Nonreciprocal transport in superconductors, particularly the diode effect, is vital for developing future electronic devices. In this study, we explore the origin of this nonreciprocity by investigating the dynamics of magnetic flux vortices in superconducting thin films with asymmetric pinning potentials. Using numerical simulations and an analytical solution to the Langevin equation, we demonstrate that asymmetric pinning leads to a significant second-harmonic resistance. Our analysis shows a distinct peak in this resistance at an intermediate magnetic field, which subsides at higher temperatures. Furthermore, we establish that an applied direct current can effectively modulate this peak. These findings are in agreement with recent experimental results (Qiaoet al2024Nano Lett.24511) and provide a quantitative framework for understanding and engineering vortex-induced nonreciprocal transport in superconducting films.

Effect of high relative permeability and high magnetic saturation flux density on dynamic performance of a plunger type solenoid valve during its start transient

A deep recurrent learning framework for predicting saturation magnetic flux density in Fe-based metallic glasses

A strong and plastic Fe-based composite alloy with extremely high saturation magnetic flux density by constructing multiscale heterogeneous structure

A multidirection three-dimensional fusion neural network for irregular defect size estimation on magnetic flux leakage detection system

Abstract Quasi-separatrix layers (QSLs) at the Sun are created in regions where channels of open magnetic flux have footpoints near regions of large-scale closed magnetic flux. These regions show rapid changes in curvature and field strength. Numerical simulations of a relaxed coronal magnetic field and solar wind using the Magnetohydrodynamic Algorithm outside a Sphere model coupled to the Energetic Particle Radiation Environment Module model indicate common sources of energetic particles over broad longitudinal distributions in the background solar wind. These regions accelerate energetic particles from QSLs and current sheets. Here, we develop an analytical framework to describe the acceleration of energetic particles due to the magnetic field changes within and near separatrix layers. The reduced field strength near the separatrix layer drives magnetic field magnitude changes that accelerate energetic particles in the presence of plasma flow along the structure. Separatrix layers are prone to magnetic reconnection, creating fluctuations in the field that propagate out from the Sun, and release material previously contained within closed magnetic field structures, which are often rich in heavy ions and 3 He ions. Thus, we present a model of energetic particles accelerated from separatrix layers in the corona. Our results provide a plausible source for seed populations near the Sun.

Abstract Bipolar magnetic regions (BMRs) that appear on the solar photosphere are surface manifestations of the Sun’s internal magnetic field. With modern observations and continuous data streams, the study of BMRs has moved from manual sunspot catalogs to automated detection and tracking methods. In this work, we present an additional module to the existing BMR tracking algorithm, the Automatic Tracking Algorithm for Bipolar Magnetic Regions (AutoTAB), which focuses on identifying emerging signatures of BMRs. Specifically, for regions newly detected on the solar disk, this module backtracks the BMRs to their point of emergence. From a total of about 12,000 BMRs identified by AutoTAB, we successfully backtracked 3080 cases. Within this backtracked sample, we find two distinct populations. One group shows the expected behavior of emerging regions, in which the magnetic flux increases significantly during the emerging phase. The other group consists of BMRs whose flux, however, does not exhibit substantial growth during their evolution, the instances where our algorithm fails to capture the initial emergence of the BMRs. We classify these as “discarded” BMRs and examine their statistical properties separately. Our analysis shows that these discarded BMRs do not display any preferred tilt angle distribution and do not show systematic latitudinal tilt dependence, in contrast to the trends typically associated with emerging BMRs. This indicates that including such regions in statistical studies of BMR properties can distort or mask the underlying physical characteristics. We therefore emphasise the importance of excluding the discarded population from the whole dataset when analysing the statistical behavior of BMRs.

Toroidal eddy currents induced in the tokamak vacuum vessel play a critical role in plasma startup, volt-second consumption, and magnetic field configuration. However, the direct and accurate measurement of these currents is challenged by the presence of strong background magnetic fields—on the order of several Tesla—generated by the central solenoid (CS) and poloidal field (PF) coils, with currents often exceeding several mega-ampere-turns. This paper presents a novel dual-loop fiber optic current sensor (FOCS) system developed specifically for the EXL-50U spherical tokamak to directly measure toroidal eddy currents. The diagnostic setup includes an inner FOCS loop dedicated to measuring the plasma current (I p), and an outer loop for detecting the total enclosed toroidal current, which comprises contributions from the plasma, all external coils, and the eddy currents. A specially designed hardware compensation coil physically cancels the dominant magnetic flux generated by the CS leads in real time, significantly enhancing the signal-to-noise ratio. Experimental results demonstrate that the system is capable of measuring eddy currents even under strong background fields. The measured waveforms are in good agreement with numerical simulations, validating both the diagnostic approach and the electromagnetic model of the device. The proposed diagnostic system offers a robust and reliable tool for optimizing plasma startup scenarios in spherical tokamaks.

Abstract Extended periods of radio pulsations have been observed for six magnetars, displaying characteristics different from those of ordinary pulsars. In this Letter, we argue that radio emission is generated in a closed, twisted magnetic flux bundle originating near the magnetic pole and extending beyond 100 km from the magnetar. The electron–positron flow in the twisted bundle has to carry electric current and, at the same time, experiences a strong drag from the radiation field of the magnetar. This combination forces the plasma into a “radiatively locked” state with a sustained two-stream instability, generating radio emission. We demonstrate this mechanism using novel first-principles simulations that follow the plasma behavior by solving the relativistic Vlasov equation with the discontinuous Galerkin method. First, using one-dimensional simulations, we demonstrate how radiative drag induces the two-stream instability, sustaining turbulent electric fields. When extended to two dimensions, the system produces electromagnetic waves, including superluminal modes capable of escaping the magnetosphere. We measure their frequency and emitted power and incorporate the local simulation results into a global magnetospheric model. The model explains key features of the observed radio emission from magnetars: its appearance after an X-ray outburst, wide pulse profiles, luminosities ∼10 30 erg s −1 , and a broad range of frequencies extending up to ∼100 GHz.

Abstract The wrist rehabilitation training device with force feedback capability can significantly enhance rehabilitation experience and therapeutic outcomes. Human wrist joint exhibits variable stiffness characteristics during movement, which imposes higher requirements on compliance and adaptability of the rehabilitation training device. Thus, this paper design a novel magnetically coupled variable stiffness joint (MCVSJ) for the wrist rehabilitation training device, which mainly consists of the active electromagnetic disk and the passive permanent magnet disk. Through modifying the drive current of the active electromagnetic disk, the MCVSJ stiffness can be quickly and continuously adjusted. Firstly, based on the Biot-Savart law, the equivalent magnetic flux density of the iron-core coil is analyzed. Then, with the spatial arrangement of the iron-core coils combined, the average magnetic flux density at the end face of the active electromagnetic disk is determined by using the mean equivalent method. Furthermore, the equivalent magnetic charge method is employed to determine the coupled magnetic force transfer relationship in the MCVSJ. Based on this, the output torque equation and stiffness characteristic equation of the MCVSJ are established. Additionally, the influences of the current and the air gap on the mechanical characteristics of the MCVSJ are systematically investigated. A prototype of the MCVSJ is then developed. Both simulation and experimental results confirm its stiffness output characteristics, showcasing rapid response, high structural stability, and a wide-range linear stiffness adjustment. These mechanical properties effectively satisfy the dynamic variable-stiffness demands of wrist rehabilitation training.

Early fault diagnosis in induction motors is important to maintain correct operation in terms of energy and efficiency, as well as to achieve a reduction in costs associated with maintenance or unexpected stoppages in production processes. These motors are widely used in industry due to their reliability, low cost, and great robustness; however, over time, they may be exposed to wear that can affect their performance, endanger the integrity of operators, or cause unexpected shutdowns that generate economic losses. Corrosion in the bearings is one of the most common failures, which is mainly triggered by high humidity in combination with high temperatures. However, despite its relevance, it has not been widely explored as a cause of failure in induction motors. Unlike failures that occur in specific or localized areas, corrosion in bearings does not manifest through specific frequencies associated with the phenomenon, since the corrosion occurs extensively on the surface of the raceway, making early diagnosis difficult with conventional techniques based on spectral analysis. Therefore, this work proposes an approach for the analysis of magnetic stray flux and vibration signals under different levels of corrosion using statistical and non-statistical parameters to capture variations in the dynamic behavior of the motors while employing genetic algorithms to select the most relevant parameters for each signal and optimize the configuration of an ensemble learning algorithm. The classification of the bearing condition is achieved using support vector machines in combination with the bagging method, which increases the robustness and accuracy of the model in the presence of signal variability. A classification accuracy between the healthy state and two gradualities greater than 99% was obtained, indicating that the proposed approach is reliable and efficient for corrosion diagnosis.

Permanent Magnet Synchronous Motors (PMSMs) are widely used in industrial and electric vehicle applications for their high efficiency, compact size, and precise controllability. However, cogging torque remains a key issue, causing vibration, noise, and performance loss, especially at variable speeds. This study presents a Finite Element Analysis (FEA)-based parametric optimization approach to improve the magnetic and structural performance of a 20-kW, 138-V, 6-pole PMSM. Instead of heuristic algorithms, the method refines key geometric parameters such as magnet thickness, pole embrace, and pole offset that strongly affect flux distribution, torque, and vibration. Using ANSYS Maxwell, simulations analyze their effects on efficiency, air-gap flux density, and cogging torque. Results indicate a decrease in cogging torque from 7.56 Nm to 4.74 Nm and an approximate 15% enhancement in efficiency, leading to improved torque smoothness and more uniform magnetic flux distribution. The study highlights the importance of precise geometric optimization for higher performance and lower noise.

The modern world is becoming increasingly vulnerable to geomagnetic storms due to the rapid development of new technologies and technical systems. This applies to all areas of human activity where power grids, GPS, the Internet, and digital communications are used. Storms can cause damage to the energy sector, aviation, navigation, satellite electronics, communication systems, industry, and the agro-industrial complex. Extreme geomagnetic storms can cause enormous economic damage and endanger to human health. Their prediction is very important, but not yet perfect enough. Extreme geomagnetic storms are typically caused by coronal mass ejections (CMEs) during powerful flares. A detailed study of their sources is very important. To study the conditions that favor the occurrence of extreme storms, we selected six active regions (ARs) that were their sources in the period from 2000 to 2024. We have analyzed the spatial and temporal evolution, morphological characteristics, magnetic field structure, and flare activity of NOAA 09393, 10484, 10486, 10501, 10696, 13664. Some ARs were located in large activity complexes. The ARs studied developed rapidly, their area and number of spots increased, their magnetic structure became more complex, and the flare activity increased. Many of these ARs had very large maximum areas exceeding 2000 millionths of a solar hemisphere. On the days when the eruptions occurred the ARs were located near the central meridian, and the Bz-component of the interplanetary magnetic field was directed south. Their area and spot number were close to their maximum, the magnetic configuration was βγδ in most cases. The sources of the CMEs were M and X class flares, which were preceded by the rapid emergence of new magnetic fluxes and their reconnection with the existing magnetic field of the region. The most powerful geomagnetic storms during the considered period with a minimum DST index less than -400 nT were observed on November 20, 2003 and May 10–11, 2024. These storms were caused by CMEs from flares occurred in ARs 10501 and 13664. These ARs were characterized by complex magnetic topology and rapid magnetic flux emergence. The storm on May 10–11, 2024, was preceded by cannibal CMEs that enhanced its strength and duration. The most powerful storm of the period under review, on November 20, 2003, with a peak Dst index of -422 nT, was caused by a CME from an M3.9 flare in the AR NOAA 10501. During the storm’s peak, auroras were observed as far south as Florida, Michigan, and Wisconsin in the United States and Greece in Europe. It was found that AR with a small area and moderate flares can produce extreme storms, while ARs with large areas and with powerful flares do not always.

Abstract Active region (AR) recurrent jets are manifestations of episodic magnetic energy release processes driven by complex interactions in the lower solar atmosphere. While magnetic flux emergence and cancellation are widely recognized as key contributors to jet formation, the mechanisms behind repeated magnetic reconnection remain poorly understood. In this Letter, we report a sequence of nine recurrent jets originating from AR 12715 during its decay phase, where the jet activity was associated with a complex distribution of fragmented magnetic flux. Nonlinear force-free field extrapolations reveal the presence of low-lying, current-carrying loops beneath overarching open magnetic fields near the jet footpoints. These magnetic structures were perturbed by: (1) emerging flux elements; and (2) interactions between oppositely polarized moving magnetic features (MMFs). To interpret these observations, we compare them with a 3D radiative MHD simulation from the Bifrost model, which reproduces jet formation driven by interacting bipolar MMFs, leading to subsequent flux cancellation in the photosphere. Our results emphasize the critical role of MMF-driven flux interactions in initiating and sustaining recurrent jet activity in ARs.

In measurements of the magnetic azimuth of the borehole axis, calculations are based on the superposition of the Earth’s magnetic field and parasitic fields from the remanent magnetization of the geophysical tool assembly and the drill string. At high latitudes the horizontal component of the geomagnetic field is very small. As a result, even weak parasitic fields — on the order of 1 % of the geomagnetic field — can cause azimuth errors of 4° or more. Many methods to mitigate this effect have been reported in the literature. However, almost all of them require either additional equipment and preliminary measurements, or knowledge of the exact values of the magnitude and inclination of the geomagnetic field at the survey location. In connection with all of the above, there is a problem of creating a compensation method that would not require preliminary measurements of the parameters of the parasitic field or the modulus and inclination of the geomagnetic field. This paper proposes using an additional magnetometer in the inclinometer to measure the gradient of the superpositional magnetic field. From simulation, and using the measured gradient, an equivalent magnetic source in the form of a circular current loop is determined. The calculated field of this loop is then subtracted from the reference magnetometer readings. In the laboratory experiments, ring neodymium magnets (three variants with different magnetic flux densities) placed on the inclinometer axis were used as parasitic-field sources. A magnetic gradiometer was formed by two magnetometer sensors spaced 0.307 m apart. In experiments, the developed algorithm identified parameters of current loops equivalent to the sources in terms of magnetic effect. This enabled compensation of the reference magnetometer readings and improved azimuth accuracy from −1°15′36″ (source 1), −3°9′36″ (source 2) and +12°30′36″ (source 3) to ±0°39′ for all sources. In the experiment the field magnitudes at the reference magnetometer location were 0.42 %, 1.59 % and 5.60 % of the geomagnetic field, respectively. The proposed method increases azimuth measurement accuracy without requiring measurements of parasitic or geomagnetic field parameters. In addition, the use of the method allows reducing the length of nonmagnetic collars on both sides of the inclinometer during drilling. Thus, the method can be implemented in a sensor that computes and compensates for parasitic fields in real time during logging or drilling.

Abstract Conventional ultrasonic rail inspection from the rail head uses reflection methods to measure thickness reduction beneath the rail web but cannot detect corrosion-induced defects on the rail foot side. To address this limitation, we propose a novel detection system that identifies magnetic field variations caused by defects using a non-contact sensor positioned above the rail foot side. Low-frequency excitation was selected because it enables deeper magnetic flux penetration and allows magnetic field changes to be detected even when the sensor is positioned several tens of millimeters away from the rail. Fundamental investigations were conducted through three-dimensional electromagnetic field analysis and laboratory experiments. A coil mounted on the rail head was energized with low-frequency current, and sensor outputs were evaluated near artificially machined defects. Numerical analysis demonstrated that, even with fastening devices present, defect presence and size can be estimated by comparing relative magnetic flux density distributions. For example, when the coil current was 0.372 A rms at 10 Hz with 84 turns, the standard deviation of relative flux density along the rail length increased from 0.246 (no defect) to 0.259 (top-surface defect, 2 mm), 0.263 (top-surface defect, 5 mm), and 0.276 (penetrating defect). Laboratory experiments showed that relative magnetic flux density along the rail length agreed well with the numerical analysis. Under higher excitation (4 V rms , 10 Hz, 168 turns), the standard deviation in the vertical direction increased from 2.58 (no defect) to 3.09, 3.64, and 5.26 for the same defect types, confirming the feasibility of defect size evaluation. These findings demonstrate that the proposed method can effectively detect corrosion-induced defects on the rail foot side, even with fastening devices. This approach offers a promising solution for non-contact inspection of regions inaccessible to ultrasonic testing and improving railway maintenance efficiency and safety.

This study offers a comprehensive in situ measurement and assessment of electromagnetic field (EMF) exposure in the central urban districts of Samsun, Türkiye, focusing on low-frequency magnetic flux density (BLF) and radiofrequency electric field strength (ERF). Drive-test measurements were performed across Atakum, İlkadım, and Canik districts to capture spatial variability and identify primary exposure sources. Band-selective analysis revealed that downlink (DL) transmissions are the main contributors to total ERF exposure, indicating that base station emissions dominate the exposed ERF levels in the environment. Six-minute averaged BLF and ERF values account for temporal fluctuations and confirm that exposure remains well below recommended limits. A one-way ANOVA test indicated that the differences in exposure levels among the three districts were not statistically significant. These findings provide a detailed spatial evaluation of EMF exposure in a large metropolitan region, demonstrating the value of integrated BLF and ERF measurements for environmental monitoring.

Context. The photospheric Evershed flow is normally oriented radially outward, yet sometimes opposite velocities are observed not only in the chromosphere but also in the photospheric layers of the penumbra. Aims. We studied the velocity field in a special case of an active region with two mature sunspots, the lesser of which formed several days after the main one. Flux emergence between the two spots is still ongoing, influencing the velocity pattern. Methods. We observed the active region NOAA 12146 on August 24, 2014, with the GREGOR Fabry-Pérot Interferometer and the Blue Imaging Channel of the GREGOR solar telescope at Observatorio del Teide on Tenerife. Context data from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory complement the high-resolution data. Results. In the penumbra of a newly formed spot, we observe opposite Doppler velocity streams of up to ±2 km s −1 very close to each other. These velocities extend beyond the outer penumbral boundary and cross the polarity-inversion line. The properties of the magnetic field do not change significantly between these two streams. Although the magnetic field is almost horizontal, we do not detect high transversal velocities in horizontal flow maps obtained via the local correlation technique. Conclusions. The ongoing emergence of magnetic flux in an active region causes flows of opposite directions that penetrate the penumbra of a preexisting sunspot.

Abstract Boron (11B) pellet injection is designated as a routine fueling technique for the EHL-2 spherical torus. The predictive modelling of 11B pellet injection for H-mode plasma fueling in EHL-2 has been performed using the three-dimensional (3D) nonlinear magnetohydrodynamic (MHD) code JOREK. The simulation results show that the 11B pellet induces rapid local cooling and temperature profile contraction. This constrains the ablation rate to a relatively low level, enabling effective penetration through the pedestal region and injection into the core up to a position of 0.35 in the normalized poloidal flux. After the pellet is completely ablated, about 90% of the 11B can be deposited inside the separatrix. The increased edge resistivity from temperature contraction modifies the poloidal magnetic flux via Ampère's law. This perturbs the toroidal current density near rational surfaces, enhances the radial gradient there and drives multiple tearing modes. Interactions among high poloidal mode (high-m) edge magnetic islands lead to magnetic stochasticity, but the stochastic layer does not expand inward beyond the pedestal during injection. Post-complete ablation, tearing mode growth ceases, suggesting pellet injection can deliver material deeply without triggering persistently growing MHD instabilities.

This paper addresses the efficiency gap in compact, self-starting electric generators for autonomous devices, where mechanical and electrical losses degrade output and lifetime (problem and relevance). We study a pulse-controlled generator with a pendulum-inertial cone rotor and dual magnetic excitation—constant field for stabilization and alternating field for adaptive energy injection – targeted at maximizing conversion from mechanical oscillations to electrical power (methods). A time-domain model with realistic losses (bearing friction, coil resistance, current/voltage limits) was implemented in Python/NumPy and validated by numerical experiments over 0–10 s. Parameter sweeps covered moment of inertia, friction coefficient, load resistance, pulse amplitude and duration, number of turns, and magnetic flux; outputs included angular speed, induced EMF, current, and accumulated energy. Our key hypothesis is that combining inertial smoothing with sparse pulse actuation increases net energy and extends steady operation versus a permanent-magnet, no-pulse baseline. The simulations confirm this, attributing gains to reduced torque ripple, selective compensation of dissipation, and recovery through a self-charging loop (hypotheses and findings). Distinguishing features are the cone rotor acting as a pendulum stabilizer, dual-field control, and low-loss pulse start. Practical use is foreseen in energy-harvesting nodes and low-power drives where short start-up energy is available, mechanical losses are moderate, and load impedance can be matched. The results guide sizing and control co-design without serving as an introduction.