部分相干电磁光束在湍流介质中传输的偏振变化

 从推广的惠更斯-菲涅尔原理出发，推导出了部分相干电磁光束的偏振态在湍流介质中传输的表达式。并以电磁高斯-谢尔模型(EGSM)光束为例，研究了湍流对电磁高斯-谢尔模型光束偏振态的影响。研究结果表明，对于轴上点，湍流介质的折射率结构常数越大，偏振度趋于最大值的速度越快，达到的最大值越小；光斑越大，偏振度达到最大值的位置离光源越远，在光斑增大的过程中，偏振度所达到的极大值会先增大后减小，最后保持与光源相同的偏振度不变。对于轴外点，一个固定的z，光的偏振度随着离轴距离的增大而逐渐下降，并最终等于零。折射率结构常数越大，偏振度随离轴距离的增大而下降得越缓慢；光斑越大，偏振度随离轴距离的增大下降得越快。     

High index of refraction via quantum interference in a three-level system of Er^3＋-doped yttrium aluminium garnet crystal

A simple three-level system is proposed to produce high index of refraction with zero absorption in an Er^3＋-doped yttrium aluminium garnet （YAG） crystal, which is achieved for a probe field between the excited state 4I13/2 and ground state 4I15/2 by adjusting a strong coherent driving field between the upper excited state 4I11/2 and 4I15/2. It is found that the changes of the frequency of the coherent driving field and the concentration of Er^3＋ ions in the YAG crystal can maximize the index of refraction accompanied by vanishing absorption. This result could be useful for the dispersion compensation in fibre communication, laser particle acceleration, high precision magnetometry and so on.     

采用多元化的教学手段,提高物理人才的综合素质——南开大学物理学基础科学人才培养基地建设经验介绍

介绍了南开大学国家物理学基础科学研究人才培养基地在十多年的建设中,通过多元化的教学手段提高学生的学习自主性,通过加强科研训练提高物理人才综合素质的经验和取得的成果.     

P schl-Teller势阱中线性与非线性光学折射率变化

利用量子力学中的密度矩阵算符理论导出了P schl-Teller势阱中的线性与三阶非线性光学折射率的解析表达式。P schl-Teller势阱中有两个可调参数κ和λ,势阱的形状及其非对称性会随势阱参数的取值不同而明显不同,从而其线性与非线性光学折射率变化的大小也会随势阱参数和入射光强的变化而呈规律性的变化。文章以典型的GaAs/AlGaAs势阱为例作了数值计算,数值计算结果表明,势阱的形状和入射光强对光学折射率有着重要的影响。     

主成分分析在地区科技竞争力评测中的应用

近年来对于科技竞争力的研究在国内方兴未艾,其中对于科技竞争力的评测是众多学者研究的重点和热点,也是各级决策者最为关心、最为重要的课题之一。本文根据科技竞争力概念和内涵来确定评测指标体系的构成要素,建立了评测指标体系,并利用主成分分析方法对采集来的数据进行分析,得到最终的评测结果。     

On a class of new and practical performance indexes for approximation of fold bifurcations of nonlinear power flow equations

Efficient measurement of the performance index (the distance of a loading parameter from the voltage collapse point) is one of the key problems in power system operations and planning and such an index indicates the severity of a power system with regard to voltage collapse. There exist many interesting methods and ideas to compute this index. However, some successful methods are not yet mathematically justified while other mathematically sound methods are often proposed directly based on the bifurcation theory and they require the initial stationary state to be too close to the unknown turning point to make the underlying methods practical.This paper first gives a survey of several popular methods for estimating the fold bifurcation point including the continuation methods, bifurcation methods and the test function methods (Seydel's direct solution methods, the tangent vector methods and the reduced Jacobian method) and discuss their relative advantages and problems. Test functions are usually based on scaling of the determinant of the Jacobian matrix and it is generally not clear how to determine the behaviour of such functions. As the underlying nonlinear equations are of a particular type, this allows us to do a new analysis of the determinants of the Jacobian and its submatrices in this paper. Following the analysis, we demonstrate how to construct a class of test functions with a predictable analytical behaviour so that a suitable index can be produced. Finally, examples of two test functions from this class are proposed. For several standard IEEE test systems, promising numerical results have been achieved.     

金属银熔体快冷过程的计算机模拟

利用分子动力学模拟技术研究了由周期性边界条件控制的500个银(Ag)原子构成的金属Ag熔体快速冷凝过程.冷却速率为8×1013K/s.模拟在FS(Finnis-Sinclair)相互作用势的基础上,通过双体分布函数、键对分析技术、键取向序等多种方法,对液银快速冷凝过程的微观结构转变特性作了分析,给出了连续快速冷凝过程中液银原子间依靠相互作用力形成的独特的微观结构图像.并考察了冷却过程中体系能量和元胞体积随温度的变化.模拟结果表明在快速冷凝过程中液Ag没有形成bcc结构的倾向.     

金属薄膜制备及物性测量系列实验

介绍了由模拟真空实验和“金属薄膜的制备”、“金属薄膜厚度的测量”、“金属薄膜电阻率的测量”,以及“金属薄膜生长过程的动态监测”等4个实验组成的金属薄膜制备与物性测量系列实验.这组实验与现代科学技术发展联系紧密,仪器设备可靠,操作简单,适合于普通物理实验阶段的研究性教学.     

中国股市长记忆的修正R/S分析

本文在比较各种长记忆检验方法优缺点的基础上,采用修正的R/S分析检验我国沪深两股市日收益和日绝对收益序列的长记忆性。结果表明在0.05的显著水平下,两股市的日收益序列均无长记忆,但深圳成指日收益序列的记忆长度比上证综指日收益序列的记忆长度长;以日绝对收益序列为代表的波动序列具有较强的长记忆性。     

关于圈的完全正矩阵实现

本文给出了一个关联图为圈的非负、半正定矩阵A为完全正的一个充要条件.我们还证明了这样的矩阵A（当A为完全正时）的分解指数即为A的阶数.