soft-computing (such as multilayer percep-
trons, radial basis functions networks, and
fuzzy systems) hold this property.
See
also
fuzzy
system
,
multilayer
perceptron
,
radial basis function
network
.
universal fuzzy approximator
a fuzzy
system approximator in a sense that it can
approximate any nonlinear function to any
degree of accuracy on any compact set.
universal fuzzy controller
a fuzzy con-
troller in a sense that it can control any nonlin-
ear plant as long as the plant can be controlled
by a smooth nonlinear control law.
universal source coding
refers to meth-
ods for source coding that do not rely on
explicit knowledge of the source statistics.
One important method for universal lossless
source coding is Ziv–Lempel coding.
universal synchronous/asynchronous re-
ceiver/transmitter (USART)
a logic de-
vice that performs the data link layer func-
tions, such as serializing, deserializing, par-
ity generation and checking, error checking,
and bit stuffing, of a serial transmission pro-
tocol for either synchronous or asynchronous
transfer modes.
universe of discourse
term associated
with a particular variable or groups of vari-
ables, it is the total problem space encom-
passing the smallest to the largest allowable
nonfuzzy value that each variable can take.
unloaded Q
dimensionless ratio of the
average over any period of time (
T =
1/frequency) of the ratio of the maximum en-
ergy stored (Umax) to the power absorbed or
dissipated in a passive component or circuit,
discounting any external effects. An ideal
resistor has an unloaded Q of zero, and ideal
capacitors or inductors have an uloaded Q of
infinity. For most applications, the higher the
unloaded Q the better the part.
unmatched uncertainty
a dynamical sys-
tem model in which the vector function that
models uncertainties in the system does not
satisfy the matching condition as, for exam-
ple, in the system model
˙x = Ax + Bu + h(t, x, u) ,
where the function h may model system un-
certainties such as modeling uncertainties,
input connection uncertainties, or additive
disturbances.
unmodeled dynamics
in control systems
design, it is often assumed that the true pro-
cess is compatible with the model used in pa-
rameter estimation. However, it frequently
happens that the true process is more com-
plex than the estimated model. This is of-
ten referred to as unmodeled dynamics. The
problem is complex, and a careful analysis
is lengthy. If a controller is able to control
processes with unmodeled dynamics and/or
disturbances, we say that the controller is ro-
bust.
unpolarized
if the amplitude of the wave
in plane perpendicular to the direction of
propagation appears to be oriented in all di-
rections with equal probability, the wave is
said to be unpolarized. Unpolarized electro-
magnetic waves are generated by atomic pro-
cesses.
unprivileged mode
one of two CPU
modes, the other being privileged mode.
Sometimes called user mode, this mode pro-
hibits access to certain instructions, data, and
registers.
unsharp masking
an edge enhancement
technique that subtracts a blurred version of
an image from the input image. See also
edge
enhancement
.
unsigned integer
an integer numeric rep-
resentation in which only positive numbers
are represented. For example, a 16-bit un-
signed integer has a range of 0 to 65535.
c
2000 by CRC Press LLC