Electrical Engineering Dictionary - part 110

maximum distance separable (MDS) code

(n, k) linear binary or nonbinary block

code, with minimum distance

min

= n −

k + 1. Except for the trivial repetition codes,
there are no binary MDS codes. Nonbinary
MDS codes such as Reed–Solomon codes do
exist.

maximum effective aperture

in antenna

theory, the ratio of the time-average power
available at the terminals of an antenna due
to power incident in the direction of the main
beam that is polarized for maximum recep-
tion to the time-average power density of the
incident field.

maximum entropy

a procedure that max-

imizes the entropy of a signal process.

maximum entropy inequality

an infor-

mation theoretic inequality, upper bounding
the possible value of entropy for probability
distributions subject to certain moment con-
straints. A common example states that for
any probability density function

f (x), sub-

ject to a power (second moment) constraint,

f (x) ≤ σ

h(f ) ≤

h(2πeσ

) .

See also

differential entropy

maximum entropy restoration

an iter-

ative method of image restoration. At each
iteration, an image is chosen whose Fourier
transform agrees with that of the principal so-
lution, i.e., the model of degradation, while
maximizing the entropy.

maximum excitation limiter

a controller

that is used to limit the maximum amount
of field current, or over-excitation, at a syn-
chronous generator. This excitation limit is
set by rotor winding heating limit.

maximum input power

the maximum in-

cident RF power that will be applied to a com-
ponent or circuit without either damage or
performance degradation, expressed in watts.

The user normally will specify whether it
is damage or degradation that is important.
If performance degradation is, then how the
degradation is manifested should be speci-
fied.

maximum likelihood estimation

to esti-

mate an unknown

x by maximizing the con-

ditional probability of the observations; that
is,

ˆx

= arg

max

p(y|x)

where

y represents an observation. x is

considered unknown; it is not a statistical
quantity.

See also

maximum matching

a defuzzification

scheme for a classification problem in which
a pattern is signed to the class outputed by the
rule that achieve the maximum firing degree.

maximum permissible exposure (MPE)
the limit adopted by a standards-setting body
for exposures of unlimited duration. Gener-
ally, some allowance is made in the standard
for time and/or space averaging of higher ex-
posure conditions.

maximum posterior probability distance

See

maximum a posteriori probability

maximum rated FET gate-to-source volt-
age

the maximum gate-to-source volt-

age that the device is designed to function
without damage due to breakdown, as deter-
mined by the device manufacturer. The ac-
tual breakdown voltage may be much larger
than this voltage, dependent process varia-
tion and manufacturer derating criteria and
margins. This voltage rating is usually in the
−2.0 volt (low noise devices) to −10 volt
(power devices) range.

maximum stable gain (MSG)

the max-

imum gain derived from a transistor, which
is obtained after making a stable condition
by adding some excess loss elements for the
case when a simultaneous matching for input

2000 by CRC Press LLC

and output of the transistor causes an unsta-
ble condition.

maximum stable power gain

figure of

merit specified as the maximum value of
transducer gain for which stability factor

is equal to one. Equivalently, this represents
the maximum value of transducer gain of a
circuit or device when the device is termi-
nated with impedance values, or by using
other methods such as feedback, and so on,
such that

K is equal to one.

maximum transducer power gain

max-

imum value of transducer power gain a cir-
cuit or device exhibits; occurs when the in-
put and output ports of the circuit are ter-
minated with simultaneous conjugate match
conditions. The transducer power gain is de-
fined as the ratio of power delivered to a load
to the power available from the source.

maximum-likelihood

the maximum of

the likelihood function,

p(y|x) or equiva-

lently, the log-likelihood function. Maximum-
likelihood is an optimality criterion that is
used for both detection and estimation.

maximum-likelihood decoding

a scheme

that computes the conditional probability for
all the code words given the received se-
quence and identifies the code word with
maximum conditional probability as the
transmitted word. Viterbi algorithm is the
simplest way to realize maximum-likelihood
decoding.

maxterm

a Boolean sum term in which

each variable is represented in either true or
complement form only once. For example,
x+y

+w+z

is a maxterm for a four variable

function.

Maxwell’s equations

a set of four vector

equations published in 1873 that govern the
generation and time evolution of electromag-
netic fields of arbitrary electric source dis-
tributions. Sometimes called the Maxwell–

Heaviside equations because Heaviside first
wrote them in their familiar vector form.

For fictitious magnetic current density

and charge density

ρ, electric field E, mag-

netic field

H, µ is the permeability and is

the dielectric constant or permittivity.

Maxwell’s equations take on the following

form:

∇ × E =

∂B

∂t

(Faraday’s law of induction)

∇ × H =

∂D

∂t

+ J (Ampere’s law)

∇ · B = 0

∇ · D = q

where

E is electric field strength, D is electric

flux density,

H is magnetic field strength, B

is magnetic flux density,

J is current density

and

q is volume charge density.

Maxwell, James Clerk

(1831–1879)

Born: Edinburgh, Scotland

Maxwell is best known as the greatest

theoretical physicist of the 19th century. It
was Maxwell who discovered, among other
things, that light consisted of waves. He de-
veloped the fundamental equations describ-
ing electromagnetic fields in his work, A Dy-
namical Theory of the Electromagnetic Field,
published in 1864. Maxwell also gave us the
mathematical foundation for the kinetic the-
ory of gases. Maxwell’s life was cut short
by cancer, and thus he was unable to see
his greatest theoretical propositions proven
by experiment.

MBE

See

molecular beam epitaxy

MBP

See

morphotropic phase boundary

McCulloch–Pitts neuron

originally a lin-

ear threshold unit that responded with a bi-
nary output at time

t + 1 to an input applied

at time

t. In current usage, usually a linear

threshold unit.

2000 by CRC Press LLC

MCM

a unit of area used to specify the

cross-sectional area of a wire, equal to 1000
circular mils .

MCM-D

See

deposited multi-chip module

MCM-L

See

laminate multi-chip module

MCP

See

motor circuit protector

MCR

See

master control relay

MCT

See

metal-oxide semiconductor

controlled thyristor

MDA

See

monochrome display adapter

MDR

See

memory data register

MDS code

See

maximum distance

separable code

MDT

See

mobile data terminal

Meachem bridge

a bridge circuit where

one of the arms (the reactance arm) is a se-
ries connection of an inductance, a capaci-
tor, and a resistor, all three other arms are
resistors. The Meachem bridge has a very
steep phase frequency characteristics in the
vicinity of the reactance arm resonance fre-
quency. The steepness increases with higher
Q-factor of the reactance arm and better tun-
ing of the bridge balance at the resonance
frequency. This combination of the bridge
and reactance selectivity properties has se-
cured the main application of the Meachem
bridge as the feedback circuit of high preci-
sion crystal oscillators.

Meachem-bridge oscillator

an oscilla-

tor where the Meachem bridge is used in the
amplifier feedback. This circuit is usually
used in design of high-frequency stability
crystal oscillators where the bridge reactance
branch is substituted by a crystal. Tuning
of the bridge allows to obtain an extremely

steep phase frequency response of the bridge
near the oscillation frequency which coin-
cides with the crystal series-mode frequency.

mean

See

mean value

mean delay

the time interval between

transmission of a pulse through a wideband
communication channel and the instant cor-
responding to the centroid of its power-delay
profile.

mean ergodic theorem

a mathematical

theorem that gives the necessary and/or suf-
ficient conditions for a random process to be
ergodic in mean. Let

x(n) be a wide-sense

stationary random process with autocorrela-
tion sequence

(k). A necessary and suffi-

cient condition for

x(n) to be ergodic in the

mean is

lim

N−>∞

N−1

k=0

(k) = 0.

The sufficient conditions for

x(n) to be er-

godic in the mean are that

(0) < ∞ and

lim

k−>∞

(k) = 0.

mean filter

a filter that takes the mean

of the various input signal components, or in
the case of an image, the mean of all the pixel
intensity values within the neighborhood of
the current pixel.

mean free path

the length of the straight

line segment travelled by a photon between
two successive hits at scattering centers of an
inhomogeneous medium.

mean of a random variable

See

expected

value of a random variable

mean of a stochastic process

the ex-

pected value of a stochastic process at some
point in time.

mean of max method

a method of de-

fuzzification in which the resultant defuzzi-

2000 by CRC Press LLC

fied quantity is obtained from the mean of the
maximum grades of membership.

mean opinion score (MOS)

(1) a subjec-

tive measure of the human-perceived quality
of a particular telecommunication parameter,
e.g., transmitted voice quality. Assessed by
methodical exposure of human test subjects
to stimuli corrupted with a known level of
technical imperfection, and then requesting
the test subjects to rate the stimuli on a sub-
jective quality scale.

(2) a subjective method of quantitatively

assessing the quality of signals. Subjects rate
the quality of presented signals (e.g., images)
on a quality or impairment scale. The mean
of these ratings is calculated as the mean
opinion score.

mean pyramids

the approach of form-

ing hierarchies by averaging over blocks of
pixels (typically 2

× 2), thus eliminating the

difficulties associated with subsampling ap-
proaches.

mean squared error (MSE)

measure of

the difference between a discrete time signal
x

, defined over

[1 . . . n], and a degraded, re-

stored or otherwise processed version of the
signal

ˆx

, defined as

MSE =

i=1

−

ˆx

)

. MSE is sometimes normalized by di-

viding by

i=1

)

mean time to failure (MTTF)

given as

the expected working lifetime for a given
part, in a given environment, as

MTTF

∞

r(t)dt

where

r(t) is a reliability function for the part.

If the failure rate

is constant, then

MTTF

1
λ

mean time to repair (MTTR)

a predic-

tion for the amount of time taken to repair a
given part or system.

mean value

the expected value of a ran-

dom variable or function. The mean value of
a function

f is defined as

= E(f ) =

∞

−∞

fp(f )df

where

p(f ) is the probability density func-

tion of

f . See also

expectation

mean-

q convergence

for a stochastic pro-

cess, the property that the mean of the ab-
solute difference between that process and
some random variable, raised to the

qth

power (

q > 0) approaches zero in time.

mean-square estimation

an estimation

scheme in which the cost function is the
mean-square error.

mean/residual

vector

quantization

(MRVQ)

an image coding technique

where a prediction is made of the original im-
age based on a limited set of data, and then a
residual image is formed by taking the differ-
ence between the prediction and the original
image. Prediction data are encoded using a
scalar quantizer and the residual image is en-
coded using a vector quantizer.

mean/residual VQ

See

mean/residual

vector quantization

measurement system

the sum of all stim-

ulus and response instrumentation, device
under test, interconnect, environmental vari-
ables, and the interaction among all the ele-
ments.

mechanical degree

the spatial angle of the

stator of a machine, expressed in radians or
degrees. Mechanical degree also represents
one revolution of the rotor (360

◦

mechanical loss