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In this paper we discuss conditions under which charged particles are confined by an axisymmetric longitudinal magnetic field with power law dependence on the radius. We derive a transcendental equation for the critical speed corresponding to the threshold between bounded and unbounded trajectories of the particles. This threshold speed shows strong dependence on the direction, and this dependence becomes more prominent as the exponent of the power law increases. The equation for threshold speed can be solved exactly for several specific values of the power exponent, but in general it requires a numerical treatment. Remarkably, if the magnetic field magnitude decreases more slowly than the inverse of the radius, charged particles remain confined no matter how large their energies may be. Key words: particle orbit theory, motion in magnetic field, escape velocity, transcendental equation, power law. Nous discutons les conditions sous lesquelles les particules chargees sont confinees par un champ magnetique longitudinal axisymetrique avec une dependance radiale en loi de puissance. Nous derivons une equation transcendantale pour la vitesse critique correspondante au seuil entre les trajectoires liees et les trajectoires libres des particules. La vitesse de seuil montre une forte dependance sur la direction et cette dependance devient plus importante lorsque l'exposant de la loi de puissance augmente. L'equation pour la vitesse de seuil peut etre solutionnee exactement pour plusieurs valeurs specifiques de l'exposant, mais en general, la solution est numerique. Il est remarquable de constater que si la magnitude du champ magnetique diminue plus lentement que l'inverse du rayon, la particule chargee reste confiner, quelle que soit son energie. [Traduit par la Redaction] Mots-cles : theorie orbitale des particules, mouvement dans un champ magnetique, vitesse de liberation ou d'echappement, equation transcendantale, loi de puissance., 1. Introduction Investigating trajectories of objects in various circumstances is one of the oldest and most fundamental problems of classical mechanics. A particular example of this problem, namely, motion of [...]

The nucleus of the Milky Way is known to harbour regions of intense star formation activity as well as a supermassive black hole (1). Recent observations have revealed regions of [...]

The spin Seebeck effect is observed when a thermal gradient applied to a spin-polarized material leads to a spatially varying transverse spin current in an adjacent non-spin-polarized material, where it [...]

Hyperpolarized nuclear states provide NMR signals enhanced by many orders of magnitude, with numerous potential applications to analytical NMR, in vivo NMR, and NMR imaging. However, the lifetime of hyperpolarized magnetization is normally limited by the relaxation time constant [T.sub.1], which lies in the range of milliseconds to minutes, apart from in exceptional cases. In many cases, the lifetime of the hyperpolarized state may be enhanced by converting the magnetization into nuclear singlet order, where it is protected against many common relaxation mechanisms. However, all current methods for converting magnetization into singlet order require the use of a high-field, high-homogeneity NMR magnet, which is incompatible with most hyperpolarization procedures. We demonstrate a new method for converting magnetization into singlet order and back again. The new technique is suitable for magnetically inequivalent spin-pair systems in weak and inhomogeneous magnetic fields, and is compatible with known hyperpolarization technology. The method involves audio-frequency pulsed irradiation at the low-field nuclear Larmor frequency, employing coupling-synchronized trains of 180[degrees] pulses to induce singlet-triplet transitions. The echo trains are used as building blocks for a pulse sequence called M2S that transforms longitudinal magnetization into long-lived singlet order. The time-reverse of the pulse sequence, called S2M, converts singlet order back into longitudinal magnetization. The method is demonstrated on a solution of [sup.15]N-labeled nitrous oxide. The magnetization is stored in low magnetic field for over 30 min, even though the [T.sub.1] is less than 3 min under the same conditions. long-lived spin states | low-field NMR | singlet states doi/ 10.1073/pnas.1010570107

The purpose of this tutorial is to derive the precessional characteristics of the magnetic moments of hydrogen nuclei in the presence of a constant external magnetic field using the Dirac bra-ket formulation of quantum mechanics (QM). This behaviour has many applications, most notably in nuclear magnetic resonance (NMR) and magnetic resonance (MR) imaging. Many NMR and MR imaging textbooks claim that the QM expectation value of the magnetic moment of a proton in a magnetic field reduces to the classical picture of a precessing magnetic dipole. This paper validates this conclusion by reducing the cumbersome QM integrals using Dirac notation and matrix algebra, and then comparing this result with the classical picture. It illustrates the connections between the quantum and classical pictures and demonstrates quantitatively how they differ and how they are similar. This tutorial targets students and researchers interested in the fundamental physics behind the MR phenomenon and assumes that the reader has a basic understanding of QM. This may be helpful for undergraduate QM students learning about spin angular momentum and Dirac notation. PACS Nos: 87.80.Lg, 87.61.-c, 32.30.Dx, 07.57.Pt, 03.65.Sq, 01.40.-d Le but de ce tutoriel est d'obtenir les caracteeristiques de precession du moment magnetique du noyau hydrogene dans un champ magnetique constant, a l'aide du formalisme bra-ket de Dirac de la mecanique quantique (MQ). Ce comportement a plusieurs applications, nommeement en resonance magnetique nucleeaire (RMN) et en imagerie a resonance magnetique (RM). Plusieurs livres traitant de RMN et d'imagerie RM soutiennent que l'espeerance mathematique en MQ du moment magnetique d'un proton dans un champ magnetique se reduit a la vision classique pour un dipole magnetique en precession. Nous validons ici cette conclusion en reduisant les lourdes integrales de la MQ a l'aide de la notation de Dirac et de l'algebre matriciel et en comparant le resultat avec le resultat classique. Nous illustrons le lien entre les visions classique et quantique et deemontrons quantitativement en quoi elles sont diffeerentes et en quoi elles sont semblables. Ce tutoriel vise les etudiants et les chercheurs interesses par la physique de base derriere le meecanisme de RM et nous supposons que le lecteur a une connaissance de base de la MQ. Il pourrait aider les etudiants de la MQ au premier cycle a mieux comprendre le moment angulaire de spin et la notation de Dirac. [Traduit par la Redaction], 1. Introduction The fundamental basis for magnetic resonance (MR) phenomena is the interaction between nuclear spins and external magnetic fields [1-4]. As shown in this tutorial, when a proton is [...]

Increasingly dense residential housing developments have spurred new concerns about electromagnetic fields. The magnetic fields generated by the underground distribution system in such a residential subdivision are assessed in this study. In particular, the magnetic flux densities above the underground cables, around the padmount transformers and junction boxes, and at the service entrance panels are measured. The largest magnetic fields of 95 mG and 148 mG are recorded on the surfaces of the transformer enclosures and junction boxes, respectively, at around 30 % to 40% of full load. The magnetic fields reduce to less than 3 mG at a distance of ~1 m from the distribution system infrastructure. Software is developed to estimate the peak magnetic field generated at full load conditions by the underground cables composed of twisted conductors. Index Terms--Electromagnetic fields, magnetic fields, power cables, underground power distribution lines.

The aim of this paper is to propose an approximate technique for the reconstruction of magnetic-field distribution in the proximity of unknown sources. The method is based on two nested optimization algorithms--the external one is responsible for the definition of the geometry of the equivalent-source system, while an internal procedure based on least-square minimization is used to identify the currents of the sources. The goal is to minimize the deviation between the reconstructed and actual field. It is shown that under magnetic quasi stationary conditions, the proposed approach is able to reconstruct the field distribution of a complex 3-D environment as medium-voltage/low-voltage substations. The main limitation is the availability of magnitude and phase of the measured magnetic field. This information is not usually provided by standard probes but can be obtained by a proper measurement setup. The proposed technique allows accurate reconstruction of the magnetic field even in the case of many sources without requiring their accurate geometrical description and is suitable for the evaluation of stray fields and the design of magnetic shielding. Index Terms--Identification, magnetic fields, equivalent-source system.

Massive stars play a crucial role in the production of heavy elements and in the evolution of the interstellar medium, yet how they form is still a matter of debate. We report high-angular-resolution submillimeter observations toward the massive hot molecular core (HMC) in the high-mass star-forming region G31.41+0.31. We find that the evolution of the gravitational collapse of the HMC is controlled by the magnetic field. The HMC is simultaneously contracting and rotating, and the magnetic field lines threading the HMC are deformed along its major axis, acquiring an hourglass shape. The magnetic energy dominates over the centrifugal and turbulence energies, and there is evidence of magnetic braking in the contracting core.

A method to evaluate the intermodulation distortion (IMD) of a ferrite element by the two-tone method is proposed in which a dual-mode resonator enables an intense RF magnetic field to be applied to the ferrite. A test fixture operating at frequencies around 2 GHz was designed and assembled based on this concept. The IMD was measured using the test fixture and different shapes of ferrites were used to show the effect of different magnetization distributions. Discussions including the data obtained in former studies clarified factors dominating the IMD of ferrite. It is anticipated that these investigations will lead to a significant reduction in IMD in ferrite circulators, as well as an increase in power-handling capability. Index Terms--Circulator, ferrites, intermodulation distortion (IMD), nonlinearities, resonators, shape.

Iron oxide nanoparticle of magnetite, one of well-known soft magnetic materials, has been investigated due to their various potential applications. In order to apply it as a magnetorheological (MR) material, composite of poly(vinyl butyral) and magnetite nanoparticles was prepared via solvent evaporation method using synthesized magnetite nanoparticles because of their proper magnetic characteristics and dispersion stability in a viscous medium. The magnetite nanoparticle was prepared via a co-precipitation method using ferrous and ferric ionic aqueous solutions. Surface and internal morphology of the composite particles were observed via scanning electron microscope and transmittance electron microscope. The MR fluid was prepared by suspending the composite particles in mineral oil. Its MR characteristics were examined via a rotational rheometer in a parallel plate geometry equipped with a magnetic field supplier. MR properties of the composite based MR fluid exhibit typical MR behavior with maximum yield stress of 800 Pa when 343 kA/m of magnetic field was applied. Index Terms--Composite, iron oxide, magnetorheology, poly(vinyl butyral).

Spin-orbit interaction induced magnetic field, which can arise from an asymmetry of the potential well, causes imbalance of carrier densities between spin-up and spin-down electrons. In the potentiometric measurement, the detected signal follows the magnetization status of the detection ferromagnet (FM1). In case of adding the neighboring ferromagnet (FM2), the measured potential is decided by both of FMs. When the magnitude of external field is between the coercive field of the FM1 and FM2, the detector reads the intermediate potential. The detector interacts with the neighboring ferromagnet and shows four levels of potential states. Index Terms--Potentiometric measurement, quantum wells, Rashba effect, spin-orbit interaction.

We report a new method that uses magnetic birefringence to enhance the contrast in a neutron interferometer. We performed model calculations for interference-fringe contrast in a Mach--Zehnder-type neutron interferometer with an improperly aligned multilayer mirror and inhomogeneous magnetic fields. Our calculations showed that, by using inhomogeneous magnetic fields, we could recover the decreased contrast caused by the improper alignment of the mirrors. OCIS codes: 030.6600, 120.1088, 120.4570, 220.1080, 220.1140, 230.2035.

We provide a representation for the scaling limit of the d = 2 critical Ising magnetization field as a (conformal) random field by using Schramm--Loewner Evolution clusters and associated renormalized area measures. The renormalized areas are from the scaling limit of the critical Fortuin--Kasteleyn clusters and the random field is a convergent sum of the area measures with random signs. Extensions to off-critical scaling limits, to d = 3, and to Potts models are also considered. continuum scaling limit | critical |sing model | FK clusters | SLE | CLE

Two variants of the advection upstream splitting method are modified to solve the equations of ideal magnetohydrodynamics. Discontinuity-sensing functions used in AUSMPW+ and M-AUSMPW+ for the magnetohydrodynamics equations are newly defined in consideration of a magnetic field. The new pressure-based weight functions are shown to effectively remove the oscillations behind a strong shock wave as well as provide a highly accurate solution for a stationary contact discontinuity. To satisfy the divergence-free constraint of a magnetic field, the hyperbolic divergence cleaning method is chosen and applied for all the test cases. Ryu and Jones' one-dimensional magnetohydrodynamics shock-tube problem and Orszag and Tang's two-dimensional magneto-hydrodynamics vortex system are evaluated to validate and show the advantages of the newly developed schemes.

A novel giant magnetoimpedance (GMI) noncontact current sensor with spiral structure double-probe is designed. Differing from the formerly reported sensors, the probes of this sensor consist of annealed commercial amorphous ribbons which are curled to spiral tubes. Two couples of permanent magnets are applied to provide bias magnetic field. The distance between the probes and the permanent magnets is fixed at 2.4 cm. The sensor shows sensitivity of 1 VIA in the current range of [+ or -] 1.5 A, measurement precision of less than 0.16% at room temperature, and good thermal stability in the temperature range between -20 and 30[degrees]C. Index Terms--Amorphous ribbon, current sensor, double-probe, giant magnetoimpedance.

The presence of crack-like defects can cause an uneven distribution of the electric current density in a cracked conductor. To investigate the perturbation of the magnetic field resulting from the disturbed electric current, computational modeling of the magnetostatics is attempted on an infinite conductive plate, which contains an elliptic hole and is subjected to uniform current flow at infinity. Both 2-D and 3-D analyses are considered in this study. The 2-D analysis requires certain crucial assumptions and the governing Maxwell's equations are solved analytically in elliptic coordinates. The 3-D numerical computation is based on superposition of the elementary solution, whose derivation utilizes the Biot-Savart law. To improve the efficiency of the 3-D calculation, an adaptive mesh refinement algorithm is implemented in the numerical discretization. Finally, through a comparative study, the validity of the introduced simplifications in the 2-D analysis is benchmarked with the 3-D computational results. The present study shows that the 2-D solution predicts the upper bound for the out-of-plane component of the magnetic field perturbed by the elliptical hole, whose semi-major axis does not exceed ten times the thickness of the plate. Index Terms--Adaptive mesh refinement, Biot-Savart law, computational electromagnetics, magnetostatics.

Magnetic shape memory alloys can be deformed in an external magnetic field by twin boundary motion. By coupling in acoustic energy the strain can be enhanced significantly, especially if the twinning stress is just above the magnetically achievable stress level. Two percent of strain can be achieved in a polycrystalline material, which showed only 0.3% strain without acoustic assistance. Index Terms--Acoustic energy, magnetic shape memory alloys, magnetomechanical effects.

A new method to simulate the steady-state magnetic fields of blocking up for induction motor is proposed. The field-circuit coupled model is combined with time-periodic finite element (FE) method to reduce the CPU time. The inductances and resistances of the stator end windings and the rotor end rings are considered in the loop circuit equations. In order to take account of the local magnetic saturation and hysteresis in the steel core, the Preisach model is incorporated in the time-periodic finite element method. An example for a two-pole three-phase induction motor is analyzed with this method. The calculation results of time-stepping method and time-periodic finite element method are compared. Index Terms--Field-circuit coupled, hysteresis, time-periodic finite element.

In this work an approach for modeling a transformer core taking into account magnetic hysteresis is presented. For this purpose, the inverse vector Jiles-Atherton hysteresis model is incorporated in a 2D finite element code. This model allows writing naturally the differential reluctivity tensor which can be directly used in the magnetic field equations. A three-phase transformer is modeled. The excitation characteristics of the transformer, as well as hysteresis loops at specific points, are presented. The proposed model was verified with obtained experimental data. Index Terms--Finite elements, hysteresis model, rotational losses, vector hysteresis.

Existence of the magnetic monopole is compatible with the fundamental laws of nature; however, this elusive particle has yet to be detected experimentally. We show theoretically that an electric charge near a topological surface state induces an image magnetic monopole charge due to the topological magneto-electric effect. The magnetic field generated by the image magnetic monopole may be experimentally measured, and the inverse square law of the field dependence can be determined quantitatively. We propose that this effect can be used to experimentally realize a gas of quantum particles carrying fractional statistics, consisting of the bound states of the electric charge and the image magnetic monopole charge.

We investigated the mechanism of nanometer-depth scratches triggering adjacent track interference (ATI) by applying DC erasure magnetic fields to scratch areas in recording media and measuring demagnetization by imaging magnetic bits using magnetic force microscopy. We found that the magnetic coercivity and anisotropy (Ku) of the scratch area is decreased to about half compared to that of a normal area. Section analysis of the recording layer under and along the scratch by transmission electron microscope revealed that the nanometer-depth scratch causes both c-axis tilt and slip of the (0001) plane of the close-packed hexagonal lattice structure of the grains. Micro-magnetic simulation indicated that the c-axis tilt only had a secondary effect on ATI but that the Ku decrease had a significant effect. On the basis of these transmission electron microscope analyses and the micro-magnetic simulation, we then concluded that the slip of crystal plane (0001) reduced Ku by introducing a stacking fault and essentially reduced coercivity, resulting in ATI. Index Terms--Adjacent track interference, demagnetization, head disk interface, perpendicular recording.

The time stepping finite element method based on the backward Euler's method has been widely used to simulate transient electromagnetic fields. Because of the numerical error of nonlinear iterations, the solutions of the derivative quantities may have very big noisy spikes. We present a modified formulation that reduces significantly the numerical error of the derivative quantities in transient finite element analysis of magnetic field computation. We also present an example that simulates the operation of an induction motor and demonstrates that the new method can successfully remove the spikes in the calculated waveforms of back electromotive force and eddy-current loss. Index Terms--Finite element method, magnetic field, nonlinear, numerical error, transient.

Field modeling becomes simpler if strong field nonuniformities are solved theoretically. The early obtained formulas for 2-D 'corner' and 'constriction' permeances pertain to right angle configurations. In this paper, using a conformal mapping, the field in the vicinity of arbitrary angle vertex is studied and the fringing permeance determined. The results are applied to permeance evaluation of lunate cross section grooves from the rotors of certain types of reluctance motors. Closed-form expressions are obtained, in good agreement with finite element analysis. Combined with the finite element method, obtained results offer the possibility to make simpler and more accurate analytical calculations of motors and other magnetic devices and to better evaluate magnetic forces that act on them. Index Terms--Conform mapping, corner permeance, fringing flux, 2-D electric and magnetic field.

This work investigates the behavior of an electroconductive plate under the action of a nonconservative load and subjected to a transversal magnetic field. The governing equation of the bending vibrations of an electroconductive plate, subjected to a transverse magnetic field and a follower type force at one edge, is presented. The assumption of an elongated plate leads to a simplified equation, which is conveniently written in dimensionless terms. For a cantilevered configuration, the characteristic equation relative to the magnetoelastic modes of vibration of the system is derived. Approximate solutions based on Galerkin method and an adjoint formulation are also presented and compared with the semi-analytical results. Root loci plots are computed as a function of the proper dimensionless parameters. The behavior of the system is very similar to the one exhibited by other structures subjected to nonconservative loads when damping is present. A relaxed definition of stability is used to regain continuity in the instability envelope. [DOI: 10.1115/1.3005573]

To design a magnetic system under a high-strength magnetic field, a nonlinear B-H relation must be considered. However, topology optimization using the nonlinear relation is rare. If the standard topology optimization formulation--varying the densities of design domain-discretizing magnetic finite elements--is used for nonlinear magnetic systems, the nonlinear material behavior will have to be interpolated. Because no consistent interpolating scheme is available, it is difficult to obtain converged distinct air-nonlinear material distributions without several trial-and-error attempts. Furthermore, the sensitivity analysis is very complicated because of the interpolated material nonlinearity. We have devised an alternative topology optimization formulation, called stacked-element connectivity parameterization (S-ECP), for the topology optimization of magnetic systems involving nonlinear B-H relations. The key idea is to discretize the design domain in terms of linear air elements, stack modified nonlinear magnetic material elements on the air elements, and control the element connectivity by varying the permeability of linearly behaving zero-length one-dimensional magnetic finks. The finks are introduced mainly to connect the air and nonlinear elements. Because a link is modeled by a linear material, the sensitivity analysis does not require complicated analysis involving the differentiation of nonlinear B-H relations, unlike the standard density method. Furthermore, it is much easier to find interpolation functions yielding converged distinct air-magnetic material states. We present numerical examples of C-shaped core design to demonstrate the effectiveness of the formulation. Index Terms--Nonlinear B-H curve, nonlinear magnetic systems, stacked element connectivity parameterization (S-ECP), topology optimization, zero-length magnetic link.

We have modeled underground isolated power cables by using magnetic eddy-current (EC) and thermal coupled formulations solved by the finite-element method (FEM). The magnetic field equation expressed in terms of magnetic vector potential (MVP) is strongly coupled with the total current density equation, which includes the source and the EC densities for taking into account skin and proximity effects. The model uses the computed EC density of losses with electric conductivity temperature dependence introduced as a heat source in the free transient thermal equation completed by the convection heat transfer. We studied single and multicircuit three-phase arrangements at various cable spaces in order to analyze the magnetic flux density and the time-space temperature evolution. Index Terms--Finite element, magnetic eddy-current thermal models, underground isolated power cables.

We describe the fabrication of a hybrid nanomagneto-electronic device, consisting of a GaAs/AlGaAs quantum wire that is bridged by a ferromagnetic gate, and study the influence of the nanomagnet fringing fields on the quantum-wire magneto-resistance. The nonplanar gate shows clear single-domain structure in magnetic-force microscopy, and a simple magnetization behavior in an external magnetic field. This behavior is reflected as a hysteretic variation of the quantum-wire magneto-resistance, whose magnitude is found to be consistent with theoretical predictions for ballistic electron transport through a spatially varying magnetic field. Index Terms--Ferromagnet, hysteresis, magneto-electronics, magneto-resistance.

This paper deals with the computation of eddy-current losses in laminated cores. In the first part we recall some approximate formulas existing in the literature and implemented in many electromagnetic computer packages. Then we assess their accuracy by making comparisons with the exact loss values obtained by numerical solution of the quasi-static Maxwell equations. In the second part we introduce a definition of an equivalent electric conductivity allowing us to replace the laminated core with a homogeneous isotropic or anisotropic medium. We compare the values of this equivalent conductivity with those obtained from some approximate formulas. Index Terms--Core losses, eddy currents, equivalent conductivity, laminated core.

Microfabricated devices formed from alternating layers of magnetic and nonmagnetic materials at combined thicknesses of a few hundred nanometers exhibit a phenomenon known as the giant magnetoresistance effect. Devices based on this effect are known as giant magnetoresistive (GMR) sensors. The resistance of a GMR is dependent on the strength of an external magnetic field, which has resulted in the widespread usage of such platforms in high-speed, high-data density storage drives. The same attributes (i.e., sensitivity, small size, and speed) are also important embodiments of many types of bioanalytical sensors, pointing to an intriguing opportunity via an integration of GMR technology, magnetic labeling strategies, and biorecognition elements (e.g., antibodies). This paper describes the utilization of GMRs for the detection of streptavidin-coated magnetic particles that are selectively captured by biotinylated gold addresses on a 2 x 0.3 cm sample stick. A GMR sensor network reads the addresses on a sample stick in a manner that begins to emulate that of a 'card-swipe' system. This study also takes advantage of on-sample magnetic addresses that function as references for internal calibration of the GMR response and as a facile means to account for small variations in the gap between the sample stick and sensor. The magnetic particle surface coverage at the limit of detection was determined to be ~2%, which corresponds to ~800 binding events over the 200 x 200 pm capture address. These findings, along with the potential use of streptavidin-coated magnetic particles as a universal label for antigen detection in, for example, heterogeneous assays, are discussed.

The effect of tower displacement of two parallel transmission lines on the magnetic field distribution is extensively studied. Two parallel lines with the same working voltage and having the same span, where artificial tower displacement is made, are modeled and the analysis of the magnetic field distribution is conducted. Natural tower displacements resulting from two parallel transmission lines with different span lengths and different voltages are also simulated to investigate the effect of displacement distance on the field distribution under and around these lines. Typical parallel lines of 275- and 132-kV, running in Kuwait, are modeled for both types of displacement and lateral magnetic field profiles are developed and analyzed. In addition to the effect of tower displacement value on the magnetic field distribution, the effects of one line disconnection, spacing between the parallel lines, phase conductors arrangements and the transmission line loading are examined. The magnetic vector potential concept, as extended to multiconductor transmission lines is used to model and calculate the magnetic field distribution under and around the parallel lines for the different mentioned operating conditions. The presented graphs are useful for setting the maximum allowable line current magnitude, for existing lines, corresponding to a certain safe level of the magnetic field at the edge of right of way. Index Terms--Environmental effect, magnetic field, magnetic vector potential, parallel transmission lines, right-of-way, tower displacement.

This paper examines high-frequency losses of thick rectangular and round wire windings due to the fringing fields of an air-gap. It derives formulas for the losses and validates them numerically using the 2-D finite-element method (FEM). It also provides a procedure for including the effect of self and proximity fields in the loss calculations, using the principle of superposition and a one-dimensional model of self and proximity fields. The paper validates the latter procedure numerically, using a 2-D finite element model. Index Terms--Eddy-current losses, inductors, losses, magnetic fields, magnetic losses, power transformers, voltage transformers, windings.

An outer magnetic field is extensively applied to drive the movement of a clinic micro-robot. However, how to produce a suitable magnetic field is a complicated problem. Commonly, the drive magnetic field is generated by a combination of power coils. This paper presents a novel method that circumferentially arrays identical permanent magnets to generate a rotational magnetic field in the center area of the array circle. First, we distribute permanent magnets uniformly in a circle, and adjust each of them at a corresponding initial angle. All of the magnets rotate in the same direction synchronously, generating a constant strength and reverse rotation magnetic field in the center area of the circle. The rotation speed of the generated magnetic field equals that of the permanent magnets. We used two models to analyze the magnetic field, and did some numerical analyses. We set up a test-bed and carried out some experiments to prove the feasibility of the novel method. The method seems to have wide applicability in designing magnets to drive micro-robots for diagnosis and treatment. Index Terms--Circumferential array, driving a micro-robot, permanent magnet, rotation magnetic field.

This paper describes a simple technique to design compact air core magnets for magnetic resonance imaging (MRI). The optimum geometry is obtained by a combination of analytical and numerical methods. The technique emphasizes achieving the required field homogeneity with a shorter magnet having a minimum amount of ampere turns. The code calculates the total inductance of the set of coils, total conductor length, force, and maximum field on each coil. The code also calculates the allowable geometrical tolerance to achieve the field uniformity. The code is flexible and can be used for various geometries. Here, we present three different cases to demonstrate the efficiency of the code. First, we present the design details of a 1.5 m long 1.5 T actively shielded magnet, where the stray field is reduced to less than 4 gauss outside the sphere of radius 3.65 m using a pair of shielded coils. A total of four pairs of coils provide a field uniform to within 5.2 parts per million (ppm) within a sphere of 50 cm diameter. Calculated values of all the higher order moments lie within a few ppm. Second, we describe optimized geometry of unshielded 1.5 T symmetric magnets having three pairs of coils. Third, we optimize the geometry of a 1.2 m long 1 T asymmetric magnet having five coils. Here, the good field region starts at 20 cm from one of the edges of the magnet, providing the attending physician better accessibility to the patient. But the ampere turns and computation time required are quite large compared to a symmetric magnet. Index Terms--Field for magnetic resonance, magnetic field analysis, optimization.

The effect of increasing Hartmann number and duct wall conductivity on the incompressible laminar flow of a liquid metal (Pb-17Li) in a rectangular duct under a transverse magnetic field has numerically been studied using usual equations of fluid dynamics coupled with the electromagnetic equations of the appropriate form. Simulations have been performed for ducts with and without electrical insulation, and the pressure drop is evaluated in each of the cases. The results of the simulation are compared with the analytical relations found in the literature. Finally, the applicability of different insulation coatings vis-a-vis their effect in reducing the magnetohydrodynamics pressure drop has been examined. Index Terms--Hartmann number, magnetohydrodynamics (MHD) flow, test blanket module (TBM).

This paper reviews recent experimental activity in the area of optimization, control, and application of laser-accelerated proton beams, carried out at the Rutherford Appleton Laboratory and the Laboratoire pour l'Utilisation des Lasers Intenses 100 TW facility in France. In particular, experiments have investigated the role of the scale length at the rear of the plasma in reducing target-normal-sheath-acceleration acceleration efficiency. Results match with recent theoretical predictions and provide information in view of the feasibility of proton fast-ignition applications. Experiments aiming to control the divergence of the proton beams have investigated the use of a laser-triggered microlens, which employs laser-driven transient electric fields in cylindrical geometry, enabling to focus the emitted protons and select monochromatic beamlets out of the broadspectrum beam. This approach could be advantageous in view of a variety of applications. The use of laser-driven protons as a particle probe for transient field detection has been developed and applied to a number of experimental conditions. Recent work in this area has focused on the detection of large-scale self-generated magnetic fields in laser-produced plasmas and the investigation of fields associated to the propagation of relativistic electron both on the surface and in the bulk of targets irradiated by high-power laser pulses. Index Terms--Ion sources, laser fusion, magnetic-field measurement, particle-beam control.

The influence of the operating parameters such as magnetic field, cathode voltage, and gas pressure on the target erosion of the rectangular planar dc magnetron is discussed in this paper. Through particle simulation for a prototype rectangular magnetron, with the same shape, stronger magnetic field could make the target erosion much sharper; with the same ratio of the field intensity in the end region to that in the straight region, stronger magnetic field could make the anomalous erosion in the curve-out region severer. Furthermore, higher cathode voltage could not only make the target erosion wider but also make the anomalous erosion weaker. Gas pressure has less influence on the target erosion in the straight region, but higher pressure could make the anomalous erosion severer. Finally, how to improve the magnetic field is discussed. Through shimming ferromagnetic and permanent magnet bars in the race track, not only the target erosion becomes wider but also the anomalous erosion could be reduced. Index Terms--Erosion, magnetron sputtering, particle simulation, plasma.

We presenta three-dimensional (3-D) torque model based on spherical harmonic functions of a Halbach array permanent-magnet (PM) spherical motor. Using the torque model, we show how to realize three-degree-of-freedom motion. We compare the Halbach array PM spherical motor and the conventional parallel magnet array spherical motor in terms of spherical harmonic component and amplitude of the torque. We discuss our study of variations of air-gap magnetic field with parallel magnetization directions along different spatial positions in each magnet segment. We also discuss the parasitic effect of the proposed spherical Halbach array magnet. We have verified our results by finite-element method. Index Terms--FEM, Halbach array PM sphericai motor, parasitic effect, pole-arc coefficient.

We present, for the fist time, an analytic method of making plane-magnetic field circuit calculations. The analytic expressions for the magnetic force, field strength, flux, potential difference, etc., are derived semi-empirically. They make possible a transition from the plane-parallel configuration to the plane-meridian one. The method takes into account the magnetic resistance of a steel. ,We compare all the results of calculations with appropriate experimental values and evaluate the corresponding errors. We also present a method for complete calculation of a separator's magnetic system. We describe an approximate method of finite size effects in multipole magnetic systems with axial pole disposition. Using the method of conformal mapping, we derive an analytic expression for the magnetic field in the inner domain of separators with radial pole disposition. We also define a precise limit when a multipole system with radial pole disposition coincides with a multipole system with axial pole configuration and show that, in this limit, analytic expressions obtained independently for both cases coincide. Taking into account the analytic expressions published earlier, we thus complete the description of the magnetic fields belonging to this class of magnetic systems. Index Terms--Conformal mapping, field calculation, magnetic circuit, separators.

The long-wave perturbation method is employed to investigate the nonlinear hydromagnetic stability of a thin electrically conductive power-law liquid film flowing down a vertical cylinder. In contrast to most previous studies presented in literature, the solution scheme employed in this study is based on a numerical approximation approach rather than an analytical method. The modeling results reveal that the stability of the film flow system is weakened as the radius of the cylinder is reduced. However, the flow stability can be enhanced by increasing the intensity of the magnetic field and the flow index. [DOI: 10.1115/1.2948375] Keywords: thin film, hydromagnetic stability analysis, power-law fluid

This paper presents a numerical analysis of the free surface liquid metal flow driven by an alternating current magnetic field in a spinning cylindrical container. The axisymmetric flow structure is analyzed for various values of the magnetohydrodynamic interaction parameter and Ekman numbers. The governing hydrodynamic equations are solved by a spectral collocation method, and the alternating magnetic field distribution is found by a boundary-integral method. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface. It is found that the container rotation may reduce the meridional flow significantly. [DOI: 10.1115/1.2948374]

We present measurements and simulations of spin-transfer torque (STT) induced magnetization dynamics in nanopillars containing a thin, circular, single-crystalline Fe nanomagnet with four-fold in-plane magnetocrystalline anisotropy as a free layer. The magnetoerystalline anisotropy inherent to bcc-Fe allows for a consecutive switching of the magnetization by 90[degrees] between parallel and antiparallel alignment to the fixed layer magnetization. Additionally, the anisotropy gives rise to steady-state precession of the magnetization at low or even zero applied magnetic field as well as at large fields exceeding the coercive field. While the low-field mode is governed by the interplay between the STT and the anisotropy, the high-field dynamics result from the STT acting against the externally applied magnetic field. Index Terms--Magnetization dynamics, magnetoerystalline anisotropy, nanomagnet, spin-transfer torque.

We have extended an earlier two-dimensional (2-D) analysis to provide a relatively simple approach to calculating the transmission of magnetic fields in three-dimensional (3-D) multilayered structures. The approach accommodates complex structures composed of an arbitrary number of layers, each of which may have an arbitrary magnetization direction and anisotropic permeability. The procedure relies on an initial transformation into the 2-D spatial frequency domain and then the use of transmission matrices to relate the fields in the different layers. The approach is general in that it provides a method for finding the field configuration for any set of 3-D magnetic sources embedded in a layered magnetic structure with a linear B-H relationship. In this paper, we concentrate on the analytical formulation and we illustrate the method by using it to determine both the external and internal fields of some relatively simple finite 3-D geometric shapes. We also derive new 3-D expressions for the flux density at the surface of a multilayered magnetic recording medium. In a companion paper, the procedure is applied to examine readback responses for a variety of 3-D magnetic recording configurations. Index Terms--Anisotropic permeability, frequency response, layered structures, magnetic fields, magnetic recording, 3-D transmission.

We have applied a technique for modeling the transmission of three-dimensional (3-D) magnetic fields through an arbitrary number of layers of a layered structure to the specific case of a recording medium in order to study and explain the readback response for a variety of perpendicular recording configurations. We examine in particular the low-frequency response associated with flux-flow in the soft underlayer and the behavior of the main response for finite read and write widths. Our work leads to a useful analytic approximation for the 3-D on-track readback response. Index Terms--Anisotropic permeability, DC null, frequency response, layered media, magnetic recording, 3-D response.