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bra brâ Fr.: bra In Dirac's notation for describing a quantum state, a vector which together with → ket constitutes the dual vector → bracket. A bra is shown by <|, the mirror image of the symbol for a ket vector. The scalar product of a bra vector < B| and a ket vector |A> is written < B|A >, i.e. as a juxtaposition of the symbols for the bra and the ket vectors, that for the bra vector being on the left, and the two vertical lines being contracted to one for brevity. From bra- the first syllable in → bracket. |
bracket brâket Fr.: bracket In Dirac's notation, an expression which is a → scalar product of the dual vectors → bra and → ket which describe a quantum state. The bra vector appears on the left of the ket vector. From M.Fr. braguette "codpiece armor." |
Brackett series seri-ye Brackett Fr.: série de Brackette A series of lines in the infrared spectrum of atomic hydrogen due to electron jumps between the fourth and higher energy levels (Br α has wavelength 4.052 μm, Br γ 2.166 μm). Named after the American physicist Frederick Brackett (1896-1980); → series. |
Bragg angle zâviye-ye Bragg Fr.: angle de Bragg The grazing angle between an incident beam of X-rays and a given set of crystal planes for which the secondary X-rays from the planes combine to give a single beam. → Bragg's law; → angle. |
Bragg's law qânun-e Bragg Fr.: loi de Bragg A parallel beam of monochromatic X-rays of wavelength λ, incident on a given set of parallel crystal planes at a grazing angle θ will give rise to a reflected beam whenever: n λ = 2d . sinθ, where n is an integer representing the difference in path length, and d is the perpendicular distance between a pair of adjacent planes. Named after William Lawrence Bragg (1890-1971), British physicist, who, in collaboration with his father, William Henry Bragg (1862-1942), joint Nobel Prize in Physics 1915, pioneered X-ray analysis and spectrometry; → law. |
brake 1) legâm, tormoz 2) legâmidan, tormoz kardan Fr.: 1) frein; 2) freiner 1) A device for slowing or stopping a vehicle or other moving mechanism by
the absorption or transfer of the energy of momentum, usually by means of friction. From O.Du. braeke "flax brake," from breken "to break." Legâm originally "a horse bit," on the model of Fr. frein "horse bit; motor brake;" and Ger. Bremse "horse bit; brake;" tormoz, loan from Russ. тормоз. |
braking legâmeš Fr.: freinage The act or fact of stopping by means of or as if by means of a brake. See: → magnetic braking; → radiative braking; → tidal braking; → braking index. Verbal noun of → brake. |
braking index dišan-e legâmeš Fr.: indice de freinage A parameter indicating the rate at which a → pulsar slows down. Neutron stars are powered by → rotational energy and lose energy by accelerating particle → winds and by emitting → electromagnetic radiation. The → rotation frequency, Ω, thus decreases with time and this slowdown is usually described by the relation Ω^{.} = - kΩn, where k is a positive constant which depends on the → moment of inertia and the → magnetic dipole moment of the → neutron star and n is the braking index. Conventionally, the braking index is derived by differentiation of the above equation, yielding n = ΩΩ^{..} / Ω^{.2}. In a highly simplified model in which the spin-down torque arises from dipole radiation at the rotation frequency, one expects n = 3 (Johnston, S., Galloway, D., 1999, arXiv:astro-ph/9905058). |
branch 1) šâxé (#); 2) šâxé zadan (#) Fr.: 1) branche; 2) se ramifier 1a) General: A shoot or arm-like limb of a tree; anything like a
limb of a tree; any offshoot from a main trunk. M.E., from O.Fr. branche, from L.L. branca "a claw, paw." 1) Šâxé "branch," from Mid.Pers šâk, cf.
Mod.Pers. šâx, šax "branch; horn," Skt. sakha-
"a branch, a limb," Arm. cax, Lit. šaka,
O.S. soxa, PIE *kakhâ "branch." |
branching šâxé-zad Fr.: branchement The act of dividing into branches. → branching ratio. |
branching ratio vâbar-e šâxé-zad Fr.: rapport de branchement A quantity used to describe a → radionuclide that has more than one → decay mode. For a particular decay mode, the ratio of the number of atoms decaying by that decay mode to the number decaying in total: BR_{i} = k_{i}/(k_{1} + k_{2} + ...) = k_{i}/k, where k is → decay constant. |
brane breyn (#) Fr.: brane In theoretical physics, an entity which can have any number of allowed spatial dimensions. It is usually accompanied by a prefix, i.e. p-brane, indicating the number of dimensions. For example, a 0-brane is a zero-dimensional point-like particle, a 1-brane is a → string, a 2-brane is a "membrane," and so forth. Our Universe is a 3-brane. Brane, short for membrane, from L. membrana "parchment," from membrum "limb, member of the body," → member. Breyn, loanword from E., as above. |
break 1) šekastan; boridan; gosastan; 2) šekast; boreš, boré;
gosast Fr.: 1) couper, rompre; 2) brisure, coupure 1) To separate into parts or fragments violently; to become broken. From break, from M.E. breken, O.E. brecan, from P.Gmc. *brekan (cf. Du. breken, O.H.G. brehhan, Ger. brechen), from PIE base *bhreg- "to break" (see also → fraction). 1) Šekastan, škan- "to break, split;"
Mid.Pers. škastan "to break;" Av. scind-, scand
"to break, cleave;" Proto-Iranian *skand- "to break, cleave;"
PIE sken- "to cut off." |
break luminosity tâbandegi-ye boré Fr.: luminosité de coupure A characteristic luminosity around which the → luminosity function of a sample of galaxies changes to a steeper slope or exponentially declines. → break; → luminosity. |
break-up velocity tondâ-ye gosast Fr.: vitesse de rupture The velocity of a → rotating star at which the → centrifugal force equals the → gravitational force. Also known as → critical velocity. The simplest expression of the break-up velocity for an OB star, ignoring the → Eddington luminosity, is given by the relation: v = (GM / R)^{1/2}, where M and R are the mass and radius of the star respectively, and G the → gravitational constant. A more realistic expression takes into account not only the → radiation pressure, but also the non-uniformity of the brightness over the stellar surface, as indicated by → von Zeipel theorem. With these conditions, the break-up velocity has a more complicated formula, corresponding to the velocity reached when somewhere on the star the → total gravity becomes zero. |
breakthrough tarâšekâft Fr.: percée 1) An act of overcoming or penetrating an obstacle or restriction. Tarâšekâft, from tarâ-, → trans-, + šekâft, past stem of šekâftan "to split, break, tear," → fission. |
breccia bereš (#) Fr.: brèche A rock composed of angular fragments (over two millimeter diameter) of older rocks melded together with a matrix of smaller particles or a mineral cement. From It. breccia "broken (rock)," from a Germanic source akin to O.H.G. brecha "a breaking," ultimately from PIE *bhreg- "to break," → fraction. Bereš, loan from Fr. |
brecciate berešidan Fr.: bréchifier To form as → breccia. |
brecciated berešidé, beršmand Fr.: bréchifié Characterized by, converted into, or resembling a breccia; especially of a rock structure marked by an accumulation of angular fragments, or of an ore texture showing mineral fragments without notable rounding. → breccia, → brecciated. |
brecciated rock sang-e berešidé Fr.: roche bréchifiée A rock formed by the process of → brecciation. → brecciated; → rock. |
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