Pair Chart Test for an Early Survival Difference

The log-rank test is commonly used in comparing survival distributions between treatment and control groups in clinical trials. However, in many studies, the treatment is only effective at the early stage of the trial. Especially when the two survival curves cross, the log-rank test has a low statistical power to show the survival difference. We propose a test statistic for detecting such an early difference between the two treatment arms. The new test has an intuitive geometric interpretation based on a pair chart and is shown to have more power than the log-rank test when the treatment effect only appears in the early phase of the study. This advantage is evaluated for finite sample sizes in simulation studies. Finally, the proposed method is illustrated with a real data example of patients with gastric cancer.     

Linear Signed-Rank Tests for Paired Survival Data Subject to a Common Censoring Time

In this paper we consider rank-based tests for paired survival data, in which pair members are subject to the same right censoring time. Linear signed-rank tests have already been developed for the two-treatment problem in which pair members receive the opposite treatments. Assuming a bivariate accelerated failure time model, we extend this class of linear signed-rank tests to the case of multiple covariates, making this methodology applicable to more complicated experimental designs. These tests can be reformulated as weighted sums of contigency table measures, giving an alternative method of computation and intuitive view of how these tests work. A simulation study of their small-sample performance relative to other tests demonstrates that the linear signed-rank tests have greater power in cases of moderately to highly correlated data.     

Modelling Aggregation on the Large Scale and Regularity on the Small Scale in Spatial Point Pattern Datasets

We consider a dependent thinning of a regular point process with the aim of obtaining aggregation on the large scale and regularity on the small scale in the resulting target point process of retained points. Various parametric models for the underlying processes are suggested and the properties of the target point process are studied. Simulation and inference procedures are discussed when a realization of the target point process is observed, depending on whether the thinned points are observed or not. The paper extends previous work by Dietrich Stoyan on interrupted point processes.     

滚珠花键副轮齿修形的有限元法研究

滚珠花键副是一种新型移动副，用于低阻力传递大扭矩。在扭矩作用下，花键副轮齿将发生变形，从而引起在不同齿之间以及在同一齿的齿宽方向载荷分布不均，造成局部应力集中，降低花键副寿命。文中利用有限元法对花键副轮齿在载荷作用下的变形进行研究，提出消除载荷集中的轮齿修形方法。     

利用贝尔测量的高效量子密钥分配协议

提出了一个建立在EPR关联之上的量子密钥分配协议。通信双方通过交换量子位和贝尔测量建立起共享的密钥,没有第三方可以窃取密钥而不被发现,因此该协议是安全的;该协议也是高效的,除了少数用作检错的量子位之外,所有的量子位都对密钥有贡献。     

城市立体交叉方案的集对分析模型研究

基于集对分析理论,提出了城市立体交叉设计方案的评价模型,运用层次分析法建立了各评价指标的层次结构,确定其权重,消除了专家评定确定权重时的人为因素干扰,提高了设计方案评价的可信度,为城市立体交叉设计方案的选优提供了简单、实用的评价方法.     

Analyses of spatial patterns and population processes of clonal plants

The nonrandom spatial structure of terrestrial plants is formed by ecological interactions and reproduction with a limited dispersal range, and in turn this may strongly affect population dynamics and population genetics. The traditional method of modelling in population ecology is either to neglect spatial pattern (e.g. in transition matrix models) or to do straightforward computer simulation. We review here three analytical mothods to deal with plant populations in a lattice-structured habitat, which propagate both by seeds that scatter over the whole habitat and by vegetative reproduction (producing runners, rhizomes, etc.) to neighboring vacant sites. [1]Dynamics of global and local densities: Dynamical equations of population density considering nearest-neighbor correlation (spatial clumping) are developed as the joint dynamics of global average density and local density (comparable to mean crowding) based onpair approximation. If there is a linear trade-off between seed production and vegetative reproduction, the equilibrium abundance of the population may be maximized by engaging both means of reproduction. This result is accurately predicted by the pair approximation method, but not by mean-field approximation (neglect of spatial structure). [2]Cluster size distributions: Using global and local densities obtained by pair approximation, we predicted cluster size distribution, i.e. the number of clusters of occupied sites of various sizes. [3]Clonal identity probability decreasing with distance: Multi-locus measurement of allozymes or other neutral molecular markers tells us whether or not a given pair of individuals belong to the same clone. From the pattern of clonal identity probability decreasing with the distance between ramets, we can estimate the relative importance of two modes of reproduction: vegetative propagation and sexual seed production.     

浅析机械工程中的虚约束

分析机械中常见的几种虚约束,说明其重要作用;由于较高的几何条件、加工和装配精度的要求,提出合理设计机构减少虚约束的方法。     

流管模型与奇异抑制

本文介绍流管模型及其最新发展,并在流管模型的基础上,研究了奇异抑制因子λ随流管半径r_o变化的规律。假定u夸克与s夸克的流质量分别为m_u=o与m_s=0.2GeV,利用λ的实验值,我们得到流管半径r_o=(0.48±0.04)fm,这个结果同用完全不同的方法所确定的r_o值符合得很好。     

基于集对分析理论确定贷款企业的信用

针对目前建于概率论基础上的企业信用评估模型 ,把不确定性问题硬性转化为确定性进行分析的缺陷 ,将一种用于解决不确定性问题的新型理论——集对分析运用于企业信用评估 ,建立了评估模型 ,并进行应用举例 ,以图探索一种更为有效的企业信用评估方法