无限长载流薄板磁场的矢势与磁感应强度计算及可视化

推导了无限长均匀薄板电流磁场的矢势和磁感应强度的解析式,将公式无量纲化,计算矢势和磁感应强度,画出中垂面上和板平面上矢势和磁感应强度曲线,并与直线电流磁场的矢势和磁感应强度进行比较,画出矢势和磁感应强度两个分量以及合磁场和方向曲面,画出了二维磁感应线,显示了磁感应强度分布规律.     

斜航向上舰船感应磁性磁场分离方法讨论

斜航向上舰船感应磁性磁场分离是舰船磁场分析中的一个难点.针对舰船龙骨下方典型测量点上的磁场特征特殊形态展开分析,可方便明晰地解决这一问题.根据相差180°的两个航向上的磁场测量数据,可分离出舰船纵向和横向感应磁性磁场的总和.在舰船龙骨下典型测量点上,舰船纵向和横向感应磁性磁场总和的纵向和垂向分量来源于纵向感应磁性,横向分量来源于横向感应磁性.最终,实现了斜航向上舰船纵向和横向感应磁性磁场的分离.     

导心轨道模拟中对磁场计算方法的改进

在导心轨道的计算中,用离散傅立叶变换对二维磁场信息沿角向进行变换,得到各阶谐波分量随极向磁通变化的拟合公式,用此生成磁场。数值模拟结果表明,该方法在精度上和传统的样条插值一致,可以在角向和极向上求任意阶导数,为磁岛和撕裂膜的计算提供了便利.     

应用坐标法求一段圆弧电流在轴线上的磁场分布

应用坐标法求出一段圆弧电流在通过圆心并与圆面垂直的轴线上的磁场分布公式 .     

"双悬线平衡法"测量地磁水平分量

采用“双悬线平衡法”,并利用外加可调磁场与地磁水平分量补偿的方法对地磁水平分量进行了测量．当磁针所受磁场力和双悬线扭力平衡时,以悬线扭力为零作为外加磁场与地磁水平分量“补偿”的判定依据,由于此时的外加磁场与地磁水平分量大小相等方向相反,从而测得地磁水平分量。     

地磁水平分量的测量

用动力学的方法测量了地磁场的水平分量.通过改变电路中电流的大小和方向,测量磁针在地磁场水平分量和外加亥姆霍兹线圈产生的合磁场的共同作用下的简谐振动周期,用作图法得到合磁场为零的电流值,从而得到地磁场水平分量.     

推导热力学关系式的几种方法

“热力学函数及其应用”一章,在热力学教学中占有重要地位。按我们的体会,学好这章的关键在于,掌握一套最基本的热力学方程──简单可压缩系统的四个热力学基本等式,八个热力学偏导数及它们之间的四对关系(麦氏关系),和几个常用的偏导数本方程和常用公式,推导出一些热力学关系式,通过这些热力学关系式,把我们感兴趣的某些热力学偏导数(中等),用能由实验测定的量如Cp和能由态式计算出的量表示出来,或者说,用三个基本偏导 (因它们直接与三个较易测定的系数a、k和Cp相联系,故叫基本编导数)表示出来。但教学实践表明,初学者在推导这样的热力学…     

磁多极场场参数的理论计算与分析

根据磁多极场的对称性，首先导出了磁多极场磁场分量的泰勒级数展开式，定义了磁多极场的场参数，然后根据毕奥-萨伐尔定律，导出了马鞍型磁多极场线圈的场参数理论计算公式.对各个场参数数量级的大小进行了分析，找出了场参数的递推规律，给出了场参数高阶导数的计算方法，从而能够准确计算整个空间的磁场值.还从简单单根导线计算结果过渡到多根导线或具有某种连续分布的情况. 这对于磁二极场、磁四极场、磁六极场等的应用提供了可靠的理论依据. 关键词： 磁多极场 场参数 马鞍型线圈     

电偶极子与单摆

电偶极子是电磁学基本模型之一,其电场强度分布颇有特点.通常教材要么给出电势然后做梯度计算,要么通过矢量叠加直接给出场强,推导比较数学化,学生难以对偶极子场强特点和物理图像获得直观理解.本文把熟知的力学单摆和偶极子联系起来,通过力电类比给出偶极子电场的两种形式,特别是不依赖坐标的场强形式,清楚阐明了各分量特点,还给出类比方法的应用实例.这种方法有助于初学者从不同角度体会知识点联系,深入理解偶极子物理图像,强化类比思维.     

电各向异性色散介质电磁散射的三维递推卷积-时域有限差分方法分析

根据递推卷积原理，将磁化等离子体的频域介电系数过渡到时域，通过引入时域复数极化率张量和时域复数电位移矢量，得到了磁化等离子体的三维时域有限差分方法迭代式. 为了验证该方法，用它计算了非磁等离子体球的后向雷达散射截面，与移位算子法结果符合很好. 应用该方法计算和分析了磁化等离子体球的电磁波散射，发现其后向散射时域波形明显出现了交叉极化分量. 关键词： 递推卷积 磁化等离子体 电磁散射 时域有限差分方法     

基于积分方程法和奇异值分解的磁性目标磁场延拓技术研究

对磁性目标磁场延拓技术进行了研究,提出了一种基于积分方程法和奇异值分解的新方法.应用该方法只需要采用积分方程法对磁性目标的结构进行较为粗略的单元划分,利用目标下方大平面上的磁场测量值,得到相应的线性方程组.采用基于奇异值分解的截断奇异值方法和修正奇异值方法对该线性方程组进行正则化求解,可实现磁性目标磁场的三维磁场重建、向上或向下延拓.该方法较以前的方法,提高了磁性目标磁场延拓的精度和可靠性,并且解决了磁性目标磁场在一定范围内向上延拓的技术难题. 关键词： 磁性目标磁场 延拓 积分方程法 奇异值分解     

火星空间环境磁场探测研究——"萤火1号"磁强计的研制与应用

文章介绍了"萤火1号"卫星对火星空问环境磁场进行探测的目的、意义及采用的方式方法.研究火星的空间环境离不开火星磁场,它对于火星弓激波、磁鞘、电离层、大气等绝大多数空间环境效应都有着深刻的影响,因此"萤火1号"卫星安装了一台重要的科学探测载荷--高精度磁强计,以满足科学研究和应用目标的需求.磁强计从原理选择到具体没计,都考虑到了火星轨道严酷的工作环境和科学目标所需的测量要求.通过"萤火1号"装星前的地面标定测试实验,验证了高精度磁强计可以在-140-75℃温度范围内测量±256nT以内的磁场,分辨率达到了0.01nT,带宽内总噪声小于0.03nT,能够胜任"萤火1号"对火星空间环境探测的科学任务."萤火1号"火星探测器将于2011年与俄罗斯的"福布斯-土壤"一同飞往火星,这是人类送往火星最精密的磁场探测器之一,将对火星空间环境磁场结构和动力学过程进行精密而详细的探测.     

Computation of demagnetizing fields and particle distribution in magnetic fluid with inhomogeneous density

A new algorithm for calculating magnetic fields in a concentrated magnetic fluid with inhomogeneous density is proposed. Inhomogeneity of the fluid is caused by magnetophoresis. In this case, the diffusion and magnetostatic parts of the problem are tightly linked together and are solved jointly. The dynamic diffusion equation is solved by the finite volume method and, to calculate the magnetic field inside the fluid, an iterative process is performed in parallel. The solution to the problem is sought in Cartesian coordinates, and the computational domain is decomposed into rectangular elements. This technique eliminates the need to solve the related boundary-value problem for magnetic fields, accelerates computations and eliminates the error caused by the finite sizes of the outer region. Formulas describing the contribution of the rectangular element to the field intensity in the case of a plane problem are given. Magnetic and concentration fields inside the magnetic fluid filling a rectangular cavity generated under the action of the uniform external filed are calculated.     

横向静磁场对电磁悬浮液滴稳定性的影响

在利用电磁悬浮技术实现液滴悬浮的过程中,液滴内部往往存在剧烈对流、外部伴随快速旋转和质心的水平位移等不稳定因素;因此,实现液滴的稳定悬浮是完善电磁悬浮技术的关键.本文采用实验观测的方法,通过U形静磁场组件对液滴所在空间施加横向静磁场,利用高速相机记录了不同磁场强度下纯铜熔融液滴的振荡变形过程;分析了横向静磁场对悬浮铜液滴振荡频率、振幅以及旋转的影响.实验发现:对于熔融前的固态铜颗粒,若静磁场强度超过0.3 T,铜颗粒几乎以静止状态悬浮.熔融后,当施加0.15 T的静磁场,与未加静磁场时相比,液滴俯视图轮廓线拟合出的椭圆分别与x轴和y轴的交点坐标之差R-、椭圆面积A和椭圆长轴长度Dmax的振幅分别减小了25%,76%和60%;随着磁场强度的继续增加,振幅和频率继续减小,但在静磁场强度为0.3 T时,相比静磁场强度为0.2 T,频率增加了1 Hz.横向静磁场还抑制了悬浮铜液滴的旋转,当磁场强度增加到0.53 T时,悬浮液滴只在10?的角度范围内摆动.这些结果表明,施加横向静磁场能够有效提高悬浮液滴的稳定性.     

磁流体数值模拟中一种消去磁场散度的方法

充分利用时空守恒元和解元（CESE）方法的特点（在CESE方法中，守恒变量及它们的空间导数都作为独立的更新量并且求解点在每个控制体边界上）给出一种用最小二乘法求解来消去磁场散度的方法.且我们进一步探究了磁场散度限制方程取不同的权重时对结果的影响.通过比较，我们发现当方程权重取为1时，可以非常有效地消去磁场散度误差.     

Seismoelectric waves in a borehole excited by an external explosive source

The conversion of energy between seismic and electromagnetic wave fields has been described by Pride’s coupled equations in porous media. In this paper, the seismoelectric field excited by the explosive point source located at the outside of the borehole is studied. The scattering fields inside and outside a borehole are analyzed and deduced under the boundary conditions at the interface between fluid and porous media. The influences of the distance of the point source, multipole components of the eccentric explosive source, and the receiving position along the axis of vertical borehole, on the converted waves inside the borehole are all investigated. When the distance from the acoustic source to the axis of a borehole is far enough, the longitudinal and coseismic longitudinal wave packets dominate the acoustic and electric field, respectively. The three components of both electric field and magnetic field can be detected, and the radial electric field is mainly excited and converted by the dipole component. Owing to the existence of borehole, the electric fields and magnetic fields in the borehole are azimuthal. The distance from the point where the maximum amplitude of the axial components of electric field is recorded, to the origin of coordinate indicates the horizontal distance from the explosive source to the axis of vertical borehole.     

Roles of Atomic Injection Rate and External Magnetic Field on Optical Properties of Elliptical Polarized Probe Light

In this paper we investigate the optical properties of an open four-level tripod atomic system driven by an elliptically polarized probe field in the presence of the external magnetic field and compare its properties with the corresponding closed system.Our result reveals that absorption,dispersion and group velocity of probe field can be manipulated by adjusting the phase difference between the two circularly polarized components of a single coherent field,magnetic field and cavity parameters i.e.the atomic exit rate from cavity and atomic injection rates.We show that the system can exhibit multiple electromagnetically induced transparency windows in the presence of the external magnetic field.The numerical result shows that the probe field in the open system can be amplified by appropriate choice of cavity parameters,while in the closed system with introduce appropriate phase difference between fields the probe field can be enhanced.Also it is shown that the group velocity of light pulse can be controlled by external magnetic field,relative phase of applied fields and cavity parameters.By changing the parameters the group velocity of light pulse changes from subluminal to superluminal light propagation and vice versa.     

General equation describing viscosity of metallic melts under horizontal magnetic field

Viscosities of pure Ga, Ga_(80)Ni_(20), and Ga_(80)Cr_(20) metallic melts under a horizontal magnetic field were investigated by a torsional oscillation viscometer. A mathematical physical model was established to quantitatively describe the viscosity of single and binary metallic melts under a horizontal magnetic field. The relationship between the viscosity and the electrical resistivity under the horizontal magnetic field was studied, which can be described as η_B = η +(2H/πΩ)B~2(η_B is the viscosity under the horizontal magnetic field, η is the viscosity without the magnetic field, H is the height of the sample,? is the electrical resistivity, and B is the intensity of magnetic field). The viscosity under the horizontal magnetic field is proportional to the square of the intensity of the magnetic field, which is in very good agreement with the experimental results. In addition, the proportionality coefficient of ηB and quadratic B, which is related to the electrical resistivity,conforms to the law established that increasing the temperature of the completely mixed melts is accompanied by an increase of the electrical resistivity. We can predict the viscosity of metallic melts under magnetic field by measuring the electrical resistivity based on our equation, and vice versa. This discovery is important for understanding condensed-matter physics under external magnetic field.     

On the relationship between the lightning electromagnetic field and the channel-base current based on the TL model

A set of approximation expressions relating the lightning channel-base current and the lightning electric and magnetic fields on earth surface are proposed respectively in the near-zone and far-zone, by employing the transmission line (TL) model. The derived expressions show that, the electric and magnetic fields waveforms can be expressed approximately by the channel-base current waveform with different factors at a certain distances, whether in the near-zone or far-zone. The factors can be expressed in terms of the return stroke wavefront speed v, the speed of light c, and the horizontal distance r between the return-stroke channel and the observation point.