ETFs及其对我国近期推出ETFs问题的分析

本文介绍了西方发达市场ETFs的运作模式,并与中国证券市场的现实特点结合起来,论述了在我国近期推出的必要性,从政策、技术、市场需求各个方面进行可行性分析,最后指出目前ETFs适宜在我国推出。     

基于PLC和无线数传电台的输油管道加热监控系统

介绍了S7-200PLC和GD数传电台构建的无线通讯监控系统在输油管道加热控制的应用.软件采用点对多点半双工通讯模式,实现了远方中控室对输油管道加热装置的自动监控,运行结果表明,系统运行可靠,节省了人力成本.     

煤层气抽采直流微网建模与稳定性分析

针对目前煤层气抽采现场用电不合理现状,构建一种新型煤层气抽采直流微网供电系统,并对该直流微网系统稳定性及控制策略进行研究。煤层气抽采直流微网供电系统分三层结构:第一层由光伏和蓄电池组成能量供给层;第二层由双向Buck/Boost变换器构成能量传输和分配层;第三层由煤层气抽采机构成负荷层。基于此架构推导了第一、二层输出阻抗Zo(s),并建立第三层煤层气抽采机电动机输入阻抗Zin(s)与受控源K??m串联的小信号模型,在此基础上得到系统全局小信号模型。考虑到呈现负阻抗特性的煤层气抽采机电动机周期性动态交变负荷引起的系统不稳定,在能量传输和分配层分析并讨论了一种基于虚拟阻抗的直流微网稳定性控制策略,以及利用下垂控制实现负荷功率动态平衡分配的方法。进一步利用阻抗匹配原则求解多项式1/(1+Zo(s)/Zin(s))主导极点,比较采取该稳定性控制策略前后的主导极点位置并分析直流微网系统稳定性。最后基于Matlab/Simulink搭建由光伏阵列、储能单元和煤层气抽采机组成的煤层气抽采直流微网系统模型,系统仿真证明了稳定性控制策略的有效性。     

谐振式强磁耦合无线能量传输及其在民用电安全方面的应用

介绍当前几种主流的无线能量传输技术方案,并比较了其优缺点.针对“谐振式强磁耦合无线能量传输”技术作一些深入的介绍,并展望其在民用电安全方面的一些应用.     

基于无线局域网的变电站在线监测系统设计

无线局域网的广泛利用大大推动了变电站的数字化建设。通过对基于无线局域网的监测管理系统的研究,提出了基于无线局域网的变电站在线检测系统的设计方案。分析了无线局域网的协议标准选取,设计了高效的现场组网方案,实现了本地无线局域网的搭建以及后继的现场信息远程传输。     

The impact of data aggregation on the performance of wireless sensor networks

With the increasing need for different energy saving mechanisms in Wireless Sensor Networks (WSNs), data aggregation techniques for reducing the number of data transmissions by eliminating redundant information have been studied as a significant research problem. These studies have shown that data aggregation in WSNs may produce various trade‐offs among some network related performance metrics such as energy, latency, accuracy, fault‐tolerance and security. In this paper, we investigate the impact of data aggregation on these networking metrics by surveying the existing data aggregation protocols in WSNs. Our aim is twofold: First, providing a comprehensive summary and comparison of the existing data aggregation techniques with respect to different networking metrics. Second, pointing out both the possible future research issues and the need for collaboration between data management and networking research communities working on data aggregation in WSNs. Copyright © 2006 John Wiley & Sons, Ltd.     

无线光通信自适应激光源研究

无线光通信由于其独特的工作原理,具有巨大的潜在应用价值,其中无线光通信的激光器光源技术是关系设备指标特性的关键技术之一。根据自适应可调节激光器的特点进行分析,介绍激光相干合成技术原理,根据无线光通信的工作原理,采用可编程控制器件,为核心设计一种可以降低各种环境干扰的可调激光源。实验结果表明设计的光源输出是稳定的。     

多跳认知无线Mesh网络中频谱决策与路由的跨层设计

灵活高效的频谱共享技术能够实现频谱资源的最大化利用,有效地缓解了无线频谱紧缺的现状。在一个与TDMA/FDMA蜂窝网络共存的多跳认知无线Mesh网络环境下,基于覆盖式（Underlay）与机会式（Overlay）相结合的频谱共享机制,提出了一种有效的链路层频谱决策与网络层路由的跨层设计方案。仿真结果表明,该方案比基于最小跳数的随机信道选择算法在网络端到端传输性能上有显著的优势。     

Long‐range wireless sensor networks with transmit‐only nodes and software‐defined receivers

Wireless sensor networks for environmental monitoring and agricultural applications often face Long‐range requirements at low bit rates together with a large numbers of nodes. This paper presents the design and test of a novel wireless sensor network that combines a large radio range with very low power consumption and cost. Our asymmetric sensor network uses ultra‐low‐cost 40‐MHz transmitters and a sensitive software‐defined radio receiver with multi‐channel capability. Experimental radio range measurements in two different outdoor environments demonstrate a single‐hop range of up to 1.8 km. A theoretical model for radio propagation at 40 MHz in outdoor environments is proposed and validated with the experimental measurements. The reliability and fidelity of network communication over longer periods is evaluated with a deployment for distributed temperature measurements. Our results demonstrate the feasibility of the transmit‐only low‐frequency system design approach for future environmental sensor networks. Although there have been several papers proposing the theoretical benefits of this approach, to the best of our knowledge, this is the first paper to provide experimental validation of such claims. Copyright © 2011 John Wiley & Sons, Ltd.     

A novel sine‐curve mobility model for intrusion detection in wireless sensor networks

Intrusion detection is prominently important for civil and military applications in wireless sensor networks (WSNs). To date, related works address the problem by assuming a straight‐line intrusion path and a Boolean sensing model. However, a straight‐line intrusion path is often not the case in reality, and the Boolean sensing model cannot resemble a real‐world sensor precisely. Results based on these assumptions are therefore not applicable with desirable accuracy in practice. In view of this, we propose a novel sine‐curve mobility model that can simulate different intrusion paths by adjusting its features (amplitude, frequency, and phase) and can be integrated into the random WSN model for intrusion detection analysis. It can also be applied to different sensor models and makes influencing factors tractable. With the model, we examine the effects of different intrusion paths on the intrusion detection probability in a random WSN, considering both Boolean and realistic Elfes sensing models. Further, we investigate the interplays between network settings and intruder's mobility patterns and identify the benefits and side effects of the model theoretically and experimentally. Simulation outcomes are shown to match well with the theoretical results, validating the modeling, analysis, and conclusions. Copyright © 2011 John Wiley & Sons, Ltd.