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 DiracDelta - Science & Engineering encyclopedia
Category: Sciences > Science & Engineering
Date & country: 01/12/2007, UK
Words: 4470


decimetre
Abbreviated as dm, unit length equal to 10-1m. See also: Decimal Prefixes, Metre.

Decrepitation
Rapid physical decomposition of some crystals when heated. Characterized by a crackling noise.

Decruitment
The rapid decline in the loudness of a tone that decreases continuously in level.

Deduction
A conclusion derived by reasoning. See also: Axiom, Conjecture.

Deep Etching
Severe etching of a metallic surface for examination at a magnification of ten diameters or less toreveal gross features such as segregation, cracks, porosity or grain flow.

Defect Structure
Relating to the kinds and concentrations of vacancies and interstitials in a ceramic compound. See also: Ceramic.

Deficient Number
A positive integer that is larger than the sum of its proper divisors. See also: Abundant Number, Divisor, Integer.

Deflagration
To cause a substance to burn rapidly, with flame.

Degas
Removing air from a liquid, usually by ultrasonic or vacuum methods. See also: Dehydrator.

Degenerate Orbital
A set of orbitals are said to be degenerate if they all have the same energy. This degeneracy can sometimes be 'lifted' by external electric or magnetic fields. See also: Orbital.

Degree of Polymerization
The average number of mer units per polymer chain molecule. See also: Mer, Polymer, Polymerization.

Degrees of Freedom
MechanicsThe number of degrees-of-freedom of a mechanical system is equal to the minimumnumber of independent co-ordinates required to define completely the positions ofall parts of the system at any instant of time. In general, it is equal to thenumber of independent displacements that are possible. A spring-mass which cannotrotate or move horizon…

Dehydrator
A separator that removes water from the system fluid. See also: Degas.

Del Operator
The del operator operates on a scalar to produce a vector. Compare the ? operation to taking the time derivative. Where d/dt means to take the derivative with respect to time and introduces a s-1 component to the units of the result, the ? operation means to take the derivative with respect to distance (in 3 dimensions) and introduces a …

Delamination
Occurs when a composite material formed from a number of layers is stressed, thermally or otherwise, such that the layers begin to separate.

Delay Line
A transmission line or circuit that imposes a desired amount of propagation delay on an incident signal. Delay lines may also be specified in terms of the phase shift they produce as a result of the propagation delay.

Deliquescence
Deliquescent compounds absorb so much moisture from the air that they dissolve.Examplescalcium chloridesodium hydroxide

Deliquium
Change of salt from a solid to a fluid state by contact with air only. See also: Deliquescence.

Delta Iron
An allotropic (polymorphic) form of iron stable above 1400°C and crystallizing in the body centred cubic lattice. See also: Body Centred Cubic, Iron.

Demodulation
The process of recovering intelligence from a signal, some parameter of which was modified to carry the intelligence.

Denaturation
The breaking down of the three-dimensional structure of a protein resulting in the loss of its function.

Denatured Alcohol
Poison is added to industrial ethanol so that the tax is not charged for industrial usage. See also: Alcohol.

Dendrite
A crystal that has a tree-like branching pattern, being most evident in cast metals slowly cooled throughthe solidification range. See also: Crystal.

Denier
A unit used in measuring the thickness (fineness) of yarn. It is the mass in grams of 9000m of yarn.ttle='Denier';xiunt='kgm-1';yiunt='denier';mconv=111.1111e-9;cconv=0.0; See also: Bolt of Cloth.

Denominator
The quantity or value on the bottom of a fraction. See also: Dividend, Improper Fractions, Numerator, Proper Fractions.

Density
The derived SI unit of density is kilogram per cubic metre, kgm-3.ttle='Density';xiunt='kgm-3';yiunt='lbft-3';mconv=16.0185;cconv=0.0;Measurement

Density Function
A mathematical function used to determine probabilities for a continuous random variable. The bell-shaped curve corresponding to a normal distribution is one example. To determine the probability of finding a value between two limits, the area under the density function between those limits is computed.

Dentils
Tooth-like ornaments used in the cornice compositions of main and porch roofs and gables.

Deoxyribonucleic Acid
The biological macromolecule that carries the genetic information of all eukaryotic and prokaryotic cells.The double-stranded DNA molecule is held together by chemical components.Adenine will bond with thymine and cytosine will bond with guanine. In living organisms, these sequences of bases that spell out the genes. See also: Nucleic Acid.

Dependent Variable
The dependent or response variable is the variable whose behaviour is to be measured as a result of an experiment. For example, in a consumer research study on the effects of types of packaging on purchase behavior (where the size, shape and colors of the box are the independent variables), the dependent variable would be the quantity of product pu…

Dephlegmation
To remove water from a solution, usually one of an acid or alcohol.

Depth Gauge
A tool used in measuring the depth of holes or recesses.Engineer's Protractor and Depth GaugePhotograph courtesy of Draper.co.ukA protractor and depth gauge. Tyre Tread Depth GaugePhotograph courtesy of Draper.co.ukA depth gauge designed specifically for measuring tyre tread depth.Vernier CaliperPhotograph courtesy of Draper.co.ukA thin rod extends…

Depth Micrometer
A micrometer in which the spindle projects through a flat accurately machined bar. Used to measure the depth of holes or recesses.

Depth of Field
The distance along the optical axis through which an object can be located and clearly defined when the lens is in focus. See also: Depth of Focus.

Depth of Focus
The distance along the optical axis through which an image can be clearly focused. See also: Depth of Field.

Depuration
To free from impurities, purify.

Derived Unit
Derived units are units constructed from a base system units. For example, the SI unit for density is kgm-3, derived from the base units kg and m. See also: Base Unit, CGS Units, SI Units.

Desalination
Removal of dissolved salts from seawater. See also: Sea Water.

Desiccator
A sealed container in which a drying agent is used to dry material that contains water. The drying effect is often enhanced by evacuation of the container.

Design Limit
The operational limit of a product, beyond which it not required to function properly.

Desquamation
The process of removing scaly crusts which form on a surface.

Detonation
Any rapid chemical reaction accompanied by noise and often heat and light, e.g., explosions.

Deuterium
An isotope of hydrogen that contains one neutron and one proton in its nucleus. In normal water a deuterium atom occurs in 1 in 6,500 hydrogen atoms. DiscoveredHarold C. Urey, F. G. Brickwedde, and G. M. Murphy.

Deutsches Institut für Normung
German national organisation for standards.

Devitrification
The process in which a glass (noncrystalline or vitreous solid) transforms to a crystalline solid.

Dew Point
The temperature at which water vapor begins to condense. See also: Absolute Humidity, Humidity, Humidity at Saturation, Relative Humidity.

Dextrorotatory
A chiral molecule which rotates plane-polarized light to the right. See also: Chirality.

Diagonal Matrix
A diagonal matrix is an n x n matrix with every off diagonal element equal to zero.This is often written showing just the diagonal elements and the upper-right and lower-left corners with a 0If we have two matrices such that: Then:If each element , thenThe eigenvalues of D are its main diagonal elements, d1, d2, d3
Dial Indicator Gauge
A dial indicator is used to measure shaft runout, shaft thrust, gear backlash, flywheel face runout, flywheel housing concentricity, and valve seat concentricity. See also: Height Gauge, Micrometer.

Dialysis
The separation of components in a mixture by passing them across a semipermeable membrane.

Diamagnetism
A weak form of induced or nonpermanent magnetism for which the magnetic susceptibility is negative. Atoms with no unpaired electrons are diamagnetic.

Diameter
The longest chord of a figure. In a circle, a diameter is a chord that passes through the centre of the circle. See also: Circle, Radius.

Diamond
A crystalline form of carbon, made of a network of covalent, tetrahedrally bound carbon atoms. In 1797, the English chemist Smithson Tennant proved that diamond is pure carbon.

Diaphoretic
Any substance which induces perspiration when administered to a patient.

Diaphram Arch
A transverse, wall-bearing arch that divides a vault or a ceiling into compartments, providing a kind of firebreak. See also: Arch.

Diastereomers
Optical isomers that are not mirror images of each other.

Diatomic Molecules
Molecules composed of two atoms eg CO.

Dichlorodiethyl Sulphide
Oily gas used in warfare. Symbol (CH2CH2Cl)2S Also known as Mustard gas, Yperite

Dichloromethane
Organic solvent often use to extract organic substances from samples. Symbol CH2Cl2 Also known as Methylene Chloride, Methylene Dichloride

Didymium
A mixture of praseodymium and neodymium believed to be an element until 1885. See also: Neodymium, Praseodymium.

Die
Mechanical EngineeringSolid or hollow form used for shaping materials by stamping, pressing, extruding, drawing or threading.When Cutting Threads with a Die, turn on 1 full turn, then back 1/2 turnElectronicsan integrated circuit chip as diced or cut from the finished wafer.

Dielectric
An insulating material. Such as the material between theplates of a capacitor. See also: Dielectric Constant, Dielectric Displacement, Dielectric Losses, Dielectric Strength, Ferroelectric.

Dielectric Constant
The ratio of the permittivity of a medium to that of a vacuum. See also: Dielectric.

Dielectric Displacement
The magnitude of charge per unit area of capacitor plate. See also: Capacitance, Capacitor, Dielectric.

Dielectric Losses
Power losses due to the conductance of dielectric materials. See also: Dielectric.

Dielectric Strength
The magnitude of an electric field necessary to cause significant current passage through a dielectric material. See also: Dielectric.

Diesel Engine
An internal-combustion engine in which the fuel is injected into the cylinder near the end of the compression stroke and is ignited by the heat of the compressed air in the cylinder.Historical Notes1892 Rudolf Diesel patents the Diesel engine.

Diesel Particulate Filter
A device which physically captures diesel particulates preventing their discharge from the tailpipe. Collected particulates need to be removed from the filter, usually by continuous or periodic oxidation in a process called regeneration.

Differential Amplifier
One whose output is proportional to the difference between two inputs.The amplifier has both an inverting and a noninverting input. See also: Amplification, Common-Mode Rejection Ratio, Common-Mode Signal, Differential Input.

Differential Equations
Linear EquationsA first order differential equation is linear if it has the form

Differential Input
Often used to reduce noise picked up by the signal leads. For each input signal there are two signal wires. A third connector allows the signals to be referenced to ground. The measurement is the difference in voltage between the two wires, any voltage common to both wires is removed. See also: Differential Amplifier.

Differential Voltage
The difference in voltages at two points as measured with respect to a common reference. See also: Voltage.

Diffraction
The spreading of waves passing through an opening or around a barrier. See also: Diffraction Grating, Refraction, Scattering, Wave.

Diffraction Grating
Grating device that splits light into a spectrum of the component wavelengths. See also: Diffraction.

Diffraction Limited
Describes an optical system in which the quality of the image is determined only by the effects of diffraction and not by lens aberrations.

Diffuse Reflection
The reflection of rays from a rough surface. The reflected rays do not leave at fixed angles. Energy is scattered uniformly in many directions and temporally dispersed. See also: Reflection, Refraction, Specular Reflections.

Diffuse Sound Field
Sound field in which the time average of the mean-square sound pressure is everywhere the same and the flow of acoustic energy in all directions is equally probable. See also: Sound.

Diffusers
A combination of sound reflection and absorption. Diffusers convex shape, with reflective surfaces, diffuse sound within a zone. Absorbers are designed to adjust the harshness of a room.The basic idea of a diffuser is to scatter the sound in a number of directions. Thus reducing the harsh reflections that might otherwise be a problem. See also: Dir…

Diffusion
AcousticsThe scattering or random reflection of a sound wave from a surface. The directions of reflected sound is changed so that listeners may have sensation of sound coming from oil directions at equal levels.ChemistryThe mixing of two substances caused by random molecular motions. Gases diffuse very quickly; liquids diffuse much more slowly, and…

Diffusion Bonding
A solid-state process for joining metals by using heat and pressure to achieve atomic bonding.

Diffusion Coefficient
The constant of proportionality between diffusion flux and the concentration gradient in Fick's first law, its magnitude is indicative of the rate of atomic diffusion. See also: Diffusion, Diffusion Rate.

Diffusion Rate
The number of randomly moving molecules that pass through a unit area per second. Diffusion rates are fastest when a large concentration difference exists on either side of the unit area. Diffusion rates increase with temperature, and decrease with increasing pressure, molecular weight, and molecular size.

Digestion
The breaking down of food.

Digit
In the decimal system, one of the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. See also: Decimal Number.

Digital Audio Broadcasting
The transmission of radio signals using digital rather than analogue methods.

Digital Circuit
A collection of logic gates used to process or generate digital signals.

Digital Signal Processing
The term used for calculations performed on digital signals. Some common digital signal processing operations are calculating the fast Fourier transform to determine the frequency content of a signal, or digital filtering to remove unwanted frequencies. See also: Signal Processing.

Digital Signatures
The electronic equivalent of a signature used for authentication.

Digital Versatile Disc
Optical disc used for data, video and audio storage. See also: Compact Disc.

Dihedral Angle
The angle formed by two planes meeting in space. See also: Plane Angle.

Dilatometer
A device for measuring volume changes. See also: Volume.

Dilute
Having a relatively low concentration.

Dimensions
All quantities can be expressed in terms of three basic quantities, mass M, length L and time T.this then gives;velocity LT-1force MLT-2energy ML2T-2

Diode
A semiconductor that allows current to flow in one direction only. It is a two-terminal device which has nonlinear and asymmetrical (about zero) voltage versus current characteristics.The Ideal DiodeIf v is negative, the diode is reversed biased and acts as a closed switch with V = 0.If a positive current is applied in the direction shown, the diod…

Diode Drop
The forward voltage developed across a diode when it is operating. See also: Diode, Zener Diode.

Diode Transistor Logic
Logic gates implemented using particular configurations of diodes and bipolar junction transistors. For the majority of today's designers, diode-transistor logic is of historical interest only. See also: Diode.

Diophantine Equation
An equation which is required to be solved by integers. Thus the diophantine equation 2x2 - 3y2 = 5 has the integer solution x=2,y=1.

Dioptre
A measure of the focal length of a mirror or lens, equal to the inverse of the focal length measured in metres. See also: Focal Length, Focal Point.

Diotically
The same signal at both ears. See also: Binaural.

Dip Angle
The vertical angle between the true horizon and the apparent horizon. See also: Apparent Horizon.