An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 48 Search : model
dirty iceball model
  مدل ِ گلوله‌ی ِ یخ   
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.

dirty; → ice; → ball; → model.

disk instability model (DIM)
  مدل ِ ناپایداری ِ گرده، ~ ~ دیسک   
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
  مدل ِ غبار   
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.

dust; → model.

dynamo model
  مدل ِ توانزا   
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.

dynamo; → model.

Einstein model
  مدل ِ اینشتین   
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: CV = 3Rx2ex/(ex -1)2, where R is the → gas constant, x = TE/T, TE = hν/k, h is → Planck's constant, and k is → Boltzmann's constant. TE 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
  مدل ِ فرگشت   
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.

forward seismic modeling
  مدل‌سازی ِ لرزه‌ای ِ پیش-سو   
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).
2) In → asteroseismology, a model that takes the physical properties of a star as input parameters and predicts the star's oscillations. Then, by finding parameters that yield oscillation frequencies (ωnlm) close to those observed, one can infer the properties of the observed star. The quantum numbers n, l, and m must be identified before any meaningful comparison between seismic data and model predictions can be made. That mode identification requires a physical interpretation of the measured frequencies.

forward; → seismic; → modeling.

inflationary model
  مدل ِ پندامی   
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.

Inflationary, adj. of → inflation; → model.

lambda cold dark matter model
  مدل ِ لامبدا-ماده‌ی-سرد ِ- تاریک   
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
  مدل ِ پتومند   
model-e patumand

Fr.:   

A stellar atmosphere model which includes metals or uses methods to reproduce their effects, → line blanketing.

line; → blanket; → model.

magnetocentrifugal model
  مدل ِ مغنات-مرکزگریز   
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
  مدل ِ کیهان‌شناختی ِ میلن   
model-e keyhânšenâxti-ye Milne (#)

Fr.: modèle cosmologique de Milne   

Same as → Milne Universe.

Milne Universe; → cosmological; → model.

model
  ۱) مدل، ترزال؛ ۲) مدل‌ساختن، ترزالیدن   
1) (n.) model, tarzâl; 2) (v.) model sâxtan, tarzâlidan

Fr.: 1) modèle; 2) modéliser   

1a) A mathematical representation of a process, system, or object developed to understand its behavior or to make predictions. The representation always involves certain simplifications and assumptions. See also → theory, → hypothesis.
1b) A mental image of a phenomenon using familiar terms (or images). For example, in the Bohr model the atom is visualized as a nucleus with electrons orbiting around it in a manner similar to the way that planets revolve around the Sun. While this model is use ul in understanding the atom, it is an over-simplified description of a real atom and does not describe/predict all of its attributes (G. Smooth, Lawrence Berkeley Lab website).
2) To make or construct a model of.

M.Fr. modelle (Fr. modèle), from It. modello "a model, mold," from V.L. *modellus, from L. modulus "measure, standard," from modus "manner, measure" (cf. Av. mad-, → mode), PIE *med- + -ulus, → -ula.

1) Model, from Fr. modèle. Tarzâl, from tarz, → mode + -âl, → -al.
2) Model sâxtan, from model + sâxtan, sâzidan "to build, make, fashion; to adapt, adjust, be fit" (from Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form;" Av. sak- "to understand, to mark," sâcaya- (causative) "to teach").
Tarzâlidan, from tarzâl + -idan infinitive suffix.

model dependence
  وابستگی به مدل، ~ ~ ترزال   
vâbastegi bé model, ~ ~ tarzâl

Fr.: dépendance du modèle   

In a theoretical analysis, the solution that does not correctly treat the intervening parameters, or neglects some crucial factors.

model. dependence, noun of → dependent.

modeling
  مدل‌سازی، ترزالش   
modelsâzi, tarzâleš

Fr.: modélisation   

The simulation of a process, concept, or operation of a system often implemented by a computer program and making use of a mathematical treatment.

Verbal noun of → model

MRN dust model
  مدل ِ MRN   
model-e MRN

Fr.: modèle MRN   

A model concerned with the distribution in size of → interstellar grains to account for observations of → interstellar extinction from 0.11 μm to 1.0 μm. The → distribution has the form N(a)da ∝ a-3.5da, where a is the grain radius. It extends from 5 nm to 1 μm for → graphite and over a narrower range for other materials.

MNR, the initials of authors J. S. Mathis, W. Rumpl, and K. H. Nordsiek (1977, ApJ 217, 425), who introduced the mode; → dust; → model.

numerical modeling
  مدل‌سازی ِ عددی، ترزال‌سازی ِ ~   
modelsâzi-ye adadi (#), tarzâlsâzi-ye ~

Fr.: modélisation numérique   

The prediction of the evolution of a system via numerical construction of approximate solutions to the governing equations.

numerical; → modeling.

oblique rotator model
  مدل ِ چرخنده ِ یکور   
model-e carxande-ye yekvar

Fr.: modèle de rotateur oblique   

A stellar model in which the rotation axis is tilted relative to the magnetic dipole axis. As the star rotates, observable quantities (e.g. the line-of-sight component of the magnetic field, stellar brightness, emission lines) are modulated according to the rotational period. Such a model was first put forward by D. Stibbs (1950, MNRAS, 110, 395).

oblique; → rotator; → model.

pancake model
  مدل ِ لواش   
model-e lavâš

Fr.: modèle des crêpes   

A model of galaxy formation in which regions of primordial gas as massive as clusters of galaxies began to collapse into thin sheets (pancakes). Within the pancakes, smaller regions of gas later collapsed to form individual galaxies.

pancake; → model.

pointing model
  مدل ِ آماجش   
model-e âmâješ

Fr.: modèle de pointage   

A mathematical model that reproduces the diurnal rotation of the Earth and is used to direct a telescope toward a precise position on the sky.

pointing; → model.

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