林产品市场模型文献综述

关于林产品市场的数量研究开始于上个世纪50年代。早期的研究主要以时间序列数据为主。近几十年来,由于经济理论在林产品市场模型中的应用,模型估计方法的改进,以及详细数据的获得,林产品市场模型越来越完善。文章对近几十年来出现的主要建模方法,及其应用作一回顾,并对这些方法的优缺点作简单的比较。     

Robustness issues in multilevel regression analysis

A multilevel problem concerns a population with a hierarchical structure. A sample from such a population can be described as a multistage sample. First, a sample of higher level units is drawn (e.g. schools or organizations), and next a sample of the sub‐units from the available units (e.g. pupils in schools or employees in organizations). In such samples, the individual observations are in general not completely independent. Multilevel analysis software accounts for this dependence and in recent years these programs have been widely accepted. Two problems that occur in the practice of multilevel modeling will be discussed. The first problem is the choice of the sample sizes at the different levels. What are sufficient sample sizes for accurate estimation? The second problem is the normality assumption of the level‐2 error distribution. When one wants to conduct tests of significance, the errors need to be normally distributed. What happens when this is not the case? In this paper, simulation studies are used to answer both questions. With respect to the first question, the results show that a small sample size at level two (meaning a sample of 50 or less) leads to biased estimates of the second‐level standard errors. The answer to the second question is that only the standard errors for the random effects at the second level are highly inaccurate if the distributional assumptions concerning the level‐2 errors are not fulfilled. Robust standard errors turn out to be more reliable than the asymptotic standard errors based on maximum likelihood.     

三维激光扫描仪在地形测量中的应用

文章从三维激光扫描仪在测量中的作用入手,详细介绍了三维激光扫描仪的工作原理和三维激光扫描系统,并说明了三维激光扫描仪配套三维数据处理软件的功能,着重介绍了三维数据的处理方法:点云的连接、特征线的提取、对地物的三维建模(TIN建模),在TIN建模中,介绍了狄洛尼三角网的构网方法。     

Preventing HIV in injection drug users: exploring the tradeoffs between interventions

Injection drug users (IDUs) transmit the human immunodeficiency virus (HIV) via both needle sharing and sex. Available interventions for this population have varying costs and effectiveness and focus on different risk behaviors. In this analysis, we look at two interventions. One is inexpensive, broad-based and provides modest risk reductions (street outreach (SO)); the other is narrowly focused, expensive and relatively effective (methadone maintenance). This analysis explores the effects of population risk behavior, intervention effectiveness, intervention costs, and decision constraints when allocating funds between these two interventions to maximize effectiveness. We develop a model of the spread of HIV, dividing IDUs into susceptibles (uninfected) and infectives, and separately portraying sex and injection risk. We simulate the epidemic in New York City for time periods from the mid-1980s to the early 1990s, and incorporate the behavioral effects of two interventions performed singly or in combination to find the allocation that maximizes the number of infections averted in the IDUs and their noninjecting sex partners, assuming interventions have increasing marginal costs. We find that the optimal allocation nearly always involves spending the maximum allowable amount on SO. This result is largely insensitive to variations in risk parameters, intervention efficacy, or cost. The model's structure, however, makes clear that many factors contribute to this insensitivity, namely the scope of the interventions, the dual drug/sex nature of HIV risk in the population, the asymmetry of sexual risk for men and women, and the potential benefits to nonIDUs.     

在工程项目管理中实施过程管理的研究

传统的建设过程彼此分裂的特性，严重影响着工程建设的效率性和有效性。本文结合过程管理的思想，分析工程项目实施和管理的系统过程，探讨工程项目管理过程的识别与建立，并在此基础上提出建立工程项目管理的过程模型的方法。     

我国水上石油物流系统优化问题探讨

随着我国石油需求量及进出口量的不断增长,研究我国水上石油物流系统的优化问题日益重要,本文首先分析了水上石油物流系统研究的必要性,对国内外关于石油物流系统研究现状进行了评述,提出了我国水上石油物流系统优化问题的研究思路和方法.     

基于遗传算法的军用集装箱装载优化

以军用集装箱装载为研究对象，在考虑实际应用中的一些约束条件下，构造了军用物资的装载优化模型，提出了一种军用集装箱三维装载的遗传算法。该算法考虑了货物放置方向、装载客积、装载质量及装载重心等约束条件。最后对一个案例进行了计算，验证了该模型的有效性，并且利用3ds max得到了装载方案的三维图。     

具纳米孔的过渡金属三维配位聚合物的合成与储气性能研究进展

综述了具有纳米孔道的过渡金属三维配位聚合物的合成方法,主要是通过选择合适的配体来增大孔道和提高配合物的热稳定性,达到增强储气性能的目的。     

《被遗弃的韦瑟罗尔奶奶》的创作手法

现代美国小说家波特的经典作品《被遗弃的韦瑟罗尔奶奶》中的意识流和互文性这些现代派文学的创作手法,不仅使人物形象更加真实、生动,而且使主题意义也得到了进一步的凸现和深化。     

我国出口企业自主创新能力不足的原因解析

我国成为世界第三大贸易国是由外资企业推动的。本文认为。我国需要内、外资企业两方面的支持，才能由制造业大国走向制造业强国；内资企业存在的主要问题在于技术引进了，吸收消化能力却未同步提高，缺乏自主知识产权导致高新技术产品出口效益低下等。