Constant External Magnetic Field Research Articles

Fluctuation Relations for Dissipative Systems in Constant External Magnetic Field: Theory and Molecular Dynamics Simulations

We illustrate how, contrary to common belief, transient Fluctuation Relations (FRs) for systems in constant external magnetic field hold without the inversion of the field. Building on previous work providing generalized time-reversal symmetries for systems in parallel external magnetic and electric fields, we observe that the standard proof of these important nonequilibrium properties can be fully reinstated in the presence of net dissipation. This generalizes recent results for the FRs in orthogonal fields—an interesting but less commonly investigated geometry—and enables direct comparison with existing literature. We also present for the first time a numerical demonstration of the validity of the transient FRs with nonzero magnetic field via nonequilibrium molecular dynamics simulations of a realistic model of liquid NaCl.

Fractional calculus approach for the phase dynamics of Josephson junction

• Phase dynamics of inline Josephson junction in voltage state is discussed. • Phase difference between the wave functions is analyzed via fractional calculus. • Hereditary effects for phase dynamics of Josephson junction are explored. • Finite element scheme is used for the simulations of governing equations. This article presents the phase dynamics of an inline long Josephson junction in voltage state under the influence of constant external magnetic field. Fractional calculus approach is used to model the evolution of the phase difference between the macroscopic wave functions of the two superconductors across the junction. The governing non-linear partial differential equation is then solved using finite difference-finite element schemes. Other quantities of interest like Josephson current density and voltage across the junction are also computed. The effects of various parameters in the model on phase difference,Josephson current density and voltage are analyzed graphically with the help of numerical simulations.

Enhancing the efficiency of the hydrogen evolution reaction utilising Fe3P bulk modified screen-printed electrodes via the application of a magnetic field.

We report the fabrication and optimisation of Fe3P bulk modified screen-printed electrochemical platforms (SPEs) for the hydrogen evolution reaction (HER) within acidic media. We optimise the achievable current density towards the HER of the Fe3P SPEs by utilising ball-milled Fe3P variants and increasing the mass percentage of Fe3P incorporated into the SPEs. Additionally, the synergy of the application of a variable weak (constant) external magnetic field (330 mT to 40 mT) beneficially augments the current density output by 56%. This paper not only highlights the benefits of physical catalyst optimisation but also demonstrates a methodology to further enhance the cathodic efficiency of the HER with the facile application of a weak (constant) magnetic field.

Dynamic Stoner–Wohlfarth Model for Time-Dependent Magnetization Analysis

In this letter, we present a numerical model of magnetization dynamics that is based on the classical Stoner–Wohlfarth model and the Landau–Lifshitz–Gilbert equation. This approach uses a series of coefficients for the interpolation of the time needed by the magnetic moment to reach equilibrium and a linear system of equations for the variation in time of the angular components of the magnetization. The dynamic Stoner–Wohlfarth model will be used to accurately replicate the dynamic behavior of macrospins with significantly improved numerical efficiency when a constant or variable external magnetic field is applied.

Mean-field BCS theory of the Meissner effect in bulk revisited

We show that the implementation of the 1/ c^2 transverse current–current interaction between electrons resulting from the non-relativistic QED into the standard self-consistent electron BCS model in bulk under thermal equilibrium in the stable superconductive phase ensures the full compensation of a constant external magnetic field by the internal magnetic field created by the electrons, i.e. one has an ideal diamagnet.Graphic

Asymptotic Growth of the Local Ground-State Entropy of the Ideal Fermi Gas in a Constant Magnetic Field

We consider the ideal Fermi gas of indistinguishable particles without spin but with electric charge, confined to a Euclidean plane {{mathbb {R}}}^2 perpendicular to an external constant magnetic field of strength B>0. We assume this (infinite) quantum gas to be in thermal equilibrium at zero temperature, that is, in its ground state with chemical potential mu ge B (in suitable physical units). For this (pure) state we define its local entropy S(Lambda ) associated with a bounded (sub)region Lambda subset {{mathbb {R}}}^2 as the von Neumann entropy of the (mixed) local substate obtained by reducing the infinite-area ground state to this region Lambda of finite area |Lambda |. In this setting we prove that the leading asymptotic growth of S(LLambda ), as the dimensionless scaling parameter L>0 tends to infinity, has the form Lsqrt{B}|partial Lambda | up to a precisely given (positive multiplicative) coefficient which is independent of Lambda and dependent on B and mu only through the integer part of (mu /B-1)/2. Here we have assumed the boundary curve partial Lambda of Lambda to be sufficiently smooth which, in particular, ensures that its arc length |partial Lambda | is well-defined. This result is in agreement with a so-called area-law scaling (for two spatial dimensions). It contrasts the zero-field case B=0, where an additional logarithmic factor ln (L) is known to be present. We also have a similar result, with a slightly more explicit coefficient, for the simpler situation where the underlying single-particle Hamiltonian, known as the Landau Hamiltonian, is restricted from its natural Hilbert space text{ L}^2({{mathbb {R}}}^2) to the eigenspace of a single but arbitrary Landau level. Both results extend to the whole one-parameter family of quantum Rényi entropies. As opposed to the case B=0, the corresponding asymptotic coefficients depend on the Rényi index in a non-trivial way.

Numerical modeling of electric arc motion in external constant magnetic field

The paper generalizes to the three-dimensional case the previously proposed two-dimensional mathematical model of the motion of a plasma formation in a constant transverse magnetic field. The complete system of single-fluid magnetogasdynamic approximation of the equations of the hydrodynamic method for plasma description under conditions of local thermodynamic equilibrium is simplified in the electromagnetic part. Instead of solving the complete system of Maxwell’s equations, Ohm’s integral law is applied to the conducting region with usage of empirical data. Earlier studies in a two-dimensional version of this model as applied to the problem of describing the motion of an arc showed its effectiveness and efficiency for the class of problems under consideration. The simulation results with proposed extended model are compared with previously obtained calculated and experimental data. Main integral and local features of flow structure are highlighted.

On the creation of charged massless fermion pair by a photon in an external constant uniform magnetic field in 2+1 dimensions

Creation of charged massless fermion pair by a photon in a constant uniform magnetic field is considered in the one-loop approximation of the [Formula: see text]-dimensional quantum electrodynamics (QED[Formula: see text]). We calculate the elastic scattering amplitude (EAS) of photon using the polarization operator of photon in the above magnetic field obtained earlier in our work. We analyze the elastic scattering amplitude of photon at various values of the photon energy and magnetic field strength. Very simple analytical formulas for EAS of photon are obtained in the so-called quasi-classical region. In the massive quantum electrodynamics the elastic scattering amplitude of photon defines its “mass” squared in the presence of external electromagnetic field and the imaginary part of EAS describes the total probability of charged massive fermion pair creation in the electromagnetic field; we assume that it is the case and in the massless quantum electrodynamics.

Interacting hadron resonance gas model in magnetic field and the fluctuations of conserved charges

In this paper we discuss the interacting hadron resonance gas (HRG) model in presence of a constant external magnetic field. The short range repulsive interaction between hadrons are accounted through Van der Waals excluded volume correction to the ideal gas pressure. Here we take the sizes of hadrons as r π (pion radius) = 0 fm, r K (kaon radius) = 0.35 fm, r m (all other meson radii) = 0.3 fm and r b (baryon radii) = 0.5 fm. We analyse the effect of uniform background magnetic field on the thermodynamic properties of interacting hadron gas. We especially discuss the effect of interactions on the behaviour of magnetization of low temperature hadronic matter. The vacuum terms have been regularized using magnetic field independent regularization scheme. We find that the magnetization of hadronic matter is positive which implies that the low temperature hadronic matter is paramagnetic. We further find that the repulsive interactions have very negligible effect on the overall magnetization of the hadronic matter and the paramagnetic property of the hadronic phase remains unchanged. We have also investigated the effects of short range repulsive interactions as well as the magnetic field on the baryon and electric charge number susceptibilities of hadronic matter within the ambit of excluded volume HRG model.

Chiral separation effect in nonhomogeneous systems

We discuss chiral separation effect in the systems with spatial nonhomogeneity. It may be caused by nonuniform electric potential or by another reasons, which do not, however, break chiral symmetry of an effective low energy theory. Such low energy effective theory describes quasiparticles close to the Fermi surfaces. In the presence of constant external magnetic field the nondissipative axial current appears. It appears that its response to chemical potential and magnetic field (the CSE conductivity) is universal. It is robust to smooth modifications of the system and is expressed through an integral over a surface in momentum space that surrounds all singularities of the Green function. In itself this expression represents an extension of the topological invariant protecting Fermi points to the case of inhomogeneous systems.

Experimental and numerical research of stress relaxation behavior of magnetorheological elastomer

The paper presents experimental research and viscoelastic modeling of stress relaxation response of isotropic magnetorheological elastomer (MRE). The isotropic MRE has been prepared based on silicone matrix filled by magnetically micro-sized carbonyl iron particles. Effects of constant strain level and external magnetic field on the stress relaxation behavior of the MRE were carefully investigated by single- and multi-step relaxation tests in shear mode using double-lap shear specimens. Results revealed that the stress relaxation response of the MRE was dependent on the applied constant strain and external magnetic field. The relaxed stress and modulus of the MRE increased with increasing the constant strain level. In addition, the values of absolute stress and modulus in the relaxation periods enhanced with the rise of magnetic flux density. A four-parameter fractional derivative viscoelastic model was used to describe the stress relaxation behavior of the MRE. The studied model was fitted well to experimental data of the MRE in both single- and multi-step relaxation tests. The fitting of shear-stress relaxation modulus for the MRE is in a very good agreement with the experimental one. Effects of applied constant strain and magnetic field intensity on the fitted parameters were discussed. Moreover, the model can be applied to predict accurately the long-term relaxation behavior of the MRE.

Magnetic line source diffraction by a conductive half‐plane in an anisotropic plasma

AbstractAn integral theory that is associated with the scattered fields is considered for the solution of H‐polarized line source diffraction by a conductive half‐plane, which is surrounded by an anisotropic plasma. As the anisotropy does not affect an E‐polarized incident wave, only one polarization case is considered. The cold plasma medium is characterized by the dielectric tensor. The constant external magnetic field producing the anisotropy in a cold plasma is applied parallel to the edge of the half‐plane. The total, scattered, and diffracted waves are derived in terms of the Fresnel functions. Therefore, finite magnitude values at the transition boundaries are obtained. The wave behaviours are investigated numerically for different quantities of the medium.

Nonlinear Waves and Coherent Structures in Laser Induced Plasmas and Polarized Vacuum

Starting from the Vlasov–Maxwell equations describing the dynamics of various species in a free quasi-neutral plasma, an exact relativistic hydrodynamic closure for a special type of water-bag distributions satisfying the Vlasov equation has been derived.It has been shown that the set of equations for the macroscopic hydrodynamic variables coupled to the wave equations for the self-consistent electromagnetic field is equivalent to the Vlasov–Maxwell system. In the case of magnetized quasi-neutral plasma, the hydrodynamic substitution has been used to derive the hydrodynamic equations for the plasma density and current velocity, coupled to the wave equations for the self-consistent electromagnetic fields. Based on the method of multiple scales, a system comprising a vector nonlinear Schrodinger equation for the transverse envelopes of the self-consistent plasma wakefield, coupled to a scalar nonlinear Schrodinger equation for the electron current velocity envelope for free plasma, has been derived. In the case of magnetized plasma, it has been shown that the whistler wave envelopes of the three basic modes satisfy a system of three coupled nonlinear Schrodinger equations. Numerical examples for typical plasma parameters have been presented, which demonstrate the relevance of the results thus obtained to the so-called shock laser-plasma acceleration. In addition, it has been shown that in the case of magnetized plasma, the whistler waves facilitate the transverse confinement considerably. The effect of the nonlinear corrections to the electric displacement vector and the intensity of the magnetic field in nonlinear electrodynamics of Heisenberg-Euler type has been studied. It has been shown that the slowly varying wave envelope in free polarized vacuum satisfies a nonlinear wave equation. In the case, where an external constant magnetic field is applied, the single nonlinear wave equation should be replaced by a system of two coupled nonlinear equations for the two independent wave polarizations. In both cases a novel effect of reduction of the speed of light can be observed, which is due to the vacuum polarization.

Room-Temperature Colossal Magnetodielectric Effect in La0.4Eu0.1Ca0.5MnO3 Manganite

The effect of an external constant magnetic field on the dielectric properties and magnetodielectric (MD) coupling in La0.4Eu0.1Ca0.5MnO3 polycrystalline manganite at room temperature (RT) has been investigated. This sample exhibits negative colossal MD values under low applied magnetic fields (− 30% and − 45% under applied fields of 0.6 T and 1.2 T, respectively). The colossal MD values as well as the relatively low dielectric loss values suggest that the La0.4Eu0.1Ca0.5MnO3 sample can be a suitable␣candidate for technological applications at RT, like magnetic field sensing and gyrators.

Branched Josephson junctions: Current carrying solitons in external magnetic fields

We consider the branched Josephson junction created by planar superconductors connected to each other through the Y-junction insulator. Assuming that the structure interacts with the external constant magnetic field, we study static sine-Gordon solitons in such system by modeling them in terms of the stationary sine-Gordon equation on metric graph. Exact analytical solutions of the problem are obtained and their stability is analyzed.

Graviton-photon mixing. Exact solution in a constant magnetic field

In this work I study the effect of graviton-photon mixing in a constant external magnetic field and find for the first time in the literature exact solution of the equations of motion. In particular, I apply the effect of graviton-photon mixing to the case of interaction of gravitational waves with an external magnetic field and calculate the intensity Stokes parameter of the produced electromagnetic radiation. The obtained results are new and extend previous results obtained by using approximation methods.

ACCELERATION OF PARTICLES BY INTENSIVE ELECTROMAGNETIC FIELDS IN A VACUUM WITH EXTERNAL MAGNETIC FIELD

The possibilities and conditions of effective interaction, in particular acceleration, of charged particles by the field of an intense plane electromagnetic wave in the presence of an external constant magnetic field are considered. It is shown that the well-known conditions of cyclotron resonances require generalization. New conditions for the resonant interaction of charged particles are formulated, which contain not only the strength of the external magnetic field (as the well-known conditions of cyclotron resonances) but also the field strength of the wave. Cases of both small wave field strengths, so large, are considered. It is shown that new resonance conditions open up new possibilities for effective particle acceleration.

Lindblad approximation and spin relaxation in quantum electrodynamics

This article is concerned with the time evolution of spin observables for generalized spin boson models. This applies in particular to a model of nuclear magnetic resonance, namely a -spin particle in a constant external magnetic field and in interaction with the quantized electromagnetic field (photons). We derive a Lindblad (or GKLS) type approximation of the spin dynamics initially in a photon vacuum state together with a precise control of the error coming from this approximation. The error term is bounded by g 2 where g is the coupling constant of the spin–photon interaction. The point here is the uniformity in time t > 0 of this error control.

Numerical Analysis of the Interaction between a Tubular Beam of Charged Particles and a Dielectric Cylinder

The effect of nonlinear stabilization of the instability of a tubular electron beam when it moves along the surface of a solid dielectric cylinder is investigated theoretically. It is assumed that the beam is nonrelativistic, infinitely thin in the radial direction, and moves along the surface of the cylinder parallel to the lines of force of an external constant magnetic field, which prevents the transverse motion of the beam electrons. The mechanism of nonlinear stabilization of azimuthally symmetric E-type electromagnetic waves with different values of radial mode indices is studied by the method of slowly varying amplitudes and phases. The physical cause of excitation of such waves is the Vavilov–Cherenkov resonance, and the nonlinear stabilization mechanism is based on the trapping of beam particles by the field of the excited wave. It is shown that, as the radial mode index of the excited wave increases, the saturation time of instability and the maxima and the “period” of amplitude oscillations at the nonlinear stage of instability saturation decrease. It is shown that, at the nonlinear stage of instability, the waves excited by the beam have elliptical polarization. Moreover, in the vacuum region, the directions of rotation of the electric field vectors of E01 and E02 waves turn out to be opposite.

Influence of an External Magnetic Field on the Morphology of a Ni-Co Alloy Obtained Electrochemically in a Deep Eutectic Solvent

The electrochemical synthesis of Ni-Co metal particles formed from through electrodeposition of Ni2+ and Co2+ was carried out from a deep eutectic solvent of choline chloride and urea in 1:2 molar ratio at 70 °C, as electrolytic medium. From the application of a constant external magnetic field (1-5 µT), the morphology of the particles formed was studied. Additionally, the kinetic and thermodynamic parameters corresponding to the formation of the new phase on the surface of the glassy carbon electrode was determined, using physicomathematical models that involve bimetallic phases [1]. Figure 1(a) and (b), show the SEM images displaying a noticeable change in the morphology after applying 5 µT. Figure (c) and (d), correspond to the elementary analysis of figures (a) and (b), respectively. Figure 1