Coherent systems based on sequential order statistics

The sequential order statistics (SOS) are a good way to model the lifetimes of the components in a system when the failure of a component at time t affects the performance of the working components at this age t. In this article, we study properties of the lifetimes of the coherent systems obtained using SOS. Specifically, we obtain a mixture representation based on the signature of the system. This representation is used to obtain stochastic comparisons. To get these comparisons, we obtain some ordering properties for the SOS, which in this context represent the lifetimes of k‐out‐of‐n systems. In particular, we show that they are not necessarily hazard rate ordered. © 2011 Wiley Periodicals, Inc. Naval Research Logistics, 2011     

‘Masters of today’: military intelligence and counterinsurgency in Colombia, 1990–2009

Military intelligence forms a vital element of counter-insurgency operations. When the Colombian military suffered setbacks at the hands of the FARC in the 1990s, military intelligence received much of the blame. It was also accused of human rights violations. With the help of US. financed Plan Colombia, military intelligence has been reorganized, expanded, strengthened with upgraded technical capabilities, constrained to operate within defined legal boundaries, and refocused to match the government's strategic priorities. Human intelligence has laid the groundwork for impressive tactical and operational results since 2006. Nevertheless, like all intelligence services, that of the Colombian military continues to experience problems of structure and political outlook.     

Counterinsurgency and the limits of state-building: An analysis of Colombia's policy of territorial consolidation, 2006–2012

Since 2002 the Colombian government has been implementing a series of policy initiatives that have sought to coordinate state resources in a neo-classical counterinsurgency approach to fight the country's main insurgent group, the Fuerzas Armadas Revolucionarias de Colombia (FARC), and recover and consolidate the territory. Despite impressive operational successes against the insurgency and other illegal groups, the government has been unable to reassert its control and build legitimacy via the state-building effort known as ‘Consolidación’, in some of the most recalcitrant areas of the country. This article examines two areas where government efforts at consolidation appear to be failing to discuss the limits of COIN theory and practice.     

The politics of defense revival in Argentina

In marked contrast with previous decades, defense issues in Argentina have started to receive increasing political attention over the last few years. The main goal of this article is to account for this new found interest in defense policy. The article contends that this revival could be accounted for by both the implementation of a neo-developmentalist strategy and a type of control that emphasizes civilian oversight over the armed forces. Both factors have promoted the implementation of policies that favored an increase in the military budget, the reconstruction of the defense industry and the establishment of a new military doctrine. This article evaluates the impact of factors that have not been previously considered by the literature on defense attention in South America.     

A combined approach to solve binary multicriteria problems

An implicit enumeration algorithm is developed to determine the set of efficient points in zero-one multiple criteria problems. The algorithm is specialized for the solution of a particular class of facility location problems. The procedure is complemented with the use of the utility function of the decision maker to identify a subset of efficient point candidates for the final selection. Computational results are provided and discussed.     

Sharp bounds for the reliability of systems and mixtures with ordered components

In this article, we study how to derive bounds for the reliability and the expected lifetime of a coherent system with heterogeneous ordered components. These bounds can be used to compare the performance of the systems obtained by permuting the components at a given system structure, that is, to study where we should place the different components at a system structure to get the most reliable system. Moreover, a similar procedure is applied to get bounds for mixtures and for the generalized proportional hazard rate model when the baseline populations are ordered. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 108–116, 2017     

Colombian Military Thinking and the Fight against the FARC-EP Insurgency, 2002–2014

This article attempts to place in historical perspective the latest effort by Colombia’s military (Colmil) to defeat the now half century old insurgency of the Fuerzas Armadas Revolucionarias de Colombia – Ejército del Pueblo (FARC-EP). It argues that the ‘surge’ initiated under President Álvaro Uribe in 2002 with the assistance of the United States can only be fully analyzed in the context of the Colmil’s intellectual framework for counter-insurgency. Specifically, this article will explain how the protracted engagement with counter-insurgency has shaped the Colmil’s understanding of the nature of the conflict, as well as its attitudes towards its adversary, civil authority and the instrumentality of force. An understanding of the Colmil’s strategic tradition can also help to explain their apprehensions about the ongoing peace negotiations with the FARC-EP.     

On the application and extension of system signatures in engineering reliability

Following a review of the basic ideas in structural reliability, including signature‐based representation and preservation theorems for systems whose components have independent and identically distributed (i.i.d.) lifetimes, extensions that apply to the comparison of coherent systems of different sizes, and stochastic mixtures of them, are obtained. It is then shown that these results may be extended to vectors of exchangeable random lifetimes. In particular, for arbitrary systems of sizes m < n with exchangeable component lifetimes, it is shown that the distribution of an m‐component system's lifetime can be written as a mixture of the distributions of k‐out‐of‐n systems. When the system has n components, the vector of coefficients in this mixture representation is precisely the signature of the system defined in Samaniego, IEEE Trans Reliabil R–34 (1985) 69–72. These mixture representations are then used to obtain new stochastic ordering properties for coherent or mixed systems of different sizes. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Tail hazard rate ordering properties of order statistics and coherent systems

We study tail hazard rate ordering properties of coherent systems using the representation of the distribution of a coherent system as a mixture of the distributions of the series systems obtained from its path sets. Also some ordering properties are obtained for order statistics which, in this context, represent the lifetimes of k‐out‐of‐n systems. We pay special attention to systems with components satisfying the proportional hazard rate model or with exponential, Weibull and Pareto type II distributions. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007