At

At
Astatine is heaviest halogen and radioactive.
at
Abbreviation for Technical Atmosphere.
Atactic
A type of polymer chain configuration wherein side groups are randomly positioned on one side of the polymer backbone or the other.
Aten Asteroids
Have orbits that lie inside the Earth′s orbit.
atm
An abbreviation of atmosphere.
atmo-m
Abbreviation of atmo-metre.
Atmometer
An instrument for measuring the rate at which water evaporates, also called an evaporimeter.
atmo-metre
Unit used in atmospheric physics to compare the "depth" or total volume of atmospheres, or components of atmospheres.
Atmometry
The science of measuring the rate at which water evaporates.
Atmosphere
The gases around a planet or star.
Atmospheric Boundary Layer
The atmospheric layer adjacent to the surface of the Earth that is affected by friction against the surface boundary.
Atmospheric Duct
An almost horizontal layer in the troposphere.
Atmospheric Engine
Also known as the Newcomen engine, this admitted steam into a cylinder which was then condensed by cold water and the piston driven by atmospheric pressure.
Atmospheric Interference
The radiofrequency electromagnetic radiation originating, principally, in the irregular surges of charge in thunderstorm lightning discharges.
Atmospheric Pressure
Atmospheric pressure is the force exerted by the weight of the atmosphere of the Earth at ground level.
Atmospheric Windows
The spectral bands in which the atmosphere least affects the transmission of radiant energy.
Atom
The smallest particle of an element that can exist and still retain the ordinary chemical properties of that element.
Atom Percent
Concentration specification on the basis of the number of moles or atoms of a particular element relative to the total number of moles or atoms of all elements within an alloy.
Atomic Clock
A timekeeping device controlled by the frequency of the natural vibrations of certain atoms.
Atomic Mass Unit
Defined as one twelfth of the mass of the most abundant isotope of carbon (12C)
Atomic Nucleus
A tiny, incredibly dense positively charged mass at the heart of the atom - normally abbreviated Nucleus.
Atomic Number
The atomic number (Z) of an element is the number of protons each atom of that element has in its nucleus.
Atomic Orbital
A wavefunction that describes the behavior of an electron in an atom.
Atomic Packing Factor
The fraction of the volume of a unit cell that is occupied by ′hard sphere′ atoms or ions.
Atomic Particle
One of the particles of which an atom is constituted.
Atomic Radius
One half the distance between nuclei of atoms of the same element, when the atoms are bound by a single covalent bond or are in a metallic crystal.
Atomic Rocket
A projected rocket engine in which the energy for the jetstream is to be generated by atomic fission or fusion.
Atomic Theory
An explanation of chemical properties and processes that assumes that tiny particles called atoms are the ultimate building blocks of matter.
Atomic Time Scale
A time scale based on an atomic definition of the second.
Atomic Unit
A system of non-SI units used in quantum chemistry to simplify calculations and mathematical expressions.
Atomic Vibration
The vibration of an atom about its normal position in a substance.
Atomic weight
The weighted average mass of the atoms in a naturally occurring element.
Atomize
To break up a liquid into extremely fine particles.
Atomus
Latin word used in medieval times to mean "a twinkling of the eye", the smallest amount of time imaginable, defined in a precise way as 1/376 minute.
ATP
Abbreviation of Adenosine Triphosphate.
ATP Synthase
An enzyme complex that forms ATP from ADP and phosphate during oxidative phosphorylation on the inner mitochondrial membrane or the bacterial plasma membrane, and during photophosphorylation in chloroplasts.
ATPase
An enzyme that hydrolyzes ATP to yield ADP and phosphate; usually coupled to some process requiring energy such as the sodium potassium ATPase.
AT-PZEV
Abbreviation for Advanced Technology Partial Zero Emission Vehicles.
ATRAC
A lossy audio coding system based on psychoacoustic principles.
Atrium
In an ancient Roman structure, a central room open to the sky, usually having a pool for the collection of rainwater.
Attached Shock Wave
An oblique or conical shock wave that appears to be in contact with the leading edge of an airfoil or the nose of a body in a supersonic flow field.
Attack
The beginning of a sound; the initial transient of a musical note.
Attenuation
The reduction of a physical quantity.
Attenuation of Sound in Air
The attenuation of sound in air at 20C due to viscous, thermal and rotational loss mechanisms is 1.6E-10fdB/m.
Attenuator
A two port circuit or device that reduces the amplitude of an input signal by a desired amount typically expressed in decibels.
Attic
The part of the entablature above the cornice, serving to hide the roof.
Attitude Angle
The angle between the steady state preload through the bearing centreline, and a line drawn between the bearing centre and the shaft centreline.
Atto
Prefix representing a multiplication of 10-18
Attometre
A distance of 10-18m.
attosecond
A time of 10-18seconds.
Attraction
The force that tends to make two objects approach each other.
Attribute
An identifiable property of an object, set, or event that is subject to being measured.
Atwood′s Machine
A weight-and-pulley system devised to measure the acceleration due to gravity at the Earth′s surface