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 Distance scaling method for accurate prediction of slowly varying magnetic fields in satellite missions

2016 ◽  
Vol 5 (2) ◽  
pp. 281-288 ◽  
Author(s):  
Panagiotis P. Zacharias ◽  
Elpida G. Chatzineofytou ◽  
Sotirios T. Spantideas ◽  
Christos N. Capsalis
Keyword(s):  
Signal To Noise Ratio ◽  
Near Field ◽  
Magnetic Behavior ◽  
Field Measurements ◽  
High Signal ◽  
Signal To Noise ◽  
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 equipment under test (EUT) consisting of multiple alternating current (AC) magnetic sources. Therefore, parameters concerning the location of the observation points (magnetometers) are studied 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 signal-to-noise ratio (SNR). Finally, the proposed method is verified by real measurements, using a mobile phone as an EUT.

scholarly journals Decaying turbulence and magnetic fields in galaxy clusters

2019 ◽  
Vol 488 (3) ◽  
pp. 3439-3445 ◽  
Author(s):  
Sharanya Sur
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Galaxy Clusters ◽  
Power Law ◽  
Dynamo Action ◽  
Wide Range ◽  
Major Merger ◽  
Decaying Turbulence ◽  
Field Decay ◽  
The Magnetic Field

Abstract We explore the decay of turbulence and magnetic fields generated by fluctuation dynamo action in the context of galaxy clusters where such a decaying phase can occur in the aftermath of a major merger event. Using idealized numerical simulations that start from a kinetically dominated regime we focus on the decay of the steady state rms velocity and the magnetic field for a wide range of conditions that include varying the compressibility of the flow, the forcing wavenumber, and the magnetic Prandtl number. Irrespective of the compressibility of the flow, both the rms velocity and the rms magnetic field decay as a power law in time. In the subsonic case we find that the exponent of the power law is consistent with the −3/5 scaling reported in previous studies. However, in the transonic regime both the rms velocity and the magnetic field initially undergo rapid decay with an ≈t−1.1 scaling with time. This is followed by a phase of slow decay where the decay of the rms velocity exhibits an ≈−3/5 scaling in time, while the rms magnetic field scales as ≈−5/7. Furthermore, analysis of the Faraday rotation measure (RM) reveals that the Faraday RM also decays as a power law in time ≈t−5/7; steeper than the ∼t−2/5 scaling obtained in previous simulations of magnetic field decay in subsonic turbulence. Apart from galaxy clusters, our work can have potential implications in the study of magnetic fields in elliptical galaxies.

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.

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 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 A MiMeS analysis of the magnetic field and circumstellar environment of the weak-wind O9 sub-giant star HD 57682

2010 ◽  
Vol 6 (S272) ◽  
pp. 188-189
Author(s):  
Jason H. Grunhut ◽  
Gregg A. Wade ◽  
Wagner L. F. Marcolino ◽  
Véronique Petit ◽  
Keyword(s):  
Magnetic Field ◽  
Field Measurements ◽  
Recent Analysis ◽  
Giant Star ◽  
Large Program ◽  
Field Geometry ◽  
Weak Wind ◽  
The Magnetic Field ◽  
Circumstellar Environment

AbstractI will review our recent analysis of the magnetic properties of the O9IV star HD 57682, using spectropolarimetric observations obtained with ESPaDOnS at the Canada-France-Hawaii telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Program. I discuss our most recent determination of the rotational period from longitudinal magnetic field measurements and Hα variability - the latter obtained from over a decade's worth of professional and amateur spectroscopic observations. Lastly, I will report on our investigation of the magnetic field geometry and the effects of the field on the circumstellar environment.

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.

Magnetic Dipole Modeling for DC and Low Frequency AC Magnetic Fields in Space Missions

2018 ◽  
pp. 71-114
Author(s):  
Sotirios Spantideas ◽  
Nikolaos Kapsalis
Keyword(s):  
Magnetic Fields ◽  
Magnetic Dipole ◽  
Near Field ◽  
Low Frequency ◽  
Magnetic Behavior ◽  
Field Measurements ◽  
Space Missions ◽  
Dipole Modeling ◽  
Magnetic Cleanliness

In this chapter, modeling methods of static and slowly varying magnetic field emissions that are generated by spacecraft equipment are analyzed and discussed. In particular, specific issues on the established methods for multiple magnetic dipole modeling (MDM) are investigated and validated via near field measurements of well-behaved magnetic sources. Moreover, a software-based calibration technique for measuring facilities, dedicated to magnetic characterization of spacecraft units, is described and implemented on a configuration consisting of 12 sensors. Due to increasingly strict magnetic cleanliness demands, the modeling of units' induced DC magnetic behavior has become a necessary requirement for various space missions. Therefore, a baseline methodology regarding the measurements and modeling of induced magnetic fields is presented. Finally, DC methods are complemented to cover AC magnetic cleanliness requirements for on-ground verification of low-frequency magnetic fields, including AC induced magnetization effects.

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.

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