A network isolation algorithm

A set of edges D called an isolation set, is said to isolate a set of nodes R from an undirected network if every chain between the nodes in R contains at least one edge from the set D. Associated with each edge of the network is a positive cost. The isolation problem is concerned with finding an isolation set such that the sum of its edge costs is a minimum. This paper formulates the problem of determining the minimal cost isolation as a 0–1 integer linear programming problem. An algorithm is presented which applies a branch and bound enumerative scheme to a decomposed linear program whose dual subproblems are minimal cost network flow problems. Computational results are given. The problem is also formulated as a special quadratic assignment problem and an algorithm is presented that finds a local optimal solution. This local solution is used for an initial bound.     

Heuristic modeling of supply availabilities in large networks

The objective of this article is to describe heuristic solutions to the problem of modeling inventories at each node of a large network in the context of a computer simulation model of that network. The heuristic solutions are compared with the mathematical solution which is too unwieldy for use in a simulation model. The Weibull cumulative distribution is used as an approximation for the heuristic models. We question whether the good performance of the Weibull is coincidence or perhaps mathematically justifiable.     

Recent articles on partial backorders: Comment

This note points out the omission of a simple but vital constraint in the recent articles on partial backlogging. Also, a simple intuitive interpretation of the “backorder” inequality of [2], [3], and [4] is provided.     

Application of disjunctive programming to the linear complementarity problem

In this article we address the question of developing deep cuts for disjunctive programs using rectilinear distance measures. The method is applied to linear complementarity problems where the matrix M need not be copositive plus. Some modifications that are needed as a computational expediency are discussed. The computation results for matrix M of size up to 30 × 30 are discussed.     

Urban violence and the militarisation of security: Brazilian ‘peacekeeping’ in Rio de Janeiro and Port-au-Prince

Despite problems of violence domestically, Brazil has played a key leadership role as part of MINUSTAH peacekeeping operations in Haiti since 2004. This article addresses how Brazil's international military engagement is shaping domestic approaches to urban security, and what may be the implications of the use of military strategies, operations, and norms to address issues of public security in Brazilian cities. It is argued that current approaches toward urban security employing military-trained peacekeepers actually represent a continuation of old paradigms, yet these recent militarised approaches are likely evolving into newer and potentially more accountable forms by constraining indiscriminate use of force and establishing a positive state presence in marginal urban areas. As such, the article connects long-established issues of dealing with urban violence in Latin America with ongoing debates in the United States and beyond about post-counterinsurgency approaches to increasingly urban conflict settings. It reflects on potential lessons to be learned from the Latin American perspective, while showing also how these have changed over the last decade. The article concludes that despite the potential utility of force in some urban conflict settings, this approach could entail a normative shift towards legitimising forceful containment of violence, and hinder democratic consolidation in Brazil.     

An assessment of the ‘democratic’ coup theory

The Egyptian military's unconstitutional removal of President Mohamed Morsi has reignited a debate regarding the theory of the ‘democratic coup’. Though coups are almost invariably condemned, many political observers and a few scholars have recently argued that coups can act as catalysts for democratisation. This paper empirically assesses the democratic coup hypothesis for Africa. Multivariate analyses from 1952 to 2012 suggest that coups statistically improve a country's democratisation prospects. Extensions of the model show that coups appear to be likely precursors for democratisation in staunchly authoritarian regimes and have become less likely to end democracy over time, and that their positive influence has strengthened since the end of the Cold War. As of 2012, countries that have experienced a recent coup are expected to be four times more likely to witness a democratic transition than those that have remained coup-free.     

The long term effects of an aging fleet on operational availability and cost: evidence from the U.S. coast guard

This paper empirically examines whether the aging of a fleet affects operational availability and operating cost using a unique data-set on the 117 47-foot Motor Lifeboats (MLBs) of the United States Coast Guard (USCG). Procured from 1997 to 2003, the 47-foot MLB is the standard lifeboat of the USCG and all 117 MLBs remain in service. The aging of the MLB fleet has resulted in higher annual operating costs and lower operational availability, although the nature of this relationship remains unclear. Our estimation strategy utilizes an error components estimator to examine these issues. We employ three variants of the dependent variables (i.e. the standard logarithmic transformation as is most commonly seen in the literature, inverse hyperbolic sine [IHS], and level outcomes). The point estimates from the standard logarithmic model finds operational availability for the MLBs decreases at a rate between 0.83 and 1.8% per year and cost increases at a rate between 0.33 and 7.81% per year. Similar effects are shown with the IHS and level outcome specifications. In terms of nonlinearity effects, we find the most pronounced changes in operational availability and cost occur for MLBs aged 15 years or more (in comparison to younger MLBs).     

Preemptive parallel‐machine scheduling with a common server to minimize makespan

We consider parallel‐machine scheduling with a common server and job preemption to minimize the makespan. While the non‐preemptive version of the problem is strongly NP‐hard, the complexity status of the preemptive version has remained open. We show that the preemptive version is NP‐hard even if there is a fixed number of machines. We give a pseudo‐polynomial time algorithm to solve the case with two machines. We show that the case with an arbitrary number of machines is unary NP‐hard, analyze the performance ratios of some natural heuristic algorithms, and present several solvable special cases. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 388–398, 2017