Page 199 - Electrical Engineering Dictionary

end frequency). The band edges are usually Terms such as dBm, dBuV, dBW indicate
defined as the highest and lowest frequencies that the decibel measurement was made rel-
within a contiguous band of interest at which ative to an established standard. A common
the loss equals L Amax , the maximum attenu- power measure reference is 0 dBm, which is
ation loss across the band. defined to be 1 mW (milliwatt, 0.001W). A
common voltage reference is 1 µV (1 micro-
decay a transformation in which an atom, volt).
nucleus, or subatomic particle changes into
two or more objects whose total rest energy decimal from the number system that has
is less than the rest energy of the original base 10 and employs 10 digits.
object.
decimation an operation that removes
decay heat the fraction of the total en- samples with certain indexes from a discrete-
ergy obtained from a nuclear fission reaction time signal and then re-indexes the remaining
which is produced by delayed neutrons and samples. Most frequently, decimation refers
by the secondary decay of fission daughters. to keeping every nth sample of a signal. Also
know as down-sampling.
decay length the average distance a
species of a particle at a given energy travels decision boundary a boundary in feature
before decaying. space which separates regions with different
interpretations or classes, e.g., the bound-
decay time in the absence of any pump or ary separating two adjacent regions charac-
other excitation mechanisms, the time after terizing the handwritten characters ‘E’ and
which the number of atoms in a particular ‘F’. In practice, the regions associated with
state falls to 1/E of its initial value. neighboring classes overlap; consequently
most decision boundaries lead to some erro-
decentralizedcontrol astructureoflarge- neous classifications, so an error criterion is
scale control systems based on system de- used to select the “best” boundary. See also
composition onto interconnected subsystems classifier, Bayesian classifier.
in order to simplify control design. Decen-
tralized control systems are usually designed decision directed the use of previously
in the form of local feedback controllers and detected information bits in an estimator, de-
are chosen to fit information structure con- tector, or adaption algorithm in an adaptive
straints imposed by the decomposition.To filter. Usually improves performance com-
ensure robustness with respect to intercon- pared to non-decision directed counterparts,
nections between subsystems, the local con- but introduces potential problems with error
trollers should be robust and/or coordination propagation (erroneous bit feed back).
should ensure robustness of the overall sys-
tem. See also decomposition. decision level the boundary between
ranges in a scalar quantizer. On one side of
decibel (dB) a unit of measure that de- the decision level, input values are quantized
scribes the ratio between two quantities in to one representative level; on the other side,
terms of a base 10 logarithm. For example, input values are quantized to a different rep-
the ratio between the power level at the in- resentative level.
put and output of an amplifier is called the
power gain and may be expressed in decibels decision mechanism rules and principles
as follows: by which the information available to a given
decision unit (control unit) is processed and
G(dB) = 10 log (P out /P in ) transformed into a decision; typical decision
10

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