Magnetic Field Model Research Articles

The Magnetic Origin of the Mystery of Rare Hα Moreton Waves

Abstract Over the past three decades, a lot of coronal fast-mode waves have been detected by space missions, but their counterparts in the chromosphere, called Moreton waves, have rarely been captured. How this happens remains a mystery. Here, to shed light on this problem, we investigate the photospheric vector magnetograms of the Moreton-wave events associated with M- and X-class solar flares during 2010–2023. The Hα data are taken with the Global Oscillation Network Group and the Chinese Hα Solar Explorer. Our statistical results show that more than 80% of the events occur at the edges of active regions and propagate nonradially, due to asymmetric magnetic fields above the flares. According to the reconstructed magnetic field and atmospheric model, Moreton waves propagate in the direction along which the horizontal fast-mode wave speed drops the fastest. This result supports the inclined magnetic configuration of the eruption being crucial for generating Moreton waves, even for X-class flares. It may explain the low occurrence rate of Moreton waves and why some X-class flares accompanied with coronal mass ejections do not generate Moreton waves.

Retracing the Cold Plasma Dispersion Law in Pulsar B0329+54: New Insights into Frequency-dependent Dispersion Measures

Abstract Multiple studies have investigated potential frequency-dependent dispersion measures (DMs) in PSR B0329+54, with sensitivities at levels of 10−3 pc cm−3 or higher, using frequencies below 1 GHz. Utilizing the extensive bandwidth of the upgraded Giant Metrewave Radio Telescope, we conducted simultaneous observations of this pulsar across a frequency range of 300–1460 MHz. Our observations reveal a distinct point in the pulse profile of PSR B0329+54 that appears to align remarkably well with the cold-plasma dispersion law, resulting in a unique measured DM across the entire frequency range. In contrast, using times of arrival from widely adopted pulsar timing techniques (e.g., FFTFIT) leads to frequency-dependent DMs. We investigated the potential causes of these frequency-dependent DMs in this pulsar and their relationship with the underlying magnetic field geometry corresponding to the radio emission. Our study reveals that all frequencies in the range 300–1460 MHz originate from a region no larger than 204 km, and the dipolar magnetic-field geometry model indicates that the emission region is centered at ~800 km from the star. This is the tightest constraint on the size of the emission region reported so far for PSR B0329+54 at the given frequencies, and it is at least 5 times more stringent than the existing emission height constraints based on the dipolar geometry model.

Nanosatellite Autonomous Navigation via Extreme Learning Machine Using Magnetometer Measurements

This work presents an algorithm to perform autonomous navigation in spacecraft using onboard magnetometer data during GPS outages. An Extended Kalman Filter (EKF) exploiting magnetic field measurements is combined with a Single-Hidden-Layer Feedforward Neural Network (SLFN) trained via the Extreme Learning Machine to improve the accuracy of the state estimate. The SLFN is trained using GPS data when available and predicts the state correction to be applied to the EKF estimates. The CHAOS-7 magnetic field model is used to generate the magnetometer measurements, while a 13th-order IGRF model is exploited by the EKF. Tests on simulated data showed that the algorithm improved the state estimate provided by the EKF by a factor of 2.4 for a total of 51 days when trained on 5 days of GPS data.

The effect of stator-rotor slot combinations on vibrations induced by tangential electromagnetic forces in HVLSPMSM

Abstract Line-starting permanent magnet synchronous motor (LSPMSM) has the advantage of induction motor and permanent magnet motor. The double-slotted stator-rotor structure can lead to the complexity of the LSPMSM air-gap magnetic field. This further leads to the variation of tangential electromagnetic force (TEMF) and cogging torque of the LSPMSM, which affects the vibration characteristics of the motor. In this paper, the effect of stator-rotor slot combinations on the TEMF of High-voltage line-starting permanent magnet synchronous motor (HVLSPMSM) is analyzed by using a 10 kV, 630 kW HVLSPMSM as an example. Firstly, a mathematical model of the air-gap magnetic field considering double slots is established by using the conformal transformation, and the harmonic distribution characteristics of the radial and tangential air-gap magnetic flux density under different stator-rotor slot combinations are obtained. Then, the expression of the TEMF density is constructed based on the Maxwell tensor method, and the conversion relationship between the TEMF density and the local tangential force is analyzed. Further, the influence of cogging torque amplitude and frequency on different stator-rotor slot combinations is derived by analyzing the TEMF density. Finally, the electromagnetic-mechanical coupling model of the HVLSPMSM is established, and the influence of TEMF on the vibration spectrum of the motor under different stator-rotor slot combinations is resolved by numerical calculations. This paper provides a reliable theoretical guide to improve the performance of HVLSPMS.

The magnetic field of the Radcliffe wave: Starlight polarization at the nearest approach to the Sun

We investigate the geometry of the magnetic field toward the Radcliffe wave, a coherent part of the nearby Local Arm of 3 kpc in length recently discovered via three-dimensional dust mapping. We used archival stellar polarization in the optical and new measurements in the near-infrared to trace the magnetic field as projected on the plane of the sky. Our new observations cover the portion of the structure that is closest to the Sun, between Galactic longitudes of ,122^∘ and 188^∘. The polarization angles of stars immediately behind the Radcliffe wave appear to be aligned with the structure as projected on the plane of the sky. The observed magnetic field configuration is inclined with respect to the Galactic disk at an angle of 18^∘. This departure from a geometry parallel to the plane of the Galaxy is contrary to previous constraints from more distant stars and polarized dust emission. We confirm that the polarization angle of stars at larger distances shows a mean orientation parallel to the Galactic disk. We discuss the implications of the observed morphology of the magnetic field for models of the large-scale Galactic magnetic field, as well as formation scenarios for the Radcliffe wave itself.

Multispheroidal model of magnetic field of uncertain extended energy-saturated technical object

Problem. The implementation of strict requirements for magnetic silence of elongated energy-saturated technical objects – such as naval vessel and submarines is largely determined by the adequacy of mathematical models to the signatures of a real magnetic field. Aim. Simplification of mathematical modeling of the magnetic field of an uncertain extended energy-saturated object based on the development and application of a multispheroidal model of its magnetic field instead of the well-known multidipole model. Methodology. Coordinates of the geometric location and magnitudes of spatial extended spheroidal harmonics of spheroidal sources of multispheroidal model of magnetic field calculated as magnetostatics geometric inverse problems solution in the form of nonlinear minimax optimization problem based on near field measurements for prediction far extended technical objects magnetic field magnitude. Nonlinear objective function calculated as the weighted sum of squared residuals between the measured and predicted magnetic field COMSOL Multiphysics software package used. Nonlinear minimax optimization problems solutions calculated based on particle swarm nonlinear optimization algorithms. Results. Results of prediction far magnetic field magnitude of extended technical objects based on designed multispheroidal model of the magnetic field in the form of spatial prolate spheroidal harmonics in prolate spheroidal coordinate system using near field measurements with consideration of extended technical objects magnetic characteristics uncertainty. Originality. For the first time the method for design of multispheroidal model of magnetic field of uncertain extended energy-saturated technical object based on magnetostatics geometric inverse problems solution and magnetic field spatial spheroidal harmonics calculated in prolate spheroidal coordinate system taking into account of technical objects magnetic characteristics uncertainties developed. Practical value. It is shown the possibility to reduce the number of spheroidal sources of the magnetic field for adequate modeling of the real magnetic field based on the developed multispheroidal model compared to the number of well-known dipole sources of the magnetic field in the multidipole model of the magnetic field. References 48, figures 4.

Constraints on axion-like particles from the gamma-ray observation of the Galactic Center

High energy photons originating from the Galactic Center (GC) region have the potential to undergo significant photon-axion-like particle (ALP) oscillation effects, primarily induced by the presence of intense magnetic fields in this region. Observations conducted by imaging atmospheric Cherenkov telescopes have detected very high energy gamma-rays originating from a point source known as HESS J1745-290, situated in close proximity to the GC. This source is conjectured to be associated with the supermassive black hole Sagittarius A*. The GC region contains diverse structures, including molecular clouds and non-thermal filaments, which collectively contribute to the intricate magnetic field configurations in this region. By utilizing a magnetic field model specific in the GC region, we explore the phenomenon of photon-ALP oscillations in the gamma-ray spectrum of HESS J1745-290. Our analysis does not reveal any discernible signature of photon-ALP oscillations, yielding significant constraints that serve as a complement to gamma-ray observations of extragalactic sources across a broad parameter region. The uncertainties arising from the outer Galactic magnetic field models have minor impacts on our results, except for ALP masses around 10-7 eV, as the dominant influence originates from the intense magnetic field strength in the inner GC region.

Impact of parameters in the toroidal blazar jet magnetic field model on axion-like particle constraints

The interaction between axion-like particles (ALPs) and photons induces ALP-photon oscillations in astrophysical magnetic fields, leading to spectral distortions in the γ-ray spectrum of blazars. The primary uncertainty of this phenomenon may originate from the magnetic field within the jet of the blazar. Many studies focus on a simple jet magnetic field model with a toroidal component exerting a predominant influence on regions far from the central region. While many investigations have explored the effects of ALP-photon oscillations using typical parameter values in this model, it is important to recognize that these parameters can be constrained by multi-wavelength observations. In this study, we utilize the high energy γ-ray spectrum of Mrk 421 obtained from MAGIC and Fermi-LAT observations. By employing multi-wavelength fitting with a one-zone synchrotron self-Compton model, we derive the parameters characterizing the simple toroidal balazar jet magnetic field model, and investigate their impacts on the ALP constraints.

Superconductivity and its Properties: Cooper Pairs, Meissner Effect, London Moment, Gravitomagnetic and Gravitoelectric Processes

The following properties of superconductivity are considered in this work: the creation and destruction of Cooper pairs, “mass defect”, Meissner effect, London moment, gravitomagnetic and gravitoelectric processes. The conducted research has shown that for explanation of the above-mentioned properties of superconductivity it is necessary to investigate the characteristics of physical vacuum. With this aim, the following physical models of physical vacuum are analyzed in the work. The Feynman model of creating of virtual photons by quantum objects, explaining the creation and destruction of Cooper pairs, “mass defect” and partly Meissner effect. The model of physical vacuum consisting of quantum oscillators by A. Einstein and O. Stern and the model of magnetic field by L. I. Sedov. The latter two models are basic for interpretation of Meissner effect, London moment, gravitomagnetic and gravitoelectric processes.

System Energy Analysis and COMSOL Simulation of a Superconducting Shielding Model

This article proposes a superconducting shielding magnetic field model based on the Meissner effect of superconductors, which blocks magnetic fields. By utilizing the shielding effect of the superconductor on the magnetic field during the phase transition, the model achieves intermittent shielding of electromagnetic force, allowing the electromagnetic force to work intermittently on the moving magnet within the model during its operation. The model is analyzed on the basis of superconducting thermodynamic theory, with a focus on the electromagnetic energy of the system. It is concluded that the energy is not conserved during the operation of the model. To verify the correctness of the analysis, electromagnetic simulations and data analysis were conducted via the COMSOL electromagnetic module and Ampère's law superconducting model parameters, which yielded identical results.

Unsteady Dungey cycle from the point of view of Stokes’ theorem

The Dungey cycle is considered from the formation of a magnetic barrier and necessary for dayside reconnection conditions till the electric field generation around the Birkeland current loop and magnetic flux circulation balance. Data-based modeling of the magnetosheath magnetic field makes it possible to quantitatively assess the main factors that control formation and destruction of the magnetospheric magnetic barrier, such as the field line draping and the field intensity increase from the bow shock to the magnetopause, as well as their dependence on the orientation of the interplanetary magnetic field (IMF). The Dungey cycle has been revised to take into account the essentially time-dependent effects of magnetic reconnection. It is shown by means of the Stokes’ theorem that a powerful electric field with an effective potential difference of several tens of kV is generated around the developing substorm current system. The emerging Birkeland current loop is an important particle acceleration element in the magnetosphere, contributing to the energization of ring current protons and electrons. The electric field that arises in the dipolarization zone magnifies the already existing ring current, and the closure of its amplified part through the ionosphere generates the Region 2 field-aligned currents. The motion of the expanding partial ring current around the magnetosphere, combined with the particle drift, transfers the magnetic flux from the night side of the magnetosphere to the dayside. At the dayside magnetopause, the reconnection is also responsible for the creation of the Birkeland loop, but now the electric field in the loop area decelerates the ring current particles, and regions of weakened ring current are formed. Closure of these weakened loop currents results in a transfer of the magnetic flux from the dayside to the night side, thus ensuring its overall balance and completing the Dungey cycle.

Diagnostic performance of DCE-MRI radiomics in predicting axillary lymph node metastasis in breast cancer patients: A meta-analysis.

Radiomics offers a novel strategy for the differential diagnosis, prognosis evaluation, and prediction of treatment responses in breast cancer. Studies have explored radiomic signatures from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) for predicting axillary lymph node metastasis (ALNM) and sentinel lymph node metastasis (SLNM), but the diagnostic accuracy varies widely. To evaluate this performance, we conducted a meta-analysis performing a comprehensive literature search across databases including PubMed, EMBASE, SCOPUS, Web of Science (WOS), Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang Data, and the Chinese BioMedical Literature Database (CBM) until March 31, 2024. The pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and the area under the receiver operating characteristic curve (AUC) were calculated. Twenty-four eligible studies encompassing 5588 breast cancer patients were included in the meta-analysis. The meta-analysis yielded a pooled sensitivity of 0.81 (95% confidence interval [CI]: 0.77-0.84), specificity of 0.85 (95%CI: 0.81-0.87), PLR of 5.24 (95%CI: 4.32-6.34), NLR of 0.23 (95%CI: 0.19-0.27), DOR of 23.16 (95%CI: 17.20-31.19), and AUC of 0.90 (95%CI: 0.87-0.92), indicating good diagnostic performance. Significant heterogeneity was observed in analyses of sensitivity (I2 = 74.64%) and specificity (I2 = 83.18%). Spearman's correlation coefficient suggested no significant threshold effect (P = 0.538). Meta-regression and subgroup analyses identified several potential heterogeneity sources, including data source, integration of clinical factors and peritumor features, MRI equipment, magnetic field strength, lesion segmentation, and modeling methods. In conclusion, DCE-MRI radiomic models exhibit good diagnostic performance in predicting ALNM and SLNM in breast cancer. This non-invasive and effective tool holds potential for the preoperative diagnosis of lymph node metastasis in breast cancer patients.

Magnetic signals from oceanic tides: new satellite observations and applications.

The tidal flow of seawater across the Earth's magnetic field induces electric currents and magnetic fields within the ocean and solid Earth. The amplitude and phase of the induced fields depend on the electrical properties of both seawater and the solid Earth, and thus can be used as proxies to study the seabed properties or potentially for monitoring long-term trends in the global ocean climatology. This article presents new global oceanic tidal magnetic field models and their uncertainties for four tidal constituents, including [Formula: see text] and even [Formula: see text], which was not reliably retrieved previously. Models are obtained through a robust least-squares analysis of magnetic field observations from the Swarm and CHAMP satellites using a specially designed data selection scheme. We compare the retrieved magnetic signals with several alternative models reported in the literature. Additionally, we validate them using a series of high-resolution global three-dimensional (3D) electromagnetic simulations and place constraints on the conductivity of the sub-oceanic mantle for all tidal constituents, revealing an excellent agreement between all tidal constituents and the oceanic upper mantle structure.This article is part of the theme issue 'Magnetometric remote sensing of Earth and planetary oceans'.

A Hybrid Analytical Model of Open-Circuit Air Gap Magnetic Field of Interior Permanent Magnet Synchronous Motor With Non-Uniform Air Gap Structure Considering Saturation Effect

A Hybrid Analytical Model of Open-Circuit Air Gap Magnetic Field of Interior Permanent Magnet Synchronous Motor With Non-Uniform Air Gap Structure Considering Saturation Effect

A method for simultaneously determining Earth's magnetic field and mantle conductivity models using MSS-1 and Swarm satellite magnetic data

A method for simultaneously determining Earth's magnetic field and mantle conductivity models using MSS-1 and Swarm satellite magnetic data

Analytical Model of Magnetic Field Generated by Racetrack Superconducting Excitation Winding Within Cylindrical Ferromagnetic Boundary Based on Mirror Method

Analytical Model of Magnetic Field Generated by Racetrack Superconducting Excitation Winding Within Cylindrical Ferromagnetic Boundary Based on Mirror Method

Large-scale Magnetic Field Model of GRB Afterglow Polarization: Effects of Field Anisotropy, Off-axis Viewing Angle, and Ordered Field

The afterglows of gamma-ray bursts are nonthermal electron synchrotron emissions from relativistic shocks. The origin of strong magnetic field in the emission region remains elusive, and two field amplification mechanisms via the plasma kinetic and magnetohydrodynamic instabilities have been discussed. The polarimetric observations are a powerful probe to distinguish these two mechanisms. So far, most theoretical works have focused on the former mechanism and constructed afterglow polarization models with microscopic-scale turbulence whose coherence length is much smaller than the thickness of the blast wave. In this work, focusing on the latter mechanism, we utilize our semianalytic model of the synchrotron polarization with large-scale turbulence whose coherence length is comparable to the thickness of the blast wave to investigate the effect of magnetic field anisotropy and the observer viewing angle. We find that the polarization in our large-scale turbulence model can exhibit both behaviors characteristic of the microscopic-scale turbulence model and those not seen in the microscopic-scale model. Then we find that the large-scale model could explain all the polarimetric observational data to date that seem to be forward shock emission. We also examine the effect of ordered-field components and find that polarization degree and polarization angle constant in time are realized only when the energy density ratio of the ordered and fluctuated components is ≳50. In this case, however, the polarization degree is much higher than the observed values.

An In-depth Analysis of Quiet-Sun IRIS Brightenings

Small-scale brightenings are ubiquitous, dynamic, and energetic phenomena found in the chromosphere. An advanced filter-detection algorithm applied to high-resolution observations from the Interface Region Imaging Spectrograph enables the detection of these brightenings close to the noise level. This algorithm also tracks the movement of these brightenings and extracts their characteristics. This work outlines the results of an in-depth analysis of a quiet-Sun data set including a comparison of a brighter domain—associated with a supergranular boundary—to the quiescent internetwork domains. Several characteristics of brightenings from both domains are extracted and analysed, providing a range of sizes, durations, brightness values, travel distances, and speeds. The “active” quiet-Sun events tend to travel shorter distances and at slower speeds across the plane of the sky than their “true” quiet-Sun counterparts. These results are consistent with the magnetic field model of supergranular photospheric structures and the magnetic canopy model of the chromosphere above. Spectroscopic analyses reveal that bright points demonstrate blueshift (as well as some bidirectionality) and that they may rise from the chromosphere into the transition region. We believe that these bright points are magnetic in nature, are likely the result of magnetic reconnection, and follow current sheets between magnetic field gradients, rather than travel along magnetic field lines themselves.

Simulating the LOcal Web (SLOW) III. Synchrotron emission from the local cosmic web

Detecting diffuse synchrotron emission from the cosmic web is still a challenge for current radio telescopes. We aim to make predictions about the detectability of cosmic web filaments from simulations. We present the first cosmological magnetohydrodynamic simulation of a 500 $h^ c$Mpc volume with an on-the-fly spectral cosmic ray (CR) model. This allows us to follow the evolution of populations of CR electrons and protons within every resolution element of the simulation. We modeled CR injection at shocks, while accounting for adiabatic changes to the CR population and high-energy-loss processes of electrons. The synchrotron emission was then calculated from the aged electron population, using the simulated magnetic field, as well as different models for the origin and amplification of magnetic fields. We used constrained initial conditions, which closely resemble the local Universe, and compared the results of the cosmological volume to a zoom-in simulation of the Coma cluster, to study the impact of resolution and turbulent reacceleration of CRs on the results. We find a consistent injection of CRs at accretion shocks onto cosmic web filaments and galaxy clusters. This leads to diffuse emission from filaments of the order $S_ $ for a potential LOFAR observation at 144 MHz, when assuming the most optimistic magnetic field model. The flux can be increased by up to two orders of magnitude for different choices of CR injection parameters. This can bring the flux within a factor of ten of the current limits for direct detection. We find a spectral index of the simulated synchrotron emission from filaments of $ -1.0 -- -1.5 in the LOFAR band.

Iterative algorithm for computing magnetic field considering remanent magnetization and demagnetization

SUMMARY Efficient and high-precision methods for performing large-scale numerical calculations under high magnetic susceptibility conditions are essential for magnetic exploration applications. This paper proposes an algorithm for magnetic field modelling considering both demagnetization and remanent magnetization. The 3-D partial differential equation of magnetic potential is reduced to a 1-D ordinary differential equation in the space-wavenumber domain through a 2-D Fourier transform in the horizontal direction. Using the quadratic interpolation finite element method to obtain the pentagonal equation, the chasing method is used to solve the equation efficiently, and a contraction operator based on electromagnetic integral equation method is introduced to ensure stable iteration convergence. The validity of the algorithm was confirmed by comparing it with analytical solutions. Numerical examples demonstrate the importance of considering demagnetization under high magnetization conditions. Test results reveal that magnetic susceptibility is the sole factor affecting convergence among the factors examined. Further analysis showed that, for the same magnetic susceptibility, the algorithm converges with the same number of iterations and higher precision is achieved with an increasing number of nodes. Under the same grid configuration, higher magnetic susceptibility requires more iterations to converge and results in lower algorithm precision. The algorithm presented in this paper shows higher efficiency compared to those based on integral equations. Moreover, we demonstrate the algorithm's high accuracy when applied to models with anomalies near boundaries. Finally, the adaptability of the algorithm to complex geological models and undulating topography is verified by combining model tests with DEM data. This algorithm presents an efficient and high-precision method for magnetic field calculations under conditions of high susceptibility and strong remanent magnetization, offering promising prospects for geoscience applications.