An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 194 Search : sit
transition disk
  گرده‌ی ِ گذرش، دیسک ِ ~   
gerde-ye gozaresh, disk-e ~

Fr.: disque de transition   

The → accretion disk of a → T Tauri star that displays very weak or no → infrared excess at → near infrared wavelengths, but shows strong excess at → intermediate infrared and longer wavelengths. This happens when the hot inner dust disk has dissipated whereas the cooler outer disk is still intact.

transition; → disk.

transition function
  کریای ِ گذرش   
karyâ-ye gozareš

Fr.: fonction de transition   

The → probability of finding the → Universe in a → state labelled X2 at a time t2, if it was in a state X1 at an earlier time t1.

transition; → function.

transition probability
  شوانایی ِ گذرشی   
šavânâyi-ye gozareši

Fr.: probabilité de transition   

The probability that a quantum-mechanical system will make a transition from a given initial state to a given final state.

transition; → probability.

transitional flow
  تچان ِ گذرشی   
tacan-e gozareši

Fr.: flux de transition   

In fluid mechanics, a flow composed of → laminar and → turbulent flows, for which the → Reynolds number is between 2300 and 4000.

transition; → flow.

transposition
  ترانهش   
tarâneheš

Fr.: transposition   

Math.: A permutation of a set of elements that interchanges two elements and leaves the remaining elements in their original positions. For example, the swapping of 2 and 5 to take the list 123456 to 153426 is a transposition.
Optics: The changing of the relative curves of a lens without changing its refractive value.

trans-; → position.

true position
  نهش ِ راستین   
neheš-e râstin

Fr.: position vraie   

The coordinates of an object for a given date, with respect to the true equator and the true equinoxes for the instant of time in question.

true; → position.

university
  دانشگاه   
dânešgâh (#)

Fr.: université   

An institution of higher education composed of several faculties for teaching and research and authorized to grant academic degrees.

M.E., from O.Fr. universitei, from M.L. universitatem (nominative. universitas), in L.L. "corporation, society," from L., "the whole, aggregate," from universus "whole, entire," → universe.

Dânešgâh, from dâneš, → science, + -gâh "place; time" (Mid.Pers. gâh, gâs "time;" O.Pers. gāθu-; Av. gātav-, gātu- "place, throne, spot;" cf. Skt. gâtu- "going, motion; free space for moving; place of abode;" PIE *gwem- "to go, come").

upper transit
  گذر ِ زبرین   
gozar-e zabarin (#)

Fr.: passage supérieur   

The movement of a celestial body across a celestial meridian's upper branch. Same as → upper culmination.

upper; → transit.

vector density
  چگالی ِ بردار   
cagâli-ye bordâr

Fr.: densité de vecteur   

A → tensor density of → order 1.

vector; → density.

vibrational transition
  گذرش ِ شیوشی   
gozareš-e šiveši

Fr.: transition vibrationnelle   

A transition between two → quantized  → levels of a → molecule that have different vibrational energies.

vibrational; → transition.

vibrational-rotational transition
  گذرش ِ چرخشی-شیوشی   
gozareš-e carxeši-šiveši

Fr.: transition vibrationnelle-rotationnelle   

A slight change in the → energy level of a → molecule due to → vibrational transition and/or → rotational transition.

vibrational; → rotational; → transition.

viscosity
  وشکسانی   
vošksâni (#)

Fr.: viscosité   

The property of a → fluid that resists the force tending to cause the fluid to flow. Viscosity may be thought of as the internal → friction of two fluid layers which flow parallel to each other at different speeds. The cause of viscosity is the transport of → momentum by the molecules from one layer to the other. Viscosity is given by η = φ.u.λ.ρ, where φ is a coefficient which depends on the nature of the interaction between the molecules, u is the average velocity of thermal motion of the molecules, λ is the → mean free path, and ρ the → density of the fluid. Also called → dynamic viscosity or → absolute viscosity. See also → kinematic viscosity.

Noun from → viscous; → -ity.

weight of a tensor density
  وزن ِ چگالی ِ تانسور   
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.

weight; → tensor; → density.

wind luminosity
  تابندگی ِ باد   
tâbandegi-ye bâd

Fr.: luminosité de vent   

The final kinetic energy of the → stellar wind expressed by: (1/2)Mdot.v2 = (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.

wind; → luminosity.

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