radiative transfer equation
hamugeš-e tarâvaž-e tâbeš
Fr.: équation de transfer radiatif, ~ ~ de rayonnement
The equation that describes the → radiative transfer. It states that the → specific intensity of radiation Iσ during its propagation in a medium is subject to losses due to → extinction and to → gains due to → emission: dIσ/dx = - μσ . Iσ + ρ . jσ, where x is the coordinate along the → optical path, μσ is the → extinction coefficient, ρ is the mass → density, and jσ is the → emission coefficient per unit mass.
Fr.: transition radiative
A transition between two states of an atomic or molecular entity, the energy difference being emitted or absorbed as photons.
Fr.: zone radiative
The region of a star in which the energy generated by → nuclear fusion in the core is transferred outward by → electromagnetic radiation and not by → convection. Such zones occur in the interior of low-mass stars, like the Sun, and the envelopes of → massive star. The radiative zone of the Sun starts at the edge of the core of the Sun, about 0.2 solar radii, and extends up to about 0.7 radii, just below the → convective zone.
radiatively driven wind
Fr.: vent radiatif
Same as → radiation-driven wind
rišé (#), rišegi (#), rišâl
1) Math.: The indicated root of a quantity, as denoted by an expression written under
the → radical sign.
M.E., from L.L. radicalis "of or having roots," from → radix "root."
Fr.: axe radical
Of two circles, the straight line containing all points P such that the lengths of the tangents from P to the two circles are equal.
nešâne-ye rišâl, ~ rišegi
Fr.: signe radical
The symbol √ placed before a number or quantity to indicate the extraction of the square root. The value of a higher (the n-th) root is indicated by a raised positive digit (n) in front of the symbol, as in 3√ (cube root). The first known occurrence of this symbol was in the book Die Cross, published in 1525, by the German mathematician Christoff Rudolff.
1); 2) râdio; 3) partow, râdio
1); 2) Short from radiophone and radio-telegraphy.
Râdio, loan from Fr., as above; partow→ ray.
Fr.: arc radio
A large number of narrow filaments in → radio continuum occurring toward the → Galactic Center, about 15 to 20 arc-minutes (some 50 parsecs in projection) north of → Sgr A*. The radio Arc is the prototype of → non-thermal filaments (NTFs) and resolves into a set of more than a dozen vertical filaments with lengths of about 30 pc distributed symmetrically with respect to the → Galactic equator (Yusef-Zadeh et al. 1984, Nature 310, 557). Among more than 100 NTFs found in the Galactic center region, the Arc is the only one known to show inverted spectrum with a → spectral index α = +0.3 (Law et al. 2008, ApJS 177, 515, and references therein). This implies a very hard energy spectrum of particles for a source of → synchrotron radiation.
râdio axtaršenâsi, axtaršenâsi-ye râdioi
Fr.: radio astronomie
The branch of astronomy that deals with the study of the Universe by means of → radio waves.
Fr.: sursaut radio
A burst of emission in the radio frequencies of the electromagnetic spectrum.
radio continuum emission
gosil-e peyvastâr-e râdio-yi
Fr.: émission de continuum radio
A → continuum emission with frequencies in the radio range of the electromagnetic spectrum.
Fr.: contrepartie radio
Fr.: émission radio
Fr.: flux radio
Total radiation in radio wavelengths going out from the 2π solid angles of a hemisphere. → flux.
radio flux density
cagâli-ye šârr-e râdioyi
Fr.: densité de flux radio
basâmad-e râdio-yi (#)
Fr.: fréquence radio
râdio kahkešân, kahkešân-e râdioyi
A galaxy that is extremely luminous at radio wavelengths between 10 MHz and 100 GHz. The radio luminosity of a strong radio galaxy (1037-1039 watts) can be up to a million times greater than the radio output of an ordinary galaxy and up to a hundred times greater than the optical luminosity of a galaxy such as the Milky Way. The optical counterparts of radio galaxies are usually an → elliptical galaxy. Radio galaxies often exhibit jet structure from a compact nucleus. They typically display two → radio lobes that are often approximately aligned with the jets observed in the optical and that may extend for millions of → light-years.
Fr.: interféromètre radio
An → interferometer designed for radio frequencies.
radio-šân, šân-e râdioyi
Fr.: jet radio
An → astrophysical jet appearing in the radio wavelengths of the electromagnetic spectrum.