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Search Results: 1 - 10 of 8500 matches for " magnetic fields "
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Creating a “Faraday Ghost” inside the Rotation Measure Synthesis Technique, through a Wide Observational “Gap” in Wavelength Coverage  [PDF]
Jacques P. Vallée
International Journal of Astronomy and Astrophysics (IJAA) , 2013, DOI: 10.4236/ijaa.2013.32011
Abstract:

Several recently published Faraday rotation measures (RM) derived using the novel RM synthesis technique are likely in error. If a set of polarimetric observations contains a large gap in the wavelength coverage, the rotation measure determination is sometimes ambiguous; this is also true even when two long wavelength ranges are observed but are separated by a wide gap. Essentially, there are 180° ambiguities in the observed Position Angle of the electric polarisation vector between the two wavelength ranges; these ambiguities are not resolved because the extent of wavelengths2 covered, within each of the two ranges, is too small to uniquely determine the RM in isolation. We find that unphysical “Faraday ghosts” can be mathematically constructed with a np ambiguity (±180° times an integer) at predictable polarization position angles when using only two wavelength ranges separated by a gap, as a function of the width of the gap (Equation (4)). Our computations suggest an empirical correlation between an observational gap between two wavelength ranges and the appearance of “Faraday ghosts”.

Fully and Partly Divergence and Rotation Free Interpolation of Magnetic Fields  [PDF]
Victor-Otto de Haan
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.57044
Abstract:

A new interpolation method for rotation and divergence free fields is presented. It is based on a suitable choice of a tricubic interpolation scheme and reaches an accuracy of third order in grid size (Δx). With the interpolation method it is possible to increase the accuracy with a factor of grid size/distance with respect to the trilinear interpolation method using exactly the same data points. Simulations for several distances of dipoles (r) to the interpolation area show that the maximum relative deviation is approximately 3(Δx/r)3 ppm.

Observational Evidences for Extremely Strong Magnetic Fields in Solar Flares  [PDF]
Vsevolod Gryhorovych Lozitsky
International Journal of Astronomy and Astrophysics (IJAA) , 2011, DOI: 10.4236/ijaa.2011.13019
Abstract: New observational data related to the X1.1/2N solar flare of 17 July 2004 were investigated and compared with some old data for other powerful flares and non-flare regions. Observations were carried out with the Echelle spectrograph of the Kyiv University Astronomical Observatory. The Stokes I ± V profiles of several metallic lines with different effective Lande factors geff have been analyzed including the FeI 5434.5 line with very low magnetic sensitivity (geff = –0.014). The obvious evidences of the emissive Zeeman effect were found as in lines with great and middle Lande factors as in FeI 5434.5 line. On the basis of all analyzed data one can conclude that upper magnetic field limit in flares can reach 70 - 90 kG, i.e. about more order higher than the well-known magnetic fields in great sunspots. The possible physical nature of such superstrong fields is discussed.
Magnetic Field Intensity/Melatonin-Molarity Interactions: Experimental Support with Planarian (Dugesia sp.) Activity for a Resonance-Like Process  [PDF]
Bryce P. Mulligan, Noa Gang, Glenn H. Parker, Michael A. Persinger
Open Journal of Biophysics (OJBIPHY) , 2012, DOI: 10.4236/ojbiphy.2012.24017
Abstract: Synergistic interactions between specific magnetic field intensities and chemical concentrations are challenging biophysical phenomena. Planarian were exposed to one of five different concentrations of melatonin and to a “geomagnetic”—patterned 7 Hz amplitude modulated magnetic field for 6 min once per hour for 8 hr during six successive nights. The peak average strengths were within the range (50 nT) or outside the range (200 nT) derived by the equation. As predicted by a resonance equation planarian displayed highly statistically significant decreased relative activity within the 50 nT, 10–7 to 10–6 M melatonin conditions compared to lower or higher concentrations. The effect explained about 30% of the variance in these changes of activity. Activity of planarian exposed to the same melatonin concentrations but to the 200 nT field did not differ significantly from each other or from those exposed to the 50 nT field in concentrations of melatonin <10–7 M or >10–6 M. These results suggest the existence of non-linear, “narrow-band” mechanisms involving the numbers of molecules within a distance determined by the boundary of the organism and the intensity of naturally-patterned magnetic fields derived from energy rather than force-based resonances.
The Efficiency of CP-Violating α2-Dynamos from Primordial Cosmic Axion Oscillation with Torsion  [PDF]
L. C. Garcia de Andrade
International Journal of Astronomy and Astrophysics (IJAA) , 2015, DOI: 10.4236/ijaa.2015.51008
Abstract: Recently torsion fields were introduced in CP-violating cosmic axion a2-dynamos [Garcia de Andrade, Mod Phys Lett A, (2011)] in order to obtain Lorentz violating bounds for torsion. Here instead, oscillating axion solutions of the dynamo equation with torsion modes [Garcia de Andrade, Phys Lett B (2012)] are obtained taking into account dissipative torsion fields. Magnetic helicity torsion oscillatory contribution is also obtained. Note that the torsion presence guarantees dynamo efficiency when axion dynamo length is much stronger than the torsion length. Primordial axion oscillations due to torsion yield a magnetic field of 109 G at Nucleosynthesis epoch. This is obtained due to a decay of BBN magnetic field of 1015 G induced by torsion. Since torsion is taken as 10–20 s–1, the dynamo efficiency is granted over torsion damping. Of course dynamo efficiency is better in the absence of torsion. In the particular case when the torsion is obtained from anomalies it is given by the gradient of axion scalar [Duncan et al., Nuclear Phys B 87, 215] that a simpler dynamo equation is obtained and dynamo mechanism seems to be efficient when the torsion helicity, is negative while magnetic field decays when the torsion is positive. In this case an extremely huge value for the magnetic field of 1015 Gauss is obtained. This is one order of magnitude greater than the primordial magnetic fields of the domain wall. Actually if one uses tDW ~ 10-4 s one obtains BDW ~ 1022 G which is a more stringent limit to the DW magnetic primordial field.
Minimum Attenuation of Physiologically-Patterned, 1 µTesla Magnetic Fields through Simulated Skull and Cerebral Space  [PDF]
Michael A. Persinger, Kevin S. Saroka
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.54024
Abstract:

To answer the queries concerning penetrability of ~1 μT, physiologically patterned, time-varying magnetic fields through the cranium, the proportions of attenuation through thicknesses and densities of ~3 times that of the human skull were measured directly. There was no reduction in the intensity of the magnetic field when two 2 cm thick dried pine boards (4.3 × 103 kg·m-3) were placed between the pairs of solenoids separated by the approximate width of the skull. Although volumes of water containing intracellular concentrations of ions did not attenuate the field intensity, placement of 290 cm2 of 2 mm sheets of duct metal reduced the amplitude by 25%. Spectra comparisons showed a clear congruence in profiles between direct measurement of the applied field and the original computer-generated pattern. These results indicate there is little validity to claims that weak, time-varying magnetic fields applied in this manner are eliminated or significantly attenuated by the human skull.

Observations of Cool-Star Magnetic Fields
Ansgar Reiners
Living Reviews in Solar Physics , 2012,
Abstract: Cool stars like the Sun harbor convection zones capable of producing substantial surface magnetic fields leading to stellar magnetic activity. The influence of stellar parameters like rotation, radius, and age on cool-star magnetism, and the importance of the shear layer between a radiative core and the convective envelope for the generation of magnetic fields are keys for our understanding of low-mass stellar dynamos, the solar dynamo, and also for other large-scale and planetary dynamos. Our observational picture of cool-star magnetic fields has improved tremendously over the last years. Sophisticated methods were developed to search for the subtle effects of magnetism, which are difficult to detect particularly in cool stars. With an emphasis on the assumptions and capabilities of modern methods used to measure magnetism in cool stars, I review the different techniques available for magnetic field measurements. I collect the analyses on cool-star magnetic fields and try to compare results from different methods, and I review empirical evidence that led to our current picture of magnetic fields and their generation in cool stars and brown dwarfs.
Solar Force-free Magnetic Fields
Thomas Wiegelmann,Takashi Sakurai
Living Reviews in Solar Physics , 2012,
Abstract: The 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 like plasma pressure gradient 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 relation 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 of large interests, as accurate measurements of the photospheric field become available from ground-based (for example SOLIS) and space-born (for example Hinode and SDO) instruments. 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.
Magnetic Structure of Sunspots
Juan M. Borrero,Kiyoshi Ichimoto
Living Reviews in Solar Physics , 2011,
Abstract: In this review we give an overview about the current state-of-knowledge of the magnetic field in sunspots from an observational point of view. We start by offering a brief description of tools that are most commonly employed to infer the magnetic field in the solar atmosphere with emphasis in the photosphere of sunspots. We then address separately the global and local magnetic structure of sunspots, focusing on the implications of the current observations for the different sunspots models, energy transport mechanisms, extrapolations of the magnetic field towards the Corona, and other issues.
Magnetic Neutral Points and Electric Lines of Force in Strong Gravity of a Rotating Black Hole  [PDF]
V. Karas, O. Kopá?ek, D. Kunneriath
International Journal of Astronomy and Astrophysics (IJAA) , 2013, DOI: 10.4236/ijaa.2013.33A003
Abstract:

Magnetic field can be amplified and twisted near a supermassive black hole residing in a galactic nucleus. At the same time magnetic null points develop near the horizon. We examine a large-scale oblique magnetic field near a rotating (Kerr) black hole as an origin of magnetic layers, where the field direction changes abruptly in the ergosphere region. In consequence of this, magnetic null points can develop by purely geometrical effects of the strong gravitational field and the frame-dragging mechanism. We identify magnetic nulls as possible sites of magnetic reconnection and suggest that particles may be accelerated efficiently by the electric component. The situation we discuss is relevant for starving nuclei of some galaxies which exhibit episodic accretion events, namely, Sagittarius A* black hole in our Galaxy.

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