Network sensor health problem

Many existing studies on the sensor health problem determine an individual sensor’s health status based on the statistical characteristics of collected data by the sensor. In this research, we study the sensor health problem at the network level, which is referred to as the network sensor health problem. First, based on the conservation principle of daily flows in a network, we separate all links into base links and non-base links, such that the flows on the latter can be calculated from those on the former. In reality, the network flow conservation principle can be violated due to the existence of unhealthy sensors. Then we define the least inconsistent base set of links as those that minimize the sum of squares of the differences between observed and calculated flows on non-base links. But such least inconsistent base sets may not be unique in a general road network. Finally we define the health index of an individual sensor as the frequency that it appears in all of the least inconsistent base sets. Intuitively, a lower health index suggests that the corresponding sensor is more likely to be unhealthy. We present the brute force method to find all least inconsistent base sets and calculate the health indices. We also propose a greedy search algorithm to calculate the approximate health indices more efficiently. We solve the network sensor health problem for a real-world example with 16 nodes and 30 links, among which 18 links are monitored with loop detectors. Using daily traffic count data from the Caltrans Performance Measurement System (PeMS) database, we use both the brute-force and greedy search methods to calculate the health indices for all the sensors. We find that all the four sensors flagged as unhealthy (high value) by PeMS have the lowest health indices. This confirms that a sensor with a lower health index is more likely to be unhealthy. Therefore, we can use such health indices to determine the relative reliability of different sensors’ data and prioritize the maintenance of sensors.     

The authors in this issue

This paper considers the main road-traffic parameters that determine air pollution, i.e. the total volume of traffic, road speeds and the composition of the vehicle fleet. Changes in the amounts of pollutants emitted, and the importance of each of the three parameters, have been computed by using a traffic assignment model, which also represents emission factors. The types of policies that may be implemented to reduce the environmental impact of transport are then considered. The study demonstrates, for example, that the impact of a deterioration in traffic conditions is limited in comparison with the effect of forecast increases in traffic and improvements in the environmental performance of vehicles. As a consequence, if cities and urban transport are to achieve sustainable development, urban expansion must take place in a controlled way.     

后张法预应力混凝土箱梁摩阻试验研究

预应力损失的合理确定是预应力混凝土结构设计的关键问题之一。基于采用后张法的20m预应力混凝土空心板和30m预应力混凝土小箱梁张拉过程中纵向预应力损失实测,对其摩阻损失和锚固损失进行了分析。结果表明：金属波纹管的孔道摩阻系数和偏差系数与国内现行的公路桥规（JTGD62—2004）[1]和铁路桥规（TB10002．3—99）[2]规定一致;对于配置曲线（直线）预应力跨径≤30m（50m）的预应力混凝土梁,采用一端张拉比两端张拉更能减小预应力损失;采用PTI《后张预应力混凝土手册》和现行公路桥规（JTGI）62—2004）给出的锚固损失计算方法进行锚固损失分析,具有较高的精度。     

柴油发电机组噪声及控制

通过分析柴油发电机组的噪声特性,提出控制柴油发电机组噪声的措施。柴油发电机组噪声得到有效控制,必将扩大柴油发电机组的应用领域。     

某型双频发电机组中频不发电故障排除剖析

对一台汽油机双频发电机组中频不发电故障现象进行了原因分析、诊断排除的描述,并对出现此类故障可能产生的故障点进行了剖析。     

柴油机发电机组在电厂中并网功能的应用分析

本文介绍了柴油发电机组与市电的正并网、反并网功能的工作原理,详细讨论了在某电厂中柴油发电机组并网功能的应用.     

基于ARM的蓄电池内阻测试仪的设计

为了评估蓄电池性能,实现单体电池内阻的在线实时监测,本文采用四线交流法进行测量,采用基于ARM单片机技术实现数据的采集和处理。文章介绍了该装置的工作原理及硬件和软件的设计。实践证明,该系统具有测量精度高、抗干扰能力强、可实现在线测量等优点,具有良好的实用价值和推广意义。     

基于粗糙集的卫星侦察监视情报保障能力评估

提出应用粗糙集理论评估卫星侦察监视情报保障能力的方法,构建了卫星侦察与监视情报保障能力的评估指标体系,并给出了评价决策表和权重的计算方法。通过对测试数据的分析,得到了约简后的评估指标和权重,克服了传统权重计算方法的主观性,使评估结果更加科学合理。     

基于犹豫度专家残缺权重补充及其群决策方法

针对直觉模糊群决策专家权重残缺的问题,在各方案平行的前提下,提出了一种基于直觉模糊数犹豫度的专家客观权重补充方法。并结合专家的主客观权重,给出决策者客观不同的专家权重公式。最后,综合各决策者的犹豫度对方案进行排序择优,并通过实例分析说明了该方法模型的具体应用及计算过程。     

舰船中压发电机组振动监测与故障诊断

中压发电机组是舰船的动力核心,中压发电机组在使用较长时间之后可能会出现振动异常的问题,通过对其进行振动检测,能够确定振动异常的位置和原因,并通过针对性的措施来解决问题,维护中压发电机的正常运行。本文以某舰船的中压发电机组故障问题为例,对中压发电机组振动监测与故障诊断进行了详细的分析。