Nonlinear 3D magnetostatic field calculation by the integralequation method with surface and volume magnetic charges

The authors present a mathematical model for the 3-D nonlinear magnetostatic field based on integral equations with fictitious surface and volume magnetic charges. The solution is performed by the extended boundary element method including surface elements and volume elements. Examples of calculation for both linear and nonlinear magnetic systems are presented. The method has been shown to be accurate and efficient     

二维非均质材料应力场的数值化计算方法

等效夹杂方法是求解含杂质材料弹性应力场的一种有效方法,但是其解析求解只适用于椭球/椭圆类杂质问题。本文提出一种基于等效夹杂方法的数值化计算方法,介绍了其基本理论,并引入共轭梯度法求解该方法的一致性条件线性方程组。该方法通过计算区域的数值离散,能够实现对二维任意形状杂质弹性场的求解。将该方法得到的结果与解析解进行比较,验证了该方法的有效性。讨论了数值化等效夹杂方法在效率以及收敛性上的表现。通过对比证明,利用共轭梯度法实现该方法,能在保持精度的同时,相较于高斯消元法具有较大的效率优势。最后通过半椭圆杂质和氧化锆/氧化铝共挤复合材料算例验证了该方法处理任意形状杂质的能力。     

Designing particular magnetic field profiles by computer

A design of specific magnetic-field profiles was performed by a power series of the general field formulas up to the 11th term. The application of this method, instead of the usual integration, was required to increase the speed of the calculation by a factor of a few hundreds and to decrease the memory capacity needed permanently for the stored data. For given magnetic parameters, the program has a self-consistent procedure to gain the prescribed homogeneity taking into account the layer distribution. The operation can be extended to the planning of strongly inhomogeneous magnetic systems as well. The elaborated method is also applicable to conventional, superconducting, multifilamentary, and high-T_c magnets     

Nonlinear magnetic field calculation using dipole approximation

A program for calculating static magnetic fields using an integral method for the iron contribution to the field is presented. To calculate the magnetic coefficients one essentially uses a simple dipole approximation. The developed formalism is applied to compute the magnetic field of toroidally shaped iron geometries. Using this formalism a program tractable on microcomputers was written with a discretization of the iron in up to 1600 elements. The results agree well with those obtained with the program TOSCA     

Finite element steady-state solutions of the traveling magnetic field problem

The paper is concerned with stability and accuracy of n-order finite element (FE) steady-state solutions of traveling magnetic field problem. It is found that the odd-order FE solutions (nis the odd number) are stable0 < sigma|u|h|nu < f(n) simeq 2.0 + 1.4(n - 1), and that the even-order FE solutions (nis the even number) are unconditionally stable. The consistent domain is also proposed, in which then-order FE solutions are stable and of 2n-order accuracy. Moreover, three-dimensional cases are dealt with, and the comparison with upwind methods is given. The merit and limits of the n-order FE method are finally cleared.     

Regular boundary element steady-state solutions of the traveling magnetic field problems

Regular boundary element method (R-BEM) is applied to analyze steady-state traveling magnetic field problems for which convective diffusion equation is considered as governing equation. We deal with a three-dimensional rectangular prism as a simple example in order to study stability and accuracy of regular boundary element (R-BE) solutions. It is found that R-BE solutions are unconditionally stable for a rectangular prism whose sides parallel to a traveling velocity are longer than those perpendicular to the velocity. Furthermore, we can show that R-BE solutions as well as conventional BE solutions have second-order accuracy. Finally, numerical precision is studied through the condition number of the system matrices used in the analysis for a few parameters. It is shown that the R-BEM is available for the analysis of three-dimensional steady-state convective diffusion equations.     

3-D magnetostatic field calculation for a magnetic circuit with no(a narrow) air gap

Noting that 3-D magnetostatic field calculations for gapless magnetic circuits are strongly affected by the discretization, the author analyzes this effect for an iron torus using a boundary integral equation based on the surface magnetization current method. The main cause of computational error is the imperfect cancellation of the permeability-free terms in the boundary integral equation due to the improper size of the analytical integration region containing a singular point. A method of reducing the computational error is presented and verified to be valid     

Influence of non-axial magnetic field in a 3D3V Particle-In-Cell plasma model

In this article we report on results obtained using a newly developed self-consistent fully 3D Particle-In-Cell code for modelling of plasma-solid interaction.The model presented here involves a hollow cylindrical chamber opened to the plasma, with a thin cylindrical guard at the inlet and a strong external magnetic field limiting access of charged particles to the cylindrical wall. This model layout might provide more insight into processes taking place during magnetron deposition of thin films onto porous media. It is also a basis for probe diagnostics in fusion plasma research.The magnetic field is either parallel or slightly inclined with respect to the cylindrical axis. The results presented are axial and azimuthal ion current densities and cumulative distribution functions of ions impinging on the cylindrical surface for several angles of magnetic field inclination. They confirm the importance of proper alignment with magnetic field in certain geometries.Efficiency and possibilities of further extensions to the 3D model are also briefly discussed.     

A method for rendering 3D finite element vector field solutionsnondivergent

The use of the method of constraints for enforcing the zero divergence condition in vectorial finite-element schemes is discussed. An earlier implementation of the method was shown to produce the correct solution for a 3-D resonant cavity problem modeled by a single finite element. Partial success in extending the method to multielement cases is reported. The reduction in matrix size alone would justify the development of the technique for general multielement grids, but it will require the implementation of a global approach to the method of constraints     

Parameterized code SHARM-3D for radiative transfer over inhomogeneous surfaces

The code SHARM-3D, developed for fast and accurate simulations of the monochromatic radiance at the top of the atmosphere over spatially variable surfaces with Lambertian or anisotropic reflectance, is described. The atmosphere is assumed to be laterally uniform across the image and to consist of two layers with aerosols contained in the bottom layer. The SHARM-3D code performs simultaneous calculations for all specified incidence-view geometries and multiple wavelengths in one run. The numerical efficiency of the current version of code is close to its potential limit and is achieved by means of two innovations. The first is the development of a comprehensive precomputed lookup table of the three-dimensional atmospheric optical transfer function for various atmospheric conditions. The second is the use of a linear kernel model of the land surface bidirectional reflectance factor (BRF) in our algorithm that has led to a fully parameterized solution in terms of the surface BRF parameters. The code is also able to model inland lakes and rivers. The water pixels are described with the Nakajima-Tanaka BRF model of wind-roughened water surface with a Lambertian offset, which is designed to model approximately the reflectance of suspended matter and of a shallow lake or river bottom.     

Bayesian analysis of computer code outputs: A tutorial

The Bayesian approach to quantifying, analysing and reducing uncertainty in the application of complex process models is attracting increasing attention amongst users of such models. The range and power of the Bayesian methods is growing and there is already a sizeable literature on these methods. However, most of it is in specialist statistical journals. The purpose of this tutorial is to introduce the more general reader to the Bayesian approach.     

Forward electric field calculation using BEM for time-varying magnetic field gradients and motion in strong static fields

A boundary element method for evaluating the electric fields induced in conducting bodies exposed to magnetic fields varying at low frequency has been developed and applied to sources of magnetic field variation that are of relevance in magnetic resonance imaging. An integral formulation based on constant boundary elements which can be used to study the effects of both temporally varying magnetic field gradients and rigid body movement in a static magnetic field is presented. The validity of this approach has been demonstrated for simple geometries with known analytical solutions and it has also been applied to the evaluation of the induced fields in more realistic models of the human head.     

Two-photon lithography for 3D magnetic nanostructure fabrication

Nano Research - Ferromagnetic materials have been utilized as recording media in data storage devices for many decades. The confinement of a material to a two-dimensional plane is a significant...     

The distribution of citations from nation to nation on a field by field basis — A computer calculation of the parameters

Following the methodology established byPrice, this paper analyzes the empirical evidence of citation matrices. Using the data cleaned and tabulated by Computer Horizons, Inc. from the Science Citation Index data banks, it is shown that the non-diagonal elements of the square citation matrices can be accounted for very satisfactorily by assigning each nation a characteristic output and input coefficient in each field measured; the ratio of these coefficients provides a measure of quality. Deviations from this simple model give measures of particular linkage strengths between nations showing some evidence of preferences and avoidances that exist for reason of language, social structure, etc. It is also shown that the diagonal data can be accounted for by the measurable phenomenon that each nation seems to publish partly for the international knowledge system and party for its own domestic purposes. Thus, three parameters and a cluster map can parsimoniously describe the citation data within the limits of random error.     

An integrated microsystem for 3-D magnetic field measurements

In this paper, we present a portable, battery-operated, three-dimensional magnetic microsystem (magneto-dosimeter), intended for monitoring the workers' exposure to magnetic fields in particular working environments, such as hospitals or physics laboratories. The proposed microsystem is based on a multichip module containing three equal channels for the three components of the magnetic field measurement, a microprocessor, and a memory. Each single-chip channel detects the magnetic field, converts it into the digital domain, and delivers the result to the microprocessor by means of an on-chip serial interface. The single-chip channel, fabricated in a 0.8-μm CMOS technology, is sensitive to magnetic fields ranging from -200 to +200 mT, achieving 12 bits of resolution, 11 bits of linearity, and an overall accuracy better than 1% in the temperature range from -20 to +80°C     

A method of calculation of a solenoid producing a given magnetic field on its axis

A method is described to calculate a sectioned solenoid generating a prescribed magnetic field on its axis. The method allows one to find a current distribution through the sections that the field obtained along the axis of the solenoid B(z) minimally deviates from a given function f(z).     

高梯度强磁力永磁磁选机磁系的研究与磁场计算

用稀土永磁材料NdFeB,研究并设计了高梯度强磁力永磁磁选机的磁系,用我们推导的磁路计算方法及公式对磁系的磁场强度、梯度及磁力进行了计算与分析,研制并优选了最佳的高梯度强磁力永磁磁选机的磁系.     

Temperature and magnetic field dependence of NbN film resistivity: 3D weak localization effects

Niobium nitride superconducting films have been deposited by reactive rf magnetron sputtering. Polyepitaxial growth on MgO-coated substrates greatly improves the superconducting properties. The overall film resistivity is found to be widely dependent on the total pressure of the gas mixture. Samples with a negative temperature coefficient of resistance exhibit 3D weak localization effects as characterized by magnetoresistance measurements. The inelastic scattering time is found to vary as T^–p with p2, in the temperature range T_c-3T_c.Laboratoire associé au C.N.R.S.