Target distance is indicated by the horizontal position of the deflection from one end of the time base. The amplitude of the vertical deflection is a function of the signal intensity.
2. In optics, a specific deviation from perfect imagery, as, for example: spherical aberration, coma, astigmatism, curvature of field, and distortion.
Ablating materials are used on the surfaces of some reentry vehicles to absorb heat by removal of mass, thus blocking the transfer of heat to the rest of the vehicle and maintaining temperatures within design limits. Ablating materials absorb heat by increasing in temperature and changing in chemical or physical state. The heat is carried away from the surface by a loss of mass (liquid or vapor). The departing mass also blocks part of the convective heat transfer to the remaining material in the same manner as transpiration cooling.
2. An aircraft, space vehicle, or the like that aborts.
3. An act or instance of aborting.
2. Complete, as in absolute vacuum.
In theory, no absolute coordinate system can be established because the reference stars are themselves in motion. In practice, such a system can be established to meet the demands of the problem concerned by the selection of appropriate reference stars.
2. Specifically, in loran, the time interval between transmission of a signal from the A-station and transmission of the next signal from the B-station.
1. A measure of the brightness of a star equal to the magnitude the star would have at a distance of 10 parsecs from the observer.
where m is apparent magnitude, and p is the parallax of the star (in seconds of arc). Absolute magnitudes may be visual, photographic, etc., according to the way in which the apparent magnitude was measured. 2. The stellar magnitude any meteor would have if placed in the observer's zenith at a height of 100 kilometers.
2. A manometer that measures absolute pressure.
In high-vacuum technology, pressure is understood to correspond to absolute pressure, not gage pressure, and therefore the term absolute pressure is rarely used.
2. Specifically, a system of electrical units put into effect by international agreement on 1 January 1948.
Prior to 1 January 1948 the international system was in effect; the two systems can be converted by the following relationships:
"Electric units, called "international," for current and resistance had been introduced by the International Electrical Congress held in Chicago in 1893, and the definitions of the international" ampere and the "international" ohm were confirmed by the International Conference of London in 1908.
Although it was already obvious on the occasion of the 8th CGPM (1933) that there was a unanimous desire to replace those "international" units by so-called "absolute" units, the official decision to abolish them was only taken by the 9th GPM (1948), which adopted for the unit of electric current, the ampere," which see.
The previous is an excerpt from WWW version of the National Institute of Standards and Technology: Physics Laboratory's International System of Units (SI).
An absolute vacuum is not obtainable.
Absolute zero may be interpreted as the temperature at which the volume of a perfect gas vanishes or, more generally, as the temperature of the cold source which would render a Carnot cycle 100 percent efficient. The value of absolute zero is now estimated to be - 273.15° Celsius, -459.67° Fahrenheit, 0° Kelvin, and 0° Rankine.
The ratio of the radiant flux absorbed by a body to that incident upon it. Also called absorption factor. Compare absorptivity.
Total absorptance refers to absorptance measured over all wavelengths.
Spectral absorptance refers to absorptance measured at a specified wavelength.
Absorption takes place only after the radiant flux enters a medium and thus acts only on the entering flux not on the incident flux, some of which may be reflected at the surface of the medium. A substance which absorbs energy may also be a medium of refraction, diffraction, or scattering; these processes, however, involve no energy retention or transformation and are to be clearly differentiated from absorption.
2. In general, the taking up or assimilation of one substance by another. See sorption, adsorption.
3. In vacuum technology, gas entering into the interior of a solid.
When the absorbing substance is a polyatomic gas, an absorption band actually is composed of a group of discrete absorption lines which appear to overlap. Each line is associated with a particular mode of vibration or rotation induced in a gas molecule by the incident radiation.
The absorption bands of oxygen and ozone are often referred to in the literature of atmospheric physics.
The important bands for oxygen are: (a) the Hopfield bands, very strong, between about 670 and 1000 angstroms in the ultraviolet; (b) a diffuse system between 1019 and 1300 angstroms; (c) the Schumann-Runge continuum, very strong, between 1350 and 1760 angstroms; (d) the Schumann-Runge bands between 1760 and 1926 angstroms; (e) the Herzberg bands between 2400 and 2600 angstroms; (f) the atmospheric bands between 5380 and 7710 angstroms in the visible spectrum; and (g) a system in the infrared at about 1 micron.
The important bands for ozone are: (a) the Hartley bands between 2000 and 3000 angstroms in the ultraviolet, with a very intense maximum absorption at 2550 angstroms; (b) the Huggins bands, weak absorption between 3200 and 3600 angstroms; (c) the Chappius bands, a weak diffuse system between 4500 and 6500 angstroms in the visible spectrum; and (d) the infrared bands centered at 4.7, 9.6 and 14.1 microns, the latter being the most intense.
(symbol 
)
1. A measure of the amount of normally incident radiant energy absorbed through a unit distance or by a unit mass of absorbing medium. Compare transmission coefficient.
The absorption coefficient is frequently identified as follows:
)1. A measure of the amount of normally incident radiant energy absorbed through a unit distance or by a unit mass of absorbing medium. Compare transmission coefficient.
The absorption coefficient is frequently identified as follows:
where ILx is the flux density of radiation of wavelength L, initially of flux density IL0, after traversing a distance x in some absorbing medium. (Substitute L for lambda.)
2. In acoustics, the ratio of the sound energy absorbed by a surface of a medium (or material) exposed to a sound field or sound radiation to the sound energy incident on the surface. The stated values of this ratio are to hold for an infinite area of the surface. The conditions under which measurements of absorption coefficients are made are to be stated explicitly.
Three types of absorption coefficients associated with three methods of measurement are: chamber absorption coefficient, obtained in a certain reverberation chamber; free-wave absorption coefficient, obtained when a plane, progressive, sound wave is incident on the surface of the medium; sabine absorption coefficient, obtained when the sound is incident from all directions on the sample.
The absorption spectrum is a characteristic of the absorbing medium, just as an emission spectrum is a characteristic of a radiator.
An absorption spectrum formed by a monatomic gas exhibits discrete dark lines, whereas that formed by a polyatomic gas exhibits ordered arrays (bands) of dark lines, which appear to overlap. This type of absorption is ften referred to as line absorption. The spectrum formed by a selectively absorbing liquid or solid is typically continuous in nature (continuous absorption).
) The capacity of a material to absorb incident radiant energy, measured as the absorptance of a specimen of the material thick enough to be completely opaque, and having an optically smooth surface.
2. The act or process of accelerating, or the state of being accelerated. Negative acceleration is called deceleration . Used for boost and G force.
By the International Gravity Formula, centimeters per second squared at sea level at latitude p. See gravity.
The standard value of gravity, or normal gravity, g, is defined as g=980.665 centimeters per second squared, or 32.1741 feet per second squared. This value corresponds closely to the International Gravity Formula value of g at 45° latitude at sea level.
An accelerometer usually uses a concentrated mass (seismic mass) which resists movement because of its inertia. The displacement of the seismic mass relative to its supporting frame or container is used as a measure of acceleration.
) The ratio of the average energy actually transferred between a surface and impinging gas molecules which are scattered by the surface to the average energy which would theoretically by transferred if the impinging molecules reached complete thermal equilibrium with the surface before leaving the surface or where a is the accommodation coefficient, Er is the energy carried away from unit surface area per second by the scattered or re-evaporated molecules, Ei is the energy per unit surface area per second carried toward the surface by the impinging molecules, and Es is the energy per unit surface area per second which would be carried away by the molecules if the molecules reached complete thermal equilibrium with the surface before leaving.
2. In computer technology, a device which stores a number and upon receipt of another number adds it to the number already stored and stores the sum. See counter.
Some acoustics Mach meters measure transit time or velocity of a sound pulse; others measure an angle, as the angle of the Mach cone.
) =speed of sound
Acoustic is used to modify terms that designate an object, or physical characteristics, associated with sound waves; acoustical is used when the term being qualified does not designate explicitly something that has such properties, dimensions, or physical characteristics.
The following terms are examples of those modified by acoustic; impedance, intertance, load (radiation field), output (sound power), energy, wave, medium, signal, conduit, absorptivity, transducer.
The following examples do not have the requisite physical characteristics and therefore take acoustical; society, method, engineer, school, glossary, symbol, problem, measurement, point of view, device.
As illustrated, the generic term is usually modified by acoustical, whereas the specific technical term calls for acoustic.
2. Those qualities of an enclosure that together determine its character with respect to distinct hearing.
2. The process of pointing an antenna or telescope so that it is properly oriented to allow gathering of tracking or telemetry data from a satellite or space probe.
Because of the particularly strong action of ultra violet radiation on photochemical processes, the term has come to be almost synonymous with ultraviolet, as in actinic rays.
Actinometers may be classified, according to the quantities which they measure, in the following manner: (a) pyrheliometer, which measures the intensity of direct solar radiation; (b) pyranometer, which measure global radiation (the combined intensity of direct solar radiation and diffuse sky radiation); and (c) pyrgeometer, which measures the effective terrestrial radiation.
2. = radioactive, as active sample .
3. = fissionable, as active material .
4. Receiving energy from some source other than a signal, as active element .
Adaptation is applied particularly to evolutionary change.
The adaptation luminance has a marked influence on an observer's estimate of the visual range because, along with the visual angle of the object under observation, it determines the observer's threshold contrast. High adaptation luminance tends to produce a high threshold contrast, thus reducing the estimated visual range. This effect of the adaptation luminance is to be distinguished from the influence of background luminance.
2. Any device, appliance or the like used to alter something so as to make it suitable for a use for which it was not originally designed.
2. An expression, usually numerical, identifying an address (sense 1).
2. = adiabatic wall temperature.
3. The final and initial temperature in an adiabatic, Carnot cycle.
Regarding the general distinction (in meteorology) between advection and convection, the former describes the predominantly horizontal, large-scale motions of the atmosphere whereas convection describes the predominantly vertical, locally induced motions.
2. Of or pertaining to the air, atmosphere, or aviation.
The problem of the effect of reentry on the trajectory of a vehicle is a problem in aeroballistics.
The aerodynamic force is proportional to the expression
where p is the fluid density; u is the velocity of the undisturbed stream relative to the body; L is a characteristic linear dimension of the body; and Rn is the Reynolds number raised to the power of n, a constant usually determined experimentally. This form for the aerodynamic force is sometimes called Rayleigh formula. The component of the aerodynamic force parallel to the direction of flow is called the drag.
Aerodynamic trails form off the tips of wings and propellers and other points of maximum pressure decrease. They are relatively rare and of short duration compared to exhaust trails.
The term is used when the context calls for discrimination from space vehicle.
2. (a) The actions and forces resulting from the movement or flow of gaseous fluids against or around bodies, as, the aerodynamics of a wing in supersonic flight . (b) The properties of a body or bodies with respect to these actions or forces, as, the aerodynamics of a turret or of a configuration .
3. The application of the principles of gaseous fluid flows and of their actions against and around bodies to the design and construction of bodies intended to move through such fluids, as a design used in aerodynamics.
2. The disease or condition caused by the formation of gas bubbles (mostly nitrogen) in the body fluids. The disease is characterized principally by neuralgic pains, cramps, and swelling, and sometimes results in death. Also call decompression sickness .
2. As a subdivision of meteorology, the study of the free atmosphere through its vertical extend, as distinguished from studies confined to the layer of the atmosphere adjacent to the earth's surface.
From a functional point of view, it is considered to be that region in which the atmosphere is so tenuous as to have a negligible, or almost negligible, effect on men and aircraft, and in which the physiological requirements of man become increasingly important in the design of aircraft and auxiliary equipment.
1. Of or pertaining to both the earth's atmosphere and space, as in aerospace industries.
2. Earth's envelope of air and space above it; the two considered as a single realm for activity in the flight of air vehicles and in the launching, guidance, and control of ballistic missiles, earth satellites, dirigible space vehicles, and the like.
Aerospace in sense 2 is used primarily by the U.S. Air Force. The term aerospace first appeared in print in the Interim Glossary; Aero-Space Terms (edited by Woodford Agee Heflin) published in February 1958 at the Air University, Maxwell Air Force Base, Alabama.
2. A section or piece of a rocket or spacecraft that enters the atmosphere unprotected behind the nose cone or other body that is protected for entry.
3. The afterpart of a vehicle.
2. The function of an afterburner, a device for augmenting the thrust of a jet engine by burning additional fuel in the uncombined oxygen in the gases from the turbine.
2. The necessary cooling of a reactor core after its shutdown by pumping a liquid or gas through it to carry off the excess heat generated by continuing radioactive decay of fission products within the core.
2. The transient decay of a plasma after the power has been turned off.
The decay time involved is a direct consequence of the charged particle loss mechanisms, such as diffusion and recombination. The magnitude of these quantities is determined by measuring the decay time under controlled conditions.
The percent by volume of those gases found in relatively constant amount in dry air near sea level in very nearly as follows:
.
| ELEMENT | % |
| nitrogen (N2) | 78.084 |
| oxygen (O2) | 20.9476 |
| argon (A) | 0.934 |
| carbon dioxide (CO2) | 0.0314 (variable) |
| neon (Ne) | 0.001818 |
| helium (He) | 0.000524 |
| methane (CH4) | 0.0002 (variable) |
| krypton (Kr) | 0.000114 |
| hydrogen (H2) | 0.00005 |
| nitruous oxide (N2O) | 0.00005 |
| xenon (Xe) | 0.0000087 |
Air breakup is sometimes provided for, as by the firing of a cartridge inside the reentry body, so as to retard the fall of certain pieces and increase the chances of their recovery. See blowoff.
Air light is not be confused with airglow .
An airborne computing system which presents a continuous indication of the aircraft position on the basis of aircraft heading, airspeed, and elapsed time.
Primary cosmic rays slowed down in the atmosphere emit bremsstrahlung photons of high energy. Each of these photons produces secondary electrons which generate more photons and the process continues until the available energy is absorbed.
Because this adjective is pronounced as the noun airspace is, it is subject to misunderstanding. Aerospace is commonly used instead.
Aircraft, in its broadest meaning, includes fixed-wing airplanes, helicopters, gliders, airships, free and captive balloons, ornithopters, flying model aircraft, kites, etc., but since the term carries a strong vehicular suggestion, it is more often applied, or recognized to apply, only to such of these craft as are designed to support or convey a burden in or through the air.
The word airframe, a carryover from aviation usage, remains appropriate for rocket vehicles since a major function of the airframe is performed during flight within the atmosphere. There is disagreement as to whether the nose cone and combustion chambers are included in the term airframe while they are attached to the vehicle.
Airglow is a chemiluminescence due primarily to the emission of the molecules O2 and N2, the radical OH, and the atoms O and Na. Emissions observed in airglow could arise from three-body atom collisions forming molecules, from two-body reactions between atoms and molecules, or from recombination of ions.
Historically, airglow has referred to visual radiation. Some recent studies use airglow to refer to radiation outside the visual range.
Airspace is sometimes particularized by altitude, as the airspace above 20,000 feet.
The Aitken nuclei play an important role in atmospheric electrical processes, for they are the particles which capture (by adsorption or other surface electrical processes) small ions and thereby form large ions. In air containing large numbers of Aitken nuclei, the small ion population is small, the large ion population is large, and the air conductivity is low.
The concept defined above is identical with reflectance. However, albedo is more commonly used in astronomy and meteorology and reflectance in physics.
Albedo is sometimes used to mean the flux of the reflected radiation as, the earth albedo is 0.64 calorie per square centimeter. This usage should be discouraged.
The albedo is to be distinguished from the spectral reflectance which refers to one specific wavelength (monochromatic radiation).
Usage varies somewhat with regard to the exact wavelength interval implied in albedo figures; sometimes just the visible portion of the spectrum is considered, sometimes the totality of wavelengths in the solar spectrum.
Near Earth, however, the magnetic field begins to be dominated by the dipole-like form of the main field generated in the Earth's core, and the combined drift due to both electric and magnetic fields tends to separate ions from electrons, steering the former to the dusk side of earth and the latter to the dawn side. This creates Alfvén layers, regions where those motions fail to satisfy charge neutrality. Charge neutrality is then restored by electrons drawn upwards as the downward region 2 current, and electrons dumped into the ionosphere (plus some ions drawn up) to create the corresponding upward currents.
For a perfectly conducting fluid with a mass density of 1 kilogram per cubic meter in a magnetic field of 10,000 gauss, the Alfvén speed is about 1,000 meters per second while the speed of sound in air is about 300 meters per second.
The dynamics of such waves are analogous to those in a vibrating string, the phase speed C being given by
where mu is the permeability; H is the magnitude of the magnetic field; and rho
is
the fluid density. alga (plural, algae)
The green algae and blue-green algae, for example, provide a possible means of photosynthesis in a closed ecological system, also a source of food.