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Much operational reliability data available, e.g., in the nuclear industry, is heavily right-censored by preventive maintenance. The common methods for dealing with right-censored data (total time on test statistic, Kaplan-Meier estimator, adjusted rank methods) assume the s-independent competing-risk model for the underlying failure process and the censoring process, even though there are, many s-dependent competing-risk models that can also interpret the data. It is not possible to identify the "correct" competing risk model from censored data. A reasonable question is whether this model uncertainty is of practical importance. This paper considers the impact of this model-uncertainty on maintenance optimization, and shows that it can be substantial. Three competing-risk model classes are presented which can be used to model the data, and determine an optimal maintenance policy. Given these models, then consider the error that is made when optimizing costs using the wrong model. Model uncertainty can be expressed in terms of the "dependence between competing risks" which can be quantified by expert judgment. This enables reformulating the maintenance optimization problem to account for model uncertainty. 相似文献
3.
Timothy Zurrer Kenneth Wong Jonathan Horlyck Emma C. Lovell Joshua Wright Nicholas M. Bedford Zhaojun Han Kang Liang Jason Scott Rose Amal 《Advanced functional materials》2021,31(9):2007624
The vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. However, a lack of straightforward methods for producing nanoparticle-encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed-metal MOF, NiMg-MOF-74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in Ni O and Mg O coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X-ray absorption fine structure and X-ray photoelectron spectroscopy. By preserving a segment of the Mg2+-containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization. 相似文献
4.
1,3,5,5-Tetranitrohexahydropyrimidine, (1), was synthesized by the oxidative nitrolysis of 1,3-diisopropyl-5,5-dinitrohexahydropyrimidine, (2), with 90% nitric acid. The course of the reaction was influenced by both the n-alkyl substituents and the nitrolyzing medium. Compound 1 was synthesized by nitrolysis of N,N-diisopropyl or dicyclohexyl substituents, while dimethyl, diethyl, or other di-n-alkyl substituents yielded ring-cleaved products 3 and/or 4. Similar effects were observed by varying the nitric acid concentration. The formation of nitramine products, rather than nitrosamine or alkyl amide products that generally result from tertiary amine nitrolysis, is attributed to conformational changes in a postulated nitronium ion-amine complex intermediate. 相似文献
5.
Li Fan Fallahi M. Zakharian A.R. Hader J. Moloney J.V. Bedford R. Murray J.T. Stolz W. Koch S.W. 《Photonics Technology Letters, IEEE》2007,19(8):544-546
We demonstrate a widely tunable vertical-external-cavity surface-emitting laser (VECSEL) with a W-shaped cavity, in which two VECSEL chips serve as fold mirrors and a birefringent filter is inserted at Brewster's angle. These two chips provide much higher modal gain and broader bandwidth of the gain than a single chip does, enhancing the VECSEL tuning range and reducing the variation of tunable output power with the tuned wavelength. This two-chip VECSEL configuration makes it possible to shape the modal gain spectra of the laser or to manipulate the tuning curve of the laser by two different chips with certain gain peak detuning (offset). Multiwatts high-brightness linearly polarized output with a tuning range of 33 nm is demonstrated in such a two-chip VECSEL 相似文献
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L Westrich S Domann B Faust D Bedford DA Hopwood A Bechthold 《Canadian Metallurgical Quarterly》1999,170(2):381-387
From a cosmid library of Streptomyces cyanogenus S136, DNA fragments encompassing approximately 35 kb of the presumed landomycin biosynthetic gene cluster were identified and sequenced, revealing 32 open reading frames most of which could be assigned through data base comparison. 相似文献
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Fallahi M. Li Fan Kaneda Y. Hessenius C. Hader J. Hongbo Li Moloney J.V. Kunert B. Stolz W. Koch S.W. Murray J. Bedford R. 《Photonics Technology Letters, IEEE》2008,20(20):1700-1702
10.
T. J. Anderson F. Ren L. Covert J. Lin S. J. Pearton T. W. Dalrymple C. Bozada R. C. Fitch N. Moser R. G. Bedford M. Schimpf 《Journal of Electronic Materials》2006,35(4):675-679
By using a frequency-tripled Nd:YVO4 laser source (355 nm) for drilling through-wafer via holes in SiC substrates, we can reduce the surface contamination and
achieve better smoothness inside the via holes compared to use of the more common 1064-nm Nd:YVO4 laser. The sheet and contact resistance of AlGaN/GaN HEMT layers grown on SiC substrates were similar after formation of
vias by 355-nm laser drilling to those of the undrilled reference sample. By sharp contrast, 1064-nm laser drilling produces
significant redeposition of ablated material around the via and degrades the electrical properties of the HEMT layers. 相似文献