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

Agar
A gel made from seaweed used to make salt bridges.

Ageing
A change in the properties of certain metals and alloys that occurs at ambient or moderately elevated temperatures after hot working, heat treatment, or a cold working operation.The ageing of aluminium alloys generally occurs slowly at atmospheric temperatures and more rapidly at higher temperatures. See also: Cold Working, Heat Treatment.

Aggravated Test
A test in which one or more conditions are set at a more stressful level that the test item will encounter in the field, in order to reduce test time or assure a margin of safety.

Agonic Line
A line joining points at which the magnetic variation is zero. The agonic line is a particular case of an isogonic line. See also: Aclinic Line.

Aileron
These are situated on the trailing (back) edge of the wing and are used to make the aircraft roll. See also: Aerofoil, Elevator, Elevon, Rudder, Wing Warping.

Air
The main constituents of air are Nitrogen, Oxygen, Argon, Carbon Dioxide, Neon, Helium along with a number of other trace gases.

Air Bearing
A bearing which uses an air cushion to separate its rotating surfaces. See also: Bearing.

Air Intake Manifold
The air intake manifold of an internal combustion engine performs a number of functions. The network of passages direct air or air-fuel mixture from the throttle body to the intake ports in the cylinder head. The flow typically proceeds from the throttle body into a chamber called the plenum, which in turn feeds individual tubes, called runners, le…

Air Intake Noise
The air intake system performs four main functions:Channel air to the enginePreferably cold air. Therefore, orifice best placed in the main airstream e.g. front of engine bay, behind headlamp unit.Filter particulatesThe filter element needs to be large enough to filter the required volume of air and achieve necessary service life.Dynamic performanc…

Air Lock
An intermediate enclosed chamber of a vacuum or pressure system through which an object may be passed without materially changing the vacuum or pressure of the system.

Air Set Cement
A cement that sets through loss of water.

Air Spring
A simple mass on an air spring.

Airbag
A bag that is inflated when an impact is detected to restrain a vehicle passenger.

Airborne Sound
Sound that arrives at the point of interest, such as one side of a partition, by propagation through air.

Airbrake
An aerodynamic control which can be extended to increase drag and slow down an aircraft. See also: Aerofoil.

Aircraft
Any structure, machine, or contrivance, especially a vehicle, designed to be supported by the air, being borne up either by the dynamic action of the air upon the surfaces of the structure or object, or by its own buoyancy; such structures, machines, or vehicles collectively.Aircraft, in its broadest meaning, includes fixed-wing airplanes, helicopt…

Airfield
An area set aside for the operation of aircraft.

Airflow
A flow or stream of air. An airflow may take place in a wind tunnel, in the induction system of an engine, etc., or a relative airflow can occur, as past the wing or other parts of a moving craft; a rate of flow, measured by mass or volume per unit of time. See also: Aerodynamic Noise, Aerofoil.

Airflow Resistance
The quotient of the air pressure difference across a specimen divided by the volume velocity of airflow through the specimen. The pressure difference and the volume velocity may be either steady or alternating.The properties of porous materials that absorb sound are related to the viscous resistance offered to small vibratory movements of air. This…

Airflow Resistivity
For a homogeneous material it is the quotient of its specific airflow resistance divided by its thickness. See also: Airflow Resistance.

Airframe
The structure of an aircraft, without power plant and systems. See also: Aircraft.

Airship
A powered lighter-than-air craft. See also: Aerostat, Aircraft, Balloon.

Airspeed
The speed of something relative to a mass of air or the speed of air relative to a fixed object. See also: Velocity.

Airy Disc
A pattern of illumination caused by diffraction at the edge of a circular aperture, consisting of a central core of light surrounded by concentric rings of gradually decreasing intensity.

Albedo
The ratio of the amount of radiation reflected from an object's surface compared to the amount that strikes it. This varies according to the texture, color, and expanse of the object's surface and is reported in percentage. Surfaces with high albedo include sand and snow, while low albedo rates include forests and freshly turned earth. See also: A…

Albedometer
An instrument used for the measurement of the reflecting power, the albedo, of a surface. A pyranometer adapted for the measurement of radiation reflected from the earth's surface is sometimes employed as an albedometer. See also: Albedo.

Alcohol
An alcohol is an organic compound with a carbon bound to a hydroxyl group.The two simplest alcohols are methanol and ethanol.ExamplesmethanolCH₃OHethanolCH₃CH₂OHpropanolCH₃CH₂CH₂OHCompounds with -OH attached to an aromatic ring are called phenols rather than alcohols.Historical Notes…

Aldehyde
Prepared by the oxidation of primary alcohols so that the OH group loses its hydrogen to give an oxygen joined by a double bond to a carbon atom.ExamplesformaldehydeHCHOacetaldehydeCH₃CHObenzaldehydeC₆H₆CHO

Alder
This wood is very durable in water and not so durable in dry conditions. Historically it was used a lot in pumps, piles and sluices.

Alfvén Waves
Waves moving perpendicularly through a magnetic field. They are caused by the oscillation of magnetic lines of force by the motions of the fluid element around its equilibrium position, which in turn is caused by the interactions between density fluctuations and magnetic variations.

Algebra
In 810AD Al-Khwarizmi writes important works on arithmetic, algebra, geography, and astronomy. In particular Hisab al-jabr w'al-muqabala (Calculation by Completion and Balancing), gives us the word 'algebra', from 'al-jabr'. From al-Khwarizmi's name, as a consequence of his arithmetic book, comes the word 'algorithm'.

Algebraic Equation
An equation of the form f(x)=0 where f is a polynomial. See also: Algebraic Number, Polynomial.

algebraic number
A number that is the root of an algebraic polynomial.Examplesqrt(2) is an algebraic number because it is a solution of the equation x²=2.

Algol
A high-level programming language developed in the 1950s. See also: Programming Languages.

Algorithm
A logical sequence of instructions that explain how to accomplish a task. It must explain exactly how to go from one step to the next and have a finite amount of steps.Historical Notes810AD Al-Khwarizmi writes important works on arithmetic, algebra, geography, and astronomy. In particular Hisab al-jabr w'al-muqabala (Calculation by Completion and B…

Aliasing
The erroneous interpretation of high-frequency signals as lower-frequency signals. Such misinterpretations are an expected result of making discrete measurements with sampling devices such as analog-to-digital (A/D) converters.In motion sequences temporal aliasing is the effect that occurs when the frame rate is not high enough for the sampling rat…

Alidade
That part of an optical measuring instrument comprising the optical system, indicator, vernier, etc.In modern practice the term is used principally to refer to a telescope mounted over a compass or compass repeater to facilitate observation of bearings, and to a surveying instrument consisting of a telescope mounted over a compass rose, for measuri…

Align
To adjust or set to a line or centre. See also: Alignment.

Alignment
A condition whereby the axes of machine components are either coincident, parallel or perpendicular, according to design requirements, during operation. See also: Align.

Aliphatic
An organic compound that does not contain ring structures.

Aliquot
A sample of precisely determined amount taken from a material.

Alkali
A substance that dissolves in water to give a solution of aqueous hydroxide ions that is capable of turning red litmus blue.The name is derived from the Arabic, al-qaliy (roasted ash), because such solutions can be made by adding water to the ashes of wood or plants. See also: Alkaline, Alkalinity.

Alkali Metal
A metal in group IA of the periodic table that form strongly alkalinehydroxides (lithium, sodium,potassium, rubidium,caesium, francium).HHeLiBeBCNOFNeNaMgAlSiPSClArKCaScTiVCrMnFeCoNiCuZnGaGeAsSeBrKrRbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIXeCsBaLaHfTaWReOsIrPtAuHgTlPbBiPoAtRnFrRaAcLanthanidesCePrNdPmSmEuGdTbDyHoErTmYbLuActinidesThPaUNpPuAmCmBkCfEsFmMdNoLr S…

Alkaline
An aqueous solution that contains a concentration of hydroxide ions and having a pH greater than 7. See also: Acid, Alkali, Base, pH.

Alkaline Earth Metal
A metal in group IIA of the periodic table(beryllium, magnesium,calcium, strontium,barium, radium).HHeLiBeBCNOFNeNaMgAlSiPSClArKCaScTiVCrMnFeCoNiCuZnGaGeAsSeBrKrRbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIXeCsBaLaHfTaWReOsIrPtAuHgTlPbBiPoAtRnFrRaAcLanthanidesCePrNdPmSmEuGdTbDyHoErTmYbLuActinidesThPaUNpPuAmCmBkCfEsFmMdNoLr See also: Periodic Table.

Alkaline Earth
An oxide of an alkaline earth metal, which produces an alkaline solution in reaction with water.

Alkalinity
A measure of a material's ability to neutralize acids. Alkalinities are usually determined using titration. See also: Acid, Alkali.

Alkaloid
A class of bitter-tasting, basic organic compounds with nitrogen-containing rings. Alkaloids often have powerful effects on living things. Examples are cocaine, nicotine, strychnine, caffeine, and morphine.

Alkane
A series of organic compounds with general formula C_nH_2n+2. Alkane names end with -ane.ExamplespropaneC₃H₈octaneC₈H₁₈

Alkene
A compound that consists of only carbon and hydrogen, that contains at least one carbon-carbon double bond.Alkene names end with -ene.ExamplesethyleneCH₂=CH₂1-propeneCH₂=CH₂CH

Alkoxide
An ionic compound formed by removal of hydrogen ions from the hydroxyl group in an alcohol using reactive metals, e. g. sodium. For example, potassium metal reacts with methanol (CH₃OH) to produce potassium methoxide (KOCH₃). See also: Alcohol.

Alkyl
A molecular fragment derived from an alkane by dropping a hydrogen atom from the formula -C_nH_2n+1.ExamplesmethylCH₃ethylCH₂CH₃CH

Alkyl Halide
An alkyl group attached to a halogen atom. See also: Alkyl.

Alkyne
A compound that consists of only carbon and hydrogen, that contains at least one carbon-carbon triple bond. Alkyne names end with -yne.ExamplesacetyleneCHCH1-propyneCH₂CH₂CH₃2-octyneCH₃CH₂CH₂(CH₂)₄CH₃

Allen Key
Photograph courtesy of Draper.co.ukA hexagonal shaped tool in cross section that is used to turn allen screws.

Allo-
A prefix that designates the more stable of a pair of geometric isomers. allo- is sometimes used less precisely to designate isomers or close relatives of a compound.

Allobar
A form of an element that has isotopic abundances that are different from the naturally occuring form. For example, 'depleted' uranium has had most of the uranium-235 removed, and is an allobar of natural uranium.

Allomer
Substances with different chemical composition but the same crystalline form. See also: Crystal.

Allosteric Effect
A change in the behavior of one part of a molecule caused by a change in another part of the molecule.

Allotriomorphic Crystal
A crystal having a normal lattice structure, but with an imperfect outward shape due to the influence of its surroundings. See also: Crystal.

Allotropy
Allotropy is the reversible phenomenon by which certain metals may exist in more than one crystal structure. If the process is not reversible, the phenomenon is termed 'polymorphism.'Generally an elemental solid.Examplegraphite and diamond are allotropes of carbon.

Allowance
The prescribed difference in dimensionsof mating parts to provide a certain class of fit.

Alloy
MetalsThe mixture of any element with a pure metal. The melting temperature of an alloy is usually less than the melting temperature of the parent metals.There are several elements regularly occurring in plain carbon steel as manufactured, such as carbon, manganese, silicon, phosphorous, sulphur, oxygen, nitrogen and hydrogen. Plain carbon steel is…

Alloying Elements
Chemical elements added for improving the properties of the finished materials. Some alloying elements are: nickel, chromium, manganese, molydenum, vanadium, silicon, copper.

Allusive Listening
Allusive listening is a presumed listening mode that may be said to occur where a listener relates moments or features of the music to similar moments or features in other musical works.

Allyl Alcohol
Used in the manufacture of resins and many pharmaceuticals this is a colourless pungent liquid. Symbol C₃H₆O

Alpakka
A nickel silver made from 65% copper, 22% zinc, 13% nickel.

Alpha Iron
The body-centered cubic (BCC) form of pure iron, stable below 910°C. See also: Body Centred Cubic, Gamma Iron, Iron.

Alpha Particle
The nucleus of helium consisting of two protons and two neutrons. Alpha particles rapidly dissipate their energy as they pass through materials, and are far less penetrating than beta particles and gamma rays.Click on an item to paste into clipboard or use clipboard symbol at end to clipboard all values alpha particle mass 6.64465598e-27 kgClip alp…

Alphametic
A cryptarithm in which the letters, which represent distinct digits, form related words or meaningful phrases.

Alphanumeric
A character set that contains both letters and digits.

Alternating Copolymer
A polymer, composed of two different repeating mers, in which the different mer units systematically alternate positions along the molecular chain. See also: Mer, Polymer.

Alternating Current
An electric current whose direction changes direction with a frequency independent of circuit components. See also: AC Brownout, AC Line, AC Line Filter, Current, Direct Current.

Altimeter
An instrument for measuring height above a reference datum. See also: Altitude.

Altitude
Height in space of an object or point relative to sea level or ground level. See also: Altimeter, Height.

Alumel
Trade name for an alloy of nickel with up to 5% aluminium, manganese and silicon, used with chromel in K-type thermocouples.

Aluminium
Aluminium and its alloys are widely used for various applications including aircraft assemblies and engine parts. It is a silvery white reactive metal which is usually covered in oxide, making it inert to acids, but it is attacked by alkalies. It is extracted from the hydrated oxide, Bauxite, by electrolysis of the oxide dissolved in molten sodium …

Aluminium Bromide
White or very pale yellow crystalline solid. Symbol Al₂Br₆

Aluminium Bronze
A copper-aluminum alloy with high tensile strength and resistance to corrosion. Sometimes contained a small amount of manganese or nickel.

Aluminium Chloride
A chloride used as a wood preservative or catalyst. Symbol AlCl₃

Aluminium Fluoride
White crystalline solid. Symbol AlF₃

Aluminium Hydride
White crystalline solid. Symbol AlH₃

Aluminium Hydroxide
White crystalline compound that occurs naturally as the mineral gibbsite.

Aluminium Iodide
White solid. Symbol Al₂I₆

Aluminium Nitride
Bluish white crystalline solid. Symbol AlN

Aluminium Oxide
Alminium oxide is the most widely used oxide ceramic, either in pure form or as raw material to be mixed with other oxides. Symbol Al₂O₃

Aluminium Sulphide
Yellow or yellow grey powder. Symbol Al₂S₃

Alvarez, Luis Walter (1911-1988)
American physicist who produced free protons with a particle accelerator. He headed a team which designed a bubble chamber for detecting short-lived subatomic particles and received the Nobel Prize for physics in 1968 for his 1960 discovery of these particles.

Amagat
The unit of density of a gas at stp equal to 44.614774 molm^-3.ttle='Density';xiunt='amagat';yiunt='molm^-3';mconv=0.0224141;cconv=0.0;The unit is named after the Dutch physicist E. H. Amagat, whose work included the study of gases under pressure. See also: Density, Mole.

Amalgam
An alloy that contains mercury. See also: Alloy, Mercury Hg.

Ambience
The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is said to be 'live'; one without much reverb is said to be 'dead'. See also: Reverberation Time.

Ambient Environment
The conditions characterizing the air or other medium that surrounds materiel.

Ambient Noise
The composite of airborne sound from many sources near and far associated with a given environment. No particular sound is singled out for interest. See also: Noise, Sound.

Ambient Temperature
The average temperature of the surroundings. See also: Temperature.

American Wire Gauge
A numbering system for standard wire diameters, often abbreviated as AWG.AWGDiameter InchesDiameter mm00000.460011.6840000000.409610.403840000.36489.26592000.32498.25246010.28937.34822020.25766.54304030.22945.82676040.20435.18922050.18194.62026060.16204.11480070.14433.66522080.12853.26390090.11442.905760100.10192.588260110.090742.304796120.080812.0…

Americium
Radioactive element of the actinide series. Symbol AmDiscoveredFirst synthesized in a series of successive neutron capture reactions in the element plutonium, 239Pu, in a nuclear reactor in 1944 by American scientists under Glenn T. Seaborg at the University of California lab in Berkeley, California.

Amicable Numbers
Two numbers are said to be amicable if each is equal to the sum of the proper divisors of the other. See also: Divisor.

Amide
The most stable of all the carbonyl functional groups. See also: Acetamide.

Amine
A class of organic compounds in which one or more of the hydrogen atoms of ammonia have been replaced by other groups of atoms.ExamplesmethylamineCH₃NH₂ dimethylamineCH₃NHCH₃trimethylamine(CH₃)₃N

Amino Acid
Amino acids are molecules that contain at least one amine group (-NH₂) and at least one carboxylic acid group (-COOH). When these groups are both attached to the same carbon, the acid is an -amino acid.Amino acids are the basic building blocks of proteins.There are about 20 naturally occurring amino acids, which are particularly importan…