Partitioning and balancing for the assembly of nozzle guide vanes in gas turbine engines

The gas turbine engine is used to power many different types of commercial and military aircraft. During the scheduled maintenance of these engines, many of the turbine components are replaced. Of particular importance to us is the replacement of nozzle guide vanes in the nozzle assembly section of the engine. Individual vanes are selected from inventory to make up sets, and each set must meet certain characteristics in order to be feasible. The vanes in each set must then be sequenced in order to meet additional criteria. In this article, we give heuristics for the above partitioning and sequencing problems. Empirical analyses, using actual data from a branch of the armed services and a major engine manufacturer, are used to evaluate the proposed heuristics. The results of these analyses indicate that the heuristics are effective.     

Multiaction maintenance under markovian deterioration and incomplete state information

Much research been devoted to modeling the replacement problem under incomplete state information. Almost no work has been done on the maintenance problem under incomplete information with multiple maintenance actions that may not return the system to as good as new. We model this problem and derive structural results concerning the optimal maintenance policy. For the case where the effect of maintenance actions is state dependent, we give conditions under which the optimal policy is finitely computable. Where maintenance is state independent we show a specific structure, consisting of monotonic waiting times and constant maintenance actions, to be optimal.     

Experience with prototype multicriteria decision support systems for pelagic fish quota determination

This article describes an attempt to use certain multiple-criteria decision-making aids to support the formulation of catch quota policies in pelagic fisheries management. A set of attributes was identified, as necessary to represent the decision-making goals. Potentially useful methods appeared to be STEM, interactive sequential goal programming (ISGP), and interactive multiple goal programming (IMGP). Prototype microcomputer-based systems were developed to implement each of the three approaches. Although experience with the implementation is still relatively limited, it has involved actual planners and decision makers from both the fishing industry and from the relevant state department. The evidence is that IMGP is particularly useful in this context, and that it does seem to facilitate the reaching of consensus between different interest groups.     

Capacitated selection problem

Optimizing the selection of resources to accomplish a set of tasks involves evaluating the tradeoffs between the cost of maintaining the resources necessary to accomplish the tasks and the penalty cost associated with unfinished tasks. We consider the case where resources are categorized into types, and limits (capacity) are imposed on the number of each type that can be selected. The objective is to minimize the sum of penalty costs and resource costs. This problem has several practical applications including production planning, new product design, menu selection and inventory management. We develop a branch‐and‐bound algorithm to find exact solutions to the problem. To generate bounds, we utilize a dual ascent procedure which exploits the special structure of the problem. Information from the dual and recovered primal solutions are used to select branching variables. We generate strong valid inequalities and use them to fix other variables at each branching step. Results of tests performed on reasonably sized problems are presented. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 19–37, 1999     

The “signature” of a coherent system and its application to comparisons among systems

Various methods and criteria for comparing coherent systems are discussed. Theoretical results are derived for comparing systems of a given order when components are assumed to have independent and identically distributed lifetimes. All comparisons rely on the representation of a system's lifetime distribution as a function of the system's “signature,” that is, as a function of the vector p= (p₁, … , p_n), where p_i is the probability that the system fails upon the occurrence of the ith component failure. Sufficient conditions are provided for the lifetime of one system to be larger than that of another system in three different senses: stochastic ordering, hazard rate ordering, and likelihood ratio ordering. Further, a new preservation theorem for hazard rate ordering is established. In the final section, the notion of system signature is used to examine a recently published conjecture regarding componentwise and systemwise redundancy. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 507–523, 1999     

Tangled up in rose? Theories of alliance entrapment and the 2008 Russo-Georgian War

Recent tensions between Russia and the United States have sparked debate over the value of the North Atlantic Treaty Organization (NATO). One controversy surrounds the extent to which NATO raises the risk of war through entrapment—a concept that scholars invoke to describe how states might drag their allies into undesirable military conflicts. Yet scholars have advanced different, even conflicting arguments about how entrapment risks arise. I offer a typology that distinguishes between the mechanisms through which entrapment risks allegedly emerge on the basis of their institutional, systemic, reputational, and transnational ideological sources. I use the 2008 Russo-Georgian War to illustrate how the purported mechanisms of entrapment fare in elucidating that conflict. In analyzing why entrapment risks emerge, and thinking counterfactually about The 2008 War, I argue that scholars need to disentangle the various mechanisms that drive both alliance formation and war to make sure that entrapment risks do indeed exist.