Page 223 - Electrical Engineering Dictionary

(2) x(t) must have a finite number of max- disconnect switch a manually operated
ima and minima during a period, and (3) x(t) switching device used to disconnect circuit
must have a finite number of (finite) discon- conductors and their associated load(s) their
tinuities in any finite interval of time. source of electrical power.

discontinuity effect an appropriate equiv-
dirty bit a status bit used to indicate if a
alent circuit model for discontinuities that
block (e.g., cache block, page, etc.) at some
have a tendency to disturb the electric and
level of the memory hierarchy has been mod-
magnetic fields in their vicinity.
ified (written) since it was first loaded in.
When the block is to be replaced with an-
discontinuity manifold See sliding
other block, the dirty bit is first checked to
surface.
see whether the block has been modified. If
it has, the block is written back to the next
discontinuous control the control law
lower level. Otherwise, the block is not writ-
that is allowed to vary discontinuously to ac-
ten back.
count for sudden switching. An example of
a discontinuous controller is
dirty page a page in memory that has been
altered since last loaded into main memory. u =−Usign(s(e)) ,
See also dirty bit.
where e is a control error and s is a function
of e, where
disable action that renders a device inca-
pable of performing its function; the opposite −1if s< 0
of enable. sign(s) = 1if s> 0.

disagreement of interests situation in
discrete cosine transform (DCT) a popu-
which there are several decision units with
lar format for video compression. The spatial
conflicting goals. Compare with consistency
signal is expanded in a cosine series, where
of interests.
the higher frequencies represent increased
video resolution.
disassembler a computer program that
The forward 2-D DCT of an n × n block
can take an executable image and convert it
is defined as
back into assembly code.
n−1 n−1
4C(u)C(v) X X
F(u, v) = f(j, k)
disc See magnetic disk. Also spelled n 2
“disk.” j=0 k=0

(2j + 1)uπ (2k + 1)vπ
cos cos
DISC Cerenkov counter stands for dif- 2n 2n
ferentialisochronousself-collimatingCerenkov
and the inverse is defined as
counter. This device is used to identify parti-
cles over a wide range of masses and can also n−1 n−1
X X
be used to give an independent calibration of f(j, k) = C(u)C(v)F(u, v)
the average momentum of a beam line. j=0 k=0

(2j + 1)uπ (2k + 1)vπ
cos cos
disco contraction of "distribution com- 2n 2n
pany," a firm which owns the electric distri- 1
bution network in a service area but neither where C(w) = √ for w = 0 and 1 for
2
generates nor transmits electric power. w = 1, 2,...,n − 1.
c
2000 by CRC Press LLC