Gold is a soft metal with a characteristic yellow colour. It is the most malleable and ductile of any element. It is unaffected by air, water, alkalis and acids.
Defined as the mean distance of the Earth from the Sun.
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Audio Amplifier
An amplifier designed specifically for amplifying audio signals in the frequency range 20Hz to 20kHz.
Audio Books
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Audio Calculations
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Audio Conversions
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Audio Frequency
Generally in the range 20Hz to 20KHz.
Audio Transducer
An electronic device that converts electrical signal variations to sound, such as a loud speaker, or sound to electrical variations, such as a microphone.
Audio Weblinks
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Graph of hearing threshold level as a function of frequency.
An instrument for measuring hearing acuity.
Auditory Anomia
A neurological disorder which causes a marked inability to name otherwise familiar acoustic stimuli such as a door bell or motor vehicle.
Auditory Area
The sensory area lying between the threshold of hearing and the threshold of feeling or pain.
Auditory Cortex
Region of the cortex devoted to the analysis of sound information.
Auditory Nerve
Bundle of nerve fibers that carry information from the cochlea to the higher stages of the auditory system.
Aufbau Principle
An approximate procedure for writing the ground state electronic configuration of atoms.
Auger Bit
A drill bit used for drilling holes in wood.
Auger Shower
A very large cosmic ray shower.
The technique of using computer-based mathematical models of an acoustic environment and 3D sound processing methods to make audible the sound field of a source in the modeled space.


A natural alloy of copper and gold.

A faint visual phenomenon associated with geomagnetic activity, which occurs mainly in the high-latitude night sky.
Aurora Australis
The aurora of the Southern Hemisphere.
Aurora Borealis
Latin for Northern Dawn, an old name for the Aurora.
Auroral Kilometric Radiation
Intense radio waves whose wavelength is of the order of a kilometre, emitted from regions above the ionosphere where the aurora is accelerated.
Auroral Oval
The region in which aurora appears at the same time, corresponding to the ring of fire around the magnetic pole.
Auroral Zone
The region on Earth where auroras are common.
Latin for gold, hence the symbol Au.
Hot deformation of metastable austenite within controlled ranges of temperature and time that avoids formation of non-martensitic transformation products.
Quenching a ferrous alloy from a temperature above the transformation range.
Face-centered cubic iron; also iron and steel alloys that have the FCC crystal structure.
Austenitic Stainless Steel
The common stainless steel, where the primary microstructure is austenite and the composition primarily iron but also includes both chromium and nickel.
Forming austenite by heating a ferrous alloy above its upper critical temperature to within the austenite phase region from the phase diagram.
Authorised Carrier Frequency
A specific carrier authorized for use, from which the actual carrier frequency is permitted to deviate, solely because of frequency instability, by an amount not to exceed a given frequency tolerance.
Auto Level
A tripod mounted optical instrument that is used for obtaining levels in construction work.
An airtight vessel constructed of thick-walled steel alloy for carrying out chemical reactions under pressure and high temperatures.
Autoclave Moulding
A moulding technique in which an entire assembly is placed into an autoclave at 50 to 100 psi, in order to consolidate layers of the part by removing entrapped air and volatiles.
A single instrument combining the functions of a telescope and a collimator to detect small angular displacements of a mirror by means of its own collimated light.
The autocorrelation function gives a measure of the extent to which a signal correlates with a displaced version of itself, as a function of the displacement.
This is the degree to which a function is correlated with itself as a function of time.
A system of heterodyne reception. The circuit combines the functions of an oscillator and detector.
An aeroplane that flies by virtue of the lift generated by freewheeling rotating wings set windmill fashion above the fuselage.
Autoigniting Propellant
Any propellant that ignites by itself without external stimulation.
Autoignition Temperature
The temperature at which combustible materials ignite spontaneously in air.
Auto-Ignition Temperature
Minimum temperature at which the vapour/air mixture over a liquid spontaneously catches fire.
Autokinetic Illusion
The illusion of a fixed object or light moving when gazed at steadily.
Automated Manual Transmission
A manual gearbox where the gear changes are decided by a computer, based on input and output torque and speeds, and the gear change is actuated using a servo.
Automated Surface Observing System
This system is a collection of automated weather instruments that collect data.
Automatic Centre Punch
Allows one-handed operation by pressing down on the tool and a spring-loaded mechanism strikes a blow.
Automatic Frequency Control
A circuit that keeps a receiver in tune with the wanted transmission.
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.
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.
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.
Automatic Transmission Fluid
Fluid for automatic, hydraulic transmissions in motor vehicles.
Automatic Weather Station
A weather station that accurately and automatically measures and records meteorological variables over extended periods.
A self-powered vehicle that travels on land typically with three or four wheels and with 2 to 9 seats.
An isomorphism from a set onto itslef.
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Automotive Battery
A battery designed to start and run automobile.
Automotive Books
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Automotive Calculations
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Automotive Conversions
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Automotive Terminal Post
A round post made of lead used on engine starter batteries.
Automotive Weblinks
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A vesicle which encloses material from inside the cytoplasm such as spent organelles or other structures and polymers to be degraded.
Transfer of a hydrogen ion between molecules of the same substance.
Autoregressive Moving Average Model
Essentially an all-pole infinite impulse response filter with some additional interpretation placed on it.
Automatic rotation of a rotary wing due to forward, or downward, movement of an autogyro.
A spectrum with the coefficients of the components expressed as the square of the magnitudes
Both primary and secondary coils have turns in common.
An organism that can synthesize its own complex molecules from simple carbon and nitrogen sources, such as CO2 and NH3.
Autotrophic Respiration
Respiration by photosynthetic organisms such as plants and algaes.
Oxidation caused by exposure to air.
Auxiliary Electrode
Another name for a Counter Electrode.
Auxiliary Firing
The addition of extra fuel into the exhaust gases of a turbine to provide an increase in heat output.
Auxiliary Power Unit
A device that converts high density fuel into electrical power.
A plant growth hormone.
A group or substructure in a molecule that influences the intensity of absorption of the molecule.