钢管相邻缺陷漏磁场相互影响的分析

实际工况中的管道缺陷是非常复杂的,用物理试验的方法研究各种缺陷漏磁场的变化规律有一定的难度。该文针对油气管道常用的钢管缺陷产生的漏磁场建立了三维有限元模型,采用有限元方法计算了几种相邻缺陷的漏磁场模型,给出了计算结果,并分析了各种相邻缺陷对漏磁场信号的影响。结果表明当相邻缺陷的中心线与磁场方向平行时,对缺陷漏磁信号的影响最小;组合型的缺陷对漏磁信号的影响最大。     

Finite mixture models with concomitant information: assessing diagnostic criteria for diabetes

The World Health Organization (WHO) diagnostic criteria for diabetes mellitus were determined in part by evidence that in some populations the plasma glucose level 2 h after an oral glucose load is a mixture of two distinct distributions. We present a finite mixture model that allows the two component densities to be generalized linear models and the mixture probability to be a logistic regression model. The model allows us to estimate the prevalence of diabetes and sensitivity and specificity of the diagnostic criteria as a function of covariates and to estimate them in the absence of an external standard. Sensitivity is the probability that a test indicates disease conditionally on disease being present. Specificity is the probability that a test indicates no disease conditionally on no disease being present. We obtained maximum likelihood estimates via the EM algorithm and derived the standard errors from the information matrix and by the bootstrap. In the application to data from the diabetes in Egypt project a two-component mixture model fits well and the two components are interpreted as normal and diabetes. The means and variances are similar to results found in other populations. The minimum misclassification cutpoints decrease with age, are lower in urban areas and are higher in rural areas than the 200 mg dl^-1 cutpoint recommended by the WHO. These differences are modest and our results generally support the WHO criterion. Our methods allow the direct inclusion of concomitant data whereas past analyses were based on partitioning the data.     

An integrated production and inventory model for a whole manufacturing supply chain involving reverse logistics with finite horizon period

This paper proposes a model and solution method for coordinating integrated production and inventory cycles in a whole manufacturing supply chain involving reverse logistics for multiple items with finite horizon period. A whole manufacturing supply chain involving reverse logistic consists of tier-2 suppliers supplying raw materials to tier-1 suppliers, tier-1 suppliers producing parts, a manufacturer which manufactures and assembles parts from tier-1 suppliers into finished products, distributors distributing finished products to retailers, retailers selling products to end customers and a third party which collects the used finished products from end customers, dissembles collected products into parts, and feed the parts back to the supply chain. In this system, we consider a finite horizon period. A mathematical model for representing the behaviors of the system is developed. Solution methods based on decentralized and a combination of decentralized and centralized decision making process, referred to as the semi-centralized decision making process, are proposed to solve the model while the centralized decision making process is solved by a mixed integer nonlinear programming method. A numerical example is used to demonstrate the model and the solutions based on the three types of the coordination.     

北宋书序作者所选择的传播因素分析

书序具有重要的传播作用,以北宋诗文集序为对象考察,书序作者在选择推动传播的因素时,对作品艺术性、知识性等文本因素的关注不如对作家身份、生平轶事等非文本因素普遍。其中原因,从书序作者的操作层面来看,是因为在书序中进行文艺批评是很难把握的;从面对读者的传播效果层面来分析,是因为非文本因素较之文本相关的评论因素可以产生显著的传播效果。于是,非文本因素在文学传播中变成了一位无形的操纵者,虽然它不是长远的传播之道,但却常常起着奇妙的传播作用,从而给书序这一文体增加活力。     

冷却剂参数对铣槽喷管低周疲劳寿命的影响

采用有限体积流固耦合计算方法、非线性有限元热结构耦合分析方法和局部应变法研究大面积比铣槽喷管三维再生冷却槽道在循环工作条件下的热结构变形与低周疲劳寿命,并对比分析了冷却剂质量流量与入口温度对铣槽喷管疲劳使用寿命的影响。计算结果表明,铣槽喷管热结构响应呈现复杂的三维效应,应变较大位置主要分布在与肋连接的内衬区域,喷管中部的残余应变量最大;冷却槽道低周疲劳寿命分布和热结构响应基本一致,最小寿命位于喷管中部与肋相连的内衬区域燃气侧;随冷却剂质量流量增加,铣槽喷管低周疲劳寿命不断提高;随冷却剂入口温度增加喷管尾部低周疲劳寿命值不断降低,而喷管中前部的低周疲劳寿命值却不断提高,当冷却剂入口温度为280K左右时,本文的铣槽喷管总体使用寿命达到最大。      

肾叶唐松草微量元素和氨基酸的测定

本文利用原子吸收光谱法测定了中药肾叶唐松草中所含14种微量元素,利用氨基酸分析仪对它所含的氨基酸进行了鉴定及含量测定,并对根、茎、叶等不同部位的微量元素和氨基酸含量分别做了比较。     

数值解法中的单元形状函数技巧

本文介绍从一组互不相关的函数中推导数值法中单元形状函数的简便而有效的算法,以特定的一维内插方法导出各种二维、三维的内插方法,它们对奇异性的模拟是有益的;为了适用于延伸到无限远的单元,假设形状函数类似于Lagrange多项式,但包含了一个按指数衰减的项。     

大熊猫主食竹种微量元素研究

用原子吸收分光光度法测定了卧龙自然保护区大熊猫主食竹种——冷箭竹(Bashania fangiana)、拐棍竹(Fargesia robusta)、华西箭竹(Fargesia nit-ida)、峨眉玉山竹(Yushaia chungii)的叶、笋——幼竹、一年杆、二年杆兵208例中的 Cu、Zn、Mn、Fe、Ca、Mg、K 等七种元素含量.找到了微量元素含量与竹类、竹龄、竹株部位、竹的生长环境(海拔高度、季节)以及与大熊猫食性等的关系。     

A modified likelihood ratio test for homogeneity in finite mixture models

Testing for homogeneity in finite mixture models has been investigated by many researchers. The asymptotic null distribution of the likelihood ratio test (LRT) is very complex and difficult to use in practice. We propose a modified LRT for homogeneity in finite mixture models with a general parametric kernel distribution family. The modified LRT has a χ-type of null limiting distribution and is asymptotically most powerful under local alternatives. Simulations show that it performs better than competing tests. They also reveal that the limiting distribution with some adjustment can satisfactorily approximate the quantiles of the test statistic, even for moderate sample sizes.     

Mixture Models in View of Evidential Analysis

In some practical inferential situations, it is needed to mix some finite sort of distributions to fit an adequate model for multi-modal observations. In this article, using evidential analysis, we determine the sample size for supporting hypotheses about the mixture proportion and homogeneity. An Expectation-Maximization algorithm is used to evaluate the probability of strong misleading evidence based on modified likelihood ratio as a measure of support.