Fr.: contraction de Lorentz
The decrease in the length of a body moving in the direction of its length as measured by an observer situated in that direction. The shortening factor is [1 - (v/c)2]1/2, where v is the relative velocity and c light speed.
Fr.: facteur de Lorentz
In → special relativity, an important parameter which appears in several equations, including → time dilation, → length contraction, and → relativistic mass. It is defined as γ = 1 / [1 - (v/c)2]1/2 = dt/dτ, where v is the velocity as observed in the reference frame where time t is measured, τ is the proper time, and c the → velocity of light. Same as Lorentz γ factor.
Fr.: fraction de masse
The fractional amount (by mass) of a given → chemical element or → nuclide in a given → chemical composition. In chemical composition studies of astrophysical objects the mass fractions of → hydrogen, → helium, and all the remaining chemical elements are usually denoted by the parameter X, Y, and Z, respectively. Their sum is defined as X + Y + Z = 1. The parameter Z is usually referred to as → heavy elements or → metals.
Fr.: impact météoritique
A striking of a meteorite against another body, especially the solar system planets or satellites.
Fr.: réaction nucléaire
A process in which the energy, composition, or structure of an atomic nucleus changes.
Fr.: réacteur nucléaire
A device in which a nuclear fission chain reaction is maintained and controlled for the production of nuclear energy or radioactive isotopes.
nulling fraction (NF)
Fr.: fraction de phase d'arrêt
Fr.: activité optique
The property possessed by some substances and their solutions of rotating the plane of vibration of → polarized light. When a beam of → linearly polarized light is sent through an optically active substance, such as crystalline quartz and sugar solution, the direction of vibration of the emerging linearly polarized light is found to be different from the original direction. Those which rotate the → plane of polarization to the right, for an observer looking in the incoming beam, are called → dextrorotatory or right handed; those which rotate it to the left, → levorotatory or left handed. Optical activity may be due to an asymmetry of molecules of a substance (solutions of cane sugar) or it may be a property of a crystal as a whole (crystalline quartz).
Fr.: optiquement actif
Relating to → optical activity.
barxe-ye anbÃ¢štegi (#)
Fr.: coefficient de tassement
The difference between the isotopic mass of a nuclide and its mass number divided by its mass number. The packing fraction is a measure of the stability of the nucleus.
Packing, from the verb pack "to put together in a pack," from the noun pack, from M.E. pak, packe, from M.D. pac or perhaps M.L.G. pak; → fraction.
Barxé, → fraction; anbÃ¢štegi quality noun of anbÃ¢štan, anbÃ¢rdan "to fill, to replete;" Mid.Pers. hambāridan "to fill;" from Proto-Iranian *ham-par-, from prefix ham- + par- "to fill;" cf. Av. par- "to fill," parav-, pauru-, pouru- "full, much, many;" O.Pers. paru- "much, many;" Mid.Pers. purr "full;" Mod.Pers. por "full, much, very;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full.
Of or pertaining to a parallax.
Adj. form of → parallax.
Fr.: angle parallactique
Of an object in the sky, the angle between the → celestial pole, the object, and the → zenith. Since parallactic angle describes the orientation on the sky of the object for a particular observer, it can be an important quantity in some observations.
Fr.: ellipse de parallaxe
The path on the sky of the apparent position of a star as seen from the Earth, due to the Earth's annual motion around the Sun.
Fr.: inégalité parallactique
An irregularity in the Moon's motion caused by the Sun's gravitational attraction, which sets the Moon ahead or behind its normal orbital position. The Moon is about 2 arcminutes ahead of its expected position at first quarter, and a similar amount behind at last quarter.
Fr.: mouvement parallactique
The proper motion of a star due to the effect of the Sun's motion relative to the → local standard of rest.
Of or pertaining to a → perigalacticon.
The point in an object's orbit around a galaxy when the object lies closest to the galactic center; opposite of → apogalacticon.
Fr.: fraction de polarisation
The ratio expressed by P = (Ipar - Iper) / (Ipar + Iper), where Ipar and Iper are the light intensities with the electric field vector respectively parallel and perpendicular to the incident beam.
That can be done or used or put into practice.
Concerned with practice, as opposed to → theory.