Page 60 - Electrical Engineering Dictionary

Armstrong is best known as the developer effects of some type of processing. See also
of frequency modulation (FM) radio and in- outlier.
ventor of the superheterodyne receiver. Arm-
strong spent most of his career at Columbia artificial constraint an additional con-
University. During his life, his inventions straint in accordance with the natural con-
made him quite wealthy. The superhetero- straints to specify desired motion or force
dyne receiver was purchased as a way for the application. An artificial constraint occurs
military to detect the spark plug ignitions of along the tangents and normals of the con-
approaching aircraft. Patent fights with Lee straint surface. An artificial force con-
DeForest and the difficulty in promoting FM straint is specified along surface normals,
radio led to bitterness and frustration which and an artificial position constraint along tan-
many felt led to his suicide. gents and hence consistency with the natu-
ral constraints is preserved. See also natural
ARQ See automatic repeat request. constraint.

array several antennas arranged together artificial dielectric a dielectric material
in space and interconnected to produce a de- that has been modified to alter its proper-
sired radiation pattern. ties. Common modifications include micro-
machining to remove material from the sub-
strate under planar patch antenna to improve
array factor in antenna theory, the re-
radiation properties and the fabrication of pe-
sulting radiation pattern of an array when
riodic arrays of holes to realize guiding or
each antenna in the array is replaced by an
photonic bandgap structures.
isotropic radiator.
artificial intelligence the study of com-
array processor an array of processor
puter techniques that emulate aspects of hu-
elements operating in lockstep in response to
man intelligence, such as speech recognition,
a single instruction and performing compu-
logical inference, and ability to reason from
tations on data that are distributed across the
partial information.
processor elements.
artificial neural network a set of nodes
array signal processing signal process-
called neurons and a set of connections be-
ing techniques used for extracting informa-
tween the neurons that is intended to perform
tion based on signals from several (identical)
intellectual operations in a manner not un-
sensors, for example an antenna array con-
like that of the neurons in the human brain.
sisting of several antenna elements.
In particular, artificial neural networks have
been designed and used for performing pat-
arrester discharge current the current
tern recognition operations. See also pattern
in an arrester during a surge.
recognition, perceptron.
arrester discharge voltage the voltage artificial neuron an elementary analog of
in an arrester during a surge. a biological neuron with weighted inputs, an
internal threshold, and a single output. When
ART network See adaptive resonance the activation of the neuron equals or exceeds
theory network. the threshold, the output takes the value +1,
which is an analog of the firing of a biological
artifact an error or aberration in a signal neuron. When the activation is less than the
that is the result of aliasing, a quantization threshold, the output takes on the value 0 (in
error, some form of noise, or the distorting the binary case) or −1 (in the bipolar case)

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