A substance that vaporizes at relatively low temperatures (e.g. H2O, CO2, CO, CH4, NH3, and so forth). The opposite of volatile is → refractory.
M.E., from M.Fr. volatile, from L. volatilis "fleeting, transitory, flying," from p.p. stem of volare "to fly," of unknown origin.
Parrâ "flying," from paridan "to fly in the air," → Volans.
Fr.: élément volatile
In → planetary science, any of a group of → chemical elements and → chemical compounds with relatively low → boiling points that are associated with a planet's or moon's → crust and/or → atmosphere. For example, H, He, C, N, O are underabundant (relative to the solar → photospheric values) in all types of → meteorites, including the C1 → carbonaceous chondrites. Any heating of the meteorite parent body subsequent to its formation would tend to drive the volatile elements out of the rock, whence it sublimated into → interplanetary medium.
Of or relating to a volcano. Characterized by volcanoes.
Fr.: éruption volcanique
The explosive ejection of superheated matter from a → volcano.
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.
dudkaš-e âtašfešâni (#)
Fr.: cheminée volcanique
From It. vulcano, from L. Vulcanus, → Vulcan.
Âtašfešân, literally "fire disperser, dispersing fire," from âtaš, → fire, + fešân contraction of afšân, from afšândan "to spread, scatter," Mid.Pers. afšân "to spread, to scatter;" ultimately from Proto-Ir. *apašan-, from root *šan- "to shake" (Cheung 2007).
The SI unit of potential difference, defined as the difference of potentials across the ends of a conductor in which a power 1 watt is liberated when a current of 1 ampere flows through it.
In honor of the Italian scientist Alessandro Volta (1745-1827), known for his pioneering work in electricity and the invention of the first battery.
Fr.: voltage, tension
The electric potential difference expressed in volts.
From → volt.
Of, relating to electricity or electric currents, especially when produced by chemical action, as in a cell. → photovoltaic detector.
Alessandro Volta (1745-1827), Italian physicist, known for his pioneering work in electricity.
The amount of space occupied by a three-dimensional object or region of space, expressed in cubic units.
M.E. volum(e), from O.Fr. volume, from L. volumen (genitive voluminis) "roll (as of a manuscript), coil, wreath," from volvere "to turn around, roll."
Gonj "volume," gonjidan "to be contained or held; to hold;" gonjâyeš "capacity, holding, containing;" Mid.Pers. winj- "to be contained;" Proto-Iranian *uiac-/*uic-; cf. Skt. vyac- "to contain, encompass," vyás- "extent, content, extension;" L. uincire "to bind."
bardid bâ gonj-e hyaddmand
Fr.: relevé limité en volume
A survey in which the observed objects are contained in a given volume of space.
von Zeipel paradox
pârâdxš-e von Zeipel
Fr.: paradoxe de von Zeipel
A → rotating star cannot simultaneously achieve → hydrostatic equilibrium and → rigid body rotation. The paradox can be solved if → baroclinic flows (essentially a → differential rotation and a → meridional circulation) are included. For a broader view of the subject see: M. Rieutord, 2006, in Stellar Fluid Dynamics and Numerical Simulations: From the Sun to Neutron Stars, ed. M. Rieutord & B. Dubrulle, EAS Publ., 21, 275, arXiv:astro-ph/0608431.
von Zeipel theorem
farbin-e von Zeipel
Fr.: théorème de von Zeipel
A theorem that establishes a relation between the → radiative flux at some → colatitude on the surface of a → rotating star and the local → effective gravity (which is a function of the → angular velocity and colatitude). For a rotating star in which → centrifugal forces are not negligible, the → equipotentials where gravity, centrifugal force, and pressure are balanced will no longer be spheres. The theorem states that the radiative flux is proportional to the local effective gravity at the considered colatitude, F(θ) ∝ geff (θ)α, where α is the → gravity darkening coefficient. As a consequence, the stellar surface will not be uniformly bright, because there is a much larger flux and a higher → effective temperature at the pole than at the equator (Teff (θ) ∝ geff (θ)β, where β is the → gravity darkening exponent. In → massive stars this latitudinal dependence of the temperature leads to asymmetric → mass loss and also to enhanced average → mass loss rates. Also called → gravity darkening. See also → von Zeipel paradox; → meridional circulation; → baroclinic instability; → Eddington-Sweet time scale.
Named for Edvard Hugo von Zeipel, Swedish astronomer (1873-1959), who published his work in 1924 (MNRAS 84, 665); → theorem.
von Zeipel's law
qanun-e von Zeipel
Fr.: loi de von Zeipel
Same as the → von Zeipel theorem.
A whirling mass of water or air.
From L. vortex, variant of vertex "whirlpool; whirlwind, an eddy of water, wind, or flame;" from stem of vertere "to turn," cognate with Pers. gardidan, as below.
Gerdšâr (on the model of gerdâb "whirlpool" and gerdbâd "whirlwind"), from gard present stem of gardidan "to turn, to change" (Mid.Pers. vartitan "to change, to turn;" Av. varət- "to turn, revolve;" cf. Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend") + šâr, from šâré, → fluid.
Of or pertaining to a → vortex.
Adj. from → vortex.
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.
A speech sound that is produced as a stream of air that is not obstructed or blocked in any way by the vocal organs, but only modulated by the position of the tongue, lips, etc.
A hypothetical small planet proposed in the 19-th century to exist in an orbit between Mercury and the Sun. In order to explain some characteristics of Mercury's orbit, the French astronomer Urbain Jean Joseph Le Verrier (1811-1877) hypothesized the presence of another planet, which he named Vulcan. Those particularities of Mercury's orbit were later explained by Albert Einstein's theory of general relativity.
L. Vulcanus in Roman mythology the blacksmith god of fire and volcanoes, a word of Etruscan origin