基于选择模式的幂律生成机制

自然界与社会生活中存在多种性质迥异的幂律分布现象,因而对它们的研究具有广泛而深远的意义．研究了一类由于人类的选择行为而产生的幂律现象,提出了人类选择行为的两个特性：理性与自利．据此,通过小球选择试验构建了模型．研究发现,这类幂律现象中随机变量服从一种近似于Zipf分布的分布．此分布为首次提出的一种新分布,将它命名为偏序分布．网络中已有的统计数据表明,偏序分布比Zipf分布更真实的反应了网络中统计变量服从的分布．文中对偏序分布进行了理论分析,并通过约束条件的改变,生成了Yule分布;表述了Yule分布的物理意义,并构造了比Yule分布更具现实意义的分布．说明了选择理论在解释幂律现象方面的普遍适用性及模型的可扩展性．文中在幂律现象的成因上支持还原论,即简单的人类选择行为导致了普遍的幂律现象． 关键词： 选择行为 幂律分布 偏序分布 Yule分布     

埋置量子点应力分布的有限元分析

通过衬底材料和外延材料的交替生长方式制备出多层排列的自组装量子点超晶格结构.这些埋置量子点的应力/应变场影响着它们的光电性能、压电性能以及力学稳定性.基于各向异性弹性理论的有限元方法,研究了埋置金字塔形应变自组织Ge/Si半导体量子点的应力/应变分布以及流体静应变和双轴应变分布,并与非埋置量子点的应力/应变分布做了比较,指出了它们之间的异同以及覆盖层对量子点应力/应变分布的影响. 关键词： 量子点 应力分布 应变分布     

密勒-库什实验过程中的气体分子分布函数

详细分析了密勒－库什实验过程中分子速率分布的变化情况，说明了实验数据与麦克斯韦速率分布之间的关系。     

Bi2223带材临界电流沿长度方向的统计分布

本文采用四引线法测量了Bi2223带材临界电流沿长度方向的分布,采用正态分布、对数正态分布、威布尔分布和最小极值分布对临界电流分布进行了拟合检验,确定了临界电流的最优统计分布模型.     

转动细杆的切向内力

本文讨论了质量离散分布和连续分布的刚性细杆在转动中切向内力的分布规律。     

L型气体分速率分布规律投影演示仪

本文介绍了Ｌ型气体分子速率分布律投影演示仪的构造．使用方法及演示效果。     

用三个分布律整合气体动理论的教学

用麦克斯韦速度分布律、玻耳兹曼分布律、自由程分布律整合了气体动理论的教学．     

相对论修正对麦克斯韦-玻耳兹曼分布律的影响

在本文中,分别推导了低速情形（E≈m0c^2＋p^2/2m0）和一般情形（E=√p^2c^2＋m0^2c^4）下考虑相对论修正的动量分布表达式和速率分布表达式,发现低速情形下修正后的动量分布形式与不考虑修正的动量分布在形式上一致,而速率分布形式发生了改变;对一般情形的动量分布函数和速率分布函数进行了数值模拟并对结果进行了必要讨论．我们发现当β减少时整个动量分布曲线向大动量区域延伸,当β较大,即温度较低使得p〈1时,一般情形将近似为低速情形．     

Matlab在麦克斯韦速率分布律中的应用

用Matlab软件对麦克斯韦速度及速率分布函数进行了编程,绘制了相应的分布曲线,讨论了不同温度和不同分子质量时麦克斯韦速率分布曲线的变化,并用Matlab的符号计算功能计算了分布在三个典型速率区间的分子数占总分子数的百分比,所有变化规律均符合热学理论中的分子运动规律,为教学提供了参考。     

增长速度对合作网络参与者节点度分布的影响

采用率方程对合作网络自组织演化模型进行解析,得到参与者节点度分布服从Yule-Simon分布,这种分布可以用漂移幂律分布近似.分析参与者节点增长速度与参与者节点度分布之间的关系,发现随节点增长速度加快,参与者节点度分布远离幂律,表明节点增长速度是除优先连接之外的另一个影响合作网络拓扑性质的重要因素.通过对城市公交网络和科研合作网络的实证研究,验证了度分布解析结果的正确性.结合实证研究,探讨了合作网络中参与者节点增长速度的形成机制及其实际意义.     

Effect of groove shape on flow characteristics around a circular cylinder with grooves

In the flow around a circular cylinder, a sudden decrease in the drag force occurs at a high Reynolds number, but the same phenomenon occurs at a lower Reynolds number in the case where there exist grooves or roughness on the circular cylinder surface. In this paper, in order to make clear the flow characteristics around a circular cylinder in the case of changing the shapes of grooves, the drag coefficient, pressure distribution, velocity distribution and turbulent distribution were measured. Moreover the flow around the cylinder was analyzed by applying the RNGk · ∈ turbulent model, and the surface flow pattern was investigated using the oil-film technique. From these results, it is clear that the drag coefficient of a circular cylinder with triangular grooves decreases by about 15% compared with that of a circular cylinder with arc grooves.     

圆孔的菲涅耳衍射

得到了圆孔菲涅耳衍射光强分布的表达式,此式由贝塞尔函数的数列(或Lommel函数)给出,因此很容易利用普及的数学软件算出结果.并且利用CCD照相机量度了衍射光强分布,与运算的结果作了比较,也与Burch在1985报导的结果作了比较.     

The steady state response of a damped circular plate driven at a diameter

The steady state response of a damped circular plate transversely or rotationally driven at a diameter is determined by the series-type method. With the reaction force or moment acting along a diameter of a circular plate regarded as an unknown harmonic load, the response of the plate to the load is expressed by the Green function. The force or moment distribution along the diameter is expanded into Fourier series with unknown coefficients, and the simultaneous linear equations for the coefficients are derived by the restraint condition on the diameter. The dynamic response of the plate is determined by solving the equations. The method is applied to circular plates driven by a sinusoidally varying transverse deflection or angular rotation at a diameter, and the steady state response of the plates is studied.     

Electrostatic potential penetration into a circular enclosure with circular apertures

Electrostatic potential penetration into a circular enclosure with circular apertures is investigated. An electrostatic boundary-value problem of the circular enclosure with circular apertures is solved based on the Hankel transform, mode matching technique, and superposition. The polarizability of the circular apertures is represented in a series and calculated in terms of the aperture geometry to understand the behaviors of potential penetration.     

高斯分布圆口径天线辐射近场分析

采用口径场法对具有高斯幅度分布的圆口径天线辐射近场进行了分析。推导了非聚焦和聚焦2种工作方式下圆口径天线轴向近场和增益的解析表达式;采用数值积分方法分析了圆口径天线非轴向近场分布特性。分析表明,对于高斯幅度分布的圆口径天线,天线轴向场在近区为振荡分布,其近场增益与口径面分布和观测点位置有关,通过聚焦可以使近场焦点处增益达到远场增益,大大提高焦点及焦点附近区域的电场幅度。     

具有环形限位夹持力的单轴式超声悬浮系统

基于超声悬浮原理,通过改变单轴式超声悬浮系统的反射和发射端的几何形状,利用凸状发射、反射面在悬浮区域周围产生环形声辐射力势阱作为限位夹持力,提高悬浮样品在驻波声场中的悬浮稳定性。基于时域有限差分法,研究不同谐振腔内的声辐射力分布,以及影响声辐射力大小的因素,优化环形限位夹持力和悬浮力。理论及实验研究结果表明,具有环形限位夹持力的超声悬浮系统可以提高普通单轴式超声悬浮装置对悬浮样品的稳定性。      

Propagation of a phase-locked circular dark hollow beams array in a turbulent atmosphere

The propagation of phase-locked circular dark hollow beams array in a turbulent atmosphere is studied. An analytical expression for the average intensity distribution at the receiving plane is obtained based on the extended Huygens-Fresnel principle. The effects of turbulence, dark parameter and beam order of the beams array on the intensity pattern are studied and analyzed. It is found that the intensity pattern of the phase-locked circular dark hollow beams array will evolve from a multiple-spot-pattern into a Gaussian beam spot under the isotropic influence of the turbulence. The intensity pattern of beam array with a larger dark parameter and beam order evolves into the Gaussian-shape faster with increasing propagation distance.     

Vibration of a membrane having a circular outer boundary and an eccentric circular inner boundary

In this paper, a method of solving vibration problems for a membrane having a circular outer boundary and an eccentric circular inner boundary is presented. The frequency equation for the membrane is given, and the dependence of the natural frequency on the eccentricity is obtained. It is shown that the result obtained from this analysis in the limit of the eccentricity being zero coincides with that of a membrane with a concentric circular inner boundary.     

Effect of a turbulent medium on the near- and far-field diffraction of a circular aperture

The near- and far-field diffraction due to a circular aperture illuminated with partially coherent light produced by a turbulent medium has been theoretically studied. Formulations are developed for investigating the near- and far-field diffraction patterns. The phase structure function, which is generated by the turbulent medium and determines the partially coherent condition of a light beam passing through it, is assumed to take both the Gaussian form and the 5/3-power law. Numerical results concerning the far-field intensity distribution and the axial intensity distribution in the near-field region are presented in diagrams and discussed.     

Far-field spectral intensity characteristics of a time-dependent gaussian pulse from a circular mask with a linear circular apertures array

The spectral characteristics of a time-dependent Gaussian pulse from a circular mask with a circular apertures array in the far field are theoretically investigated and presented with numerical results. A rigorous treatment, with the Fresnel diffraction integral, to the spectral changes of a time-dependent Gaussian-shaped pulse passing through a circular mask with a linear circular apertures array is given and some properties of the spectral intensity under different situations are provided. Also an accurate and concrete criteria judging the condition for the red shift, blue shift of spectral intensity distributions is obtained as well.