On Exact K-optimal Designs Minimizing the Condition Number

A new design criterion based on the condition number of an information matrix is proposed to construct optimal designs for linear models, and the resulting designs are called K-optimal designs. The relationship between exact and asymptotic K-optimal designs is derived. Since it is usually hard to find exact optimal designs analytically, we apply a simulated annealing algorithm to compute K-optimal design points on continuous design spaces. Specific issues are addressed to make the algorithm effective. Through exact designs, we can examine some properties of the K-optimal designs such as symmetry and the number of support points. Examples and results are given for polynomial regression models and linear models for fractional factorial experiments. In addition, K-optimal designs are compared with A-optimal and D-optimal designs for polynomial regression models, showing that K-optimal designs are quite similar to A-optimal designs.     

A note on non-negative continuous time processes

Summary.  Recently there has been much work on developing models that are suitable for analysing the volatility of a continuous time process. One general approach is to define a volatility process as the convolution of a kernel with a non-decreasing Lévy process, which is non-negative if the kernel is non-negative. Within the framework of time continuous autoregressive moving average (CARMA) processes, we derive a necessary and sufficient condition for the kernel to be non-negative. This condition is in terms of the Laplace transform of the CARMA kernel, which has a simple form. We discuss some useful consequences of this result and delineate the parametric region of stationarity and non-negative kernel for some lower order CARMA models.     

《函数迭代与一维动力系统》中一个定理的注记

指出文献<函数迭代与一维动力系统>中关于定理19.6的证明的错误部分,并给出此部分的证明.     

可持续发展与西部大开发

本文联系实际,重点阐述了可持续发展理论的由来及其内涵,指出西部大开发必须走可持续发展道路,西部各省市自治区必须高举十六大旗帜,实施可持续发展战略,西部地区才能跳出贫困怪圈,全面建设小康社会,加快推进社会主义现代化建设。     

Impact of students’ behavior on continuous assessment in Higher Education

The aim of this study is to analyze students’ academic results following the introduction of a continuous assessment system in Higher Education. This study examines a large sample that consists of third-year students’ grades across nine subjects in the Bachelor of Business Administration program at the University of Castilla-La Mancha (Spain). Specifically, this paper studies the relations among three types of grades (i.e. final exam grades (FEGs), continuous assessment activities grades (excluding the final exam) and GAGs, which are calculated as the weighted averages of the FEGs and the continuous assessment activities grades) and the influence of the number of students who actively participate in a subject and the date of the final exam on students’ grades. Generally, this study reveals a positive effect of continuous assessment activities on students’ academic success. Furthermore, there is a statistically significant positive relation between the number of students who actively follow a subject and their GAGs. Finally, the earlier the students completed the final exam, the higher their grades were on this exam.     

International surveys of educational achievement: how robust are the findings?

Summary.  International surveys of educational achievement and functional literacy are increasingly common. We consider two aspects of the robustness of their results. First, we compare results from four surveys: the Trends in International Maths and Science Study, the Programme for International Student Assessment, the Progress in International Reading Literacy Study and the International Adult Literacy Survey. This contrasts with the standard approach which is to analyse just one survey in isolation. Second, we investigate whether results are sensitive to the choice of item response model that is used by survey organizers to aggregate respondents' answers into a single score. In both cases we focus on countries' average scores, the within-country differences in scores and on the association between the two.     

Determinants of obesity: The case of Germany

Obesity now has the rank of a global epidemic, but finds its severest expression in the economically advanced parts of the world. This study offers an interdisciplinary analysis of obesity in Germany, including socio-economic factors. In comparison to related studies, it uses a continuous BMI variable as well as an improved empirical design. The coefficient of the term for sport activities is significantly negative, and the coefficient for the age terms are significantly positive. The results for the income variable are ambiguous. Cigarette consumption does not indicate negative relationships with individual BMI-levels. No evidence was found for systematic differences in BMI between the eastern and western regions in reunified Germany.     

CCEW对16Mn钢焊接接头组织和力学性能的影响

本文利用ＣＣＥＷ技术，采用直长型焊条（ＬＣＣＥＪ５０７）对１６Ｍｎ钢进行双面焊和单面焊双面成形对接，分析焊缝宏观质量和缺陷，检验显微组织，测试其力学性能。结果表明：接头外观质量良好，焊缝的显微组织正常，力学性能符合国际。对１２ｍｍ厚的板材，可以实现预留间隙双面焊一次焊透，省去开坡口工序，从而提高生产效率，值得推广应用。     

两种不同类型随机变量混合函数的分布

文章主要讨论了由两种不同类型随机变量构成一个随机变量函数的分布,并着重给出了相互独立的一个连续型随机变量和一个离散型随机变量相乘构成的随机变量函数的分布的计算方法。     

Numerical Method for Reliability Analysis of Phased-Mission System Using Markov Chains

This article presents a numerical method for solving continuous time Markov chain (CTMC) model for reliability evaluation of phased-mission system. The method generates infinitesimal matrix based on the statistical independence of subsystem failure and repair process. The infinitesimal generator matrix is stored by the use of sparse matrix-compressed storage schemes, and the transient solution of the CTMC model is obtained by using three methods including the uniformization method, forward Euler method, and Runge-Kutta method, which take advantage of the sparseness of the infinitesimal generator matrix. An example PMS is used to compare the preconditioning methods for sparse matrix and numerical methods. Experiment results show that compressed row storage scheme (CRS) saves more storage than other storage formats, and uniformization method combined with CRS achieves the best efficiency and accuracy.