An → engine that works by taking in air at the front and expelling exhaust gases at the rear so that the reaction to this exhaust propels the vehicle forward.
Fr.: lancement de jet
The mechanism whereby → astrophysical jets are thrown out of → accretion disks . Observed correlations between emission from the accretion disk and from the jet provide evidence that the jets are launched from the disks directly. As the energy emitted from the jets is a → synchrotron radiation, the presence of a → magnetic field is deduced for the ejection. The most promising model for such "accretion-ejection" structures is based on a scenario where a large-scale magnetic field threads an accretion disk. This model, using a → magnetohydrodynamic (MHD) approach, shows that the magnetic field can azimuthally brake the matter inside the disk (carrying off → angular momentum allowing accretion) and accelerate matter above the disk surface. The → collimation of the flow is achieved via → magnetic tension due to the presence of a → toroidal component of the magnetic field. The magnetic field provides an effective alternative to the radially outward transport of disk angular momentum by → viscosity. The interaction of the magnetic structure with the disk plasma can create a MHD → Poynting flux leaving the disk along the magnetic surface. This energy flux can then be converted into → kinetic energy of the matter within the jet. Because the → mass density in the jet is smaller than in the disk, it is thereby possible to reach high → terminal velocities for a given amount of angular momentum removed from the disk (Casse & Keppens, 2002, ApJ 581, 988, and references therein).
jet (#), havâpeymâ-ye ~ (#)
Fr.: avion à réaction
An airplane moved by → jet propulsion.
→ jet; plane, short for airplane, from Fr. aeroplane, from aero-, → air, + plane feminine of plan "flat, level," from L. planus, perhaps by association with forme plane; apparently coined and first used by Fr. sculptor and inventor Joseph Pline in 1855.
→ jet; havâpeymâ "airplane," from havâ, → air, + peymâ "travelling; traveller," from peymudan, peymâyidan "to travel, traverse, pass over," from Mid.Pers. patmudan, paymudan "to measure (against)," from *pati-māya-. The first element *pati- "against, back" (cf. Mod.Pers. pâd- "against, contrary to;" Mid.Pers. pât-; O.Pers. paity "agaist, back, opposite to, toward, face to face, in front of;" Av. paiti; Skt. práti "toward, against, again, back, in return, opposite;" Pali pati-; Gk. proti, pros "face to face with, toward, in addition to, near;" PIE *proti). The second element from *mā- "to measure;" O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure." Apart from peymâ, several other terms in Mod.Pers. are related to this second element, which occurs also as mun, mân, man, mâ, mu, and mây: pirâmun "perimeter," âzmun, âzmây- "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," man "a measure weighing forty seers)," nemudan, nemâ- "to show, display," âmâdan, âmây- "to prepare."
Fr.: propulsion par réaction
Powerful, forward thrust that results from the rearward expulsion of a jet of fluid, especially propulsion by jet engines.
Fr.: jet stream
Meteo.: An area of relatively strong winds that are concentrated in a narrow band in the upper troposphere of the middle latitudes and subtropical regions of the Northern and Southern Hemispheres.
gâhšomâr-e yahud (#)
Fr.: calendrier juif
Same as → Hebrew calendar
Jewish, adj. of jew, from M.E. jewe, giu, gyu, ju, from O.Fr. juiu, juieu, gyu, from L.L. judeus, from L. juaeus, from Gk. ioudaios, from Aramaic yehudhai, from Heb. yəhudhi "Jew," from Yəhudah "Judah," literally "celebrated," name of Jacob's fourth son and of the tribe descended from him; → calendar.
Gâhšomâr→ calendar; yahud, from Ar., from Heb., as above.
Fr.: système JHK
1) Three → atmospheric windows in the
→ near infrared portion of the
→ electromagnetic spectrum at 1.25 (J), 1.65 (H), and
2.20 (K) μm.
Letters of alphabet, used conventionally; → system.
šahâbsang-e jilin (#)
Fr.: météorite de Jilin
The biggest meteorite ever witnessed falling and the largest stone meteorite known. It happened near Jilin, an industrial port city located northeastern China, on March 8, 1976. Of the four tons of fragments of the type H5 chondrite recovered, one piece weighs 1.774 tons and measures about 100 x 80 x 50 cm. The meteorite exploded in the sky and produced a shower covering an area of more than 500 square kilometers.
Jilin, from the name of the Chinese city, known also as Chi-lin City or Kirin City. → meteorite.
Fr.: scintillement, vacillement
Short term random variations either in amplitude or phase of a radio signal.
Jitter, may be variant of chitter "tremble, shiver," from M.E. chiteren "to twitter, chatter."
Jastojah, from jast and jah past and present stems of jahidan "to jump, leap, spring forward; to shake or tremble," from Mid.Pers. jastan, jahidan "to jump," figuratively "to happen, occur;" Av. yaēš-, yas- "to boil;" cf. Skt. yas-, yásyati "to boil, to heat; to make effort" + -o- euphonic infix, on the model of kandokâv, oftoxiz, and so on.
A mode of observation in which a series of short exposures are used to enhance the final image quality through appropriate data processing. The first exposure is assumed to be centered on the point of interest; the following ones are slightly offset from the first position with separations not larger than a reasonably small fraction of the detector size. The offsets should be optimally distributed on the sky in order to maximize the chances of being able to filter out the sky background.
jofteš-e jj, jafsari-ye ~
Fr.: couplage jj
A coupling scheme of electronic → spin angular momenta and → orbital angular momenta for heavy atoms (generally Z > 30), where the spin and orbital angular momenta of individual electrons couple strongly, and therefore the → LS coupling scheme does not apply. The coupling between spin and orbital angular momentum of each electron is much stronger than the coupling between different electrons. Therefore, the total angular momentum, ji, for the i-th electron is obtained by combining li and si and then coupling these j's together to give the total angular momentum J = Σi ji. In the jj coupling scheme the total orbital angular momentum quantum number, L, and the total spin angular momentum number, S, are not specified.
j referring to the symbol of the total angular momentum for individual electrons; → coupling.
nufe-ye Johnson-Nyquist (#)
Fr.: bruit de Johnson-Nyquist
The random fluctuation of voltage across a resistor caused by the thermal excitation of electrons within it, and the dissipation of power associated with these fluctuations. More generally, an intrinsic noise generated by thermal agitation of electrons by all bodies whose temperature is above 0 K. Also called → thermal noise, Johnson noise, or Nyquist noise.
Named after John Bertrand Johnson (1887-1970) and Harry Nyquist (1889-1976) Swedish-born American engineers and physicists, who did important work on thermal noise and information theory. → noise.
mâtris-e Jordan (#)
Fr.: matrice de Jordan
A square matrix with a constant value λ (nonzero) along the diagonal, 1's on the superdiagonal, and all other elements 0.
Named after Marie Ennemond Camille Jordan (1838-1922), French mathematician who pioneered group theory, wrote on the theory of linear differential equations, and on the theory of functions, which he applied to the curve which bears his name. → matrix.
Fr.: théorie de Jordan-Brans-Dicke
A relativistic theory of gravitation which involves a → scalar field in addition to the → metric (→ tensor field) used in rarr; general relativity. It obeys the → equivalence principle, but tries at the same time to comply with → Mach's principle owing to possible spatial and temporal variations of the → gravitational constant, which is inversely proportional to the scalar field. The theory uses a new dimensionless parameter to determine the discrepancy between its predictions and those of general relativity. So far there is no firm indication of its validity. Same as → scalar-tensor theory.
Named after the creators, Carl Brans (1935-) and Robert Dicke (1916-1997), who presented the theory in 1961, based on the initial work of Pascual Jordan (1902-1980); → theory.
Fr.: effet Josephson
Named after the British physicist Brian David Josephson, who predicted the existence of the effect in 1962; → effect.
juhe-ye Josephson (#)
Fr.: jonction Josephson
A unit of → energy in the → International System of Units equal to the → work performed by one → newton over a distance of 1 → meter. 1 J is equivalent to 107 ergs = 1 Watt second = 2.78 × 10-7 kWh = 0.2389 calories = 6.24 × 1018 eV.
In honor of the English physicist James Prescott Joule (1818-1889), who established that the various forms of energy (mechanical, electrical, and heat) are basically the same and can be changed, one into another.
Joule is in Pers. pronounced as žul, loaned from the Fr. rendering of the E. name.
Fr.: effet Joule
pâyâ-ye Joule (#)
Fr.: constante de Joule
The proportional relationship of mechanical energy to thermal energy, equal to 4.184 joules per calorie. Also called mechanical equivalent of heat.
Fr.: effet Joule-Thomson
The change in the temperature of a gas in the → throttling process.