scholarly journals Magnetic Fields in the Irregular Galaxy LMC

1993 ◽  
Vol 157 ◽  
pp. 317-319
Author(s):  
Richard Wielebinski
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Radio Continuum ◽  
The South ◽  
Irregular Galaxy ◽  
New Radio ◽  
The Magnetic Field

New radio continuum surveys allowed the determination of the magnetic field in the Large Magellanic Cloud. The magnetic field is filamentary, extending to the south of the 30 Doradus nebula. Some possible explanations for this unusual morphology are discussed.

MRE Damping Characteristics Evaluation

2016 ◽  
Vol 699 ◽  
pp. 31-36 ◽  
Author(s):  
Eduard Chirila ◽  
Ionel Chirica ◽  
Doina Boazu ◽  
Elena Felicia Beznea
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Smart Materials ◽  
Magnetorheological Elastomers ◽  
Damping Characteristics ◽  
The Subject ◽  
Energy Absorbing ◽  
The Magnetic Field ◽  
Material Form

The paper addresses the study of the damping characteristics estimation and behaviour of the magnetorheological elastomers (MREs) in the absence of magnetic field. This type of material actively changes the size, internal structure and viscoelastic characteristics under the external influences. These particular composite materials whose characteristics can vary in the presence of a magnetic fields are known as smart materials. The feature which causes the variation of properties in magnetic fields is explained by the existence of polarized particles which change the material form by energy absorbing. Damping is a special characteristic that influences the vibratory of the mechanical system. As an effect of this property is the reducing of the vibration amplitudes by dissipating the energy stored during the vibratory moving. The main characteristic that is based on the determination of the damping coefficient is the energy loss, which is the subject of the present paper. Before to start the characteristics determination in the presence of the magnetic field, it is necessary to study these characteristics in the absence of magnetic field. The MRE specimens have been manufactured and tested under the light conditions (non magnetic field). A special experimental test rig was built to investigate the response of the MRE specimens under the charging force. The experimental results show that the loss energy of the MRE specimen can be determined from the charging-discharging curves versus displacement. The results of the MRE specimen are presented in this paper: MRE with feromagnetic particles not exposed in magnetic field during fabrication.

scholarly journals Linearly Polarised Radio Emission from M83 (NGC 5236) and NGC 891

1990 ◽  
Vol 140 ◽  
pp. 215-218 ◽  
Author(s):  
S. Sukumar ◽  
R.J. Allen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Radio Emission ◽  
Galactic Plane ◽  
Radio Continuum ◽  
The Galaxy ◽  
The Magnetic Field

Recent VLA 20 cm radio continuum observations of the southern face-on barred spiral M83 reveal that the magnetic field is very highly aligned at the outer regions (~12 kpc radius) and totally disrupted in the inner regions (<6 kpc) of the galaxy. The RM variation suggests an axisymmetric morphology for the magnetic field. VLA 6 cm continuum polarization observations of the edge-on spiral NGC 891 reveal ordered magnetic fields at large Z-distances (~3 kpc) from the galactic plane, probably emanating from the disk through instabilities.

scholarly journals Numerical determination of the cutoff frequency in solar models

2020 ◽  
Vol 640 ◽  
pp. A4 ◽  
Author(s):  
T. Felipe ◽  
C. R. Sangeetha
Keyword(s):  
Magnetic Field ◽  
Wave Propagation ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
Acoustic Waves ◽  
Cutoff Frequency ◽  
Quiet Sun ◽  
Radiative Losses ◽  
The Magnetic Field

Context. In stratified atmospheres, acoustic waves can only propagate if their frequency is higher than the cutoff value. The determination of the cutoff frequency is fundamental for several topics in solar physics, such as evaluating the contribution of the acoustic waves to the chromospheric heating or the application of seismic techniques. However, different theories provide different cutoff values. Aims. We developed an alternative method to derive the cutoff frequency in several standard solar models, including various quiet-Sun and umbral atmospheres. The effects of magnetic field and radiative losses on the cutoff are examined. Methods. We performed numerical simulations of wave propagation in the solar atmosphere using the code MANCHA. The cutoff frequency is determined from the inspection of phase-difference spectra computed between the velocity signal at two atmospheric heights. The process is performed by choosing pairs of heights across all the layers between the photosphere and the chromosphere to derive the vertical stratification of the cutoff in the solar models. Result. The cutoff frequency predicted by the theoretical calculations departs significantly from the measurements obtained from the numerical simulations. In quiet-Sun atmospheres, the cutoff shows a strong dependence on the magnetic field for adiabatic wave propagation. When radiative losses are taken into account, the cutoff frequency is greatly reduced and the variation of the cutoff with the strength of the magnetic field is lower. The effect of the radiative losses in the cutoff is necessary to understand recent quiet-Sun and sunspot observations. In the presence of inclined magnetic fields, our numerical calculations confirm that the cutoff frequency is reduced as a result of the reduced gravity experienced by waves that propagate along field lines. An additional reduction is also found in regions with significant changes in the temperature, which is due to the lower temperature gradient along the path of field-guided waves. Conclusions. Our results show solid evidence that the cutoff frequency in the solar atmosphere is stratified. The cutoff values are not correctly captured by theoretical estimates. In addition, most of the widely used analytical cutoff formulae neglect the effect of magnetic fields and radiative losses, whose role is critical for determining the evanescent or propagating nature of the waves.

scholarly journals The NGC 346 massive star census

2020 ◽  
Vol 634 ◽  
pp. A6 ◽  
Author(s):  
P. L. Dufton ◽  
C. J. Evans ◽  
D. J. Lennon ◽  
I. Hunter
Keyword(s):  
Magnetic Field ◽  
Massive Star ◽  
Main Sequence ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Evolutionary Models ◽  
Qualitative Comparison ◽  
Single Star ◽  
Early Type Stars ◽  
The Magnetic Field

Previous analyses of two large spectroscopic surveys of early-type stars in the Large Magellanic Cloud (LMC) have found an excess of nitrogen enriched B-type targets with a ve sin i ≤ 40 km s−1 compared with the predictions of single star evolutionary models that incorporate rotational mixing. By contrast, the number of such targets with 40 <  ve sin i ≤ 80 km s−1 was consistent with such models. We have undertaken a similar analysis for 61 B-type targets which lie towards the young cluster, NGC 346 in the Small Magellanic Cloud (SMC). These again have projected rotational velocities, ve sin i ≤ 80 km s−1, are not classified as supergiants, and are apparently single. Approximately 65% of these SMC targets could have nitrogen enhancements of less than 0.3 dex, which is consistent with them having experienced only small amounts of mixing due to their low rotational velocities. However, as with the previous LMC surveys, an excess of stars with low projected rotational velocities, ve sin i ≤ 40 km s−1, and significant nitrogen enrichments is found. This is estimated to be approximately 5% of the total population of apparently single B-type stars or 40% of all stars with current rotational velocities of less than 40 km s−1; these percentages are similar to those found previously for the two LMC samples. For all three surveys, the presence of undetected binaries and other uncertainties imply that these percentages might be underestimated and that it is indeed possible for all the single stars with current rotational velocities of less than 40 km s−1 to be nitrogen enriched. Two possible explanations incorporate the effects of the magnetic field, via either a stellar merger followed by magnetic braking or the evolution of a single star with a large magnetic field. Both mechanisms would appear to be compatible with the observed frequency of nitrogen-enriched stars in the Magellanic Clouds. Differences in the properties of the nitrogen-enriched stars compared with the remainder of the sample would be consistent with the former mechanism. For the latter, a qualitative comparison with Galactic evolutionary models that incorporate magnetic fields is encouraging in terms of the amount of nitrogen enrichment and its presence in stars near the zero-age main sequence.

scholarly journals Experimental Installation for Determination of Attenuation Coefficient of Permanent Magnetic Field by Protective Materials

2021 ◽  
Vol 12 (1) ◽  
pp. 7-12
Author(s):  
V. M. Fedosyuk
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Electromagnetic Radiation ◽  
Attenuation Coefficient ◽  
Magnetic Circuit ◽  
Permanent Magnetic Field ◽  
Experimental Installation ◽  
Closed Magnetic Circuit ◽  
The Magnetic Field

The permanent magnetic field in addition to electromagnetic radiation has a significant effect on performance of devices. This is particularly true for highly sensitive precision measuring equipment, such as, for example, magnetometers or photomultiplier tubes. In this regard a new high-performance materials for protection against permanent fields and electromagnetic radiation need to be developed. The purpose of this paper is a development of a hardware and software complex for high-precision determination of permanent magnetic field attenuation coefficient and certification of protective materials.This paper describes an experimental installation for determining the attenuation coefficient of a permanent magnetic field using materials and coatings on standard package for electronic equipment. The installation ensures a uniform magnetic field flow in the measurement volume. The advantage of the measuring device is the ability to measure magnetic field in three coordinates due to the use of three pairs of Helmholtz coils and a three-dimensional Hall sensor. The software will enable to control of the magnetic field in all three directions, simulating the real operating conditions of devices that require protection from such influences. In addition, a movable positioning system makes it possible to compensate for the Earth's magnetic field, which increases the accuracy of estimating the attenuation coefficient by protective materials in weak magnetic field.An alternative use of the capabilities of the installation is to test the performance of the devices in a permanent magnetic field and evaluate the electromagnetic compatibility. Experimental results of the work includes determination of the magnetic field attenuation coefficient using standard photomultiplier tube package made of electrolytically deposited permalloy and the sheet of annealed permalloy. Thus, the effect of annealing and closed magnetic circuit on the degree of weakening of the magnetic field is shown. It has been demonstrated that annealing which causes a significant increase in the magnetic permeability promotes an effective attenuation of weak magnetic fields (up to 1 mT). In magnetic fields with an induction of 1 mT or more, effective attenuation is provided by a closed magnetic circuit.

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 Magnetic Fields and Halos in Spiral Galaxies

Galaxies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 54 ◽  
Author(s):  
Marita Krause
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Field Pattern ◽  
Dynamo Action ◽  
Disk Plane ◽  
The Magnetic Field

Radio continuum and polarization observations reveal best the magnetic field structure and strength in nearby spiral galaxies. They show a similar magnetic field pattern, which is of spiral shape along the disk plane and X-shaped in the halo, sometimes accompanied by strong vertical fields above and below the central region of the disk. The strength of the total halo field is comparable to that of the disk. The small- and large-scale dynamo action is discussed to explain the observations with special emphasis on the rôle of star formation on the α − Ω dynamo and the magnetic field strength and structure in the disk and halo. Recently, with RM-synthesis of the CHANG-ES observations, we obtained the first observational evidence for the existence of regular magnetic fields in the halo. The analysis of the radio scale heights indicate escape-dominated radio halos with convective cosmic ray propagation for many galaxies. These galactic winds may be essential for an effective dynamo action and may transport large-scale magnetic field from the disk into the halo.

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