An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 26 Search : pressure
acoustic pressure
  فشار ِ صدا   
fešâr-e sedâ

Fr.: pression acoustique   

Same as → sound pressure.

acoustic; → pressure.

Coulomb pressure
  فشار ِ کولن   
fešâr-e Coulomb

Fr.: pression de Coulomb   

The repulsive interaction due to the → Coulomb energy between two ions. If the ionic charge is Z, then the Coulomb potential energy is Z2e2/a, where a is some typical separation between the ions. The Coulomb pressure is expected to become important when the ratio ΓC = Z2e2/akT is much larger than 1. In that case, Coulomb effects dominate those of → thermal agitation and the gas settles down into a → crystal.

Coulomb; → pressure.

degeneracy pressure
  فشار ِ واگنی   
fešâr-e vâgeni (#)

Fr.: pression de dégénérescence   

Pressure in a degenerate electron or neutron gas. → degenerate matter.

degeneracy; → pressure.

dynamic pressure
  فشار ِ توانیک   
fešâr-e tavânik

Fr.: pression dynamique   

A property of a moving → fluid defined by (1/2)ρv2 in → Bernoulli's law, where ρ is → density of fluid and v is → velocity. Dynamic pressure is the difference between → total pressure and → static pressure. Also called → velocity pressure. → ram pressure.

dynamic; → pressure.

Fermi pressure
  فشار ِ فرمی   
fešâr-e Fermi

Fr.: pression de Fermi   

Same as → degeneracy pressure.

fermi; → pressure.

hydrostatic pressure
  فشار ِ هیدروتوانیک   
fešâr-e hidrotavânik

Fr.: pression hydrodynamique   

The term ρgz in the → Bernoulli equation. It is not pressure in a real sense, because its value depends on the reference level selected.

hydrostatic; → pressure.

magnetic pressure
  فشار ِ مغناتیسی   
fešâr-e meqnâtisi (#)

Fr.: pression magnétique   

The pressure exerted by a magnetic field on the material that contains the field.

magnetic; → pressure.

negative pressure
  فشار ِ ناییدار   
fešâr-e nâyidâr

Fr.: pression négative   

A kind of pressure that contrarily to ordinary pressure pushes inward. In contrast with the → Newtonian mechanics, in → general relativity there are situations in which pressure can be negative. Positive pressure gives rise to attractive gravity, whereas negative pressure creates → repulsive gravity.

negative; → pressure.

osmotic pressure
  فشارِ ترارانی   
fešâr-e tarârâni

Fr.: pression osmotique   

The hydrostatic pressure produced on the surface of a partially permeable membrane by osmosis.

osmotic; → pressure.

fešâr (#)

Fr.: pression   

The force per unit area.

M.E., from O.Fr. pressure, from L. pressura "action of pressing," from pressus, p.p. of premere "to press, compress."

Fešâr "squeezing, constriction, compression," verb fešordan, fešârdan "to press, squeeze;" phonetic variants Lori xošâr, Aftari xešâr, Qazvini, Qomi xošâl; cf. Khotanese ssarr- "to exhilarate;" loaned in Arm. ôšarak, in Ar. afšaraj "juice."

pressure broadening
  پهنش ِفشاری   
pahneš-e fešâri

Fr.: élargissement par pression   

A broadening of spectral lines caused mainly by the stellar atmospheric density and the surface gravity of the star. The line strength of a spectral line depends on the number of atoms in the star's atmosphere capable of absorbing the wavelength in question. For a given temperature, the more atoms there are, the stronger and broader the spectral line appears. Denser stars with higher surface gravity will exhibit greater pressure broadening of spectral lines.

pressure; → broadening.

pressure gradient
  زینه‌ی ِ فشار   
zine-ye fešâr

Fr.: gradient de pression   

The pressure difference between two adjacent regions of a fluid that results in a force being exerted from the high pressure region toward the low pressure region.

pressure; → gradient.

pressure gradient force
  نیروی ِ زینه‌ی ِ فشار   
niru-ye zine-ye fešâr

Fr.: force du gradient de pression   

A force resulting from → pressure gradient that is directed from high to low pressure.

pressure; → gradient; → force.

pressure ionization
  یونش ِ فشاری   
yoneš-e fešâri

Fr.: ionisation par pression   

A physical state of dense matter in which the electrostatic field of one atom should influence a neighboring atom and hence disturb atomic levels. In extreme case, such as white dwarfs, electron clouds practically rub and electrons are ionized off the parent atoms.

pressure; → ionization.

pressure scale height
  بلندی ِ مرپل ِ فشار   
bolandi-ye marpel-e fešâr

Fr.: hauteur d'échelle de pression   

A basic ingredient of the → mixing length theory that scales with the → mixing length. It is defined by the relation: HP = -dr/dln P = -Pdr/dP , where r is the height and P the pressure. See also → scale height.

pressure; → scale; → height.

radiation pressure
  فشار ِ تابش   
fešâr-e tâbeš

Fr.: pression de radiation   

The → momentum carried by → photons to a surface exposed to → electromagnetic radiation. Stellar radiation pressure on big and massive objects is insignificant, but it has considerable effects on → gas and → dust particles. Radiation pressure is particularly important for → massive stars. See, for example, → Eddington limit, → radiation-driven wind , and → radiation-driven implosion. The → solar radiation pressure is also at the origin of various physical phenomena, e.g. → gas tails in → comets and → Poynting-Robertson effect.

radiation; → pressure.

ram pressure
  فشار ِ قوچ‌وار   
fešâr-e qucvâr

Fr.: pression dynamique   

The pressure exerted on a body moving through a → fluid medium. For example, a → meteor traveling through the Earth's atmosphere produces a → shock wave generated by the extremely rapid → compression of air in front of the → meteoroid. It is primarily this ram pressure (rather than → friction) that heats the air which in turn heats the meteoroid as it flows around the meteoroid. The ram pressure increases with → velocity according to the relation P = (1/2)ρv2, where ρ is the density of the medium and v the relative velocity between the body and the medium. Similarly, → ram pressure stripping produces → jellyfish galaxies. Same as → dynamic pressure.

ram; → pressure.

ram pressure stripping
  لختکرد با فشار ِ قوچ‌وار   
loxtkard bâ fešâr-e qucvâr

Fr.: balayage par la pression dynamique   

A process proposed to explain the observed absence of gas-rich galaxies in → galaxy clusters whereby a galaxy loses its gas when it falls into a cluster. There is a tremendous amount of hot (~ 107 K) and tenuous (~ 10-4 cm-3) gas (several 1013 → solar masses) in the → intracluster medium (ICM). Ram pressure stripping was first proposed by Gunn & Gott (1972) who noted that galaxies falling into clusters feel an ICM wind. If this wind can overcome the → gravitational attraction between the stellar and gas disks, then the gas disk will be blown away. The mapping of the gas content of spiral galaxies in the → Virgo cluster showed that the → neutral hydrogen (H I) disks of cluster spiral galaxies are disturbed and considerably reduced. Their molecular gas, more bound to the galaxy, is less perturbed, but still may be swept out in case of very strong ram pressure. These observational results indicate that the gas removal due to the rapid motion of the galaxy within the intracluster medium is responsible for the H I deficiency and the disturbed gas disks of the cluster spirals (e.g., J. A. Hester, 2006, ApJ 647:910).

ram; → pressure; → strip.

solar radiation pressure
  فشار ِ تابش ِ خورشید   
fešâr-e tâbeš xoršid (#)

Fr.: pression du rayonnement solaire   

The → radiation pressure of solar photons, which pushes a comet's dust outward to form a → dust tail.

solar; → radiation; → pressure.

sound pressure
  فشار ِ صدا   
fešâr-e sedâ

Fr.: pression de son   

The periodic fluctuation above and below atmospheric pressure created by an oscillating body which provides the → sound power. Instantaneous sound pressure is the peak value of air pressure.

sound; → pressure.

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