diyâri, padidâri (#)
1) General: The state or fact of being visible.
→ crescent Moon visibility,
→ Venus visibility.
karyâ-ye diyâri, ~ padidâri
Fr.: fonction de visibilité
hâmon-e diyâri, ~ padidâri
Fr.: plan de visibilité
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 km3.
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.
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.
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.: 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.
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 ≤ CJ. The surface that limits this region, defined by U = CJ, is called the zero-velocity surface.