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Electrical Engineering Dictionary - part 148

reference white level

picture signal level

corresponding to a specified maximum limit
for white peaks.

reflectance

the physical property of mat-

ter to reflect light, defined (punctually) as the
ratio between the intensity

I (x) of a point x

of an image and the irradiance

L(x) in the

same point.

reflected power

power in the reflected

part of an electromagnetic wave.

reflected wave

the result that ensues when

a high-speed electromagnetic wave reaches
the end of a transmission line, when the line
is not terminated with an impedance match-
ing the surge impedance of the line. When a
surge reaches an open circuited line terminal,
the reflected voltage wave equals the incident
voltage wave, resulting in a doubling of the
level of the voltage surge at that point.

reflection

in electromagnetic wave propa-

gation, the change in direction of propagation
of a plane wave due to the wave being inci-
dent on the surface of a material. Typically,
the effect is greater in the case of a material
that has a high electrical conductivity.

reflection coefficient

(1) the ratio of the

reflected field to the incident field at a mate-
rial interface.

(2) another way of expressing the impe-

dance. The reflection coefficient is defined
as how much signal energy would be re-
flected at a given frequency. Like impedance,
the reflection coefficient will vary with fre-
quency if inductors or capacitors are in the
circuit. The reflection coefficient is always
defined with respect to a reference or charac-
teristic impedance (

= (Z − Z

)/(Z + Z

)).

For example, the characteristic impedance
of one typical TV transmission line is 75
ohms, whereas another type of TV trans-
mission line has a characteristic impedance
of 300 ohms. Hooking up a 75-ohm trans-
mission line to a 300-ohm transmission line
will result in a reflection coefficient of value

(300 − 75)/(300 + 75) = 0.6, which means
that 60% of the energy received from the an-
tenna.

reflection grating

a diffraction grating

that operates in reflection, i.e., the diffracted
light is obtained by reflecting off the grating.

reflective notching

an unwanted notching

or feature size change in a photoresist pattern
caused by the reflection of light off nearby
topographic patterns on the wafer.

reflectivity

a property that describes the

reflected energy as a function of the incident
energy of an EM wave and a material body.
The property may be quantified in terms of
the magnitude of the reflection coefficient or
the ratio of the incident to the reflected field.

reflectometer

instrument that measures

reflected power.

reflector antenna

an antenna comprised

of one or more large reflecting surfaces used
to focus intercepted power around a small
region where a primary feed antenna is then
used to input the power to the receiver elec-
tronics. Also used to transmit power in nar-
row angular sectors.

reflex klystron

a high-power microwave

tube oscillator.

refraction

the process undertaken by

an electromagnetic wave wherein the wave
changes direction of propagation as it is in-
cident on the edge of a material. The wave
undergoes a “bending” action, sometimes re-
ferred to as knife edge refraction, and the
“bending” angle is less than 90 degrees. Re-
fraction may also occur as a wave propagates
through a media such as the atmosphere.

refractive index

a parameter of a medium

equal to the ratio of the velocity of propaga-
tion in free space to the velocity of propaga-
tion in the medium. It is numerically equal to
the square root of the product of the relative

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permittivity and relative permeability of the
medium. See also

index of refraction

refractivity

the refractive index minus 1.

refractory period

a period of time af-

ter the initiation of an action during which
further excitation is impossible (absolute re-
fractory period) or requires a greater stimulus
(relative refractory period).

refresh

refers to the requirement that dy-

namic RAM chips must have their contents
periodically refreshed or restored. Without a
periodic refresh, the chip loses its contents.
Typical refresh times are in the 5–10 millisec-
ond range. See also

memory refresh

refresh cycle

(1) a periodically repeated

procedure that reads and then writes back the
contents of a dynamic memory device. With-
out this procedure, the contents of dynamic
memories will eventually vanish.

(2) the period of time taken to “refresh” a

portion of a dynamic RAM chip’s memory.
See also

refresh

refresh period

the time between the be-

ginnings of two consecutive refresh cycles
for dynamic random access memory devices.

regeneration

the process of returning en-

ergy back into a system during a portion of
the machine’s operating cycle.

regeneration loop

a water purification

system used to maintain proper conditions of
the cooling liquid for a power vacuum tube.

regenerative braking

a method for ex-

tracting kinetic energy from the load, con-
verting it back to electricity, and returning it
to the supply. Used widely in electric train
drives and electric vehicles.

region growing

the grouping of pixels

or small regions in an image into larger re-
gions.

Region growing is one approach

to image segmentation. See also

region of absolute convergence

the set

of complex numbers

s for which the mag-

nitude of the Laplace transform integral is
finite. The region can be expressed as

< Re(s) < σ

−

where

and

−

denote real parameters that

are related to the causal and anticausal com-
ponents, respectively, of the signal whose
Laplace transform is being sought.

Re(s)

represents the real part of

region of asymptotic stability

See

region

of attraction

region of attraction

the region around an

equilibrium state of a system of differential
or difference equations such that the trajec-
tories originating at the points in the region
converge to the equilibrium state. Trajecto-
ries starting outside the region of attraction of
the given equilibrium state may “run away”
from that equilibrium state.

region of convergence (ROC)

(1) an area

on a display device where the image dis-
played meets an accepted criteria for raster
coordinate deviation. See

region of absolute

convergence

(2) the set of complex numbers

s = a +

jb for which the magnitude of the Laplace
transform integral is finite. The region can
be expressed as:

−

< Real(s) < σ

where

−

and

denote real parameters that

are related to the causal and anticausal com-
ponents, respectively, for the signal whose
Laplace transform is being sought.

(3) the set of complex numbers

z = e

for which the magnitude of the

z-transform

sum is finite. The region can be expressed
as:

−

< |z| < R

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where

−

and

denote real parameters that

are related to the causal and anticausal com-
ponents, respectively, for the signal whose

transform is being sought.

region of interest (ROI)

a restricted set

of image pixels upon which image process-
ing operations are performed. Such a set of
pixels might be those representing an object
that is to be analysed or inspected.

region of support

the region of variable

or variables where the function has non-zero
value.

register

a circuit formed from identical

flip-flops or latches and capable of storing
several bits of data.

register alias table

See

virtual register

register direct addressing

an instruction

addressing method in which the memory ad-
dress of the data to be accessed or stored is
found in a general purpose register.

register file

a collection of CPU registers

addressable by number.

register indirect addressing

an instruc-

tion addressing method in which the register
field contains a pointer to a memory location
that contains the memory address of the data
to be accessed or stored.

register renaming

dynamically allocat-

ing a location in a special register file for an
instance of a destination register appearing in
an instruction prior to its execution. Used to
remove antidependencies and output depen-
dencies. See also

reorder buffer

register transfer notation

a mathemat-

ical notation to show the movement of data
from one register to another register by using
a backward arrow. Notation used to describe
elementary operations that take place during
the execution of a machine instruction.

register window

in the SPARC architec-

ture, a set or window of registers selected out
of a larger group.

registration

the process of aligning mul-

tiple images obtained from different modali-
ties, at different timepoints, or with different
image acquisition parameters. See

fusion

regression

the methods that use backward

prediction error as input to produce an esti-
mation of a desired signal. Quantitatively,
the regression of

y on X, denoted by r(y), is

defined as the first conditional moment, i.e.,

r(y) = E(X|y).

regular controllability

a dynamical sys-

tem is said to be regularly controllable in time
interval

, t

] if every dynamical system of

the form

(t) = Ax(t)x(t) + b

(t)

j = 1, 2, . . . , m

is controllable where

is the

jth column

of the matrix

B and u

(t) is the jth scalar

admissible control.

regular cue

any regular recurring

point/element of a signal that can be used to
signal the start of a new signal sequence; e.g.,
the leading edge of a 60-Hz square wave is a
regular cue.

regular form

a particular form of the

state space description of a dynamical sys-
tem.

This form is obtained by a suitable

transformation of the system state. The reg-
ular form is useful in control design.

regularization

a procedure to add a con-

straint term in the optimization process that
has a stabilizing effect on the solution.

regulation

the change in voltage from no-

load to full-load expressed as a percentage of
full-load voltage.

2000 by CRC Press LLC

regulator

a controller designed to main-

tain the state of the controlled variable at
a constant value, despite fluctuations of the
load.

reinforcement learning

learning on the

basis of a signal that tells the learning system
whether its actions in response to an input (or
series of inputs) are good or bad. The signal
is usually a scalar, indicating how good or
bad the actions are, but may be binary.

rejection criteria

criteria such as poor

surface texture, existence of scratch marks,
and out-of-tolerance distance measures, which
constitute reasonable grounds for rejecting a
product from a product line.

relational model

a logical data struc-

ture based on a set of tables having common
keys that allows the relationship between data
items to be defined without considering the
physical database organization.

relative addressing

an addressing mech-

anism for machine instructions in which the
address of the target location is given by the
contents of a specific register and an offset
held as a constant in the instruction added
together. See also

PC-relative addressing

index register

base address

relative-address coding

in facsimile cod-

ing, represents the transition between levels
on a particular scan line relative to transi-
tions on the preceding scan line. A relative-
address coding system has a pass mode code-
word for indicating where a pair of transi-
tions on the previous line does not have cor-
responding transitions on the current line and
a runlength coding mode applied when there
is no nearby suitable transition on the previ-
ous line. CCITT Group IV facsimile uses a
form of relative-address coding.

relative controllability

a dynamical sys-

tem with delays in which for a given time
interval

[0, t

] if for any initial condition

(x(0), x

) and any final vector x

∈ R

there

exists an admissible control

u(t), t ∈ [0, t

such that the corresponding trajectory satis-
fies the condition

x (t

, x(0), x

, u) = x

relative entropy

information theoretic

quantity representing the “distance” between
two probability distribution functions. Also
known as the Kullback–Liebler distance. For
two probability mass functions

p(x) and

q(x), the relative entropy D(p||q) is given
by

D(p||q) =

p(x) log

p(x)

q(x)

This quantity is only a pseudo-distance, as
D(p||q) 6= D(q||p).

relative intensity noise

noise resulting

from undesirable fluctuations of the optical
power detected in an optical communication
system.

relative permeability

the complex per-

meability of a material divided by the per-
meability of free space:

= µ/µ

relative permittivity

the complex permit-

tivity of a material divided by the permittivity
of free space:

= /

relative refractive index difference

the

ratio

2
1

− n

2
2

)/2n

2
1

≈ (n

− n

)/n

where

> n

and

are refractive indices.

relative sensitivity

denoted S

(y, x) and

defined as follows:

(y, x) =

∂y
∂x

x
y

∂y/y
∂x/x

∂ln y
∂ln x

It is usually used to establish the approximate
relationship between the relative changes
δy = 1y/y and δx = 1x/x. Here 1y and

1x are absolute changes. If these relative
changes are small, one writes that

δy ≈

δx

2000 by CRC Press LLC

Content .. 146 147 148 149 ..