Page 238 - Electrical Engineering Dictionary

duty cycle (1) the ratio of the turn-on time of a subroutine; this allocation is performed
of a semiconductor switch to the sum of the upon entry to the subroutine.
turn-on and turn-off times;
dynamic beam control a circuit in a
Turn-on / (Turn-on + Turn-off)
camera designed to instantaneously increase
beam current to handle highlights in a scene.
(2) the mode of operation that an elec-
tric machine is classified, in consideration of
dynamic brake the braking operation of
thermal limits, e.g., continuous operation, in-
a machine by extracting electrical energy and
termittent operation.
then dissipating it in a resistor.
Also known as duty ratio.
duty ratio See duty cycle. dynamic braking since AC motors do not
have separate field excitation, dynamic brak-
ing is accomplished by continuing to excite
the motor from the drive. This causes a gen-
DVM See digital voltmeter. erative current to the drives DC intermediate
bus circuit. The dynamic brake resistors are
DWT See discrete wavelet transform. then placed across the DC bus to dissipate the
power returned. The brake resistor is usually
DX-center stands for defect unknown(X)/ switchedbyatransistororotherpowerswitch
complex. Name originally given to de- controlled by the drive.
fects that caused persistent photoconductiv-
ity (PPC) in GaAs. The term is now com-
dynamic channel assignment (DCA) a
monly applied to similar defects in both
technique of assigning or reassigning radio
III-V and II-VI compound semiconductors.
channels in a communications system in or-
The presently accepted interpretation of the
der to respond to current interference or prop-
microscopic nature of the DX-center is a
agation conditions. Such assignment or reas-
large deformation associated with a nega-
signment may be made before or during radio
tively charged substitutional impurity.
transmission. DCA is typically implemented
in a distributed fashion, with mobile termi-
dyadic decomposition wavelet decompo-
nals and/or fixed cell sites taking measure-
sition in which the dilation is a dyadic num- ments to determine local interference levels,
j
ber, i.e., 2 with j being the decomposition
and then applying an algorithm to choose the
level; this corresponds to a octave frequency
best radio channel on which to initiate or re-
band division in the frequency domain.
assign communication.
dyadic Green’s functions Green’s func-
dynamic convergence the process of
tions that relate together vector field quanti-
making the electron beam fall on a specified
ties.
surface during scanning, as in the case of a
dyed resist a photoresist with an added CRT. This process is necessary for all three-
nonphotosensitive chemical that absorbs gun CRTs that do not have in-line video dis-
light at the exposing wavelength. plays or CRTs.
dynamic allocation allocation of memory dynamic linking deferring the determi-
space that is determined during program ex- nation of the association between a symbol
ecution. Dynamic allocation can be used to used in a program module and the object to
designate space on the stack to store objects which it refers until that object must be ac-
whose lifetimes match the execution interval cessed (i.e., during program execution).

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2000 by CRC Press LLC