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: 144 Search : magnet
electromagnetic wave
  موج ِ برقامغناتی   
mowj-e barqâmeqnâti

Fr.: onde électromagnétique   

A wave produced by oscillation or acceleration of an electric charge. → electromagnetic radiation.

electromagnetic; → wave.

electromagnetism
  برقامغنات، برقامغناتیس   
barqâmeghnât, barqâmeghnâtis

Fr.: électromagnétisme   

1) The science dealing with the physical relations between → electricity and → magnetism. Same as → electromagnetic theory.
2) One of the four fundamental forces of nature, governing the electric and magnetic interaction between particles.

electro-; → magnetism.

ferromagnet
  آهن‌مغنات   
âhanmeqnât

Fr.: ferro-aimant   

A ferroamagnetic substance, which possesses → ferromagnetism.

ferro-; → magnet.

ferromagnetic
  آهن‌مغناتی   
âhanmeqnâti

Fr.: ferromagnétique   

Relative to or characterized by → ferromagnetism.

ferro-; → magnetic.

ferromagnetism
  آهن‌مغنات‌مندی   
âhanmegnâtmandi

Fr.: ferromagnétisme   

A property of certain substances which are enormously more magnetic than any other known substance. Ferromagnetic substances, such as the chemical elements iron, nickel, cobalt, some of the rare earths, and ceratin alloys, achieve maximum → magnetization at relatively low magnetic field strengths. Their large → magnetic permeabilityies (greater than unity) vary with the strength of the applied field. When the temperature of a ferromagnet is increased the property vanishes gradually due to randomizing effects of thermal agitation. Beyond a definite temperature for each substance ( → Curie temperature) it ceases to behave as a ferromagnet and becomes a → paramagnet. Ferromagnetism is due to the alignment of the → magnetic moments of uncompensated electrons in the crystal lattice. Under the influence of an external magnetizing field, all of the uncompensated electrons line up with their → spins in the direction of the field. In contrast with paramagnetic substances, in which spins interact only with an external magnetic field, in ferromagnets the spins interact with each others, each of them trying to align the others in its own direction. This coupling gives rise to a spontaneous alignment of the moments over macroscopic regions called domains. The domains undergo further alignment when the substance is subjected to an applied field. Ferromagnets retain their magnetisation even when the external magnetic field has been removed. See also → antiferromagnetism ; → diamagnetism; → magnetism.

ferro-; → magnetism.

force-free magnetic field
  میدان ِ مغناتیسی ِ بی‌نیرو   
meydân-meqnâtisi-ye bi-niru

Fr.: champ magnétique sans force   

The condition in a plasma when the → Lorentz force is zero, that is when the electric current flows along the magnetic field. Force-free magnetic fields are encountered in astrophysical plasmas with negligible gas pressure. The solar corona is the best available example of such fields in action in a plasma.

force; → free; → magnetic; → field.

fossil magnetic field
  میدان ِ مغناتیسی ِ سنگواره، ~ ~ سنگواره‌ای   
meydân-e meqnâtisi-ye sangvâré, ~ ~ sangvâre-yi

Fr.: champ magnétique fossile   

In a physical system, the → magnetic field belonging to an earlier magnetic process or event. A fossil magnetic field may be a vanished one or exist in relic forms. As an example, the solar magnetic field, which was present during the formation of the Sun, has disappeared over the last 4.6 billions years.

fossil;→ magnetic; → field;

frozen magnetic field line
  خط ِ میدان ِ مغناتیسی ِ یخ‌بسته، ~ ~ ~ رچیده   
xatt-e meydân-e meqnâtisi-ye yax basté, ~ ~ ~ rocidé

Fr.: ligne de champ magnétique gelée   

A → magnetic field line in a → fluid when the motion of the fluid carries the magnetic field along with it.

Frozen, p.p. of → freeze; → magnetic; → line.

Gauss's law for magnetism
  قانون ِ گاؤس در مغنات‌مندی   
qânun-e Gauss dar meqnâtmandi

Fr.: loi de Gauss en magnétisme   

The → magnetic flux through an arbitrary closed surface equals zero. Mathematically, in differential form: ∇ . B = 0 and in integral form: ΦB = ∫B.dS = 0 (closed surface integral). This is one of the four → Maxwell's equations. This law expresses the fact that there are no free magnetic poles (→ monopoles) in nature and that all the lines of force of a magnetic field are closed curves.

gauss; → law; → magnetism.

geomagnetic
  زمین‌مغناتیسی، زمین‌مغناتی   
zamin-meqnâtisi, zamin-meqnâti

Fr.: géomagnétique   

Of or pertaining to → geomagnetism.

geo-; → magnetic.

geomagnetic activity
  ژیرندگی ِ زمین‌مغناتیسی، ~ زمین‌مغناتی   
žirandegi-ye zamin-meqnâtisi, ~ zamin-meqnâti

Fr.: activité géomagnétique   

The natural variations in the → geomagnetic field due to interactions of the Earth's field and → magnetosphere with energetic particles from the Sun.

geomagnetic; → activity.

geomagnetic excursion
  زچار ِ زمین‌مغناتی   
zocâr-e zamin-meqnâti

Fr.: excursion géomagnétique   

A geophysical event, distinguished from the → magnetic reversal, in which the Earth's magnetic field departs for a relatively short time from its usual near axial configuration, without establishing a reversed direction. During the excursion the intensity and direction of the Earth's magnetic field undergo drastic changes. Palaeomagnetic measurements have revealed that since the last full reversal the Earth's magnetic field has, for brief intervals, deviated from the behavior expected during "normal" secular variation.

geomagnetic; → excursion.

geomagnetic field
  میدان ِ زمین‌مغناتیسی، ~ زمین‌مغناتی   
meydân-e zamin-meqnâtisi, ~ zamin-meqnâti

Fr.: champ géomagnétique   

The magnetic field that is generated within the Earth and extends out around the Earth. The intensity of the magnetic field at the Earth's surface is about 0.32 → gauss at the equator and 0.62 gauss at the north pole.

geomagnetic; → field.

geomagnetic storm
  توفان ِ زمین‌مغناتیسی، ~ زمین‌مغناتی   
tufân-e zamin-meqnâtisi, ~ zamin-meqnâti

Fr.: orage géomagnétique   

A violent disturbance of the Earth's magnetic field, distinct from regular diurnal variations, following a → solar flare or → coronal mass ejection.

geomagnetic; → storm.

geomagnetism
  زمین‌مغنات‌مندی   
zamin-meqnâtmandi

Fr.: géomagnetsme   

A branch of geophysics concerned with the study of the Earth's → geomagnetic field, including its origin, spatial extent, and variations in time.

geo-; → magnetism.

giant magnetoresistance (GMR)
  مغنات-ایستادگی ِ کلان، ایستادگی ِ مغناتیسی ِ ~   
meqnât-istâdegi-ye kalân, istâdegi-ye meqnâtisi-ye ~

Fr.: magnétorésistance géante   

A quantum mechanical phenomenon where the resistance of certain materials drops dramatically upon application of a magnetic field in certain structures composed of alternating layers of magnetic and nonmagnetic metals. The basis of the GMR is the dependence of the electrical resistivity of electrons in a magnetic metal on the direction of the electron spin, either parallel or anti-parallel to the magnetic moment of the layers. The 2007 Nobel Prize in physics was awarded to the French physicist Albert Fert (1938-) and German physicist Peter Grünberg (1939-) for the discovery of GMR.

giant; magneto- combining form of → magnet; → resistance.

hydromagnetics
  هیدرومغناتیک   
hidromeqnâtik

Fr.: hydromagnétisme   

Same as → magnetohydrodynamics.

hydro-; → magnetics.

ideal magnetohydrodynamics (MHD)
  مغنات-و-هیدروتوانیک ِ آرمانی، ~ مینه‌وار   
meqnâtohidrotavânik-e ârmâni, ~ minevâr

Fr.: magnétohydrodynamique idéale   

Magnetohydrodynamics of a → plasma with very large (infinite) → conductivity. In this condition, → Ohm's law reduces to E = -v × B, where E represents → electric field, B → magnetic field, and v the → fluid velocity. Ideal MHD is the simplest model to describe the dynamics of plasmas immersed in a magnetic field. It is concerned with → one-fluid magnetohydrodynamics and neglects → resistivity. This theory treats the plasma composed of many charged particles with locally neutral charge as a continuous single → fluid. Ideal MHD does not provide information on the velocity distribution and neglects the physics relating to wave-particle interactions, as does the two-fluid theory as well. It does have the advantage that the macroscopic dynamics of the → magnetized plasma can be analyzed in realistic three-dimensional geometries (K. Nishikawa & M. Wakatani, 2000, Plasma Physics, Springer). See also → non-ideal magnetohydrodynamics.

ideal; → magnetohydrodynamics.

interplanetary magnetic field
  میدان ِ مغناتیسی ِ اندرسیاره‌ای   
meydân-e meqnâtisi-ye andarsayyârei

Fr.: champ magnétique interstellaire   

The magnetic field that is carried along with the solar wind and fills the solar system space. It is wound into a spiral structure by the rotation of the Sun. At the Earth's distance from the Sun, it has a strength of about 5 x 10-5 gauss.

interplanetary; → magnetic; → field.

interstellar magnetic field
  میدان ِ مغناتیسی ِ اندر-اختری   
meydân-e meqnâtisi-ye andaraxtari

Fr.: champ magnétique interstellaire   

A large-scale, weak magnetic field, with an estimated strength of about 1 to 5 microgauss, that pervades the disk of the Milky Way Galaxy and controls the alignment of interstellar dust grains.

interstellar; → magnetic; → field.

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