logic gate
a basic building block for logic
systems that controls the flow of pulses.
logic level
the high or low value of voltage
variable that is assigned to be a 1 or 0 state.
logical operation
the machine-level in-
struction that performs Boolean operations
such as AND, OR, and COMPLEMENT.
logical register
See
virtual register
.
logical shift
a shift in which all bits of
the register are shifted. See also
arithmetic
shift
.
long code
in a spread-spectrum system,
a (periodic) spreading code (spreading se-
quence) with a period (substantially) longer
than a bit duration. See also
short code
.
long duration
See
voltage variation
.
long integer
an integer that has double
the number of bits as a standard integer on
a given machine. Some modern machines
define long integers and regular integers to
be the same size.
long-term stability
a measure of a power
system’s long-term response to a disturbance
after all post-disturbance transient oscilla-
tions have been damped out, often associated
with boiler controls, power plant and trans-
mission system protection, and other long-
period factors.
longitudinal excitation
laser pumping
process in which the pump power is intro-
duced into the amplifying medium in a direc-
tion parallel to the direction of propagation of
the resulting laser radiation.
longitudinal mode
term (somewhat mis-
leading) used in referring to the longitudinal
structure or index of the mode of a laser os-
cillator.
longitudinal modelocking
forcing the
longitudinal modes of a laser oscillator to be
equally spaced in frequency and have a fixed
phase relationship; useful for obtaining very
short and intense pulsations.
longitudinal phase velocity
phase veloc-
ity of microwave propagation in the axial di-
rection of a slow-wave structure of traveling
wave tube.
longitudinal redundancy check
an error
checking character written at the end of each
block of information on a track of magnetic
tape. The character is calculated by counting
the number of one on a track and adding ei-
ther an additional one or zero in the character
so that the total number of ones in the block
is even.
longitudinal section
electric and mag-
netic modes (LSE, LSM) are alternative
choices for the electromagnetic potentials.
For a waveguiding structure, the most com-
mon choices are potentials directed in the
propagation direction (i.e., TE and TM
modes). Sometimes, especially when lay-
ered dielectric are present, it is more con-
venient to consider the LSE, LSM potential,
perpendicular to the longitudinal section.
look-ahead carry
the concept (frequently
used for adders) of breaking up a serial com-
putation in which a carry may be propa-
gated along the entire computation into sev-
eral parts, and trying to anticipate what the
carry will be, to be able to do the computa-
tion in parallel and not completely in series.
look-up table model
a model in which
measured data is stored in a data base, allow-
ing the user to access the data and interpo-
late or extrapolate performance based on that
data. S-parameter data is an example that is
encountered frequently in RF and microwave
design. Sophisticated look-up tables may re-
duce the data by polynomial curve fitting and
retaining only the coefficients. Look-up table
c
2000 by CRC Press LLC