From wide, M.E., O.E. wid (cf. Du. wijd, O.H.G. wit, Ger. weit) + -th a suffix forming nouns of quality or condition, M.E. -th(e); O.E. -thu, -th.
Pahnâ, from pahn "wide, broad," from Mid.Pers. pah(a)n; Av. paθana- "broad, wide, spacious."
Fr.: loi Wiedemann-Franz
For all metals the ratio of the → thermal conductivity, κ, to the → electrical conductivity, σ, is directly proportional to the absolute temperature: K/σ = (1/3)(πk/e)2T, where k is → Boltzmann's constant and e the electron's charge.
Named after the German physicists Gustav Heinrich Wiedemann (1826-1899) and Rudolph Franz (1826-1902); → law.
Wien's displacement law
qânun-e jâ-be-jâyi-ye Wien (#)
Fr.: loi du déplacement de Wien
The wavelength corresponding to the maximum emissive power of a black body is inversely proportional to the absolute temperature of the body: λmax.T = 0.29 cm-deg. Wien's law explains why objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer. Wien's law was an early attempt to describe the → blackbody radiation. The law closely approximated the true shape of the blackbody spectrum at short wavelengths, but ultimately failed because it relied solely on classical physics. It was superseded by → Planck's radiation law, which correctly describes the blackbody spectrum at all wavelengths.
Fr.: théorème de Wiener-Khintchine
A theorem used in signal processing whereby the → spectral density of a random signal is the → Fourier transform of the corresponding → autocorrelation function. In other words, the autocorrelation function and the spectral density function constitute a → Fourier transform pair. The Wiener-Khinchin theorem allows one to estimate the spectral density function from the Fourier transform of the autocorrelation function, which is easier to handle. The theorem has an important application particularly in radio astronomy. The two following → Fourier integrals are called the Wiener-Khinchin relations: K(τ) = ∫ J(f)e-iωτdf and J(f) = ∫ K(τ)eiωτdτ (both summed over -∞ to +∞), where K(τ) is the autocorrelation function and J(f) is the spectral density.
Named after Norbert Wiener (1894-1964), American mathematician, who first published this theorem in 1930, and Aleksandr Khinchin (1894-1959), Russian mathematician, who did so independently in 1934; → theorem.
Wilkinson Microwave Anisotropy Probe (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.
Fr.: effet de Wilson-Bappu
The strong correlation between the equivalent width of Ca II → H and K lines of a late-type giant or supergiant star with the absolute visual magnitude of the star.
O. C. Wilson & M. K. Vainu Bappu (1957, ApJ 125, 661); → effect.
A member of a broad class of hypothetical elementary particles moving with non-relativistical speeds at the time of structure formation in the early Universe. WIMPs have nonzero rest mass and participate only in the weak nuclear interaction. WIMPs are expected to have collapsed into a roughly isothermal, spherical halo within which the visible portion of our galaxy resides. → dark halo. The → neutralino, predicted by supersymmetric theories is the favorite WIMP candidate. Another candidate is the → axion. WIMPs are candidates for dark matter.
1) bâd (#); 2) picidan
Fr.: 1) vent; 2) s'enrouler
1a) Meteo.: Air in motion, especially a natural and perceptible movement of air
relative to the ground.
1) M.E., O.E. wind (cf. O.S., O.Fris., Du. wind, O.H.G. wind,
Ger. Wind, Goth. winds).
1) Bâd, from Mid.Pers. wâd "wind;" Av. vāta- "wind;"
cf. Skt. vāta- "wind, god of wind;" Gk. anemos "wind;"
L. ventus "wind" (Fr. vent); cognate with E. wind, as above.
farbâl-e bâdi, ~ pat bâd
Fr.: accrétion par vent
A quasi-spherical accretion that is likely to occur in a → high-mass X-ray binary (HMXB) when the optical star of → early spectral class (O-B) does not fill its → Roche lobe, but has a significant → mass loss via → stellar wind. In → close binary systems another accretion regime, → disk accretion, occurs when the optical star overfills its Roche lobe.
Fr.: effet de couverture du vent
A process whereby dense winds of very luminous O type stars modify the temperature and internal structure of the underlying photosphere by scattering back a considerable part of the coming photospheric radiation. Not to be confused with → line blanketing .
Thus called because the wind acts like a blanket and heats the photosphere * by reflecting its radiation; → wind.
Fr.: grumelage de vent
Fr.: luminosité de vent
The final kinetic energy of the → stellar wind expressed by: (1/2)Mdot.v∞2 = (1/2)(v∞/c)L For an O6 star, L ~ 3 x 105Lsun and v∞ ~ 2000 km s-1, which give a wind luminosity of ~ 1 x 1037 erg s-1, about 1% of the → stellar luminosity. See also → photon tiring limit.
Fr.: moment angulaire de vent
Fr.: rose des vents
A diagram showing the relative frequency of winds blowing from each of the 8 or 16 main points of the compass, sometimes within specified speed ranges, at a given location over a considerable period.
An object that is balanced on a rotating axis and indicates the direction of the wind. Also called a weather vane.
→ wind + vane "a blade, plate," O.E. fanafana "piece of cloth," O.H.G. fano, Ger. Fahne "flag, standard."
Fr.: vitesse de vent
The speed at which the → stellar wind is forced away from the star. Wind velocities of → hot stars are directly measured from → P Cygni profiles, which indicate velocities from several hundred to several thousand km s-1. See also → escape velocity, → terminal velocity, → velocity law, → radiation-driven wind, → CAK model.
Fr.: problème d'enroulement
The problem encountered in the explanation of the → spiral arms of galaxies if the material making up a spiral arm is static, that is remains in the arm. Since galaxies exhibit → differential rotation, stars near the center take less time to orbit the center than those farther from the center. The arm would, after a few → galactic rotations, become increasingly curved and wind around the → galaxy ever tighter until it ultimately disappears. This is inconsistent with observations.
1) Anything likened to a window in appearance or function.
Rowzané, from rowzan "window, aperture;" Mid.Pers. rocânak "window," rôšn "light; bright, luminous," from Av. raocana- "bright, shining, radiant," raocah- "light, luminous; daylight," related to Mod.Pers. ruz "day," from Mid.Pers. rôc, O.Pers. raucah-; akin to Skt. rocaná- "bright, shining," roka- "brightness, light;" Gk. leukos "white, clear;" L. lux "light" (also lumen, luna); PIE base *leuk- "light, brightness." The Persian words rowšan "bright, clear," foruq "light," and afruxtan "to light, kindle" also belong to this family, as well as the E. light, Ger. Licht, and Fr. lumière; forusorx→ infrarouge.
Fr.: fonction fenêtre
A function whose value is zero outside a given interval. Applications of window functions include signal filtering and spectral analysis. The various types of windw functions include: → rectangular window, cosine window, triangular window, Gaussian window, Hanning window, and so on.
mey (#), bâdé (#), nabid (#)
The fermented juice of grapes, made in many varieties, such as red, white, sweet, dry, still, and sparkling, for use as a beverage, in cooking, in religious rites, etc., and usually having an alcoholic content of 14 percent or less (Dictionary.com).
M.E., O.E. win, cognate with O.H.G. win, Du. wijn, Ger. Wein, from L. vinum "wine," from PIE *woin-o-, related Gk. word oinos.
Mey, variant mol "wine;" Mid.Pers. mad, may "wine;"
Av. maδu- "wine;" cf. Skt. madhu- "wine, sweet drink, sweet;"
Gk. methy "wine;" O.C.S. medu; Lith. medus "honey;"
O.Irish mid; Welsh medd; Breton mez "mead;"
O.E. medu; E. mead "fermented honey drink;" Russ. medved