Field Generation Research Articles

Orthonormalization of phase-only basis functions

Generation of orthonormal optical fields using phase-only spatial light modulators (SLM) or amplitude-only digital micromirror devices (DMD) is an active and diverse research field, with a wide variety of applications. However, these approaches typically come with limited accuracy, and a significant loss in resolution and intensity. We present a different approach: we construct orthonormal fields that can be generated exactly on phase-only hardware without loss of resolution or intensity. Our method can use any set of fields as a starting point and orthonormalize them. Our approach allows control over application-specific requirements such as smoothness, symmetry and overall shape. In many use cases, sets of orthonormal fields can be used as a ‘drop-in replacement’ for other sets of fields. We demonstrate the practical benefit of our approach in a wavefront shaping experiment, achieving a factor 1.5 increase in performance over a non-orthonormal phase-only basis.

Electromagnetically induced transparency and second-order sideband Effects in a Laguerre-Gaussian cavity optorotational system with Kerr medium

Abstract In this paper, we investigate the phenomena of electromagnetically induced transparency (EIT) and the generation of second-order sideband in a Laguerre-Gaussian (LG) cavity optorotational sys tem with a Kerr nonlinear medium. Using the perturbation method, we analyze the first- and second order sideband generations in the output field from the system under the actions of a strong control
field and a weak probe field. Numerical simulations show that the Kerr nonlinearity can lead to the occurrence of the asymmetric line shape in the transmission of the probe field and the efficiency of second-order sideband generation, and the Kerr nonlinearity can enhance the efficiency of the second order sideband generation. Comparing with traditional scheme for generating the second-order sideband, our spectral shape of the second-order sideband is amplified and becomes asymmetric, which has potential applications in precision measurement, high-sensitivity devices, and frequency conversion.

Influence of oxygen on electronic correlation and transport in iron in the Earth’s outer core

Knowing the transport properties of iron at the Earth’s core conditions is essential for the geophysical modeling of Earth’s magnetic field generation. Besides by extreme pressures and temperatures (which cause scattering by thermal disorder to dominate), transport may be also influenced by the presence of light elements and electron-electron scattering. We used a combination of molecular dynamics, density functional theory, and dynamical mean-field theory methods to examine the impact of oxygen impurities on the electronic correlations and transport in the Earth’s liquid outer core. We find electronic correlations to be moderately enhanced by oxygen admixture. At realistic 10 atomic% of oxygen, the thermal conductivity suppression by electronic correlations (about 20%) is of the same magnitude as that due to oxygen inclusion. Hence, both play an equally important role in reducing the conductivity and stabilizing the geodynamo. We also explain the reduction of Lorenz ratio in core matter.

Twist-angle dependent pseudo-magnetic fields in monolayer CrCl2/graphene heterostructures.

The generation of pseudo-magnetic fields in strained graphene leads to quantized Landau levels in the absence of an external magnetic field, providing the potential to achieve a zero-magnetic-field analogue of the quantum Hall effect. Here, we report the realization of a pseudo-magnetic field in epitaxial graphene by building a monolayer CrCl2/graphene heterointerface. The CrCl2 crystal structure exhibits spontaneous breaking of three-fold rotational symmetry, yielding an anisotropic displacement field at the interface. Using scanning tunneling spectroscopy, we have discovered a sequence of pseudo-Landau levels associated with massless Dirac fermions. A control experiment performed on the CrCl2/NbSe2 interface confirms the origin as the pseudo-magnetic field in the graphene layer that strongly interacts with CrCl2. More interestingly, the strength of the pseudo-magnetic fields can be tuned by the twist angle between the monolayer CrCl2 and graphene, with a variation of up to threefold, depending on the twist angle of 0° to 30°. This work presents a rare 2D heterojunction for exploring PMF-related physics, such as the valley Hall effect, with the advantage of easy and flexible implementation.

Gravitational-wave signatures of gravito-electromagnetic couplings

Gravitational waves (GWs) can undoubtedly serve as a messenger from the early Universe acting as well as a novel probe of the underlying gravity theory. In this work, motivated by one-loop vacuum-polarization effects on curved spacetime, we investigate a gravitational theory with non-minimal curvature-electromagnetic coupling terms of the form ξR/M Pl2 F μν F μν , where M Pl is the reduced Planck mass, R is the scalar curvature and F μν the Faraday tensor, being responsible for the generation of primordial electromagnetic fields. We study then the GW signatures of such coupling terms deriving in particular for the first time to the best of our knowledge the modified tensor modes equation of motion. Remarkably, we find a universal infrared (IR) frequency scaling f 5 of the electromagnetically induced GW (EMIGW) signal, which, depending on the energy scale of inflation, the duration of inflation and reheating as well as the dynamical behaviour of the coupling function ξ, can be well within the detection sensitivity bands of GW experiments such as SKA, LISA, ET and BBO, being thus potentially detectable in the future by GW observatories.

Research on Magnetic Field Generator and Vibration Measurement Errors in the Development of Eco-friendly Vehicle Noise and Vibration

Research on Magnetic Field Generator and Vibration Measurement Errors in the Development of Eco-friendly Vehicle Noise and Vibration

Force free magnetic flux rope with a high current density on the axis

A new model of a force-free magnetic flux rope with a high concentration of electric current on the axis is presented. The general property of axisymmetric force-free magnetic ropes is that with the exit of the top of the magnetic loop-rope into the corona, the external pressure that keeps it from lateral expansion steadily decreases, and with some critical decrease in this pressure, the longitudinal magnetic field of the rope becomes zero on the surface where the electric current changes its sign (it is current inversion surface — CIS). In this case, the force-free parameter α(r) and the azimuthal electric current experience a second-order discontinuity on this surface, so that in the vicinity of CIS their values begin to increase without limit. The current (drift) speed of electrons here will inevitably exceed the speed of ion sound. This serves as a trigger for the heating of non-isothermal plasma (so it turns out Te Ti) and the excitation of plasma ion-acoustic instability of the plasma not only near the CIS, but also in the central region of the rope, on its axis, where the current density is especially high. The appearance of anomalous resistance leads to rapid dissipation of the magnetic field and the generation of a super-Dreicer electric field. The Parker effect, associated with the equalization (with some delay) of the torque along the axis of the rope due to the transfer of the azimuthal field to the region of energy release, leads to quasiperiodic pulsations of hard flare radiation and, ultimately, ensures the flare release of the most part of free magnetic energy accumulated in the rope.

On machine learnability of local contributions to interatomic potentials from density functional theory calculations

Machine learning interatomic potentials, as a modern generation of classical force fields, take atomic environments as input and predict the corresponding atomic energies and forces. We challenge the commonly accepted assumption that the contribution of an atom can be learned from the short-range local environment of that atom. We employ density functional theory calculations to quantify the decay of the induced electron density and electrostatic potential in response to local perturbations throughout insulating, semiconducting and metallic samples of different dimensionalities. Molecules and thin layers are shown to fail keeping such disturbances localized. Therefore, the learnability of local atomic contributions, which guarantees scalability and transferability of a machine learning interatomic potential, is questionable in the case of molecules and low-dimensional samples. Similarly, the induced electrostatic effects due to substituted impurities or vacancy sites in a crystalline bulk are weakly damped and remain significant beyond several interatomic distances. However, geometric deformations in bulks are practically local within the first neighbors and induce a Yukawa-type electrostatic potential that exponentially vanishes. The practical importance of this finding is that it limits the application of the machine learning interatomic potentials to conformational search or thermal properties of bulk materials and so on, where only purely geometrical deformations are involved. Once chemically impactful defects like aliovalent impurities or vacancies are present, the interatomic potentials trained on local environments need to be corrected for long-range effects.

Diamagnetic levitation of water realized with a simple device consisting of ordinary permanent magnets

Diamagnetic levitation is an appealing technique for levitating objects at room temperature without subjecting the sample to potentially damaging control fields, such as high-intensity laser light or sound pressure. However, owing to the extremely low magnetic susceptibility of diamagnetic materials, except for bismuth and graphite, diamagnetic levitation generally necessitates the use of exceptionally strong magnets, such as those found in world-class high-field facilities. This study simulated the magnetic field distribution in a narrow valley formed between two adjacent rectangular cuboid magnets with antiparallel magnetizations, at a spatial resolution of 5 μm. The simulations indicated the generation of a strong magnetic force field, B∂B/∂z(>40 000 T2/m), which could lift not only light organic compounds but also dense metallic compounds. Moreover, the addition of another pair of smaller sized magnets provided a local potential minimum that satisfied the conditions for non-contact levitation. Based on these results, a compact magnetic levitation system was developed by combining four small commercially available magnets. Experimental results showed that a water droplet of approximately 0.3 mm diameter was levitated. The experimental space was nearly sealed and highly resistant to external disturbances, such as vibrations, allowing the water to remain in a non-contact levitated state unless the operator intentionally shook the experimental table or directed airflow to displace the water away. The device is expected to facilitate various applications in materials science and fluid dynamics as well as promote preliminary ground-based research on space-related experiments designed to be conducted in microgravity environments.

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

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

FEATURES OF GENERATION OF SPONTANEOUS MAGNETIC FIELDS IN FULLY IONIZED PLASMA

In this paper, magnetic field generation in a fully ionized plasma is discussed both in the presence and absence of an external constant magnetic field. Considering the dependence of the transfer coefficients on the magnetic field, Braginsky's equations are applied to describe collective processes in plasma. Criteria for the formation of instabilities and, consequently, the generation of magnetic fields are obtained, taking into account convective heat transfer and thermomagnetic phenomena. We derive expressions for the growth rate of perturbations in the magnetic field and the temperature in the short-wave range.

Origin of fast charging in solid-state batteries revealed by Cryo-transmission X-ray microscopy

The interface issue poses a limitation on the fast charging of solid-state batteries (SSBs), with the high-impedance non-Faraday electric field serving as a pivotal factor. However, the mechanism of fast-charging capability degradation triggered by the dynamic evolution of non-Faraday electric fields remains unclear due to the lack of particle-scale nondestructive detection techniques. Here, we dissect the generation and elimination processes of non-Faradaic electric field in segments using the developed operando cryogenic transmission X-ray microscopy (Cryo-TXM). This method accurately tracks the ion self-balancing pathways in LiNi0.8Co0.1Mn0.1O2 (NCM811) post-fast-charging, elucidating the high polarization during late charging caused by exacerbated irreversible local electric field. By intermittently applying reverse potential during fast charging to alleviate the exacerbation of non-Faradaic electric field at the cathode interface, we achieved a roughly 400% reversible capacity increase of SSBs at 10 C. This insightful dynamic imaging method effectively captures and resolves the transient, opaque signals within SSBs, significantly enhancing their fast-charging performance.

Mass Transfer and MHD Free Convection Flow Across a Stretching Sheet with a Heat Source and Chemical Reaction

This work examines mass transfer and MHD free convective flow across a stretching sheet in the presence of a heat source and a chemical reaction. The sheet's stretching action propels the flow, while a magnetic field applied perpendicular to the flow direction influences it. The effects of gradients in temperature and concentration on buoyant forces are also taken into account. The continuity, momentum, energy, and concentration equations are among the coupled nonlinear partial differential equations that regulate the system. Similarity transformations are used to convert these equations into a system of ordinary differential equations, which are then numerically solved using bvp4c techniques. In this investigation, magnetic, buoyancy, chemical reaction rate, and heat source factors are the main parameters of interest. The outcomes show the influence of these parameters on the boundary layer's temperature, concentration, and velocity profiles. To quantify the mass transfer rate, heat transfer rate, and shear stress at the sheet surface, the skin friction coefficient, Nusselt number, and Sherwood number are calculated. By manipulating the magnetic field, chemical reactions, and heat generation, the work offers important new insights into how to best utilise MHD flows in industrial processes, such as polymer manufacturing, chemical reactors, and cooling systems.

Emulation of f(R) modified gravity from ΛCDM using conditional GANs

Abstract A major aim of cosmological surveys is to test deviations from the standard ΛCDM model, but the full scientific value of these surveys will only be realised through efficient simulation methods that keep up with the increasing volume and precision of observational data. N-body simulations of modified gravity (MG) theories are computationally expensive since highly non-linear equations must be solved. This represents a significant bottleneck in the path to reach the data volume and resolution attained by equivalent ΛCDM simulations. We develop a field-level neural network-based emulator that generates density and velocity divergence fields under the f(R) gravity MG model from the corresponding ΛCDM simulated fields. Using attention mechanisms and a complementary frequency-based loss function, our model is able to learn this intricate mapping. We use the idea of latent space extrapolation to generalise our emulator to f(R) models with differing field strengths. The predictions of our emulator agree with the f(R) simulations to within 5% for matter density and to within 10% for velocity divergence power spectra up to k ∼ 2 h Mpc−1. But for a few select cases, higher-order statistics are reproduced with ≲10% agreement. Latent extrapolation allows our emulator to generalise to different parameterisations of the f(R) model without explicitly training on those variants. Given a ΛCDM simulation, the GPU-based emulator can reproduce the equivalent f(R) realisation ∼600 times faster than full N-body simulations. This lays the foundations for a valuable tool for realistic yet rapid mock field generation and robust cosmological analyses.

Magnetic seed generation by plasma heat flux in accretion disks

Magnetic batteries are potential sources that may drive the generation of a seed magnetic field, even if this field is initially zero. These batteries can be the result of nonaligned thermodynamic gradients in plasmas, as well as of special and general-relativistic effects. So far, magnetic batteries have only been studied in ideal magnetized fluids. We studied the nonideal fluid effects introduced by the energy flux in the vortical dynamics of a magnetized plasma in curved space-time. We propose a novel mechanism for generating a heat-flux-driven magnetic seed within a simple accretion disk model around a Schwarzschild black hole. We used the 3+1 formalism for the splitting of the space-time metric into space-like and time-like components. We studied the vortical dynamics of a magnetized fluid with a heat flux in the Schwarzschild geometry in which thermodynamic and hydrodynamic quantities are only dependent on the radial coordinate. Assuming that the magnetic field is initially zero, we estimated the linear time evolution of the magnetic field due to the inclusion of nonideal fluid effects. When the thermodynamic and hydrodynamic quantities vary only radially, the effect of the coupling between the heat flux, the space-time curvature, and the fluid velocity acts as the primary driver for an initial linearly time-growing magnetic field. The plasma heat flux completely dominates the magnetic field generation at a specific distance from the black hole, where the fluid vorticity vanishes. This distance depends on the thermodynamical properties of the Keplerian plasma accretion disk. These properties control the strength of the nonideal effects in the generation of seed magnetic fields. We find that heat flux is the main driver of a seed magnetic field in black hole accretion disks if the geometry, plasma dynamics, and thermodynamics share the same axial symmetry. This suggests that nonideal fluid effects may play a major role in the magnetization of astrophysical plasmas.

A game-theoretic driver steering model with individual risk perception field generation

Driver-automation shared steering control (SSC) has emerged as a promising technology for enhancing vehicle safety, but desire to achieve seamless collaboration between the driver and automation requires an in-depth understanding of driver steering behavior in interaction with automation. In this paper, we introduce a game-theoretic driver steering model with individual risk perception field generation. Firstly, a driver risk perception field is developed based on a novel concept of potential injury risk (PIR) to provide a quantitative estimation of the driver’s perceived driving risk. This approach offers an explicit and physically meaningful structure for simulating the driver’s risk perception process and elucidating the reasons for discrepancies in risk perception. Then, this driver risk perception field is integrated into the framework of non-cooperative Nash game to model the steering interaction between the driver and automation, and the analytical expression of Nash equilibrium is derived in detail. The resulting combined driver model effectively captures the driver adaptation at both the control and planning levels. Next, the key parameters of the combined driver model and its comparators are identified using measured driver steering behavior data from thirty subjects in a series of driving simulator experiments. Finally, the effectiveness and superiority of the combined driver model is validated through a comprehensive comparative analysis. The results demonstrate that the combined driver model achieves the lowest prediction errors compared to its comparators and effectively captures the individual differences in risk perception and steering behavior.

Relationship of Asymmetries in the Distribution of Solar Tracer Activity and Generation of the Solar Magnetic Field

Relationship of Asymmetries in the Distribution of Solar Tracer Activity and Generation of the Solar Magnetic Field

The Role of Accelerated Electron Beams in the Generation of Intense Current Structures and Nonideal Electric Fields in the Outer Region of the Plasma Sheet

The Role of Accelerated Electron Beams in the Generation of Intense Current Structures and Nonideal Electric Fields in the Outer Region of the Plasma Sheet

Axial Field of View Expansion by Switchable Halbach Dipole Rings: A Simulation Study

Abstract In Magnetic particle imaging (MPI), the spatial encoding of the particle response is achieved by a magnetic gradient field called selection field. In this work a selection field generator based on two pairs of nested and freely rotatable Halbach cylinders in dipole configuration generating a gradient field in form of a linear field free region (FFR) is proposed. Through adequate rotation of the Halbach dipoles the FFR can be moved continuously along the cylinder axis. To understand and evaluate the movement of the FFR for different sequences of dipole rotations a simulation study is conducted. The simulation is based on the approximation of a permanent magnet’s field as a magnetic dipole field, so that the Halbach cylinder field results from the superposition of circularly arranged magnetic dipole moments. By the summation of four Halbach dipole fields the selection field can be calculated. It has turned out that the opposite rotation and the matching field strengths of the dipoles of a pair are prerequisites for the movement of the FFR. With regard to the gradient field strengths and the movement speed of the FFR within a potential imaging area, a phase-shifted rotation of two pairs seems promising for the use in MPI.

Stable Stratification of the Helium Rain Layer Yields Vastly Different Interiors and Magnetic Fields for Jupiter and Saturn

At sufficiently high pressures (∼Mbar) and low temperatures (∼103–104 K), hydrogen and helium become partly immiscible. Interpretations of Jupiter’s and Saturn’s magnetic fields favor the existence of a statically stable layer near the Mbar pressure level. From experimental and computational data for the hydrogen–helium phase diagram, we find that moist convection and diffusive convection are inhibited, implying a stable helium rain layer in both Jupiter and Saturn. However, we find a significant difference in terms of structure and evolution: in Jupiter, helium settling leads to a stable yet superadiabatic temperature gradient that is limited by conductive heat transport. The phase separation region should extend only a few tens of kilometers, instead of thousands in current-day models, and be characterized by a sharp increase of the temperature of about 500 K for standard phase separation diagrams. In Saturn, helium rains occur much deeper, implying a larger helium flux relative to planetary mass. We find that the significant latent heat associated with helium condensation implies that a large fraction, perhaps close to 100%, of the planet’s intrinsic heat flux may be locally transported by the sinking helium droplets. This implies that Saturn may possess a much more extended helium rain region. This also accounts, at least qualitatively, for the differences in strength and characteristics of the magnetic fields of the two planets. Dedicated models of magnetic field generation in both planets may offer observational constraints to further refine these findings.