differential image motion monitor (DIMM) pahregar-e jonbeš-e degarsâneyi-ye tasvir Fr.: moniteur de mouvements d'images différentiels,
moniteur seeing A device that is commonly used to measure the → seeing at optical astronomical sites. The DIMM delivers an estimate of the → Fried parameter based on measuring the variance of the differential image motion in two small apertures, usually cut out in a single larger telescope pupil by a mask. The DIMM concept was introduced by Stock & Keller (1960, in Stars and Stellar Systems, Vol. 1, ed. G. P. Kuiper & B. M. Middlehurst, p. 138), whereas its modern implementation was first described by Sarazin & Roddier (1990, A&A 227, 294). → differential; → image; → motion; → monitor. |
dim tiré (#) Fr.: faible, pâle, mat(e) Not bright; obscure from lack of light. O.E. dimm "dark, gloomy, obscure," from P.Gmc. *dimbaz. Tiré, from Mid.Pers. têrag, variant of târig "dark," Av. taθra- "darkness," taθrya- "dark," cf. Skt. támisrâ- "darkness, dark night," L. tenebrae "darkness," Hittite taš(u)uant- "blind," O.H.G. demar "twilight." |
dimension vâmun Fr.: dimension 1) Math.: Independent extension in a given direction; a property of space. From L. dimensionem (nom. dimensio), from stem of dimetri "to measure out," from → dis- + metri "to measure." Vâmun, from vâ-, → dis-, + mun, variant mân "measure" (as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl"), from O.Pers./Av. mā(y)- "to measure;" PIE base *me- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum. |
dimensional vâmuni Fr.: dimensionnel Of or pertaining to → dimension. |
dimensional analysis ânâlas-e vâmuni, ânâkâvi-ye ~ Fr.: analyse dimensionnelle A technique used in physics based on the fact that the various terms in a
physical equation must have identical → dimensional formulae
if the equation is to be true for all consistent systems of unit. Its main uses are: → dimensional; → analysis. |
dimensional formula disul-e vâmuni Fr.: formule dimensionnelle Symbolic representation of the definition of a physical quantity obtained from its units of measurement. For example, with M = mass, L = length, T = time, area = L^{2}, velocity = LT^{-1}, energy = ML^{2}T^{-2}. → dimensional analysis. → dimensional; → formula. |
dimensionless quantity candâ-ye bivâmun Fr.: quantité sans dimension A quantity without an associated → physical dimension. Dimensionless quantities are defined as the ratio of two quantities with the same dimension. The magnitude of such quantities is independent of the system of units used. A dimensionless quantity is not always a ratio; for instance, the number of people in a room is a dimensionless quantity. Examples include the → Alfven Mach number, → Ekman number, → Froude number, → Mach number, → Prandtl number, → Rayleigh number, → Reynolds number, → Richardson number, → Rossby number, → Toomre parameter. See also → large number. → dimension + -less M.E. from O.E. læs (adv.), læssa (adj.), akin to O.Fr. les "less." |
dimer dimer Fr.: dimère A molecule resulting from combination of two identical molecules. From → di- "two, twice, double," + -mer a combining form denoting member of a particular group, → isomer. |
disk instability model (DIM) model-e nâpâydâri-ye gerdé, ~ ~ disk Fr.: modèle d'instabilité de disque A model describing → dwarf novae and → Soft X-ray Transient (SXT)s. Accordingly, these objects are triggered by an → accretion disk instability due to an abrupt change in opacities (→ opacity) at → temperatures at which hydrogen is partially ionized. All versions of the DIM have this ingredient. They differ in assumptions about → viscosity, and about what happens at the inner and outer disk radii. Basically, during → quiescence, material accumulates in the accretion disk until a critical point is reached. The disk then becomes unstable and is dumped onto the → compact object, releasing a burst of → X-rays. However, the greater duration of SXT bursts (months) and the time interval between bursts (decades) cannot be accounted for by the standard disk instability model used for dwarf novae, and additional factors such as X-ray illumination and irradiation of the accretion disk are required for the model to match the observed properties of SXTs (J-P Lasota and J-M Hameury, 1995). → disk; → instability; → model. |
embodiment tanigâneš Fr.: incarnation, incorporation, personnification The act of embodying; the state or fact of being embodied. verbal noun of → embody. |
four-dimensional operator âpârgar-e cahâr-vâmuni Fr.: opérateur à quatre dimensions An operator defined as: ▫ = (∂/∂x, ∂/∂y, ∂/∂z, 1/(jc∂/∂t). → four; → dimensional; → operator. |
nondimensional equation hamugeš-e nâvâmuni Fr.: équation non-dimensionnelle An equation that is independent of the units of measurement as it only involves nondimensional numbers, parameters, and variables. → non-; → dimensional; → equation. |
one-dimensional flow tacân-e yek-vâmuni Fr.: écoulement uni-dimensionnel A hypothetical flow in which all the flow parameters may be expressed as functions of time and one space coordinate only. This single space coordinate is usually the distance measured along the center-line of some conduit in which the fluid is flowing (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006). → one; → dimensional; → flow. |
physical dimension vâmun-e fiziki Fr.: dimension physique Any of basic physical quantities, such as mass, length, time, electric charge, and temperature in terms of which all other kinds of quantity can be expressed. |
sediment nehešt (#) Fr.: sédiment Mineral or organic material which has been transported and deposited by an agent of erosion such as water, wind, and ice. From Fr. sédiment, from L. sedimentum "a settling, sinking down," from stem of sedere "to settle, sit" Nehešt past stem of neheštan "to place, deposit," from ne- "down, below," → ni- (PIE), + heštan "to place, put" from Mid.Pers. hištan, hilidan "to let, set, leave, abandon;" Parthian Mid.Pers. hyrz; O.Pers. hard- "to send forth," ava.hard- "to abandon;" Av. harəz- "to discharge, send out; to filter," hərəzaiti "releases, shoots;" cf. Skt. srj- "to let go or fly, throw, cast, emit, put forth;" Pali sajati "to let loose, send forth." |
sedimentary nehešti (#) Fr.: sédimentaire Of, pertaining to, or of the nature of sediment. Adj. of → sediment. |
sedimentary rock sang-e nehešti Fr.: roche sédimentaire A rock composed of materials that were transported to their present position by wind or water. → Sandstone, → shale, and → limestone are sedimentary rocks. → sedimentary; → rock. |
three-dimensional flow tacân-e sé-vâmuni Fr.: écoulement tri-dimensionnel A flow whose parameters (velocity, pressure, and so on) vary in all three coordinate directions. Considerable simplification in analysis may often be achieved, however, by selecting the coordinate directions so that appreciable variation of the parameters occurs in only two directions, or even only one (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006). → three; → dimensional; → flow. |
two-dimensional flow tacân-e do-vâmuni Fr.: écoulement bi-dimensionnel A flow whose parameters are functions of time and two space coordinates (x and y) only. There is no variation in the z direction and therefore the same → streamline pattern could at any instant be found in all planes in the fluid perpendicular to the z direction (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006). → two; → dimensional; → flow. |
X-ray Dim Isolated Neutron Star (XDINS) setâre-ye notroni bâ partowhâ-ye X-e nazâr Fr.: étoile à neutron de faibles rayons X A member of a class of isolated, radio-silent → pulsars with peculiar properties. They show a purely thermal spectrum at X-ray energies with no evidence for a high-energy, power-law component often detected in other → isolated neutron star classes. The X-ray luminosity is 10^{31} - 10^{32} erg s^{-1}, fully consistent with surface blackbody emission with temperatures ~ 40-100 eV and (radiation) radii of a few kilometers, as derived from X-ray spectral fits. With the only exception of RX J1856.5-3754, broad absorption features have been found in all XDINSs. These features have energies ~ 300 - 700 eV, equivalent widths of ~ 50 - 150 eV and, as in the case of RX J0720.4-3125, may be variable. |