Page 29 - Electrical Engineering Dictionary

dump. This is generally done to prevent in- absolute sensitivity denoted S(y, x),is
jury to some personnel or damage to acceler- simply the partial derivative of y with respect
ator components. to x, i.e., S(y, x) = ∂y/∂x, and is used to
establish the relationships between absolute
ABR See available bit rate. changes. See sensitivity, sensitivity measure,
relative sensitivity, semi-relative sensitivity.
absolute address an address within an
instructionthatdirectlyindicatesalocationin absolute stability occurs when the net-
the program’s address space. Compare with work function H(s) has only left half-plane
relative addressing. poles.

absolute addressing an addressing mode absorber generic term used to describe
where the address of the instruction operand material used to absorb electromagnetic en-
in memory is a part of the instruction so that ergy. Generally made of polyurethane
no calculation of an effective address by the foam and impregnated with carbon (and fire-
CPU is necessary. retardant salts), it is most frequently used to
For example, in the Motorola M68000 ar- line the walls, floors and ceilings of anechoic
chitectureinstructionADD5000,D1, a16-bit chambers to reduce or eliminate reflections
word operand, stored in memory at the word from these surfaces.
address 5000, is added to the lower word in
register D1. The address “5000” is an exam- absorbing boundary condition (ABC) a
ple of using the absolute addressing mode. fictitious boundary introduced in differential
See also addressing mode. equation methods to truncate the computa-
tional space at a finite distance without, in
absolute encoder an optical device principle, creating any reflections.
mounted to the shaft of a motor consisting
of a disc with a pattern and light sources and absorption (1) process that dissipates en-
detectors. The combination of light detectors ergy and causes a decrease in the amplitude
receiving light depends on the position of the and intensity of a propagating wave between
rotor and the pattern employed (typically the an input and output reference plane.
Gray code). Thus, absolute position infor- (2) reduction in the number of photons of a
mation is obtained. The higher the resolution specific wavelength or energy incident upon
required, the larger the number of detectors a material. Energy transferred to the material
needed. See also encoder. may result in a change in the electronic struc-
ture, or in the relative movement of atoms in
absolute moment The pth order absolute the material (vibration or rotation).
moment µ p of a random variable X is the (3) process by which atoms or molecules
expectation of the absolute value of X raised stick to a surface. If a bond is formed, it is
to the pth power: termed chemisorption, while the normal case
isphysisorption. Theabsorptionprocesspro-
p
µ p = E[|X|] . ceeds due to, and is supported by, the fact that
this is a lower energy state.
See also central moment, central absolute
moment. See also expectation. absorption coefficient (1) inapassive de-
vice, the negative ratio of the power absorbed
absolute pressure units to measure gas (p absorbed = p in −p out ) ratioed to the power in
pressure in a vacuum chamber with zero be- (p in = p incident − p reflected ) per unit length (l),
ing a perfect vacuum. Normally referred to usually expressed in units of 1/wavelength or
as psia (pounds per square inch absolute). 1/meter.

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2000 by CRC Press LLC