An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 544

Fr.: thermalisation   

1) The process by which a system reaches → thermal equilibrium. Thermalization results from energy exchange between the components constituting the system and their exchange with the outside medium. In a gas at a given temperature, molecules move with different velocities. The gas temperature corresponds to the mean velocity of the molecules, but individual molecules may deviate largely from the mean velocity. Some move very fast others slowly and change velocity upon collisions. Collisions reduce the energy of fast moving molecules and increase that of slow ones. In the process of thermalization → matter and → radiation are in constant interaction such that their → temperatures become identical. The process goes on until energy distribution reaches → equilibrium. The system is said to be → thermalized.
2) The condition where in an → atomic or → molecular → transition the → Boltzmann factor for the two → levels of transition takes on the value it would have in → thermodynamic equilibrium.

Verbal noun of → thermalize.


Fr.: thermaliser   

To bring neutrons into → thermal equilibrium with their surroundings; to produce → thermal neutrons.

From → thermal + → -ize.

Yekgarmâyidan, literally "equal warming," from yek-, → one, + garmâyidan, infinitive from garmâ, → thermo-.

thermalized line
  خط ِ یکگرماییده   
xatt-e yekgarmâyidé

Fr.: raie thermalisée   

A collisionally excited spectral line formed in high density condition well above the → critical density. At such densities the → excitation temperature is at (or very near) the → kinetic temperature of the gas. At low densities, below the critical density, the excitation temperature will be only slightly above the radiation temperature and the emission line will be practically invisible.

Thermalized, p.p. of → thermalize; → line.


Fr.: thermion   

An electron that has been emitted from a heated body such as the hot cathode of an electron tube.

From therm- variant of → thermo- before a vowel + → ion.

thermionic emission
  گسیل ِ گرمایونی   
gosil-e garmâyoni

Fr.: émission thermionique   

Electrons gaining enough thermal energy to escape spontaneously from the cathode or dynodes and mimic photoelectrons.

thermion; → emission.

garmâ- (#)

Fr.: thermo-   

A combining form meaning "heat, hot," used in the formation of compound words. Also therm- before a vowel.

From Gk. therme "heat," thermos "hot;" cf. L. fornax "oven, kiln," related to fornus, furnus "oven," and to formus "warm;" cognate with Pers. garm "warm," as below; P.Gmc. *warmaz (O.E. wearm; E. warm; O.H.G., Ger. warm).

Garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" cognate with Gk. therme, thermos, as above; PIE *ghworm-/*ghwerm- "warm."

damâšib (#)

Fr.: thermocline   

A layer in a large body of water, such as a lake, in which temperature changes more rapidly with depth than it does in the layers above or below.

thermo- + → -cline.

damâjoft (#)

Fr.: thermocouple   

Electrical circuit consisting of two dissimilar metals, in which an electromotive force is produced when the two junctions are at different temperatures.

thermo- + → couple.


Fr.: thermodynamique   

Of or pertaining to → thermodynamics.

thermo-; → dynamic.

thermodynamic equilibrium
  ترازمندی ِ گرماتوانیک   
tarâzmandi-ye garmâtavânik

Fr.: équilibre thermodynamique   

The condition of a → thermodynamic system in which the available → energy is distributed uniformly among all the possible forms of energy. Furthermore, all → thermodynamic process es must be exactly balanced by their reverse processes. For example, inside a star there will be as many → ionizations of helium per second as there are → recombinations of free electrons and helium ions. Se also → local thermodynamic equilibrium (LTE).

thermodynamic; → equilibrium.

thermodynamic path
  په ِ گرماتوانیک   
pah-e garmâtavânik

Fr.: chemin thermodynamique   

The loci of various changes between two → states through which a → thermodynamic system passes during a → thermodynamic process.

thermodynamic; → path.

thermodynamic potential
  توند ِ گرماتوانیک   
tavand-e garmâtavânik

Fr.: potentiel thermodynaique   

A measure of the energy level of a → thermodynamic system. It represents the amount of → work obtainable when the system undergoes a → change. The main types of thermodynamic potential are: → internal energy, → enthalpy, the → Helmholtz free energy, and the → Gibbs free energy.

thermodynamic; → potential.

thermodynamic process
  فراروند ِ گرماتوانیک   
farâravand-e garmâtavânik

Fr.: processus thermodynamique   

An ordered set of → equilibrium states undergone by a → thermodynamic system. Thermodynamics processes have various types: → cyclic process, → reversible process, and → irreversible process, → isothermal process, → adiabatic process, → isentropic process.

thermodynamic; → process.

thermodynamic system
  راژمان ِ گرماتوانیک   
râžmân-e garmâtavânik

Fr.: système thermodynamique   

A quantity of substance or a working machine which in a well-defined way is set apart from its → environment. The boundary between the system and its surroundings can be real or an imaginary mathematical envelope. A thermodynamic system is not necessarily bound to a predefined geometry. Thermodynamic systems can be divided into three types: → open systems, → closed systems, and → isomated systems.

thermodynamic; → system.


Fr.: thermodynamique   

A branch of physics concerned with the relations between heat and other forms of energy and how these affect temperature, pressure, volume, mechanical action, and work.

thermo-; → dynamics, coined by the Scottish physicist William Thomson (Lord Kelvin, 1824-1907), in 1849.

damâbarqi (#)

Fr.: thermo-électrique   

Of, relating to, or produced by electric phenomena occurring in conjunction with a flow of heat.

thermo- + → electric.

thermoelectric effect
  اسکر ِ دمابرقی   
oskar-e damâbarqi

Fr.: effet thermo-électrique   

A phenomenon occurring when temperature differences exist in an electrical circuit, such as the → Peltier effect, the → Seebeck effect, and the → Thomson effect,

thermoelectric; → effect.

damâbarq (#)

Fr.: thermo-éléctricité   

The electricity produced by heat or temperature difference in a conductor.

thermo- + → electricity.

thermohaline convection
  همبز ِ گرماشور   
hambaz-e garmâšur

Fr.: convection thermohaline   

An instability in the ocean water that occurs when a layer of warm salt water is above a layer of fresh cold water of slightly higher density. In this process the hot salt water cools off and then, after having reached a higher density than the fresh water, sinks down even in the presence of stabilizing temperature gradients. This phenomenon explains the large-scale water movements in the oceans called themohaline circulation. First discussed by Melvin E. Stern (1960, Tellus 12, 172). → thermohaline mixing.

Thermohaline, from → thermo- + haline, from Gk. hals (genitive halos) "salt, sea;" cf. L. sal; O.Ir. salann; Welsh halen; O.C.S. sali "salt;" O.E. sealt; cf. O.N., O.Fris., Goth. salt, Du. zout, Ger. Salz from PIE *sal- "salt."

Garmâšur, from garmâ-thermo- + šur "salty" (Mid.Pers. šôr "salty," šorag "salt land;" cf. Skt. ksurá- "razor, sharp knife;" Gk. ksuron "razor;" PIE base *kseu- "to rub, whet").

thermohaline mixing
  آمیزش ِ گرماشور   
âmizeš-e garmâšur

Fr.: mélange thermohaline   

In stars, an instability phenomenon, reminiscent of the → thermohaline convection in the oceans, that takes place when layers of higher molecular weight occur above a region of lower molecular weight. A situation of heavier material being above lighter gas in a star can occur during the → helium flash when → helium burning does not start in the center but in the shell. Similarly, in → close binary systems it may happen that helium-rich material is transferred to a → main sequence star. Then a helium-rich outer layer is formed and the instability occurs at the interface between that layer and the original stellar material. This process can explain several surface abundance variations in stars. First discussed by S. Kato (1966, Publ. Astron. Soc. Japan 18, 374).

thermohaline; → mixing.

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