18WuD2x

jogging • J rule 387
jogging Rapid, repetitive switching of power to a
motor to advance its shaft by small amounts.
Also called inching.
Johnson counter See RING COUNTER.
Johnson curve A spectral curve (important in appraising
solar cell performance) for air mass zero
(i.e., for conditions beyond the earth’s atmosphere).
Johnson-Lark-Horowitz effect The resistivity
gained by a metal or degenerate semiconductor
(one in which conduction is nearly equal to that
of a simple metal) because of electron scattering
by impurity atoms.
Johnson noise See THERMAL NOISE.
Johnson-Q feed system See Q-ANTENNA.
join Also called disjunction. The logical inclusive-
OR operation.
joined actuator A form of multiple circuit breaker
in which the opening of one circuit results in the
opening of all circuits.
joint See JUNCTION, 1.
joint circuit A communications circuit shared by
two or more services.
joint communications Communication facilities
being used by more than one service of the same
country.
joint denial The logical NOR (NOT-OR) operation.
joint-force sensor A feedback servo device that prevents
a robot joint from exerting excessive force. It
works by detecting the mechanical resistance the
robot arm encounters. If the resistance becomes
too great, the joint force is reduced or removed.
jolt 1. Colloquialism for KILOVOLT. 2. Colloquialism
for ELECTRIC SHOCK. 3. Colloquialism for
TRANSIENT. 4. Colloquialism for a lightning discharge.
Joly transformer A frequency-tripling transformer
whose frequency-multiplying action depends on
the nonlinearity of the magnetic induction curve
of the core material.
Jones plug A special form of polarized receptacle
having numerous contacts.
joule Abbreviation, J. The SI unit of work. One
joule is the work performed when the point of application
of one newton is moved one meter in the
direction of the applied force. Also see NEWTON.
Joule calorimeter A heat-measuring device that
operates electrically.
Joule constant See MECHANICAL EQUIVALENT
OF HEAT.
Joule effect 1. The heat resulting from current
flowing through a resistance. 2. See MAGNE-
TOSTRICTION.
joule heat See JOULE EFFECT, 1.
joule heat gradient The rate of change in the temperature
of a resistive object through which a
current flows.
joule meter An integrating wattmeter producing
readings in joules.
Joule’s law The rate at which heat is produced by
current flowing in a constant-resistance circuit is
proportional to the square of the current.
journal A file of messages within an operating system,
providing information for restarts and historical
analysis of system functioning.
joystick A two- or three-dimensional potentiometer
with a movable lever, allowing control of a parameter,
according to the position of the lever in
the up/down and left/right directions. It is often
used in computer games for the purpose of manipulating
images on a screen. In some such
devices, the lever can be rotated clockwise or
counterclockwise to obtain additional functions.
joystick
Jones plug
j operator See J.
Josephson effect The phenomenon, predicted by
Brian Josephson, wherein a current flows across
the gap between the tips of two superconductors
brought close together; a high-frequency wave is
generated.
Joshi effect The phenomenon whereby current in
a gas changes as the result of irradiation by light.
JPEG Abbreviation of Joint Photographic Experts
Group.
JPEG image compression An image-compression
scheme that eliminates redundancies, greatly reducing
the necessary digital storage space. The
process is fast enough to allow animated graphics
at moderate speed.
JPL Abbreviation of Jet Propulsion Laboratory.
J-pole antenna See J ANTENNA.
J rule During transitions of orbital electrons from
higher to lower energy states (accompanied by
the emission of photons), changes in the inner
quantum number can only be by a factor of 0 or
+1, or –1.