An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 46 Search : flow
accretion flow
  تچان ِ فربال   
tacân-e farbâl

Fr.: flot d'accrétion   

1) Flow of matter during an accretion process.
2) In a → binary system, flow of matter from the losing-mass → companion toward the compact one. The flow can be from a → stellar wind or through the → inner Lagrangian point.
3) → cold accretion flow, → hot accretion flow.

accretion; → flow.

bipolar flow
  تچان ِ دوقطبی   
tacân-e doqotbi

Fr.: flot bipolaire   

Same as → bipolar outflow.

bipolar; → flow.

bipolar outflow
  ا ُستچان ِ دوقطبی   
ostacân-e doqotbi

Fr.: flot bipolaire   

A flow of gaseous material in two opposite directions emanating from protostellar regions or from → evolved stars during the early post-→ AGB evolution. In protostellar regions → molecular outflows are pushed by → bipolar jets.

bipolar; → outflow.

Ostacân, → outflow; doqotbibipolar.

champagne flow
  تچان ِ شامپانی   
tacân-e šâmpâyn

Fr.: flot champagne   

The flow of → ionized gas escaping from a → molecular cloud due to the → champagne effect.


circumstellar outflow
  استچان ِ پیراستاره‌ای   
ostacân-e pirâsetâreyi

Fr.: flot circumstellaire   

A stream of matter into the interstellar medium from a central star.

circumstellar; → outflow.

cold accretion flow
  تچان ِ فربال ِ سرد   
tacân-e farbâl-e sard

Fr.: écoulement d'accrétion froid   

1) A type of → accretion flow by a → compact object such as a → black hole that consists of cool → optically thick gas and has a relatively high mass → accretion rate, in contrast to → hot accretion flows.
2) Gas accreting from the → intergalactic medium (IGM) onto → galactic haloes with sufficiently low velocities so that it will not be shocked to the → virial temperature of the halo, but will instead flow at a relatively low temperature (T ~ 104 K). Galaxies grow by accreting gas from → cosmic filaments. Feedback from star formation and → active galactic nuclei returns a significant fraction of the → interstellar medium (ISM) to the halo and may even blow it out of the halo into the IGM. This "cold accretion" will happen if the cooling time of → virialized gas is too short to maintain a hot, → hydrostatic halo. The existence of such a cold accretion mode has been confirmed by simulations, which have furthermore demonstrated that cold mode accretion can also be important for halos sufficiently massive to contain hot, hydrostatic gas. Because gas accretes preferentially along the filaments of the cosmic web, the streams of infalling gas have relatively high gas densities and correspondingly low cooling times. This allows the cold streams to penetrate the hot, hydrostatic halos surrounding massive galaxies, particularly at → high redshifts (F. van de Voort et al., 2012, MNRAS 421, 2809).

cold; → accretion; → flow.

compressible flow
  تچان ِ تنجیدنی، ~ تنجش‌پذیر   
tacân-e tanjidani, ~ tanješpazir

Fr.: flot compressible   

A flow in which changes of the density, induced by velocities and their fluctuations, are not negligible.

compressible; → flow.

cooling flow
  تچان ِ سردش   
tacân-e sardeš

Fr.: flot de refroidissement   

A phenomenon observed in a → cluster of galaxies, whereby the cluster core loses energy via X-ray radiation because of the collisions between the gas particles. The radiation rate is proportional to the square of the density, and the → cooling time, which remains in the outer parts too large, becomes smaller than the → Hubble time in the core. As a result, the central regions of clusters of galaxies cool down; and since in the center of a cluster gas pressure and gravitational attraction are in equilibrium, the gas density has to rise to maintain the pressure necessary for supporting the outer layers of gas. To cause its density to rise, the cooled gas has to flow inward. As the densest gas, which cools quickest, is already concentrated in the center of the cluster, the inward flow will start at the center, soon followed by the outer layers. This flow of gas is called the cooling flow. Cooling flows are moderated through feedback due to the → supermassive black hole in the nucleus of the central galaxy. The gas inflow to the center fuels the → active galactic nucleus (AGN). The latter then heats again the gas through its → radio jets.

cooling; → flow.

Couette flow
  تچان ِ کویءت   
tacân-e Couette

Fr.: écoulement de Couette   

In fluid dynamics, the motion of an → incompressible → laminar flow passing between two parallel plates, when the upper plate is moving with some velocity while the lower one is stationary. The flow is driven owing to the fluid → viscosity and the applied pressure gradient parallel to the plates. See also → Taylor-Couette flow.

Named after Maurice Marie Alfred Couette (1858-1943), a French physicist who dealt mainly with fluid mechanics; → flow

Couette-Taylor flow
  تچان ِ کویءت-تیلر   
tacân-e Couette-Taylor

Fr.: écoulement de Couette-Taylor   

In fluid mechanics, the motion of a fluid between two concentric cylinders when one or both of the cylinders rotate.

Couette flow; Geoffrey Ingram Taylor (1886-1975), British physicist; → flow.


Fr.: contreflot   

The movement of a fluid in the opposite direction to a fluid flowing in the same cross section of a turbulent medium.

counter-; → flow.

  ۱) تچان؛ ۲) تچیدن   
1) tacân; 2) tacidan

Fr.: 1) flot, écoulement; 2) couler, s'écouler   

1a) Moving along in a → stream; going as in a stream.
1b) A → dynamical system that evolves continuously with time.
1c) The transference of energy.
2) The corresponding verb.

O.E. flowan, from P.Gmc. *flo- (cf. Du. vloeien "to flow," O.H.G. flouwen "to rinse, wash"), probably from PIE *pleu- "to flow, float" (cf. Skt. plavate "navigates, swims," plavayati "overflows;" Gk. plyno "I wash," pleo "swim, go by sea;" L. pluere "to rain;" Arm. helum "I pour;" Lith. pilu "to pour out").

1) Tacân, from tac- variant tâz- present stem of tacidan, tâxtan, tâzidan "to run; to hasten; to assault," + noun and adj. suffix -ân. Related to the first component are Mod.Pers. tajan name of a river (initially "flowing, streaming, stream"), tâzi "swift (greyhound)," tak "running, rush," from Mid.Pers. tâz-, tâxtan "to flow, to cause to walk," tc- "to flow, to walk," tag "running, attack," tâzig "swift, fast;" Khotanese ttajs- "to flow, to walk;" Av. tac- "to run, to flow," taciāp- "flowing water," tacinti (3pl.pers.act.) "to flow," tacar- "course," tacan "current, streaming;" cf. Skt. tak- "to rush, to hurry," takti "runs;" O.Ir. tech- "to flow;" Lith. teketi "to walk, to flow;" O.C.S. tešti "to walk, to hurry;" Tokharian B cake "river;" PIE base *tekw- "to run; to flow."
2) Verbal form.

flow line
  خط ِ تچان   
xatt-e tacân

Fr.: ligne d'écoulement   

Same as → streamline.

flow; → line.

flow rate
  نرخ ِ تچان   
nerx-e tacân

Fr.: débit   

The amount of a substance, specifically a → fluid, moving across a specified unit → area in a given amount of → time.

flow; → rate.

flow tube
  لوله‌ی ِ تچان   
lule-ye tacân

Fr.: tube d'écoulement   

Same as → stream tube.

flow; → tube.


Fr.: aptitude à s'écouler, coulabilité   

The ability of a body of matter (liquid, gas, loose particulate solid) to flow.

From flowable, adj. from → flow + → -able + → -ity.

Tacandegi, from tacandé (originally tacandag), agent noun of tacidan, → flow, + noun suffix -i.

forced flow
  تچان ِ زوری   
tacân-e zuri

Fr.: écoulement forcé   

A fluid flow generated when external forces cause the fluid to flow, for example when a flow is caused by a pump. It contrasts with → free flow.

forced; → flow.

free flow
  تچان ِ آزاد   
tacân-e âzâd

Fr.: écoulement libre   

A fluid flow which develops when density differences within the fluid are the only driving forces. See also → forced flow.

free; → flow.

galactic outflow
  استچان ِ کهکشانی   
ostacân-e kahkešâni

Fr.: flot galactique   

galactic-scale outflow.

galactic; → outflow.

galactic-scale outflow
  استچان با مرپل ِ کهکشانی   
ostacân bâ marpel-e kahkešâni

Fr.: flot à l'échelle galactique   

The enormous amounts of → mass and → energy released from active galaxies into the → intergalactic medium. → Supermassive black holes, believed to exist at the centres of active galaxies (→ active galaxy), → accrete matter and liberate huge quantities of energy. The energy output is often observed as → active galactic nuclei (AGN) outflows in a wide variety of forms, e.g. → collimated  → relativistic jets and/or huge overpressured cocoons in → radio, → blueshifted broad → absorption lines in the → ultraviolet and → optical, → warm absorbers and ultrafast outflows in → X-rays, and → molecular gas in → far infrared. Moreover, the processes of → star formation and → supernova explosions release mass/energy into the surroundings. This → stellar feedback heats up, ionizes and drives gas outward, often generating large-scale outflows/→ winds. Galactic outflows are observed at low redshifts reaching a velocity as large as 1000 km s-1 and at high-z up to z ~ 5, sometimes extending over distances of 60-130 kpc. Galactic-scale outflows may be a primary driver of galaxy evolution through the removal of cool gas from star-forming regions to a galaxy's → halo or beyond.

galactic; → scale; → outflow.

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