radial velocity method
raveš-e tondâ-ye šo'â'i
Fr.: méthode de vitesses radiales
The technique based on the analysis of the → radial velocity curve, used to detect the presence of an invisible secondary around a host star. This method holds the majority of exoplanet discoveries.
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.
radio flux density
cagâli-ye šârr-e râdioyi
Fr.: densité de flux radio
The spontaneous disintegration of certain atomic nuclei, which is accompanied by the emission of either α- or β- particles and/or a γ rays.
Fr.: instabilité Rayleigh-Taylor
A type of hydrodynamical instability between two fluids of different densities, which occurs when the heavy fluid lies above the lighter fluid in a gravitational field. More generally a material interface is said to be Rayleigh-Taylor unstable whenever the fluid acceleration has an opposite direction to the density gradient.
1) General: The quality or condition of being reactive.
1) The state or quality of being real. A real thing or fact.
tondâ-ye dur šodan
Fr.: vitesse d'éloignement
The velocity with which an object moves away from another object or a reference point.
Fr.: théorème de réciprocité
1) General: Any theorem that expresses various reciprocal relations for the
behavior of some physical systems, in which input and output can be
interchanged without altering the response of the system to a given
The quality of being → refutable.
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.: humidité relative
The amount of moisture in the air compared to what the air can "hold" at that temperature. It is given by the ratio of the partial pressure of water vapor in the mixture to the saturated vapor pressure of water at a specific temperature.
Fr.: perméabilité relative
Fr.: vitesse relative
For two objects A and B, the velocity which B, supposing itself at rest, assigns to A.
Fr.: vitesse relativiste
The velocity of a body when it is a significant fraction of the → speed of light.
relativity of simultaneity
Fr.: relatitivité de simultanéité
Fr.: principe de relativité
The requirement employed by Einstein in his relativity theories, that the equations describing the laws of physics are the same in all frames of reference. This statement and that of the constancy of the speed of light constitute the founding principles of special relativity.
Relativity; → principle.