parâš-e Fresnel (#)
Fr.: diffraction de Fresnel
The diffraction effects obtained when either the source of light or observing screen, or both, are at a finite distance from diffracting aperture or obstacle. → Fraunhofer diffraction.
Named after Jean Augustin Fresnel (1788-1827), French physicist, a key figure in establishing the wave theory of light. His earlier work on interference was carried out in ignorance of that of Thomas Young (1773-1829), English physician and physicist, but later they corresponded and were allies; → diffraction.
Fr.: interaction fondamentale
Any of the four interactions in nature between bodies of matter and that are mediated by one or more particles. Also called the → fundamental force. In order of decreasing strength, the four fundamental interactions are the → strong interaction, the → electromagnetic interaction, the → weak interaction, and the → gravitational interaction.
Fr.: réfraction géodésique
The limiting case of → astronomical refraction when the light path is entirely within the Earth's atmosphere.
Fr.: attraction gravitationnelle
The force that pulls material bodies toward one another because of → gravitation.
Fr.: contraction gravitationnelle
Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force.
Fr.: interaction gravitationnelle
Mutual attraction between any two bodies that have mass.
šekast-e ofoqi (#)
Fr.: réfraction horizontale
The angular distance of an object below the horizon when it appears to lie on the horizon.
index of refraction
Fr.: indice de réfraction
Same as → refractive index.
General: Mutual or reciprocal action or influence.
Capable of acting on or influencing each other
Fr.: fractionnement isotopique
A slight difference between the → abundances of → isotopes of the same → chemical element owing to → physical or → chemical → processes. It results in the → enrichment or → depletion of an isotope. Same as → isotopic fractionation.
Fr.: fractionnement isotopique
Same as → isotope fractionation.
Fr.: contraction de Kelvin-Helmholtz
After the Scottish physicist William Thomson, also known as Lord Kelvin (1824-1907) and the German physicist and physician Hermann Ludwig Ferdinand von Helmholtz (1821-1894), who made important contributions to the thermodynamics of gaseous systems; → contraction.
law of refraction
qânun-e šekast (#)
Fr.: loi de réfraction
One of the two laws governing → refraction of light when it enters another transparent medium: a) The → incident ray, normal to the surface, and refracted ray, all lie in the same plane. b) → Snell's law is satisfied.
Fr.: contraction de longueur
Same as → Lorentz contraction.
line of action
xatt-e žireš, ~ koneš
Fr.: ligne d'action
Of a force, the straight line along which the force → vector is directed. The action of a force on a → rigid body does not change when its point of application is displaced along the line of action. Hence, forces applied to a rigid body can be regarded as non-localized, or sliding, vectors.
1) The act or process of liquefying or making liquid.
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.: 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.: réaction nucléaire
A process in which the energy, composition, or structure of an atomic nucleus changes.