quantum phase transition (QPT)
gozareš-e fâz-e kuântomi
Fr.: transition de phase quantique
A phase transitions that occurs at zero temperature as a function of a non-thermal parameter like → pressure, → magnetic field, or → chemical composition. In contrast to ordinary → phase transitions, which are associated with passage through a critical temperature, quantum phase transitions are associated with → quantum fluctuations, a consequence of → Heisenberg's uncertainty principle. For example, see → Bose-Einstein condensation.
quark-hadron phase transition
gozareš-e fâz-e kuârk-hâdron
Fr.: transition de phase quark-hadron
A phase transition, predicted by cosmological models, to have occurred at approximately 10-5 seconds after the Big Bang to convert a plasma of free quarks and gluons into hadron.
Fr.: intensité de rayonnement
A measure of the amount of radiation emitted from a point expressed as the radiant flux per unit solid angle leaving this source.
radiation density constant
pâypa-ye cagâli-ye tâbeš
Fr.: constante de rayonnement
The constant related to the total energy radiated by a → blackbody and defined as: a = 4σ/c, where σ is the → Stefan-Boltzmann constant and c the → speed of light. Its value is a = 7.5657 x 10-15 erg cm-3 K-4. Same as → radiation constant.
Fr.: transition radiative
A transition between two states of an atomic or molecular entity, the energy difference being emitted or absorbed as photons.
radio flux density
cagâli-ye šârr-e râdioyi
Fr.: densité de flux radio
Fr.: densité relative
The ratio of the density of a substance to the density of a given reference material. For a solid or liquid, it is the density (at 20°C) relative to the maximum density of water (at 4°C). For a gas is its density divided by the density of hydrogen (or sometimes dry air) at the same temperature and pressure. Also called → specific density.
Fr.: effet Rossiter-McLaughlin
A → spectroscopic phenomenon observed when either an → eclipsing binary's → secondary star or an → extrasolar planet is seen to → transit across the face of the → primary body. Because of the rotation of the star, an asymmetric distortion takes place in the → line profiles of the stellar spectrum, which changes during the transit. The measurement of this effect can be used to derive the → alignment of the → orbit of the transiting exoplanet with respect to the → rotation axis of the star.
Named after Richard Alfred Rossiter (1886-1977) and Dean Benjamin McLaughlin (1901-1965), American astronomers.
Fr.: transition rotationnelle
A slight change in the energy level of a molecule due to the rotation of its constituent atoms about their center of mass.
Fr.: densité scalaire
Fr.: transition semi-interdite
Endowed with sensation; having perception through the senses. Responding to a stimulus.
From M.Fr. sensitif, from M.L. sensitivus "capable of sensation," from L. sensus, p.p. of sentire "feel perceive," → sense.
hessmand, from hess, → sense + -mand possession suffix.
1) The required brightness for an object in order to be detected by an observing instrument.
A highly sensitive telescope can detect dim objects, while a telescope
with low sensitivity can detect only bright ones.
State noun from → sensitive.
1) To rest with the body supported by the buttocks or thighs; be seated.
Nešastan "to sit down; to settle down; to sink;" Mid.Pers. nišastan "to sit;" O.Pers. nišādayam [1 sg.impf.caus.act.] "to sit down, to establish," hadiš- "abode;" Av. nišasiiā [1 sg.subj.acr.] "I shall sit down," from nihad- "to sit down," from → ni- "down; into" + had- "to sit;" PIE base *sed- "to sit;" cf. Skt. sad- "to sit," sidati "sits;" Gk. hezomai "to sit," hedra "seat, chair;" L. sedere "to sit;" O.Ir. suide "seat, sitting;" Welsh sedd "seat;" Lith. sedmi "to sit;" Rus. sad "garden;" Goth. sitan, Ger. sitzen; E. sit. See also: → reside, → settle.
The position or location of a building, observatory, etc. especially as to its environment. → astronomical site.
M.E., from L situs "position, arrangement, site," from sinere "to let, leave alone, permit," cognate with Av. šiti- "place, abode, residence," as below.
Sit, from Av. šiti- "place, abode, residence," šitāy- "habitation, dwelling," from ši- "to live;" cognate with Skt. ksay- "to live, to stay," kséti "he dwells;" Gk. ktizein "to inhabit, build;" L. situs "position, site; situated."
Fr.: sélection de site
The process of choosing a site for an astronomical observatory based on meteorology, seeing conditions, and access to the site.
→ site; → selection.
To place in a site or context; to locate.
From M.L. situatus, p.p. of situare "to place, locate," from L. situs "place, position."
Sitidan, from sit, → site, + -idan infinitive suffix.
Having a site, situation or location.
P.p. of → situate.
1) The manner of being placed with respect to surroundings.
Verbal noun of → situate.
tâbandegi-ye xoršid (#)
Fr.: luminosité solaire
The total → radiant energy, in all wavelengths, emitted by the Sun in all directions. It is 3.828 × 1026 W or 3.828 × 1033 erg sec-1 (International Astronomical Union, Resolution B3, 14 August 2015, Honolulu, USA). This is the luminosity unit conventionally used to give the luminosities of stars. See also: → solar constant. When the Earth first formed, 4.56 billion years ago, the Sun radiated 30% less energy than it does today, thus giving rise to the so-called → faint early Sun paradox. Ever since then, its power has increased by 7% every billion years (I. Ribas, 2009, arXiv:0911.4872).