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

Ammeter
Instrument for measuring the current in amps, milliamps or microamps by an indicator activated by the movement of a coil in a magnetic field or by the longitudinal expansion of a wire carrying the current. The ideal ammeter has zero resistance. See also: Ampere.

Ammine
A metal ion complex containing ammonia as a ligand. The ammonia nitrogen is bound directly to a metal ion in ammines; amines differ in that the ammonia nitrogen is directly bound to a carbon atom. See also: Amine, Ammonia.

Ammonia
Obtained from nitrogen using the Haber process and used in the manufacture of fertilizers and explosives. Pure NH₃ is a colorless gas with a sharp, characteristic odor. It is easily liquified by pressure, and is very soluble in water. Ammonia acts as a weak base. Symbol NH₃

Ammonium Carbonate
Colorless crystal or white powder with a strong ammonia-like odor. Soluble in water and decomposes in hot water. Symbol (NH₄)₂CO₃

Ammonium Chloride
A clear white water-soluble crystalline salt with a biting, slightly sour taste. Symbol NH₄Cl Also known as Sal Ammoniac, salmiac, nushadir salt, zalmiak, sal armagnac, sal armoniac, salmiakki, salmiak, salt armoniack

Ammonium Fluoride
Crystallizes as small prisms, having a sharp saline taste, and is exceedingly soluble in water. Symbol NH₄F Also known as Neutral ammonium fluoride

Ammonium Hydrogenphosphate
Used as a nutrient for the yeast in brewing. Symbol (NH₄)₂HPO₄

Ammonium Hydroxide
A solution of ammonia in water. Symbol NH₄OH

Ammonium Iodide
Used in photographic chemicals and some medications. Symbol NH₄I

Ammonium Nitrate
The best known chemical property of ammonium nitrate is its combustability. This also makes it a very dangerous compound to work with. Symbol NH₄NO

Ammonium Sulphate
Fine granulated, off white or brown crystals. There may be a slight ammonia like odour. Sulphate of ammonia is a chemical fertilizer. Symbol (NH₄)₂SO₄

Amorphography
The branch of science concerned with the determination of amorphous solid structures and their systemmatic classification.

Amorphous
Non-crystalline, without long-range order. Does not have a repeating, regular three-dimensional arrangement of atoms, molecules, or ions.

Ampere
The SI unit of Electric currentThe ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce a force between the conductors equal to 2x10^-7 newton per metre of length.The official symbol is A.Named af…

Ampere Andre Marie
Permanent place in the history of science because it was his name that was given to the unit by which we measure electrical current. See also: Ampere.

Ampere-Hour
Symbol Ah. An alternative unit of electrical charge. One ampere-hour = 3,600 coulombs.Often used to state the capacity of a battery.ttle='Ampere-Hour';xiunt='C';yiunt='Ah';mconv=3600;cconv=0.0; See also: Coulomb.

Amperometry
Determining the concentration of a material in a sample by measuring electric current.

Ampersand
The character &

Amphi-
A prefix used to name certain members of a series of geometric isomers or stereoisomers.

Amphiprotic Solvent
Solvents that exhibit both acidic and basic properties; amphiprotic solvents undergo autoprotolysis.Examples:waterammoniaethanol

Amplification
ElectronicsAmplifiers are used to provide a number of functions:Increase or attenuate magnitude of a physical quantity.Transform signals from one physical variable to another (e.g. charge tovoltage).Remove DC biases.Provide impedance matching. Care should be taken to ensure:Linearity.Satisfactory frequency response.Satisfactory 'slew rate' i.e. res…

Amplifier
A circuit or element that provides gain. See also: Amplification, Direct Current Amplifier, Operational Amplifier.

Amplitude
The maximum distance from the equilibrium position that occurs in periodic motion. Peak amplitudeThe difference between the maximum excursion and the equilibrium point.Peak-to-peak amplitudeThe difference between the maximum positive and maximum negative points of excursion.RMS amplitudeThe standard deviation of all values.

Amplitude Distortion
A distortion of the wave shape of a signal.

Amplitude Envelope
The function describing how the maximum amplitude of a waveform evolves over time. In acoustics the amplitude envelope is often characterized as consisting of four parts:The attack portion - the part during which the amplitude is rapidly increasingThe decay portion - the 'backside' of the attack, during which the amplitude is rapidly diminishingThe…

Amplitude Modulation
Where audio signals increase and decrease the amplitude of the 'carrier wave'.The carrier wave contains most of the transmitted power, but no signal information.The envelope is the information and so an envelope detector is a sufficient demodulator.

Anaerobe
An organism that lives without oxygen and uses another chemical species as a terminal electron acceptor.Obligate AnaerobesDie when exposed to oxygen.Facultative AnaerobesCan live in both aerobic and anaerobic environments.

Anaerobic
Occurring in the absence of air or oxygen. See also: Aerobic, Anaerobe, Oxygen.

Anaerobic Adhesive
An adhesive which hardens in the absence of air, such adhesives are often used as a thread locking medium. See also: Adhesive.

Analog to Digital Converter
A circuit that converts an analog signal, having a continuously varying amplitude, to a digitally quantized representation using binary output signals. The sampling frequency must be at least twice as high as the highest frequency present in the signal to prevent aliasing errors. See also: Anti-Aliasing Filter, Quantization Error, Sampling Frequenc…

Analogue
Any representation of a physical quantity (e.g. displacement) in terms of a continuous variation of a second physical quantity (e.g. voltage) is known as analogue representation. Most measurement devices (e.g. accelerometers, strain gauges, thermocouples and microphones) generate analogue signals.Quantities in two separate physical systems having c…

Analyte
The sample constituent whose concentration is sought in a chemical analysis.

Anchor
A weighty grappling hook used for holding a ship fast.

Ancillaries
Name given to components such as alternator, power steering pump and air conditioning compressor driven by the engine. See also: Internal Combustion Engine.

AND Gate
Gate that produces a logic 1 when all of its inputs are 1. In all other cases the output is 0.The truth table for the AND Gate is:The AND Gate can be made from NAND Gates:

Anechoic
Without echo. See also: Anechoic Chamber, Reverberant Sound Field.

Anechoic Chamber
Literally meaning 'without echo'. A room whose boundaries effectively absorb all incident sound over the frequency range of interest, thereby creating essentially free field conditions. This allows measurements to be made without them being contaminated with reflected waves from the walls, ceiling and floor.Rooms of this type are used to test audio…

Anelasticity
The property of a solid in which deformation depends on the time rate of change of stress as well as on the stress itself.

Anemometer
A sensor that measures wind speed. Cup, propeller, and sonic anemometers are available.Historical Notes1450 The first anemometer, a disc placed perpendicular to the wind, was invented by the Italian architect Leon Battista Alberti. Robert Hooke, an English physicist, later reinvented the anemometer.1846 John Thomas Romney Robinson, an Irish physici…

Angle grinder
Photograph courtesy of Draper.co.ukA handheld powered tool with a geared head at a right-angle on which is mounted an abrasive disc. See also: Abrasive Wheel.

Angle Iron
An iron or steel structural member that has been cast, rolled, or folded so that its cross section is L-shaped. See also: Iron.

Angle of Attack
The angle at which a wing strikes the air stream.The ability to create lift is dependent on the airflow remaining smooth around the airfoil. At zero degrees angle of attack there is just a small turbulent wake.As the angle of attack is increased the lift increase and the point at which the airflow separates from the upper surface of the wing moves …

Angle of Incidence
Angle between direction of motion of waves and a line perpendicular to the surface the waves are striking. See also: Angle of Reflection.

Angle of Reflection
Angle between direction of motion of waves and a line perpendicular to surface the waves are reflected from. See also: Angle of Incidence, Snells Law.

Angle Plate
A precision holding fixture made of cast iron, steel, or granite. The two principal faces are at right angles and may be slotted for holding the work or clamping to a table.

Angles
The inclination of one line to another. One complete revolution equals 360° (degrees)or 2p radians. See also: Obtuse Angle, Radian, Reflex Angle, Supplementary Angles.

Angular Frequency
The frequency of a steady recurring phenomenum in radians per second. Also known as Circular Frequency.wheref = frequency [Hz]t = period [s]

Angular Momentum
A vector quantity giving the rotational momentum. For an object orbiting apoint, the angular momentum is the product of the linear momentum and theradius of the path. For a solid body, it is the product of the rotationalinertia and the rotational velocity. [kgm²rads^-1]whereI = moment of inertia [kgm²]? = angular v…

Angular Rate Sensor
A sensor that measures rotational velocity around its sensitive axis. See also: Angular Frequency, Angular Velocity.

Angular Velocity
The rate of change of angle turned in radians.where? = angular velocity [rads^-1]? = angle turned [rad]t = time taken [s]

Anharmonic
Of or pertaining to an oscillating system that is not undergoing simple harmonic motion.

Anhydrous
A compound with all water removed, especially water of hydration.Examples:strongly heating copper(II) sulphate pentahydrate (CuSO₄·5H₂O) produces anhydrous copper(II) sulphate (CuSO₄).

Aniline
Used in the manufacture of drugs and plastics. Symbol C₆H₇N Also known as Phenylamine, aminobenzene

Aniline Number
The lowest temperature at which equal parts of aniline and a sample of oil are completely miscible, or the temperature at which the mixture becomes turbid or cloudy. See also: Aniline.

Anion
Ions with a negative charge. Non-metals typically form anions. See also: Cations.

Anisochrony
A sequence of events where the time seperating each pair is not equal. See also: Isochrony.

Anisole
An aromatic smell and used in perfumes. Symbol C₇H₈O Also known as Methyl Phenyl Ether

Anisotropic
Unequal physical properties along different axes.

Annealing
Heating to and holding at a suitable temperature and then cooling at a suitable rate, for such purposes as reducing hardness, improving machinability, facilitating cold working, producing a desired microstructure, orobtaining desired mechanical, physical or other properties.When applied to ferrous alloys, the term 'annealing,' without qualification…

Annealing Twin
A twin formed in a crystal during recrystallization. See also: Annealing.

Annihilation
A process in which a particle meets its corresponding antiparticle and both disappear. The energy appears in some other form, perhaps as a different particle and its antiparticle (and their energy), perhaps as many mesons, perhaps as a single neutral boson. The produced particles may be any combination allowed by conservation of energy and momentum…

Annual Aberration
The component of stellar aberration resulting from the motion of the Earth about the Sun. See also: Aberration, Diurnal Aberration.

Annulus
The region enclosed by two concentric circles. See also: Circle.

Anode
The electrode where electrons are lost (oxidized) in redox reactions.The electrode of an electrolyte cell at which oxidation occurs, electrons flow away from the anode in the external circuit, it is usually at the electrode that corrosion occurs and metal ions enter solution. See also: Anodic Reaction, Cathode, Electrochemistry, Electrodes, Electro…

Anodic Protection
A technique to reduce the corrosion rate of a metal by polarizing it into its passive region, where dissolution rates are low. See also: Cathodic Protection.

Anodic Reaction
Electrode reaction equivalent to a transfer of positive charge from the electronic to the ionic conductor; an anodic reaction is an oxidation process. See also: Anode.

Anodize
To coat a metal with a protective film by electrolysis. See also: Electrolysis.

Anomalous Dispersion
A sudden change in the refractive index of a material for wavelengths in the vicinity of absorption bands in the spectrum of the material.

Anomia
A neurological disorder which causes a marked inability to name otherwise familiar stimuli. See also: Auditory Anomia.

Antenna
A length of wire or similar that radiates (such as a transmitting antenna) or absorbs (such as a radio antenna) radio waves.

Anthocyanin
A family of pigments that give flowers, fruits, and leaves of some plants their red or blue colouring.

Anthracene
White crystalline with a blue fluorescence used in the manufacture of dyes. Symbol C₁₄H₁₀

Anthracite
Type of coal with highest carbon content (86% to 98%) and thus highest heat value .

Anthraquinone
Yellow powder derived from Anthracene and used as a dye. Symbol C₁₄H₈O

Anthropic Principle
Weak anthropic principleThe conditions necessary for the development of intelligent life will be met only in certain regions that are limited in space and time. That is, the region of the Universe in which we live is not necessarily representative of a purely random set of initial conditions; only those favorable to intelligent life would actually …

Anti Lock Brake System
A system that can modulate the brake pressure under hard braking conditions to avoid a brake locking and resultant skidding.

Anti Resonance
In multi degree of freedom systems (e.g. 2 or more spring-masses) or continuous systems (e.g. beams) there will exist frequencies at which a dynamic force applied at a point will not cause any motion of the system at that point. These frequencies are known as anti-resonance's. See also: Antinode, Resonance.

Anti-Aliasing Filter
A device that attenuates signal content outside the desired bandwidth. It precedes the analog-to-digital converter (ADC) in instrumentation designs theoretically allowing only frequencies in the pass-band to be sampled by the ADC.It consists of a low pass filter designed to stop frequencies higher than the ½ the sample rate, in order to minimize al…

Antibaryon
The antiparticle of a baryon, having baryon number -1 and charge, strangeness, and other quantum numbers opposite in sign to those of the baryon. See also: Baryon.

Antichlor
A chemical compound that reacts with chlorine-based bleaches to stop the bleaching. Thiosulfate compounds are antichlors. See also: Chlorine.

Antiferromagnetism
A phenomenon observed in some materials in which complete magnetic moment cancellation occurs as a result of antiparallel coupling of adjacent atoms or ions. The macroscopic solid possesses no net magnetic moment.

Antimatter
Material made from antifermions. We define the fermions that are common in our universe as matter and their antiparticles as antimatter. In the particle theory there is no a priori distinction between matter and antimatter. The asymmetry of the universe between these two classes of particles is a deep puzzle for which we are not yet completely sure…

Antimony
Photograph of stibnite courtesy of MineraliteGenerally found in one of two allotropes and has both metallic and non-metallic properties. From latin 'antimonium' used by Constantinius Africanus (c. 1050) to refer to Stibnite. The main source of this element is Stibnite (Sb₂ S₃), a widely distributed but not very plentiful ore. …

Antimony Hydride
Poisonous gas. Symbol SbH₃ Also known as Stibine

Antinode
Point of maximum displacement. The location may change with time and frequency for complex systems. If dealing with sound waves, this is the point where the sound is the loudest. See also: Anti Resonance.

Antiparticle
A subatomic particle with the same-size properties as those of the particle although some may have the opposite sign. The positron is the antiparticle of the electron.Bosons also have antiparticles except for those that have zero value for all charges, for example a photon or a composite boson made from a quark and its corresponding antiquark. In t…

Antipyretic
A substance that can lessen or prevent fever.

Antiquark
The antiparticle of a quark. See also: Antimatter, Antiparticle, Quark.

Antistatic
Of or pertaining to the ability to either prevent the accumulation of or to enable the dissipation of static charge.

Anvil
A heavy iron or steel block upon which metal is forged or hammered.Photograph courtesy of Draper.co.ukThe fixed jaw on a micrometer against which parts are measured.

Anyon
An elementary particle or particle-like excitation having properties intermediate between those of bosons and fermions. See also: Bosons.

Aperiodic
Vibrations or oscillations with no apparent period. See also: Periodic, Vibration.

Aperture
An opening through which radiation can pass.

Aperture Delay
In an analog-to-digital converter (ADC), the delay in time from when the user requests the analog input to be sampled (that is, when the user puts the ADC's track/hold in 'hold' mode) and the actual time when this occurs. See also: Aperture Jitter.

Aperture Jitter
The amount of variance in the aperture delay. This value is typically much smaller than that of the aperture delay. See also: Aperture Delay.

Apgar Scale
A simple, easy-to-perform, standardized scale that is used to determine the physical status of an infant at birth. The Apgar scale is administered to a newborn at one minute after birth and five minutes after birth.It scores the baby's heart rate, respiration, muscle tone, reflex response, and color. This test quickly alerts medical personnel that …

Apgar, Virginia (1909-1974)
Professor of anesthesiology at the New York Columbia-Presbyterian Medical Center, devised the Apgar Scale in 1953.The Apgar scale is a simple, easy-to-perform, standardized scale that is used to determine the physical status of an infant at birth. The Apgar scale is administered to a newborn at one minute after birth and five minutes after birth.It…

Aphelion
The point in a planet's orbit furthest from the Sun (Helios is Greek for Sun). See also: Perihelion.

API Gravity
An arbitrary scale adopted by the American Petroleum Institute to designate the specific gravity of mineral oils. Diesel fuels range from 18 to 41 API. See also: Cetane Number.

Apocentre
The point on a spacecraft's orbit at which it is furthest away from the body it is orbiting. See also: Orbit.