Constant External Field Research Articles

Experimental study on screening-current induced strain in REBCO insert coils: under critical current control and operation current cycles

The screening-current effect is an inhomogeneous distribution of current density inside the REBCO conductors. The additional strain induced by the screening current, known as screening-current induced strain (SCS), is considered to affect the structural integrity of REBCO windings, especially when operating high-field REBCO insert magnets. In this work, we wound and tested a series of 50-turn REBCO coils inside a 10 T LTS external to investigate the influencing mechanism of multiple electromagnetic factors on SCS. We varied the critical current in different coils by different heat treatment procedures. Each coil was tested individually, experiencing a external field cycle and multiple operation current cycles at constant external fields. The extreme scenario for each coil was being energized to 400 A while the external field was 10 T. We adapted the discrete-coupled model to estimate the hoop strain distribution, monitored the experimental results by multiple strain gauges at the outermost turn. Test coil with a lower critical current endured a lower maximum hoop strain. When we were energizing the test coils, hoop strain increased at the edge of REBCO tapes while remaining nearly constant in the middle region. Additionally, the maximum hoop strain at the outermost turn decreased after each excitation cycle. This work could be an experimental reference for optimizing the electromagnetic design and the excitation scheme during the development of high-field REBCO magnets.

On graviton–photon conversions in magnetic environments

Graviton–photon conversions in a given external electric or magnetic field, known as the Gertsenshtein mechanism, are usually treated using the four-potential for photons. In terms of the electric and magnetic (EM) fields, however, proper identification of the fields in curved spacetime is important. By misidentifying the fields in Minkowski form, as is often practiced in the literature, we show that the final equation for photon conversion is correct in transverse-tracefree gauge only for planar gravitational waves in a uniform and constant external field. Even in the former method, to recover the EM fields from the four-potential in curved spacetime, one should properly take into account the metric involved in the relation. By including the metric perturbation in the graviton conversion equation, we show that a magnetic environment can cause tachyonic instability term in gravitational wave equation.

Optical gain and entanglement through dielectric confinement and electric field in InP quantum dots.

Quantum dots are widely recognized for their advantageous light-emitting properties. Their excitonic fine structure along with the high quantum yields offers a wide range of possibilities for technological applications. However, especially for the case of colloidal QDs, there are still characteristics and properties which are not adequately controlled and downgrade their performance for applications which go far beyond the simple light emission. Such a challenging task is the ability to manipulate the energetic ordering of exciton and biexciton emission and subsequently control phenomena such as Auger recombination, optical gain and photon entanglement. In the present work we attempt to engineer this ordering for the case of InP QDs embedded in polymer matrix, by means of their size, the dielectric confinement and external electric fields. We employ well tested, state of the art theoretical methods, in order to explore the conditions under which the exciton-biexciton configuration creates the desired conditions either for optical gain or photon entanglement. Indeed, this appears to be feasible for QDs with small diameters (1 nm, 1.5 nm) embedded in a host material with high dielectric constant and additional external electric fields. These findings offer a new design principle which might be complementary to the well-established type II core-shell QDs approach for achieving electron-hole separation.

Radially transverse isotropic inclusions in isotropic conductive media: Local fields, effective properties, neutral inclusions

Spherical radially transverse isotropic heterogeneous inclusions in homogeneous isotropic conductive host media are considered. The volume integral equation for the field in the medium with an isolated inclusion subjected to a constant external field is solved using Mellin-transform technique. The method allows revealing tensor structure of the solution with precision to one scalar function of radial coordinate. Differential equation for this function arises in the process of realization of the method. For multilayered radially transverse isotropic inclusions, an efficient algorithm of solution is presented. Neutral inclusions that do not disturb constant external fields in the host medium are considered. For neutral inclusions, relations between the conductivity coefficients of the inclusion and the host medium are indicated. It is shown that homogeneous inclusions with a layer of other material at the inclusion interface can be neutral (invisible for external observers). For neutral inclusions, thin boundary layers can be changed with specific boundary conditions at the inclusion interface (singular models of thin layers). Parameters of the singular models are indicated in terms of conductivity coefficients of the inclusion, layer, and host medium. The effective field method is used for calculation of the effective conductivity of homogeneous isotropic media containing random sets of radially transverse isotropic inclusions. Influence of volume fractions and conductivity coefficients of the inclusions on the effective conductivity of the composite is studied.

Bilayer thermal metadevices that mold transient heat flows

Thermal manipulation has been widely researched due to its potential in novel functions, such as cloaking, illusion and sensing. To avoid the spatially inhomogeneous and anisotropic heat conductivity tensors (introduced by transformation thermodynamics), several thermal cloaks based on scattering cancellation (SC) approach are designed and experimentally demonstrated. However, the current SC cloak is only effective in the steady-state heat transfer condition as the heat capacity terms are neglected by the requirement of constant external fields. In order to expand the SC cloak to the transient regime, a bilayer scheme is introduced to achieve the accurate solutions of the camouflage equations considering time factors. Indeed, there are two equations to solve with two unknown quantities: first the thermal conductivity and second the product of specific heat capacity by the density. We construct thermal camouflage devices and verify their ability to mold dynamic heat flows both by simulations and experiments. Our proposed method paves an efficient avenue to extend SC approach to dynamic heat transfer regime.

Scalar particle creation in a quantum gravity perspective

In gravity’s rainbow perspective (GRP), we intend to analyze the particle production coming from electromagnetic and gravitational fields of the spin-0 (scalar) particles. In accordance with this purpose, a constant external electric field is taken into account together with a rainbow metric with non-isotropic expansion. We obtain the number density of the created Klein–Gordon particles in terms of particle mass, particle charge, external electric field parameter, rainbow functions and particle momentum by using the Bogoliubov transformation method. We display that the number density of the created scalar particles becomes thermal both in the absence of the external constant electric field and in the massless case. We also provide a graphical analysis to scrutinize the particle creation process in the GRP. In this context, it has been observed that rainbow functions drastically alter the number density of the created scalar particles.

Effect of the Applied Electric Field on the Thermal Properties of the Relativistic Harmonic Oscillator in One Dimension

We study the relativistic harmonic oscillators (Dirac and Klein–Gordon ones) in a constant external electric field. The solutions obtained are exact. These solutions allowed us to focus on the effect of the external electric field on the thermal properties of such oscillators. These properties are calculated by means of the Zeta-based method. Some figures have been built to show the mentioned effect.

Newton’s equations from quantum mechanics for a macroscopic body in the vacuum

Newton’s force law [Formula: see text] is derived from the Schrödinger equation for isolated macroscopic bodies, composite states of e.g. [Formula: see text] atoms and molecules, at finite body temperatures. We first review three aspects of quantum mechanics (QM) in this context: (i) Heisenberg’s uncertainty relations for their center of mass (CM), (ii) the diffusion of the CM wave packet, and (iii) a finite body temperature which implies a metastable (mixed-) state of the body: photon emissions and self-decoherence. They explain the origin of the classical trajectory for a macroscopic body. The ratio between the range [Formula: see text] over which the quantum fluctuations of its CM are effective, and the body’s (linear) size [Formula: see text], [Formula: see text] or [Formula: see text], tells whether the body’s CM behaves classically or quantum mechanically, respectively. In the first case, Newton’s force law for its CM follows from the Ehrenfest theorem. We illustrate this for weak gravitational forces, a harmonic-oscillator potential, and for constant external electromagnetic fields slowly varying in space. The derivation of the canonical Hamilton equations for many-body systems is also discussed. Effects due to the body’s finite size such as the gravitational tidal forces appear in perturbation theory. Our work is consistent with the well-known idea that the emergence of classical physics in QM is due to the environment-induced decoherence, but complements and completes it, by clarifying the conditions under which Newton’s equations follow from QM, and by deriving them explicitly.

Dynamics of Bloch–Zener Oscillations with Tuning Gap

AbstractIn this study, the transient dynamics of Bloch–Zener oscillations (BZOs) in a 1D qubit chain with a controllable band gap are explored. The chain consists of alternating site energies and is subjected to a constant external field. Several tight‐binding models were analyzed, including Bloch and Landau–Zener models, to understand the BZOs mechanism. The findings revealed that the band gaps played a crucial role in bridging the intriguing interplay between Bloch oscillations and Landau–Zener transitions. The motion of carriers in real and quasi‐momentum spaces is explored and the time evolution of occupancy in mini‐bands is calculated. A linearly time‐dependent way of tuning the gap is also proposed and non‐periodic motion is observed. When the chain is coupled to dispersionless optical phonons, strong coupling leads to large phonon displacements and localizes the carrier wave packets of the qubit states. The findings provide new insights into the behavior of BZOs in complex systems and suggest avenues for future studies.

Investigating simultaneous effects of temperature, surface heterogeneity and geometry on fluid mixing in electroosmotic flow considering temperature dependent properties by Nernst–Planck Poisson method

Numerical study of the effect of temperature and heat transfer as well as surface heterogeneity effects on mixing and electroosmotic flow in microchannels with convergent/divergent and straight mixing chamber is carried out. The fluid properties and surface zeta potentials are assumed to be temperature dependent. Based on the Nernst–Planck Poisson model, the governing equations of this problem include the Laplace equation, Poisson equation, Navier–Stokes and the propagation equation as well as the energy equation, respectively for the distribution of external electric field, distribution of internal electric field due to the charge of ions, fluid motion, concentration field and temperature distribution, which are solved by the finite element method. Flow rate, the mixing efficiency and a new parameter called mixing capacity, which is achieved by multiplying flow rate by mixing efficiency, are obtained for convergent/divergent and straight microchannels in a constant external electric field distributed under different wall temperatures, and performance of the geometries in flow transfer and mixing development is investigated. For electroosmotic flow, heterogeneous microchannels create vortices which improve mixing. Different arrangements of heterogeneous pieces of the surface create different patterns of vortices, each of which has different effects in the various geometries on fluid flow and mixing. Also, the dependence of the molecular diffusion on temperature causes increasing the mixing of species with the temperature increment. The results show that divergent microchannels have the maximum flow rate and the minimum mixing efficiency, but this efficiency can be increased by increasing the wall temperature. Convergent microchannels also have high mixing efficiency due to low flow rates and sufficient time for mixing even at low and near ambient temperatures, although their mixing capacity is less than the divergent microchannels.

Structural and magnetic ordering properties of TbFexMn12-x (x = 6.0–9.0) intermetallic compounds

In this work, single-phase TbFexMn12-x compounds with the optimized composition (x = 6.0–9.0) were prepared, and their structural and magnetic ordering properties were investigated. It was found that the Tb-(Mn, Fe) coupling strength was significantly enhanced by the introduction of Fe, which finally significantly increased the magnetic ordering temperature of the R sublattice and induced interesting magnetic behaviors. When x ≤ 8.0, negative magnetization was observed in the M-T curves when decreasing the temperature in a constant positive external field. When x = 6.0, the M-T curve seemed the M-T curves of normal ferromagnetic materials because the net magnetization of the (Fe, Mn) magnetic sublattice was too small to induce the Tb magnetization to align in the opposite direction of the external magnetic field. Lateral and longitudinal offsets in the hysteresis loops, namely exchange-bias-like behavior, were observed, and with the increase of the maximum measurement field, the lateral and longitudinal offsets become smaller. The estimated minimum magnetic field required to cancel the offset was 110 kOe. In addition, AC susceptibility measurement results showed that all samples had the characteristics of spin-glass state at temperature just below the (Fe, Mn) sublattice ordering temperature due to the fluctuations in exchange interaction and anisotropy caused by the introduction of Fe in the (Fe, Mn) sublattice.

Janus Type Monolayers of S-MoSiN2 Family and Van Der Waals Heterostructures with Graphene: DFT-Based Study.

Novel representative 2D materials of the Janus type family X-M-ZN2 are studied. These materials are hybrids of a transition metal dichalcogenide and a material from the MoSi2N4 family, and they were constructed and optimized from the MoSi2N4 monolayer by the substitution of SiN2 group on one side by chalcogen atoms (sulfur, selenium, or tellurium), and possibly replacing molybdenum (Mo) to tungsten (W) and/or silicon (Si) to germanium (Ge). The stability of novel materials is evaluated by calculating phonon spectra and binding energies. Mechanical, electronic, and optical characteristics are calculated by methods based on the density functional theory. All considered 2D materials are semiconductors with a substantial bandgap (>1 eV). The mirror symmetry breaking is the cause of a significant built-in electric field and intrinsic dipole moment. The spin-orbit coupling (SOC) is estimated by calculations of SOC polarized bandstructures for four most stable X-M-ZN2 structures. The possible van der Waals heterostructures of considered Janus type monolayers with graphene are constructed and optimized. It is demonstrated that monolayers can serve as outer plates in conducting layers (with graphene) for shielding a constant external electric field.

Thermoelectric phenomena in a one-dimensional diffusive quantum medium

The quantum diffusion in a one-dimensional lattice in a tunneling regime under the influence of spatially inhomogeneous Gaussian noise is studied theoretically. It is shown that the thermopower appears at an arbitrary value of the tunneling coupling. In the strong tunneling regime at an extremely high temperature, when the drift component of the charge transport can be neglected, the thermoelectric effect takes place only in the presence of a constant external electric field. The Seebeck and Peltier coefficients for the closed-circuit mode are obtained for a one-dimensional quantum diffusion medium in the tunneling regime. In the strong tunneling regime, both the thermopower and the Peltier effect are essentially nonlinear phenomena.

Numerical Solutions of the External Field Effect on the Radial Acceleration in Disk Galaxies

Abstract In modified Newtonian dynamics (MOND)-based theories, the strong equivalence principle is generically broken in an idiosyncratic manner, manifested in the action of an “external field effect” (EFE). The internal dynamics in a self-gravitating system is affected even by a constant external field. In disk galaxies, the EFE can induce warps and modify the rotational speeds. Due to the nonlinearity of MOND, it is difficult to derive analytic expressions of this important effect in a disk. Here we study numerically the EFE in two nonrelativistic Lagrangian theories of MOND: the “Aquadratic–Lagrangian” theory (AQUAL) and “Quasilinear MOND” (QUMOND). For AQUAL, we consider only the axisymmetric field configurations with the external field along the disk axis, or a spherical galaxy with test-particle orbits inclined to the external field. For the more manageable QUMOND, we also calculate the three-dimensional field configurations, with the external field inclined to the disk axis. We investigate in particular to what degree an external field modifies the quasi-flat part of rotation curves. While our QUMOND results agree well with published numerical results in QUMOND, we find that AQUAL predicts weaker EFE than published AQUAL results. However, AQUAL still predicts stronger EFE than QUMOND, which demonstrates current theoretical uncertainties. We also illustrate how the MOND prediction on the rising part of the rotation curve, in the inner parts, depends largely on disk thickness but only weakly on a plausible external field for a fixed galaxy model. Finally, we summarize our results for the outer parts as an improved, approximate analytic expression.

Catalysis and inverse electric catalysis in a scalar theory

In this article we explore the phase diagram associated to the symmetry breaking of a scalar self-interacting theory, induced by temperature and the presence of an external electric field. For such purpose, first we obtain the boson propagator, in the presence of a constant external electric field, both in the weak and strong field strength limits. Novel expansions are derived for the effective potential, valid for the whole range of temperature. We found inverse electric catalysis for the weak field region, i.e., a situation where the critical temperature diminishes as function of the strength of the electric field whereas for a strong field electric catalysis emerges. These behaviors, in the weak and strong intensity sectors, are valid for all possible values of temperature.

Феррозондовые преобразователи слабого магнитного поля на основе стержневых сердечников из аморфных сплавов

Ferroprobe magnetic field converters (MFC) are used in the tasks of geophysical and radiophysical research, in the development of civil and special equipment. The MFC is the main element of magnetometric sensor systems. The principle of operation of ferroprobe MFC is based on the transformation of the external constant field strength into an EMF with frequency multiple of the frequency of the alternating current feeding it. The transformation is possible due to the non-linearity of the magnetic characteristics of its cores. In this work, the main results of experimental studies of the developed ferroprobe MFC are presented. This MFC design was implemented based on the use of cores made of amorphous alloys with high magnetic permeability. Structural and circuit design solutions that provide an increase in the transfer function of a ferroprobe MFC when operating at a higher core excitation frequency were investigated. It was stated that the operating frequency of excitation of the cores of the ferroprobe MFC is determined by the magnetic properties of the material from which they are made. It has been established that for sensitive ferroprobe MFC creation, it is advisable to use cores made of amorphous alloys of the AMAG-170 type, which provide operation in the frequency band up to 100 kHz, and therefore have the possibility of potentially increasing the conversion coefficient of the ferroprobe MFC by increasing the core excitation frequency. The highly sensitive ferroprobe MFCs are promising for sensor systems creation.

Generation of unipolar pulses of terahertz radiation with a large electric area

A physical situation is proposed and theoretically analyzed, in which, in our opinion, it is possible to generate unipolar terahertz pulses with a large electric area. In this case, the gas in the tube is excited by a femtosecond IR laser pulse. In this case, the tube with gas is placed in a constant external electric field. The generation of a unipolar pulse is based on "three-step scheme" --- ionization of gas atoms by a femtosecond pulse, subsequent acceleration of a free electron in a dc external field and subsequent annihilation of an electron upon collision with a tube wall or another atom (ion). Keywords: unipolar pulses, ultrafast optics, electric pulse area, terahertz radiation, three-step model.

Генерация униполярных импульсов терагерцового излучения с большой электрической площадью

A physical situation is proposed and theoretically analyzed, in which, in our opinion, it is possible to generate unipolar terahertz pulses with a large electric area. In this case, the gas in the tube is excited by a femtosecond IR laser pulse. In this case, the tube with gas is placed in a constant external electric field. The generation of a unipolar pulse is based on ”three-step scheme" - ionization of gas atoms by a femtosecond pulse, subsequent acceleration of a free electron in a dc external field and subsequent annihilation of an electron upon collision with a tube wall or another atom (ion).

Critical analysis of generalized Maxwell homogenization schemes and related prospective problems

A linear composite medium consisting of a homogeneous matrix containing either the periodic or random set of heterogeneities is considered. Both the original and generalized Maxwell schemes are analyzed by reducing the problem to calculation of elastic fields in a finite volume of the composite embedded in the infinite homogeneous matrix medium and subjected to a constant external stress or strain field at infinity. We investigate (qualitatively and quantitatively) a correspondence between the Maxwell schemes (the original and generalized versions) and other different basic assumptions, conceptions, and methods of analytical micromechanics such as effective field method (EFM) and Mori–Tanaka method (MTM). Some deficiencies and inconsistencies of generalized Maxwell schemes in particular examples are detected and explained how the mentioned difficulties can be easily overcome by the classical micromechanical methods EFM and MTM. For the modeling of both periodic and random structure composites, the generalized Maxwell schemes taking into account the inclusion interactions inside the cluster are analyzed. The incorrectness of using of some generalized Maxwell schemes for the modeling of random structure composite materials (CMs) is shown and the directions for its improvements in the framework of the second background of analytical micromechanics are proposed.

Effective conductivity of anisotropic media with crack-like inclusions and cracks of arbitrary shapes

The effective field method is applied to solution of the homogenization problem for anisotropic media containing random sets of thin inclusions of low conductivity (crack-like inclusions) or cracks. The derived expression for the tensor of effective conductivity of cracked media on the one hand, takes into account peculiarities of shapes and conductivity of thin inclusions, and on the other hand, reflect statistical properties of the inclusion distributions in the host medium. The crucial part of realization of the method is solution of the so-called one-particle problem that is the conductivity problem for an isolated inclusion embedded into an anisotropic host medium and subjected to a constant external field. This problem is reduced to solution of the integral equation for the potential jump on the middle surface of a thin inclusion. An efficient numerical method of solution of this equation is proposed. The integral equation is discretized by Gaussian approximating functions and reduced to a linear algebraic system for the coefficients of the approximation (the discretized problem). For Gaussian functions, the elements of the matrix of the discretized problem are calculated in explicit analytical forms (for isotropic host media) or they reduce to a standard 1D-integral (for arbitrary anisotropic host media) that can be tabulated. As a result, the matrix of the discretized problem is calculated fast. For inclusions with planar middle surfaces and regular grids of approximated nodes, this matrix has Toeplitz’ structure, and fast Fourier transform algorithm can be used for iterative solution of the discretized problem. The cases of a strongly anisotropic medium with circular, annular and square cracks are considered. Examples of solution of the homogenization problems for the medium containing cracks of various shapes are presented.