18WuD2x

270 expandable gate • exponential horn
expandable gate In digital logic, a gate that can be
provided with an unlimited number of input lines
by electrical interconnection with other gates.
expanded memory In personal computer systems,
memory beyond the basic 640 kilobytes (640 kb),
up to one megabyte (1 MB). This memory resides
in integrated circuits (ICs) in the computer, and is
normally volatile (i.e., it is not retained when
power is removed). Compare EXTENDED MEM-
ORY.
expanded-scale meter A meter having a scale designed
to display a narrow range of values. Such
a meter used for monitoring the 117-V power line
might have a scale reading 100 to 140 V, instead
of a conventional scale beginning at zero.
expanded sweep 1. In an oscilloscope, speeding
up the deflection of the beam during a selected
portion of the trace. 2. The circuit for the action
described in 1.
expander A circuit for increasing the dynamic
range over which a signal or quantity can vary. A
typical example is the volume expander, a device
that greatly increases the amplitude of strong signals
while weakening, or having no effect on, signals
of low amplitude.
expansion 1. In communications, the process of
increasing the bandwidth of a signal, restoring it
to normal bandwidth after it has been compressed.
2. In communications, a process in
which stronger components are amplified more
than weak ones, restoring a signal to its normal
dynamic range after it has been compressed.
3. In computer operations, the restoration of a file
to full or normal size after it has been compressed.
4. The widening of a meter scale. 5. The widening
or magnification of an oscilloscope trace. Compare
COMPRESS.
expansion chamber A cloud chamber for viewing
the paths of radioactive particles. It consists of a
closed glass cylinder containing humid air and a
piston. An electrostatic field is applied through
the cylinder, the piston is pulled quickly, and the
volume of the chamber expands. The temperature
inside falls below the dew point, a cloud is
formed, and droplets of water condense on ions,
making their paths visible for observation or photography
through the cylinder walls.
expansion ratio In communications, the inverse of
COMPRESSION RATIO.
expansion time For an expansion chamber, the
interval during which expansion occurs. The
interval is kept short to ensure that the temperature
will drop low enough for vapor condensation,
and to minimize the possibility of
continuing gas motion distorting the track of a
particle.
expectation In probability theory, the middle
value (average or mean) of a random variable.
expendable A component or system that, for economy,
is best discarded instead of repaired when it
fails. Also called DISPOSABLE COMPONENT.
experiment One or a series of carefully planned
tests carried out under controlled conditions to
obtain data or to check performance.
experimental chassis See ELECTRONIC CHASSIS.
experimental model A prototype of an electronic
circuit or device, produced solely for operational
tests or as a model against which theory and design
can be checked.
experimental service A special, nonamateur radio
service intended for on-the-air testing of new
methods and equipment.
experimental station A station specially licensed
to operate on specific frequencies in the experimental
service.
expert system Also called rule-based system. A
form of artificial intelligence (AI) that allows a
computer or smart robot to act as a highly talented
specialist in a specific field. An example is
the use of a computer to help a physician diagnose
a complex disease. A smart robot might be
used as a surgical assistant.
exploring coil A pickup coil for sensing a signal or
magnetic field. Sometimes called a sniffer.
exploring electrode 1. A sampling electrode sealed
in a discharge tube for measuring ionization at
the point of insertion. 2. Broadly, a test probe.
explosion-proof device A device that is housed
and operated so that its sparking, heating, or
production of radiant energy will not cause materials
in the environment to explode.
exponent A number written as a superscript indicating
the power to which another number (called
the base) is to be raised. For example, 2 2 is the
square (second power) of 2; x 3 is the cube (third
power) of x.
exponential 1. A base (such as the natural number
e) modified by an exponent. 2. Related to a
change in value as determined by an exponent.
Thus, using increments for x in the equation y =
e x produces an exponential curve.
exponential curve A curve based on powers of a
number (such as for y = e x ). Also see EXPONEN-
TIAL, EXPONENTIAL DECREASE, and EXPO-
NENTIAL INCREASE.
exponential damping Damping action described
by an exponential curve.
exponential decay See EXPONENTIAL DE-
CREASE.
exponential decrease The continuous reduction
in the value of a quantity, according to the equation
y = e -x , which depicts the natural decay
curve.
exponential function A function, such as f (x) = e x ,
that varies exponentially. See, for example, EX-
PONENTIAL DECAY, EXPONENTIAL GROWTH,
and EXPONENTIAL SERIES.
exponential horn A horn of circular or rectangular
cross section, whose cross-sectional area S at any
point x feet along its axis is given by the formula
S = S 0 e mx , where S 0 is the cross-sectional area at
the throat, e is the natural logarithm base