Fr.: inversion magnétique
A change in the Earth's → magnetic field in which the → magnetic north pole is transformed into a → magnetic south pole and the magnetic south pole becomes a magnetic north pole. There are geological proofs indicating that the Earth's magnetic field has undergone numerous reversals of → polarity in the past. In the last 10 million years, there have been, on average, 4 or 5 reversals per million years. At other times, for example during the → Cretaceous era, there have been much longer periods when no reversals occurred. Over the past two centuries, Earth's magnetic field has weakened by 15%. Risks of a weak magnetic field include more deaths from cancer due to increased radiation, electrical grid collapse from severe solar storms, climate change, and temporary ozone holes.
magnetic Reynolds number
adad-e Reynolds-e meqnâtisi
Fr.: nombre de Reynolds magnétique
A → dimensionless quantity used in → magnetohydrodynamics to describe the relative balance of → magnetic advection to → magnetic diffusion. It is given by: Rm = σμ0νLU0, where σ is the → conductivity of the fluid, μ0 is the → magnetic permeability of the fluid, L is he characteristic length scale of the fluid flow, and U0 the characteristic velocity of the flow. A typical value for the Earth is Rm ~ 200.
Fr.: rigidité magnétique
In → plasma physics, a → quantity that describes the → resistance of a → charged particle to change its direction of motion under the influence of a perpendicular → magnetic field. Rigidity is defined as: R = rLBc = (pc)/(Ze), where rL is the → Larmor radius, B is → magnetic induction, c is the → speed of light, p is the → momentum of the particle, Z is → atomic number, and e the → electron charge. Since pc has the dimensions of energy and e the dimensions of charge, rigidity has the dimensions of → volts (a 10 GeV proton has a rigidity of 10 GV). In → cosmic ray studies, the energies of cosmic rays are often quoted in terms of their rigidities, rather than their energies per nucleon.
magnetic south pole
qotab-e daštar-e meqnâtisi
Fr.: pôle sud magnétique
setâre-ye meqnâtisi (#)
Fr.: étoile magnétique
A star (usually of spectral type A) with strong integrated magnetic field ranging up to 30,000 gauss.
tufân-e meqnâtisi (#)
Fr.: orage magnétique
A temporary, worldwide disturbance of the Earth's magnetic field by streams of charged particles from the Sun. Magnetic storms are frequently characterized by a sudden onset, in which the magnetic field undergoes marked changes in the course of an hour or less, followed by a very gradual return to normalcy, which may take several days.
Fr.: susceptibilité magnétique
Fr.: bande magnétique
A continuous, flexible ribbon impregnated or coated with magnetic-sensitive material on which information (sound, images, data, etc.) may be recorded.
magnetic vector potential
tavand-e bordâri-ye meqnâtisi
Fr.: vecteur potentiel magnétique
tâbeš-e doqotbe-ye meqnâtisi (#)
Fr.: rayonnement du dipôle magnétique
Radiation emitted by a rotating magnet.
The study of magnetic phenomena, comprising magnetostatics and electromagnetism.
The science of magnetic phenomena, including the fields and forces produced by magnets and, more generally, by moving electric charges.
Verbal noun of → magnetize.
To make a magnet of, or impart the properties of a magnet to.
Having been made magnetic; magnetic properties imparted to.
Past participle of → magnetize.
Fr.: plasma magnétisé
Fr.: vide magnétisé
Fr.: magnéto-, magnét-
Fr.: accelération magnetocentrifuge
The acceleration exerted on the plasma particles according to the → magnetocentrifugal model.
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.