Page 57 - Electrical Engineering Dictionary

apparent mean thermal conductivity ceiver. A library of patterns is maintained for
the effective thermal conductivity of an as- continuous checking. See also exact coding.
semblage of material (Pearlite, super insula-
tion) between specified temperatures.
approximate reasoning an inference
procedure used to derive conclusions from
apparent power (1) in an AC system,
a set of fuzzy if-then rules and some con-
the product of voltage, E and current, I. Ap-
ditions (facts). The most used approximate
parent power (or total power) is composed of
reasoning methods are based on the general-
two mutually independent components — an
ized modus ponens. See also fuzzy IF-THEN
active component (real power), and a reac-
rule, generalized modus ponens, linguistic
tive component (imaginary power). Appar-
variable.
ent power is denoted by S, and has the unit
of voltamperes.
(2) the scalar product of the voltage and approximately controllable system
current delivered to the load. It can also be an infinite-dimensional stationary linear dy-
expressed as the vector S = P + jQ, where namical system where the attainable set K ∞
P = real power and Q = reactive power. is dense in the infinite-dimensional state
space X. The set is said to be approximately
application-specific integrated circuit controllable in [0,T ] if the attainable set
(ASIC) an integrated circuit designed for K(0,T ) is dense in the infinite-dimensional
one particular application. state space X.

Approximate controllability in [0,T ] al-
appropriate technology the technology
ways implies approximate controllability.
that will accomplish a task adequately given
The converse statement is not always true.
the resources available. Adequacy can be
verified by determining that increasing the
technological content of the solution results Ar+ laser laser in which the active
in diminishing gains or increasing costs. medium consists of singly ionized argon
atoms. Ar+ lasers have several wavelengths
approximate coding a process, defined in the visible portion of the spectrum.
with respect to exact coding, that deals with
irreversible and information-lossy process-
Arago, Dominique Francois (1786–
ingoftwo-levelpicturestoimprovecompres-
1853) Born: Estagel, France
sion ratio with significant degradation of pic-
ture quality. Exact coding schemes depend Arago is best known for the breadth and
on the ability to predict the color of a pixel the volume of his contribution to the study
or the progression of a contour from line to of light and for his work with Ampere on the
line. Irreversible processing techniques try to development of electrodynamics. Arago dis-
reduce prediction errors by maintaining the covered that iron could be magnetized by the
continuity of the contours from line to line. passage of current through a wire and, the
With predictive coding the number of pix- phenomenon of magnetic rotation. It was
els can be changed to reduce those having left to Michael Faraday to properly explain
nonzero prediction error. With block coding this phenomenon. Arago spent a significant
the compression efficiency can be improved amount of time involved in politics and suc-
by increasing the probability of occurrence ceeded Jean Fourier as the permanent secre-
of the all zero block. The third approximate tary to The Academy of Sciences in 1830. It
block coding scheme is pattern matching. In has been suggested that Arago’s enthusiasm
this scheme the identification codes of the and work ethic were an inspiration to many
repeated patterns are transmitted to the re- contemporary scientists.

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2000 by CRC Press LLC