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Exceptional points (EPs) in non-Hermitian systems have recently attracted wide interest and spawned intriguing prospects for enhanced sensing. However, EPs have not yet been realized in thermal atomic ensembles, which is one of the most important platforms for quantum sensing. Here we experimentally observe EPs in multilevel thermal atomic ensembles and realize enhanced sensing of the magnetic field for 1 order of magnitude. We take advantage of the rich energy levels of atoms and construct effective decays for selected energy levels by employing laser coupling with the excited state, yielding unbalanced decay rates for different energy levels, which finally results in the existence of EPs. Furthermore, we propose the optical polarization rotation measurement scheme to detect the splitting of the resonance peaks, which makes use of both the absorption and dispersion properties and shows an advantage with enhanced splitting compared with the conventional transmission measurement scheme. Additionally, in our system both the effective coupling strength and decay rates are flexibly adjustable, and thus the position of the EPs are tunable, which expands the measurement range. Our Letter not only provides a new controllable platform for studying EPs and non-Hermitian physics, but also provide new ideas for the design of EP-enhanced sensors and opens up realistic opportunities for practical applications in the high-precision sensing of magnetic field and other physical quantities.

Magnetic reconnection is a process that can rapidly convert magnetic field energy into plasma thermal energy and kinetic energy, and it is also an important energy conversion mechanism in space physics, astrophysics and plasma physics. Research related to analytical solutions for time-dependent three-dimensional magnetic reconnection is extremely difficult. For decades, several mathematical descriptions have been developed regarding different reconnection mechanisms, in which the equations based on magnetohydrodynamics theory outside the reconnection diffusion region are widely accepted. However, the equation set cannot be analytically solved unless specified constraints are imposed or the equations are reduced. Based on previous analytical methods for kinematic stationary reconnection, here the analytical solutions for time-dependent kinematic three-dimensional magnetic reconnection are discussed. In contrast to the counter-rotating plasma flows that existed in steady-state reconnection, it is found that spiral plasma flows, which have never been reported before, can be generated if the magnetic field changes exponentially with time. These analyses reveal new scenarios for time-dependent kinematic three-dimensional magnetic reconnection, and the deduced analytical solutions could improve our understanding of the dynamics involved in reconnection processes, as well as the interactions between the magnetic field and plasma flows during magnetic reconnection., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Chen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Magnetic resonance imaging (MRI) is an imaging technique derived from radiofrequency (RF) signals of proton that are magnetized by a strong magnetic field. These protons typically originate from water, fat, or metabolites. The application of RF pulses is used to excite the magnetization, whereas pulsed magnetic field gradients are used to provide spatial localization. This chapter describes the fundamental principles giving rise to MR images. Furthermore, the connection between relaxation and image contrast is discussed.

Claims that magnetic fields can be used to manipulate biological systems contradict some basic laws of physics., Competing Interests: The authors declare that no competing interests exist.

A general master equation is derived to describe an electromechanical single-dot transistor in the Coulomb blockade regime. In the equation, Fermi distribution functions in the two leads are taken into account, which allows one to study the system as a function of bias voltage and temperature of the leads. Furthermore, we treat the coherent interaction mechanism between electron tunneling events and the dynamics of excited vibrational modes. Stationary solutions of the equation are numerically calculated. We show that current through the oscillating island at low temperature appears to have step-like characteristics as a function of the bias voltage and the steps depend on the mean phonon number of the oscillator. At higher temperatures the current steps would disappear and this event is accompanied by the emergence of thermal noise of the charge transfer. When the system is mainly in the ground state, the zero frequency Fano factor of current manifests sub-Poissonian noise and when the system is partially driven into its excited states it exhibits super-Poissonian noise. The difference in the current noise would almost be removed for the situation in which the dissipation rate of the oscillator is much larger than the bare tunneling rates of electrons., (© 2012 IOP Publishing Ltd)

The magnetohydrodynamic (MHD) equations in the presence of a guiding magnetic field are investigated by means of direct numerical simulations. The basis of the investigation consists of nine runs forced at the small scales. The results demonstrate that for a large enough uniform magnetic field the large scale flow behaves as a two-dimensional (2D) (non-MHD) fluid exhibiting an inverse cascade of energy in the direction perpendicular to the magnetic field, while the small scales behave like a three-dimensional (3D) MHD fluid cascading the energy forwards. The amplitude of the inverse cascade is sensitive to the magnetic field amplitude, the domain size, the forcing mechanism, and the forcing scale. All these dependences are demonstrated by the varying parameters of the simulations. Furthermore, in the case that the system is forced anisotropically in the small parallel scales an inverse cascade in the parallel direction is observed that is feeding the 2D modes k(//)=0.

The secular variation of the geomagnetic field as observed at the Earth's surface results from the complex magnetohydrodynamics taking place in the fluid core of the Earth. One way to analyze this system is to use the data in concert with an underlying dynamical model of the system through the technique of variational data assimilation, in much the same way as is employed in meteorology and oceanography. The aim is to discover an optimal initial condition that leads to a trajectory of the system in agreement with observations. Taking the Earth's core to be an electrically conducting fluid sphere in which convection takes place, we develop the continuous adjoint forms of the magnetohydrodynamic equations that govern the dynamical system together with the corresponding numerical algorithms appropriate for a fully spectral method. These adjoint equations enable a computationally fast iterative improvement of the initial condition that determines the system evolution. The initial condition depends on the three dimensional form of quantities such as the magnetic field in the entire sphere. For the magnetic field, conservation of the divergence-free condition for the adjoint magnetic field requires the introduction of an adjoint pressure term satisfying a zero boundary condition. We thus find that solving the forward and adjoint dynamo system requires different numerical algorithms. In this paper, an efficient algorithm for numerically solving this problem is developed and tested for two illustrative problems in a whole sphere: one is a kinematic problem with prescribed velocity field, and the second is associated with the Hall-effect dynamo, exhibiting considerable nonlinearity. The algorithm exhibits reliable numerical accuracy and stability. Using both the analytical and the numerical techniques of this paper, the adjoint dynamo system can be solved directly with the same order of computational complexity as that required to solve the forward problem. These numerical techniques form a foundation for ultimate application to observations of the geomagnetic field over the time scale of centuries.

The effect of a constant and uniform horizontal magnetic field on the flow in a cylindrical cavity heated from below, with a free surface at the top, is numerically investigated. The azimuthal modes, which usually trigger convection in a cylinder, are changed by the horizontal magnetic field to oriented modes, either parallel or perpendicular to the magnetic field direction. The corresponding primary thresholds increase with the Hartmann number Ha. This increase, however, depends on the structure of the modes and is the weakest for the parallel modes and the strongest for the perpendicular modes. The changes that affect the evolution of the primary thresholds with the aspect ratio for nonzero Ha are also emphasized. The nonlinear evolution of the convection with a horizontal magnetic field is presented through bifurcation diagrams for different values of the Prandtl number Pr. For Pr=1 and small values of Ha, the structuring effect of the horizontal magnetic field, which involves modifications of the flow structures and bifurcation points, is put into light. Results are finally shown for smaller Pr values corresponding to liquid metals.

Ferrofluids are colloidal suspensions of magnetic nanoparticles that exhibit normal liquid behavior in the absence of magnetic fields but respond to imposed magnetic fields by changing their viscosity without loss of fluidity. The response of ferrofluids to constant shear and magnetic fields has received a lot of attention, but the response of ferrofluids to oscillatory shear remains largely unexplored. In the present work we used rotational Brownian dynamics to study the dynamic properties of ferrofluids with thermally blocked nanoparticles under oscillatory shear and constant magnetic fields. Comparisons between simulations and modeling using the ferrohydrodynamics equations were also made. Simulation results show that, for small rotational Péclet number, the in-phase and out-of-phase components of the complex viscosity depend on the magnitude of the magnetic field and frequency of the shear, following a Maxwell-like model with field-dependent viscosity and characteristic time equal to the field-dependent transverse magnetic relaxation time of the nanoparticles. Comparison between simulations and the numerical solution of the ferrohydrodynamic equations shows that the oscillatory rotational magnetoviscosity for an oscillating shear field obtained using the kinetic magnetization relaxation equation quantitatively agrees with simulations for a wide range of Péclet number and Langevin parameter but has quantitative deviations from the simulations at high values of the Langevin parameter. These predictions indicate an apparent elastic character to the rheology of these suspensions, even though we are considering the infinitely dilute limit in which there are negligible particle-particle interactions and, as such, chains do not form. Additionally, an asymptotic analytical solution of the ferrohydrodynamics equations, valid for Pe<<2, was used to demonstrate that the Cox-Merz rule applies for dilute ferrofluids under conditions of small shear rates. At higher shear rates the Cox-Merz rule ceases to apply.

Using different analytical methods (the quasilinear approach, the path-integral technique, and the tau-relaxation approximation) we develop a comprehensive mean-field theory for a pumping effect of the mean magnetic field in homogeneous nonrotating helical turbulence with imposed large-scale shear. The effective pumping velocity is proportional to the product of α effect and large-scale vorticity associated with the shear, and causes a separation of the toroidal and poloidal components of the mean magnetic field along the direction of the mean vorticity. We also perform direct numerical simulations of sheared turbulence in different ranges of hydrodynamic and magnetic Reynolds numbers and use a kinematic test-field method to determine the effective pumping velocity. The results of the numerical simulations are in agreement with the theoretical predictions.

We review the evidence for and against the possibility that a strong enough poloidal field stabilizes an axisymmetric magnetostatic field configuration. We show that there does exist a class of resonant magnetohydrodynamic (MHD) waves which produce instability for any value of the ratio of poloidal and toroidal field strength. We argue that recent investigations of the stability of mixed poloidal and toroidal field configurations based on three-dimensional numerical simulations can miss this instability because of the very large azimuthal wave numbers involved and its resonant character.

The decay of current autocorrelation functions is investigated for quantum systems featuring strong interactions. Here the term "interaction" refers to that part of the Hamiltonian causing the (major) decay of the current. On the time scale before the (first) zero crossing of the current, its relaxation is shown to be well described by a suitable perturbation theory in the lowest orders of the interaction strength, particularly if interactions are strong. In this description the relaxation is found to be rather close to a Gaussian decay and the resulting diffusion coefficient approximately scales with the inverse interaction strength. These findings are confirmed by numerical results from exact diagonalization for several one-dimensional transport models including spin transport in the Heisenberg chain with respect to different spin quantum numbers, anisotropy, next-nearest-neighbor interaction, or alternating magnetic field; energy transport in the Ising chain with tilted magnetic field; and transport of excitations in a randomly coupled modular quantum system. The impact of these results for weak interactions is discussed.

The symmetry properties of split ring resonators (SRRs) are exploited for the implementation of novel sensing devices. The proposed structure consists of a coplanar waveguide (CPW) loaded with movable SRRs on the back substrate side. It is shown that if the SRRs are placed with the slits aligned with the symmetry plane of the CPW, the structure is transparent to signal propagation. However, if the symmetry is broken, a net axial magnetic field can be induced in the inner region of the SRRs, and signal propagation is inhibited at resonance. The proposed structures can be useful as alignment sensors, position sensors and angle sensors. This novel sensing principle is validated through experiment.

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]

Going beyond the conventional theory, non-Abelian band topology reveals the global quantum geometry of multiple Bloch bands and unveils a new paradigm for topological physics. However, to date, experimental studies on non-Abelian topological states beyond one dimension are still restricted to systems with time-reversal (T ) symmetry. Here, exploiting a designer gyromagnetic photonic crystal, we find rich T -broken non-Abelian topological phases and their transitions with an unexpected connection to multigap antichiral edge states. By in-situ tuning the magnetic field in the gyromagnetic photonic crystal, we can create, braid, merge, and split the non-Abelian topological nodes in a unique way. Alongside this process, the multigap antichiral edge states can be tuned versatilely, giving rise to topological edge waveguiding with frequency-dependent directionality. These findings open a new avenue for non-Abelian topological physics and topological photonics. Non-Abelian band topology reveals the global quantum geometry of multiple Bloch bands and unveils a new paradigm for topological physics. Here, authors find rich T-broken non-Abelian topological phases and their transitions with an unexpected connection to multigap antichiral edge states. [ABSTRACT FROM AUTHOR]

Non-Hermitian skin effect (NHSE) is an intrinsic non-Hermitian phenomenon where an extensive number of eigenmodes, called skin modes, are localized at the boundary of a system. Recent theories have suggested that the NHSE can be well-tuned by external fields, opening a route to manipulating wave localization. Here, we experimentally demonstrate the diverse interactions between NHSE and synthetic magnetic fields (SMFs) in coupled acoustic ring resonator lattices. We observe that the NHSE and SMFs can, via different physical mechanisms, compete or synergize, resulting in either the suppression or the creation of NHSE. With the aid of the complex frequency excitation technique, we experimentally observe that SMFs can suppress the NHSE by introducing Landau quantization, causing localization to move toward the bulk. In contrast, we show that the presence of SMF generates topological edge modes in the lattice, which then become corner skin modes by the second-order NHSE. Our results evidence the rich physics and diverse consequences that arise from the interplay of magnetic fields and NHSE, paving the way for actively controlling wave localization. [ABSTRACT FROM AUTHOR]

The magnetic topology is a critical issue in fusion plasma research. An example is the Resonant Magnetic Perturbation (RMP), which controls the edge transport in tokamaks. However, the physics of how the RMP affects edge transport is not clear. One reason is the transport process on the stochastic magnetic field is poorly understood. This study examines anisotropic heat diffusion numerically to understand heat transport in stochastic magnetic fields. We developed a numerical model of an anisotropic temperature diffusion model, where the significant deviation of the parallel and perpendicular thermal conductivity exists. We applied this implementation to the realistic stellarator geometry with the stochastic magnetic field in the edge. The smooth temperature profile is obtained for the large perpendicular diffusion, although the magnetic field is stochastic. However, for another case of significant parallel diffusion, the small flattening of the temperature on the magnetic island in the stochastic region appears. That result suggests that the stochastic magnetic field can keep the finite temperature gradient if the connection length of the magnetic field line in the stochastic region is sufficiently long. [ABSTRACT FROM AUTHOR]

Nanofluids (NFs) have emerged as a revolutionary medium for enhancing heat transfer, with magnetohydrodynamics (MHD) gaining particular attention for its potential to improve system efficiency. Despite this growing interest, a critical gap remains in understanding the combined impact of Fe3O4 and its hybrid nanofluids under magnetic fields, especially in turbulent and transition flow regimes of internal forced convection. This review offers an in-depth exploration of MHD-NF internal forced convection, addressing key aspects such as magnetic field dynamics, nanoparticle clustering, stability, dispersion, flow control, and responsive rheology. Leveraging a comprehensive bibliographic analysis of 100 experimental studies from 2010 to the 2024, along with data from the Scopus® database, this work highlights how optimized nanofluid volume concentrations, magnetic field intensities, and frequencies significantly enhance heat transfer coefficients. The findings underscore that both magnetic field strength and nanoparticle concentration critically influence particle motion, flow patterns, entropy generation, thermal performance, and pressure drops, offering new insights into system design. The versatility of MHD-NF systems presents promising applications in fields ranging from advanced cooling technologies to solar thermal systems and material processing. Furthermore, this review addresses ongoing debates on the efficacy of alternating versus constant magnetic fields, advocating for customized magnetic field configurations to unlock the full potential of MHD-enhanced heat transfer. This work not only identifies existing gaps but also lays the foundation for future breakthroughs in magnetically influenced nanofluid systems.

Stellarator plasmas are externally controlled to a degree unparalleled by any other fusion concept, magnetic or inertial. This control is largely through the magnetic fields produced by external coils. The development of fusion energy could be expedited by carrying out remarkably straight-forward computations to define strategies for exploiting this external control. In addition to these computations, which have a reliability limited only by competence, certain physics areas that affect the development of stellarator power plants should have a more intense study. The low cost and speed with which computations can be carried out relative to experiments have implications for the development of fusion. Computations should be used to develop a strategy that to the extent possible allows major issues to be circumvented. Required computations for this strategy are the subject of this paper. [ABSTRACT FROM AUTHOR]

Excitons in two-dimensional (2D) semiconductors have offered an attractive platform for optoelectronic and valleytronic devices. Further realizations of correlated phases of excitons promise device concepts not possible in the single particle picture. Here we report tunable exciton "spin" orders in WSe2/WS2 moiré superlattices. We find evidence of an in-plane (xy) order of exciton "spin"—here, valley pseudospin—around exciton filling vex = 1, which strongly suppresses the out-of-plane "spin" polarization. Upon increasing vex or applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic (FM-z) spin order that spontaneously enhances the "spin" polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose–Hubbard model and is distinct from the fermion case. Our study paves the way for engineering exotic phases of matter from correlated spinor bosons, opening the door to a host of unconventional quantum devices. Control of correlated excitonic states is a key goal of modern optoelectronic physics. Here, the authors demonstrate filling- and field-tunable exciton valley-pseudospin orders in a moiré heterostructure. [ABSTRACT FROM AUTHOR]

We study the physical origins of parallel guiding center drift and parallel velocity-dependent effective magnetic field ( B ‖ * ) appearing in the Hamiltonian formulation of a particle motion in a curved magnetic field. The magnetic twist term is shown to be responsible for both of them. The parallel guiding center drift originates from the change in the effective parallel velocity due to the combined effect of the initial perpendicular motion (v⊥0) and the magnetic twist. The effective magnetic field arises from the collated effect of the change in v⊥0 due to its initial parallel guiding center motion and the conservation of magnetic moment. This understanding clearly shows that the appearance of B ‖ * is a consequence of magnetic moment conservation in curved magnetic fields. [ABSTRACT FROM AUTHOR]

The basic physics of magnetic fields is presented for a target audience of NMR workers. This group often does not have formal training in electromagnetism, but could benefit from an understanding of a selected subset of topics. The focus here is on a relatively non-mathematical view, intended to deliver an intuitive understanding of the topic. The covered topics start with the fields arising from simple idealized currents, including long straight wires, short flat coils, infinite current sheets, long solenoids, and magnetic dipole moments. The generation of field gradients and shim fields is discussed. All of these can be unified by considering the divergence and curl of the magnetic field. Magnetic materials are treated, both linear magnetizable materials (including the sample itself) and permanently magnetized materials; the approaches of equivalent currents and Ampere's theorem for magnetic circuits are presented.

We formulate a Majorana mean-field theory for the extended JKΓ Kitaev model in a magnetic Zeeman field of arbitrary direction, and apply it for studying spatially inhomogeneous states harboring vortices. This mean-field theory is exact in the pure Kitaev limit and captures the essential physics throughout the Kitaev spin liquid phase. We determine the charge profile around vortices and the corresponding quadrupole tensor. The quadrupole-quadrupole interaction between distant vortices is shown to be either repulsive or attractive, depending on parameters. We predict that electrically biased scanning probe tips enable the creation of vortices at preselected positions. Our results paves the way for the electric manipulation of Ising anyons in Kitaev spin liquids. [ABSTRACT FROM AUTHOR]

Continuum Landau modes — predicted recently in a non-Hermitian Dirac Hamiltonian under a uniform magnetic field — are continuous bound states with no counterparts in Hermitian systems. However, they have still not been confirmed in experiments. Here, we report an experimental observation of continuum Landau modes in non-Hermitian electric circuits, in which the non-Hermitian Dirac Hamiltonian is simulated by non-reciprocal hoppings and the pseudomagnetic field is introduced by inhomogeneous complex on-site potentials. Through measuring the admittance spectrum and the eigenstates, we successfully verify key features of continuum Landau modes. Particularly, we observe the exotic voltage response acting as a rainbow trap or wave funnel through full-field excitation. This response originates from the linear relationship between the modes' center position and complex eigenvalues. Our work builds a bridge between non-Hermiticity and magnetic fields, and thus opens an avenue to explore exotic non-Hermitian physics. Non-Hermitian systems have many physical properties without Hermitian counterparts. Here, the authors demonstrate a non-Hermitian topolectrical circuit hosting continuous bound states under pseudomagnetic fields with no counterparts in Hermitian systems. [ABSTRACT FROM AUTHOR]

2023 marks the 25th anniversary of the formation of the Department of Nonlinear Physics of Saratov State University. The department has developed and implements training programs on the general course of physics, physics of nonlinear processes, physics of wave processes in magnetic fields and structures.

Rapid magnetic reconnection was experimentally observed to occur within a microsecond timescale, leading to the field-reversed configuration (FRC) comprising a single closed magnetic field structure. The compressibility of the plasma within the FRC played a crucial role in accelerating the coalescence process, making it considerably faster than the resistive process. A strong similarity between the observed experimental results and those of the coalescence of solar flare loops indicates that astrophysical phenomena and laboratory plasmas are governed by a common physics. [ABSTRACT FROM AUTHOR]

Abstract Magnetic fields are proposed to be a clean and powerful tool to boost the heterogeneous reaction processes, from the simple two‐electron transfer hydrogen evolution to the complicated proton‐coupling of multi‐electron transfer reactions. Although many mechanisms are proposed to explain the field‐assistant enhancement of activities, it remains an open question of how to understand the contradictory experiment results. In this study, the interplay between the alternating magnetic field (AMF) and the working electrodes from the viewpoint of their relative geometric positions is investigated. It is found that the HER current is almost doubled at an AMF of 25 mT when Pt foil and AMF are parallelly arranged, which is more significant than the perpendicularly arranged configuration. A significant increase in solution resistance is observed, which is in contradiction to previous works. The changing of currents with the AMF strength is investigated for the diamagnetic Cu, ferromagnetic Ni, and paramagnetic Ti and Pt wire, all suggesting the vital role of the induced electromotive force, which is a result of the relative geometric positions between the electrode and AMF. The findings provide an alternative mechanism for the magnetic field‐assisted electrocatalytic processes, which is helpful for the rational design of high‐performance catalysts.

High-precision radial-velocity measurements in the near-infrared allow one to search for exoplanet signals around the lowest-mass stars, including young ones. Because these stars can be among the most active ones, it is essential to characterize their magnetic activity. SPIRou, installed at the Canada–France–Hawai’i telescope, was designed to explore such planetary systems and characterize their properties. With a wide spectral range and large resolving power, SPIRou is also optimized for transmission spectroscopy and for investigating the chemical composition of exoplanetary atmospheres.

Axion-like particles (ALPs) are well-motivated extensions of the Standard Model of Particle Physics and a generic prediction of some string theories. X-ray observations of bright active galactic nuclei (AGNs) hosted by rich clusters of galaxies are excellent probes of very-light ALPs, with masses log (m a / eV) < − 12.0. We evaluate the potential of future X-ray observatories, particularly Athena and the proposed AXIS, to constrain ALPs via observations of cluster-hosted AGNs, taking NGC 1275 in the Perseus cluster as our exemplar. Assuming perfect knowledge of the instrument calibration, we show that a modest exposure (200 ks) of NGC 1275 by Athena permits us to exclude all photon–ALP couplings g a γ > 6.3 × 10−14 GeV−1 at the 95% confidence level, as previously shown by Conlon et al., representing a factor of 10 improvement over current limits. We then proceed to assess the impact of realistic calibration uncertainties on the Athena projection by applying a standard Cash likelihood procedure, showing the projected constraints on g a γ weaken by a factor of 10 (back to the current most sensitive constraints). However, we show how the use of a deep neural network can disentangle the energy-dependent features induced by instrumental miscalibration and those induced by photon–ALP mixing, allowing us to recover most of the sensitivity to the ALP physics. In our explicit demonstration, the machine learning applied allows us to exclude g a γ > 2.0 × 10−13 GeV−1, complementing the projected constraints of next-generation ALP dark matter birefringent cavity searches for very-light ALPs. Finally, we show that a 200 ks AXIS/on-axis observation of NGC 1275 will tighten the current best constraints on very-light ALPs by a factor of 3. [ABSTRACT FROM AUTHOR]

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The discovery of the quantum Hall effect (QHE) in 1980 marked a turning point in condensed matter physics: given appropriate experimental conditions, the Hall conductivity σ x y of a two-dimensional electron system is exactly quantized. But what happens to the QHE in three dimensions (3D)? Experiments over the past 40 years showed that some of the remarkable physics of the QHE, in particular plateau-like Hall conductivities σ x y accompanied by minima in the longitudinal resistivity ρ x x , can also be found in 3D materials. However, since typically ρ x x remains finite and a quantitative relation between σ x y and the conductance quantum e 2 / h could not be established, the role of quantum Hall physics in 3D remains unsettled. Following a recent series of exciting experiments, the QHE in 3D has now returned to the center stage. Here, we summarize the leap in understanding of 3D matter in magnetic fields emerging from these experiments. [ABSTRACT FROM AUTHOR]

The nature of light, the existence of magnetism, and the physical meaning of a vacuum are the problems so deeply related to philosophy that they have been discussed for thousands of years. In this paper, we concentrate ourselves on a question that concerns the three of them: does light speed in a vacuum change when a magnetic field is present? The experimental answer to this fundamental question has not yet been given even if it has been stated in modern terms for more than a century. To fully understand the importance of such a question in physics, we review the main facts and concepts from the historical point of view. [ABSTRACT FROM AUTHOR]

The influence of various mechanical influences (transfusion, stirring, vibration, shaking, etc.) and magnetic installations (used in the application of spin chemistry methods) on colloidal solutions of protein and water, which are often used in pharmaceutical production, was studied. It has been shown that when mechanical influences are applied, physical and chemical properties of water and aqueous colloids of the IgG protein are changed. Magnetic fields do not have a significant effect on water; however, variation in a number of physical and chemical characteristics is observed in protein colloids. Moreover, the effect after exposure to magnetic fields with a frequency of 8 Hz is higher compared to the effect after exposure to magnetic fields with a frequency of 50 Hz. This effect persists even at extremely low concentrations of IgG protein molecules. The measurement system proposed in this work makes it possible to monitor the state of protein molecules in a non-invasive mode. In the future, optical and potentiometric methods built into flow systems can be used at all stages of the production of protein pharmaceuticals.

Both analytical and numerical methods have proven to be suitable for describing radiation transport and interactions. The standard Boltzmann formalism derived from statistical mechanics requires to be specifically re-formulated to account for the interactions with external electromagnetic fields. Verifying the proper implementation of the external electromagnetic field coupling in Monte Carlo simulation codes is a key issue to confirm the feasibility of using such a tool to describe complex applications like image-guided radiotherapy based on integrating magnetic resonance scanner to the radiant field of ionizing radiation along with the subsequent dosimetric effects. The present work reports on the feasibility and reliability of the Monte Carlo FLUKA and PENELOPE main codes to assess electron trajectory in presence of strong magnetic fields. The obtained results confirm the ability of FLUKA and PENELOPE to model the alterations in the electron trajectories due to external magnetic field effects, also demonstrating an excellent agreement between both codes and with the theoretical-analytical model.

Solar eruptions often show the rotation of filaments, which is a manifestation of the rotation of erupting magnetic flux rope (MFR). Such a rotation of MFR can be induced by either the torque exerted by a background shear-field component (which is an external cause) or the relaxation of the magnetic twist of the MFR (an internal cause). For a given chirality of the erupting field, both the external and internal drivers cause the same rotation direction. Therefore, it remains elusive from direct observations which mechanism yields the dominant contribution to the rotation. In this paper, we exploit a full MHD simulation of solar eruption by tether-cutting magnetic reconnection to study the mechanism of MFR rotation. In the simulation, the MFR’s height–rotation profile suggests that the force by the external shear-field component is a dominant contributor to the rotation. Furthermore, the torque analysis confirms that it is also the only factor in driving the counterclockwise rotation. On the contrary, the Lorentz torque inside the MFR makes a negative effect on this counterclockwise rotation.

Abstract Stable all‐inorganic CsPbX3 perovskite nanocrystals (PNCs) with high optical yield can be used in combination with graphene as photon sensors with high responsivity (up to 106 A W−1) in the VIS‐UV range. The performance of these perovskite/graphene field effect transistors (FET) is mediated by charge transfer processes at the perovskite – graphene interface. Here, the effects of high electric (up to 3000 kV cm−1) and magnetic (up to 60 T) fields applied perpendicular to the graphene plane on the charge transfer are reported. The authors demonstrate electric‐ and magnetic‐field dependent charge transfer and a slow (>100 s) charge dynamics. Magneto‐transport experiments in constant (≈0.005 T s−1) and pulsed (≈1000 T s−1) magnetic fields reveal pronounced hysteresis effects in the transfer characteristics of the FET. A magnetic time is used to explain and model differences in device behavior under fast (pulsed) and slowly (continuous) changing magnetic fields. The understanding of the dynamics of the charge transfer in perovskite/graphene heterostructures developed here is relevant for exploitation of these hybrid systems in electronics and optoelectronics, including ultrasensitive photon detectors and FETs for metrology.

This article proposes the study of Ampere's Law, which is taught in the Physics course of undergraduate engineering courses in Brazil, using the hypothesis of the finite-length conductor instead of the infinite-length conductor. For this, it is necessary to use Stokes' Theorem, which in the case of infinite conductor is dispensed with. The feasibility of this proposal is supported by the fact that the techniques to calculate the line integrals and flux integrals, necessary in our proposal, are taught in the disciplines of Calculus. This approach allows a clear distinction between the "current enclosed" by the closed curve of the amperian line integral and the current actually flowing through the conductor. With the assumption of the infinite length conductor these two currents are indistinguishable. Another benefit of this approach is that the displacement current can be introduced intuitively as the flux integral of the curl of the magnetic field that appears in one of the members of the Stokes equation. [ABSTRACT FROM AUTHOR]

Basic science courses, such as physics, are fundamental to precollege studies. For instance, in different engineering applications, electricity and magnetism require comprehending subjects such as electrical circuits and power electronics. However, abstract concepts such as electric or magnetic fields are often difficult to explain without visual tools. Computer programs designed for learning physics fundamentals are useful in this area because they allow the visualization, interaction and reinforcement of main concepts in a better way than using only blackboard. In this work, an interactive MATLAB based program to visualize a magnetic field in 3D was presented. The measurements were sampled by a computer-controlled Cartesian robot with a Hall effect sensor. The magnetic field was generated by an energized electromagnet to show the relationship between electricity and magnetism. The designed graphical user interface aims to stimulate interest in electromagnetism in precollege students. [ABSTRACT FROM AUTHOR]

By using the non-Markovian Quantum State Diffusion method, the non-Markovian dynamics of entanglement, quantum dense coding and quantum teleportation in the spin chain system with Kaplan-Shekhtman-Entin-wohlman-Aharony interactions and Dzyaloshinskii-Moriya in- teractions are studied. In particular, the joint effects of Kaplan-Shekhtman-Entin-wohlman-Aharony interactions and different external magnetic fields are discussed under zero and finite temperatures, respectively. The results show that the concurrence, channel capacity of quantum dense coding and average fidelity of quantum teleportation can be effectively increased via the increasing of Kaplan-Shekhtman-Entin-wohlman-Aharony interactions along the z-direction which can be attributed to the constructive role of Kaplan-Shekhtman-Entin-wohlman-Aharony interactions on the O(3) invariance in the spin chain. Non-uniform magnetic fields with the combination of Kaplan-Shekhtman-Entin-wohlman-Aharony interactions are found to be more effective in the increasing of the parameters under discussion.

We present the magnetically shielded room (MSR) for the n2EDM experiment at the Paul Scherrer Institute, which features an interior cubic volume with each side of length 2.92 m, thus providing an accessible space of 25 m3. The MSR has 87 openings of diameter up to 220 mm for operating the experimental apparatus inside and an intermediate space between the layers for housing sensitive signal processing electronics. The characterization measurements show a remanent magnetic field in the central 1 m3 below 100 pT and a field below 600 pT in the entire inner volume, up to 4 cm to the walls. The quasi-static shielding factor at 0.01 Hz measured with a sinusoidal 2 μT peak-to-peak signal is about 100 000 in all three spatial directions and increases rapidly with frequency to reach 108 above 1 Hz. [ABSTRACT FROM AUTHOR]

We perform a geomagnetic event simulation using a newly developed magnetohydrodynamic with adaptively embedded particle‐in‐cell (MHD‐AEPIC) model. We have developed effective criteria to identify reconnection sites in the magnetotail and cover them with the PIC model. The MHD‐AEPIC simulation results are compared with Hall MHD and ideal MHD simulations to study the impacts of kinetic reconnection at multiple physical scales. At the global scale, the three models produce very similar SYM‐H and SuperMag Electrojet indexes, which indicates that the global magnetic field configurations from the three models are very close to each other. We also compare the ionospheric solver results and all three models generate similar polar cap potentials and field‐aligned currents. At the mesoscale, we compare the simulations with in situ Geotail observations in the tail. All three models produce reasonable agreement with the Geotail observations. At the kinetic scales, the MHD‐AEPIC simulation can produce a crescent shape distribution of the electron velocity space at the electron diffusion region, which agrees very well with MMS observations near a tail reconnection site. These electron scale kinetic features are not available in either the Hall MHD or ideal MHD models. Overall, the MHD‐AEPIC model compares well with observations at all scales, it works robustly, and the computational cost is acceptable due to the adaptive adjustment of the PIC domain. It remains to be determined whether kinetic physics can play a more significant role in other types of events, including but not limited to substorms. Key Points: We perform a global simulation of a geomagnetic storm event with kinetic modeling of the magnetotail reconnectionThe kinetic region is adaptively embedded to the magnetohydrodynamic model and the reconnection sites are identified by physical criteria during the runtimeThe global scale, mesoscale, and electron scale features are observed simultaneously in one simulation [ABSTRACT FROM AUTHOR]

In this paper, the standing magnetohydrodynamic slow waves in the magnetic flux tubes are investigated under coronal conditions. The temperature and equilibrium plasma density of the tube is assumed to be homogeneous and constant and the compressive viscosity is considered as the damping mechanism. Also, the plasma flow is considered in the flux tube. Assuming that the damping rate to be much smaller than the oscillation frequency of the waves, the perturbation method is used to solve the problem. The oscillation frequency and the eigenfunctions are found from the first-order perturbation while the damping rate is determined from the second-order perturbation. To increase the flow speed makes the oscillation frequency decreases and the damping rate increases. Also, increasing each of the flow speed and background temperature of the tube, decreases the ratio of the damping time to the oscillation period. But this ratio increases due to the increasing the length of the tube The results found here are consistent with the theoretical results obtained earlier. Also, the obtained results can justify some observational cases.

Background: The literature on the use of static magnetic field (SMF), particularly in orthodontics, has certain gaps. Furthermore, the mechanism by which SMF affects orthodontic tooth movement (OTM) is still unclear and quite contradictory. Thus, the goal of this systematic review and meta-analysis was to assess SMF’s effect on OTM. This study also sought to analyse the variability of the studies included in the analysis and the size of the impact of SMF on OTM. Methods: Using the PRISMA guidelines, reviewers implemented a search strategy across several online databases, filtering out the initial articles that were obtained by applying relevant inclusion and exclusion criteria. Results: The overall effect size for the odds ratio was found to be 0.58, with a 95% confidence interval ranging from 0.40 to 0.86. This indicates that exposure to static magnetic fields is associated with a significantly reduced likelihood of orthodontic tooth movement in the animal studies analysed. Similarly, the overall effect size for the risk ratio was calculated to be 0.71, with a 95% confidence interval ranging from 0.55 to 0.91. The risk ratio also suggests a significant impact of SMF on OTM, with animals exposed to magnetic fields being at a lower risk of experiencing substantial tooth movement compared to those not exposed. However, it is important to note that moderate heterogeneity was observed among the included studies. Conclusion: The findings of this systematic review and meta-analysis indicate that there may be a causal relationship between OTM and SMF. However, the small number of studies included in this review and their poor methodological quality limit the available data, highlighting the need for further well-designed research to support these conclusions.

Homogeneous magnetic field is widely used in various applications, and Helmholtz and Merritt coils are the most commonly used homogeneous field generators. However, only the field homogeneity at the center point is concerned in their design, which leads to restriction for most applications, where a certain volume of homogeneous field is required. This indicates that traditional coil configurations can be further optimized. Based upon a comprehensive definition of homogeneous field, improved three-s and four-coil configurations are proposed in this article. Practical formulae with normalized coil parameters are given to provide a convenient tool for designers. These formulae establish relationships between coil parameters and the required homogeneous field. The accuracy of the formulae is verified by the finite-element analysis. Comparisons with Merritt coils show that, when getting the same homogeneous field, the improved coils can reduce both power loss and conductor mass by up to 24.8%. Through a comparison among main coil configurations, the improved four-coil configuration is recommended for homogeneous magnetic field generation. For high-intensity magnetic field applications, the winding cross-section effect is analyzed. At last, experiments are performed to verify the theoretical analysis, and the reason why the improved coils have better performance than traditional ones is revealed. [ABSTRACT FROM AUTHOR]

The Australian MRI-Linac prototype radiotherapy system has been shown to generate significant entry skin or surface dose increases. This arises from electron contamination focusing toward the isocenter caused by the 1 T MRI field being in-line with the x-ray beam. The aim of this study is to present accurate Monte Carlo modeling of these skin dose changes and to compare them with previous experimental measurements. Accurate skin dose modeling will improve confidence in the pathway forward to treatment planning for clinical trials. A COMSOL Multiphysics model of the Australian MRI-Linac system was used to generate a 3D magnetic field map to be used in corresponding Geant4 Monte Carlo simulations. The Geant4 simulations included the x-ray source (6 MV Linac), multileaf collimators (MLCs), and a 30 cm × 30 cm × 30 cm water phantom located with its front surface at the beam isocenter. Simulations were performed with a source to surface distance (SSD) of 1,819 mm for nominal field sizes 2 cm × 2 cm, 6 cm × 6 cm, and 10 cm × 10 cm. Central axis percentage depth dose (PDD) and surface (or skin) doses at 70 μm depth were calculated by using high-resolution scoring voxels of 10 μm thickness. The results were compared with corresponding experimental data collected using MOSkin™ on the Australian MRI-Linac prototype system. The accurate modeling provides great detail into how the electron contamination is heavily confined and focused toward the beam central axis due to the presence of in-line magnetic field. This concentration significantly increases the skin dose up to 320% for the field size of 10 cm × 10 cm. For 2 cm × 2 cm and 6 cm × 6 cm, the surface skin dose is 128% and 217%, respectively, as compared to the skin dose in the absence of the magnetic field. The simulation results are in generally good agreement, ±10%, with previously collected experimental data for the same nominal field sizes. For the first time, detailed Geant4 Monte Carlo simulations of the electron contamination in the Australian MRI-Linac system have been performed and confirmed to be sufficiently accurate. These simulations will provide a solid framework for estimating the skin dose changes in more clinically relevant treatment plan scenarios that are envisaged in the near future.

Alfvénic component of MHD turbulence damps Alfvénic waves. The consequences of this effect are important for many processes, from cosmic ray (CR) propagation to launching outflows and winds in galaxies and other magnetized systems. We discuss the differences in the damping of the streaming instability by turbulence and the damping of a plane parallel wave. The former takes place in the system of reference aligned with the local direction of magnetic field along which CRs stream. The latter is in the reference frame of the mean magnetic field and traditionally considered in plasma studies. We also compare the turbulent damping of streaming instability with ion-neutral collisional damping, which becomes the dominant damping effect at a sufficiently low ionization fraction. Numerical testing and astrophysical implications are also discussed.