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
The process goes on until energy distribution reaches
The system is said to be → thermalized.
Verbal noun of → thermalize.
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.
An electron that has been emitted from a heated body such as the hot cathode of an electron tube.
Fr.: émission thermionique
Electrons gaining enough thermal energy to escape spontaneously from the cathode or dynodes and mimic photoelectrons.
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."
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.
Electrical circuit consisting of two dissimilar metals, in which an electromotive force is produced when the two junctions are at different temperatures.
Of or pertaining to → thermodynamics.
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).
Fr.: chemin thermodynamique
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.
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.
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.
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.
Of, relating to, or produced by electric phenomena occurring in conjunction with a flow of heat.
Fr.: effet thermo-électrique
The electricity produced by heat or temperature difference in a conductor.
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").
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).