A preventive maintenance policy for a continuously monitored system with correlated wear indicators

A continuously monitored system is considered, that gradually and stochastically deteriorates according to a bivariate non-decreasing Lévy process. The system is considered as failed as soon as its bivariate deterioration level enters a failure zone, assumed to be an upper set. A preventive maintenance policy is proposed, which involves a delayed replacement, triggered by the reaching of some preventive zone for the system deterioration level. The preventive maintenance policy is assessed through a cost function on an infinite horizon time. The cost function is provided in full form, and tools are provided for its numerical computation. The influence of different parameters on the cost function is studied, both from a theoretical and/or numerical point of view.     

Fluorescent pH Indicator. Spectral Changes of 4-Methylumbelliferone

Abstract

4-Methylumbelliferone is a useful acid-base fluorescent indicator with a midpoint of its transition interval at pH 7.6. Both anionic and neutral forms fluoresce in the blue with high quantum yield (70%). The indicator properties are based on a blue shift of the absorption spectrum in acid. Depending on the excitation wavelength employed, one has the option of following either an increase or a decrease in fluorescence as the pH changes.     

新疆区域农业品牌价值最大化及其评价指标与模型

基于对区域农业品牌和新疆区域农业品牌发展的研究综述,应用产品整体概念理论探讨了新疆农产品多层面产品要素的品牌化和综合品牌价值最大化,分析了支撑新疆农产品品牌价值最大化的产业链管理与创新,构建了新疆农业品牌价值最大化评价指标体系,并请新疆的11位农业专家进行评分,应用AHP方法得到了各指标的权重,构建了定量评价模型,以库尔勒香梨为案例,应用模糊综合评价方法测度了特定农产品品种的区域品牌价值,明确了新疆区域农业品牌发展面临的薄弱环节,为新疆政府和企业的品牌农业决策提供了理论依据.     

随机次自相似集的表示

本文引进了随机次自相似集与随机推移集的概念,讨论了随机次自相似集的结构,并证明了任一随机集是随机次自相似集的充分必要条件是：该随机集可以表为某一个随机推移集的某个像集。     

非标记电化学DNA杂交指示剂

电化学DNA杂交检测技术因其快速、灵敏、低消耗和易于操作等优点而在临床医学、环境监测和药物分析等领域受到普遍关注。电化学DNA杂交指示剂是DNA电化学杂交传感器的重要组成部分,能与单链DNA和双链DNA通过不同的模式和作用力进行差异性结合。本文介绍了电化学杂交指示剂的定义及其在DNA电化学传感器中的重要性,根据分子结构上的特征差异,将非标记型电化学杂交指示剂分为有机染料（荧光素）、药物分子和金属配合物三类,并从中选取了各个类型中具有代表性的指示剂对它们的工作原理、研究进展和应用现状进行了比较和评述。对杂交指示剂的设计和开发前景,特别是满足基因芯片应用等方面做出了展望。     

Smart Biopolymer-Based Nanocomposite Materials Containing pH-Sensing Colorimetric Indicators for Food Freshness Monitoring

Nanocomposite biopolymer materials containing colorimetric pH-responsive indicators were prepared from gelatin and chitosan nanofibers. Plant-based extracts from barberry and saffron, which both contained anthocyanins, were used as pH indicators. Incorporation of the anthocyanins into the biopolymer films increased their mechanical, water-barrier, and light-screening properties. Infrared spectroscopy and scanning electron microscopy analysis indicated that a uniform biopolymer matrix was formed, with the anthocyanins distributed evenly throughout them. The anthocyanins in the composite films changed color in response to alterations in pH or ammonia gas levels, which was used to monitor changes in the freshness of packaged fish during storage. The anthocyanins also exhibited antioxidant and antimicrobial activity, which meant that they could also be used to slow down the degradation of the fish. Thus, natural anthocyanins could be used as both freshness indicators and preservatives in biopolymer-based nanocomposite packaging materials. These novel materials may therefore be useful alternatives to synthetic plastics for some food packaging applications, thereby improving the environmental friendliness and sustainability of the food supply.     

一类输水线路的最佳布线问题

主要解决了如下问题 :对于从河流 L取水并输送到 L同岸的两个用水点 A,B的输水工程(图 1) ,当修建各段输水管道的耗资系数分别为 k1,k2 ,k3 时 ,如何确定抽水点 P及分水点 O才能使加权和值w =k1OA+ k2 OB+ k3OP为最小 .     

The effect of bioindicator preparation and storage on thermal resistance of Bacillus stearothermophilus spores

Paper strips inoculated with spores of Bacillus stearothermophilus ATCC 7953 were conventionally dried (lot 1) and lyophilized (lot 2); stored in defined environments of 32 and 86% relative humidity at 10, 25 and 33°C for 210 d; and submitted to moist heat treatments at 121°C. A significant decrease in thermal resistance from initial starting levels was found for lyophilized bioindicators stored at 86% relative humidity. The respective average D _121°C values were 1.55 ± 0.05 and 1.37 ± 0.10 min for lyophilized bioindicators stored at 32 and 86% relative humidity; and 1.65±0.15min and 1.57 ± 0.11 min for dried bioindicators stored in the same environments.     

示波中和滴定指示剂的研究（Ⅲ）

本文介绍了对酸性示波中和指示剂刚果红、百里酚兰和对、间、邻－硝基酚等指示滴定终点时切口随变化的原理的探讨。