Preemptive parallel‐machine scheduling with a common server to minimize makespan

We consider parallel‐machine scheduling with a common server and job preemption to minimize the makespan. While the non‐preemptive version of the problem is strongly NP‐hard, the complexity status of the preemptive version has remained open. We show that the preemptive version is NP‐hard even if there is a fixed number of machines. We give a pseudo‐polynomial time algorithm to solve the case with two machines. We show that the case with an arbitrary number of machines is unary NP‐hard, analyze the performance ratios of some natural heuristic algorithms, and present several solvable special cases. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 388–398, 2017     

Scheduling combat logistics force replenishments at sea for the US Navy

The Replenishment at Sea Planner (RASP) is saving the U.S. Navy millions of dollars a year by reducing fuel consumption of its Combat Logistics Force (CLF). CLF shuttle supply ships deploy from ports to rendezvous with underway U.S. combatants and those of coalition partners. The overwhelming commodity transferred is fuel, ship‐to‐ship by hoses, while other important packaged goods and spare parts are high‐lined, or helicoptered between ships. The U.S. Navy is organized in large areas of responsibility called numbered fleets, and within each of these a scheduler must promulgate a daily forecast of CLF shuttle operations. The operational planning horizon extends out several weeks, or as far into the future as we can forecast demand. We solve RASP with integer linear optimization and a purpose‐built heuristic. RASP plans Replenishment‐at‐Sea (RAS) events with 4‐hour (Navy watch) time fidelity. For five years, RASP has served two purposes: (1) it helps schedulers generate a daily schedule and animates it using Google Earth, and (2) it automates reports command‐to‐ship messages that are essential to keep this complex logistics system operating.     

A branch‐and‐price approach for the stochastic generalized assignment problem

In this article, we address a stochastic generalized assignment machine scheduling problem in which the processing times of jobs are assumed to be random variables. We develop a branch‐and‐price (B&P) approach for solving this problem wherein the pricing problem is separable with respect to each machine, and has the structure of a multidimensional knapsack problem. In addition, we explore two other extensions of this method—one that utilizes a dual‐stabilization technique and another that incorporates an advanced‐start procedure to obtain an initial feasible solution. We compare the performance of these methods with that of the branch‐and‐cut (B&C) method within CPLEX. Our results show that all B&P‐based approaches perform better than the B&C method, with the best performance obtained for the B&P procedure that includes both the extensions aforementioned. We also utilize a Monte Carlo method within the B&P scheme, which affords the use of a small subset of scenarios at a time to estimate the “true” optimal objective function value. Our experimental investigation reveals that this approach readily yields solutions lying within 5% of optimality, while providing more than a 10‐fold savings in CPU times in comparison with the best of the other proposed B&P procedures. © 2014 Wiley Periodicals, Inc. Naval Research Logistics 61: 131–143, 2014     

Military expenditure,economic growth and structural instability: a case study of South Africa

This paper contributes to the growing literature on the milex-growth nexus, by providing a case study of South Africa and considering the possibility of structural breaks by applying newly developed econometric methods. Using full sample bootstrap Granger non-causality tests, no Granger causal link is found between military expenditure and GDP for 1951–2010, but parameter instability tests show the estimated VARs to be unstable. Using a bootstrap rolling window estimation procedure, however, finds evidence of bidirectional Granger causality in various subsamples. This implies standard Granger non-causality tests, which neither account for structural breaks nor time variation may be invalid.     

THE HARD CASES

Many countries received Soviet-origin highly enriched uranium (HEU) for civilian nuclear research purposes. Because of inadequate nuclear security at a number of the research sites, U.S. policy has sought to remove or otherwise safely dispose of their HEU stocks as quickly as possible. Although the pace of HEU disposition has accelerated significantly in recent years, several sites have posed formidable technical, economic, and political challenges. This article identifies the major obstacles to HEU removal at two key installations—Kharkiv in Ukraine, and Sosny in Belarus—and recommends a strategy for overcoming these impediments. Key components for a successful disposition strategy include: treating these cases with the urgency they deserve, expanding potential compensation packages, explicitly addressing the institutional and political issues involved, engaging high-level political leaders, working with third parties, and promoting these efforts as part of a nondiscriminatory initiative to phase out HEU in the civilian nuclear sector globally.     

UNDER THE RADAR?

Missile Contagion: Cruise Missile Proliferation and the Threat to International Security, by Dennis M. Gormley. Praeger Security International, 2008. 272 pages, $54.95.     

Japan's plutonium policy: Consequences for nonproliferation

ABSTRACT

What do we mean by nuclear proliferation? What does it mean to proliferate? This article investigates both the literal and figurative meaning of the term “proliferation.” It argues that many of the definitions and conceptualizations of nuclear proliferation often used by scholars are either limited in their utility or logically inconsistent. It then reconceptualizes and redefines the term, incorporating an understanding of both its etymological origins and the geopolitical context in which the phenomenon occurs. It concludes by exploring the potential impact that the politicization of the phenomenon may have on the identification of occurrences of proliferation, from both an academic and a policy-making perspective.