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181.
Hollander, Park, and Proschan define a survival function S of a positive random variable X to be new better than used at age t0 (NBU-{t0}) if S satisfies $ \begin{array}{*{20}c} {\frac{{S(x + t_0)}}{{S\left({t_0} \right)}} \le S\left(x \right),} & {{\rm for}\,{\rm all}\,x\, \ge \,0,} \\ \end{array}$ where S(x) = P(X > x). The NBU-{t0} class is a special case of the NBU-A family of survival distributions, where A is a subset of [0, ∞). These families introduce a variety of modeling possibilities for use in reliability studies. We treat problems of nonparametric estimation of survival functions from these classes by estimators which are themselves members of the classes of interest. For a number of such classes, a recursive estimation technique is shown to produce closed-form estimators which are strongly consistent and converge to the true survival distribution at optimal rates. For other classes, additional assumptions are required to guarantee the consistency of recursive estimators. As an example of the latter case, we demonstrate the consistency of a recursive estimator for S ∈ NBU-[t0, ∞) based on lifetime data from items surviving a preliminary “burn-in” test. The relative precision of the empirical survival curve and several recursive estimators of S are investigated via simulation; the results provide support for the claim that recursive estimators are superior to the empirical survival curve in restricted nonparametric estimation problems of the type studied here. 相似文献
182.
This article considers the problem of scheduling parallel processors to minimize the makespan. The article makes two key contributions: (1) It develops a new lower bound on the makespan for an optimal schedule, and (2) it proposes an efficient two-step algorithm to find schedules of any desired accuracy, or percent above optimal. In addition, a posterior bound on LPT (longest processing time) sequencing is developed in the article. It is proved that this bound dominates the previously reported bounds on LPT sequencing. 相似文献
183.
This article deals with the statistical analysis of an N-component series system supported by an active standby and one repair facility. Assuming that the life and repair times of the components are independent exponential random variables, the probability distribution of the first passage to the system failure time is shown to be a convolution of two independent exponential distributions. Three observation schemes are considered to obtain the maximum likelihood estimates of the survival function. Information matrices are supplied. Numerical results based on Monte Carlo simulation are presented. It is noted that component level information (failure rate, repair rate) is not necessary for estimating the survival function of the system. 相似文献
184.
The gas turbine engine is used to power many different types of commercial and military aircraft. During the scheduled maintenance of these engines, many of the turbine components are replaced. Of particular importance to us is the replacement of nozzle guide vanes in the nozzle assembly section of the engine. Individual vanes are selected from inventory to make up sets, and each set must meet certain characteristics in order to be feasible. The vanes in each set must then be sequenced in order to meet additional criteria. In this article, we give heuristics for the above partitioning and sequencing problems. Empirical analyses, using actual data from a branch of the armed services and a major engine manufacturer, are used to evaluate the proposed heuristics. The results of these analyses indicate that the heuristics are effective. 相似文献
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186.
Susanna D. Wing 《Small Wars & Insurgencies》2016,27(1):59-80
The March 2012 coup in Mali opened the door to expanded territorial occupation in northern Mali by Tuareg separatists and subsequently armed Islamist extremists. French forces intervened at the behest of the interim government in Mali. This article examines how various actors frame the conflict to their advantage. While the Malian government and France are allies, the position of various Tuareg actors shift over time as they strategize and weigh the value of allegiance with the French. Local extremist organizations are labeled as terrorists and are targeted as enemies. This article argues that the conflict has been decontextualized and framed within the ‘war on terror’. France’s decision to intervene and to expand their regional military presence, rather than exit, is legitimized by the framing of their intervention as integral to counterterrorism efforts. 相似文献
187.
A single server is faced with a collection of jobs of varying duration and urgency. Each job has a random lifetime during which it is available for nonpreemptive service. Should a job's lifetime expire before its service begins then it is lost from the system unserved. The goal is to schedule the jobs for service to maximize the expected number served to completion. Two heuristics have been proposed in the literature. One (labeled πS) operates a static priority among the job classes and works well in a “no premature job loss” limit, whereas the second (πM) is a myopic heuristic which works well when lifetimes are short. Both can exhibit poor performance for problems at some distance from the regimes for which they were designed. We develop a robustly good heuristic by an approximative approach to the application of a policy improvement step to the asymptotically optimal heuristic πS, in which we use a fluid model to obtain an approximation for the value function of πS. The performance of the proposed heuristic is investigated in an extensive numerical study. © 2010 Wiley Periodicals, Inc. Naval Research Logistics 2010 相似文献
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189.
Irrespective our views on the rationality of our opponent's continuing to conduct operations against us, unless utterly extirpated, he retains a vote on when and how conflict will end. This is because war is about power — compelling another actor to do something he would not otherwise do, or to cease doing something he would otherwise prefer to do. In planning for conflict termination we should account for the peculiarities of opponents who may decide not to quit when we have beat them fair and square. We do not desire that they cease conventional fighting, but that they cease fighting altogether. 相似文献
190.
Allan D. English 《战略研究杂志》2013,36(3):408-431
This article borrows from the work of Clausewitz to posit two general approaches to the pursuit of limitation in war, one being political and the other technical. The political approach seeks to control escalation via consensual arrangements with the adversary, while the technical approach seeks to forestall escalation by peremptorily destroying the enemy's military capability. It is argued that the 'Revolution in Military Affairs' (RMA) instantiates the second, technical, approach to war limitation. By exploiting advanced technology, the US armed forces hope to limit the costs of war by defeating their adversaries in a rapid, decisive manner. The problems associated with this approach are discussed in relation to the nature of the conflicts that the US is likely to face in the foreseeable future. The article concludes by suggesting that such conflicts will require that more attention be paid to the political sources of limitation in war. 相似文献