Diagnostic Acceptability Measure
Scores are based on results of test methods evaluating the quality of a communication system based on the acceptability of speech as perceived by a trained normative listener.
Diagnostic Rhyme Test
An intelligibility measure where the subject′s task is to recognize one of two possible words in a set of rhyming pairs.
In a polygon, the line segment joining a vertex with another (non-adjacent) vertex is called a diagonal.
Diagonal Matrix
A diagonal matrix is an n x n matrix with every off diagonal element equal to zero.
Dial Indicator Gauge
Used to measure shaft runout or deviation from a nominal position.
Dialog Unit
A unit of relative distance used in computer graphics.
Dialuminium Hexachloride
Alternative name for Aluminium Chloride.
Dialuminium Trisulphide
Alternative name for Aluminium Sulphide.
The separation of components in a mixture by passing them across a semipermeable membrane.
A weak form of induced or nonpermanent magnetism for which the magnetic susceptibility is negative.
The longest chord of a figure. In a circle, a diameter is a chord that passes through the centre of the circle.
A crystalline form of carbon, made of a network of covalent, tetrahedrally bound carbon atoms.
Diamond Point Chisel
Used for cleaning out corners or difficult places and pulling over centre punch marks wrongly placed for drilling.
Any substance which induces perspiration when administered to a patient.
Flexible material usually made of thin metal, rubber or plastic.
Diaphragm Valve
A bi-directional valve which is operated by applying an external force to a flexible element or diaphragm.
Diaphram Arch
A transverse, wall-bearing arch that divides a vault or a ceiling into compartments, providing a kind of firebreak.
Optical isomers that are not mirror images of each other.
Diatomic Molecules
Molecules composed of two atoms eg CO.
Diazonium Salt
A compound with general form Ar-NN+X-, where Ar represents a substituted benzene ring and X- is a halide ion such as chloride.
A reaction that converts an -NH2 group connected to a phenyl ring to a diazonium salt.
Dicaesium Oxide
Old name for Caesium Oxide.
Dicaesium Peroxide
Old name for Caesium Peroxide.
Dicaesium Sulphide
Old name for Caesium Sulphide.
Dichlorodiethyl Sulphide


Oily gas used in warfare. Also known as mustard gas or yperite.

Alternative name for Germanium II Chloride.


Organic solvent often use to extract organic substances from samples.

Listening condition in which different signals are applied to the two ears.
Dicobalt Trioxide
Alternative name for Cobalt III Oxide.
Didot Point
A unit of distance used in typography.
A mixture of praseodymium and neodymium believed to be an element until 1885.
Solid or hollow form used for shaping materials by stamping, pressing, extruding, drawing or threading.
Die Casting
Casting process wherein molten metal is forced under high pressure into the cavity of a metal mould.
Die Lines
Lines of markings caused on drawn or extruded products by minor imperfections in the surface of the die.
Die Stock
The frame and two handles which hold the dies used for cutting external screw threads.
diebus alternis
Latin for every other day.
diebus tertius
Latin for every third day.
An insulating material. Such as the material between the plates of a capacitor.
Dielectric Breakdown Voltage
Voltage an insulating material will withstand before flashover (arcing) or puncture.
Dielectric Constant
The ratio of the permittivity of a medium to that of a vacuum.
Dielectric Displacement
The magnitude of charge per unit area of capacitor plate.
Dielectric Heating
The phenomenon in which radiowave or microwave electromagnetic radiation heats a dielectric material, especially as caused by dipole rotation.
Dielectric Hysteresis Loss
Power loss of a capacitor because of the changes in orientation of electron orbits in the dielectric; the changes in orientation are caused by rapid reversal in polarity of line voltage.
Dielectric Losses
Power losses due to the conductance of dielectric materials.
Dielectric Strength
The magnitude of an electric field necessary to cause significant current passage through a dielectric material.
Dielectric Withold Volatge
Voltage an insulating material will withstand before flashover (arcing) or puncture.
Fossil diesel is produced from the fractional distillation of crude oil between 200°C and 350°C at atmospheric pressure, resulting in a mixture of carbon chains that typically contain between 8 and 21 carbon atoms per molecule.

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.
Diesel Particulate Filter
A device which physically captures diesel particulates preventing their discharge from the tailpipe.
Diesel, Rudolf
Inventor of the diesel engine.
Dietary Fibre
This helps food to pass through the alimentary canal.
Diethyl Ether


A clear, colourless, and highly flammable liquid with a low boiling point and a characteristic odor.

The difference between two numbers is what you get when you subtract one from the other.
Geared device between the driven wheels to allow varying rotational speeds of the wheels around corners.
Differential Amplifier
One whose output is proportional to the difference between two inputs.
Differential Calculus
That part of calculus that deals with the operation of differentiation of functions.
Differential Equations
Equations that express the rate of change of an equation.
Differential GPS
A technique for overcoming GPS position determination errors.
Differential Input
Often used to reduce noise picked up by the signal leads.
Differential Pressure Indicator
An indicator which signals the difference in pressure between two points, typically between the upstream and downstream sides of a filter, valve or expansion element.
Differential Pressure Valve
A valve whose primary function is to limit differential pressure.
Differential Scanning Calorimeter
A thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature.
Differential Thermal Analysis
A technique that is often used to analyze materials that react or decompose at higher temperatures.
Differential Voltage
The difference in voltages at two points as measured with respect to a common reference.
A mathematical operation that differentiates a signal or function.
The spreading of waves passing through an opening or around a barrier.
Diffraction Grating
Grating device that splits light into a spectrum of the component wavelengths.
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.
Diffraction Region
The space beyond the radio horizon which is shadowed from direct rays by the curvature of the earth or terrain irregularities or objects.
Diffuse Insolation
Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. Opposite of direct insolation.
Diffuse Reflection
The reflection of rays from a rough surface. The reflected rays do not leave at fixed angles.
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.
The divergent section of a duct which slows down airflow to reduce pressure loss.
A combination of sound reflection and absorption.
The mixing of two substances caused by random molecular motions.
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.
Diffusion Flux
The quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time.
Diffusion Furnace
Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.
Diffusion Length
The mean distance a free electron or hole moves before recombining with another hole or electron.
Diffusion Rate
The number of randomly moving molecules that pass through a unit area per second.
The breaking down of food.
A cryptarithm in which digits represent other digits.
In the decimal system, one of the numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
Literally means to do with numbers.
Digital Audio
The use of sampling and quantization techniques to store or transmit audio information in binary form.
Digital Audio Broadcasting
The transmission of radio signals using digital rather than analogue methods.
Digital Audio Compression
Any of several algorithms designed to reduce the number of bits required for accurate digital audio storage and transmission.
Digital Caliper
A caliper with a digital readout. Able to measure inside, outside and depth.
Digital Camera
An electronic camera that captures images using a solid-state image sensor, and then outputs a digital signal representing the images or records the images on a digital storage medium.
Digital Circuit
A collection of logic gates used to process or generate digital signals.
Digital Computer
A computer that operates on discrete data by performing arithmetic and logic processes on these data.
Digital Filter
Any filter accomplished in the digital domain.
Digital Rights Management
Software intended to prevent the unauthorised duplication of copyrighted video or audio, usually built into a computer's operating system.
Digital Signal Processing
The term used for calculations performed on digital signals.
Digital Signatures
The electronic equivalent of a signature used for authentication.
Digital Theatre System
A multi-channel encoding/decoding system. Used in some movie theatres. Also now included in some home-theatre processors.
Digital Versatile Disc
Optical disc used for data, video and audio storage.
Digital Visual Interface
A video interface standard designed to provide very high visual quality on digital displays.
Digital-to-Analogue Converter
Converts a digital number into a corresponding analogue voltage or current.
Any conversion of analog information into a digital form.
Angle which the spanwise axis of an aerofoil makes to the fuselage when the wing or tailplane tip is higher than its root attachment point.
Dihedral Angle
The angle formed by two planes meeting in space.
Another name for Dodecane.
Dihydrogen Monoxide
More commonly known as water.
Dihydrogen Selenide
Old name for Hydrogen I Selenide.
A device for measuring volume changes.
Dilithium Oxide
Old name for Lithium I Oxide.
Dilithium Peroxide
Old name for Lithium I Peroxide.
Having a relatively low concentration.
Adding solvent to a solution to lower its concentration.
Dimanganese Heptoxide
Alternative name for Manganese VII Oxide.
The indication of how far something extends in space.
Dimension of a Subspace
The dimension of a subspace W is the number of vectors in any basis of W.
All quantities can be expressed in terms of three basic quantities, mass M, length L and time T.
Dimercury Dichloride
Another name for Mercury I Chloride.
Dimethyl Ether


Simplest ether, it is a colourless gas that is a useful precursor to other organic compounds and an aerosol propellant.

Dimethyl Ketone
Also known as acetone.
Dimethyl Oxide
Alternative name for Dimethyl Ether.
Alternatively known as Xylol.
Abbreviation of Dual In-line Memory Module.
Abbreviation of Deutsches Institut für Normung.
A semiconductor that allows current to flow in one direction only.
Diode Drop
The forward voltage developed across a diode when it is operating.
Diode Transistor Logic
Logic gates implemented using particular configurations of diodes and bipolar junction transistors.
Diophantine Equation
An equation which is required to be solved by integers.
A measure of the focal length of a mirror or lens.
The same signal at both ears.
Abbreviation of Dual Inline Package.
Dip Angle
The vertical angle between the true horizon and the apparent horizon.
Dip Brazing
A brazing process in which bonding is produced by heating in a molten chemical or metal bath.
Dip Equator
Another name for Aclinic Line or Magnetic Equator.
A circuit or system that allows the ability to transmit and receive two distinct signals simultaneously.
Having two sets of genetic information; describing a cell with two chromosomes of each type.
A pair of equal yet opposite electrical charges that are separated by a small distance.
Dipole-Dipole Interaction
Electrostatic attraction between oppositely charged poles of two or more dipoles.
Dipotassium Oxide
Old name for Potassium Oxide.
Dipotassium Peroxide
Old name for Potassium Peroxide.
Diprotic Acid
An acid having two dissociable protons.
The metal rod that passes into the oil sump it is used to determine the quantity of oil in the engine.
Dirac Delta Function
The limiting case of a pulse with unit area that is infinitely short and at the same time infinitely high.
Dirac, Paul
English physicist; published Principles of Quantum Mechanics in 1930.
Dirac′s Constant
Equal to Planck′s constant divided by 2 pi.
Direct Chill Casting
A continuous method of making ingots or billets for sheet or extrusion by pouring the metal into a short mould.
Direct Coupled Amplifier
An amplifier in which the output of one stage is coupled to the input of the next without the use of a capacitor.
Direct Coupling
A coupling system which provides a direct path for DC or AC signals between one circuit and another, without intervening series inductors or capacitors, except when shunted by resistors.
Direct Current
A current that does not change in direction.
Direct Current Amplifier
A direct coupled amplifier that can provide gain for zero-frequency signals.
Direct Current Restorer
A damper circuit which restores the DC level to a signal waveform.
Direct Fuel Cell
A type of fuel cell in which a hydrocarbon fuel is fed directly to the fuel cell stack, without requiring an external reformer to generate hydrogen.
Direct Insolation
Sunlight falling directly upon a collector. Opposite of diffuse insolation.
Direct Measurement
A process of obtaining the measurement of some entity by reading a measuring tool, such as a ruler for length, a scale for weight, or a protractor for angle size.
Direct Methanol Fuel Cell
A direct methanol fuel cell functions in a similar way to a PEMFC and uses the same electrolyte, but reforms methanol directly on its electrode to form hydrogen.
Direct Proportion
Two variables are said to be in a direct proportion if the proportions of corresponding pairs of values are always equal.
Direct Quenching
Quenching carburized parts directly from the carburizing operation.
Direct Sequence Modulation
A spread spectrum modulation scheme that directly modulates the information-bearing data with a spreading code sequence.
Direct Short
A short circuit.
Direct Sound
Sound reaching the listening location without reflections.
The way a number goes - positive or negative.
Directional Antenna
An antenna that radiates most effectively in only one direction.
Directional Gyro
A two-degree-of-freedom gyro with a provision for maintaining its spin axis approximately horizontal.
Directive Gain
4π times the ratio of the radiation intensity in that direction to the total power radiated by the antenna.
Directivity Factor
The ratio of the sound pressure squared, radiated directly ahead of a sound source, to the sound pressure squared radiated in all directions.
Directivity Index
The difference between sound pressure level in any given direction in the acoustic far field and the average sound pressure level in that field.
A circle together with its interior.
Disc Brake
A type of brake in which two friction pads grip a steel disc that is attached to the wheel, with one pad on each side.
Disc Clutch
A disc on the end of the input shaft with a friction surface and a disc on the end of the output shaft.
To relieve of a charge, the conversion of the chemical energy of a battery into electrical energy.
Discharge Curve
Graphical representation of the change in output voltage over time under various loads and/or temperature.
Discharge Factor
A number equivalent to the time in hours during which a battery is discharged at constant current, usually expressed as a percentage of the total battery capacity, i.e., C/3 indicates a discharge factor of 3 hours.
The disclaimer for the Science and Engineering Encyclopaedia.
A break in sequence or continuity of anything.
Discontinuous Graph
A line in a graph that is interrupted, or has breaks in it forms a discontinuous graph.
A pair of cases for two ordered data variables in which the value of one variable for the first case is higher or lower than its value in the second case, and the relative relationship is switched for the second variable.
A type of random variable which may take on only a limited set of values, such as 1,2,3,...,10.
Discrete Components
Individual transistors, diodes, resistors, capacitors, and inductors.
Discrete Fourier Transform
The digital version of the fourier transform.
Discrete Gabor Transform
An algorithm for transforming data from the discrete time domain to the joint time-frequency domain.
Discrete Tone
A prominent single frequency component within a broadband noise signal.
Disilver Sulphide
Old name for Silver Sulphide.
A substance that kills or stops the growth of microbes.
Disjoint Events
Two events are disjoint if they can't both happen at the same time.
Disk Operating System
Program used to control the transfer of information to and from a disk, such as MS DOS.
A linear crystalline defect around which there is an atomic misalignment.
Dislocation Line
The line that extends along the end of the extra half-plane of atoms for an edge dislocation, and along the center of the spiral of a screw dislocation.
Disodium Oxide
Old name for Sodium Oxide.
An additive that reduces deposits on oil-wetted surfaces primarily through suspension of particles.
The spreading of light into a spectrum of colour. The variation in the speed of a periodic wave due to its wavelength or frequency.
Dispersion Forces
Also known as London Forces, an intermolecular attraction force that exists between all molecules.
Dispersion Model
A computerized set of mathematical equations that uses emissions and meteorological information to simulate the behavior and movement of air pollutants in the atmosphere.
Displacement is a vector quantity that specifies the change of position of a body or particle and is usually measured from the mean position or position of rest.
Displacement Current
The current that appears to flow through a capacitor.
Displacement Reaction
A reaction in which a fragment of one reactant is replaced by another reactant or by a fragment of another reactant.
Displacements per Atom
A measure of the damage to a crystalline material caused by bombarding the material with energetic particles.
Display Resolution
Refers to the number of distinct pixels in each dimension that can be displayed.
Disposable Filter
A filter element intended to be discarded and replaced after one service cycle.
A reaction involving a substance that produces two different forms of the substance, one more oxidized and the other more reduced than the original.
Disruptive Discharge Coil
A Tesla oscillator which incorporates some form of spark gap switching device to discharge the primary capacitor(s) through the primary inductor.
Breaking down of a compound into its components.
To mix a solid and a liquid to form a solution.
Dissolved Oxygen
The amount of oxygen dissolved in a solvent (usually water).
Distance Between Two Points
The straight line distance between two points in cartesian coordinates.
Distance Double Law
In pure spherical divergence of sound from a point source in free space, the sound pressure level decreases 6 dB for each doubling of the distance.
Distance Factor
An indication of a directional microphone′s increased working distance.
The vapour collected and condensed from a distillation.
A process used to separate a liquid from a solution.
Distillation Per Ascensum
Distillation with the collecting vessel above the heated vessel.
Distillation Per Decensum
Any distillation where the collecting vessel is below the heated vessel.
Distillation Per Obliquium
Distillation in a retort used for substances of relatively low vapor pressure and other properties that make distillation difficult.
Distillation with Addition
Adding some substance prior to distillation that will aid the process.
Any change in the waveform or harmonic content of an original signal as it passes through a device.
Distributed Capacitance
Capacitance that is not concentrated within a lumped capacitor, but spread over a circuit or group of components.
Distributed Computing Environment
The services that support the creation and maintenance of distributed applications.
Distributed Constants
The constants of inductance, capacitance, and resistance in a transmission line.
Distributed Inductance
Inductance that is not concentrated within a lumped inductor, but spread over a circuit or group of components.
Distributed Load
An external force which acts over a region of length, surface, or area: essentially any external force which is not a concentrated force.
A probability function which describes the relative frequency of occurrence of data values when sampled from a population.
Distribution Circuit Breaker
A device used for overload and short current protection of loads connected to a main distribution device.
Distribution Panel
The main electrical control center, which contains switches or circuit breakers, is connected to the service wires and delivers current to the various branch circuits.
Distributive Law
States that if a group of terms connected by like operators contains the same variable, the variable may be removed from the terms and associated with them by the appropriate sign of operation.
Old name for Hydrogen Persulphide.
Disulphur Dioxide


Unstable with a lifetime of a few seconds.

The noise added to a signal prior to quantization which reduces the distortion and noise modulation resulting from the quantization process.
Diurnal Aberration
The component of stellar aberration resulting from the observer′s diurnal motion about the center of the Earth.
Diurnal Temperature Range
The difference between the maximum and minimum temperature during a day.
Binds to two other things: atoms, molecules, ions, or electrons.
Divalent Anion
An ion with a charge of -2.
Divalent Cation
An ion with a charge of +2.
Dive Brake
Drag-inducing surface deployed in a dive to maintain speed below structural limitations, or improve controllability.
The divergence operation is performed on a vector and produces a scalar.
Diversion Channel
A bypass created to divert water around a dam so that construction can take place.
Diverter Valve
A valve which can change the direction of the flow of a medium to two or more different directions.
A number or quantity that is to be divided by another number or quantity.
Dividing Head
A machine tool holding fixture which positions the work for accurately space holes, slots, flutes and gear teeth and for making geometric shapes
Another name for 1,3-Butadiene.
The binary operation of finding the quotient of two quantities.
A number or quantity that is to be divided into another number or quantity.