longitudinal magnetic field
meydân-e meqnâtisi-ye derežnâyi
Fr.: champ magnétique longitudinal
1) A → magnetic field whose lines of force
(→ line of force)
run parallel to the long axis of the → magnet.
of a component can be accomplished using the longitudinal field set
up by a → coil or
→ solenoid. It can also be accomplished using
permanent magnets or electromagnets.
âhanrobâ (#), meqnâtis (#)
An object that produces a magnetic field around itself.
From L. magnetum (nom. magnes) "lodestone," from Gk. ho Magnes lithos "the Magnesian stone," from Magnesia region in Thessaly where magnetized ore was obtained.
Âhanrobâ, literally "iron attracting, iron robbing," from âhan→ iron + robâ agent noun of robudan, robâyidan
"to attract, to grab, rob;" Av. urūpaiieinti "to cause racking
pain(?);" cf. Skt. rop- "to suffer from abdominal pain,"
rurupas "to cause violent pain," ropaná- "causing
racking pain," rópi- "racking pain;" L. rumpere
"to break;" O.E. reofan "to break, tear."
A highly magnetized → neutron star with fields a thousand times stronger than those of → radio pulsars. There are two sub-classes of magnetars, → anomalous X-Ray pulsar (AXP)s and → soft gamma repeater (SGR)s, that were thought for many years to be separate and unrelated objects. In fact SGRs and AXPs are both neutron stars possessing → magnetic fields of unprecedented strength of 1014 - 1016 G, and that show both steady X-ray pulsations as well as soft gamma-ray bursts. Their inferred steady X-ray luminosities are about one hundred times higher than their → spin-down luminosities, requiring a source of power well beyond the magnetic dipole spin-down that powers → rotation-powered pulsar (RPP)s. New high-energy components discovered in the spectra of a number of AXPs and SGRs require non-thermal particle acceleration and look very similar to high-energy spectral components of young rotation-powered pulsars (A. K. Harding, 2013, Front. Phys. 8, 679).
meqnâtisi (#), meqnâti, âhanrobâyik
Of or pertaining to a magnet or magnetism.
Fr.: advection magnétique
The transport of the magnetic field by a fluid. It is given by the term ∇ x (v x B) in the → induction equation.
Fr.: axe magnétique
botri-ye meqnâtisi (#)
Fr.: bouteille magnétique
Fr.: freinage magnétique
The process whereby a star which loses mass slows down under the action of its → magnetic field. The stellar material follows the → magnetic field lines extending well beyond the stellar surface. The material gain → angular momentum and the underlying object is slowed down. Magnetic braking is an efficient mechanism for removing angular momentum from the the rotating object. See also → disk locking.
magnetic braking catastrophe
negunzâr-e legâmeš-e meqnâtisi
Fr.: catastrophe du freinage magnétique
The failure of numerical star formation calculations to produce rotationally supported → Keplerian disks because of the → magnetic braking effect, when → magnetic fields of strengths comparable to those observed in → molecular clouds are accounted for. The formation and early evolution of disks is a long-standing fundamental problem in → star formation models. Early work in the field had concentrated on the simpler problem of disk formation from the → collapse of a rotating dense core in the absence of a magnetic field. However, dense star-forming cores are observed to be significantly magnetized. There is increasing theoretical evidence that disk formation is greatly modified, perhaps even suppressed, by a dynamically important magnetic field. This has been found in analytic studies, axisymmetric numerical models and in 3D calculations using → ideal magnetohydrodynamics. By contrast, recent observations suggest the presence of massive, 50-100 AU disks and evidence for associated → outflows in the earliest (→ class 0) stages of star formation around both low and high mass stars. Two primary solutions have been proposed: → turbulence and → non-ideal magnetohydrodynamics. Calculations of the collapse of a massive 100 Msun core have shown that 100 AU scale disk formation in the presence of strong magnetic fields was indeed possible, with some argument over whether this is caused by turbulent reconnection or another mechanism. Studies, using simulations of collapsing 5 Msun cores, have found that turbulence diffuses the strong magnetic field out of the inner regions of the core, and that the non-zero → angular momentum of the turbulence causes a misalignment between the rotation axis and the magnetic field. Both of these effects reduce the magnetic braking, and allow a massive disk to form (Wurster et al. 2016, arxiv/1512.01597 and references therein).
Fr.: rayonnement de freinage magnétique
Same as → synchrotron radiation.
Fr.: flottabilité magnétique
The phenomenon whereby the presence of a → magnetic field can make a portion of → compressible fluid less dense than its surroundings, so that it floats upward under the influence of gravity. This magnetic buoyancy is thought, in fact, to be the mechanism by which magnetic flux tubes rise through the Sun's → convection zone and break at the surface in the form of → sunspots. The Sun's rotation would have a major effect on the rate at which these magnetic flux tubes rise. The rotation substantially lengthen the time taken for the flux tubes to reach the surface (D. J. Acheson, 1979, Nature 277, 41).
magnetic cataclysmic binary
dorin-e gatluri-ye meqnâtisi
Fr.: binaire cataclysmique magnétique
A cataclysmic binary in which the white dwarf primary has a strong magnetic field that radically affects the accretion flow in the system. → polar
Fr.: nuage magnétique
A transient ejection in the → solar wind having an enhanced field, a large and smooth change in field direction, and a low → proton temperature compared to the ambient proton temperature (L. F. Burlaga, 1995, Interplanetary Magnetohydrodynamics, Oxford Univ. Press, 89-114).
Fr.: compas magnétique
Fr.: connectivité magnétique
Of magnetic field lines, the condition for them to be connected or the process whereby they become connected or connective.
pâyâ-ye meqnâtisi (#)
Fr.: constante magnétique
A physical constant relating mechanical and electromagnetic units of measurement. It has the value of 4π × 10-7 henry per meter. Also called the permeability of free space, or → absolute permeability.
Fr.: convection magnétique
Thermal → convection modified by the presence of magnetic fields.
Fr.: déclinaison magnétique
Fr.: diffusion magnétique
The process whereby the magnetic field tends to diffuse across the plasma and to smooth out any local inhomogeneities under the influence of a finite resistance in the plasma. For a stationary plasma the → induction equation becomes a pure → diffusion equation: ∂B/∂t = Dm∇2B, where Dm = (μ0σ0)-1 is the → magnetic diffusivity.
Fr.: diffusivité magnétique