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FOSDIC • fps system of units 297
FOSDIC Acronym for film optical scanning devices
for input to computer.
Foster-Seeley discriminator A discriminator circuit
in which the diodes are operated from a
single-tuned, center-tapped secondary of the input
transformer. The center tap is also capacitively
coupled to the top of the transformer’s primary
coil. Compare TRAVIS DISCRIMINATOR.
From
limiter
C1
E p
B+
T1
C2
E1
E2
C3
R2
A
+
−
R3
Foster-Seeley discriminator
Audio
output
C4
Foucault currents See EDDY CURRENTS.
four-address instruction A computer instruction
in which the address is comprised of four addresses:
two for operands, one for the result of
the operation, and one for the upcoming instruction.
four-channel sound system Also called quadraphonic
sound system. A high-fidelity, stereophonic
sound reproduction system, in which
there are four channels, rather than the usual
two. The channels are generally designated left
front, left rear, right front, and right rear. The
four-channel system is an enhancement of twochannel
stereo.
four-dimensional continuum 1. In relativistic
theory, the space-time continuum. There are
three spatial dimensions and one time dimension.
A point in the continuum can be uniquely
defined by three space coordinates and one time
coordinate. 2. Any continuum that requires four
and only four coordinates to uniquely determine
the position of a point.
Fourier analysis Use of the FOURIER SERIES to
evaluate the components of a complex wave, or to
define a complex wave in terms of its components.
Fourier series An infinite mathematical series that
shows any periodic function to be a combination
of sine terms and cosine terms. Any complex
wave (e.g., a square wave) consists of fundamental
and harmonic sine-wave components. In simplified
form, the series is:
f(x) = A 0 /2 + A 1 cos x + B 1 sin x + A 2 cos 2x + B 2
sin 2x + A 3 cos 3x + B 3 sin 3x + . . .
In general, the more terms to which the series is
calculated, the better the approximation of a
complex waveform.
C5
four-layer diode A dual-terminal npnp device that
is usable as a bistable switch, sawtooth or pulse
generator, memory device, etc.
four-layer transistor A transistor in which the
wafer or block has four processed regions; however,
the device might have only three terminals.
Some examples are the silicon-controlled rectifier,
silicon-controlled switch, and thyristor.
four-level laser A laser identical to the three-level
laser, except for the addition of one excited state.
four-phase system A two-phase system in which
the center taps of the coils are interconnected.
Also called QUARTER-PHASE SYSTEM.
four-terminal network A network having two input
terminals and two output terminals. One input
terminal can be internally connected to one
output terminal (as when a common ground is
present), but this is not mandatory.
four-space 1. A mathematical space in which four
coordinates (w,x,y,z) are necessary to uniquely
define a point. 2. Three-dimensional space with
the addition of time as a fourth dimension; coordinates
are, for example, (x,y,z) for space and t for
time.
four-space coordinates 1. A system of coordinates
for uniquely determining points in four-space.
Such a system can be Euclidean or non-
Euclidean, as with space of any number of
dimensions. 2. The set of numbers that defines a
particular point uniquely in four-space; for example,
P = (3,–15,0,–7).
four-sphere The set of all points equidistant from a
given point P in four-space. Formula is w 2 + x 2 +
y 2 + z 2 = r 2 , where r is the radius and the coordinates
are (w,x,y,z) in the Euclidean, Cartesian system.
four-track recording A tape recording in which
four channels are recorded in two adjacent tracks
on the tape. Usually, tracks number 1 and 3 are
in the forward direction, and tracks number 2
and 4 are in the reverse direction.
four-track tape A magnetic tape with four parallel
sound paths.
four-wire wye system A three-phase system in
which three wires supply the respective phases, a
fourth being the neutral conductor.
F p Symbol for POWER-LOSS FACTOR.
fp Abbreviation of FREEZING POINT.
FPC Abbreviation of Federal Power Commission.
FPI Abbreviation of FUEL-PRESSURE INDICATOR.
FPIS Abbreviation of forward propagation by ionospheric
scatter. See FORWARD SCATTER.
fpm Abbreviation of feet per minute.
fps 1. Abbreviation of feet per second. 2. Abbreviation
of frames per second. 3. Abbreviation of footpound-second
(fps), a chiefly British system of
units.
fps system of units The British system of units of
measurement that uses the foot for length, the
pound for mass, and the second for time. Compare
CENTIMETER-GRAM-SECOND and INTER-
NATIONAL SYSTEM OF UNITS.