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The study of magnetic interactions is crucial in understanding magnetic materials, where both exchange coupling and dipole interactions significantly affect the magnetic properties of composite materials. Separating and utilizing these two types of interactions have consistently been a research focus. In this study, FINEMET/Fe35Ni65 composite ribbons with varying coating thicknesses were fabricated using magnetron sputtering. Notably, obvious four-peak giant magnetoimpedance profiles can be observed as the Fe35Ni65 film thickness varied from 10 to 50 nm. Additionally, the manifestation of the four-peak profile was attributed to the variation in the magnetic properties in the FINEMET ribbon induced by exchange coupling and dipole interaction. This analysis is crucial for advancing our understanding of the underlying physical mechanisms of magnetic interactions in composite ribbons. [ABSTRACT FROM AUTHOR]

Temperature-dependent Raman spectral studies of BiFeO3 (BFO) films coated on three different substrates, viz., conducting Si (BFO-Si), sapphire (BFO-SAP), and fluorine-doped tin oxide (BFO-FTO), are reported between 123 and 773 K. The activity of Bi–O and Fe–O modes in these samples as a function of temperature shows different spectral features despite having synthesized from the same precursor. To understand the source of these variations, the spectra obtained on the above films were compared with those of bulk BiFeO3 (BFO-bulk) prepared via spark-plasma sintering. As the temperature increases, modes corresponding to the Bi–O activity at low frequency (120–180 cm−1) exhibit a redshift in their positions in all the samples. Between 350 and 550 K, BFO-SAP and BFO-Si samples show discernible anomalies in the positions of modes corresponding to the Fe–O activity (200–500 cm−1), which is not observed in the BFO-bulk and BFO-FTO samples. These anomalies are more pronounced for the modes between 350 and 500 cm−1, suggesting alterations in the Néel transition temperature (∼643 K for BiFeO3). Concurrently, another composite film of BiFeO3–CoFe2O4 coated on the Si substrate is explored. Raman studies on the composite film are used to compare and verify the influence of the substrate and defects on the magnetic ordering as a function of temperature. Our study highlights the significance and relevance of using Raman spectroscopy as a tool to discern various factors leading to local structural and magnetic variation in a given compound. [ABSTRACT FROM AUTHOR]

This study investigates an axial extension mode magnetoelectric antenna designed for near-field communication in dielectric cluttered environments. The antenna configuration consists of two magnetostrictive Metglas-polymer composites bonded on opposite sides of a PZT-5A actuator, creating a dumbbell configuration. Operating at its 88 kHz mechanical resonance, the antenna emits electromagnetic radiation in the near field by applying an AC voltage to the piezoelectric material, generating an acoustic wave that propagates through the volume and induces oscillating magnetizations. The design uses a system of uncoupled models: an electrostatic finite element model to predict strain that feeds into a Landau–Lifshitz–Gilbert micromagnetic model to predict magnetic moment changes and, subsequently, a dipole model to forecast near-field radiation characteristics. Measurements were conducted on the antenna's impedance, quality factor, mechanical resonance, transmitted magnetic signal strength, and radiation patterns, with variations in the bias magnetic field, frequency, and applied voltage. The results exhibit a strong correlation with model predictions, and the radiated signal strengths compare favorably with those of state-of-the-art pacemaker communication devices. Computational parametric studies using Galfenol and Terfenol-D suggest the potential for up to a three order of magnitude reduction in the antenna's volume, which is critical for implanted medical devices. [ABSTRACT FROM AUTHOR]

The Sun exhibits episodic surges of magnetic activity across a range of temporal and spatial scales, the most prominent of which is the 11-th year modulation of sunspot production. Beside the ∼170 (min to max) decadal variation in sunspot production there is a less-explored quasi-annual variation in the range of 25-50 sunspots/year in magnitude. In addition, there is there is a slower, ∼80 year period, 10-50 variation in the sunspot number, that is commonly referred to as the "Gleissberg Cycle." Using a suite of contemporary and historical observations we will illustrate these elements of our star's episodic behavior and present a hypothesis that may provide a consistent physical link between the observed "climatic," "decadal," and "seasonal" magnetic variation of our star. [ABSTRACT FROM AUTHOR]

We aimed to compare the accuracy and reliability of two segmentation tools for magnetic resonance (MR) volumetry (FreeSurfer and Neurophet AQUA) at two magnetic field strengths (1.5T and 3T). We included 101 patients for the 1.5T–3T dataset and 112 for the 3T–3T dataset from three hospitals and five open-source datasets. The mean volume difference and average volume difference percentage with the change in magnetic field strength were compared between the methods. The hippocampus volume was larger with FreeSurfer than the Neurophet AQUA. In most brain regions, the Neurophet AQUA yielded a smaller average volume difference percentage (all < 10%) than FreeSurfer (all > 10%). The Neurophet AQUA exhibited more stable connectivity and regularity of the segmented components. Regarding volume, the Neurophet AQUA had effect sizes and ICCs comparable to those of FreeSurfer across the magnetic field strengths. With FreeSurfer, the original volume difference was small, whereas the average volume difference percentage was small with the Neurophet AQUA. Image segmentation took 1 h with FreeSurfer and 5 min with the Neurophet AQUA. When choosing an automatic segmentation method, the differences in image processing time and volume variability due to changes in the magnetic field strength of these methods should be considered. [ABSTRACT FROM AUTHOR]

We have developed a 3-D forward modeling method for the magnetometric resistivity (MMR) technique, specially focusing on the marine MMR method, which utilizes a vertical bipole source and seafloor receivers to measure magnetic field variations. The bipole source generates an artificial electric current between two electrodes: one on the sea surface and another on the seafloor. When computing the electric potential using the relaxation method, while conserving electric current, singularities arise at the electrode locations. To address this issue, we introduce two electrical resistivity structures to mitigate the effects of these singularities and to obtain magnetic field anomalies caused by arbitrary 3-D electrical resistivity anomalies beneath the seafloor. By determining the sign of the magnetic field anomaly, we can infer whether the electrical resistivity of the anomalous body is more conductive or more resistive compared to the surrounding oceanic crust. Furthermore, we demonstrate that increasing the number of bipole sources is more effective in exploring anomalous bodies than increasing the number of receivers. [ABSTRACT FROM AUTHOR]

We have developed replicate paleomagnetic secular variation (PSV) records for MIS 6–7 (130–244 ka) from IODP Ex. 3 23 Sites 1,343, 1,344, and 1,345 (Bering Sea). We can correlate the PSV at all three sites and identify 90 inclination features and 64 declination features. We have developed relative paleointensity records for all three sites by normalizing the demagnetized natural remanence to magnetic susceptibility. Paleointensity highs/lows can be tied to the PISO‐1500 global oxygen‐isotope‐dated paleointensity record. This provides a significant increase in chronostratigraphic resolution for these sites. Only one excursion is recorded in the MIS 6–7 sediments of the Bering Sea—the Iceland Basin Excursion (∼196 ± 3 ka). Replicate records of the inclinations and declinations both flip quickly to reversed polarity directions, stay there for several hundred years and then flip quickly back to normal polarity directions. However, the inclination flips occur without significant declinations changes and visa versa. A statistical PSV study was carried out by averaging the data in 3 ky and 9 ky windows. There is a distinctive bimodal pattern to the angular dispersions with most time spent with low angular dispersion values (∼10°–15°), but there is an interval of more than 30 ky (185–220 ka) with angular dispersions averaging two to three times higher amplitudes (∼25°–35°). This interval also has low paleointensities and the Iceland Basin Excursion. This same, coupled pattern of high angular dispersion, low paleointensity, and excursions is noted synchronously in the central North Atlantic Ocean and may indicate a global pattern to the geomagnetic field. Plain Language Summary: We have developed records of the Earth's paleomagnetic field variation for the interval 130,000–244,000 years ago recorded in deep‐sea sediments deposited in the Bering Sea. We recovered these sediment records as part of the Integrated Ocean Drilling Program Expedition 323. We can date the ages of these sediments by comparing the pattern of microfossil variations and magnetic field intensity variations with other dated deep‐sea sediment records from around the world. We find evidence for one short (several hundred year) interval with directions that point far from the North Pole. This is termed the Iceland Basin Excursion. We have measured the long‐term variability in secular variation as part of this study. We find that the field directions normally vary by 10°–15° over a few thousand years. But, there is an interval of about 30,000 years surrounding the Iceland Basin Excursion where the field directions vary by three times greater than normal (25°–35°) and have lower than average field intensity values. We think this interval of weak field intensity, an excursion, and high variability in directions occurs elsewhere in the World at the same time and indicates an unusual interval of global magnetic field variability. Key Points: we develop replicate long paleomagnetic secular variation records from the Bering SeaWe have replicate records of the Iceland Basin Excursion. It is very unusual in its directional pattern of variabilityWe find a long ∼30ky interval of anomalously high‐amplitude directional variability and low paleointensity [ABSTRACT FROM AUTHOR]

The article examines the properties of a statistical functional constructed from a set of measurements of the H-component of magnetic field measurements. A set of quasilinear objects with very similar parameters has been identified. Based on the hypothesis of the correspondence of these structures to seismic processes, authors estimate the characteristic time intervals for the phases of increase and decrease in the level of compression of lithospheric plates in probable preparation zones for impending earthquakes. It is shown that the statistical approach in geophysical problems can be used to assess seismic hazard in a given region in near real time. [ABSTRACT FROM AUTHOR]

The disturbances of the geomagnetic field in the surface atmosphere were considered during a series of strong earthquakes that occurred on April 2–3, 2024, in the vicinity of the island of Taiwan. The data from the Mikhnevo Geophysical Observatory of the Sadovskii Institute of Geosphere Dynamics, Russian Academy of Sciences, and the observatories of the international INTERMAGNET network were analyzed. It was shown that in the absence of sole-related global disturbances of the Earth's magnetic field, earthquakes were accompanied by geomagnetic variations with a maximum amplitude of ~10 nT and a total duration of about four hours. The delay time of the magnetic effect relative to the main shock of the first earthquake was ~60 min. The ionospheric effect of the event considered was established in the form of variations in the critical frequency of the F2 layer of the ionosphere on the basis the ionograms of height–frequency sounding obtained at the Okinawa ionospheric monitoring station and freely available on the website of the Japanese National Institute of Information and Communication Technologies. [ABSTRACT FROM AUTHOR]

Geomagnetic field data from six magnetic observatories in and adjacent to the South Atlantic Anomaly were individually analysed to detect abrupt secular variation changes occurring on timescales of less than a year and to explore any correlation with the evolution of the South Atlantic Anomaly. After applying external field corrections by means of the CHAOS-7 model, 12-month differences of the respective observatory monthly mean of the eastward component Y revealed evidence of several geomagnetic jerks with varying amplitudes during the period 2000–2020. These observations were compared to the CHAOS-7 spherical harmonic model and previous studies of the South Atlantic Anomaly's evolution. It emerged from this study that global field models like CHAOS are not very effective in identifying rapid localized changes in the geomagnetic field, highlighting the importance of using observatory data in conjunction with satellite data when studying geomagnetic jerks. [ABSTRACT FROM AUTHOR]

The ratio of the magnetic power spectrum and the secular variation spectrum measured at the Earth's surface provides a timescale |$\tau _{\rm sv}(l)$| as a function of spherical harmonic degree l. |$\tau _{\rm sv}$| is often assumed to be representative of timescales related to the dynamo inside the outer core and its scaling with l is debated. To assess the validity of this surmise and to study the time variation of the geomagnetic field |$\dot{\boldsymbol {B}}$| inside the outer core, we introduce a magnetic timescale spectrum |$\tau (l,r)$| that is valid for all radius r above the inner core and reduces to the usual |$\tau _{\rm sv}$| at and above the core–mantle boundary (CMB). We study |$\tau$| in a numerical geodynamo model. At the CMB, we find that |$\tau \sim l^{-1}$| is valid at both the large and small scales, in agreement with previous numerical studies on |$\tau _{\rm sv}$|⁠. Just below the CMB, the scaling undergoes a sharp transition at small l. Consequently, in the interior of the outer core, |$\tau$| exhibits different scaling at the large and small scales, specifically, the scaling of |$\tau$| becomes shallower than |$l^{-1}$| at small l. We find that this transition at the large scales stems from the fact that the horizontal components of the magnetic field evolve faster than the radial component in the interior. In contrast, the magnetic field at the CMB must match onto a potential field, hence the dynamics of the radial and horizontal magnetic fields are tied together. The upshot is |$\tau _{\rm sv}$| becomes unreliable in estimating timescales inside the outer core. Another question concerning |$\tau$| is whether an argument based on the frozen-flux hypothesis can be used to explain its scaling. To investigate this, we analyse the induction equation in the spectral space. We find that away from both boundaries, the magnetic diffusion term is negligible in the power spectrum of |$\dot{\boldsymbol {B}}$|⁠. However, |$\dot{\boldsymbol {B}}$| is controlled by the radial derivative in the induction term, thus invalidating the frozen-flux argument. Near the CMB, magnetic diffusion starts to affect |$\dot{\boldsymbol {B}}$| rendering the frozen-flux hypothesis inapplicable. We also examine the effects of different velocity boundary conditions and find that the above results apply for both no-slip and stress-free conditions at the CMB. [ABSTRACT FROM AUTHOR]

Structural safety performance is intricately tied to the stress level of rebars. The force-magnetic coupling relationship of rebar is a current focal point. Research gaps exist in the influence pattern of the appearance and shape of rebars on the mechanical and magnetic properties. This study conducted axial tensile failure tests on HRB400 ribbed rebars and HPB300 round rebars with different diameters. Variations in mechanical and magnetic indices were monitored and recorded to analyze the force-magnetic coupling effect in rebars. Results reveal that, concerning mechanical properties, increasing rebar diameter led to higher yield and ultimate strains, resulting in increased ultimate deformation. Ribbed rebars with a bumpy cross section differed from the smooth cross section of round rebars, leading to variations in the curves of tensile elongation percentage (l) versus section reduction percentage (r) for different rebar types. Regarding magnetic properties, the self-magnetic flux leakage (SMFL) intensity of ribbed rebar surpassed that of round rebar. SMFL curves in the elastic-plastic articulation stage exhibited contrast wave peaks, with rebar diameter positively correlating with the fluctuation range. Variations in leakage gradient curves indicated a stronger force-magnetic coupling relationship in the elastic and yielding stages and a weaker relationship in the strengthening stage. This research establishes the groundwork for nondestructive testing of rebar stress and enhances understanding of force-magnetic coupling in different rebar types. [ABSTRACT FROM AUTHOR]

The Geomagnetism Group at the National Centers for Environmental Information (NCEI), in collaboration with the Cooperative Institute for Research in Environmental Sciences (CIRES), along with various government and industry partners, specializes in developing and providing access to Earth's internal magnetic field models. These models are crucial for applications such as compass navigation and wellbore positioning, offering reference values for the geomagnetic field (total field, dip or inclination, and declination) at any location across the Earth. This study assesses the Weimer geomagnetic perturbation model, proposed by Weimer in 2013, which is an empirical model of magnetic field variations at high latitudes driven by solar wind measurements, as a candidate for capturing geomagnetic field variations in high‐latitude areas. We compare the geomagnetic field variations predicted by the Weimer model against data from the INTERMAGNET and SuperMAG observatory networks. Our findings indicate that the Weimer model achieves a reduction in the standard deviations of high‐latitude magnetic field variations by approximately 20%–30% once quiet‐time baselines are removed from the data set. Furthermore, we compare the performance of the Weimer model against the Space Weather Modeling Framework's Geospace model during specific geomagnetic storms in 2017 and 2018, and we find that the Weimer model is more effective in predicting magnetic variations at high latitudes than the Geospace model during these storms. Additionally, comparisons to magnetometer data collected from high‐latitude directional‐drilling operations align with the trends observed in comparisons with INTERMAGNET and SuperMAG observatory data, confirming the Weimer model's reliability and effectiveness for such applications. Plain Language Summary: The Geomagnetism Group at the National Centers for Environmental Information (NCEI), in collaboration with the Cooperative Institute for Research in Environmental Sciences (CIRES), along with various government and industry partners, develops geomagnetic models that are used for navigation and oil drilling applications. At high latitudes, geomagnetic variations caused by the interaction between the solar wind and the Earth's magnetic field increases uncertainty in the models. This study assesses the Weimer geomagnetic perturbation model as a candidate to compensate for these geomagnetic variations. We compare the model to scientific ground observatories, and show that the model captures 20%–30% of the variation. We also demonstrate that the model is useful in applied setting by comparing the model to data collected from oil drilling operations. Key Points: The Weimer Geomagnetic Perturbation Model is evaluated for real‐time prediction of geomagnetic disturbances at high latitudesThe Weimer model reduces geomagnetic reference errors at high latitudes by 20%–30% based on comparisons to observatory dataMeasurement‐while‐drilling data show that the Weimer model can save valuable rig time by reducing geomagnetic reference model errors [ABSTRACT FROM AUTHOR]

In this article, we report a novel pressure sensing method based on the Hall effect and a hard magnet magnetorheological elastomer (hmMRE). The elastic property of the MRE under pressure was used to generate spatial variation in the magnetic flux density around the MRE, and the variation was detected by the Hall effect device underneath. As the first development in this kind of pressure sensing mechanism, we conducted research for the following three purposes: (1) to verify the Hall effect on the output signal, (2) to understand the sensor output variations under different modes of operation, and (3) to utilize the mechanism as a pressure sensor. We characterized the sensor with its operation parameters, such as signal polarity switching depending on wiring directions, signal amplitude, and offset shift depending on the input voltage. Based on the analyses, we concluded that the Hall voltage represents the pressure applied on the hmMRE, and the new pressure sensing mechanism was devised successfully. [ABSTRACT FROM AUTHOR]

The generation of cosmic ray particles with ultra‐relativistic energies is a crucial issue in astrophysical and space physics. Shocks have been acknowledged as efficient accelerators in the universe which can produce energetic particles through a variety of mechanisms, such as diffusive shock acceleration (DSA), shock surfing acceleration (SSA) and shock drift acceleration (SDA). Using the data set obtained by the Magnetospheric Multiscale mission, we report an unusually sharp enhancement of energetic electron flux in the upstream region of Earth's bow shock, associated with a bipolar variation of the interplanetary magnetic field. To explain these observations, we propose a two‐step acceleration scenario where electrons trapped in a flux rope (FR) first undergo head‐on collisions and are further accelerated by FR contraction as the FR crosses the shock. Such a scenario can well explain the spacecraft observations. This work can improve our understanding of particle acceleration processes at shocks. Plain Language Summary: The cosmic ray comprises ions and electrons with energies up to 1,020 eV and thus its generation mechanism is an important issue. A conventional theory known as diffusive shock acceleration is a promising candidate but it needs seed electrons with sufficient initial energies. How these electrons are generated is still unclear. In this study, we report an unusually sharp enhancement of energetic electron flux with a large variation of magnetic field direction in the upstream region of Earth's bow shock, and propose a two‐step acceleration scenario to explain the spacecraft measurements. Electrons first gain energies from the head‐on collisions with the bow shock, and then bounce between the two ends of a circular magnetic field of shrinkage, analogous to a ball reflecting between two converging walls. This scenario has been mathematically confirmed and shows good agreement with the spacecraft measurements. Key Points: Efficient electron acceleration is observed when a flux rope collides with the Earth's bow shockElectrons trapped in the flux rope are successively accelerated by the head‐on reflection at shock front and the flux rope contractionThis two‐step acceleration scenario is mathematically reproduced and fit the spacecraft observations well [ABSTRACT FROM AUTHOR]

Regional magnetic data in the southeastern segment of the Nigerian Niger Delta were evaluated with the aim of mapping deep-seated tectonic elements. Enhanced filtering operations and 3D forward modelling were applied on the magnetic data. These geologic features triggered the formation of rollover anticlines and faults that serve as structural traps in the study area. The filtered residual magnetic data revealed geologic structures characterized with NE -- SW, N -- S, and E -- W orientations. The 3-D models detected the faulted crustal blocks, gradient zones, and intra-basement compositional magnetic variations. Furthermore, some prominent horst and graben structures as well as related normal faults characterized with distinct magnetic signatures were observed. Faults of base magnetic (of various compositions) were observed to be the fabricating mechanisms of the magnetic anomalies. Collectively, these structures influenced the patterns of magnetic anomalies with direct effects on the hydrocarbon trapping systems, as well as the pathways and accumulation zones for hydrothermal minerals. On the whole, the interpreted results revealed that the basement surface is rippling. Additionally, the depth result showed sedimentary thicknesses that ranged from 4-10 km. Again, the estimated crustal thickness varied from 14 to 19 km. This study has displayed the capabilities of the magnetic method in mapping the depth and configuration of basement rocks, which are crucial in controlling the formation of structural traps. Identifying these basement structures early helps in understanding the overall geological framework and potential hydrocarbon systems. [ABSTRACT FROM AUTHOR]

The effect of plastic deformation on the structure, phase composition, and magnetic parameters of maraging steel 08Kh15N5D2T was studied. The hysteresis, electromagnetic, and magnetostrictive characteristics were measured both in a closed magnetic circuit using the Remagraph C-500 hysteresis graph and by means of attached magnetic transducers. The regions of plastic deformation are experimentally determined in which the behavior of the magnetic parameters and their relationship vary with changes in structure and phase composition. Informative parameters are proposed that can be used to control variations in the structure and phase composition of the studied steel. [ABSTRACT FROM AUTHOR]

How to induce magnetism for two-dimensional materials has always been a focus of research in nanomaterials science. In this work, employing density functional theory, we investigated the structural stability and electronic-magnetic properties of antimonene-phosphorene (SbP) nanoribbons doped with B, C, N, and O atoms. Additionally, we investigated the effects of vacancy defects along with impurity atoms doping on antimonene-phosphorene nanoribbons. Our analysis revealed that all doped and defected structures displayed robust structural stability, as evidenced by negative binding and formation energies. It was found that the substitution of impurity atoms in either P or Sb positions of the SbP nanoribbon leads to different behaviors, and only the SbP nanoribbons doped with C atom in P position and doped with O atom in Sb position show magnetic properties. Moreover, we observed that the magnetic properties of vacancy structures doped with impurity atoms varied based on the number of doping atoms in P or Sb positions. For instance, spin polarization behavior can be realized in P-vacancy nanoribbons doped with one and two N atoms, and the magnetic moment variations in Sb-vacancy nanoribbon doped with N atoms are nearly three times greater than those of the P-vacancy nanoribbon. Furthermore, the effects of the transverse electric field have also been calculated, and we found that applying an electric field to the system can reduce the band gap and modulate the magnetic moment. Intriguingly, we observed negative differential resistance behavior and an 80% spin filtering effect in antimonene-phosphorene nanoribbons with a phosphorus vacancy. Overall, these findings offer new insights into designing next-generation nano spintronic devices within antimonene-phosphorene nanoribbons. [ABSTRACT FROM AUTHOR]

The study of the physical properties of the topside ionosphere is fundamental to investigating the energy balance of the ionosphere and developing accurate models to predict relevant phenomena, which are often at the root of Space Weather effects in the near-Earth environment. One of the most important physical parameters characterising the ionospheric medium is electrical conductivity, which is crucial for the onset and amplification of ionospheric currents and for calculating the power density dissipated by such currents. We characterise, for the first time, electrical conductivity in the direction perpendicular to the geomagnetic field, namely Pedersen and Hall conductivities, in the topside ionosphere at an altitude of about 450 km. For this purpose, we use eight years of in situ simultaneous measurements of electron density, electron temperature and geomagnetic field strength acquired by the Swarm A satellite. We present global statistical maps of perpendicular electrical conductivity and study their variations depending on magnetic latitude and local time, seasons, and solar activity. Our findings indicate that the most prominent features of perpendicular electrical conductivity are located at low latitudes and are probably driven by the complex dynamics of the Equatorial Ionisation Anomaly. At higher latitudes, perpendicular conductivity is a few orders of magnitude lower than that at low latitudes. Nevertheless, conductivity features are modulated by solar activity and seasonal variations at all latitudes. [ABSTRACT FROM AUTHOR]

The motor parameters of permanent magnet synchronous motor (PMSM) can be mismatched in operation due to temperature variations and magnetic saturation. The parameter mismatch leads to a significant decrease in the robustness of traditional deadbeat predictive current control (DPCC), which leads to issues such as current static error and motor vibration noise. In this paper, a model-free predictive current control (MFPCC) method based on an improved sliding mode disturbance observer (SMDO) was proposed. The method estimated the total disturbance of the system using the improved SMDO, which could effectively suppress sliding mode chattering and accelerate the convergence speed of current errors. Subsequently, the predicted control voltage was calculated using a hyper-local model and compensated for the time delay. The experimental results demonstrated that the improved MFPCC-SMDO method generated lower motor noise compared to the traditional DPCC method when the controller's inductance parameters are mismatched. [ABSTRACT FROM AUTHOR]

Copyright of Acta Scientiarum Naturalium Universitatis Pekinensis is the property of Editorial Office of Acta Scientiarum Naturalium Universitatis Pekinensis and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, we present the results of an analysis of the morphological features of Equatorial Plasma Bubbles (EPBs) over South America. In this context, we analyzed data from the Disturbance Ionosphere indeX (DIX) maps calculated using around 450 Global Navigation Satellite System (GNSS) stations. To mitigate the influence of magnetic disturbances on bubble development, only data from geomagnetically quiet days were utilized. This study covered the period from the post‐peak of solar cycle 24 (2015) to the pre‐peak of solar cycle 25 (2023), totaling 1321 nights with EPB occurrences, representing the largest data set of EPBs ever compiled for South America. Our analysis unveiled several key findings regarding EPBs and their behavior over the South American region. First, we observed that the amplitude of plasma depletions, as reflected in the DIX values, and the EPB latitudinal development follow an approximately 11‐year cycle driven by solar radiation levels. Furthermore, our analysis highlights the significant influence of factors such as the angle between the solar terminator and the magnetic meridian (T‐M angle), which varies inversely with the vertical plasma drift velocity during the pre‐reversal enhancement (PRE). Additionally, we discuss the longitudinal variations associated with magnetic declination, as well as the saturation behavior of EPB development with extreme solar flux. Key Points: EPBs exhibit a cycle linked with solar flux, impacting depletion amplitudes and latitudinal development according to magnetic declinationDuring geomagnetically quiet periods, EPB development saturates with high solar flux valuesSignificant longitudinal variations in EPB development can be primarily attributed to the influence of the South America Magnetic Anomaly [ABSTRACT FROM AUTHOR]

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Himalayas are a region of geomagnetic importance, as they impact the geomagnetic field of Earth and space weather, as it is one of the largest mountain belts in the world. Due to its huge mass, it may influence the dynamics of the Earth's core, the primary source of the geomagnetic field. In Indian longitudes, the mean location of the solar quiet (Sq) focus lies in latitudes closer to the Hanle region. Therefore, monitoring the magnetic field in the Hanle region is important. Ideally, a zero magnetic gradient or low magnetic gradient of the order of a few nT/m or less is preferred; this low gradient helps reduce the effects of local magnetic variations. Hence, to establish a continuous geomagnetic observation setup, a magnetic survey was conducted at Hanle, Ladakh, to identify the location of the low magnetic gradient. From the magnetic survey, the eastern part of the selected hillock was identified that has the least magnetic gradient. After checking other logistics, the chosen site is suitable for setting magnetic field observations. The proposed magnetic observatory at Hanle will be useful for studies related to unusual space weather phenomena, such as the citing of Auroras (of 22–23 April 2023 and 10–11 May 2024) in the Ladakh region, geomagnetic field monitoring in low-mid transitional regions, or magnetic exploration. [ABSTRACT FROM AUTHOR]

Worldwide, Quaternary loess-paleosol sequences archive terrestrial paleoenvironmental information. The Palouse loess in the northwestern USA is one such deposit representing at least a million years of sediment accumulation. Loess paleosol sequences are often studied via the magnetic susceptibility of sediments and the changes in susceptibility with depth. However, since variations in magnetic susceptibility can have different underlying causes, the interpretation of the magnetic susceptibility of loess depends on factors specific to each major loess region. We measured the magnetic susceptibility of sediments along depth profiles in a well-studied exposure of the Palouse loess in eastern Washington, USA (the "CLY-2 site," 46.3131° N, 118.4874° W, WGS84). Our measurements show that the magnetic susceptibility of sediments in the Palouse loess varies systematically and predictably with depth and can be correlated with other magnetic susceptibility profiles at the outcrop scale and at the regional scale. We also measured changes in grain size, elemental abundance, mineralogy, and other magnetic properties to determine the most likely cause of the magnetic susceptibility signal. Based on these results, variations in magnetic susceptibility in the Palouse are likely driven mostly by changes in coarse sediment supply and accumulation of tephra rather than changes in weathering. Magnetic susceptibility is useful as an inexpensive, non-destructive tool for stratigraphic correlation of Quaternary loess deposits in the Palouse, especially in combination with paleosol stratigraphic markers and known tephra deposits. [ABSTRACT FROM AUTHOR]

Magnetism in Croatian caves has been significantly underexplored, despite the well-documented preservation of cave sediments. This study investigates whether magnetic susceptibility can be effectively recorded in Croatian caves and, if so, whether there are differences between in situ and laboratory measurements, as well as the extent of these differences. The focus is on two prominent sites within the Velebit Mountain range of the Dinaric Karst: the deep Slovačka Cave and the extensive Crnopac Cave System (ex. Kita Gaćešina Cave). Magnetic susceptibility was measured in soft sediments using the Kappameter KM-7 for in situ assessments and the Bartington MS2B System for laboratory analyses. The comparison of the two devices aimed to evaluate the feasibility of detecting magnetic susceptibility variations within carbonate sediments. Sampling locations were selected based on preliminary assessments of magnetic susceptibility variations and accessibility for sampling. Characteristic samples from each profile underwent X-ray powder diffraction analysis. Results revealed significant variations in magnetic susceptibility across each profile under both in situ and laboratory conditions. In situ measurements ranged from −45 × 10−5 SI to 120 × 10−5 SI, while laboratory measurements ranged from 4.00 × 10−5 SI to 99.40 × 10−5 SI. The portable Kappameter KM-7 provided satisfactory results for preliminary investigations, while the Bartington MS2B System demonstrated high precision in analyzing these variations in detail. These findings support the potential for further investigations into magnetic susceptibility in karst cave environments, with an emphasis on understanding depositional history and the timeline of climate and tectonic changes. [ABSTRACT FROM AUTHOR]

In this study, we consider historical geomagnetic satellite data obtained during a strong magnetic storm on March 8−9, 1970. In addition to the data of the Soviet satellite Kosmos-321, data from the American satellite OGO-6, which performed geomagnetic measurements at the same time, were used. We analyzed time variations of external magnetic fields recorded in satellite and ground-based observations of the magnetic field. The research also gave impetus to the creation of the improved software implementation of the auroral oval model APM, which enables reconstruction of its position and precipitation intensity in both the past and near real time. The magnetic variations originating in the near-Earth space from various sources were identified. In particular, we revealed the signatures of the storm-time ring current and equatorial and auroral electrojects. The paper highlights the enduring value of historical data of magnetic field observations stored in data centers and continuously digitized by their staff. [ABSTRACT FROM AUTHOR]

Some rock and soil samples exhibit significant loss of magnetic susceptibility (χ) with increasing applied field amplitude even at relatively low (10–100s of A/m) fields, a behavior which remains unexplained. Exceptionally strong negative field‐dependence of susceptibility (χHD) is present in sandstones and altered intermediate‐felsic igneous rocks in several cores from the northeastern Oklahoma subsurface. These same rocks also show elevated frequency‐dependence of susceptibility (χFD), with reasonable correlation of χHD to χFD, and frequency‐dependent χHD. Results from multiple characterization methods indicate that strongly negative χHD in these rocks is linked to a yet‐unidentified phase which begins the approach to magnetic saturation in low fields (<1 mT/800 A/m), shows elevated χFD to low temperatures, is unstable at high temperatures, possesses significant anisotropy of magnetic susceptibility, and becomes paramagnetic above ∼83°C. Clear associations with fluid alteration features indicate that this material may be highly relevant to rock alteration, diagenetic, and environmental studies. Plain Language Summary: Magnetic susceptibility is usually measured using weak magnetic fields, and in many geological materials the value depends on the strength of the field used. In the low‐field range, this usually results in slightly higher susceptibility values as field strength increases. In some rocks and soils, however, susceptibility decreases with increasing applied field, which has not been explained. The lowermost sandstones and uppermost igneous rocks in the northeastern Oklahoma subsurface have been found to provide prominent examples of this "negative field‐dependence" of susceptibility. When susceptibility of the same rocks is measured using an alternating‐current field, the results are also highly dependent on the frequency of that field. The strength of these behaviors is correlated, and both are found to be associated with a yet‐unidentified magnetization carrier with an apparent Curie temperature of ∼83°C. Through direct‐current measurements, it is apparent that the negative field‐dependence is due to this mineral approaching magnetic saturation at unusually low fields relative to most natural materials. The magnetic behavior is associated with other evidence of water‐rock interaction, which may prove to be a useful indicator of chemical conditions of alteration, diagenesis, and weathering. Key Points: Negative field‐dependence of magnetic susceptibility is poorly understood and occurs in rocks near the basement unconformity of NE OklahomaThis behavior is due to low‐field magnetic saturation of an unknown magnetic carrier with a magnetic ordering temperature near 80°CThe carrier is associated with frequency‐dependence of susceptibility and fluid alteration and may complicate environmental studies [ABSTRACT FROM AUTHOR]

SUMMARY: The geocentric axial dipole (GAD) hypothesis is key to many palaeomagnetic applications, for example plate-tectonic reconstructions; however, the validity of this hypothesis at high latitudes is not fully resolved. To address this, in this paper we determined the palaeomagnetic directional data of 156 lava units in Eyjafjarðardalur, Iceland, with the aim of determining the validity of the GAD hypothesis at high latitudes using time-averaged field (TAF) analysis. In addition to the palaeomagnetic directional data, we constructed an age model for the sequences using new 40Ar/39Ar dates, magnetostratigraphy and field data. The sequence age range is 2.6–8.0 Ma. We show that the mean virtual geomagnetic pole (VGP) for our data does not agree with the GAD theory at 95 per cent confidence, when only the standard tilt and tectonic corrections are made; however, when inclination-shallowing processes are accounted for, for example thermoremanence (TRM) anisotropy and refraction effects, the mean VGP can align with GAD at 95 per cent confidence. These inclination-shallowing processes are shown to reduce the inclination by up to 14° for some of the basaltic units. Applying the inclination-shallowing correction also reduces VGP dispersion to levels that agree with global model predictions. We propose that much of the scatter within the palaeomagnetic directional databases are due to inclination-shallowing process effects, which become more important as the natural remanent magnetization (NRM) intensity is high, for example >2 A m−1. We propose that inclination-shallowing processes can be identified and corrected for by examining the NRM intensity and dispersion. [ABSTRACT FROM AUTHOR]

As a new type of braking method, the eddy current brake (ECB) is nowadays widely applied in life and military. The ECB can generate the strong resistance by the magnetic field, and obtaining the accurate magnetic induction distribution is essential in the ECB modeling. This paper proposes an analytical model of a cylinder ECB used in the artillery that operates under the intense impact load. This model takes the axial edge effects into consideration in both static and dynamic conditions. Firstly, this paper introduces the structure and working principle of this ECB. Secondly, a multilayer theory with virtual region is proposed to calculate the magnetic induction distribution considering the end effect. Thirdly, Finite Element Method (FEM) model is established to describe the spatial variation of the magnetic field in different conditions. Finally, the analytical model is compared with the FEM model to prove its validity and predict the working characteristic of the ECB under the intense impact load, the max recoil displacement and speed range both meet design and work requirements. [ABSTRACT FROM AUTHOR]

Paleomagnetic analyses have suggested that the lunar magnetic field underwent a significant change from 4.25 to 3.19 Ga, indicating the rapid transition of the lunar dynamo mechanism. We used the van der Pauw (vdP) method to measure the electrical resistivity of Fe‐S‐P alloys under conditions relevant to the lunar core and estimated the thermal conductivity of the Fe‐S‐P lunar core. These values were incorporated into thermal and dynamo models to investigate the evolution of the lunar core. Our model indicates that the inner core began to grow as early as 4.35 Ga, the solidification regime switched at 3.50 Ga, and the thermal dynamo ceased between 3.78 and 3.51 Ga. The cessation of the dynamo could be due to a low buoyancy flux and insufficient entropy dissipation. Thermal and compositional dynamos cannot sustain the ancient strength of the Moon's magnetic field, and require other energy sources. Plain Language Summary: The transport properties of planetary core materials dominate heat transfer through thermal convection, which is closely linked to the geodynamo of the planetary core. The van der Pauw (vdP) method was used to measure the electrical resistivity of Fe‐S‐P alloy, and we assessed the effects of pressure, temperature, and light elements (sulfur and phosphorus) on the electrical resistivity of these alloys. We estimated the thermal conductivity of the Fe‐S‐P lunar core and modeled the growth of the lunar core. We found that the inner core nucleated at 4.35 Ga in the center and then solidified at the core‐mantle boundary (CMB) at 3.50 Ga. The adiabatic heat conduction at the lunar CMB indicated that a thermally driven dynamo persisted until 3.78–3.51 Ga in the Moon's history. We discuss the cessation of the lunar core dynamo in relation to the buoyancy flux, entropy, Reynolds number and Elsasser number and explain the variation in the magnetic field in conjunction with the previous dynamo mechanism. Key Points: The electrical resistivity and thermal conductivity of Fe‐S‐P alloys were determined at 3 and 5 GPaA low thermal conductivity Fe‐S‐P core nucleated earlier and the bottom‐up growth regime switched to a top‐down regime at 3.50 GaMultiple dynamo mechanisms worked together to generate a high magnetic field, low buoyancy flux and entropy dissipation causing the dynamo to cease [ABSTRACT FROM AUTHOR]

The corrosion damage of rebars is a leading cause of structural failure in reinforced concrete structures. Timely detection and evaluation of corrosion damage are crucial for ensuring structural safety. The self-magnetic flux leakage (SMFL) technology is often used due to its unique advantages in detecting corrosion damage of rebars. However, challenges persist in theoretically characterizing corrosion damage and exploring influencing factors. Therefore, the magnetic dipole theory model coupled with multiple-shaped defects is proposed and the influence of corrosion expansion force on the detection of corrosion damage is analyzed. The results show that the standard deviation of the magnetic field intensity induced by corrosion varied by up to 833%, while that induced by corrosion expansion force did not exceed 10%. So the changes in the SMFL field induced by corrosion damage play the dominant role and the influence of corrosion expansion force can be ignored. In addition, corrosion damage experiments on reinforced concrete based on the SMFL technology were conducted. The results indicate that the SFML curves of rebars change monotonically with the increasing corrosion degree. Significant variations in the curves correspond well with the locations of severe corrosion on the rebars. There is a positive relationship between the proposed magnetic parameters and the corrosion degree of the rebars. Furthermore, a corrosion damage evaluation model considering multiple parameters is developed to predict the corrosion degree of rebars. The prediction results demonstrate high accuracy, with an average absolute error of only 8.33%, which is within 10%. [ABSTRACT FROM AUTHOR]

The aim of this work is to optimize the sensor positions of a sensor–actuator measurement system for identifying local variations in the magnetic permeability of cut steel sheets. Before solving the actual identification problem, i.e., finding the material distribution, the sensor placement of the measurement setup should be improved in order to reduce the uncertainty of the identification of the material distribution. The Fisher information matrix (FIM), which allows one to quantify the amount of information that the measurements carry about the unknown parameters, is used as the main metric for the objective function of this design optimization. The forward problem is solved by the finite element method. The results show that the proposed method is able to find optimal sensor positions as well as the minimum number of sensors to achieve a desired maximum parameter uncertainty. [ABSTRACT FROM AUTHOR]

Electrochemical machining has shown advantages over conventional processing for difficult-to-process materials. In this study, electrochemical machining methods were applied to the surface treatment of 2Cr13 stainless steel. Magnetic field assistance was employed for the experiments and the variations in magnetic induction intensity were taken into consideration. The surface roughness of machined samples was detected and the surface morphology was observed. The results showed that electrochemical machining was an effective treatment for surface roughness reduction. After the introduction of a magnetic field of 200 mT, lower surface roughness was realized for the same machining time, which indicated that the magnetic field helped to promote the improvement of processing efficiency. Moreover, the processing efficiency was further enhanced with the increase of the magnetic induction intensity to 300 mT. In the regime of magnetic field-assisted electrochemical machining for 20 min, a high-precision surface with a roughness of 0.28 μm was achieved for 2Cr13 stainless steel. The simulation results demonstrated that the magnetic field increased the current density at the anode surface and accelerated electrochemical anodic dissolution. With the increase of the magnetic induction intensity, the current density reinforcement became significant. The enhancement mechanism of magnetic field-assisted electrochemical machining was revealed by employing the theory of magnetohydrodynamics. [ABSTRACT FROM AUTHOR]

This paper presents an experimental setup of magnetic field taper variations to optimize the efficiency of a Ka-band pulsed gyrotron. Experimental optimization of the gyrotron's efficiency is presented. The efficiency dependence on three input parameters—beam current, magnetic field amplitude, and variations in the magnetic field taper profile—is studied. A gyrotron electron efficiency improvement from 25.4% for a non-tapered magnetic curve to 36.4% for a tapered magnetic curve is measured. The stability of the millimeter wave excitation in the cavity is also affected by the magnetic taper gradient. The magnetic taper is obtained by a practical modification of the solenoid that leads to an 11% electron efficiency improvement. Magnetic tapering can be combined with other types of efficiency enhancement concepts to obtain an overall improved efficiency that can be important for industrial applications. [ABSTRACT FROM AUTHOR]

The FormoSat-7/Constellation Observing System for Meteorology, Ionosphere, and Climate II (FS7/COSMIC2) program has acquired over three hundred thousand equatorial plasma bubble (EPB) observations from 2019 to 2023 in the equatorial and near low-latitude regions. The huge FS7/COSMIC2 database offers an opportunity to perform statistical inspections of the proposed hypothesis on seasonal versus longitudinal variability of EPB occurrence rates relevant to the Rayleigh–Taylor (R-T) instability. The detected EPBs are distributed along the magnetic equator with a half width of ~20° in geomagnetic latitude. The obtained EPB occurrence rates in local time (LT) rose rapidly after sunsets, and could be deconstructed into two overlapped Gaussian distributions resembling a major peak around 23:00 LT and a minor peak around 20:20 LT. The two groups of Gaussian-distributed EPBs in LT were classified as first- and second-type EPBs, which could be caused by different mechanisms such as sporadic E (Es) instabilities and pre-reversal enhancement (PRE) fields. The obtained seasonal–longitudinal distributions of both types of EPBs presented two diffused traces of high occurrence rates, which happened near the days and longitudes when and where the angle between the two lines of magnetic declination and solar terminator at the magnetic equator was equal to zero. Finally, we analyzed the climatological and seasonal–longitudinal variability of EPB occurrences and compared the results with the physical R-T instability model controlled by Es instabilities and/or PRE fields. [ABSTRACT FROM AUTHOR]

On 18 June 2023, comprehensive observations were conducted to an altitude‐triggered lightning flash. Upward positive leader (UPL) and downward negative leader (DNL) in a bi‐directional development system were detected simultaneously by a high‐speed camera, together with the coordinated measurements of magnetic field and very‐high‐frequency (VHF) emissions. High‐speed images reveal, for the first time, the enhancement of the UPL's propagation speed by DNL in the bi‐directional leader system. Concretely, the upward positive leader initially originates from a suspended wire tip and propagates at a two dimensional (2D) speed of 5.32 × 104 m/s, and after about 6.3 ms, its propagation speed was enhanced to 1.12 × 105 m/s when the stepped DNL started advancing at an average speed of 1.44 × 105 m/s. Additionally, based on the evolution of channel luminosity and the variations of magnetic radiation, it is found that there is a consistency in luminosity variation between the ascending channel and the descending channel in the bi‐directional leader system, and the amplitude of the magnetic field increases when the negative discharges start at the bottom wire end with intensive VHF emissions. Those facts indicate that the DNL has an effect, may be a positive one, on the UPL's development in the early stage of altitude‐triggered lightning. Plain Language Summary: The proposal and verification of the bi‐directional leader development shed light on the understanding of lightning initiation and extension. However, the study on the initiation and propagation of bi‐directional leader is limited as a result of the destitution of close and detailed observations due to its random occurrence time and position. Therefore, the comprehensive observation on the discharges in the initial stage of the altitude‐triggered lightning through simultaneous optical images, and magnetic field and very‐high‐frequency emissions measurements at close range is of great value for distinctly clarifying the evolution of the bi‐directional leader's propagation manner and the associated electromagnetic radiation. In this paper, we analyzed the initiation process and propagation manner of the bi‐directional leader in an altitude‐triggered lightning flash using high‐speed imaging and concurrent measurements of the associated magnetic radiation. It aims to understand the initiation and propagation process of the bi‐directional leader and revealing the evolution of discharges in the early stage of the altitude‐triggered lightning. Key Points: Bi‐directional leader's initiation and propagation in altitude‐triggered lightning was documented by coordinated observationsPropagation speed of upward positive leader (UPL) is enhanced as fast as the DNL's propagation in the bi‐directional leader systemDownward negative leader has a possible positive effect on the UPL's development in the early stage of altitude‐triggered lightning [ABSTRACT FROM AUTHOR]

Magnetotelluric (MT) impedances from 62 sites in southern South Island of Aotearoa New Zealand have been used to model geomagnetically induced currents (GIC) in four transformers during two solar storms. Induced electric fields during the storms are calculated from the MT impedances using the magnetic fields measured at the Eyrewell (EYR) geomagnetic observatory, approximately 200 km north of the study area. Calculated GIC during the sudden storm commencements (SSC) give a generally good match to GIC measured by the network operator, Transpower New Zealand. Long period GIC (periods longer than about 10,000 s) are less well modeled. Calculations based on thin‐sheet modeling, which has restrictions on the shortest period of variation which can be modeled, perform less well for the GIC associated with SSC, but are equally good, if not better, at modeling longer period GIC. Consistent underestimation of large GIC at one transformer (HWBT4) near Dunedin are likely to be the result of uncertainty in the assumed values of line, transformer, and earthing resistances. The assumption of a spatially uniform magnetic field across the study area, which is implied by use of the magnetic field measured at EYR as a basis for calculation, may also lead to incorrect calculation of GIC. For one storm use of magnetic field data from a magnetometer within the study area leads to much improved modeling of the observed GIC. This study compares modeled and measured GIC using specifically measured MT impedance data. Plain Language Summary: Variations in the Earth's magnetic field during magnetic storms produce induced currents (geomagnetically induced currents–GIC) in the ground which can present a risk to electricity transmission networks. Long period magnetotelluric measurements made at 62 sites in southern South Island of Aotearoa New Zealand have been used to model GIC observed during two magnetic storms. It is found that large GIC occurring over short periods of time associated with the commencement of a storm can be well modeled. GIC occurring over longer periods are less well modeled. Uncertainty in values of resistances incorporated in the model of the transmission network are likely to be the reason why the size of GIC is consistently underestimated at some locations. The assumption that the magnetic field variations are uniform across the study area is also found to not always be valid. Key Points: Magnetotelluric impedances from 62 sites across southern South Island of Aotearoa New Zealand have been used to model geomagnetically induced currents (GIC) during two stormsCalculated GIC are compared to observed values at 4 transformers and GIC during sudden storm commencements are captured by MT‐based modelsQuantitative comparison between simulations confirms that consideration of spatial variations in the magnetic field is important [ABSTRACT FROM AUTHOR]

The rotor magnetic shunt structure hybrid excitation synchronous motor (RMS-HESM) has been widely used in marine propulsion due to its advantages of low loss and high efficiency. The objective of this paper is to improve the output torque capability of the hybrid excitation motor with a rotor magnetic shunt structure by conducting a multi-objective optimization design for the magnetic permeability structure. The first step involved establishing a mathematical analytical model of average torque and torque ripple based on the fundamental principle of motor magnetization. Next, the parameters of the magnetic permeability structure were designed and analyzed using the finite element simulation method. The impact of the variations in the parameters of the magnetic permeability structure on motor torque and no−load back electromotive force was examined. Additionally, a sensitivity analysis was performed on the design variables of the magnetic permeability structure, leading to the determination of optimization parameters based on the obtained results. The adaptive inertia weight-based particle swarm algorithm (PSO) was employed to conduct a multi-objective optimization design analysis. A comparative analysis on the average torque, torque ripple, and no−load back electromotive force of the motor before and after optimization was performed using the Maxwell and Workbench and Optislong joint simulation tools. This enhancement significantly improves the torque performance of the marine motor while simultaneously optimizing the no−load back electromotive force. [ABSTRACT FROM AUTHOR]

Localized dynamic pressure enhancements arising from kinetic processes are frequently observed downstream of the Earth's bow shock. These structures, called jets, modify their plasma surroundings and participate in particle energization. Here, we report the first observations of jet-like structures in a non-planetary shock environment: downstream of interplanetary shocks. We introduce an analysis approach suitable for such conditions and apply it to Wind spacecraft data. We present one event with a Mach number similar to the Earth's bow shock as a benchmark, as well as two low Mach number, low beta shocks: a parameter range that is difficult to access at planets. The jet-like structures we find are tens of ion inertial lengths in size, and some are observed further away from the shock than in a limited magnetosheath. We find that their properties are similar to those of magnetosheath jets: in the frame of the shock these structures are fast, cold, and most have no strong magnetic field variations. All three interplanetary shocks feature foreshock activity, but no strongly compressive waves. We discuss the implications, these findings have for the proposed jet formation mechanisms. [ABSTRACT FROM AUTHOR]

Ground magnetic field variations have been used to investigate ionospheric dynamics for more than a century. They are usually explained in terms of an electric circuit in the ionosphere driven by an electric field, but this is insufficient to explain how magnetic field disturbances are dynamically established. Here we explain and simulate how the ionosphere dynamically responds to magnetospheric forcing and how it leads to magnetic field deformation via Faraday's law. Our approach underscores the causal relationships, treating the magnetic field and velocity as primary variables (the B, v paradigm), whereas the electric field and current are derived, in contrast to the E, j paradigm commonly used in ionospheric physics. The simulation approach presented here could be used as an alternative to existing circuit‐based numerical models of magnetosphere‐ionosphere coupling. Plain Language Summary: Ground magnetic field variations have been used to investigate ionospheric dynamics for more than a century. They are usually explained in terms of an electric circuit in the ionosphere driven by an electric field; similar to how we would explain the magnetic field of a current‐carrying wire. However, this approach oversimplifies the complex reality in space plasmas. Here, the relationship between currents and magnetic fields is reversed: currents should be understood as a consequence of the magnetic field, and not the other way around. In this paper we explain and simulate how the ionosphere dynamically responds to forcing from above, and how it leads to magnetic field deformation that corresponds to an electrical current. Key Points: We present a model and simulation of how the magnetic field in the ionosphere dynamically changes in response to external forcingOur model emphasizes the causal relationships, treating B and v as primary instead of E and j, as is commonly done in ionospheric physicsSimulation results highlighting the self‐consistent ionospheric response in the B, v paradigm are presented [ABSTRACT FROM AUTHOR]

The generation of topological spin textures under ultrafast laser pulse excitations and field-free manipulation of topological transitions between different spin textures has attracted enormous interest from the perspective of spintronic applications. Here, we utilize ultrafast electron microscopy to showcase the femtosecond laser pulses excitation on magnetic materials and have generated multiple topological spin textures in an amorphous ferrimagnetic TbFeCo film. Furthermore, the following field-free topological transitions between skyrmions and bubbles with diversified topology are identified via in situ heating the sample in Lorentz transmission electron microscopy. The critical role of uniaxial anisotropy variation on changing the magnetic textures during the heating process is confirmed by micromagnetic simulations. Our results provide a perspective on the generation and transformation of topological spin textures. [ABSTRACT FROM AUTHOR]

Coils are one of the basic elements employed in devices. They are versatile, in terms of both design and manufacturing, according to the desired inductive specifications. An important characteristic of coils is their bidirectional action; they can both produce and sense magnetic fields. Referring to sensing, coils have the unique property to inductively translate the temporal variation of magnetic flux into an AC voltage signal. Due to this property, they are massively used in many areas of science and engineering; among other disciplines, coils are employed in physics/materials science, geophysics, industry, aerospace and healthcare. Here, we present detailed and exact mathematical modeling of the sensing ability of the three most basic scalar assemblies of coaxial pick-up coils (PUCs): in the so-called zero derivative configuration (ZDC), having a single PUC; the first derivative configuration (FDC), having two PUCs; and second derivative configuration (SDC), having four PUCs. These three basic assemblies are mathematically modeled for a reference case of physics; we tackle the AC voltage signal, VAC (t), induced at the output of the PUCs by the temporal variation of the magnetic flux, Φ(t), originating from the time-varying moment, m(t), of an ideal magnetic dipole. Detailed and exact mathematical modeling, with only minor assumptions/approximations, enabled us to obtain the so-called sensing function, FSF, for all three cases: ZDC, FDC and SDC. By definition, the sensing function, F S F , quantifies the ability of an assembly of PUCs to translate the time-varying moment, m(t), into an AC signal, VAC (t). Importantly, the F S F is obtained in a closed-form expression for all three cases, ZDC, FDC and SDC, that depends on the realistic, macroscopic characteristics of each PUC (i.e., number of turns, length, inner and outer radius) and of the entire assembly in general (i.e., relative position of PUCs). The mathematical methodology presented here is complete and flexible so that it can be easily utilized in many disciplines of science and engineering. [ABSTRACT FROM AUTHOR]

In a multi-source permanent magnet synchronous motor (PMSM) drive, three distinct winding structures can be implemented: multi-sector, multi-three-phase, and highly coupled. However, due to variations in the magnetic coupling between windings, their low-frequency DC-link current ripple components differ. This paper presents a method to identify the phenomena associated with each low-frequency harmonic content. Three analytical models are developed for the DC current ripple induced by unbalanced winding, counter-electromotive force (back-EMF) harmonics and aliasing effects, respectively, with the results validated through simulations. Experimental validation is conducted for highly coupled winding drives, demonstrating agreement with the analytical models and simulations. The maximum DC current ripple ratio found in the analytical model, the simulation and the experiments is less than 15 % , which is deemed acceptable for motor drive applications. [ABSTRACT FROM AUTHOR]

Featured Application: Detection of superficial semi-elliptical defects in steel pipes using the variation in the self-magnetic flux leakage based on the metal magnetic memory method. Ferromagnetic pipes are widely used for fluid transportation in various industries. The failure of these ferromagnetic pipes due to surface defects can generate industrial accidents, economic losses, and environmental pollution. Non-destructive testing techniques are required to detect these surface defects. An alternative is the metal magnetic memory (MMM) method, which can be employed to detect surface flaws in ferromagnetic structures. Based on this method, we present an analysis of experimental results of the magnetic field variations around five different surface semi-elliptical defects of an ASTM A36 steel pipe. A measurement system of MMM signals is implemented with a rotatory mechanism, a magnetoresistive sensor, a data processing unit, and a control digital unit. The MMM method does not require expensive equipment or special treatment of the ferromagnetic structures. In order to research a potential relationship between the defect sample size and the measured MMM signals, variable defect dimensions are experimentally considered. According to these results, the shape and magnitude of the normal and tangential MMM signals are altered by the superficial semi-elliptical defects. In particular, the maximum and mean tangential components and the maximum and minimum normal components are related to the defect dimensions. The proposed measurement system can be used to study the behavior of magnetic field variations around surface defects of ferromagnetic pipes. This system can be adapted to measure the position and damage level of small defects on the surface of ferromagnetic pipes. [ABSTRACT FROM AUTHOR]

The propagation velocities of geomagnetic Pc5 pulsations in the azimuthal and meridional directions were analyzed for a series of events. Two methods were used: based on the phase delays of the signal between stations and the displacement of vortex centers of their equivalent current systems. The analysis showed that the propagation of pulsations and vortices coincides in direction—along the meridian, they predominantly propagate northward. In most cases, the propagation velocity is 5 km/s for pulsations and 2 km/s for vortices. In the azimuthal direction, pulsations and vortices propagate westward, with pulsation propagation velocity of 10 km/s and vortex propagation velocity of 3 km/s. However, the distributions of azimuthal velocities for both pulsations and vortices exhibit comparable maxima corresponding to eastward propagation: pulsations at a velocity of 10 km/s and vortices at 5 km/s. It is concluded that the measured phase velocities of pulsations at the ionospheric level are approximately twice the group velocities of vortices. [ABSTRACT FROM AUTHOR]

PBC J0801.2–4625 is an intermediate polar with a primary spin frequency of 66.08 d−1 and an unknown orbital period. The long-term All Sky Automated Survey for Supernovae (ASAS-SN) light curve of this system reveals four bursts, all of which have similar peak amplitudes (∼2 mag) and durations (∼2 d). In this work, we primarily study the timing properties of this system's 2019 February burst, which was simultaneously observed by both ASAS-SN and the Transiting Exoplanet Survey Satellite (TESS). Pre-burst, a frequency of 4.064 ± 0.002 d−1(5.906 ± 0.003 h period), likely attributed to the binary orbit, is identified in addition to previous measurements for the white dwarf's spin. During the burst, however, we find a spin frequency of 68.35 ± 0.28 d−1. Post-burst, the spin returns to its pre-brust value but with a factor 1.82 ± 0.05 larger amplitude. The burst profile is double-peaked, and we estimate its energy to be 3.3 × 1039 erg. We conclude that the burst appears most consistent with thermonuclear runaway (i.e. a 'micronova'), and suggest that the spin variations may be an analogue to burst oscillations (i.e. 'micronova oscillations'). However, we also note that the above findings could be explained by a dwarf nova outburst. With the available data, we are unable to distinguish between these two scenarios. [ABSTRACT FROM AUTHOR]

In this work, it is shown that early warning signals were recorded prior to a 6.4 magnitude earthquake that took place on December 29, 2020, near the Croatian city of Petrinja. The study relied on analyzing property changes in small-scale probability density fluctuations in three parameters of the Earth's magnetic field: X, Y and Z. The applied technique made it possible to identify a set of these precursors in intervals ranging from two and a half days to one day to less than one hour before this event. It has been observed that the three magnetic variation stations located at distances of approximately 300, 1000, and 1500 km from the epicenter exhibit significant differences in the occurrence of early warning signs and critical phenomena during an impending earthquake. These differences are related to the intensity and frequency of the effects observed at each station. [ABSTRACT FROM AUTHOR]

The hour-long, gradual phase of solar flares is well observed across the electromagnetic spectrum, demonstrating many multiphase aspects, where cold condensations form within the heated post-flare system, but a complete 3D model is lacking. Using a state-of-the-art 3D magnetohydrodynamic simulation, we identify the key role played by the Lorentz force through the entire flare lifespan, and show that slow variations in the post-flare magnetic field achieve the bulk of the energy release. Synthetic images in multiple passbands closely match flare observations, and we quantify the role of conductive, radiative, and Lorentz force work contributions from flare onset to decay. This highlights how the non-force-free nature of the magnetic topology is crucial to trigger Rayleigh–Taylor dynamics, observed as waving coronal rays in extreme ultraviolet observations. Our C-class solar flare reproduces multiphase aspects such as post-flare coronal rain. In agreement with observations, we find strands of cooler plasma forming spontaneously by catastrophic cooling, leading to cool plasma draining down the post-flare loops. As there is force balance between magnetic pressure and tension and the plasma pressure in gradual-phase flare loops, this has potential for coronal seismology to decipher the magnetic field strength variation from observations. [ABSTRACT FROM AUTHOR]