Debye model model-e Debye (#) Fr.: modèle de Debye An extension of the → Einstein model accounting for → specific heats, based on the concept of → elastic waves in → crystals. In this model specific heat is given by: C_{V} = 9R[(4/x^{2})∫ y^{2}/(e^{y} - 1)dy - x/(e^{x} - 1)], integrating from 0 to x, where R is the → gas constant, k is → Boltzmann's constant, x = hν_{max}/k, and y = hν/k. The parameter T_{D} = hν_{max}/k is the characteristic → Debye temperature of the crystal. At low temperatures the specific heat prediction by this model is in good agreement with observations (→ Debye law), in contrast to Einstein's model. → debye; → temperature. |
decay mode tarz-e tabâhi, mod-e ~ Fr.: mode de désintégration A possible type of decay of a → radionuclide or → elementary particle. In general, a given particle may decay by more than one decay mode. Usually the number of decay modes is one or two. There are, however, → nuclides which have many decay modes; for example the nuclide ^{11}Li has seven decay modes. |
dirty iceball model model-e golule-ye yax Fr.: modèle de la boule de glace sale A model for a → cometary nucleus proposed by Fred Whipple (1950-51), according to which the nucleus is a solid body (a few kilometers across) made up of various → ices (→ frozen water, → methane, → ammonia, → carbon dioxide, and → hydrogen cyanide) in which → dust is embedded. Dust particles are liberated when the ices vaporize as the → comet approaches the → Sun, and they get blown away by → solar radiation pressure, often forming impressive, gently curved → dust tails. |
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. |
dust model model-e qobâr Fr.: modèle de poussière A model of → dust grains conceived to describe the observed → interstellar extinction properties. It is characterized by the abundance of the different → chemical elements locked up in the dust, and by the → composition, → morphology, and → size distribution of its individual grains. For example, → MRN dust model. |
dynamo model model-e tavânzâ Fr.: modèle dynamo A theory for the generation of a star's or planet's magnetic field by the circulation of conducting fluids inside it. → solar dynamo. |
E-mode polarization qotbeš-e tarz-e E Fr.: polarisation en mode E A → polarization component in the → cosmic microwave background radiation that depends only on → gradient, is independent of → curl and does not have → handedness. In contrast to the → B-mode, the E-mode may be due to both the → scalar perturbations and → tensor perturbations. E, indicating electric-field like; → mode; → polarization. |
Einstein model model-e Einstein Fr.: modèle d'Einstein A model for the → specific heat of solids in which the specific heat is due to the vibrations of the atoms of the solids. The vibration energy is → quantized and the atoms have a single frequency, ν. Put forward in 1907 by Einstein, this model was the first application of → quantum theory to the solid state physics. The expression for the specific heat is given by: C_{V} = 3Rx^{2}e^{x}/(e^{x} -1)^{2}, where R is the → gas constant, x = T_{E}/T, T_{E} = hν/k, h is → Planck's constant, and k is → Boltzmann's constant. T_{E} is called the → Einstein temperature. This model could explain the temperature behavior of specific heat but not very satisfactorily at low temperatures. It has therefore been superseded by the → Debye model. See also → Dulong-Petit law. Albert Einstein in 1907; → model. |
evolutionary model model-e fargašt (#) Fr.: modèle d'évolution A model, based on theoretical calculations, which predicts the behavior of an astronomical entity (stars, galaxies, Universe) over time. → evolutionary; → model. |
f mode tarz-e f, mod-e ~ Fr.: mode f Waves that propagate only on the stellar surface. See also: → oscillation mode; → g mode; → p mode. f referring to → fundamental; → mode. |
forward seismic modeling modelsâzi-ye larze-yi-ye piš-su Fr.: 1) Geology: The process whereby a geologic section (subsurface model
of one-, two-, or three dimensions) is transformed into a synthetic seismogram
(synthetic seismic record). |
g mode tarz-e g, mod-e ~ Fr.: mode g Waves trapped inside stars, whose restoring force is the → buoyancy. Same as → gravity mode. See also: → oscillation modes; → p mode; → f mode. g referring to gravity; → mode. |
gravity mode tarz-e gerâni, mod-e ~ Fr.: mode gravité Same as → g mode |
inflationary model model-e pandâmi Fr.: modèle d'inflation A class of → Big Bang models of the Universe that include a finite period of accelerated expansion in their early histories. Such an event would have released enormous energy, stored until then in the vacuum of space-time. The horizon of the Universe expanded, temporarily, much faster than the speed of light. → inflaton field. |
jitter mode mod-e jastojah Fr.: A mode of observation in which a series of short exposures are used to enhance the final image quality through appropriate data processing. The first exposure is assumed to be centered on the point of interest; the following ones are slightly offset from the first position with separations not larger than a reasonably small fraction of the detector size. The offsets should be optimally distributed on the sky in order to maximize the chances of being able to filter out the sky background. |
lambda cold dark matter model model-e lâmbdâ-mâde-ye-sard-e-târik Fr.: modèle ΛCDM The → standard model of → Big Bang that incorporates both → dark matter and → dark energy. See also → cold dark matter (CDM). → lambda, → cosmological constant; → cold; → dark; → matter; → model. |
line-blanketed model model-e patumand Fr.: A stellar atmosphere model which includes metals or uses methods to reproduce their effects, → line blanketing. |
magnetocentrifugal model model-e meqnât-markazgoriz Fr.: modèle magnétocentrifuge A → magnetohydrodynamic model devised to account for the → bipolar jets and → outflows observed around → protostars. Basically, a → poloidal magnetic field is frozen into a rotating → accretion disk. If the angle between the magnetic field lines threading the disk and the rotation axis of the disk is larger than 30°, the plasma can be accelerated out of the accretion disk along the field lines. The field lines rotate at a constant → angular velocity, and as the gas moves outward along the field lines, it is accelerated by an increasing → centrifugal force (magnetocentrifugal acceleration). At some point, when the rotation velocity is about the same as the → Alfven velocity in the gas, the field lines get increasingly wound up by the inertia of the attached gas and a strong → toroidal magnetic field component is generated. The toroidal component is the main agent in collimating the flow into a direction along the → open magnetic field lines. The earliest version of the model was proposed by Blandford & Payne (1982, MNRAS 199, 883). It has two main versions: → X-wind and → disk wind models. See also → magnetorotational instability. → magneto-; → centrifugal; → model. |
Milne cosmological model model-e keyhânšenâxti-ye Milne (#) Fr.: modèle cosmologique de Milne Same as → Milne Universe. → Milne Universe; → cosmological; → model. |
mode tarz, mod Fr.: mode 1) Physics: Any of the distinct patterns of oscillation that a
given periodically varying system can have. Mode, from Fr. mode, from L. modus "measure, rhythm, song, manner," from PIE base *med- "to measure, limit, judge, advise;" cf. L. meditari "to think or reflect upon, consider;" Av. mad- "to measure out, apportion, allot;" Gk. medein "to rule;" O.E. metan "to measure out." Tarz "manner, mode," Arabicized as |