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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unitary transformation
  ترادیس ِ یکایی، ~ یکانی   
tarâdis-e yekâyi, ~ yekâni

Fr.: transformation unitaire   

A transformation whose reciprocal is equal to its Hermitian conjugate.

unitary; → transformation.

universal gas constant
  پایای ِ هرگانی ِ گاز‌ها   
pâyâ-ye hargâni-ye gâzhâ

Fr.: constante universelle des gaz   

Same as → gas constant.

universal; → gas; → constant.

upper culmination
  بالست ِ زبرین   
bâlest-e zabarin

Fr.: culmination supérieure   

Same as → superior culmination.

upper; → culmination.

uranium conversion
  هاگرد ِ اورانیوم   
hâgard-e urâniom

Fr.: convesrion de l'uranium   

A chemical process converting the → yellowcake to → uranium hexafluoride. The uranium hexafluoride is heated to become a gas and loaded into cylinders. When it cools, it condenses into a solid.

uranium; → conversion.

utilization
  هودش   
hudeš

Fr.: utilisation   

The act or process of utilizing.

Verbal noun of → utilize.

vacuum polarization
  قطبش ِ خلاء   
qotbeš-e xala'

Fr.: polarisation du vide   

A quantum field theory a process in which an electromagnetic field gives rise to virtual electron-positron pairs that in turn exert electromagnetic fields of their own, in a manner similar to classical dielectric polarization.

vacuum; → polarization.

valence electron
  الکترون ِ ارزایی   
elektron-e arzâyi

Fr.: électron de valence   

An electron of an atom lying farthest from the nucleus. Valence electrons are shared when atoms combine to form molecules.

valence; → electron.

van der Waals equation
  هموگش ِ وان در والس   
hamugeš-e van der Waals

Fr.: équation de van der Waals   

An → equation of state that satisfactorily describes the behavior of → real gass over a wide range of temperatures and pressures. It is derived from considerations based on kinetic theory, taking into account to a first approximation the size of a molecule and the cohesive forces between molecules: (P + a / V2) (V - b) = RT, where P, V, and T are pressure, volume, and temperature and R the gas constant. a and b are characteristic constants for a given substance. For a = b = 0, the van der Waals equation reduces to the characteristic equation of an → ideal gas. See also → Dieterici equation.

Named after Dutch physicist Johannes Diderik van der Waals (1837-1923), Nobel Prize in Physics 1910; → equation.

vaporization
  بخارش   
boxâreš

Fr.: vaporisation, évaporation   

The act of vaporizing. The state of being vaporized.
The rapid change of water into steam.

Verbal noun of → vaporize.

variable star designation
  نامگزینی ِ ستاره‌ی ِ ورتنده   
nâmgozini-ye setâre-ye vartandé

Fr.: designation des étoiles variables   

A set of conventions used for naming → variable stars. Stars with existing → Bayer designations are not given new designations. Alternatively, the letters R through Z are used followed by the Latin genitive of the name of the hosting constellation. Otherwise, two letters of alphabet are used (334 combinations) with the Latin genitive of the name of the constellation. Finally, the letter V (variable) is used followed by numbers 335, 336, and so on. Some examples are: → P Cygni, → T Tauri, → FU Orionis, → EX Lupi, and → V2052 Oph.

variable; → star; → designation.

variation
  ورتش   
varteš

Fr.: variation   

1) General: An instance of changing, or something that changes.
2) Astro.: The periodic inequality in the Moon's motion that results from the combined gravitational attraction of the Earth and the Sun. Its period is half the synodic month, that is 14.77 days, and the maximum longitude displacement is 39'29''.9.
See also: → calculus of variations, → annual variation, → secular variation.

M.E., from O.Fr. variation, from L. variationem (nominative variatio) "difference, change," from variatus, p.p. of variare "to change," → vary.

Varteš, verbal noun from vartidan, → vary.

variational
  ورتشی   
varteši

Fr.: variationnel   

Of or describing a → variation.

variation; → -al.

variational principle
  پروز ِ ورتشی   
parvaz-e varteši

Fr.: principe variationnel   

Any of the physical principles that indicate in what way the actual motion of a state of a mechanical system differs from all of its kinematically possible motions or states. Variational principles that express this difference for the motion or state of a system in each given instant of time are called → differential. These principles are equally applicable to both → holonomic and → nonholonomic systems. Variational principles that establish the difference between the actual motion of a system during a finite time interval and all of its kinematically possible motions are said to be → integral. Integral variational principles are valid only for holonomic systems. The main differential variational principles are: the → virtual work principle and → d'Alembert's principle.

variational; → principle.

Varignon's theorem
  فربین ِ وری‌نیون   
farbin-e Varignon

Fr.: théorème de Varignon   

The → moment of the resultant of a → coplanar system of → concurrent forces about any center is equal to the algebraic sum of the moments of the component forces about that center.

Named after Pierre Varignon (1654-1722), a French mathematician, who outlined the fundamentals of statics in his book Projet d'une nouvelle mécanique (1687).

vector boson
  بوسون ِ برداری   
boson-e bordâri

Fr.: boson vectoriel   

In nuclear physics, a → boson with the spin quantum number equal to 1.

vector; → boson.

vector function
  کریای ِ برداری   
karyâ-ye bordâri

Fr.: fonction vectorielle   

A function whose value at each point is n-dimensional, as compared to a scalar function, whose value is one-dimensional.

vector; → function.

vector meson
  مسون ِ برداری   
mesoon-e bordâri

Fr.: meson vectoriel   

Any particle of unit spin, such as the W boson, the photon, or the rho meson.

vector; → meson.

vector perturbation
  پرتورش ِ برداری   
partureš-e bordâri

Fr.: perturbation vectorielle   

The perturbation in the → primordial Universe plasma caused by → vorticity. These perturbations cause → Doppler shifts that result in → quadrupole anisotropy.

vector; → perturbation.

vegetation
  گیاهش   
giyâheš

Fr.: végétation   

1) All the plants or plant life of a place.
2) (Botany) Plant life as a whole, especially the plant life of a particular region.
3) The act or process of vegetating.

Verbal noun from → vegetate.

velocity dispersion
  پاشش ِ تندا   
pâšeš-e tondâ

Fr.: dispersion de vitesses   

The → standard deviation of a velocity → distribution. It indicates how objects of the sample move relative to one another. Objects with similar velocities have a small velocity dispersion, whereas objects with very different velocities have a large velocity dispersion.

velocity; → dispersion.

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