J

Source edition 1965. Please read the Introduction to find out about this dictionary and our plans for it. Caution, many entries have not been updated since the 1965 edition.
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jacket: 1. A covering or casing of some kind.; 2. Specifically, a shell around the combustion chamber of a liquid-fuel rocket, through which the propellant is circulated in regenerative cooling.; 3. A coating of one material over another to prevent oxidation, micrometeoroid penetration, etc.
Jacobian: The determinant formed by the n<² partial derivatives of n functions of n variables, when the derivatives of each function occupy one row of the determinant. For the case of two functions f(x,y) and g(x,y) , the Jacobian J(f,g) is Sometimes written .
jamming: Intentional transmission or reradiation of radio signals in such a way as to interfere with reception of desired signals by the intended receiver.
J-antenna: A half-wave antenna, end fed by a parallel-wire quarter-wave section having the configuration of a J.
JATO, Jato, or jato: (From jet-assisted take-off ).; 1. A take-off utilizing an auxiliary jet-producing unit or units, usually rockets, for additional thrust. Hence JATO bottle, Jato unit , etc.; a rocket or unit so used. Where rockets are the auxiliary units, RATO (which see) is the more specific term.; 2. A JATO bottle or unit; the complete auxiliary power system used for assisted take-off.
J-display: In radar, a modified A-display in which the time base is a circle. The target signal appears as a radial deflection from the time base. Also called J-scan, J-scope, J-indicator.
jerk: A vector that specifies the time rate of change of the acceleration; the third derivative of displacement with respect to time.
jerkmeter: An instrument for measuring the magnitude of the time rate of change of acceleration.
jet: 1. A strong well-defined stream of fluid either issuing from an orifice or moving in a contracted duct, such as the jet of combustion gases issuing from a reaction engine, or the jet in the test section of a wind tunnel. See free jet.; 2. A tube, nozzle, or the like through which fluid passes, or from which it issues, in a jet, such as a jet in a carburetor. See metering jet.; 3. A jet engine, as, an airplane with jets slung in pods.
jetavator: A control surface that may be moved into or against a rocket's jetstream, used to change the direction of the jet flow for thrust vector control. Compare jet vane.
jet engine: 1. Broadly, and engine that ejects a jet or stream of gas or fluid, obtaining all or most of its thrust by reaction to the ejection. See reaction engine.; 2. Specifically, an aircraft engine that derives all or most of its thrust by reaction to its ejection of combustion products (or heated air) in a jet and that obtains oxygen from the atmosphere for the combustion of its fuel (or outside air for heating, as in the case of the nuclear jet engine), distinguished in this sense from a rocket engine. A jet engine of this kind may have a compressor, commonly turbine-driven, to take in and compress air (turbojet), or it may be compressorless, taking in and compressing air by other means ( pulsejet, ramjet).
jet nozzle: A nozzle, usually specially shaped, for producing a jet, such as the exhaust nozzle on a jet or rocket engine. See rocket nozzle.
jet propulsion: 1. The propulsion of a rocket or other craft by means of a reaction engine.; 2. = duct propulsion.; Duct propulsion and rocket propulsion are the two forms of jet propulsion.
jetstream: A jet issuing from an orifice into a medium with much lower velocity, such as the stream of combustion products ejected from a reaction engine.; In the meteorological sense jet stream is two words, see following definition, but in the sense defined above, one word.
jet stream: A strong band of wind or winds in the upper troposphere or in the stratosphere, moving in a general direction from west to east and often reaching velocities of hundreds of miles an hour. See jetstream, note.
jet thrust: The thrust of a fluid, especially as distinguished from the thrust of a propeller. The thrust of a rocket engine is calculated in the same manner as gross thrust of a jet engine. See gross thrust.
jet vane: A vane, either fixed or movable, used in a jetstream, especially in the jetstream of a rocket, for purposes of stability or control under conditions where external aerodynamic controls are ineffective. Also called blast vane. Compare air vane.
J-indicator = J-display.
jitter: 1. Instability of the signal or trace of a cathode-ray tube.; 2. Small rapid variations in a waveform due to deliberate or accidental electrical or mechanical disturbances or to changes in the supply voltages, in the characteristic of components, etc.
Jodrell Bank: The site of a large radio telescope, located near Manchester, England; by extension, the radio telescope itself.; The radio telescope has a paraboloidal receiver 250 feet in diameter, 60 feet deep.
Johnson noise: See thermal noise.
Joint Long Range Proving Ground: The earliest predecessor organization and facility of the Atlantic Missile Range, activated at Cape Canaveral 1 October 1949 as a joint undertaking of the Air Force, Army, and Navy under the executive control of the Chief of Staff, USAF.; This facility became the sole responsibility of the Air Force on 16 May 1950, and became known as the Florida Missile Test Range.
joule (abbr j): A unit of energy or work in the MKS system; the work done when the point of application of 1 newton is displaced a distance of 1 meter in the direction of the force.; 1 joule = 10E7 ergs = 1 watt second.
Joule constant: The ratio between heat and work units from experiments based on the first law of thermodynamics: 4.1858 X 10E7 ergs per 15 degrees calorie. Also called mechanical equivalent of heat.
Joule cycle: (After James Prescott Joule, 1818-89, English physicist). An ideal cycle for engines consisting of isentropic compression of the working substance, addition of heat at constant pressure, isentropic expansion to ambient pressure, and exhaust at constant pressure. Also called Brayton cycle.
Joule-Kelvin effect = Joule-Thomson effect.
Joule-Thomson coefficient (symbol μ): See Joule-Thomson effect.
Joule-Thomson effect: The decrease in temperature which takes place when a gas expands through a throttling device as a nozzle. Also called Joule-Kelvin effect.; The rate of change of temperature T with pressure p in the Joule-Thomson effect is called the Joule-Thomson coefficient (symbol μ): where h denotes constant enthalpy. For the Joule-Thomson effect to take place the gas must initially be below its inversion temperature; if above the inversion temperature, the gas will gain heat on expansion. The inversion temperature of hydrogen, for example, is approximately -183 degrees C.
Jovian: (Latin Jovis, genitive of Jupiter) Of or pertaining to the planet Jupiter; associated with Jupiter; or similar to Jupiter, as in Jovian planet.
Jovian planet: Any one on the giant planets: Jupiter, Saturn, Uranus, or Neptune. Usually in plural Jovian planets.
JP (abbr) = jet propulsion: Compare RP.
JP-4: A liquid fuel for jet and rocket engines, the chief ingredient of which is kerosene.
J-scan = J-display.
J-scope = J-display.
Julian day: The number of each day, as reckoned consecutively since the beginning of the present Julian period on January 1, 4713 B.C.; The Julian day is used primarily by astronomers to avoid confusion due to the use of different calendars at different times and places. The Julian day begins at noon, 12 hours later than the corresponding civil day. The day beginning at noon January 1, 1965, is Julian day 2,438,395.
Julian period: See Julian day.
jump: In computer programming, to cause the next instruction to be selected conditionally or unconditionally from a specified storage location.
jumper: A short length of conductor used to complete an electrical circuit, usually temporary, between terminals, or to bypass an existing circuit.
junction: In a semiconductor device, a region of transition between semiconducting regions of different electrical properties.
junction point = node.
June solstice = summer solstice.
Jupiter: See planet, table.
Jupiter I = Io.
Jupiter II = Europa.
Jupiter III = Ganymede.
Jupiter IV = Callisto.

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