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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, 相似文献
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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. 相似文献
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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. 相似文献
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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。 相似文献
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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. 相似文献
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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. 相似文献
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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。 相似文献
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