Continuous-time markov decision processes with nonzero terminal reward

In this article we consider a continuous-time Markov decision process with a denumerable state space and nonzero terminal rewards. We first establish the necessary and sufficient optimality condition without any restriction on the cost functions. The necessary condition is derived through the Pontryagin maximum principle and the sufficient condition, by the inherent structure of the problem. We introduce a dynamic programming approximation algorithm for the finite-horizon problem. As the time between discrete points decreases, the optimal policy of the discretized problem converges to that of the continuous-time problem in the sense of weak convergence. For the infinite-horizon problem, a successive approximation method is introduced as an alternative to a policy iteration method.     

The demilitarization of public security in Panama

The Author, a former Vice‐President and Minister of Government and Justice in Panama, describes the demilitarization process in his country since 1989. A historical summary traces militarization up to the fall of General Noriega and his Panamanian Defense Forces. The factors and stages in demilitarizing the latter back to a civilian police force are described together with the personnel, financial and educational policies implemented. A conclusion argues that better pay and greater professionalization will improve the police's self‐image even more.     

Tripwires and free-riders: Do forward-deployed U.S. troops reduce the willingness of host-country citizens to fight for their country?

This article investigates the relationship between U.S. overseas troops and the willingness of the citizens of host states to fight for their country. The study joins the long-running debate about burden-sharing and free-riding among U.S. allies. Unlike most previous empirical studies, we focus on non-material or intangible measures of the underlying concepts. Our dependent variable estimates the proportion of citizens expressing a willingness to fight for their country. Scores at the aggregate-national as well as the individual level are shaped by the presence of U.S. military forces, which act as a “tripwire” signaling credible security commitments. This increases opportunities of (non-material) free-riding. We present both bivariate and multivariate analyses covering the period 1981–2014 to test this supposition. Findings indicate that once U.S. troop levels reach a certain threshold (between 100 and 500 troops), citizens’ willingness to fight drops significantly. This likely reflects non-material free-riding.     

Optimal base stock policies and truck capacity in a two-echelon system

With the recent trend toward just-in-time deliveries and reduction of inventories, many firms are reexamining their inventory and logistics policies. Some firms have dramatically altered their inventory, production, and shipping policies with the goal of reducing costs and improving service. Part of this restructuring may involve a specific contract with a trucking company, or it may entail establishing in-house shipping capabilities. This restructuring, however, raises new questions regarding the choice of optimal trucking capacity, shipping frequency, and inventory levels. In this study, we examine a two-level distribution system composed of a warehouse and a retailer. We assume that demand at the retailer is random. Since the warehouse has no advance notice of the size of the retailer order, inventory must be held there as well as at the retailer. We examine inventory policies at both the warehouse and the retailer, and we explicitly consider the trucking capacity, and the frequency of deliveries from the warehouse to the retailer. Both linear and concave fixed transportation costs are examined. We find the optimal base stock policies at both locations, the optimal in-house or contracted regular truck capacity, and the optimal review period (or, equivalently, delivery frequency). For the case of normally distributed demand we provide analytical results and numerical examples that yield insight into systems of this type. Some of our results are counterintuitive. For instance, we find some cases in which the optimal truck capacity decreases as the variability of demand increases. In other cases the truck capacity increases with variability of demand. © 1993 John Wiley & Sons, Inc.     

A O(nm log(U/n)) time maximum flow algorithm

In this paper, we present an O(nm log(U/n)) time maximum flow algorithm. If U = O(n) then this algorithm runs in O(nm) time for all values of m and n. This gives the best available running time to solve maximum flow problems satisfying U = O(n). Furthermore, for unit capacity networks the algorithm runs in O(n^2/3m) time. It is a two‐phase capacity scaling algorithm that is easy to implement and does not use complex data structures. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 511–520, 2000     

An Integro-Differential Approach To Terrorism Dynamics

This article introduces integro-differential equations as a new technique to study terrorism dynamics. An integro-differential equation is a mathematical expression that contains derivatives of the required function and its integral transforms. The technique is applied to two different dynamic models in terrorism: terrorism and tourism, and terrorist innovations. In the first model the number of tourists that appears in an integral term and also in a derivative term is impacted by the number of terrorists. In the second model the integro-differential equation for terrorist innovations relates them to terrorist attacks. The article shows how to solve, analyze, interpret, and deal with integro-differential equations. Integro-differential equations shed light on aspects of the models ignored when other techniques are used. This is particularly important for the evaluation of current counterterrorist policies, as well as to the formulation of new ones.     

Counterterrorism And Its Impact On Terror Support And Recruitment: Accounting For Backlash

This article presents a dynamic model in which counterterrorism policies have the potential to generate positive public support for terrorism via a backlash that may fuel terror recruitment. For an optimizing government aiming at maximizing security, this phenomenon produces a natural bound on proactive counterterror policy that is related to the dynamic path of conflict. Moreover, terror is a persistent phenomenon that requires patience on the part of the target government for optimal counterterror policies to be realized. Finally, the potential for backlash yields insights into the need for target governments to fight an information war to change public opinion regarding its own policies and the ultimate effect of terror attacks.     

Waiting time distributions for transient bulk queues with general vehicle dispatching strategies

A numerical approach is presented for determining the waiting time distribution in a transient bulk-arrival, bulk-service queue. Vehicle departures from the queue are governed by a general dispatch strategy that includes holding with a variable release function and vehicle cancellations. The waiting time distribution of a customer (in a group) arriving at a given point in time is calculated by simulating the process in discrete time and determining at each step the probability the customer has left the system. The dispatch strategies require knowing the total length of the queue as well as the position a customer holds in the queue. An exact approach is compared to an accurate approximation which is 50 to 100 times faster. Comparisons are made with other approaches in the context of steady-state systems.     

Synthesis and properties of novel nitro-based thermally stable energetic compounds

This paper reviews the achievements in the field of synthesis of new thermally resistant explosive compounds in the years 2009 through 2019. The performance characteristics of these compounds (sensitivity, thermal decomposition parameters, and detonation parameters) were compared with those of 1,3,5-triamino-2,4,6-trinitrobenzene, which still seems to be an unrivalled model of a thermally resistant and generally low-sensitivity explosive material. New thermally stable explosives (TSEs) were found among macromolecular compounds with tri- and dinitrophenyl groups, nitro and amine-nitro derivatives of azoles, and polynitro derivatives of calixarenes. Some of them match TATB in terms of thermal resistance and additionally have higher detonation parameters.     

The Persistent Deficit of Militia Officers in the Swiss Armed Forces: An Opportunity Cost Explanation

The Swiss Armed Forces are suffering from a structural deficit of militia officers despite good pay and a general supportive attitude in the population. Whereas, prior studies have focused on motivation to explain understaffing in armed forces, we offer an alternative approach based on opportunity cost. We model decision alternatives both within and outside a military organization, taking private sector employment as the reference point. We then monetize opportunity costs of leisure, fringe benefits, and private sector income not compensated. Our results suggest that in terms of opportunity cost, service as a militia officer is the least attractive option, an effect that we believe explains the persistent staff deficit. Implications of these findings for the literature and recruitment policy are discussed.