On the orbit characteristics of the M/G/ 1 retrial queue

In teletraffic applications of retrial queues only the service zone is observable. Another part of a retrial queue, the orbit, which represents the delay before repeated attempts to get service, cannot be observed. Thus, it is very important to get general results about behavior of the orbit. We investigate two characteristics of the orbit, namely, the orbit busy period and the orbit idle period, which seem to be very useful from this point of view. © 1996 John Wiley & Sons, Inc.     

On the busy period of the M/G/1 retrial queue

The M/G/1 queue with repeated attempts is considered. A customer who finds the server busy, leaves the service area and joins a pool of unsatisfied customers. Each customer in the pool repeats his demand after a random amount of time until he finds the server free. We focus on the busy period L of the M/G/1$ retrial queue. The structure of the busy period and its analysis in terms of Laplace transforms have been discussed by several authors. However, this solution has serious limitations in practice. For instance, we cannot compute the first moments of L by direct differentiation. This paper complements the existing work and provides a direct method of calculation for the second moment of L. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 115–127, 2000     

Approximation for the departure process of a queue in a network

A simple renewal process is identified to approximate the complex departure process of a queue often found in queueing network models. The arrival process to the queue is the superposition or merging of several independent component-renewal processes that are approximations of departure processes from other queues and external arrival processes; there is a single server with exponential service times, and the waiting space is infinite. The departure process of this queue is of interest because it is the arrival process to other queues in the network. The approximation proposed is a hybrid; the mean and variance of the approximating departure intervals is a weighted average of those determined by basic methods in Whitt [41] with the weighting function empirically determined using simulation. Tandem queueing systems with superposition arrival processes and exponential service times are used to evaluate the approximation. The departure process of the first queue in the tandem is approximated by a renewal process, the tandem system is replaced by two independent queues, and the second queue is solved analytically. When compared to simulation estimates, the average absolute error in hybrid approximations of the expected number in the second queue is 6%, a significant improvement over 22–41% in the basic methods.     

The threshold policy in the M/G/1 queue with server vacations

This article deals with the M/G/1 queue with server vacations in which the return of the server to service depends on the number of customers present in the system. The main goal is optimization, which is done under the average cost criterion in the multiple- and single-vacation models as well as for the “total cost for one busy cycle” criterion in the multiple-vacation case. Expressions that characterize the optimal number of customers, below which the server should not start a new service period, are exhibited for the various cases. It is found that under the average cost criterion, the expression may be universal in the sense that it may hold for a general class of problems including such that arise in production planning and inventory theory (for the particular cost structure discussed).     

On the behavior of the batch arrival queue Mx/M/1 during a busy period

The queue size process (^t)⁰≤^t≤^t0 of the batch arrival queue M^X/M/1 is studied under the condition that the duration of its busy period is larger than t⁰. Explicit formulas for the transition probabilities are given and the limiting Markov process for t⁰ → ∞ is investigated. Several properties of this process are considered. Its transition probabilities and moments and the distribution of its minimum are derived and a functional limit theorem for the rescaled process is proved. © 1994 John Wiley & Sons, Inc.     

On the design of a tandem queue with blocking: Modeling,analysis, and gradient estimation

We demonstrate here how recent advances in the study of discrete-event stochastic systems provide fruitful results for the modeling, analysis, and design of manufacturing systems. We consider a multistage make-to-stock system where outputs from the final stage are used to satisfy customer demands. We address the problem of finding the appropriate trade-off between reduced order waiting time and increased process speeds. Using the idea of infinitesimal perturbation analysis (IPA), we establish a simple procedure where sample-path derivatives can be obtained along an arbitrary sample path. Under suitable conditions, we demonstrate that these derivative estimators are unbiased and strongly consistent and can be used in a classical stochastic optimization scheme to solve the problem. The role of continuity and convexity on the validity of the estimator is also addressed. Although the focus of this article is not to solve for the optimal solution, we provide a theoretical justification for such a pursuit. The approach is appealing as it is numerically stable, easy to implement, and can be extended to other system performance measures. © 1994 John Wiley & Sons, Inc.     

The causal nexus between military spending and unemployment in the G7: a bootstrap panel causality test

We revisit the causal relationship between military spending and unemployment in the G7 countries applying a bootstrap panel causality analysis that accounts for both cross-sectional dependence and for heterogeneity across countries. Using per capita real GDP as a controlled variable, we found a unidirectional causality running from military spending to unemployment for Canada, Japan, and the US, one-way causality running from unemployment to military spending for France and Germany, and bidirectional causality for Italy and the UK. The empirical evidence does not seem to provide consistent results regarding the causal relationship between military spending and unemployment in G7 countries.     

20世纪50年代人民解放军建设取得辉煌成就的原因浅探

20世纪50年代,是新中国成立后人民解放军建设的第一个时期,也是新中国成立后人民解放军建设取得辉煌成就的一个时期。从1949年10月中华人民共和国成立,到20世纪50年代末,仅10年左右的时间,人民解放军迅速从以步兵为主的单一陆军发展成为具有海军、空军和陆军各技术兵种合成的现代化、正规化的强大国防军,是人民解放军历史上技术装备水平与当时世界发达国家军队相比,差距最小的时期。这一时期,人民解放军建设之所以能够取得如此辉煌的成就,分析研究其原因,主要有如下几点。一、建设现代化、正规化强大国防军的明确目标牵引随着1949年10月新中…     

Bounds and properties of the expected value of sample information for a project-selection problem

In this article we extend the work of Mehrez and Stulman [5] on the expected value of perfect information (EVPI) to the expected value of sample information (EVSI) for a class of economic problems dealing with the decision to reject or accept an investment project. It is shown that shifting the mean of the underlying a priori distribution of X, the project's monetary value from zero in either direction will decrease the associated EVSI of Y, the random sampled information. A theorem is then presented which gives an upper bound on the EVSI over all distributions of Y, as well as the structure of the posterior mean E[X|Y] for which this upper bound is achieved. Finally, the case where E[X|Y] is linear in Y is discussed and its performance compared with that of the optimal case.     

地暖采暖空间中庭火灾烟气流动规律探究

在理论研究采用地暖采暖空间的垂直温度场分布规律的基础上,对此类环境火灾情况下烟气蔓延和流动规律进行小尺寸试验,并进行数据分析。通过对比分析得到烟气在地暖采暖空间中庭下降速度要比普通的均匀无采暖环境迅速。为此类环境的防烟设计提供理论依据。     

某大型商业综合体建筑安全疏散性能化消防设计探析

对选定的大型商业综合体建筑功能特点及防火设计问题进行分析,运用消防安全工程学原理,选择适当的分析方法,采用可靠的技术手段和分析软件,设定全面客观的火灾与疏散场景,对烟气流动和人员疏散进行模拟分析.在对该项目拟定的消防设计方案进行调整并设置必要的消防设施保障后,能达到性能化设计提出的保证人员生命安全和限制火灾大规模蔓延的设计目标.     

Design and analysis of a scheme for the naval gun test shell entering the bore

The test shell without projectile belt is widely used in the teaching, inspection and maintenance of modern automatic naval guns. In order to ensure the normal work of each mechanism, it is very important to design the buffer and limit of the test shell during the process of entering the bore. Taking a certain type of medium caliber naval gun as the research object, the design of colloidal fluid damper and cartridge lock was proposed to ensure the reliability of entering the bore and closing the breechblock. By combining the simulation methods of computational fluid dynamics (CFD) and multibody system dy-namic (MBD), it was analyzed whether the structural design can meet the engineering requirements. The research results show that the colloidal fluid damper can dissipate a large amount of kinetic energy of the shell, and the cartridge lock can limit the rebound movement. The combination of the two ensures the smooth process of closing the breechblock. The research provides a design method for the process of the test shell entering the bore, and provides theoretical support for the feasibility of the method.     

大型商业综合体内影院消防设计探讨

重点介绍了某大型商业综合体内影院的消防设计方案,并进行烟气流动和人员疏散的数值模拟分析,得出该影院消防设计是安全可行的.为确保此类影院的消防安全,建议其疏散楼梯设计不受商场营业与否的影响,且应定期维护保养消防系统.     

中庭式建筑防火设计探讨

根据消防实际工作经验,以某星级饭店为工程研究对象,就中庭式建筑的火灾危险性以及规范中关于中庭防火设计问题存在的不明确之处进行探讨,并提出了一些建议和解决对策.     

航站楼消防设计若干问题探讨

消防设计的合理性对于航站楼安全运行具有重要意义。目前,国内尚未出台航站楼设计防火规范,因此,航站楼消防设计还处于探索和积累经验的阶段。介绍了航站楼消防设计四个阶段、重要设计难点,结合工程实际问题,对消防设计思路系统化进行了梳理,力图为设计者提供少许帮助。     

英国关于滇缅战场的具体设想

第二次世界大战中英国在东南亚的战绩不佳,根源在于英国的"先欧后亚"大战略。第一次魁北克会议后,丘吉尔倾心于"长炮"计划,设想绕过缅甸,利用两栖作战夺取苏门答腊北端,为攻打新加坡建立前进基地。而英国军方——参谋长委员会(C.O.S)则认为在东南亚作战需要美国的支持,因此要在遵从第一次魁北克会议决议的基础上,进行两栖作战,夺取安达曼群岛,可行方案是"海盗"计划。双方争论不休。到第一次开罗会议,中美两国认可了"海盗"计划,但由于德黑兰会议关于欧洲战场的安排,让英国得以在第二次开罗会议时说服美国放弃"海盗"计划。英国得以致力于欧洲战场,而1944年由英国主导的东南亚战区则没有明确的作战计划,对战后英国在东南亚的影响力,以及中英关系都有消极影响。     

超大型购物中心人员疏散设计有关问题探讨

从超大型购物中心人员疏散设计中存在的疏散宽度不足、疏散距离过长等问题入手,在保证人员安全疏散的前提下,就如何合理地进行人员疏散设计进行了深入探讨,以期达到安全性和经济性的最大统一。     

一个新型数据采集处理系统在电机试验中的应用

介绍了一个用于电机试验的新型数据采集处理系统 ,并举例说明了该系统在电机试验中的功能及应用