de Broglie Wavelength
The wavelength associated with a particle or body.
Dead Centre
A centre that does not rotate.
Dead Room
Room characterized by a relatively large amount of sound absorption and a relatively short reverberation time.
Dead Short
A short circuit having minimum resistance.
Dead Time
In radar, the interval following a pulse transmission during which the receiver is unable to respond to an incoming signal.
The enzymatic removal of amino groups from biomolecules such as amino acids or nucleotides.
To correct mistakes in both software and hardware.
To remove sharp edges.
Unit of dipole moment.
Debye, Peter
Dutch physicist and physical chemist famous for his research on polar molecules. Nobel laureate in Chemistry.
Prefix representing a multiplication of 10.
Ten times any quantity or frequency range. The range of the human ear is about 3 decades.
A polygon with ten sides.
A decrease in temperature that occurs while heating metal through a range in which change in structure occurs.
Abbreviated as dam, unit length equal to 10m.


Decane is one of the components of petrol. Like other alkanes, it is nonpolar and therefore will not dissolve in polar liquids such as water.

To a separate the supernatant liquid from a solid precipitate by pouring the liquid off, being careful that all of the solid remains in the vessel.
The loss of carbon from the surface of a ferrous alloy.
Decay Rate
The rate at which a population of radioactive atoms decays into stable daughter atoms.
Decay Time
The time required for an exponentially decaying process to decrease to 1/e = 36.7879% of its original value.
Decaying Orbit
An unstable orbit from which the orbiting object will gradually spiral into the body it is orbiting.
Negative acceleration is called deceleration .
A unit of time equal to 10 years.
Prefix representing a multiplication of 10-1
A metric unit of pressure equal to 0.1 bar or 10 kilopascals.
The human ear responds logarithmically and it is convenient to deal in logarithmic units in audio systems.
A metric unit of mass equal to 100 milligrams.
The 10th, 20th, 30th, ...90th percentile points.
Abbreviated as dl, unit volume equal to 10-1litre.
A number equal to 1033.
Pertaining to the number representation system with a radix of ten.
Decimal Number
A number written to the base 10.
Decimal Point
The period in a decimal number separating the integer part from the fractional part.
Decimal Prefixes
The decimal prefixes from pico to tera.
.. 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 oder to compact the data or to match the sampling rate to another data set.
Abbreviated as dm, unit length equal to 10-1m.
An empirical unit of indoor air pollution.
Decision Tree
A graphical representation of a hierarchical set of rules that describe how one might evaluate or classify an object of interest based on the answers to a series of questions.
Supported roadway on a bridge.
Deck-Stiffened Arch
An arch connected by vertical elements to a deck beam that stiffens the arch in such a way that the arch carries almost no bending moments and can therefore be thin.
Continuous application of boiling heat to a reaction mixture.
Extracts intelligence from a coded signal.
Decomposition Reaction
A reaction in which a compound is broken down into simpler compounds or elements.
Doubly compounded, or composed of three or more substances.
Rapid physical decomposition of some crystals when heated. Characterized by a crackling noise.
The rapid decline in the loudness of a tone that decreases continuously in level.
A conclusion derived by reasoning.
Filtering applied to an audio signal after storage or transmission to undo a linear distortion due to emphasis.
Deep Cycle Battery
A battery that is designed to withstand repetitive discharges to less than 20% State of Charge and to continue providing its rated capacity after hundreds of cycles.
Deep Drawing
Forming a deeply recessed part by forcing sheet metal to undergo plastic flow between dies.
Deep Etching
Severe etching of a metallic surface for examination.
Deep Lake Water Cooling
The heat is rejected to deep lake regions to cool homes and offices, reducing the energy costs.
Defect Structure
Relating to the kinds and concentrations of vacancies and interstitials in a ceramic compound.
Defective Matrix
A matrix A is defective if A has an eigenvalue whose geometric multiplicity is less than its algebraic multiplicity.
Deficient Number
A positive integer that is larger than the sum of its proper divisors.
Definite Time Relay
A relay in which the operating time is substantially constant regardless of the input quantity.
Definition of a Sound
This may be described by the time at which the sound arrives at the listening position.
To cause a substance to burn rapidly, with flame.
Deflection Coils
In a cathode-ray tube, coils used to bend an electron beam a desired amount.
Deflection Plates
Two pairs of parallel electrodes, one pair set forward of the other and at right angles to each other, parallel to the axis of the electron stream within an electrostatic cathode-ray tube.
A change in the shape of an object or material.
Deformation Energy
Energy required to deform a material a specified amount.
Deformation Under Load
Measure of the ability of rigid plastics to withstand permanent deformation and the ability of nonrigid plastics to return to original shape after deformation.
Deformation-Type Thermometer
A thermal sensor with a sensing element that bends or deforms by an amount which is a function of temperature.
Removing air from a liquid, usually by ultrasonic or vacuum methods.
Degenerate Code
The genetic code is degenerate because there are many instances in which different codons specify the same amino acid.
Degenerate Orbital
A set of orbitals are said to be degenerate if they all have the same energy.
The process whereby a part of the output signal of an amplifying device is returned to its input circuit in such a manner that it tends to cancel part of the input.
Degenerative Feedback
Feedback in which the feedback signal is out of phase with the input signal.
A decrease in the quality of a desired signal as the result of interference, noise or distortion.
To remove oil and grease from the surface of a part.
A unit describing a plane angle, 1 degree = 1/90 right angle.
Degree Day
A unit used in meteorology and engineering to measure the demand for heating or cooling.
Degree of Polymerization
The average number of mer units per polymer chain molecule.
Degrees of Freedom
The number of degrees-of-freedom of a mechanical system is equal to the minimum number of independent co-ordinates required to define completely the positions of all parts of the system at any instant of time.
A machine that removes moisture from the air.
A separator that removes water from the system fluid.
Deionization Potential
The potential at which ionization of the gas within a gas-filled tube ceases and conduction stops.
Deionization Time
In a spark gap, the time required for ionized gas to return to its neutral state after the spark is removed.
Del Operator
The del or grad operation means to take the derivative with respect to distance, in 3 dimensions.
Occurs when a composite material formed from a number of layers is stressed, thermally or otherwise, such that the layers begin to separate.
Delamination Strength
Measure of the node-to-node bond strength of honeycomb core materials.
Delay Line
A transmission line or circuit that imposes a desired amount of propagation delay on an incident signal.
Deletion Mutation
A mutation resulting from the deletion of one or more nucleotides from a gene.
Deliquescent compounds absorb so much moisture from the air that they dissolve.
Change of salt from a solid to a fluid state by contact with air only.
Delivery Stroke
The stroke of a pump during which the fluid in the pump is forced out of the cylinder.
Delphi Techniques
These techniques involve processes for combining expert opinions from different sources into a model for estimating risk.
A letter of the Greek alphabet.
Delta Connection
A three phase connection in which the start of each phase is connected to the end of the next phase, forming the triangle-shaped Greek letter Delta.
Delta Iron
An allotropic form of iron stable above 1400°C.
Delta T
A reference to a temperature difference. It is used to describe the difference in temperature of a heating or cooling fluid as it enters and as it leaves a system.
Delta Wing
An aircraft wing that when viewed in plan has the shape of an isosceles triangle.
Delta-Sigma Modulating ADC
A high-accuracy circuit that samples at a higher rate and lower resolution than is needed and pushes the quantization noise above the frequency range of interest.
Alternative name for Dimethyl Ether.
The process of recovering intelligence from a signal, some parameter of which was modified to carry the intelligence.
de Moivre
Named after the analyst and probability theorist Abraham de Moivre.
A loss of chemical function, usually due to some heat or chemically-induced structural change.
Denatured Alcohol
Poison is added to industrial ethanol so that the tax is not charged for industrial usage.
A crystal that has a tree-like branching pattern.
Tree-ring dating is the method of scientific dating based on the analysis of tree-ring growth patterns.
Denial of Service
A form of attack on an internet service, which aims to prevent the service from operating properly, often by bombarding it with more information than it can process.
A unit used in measuring the thickness (fineness) of yarn. It is the mass in grams of 9000m of yarn.
The quantity or value on the bottom of a fraction.
Dense Line
The line that contains the shortest path between two points.
The derived SI unit of density is kgm-3
Density Function
A mathematical function used to determine probabilities for a continuous random variable.
Density Functional Theory
A model that describes the electronic structure of an atom or molecule by approximating the total energy as a function of electron density.
A sharply defined surface impression on the metal which may be caused by a blow from another object.
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.
Dependent Suspension
Any suspension scheme using a single axle to connect both wheels, such that movement of one wheel also directly affects the other wheel.
Dependent Variable
The dependent or response variable is the variable whose behaviour is to be measured as a result of an experiment.
To remove water from a solution, usually one of an acid or alcohol.
Dephlogisticated Air
An old name for oxygen.
Depletion Region
The region in a semiconductor where essentially all free electrons and holes have been swept out by the electrostatic field which exists there.
Deposit Corrosion
Corrosion occurring under or around a deposit on a metallic surface. Also called Poultice Corrosion.
Depth Filter
A filter medium that retains contaminants primarily within tortuous passages.
Depth Filter Media
Porous materials which primarily retain contaminants within a tortuous path, performing the actual process of filtration.
Depth Gauge
A tool used in measuring the depth of holes or recesses.
Depth Micrometer
A micrometer in which the spindle projects through a flat accurately machined bar.
Depth of Cut
Distance between the bottom of the cut and the uncut surface of the workpiece, measured in a direction at right angles to the machined surface of the workpiece.
Depth of Discharge
The amount of energy that has been removed from a battery.
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.
Depth of Focus
The distance along the optical axis through which an image can be clearly focused.
To free from impurities, purify.
Derated Engine
An engine with a restricted power output.
Derived SI Units
These are multiplications and divisions of the basic units to form derived units.
Derived Units
Derived units are units constructed from a base system of units.
Removal of dissolved salts from seawater.
Descartes, Rene
Considered the father of analytic geometry, he formulated the Cartesian system of coordinates.
Descartes Rule of Signs
The number of positive real zeros of a polynomial is either equal to the number of variations in sign of the coefficients or else less than that number by a positive even integer.
Any absorbent or adsorbent, liquid or solid, that will remove water or water vapor from a material.
A sealed container in which a drying agent is used to dry material that contains water.
Design Limit
The operational limit of a product, beyond which it not required to function properly.
Design Pressure
Highest or most severe pressure expected during operation.
Design Working Pressure
The maximum allowable working pressure for which a specific part of a system is designed.
Desktop Computer
A computer designed to sit on a desk.
In aqueous solution, the release of bound water surrounding a solute such as an enzyme.
The opposite process of adsorption.
The process of removing scaly crusts which form on a surface.
Destructive Hydrogenation
The hydrocarbon chains are ruptured and hydrogen is added where the breaks have occurred.
Destructive Interference
When the peaks of one wave match the troughs of another, the waves interfere destructively.
A device that receives energy in one form and supplies an ouput in another form.
Detent Ball and Spring
A spring loaded ball that snaps into a groove or notch to hold some sliding object in position.
Detergent Additive
In lubrication technology, a surface active additive that helps to keep solid particles suspended in an oil.
Determinism Principle
The principle that if one knows the state to an infinite accuracy of a system at one point in time, one would be able to predict the state of that system with infinite accuracy at any other time, past or future.
Deterministic Signal
For a deterministic signal the physical phenomenon can be represented by a mathematical relationship to a reasonable degree of accuracy.
Any rapid chemical reaction accompanied by noise and often heat and light, e.g., explosions.
An isotope of hydrogen that contains one neutron and one proton in its nucleus.
Nucleus of a deuterium atom.
Deutsches Institut für Normung
German national organisation for standards.
Deviation Ratio
Ratio of the maximum frequency deviation to the maximum modulating frequency of a frequency modulation system, under specified conditions.
The process in which a glass (noncrystalline or vitreous solid) transforms to a crystalline solid.
The geological period from 408 million to 360 million years ago.
Dew Point
The temperature at which water vapour begins to condense.
Dew Point Depression
The difference between dry bulb and dew point temperatures.
Dew Point Hygrometer
An instrument used for determining the dewpoint.
A chiral molecule which rotates plane-polarized light to the right.
Corrosive removal of zinc from a brass surface, leaving rough copper.