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     

Network reliability assessment in a random environment

In this paper we consider networks that consist of components operating under a randomly changing common environment. Our work is motivated by power system networks that are subject to fluctuating weather conditions over time that affect the performance of the network. We develop a general setup for any network that is subject to such environment and present results for network reliability assessment under two repair scenarios. We also present Bayesian analysis of network failure data and illustrate how reliability predictions can be obtained for the network. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 574–591, 2003     

How long until midnight? Intelligence-policy relations and the United States response to the Israeli nuclear program, 1959–1985

Why did the United States fail to stop Israeli acquisition of nuclear weapons? Existing research argues that patrons such as the U.S. should have an easy time halting proliferation by militarily and economically vulnerable clients. Nevertheless, Israel acquired nuclear weapons with relatively little American opposition. Utilizing extensive primary source research, we argue that problematic intelligence-policy relations hindered U.S. efforts to arrest Israeli proliferation as (1) policymakers often gave mixed guidance to the intelligence community, resulting in (2) limited information on Israeli efforts that reinforced policy ambiguity. The results carry implications for understanding the dynamics of nuclear proliferation and intelligence-policy relations.     

The conditional p-center problem in the plane

An algorithm is given for the conditional p-center problem, namely, the optimal location of one or more additional facilities in a region with given demand points and one or more preexisting facilities. The solution dealt with here involves the minimax criterion and Euclidean distances in two-dimensional space. The method used is a generalization to the present conditional case of a relaxation method previously developed for the unconditional p-center problems. Interestingly, its worst-case complexity is identical to that of the unconditional version, and in practice, the conditional algorithm is more efficient. Some test problems with up to 200 demand points have been solved. © 1993 John Wiley & Sons, Inc.     

Setting military reenlistment bonuses

The United States military frequently has difficulty retaining enlisted personnel beyond their initial enlistment. A bonus program within each service, called a Selective Reenlistment Bonus (SRB) program, seeks to enhance reenlistments and thus reduce personnel shortages in critical military occupational specialties (MOSs). The amount of bonus is set by assigning “SRB multipliers” to each MOS. We develop a nonlinear integer program to select multipliers which minimize a function of deviations from desired reenlistment targets. A Lagrangian relaxation of a linearized version of the integer program is used to obtain lower bounds and feasible solutions. The best feasible solution, discovered in a coordinate search of the Lagrangian function, is heuristically improved by apportioning unexpended funds. For large problems a heuristic variable reduction is employed to speed model solution. U.S. Army data and requirements for FY87 yield a 0-1 integer program with 12,992 binary variables and 273 constraints, which is solved within 0.00002% of optimality on an IBM 3033AP in less than 1.7 seconds. More general models with up to 463,000 binary variables are solved, on average, to within 0.009% of optimality in less than 1.8 minutes. The U.S. Marine Corps has used a simpler version of this model since 1986. © 1993 John Wiley & Sons, Inc.     

UNFPA and population assistance

International population assistance in the UN is a relatively recent development; it is only since 1966 that a broad-based technical assistance program in population was authorized by the General Assembly. The desire of developing country members for accelerated economic growth ultimately brought about a change in the views on population. In 1967, the Secretary General established a trust fund for population activities, later renamed the United Nations Fund for Population Activities (UNFPA). 3 principles have guided UNFPA work since its inception: 1) national sovereignty in population matters is to be resspected and adhered to at all times, 2) individuals and couples are to be provided the information and services necessary to determine freely and responsibly the number and spacing of their children, and 3) population goals and policies are integral parts of socioeconomic defelopment. The areas of assistance by the UNFPA consist of 1) family planning, 2) communication and education, 3) population dynamics, 4) basic data collection, 5) population policy formulation and implementation, and 6) special programs such as those for women and the aging population. In 16 years, the UNFPA has received about $1.4 billion for transfer to developing countries as population assistanceand has financed 4373 population projects in 149 countries and territories. The relation between the US government and UNFPA is tenuous and likely to remain so as long as the US cannot resolve its own domestic controversies over famly planning, foreign population assistance, abortion, which, ironically, is legalin the country. There will always be some sort of domestic controversy over population; the UN has overcome domestic difficulties by framing the arguments properly within the demographic, social, economic, ecological, and political concerns of countries and applying the fundamental principles of national sovereignty, freedom of individual choice, and the link of population and development,to reconcile differences.     

Optimal stocking policies for low usage items in multi-echelon inventory systems

Multi-echelon logistic systems are essential parts of the service support function of high technology firms. The combination of technological developments and competitive pressures has led to the development of services systems with a unique set of characteristics. These characteristics include (1) low demand probabilities: (2) high cost items; (3) complex echelon structures; (4) existence of pooling mechanisms among stocking locations at the same echelon level; (5) high priority for service, which is often expressed in terms of response time service levels for product groups of items: (6) scrapping of failed parts; and (7) recycling of issued stock due to diagnostic use. This article develops a comprehensive model of a stochastic, multi-echelon inventory system that takes account of the above characteristics. Solutions to the constrained optimization problem are found using a branch and bound procedure. The results of applying this procedure to a spare parts inventory system for a computer manufacturer have led to a number of important policy conclusions.