Machine maintenance with workload considerations

Machine maintenance is modeled in the setting of a single‐server queue. Machine deterioration corresponds to slower service rates and failure. This leads to higher congestion and an increase in customer holding costs. The decision‐maker decides when to perform maintenance, which may be done pre‐emptively; before catastrophic failures. Similar to classic maintenance control models, the information available to the decision‐maker includes the state of the server. Unlike classic models, the information also includes the number of customers in queue. Considered are both a repair model and a replacement model. In the repair model, with random replacement times, fixed costs are assumed to be constant in the server state. In the replacement model, both constant and variable fixed costs are considered. It is shown in general that the optimal maintenance policies have switching curve structure that is monotone in the server state. However, the switching curve policies for the repair model are not always monotone in the number of customers in the queue. Numerical examples and two heuristics are also presented. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007     

Force protection and society

Wars have long been fought with a firm focus upon armies' domestic contexts. These socio-political foundations have underpinned decisions regarding embarking upon war as well the conduct of war itself. Of particular importance among liberal democracies is the emphasis which is now placed upon force protection; broadly conceived as the range of measures employed to ensure the protection of servicemen and women on operations. Decisions surrounding protective equipment, deployed locations and wartime activities all face detailed scrutiny in contemporary operating environments. The attitudes of the government, the military and the civilian population combine to create a complex and dynamic backdrop of harmony and tension to this most sensitive characteristic of modern wars.     

Product commonality in multiple‐period,make‐to‐stock systems

It is well known that replacing several products by a single common product can reduce required safety stock levels due to the benefits of risk pooling. Recent research utilizing single‐period models has investigated the cost savings (or losses) from doing so. This paper uses a very general multiple‐period model, with general demand distributions, any number of products, and the objective of minimizing production, holding, and shortage costs. Two scenarios are considered—one that utilizes a common product and one that does not. Prior results utilizing single‐period models indicate that even if the common product is more expensive than the products it replaces, there are many circumstances under which it is still worthwhile to employ. Surprisingly, this paper will show that this is almost never the case in a multiple‐period model. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 737–751, 1999     

An extensible modeling framework for dynamic reassignment and rerouting in cooperative airborne operations

Unmanned aerial vehicles (UAVs), increasingly vital to the success of military operations, operate in a complex and dynamic environment, sometimes in concert with manned aircraft. We present an extensible modeling framework for the solution to the dynamic resource management (DRM) problem, where airborne resources must be reassigned to time‐sensitive tasks in response to changes in battlespace conditions. The DRM problem is characterized by diverse tasks with time windows, heterogeneous resources with fuel‐ and payload‐capacity limitations, and multiple competing objectives. We propose an integer linear programing formulation for this problem, where mathematical feasibility is guaranteed. Although motivated by airborne military operations, the proposed general modeling framework is applicable to a wide array of settings, such as disaster relief operations. Additionally, land‐ or water‐based operations may be modeled within this framework, as well as any combination of manned and unmanned vehicles. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010     

Was World War Two a Completely Just War?

ABSTRACT

According to Brian Orend’s binary political model, minimally just states possess a robust set of moral rights, while other states essentially exist in a moral vacuum in which they possess no moral rights. I argue that a more plausible comparative model would allow for a state to acquire (or lose) discrete moral rights as it improves (or damages) its moral record. This would generate a more accurate portrayal of both domestic policy within states and military conflict between states; including, in particular, the role of the Allied forces during World War Two.