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


Engineering Ceramics
Technical ceramics for structural applications. See also: Ceramic.

Engineering Units
Units that are decided upon by an individual user or by agreement among users. See also: Conversions, Unit.

Enthalpy
Change in heat. See also: Heat, Hess's Law, Stagnation Enthalpy.

Enthalpy of Fusion
The enthalpy change that occurs to melt a solid at its melting point.The kinetic energy of the molecules remains the same, the latent heat is used to overcome the potential energy of the intermolecular forces.

Entropy
Measure of the disorder of a system.whereS = Experimental entropydQrev = Heat supplied to system, reversible changedQ = Heat supplied to systemT = Temperature

Entropy
The average amount of information represented by a symbol in a message, is a function of the model used to produce that message and can be reduced by increasing the complexity of the model so that it better reflects the actual distribution of source symbols in the original message. Entropy is a measure of the information contained in message, it's …

Entropy Coding
Variable length lossless coding of the digital representation of a signal to reduce statistical redundancy. See also: Arithmetic Coding.

Enumerable Set
A countable set.

Environmental Lapse Rate
The rate at which the air temperature decreases as you move higher in the atmosphere.The rate at which a parcel of air cools as it rises depends on the relative humidity of the air contained in the parcel. If a parcel has a relative humidity less than 100% we say it is dry.A dry parcel cools at a constant rate known as the dry adiabatic lapse rate …

Enzyme
Protein or protein-based molecules that speed up chemical reactions occurring in living things. Enzymes act as catalysts for a single reaction, converting a specific set of reactants (called substrates) into specific products. Without enzymes life as we know it would be impossible.The increase in rate can be as much as 1010 times that of…

Epitaxial
Of or pertaining to a layer of single crystal material grown on a crystalline substrate, with the same crystal orientation in both regions. See also: Crystal.

Epoxy Glue
A two-part resin/hardener glue that is extremely strong. It is generally available in 6 and 30-minute formulas.Uses:Plastic to plastic/wood, metal to metal/wood.Pros:Strong - note that longer setting time epoxy is often stronger and more durable.Cons:Difficult to sand - be careful if using it where it will need sanding to get a finish.

Equal Loudness Contour
A contour representing a constant loudness for all audible frequencies. The contour having a sound pressure level of 40 dB at 1000 Hz is arbitrarily defined as the 40-phon contour. High frequency sounds above 2000 Hz are more annoying. Human hearing is less sensitive to low frequency sound. The graph shows the equal loudness contours according to I…

Equality
Symbol : The relationship between two quantities that have the same value or values. If two quantities are not equal, the symbol is used. When the equality is only approximate, the symbol is used. When two expressions are exactly equivalent, the symbol is used.

Equations of Motion
There are four basic equations that describe the motion of a body moving withconstant acceleration.whereu = then velocity at time, t = 0v = velocity at time ta = constant accelerations = the distance travelled during time t

Equations of Rotational Motion
Similar to the four basic equations that describe the motion of a body moving withconstant acceleration the rotational forms are:where?0 = angular velocity at time t=0s [rads-1]? = angular velocity at time t [rads-1]a = constant angular acceleration [rads-2]? = angle turned through in time t [rad]t = time…

Equatorial Axis
Among the two mutually perpendicular axes of a telescope, the one that points at the celestial pole. To keep a star in view, the telescope must be rotated around this axis at the same rate as the Earth turns.

Equidistant
The same distance from something. See also: Equilateral.

Equilateral
Equal in length. See also: Equidistant.

Equilateral Triangle
A triangle with three equal sides. See also: Triangle.

Equilibrium
MechanicsA body may be in one of three states of equilibrium: stable, unstable and neutral.Stable EquilibriumA body is in stable equilibrium if it returns to its equilibrium position after it has been displaced slightly.Unstable EquilibriumA body is in unstable equilibrium if it does not return to its equilibrium position and does not remain in the…

Equilibrium Constant
Value that expresses how far the reaction proceeds before reaching equilibrium. A small number means that the equilibrium is towards the reactants side while a large number means that the equilibrium is towards the products side. See also: Equilibrium.

Equivalence Point
Occurs when the moles of acid equal the moles of base in a solution. In a titration the equivalence point is when enough titrant has been added to react completely with the analyte. See also: Acid, Base.

Equivalence Principle
Constant acceleration is completely equivalent to a uniform gravitational field.

Equivalent Continuous Sound Level
The steady state dB(A) level which would produce the same A-weighted sound energy over a stated period of time as a specified time-varying sound.Equivalent continuous A-weighted sound pressure level is widely used around the world as an index for noise. It is defined as 'the A-weighted sound pressure level of a noise fluctuating over a period of ti…

Eratosthenes
Around 230BC developed a method for finding all prime numbers. See also: Prime Numbers.

Erbium
A member of the lanthanide group of elements, erbium is a silver grey metal. It has high electrical resistivity and has properties similar to holmium and dysprosium. It is always found in combination with other rare earths, being found in small quantities in the same minerals as dysprosium (gadolinite, fergusonite and xenotime). It slowly tarnishes…

Erg
Unit of energy equal to 100.0x10-9J.ttle='Energy';xiunt='erg';yiunt='joule';mconv=10000000;cconv=0.0; See also: Energy, Joule, Therm.

Ergodic Process
An ergodic process is a random process that is stationary and of such a nature that all possible time averages performed on one signal are independent of the signal chosen and hence are representative of the time averages of each of the other signals of the entire random process.

Ergosphere
The region around a rotating black hole, between the event horizon and the static limit, where rotational energy can be extracted from the black hole. See also: Black Hole, Event Horizon, Static Limit.

Erosion
The natural wearing away of rocks. See also: Acid Rain, Weathering.

Error Correction
A method using a coding system to correct data errors by use of redundant data within a data block. Often data is interleaved for immunity to burst errors. Corrected data is identical to the original.

Errors
No measurement is exact, they all contain some degree of errors.Types of errors:BlunderA gross mistake caused by carelessness or poor judgement.e.g. when recording a distance you write 3.01m instead of 3.1mErratic ErrorAn error caused by an incomplete element in an instrument.e.g. backlash in a gear train.Inherited ErrorThe error in initial values …

Escape Velocity
This is the initial velocity that an object would have to have if projected from the surface of a body (e.g. Earth) to reach infinity before coming to rest.Escape velocity,Wherev = escape velocity [ms-1]G = universal gravitational constant = 6.67x10-11Nm2kg-2m = mass of body from which object is projected…

Essential Oil
Any oil that smells the same as the vegetable from which it was obtained and has a low boiling point.

Ester
Compound formed by the reaction between an alcohol and an acid, with the elimination of water. See also: Acid, Alcohol.

Estimate
An indication of the value of an unknown quantity based on observed data. See also: Estimation, Estimator.

Estimation
The process by which sample data are used to indicate the value of an unknown quantity in a population.The results of an estimation can be expressed as a single value, known as a point estimate; or a range of values, known as a confidence interval.

Estimator
Any quantity calculated from the sample data which is used to give information about an unknown quantity in the population. For example, the sample mean is an estimator of the population mean.

Etching
Chemical surface corrosion, usually conducted in a controlled fashion on a polished surface of a material sample to reveal details of the microstructure or to selectively remove any material not protected by a resist using an appropriate solvent or acid. In some cases the unwanted material is removed using an electrolytic process.

Ethane
Second member of the alkane series, a colourless, odourless gas. Symbol C2H6

Ethanol
Prepared by the fermentation of sugar. Symbol C2H5OH

Ethanol E10
Ethanol mixture that contains 10% ethanol, 90% unleaded gasoline.

Ethanol E85
Refers to a fuel blend of 85 percent ethanol and 15 percent gasoline.

Ether
A hypothetical elastic fluid postulated to support the transmission of light. See also: Caloric, Phlogiston.

Ethyl
The monovalent radical -C2H5

Ethyl Acetate
A flammable liquid with a fruity odour, used in flavourings and as a solvent. Symbol CH3COOCH2CH3

Ethylamine
Widely used in chemical industry and organic synthesis, it has a strong ammonia-like odor. Symbol CH3CH2NH2

Ethylene
A colourless inflammable gas with a sweet smell used as an anaesthetic and in the manufacture of polythene. Symbol C2H4 Also known as Ethene

Euclid
Euclid was a Greek mathematician; he taught in Alexandria, circa 300 BC. There is evidence that he wrote a number of works, but they have been lost to us. His work, Elements, however, was found, the Arabian mathematicians having carefully preserved it for the rest of us, as western man struggled through his dark ages; it was translated from Arabic …

Euclidean Algorithm
A set of rules which when applied to two integers produces their common divisor. See also: Algorithm.

Euler Codes
Computer software that is a mathematical representation of the motion of a fluid whose behavior and properties are described at fixed points in a coordinate system.

Euler's Constant
? = 0.577215664901532860606512 .......ttle='Eulers Constant';consttxt='g';constval=0.577215664901532860606512;constunt='';given by: Also known as the Euler-Mascheroni Constant.

Europium
The most reactive member of the lanthanide group of elements. Europium is a ductile silvery metal which reacts rapidly with air and water. As a result of its reactive nature, the metal has limited applications, but some is used in the manufacture of thin-film superconductor alloys. Europium is also used as control rod material in nuclear reactors d…

Eutectic (Eutectoid)
An isothermal reversible reaction in which a liquid solution is converted into two or moreintimately mixed solids on cooling, the number of solids formed being the same as the number of components inthe system. An alloy having the composition indicated by the eutectic/eutectoid point on an equilibrium diagram.An alloy structure of intermixed solid …

Eutectic Mixture
A mixture of two or more substances with melting point lower than that for any other mixture of the same substances. See also: Mixture.

Evaporation
The physical process by which a liquid, such as water is transformed into a gaseous state, such as water vapor. It is the opposite physical process of condensation.The kinetic interpretation of evaporation is molecules escape from the surface of the liquid until equilibrium with the saturated vapour is reached. See also: Atmometry, Condensation, Ph…

Evaporative Emissions
Hydrocarbon vapours that escape from a fuel storage tank, a vehicle fuel tank or vehicle fuel system. See also: Internal Combustion Engine.

Even Function
A function f(x) is called an even function if f(x)=f(-x) for all x.

Even Number
An integer that is divisible by 2. See also: Odd Number.

Event Horizon
The radius that a spherical mass must be compressed to in order to transform it into a black hole, or the radius at which time and space switch responsibilities. Once inside the event horizon, it is fundamentally impossible to escape to the outside. Furthermore, nothing can prevent a particle from hitting the singularity in a very short amount of p…

Evolution
A theory that tries to explain the variety of all living things. It suggests that living things adapt so that they can survive in their environment. See also: Darwin, Charles.

Excitation
Excitation is an external force or motion (or other input) applied to a system that causes the system to respond in some way.

Excitotoxin
An excitotoxin is a toxic molecule that stimulates nerve cells so much that they are damaged or killed. Domoic acid and glutamate are examples of excitotoxins.

Exclusion Principle
No two electrons can have the same set of quantum numbers. This statement also applies to protons, neutrons, and other baryons. See also: Bose-Einstein Statistics, Electron, Hadrons, Neutron, Proton.

Exclusive Or Gate
Logic element that features two inputs. The output will be 1 onlywhen one or the other (but not both) is logic 1. In all other cases the output is 0.The truth table for the Exclusive Or Gate:The Exclusive Or Gate can be built using NAND Gates as shown in the following diagram:

Excretion
The removal of waste substances from living things. See also: Kidney.

Exergonic
Refers to a reaction for which the free energy of the system decreases. See also: Endergonic.

Exhaust
An exhaust system of an internal combustion engine performs a number of functions. The main features that must be considered are:Acoustic design - Acoustic Ducts, Acoustic Filter Elements.CostConstruction and manufacturing processDurabilityDynamic tuneEmissions controlExhaust system backpressure Orifice positionPackaging Shell radiated noiseSystem …

Exhaust Catalyst
A catalytic converter is known to have two distinct acoustic effects:Reactive Effect Acoustic wave reflections caused by cross-sectional area changes within the catalyst can and the catalyst brick.Resistive Effect Acoustic wave dissipation caused by viscous losses. The resistive effect is frequency-dependent, that is, the catalytic converter acoust…

Exhaust Noise
The exhaust system of an internal combustion engine has a number of functions, one of which is to reduce the noise of the waste gases as they are expelled from the engine to the atmosphere.The three basic exhaust noise mechanisms are:Exhaust orifice noise - this is the noise radiated from the duct as it opens into the atmosphere.Structure borne noi…

Exhaust Tailpipe
The final pipe that the exhaust gas passes through before mixing with the atmosphere. There are a number of issues that must be taken into account:Positioned so that the exhaust gases exit into the moving air stream so that they are then taken clear of the vehicle.Designed so that it does not generate high levels of flow noise from the high speed e…

Exobiology
The study of biological processes that have or could have evolved away from the Earth.

Exosphere
This region is considered the very outer limits of the earth's atmosphere. Its lower boundary is often called the critical level of escape, where gas atoms are so widely spaced that they rarely collide with one another and have individual orbits. It is roughly 640000 metres above the surface of the Earth.

Exothermic
Reaction that gives off heat to the environment. See also: Combustion Reaction, Endothermic, Spontaneous Reaction.

Expansion Chamber
The expansion chamber can be considered as a simple low pass filter. The transmission loss performance is determined by the cross-sectional area ratio between the inlet and outlet ducts and the volume. With the single expansion chamber the transmission loss falls to zero when a half wavelength or multiple thereof equates to the length of the chambe…

Experiment
A process or study that results in the collection of data, the outcome of which is unknown.

Explosion
The sudden production of a large quantity of gas, usually hot, from a much smaller amount of a gas, liquid, or solid. See also: Explosive Decompression, Implosion.

Explosive Decompression
A very rapid reduction of air pressure inside a cabin, coming to a new static condition of balance with the external pressure. See also: Explosion.

Exponent
In the expression am, m is the exponent and a is the base. am is the mth power of a. If this is set equal to y (y=am) then this is called an exponential function. where

Exponential Constant
The base of natural (Napierian) logarithmse = 2.718281828459045235360287471352 .......ttle='Exponential Constant';consttxt='g';constval=2.718281828459045235360287471352;constunt='';'The letter e may now no longer be used to denote anything other than this positive universal constant.'Edmund Landau (1877-1938)

Exponential Smoothing
A statistical technique commonly used to forecast time series data or to smooth the values on a control chart. A forecast function is estimated from previous data using a weighted least squares technique. The degree to which data in the far past is weighted relative to the near past is governed by the value of one or more smoothing constants, which…

Extensible Markup Language
Better known in the abbreviated form as XML. XML is a markup language much like HTML and was designed to describe data.

Extensive Properties
Properties which are dependent on the amount of the substance.e.g. volume, mass, total energy.Extensive properties per unit mass are called specific properties.Specific volumewherev = specific volume [m3 kg-1]V = volume [m3]m = mass [kg]Specific energywheree = specific energy [kJ kg-1]E = energy [kJ]m = m…

Exterior Noise
Noise produced by a vehicle and radiating to its surroundings.

External Force
A surface force or body force acting on an object. External forces are sometimes called applied forces. See also: Body Force, Force, Internal Force, Line of Action, Surface Force.

External Thread
A screw thread which is formed on an external cylinder,e.g. bolts, screws, studs. See also: Thread.

Extinction
The attenuation of light, the reduction of illuminance of a collimated beam of light as the light passes through a medium wherein absorption and scattering occur.

Extragalactic
Outside the Milky Way. See also: Extraterrestrial.

Extraterrestrial
A term used to describe anything which does not originate on the Earth. See also: Earth, Extragalactic.

Extreme Ultraviolet
A portion of the electromagnetic spectrum from approximately 100 to 1000 angstroms. See also: Ultraviolet Light.

Extremely Low Frequency
That portion of the radio frequency spectrum from 30 to 3000 hertz. See also: Frequency.

Extrinsic Semiconductor
A semi-conducting material for which the electrical behavior is determined by impurities. See also: Semiconductor.

Extruded
A material that has been shaped by forcing through a die. See also: Extrusion.

Extrusion
A forming technique whereby a material is forced, by compression, through a die orifice. See also: Extruded.

Eye
An organ which is sensitive to light. See also: Ear, Ocular, Oculogyric, Visible Light.

Face
To machine a flat surface as in the end of a shaft in the lathe. See also: Facing, Lathe.

Face Centred Cubic
A crystal structure found in some of the common elemental metals; within the cubic unit cell atoms are located at all corner and face-centered positions. Roughly 20% of the elements crystallize with face centred cubic structures.Volume of conventional cella3Lattice points per cell4Volume of primitive cell1/4a3<…

Faceplate
A large circular plate with slots and holes for mounting the workpiece to be machined. It is attached to the headstock of a lathe. See also: Lathe.

Facing
The process of making a flat or smooth surface on the end of a piece of material. See also: Face.