Exact solutions to the Behrens–Fisher Problem: Asymptotically optimal and finite sample efficient choice among

The problem of testing the equality of two normal means when variances are not known is called the Behrens–Fisher Problem. This problem has three known exact solutions, due, respectively, to Chapman, to Prokof’yev and Shishkin, and to Dudewicz and Ahmed. Each procedure has level alpha and power beta when the means differ by a given amount delta, both set by the experimenter. No single-sample statistical procedures can make this guarantee. The most recent of the three procedures, that of Dudewicz and Ahmed, is asymptotically optimal. We review the procedures, and then compare them with respect to both asymptotic efficiency and also (using simulation) in finite samples. Of these exact procedures, based on finite-sample comparisons the Dudewicz–Ahmed procedure is recommended for practical use.     

缝洞型油藏三重介质数值试井模型

基于多重介质渗流的概念模型和数学模型，建立了缝洞型油藏三重介质数值试井模型。该模型是一般三重介质模型的推广，可以很好地反映缝洞型油藏的各种非均质特征，能灵活处理油藏中各种断层和边界，且允许产量的任意变化。采用基于积分的有限差分方法求解，得到三重介质油藏试井响应曲线，分析了其渗流规律：三重介质不同的渗透性致使在半对数曲线上出现两个台阶、导数曲线上出现两个下凹。分别计算了层状非均质地层模型、直线断层模型、变产量模型、复合模型等几个复杂模型的试井响应。该数值试井模型可以进一步考虑缝洞型油藏中具体的裂缝和溶洞，进而推广至缝洞型油藏的两相流试井。     

A Note on Screening Regression Equations

Consider developing a regression model in a context where substantive theory is weak. To focus on an extreme case, suppose that in fact there is no relationship between the dependent variable and the explanatory variables. Even so, if there are many explanatory variables, the R ² will be high. If explanatory variables with small t statistics are dropped and the equation refitted, the R ² will stay high and the overall F will become highly significant. This is demonstrated by simulation and by asymptotic calculation.     

S–S method for stochastically ordered multinomial populations with missing data

Stochastic ordering is a useful concept in order restricted inferences. In this paper, we propose a new estimation technique for the parameters in two multinomial populations under stochastic orderings when missing data are present. In comparison with traditional maximum likelihood estimation method, our new method can guarantee the uniqueness of the maximum of the likelihood function. Furthermore, it does not depend on the choice of initial values for the parameters in contrast to the EM algorithm. Finally, we give the asymptotic distributions of the likelihood ratio statistics based on the new estimation method.     

组件技术在分布式测试系统与测试工具集成中的应用

设计了一种分布式测试系统软件体系结构,对测试过程及测试工具进行统一管理.通过组件对象模型技术建立了分布式软件测试环境,并在组件的基础上开发了用于第三方测试工具集成的API接口及配置工具.当集成新的测试工具时,只需利用API接口开发工具组件及修改配置文件,测试平台完全不用修改,系统具有二次开发能力.     

老年肺心病患者高危死亡因素分析

目的探讨老年肺心病患者死亡的高危因素.方法回顾性分析198例住院老年肺心病患者临床资料,并进行相关因素分析.结果1.死亡组平均年龄、病程、吸烟指数、体重指数(BMI)、入院时氧合指数(PaO2/FiO2)、二氧化碳分压(PaCO2)、pH、ls用力呼气容积占预计值百分比(FEV1%)和FEV1/用力肺活量(FEV1/FVC)与缓解出院组比较,具有显著性差异;2.缓解出院组以单纯性酸碱失调为主,且以呼酸为多,而死亡组主要表现为混合性酸碱失调.结论测定相关指标,加强监护与治疗,对老年肺心病患者预后至关重要.     

The Assessment of Radiation Exposures in Native American Communities from Nuclear Weapons Testing in Nevada

Native Americans residing in a broad region downwind from the Nevada Test Site during the 1950s and 1960s received significant radiation exposures from nuclear weapons testing. Because of differences in diet, activities, and housing, their radiation exposures are only very imperfectly represented in the Department of Energy dose reconstructions. There are important missing pathways, including exposures to radioactive iodine from eating small game. The dose reconstruction model assumptions about cattle feeding practices across a year are unlikely to apply to the native communities as are other model assumptions about diet. Thus exposures from drinking milk and eating vegetables have not yet been properly estimated for these communities. Through consultations with members of the affected communities, these deficiencies could be corrected and the dose reconstruction extended to Native Americans. An illustration of the feasibility of extending the dose reconstruction is provided by a sample calculation to estimate radiation exposures to the thyroid from eating radio-iodine-contaminated rabbit thyroids after the Sedan test. The illustration is continued with a discussion of how the calculation results may be used to make estimates for other tests and other locations.     

在数控车床实习中进行技能测试的探讨

从数控车床实习教学的特点出发,通过对目前在教学中存在的一些不足的分析,提出数控车实习教学改革应该以实际操作为重点,通过对教学内容和教学方法的改进和优化,增加技能测试环节,达到改善教学效果。     

焦虑对体育高考考生的影响

通过问卷调查法对参加体育高考考生的考前产生焦虑的原因作了初步研究，分析了运动水平、考生离考试时间的远近、考生考试的专项、考生对成绩的归因以及考生是否懂得自我调节与焦虑的关系，并提出了克服体育高考考生焦虑的调控方法。为教练员及考生的心理训练提供参考建议。