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cross dispersion pâšeš-e calipâyi, ~ xâji Fr.: dispersion croisée Dispersion of a light beam by using two dispersing elements (grating, grism), one for separating spectral orders, the other for resolving spectral features within an order. → cross; → dispersion. |
cross identification idâneš-e calipâyi Fr.: identification croisée The identification of an object in a data base or catalog and matching it with the same object identified in another catalog. → cross; → identification. |
cross section sekanjgâh Fr.: 1) section plane; 2) section efficace 1) Math: The intersection of a plane with a geometric figure,
usually at right angles to an axis of symmetry. In classical mechanics, the cross section for the collision of a point particle with a hard sphere is just be the surface of a section through the middle of the sphere. This explains the name "cross section." → cross; → section. |
crystallization bolureš Fr.: cristallisation A process by which a homogeneous solution becomes crystal. Noun from crystallize, → crystal. Noun from bolur, from verb boluridan "to crystallize" + verbal noun suffix -eš. |
cubic equation hamugeš-e kâbi Fr.: équation cubique An equation containing unknowns of the third power; the general form: ax^{3} + bx^{2} + cx + d = 0. |
cubic function karyâ-ye kâbi Fr.: fonction cubique A function defined by a → polynomial of → degree three. Its generalized form is: f(x) = ax^{3} + bx^{2} + cx + d, where a, b, c and d are constants, and a≠ 0. |
culmination bâlest Fr.: culmination The act of culminating or the instant at which a celestial object reaches its highest altitude above the horizon by crossing the observer's meridian. → upper culmination; → lower culmination. Verbal noun of → culminate. Bâlest, from Mid.Pers. bâlist "culmination point of a star; highest, summit," from bâlây "high" + -ist superlative suffix, Av. barəzišta- "highest," from barəz- "high, mount" (Skt. bhrant- "high," O.E. burg, burh "castle, fortified place," from P.Gmc. *burgs "fortress," Ger. Burg "castle," Goth. baurgs "city," E. burg, borough, Fr. bourgeois, bourgeoisie, faubourg; PIE base *bhergh- "high") + -išta- superlative suffix (Skt. -istha-, Gk. -istos, O.H.G. -isto, -osto, O.E. -st, -est, -ost). |
cumulative distribution function karyâ-ye vâbâžeš-e kumeši Fr.: fonction de distribution cumulée A function that gives the probability that a → random variable X is less than or equal to x, at each possible outcome: F(x) = P(X ≤ x), for -∞ < x < ∞. Same as → distribution function. → cumulative; → distribution; → function. |
Cygnus OB association âhazeš-e OB Mâkiyân Fr.: association OB Cygne One of nine → OB associations located in the Cygnus → constellation. The central association, → Cygnus OB2, is the most famous and the youngest of the Cygnus region. (L. Mahy et al. 2013, astro-ph/1301.0500 and references therein). → Cygnus; → OB star; → association. |
D-type ionization front pišân-e yoneš-e gune-ye D Fr.: front d'ionisation de type D An → ionization front of → H II regions whose expansion speed is comparable to the → sound speed in the gas (~ 10 km/sec for hydrogen at 10^{4} K). A D-type ionization front results from → R-type ionization front when its propagation speed decreases as the volume of gas ahead of the ionization front grows. If front velocity is equal to a lower limit (C_{1}^{2} / 2C_{2}, where C_{1} and C_{2} are the sound speed ahead and behind the front respectively), the front is called D critical. D referring to a dense gas; → type; → ionization; → front. |
dark adaptation niyâveš bé târiki Fr.: adaptation à l'obscurité The automatic adjustment of the iris and retina of the eye to allow maximum vision in the dark, following exposure of the eye to a relatively brighter illumination. → dark; → adaptation. |
dark matter annihilation nâbudi-ye mâde-ye târik Fr.: annihilation de la matière noire A hypothetical process whereby hypothetical → non-baryonic dark matter particles undergo → annihilation interactions with themselves. The process results in observable by-products such as high-energy photons, neutrinos, and other detectable particles. See also → dark matter decay. → dark; → matter; → annihilation. |
data acquisition alfanješ-e dâdehâ Fr.: acquisition de données The process of controlling telescope operations during observation and obtaining data. → data; acquisition, from L. acquisitionem, from acquirere "get in addition," from → ad- "extra" + quærere "to search for, obtain." Alfanješ, verbal noun of alfanjidan (variant alfaqdan) "to acquire, get," Bactrian αλφανζ "to acquire," Sogdian δβ'yz "to acquire, gain, get" (Cheung 2007); → data. |
data reduction bâzhâzeš-e dâdehâ Fr.: réduction de données The process of converting crude observational data into usable information for scientific interpretation, by correcting, rearranging, ordering, and simplifying. |
de Broglie equation hamugeš-e de Broglie Fr.: équation de de Broglie According to the → de Broglie hypothesis,
which has been verified by experiments, every → particle
of matter, whatever its nature, has a characteristic → wavelength
associated with its wavelike quantum aspect. The de Broglie equation gives the
equivalent wavelength of a moving particle: λ = h/mv, where h is
→ Planck's constant, m the mass of the particle,
and v its velocity. Named after Louis Victor de Broglie (1892-1987), French physicist, creator of a new field in physics, wave mechanics, who won the Nobel prize in physics in 1929. → equation |
de-excitation foru-angizeš Fr.: désexcitation Transition from an excited energy state to a lower energy level, as in spectral line formation or particle emission from an atomic nucleus. From → de- + → excitation. |
de-projection vâ-farâšâneš Fr.: déprojection A method for estimating the real orientation of a field and/or related velocities/separations from two-dimensional images. → de-; → projection. |
deceleration vâšetâb (#) Fr.: décéleration The act or process of moving, or of causing to move, with decreasing speed. Sometimes called negative acceleration. Verbal noun of decelerate. |
deceleration parameter pârâmun-e vâšetâb Fr.: paramètre de décéleration A parameter designating the rate at which the expansion of the Universe would slow down owing to the braking gravitational effect of the matter content of the Universe. It is expressed by: q(t) = -R(t)R^{ ..}(t)/R^{ .}^{2}(t), where R(t) represents the size of the Universe at time t. See also → expansion parameter; compare with → acceleration parameter. → deceleration; → parameter. |
decimal fraction barxe-ye dahdahi Fr.: fraction décimale A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction. |
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