External Uniform Magnetic Field Research Articles

Steady MHD Flow of Viscous Fluid between Two Parallel Porous Plates with Heat Transfer in an Inclined Magnetic Field

The steady flow behavior of a viscous, incompressible and electrically conducting fluid between two parallel infinite insulated horizontal porous plates with heat transfer is investigated along with the effect of an external uniform transverse magnetic field, the action of inflow normal to the plates, the pressure gradient on the flow and temperature. The fluid viscosity is supposed to vary exponentially with the temperature. A numerical solution for the governing equations for both the momentum transfer and energy transfer has been developed using the finite difference method. The velocity and temperature distribution graphs have been presented under the influence of different values of magnetic inclination, fluid pressure gradient, inflow acting perpendicularly on the plates, temperature dependent viscosity and the Hartmann number. In our study viscosity is shown to affect the velocity graph. The flow parameters such as viscosity, pressure and injection of fluid normal to the plate can cause reverse flow. For highly viscous fluid, reverse flow is observed. The effect of magnetic force helps to restrain this reverse flow.

Propagators of charged particles in an external magnetic field, expanded over Landau levels

Various forms of expressions for the propagators of charged particles in a constant magnetic field that should be used for investigations of electroweak processes in an external uniform magnetic fields are discussed. Formulas for the propagators of the Standard Model charged [Formula: see text]- and scalar [Formula: see text]-bosons in an arbitrary [Formula: see text]-gauge, expanded over Landau levels, are derived for the first time.

Characteristics of laminar MHD fluid hammer in pipe

As gradually wide applications of MHD fluid, transportation as well as control with pumps and valves is unavoidable, which induces MHD fluid hammer. The paper attempts to combine MHD effect and fluid hammer effect and to investigate the characteristics of laminar MHD fluid hammer. A non-dimensional fluid hammer model, based on Navier–Stocks equations, coupling with Lorentz force is numerically solved in a reservoir–pipe–valve system with uniform external magnetic field. The MHD effect is represented by the interaction number which associates with the conductivity of the MHD fluid as well as the external magnetic field and can be interpreted as the ratio of Lorentz force to Joukowsky force. The transient numerical results of pressure head, average velocity, wall shear stress, velocity profiles and shear stress profiles are provided. The additional MHD effect hinders fluid motion, weakens wave front and homogenizes velocity profiles, contributing to obvious attenuation of oscillation, strengthened line packing and weakened Richardson annular effect. Studying the characteristics of MHD laminar fluid hammer theoretically supplements the gap of knowledge of rapid-transient MHD flow and technically provides beneficial information for MHD pipeline system designers to better devise MHD systems.

Skyrmion lattice in a magnetic film with spatially modulated material parameters

The problem of the skyrmion stability in the magnetic film with perpendicular anisotropy inside the area with the changed material parameters is considered. The solution describing the conditions of such stabilization in the absence of Dzyaloshinskii–Moriya interaction is obtained analytically. The easy method of nanomodification of ordinary magnetic perpendicular media such as Co,Fe/Pt,Pd,Ru superlattices allowing the formation of the dense enough (with the period less than 100nm) skyrmion lattices is suggested. By micromagnetic simulations it is shown that the skyrmion lattices can be initialized in the system by simple magnetization in the uniform external magnetic field.

Oblique propagation of longitudinal waves in magnetized spin-1/2 plasmas: Independent evolution of spin-up and spin-down electrons

We consider quantum plasmas of electrons and motionless ions. We describe separate evolution of spin-up and spin-down electrons. We present corresponding set of quantum hydrodynamic equations. We assume that plasmas are placed in an uniform external magnetic field. We account different occupation of spin-up and spin-down quantum states in equilibrium degenerate plasmas. This effect is included via equations of state for pressure of each species of electrons. We study oblique propagation of longitudinal waves. We show that instead of two well-known waves (the Langmuir wave and the Trivelpiece–Gould wave), plasmas reveal four wave solutions. New solutions exist due to both the separate consideration of spin-up and spin-down electrons and different occupation of spin-up and spin-down quantum states in equilibrium state of degenerate plasmas.

Spin Excitations in Chiral Model of Graphene

We consider the generalization of the scalar chiral model of graphene, the 8-spinor field being included for the description of spin and quasi-spin excitations. The invariant Lagrangian density quadratic in derivatives is constructed using the principle of energy positivity and that of correspondence with the scalar model. The electromagnetic interaction is included through the extension of derivatives, the Pauli direct interaction term being added. We consider in detail an example of interaction with the external uniform static magnetic field.

Magnetohydrodynamic Flow of Liquid-Metal in Circular Pipes for Externally Heated and Non-Heated Cases

The Computational Fluid Dynamics (CFD) study of external magnetic field effect on the steady, laminar, incompressible flow of an electrically conducting liquid-metal fluid in a pipe has been performed. The MHD Module of ANSYS Fluent commercial programme has been used to compute the flow and temperature fields. Na 22 K 78 (sodium potassium) alloy has been used as operating fluid, which is liquid in room temperature. The simulations are performed for two different cases, first a non-heated pipe flow and secondly an externally heated pipe flow. For both cases, three different magnitude uniform external magnetic field, B0, applied (which are B0 = 0.5 T, 1.0 T and 1.25 T, T represents Tesla). The results are compared for the MHD effect on the flow variables in two cases separately, but also compared for heated and non-heated cases in order to analyze the temperature effect on MHD flows, as well. It is observed that heating is reducing the magnetic effect on the flow field. While in nonheated cases it is observed that very well-known slowing down effect of MHD on fluid flow, in heated case the velocity field shows a tendency to behave as if it were MHD is not applied. Towards the end of the physical length the heating seems dominating the MHD effect. It is shown that in heated case temperature differences and entropy differences are in tendency to behave as if it were MHD is not applied.

Influence of quantized massive matter fields on the Casimir effect

Charged massive matter fields of spin-0 and spin-[Formula: see text] are quantized in the presence of an external uniform magnetic field in a spatial region bounded by two parallel plates. The most general set of boundary conditions at the plates, that is required by mathematical consistency and the self-adjointness of the Hamiltonian operator, is employed. The vacuum fluctuations of the matter field in the case of the magnetic field orthogonal to the plates are analyzed, and it is shown that the pressure from the vacuum onto the plates is positive and independent of the boundary condition, as well as of the distance between the plates. Possibilities of the detection of this new-type Casimir effect are discussed.

Spin-Zero Cox's particle With Intrinsic Structure: General Analysis in External Electromagnetic and Gravitational Fields

The relativistic theory of Cox’s scalar non-point particle with intrinsic structure in the Proca approach in external uniform magnetic and electric fields in the Minkowski space is developed. A generalized Klein–Gordon–Fock equation is derived and is detailed in the presence of uniform magnetic and electric fields. The extension of this formalism to the arbitrary Riemannian space-time background is given. For a special class of curved metrics allowing for the existence of nonrelativistic wave equations, a generalized Schr¨odinger-type quantum mechanical equation for Cox’s particle is derived. This generally covariant formalism is suitable in the presence of external magnetic and electric fields. It is shown that, in the most general form, the extended first-order Proca-like system of tensor equations contains non-minimal interaction terms through the electromagnetic tensor FaB and the Ricci tensor RaB.

Meron-cluster simulation of the quantum antiferromagnetic Heisenberg model in a magnetic field in one- and two-dimensions

Motivated by the numerical simulation of systems which display quantum phase transitions, we present a novel application of the meron-cluster algorithm to simulate the quantum antiferromagnetic Heisenberg model coupled to an external uniform magnetic field both in one and in two dimensions. In the infinite volume limit and at zero temperature we found numerical evidence that supports a quantum phase transition very close to the critical values $B_{c}=2$ and $B_{c}=4$ for the system in one and two dimensions, respectively. For the one dimensional system, we have compared the numerical data obtained with analytical predictions for the magnetization density as a function of the external field obtained by scaling-behaviour analysis and Bethe Ansatz techniques. Since there is no analytical solution for the two dimensional case, we have compared our results with the magnetization density obtained by scaling relations for small lattice sizes and with the approximated thermodynamical limit at zero temperature guessed by scaling relations. Moreover, we have compared the numerical data with other numerical simulations performed by using different algorithms in one and two dimensions, like the directed loop method. The numerical data obtained are in perfect agreement with all these previous results, which confirms that the meron-algorithm is reliable for quantum Monte Carlo simulations and applicable both in one and two dimensions. Finally, we have computed the integrated autocorrelation time to measure the efficiency of the meron algorithm in one dimension.

Magnetization plateaus in the antiferromagnetic Ising chain with single-ion anisotropy and quenched disorder

We have studied the presence of plateaus on the low-temperature magnetization of an antiferromagnetic spin-1 chain, as an external uniform magnetic field is varied. A crystal-field interaction is present in the model and the exchange constants follow a random quenched (Bernoulli or Gaussian) distribution. Using a transfer-matrix technique we calculate the largest Lyapunov exponent and, from it, the magnetization at low temperatures as a function of the magnetic field, for different values of the crystal field and the width of the distributions. For the Bernoulli distribution, the number of plateaus increases, with respect to the uniform case [Litaiff etal., Solid State Commun. 147, 494 (2008)] and their presence can be linked to different ground states, when the magnetic field is varied. For the Gaussian distributions, the uniform scenario is maintained, for small widths, but the plateaus structure disappears as the width increases.

MHD orthogonal stagnation-point flow of a micropolar fluid with the magnetic field parallel to the velocity at infinity

An exact solution is obtained for the steady MHD plane orthogonal stagnation-point flow of a homogeneous, incompressible, electrically conducting micropolar fluid over a rigid uncharged dielectric at rest. The space is permeated by a not uniform external magnetic field He and the total magnetic field H in the fluid is parallel to the velocity at infinity. The results obtained reveal many interesting behaviours of the flow and of the total magnetic field in the fluid and in the dielectric. In particular, the thickness of the layer where the viscosity appears depends on the strength of the magnetic field. The effects of the magnetic field on the velocity and on the microrotation profiles are presented graphically and discussed.

Chiral Current in the Lattice Model of Weyl Semimetal**Supported by the National Natural Science Foundation of China under Grant No 11275180, and the China Government Project under Grant No CSC-201206340089.

We demonstrate the existence of the chiral magnetic effect in a simple lattice model of Weyl semimetal, which is a hallmark of chiral anomaly in the Weyl semimetal, by calculating the anomalous charge current directly. We identify that the uniform external magnetic field can induce a non-dissipative charge current along its direction in Weyl semimetal, even in the absence of an external electric field if the right and left handed Weyl points are separated in energy, and that the anomalous current is proportional to the strength of the magnetic field and the energy separation with a universal coefficient e2/h2, which coincide with the ones predicted on the basis of the field theory treatment. Our results give the possibility to detect these nontrivial electrodynamic phenomena in real materials of Weyl semimetal.

Diffusive and thermodiffusive transfer of magnetic nanoparticles in porous media.

Experimental results on mass transfer within a thin porous layer saturated with ferrofluid are outlined in this paper. From the analysis of particle concentration distribution across the layer it is shown that both the mass diffusion and the Soret coefficients of nanoparticles are remarkably less than those measured in free fluid. The particle transport coefficient changes due to an external uniform magnetic field qualitatively well agree with the predictions of existing theoretical research. The magnetic field that is oriented transversely to the porous layer causes an increase in the diffusion coefficient and a decrease in the Soret coefficient whilst the longitudinal field causes a reduction of the mass diffusion and an intensification of the particle thermodiffusion.

Finite isospin chiral perturbation theory in a magnetic field

The phase diagram of finite isospin, zero temperature QCD with the pions coupled to photons in a uniform external magnetic field is explored in the low field, small isospin density regime for which chiral perturbation theory is a valid description. For realistic pion masses, the system behaves as a type-II superconductor: a uniform superconducting state is formed at low-enough magnetic fields, a vortex state for intermediate magnetic fields and finally a normal state for large magnetic fields. In each these phases (including the vortex phase), the $\pi^{0}$ remains uncondensed just as in the zero-external field problem. The critical magnetic field where the phase transition from the uniform superconducting state to a vortex state occurs was found numerically.

Energy Levels and Eigenfunctions for Two-Dimensional Electron Systems with Confining Square Well Potentials and Spin-Orbit Interactions in the Presence of Magnetic Field

Solutions of the Schr¨odinger equation are obtained for electrons in two-dimensional circular semiconductor quantum dots and rings in the presence of both external uniform constant magnetic field and the Rashba and Dresselhaus spin-orbit interactions of equal strengths. Confinement is simulated by realistic square well potentials. The dependence of the energy levels on the magnetic field and the strength of spin-orbit interaction is presented in detail.

Polarization operator in the 2+1 dimensional quantum electrodynamics with a nonzero fermion density in a constant uniform magnetic field

The polarization operator (tensor) for planar charged fermions in a constant uniform magnetic field is calculated in the one-loop approximation of $$2+1$$ -dimensional quantum electrodynamics (QED $$_{2+1}$$ ) with a nonzero fermion density. We construct the Green function of the Dirac equation with a constant uniform external magnetic field in QED $$_{2+1}$$ at a finite chemical potential, find the imaginary part of this Green function, and then obtain the polarization tensor related to the combined contribution from real particles occupying the finite number of energy levels and magnetic field. We expect that some physical effects under consideration seem likely to be revealed in a monolayer graphene sample in the presence of an external constant uniform magnetic field $$B$$ perpendicular to it.

Effect of magnetization force on ferrofluid flow due to a rotating disk in the presence of an external magnetic field

The flow characteristics of ferrofluid due to a rotating disk in the presence of an external uniform magnetic field, which is subjected in the radial and axial directions, are studied. In the presence of 10 and 100T magnetization force, contour and surface plots are presented here for radial, tangential and axial velocity profiles, and these results are compared with the case when the external applied magnetic field is absent. The results are also drawn for the variation of the magnetic field intensity in the flow due to a rotating disk.

Magnetic field instability in a neutron star driven by the electroweak electron-nucleon interaction versus the chiral magnetic effect

We show that the Standard Model electroweak interaction of ultrarelativistic electrons with nucleons ($eN$ interaction) in a neutron star (NS) permeated by a seed large-scale helical magnetic field provides its growth up to $\gtrsim 10^{15}\thinspace\text{G}$ during a time comparable with the ages of young magnetars $\sim 10^4\thinspace\text{yr}$. The magnetic field instability originates from the parity violation in the $eN$ interaction entering the generalized Dirac equation for right and left massless electrons in an external uniform magnetic field. We calculate the averaged electric current given by the solution of the modified Dirac equation containing an extra current for right and left electrons (positrons), which turns out to be directed along the magnetic field. Such current includes both a changing chiral imbalance of electrons and the $eN$ potential given by a constant neutron density in NS. Then we derive the system of the kinetic equations for the chiral imbalance and the magnetic helicity which accounts for the $eN$ interaction. By solving this system, we show that a sizable chiral imbalance arising in a neutron protostar due to the Urca-process $e^-_\mathrm{L} + p\to N + \nu_\mathrm{eL}$ diminishes very rapidly because of a huge chirality flip rate. Thus the $eN$ term prevails the chiral effect providing a huge growth of the magnetic helicity and the helical magnetic field.

Combined Resonances in Cyclotron Masers With Periodic Slow-Wave Structures

It is shown that electrons moving along helical trajectories in an external uniform magnetic field and propagating in periodic slow-wave circuits can simultaneously interact with several space harmonics of such waves. The linear theory describing combined resonances in such systems is developed. Our treatment is limited by consideration of four resonances: 1) two cyclotron resonances at the fundamental and second cyclotron harmonics; 2) the Cherenkov resonance at the zero space and zero cyclotron harmonics; and 3) the cyclotron resonance under the anomalous Doppler effect condition at the minus first cyclotron harmonic. It is shown that the growth rate and the bandwidth in the cases of such a combined resonance, in which the dominant role is, as a rule, played by the cyclotron resonance at the fundamental and the Cherenkov resonance, can be much larger than in the case of single resonances.