渔业资源的变动模型与捕捞策略

为描述鱼群中鱼量在复杂因素影响下的变动规律,建立了定量化的数学模型,并给出定率捕捞、分段减率、集中峰率等3种可操作的捕捞策略,提供了在可持续生产的条件下,寻求最大收获量及其决策数据的计算公式与搜索算法。该算法简便易行,既适用于单年生产,也适用于多年承包。最后,对各种捕捞策略做出了定性评价。     

Graphical Representation of Missing Data Problems

Rubin’s classic missingness mechanisms are central to handling missing data and minimizing biases that can arise due to missingness. However, the formulaic expressions that posit certain independencies among missing and observed data are difficult to grasp. As a result, applied researchers often rely on informal translations of these assumptions. We present a graphical representation of missing data mechanism, formalized in Mohan, Pearl, and Tian (2013). We show that graphical models provide a tool for comprehending, encoding, and communicating assumptions about the missingness process. Furthermore, we demonstrate on several examples how graph-theoretical criteria can determine if biases due to missing data might emerge in some estimates of interests and which auxiliary variables are needed to control for such biases, given assumptions about the missingness process.     

Implementing Restricted Maximum Likelihood Estimation in Structural Equation Models

Structural equation modeling (SEM) is now a generic modeling framework for many multivariate techniques applied in the social and behavioral sciences. Many statistical models can be considered either as special cases of SEM or as part of the latent variable modeling framework. One popular extension is the use of SEM to conduct linear mixed-effects modeling (LMM) such as cross-sectional multilevel modeling and latent growth modeling. It is well known that LMM can be formulated as structural equation models. However, one main difference between the implementations in SEM and LMM is that maximum likelihood (ML) estimation is usually used in SEM, whereas restricted (or residual) maximum likelihood (REML) estimation is the default method in most LMM packages. This article shows how REML estimation can be implemented in SEM. Two empirical examples on latent growth model and meta-analysis are used to illustrate the procedures implemented in OpenMx. Issues related to implementing REML in SEM are discussed.     

A Two-Stage Approach to Missing Data: Theory and Application to Auxiliary Variables

A well-known ad-hoc approach to conducting structural equation modeling with missing data is to obtain a saturated maximum likelihood (ML) estimate of the population covariance matrix and then to use this estimate in the complete data ML fitting function to obtain parameter estimates. This 2-stage (TS) approach is appealing because it minimizes a familiar function while being only marginally less efficient than the full information ML (FIML) approach. Additional advantages of the TS approach include that it allows for easy incorporation of auxiliary variables and that it is more stable in smaller samples. The main disadvantage is that the standard errors and test statistics provided by the complete data routine will not be correct. Empirical approaches to finding the right corrections for the TS approach have failed to provide unequivocal solutions. In this article, correct standard errors and test statistics for the TS approach with missing completely at random and missing at random normally distributed data are developed and studied. The new TS approach performs well in all conditions, is only marginally less efficient than the FIML approach (and is sometimes more efficient), and has good coverage. Additionally, the residual-based TS statistic outperforms the FIML test statistic in smaller samples. The TS method is thus a viable alternative to FIML, especially in small samples, and its further study is encouraged.     

关于对数Poisson分布性质的研究

针对经典的Piosson分布,利用对数正态分布的思想,给出了对数Poisson分布的定义以及对数Poisson分布的概率分布律,讨论了对数Poisson分布的矩的性质及其分布的偏度和峰度系数。在对数Poisson分布的点估计的研究中,得到了参数的极大似然估计量具有无偏性、有效性、相合性和充分性等优良性质。     

万年油对果蝇的急性与慢性毒性效应

本实验初步研究万年油对红眼果蝇的7天急性毒性效应及对红眼雌性处女蝇的22天慢性毒性效应。采用野生型黑腹红眼果蝇,在其培养基中加入浓度分别为2%、20%的万年油,以2%的未加热食用油作为阴性对照组,计算平均寿命,最高平均寿命和死亡率,作为3个毒性指标。结果显示通过急性毒性试验计算出万年油的半数致死剂量为2.86%。慢性实验结果显示,与对照组相比,2%组3个毒性指标有显著性差异;20%万年油组3个毒性指标存在极显著性差异。结果说明万年油对红眼果蝇有较强毒性,且含油量越高,其毒性效应越大。     

用纹理分析方法作肝脏检查

采用共生矩阵分析B超肝脏图橡钓改狸结构,从中找出有关的特征参数,作为医生区分肝脏有否病患的依据。     

基于粒子群优化算法的结构系统辨识

针对一般智能理论辨识方法在结构系统辨识中存在的问题,提出一种基于粒子群优化算法(PSO)的辨识方法。用粒子群中的粒子表征结构物理参数,以最大似然准则为粒子群优化算法的适应度函数,建立了结构系统的辨识模型。数值仿真分析表明,粒子群优化算法可以精确辨识出结构系统的物理参数。     

最大气泡法测定液体表面张力实验装置的改进

基于物理化学实验教材“最大气泡法测定液体的表面张力”实验中毛细管与液面相切难控制、毛细管鼓泡速率难控制的缺点提出了改进方案.由注射器代替滴管控制液体加入量,较容易使毛细管与液面刚好相切;采用带活塞的锥形瓶与注射器联用取代滴流瓶控制减压操作气泡形成的速率;用计算机取代人工处理实验数据和绘图.改进后的实验数据准确度和精密度均有所提高.     

等价限制线性模型中极大似然估计的稳健性

稳健性分析是判断估计值与真实值之间差异是否重要的一种方法。限制线性模型下的极大似然估计的稳健性是当前大家比较感兴趣的一个问题。笔者在前人的基础上,给出限制线性模型中极大似然估计对随机误差协方差矩阵的稳健性统计量,并对其进行分析,得出限制线性模型中极大似然估计对随机误差协方差矩阵不敏感。