Composite unimodality

This article defines a class of univariate functions termed composite unimodal, and shows how their minimization admits an effective search procedure, albeit one not as efficient as is Fibonacci search for unimodal functions. An approximate Lagrangian approach to an important real-world logistics problem is seen to yield a surrogate problem whose objective function is composite unimodal. The mathematical form of this objective function is likely to be encountered in solving future real-world problems. © 1993 John Wiley & Sons, Inc.     

Replacing nonidentical vital components to extend system life

We consider a system that depends on a single vital component. If this component fails, the system life will terminate. If the component is replaced before its failure then the system life may be extended; however, there are only a finite number of spare components. In addition, the lifetimes of these spare components are not necessarily identically distributed. We propose a model for scheduling component replacements so as to maximize the expected system survival. We find the counterintuitive result that when comparing components' general lifetime distributions based on stochastic orderings, not even the strongest ordering provides an a priori guarantee of the optimal sequencing of components. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Estimating the probability that a simulated system will be the best

Consider a stochastic simulation experiment consisting of v independent vector replications consisting of an observation from each of k independent systems. Typical system comparisons are based on mean (long‐run) performance. However, the probability that a system will actually be the best is sometimes more relevant, and can provide a very different perspective than the systems' means. Empirically, we select one system as the best performer (i.e., it wins) on each replication. Each system has an unknown constant probability of winning on any replication and the numbers of wins for the individual systems follow a multinomial distribution. Procedures exist for selecting the system with the largest probability of being the best. This paper addresses the companion problem of estimating the probability that each system will be the best. The maximum likelihood estimators (MLEs) of the multinomial cell probabilities for a set of v vector replications across k systems are well known. We use these same v vector replications to form v^k unique vectors (termed pseudo‐replications) that contain one observation from each system and develop estimators based on AVC (All Vector Comparisons). In other words, we compare every observation from each system with every combination of observations from the remaining systems and note the best performer in each pseudo‐replication. AVC provides lower variance estimators of the probability that each system will be the best than the MLEs. We also derive confidence intervals for the AVC point estimators, present a portion of an extensive empirical evaluation and provide a realistic example. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 341–358, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10019     

Dominating sets for rectilinear center location problems with polyhedral barriers

In planar location problems with barriers one considers regions which are forbidden for the siting of new facilities as well as for trespassing. These problems are important since they model various actual applications. The resulting mathematical models have a nonconvex objective function and are therefore difficult to tackle using standard methods of location theory even in the case of simple barrier shapes and distance functions. For the case of center objectives with barrier distances obtained from the rectilinear or Manhattan metric, it is shown that the problem can be solved in polynomial time by identifying a dominating set. The resulting genuinely polynomial algorithm can be combined with bound computations which are derived from solving closely connected restricted location and network location problems. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 647–665, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10038     

Epidemics,national security,and US immigration policy

What are relationships between epidemics, national security, and US immigration policy? This question is important because it sheds light on transnational or nontraditional security areas, American immigration policy, and a pressing issue for US leaders who have recently faced epidemics such as the West Africa Ebola outbreak that began in 2013. This article answers it and lays ground in the area by reviewing epidemics in world history, using International Relations and Security Studies works to specify dangers of contagions for states, and identifying three general immigration measures that American leaders have utilized from the seventeenth century to the present day to protect against contagions, which are (1) policies restricting entrance of foreigners thought to carry specified diseases, (2) the isolation or quarantining of immigrants with contagious disease, and (3) delegating the President with authority to stop immigration in the event of an epidemic abroad. This study has implications for research and contemporary US immigration policy.     

Nuclear deterrence and cyber warfare: coexistence or competition?

Nuclear deterrence and cyber war seem almost antithetical in their respective intellectual pedigrees. Nuclear weapons are unique in their ability to create mass destruction in a short time. Information or “cyber” weapons, at least for the most part, aim at sowing confusion or mass disruption instead of widespread physical destruction. Nevertheless, there are some intersections between cyber and nuclear matters, and these have the potential to become troublesome for the future of nuclear deterrence. For example, cyber attacks might complicate the management of a nuclear crisis. As well, information attacks on command-control and communications systems might lead to a mistaken nuclear launch based on false warnings, to erroneous interpretations of data or to panic on account of feared information blackout. It is not inconceivable that future nuclear strike planning will include a preliminary wave of cyber strikes or at least a more protracted “preparation of the battlefield” by roaming through enemy networks to plant malware or map vulnerabilities.     

Timely Verification at Large-Scale Gas Centrifuge Enrichment Plants

This article examines challenges in international nuclear safeguards pertaining to the timely detection of highly enriched uranium production at large-scale gas centrifuge enrichment plants. To establish where present gas centrifuge enrichment plant safeguards measures and approaches could be strengthened, we have created a discrete time model for simulating hypothetical misuse scenarios, both through transient phases and at steady-state. We find that timely detection of misuse at modern large-scale facilities presents a challenge for international safeguards. A toolbox of unattended measurement systems, along with remote monitoring, however, could be used to improve detection timeliness, enabling the initiation of follow-up activities, potentially on a rapid time scale. These measures, which would need very low false alarm rates, should be implemented in a graded approach, depending on the characteristics of each enrichment plant and an analysis of plausible acquisition paths for the State in which it is situated. Some of these technologies could provide significant benefit to plant operators.     

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).     

John Brown as guerrilla terrorist

John Brown is usually not considered to have been a terrorist, and even recent analyses of his activities consider him to be a guerrilla fighter or insurgent in his activities in Kansas. Brown, however, meets the criteria of a terrorist more than a guerrilla fighter when his activities in the Kansas Territory are considered. His raid on Harpers Ferry, however, is more in line with guerrilla operations or insurgent activities.