Bayesian enhanced decision making for deteriorating repairable systems with preventive maintenance

Since a system and its components usually deteriorate with age, preventive maintenance (PM) is often performed to restore or keep the function of a system in a good state. Furthermore, PM is capable of improving the health condition of the system and thus prolongs its effective age. There has been a vast amount of research to find optimal PM policies for deteriorating repairable systems. However, such decisions involve numerous uncertainties and the analyses are typically difficult to perform because of the scarcity of data. It is therefore important to make use of all information in an efficient way. In this article, a Bayesian decision model is developed to determine the optimal number of PM actions for systems which are maintained according to a periodic PM policy. A non‐homogeneous Poisson process with a power law failure intensity is used to describe the deteriorating behavior of the repairable system. It is assumed that the status of the system after a PM is somewhere between as good as new for a perfect repair and as good as old for a minimal repair, and for failures between two preventive maintenances, the system undergoes minimal repairs. Finally, a numerical example is given and the results of the proposed approach are discussed after performing sensitivity analysis. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

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     

Estimating the probability that a simulated system will be the best

Consider a stochastic simulation experiment consisting of v independent vector replications consisting of an observation from each of k independent systems. Typical system comparisons are based on mean (long‐run) performance. However, the probability that a system will actually be the best is sometimes more relevant, and can provide a very different perspective than the systems' means. Empirically, we select one system as the best performer (i.e., it wins) on each replication. Each system has an unknown constant probability of winning on any replication and the numbers of wins for the individual systems follow a multinomial distribution. Procedures exist for selecting the system with the largest probability of being the best. This paper addresses the companion problem of estimating the probability that each system will be the best. The maximum likelihood estimators (MLEs) of the multinomial cell probabilities for a set of v vector replications across k systems are well known. We use these same v vector replications to form v^k unique vectors (termed pseudo‐replications) that contain one observation from each system and develop estimators based on AVC (All Vector Comparisons). In other words, we compare every observation from each system with every combination of observations from the remaining systems and note the best performer in each pseudo‐replication. AVC provides lower variance estimators of the probability that each system will be the best than the MLEs. We also derive confidence intervals for the AVC point estimators, present a portion of an extensive empirical evaluation and provide a realistic example. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 341–358, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10019     

Designing a screening experiment for highly reliable products

Within a reasonable life‐testing time, how to improve the reliability of highly reliable products is one of the great challenges to today's manufacturers. By using a resolution III experiment together with degradation test, Tseng, Hamada, and Chiao (1995) presented an interesting case study of improving the reliability of fluorescent lamps. However, in conducting such an experiment, they did not address the problem of how to choose the optimal settings of variables, such as sample size, inspection frequency, and termination time for each run, which are influential to the correct identification of significant factors and the experimental cost. Assuming that the product's degradation paths satisfy Wiener processes, this paper proposes a systematic approach to the aforementioned problem. First, an intuitively appealing identification rule is proposed. Next, under the constraints of a minimum probability of correct decision and a maximum probability of incorrect decision of the proposed identification rule, the optimum test plan (including the determinations of inspection frequency, sample size, and termination time for each run) can be obtained by minimizing the total experimental cost. An example is provided to illustrate the proposed method. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 514–526, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10024     

Minimizing weighted earliness and tardiness penalties in single‐machine scheduling with idle time permitted

In this paper, a single‐machine scheduling problem with weighted earliness and tardiness penalties is considered. Idle time between two adjacent jobs is permitted and due dates of jobs could be unequal. The dominance rules are utilized to develop a relationship matrix, which allows a branch‐and‐bound algorithm to eliminate a high percentage of infeasible solutions. After combining this matrix with a branching strategy, a procedure to solve the problem is proposed. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 760–780, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10039     

The National resistance army (NRA) as a guerrilla force

Africa has had no shortage of guerrilla movements since 1975. However, very few have been successful that have not fought against European colonial rule or white minority regimes. Fundamentally, without external support, these movements have been almost universally failures. One major exception to this rule was the National Resistance Army of Uganda, which overthrew the regime led by General Tito Okello in 1986. What made the National Resistance Army a success and distinct from other guerrilla armies were its sound leadership, its superior organization and its creative strategy.     

Reviews

A. Hamish Ion and E.J. Errington (eds.), Great Powers and Little Wars: the Limits of Power. Westport, CT: Praeger, 1993. Pp.246, select biblio, index. $49.95. ISBN 0275–93965–0

John M. Rothgeb, Jr., Defining Power: Influence and Force in the Contemporary International System. New York: St. Martin's Press, 1993. Pp.205. $39.95 (hbk); $18.70 (pbk). ISBN 0312–086–822 and 061–056

Brian L. Job (ed.), The Insecurity Dilemma: National Security in Third World States. Boulder, CO: Lynne Rienner Publishers, 1992, Pp.257. $37. ISBN 1–55587–267–0

Edwin G. Corr and Stephen Sloan (eds.), Low‐Intensity Conflict: Old Threats in a New World. Westview Studies in Regional Security, Boulder, CO: Westview, 1992. Pp.310, maps, figures, index. $55 (hbk); $18.85 (pbk). ISBN 0–8133–8593–8 and 8594–6     

Israel's Northern eyes and shield: The strategic value of the Golan Heights revisited

According to common wisdom, the Golan provides Israel with an ideal platform for its warning stations as well as the best available defense line against a massive Syrian ground attack. Challenging this belief, this article compares the present situation with an alternative defined by (a) a complete Israeli withdrawal from the Golan, (b) a complete demilitarization of the evacuated territory, and (c) considerable limitations on Syrian military presence in the area between the Golan and Damascus. The article reaches two conclusions. First, that a combination of means, primarily airborne and space‐based platforms, can effectively answer Israel's northern intelligence needs. Second, the security arrangements set above, combined with recent revolutionary military technologies and its relative advantage in this domain, offer Israel an effective ‐ in some respects even a better ‐ alternative, to the present defense line.