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longitudinal mass jerm-e derežnâyi Fr.: masse longitudinale In special relativity theory, the mass of a body when the acceleration is parallel or anti-parallel to velocity: m_{l} = m_{0} / [1 - (v/c)^{2}]^{3/2}, where m_{0} is the → rest mass, v is the velocity, and c the → velocity of light. → transverse mass. → longitudinal; → mass. |
longitudinal wave mowj-e derežnâyi Fr.: onde longitudinale A wave vibrating along the direction of propagation, such as a → sound wave. → transverse wave. → longitudinal; → wave. |
longitudinal Zeeman effect oskar-e Zeeman-e derežnâyi Fr.: effet Zeeman longitudinal The → Zeeman effect when the emitting source is viewed in the direction of the magnetic field. In the normal longitudinal effect, each spectral line is split into two components with frequencies ν ± Δν. The line with the frequency ν - Δν shows left-hand → circular polarization and that with frequency ν + Δν shows right-hand circular polarization. → transverse Zeeman effect. → longitudinal; → Zeeman effect. |
look negâh (#) Fr.: regard The act or instance of looking. Look, from W.Gmc. *lokjan (cf. O.S. lokon, M.Du. loeken, O.H.G. luogen, Ger. dialectal lugen "to look out"), of unknown origin. Negâh "look," from Mid.Pers. nikâh "look, glance, observation;" Proto-Iranian *ni-kas- "to look down," from ni- "down," → ni- (PIE), + *kas- "to look, appear;" cf. Av. nikā-, nikāta- (in the name of the 15-th nask) "that which is observed," ākas- "to look;" Mid.Pers. âkâh, Mod.Pers. âgâh "aware, knowing;" Skt. kāś- "to become visible, appear;" Ossetic kast/kaesyn "to look." |
look-back time zamân-e negâh bé gozašté Fr.: temps de retour en arrière The time that has elapsed since the light was emitted from a distant object (of → redshift z). Because → light moves at a → constant → speed, it takes a finite time to travel from distant objects. Hence, we "see" distant objects at a point in time in their past. In other words, look-back time is the difference between the age of the Universe now and the age of the Universe at the time the photons were emitted from the object. See also → comoving distance. Zamân, → time; negâh, → look; gozašté "past, passed" (from gozaštan "to pass, proceed, go on," variant gozâštan "to put, to place, let, allow;" Mid.Pers. widardan, widâštan "to pass, to let pass (by);" O.Pers. vitar- "to pass across," viyatarayam "I put across;" Av. vi-tar- "to pass across," from vi- "apart, away from" (O.Pers. viy- "apart, away;" Av. vi- "apart, away;" cf. Skt. vi- "apart, asunder, away, out;" L. vitare "to avoid, turn aside") + O.Pers./Av. tar- "to cross over"). |
loop gerdâl Fr.: boucle General:
Anything shaped more or less like a loop, i.e. portion of a cord, ribbon, etc.,
folded or doubled upon itself. Probably of Celtic origin (cf. Gael. lub "bend," Ir. lubiam), influenced by O.N. hlaup "a leap, run." Gerdâl, from gerd "round, a circle" (Mid.Pers. girdag "disk, round," from gird/girt "round, all around," Proto-Iranian *gart- "to twist, to wreathe," cf. Skt krt "to twist threads, spin; to wind; to surround;" kata- "a twist of straw," Pali kata- "ring, bracelet," Gk. kartalos "a kind of basket," kyrtos "curved") + → -al. |
loop prominence zabâne-ye gerdâli Fr.: protubérance en boucle A very bright active prominence in the form of a loop seen in Hα after a rather big flare. Also called "post-flare loops," they connect the feet where the two-ribbon flares were seen. The lifetime of loop prominences is several hours. → loop; → prominence. |
lord xâvand (#) Fr.: seigneur 1) A person who has authority, control, or power over others; a master, chief, or ruler. M.E. lord, loverd, O.E. hlâford, hlâfweard, literally "loaf-keeper," from hlaf "bread, loaf" + weard "keeper, guardian." Xâvand, contraction of xodâvand "lord, master, god," from xodâ "lord, master," → God, + suffix -vand. |
Lorentz Lorentz Fr.: Lorentz Contraction of the full name of Hendrik Antoon Lorentz (1853-1928), a Dutch physicist, who made important contribution to physics. He won (with Pieter Zeeman) the Nobel Prize for Physics in 1902 for his theory of electromagnetic radiation, which, confirmed by findings of Zeeman, gave rise to Albert Einstein's special theory of relativity. |
Lorentz contraction terengeš-e Lorentz Fr.: contraction de Lorentz The decrease in the length of a body moving in the direction of its length as measured by an observer situated in that direction. The shortening factor is [1 - (v/c)^{2}]^{1/2}, where v is the relative velocity and c light speed. → Lorentz; → contraction. |
Lorentz factor karvand-e Lorentz Fr.: facteur de Lorentz In → special relativity, an important parameter which appears in several equations, including → time dilation, → length contraction, and → relativistic mass. It is defined as γ = 1 / [1 - (v/c)^{2}]^{1/2} = dt/dτ, where v is the velocity as observed in the reference frame where time t is measured, τ is the proper time, and c the → velocity of light. Same as Lorentz γ factor. |
Lorentz force niru-ye Lorentz (#) Fr.: force de Lorentz The force acting upon a → charged particle as it moves in a → magnetic field. It is expressed by F = q.v x B, where q is the → electric charge, v is its → velocity, and B the → magnetic induction of the field. This force is perpendicular both to the velocity of the charge and to the magnetic field. The magnitude of the force is F = qvB sinθ, where θ is the angle between the velocity and the magnetic field. This implies that the magnetic force on a stationary charge or a charge moving parallel to the magnetic field is zero. The direction of the force is given by the → right-hand rule. |
Lorentz invariance nâvartâyi-ye Lorentz Fr.: invariance de Lorentz Of a physical law, invariance with respect to a → Lorentz transformation. → Lorentz; → invariance. |
Lorentz resonance bâzâvâyi-ye Lorentz Fr.: résonance de Lorentz A repeated electromagnetic force on an electrically charged ring particle, nudging the particle in the same direction and at the same point in its orbit. Lorentz resonances are especially important for tiny ring particles whose charge-to-mass ratio is high and whose orbit periods are a simple integer fraction of the rotational period of the planet's magnetic field (Ellis et al., 2007, Planetary Ring Systems, Springer). |
Lorentz transformation tarâdis-e Lorentz Fr.: transformation de Lorentz A set of linear equations that expresses the time and space coordinates of one → reference frame in terms of those of another one when one frame moves at a constant velocity with respect to the other. In general, the Lorentz transformation allows a change of the origin of a coordinate system, a rotation around the origin, a reversal of spatial or temporal direction, and a uniform movement along a spatial axis. If the system S'(x',y',z',t') moves at the velocity v with respect to S(x,y,z,t) in the positive direction of the x-axis, the Lorentz transformations will be: x' = γ(x - vt), y' = y, z' = z, t' = γ [t - (vx/c^{2})], where c is the → velocity of light and γ = [1 - (v/c)^{2}]^{-1/2}. For the special case of velocities much less than c, the Lorentz transformation reduces to → Galilean transformation. → Lorentz; → transformation. |
Lorentzian profile farâpâl-e Lorentzi Fr.: profil lorentzien A spectral profile in which the intensity distribution follows a specific mathematical function (Lorentz or Cauchy probability). Compared to the normal or Gaussian profile, Lorentzian has a pointed peak and more important wings. |
Lorimer burst belk-e Lorimer Fr.: sursaut Lorimer, impulsion ~ The first ever discovered → fast radio burst. It was done during a search of archival data from a 1.4-GHz survey of the → Magellanic Clouds using the multi-beam receiver on the 64-m Parkes Radio Telescope in Australia. D. R. Lorimer et al., 2007, Science, 318, 777; → burst. |
Loschmidt's number adad-e Loschmidt Fr.: nombre de Loschmidt The number of molecules in 1 cm^{3} of an ideal gas (2.687 x 10^{19} per cm^{3}). Joseph Loschmidt (1821-1895), Austrian physicist. |
loss dastraft Fr.: perte In physics, a measure of the energy, mass, or other physical quantities lost in a system, by conversion or external effects. From O.E. los "loss, destruction," from P.Gmc. *lausa, from PIE base *leu- "to loosen, divide, cut apart, untie, separate" (cf. Gk. lyein "to loosen, untie, slacken," lysus "a loosening;" L. luere "to loose, release, atone for;" Skt. lunati "cuts, cuts off," lavitram "sickle;" Pers. las "loose," lâ "slit, cut;" → analysis). Dastraft, literally "gone from hand," from dast "hand" (Mid.Pers. dast; O.Pers. dasta-; Av. zasta-; cf. Skt. hásta-; Gk. kheir; L. praesto "at hand;" Arm. jern "hand;" Lith. pa-žastis "arm-pit;" PIE *ghes-to-) + raft p.p. of raftan "to go, elapse, glide by, depart" (Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack"). |
loud boland (#) Fr.: fort, sonore, bruillant High in volume of sound. M.E., O.E. hlud "making noise, sonorous" (cf. M.Du. luut, Du. luid, O.H.G. hlut, Ger. laut "loud"), from PIE *klutos- (cf. Skt. sruta-, Gk. klytos "heard of, celebrated," Arm. lu "known." Boland, → high. |
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