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

Austempering
Quenching a ferrous alloy from a temperature above the transformation range, in a medium having a rate of heat abstraction high enough to prevent the formation of high-temperature transformation products, and then holding the alloy, until transformation is complete. The advantages of this method of interrupted quenching are increased ductility and …

Austenite
Non-magnetic face-centered cubic iron. Also iron and steel alloys that have the face-centered cubic crystal structure.It is produced by heating steel above the upper critical temperature and has a high solid solubility for carbon and alloying elements. This temperature or temperature range is called the austenitizing temperature and must be attaine…

Auto-Ignition Temperature
Minimum temperature at which the vapour/air mixture over a liquid spontaneously catches fire. i.e. without the application of a flame or spark. See also: Flash Point.

Autoclave
An airtight vessel constructed of thick-walled steel alloy for carrying out chemical reactions under pressure and high temperatures. Auto-claves are used for the industrial processing of composite materials.

Autocorrelation
The autocorrelation function gives a measure of the extent to which a signalcorrelates with a displaced version of itself, as a function of the displacement.whereR_AA(t) = autocorrelation of signal A as a function of displacementf_A(t) = signal A as a function of timeT = length of signal over which each correlation is calculated…

Autocovariance
This is the degree to which a function is correlated with itself as a function of time. See also: Autocorrelation.

Autogyro
An aeroplane that flies by virtue of the lift generated by freewheeling rotating wings set windmill fashion above the fuselage. The forward motion of the autogiro provides the force to keep the rotors turning so unlike a helicopter the autogiro cannot hover. See also: Aircraft, Helicopter.

Automatic Gain Control
A circuit that adjusts the gain of a stage so that the volume is constant even though the input signal may vary over a wide range. Signals are amplified or attenuated according to some measure of their amplitude or intensity, often by the mean square, or root mean square amplitude.

Automatic Gearbox
A gearbox where the ratio between input and output shafts is changed automatically based on load, throttle application, engine speed and road speed. See also: Continuously Variable Transmission, Gear Design, Gear Mesh Frequency, Gear Noise.

Automatic Stop
A device which may be attached to any of several parts of a machine tool to stop the operation of the machine at any predetermined point.

Automobile
A self-powered vehicle that travels on land typically with three or four wheels and with 2 to 9 seats.Historical Notes1769 Cugnot's carriage is the first large steam tractor. It was slow, clumsy and difficult to control.1801 Richard Trevithick built a road carriage powered by steam.1863 Jean-Joseph-Etienne Lenoir builds a horseless carriage that us…

Autospectrum
A spectrum with the coefficients of the components expressed as the square of the magnitudes. See also: Cross Spectrum.

Autoxidation
Oxidation caused by exposure to air. Rust is an example of autoxidation. Autoxidation makes ether taken from half-filled bottles very dangerous, because air oxidizes ether to highly explosive organic peroxides. See also: Oxidation Reaction.

Auxochrome
A group or substructure in a molecule that influences the intensity of absorption of the molecule.

Avalanche
A cumulative ionization process in which the ions and electrons of one generation undergo collisions that produce a greater number of ions and electrons in succeeding generations. See also: Breakdown Voltage.

Average
A statistic calculated by summing a set of data values and dividing by the number of values. Used to measure the centre of a sample of variable data.It can also denote the median, the mode, the geometric mean, and weighted means, among other things. See also: Arithmetic Mean, Moving Average.

Average Deviation
The absolute value of the difference from the mean for each data value, summed, then divided by the number of values. A somewhat more robust estimator of the of the so-called 'second moment' than standard deviation. See also: Mean, Standard Deviation, Statistic.

Average Room Absorption Coefficient
Total room absorption in sabins or metric sabins, divided by total room surface area in consistent units of square feet or square metres. See also: Metric Sabin, Room Acoustics, Sabin, Sound Absorption.

Average Speed
The distance traveled divided by the time taken. See also: Time, Velocity.

Averaging
In any process it is often necessary to average a number of measurements to gain any confidence in the measured value. As the number of measurements increases confidence will also increase. However, care must be taken to ensure that the quantity being measured remains stationary over the averaging time. In performing spectrum analysis, regardless o…

Averroes, Ibn Roshd (1126-1198)
An Arabian philosopher and physician who helped to advance the science of his time and has been called the Aristotle of the Middle Ages.

Avogadro, Armedeo (1776-1856)
The Italian scientist after which is named the Avogadro's Law, viz,. 'equal volumes of different gases, pressure and temperature being equal, contain the same number of molecules'; or, 'equal volumes of gases or vapours contain the same number of molecules'.He proposed a correct molecular explanation for Gay-Lussac's law of combining volumes. His w…

Avogadro's Law
Equal volumes of an ideal gas contain equal numbers of molecules, if both volumes are at the same temperature and pressure. For example, 1 L of ideal gas contains twice as many molecules as 0.5 L of ideal gas at the same temperature and pressure.It is, in fact, only true for ideal gases. See also: Avogadro, Armedeo, Dalton's Law of Partial Pressure…

Avogadro's Number
The number of items in a sample of a substance which is equal to the number of atoms or molecules in a sample of an ideal gas which is at standard temperature and pressure. It is equal to about N = 6.022045x10²³ mol^-1ttle='Avogadros Number';consttxt='N';constval=6.022045e23;constunt='mol^-1'; See also: Avogadro, Arme…

Axial
In the same direction as the shaft centreline.

Axial Float
Also known as End Float. Movement of one shaft along its centreline due to the freedom of movement permitted by a journal bearing or a sleeve bearing. This adjustment should be set before performing vertical or horizontal moves. The degree of axial float can be adjusted by the position of the stops, or whatever limits the motion.

Axial Load
A load applied along or parallel to and concentric with the primary axis.

Axial Mode
The room resonances associated with each pair of parallel walls.Dimensions x=5m, y=4m, z=3mmode: n_x=1, n_y=0, n_z=0

Axicon Lens
A conical lens which, when followed by a conventional lens, can focus laser light to a ring shape. See also: Laser, Lens.

Axiom
A statement assumed to be true without the need for proof. See also: Deduction.

Axis
The line, real or imaginary, passing through the centre of an object about which it could rotate; a point of reference. See also: x axis, y axis.

Axis of Symmetry
A line that passes through a graph or figure such that one side of the figure is an exact mirror image of the other.

Axle
An axle is a shaft on which a part rotates. See also: Wheel.

Azeotrope
A solution that does not change composition when distilled. For example, if a 95% (w/w) ethanol solution in water is boiled, the vapour produced also is 95% ethanol- and it is not possible to obtain higher percentages of ethanol by distillation.

Azobenzene
Red insoluble crystalline powder. Symbol C₁₂H₁₀N₂

Babbage, Charles (1791-1871)
The British inventor known to some as the 'Father of Computing' for his contributions to the basic design of the computer through his Analytical Engine. His previous computer, the Difference Engine, was a special purpose device intended for the production of mathematical tables.Babbage also invented the cowcatcher, the dynamometer, standard railroa…

Babbitt
A soft antifriction metal used to line bearings. Made of tin, antimony, lead, and copper.

Back Electromotive Force
The emf that opposes the normal flow of current in a circuit. See also: Electromotive Force.

Back Gears
Gears fitted to a machine to increase the number of spindle speeds obtainable with a cone or step pulley belt drive.

Back Titration
Determining the concentration of an analyte by reacting it with a known number of moles of excess reagent. The excess reagent is then titrated with a second reagent. The concentration of the analyte in the original solution is then related to the amount of reagent consumed. Also known as indirect titration. See also: Titration.

Background Noise
Noise from all sources unrelated to a particular sound that is the object of interest. Background noise may include airborne, structureborne, and instrument noise.

Backing Weld
A weld bead applied to the root of a single groove joint to assure complete root penetration.

Backlash
The lost motion or looseness (play) between the faces of meshing gears or threads. In the case of gears, it refers to how much one gear can be moved back and forth without moving the gear into which it is meshed. It may be measured in degrees. See also: Gear Design.

Backscattering
Primary radiation deflected or secondary radiation emitted in the general direction of the incident radiation beam.

Backward Recognition Masking
This is Also known as informational masking. The reduction in the ability to recognize a sound pattern due to the subsequent presentation of another sound pattern with similar information content. This kind of masking is thought to result from a process different from that or normal (sensory) masking.

Bacon, Francis (1561-1626)
An English natural philosopher, who reached his conclusions through the process of induction from facts, thus breaking away from contemporary scholasticism. He stated (1620) that experiments are of fundamental importance in acquiring scientific knowledge, since experiments enable us to establish causes that determine an occurrence and enable us to …

Bacteria
A group of small living organisms made of just one cell.

Baffle
AcousticsA movable barrier used to achieve separation of signals from different sources.LoudspeakersThe surface or board upon which a loudspeaker is mounted.

Bainite
An austenitic transformation product found in some steels and cast irons; it forms at temperatures between those at which pearlite and martensite transformations occur; the microstructure consists of alpha-ferrite and a fine dispersion of cementite.This term is used by metallurgists to describe a particular structure of steel when the steel is poli…

Bakelite
A plastic, a dense synthetic polymer (a phenolic resin) that was used to make jewellery, game pieces, engine parts, radio boxes, switches, and many, many other objects. Bakelite was the first industrial thermoset plastic (a material that does not change its shape after being mixed and heated). Bakelite plastic is made from carbolic acid (phenol) an…

Baker's Dozen
Thirteen pieces of something. See also: Dozen.

Balanced Construction
A method of constructing manufactured wood products so that moisture content changes will be uniformly distributed and therefore will not cause warping. An example would be symmetrical construction of plywood in which the grain direction of each ply is perpendicular to that of adjacent plies. See also: Plywood.

Balancing
A procedure for adjusting the mass distribution of a rotor so that vibration of journals, or the forces on the bearings at once-per-revolution, are reduced or controlled. See also: Counter Weight.

Balconet
A false balcony constructed with a low railing outside a window. See also: Balcony, Window.

Balcony
A projection from an upper story window or door surrounded by railing. See also: Balconet, Window.

Ball
A sphere together with its interior. See also: Sphere.

Ballistics
Ignoring the curvature of the Earth, frictional losses and that g is constant it is possible to calculate the trajectory of a projectile that is fired with a given initial velocity and elevation.VelocityTrajectoryMaximum HeightHorizontal Rangewherev = velocity at t [ms^-1]v₀ = initial velocity [ms^-1]a = elevation ang…

Balloon
A lighter than air craft. The Montgolfier brothers made the first flight in a hot air balloon in 1783.Historical Notes19 September 1783 Pilatre De Rozier launches the first hot air balloon with a sheep, a duck and a rooster as passengers.21 November 1783 The Montgolfier brothers make the first flight in a hot air balloon.1785 The first balloon cros…

Ballscrew
A threaded shaft and nut assembly supported by angular contact bearings, normally found on machine tools.

Balmer Series
A series of lines in the emission spectrum of hydrogen that involve transitions to the n=2 state from states with n>2. Four of the lines are in the visible spectrum, and the remainder are in the ultraviolet. First discovered by Balmer in 1885.The frequency of the visible lines is given by:whereR_H = Rydberg constant for hydrogen = 1.097x1…

Balsa Wood
The wood from Ochroma Lagopus it is used in model making as it is very light and easily worked.

Balsam
Light oily aromatic extracts from trees which cure into resins.

Balun
A transformer circuit that couples a balanced transmission line to an unbalanced transmission line.

Balusters
Small turned, square, or flat column that supports a rail; also used to form chair backs. See also: Balustrade, Bannister.

Balustrade
A series of balusters supporting the railing of a stairs or balcony. See also: Balusters, Bannister.

Bamboo
A natural material with a great strength to weight ratio. It was used in the early construction of aircraft wings and fuselages.

Band Gap Energy
For semiconductors and insulators, the energies that lie between the valence and conduction bands.

Band Stop Filter
An electronic network which passes signals having frequencies above and below the band-elimination frequency span. See also: Bandpass Filter, Filter.

Bandgap
For semiconductors and insulators, this is the range of energies between existing energy bands where no energy levels exist. For intrinsic materials, electrons are forbidden to have energies within this range.

Bandpass Filter
An electronic network which transfers through it a specific band of signal frequencies, attenuating signals both below and above the desired passband. See also: Band Stop Filter, Filter, Frequency.

Bandsaw
Photograph courtesy of Draper.co.ukA power saw, the blade of which is a continuous, narrow, steel band having teeth on one edge and passing over two large pulley wheels.

Bandwidth
CommunicationsThe difference between the lowest and highest frequency components of a signal or device. The bandwidth of optical fibre is in the gigabit or billions of bits per second range, while ethernet coaxial cable is in the megabit or millions of bits per second range. FilterThe bandwidth of a filter is the separation between the lower and up…

Bandwidth Time Product
The bandwidth-time product is used in calculating the confidence limit of a measurement. Confidence limits describe the uncertainty in measuring the level of random signals in finite periods of time.

Bannister
A handrail with supporting posts on a stairway. See also: Balusters, Balustrade.

Bar Chart
A strong graphical representation of data.

Bar Code
Coded labels that contain information about the item they are attached to, the information is contained in a numerical code, usually containing 12 digits.

Bar Stock
Metal bars of various lengths, made in flat, hexagon, octagon, round, and square shapes from which parts are machined.

Bargeboard
The finish board covering the projecting portion of a gable roof.

Barium
Elemental barium does not occur naturally. It is obtained by heating BaO with Al and, once refined, barium is a silvery white, soft metal which oxidises readily in air and water. Barium compounds, particularly BaSO₄ , are used for various applications, including the manufacture of paint, as an addition to heavy duty drilling oils and in …

Barium Dioxide
A white toxic powder obtained by heating barium oxide in air.

Barium Oxide
An oxide of barium; a whitish toxic powder. Used in optical glass.

Barium Sulphate
A white insoluble solid used as a pigment and filler in plastics. Most commonly found as the mineral Barite. Symbol BaSO₄ Also known as Ponderous Spar.

Bark
This is based on critical bandwidths and is a subjective representation of frequency. This is not an exact representation of what happens in the ear, but is a good starting point in basic modelling and psychoacoustic metric development.The relationship between frequency and the Bark scale is:wherez = barksf = frequency [Hz]

Barn
A unit of nuclear cross section, equal to 10^-28m² has been named the Barn.1 Barn (b) = 10^-28m²

Barometer
A device for measuring atmospheric pressure. It measures the weight of the column of air that extends from the instrument to the top of the atmosphere. There are two types of barometers commonly used today:Mercury BarometerConsists of a closed tube filled with mercury inverted in a mercury reservoir. The height of the mercury column indicates atmos…

Baromil
The unit of length used in graduating a mercury barometer in the centimetre-gram-second system. If the barometer is located at 45 latitude at sea level and its temperature is 0°C, a length increment of one baromil will correspond to a pressure increment of one millibar. Corrections must be applied at other locations. See also: Pressure.

Barrel (petroleum)
A unit of capacity in the oil industry.Conversions1 barrel (petroleum)=35 gallon (UK)1 barrel (petroleum)=42 gallon (US)1 barrel (petroleum)=0.1589873 m³ ttle='Barrel';xiunt='m³';yiunt='barrel (petroleum)';mconv=0.1589873;cconv=0.0;Oil consumption is measured in millions of barrels per day.World oil consumption.

Barrique
A large French wine barrel holding 225 litres.

Bartels Rotation Number
The serial number assigned to 27-day recurrence periods of solar and geophysical parameters. The equatorial rotation rate of the Sun is very close to 27 days. Rotation 1 Day 1 in this sequence was assigned arbitrarily by J. Bartels to February 8, 1832. See also: Sun.

Barycentre
This is the centre of gravity of 2 or more masses; the centre of mass of the Earth and Moon and is actually located within the Earth. See also: Earth, Moon.

Barye
The CGS unit of pressure, equal to 1 dyne per square centimetre.Conversions1 barye=0.1 pascal1 barye=0.1 Nm^-2ttle='Bayre';xiunt='barye';yiunt='Nm^-2';mconv=10;cconv=0.0; See also: CGS Units, Pressure.

Baryon
A particle with spin 1/2 (or 3/2) which consists of three elementary particlesknown as quarks. Baryons are the nucleons (protons and neutrons) which form atomicnuclei and also very shortlived (

Baryta
Any of several compounds of barium. See also: Barium, Barium Dioxide, Barium Oxide.

Base
ChemistrySubstance which gives off hydroxide ions (OH^-) in solution.MathematicsIn the expression x^y, x is called the base and y is the exponent.

Base Metal
The metal to be welded or cut. In alloys, it is the metal present in the largest proportion. See also: Alloy.

Base Unit
Base units are units that are fundamental building blocks in a system of measurement. There are seven base units in the SI system.

Baseplate
The surface to which the feet of a machine are attached.

Basis Function
A mathematical function that can be used to build a description of wavefunctions for electrons in atoms or molecules.

Basis Set
A set of mathematical functions that are combined to approximate the wavefunctions for electrons in atoms and molecules.

Bass
The lower range of audible frequencies. See also: Acoustics, Treble.