Polariton vortex Chern insulator [Invited

Introduction. When heating with high-frequency currents (HFCs) at high speeds, more significant strengthening effects can be observed compared to using machine generators. Therefore, hardening at high frequencies is more efficient. However, the increase in the generator frequency results in a decrease in the depth of penetration of eddy currents and an increased unevenness of heating across the cross-section. The application of a constant external magnetic field during HFC hardening can increase the depth of eddy current penetration and create more uniform heating. Unfortunately, there is not enough information available on the effect of the external magnetic field on HFC heating processes and phase transformations in steel. Currently, there are no quantitative estimates for the impact of an external magnetic field on changes in the kinetics of electric heating and the penetration depth of eddy currents. In connection with the above, the aim of this paper is to investigate changes in the kinetics of high-frequency heating of iron-carbon alloys when an external constant magnetic field is applied and, and, based on this, to consider the potential for technological applications. Materials and Methods. Theoretical assessment of the influence of an external magnetic field on the change in the kinetics of electric heating and the penetration depth of eddy currents is based on the general theory of induction heating kinetics. An experimental study of the influence of a magnetic field on the kinetics of high-frequency current heating was performed on samples of 45 steel, pearlitic gray (SCh30), and ferritic malleable cast iron (KCh30-6). The temperature distribution over the cross-section of ferromagnetic materials during induction heating with an external magnetic field has been studied using special samples of iron, 45 steel, and SCh30 gray pearlitic cast iron. Electric tempering processes have been investigated on samples of U8A steel using a vacuum tube generator (heating temperature — 450℃, heating rate — 750℃/s). Changes in austenite grain size after high-speed heating with external magnetization have been examined on samples of reduced-hardenability 55PP steel. To study the processes of thermal treatment in a magnetic field during experiments involving heating samples using high-frequency currents, a specially designed electromagnet was created to apply an external constant magnetic field. Results. Theoretical curves were constructed for heating conditions with and without an external constant magnetic field. Experimental data on the effect of an external constant magnetic field on induction heating in the surface layer of various materials were summarized in kinetic diagrams. Evidence that the observed changes were due to increased depth of penetration of eddy currents came from experiments on cylindrical samples of 45 steel with different wall thicknesses. Kinetic curves were provided for estimating the temperature field (at 6 points at different depths) during high-frequency current heating with and without external magnetization. The paper presents experimental data on the micro-hardness distribution across the cross-section of a U8 steel sample after quenching, quenching and electric tempering, quenching and electric tempering with external magnetization, and quenching and bulk tempering. It also includes the results of the study of the austenite grain size of 55PP steel after high-speed heating with external magnetization and conventional (slow) deep heating. Discussion. The application of a high-intensity external constant magnetic field during the first quasi-stationary process resulted in a decrease in the rate of induction heating of the ferromagnetic material and an increase in the depth of its uniform heating. However, above the Curie point, the effect of the magnetic field was negligible due to the low magnetic susceptibility of the material, and the heating rate remained unchanged as if there was no field present. In addition, due to the insignificant difference in the values of magnetic permeability below and above the Curie point during heating in the field, the thermal curve did not exhibit the characteristic inflection typical of kinetic curves observed during the transition of the surface layer to a paramagnetic state. Experiments with electric tempering have demonstrated that by applying an external field, it was possible to temper a material to the desired depth and it could be done on a single high-frequency current setup. The size of the austenite grains after high-speed heating with magnetization was reduced compared to conventional deep heating of steel with low hardenability, eliminating the issue of induction heating for low-hardenability steel. Conclusion. The results of the study demonstrated that the use of an external magnetic field enabled the achievement of strengthening effects during heating at higher frequencies, thereby eliminating the drawbacks of such heating methods.

AC losses are numerically evaluated for a Bi-2223 tape-shaped wire in combined alternating transport current and external AC magnetic field with a phase shift. It is considered that the external field is applied only parallel to the wide surface of tape. Since the multifilamentary wire without twisting is assumed, a solenoidal coil is simplified as a homogeneous superconducting sheet with infinitely wide surfaces. The electromagnetic quantities are numerically calculated by solving Maxwell's equations and the voltage-current characteristics represented by the power law simultaneously. The calculations of AC losses are carried out as a function of both amplitudes of transport current and external magnetic field. The obtained results are plotted on a master curve for the maximum magnetic field applied to the wire.

We derive the polarization tensor for a system of charged spin-one bosons and antibosons in the case of no external magnetic field. This requires a thorough exposition of relativistic spin-one quantum mechanics, and thus we initially focus upon the Sakata-Taketani equation and its free-field solutions. We employ these results to evaluate the matrix elements required for the calculation of the polarization tensor, which itself is derived via the self-consistent random-phase approximation (RP A) method. It is from this tensor that we obtain the longitudinal and transverse dielectric response functions for this plasma. We evaluate these response functions at zero temperature, and exhibit the characteristic modes of oscillation. Finally, we discuss possible generalizations of this work, in particular to a finite-temperature plasma, and to one with an external magnetic field. In this paper, we present a study of the relativistic spin-one particle-antiparticle plasma, in the presence of no external magnetic field. The course of the investigation begins with a review of single particle theories of spin-one (vector) bosons, which we present in § 2 of this work. In § 3 of the paper, we present a detailed treatment of the six-component formalism for spin-one bosons, first developed by Sakata and Taketani/) which we then employ in our linear response theory calculations for the plasma. To our knowledge, this particular formalism is under-represented in the literature pertinent to spin-one bosons, and hence our exposition is an attempt to clarify its general features, and underscore its particular utility in work of the nature we have undertaken. The latter part of the paper (§§ 4 and 5) contains the linear response calculations proper. We set about deriving the polarization four-tensor, employing a method first· proposed by Harris,z) this being the self-consistent random-phase approximation (RPA) method. We then obtain the characteristic modes of oscillation of the plasma. At present, we concern ourselves solely with the plasma properties of the polari­ zation tensor, leaving a complete study of the vacuum modes of oscillation and their renormalization to a later paper, in which we also propose to introduce the presence of an external magnetic field. Employing our plane-wave solutions of the Sakata­ Taketani equation for the case of no external fields, we proceed to calculate the longitudinal and transverse dielectric response functions, which are obtained via the employment of the relationship between the covariant polarization four-tensor and the dielectric three-tensor. In the case of the longitudinal response function, we present the formal result which is valid for all temperatures, and we then evaluate the longitudinal and transverse response functions at zero temperature, from which we obtain the modes of oscillation. Our work follows on from that of Kowalenko, Frankel and Hines (KFH),3) who studied the spin-zero pair plasma by employing a self-consistent field method to find

New magnetic phenomena in Bi-based dielectrics

This thesis deals with various aspects of domain wall structures in a ferromagnet. The ferromagnet is described within the framework of a classical continuum model. Its energy contains exchange terms, a uniaxial anisotropy and the coupling to the external magnetic field. The demagnetizing field is treated within the approximation of a hard axis anisotropy. First we present a family of static planar structures in the presence of an external magnetic field. These structures fall into two classes: Spatially aperiodic solutions like a kink-kink or kink-antikink pair and spatially periodic solutions. Some of the latter can be interpreted as nonuniform static structures in a sample of finite length. The stability of a kink-kink pair and a kink-antikink pair is investigated. It is shown that the kink-antikink pair has exactly one unstable mode identifying it as a nucleation center of planar symmetry. The kink-kink pair also exhibits an instability for large external fields against out of easy plane distortions. The dynamics of such pairs of domain walls in the absence of external fields is investigated analytically. Somewhat unexpected is the existence of a breather describing an oscillating bound pair of equally twisted domain walls. Its energy is higher than that of two freely moving domain walls. This situation has no known analogy in other nonlinear field theories. It corresponds to a bound state of two domain walls with equal sense of twist and an energy which is higher than that of two freely moving domain walls. Finally transition rates of magnetization reversal are calculated. For an external magnetic field slightly less than the anisotropy field, thermal fluctuations lead to a decay of a state homogeneously magnetized antiparallel to the external field. Thereby the system has to surmount a saddle point of lowest energy. In case of a planar symmetry this saddle point is the kink-antikink pair. Magnetization reversal rates are calculated for large and moderate effective damping. The latter case involves the determination of the escape frequency of the dynamical unstable mode. Apart from numerical results a very accurate approximation for this escape frequency is given. In both cases the nucleation rates are evaluated analytically in the limit of small and large nucleation centers, for intermediate values of external fields numerical results are obtained.

The motion of impurities and the spectrum of excitations in liquid helium-four

Purpose – The purpose of this paper is to discuss the operation of new generation electromagnetic current-to-voltage transducer. The aim of research was analysis of behaviour of considered current-to-voltage transducers during operation. The main problem was to estimate whether the external fields are able to change the value of the secondary voltage and that the replacement of the casing material by a conductive or ferromagnetic material will increase the immunity of the transducer to external magnetic fields. The immunity of current-to-voltage transducers to the external fields is very important because it influences the proper functioning of the protection system. Design/methodology/approach – The use of analytical methods to assess the influence of external fields was impossible due to the complexity of the geometry. The 3D computations were necessary because of different cross sections of circuit boards at different heights. Therefore the numerical 3D field-and-circuit method based on finite element method was applied. The wide range of dimensions in computation system, ranging from 0.15 mm (print paths) to 0.22 m, made it necessary to use the mesh of millions of elements. The division of this type of system into elements requires a diverse and extremely dense mesh in the area of printed circuits board (PCBs). Findings – The 3D analysis of magnetic field distribution was performed for different external field effect upon a current-to-voltage transducer. The magnetic field distributions and the induced secondary voltage for several different cases were presented. As a conclusion it can be said that in this particular case the magnetic shield is most effective. The influence of external magnetic fields caused by currents passing through the other neighbouring phase bars near are insignificant for the transducer with non-magnetic core. Practical implications – Commonly used in measuring and protection systems of the transmission lines are induction instrument transformers. The instrument transformers are very precise devices and their errors are counted in tenths of a per cent, and phase displacement of signals in minutes. Especially in HV systems they are very big and their cores are heavy. Replacement of instrument transformers by the current to voltage transducers cooperating with electronic measuring systems will reduce the size and cost of devices. Originality/value – The requirements set for protective current transformers concern the transformation of currents, with high accuracy, especially at transient states. Therefore magnetic characteristics of their cores should be linear. It causes that cores are large and have some air gaps. Current-to-voltage transducers based on Rogowski coil are particularly suitable for the replacement of the protective current transformers because of their linearity. The traditional technologies used for making Rogowski coil consisted in winding a wire on a non-magnetic carcass. The development of technology has enabled the use of new technologies PCB high density interconnect in the production of Rogowski coil.

AC transport losses in a biaxially aligned YBCO-123 tape (10 cm in length) were measured (at 77 K) as a function of frequency and amplitude of a sinusoidally varying transport current. In the frequency range of 30-320 and the transport current losses are hysteretic in nature. The measurements of the self-field losses caused by the AC transport current as a function of the magnitude and orientation of the applied low external DC magnetic field (up to 150 mT) are also reported. The external magnetic field was rotated in the range of +120 to -120 degrees with respect to the plane of the tapes, and was in all cases perpendicular to the transport current flow. Strong anomaly in angular critical current dependence on external magnetic field was observed.

Dispersion property of electromagnetic wave in 1D magnetized ferrites photonic crystals for TE mode in longitudinal magnetization configuration

We present a study of the effects of external magnetic fields on the dynamics of ferrofluid droplets in suspension and its impacts on the rheology of dilute magnetic emulsions. Our analysis considers a single two-dimensional droplet of a superparamagnetic ferrofluid in an immiscible, non-magnetizable liquid. The two-phase system is confined in a channel between parallel plates and undergoes a simple shear flow under the influence of a uniform external magnetic field. We present a theoretical formulation for the stress tensor of dilute suspensions of ferrofluid droplets in which the stresslet accounts for a magnetic field-induced traction across the droplet surface. Remarkably, the stresslet is no longer symmetric in the presence of external magnetic fields. The complex configuration of the droplet leads to a misalignment between the bulk magnetization and the external magnetic field. As a result, internal torques appear in the magnetic emulsion even when both liquid phases are symmetric fluids. We also present a comprehensive investigation of the configuration and magnetization of the suspended ferrofluid droplet as a function of the intensity and direction of the external field. Then, the stresslet is used to explore how external magnetic fields affect the rheology of dilute magnetic emulsions in terms of the shear viscosity, rotational viscosity, and first normal stress difference. Our predictions show that external magnetic fields can be effectively adjusted to control the dynamics at the droplet level and the rheology of magnetic emulsions.

Spectrum of coupled spin, acoustic, electro-dipole and electromagnetic waves in orthorhombic perovskite multiferroics placed in external electric and magnetic field has been calculated. Frequency and field dependencies of electric, magnetic, and magnetoelectric susceptibilities of multiferroics with cycloidal antiferromagnetic structure in external electric and magnetic fields have been investigated as well. The spectrum of coupled waves has a band structure. Width and frequency ranges of bands depend on external fields. The possibility of control of electrodynamic properties of orthorhombic perovskite multiferroics with cycloidal antiferromagnetic structure by external electric and magnetic fields has been shown.

Magnetotactic bacteria are ubiquitous and can be found in both freshwater and marine environments. Due to intracellular chains of magnetic single domain particles, they behave like swimming compass needles. In external magnetic fields like the Earth's magnetic field, a torque is acting on the chain. This will cause the bacterium to be rotated and aligned with the external field. The swimming direction of magnetotactic bacteria can be controlled with external magnetic fields, which makes it convenient to study them under a light microscope. Usually, a special set of coils arranged around a light microscope is used to control the swimming magnetotactic bacteria. Here, we present a simple mechanical system with a permanent magnet, which produces a rotating magnetic field of nearly constant amplitude in the focal plane of a light microscope. The device is placed beside the light microscope and easily adaptable to almost any microscope and thus convenient for field experiments. To describe the trajectories qualitatively, a theoretical model of the trajectories is presented. This device can be used to control the swimming direction of magnetotactic bacteria and also for studying their magnetic and hydrodynamic properties.

The arrangements of molecular layers I—Cd—I, which may be regarded as “faulted” for CdI2 polytypic crystals, are analyzed. Tentative classification of faults into those which are intermediate structure between the basic polytypes 2H and 4H and faults occurring between different blocks of pure structure 4H is proposed. The connection between some growth parameters and the structure of faults in CdI2 crystals grown from solutions is discussed. It is shown that the geometrical classification of stacking faults used for layered inorganic crystals is not appropriate for the description of the faults existing in polytypic crystals of MX2 type. The effect of weak external electric and magnetic fields on the polytypic structure of CdI2 is analyzed. The experiments performed for several hundred of polytypes of CdI2 showed that the external fields may, in some conditions, affect the organization of the polytypic structure of crystals very strongly. In particular, it was found that the external fields may change the period of polytype cells and that the relative number of hexagonal and rhombohedral polytypes differ very strongly for crystals grown in the absence and in the presence of external electric and magnetic fields.

The magnetic hyperfine interaction of iron atoms isolated in a xenon matrix in the presence of an external magnetic field

This tutorial chapter provides an introduction to the vibrant field of cold molecular collisions in the presence of external electromagnetic fields. The kinetic energy of molecules confined in electromagnetic traps is small compared to their interactions with external fields, so the influence of molecule -field interactions on molecular collisions at ultralow temperatures can no longer be neglected or treated perturbatively. The intricate topology of spin-dependent, multidimensional intermolecular interactions makes it necessary to use accurate, non-perturbative quantum scattering techniques for solving the Schrodinger equation for molecules colliding in the presence of external fields. The primary goal of this chapter is to provide an overview of multichannel quantum scattering theory of molecular collisions in external fields, with a focus on rigorous coupled-channel methodology applied to molecules of current experimental interest. We also present an overview of the mechanisms for controlling elastic and inelastic molecular collisions with external magnetic fields.