tâbeš-e Čerenkov (#)
rayonnement de Čerenkov
Visible radiation emitted when → charged particles pass through a transparent medium faster than the speed of light in that medium.
Named after Pavel A. Čerenkov (1904-1990), Russian physicist, who discovered the phenomenon. He shared the Nobel prize 1958 in physics with Ilya Frank and Igor Tamm, who in 1937 gave the theoretical explanation for this radiation.
Fr.: figure de Chladni
Named after Ernst Chladni (1756-1827), German physicist; → figure.
Being, having, characterized by, or occurring in approximately 24-hour periods or cycles, as of biological activity or function (Merriam-Webster.com).
Fr.: rythme circardien
Any of several physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism's environment. Circadian rhythms are found in most living things, including animals, plants and many tiny microbes.
Fr.: échelle CO
A spectral line energy distribution which plots the intensity of each → carbon monoxide (CO) transition as a function of the upper J number. This type of → diagram is a powerful diagnostic tool, where models show that these CO ladders have very different shapes depending on the type of excitation (i.e. photon dominated region, PDR or X-ray dominated region, XDR) as well as density and radiation environment.
vine-ye hamafzudé, tasvir-e ~
Fr.: image intégrée
An image made up of several individual images of relatively short exposure times which are added together in order to produce a final image of higher quality.
compact radio source
xan-e râdioyi-ye hampak
Fr.: source radio compacte
An object emitting intense energy in radio wavelength from a small, unresolved central region.
1) The act of contradicting; assertion of the contrary or opposite.
M.E., from O.Fr. contradiction or directly from L. contradictionem "objection, counterargument," from contradicere, from contra dicere "to speak against," from → contra- "against" + dicere "to speak," akin to Pers. dis, → form.
Asserting the contrary or opposite; contradicting; inconsistent; logically opposite (Dictionary.com).
Adjective from → contradiction.
Fr.: rayon de corotation
1) In the → X-wind model of → accretion,
the distance from the star where the → centrifugal force
on a particle corotating with the star balances the
→ gravitational attraction; in other words, where the
→ accretion disk rotates at the same
→ angular velocity as the star.
Fr.: rayonnement corpusculaire
A stream of atomic or subatomic particles.
cosmic background radiation
tâbeš-e paszaminé-ye keyhâni
Fr.: rayonnement du fond cosmique
cosmic microwave background radiation (CMBR)
tâbeš-e rizmowj-e paszaminé-ye keyhâni
Fr.: rayonnement du fond cosmique microonde
The diffuse → electromagnetic radiation in the → microwave band, coming from all directions in the sky, which consists of relic photons left over from the very hot, early phase of the → Big Bang. More specifically, the CMBR belong to the → recombination era, when the → Universe was about 380,000 years old and had a temperature of about 3,000 K, or a → redshift of about 1,100. The photons that last scattered at this epoch have now cooled down to a temperature of 2.73 K. They have a pure → blackbody spectrum as they were at → thermal equilibrium before → decoupling. The CMB was discovered serendipitously in 1965 by Penzias and Wilson (ApJ L 142, 419) and was immediately interpreted as a relic radiation of the Big Bang by Dicke et al. (1965, ApJL 142, 383). Such a radiation had been predicted before by Gamow (1948, Nature 162, 680) and by Alpher and Herman (1948, Nature 162, 774). This discovery was a major argument in favor of the Big Bang theory. In 1992, the satellite → Cosmic Background Explorer (COBE) discovered the first anisotropies in the temperature of the CMB with an amplitude of about 30 µK. See also: → cosmic microwave background anisotropy, → dipole anisotropy, → CMB lensing, → CMB angular power spectrum, → acoustic peak, → baryon acoustic oscillation, → WMAP.
cosmic radio noise
nufe-ye râdioyi-ye keyhâni
Fr.: bruit radio cosmique
Radio waves emanating from extraterrestrial sources.
1) A bed for a baby that is usually designed to rock back and forth when pushed gently.
→ Newton's cradle.
M.E. cradel, from O.E cradol akin to O.H.G. kratto "basket," Ger. Krätze "basket carried on the back;" Pers. gereh "knot;" Skt. granth- "to tie a knot" (Cheung 2007).
Gahvâré "cradle," variants gâhvâré, gowvâré, govâré, from Mid.Pers. gâhwârag "cot, cradle."
Fr.: radical cyano
A diatomic chemical radical composed of carbon and nitrogen atoms. The triple bonds of C to H leave one electron available, which makes the CN radical very reactive. Organic molecules with the -CN group are potential sources of → prebiotic amino acids. Same as the → CN molecule. The CN radical was first identified by Gay-Lussac, who in 1815 published an extensive study of the derivatives of prussic acid (→ hydrogen cyanide). He showed that the cyano radical remained intact throughout a series of chemical transformations. Also called cyanogen radical.
Fr.: quadrilatère cyclique
A quadrilateral in which all four vertices lie on the circumference of a circle.
Fr.: rayon de cyclotron
Same as → Larmor radius.
Fr.: paradoxe de d'Alembert
A hydrodynamical paradox arising from the neglect of → viscosity in the → steady flow of a fluid around a submerged solid body. According to this paradox, the submerged body would offer no resistance to the flow of an → inviscid fluid and the pressure on the surface of the body would be symmetrically distributed about the body. This paradox may be traced to the neglect of the viscous forces, which are indirectly responsible for fluid resistance by modifying the velocity field close to a solid body (Meteorology Glossary, American Meteorological Society).
niyâveš bé târiki
Fr.: adaptation à l'obscurité
The automatic adjustment of the iris and retina of the eye to allow maximum vision in the dark, following exposure of the eye to a relatively brighter illumination.