Kinds Of Magnetic Fields Research Articles

Wide-angle energy steering and magnetic information detection-coding of stacked ferrite-based elements in the gradient magnetic domain

By stacking ferrite-based elements (FBEs) with three kinds of magnetic fields, a tunable optical multifunctional device with wide-angle energy steering and magnetic information detection-coding is designed. For the transverse electric (TE) wave, the effective refractive index and properties of FBEs in a constant magnetic field are investigated theoretically. Based on this, we analyze the abilities of FBEs to control the energy of the electromagnetic (EM) wave in a gradient magnetic domain systematically. The computed results show that the ultra-wideband absorption and the transmission window in the absorption band are realized within the incident angle of 0−60° for the forward propagation. Reciprocal energy coexistence of absorption and transmission can be also available by expanding the applied magnetic field into the pairwise symmetric distribution. In addition, the transmission window is utilized to achieve magnetic intensity detection and the detection results (with or without absorption peak) are coded with logical values “0” and “1”. Finally, a logic gate is formed in which continuous random magnetic information can be encoded. Those calculated results can apply for wide-angle reciprocal energy steering, multipurpose magnetic detection, and coding.

Account of the baryonic feedback effect in γ-ray measurements of intergalactic magnetic fields

Aims. Intergalactic magnetic fields in the voids of the large-scale structure can be probed via measurements of secondary γ-ray emission from γ-ray interactions with extragalactic background light. Lower bounds on the magnetic field in the voids were derived from the nondetection of this emission. It is not clear a priori what kind of magnetic field is responsible for the suppression of the secondary γ-ray flux: a cosmological magnetic field that might be filling the voids, or the field spread by galactic winds driven by star formation and active galactic nuclei. Methods. We used IllustrisTNG cosmological simulations to study the effect of magnetized galactic wind bubbles on the secondary γ-ray flux. Results. We show that within the IllustrisTNG model of baryonic feedback, galactic wind bubbles typically provide energy-independent secondary flux suppression at a level of about 10%. The observed flux suppression effect has to be due to the cosmological magnetic field in the voids. This might not be the case for the special case when the primary γ-ray source has a hard intrinsic γ-ray spectrum that peaks in the energy range above 50 TeV. In this case, the observational data may be strongly affected by the magnetized bubble that is blown by the source host galaxy.

Development and application of OpenFOAM based magnetohydrodynamic solver

We develop a compressible magnetohydrodynamic solver to simulate the transonic flows based on an open-source computational fluid dynamics platform OpenFOAM. The solver is achieved by modifying the density-based Riemann solver <i>rhoCentralFoam</i> which adopts a central scheme and is available in OpenFOAM. To improve simulation accuracy and avoid non-physical oscillations, a specialized pressure-implicit algorithm with the splitting of operators is implemented to guarantee the incompressibility of magnetic field. The solver is benchmarked and the convergence rate is between the first and the second order. After benchmark, we apply this solver to magnetohydrodynamic simulations of intense-laser-produced plasma. The influences of uniform axial magnetic field and nonuniform coil-current-induced magnetic field on laser-produced plasma jets are investigated. With the uniform axial magnetic field, the positions of nozzle and the distance between knots are linearly related to square root of thermal over magnetic pressure. With the nonuniform magnetic field generated in the coil, knots are nonlinearly distributed in space and the nozzle position is modulated according to preliminary simulations. In the two kinds of magnetic fields, when the B-field strength is the same at coil center, the magnetic field of relatively small coils can shorten the times of forming nozzles and knots, suggesting that the coil magnetic field is equivalent to a higher uniform one. The simulations can be used as a reference for our future experiment on magnetized laser-produced plasma jet. Meanwhile, our simulation investigation shows that this magnetohydrodynamic solver is suitable for engineering calculation for laser plasma experiments and can deal with the situation with relatively complex configurations.

Effect of magnetic field waveform on microstructure and properties of laser cladding

Ni60 coating-45 steel substrate was prepared by magnetic field assisted laser cladding with four waveforms:steady magnetic field (SMF), alternating magnetic field (AMF), pulsed magnetic field (PMF). The effects of four kinds of magnetic fields on the morphology, microstructure, phase composition and microhardness of the coating were studied, and the magnetic field mechanism on the coating was briefly analyzed. Results revealed that the addition of magnetic field can significantly reduce the number of cracks, facilitate grain refinement and improve the coating hardness. The improvement degree of four kinds of magnetic fields on the coating performance is: PMF > APMF > AMF > SMF. Among them, the coating performance is prominently improved by PMF, but there is a serious segregation of hard phase; The segregation of hard phase and the slender of the structure occur in the APMF.

Fine Filament Structure of a Quiescent Solar Prominence

A theoretical model of a cold and dense isolated solar prominence is presented. The thermodynamic parameters of a filament (gas pressure, density and temperature) are calculated from a specified magnetic field structure. The filament lies above the photospheric polarization separation line and its magnetic field falls off rapidly with distance from the axis, so that the total electric current along the axis of the filament equals zero. The prominence has a helical magnetic field structure divided into separate thin filaments. The density and temperature distributions of the prominence derived from the equilibrium conditions for this kind of magnetic field correspond well to the known observed parameters.

Modeling for detecting weld defects based on magneto-optical imaging.

A magneto-optical (MO) imaging nondestructive testing (NDT) method for ferromagnetic weldments has been proposed. The mechanism of MO imaging was analyzed by the Faraday MO effect, magnetic domain theory, and magnetic hysteresis loops. Then, the relation between MO images and their corresponding excitation voltages was investigated. To explain the MO imaging system, magnetic domain distribution models of various welding states were established. These models are excited by two kinds of magnetic fields. One is the external magnetic field (Hex), and the other is a weldment remanence field (Mr) after Hex is removed. Relations of magnetic field excitation voltages, thickness of the spacer plate, and the corresponding MO images were also researched, which indicates the proposed NDT method can be used to detect incomplete penetration defect. Then, an experiment that uses MO imaging to detect the defects of high-strength steel (HSS) weldment was performed. Experimental results proved this method can detect crack, sag, and incomplete penetration of weldment effectively. Finally, a series of welded joint MO images of the HSS weldment were captured, which are used as the input data of the defect classification model established by using principal component analysis and an error backpropagation neural network, and the accuracy of this classification model can achieve 92.8%.

Nonlinear vibration of a rotating cantilever beam in a surrounding magnetic field

The nonlinear vibrations of a rotating cantilever beam made of magnetoelastic materials surrounded by a uniform magnetic field are investigated. The kinetic energy, potential energy and work done by the electromagnetic force are obtained. A nonlinear dynamic model, based on the Hamilton principle, which includes the stretching vibration and bending vibration is presented. The Galerkin method is adopted to discretize the dynamic equations. The proposed method is validated by comparison with the literature. The nonlinear behaviors of the responses are studied. Then simulations for different kinds of magnetic field are conducted. The effects of magnetic field parameters, including the amplitude, plane angle, spatial angle and time-varying frequency, on the dynamic behaviors of the stretching motion and bending motion are investigated in detail. The results illustrate that the interaction effects between the rotating cantilever beam and the magnetic field will increase the vibration amplitude and fluctuation of the beam. In particular, we found that: collinear magnetic fields with equal amplitude lead to the same dynamic responses; the amplitude of magnetic field intensity increases the dynamic responses remarkably; the response amplitude changes nonlinearly with the plane angle and spatial angle of the magnetic field; and the increase of time-varying frequency enhances dynamic responses of the rotating cantilever beam.

Forced convection heat transfer in a channel under the influence of various non-uniform transverse magnetic field arrangements

Magnetic nanofluids (MNFs) are suspensions, comprising a non-magnetic base fluid and magnetic nanoparticles. In modern set of suspensions called smart or functional fluids, fluid flow, particle movement, and heat transfer process can be controlled by magnetic fields. The present study investigated hydro-thermal characteristics of ferrofluid (water and Fe3O4) in a rib-channel exposed to several non-uniform transverse magnetic fields generated by an electric current going through several wires located perpendicularly in the flow between ribs. Two-phase mixture model and control volume technique were used to carry out the study. The effect of transverse magnetic field on heat transfer, consequent pressure loss, and wall shear stress resulting from this kind of magnetic field along the channel was investigated as well as the effect of various magnetic field arrangements. The results showed that magnetic field would have an unexpected influence on increasing Nusselt number in the channel, and raising the strength of magnetic field would cause an increase in minimum and maximum local Nusselt numbers, especially in rib regions. Furthermore, applying external magnetic field could noticeably affect fluid cooling at low Reynolds numbers. The influence of magnetic field on pressure drop and skin friction also are investigated in this study and it is illustrated that applying magnetic field increased skin friction especially in the case which whole magnetic wire located in one side on channel.

Temporally asymmetric laser pulse for magnetic-field generation in plasmas

Of particular interest in this article, the case study of an asymmetric laser pulse interaction with a plasma for magnetic field enhancement has been investigated. The strong ponderomotive force due to the short leading edge of the propagating laser pulse drives a large nonlinear current, producing a stronger quasistatic magnetic field. An analytical expression for the magnetic field is derived and the strength of the magnetic field is estimated for the current laser-plasma parameters. The theoretical results are validated through the particle-in-cell (PIC) simulations and are in very close agreement with the simulation based estimations. This kind of magnetic field can be useful in the plasma based accelerators as well as in the laser-fusion based experiments.

Case studies of EUV cyclones and their associated magnetic fields

EUV cyclones are rotating structures in the solar corona, and they are usually rooted in the underlying rotating network magnetic fields in the photosphere. However, their connection with the surrounding magnetic fields remains unknown. Here we report an observational study of four typical cyclones which are rooted in different kinds of magnetic fields. We use Solar Dynamics Observatory/Atmospheric Imaging Assembly data to investigate the rotation of EUV features in cyclones and Helioseismic and Magnetic Imager data to study the associated magnetic fields. The results show that, (1) an EUV cyclone rooted in a sunspot rotates with the photospheric magnetic field; (2) two EUV cyclones in two faculae of an active region are connected to the same sunspot of the active region but rotate oppositely; (3) an EUV cyclone is rooted in a coronal hole with weak open magnetic fields; (4) a pair of conjugated cyclones is rooted in magnetic fields that have opposite polarity with opposite directions of rotation. The differences in the spatial extent of a cyclone, characteristics of its rotation and underlying fields indicate that cyclones are ubiquitous over the solar atmosphere and that the magnetic structures relevant to the cyclones are more complicated than expected.

Andrzej Więcek: east meets west in nephrology

Andrzej Więcek: east meets west in nephrology

ChemInform Abstract: Manipulation of Micro‐ and Nanostructure Motion with Magnetic Fields

AbstractReview: 117 refs.

Manipulation of micro- and nanostructure motion with magnetic fields

In this review we will focus on how magnetic fields can be used to manipulate the motion of various micro- and nanostructures in solution. We will distinguish between ferromagnetic, paramagnetic and diamagnetic materials. Furthermore, the use of various kinds of magnetic fields, such as homogeneous, inhomogeneous and rotating magnetic fields, is discussed. To date most research has focused on the use of ferro- and paramagnetic materials, but here we also describe the possibilities of magnetic manipulation of diamagnetic materials. Since the vast majority of soft matter is diamagnetic, this paves the way for many new applications to manipulate the motion of micro- and nanostructures.

Spin waves in easy-axis antiferromagnets with precessing domain walls

Equations for the antiferromagnetism vector are used to study the spectrum and scattering of spin waves on a domain wall with precessing spins in an easy-axis antiferromagnet with a constant magnetic field directed along the easy axis. It is shown that this kind of magnetic field can be completely eliminated from the equations of motion, so that they can be reduced to a Lorentz invariant form. The spectral problem for weak excitation of a precessing domain wall is solved and exact solutions are found for the linearized equations describing the propagation of spin waves in antiferromagnets with this kind of domain wall. An explicit expression is found for the reflection coefficient of spin waves from a domain wall as a function of the wave vectors of the incident and transmitted waves, along with its dependence on the spin wave frequency. The range of frequencies within which the spin waves are fully reflected is found and it is shown that the reflection coefficient falls off sharply above the upper limit of this range. These results can be generalized to the case of a moving domain wall in a three-dimensional crystal.

Effect of Magnetic Fields on Oscillatory Marangoni Convection in a Half-Zone of an Electric Conducting Liquid Bridge

Three-dimensional numerical computations have been carried out for oscillatory Marangoni convection of an electric conducting liquid sustained between parallel circular plates having temperature difference in the presence of three kinds of magnetic fields. For the sake of simplicity, the buoyancy effect is ignored and the free-surface shape is assumed to be perfectly cylindrical. Axial, horizontal or cusp-shaped magnetic field is applied to this configuration. The Marangoni convection exhibits transition from axisymmetric flow to three-dimensional oscillatory flow depending on the Reynolds and Hartmann number as well as the type of magnetic field. The transition process can be recognized by the growth rate of the azimuthal velocity. Three-dimensional oscillatory flows can be stabilized to steady flows when the Hartmann number is large enough compared to the Marangoni number in spite of the three kinds of magnetic field. The axial or cusp-shaped magnetic field damps out the velocity effectively and axisymmetric steady flows take place, while the horizontal magnetic field tends to restrict the flow aligning parallel to the magnetic field line.

Calculation of Performance for Brushless Doubly-Fed Machine as Generator Based on Finite-Element Model

For Brushless Doubly-fed Machine(BDFM), the main feature of field is that there are two kinds of magnetic fields differing in pole number in the machine’s iron circuit and the two fields have the same order of magnitude. Hence, it is difficult to calculate the machine’s performance accurately using conventional analytic method. In this paper, the author constructed one finite-element model of BDFM, and analyzed the machine’s performance using transient solver. The author also compared the finite-element method with experiment and conventional analytic method. Because taking into account the saturation, the results of finite-element method are closer to the measurements than that of conventional analytic method. The validity of model is verified.

Effect of Axial and Transverse Magnetic Fields on the Arc Duration and Material Transfer

Axial and transverse magnetic fields are widely used in many kinds of switches to decrease the arc erosion. In this paper, the influence of these two kinds of magnetic fields on the arc phase transition was studied particularly for AgSnO2 contacts breaking a 28V/25A circuit. The experiments were carried out under resistive and inductive loads in an atmospheric environment. The relationships between flux densities ranging from 0 to 200mT and the arc duration were obtained. It was found that the transverse magnetic field was more efficient in balancing the arc phases and decreasing the arc erosion. The results can be used to guide the design of arc extinguishment systems in DC high power relays.

The Effect of the Magnetic Field’s Direction to Polishing in a Magnetic-Electrochemical Compound Polishing

Magnetic-electrochemical compound polishing is applied in difficult-to-process materials little by little. The influence of the magnetic field to electrochemical process is very complicated. In the paper, using Coulomb laws and Lorentz force, the two kinds of math model of the movement of the charged particles are established according to the different magnetic field whose direction is vertical or parallel to the electrical field. The velocity equations and loci equations of three typical particles are concluded in two kinds of magnetic field’s directions. To be compared and analyzed carefully, the influence of the magnetic field’s direction to polishing is concluded. This study can guide how to determine the magnetic field’s direction in magnetic-electrochemical compound polishing, and build the theoretical basis to study the mechanism of magnetic-electrochemical compound polishing.

Effects of gradient magnetic force and diamagnetic torque on formation of osteoclast-like giant cell

In bone tissue, two kinds of cells, osteoblast (OB) and osteoclast (OC), contribute to remodeling of bone. In the present study, a co-culture system of bone-forming cell (OB) and -dissolving cell (OC) was incubated in static magnetic fields of horizontal 14 T and vertical gradient 10 T. Effect of two kinds of magnetic fields was an inhibition of OC formation. Three kinds of mechanisms, magnetic orientation of OB, diamagnetic torque force acting on OC, and possible reduction of earth's gravity were discussed.

Three-dimensional modelling of GeSi growth in presence of axial and rotating magnetic fields

A three-dimensional numerical simulation has been performed to study the growth of Ge 0.98Si 0.02 by the Traveling Solvent Method. We attempted to suppress the buoyancy convection, in the Ge 0.98Si 0.02 melt zone, by applying axial and rotating magnetic fields. The effects of the applied magnetic field intensity, on the transport structures in the melt (flow and concentration fields, heat and mass transfer), have been investigated in detail. The steady-state full Navier–Stokes equations, as well as energy, mass species transport and continuity equations are numerically solved using the finite element method. By applying an axial magnetic field of various intensities (2, 10, and 22 mT), we found that as the axial magnetic field increases, the silicon distribution nearby the growth interface becomes more uniform. In the case of a rotating magnetic field, with different applied rotational speeds (2, 7 and 10 rpm), we found that such kind of magnetic field has a marked effect on the silicon concentration, which changes its shape from a convex one to a nearly flat shape as the magnetic field intensity increases. An alternative method to reduce or suppress buoyancy convection, in the melt zone, is the growing of the sample in a microgravity environment, with a gravity level of at least 10 −4 the earth normal gravity level; in this case the results revealed smooth and almost perfect straight concentration contours, due to the buoyancy convection weakness.