基于幅值和梯度约束的磁化向量反演方法

基于磁异常数据的反演可以获得地下目标体的形状、位置、磁化等信息。传统的反演方法假设反演的物体中不存在剩磁、自退磁等情况,磁化均是由地磁场感应得到,当其被应用于物体中包含剩磁的反演时,结果将产生偏差。而磁化向量反演不需要已知磁化方向,其将未知的磁化向量分解成3个已知方向的标量分量进行反演,然后将反演的标量分量结果再合成矢量,其可以应用于物体磁化复杂的情况。

核磁共振断层成像在医学上的应用

核磁共振成像,是继X射线CT、单光子发射CT(SPECT)和正电子发射CT(PET)等计算机断层成像方法之后,在80年代崛起的最先进的成像技术。它初露崭头就已具备了许多优势,正日趋广泛地用于临床诊断和生理、病理研究,其前景相当喜人。这个全新的成像原理是首先由美国纽约洲立大学的P.C.

Three-dimensional transformation of magnetization direction and magnetic field component at low latitudes based on vertical relationship

The transformation of the magnetization direction and the magnetic fi eld component is one of the important methods in magnetic data processing and transformation,which can be conducted in both wavenumber and spatial domains.The transformation method in the wavenumber domain has simpler processing expression and higher processing effi ciency than in the spatial domain;however,they are unstable at low latitude.In this paper,the conclusion that the sum is 0 of two vertical magnetic fi eld components(magnetization inclinations are also perpendicular)in 2D is used for the 3D transformation of the magnetization direction and the magnetic field component.In addition,the transformation method at low latitudes based on vertical relationship(VMT)is proposed,which is an iterative algorithm that converts the transformation of the magnetization direction and the magnetic field component at the low latitude into the high latitude.This method restrains the instability of transformation of constant and variable magnetization direction and magnetic fi eld components in low latitudes.The accuracy,stability,and practicality are verifi ed from synthetic models and real data.

Vacuum Susceptibility Calculation

The vector susceptibility is investigated numerically in the Dyson-Schwinger approach. The results agree with those obtained analytically previously by using a simple gluon propagator.

New analytical solution for the analysis and design of permanent magnet thrust bearings

On the basis of the current sheet model, a new analytical solution for permanent magnet （PM） bearings is developed. Compared with analytical methods based on the coupling energy model and the magnetic dipole model, the proposed one is more physically intuitive and convenient for engineering designers. According to the analytical model, the thrust characteristics of a novel PM thrust bearing is studied and verified by finite element analysis （FEA）. In the proposed thrust bearing configuration, the rotor is composed of stacked PM tings with alternative axial magnetization directions, and the stator with alternative radial magnetization directions while copper rings are used to separate adjacent PM rings. A prototype PM thrust bearing with the proposed configuration is designed and fabricated. The performances of the PM thrust beating are experimentally validated. It is shown that the calculation accuracy of the presented analytical solution is satisfying.

Thickness-driven spin reorientation transition in ultrathin films

We review recent studies by different experimental means of ultrathin films,exhibiting thickness-driven spin reorientation transitions(SRTs).The stage is set by determining,via phenomenological thermodynamic description,of the relevant phase diagrams for the possible types of SRT with and without applied magnetic field.Suitable representation may be chosen such that best use is made of the linear character(under thickness variation) of the system's path in anisotropy space.The latter involves higher-order bulk and surface anisotropies in a substantial way.We examine sensitive experimental techniques for the detection and quantification of SRTs,such as hysteresis measurements with magneto-optical Kerr effect(MOKE),micromagnetic studies utilizing scanning electron microscopy with polarization analysis(SEMPA),photoemission electron microscopy(PEEM) and spin-polarized low-energy electron microscopy(SPLEEM) as well as ac magnetic susceptibility measurements via MOKE.Key issues are conclusively discussed including the identification of reliable experimental fingerprints about whether a given SRT proceeds via a phase of coexistence or via a cone(canted) phase.We demonstrate how the application of the general theoretical ideas to carefully designed measurements leads to the determination of the most important material parameters in any ultrathin-film SRT,namely,the surface(interface) magnetic anisotropy constants.The review concludes by our personal outline for future promising work on SRTs.

Large and anisotropic linear magnetoresistance in bulk stoichiometric Cd_3As_2 crystals

Cd3As2 was recently identified as a novel three-dimensional （3D） topological semimetal hosting the long-pursuing 3D Dirac Fermion. Crystals of Cd3As2 grown preferentially along the [100] and [112] directions were obtained through the modified chemical vapor transfer growth method, thus allowing the examination of transport anisotropy. The resistivity and magnetore- sistance （MR） are basically linear with respect to magnetic field （H） in the measured temperature range of 2-300 K irrespective of the directions. The linear resistivity and MR are significantly anisotropic not only along [100] and [112] directions but also with respect to tilt angle between the growth directions and H, thus providing transport signatures of the 3D Dirac Fermion as well as the possible linear and anisotropic change of Weyl Fermi surface in H. Very large MR along the [100] direction is observed, even approaching 3100% at 2 K and 14 kOe （10e = 79.5775 A m^-l）. The results would be helpful in renewing interest in studying emergent phenomena arising from bulk 3D Dirac Fermion as well as in paving the way for Cd3As2 to be used in magnetoelectronic sensors.