红磷烟雾对10.6μm激光的消光分析

本文简要叙述了红磷形成烟雾的过程及性质,并用 Mie 理论计算了不同温度条件下红磷烟雾对10.6μm 激光的质量消化系数α_c 和质量散射系数α。理论计算与实验测得的α_c 有较好的一致性。     

Identifiable finite mixtures of location models for clustering mixed-mode data

For clustering mixed categorical and continuous data, Lawrence and Krzanowski (1996) proposed a finite mixture model in which component densities conform to the location model. In the graphical models literature the location model is known as the homogeneous Conditional Gaussian model. In this paper it is shown that their model is not identifiable without imposing additional restrictions. Specifically, for g groups and m locations, (g!)m–1 distinct sets of parameter values (not including permutations of the group mixing parameters) produce the same likelihood function. Excessive shrinkage of parameter estimates in a simulation experiment reported by Lawrence and Krzanowski (1996) is shown to be an artifact of the model's non-identifiability. Identifiable finite mixture models can be obtained by imposing restrictions on the conditional means of the continuous variables. These new identified models are assessed in simulation experiments. The conditional mean structure of the continuous variables in the restricted location mixture models is similar to that in the underlying variable mixture models proposed by Everitt (1988), but the restricted location mixture models are more computationally tractable.     

非线性波动方程的孤波解及余弦周期波解

利用假设待定法,求出了非线性波动方程的具有双曲正割函数分式形式且渐近值不为零的精确孤波解和余弦函数周期波解,并分别讨论了它们的有界性,揭示了行波波速改变对钟状孤波解与余弦函数周期波解波形变化的影响.     

指数基金投资策略研究

长期来看,绝大部分基金都不能跑赢指数基金,因此,普通投资者的最佳选择是投资指数基金.但投资指数基金应避免两个误区:一是在局部地区的长期熊市中不适合长期投资指数基金,二是在全球股市的长期熊市中不适合长期投资指数基金.而指数基金投资波段操作策略可有效避免以上两个投资误区,即每年5月至10月空仓、11月至次年4月投资指数基金.     

平面波照明正交光栅时的Talbot效应

本文根据菲涅尔衍射理论,讨论了平面波照明时,两方向周期d_x≠d_y的正交光栅的Talbot效应。指出,两方向周期满足k_x/k_y=(d_y~2)/(d_x~2)的关系时,才能得到完整信息的Talbot像。并据此,引入了混合Talbot像的新概念。给出了一种较Szwaykowski的方法优越的产生正交光栅的方法。并扩展了Szwaykowski的理论。实验结果和理论吻合很好。     

弱位相光栅的自成像研究

本文从理论上对球面波照明弱位相光栅时的自成像现象进行了研究，发现当相对位相分布（x）＜＜1弧度时，位相光栅也存在自成像现象。     

血流脉搏波的特征与生理因素的相关性研究

从动脉血管系统的血管壁、血液以及动脉血管周围组织的生理物性出发,建立了脉搏波波形特征的数学表达式,从物理学以及数学的角度在理论上分析了脉搏波波形的特征随生理参数的变化情况。改变血管的杨氏模量,血液的粘度以及血管半径参数后发现所得的脉搏图与能较好的反映生理信息,本文所得到的结果为脉搏波的波形特征的进一步研究奠定了理论基础,也有助于临床上利用脉搏波的传播特性来分析和诊断相关的疾病。     

A stochastic approximation algorithm for maximum-likelihood estimation with incomplete data

We propose a new stochastic approximation (SA) algorithm for maximum-likelihood estimation (MLE) in the incomplete-data setting. This algorithm is most useful for problems when the EM algorithm is not possible due to an intractable E-step or M-step. Compared to other algorithm that have been proposed for intractable EM problems, such as the MCEM algorithm of Wei and Tanner (1990), our proposed algorithm appears more generally applicable and efficient. The approach we adopt is inspired by the Robbins-Monro (1951) stochastic approximation procedure, and we show that the proposed algorithm can be used to solve some of the long-standing problems in computing an MLE with incomplete data. We prove that in general O(n) simulation steps are required in computing the MLE with the SA algorithm and O(n log n) simulation steps are required in computing the MLE using the MCEM and/or the MCNR algorithm, where n is the sample size of the observations. Examples include computing the MLE in the nonlinear error-in-variable model and nonlinear regression model with random effects.     

EM浸种处理对玉米叶色值的影响

以玉米品种农大108为试验材料,用SPAD-502仪分别测定了不同浓度EM稀释液浸种处理后的叶色值。试验结果表明:利用不同浓度EM(有效微生物群)稀释液浸种及在玉米拔节期叶面喷施并灌根,可显著提高玉米叶片的叶绿素含量。并遴选出玉米施用EM的最佳浓度为500倍稀释液。     

色散特性对毫米波频率步进雷达影响的研究

对影响毫米波频率步进雷达分辨率的主要因素进行了分析。除目标速度以外,为毫米波频率步进雷达提供频率信号的频率源的色散特性也会对雷达分辨率造成恶化影响。微波频段上的色散特性会被搬移到毫米波频段,导致毫米波发射信号和本振信号的初始相位差不为常数,对雷达系统尤其是距离分辨率造成严重影响。仿真结果与实验结果一致。为了抵消色散特性对雷达分辨率的恶化影响,可以通过对色散特性的补偿来实现。色散特性补偿的方法被应用到实现W波段频率步进频率源的设计中,满足了0.45m距离分辨率的要求。