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pulsational pair-instability supernova abar-novâ-ye nâpâydâri-ye tapeši-ye joft,
abar-now-axtar-e ~ ~ ~ Fr.: supernova à instabilité pulsationnelle de paires A → supernova resulting from the → pair instability that generates several successive explosions. According to models, a first pulse ejects many solar masses of hydrogen layers as a shell. After the first explosion, the remaining core contracts and searches for a stable burning state. When the next explosion occurs a few years later, several solar masses of material are again ejected, which collide with the earlier ejecta. This collision can radiate 10^{50} erg of light, about a factor of ten more than an ordinary → core-collapse supernova. After each pulse, the remaining core contracts, radiates neutrinos and light, and searches again for a stable burning state. Later ejections have lower mass, but have higher energy. They quickly catch up with the first shell, where the collision dissipates most of their kinetic energy as radiation. The first SNe from → Population III stars are likely due to pulsational pair instability (Woosley et al. 2007, Nature 450, 390). See also → pair-instability supernova. → pulsational; → pair; → instability. |
pycnonuclear reaction vâžireš-e cagâl-hasteyi Fr.: réaction pycnonucléaire A nuclear reaction that takes place at high densities and relatively low temperatures. Pycnonuclear reactions are almost temperature independent and occur even at zero temperature. These reactions are extremely slow at densities typical for normal stars but intensify with increasing density. For example, carbon burns into heavier elements at densities over 10^{10} g cm^{-3}. Pycnonuclear, from pycno- a combining form meaning "dense, thick," from Gk. pyknos "dense, solid" + → nuclear; → reaction. Vâžireš, → reaction; cagâl-hasteyi, from cagâl, → dense, + hasteyi, → nuclear. |
quadratic equation hamugeš-e câruši Fr.: équation quadratique An equation with the general form of ax^{2} + bx +c = 0, in which the highest power of the unknown is the second power (square). |
qualification cunâyeš Fr.: qualification 1) A quality, accomplishment, etc., that fits a person for some function,
office, or the like. |
quantification candâyeš Fr.: quantification The fact or process of quantifying. Verbal noun of → quantify. |
quantization kuântomeš (#) Fr.: quantification 1) The procedure of restricting a continuous quantity to certain discrete values. Verbal noun of → quantize. |
quantum fluctuation oftâxiz-e kuântomi Fr.: fluctuation quantique The temporary variation in a → quantum field due to the → uncertainty principle. → quantum; → fluctuation. |
quantum information azdâyeš-e kuântomi Fr.: information quantique The science concerned with the transmission, storage, and processing of information using quantum mechanical systems. It exploits the notion of → quantum entanglement between systems and joins several fields of knowledge, mainly quantum physics, information, computation, and probability. → quantum; → information. |
quantum of action kuântom-e žireš Fr.: quantum d'action Since → Planck's constant has the dimension of → energy × → time, its sometimes called the quantum of → action. |
quantum phase transition (QPT) gozareš-e fâz-e kuântomi Fr.: transition de phase quantique A phase transitions that occurs at zero temperature as a function of a non-thermal parameter like → pressure, → magnetic field, or → chemical composition. In contrast to ordinary → phase transitions, which are associated with passage through a critical temperature, quantum phase transitions are associated with → quantum fluctuations, a consequence of → Heisenberg's uncertainty principle. For example, see → Bose-Einstein condensation. → quantum; → phase; → transition. |
quark-hadron phase transition gozareš-e fâz-e kuârk-hâdron Fr.: transition de phase quark-hadron A phase transition, predicted by cosmological models, to have occurred at approximately 10^{-5} seconds after the Big Bang to convert a plasma of free quarks and gluons into hadron. → quark; → hadron; → phase; → transition. |
quartic equation hamugeš-e câromik Fr.: équation quartique An equation containing unknowns of the fourth power; the general form: ax^{4} + bx^{3} + cx^{2} + dx + e = 0. From L. quart(us) "fourth" (→ quarter) + → -ic; → equation. hamugeš, → equation; câromân, from cârom "fourth," from câr, cahâr "four" + -om "-th" + -ik, → -ic. |
quasi-single-scattering approximation nazdineš-e cunân-tak-parâkaneš Fr.: A model of radiative transfer that ignores forward scattering of photons; assuming forward-scattered light as un-scattered. → quasi-; → single; → scattering; → approximation. |
quasiperiodic motion jonbeš-e cunân-dowreyi Fr.: mouvement quasipériodique In a dynamical system, a form of motion that is regular but never exactly repeating. Quasiperiodic motion appears when the system contains two or more incommensurate frequencies. |
quintic equation hamugeš-e panjomik Fr.: équation quintique An equation containing unknowns of the fifth power. |
R association âhazeš-e R Fr.: association R A → stellar association containing a number of → reflection nebulae. The stars are of low or intermediate mass and young, less than a million years old. They are still surrounded by patches of dust that reflect and absorb light from the interstellar cloud in which they formed. This type of association was first suggested by Sidney van den Bergh (1966, AJ 71, 900). R, from → reflection; → association. |
R-type ionization front pišân-e yoneš-e gune-ye R Fr.: front d'ionisation de type R A spherical → ionization front of → H II regions that moves radially outward from the → exciting star at a velocity much higher than → sound speed in the surrounding cold neutral gas of uniform density (ahead of the front). R-type ionization fronts corresponds to early evolution of H II regions, and will eventually transform into → D-type ionization fronts. If the motion of the front is supersonic relative to the gas behind as well as ahead of the front, the front is referred to as weak R. The strong R front correspond to a large density increase across the front. R referring to a rarefied gas; → type; → ionization; → front. |
radial migration kuc-e šo'â'i Fr.: migration radiale The process whereby a → disk star changes its → galactocentric distance. Radial migration involves → angular momentum transfer, resulting from → resonances created by transient → density waves such as → bars or → spiral arms in → galactic disks. According to → galactic dynamics models, → churning is the main cause of radial migration. Radial migration of stars plays an important role in shaping the properties of galactic disks. |
radial motion jonbeš-e šo'â'i Fr.: mouvement radial A motion away from or toward a central point or axis. |
radiation tâbeš (#) Fr.: radiation, rayonnement The emission of any → rays, → waves, or → particles from a source; usually applied to the → emission of → electromagnetic energy. Verbal noun of → radiate. |
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