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Fluid Mechanics. A fluid is a substance that deforms continuously when subjected to a tangential or shear stress, however small the shear stress may be. Such a continuous deformation under the stress constitutes a flow. Fluid mechanics is therefore the study of mechanics of such matter. As such, it pertains mostly to the study of liquids and gases, however the general theories may be applied to the study of amorphous solids, colloidal suspensions and gelatinous materials.
Fluid mechanics is a subdivision of continuum mechanics. Consequentially, fluids are considered continuous media for analysis, and their discrete nature is of no consequence for most applications. This assumption is valid mostly on length scales much larger than intramolecular distances. The departure from continuum is characterised by a dimensionless parameter, the Knudsen Number, defined by
formula_1, where L is a characteristic length scale of the flow. The continuum hypothesis holds good if Kn < 0.01. However, recent applications in nanotechnology and biotechnology are demonstrating that the governing equations are still relevant on smaller scales, specifically when they are modified to include the effects of electrostatic, magnetic, colloidal and surface-tension driven forces.
Some fluid mechanics problems can be solved by applying conservation laws (mass, momentum, energy) of mechanics to a finite control volume. However, in general, it is necessary to apply those laws to an infinitesimal control volume, then use the resulting differential equations.
Additionally, boundary values, initial conditions and thermodynamic state equations are generally necessary to obtain numeric or analytic solutions.
Brief History.
Fluid interactions help fish in a school swim faster. The collective motion of a fish school results from every animal responding solely to the motion of it's neighbour. This is what happens to bird flocks, but unlike the birds, fish usually move in a liquid which may be a river, lake or fish pond. A group of researchers recently used computer simulations to explain the water flow that fish induce can have a substantial influence on the coordinated patterns that they do create. Schooling of fish, shown by nearly half of the known species of fish can take various forms (Hemelrijk et al., 2015). The group can just swarm together with no string degree of alignment, or the fish can swim in collectively oriented rings, streams, or balls. These particular motions are thought to help in avoiding predators as well as foraging.
Use of Theoretical models can assist in understanding this by reproducing this fish schooling behaviour with no need for any large institution. They hold an assumption that every fish follows a simple “local “rules like aligning itself with the average orientation of the fish that are near it. Fish have the ability to sense fluid flow through the use of their lateral line. The lateral line is a series of tiny, hair-like sensory organs that are distributed evenly along the sides of the fish body (Ball, 2018). Also, each can enhance its swimming efficiency by swimming in the clip steam of another. But how and if these hydrodynamic effects impact the collective motion of fish schools has not been studied much by scholars and researchers.
Christophe Eloy, a member of the “Ecole Centrale Marseille” in France and his colleagues, studied the effects of fluid dynamics through the use of virtual fish moving in dual dimensions (Hemelrijk et al., 2015). Similar to the preceding model, the researchers held an assumption that the fish attract each other and to orient themselves to a certain extent with others in their field of view. Again, they assume that there is a smooth flow, such that turbulent vortices in the wake are overlooked.
Under these conditions or assumptions, the researchers found out that fish portray four different joint motion modes, which depend on the parameters of the rule of behavior. These include random and cohesive swarming; aligned, mainly swimming in a straight line or schooling; collective circle swimming or milling; and rapid, aligned swimming with a regular spontaneous turn or turning (Ball, 2018). The average speed of fish is higher with the fluid included. "Turning" resulted from noise or greater rotational randomness caused by hydrodynamic effects. What may appear to be a consequence of behavior, the fish's free will may actually be an outcome of fluid dynamics. This research can be furthered by relating the modelling results to an observation which are real.
References
Ball, P. (2018). Fluid Interactions Help Fish in a School Swim Faster. Physics Online Journal, 11.
Hemelrijk, C. K., Reid, D. A. P., Hildenbrandt, H., & Padding, J. T. (2015). The increased efficiency of fish swimming in a school. Fish and Fisheries, 16(3), 511-521. | 1,086 |
Strength of Materials. This book is a first course in the analysis of structures. Although most of the material should be accessible to all students who have had a mechanics course, a previous exposure to Engineering Mechanics would be useful. There are no mathematical prerequisites, though some elementary calculus would be useful in certain sections which can be skipped without affecting the flow of the book.
To do.
Author Resources.
The following are free resources available online that may be helpful in completing the writing of this text. Of course each source must be evaluated for accuracy and copyrights must be respected.
Strength of Material Textbooks.
John P. Kottcamp (1919) Strength of Materials http://books.google.com/books?id=f580AAAAMAAJ&dq=strength%20of%20materials&pg=PP1#v=onepage&q&f=false
James E. Boyd (1911) Strength of Materials http://books.google.com/books?id=07w0AAAAMAAJ&dq=strength%20of%20materials&pg=PP1#v=onepage&q&f=false
Arthur Morely (1913) Strength of Materials http://books.google.com/books?id=BT9DAAAAIAAJ&dq=strength%20of%20materials&pg=PR8#v=onepage&q&f=false
Open Courseware.
MIT Opencourseware 3.11 Mechanics of Materials http://ocw.mit.edu/courses/materials-science-and-engineering/3-11-mechanics-of-materials-fall-1999/modules/ Graduate level course. Includes multiple pdfs with over 300 pages of content.
Video Lectures.
Prof. S.P. Harsha. Strength of Materials Lectures. NPTEL Indian Institute of Technology, Roorke http://freevideolectures.com/Course/2361/Strength-of-Materials. This includes 40 lectures averaging between 50 and 60 minutes long.
Prof. S.K. Bhattacharyya (2005) Strength of Materials Lectures. NPTEL Indian Institute of Technology, Kharagpur http://nptel.iitm.ac.in/video.php?subjectId=105105108 This includes 40 lectures averaging between 50 and 60 minutes long taught in the civil engineering department. | 627 |
Geometry/Quadrilaterals. A quadrilateral is a polygon that has four sides.
Special Types of Quadrilaterals.
One of the most important properties used in proofs is that the sum of the angles of the quadrilateral is always 360 degrees. This can easily be proven too:
If you draw a random quadrilateral, and one of its diagonals, you'll split it up into two triangles. Given that the sum of the angles of a triangle is 180 degrees, you can sum them up, and it'll give 360 degrees. | 133 |
Cryptography/Atbash cipher. Atbash is an ancient encryption system created in the Middle East. It was originally used in the Hebrew language; some historians and cryptographers believe there are such examples in the Bible. The name "Atbash" comes from the first Hebrew letter Aleph and the last Taff. The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards. Atbash is also a substitution cipher. Since each letter corresponds to another, it offers very little security. The first letter is replaced with the last letter, the second with the second-last, and so on. The completed cypher looks like so:
Plain: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Cipher: ZYXWVUTSRQPONMLKJIHGFEDCBA
An example plaintext to ciphertext using Atbash:
Plain: MEETMEATONE
Cipher: NVVGNVZGLMV
As one can see, and as mentioned previously, the Atbash cipher offers no security once the cipher method is found. | 266 |
XML - Managing Data Exchange/The many-to-many relationship. Introduction.
In the previous chapters, you learned how to use XML to structure and format data based on one-to-one and one-to-many relationships. Because XML provides the means to model data using hierarchical parent-child relationships, the one-to-one and one-to-many relationships are relatively simple to represent in XML. However, this hierarchical parent-child structure is difficult to use to model the many-to-many relationship, a common relationship between entities in many situations.
In this chapter, we will explore the pros and cons of a few methods that are used to model a many-to-many relationship in XML; these methods offer compromises in overcoming the problems that arise when applying this relationship to XML. In particular, we will see examples of how to model the many-to-many relationship using two different methods, "Eliminate" and "ID/IDREF." Additionally, in the XML stylesheet, we will learn how to implement the key function to display the data that was modeled using the "ID/IDREF" method.
Problems: many-to-many relationship.
In XML, the parent-child relationship is most commonly used to represent a relationship. This can easily be applied to a one-to-one or one-to-many relationship. A many-to-many relationship is not supported directly by XML; the parent-child relationship will not work as each element may only have a single parent element. There are couple of possible solutions to get around this.
Solutions: many-to-many relationship.
Eliminate.
Create XML documents that eliminate the need for a many-to-many relationship<br>
By limiting the extent of information that is conveyed, you can get around the need for a many-to-many relationship. Instead of trying to have one XML document encompass all of the information, separate the information where one document describes only one of the entities that participates in the many-to-many relationship. Using our tourGuide relationship for example, one way for us to accomplish this would be creating a separate XML document for each hotel. The relationship with amenity would ultimately then become a one-to-many. This method is more suitable for situations in which the scope of data exchange can be limited to subsets of data. However, using this method for more broadly scoped data exchange, you may repeat data several times, especially if there are many attributes. To avoid this redundancy, use the ID/IDREF method.
ID/IDREF.
Represent the many-to-many relationship using unique identifiers<br>
Although not the most user-friendly way to handle this problem, one way of getting around the many-to-many relationship is by creating keys that would uniquely identify each entity. To do this, an element with ID or IDREF attributes-types must be specified within the XML schema. To use a data modeling analogy, ID is similar to the primary key, and IDREF is similar to the foreign key.
Many-to-many relationship data model.
Exhibit 1: Data model for a m:m relationship<br>
The relationship reads, "a hotel can have many amenities, and an amenity can exist at many hotels".
As you will notice, in order to represent a many-to-many relationship, two entities were added. The middle entity is necessary for the data model to represent an associative entity that stores data about the relationship between hotel and amenity. Using our Tour Guide example, "Amenity" was added to represent a list of possible amenities that a hotel can possess.
The following examples illustrate methods to represent a many-to-many relationship in XML.
Eliminate: sample solution.
In this example, the many-to-many relationship has been converted to a one-to-many relationship.
XML schema.
Exhibit 2: XML schema for "Eliminate" method
<?xml version="1.0" encoding="UTF-8" ?>
Document : amenity1.xsd
Created on : February 4, 2006
Author : Dr. Rick Watson
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="unqualified">
<xsd:element name="hotelGuide">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="hotel" type="hotelDetails" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:simpleType name="emailAddressType">
<xsd:restriction base="xsd:string">
<xsd:pattern value="\w+\W*\w*@{1}\w+\W*\w+.\w+.*\w*"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:complexType name="hotelDetails">
<xsd:sequence>
<xsd:element name="hotelPicture"/>
<xsd:element name="hotelName" type="xsd:string"/>
<xsd:element name="streetAddress" type="xsd:string"/>
<xsd:element name="postalCode" type="xsd:string" minOccurs="0"/>
<xsd:element name="telephoneNumber" type="xsd:string"/>
<xsd:element name="emailAddress" type="emailAddressType" minOccurs="0"/>
<xsd:element name="websiteURL" type="xsd:anyURI" minOccurs="0"/>
<xsd:element name="hotelRating" type="xsd:integer" default="0"/>
<xsd:element name="lowerPrice" type="xsd:positiveInteger"/>
<xsd:element name="upperPrice" type="xsd:positiveInteger"/>
<xsd:element name="amenity" type="amenityValue" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="amenityValue">
<xsd:sequence>
<xsd:element name="amenityType" type="xsd:string"/>
<xsd:element name="amenityOpenHour" type="xsd:time"/>
<xsd:element name="amenityCloseHour" type="xsd:time"/>
</xsd:sequence>
</xsd:complexType>
</xsd:schema>
XML document.
Exhibit 3: XML document for "Eliminate" method
<?xml version="1.0" encoding="UTF-8"?>
Document : amenity1.xml
Created on : February 4, 2006
Author : Dr. Rick Watson
<hotelGuide xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="amenity1.xsd">
<hotel>
<hotelPicture/>
<hotelName>Narembeen Hotel</hotelName>
<streetAddress>Churchill Street</streetAddress>
<telephoneNumber>+61 (08) 9064 7272</telephoneNumber>
<emailAddress>[email protected]</emailAddress>
<hotelRating>1</hotelRating>
<lowerPrice>50</lowerPrice>
<upperPrice>100</upperPrice>
<amenity>
<amenityType>Restaurant</amenityType>
<amenityOpenHour>06:00:00</amenityOpenHour>
<amenityCloseHour>22:00:00 </amenityCloseHour>
</amenity>
<amenity>
<amenityType>Pool</amenityType>
<amenityOpenHour>06:00:00</amenityOpenHour>
<amenityCloseHour>18:00:00 </amenityCloseHour>
</amenity>
<amenity>
<amenityType>Complimentary Breakfast</amenityType>
<amenityOpenHour>07:00:00</amenityOpenHour>
<amenityCloseHour>10:00:00 </amenityCloseHour>
</amenity>
</hotel>
<hotel>
<hotelPicture/>
<hotelName>Narembeen Caravan Park</hotelName>
<streetAddress>Currall Street</streetAddress>
<telephoneNumber>+61 (08) 9064 7308</telephoneNumber>
<emailAddress>[email protected]</emailAddress>
<hotelRating>1</hotelRating>
<lowerPrice>20</lowerPrice>
<upperPrice>30</upperPrice>
<amenity>
<amenityType>Pool</amenityType>
<amenityOpenHour>10:00:00</amenityOpenHour>
<amenityCloseHour>22:00:00 </amenityCloseHour>
</amenity>
</hotel>
</hotelGuide>
ID/IDREF: sample solution.
To avoid redundancy, we create a separate element, "amenity," which is included at the top of the schema along with "hotel." Remember, the data types ID and IDREF are synonymous with the primary key and foreign key, respectively. For every foreign key (IDREF), there must be a matching primary key (ID). Note that the IDREF data type has to be an alphanumeric string.
The following example illustrates the ID/IDREF approach. Notice that the ID for the amenity pool is defined as "k1," and every hotel with a pool as an amenity references "k1," using IDREF. If the IDREF does not match any ID, then the document will not validate.
XML schema.
Exhibit 4: XML schema for "ID/IDREF" method
<?xml version="1.0" encoding="UTF-8" ?>
Document : amenity2.xsd
Created on : February 4, 2006
Author : Dr. Rick Watson
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="unqualified">
<xsd:element name="hotelGuide">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="hotel" type="hotelDetails" minOccurs="1" maxOccurs="unbounded"/>
<xsd:element name="amenity" type="amenityList" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:simpleType name="emailAddressType">
<xsd:restriction base="xsd:string">
<xsd:pattern value="\w+\W*\w*@{1}\w+\W*\w+.\w+.*\w*"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:complexType name="hotelDetails">
<xsd:sequence>
<xsd:element name="hotelPicture"/>
<xsd:element name="hotelName" type="xsd:string"/>
<xsd:element name="streetAddress" type="xsd:string"/>
<xsd:element name="postalCode" type="xsd:string" minOccurs="0"/>
<xsd:element name="telephoneNumber" type="xsd:string"/>
<xsd:element name="emailAddress" type="emailAddressType" minOccurs="0"/>
<xsd:element name="websiteURL" type="xsd:anyURI" minOccurs="0"/>
<xsd:element name="hotelRating" type="xsd:integer" default="0"/>
<xsd:element name="lowerPrice" type="xsd:positiveInteger"/>
<xsd:element name="upperPrice" type="xsd:positiveInteger"/>
<xsd:element name="amenities" type="amenityDesc" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="amenityDesc">
<xsd:sequence>
<xsd:element name="amenityIDREF" type="xsd:IDREF"/>
<xsd:element name="amenityOpenHour" type="xsd:time"/>
<xsd:element name="amenityCloseHour" type="xsd:time"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="amenityList">
<xsd:sequence>
<xsd:element name="amenityID" type="xsd:ID"/>
<xsd:element name="amenityType" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:schema>
XML document.
Exhibit 5: XML document for "ID/IDREF" method
<?xml version="1.0" encoding="UTF-8"?>
Document : amenity2.xml
Created on : February 4, 2006
Author : Dr. Rick Watson
<?xml-stylesheet href="amenity2.xsl" type="text/xsl" media="screen"?>
<hotelGuide xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="amenity2.xsd">
<hotel>
<hotelPicture/>
<hotelName>Narembeen Hotel</hotelName>
<streetAddress>Churchill Street</streetAddress>
<telephoneNumber>+61 (08) 9064 7272</telephoneNumber>
<emailAddress>[email protected]</emailAddress>
<hotelRating>1</hotelRating>
<lowerPrice>50</lowerPrice>
<upperPrice>100</upperPrice>
<amenities>
<amenityIDREF>k2</amenityIDREF>
<amenityOpenHour>06:00:00</amenityOpenHour>
<amenityCloseHour>22:00:00 </amenityCloseHour>
</amenities>
<amenities>
<amenityIDREF>k1</amenityIDREF>
<amenityOpenHour>06:00:00</amenityOpenHour>
<amenityCloseHour>18:00:00 </amenityCloseHour>
</amenities>
<amenities>
<amenityIDREF>k5</amenityIDREF>
<amenityOpenHour>07:00:00</amenityOpenHour>
<amenityCloseHour>10:00:00 </amenityCloseHour>
</amenities>
</hotel>
<hotel>
<hotelPicture/>
<hotelName>Narembeen Caravan Park</hotelName>
<streetAddress>Currall Street</streetAddress>
<telephoneNumber>+61 (08) 9064 7308</telephoneNumber>
<emailAddress>[email protected]</emailAddress>
<hotelRating>1</hotelRating>
<lowerPrice>20</lowerPrice>
<upperPrice>30</upperPrice>
<amenities>
<amenityIDREF>k1</amenityIDREF>
<amenityOpenHour>10:00:00</amenityOpenHour>
<amenityCloseHour>22:00:00 </amenityCloseHour>
</amenities>
</hotel>
<amenity>
<amenityID>k1</amenityID>
<amenityType>Pool</amenityType>
</amenity>
<amenity>
<amenityID>k2</amenityID>
<amenityType>Restaurant</amenityType>
</amenity>
<amenity>
<amenityID>k3</amenityID>
<amenityType>Fitness room</amenityType>
</amenity>
<amenity>
<amenityID>k4</amenityID>
<amenityType>Complimentary breakfast</amenityType>
</amenity>
<amenity>
<amenityID>k5</amenityID>
<amenityType>in-room data port</amenityType>
</amenity>
<amenity>
<amenityID>k6</amenityID>
<amenityType>Water slide</amenityType>
</amenity>
</hotelGuide>
Key function: XML stylesheet.
In order to set up an XML stylesheet using the ID/IDREF method for a many-to-many relationship, the key function should be used. In the stylesheet, the <xsl:key> element specifies the index, which is used to return a node-set from the XML document.
A key consists of the following:
1. the node that has the key<br>
2. the name of the key<br>
3. the value of a key
The following XML stylesheet illustrates how to use the key function to present content that is structured in a many-to-many relationship.
XML stylesheet.
Exhibit 6: XML stylesheet for "ID/IDREF" method
<?xml version="1.0" encoding="UTF-8"?>
Document : amenity2.xsl
Created on : February 4, 2006
Author : Dr. Rick Watson
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:key name="amList" match="amenity" use="amenityID"/>
<xsl:output method="html"/>
<xsl:template match="/">
<html>
<head>
<title>Hotel Guide</title>
</head>
<body>
<h2>Hotels</h2>
<xsl:apply-templates select="hotelGuide"/>
</body>
</html>
</xsl:template>
<xsl:template match="hotelGuide">
<xsl:for-each select="hotel">
<xsl:value-of select="hotelName"/>
<br/>
<xsl:for-each select="amenities">
<xsl:value-of select="key('amList',amenityIDREF)/amenityType"/>
<xsl:text> </xsl:text>
<xsl:value-of select="amenityOpenHour"/> -
<xsl:value-of select="amenityCloseHour"/>
<BR/>
</xsl:for-each>
<br/>
<br/>
</xsl:for-each>
<br/>
</xsl:template>
</xsl:stylesheet>
References.
http://www-128.ibm.com/developerworks/xml/library/x-xdm2m.html
http://www.w3.org/TR/xslt#key | 5,850 |
Russian/Lesson 2. Произноше́ние - Pronunciation.
Usually, Russian is pronounced as you see it. However, there are some exceptions, usually changes in the pronunciation of vowels based on where they are in relation to the stressed syllable.
If you pronounce these letters without reducing them you will be understandable, but will sound strange.
Voiced consonants at the end of the word become unvoiced. So, таз sounds like 'tas', взвод sounds like 'vzvot', etc. The same thing happens if a voiced consonant is followed by an unvoiced one. For example, подско́к sounds like 'patskók', and водка sounds like 'votka'.
Диало́г - Dialogue.
Unlike modern English, Russian has two words for 'you': ты and вы. You use вы when the person you're talking to is someone you don't know, someone you want to show respect to (such as a teacher or elder), or a group of people. In this sense, it is both a more polite form of ты, and a plural form. So you would only use ты to talk to a single person who you know well. In written Russian, a capitalised Вы is used when being respectful, while the lower-case вы is used when talking to many people.<br>
You can also to the audio version of this dialogue.
Note: The Russian for 'glad' is рад ('rat') when spoken by a male, or ра́да (rada) when spoken by a female
Note: This literally means "Me (they) call Joanne, and you?", or "They call me Joanne, and you?" and is the Russian construction of asking someone's name.
Lesson 3 » | 409 |
Invertebrate Zoology/Mollusks. Introduction to the Mollusks.
Mollusks are metazoan animals that take a variety of forms. However, almost all mollusks are characterized by a body with several main regions: a muscular foot, a visceral mass covered by a mantle that secretes a shell, paired gills (called ctenidia) and a unique feeding organ called a radula. The radula is a tongue-like organ that is covered with a chitinous ribbon with numerous rows of teeth, which are used to tear food off substrate and bring it into the mouth. In terms of species, they are the second-most diverse phylum next to the Arthropods, but few phyla can rival their diversity in form, from giant clams to minute sea slugs to fast moving squid.
Commonly accepted molluscan classes include:<br>
Aplacophora <br>
Monoplacophora <br>
Polyplacophora (chitons)<br>
Gastropoda (snails and slugs)<br>
Cephalopoda (squid, octopus, nautilus)<br>
Bivalvia (clams, oysters, mussels)<br>
Scaphopoda (Tusk shells) | 329 |
Electronics/Scratch pad. Parts list and theory.
Voltage = potential between two charges.
Defined as the derivative of the flux linkage:
formula_1
Current = flow of electrons
Defined as the rate of change of the charge:
formula_2
There are 3 parameters in an electrical circuit:
Resistance =
formula_3
In a resistor voltage and current are in sync.
formula_4
In capacitors voltage leads current. Capacitors are good as a low pass filter.
formula_5
In inductors current leads voltage. Current equals the negative derivative of the voltage. Inductors are good as a high pass filter.
formula_6
relationship between voltage and current
formula_7
in a circuit
in series voltage drops and current stays constant
in parallel voltage stays constant and current divides according to the resistance
voltage stays constant in parallel and current drops in p
pizoelectric = a crystal under compression creates current
transformers
vacuum tube = electron emitter in a vacuum
integrated circuit a semiconductor doped with impurities
group 4 elements doped with group 3 and 5
electrons and holes
ground
applications.
Resistors in series (Christmas lights, stove)
computer
3.5, 5, 12 Volts
lamp
monitor
power distribution (three phase power)
radio
modem
speaker
circuit design.
bandgap
cmos
flip flop
computer parts
leakage current | 360 |
Electronics/Ohm's Law. Ohm's law describes the relationship between voltage, current, and resistance.
Voltage and current are related such that voltage is equal to current times resistance:
formula_1
Common units used in electronics calculations are:
V = mA × kΩ
the current going through any point in the circuit, I, will be equal to the voltage V divided by the resistance R.
In this example, the voltage across the resistor, V, will be equal to the supplied current, I, times the resistance R.
SUMMARY: | 128 |
Electronics/Capacitors. General remarks.
Capacitors are a good example of the fact that even the simplest device can become complicated given 250 years of evolution. (Citation J. Ho, T. R. Jow, St. Boggs, Historical Introduction to Capacitor Technology)
Capacitors, together with resistors, inductors and memristors, belong to the group of "passive components" for electronic equipment. Although in absolute figures the most common capacitors are integrated capacitors, e.g. in DRAMs or in flash memory structures, this article is concentrated on discrete components.
Capacitors.
Theory of conventional construction.
A capacitor (historically known as a "condenser") is a device that stores energy in an electric field, by accumulating an internal imbalance of electric charge. It is made of two conductors separated by a dielectric (insulator). Using the same analogy of water flowing through a pipe, a capacitor can be thought of as a tank, in which the charge can be thought of as a volume of water in the tank. The tank can "charge" and "discharge" in the same manner as a capacitor does to an electric charge. A mechanical analogy is that of a spring. The spring holds a charge when it is pulled back.
When voltage exists one end of the capacitor is getting drained and the other end is getting filled with charge.This is known as charging. Charging creates a charge imbalance between the two plates and creates a reverse voltage that stops the capacitor from charging. As a result, when capacitors are first connected to voltage, charge flows only to stop as the capacitor becomes charged. When a capacitor is charged, current stops flowing and it becomes an open circuit. It is as if the capacitor gained infinite resistance.
You can also think of a capacitor as a fictional battery in series with a fictional resistance. Starting the charging procedure with the capacitor completely discharged, the applied voltage is not counteracted by the fictional battery, because the fictional battery still has zero voltage, and therefore the charging current is at its maximum. As the charging continues, the voltage of the fictional battery increases, and counteracts the applied voltage, so that the charging current decreases as the fictional battery's voltage increases. Finally the fictional battery's voltage equals the applied voltage, so that no current can flow into, nor out of, the capacitor.
Just as the capacitor charges it can be discharged. Think of the capacitor being a fictional battery that supplies at first a maximum current to the "load", but as the discharging continues the voltage of the fictional battery keeps decreasing, and therefore the discharge current also decreases. Finally the voltage of the fictional battery is zero, and therefore the discharge current also is then zero.
This is not the same as dielectric breakdown where the insulator between the capacitor plates breaks down and discharges the capacitor. That only happens at large voltages and the capacitor is usually destroyed in the process. A spectacular example of dielectric breakdown occurs when the two plates of the capacitor are brought into contact. This causes all the charge that has accumulated on both plates to be discharged at once. Such a system is popular for powering tasers which need lots of energy in a very brief period of time.
Theory of electrochemical construction.
Besides the conventional static storage of electric energy in an electric field, two other storage principles to store electric energy in a capacitor exist. They are so-called electrochemical capacitors. In contrast to ceramic, film and electrolytic capacitors, supercapacitors, also known as electrical double-layer capacitors (EDLC) or ultracapacitors do not have a conventional dielectric. The capacitance value of an electrochemical capacitor is determined by two high-capacity storage principles. These principles are:
The ratio of the storage resulting from each principle can vary greatly, depending on electrode design and electrolyte composition. Pseudocapacitance can increase the capacitance value by as much as an order of magnitude over that of the double-layer by itself.
Capacitance.
The capacitance of a capacitor is a ratio of the amount of charge that will be present in the capacitor when a given potential (voltage) exists between its leads. The unit of capacitance is the farad which is equal to one coulomb per volt. This is a very large capacitance for most practical purposes; typical capacitors have values on the order of microfarads or smaller.
<br>
Where "C" is the capacitance in farads, "V" is the potential in volts, and "Q" is the charge measured in coulombs. Solving this equation for the potential gives:
Capacitor & Direct Current Voltage (DC).
Charge Building
Storing Charge
Charge discharge
Therefore, a Capacitor is a device that can Build up Charge , Store Charge and Release Charge
Capacitor & Alternating Current Voltage (AC).
Reactance.
Reactance is defined as the ratio of Voltage over Current
Impedance.
Impedance is defined as the sum of Capacitor's Resistance and Reactance
Angle of Difference between Voltage and Current.
For Lossless Capacitor
For Lossy Capacitor
Changing the value of R and C will change the value of Phase Angle, Angular Frequency, Frequency and Time
Capacitor Connection.
Capacitors in Series.
Capacitors in series are the same as increasing the distance between two capacitor plates. As well, it should be noted that placing two 100 V capacitors in series results in the same as having one capacitor with the total maximum voltage of 200 V. This, however, is not recommended to be done in practice, especially with capacitors of different values. In a capacitor network in series, all capacitors can have a different voltage over them.
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In a series configuration, the capacitance of all the capacitors combined is the reciprocal of the sum of the reciprocals of the capacitance of all the capacitors.
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Capacitors in Parallel.
Capacitors in parallel are the same as increasing the total surface area of the capacitors to create a larger capacitor with more capacitance. In a capacitor network in parallel, all capacitors have the same voltage over them.
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In a parallel configuration, the capacitance of the capacitors in parallel is the sum of the capacitance of all the capacitors.
RC Circuit.
Introduction.
An RC circuit is short for 'Resistor-Capacitor' circuit. A capacitor takes a finite amount of time to discharge through a resistor, which varies with the values of the resistor and capacitor. A capacitor acts interestingly in an electronic circuit, practically speaking as a combination of a voltage source and a variable resistor.
Basics.
Below is a simple RC Circuit:<br>
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There is a capacitor in parallel with the resistor and current probe. The way the capacitor functions is by acting as a very low resistance load when the circuit is initially turned on. This is illustrated below:<br>
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Initially, the capacitor has a very low resistance, almost 0. Since electricity takes the path of least resistance, almost all the electricity flows through the capacitor, not the resistor, as the resistor has considerably higher resistance.<br>
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As a capacitor charges, its resistance increases as it gains more and more charge. As the resistance of the capacitor climbs, electricity begins to flow not only to the capacitor, but through the resistor as well:<br>
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Once the capacitor's voltage equals that of the battery, meaning it is fully charged, it will not allow any current to pass through it. As a capacitor charges its resistance increases and becomes effectively infinite (open connection) and all the electricity flows through the resistor.<br>
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Once the voltage source is disconnected, however, the capacitor acts as a voltage source itself:<br>
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As time goes on, the capacitor's charge begins to drop, and so does its voltage. This means less current flowing through the resistor:<br>
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Once the capacitor is fully discharged, you are back to square one:<br>
If one were to do this with a light and a capacitor connected to a battery, what you would see is the following:
This is how a capacitor acts. However, what if you changed the values of R1? C1? The voltage of the battery? We will examine the mathematical relationship between the resistor, capacitor, and charging rate below.
Time Constant.
In order to find out how long it takes for a capacitor to fully charge or discharge, or how long it takes for the capacitor to reach a certain voltage, you must know a few things. First, you must know the starting and finishing voltages. Secondly, you must know the time constant of the circuit you have. Time constant is denoted by the Greek letter 'tau' or τ. The formula to calculate this time constant is:<br><br>
So this means that the time constant is how long it takes for a capacitor to charge to 63% of its full charge. This time, in seconds, is found by multiplying the resistance in ohms and the capacitance in farads.
According to the formula above, there are two ways to lengthen the amount of time it takes to discharge. One would be to increase the resistance, and the other would be to increase the capacitance of the capacitor. This should make sense. It should be noted that the formula compounds, such that in the second time constant, it charges another 63%, based on the original 63%. This gives you about 86.5% charge in the second time constant. Below is a table.
For all practicality, by the 5th time constant it is considered that the capacitor is fully charged or discharged.
put some stuff in here about how discharging works the same way, and the function for voltage based on time
formula_14
Where "i"("t") is the current flowing through the capacitor as a function of time.
This equation is often used in another form. By differentiating with respect to time:
formula_15
Substituting v/r for i(t) and integrating the above equation gives you an equation used to describe the charging and discharging characteristics of RC circuits. A charging characteristic curve exponentially increases from 0% (0 volts) and approaches 100% full (maximum voltage), similarly, a discharge curve starts at the theoretical 100% (maximum voltage) and exponentially falls back to 0% (0 volts).
Capacitors - general remarks.
Common capacitors and their names.
Capacitors are divided into two mechanical groups: Fixed capacitors with fixed capacitance values and variable capacitors with variable (trimmer) or adjustable (tunable) capacitance values.
The most important group is the fixed capacitors. Many got their names from the dielectric. For a systematic classification these characteristics can't be used, because one of the oldest, the electrolytic capacitor, is named instead by its cathode construction. So the most-used names are simply historical.
The most common kinds of capacitors are:
Capacitors in each family have similar physical design features, but vary, for example, in the form of the terminals.
In addition to the above shown capacitor types, which derived their name from historical development, there are many individual capacitors that have been named based on their application. They include:
Often, more than one capacitor family is employed for these applications, e.g. interference suppression can use ceramic capacitors or film capacitors.
Specialized devices such as built-in capacitors with metal conductive areas in different layers of a multi-layer printed circuit board and kludges such as twisting together two pieces of insulated wire also exist.
Dielectrics.
The most common dielectrics are:
All of them store their electrical charge statically within an between two (parallel) electrodes.
Beneath this conventional capacitors a family of electrochemical capacitors called s was developed. Supercapacitors don't have a conventional dielectric. They store their electrical charge statically in
and additional electrochemical with faradaic charge transfer
The most important material parameters of the different dielectrics used and the appr. Helmholtz-layer thickness are given in the table below.
The capacitor's plate area can be adapted to the wanted capacitance value. The permittivity and the dielectric thickness are the determining parameter for capacitors. Ease of processing is also crucial. Thin, mechanically flexible sheets can be wrapped or stacked easily, yielding large designs with high capacitance values. Razor-thin metallized sintered ceramic layers covered with metallized electrodes however, offer the best conditions for the miniaturization of circuits with SMD styles.
A short view to the figures in the table above gives the explanation for some simple facts:
Capacitance and voltage range.
Capacitance ranges from picofarad to more than hundreds of farad. Voltage ratings can reach 100 kilovolts. In general, capacitance and voltage correlates with physical size and cost.
Miniaturization.
As in other areas of electronics, volumetric efficiency measures the performance of electronic function per unit volume. For capacitors, the volumetric efficiency is measured with the "CV product", calculated by multiplying the capacitance (C) by the maximum voltage rating (V), divided by the volume. From 1970 to 2005, volumetric efficiencies have improved dramatically.
Overlapping range of applications.
These individual capacitors can perform their application independent of their affiliation to an above shown capacitor type, so that an overlapping range of applications between the different capacitor types exists.
Capacitor - types and styles.
Ceramic capacitors.
A ceramic capacitor is a non-polarized fixed capacitor made out of two or more alternating layers of ceramic and metal in which the ceramic material acts as the dielectric and the metal acts as the electrodes. The ceramic material is a mixture of finely ground granules of paraelectric or ferroelectric materials, modified by mixed oxides that are necessary to achieve the capacitor's desired characteristics. The electrical behavior of the ceramic material is divided into two stability classes:
The great plasticity of ceramic raw material works well for many special applications and enables an enormous diversity of styles, shapes and great dimensional spread of ceramic capacitors. The smallest discrete capacitor, for instance, is a "01005" chip capacitor with the dimension of only 0.4 mm × 0.2 mm.
The construction of ceramic multilayer capacitors with mostly alternating layers results in single capacitors connected in parallel. This configuration increases capacitance and decreases all losses and parasitic inductances. Ceramic capacitors are well-suited for high frequencies and high current pulse loads.
Because the thickness of the ceramic dielectric layer can be easily controlled and produced by the desired application voltage, ceramic capacitors are available with rated voltages up to the 30 kV range.
Some ceramic capacitors of special shapes and styles are used as capacitors for special applications, including RFI/EMI suppression capacitors for connection to supply mains, also known as safety capacitors, X2Y® capacitors for bypassing and decoupling applications, feed-through capacitors for noise suppression by low-pass filters and ceramic power capacitors for transmitters and HF applications.
Film capacitors.
Film capacitors or plastic film capacitors are non-polarized capacitors with an insulating plastic film as the dielectric. The dielectric films are drawn to a thin layer, provided with metallic electrodes and wound into a cylindrical winding. The electrodes of film capacitors may be metallized aluminum or zinc, applied on one or both sides of the plastic film, resulting in metallized film capacitors or a separate metallic foil overlying the film, called film/foil capacitors.
Metallized film capacitors offer self-healing properties. Dielectric breakdowns or shorts between the electrodes do not destroy the component. The metallized construction makes it possible to produce wound capacitors with larger capacitance values (up to 100 µF and larger) in smaller cases than within film/foil construction.
Film/foil capacitors or metal foil capacitors use two plastic films as the dielectric. Each film is covered with a thin metal foil, mostly aluminium, to form the electrodes. The advantage of this construction is the ease of connecting the metal foil electrodes, along with an excellent current pulse strength.
A key advantage of every film capacitor's internal construction is direct contact to the electrodes on both ends of the winding. This contact keeps all current paths very short. The design behaves like a large number of individual capacitors connected in parallel, thus reducing the internal ohmic losses (ESR) and parasitic inductance (ESL). The inherent geometry of film capacitor structure results in low ohmic losses and a low parasitic inductance, which makes them suitable for applications with high surge currents (snubbers) and for AC power applications, or for applications at higher frequencies.
The plastic films used as the dielectric for film capacitors are Polypropylene (PP), Polyester (PET), Polyphenylene sulfide (PPS), Polyethylene naphthalate (PEN), and Polytetrafluoroethylene or Teflon (PTFE). Polypropylene film material with a market share of something about 50% and Polyester film with something about 40% are the most used film materials. The rest of something about 10% will be used by all other materials including PPS and paper with roughly 3%, each.
Some film capacitors of special shapes and styles are used as capacitors for special applications, including RFI/EMI suppression capacitors for connection to the supply mains, also known as safety capacitors, Snubber capacitors for very high surge currents, Motor run capacitors, AC capacitors for motor-run applications
Film power capacitors.
A related type is the power film capacitor. The materials and construction techniques used for large power film capacitors mostly are similar to those of ordinary film capacitors. However, capacitors with high to very high power ratings for applications in power systems and electrical installations are often classified separately, for historical reasons. The standardization of ordinary film capacitors is oriented on electrical and mechanical parameters. The standardization of power capacitors by contrast emphasizes the safety of personnel and equipment, as given by the local regulating authority.
As modern electronic equipment gained the capacity to handle power levels that were previously the exclusive domain of "electrical power" components, the distinction between the "electronic" and "electrical" power ratings blurred. Historically, the boundary between these two families was approximately at a reactive power of 200 volt-amps.
Film power capacitors mostly use polypropylene film as the dielectric. Other types include metallized paper capacitors (MP capacitors) and mixed dielectric film capacitors with polypropylene dielectrics. MP capacitors serve for cost applications and as field-free carrier electrodes (soggy foil capacitors) for high AC or high current pulse loads. Windings can be filled with an insulating oil or with epoxy resin to reduce air bubbles, thereby preventing short circuits.
They find use as converters to change voltage, current or frequency, to store or deliver abruptly electric energy or to improve the power factor. The rated voltage range of these capacitors is from approximately120 V AC (capacitive lighting ballasts) to 100 kV.
Electrolytic capacitors.
Electrolytic capacitors have a metallic anode covered with an oxidized layer used as dielectric. The second electrode is a non-solid (wet) or solid electrolyte. Electrolytic capacitors are polarized. Three families are available, categorized according to their dielectric.
The anode is highly roughened to increase the surface area. This and the relatively high permittivity of the oxide layer gives these capacitors very high capacitance per unit volume compared with film- or ceramic capacitors.
The permittivity of tantalum pentoxide is approximately three times higher than aluminium dioxide, producing significantly smaller components. However, permittivity determines only the dimensions. Electrical parameters, especially conductivity, are established by the electrolyte's material and composition. Three general types of electrolytes are used:
Internal losses of electrolytic capacitors, prevailing used for decoupling and buffering applications, are determined by the kind of electrolyte.
The large capacitance per unit volume of electrolytic capacitors make them valuable in relatively high-current and low-frequency electrical circuits, e.g. in power supply filters for decoupling unwanted AC components from DC power connections or as coupling capacitors in audio amplifiers, for passing or bypassing low-frequency signals and storing large amounts of energy. The relatively high capacitance value of an electrolytic capacitor combined with the very low ESR of the polymer electrolyte of polymer capacitors, especially in SMD styles, makes them a competitor to MLC chip capacitors in personal computer power supplies.
Bipolar electrolytics (also called Non-Polarized capacitors) contain two anodized aluminium foils, behaving like two capacitors connected in series opposition.
Electolytic capacitors for special applications include motor start capacitors, flashlight capacitors and audio frequency capacitors.
Supercapacitors.
Supercapacitors (SC), comprise a family of electrochemical capacitors. Supercapacitor, sometimes called ultracapacitor is a generic term for electric double-layer capacitors (EDLC), pseudocapacitors and hybrid capacitors. They don't have a conventional solid dielectric. The capacitance value of an electrochemical capacitor is determined by two storage principles, both of which contribute to the total capacitance of the capacitor:
The ratio of the storage resulting from each principle can vary greatly, depending on electrode design and electrolyte composition. Pseudocapacitance can increase the capacitance value by as much as an order of magnitude over that of the double-layer by itself.
Supercapacitors are divided into three families, based on the design of the electrodes:
Supercapacitors bridge the gap between conventional capacitors and rechargeable batteries. They have the highest available capacitance values per unit volume and the greatest energy density of all capacitors. They support up to 12,000 Farads/1.2 Volt, with capacitance values up to 10,000 times that of electrolytic capacitors. While existing supercapacitors have energy densities that are approximately 10% of a conventional battery, their power density is generally 10 to 100 times greater. Power density is defined as the product of energy density, multiplied by the speed at which the energy is delivered to the load. The greater power density results in much shorter charge/discharge cycles than a battery is capable, and a greater tolerance for numerous charge/discharge cycles. This makes them well-suited for parallel connection with batteries, and may improve battery performance in terms of power density.
Within electrochemical capacitors, the electrolyte is the conductive connection between the two electrodes, distinguishing them from electrolytic capacitors, in which the electrolyte only forms the cathode, the second electrode.
Supercapacitors are polarized and must operate with correct polarity. Polarity is controlled by design with asymmetric electrodes, or, for symmetric electrodes, by a potential applied during the manufacturing process.
Supercapacitors support a broad spectrum of applications for power and energy requirements, including:
Supercapacitors are rarely interchangeable, especially those with higher energy densities. IEC standard 62391-1 "Fixed electric double layer capacitors for use in electronic equipment" identifies four application classes:
Exceptional for electronic components like capacitors are the manifold different trade or series names used for supercapacitors like: "APowerCap, BestCap, BoostCap, CAP-XX, DLCAP, EneCapTen, EVerCAP, DynaCap, Faradcap, GreenCap, Goldcap, HY-CAP, Kapton capacitor, Super capacitor, SuperCap, PAS Capacitor, PowerStor, PseudoCap, Ultracapacitor" making it difficult for users to classify these capacitors.
Miscellaneous capacitors.
Beneath the above described capacitors covering more or less nearly the total market of discrete capacitors some new developments or very special capacitor types as well as older types can be found in electronics.
Variable capacitors.
Variable capacitors may have their capacitance changed by mechanical motion. Generally two versions of variable capacitors has to be to distinguished
Variable capacitors include capacitors that use a mechanical construction to change the distance between the plates, or the amount of plate surface area which overlaps. They mostly use air as dielectric medium.
Semiconductive variable capacitance diodes are not capacitors in the sense of passive components but can change their capacitance as a function of the applied reverse bias voltage and are used like a variable capacitor. They have replaced much of the tuning and trimmer capacitors.
Market.
Discrete capacitors today are industrial products produced in very large quantities for use in electronic and in electrical equipment. Globally, the market for fixed capacitors was estimated at approximately US$18 billion in 2008 for 1,400 billion (1.4 × 1012) pieces. This market is dominated by ceramic capacitors with estimate of approximately one trillion (1 × 1012) items per year.
Detailed estimated figures in value for the main capacitor families are:
All other capacitor types are negligible in terms of value and quantity compared with the above types.
Capacitor - Electrical characteristics.
Series-equivalent circuit.
Discrete capacitors deviate from the ideal capacitor. An ideal capacitor only stores and releases electrical energy, with no dissipation. Capacitor components have losses and parasitic inductive parts. These imperfections in material and construction can have positive implications such as linear frequency and temperature behavior in class 1 ceramic capacitors. Conversely, negative implications include the non-linear, voltage-dependent capacitance in class 2 ceramic capacitors or the insufficient dielectric insulation of capacitors leading to leakage currents.
All properties can be defined and specified by a series equivalent circuit composed out of an idealized capacitance and additional electrical components which model all losses and inductive parameters of a capacitor. In this series-equivalent circuit the electrical characteristics are defined by:
Using a series equivalent circuit instead of a parallel equivalent circuit is specified by IEC/EN 60384-1.
Standard values and tolerances.
The "rated capacitance" CR or "nominal capacitance" CN is the value for which the capacitor has been designed. Actual capacitance depends on the measured frequency and ambient temperature. Standard measuring conditions are a low-voltage AC measuring method at a temperature of 20 °C with frequencies of
For supercapacitors a voltage drop method is applied for measuring the capacitance value. .
Capacitors are available in geometrically increasing preferred values (E series standards) specified in IEC/EN 60063. According to the number of values per decade, these were called the E3, E6, E12, E24 etc. series. The range of units used to specify capacitor values has expanded to include everything from pico- (pF), nano- (nF) and microfarad (µF) to farad (F). Millifarad and kilofarad are uncommon.
The percentage of allowed deviation from the rated value is called tolerance. The actual capacitance value should be within its tolerance limits, or it is out of specification. IEC/EN 60062 specifies a letter code for each tolerance.
The required tolerance is determined by the particular application. The narrow tolerances of E24 to E96 are used for high-quality circuits such as precision oscillators and timers. General applications such as non-critical filtering or coupling circuits employ E12 or E6. Electrolytic capacitors, which are often used for filtering and bypassing capacitors mostly have a tolerance range of ±20% and need to conform to E6 (or E3) series values.
Temperature dependence.
Capacitance typically varies with temperature. The different dielectrics express great differences in temperature sensitivity. The temperature coefficient is expressed in parts per million (ppm) per degree Celsius for class 1 ceramic capacitors or in % over the total temperature range for all others.
Frequency dependence.
Most discrete capacitor types have more or less capacitance changes with increasing frequencies. The dielectric strength of class 2 ceramic and plastic film diminishes with rising frequency. Therefore their capacitance value decreases with increasing frequency. This phenomenon for ceramic class 2 and plastic film dielectrics is related to dielectric relaxation in which the time constant of the electrical dipoles is the reason for the frequency dependence of permittivity. The graphs below show typical frequency behavior of the capacitance for ceramic and film capacitors.
For electrolytic capacitors with non-solid electrolyte, mechanical motion of the ions occurs. Their movability is limited so that at higher frequencies not all areas of the roughened anode structure are covered with charge-carrying ions. As higher the anode structure is roughned as more the capacitance value decreases with increasing frequency. Low voltage types with highly-roughened anodes display capacitance at 100 kHz approximately 10 to 20% of the value measured at 100 Hz.
Voltage dependence.
Capacitance may also change with applied voltage. This effect is more prevalent in class 2 ceramic capacitors. The permittivity of ferroelectric class 2 material depends on the applied voltage. Higher applied voltage lowers permittivity. The change of capacitance can drop to 80% of the value measured with the standardized measuring voltage of 0.5 or 1.0 V. This behavior is a small source of non-linearity in low-distortion filters and other analog applications. In audio applications this can be the reason for harmonic distortion.
Film capacitors and electrolytic capacitors have no significant voltage dependence.
Rated and category voltage.
The voltage at which the dielectric becomes conductive is called the breakdown voltage, and is given by the product of the dielectric strength and the separation between the electrodes. The dielectric strength depends on temperature, frequency, shape of the electrodes, etc. Because a breakdown in a capacitor normally is a short circuit and destroys the component, the operating voltage is lower than the breakdown voltage. The operating voltage is specified such that the voltage may be applied continuously throughout the life of the capacitor.
In IEC/EN 60384-1 the allowed operating voltage is called "rated voltage" or "nominal voltage". The rated voltage (UR) is the maximum DC voltage or peak pulse voltage that may be applied continuously at any temperature within the rated temperature range.
The voltage proof of nearly all capacitors decreases with increasing temperature. For some applications it is important to use a higher temperature range. Lowering the voltage applied at a higher temperature maintains safety margins. For some capacitor types therefore the IEC standard specify a second "temperature derated voltage" for a higher temperature range, the "category voltage". The category voltage (UC) is the maximum DC voltage or peak pulse voltage that may be applied continuously to a capacitor at any temperature within the category temperature range.
The relation between both voltages and temperatures is given in the picture right.
Impedance.
In general, a capacitor is seen as a storage component for electric energy. But this is only one capacitor function. A capacitor can also act as an AC resistor. In many cases the capacitor is used as a decoupling capacitor to filter or bypass undesired biased AC frequencies to the ground. Other applications use capacitors for capacitive coupling of AC signals; the dielectric is used only for blocking DC. For such applications the AC resistance is as important as the capacitance value.
The frequency dependent AC resistance is called impedance formula_16 and is the complex ratio of the voltage to the current in an AC circuit. Impedance extends the concept of resistance to AC circuits and possesses both magnitude and phase at a particular frequency. This is unlike resistance, which has only magnitude.
The magnitude formula_18 represents the ratio of the voltage difference amplitude to the current amplitude, formula_19 is the imaginary unit, while the argument formula_20 gives the phase difference between voltage and current.
In capacitor data sheets, only the impedance magnitude |Z| is specified, and simply written as "Z" so that the formula for the impedance can be written in Cartesian form
where the real part of impedance is the resistance formula_22 (for capacitors formula_23) and the imaginary part is the reactance formula_24.
As shown in a capacitor's series-equivalent circuit, the real component includes an ideal capacitor formula_25, an inductance formula_26 and a resistor formula_27. The total reactance at the angular frequency formula_28 therefore is given by the geometric (complex) addition of a capacitive reactance (Capacitance) formula_29 and an inductive reactance (Inductance): formula_30.
To calculate the impedance formula_16 the resistance has to be added geometrically and then formula_32 is given by
to calculate either the peak or the effective value of the current or the voltage.
In the special case of resonance, in which the both reactive resistances
have the same value (formula_36), then the impedance will only be determined by formula_37.
The impedance specified in the datasheets often show typical curves for the different capacitance values. With increasing frequency as the impedance decreases down to a minimum. The lower the impedance, the more easily alternating currents can be passed through the capacitor. At the apex, the point of resonance, where XC has the same value than XL, the capacitor has the lowest impedance value. Here only the ESR determines the impedance. With frequencies above the resonance the impedance increases again due to the ESL of the capacitor. The capacitor becomes to an inductance.
As shown in the graph, the higher capacitance values can fit the lower frequencies better while the lower capacitance values can fit better the higher frequencies.
Aluminum electrolytic capacitors have relatively good decoupling properties in the lower frequency range up to about 1 MHz due to their large capacitance values. This is the reason for using electrolytic capacitors in standard or switched-mode power supplies behind the rectifier for smoothing application.
Ceramic and film capacitors are already out of their smaller capacitance values suitable for higher frequencies up to several 100 MHz. They also have significantly lower parasitic inductance, making them suitable for higher frequency applications, due to their construction with end-surface contacting of the electrodes. To increase the range of frequencies, often an electrolytic capacitor is connected in parallel with a ceramic or film capacitor.
Many new developments are targeted at reducing parasitic inductance (ESL). This increases the resonance frequency of the capacitor and, for example, can follow the constantly increasing switching speed of digital circuits. Miniaturization, especially in the SMD multilayer ceramic chip capacitors (MLCC), increases the resonance frequency. Parasitic inductance is further lowered by placing the electrodes on the longitudinal side of the chip instead of the lateral side. The "face-down" construction associated with multi-anode technology in tantalum electrolytic capacitors further reduced ESL. Capacitor families such as the so-called MOS capacitor or silicon capacitors offer solutions when capacitors at frequencies up to the GHz range are needed.
Inductance (ESL) and self-resonant frequency.
ESL in industrial capacitors is mainly caused by the leads and internal connections used to connect the capacitor plates to the outside world. Large capacitors tend to have higher ESL than small ones because the distances to the plate are longer and every mm counts as an inductance.
For any discrete capacitor, there is a frequency above DC at which it ceases to behave as a pure capacitor. This frequency, where formula_38 is as high as formula_39, is called the self-resonant frequency. The self-resonant frequency is the lowest frequency at which the impedance passes through a minimum. For any AC application the self-resonant frequency is the highest frequency at which capacitors can be used as a capacitive component.
This is critically important for decoupling high-speed logic circuits from the power supply. The decoupling capacitor supplies transient current to the chip. Without decouplers, the IC demands current faster than the connection to the power supply can supply it, as parts of the circuit rapidly switch on and off. To counter this potential problem, circuits frequently use multiple bypass capacitors—small (100 nF or less) capacitors rated for high frequencies, a large electrolytic capacitor rated for lower frequencies and occasionally, an intermediate value capacitor.
Ohmic losses, ESR, dissipation factor, and quality factor.
The summarized losses in discrete capacitors are ohmic AC losses. DC losses are specified as "leakage current" or "insulating resistance" and are negligible for an AC specification. AC losses are non-linear, possibly depending on frequency, temperature, age or humidity. The losses result from two physical conditions:
The largest share of these losses in larger capacitors is usually the frequency dependent ohmic dielectric losses. For smaller components, especially for wet electrolytic capacitors, conductivity of liquid electrolytes may exceed dielectric losses. To measure these losses, the measurement frequency must be set. Since commercially available components offer capacitance values cover 15 orders of magnitude, ranging from pF (10−12 F) to some 1000 F in supercapacitors, it is not possible to capture the entire range with only one frequency. IEC 60384-1 states that ohmic losses should be measured at the same frequency used to measure capacitance. These are:
A capacitor's summarized resistive losses may be specified either as ESR, as a dissipation factor(DF, tan δ), or as quality factor (Q), depending on application requirements.
Capacitors with higher ripple current formula_40 loads, such as electrolytic capacitors, are specified with equivalent series resistance ESR. ESR can be shown as an ohmic part in the above vector diagram. ESR values are specified in datasheets per individual type.
The losses of film capacitors and some class 2 ceramic capacitors are mostly specified with the dissipation factor tan δ. These capacitors have smaller losses than electrolytic capacitors and mostly are used at higher frequencies up to some hundred MHz. However the numeric value of the dissipation factor, measured at the same frequency, is independent on the capacitance value and can be specified for a capacitor series with a range of capacitance. The dissipation factor is determined as the tangent of the reactance (formula_41) and the ESR, and can be shown as the angle δ between imaginary and the impedance axis.
If the inductance formula_42 is small, the dissipation factor can be approximated as:
Capacitors with very low losses, such as ceramic Class 1 and Class 2 capacitors, specify resistive losses with a quality factor (Q). Ceramic Class 1 capacitors are especially suitable for LC resonant circuits with frequencies up to the GHz range, and precise high and low pass filters. For an electrically resonant system, Q represents the effect of electrical resistance and characterizes a resonator's bandwidth formula_44 relative to its center or resonant frequency formula_45. Q is defined as the reciprocal value of the dissipation factor.
A high Q value is for resonant circuits a mark of the quality of the resonance.
Limiting current loads.
A capacitor can act as an AC resistor, coupling AC voltage and AC current between two points. Every AC current flow through a capacitor generates heat inside the capacitor body. These dissipation power loss formula_47 is caused by formula_48 and is the squared value of the effective (RMS) current formula_49
The same power loss can be written with the dissipation factor formula_51 as
The internal generated heat has to be distributed to the ambient. The temperature of the capacitor, which is established on the balance between heat produced and distributed, shall not exceed the capacitors maximum specified temperature. Hence, the ESR or dissipation factor is a mark for the maximum power (AC load, ripple current, pulse load, etc.) a capacitor is specified for.
AC currents may be a:
Ripple and AC currents mainly warms the capacitor body. By this currents internal generated temperature influences the breakdown voltage of the dielectric. Higher temperature lower the voltage proof of all capacitors. In wet electrolytic capacitors higher temperatures force the evaporation of electrolytes, shortening the life time of the capacitors. In film capacitors higher temperatures may shrink the plastic film changing the capacitor's properties.
Pulse currents, especially in metallized film capacitors, heat the contact areas between end spray (schoopage) and metallized electrodes. This may reduce the contact to the electrodes, heightening the dissipation factor.
For safe operation, the maximal temperature generated by any AC current flow through the capacitor is a limiting factor, which in turn limits AC load, ripple current, pulse load, etc.
Ripple current.
A "ripple current" is the RMS value of a superimposed AC current of any frequency and any waveform of the current curve for continuous operation at a specified temperature. It arises mainly in power supplies (including switched-mode power supplies) after rectifying an AC voltage and flows as charge and discharge current through the decoupling or smoothing capacitor. The "rated ripple current" shall not exceed a temperature rise of 3, 5 or 10 °C, depending on the capacitor type, at the specified maximum ambient temperature.
Ripple current generates heat within the capacitor body due to the ESR of the capacitor. The ESR, composed out of the dielectric losses caused by the changing field strength in the dielectric and the losses resulting out of the slightly resistive supply lines or the electrolyte depends on frequency and temperature. Higher frequencies heighten the ESR and higher temperatures lower the ESR slightly.
The types of capacitors used for power applications have a specified rated value for maximum ripple current. These are primarily aluminum electrolytic capacitors, and tantalum as well as some film capacitors and Class 2 ceramic capacitors.
Aluminium electrolytic capacitors, the most common type for power supplies, experience shorter life expectancy at higher ripple currents. Exceeding the limit tends to result in explosive failure.
Tantalum electrolytic capacitors with solid manganese dioxide electrolyte are also limited by ripple current. Exceeding their ripple limits tends to shorts and burning components.
For film and ceramic capacitors, normally specified with a loss factor tan δ, the ripple current limit is determined by temperature rise in the body of approximately 10 °C. Exceeding this limit may destroy the internal structure and cause shorts.
Pulse current.
The rated pulse load for a certain capacitor is limited by the rated voltage, the pulse repetition frequency, temperature range and pulse rise time. The "pulse rise time" formula_53, represents the steepest voltage gradient of the pulse (rise or fall time) and is expressed in volts per μs (V/μs).
The rated pulse rise time is also indirectly the maximum capacity of an applicable peak current formula_54. The peak current is defined as:
where: formula_54 is in A; formula_25 in µF; formula_53 in V/µs
The permissible pulse current capacity of a metallized film capacitor generally allows an internal temperature rise of 8 to 10 °K.
In the case of metallized film capacitors, pulse load depends on the properties of the dielectric material, the thickness of the metallization and the capacitor's construction, especially the construction of the contact areas between the end spray and metallized electrodes. High peak currents may lead to selective overheating of local contacts between end spray and metallized electrodes which may destroy some of the contacts, leading to increasing ESR.
For metallized film capacitors, so-called pulse tests simulate the pulse load that might occur during an application, according to a standard specification. IEC 60384 part 1, specifies that the test circuit is charged and discharged intermittently. The test voltage corresponds to the rated DC voltage and the test comprises 10000 pulses with a repetition frequency of 1 Hz. The pulse stress capacity is the pulse rise time. The rated pulse rise time is specified as 1/10 of the test pulse rise time.
The pulse load must be calculated for each application. A general rule for calculating the power handling of film capacitors is not available because of vendor-related internal construction details. To prevent the capacitor from overheating the following operating parameters have to be considered:
Higher pulse rise times are permitted for pulse voltage lower than the rated voltage.
Examples for calculations of individual pulse loads are given by many manufactures, e.g. WIMA and Kemet.
AC current.
An AC load only can be applied to a non-polarized capacitor. Capacitors for AC applications are primarily film capacitors, metallized paper capacitors, ceramic capacitors and bipolar electrolytic capacitors.
The rated AC load for an AC capacitor is the maximum sinusoidal effective AC current (rms) which may be applied continuously to a capacitor within the specified temperature range. In the datasheets the AC load may be expressed as
The rated AC voltage for film capacitors is generally calculated so that an internal temperature rise of 8 to 10 °K is the allowed limit for safe operation. Because dielectric losses increase with increasing frequency, the specified AC voltage has to be derated at higher frequencies. Datasheets for film capacitors specify special curves for derating AC voltages at higher frequencies.
If film capacitors or ceramic capacitors only have a DC specification, the peak value of the AC voltage applied has to be lower than the specified DC voltage.
AC loads can occur in AC Motor run capacitors, for voltage doubling, in snubbers, lighting ballast and for power factor correction PFC for phase shifting to improve transmission network stability and efficiency, which is one of the most important applications for large power capacitors. These mostly large PP film or metallized paper capacitors are limited by the rated reactive power VAr.
Bipolar electrolytic capacitors, to which an AC voltage may be applicable, are specified with a rated ripple current.
Insulation resistance and self-discharge constant.
The resistance of the dielectric is finite, leading to some level of DC "leakage current" that causes a charged capacitor to lose charge over time. For ceramic and film capacitors, this resistance is called "insulation resistance Rins". This resistance is represented by the resistor Rins in parallel with the capacitor in the series-equivalent circuit of capacitors.
Insulation resistance must not be confused with the outer isolation of the component with respect to the environment.
The time curve of self-discharge over insulation resistance with decreasing capacitor voltage follows the formula
With stored DC voltage formula_60 and self-discharge constant
Thus, after formula_62 voltage formula_60 drops to 37% of the initial value.
The self-discharge constant is an important parameter for the insulation of the dielectric between the electrodes of ceramic and film capacitors. For example, a capacitor can be used as the time-determining component for time relays or for storing a voltage value as in a sample and hold circuits or operational amplifiers.
Class 1 ceramic capacitors have an insulation resistance of at least 10 GΩ, while class 2 capacitors have at least 4 GΩ or a self-discharge constant of at least 100 s. Plastic film capacitors typically have an insulation resistance of 6 to 12 GΩ. This corresponds to capacitors in the uF range of a self-discharge constant of about 2000–4000 s.
Insulation resistance respectively the self-discharge constant can be reduced if humidity penetrates into the winding. It is partially strongly temperature dependent and decreases with increasing temperature. Both decrease with increasing temperature.
In electrolytic capacitors, the insulation resistance is defined as leakage current.
Leakage current.
For electrolytic capacitors the insulation resistance of the dielectric is termed "leakage current". This DC current is represented by the resistor Rleak in parallel with the capacitor in the series-equivalent circuit of electrolytic capacitors. This resistance between the terminals of a capacitor is also finite. Rleak is lower for electrolytics than for ceramic or film capacitors.
The leakage current includes all weak imperfections of the dielectric caused by unwanted chemical processes and mechanical damage. It is also the DC current that can pass through the dielectric after applying a voltage. It depends on the interval without voltage applied (storage time), the thermic stress from soldering, on voltage applied, on temperature of the capacitor, and on measuring time.
The leakage current drops in the first minutes after applying DC voltage. In this period the dielectric oxide layer can self-repair weaknesses by building up new layers. The time required depends generally on the electrolyte. Solid electrolytes drop faster than non-solid electrolytes but remain at a slightly higher level.
The leakage current in non-solid electrolytic capacitors as well as in manganese oxide solid tantalum capacitors decreases with voltage-connected time due to self-healing effects. Although electrolytics leakage current is higher than current flow over insulation resistance in ceramic or film capacitors, the self-discharge of modern non solid electrolytic capacitors takes several weeks.
A particular problem with electrolytic capacitors is storage time. Higher leakage current can be the result of longer storage times. These behaviors are limited to electrolytes with a high percentage of water. Organic solvents such as GBL do not have high leakage with longer storage times.
Leakage current is normally measured 2 or 5 minutes after applying rated voltage.
Microphonics.
All ferroelectric materials exhibit piezoelectricity a piezoelectric effect. Because Class 2 ceramic capacitors use ferroelectric ceramics dielectric, these types of capacitors may have electrical effects called microphonics. Microphonics (microphony) describes how electronic components transform mechanical vibrations into an undesired electrical signal (noise). The dielectric may absorb mechanical forces from shock or vibration by changing thickness and changing the electrode separation, affecting the capacitance, which in turn induces an AC current. The resulting interference is especially problematic in audio applications, potentially causing feedback or unintended recording.
In the reverse microphonic effect, varying the electric field between the capacitor plates exerts a physical force, turning them into an audio speaker. High current impulse loads or high ripple currents can generate audible sound from the capacitor itself, draining energy and stressing the dielectric.
Dielectric absorption (soakage).
Dielectric absorption occurs when a capacitor that has remained charged for a long time discharges only incompletely when briefly discharged. Although an ideal capacitor would reach zero volts after discharge, real capacitors develop a small voltage from time-delayed dipole discharging, a phenomenon that is also called dielectric relaxation, "soakage" or "battery action".
In many applications of capacitors dielectric absorption is not a problem but in some applications, such as long-time-constant integrators, sample-and-hold circuits, switched-capacitor analog-to-digital converters, and very low-distortion filters, it is important that the capacitor does not recover a residual charge after full discharge, and capacitors with low absorption are specified.
The voltage at the terminals generated by the dielectric absorption may in some cases possibly cause problems in the function of an electronic circuit or can be a safety risk to personnel. In order to prevent shocks most very large capacitors are shipped with shorting wires that need to be removed before they are used.
Energy density.
The capacitance value depends on the dielectric material (ε), the surface of the electrodes (A) and the distance (d) separating the electrodes and is given by the formula of a plate capacitor:
The separation of the electrodes and the voltage proof of the dielectric material defines the breakdown voltage of the capacitor. The breakdown voltage is proportional to the thickness of the dielectric.
Theoretically, given two capacitors with the same mechanical dimensions and dielectric, but one of them have half the thickness of the dielectric. With the same dimensions this one could place twice the parallel-plate area inside. This capacitor has theoretically 4 times the capacitance as the first capacitor but half of the voltage proof.
Since the energy density stored in a capacitor is given by:
thus a capacitor having a dielectric half as thick as another has 4 times higher capacitance but ½ voltage proof, yielding an equal maximum energy density.
Therefore, dielectric thickness does not affect energy density within a capacitor of fixed overall dimensions. Using a few thick layers of dielectric can support a high voltage, but low capacitance, while thin layers of dielectric produce a low breakdown voltage, but a higher capacitance.
This assumes that neither the electrode surfaces nor the permittivity of the dielectric change with the voltage proof. A simple comparison with two existing capacitor series can show whether reality matches theory. The comparison is easy, because the manufacturers use standardized case sizes or boxes for different capacitance/voltage values within a series.
In reality modern capacitor series do not fit the theory. For electrolytic capacitors the sponge-like rough surface of the anode foil gets smoother with higher voltages, decreasing the surface area of the anode. But because the energy increases squared with the voltage, and the surface of the anode decreases lesser than the voltage proof, the energy density increases clearly. For film capacitors the permittivity changes with dielectric thickness and other mechanical parameters so that the deviation from the theory has other reasons.
Comparing the capacitors from the table with a supercapacitor, the highest energy density capacitor family. For this, the capacitor 25 F/2.3 V in dimensions D × H = 16 mm × 26 mm from Maxwell HC Series, compared with the electrolytic capacitor of approximately equal size in the table. This supercapacitor has roughly 5000 times higher capacitance than the 4700/10 electrolytic capacitor but ¼ of the voltage and has about 66,000 mWs (0.018 Wh) stored electrical energy, approximately 100 times higher energy density (40 to 280 times) than the electrolytic capacitor.
Long time behavior, aging.
Electrical parameters of capacitors may change over time during storage and application. The reasons for parameter changings are different, it may be a property of the dielectric, environmental influences, chemical processes or drying-out effects for non-solid materials.
Aging.
In ferroelectric Class 2 ceramic capacitors, capacitance decreases over time. This behavior is called "aging". This aging occurs in ferroelectric dielectrics, where domains of polarization in the dielectric contribute to the total polarization. Degradation of polarized domains in the dielectric decreases permittivity and therefore capacitance over time. The aging follows a logarithmic law. This defines the decrease of capacitance as constant percentage for a time decade after the soldering recovery time at a defined temperature, for example, in the period from 1 to 10 hours at 20 °C. As the law is logarithmic, the percentage loss of capacitance will twice between 1 h and 100 h and 3 times between 1 h and 1,000 h and so on. Aging is fastest near the beginning, and the absolute capacitance value stabilizes over time.
The rate of aging of Class 2 ceramic capacitors depends mainly on its materials. Generally, the higher the temperature dependence of the ceramic, the higher the aging percentage. The typical aging of X7R ceramic capacitors is about 2.5&nbs;% per decade. The aging rate of Z5U ceramic capacitors is significantly higher and can be up to 7% per decade.
The aging process of Class 2 ceramic capacitors may be reversed by heating the component above the Curie point.
Class 1 ceramic capacitors and film capacitors do not have ferroelectric-related aging. Environmental influences such as higher temperature, high humidity and mechanical stress can, over a longer period, lead to a small irreversible change in the capacitance value sometimes called aging, too.
The change of capacitance for P 100 and N 470 Class 1 ceramic capacitors is lower than 1%, for capacitors with N 750 to N 1500 ceramics it is ≤ 2%. Film capacitors may lose capacitance due to self-healing processes or gain it due to humidity influences. Typical changes over 2 years at 40 °C are, for example, ±3 % for PE film capacitors and ±1 % PP film capacitors.
Life time.
Electrolytic capacitors with non-solid electrolyte age as the electrolyte evaporates. This evaporation depends on temperature and the current load the capacitors experience. Electrolyte escape influences capacitance and ESR. Capacitance decreases and the ESR increases over time. In contrast to ceramic, film and electrolytic capacitors with solid electrolytes, "wet" electrolytic capacitors reach a specified "end of life" reaching a specified maximum change of capacitance or ESR. End of life, "load life" or "lifetime" can be estimated either by formula or diagrams or roughly by a so-called "10-degree-law". A typical specification for an electrolytic capacitor states a lifetime of 2,000 hours at 85 °C, doubling for every 10 degrees lower temperature, achieving lifespan of approximately 15 years at room temperature.
Supercapacitors also experience electrolyte evaporation over time. Estimation is similar to wet electrolytic capacitors. Additional to temperature the voltage and current load influence the life time. Lower voltage than rated voltage and lower current loads as well as lower temperature extend the life time.
Failure rate.
Capacitors are reliable components with low failure rates, achieving life expectancies of decades under normal conditions. Most capacitors pass a test at the end of production similar to a "burn in", so that early failures are found during production, reducing the number of post-shipment failures.
Reliability for capacitors is usually specified in numbers of Failures In Time (FIT) during the period of constant random failures. FIT is the number of failures that can be expected in one billion (109) component-hours of operation at fixed working conditions (e.g. 1000 devices for 1 million hours, or 1 million devices for 1000 hours each, at 40 °C and 0.5 UR). For other conditions of applied voltage, current load, temperature, mechanical influences and humidity the FIT can recalculated with terms standardized for industrial or military contexts.
Additional information.
Soldering.
Capacitors may experience changes to electrical parameters due to environmental influences like soldering, mechanical stress factors (vibration, shock) and humidity. The greatest stress factor is soldering. The heat of the solder bath, especially for SMD capacitors, can cause ceramic capacitors to change contact resistance between terminals and electrodes; in film capacitors, the film may shrink, and in wet electrolytic capacitors the electrolyte may boil. A recovery period enables characteristics to stabilize after soldering; some types may require up to 24 hours. Some properties may change irreversibly by a few per cent from soldering.
Electrolytic behavior from storage or disuse.
Electrolytic capacitors with non-solid electrolyte are "aged" during manufacturing by applying rated voltage at high temperature for a sufficient time to repair all cracks and weaknesses that may have occurred during production. Some electrolytes with a high water content react quite aggressively or even violently with unprotected aluminum. This leads to a "storage" or "disuse" problem of electrolytic capacitors manufactured before the 1980s. Chemical processes weaken the oxide layer when these capacitors are not used for too long. New electrolytes with "inhibitors" or "passivators" were developed during the 1980s to solve this problem.
As of 2012 the standard storage time for electronic components of two years at room temperature substantiates (cased) by the oxidation of the terminals will be specified for electrolytic capacitors with non-solid electrolytes, too. Special series for 125 °C with organic solvents like GBL are specified up to 10 years storage time ensure without pre-condition the proper electrical behavior of the capacitors.
For antique radio equipment, "pre-conditioning" of older electrolytic capacitors may be recommended. This involves applying the operating voltage for some 10 minutes over a current limiting resistor to the terminals of the capacitor. Applying a voltage through a safety resistor repairs the oxide layers.
IEC/EN standards.
The tests and requirements to be met by capacitors for use in electronic equipment for approval as standardized types are set out in the generic specification IEC/EN 60384-1 in the following sections.
Ceramic capacitors
Film capacitors
Electrolytic capacitors
Supercapacitors
Markings.
Imprinted.
Capacitors, like most other electronic components and if enough space is available, have imprinted markings to indicate manufacturer, type, electrical and thermal characteristics, and date of manufacture. If they are large enough the capacitor is marked with:
Polarized capacitors have polarity markings, usually "-" (minus) sign on the side of the negative electrode for electrolytic capacitors or a stripe or "+" (plus) sign, see #Polarity marking. Also, the negative lead for leaded "wet" e-caps is usually shorter.
Smaller capacitors use a shorthand notation. The most commonly used format is: XYZ J/K/M VOLTS V, where XYZ represents the capacitance (calculated as XY × 10Z pF), the letters J, K or M indicate the tolerance (±5%, ±10% and ±20% respectively) and VOLTS V represents the working voltage.
Examples:
Capacitance, tolerance and date of manufacture can be indicated with a short code specified in IEC/EN 60062. Examples of short-marking of the rated capacitance (microfarads): µ47 = 0,47 µF, 4µ7 = 4,7 µF, 47µ = 47 µF
The date of manufacture is often printed in accordance with international standards.
For very small capacitors like MLCC chips no marking is possible. Here only the traceability of the manufacturers can ensure the identification of a type.
Colour coding.
Capacitors do not use color coding.
Polarity marking.
Aluminum e-caps with non-solid electrolyte have a polarity marking at the cathode (minus) side. Aluminum, tantalum, and niobium e-caps with solid electrolyte have a polarity marking at the anode (plus) side. Supercapacitor are marked at the minus side. | 14,985 |
Electronics/Resistors. Resistor.
A resistor is a block or material that limits the flow of current. The greater the resistance, the lower the current will be, assuming the same voltage imposed on the resistor. The hydraulic analogy of a resistor would be the pipe with water flowing through it. The wider the diameter of a pipe, the higher the water flow through the pipe, assuming the same pressure difference on the terminals of a pipe.
Resistor's Symbol.
Resistors have two leads (points of contact) to which the resistor can be connected to an electrical circuit. A symbol for a resistor used in electrical circuit diagrams is shown below.
The endpoints at the left and right sides of the symbol indicate the points of contact for the resistor. The ratio of the voltage to current will always be positive, since a higher voltage on one side of a resistor is a positive voltage, and a current will flow from the positive side to the negative side, resulting in a positive current. If the voltage is reversed, the current is reversed, leading again to a positive resistance.
Resistance.
Resistance is a characteristic of Resistor indicates the measurement of current opposition . Resistance has a symbol R measured in Ohm (Ω) . The ratio of voltage to current is referred to as Ohm's Law, and is one of the most basic laws that govern electronics.
An ohm is the amount of resistance which passes one ampere of current when a one volt potential is placed across it. (The ohm is actually defined as the resistance which dissipates one watt of power when one ampere of current is passed through it.)
Resistance can vary from very small to very large. A superconductor has zero resistance, while something like the input to an op-amp can have a resistance near 1012 Ω, and even higher resistances are possible.
Resistance and Temperature.
For most materials, resistance increases with increasing Temperature
Resistance and Electric Power Loss.
Resistance converts Electrical Energy into Heat this causes Electric Energy Loss.
NOTE : Resistors which dissipate large amounts of power are cooled so that they are not destroyed, typically with finned heatsinks.
If Electric Energy Supply is Pv and Electric Energy Loss is Pr Then, Electric Energy Delivered is
The ratio of Electric Energy Delivered over Electric Energy Supplied indicates the Efficiency of Electric Power Supply
Resistor's Labeling (See also Identification).
A manufactured resistor is usually labeled with the nominal value (value to be manufactured to) and sometimes a tolerance. Rectangular resistors will usually contain numbers that indicate a resistance and a multiplier. If there are three or four numbers on the resistor, the first numbers are a resistance value, and the last number refers to the number of zeroes in the multiplier. If there is an R in the value, the R takes the place of the decimal point.
Cylindrical resistors (axial) usually have colored bands that indicate a number and a multiplier. Resistance bands are next to each other, with a tolerance band slightly farther away from the resistance bands. Starting from the resistance band side of the resistor, each colour represents a number in the same fashion as the number system shown above.
Colour System
Clue : B.B.ROY of Great Britain was a Very Good Worker.
Additional Colours: A gold band in the multiplier position means 0.1, but means a 5% tolerance in the tolerance position. A silver band in the multiplier position means 0.01, but means 10% in the tolerance position.
Resistor's Construction.
The resistance "R" of a component is dependent on its physical dimension and can be calculated using:
where
If you increase "ρ" or "L" you increase the resistance of the material, but if you increase "A" you decrease the resistance of the material.
Resistivity of the Material.
Every material has its own resistivity, depending on its physical makeup. Most metals are conductors and have very low resistivity; whereas, insulators such as rubber, wood, and air all have very high resistivity. The inverse of resistivity is conductivity, which is measured in units of Siemens/metre (S/m) or, equivalently. mhos/metre.
In the following chart, it is not immediately obvious how the unit ohm-meter is selected. Considering a solid block of the material to be tested, one can readily see that the resistance of the block will decrease as its cross-sectional area increases (thus widening the conceptual "pipe"), and will increase as the length of the block increases (lengthening the "pipe"). Given a fixed length, the resistance will increase as the cross-sectional area decreases; the resistance, multiplied by the area, will be a constant. If the cross-sectional area is held constant, as the length is increased, the resistance increases in proportion, so the resistance divided by the length is similarly a constant. Thus the bulk resistance of a material is typically measured in ohm meters squared per meter, which simplifies to ohm - meter (Ω-m).
Silver, copper, gold, and aluminum are popular materials for wires, due to low resistivity. Silicon and germanium are used as semiconductors. Glass, rubber, quartz crystal, and air are popular dielectrics, due to high resistivity.
Many materials, such as air, have a non-linear resistance curve. Normal undisturbed air has a high resistance, but air with a high enough voltage applied will become ionized and conduct very easily.
The resistivity of a material also depends on its temperature. Normally, the hotter an object is, the more resistance it has. At high temperatures, the resistance is proportional to the absolute temperature. At low temperatures, the formula is more complicated, and what counts as a high or low temperature depends on what the resistor is made from. In some materials the resistivity drops to zero below a certain temperature. This is known as superconductivity, and has many useful applications.
For all resistors, the "change" in resistance for a "small" increase in temperature is "directly proportional" to the "change" in temperature.
Current passing through a resistor will warm it up.
Many components have heat sinks to dissipate that heat. The heatsink keeps the component from melting or setting something on fire.
Length.
The length of an object is directly proportional to its resistance. As shown in the diagram below, 1 unit cubed of material has 1 ohm of resistance. However, when 4 units are stacked lengthwise and a connection is made to the front and back sides respectively, the total resistance is 4 ohms. This is because the length of the unit is 4, whereas the cross-sectional area remains 1. However, if you were to make connections on the sides, the exact opposite would be true: the cross-sectional area would be 4 and the length 1, resulting in 0.25 ohms total resistance.
Cross-Sectional Area.
Increasing area is the same as having resistors in parallel, so as you increase the area you add more paths for current to take.
The resistance of a material is inversely proportional to its cross-sectional area. This is shown in the diagram below, where 1 unit cubed has one ohm of resistance. However, if 4 units cubed are stacked on top of each other in the fashion such that there is 4 units squared of cross-sectional area, and the electrical connections are made to the front and back such that the connections are on the largest sides, the resultant resistance would be 0.25 ohms.
Additional note: There are two reasons why a small cross-sectional area tends to raise resistance. One is that the electrons, all having the same negative charge, repel each other. Thus there is resistance to many being forced into a small space. The other reason is that they collide, causing "scattering," and therefore they are diverted from their original directions. (More discussion is on page 27 of "Industrial Electronics," by D. J. Shanefield, Noyes Publications, Boston, 2001.)
Example.
For instance, if you wanted to calculate the resistance of a 1 cm high, 1 cm wide, 5 cm deep block of copper, as shown in the diagram below:
You would first need to decide how it's oriented. Suppose you want to use it from front to back (lengthwise), like a piece of wire, with electrical contacts on the front and rear faces. Next you need to find the length, L. As shown, it is 5 cm long (0.05 m). Then, we look up the resistivity of copper on the table, 1.6×10-8 Ω-meters. Lastly, we calculate the cross-sectional area of the conductor, which is 1 cm × 1 cm = 1 cm2 (0.0001 m2). Then, we put it all in the formula, converting cm to m:
formula_12
units m2 cancel:
formula_13
Which, after evaluating, gives you a final value of 8.0×10-6 Ω, or 8 microohms, a very small resistance. The method shown above included the units to demonstrate how the units cancel out, but the calculation will work as long as you use consistent units.
Resistor Connection.
Resistors in Series.
Resistors in series are equivalent to having one long resistor. If the properties of two resistors are equivalent, except the length, the final resistance will be the sum of the two construction methods:
This means that the resistors add when in series.
Resistors in Parallel.
In a parallel circuit, current is divided among multiple paths. This means that two resistors in parallel have a lower equivalent resistance than either of the parallel resistors, since both resistors allow current to pass. Two resistors in parallel will be equivalent to a resistor that is twice as wide:
Since conductances (the inverse of resistance) add in parallel, you get the following equation:
For example, two 4 Ω resistors in parallel have an equivalent resistance of only 2 Ω.
To simplify mathematical equations, resistances in parallel can be represented with two vertical lines "||" (as in geometry). For two resistors the parallel formula simplifies to:
Combinations of series and parallel.
Resistors in parallel are evaluated as if in a mathematical set of "parentheses." The most basic group of resistors in parallel is evaluated first, then the group in series with the new equivalent resistor, then the next group of resistors in parallel, and so on. For example, the above portion would be evaluated as follows:
Specifications.
Resistors are available as pre-fabricated, real-world components. The behavior of such components deviates from an ideal resistor in certain ways. Therefore, real-world resistors are not only specified by their resistance, but also by other parameters. In order to select a manufactured resistance, the entire range of specifications should be considered. Usually, exact values do not need to be known, but ranges should be determined.
Nominal Resistance.
The nominal resistance is the resistance that can be expected when ordering a resistor. Finding a range for the resistance is necessary, especially when operating on signals. Resistors do not come in all of the values that will be necessary. Sometimes resistor values can be manipulated by shaving off parts of a resistor (in industrial environments this is sometimes done with a LASER to adjust a circuit), or by combining several resistors in series and parallel.
Available resistor values typically come with a resistance value from a so called resistor series. Resistor series are sets of standard, predefined resistance values. The values are actually made up from a geometric sequence within each decade. In every decade there are supposed to be formula_23 resistance values, with a constant step factor. The standard resistor values within a decade are derived by using the step factor formula_24
rounded to a two digit precision. Resistor series are named Eformula_23, according to the used value of formula_23 in the above formula.
n Values/Decade Step factor i Series
6 1.47 E6
12 1.21 E12
24 1.10 E24
48 1.05 E48
For example, in the E12 series for formula_28, the resistance steps in a decade are, after rounding the following 12 values:
1.00, 1.20, 1.50, 1.80, 2.20, 2.70,
3.30, 3.90, 4.70, 5.60, 6.80, and 8.20
and actually available resistors from the E12 series are for example resistors with a nominal value of 120Ω or 4.7kΩ.
Tolerances.
A manufactured resistor has a certain tolerance to which the resistance may differ from the nominal value. For example, a 2kΩ resistor may have a tolerance of ±5%, leaving a resistor with a value between 1.9kΩ and 2.1kΩ (i.e. 2kΩ±100Ω). The tolerance must be accounted for when designing circuits. A circuit with an absolute voltage of 5V±0.0V in a voltage divider network with two resistors of 2kΩ±5% will have a resultant voltage of 5V±10% (i.e. 5V±0.1V). The final resistor tolerances are found by taking the derivative of the resistor values, and plugging the absolute deviations into the resulting equation.
The above mentioned E-series which are used to provide standardized nominal resistance values, are also coupled to standardized nominal tolerances. The fewer steps within a decade there are, the larger the allowed tolerance of a resistor from such a series is. More precises resistors, outside of the mentioned E-series are also available, e.g. for high-precision measurement equipment. Common tolerances, colors and key characters used to identify them are for example:
Series Values/Decade Tolerance Color Code Character Code
E6 6 ±20% [none] [none]
E12 12 ±10% silver K
E24 24 ±5% gold J
E48 48 ±2% red G
- - ±1% brown F
- - ±0.5% - D
- - ±0.25% - C
- - ±0.1% - B
Resistor manufacturers can benefit from this standardization. They manufacture resistors first, and afterwards they measure them. If a resistor does not meet the nominal value within the defined tolerance of one E-series, it might still fit into a lower series, and doesn't have to be thrown away, but can be sold as being compliant to that lower E-series standard. Although typically at a lower price.
Series: Resistors that combine in series add the nominal tolerances together.
Parallel: Resistors that combine in parallel have a combined tolerance that is slightly more complex.
Power Rating.
Because the purpose of a resistor is to dissipate power in the form of heat, the resistor has a rating (in watts) at which the resistor can continue to dissipate before the temperature overwhelms the resistor and causes it to overheat. When a resistor overheats, the material begins to melt away, which will cause the resistance to increase (usually), until the resistor breaks.
Operating Temperature.
Related to power rating, the operating temperature is the temperature that the resistor can continue to operate before being destroyed.
Maximum Voltage.
In order to avoid sparkovers or material breakdown a certain maximum voltage over a resistor must not be exceeded. The maximum voltage is part of a resistor's specification, and typically a function of the resistor's physical length, distance of the leads, material and coating.
For example, a resistor with a maximum operating voltage of 1kV can have a length in the area of 2", while a 0.3" resistor can operate under up to several tens of volts, probably up to a hundred volts. When working with dangerous voltages it is essential to check the actual specification of a resistor, instead of only trusting it because of the length.
Temperature Coefficient.
This parameter refers to the constant in which the resistance changes per degree Celsius (units in C-1). The change in temperature is not linear over the entire range of temperatures, but can usually be thought of as linear around a certain range (usually around room temperature). However, the resistance should be characterized over a large range if the resistor is to be used as a thermistor in those ranges. The simplified linearized formula for the affect on temperature to a resistor is expressed in an equation:
Capacity and Inductance.
Real world resistors not only show the physical property of resistance, but also have a certain capacity and inductance. These properties start to become important, if a resistor is used in some high frequency circuitry. Wire wound resistors, for example, show an inductance which typically make them unusable above 1kHz.
Packaging.
Resistors can be packaged in any way possible, but are divided into surface mount, through hole, soldering tag and a few more forms. Surface mount is connected to the same side that the resistor is on. Through hole resistors have leads (wires) that typically go through the circuit board and are soldered to the board on the side opposite the resistor, hence the name. Resistors with leads are also used in point-to-point circuits without circuit boards. Soldering tag resistors have lugs to solder wires or high current connectors onto.
Usual packages for surface mount resistors are rectangular, referenced by a length and a width in mils (thousands of an inch). For instance, an 0805 resistor is a rectangle with length .08" x .05", with contacts (metal that connects to the resistor) on either side. Typical through hole resistors are cylindrical, referenced either by the length (such as 0.300") or by a typical power rating that is common to the length (a 1/4W resistor is typically 0.300"). This length does not include the length of the leads. | 4,199 |
Microeconomics. Preface.
The goal of this book is to explain how people interact economically, understanding the relationship between people, supply and demand, markets, and efficiency. We will do this by first understanding the nature of the basics concepts of microeconomics, then proceeding to the application of the concepts in specific types of situations.
Readers are expected to have an understanding of arithmetics as well as basic differential calculus. Where needed, we use R for statistical programming. The graphics are also created using R, the needed code can be revealed by clicking on the graphic. | 124 |
Electronics/RC. Introduction.
An RC circuit is short for 'Resistor-Capacitor' circuit. A capacitor takes an infinite amount of time to discharge through a resistor, which varies with the values of the resistor and capacitor. A capacitor acts interestingly in an electronic circuit, practically speaking as a combination of a voltage source and a variable resistor.
Basics.
Below is a simple RC circuit:<br>
<br>
There is a capacitor in parallel with the resistor and current probe. The way the capacitor functions is by acting as a very low resistance load when the circuit is initially turned on. This is illustrated below:<br>
<br>
Initially, the capacitor has a very low resistance, almost 0. Since electricity takes the path of least resistance, almost all the electricity flows through the capacitor, not the resistor, as it has considerably higher resistance. As a capacitor charges, its resistance increases as it gains more and more charge. As the resistance of the capacitor climbs, electricity begins to flow not only to the capacitor, but through the resistor as well:<br>
<br>
Once the capacitor's voltage equals that of the battery, meaning it is fully charged, it will not allow any current to pass through it. All the electricity eventually flows through the resistor.<br>
<br>
A capacitor's resistance becomes higher and higher as it becomes more charged. Once it is fully charged, for all practical reasons, it has infinite resistance (an open connection). Once the voltage source is disconnected, however, the capacitor acts as a voltage source itself:<br>
<br>
As time goes on, the capacitor's charge begins to drop, and so does its voltage. This means less current through the resistor:<br>
<br>
Once the capacitor is fully discharged, you are back to square one:<br>
<br>
If one were to do this with a light and a capacitor connected to a battery, what you would see is the following:
This is how a capacitor acts. However, what if you changed the values of R1? C1? The voltage of the battery? We will examine the mathematical relationship between the resistor, capacitor, and charging rate below.
The Time Constant.
In order to find out how long it takes for a capacitor to fully charge or discharge, or how long it takes for the capacitor to reach a certain voltage, you must know a few things. First, you must know the starting and finishing voltages. Secondly, you must know the time constant of the circuit you have. Time constant is denoted by the Greek letter 'tau' or τ. The general formula for percentage change is:<br> | 667 |
Puzzles/Arithmetical puzzles/Hotel Refund. Puzzles | Arithmetical puzzles | Hotel refund
Three men stop at a hotel. There's only one room left, so they agree to share. The desk clerk charges them thirty dollars, and they each give him ten dollars.
Later, the clerk realizes he's over-charged them by five dollars. He gives the bell-boy five one-dollar bills, and tells him to return the money to the three men. The bell-boy keeps two dollars for himself, and gives one dollar to each of the three men.
So, the men paid nine dollars each for the room, for a total of twenty-seven dollars. The bell-hop has two dollars, and that makes twenty-nine. What happened to the other dollar?
And another thing. Two men stop at the same hotel. There's only one room left, so they agree to share. The desk clerk charges them thirty dollars, and they each give him fifteen dollars.
Later, the clerk realizes that once "again" he has over-charged by five dollars. He gives the bell-boy five one-dollar bills, and tells him to return the money to the two men. The bell-boy, feeling slightly more daring, keeps three dollars for himself, and gives one dollar to each of the two men.
So, the men paid fourteen dollars each for the room, for a total of twenty-eight dollars. The bell-boy has three dollars, and that makes thirty-one. Where did the other dollar come from? And, no, you better not answer that it came from the first puzzle.
solution | 367 |
Puzzles/Arithmetical puzzles/Hotel Refund/Solution. Puzzles | Arithmetical puzzles | Hotel refund | Solution
The men paid $27 dollars. The desk clerk has $25 dollars and the bell-hop pocketed $2.
The mistake is expecting that what the men paid and what the bell-boy kept to add up to what the men initially gave the desk clerk. In fact, it is the amount that the room effectively cost them, plus the amount they received back, that should add to $30.
The second puzzle is very similar: $25 is sitting with the clerk, $2 with the men, and $3 with the bellhop. That adds to the required $30. | 163 |
Cell Biology/History. Some History of the development of understanding of the Cell.
The origin of the idea that living organisms are made of cells is often traced back to observations of thin slices of cork. In 1665 the book "Micrographia: Some physiological descriptions of minute bodies made by magnifying glasses" was published by Robert Hooke. He wrote:
We now know that the "cells" Hooke observed were an indication of the cellular structure of multi-cellular organisms. During the 1670s, Antony van Leeuwenhoek used microscopes to observe sperm, red blood cells, and protozoa. While many cells are about 10 microns in diameter, some protozoa are visible to the naked eye, reaching over 1 millimeter in length. Leewenhoek is the inventor of the microscope. Thus, while it is true that the small size of most cells made it difficult to develop the theory that all living organisms are composed of cells, it was also difficult to recognize that living cells have certain functional components such as the nucleus and a surface membrane that allow cells to exist as the basic functional components of all living organisms. In 1833 Robert Brown published a report describing microscopic observations of plant cells in which he used first used the term "cell nucleus":
Such observations of the microscopic cellular components of cells helped make it possible for Schleiden and Schwann to propose a cell theory specifying that nucleated cells are key structural and functional units in plants and animals (1832-1838). However, they did not understand cell reproduction. About this time microscopists such as the Belgian botanist Barthelemy C. Dumortier observed and reported the binary fission of cells. By 1879 the zoologist Walther Flemming was using chemical staining of "fixed" cells to allow clear visualization of chromosomes during cell division.
During the 1890s, Ernest Overton, developed a theory of lipid membrane structure and function, based largely on the osmotic properties of cells. Visualization of lipid bilayer membranes at the surface of cells had to wait until the development of electron microscopy. | 501 |
Electronics/Static Electricity. Static Electricity.
"This is a rough draft."
"As this is a book, it should have historical stories and stuff to make it more interesting. Greeks and amber in this section, for instance."
When a solitary atom has the same number of electrons and protons, it has no overall charge. The individual charges cancel out. It is said to be "neutral".
An atom that has more electrons than protons is negatively charged. The atom will have a tendency to attract other particles that have a positive charge, and repel particles with a negative charge.
An atom that has less electrons than protons is positively charged. The atom will attract negative particles (like solitary electrons or negatively charged atoms) and repel positive particles (like solitary protons or positively charged atoms).
If a solitary proton and electron are placed near each other (or even far away, as long as nothing else is nearby), they will move closer together, until the electron becomes "attached" to the proton and they form a hydrogen atom. An atom of metal that is positively charged (missing electrons) and a free electron will behave the same way.
The same goes for macroscopic objects. A metal sphere that has a significant amount of atoms that have the same number of electrons and protons is neutral. Also, if there are several atoms that are positively charged or negatively charged, it is said that the whole object is charged. This may not be noticeable if only a few atoms on the object are charged.
Charged metal spheres will attract and repel each other according to the same rules as individual particles.
A solitary metal sphere with an excess of electrons will tend to have the extra electrons spread out evenly across the surface of the sphere (not in the interior). This is because the electrons repel each other, and try to get as far apart as possible. On a positively charged sphere, the positive charge (absence of electrons) also spreads evenly across the surface due to its lack of electrons. (Talk about the neat shielding properties of Faraday cages) In the space inside to the sphere there is no charge.
In the case of insulating spheres charge does not move throughout the object, it just sits there. The electrons in this object are not constantly moving from atom to atom, so the empty holes have no way to be filled by their neighbors.
A Van de Graaff generator is basically a pump for electrons (or a "charge pump"). It uses the triboelectric effect to take electrons from one conductor and deposit them on another. The triboelectric effect is caused when two different materials are brought into contact and then separated. One material will have more of a tendency to attract extra electrons, and some of the electrons will transfer from one material to the other. The Van de Graaff generator accomplishes this with a silk or rubber belt held tightly between two rollers of different materials. As the belt comes into contact with one roller and then separates, it picks up charge from the roller. When it comes into contact with the other roller and then separates, it deposits the charge.
It thus makes one roller positively charged and the other negatively charged. The electrons are supplied to one roller and extracted from the other by metal brushes, connected to the large conductors. This creates a voltage between the conductors, due to their distance.
"(Should we really be going into so much detail about it though?... I guess as an example of a very basic electric circuit, it is a good example. Maybe we could just link to Wikipedia triboelectric effect? That's the thing I don't like about wikibooks. You have to provide all of the background instead of just directing them to it.)" | 837 |
Electronics/Formulas. Resistance and Temperture.
Resistance of a conductor increase with increasing temperature
Power Delivered.
Electric Power delivered through resistive network is equal to Electric Power Supply minus Electric Power Loss as Heat through resistance of the resistive network | 62 |
Electronics/TTL. Introduction.
<br>
TTL stands for Transistor-Transistor Logic. It is the system based on combining transistors in such a way that they can be used for logic gates. Transistors have the capability of becoming parts of very complex devices when combined. An average microprocessor uses upwards of 40 million transistors. Transistors in microprocessors, however, are microscopic as opposed to the discrete components used in consumer electronics and circuitboards.
The NOT Gate.
The NOT gate works by inverting the input. The TTL version of the NOT gate contains one transistor, seen below: <br>
When the input, A, is high (+5V), the base of the transistor is saturated, allowing current to flow from the collector of the transistor to the emitter. Since this is possible, the current does not take the higher resistance path through the output (assuming it has a resistive load attached to it such as an LED). When the input is low (0V), the current has no choice but to flow out of the inverted A output (the A with the line overtop to indicate it is negated). The two resistors in the circuit are for limiting current as to not destroy the transistor, and sometimes may not even be required depending on the transistor.
To further explain, the NOT gate has been integrated into a circuit by connecting it to a current probe and a battery. When the switch for the input of the not gate is not hit, the current flows in the path indicated by the red diagram below. The current flows through the resistor because the transistor does not conduct when the base is not saturated.:<br>
However, when the switch is hit, making the input high, the circuit is shorted and current flows directly from one terminal of the battery through the transistor, to the other terminal. This is illustrated further in the next figure:<br><br>
<br><br>
In real logic gates, several more transistors are used in order to stabilize the input and output. Although this may seem like a large hike in complexity and price, creating transistors in ICs is a lot cheaper and easier to do, as they do not have to even have a shell or casing, and are a lot smaller. | 540 |
Russian/Lesson 3. This means "I am a student" in Russian.
Examples
Russian has eight personal pronouns altogether:
Grammar vs. vocabulary; "getting by" vs. "good Russian".
Are you learning Russian to "get by" on a one-week business trip to Moscow? Or do you want to learn "good Russian"?
To "get by" you need basic grammar, but not the byzantine grammar of "good Russian." You could treat all nouns as if they were masculine, and all verbs as if you are the person doing the action, and Russians would understand your meaning. But you should read over the many grammar rules so that you have a clue what Russians are saying. E.g., you should be able to recognize when a Russian uses the prepositional case, even if you only use the nominative case.
If you want to marry a Russian, learn good Russian. Russians (and people all over the world) are impressed by good language skills. Note that in English the words "conjugate" (to produce the different forms of a verb) and "conjugal" (relating to marriage) come from the same root word (meaning "to join together"). In other words, Russians think that someone who can say "I study, you study, he studies, she studies, we study, they study" correctly (in Russian) will make a good spouse!
Native speakers learn grammar as children, by listening to adults talk, and being corrected by their peers. A child who reads a lot, and whose parents speak correctly, doesn't need to learn grammar rules. As an adult learning Russian, you'll learn best if a native Russian listens to you and corrects your mistakes. But the grammar rules will act as shortcuts, to help you learn faster.
When learning anything, some people are auditory learners, some are visual, and some are movement learners. (See "The Open Mind," by Dawna Marcova, for more about this.) But all three learning styles are needed for organizing and committing to long-term memory. You may prefer to hear spoken Russian, or see written Russian, or (for movement learners) write a Russian word and then write how it sounds in English. You may need to do an activity, such as cooking dinner, to pay attention. But all of us need to do all of these things to learn well.
Gender.
You may guess correctly that the correct way to say ""He" is a student" in Russian is "Он студент." However, things change a bit when talking about "она". As in many Indo-European languages—including English until several hundred years ago—"gender" is an important feature of Russian grammar. Every noun, as well as the three third-person singular pronouns, has a characteristic gender: masculine, feminine, or neuter.
Masculine nouns end in a consonant. Remember that й is a consonant.
Feminine nouns end in а or я.
Neuter nouns end in о or е.
Nouns ending in ь can be masculine or feminine. Nouns ending in ь that describe abstract concepts are generally feminine, but otherwise there's no rule; you just have to memorize these words.
quiz.
<quiz display=simple>
- masculine
+ feminine
- neuter
</quiz>
Formal and Informal.
Russians differentiate between formal and informal social relationships. Two words translate to "you": Вы (pronounced "vee" but make it short, don't draw out the vowel) is how you say "you" to a teacher, police officer, etc. Ты (pronounced "tee") is how you say "you" to a friend or family member. Russians are more formal than Americans, so if in doubt use Вы!
Вы is also "you plural" or "you all." In other words, you address a superior person as if he or she were several people.
The greeting здравствуйте (formal) and здравствуй (informal) has two forms.
The word "your" also comes in formal and informal: ваш (formal) and твой (informal).
quiz.
<quiz display=simple>
- formal
+ informal
+ formal
- informal
</quiz>
Russian names.
Russians use three names: first name, or имя; middle or patronymic name, or отчество, which is their father's first name plus a suffix meaning "son of" (ович) or "daughter of" (овна); and the last name or family name, or фамилия. Women's last names add an а to the masculine form of the name.
To address a Russian formally, don't use "Mr." or "Ms." Instead, address the person using his or her first name and patronymic.
Russians use relatively few first names. There are only a dozen or so men's first names, and maybe three dozen women's first names. Creativity in baby-naming isn't encouraged.
Russians also use diminutives or nicknames. Each name typically has a version used by your best friend, another used by your other friends, another used by your teachers, another used by your grandmother, another used when you are scolded, etc.
Noun Cases.
English uses word order to indicate a sentence's subject and object. E.g., "Bob eats lunch" and "Lunch eats Bob" have different meanings in English. Word order is less important in Russian. Instead, meaning is conveyed by suffixes. It would be like an eaten lunch becoming "lunchoo," so you could say "Bob eats lunchoo" or "Lunchoo eats Bob," and still make it clear that it's the lunch that is eaten (not Bob).
This would be straightforward enough if there were simply one case for the subject of a sentence, and a second case for the object of the sentence. Instead, Russian has six cases, conveying such meanings as where you are vs. where you're going, or whether the object of the sentence is animate or inanimate!
Nominative case.
The primary case, used for the subject of the sentence ("Bob"), is called the nominative case. This is the case you find in dictionaries.
Accusative case.
"Lunch" is the direct object of "Bob eats lunch." The direct object is used in the accusative case. Inanimate masculine and neuter nouns in the accusative case are the same as nouns in the nominative case. Feminine nouns change their а or я ending to у or ю, respectively. E.g., "car" is машина (pronounced "masheena") in nominative case, and машину (pronounced "masheenoo")in the accusative case.
Prepositional case.
When a sentence contains a complement of location, the noun is in the prepositional case. In general, you add е (pronounced "yeh") to end of the word. E.g., "I live in Michigan" becomes "I live in Michigane." If the word ends in й, а, or я, replace that letter with е. E.g., "She works in Minnesota" becomes "She works in Minnesote."
There are two exceptions to the е ending. Never write ие, instead write ии (yes, Russians pronounce both, like "ee-ee"). The other exception is foreign nouns ending in о, и, or у. These look the same as the nominative case. E.g., Colorado, Kentucky, and Peru don't change.
Nouns in the prepositional case are always preceded by "in" or "about." Each word comes in two versions. If "in" is an activity, or a place where an activity is done (for example, the ballet) use на (pronounced "na"). For other places, use в (pronounced "veh" or pronounced with the next word if it starts with a vowel, e.g., "in Atlante" would be "vatlante").
"About" is о, or, if the following word starts with a vowel, об. There are several cases when "about" is обо, e.g. обо мне.
Куда vs. где.
Куда asks "where (whither) are [you/he/she/etc.] going?" It's pronounced "koodá.".
Где asks "where are [you/he/she/etc.]?" I.e., куда is moving, где is static. It's pronounced "gdye," with the d palatalized.
Statements that could answer the question куда are in the accusative case. E.g., "We're driving to St. Petersburg, Florida" would be in the accusative case, if you said it in Russian.
Statements that could answer the question где are in the prepositional case. E.g., "We live in Moscow, Idaho" would be in the prepositional case.
This is easy to remember because the vowels in Куда are у and а—nouns that end in а (feminine nouns) change to у in the accusative case. The vowel in где is е, the letter you add to end nouns in the prepositional case.
Genitive case.
The genitive case is used to show possession, negation, and quantity such as numbers. E.g., <q>I have six chairs</q> (У меня есть шесть стульев) is plural both in English and in Russian! It's genitive case.
Genitive nouns.
Masculine and neuter nouns form the genitive case the same way: add а at the end. E.g., стол (sing. table) becomes стола́, but столы́ (pl. tables) becomes столо́в. The exceptions are masculine words ending in й or ь add я. if the word ends in a vowel, drop the vowel then add a.
Feminine nouns drop the а and add ы. E.g., лампа (lamp) becomes лампы. The exceptions are if the word ends in я or ь, or for the 7-letter spelling rule, add и.
Genitive adjectives.
Masculine and neuter adjectives form the genitive case the same way: change the ending to ого. This is pronounced "ovo"! The exceptions are masculine words ending in й or ь, or for the 5-letter spelling rule with the ending unstressed, change to его (pronounced "yevo").
Feminine adjectives change the ending to ой (rhymes with "boy"). The exceptions are feminine words ending in й or ь, or for the 5-letter spelling rule with the ending unstressed, change to ей (pronounced "yay").
Genitive case of possessive pronouns.
The possessive pronouns его́, её, and их (his, hers, theirs) never change.
"I have something".
Genitive case is also used for saying you have something, or you don't have something. To say that you have something, start with У (means <q>by</q> or <q>next to</q>). Then change the pronoun (я, ты, вы, etc.) to the following:
In many cases, the genitive ого́ ending is irregularly pronounced ovo.
In other words, Russians don't say <q>Ivan has a dacha,</q> but rather say <q>By Ivan is dacha.</q>
"No something".
In Russian, you use genitive instead of nominative with negative word нет "n'et" "no" when you want to say that there isn't something or one does not have something. If there is none of it, it can't be the subject, right?
Dative case.
Dative case is used with the indirect object of a sentence. It is, when people want <q>to say something to her</q> or <q>to give(to sell, to show and etc.) something to him</q>, etc. (for example: He shows to her this beautiful picture (Он пока́зывает ей э́ту прекра́сную карти́ну). Note here the difference between the direct object from earlier and the indirect object: Ivan gives a "letter" (direct object, accusative case) to his "sister" (indirect object, dative case; also depending on the vowel. If it is silent or not. But that rarely happens in modern Russian)
Dative case quiz.
/Dative case quiz/
Russian lacks "a," "the," and "to be".
Russian lacks the articles "a," "an," and "the." English uses the definite article "the" to indicate a specific place, thing, etc.: "I ate the orange" suggests there was only one orange, or it was special or something. English uses the indefinite articles "a" and "an" to indicate that the following noun is not a specific, e.g., "I ate an orange" suggests there were several oranges.
Russian also lacks the verb "to be," and its conjugations "am," "are," and "is."
Thus the English four-word sentence "I am a student" is just two words in Russian: "Я студент." In written Russian, when a sentence has two nouns in a row, a — is written between the nouns to indicate the verb "to be." E.g., "Tanya is a student" translates to "Таня — студентка."
"This," "these," and "those".
Russian has the adjectives "this" and "these." To "get by" in Russian use это (pronounced "eta") for both "this" (singular) and "these" (plural). To speak "good Russian" it gets confusing. If a word is between "this" (or "these") and the noun ("This is my suitcase") then это doesn't change. But if the noun immediately follows "this" or "these" ("This suitcase is mine") then, if the noun is masculine, это changes to этот (pronounced "etot") ; if the noun is feminine then это changes to эта (pronounced "eta") ; if the noun is neuter then это doesn't change; and if the noun is plural ("these") then это changes to эти (pronounced "etee") .
Russian also has the adjective "those": те. This follows the conjugation for 'that', implying that the noun is in a remote location (not here). Masculine is тот, Feminine is та, Neuter is то, and Plural is те.
this these and those quiz.
This these and those quiz
Plural nouns.
In English we add "s" (or "es") to indicate that a noun is plural. Russian isn't so simple.
Masculine nouns ending in a "hard" consonant add ы. E.g., студент (student) becomes студенты (students).
Masculine nouns ending in the "soft" consonants й or ь add и. E.g., словарь (dictionary) becomes словари (dictionaries).
If you speak Russian (without writing) you can "get by" without learning this distinction, as ы and и sound similar.
Feminine nouns ending in а change the а to ы. This is not always the case. Sometimes а is replaced by и e.g. груша → груши.
Feminine nouns ending in я change the я to и.
Thus masculine and feminine nouns follow a similar pattern for plural. Again, if you only want to speak "get by" Russian you can ignore this distinction because a and я sound similar.
Neuter nouns have a different pattern for plural.
Neuter nouns ending in o change the o to a. This is not always the case. Sometimes o is replaced by и e.g. яблоко → яблоки.
Neuter nouns ending in e change the e to я.
Thus, neuter plural nouns look like feminine singular nouns.
Note that these rules are for plural nouns. Plural adjectives follow different rules.
The 7-letter spelling rule.
Now it gets complicated.
After the letters к, г, х, ш, щ, ж, and ч, always add (or change a or я to) и, not ы. E.g., книга (book) becomes книги (books).
Exceptional plurals.
Some masculine nouns drop the last vowel before adding ы or и. E.g., подарок (present or gift) becomes подарки.
Some masculine nouns add a for plural. E.g., дом (house) becomes дома (houses).
Words of foreign origin ending in o, и, or у don't change between singular and plural. E.g., радио means "radio" or "radios." Note that foreign nouns with these endings also don't change in prepositional case (e.g., Colorado, Kentucky, and Peru).
The personal pronouns "he," "she," and "it".
The personal pronouns are straightforward:
"He" (masculine) is он.
"She" (feminine) is она.
"It" (neuter) is оно.
"They" (plural) is они.
Note that in English we use "he" and "she" for animate objects (people and animals) and "it" for everything else, but Russians use "he" for all masculine nouns, "she" for all feminine nouns, and "it" for all neuter nouns. Thus, a car (машина) is always "she" because машина is feminine.
"Whose?".
The English question word "whose" translates to four Russian words, depending on gender:
чей (pronounced "chey") is masculine.
чья (pronounced "chyah") is feminine.
чьё (pronounced "chyo") is neuter.
чьи (pronounced "chyee") is plural.
If you just want to "get by," say "chee" and you'll be right about 50% of the time.
The possessive pronouns "my," "your," "our," "his," "her," and "their".
To learn to conjugate verbs as well as possessive pronouns, memorize the following order of pronouns:
я (I)
ты (you, informal)
он/она (he/she)
мы (we)
вы (you, formal and plural)
они (they)
In this order, in English the possessive pronouns are "my, your, his, her, our, (no formal your), their." Russian makes this complicated because four of these words change depending on whether the following noun is masculine, feminine, neuter, or plural. Three don't change.
The three possessive pronouns that don't change are "his," "her," and "their." In Russian these are его ("his"), pronounced "yehvo" (not "yehgo"); её, pronounced "yehyo" ("her yo-yo" would sound like "yeh-yo yo-yo"); and их (pronounced "eech," like the German word for "I").
The four possessive pronouns that change are "my," "your" (informal and formal), and "our."
"My" is мой (masculine, pronounced "moy," which sounds vaguely like a New York Yiddish version of "my"); моя (feminine, pronounced "mo-yah"); моё (neuter, pronounced "mo-yo"), and мои (plural, pronounced "mo-ee").
"Your" (informal Ты) is твой (masculine, pronounced "tvoy"); твоя (feminine, pronounced "tvo-yah"); твоё (neuter, pronounced "tvo-yo"), and твои (plural, pronounced "tvo-ee").
"Our" (Мы) is наш (masculine, pronounced "nash," not like "Nashville" but rhymes with "wash"); наша (feminine, pronounced "nasha"); наше (neuter, pronounced "nashyeh"), and наши (plural, pronounced "nashee").
"Your" (formal Вы) is ваш (masculine, pronounced "vash", rhymes with "wash"); ваша (feminine, pronounced "vasha"); ваше (neuter, pronounced "vash-yeh"), and ваши (plural, pronounced "vashee"). A memory aid is "your car is a washing machine." Picture opening the hood of a car and finding a washing machine where the engine should be. "Your car" is ваша машина (sounds like "washing machine").
Adjective endings (nominative case).
Russian adjectives agree with their nouns in gender, number, and case. Here we will learn the adjective endings for gender and number (singular vs. plural). (Cases will be later.)
The dictionary form of adjectives end in ый (pronounced "ee"). This is the ending with masculine nouns. E.g., "new pencil" is новый карандаш (pronounced "no-vee karandash").
With feminine nouns, the adjective ends in ая. E.g., "new car" is новая машина (pronounced "no-vah-yah masheena").
With neuter nouns, the adjective ends in ое. E.g., "new dress" is новое платье (pronounced "no-vo-yeh plat-yeh"). As a memory aid, think of "oh yeah."
With plural nouns, the adjective ends in ые. E.g., "new students" is новые студенты (pronounced "no-vih-yeh studentih"). As a memory aid, think of plural as one masculine and one neuter object. Take the first letter from the masculine ending (ы) and the second letter from the neuter ending (е) and you get ые.
Adjectives with "soft endings" (й or ь) have the same second letter in their endings, but the first letter of the endings change. The masculine ending ый becomes ий, the feminine ending ая becomes яя, the neuter ending ое becomes ее (like the "yeah-yeah" chorus of 1965 Beatles songs), and the plural ending ые becomes ие (maintaining the memory aid that you take a masculine object and a neuter object to get two objects).
5- and 7-letter spelling rules.
Recall that with plurals, after the letters г, ж, к, х, ч, ш, and щ, you use и, not ы. This 7-letter spelling rule also applies to adjectives. As a memory aid, ч, ш, and щ are together in the alphabet.
The 5-letter spelling rule is that after the letters ж, ц, ч, ш, and щ, don't write an unstressed o, but instead write e. As a memory aid, ц, ч, ш, and щ are together in the alphabet.
"What?" and "which?".
Что (pronounced "shto," not "chto") and какой both mean "what." As a loose rule, какой means "which." The correct rule is that if a noun follows "what," use какой. If no noun follows "what," use что.
As a memory aid, the following noun's gender and number change какой. Какой precedes masculine nouns, какая precedes feminine nouns, какое precedes neuter nouns, and какие precedes plural nouns. Because что does not modify nouns, it does not change according to gender.
If you just want to "get by," always use что for "what."
Showing Ownership.
In English, "my" and "I have" are different, just as "your" and "you have" are different. Russian makes a similar distinction—but it's more complicated.
First, the pronoun is in the genitive case (меня, тебя etc.), which indicates possession/ownership. The preposition used with the genitive pronouns to indicate ownership is У (pronounced "oo"), meaning roughly "with".
The forms are as follows:
"I have": У меня (pronounced "oo meen-yah", meaning roughly "with me")
"You have" (informal): У тебя (pronounced "oo teeb-yah", meaning roughly "with you")
"You have" (formal): у вас (pronounced "oo vas")
"He has": у него (pronounced "oo nee-go", meaning "with him")
"She has": у неё (pronounced "oo nee-yo", meaning "with her")
"We have": у нас (pronounced "oo nas", meaning "with us")
"They have": у них (pronounced "oo neech", meaning "with them")
Thus the question "У тебя есть карандаш?" when interpreted rather literally, means "With you is a pencil?" It is easy to see how this can be correctly interpreted as "Do you have a pencil (with you)?" or even just "Do you own a pencil?"
These three phrases are sometimes followed by есть (pronounced "yehst", meaning "is"). Есть questions the existence of something, e.g., У вас есть синий костюм? ("Do you have a blue suit?").
Verb conjugation, present tense.
In English we say, "I study," "you study," "he studies," "she studies," "we study," "they study." Note that some pronouns use "study," while other pronouns use "studies." "Verb conjugation" is how verbs change with pronouns. English has simple two-form verb conjugation for the present tense.
Russian verbs conjugate in six forms, for "I", "you (singular and informal)", "he" and "she", "we", "you (plural and formal singular)" and "they". In addition, Russian verbs conjugate in either of two ways. In other words, some verbs are first conjugation, when others are second conjugation.
All verbs have an infinitive form, which is listed in dictionaries. Typically this form ends in -ть.
First-conjugation verbs usually end in something other than -ить (e.g. in -ать). These verbs conjugate by dropping the ть and replacing it with the following endings:
Second-conjugation verbs usually end in -ить. These verbs conjugate by dropping the -ть and replacing it with the following endings:
Verb conjugation, past tense.
Past tense verbs are somewhat simpler. They conjugate with the gender (or number) of the pronoun. Thus, "I understood" changes depending on whether the speaker is a man or a woman. But the verb is the same for "he understood" or for "I understood," where the speaker is a man. "We understood" and "they understood" are the same.
To form a past tense verb, drop the ть and add л (pronounced "l") for masculine pronouns ("I," "you," "he"), ла (pronounced "la") for feminine pronouns ("I," "you," "she"), and ли (pronounced "lee") for plural pronouns (мы, они, "we," "they"). (Neuter subjects can't talk.)
Verb conjugation, future tense.
Russian future tense is incredibly more complex in meaning than English future tense. Russian future tense also contains information pertaining to the aspect of the verb.
Imperfective Aspect
The simplest, and imperfective aspect of a verb can be attained by the use of the verb "быть." By placing the correct form of "быть," in front of a Russian infinitive, you can create a verb in imperfective future tense.
Form будь is imperative of to be, but in this case it roughly means "will"
Can you decipher these?
As an FYI, the imperfective aspect in Russian refers to a habitual action that we would not go out of our way to delineate. While "Я играю в игру" (I am playing the game) shows current action in a way not unlike English, "Я играла в игру" (I played-feminine the game) relates a habitual action to the playing of the game in the past. English leaves this ambiguous.
Perfective aspect
For perfective aspect verbs, just use the table above for present tense endings, and you will get future tense (do you remember that perfective verbs have no present tense?) E.g. заиграть 'to begin playing' - я заиграю 'I shall begin to play'.
Prepositional case adjectives.
Recall that the prepositional case is used when the object of a sentence is a location. Earlier you learned how to modify nouns (usually by adding е).
Russian adjectives must agree with their following noun in gender, number, and case.
With a masculine noun in the prepositional case, a preceding adjective usually ends in ом. The ending is ем for the 5-letter spelling rule, and for soft-ending (й or ь) adjectives.
With a feminine noun in the prepositional case, a preceding adjective usually ends in ой (pronounced "oy"). The ending is ей (pronounced ("yee") for the 5-letter spelling rule, and for soft-ending (й or ь) adjectives.
Prepositional case plural adjectives and nouns.
With a plural noun in the prepositional case, a preceding adjective usually ends in ых (pronounced "eeh"). The ending is их (pronounced ("ih") for the 7-letter spelling rule, and for soft-ending (й or ь) adjectives.
Plural nouns in the prepositional case usually end in ах (pronounced "ach"). The ending is ях (pronounced ("yach") for soft-ending (й or ь) nouns.
Prepositional case personal pronouns.
The personal pronouns change (considerably!) in the prepositional case.
Я ("I") becomes обо мне (pronounced "obo mnyeh").
Ты ("you" informal) becomes о тебе (pronounced "o tyehbyeh").
Он ("he") becomes о нём (pronounced "o nyom").
Она ("she") becomes о ней (pronounced "o nyee").
Мы ("we") becomes о нас (pronounced "o nas").
Вы ("you" formal) becomes о вас (pronounced "o vas").
Они ("they") becomes о них (pronounced "o neech").
Prepositional case possessive pronouns.
If the object possessed is masculine or neuter, use the following possessive pronouns: моём ("my"), твоём ("your" informal), нашем ("our'), вашем ("your" formal), чьём ("whose?"), этом ("this").
If the object possessed is feminine, use the following possessive pronouns: моей ("my"), твоей ("your" informal), нашей ("our'), вашей ("your" formal), чьей ("whose?"), этой ("this").
If the objects possessed are plural, use the following possessive pronouns: моих ("my"), твоих ("your" informal), наших ("our'), ваших ("your" formal), чьих ("whose?"), этих ("this").
Prepositional case question words.
Some question words change in the prepositional case. Что ("what," pronounced "shto") changes to о чём (pronounced "o chyom"). Кто ("who," pronounced "kto") changes to о ком.
Conjunctions: "and," "yes but," and "but".
Let's do something simpler.
И (pronounced "ee") means "and."
А (pronounced "ah") means "yes, but."
Но (pronounced "no") means "but."
Reflexive verbs.
In English we add "self" to a pronoun to indicate reflexive action. E.g., "I wash myself" is different from "I wash my dog." In Russian, reflexive action is in the verb, not in the pronoun. E.g., a Russian would say something like "I washself."
This reflexive action is indicated by the suffix ся added to the verb, if the verb ends in a consonant. But if the verb ends in a vowel you instead add сь. Note that the former adds a syllable but the latter doesn't!
The verb учиться means "study" (pronounced "oo-cheet-syah"). The verb conjugates:
Three words for "study".
Russia has three words that translate to "study." (You can imagine that Russians must study three times harder than Americans to learn language skills!)
Учиться (pronounced "oo-cheet-syah") usually refers to where you go to school, e.g., "I go to Harvard University." As a memory aid, picture that Russians students cheat.
Изучать (pronounced "ee-zoo-chat") usually refers to the subject you study, e.g., "I study physics." As a memory aid, think that the zoo is where you study subjects such as monkeys, elephants, etc.
заниматься (pronounced "zan-ee-mat-syah") usually refers to doing homework, e.g., "I'm studying at the library." As a memory aid, think that your "zany mother makes you do your homework."
There is also a fourth verb, готовиться (perf. подготовиться), which means to prepare yourself, in this case to study for something, e.g. an exam. This is used with the preposition к + dative case. Например: Я готовлюсь к экзамену по русскому языку.
Two words for "also".
Russian has two words that translate to "also."
Тоже (pronounced "to-zheh") means that two people are doing the same thing (e.g., "I'm a student and my sister is also a student").
Также (pronounced "takzheh") means that one person does two different things (e.g., "I'm a student and I also work part-time").
As a memory aid, picture that Emperor Tojo of Japan is also the emperor of Russia. He has a reclusive brother Takzhye who only does things by himself.
Going by foot, by car, and going regularly.
Russian has three words that translate to "going."
Идти (pronounced "eed-tee") means to go by foot. As a memory aid, think the conjugation он идёт ("he walks," pronounced "on eed-dyot") which sounds like "he's an idiot to walk (with the traffic so dangerous)."
ехать (pronounced "ee-hot") means to go by car, bus, etc. Note that conjugations are еду, едешь, едет, едем, едете, едут—none have the х!
ходить (pronounced "hod-deet") means to go back and forth habitually, e.g., "I go to school every day." As a memory aid, think of hod carriers going back and forth up and down ladders (a hod carrier carries morter to a bricklayer).
Necessity and freedom.
"I have to" translates to я должен (pronounced "dol-zhen," sort of like "dolphin")—if the subject is masculine! If the subject is feminine, it's должна. If the subject is neuter, it's должно. If the subject is plural, it's должны.
Remember that "have to" is an adjective, not a verb! Don't try to conjugate it as a verb.
The opposite of "have to" is freedom. E.g., "I'm free this evening" means there's nothing you have to do. The adjectives are свободен (masculine, pronounced "sva-bod-den"), свободна (feminine, pronounced "sva-bod-na"), свободно (neuter, pronounced "sva-bod-no") and свободны (plural, pronounced "sva-bod-nih").
Note that вы ("you" formal, and "y'all") uses the plural forms, regardless of the gender of the person you're addressing.
Note that кто ("who") uses the masculine form, regardless of the gender of the person you're asking about
Lesson 4 » | 8,833 |
Animal Care/Guinea pig. Guinea Pigs (also called cavies after their scientific name) are rodents belonging to the family Caviidae and the genus Cavia. Despite their common name, the animals are not pigs, nor do they come from Guinea. Male guinea pigs are called "boars", females "sows" and babies are called "pups". They are originally native to the Andes, and while they are no longer extant in the wild, they are closely related to several species which are commonly found in the grassy plains and plateaus of this region. The guinea pig plays an important role in the folk culture of indigenous South Americans, especially as a food source, but also in folk medicine and in community religious ceremonies. Since the 1960s, the guinea pig has become increasingly important as a staple food in the Andes, and efforts have been made to increase consumption of the animal outside South America. See the for links to recipes.
In Western societies, the guinea pig has enjoyed widespread popularity as a household pet since its introduction by European traders in the sixteenth century. Because of its docile nature, the relative ease of caretaking, and its responsiveness to handling and feeding, the guinea pig remains a popular pet choice. Organizations devoted to competitive breeding of guinea pigs have been formed worldwide, and a large number of specialized breeds of guinea pig, with varying coat colors and compositions, are cultivated by breeders.
Choosing a Guinea Pig.
Taking care in choosing your guinea pig and its possible companions is the first, and possibly the most important, step in keeping guinea pigs. Make sure your guinea pigs are either of the same sex or neutered/spayed.
Health.
As prey animals, guinea pigs have evolved to hide any signs of illness, as long as possible in order to avoid becoming the main targets of the dangerous predation. This can make it difficult to recognize an illness or ailment. The best way to check for them is to place the cavy carefully on its back and check the belly. Their feet should be clean-looking and not red or irritated; with no broken or extraordinarily long nails. Check their teeth for length and evenness (see section below). It is also important to check their eyes and nose, to make sure that there is no mucus or crust there. These are signs of an upper respiratory infection, or URI, and can be deadly if left untreated.
Breed.
The most common kinds of guinea pig (especially in pet stores) are the short-haired "American" or "Self" breed and the "Abyssinian", which has curly, cow-licked hair. Long-haired guinea pigs (the Sheltie/Silky and Peruvian breeds) are very beautiful pets, but they need daily grooming to be healthy, thus making them not usually suitable for children. The hair near the rear of the Guinea Pig must be cut and cleaned on a regular basis, or it will get caked with feces and the bedding from the cage. Short hair guinea pigs take less effort in the hygienic and cosmetic categories, but still need to be properly cared for. Therefore, the Peruvian guinea pig breed is the most difficult breed to care for due to the long hair. It gets tangled extremely easily, and is not recommended for anyone without extensive time to care for the cavy's hair every day.
How many?
The vast majority of rescues, knowledgeable vets, household breeders and scientists will tell you that guinea pigs should be housed in groups of two or more. Not only is making sure your guinea pigs have companions important for their health and happiness, keeping multiple guinea pigs will improve the fun of having these animals as pets as you watch them interact. In practice, the best option is usually a pair of guinea pigs. Of course, the most important factor in choosing groups is to make sure you will not have any unwanted babies, so make sure your pets are either of the same gender or spayed/neutered. If you are not confident in sexing guinea pigs, buy/adopt whatever guinea pigs you so desire, and then take it to your vet or a cavy-specific rescue to have its gender confirmed "before introducing them at all". While groups of boars might get along (provided no females are present and they are carefully introduced), and groups of females are often fine, the easiest combination is one neutered boar (neutering is cheaper and safer than spaying) and one or more females. The personality of individual guinea pigs varies; with some being very amicable to company and others incapable of showing anything but hostility to other cavies.
Behavior.
Guinea pigs are active during the day, but are actually crepuscular (most active at dawn and dusk). Guinea pigs are very gentle, and even untamed guinea pigs will not bite unless you are causing them pain or they have been abused in the past.
Guinea pigs have a poor sense of sight, but well-developed senses of hearing and smell. Vocalization is the primary means of communication between members of the species.
The Cage or Living Environment.
While some older guinea pig resources may say that housing them outdoors is acceptable, this is simply not the case. Wind can blow a hutch over easily; it is also the perfect place for molds to grow. Spiders and insects may bite guinea pigs left outside. There is also no guarantee that temperatures will be acceptable for your guinea pigs to live in. It is also very hard to notice signs of disease in guinea pigs if they are constantly out of sight, and out of mind. Even indoors, sudden drafts or radical shifts in temperature may adversely affect the health of your guinea pig. Outdoors, guinea pigs may still be subject to predators such as raccoons, opossums, birds of prey and cats. Even a guinea pig physically protected from a predator may suffer from the ill effects of stress from the presence of a predator. Guinea pigs in the Andean region of South America are often kept outside on roofs or in milk crates. But these are livestock, not pets. A pet guinea pig is a member of your family and will benefit from the most interaction available. Being inside your home will make it easier and more appealing to care for and play with your guinea pig. Additionally, most secure hutches are designed for rabbits, and as such have mostly wood or wire floors that are unsuitable for guinea pigs. These wire floors are extremely painful for rabbits and cavies alike, and will damage their delicate feet.
Indoor housing can consist of a large cage, with a plastic base (not metal mesh, this can damage the guinea pig's feet; wood will soak up urine permanently) and a large metal top half. As guinea pigs are not climbers, a top is only absolutely necessary if other pets are present in the house. A pet store cage is nowhere near adequate size for a happy guinea pig, and will cost in upwards of $45–50. The minimum size cage for 1-2 guinea pigs is 7.5 square feet. A good cheap option is buying or making a "C&C" cage made of metal mesh cubes (the organizer kind with small plastic connectors, for the outside) and Coroplast (the floor and walls) which is basically plastic cardboard you can buy at any sign store for a very low price. There are instructions at Cavy Cages
Bedding.
The housing should be lined with bedding at a minimum of 1 inch deep, ideally deeper in the sleeping areas. You should never use softwoods such as pine or cedar shavings for bedding, as these emit harmful odors called phenols that cause your guinea pig respiratory problems. Hardwoods such as aspen are fine. Other options for bedding are recycled paper products such as Carefresh; these are more expensive, but also stay clean for longer than shavings and are easier on a guinea pig's feet. A cage needs to be cleaned generally every week at the very minimum, but more often as needed.
A newer form of guinea pig bedding is polar or anti-pill fleece. While this may seem strange at first, it is a very hygienic and cost-effective form of bedding. First, an absorbent layer must be in the bottom of the cage, because the function of fleece is to wick the urine away from the guinea pigs' feet. Most fleece users are happy to use 1-2 layers of towels on the bottom of their cage, topped with a single layer of fleece. So, when a guinea pig urinates on fleece bedding, the urine is wicked through the fleece and into the towels, where it is absorbed. Fleece needs to be washed at least once weekly, without fabric softener; it inhibits the fleece's ability to wick urine. It is also a good idea to wash it with an unscented detergent, and some white vinegar to absorb odors. For more information on using fleece as a bedding, please visit
Other essential accessories.
Other items needed for your guinea pig's home will be a gravity-fed water bottle (cavies tend to spill and defecate in water bowls), a small bowl for pellets and other food, and "hidey houses". Wild cavy species and feral guinea pigs naturally use dens made by other animals, and all domestic guinea pigs should be provided a safe place to hide in. As they are prey animals, they will feel much more secure in their environments if they have places to hide. This can be a plastic "igloo" or wood house from a pet store, or simply a towel tent. Be aware that some cardboard is put together using glues that can be harmful to your guinea pig, so it is best to avoid these if you can. If you have more than one guinea pig, having both an entrance and an exit to any hiding places can prevent fights between cornered guinea pigs. The more hiding places, the merrier! It is also better for your guinea pigs to keep borders around the cage clear, so that they can run laps.
Toys.
Unlike hamsters or rats, guinea pigs don't need fancy toys such as running balls or exercise wheels. Wheels and balls may have a picture of a guinea pig on the box, but you should not buy one for them to play with. A cavy's spine (and other bones) is much more fragile than other pet rodents, its feet are too soft, the balls are not properly ventilated for a larger animal such as a cavy. Mostly they like simple things like cardboard shoe boxes, towel tents, oatmeal tubes, paper bags and other tunnels or places to hide and chew on. Some owners give bird toys, but chewing the plastic is very bad for guinea pigs. Mirrors can be hung from outside the cage, however.
An item that is very dangerous and should be avoided is a guinea pig leash. Guinea pigs cannot be trained to walk, and it shouldn't be attempted. While this may seem like a good way to let them run about the yard safely, it is merely dangerous. They have very delicate spines and bones, which are easily damaged by a leash or harness.
An alternative way to get fresh air and fresh grass is an outdoor pen, but it should be used when you will be outside with the guinea pig the entire time. It is good to place their igloo/hut in there with them so if they become startled, they can hide. The igloo/hut will not suffice for sun protection, however, as it will keep in too much heat. You must be careful where you place the pen and must stay with the guinea pig at all times while they are outside in it. Also, it should be noted that if a guinea pig is to be outside, the grass it will be on cannot have had any pesticides or fertilizers on it. These chemicals will kill your guinea pig, and are very dangerous.
Food.
A guinea pig's diet should be comprised of three basic groups; grass hay, pellets, and fresh treats. Most importantly, a guinea pig cannot make their Vitamin C (just like people) and will need it either in vitamin supplements (not droplets, these don't work as the C dissolves too rapidly in water) or in plenty of the right fruits and veggies. Of course, every guinea pig needs a water bottle (they tend to poop in water bowls, and it could get very unhealthy).
You should give one adult guinea pig approximately 1/8 cup pellets every day, possibly more for young ones. Pellets should be Timothy hay-based (little green ones), and not a seed mix. They can easily choke on seeds, and seeds are too fatty. Alfalfa-based hay pellets have too much calcium, and should not be fed for guinea pigs over 6 months of age.
Providing your guinea pig as much Timothy hay or orchard grass as it can eat is very important for its health and happiness. Hay provides important digestive fiber and can prevent a condition in older boars where they lose the ability to defecate properly. Also, guinea pigs have a natural inclination to forage for food almost constantly, not giving them proper hay can cause them stress and result in barbering (chewing their own hair) and other behavioral problems. Alfalfa hay can be fed to guinea pigs younger than 6 months, but should not be fed to older guinea pigs other than the occasional treat. If you do not know the age of your guinea pig, or are unsure, use a different hay that is safe.
If you ever have a question about whether your guinea pig can eat a certain vegetable or fruit, and in which quantities, please visit this link: . It was made by a guinea pig dietary specialist, and is very helpful!
Guinea pigs like to eat lots of green veg, and on the whole this is very good for them, but there are a few things that should be left off your pets menu. Iceberg Lettuce causes bloat and gas, and so should be avoided, no exception. Tomato leaves are also not good for piggies. Carrot in excess can cause liver problems due to the excessive amounts of vitamin A, and in the pregnant cavy can cause birth defects. However, in small amounts to a non pregnant guinea pig, this is fine. Mushrooms and Rhubarb are poisonous. The best fruits and veggies for Vitamin C are Romaine lettuce, Carrot, Kale, Mustard greens, Red bell pepper, Spinach and many others. Oddly, oranges do not have very much vitamin C and can even cause the runs in guinea pigs. They need 10-20 MG of Vitamin C a day if they are healthy. If they are unhealthy, pregnant, or under 3 months, they should get 30-50 MG. For additional vitamin C, you can purchase vitamin C tablets. It is very important that you do not use vitamin C drops, as these can result in dehydration in guinea pigs. Do not give them multivitamins. These can be bad for them and even poisonous.
Problems.
Before you bringing home your new guinea pig, you should locate your nearest veterinarian, and go in to the practice to pick up any leaflets or advice sheets on basic first aid for guineas. Staff should be knowledgeable, and will be able to help you with any other queries you might have about your guinea pigs. Make sure to visit a knowledgeable exotic pet veterinarian, as many regular cat and dog veterinarians have limited knowledge of cavies and some may refuse to treat them altogether.
Pain
As guinea pigs are naturally prey animals, they instinctively hide pain to prevent appearing as a weak animal within the group. As a result it may be difficult to tell if they are hurting. If you notice changes in behavior, or unusual avoidance of handling, call your veterinarian for advice.
Parasites
Guinea pigs can occasionally harbor skin (ecto-) parasites, which may not always be visible to the naked eye. Fortunately these parasites are not zoonotic, meaning your guinea pig cannot give them to you. Treatment with a topical product called Revolution(R) (active ingredient, selamectin) is a very effective method of controlling ectoparasites. Ivermectin is also effective, and is given either as an injection or orally. These medications must be prescribed by your veterinarian. It is not uncommon for pet store bought guinea pigs will harbor lice or mites. For this reason, it is a good idea to have a newly acquired guinea pig examined by a veterinarian before introducing the new cavy to other cavies in your home.
Teeth
As guinea pigs are rodents, their teeth grow constantly. The constant availability of roughage (grass hay) is of critical importance in maintaining your guinea pig's dental health. It is also helpful, and fun for your guinea pig, if you include a chew stick (available in most pet shops) or piece of fruit wood for them to gnaw on. Dental examinations are an important part of your guinea pig's health plan. You can easily monitor the incisors (front teeth), but it is difficult to see the premolars and molars (cheek teeth) without an oral speculum. To see the incisors, hold your guinea gently but firmly in one hand, with one finger behind the head to support, lean your pet back. If this doesn't expose the teeth, gently push on the lips to show them. The teeth should appear straight; the top and bottom teeth should overlap only slightly (top over bottom- if they are the other way round, you should consult with your veterinarian). Normal incisors are off-white to yellow in color. Normal mandibular (lower) incisors often appear quite long to the untrained eye. If the incisors curve away from each other or are excessively long, consult your veterinarian. "Never" attempt to trim or clip your guinea pig's incisors by yourself. This may result in a fractured incisor, which is painful, and may cause further dental problems in the future.
Guinea pigs and other pets
Obviously, cats, dogs and ferrets are predators and may kill a small furry creature. However, there are cases of guinea pigs getting along with them, and often as not cats may not know what to think of a guinea pig or even be scared of it. Dogs may be trained to accept guinea pigs as well. Chiefly, never leave a guinea pig alone with any predatory animal, however well-trained. Cohousing of guinea pigs with other rodents such as gerbils, rats and hamsters may increase instances of respiratory and other infections, and such rodents may act aggressively towards the guinea pig. Opinion is divided over the cohousing of guinea pigs and domestic rabbits. Some published sources say that guinea pigs and rabbits complement each other well when sharing a cage. However, as lagomorphs, rabbits have different nutritional requirements, and so the two species cannot be fed the same food. Rabbits may also harbor diseases (such as the respiratory infections Bordetella and Pasteurella), which guinea pigs are susceptible to. Even a dwarf rabbit is much stronger and more aggressive than the guinea pig and may cause intentional or inadvertent injury.
Breeding
Pregnant sows have a 25% chance of having a fatal pregnancy complication. It is advisable to not breed guinea pigs, unless you know 100% of what you're doing, you're able to find homes for them, and you know what breeds can cause problems if they cross. | 4,501 |
Organic Chemistry/Introduction to reactions/THF. THF stands for Tetrahydrofuran, and is a common ether-type solvent.
Structure.
It is a 5 membered ring containing 4 carbons and one oxygen. It is very inert and thus makes a good solvent for many reactions. | 72 |
Electronics/Aim. The aim of this textbook is to explain the design and function of electronic circuits and components. The text covers electronic circuit components, DC analysis, and AC analysis.
It should be useful to beginner hobbyists as well as beginner engineering students, teaching both theory and practical applications.
It should be thought of as a companion project to the Wikipedia articles about electronics. While Wikipedia covers many details about the technology used in electronics components and related fields, the Electronics Wikibook covers a lot of the "how-to" aspects that aren't covered in an encyclopedia. The book will focus on how to use the components to build useful circuits. | 148 |
Electronics/Definitions. "Get ideas from here:"
http://en.wikipedia.org/wiki/List_of_electronics_topics
"(BUT WE ONLY WANT THINGS THAT MATTER TO A TWO YEAR LEVEL. No "quadrature amplitude modulation" or anything like that.)"
SI Units and derived units
Definitions in Alphabetical Order:
"Another order could be definitions by subject such as DC, AC, radio, integrated circuit, etc."
to be merged.
superfluous stuff from "overview of electronics", which should be merged in with these definitions:
Charge: Particles can have three possible types of charge: positive, negative, or neutral (no charge). Electrons are negatively charged, protons are positively charged, and neutrons are (surprise!) neutral. Opposite charges tend to attract, while particles with the same charge (both positive or negative) tend to repel.
Electricity: the flow of electrons.
Electronics: is the study of gadgets that use electricity, typically creating or handling signals, not just switching power.
??? are devices which take in input, perform some function, and return some output, through the use of electricity.
Circuit: The path electrons take as they are pushed by some power source, flow through various electrical components in a gadget, and return to the power source.
Electric Field: field created by the presence of charge. The field represents the force that would be felt by a positive charge.
Voltage: Accelerates charge.
Voltage is a gravity-like potential due to the separation of a negative and a positive charge. Voltage accelerates negatively charged electrons from the negative to the positive charge, and accelerates positive charged protons and ions the other way. Pushing accelerates the charges in what is known as current.
Resistance: When moving electrons (current) collide with atoms, energy is given off as heat. Resistance is the measure of a material's tendency to cause this type of energy loss. Resistance acts to limit the flow of current due to a given voltage. As the resistance becomes infinite the current stops flowing and becomes an open circuit. When there is no resistance the circuit shorts and the current becomes infinite. (Current 'prefers' the path with the lowest possible resistance.)
Resistor: A device whose primary use is to provide resistance.
Short Circuit: there is no resistance between two points. Current flows without a change in voltage.
Open Circuit: there is infinite resistance between two points. Current is unable to flow, but there is still a voltage between the two points.
Voltage Source creates a voltage, which creates a current.
Current Source, which creates a current and a voltage for the current.
Voltage Drop When the current goes through resistance it loses some of the push of the voltage.
When the current comes to an intersection it has multiple paths it can take and flows according to its resistance.
Permittivity: (ε) A measure of how much energy a material absorbs in response to an electric field. Materials (εr) absorb more energy than the vacuum (ε0). The permittivity of a material is known as its dielectric constant.
Cell: Two materials with a voltage difference between them.
Capacitor: Two metal plates with a gap between them. Voltage causes charge to drain from one plate and accumulate on the other plate. This charge separation creates a voltage in the capacitor that opposes the other voltage and stops the flow of current. When a dielectric is placed between the plates it weakens the electric field between the plates and allows more charge to accumulate.
Capacitance: Any two pieces of conducting material separated by some distance have capacitance. Simply, a measure of the tendency of some configuration of metal to act as a capacitor.
Inductor: A coil of wire. Current starts to flow through the wire and creates a magnetic field. This magnetic field creates an opposing magnetic field which stops the current through the wire. Over time the inductor stops opposing current and turns into a wire.
Transformer Two connected inductors, which operate through mutual inductance. Current flows through the first inductor and creates a magnetic field that is fed to the second inductor. In response the second inductor creates an opposing magnetic field and current. Having a permanent magnet between the two inductors intensifies their magnetic fields.
Vacuum tube: An arrangement of two or more electrodes in a vacuum. Typically placed in a glass bulb to keep air from leaking in.
Triode: The first electrical amplification device. A triode is a type of vacuum tube with three connections:
Diode: A 2 wire device that allows current to flow easily in only one direction.
Transistor: A 3 wire device, with one wire (the "base" or "gate") that controls the flow of electrons between the other 2 wires. Replaced vacuum tubes.
Light waves: (Electromagnetic waves) | 1,113 |
Trigonometry/The Unit Circle. The Unit Circle is a circle with its center at the origin (0,0) and a radius of one unit.
Angles are always measured from the positive x-axis (also called the "right horizon"). Angles measured counterclockwise have "positive" values; angles measured clockwise have "negative" values.
Defining sine and cosine in terms of the unit circle.
In the unit circle shown here, a unit-length radius has been drawn from the origin to a point (x, y) on the circle.
A line perpendicular to the x-axis, drawn through the point (x, y), intersects the x-axis at the point with the abscissa "x". Similarly, a line perpendicular to the y-axis intersects the y-axis at the point with the ordinate "y". The angle between the x-axis and the radius is formula_1.
So, we can say that the sine of an angle is the ordinate of the point on the unit circle at that angle, and the cosine of an angle is the abscissa of the point on the unit circle at that angle.
We define the basic trigonometric functions of any angle formula_1 as follows:
formula_3
formula_4 can be algebraically defined.
formula_5
formula_6
These three trigonometric functions can be used whether the angle is measured in degrees or radians as long as it specified which, when calculating trigonometric functions from angles or vice versa.
Alternative definitions.
formula_10
It is important to know why the above equations are true. Knowing formula_11, formula_12. The same could be said for the definition for formula_13. Finally, the final line is the Pythagorean identity.
Video links.
More about this topic can be found at the "'Khan Academy":'
Some values for sine and cosine.
A unit circle with certain exact values marked on it is below:
Unit circles form the basis of most analog clocks and animations on computers since the cos and sin correspond to the x and y positions of the end of the line segments representing the hands of the clock.
The unit circle on the left has the degree, the radian, and the coordinate value on the unit circle. For a coordinate value formula_14, if walking around the circle formula_15 radians anti-clockwise from the horizontal axis, the coordinate value at which the person walked around the circle is formula_16.
Remember that on a unit circle, the angle formula_17 anti-clockwise from the horizontal axis gives formula_18 and formula_19. The same is true for radians. As such, for formula_14 corresponding to formula_21 on the unit circle, formula_15 radians when substituted in the cosine or sine function is the coordinate value on the unit circle. That is:
The unit circle is very useful to your mathematical studies of trigonometry because it tells you the EXACT value of certain angles. Later, you will learn how to find other ratios of angles and radians without needing to rely on the special values of the unit circle – 30, 45, 60, and 90.
It is worth your time memorizing some of the values of sine and cosine on the unit circle (cosine is equal to formula_25 while sine is equal to formula_13). You should at least become familiar with the values for formula_27 and know where formula_28 are on the unit circle.
If you have some trouble memorizing the values, here are some helpful hints and patterns. Try to find some more other than what is listed.
If you are to ever be tested on this, make a quick sketch of the first quadrant of the circle, and remember the pattern that underlies the unit circle. | 868 |
Trigonometry/Geometric Definitions of Trig Functions. Geometrically defining tangent.
In the previous section, we algebraically defined tangent as formula_1, and this is the definition that we will use most in the future. It can, however, be helpful to understand the tangent function from a geometric perspective.
A line is drawn at a tangent to the unit circle: (i.e. formula_2). Another line is drawn from the point on the radius of the circle where the given angle falls, through the origin(O), to a point (Q) on the drawn tangent. The ordinate (QP) of this point is called the tangent of the angle.
The slope of the line OQ = formula_3 and as we mentioned before
KC = sin(θ) ,
OC = cos(θ)
Hence , the Slope of the line OQ = formula_4
and also the slope of OQ = formula_5 = formula_6 = formula_7 = tan(θ)
Hence , we can deduce that tan(θ) = formula_3 = formula_4 = QP = the ordinate of the point Q = the slope of OQ
Domain and range of circular functions.
Any size angle, positive or negative, can be the input to sine or cosine — the result will be as if the largest multiple of 2π (or 360°) were subtracted from or added to the angle. The output of the two functions is limited by the absolute value of the radius of the unit circle, formula_10.
formula_11
"R" represents the set of all real numbers.
No such restrictions apply to the tangent, however, as can be seen in the diagram in the preceding section. The only restriction on the domain of tangent is that odd integer multiples of formula_12 are undefined, as a line parallel to the tangent will never intersect it.
formula_13
for a deep understanding of trigonometric functions explore this Applet
Applying the trigonometric functions to a right-angled triangle.
If you redefine the variables as follows to correspond to the sides of a right triangle:
• x = a (adjacent)
• y = o (opposite)
• a = h (hypotenuse)
"Next Page: Right Angle Trigonometry" | 527 |
Trigonometry/Thales Theorem. = Construction of Right Triangles =
Right triangles are easily constructed. Recall that a "diameter" is a straight line which starts at one point on the circle and goes through the center to the other side. Using this property of a circle:
Provided the above three directions are followed, the resulting triangle Δ"abc" will be a right triangle. This result is known as Thales' theorem.
This right triangle can be further divided into two isosceles triangles by adding a line segment from "b" to the center of the circle.
To simplify the following discussion, we specify that the circle has diameter 1 and is oriented such that the diameter drawn above runs left to right. We shall denote the angle of the triangle at the right "θ" and that at the left "φ". The sides of the right triangle will be labeled, starting on the right, "a, b, c," so that "a" is the rightmost side, "c" the leftmost, and "b" the diameter. We know from earlier that side "b" is opposite the right angle and is called the hypotenuse. Side "a" is opposite angle "φ", while side "c" is opposite angle "θ". We reiterate that the diameter, now called "b", shall be assumed to have length 1 except where otherwise noted.
By constructing a right angle to the diameter at one of the points where it crosses the circle and then using the method outlined earlier for producing binary fractions of the right angle, we can construct one of the angles, say "θ", as an angle of known measure between 0 and "π" / 2. The measure of the other angle "φ" is then "π" - "π"/2 - "θ" = "π"/2 - "θ", the complement of angle "θ". Likewise, we can bisect the diameter of the circle to produce lengths which are binary fractions of the length of the diameter. Using a compass, a binary fractional length of the diameter can be used to construct side "a" (or "c") having a known size (with regard to the diameter "b") from which side "c" can be constructed.
= Using Right Triangles to find Unknown Sides =
Finding unknown sides from two other sides.
From the Pythagorean Theorem, we know that:
Recall that c (the diameter/hypotenuse in the above example) has been defined as having a length of one, therefore:
permits us to calculate the length of b squared. It may happen that b squared is a fraction such as 1/4 for which a rational square root can be found, in this case as 1/2, alternatively, we could use Newton's Method to find an approximate value for b.
Finding unknown sides from one side and one (non-right) angle.
As any triangle could be compared to our basic triangle (formed from a circle with a diameter of one), a table enumerating the relationships between angles and side lengths would be very useful to understanding the properties of any triangle. However, such a table would be unwieldy in practice and it is often not necessary to know the exact value.
Of course, given an angle formula_3, we could construct a right angled triangle using ruler and compass that had formula_4 as one of its angles, we could then measure the length of the side that corresponds to a to evaluate the formula_5 function. Such measurements would necessarily be inexact; it would be a problem in physics to see how accurately such measurements can be made; using trigonometry we can make precise predictions with which the results of these physical measurements can be compared.
The most common way of communicating the idea that relationships exist without providing exact details takes the form of a 'function'. A function is like a machine that takes some simple input and produces some simple output. Usually a function defines some kind of rule ([Function]) and provides us a handy notation useful in trigonometry. That way, we know that we're using a certain relationship without needing to know the exact numerical values. Basic trigonometric functions are simply stand-ins for the relationship between angles and sides of a triangle.
One such function, which allows us to know the relationship between any value of formula_4 and the corresponding value of formula_7 is called the "cosine" or formula_8. This universal relationship is represented as: formula_9 which would save us the work of constructing angles and lengths and making difficult deductions from them.
This means that if you know the cosine of an angle, you also know the relationship between the lengths of the sides. The actual size of the triangle can be bigger or smaller, but the mathematical relationship represented by the cosine does not change so long as the size of the angle remains constant.
Cosine example.
Some explicit values for the cos function are known. For formula_10, sides formula_7 and formula_12 coincide: formula_13, so formula_14. For formula_15, sides formula_16 and formula_12 coincide and are of length 1, and side formula_7 is of zero length, consequently formula_19, formula_20. formula_21 and formula_22.
The simplest right angle triangle we can draw is the isosceles right angled triangle, it has a pair of angles of size formula_23 radians, and if its hypotenuse is considered to be of length one, then the sides formula_7 and formula_25 are of length formula_26 as can be verified by the theorem of Pythagoras. If the side formula_7 is chosen to be the same length as the radius of the circle containing the right angled triangle, then the right hand isosceles triangle obtained by splitting the right angled triangle from the circumference of the circle to its center is an equilateral triangle, so formula_3 must be formula_29, and formula_30 must be formula_31 and formula_32 must be formula_33.
= Properties of the cosine and sine functions=
Period.
A full revolution is an angle of 2π radians, so increasing an angle by this amount gets you exactly back to your starting point. Therefore, a perfect circle is maintained, along with the relationships formed by triangles within, by adding 2π to any angle θ. This is called the "period," --the size of the angle or the time period over which the relationships begin to repeat (correlating the two is complex, and allows us to talk about wave theory).
Using functions, we can represent this fact in terms of the cosine function by stating that : formula_34
Knowing the period of the sine and cosine functions (and by derivation, that of other functions) is useful because it means that we can substitute one angle for another when we know that the period is the same. This helps in calculations, such as when there is the need to add or subtract angles.
Half Angle and Double Angle Formulas.
We can derive a formula for cos(θ/2) in terms of cos(θ) which allows us to find the value of the cos() function for many more angles. To derive the formula, draw an isosceles triangle, draw a circle through its corners, connect the center of the circle with radii to each corner of the isoceles triangle, extend the radius through the apex of the isoceles triangle into a diameter of the circle and connect the point where the diameter crosses the other side of the circle with lines to the other corners of the isoceles triangle.
Therefore:
formula_35
which gives a method of calculating the cos() of half an angle in terms of the cos() of the original angle. For this reason * is called the "Cosine Half Angle Formula".
The half angle formula can be applied to split the newly discovered angle which in turn can be split again ad infinitum. Of course, each new split involves finding the square root of a term with a square root, so this cannot be recommended as an effective procedure for computing values of the cos() function.
Equation * can be inverted to find cos(θ) in terms of cos(θ)/2:
formula_36
substituting formula_37 gives:
formula_38
that is a formula for the cos() of double an angle in terms of the cos() of the original angle, and is called the "cosine double angle sum formula".
"Next Page: ../Trigonometric identities/" | 1,887 |
Engineering Thermodynamics/Applications. One Component Systems.
All materials can exist in three phases: "solid", "liquid", and "gas". All one component systems share certain characteristics, so that a study of a typical one component system will be quite useful.
For this analysis, we consider heat transferred to the substance at constant pressure. The above chart shows temperature vs. specific volume (1/density) curves for at three different constant pressures. The three line-curves labeled p1, p2, and pc above are isobars, showing conditions at constant pressure. When the liquid and vapor coexist, it is called a saturated state. There is no change in temperature or pressure when liquid and vapor are in equilibrium, so that the temperature is called "saturation temperature" and the pressure is called "saturation pressure". Saturated states are represented by the horizontal lines in the chart. In the temperature range where both liquid and vapor of a pure substance can coexist in equilibrium, for every value of saturated temperature, there is only one corresponding value of saturation pressure. If the temperature of the liquid is lower than the saturation temperature, it is called "subcooled liquid". If the temperature of the vapor or gas is greater than the saturation temperature it is called "superheated vapor".
The amount of liquid and vapor in a saturated mixture is specified by its "quality x", which is the fraction of vapor in the mixture. Thus, the horizontal line representing the vaporization of the fluid has a quality of "x=0" at the left endpoint where it is 100% liquid and a quality of "x=1" at the right endpoint where it is 100% vapor. The blue curve in the preceding diagram shows saturation temperatures for saturated liquid i. e. where x=0. The green curve in the diagram shows saturation temperatures for saturated vapor i. e. where x=1. These curves are not isobars.
formula_1
formula_2
formula_3
If you also consider the solid state, then we get the phase diagram for the material. The point where the solid, liquid, and the vapor state exist in equilibrium is called the "triple point". Note that as the saturation temperatures increase, the liquid and vapor specific volumes approach each other until the blue and green curves come together and meet at point C on the pc isobar. At that point C, called the "critical point", the liquid and vapor states merge together and all their thermodynamic properties become the same. The critical point has a certain temperature Tc, and pressure pc, which depend on the substance in question. At temperatures above the critical point, the substance is considered a super-heated gas.
This diagram is based on the diagram for water. Other pure (one-component) substances have corresponding temperature vs. specific volume diagrams which are fairly similarly shaped, but the temperatures, pressures, and specific volumes will vary.
The thermodynamic properties of materials are given in charts.
One commonly used chart is the "Mollier Chart", which is the plot of enthalpy versus entropy.
The pressure enthalpy chart is frequently used in refrigeration applications.
Charts such as these are useful because many processes are isenthalpic, so obtaining values would be as simple as drawing a straight line on the chart and reading off the data.
"Steam tables" give the values of specific volume, enthalpy, entropy, and internal energy for different temperatures for water.
They are of great use to an engineer, with applications in steam turbines, steam engines, and air conditioning, among others.
"Gas tables" give the same equations for common gases like air.
Although most gases roughly obey the ideal gas equation, gas tables note the actual values which are more accurate in many cases.
They are not as important as steam tables, but in many cases it is much easier to lookup from a table rather than compute answers.
Gibbs Phase Rule.
"Gibbs phase rule" states that for a heterogeneous system in equilibrium with "C" components in "P" phases, the degree of freedom "F = C - P + 2".
Thus, for a one component system with two phases, there is only one degree of freedom.
F=1-2+2
F =1
That is, if you are given either the pressure or temperature of wet steam, you can obtain all the properties, while for superheated steam, which has just one phase, you will need both the pressure and the temperature.
Psychrometry.
"Psychrometry" is the study of air and water vapor mixtures for air conditioning.
For this application, air is taken to be a mixture of nitrogen and oxygen with the other gases being small enough so that they can be approximated by more of nitrogen and oxygen without much error. In this psychrometry section, vapor refers to water vapor. For air at normal (atmospheric) pressure, the saturation pressure of vapor is very low. Also, air is far away from its critical point in those conditions. Thus, the air vapor mixture behaves as an ideal gas mixture. If the partial pressure of the vapor is smaller than the saturation pressure for water for that temperature, the mixture is called unsaturated. The amount of moisture in the air vapor mixture is quantified by its "humidity".
The absolute humidity "ω" is the ratio of masses of the vapor and air, "i.e.", "ω = mv/ma".
Now, applying ideal gas equation, "pV = mRT" for water vapor and for air, we have, since the volume and temperature are the same, "ω = 0.622 pv/pa". The ratio of specific gas constants (R in preceding equation) of water vapor to air equals 0.622 .
The "relative humidity" "φ" is the ratio of the vapor pressure to the saturation vapor pressure at that temperature, "i.e.", "φ = pv/pv,sat".
The "saturation ratio" is the ratio of the absolute humidity to the absolute humidity at saturation, or, "ψ = ω/ωsat".
It is easy to see that the saturation ratio is very close to the value of relative humidity.
The above plot shows the value of absolute humidity versus the temperature.
The initial state of the mixture is 1, and it is cooled isobarically, and at constant absolute humidity.
When it reaches 2, it is saturated, and its absolute humidity is "ωa".
Further cooling causes condensation and the system moves to point 3, where its absolute humidity is "ωb".
The temperature at 2 is called the "dew point".
It is customary to state all quantities in psychrometry per unit mass of dry air.
Thus, the amount of air condensed in the above chart when moving from 2 to 3 is "ωb − ωa".
Adiabatic Saturation.
Consider an unsaturated mixture entering a chamber.
Suppose water was sprayed into the stream, so that the humidity increases and it leaves as a saturated mixture.
This is accompanied by a loss of temperature due to heat being removed from the air which is used for vaporization.
If the water supplied is at the temperature of exit of the stream, then there is no heat transfer from the water to the mixture.
The final temperature of the mixture is called "adiabatic saturation temperature".
Wet Bulb Temperature.
The relative humidity of air vapor mixtures is measured by using dry and wet bulb thermometers.
The dry bulb thermometer is an ordinary thermometer, while the wet bulb thermometer has its bulb covered by a moist wick.
When the mixture flows past the two thermometers, the dry bulb thermometer shows the temperature of the stream, while water evaporates from the wick and its temperature falls.
This temperature is very close to the adiabatic saturation temperature if we neglect the heat transfer due to convection.
Psychrometric Chart.
This chart gives the value of absolute humidity versus temperature, along with the enthalpy.
From this chart you can determine the relative humidity given the dry and wet bulb temperatures.
We have, from the first law, that for a flow system with no heat transfer, the enthalpy is a constant.
Now, for the adiabatic saturation process, there is no heat transfer taking place, so that the adiabatic saturation lines are the same as the wet bulb temperature and the constant enthalpy lines.
Questions
1. The temperature at Phoenix is 35 °C with a relative humidity of 40%. Can a room be cooled using a conventional air cooler?
2. The temperature of Los Angeles is 37 °C with relative humidity of 83%. To what temperature can a room be cooled using a conventional air cooler?
Air Conditioning.
The human body can work efficiently only in a narrow range of conditions.
Further, it rejects about 60 W of heat continuously into the surroundings, and more during heavy exercise.
The temperature of the body is maintained by the evaporation of sweat from the body.
Thus, for comfort, both the temperature and the relative humidity should be low.
Conventional air conditioning consists of setting the humidity at an acceptable level, while reducing the temperature.
Reducing the humidity to zero is not the ideal objective.
For instance, low humidity leads to issues like high chances of static electricity building up, leading to damage of sensitive electronic equipment.
A humidity level of 50% is more acceptable in this case.
The most common method of reducing humidity is to cool the air using a conventional air conditioner working on a reversed Carnot cycle.
The vapor that condenses is removed.
Now, the air that is produced is very cold, and needs to be heated back up to room temperature before it is released back to the air conditioned area.
Common Thermodynamic Cycles.
Several thermodynamic cycles used in machines can be approximated with idealized cycles.
It was shown previously that a Carnot engine was the most efficient engine operating between two thermal reservoirs.
However, due to practical difficulties, Carnot cycle cannot be implemented in all situations.
The following sections deal with idealized (non Carnot) systems found in practice.
Rankine Cycle.
In the Rankine cycle, also called the "standard vapor power cycle", the working fluid follows a closed cycle.
We will consider water as a working substance. Other materials can be also used, for example organic one (see Organic Rankine Cycle); properties of the working fluids in use has great influence on the actual process.
In the Rankine cycle, water is pumped from a low pressure to a high pressure using a liquid pump.
This water is then heated in the boiler at constant pressure where its temperature increases and it is converted to superheated vapor.
This vapor is then expanded in an expander to generate work. This expander can be a turbine or a reciprocating (i.e. piston) machine such as those used in older steam locomotive or ship.
The output of the expander is then cooled in a condenser to the liquid state and fed to the pump.
The Rankine cycle differs from the Carnot cycle in that the input to the pump is a liquid (it is cooled more in the condenser).
This allows the use of a small, low power pump due to the lower specific volume of liquid compared to steam.
Also, the heat transfer in the boiler takes place mainly as a result of a phase change, compared to the isothermal heating of the ideal gas in the Carnot cycle, so that the efficiency is quite good (even though it is still lower than the Carnot efficiency).
The amount of heat transferred as the liquid is heated to its boiling point is very small compared to the heat transfer during phase change.
The steam is superheated so that no liquid state exists inside the turbine.
Condensation in the turbine can be devastating as it can cause corrosion and erosion of the blades.
There are several modifications to the Rankine cycle leading to even better practical designs.
In the "reheat cycle" there are two expanders working in series, and the steam from the high pressure stage is heated again in the boiler before it enters the low pressure expander.
This avoids the problem of moisture in the turbine and also increases the efficiency. The "regenerative cycle" is another modification to increase the efficiency of the Rankine cycle.
In many Rankine cycle implementations, the water enters the boiler in the subcooled state, and also, the large difference in temperature between the one at which heat is supplied to the boiler and the fluid temperature will give rise to irreversibilities which will cause the efficiency to drop.
In the regenerative cycle, the output of the condenser is heated by some steam tapped from the expander.
This causes the overall efficiency to increase, due to the reasons noted above.
Otto Cycle.
The "Otto Cycle" is the idealization for the process found in the reciprocating internal combustion engines which are used by most automobiles.
While in an actual engine the gas is released as exhaust, this is found to be a good way to analyze the process.
There are, of course, other losses too in the actual engine.
For instance, partial combustion and aspiration problems for a high speed engine.
The working material in the idealized cycle is an ideal gas, as opposed to the air fuel mixture in an engine.
Analysis.
Heat is transferred at constant volume in 1-2, so that "Q1-2 = m cv(T2 − T1)".
Similarly, the heat rejected in 3-4 is "Q3-4 = m cv (T3 − T4)".
The thermal efficiency of the Otto cycle is thus
"ηth = (Q1-2 − Q3-4)/Q1-2"
"ηth = 1 − Q3-4/Q1-2"
"ηth = 1 − (T3 − T4)/(T2 − T1)"
Since 2-3 and 4-1 are reversible adiabatic processes involving an ideal gas, we have,
"T2/T3 = (V3/V2)γ − 1"
and
"T4/T1 = (V1/V4)γ − 1"
But,
"V1 = V2"
and
"V3 = V4"
So, we have
"T2/T3 = T1/T4"
Thus,
"ηth = 1 − (T3/T2)(1 − T4/T3)/(1 − T1/T2)"
Or
"ηth = 1 − T3/T2"
If we introduce the term "rc = V3/V2" for the compression ratio, then we have,
"ηth = 1 − rc1 − γ"
As can be seen, increasing the compression ratio will improve thermal efficiency.
However, increasing the compression ratio causes the peak temperature to go up, which may cause spontaneous, uncontrolled ignition of the fuel, which leads to a shock wave traveling through the cylinder, and is called "knocking".
Diesel Cycle.
The Diesel cycle is the idealized cycle for compression ignition engines (ones that don't use a spark plug).
The difference between the Diesel cycle and the Otto cycle is that heat is supplied at constant pressure.
Analysis.
Heat is transferred to the system at constant pressure during 1-2 so that
"Qin = m cp (T2 − T1)"
Heat is rejected by the system at constant volume during 3-4:
"Qout = m cv (T3 − T4)"
Thus, the efficiency of the Diesel cycle is
"ηth = (Qin − Qout)/Qin"
"ηth = 1 − Qout/Qin"
"ηth = 1 − (cv (T3 − T4))/(cp (T2 − T1))"
"ηth = 1 − (1/γ) (T3 − T4)/(T2 − T1)"
formula_4
We define the cutoff ratio as "rt = V2/V1", and since the pressures at 1 and 2 are equal, we have, applying the ideal gas equation, "T2/T1 = rt".
Now, for the adiabatic processes 2-3 and 4-1 we have,
formula_5
formula_6
Since "V3 = V4", we have
formula_7
formula_8
formula_9
Dual Cycle.
The dual cycle is sometimes used to approximate actual cycles as the time taken for heat transfer in the engine is not zero for the Otto cycle (so not constant volume).
In the Diesel cycle, due to the nature of the combustion process, the heat input does not occur at constant pressure.
Gas Turbine Cycle (or Joule-Brayton Cycle).
Gas turbines are rotary internal combustion engines.
As the first stage air is drawn in from outside and compressed using a compressor.
Then the fuel is introduced and the mixture is ignited in the combustion chamber.
The hot gases are expanded using a turbine which produces work.
The output of the turbine is vented outside as exhaust.
The ideal gas turbine cycle is shown above.
The four stages are
Large amount of work is consumed in process 4-1 for a gas turbine cycle as the working material (gas) is very compressible.
The compressor needs to handle a large volume and achieve large compression ratios.
Analysis.
The heat input in a gas turbine cycle is given by "Qin = m cp (T2 - T1)" and the heat rejected "Qout = m cp (T3 - T4)".
Thus the thermal efficiency is given by
formula_10
formula_11
formula_12
Since the adiabatic processes take place between the same pressures, the temperature ratios are the same
formula_13
Or
formula_14
Where "rp" is the pressure ratio and is a fundamental quantity for the gas turbine cycle.
Refrigeration Cycles.
The ideal refrigeration cycle is reverse of Carnot cycle, working as a heat pump instead of as a heat engine.
However, there are practical difficulties in making such a system work.
The "gas refrigeration cycle" is used in aircraft to cool cabin air.
The ambient air is compressed and then cooled using work from a turbine.
The turbine itself uses work from the compressed air, further cooling it.
The output of the turbine as well as the air which is used to cool the output of the compressor is mixed and sent to the cabin.
The Rankine vapor-compression cycle is a common alternative to the ideal Carnot cycle.
A working material such as Freon or R-134a, called the "refrigerant", is chosen based
on its boiling point and heat of vaporization.
The components of a vapor-compression refrigeration system are the compressor, condenser, the expansion (or throttling) valve, and the evaporator.
The working material (in gaseous form) is compressed by the compressor, and its output is cooled to a liquid in the condenser.
The output of the condenser is throttled to a lower pressure in the throttling valve, and sent to the evaporator which absorbs heat.
The gas from the evaporator is sent to the compressor, completing the cycle.
Standard refrigeration units use the throttling valve instead of a turbine to expand the gas as the work output that would be produced is not significant to justify the cost of a turbine.
There are irreversibilities associated with such an expansion, but it is cost effective when construction costs are considered. | 4,529 |
Electronics/Template. "This page is for editors of the book, and deals with drawing circuit diagrams for illustration."
Inkscape.
There is a SVG electrical components library available, which should provide a possibility to draw the images in Inkscape or similar vector graphics editor:
The images remain editable, look nice even when scaled or printed and take small amount of space.
You can edit this template and add more components, of course. See the image description page for more info.
See the Category:Created_with_electrical_symbols_library for examples.
Klunky.
Special Klunky pictures courtesy of
Any requests?
I recommend using Klunky schematic editor to do diagrams, and have contacted the author to see about making my own version, with more parts and easier to get into 2-color PNG with transparency, etc. See my Wikipedia page () for some of the stuff I have done with it, and feel free to give me style suggestions or recommend other drawing programs/sites. -
For instance, the above would look like this, Klunkified, and took me this long to make. (6 minutes? That seems longer than it actually took.) It is pretty nice for web graphics:
"Not bad. The question is how big we want our pictures to be?
What would really be nice is to have some sort of circuit builder. That would be a great way to teach electronics, but it would probably be a lot of work.
Circuit builder of choice: mspaint.exe"
Instructions for making a Klunky drawing in Windows with the help of MSPaint:
More detailed instructions are available at http://www.qsl.net/wd9eyb/klunky/guide.html
Note that there are many ways to streamline this process (steps 3 through 9), such as screen capture programs, etc. I use Paint Shop myself, but it is certainly not the best solution. I just use it out of habit.
Here are some others I made:
I don't actually recommend that ugly 4 way connection. That is just something I sent to the author of the program since he doesn't include a 4 way because it might get confused with the non contacting wires. i think it is not very confusing, and you should just use a regular 4 way connection. in fact, i will make one:
Modified Klunky.
I modified the Klunky available on the web. I added a bunch of new symbols (all of the above symbols, like ideal sources, cells, etc.), and tweaked a few so they were better, in my opinion. Plus you can run it from your own machine, which is much faster. You can download it from http://mysite.verizon.net/negatron/klunky.zip Just unzip it into a folder and then open klunky.html (however that site seems to be down. keep checking and i will see if it is something i can fix.) Or you can give me your email address and I will send it. -
TeX-based diagrams?
Is there a way to create diagrams with a TeX-like language? They are adding musical notation, hieroglyphs, etc. to the mediawiki. I don't understand all the details but here is something similar: . - 20:59, 26 May 2004 (UTC) | 755 |
General Mechanics/Energy Analysis. Energy Analysis.
Figure 11.2: Potential, kinetic, and total energy of a one-dimensional harmonic oscillator plotted as a function of spring displacement.
For a spring, Hooke's law says the total force is proportional to the displacement, and in the opposite direction.
Since this is independent of velocity, it is a conservative force. We can integrate to find the potential energy of the mass-spring system,
formula_2
Since a potential energy exists, the total energy
is conserved, i. e., is constant in time.
We can now use energy conservation to determine the velocity in terms of the position
We could integrate this to determine the position as a function of time, but we can deduce quite a bit from this equation as it is.
It is fairly evident how the mass moves. From Hooke's law, the mass is always "accelerating" toward the "equilibrium position", so we know which sign of the square root to take.
The velocity is zero when
If "x" were larger than this the velocity would have to be imaginary, clearly impossible, so the mass must be confined between these values. We can call them the turning points.
If the mass is moving to the left, it slows down as it approaches the left turning point. It stops when it reaches this point and begins to move to the right. It accelerates until it passes the equilibrium position and then begins to decelerate, stopping at the right turning point, accelerating toward the left, etc. The mass thus oscillates between the left and right turning points.
How does the period of the oscillation depend on the total energy of the system?
We can get a general idea without needing to solve the differential equation.
There are only two parameters the period, "T", could depend on; the mass, "m", and the spring constant, "k".
We know "T" is measured in seconds, and "m" in kilograms. For the units in Hooke's law to match, "k" must be measured in N·m-1, or equivalently, in kg·s-2.
We immediately see that the only way to combine "m" and "k" to get something measured in seconds is to divide, cancelling out the kg's.
Therefore "T"∝formula_6
We have established the general way the period depends on the parameters of the problem, without needing to use calculus.
This technique is called "dimensional analysis", and has wide application. E.g., if we couldn't calculate the proportionality constant exactly, using calculus, we'd be able to deduce by doing one experiment. Without dimensional analysis, if calculus failed us we'd have to do scores of experiments, each for different combinations of "m" and "k".
Fortunately, the proportionality constants are typically small numbers, like formula_7 or formula_8. | 652 |
Electronics/Electrons. "Two atoms are walking down the street. The first atom says to the second atom "I think I lost an electron!" The second says "Are you sure?" To which the first states "I'm positive!""
Electrons.
"This is a rough draft"
Electronics is the study and use of devices that control the flow of electrons (or other charged particles). These devices can be used to process information or perform tasks using electromagnetic power.
Atoms, the smallest particles of matter "(which cannot be divided and still blah blah)", are made of protons, electrons, and neutrons.
Electrons have a negative charge, and protons have a positive charge. Neutrons have no charge. The notation that a charge is positive or negative is arbitrary.
Particles that have the same charge (such as two electrons) have a tendency to push each other away; to "repel". Particles with opposite charge (such as a proton and an electron) tend to move closer together, or "attract". This effect extends from every particle to infinity, although it decreases with distance. It is called the particle's "electric field".
Protons and neutrons combine to form the atom's nucleus, with electrons circling them at a relatively great distance (held near the protons by the fact that they are oppositely charged).
All atoms have electrons surrounding them, which tend to exist in several layers. (The modern model of the atom, which involves quantum mechanics, is more complicated, but both models are equally valid for electronics, so we will use the vastly simpler classical model for our introduction to electronics.) The outermost electrons are free to move from atom to atom. The inner shells of electrons are held tightly to just one atom. The electrons that are free to move are called "valence electrons".
Electronic devices are based on the following principles:
The most commonly used conductors are metals. Metals have electrons that are very free to move from atom to atom, and do so constantly. This is sometimes thought of as many atomic nuclei surrounded by a "sea of electrons". | 477 |
Electronics/Voltage and Current. Voltage.
"This is a rough draft."
This section talks about the nature of voltage and current. Voltage and current sources and series and parallel voltage and current belong in the DC section. I'm not sure where voltage drops should go.
Voltage is a potential in an electric field between two charges. A voltage drop is a change in potential. Voltages add or subtract in series. (Relate this to voltage symbol)
"(Moved to talk page)"
Two electrically charged particles separated by a distance will have a potential energy associated with them,
Potential energy between two charges, where k is a constant, q and Q are the value of the two charges and r is the distance. Note that potential falls off as 1/r.
formula_1
The potential divided by the amount of charge is the voltage:
formula_2
formula_3
Ideal voltage sources.
An ideal voltage source is a fundamental electronics component that creates a constant voltage between two points regardless of whatever else is connected to it. Since it is ideal, some circuit configurations are not allowed.
"Real" voltage sources, such as batteries, power supplies, piezoelectric disks, generators, etc. have an internal source impedance (in series with the source), which is very important to understand.
hfdh
Current.
It is sometimes taught that current in electric circuits is composed of electrons, which flow from the negative terminal of the power source to the positive at the speed of light. This is not (completely) true.
(Section relating voltage to current.) As you increase voltage you apply an electric field to electrons and they travel from the negative to the positive potential. This is why increasing voltage directly increases current. Reversing the voltage reverses the current. Without resistance this is effectively a short meaning the electrons flow unhindered.
(section where you have voltage but no current.) Sometimes you have voltage but no current. Describe its effects on circuits.
So, negative particles drift from negative to positive voltage, and positive particles drift in the opposite direction from positive to negative voltage. The particles drift at different speeds in different materials. speed of "holes" based on bandgap. Given the presence of holes we tend to ignore the particles and focus on the current flow. Current is measured by the amount of charge flow per unit time and represents the speed of the electromagnetics waves. In talking about current we will mainly talk about electrons flowing, as they are the predominant charge carriers in metal and many circuit components.
Voltage = potential between two charges.
Defined as the derivative of the flux linkage:
formula_4
Current = flow of electrons
Defined as the rate of change of the charge:
formula_5
Ideal current sources.
An ideal voltage source is a fundamental electronics component that creates a constant current through a section of circuit, regardless of whatever else is connected to it. Since it is ideal, some circuit configurations are not allowed.
"Real" current sources, such as batteries, power supplies, piezoelectric disks, generators, etc. have an internal source impedance (in parallel with the source), which is very important to understand. | 714 |
Python Programming/Getting Python. To program in Python, you need a Python interpreter to run your code—we will discuss interpreters later. If it's not already installed, or if the version you are using is obsolete, you will need to obtain and install Python using the methods below. The current Python versions are 3.x; versions 2.x are discontinued and no longer maintained.
Installing Python in Windows.
Go to the Python Homepage and get the proper version for your platform. Download it, read the instructions and get it installed.
To run Python from the command line, you will need to have the python directory in your PATH. You can instruct the Python installer to add Python to the path, but if you do not do that, you can add it manually. The PATH variable can be modified from the Window's System control panel. To expand the PATH in Windows 7:
If you prefer having a temporary environment, you can create a new command prompt short-cut that automatically executes the following statement:
PATH %PATH%;c:\python27
If you downloaded a different version (such as Python 3.1), change the "27" for the version of Python you have (27 is 2.7.x, the current version of Python 2.)
Cygwin.
By default, the Cygwin installer for Windows does not include Python in the downloads. However, it can be selected from the list of packages.
Installing Python on Mac.
Users on Mac OS X will find that it already ships with Python 2.3 (OS X 10.4 Tiger) or Python 2.6.1 (OS X Snow Leopard), but if you want the more recent version head to Python Download Page follow the instruction on the page and in the installers. As a bonus you will also install the Python IDE.
Installing Python on Unix environments.
Python is available as a package for most Linux distributions. In some cases, the distribution CD will contain the python package for installation, while other distributions require downloading the source code and using the compilation scripts.
Gentoo Linux.
Gentoo includes Python by default—the package management system "Portage" depends on Python.
Ubuntu Linux.
Users of Ubuntu will notice that Python comes installed by default, only it sometimes is not the latest version. To check which version of Python is installed, type python -V into the terminal.
Arch Linux.
Arch Linux does not come with Python pre-installed by default, but it is easily available for installation through the package manager to pacman. As root (or using sudo if you've installed and configured it), type:
pacman -S python
This will be update package databases and install Python 3. Python 2 can be installed with:
pacman -S python2
Other versions can be built from source from the Arch User Repository.
Source code installations.
Some platforms do not have a version of Python installed, and do not have pre-compiled binaries. In these cases, you will need to download the source code from the official site. Once the download is complete, you will need to unpack the compressed archive into a folder.
To build Python, simply run the configure script (requires the Bash shell) and compile using make.
Other Distributions.
Python, also referred to as CPython to avoid confusion, is written in the , and is the official reference implementation. CPython can run on various platforms due to its portability.
Apart from CPython there are also other implementations that run on top of a virtual machine. For example, on Java's JRE (Java Runtime Environment) or Microsoft's .NET CLR (Common Language Runtime). Both can access and use the libraries available on their platform. Specifically, they make use of reflection that allows complete inspection and use of all classes and objects for their very technology.
"Python Implementations (Platforms)"
Integrated Development Environments (IDE).
It's common to use a simple text editor for writing Python code, but you may feel the need to upgrade to a more advanced "IDE". CPython ships with IDLE; however, IDLE is not considered user-friendly. For Linux, KDevelop and Spyder are popular. For Windows, PyScripter is free, quick to install, and comes included with PortablePython.
"Some Integrated Development Environments (IDEs) for Python"
The Python official wiki has a complete list of IDEs.
There are several commercial IDEs such as Komodo, BlackAdder, Code Crusader, Code Forge, and PyCharm. However, for beginners learning to program, purchasing a commercial IDE is unnecessary.
Trying Python online.
You can try Python online, thereby avoiding the need to install. The online Python shell at Python's official site provides a web Python REPL (read–eval–print loop).
Keeping Up to Date.
Python has a very active community and the language itself is evolving continuously. Make sure to check python.org for recent releases and relevant tools. The website is an invaluable asset.
Public Python-related mailing lists are hosted at mail.python.org. Two examples of such mailing lists are the Python-announce-list to keep up with newly released third party-modules or software for Python and the general discussion list Python-list. These lists are mirrored to the Usenet newsgroups comp.lang.python.announce & comp.lang.python. | 1,230 |
Python Programming/Basic Syntax. There are five fundamental concepts in Python.
Semicolons.
Python does not normally use semicolons, but they are allowed to separate statements on the same line, if your code has semicolons; your code isn't "Pythonic"
Case Sensitivity.
All variables are case-sensitive. Python treats 'number' and 'Number' as separate, unrelated entities.
Spaces and tabs don't mix.
Instead of block delimiters (braces → "{}" in the C family of languages), indentation is used to indicate where blocks begin and end. Because whitespace is significant, remember that spaces and tabs don't mix, so use only one or the other when indenting your programs. A common error is to mix them. While they may look the same in editor, the interpreter will read them differently and it will result in either an error or unexpected behavior. Most decent text editors can be configured to let tab key emit spaces instead.
Python's Style Guideline described that the preferred way is using 4 spaces.
Tips: If you invoked python from the command-line, you can give -t or -tt argument to python to make python issue a warning or error on inconsistent tab usage.
pythonprogrammer@wikibook:~$ python -tt myscript.py
This will issue an error if you have mixed spaces and tabs.
Objects.
In Python, like all object-oriented languages, there are aggregations of code and data called "objects", which typically represent the pieces in a conceptual model of a system.
Objects in Python are created (i.e., instantiated) from templates called "classes" (which are covered later, as much of the language can be used without understanding classes). They have "attributes", which represent the various pieces of code and data which make up the object. To access attributes, one writes the name of the object followed by a period (henceforth called a dot), followed by the name of the attribute.
An example is the 'upper' attribute of strings, which refers to the code that returns a copy of the string in which all the letters are uppercase. To get to this, it is necessary to have a way to refer to the object (in the following example, the way is the literal string that constructs the object).
'bob'.upper
Code attributes are called "methods". So in this example, upper is a method of 'bob' (as it is of all strings). To execute the code in a method, use a matched pair of parentheses surrounding a comma separated list of whatever arguments the method accepts (upper doesn't accept any arguments). So to find an uppercase version of the string 'bob', one could use the following:
'bob'.upper()
Scope.
In a large system, it is important that one piece of code does not affect another in difficult to predict ways. One of the simplest ways to further this goal is to prevent one programmer's choice of a name from blocking another's use of that name. The concept of scope was invented to do this. A scope is a "region" of code in which a name can be used and outside of which the name cannot be easily accessed. There are two ways of delimiting regions in Python: functions or modules. They each have different ways of providing their content outside of their scope. Functions return data as the result of execution. Modules leads us to another concept, namespace.
Namespaces.
It would be possible to teach Python without the concept of namespaces because they are so similar to attributes, which we have already mentioned, but the concept of namespaces is one that transcends any particular programming language, and so it is important to teach. To begin with, there is a built-in function dir() that can be used to help one understand the concept of namespaces. When you first start the Python interpreter (i.e., in interactive mode), you can list the objects in the current (or default) namespace using this function.
Python 2.3.4 (#53, Oct 18 2004, 20:35:07) [MSC v.1200 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
»> dir()
['__builtins__', '__doc__', '__name__']
This function can also be used to show the names available within a module's namespace. To demonstrate this, first we can use the type() function to show what kind of object __builtins__ is:
»> type(__builtins__)
<type 'module'>
Since it is a module, it has a namespace. We can list the names within the __builtins__ namespace, again using the dir() function (note that the complete list of names has been abbreviated):
»> dir(__builtins__)
['ArithmeticError', ... 'copyright', 'credits', ... 'help', ... 'license', ... 'zip']
Namespaces are a simple concept. A namespace is a particular place in which names specific to a module reside. Each name within a namespace is distinct from names outside of that namespace. This layering of namespaces is called scope. A name is placed within a namespace when that name is given a value. For example:
»> dir()
['__builtins__', '__doc__', '__name__']
»> name = "Bob"
»> import math
»> dir()
['__builtins__', '__doc__', '__name__', 'math', 'name']
Note that I was able to add the "name" variable to the namespace using a simple assignment statement. The import statement was used to add the "math" name to the current namespace. To see what math is, we can simply:
»> math
<module 'math' (built-in)>
Since it is a module, it also has a namespace. To display the names within this namespace, we:
»> dir(math)
['__doc__', '__name__', 'acos', 'asin', 'atan', 'atan2', 'ceil', 'cos', 'cosh', 'degrees', 'e',
'exp', 'fabs', 'floor', 'fmod', 'frexp', 'hypot', 'ldexp', 'log', 'log10', 'modf', 'pi', 'pow',
'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh']
If you look closely, you will notice that both the default namespace and the math module namespace have a '__name__' object. The fact that each layer can contain an object with the same name is what scope is all about.
To access objects inside a namespace, simply use the name of the module, followed by a dot, followed by the name of the object. This allows us to differentiate between the __name__ object within the current namespace, and that of the object with the same name within the math module. For example:
»> print (__name__)
__main__
»> print (math.__name__)
math
»> print (math.__doc__)
This module is always available. It provides access to the
mathematical functions defined by the C standard.
»> print (math.pi)
3.1415926535897931 | 1,672 |
Haskell/Beginning. Haskell is a programming language. If you can write and understand Haskell, you can create new computer programs and understand and modify programs others have written. Learning to program is a fairly complex task, but Haskell is a great way to start because it is fairly simple and predictable. Even if you end up doing most of your programming in other languages, a significant portion of your knowledge will carry over. Haskell is more than a beginning language, however; it is also one of the most advanced and powerful.
Haskell Software.
To begin using any programming language, you will need some special software to make up your "development toolchain". At the minimum, you will need a compiler or an interpreter.
First, we need to reveal a little about how computers work. You may have heard of CPUs(Central Processing Units). They are pieces of hardware responsible for interpreting data known as machine language stored in the computer's memory. Machine language encodes simple instructions which, when processed by the CPU, cause the computer to do useful things such as bring you to this Web page. In other words, it is a programming language. The programs your computer executes, and the data they operate on, are stored in the same manner.
One significant consequence of this architecture is that programs can write other programs. That is how interpreters and compilers work. They translate programs written in a language such as Haskell into programs written in machine language which can then be directly executed by the computer.
The difference between a compiler and an interpreter has to do with the internal workings of the software, and you don't need to worry about it too much. Today, the difference is becoming increasingly unclear and irrelevant.
For Haskell, we use the Glasgow Haskell Compiler (GHC). It is a free/libre/open-source program, available for all major operating systems. Download
The REPL: Using Haskell as a Calculator.
GHC includes a program known as GHCi, or "GHC Interactive." This program lets you type in small Haskell programs on one line, and executes them when you hit Enter. Consult the GHC documentation for info on how to start GHCi, and do so.
You should have a prompt, which says something such as codice_1, in front of you. (Don't be alarmed if it says something else, such as codice_2). When GHCi is in this state, it is ready to accept and execute a program. Try typing in the following simple program: GHCi should respond by displaying the number two. This is, in fact, the purpose of this program: to compute the sum of 1 and 1, and display it. Programs that compute things and display them are called "expressions", and they make up the larger part of Haskell. When you execute an expression to determine the value it produces, it is referred to as "evaluating" that expression.
Note that, once you've evaluated an expression, you can do more than simply display it; in fact, there are a variety of ways in which the values expressions produce can be used. We will encounter these various techniques later on. For now, simply be aware that they exist.
Moving back to less theoretical matters, at this point, your interaction with GHCi should look something like this:
When showing examples, we will display interactions with GHCi this way, as well. A program will generally be included with its result, and preceded by a codice_1 prompt. You can duplicate the same interaction with GHCi by typing in the program on the prompt.
More Arithmetic.
As you may have guessed, Haskell supports a full complement of arithmetic operators; addition (codice_4), subtraction (codice_5), multiplication (codice_6), and division (codice_7). Numbers can be notated in the usual way, as integers or real numbers, with one catch; no number may be written without numbers before the decimal point. That is, for instance, codice_8 should always be written as codice_9. The operators follow the normal order of operations, and parentheses can be used in the usual way. You can also use a variety of constants and functions, such as codice_10, codice_11, codice_12, codice_13, codice_14, and codice_15.
Go ahead and try out a few expressions; you can't break anything if you mess up. Here are some simple examples:
Note that the spaces in the examples are not necessary; the first one could have been written codice_16, and the fifth codice_17, for instance. In general, Haskell isn't picky about spaces, except where otherwise noted. When in doubt, however, use more spaces, rather than fewer.
Errors.
Any computer user is familiar with errors. You can get them when programming, as well. Try this little experiment:
When you make a mistake in your program, GHCi will notify you, and tell you what it perceives to be the problem. Unfortunately, it doesn't always guess correctly, and it's usually rather cryptic about its diagnosis. In this example, aside from the useless comment about indentation, it's on the right track, but it still has the latter problem of being rather cryptic. So, what is a "parse error?"
A parser is the part of a compiler responsible for breaking the program down into logical pieces, and converting it to a format suitable for translation into machine language. A "parse error," then, is when the compiler can't make sense of your program; this means that there's a problem with your program.
So, what's this business: codice_18? The first part, codice_19, means that it's reporting an error from the program you just typed. The first number is the number of the line that the error occurred on; it will always be 1 for interactively entered programs, so, again, it is of little use to us. The second is the column in which GHC thinks the erroneous piece of code occurs (actually, the first column is numbered zero, so it's the offending code's column number minus one). Here it points to the fourth column, just after the plus sign; this is correct, because the problem is that we omitted a right operand for the operator. (By the way, in general, do not take these numbers as Gospel; GHC sometimes gives you numbers that are slightly off.)
Now, what about when GHC guesses the problem incorrectly? Let's consider a slightly modified version of the mistake above:
We made a small change, and the error message changed completely. In addition, the message now diagnoses a problem completely different than the actual one, and refers to fairly advanced features of Haskell which you have yet to learn. An unfortunately large class of errors produces messages like this one; dealing with these messages is a more challenging aspect of learning Haskell. (Other programming systems share this problem, as well, but most are somewhat better off than Haskell.)
Of course, this was an extreme example; most of the time, the messages will not be so far off-target as this one.
Try typing in a few invalid programs and see what kinds of error messages you get back, just to get a feel for them. Again, you can't break anything, so don't worry about it. Here are some examples:
Variables.
Haskell supports a feature called variables. These are similar to the variables of algebra, but there are more restrictions on their usage.
A variable is named by one or more letters; codice_20, codice_21, codice_22, and codice_23 are all acceptable names for variables. They can contain uppercase letters, as well, but not as the first letter; codice_24, for instance, is not an acceptable variable name, although codice_25 is. The typical use of uppercase letters is to delimit words in names; for instance, instead of writing codice_26, it is customary to write codice_27, which is easier on the eyes.
You can assign values to variables with a program of the form:
let "variable name" = "value"
For instance, the program codice_28 defines codice_20 to be five. The value can also be an arbitrary expression, such as codice_30.
Notice that the name of a variable is the "only" thing that can appear on the left side of an equals sign. These programs all work incorrectly:
Curiously, GHCi generates no errors for the latter two. That's because they're valid Haskell; they just don't do what you expect. For instance, after executing the second statement, codice_31 is five, and, after executing the third statement, attempting to find the value of codice_20 will result in GHCi hanging. (Press ctrl+c in UNIX, ctrl+. in Mac OS X, and ctrl+break in Windows to stop it.)
Bottom line: Haskell isn't exactly algebra; don't use it as such.
Once you've established a variable's value, you can use that variable in following expressions; each occurrence of the variable will be substituted for its value. For instance:
Multiple variables can be established in one codice_33 by delimiting the assignments with a semicolon. For instance, the previous example could be rewritten as:
Functions.
While you've made it through quite a bit of material, you may feel like you're not much closer to programming your computer. The programs we've written so far haven't accomplished much; you'd do just as well with pencil and paper or a conventional pocket calculator. By the end of this chapter, you will be able to do less trivial things, but the examples will still be quite contrived. However, at this point, you have nowhere to go but up; the variety and complexity of the programs you can write will begin to grow exponentially from here, and continue for the next several chapters, as you learn about new kinds of expressions, and new ways to combine expressions.
Haskell supports functions. To begin with, don't assume any preconceptions of this word related to mathematical functions; Haskell's functions are somewhat distinct.
A better match to Haskell functions is Haskell variables. A variable stands in for an expression. A function stands in for an expression, as well, with one twist: it takes an argument; a variable which is defined inside the function, supplied when the function is used. This concept is perhaps best understood by example: This code defines the function codice_34, with the argument codice_20.
What can we do with codice_34? We can "apply" it to an argument. Suppose the argument is to be 4. The code for this is:
What's going on here? Let's refer back to the definition of codice_34:
The expression codice_38 is substituted by the definition of codice_34, with codice_20 substituted by four. Thus, it becomes codice_41, which is, of course, 7.
The general form of a function definition is:
let "function" "argument" = "definition"
And the general form of a function application is:
"function" "argument"
Notice that, in these definitions, the word "argument" is used in two different ways. The first is the kind the function has attached to its definition; simply a name standing in for a value that is supplied when it is applied. The second is the actual value that ousts the previous type of argument when the function is applied, resulting an expression which can be evaluated.
A few more examples:
Again, there is a simple technique for figuring out the value of a function expansion by hand:
Functions With Several Arguments.
The function notation suggests that it might be possible to create a function with more than one argument. In fact, this is possible, and works exactly as you might expect:
One "gotcha" to watch out for when programming with multi-argument functions is giving too many arguments, or not enough arguments, to a function. These examples demonstrate the problem:
Both of these errors look fairly similar. In general, if you get an error of this form, check that you gave the right number of arguments to your functions.
Functions in Expressions.
Up until now, we have only given numbers as arguments to functions. However, you can give expressions as arguments, as well, and use function applications as expressions:
Function applications are evaluated before operators; thus, f 4 + 2 is equivalent to (f 4) + 2, not f (4 + 2).
Since function applications are expressions, they can be used in function definitions. For instance:
There are several small points to note here:
Conditional Tests.
We promised that, as you read more of this book, you would learn to write newer, more exciting types of programs. In this chapter, we will fill in another missing piece of the puzzle.
The programs you have written so far have seemed somewhat simplistic; they haven't been able to make choices, to do different things at different times. An easy to achieve simple choice-making is to use an if expression. These expressions take the following form:
if "test" then "expression" else "expression"
The test part can take one of the following forms:
"expression" == "expression"
"expression" /= "expression"
"expression" < "expression"
"expression" > "expression"
"expression" <= "expression"
"expression" >= "expression"
Each form describes some sort of relation between the two expressions; for instance, < is the mathematical less-than test. Each is a plain-text corruption of some mathematical operator:
When an if expression is evaluated, if the "test" part states something true (e.g. 5 < 6), then it evaluates to the "then" expression; otherwise, if the "test" part states something false (e.g. 5 == 6), then it evaluates to the "else" expression. This is demonstrated in these examples:
Note that, in the last three examples, the parentheses were not necessary; however, if the last example had been written with the operands to the plus sign reversed, the parentheses would have been necessary; thus, it would be
If it were written without the parentheses, it would evaluate to:
Examples.
Here are a few examples of functions using if expressions.
Numerical Three-Way Tests.
This function corresponds to the following mathematical function:
formula_1
The last test, instead of being if x < 0 then n, is simply else n. This is because, by the definition of the numeric relations, if x is neither less than or equal to zero, it must be greater than zero, so the test will always be true. Furthermore, every if needs an "else" clause, and what would you put in an "else" clause that can never be reached?
Actually, Haskell has a tool for these cases; undefined. This is the name of a special value that, when produced as an answer from an expression, simply flags an error. It is a good value to put in "impossible" cases of your if expressions.
Sign.
This function corresponds to the following mathematical function:
formula_2
We could have defined it like this:
However, since nif turns out to be a generalization of the sign function, it is simpler to define it as an application of nif. In fact, expanding nif into the function's body leaves you with exactly the above code!
References.
/Not in book | 3,521 |
Electronics/Simplifying Capacitor/Inductor Networks. Introduction.
<br>
Capacitors and inductors follow similar laws as resistors when it comes to simplification.
Simplifying Capacitor Configurations.
Capacitors in Parallel.
<br>
Capacitors in parallel are the same as increasing the total surface area of the capacitors to create a larger capacitor with more capacitance. In a capacitor network in parallel, all capacitors have the same voltage over them.
<br>
<br>
In a parallel configuration, the capacitance of the capacitors in parallel is the sum of the capacitance of all the capacitors.
Capacitors in Series.
<br>
Capacitors in series are the same as increasing the distance between two capacitor plates. As well, it should be noted that placing two 100V capacitors in series results in the same as having one capacitor with the total maximum voltage of 200V. This, however, is not recommended to be done in practice. Especially with capacitors of different values. In a capacitor network in series, all capacitors can have the a different voltage over them.
<br>
<br>
In a series configuration, the capacitance of all the capacitors combined is the sum of the reciprocals of the capacitance of all the capacitors.
Simplifying Inductor Configurations.
An inductor works by opposing current change
Inductors in Parallel.
Each inductor has a decreased amount of current flowing through it.<br>
Take two inductors of the same strength that are in parallel. This divides the current so half the current is flowing through each inductor.
formula_3
Inductors in Series.
Inductors in series are just like resistors in series. Simply add them up. | 449 |
MATLAB Programming/Advanced Topics/Toolboxes and Extensions/Simulink. Sample Time Colors.
By selecting Format->Sample Time Colors, you can get Simulink to color code signal lines according to their sample times. Colors are only updated when the model is "updated" or simulated.
The most common colors are:
For the rest of the colors and other information, see Enabling Sample Time Colors (the Mathworks website)
"Note: Constant sample time will only be displayed if Inline Parameters is checked in the Advanced Tab of Simulation->Simulation Parameters. This is because constant blocks can have variables as their arguments." | 147 |
Starting and Running a Wiki Website. This short book is a guide on how to start a wiki website and run it, including the choice of wiki software, whether to host the wiki yourself or go for a hosted wiki, and what choices there are of hosted wikis. | 60 |
William Shakespeare's Works/Tragedies/Othello/Iago. The name Iago is a Spanish name, in English the name is James. When England was under attack by Spain the King was King Iago so to the British the name had a bad connotation. | 59 |
Robotics. Robotics brings together several very different engineering areas and skills. There is metalworking for the body. There is mechanics for mounting the wheels on the axles, connecting them to the motors and keeping the body in balance. You need electronics to power the motors and connect the sensors to the controllers. At last you need the software to understand the sensors and drive the robot around.
This book tries to cover all the key areas of robotics as a hobby. When possible examples from industrial robots will be addressed too.
You'll notice very few "exact" values in these texts. Instead, vague terms like "small", "heavy" and "light" will be used. This is because most of the time you'll have a lot of freedom in picking these values, and all robot projects are unique in available materials.
Design Basics.
"Note to potential contributors: this section could be used to discuss the basics of robot design/construction."
Physical Construction.
"This section could be used to discuss various means through which robots are constructed."
Robot control.
"This section could be used to discuss the control method and control algorithm introduces and analyzes the robot, including the position control, trajectory control, force control, torque control, compliance control, hybrid force / position control, decomposition motion control, variable structure control, adaptive control and hierarchical control, fuzzy control, learning control, neural control and evolutionary control, intelligent control."
Components.
"This section could be used to discuss components used in robotics or the making of robots."
Computer Control.
"This section could be used to discuss the things involved with controlling robots via computers."
Sensors.
Sensors that a robot uses generally fall into three different categories:
Sensors aren't perfect. When you use a sensor on your robot there will be a lot of times where the sensors acts funny. It could miss an obstacle, or see one where none is. Key to successfully using sensors is knowing how they function and what they "really" measure.
Exotic Robots.
"This section could be used to cover "special" robots." | 470 |
XML - Managing Data Exchange/Introduction/Answers. Exercise 1.
Use NetBeans to create a markup file describing a restaurant. The markup should identify the name and address of the restaurant and the type of food or foods in which it specializes.
Answer.
Submitted by Princess Anne Rayborn<br>
Exercise 2.
Let's assume we want to create a personnel file for a smaller company.
What kind of data do we have?
Analyse the data from following table. Our goal is to transform it into a markup file.
Name of the company: 'Exercises inc.'
Answer.
Submitted by Stefan Meyer (Team 1)<br> | 164 |
XML - Managing Data Exchange/The one-to-many relationship/Answers. Chapter.
To return to the chapter, follow this link: One-to-many relationship
Exercises.
To view the exercises, follow this link: exercises
Answer - Exercise 1.
XML schema:
XML document:
Answer - Exercise 2.
XML schema:
XML document:
Answer - Exercise 3.
XML schema:
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="unqualified">
<!-- Spa Finder -->
<xsd:element name="spaFinder">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="spa" type="spaDetails" minOccurs="1"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<!-- Spa -->
<xsd:complexType name="spaDetails">
<xsd:sequence>
<xsd:element name="spaName" type="xsd:string"/>
<xsd:element name="spaOwner" type="xsd:string"/>
<xsd:element name="spaPhone" type="xsd:string"/>
<xsd:element name="spaCity" type="xsd:string"/>
<xsd:element name="spaState" type="xsd:string"/>
<xsd:element name="spaAddress" type="xsd:string"/>
<xsd:element name="startedIn" type="xsd:date"/>
<xsd:element name="spaType" type="xsd:string"/>
<!--Activity is a complexType defined in the Spa to
indicate the one-to-many relationship between spa and activities.-->
<xsd:element name="activity" type="activityDetails" minOccurs="1"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<!-- Activity -->
<xsd:complexType name="activityDetails">
<xsd:sequence>
<xsd:element name="activityName" type="xsd:string"/>
<xsd:element name="description" type="xsd:string"/>
<xsd:element name="price" type="xsd:decimal" />
<!--Offering is a complexType defined in the Activities to
indicate the one-to-many relationship between activities and offerings.-->
<xsd:element name="offering" type="offeringDetails" minOccurs="1"
maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<!-- Offering -->
<xsd:complexType name="offeringDetails">
<xsd:sequence>
<xsd:element name="days" type="xsd:string"/>
<xsd:element name="time" type="xsd:string"/>
<xsd:element name="practitioner" type="xsd:string" />
<xsd:element name="floor" type="xsd:integer"/>
<xsd:element name="room" type="xsd:string" />
</xsd:sequence>
</xsd:complexType></xsd:schema>
Exercises.
To view the exercises, follow this link: exercises | 1,048 |
GCSE Science/Parallel and series circuits answers. Answers to practice questions on series circuits.
So R2 = 3Ω
Answers to Questions on Parallel Circuits.
Yes it does.
Ideally it should not make any difference. The brightness of the lit bulb should remain the same. "(In practice the bulb will probably dim a tiny bit because of the internal resistance of the battery, but that's more advanced than this course)"
It certainly would.
R1 + R2 = 1 + 1 = 2 Ω
Let the Voltage be V.
From Ohm's Law
So the total Current I = V/2+V/3
Now we Apply Ohm's Law to the circuit again only this time using the total current so that we know what the total resistance is-
R = V/I
Rather than going through the whole procedure for Q8 again we note that -
1/R = 1/R1 + 1/R2 + 1/R3
So R = 3/4 Ω | 242 |
XML - Managing Data Exchange/Namespace. Learning Objectives.
Upon completion of this chapter, you will:
What is Namespace?
An XML namespace is a collection of names that are identified by a Uniform Resource Identifier (URI) reference, which are used in XML documents as element types and attribute names. URIs were used simply because they are a well-known system for creating unique identifiers. Namespaces consist of several parts including local names, namespace URIs, prefixes and declarations. The combination of a local name and a namespace is called a universal name.
You might find it easier to think of a namespace as a dictionary that is a source of definitions for items that you use within an XML document.
All schemas include the namespace http://www.w3.org/2001/XMLSchema-instance. You can think of this as the master dictionary to which all schemas must refer because it defines the fundamental items of an XML schema. The namespace's address looks like a URL, but in XML we use the broader term Uniform Resource Identifier (URI).
Because a document can refer to multiple namespace, we need a convenient short form for referencing the namespace. One of the common forms used is xsd as illustrated in the following.
xmlns:xsd="http://www.w3.org/2001/XMLSchema-instance"
The "xlmns" informs XML that you are referencing a name space, and the "xsd" indicates this is the short form of the namespace.
For example, you might use the following line of code in an XML schema
<xsd:element name="item" type="xsd:string">
The previous line of code states that the definition of element name and string are found in "http://www.w3.org/2001/XMLSchema-instance"
Namespace enables you to use elements described in multiple schemas within your XML document, so the short form of a namespace's URI is useful for identifying the namespace to which you are referring.
History.
Namespace in XML was a new W3C recommendation in January, 1999. Namespace was created to be a pretty simple method to distinguish names used in XML documents. The main purpose of Namespace is to provide programmers a method for which to grab elements and attributes that they want, leaving behind other tags that they do not need. These programmer-friendly names will be unique across the Internet. The XML namespaces recommendation does not define anything except a two-part naming system for element types and attributes.
For additional information regarding the W3C recommendation, follow this link: http://www.w3.org/TR/REC-xml-names/.
When would you use Namespace?
It would mainly be used to avoid naming conflicts. If you don’t have any duplicate elements or attributes in the XML that you use, namespaces are not necessary. It is however beneficial if you have duplicate elements or attributes. It basically makes two part structures that make it unique. Instead of just defining element A, for example, you have to define element A with some other type of identifier. That is where the URI comes into play. The URI in combination with the element or attribute creates your namespace and it is then a universal name.
Namespace Structure.
XML namespaces differ from the "namespaces" conventionally used in computing disciplines in that the XML version has internal structure and is not, mathematically speaking, a set.
This is an example of 2 Namespace declarations:
<Organization
xmlns:addr="http://www.example.com/addresses"
xmlns="http://www.example.com/files">
The first declaration associates the addr prefix with the “www.example.com/addresses” URI.
The second declaration defines www.example.com/files as the default namespace. If there is not a prefix defined for that element, a default namespace is applied. This default namespace is applied to all elements without a prefix. Please note, however, that default namespaces do not apply directly to attributes.
How Does It Work?
When specifying a universal name in an XML document, you use an abbreviation based on an optional prefix that's attached to the local name. This abbreviation is called the qualified name or qname.
To declare an XML namespace, you use an attribute whose name has the form:
xmlns:prefix
These attributes are often called xmlns attributes and their value is the name of the XML namespace being declared. This is a Uniform Resource Identifier. The first form of the attribute (xmlns:prefix) declares a prefix to be associated with the XML namespace. The second form (xmlns) declares that the specified namespace is the default XML namespace.
Example of Namespace Use.
Let’s say we are going to be pulling address values from two different sources and address from one source pulls in a mailing address while from the other source, it pulls in a computer IP address. We’ll need to create a Namespace so that we can distinguish the two addresses elements.
Postal Address XML document
<address>100 Elm St., Apt#1</address>
IP Address XML document
<address>172.13.5.7</address>
How do we distinguish these Address elements in the case that they need to be combined into the same document?
We would assign each address name to a namespace. Therefore, it becomes defined in two parts, the address element and the XML namespace. Every time the element Address comes up, it will have to look at two things instead of one for definition, but this look up only has to be performed one time because the combination is universally unique.
In this instance, we could create Namespaces for the address element:
<Example Organization
xmlns: addr="http://www.example.com/postal_addresses"
xmlns="http://www.example.com/ip_addresses">
The first declaration associates the prefix 'addr' with the URI, "www.example.com/postal_addresses and the second declaration sets "www.example.com/ip_addresses" as the default namespace. So, where a the prefix 'addr' is used, it will pull the postal address and for others, it will pull the IP address.
Defining the location of an XML schema.
Assume you have created a schema, example.xsd, that is located in the same directory as your XML document, example.xml. In the XML document you will indicate the location of the schema with the following code.
<xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xsi:noNamespaceSchemaLocation='example.xsd'>
Of course, if example.xsd is stored somewhere other than the same directory as example.xml, you specify the full path. | 1,537 |
Bioeconomics. Bioeconomics is the theory of economic exploitation of living resources, dealing with two dynamic systems: population dynamics and the dynamics of economic systems. Bioeconomics therefore leans on two traditional university disciplines, biology and economics.
Short reference to production theory.
Production theory is a central element in microeconomics and describes simply the conversion of inputs ("v") into outputs ("Q"):
There are several ways of specifying this function. One is as an additive production function:
where "p0", "p1", ... "pn" are parameters that are determined empirically.
Another is as a Cobb-Douglas production function (multiplicative):
Other forms include the constant elasticity of substitution production function (CES) which is a more general formulation including the Cobb-Douglas function, and the quadratic production function which is a specific type of additive function. The best form of the equation to use and the values of the parameters vary from company to company and industry to industry.
In a short run production function at least one of the (inputs) is fixed. In the long run all factor inputs are variable, in principle at the discretion of management.
In classical theory production may involve three types of input: Labour ("L"), Capital ("K") and Natural resources ("R"). Some classical works splits the latter into two: Natural resources and Energy resources ("E").
More often outputs from other production processes are used as inputs others. But in principle it should be possible to separate all inputs down to the three or four basic types of input.
Catch production in the short run.
The simplest model of catch production involves only two input factor: A natural resource ("x") and a fishing activity (fishing effort, "F").
Production of fishing effort.
Let us start to discuss the production of a certain quantity of fishing effort. Further let us assume that human labour input (which could be regarded as a natural resource, but is more practically described as labour) and Capital (boats, fishing gears, etc.) is the two basic types of input in the production of fishing effort. Also assume one of the two factors could be perfectly substituted by the other in a certain quantity.
While limiting the input factor to two, the substitution rates can easily be viewed in a contour plot, often referred to as isocurves of production (Fig. 3.1).
The concept of efficient production.
Equation 3.1 is simply giving a technical description on how "F" is produced by the input factor "L" and "K" and does not give us any suggestions on which mix of input factors are to be preferred. In order to prioritize between different alternatives of producing a specific quantity of "F", it is convenient to look at the cost of the two input factors. Let the unit cost of labour ("L") be "w" and the unit cost of capital ("K") be "r". The total cost of production ("C") then is:
Lagrange's method can be used in order to maximise the production of fishing effort at a cost constraint, which is the dual problem of minimising the cost at a given production. The Lagrange equation will be:
where "C"0 is the given cost and "formula_1" the Lagrange multiplier.
The first order condition when maximising the Lagrange equation, is that the partial derivatives of the equation with respect of "L" and "K" equals 0, from which follows:
This expression is referred to as the marginal rate of technical substitution ("MRTS"). In the most cost-efficient production "MRTS" should according to Eq. (3.4) equal the price ratio of the two input factors. Cost efficient solutions of different levels of production are shown in Figure 3.2.
Producing fish harvest by two input factors.
By regarding production of fishing effort as an independent production process, production of ("h", fish harvest) can be expressed by the two input factors "x" and "F":
It is reasonable to assume that "x" and "F" is substitutable in the same way as "L" and "K" in Figure 3.1. In order to fish a certain quantity, say one kilo fish, when the stock biomass is low (low "x"-value), one has to input a larger fishing effort than in the case of a higher stock density (large "x"-value).
Eq. (3.5) therefore is of the same type as Eq. (3.1) and in principle we have the same type of continuous substitution as indicated in Figure 3.1.
Market failures while using common resources.
The first problem makes it impossible to continue along the normal methods of identifying cost efficient solutions. Since the scarcity of the natural resource is not reflected in a price, we lack the value information on this factor. The other problem is also corrupting our model, as it attacks the basic assumption of independency in availabilities of the two input factors. In the long run in fact we have:
The straight forward implication of this is obvious from Eq. (3.5):
showing that in the long run (keeping fishing effort constant over a sufficient period of time) catch will be determined by the fishing effort alone.
The crucial relationship to investigate further therefore is the "x"-"F" relationship. How the stock biomass "x" be defined as a function of fishing effort "F"? At this point we have to turn to biology and population dynamics.
Population growth.
Population dynamics is the study of marginal and long term changes in numbers, individual weights and age composition of individuals in one or several populations, and biological and environmental processes influence those changes. In idealized population growth models one differs between compensatory growth and decompensatory growth, the first one is regarded as normal growth.
The logistic growth model is a widely-used compensatory growth model.
Logistic growth.
Let us assume annual biomass growth of a fish population to follow logistic growth (first proposed as a demographic model by Verhulst, 1838. (Applied as a biomass growth model by Pearl, 1934.) The population dynamics is described by a differential equation where biomass ("x") is a function of time ("t") and the time derivative of population biomass is:
Note that the two parameters (constants), "r" often referred to as the intrinsic growth rate and "K" the population biomass at natural equilibrium, are not the same as the parameter "r" and the variable "K" above (in pnt. 3).
The parabolic function (square function) in Eq. 4.1, shown in Figure 4.1, describe and increasing biomass growth as the population biomass increases, up to a certain population size (which is easy to identify as "K"/2), where the biomass growth starts declining to reach zero at biomass level "K". "K" therefore represents a natural equilibrium biomass of an unexploited stock.
Biomass growth as a function of time.
The differential equation (4.1) has a unique solution ( = INTEGRAL):
"x"0 being the biomass at "t"=0.
Catch production in the long run.
Let us start with catch production in the short run as discussed above. Eq. (3.5) defines catch as an output from of production process where stock biomass, "x", and fishing effort, "F", are input factors. "x" can be substituted by "F". This assumption of substitution is taken care of in the so-called Schaefer production equation:
"q" is a constant (parameter) often referred to as the "catchability coefficient". By referring to Eq. (2.3) we see that the Schaeffer production equation is of the Cobb-Douglas type, with powers set equal to 1. Later we will investigate the consequences of the choice of power values.
The biomass growth equation (4.1) now has to be adjusted to include catch. The annual biomass growth will be the natural growth (right hand side of 4.1) minus the harvested biomass (e.g. 5.1):
As Eq. (4.1) identify "K" as the natural biomass equilibrium when formula_2, Eq. (5.2) also identify an equilibrium biomass when keeping "F" constant over an infinite number of years. The equilibrium is defined by
from which follows (in the case of Eq. 5.2):
Skipping the trivial solution "x"=0, the stock biomass - fishing effort relationship is given directly from Eq. (5.4):
The long term catch equation is finally found by inserting Eq. (5.5) into the short term catch equation defined by Eq. (5.1): | 1,942 |
Authoring Webpages. __NOEDITSECTION__
Foreword.
The World Wide Web (often simply called "the Web") is a means of communication using inter-linked pages of text called "web pages". A coherent group of such pages is called a "website". This short course will attempt to provide a hands-on approach to teach you how to make high-quality web pages. After a short introduction, you will be thrown in at the deep end and start making web pages yourself.
Rationale.
Many textbooks approach the creation of webpages and websites as a computing task. Many others approach it as a graphical design challenge. Both approaches are rooted in treating the web as if it were a computational or graphical medium. Rooting the web in a understandable metaphor may be comforting, it is also misleading.
The web is a new medium, that requires a completely new approach to building parts of it. Although students will often pick up some of the right concepts while studying the 'programming' and 'designing' books, it is often better to start with the right concepts, and deal with the computational and graphical aspects of the web later.
What this textbook therefore tries to accomplish, is providing the student with a strong basis for learning more about building webpages. This book will try and do this in a practical, hands-on way. Almost from the get-go, students will start authoring their own webpages. | 312 |
Authoring Webpages/Requirements. = Requirements =
In order to use this tutorial, you must have a web browser and a text editor. (Most operating systems come shipped with both.)
If you use Microsoft Windows, you will find an editor called Notepad in your Accessories.
Note: a text editor is not the same as a word processor. Do not use a word processor for this course.
Once you get more comfortable authoring webpages, you may want to acquire a more powerful text editor. For now, however, editors like Notepad, Simpletext (Apple Macintosh) or Nano (GNU/Linux) suffice.
Also, some minimal computing knowledge is assumed. If you do not know how to operate a computer, this course is not for you, yet.
Testing: Your first Webpage.
In order to test whether you fulfil the requirements, you will now create your first web page in the following simple steps.
This doesn't look very impressive, does it? Well, it will get much more impressive soon, and the good news is that it will not get much more difficult.
To reach true impressiveness though, you need to be able to reach your audience. To reach your audience, a webserver program needs to know about your webpages, so that it can serve your pages to all who ask for them.
Webservers.
You could run your own webserver, but setting up such a program is beyond the scope of this tutorial.
If you follow this course in a class, the teacher will have set up a webserver for you.
If you follow this course by yourself, please check the website hosting options your Internet Service Provider (ISP) has available. (The ISP is the company that connects you to the internet. If you are connected through your work or college, consult with your systems administrator about hosting possibilities.) A form of web hosting may even be a free service your ISP offers you as part of your access package.
Recapitulation.
In short, you need:
The first two items you need right away, the last you need when you want to publish your webpages on the World Wide Web.
Up: Table of Contents - Next: Introduction | 485 |
Authoring Webpages/Teacher's Guide. Goals of this course.
This course has only one goal: to teach the practice of creating webpages.
If you want to teach your pupils about computing, networking, the internet, HTML et cetera, I would like to refer you to other WikiBooks.
Requirements.
In order to be able to teach this course, you need to:
Optional:
Web browsers.
The web browsers you use should be able to handle HTML 4 or better. Web browsers that are shipped with current operating systems are acceptable for this goal.
There are lessons in this course that deal with graphical presentation of web pages. You may skip these lessons, but if you don't, you need to provide a so-called graphical web browser. Well known such browsers are for instance , , , and Microsoft Internet Explorer. These browsers are either provided with your operating system, or can be downloaded and used freely.
If you need to download and install a web browser, we recommend the family of web browsers.
Ideally you will provide your students with several web browsers on side-by-side computers. This will allow them to see how the rendering of web pages varies between different browsers.
Text editors.
The text editors that generally accompany an operating system are all that is needed to create webpages in this course.
Although you may use editors that are specifically geared towards creating and editing websites, we advise against this. It might make your students dependent on such editors. Even if all they will use after they finished the course is such an editor, learning the basics of creating a webpage can be very helpful during trouble shooting.
Webservers.
None of the practice projects are so complex that they require a certain server set-up. Later versions of this course may require more advanced webservers. If you do not know how to set up a webserver, consult your systems administrator.
One thing to keep in mind is that you may wish to run your webserver solely on an intranet. That way, your students cannot abuse the school's Internet connection to publish information the school does not wish to be associated with.
If you are the systems administrator, you might find
or more generally
helpful.
On the other hand, using a
is likely to be easier than setting up even the easiest intranet web server.
It may help student motivation to see that their work is becoming part of the "real" WWW that anyone in the world can immediately read,
and not just another homework assignment that only the teacher can read.
Although some hosting services provide "templates" and "wizards" for creating websites, we recommend against using those tools -- it might make students dependent on that hosting service.
Instead, use ordinary file uploads.
Storage space.
The practice projects are all reasonably small. You may devise a large end-of-course project though. Also, your students may wish to study webpages they created earlier on. For these reasons, it could be handy to provide your students with storage space to keep their projects on and reference later.
The HTML and CSS and JavaScript files (which does not include image files, MP3s, videos, etc.) for one larger than average web site is under 8 MB.
"Does this need to be separate from the files on the web server?"
Previous knowledge.
If your students are new to computing, you may want to spend the first lesson acquainting them with some general principles of computing. At the very least, they should know how to:
Class project.
Since this is a work book as much as a text book, students will benefit from having engaging projects in which they can test their skills to the fullest.
Many of the exercises in this book are designed to provide such project but will probably be found lacking by almost all students. The exercises are limited by their nature: they must assume incomplete knowledge in the earlier chapters of the book, and they must be finishable within the time set for homework.
Therefore, it would be advisable to have an end-project in which the students can test all the skills and knowledge they acquired during this course.
The teacher is free to invent such a project, and hopefully in the course of time, many cool project proposals will be added to this Wikibook.
However, a teacher of minors can also choose to participate in the six-monthly ThinkQuest competition. ThinkQuest is a website creation competition for elementary and secondary school students that has produced some of the finest sites on the web today. Students are pitted against other students from all over the world. The competition is fierce and the participants need to use all they've got to have a chance at winning. All participating teams must have a school teacher as team leader, but the students themselves must do all the work.
In due time, this Wikibook will provide all the basic knowledge required for participating in and winning a ThinkQuest competition with one major exception: this book will not deal with embeddable content, such as images, animation, video et cetera.
These form an important part of the web, but they fill a whole separate book on their own: the Web Design book.
The students who are following this course on their own, are encouraged to think up their own projects. If you come up with fun projects, please share them by posting their descriptions here. | 1,165 |
Robotics/Computer Control/The Interface/Microcontrollers. Microcontrollers are the core of many robots. They have considerable processing power packed on to one chip, allowing lots of freedom for programmers. Microcontrollers are low level devices and it is common to program them using an assembly language, this provides a great deal of control over the hardware connected to the controller. Many manufacturers also provide high-level language compilers for their chips, including BASIC and C.
What's the difference between a
', ', and a "" ?
The CPU is the part which actually executes the instructions (add, subtract, shift, fetch, etc.).
A "microprocessor" is any CPU on a single chip.
A "microcontroller" is a kind of microprocessor, because it includes a CPU, but it typically also contains all of the following components on the same single chip:
Some microcontrollers even include on board Analog-to-Digital converters (ADCs). This allows analog sensors to be directly connected to the microcontroller.
With this capability, microcontrollers are quite convenient pieces of silicon.
The outputs of a microcontroller can be used to drive many things, common examples include and . The outputs on a microcontroller are generally low power. Transistors are used to switch higher power devices (such as motors) on and off.
All CPUs are useless without software.
Most software for a PC is stored on the hard drive. But when you first turn one on, it starts executing the software in the boot ROM. If you wanted to change that software, you would have to pull out the ROM chip, program a new ROM chip (in a "chip programmer"), and then plug the new chip into the PC.
Most robots don't have a hard drive -- all their software is stored in ROM.
So changing that software is exactly like changing the boot code of a PC.
(If your robot has an external ROM chip, then that is the one that is pulled and replaced. If your robot uses a microcontroller with internal ROM, then the microcontroller is pulled and replaced).
Many recent PC motherboards and microcontrollers use instead of ROM. That allows people to change the program without pulling out or putting in any chips. They can be rewritten with new data, like a memory chip, but permanently, and only a certain number of times (10,000 to 100,000 erase/write cycles).
Here are a few pages about specific µcontrollers: | 550 |
Electronics/Voltage Dividers. Ideal case.
Consider the illustration below. Assume initially that no current is flowing in or out of the terminal marked Vout. In this case, the only path for current is from Vin through R1 and R2 to GND. The equivalent resistance of this configuration is R1+R2 since these are resistors in series. From Ohm's law the current flowing through both resistors is
formula_1.
Also from Ohm's law, we know that the voltage drops across the resistors are I*R1 and I*R2 respectively. A quick check shows that the sum of the voltage drops across the resistors adds up to Vin. Now we can calculate the voltage at Vout (still assuming that no current flows through the terminal Vout). In this case the voltage is just
formula_2
where the 0V is the voltage at GND. If we substitute what we calculated for I, we obtain
formula_3.
This is the "voltage divider equation" for the ideal case where no current flows through the output. Another way of saying that no current flows through the output is that the output has infinite resistance. A quick mental check using formula_4 shows that the voltage calculated divided by infinity equals zero
Non-ideal case - finite resistance outputs.
In the non-ideal case, we need to consider the resistance of the output. If we assume that the resistance of the output is R3 (and it is connected only to GND), we need to modify our analysis as follows. Now we have two resistors in parallel from the Vout junction to GND. The equivalent resistance of the parallel resistors then is
formula_5
and the equivalent resistance of the entire circuit is
formula_6.
This yields a current of
formula_7.
Now we multiply this by formula_8 calculated above to obtain the output voltage:
formula_9
Normally R2 will be much smaller than R3 so Req will be approximately equal to R2. Keep in mind that a resistance R3 that is 100 times as large as R2 results in a voltage sag of about 1% and that a resistance R3 that is 10 times as large as R2 results in an almost 10% voltage sag.
Non-ideal case - complex impedance.
Both voltage divider equations hold for complex impedances. Just substitute Z's for R's and do the complex arithmetic. The resulting equations are just the following:
formula_10 - ideal case
formula_11 - non-ideal case | 575 |
Unsolved Problems in Biology/Grist. Top of the list of questions.
Explain the Paradox of the plankton. How the high diversity of phytoplankton seems to violate the competitive exclusion principle.
What are the current drawbacks and adverse effects to telomerase bio-genesis inhibition technology?
Is natural selection capable of producing the major innovations we see in the living world, or only minor variations within species boundaries?
Why age? Why must all organisms die? Why do cells of different organisms age on different time scales?
Is the biology of chimps enough like that of humans that we should grant them human rights?
Does it make sense to think about moving living organisms from Earth to other planets like Mars or Venus in order to terraform them?
Can you engineer a tree so that it makes electricity...so that you could have a tree in your yard that would be able to charge a chemical battery?
What is the upper limit (if any) on how long a human can live?
Will it ever be possible to transfer a human mind to a robotic brain and body? | 246 |
Botany/Bryology. Chapter 11
Chapter 11. Bryology ~ The Liverworts and Mosses
"Bryology" is the study of nonvascular complex plants classified in the Division Bryophyta.
The Bryophytes have several adaptations that allow them to grow on land, but are still tied to moisture for their reproduction. Their size is also restricted because they do not have vascular tissues, which limits their height and keeps them close to the nutrition and moisture of the ground. Rhizoids anchor them to the ground, but do not conduct water or nutrients as roots do. Some mosses have developed pores, but they do not open and close as stomata do.
Most mosses look like undifferentiated green mold on rocks, but while they are non vascular, they have complex forms and parts. They have what appear to be leaves coming off their stalks, but are not leaves because they have no veins. Most notable in their anatomy is the peculiarity of their life cycle. The haploid organism is actually most of what we would call the moss. That green mat is the gameteophyte contains half of the DNA, or one full set of chromosomes. When the female gametophyte is fertilized with motile sperm from the male gametophyte, the diploid sporophyte grows directly out of the gametophyte. So out of an ordinary spiky green moss stalk, a tall curved stalk grows, with a large cap on it. That structure is the sporophyte. It will produce spores (that are haploid) that will propagate more haploid mosses. Each successive evolutionary adaptation of plants has reduced the haploid stage in size, and increased the diploid, or sporophyte stage. In ferns, the next evolutionary innovation based in bryophytes, the gametophyte stage functions the same way as here, the haploid spores make a haploid organism, which after fertilization grows a full diploid sporophyte from it. However, what we know as a fern is the diploid organism, the gametophyte is a very small heart shaped organism at the base of the fern.
Read:
"Questions"
11.1 Out of the mosses, the liverworts and the hornworts, do any of these have seeds?
11.2 How are bryophytes similar to the algae? How are they different?
11.3 How is a spore different from a seed? How many sets of chromosomes does a spore have (1N or 2N)? | 624 |
Botany/Equisetophyta. Chapter 13
Chapter 13. Equisetophyta ~ The Club Mosses and Horsetails.
The Equisetophyta is a very old division—the plants of this division were among the first plants to grow on land. Equisetophyta are sometimes referred to as fern allies, as they have the same life cycles as ferns, and have similar developments that allow them to grow taller than the bryophytes.
Read: | 117 |
Electronics/KCL. Kirchoff's Current Law.
Current is conserved.
Current flowing into a junction is equal to that flowing out.
I1 = I2 + I3
Current is the flow of electrons through a piece of metal. Given the sheer number of electrons involved it is similar to the flow of water through a pipe. When the pipe branches the water has multiple paths to travel. The only rule is that the amount of water entering any place has to be equal to the amount of water leaving any that place. Otherwise the pipe would explode from the pressure or the water would cease to exist.
Here is more about which can be integrated here | 143 |
Electronics/KVL. Kirchoff's Voltage Law.
Kirchoff's laws can be described with a sentence as, What comes in, must go out. It's that simple. You have a potential on one side of a battery, then you need the negative potential on the other side of the battery. You have a current into a junction, the same current must go out of the junction.
in a circuit
in series voltage drops and current stays constant
in parallel voltage stays constant and current divides according to the resistance
voltage stays constant in parallel and current drops in p
Voltage is the potential between two charges.
The nice things about potentials is you can add or subtract them in series to make a larger or smaller potential as is commonly done in batteries.
In parallel voltage...
The flow a circuit is that of a potential drop. Electrons flow from areas of high potential to ground which is low potential. At a given place in a circuit there are numerous paths to ground. Each of them has the same voltage as they have the same potential from ground.
All the components of a circuit have resistance that acts as a potential drop. | 253 |
Electronics/Diodes. Diode.
Theoretically, a diode allows current flow in only one direction. An ideal diode acts as a perfect insulator for currents flowing in one direction and as a perfect conductor for currents flowing through it in the other direction. The direction in which the diode allows current to flow is called the forward bias direction and that in which current is resisted is called reverse bias direction. Diode has a symbol as shown
Construction.
The modern semiconductor diode consists of two regions of semiconductor each having impurities of different types such that one side has excess holes (p-region) and the other has excess electrons (n-region). Such a junction of p and n regions is called a pn junction diode. The p-region has about twice as much area as the n-region to compensate for the lesser mobility of holes compared to electrons.
Operation.
I V Curve.
As seen in the graph above the diode actually works in both the forward region and the backward region. In the forward region the value of I and V are positive and in the backward region I and V are negative.
Ideal Diode.
The real diode approaches the ideal diode in the sense that the reverse current is extremely small (less than 1fA) at least for a significant part of the characteristic, and the forward current is very high (on the order of 1mA). Although a real diode does not have the characteristics as the ideal diode, in theory it is possible to make an ideal diode if the concentrations of dopants in both the regions are infinite. However, there is no way of actually doing this and experiments do not agree.
The Shockley equation.
The diode reverse ("saturation") current is governed by the doping concentration. The current flowing through the device varies as the voltage applied across it changes as given by the Shockley diode equation (not to be confused with Schottky):
formula_2
In the equation above formula_3 is defined as formula_4, where formula_5 is Boltzmann's constant, formula_6 is the temperature in Kelvin, and formula_7 is the magnitude of the charge on an electron.
In the forward bias direction, current flows with low voltage. If one draws a characteristic for this equation, a sharp increase in current can be seen at a particular voltage called the "cut-in voltage" or the "on-voltage".
In the reverse bias mode, the diode current is approximately formula_8. This is called the reverse "saturation" current because it looks like the diode is saturated with charge and cannot allow more current in the reverse bias direction than this.
It initially appears that as the temperature formula_6 increases, the total diode current would decrease. However, the saturation current formula_10 increases with temperature faster than the formula_3 term decreases the current. This leads to a negative temperature coefficient for the entire device: as the diode heats up, it will pass more current.
Break-down.
However, a break from the above equation takes place at a point called "break-down voltage". One could think of it as the point where the Shockley equation "breaks down" and is no longer valid. There are two reasons for breakdown to occur.
Avalanche Breakdown
Zener Breakdown
See also Zener diodes
Summary.
So basically, there are three modes in which a diode operates:
Forward
Reverse
Breakdown
When there is no voltage applied, the excess electrons of the N type semiconductor flow into the holes of the P type semiconductor. This creates a depletion region that acts as a voltage.
Diode Variations.
Bridge Rectifier:
LED (Light Emitting Diode)
Schottky:
Zener:
Varicap: | 854 |
Human Anatomy. See also.
This book incorporates text from the public domain 1918 Gray's Anatomy. Update as needed. | 34 |
Electronics/Units. These are the units you would find when doing problems in electronics.<br>
The majority of these units are named after famous people in the field who either discovered the units or had someone else name the units after them.
One reason people don't understand math or Physics very well is that it literally is Greek to them.
"(Do we want these separated from the definitions page? or should we include all of these on the definitions page and just have a separate units page too?)"
"My take on the units page is that it is a guide for doing math problems. Imagine doing a math problem and coming across Ξ. That's where the units page comes in handy as you only have to search through a small number of units to find the unit you want. Ideally all the definitions in Units should find their way into the main definitions page."
"Ok. So we should copy all of these to the definitions page as well? Things like frequency, length, time and wavelength are not units; they should be in the definitions section and not here. Hertz, meters, and seconds are units."
Ampere, Amp (A): The SI unit for current I. Equals a coulomb (1 C) of charged particles moving past a point in one second (1 s).<br>
formula_1
Coulomb (C): The SI unit for charge Q.<br>
1 C = 6.24 x 1018 Q
Cycles per second (cps): As the name implies, a measurement of frequency in full cycles of a wave per second. This is equivalent to Hertz, but Hertz is the official unit. The unit cps (or kilocycles, megacycles, etc.) is more often seen in older documents.
Farad (F): The SI unit for Capacitance (C). One Farad equals a capacitor that has a Coulomb (1 C) of charge on it with a voltage separation of a Volt (1 V).<br>
formula_2
Inductance
Henry (H): The SI unit for inductance. <br>
formula_3
Frequency
Hertz (Hz): The SI unit for frequency. One Hz is one cycle per second.
Horse Power (HP): The power a horse can achieve.<br>
1 HP = 746 W
Joule (J): The work required to move a Newton (1 N) a meter (1 m).<br>
J = N m
Length: (l): The symbol for distance in meters (m).
Meter (m): The SI unit for distance. The distance light travels in 1/299,792,458 second.
Ohm (Ω): A measure of resistance or impedance.<br>
1 Ohm =
Second (s): The SI unit for time.
SI: The standard system of units.
Time (t): The symbol for time in seconds (s).
Volt (V): A potential due to an electric field.<br>
formula_4
Watt (W): A measure of power (P). A Watt is a Joule (1 J) of work done in a second (1 s). <br>
formula_5
Wavelength (λ): The distance between two peaks of a cycle. | 788 |
Human Anatomy/Osteology/Introduction. The framework of the body is built upon a series of bones, supplemented in certain regions by cartilage; the bony part of the framework constitutes the skeleton.
The skeletal system serves several functions, among them are:
In the skeleton of the adult there are generally 206 distinct bones:
Axial Skeleton:
Appendicular Skeleton:
Total 206
Types of Bones.
Bones are divisible into four classes: Long, Short, Flat, and Irregular. Long Bones are found in the limbs and function as levers, they are longer than they are wide. Short Bones transfer forces of movement and are cube shaped as in the carpus and tarsus. Flat Bones are used for either extensive protection or the provision of broad surfaces for muscular attachment. The bones expand into broad, flat plates, as in the skull and the scapula. Irregular Bones have peculiar forms, cannot be grouped under the preceding heads, and are used for muscle attachment and articulation. Some irregular bones include the vertebræ, sacrum and coccyx.
LONG BONE.
Long bones consists of a body or shaft and two extremities. The body, or diaphysis is cylindrical, with a central cavity termed the medullary cavity. The wall consists of dense, compact tissue of considerable thickness in the middle part of the body, but becoming thinner toward the extremities. Within the medullary cavity is adipose tissue or "yellow bone marrow".
The extremities are refered to as the epiphysis. Within the epiphysis is the "spongy bone" also known as "red bone marrow". It is within this marrow that red blood cells are produced at an average rate of 2.5 million per second. Running horizontally across the spongy bone of this region is the Epiphyseal line which is a region of cell growth responsible for lateral bone growth during youth, when growth is complete this line calcifies and becomes known as the epiphyseal plate.
Nutrient foramen run through the compact bone and allow the passage of nutrients in and out of the bone. There is a thin outer layer of connective tissue called the PERIOSTEUM which is highly vascular and allows for muscle and tendon attachment, it is bound to the bone itself by PERFORATING FIBERS which are composed of collagen. This layer does not cover the articulating regions of the bone. The bones belonging to this class include: the clavicle, humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges.
it is strongest largest of all body bones.
SHORT BONE.
Short bones are generally equal in length, width, and thickness. They are found in the wrists and ankles. Aside from points of insertion and vascular areas, short bones are almost completely covered by articular surfaces.
FLAT BONE.
These bones are composed of two thin layers of compact tissue enclosing between them a variable quantity of spongy bone. They generally offer protection, as is the case with the bones of the cranium and with the ribs and sternum. | 734 |
Electronics/RCL. RLC Series.
An RLC series circuit consists of a resistor, inductor, and capacitor connected in series:
By Kirchhoff's voltage law the differential equation for the circuit is:
or
Leading to:
with
There are three cases to consider, each giving different circuit behavior,
formula_8 .
Equation above has only one real root
Equation above has only two real roots
Equation above has only two complex roots
Circuit Analysis.
R = 0.
If R = 0 then the RLC circuit will reduce to LC series circuit . LC circuit will generate a standing wave when it operates in resonance; At Resonance the conditions rapidly convey in a steady functional method.
R = 0 ZL = ZC.
If R = 0 and circuit above operates in resonance then the total impedance of the circuit is Z = R and the current is V / R
At Resonance
At Frequency
Plot the three value of I at three I above we have a graph I - 0 At Resonance frequency formula_32 the value of current is at its maximum formula_38 . If the value of current is half then circuit has a stable current formula_41does not change with frequency over a Bandwidth of frequencies É1 - É2 . When increase current above formula_41 circuit has stable current over a Narrow Bandwidth . When decrease current below formula_41 circuit has stable current over a Wide Bandwidth
Thus the circuit has the capability to select bandwidth that the circuit has a stable current when circuit operates in resonance therefore the circuit can be used as a Resonance Tuned Selected Bandwidth Filter | 376 |
Electronics/RCL time domain. "Figure 1: RCL circuit"
When the switch is closed, a voltage step is applied to the RCL circuit. Take the time the switch was closed to be 0s such that the voltage before the switch was closed was 0 volts and the voltage after the switch was closed is a voltage V. This is a step function given by formula_1 where V is the magnitude of the step and formula_2 for formula_3 and zero
otherwise.
To analyse the circuit response using transient analysis, a differential equation which describes the system is formulated. The voltage around the loop is given by:
formula_4
where formula_5 is the voltage across the capacitor, formula_6 is the voltage across the inductor and formula_7 the voltage across the resistor.
Substituting formula_8 into equation 1:
formula_9
formula_10
The voltage formula_5 has two components, a natural response formula_12 and a forced response formula_13 such that:
formula_14
substituting equation 3 into equation 2.
formula_15
when formula_16 then formula_2:
formula_18
formula_19
The natural response and forced solution are solved separately.
Solve for formula_20
Since formula_21 is a polynomial of degree 0, the solution formula_13 must be a constant such that:
formula_23
formula_24
formula_25
Substituting into equation 5:
formula_26
formula_27
formula_28
Solve for formula_12:
Let:
formula_30
formula_31
formula_32
Substituting into equation 4 gives:
formula_33
formula_34
formula_35
formula_36
Therefore formula_12 has two solutions formula_38 and formula_39
where formula_40 and formula_41 are given by:
formula_42
formula_43
The general solution is then given by:
formula_44
Depending on the values of the Resistor, inductor or capacitor the solution has three posibilies.
1. If formula_45 the system is said to be overdamped
2. If formula_46 the system is said to be critically damped
3. If formula_47 the system is said to be underdamped
Example.
Given the general solution
formula_48
formula_49
formula_50
formula_51
formula_52
Thus by Euler's formula (formula_53):
formula_54
formula_55
Let formula_56 and formula_57
formula_58
Solve for formula_59 and formula_60:
From equation \ref{eq:vf}, formula_61 for a unit step of magnitude
1V. Therefore substitution of formula_62 and formula_12 into equation \ref{eq:nonhomogeneous} gives:
formula_64
for formula_65 the voltage across the capacitor is zero, formula_66
formula_67
formula_68
for formula_65, the current in the inductor must be zero, formula_70
formula_71
formula_72
formula_73
substituting formula_59 from equation \ref{eq:B1} gives
formula_75
For formula_76, formula_5 is given by:
formula_78
formula_79 is given by:
formula_80
formula_81
For formula_76, formula_79 is given by:
formula_84 | 886 |
Latin/Lesson 8-Imperfect and Future. = Imperfect and Future constructs =
Warning: Beyond the imperfect, this page is not entirely clear. Do not use it beyond the basic imperfect if you are a first time Latin student. See discussion for my thoughts on this.
Imperfect Active Indicative.
The imperfect is a construct like:
In Latin it would look like this:
English has a similar construct called progressive past. Actions seem incomplete, and so the imperfect label. For example, "I was running," "We were sailing," "They were calling." Note that 'to be' is always there. Latin, however, would sometimes use imperfect like simple past; accordingly, "We were sailing" could be translated as "We sailed." Other translations of imperfect can be used to/kept such as "We used to sail/We kept sailing."
Regardless of language, the concept of an imperfect is important. Imperfect is called imperfect for a reason - in Latin, the verb "perficere" means to finish/complete, which is what perfect is from. Thus, imperfect, in the grammatical sense, means not finished - that the action could be or could not be completed. Perfect instead means it has been finished - I saw. You have already seen, and it is now completed. I was seeing implies that the action is not yet completed.
The perfect tense, which we will learn later, is a more immediate reference to the past. The name, imperfect, helps you remember its use: in situations where you can't say when an event started or ended or happened, you must use the imperfect.
In situations where you can know when an event started or ended or happened, use the perfect.
You conjugate the imperfect tense this way:
verb + -bā- + personal ending
The endings for imperfect are:
Sg.
Pl.
Note that the only thing we add are ba + the personal endings (the same as in the present tense) to the infinitive stem. This gives us the imperfect conjugation.
Note that in third and fourth conjugations, you will have to form it differently. There is *no* rule to explain this, it just is, although there are memorization techniques that can help.
venire is 4th conjugation and is formed like:
For third conjugation -iō stem verbs, the imperfect is like so: capere (to capture or seize)
Note that it is easiest to think of what the endings -ere and ire lack. The imperfect -bā- + the personal ending, which we can call the imperfect conjugation, must be prefixed by -iē-.
A few examples:
Future I, Active.
Future active is a tense which, unsurprisingly, refers to something which has not yet happened. The endings are fairly basic, and follow fairly regular rules - however, the future endings used in 1st and 2nd conjugation differ from the endings of 3rd, 3rd-iō, and 4th.
For example - "amō, amāre" (1st conjugation) would be
NOTE: 1st person singular and 3rd person plural use -bō and -bunt, not -bi-.
NOTE: the B and the BIs - the distinguishing feature of future tense in Latin.
With "veniō, venīre" (4th conjugation), however, the endings are different. In future, this is what they look like:
[deleted paragraphs go here. deleted to maintain rigorous accuracy, which we will go back to striving for.)
To clarify: venīre, veniō.. we know it is 4th conjugation verb and if we look at its first person singular conjugation, we see that it is an -iō verb, because the conjugation of the first person singular is "venio". (an io category exists within 3rd and fourth conjugations and is a more general concept which we will briefly introduce here by using venire, venio as an example).
Let's first identify what we know.
We know it is 4th conjugation -io because it ends in īre, which tells us that it is 4th conjugation, and io because its first person singular ends in io (venio). Because it is -iō, we leave the -i- in. So, when we are asked (as all textbooks should phrase these new questions):
What are the steps to form the future 2nd person conjugation?
We say:
What is the form for venīre, in the future tense, in the 2nd person?
The answer is veniēs.
Future conjugation.
Example: I will love:
The table at the end of this page tries to summarize the future tense, with both sets of personal endings. As the warning notes, this summary may confu panda
As an aid to your understanding, this table only applies to the future tense. Do not assume the table is displaying a pattern that is somehow applicable to all of Latin.
The A- and the E- conjugation are (relatively) straight-forward. The others are more advanced, and as the warning notes, could confuse a first-time student. Commercial textbooks probably explain it better at this point, although laying their explanation in a table like the one below is well-advised. Leave items marked with a ? in until issues are resolved.
Take a look at the following table:
The vocabulary mostly consists of verbs, and can easily be looked up in a dictionary. We will give a limited translation below, and the rest, for those who are particularly adept at language learning, can be learned through immersion. | 1,289 |
C Programming/Operators and type casting. Operators and Assignments.
C has a wide range of operators that make simple math easy to handle. The list of operators grouped into precedence levels is as follows:
Primary expressions.
"Identifiers" are names of things in C, and consist of either a letter or an underscore ( _ ) optionally followed by letters, digits, or underscores. An identifier (or variable name) is a primary expression, provided that it has been declared as designating an object (in which case it is an lvalue [a value that can be used as the left side of an assignment expression]) or a function (in which case it is a function designator).
A "constant" is a primary expression. Its type depends on its form and value. The types of constants are character constants (e.g. codice_1 is a space), integer constants (e.g. codice_2), floating-point constants (e.g. codice_3), and enumerated constants that have been previously defined via codice_4.
A "string literal" is a primary expression. It consists of a string of characters within double quotes ( " ).
A parenthesized expression is a primary expression. It consists of an expression within parentheses ( ( ) ). Its type and value are those of the non-parenthesized expression within the parentheses.
In C11, an expression that starts with _Generic followed by an initial expression, a list of values of the form "type: expression" where type is either a named type or the keyword default, and constitutes a primary expression. The value is the expression that follows the type of the initial expression or the default if not found.
Postfix operators.
First, a primary expression is also a postfix expression. The following expressions are also postfix expressions:
A postfix expression followed by a left square bracket (codice_5), an expression, and a right square bracket (codice_6) in sequence constitutes an invocation of the "array subscript operator". One of the expressions shall have type "pointer to object type" and the other shall have an integer type; the result type is type. Successive array subscript operators designate an element of a multidimensional array.
A postfix expression followed by parentheses or an optional parenthesized argument list indicates an invocation of the "function call operator". The value of the function call operator is the return value of the function called with the provided arguments. The parameters to the function are copied on the stack by value (or at least the compiler acts as if that is what happens; if the programmer wanted the parameter to be copied by reference, then it is easier to pass the address of the area to be modified by value, then the called function can access the area through the respective pointer). The trend for compilers is to pass the parameters from right to left onto the stack, but this is not universal.
A postfix expression followed by a dot (codice_7) followed by an identifier selects a member from a structure or union; a postfix expression followed by an arrow (codice_8) followed by an identifier selects a member from a structure or union who is pointed to by the pointer on the left-hand side of the expression.
A postfix expression followed by the increment or decrement operators (codice_9 or codice_10 respectively) indicates that the variable is to be incremented or decremented as a side effect. The value of the expression is the value of the postfix expression "before" the increment or decrement. These operators only work on integers and pointers.
Unary expressions.
First, a postfix expression is a unary expression. The following expressions are all unary expressions:
The increment or decrement operators followed by a unary expression is a unary expression. The value of the expression is the value of the unary expression "after" the increment or decrement. These operators only work on integers and pointers.
The following operators followed by a cast expression are unary expressions:
Operator Meaning
& Address-of; value is the location of the operand
* Contents-of; value is what is stored at the location
- Negation
+ Value-of operator
! Logical negation ( (!E) is equivalent to (0==E) )
~ Bit-wise complement
The keyword codice_11 followed by a unary expression is a unary expression. The value is the size of the type of the expression in bytes. The expression is not evaluated.
The keyword codice_11 followed by a parenthesized type name is a unary expression. The value is the size of the type in bytes.
Cast operators.
A unary expression is also a cast expression.
A parenthesized type name followed by any expression, including literals, is a cast expression. The parenthesized type name has the effect of forcing the cast expression into the type specified by the type name in parentheses. For arithmetic types, this either does not change the value of the expression, or truncates the value of the expression if the expression is an integer and the new type is smaller than the previous type.
An example of casting an int as a float:
int i = 5;
printf("%f\n", (float) i / 2); // Will print out: 2.500000
Multiplicative and additive operators.
First, a multiplicative expression is also a cast expression, and an additive expression is also a multiplicative expression. This follows the precedence that multiplication happens before addition.
In C, simple math is very easy to handle. The following operators exist: + (addition), - (subtraction), * (multiplication), / (division), and % (modulus); You likely know all of them from your math classes - except, perhaps, modulus. It returns the remainder of a division (e.g. 5 % 2 = 1). (Modulus is not defined for floating-point numbers, but the "math.h" library has an "fmod" function.)
Care must be taken with the modulus, because it's not the equivalent of the mathematical modulus: (-5) % 2 is not 1, but -1. Division of integers will return an integer, and the division of a negative integer by a positive integer will round towards zero instead of rounding down (e.g. (-5) / 3 = -1 instead of -2). However, it is always true that for all integer a and nonzero integer b, ((a / b) * b) + (a % b) == a.
There is no inline operator to do exponentiation (e.g. 5 ^ 2 is not 25 [it is 7; ^ is the exclusive-or operator], and 5 ** 2 is an error), but there is a
power function.
The mathematical order of operations does apply. For example (2 + 3) * 2 = 10 while 2 + 3 * 2 = 8. Multiplicative operators have precedence over additive operators.
int main(void)
int i = 0, j = 0;
/* while i is less than 5 AND j is less than 5, loop */
while( (i < 5) && (j < 5) )
/* postfix increment, i++
* the value of i is read and then incremented
printf("i: %d\t", i++);
* prefix increment, ++j
* the value of j is incremented and then read
printf("j: %d\n", ++j);
printf("At the end they have both equal values:\ni: %d\tj: %d\n", i, j);
getchar(); /* pause */
return 0;
will display the following:
The shift operators (which may be used to rotate bits).
A shift expression is also an additive expression (meaning that the shift operators have a precedence just below addition and subtraction).
Shift functions are often used in low-level I/O hardware interfacing.
Shift and rotate functions are heavily used in cryptography and software floating point emulation.
Other than that, shifts can be used in place of division or multiplication by a power of two.
Many processors have dedicated function blocks to make these operations fast -- see Microprocessor Design/Shift and Rotate Blocks.
On processors which have such blocks, most C compilers compile shift and rotate operators to a single assembly-language instruction -- see X86 Assembly/Shift and Rotate.
shift left.
The codice_13 operator shifts the binary representation to the left, dropping the most significant bits and appending it with zero bits.
The result is equivalent to multiplying the integer by a power of two.
unsigned shift right.
The unsigned shift right operator, also sometimes called the logical right shift operator.
It shifts the binary representation to the right, dropping the least significant bits and prepending it with zeros.
The codice_14 operator is equivalent to division by a power of two for unsigned integers.
signed shift right.
The signed shift right operator, also sometimes called the arithmetic right shift operator.
It shifts the binary representation to the right, dropping the least significant bit, but prepending it with copies of the original sign bit.
The codice_14 operator is not equivalent to division for signed integers.
In C, the behavior of the codice_14 operator depends on the data type it acts on.
Therefore, a signed and an unsigned right shift looks exactly the same, but produces a different result in some cases.
rotate right.
Contrary to popular belief, it is possible to write C code that compiles down to the "rotate" assembly language instruction (on CPUs that have such an instruction).
Most compilers recognize this idiom:
unsigned int x;
unsigned int y;
y = (x » shift) | (x « (32 - shift));
and compile it to a single 32 bit rotate instruction.
On some systems, this may be "#define"ed as a macro or defined as an inline function called something like "rightrotate32" or "rotr32" or "ror32" in a standard header file like "bitops.h".
rotate left.
Most compilers recognize this idiom:
unsigned int x;
unsigned int y;
y = (x « shift) | (x » (32 - shift));
and compile it to a single 32 bit rotate instruction.
On some systems, this may be "#define"ed as a macro or defined as an inline function called something like "leftrotate32" or "rotl32" in a header file like "bitops.h".
Relational and equality operators.
A relational expression is also a shift expression; an equality expression is also a relational expression.
The relational binary operators codice_17 (less than), codice_18 (greater than), codice_19 (less than or equal), and codice_20 (greater than or equal) operators return a value of 1 if the result of the operation is true, 0 if false. The result of these operators is type codice_21.
The equality binary operators codice_22 (equals) and codice_23 (not equals) operators are similar to the relational operators except that their precedence is lower. They also return a value of 1 if the result of the operation is true and 0 if it is false.
One thing with floating-point numbers and equality operators: Because floating-point operations can produce approximations (e.g. 0.1 is a repeating decimal in binary, so 0.1 * 10.0 is hardly ever 1.0), it is unwise to use the codice_22 operator with floating-point numbers. Instead, if a and b are the numbers to compare, compare codice_25 to a fudge factor.
Bitwise operators.
The bitwise operators are codice_26 (and), codice_27 (exclusive or) and codice_28 (inclusive or). The codice_26 operator has higher precedence than codice_27, which has higher precedence than codice_28.
The values being operated upon must be integral; the result is integral.
One use for the bitwise operators is to emulate bit flags. These flags can be set with OR, tested with AND, flipped with XOR, and cleared with AND NOT. For example:
/* This code is a sample for bitwise operations. */
unsigned bitbucket = 0U; /* Clear all */
bitbucket |= BITFLAG1; /* Set bit flag 1 */
bitbucket &= ~BITFLAG2; /* Clear bit flag 2 */
bitbucket ^= BITFLAG3; /* Flip the state of bit flag 3 from off to on or
vice versa */
if (bitbucket & BITFLAG3) {
/* bit flag 3 is set */
} else {
/* bit flag 3 is not set */
Logical operators.
The logical operators are codice_32 (and), and codice_33 (or). Both of these operators produce 1 if the relationship is true and 0 for false. Both of these operators short-circuit; if the result of the expression can be determined from the first operand, the second is ignored. The codice_32 operator has higher precedence than the codice_33 operator.
codice_32 is used to evaluate expressions left to right, and returns a 1 if "both" statements are true, 0 if either of them are false. If the first expression is false, the second is not evaluated.
int x = 7;
int y = 5;
if(x == 7 && y == 5) {
Here, the codice_32 operator checks the left-most expression, then the expression to its right. If there were more than two expressions chained (e.g. codice_38), the operator would check x first, then y (if x is nonzero), then continue rightwards to z if neither x or y is zero.
Since both statements return true, the codice_32 operator returns true, and the code block is executed.
if(x == 5 && y == 5) {
The && operator checks in the same way as before, and finds that the first expression is false.
The && operator stops evaluating as soon as it finds a statement to be false, and returns a false.
codice_33 is used to evaluate expressions left to right, and returns a 1 if "either" of the expressions are true, 0 if both are false. If the first expression is true, the second expression is not evaluated.
/* Use the same variables as before. */
if(x == 2 || y == 5) { // the || statement checks both expressions, finds that the latter is true, and returns true
The codice_33 operator here checks the left-most expression, finds it false, but continues to evaluate the next expression.
It finds that the next expression returns true, stops, and returns a 1.
Much how the codice_32 operator ceases when it finds an expression that returns false, the codice_33 operator ceases when it finds an expression that returns true.
It is worth noting that C does not have Boolean values (true and false) commonly found in other languages. It instead interprets a 0 as false, and any nonzero value as true.
Conditional operators.
The ternary codice_44 operator is the conditional operator. The expression codice_45 has the value of codice_46 if codice_47 is nonzero, codice_48 otherwise.
Example:
int x = 0;
int y;
y = (x ? 10 : 6); /* The parentheses are technically not necessary as assignment
has a lower precedence than the conditional operator, but
it's there for clarity. */
The expression codice_47 evaluates to 0. The ternary operator then looks for the "if-false" value, which in this case, is 6. It returns that, so codice_46 is equal to six. Had codice_47 been a non-zero, then the expression would have returned a 10.
Assignment operators.
The assignment operators are codice_52, codice_53, codice_54, codice_55, codice_56, codice_57, codice_58, codice_59, codice_60, codice_61, and codice_62 . The codice_52 operator stores the value of the right operand into the location determined by the left operand, which must be an lvalue (a value that has an address, and therefore can be assigned to).
For the others, codice_64 is shorthand for codice_65 . Hence, the following expressions are the same:
1. x += y - x = x+y
2. x -= y - x = x-y
3. x *= y - x = x*y
4. x /= y - x = x/y
5. x %= y - x = x%y
The value of the assignment expression is the value of the left operand after the assignment. Thus, assignments can be chained; e.g. the expression codice_66 would assign the value zero to all three variables.
Comma operator.
The operator with the least precedence is the comma operator. The value of the expression codice_67 will evaluate both codice_47 and codice_46, but provides the value of codice_46.
This operator is useful for including multiple actions in one statement (e.g. within a for loop conditional).
Here is a small example of the comma operator:
int i, x; /* Declares two ints, i and x, in one declaration.
Technically, this is not the comma operator. */
/* this loop initializes x and i to 0, then runs the loop */
for (x = 0, i = 0; i <= 6; i++) {
printf("x = %d, and i = %d\n", x, i); | 4,121 |
Authoring Webpages/Introduction. = Introduction =
The Internet.
The World Wide Web is only one of many Internet services. The Internet is a network of computers. ("Net" is short for "network".)
The Internet provides the means to pass packets of data around the globe. In order to make sense of these packets, you need services: protocols (sets of rules) that tell you what a certain piece of data means, and computer programs (software) that allow access to data based on such protocols.
The web is one such service, as are e-mail, FTP, torrents, Instant Messaging, etc. All these services require particular programs that understand their protocols, although some programs can work with multiple services. For instance, a web browser may also be capable of downloading files from an FTP site or managing e-mail.
The World Wide Web.
The web was created to make finding and exchanging documents across the Internet easier. Before the web, if you had a document to offer through the Internet (for instance, a scientific paper, or a list of jokes, or a recipe, or your curriculum vitae), you had to put it up on an FTP site and then pass the address of that FTP site to someone else.
With the web, you embedded the address into the page, instead of passing it around. More than that, you could hide the real address from view by wrapping it in descriptive text. Instead of typing in a bunch of numbers in your FTP client, and then moving from folder to folder until you stumbled on a file called ppr_john.ps, you could create a 'link' called "John's paper on astroturf" that would take you directly to the desired file.
Hypertext.
HTML stands for "HyperText Markup Language". But what is "hypertext"?
Webpages are documents. They are files on computers. When displayed in a browser, they are displayed as "hypertext". The definition of files and computers is outside the scope of this textbook, but hypertext needs to be explained before we can continue.
On a computer, a text file behaves like print: like a book or a magazine. You can scroll through the file instead of having to turn pages, but the text behaves the same way it would if it were printed. It simply sits on the page and you read it. Hypertext, on the other hand, has additional functionality; mainly, the use of "hyperlinks". ("Hyperlinks" are commonly referred to simply as "links".) A link is a part of the page that, when clicked on by a mouse (or tapped with a finger on a touchscreen), takes the reader to a different part of the document, or to an entirely different document. Typically, links are clickable parts of text, but they can also be images. For instance, clicking a chapter heading in the table of contents could take you to that chapter; a linked phrase could take you to a footnote or a reference document for further information.
Probably the first description of "hypertext" appeared in 1945, when Vannevar Bush wrote an article in The Atlantic Monthly called "As We May Think," about a futuristic device he called a "Memex". He described the device as electronically linked to a library and able to display books and films from the library. The Memex also gave the reader the ability to automatically follow references to the work referenced.
The Memex did more than offer linked information to a user, though. It was a tool for establishing links as well as following them.
HTML was designed by Tim Berners-Lee with similar goals in mind: to provide a way for scientists to create a huge library of interlinked works and to provide a way for the users of this library to alter certain documents: for instance, to add annotations or links.
The latter part of Berners-Lee's dream never really materialized until the invention of the first wiki, Wiki-Wiki Web. Wiki pages are special types of web pages that allow the reader to edit them. For example, this textbook is part of a wiki. Anybody can change the contents of this textbook on its website.
Since hypertext is so different from normal text, there are certain things that need to be considered when writing it.
Where hypertext links to another document, the author needs to make clear what it links to. (The dreaded "click here" is, without a doubt, the worst way to create a hyperlink, as it tells the user absolutely nothing about the linked document.)
Where a hypertext document is part of a larger whole (say, a website), it is often helpful to the users if they can find out which part of a larger whole it is. The document should link to a home page. The home page is a web page that forms the "front", or table of contents, of a website. The home page usually contains information about the website and has menus of links that allow the user to navigate to various parts of the website.
For instance, a home page might say: "This is the personal home page of Clarence Wiley". This suggests to the visitor that the web pages found there are probably of a personal nature, most likely created by Clarence, and of some value to Clarence.
Similarly, web pages that are part of a website often use a uniform style. Since arriving at a uniform writing style is not always easy or convenient (think of a web page with dozens of authors), other hints may be employed that tell visitors where they are. One of these hints is explained in the following chapter.
Dangerous metaphors.
Calling web documents "pages" is a metaphor. They aren't really "pages", as in a book. However, it is useful to explain characteristics of the new and unknown by comparing them with similar characteristics of the old and known. As such, metaphors can be a useful and powerful device. However, the new and unknown has traditionally suffered harshly from a heavy stamping of the metaphor on the subject.
It is said by some that when television was invented, it took fifty years for the new medium to escape from being a stage in a box. Far into the twentieth century, television was made by aiming a camera at a stage (a 'set' in television and cinema terms) and just passing on to the viewer what went on.
Oddly enough, the things that are possible on television, but not on stage, were already possible when the first consumer grade television sets were being produced: broadcasting with a time-delay (record now, broadcast later), editing a program, using unusual viewpoints, animation, overlaying images et cetera. Of course there were a few 'revolutionaries' who used these techniques, but in general the metaphor (television is like a stage) held the new medium captive.
Even today, news anchors can sit behind their desk clad in nothing but underwear below the waist, safe in the knowledge that the camera will never do anything the audience of a stage play wouldn't do.
Today, the web has been struck similarly hard by failing metaphors. Since the web is clearly tied to computers, a lot of people confuse authoring web pages with programming. Since a lot of web content was written from the start by people using graphical web browsers, designing a web page is often primarily considered a graphical design task. (Contrary to popular belief, the first web browser displayed images and used an early form of stylesheets. )
False metaphor #1: Programming.
Programming is the art of creating a computer program. A computer program is something that tells the computer what to do. Usually, a computer program is a list of instructions. For instance, a computer programmer can write a program that tells the computer to open a window on a screen, and display a large, bold text in the top-left corner.
A hypertext document can be implemented as a computer program. A modern day example of programming hypertext would be PDF, the Adobe originated format for distributing print documents across computer networks and to printers. However, HTML, the hypertext language for the web, is not a programming language. Instead, it is a Markup language: it allows one to "mark up" the structure of a document. (You may want to revisit this section later, once you have "marked up" a few web pages yourself.) HTML is a way to tell a web browser what the different parts of a document are. For example, one part of a web page could be a paragraph and another part could be a list.
Viewing HTML as a programming language means that you view its constructs, its labels, its mark-up, as instructions to the browser. For instance, you may want to indicate that a particular piece of text should be printed in large and bold letters. You could use the HTML code for headings for this, because most graphical browsers will display a heading as large, bold text. However, you may get visitors with browsers who don't display a heading as large bold text. That's the moment when the trap of the false metaphor closes around you.
The important thing to remember is that HTML tells a web browser what the different parts of a page "are", not how they should "look".
False metaphor #2: web authoring as graphical design.
To view the web as a graphical medium is a much more insidious problem, because it is largely a correct view. Most web pages are browsed through a graphical browser. On such occasions, the graphical design of a web page can have a decisive influence on how well the content of that page is perceived and received by the visitor.
The problem lies not so much in seeing the web as a graphical medium, but in our assumptions on what a "graphical medium" is. Since web pages are often displayed on a computer screen, web page authors often design a layout grid with certain dimensions. Not everybody may be using the same dimensions, though, and visitors are hardly ever willing to change the dimensions of their windowing system to accommodate the wishes of a website's author.
The web can be displayed on a vast array of devices, some of which are not graphical at all: think of speaking browsers or touch browsers (Braille rules for the blind). You need to adjust your assumptions on what a graphical medium means to write good web pages.
The practice of creating web pages that can be accessed by a wide variety of types of browsers is called "accessibility". As the web grows, accessibility becomes more and more important.
Other, less damaging metaphors.
It is clear that when we wish to see the web in the light of another, better-understood invention, we need to do this with care, and clearly delineating the limits of our comparisons.
I would like to propose a few metaphors that are just as useful as the ones before, but that have less potential for damage.
The media that are perhaps the most natural candidates for comparing the web to are unsurprisingly other Internet services. They all share with each other that they provide a way for people to talk directly to other people without intervention of middlemen such as editors and publishers. This possibility for direct contact stems from the underlying low-level protocols of the Internet. On the Internet, every computer can talk to any other computer.
Other systems for sharing information in the free-form manner the web allows, are abundant in real life. Just try to imagine all the possibilities you have when you want to announce a neighborhood party to strangers, or when you want to share your daily troubles with relative strangers: letter pages, bulletin boards, pen pal magazines, etc. spring to mind.
Conclusion.
The important idea to take away from this chapter is that the web is a way of sharing information. There is nothing wrong with running programs on the web, or with presenting graphical design on it. These are well-understood and accepted uses of the web. What you should make a distinction between, though, is the web as a way to present information and the form and shape that information takes.
Your need to share --> Your way of sharing it --> An audience.
Questions and Exercises.
1. Collect examples of typical web pages. How do they fit into the web? Which role do they play?
2. Find a web page. Make a list of all of the page's possible users, and write down how they would experience the page. Would they find the information they were looking for? Which information would they not be able to find? Would they have an easy way of finding more information through hyperlinks?
If you follow this course as part of a class, let the teacher pick a web page and see how many different audiences the students can come up with.
If you follow this course by yourself, you could go to http://www.google.com and enter a random word in its search box, then activate the "I'm Feeling Lucky" link. I find that the names of kitchen things often make great 'random' words ('ladle', 'cinnamon', 'fridge', 'stove', etc).
3. Try to view a web page using a non-graphical browser, or a browser, such as Opera, with all graphics capabilities switched off. If this exercise is done as part of a class, form duos: let one student face away, let the other read out what's going on in the web page. Let the student who cannot read the web page give instructions and see how hard or easy it is to use the website.
4. Try to think of a subject you would like to create a web page or a website about. Go to a search engine and try to find web pages about this or similar subjects. For instance, if you would like to create a website for your football club, try to find the websites of other local and internationally famous clubs. According to your personal taste and opinions, what have the authors of these sites done right? What have they done wrong?
Answers.
For answers, see Answers to Questions and Exercises.
Previous: Requirements - Up: Table of Contents - Next: Creating a simple page | 3,082 |
Electronics/Resonance. Resonance is where the reactance of capacitors and inductors cancel at a specific frequency.
This frequency is called Resonance Frequency usually, denoted as formula_4 | 46 |
Geometry/Differential Geometry/Introduction. Differential geometry studies geometry by considering differentiable paramaterizations of curves, surfaces, and higher dimensional objects. Prerequisites include vector calculus, linear algebra, analysis, and topology.
One goal of differential geometry is to classify and represent differentiable curves in ways which are independent of their paramaterization. For example consider the curve represented by formula_1. Although formula_2 and formula_3 are different paramterizations, they both represent the same curve. More generally, we consider the slope of the curve
formula_4.
We call this type of curve a line. We can even rotate, and move it around, but it is still a line. The goal of Differential Geometry will be to similarly classify, and understand classes of differentiable curves, which may have different paramaterizations, but are still the same curve.
By adding sufficient dimensions, any equation can become a curve in geometry. Therefore, the ability to discern when two curves are unique also has the potential for applications in distinguishing information from noise. There may be multiple ways of receiving the same information--in different paramterizations, but we want to distinguish if the information is actually unique. | 263 |
GCSE Science/Edexcel/Chemical Patterns. This edexcel module is splt into three sub-models. You should study all three of them to complete all the material in the module. | 44 |
Electronics/Transistors. Transistor.
A transistor is a solid state device made by joining three positive-type and negative-type semiconductors together. In general, all transistors have three pins: base, collector, and emitter. Transistor is a bi-polar device that is a transistor with two junctions namely BE and CE DE EE FE. In theory we take a specified formulae incorporate this with using any type of meter in figuring the mathematical solution.
Construction.
A lightly doped region called base is sandwiched between two regions called the emitter and collector respectively. The collector handles large quantities of current, hence its dopant concentration is the highest. The emitter's dopant concentration is slightly lesser, but its area is larger to provide for more current than the collector. The collector region should be heavily doped because electron-hole pairs recombine in that region, while the emitter is not such a region. We can have two varieties in this kind of transistor.
NPN Transistor.
An NPN transistor is made by joining one positive-type semiconductor in between two negative-type semiconductors. Here a lightly doped p-type semiconductor (semiconductor with more holes than electrons) is sandwiched between two well-doped n-type regions. It is like two pn-junctions facing away. An IEEE symbol for the NPN transistor is shown here. The arrow between the base and emitter is in the same direction as current flowing between the base-emitter junction. Power dissipated in the transistor is
PNP Transistor.
A PNP transistor is made by sandwiching a negative-type semiconductor in between two positive-type semiconductors.
Transistor Operation.
Amplifier.
A transistor conducts current when the base voltage is greater than BE junction's voltage. Current is non zero.
Switch.
A transistor conducts current when the base voltage is greater than BE junction's voltage. Current is non zero. This corresponds to a closed switch. A transistor does not conduct current when the base voltage is less than BE junction's voltage. Current is zero. This correspond to an open switch. | 517 |
Electronics/RCL time domain simple. "Figure 1: RCL circuit"
When the switch is closed, a voltage step is applied to the RCL circuit. Take the time the switch was closed to be 0s such that the voltage before the switch was closed was 0 volts and the voltage after the switch was closed is a voltage V. The voltage across the capacitor consists of a forced response formula_1 and a natural response formula_2 such that:
formula_3
The forced response is due to the switch being closed, which is the voltage V for formula_4. The natural response depends on the circuit values and is given below:
Define the pole frequency formula_5 and the dampening factor formula_6 as:
formula_7
formula_8
Depending on the values of formula_6 and formula_5 the system can be characterized as:
1. If formula_11 the system is said to be overdamped. The solution for the system has the form:
formula_12
2. If formula_13 the system is said to be critically damped The solution for the system has the form:
formula_14
3. If formula_15 the system is said to be underdamped The solution for the system has the form:
formula_16
How do you calculate these equations?
Example.
Given the following values what is the response of the system when the switch is closed?
First calculate the values of formula_6 and formula_5:
formula_19
formula_20
From these values note that formula_15. The system is therefore underdamped. The equation for the voltage across the capacitor is then:
formula_22
Before the switch was closed assume that the capacitor was fully discharged. This implies that v(t)=0 at the instant the switch was closed (t=0). Substituting t=0 into the previous equation gives:
formula_23
Therefore formula_24. Similarly at the instant the switch is closed, the current in the inductor must be zero as the current can not instantly change. Substituting the equation for formula_25 into the equation for the inductor and solving at the instant the switch was closed (t=0) gives:
formula_26
formula_27
Therefore formula_28. Once formula_25 is known, the voltage across the inductor and resistor (formula_30) is given by:
formula_31
You have missed a lot of steps, where are they?
"Figure 2: Underdamped Resonse"
File:Example1 underdamped.png | 595 |
Electronics/Inductors. Inductor.
An inductor is a passive electronic component dependent on frequency used to store electric energy in the form of a magnetic field. An inductor has the symbol
Inductance.
Inductance is the characteristic of the Inductor to generate a magnetic field for a given current. Inductance has a letter symbol L and measured in units of Henry (H).
This section list formulas for inductances in specific situations. Beware that some of the equations are in Imperial units.
The permeability of free space, "μ0", is constant and is defined to be exactly equal to 4"π"×10-7 H m-1.
The self-inductance of a straight, round wire in free space.
If you make the assumption that "b" » "a" and that the wire is nonmagnetic (formula_5), then this equation can be approximated to
The inductance of a straight wire is usually so small that it is neglected in most practical problems. If the problem deals with very high frequencies ("f" > 20 GHz), the calculation may become necessary. For the rest of this book, we will assume that this self-inductance is negligible.
Flat spiral air core coil.
Hence a spiral coil with 8 turns at a mean radius of 25 mm and a depth of 10 mm would have an inductance of 5.13µH.
Quality of good inductor.
There are several important properties for an inductor that may need to be considered when choosing one for use in an electronic circuit. The following are the basic properties of a coil inductor. Other factors may be important for other kinds of inductor, but these are outside the scope of this article.
The inductance is determined by several factors.
Coil's Characteristics.
For a Coil that has the following dimension
The magnetic flux density, "B", inside the coil is given by:
We know that the flux linkage in the coil, λ, is given by;
Thus,
The flux linkage in an inductor is therefore proportional to the current, assuming that "A, N, l" and "μ" all stay constant. The constant of proportionality is given the name inductance (measured in Henries) and the symbol "L":
Taking the derivative with respect to time, we get:
Since "L" is time-invariant in nearly all cases, we can write:
Now, Faraday's Law of Induction states that:
We call formula_19 the electromotive force (emf) of the coil, and this is opposite to the voltage "v" across the inductor, giving:
This means that the voltage across an inductor is equal to the rate of change of the current in the inductor multiplied by a factor, the inductance. note that for a constant current, the voltage is zero, and for an instantaneous change in current, the voltage is infinite (or rather, undefined). This applies only to ideal inductors which do not exist in the real world.
This equation implies that
An inductor works by opposing current change. Whenever an electron is accelerated, some of the energy that goes into "pushing" that electron goes into the electron's kinetic energy, but much of that energy is stored in the magnetic field.
Later when that or some other electron is decelerated (or accelerated the opposite direction), energy is pulled back out of the magnetic field.
Inductor and Direct Current Voltage (DC).
When a coil of several turns is connected to an electricity source in a closed loop, the current in the circuit induces a magnetic field that has the same properties as a Magnetic Field of a Magnet.
When the current is turned off, the Magnetic Field does not exist.
Conducting Coil is called ElectroMagnet
Inductor and Alternating Current Voltage (AC).
Angle Difference Between Voltage and Current.
For Lossless Inductor
For Lossy Inductor
Changing the value of L and RL will change the value of Angle of Difference, Angular Frequency, Frequency and Time.
Quality factor.
Quality factor denoted as Q is defined as the ability to store energy to the sum total of all energy losses within the component | 976 |
Electronics/LR. LR Circuits.
An LR circuit has an inductor and a resistor.
When the circuit is turned on the inductor will initially oppose the flow of electrons and no current will flow. Over time the inductor will stop opposing the current and will act as a short allowing current to flow unhindered.
Once the current is shut off the inductor will oppose the decrease in current.
This only happens if there is a resistor to bleed off the current. | 113 |
Electronics/RF Basics. Originally people thought that radio waves propagate through the ether.
The ether was disproved by showing that it did not flow. | 38 |
Electronics/Signal Modulation. Modulation and Mixing.
Put simply, modulation is the change of an electric signal based on the change in another signal. Another way to look at it practically, is the use of electric signals to carry information.
mixing is the addition and subtraction of signals.
Magic equation:<br>
formula_1<br>
Has strange effects on bandwidth and creates sidebands.
AM (Amplitude Modulation).
simpler than FM. An AM receiver detects the power of the radio wave, and amplifies changes in the power measurement to drive a speaker or earphones.
AM radio. known as medium wave. started in the 1920s. has a long enough wavelength that it diffracts and follows the curvature of the earth traveling a great distance. lower audio fidelity. used for broadcasts. Affected by light and solar flares, and works better during the night. Clear channel stations are allowed to broadcast all the time, but other stations are only allowed to broadcast during the day.
SSB (Single SideBand).
AM with only one side band. carrier.The other one sideband block or can be use for other information transmission.
[email protected]
FM (Frequency Modulation).
In FM modulation, frequence of carrier signal vairy according to the audio frequency signal(Which is our actual signal).
PM (Phase Modulation).
Change phase by modifying capacitor and inductor values. Since capacitors and inductors are 180 degrees out of phase. | 357 |
Electronics/Symbols. Switches.
"See here for more examples:"
Greek characters.
One reason people don't understand math or Physics very well is that it literally is Greek to them. | 47 |
Electronics/RCL time domain1. "Figure 1: RCL circuit"
When the switch is closed, a voltage step is applied to the RCL circuit. Take the time the switch was closed to be 0s such that the voltage before the switch was closed was 0 volts and the voltage after the switch was closed is a voltage V. This is a step function given by formula_1 where V is the magnitude of the step and formula_2 for formula_3 and zero
otherwise.
To analyse the circuit response using transient analysis, a differential equation which describes the system is formulated. The voltage around the loop is given by:
formula_4
where formula_5 is the voltage across the capacitor, formula_6 is the voltage across the inductor and formula_7 the voltage across the resistor.
Substituting formula_8 into equation 1:
formula_9
formula_10
The voltage formula_5 has two components, a natural response formula_12 and a forced response formula_13 such that:
formula_14
substituting equation 3 into equation 2.
formula_15
when formula_16 then formula_2:
formula_18
formula_19
The natural response and forced solution are solved separately.
Solve for formula_20
Since formula_21 is a polynomial of degree 0, the solution formula_13 must be a constant such that:
formula_23
formula_24
formula_25
Substituting into equation 5:
formula_26
formula_27
formula_28
Solve for formula_12:
Let:
formula_30
formula_31
formula_32
Substituting into equation 4 gives:
formula_33
formula_34
formula_35
formula_36
Therefore formula_12 has two solutions formula_38 and formula_39
where formula_40 and formula_41 are given by:
formula_42
formula_43
The general solution is then given by:
formula_44
Depending on the values of the Resistor, inductor or capacitor the solution has three posibilies.
1. If formula_45 the system is said to be overdamped. The system has two distinct real solutions:
formula_46
2. If formula_47 the system is said to be critically damped. The system has one real solution:
formula_48
formula_50
3. If formula_51 the system is said to be underdamped. The system has two complex solutions:
formula_52
formula_53
formula_54
formula_56
formula_59 | 647 |
Electronics/RCL time domain2. "Figure 1: RCL circuit"
Example.
Given the following values what is the response of the system when the switch is closed?
formula_1
formula_2
formula_3
Solve for formula_4 and formula_5:
From equation \ref{eq:vf}, formula_6 for a unit step of magnitude
1V. Therefore substitution of formula_7 and formula_8 into equation \ref{eq:nonhomogeneous} gives:
formula_9
for formula_10 the voltage across the capacitor is zero, formula_11
formula_12
formula_13
for formula_10, the current in the inductor must be zero, formula_15
formula_16
formula_17
formula_18
substituting formula_4 from equation \ref{eq:B1} gives
formula_20
For formula_21, formula_22 is given by:
formula_23
formula_24 is given by:
formula_25
formula_26
For formula_21, formula_24 is given by:
formula_29 | 279 |
Electronics/Signal Propagation. Generation.
AC source alternates on a piece of wire. This creates an electric field that creates a magnetic field that creates an electric field. These waves are known as Electro-Magnetic waves, and are photons that travel through free space.
Propagation.
Originally people thought that photons propagate through an aether wind. The aether was disproved by showing that it was not flowing from any direction even though the earth is moving.
"My first tie in with other books. The idea is to have a short intro which motivates the other books so people will be interested in reading them. "
In showing that the aether did not exist came the realization that light travels at the same speed regardless of how fast you are moving and that time is relative and events do not happen at the same time. With that knowledge came the famous E=MC2 equation, time travel, the secrets behind blackholes, and how gravity and energy warp time and space. Click Here to unlock these secrets of the universe.
Antennas.
You only need a quarter wavelength antenna to resolve a full wavelength. It is hard to resolve wavelengths of 200 meters. Use powerlines. Fractal antennas allow to compress the antenna size. As long as the antenna is long enough for a standing wave it does not matter how it is compressed.
Range.
The earth behaves like a conductor. The ionosphere also behaves like a conductor. Both can reflect radio waves. | 330 |
Authoring Webpages/Creating a simple page. = Creating a simple webpage =
Time to get our hands dirty! (In a manner of speaking.)
Text structures.
In the first chapter, which stated the requirements for following this course, a small exercise was printed, in which you created your first simple web page. If you haven't done that exercise yet, go there now and do it.
Text entered into a text editor and saved to a hard disk, or other form of storage, is often called a "plain text file". Plain text files generally provide three small ways for separating text. Tabs and spaces are used for separating words and returns are used for separating paragraphs.
People have found creative ways of producing intricate layouts using just these small methods of markup. In web pages, however, this method of laying out text doesn't work. A web browser will collapse all consecutive spaces, tab stops and returns into one single space or soft return, depending on where on the line the word occurs. HTML does layout a much different way, which will be discussed later.
When you structure a text, you generally do so to make it easier to digest and to read. By making chapter and section headings more pronounced, you allow the reader to skim over a text until they find an especially interesting part. By using introductions and abstracts, you allow a reader to decide if this text will be interesting to them. You can use illustrations, because sometimes people will much sooner understand what's going on when they can see what's going on.
HTML, the HyperText Markup Language for the web, and its successor XHTML, the eXtensible HyperText Markup Language, allow you to impose a structure on a plain text document. It replaces the few simple mark-up methods plain text allows you by its own. (Note: XHTML has been superceded by HTML5.)
The way HTML lets you do all this, is by letting you label certain parts of the text as a heading, a paragraph, an image, a table, a list, etc. Some structures are not supported by HTML, since it is a relatively simple markup language. For instance, there is no element for introductions or leads. The reader will have to infer from the position in a text which is the introduction, the lead or the abstract.
Each part of an HTML document is called an "element". Elements are separated from each other by a type of label called "tags".
An example:
<p>This is an <em>important</em> example.</p>
What you see above is a paragraph element with an embedded emphasis element. The paragraph element starts with a <p> tag and ends with a </p> tag. The emphasis element starts with an <em> tag and ends with an </em> tag.
A web page by any other name....
There are several versions of the HTML standard. The most current is HTML5. However, web browsers should also support older versions of the standard, so that examples such as the one given in the Requirements chapter are considered valid HTML documents.
Every web page must have a codice_1 element (under older versions of HTML this was the only required element):
<title>My webpage</title>
The title is the text by which the browser window will be named. It is the text that appears at the top of your browser window, and it is the default name of the bookmark (or favorite) used by the browser. It is also the title by which the page will be listed by a search engine.
Find a descriptive title. The heading of your page will often do just fine. The heading of this chapter is "Creating a simple web page", so its title could be the same text. Since this web page explains to you how to create a simple web page, that would be an excellent title.
Bad titles abound on the web. For example, a company might name their page
<title>Big Fridge Manufacturer Inc.</title>
If you are lucky, they will even add in a bit of information related to the web page you are visiting, for instance:
<title>Big Fridge Manufacturer Inc. - Manual of the Cool 3000 ice box</title>
Better for the visitor is:
<title>Manual of the Cool 3000 ice box - Big Fridge Manufacturer Inc.</title>
After all, it is much more likely that the visitor who gets to this page is searching for the manual, rather than for company info.
So, the lesson is: always put the important information first. Often, you only have a limited amount of characters available to you in your bookmarks menu, in the search engine listing or in the window title bar; utilize that space to the maximum.
An HTML document with only a title element is not very useful. We will now introduce you to a couple of elements that will allow you to make good use of 90% of the power of the web.
A simple linking webpage.
With these elements, we can make the following simple web page:
<!DOCTYPE html>
<html>
<head>
<title>Friends and family of Clemence Wylie</title>
</head>
<body>
<h1>Friends and family</h1>
<p>The following are links to the websites of my friends and family</p>
<h2>Friends</h2>
<p><a href="http://www.tomsawyer.us">Tom Sawyer</a></p>
<h2>Family</h2>
<p><a href="http://www.tantejeanette.ca">Aunt Jeanette</a></p>
</body>
</html>
Exercise 2-1.
Copy the above sample code to your text editor. Save it as exercise2-1.html. Open it in a web browser. Does it display like you expected?
Answers.
For answers, see .
Creating a link.
The codice_2 tags in the previous example have a special purpose. They create anchors. (Anchors are more commonly referred to as "links".) They contain "attributes" with attached values. Attributes are part of a tag that give the browser additional information about the element. Each attribute is followed by an equals sign (=) and a value in quotation marks (").
codice_2 tags have several possible attributes. The most important are codice_4 and codice_5. codice_4 is the attribute that defines the URL (Uniform Resource Locater) or URI (Uniform Resource Indicator) (more commonly known as an "address"). This is the destination that the link leads to: another document, or a location within the same document. Commonly, addresses are called URLs; however, this practice has become deprecated, and it is now recommended that you use the broader term "URI", instead.
The codice_5 is a unique name for the link, which can be used by other links to refer to it.
URIs typically have the following form:
codice_10
For example
codice_11
The protocol for web pages is usually codice_12 (HyperText Transfer Protocol) or its secure variant codice_13. In this example, the link would take you to the codice_14 section of the codice_15 document on the codice_16 domain, using codice_13.
Note, however, that most parts of this are optional, depending upon how you want to use the URI. URIs can be relative or absolute. An absolute URI will include the domain as part of the address. (The codice_16 part.)
An codice_4 can just be a relative path (for example codice_20): in that case, the address will be calculated from the page that contains the link.
An codice_4 can also just be a domain name: codice_22 leads to a website with that address; the web server of that site is supposed to figure out which document you want. This typically defaults to codice_23 or codice_24.
Elements deconstructed.
An HTML document consists of elements. These elements are constructed as follows:
<tag>;contents</tag>
An opening tag may contain attributes. Attributes often have values.
<tag attribute1="value" attribute2="value2" attribute3>
The tag that closes an element is just like the opening tag, but has a slash in front of the name, and cannot contain attributes:
</tag>
Some elements cannot contain other elements. The HTML standard defines which elements can be contained by an element. The permitted combinations vary from version to version.
Elements are either "block-level" elements or "inline" elements. With block-level elements, the browser sets off the element in its own "block". It has a return placed both before and after it. Some examples of this are headings (codice_25, codice_26, codice_27, and so on), paragraphs (codice_28), and list items (codice_29). Inline elements are not treated this way, so (for example) they can be inserted into paragraphs without disrupting the flow of the paragraph. Good examples of this are anchors (codice_2), emphasis (codice_31), and images (codice_32).
Block-level elements can contain inline elements, but inline elements cannot contain block-level elements.
For instance, the following is valid HTML:
<h1><a>Valid HTML</a></h1>
But this is not:
<syntaxhighlight lang="html">
Invalid: invalid HTML
</syntax>
Validity.
The term "valid HTML" has already been mentioned a few times. Since web pages are authored by people, and people make mistakes, web browsers tend to be extremely forgiving towards those mistakes. They will even try to correct your mistakes.
Still, there are several reasons why you should try to mark up a web page with valid HTML:
The organization responsible for maintaining the HTML standard is the World Wide Web Consortium. It runs a validation service that you can use to check if your HTML is valid. You can find it at http://validator.w3.org. It is a good practice to validate your HTML with this service.
A common mistake is forgetting to start every document with a DOCTYPE. A document without a DOCTYPE is automatically invalid (HTML version information). Note: many texts erroneously state that the DOCTYPE is optional. It is true that all major browsers will forgive the absence of a DOCTYPE, but this does not make the page valid. The appearance of a page may vary noticeably between different browsers if the DOCTYPE is omitted, because each browser has its own peculiarities when rendering such pages.
Exercises.
Time to have some fun. The following exercises will let you make some simple web pages and websites. The goal is to teach you the power of several different ways of linking.
Exercise 2-2.
Copy the example web page above to the clipboard and open http://validator.w3.org. Paste the example in to the 'Validate by Direct Input' section and click on 'Check'. Is the example valid?
Exercise 2-3.
If you have an anchor codice_33, then codice_34 will link to it. That means that when you activate the link, the web page will be displayed starting at the anchor (rather than as usual from the top).
Make a copy of the web page you created in Exercise 2-1 and save it as codice_35. Change this file to include a 'menu' of anchors at the top that link to the headings of the different subsections (Family, Friends).
Exercise 2-4.
There is a hybrid form of book and game called Choose Your Own Adventure (CYOA). In such a game-book, you read a bit of text as in a normal book, but after a while, you get to make a choice as to how to continue.
For instance:
You are sitting in the tub, soaking and relaxing. Your rubber ducky is chattering away happily when suddenly a pike grabs it from below and drags it down.
- If you dive into to the water to save the ducky, go to page 89
- If you pull the plug to empty the bath, go to page 24
In this exercise, you will write a short CYOA, in which the choices are represented by anchors that will lead to the text continuing from that choice. Every "chapter" must be a separate web page.
Keep it snappy and don't spend too much time on this. Ten to twenty web pages should be sufficient. The story does not need to be good or finished.
Tip: Create a template HTML file which you can use to base all subsequent chapters.
Exercise 2-5.
Create a web page and save it as "exercise2-5.html". The web page should contain a short, informative text about a subject of your choice. It should contain at least three working links to external websites about the subject.
Answers.
For answers, see .
Images.
Including an image on a webpage is done using the codice_32 element. codice_32 is one of a class of elements referred to as "self-closing". Self-closing elements don't have a closing tag. Instead, they end with codice_38. (In HTML5, the slash is optional; however, it is considered a best practice to include it.)
The codice_32 element has two obligatory attributes: codice_40 and codice_41.
codice_40 takes a URI as its value. In this case, the URI will be the "address" (location) of the image.
Since URIs can be relative, if the image is located in the same folder as the web page that includes it, the URI can consist merely of the file name of the image. More commonly, the image will be located with other images in a directory called codice_32. It is a good practice to keep your images in a separate directory, because it will make your site better organized.
The codice_41 attribute contains a textual description that appears when the image cannot be displayed. For instance, if the image is a photo of a lake with a castle, you could have the following code:
codice_45
When the purpose of the image is decorative, you might want to use an empty alt value. That way, when the page is displayed, the "decorative" text will not interrupt the flow of the page's main text.
codice_46
However, when the image has a function to fulfill on a webpage, the presence of alt text is very important for visitors who can't see the image. For instance, many webpages have navigation built from menus of links, where the links are represented by images. If the images can't be displayed and there's no alt text, users won't be able to use the navigation.
codice_47
The codice_32 element lets you embed an image on a page. You can of course also link to an image that you do not want to display on the page, because it has no role there. For instance, if you want to offer people the chance to download photos you made, you can offer links to those photos. For that you use the same codice_2 element that we have been using to link to other webpages:
codice_50
Note how you can create links to every file that can be located using a URL. By indicating that a photo is stored in the JPEG format (a very common file format for photos) and by indicating the file size, we give visitors the opportunity to decide whether they A) can use a file of this format and B) whether they are willing to download a file of this size.
Pre-formatted text.
HTML contains many more elements (for example, HTML 4.01, contains 91 different elements), but for now we will discuss only one more before moving on to the style of web-writing.
The codice_51 element allows you to retain plain text formatting (as discussed shortly at the beginning of this chapter). This means that within the element, consecutive spaces, tabs and hard returns will not be collapsed into a single space or soft return.
There is little use for this element. It stops the text from reflowing neatly when the browser width is reduced or expanded, causing visitors to scroll horizontally, which web-surfers generally hate to do. HTML and its companion layout language CSS have plenty of options to display line-breaks and indentation. Also, it is pretty meaningless in non-visual browsers.
However, when you wish to copy pre-formatted text from other documents, it may be handy to use the codice_51 element until you have the time to mark that text up.
Example:
Further reading.
Later during this course, we will discuss further elements. However, the intention of this course is not to make you fluent in HTML; it is to make you fluent in authoring webpages.
Generally, to fully comprehend something requires that you fully comprehend its form first. You cannot be a successful karateka if you cannot perform the various moves. You cannot be a successful French speaker if you have not mastered its grammar and vocabulary first. However, knowing all the ways to hit someone does not make you a good karateka, and knowing all the words and rules of the French language does not prevent you from becoming a mumbling baboon the next time you need to speak French.
To fully comprehend authoring webpages, you need to look beyond the language in which you write them. This is what we will do in most of the further chapters of this book.
The official HTML5 Recommendation of the World Wide Web Consortium can be found here. Although this documentation can, at times, be pretty hard to read, it represents the last word on any discussion of what is valid HTML5 and what is not.
Further, one the authors of the HTML 4.01 Recommendations, Dave Ragett, has written a couple of handy guides to HTML and its companion layout language CSS, which you can find at http://www.w3.org/MarkUp/#tutorials. If there are points in this and later chapters that you do not fully comprehend, you could do worse than study Dave's texts. They are much clearer than the official specifications, and short enough to study alongside this text.
More exercises.
The following exercises are optional. You can use them to practice putting images on your webpages.
Exercise 2-6.
Download the following images, and put them all on a webpage that you will save as 'exercise2-6.html'. Think of useful codice_41 texts.
To download linked files, a lot of browsers contain a Save Link As function. In graphical browsers using a mouse, this function is often part of the context menu. On the PC this means you have to click you right mouse button, on Mac OS this means you have to press the codice_54-key and press the mouse button.
"(images to follow later)"
Answers.
For answers, see Answers to Questions and Exercises.
References.
Previous: Introduction - Up: Table of Contents - Next: How to write for the web | 4,537 |
Electronics/RCL frequency domain. "Figure 1: RCL circuit"
Define the pole frequency formula_1 and the dampening factor formula_2 as:
formula_3
formula_4
To analyze the circuit first calculate the transfer function in the s-domain H(s). For the RCL circuit in figure 1 this gives:
formula_5
formula_6
When the switch is closed, this applies a step waveform to the RCL circuit. The step is given by formula_7. Where V is the voltage of the step and u(t) the unit step function. The response of the circuit is given by the convolution of the impulse response h(t) and the step function formula_7. Therefore the output is given by multiplication in the s-domain H(s)U(s), where formula_9 is given by the Laplace Transform available in the appendix.
The convolution of u(t) and h(t) is given by:
formula_10
Depending on the values of formula_2 and formula_1 the system can be characterized as:
3. If formula_13 the system is said to be underdamped The solution for h(t)*u(t) is given by:
formula_14
Example.
Given the following values what is the response of the system when the switch is closed?
First calculate the values of formula_2 and formula_1:
formula_17
formula_18
From these values note that formula_13. The system is therefore underdamped. The equation for the voltage across the capacitor is then:
formula_20
"Figure 2: Underdamped Resonse" | 382 |
Authoring Webpages/How to write for the web. Introduction.
In the previous chapter, you have learned how to actually create a webpage.
To reiterate, you should have learned
In other words, you have learned some of the mechanics of creating a webpage, and if you have followed the exercises, you actually gained some experience in writing webpages.
Now, you will begin to learn how to apply that knowledge in a meaningful way.
As we observed before, there is no right or wrong way to make a webpage. The page may consist of valid or invalid HTML, but whether a page is successful depends solely on the goals you have set yourself and whether they were met. However, we have also noted that there is no way of knowing whether the goals were met for all visitors.
Generally, your goal will be to tell the world a story.
If you manufacture lawnmowers, your goal with a webpage may be:
This list is endless. Who knows why somebody makes a webpage? There could be a million reasons.
But once you have committed yourself to telling your story, it would help if you could get your story across.
General writing skills are beyond the scope of this textbook. There are other Wikibooks (under development at the time of writing) that teach you exactly this. See for instance How to write an essay.
Reading problems on the web.
Although few hard facts are known about this, it is generally assumed that reading from a screen is harder than from paper. For instance, it takes about 30% more time to read a text off a screen than off paper. Although little is known about the reason for this, it could be because most screens are static, while readers who use paper generally can move the paper around. Another theory holds that because the resolution of text on paper is much higher than that on screen (300dpi vs. 100dpi), it is 'easier for the eye' to read text off paper.
Most visitors browse websites using a browser that displays the contents of a webpage on a screen. The standard typography of web browsers seems to accommodate for a harder reading experience: paragraphs are separated by empty lines.
Regardless of how difficult it appears to be to read off a screen, web surfers have shown a marked preference for lay-outs that make it easier to scan a text for important points. Some of the qualities of these lay-outs are:
Often, visitors will print out text that they want to read with attention, while they skim over text that does not warrant such close scrutiny.
Information scent.
Whatever they are searching for, most web surfers follow a similar strategy in hopping from page to page. They will 'scan' (skim through) a webpage, looking for interesting information. They will seek out elements that seem most promising to deliver that information, such as headings, emphasized text, and hyperlinks. If within the first few seconds a webpage does not seem to promise interesting information, the visitor will hop on the most promising hyperlink out of there. If there are no promising hyperlinks, visitors may even use the Back function of their browsers to return to a previous page.
The trail of promising elements is similar to the trail a bloodhound follows when hunting prey. It is therefore said that elements on a webpage emit an 'information scent'. The stronger that scent, the more likely the user is to follow it.
However, if a certain type of element has been producing false trails often, users will start turning away from such elements. For instance, although animated content is much more attention grabbing than static content, visitors turn away from animations more and more. This may be because web surfers have started to equate animations with advertisements; and advertisements rarely contain the sort of information the visitor was looking for.
By knowing how to make a webpage more accessible to those who use graphical browsers, and by knowing how to apply the right amount of 'scent' to certain elements on a page, the webpage author arms himself with the right tools to reach his audience optimally.
In the following, we will take a look at a couple of such tools.
Links vs. Text.
The term Hypertext consists of two parts: 'hyper' and 'text'. Hyper is originally a Greek word meaning 'over', 'beyond'. Hypertext is something that takes text to a new level; but it still remains text. Hypertext has all the properties text has, and then some.
Although the title of this section makes it seem so, the extra properties of text, i.e. the (hyper)links, are not at war with the original text. At least not all the time.
When the theories of the web experts are correct, a web user surfs from page to page, following a trail of information scent. Whether that user is looking for a specific piece of information and trying all likely avenues that may lead to that piece; whether a user is looking for specific information, but gets side-tracked by other information; or whether a user is not looking for information at all, but just for some fun; all seem to be using the same strategy of following a trail of promising leads.
The longer a visitor stays on a page that does not hold his interest, the more the likelihood increases that the visitor starts looking for a way to escape. Although the promised information or fun may lie in the plain text that is presented on a webpage, all the escape routes are embedded in hyperlinks. Chances are, therefore, that any text that does not immediately captivate a visitor's attention, is unlikely to be read later on, unless much of the preceding text has already made abundantly clear to the visitor that this is where he wants to stay.
Let me repeat again that it is not the author's task to entertain the reader. But an author who does not want to entertain readers, will find himself without an audience. Similarly, an author who sets out to maximize the sense of reward someone gets from reading his work, will reach the maximum audience for that type of work.
"???more to follow"
The fold.
The fold is a term that could in some sense be used for all media, but is pretty useless when speaking of streamed media such as speech. It is a term used for visual browsers, meaning the bottom edge of the first displayed part of a webpage.
For instance, if a webpage consists of fifty lines of text, but only the first twenty are displayed, the fold is beneath the twentieth and above the twenty-first line.
That may seem to be an arbitrary position to give its own name, but it is not, because webpage visitors will generally look at what's above the fold, not at what's beyond.
Unfortunately, it is not a very useful metric, as each visitor has his web browser set up in different ways, and so for each visitor the position of the fold may differ.
However, it teaches us that things that need to be viewed by as many visitors as possible, need to be as high up on a page as possible.
The inverted pyramid.
So far we have discussed the difficulty with which a visitor reads a webpage off a screen, and with which haste he does so. Forget to grab the right person's attention, and he will disappear to the greener grass on other webpages. The web is quite vicious like that: all your competitors are your direct neighbour.
In the section about the fold we discussed how it is important to maximize your readership by putting important information at the top.
The method of writing a text with the most important sentence first, the second most important sentence second, the third most important sentence third, etcetera, is called the Inverted Pyramid.
Traditional essay writing holds that a piece is structured as follows: introduction, expansion, conclusion. For most of us, it is pretty common practice to sit on important facts for awhile, and only reveal them as the piece progresses. As readers, we have become accustomed to text being structured like this, and are willing to show a certain amount of forgiveness when an author does not come to the point right away. On the web, we click away without even blinking our eyes when we encounter a text that does not immediately tell us what we want to know.
Pitfalls.
So far, we have been stressing what happens when a visitor does not find the information he is looking for. But what happens when the visitor does find what he is looking for: does web text still need to be as oddly contorted as described before in order to appeal to the visitor?
One would hope not. How would Alice in Wonderland read if we had put the most important facts first? If we had put links to more interesting literature in the text? If we had forgone all artistic ambition just to satisfy some weary surfer, who wasn't going to read our text anyway?
The usability extremists would say, yes, there are no artistic values--just a new world, with new rules.
Unfortunately for them, people do read on the web. They are moved by what they encounter. They have ways to circumvent the difficulties of the web medium. For instance, people who find an interesting text on the web often print it out, so that they can read it from an easier medium.
I would also argue, without any facts to back me up, that the nature of a text plays a role. Informative and persuasive texts may be constructed according to the guidelines given before, whereas entertaining texts may be constructed in the old-fashioned, pre-web way.
If you are trying to sell me something, for instance, there's really no need to fluff up your text with "marketese". More likely than not, I will hit the Back button of my browser faster than you can say 'percentage'.
If you are trying to inform me of something, I might be more lenient. The trade we are making (you get my attention, I get your insights) is much more immediate, and therefore worth more to me.
But even the authors of entertaining webpages can learn something here. The most important thing: you write for an audience. The medium plays a role in that. A hard rock band must use loud speakers. It's what the audience expects. (And of course, the hard rock band that knows this can play on this, and show their soft side in an 'unplugged' session--but such things are better only tried by those who understand their medium.)
Even if the entertaining text is going to be printed out, even if the user is going to sit in front of his screen and persevere through your entire, brilliant play, some of the methods outlined before make sense.
Should you not use the inverted pyramid, you should at least use headings for headings, don't fiddle with font sizes (yes, this is unfortunately possible), let paragraphs stay separated by blank lines, etcetera. It is not rare to find that some author of science fiction stories has found out a way to display their story the same as on paper--forgetting in the mean time that he is not publishing on paper, and losing part of his audience.
Most of the promotional value of an entertaining text is in the text itself. Entertainment is highly valued: if what you wrote is good, others will link to it, including search engines.
Usability and Accessibility.
The World Wide Web Consortium has produced a set of Web Content Accessibility Guidelines that provide guidance on some areas of writing web pages. The guidelines are quite daunting at first. Don't try to understand them all in a single reading. Some guidelines are easy to follow whilst others can require significant effort.
Watchfire's WebXACT is a popular free online tool for checking pages for accessibility. Although it can only check some of the guidelines and occasionally fails pages that do meet the guidelines it is a good starting point for learning the guidelines.
Checkpoint 10.4, "Until user agents handle empty controls correctly, include default, place-holding characters in edit boxes and text areas.", is now considered unnecessary and has been removed from the draft of the next version of the guidelines. See the UK's Royal National Institute for the Blind's article Place-holding text in form elements for more information.
Checkpoint 4.2, "Specify the expansion of each abbreviation or acronym in a document where it first occurs." It is now considered good practice to markup all occurrences of an abbreviation instead of just the first occurrence. HTML 4.01 and XHTML1.0/1.1 have two elements for marking-up abbreviations. The codice_1 element is used to markup any abbreviation. The codice_2 element can be used to markup acronyms. Since acronyms are a special type of abbreviation they can also be marked-up with codice_1. Abbreviations that are not acronyms should not be marked-up with codice_2.
Questions and Exercises.
Exercise 3-1.
Behold the following text: "It is always the dead that are praised, or so claim those who are unsuccessful while alive. Perhaps this is so, partly because some people only revere that which has passed. However, works that have withstood the test of time, have withstood its scrutiny. Long-dead authors that are still remembered, are remembered because of the quality of their work. And no work can be stiled that of a genius, until other works have come along against which it can be compared." (Free after Samuel Johnson's "Preface to Shakespeare".)
Rewrite this paragraph using the inverted pyramid.
Answers.
For answers, see Answers to Questions and Exercises.
Previous: Creating a simple page - Up: Table of Contents - Next: Adapting a webpage for visual browsers | 3,037 |
Electronics/Humor. Sample joke: (rough draft)
Q: How do you tell the difference between elementary particles?<br>
A: Protons are positivists, electrons are negativists, and neutrons have no opinion.
Two atoms are walking down the street. The first atom says to the second atom "I think I lost an electron!" The second says "Are you sure?" To which the first states "I'm positive!" | 103 |
Organic Chemistry/Introduction to reactions/Halohydrins. Halohydrins are formed in addition reactions with alkenes, and either an aqueous solution of a halogen or the corresponding hypohalous acid (eg HOBr or HOCl).
Halohydrin formation uses a cyclic bridged ion as an intermediate. Because of this, the stereochemistry of the reaction process is "anti". | 92 |
Norwegian/Introduction. Welcome to the course.
Welcome to a course in Norwegian. When you have completed this course, you should have enough knowledge to speak, read and write the language rather well. In order to learn a language properly, you must take action, you must "do" something. So I suggest, after you've learnt the basics, that you look up some simple, easy Norwegian literature, and start reading. Knowing what is easy is not easy if you don't know any Norwegian at all though. If you know somebody who is Norwegian, they might be able to help you to some nice reading. I will also try to put up some links to read like easy articles here later.
General remarks about Norwegian.
Written Norwegian is, in contrast to English, very close to pronunciation in spelling. This means that, like Spanish, it is always possible to guess how a word is pronounced in Norwegian. Although Norwegian can only be written in two ways, Bokmål and Nynorsk; how one speaks it is usually reflected in where you come from, by your dialect. There are nine vowels in Norwegian:
and 15 consonants:
The consonants c, q, w, x and z appear only in words of foreign origin.
Finally, there are 7 diphthongs:
Syllable division.
Syllable division marks the natural break in a word. When you know where the syllables divide, you can divide a word into its natural sections. This makes speaking correctly easier. You also get a correct speech rhythm. The general rule for syllable division is that each syllable contains one vowel each.
Information about the language.
First of all, if you're a native English speaker, German speaker, or native in any other Germanic language, learning Norwegian shouldn't be too difficult, as it will have some common traits with your own. I am not saying, however, that it will be easy just because of it.
Alphabet.
The Norwegian alphabet is almost the same as in English, except for three additional letters, æ/Æ, ø/Ø and å/Å. These have no special function in sentences/words, they are normal letters, and you will see them in use nearly as much as any other letters would be in use in English.
Here's how to say the alphabet letter by letter (note that these are the "names" of the letters, not how they are pronounced when they appear in words):
Wikipedia has more information about the use of the letters Æ, Ø, and Å.
Bokmål and Nynorsk.
There are two official written forms of the Norwegian language. This specific course will teach you Bokmål, which is the most widely used (85%). However, the two forms are very similar and you should not have great difficulties in understanding written Nynorsk. For more information about this, check out the Wikipedia article on the Norwegian language.
Getting Started.
Okay, if you're ready, all you gotta do is proceed to Lesson 1! | 689 |
Norwegian/Lesson 1. Pronunciation Guide.
Pronunciation in Norwegian can be quite different from English pronunciation. There are three extra letters: æ, ø, and å (sometimes written "aa"). The letter "æ" is pronounced like the letter "a" in the English word "mad". The letter "ø" is pronounced like the letters "e" and "u" together. The sound is prominent in French words, as in the words "peu" and "deux". The letter "å" is pronounced like "aw". The best way to make this sound is to form one's mouth as if one were going to say the short "o" sound in English, but then making an English "a" sound. There are also other variations in Norwegian pronunciation. The letter "s" becomes a "sh" sound when followed by the letter "l" or when following the letter "r" (i.e. norsk is pronounced "norshk"). The letter "r" is pronounced like the Spanish "r", but is never rolled. The "r" sound in Norsk is produced simply by rapping the tongue against the hard palate once. The letter "g" is pronounced like 'g' in "good", but like 'y' in "yes" before i or j, and silent at the end of some words. The letter "j" is like the English letter "y". The letter "d" is pronounced like the English "d", but is in most cases silent at the end of a syllable or at the end of a word. The letters "q", "w", "z", "x", and "c" are generally only found in foreign words and have no real function in Norsk.
Part One.
Dialogue One.
Arne: God Dag! (Goo dahg)
Bente: God Dag! Hvordan har du det? (Goo dahg! Vor-DAN har deuh deh?)
Arne: Jeg har det bra, takk. Og du? (Yai har deh bra, takk. Aw doo?)
Bente: Bare bra, takk. (Ba-reh bra, takk)
Arne: Hva gjør du? (va yuhr doo?)
Bente: Jeg studerer. (Yai stu-derer.)
Vocabulary.
Bare [Ba-re]: Just/Only
Bra [bra]: Good/Fine
Dag [dag]: Day
Det [deh]: It
Du [doo]: You
Gjør [yuhr]: Doing
God [goo]: Good
Har [har]: Have
Hva [va]: What
Hvordan [vor-DAHN]: How
Jeg [yai]: I
Og [aw]: And
Studerer [stu-DARE-er]: Study
Takk [tahk]: Thanks
Phrases.
Hva gjør du? - What are you doing?
Hvordan har du det? - How are you? (Literally: How do you have it?)
Jeg har det bra. - I'm fine. (Literally: I have it good)
God Dag: - Good morning (Literally: Good day)
Exercises.
Translate the following words/phrases from Norwegian into English.
1 - "Jeg har det bra"
2 - "Du"
3 - "Hva"
4 - "God Dag"
5 - "Takk"
Extra Vocabulary.
Here are a few more words which will increase your Norwegian vocabulary.
Engelsk [en-GELSK]: English
Norsk [norshk]: Norwegian
Norge [nor-GAH]: Norway
Oslo [Osh-lo]: Oslo (The capital of Norway)
Dialogue Two.
You should be able to understand this conversation fairly well now.
Bente: God Dag!
Arne: God Dag! Hva gjør du?
Bente: Jeg studerer.
Arne: Hva studerer du?
Bente: Jeg studerer norsk. Og du? Hva studerer du?
Arne: Jeg studerer engelsk.
Part Two.
Dialogue Three.
Emma: Hei! Jeg er norsk.
Bjørn: Hei, jeg er også norsk.
Emma: Hvor bor du?
Bjørn: Jeg bor i Oslo. Hvor bor du?
Emma: Jeg bor i Bergen, men jeg kommer fra Tromsø.
Bjørn: Hvor er Tromsø?
Emma: Tromsø er i Nord-Norge.
Vocabulary.
Bergen [BAR-yen]: Bergen, A large city on the western coast of Norway
Bor [boor]: Live/Living
Er [ar]: Is/Am/Are
Fra [fra]: From
Hei [hai]: Hi/Hello
Hvor [voor]: Where
I [ee]: In
Kommer [COME-mer]: Come/Coming
Men [men]: But
Nord [noort]: North
Nord-Norge [noort-nor-gah]: Northern Norway
Også [OH-saw]: Also
Tromsø [TROHM-seuh]: Tromso, a city in far northern Norway.
Phrases.
Jeg kommer fra... I come from...
Jeg bor i... I live in...
Hvor kommer du fra? Where do you come from?
Hvor bor du? Where do you live?
Gender.
In Norwegian, every noun (a person, place, thing, or idea) has a gender assigned to it. There are three genders in Norwegian - Masculine, Feminine, and Neuter. There are very few feminine nouns used in Norwegian, and many people simply treat them as masculine nouns, so in this course, we will combine the masculine and feminine genders into the "common gender".
Below are two nouns - One neuter noun, one common noun.
Vin [veen]: Wine
Øl [euhl]: Beer
Vin is common, and Øl is neuter. Why does this matter? It matters because it affects the way you treat these words. An example is with the Norwegian word for "one", which can either be "en" or "ett".
En vin [en veen]: A wine [en vin]
Ett øl [et euhl]: A beer
Common gender words use "en" for one, while Neuter gender words use "ett" for one. We will cover more on gender later.
Forming Questions.
To form a question in Norwegian, invert the verb and noun. For instance...
Du kommer fra: You come from (A statement)
Kommer du fra: Do you come from (lit: come you from) (A question)
You can also form a question by adding a question word (what, where, who, etc.). So far, you have learned the words "hvordan", "hva", and "hvor".
Hva lærer du? What are you learning?
Hvordan har du det? How are you?
Hvor kommer du fra? Where do you come from?
Exercises.
Turn the following statements into questions.
1. "Du er norsk."
2. "Jeg er engelsk."
3. "Du bor i Bergen."
4. "Du har det bra."
5. "Du studerer engelsk i London."
6. "Jeg kommer fra Norge."
7. "Jeg heter ali."
Extra Vocabulary.
(En) Kaffe [KAH-fuh]: Coffee
(En) Fisk [fisk]: Fish
Liker [LEE-care]: Like/Likes
Dialogue Four.
You should be able to understand the following dialogue given your current knowledge of Norwegian.
Emma: God Dag! Hvordan har du det?
Bjørn: Bare bra, takk. Og du?
Emma: Jeg har det bra. Hva har du?
Bjørn: Jeg har en fisk.
Emma: Liker du fisk?
Bjørn: Ja, jeg liker fisk. Liker du kjøtt?
Emma: Nei, men jeg liker kaffe.
Bjørn: Jeg liker også kaffe, og jeg liker øl og vin.
Emma: Hvor bor du?
Bjørn: Jeg bor i Oslo. Og du?
Emma: Jeg bor i Tromsø i Nord-Norge. | 2,043 |
Norwegian/Lesson 2. Gender of Nouns.
Norwegian Bokmål has three genders - feminine, masculine and neuter. Each noun is associated with one specific gender only. There are no simple rules for knowing which noun belongs to which gender; the only way to learn which is which is to memorize it. However nearly all feminine words can also be used as masculine words. In fact the dialect of Bergen, the second largest city in Norway, has no feminine gender and the same goes for the moderate version of Bokmål and Riksmål (the traditional written form of Bokmål, still is used by many). For example the noun ‘dame’ (‘lady’ or ‘woman’) can be inflected as: "ei dame/en dame - dama/damen" (a woman - the woman) and ‘dør’ as "ei dør/en dør - døra/døren" (a door - the door). In addition very few common words actually belong to neuter. That means that you can assume that nouns are masculine and just memorize those that are neuter.
In English nouns are inflected only by using a/an/the. That is because the word ‘cat’/cats’, for example, is the same in both the indefinite and the definite form. In Norwegian it is done by inflecting the noun instead. Notice also that the ending 't' of the definite singular neuter is silent.
Basic inflectional patterns.
Here are examples from each of the three genders. Inflection pattern is marked with bold text.
However, in Norwegian Bokmål, there's an alternative method of inflecting nouns, which basically turns feminine nouns into masculine. This is both accepted and common to do. If you choose to do this, you should also avoid using the a-form of the definite plural neuter.
When speaking, native speakers will often mix between masculine and feminine inflection of nouns. For example, you could say: "en klokke" - "klokka" (a clock - the clock). Here, the indefinite singular form is in the masculine ("en klokke" instead of "ei klokke") while the definite singular form is in the feminine.
Check out Appendix 1: Advanced Noun Inflection to see all the ways the nouns can be inflected.
Definite and Indefinite Articles.
The Indefinite Article.
In English the indefinite articles are "a" and "an" (singular) or "some" (plural).
In Norwegian, the indefinite singular articles are dependent upon the gender of the noun being addressed. The indefinite plural article is the same for all genders. In the previous tables, you've already been introduced to the singular indefinite articles.
Personal Pronouns.
These are very similar to the English personal pronouns. You'll quickly recognize them
The Polite 2nd Person Singular forms 'De' and 'Dem' and the Polite 2nd Person Plural form 'Dere' are always capitalized, unlike the other pronouns, which follow normal rules for casing. For example whilst "Jeg elsker dem" means "I love them", "Jeg elsker Dem" means "I love you". As a sidenote, the use of these polite forms is becoming rarer and they are very seldom used in everyday language.
Both “den” and “det” mean “it”. If the noun is masculine or feminine “den” is used and “det” is used if the noun is neuter.
Verbs.
Learning verbs in Norwegian is easier than most other things you have learnt so far. Unlike English, verbs in Norwegian inflect only for tense and mood. Here's an example - the verbs "to be" and "to run": | 911 |
Norwegian/Appendix 1. Appendix A: Advanced Noun Inflections.
Unfortunately, there is not just one way to inflect a noun per gender. Each gender has several patterns, not to mention that there are plenty of irregular nouns as well.
Feminine Specific Inflection Patterns.
There are three feminine inflection patterns.
Masculine Specific Inflection Patterns.
There are seven masculine inflection patterns.
Neuter Specific Inflection Patterns.
There are eleven neuter inflection patterns | 118 |
XML - Managing Data Exchange/Data schemas. Introduction.
Data schemas are the foundation of all XML pages. They define objects, their relationships, their attributes, and the structure of the data model. Without them, XML documents would not exist.
In this chapter, you will come to understand the purpose of XML data schemas, their intricate parts, and how to utilize them. Also, examples will be included for you to copy when creating your own data schema, making your job a lot easier. At the bottom of this Web page a whole Schema has been included, from which parts have been included in the different sections throughout this chapter. Refer to it if you would like to see how the whole Schema works as one.
Overview of Data Schemas.
The data schema, all technicalities aside, is the data model with which all the XML information is conveyed. It has a hierarchy structure starting with a root element (to be explained later) and goes all the way down to cover even the most minute detail of the model with detailed steps in between.
Data schemas have two main parts, the entities and their relationships. The entities contained in a data schema represent objects from the model. They have unique identifiers, attributes, and names for what kind of object they are. The relationships in the schema represent the relationships between the objects, simple enough. Relationships can be one to one, one to many, many to many, recursive, and any other kind you could find in a data model.
Now we will begin to create our own data schema.
Starting your schema the right way.
All schemas begin the same way, no matter what type of objects they represent. The first line in every Schema is this declaration:
<?xml version="1.0" encoding="UTF-8"?>
Exhibit 1 simply tells the browser or whatever file/program accessing this schema that it is an XML file and uses the encoding structure "UTF-8". You can copy this to use to start your own XML file.
Next comes the Namespace declaration:
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="unqualified">
Namespaces are basically dictionaries containing definitions of most of the coding in the schema. For example, when creating a schema, if you declare an object to be of type "String", the definition of the type "String" is contained in the Namespace along with all of its attributes. This is true for most of the code you write. If you have made or seen other schemas, most of the code is prefaced by "xsd:". A good example is something like "xsd:sequence" or "xsd:complexType". sequence and complexType are both objects defined in the Namespace that has been linked to the prefix "xsd". In fact, you could theoretically name the default Namespace anything, as long as you referenced it the same way throughout the Schema. The most common Namespace which contains most of the XML objects is http://www.w3.org/2001/XMLSchema. Now onto Exhibit 2.
The first part lets any file/program know that this file is a schema. Pretty easy to understand. Like the XML declaration, this is universal to XML schemas and you can use it in yours. The second part is the actual Namespace declaration; xmlns stands for XML NameSpace. This defines the Schema's default Namespace and is usually the one given in the code. Again, I would recommend using this code to start your Schemas. The last part is difficult to understand, but here is a pretty detailed explanation. Using "unqualified" is most applicable until you get to some really complicated code.
Entities in general.
Entities are basically the objects a Schema is created to represent. As stated before, they have attributes and relationships. We will now go much further into explaining exactly what they are and how to write code for them.
There are two types of Entities: simpleType and complexType. A simpleType object has one value associated with it. A string is a perfect example of a simpleType object as it only contains the value of the string. Most simpleTypes used will be defined in the default Namespace; however, you can define your own simpleType at the bottom of the Schema (this will be brought up in the restrictions section). Because of this, the only objects you will most often need to include in your Schema are complexTypes. A complexType is an object with more than one attribute associated with it, and it may or may not have a child elements attached to it. Here is an example of a complexType object:
<xsd:complexType name="GenreType">
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="description" type="xsd:string"/>
<xsd:element name="movie" type="MovieType" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
This code begins with the declaration of a complexType and its name. When other entities refer to it, such as a parent element, it will refer to this name. The 2nd line begins the sequence of attributes and child elements, which are all declared as an "element". The elements are declared as elements with the 1st part of the line of code, and their name to which other documents will refer is included as the "name" as the 2nd part. After the first two declarations comes the "type" declaration. Note that for the "name" and "description" elements their type is "xsd:string" showing that the type string is defined in the Namespace "xsd". For the "movie" element, the type is "MovieType", and because there is no Namespace before "MovieType", it is assumed that this type is included in this Schema. (it could refer to a type defined in another Schema if the other Schema was included at the top of the Schema. don't worry about that now) "minOccurs" and "maxOccurs" represents the relationship between Genre's and MovieTypes. "minOccurs" can be either 0 or an arbitrary number, depending only on the data model. "maxOccurs" can be either 1 (a one to one relationship), an arbitrary number (a one to many relationship), or "unbounded" (a one to many relationship).
For each schema, there must be one root element. This entity contains every other entity underneath it in the hierarchy. For instance, when creating a schema to include a list of movies, the root element would be something like MovieDatabase, or maybe MovieCollection, just something that would logically contain all the other objects (like genre, movie, actor, director, plotline, etc.) It is always started with this line of code: codice_1 showing that it is the root element and then goes on as a normal complexType. All other objects will begin with either simpleType or complexType. Here is sample code for a MovieDatabase root element:
<xsd:element name="MovieDatabase">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="Genre" type="GenreType" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
This represents a MovieDatabase where the child element of MovieDatabase is a Genre. From there it goes onto movie, etc. We will continue to use this example help you better understand.
The Parent / Child Relationship.
The Parent / Child Relationship is a key topic in Data Schemas. It represents the basic structure of the data model's hierarchy by clearly laying out the top down configuration. Look at this piece of code which shows how movies have actors associated with them:
<xsd:complexType name="MovieType">
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="actor" type="ActorType" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="ActorType">
<xsd:sequence>
<xsd:element name="lname" type="xsd:string"/>
<xsd:element name="fname" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
Within each MovieType, there is an element named "actor" which is of "ActorType". When the XML document is populated with information, the surrounding tags for actor will be codice_2 and not codice_3. To keep your Schema flowing smoothly and without error, the "type" field in the Parent Element will always equal the "name" field in the declaration of the complexType Child Element.
Attributes and Restrictions.
An attribute of an entity is a simpleType object in that it only contains one value. codice_4 is a good example of an attribute. It is declared as an element, has a name associated with it, and has a type declaration. Located in the appendix of this chapter is a long list of simpleTypes built into the default Namespace. Attributes are incredibly simple to use, until you try and restrict them.
In some cases, certain data must abide by a standard to maintain data integrity. An example of this would be a Social Security number or an email address. If you have a database of email addresses that sends mass emails to, you would need all of them to be valid addresses, or else you'd get tons of error messages each time you send out that mass email. To avoid this problem, you can essentially take a known simpleType and add a restriction to it to better suit your needs. Now you can do this two ways, but one is simpler and better to use in Data Schemas. You could edit the simpleType within its declaration in the Parent Element, but it gets messy, and if another Schema wants to use it, the code must be written again. The better way to do it is to list a new type at the bottom of the Schema that edits a previously known simpleType. Here is an example of this with a Social Security number:
<xsd:simpleType name="emailaddressType">
<xsd:restriction base="xsd:string">
<xsd:pattern value="[^@]+@[^\.]+\..+"/>
</xsd:restriction>
</xsd:simpleType>
<xsd:simpleType name="ssnType">
<xsd:restriction base="xsd:string">
<xsd:pattern value="\d{3}-\d{2}-\d{4}"/>
</xsd:restriction>
</xsd:simpleType>
This was included in the Schema below the last Child Element and before the closing codice_5. The first line declares the simpleType and gives it a name, "ssnType". You could name yours anything you want, as long as you reference it correctly throughout the Schema. By doing this, you can use this type anywhere in the Schema, or anywhere in another Schema, provided the references are correct. The second line lets the Schema know it is a restricted type and its base is a string defined in the default Namespace. Basically, this type is a string with a restriction on it, and the third line is the actual restriction. It can be one of many types of restrictions, which are listed in the Appendix of this chapter. This one happens to be of type "pattern". A "pattern" means that only a certain sequence of characters will be allowed in the XML document and is defined in the value field. This particular one means three digits, a hyphen, two digits, a hyphen, and four digits. To learn more about how to use restrictions, follow this link to the W3 school's section on restrictions.
Not of little import: Introducing the codice_6 tag.
The codice_6 tag is used to import a schema document and the namespace associated with the data types defined within the schema document. This allows an XML schema document to reference a type library using namespace names (prefixes). Let's take a closer look at a simple XML instance document for a store that uses these multiple namespace names:
<?xml version="1.0" encoding="UTF-8"?>
<store:SimpleStore xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opentourism.org/xmltext/SimpleStore.xsd"
xmlns:store="http://www.opentourism.org/xmltext/Store"
xmlns:MGR="http://www.opentourism.org/xmltext/CoreSchema">
<!-- Note the explicitly defined namespace declarations, the prefix store
represents data types defined in the
codice_8 namespace and the
prefix MGR represents data types defined in the
codice_9 namespace.
Also, notice that there is no default namespace declaration – every element
and attribute must be associated with a namespace (we will see this is
necessary weh we examine the schema document)
<store:Store>
<MGR:Name xmlns:MGR=" http://www.opentourism.org/xmltext/CoreSchema ">
<MGR:FirstName>Michael</MGR:FirstName>
<MGR:MiddleNames>Jay</MGR:MiddleNames>
<MGR:LastName>Fox</MGR:LastName>
</MGR:Name>
<store:StoreName>The Gap</store:StoreName>
<store:StoreAddress>
<store:Street>86 Nowhere Ave.</store:Street>
<store:City>Los Angeles</store:City>
<store:State>CA</store:State>
<store:ZipCode>75309</store:ZipCode>
</store:StoreAddress>
<!-- More store information would go here. -->
</store:Store>
<!-- More stores would go here. -->
</store:SimpleStore>
Let's look at the schema document and see how the codice_6 tag was used to import data types from a type library (external schema document).
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns="http://www.opentourism.org/xmltext/Store.xml"
xmlns:MGR="http://www.opentourism.org/xmltext/CoreSchema"
targetNamespace="http://www.opentourism.org/xmltext/Store.xml" elementFormDefault="qualified">
<!-- The prefix MGR is bound to the following namespace name:
codice_9
The managerTypeLib.xsd schema document is imported by associating the
schema with the codice_9
namespace name, which was bound to the MGR prefix.
The elementFormDefault attribute has the value ‘qualified' indicating that
an XML instance document must use qualified names for every element(default
namespace can not be used)
<!-- The target namespace and default namespace are the same -->
<xsd:import namespace="http://www.opentourism.org/xmltext/CoreSchema"
schemaLocation="ManagerTypeLib.xsd"/>
<xsd:element name="SimpleStore">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="Store" type="StoreType" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType name="StoreType">
<xsd:sequence>
<xsd:element ref="MGR:Name"/>
<xsd:element name="StoreName" type="xsd:string"/>
<xsd:element name="StoreAddress" type="StoreAddressType"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="StoreAddressType">
<xsd:sequence>
<xsd:element name="Street" type="xsd:string"/>
<xsd:element name="City" type="xsd:string"/>
<xsd:element name="State" type="xsd:string"/>
<xsd:element name="ZipCode" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:schema>
Like the include tag and the redefine tag, the import tag is another means of incorporating any data types from an external schema document into another schema document and must occur before any element or attribute declarations. These mechanisms are important when XML schemas are modularized and type libraries are being maintained and used in multiple schema documents.
When the whole is greater than the sum of its parts:<br> Schema Modularization.
Now that we have covered all three methods of incorporating external XML schemas, let’s consider the importance of these mechanisms. As is typical with most programming code, redundancy is frowned upon; this is true for custom data type definitions as well. If a custom data type already exists that can be applied to an element in your schema document, does it not make sense to use this data type rather than create it again within your new schema document? Moreover, if you know that a single data type can be reused for several applications, should you not have a method for referencing that data type when you need it?
The idea behind modular schemas is to examine what your schema does, determine what data types are frequently used in one form or another and develop a type library. As your needs for more complex schemas increase you can continue to add to your library, reuse data types in your type library, and redefine those data types as needed. An example of this reuse would be a schema for customer information – different departments would use different schemas as they would need only partial customer information. However most, if not all, departments would need some specific customer information, like name and contact information, which could be incorporated in the individual departmental schema documents.
Schema modularization is a “best practice”. By maintaining a type library and reusing and redefining types in the type library, you can help ensure that your XML schema documents don't become overwhelming and difficult to read. Readability is important, because you may not be the only one using these schemas, and it is important that others can easily understand your schema documents.
“Choose, but choose wisely…”: Schema alternatives.
Thus far in this book we have only discussed XML schemas as defined by the World Wide Web Consortium (W3C). Yet there are other methods of defining the data contained within an XML instanced document, but we will only mention the two most popular and well known alternatives: Document Type Definition (DTD) and Relax NG Schema.
We will cover DTDs in the next chapter. Relax NG schema is a newer and has many of the same features that W3C XML schema have; Relax NG also claims to be simpler, and easier to learn, but this is very subjective.
For more about Relax NG, visit: http://www.relaxng.org/
Appendix.
First is the full Schema used in the examples throughout this chapter:
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
elementFormDefault="unqualified">
<xsd:element name="MovieDatabase">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="Genre" type="GenreType" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:complexType name="GenreType">
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="description" type="xsd:string"/>
<xsd:element name="movie" type="MovieType" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="MovieType">
<xsd:sequence>
<xsd:element name="name" type="xsd:string"/>
<xsd:element name="rating" type="xsd:string"/>
<xsd:element name="director" type="xsd:string"/>
<xsd:element name="writer" type="xsd:string"/>
<xsd:element name="year" type="xsd:int"/>
<xsd:element name="tagline" type="xsd:string"/>
<xsd:element name="actor" type="ActorType" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="ActorType">
<xsd:sequence>
<xsd:element name="lname" type="xsd:string"/>
<xsd:element name="fname" type="xsd:string"/>
<xsd:element name="gender" type="xsd:string"/>
<xsd:element name="bday" type="xsd:string"/>
<xsd:element name="birthplace" type="xsd:string"/>
<xsd:element name="ssn" type="ssnType"/>
</xsd:sequence>
</xsd:complexType>
<xsd:simpleType name="ssnType">
<xsd:restriction base="xsd:string">
<xsd:pattern value="\d{3}-\d{2}-\d{4}"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:schema>
It’s time to go back to the beginning…and review all of the schema data types, elements, and attributes that we have covered thus far (and maybe a few that we have not). The following tables will detail the XML data types, elements and attributes that can be used in an XML Schema.
Primitive Types
This is a table with all the primitive types the attributes in your schema can be.
Schema Elements <br> ( from http://www.w3schools.com/schema/schema_elements_ref.asp )
Here is a list of all the elements which can be included in your schemas.
Schema Restrictions and Facets for data types<br>( from http://www.w3schools.com/schema/schema_elements_ref.asp )
Here is a list of all the types of restrictions which can be included in your schema.
Regex <br>
Special regular expression (regex) language can be used to construct a pattern. The regex language in XML Schema is based on Perl's regular expression language. The following are some common notations:
Instance Document Attributes These attributes do NOT need to be declared within the schemas
For more information on XML Schema structures, data types, and tools you can visit http://www.w3.org/XML/Schema. | 5,868 |
Calculus/Sequences. A sequence is an ordered list of objects (or events). Like a set, it contains members (also called "elements" or "terms"), and the number of terms (possibly infinite) is called the "length" of the sequence. Unlike a set, order matters, and exactly the same elements can appear multiple times at different positions in the sequence.
For example, (C, R, Y) is a sequence of letters that differs from (Y, C, R), as the ordering matters. Sequences can be "finite", as in this example, or "infinite", such as the sequence of all even positive integers (2, 4, 6...).
Examples and notation.
There are various and quite different notions of sequences in mathematics,
some of which (e.g., exact sequence) are not covered by the notations introduced below.
A sequence may be denoted ("a"1, "a"2, ...). For shortness, the notation ("a""n") is also used.
A more formal definition of a finite sequence with terms in a set "S" is a function from {1, 2, ..., "n"} to "S" for some "n" ≥ 0. An infinite sequence in "S" is a function from {1, 2, ...} (the set of natural numbers without 0) to "S".
Sequences may also start from 0, so the first term in the sequence is then "a"0.
A finite sequence is also called an n-tuple. Finite sequences include the "empty sequence" ( ) that has no elements.
A function from all integers into a set is sometimes called a bi-infinite sequence, since it may be thought of as a sequence indexed by negative integers grafted onto a sequence indexed by positive integers.
The sequence formula_1 is called the harmonic sequence.
If "c" and "d" are given numbers, the sequence formula_2 is an arithmetic sequence.
If "b" and "r" ≠ 0 are given, the sequence formula_3 is a geometric sequence.
Types and properties of sequences.
A subsequence of a given sequence is a sequence formed from the given sequence by deleting some of the elements (which, as stated in the introduction, can also be called "terms") without disturbing the relative positions of the remaining elements.
If the terms of the sequence are a subset of an ordered set, then a "monotonically increasing" sequence is one for which each term is greater than or equal to the term before it; if each term is strictly greater than the one preceding it, the sequence is called "strictly monotonically increasing". A monotonically decreasing sequence is defined similarly. Any sequence fulfilling the monotonicity property is called monotonic or "monotone". This is a special case of the more general notion of a monotonic function. A sequence that both increases and decreases (at different places in the sequence) is said to be "non-monotonic" or "non-monotone".
The terms "non-decreasing" and "non-increasing" are often used in order to avoid any possible confusion with strictly increasing and strictly decreasing, respectively.
If the terms of a sequence are integers, then the sequence is an integer sequence.
If the terms of a sequence are polynomials, then the sequence is a polynomial sequence.
If "S" is endowed with a topology (as is true of real numbers, for example), then it becomes possible to consider the "convergence" of an infinite sequence in "S". Such considerations involve the concept of the "limit of a sequence".
It can be shown that bounded monotonic sequences must converge.
Sequences in analysis.
In analysis, when talking about sequences, one will generally consider sequences of the form
which is to say, infinite sequences of elements indexed by natural numbers.
(It may be convenient to have the sequence start with an index different from 1 or 0. For example, the sequence defined by "xn" = 1/log("n") would be defined only for "n" ≥ 2.
When talking about such infinite sequences, it is usually sufficient (and does not change much for most considerations) to assume that the members of the sequence are defined at least for all indices large enough, that is, greater than some given "N".)
The most elementary type of sequences are numerical ones, that is, sequences of real or complex numbers. | 993 |
Norwegian/Numbers. The norm in Norwegian is to write numbers from one to twelve using letters and the numbers from 13 and above using numbers. It is recommended not to mix letters and numbers within the same sentence (or even within the same paragraph or the same document), so it would be better to write “from one to fifty cars” or “from 1 to 50 cars” than “from one to 50 cars”. When spelt with letters, they are either spelt in one word ("hundreogtrettito") or separately ("hundre og tretti to").
The decimal mark in Norwegian is the comma and the thousands separator is a blank space, so 987654 divided by 100 equals 9 876,54. Not all Norwegians follow these rules, so pay attention when a website prompt you for a number as the website will usually tell you what decimal mark to use (or even prompt for the decimals in a separate field).
In Old Norse, numbers one through four were all inflected in three genders (masculine, feminine and neuter) and four cases (nominative, accusative, dative and genitive). In modern Norwegian, most of the inflection is gone. The official orthography only contains inflected forms of "one", but some dialects have kept a larger portion. However, the case inflection is gone everywhere. The early Nynorsk orthography kept the gender inflection of all four numbers, but the forms gradually merged. | 332 |
Norwegian/Appendix 2. Appendix P: Norwegian Pronunciation.
The pronunciation is indicated in IPA. The sounds are best learned from a native speaker. Whenever possible, practice these with a native speaker. Reading aloud will also help your confidence. Note that the Norwegian language is full of dialects, so there are several ways of pronouncing the words. Foreign learners are usually taught to speak the way that people in the Oslo-area speak.
Vowels.
The Norwegian vowels:
The main rule is that long vowels occur before single consonants, short vowels occur before double consonants. This is no absolute rule, though, as you will see in the examples below. Notice: the short o sound is rarely represented in written form with an "o"! (It's usually represented by "u")
Consonants.
The Norwegian consonants
Most consonants in the Norwegian language are pronounced like the English consonants.
Plosives.
In Norwegian, there are six plosives, all equal to the English version of them.
Fricatives.
These are also quite equal to the English language, except that Norwegian does not have ', (as in "thin") ' (as in "this") ' (as in "measure") and ', (as in "zing") but at the other hand, Norwegians have the ' sound, which is sort of a "stiffer" version of the ' sound (as in German "ich"). The ç sound is similar to the "h" in many English dialects' pronunciation of "huge".
Diphthongs.
Vowels also appear in set combinations. These are called diphthongs. They are two vowel sounds pronounced after the other as a continuous sound
Tonemes.
Norwegian has two contrasting tonemes. These are kind of hard to describe using text, and some also say that foreigners (to Norway) are even unable to distinguish one from the other. However, they do exist. In the words indicated with 1 and a hacek, the tone is normal in the first part of the word, and rises in the last part of the word. In the words indicated with 2, the word is pronounced like any other normal word. (In other words, it's very hard to say 1 words in a monotone voice) Here are two examples:
Notice: The two last examples are "very" similar to each other even though they are different, and I am actually somewhat unsure if it's loven or låven which is the more "special" one. | 581 |
Puzzles/Action sequences/Three Bottles. Puzzles | Action sequences | Three Bottles
Suppose you have a full bottle containing twenty-four ounces of liquid. You also have three empty bottles: one of five ounces, one of eleven ounces, and one of thirteen ounces. How could you divide the twenty-four ounces of liquid into three equal parts, so that you have three bottles containing eight ounces of liquid each?
Solution | 106 |
Electronics/Prereq. Prerequisite Topics.
Most important / Required knowledge
Moderately Important / Aids in comprehension
Slightly Important / Related or helpful
Mathematics
Physics
Other Useful Topics | 58 |
Electronics/Conventional Current. An electronic circuit is a system in which electrons flow from a negative terminal of a source, through a load, to the positive terminal. Unfortunately for electronics students, pioneers in the fields of electricity and magnetism believed that positive charge flowed, so many of the conventions in physics and electronics assume that current flows from positive to negative, even though the particles that are moving are actually negatively charged electrons moving from negative to positive. ("conventional current is covered in the voltage and current section. should we take it out of here and just leave it there?")
"Talking about conventional current here sounds like a good idea. The discussion should include a blurb on the relationship between conventional current and voltage."
If you are having trouble imagining this, consider what happens if you pass helium filled balloons to another person while you both are standing on scales. If the balloons are very large, then the person receiving the balloon actually loses weight and you who gave the balloon gain weight -- as measured by the scales. (This is because the balloons are pulling up on you.) In other words, the person who gives the balloon seems to have received weight and the person who receives the balloon seems to have lost weight. In the same way, when something gives electrons it seems to have received positive charge.
If this all seems confusing, rest assured that you will find a way to think about it that works for you. Many people just ignore the electrons altogether and think of positive charge flowing around. Except in rare cases this is completely fine.
So, different types of negative particles drift from negative to positive, and positive particles drift in the opposite direction, at different speeds in different materials. How to make sense of this? Conventional current. We define current as flowing from positive to negative, and ignore the particles that make it up (for most purposes), paying attention only to the amount of charge flow per unit time, and the speed of the electromagnetic waves. We will sometimes still talk about electrons flowing, since they are the predominant charge carriers in metal, and many circuit components. Just keep these principles in mind.
Current i / I is represented in Amperes / Amps / A and equals x number of y | 481 |
XML - Managing Data Exchange/The many-to-many relationship/Answers. Many-to-Many Chapter => The Many-to-Many Relationship
Many-to-Many Exercises => Exercises
1) Movie Collection.
Use the following data model:
2) Student/Class Directory.
the Stylesheet.
Many-to-Many Chapter => The Many-to-Many Relationship
Many-to-Many Exercises => Exercises | 116 |
MATLAB Programming/char. "char" is used to convert numbers and cells to character arrays, i.e. strings. It uses the standard ASCII codes. Matlab R12.1 on Windows gives the following output for this code:
Code.
for i = -1:257
disp([num2str(i) ': ' char(i)])
end
Output.
Warning: Out of range or non-integer values truncated during conversion from
double to character.
-1:
0:
1: �
2: �
3: �
4: �
5: �
6: �
7:
8:
9:
10:
11: �
12: �
13:
14: �
15: �
16: �
17: �
18: �
19: �
20: �
21: �
22: �
23: �
24: �
25: �
26: �
27: �
28: �
29: �
30: �
31: �
32:
33: !
34: "
35: #
36: $
37: %
38: &
39: '
40: (
41: )
42: *
43: +
44: ,
45: -
46: .
47: /
48: 0
49: 1
50: 2
51: 3
52: 4
53: 5
54: 6
55: 7
56: 8
57: 9
58: :
59: ;
60: <
61: =
62: >
63: ?
64: @
65: A
66: B
67: C
68: D
69: E
70: F
71: G
72: H
73: I
74: J
75: K
76: L
77: M
78: N
79: O
80: P
81: Q
82: R
83: S
84: T
85: U
86: V
87: W
88: X
89: Y
90: Z
91: [
92: \
93: ]
94: ^
95: _
96: `
97: a
98: b
99: c
100: d
101: e
102: f
103: g
104: h
105: i
106: j
107: k
108: l
109: m
110: n
111: o
112: p
113: q
114: r
115: s
116: t
117: u
118: v
119: w
120: x
121: y
122: z
123: {
124: |
126: ~
127:
128: €
129: ?
130: ‚
131: ƒ
132: „
133: …
134: †
135: ‡
136: ˆ
137: ‰
138: Š
139: ‹
140: Œ
141: ?
142: ?
143: ?
144: ?
145: ‘
146: ’
147: “
148: ”
149: •
150: –
151: —
152: ˜
153: ™
154: š
155: ›
156: œ
157: ?
158: ?
159: Ÿ
160:
161: ¡
162: ¢
163: £
164: ¤
165: ¥
166: ¦
167: §
168: ¨
169: ©
170: ª
171: «
172: ¬
173:
174: ®
175: ¯
176: °
177: ±
178: ²
179: ³
180: ´
181: µ
182: ¶
183: ·
184: ¸
185: ¹
186: º
187: »
188: ¼
189: ½
190: ¾
191: ¿
192: À
193: Á
194: Â
195: Ã
196: Ä
197: Å
198: Æ
199: Ç
200: È
201: É
202: Ê
203: Ë
204: Ì
205: Í
206: Î
207: Ï
208: Ð
209: Ñ
210: Ò
211: Ó
212: Ô
213: Õ
214: Ö
215: ×
216: Ø
217: Ù
218: Ú
219: Û
220: Ü
221: Ý
222: Þ
223: ß
224: à
225: á
226: â
227: ã
228: ä
229: å
230: æ
231: ç
232: è
233: é
234: ê
235: ë
236: ì
237: í
238: î
239: ï
240: ð
241: ñ
242: ò
243: ó
244: ô
245: õ
246: ö
247: ÷
248: ø
249: ù
250: ú
251: û
252: ü
253: ý
254: þ
255: ÿ
256:
257: �
@import ( reference ) '@wikimedia/codex-design-tokens/theme-wikimedia-ui.less';
@import ( reference ) '@wikimedia/codex/mixins/link.less';
.my-custom-link {
.cdx-mixin-link(); | 1,986 |
Electronics/Inductance. A electron moving through space creates a magnetic field that spins around the charge according to the right hand rule. The magnetic field is created by the spin of the moving electron. If the wire is bent in the shape of a ring, when its current is flowing it magnetic field will resemble water flowing through a hose. In order for the ring to have a magnetic field, its magnetic field must first displace the magnetic field that is already there. This is why inductors initially resist any changes in current when a voltage is applied. Over time the magnetic field changes to reflect the magnetic field of the ring and current starts flowing.
Inductors resist changes in current and take time to adjust.
A popular example of inductance is an electromagnet. It is essentially an inductor connected to dc with a piece of metal in its core. The flow of current creates a magnetic flow that mimicks a magnet. The direction of current determines the polarity of the magnet.
The nice thing about electromagnets is the strength of the current determines the strength of the magnetic field, so the more current the more magnetic field. Also reversing the direction of the current switches the polarity of the electromagnet.
This property allows electromagnets to be used as switches. As the current increases the magnet becomes more repulsive to other magnets.
Electromagnets are also used in loudspeakers. You have a voltage that is dependent on distance so as the distance decreases the voltage increases and as the distance increases the voltage decreases. The result is the ability to program the loudspeaker according to a vibration pattern. | 353 |
Electronics/Mutual Inductance. Mutual inductance is just like inductance except that there is a hose at the other end to collect the magnetic flow. So current through a ring generates a magnetic field which is collected by the other ring and is turned into current that moves the opposite direction. Mutual inductance relies on AC as DC does not disturb the magnetic field enough. Nominally the inductance can flow through air, but the inductance is more effective when it flows through a magnetic core such as iron. | 115 |
Electronics/Transformers. Transformer.
Description
A transformer is a device that is used to either raise or lower voltages and currents in an electrical circuit. In modern electrical distribution systems, transformers are used to boost voltage levels so as to decrease line losses during transmission.
Theory of Operation
Transformers rely on Faraday's Law, which states that a time-varying magnetic field can induce a time-varying voltage in a loop of wire. In a transformer, this is accomplished by wrapping multiple turns of wire around some type of ferromagnetic material. Usually, there are two sets of windings: a primary and a secondary. The primary winding is attached to the generator; the secondary side is attached to the load. When a time-varying voltage is applied to the primary, a magnetic field is created inside the ferromagnetic core. The ferromagnetic material serves to concentrate the magnetic flux within the windings. The magnetic flux on the outside of the windings is reduced and the efficiency of the device is increased.
The time-varying magnetic field induces a voltage in the secondary winding.
The magnitude of the secondary voltage depends on the turns ratio of the primary and secondary windings. Suppose that the secondary winding of a transformer has 100 turns, while the primary winding has only 50 turns. The resulting secondary voltage will be twice that of the primary voltage. Likewise, if the primary has 100 turns, and the secondary has 50 turns, the secondary voltage would be half that of the primary.
At this point it may seem that we're getting something for nothing, but this is not the case. Recall that energy can neither be created nor destroyed. We know that the electrical power flowing into the primary windings is the product of the current and voltage. Similarly, the power flowing out of the transformer must also be product of its current and voltage. Neglecting losses in the transformer core, the power entering the transformer must also be the power leaving the transformer. This means that in order to raise the voltage, we must decrease the current. Likewise, by lowering the voltage, we increase the current. As with the transformer voltages, the ratios of the currents depend on the ratios of the primary and secondary windings. However, when dealing with currents, it is important to remember that the side with the larger number of turns has the smaller current and vice versa. Consider the transformer mentioned above with a primary to secondary turns ratio of 1:2. A 100-A current flowing into the primary would result in a 50-A current flowing out of the secondary.
Uses
The most obvious application of the electrical transformer is in power distribution. Recall that in an electrical circuit, formula_1. Therefore, the power consumed by a circuit element is proportional to the "square" of the current flowing through it. In a transmission line, this is important because the line itself has some characteristic impedance. In order to reduce power losses in the transmission line, it is desirable to transmit the least amount of current possible. For a given amount of power, the best way to do this is by increasing the voltage.
The transformer is also used for impedance matching. Given a voltage source and a transmission line with a characteristic impedance, it is possible to use a transformer to make the load appear larger or smaller so that the load receives maximum power. Note that maximum power is not equal to maximum efficiency. For maximum efficiency in the use of electrical energy, the load should have extreme resistance so that the energy lost in the rest of the circuit will be negligible. Looking into the equations, however, the load of extreme resistance will receive negligible power (though much higher than the rest of the circuit). For any given constant voltage across any load, the power received by the load is given by formula_2, thus the relationship. Note again that the equation used here is the one above transformed with Ohm's Law, and is the only appropriate since Current will drop in this case if the resistance increases.
3-phase transformers.
These are, in essence, 3 single-phase transformers that have one of their terminals connected to a common terminal, called the neutral, which usually is connected to earth/ground. Their voltages are 120 degrees out of phase from the other two. | 942 |
General Mechanics/Analysis Using Newton's Laws. Analysis Using Newton's Laws.
The acceleration of the mass at any time is given by Newton's second law
An equation of this type is known as a "differential equation" since it involves a derivative of the dependent variable . Equations of this type are generally more difficult to solve than algebraic equations, as there are no universal techniques for solving all forms of such equations. In fact, it is fair to say that the solutions of most differential equations were originally obtained by "guessing"!
There are systematic ways of solving simple differential equations, such as this one, but for now we will use our knowledge of the physical problem to make an intelligent guess.
We know that the mass oscillates back and forth with a period that is independent of the amplitude of the oscillation. A function which might fill the bill is the sine function. Let us try substituting,
where ω is a constant, into this equation.
We get
Notice that the sine function cancels out, leaving us with formula_1 . The guess thus works if we set
This constant is the angular oscillation frequency for the oscillator, from which we infer the period of oscillation to be
This agrees with the result of the dimensional analysis. Because this doesn't depend on formula_2 , we can see that the period is independent of amplitude.
It is easy to show that the cosine function is equally valid as a solution,
for the same formula_3 .
In fact, the most general possible solution is just a combination of these two, i.e.
The values of formula_4 depend on the position and velocity of the mass at time formula_5 . | 370 |
Electronics/Urban Legends. Various legends and their status as true or false.
1. Touching both ends of a 12 Volt car battery will kill me.
False. The human body has millions of ohms of resistance so unless you are wet or are bleeding you should be ok. Millions of ohms of resistance means that the amount of current flowing will be astronomically small.
2. Cell phones cause cancer or brain damage.
Probably false. A cell phone operates at 900 MHz and 3GHz. Visible light has a frequency of 1 Petillion 10^15 Hz. Just below that is UV where you get sunburns. That's a million times the frequency. So if cell phones hurt you than what must visible light be doing to you? If you believe it will hurt you than your only hope is to live in darkness inside a Faraday cage like a CHUD. No microwave, infared, or visible light for you.
3. One time a cell phone caused a fire at a gas station.
4. CRTs are bad for you and expose you to x-rays. False, there are some x rays that get through occasionally, but not frequently enough to cause real damage. | 276 |