<< < -it ang bis cit cre dim ele flu gra ima iso lum men nec opt per pri rad rel sim spe the uti vis > >>
visibility diyâri, padidâri (#) Fr.: visibilité 1) General: The state or fact of being visible.
→ crescent Moon visibility,
→ Venus visibility. |
visibility function karyâ-ye diyâri, ~ padidâri Fr.: fonction de visibilité The → Fourier transform of a source's → brightness distribution, weighted by the characteristics of the → interferometer's antennas. → visibility; → function. |
visibility plane hâmon-e diyâri, ~ padidâri Fr.: plan de visibilité In → interferometry, the projection of a → baseline onto the plane normal to the source direction defining a vector in (u,v) space, measured in wavelength units. → visibility; → plane. |
visual acuity tiznâyi-ye did Fr.: acuité visuelle Same as → acuity of vision. |
volcanic explosivity index (VEI) dišan-e oskaftandegi-ye âtašfešâni Fr.: indice d'explosivité volcanique A logarithmic scale, ranging from 1 to 8, used to measure the intensity of volcano eruptions. The VEI is based on several factors: the degree of fragmentation of the volcanic products released by the eruption, the amounts of sulfur-rich gases that form stratospheric aerosols, the volume of the eruptions, their duration, and the height is reached. The largest eruptions (8) produce an amount of bulk volume of ejected → tephra of ~ 1,000 km^{3}. → volcanic; → explosivity; → index. |
vorticity gerdšârigi Fr.: vorticité In fluid mechanics, a measure of the rate of rotational spin in a fluid.
Mathematically, vorticity is a vector field defined as the curl of the velocity field:
ω = ∇ x v. |
wave-particle duality dogânegi-ye mowj-zarré Fr.: dualité onde-particule The principle admitted in → quantum mechanics that
all particles have a wave-like nature and that waves have a particle aspect.
The wave-particle duality is of fundamental importance in obtaining a realistic picture of
the → elementary particles. |
weight of a tensor density vazn-e cagâli-ye tânsor Fr.: poids d'une densité de tenseur A constant the value of which is characteristic for any given → tensor density. |
wind luminosity tâbandegi-ye bâd 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 10^{5}Lsun and v_{∞} ~ 2000 km s^{-1}, which give a wind luminosity of ~ 1 x 10^{37} erg s^{-1}, about 1% of the → stellar luminosity. See also → photon tiring limit. → wind; → luminosity. |
wind velocity tondâ-ye bâd 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. |
zero-velocity surface ruye-ye tondâ-ye sefr Fr.: surface de vitesse nulle In the → restricted three-body problem, a surface which limits the region of space in which a small body can move. In the expression for the → Jacobi integral, the left side value is always positive or nul; hence the particle motion is confined to the region where U ≤ C_{J}. The surface that limits this region, defined by U = C_{J}, is called the zero-velocity surface. |
<< < -it ang bis cit cre dim ele flu gra ima iso lum men nec opt per pri rad rel sim spe the uti vis > >>