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991.
992.
Michael Bartholomew-Biggs Bruce Christianson Ming Zuo 《Computational Optimization and Applications》2006,35(2):261-279
We deal with the problem of scheduling preventive maintenance (PM) for a system so that, over its operating life, we minimize
a performance function which reflects repair and replacement costs as well as the costs of the PM itself. It is assumed that
a hazard rate model is known which predicts the frequency of system failure as a function of age. It is also assumed that each PM produces
a step reduction in the effective age of the system.
We consider some variations and extensions of a PM scheduling approach proposed by Lin et al. [6]. In particular we consider
numerical algorithms which may be more appropriate for hazard rate models which are less simple than those used in [6] and
we introduce some constraints into the problem in order to avoid the possibility of spurious solutions. We also discuss the
use of automatic differentiation (AD) as a convenient tool for computing the gradients and Hessians that are needed by numerical
optimization methods.
The main contribution of the paper is a new problem formulation which allows the optimal number of occurrences of PM to be determined along with their optimal timings. This formulation involves the global minimization
of a non-smooth performance function. In our numerical tests this is done via the algorithm DIRECT proposed by Jones et al.
[19]. We show results for a number of examples, involving different hazard rate models, to give an indication of how PM schedules
can vary in response to changes in relative costs of maintenance, repair and replacement.
Part of this work was carried out while the first author was a Visiting Professor in the Department of Mechanical Engineering
at the University of Alberta in December 2003. 相似文献
993.
994.
Four common mesostructured aluminosilicates (e.g. AlMCM‐41, AlMCM‐48, AlMSU‐1 and AlSBA‐15, Si/Al = 7.5) with different pore framework structures were prepared via post‐synthetic method utilizing aluminum isopropoxide as the aluminating agent and characterized by 27Al MAS NMR, XRD, N2‐adsorption isotherm and NH3‐TPD. It was found that, on the basis of the above analysis results, AlMCM‐41, AlMSU‐1 and AlSBA‐15 retained more mesoporosity than cubic Al/MCM‐48 after exposure to pure steam at 800 °C, which may be responsible for their much higher activities in bulky 1,3,5‐triisopropylbenzene (TIPB) conversion. 相似文献
995.
球面上5点分布问题的数值解法 总被引:1,自引:0,他引:1
针对物理学家Thomson在研究核电子的平衡时提出球面上点的分布问题,本文设计了一个新型群体分裂演化算法PDEA(PoPulation-Decomposition Evolutionary Algorithm)来求解该问题在各种能量意义下的5点分布问题:minVs(X,α),得到了令人惊喜的结果:这些点的分布为两个点位于球的两极,其余3点位于赤道上形成一个等边三角形.特别是当α=1时,即Thomson问题minVs(X,1),这时达到最小能量Vs(X,1)=6.474691。 相似文献
996.
介绍一种基于高斯光束传输特性对Mie散射激光雷达回波信号校正的新方法.首先根据发射激光束的高斯光束特性,对大气激光雷达回波信号作高斯修正,然后在大气近似均匀假定下,对近场区经高斯修正的回波信号距离校正函数进行二次曲线拟合,实现对交叠面积影响的修正,实际计算表明,用此方法对Mie散射激光雷达回波近场信号进行处理,可获得与实际更为接近的反演结果.
关键词:
大气激光雷达
高斯光束
回波近场信号修正
大气消光系数 相似文献
997.
998.
Zuo Liang Zhang Yu-dong Zhao Xiang He Chang-shu Claude Esling 《Frontiers of Physics in China》2006,1(1):85-91
This paper summarizes our recent work on the application of high static magnetic fields to the austenite-to-ferrite transformation
and the tempering processes in hot-rolled 42CrMo steel. The thermodynamic and kinetic effects of the high magnetic fields
on austenite decomposition and the influences of the high magnetic field on carbide precipitation and the matrix recovery
during high- and low-temperature tempering are briefly outlined. Insight into these aspects may provide better understanding
of the effects of high magnetic fields on diffusional phase transformations and is of both theoretical significance and technical
interest. 相似文献
999.
记Jn,kr为具有如下性质的n维未定向上协边类α构成的集合:存在α的一个代表元Mn及(Z2)k在Mn上的作用,其不动点集为常余维数r .记Jn,kr=∑nJn,kr,则Jn,kr为未定向上协边环MOn= 相似文献
1000.