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