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DiracDelta - Science & Engineering encyclopedia
Category: Sciences > Science & Engineering
Date & country: 01/12/2007, UK
Words: 4470
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Cross AssemblerAn assembler program that runs on a different kind of computer thanthat for which it generates code. See also: Assembler, Compiler.
Cross CorrelationThe cross-correlation function gives a measure of the extent to which two signals correlate with each other as a function of the time displacement between them. If the signals are identical, the cross correlation will be one, and if they are completely dissimilar, the cross correlation will be zero.The cross correlation of two functions f
x
Cross Section
A view showing an internal structure as it would be revealed by cutting through the piece in any plane.
Cross Spectrum
The cross spectrum Fxy(f) of fx(t) and fy(t) is the forward Fourier Transformof the cross correlation function Rxy(T). The cross spectrum is in generalcomplex. The cross spectrum can also be obtained from the individual Fourier spectra Fx(f) and Fy(f)Fxy(f)=F'
Cross Talk
Unwanted breakthrough of one channel into another.Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.
Crosslinked Polymer
A polymer in which adjacent linear molecular chains are joined at various positions by covalent bonds. See also: Covalent Bond, Polymer.
Crossover Frequency
In a loudspeaker with multiple radiators, the crossover frequency is the 3dB point of the network dividing the signal energy. See also: Loudspeaker.
Crosswall
An interior dividing wall of a castle.
Crosswind
Any wind that is blowing perpendicular to a line of travel.
Crowbar
Circuit used to protect the output of a source from a short circuited load. Load current is limited to a value the source can deliver without damage.
Crown Glass
A silicate glass containing oxides of sodium and potassium, used in compound lenses and spectacles; harder than flint glass, with low index and low dispersion.
Cruise Control
Control system used to maintain the vehicle speed without the invention of a driver.
Cryogenic Gas
A gas that has been liquified by lowering the temperature, usually to a temperature under about -100°C. See also: Cryostat, Gas.
Cryostat
Container used to isolate thermally a fluid from its environment and maintain it at low temperatures. See also: Cryogenic Gas.
Cryptarithm
A number puzzle in which an indicated arithmetical operation has some or all of its digits replaced by letters or symbols and where the restoration of the original digits is required. Each letter represents a unique digit.
Cryptography
Field of mathematics and computer science concerned with information security and related issues, particularly encryption and authentication.Code as intercepted from a German Enigma machine during WWII:'NCZW VUSX PNYM INHZ XMQX SFWX WLKJ AHSH NMCO CCAK UQPM KCSM HKSE INJU SBLK IOSX CKUB HMLL XCSJ USRR DVKO HULX WCCB GVLI YXEO AHXR HKKF VDRE WEZL XO…
Crystal
A material in which the atoms are arranged in a definite geometric pattern. These arrangements have a direct effect on the physical properties of the material. These arrangements commonly take the form of cubes, rectangular solids, hexagonal solids.....etc. Most crystals contain defects that can strongly affect their optical and electrical properti…
Crystal Controlled Oscillator
Oscillator that uses a quartz crystal in its feedback path to maintain a stable output frequency. See also: Frequency.
Crystal Structure
For crystalline materials, the manner in which atoms or ions are arrayed in space. It is defined in terms of the unit cell geometry and the atom positions within the cell. See also: Crystal.
Crystal System
A scheme by which crystal structures are classified according to unit cell geometry. See also: Crystal.
Crystalline
The state of a solid material characterized by a periodic and repeating three-dimensional arrays of atoms, ions, or molecules. See also: Crystal, Crystallization.
Crystallite
A region within a crystalline polymer in which all the molecular chains are ordered and aligned. Real crystals are usually built of a large number of crystallites. See also: Crystal, Polymer.
Crystallization
Act or process of forming crystals or bodies by elements or compounds solidifying so they are bounded by plane surfaces, symmetrically arranged, and are external expressions of definite internal structure. See also: Crystal, Crystalline.
Cube
A solid figure bounded by 6 congruent squares.A number raised to the power 3, ie 2 x 2 x 2 = 23 = 8
Cubic Centimetre
Abbrieviated as cm3 or cc.ttle='Volume';xiunt='cubic centimetre';yiunt='m3';mconv=1000;cconv=0.0; See also: Cubic Inch, Volume.
Cubic Equation
An equation of the third order.Note that the first root is real and roots 1 and 2 are complex.
Cubic Foot
1 cubic foot = 0.0283168 m3ttle='Volume';xiunt='cubic foot';yiunt='m3';mconv=1/0.0283168;cconv=0.0; See also: Cubic Foot per Minute, Cubic Foot per Second, Volume.
Cubic Foot per Minute
British imperial unit of flow rate. Abbreviated to cfm.Actual Cubic Feet per Minute (acfm) or Standard Cubic Feet per Minute (scfm) is used to denote that the air is at standard pressure and temperature. The standard pressure is 1 atmosphere and temperature 0°C or 20°C. The petroleum industry uses a standard temperature of 15.6°C for natural gas.Co…
Cubic Foot per Second
British imperial unit of flow rate.Conversions1 ft3s-1=0.02832m3s-11 ft3s-1=1 cusec1 cufm=1.699m3h-11 cufm=28.32 litre min-11 ft3s-1=28.32 litre s-11 cubic foot per minute=1 cufmttle='Flow Rate';xiunt='m3s
Cubic Inch
There are a number of derived units of volume in the British system of units and theSI system of units. The cubic inch has traditionally been used in American to define the swept volumeof internal combustion engines.ttle='Volume';xiunt='cubic inch';yiunt='cm3';mconv=1/16.3871;cconv=0.0; See also: Cubic Centimetre, Volume.
Cubic Yard
1 cubic yard = 0.764555 m3ttle='Volume';xiunt='cubic yard';yiunt='m3';mconv=1/0.764555;cconv=0.0; See also: Volume, Yard.
Cubit
Unit of length equal to 0.4572m.ttle='Length';xiunt='cubit';yiunt='m';mconv=2.1872265966754156;cconv=0.0; See also: Length, Metre, SI Units.
Cumulative Frequency
The number of observations falling in a given class in a frequency table, plus all observations falling in earlier classes. See also: Cumulative Relative Frequency, Histogram.
Cumulative Probability
The probability that a random variable will be less than or equal to a specified value. For example, the cumulative probability equals 0.5 for the median. See also: Probability.
Cumulative Relative Frequency
The number of observations falling in a given class in a frequency table, plus all observations falling in earlier classes, divided by the total number of observations. See also: Cumulative Frequency.
Cure
To irreversibly polymerize a thermosetting plastic by subjecting it to a time-temperature profile.
Curie
Named after Pierre and Marie Curie.One Curie equals the radioactivity of a source with equal radioactivity as 1g of 226Ra86 in secular equilibrium with 222Rn86.ci = 3.7x1010Bq
Curie Constant
A characteristic constant, dependent on the material in question, which indicates the proportionality between its susceptibility and its thermodynamic temperature. See also: Weiss Constant.
Curie Temperature
The temperature above which a ferromagnetic or ferrimagnetic material becomes paramagnetic.Click on an item to paste into clipboard or use clipboard symbol at end to clipboard all values Iron 1033 KClip Nickel 629 KClip paste all data into clipboard See also: Paramagnetism.
Curium
Manmade radioactive element produced from americium. Symbol Cm
Current
Current is often used to transmit signals in noisy environments because it is much less affected by environmental noise pick-up. Before analogue to digital conversion the current signals are usually turned into voltage signals by a current-sensing resistor. See also: Alternating Current, Ampere, Current Density, Current Sink, Current Source, Eddy C…
Current Density
Amperes per unit area. See also: Ampere, Area, Current.
Current Sink
This refers to a sensor output configuration which switches a voltage to the negative side of the power supply. Since the current is being supplied through the load connected to the positive side of the supply, it is said to ‘sink` the current to negative. See also: Current, Current Source.
Current Source
This refers to a sensor output configuration which provides a source of current to the load. Since the current passes through the circuit to the load, it is said to ‘source` the current to the load. See also: Current, Current Sink.
Cursor
A bright figure used as a pointer on a computer screen.
Curtain Wall
A connecting wall hung between towers of a castle.
Curvature
Departure from flatness of a surface. Defined as the reciprocal of the radius of curvature.
Curve Sketching
When sketching a curve there are a number of general features to look for:Symmetry (even in x or even in y)Points where y = 0 and where y changes sign, the same for xLook at behaviour as x ? ±8Look at behaviour near special points, eg assymtotesExamplesketch the following example:y changes sign at x = 0, x = 2, x = 3also, y>0 when x>0y = 0 at x = 0…
Cutoff Frequency
AbsorptionThe cutoff frequency of an anechoic wedge or set of wedges is the lowest frequency above which the normal incidence sound absorption coefficient is at least .990Duct AcousticsPlane wave propagation will occur in ducts up until ka~1.84
Cutting Fluid
A liquid used to cool and lubricate the cutting to improve the work surface finish. See also: Cutting Speed, Cutting Tool.
Cutting Speed
The surface speed of the workpiece in a lathe or a rotating cutter. See also: Cutting Fluid, Cutting Tool.
Cutting Tool
A hardened piece of metal that is machined and ground so that it has the shape and cutting edges appropriate for the operation for which it is to be used. See also: Cutting Fluid, Cutting Speed.
Cutting Torch
A device used in gas cutting for controlling the gases used for preheating and the oxygen used for cutting the metal. See also: Gas Welding.
Cyanoacrylate
Perhaps more commonly known as 'Super Glue' or 'Instant Glue'. Many different types fast set, medium set, slow set. Many different viscosities: thin, medium thick all used for different jobs. Slow sets are generally stronger.Uses:paper, cardboard, all forms of wood, metal to metal, metal to wood and most plastics.Pros:Easy to use - with care, insta…
Cyanogen
Colourless very poisonous gas that smells of bitter almonds. Symbol C2N2
Cycle
One complete repetition of a periodic motion. It may start anywhere in the motion. See also: Frequency, Period, Periodic.
Cycle Counting
Cycle counting is used to summarize lengthy, irregular load-versus-time histories by providing the number of times cycles of various amplitudes occur. The definition of a cycle varies with the method of cycle counting. In fatigue analysis, a cycle is the load variation from the minimum to the maximum and then to the minimum load. Cycle counts can b…
Cyclic Polygon
A polygon whose vertices lie on a circle. See also: Circle, Polygon.
Cycloalkanes
Saturated compounds containing only carbon and hydrogen atoms in which the carbon backbone forms a ring structure.
Cyclotron
A type of particle accelerator in which an ion introduced at the centre is accelerated in an expanding spiral path by use of alternating electrical fields in the presence of a magnetic field. See also: Particle Accelerator.
Cylinder
A right angle circular cylinder.
Cylindrical Wave
A wave in which the surfaces of constant phase are coaxial cylinders. A line of closely-spaced sound sources radiating into an open space produces a free sound field of cylindrical waves. See also: Longitudinal Wave, Transverse Wave.
Cytoplasm
A jelly like material found in a living cell.
Dalton, John (1766-1844)
English chemist and physicist, colourblind and mostly self-taught. Professor of mathematics and natural philosophy. He developed atomic theory that accounts for the law of conservation of mass, law of definite proportions and law of multiple proportions. He produced the first table of atomic weights.
Dalton's Law of Partial Pressures
The total pressure of a mixture of gases, which do not interact chemically, is equal to the sum of the partial pressures. The sum of the pressures that each gas would exert if it alone occupied the volume containing the mixture.ExampleDry oxygen gas at 713 torr is saturated with water vapour at 25 torr, the pressure of the wet gas is 738 torr.
Damped Natural Frequency
The frequency at which a damped system will oscillate in a free vibration situation. See also: Damping, Natural Frequency.
Damping
Dissipation of energy in a system, either through time or distance.Constrained-layer damperA treatment to control the vibration of a structure by bonding a layer of damping material between the structure`s surface and an additional elastic layer (that is, the constraining layer), whose relative stiffness is greater than that of the damping material…
Damping Factor
The ratio of actual damping in a system to its critical damping. See also: Damping.
Damping Pad
Material applied to add damping to another material to reduce structural vibrations. This layer may be constrained or unconstrained. See also: Damping.
Damps
Any dangerous vapours in caves, mines etc.
Darcets Alloy
A low melting point alloy.
Dark Matter
Matter that is in space but is not visible to us because it emits no radiation by which to observe it. The motion of stars around the centers of their galaxies implies that about 90% of the matter in a typical galaxy is dark. Physicists speculate that there is also dark matter between the galaxies but this is harder to verify.It has been proposed t…
Darwin, Charles (1809-82)
Darwin struck upon the theory of evolution. All things have slowly evolved over an unimaginable amount of time, into what they are today. This natural law is a process which Darwin called natural selection. This theory was supported by real evidence, meaning we no longer had to subscribe to the notion that every species had been created, by some un…
Data
A series of facts or statements that may have been collected, stored, processed or manipulated but have not been organized. See also: Data Mining, Database, Time History.
Data Mining
Using automated data anlysis techniques to find themes or relationships. See also: Data, Database.
Database
Information organised into interrelated tables of data and information. See also: Data.
Daughter Isotope
In a nuclear equation the compound remaining after the parent isotope (the original isotope) has undergone decay. A compound undergoing decay, such as alpha decay, will break into an alpha particle and a daughter isotope. See also: Isotopes, Parent Isotope.
Davisson-Germer Experiment
An experiment that conclusively confirmed the wave nature of electrons. Diffraction patterns were observed by an electron beam penetrating into a nickel target. See also: Electron, Wave Particle Duality.
dB(A)
A sound-level meter reading with an A-weighting network simulating the human-ear response at a loudness level of 40 phons.Enter frequency and level in either dB or dB(A) to get conversion and weighting or frequency only to get weighting.
dB(B)
A sound-level meter reading with a B-weighting network simulating the human-ear response at a loudness level of 70 phons.Enter frequency and level in either dB or dB(A) to get conversion and weighting or frequency only to get weighting.
DC Component
The dc value of an waveform that has a value other than zero. See also: Waveform.
DC DC Converter
A circuit or device that changes a dc input signal value to a different dc output signal value.
de Broglie Wavelength
Considers an atom behaving as a wave rather than a particle.The effective wavelength of a particle would be inversely proportional to its momentum, where the constant of proportionality is the Planck constant.whereh = Plancks constant = 6.63x10-34Jsm = mass [kg]h = speed [ms-1]
De Moivre's Theorem
De Moivre's theorem can be expressed as;for all values of n.
De-Emphasis
Filtering applied to an audio signal after storage or transmission to undo a linear distortion due to emphasis. See also: Emphasis.
Dead Room
Room characterized by a relatively large amount of sound absorption and a relatively short reverberation time. See also: Anechoic Chamber, Warmth.
Debug
To correct mistakes in both software and hardware. See also: Bug.
Deburr
To remove sharp edges.
Debye
A common non-SI unit of dipole moment, named for Dutch physical chemist Peter Debye. A charge separation equal to one electron charge placed one Ångstrom unit apart has a dipole moment of 4.8D. In SI units, 1D = 3.338×10-30 coulomb metre. See also: SI Units.
Decade
Ten times any quantity or frequency range. The range of the human ear is about 3 decades.
Decagon
A polygon with ten sides. Each internal angle is 144° and the sum of the internal angles is 1440°. See also: Polygon, Regular Polygon.
Decalescence
A decrease in temperature that occurs while heating metal through a range in which change in structure occurs.
decametre
Abbreviated as dam, unit length equal to 10m. See also: Decimal Prefixes, Metre.
Decarburization
The loss of from the surface of a ferrous alloy as a result of heating in a medium thatreacts with the carbon at the surface.
Decaying Orbit
An unstable orbit from which the orbiting object will gradually spiral into the body it is orbiting. See also: Orbit, Roche Limit.
Decibel
The human ear responds logarithmically and it is convenient to dealin logarithmic units in audio systems. The bel is the logarithm of theratio of two powers, and the decibel is one tenth of a bel.The decibel scale is often used to express the signal to noise ratio, frequency and amplitude response limits in the majority of instrument specifications…
decilitre
Abbreviated as dl, unit volume equal to 10-1litre. See also: Decimal Prefixes, Litre.
Decillion
A number equal to 1033. See also: Googol, Nonillion.
Decimal Number
A number written to the base 10.Historical Notes1360BC A decimal number system with no zero starts to be used in China.594AD Decimal notation is used for numbers in India. This is the system on which our current notation is based.
Decimation
.. to lose one tenth of one's military forces in battle or as punishment... Decimation is a terminology used in signal processing for the discarding of data in order to compact the data or to match the sampling rate to another data set. See also: Downsampling.
