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


Earplug
Hearing protector that is inserted into the ear canal. See also: Ear, Earmuff, Hearing, Hearing Protector.

Earth
The third planet from the sun in the solar system. Other planets possess oceans or/and an atmosphere, but Earth is so far the only planet known to be inhabited by carbon based life.The Earth revolves around the sun on an elliptical orbit. One orbit takes 365.2422 days to complete.

earth
Can mean a connection to the earth itself or the negative lead to the chassis or any point to zero voltage.

Earth Rate Unit
Unit of angular velocity equal to 15° per hour. This is the rate at which the earth rotates on its axis. It is used to measure the drift rate of a gyroscope and various pointing devices in aerospace engineering.

Eave
This is the part of a roof which overhangs the exterior walls.

Ebony
A very dark, hard and smooth wood used for ornamental work.

Ebulliometry
Determination of average molecular weight of a dissolved substance from the boiling point elevation of the solution. See also: Molecular Weight.

Ebullition
The agitating, bubbling action of a liquid that is undergoing rapid, active boiling. See also: Boiling Point.

Eccentric
A circle not having a geometric centre.Also, a device such as a crankshaft or a cam for converting rotary motion to reciprocating motion. See also: Cam.

Eccentricity
The variation of the outer diameter of a shaft surface when referenced to the true geometric centreline of the shaft. Often described as Out-of-roundness. See also: Eccentricity Ratio, Off Centre.

Eccentricity Ratio
The vector difference between the bearing centreline and the average steady-state journal centreline. See also: Eccentricity.

Echo
A delayed return of sound that is perceived by the ear as a discrete sound image. Typically >90 milliseconds to be perceived as distinct from that directly transmitted. See also: Cepstrum, Echo Location, Echograms, Flutter Echo, Reflected Sound.

Echo Location
Determining the location of a target relative to the sensor face by means of measuring the time it takes for a sound wave to travel to the target and be reflected back to the sensor. See also: Cepstrum, Echo.

Echograms
A record of the very early reverberatory decay of sound in a room. See also: Echo.

Eclipse
A chance alignment between the Sun and two other celestial objects within the solar system in which one body blocks the light of the Sun from the other. In effect, the outer object moves through the shadow of the inner object.Lunar EclipseWhen the Moon enters the Earth's shadow as the Earth moves between the Sun and the Moon.Solar EclipseWhen the E…

Ecology
The study of living things in their environment. See also: Ecosystem.

Ecosystem
A community of living things together with their environment. See also: Ecology.

Eddington Limit
The theoretical limit at which the photon pressure would exceed the gravitational attraction of a light-emitting body. That is, a body emitting radiation at greater than the Eddington limit would break up from its own photon pressure. See also: Photons.

Eddy Currents
Circulating currents within inductor core material caused by magneticlines of force cutting across the core in a direction which induces a voltagein the core material.They are the main cause of heating in electric motors and transformers. For this reason iron cores are made from many thin layers that are insulated from each other so that the eddy c…

Effective Address
The final memory address used by an instruction. The instruction may require the microprocessor to perform several operations to generate the effective address.

Effective Nuclear Charge
The nuclear charge experienced by an electron when other electrons are shielding the nucleus. See also: Atomic Number.

Efficiency
A measure of how well a machine changes energy into useful energy.ObjectEfficiencyDry plate clutch (transmission efficiency)0.99Driveshaft joints (transmission efficiency)0.99Straight gears (transmission efficiency)0.95 to 0.98 See also: Energy.

Efflorescent
Efflorescent substances lose water of crystallization to the air. The loss of water changes the crystal structure, often producing a powdery crust. See also: Deliquescence.

Effusion
Movement of gas molecules through a small opening. They also move in straight-line trajectories through the hole.

Egyptian Fraction
A number of the form 1/x where x is an integer is called an Egyptian fraction. See also: Fraction.

Ehrenfest Paradox
The special relativistic 'paradox' involving a rapidly rotating disc. Since any radial segment of the disc is perpendicular to the direction of motion, there should be no length contraction of the radius; however, since the circumference of the disc is parallel to the direction of motion, it should contract.

Eigenvalue
Possible values for a parameter of an equation for which the solutions will be compatible with the boundary conditions.In quantum mechanics the energy eigenvalues for the Schrödinger equation are the possible energy levels for the system.

Einstein Field Equation
The cornerstone of Einstein's general theory of relativity, relating the gravitational tensor G to the stress-energy tensor T by the simple equation

Einstein, Albert (1879-1955)
Einstein thought in another dimension, unknown and practicably unknowable to most of us.1905 Einstein published papers on Brownian motion, the photoelectric effect, and the special theory of relativity. 1907 Einstein publishes his principle of equivalence, in which says that gravitational acceleration is indistinguishable from acceleration caused b…

Einsteinium
An artificial radioactive element found in the debris of an H bomb. Symbol Es

Elastic Collisions
When two bodies collide their total momentum is conserved unless external forces act on them. In most real situations their is some loss of energy in the form of heat, sound or permanent deformation of one of the bodies. See also: Collision, Inelastic.

Elasticity
A material is elastic if it returns to its original shape after being deformed. The maximum load that a body can experience and still return to its original shape is known as the Elastic Limit.MetalsThe elastic limit is defined as the 0.2% offset yield strength. This represents the stress at which the stress-strain curve for uniaxial tensile loadin…

Elastomer
A polymeric material that may experience large and reversible elastic deformations.

Electric Charge
A property used to explain attractions and repulsions between certain objects. Two types of charge are possible: negative and positive. Objects with different charge attract; objects with the same charge repel each other. See also: Electric Dipole Moment, Electron.

Electric Constant
Electric Constant = 1/µ0c2 = e0 = 8.854187817x10-12Fm-1

Electric Dipole Moment
A measure of the degree of polarity of a polar molecule. Dipole moment is a vector with magnitude equal to charge separation times the distance between the centers of positive and negative charges. Chemists point the vector from the positive to the negative pole; physicists point it the opposite way. Dipole moments are often expressed in units call…

Electric Motor Noise
There are numerous applications of electric motors and the type of noise produced by each may be very specific to the installation and type of motor. There are a number of reasons why the motor is perceived as being noisy:The loudness level of the soundPeriodic variation of sound pitch due to motor speed variationNon-periodic variation of sound pit…

Electric Motors
There are a number of different types of electric motor:AC Induction MotorsBrush Direct Current MotorsBrushless Direct Current MotorsStepper MotorsDesign factors to consider when choosing an electric motor:ApplicationEnvironmentCommutation methodDuty cycleNo-load speedWeightStall torqueLifetimeLoad (operating) pointTorque ripplePower sourceControll…

Electrical Impedance
Impedance of a linear circuit element with two terminals is the ratio of the complex sinusoidally varying voltage applied across the terminals to the complex current that flows in response.If the circuit element is a pure resistance the impedance is simply the resistance of the element.

Electrical Length
Physical length expressed in terms of the wavelength of a signal for the medium in which the component or structure is situated. The units are degrees, radians or grads. See also: Wavelength.

Electrical Screen
A metal shield which isolates a device from external fields.

Electrochemistry
The study of the interchange of chemical and electrical energy. See also: Anode, Battery, Cathode.

Electrodes
Device that moves electrons into or out of a solution by conduction. See also: Anode, Cathode, Electrolysis.

Electroform
To form shaped objects by electro-deposition on a mould.

Electrolysis
Changing the chemical structure of a compound using electrical energy. See also: Anodize.

Electrolyte
A substance that dissociates fully or partially into ions when dissolved in a solvent, producing a solution that conducts electricity.Strong ElectrolyteA strong electrolyte is a solute that completely dissociates into ions in solution. Solutions of strong electrolytes conduct electricity. Most soluble ionic compounds are strong electrolytes. Strong…

Electrolytic Capacitor
A type of capacitor that has a liquid or paste between the plates to increase its capacitance. See also: Capacitance, Capacitor, Ceramic Capacitor, Greencap Capacitor.

Electrolytic Cell
A cell that uses electrical energy to produce a chemical change that would otherwise not occur spontaneously.

Electromagnet
A magnet formed by an inductor having current flow through it.

Electromagnetic Compatibility
The capability of different electrical systems to coexist in the electromagnetic environment without causing or being subjected to interference.

Electromagnetic Field
Electric and magnetic forces that exist in a physical volume. See also: Electromagnetic Radiation.

Electromagnetic Radiation
The emanation of an electromagnetic field from a source through space. See also: Electromagnetic Field.

Electromotive Force
The difference of potential produced by an electrical source to drive a current through an external electrical circuit. The SI units of electromotive force is the volt. The potential difference between points a and b is:wherefa = potential at point afb = potential at point bE = electric fielddl = line element

Electromotive Series
The electrode potential of a material according to decreasing tendency to release electrons with hydrogen as zero.Click on an item to paste into clipboard or use clipboard symbol at end to clipboard all values Aluminium 1.67 VClip Antimony -0.1 VClip Arsenic -0.3 VClip Barium 2.9 VClip Beryllium 1.7 VClip Bismuth -0.226 VClip Brass -0.47 VClip Brom…

Electron
The least massive electrically-charged particle, hence absolutely stable.It is the most common lepton, with electric charge -1.A unit of energy equal to the kinetic energy acquired by an electron or protonfalling through an electric potential difference of 1 volt.Electrons surround the atom's positively charged nucleus and determine the atom's chem…

Electron Affinity
The measure of an atom's tendency to gain an electron. Thermal energy is released from most atoms when they gain an electron. The higher the electron affinity number, the more likely to gain an electron.

Electron Beam Welding
A technique for joining materials in which components to be welded are heated by a concentrated beam of high-velocity electrons in a vacuum. See also: Electron, Welding.

Electron Capture
A decay process in which an inner atomic electron is captured by the nucleus. The daughter nucleus has the same number of nucleons but one fewer proton. See also: Electron, Nucleus.

Electron Volt
Unit of energy of moving particles. Given by the kinetic energy acquired by an electron losing one volt of potential.eV = 1.60217733×10-19Jttle='Electron Volt';consttxt='eV';constval=1.60217733e-19;constunt='J';Electronvolts are used as a measure of the energy of cosmic rays and high-energy photons.ExampleX-rays can have energies of 1000…

Electron-Positron Annihilation
When an electron and its anti-particle, a positron, collide, they annihilate emitting a pair of gamma-ray photons each with an energy of 511 keV. See also: Electron, Positron.

Electronegativity
Measure of a substances' ability to attract electrons, also a term to describe non-metallic elements.

Electronics Books
Transistors: from Crystals to Integrated Circuits By M. Levinshtein, G. Simin, Published By: World Scientific Publishing.The Art of Electronics By Paul Horowitz, Winfield Hill, Published By: Cambridge University Press.Handbook of Modern Sensors By Jacob Fraden, Published By: Springer-Verlag Berlin and Heidelberg GmbH & Co. KG.Discrete-time Signal P…

Electronics Calculations
BAn abbreviation of bel, the logarithm of the ratio of two powers. The decibel is one tenth of a bel.belThe bel is the logarithm of the ratio of two powers, and the decibel is one tenth of a bel.ResistanceThe electrical resistance of a conductor.ResistorPassive component with a known resistance. The value of resistance is usually shown by a set of …

Electronics Conversions
AbampereThe CGS electromagnetic unit of current equal to 10 Amperes.AbcoulombThe CGS unit of electric charge equal to 10 Coulomb.AbhenryThe CGS unit of inductance equal to 1.0x10-9Henry.AbmhoThe CGS unit that is the reciprocal of the ohm equal to 1.0x109Siemens.AbohmThe CGS unit of electrical resistance equal to 1.0x10-9<…

Electrophile
A species that loves electrons. Since the electrons are negatively charged, electrophiles are positively charged or bear a partial positive charge. Examples are carbocations or protons. See also: Electron, Proton.

Electropositive
For an atom, having a tendency to release valence electrons, also a term to describe metallic elements.

Electrostatic Sensitivity
The degree to which a component or device is susceptible to damage by electrostatic discharge.

Electroweak Interaction
In the Standard Model, electromagnetic and weak interactions are related (unified); physicists use the term electroweak to encompass both of them. See also: Standard Model, W Particles.

Electrum
An alloy of 75% gold and 25% silver along with small quantities of other metals such as copper.

Element
A pure substance which cannot be broken down into simpler substances by chemical means. Set of stable atoms from which all known molecules are made. These atoms are organised as a function of their chemical properties in the so-called `Periodic Table of the Elements'.ActiniumAcAluminiumAlAmericiumAmAntimonySbArgonArArsenicAsAstatineAtBariumBaBerkel…

Elementary Charge
The electric charge on an electron particle.e = 1.602176462x10-19Cttle='Elementary Charge';consttxt='e';constval=1.602176462e-19;constunt='C';

Elementary Particles
The particles which form the building blocks of atoms and those which carry energy.

Elevator
Movable control surface, attached to the trailing edge of an aircraft tailplane to control pitching movements. See also: Aileron, Canard, Elevon, Rudder.

Elevon
Movable control surfaces which act collectively as elevators, but differentially as ailerons. See also: Aileron, Aircraft, Elevator.

Ellipse
A plane through a right angle cone.The equation of an ellipse is given bywhereThis may be approximated as

Elliptical Orbit
An orbit which describes an ellipse or oval shape. See also: Orbit.

Elm
A hard, durable and coarse grained wood. Durable even when constantly wet and so used for ship building, piles and paddle wheels.

Elongation
Increase in length which occurs before a metal is fractured, when subjected to stress.This is usually expressed as a percentage of the original length and is a measure of the ductility of the metal. See also: Stress.

Embrasure
A splayed opening in a wall that enframes a doorway or a window.

Emery
A natural abrasive used for grinding or polishing. See also: Emery Cloth.

Emery Cloth
Fabric backed abrasive paper. See also: Abrasive, Emery, Sandpaper, Wire Brush.

Emission Nebula
A type of nebula that shines by emitting light when electrons recombine with protons to form hydrogen atoms. The electron frequently approaches the proton in steps emitting energy as light as it gets pulled in. In one of the most common 'steps,' the recombining electron emits a photon of red light. Since many atoms in the nebula do this all at once…

Emission Spectrum
The collection of discrete wavelengths emitted by atoms that have been excited by heating or by electric currents.

Emphasis
Filtering applied to an audio signal before storage or transmission to improve the signal-to-noise ratio at high frequencies. See also: De-Emphasis.

Empirical Law
A law strictly based on experiment, which may lack theoretical foundation.

Empty Set
The set with no elements in it.

Enantiomers
Stereoisomers that are nonsuperimposable complete mirror images of each other. See also: Racemic Mixture, Stereoisomerism.

Encastre
A term which describes the constraints imposed on a structure where it joins its foundations. An encastré beam has no translation or rotation at its supports. This is Also known as a clamped support.

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

Endothermic
Reaction that absorbs heat from its surroundings as the reaction proceeds. See also: Exothermic, Spontaneous Reaction.

Endurance Limit
In fatigue testing, the number of cycles which may be withstood without failure at a particular level of stress.Generally 'infinite' life means more than 107 cycles to failure.If the term is used without qualification, the cycles of stress are usually such as to produce complete reversal of flexural stress. Above this limit failure occur…

Energy
Energy is defined as the capacity of a body for doing work. The SI unit of energy is the joule. 1 joule is the work done by a force of 1 newton moving a distance of 1 metre in the direction of the force.Conversions1 calorie=4.1868 joules1 kilowatt hour=3.6x106 J1 therm (EEC)=105.506x106 J1 therm (US)=105.4804x106 J1…

Energy Band
A collection of closely spaced energy levels.

Energy Density
Characteristic parameter of a battery/electrical power source indicating the amount of electrical energy stored per unit weight or volume.Specific Energy or Gravimetric Energy DensityWeight based power density [watt-hour/kg].Power Density or Volumetric Power DensityVolume based power density [watt-hour/litre or watt-hour/m3].Note: the te…

Engine
A machine which produces power to do work, particularly one that converts heat into mechanical work.Diesel EngineAn 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.Four-Stroke EngineAn engine operating on a cycle which …

Engine Bay
The enclosure in which an engine is installed in a vehicle. See also: Engine.

Engine Configurations
Various configurations of engine have been developed over the years for power, low noise and vibration, economy or weight.Single Cylinder - HorizontalThe first internal combustion engines were single cylinder designs and mostly stationary engines.Inline TwinThis particular engine is a model two-stroke glow plug engine.Opposed TwinA model engine bui…

Engine Excitation Mechanisms
Single Cylinder EngineInertia Force - The displacement of the piston with respect to crank angle can be derived from simple trigonometry. This can then be differentiated to yield velocity and acceleration of the piston. The expressions obtained tend to be very complicated and can be simplified into the expression containing only first order (once p…

Engine Orders
Engine orders are simply the amplitudes of the frequency components which are the multiples of the rotating frequency. Engine orders, which are determined by an order analysis are extensively used in the vibration and noise work to identify the source of excitation (order) and, hence, its frequency of an engine induced problem. For example, a four …

Engine Radiated Noise
Some empirical noise prediction models have been derived from a sample of 1m radiated engine noise measurements.Normally aspirated direct injection dieselTurbocharged direct injection dieselIndirect injection dieselPetrol engines (lean burn)Petrol engine formula updated for 1990'sThe updated formula for petrol engine radiated noise shows that the n…