聚丙烯接枝马来酸酐增容聚酰胺6／聚丙烯体系吸湿性能及力学性能的研究

以聚丙烯接枝马来酸酐(PP-g-MAH)为相容剂，利用其与聚酰胺6(PA6)在共混过程中的反应增容作用，实现了与聚丙烯(PP)之间的相容性共混，改变其用量，制备了系列具有不同组成的PA6／PP合金，研究了不同组成合金材料的吸湿性能及其在干态和充分吸湿状态时的冲击强度和拉伸性能。结果表明，向PA6／PP合金体系中加入相容剂PP-g-MAH后，可以改善合金的相界面，形成相容性的合金结构，明显降低合金材料的吸湿量及吸湿速率，但进一步增大相容剂PP-g-MAH的用量时，只能明显降低合金材料吸湿过程初期的吸湿速率，不能进一步显著降低合金材料的吸湿量。在相容剂PP-g-MAH用量一定时，随着PA6／PP合金体系中PA6组分含量的提高，合金在干、湿态条件下的冲击强度、拉伸强度、断裂伸长率均呈近似线性变化。对于具有相同基本组成的合金，随着相容剂PP-g-MAFI用量的增加，材料在干、湿态条件下的拉伸强度均有提高，杨氏模量则在干态时有所提高，在湿态时影响不显著，在干、湿态时断裂伸长率以及冲击强度均没有产生显著影响。     

On Designing Time‐delay Feedback Controller for Master‐Slave Synchronization of Lur'e Systems

This paper is concerned with the problem of designing a time‐delay output feedback controller for master‐slave synchronization of Lur'e systems. The time delay is divided into two intervals and different energy functions are defined in each interval, which together provide a new Lyapunov–Krasovskii functional and derive a new delay‐dependent synchronization criterion. A sufficient condition for the existence of such a feedback controller is given, and an explicit expression of such a controller is also achieved. These algorithms are formulated in terms of linear matrix inequalities that can be solved easily. Chua's circuit is used to illustrate the effectiveness of the design method.     

A generalized robust H ∞ filtering for singular Markovian jump systems and its applications

In this paper, a generalized robust H _∞ filtering method is proposed for a class of singular Markovian jump systems, whose generality is mainly embodied that the desired filter could bear perturbances in terms of uncertainties on its parameter matrices. Firstly, an LMI condition of robust mode‐dependent filter is developed. Based on the given result, a new approach to mode‐independent H _∞ filter is presented, which establishes a direct connection between mode‐dependent and mode‐independent filters. Secondly, when the transition rate matrix is with elementwise bounded uncertainties or partially unknown, sufficient conditions of such robust mode‐dependent and mode‐independent filters are all developed within LMI frameworks. Finally, a numerical example is used to demonstrate the effectiveness of the proposed methods. Copyright © 2013 John Wiley & Sons, Ltd.     

Observer‐based H ∞ output tracking control for networked control systems

This paper is concerned with observer‐based H _∞ output tracking control for networked control systems. An observer‐based controller is implemented through a communication network to drive the output of a controlled plant to track the output of a reference model. The inputs of the controlled plant and the observer‐based tracking controller are updated in an asynchronous way because of the effects of network‐induced delays and packet dropouts in the controller‐to‐actuator channel. Taking the asynchronous characteristic into consideration, the resulting closed‐loop system is modeled as a system with two interval time‐varying delays. A Lyapunov–Krasovskii functional, which makes use of information about the lower and upper bounds of the interval time‐varying delays, is constructed to derive a delay‐dependent criterion such that the closed‐loop system has a desired H _∞ tracking performance. Notice that a separation principle cannot be used to design an observer gain and a control gain due to the asynchronous inputs of the plant and the controller. Instead, a novel design algorithm is proposed by applying a particle swarm optimization technique with the feasibility of the stability criterion to search for the minimum H _∞ tracking performance and the corresponding gains. The effectiveness of the proposed method is illustrated by an example. Copyright © 2013 John Wiley & Sons, Ltd.     

Observer‐based H ∞ control for networked systems with bounded random delays and consecutive packet dropouts

This paper is concerned with the H _∞ control problem for a class of systems with bounded random delays and consecutive packet dropouts that exist in both sensor‐to‐controller channel and controller‐to‐actuator channel during data transmission. A new model is developed to describe possible random delays and packet dropouts by two groups of Bernoulli distributed stochastic variables. To avoid the state augmentation, a full‐order observer‐based feedback controller is designed via LMI approach. Based on the Lyapunov theory, a sufficient condition is provided to guarantee the closed‐loop networked system to be asymptotically mean‐square stable and achieve the prescribed H _∞ disturbance‐rejection‐attenuation level. The simulation examples illustrate the effectiveness of the proposed method. Copyright © 2013 John Wiley & Sons, Ltd.     

H ∞ control for discrete‐time nonlinear Markov jump systems with multiplicative noise and sector constraint

This paper addresses the finite horizon H _∞ control problem for a class of discrete‐time nonlinear Markov jump systems with multiplicative noise and nonlinear feedback device. The system nonlinearity occurs in a random way specified by a Bernoulli process, whereas the actuator and sensor nonlinearities are restricted to a sector region. Both the state and the dynamic output feedback H _∞ controllers are devised in terms of difference LMIs. The proposed approach not only allows the resulting system to achieve a prescribed disturbance attenuation level, but also enables the output of actuator/sensor to meet the designated sector condition. Moreover, it is also shown that our approach is well‐adapted for dealing with the discrete‐time Markov jump systems with saturated actuator and sensor. Finally, a backward iterative algorithm is provided to solve the obtained difference LMIs and a numerical example is presented to verify the efficiency of the theoretical results. Copyright © 2013 John Wiley & Sons, Ltd.     

Robust adaptive control for a class of cascaded nonlinear systems with applications to space interception

This paper proposes a robust H _∞ ‐based adaptive backstepping control scheme for the output stabilization of a special class of cascaded nonlinear systems. This kind of systems possess the feature that the first sub‐equation is a linear perturbed system, whereas the rest ones perform a general semi‐strict feedback form. Different from the conventional backstepping design approach, the special cascaded structure ensures to introduce the H _∞ technique to the backstepping procedure such that both the robust performance and the robust stability can be simultaneously guaranteed. Within the Lyapunov framework, the proposed control scheme is proved to guarantee (i) the uniformly ultimate boundedness of the system signals with a bound that can be made arbitrarily small by suitably choosing control parameters; (ii) asymptotic output stabilization as long as the uncertain nonlinearities and external disturbances vanish; and (iii) ‐performance of the closed‐loop system. A space interception scenario is utilized to demonstrate the effectiveness of the proposed control scheme. Copyright © 2013 John Wiley & Sons, Ltd.     

基于IEEE 80211e EDCA的下行信道动态无竞争接入机制*

为了改善无线局域网络服务质量,IEEE工作组形成了增补标准IEEE 802.11e,但是其增强的接入机制仍然不能完全满足IPTV、视频点播等类似场景的应用。为此提出了针对这一类应用场景的一种新的简单易行的下行信道动态无竞争接入机制,该机制基于MAC层队列长度信息动态调整下行信道接入参数,能有效地保护下行流媒体数据的传输,通过仿真结果验证了该机制有效并且实用。     

IEEE802.16e中的卷积Turbo码编译码算法研究

为了分析不同设计参数对IEEE802.16e中卷积Turbo码(CTC)性能的影响以及对比IEEE802.16e支持的CTC和卷积码的编码性能,介绍了IEEE802.16e中的CTC的编码过程,给出了编码过程中的循环状态确定方法的推导过程,分析了CTC的迭代译码结构和译码算法,最后对CTC的性能进行了仿真.仿真结果表明:在相同码率和相同调制方式下CTC的编码增益要比卷积码大,采用CTC比采用卷积码有着明显的性能优势.因此在码率较低、信道状况较好或对系统实时性要求严格的情况下,可考虑使用卷积码,以降低信道编码的复杂度;而在码率较高、信道状况较差或对误码率要求严格时,可考虑选用CTC编码方案,以保证通信的可靠性.     

基于MDT的汽车覆盖件反求研究

汽车工业是21世纪的主导产业,模具作为车身生产的基础工艺装备,将直接制约产品的质量和新产品的开发.文章以MDT软件为基础,利用三坐标测量仪的三维数据点通过圆率法完成了曲线曲面的光顺、拼接与合成,实现了汽车覆盖件的反求工程,从而为模具设计奠定了基础.