Scheduling with earliest start and due date constraints on multiple machines

We consider the scheduling of n jobs on m identical machines when the jobs become available for processing at ready times a_i, a_i, ? 0, require d_i time units for processing and must be completed by times b_i for i = 1, 2, … n. The objective chosen is that of minimizing the total elapsed time to complete all jobs subject to the ready time and due date constraints, preemption is not allowed. We present a multi-stage solution algorithm for this problem that is based on an implicit enumeration procedure and also uses the labelling type algorithm which solves the problem when preemption is allowed.     

On sequencing with earliest starts and due dates with application to computing bounds for the (n/m/G/Fmax) problem

Recent efforts to improve lower bounds in implicit enumeration algorithms for the general (n/m/G/F_max) sequencing problem have been directed to the solution of an auxiliary single machine problem that results from the relaxation of some of the interference constraints. We develop an algorithm that obtains optimal and near optimal solutions for this relaxed problem with relatively little computational effort. We report on computational results achieved when this method is used to obtain lower bounds for the general problem. Finally, we show the equivalence of this problem to a single machine sequencing problem with earliest start and due date constraints where the objective is to minimize the maximum lateness.     

Stochastic leadtimes in continuous-time inventory models

This paper shows that one of the fundamental results of inventory theory is valid under conditions much broader than those treated previously. The result characterizes the distributions of inventory level and inventory position in the standard, continuous-time model with backorders, and leads to the relatively easy calculation of key performance measures. We treat both fixed and random leadtimes, and we examine both stationary and limiting distributions under different assumptions. We consider demand processes described by several general classes of compound-counting processes and a variety of order policies. For the stochastic-leadtime case we provide the first explicit proof of the result, assuming the leadtimes are generated according to a specific, but plausible, scenario.     

Optimal timing of switches between product sales for sports and entertainment tickets

Like airlines and hotels, sports teams and entertainment venues can benefit from revenue management efforts for their ticket sales. Teams and entertainment venues usually offer bundles of tickets early in their selling horizon and put single‐event tickets on sale at a later date; these organizations must determine the best time to offer individual tickets because both types of ticket sales consume the same fixed inventory. We model the optimal a priori timing decision for a seller with a fixed number of identical tickets to switch from selling the tickets as fixed bundles to individual tickets to maximize the revenue realized before the start of the performance season. We assume that bundle and single‐ticket customers each arrive according to independent, nonhomogeneous Markovian death processes with a linear death rate that can vary over time and that the benefit from selling a ticket in a package is higher than from selling the ticket individually. We characterize the circumstances in which it is optimal for the seller to practice mixed bundling and when the seller should only sell bundles or individual tickets, and we establish comparative statics for the optimal timing decision for the special case of constant customer arrival rates. We extend our analytical results to find the optimal time for offering two groups of tickets with high and low demand. Finally, we apply the timing model to a data set obtained from the sports industry. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Robust shortest path problems with two uncertain multiplicative cost coefficients

We consider a robust shortest path problem when the cost coefficient is the product of two uncertain factors. We first show that the robust problem can be solved in polynomial time by a dual‐variable enumeration with shortest path problems as subproblems. We also propose a path enumeration approach using a K ‐shortest paths finding algorithm that may be efficient in many real cases. An application in hazardous materials transportation is discussed, and the solution methods are illustrated by numerical examples. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013     

Westmoreland was right: learning the wrong lessons from the Vietnam War

Fourth Generation Warfare is a theory of contemporary warfare that posits a number of different ideas that are able to shed light on current conflicts. Whilst much of the debate has been concentrated on the linear development of warfare and also on analysis of the current situation of US forces in Iraq, it has resonance for a number of different conflicts taking place in Africa, if only because the US has become involved in contemporary conflicts in Somalia and the Mahgreb. There are clearly significant issues with the US-centric, flawed linear approach to history, but the actual analysis of modes of warfare has much to offer policymakers in a continent that is under-represented in the literature, and is also in danger of being forgotten in the shadow of analysis of Iraq. This paper moves on from criticising the stepped approach to history and looks at patterns of warfare in contemporary Africa, arguing that there is much in the theory that could be used to explain seemingly illogical tactics or patterns, and thus has much to tell policymakers engaged in conflict analysis.

Rebellions can be made 2 per cent active in a striking force, and 98 per cent passively sympathetic.1 ?1. T.E. Lawrence, ‘Science of Guerrilla Warfare’, 1929, published in Malcolm Brown (ed) T.E. Lawrence in War and Peace: An Anthology of the Military Writings of Lawrence of Arabia (London: Greenhill Books, 2005) p.284.      

Capacity and competence: full-spectrum counterinsurgency in the Horn of Africa

From 2006 to 2011, al Qaeda's East African proxy, al Shabaab, served as de facto ruling party of Somalia despite the efforts of the internationally recognized Transitional Federal Government (TFG). During these five years, a violent struggle between al Shabaab and the Burundian and Ugandan Peacekeepers of the African Union Mission in Somalia (AMISOM) resulted in thousands of dead civilians, hundreds of thousands of internally displaced persons, and a strategic environment inhospitable to reconciliation, recovery, or development. Beginning in August 2011, AMISOM was able to break the deadlock and force al Shabaab from Mogadishu, then subsequently, Kismayo, and ultimately to consolidate and reorganize in the Somali hinterland. In order to continue the momentum, the African Union and other partner nations must support the newly recognized Somali Federal Government (SFG), neutralize al Shabaab, and provide good governance to its constituents. Al Shabaab's revenue streams must be shut down and their offensive capability must be degraded while the strategic environment is shaped to ensure that conditions conducive to a revival do not exist. Failure to do so will likely see Somalia continuing to produce Islamic extremists and pirates to menace international maritime traffic in the Western Indian Ocean, destabilize East Africa, and adversely impact millions.