mum phase deviation in the modulating sig-
nal.
modulation property
a property of the
Fourier transform in which the Fourier trans-
form of a modulated signal
c(t)e
jw
o
t
is equal
to
C(w − w
o
), where C(w) is the Fourier
transform of
c(t).
modulation transfer function (MTF)
for
an imaging system the Fourier transform of
the system line spread function. The MTF
describes the spatial frequency resolution of
the system.
modulator
device that varies the ampli-
tude or phase of an electromagnetic wave.
modus ponens
a rule of reasoning which
states that given that two propositions,
A and
A ⇒ B (implication), are true, then it can be
inferred that
B is also true.
modus tollens
a rule of reasoning which
states that if a proposition
B is not true and
given that
A ⇒ B, then it can be inferred that
A is also not true.
Moire pattern
image caused by a combi-
nation of two effects, sampling rate and re-
construction filter shape; they occur in image
signals when two conditions are met. First,
when the sampling frequency is close to the
Nyquist Frequency for the signal (i.e., two
times the highest frequency in the image sig-
nal). Second, the cutoff frequency of the re-
construction filter is located beyond one half
the sampling frequency (e.g., a first order fil-
ter). These two problems result in mirror
images of frequency components around the
sampling frequency causing banding in the
image signal. The Moire effect is seen in
practical applications due to real world prob-
lems of finite filter lengths and errors in sam-
pling rates.
molded case circuit breaker
a low-
voltage air circuit breaker that includes ther-
mal and/or magnetic overcurrent sensing
which directly trips the breaker. The molded
case circuit breaker is nearly always manu-
ally closed, opened, and reset.
molecular beam
a source of molecules
traveling primarily in one direction. In prac-
tice, molecular beams are usually realized by
expansion of an atomic or molecular vapor
into a vacuum through a small aperture. The
resulting expanding cloud of molecules is
usually made nearly unidirectional by a col-
limator that blocks or otherwise removes all
molecules not propagating within a narrow
range of angles.
molecular beam epitaxy (MBE)
a ma-
terial growth technique that uses atomic or
molecular beams in an ultra high vacuum
chamber to grow a variety of II-VI, III-V, and
group IV materials with atomic layer con-
trol. Individual molecules or atoms are ex-
cited from heated sources (effusion cells) and
attach to the substrate in an ordered manner.
High quality growth is achieved when the sur-
face diffusion coefficient is sufficiently high
that the atoms can arrange themselves coher-
ently on the surface.
Used to create material structures for a va-
riety of electronic and optical devices using
quantum wells, heterostructures, and super-
lattices.
molecular transition
coupling of energy
levels in an atom by means of absorption or
emission processes.
molecular vapor
a material composed of
molecules in the vapor phase.
Mollow gain
gain that originates when
a 2-level system is driven by a strong, near
resonant, electromagnetic field.
MOM
See
method of moments
.
moment
a statistic of a random variable.
For example, the first moment is called the
mean. In general, the
nth moment is given
c
2000 by CRC Press LLC