Transporting jobs through a two‐machine open shop

We consider the two‐machine open shop scheduling problem in which the jobs are brought to the system by a single transporter and moved between the processing machines by the same transporter. The purpose is to split the jobs into batches and to find the sequence of moves of the transporter so that the time by which the completed jobs are collected together on board the transporter is minimal. We present a ‐approximation algorithm. © 2008 Wiley Periodicals, Inc. Naval Research Logistics 2009     

Transient solution of a finite-capacity M/Ga,b/1 queueing system

In this article we consider a single-server, bulk-service queueing system in which the waiting room is of finite capacity. Arrival process is Poisson and all the arrivals taking place when the waiting room is full are lost. The service times are generally distributed independent random variables and the distribution is depending on the batch size being served. Using renewal theory, we derive the time-dependent solution for the system-size probabilities at arbitrary time points. Also we give expressions for the distribution of virtual waiting time in the queue at any time t.     

A nonlinear approach to the multiorigin,multidestination fleet deployment problem

The problem of minimal-cost operation of a fleet of ships carrying a specific amount of bulk cargo from several origin ports to several destination ports during a specified time interval is examined. The fuel oil cost, a major component of the total operating cost, is realistically modeled as a nonlinear function of the vessels' operating speeds. Introduction of both full load and ballast speeds as independent variables results in a nonlinear optimization problem in which the vessels' allocation to the available routes and the optimal speed selection problem are coupled. Within the framework of our model, each vessel of the fleet may load at any origin, unload at a destination and return to the same origin. The solution method developed utilizes specific features of the above fleet deployment model, and may reduce substantially the dimensionality of the problem. Under certain conditions, decoupling of the speed selection from the vessel allocation problem can be achieved, and linear programming can be used to obtain an optimal solution. In the general case, a projected Lagrangian method appears to be more appropriate for the problem under consideration.     

Principal-agent maintenance problem

This article studies a maintenance problem that is applicable for multidivision organizations on lessee-lessor relationships. It is assumed that the parties sign a contract for a fixed time period. Within the period, the lessor is allowed to use the equipment supplied by the lessee. The availability of the equipment that may suffer from breakdown depends on the preventive maintenance policy adopted by the lessor. The properties of this policy as well as other features of the problem are analyzed using a one-period model that takes into account the economic value of the contract as perceived by the lessor and the lessee. The optimal contracting arrangements are analyzed from the perspective of efficient risk sharing and incentive provisions.     

Spaghetti: systems thinking and the US Army

In the mid-2000s, the United States Army was embroiled in counterinsurgency missions in Iraq and Afghanistan that required deeper understanding of local social systems. The Army turned to systems thinking and design thinking to model and understand the world, define problems, and develop approaches to strategic and operational challenges. However, the Army’s approach as expressed in publications and doctrine encourages the development of complicated, unsupported, and unfalsifiable hypotheses. The risk is that the Army will act on incorrect assumptions and develop plans that are fragile.     

Algorithm to solve a chance‐constrained network capacity design problem with stochastic demands and finite support

We consider the problem of determining the capacity to assign to each arc in a given network, subject to uncertainty in the supply and/or demand of each node. This design problem underlies many real‐world applications, such as the design of power transmission and telecommunications networks. We first consider the case where a set of supply/demand scenarios are provided, and we must determine the minimum‐cost set of arc capacities such that a feasible flow exists for each scenario. We briefly review existing theoretical approaches to solving this problem and explore implementation strategies to reduce run times. With this as a foundation, our primary focus is on a chance‐constrained version of the problem in which α% of the scenarios must be feasible under the chosen capacity, where α is a user‐defined parameter and the specific scenarios to be satisfied are not predetermined. We describe an algorithm which utilizes a separation routine for identifying violated cut‐sets which can solve the problem to optimality, and we present computational results. We also present a novel greedy algorithm, our primary contribution, which can be used to solve for a high quality heuristic solution. We present computational analysis to evaluate the performance of our proposed approaches. © 2016 Wiley Periodicals, Inc. Naval Research Logistics 63: 236–246, 2016     

Ethnic groups,political exclusion and domestic terrorism

This study examines whether the exclusion of ethnic groups from political power is an important contributing factor to domestic terrorism. To empirically test this question, we employ a negative binomial regression estimation on 130 countries during the period from 1981 to 2005. We find that countries in which certain ethnic populations are excluded from political power are significantly more likely to experience domestic terrorist attacks and to suffer from terrorist casualties; furthermore, ethnic group political exclusion is a more consistent and substantive predictor of domestic terrorist activity than general political repression or economic discrimination.     

Child Soldiering in Colombia: Does Poverty Matter?

Child soldiering remains a challenge for the international community, and non-state armed groups are the most persistent offenders, but its drivers are poorly understood. Recent contributions suggest that decisions by armed groups are the key to explain child soldiering and that contextual variables are less relevant. This article exploits the availability of subnational, longitudinal data on child soldiering in Colombia, where insurgents and private militias have recruited children at least since the 1990s. The analysis shows that child recruitment is more likely in poorer municipalities, with limited access to education, and where coca crops are grown.     

Military Spending and Growth: The Role of Institutions

Recent literature on whether military spending affects economic growth argues that the relationship may be a conditional one. We add to this literature by considering the role that ‘good institutions’ play in the effect of military spending on growth. Using data from a sample of over 100 countries from 1988 to 2010, our analysis suggests that the effect of military spending on growth is generally negative or zero at best, and this effect is mitigated in the presence of good economic and political institutions.     

Optimal shift scheduling: A branch‐and‐price approach

We present a branch‐and‐price technique for optimal staff scheduling with multiple rest breaks, meal break, and break windows. We devise and implement specialized branching rules suitable for solving the set covering type formulation implicitly, using column generation. Our methodology is more widely applicable and computationally superior to the alternative methods in the literature. We tested our methodology on 365 test problems involving between 1728 and 86400 shift variations, and 20 demand patterns. In a direct comparison with an alternative method, our approach yields significant improvements both in cpu time and in the number of problem instances solved to optimality. The improvements were particularly marked for problems involving larger numbers of feasible shifts. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 185–200, 2000