External Uniform Magnetic Field Research Articles

Magnetic Field Inhibition of Convective Heat Transfer in Magnetic Nanofluid

Natural convection is the main mechanism of heat transfer in many natural and technological processes, which makes it urgent to study the possibilities of controlling it. In this work, the processes of development and damping of thermal convection in a flat vertical quasi-two-dimensional layer of magnetic nanofluid are considered experimentally. The presence of the magnetic properties of the nanofluid makes it possible to effectively apply the external magnetic fields to regulate convective heat transfer. The magnetic nanofluid layer was heated from below. It was shown in this work that the imposition of an external uniform stationary magnetic field perpendicular to the temperature gradient leads to the suppression of convection. The processes of heating and cooling the metal plates in a magnetic nanofluid are studied. It is demonstrated that the suppression of convection by a magnetic field leads to a slowdown in the heating of cold and cooling of hot metal plates in a magnetic nanofluid. The obtained results can be considered as a model for understanding similar exchange processes in liquids under the action of magnetic field.

Depletion-Induced Chiral Chain Formation of Magnetic Spheres

Experimental evidence is presented for the spontaneous formation of chiral configurations in bulk dispersions of magnetized colloids that interact by a combination of anisotropic dipolar interactions and isotropic depletion attractions. The colloids are superparamagnetic silica spheres, magnetized and aligned by a carefully tuned uniform external magnetic field; isotropic attractions are induced by using poly(ethylene oxide) polymers as depleting agents. At specific polymer concentrations, sphere chains wind around each other to form helical structures–of the type that previously have only been observed in simulations on small sets of unconfined dipolar spheres with additional isotropic interactions.

Magnetization textures in twisted bilayer CrX3 ( X =Br, I)

Motivated by the recent experiment demonstration of stacking dependent interlayer magnetic interaction [T. Song et al., Nat. Mater. 18, 1298 (2019); T. Li et al., Nat. Mater. 18, 1303 (2019); W. Chen et al., Science 366, 983 (2019)], we investigate the magnetization textures and the control possibilities in the moir\'{e} pattern formed of twisted bilayer two-dimensional (2D) magnets CrX$_3$ (X=Br, I). We find that the stacking dependent interlayer magnetic interaction results in the formation of periodic magnetization domains in a long-period moir\'{e} pattern. Magnetization textures with various topological numbers can be constructed, depending on the winding of the textures around the domain walls. A uniform external magnetic field competes with the lateral modulated interlayer magnetic interaction and can be utilized to tune the magnetization textures.

Relativistic Dynamics of Oppositely Charged Two Fermions Interacting with External Uniform Magnetic Field

We investigated the relativistic dynamics of oppositely charged two fermions interacting with an external uniform magnetic field. We chose the interaction of each fermion with the external magnetic field in the symmetric gauge, and obtained a precise solution of the corresponding fully-covariant two-body Dirac equation that derived from Quantum Electrodynamics via Action principle. The dynamic symmetry of the system we deal with allowed us to determine the relativistic Landau levels of such a spinless composite system, without using any group theoretical method. As a result, we determined the eigenfunctions and eigenvalues of the corresponding two-body Dirac Hamiltonian

Peristaltic flow of Herschel Bulkley nanofluid through a non-Darcy porous medium with heat transfer under slip condition

In this work, we focused on the peristaltic unsteady flow of non-Newtonian nanofluid with heat transfer through a non-uniform vertical duct. The flow obeys Herschel Bulkley model through a non-Darcy porous medium under the effects of mixed convection and thermal diffusion. Moreover, the effects of thermal radiation, heat generation, Ohmic dissipation, chemical reaction and uniform external magnetic field are investigated. The derived equations that describe the velocity, temperature and nanoparticles concentration are simplified under the assumptions of long wave length and low Reynolds number. These equations have been solved by using a numerical technique with the help of shooting method. The obtained solutions are functions of the physical parameters entering the problem. The effects of these parameters and the obtained solutions are explained and discussed through a set of graphs. It is found that the increment in Prandtl number or Thermophoresis parameter reduces the spread of the nanoparticles (concentration increased) within the fluid along with the thermal diffusivity through the fluid layers. Also the non-Darcy effect supports the inertial forces, and in order to maintain Reynolds number, the viscous forces are motivated and the axial velocity is damped. Moreover, for the validation of the current methodology, this model is reduced to power law model (no yield stress) and compared with the work of Eldabe et al. [16].

Aggregation Kinetics and Macroscopic Properties of an Athermal Suspension in Uniaxial Magnetic Field

In this letter, the aggregation kinetics in a magnetic fluid emulsion as a model system under the action of an external uniform stationary magnetic field is studied experimentally. The process of structure formation is analyzed by measuring the macroscopic magnetic permeability of a three-dimensional sample of the emulsion. This makes it possible to obtain information on the aggregation kinetics in an athermal polydisperse unbounded suspension. It is shown that the emulsion macroscopic properties change has a time scale corresponding to the predictions of the hierarchical model $t^*\approx1$ /( $H\varphi^{1/2}$ ), where $t^*$ is the time scale, $H$ is the magnetic field strength, and ϕ is the emulsion volume fraction. The dependences of the magnetic permeability relative change on dimensionless time can be collapsed onto a master curve when these dependences are normalized to their maximum value. The obtained results are discussed using a two-dimensional computational finite-difference model of suspension permeability.

MHD mixed convection on an inclined stretching plate in Darcy porous medium with Soret effect and variable surface conditions

AbstractThis work is concerned with a steady 2D laminar MHD mixed convective flow of an electrically conducting Newtonian fluid with low electrical conductivity along with heat and mass transfer on an isothermal stretching semi-infinite inclined plate embedded in a Darcy porous medium. Along with a strong uniform transverse external magnetic field, the Soret effect is considered. The temperature and concentration at the wall are varying with distance from the edge along the plate, but it is uniform at far away from the plate. The governing equations with necessary flow conditions are formulated under boundary layer approximations. Then a continuous group of symmetry transformations are employed to the governing equations and boundary conditions which determine a set of self-similar equations with necessary scaling laws. These equations are solved numerically and similar velocity, concentration, and temperature for various values of involved parameters are obtained and presented through graphs. The momentum boundary layer thickness becomes larger with increasing thermal and concentration buoyancy forces. The flow boundary layer thickness decreases with the angle of inclination of the stretching plate. The concentration increases considerably for larger values of the Soret number and it decreases with Lewis number. The skin friction coefficient increases for increasing angle of inclination of the plate, magnetic and porosity parameters, however it decreases for rise of thermal and solutal buoyancy parameters. In this double diffusive boundary layer flow, Nusselt and Sherweed numbers increase for rise of thermal and solutal buoyancy parameters, Prandtl number, but they behave opposite nature in case of angle of inclination of the plate, magnetic and porosity parameters. The Sherwood number increases for increasing Lewis number but it decreases for increasing Soret number.

Lattice Boltzmann Simulation of MHD Rayleigh-Bénard Natural Convection in a Cavity Filled With a Ferrofluid

In this study, we examine the effect of a uniform external magnetic field on Rayleigh-Bénard convection in a square cavity filled with a ferrofluid. Numerical simulations are based on the Lattice Boltzmann method. The effects of physical parameters, which are the Rayleigh number, the Hartmann number, and the angle of inclination of the magnetic field are studied. The results obtained are graphically illustrated and discussed for a volume fraction of four percent. These results show that the rate of heat transfer decreases by increasing the Hartmann number. For high Rayleigh number values, the maximum heat transfer rate was obtained for a specific Hartmann number when the Lorentz and buoyancy forces are perpendicular

Attenuation properties of EM wave by magnetized nonuniform plasma slab coated on perfect conductor plane

AbstractThe total amplitude reflection coefficient of EM wave in a nonuniform plasma slab coated on perfect conductor plane is newly derived by using the scattering matrix method (SMM), and the attenuation is calculated. Three types of plasma electron density profile, that is the hyperbolic, sinusoidal, and linear profiles, are used. The external magnetic field and plasma parameters such as the maximum electron density and collision frequencies are discussed to calculate the attenuation of EM wave. The calculation results show that the plasma electron density profile and maximum electron density exert a large effect to the attenuation of EM wave and the attenuation under the uniform external magnetic field is taken place by the electron cyclotron resonance absorption, the up hybrid resonance absorption and geometric resonances absorption.

Metal-insulator transition and band magnetism in the spin-1∕2 Falicov-Kimball model on a triangular lattice with external magnetic field

Ground state properties of the spin$-1/2$ Falicov-Kimball model on a triangular lattice in the presence of uniform external magnetic field are explored. Both the orbital and the Zeeman field-induced effects are taken into account and in each unit cell only rational flux fractions are considered. Numerical results, obtained with the help of Monte Carlo simulation algorithm, reveal that the ground state properties strongly depend on the onsite Coulomb correlation between itinerant and localized electrons, orbital magnetic field as well as the Zeeman splitting. Strikingly, for the on-site Coulomb correlation $U/t \approx 1$, the Zeeman splitting produces a phase transition from paramagnetic metal/insulator to ferromagnetic insulator/metal transition in the itinerant electron subsystem accompanied by the phase segregation to the bounded/regular phase in the localized electrons subsystem. For the onsite Coulomb correlation $U/t \approx 5$, although no metal to insulator transition is observed but a magnetic phase transition from paramagnetic phase to ferromagnetic phase in the itinerant electron subsystem is observed with the Zeeman splitting. These results are applicable to the layered systems e.g. cobaltates, rare earth and transition metal dichalcogenides, $GdI_{2}$, $NaTiO_{2}$, $NaVO_{2}$ and $Be_{x}Zn_{1-x}O$ etc. It has been also proposed that the results can be realized in the optical lattices with mixtures of light atoms and heavy atoms using the cold atomic techniques.

Magnetohydrodynamic Moving Liquid Plug Within a Microchannel: Analytical Solutions.

The wide applications of plug flows in microscale in science and engineering help them attract a great deal recent interest. An analytical study is undertaken here to study the impacts of a transversely applied external uniform magnetic field affecting the motion of liquid in the plug in terms of hydrodynamic mixing properties. The well-known symmetric vortex structure occurring in a long plug with moderate aspect ratio is observed to be preserved, while the recirculation phenomenon is highly affected by the action of the magnetic field. The decelerating feature of Lorentz force on the liquid motion is illuminated by reducing the strength of the recirculating vortex moving towards the upper and lower walls. The effects of magnetic field on the flow resistance of the liquid plug as well as on the plug circulation rate and on the axial flux are also clarified. The liquid plug considered here is shown to be fully consistent with the continuous liquid flow in a channel whose exact solution is further extracted.

Exact solutions of a quantum system placed in a Kratzer potential and under a uniform magnetic field

We propose Whittaker function approach as a theoretical method for finding exact solutions of a quantum mechanical system placed in the Kratzer potential. We then show that the effect of an external uniform magnetic field on this system can be satisfactorily determined using variational method. By following the one-step treatment suggested in this study, we increase the reliability and the accuracy of the solutions of Schrodinger equation for a quantum mechanical system placed in potential energy and perturbed by a uniform magnetic field that proves to be useful in modelling physical phenomena. We find that the achieved numerical and analytical results agree very well with those already published and those calculated using the Numerov method.

MHD Peristaltic Transport of Bingham Blood Fluid with Heat and Mass Transfer Through a Non-Uniform Channel

In the present work, the flow of non-Newtonian Bingham blood fluid through non-uniform channel is investigated. The fluid is electrically conducting, and the external uniform magnetic field is applied on this motion. The heat and mass transfer are taken in consideration, so, Soret and Dufour effects are studied. The problem is modulated mathematically by a system of non-linear partial differential equations which govern the velocity, temperature and concentration distributions. The system of these equations is simplified under the assumptions of long wavelength and low Reynolds number, then it is solved analytically by using homotopy perturbation technique. These distributions are obtained as a function of the physical parameters of the problem. The effects of these parameters on the obtained solutions are discussed numerically and illustrated graphically through a set of figures. These parameters play an important role to control the values of solutions. The used Bingham model is applicable for the physiological transportation of blood in arteries.

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.

A magnetic field coupling lattice Boltzmann model and its application on the merging process of multiple-ferrofluid-droplet system

The present study concerns the dynamics of ferrofluid droplets in a Newtonian fluid. The incompressible Navier-Stokes (NS) equations are applied for the dynamics of the immiscible magnetic and Newtonian fluids while the Cahn-Hilliard (C-H) equation is adopted to describe the behavior of their interface. A magnetic field coupling lattice Boltzmann (LB) model is developed to solve both the NS equations and the C-H equation. Specially, a mass-correcting term is introduced into the C-H equation, which strongly enforces the mass conservation. The magnetic field is evaluated by a Poisson equation solver with a self-correcting procedure for the static Maxwell equations. The magnetic dipole force is transformed into the magnetic surface force by a rigorous mathematical procedure, which can physically describe the magnetic effect on the interface. Moreover, the magnetic force after this treatment becomes easy-to-implement, which can be directly incorporated into the external force term of the LB model. The capability of the present combination method to simulate the magnetic multiphase flows is demonstrated by three typical numerical examples, i.e., Laplace law for a stationary droplet, a stationary cylinder under an external uniform magnetic field, the deformation of a single ferrofluid droplet. Further, the merging process of multiple-ferrofluid-droplet system in organic oil is investigated. It is found that the elongation of ferrofluid droplet in the direction of magnetic field shows positive impact on the merging process when the orientation of ferrofluid droplets is parallel to the external magnetic field, while negative impact on the merging process when their orientation is perpendicular to the external magnetic field.

Chaos in positive ion–negative ion magnetized plasmas

The dynamical behaviour of weakly nonlinear, low-frequency sound waves are investigated in a plasma composed of only positive and negative ions incorporating the effects of a weak external uniform magnetic field. In the plasma model the mass (temperature) of the positive ions is smaller (larger) than that of the negative ions. The dynamics of the nonlinear wave is shown to be governed by a novel nonlinear equation. The stationary plane wave (analytical and numerical) nonlinear analysis on the basis of experimental parameters reveals that the nonlinear wave does have quasi-periodic and chaotic solutions. The Poincarè return map analysis confirms these observed complex structures.

Spin 3/2 particle: Puali – Fierz and Fradkin models, interaction with external fields

In the frame of the general Gel’fand – Yaglom formalism, the Fradkin theory for a spin 3/2 particle in presence of external fields is investigated. Applying the standard requirements of relativistic invariance, P-symmetry, existence of a Lagrangian for the model, we derive a set of spinor equations, first in absence of external fields. The wave function consists of a bispinor and a vector-bispinor. It is shown that in absence of external fields the Fradkin model is reduced to the Pauli – Fierz theory. Taking into account the presence of external electromagnetic fields, the Fradkin theory can be turned to the minimal form of the equation for the main bispinor. This equation contains an additional interaction term governed by the electromagnetic tensor F αβ . Meanwhile, there appears a parameter in the Fradkin equation related to any characteristic of the particle additional to its charge. The theory is generalized for taking into account the pseudo-Riemannian space-time geometry. In this case, the Fradkin equation contains an additional interaction term, governed by the Ricci tensor R αβ . If the electric charge of the particle is zero, the Fradkin model remains correct and describes a neutral spin 3/2 particle of the Majorana type interacting nonminimally with the geometrical background through the Ricci tensor. To clarify the meaning of the additional physical characteristics underlying the Fradkin model in contrast to the Pauli – Fierz one we have considered nonrelativistic approximation for both theories in presence of an external uniform magnetic field, and found respective energy spectra. The structure of the ninrelativistic Fradkin equation permits to consider such an additional parameter as polarizability.

MHD peristaltic flow of non-Newtonian power-law nanofluid through a non-Darcy porous medium inside a non-uniform inclined channel

In this work, we studied the peristaltic motion of steady non-Newtonian nanofluid flow with heat transfer through a non-uniform inclined channel. The flow in this discussion obeys the power law model through a non-Darcy porous medium. Moreover, the effects of thermal radiation, heat generation, Ohmic dissipation and a uniform external magnetic field are taken in consideration. The governing equations that describe the velocity, temperature and nanoparticles concentration are simplified under the assumptions of long wave length and low-Reynolds number. These equations have been solved numerically by using Runge–Kutta–Merson method with the help of shooting and matching technique. The solutions are obtained as functions of the physical parameters entering the problem. The effects of these parameters on the obtained solutions are discussed and illustrated graphically through a set of figures. It is found that as Brownian motion parameter increases, the axial velocity decreases, whereas the nanoparticles concentration increases and it has a dual effect on the temperature distribution. Moreover, the axial velocity and temperature increase as Prandtl number increases, while the nanoparticles decrease.

Shunting the electric arc helical spiral turns (numerical simulation)

A numerical simulation was performed for an open direct current (dc) electric arc in a uniform external axial magnetic field. The calculation was carried out in the frameworks of a non-stationary three-dimensional mathematical model in approximation of partial local thermodynamic equilibrium of plasma. The model does not presuppose a helical shape of the arc, as is customary in theoretical studies based on linear perturbation theory. It was shown that the helical shape of an open arc is not constant in time and periodically collapses with subsequent restoration. In a certain range of external parameters of the arc (current strength, inter-electrode distance, and external axial magnetic field), a new mode of destruction of a regular structure was revealed – the arc section shunting between the spiral turns. Shunting can be single or double when the breakdown occurs simultaneously in two places. Apparently, it is caused by convective heat transfer by plasma flows as well as by the sliding of the arc thermal field. The appeared thermal field creates a zone of electric conductivity in which the breakdown occurs.

Quantum dynamics of spin-0 scalar particle with a uniform magnetic field and scalar potential in spinning cosmic string space-time and AB-effect

The relativistic quantum dynamics of a spin-0 scalar massive charged particle with an external uniform magnetic field including a magnetic quantum flux in a spinning cosmic string with a scalar potential is studied. We compute the energy eigenvalues and eignfunctions and analyze a relativistic analogue of the Aharonov-Bohm (AB) effect for bound states.