A constrained optimization problem for a processor sharing queue

In this article we discuss a processor sharing queueing model for a stored program controlled telephone exchange. The model incorporates the effects of both call requests and operator tasks on the load of the processor. Newly arriving call requests and operator tasks can either be admitted or rejected and for this decision the state of the queue at the moment of arrival is available as information. To guarantee a high level of service, we formulate a constrained optimization problem. Two types of access control, viz., partitioning policies and sharing policies, are considered. The optimization problem is solved for partitioning policies and the performance of both types of policies is compared. © 1993 John Wiley & Sons, Inc.     

Linear programming and the reliability of multicomponent systems

Several problems in the assignment of parallel redundant components to systems composed of elements subject to failure are considered. In each case the problem is to make an assignment which maximizes the system reliability subject to system constraints. Three distinct problems; are treated. The first is the classical problem of maximizing system reliability under total cost or weight constraints when components are subject to a single type of failure. The second problem deals with components which are subject to two types of failure and minimizes the probability of one mode of system failure subject to a constraint on the probability of the other mode of system failure. The third problem deals with components which may either fail to operate or may operate prematurely. System reliability is maximized subject to a constraint ori system safety. In each case the problem is formulated as an integer linear program. This has an advantage over alternative dynamic programming formulations in that standard algorithms may be employed to obtain numerical results.     

An application of servomechanisms to inventory

In recent years, some attention has been devoted to the application of techniques of control theory to inventory management. In particular, H. Vassian (1955) developed a model for a periodic review inventory system utilizing techniques of discrete variable servomechanisms to analyze the system in a cost-free structure. The resulting model is inherently deterministic, however, and emphasizes the control of inventory fluctuation about a safety level by selecting an appropriate order policy. Such an order policy is defined only up to an arbitrary method of forecasting customer demands. The present paper is a continuation of the model developed by Vassian in which exponential smoothing is used as a specific forecasting technique. Full recognition of the probabilistic nature of demand is taken into account and the requirement of minimizing expected inventory level is imposed. In addition, explicit formulas for the variance in inventory are derived as functions of the smoothing constant and the tradeoff between small variance and rapid system response is noted. Finally, in an attempt to remove the bias inherent in exponential smoothing, a modification of that technique is defined and discussed as an alternate forecasting method.     

Scheduling customer arrivals to a stochastic service system

An efficient algorithm for determining the optimal arrival schedule for customers in a stochastic service system is developed. All customers arrive exactly when scheduled, and service times are modeled as iid Erlang random variables. Costs are incurred at a fixed rate per unit of time each customer waits for service, and an additional cost is incurred for every unit of time the server operates beyond a scheduled closing time. The objective is to minimize total operating cost. This type of problem arises in many operational contexts including transportation, manufacturing, and appointment‐based services. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 549–559, 1999     

Facing ‘people's war’: Moltke the elder and Germany's military options after 1871

Prof. Dr Werner Hahlweg (ed.), Carl von Clausewitz: Vom Kriege. Neunzehnte Auflage. Bonn: Duemmler, 1980. Pp. 1406; DM. 98.00.*

Tony Ashworth, Trench Warfare 1914–1918. The Live and Let Live System. London: The Macmillan Press, 1980. Pp. 226; £15.

Stephen Roskill, Admiral of the Fleet: Earl Beatty. London: Collins, 1980. Pp. 430; £12.95.

R.J. Overy, The Air War 1939–1945. London: Europa Publications, 1980. Pp. 250; £12.50.

Martin Binkin and Irene Kynakopoulos, Youth or Experience? Manning the Modern Military. Washington, D.C.: The Brookings Institution, 1980. Pp. 84; NP.

Amos Perlmutter and Valerie Bennett (eds), The Political Influence of the Military. New Haven and London: Yale University Press, 1980. Pp. 508; £22.50; £6.90 (paperback).

Edward M. Spiers, The Army and Society 1815–1914. Themes in British Social History. London: Longman, 1980. Pp. 318; £9.95, £5.75 (paperback).

Richard K. Ashley, The Political Economy of War and Peace: The Sino‐Soviet‐American Triangle and the Modern Security Problematique. London: Frances Pinter, 1980. Pp. 384; £15.     

Counter-terrorism in the Horn of Africa: New security frontiers,old Strategies

The US-led ‘war on terror’ dramatically changed America's security strategy towards Africa. But more fundamentally, it threw the Horn of Africa on the centre stage of global counter-terrorism. A double-edged blade, counter-terrorism has at once catalysed peace processes and intensified insecurity, with Islamic radicalism at the core of the regional storm. Governments utilised the threat of terrorism for political ends, defending old security paradigms that prioritised regime stability over human security. Africa integrated counter-terrorism into its emerging security agenda, but insufficient funds, operational constraints and poor coordination with international initiatives have hampered meaningful progress. Washington, laudably, launched a robust counter-terrorist campaign, but its high-handed military-heavy style put fragile democracies at risk while lapses in its overall policy risk triggering proxy wars. This essay examines the impact of counter-terrorism on security in the Horn of Africa. It argues for stronger coordination between national, regional and international initiatives to curb international terrorism.