Estimating failure time distribution and its parameters based on intermediate data from a Wiener degradation model

Instead of measuring a Wiener degradation or performance process at predetermined time points to track degradation or performance of a product for estimating its lifetime, we propose to obtain the first‐passage times of the process over certain nonfailure thresholds. Based on only these intermediate data, we obtain the uniformly minimum variance unbiased estimator and uniformly most accurate confidence interval for the mean lifetime. For estimating the lifetime distribution function, we propose a modified maximum likelihood estimator and a new estimator and prove that, by increasing the sample size of the intermediate data, these estimators and the above‐mentioned estimator of the mean lifetime can achieve the same levels of accuracy as the estimators assuming one has failure times. Thus, our method of using only intermediate data is useful for highly reliable products when their failure times are difficult to obtain. Furthermore, we show that the proposed new estimator of the lifetime distribution function is more accurate than the standard and modified maximum likelihood estimators. We also obtain approximate confidence intervals for the lifetime distribution function and its percentiles. Finally, we use light‐emitting diodes as an example to illustrate our method and demonstrate how to validate the Wiener assumption during the testing. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Optimal control of a production process subject to AOQL constraint

A production process which exhibits a decreasing pattern in the mean quality during the course of production is considered. A lower limit is specified for the quality characteristic of interest, and an item is classified as defective if its quality characteristic is below this lower limit. The major concern of the manufacturer is the average outgoing quality (AOQ). Hence, the process has to be adjusted after a time to avoid producing a large proportion of defective items due to deteriorating quality. To meet consumer specifications, an average outgoing quality limit (AOQL) is specified. A process-control scheme is developed in which decisions as to the upper and lower limit of the process mean are made based upon the choice of an AOQL. We discuss the decision problem of selecting the starting level of the process mean, and the level at which the process mean should be adjusted back to the starting level, so that the AOQ is not larger than AOQL. We consider a cost model which includes a fixed cost for adjustment, and a production cost which is assumed to be a function of the quality level. Due to the complexity of the model, a search procedure is used to find the optimal solution. In addition, an approximate solution which requires only simple calculations is developed, and is shown to be very effective in finding near-optimal solutions.     

论东北战场1947年夏季攻势

全国解放战争时期,东北战场最先揭开战略反攻序幕,民主联军从吉林以东、长春以西、郑家屯以北、梅河口以南及辽南、热西、冀东等七个重点方向上同时发动进攻,其势如潮涌,纵横关内外。大战结果,民主联军于战略上贯通南北满,一举扭转东北战局,开始掌握战场主动权,迫使东北国民党军转入战略防御,有力地支援了关内战场作战。     

Determination of burn‐in parameters and residual life for highly reliable products

Today, many products are designed and manufactured to function for a long period of time before they fail. Determining product reliability is a great challenge to manufacturers of highly reliable products with only a relatively short period of time available for internal life testing. In particular, it may be difficult to determine optimal burn‐in parameters and characterize the residual life distribution. A promising alternative is to use data on a quality characteristic (QC) whose degradation over time can be related to product failure. Typically, product failure corresponds to the first passage time of the degradation path beyond a critical value. If degradation paths can be modeled properly, one can predict failure time and determine the life distribution without actually observing failures. In this paper, we first use a Wiener process to describe the continuous degradation path of the quality characteristic of the product. A Wiener process allows nonconstant variance and nonzero correlation among data collected at different time points. We propose a decision rule for classifying a unit as normal or weak, and give an economic model for determining the optimal termination time and other parameters of a burn‐in test. Next, we propose a method for assessing the product's lifetime distribution of the passed units. The proposed methodologies are all based only on the product's initial observed degradation data. Finally, an example of an electronic product, namely contact image scanner (CIS), is used to illustrate the proposed procedure. © 2002 Wiley Periodicals, Inc. Naval Research Logistics, 2003     

柔性制造单元监控系统总体设计与研究

本文就监控与诊断技术的发展现状与趋势进行了综述。设计并研制FMS/FMC监控系统CMFDS,给出系统的组成、功能、配制、硬软件系统、总体结构及系统的技术特点。在加工中心、FMS上的实验表明了该系统良好的通用性和简洁性,体现了集成化、智能化现代监控技术发展的趋势。     

包带式星箭紧锁预紧力分析

根据星箭连接处受力情况及紧锁装置的特点,分析了星箭连接处发生松动的可能性,导出了星箭紧锁所需包带预紧力计算公式,提出了解决包带应力分布不均匀的方法。通过与两种型号的实验结果对比,证明了本文分析方法的正确性和计算公式的可信性。本文所得结论为包带式星箭紧锁结构设计提供了依据。     

面向 MPP Fortran 的程序自动并行化初探

ＭＰＰＦｏｒｔｒａｎ是由Ｃｒａｙ公司推出的一种较有代表性的数据并行语言,本文首先介绍了ＭＰＰＦｏｒｔｒａｎ的主要特点,然后,以该语言为例,对面向ＭＰＰ系统程序自动并行化的主要内容进行了初步的探讨。     

基于神经元的动态系统模糊关系模型及其学习算法

本文直接针对模糊集,提出了三种基于模糊集运算的逻辑神经元,即ＡＮＤ．ＯＲ和ＡＮＤ／ＤＲ．基于上述神经元,提出了一种应用于动态系统建模的实用的模糊关系网络模型,通过一个简单实例,证实了上述模型建模算法的学习能力和快速计算能力。     

矩阵形式的快速沃尔什变换法

本文用矩阵形式,建立系统地快速沃尔什变换(FWT)运算方法,它应用了二进制顺序Walsh-paley,列率顺序Walsh-Kaczmarz和Kronecker顺序Walsh-Hadamard变换。由文献可知,某些FWT运算是借助于一定的矩阵编制计算程序的新方法,这样的变换法,可作为数字计算机的辅助设备。     

用沃尔什变换解差分方程

本文证明了关于二进时移函数和非二进时移函数的walsh变换的几个定理。同时论证了这两种变换之间的关系。用walsh变换方法,讨论了线性、常系数差分方程在列率(Sequency)域上的解法,文章给出解的一般表达式。