单磁悬浮系统的纵向解耦控制研究

磁悬浮系统是复杂的强耦合系统,研究中未充分考虑轨道的弹性形变,会造成磁浮列车和轨道之间产生耦合振动的现象,而考虑这一因素对系统的影响无疑增加了研究的难度;为了便于问题的求解,采用非线性系统理论解耦的方法,对单电磁铁悬浮系统进行纵向解耦控制,并对解耦后的子系统进行极点配置使其满足要求的性能指标;仿真结果表明该方法有效地使复杂问题简单化,并且能够实现系统的全局稳定和良好的动态性能.     

Compensation of hysteresis in piezoelectric actuator with iterative learning control

This paper presents the application of iterative learning control (ILC) to compensate hysteresis in a piezoelectric actuator. The proposed controller is a hybrid of proportional-integral-differential (PID) control, whose main function is for trajectory tracking, and a chatter-based ILC, whose main function is for hysteresis compensation. Stability analysis of the proposed ILC is presented, with the PID included in the dynamic of the piezoelectric actuator. The performance of the proposed controller is analysed through simulation and verified with experiment with a piezoelectric actuator.     

PeerDetector:一种基于连接模式的P2P流检测算法

基于NetFlow技术,提出一种基于连接模式的流量检测算法PeerDetector,能够从本地网络的所有流量中有效地检测出P2P流量,PeerDetector算法先用HTD算法检测出HTIP流量,再根据P2P连接的单连接特性识别设计了PTD算法区分开P2P流量和传统网络应用流量,检测出P2P流量.对算法和适合数据处理的数据库进行了设计和实现,用Dynamips仿真Cisco路由器搭建了试验床.经过实验测试,P2P流量检测工具工作效果良好,能够有效检测出绝大多数的P2P流量,误检概率和错检概率非常小.     

基于PolyTrans的IGES文件简化

CAD软件与基于多边形的3D软件之间数据转换需求不断增加,但是CAD模型复杂度和精细度却越来越高,数据转换的难度变大.为了解决这一难题,结合PolyTrans,分析如何解决一般3D软件难以导入大型的IGES(Initial Graphics Exchange Specifi-cation)文件的问题.从PolyTrans模型简化模块的理论依据着手,研究如何控制多边形的数量、降低文件的复杂性和减少文件的数量,使大型CAD装配模型能顺利地以单个实体形式导入Lightwave、3DS MAX以及Maya类的3D软件.并结合具体科研项目,给出了模型优化前后各指标参数对比情况.     

一种统计可靠的监控系统样本同步机制

针对分布式监控系统的样本库同步机制提出一种基于流行病理论的样本信息层次化扩散算法.样本信息在扩散过程中模仿流行病在生物群体中的传播方式.扩散分两个阶段,其一是信息以改进的Rumor Mongering方式在系统内进行扩散;其二是采用Anti-entropy方式补充各节点未收到的信息.该同步机制充分考虑了分布式监控节点的层次性、簇集性,为样本信息同步提供统计意义上的可靠性保证.最后,通过仿真验证了理论分析的正确性.     

Characterization and humidity sensing properties of Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 powder synthesized by metal-organic decomposition

Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃ (BNT-BKT) powder is synthesized by a metal-organic decomposition method and characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). A humidity sensor, which is consisted of five pairs of Ag-Pd interdigitated electrodes and an Al₂O₃ ceramic substrate, is fabricated by spin-coating the BNT-BKT powder on the substrate. Good humidity sensing properties such as high response value, short response and recovery times, and small hysteresis are observed in the sensing measurement. The impedance changes more than four orders of magnitude within the whole humidity range from 11% to 95% relative humidity (RH) at 100 Hz. The response time and recovery time are about 20 and 60 s, respectively. The maximum hysteresis is around 4% RH. The results indicate that BNT-BKT powder is of potential applications for fabricating high performance humidity sensors.     

Hydrothermal synthesis of hollow ZnSnO3 microspheres and sensing properties toward butane

Hollow ZnSnO₃ microspheres were successfully prepared by hydrothermal method at 160 °C for 12 h. The prepared material was characterized by field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and X-ray diffraction measurements (XRD). The average diameter of the hollow ZnSnO₃ microspheres was in the range of 400-600 nm. Compared with solid ZnSnO₃ microspheres structure, the hollow ZnSnO₃ microspheres showed better response (S) to butane. To 500 ppm butane, the sensor response (S) of the hollow ZnSnO₃ microspheres was 5.79 at the optimum operating temperature of 380 °C, and the response and recovery time were 0.3 s and 0.65 s, respectively. The sensitivities of sensors based on this material were linear with the concentration of butane in the range of 100-1000 ppm.     

Measurement of static and dynamic mechanical behavior of micro and nano-scale thin metal films: using micro-cantilever beam deflection

We present the results of a novel micro-beam deflection test used to investigate the static and dynamic mechanical behavior of submicron-thick metal films. The method demonstrated in this study allows researchers to observe the motion of micro and nano-scale thin films responding to electrostatic loads, by means of laser reflection measurements at frequency rates of up to 500 Hz. Researchers fabricated a supporting frame and a novel triangular shaped “paddle” beam designed to provide uniform plane stress distribution while undergoing deflection. A simple geometric calculation, based on cantilever deflection, enabled the degree of strain to be determined, which in turn provided the Young’s modus for aluminum film of a given thickness. We also studied the dynamic behavior using the dynamic frequency response of the beam, generated by electrostatic forces under various loads and vacuum pressure conditions. Our results showed that air damping has a significant influence on the free damping behavior of specimens, and only a minor influence on damping frequency. We determined the loss angle and frequency using sweep frequency and free damping methods, which were very consistent with paddle resonant frequencies. The loss angle obtained from a simple silicon micro-beam was 2.001 × 10^−4°using the free damping method and 2.23 × 10^−4°using the sweep frequency method. The dynamic response loss mechanism measured in this experiment provides incentive for the further study of grain boundary motion and dislocation motion in thin films.     

木马隐藏技术与防范方法

为加固网络安全、防范木马攻击,结合实例研究了一种木马隐藏技术,实现了基于加载三级跳和线程守护的隐藏技术,增强了木马的隐蔽性与抗毁性,并提出了该技术相应的防范措施和清除方法。实验结果表明,融入该隐藏技术的木马程序完成了预期的隐藏功能并可以穿透最新的瑞星杀毒软件、瑞星防火墙及硬件防火墙,表明了该隐藏技术的可行性与有效性。     

Toward effective service composition for real-time SOA-based systems

Many application domains are increasingly leveraging service-oriented architecture (SOA) techniques to facilitate rapid system deployment. Many of these applications are time-critical and, hence, real-time assurance is an essential step in the service composition process. However, there are gaps in existing service composition techniques for real-time systems. First, admission control is an essential technique to assure the time bound for service execution, but most of the service composition techniques for real-time systems do not take admission control into account. A service may be selected for a workflow during the composition phase, but then during the grounding phase, the concrete service may not be able to admit the workload. Thus, the entire composition process may have to be repeated. Second, communication time is an important factor in real-time SOA, but most of the existing works do not consider how to obtain the communication latencies between services during the composition phase. It is clear that maintaining a full table of communication latencies for all pairs of services is infeasible. Obtaining communication latencies between candidate services during the composition phase can also be costly, since many candidate services may not be used for grounding. Thus, some mechanism is needed for estimating the communication latency for composite services. In this paper, we propose a three-phase composition approach to address the above issues. In this approach, we first use a highly efficient but moderately accurate algorithm to eliminate most of the candidate compositions based on estimated communication latencies and assured service response latency. Then, a more accurate timing prediction is performed on a small number of selected compositions in the second phase based on confirmed admission and actual communication latency. In the third phase, specific concrete services are selected for grounding, and admissions are actually performed. The approach is scalable and can effectively achieve service composition for satisfying real-time requirements. Experimental studies show that the three-phase approach does improve the effectiveness and time for service composition in SOA real-time systems. In order to support the new composition approach, it is necessary to effectively specify the needed information. In this paper, we also present the specification model for timing-related information and the extension of OWL-S to support this specification model.