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1.
Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
2.
In survival or reliability studies, the mean residual life or life expectancy is an important characteristic of the model. Whereas the failure rate can be expressed quite simply in terms of the mean residual life and its derivative, the inverse problem—namely that of expressing the mean residual life in terms of the failure rate—typically involves an integral of a complicated expression. In this paper, we obtain simple expressions for the mean residual life in terms of the failure rate for certain classes of distributions which subsume many of the standard cases. Several results in the literature can be obtained using our approach. Additionally, we develop an expansion for the mean residual life in terms of Gaussian probability functions for a broad class of ultimately increasing failure rate distributions. Some examples are provided to illustrate the procedure. 相似文献
3.
The purpose of this paper is to review the mechanisms and available theoretical methods for modeling the strength and failure of thin film/substrate systems 相似文献
4.
This paper investigates regression quantiles (RQ) for unstable autoregressive models. The uniform Bahadur representation of the RQ process is obtained. The joint asymptotic distribution of the RQ process is derived in a unified manner for all types of characteristic roots on or outside the unit circle. It involves stochastic integrals in terms of a sequence of independent and identically distributed multivariate Brownian motions with correlated components. The related L-estimator is also discussed. The asymptotic distributions of the RQ and the L-estimator corresponding to the nonstationary componentwise arguments can be transformed into a function of a normal random variable and a sequence of i.i.d. univariate Brownian motions. This is different from the analysis based on the LSE in the literature. As an auxiliary theorem, a weak convergence of a randomly weighted residual empirical process to the stochastic integral of a Kiefer process is established. The results obtained in this paper provide an asymptotic theory for nonstationary time series processes, which can be used to construct robust unit root tests. 相似文献
5.
Xinyu Huang Roham Solasi Yue Zou Matthew Feshler Kenneth Reifsnider David Condit Sergei Burlatsky Thomas Madden 《Journal of Polymer Science.Polymer Physics》2006,44(16):2346-2357
The life of proton exchange membrane fuel cells (PEMFC) is currently limited by the mechanical endurance of polymer electrolyte membranes and membrane electrode assemblies (MEAs). In this paper, the authors report recent experimental and modeling work toward understanding the mechanisms of delayed mechanical failures of polymer electrolyte membranes and MEAs under relevant PEMFC operating conditions. Mechanical breach of membranes/MEAs in the form of pinholes and tears has been frequently observed after long‐term or accelerated testing of PEMFC cells/stacks. Catastrophic failure of cell/stack due to rapid gas crossover shortly follows the mechanical breach. Ex situ mechanical characterizations were performed on MEAs after being subjected to the accelerated chemical aging and relative humidity (RH) cycling tests. The results showed significant reduction of MEA ductility manifested as drastically reduced strain‐to‐failure of the chemically aged and RH‐cycled MEAs. Postmortem analysis revealed the formation and growth of mechanical defects such as cracks and crazing in the membranes and MEAs. A finite element model was used to estimate stress/strain states of an edge‐constrained MEA under rapid RH variations. Damage metrics for accelerated testing and life prediction of PEMFCs are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2346–2357, 2006 相似文献
6.
Kyle Siegrist 《Journal of Theoretical Probability》1994,7(4):725-737
Three fundamental characterizations of the standard exponential distribution on [0, ) are the remaining life, memoryless and constant failure properties. Analogs of these properties are studied for distributions on a class of semigroups in which the semigroup operation replaces addition, a compatible partial order replaces the ordinary order, and a left-invariant measure replaces Lebesgue measure. Partial characterizations of exponential distributions on such semigroups are obtained and the semigroup formulation provides new characterizations of certain aging properties studied in reliability-increasing failure rate, new better than used, and increasing failure rate average. 相似文献
7.
8.
HOU A-li MENG Qing-fan AN Jin-shuang ZHU Kai FENG Yun TENG Li-rong College of Life Science Jilin University Changchun P. R. China 《高等学校化学研究》2008,24(5):584-587
The crude polysaccharide was obtained by means of the decolorization of porphyrized Cordyceps minlitaris stroma with organic solvent, extraction with hot water, precipitation in 80% ethanol, and protein removal with the Sevag method. After purification with Sephadex G-75, two of its components, CMP-1 and CMP-2, were obtained. Through the assay of gel chromatography and polarimetry, CMP-1 was identified as pure polysaccharide. The results demonstrated that CMP-1 had favorable oxidation resistance activity, which could scavenge not only oxygen-free radicals in the self-oxidation system of pyrogallic acid, but also the hydroxide-free radicals in the Fenton system. The study focused on the effects of low, medium, and high dosages of CMP-1 in rat blood serum on the proliferation of glomerular mesangial cells in vitro. Through MTT Colorimetric analysis, the activities were compared among the blank control group and the Niaoduqing positive control group CMP-1 and CMP-2. The results shows that CMP-1 was able to inhibit the proliferation of rat glomerular mesangial cells effectively. Therefore, CMP-1, one component of polysaccharides of Cordyceps minlitaris, was certainly a potential remedy for hyperplastic glomerular nephritis, whose antioxidant activity could slow down the process of chronic renal failure(CRF) to some extent. 相似文献
9.
This study addresses the effectiveness of a simple stiffness tailoring concept to delay damage initiation, control damage progression, and improve residual strength in tensile-loaded composite plates with a central circular cutout. The tailoring concept is to simply reposit all axially oriented (0°) material into regions near the edge of the plate away from the cutout. This tailoring is done in a way so as not to affect the weight of the plate. This accomplishes several beneficial changes in the way that the plate resists loading with no increases in material cost or weight. Lowering the axial stiffness of the laminate surrounding the cutout lowers the stress concentration. Increasing the axial stiffness near edges of the plate attracts loading away from the vicinity of the cutout to further lower stresses in the critical cutout region. This study focuses on in-plane response including damage progression and residual strength as a function of the degree of tailoring and cutout size. Strength and stiffness properties typical of IM7/8551-7 preperg material were assumed and a modified version of the Hashin failure criteria was used to identify the local damage. Results show that tailoring can significantly increase the damage initiation load and the residual strength. In some cases, observed evidence shows that tailoring performs as a damage arrest mechanism. 相似文献
10.
系统可靠性建模分析是开展可靠性分配、预计、故障树分析及可靠性优化设计的基础。介绍了一种光电系统可靠性建模分析方法,针对光电系统中部分分系统具有多种失效模式且各失效模式均服从指数分布的特点,依据齐次马尔科夫理论,采用马尔科夫状态转移图方法建立了产品的可靠性模型,并给出解析表达式、数值计算方法和Monte Carlo仿真方法。最后,将其应用于某机载光电系统供电回路的实例分析中。采用两种计算方法及Monte Carlo仿真方法分别进行计算,并将结果进行对比分析,证明了该方法的正确性及可行性。 相似文献