Effect of crystal potential on electric field gradient calculations due to impurities in cubic metals

The electric field gradients caused by interstitial and substitutional point defects in f.c.c. metals have been studied. The perturbation on the host electron distribution has been calculated self-consistently using density functional formalism. The effect of strain caused by size difference between host and impurity atoms is treated in the point-ion model. The influence of the host potential on impurity perturbation is incorporated within the spherical solid approximation. The theory is applied to positive muon and mono-vacancy in Al and Cu hosts. The theoretical results are in good agreement with experiment and illustrate the importance of both strain and conduction electron contribution to the electric field gradient.     

强电场作用下反铁电锆钛酸铅的介电行为研究

采用电滞回线方法和偏置直流电场中叠加小交变电场方法研究了锆钛酸铅反铁电陶瓷材料在强电场作用下的介电行为.测量结果显示，锆钛酸铅反铁电材料的介电常数随外加电场强度呈非线性变化，在反铁电 铁电转变的电场区间形成介电峰.表征极化强度随电场强度变化率的微分介电常数εd峰值出现在反铁电 铁电转换电场强度处，最高达到41000.随着偏置电场增加反铁电向铁电体转变过程中，小信号介电常数εc减小；在电场降低铁电回复成反铁电过程中，小信号介电常数εc增大，小信号介电常数εc峰先于微分介电常数εd峰出现.根据电场作用下反铁电 关键词： 锆钛酸铅反铁电陶瓷 介电行为 强电场条件     

Smoothing of Doppler spectra line shapes in electrophoretic analysis of biological cell suspensions

The study of cell and particle electrophoresis by laser Doppler techniques requires the application of an electric field to a conducting solution. Steady d.c. electric fields are usually not possible because of electrode surface reactions. Hence, it has been common practice to apply temporally varying electric fields, either pulses of alternating polarity or square-wave fields of constant amplitude. Oscillating particle motion leads to harmonic structure (multiples of the square-wave electric field frequency) in the scattered light spectra. This harmonic structure may be considerably smoothed by a suitable variation of the period of the applied square-wave field. The application of a pseudo-random period oscillating electric field yields line shapes that approach the line shapes to be expected from the application of a continuous d.c. electric field.     

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.     

Regular Electric Field in Electromagnetic Coupled to a Scalar Field

In the framework of an electromagnetic field coupled nonminimally with a scalar field in flat spacetime, the existence of a non-singular electric field is proved for a point electric charge or electric monopole. In analogy with the Maxwell-dilaton system introduced by Gibbons and Wells, first, a Maxwell-anti-dilaton system is constructed where the radial electric field of a static electric monopole is coupled to an anti-dilaton. The field equations are solved analytically for the electric and dilaton fields and observe the nonsingular electric field. Also, the self-energy of the electric monopole is found to be finite. Furthermore, the formalism to a Maxwell-scalar field is generalized where a mechanism is introduced upon which the coupled regular-electric field and scalar field is obtained. The formalism shows that for a given regular electric field there are two supersymmetric coupling functions corresponding to a scalar and a phantom field.     

基于OpenGL的三维电场线模拟

在Visual C＋＋环境下,设计了一种基于OpenGL的三维电场线模拟软件。该软件采用微分方程法来生成电场线,可以准确地模拟不同观察视角下,静止点电荷的三维电场线。用户可以拖动鼠标随意转动观察视角,并可随意设置电荷个数、分布以及大小。     

一种简单精准的渐变折射率分布光波导分析方法

渐变折射率分布的光波导分析对光波导器件的设计和研究至关重要, 近年来已提出了多种分析方法, 然而在简便性或准确性上都存在着不足. 为此, 提出了一种分析渐变折射率分布光波导的方法, 能够结合现有的Wentzel-Kramers-Brillouin近似法和离散化的波动方程, 构建模场分布, 再结合变分运算方程和修正的模式本征方程, 计算出较为精确的有效折射率. 与其他分析方法相比, 该方法较为简单, 而且有一定的精度.     

常气压辉光放电等离子体对边界层流动的影响

基于Shyy提出的常气压下均匀辉光放电等离子体与空气干扰的物理模型,通过求解电位势方程得到电场分布及作用于流体上的电场力.以NACA0015翼型低速绕流为对象,通过数值求解考虑等离子体作用的流体运动控制方程,研究等离子体位置和个数控制对翼型绕流分离的影响.位于分离点上游的等离子体能够有效地抑制流动分离,而在分离区的等离子体对流动影响很弱,这一结论同实验观察一致,并给出等离子体对翼型壁面压力和气动力影响的规律.     

感生电场与动生电场的等效性探究

本文认为在感生电场的情况下,磁场的强弱变化可以引起磁场自身的横向运动,使得线圈中电子相对于磁场发生运动,从而等效为一个动生电场,受到洛伦兹力的作用.借助磁感线模拟磁场的运动方式,得到圆形回路中任意一点与磁场相对运动速度的表达式,进而推得该＂等效动生电场＂中的洛伦兹力.以螺线管为例,验证该方法可以解释感生电场所满足的规律.将感生电场与动生电场的产生原因统一为导体中电子与磁场的相对运动,相应电动势的非静电力统一为洛伦兹力.     

AlGaN合金中局域态和极化电场的竞争机制

通过MOVPE方法生长了不同Al组分的3块Al_xGa_1-xN样品,利用稳态光谱和时间分辨光谱对其样品的光学特性进行了分析。鉴于影响氮化物发光性质的极化电场或局域态的单一机制不能充分解释我们的实验现象,提出了局域态-内部极化电场竞争的机制。通过对实验数据的分析,得出如下重要结论：样品PL峰位蓝移的温度起点基本对应于局域态和极化电场起作用的交替点,PL峰位发生蓝移的温度起点与光强-温度曲线的斜率出现明显变化的温度点一致;随着温度的升高,若AlGaN合金样品中PL峰位存在二次蓝移,则说明样品中电场分布不均匀。     

Reduction of the error of hydrophone calibration with respect to the field in a hydroacoustic tank by the reciprocity method

A hydrophone calibration procedure that considerably reduces the error caused by the acoustic field distortions in a hydroacoustic tank is proposed. The procedure is based on the definition of the reduced electric transfer impedances of transducers (i.e., the electric transfer impedances reduced to the spherical wave propagation law) and consists in measuring the electric transfer impedances for different distances between hydroacoustic transducers. The sensitivity of the hydrophone under calibration is calculated from the far-field values of the reduced electric transfer impedances. The latter are determined using a mathematical model of the hydrophone in the form of a system that contains a point sensing element and a finite number of point sources of acoustic signals (point reflectors). A method of determining the number and coordinates of the point reflectors from the analysis of the acoustic “images” of the hydrophone’s reflecting surface is proposed. The measuring technique, the algorithms of mathematical processing, and the results of experimental studies are considered. A comparative analysis of the results of the hydrophone calibration with respect to the field by the reciprocity method is performed for the cases of using the conventional technique and the proposed method.     

Aspects of electrostatics in a weak gravitational field

Several features of electrostatics of point charged particles in a weak, homogeneous, gravitational field are discussed using the Rindler metric to model the gravitational field. Some previously known results are obtained by simpler and more transparent procedures and are interpreted in an intuitive manner. Specifically: (a) We discuss possible definitions of the electric field in curved spacetime (and noninertial frames), argue in favour of a specific definition for the electric field and discuss its properties. (b) We show that the electrostatic potential of a charge at rest in the Rindler frame (which is known and is usually expressed as a complicated function of the coordinates) is expressible as A ₀ = q/λ where λ is the affine parameter distance along the null geodesic from the charge to the field point. (c) This relates well with the result that the electric field lines of a charge coincide with the null geodesics; that is, both light and the electric field lines ‘bend’ in the same manner in a weak gravitational field. We provide a simple proof for this result as well as for the fact that the null geodesics (and field lines) are circles in space. (d) We obtain the sum of the electrostatic forces exerted by one charge on another in the Rindler frame and discuss its interpretation. In particular, we compare the results in the Rindler frame and in the inertial frame and discuss their consistency. (e) We show how a purely electrostatic term in the Rindler frame appears as a radiation term in the inertial frame. (In part, this arises because charges at rest in a weak gravitational field possess additional weight due to their electrostatic energy. This weight is proportional to the acceleration and falls inversely with distance—which are the usual characteristics of a radiation field.) (f) We also interpret the origin of the radiation reaction term by extending our approach to include a slowly varying acceleration. Many of these results might have possible extensions for the case of electrostatics in an arbitrary static geometry.     

利用Matlab模拟点电荷系的电场线和等势面

根据电场叠加原理,利用Matlab的绘图功能,绘出二维平面内点电荷系的等势面和电场线。以三个点电荷为例,模拟了它们的电场线和等势面,并通过改变电荷的位置和电荷量的大小对电场的分布情况进行分析比较,在教学中能起到很好的演示作用。     

Current induced Kerr effect in weakly ionized gases in the presence of a magnetic field

The current induced Kerr effect in the presence of a homogeneous magnetic field is treated for binary mixtures of neutral molecules and ions. The starting point is a system of moment equations derived from the linearized Waldmann-Snider equation. The dialectric tensor is calculated and studied in particular for a lorentzian mixture in perpendicular electric and magnetic fields. It is shown that the magnetic field causes a decrease of briefringence as well as a rotation of the principal axes of the dielectric tensor.     

电场条件下氧化锌结晶特性及极化产物的拉曼光谱分析

开展高压电场调控纳米材料结构形貌和性能研究在功能材料领域具有重要的理论和实际意义.本文在高压电场条件下合成了氧化锌纳米粉体,并对粉末试片进行了后期电场极化处理,研究了电场对氧化锌的结构形貌、点缺陷、拉曼光谱的影响.以X射线衍射仪(XRD)、扫描电镜(SEM)和拉曼光谱仪对产物的结构形貌、拉曼位移、缺陷分布等进行了表征.结果表明,高压电场条件下氧化锌的完全晶化时间和温度比未施加电场时明显延长和升高,直流电场能够显著促进前驱物中氧化锌的形核,并降低晶化速度.不同电场强度下氧化锌具有不同的显微形貌.纳米氧化锌粉末试片在直流电场中极化后,其阴极面和阳极面的拉曼光谱表现出明显的差异.有明显漏电电流的情况下,阳极面在1050 cm~(–1)处的二级光学声子模A_1(LO)的强度显著提高,且拉曼强度I_1=438 cm~(–1)和I_2=1050 cm~(–1)的比值与极化电场的场强呈线性关系.当调转试片正反面进行二次极化时,原来在阳极面尖锐的1050 cm~(–1)峰经过阴极极化而消失.阳极面1050 cm~(–1)拉曼峰的锐化与氧化锌晶粒内的缺陷重新分布和双肖脱基势垒有关.     

静电场中电场强度的数值意义

“近场强远场弱”是静电场的普遍特点,宏观带电体的静电场是点电荷电场叠加的结果.本文以静电场中两个实际的电场强度问题为例,用相对数值比较了电荷分布对电场强度的贡献,阐述电场强度“近场强远场弱”的数值意义.     

Radiation from electrons in graphene in strong electric field

We study the interaction of electrons in graphene with the quantized electromagnetic field in the presence of an applied uniform electric field using the Dirac model of graphene. Electronic states are represented by exact solutions of the Dirac equation in the electric background, and amplitudes of first-order Feynman diagrams describing the interaction with the photon field are calculated for massive Dirac particles in both valleys. Photon emission probabilities from a single electron and from a many-electron system at the charge neutrality point are derived, including the angular and frequency dependence, and several limiting cases are analyzed. The pattern of photon emission at the Dirac point in a strong field is determined by an interplay between the nonperturbative creation of electron–hole pairs and spontaneous emission, allowing for the possibility of observing the Schwinger effect in measurements of the radiation emitted by pristine graphene under DC voltage.     

On the Averaged Forces in Bounded Plasma in Parallel Electric and Magnetic Fields

Averaged forces of Miller's type, acting on the particles of a bounded plasma in parallel external a. c. electric and d. c. magnetic fields, are found on the basis of the equations of the two-component MHD. It is assumed, that standing transverse waves are excited in the plasma by the external source before the a. c. electric field is switched on.     

VELOCITY AND TEMPERATURE FIELDS IN A PLANE POISEUILLE FLOW WITH VOLUME HEATING: MEASUREMENTS UNDER ELECTRIC FIELD

This study concerns the measurement of the velocity and temperature fields in a laminar flow within a vertical channel of rectangular cross section. The fluid is heated in volume by direct electric conduction induced by an alternating electric field. Particular attention is paid to the procedure for temperature measurement under an electric field. The feasibility of such a measurement technique is shown, and specific aspects of the mixed convection regime are analyzed. Flow and temperature fields are also calculated by solving numerically the complete Navier-Stokes and energy equations for comparison with the experimental results. Differences between the experimental and numerical results are discussed, and the underlying physical mechanisms are analyzed.     

6H-SiC高场输运特性的多粒子蒙特卡罗研究

采用非抛物性能带模型,对6H-SiC高场电子输运特性进行了多粒子蒙特卡罗(Ensemble Monte Carlo)研究.研究表明：温度为296 K时,电子横向漂移速度在电场为2.0×104 V/cm处偏离线性区,5.0×105 V/cm处达到饱和.由EMC方法得到的电子横向饱和漂移速度为1.95×107 cm/s,纵向为6.0×106 cm/s,各向异性较为显著.当电场小于1.0×106 V/cm时,碰撞电离效应对高场电子漂移速度影响较小.另一方面,高场下电子平均能量的各向异性非常明显.电场大于2.0×105 V/cm时,极化光学声子散射对电子横向能量驰豫时间影响较大.当电场一定时,c轴方向的电子碰撞电离率随着温度的上升而增大.对非稳态高场输运特性的分析表明：阶跃电场强度为1.0×106 V/cm时,电子横向瞬态速度峰值接近3.0×107 cm/s,反应时间仅为百分之几皮秒量级.