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51.
In this article, we discuss the optimal allocation problem in a multiple stress levels life‐testing experiment when an extreme value regression model is used for statistical analysis. We derive the maximum likelihood estimators, the Fisher information, and the asymptotic variance–covariance matrix of the maximum likelihood estimators. Three optimality criteria are defined and the optimal allocation of units for two‐ and k‐stress level situations are determined. We demonstrate the efficiency of the optimal allocation of units in a multiple stress levels life‐testing experiment by using real experimental situations discussed earlier by McCool and Nelson and Meeker. Monte Carlo simulations are used to show that the optimality results hold for small sample sizes as well. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2007 相似文献
52.
Chen and Bhattacharyya [Exact confidence bounds for an exponential parameter under hybrid censoring, Commun Statist Theory Methods 17 (1988), 1857–1870] considered a hybrid censoring scheme and obtained the exact distribution of the maximum likelihood estimator of the mean of an exponential distribution along with an exact lower confidence bound. Childs et al. [Exact likelihood inference based on Type‐I and Type‐II hybrid censored samples from the exponential distribution, Ann Inst Statist Math 55 (2003), 319–330] recently derived an alternative simpler expression for the distribution of the MLE. These authors also proposed a new hybrid censoring scheme and derived similar results for the exponential model. In this paper, we propose two generalized hybrid censoring schemes which have some advantages over the hybrid censoring schemes already discussed in the literature. We then derive the exact distribution of the maximum likelihood estimator as well as exact confidence intervals for the mean of the exponential distribution under these generalized hybrid censoring schemes. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004 相似文献
53.
Joanna R.Hall Olivia Matthews Timothy N.Volonakis Eric Liggins Karl P.Lymer Roland Baddeley Innes C.Cuthill Nicholas E.Scott-Samuel 《防务技术》2021,17(6):1833-1839
The human visual system is still an important factor in military warfare; military personnel receive training on effective search strategies, and camouflage that can effectively conceal objects and personnel is a key component of a successful integrated survivability strategy. Previous methods of camouflage assessment have, amongst others, used psychophysics to generate distinctiveness metrics. However, the population from which the human observers are drawn is often not well defined, or necessarily appropriate. In this experiment we designed a new platform for testing multiple patterns based on a camouflaged object detection task, and investigate whether trained military observers perform better than civilians. We use a two-alternative forced choice paradigm, with participants searching images of woodland for a replica military helmet displaying Olive Green, Multi Terrain Pattern, US Marine Pattern or, as a conspicuous control, UN Peacekeeper Blue. Our data show that there is no difference in detection performance between the two observer groups but that there are clear differences in the effectiveness of the different helmet colour patterns in a temperate woodland environment. We conclude that when tasks involve very short stimulus presentation times, task-specific training has little effect on the success of target detection and thus this paradigm is particularly suitable for robust estimates of camouflage efficacy. 相似文献
54.
This article explores the drilling behavior of polymer nanocomposites reinforced by Graphene oxide/Carbon fiber using a hybrid method of Grey theory and Principal component analysis (GR-PCA). An online digital dynamometer was employed for the evaluation of Thrust Force and Torque. The image processing technique computes the delamination. Response surface methodology (RSM) considers the parameters, namely, drilling speed (S), feed rate (F), Graphene Oxide wt.% (G) in designing the experimentation array. Principal component analysis (PCA) was used to tackle the response priority weight during the combination of multiple functions. Analysis of variance (ANOVA) scrutinized the influence of parameters and intended the regression models to predict the response. GR-PCA evaluated the optimal parametric setting and remarked that feed rate acts as the most predominant factor. The higher feed rate and wt.% of G is responsible for surface damages like fiber pull-out, fiber fracture and cracks. A significant improvement in drilling responses has been obtained and also validates through confirmatory test and microstructure investigations. 相似文献
55.
The present article discusses the properties of the mean residual life function in a renewal process. We examine the relationship this function has with the failure rate function and the conventional mean, variance and coefficient of variation of residual life. We also discuss some monotonicity properties of the mean residual life function. A partial order based on the renewal mean residual function is introduced along with its interrelationship with some existing stochastic orders. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 相似文献
56.
In this paper, we derive new families of facet‐defining inequalities for the finite group problem and extreme inequalities for the infinite group problem using approximate lifting. The new valid inequalities for the finite group problem include two‐ and three‐slope facet‐defining inequalities as well as the first family of four‐slope facet‐defining inequalities. The new valid inequalities for the infinite group problem include families of two‐ and three‐slope extreme inequalities. These new inequalities not only illustrate the diversity of strong inequalities for the finite and infinite group problems, but also provide a large variety of new cutting planes for solving integer and mixed‐integer programming problems. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008 相似文献
57.
John P. Cann 《Small Wars & Insurgencies》2013,24(1):196-225
In its colony of Angola, Portugal during its colonial wars (1961–1974) was able to exploit the economic dependence and divided population loyalties of its hostile neighbours the Congo and Zambia as well as the cleavages within the nationalist movements to prevent a crippling insurgency. The rulers of both countries were largely dependent on Angola for trade, and were eager to have the side effects of the robust Angolan economy with its 11% annual growth brush off on their own moribund ones. While relationships were never comfortable, the sponsors of revolution were forced to reign in their ‘freedom fighters’ in order to maintain the functioning of their export-dependent economies. Portuguese leadership also played a vital role, as it was able to bring together diverse elements of national power in a concerted policy for dealing with these enemies, whether they were insurgents or their sanctuary countries. This policy of leveraging national power and playing on the vulnerabilities of its opponents worked well during its war in Angola and still holds valuable lessons for countries that find themselves in similar circumstances. 相似文献
58.
John P. Cann 《Small Wars & Insurgencies》2013,24(3):500-516
On 4 January 1961 in Baixa do Cassange, in the north of Angola, the blacks who worked in the cotton fields began a strike. The army with air support was called to quell the rebellion, and the article emphasizes the importance of air support tethered to the ground forces, particularly in a remote and vast area of operations in the tropical rainy season. In this case, the support originally came in the form a squadron of Lockheed PV-2 Harpoons from Luanda, some 300 kilometers away. These open-ocean reconnaissance aircraft and their crews were ill-suited for the task. When this became apparent, four small Auster D5/160s were relocated from Negage to Malange, among the ground forces. The Austers flew reconnaissance missions over the troubled zones, dropped provisions and messages to the advancing ground forces, and served as a backup communications link. When the strike ceased after three weeks, the Austers assumed a humanitarian role in support of the starving population. The conclusion is that air support to ground forces is indispensable, must be properly tailored to the job, and must operate as an integral part of the ground forces. 相似文献
59.
Marc-Antoine Pérouse de Montclos 《Small Wars & Insurgencies》2013,24(5-6):863-885
ABSTRACTThis article discusses the shortcomings of the “de-radicalization doctrine” in sub-Saharan Africa. The issues raised are illustrated by the war against Boko Haram, which involves Nigeria, Niger, Chad and Cameroon. Relying on interviews with security officers, insurgents, civil servants, displaced people, humanitarian workers and Muslim and Christian clerics in Nigeria, Niger and Chad since 2005, the investigation shows that the four states focused on repression rather than demobilisation programs in prison or outdoors. The Boko Haram crisis is mainly a story of mismanagement. The article thus challenges the assumptions of the “de-radicalization doctrine” in Muslim Africa South of the Sahara. First, attempts to de-radicalize jihadi terrorists tend to focus too much on religious fanaticism and the exegesis of the Quran. Secondly, they are neither feasible nor efficient. Finally, they obscure priorities that are more important to counter extremism and demobilize insurgents. 相似文献
60.
Greece has regularly ranked as the country with the highest defence burden in NATO and the European Union. Over the past decades she has allocated an averatge 6% of GDP to defence yearly. This study using neural networks examines the external security determinants of Greek military expenditure in the context of the ongoing Greek‐Turkish conflict. 相似文献