B2H6分子在C2v势阱中的频率分解及其各向异性效应

依据杨-泰勒效应理论、量子理论和群论探讨了具有D3h对称性构型的B2H6分子的E  e′系统在C2v势阱中的频率分解及其各向异性现象。借助么正平移变换和标度变换计算出了杨-泰勒畸变后的系统振动频率,结果表明,畸变导致系统二重简并的振动模式e′的振动频率发生了分解,对于系统的4个C2v势阱而言,无论系统处在哪一个势阱中,畸变所导致的频率分解都是相同的;畸变同时还导致系统的振动基态能量比畸变前降低了。正是这种基态能量的降低,使得畸变后系统就达到了一个更加稳定的状态。文中利用群论进一步探讨了系统的频率分解,结果发现,畸变导致系统的二重简并振动态e′分解为两种非简并的振动态,它们分别具有C2v群下的a1与b2对称性。系统的频率分解与基态能量的降低就意味着系统的各向同性遭到破坏而呈现出各向异性。     

An investigation on the sensitivity and stability radius of returns to scale and efficiency in data envelopment analysis

An issue which has received widespread attention in rapidly growing field of DEA is the sensitivity of the results of analysis to perturbations in the data.     

基于归属不确定性的变规模网络重叠社区识别

 拓扑势理论是一种新的复杂网络社区识别理论.针对该理论和方法存在的应用范围不明确和社区重叠节点数量过少等问题,提出基于归属不确定性的变规模网络重叠社区识别方法.在证明拓扑势熵最小值点存在性的基础上,该方法通过提出重叠节点社区归属不确定性测度以及变规模社区的概念和思想,实现社区的有效识别.通过实验验证了该测度的合理性和有效性.实验结果表明,该方法不但具有识别变规模重叠社区的能力,而且还可获得与拓扑势方法相当的社区识别效果.     

黑碳气溶胶的光散射特性研究

利用光电检测法研究黑碳气溶胶粒子的光散射特性,根据粒子的光散射特性来分析它的尺度谱.黑碳气溶胶粒子在激光的作用下产生散射光,利用光电检测器检测黑碳气溶胶粒子发出的散射光.提出了利用散射光信号的前沿部分进行拟合,得到粒子散射光信号的完整高斯分布.     

WLCSP中微焊球结构尺寸对其热应力的影响

晶圆级芯片尺寸封装(WLCSP)微焊球结构尺寸对其热机械可靠性有重要的影响。通过二维有限元模拟筛选出对WLCSP微焊球及其凸点下金属层(UBM)中热应力影响显著的参数,采用完全因子实验和多因子方差统计分析定量评估各种因子影响的显著性,最后建立三维模型,用子模型技术研究关键尺寸因子对热应力变化的影响。研究发现,焊球半径是影响焊球热应力的最关键尺寸因子,电镀铜开口和铜焊盘厚度对焊球热应力的影响也较显著;钝化层开口和焊球半径是影响UBM热应力的最关键尺寸因子。随着焊球半径增大,焊球热应力减小。     

完全子图的邻域重叠社团结构探测

为了能够更准确地对邻域重叠网络进行社团结构探测,研究人员对基于完全子图的社团探测算法进行了改进。在合并完全子图团簇时,计算每一对完全子图的重叠节点个数,设置合并完全子图的阈值,如果大于阈值,则合并。在处理不在团簇内的其他节点时,采用按照比例系数大小来划分规则进行划分。算法应用5-空手道俱乐部和科学家合作网当中,验证算法可以更准确地探测邻域重叠社团结构。     

一种基于特征的自适应水印算法

基于图像多尺度空间理论和扩频机制以及视觉感知模型的特性,给出一种基于特征的数字图像水印算法。算法采用尺度不变特征变换算子提取图像的局部不变特征区域,根据信噪比特点自适应选取水印嵌入强度因子,将一幅二值水印图像嵌入到原始图像中,实现了数字水印的不可感知性和鲁棒性。仿真结果表明,该算法对添加噪声、压缩、旋转等常见的图像处理攻击具有较强的鲁棒性。     

The search for a primordial magnetic field

Magnetic fields appear wherever plasma and currents can be found. As such, they thread through all scales in Nature. It is natural, therefore, to suppose that magnetic fields might have been formed within the high temperature environments of the big bang. Such a primordial magnetic field (PMF) would be expected to arise from and/or influence a variety of cosmological phenomena such as inflation, cosmic phase transitions, big bang nucleosynthesis, the cosmic microwave background (CMB) temperature and polarization anisotropies, the cosmic gravity wave background, and the formation of large-scale structure. In this review, we summarize the development of theoretical models for analyzing the observational consequences of a PMF. We also summarize the current state of the art in the search for observational evidence of a PMF. In particular, we review the framework needed to calculate the effects of a PMF power spectrum on the CMB and the development of large scale structure. We summarize the current constraints on the PMF amplitude _Bλ$B_{\lambda }$ and the power spectral index _nB$n_B$ and discuss prospects for better determining these quantities in the near future.     

CMB fluctuations and string compactification scales

We propose a mechanism for the generation of temperature fluctuations of cosmic microwave background. We consider a large number of fields, such as Kaluza-Klein modes and string excitations. Each field contributes to the gravitational potential by a small amount, but an observable level of temperature fluctuations is achieved by summing up the contribution of typically of order 10¹⁴ fields. Tensor fluctuations are hardly affected by these fields. Our mechanism is based on purely quantum effects of the fields which are classically at rest, and is different from the one in slow-roll inflation. Using the observed data, we find constraints on the parameters of this model, such as the size of the extra dimensions and the string scale. Our model predicts a particular pattern of non-gaussianity with a small magnitude.     

Mesoscopic approach to minority games in herd regime

We study minority games in efficient regime. By incorporating the utility function and aggregating agents with similar strategies we develop an effective mesoscale notion of the state of the game. Using this approach, the game can be represented as a Markov process with substantially reduced number of states with explicitly computable probabilities. For any payoff, the finiteness of the number of states is proved. Interesting features of an extensive random variable, called aggregated demand, viz. its strong inhomogeneity and presence of patterns in time, can be easily interpreted. Using Markov theory and quenched disorder approach, we can explain important macroscopic characteristics of the game: behavior of variance per capita and predictability of the aggregated demand. We prove that in the case of linear payoff many attractors in the state space are possible.