| magnetic confinement fusion | <physics> Method of fusion which uses magnetic fields / magnetic bottles to confine a hot plasma until fusion occurs. (09 Oct 1997) |
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| magnetic field | The sphere of influence of a magnet. (05 Mar 2000) |
| magnetic field gradient | In magnetic resonance imaging, a magnetic field that varies with location, superimposed on the uniform field of the magnet, to alter the resonant frequency of nuclei and allow recovery of their spatial position. Synonym: field gradient. (05 Mar 2000) |
| magnetic implant | A tissue-tolerated, magnetised metal placed within the bone to aid in denture retention; a similar magnet is placed in the overlying denture to complete the field. (05 Mar 2000) |
| magnetic inertia | <physics> A lagging or retardation of the effect, when the forces acting upon a body are changed, as if from velocity or internal friction; a temporary resistance to change from a condition previously invuced, observed in magnetism, thermoelectricity, etc, on reversal of polarity. Origin: NL, fr. Gr. To be behind, to lag. Source: Websters Dictionary (01 Mar 1998) |
| magnetic island | <physics> A magnetic topology near a rational surface where the flux surface is broken up into tubes which are not connected with each other poloidally. Islands may develop in non-ideal magnetohydrodynamic fluids, where electrical resistance becomes important and magnetic field lines are no longer frozen-in to the fluid. Then magnetic tearing and reconnection may allow field lines to link up and form islands with a local magnetic axis in a narrow region near a rational surface. (See also magnetohydrodynamic, frozen-in law). The development of islands may be caused by a small perturbation, whether internal or external, whether deliberate or accidental, and is usually associated with enhanced transport (i.e., reduced confinement). The centres of the islands are magnetic O-points, while the boundaries between islands are marked by X-points. (09 Oct 1997) |
| magnetic mach number | <physics> A dimensionless number equal to the ratio of the velocity of a fluid to the velocity of Alfven waves in that fluid. (13 Nov 1997) |
| magnetic moment | <physics> (a) A vector associated with a magnet, current loop, or particle, the cross product of this vector with the magnetic field is equal to the torque which the field exerts on the system. (b) The adiabatic invariant associated with the rapid gyromotion of a charged particle in a slowly varying magnetic field. (The value of the magnetic moment in sense (b) is the magnitude of the vector in sense (a).) (13 Nov 1997) |
| magnetic probe | <radiobiology> A conducting coil (sometimes insulated and inserted into the plasma) will have an induced voltage due to changes in the magnetic flux through the coil, and can therefore be used to measure changes in magnetic field strength. Small coils used to measure the local field strength are known as probes. (Other plasma diagnostics using this effect are the Rogowski coil, the voltage loop, and the diamagnetic loop.) Magnetic probes placed outside a toroidal plasma which are used to measure the poloidal magnetic field are also called Mirnov coils. (09 Oct 1997) |
| magnetic pumping | <radiobiology> Form of plasma heating where the plasma is successively compressed and expanded by means of a fluctuating external magnetic field. (See also adiabatic compression, frozen-in law.) (09 Oct 1997) |
| magnetic reconnection | When a plasma has some resistivity, then the frozen-in flow requirement is relaxed (see frozen-in flow). In that case, the magnetic field can move through the plasma fluid on the resistive (magnetic diffusion) time scale. (Typically slow compared to magnetohydrodynamic timescales.) This allows field lines to reconnect with each other to change their topology in response to magnetic and other forces in the plasma. (see also Helicity, which is not conserved when reconnection is significant.) The predominant theory for solar flares is based on the transfer of energy from magnetic fields to plasma particles which can occur in reconnection. Reconnection can also be studied in the laboratory. (09 Oct 1997) |
| magnetic resonance angiography | Non-invasive method of vascular imaging and determination of internal anatomy without injection of contrast media or radiation exposure. The technique is used especially in cerebral angiography as well as for studies of other vascular structures. (12 Dec 1998) |
| Magnetic Resonance Imaging | A special imaging technique used to image internal stuctures of the body, particularly the soft tissues. An MRI image is often superior to a normal X-ray image. It uses the influence of a large magnet to polarize hydrogen atoms in the tissues and then monitors the summation of the spinning energies within living cells. Images are very clear and are particularly good for soft tissue, brain and spinal cord, joints and abdomen. These scans may be used for detecting some cancers or for following their progress. Acronym: MRI (11 Nov 1997) |
| magnetic resonance imaging, cine | A type of imaging technique used primarily in the field of cardiology. By coordinating the fast gradient-echo mri sequence with retrospective ecg-gating, numerous short time frames evenly spaced in the cardiac cycle are produced. These images are laced together in a cinematic display so that wall motion of the ventricles, valve motion, and blood flow patterns in the heart and great vessels can be visualised. (12 Dec 1998) |
| magnetic resonance scanning | A special imaging technique used to image internal stuctures of the body, particularly the soft tissues. An MRI image is often superior to a normal X-ray image. It uses the influence of a large magnet to polarize hydrogen atoms in the tissues and then monitors the summation of the spinning energies within living cells. Images are very clear and are particularly good for soft tissue, brain and spinal cord, joints and abdomen. These scans may be used for detecting some cancers or for following their progress. Acronym: MRI (11 Nov 1997) |