A nonparametric Bayes approach to decide system burn-in time

Burn-in is the preconditioning of assemblies and the accelerated power-on tests performed on equipment subject to temperature, vibration, voltage, radiation, load, corrosion, and humidity. Burn-in techniques are widely applied to integrated circuits (IC) to enhance the component and system reliability. However, reliability prediction by burn-in at the component level, such as the one using the military (e.g., MIL-STD-280A, 756B, 217E [23–25]) and the industrial standards (e.g., the JEDEC standards), is usually not consistent with the field observations. Here, we propose system burn-in, which can remove many of the residual defects left from component and subsystem burn-in (Chien and Kuo [6]). A nonparametric model is considered because 1) the system configuration is usually very complicated, 2) the components in the system have different failure mechanisms, and 3) there is no good model for modeling incompatibility among components and subsystems (Chien and Kuo [5]; Kuo [16]). Since the cost of testing a system is high and, thus, only small samples are available, a Bayesian nonparametric approach is proposed to determine the system burn-in time. A case study using the proposed approach on MCM ASIC's shows that our model can be applied in the cases where 1) the tests and the samples are expensive, and 2) the records of previous generation of the products can provide information on the failure rate of the system under investigation. © 1997 John Wiley & Sons, Inc. Naval Research Logistics 44: 655–671, 1997     

Algorithms for computing waiting time distributions under different queue disciplines for the D-BMAP/PH/1

A queueing system characterized by the discrete batch Markovian arrival process (D-BMAP) and a probability of phase type distribution for the service time is one that arises frequently in the area of telecommunications. Under this arrival process and service time distribution we derive the waiting time distribution for three queue disciplines: first in first out (FIFO), last in first out (LIFO), and service in random order (SIRO). We also outline efficient algorithmic procedures for computing the waiting time distributions under each discipline. © 1997 John Wiley & Sons, Inc. Naval Research Logistics 44: 559–576, 1997     

Stage life testing

In progressive censoring, items are removed at certain times during the life test. Commonly, it is assumed that the removed items are used for further testing. In order to take into account information about these additional testing in inferential procedures, we propose a two‐step model of stage life testing with one fixed stage‐change time which incorporates information about both the removed items (further tested under different conditions) and those remaining in the current life test. We show that some marginal distributions in our model correspond either to progressive censoring with a fixed censoring time or to a simple‐step stress model. Furthermore, assuming a cumulative exposure model, we establish exact inferential results for the distribution parameters when the lifetimes are exponentially distributed. An extension to Weibull distributed lifetimes is also discussed.     

Insurgent courts in civil wars: the three pathways of (trans)formation in today’s Syria (2012–2017)

As part of research on the meso-foundations of conflict, the field of ‘rebel governance’ examines political institutions that regulate the affairs of civilians in wartime as well as their relations with armed actors. Judicial institutions play an important role in this and research has shown that they are widespread among both historical and current insurgencies. However, usually these bodies have been analysed in the context of one hegemonic faction like the Tamil Tigers in Sri Lanka and the Afghan Taliban. What is missing so far is an analysis of different pathways of (trans)formation of rebel courts. As exemplified by the three case studies of judicial institutions in Eastern Ghouta, Idlib and Aleppo, these are shaped by the distribution of power between ‘same-side’ groups, yielding unipolar, bipolar, or multipolar constellations. The analysis is located on the meso or movement level of insurgent social structures, complementing research on the micro and macro levels.     

相似分布特性准则下的高斯混合项聚类-合并算法

针对高斯混合模型估计非高斯系统时高斯混合项呈指数级增长问题,提出一种基于相似分布特性准则的聚类-合并方法。通过分析高斯混合项的分布特性,基于扩展积分均方误差代价函数搜索最优置信范围,并对混合项进行高斯聚类,进而获得具有不同分布特性的高斯簇。为防止高斯簇间对高斯子项的重复利用,引入局部最近邻思想对交叉高斯项进行重新分配。采用并行多元素合并方法对高斯簇中的混合项进行合并,在保证无偏性基础上减少下一时刻混合项数量。仿真结果表明,改进算法在保证跟踪精度的同时还可有效提高算法效率。     

指数寿命产品可靠性增长试验的Bayes分析

针对指数寿命产品的定时、定数截尾试验方案,推广了Mazzuchi-Soyer模型的应用范围。首先引入模型假设,以狄氏分布作为先验分布,综合利用产品研制的历史信息和专家信息,结合产品研制各阶段试验数据,给出了各阶段可靠性的联合后验分布。然后利用Gibbs抽样算法解决后验推断计算问题,得到各阶段产品可靠性的Bayes点估计和区间估计。最后给出产品可靠性增长分析实例,表明了模型的优越性。     

基于矢量分配的组合导航容错联邦滤波算法

针对高动态环境下飞行器组合导航系统因不确定故障导致导航精度下降的问题,提出了一种基于矢量信息分配的容错联邦滤波算法。设计矢量形式的故障检测函数,对各观测量进行单独的故障程度划分,克服了将故障子系统所有观测量同时隔离的缺陷;根据观测量是否异常,重构时变量测噪声矩阵和信息分配矢量系数,对子滤波器的状态变量进行信息分配,在隔离故障子系统异常观测量的同时,最大限度地利用正确观测信息。仿真结果表明,采用该算法能够充分发挥各导航子系统的优势,极大提高了导航子系统信息利用率,具有较高的精确性和容错性。     

Scheduling of depalletizing and truck loading operations in a food distribution system

This paper studies a scheduling problem arising in a beef distribution system where pallets of various types of beef products in the warehouse are first depalletized and then individual cases are loaded via conveyors to the trucks which deliver beef products to various customers. Given each customer's demand for each type of beef, the problem is to find a depalletizing and truck loading schedule that fills all the demands at a minimum total cost. We first show that the general problem where there are multiple trucks and each truck covers multiple customers is strongly NP‐hard. Then we propose polynomial‐time algorithms for the case where there are multiple trucks, each covering only one customer, and the case where there is only one truck covering multiple customers. We also develop an optimal dynamic programming algorithm and a heuristic for solving the general problem. By comparing to the optimal solutions generated by the dynamic programming algorithm, the heuristic is shown to be capable of generating near optimal solutions quickly. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2003     

Analysis of a machine repair problem with an unreliable server and phase type repairs and services

In this paper we study a machine repair problem in which a single unreliable server maintains N identical machines. The breakdown times of the machines are assumed to follow an exponential distribution. The server is subject to failure and the failure times are exponentially distributed. The repair times of the machine and the service times of the repairman are assumed to be of phase type. Using matrix‐analytic methods, we perform steady state analysis of this model. The time spent by a failed machine in service and the total time in the repair facility are shown to be of phase type. Several performance measures are evaluated. An optimization problem to determine the number of machines to be assigned to the server that will maximize the expected total profit per unit time is discussed. An illustrative numerical example is presented. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 462–480, 2003     

Hopfield神经网络的防空火力最优分配问题

火力的最优分配是作战计划的重要内容,它包含火力单位特性、目标单位特性、最优准则、射击条件四个方面的内容。简要介绍了Hopfield神经网络的基础知识,建立了防空自动化指挥系统中火力分配的Hopfield神经网络算法一般模型,在此基础上,阐述了利用该算法在火力分配中的一般应用,并通过在计算机上借助C语言编程实现了这一模型,得出了一种比较合理可行的火力分配方案。