Preventive replacement policies with time of operations,mission durations,minimal repairs and maintenance triggering approaches

When a mission arrives at a random time and lasts for a duration, it becomes an interesting problem to plan replacement policies according to the health condition and repair history of the operating unit, as the reliability is required at mission time and no replacement can be done preventively during the mission duration. From this viewpoint, this paper proposes that effective replacement policies should be collaborative ones gathering data from time of operations, mission durations, minimal repairs and maintenance triggering approaches. We firstly discuss replacement policies with time of operations and random arrival times of mission durations, model the policies and find optimum replacement times and mission durations to minimize the expected replacement cost rates analytically. Secondly, replacement policies with minimal repairs and mission durations are discussed in a similar analytical way. Furthermore, the maintenance triggering approaches, i.e., replacement first and last, are also considered into respective replacement policies. Numerical examples are illustrated when the arrival time of the mission has a gamma distribution and the failure time of the unit has a Weibull distribution. In addition, simple case illustrations of maintaining the production system in glass factories are given based on the assumed data.     

Reward optimization of a repairable system

This paper analyzes a system subject to repairable and non-repairable failures. Non-repairable failures lead to replacement of the system. Repairable failures, first lead to repair but they lead to replacement after a fixed number of repairs. Operating and repair times follow phase type distributions (PH-distributions) and the pattern of the operating times is modelled by a geometric process. In this context, the problem is to find the optimal number of repairs, which maximizes the long-run average reward per unit time. To this end, the optimal number is determined and it is obtained by efficient numerical procedures.     

应用陶瓷型人工髋关节治疗中青年髋关节伤病

目的比较陶瓷型与生物固定型人工髋关节治疗中青年髋关节创病的中短期应用结果，以探讨陶瓷型人工髋关节假体的临床应用价值。方法对人工全髋关节置换术132例164髋进行随访，其中生物固定型超高分子聚乙烯-钻铬钼合金全髋假体97例99髋，陶瓷-陶瓷非骨水泥型假体35例35髋，应用Harris评分进行功能评价，应用Gruen股骨分区与髋臼Delee—charnly分区方法进行影像学评价。结果Harris功能评分两组患者之间未见显著性差异，但是影象学上，超高分子聚乙烯-钻铬钼合金假体的松动范围或程度要大于陶瓷假体。结论对于年轻患者，陶瓷-陶瓷假体中短期效果良好，影象学松动率明显低于超高分子聚乙烯-钻铬钼合金假体。但是由于其价格昂贵，使用范围受到限制，而且远期结果有待于临床观察。     

建设电动汽车电池更换式充电站的可操作性分析

电池更换充电模式在当前的科技水平条件下成为电动汽车推广普及的快捷方式。本文根据前人的研究成果。从现实可操作性的角度对电池更换式充电站的建设、管理、标准化等环节作出分析,并在充电时间、电池流通管理、充电安全等方面进行了比较论证,证明了电池更换式充电站的现实可操作性较强。     

高斯噪声与窄带干扰同时抑制技术

为了抑制接收信号中的高斯噪声和窄带干扰,在进一步分析边带相关置换（SCR）算法的基础上,提出了一种新的高斯噪声和窄带干扰抑制算法——循环边带相关置换（CSCR）算法. CSCR算法将SCR思想引入循环谱相关理论中,利用循环谱相关可有效抑制高斯噪声的技术优势,在接收信号的谱相关密度函数中用相对于窄带干扰的边带对称值代替干扰值来重构期望信号,从而实现了高斯噪声和窄带干扰的同时抑制. 该算法对谱相关密度谱对称的调制方式均适用. 通过对2PSK信号的计算机仿真表明,循环边带相关置换算法可以有效抑制高斯噪声和窄带干扰.     

软弱地基不同置换深度及宽度对堤防应力变形及稳定性影响研究

软弱地基对堤防稳定性有很大影响。本文采用数值计算方法分析了不同置换深度、不同的坡脚外置换宽度对堤防应力变形及稳定性影响规律。结果表明,当软土厚度一定时,随着置换厚度增大,新填筑堤防地基表面沉降减小,安全系数有所增大;当置换厚度一定时,增大堤脚外地基置换宽度对加固区堤身及地基变形影响不大,但对稳定性影响较大;置换深度越小,堤脚外加固宽度就越大。其成果对软基置换设计具有一定指导意义。     

一种面向固态硬盘的Cache置换算法

固体硬盘的出现改变了现有存储子系统的框架,也逐渐成为了嵌入式应用的主流存储设备.但是其自身的写机制由于需要先擦后写,成为了影响SSD性能的瓶颈.针对此问题,出于减少写操作次数这一思路提出了LRU-AB算法,力图在基于Cache数据的访问频度上改进SSD置换算法.同时对现有算法进行了分析.     

Web proxy cache replacement scheme based on back-propagation neural network

Web proxy caches are used to reduce the strain of contemporary web traffic on web servers and network bandwidth providers. In this research, a novel approach to web proxy cache replacement which utilizes neural networks for replacement decisions is developed and analyzed. Neural networks are trained to classify cacheable objects from real world data sets using information known to be important in web proxy caching, such as frequency and recency. Correct classification ratios between 0.85 and 0.88 are obtained both for data used for training and data not used for training. Our approach is compared with Least Recently Used (LRU), Least Frequently Used (LFU) and the optimal case which always rates an object with the number of future requests. Performance is evaluated in simulation for various neural network structures and cache conditions. The final neural networks achieve hit rates that are 86.60% of the optimal in the worst case and 100% of the optimal in the best case. Byte-hit rates are 93.36% of the optimal in the worst case and 99.92% of the optimal in the best case. We examine the input-to-output mappings of individual neural networks and analyze the resulting caching strategy with respect to specific cache conditions.     

Performance evaluation of Web proxy cache replacement policies

The continued growth of the World-Wide Web and the emergence of new end-user technologies such as cable modems necessitate the use of proxy caches to reduce latency, network traffic and Web server loads. In this paper we analyze the importance of different Web proxy workload characteristics in making good cache replacement decisions. We evaluate workload characteristics such as object size, recency of reference, frequency of reference, and turnover in the active set of objects. Trace-driven simulation is used to evaluate the effectiveness of various replacement policies for Web proxy caches. The extended duration of the trace (117 million requests collected over 5 months) allows long term side effects of replacement policies to be identified and quantified.

Our results indicate that higher cache hit rates are achieved using size-based replacement policies. These policies store a large number of small objects in the cache, thus increasing the probability of an object being in the cache when requested. To achieve higher byte hit rates a few larger files must be retained in the cache. We found frequency-based policies to work best for this metric, as they keep the most popular files, regardless of size, in the cache. With either approach it is important that inactive objects be removed from the cache to prevent performance degradation due to pollution.