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Near-zero magnetic shielding systems (MSSs) can provide basic experimental environments for extremely weak magnetic measurements. Reducing the internal magnetic field of MSS is the crucial element of high-sensitivity measurements, which is related to the shielding material flux. As an effective way to regulate the material remanence, degaussing reconstructs the magnetic balance with the geomagnetic field. However, previous research studies mainly focused on the optimization of material degaussing, with few considering the practical application scenarios of MSS. In this work, a numerical modeling method is proposed to realistically depict the balancing process, and the mapping relationship between the internal magnetic field of the MSS and the degaussing current is established. First, the magnetic field source analysis is carried out, and the internal magnetic field fluctuations of the MSS during degaussing are decomposed into multi-harmonic components. Then, the phase and amplitude changes of the hysteresis loop are simulated to predict the residual field. Thereafter, the effectiveness of the method is verified by a magnetic shielding cylinder. The experimental results indicate that the slight difference in material remanence has a negligible effect on the residual field. This work has potential application value in the research of degaussing technology. [ABSTRACT FROM AUTHOR]

Electron spin relaxation is, on many occasions, considered an elephant in the room that challenges the idea of a radical-pair compass, a leading hypothesis for the navigation of migratory avian species. It has been widely recognized that an effective radical-pair magnetoreceptor requires a relaxation time that is long enough for an external magnetic field as weak as the geomagnetic field to significantly modify the coherent spin dynamics. However, previous studies proposed that certain spin relaxation, far quicker than the radical recombination reactions, could enhance, rather than degrade, the directional sensitivity of a radical-pair magnetoreceptor. Here, I investigate relaxation effects on the singlet–triplet interconversion of a model radical pair and find that the enhancement effect originates from population relaxation over a period of several microseconds as a result of efficient spin decoherence. Insights into the truncated spin systems shed light on the physics behind them. I further investigate the possibilities of such enhancement in cryptochrome-based magnetoreception, in which electron hopping takes place between tryptophan residues. [ABSTRACT FROM AUTHOR]

Geomagnetic navigation has become a hot spot in current research because of its characteristics of passiveness and good concealment. However, the magnetic interference from various ferromagnetic substances, electronic equipment, etc., of the carrier will be superimposed on the geomagnetic field, causing magnetometer measurement errors, thus affecting navigation accuracy. In practice, due to the limited maneuverability of the carrier, sufficient geomagnetic observation data cannot be obtained, resulting in the observation equation used for carrier magnetic interference compensation to be seriously pathological. To achieve the compensation of carrier magnetic interference, this paper proposes the total least squares method based on the ridge regression using the L curve to solve ridge parameters. This method can effectively suppress the measurement noise that exists on both sides of the observation equation, and is suitable for alleviating the pathological effects of carrier magnetic interference compensation. Experimental results show that the compensated magnetometer measurement error is reduced to 3% of the carrier magnetic interference by using the method proposed in this paper, which obtains more stable and accurate parameter estimates. [ABSTRACT FROM AUTHOR]

Low-noise fluxgate magnetometers are normally comprised of three separate devices: a power supply, the sensor head/electronics and an analog-to-digital converter (ADC). This paper presents a parallel rod fluxgate magnetometer in a single printed circuit board of size = 5 × 12 cm, weight = 45 g, and sensor head average power dissipation = 40 mW. The open-loop noise spectral density = 5 p T r m s / Hz @ 1 Hz , competitive with state-of-the-art devices. This is realized using a new amorphous wire core material and programmable mixed-signal electronics with low amplifier and ADC noise. We have compared the sensor performance to a low-noise observatory magnetometer and found sub-nT correlation when tracking the Y (East-West) component of the Earth's geomagnetic field. [ABSTRACT FROM AUTHOR]

This work follows on from studies carried out by Jiles and Atherton on magnetic hysteresis and on the magnetomechanical effect. The Jiles–Atherton equation, which models the rate of change of magnetization with respect to stress, was solved numerically in the forward and reverse directions for stress up to 90 MPa, suggesting that stressing carbon steel will cause a lasting change in the magnetization of the sample. This was confirmed experimentally by measuring the B-field in proximity to samples of C45 steel while undergoing tensile stress, with the pattern of magnetization suggesting that the magnetic domains reorient themselves in the geomagnetic field when stressing loosens their pinning. A further experiment on two samples confirms this, with the B-field around the samples showing strong changes according to their orientation in the geomagnetic field at the time of the stressing. This work has relevance to the non-destructive testing of steel structures such as pipelines, and the relevance of the experiments to this work is considered, as well as future prospects. [ABSTRACT FROM AUTHOR]

The Earth's outer core dynamics involve convective fluid motion generating an observable geomagnetic field. The velocity and magnetic fields exhibit characteristic spatiotemporal features possessing geophysical significance for which extensive datasets are available from direct observations and computational simulations. This study demonstrates the robustness of proper orthogonal decomposition (POD), a data-driven technique, in detecting prominent and relevant features in these datasets. Improvising on previous practices, the POD efficiently detects infinitesimal instabilities at the onset of convection, providing an accurate and objective methodology to determine the convective threshold, even for heterogeneous buoyancy forcing. Time evolution of paired, phase-shifted modes efficiently reconstructs the azimuthally drifting of traveling wave instabilities. Simultaneously reduced order modeling of velocity components clearly distinguish the equatorial and polar coherent flow structures. Supercritical convection-driven magnetic field data over long periods, generated using numerical simulations, produce dominant modes that are more accurately representative of time-averaged patterns than geocentric axial dipole patterns. Moreover, the quantitative significance of the dominant modes determines the extent of dimensional reduction complementing established diagnostics for dipolarity. Finally, analysis of observational geomagnetic field data reveals long-lived dominant patterns influenced by thermal core–mantle interaction consistent with numerical models employing tomographic heat flux boundary conditions in present as well as previous studies. [ABSTRACT FROM AUTHOR]

We perform a novel linear simulation of the feedback instability by applying a gyrokinetic model to the magnetosphere, where the geomagnetic field is modeled by a dipole magnetic field. In order to avoid huge numerical calculation costs, the effect of the fluctuating mirror force is neglected. It is found that kinetic effects, such as the finite Larmor radius effect and the electron Landau damping, strongly stabilize the feedback instability and form a peak in the perpendicular wave number spectrum of the growth rate. During the linear growth, it is observed that electron free energy has a much larger value than the electromagnetic field perturbation energy. Since such large electron free energy may lead to electron heating and acceleration, it is important to understand its generation mechanism. Analyses based on the energy conservation reveal that the coupling of the non-uniformity of the equilibrium fields along the geomagnetic field and the fluctuating electron distribution gives rise to thermodynamic power generating the electron free energy. A fine velocity space structure around an average Alfvén velocity of the fluctuating electron distribution mainly contributes to drive the thermodynamic power. [ABSTRACT FROM AUTHOR]

Many modern accelerators rely on superconducting radio-frequency (SRF) cavities to accelerate particles. When these cavities are cooled to the superconducting state, a fraction of the ambient magnetic field (e.g., Earth's magnetic field) may be trapped in the superconductor. This trapped flux can significantly increase the power dissipation of the SRF cavities. It is, therefore, crucial to understand the underlying mechanism of how magnetic flux is trapped and what treatments and operating conditions can reduce the flux-trapping efficiency. A new experiment was designed that enables a systemic investigation of flux trapping. It allows for independent control of cooldown conditions, which might have an influence on flux trapping: temperature gradient across the superconductor during cooldown, cooldown rate, and ambient magnetic field. For exhaustive studies, the setup was designed for quick thermal cycling, permitting up to 300 superconducting transitions in one day. In this paper, the setup and operation is described in detail and an estimation of the measurement errors is given. Exemplary data are presented to illustrate the efficacy of the system. [ABSTRACT FROM AUTHOR]

This document explores the experimental and theoretical aspects of a magnetically coupled oscillator system with two swinging magnets. The setup is designed to allow for long-lasting oscillations and is cost-effective by utilizing a smartphone magnetometer to measure the dipole moment of the magnet and record the period of the oscillations. The document discusses various setups and approaches used in studying magnetically coupled oscillators, and presents a simplified setup that uses a low-friction pivot and a smartphone for data recording. The physical setup, theoretical model, and experimental results are described in detail. The document concludes by suggesting that this setup can be a valuable addition to existing experiments on coupled oscillators. [Extracted from the article]

Cryptochrome photoreceptors contain a photochemically generated radical pair, which is thought to mediate sensing of the geomagnetic field direction in many living organisms. To gain insight into the response of the cryptochrome to a weak magnetic field, we have studied the quantum-mechanical hyperfine spin states of the radical pair. We identify quantum states responsible for the precise detection of the magnetic field direction, taking into account the strongly axial hyperfine interactions of each radical in the radical pair. The contribution of these states to the formation of the cryptochrome signaling state sharply increases when the magnetic field becomes orthogonal to the hyperfine axis of either radical. Due to such a response, the radical pair may be able to detect the particular field direction normal to the plane containing the hyperfine axes of the radicals. [ABSTRACT FROM AUTHOR]

The article discusses the impact of ferromagnetic materials on the flux density of a solenoid, emphasizing the need for students to understand physics concepts beyond memorizing equations. It highlights the importance of using open-source software and applications in theoretical physics classes to enhance the teaching and learning process. Through an experimental analysis using a smartphone with a magnetometer app, the relationship between a magnetic core and the measured magnetic field amplitude is explored, shedding light on the efficiency of transformers. The study aims to encourage students to engage in hands-on learning experiences and make meaningful discoveries in physics education. [Extracted from the article]

This article provides a detailed analysis of the geomagnetic field, which is the magnetic field associated with Earth. It explains how convection currents in the liquid outer core generate this field, which is almost parallel to Earth's axis of rotation. The article explores the total energy of the geomagnetic field and its importance in protecting the planet from space weather. It also discusses geomagnetic reversals and provides equations and calculations to estimate the energy of the field. The article concludes by discussing different models for estimating the field's energy and the limitations of these models. The author, Christopher Provatidis, is a professor with scientific interests in various fields. [Extracted from the article]

All organisms on Earth live in the weak but ubiquitous geomagnetic field. Human beings are also exposed to magnetic fields generated by multiple sources, ranging from permanent magnets to magnetic resonance imaging (MRI) in hospitals. It has been shown that different magnetic fields can generate various effects on different tissues and cells. Among them, stem cells appear to be one of the most sensitive cell types to magnetic fields, which are the fundamental units of regenerative therapies. In this review, we focus on the bioeffects of static magnetic fields (SMFs), which are related to regenerative medicine. Most reports in the literature focus on the influence of SMF on bone regeneration, wound healing, and stem cell production. Multiple aspects of the cellular events, including gene expression, cell signaling pathways, reactive oxygen species, inflammation, and cytoskeleton, have been shown to be affected by SMFs. Although no consensus yet, current evidence indicates that moderate and high SMFs could serve as a promising physical tool to promote bone regeneration, wound healing, neural differentiation, and dental regeneration. All in vivo studies of SMFs on bone regeneration and wound healing have shown beneficial effects, which unravel the great potential of SMFs in these aspects. More mechanistic studies, magnetic field parameter optimization, and clinical investigations on human bodies will be imperative for the successful clinical applications of SMFs in regenerative medicine. [ABSTRACT FROM AUTHOR]

Atomic transport properties of liquid iron are important for understanding the core dynamics and magnetic field generation of terrestrial planets. Depending on the sizes of planets and their thermal histories, planetary cores may be subject to quite different pressures (P) and temperatures (T). However, previous studies on the topic mainly focus on the P–T range associated with the Earth's outer core; a systematic study covering conditions from small planets to massive exoplanets is lacking. Here, we calculate the self-diffusion coefficient D and viscosity η of liquid iron via ab initio molecular dynamics from 7.0 to 25 g/cm3 and 1800 to 25 000 K. We find that D and η are intimately related and can be fitted together using a generalized free volume model. The resulting expressions are simpler than those from previous studies where D and η were treated separately. Moreover, the new expressions are in accordance with the quasi-universal atomic excess entropy (Sex) scaling law for strongly coupled liquids, with normalized diffusivity D⋆ = 0.621 exp(0.842Sex) and viscosity η⋆ = 0.171 exp(−0.843Sex). We determine D and η along two thermal profiles of great geophysical importance: the iron melting curve and the isentropic line anchored at the ambient melting point. The variations of D and η along these thermal profiles can be explained by the atomic excess entropy scaling law, demonstrating the dynamic invariance of the system under uniform time and space rescaling. Accordingly, scale invariance may serve as an underlying mechanism to unify planetary dynamos of different sizes. [ABSTRACT FROM AUTHOR]

Geomagnetic indices including AE (Auroral Electrojet), AU (Upper envelopes of AE), AL (Lower envelopes of AE), and Dst (Disturbance Storm Time) are widely considered signatures of geomagnetic storms or substorms that are triggered by solar wind plasma fluids and magnetic fields impinging the Earth's magnetosphere. They are crucial for comprehending and predicting the particle dynamics within the near-Earth space. In the present study, a forecast model utilizing a Long Short-Term Memory (LSTM) Neural Network was constructed by training more than five decades of measurements of solar wind parameters near the first Lagrangian point (L1). Note that it is the first deep learning model to forecast the AE, AU, and AL indices, the overall correlation coefficient (R) between the 1-h-ahead forecast results and the observations reached > 0.85, and the root mean squared error (RMSE) reached 0.05. For the Dst prediction, the model achieves better performance with R and RMSE values reaching 0.981 and 0.011, respectively. It also exhibited an extremely high level in predicting 3-h-ahead Dst, as indicated by R and RMSE values of approximately 0.91 and 0.023, respectively. Further analysis presents that the predictions of the model can be used to precisely track the overall changes in AE and Dst during both quiet times and different stages of geomagnetic storms. It can be easily implemented to supply essential guidelines for examining and estimating the variations in inner magnetospheric particles and solar wind-magnetosphere couplings. [ABSTRACT FROM AUTHOR]

The radiation belt energetic electrons that are trapped by the geomagnetic field are one kind of space plasma and magnetic fluid. We quantitatively study the competition process between source and loss processes of radiation belt "source" (a few to tens of keV), "seed" (hundreds of keV), and "relativistic" (>1 MeV) electrons when a typical magnetic cloud (MC) event impinged on the magnetosphere on 19–20 July 2016. A very weak geomagnetic storm with SymHmin = −32 nT was driven by this magnetic cloud event. With the MC-driven shock arrival, the relativistic electrons experienced a "one-kick" energization at lower L-shells while having a moderate dropout at higher L-shells. The dropout became pronounced during the weak storm main phase. However, the seed electrons had a slight depletion after the shock and recovered to the pre-event level in the main phase, while the source electrons continued increasing during the entire event. Further analysis demonstrates that the loss processes (magnetopause shadowing and ultralow-frequency waves-driven outward transport) were competing with the source processes (shock-induced energization, substorm ejections, and wave–particle interactions), which are strongly sensitive to electron energy and L-shells. It is found that L*= ∼ 4 and μ = 102–102.5 MeV/G could be typical values at which the source and loss processes arrived at dynamic equilibrium. Our study first provides the "balance lines" in both energy channels and L* of the radiation belt source, seed, and relativistic electrons in response to magnetic cloud events. The quantitative results could be a key factor when investigating MC–magnetosphere coupling. [ABSTRACT FROM AUTHOR]

Existence of an axial (poloidal) component of magnetic field in the dense plasma focus has been inferred using multiple diagnostics in many laboratories since 1979. It has not received much attention because its origin as well as role in plasma focus physics was unclear till recently. Recent discovery of long-lasting neutron emission perpendicular to the axis in PF-1000 and neutron fluence ratio (end/side) less than unity in Gemini shows that azimuthally accelerated and radially confined deuterons play an observable role in fusion reactions. A spontaneously generated poloidal magnetic field can provide both the azimuthal electric field necessary for acceleration and radial confinement of the ions being accelerated in the acceleration zone. A comprehensive survey of plasma focus research also confirms the role of spontaneously self-organized plasma objects in the fusion reaction process where their three-dimensional magnetic field structure provides a mechanism for accelerating and trapping ions making them repeatedly pass through a dense plasma target. With emerging appreciation of the likely role of the axial magnetic field in plasma focus neutron emission, it becomes imperative to consider models for its origin. This Letter proposes a partial theory of growth of the axial (poloidal) magnetic field via a simple dynamo, with the geomagnetic field as the seed, which converts the kinetic energy of the plasma into energy of the poloidal magnetic field. This theory leads to an experimentally testable proposition. [ABSTRACT FROM AUTHOR]

In systems of more than two reactive radicals, the radical recombination probability can be magnetosensitive due to the mere effect of the inter-radical electron–electron dipolar coupling. Here, we demonstrate that this principle, previously established for three-radical systems, generalizes to n-radical systems. We focus on radical systems in the plane and explore the effects of symmetry, in particular its absence, on the associated magnetic field effects of the recombination yield. We show, by considering regular configurations and slightly distorted geometries, that the breaking of geometric symmetry can lead to an enhancement of the magnetosensitivity of these structures. Furthermore, we demonstrate the presence of effects at low-field that are abolished in the highly symmetric case. This could be important to the understanding of the behavior of radicals in biological environments in the presence of weak magnetic fields comparable to the Earth's, as well as the construction of high-precision quantum sensing devices. [ABSTRACT FROM AUTHOR]

The article explores the practical application of using smartphones equipped with magnetometer apps to measure the AC current of household appliances. By eliminating background magnetic fields, researchers were able to establish a linear relationship between the magnetic field and electric current, aligning with Ampere's law. The study demonstrates how smartphones can be used to directly measure AC current based on this relationship, providing a practical tool for merging abstract physics knowledge with real-world experiments. The research was conducted in Thailand and received financial support from The Royal Thai Government Scholarship under the Thailand-Laos PDR Bilateral Development Cooperation. [Extracted from the article]

The mechanism of the magnetic compass sense of migratory songbirds is thought to involve magnetically sensitive chemical reactions of light-induced radical pairs in cryptochrome proteins located in the birds' eyes. However, it is not yet clear whether this mechanism would be sensitive enough to form the basis of a viable compass. In the present work, we report spin dynamics simulations of models of cryptochrome-based radical pairs to assess whether accumulation of nuclear spin polarization in multiple photocycles could lead to significant enhancements in the sensitivity with which the proteins respond to the direction of the geomagnetic field. Although buildup of nuclear polarization appears to offer sensitivity advantages in the more idealized model systems studied, we find that these enhancements do not carry over to conditions that more closely resemble the situation thought to exist in vivo. On the basis of these simulations, we conclude that buildup of nuclear polarization seems unlikely to be a source of significant improvements in the performance of cryptochrome-based radical pair magnetoreceptors. [ABSTRACT FROM AUTHOR]

Magnetotactic bacteria (MTB) are aquatic microorganisms that are able to biomineralize membrane-enclosed magnetic nanoparticles called magnetosomes. Inside the MTB, magnetosomes are arranged in a chain that allows MTB to align and navigate along the Earth's magnetic field. When isolated from the MTB, magnetosomes display a number of potential applications for targeted cancer therapies, such as magnetic hyperthermia, localized drug delivery, or tumor monitoring. The characteristics and properties of magnetosomes for these applications exceed in several aspects those of synthetic magnetic nanoparticles. Likewise, the whole MTB can also be considered as promising agents for cancer treatment, taking advantage of their self-propulsion capability provided by their flagella and the guidance capabilities ensured by their magnetosome chain. Indeed, MTB are envisaged as nanobiots that can be guided and manipulated by external magnetic fields and are naturally attracted toward hypoxic areas, such as the tumor regions, while retaining the therapeutic and imaging capacities of the isolated magnetosomes. Moreover, unlike most of the bacteria currently tested in clinical trials for cancer therapy, MTB are not pathogenic but could be engineered to deliver and/or express specific cytotoxic molecules. In this article, we will review the progress and perspectives of this emerging research field and will discuss the main challenges to overcome before the use of MTB can be successfully applied in the clinic. [ABSTRACT FROM AUTHOR]

This article discusses the challenges faced by teachers when explaining permanent magnetism to students without a background in quantum physics. While magnetic materials have been studied for centuries, a satisfactory explanation of their properties requires an understanding of quantum mechanics. Teachers often use simplified models, such as magnetic poles, to explain magnetic phenomena, but these models do not fully capture the complexity of magnetic materials. The article suggests that teachers should present the concept of electron spin as an intrinsic property of electrons, rather than relying on classical models. It emphasizes the importance of presenting the material in a consistent and physically correct manner to avoid misconceptions. [Extracted from the article]

We present the results of a numerical model for VLF chorus emissions generation based on the EPOCH PIC code. The initial distribution function of energetic elections is assumed to have a finite-width step-like deformation in the velocities parallel to the geomagnetic field. This allows us to verify and generalize the analytical and numerical results obtained earlier within the framework of a backward wave oscillator model in which a sharp step feature is assumed. We show that in the presence of a sharp or smooth step, chorus emissions can be generated for realistic flux of energetic electrons even if the initial velocity distribution (without the step) is isotropic. Simulated chorus emissions behave very similarly for both sharp and finite-width steps. In particular, the generation of repetitive chirping chorus elements occurs if the coupling parameter exceeds the linear generation threshold several times. For smaller threshold excess, quasi-stationary or relaxation oscillation regimes take place. For the first time, we systematically study the dependence of the chorus emissions properties on the energetic electron distribution parameters, in particular, on the step width and the effective wave-particle coupling parameter proportional to the energetic electron flux and step height. We show that the functional dependences of the linear growth rate on the coupling parameter is the same for a smooth step gradient as those obtained for the sharp step within the framework of the backward wave oscillator model. The threshold flux of energetic electrons, above which whistler mode waves are generated, increases very fast with increasing step width. With a fixed relative step height, the threshold flux is about an order of magnitude higher for a step width of 8% than for a sharp step. [ABSTRACT FROM AUTHOR]

In this study, the cosmic ray stuff and its associations with the solar flare index, coronal index, and geomagnetic indices, such as Kp, auroral electrojets, Ap, disturbance storm time (Dst), polar cap, Lyman-alpha, Hp60, and Ap60 indices, were studied using wavelet-based approaches over KIEL and MOSC stations during 2003 and 2004. The cosmic ray data used in this study were obtained from ground-based neutron monitor stations. Different sources are also used to get data on the different indices used in this study. The yearly variation in cosmic ray intensity revealed that the intensity of cosmic rays over KIEL and MOSC stations was greater in 2004 and lower in 2003. This variation might be due to the ring current's asymmetry, which causes an enormous asymmetry in the storm-time cosmic-ray increase. The wavelet coherence transform shows a positive and negative correlation as well as cosmic ray lags with solar flares and coronal indices throughout different months of the 2003 and 2004 periods over both suggested stations. The results of cross correlation indicate that cosmic ray intensity is positively correlated with all geomagnetic indices. However, cosmic ray intensity was negatively associated with the Dst index during 2003 and 2004 over both suggested stations. Moreover, multi-resolution analysis and power spectral density (PSD) analysis are consistent with wavelet analysis. Using the PSD result, we have seen high-power wavelet regions during geomagnetically quiet months and low-power wavelets during disturbed months at a common frequency over both stations during 2003 and 2004. [ABSTRACT FROM AUTHOR]

Non-destructive defect testing with a passive magnetic detection technique is crucial for magnetic materials, which can be exempt from the extra excitation magnetic field or developer replenisher contamination. We demonstrate a novel and high-resolution non-destructive defect testing of a magnetic turbine blade in the earth's magnetic field using a passive magnetic detection technique and a precisely controlled experimental system. The variation in the turbine blade's magnetic field, measured by a three-dimensional and sensitive sensor mounted on a translation system, was numerically processed and visually demonstrated according to the experimental data. The element differential method was used for simulation and analysis, and we found that a feasible distance and an optimal signal-to-noise ratio can be reached at a testing distance of h = 1 mm. The magnetic characteristics obtained experimentally are in good agreement with those of the sample defect spots with the best spatial resolution of 0.1 mm. The major sources of systematic errors including dead zones and sensor orthogonality were also briefly discussed along with the possible solutions. [ABSTRACT FROM AUTHOR]

The ability of night-migratory songbirds to sense the direction of the Earth's magnetic field is increasingly attributed to a photochemical mechanism in which the magnetic field acts on transient radical pairs in cryptochrome flavoproteins located in the birds' eyes. The magnetically sensitive species is commonly assumed to be [ FAD • − TrpH • + ], formed by sequential light-induced intraprotein electron transfers from a chain of tryptophan residues to the flavin adenine dinucleotide chromophore. However, some evidence points to superoxide, O 2 • − , as an alternative partner for the flavin radical. The absence of hyperfine interactions in O 2 • − could lead to a more sensitive magnetic compass, but only if the electron spin relaxation of the O 2 • − radical is much slower than normally expected for a small mobile radical with an orbitally degenerate electronic ground state. In this study we use spin dynamics simulations to model the sensitivity of a flavin-superoxide radical pair to the direction of a 50 μT magnetic field. By varying parameters that characterize the local environment and molecular dynamics of the radicals, we identify the highly restrictive conditions under which a O 2 • − -containing radical pair could form the basis of a geomagnetic compass sensor. We conclude that the involvement of superoxide in compass magnetoreception must remain highly speculative until further experimental evidence is forthcoming. [ABSTRACT FROM AUTHOR]

We demonstrated a scalar atomic magnetometer using a microfabricated Cs vapor cell. The atomic spin precession is driven by an amplitude-modulated circularly-polarized pump laser resonant on the D1 transition of Cs atoms and detected by an off-resonant linearly-polarized probe laser using a balanced polarimeter setup. Under a magnetic field with amplitude in the Earth's magnetic field range, the magnetometer in the gradiometer mode can reach sensitivities below 150 fT / Hz , which shows that the magnetometer by itself can achieve sub - 100 fT / Hz sensitivities. In addition to its high sensitivity, the magnetometer has a bandwidth close to 1 kHz due to the broad magnetic resonance inside the small vapor cell. Our experiment suggests the feasibility of a portable low-power and high-performance magnetometer which can be operated in the Earth's magnetic field. Such a device will greatly reduce the restrictions on the operating environment and expand the range of applications for atomic magnetometers, such as detection of nuclear magnetic resonance in low magnetic fields. [ABSTRACT FROM AUTHOR]

Birds appear to be equipped with an innate magnetic compass. One biophysical model of this sense relies on spin dynamics in photogenerated radical pairs in the protein cryptochrome. This study employs a systematic approach to predict the dependence of the compass sensitivity on the relative orientation of the constituent radicals for spin systems comprising up to 21 hyperfine interactions. Evaluating measures of compass sensitivity (anisotropy) and precision (optimality) derived from the singlet yield, we find the ideal relative orientations for the radical pairs consisting of the flavin anion (F•−) coupled with a tryptophan cation (W•+) or tyrosine radical (Y•). For the geomagnetic field, the two measures are found to be anticorrelated in [F•− W•+]. The angle spanned by the normals to the aromatic planes of the radicals is the decisive parameter determining the compass sensitivity. The third tryptophan of the tryptophan triad/tetrad, which has been implicated with magnetosensitive responses, exhibits a comparably large anisotropy, but unfavorable optimality. Its anisotropy could be boosted by an additional ∼50% by optimizing the relative orientation of the radicals. For a coherent lifetime of 1 µs, the maximal relative anisotropy of [F•− W•+] is 0.27%. [F•− Y•] radical pairs outperform [F•− W•+] for most relative orientations. Furthermore, anisotropy and optimality can be simultaneously maximized. The entanglement decays rapidly, implicating it as a situational by-product rather than a fundamental driver within the avian compass. In magnetic fields of higher intensity, the relative orientation of radicals in [F•− W•+] is less important than for the geomagnetic field. [ABSTRACT FROM AUTHOR]

Measurements of lighter, low-energy charged particles in a laboratory beamline are complicated due to the influence of Earth's magnetic field. Rather than nulling out the Earth's magnetic field over the entire facility, we present a new way to correct particle trajectories using much more spatially limited Helmholtz coils. This approach is versatile and easy to incorporate in a wide range of facilities, including the existing ones, enabling measurements of low-energy charged particles in a laboratory beamline. [ABSTRACT FROM AUTHOR]

Navigation and positioning technologies play a key role in modern human activities. Currently, navigation devices are mostly dependent on the global navigation satellite systems, for example, the global positioning system (GPS). However, it is known that GPS signals can be jammed or spoofed or otherwise fail. As the need for GPS independent navigation increases in some practical application scenarios, novel navigation techniques based on the geomagnetic field have been developed. A main task of geomagnetic navigation is to obtain the amplitude and direction of the geomagnetic field accurately. Here, we introduce an alternative scheme for vectorial measurements of the local geomagnetic field for magnetic positioning based on the biological ferric sulfide cluster, which exists in the magnetoreceptor protein/cryptochrome complex in certain avian species. We find that by observing the number of peaks and the proportional rate of spectrum on resonance, both the direction and intensity of the magnetic field can be determined. Therefore, our findings may provide a fresh insight into magnetic field measurement and also suggest further guidelines for the design and operation of satellite-free navigation systems based on the electrically tunable inorganic biological molecules. [ABSTRACT FROM AUTHOR]

The electronic thermal conductivity of iron at the Earth's core conditions is an extremely important physical property in the geophysics field. However, the exact value of electronic thermal conductivity of iron under extreme pressure and temperature still remains poorly known both experimentally and theoretically. A few recent experimental studies measured the value of the electronic thermal conductivity directly and some theoretical works have predicted the electronic thermal conductivity of iron at the Earth's core conditions based on the Kubo-Greenwood method. However, these results differ largely with each other. A very recent research has confirmed that for iron at the Earth's core conditions, the strength of electron-electron scattering could be comparable to that for electron-phonon scattering, meaning that the electron-electron scattering should also be considered when evaluating the electronic thermal conductivity in the Earth's core situations. Here, by utilizing a newly developed methodology based on direct non-equilibrium ab initio molecular dynamics simulation coupled with the concept of electrostatic potential oscillation, we predict the electronic thermal conductivity of iron in h.c.p. phase. Our methodology inherently includes the electron-phonon and electron-electron interactions under extreme conditions. Our results are comparable to the previous theoretical and experimental studies. More importantly, our methodology provides a new physical picture to describe the heat transfer process in ϵ -iron at the Earth's core conditions from the electrostatic potential oscillation point of view and offers a new approach to study the thermal transport property of pure metals in the planet's cores with different temperature and pressure. [ABSTRACT FROM AUTHOR]

On the left is one, ca. 1910, that is in my collection of early physics teaching apparatus.[3] Two light bulbs illuminate a postcard that serves as an object for the lens, and an image is projected on a white sheet. 1 has an objective lens with a focal length of 15 cm and a second lens with a focal length of 7 cm. The second lens is placed 5 cm inside a smaller sliding box. In this note, I will describe five pieces of apparatus: a telescope, a microscope, a galvanometer, an opaque projector, and an air table that I built for my boys to bring them into the worlds of physical science. The image formed by the first lens was inverted, and the magnified image obtained with the second lens was similarly inverted. [Extracted from the article]

In the field of aviation anti-submarine warfare, magnetic detection systems often result in a large number of false alarms due to the inability to effectively distinguish between a local geomagnetic anomaly in the background field and a target magnetic anomaly. To address this problem, this paper proposes a matching detection method for the magnetic anomaly of underwater targets. This method is based on the measured data of the magnetic anomaly in the sea area, and the geomagnetic reference map of the area is generated by interpolation of the Kriging method; then, the background field signal extracted from the geomagnetic reference map and the real-time signal acquired by detection are matched by the similarity metric algorithm; finally, the target detection is realized by using the feature fusion-isolation forest algorithm. Compared with the conventional detection methods, such as time–frequency analysis, the detection rate is improved by nearly 15% and the false alarm rate is reduced by about 40%, indicating that matching detection can effectively filter out the magnetic anomaly in the background field, reduce the false alarm, and improve the detection rate in the real geomagnetic environment, which has certain application value. [ABSTRACT FROM AUTHOR]

Magnetic anomaly detection is a new technology for underground or underwater ferromagnetic targets using the physical principle that ferromagnetic targets will be long-term magnetized by the geomagnetic field to generate abnormal magnetic fields. This technology is often used in underwater security, mineral exploration, and other areas. But it is quite challenging to effectively detect weak magnetic anomaly signals in a complex underwater environment. Therefore, we propose an adaptive cascade weak magnetic anomaly detection method based on Marine Predators Algorithm-Stochastic Resonance (MPA-SR). According to the characteristics of magnetic anomaly signals, the cascade detection method of low-pass filtering, stochastic resonance, and threshold detection is designed to improve the detection probability of magnetic anomaly signals. In addition, the Marine predator algorithm with optimized initialization strategy and step size control parameters is used to improve the stochastic resonance system to adaptively detect the magnetic anomaly signal in more applications. The simulation results show that the signal-to-noise ratio (SNR) of the output signal of the MPA-SR method is 2.41 dB higher than the input signal, and the detection probability of the method is 57% higher than that of the minimum entropy (ME) method under the same low SNR environment. The method can provide the theoretical basis and empirical reference for further application of magnetic anomaly data like identifying, locating, and tracking underwater magnetic targets. [ABSTRACT FROM AUTHOR]

The dynamics of head-on collision of two magnetosonic solitary waves in ionosphere plasma of the Earth is investigated. A geomagnetic field model standing for the relation between a magnetic field and latitude is used to study nonlinear magnetosonic waves in the ionosphere of Earth. The linear and weakly nonlinear properties of magnetosonic waves are studied by the dispersion relation and the extended Poincaré–Lighthill–Kuo (PLK) method, respectively. Two coupled damped Korteweg–de Vries equations (dKdV) are derived for oppositely propagating magnetosonic solitary waves. The explicit solitary wave solutions are obtained in the weak collision limit, and the trajectories and phase shifts of two magnetosonic solitary waves are derived, which show that collisional dynamics and their phase shifts are dependent on the collision caused by neutral particles and the properties of the ionosphere. This study is applied to investigate the two-counterpropagating magnetosonic solitary waves located in the F2-region of the Earth's ionosphere at low latitude. This study should be beneficial to understand the interaction dynamics of the head-on nonlinear magnetosonic waves located in the F2 layer of the ionosphere when collision effects caused by neutral particles and geomagnetic field distribution are considered. [ABSTRACT FROM AUTHOR]

In this work, we consider the geomagnetic field inversion model proposed by Gissinger et al. [Europhys. Lett. 90(4), 49001 (2010)], where a quadratic term is added for symmetry control purposes. The resulting system is explored in both symmetric and asymmetric modes of operation. In the symmetric case, we report a bursting phenomenon and heterogeneous multistability of six and four different attractors. We show that the model owns an offset adjustment feature. In the asymmetric case, the model develops different phenomena, such as the coexistence of (four and three) asymmetric attractors, asymmetric (periodic and chaotic) bursting oscillation, and transient asymmetric bursting phenomenon. The effect of symmetry breaking is also manifested in the bubbles of bifurcation. It is shown that this system can leave from the multistable state to a monostable state by adjusting the coupling parameter of a linear controller. Moreover, microcontroller-based implementation of the system is considered to check the correctness of the numerical results. [ABSTRACT FROM AUTHOR]

A recent comprehensive review paper has summarized the current experimental state of knowledge on the question of existence of a poloidal component of magnetic field in the dense plasma focus and indirect evidence indicating its prominent role in neuron emission. This Letter looks at the role of the plasma as a curved, azimuthally continuous conductor moving in a small but nonzero geomagnetic field with a component along the device axis. The motional electric field then has an azimuthal component arising from the radial velocity, outward-directed near the cathode throughout the discharge, and inward directed in the radial implosion phase near the anode. This would drive an azimuthal current in the plasma. The electromechanical work done against the associated magnetic force density converts the kinetic energy into the associated magnetic energy density. This would act as a source of poloidal magnetic flux emission from a dense plasma focus, which has been experimentally demonstrated recently. [ABSTRACT FROM AUTHOR]

Energetic electron scattering and precipitation from the Earth's plasma sheet to the ionosphere is an important contributor to magnetosphere–ionosphere coupling. In this study, we investigate the role of one of the most intense wave emissions, kinetic Alfvén waves (KAWs), in energetic electron scattering. We have evaluated the effect of KAWs on energetic electrons within a curved magnetic field configuration exhibiting sharp cross field gradients. The magnetic field in Earth's magnetotail plasma sheet with an embedded dipolarization front is used as a working example. Taking into account electron bounce motion and perpendicular guiding-center drifts, we have shown that electrons with energies of tens to hundreds of keV can be scattered by KAWs in pitch angle and momentum through Doppler-shifted Landau resonance near the magnetic equator. The bounce-averaged pitch-angle diffusion coefficients for near-loss-cone (∼2°) electrons are on the order of 10–7–10–6 rad2/s for a characteristic KAW amplitude of 1 mV/m and approach the strong diffusion limit of ∼10–4 rad2/s for amplitudes of greater than 10 mV/m. These results suggest that under such ambient conditions, KAWs can pitch-angle scatter energetic electron population into the loss cone. In Earth's plasma sheet, this scattering is, thus, very likely to cause significant precipitation during active times. The diffusion coefficients of energetic electrons at large pitch angles (∼45°–∼80°) are more than two orders of magnitude larger than those of electrons near the loss cone, suggesting that KAWs contribute to isotropization of anisotropic electrons due to adiabatic heating should they drift into the vicinity of the magnetic field gradient. [ABSTRACT FROM AUTHOR]

To analyze the characteristics of the aeromagnetic scalar gradient detection method, a uniformly magnetized ellipsoid is used to simulate an unexploded ordnance, and a magnetic field detection model is established in the International Geomagnetic Reference Field based on rotation matrices. Furthermore, the spatial distribution of the target's magnetic field is simulated. The results indicate that the scalar gradient detection curve is closely related to the unmanned aerial vehicle (UAV) heading, geomagnetic direction, and target attitude. According to the measured data, the aeromagnetic detection system exhibits differences in the detection of different headings, indicating that some "blind areas" exist in the scalar gradient magnetic detection method. The experimental measurement by a quadrotor UAV equipped with two optical pump magnetometers verifies that the scalar gradient detection method can effectively eliminate the geomagnetic field as well as the interferences of the UAV itself. Furthermore, the angular relationship between the target magnetic field contour distribution and the heading is found to be the main reason that the scalar gradient detection system enters the "blind detection area." Therefore, a flight strategy of "positive direction + orthogonal grid" is proposed. This method effectively reduces the missed detection rate of scalar gradient detection and provides strategic guidance for the detection path of aeromagnetic scalar gradient system. [ABSTRACT FROM AUTHOR]

The sensitive, broadband seismometer described in this paper is based on frequency modulation and a two-dimensional (2D) Fourier transform method to obtain time vs frequency (and seismic amplitude) recordings. The intent was to develop an instrument that could compare seismic recordings with variables (as signals) that, for rational reasons, might be active before a seismic rupture and, thus, possibly serve as quake warning indicators. Five such variables were eventually incorporated into the instrument and tested as amplitudes: electric field changes, the electromagnetic spectrum between 3 and 30 Hz (extremely low frequency as Schumann-like emissions), the electromagnetic spectrum between 0.3 and 3 Hz (possibly ionospheric Alfvén waves acting through the geomagnetic field), and short period seismic resonances at 10.1 and 15.9 Hz. All five of the sensors actually detected possible precursors of the seismic events that followed them. However, the 3–30 Hz electromagnetic signals showed up in less than 10% of the recorded earthquakes. The signals of the 0.3–3 Hz band were also not in all quake recordings. Broadband strobing was recorded before several earthquakes and was especially prominent for hours before a quake near Wyatt MO and Bardwell KY on 2017-03-19. The strobe issue appears to be worthy of further scrutiny. The lack of a good electric conduction mechanism between earthquake hypocenters and the earth–ionosphere cavity may be the reason why the Schumann-like emissions of the 3–30 Hz band were not observed for most earthquakes. A magnetometer is a preferred next step because it could increase the percentage of quakes with observable effects. In addition, a short period seismic resonator for 20 Hz is another desirable addition. [ABSTRACT FROM AUTHOR]

10.1119/5.0074846.1 The Earth's magnetic field can be decomposed into spherical harmonics, and the exact coefficients of the decomposition can be determined through a few measurements of its value at different locations. Using measurements from a magnetometer on board the International Space Station, we computed the multipolar moments of an expansion in spherical harmonics to order 3, calculated the location of the magnetic dip poles, and produced an intensity map of the magnetic field across the globe. The accuracy of the results was evaluated by comparison with data from the International Geomagnetic Reference Field. [ABSTRACT FROM AUTHOR]

On 6 July 2017, the four Magnetospheric Multiscale spacecrafts were positioned within an electron diffusion region (EDR) just northward of a reconnection X line. The EDR was identified by electron crescent distributions, out-of-plane current, and energy conversion. From this position, the three spacecrafts closest to the X line (within about three electron inertial lengths) were able to accurately measure the reconnection electric field and the electron inflow velocity. The reconnection rates derived from the electric field and inflow velocity measurements agree with theoretical estimates (0.11–0.17) and a previous measurement of EM in a tail reconnection event on 11 July 2017. [ABSTRACT FROM AUTHOR]

The magnetic anomalies generated by the ferromagnetic targets are usually buried within uncontrollable interference sources, such as the power frequency and random noises. In particular, the variability of the geomagnetic field and the low signal-to-noise ratio (SNR) of the magnetic anomalies cannot be avoided. In this paper, to improve the performance of magnetic anomaly detection (MAD) with a low SNR, we propose a novel structured low-rank (SLR) decomposition-based MAD method. In addition, a new framework based on the SLR and singular value decomposition (SVD) is constructed, dubbed SLR-SVD, and the corresponding working principle and implemented strategy are elaborated. Through comparing the SLR-SVD with two state-of-the-art methods, including principal component analysis and SVD, the results demonstrate that the proposed SLR-SVD can not only suppress the noise sufficiently, i.e., improving 55.26% approximately of the SNR, but also retain more boundary information of magnetic anomalies, i.e., decreasing approximately 68.05% of the mean squared error and improving approximately 28.47% of the structural similarity index. [ABSTRACT FROM AUTHOR]