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tâbeš-e siyah-jesm (#)
Fr.: rayonnement de corps noir
Fr.: région bleue
The portion of the → visible spectrum lying between 455 and 492 nm.
Fr.: classification de Boeshaar-Keenan
A system for the classification of → S-type stars. The system involves the designations of a C/O index and a temperature type. Moreover, when possible, it uses intensity estimates for → ZrO bands, the → TiO bands, the → Na I D-lines, the YO bands, and the Li I 6708 line.
Philip C. Keenan & Patricia C. Boeshaar, 1980, ApJS, 43, 379; → classification.
aršâyeš-e tafsanji, ~ tafsanjik
Fr.: correction bolométrique
Fr.: équation de Boltzmann
1) An equation that expresses the relative number (per unit volume) of → excited atoms in different states as a function of the temperature for a gas in → thermal equilibrium: Nu/Nl = (gu/gl) exp (-ΔE/kTex), where Nu and Nl are the upper level and lower level populations respectively, gu and gl the → statistical weights, ΔE = hν the energy difference between the states, k is → Boltzmann's constant, and h → Planck's constant.
Fr.: relation de Boltzmann
A relation between the → entropy of a given → state of a → thermodynamic system and the → probability of the state: S = k . ln Ω where S is the entropy of the system, k is → Boltzmann's constant, and Ω the thermodynamic probability of the state. Boltzmann's relation connects → statistical mechanics and → thermodynamics. Ω is the number of possible → microstates of the system, and it represents the → randomness of the system. The relation also describes the statistical meaning of the → second law of thermodynamics. This expression has been carved above Boltzmann's name on his tombstone in Zentralfreihof in Vienna. Same as → Boltzmann's entropy formula.
Fr.: accrétion de Bondi-Hoyle
The → accretion of mass by a star (assumed as point particle) moving at a steady speed through an infinite, uniform gas cloud. It is directly proportional to the star mass (M) and the medium density (ρ) and inversely proportional to the relative star/gas velocity (v). In its classical expression: 4πρ(G M)2 / v3, where G is the → gravitational constant. See Bondi & Hoyle (1944, MNRAS 104, 273) and Bondi (1952, MNRAS 112, 195). For a recent treatment of accretion in a turbulent medium see Krumholtz et al. 2006 (ApJ 638, 369).
Named after Hermann Bondi (1919-2005), an Anglo-Austrian mathematician and cosmologist and Fred Hoyle (1915-2001), British mathematician and astronomer best known as the foremost proponent and defender of the steady-state theory of the universe; → accretion.
Bondi-Hoyle accretion radius
šo'â'-e farbâl-e Bondi-Hoyle
Fr.: rayon de l'accrétion de Bondi-Hoyle
In the → Bondi-Hoyle accretion process, the radius where the gravitational energy owing to star is larger than the kinetic energy and, therefore, at which material is bound to star. The Bondi-Hoyle accretion radius is given by RBH = 2 GM / (v2 + cs2) where G is the gravitational constant, M is the stellar mass, v the gas/star relative velocity, and cs is the sound speed.
Bose-Einstein condensation (BEC)
Fr.: condensation de Bose-Einstein
A → quantum phase transition during which the → bosons constituting a sufficiently cooled boson gas are all clustered in the → ground energy state. The phase transition results in a → Bose-Einstein condensate. This phenomenon occurs when the temperature becomes smaller than a critical value given by: Tc = (2πħ2 / km)(n / 2.612)2/3, where m is mass of each boson, ħ is the → reduced Planck's constant, k is → Boltzmann's constant, and n is the particle number density. When T ≤ Tc, the → de Broglie wavelength of bosons becomes comparable to the distance between bosons.
Fr.: distribution de Bose-Einstein
bottom-up structure formation
diseš-e sâxtâr az pâyin bé bâlâ
Fr.: formation des structures du bas vers le haut
Fr.: transition liée-liée
Fr.: transition liée-libre
butârhâ-ye karân, ~ karâni
Fr.: conditions à la limite
1) Math: Restriction on the limits of applicability of an equation.
In a differential equation, conditions that allow to fix the constant
of integration and reach a unique solution. The number of boundary conditions
necessary to determine a solution matches the order of the equation.
karyâ-ye karânmand, ~ karândâr
Fr.: fonction bornée
The function y = f(x) in a given range of the argument x if there exists a positive number M such that for all values of x in the range under consideration the inequality | f(x) | ≤ M will be fulfilled. → unbounded function.
Fr.: approximation de Boussinesq
A simplification in the equations of → hydrodynamics that treats the density as constant except in the → buoyancy term. This approximation is motivated by the fact that when pressure and temperature differences in a flow are small, then it follows from the thermodynamic → equation of state that a change in the density is also small.
Named after Joseph Valentin Boussinesq (1842-1929), a French physicist who made significant contributions to the theory of hydrodynamics, vibration, light, and heat; → approximation.
The formation of → breccia.
Verbal noun of → brecciate.
Fr.: distribution de brillance
A statistical distribution of the brightness of an astronomical extended object.
Fr.: fonction de Brillouin
An international collaboration between Austria, Canada, and Poland, currently comprising five nano-satellites to investigate stellar structure and evolution of the brightest stars in the sky and their interaction with the local environment. BRITE is also used to study micropulsation, wind phenomena, and other forms of stellar variability. These nano-satellites aim to monitor stars brighter than V ~ 5 mag using two color pass-bands, over various observing campaigns. Each nano-satellite hosts a 3 cm telescope, providing a wide field of view (24° x 20°) to simultaneously observe up to a few dozen stars (Weiss et al. 2014).