Robustness of efficient server assignment policies to service time distributions in finite‐buffered lines

We study the assignment of flexible servers to stations in tandem lines with service times that are not necessarily exponentially distributed. Our goal is to achieve optimal or near‐optimal throughput. For systems with infinite buffers, it is already known that the effective assignment of flexible servers is robust to the service time distributions. We provide analytical results for small systems and numerical results for larger systems that support the same conclusion for tandem lines with finite buffers. In the process, we propose server assignment heuristics that perform well for systems with different service time distributions. Our research suggests that policies known to be optimal or near‐optimal for Markovian systems are also likely to be effective when used to assign servers to tasks in non‐Markovian systems. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010     

National security,military spending and the business cycle

This paper develops a Dynamic Stochastic General Equilibrium model where national security is an argument in the agent’s utility function and the government chooses optimally the level of military spending to maximize social welfare. National defense depends on military expenditure and on the strategic environment reflecting a potential hostile external threat. We use aggregate data on consumption, investment, and military spending for the US economy to estimate the parameters of the model. Estimation results suggest that consumption and national defense are complements and that military spending variability is mainly explained by external threat shocks although it also depends on the macroeconomic conditions. We compute impulse response functions of the main macroeconomic variables to several shocks: a total factor productivity shock, a defense technology shock, and a strategic environment shock. Surprisingly, we find that the optimal response to an increase in the external threat (a worsening in the strategic environment) will rise output by reducing consumption and increasing investment.     

Piracy,state capacity and root causes

By comparing the Somali experience of piracy with the emerging situation in the Gulf of Guinea, I show that increases in the enforcement aspects of state capacity in the Gulf of Guinea states are necessary but not sufficient tools to combat the emergence, growth, and institutionalisation of piracy. Such tools would require state-building measures that would minimise the incentives of individuals to join piracy organisations and they would have to effectively deal with youth unemployment, income inequality, and environmental degradation.     

Fully sequential procedures for comparing constrained systems via simulation

We consider the problem of finding the system with the best primary performance measure among a finite number of simulated systems in the presence of a stochastic constraint on a single real‐valued secondary performance measure. Solving this problem requires the identification and removal from consideration of infeasible systems (Phase I) and of systems whose primary performance measure is dominated by that of other feasible systems (Phase II). We use indifference zones in both phases and consider two approaches, namely, carrying out Phases I and II sequentially and carrying out Phases I and II simultaneously, and we provide specific example procedures of each type. We present theoretical results guaranteeing that our approaches (general and specific, sequential and simultaneous) yield the best system with at least a prespecified probability, and we provide a portion of an extensive numerical study aimed at evaluating and comparing the performance of our approaches. The experimental results show that both new procedures are useful for constrained ranking and selection, with neither procedure showing uniform superiority over the other.© 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010     

Ireland's Ho Chi Minh trail? The Republic of Ireland's role in the Provisional IRA's bombing campaign, 1970–1976

A common criticism levelled at successive governments of the Republic of Ireland during the Northern Ireland ‘Troubles’ was their alleged inactivity in the face of a ferocious Provisional IRA campaign. Such criticisms were based in large part on the perception of the southern state as a supply base for militant republicanism. The Republic was undoubtedly a formidable logistics hinterland for such militants. However, criticisms of the reactions of authorities in the south are unfair. This article considers the explosives capabilities of the IRA during the first six years of their campaign. It does so with reference to their attempts to obtain commercial explosives as well as measures employed by them to obtain homemade explosives. The article also considers countermeasures employed by the southern government and reveals the extent to which they sought to shut down IRA capabilities in the south. It is argued that, ultimately, the IRA's campaign in this regard could only be contained and never unilaterally halted.     

The solution to an open problem for a caching game

In a caching game introduced by Alpern et al. (Alpern et al., Lecture notes in computer science (2010) 220–233) a Hider who can dig to a total fixed depth normalized to 1 buries a fixed number of objects among n discrete locations. A Searcher who can dig to a total depth of h searches the locations with the aim of finding all of the hidden objects. If he does so, he wins, otherwise the Hider wins. This zero‐sum game is complicated to analyze even for small values of its parameters, and for the case of 2 hidden objects has been completely solved only when the game is played in up to 3 locations. For some values of h the solution of the game with 2 objects hidden in 4 locations is known, but the solution in the remaining cases was an open question recently highlighted by Fokkink et al. (Fokkink et al., Search theory: A game theoretic perspective (2014) 85–104). Here we solve the remaining cases of the game with 2 objects hidden in 4 locations. We also give some more general results for the game, in particular using a geometrical argument to show that when there are 2 objects hidden in n locations and n→∞, the value of the game is asymptotically equal to h/n for h≥n/2. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 23–31, 2016     

Waiting time analysis of the M/G/1 queue with finite retrial group

We consider an M/G/1 retrial queue with finite capacity of the retrial group. First, we obtain equations governing the dynamic of the waiting time. Then, we focus on the numerical inversion of the density function and the computation of moments. These results are used to approximate the waiting time of the M/G/1 queue with infinite retrial group for which direct analysis seems intractable. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007     

The ‘Third’ US Offset Strategy and Europe’s ‘Anti-access’ Challenge

Over the last two decades, a number of countries (most notably China, Russia and Iran) have been developing so-called anti-access and area denial (A2/AD) capabilities, such as ballistic and cruise missiles, offensive cyber-weapons, electronic warfare, etc. The development of A2/AD capabilities by non-Western countries undermines the foundations of US power projection and global military-technological supremacy. In order to overcome, or at least mitigate, the impending A2/AD challenge, the US Department of Defense (DoD) began to roll out its so-called ‘third’ offset strategy in late 2014. The strategy aims to bring about innovative operational concepts and technologies and spur new doctrinal and organisational debates. This article assesses which of the operational concepts and capabilities informing current US discussions on offset may be relevant in the context of the A2/AD challenges Europeans face on their eastern ‘flank‘ and in their ‘extended southern neighbourhood‘, and which may not. Europeans must grapple with the same conceptual puzzle as the US: how to strike the right balance between defeating A2/AD capabilities and hedging against them, i.e. through alternative strategies that are less dependent on unhindered access and resort to asymmetric forms of warfare. However, they must take into account the geographical features of their eastern flank and extended southern neighbourhood, the level of technological maturity of their challengers, and their own military-technological prowess and political limitations. This suggests a somewhat different approach to offsetting A2/AD than that adopted by the US.     

Revenue maximization in two-station tandem queueing systems

We study optimal pricing for tandem queueing systems with finite buffers. The service provider dynamically quotes prices to incoming price sensitive customers to maximize the long-run average revenue. We present a Markov decision process model for the optimization problem. For systems with two stations, general-sized buffers, and two or more prices, we describe the structure of the optimal dynamic pricing policy and develop tailored policy iteration algorithms to find an optimal pricing policy. For systems with two stations but no intermediate buffer, we characterize conditions under which quoting either a high or a low price to all customers is optimal and provide an easy-to-implement algorithm to solve the problem. Numerical experiments are conducted to compare the developed algorithms with the regular policy iteration algorithm. The work also discusses possible extensions of the obtained results to both three-station systems and two-station systems with price and congestion sensitive customers using numerical analysis.     

A PRODUCTIVITY AND EFFICIENCY ANALYSIS OF THE SECURITY AND DEFENCE TECHNOLOGICAL AND INDUSTRIAL BASE IN SPAIN

This study analyses the performance of the productivity of the main industrial subsectors composing the security and defence technological and industrial base (SDTIB) in Spain from 1996 to 2009. Accordingly, we have used the non-parametric data envelopment analysis and bootstrapping techniques to compute Malmquist productivity indexes that allow us to split productivity growth into efficiency change and technical progress. The results obtained show productivity improvement in the SDTIB as a whole due mainly to advances in technology and to a lesser extent to the contribution of technical efficiency. The bootstrap approach yields further evidence, as for many cases, productivity growth or decline, is not statistically significant. This is the first time a study of this kind has been carried out on the production process of this sector in Spain.