scholarly journals Tracing magnetic field with synchrotron polarization gradients: parameter study

2019 ◽  
Vol 486 (4) ◽  
pp. 4813-4822 ◽  
Author(s):  
Jian-Fu Zhang ◽  
Alex Lazarian ◽  
Ka Wai Ho ◽  
Ka Ho Yuen ◽  
Bo Yang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Milky Way ◽  
Low Frequency ◽  
Parameter Study ◽  
New Techniques ◽  
Polarization Gradient ◽  
Local Magnetic Fields ◽  
Magnetohydrodynamic Simulations ◽  
Tomographic Slice

ABSTRACT We employ synthetic observations obtained with magnetohydrodynamic simulations to study how to trace the distribution of turbulent magnetic fields using the synchrotron polarization gradient techniques suggested by Lazarian & Yuen. Both synchrotron polarization gradients and its derivative gradients with regard to the squared wavelength λ2 are used to explore the probing ability of the technique in magnetic fields from sub- to super-Alfvénic turbulence. We focus on studies that involve multifrequency measurements in the presence of strong Faraday rotation and show the ways of how to recover the projected mean magnetic fields in the plane of the sky and the local magnetic fields within a tomographic slice. We conclude that the new techniques can successfully reconstruct the 3D magnetic field within our Milky Way and other galaxies. This paper opens an avenue for applying our new techniques to a large number of data cubes such as those from the Low-Frequency Array for radio astronomy and the Square Kilometre Array.

scholarly journals Effect of magnetic fields on cryptochrome-dependent responses in Arabidopsis thaliana

2009 ◽  
Vol 6 (41) ◽  
pp. 1193-1205 ◽  
Author(s):  
Sue-Re Harris ◽  
Kevin B. Henbest ◽  
Kiminori Maeda ◽  
John R. Pannell ◽  
Christiane R. Timmel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Arabidopsis Thaliana ◽  
Magnetic Fields ◽  
Low Frequency ◽  
Zero Field ◽  
Experimental Conditions ◽  
Replication Studies ◽  
Weak Magnetic Fields ◽  
Simultaneous Control ◽  
Independent Replication

The scientific literature describing the effects of weak magnetic fields on living systems contains a plethora of contradictory reports, few successful independent replication studies and a dearth of plausible biophysical interaction mechanisms. Most such investigations have been unsystematic, devoid of testable theoretical predictions and, ultimately, unconvincing. A recent study, of magnetic responses in the model plant Arabidopsis thaliana , however, stands out; it has a clear hypothesis—that seedling growth is magnetically sensitive as a result of photoinduced radical-pair reactions in cryptochrome photoreceptors—tested by measuring several cryptochrome-dependent responses, all of which proved to be enhanced in a magnetic field of intensity 500 μT. The potential importance of this study in the debate on putative effects of extremely low-frequency electromagnetic fields on human health prompted us to subject it to the ‘gold standard’ of independent replication. With experimental conditions chosen to match those of the original study, we have measured hypocotyl lengths and anthocyanin accumulation for Arabidopsis seedlings grown in a 500 μT magnetic field, with simultaneous control experiments at 50 μT. Additionally, we have determined hypocotyl lengths of plants grown in 50 μT, 1 mT and approximately 100 mT magnetic fields (with zero-field controls), measured gene ( CHS , HY5 and GST ) expression levels, investigated blue-light intensity effects and explored the influence of sucrose in the growth medium. In no case were consistent, statistically significant magnetic field responses detected.

scholarly journals Measurements of local magnetic fields in a solar flare by splitting of emissive peaks in cores of spectral lines

2018 ◽  
pp. 47-52 ◽  
Author(s):  
V. Lozitsky
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Flare ◽  
Filling Factor ◽  
Spectral Lines ◽  
Local Fields ◽  
Strong Component ◽  
Component Structure ◽  
Local Magnetic Fields ◽  
The Magnetic Field

We present study of solar flare of 19 July 2000 which arose in active region NOAA 9087 and had M 5.6 / 3N importance. Observational material was obtained with the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. The local magnetic fields in this flare were measured by the splitting of emissive peaks of the FeI 5269.54, FeII 4923.93, Нα, Нβ, Нγand D3 HeI lines. The basic idea of the method is based on the fact that the flare emission in some spectral lines is clearly divided into two components: (1) wider and unpolarized, and (2) more narrow and polarized, with significant Zeeman splitting. This is indication to the two-component structure of the magnetic field, with substantially different magnetic fields and thermodynamical conditions in these two components. Due to the fact that the polarized emission is quite confidently separated from the unpolarized, it is possible to measure the local magnetic fields directly in the second (strong) component regardless of the filling factor. It was found that in the bright place of this flare, which was projected on the sunspot penumbra, the effective magnetic field Beff in the FeI 6301.5 i 6302.5 lines measured by splitting of the Fraunhofer profiles, was 900 G. However, the splitting of emissive peaks in Нα, Нβ, Нγ and D3 lines corresponds to 1000 G, 1400 G, 1450 G and about zero, respectively, with errors of 30-50 G for abovenamed FeI lines and about 100–150 G for other lines. This difference in the results is probably due to the fact that in the case of FeI 6301.5 i 6302.5 lines, the Beff value represents several parameters, including the value of the background field, the filling factor, and the intensity of the local fields in the strong component. In contrast, data on the Нα, Нβ, Нγ, and D3 lines mainly reflect local fields in the strong component and indicate the nonmonotonous distribution of the magnetic field with height in solar atmosphere, with its maximum at the chromospheric level. Earlier in this flare, when constructing its semi-empirical model, local amplification of the magnetic field at the photospheric level was discovered, and its value reached 1500 G. These data are confirmed by direct measurements of splitting of emissive peaks in FeI 5269.54 and FeII 4923.93 lines, according to which the magnetic field in the flare was 1250 ± 100 G. Thus, in this flare there were at least two regions (possibly two flat layers) of local amplification of the magnetic field.

scholarly journals Measurements of Cosmic Magnetism with LOFAR and SKA

2007 ◽  
Vol 5 ◽  
pp. 399-405 ◽  
Author(s):  
R. Beck
Keyword(s):  
Magnetic Fields ◽  
Interstellar Medium ◽  
Milky Way ◽  
Intergalactic Medium ◽  
Low Frequency ◽  
Radio Telescopes ◽  
New Era ◽  
Origin And Evolution ◽  
Central Regions ◽  
Nearby Galaxies

Abstract. The origin of magnetic fields in stars, galaxies and clusters is an open problem in astrophysics. The next-generation radio telescopes Low Frequency Array (LOFAR) and Square Kilometre Array (SKA) will revolutionize the study of cosmic magnetism. "The origin and evolution of cosmic magnetism" is a key science project for SKA. The planned all-sky survey of Faraday rotation measures (RM) at 1.4 GHz will be used to model the structure and strength of the magnetic fields in the intergalactic medium, the interstellar medium of intervening galaxies, and in the Milky Way. A complementary survey of selected regions at around 200 MHz is planned as a key project for LOFAR. Spectro-polarimetry applied to the large number of spectral channels available for LOFAR and SKA will allow to separate RM components from distinct foreground and background regions and to perform 3-D Faraday tomography of the interstellar medium of the Milky Way and nearby galaxies. – Deep polarization mapping with LOFAR and SKA will open a new era also in the observation of synchrotron emission from magnetic fields. LOFAR's sensitivity will allow to map the structure of weak, extended magnetic fields in the halos of galaxies, in galaxy clusters, and possibly in the intergalactic medium. Polarization observations with SKA at higher frequencies (1–10 GHz) will show the detailed magnetic field structure within the disks and central regions of galaxies, with much higher angular resolution than present-day radio telescopes.

scholarly journals Trichomonas vaginalis and Giardia lamblia Growth Alterations by Low-Frequency Electromagnetic Fields

2019 ◽  
Author(s):  
Abraham Octavio RODRÍGUEZ-DE LA FUENTE ◽  
Ricardo GOMEZ-FLORES ◽  
José Antonio HEREDIA-ROJAS ◽  
Edna Marbella GARCÍA-MUÑOZ ◽  
Javier VARGAS-VILLARREAL ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electromagnetic Fields ◽  
Giardia Lamblia ◽  
Trichomonas Vaginalis ◽  
Low Frequency ◽  
Antagonistic Effect ◽  
Logarithmic Phase ◽  
Physical Factors ◽  
Field Exposure

Background: There is an increasing interest in using physical factors such as magnetic fields as antimicrobial strategy, with variable results. The current study was aimed to evaluate the influence of extremely low-frequency electromagnetic fields (ELF-EMFs) on the axenically-cultured parasite protozoans Trichomonas vaginalis and Giardia lamblia growth. Methods: Bioassays were developed using T. vaginalis, GT-13 and G. lamblia IMSS-0989 strains cultured at 37 ºC in TYI-S-33 medium. The following treatment regimens and controls were considered: (a) cells exposed to ELF-EMFs, (b) untreated cells, (c) cells treated with Metronidazole, used as positive controls, and (d) cells co-exposed to ELF-EMFs and Metronidazole. When cultures reached the end of logarithmic phase, they were exposed to ELF-EMFs for 72 h, in a standardized magnetic field exposure facility. For determining cytotoxic effects, trophozoite density was blindly evaluated in a Neubauer chamber. Results: A significant decrease in trophozoite growth was observed for T. vaginalis, in magnetic field-treated cultures. On the other hand, cultures co-exposed to ELF-EMFs and Metronidazole showed no significant differences when compared with cultures treated with Metronidazole alone. On the contrary, an increased trophozoite density was observed in G. lamblia cultures after exposure to magnetic fields. An absence of a synergistic or antagonistic effect was observed. Conclusion: ELF-EMFs induced T. vaginalis and G. lamblia growth alterations, indicating a potential effect in cell cycle progression.

scholarly journals Massive core/star formation triggered by cloud–cloud collision: Effect of magnetic field

2020 ◽  
Author(s):  
Nirmit Sakre ◽  
Asao Habe ◽  
Alex R Pettitt ◽  
Takashi Okamoto
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Strong Magnetic Field ◽  
Molecular Clouds ◽  
Weak Magnetic Field ◽  
Dense Cores ◽  
Cloud Models ◽  
Low Mass ◽  
Magnetohydrodynamic Simulations

Abstract We study the effect of magnetic field on massive dense core formation in colliding unequal molecular clouds by performing magnetohydrodynamic simulations with sub-parsec resolution (0.015 pc) that can resolve the molecular cores. Initial clouds with the typical gas density of the molecular clouds are immersed in various uniform magnetic fields. The turbulent magnetic fields in the clouds consistent with the observation by Crutcher et al. (2010, ApJ, 725, 466) are generated by the internal turbulent gas motion before the collision, if the uniform magnetic field strength is 4.0 μG. The collision speed of 10 km s−1 is adopted, which is much larger than the sound speeds and the Alfvén speeds of the clouds. We identify gas clumps with gas densities greater than 5 × 10−20 g cm−3 as the dense cores and trace them throughout the simulations to investigate their mass evolution and gravitational boundness. We show that a greater number of massive, gravitationally bound cores are formed in the strong magnetic field (4.0 μG) models than the weak magnetic field (0.1 μG) models. This is partly because the strong magnetic field suppresses the spatial shifts of the shocked layer that should be caused by the nonlinear thin shell instability. The spatial shifts promote the formation of low-mass dense cores in the weak magnetic field models. The strong magnetic fields also support low-mass dense cores against gravitational collapse. We show that the numbers of massive, gravitationally bound cores formed in the strong magnetic field models are much larger than in the isolated, non-colliding cloud models, which are simulated for comparison. We discuss the implications of our numerical results on massive star formation.

Investigation of the spectral characteristics of low-frequency magnetic fields in different modes of operation of magnetic resonance imaging

2020 ◽  
pp. 727-727 ◽  
Author(s):  
L. V. Pokhodzey ◽  
E. A. Rudneva ◽  
Yu. P. Paltzev
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Field ◽  
Magnetic Resonance ◽  
Magnetic Fields ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Resonance Imaging ◽  
Gradient Coils ◽  
Modes Of Operation ◽  
Frequency Magnetic Field

The features of the amplitude-frequency and temporal parameters of magnetic fields created by MRI 3 T the gradient coils under various modes of its operation has studied. Low-frequency magnetic field induction changes has pulsed form - single pulses and various pulses shapes, different polarities and durations. Adequate controlled parameters for their hygienic evaluation are proposed

scholarly journals Cosmic magnetic field observations with next generation instrumentation

2009 ◽  
Vol 5 (H15) ◽  
pp. 430-431
Author(s):  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Milky Way ◽  
Low Frequency ◽  
Radio Telescopes ◽  
Radio Waves ◽  
Huge Number ◽  
Fundamental Physics ◽  
New Era ◽  
Weak Magnetic Fields ◽  
The Universe

AbstractThe origin of magnetic fields in the Universe is an open problem in astrophysics and fundamental physics. Forthcoming radio telescopes will open a new era in studying cosmic magnetic fields. Low-frequency radio waves will reveal the structure of weak magnetic fields in the outer regions and halos of galaxies and in intracluster media. At higher frequencies, the EVLA and the SKA will map the structure of magnetic fields in galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures (RM) towards a huge number of polarized background sources with the SKA and its pathfinders will allow us to model the structure and strength of the regular magnetic fields in the Milky Way, the interstellar medium of galaxies, in galaxy clusters and the intergalactic medium.

scholarly journals Magnetic field of complex helical conductors

2013 ◽  
Vol 62 (4) ◽  
pp. 533-540 ◽  
Author(s):  
Krzysztof Budnik ◽  
Wojciech Machczyński
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electric Power ◽  
Electromagnetic Compatibility ◽  
Complex Geometry ◽  
Phase Distribution ◽  
Low Frequency ◽  
Software Tool ◽  
Helical Structure ◽  
Analytical Formulas

Abstract Transmission of the electric power is accompanied with generation of low - frequency electromagnetic fields. Electromagnetic compatibility studies require that the fields from sources of electric power be well known. Unfortunately, many of these sources are not defined to the desired degree of accuracy. This applies e.g. to the case of the twisted-wire pair used in telephone communication; already practiced is twisting of insulated high-voltage three phase power cables and single-phase distribution cables as well. The paper presents a theoretical study of the calculation of magnetic fields in vicinity of conductors having helical structure. For the helical conductor with finite length the method is based on the Biot-Savart law. Since the lay-out of the cables is much more similar to a broken line than to strait line, in the paper the magnetic flux densities produced by helical conductor of complex geometry are also derived. The analytical formulas for calculating the 3D magnetic field can be used by a software tool to model the magnetic fields generated by e.g. twisted wires, helical coils, etc.

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