An exact aggregation/disaggregation algorithm for large scale markov chains

Many Markov chain models have very large state spaces, making the computation of stationary probabilities very difficult. Often the structure and numerical properties of the Markov chain allows for more efficient computation through state aggregation and disaggregation. In this article we develop an efficient exact single pass aggregation/disaggregation algorithm which exploits structural properties of large finite irreducible mandatory set decomposable Markov chains. The required property of being of mandatory set decomposable structure is a generalization of several other Markov chain structures for which exact aggregation/disaggregation algorithms exist. © 1995 John Wiley & Sons, Inc.     

Algorithms for the design of finite-capacity service units

Finite-capacity queues arise naturally in many practical situations, notably in communications and manufacturing engineering. In this article, the matrix formalism of probability distributions of phase type is used to develop fast algorithms to compute various steady-state distributions for the finite-capacity PH/PH/1 queue. This algorithm is an important ingredient in solving nontraditional but significant design problems. Some of these are described as illustrative examples.     

Note: Pairwise rearrangements in reliability structures

Boland, Proschan, and Tong [2] used the notion of criticality of nodes in a coherent system to study the optimal component arrangement of reliability structures. They also provided a sufficient minimal cut (path) based criterion for verifying the criticality ordering of two nodes. We develop a necessary and sufficient condition for two nodes to be comparable and provide specific examples illustrating our result's applicability. As a corollary, certain optimal arrangement properties of well-known systems are derived. © 1994 John Wiley & Sons, Inc.     

An interactive paired comparison method for bicriterion integer programming

This article proposes an interactive paired comparison region elimination method for bicriterion integer mathematical programming problems. The new method isolates the best compromise solution by successively evaluating a pair of associated supported non-dominated solutions. The efficiency of the method is tested by solving randomly generated problems based on varying shapes of efficient frontiers. When compared with the existing branch-and-bound method, the method was effective in reducing the burden on the decision maker. © 1994 John Wiley & Sons, Inc.     

Employment and utilization of engineers among defense contractors

Defense contractors retain engineers for two reasons. First, engineers work on current-period production contracts. Second, engineers conduct independent research and development (IR&D) and write bids and proposals (B&P) for future contracts. The amount of IR&D/B&P activity, however, understates the amount of effort devoted to learning that reduces the cost of future production. Even some engineers who work on current-period production may engage in learning, as a by-product of their efforts. This article develops and implements a model for estimating the volume of learning activity undertaken by four large manufacturers of military aircraft. © 1994 John Wiley & Sons, Inc.     

Hybrid minimal repair and age replacement maintenance policies,with nonnegligible repair times

A system undergoes minimal repair during [0, T] with a failure replacement on first failure during [T, a], or a planned replacement if the system is still functioning at elapsed time a. Repairs and replacements are not necessarily instantaneous. An expression is obtained for the asymptotic expected cost rate, and sufficient conditions are obtained for the optimum T* > 0. Several special cases are considered. A numerical investigation for a Weibull distributed time to first failure compares this elapsed-time policy with replacement on failure only, and also a policy based on system operating time or age. It is found that in many cases the elapsed-time-based policy is only marginally worse than one based on system age, and may therefore be preferred in view of its administrative convenience. © 1994 John Wiley & Sons, Inc.     

Casualty Rates of US Military Personnel During the Wars in Iraq and Afghanistan

Abstract

In Operation Iraqi Freedom, which ended in August 2010, nearly 3500 hostile deaths occurred among US military personnel and 32,000 more were wounded in action (WIA). More than 1800 hostile deaths occurred during Operation Enduring Freedom (in and around Afghanistan) through 2014 and about 20,000 were WIA. A larger proportion of wounded personnel survived in Iraq and Afghanistan than during the Vietnam War, but the increased survival rates were not as high as some studies have asserted. The survival rates were 90.2% in Iraq and 91.6% in Afghanistan, compared with 86.5% in Vietnam. The casualty rates varied between the conflicts in Iraq and Afghanistan and before, during, and after the respective surges. Amputation rates are difficult to measure consistently, but I estimate that 2.6% of all WIA and 9.0% of medically evacuated WIA from the Iraq and Afghanistan theaters combined resulted in the major loss of a limb. Elevated non-hostile death rates (including deaths due to accidents, illnesses, homicides, or suicides) resulted in about 220 more deaths in Iraq and about 200 more deaths in Afghanistan than would have been expected in peacetime among populations of the size deployed to those two conflicts.     

A facility reliability problem: Formulation,properties, and algorithm

Having a robustly designed supply chain network is one of the most effective ways to hedge against network disruptions because contingency plans in the event of a disruption are often significantly limited. In this article, we study the facility reliability problem: how to design a reliable supply chain network in the presence of random facility disruptions with the option of hardening selected facilities. We consider a facility location problem incorporating two types of facilities, one that is unreliable and another that is reliable (which is not subject to disruption, but is more expensive). We formulate this as a mixed integer programming model and develop a Lagrangian Relaxation‐based solution algorithm. We derive structural properties of the problem and show that for some values of the disruption probability, the problem reduces to the classical uncapacitated fixed charge location problem. In addition, we show that the proposed solution algorithm is not only capable of solving large‐scale problems, but is also computationally effective. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2010     

Coercive diplomacy and the Donbas: Explaining Russian strategy in Eastern Ukraine

What were Russia’s objectives in Eastern Ukraine, and why was it seemingly unable to achieve a successful or decisive outcome? In contrast to Russia’s seizure of Crimea, the uprising in Eastern Ukraine was marked by disorganization and chaos. Using proxy and surrogate actors, along with military exercises and the injection of Russian troops, Russia sought to institutionalize a political entity inside Ukraine to influence its domestic politics. In this article, I analyze the mechanisms by which Russia attempted to implement, and later salvage, its strategy. The article contributes to clearer theoretical and practical understanding of limited force in coercive diplomacy, signaling, and a more rigorous treatment of the role and uses of proxy actors.