Effects of inhomogeneous regions on electric potentials and magnetic fields: Two special cases

1982 ◽  
Vol 53 (12) ◽  
pp. 9192-9197 ◽  
Author(s):  
B. Neil Cuffin
Keyword(s):  
Magnetic Fields ◽  
Special Cases ◽  
Electric Potentials

Olfactory evoked electric potentials and magnetic fields in human

1992 ◽  
Vol 17 ◽  
pp. 267
Author(s):  
Mitsuo Tonoike ◽  
Mari Nakamura ◽  
Masamine Takebayashi
Keyword(s):  
Magnetic Fields ◽  
Electric Potentials

Correlation and comparison of magnetic and electric detection of small intestinal electrical activity

1997 ◽  
Vol 272 (5) ◽  
pp. G1159-G1167 ◽  
Author(s):  
L. A. Bradshaw ◽  
S. H. Allos ◽  
J. P. Wikswo ◽  
W. O. Richards
Keyword(s):  
Magnetic Fields ◽  
Quantum Interference ◽  
Rabbit Model ◽  
Field Measurements ◽  
Squid Magnetometer ◽  
Electrical Insulator ◽  
Electrode Recording ◽  
Electric Potentials ◽  
Small Intestinal ◽  
Highly Correlated

The small intestinal basic electrical rhythm (BER) was detected simultaneously with serosal electrodes and a transabdominal superconducting quantum interference device (SQUID) magnetometer in anesthetized rabbits. We induced mesenteric ischemia to correlate serosal electrode recording of changes in BER with the SQUID magnetometer. The BER frequency was obtained by spectral analysis of the data using Fourier and autoregressive techniques. There was a high degree of correlation (r = 0.96) between the BER frequency determined using the serosal electrodes and the BER frequency ascertained from SQUID data. Additionally, the effects of an electrical insulator on the external electric and magnetic fields were studied in the rabbit model. The presence of an insulator profoundly attenuates external electric potentials recorded by cutaneous electrodes but does not significantly affect external magnetic fields or serosal potentials. We conclude that SQUID magnetometers could noninvasively record small intestinal BER that was highly correlated with the activity recorded by invasive serosal electrodes. The advantages of magnetic field measurements have encouraged us to investigate clinical applications.

scholarly journals The Association of Flares to Cancelling Magnetic Features on the Sun

1989 ◽  
Vol 104 (1) ◽  
pp. 197-214
Author(s):  
Silvia H. B. Livi ◽  
Sara Martin ◽  
Haimin Wang ◽  
Guoxiang Ai
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Common Factor ◽  
Solar Observatory ◽  
The Other ◽  
Line Of Sight ◽  
Evolutionary Changes ◽  
Special Cases ◽  
Close Proximity ◽  
Polarity Inversion Line

AbstractPrevious work relating flares to evolutionary changes of photospheric solar magnetic fields are reviewed and reinterpreted in the light of recent observations of cancelling magnetic fields. In line-of-sight magnetograms and H-alpha filtergrams from Big Bear Solar Observatory, we confirm the following 3 associations: (a) the occurrence of many flares in the vicinity of emerging magnetic flux regions (Rust, 1974), but only at locations where cancellation has been observed or inferred; (b) the occurrence of flares at sites where the magnetic flux is increasing on one side of a polarity inversion line and concurrently decreasing on the other (Martres et al, 1968; Ribes, 1969); and (c) the occurrence of flares at sites where cancellation is the only observed change in the magnetograms for at least several hours before a flare (Martin, Livi, and Wang, 1985). Because cancellation (or the localized decrease in the line-of-sight component of magnetic flux) is the only common factor in all of these circumstances, suggest that cancellation is the more general association that includes the other associations as special cases. We propose the hypothesis that cancellation is a necessary, evolutionary precondition for flares. We also confirm the observation of Martin, Livi, and Wang (1985) that the initial parts of flares occur in close proximity to cancellation sites but that during later phases, the flare emission can spread to other parts of the magnetic field that are weak, strong, or not cancelling.

The generalized Balescu-Lenard collision Operator

1988 ◽  
Vol 39 (2) ◽  
pp. 303-317 ◽  
Author(s):  
Harry E. Mynick
Keyword(s):  
Diffusion Coefficient ◽  
Magnetic Fields ◽  
Anomalous Diffusion ◽  
Particle Motion ◽  
Collision Operator ◽  
Related Structure ◽  
Standard Operator ◽  
Simple Geometry ◽  
Special Cases ◽  
Generalized Operator

The generalization of the Balescu-Lenard collision operator to its fully electromagnetic counterpart in Kaufman's action-angle formalism is derived and its properties investigated. The general form may be specialized to any particular geometry where the unperturbed particle motion is integrable, and thus includes cylindrical plasmas, inhomogeneous slabs with non-uniform magnetic fields, tokamaks and the particularly simple geometry of the standard operator as special cases. The general form points to the commonality between axisymmetric, turbulent and ripple transport, and implies properties (e.g. intrinsic ambipolarity) that should be shared by them, under appropriate conditions. Along with a turbulent ‘anomalous diffusion coefficient’ calculated for tokamaks in previous work, an ‘anomalous pinch’ term of closely related structure and scaling is also implied by the generalized operator.

scholarly journals Solar force-free magnetic fields

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Thomas Wiegelmann ◽  
Takashi Sakurai
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Free Field ◽  
Coronal Magnetic Field ◽  
Electric Currents ◽  
Magnetic Forces ◽  
Special Cases ◽  
Field Lines ◽  
The Magnetic Field ◽  
Force Free Field

AbstractThe structure and dynamics of the solar corona is dominated by the magnetic field. In most areas in the corona magnetic forces are so dominant that all non-magnetic forces such as plasma pressure gradients and gravity can be neglected in the lowest order. This model assumption is called the force-free field assumption, as the Lorentz force vanishes. This can be obtained by either vanishing electric currents (leading to potential fields) or the currents are co-aligned with the magnetic field lines. First we discuss a mathematically simpler approach that the magnetic field and currents are proportional with one global constant, the so-called linear force-free field approximation. In the generic case, however, the relationship between magnetic fields and electric currents is nonlinear and analytic solutions have been only found for special cases, like 1D or 2D configurations. For constructing realistic nonlinear force-free coronal magnetic field models in 3D, sophisticated numerical computations are required and boundary conditions must be obtained from measurements of the magnetic field vector in the solar photosphere. This approach is currently a large area of research, as accurate measurements of the photospheric field are available from ground-based observatories such as the Synoptic Optical Long-term Investigations of the Sun and the Daniel K. Inouye Solar Telescope (DKIST) and space-born, e.g., from Hinode and the Solar Dynamics Observatory. If we can obtain accurate force-free coronal magnetic field models we can calculate the free magnetic energy in the corona, a quantity which is important for the prediction of flares and coronal mass ejections. Knowledge of the 3D structure of magnetic field lines also help us to interpret other coronal observations, e.g., EUV images of the radiating coronal plasma.

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