一种改进的即时消息传递系统认证方案

即时消息传递（IM—Instant messaging）是Internet上日渐普及的一种通信方法。在介绍IM系统工作方式的基础上,详。细分析了当前IM系统在认证方案上的不足以及由此引起的潜在安全威胁。结合数据摘要技术和一次性口令认证方法,对IM系统层对层文件传输提出了一种改进的系统认证方案。该方案面向企业级应用,能够满足安全性要求较高的领域。     

基于滑模与自适应观测器的感应电机非线性控制新策略

提出一种结合滑模变结构和自适应观测技术的感应电机非线性控制新方法. 以定子电流与定子磁链为状态变量建立感应电机模型, 采用非线性分析方法建立转矩与磁链误差方程, 使用自适应滑模技术设计转矩与磁链控制器, 推导出定子电压控制量. 基于模型参考技术设计自适应观测器, 向控制器提供准确的转速辨识与磁链观测值,并给出了控制系统的稳定性证明. 该方法具有转矩脉动小、定子磁链畸变不明显的优点, 低速时也具有良好的控制性能, 且对参数与负载变化有较强的鲁棒性. 仿真与实验结果证明了该控制策略的正确性与有效性.     

一种多媒体服务器混合缓存策略

提高视频点播系统性能的一个有效途径是提高缓存的利用率，进而使系统可容纳更多的媒体流．间隔缓存(Interval Caching)是一种有效的缓存策略．在间隔缓存的基础上提出了一种混合了静态和动态缓存策略特点的混合缓存策略．通过对该策略进行缓存模型分析，对比了混合策略同间隔缓存策略的相关指标，结果说明，混合策略较间隔缓存策略有明显的改善．     

A robust sensorless output feedback controller of the induction motor drives: new design and experimental validation

In this article, a sensorless output feedback controller is designed in order to drive the induction motor (IM) without the use of flux and speed sensors. First, an observer that uses only the measured stator currents is synthesised to estimate the mechanical variables (speed and load torque) and the magnetic variables (fluxes) by structurally taking into account the unobservability phenomena of the sensorless IM (SIM) and the parametric uncertainties. Second, a current-based field-oriented sliding mode control that uses the flux and the speed estimates given by the former observer is developed so as to steer the estimated speed and flux magnitude to the desired references. Since the observer error dynamic is independent from the known input control and depends on the IM parametric uncertainties, a kind of separation principle is introduced to guarantee the practical stability of the whole closed-loop system ‘observer–controller’ (‘O-C’) according to observability and unobservability time variation. A significant benchmark taking into account the unobservability phenomena of the SIM is presented to show the performances of the whole control scheme against experimental set-up.     

Survey on Passivity Based Control of Induction Machine

Induction machines (IM) constitute a theoretically interesting and practically important class of nonlinear systems. They are frequently used as wind generators for their power/cost ratio. They are described by a fifth‐order nonlinear differential equation with two inputs and only three state variables available for measurement. The control task is further complicated by the fact that IM are subject to unknown (load) disturbances and the parameters can be of great uncertainty. One is then faced with the challenging problem of controlling a highly nonlinear system, with unknown time‐varying parameters, where the regulated output, besides being unmeasurable, is perturbed by an unknown additive signal. Passivity‐based control (PBC) is a well‐established structure‐preserving design methodology which has shown to be very powerful to design robust controllers for physical systems described by Euler‐Lagrange equations of motion. PBCs provide a natural procedure to "shape" the potential energy yielding controllers with a clear physical interpretation in terms of interconnection of the system with its environment and are robust vis á vis to unmodeled dissipative effects. One recent approach of PBC is the Interconnection and Damping Assignment Passivity‐Based Control (IDA‐PBC) which is a very useful technique to control nonlinear systems assigning a desired (Port‐Controlled Hamiltonian) structure to the closed‐loop. The aim of this paper is to give a survey on different PBC of IM. The originality of this work is that the author proves that the well known field oriented control of IM is a particular case of the IDA‐PBC with disturbance.     

Calibration-free and model-independent method for high-DOF image-based visual servoing

This paper presents a novel method to improve the performance of high-DOF image base visual servoing (IBVS) with an uncalibrated camera. Firstly, analysis and comparison between point-based and moment-based features are carried out with respect to a 4-DOF positioning task. Then, an extended interaction matrix (IM) related to the digital image, and a Kalman filter (KF)-based estimation algorithm of the extended IM without calibration and IM model are proposed. Finally, the KF-based algorithm is extended to realize an approximation to decoupled control scheme. Experimental results conducted on an industrial robot show that our proposed methods can provide accurate estimation of IM, and achieve similar performance compared with traditional calibration-based method. Therefore, the proposed methods can be applied to any robot control system in variational environments, and can realize instant operation to planar object with complex and unknown shape at large displacement.     

SLIDING‐MODE LINEARIZATION TORQUE CONTROL OF AN INDUCTION MOTOR

This paper proposes a sliding‐mode linearization torque control (SMLTC) for an induction motor (IM). An ideal feedback linearization torque control method is firstly adopted in order to decouple the torque and flux amplitude of the IM. However, the system parameters are uncertainties, which will influence the control performance of the IM in practical applications. Hence, to increase the robustness of the IM drive for high‐ performance applications, this SMLTC aims to improve the immunity of those uncertainties. We modify the flux observer of Benchaib and Edwards [15] by means of the adaptive sliding‐mode method. This not only eliminates the estimation of the uncertainty bounds, but also improves the performance of sliding control. In addition, a practical application of the proposed SMLTC, with a model reference adaptive control (MRAC) scheme incorporated as the inner and outer loop controller used for position control, is also presented. Some experiments are presented to verify the control theory and demonstrate the robustness and effectiveness of the proposed SMLTC.     

一种可防止合谋攻击的门限签名方案

针对现有门限签名方案在抵抗合谋攻击上的弱点,基于离散对数问题提出了一个（t,n）门限签名方案。在该方案中,t个或t个以上的内部成员合作可以代表群体产生有效的门限签名,但不能获取系统秘密,从而有效地阻止了内部恶意成员的合谋攻击。方案还能够防止伪造攻击,并具有可追踪性。     

一种基于双层管理机制的MIPv6安全通信方案

通过对现有的基于IPv6亲密伙伴的安全通信方案进行了研究和分析,结合移动IPv6网络中移动节点的特性,提出了一种基于移动节点预测驻留时间构造上层节点的双层管理机制。通过在移动网络中构造一个动态管理节点,妥善地解决了原方案在移动IPv6网络中的扩展问题。最后对新方案进行了仿真和分析。     

基于时间尺度的感应电机自抗扰控制器的参数整定

自抗扰控制器(ADRC)在感应电机控制中取得了优良的控制效果, 但控制器参数整定比较困难. 本文从时间尺度的概念入手分析ADRC参数整定问题, 通过理论分析得出感应电机的时间尺度, 并结合时间尺度与ADRC参数的关系进行参数整定, 得到了感应电机按定子磁场定向矢量控制的ADRC控制器参数整定方法, 该方法尤其适于多台电机的参数整定. 仿真结果表明该方法可行, 为感应电机ADRC提供了一种参数整定方法.