Optimal block replacement policies with multiple choice at failure

In this article we consider block replacement policies where the operating item is replaced by a new one at times kT, k = 1, 2, …, independently of its failure history. At failure the item is either replaced by a new or a used one or remains inactive until the next planned replacement. The mathematical model is defined and general analytical results are obtained. Computations are carried out for the case where the underlying life distribution is gamma or Weibull.     

Noncombatant Immunity and the Ethics of Blockade

This article counters Michael Walzer's argument against tight blockades. It shows that the interdiction of food shipments need not violate the principle of noncombatant immunity. Whether it is morally permissible to impose a strict blockade depends on the circumstances of the target state. The more self-sufficient a country is, the more acceptable it should be for a belligerent to cut the enemy's external lines of supply. The Allied blockade of Germany during the First World War illustrates the argument. Fault in this case should be assigned to the German government for the loss of civilian lives.     

Design and control of agile automated CONWIP production lines

In this article, we study the design and control of manufacturing cells with a mix of manual and automated equipment, operating under a CONWIP pull protocol, and staffed by a single agile (cross‐trained) worker. For a three‐station line with one automated station, we fully characterize the structure of the optimal control policy for the worker and show that it is a static priority policy. Using analytical models and extensive simulation experiments, we also evaluate the effectiveness of practical heuristic control policies and provide managerial insights on automation configuration design of the line. This characterization of the worker control policy enables us to develop managerial insights into the design issues of how best to locate and concentrate automation in the line. Finally, we show that, in addition to ease of control and greater design flexibility, the CONWIP protocol also offers higher efficiency and robustness than does the push protocol. © 2008 Wiley Periodicals, Inc. Naval Research Logistics 2009     

An exact ceiling point algorithm for general integer linear programming

We present an algorithm called the exact ceiling point algorithm (XCPA) for solving the pure, general integer linear programming problem (P). A recent report by the authors demonstrates that, if the set of feasible integer solutions for (P) is nonempty and bounded, all optimal solutions for (P) are “feasible 1-ceiling points,” roughly, feasible integer solutions lying on or near the boundary of the feasible region for the LP-relaxation associated with (P). Consequently, the XCPA solves (P) by implicitly enumerating only feasible 1-ceiling points, making use of conditional bounds and “double backtracking.” We discuss the results of computational testing on a set of 48 problems taken from the literature.     

Military Debt: Perspectives from the Experience of Arab Countries

The sectoral production function model of Feder (1983) has been widely used to examine the link between defence spending and economic growth. In this paper, the model, for which too much has been claimed in some past work, is examined, and the case is made for using growth in real non‐defence output rather than growth in real aggregate output (inclusive of military spending) as the dependent variable. Attention is restricted to a small group of OECD countries for which reliable labour force and capital stock (as well as defence) data are obtainable. With non‐defence output as the dependent variable and using only high quality data, no evidence in favour of the underconsumptionist (as opposed to the defence as a burden) position is found.     

How not to pay for the war

As a result of allied subsidy and the influence of sunk costs, the marginal cost of the Gulf War to the US was reduced to negligible size. This result is at variance with the Olson‐Zeckhauser thesis that in an alliance “the small exploit the large.” A game theoretic alternative explanation suggests that the relation between allies resembles the game of Chicken, successfully played by the US. The ability to shift the marginal costs of war in the short term raises questions about the possible underestimation of long term effects.     

Statistical equivalency and optimality of simple step‐stress accelerated test plans for the exponential distribution

Accelerated life testing (ALT) is commonly used to obtain reliability information about a product in a timely manner. Several stress loading designs have been proposed and recent research interests have emerged concerning the development of equivalent ALT plans. Step‐stress ALT (SSALT) is one of the most commonly used stress loadings because it usually shortens the test duration and reduces the number of required test units. This article considers two fundamental questions when designing a SSALT and provides formal proofs in answer to each. Namely: (1) can a simple SSALT be designed so that it is equivalent to other stress loading designs? (2) when optimizing a multilevel SSALT, does it degenerate to a simple SSALT plan? The answers to both queries, under certain reasonable model assumptions, are shown to be a qualified YES. In addition, we provide an argument to support the rationale of a common practice in designing a SSALT, that is, setting the higher stress level as high as possible in a SSALT plan. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2013