Journal articles: 'The origin of magnetic field'

1

Dolginov, A. Z., and A. F. Ioffe. "Origin of the Magnetic Field." International Astronomical Union Colloquium 90 (1986): 11–21. http://dx.doi.org/10.1017/s0252921100091120.

Full text

Abstract:

Some progress has been achieved in recent years in the theory of the stellar magnetic field generation but a lot of questions remain unanswered. I would like to give here a brief critical review of the current state of the problem.

APA, Harvard, Vancouver, ISO, and other styles

2

Gvaramadze, V. V., J. G. Lominadze, A. A. Ruzmaikin, D. D. Sokoloff, and A. M. Shukurov. "Magnetic field origin in astrophysical jets." Advances in Space Research 8, no. 2-3 (January 1988): 621–24. http://dx.doi.org/10.1016/0273-1177(88)90467-x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Neiner, Coralie, Stéphane Mathis, Evelyne Alecian, Constance Emeriau, and Jason Grunhut. "The origin of magnetic fields in hot stars." Proceedings of the International Astronomical Union 10, S305 (December 2014): 61–66. http://dx.doi.org/10.1017/s1743921315004524.

Full text

Abstract:

AbstractObservations of stable mainly dipolar magnetic fields at the surface of ~7% of single hot stars indicate that these fields are of fossil origin, i.e. they descend from the seed field in the molecular clouds from which the stars were formed. The recent results confirm this theory. First, theoretical work and numerical simulations confirm that the properties of the observed fields correspond to those expected from fossil fields. They also showed that rapid rotation does not modify the surface dipolar magnetic configurations, but hinders the stability of fossil fields. This explains the lack of correlation between the magnetic field properties and stellar properties in massive stars. It may also explain the lack of detections of magnetic fields in Be stars, which rotate close to their break-up velocity. In addition, observations by the BinaMIcS collaboration of hot stars in binary systems show that the fraction of those hosting detectable magnetic fields is much smaller than for single hot stars. This could be related to results obtained in simulations of massive star formation, which show that the stronger the magnetic field in the original molecular cloud, the more difficult it is to fragment massive cores to form several stars. Therefore, more and more arguments support the fossil field theory.

APA, Harvard, Vancouver, ISO, and other styles

4

Qi Wei-Hua, Li Zhuang-Zhi, Ma Li, Tang Gui-De, Wu Guang-Heng, and Hu Feng-Xia. "Molecular field origin for magnetic ordering of magnetic materials." Acta Physica Sinica 66, no. 6 (2017): 067501. http://dx.doi.org/10.7498/aps.66.067501.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Wanas, M. I. "Non-Conventional Origin of Large-Scale Magnetic Fields." Symposium - International Astronomical Union 140 (1990): 518. http://dx.doi.org/10.1017/s0074180900191041.

Full text

Abstract:

One of the models constructed (Wanas, 1985) within the framework of the generalized field theory (Mikhail and Wanas, 1977) is found to give results in favour of Blackett's speculation concerning rotation and the origin of magnetic fields. The formula giving the surface polar magnetic field of a spherical body of mass M, radius R, and uniform rotational velocity w is given by (Mikhail and Wanas, 1989) In case of a typical galaxy, the model gives a magnetic field of the order of 10-5 Gauss.

APA, Harvard, Vancouver, ISO, and other styles

6

Wicht, J., M. Mandea, F. Takahashi, U. R. Christensen, M. Matsushima, and B. Langlais. "The Origin of Mercury’s Internal Magnetic Field." Space Science Reviews 132, no. 2-4 (October 2007): 261–90. http://dx.doi.org/10.1007/s11214-007-9280-5.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Kulsrud, R. M. "The origin of our galactic magnetic field." Astronomische Nachrichten 331, no. 1 (January 2010): 22–26. http://dx.doi.org/10.1002/asna.200911295.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Benevolenskaya, E. E. "Origin of the polar magnetic field reversals." Solar Physics 167, no. 1-2 (August 1996): 47–55. http://dx.doi.org/10.1007/bf00146327.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Spruit, Hendrik C. "The source of magnetic fields in (neutron-) stars." Proceedings of the International Astronomical Union 4, S259 (November 2008): 61–74. http://dx.doi.org/10.1017/s1743921309030075.

Full text

Abstract:

AbstractSome arguments, none entirely conclusive, are reviewed about the origin of magnetic fields in neutron stars, with emphasis of processes during and following core collapse in supernovae. Possible origins of the magnetic fields of neutron stars include inheritance from the main sequence progenitor and dynamo action at some stage of evolution of progenitor. Inheritance is not sufficient to explain the fields of magnetars. Energetic considerations point to differential rotation in the final stages of core collapse process as the most likely source of field generation, at least for magnetars. A runaway phase of exponential growth is needed to achieve sufficient field amplification during relevant phase of core collapse; it can probably be provided by a some form of magnetorotational instability. Once formed in core collapse, the field is in danger of decaying again by magnetic instabilities. The evolution of a magnetic field in a newly formed neutron star is discussed, with emphasis on the existence of stable equilibrium configurations as end products of this evolution, and the role of magnetic helicity in their existence. A particularly puzzling problem is the large range of field strengths observed in neutron stars (as well as in A stars and white dwarfs). It implies that a single, deterministic process is insufficient to explain the origin of the magnetic fields in these stars.

APA, Harvard, Vancouver, ISO, and other styles

10

Kawka, Adela. "Clues to the origin and properties of magnetic white dwarfs." Proceedings of the International Astronomical Union 15, S357 (October 2019): 60–74. http://dx.doi.org/10.1017/s1743921320000745.

Full text

Abstract:

AbstractA significant fraction of white dwarfs possess a magnetic field with strengths ranging from a few kG up to about 1000 MG. However, the incidence of magnetism varies when the white dwarf population is broken down into different spectral types providing clues on the formation of magnetic fields in white dwarfs. Several scenarios for the origin of magnetic fields have been proposed from a fossil field origin to dynamo generation at various stages of evolution. Offset dipoles are often assumed sufficient to model the field structure, however time-resolved spectropolarimetric observations have revealed more complex structures such as magnetic spots or multipoles. Surface mapping of these field structures combined with measured rotation rates help distinguish scenarios involving single star evolution from other scenarios involving binary interactions. I describe key observational properties of magnetic white dwarfs such as age, mass, and field strength, and confront proposed formation scenarios with these properties.

APA, Harvard, Vancouver, ISO, and other styles

11

Schuck, Peter W., Mark G. Linton, Kalman J. Knizhnik, and James E. Leake. "On the Origin of the Photospheric Magnetic Field." Astrophysical Journal 936, no. 1 (September 1, 2022): 94. http://dx.doi.org/10.3847/1538-4357/ac739a.

Full text

Abstract:

Abstract This article presents results that challenge the paradigms that (1) the convection zone is the source of the radial magnetic field in the photosphere and (2) that coronal currents are neutralized from the perspective of the photosphere. We demonstrate, using a new analysis tool applied to simulations and observations, that bare or partially dressed current channels are supported by the solar corona and that fingerprints of these coronal current systems can be detected in the photosphere. These coronal current channels can be a significant source of the radial component of the magnetic field in the photosphere. The roots of these coronal current channels in the photosphere are the source of the magnetic field component parallel to the polarity inversion line in active region NOAA 12673. These analyses and observations transform our theoretical understanding of coronal evolution and argue for a reexamination of the present paradigm in which the convection zone is the sole source of the photospheric magnetic field.

APA, Harvard, Vancouver, ISO, and other styles

12

Parker, E. N. "The Magnetic Field of the Sun: An Object Lesson." Symposium - International Astronomical Union 140 (1990): 1–12. http://dx.doi.org/10.1017/s0074180900189375.

Full text

Abstract:

The magnetic field of the sun is created by a magnetohydrodynamic dynamo under conditions bearing some qualitative similarities to the apparent generation of the galactic field in the gaseous disk of the galaxy. There is a similarity, too, in the extension of bipolar lobes of the solar field above the surface of the sun and the extension of bipolar lobes of the galactic field outward from both sides of the disk. Hence one can learn a lot about the expected origin and activity of the galactic field by studying the behavior of the magnetic field of the sun. In particular, the mysteries associated with the “simple” circumstances of the origin of the solar magnetic field far below the surface are no less than the mysteries in the theoretical origin of the galactic field, where there is so little direct observation of the small scale motions and magnetic fields. There is reason to think that the activity of the magnetic field of the sun, producing prominences, flares and X-ray corona, a solar wind, and coronal mass ejection may all have counter parts in the activity of the galactic field above the surface of the gaseous disk.

APA, Harvard, Vancouver, ISO, and other styles

13

Abe, Haruo. "The Origin of SO2 Afterglows as Revealed by Magnetic Field Effects." Laser Chemistry 13, no. 3-4 (January 1, 1994): 223–39. http://dx.doi.org/10.1155/1994/46176.

Full text

Abstract:

The chemiluminescence intensity in the low pressure diffusion flame of the CS2 + O/N2 system was found to be considerably affected by external magnetic fields. The emitter in the flame was identified as the main emitter in the SO2 afterglow. The measurements of the field strength dependence, collisional effect, and spectral distribution of the magnetic field effect revealed the major emitter as the SO2 in the C˜ state. External magnetic fields were also found to quench fluorescence remarkably emitted from the vibronic levels just below the predissociation threshold in the C˜ state. From the observed vibrational-level, field-strength, and pressure dependences of the magnetic quenching, it became evident that the major emitter of chemiluminescence in the flame could be assigned to the SO2 molecule in the vibronic levels located at about 800 cm–1 below the predissociation threshold in the C˜ state

APA, Harvard, Vancouver, ISO, and other styles

14

POLLOCK, M. D. "ON THE ORIGIN OF THE COSMIC MAGNETIC FIELD." International Journal of Modern Physics D 03, no. 02 (June 1994): 499–511. http://dx.doi.org/10.1142/s0218271894000666.

Full text

Abstract:

It is shown how a cosmic magnetic field Bc can arise in the dimensionally reduced, heterotic superstring theory, via the logarithmic variation with temperature of the string gauge coupling parameter, assuming the ansatz where the asantaz ḡ≡0(α1α2α3)1/6, where the αi are the fine-structure constants of the electroweak and strong interactions. If [Formula: see text], where H0=100h km s −1 Mpc −1 is the Hubble parameter and s≫1 is a constant, then [Formula: see text]. Thus, for example, if s=3×103, then B c ≈3×10−6 G .

APA, Harvard, Vancouver, ISO, and other styles

15

Zhang, Qiushu, Bei Peng, Jintao Xu, and Mengqi Chu. "Origin of Magnetically Induced Optical Transmission of Magnetic Nanocomposite Films." Polymers 12, no. 11 (October 29, 2020): 2533. http://dx.doi.org/10.3390/polym12112533.

Full text

Abstract:

Herein, we present an investigation on the origin of the magnetically induced optical transmission of composite films comprised of polydimethylsiloxane and magnetic nanofillers via experiment and simulation. Structured and unstructured films were used in the study, which were fabricated with and without magnetic fields, respectively. Altered optical transmittance was observed from both types of films when they were subjected to an external magnetic field. Numerical analyses were performed to investigate the effect of the particle movement under magnetic field and the film magnetostriction on the film optical transmittance. The simulation results show that the changed light transmission under magnetic field is mainly due to a variation in the film thickness resulting from the film magnetostriction. The ellipsometric analysis results confirm the altered film thickness in response to the external magnetic field, and the measurements of the film magnetostrictive stresses validate that there is magnetostriction in the magnetic composite films. Additionally, it is indicated that there might be some relationship between the magnetically induced optical transmission and the film magnetostrictive stress under certain conditions.

APA, Harvard, Vancouver, ISO, and other styles

16

Istomin, Ya N. "Origin of Giant Radio Pulses." Symposium - International Astronomical Union 218 (2004): 369–72. http://dx.doi.org/10.1017/s0074180900181392.

Full text

Abstract:

A model for the origin of giant radio pulses is suggested. Radio emission is generated by the electric discharge taking place due to the magnetic reconnection of field lines connecting the opposite magnetic poles. The reconnection occurs in the region of the light cylinder near the zero line of the magnetic field. The coherent mechanism of radiation is pure maser amplification of Alfvén waves. The radiated frequencies are found.

APA, Harvard, Vancouver, ISO, and other styles

17

Zweibel, Ellen G. "Magnetic Fields in Galaxies." Proceedings of the International Astronomical Union 6, S271 (June 2010): 135–44. http://dx.doi.org/10.1017/s1743921311017546.

Full text

Abstract:

AbstractThe origin and evolution of magnetic fields in the Universe is a cosmological problem. Although exotic mechanisms for magneotgenesis cannot be ruled out, galactic magnetic fields could have been seeded by magnetic fields from stars and accretion disks, and must be continuously regenerated due to the ongoing replacement of the interstellar medium. Unlike stellar dynamos, galactic dynamos operate in a multicomponent gas at low collisionality and high magnetic Prandtl number. Their background turbulence is highly compressible, the plasma β ~ 1, and there has been time for only a few large exponentiation times at large scale over cosmic time. Points of similarity include the importance of magnetic buoyancy, the large range of turbulent scales and tiny microscopic scales, and the coupling between the magnetic field and certain properties of the flow. Understanding the origin and maintenance of the large scale galactic magnetic field is the most challenging aspect of the problem.

APA, Harvard, Vancouver, ISO, and other styles

18

Ruzmaikin, A. A. "Dynamo in Astrophysics." Symposium - International Astronomical Union 140 (1990): 83–89. http://dx.doi.org/10.1017/s0074180900189636.

Full text

Abstract:

The fast dynamo acting in a turbulent flow explains the origin of magnetic fields in astrophysical objects. Stellar cycles and large-scale magnetic fields in spiral galaxies reflect the behaviour of a mean magnetic field. Intermittent magnetic structures in clusters of galaxies are associated with random magnetic field.

APA, Harvard, Vancouver, ISO, and other styles

19

Bera, Prasanta, Anvar Shukurov, and Kandaswamy Subramanian. "The Origin of Large-Scale Magnetic Fields in Low-Mass Galaxies." Galaxies 7, no. 4 (November 29, 2019): 91. http://dx.doi.org/10.3390/galaxies7040091.

Full text

Abstract:

The origin of large-scale magnetic fields, detected in some low-mass (dwarf and irregular) galaxies via polarised synchrotron emission and Faraday rotation, has remained unexplained for a long time. We suggest that mean-field dynamos can be active in galaxies of this class despite their slow rotation because their discs are relatively thick. Earlier assessments of the possibility of the mean-field dynamo action in low-mass galaxies relied on estimates applicable to thin discs, such as those in massive spiral galaxies. Using both order-of-magnitude estimates and numerical solutions, we show that the strength of differential rotation required to amplify magnetic field reduces as the aspect ratio of the galactic gas layer increases. As in a thin disc, quadrupolar magnetic fields dominate in thick discs. Thus, the origin of large-scale magnetic fields in low-mass galaxies has been clarified. This class of galaxies provides a new ground for testing our understanding of galactic magnetism.

APA, Harvard, Vancouver, ISO, and other styles

20

West, J. L., R. N. Henriksen, K. Ferrière, A. Woodfinden, T. Jaffe, B. M. Gaensler, and J. A. Irwin. "Helicity in the large-scale Galactic magnetic field." Monthly Notices of the Royal Astronomical Society 499, no. 3 (October 8, 2020): 3673–89. http://dx.doi.org/10.1093/mnras/staa3068.

Full text

Abstract:

ABSTRACT We search for observational signatures of magnetic helicity in data from all-sky radio polarization surveys of the Milky Way Galaxy. Such a detection would help confirm the dynamo origin of the field and may provide new observational constraints for its shape. We compare our observational results to simulated observations for both a simple helical field, and for a more complex field that comes from a solution to the dynamo equation. Our simulated observations show that the large-scale helicity of a magnetic field is reflected in the large-scale structure of the fractional polarization derived from the observed synchrotron radiation and Faraday depth of the diffuse Galactic synchrotron emission. Comparing the models with the observations provides evidence for the presence of a quadrupolar magnetic field with a vertical component that is pointing away from the observer in both hemispheres of the Milky Way Galaxy. Since there is no reason to believe that the Galactic magnetic field is unusual when compared to other galaxies, this result provides further support for the dynamo origin of large-scale magnetic fields in galaxies.

APA, Harvard, Vancouver, ISO, and other styles

21

Yuan, Lu, Baomin Wang, Dezhi Zha, Chenxu Liu, Mengchao Li, Yali Xie, Huali Yang, Yanwei Cao, Hui Xu, and Run-Wei Li. "Origin of magnetic field-induced magnetic anisotropy in amorphous CoFeB thin films." AIP Advances 12, no. 4 (April 1, 2022): 045203. http://dx.doi.org/10.1063/5.0086805.

Full text

Abstract:

Magnetic anisotropy (MA) is an important property of magnetic materials, which not only determines the orientation of the magnetic moment in the magnetic material but also influences the working frequency of magnetoelectric devices. Unrevealing the origin of MA has become an important topic and attracts lasting interest. Here, we report a quite significant magnetic field-induced uniaxial MA in amorphous CoFeB thin films containing double ferromagnetic atoms. The thickness independence of MA was obtained by observing a series of hysteresis loops and magnetic domains. The MA is proved subtly to be related to the variation of orbital magnetic moment acquired by ferromagnetic resonance. Furthermore, we found that atoms combine into clusters and incline to an order in amorphous CoFeB thin films with field-induced MA. Based on these experimental results, we proposed a direction-like order model to interpret the origin of magnetic field-induced MA in amorphous CoFeB thin films well.

APA, Harvard, Vancouver, ISO, and other styles

22

Wiechen, H., G. T. Birk, and H. Lesch. "The origin of primeval magnetic fields: Self-consistent simulation of magnetic field generation and amplification." Physics of Plasmas 7, no. 2 (February 2000): 701–5. http://dx.doi.org/10.1063/1.873855.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Wurster, James, Matthew R. Bate, Daniel J. Price, and Ian A. Bonnell. "On the origin of magnetic fields in stars – II. The effect of numerical resolution." Monthly Notices of the Royal Astronomical Society 511, no. 1 (January 18, 2022): 746–64. http://dx.doi.org/10.1093/mnras/stac123.

Full text

Abstract:

ABSTRACT Are the kG-strength magnetic fields observed in young stars a fossil field left over from their formation or are they generated by a dynamo? Our previous numerical study concluded that magnetic fields must originate by a dynamo process. Here, we continue that investigation by performing even higher numerical resolution calculations of the gravitational collapse of a 1 M⊙ rotating, magnetized molecular cloud core through the first and second collapse phases until stellar densities are reached. Each model includes Ohmic resistivity, ambipolar diffusion, and the Hall effect. We test six numerical resolutions, using between 105 and 3 × 107 particles to model the cloud. At all but the lowest resolutions, magnetic walls form in the outer parts of the first hydrostatic core, with the maximum magnetic field strength located within the wall rather than at the centre of the core. At high resolution, this magnetic wall is disrupted by the Hall effect, producing a magnetic field with a spiral-shaped distribution of intensity. As the second collapse occurs, this field is dragged inward and grows in strength, with the maximum field strength increasing with resolution. As the second core forms, the maximum field strength exceeds 1 kG in our highest resolution simulations, and the stellar core field strength exceeds this threshold at the highest resolution. Our resolution study suggests that kG-strength magnetic fields may be implanted in low-mass stars during their formation, and may persist over long time-scales given that the diffusion time-scale for the magnetic field exceeds the age of the Universe.

APA, Harvard, Vancouver, ISO, and other styles

24

Genestreti, Kevin J., Xiaocan Li, Yi-Hsin Liu, James L. Burch, Roy B. Torbert, Stephen A. Fuselier, Takuma Nakamura, et al. "On the origin of “patchy” energy conversion in electron diffusion regions." Physics of Plasmas 29, no. 8 (August 2022): 082107. http://dx.doi.org/10.1063/5.0090275.

Full text

Abstract:

During magnetic reconnection, field lines interconnect in electron diffusion regions (EDRs). In some EDRs, the reconnection and energy conversion rates are controlled by a steady out-of-plane electric field. In other EDRs, the energy conversion rate [Formula: see text] is “patchy,” with electron-scale large-amplitude positive and negative peaks. We investigate 22 EDRs observed by NASA's Magnetospheric Multiscale mission in a wide range of conditions to determine the cause of patchy [Formula: see text]. The patchiness of the energy conversion is quantified and correlated with seven parameters describing various aspects of the asymptotic inflow regions that affect the structure, stability, and efficiency of reconnection. We find that (1) neither the guide field strength nor the asymmetries in the inflow ion pressure, electron pressure, nor number density are well correlated with the patchiness of the EDR energy conversion; (2) the out-of-plane axes of the 22 EDRs are typically fairly well aligned with the “preferred” axes, which bisect the time-averaged inflow magnetic fields and maximize the reconnection rate; and (3) the time-variability in the upstream magnetic field direction is best correlated with the patchiness of the EDR [Formula: see text]. A 3D fully kinetic simulation of reconnection with a non-uniform inflow magnetic field is analyzed; the variation in the magnetic field generates secondary X-lines, which develop to maximize the reconnection rate for the time-varying inflow magnetic field. The results suggest that magnetopause reconnection, for which the inflow magnetic field direction is often highly variable, may commonly be patchy in space, at least at the electron scale.

APA, Harvard, Vancouver, ISO, and other styles

25

Sofue, Yoshiaki. "Vertical Magnetic Fields in Spiral Galaxies." Symposium - International Astronomical Union 140 (1990): 227–32. http://dx.doi.org/10.1017/s0074180900190060.

Full text

Abstract:

Evolution of a vertical magnetic field which may have existed in the primeval galaxy is discussed based on a primordial-origin hypothesis for the bisymmetric spiral configuration of magnetic fields in spiral galaxies. The vertical field is accumulated toward the nucleus and forms a strong poloidal field, which may trigger activities like jets. Quasar jets are suggested to be the result of such strong vertical fields in the cores of primeval galaxies.

APA, Harvard, Vancouver, ISO, and other styles

26

Xu, J., and J. L. Han. "Evidence for Strong Intracluster Magnetic Fields in the Early Universe." Astrophysical Journal 926, no. 1 (February 1, 2022): 65. http://dx.doi.org/10.3847/1538-4357/ac4095.

Full text

Abstract:

Abstract The origin of magnetic fields in clusters of galaxies is still a matter of debate. Observations for intracluster magnetic fields over a wide range of redshifts are crucial to constrain possible scenarios for the origin and evolution of the fields. Differences in Faraday rotation measures (RMs) of an embedded double radio source, i.e., a pair of lobes of mostly Fanaroff–Riley type II radio galaxies, are free from the Faraday rotation contributions from the interstellar medium inside the Milky Way and the intergalactic medium between radio galaxies and us, and hence provide a novel way to estimate average magnetic field within galaxy clusters. We have obtained a sample of 627 pairs whose RMs and redshifts are available in the most updated RM catalogs and redshift databases. The RM differences of the pairs are derived. The statistically large RM differences for pairs of redshifts z > 0.9 indicate that intracluster magnetic fields are as strong as about 4 μG. Such strong magnetic fields in the intracluster medium at the half age of the universe, comparable to the intracluster field strength in nearby galaxy clusters, pose a challenge to the theories of the origin of cosmic magnetic fields.

APA, Harvard, Vancouver, ISO, and other styles

27

Hubrig, Swetlana, Markus Schöller, and Silva P. Järvinen. "Magnetic massive stars in star forming regions." Proceedings of the International Astronomical Union 14, A30 (August 2018): 132. http://dx.doi.org/10.1017/s174392131900382x.

Full text

Abstract:

AbstractOne idea for the origin of magnetic fields in massive stars suggests that the magnetic field is the fossil remnant of the Galactic ISM magnetic field, amplified during the collapse of the magnetised gas cloud. A search for the presence of magnetic fields in massive stars located in active sites of star formation led to the detection of rather strong magnetic fields in a few young stars. Future spectropolarimetric observations are urgently needed to obtain insights into the mechanisms that drive the generation of kG magnetic fields during high-mass star formation.

APA, Harvard, Vancouver, ISO, and other styles

28

Tout, C. A., D. T. Wickramasinghe, J. Liebert, L. Ferrario, and J. E. Pringle. "Binary star origin of high field magnetic white dwarfs." Monthly Notices of the Royal Astronomical Society 387, no. 2 (June 2008): 897–901. http://dx.doi.org/10.1111/j.1365-2966.2008.13291.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Dionne, Gerald F. "Origin of exchange field reductions in diluted magnetic garnets." Journal of Applied Physics 85, no. 8 (April 15, 1999): 4627–29. http://dx.doi.org/10.1063/1.370429.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Salsbury, Freddie R., and Robert A. Harris. "The origin of the magnetic-field-dependent quadrupolar splitting." Journal of Chemical Physics 109, no. 19 (November 15, 1998): 8338–41. http://dx.doi.org/10.1063/1.477627.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Braithwaite, Jonathan. "The nature and origin of magnetic fields in early-type stars." Proceedings of the International Astronomical Union 9, S302 (August 2013): 255–64. http://dx.doi.org/10.1017/s1743921314002221.

Full text

Abstract:

AbstractI review our current knowledge of magnetic fields in stars more massive than around 1.5 M⊙, in particular their nature and origin. This includes the strong magnetic fields found in a subset of the population and the fossil field theory invoked to explain them; the subgauss fields detected in Vega and Sirius and their possible origin; and what we can infer about magnetic activity in massive stars and how it might be linked to subsurface convection.

APA, Harvard, Vancouver, ISO, and other styles

32

Vlemmings, Wouter. "Magnetic fields of AGB and post-AGB stars." Proceedings of the International Astronomical Union 14, S343 (August 2018): 19–26. http://dx.doi.org/10.1017/s1743921318005367.

Full text

Abstract:

AbstractThere is ample evidence for the presence of strong magnetic fields in the envelopes of (post-)Asymptotic Giant Branch (AGB) stars as well as supergiant stars. The origin and role of these fields are still unclear. This paper updates the current status of magnetic field observations around AGB and post-AGB stars, and describes their possible role during these stages of evolution. The discovery of magnetically aligned dust around a supergiant star is also highlighted. In our search for the origin of the magnetic fields, recent observations show the signatures of possible magnetic activity and rotation, indicating that the magnetic fields might be intrinsic to the AGB stars.

APA, Harvard, Vancouver, ISO, and other styles

33

Zhu, Jun Feng, Xin Yan, Ling Ling Zhou, and Xiao Xin Zhao. "Measurement of Helmholtz Coil." Applied Mechanics and Materials 738-739 (March 2015): 893–98. http://dx.doi.org/10.4028/www.scientific.net/amm.738-739.893.

Full text

Abstract:

Based on the basic principles of electromagnetism, the application of Shanghai Fudan-day Welcomes UNESCO Instruments Ltd. THQHC-1 type Helmholtz coil magnetic field measuring instrument for measuring coil uniform magnetic field generates a magnetic field on the carrier to get round the coil axis, online circle center at (coordinate origin) at the maximum magnetic field strength. Starting from the coordinate origin, to the sides, the magnetic field lines accelerate the decline, when the distance exceeds the coil radius, the decelerating decline. Conclusions for the understanding of a uniform magnetic field reference.

APA, Harvard, Vancouver, ISO, and other styles

34

TAMURA, HIDEO. "NORM RESOLVENT CONVERGENCE TO MAGNETIC SCHRÖDINGER OPERATORS WITH POINT INTERACTIONS." Reviews in Mathematical Physics 13, no. 04 (April 2001): 465–511. http://dx.doi.org/10.1142/s0129055x01000697.

Full text

Abstract:

The Schrödinger operator with δ-like magnetic field at the origin in two dimensions is not essentially self-adjoint. It has the deficiency indices (2, 2) and each self-adjoint extension is realized as a differential operator with some boundary conditions at the origin. We here consider Schrödinger operators with magnetic fields of small support and study the norm resolvent convergence to Schrödinger operator with δ-like magnetic field. We are concerned with the boundary conditions realized in the limit when the support shrinks. The results obtained heavily depend on the total flux of magnetic field and on the resonance space at zero energy, and the proof is based on the analysis at low energy for resolvents of Schrödinger operators with magnetic potentials slowly falling off at infinity.

APA, Harvard, Vancouver, ISO, and other styles

35

Subramanian, Kandaswamy. "Origins of Cosmic magnetism." Proceedings of the International Astronomical Union 14, A30 (August 2018): 291–94. http://dx.doi.org/10.1017/s1743921319004435.

Full text

Abstract:

AbstractThe standard picture for the origin of magnetic fields in astrophysical systems involves turbulent dynamo amplification of a weak seed field. Dynamos convert kinetic energy of motions to magnetic energy. While it is relatively easy for magnetic energy to grow, explaining the observed degree of coherence of cosmic magnetic fields generated by turbulent dynamos, remains challenging. We outline potential resolution of these challenges. Another intriguing possibility is that magnetic fields originated at some level from the early universe.

APA, Harvard, Vancouver, ISO, and other styles

36

Lèbre, Agnès, Michel Aurière, Nicolas Fabas, Denis Gillet, Fabrice Herpin, Pascal Petit, and Renada Konstantinova-Antova. "Search for surface magnetic fields in Mira stars: first results on χ Cyg." Proceedings of the International Astronomical Union 9, S302 (August 2013): 385–88. http://dx.doi.org/10.1017/s1743921314002579.

Full text

Abstract:

AbstractSo far, surface magnetic fields have never been reported on Mira stars, while observational facilities allowing detection and measurement of weak surface fields through the Zeeman effect have become available. Then, in order to complete the knowledge of the magnetic field and of its influence during the transition from Asymptotic Giant Branch (AGB) to Planetary Nebulae (PN) stages, we have undertaken a search for magnetic fields at the surface of Miras. We present the first spectropolarimetric observations (performed with the Narval instrument at Télescope Bernard Lyot-TBL, Pic du Midi, France) of the S-type Mira star χ Cyg. We have detected a polarimetric signal in the Stokes V spectra and we have established its Zeeman origin. We claim that it is likely to be related to a weak magnetic field present at the photospheric level and in the lower part of the stellar atmosphere. The origin of this magnetic field is discussed in the framework of shock waves periodically propagating throughout the atmosphere of a Mira.

APA, Harvard, Vancouver, ISO, and other styles

37

Blackman, Eric G., and George B. Field. "Mean Field Dynamo Saturation: Toward Understanding Conflicting Results." Highlights of Astronomy 12 (2002): 736–38. http://dx.doi.org/10.1017/s1539299600014830.

Full text

Abstract:

AbstractMean field dynamos may explain the origin of large scale magnetic fields of galaxies, but controversy arises over the extent of dynamo quenching by the growing field. Here we explain how apparently conflicting results may be mutually consistent, by showing the role of magnetic helicity conservation and boundary terms usually neglected. We estimate the associated magnetic energy flowing out of the Galaxy but emphasize that the mechanism of field escape needs to be addressed.

APA, Harvard, Vancouver, ISO, and other styles

38

Baag, Czango, and Deok Kyo Lee. "Absence of magnetic anomalies due to seepage‐induced “magnetoelectric effects” and implications for sulfide self‐potentials." GEOPHYSICS 54, no. 9 (September 1989): 1174–79. http://dx.doi.org/10.1190/1.1442752.

Full text

Abstract:

The magnetic field due to an azimuthally symmetric distribution of subsurface electric current, which may be associated with vertical hydrocarbon seepage, vanishes above the ground surface. However, geologic conditions in general do not provide perfect isotropic conditions, and, in theory, some magnetic fields can be generated by the magnetoelectric effect. Sedimentary rock sections are relatively isotropic, particularly in the stratigraphic plane. Thus, hydrocarbon seepage‐induced magnetic fields above the ground surface may never be significant, even if strong electric currents are associated with the seepage. All current‐generated magnetic fields, of whatever origin, must obey Ampère’s law; no line integral operation can distinguish a magnetic field having one origin from that of any other origin. Therefore, seepage‐induced magnetic anomalies, if they exist at all, are probably useless for hydrocarbon exploration because it is virtually impossible to distinguish them from other anomalies of unknown origin. Thus, even if hydrocarbon seepage is capable of producing oxidized and reduced zones, the significance of any generated electric currents is very doubtful. Since the seepage‐induced electrochemical model lacks a conducting mass in the columnar reducing zone and/or an electric barrier around the reducing zone, electric potential due to excess electric charges developed between the two zones would tend to dissipate.

APA, Harvard, Vancouver, ISO, and other styles

39

Crandpierro, Attila. "On the Inadequacies of the Magnetic Flare Theories and the Resolution of these Problems with the Convective Flare Theory." International Astronomical Union Colloquium 104, no. 2 (1989): 365–68. http://dx.doi.org/10.1017/s0252921100154557.

Full text

Abstract:

I give here a short review of some of the main problems of the magnetic theories for the flare origin. I point out that the magnetic theories are unable to solve the problems of the energetics, height and compactness of the acceleration region, compresslve inflows, magnetic field structures, particle numbers, preflare upflows and the global cause of the flare origin. Then I outline the convective flare theory which have proposals for the solutions of these problems. I show here what is the role of the magnetic field at flare origins in the frame of the convective flare theory. The convective flare theory gives a deeper level understanding than the magnetic theories and therefore it also can supply us with the derivation of some input parameters and assumptions used for the magnetic theories and so it offers a wider perspective to understand the physics of the explosive astrophysical processes.

APA, Harvard, Vancouver, ISO, and other styles

40

Irrgang, Christopher, Jan Saynisch-Wagner, and Maik Thomas. "Depth of origin of ocean-circulation-induced magnetic signals." Annales Geophysicae 36, no. 1 (January 29, 2018): 167–80. http://dx.doi.org/10.5194/angeo-36-167-2018.

Full text

Abstract:

Abstract. As the world ocean moves through the ambient geomagnetic core field, electric currents are generated in the entire ocean basin. These oceanic electric currents induce weak magnetic signals that are principally observable outside of the ocean and allow inferences about large-scale oceanic transports of water, heat, and salinity. The ocean-induced magnetic field is an integral quantity and, to first order, it is proportional to depth-integrated and conductivity-weighted ocean currents. However, the specific contribution of oceanic transports at different depths to the motional induction process remains unclear and is examined in this study. We show that large-scale motional induction due to the general ocean circulation is dominantly generated by ocean currents in the upper 2000 m of the ocean basin. In particular, our findings allow relating regional patterns of the oceanic magnetic field to corresponding oceanic transports at different depths. Ocean currents below 3000 m, in contrast, only contribute a small fraction to the ocean-induced magnetic signal strength with values up to 0.2 nT at sea surface and less than 0.1 nT at the Swarm satellite altitude. Thereby, potential satellite observations of ocean-circulation-induced magnetic signals are found to be likely insensitive to deep ocean currents. Furthermore, it is shown that annual temporal variations of the ocean-induced magnetic field in the region of the Antarctic Circumpolar Current contain information about sub-surface ocean currents below 1000 m with intra-annual periods. Specifically, ocean currents with sub-monthly periods dominate the annual temporal variability of the ocean-induced magnetic field. Keywords. Electromagnetics (numerical methods) – geomagnetism and paleomagnetism (geomagnetic induction) – history of geophysics (transport)

APA, Harvard, Vancouver, ISO, and other styles

41

Tajima, T., and K. Shibata. "On the Origin of Cosmic Magnetic Fields." Symposium - International Astronomical Union 140 (1990): 531–32. http://dx.doi.org/10.1017/s0074180900191077.

Full text

Abstract:

In the past investigations of cosmological magnetic fields, Harrison (1970) assumed primordial turbulence with nonzero vorticity. More recently this idea lost favor with most cosmologists, primarily because vortices decay during the cosmic expansion (Rees, 1987). In contrast to these works we resort to no assumption as for the primordial condition but for the thermal equilibrium in the following. A plasma with temperature T in the early universe sustains fluctuations of electromagnetic fields and density even if it is in a thermal equilibrium. The level of fluctuations in the plasma for a given wavelength of electromagnetic fields, for example, can be rigorously computed by the fluctuation-dissipation theorem (Geary et al. 1986; Kubo 1957; Sitenko 1967). In particular, without assuming any turbulence we show that very low (or ~ zero) frequency magnetic fluctuations can also be excited and the level of these is computedr where summation on k is over all the available wavenumbers V the volume of the Universe, and ωp the plasma frequency (4πe2n/m)1/2. The level of fluctuation is given approximately by the equipartition value of T/2 for kωωp/c and much less than that for k>ωp/c. These fields at the early radiation epoch t=10°sec (we call the radiation epoch in which the radiation effects dominate that of gravity in the universe as the plasma epoch: tε10−2 − 1013 sec) can act as seed fields and can evolve during the plasma epoch. The result is shown in Fig. 1. We show that magnetic fields with the size of λ≤108cm can be amplified by the dynamo effect and that the field strength corresponding to this size is greater than 10–19 Gauss.

APA, Harvard, Vancouver, ISO, and other styles

42

Ponomarev, Andrey A., Marsel A. Kadyrov, Yuri V. Vaganov, Valeria A. Cheymetova, Vadim M. Aleksandrov, and Aleksandr V. Morev. "Controversial Issues of Hydrocarbon Field Formation and the Role of Geomagnetic Fields." International Journal of Geophysics 2022 (December 27, 2022): 1–12. http://dx.doi.org/10.1155/2022/2834990.

Full text

Abstract:

This review paper presents controversial issues on the formation of hydrocarbon deposits. We look into the geological contradictions of the abiogenic and biogenic theories of petroleum origin, indicating the connection between hydrocarbon deposits and disjunctive dislocations, as well as present disputes about the geological period over which hydrocarbon deposits have been formed. We further overviewed the radical chain mechanism of hydrocarbon generation from organic matter as proposed by Prof. Nesterov. It is noted that the petroleum generation process in reservoir conditions occurs almost instantly in the presence of discrete geomagnetic fields and does not require a long geological time. This is explained by spin magnetic effects (spin catalysis, magnetic isotope properties). We briefly highlight the effect of magnetic fields on chemical reactions involving organic compounds and the use of magnetic fields to enhance oil recovery. We also present the leading causes of discrete magnetic fields in the sedimentary cover: Earth’s geomagnetic reversals, generation of ferromagnetic minerals in oil deposits, electromechanical effects of rock friction near faults, and intermixing of reservoir waters with different mineralization (spontaneous ion polarization). Based on the material reported, we conclude that the radical chain mechanism of petroleum generation processes explains some contradictions of the abiogenic and biogenic theories of petroleum origin. Elaborating this research area has excellent prospects for developing new criteria for hydrocarbon prospecting and devising innovative methods to enhance the oil recovery for shale oil production.

APA, Harvard, Vancouver, ISO, and other styles

43

Xu, Yan, Jun Xu, Wei Hua Zhu, Xia Feng, and Hai Yan Xie. "3-D Modeling the Magnetic Field due to Ocean Tidal Flow O1." Advanced Materials Research 658 (January 2013): 471–74. http://dx.doi.org/10.4028/www.scientific.net/amr.658.471.

Full text

Abstract:

The tidal motion of the ocean water through the ambient magnetic field, generates secondary electric and magnetic field. The magnetic fields generated by the diurnal (O1) ocean flow can be clearly detected. We simulate the magnetic signals for tidal constituents –diurnal (O1) tides. The idea of exploiting tidal signals for EM studies of the Earth is not new, but so far it was used only for interpretation of inland and transoceanic magnetic field data due to O1. Emphasis in this work is made on a discussion of sea bottom electric field of the same origin.

APA, Harvard, Vancouver, ISO, and other styles

44

Farrell, Eoin, Adam S. Jermyn, Matteo Cantiello, and Daniel Foreman-Mackey. "The Initial Magnetic Field Distribution in AB Stars." Astrophysical Journal 938, no. 1 (October 1, 2022): 10. http://dx.doi.org/10.3847/1538-4357/ac8423.

Full text

Abstract:

Abstract Stars are born with magnetic fields, but the distribution of their initial field strengths remains uncertain. We combine observations with theoretical models of magnetic field evolution to infer the initial distribution of magnetic fields for AB stars in the mass range of 1.6–3.4 M ⊙. We tested a variety of distributions with different shapes and found that a distribution with a mean of ∼800 G and a full width of ∼600 G is most consistent with the observed fraction of strongly magnetized stars as a function of mass. Our most-favored distribution is a Gaussian with a mean of μ = 770 G and standard deviation of σ = 146 G. Independent approaches to measure the typical field strength suggest values closer to 2–3 kG, a discrepancy that could suggest a mass-dependent and bimodal initial field distribution, or an alternative theoretical picture for the origin of these magnetic fields.

APA, Harvard, Vancouver, ISO, and other styles

45

Fioranelli, Massimo, Maria Grazia Roccia, Aroonkumar Beesham, Dana Flavin, and Somayyeh Shoorvazi. "The Physical Origin of Waves in Magnetocardiography Technique and their Applications in Imaging." NeuroQuantology 20, no. 5 (May 10, 2022): 886–91. http://dx.doi.org/10.14704/nq.2022.20.5.nq22294.

Full text

Abstract:

In this research, we propose a theoretical model which helps us to consider evolutions of some special heart cells by using superconducting quantum interface devices (SQUID) in a magnetocardiography (MCG) technique. In this model, each cell has its own special electrical structure including ions and charges. These charges move within or outside the cell and emit some magnetic fields. Also, some charges have spins which emit spinning magnetic fields. Summing over these biofields produces the real biofield of a cell. All cellular magnetic fields are summed and enter into the sensor (SQUID) and form the observed pulse on the scope. On the other hand, each biofield induces a current on the superconductor of detector. To consider evolutions of a special cell, one can produce some currents, equal and in opposite directions of currents which are induced by other cells. These currents cancel effects of other cells and only the current and magnetic field of a desired cell is remained. Thus, one can analyze the behavior of one special cell. For example, if a cell converts to a tumor one, its radiated charges and magnetic fields are changed. These changes could be detected by SQUID and tumors could be diagnosed fast.

APA, Harvard, Vancouver, ISO, and other styles

46

Rees, M. J. "Origin of cosmic magnetic fields." Astronomische Nachrichten 327, no. 5-6 (June 2006): 395–98. http://dx.doi.org/10.1002/asna.200610540.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Kuperus, M., and J. Harvey. "Commission 12: Radiation and Structure of the Solar Atmosphere (Radiation et Structure De L’atmosphere Solaire)." Transactions of the International Astronomical Union 20, no. 1 (1988): 91–94. http://dx.doi.org/10.1017/s0251107x00006994.

Full text

Abstract:

Solar Physics has been traditionally divided into Structure and Radiation of the Solar Atmosphere (commission 12) and Solar Activity (commission 10). There has been increasing evidence that solar activity, which is basically of magnetic origin, occurs on a great variety of scales arid thus immediately touches upon the structure of the solar atmosphere as well as the structure and dynamics of the convection zone. As a consequence progress in the field of origin and evolution of solar magnetic fields from a large scale, ‘the dynamo’, to small scale is included in this report. In the past few years particular attention has been paid to the fact that the fluctuations in the magnetic field are much larger than the mean field and that the dynamo modes may be stochastically excited. The question whether there is a magnetic reservoir at the bottom of the convection zone still remains to be resolved. The interaction of the convection and the magnetic field resulting in an enhancement of the magnetic field in the intergranular lanes is studied by numerical modelling.

APA, Harvard, Vancouver, ISO, and other styles

48

TEH, ROSY, BAN-LOONG NG, and KHAI-MING WONG. "FINITE ENERGY ONE-HALF MONOPOLE SOLUTIONS." Modern Physics Letters A 27, no. 40 (December 19, 2012): 1250233. http://dx.doi.org/10.1142/s0217732312502331.

Full text

Abstract:

We present finite energy SU(2) Yang–Mills–Higgs particles of one-half topological charge. The magnetic fields of these solutions at spatial infinity correspond to the magnetic field of a positive one-half magnetic monopole at the origin and a semi-infinite Dirac string on one-half of the z-axis carrying a magnetic flux of [Formula: see text] going into the origin. Hence the net magnetic charge is zero. The gauge potentials are singular along one-half of the z-axis, elsewhere they are regular.

APA, Harvard, Vancouver, ISO, and other styles

49

Kaphle, Kishor, Gyanendra Karki, and Amrit Panthi. "Alternative Approach for the Calculation of Magnetic Field due to Magnet for Magnetic Field Visualization and Evaluation." Journal of the Institute of Engineering 15, no. 1 (February 16, 2020): 150–60. http://dx.doi.org/10.3126/jie.v15i1.27724.

Full text

Abstract:

The magnetic field of different geometry of the permanent magnet is analytically calculated by using basic principles of the magnetism in very easier approach. Concept of origin shifting and geometrical shape transformation are used to formulate the formula for cuboidal, cubical and cylindrical permanent magnets. This concept can be used for the analysis of magnetic field distribution in space around for permanent magnet as well as electromagnet in a very easier approach. Handy and simplified software is made to calculate the magnetic field due to permanent magnet and electromagnet at any desired position on space. Magnetic field visualization is also done in both magnitude and direction by using MATLAB.

APA, Harvard, Vancouver, ISO, and other styles

50

Romanova, M. M. "Origin of Blazar Activity." Symposium - International Astronomical Union 194 (1999): 256–68. http://dx.doi.org/10.1017/s0074180900162084.

Full text

Abstract:

Models of Blazars based on the propagation of finite discontinuities or fronts in the Poynting flux jet from the innermost regions of an accretion disk around a black hole are discussed. Such fronts may be responsible for short time–scale (from less than hours to days) flares in different wavebands from high frequency radioband to TeV, with delay in low radio frequencies as a result of synchrotron self-absorption. The cases of magnetic fields of one and opposite polarities across the front are investigated. We find that annihilation of magnetic field in the front leads to higher energy spectrum of leptons and possibility of strong TeV flares. Electron–positron pairs form in most cases as a result of interaction between numerous synchrotron photons and SSC photons, and constitute the majority species, compared with the ions at subparsec scales. Frequent weak outbursts may be responsible for flickering core radiation in all wavebands, while the stronger outbursts may be observed as short time–scale flares.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'The origin of magnetic field'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles