Strong Constant Magnetic Field Research Articles

The crystallization mode influence and magnetic field action upon the mechanical and thermal properties of composite materials on the basis of polymers and magnetic additives

The results of investigations of the temperature-time mode of the crystallization influence and magnetic field action upon the mechanic strength, magnetic permeability, and thermal properties of composites on the basis of polymers (PEHD, PVDF) and the magnetic additive BaO(Fe2O3)6 have been presented. It has been shown that the changes of the mechanical strength, magnetic permeability, and the thermal properties of the magnetic composites being studied, with regard to the temperature-time mode of crystallization and processing in a strong constant magnetic field, can be interrelated with the change of the polymer matrix supermolecular structure, the degree of the phase interaction, and the interphase layer thickness.

Nonlinear generation mechanism for the vortical electric field in magnetized plasma media

A physical mechanism and nonlinear mathematical formalism for study of generation and further amplification of the vortical electric field in the magnetized plasma are proposed. A modulation instability process in a plasma medium is considered in a strong constant magnetic field. The plasmon condensate is modulated not by a low-frequency ionic sound as is usually done, but by the beating of two high-frequency transverse electromagnetic waves propagating along the external magnetic field. Conditions in which aperiodic instability occurs are found and its increment is defined. This instability leads to a decrease in the scale of Langmuir turbulence along the external magnetic field and to the generation of electromagnetic fields. Dissipative property of the medium increases an amplitude threshold of the pumping waves. It is shown that for sufficiently large amplitudes of pumping waves the effect described in the paper is the defining nonlinear process.

Equivalent circuits for two‐state quantum systems

AbstractThe development of nanocircuits designed to ultimately interact with classical electromagnetic environments demands a description of their performance in circuit terms, i.e. in terms of voltages and currents for incident, reflected and transmitted waves. A class of quantum systems which are particularly promising for applications (e.g. in spintronics) and at the same time easy to analyse and to understand physically are the two‐state systems. Here, we present equivalent circuits for a generic two‐state quantum system imbedded in a one‐port or two‐port structure guiding a linearly polarized electromagnetic wave. For the sake of concreteness we explicitly refer to a system of spin ½ particles whose magnetic moments are aligned with the axis of the guiding structure by a strong constant magnetic field; but the formalism can be easily extended to particles endowed with electric dipole moments or any other system with two degrees of freedom. Copyright © 2007 John Wiley & Sons, Ltd.

Nonlinear mechanism for the generation of electromagnetic fields in a magnetized plasma by the beatings of waves

The modulational instability in a plasma in a strong constant external magnetic field is considered. The plasmon condensate is modulated not by conventional low-frequency ion sound but by the beatings of two high-frequency transverse electromagnetic waves propagating along the magnetic field. The instability reduces the spatial scales of Langmuir turbulence along the external magnetic field and generates electromagnetic fields. It is shown that, for a pump wave with a sufficiently large amplitude, the effect described in the present paper can be a dominant nonlinear process.

Nonlinear mechanism for electromagnetic field generation in modulation-unstable magnetized plasma media

A modulation instability process in a plasma medium is considered in a strong constant magnetic field. The plasmon condensate is modulated not by a low-frequency ionic sound as is usually done, but by the beating of two high-frequency transverse electromagnetic waves propagating along the external magnetic field. Conditions in which aperiodic instability occurs are found and its increment is defined. Instability leads to a decrease of the scale of Langmuir turbulence along the external magnetic field and to the generation of electromagnetic fields. Dissipative property of the medium increases an amplitude threshold of the pumping waves. It is shown that for sufficiently large amplitudes of pumping waves the effect described in the Letter is the defining nonlinear process.

NONCOMMUTATIVITY VS. TRANSVERSALITY IN QED IN A STRONG MAGNETIC FIELD

Quantum electrodynamics (QED) in a strong constant magnetic field is investigated from the viewpoint of its connection with noncommutative QED. It turns out that within the lowest Landau level (LLL) approximation the 1-loop contribution of fermions provides an effective action with the noncommutative U(1) NC gauge symmetry. As a result, the Ward identities connected with the initial U(1) gauge symmetry are broken down in the LLL approximation. On the other hand, it is shown that the sum over the infinite number of the higher Landau levels (HLL's) is relevant despite the fact that each contribution of the HLL is suppressed. Owing to this nondecoupling phenomenon the transversality is restored in the whole effective action. The kinematic region where the LLL contribution is dominant is also discussed.

Nondecoupling phenomena in QED in a magnetic field and noncommutative QED

The dynamics in QED in a strong constant magnetic field and its connection with the noncommutative QED are studied. It is shown that in the regime with the lowest Landau level (LLL) dominance the U(1) gauge symmetry in the fermion determinant is transformed into the noncommutative U(1)nc gauge symmetry. In this regime, the effective action is intimately connected with that in noncommutative QED and the original U(1) gauge Ward identities are broken (the LLL anomaly). On the other hand, it is shown that although a contribution of each of an infinite number of higher Landau levels is suppressed in an infrared region, their cumulative contribution is not (a nondecoupling phenomenon). This leads to a restoration of the original U(1) gauge symmetry in the infrared dynamics. The physics underlying this phenomenon reflects the important role of a boundary dynamics at spatial infinity in this problem.

Intermartensitic phase transformations in Ni–Mn–Ga studied under magnetic field

The Heusler-type ferromagnetic shape memory Ni 52.6Mn 23.6Ga 23.8 single crystal has been found to undergo a sequence of temperature-induced reversible intermartensitic transformations (IMTs) in addition to the martensitic transformation (MT). The temperature dependencies of the magnetization and electrical resistivity, as well as the magnetization curves have been studied for this alloy. In contrast to the MT, no anomalies of the saturation magnetization have been observed for any of the two IMTs. Nevertheless, application of a strong constant magnetic field is shown both experimentally and theoretically to induce similar shifts of the IMTs and MT temperatures.

Theory of reflection and absorption of light by low-dimensional semiconductor objects in a strong magnetic field under monochromatic and pulsed excitations

The theoretical principles of reflection and absorption of light by low-dimensional semiconductor objects (quantum wells, quantum wires, quantum dots) under monochromatic and pulsed excitations with an arbitrary pulse shape are developed. A semiconductor object can be placed in a strong constant magnetic field. The normal incidence of light on a quantum well whose width can be comparable to the light wavelength and for which the number of levels of electronic excitations can be arbitrary is considered as an example. An integral equation similar to the Dyson equation is derived for the Fourier components of the electric fields. The solutions to this equation are given for a number of special cases.

The Magnetisation of Large Atoms in Strong Magnetic Fields

In this paper we study the asymptotic form of the magnetisation and current of large atoms in strong constant magnetic fields. We prove that the Magnetic Thomas–Fermi theory gives the right magnetisation/current for magnetic field strengths which satisfy B≤Z 4/3.

Coordinate noncommutativity in strong nonuniform magnetic fields

Noncommuting spatial coordinates are studied in connection with the motion of a charged particle in a strong generic magnetic field. We derive a relation involving the commutators of the coordinates, which generalizes the one realized in a strong constant magnetic field. As an application, we discuss the coordinate noncommutativity in a slowly varying magnetic field.

Polarization of the Electron–Positron Vacuum by a Strong Magnetic Field in the Theory with a Fundamental Mass

In the framework of the theory with a fundamental mass in the one-loop approximation, we evaluate the exact Lagrange function of the strong constant magnetic field, replacing the Heisenberg–Euler Lagrangian in the traditional QED. We establish that the derived generalization of the Lagrange function is real for arbitrary values of the magnetic field. In the weak field, the evaluated Lagrangian coincides with the known Heisenberg–Euler formula. In extremely strong fields, the field dependence of the Lagrangian completely disappears; in this range, the Lagrangian tends to the limit value determined by the ratio of the fundamental and lepton masses.

On the Semiclassical Asymptotics of the Current and Magnetic Moment of a Non-Interacting Electron Gas at Zero Temperature in a Strong Constant Magnetic Field

We calculate the asymptotic form of the quantum current and magnetic moment of a non-interacting electron gas at zero temperature. The calculation uses coherent states and a novel commutator identity for the current operator.

SEMICLASSICS OF THE QUANTUM CURRENT IN A STRONG CONSTANT MAGNETIC FIELD

We study the current of the Pauli operator in a strong constant magnetic field. We prove that in the semi-classical limit the persistent current and the current from the interaction of the spin with the magnetic field cancel, in the case where the magnetic field is very strong. Furthermore we calculate the next term in the asymptotics and estimate the error. Finally, we discuss the connection between this work and the semi-classical estimate of the energy in strong magnetic fields proved by Lieb, Solovej and Yngvason [8]. *Partially supported by the European Union, grant FMRX-960001.

The Magnetisation of Large Atoms¶in Strong Magnetic Fields

In this paper we study the asymptotic form of the magnetisation and current of large atoms in strong constant magnetic fields. We prove that the Magnetic Thomas–Fermi theory gives the right magnetisation/current for magnetic field strengths which satisfy B≤Z 4/3.

THE GYROKINETIC APPROXIMATION FOR THE VLASOV–POISSON SYSTEM

Consider a plasma in a strong constant magnetic field with self-consistent electric field. We present here the formal derivation that leads to the so-called guiding center approximation, and justify it in the case of a well-prepared initial density of particles. More precisely, we prove that the motion of the particles can be approximatively decomposed as the sum of a fast rotation on Larmor circles, an advection along the magnetic lines and a small drift orthogonal to both electric and magnetic fields.

Convergence of the vlasov-poisson system to the incompressible euler equations

We consider the displacement of an electronic cloud generated by the local difference of charge with a uniform neutralizing background of non-moving ions. The equations are given by the Vlasov-Poisson system, with a coupling constant where τ is the (constant) oscillation period of the electrons. In the so-called quasi-neutral regime, namely as 0, the current is expected to converge to a solution of the incompressible Euler equations, at least in the case of a vanishing initial temperature. This result is proved by adapting an argument used by P.-L. Lions [Li] to prove the convergence of the Leray solutions of the 3d Navier-Stokes equation to the so-called dissipativesolutions of the Euler equations. For this purpose, the total energy of the system is modulated by a test-function. An alternative proof is given, based on the concept of measure-valued (mv) solutions introduced by DiPerna and Majda [DM] and already used by Brenier and Grenier [BG], [Gr2] for the asymptotic analysis of the Vlasov-Poisson system in the quasi-neutral regime. Through this analysis, a link is established between Lions' dissipative solutions and Diperna-Majda's (mv)solutions of the Euler equations. A second interesting asymptotic regime, still leading to the Euler equations, known as the gyrokinetic limit of the Vlasov-Poisson system, is obtained when the electrons are forced by a strong constant external magnetic field and has been investigated in [Gr3], [GSR]. As for the quasi-neutral limit, we jus- tify the gyrokinetic limit by using the concepts of dissipative solutions and modulated total energy.

A strong constant magnetic field affects muscle tension development in bullfrog neuromuscular preparations.

Effects of a constant magnetic field (CMF) of 0.65 T on muscle tension over 9 h were studied in the neuromuscular preparation of the bullfrog sartorius muscle. Tension was developed every 30 min by stimulation of the sciatic nerve (nerve stimulation) or of the sartorius muscle itself (muscle stimulation). In sciatic nerve stimulation, tension decreased rapidly for the first 3-4 h at a similar rate in both test (exposed to CMF) and control muscles. However, the rate of decrease became smaller and almost leveled off after 3-4 h in the test muscles, whereas tension continued to decrease monotonically in control muscles. The slope of the decrease for these later periods was significantly different between the test and the control conditions. Accordingly, tension was larger in test than in control muscles. In muscle stimulation, tension decreased monotonically from the start of experiments in control muscles, while tension in test muscles maintained their initial values for almost 3 h. Thereafter they started to decrease with a similar rate to the control. Hence, tension was always larger in test than in control muscles. A similar pattern of temporal change was observed for the rate of rise of the maximum tension for nerve or muscle stimulation. However, a significant difference was detected only in the case of muscle stimulation. The present results showed that a strong CMF of 0.65 T had biological effects on tension development of the bullfrog sartorius muscle by stimulation of the sciatic nerve as well as by stimulation of muscle itself. The presence of a small AC magnetic field component leaves open the possibility of an AC, rather than a CMF effect.

QED2+1 radiation effects in a strong magnetic field

We develop the eigenfunction method for the Dirac operator in a background magnetic field in the (2+1)-dimensional quantum electrodynamics (QED2+1). In the eigenfunction repressentation, we find the exact solutions and the Green's functions of the Dirac equation in a strong constant homogeneous magnetic field in 2+1 dimensions. In the one-loop QED2+1 approximation, we derive the effective Lagrangian, the density of vacuum fermions induced by the field, and the electron mass operator in a homogeneous background magnetic field.

Ergodic theorem for an impurity spin subsystem in a paramagnet

A model for verifying and developing the fundamental ideas underlying the ergodic hypothesis is proposed. The model describes the dynamics of the spin subsystem formed by impurity charges with spin I and a small g factor in a crystal immersed in a strong constant external magnetic field under conditions where the spin system of the nuclei in the crystal is isolated from the other degrees of freedom. The additive integral of motion is the projection of the total spin of the subsystem onto the external field. Attention is focused mainly on the case of I=1/2. It is shown that the ergodic hypothesis holds if the correlation radius is finite in the initial state and that the ergodic hypothesis is violated if the initial state is sharply localized or has global correlation. The nonergodicity of the 8Li− 6Li spin subsystem, which is a convenient object for experimental investigations of spin dynamics, is revealed. An estimate is obtained for the time for transition from a sharply localized disturbance of the canonical distribution to a quasiequilibrium state.