Optimizing Preventive Maintenance Models

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.     

Optical matching layer structures in evanescent coupling photodiodes at a wavelength of 1.55μm： physics,design and simulation

We have studied the optical matching layers (OMLs) and external quantum efficiency in the evanescent coupling photodiodes (ECPDs) integrating a diluted waveguide as a fibre-to-waveguide coupler, by using the semi-vectorial beam propagation method (BPM). The physical basis of OML has been identified, thereby a general designing rule of OML is developed in such a kind of photodiode. In addition, the external quantum efficiency and the polarization sensitivity versus the absorption and coupling length are analysed. With an optical matching layer, the absorption medium with a length of 30μm could absorb 90% of the incident light at 1.55μm wavelength, thus the total absorption increases more than 7 times over that of the photodiode without any optical matching layer.     

Infinite-dimensional Frobenius manifolds underlying the Toda lattice hierarchy

Following the approach of Carlet et al. (2011) [9], we construct a class of infinite-dimensional Frobenius manifolds underlying the Toda lattice hierarchy, which are defined on the space of pairs of meromorphic functions with possibly higher-order poles at the origin and at infinity. We also show a connection between these infinite-dimensional Frobenius manifolds and the finite-dimensional Frobenius manifolds on the orbit space of extended affine Weyl groups of type A defined by Dubrovin and Zhang.     

A decoupling two‐grid algorithm for the mixed Stokes‐Darcy model with the Beavers‐Joseph interface condition

In this article, a decoupling scheme based on two‐grid finite element for the mixed Stokes‐Darcy problem with the Beavers‐Joseph interface condition is proposed and investigated. With a restriction of a physical parameter α, we derive the numerical stability and error estimates for the scheme. Numerical experiments indicate that such two‐grid based decoupling finite element schemes are feasible and efficient. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 1066–1082, 2014     

刚体转动惯量实验误差分析

本文指出,在单通道计时法测量刚体转动惯量的实验中,当刚体系轴上摩擦力矩较小时,可通过取较大的予置数Ｎ,来减少由于测量时间的涨落引起的转动惯量的测量误差;同时指出,外力矩中不考虑物体下落的加速度ａ时所引起的转动惯量测量偏差不能忽略;前者使测量结果偏小,后者使测量结果偏大,ａ的计入使总的测量误差变小。     

丁基橡胶母炼胶的成分分析

对一种丁工橡胶母炼胶，采用溶剂萃取方法进行成分分离，然后综合利用傅里叶变换红外光谱、气相色谱、X荧光光谱等手段对分离后的组分进行分析鉴定，从而确定了其配方，获得了满意的结果。     

微型铒玻璃激光器研究

报道了微型铒玻璃激光器的阶段性研究成果，研究了在自由振荡情况下输出膜片反射率、氙灯气压以及激光电容的大小对激光输出的影响。采用电光调Ｑ，获得了８ｍＪ的巨脉冲输出；采用转镜调Ｑ，获得了１２ｍＪ的巨脉冲输出，脉宽８０ｎｓ。