Scattering of particles in wave beam based on series expansion

Based on the orthogonalities of the vector wave functions, the expressions of scattering fields are developed as the particle in the zero order field and in the first order fields of x, y, and z, respectively. A general relation between the expansion coefficients of scattering field and incident field is presented. Taking the elliptical beam for example, the scattering property of a particle in beam is investigated. After analyzing the effects of the beam waist, irradiating distance, etc. on scattering property, the validity of the proposed algorithm is demonstrated. Results show that the beam waist may improve the particle identification property and the particle has a strong scattering both in the forward direction and in the backward direction. The method proposed is simple and is a new way of researching the scattering from particles in electromagnetic beams.     

双向隐形传态方案及安全性分析

基于位函数的引入与介质参量无关,将各向异性目标内外的电场展为级数形式,得到了任意各向异性目标n阶散射场、目标内场的递推表达式,给出了介电常量张量的变换关系,在平面波任意入射的条件下,并给出了传播单位矢量与极化单位矢量的一般关系.以磁化冷等离子体为例,给出了一阶散射场的具体表达式,并对二阶散射场引起的误差进行了评估.在THz波段和光波段,对所得结果进行了部分仿真.结果表明:微分散射对电波频率和极化状态等因素的影响较为敏感,介电常量张量的非对角元素对散射的影响不大,当波长与目标尺寸一定时,仿真结果不仅适用于THz波段,对其它波段也成立.     

面向低强度无线网络信号接收谱参数估计研究

针对以北斗卫星导航信号为代表的亚纳秒级的低强度无线网络信号在定位中难以获取精确时间估计及角度估计,且易受环境噪声影响,使其定位精度不高等难题,本文提出了基于亚纳秒级的低强度无线网络信号接收谱参数估计方法。首先通过抽样方式,将发射信号抽样为多维独立子信号并独立建模,通过构造噪声空间与子信号空间在对应列向量正交化的基础上精确获取TOA估计;随后利用复数域映射,在获取TOA估计基础上采取比对方式精确地获取DOA估计。最后对本文参数估计方法进行了精度分析。测试数据显示：与 PM算法、ESPRIT算法相比,本文技术在TOA及DOA估计上更为精确;同时在信号强度低且背景噪声干扰严重的情况下,本文方法仍可有效的维持参数估计精度。     

创设教学情境案例三则

建构主义学习观认为,学习是在一定情境中的意义建构．学习是个人建构自己知识的过程,学生要对所学的知识作主动的选择和加工,外部信息本身没有意义,意义是学生在经过以自己原有的经验为皋础,对新的信息加以分析吸收而进行自己的理解．当问题呈现给学生时,     

Gravitational quasinormal modes of static Einstein-Gauss-Bonnet anti-de Sitter black holes

In this paper, we describe quasinormal modes(QNMs) for gravitational perturbations of Einstein-GaussBonnet black holes(BHs) in higher dimensional spacetimes, and derive the corresponding parameters of such black holes in three types of spacetime(flat, de Sitter(d S) and anti-de Sitter(Ad S)). Our attention is concentrated on discussing the(in)stability of Einstein-Gauss-Bonnet Ad S BHs through the temporal evolution of all types of gravitational perturbation fields(tensor, vector and scalar). It is concluded that the potential functions in vector and scalar gravitational perturbations have negative regions, which suppress quasinormal ringing. Furthermore,the influences of the Gauss-Bonnet coupling parameter α, the number of dimensions n and the angular momentum quantum number l on the Einstein-Gauss-Bonnet Ad S BHs quasinormal spectrum are analyzed. The QNM frequencies have greater oscillation and lower damping rate with the growth of α. This indicates that QNM frequencies become increasingly unstable with large α. Meanwhile, the dynamic evolutions of the perturbation field are compliant with the results of computation from the Horowitz and Hubeny method. Because the number of extra dimensions is connected with the string scale, the relationship between α and properties of Einstein-Gauss-Bonnet Ad S BHs might be beneficial for the exploitation of string theory and extra-dimensional brane worlds.     

等离子体风洞中释放二氧化碳降低电子密度

航天器从近地空间进入大气层过程中,由于激波加热,会在航天器外表面形成等离子体鞘套,导致航天器与地面之间的无线电通信中断,即“黑障”效应.为了缓解“黑障”效应,国内外学者进行了多方面的技术研究,其中化学物质释放被认为是一种有效的方法.以往,主要针对卤族元素和水开展理论和实飞研究.本文基于二氧化碳不易在高温流场中发生裂解的特性,利用电弧和高频风洞产生等离子体流场,主动释放二氧化碳降低等离子体电子密度.结果表明,在风洞等离子体中,释放不同流量的二氧化碳可使电子密度下降1—2个量级,为解决再入过程中黑障问题提供了一种可行方法.     

Gravitational quasi-normal modes of static R~2 Anti-de Sitter black holes

In this paper, we study the gravitational quasi-normal modes(QNMs) for a static R~2 black hole(BH) in Anti-de Sitter(AdS) spacetime. The corresponding master equation of odd parity is derived and the QNMs are evaluated by the Horowitz and Hubeny method. Meanwhile the stability of such BH is also discussed through the temporal evolution of the perturbation field. Here we mainly consider the coefficient λ, which is related to the radius of AdS black hole, on the QNMs of the R~2 AdS BH. The results show that the Re(ω) and |Im(ω)| of the QNMs increase together as |λ| increases for a given angular momentum number l. That indicates with a larger value of |λ| the corresponding R~2 AdS BH returns to stable much more quickly. The dynamic evolution of the perturbation field is consistent with the results derived by the Horowitz and Hubeny method. Since in the conformal field theory the QNMs can reflect its approach to equilibrium, so our related results could be referential to studies of the AdS/CFT conjecture. The relationship between λ and the properties of the static R~2 BH might be helpful for the development of R~2 gravitational theory.     

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给出了不同坐标系中介质参数张量的变换,得到了磁化冷等离子体球电场的表达式,得出了任意各向异性目标散射场的表达式,研究了磁化冷等离子体球的微分散射截面、散射截面等的函数关系,仿真结果与有关文献一致,表明了本算法的有效性,从而为各向异性目标识别等提供理论支持。     

磁化冷等离子体球的太赫兹散射特性

基于位函数的引入与介质参量无关,将各向异性目标内外的电场展为级数形式,得到了任意各向异性目标n阶散射场、目标内场的递推表达式,给出了介电常量张量的变换关系,在平面波任意入射的条件下,并给出了传播单位矢量与极化单位矢量的一般关系.以磁化冷等离子体为例,给出了一阶散射场的具体表达式,并对二阶散射场引起的误差进行了评估.在THz波段和光波段,对所得结果进行了部分仿真.结果表明:微分散射对电波频率和极化状态等因素的影响较为敏感,介电常量张量的非对角元素对散射的影响不大,当波长与目标尺寸一定时,仿真结果不仅适用于THz波段,对其它波段也成立.     

提升现代民营企业管理水平的对策

现代民营企业是最具普遍意义的企业组织形态,其自身的众多特点为企业的建立和初期的发展具有功不可没的作用,但随着社会分工的精细化和经营的国际化,现代民营企业要想永葆青春、不断飞跃,必须做好改革与创新。