A single server queue with arrival rate dependent on server breakdowns

This paper considers a single server queueing system that alternates stochastically between two states: operational and failed. When operational, the system functions as an M/E_k/1 queue. When the system is failed, no service takes place but customers continue to arrive according to a Poisson process; however, the arrival rate is different from that when the system is operational. The durations of the operating and failed periods are exponential with mean 1/cβ and Erlang with mean 1/cβ, respectively. Generating functions are used to derive the steady-state quantities L and W, both of which, when viewed as functions of c, decrease at a rate inversely proportional to c². The paper includes an analysis of several special and extreme cases and an application to a production-storage system.     

Incorporating learning curve costs in acquisition strategy optimization

Each year, the U.S. Army procures billions of dollars worth of weapons and equipment. The process of deciding what to buy, when to buy, and in what quantities is extremely complex, requiring extensive analysis. Two techniques used in this analysis are mathematical programming and cost estimation. Although they are related through constraints on available procurement funds, the use of nonlinear cost learning curves, which better represent system costs as a function of quantity produced, have not been incorporated into the mathematical programming formulations that compute the quantities of items to be procured. As a result, the solutions obtained could be either suboptimal, or even infeasible with respect to budgetary limitations. In this paper we present a piecewise linear approximation of the learning curve costs for a more accurate portrayal of budgetary constraints used in a mixed integer linear programming for acquisition strategy optimization. In addition, implementation issues are discussed, and performance results are given. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 255–271, 1999     

Replacing nonidentical vital components to extend system life

We consider a system that depends on a single vital component. If this component fails, the system life will terminate. If the component is replaced before its failure then the system life may be extended; however, there are only a finite number of spare components. In addition, the lifetimes of these spare components are not necessarily identically distributed. We propose a model for scheduling component replacements so as to maximize the expected system survival. We find the counterintuitive result that when comparing components' general lifetime distributions based on stochastic orderings, not even the strongest ordering provides an a priori guarantee of the optimal sequencing of components. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Unity is the exception. Alliance formation and de-formation among armed actors in Northern Mali

Our paper investigates the political trajectories of armed actors in Mali since 2012, using recent theoretical advances on alliance formation and collapse in civil wars. Our paper establishes an analytically productive distinction between levels of wartime cleavages and factors shaping groups’ trajectories. Strategic alliances, we argue, emerge from anticipated benefits on the national political scene as well as in the local political economy. The two sets of considerations do not necessarily converge. This dual logic is studied through the cases of two armed groups, both siding with the government after originally aligning with jihadi and separatist coalitions respectively.     

Rising Tide,Dispersing Waves: Opportunities and Challenges for Chinese Seapower Development

Abstract

This article surveys China’s current naval forces and considers key dynamics and possible Chinese naval futures to 2020, the projected end of Beijing’s ‘strategic window of opportunity’, the idea that a peaceful external environment for economic development, globalization, and integration of China into the global economy allows China to benefit from diversion of US attention to countering terrorism. It considers broad possibilities through 2030, the general limit of public US government projections, and by which time multiple factors will likely slow China’s growth and compete for leadership focus and resources.     

THE HUMAN CAPITAL PEACE: DEVELOPMENT AND INTERNATIONAL CONFLICT

This paper explores the relationship between human capital and international conflict. In theory, human capital may increase the opportunity cost of military service and the economic cost of injury and loss of life in combat; it may decrease the benefits of conflict as human capital cannot be easily appropriated or transferred; it may affect societal norms toward peace and war; and it may alter military productivity through new technology and complementarities between military technology and personnel. Using a panel of politically relevant dyads, I find robust empirical evidence that human capital may significantly decrease the likelihood of militarized conflict between nations. In short, the findings suggest that promoting human capital‐oriented development may help to increase peace in the world.     

ADVANCED US CONVENTIONAL WEAPONS AND NUCLEAR DISARMAMENT

The Obama administration has made a great effort to increase the role of advanced conventional weaponry in US national security thinking and practice, in part to help reinvigorate the global nuclear disarmament agenda by reducing the role played by nuclear weapons in the US defense posture. However, such a strategy is fundamentally flawed because increases in US conventional superiority will exacerbate US relative strength vis-à-vis other powers, and therefore make the prospect of a nuclear weapon-free world seem less attractive to Washington's current and potential nuclear rivals. Consequently, it is highly likely that the impact of efforts to increase US advanced conventional superiority through ballistic missile defense and a conventional “prompt global strike” program will ensure that the Obama administration is adopting a pathway to nuclear abolition on which it is the sole traveler for the foreseeable future.