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wave equation hamugeš-e mowj Fr.: équation d'onde The partial differential equation ∂^{2}U / ∂^{2}x + ∂^{2}U / ∂^{2}y + ∂^{2}U / ∂^{2}z = (1/c^{2}) ∂^{2}U / ∂^{2}t or its counterparts in one or two dimensions or in other coordinates, the solution of which represents the propagation of displacementU as waves with velocity c. |
wave function karyâ-ye mowj Fr.: fonction d'onde In → quantum mechanics, the function of space and time that satisfies → Schrodinger equation. The square of the modulus of its amplitude at any point represents the probability of finding a particle there. → wave; → function. |
wavefront pišân-e mowj, mowj-pišân Fr.: front d'onde The locus of adjacent points possessing the same phase in the path of a wave motion. Its surface is uniform (spherical or plane) and normal to propagation direction in an isotropic medium. → wavefront distortion. |
wavefront correction aršâyeš-e pišân-e mowj Fr.: correction de front d'onde In → adaptive optics, eliminating the effects of atmospheric turbulence on the wavefront of the object being observed. → wavefront distortion. → wavefront; → correction. |
wavefront distortion cowlegi-ye pišân-e mowj Fr.: distortion de front d'onde The disruption of the spherical shape of a wavefront due to atmospheric turbulence which makes the adjacent points in the wavefront out of phase. → wavefront; → distortion. |
wavefront sensor hessgar-e pišân-e mowj Fr.: analyseur de front d'onde In adaptive optics, a device that analyzes the light sample coming from the wavefront and determines the error in each part of the beam. The wavefront sensor used in adaptive optics is a → Shack-Hartmann type, which works in conjunction with a deformable mirror. |
wavefront tilt gerâ-ye pišân-e mowj Fr.: inclinaison du front d'onde The average slope in both the X and Y directions of a → wavefront or phase profile across the pupil of an optical system. |
waxing moon mâng-e fazâyandé (#) Fr.: lune montante The circumstance when the phase of the Moon is increasing from → new moon to → full moon. |
weak emission-line central star (wel) setâre-ye markazi bâ xatt-e gosili-ye nezâr Fr.: étoile centrale à faibles raies d'émission A member of a class of cntral stars of planetary nebula, → CSPN, which have weaker and narrower emission lines than → Wolf-Rayet-like CSPNe (Tylenda et al. 1993, A&AS 102, 595). |
weak gravitational lensing lenzeš-e gerâneši-ye nezâr Fr.: effet de lentille gravitationnelle faible A gravitational bending of light by structures in the Universe that distorts the images of distant galaxies. The distortion allows the distribution of → dark matter and its evolution with time to be measured, thereby probing the influence of → dark energy on the growth of structures. Weak gravitational lensing is generally difficult to identify in individual images, in contrast to → strong gravitational lensing (see, e.g., Bartelmann & Peter Schneider, 2001, Phys. Rept. 340, 291). → weak; → gravitational; → lensing. |
weak interaction andaržireš-e nezâr, ~ kamzvr Fr.: interaction faible One of the fundamental forces of nature that accounts for some particle interaction, such as → beta decay (→ radioactivity), the decay of free → neutrons, → neutrino interactions, and so forth. It is short-ranged, dominating at distances of 10^{-16} cm and occurs at a rate slower than that of the → strong interaction by a factor of about 10^{-13}, hence its name. Although the weak interaction also includes interactions in which no neutrinos are emitted, neutrino emission accompanies all weak interactions of interest to astrophysics. Weak interaction plays an important role in the evolution of the stars from birth to death. For example, the → proton-proton reaction is a weak interaction. Also called → weak force or → weak nuclear force. → weak; → interaction. |
Weierstrass approximation theorem farbin-e nazdineš-e Weierstrass Fr.: théorème d'approximation de Weierstrass If a function φ(x) is continuous on a closed interval [a,b], then for every ε > 0 there exists a polynomial P(x) such that |f(x) - P(x)| <ε, for every x in the interval. After German mathematician Karl Wilhelm Theodor Weierstrass (1815-1897); → approximation; → theorem. |
weight concentration dabzeš-e vazni Fr.: concentration en poids of a gas included in the composition of a → gas mixture, the ratio of mass of this gas to the mass of the whole mixture. Same as → weight fraction and → weight-fraction concentration. → weight; → concentration. |
weight fraction barxe-ye vazni Fr.: fraction en poids Same as → weight concentration. |
weight-fraction concentration barxe-ye vazni-ye dabzeš Fr.: concentration en poids Same as → weight concentration. → weight; → fraction; → concentration. |
western elongation derâzeš-e bâxtari Fr.: élongation ouest The position of a planet when it is visible in the eastern sky before dawn. → western; → elongation. |
Wheatstone bridge pol-e Wheatstone Fr.: pont de Wheatstone An device consisting of four → resistances in series, used to determine the value of an unknown electrical resistance when the other three resistances are known. Named after Charles Wheatstone (1802-1875), British physicist, who extensively used the circuit (1843) but was not its inventor. Such an arrangement of four resistances was first used by Samuel Hunter Christie (1784-1865) in 1833; → bridge. |
Wheeler-DeWitt equation hamugeš-e Wheeler-DeWitt Fr.: équation de Wheeler-DeWitt In → quantum gravity, an equation that describes the → wave function of the → Universe. It is an adaptation of the → Schrodinger equation but includes the curved space attributes of → general relativity. Named after American theoretical physicists John Archibald Wheeler (1911-2008) and Bryce Seligman DeWitt (1923-2004). |
white dwarf crystallization bolureš-e sefid kutulé Fr.: cristallisation de naine blanche The most important phenomenon occurring during → white dwarf evolution, which results from its cooling. Crystallization is a → phase transition whereby → latent heat is released. At the cooler end of a white dwarf's life (→ cooling time), the → thermal energy of nuclei, which are positively charged ions, becomes small and the effects of electrostatic interaction on the motion of ions become important. The ions repel each other and their distribution will be such that the → Coulomb energy per ion is a minimum. This will cause the ions to form crystal-like lattice structures. As the star cystallizes it releases latent heat, providing an additional energy source that slows the cooling process compared to the → Mestel theory. Once the bulk of the white dwarf is crystalline, heat can travel through the star more easily and the white dwarf cools faster. → white; → dwarf; → crystallization. |
Wilkinson Microwave Anisotropy Probe (WMAP) WMAP Fr.: WMAP A space telescope launched by NASA in 2001 which measures the temperature fluctuations in the → cosmic microwave background (CMB) radiation. It creates a full-sky map of the CMB, with a 13 arcminute resolution via multi-frequency observations. WMAP is the first mission to use a → Lagrangian point L2 as its permanent observing station at a distance of 1.5 million km. WMAP completed its prime two years of mission operations in September 2003 and is continuing in 2009 its observations for still several years to come. WMAP's measurements have played a considerable role in establishing the current standard model of cosmology. They are consistent with a Universe that is dominated by → dark energy, with negative pressure or a → cosmological constant. In this model, the age of the Universe is 13.73 ± 0.12 billion years. The current expansion rate of the Universe measured by the Hubble constant, is 70.5 ± 1.3 km·s^{-1} Mpc^{-1}. The content of the Universe consists of 4.56% ± 0.15% ordinary → baryonic matter, 22.8% ± 1.3% → cold dark matter, and 72.6% ± 1.5% of → dark energy, that accelerates the → expansion of the Universe. WMAP, short for Wilkinson Microwave Anisotropy Probe, in honor of David Todd Wilkinson (1935-2002), who had been a member of the mission's science team. |
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