A m‐parallel crane scheduling problem with a non‐crossing constraint

In this paper, we study a m‐parallel machine scheduling problem with a non‐crossing constraint motivated by crane scheduling in ports. We decompose the problem to allow time allocations to be determined once crane assignments are known and construct a backtracking search scheme that manipulates domain reduction and pruning strategies. Simple approximation heuristics are developed, one of which guarantees solutions to be at most two times the optimum. For large‐scale problems, a simulated annealing heuristic that uses random neighborhood generation is provided. Computational experiments are conducted to test the algorithms. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2007.     

Weakest‐link attacker‐defender games with multiple attack technologies

In this article, we examine a model of terrorism that focuses on the tradeoffs facing a terrorist organization that has two qualitatively different attack modes at its disposal. The terrorist organization's objective is to successfully attack at least one target. Success for the target government is defined as defending all targets from any and all attacks. In this context, we examine how terrorist entities strategically utilize an efficient but discrete attack technology — e.g., suicide attacks — when a more conventional mode of attack is available, and the optimal anti‐terrorism measures.© 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012     

General Dostum and the Mazar i Sharif Campaign: new light on the role of Northern Alliance warlords in Operation Enduring Freedom

This report sheds new light on the CIA and US Special Forces' covert campaign alongside Afghan Northern Alliance leader General Dostum's horse-mounted Uzbeks during 2001's Operation Enduring Freedom. In 2003 and 2005 the author traveled over the Hindu Kush Mountains to the plains of Northern Afghanistan and lived with the legendary Northern Alliance opposition leader General Dostum. His aim was to recreate Dostum's campaign alongside the CIA and Special Forces to seize the holy city of Mazar i Sharif from the Taliban in November 2001. Based on interviews with Dostum and his Uzbek commanders, this article recreates this proxy offensive that saw the Northern Alliance opposition break out of the mountains, seize this shrine town and bring the Taliban house of cards falling down in a matter of weeks. Up until now the indigenous Afghan Uzbeks, who played a crucial role as a ‘boots on the ground’ fighting force for Centcom, have been cast as a mere backdrop for American heroics. Now their side of the story and their links to the mysterious shrine of Mazar i Sharif are for the first time revealed.     

COURTING THE GLOBAL SOUTH WITH “DUAL-BENEFIT” NONPROLIFERATION ENGAGEMENT

President Barack Obama and an array of other Western leaders continue to assert that the spread of weapons of mass destruction (WMD) to non-state actors is one of most pressing challenges to global security today. Yet, Western efforts to engage governments—particularly governments across the global South—in a practical nonproliferation dialogue have largely yielded disappointing results. This viewpoint examines the need for a new strategy to engage the developing world in nonproliferation programs. It argues that strategies focused strictly on WMD nonproliferation are unsustainable, and ultimately are destined for failure. An alternative “dual-benefit” nonproliferation engagement strategy utilizes the enlightened self-interest of partner governments needed to achieve broad-based buy-in among all partners. In a concluding section, we recommend that the “Group of 8” Global Partnership Against the Spread of Weapons and Materials of Mass Destruction standardize this model of nonproliferation engagement as it sets out to identify and fund WMD nonproliferation capacity-building initiatives beyond the states of the former Soviet Union.     

Properties of the geometric and related processes

Some properties of the geometric process are studied along with those of a related process which we propose to call the α‐series process. It is shown that the expected number of counts at an arbitrary time does not exist for the decreasing geometric process. The decreasing version of the α‐series process does have a finite expected number of counts, under certain conditions. This process also has the same advantages of tractability as the geometric process; it exhibits some properties which may make it a useful complement to the increasing geometric process. In addition, it may be fit to observed data as easily as the geometric process. Applications in reliability and stochastic scheduling are considered in order to demonstrate the versatility of the alternative model. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

Crane scheduling with spatial constraints

In this work, we examine port crane scheduling with spatial and separation constraints. Although common to most port operations, these constraints have not been previously studied. We assume that cranes cannot cross, there is a minimum distance between cranes and jobs cannot be done simultaneously. The objective is to find a crane‐to‐job matching which maximizes throughput under these constraints. We provide dynamic programming algorithms, a probabilistic tabu search, and a squeaky wheel optimization heuristic for solution. Experiments show the heuristics perform well compared with optimal solutions obtained by CPLEX for small scale instances where a squeaky wheel optimization with local search approach gives good results within short times. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004.     

An efficient SPH methodology for modelling mechanical characteristics of particulate composites

Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical, automobile, aerospace including defence technology. Variety of modelling techniques have been adopted in the past to model mechanical behaviour of particulate composites. Due to their favourable properties, particle-based methods provide a convenient platform to model failure or fracture of these composites. Smooth particle hydrodynamics (SPH) is one of such methods which demonstrate excellent potential for modelling failure or fracture of particulate composites in a Lagrangian setting. One of the major challenges in using SPH method for modelling composite materials depends on accurate and efficient way to treat interface and boundary conditions. In this paper, a master-slave method based multi-freedom constraints is proposed to impose essential boundary conditions and interfacial displacement constraints in modelling mechanical behaviour of composite materials using SPH method. The proposed methodology enforces the above constraints more accurately and requires only smaller condition number for system stiffness matrix than the procedures based on typical penalty function approach. A minimum cut-off value-based error criteria is employed to improve the compu-tational efficiency of the proposed methodology. In addition, the proposed method is further enhanced by adopting a modified numerical interpolation scheme along the boundary to increase the accuracy and computational efficiency. The numerical examples demonstrate that the proposed master-slave approach yields better accuracy in enforcing displacement constraints and requires approximately the same computational time as that of penalty method.     

Monotone optimal preventive maintenance policies for stochastically failing equipment

This paper examines various models for maintenance of a machine operating subject to stochastic deterioration. Three alternative models are presented for the deterioration process. For each model, in addition to the replacement decision, the option exists of performing preventive maintenance. The effect of this maintenance is to “slow” the deterioration process. With an appropriate reward structure imposed on the processes, the models are formulated as continuous time Markov decision processes. the optimality criterion being the maximization of expected discounted reward earned over an infinite time horizon. For each model conditions are presented under which the optimal maintenance policy exhibits the following monotonic structure. First, there exists a control limit rule for replacement. That is, there exists a number i* such that if the state of machine deterioration exceeds i* the optimal policy replaces the machine by a new machine. Secondly, prior to replacement the optimal level of preventive maintenance is a nonincreasing function of the state of machine deterioration. The conditions which guarantee this result have a cost/benefit interpretation.