scholarly journals Magnetic Fields in Filaments

1998 ◽  
Vol 167 ◽  
pp. 78-85
Author(s):  
P. Démoulin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Coronal Mass Ejections ◽  
Cold Plasma ◽  
Field Measurements ◽  
The Other ◽  
Observational Constraints ◽  
Large Set ◽  
Photospheric Field ◽  
The Magnetic Field

AbstractFilaments are present in highly non-potential magnetic configurations. On one hand, the complexity of modeling such 3-D configurations makes a useful comparison between observations and models difficult. On the other hand such highly sheared regions are more interesting and challenging for understanding eruptive phenomena like flares and coronal mass ejections. Fortunately, the presence of cold plasma allows us to measure the magnetic field inside prominences. Together with photospheric field measurements and other morphological observations, these provide a large set of puzzling constraints for plausible models of the magnetic configurations. Models are reviewed in the framework of present observational constraints with the aim to clarify a piece of the mystery which surrounds the magnetic configuration of filaments.

scholarly journals Discovery of weak magnetic fields in four DZ white dwarfs in the local 20 pc volume

2019 ◽  
Vol 630 ◽  
pp. A65 ◽  
Author(s):  
S. Bagnulo ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Dwarfs ◽  
Field Measurements ◽  
Weak Magnetic Fields ◽  
Polluted Atmosphere ◽  
Highly Sensitive ◽  
Cool White Dwarfs ◽  
The Magnetic Field ◽  
Made In

We report the discovery of weak magnetic fields in three white dwarfs within the local 20 pc volume (WD 0816−310, WD 1009−184, and WD 1532+129), and we confirm the magnetic nature of a fourth star (WD 2138−332) in which we had previously detected a field at a 3σ level. The spectra of all these white dwarfs are characterised by the presence of metal lines and lack of H and He lines, that is, they belong to the spectral class DZ. The polarisation signal of the Ca II H+K lines of WD 1009−184 is particularly spectacular, with an amplitude of 20% that is due to the presence of a magnetic field with an average line-of-sight component of 40 kG. We have thus established that at least 40% of the known DZ white dwarfs with an He-rich atmosphere contained in the 20 pc volume have a magnetic field, while further observations are needed to establish whether the remaining DZ white dwarfs in the same volume are magnetic or not. Metal lines in the spectra of DZ white dwarfs are thought to have originated by accretion from rocky debris, and it might be argued that a link exists between metal accretion and higher occurrence of magnetism. However, we are not able to distinguish whether the magnetic field and the presence of a polluted atmosphere have a common origin, or if it is the presence of metal lines that allows us to detect a higher frequency of magnetic fields in cool white dwarfs, which would otherwise have featureless spectra. We argue that the new highly sensitive longitudinal field measurements that we have made in recent years are consistent with the idea that the magnetic field appears more frequently in older than in younger white dwarfs.

Die Wirkung eines homogenen Magnetfeldes auf das Wachstum von Micrococcus denitrificans / The Influence of Homogeneous Magnetic Fields on the Growth of Micrococcus denitrificans

1970 ◽  
Vol 25 (9) ◽  
pp. 1020-1023 ◽  
Author(s):  
Wolfram Thiemann ◽  
Erich Wagner
Keyword(s):  
Magnetic Field ◽  
Saccharomyces Cerevisiae ◽  
Growth Rate ◽  
Magnetic Fields ◽  
The Other ◽  
Anaerobic Conditions ◽  
Inhibition Of Growth ◽  
Significant Acceleration ◽  
In The Beginning ◽  
The Magnetic Field

The influence of strong homogeneous magnetic fields in the range of 5000 to 8000 Gauss on the growth of Saccharomyces cerevisiae and Micrococcus denitrificans was studied. In the case of yeast growing under nearly anaerobic conditions an inhibition of growth rate was observed in the beginning of incubaton while some hours later the growth accelerated and surpassed the control. M. denitrificans on the other hand grew with the same rate as the controls during the first 2 - 3 hours of experiment; thereafter the magnetic field resulted in a significant acceleration of growth rate measured by a 5.8 to 13.3% increase of oxygen consumption after 5 - 6 hours run of experiment. Until now only inhibition of bacterial growths by magnetic fields is reported elsewhere in the literature.

scholarly journals Magnetotellurics with a remote magnetic reference

Geophysics ◽  
1979 ◽  
Vol 44 (1) ◽  
pp. 53-68 ◽  
Author(s):  
T. D. Gamble ◽  
W. M. Goubau ◽  
J. Clarke
Keyword(s):  
Magnetic Field ◽  
Standard Deviation ◽  
Magnetic Fields ◽  
Apparent Resistivity ◽  
The Other ◽  
Impedance Tensor ◽  
Free Data ◽  
Electric And Magnetic Fields ◽  
Conventional Methods ◽  
The Magnetic Field

Magnetotelluric measurements were performed simultaneously at two sites 4.8 km apart near Hollister, California. SQUID magnetometers were used to measure fluctuations in two orthogonal horizontal components of the magnetic field. The data obtained at each site were analyzed using the magnetic fields at the other site as a remote reference. In this technique, one multiplies the equations relating the Fourier components of the electric and magnetic fields by a component of magnetic field from the remote reference. By averaging the various crossproducts, estimates of the impedance tensor not biased by noise are obtained, provided there are no correlations between the noises in the remote channels and noises in the local channels. For some data, conventional methods of analysis yielded estimates of apparent resistivities that were biased by noise by as much as two orders of magnitude. Nevertheless, estimates of the apparent resistivity obtained from these same data, using the remote reference technique, were consistent with apparent resistivities calculated from relatively noise‐free data at adjacent periods. The estimated standard deviation for periods shorter than 3 sec was less than 5 percent, and for 87 percent of the data, was less than 2 percent. Where data bands overlapped between periods of 0.33 sec and 1 sec, the average discrepancy between the apparent resistivities was 1.8 percent.

B-fields and gas motion in the L1689 region: an interpretation of Planck polarization data

2018 ◽  
Vol 14 (A30) ◽  
pp. 107-107
Author(s):  
Masafumi Matsumura ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Position Angle ◽  
The Other ◽  
Spatial Gradient ◽  
East Side ◽  
Polarization Data ◽  
The West ◽  
Complete Survey ◽  
The Magnetic Field

AbstractWith using the Planck polarization data (PR2, 2016A A…596A.109P), we investigate the magnetic fields in L1689 and associated clouds, and compare them with centroid velocities VLSR of 12CO and 13CO from the COMPLETE survey (2006AJ….131.2921R). We observe two components in this elongated region: in one component, the position angle of the magnetic field varies from –10 to 110 degrees in the galactic coordinate, while VLSR is rather constant (=4 ± 0.5 km/s). In the other component with the position angle being constant (=110 ± 15 degrees), the velocity VLSR shows a spatial gradient from 3 to 5 km/s, as one goes from west to east along the direction of elongation. If the east side of the component is more distant from us than the west, this gradient suggests that this component is stretching. This work is supported by JSPS KAKENHI Grant Number JP18H03720 (PI: Koji S. Kawabata).

Slipping stream instability in anisotropic plasma with magnetic shear

1968 ◽  
Vol 2 (2) ◽  
pp. 181-187 ◽  
Author(s):  
S. S. Rao ◽  
G. L. Kalra ◽  
S. P. Talwar
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Tangential Velocity ◽  
Anisotropic Plasma ◽  
The Other ◽  
Magnetic Shear ◽  
Velocity Discontinuity ◽  
Special Case ◽  
The Magnetic Field ◽  
Stream Instability

Starting with the Chew, Goldberger & Low equations, an analysis is made of instability arising due to a tangential velocity discontinuity in a dilute plasma. The velocities on either side are parallel but oppositely directed. Two cases are considered: (i) the magnetic field is uniform and everywhere transverse to the motion, and (ii) the magnetic field vectors on either side are orthogonal, being parallel to the motion on one side and perpendicular on the other. The conditions for instability are obtained and it is found that the effect of magnetic field is destabilizing in both cases. The effect of orthogonality of magnetic fields on the conventional fire-hose instability for a uniform, static plasma is also discussed as special case.

scholarly journals Properties of MHD turbulence and its consequences for the ISM and ICM

2009 ◽  
Vol 5 (H15) ◽  
pp. 464-465
Author(s):  
D. Falceta-Gonçalves ◽  
G. Kowal ◽  
A. Lazarian
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Collisionless Plasma ◽  
The Other ◽  
Mhd Turbulence ◽  
The Media ◽  
The Magnetic Field ◽  
Theoretical Results ◽  
Ism Magnetic Fields

AbstractIt is well known that the interstellar (ISM) and intergalactic (ICM) media are threaded by large scale magnetic fields. The understanding of its role on the dynamics of the media is, however, still in progress. For the ISM, magnetic fields may control or, at least, play a major role on the turbulence cascade leading to the star formation process. The ICM, on the other hand, is assumed to be thermally dominated but still the magnetic field may play an important role on the processes of acceleration and propagation of cosmic rays. In this work we provide a review of the latest theoretical results on the evolution of MHD turbulence under collisional and collisionless plasma approaches.

scholarly journals Distance Scaling Method for Accurate Prediction of Slowly Varying Magnetic Fields in Satellite Missions

2016 ◽  
Author(s):  
P. P. Zacharias ◽  
E. G. Chatzineofytou ◽  
S. T. Spantideas ◽  
C. N. Capsalis
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Power Law ◽  
Near Field ◽  
Magnetic Behavior ◽  
Field Measurements ◽  
Scaling Method ◽  
Magnetic Signature ◽  
The Magnetic Field

Abstract. In the present work, the determination of the magnetic behavior of localized magnetic sources from near field measurements is examined. The distance power law of the magnetic field fall-off is used in various cases to accurately predict the magnetic signature of an EUT consisting of multiple AC magnetic sources. Therefore, parameters concerning the location of the observation points (magnetometers) are stud ied towards this scope. The results clearly show that these parameters are independent of the EUT's size and layout. Additionally, the techniques developed in the present study enable the placing of the magnetometers close to the EUT, thus achieving high SNR. Finally, the proposed method is verified by real measurements, using a mobile phone as an EUT.

scholarly journals Observations of Magnetic Fields in Quiescent Prominences

1971 ◽  
Vol 43 ◽  
pp. 192-200 ◽  
Author(s):  
Einar Tandberg-Hanssen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Component ◽  
Zeeman Effect ◽  
Mean Value ◽  
Longitudinal Component ◽  
The Other ◽  
Magnetic Field Component ◽  
The Magnetic Field

The longitudinal component of the magnetic field, B∥, has been recorded in about 135 quiescent prominences observed at Climax during the period 1968–1969. The measurements were obtained with the magnetograph which records the Zeeman effect on hydrogen, helium and metal lines. The following lines were used, Hα; He I, D3, He I, 4471 Å; Na I, D1 and D2, and the observed magnetic field component in these prominences was independent of the line. The overall mean value of the field B∥ for all the prominences was 7.3G. As a rule, the magnetic field enters the prominence on one side and exits on the other, but in traversing the prominence material, the field tends to run along the long axis of the prominence.

scholarly journals Magnetism and the Invisible Man: The mysteries of coronal cavities

2013 ◽  
Vol 8 (S300) ◽  
pp. 139-146 ◽  
Author(s):  
Sarah Gibson
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Interplanetary Space ◽  
Three Dimensional ◽  
Field Measurements ◽  
Coronal Magnetic Field ◽  
Magnetic Structures ◽  
Coronal Magnetic Fields ◽  
Multiple Wavelengths ◽  
The Magnetic Field

AbstractMagnetism defines the complex and dynamic solar corona. Twists and tangles in coronal magnetic fields build up energy and ultimately erupt, hurling plasma into interplanetary space. These coronal mass ejections (CMEs) are transient riders on the ever-outflowing solar wind, which itself possesses a three-dimensional morphology shaped by the global coronal magnetic field. Coronal magnetism is thus at the heart of any understanding of the origins of space weather at the Earth. However, we have historically been limited by the difficulty of directly measuring the magnetic fields of the corona, and have turned to observations of coronal plasma to trace out magnetic structure. This approach is complicated by the fact that plasma temperatures and densities vary among coronal magnetic structures, so that looking at any one wavelength of light only shows part of the picture. In fact, in some regimes it is the lack of plasma that is a significant indicator of the magnetic field. Such a case is the coronal cavity: a dark, elliptical region in which strong and twisted magnetism dwells. I will elucidate these enigmatic features by presenting observations of coronal cavities in multiple wavelengths and from a variety of observing vantages, including unprecedented coronal magnetic field measurements now being obtained by the Coronal Multichannel Polarimeter (CoMP). These observations demonstrate the presence of twisted magnetic fields within cavities, and also provide clues to how and why cavities ultimately erupt as CMEs.

scholarly journals New magnetic field measurements of β Cephei stars and slowly pulsating B stars

2008 ◽  
Vol 4 (S259) ◽  
pp. 389-390
Author(s):  
Swetlana Hubrig ◽  
M. Briquet ◽  
P. De Cat ◽  
M. Schöller ◽  
T. Morel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Main Sequence ◽  
Field Measurements ◽  
Clear Picture ◽  
Magnetic Survey ◽  
B Stars ◽  
Pulsating Stars ◽  
Magnetic Field Measurements ◽  
The Magnetic Field

AbstractWe present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B-type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B stars. Roughly one third of the studied β Cephei stars have detected magnetic fields. The fraction of magnetic Slowly Pulsating B and candidate Slowly Pulsating B stars is found to be higher, up to 50%. We find that the domains of magnetic and non-magnetic pulsating stars in the H-R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence.

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