On the assignment and sequencing of operations on a crew-served project

This paper is concerned with assigning and sequencing a set of activities for some or all members of a crew of operators so that the completion time of all such operations is minimized. It is assumed that each of the operators in the crew possesses, initially, certain tasks that only he can perform. A branch-and-bound scheme is proposed to treat the problem, and suitable computational experience is provided.     

The effect of correlated exponential service times on single server tandem queues

An investigation via simulation of system performance of two stage queues in series (single server, first-come, first-served) under the assumption of correlated exponential service times indicates that the system's behavior is quite sensitive to departures from the traditional assumption of mutually independent service times, especially at higher utilizations. That service times at the various stages of a tandem queueing system for a given customer should be correlated is intuitively appealing and apparently not at all atypical. Since tandem queues occur frequently, e.g. production lines and the logistics therewith associated, it is incumbent on both the practitioner and the theoretician that they be aware of the marked effects that may be induced by correlated service times. For the case of infinite interstage storage, system performance is improved by positive correlation and impaired by negative correlation. This change in system performance is reversed however for zero interstage storage and depends on the value of the utilization rate for the case where interstage storage equals unity. The effect due to correlation is shown to be statistically significant using spectral analytic techniques. For correlation equal unity and infinite interstage storage, results are provided for two through twenty-five stages in series to suggest how adding stages affects system performance for ρ>0. In this extreme case of correlation, adding stages has an effect on system performance which depends markedly on the utilization rate. Recursive formulae for the waiting time per customer for the cases of zero, one, and infinite interstage storage are derived.     

A note on the optimal scheduling of two parallel processors

The problem of minimizing mean flow time of two parallel processors is discussed. Prior results are briefly reviewed. A dynamic programming algorithm is presented which minimizes mean flow time for a set of n preordered jobs on two nonequivalent parallel processors. The algorithm is illustrated with an example problem. The computational experience is presented which illustrates the efficiency of the algorithm.     

An algorithm for maximizing target achievement in the stochastic knapsack problem with normal returns

We consider the stochastic linear knapsack problem in which costs are known with certainty but returns are independent, normally distributed random variables. The objective is to maximize the probability that the overall return equals or exceeds a specified target value. A previously proposed preference order dynamic programming-based algorithm has been shown to be potentially suboptimal. We offer an alternative hybrid DP/branch-and-bound algorithm that both guarantees optimality and significantly outperforms generating the set of Pareto optimal returns.© 1993 John Wiley & Sons, Inc.     

An inventory model of incentives for on-time delivery in just-in-time purchasing contracts

This article formulates an analytic model of just-in-time purchasing contracts and compares the minimum cost solution with the cost attainable through vertical integration. The models use standard inventory theory cost parameters and decision variables. The results quantify the increase in cost of buying an item rather than making it. Optimal incentives are characterized when JIT purchasing contracts are used. When JIT purchasing is implemented, buffer inventories are typically reduced. This inventory reduction makes on-time delivery critical to the buyer; yet timeliness is controlled by the supplier. As an incentive to provide on-time delivery, the buyer offers the supplier a bonus for on-time delivery. The supplier chooses a flow time allowance based upon the bonus offered. First- and second-order conditions are characterized in general, and examples are provided for exponentially and uniformly distributed flow times. The delivery timeliness obtainable in a vertically integrated firm is determined and compared with timeliness obtainable between separate firms. This comparison indicates that buyers who choose to purchase materials from a separate firm are more likely to experience late deliveries. The relationship between the value of the bonus and the proportion of on-time deliveries is also considered. The bonus required to achieve the same probability of on-time delivery as under vertical integration is also determined. © 1993 John Wiley & Sons, Inc.     

Whose Hearts and Whose Minds? The Curious Case of Global Counter-Insurgency

Traditionally regarded as a secondary activity in military thinking and practice, the notion of counter-insurgency (COIN) has undergone a remarkable renaissance. This analysis traces the origins of this renaissance to two distinctive schools: a neo-classical school and a global insurgency school. The global insurgency school critiques neo-classical thought and presents itself as a more sophisticated appreciation of current security problems. An examination of the evolution of these two schools of counter-insurgency reveals how the interplay between them ultimately leaves us with a confused and contradictory understanding of the phenomenon of insurgency and the policies and strategies necessary to combat it.     

Reviews

Ian Castle and Ian Knight, Fearful Hard Times: The Siege and Relief of Eshowe, 1879. Greenhill Books, London 1994, Pp.256, 85 illus, 6 maps, index. £17.95. ISBN 1–85367–180–0.

Michael E. Brown (ed.), Ethnic Conflict and International Security. Princeton: Princeton University Press, 1993, Pp.263, selected biblio, index. $45/£30 (cloth); $14.95/£12.95 (paper). ISBN 0–691–03368 and 00068–9.

Deborah Poole and Gerardo Renique, Peru: Time of Fear. London: Latin American Bureau (Research and Action) Ltd., 1992. Pp.212, 7 maps, photographs, glossary, sources/further reading, index. £17.99 ISBN 0–906156–70‐X and ‐71–8.

David A. Charters (ed.), Peacekeeping and the Challenge of Civil Conflict Resolution. Center for Conflict Studies, University of New Brunswick, 1994. Pp.viii+220. NP.

Joachim Remak, A Very Civil War: The Swiss Sonderbund War of 1847. Boulder, Colorado: Westview Press, 1993. Pp.xvi+221, 6 map's, 68 illus, biblio, index. $24.95/£16.95.     

The impact of superpower arms transfers on conflict in the Middle East

I explore the relationship between superpower arms transfers and the Arab‐Israeli rivalry. My empirical analysis suggests that Soviet arms transfers to the Middle East, more than American transfers, have exacerbated interstate rivalry in the region. It also suggests that Soviet arms transfers, again more than American transfers, have encouraged compensatory arming by the other superpower. These conclusions derive from the results of cross‐correlation analysis, Granger‐causality tests, and variance decompositions, and are quite robust. While my findings paint a rather unflattering portrait of the effects of superpower involvement in the region, they do constitute grounds for optimism in light of current developments.