AN EXPERIMENTAL INVESTIGATION OF THE GROWTH OF SMALL CORNER FATIGUE CRACKS IN ALUMINIUM 6061-T651

Results of an experimental investigation of the fatigue growth of small corner cracks emanating from small flaws are presented. Growth-arrest behaviour was observed, and increases in crack length during growth periods were of the order of the transverse grain size. For the test material, the corner crack front intersects, on average, only three–six grains in the small crack regime monitored, so only a small number of constrained, interior grains is encountered. It is suggested that the presence of partially constrained surface grains may contribute to the 'anomalous' growth behaviour which has been observed by a number of investigators.
The crack growth histories of the test data presented exhibit considerable scatter. It is shown that a Student's t -test can be used to estimate confidence intervals in order to provide a measure of the observed scatter. The variation in confidence intervals in the transition from small to long fatigue crack growth is discussed.     

电子学档在计算机基础课程教学中的应用

对大学计算机基础课程教学活动中引入电子学档来辅助教学,从而构建一种基于电子学档的信息化教学活动进行了探讨。并以《网页设计基础》课程的教学活动为案例,分析了在计算机基础课程教学中引入电子学档的可行性、必要性。最后,使用平均数差异显著性T检验来测量两组学生的学习情况,对使用电子学档提高学生的学习效率进行了量化评价。     

方差分析用于农宅供热能耗影响因素研究

北方农宅供热能耗影响因素的研究可为农宅供热节能改造、国家节能政策和相关规范的制定提供有力的依据.影响农宅供热能耗的因素种类繁多,并且影响程度不同.本文运用SPSS19.0软件,采用独立样本t检验、单因素方差分析以及控制供暖系统组成形式下的双因素方差分析,进行农宅供热能耗影响因素的筛选及其影响程度的深度剖析.初步统计研究结果表明在0.05显著性水平上的农宅供热能耗主要影响因素为冬季炊事频率、所在地区、家庭常住人口数和供热系统组成形式.     

砚瓦川流域1981-2012年降水特性及趋势分析

我国西北地区流域降水特性及趋势对当地雨养农业及水土流失有重要的影响。选用1981-2012年马莲河砚瓦川流域的降水量资料,以集中度、变差系数、逐年距平、M-K非参数统计检验以及滑动t检验等方法分析了降水年内、年际、突变变化特征。结果表明:砚瓦川流域降水量年内分配不均,集中度较高,降水多分布在7、8月;年际变化较小,流域多年平均降水量为523.0mm,变差系数约为0.2。M-K非参数统计检验表明,整体变化趋势并不明显,与距平和变差系数分析的结果一致;滑动t检验和M-K检验的结果显示年降雨量序列没有出现突变值。     

Multiple change-point detection with a genetic algorithm

 A common change-point problem is considered where the population mean of a random variable is suspected of undergoing abrupt changes in course of a time series. It is usual in practice that no information on positions or number of such shifts is available beforehand. Finding the change points, i.e. the positions of the shifts, in such a situation is a delicate statistical problem since any considered sample may actually represent a mixture of two or more populations where values from both sides of a yet unrecognized change point are unconsciously assembled. If this is the case, underlying assumptions of an employed statistical two-sample test are usually violated. Consequently, no definite decision should be based on just one value of the test statistic. Such a value is rather, as a precaution, to be regarded as an only approximate indicator of the quality of a hypothesis about change-point positions. Given these conclusions, it is found imperative to treat the problem of multiple change-point detection as one of global optimization. A cost function is constructed in such a manner that the change-point configuration yielding the global optimum is compliant with statistical-theoretical requirements to the utmost extent. The used advanced optimization tool, a genetic algorithm, is both efficient – as it takes advantage of the information about promising change-point positions encountered in previously investigated trial configurations – and flexible (as it is open to any modification of the change-point configuration at any time). Experiments using numerical simulation confirm adequate performance of the method in an application where a common change-point detection procedure based on Student's two-sample t-test is used to detect an arbitrary number of shifts in the mean of a normally distributed random variable.     

应用便携式快速水质检测仪测定废水中的六价铬

采用二苯碳酰二肼分光光度法利用便携式快速水质检测仪测定废水中的六价铬,具有方便快速的特点,通过数理统计t检验发现,与国标方法二苯碳酰二肼分光光度法(GB7467-87)相比,没有显著性差异。     

基于词频统计的中文分词的研究

论文介绍了一个基于词频统计的中文分词系统的设计和实现。通过这个系统,可以将输入的连续汉字串进行分词处理,输出分割后的汉语词串,一般是二字词串,并得到一个词典。词典中不重复地存储了每次处理中得到的词语,以及这些词语出现的频率。这个系统选用了三种统计原理分别进行统计:互信息,N元统计模型和t-测试。文中还对这三种原理的处理结果进行了比较,以分析各种统计原理的统计特点,以及各自所适合的应用场合。     

基于像元与对象分类的景观指数差异性分析

景观指数分析是进行遥感监测土地利用及变化空间格局的重要方法之一,而因为遥感分类方法的不同,所计算出的同一景观指数所揭示的土地变化模式可能出现较大差异。以北京市密云县为研究区,对影像分别进行了面向对象分类与基于像元的监督分类,并对两种分类进行景观指数计算,利用配对样本t检验方法对各景观指数进行了差异显著性分析。分析结果显示地类面积比例(PLAND)和最大斑块指数(LPI)在两种分类方法之间差异不显著;边缘密度(ED)略有显著差异性;而斑块数量(NP)、斑块面积平均值(AREA_MN)、聚合度(AI)与周长面积分维数(PAFRAC)在两种分类方法之间差异显著。     

计量保证方案中的测量过程控制

本文对计量保证方案（MAP）的核心──测量过程的统计控制进行研究．探讨测量过程的主要控制技术：t检验和F检验，把t分布和F分布的分位数的计算问题统一地归结为了1/2整数倍贝塔分布的分位数计算．并设计编制计算程序，快速、系统地算得任意自由度t分布和F分布的分位数，为测量过程的控制和计量保证方案的实施提供了一个有效的数据处理方法．     

基于STM32的远程脉象复放系统的设计

为了实现远程脉象诊断,设计了一套远程脉象复放系统。针对当前脉象复放装置反应慢、控制复杂的不足,设计了新型的机械与液路相结合的脉象复放装置;针对复放脉象不能根据"浮、中、沉"不同压力产生变化的缺陷,设计了智能压力反馈模块,运用自适应逆控制算法对输出误差进行校正。设计实验对比复放脉象和采集脉象,分析两者相关性并对脉搏波特征参数进行t-检验分析。结果表明:复放波形和采集波形之间脉搏波特征参数无显著性差异,且2种波形相关系数大于0.91,具有显著相关性。邀请3名老中医对系统进行盲测,正确率均在93%以上,证明该系统可以准确实现远程条件下脉象的复放,可应用于中医远程脉诊及中医教学领域。