热变形对合金钢A_（e3）影响的热力学计算

以超组元（Ｓｕｐｅｒｅｌｅｍｅｎｔ）模型为基础，开发了计算热变形后Ｆｅ－ΣＸ_ｉ－Ｃ（Ｘ_ｉ＝Ｍｎ，Ｓｉ，Ｍｏ，Ａｌ，Ｃｕ，Ｎｉ，Ｃｏ，Ｃｒ等）多组元合金钢的Ａ（ｅ３）的方法，并着重分析了γ相热变形对Ａ（ｅ３）的影响，未变形合金钢Ａ（ｅ３）的计算值，与前人的实测值基本符合．     

渭河流域降水时空变化与干旱特征分析

以渭河流域14个典型气象站降水资料为基础,应用Mann-Kendall趋势检验法、频率分析法、差积曲线法以及游程分析法对研究区的降水变化规律及少水概率特征进行了研究。结果显示:40多年来渭河流域降水量呈明显减少趋势,以春、秋两季最为明显,这增加了区域发生干旱的可能性;流域降水过程呈丰枯交替的周期性现象,连丰或连枯较易发生,且存在干旱与洪涝并发现象;连枯年的概率比连丰年概率大,且少水期常持续2~3a,引发的干旱强度较大;1991年以后渭河流域干旱事件的频率、强度和烈度均有增加趋势,未来渭河流域的农业发展与水安全将面临更大的威胁,必须予以高度关注。     

Improving the Performance and Energy E?ciency of Phase Change Memory Systems

Phase change memory (PCM) is a promising technology for future memory thanks to its better scalability and lower leakage power than DRAM (dynamic random-access memory). However, adopting PCM as main me...     

Performance control for interconnection of identical systems: Application to PLL network design

In this paper, the problem of the control law design for interconnected identical systems ensuring the global stability and the global performance properties is under consideration. Inspired by the decentralized control law design methodology using the dissipativity input–output approach, the problem is reduced to the problem of satisfying two conditions: (i) the condition on the interconnection and (ii) the condition on the local subsystem dynamics. Both problems are efficiently solved applying a (quasi‐) convex LMI optimization and standard H_∞ synthesis. The proposed design methodology is applied to the control law design of a synchronous PLL network. Copyright © 2014 John Wiley & Sons, Ltd.     

Robust grid‐oriented control of high voltage DC links embedded in an AC transmission system

Several studies have shown that the way to design controllers for the high‐voltage direct current (HVDC) links impacts the transient behavior of the electric system in which the latter are inserted. This can be exploited to improve the performances of the stability of the power system. In this paper, a robust multivariable control design for the converters of an HVDC link is proposed. It is based on the coordination of the control actions of the HVDC converters and the use of a control model. The latter takes into consideration, in addition to the dynamics that mostly impact the stability of the neighbor zone of the HVDC link, several cases of faulted situations modeled as uncertainties. An H_∞ controller allowed us to achieve robustness against such uncertainties. The new controller is tested in comparison with the standard vector control and an optimal linear quadratic controller using the EUROSTAG simulation software (Tractebel Engineering, Brussels, Belgium and Réseau de Transport d'Electricité (RTE) ‐ France) on both academic and realistic large‐scale power systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Design of a robust observer‐based memoryless H∞ control for internet congestion

This work is concerned with the transmission control protocol(TCP)‐based active queue management for alleviating Internet congestion. To achieve the objective, a novel robust observer‐based H_∞ control scheme is proposed to stabilize the data queue length of the router to a given target. The robust observer is advocated to reconstruct a substitution state of the TCP window size under uncertain Internet environments, wherein the TCP window size is almost impossible to be explicitly measured in practise. Meanwhile, a memoryless H_∞ controller is employed to guarantee the system asymptotical stability and further enhance the robustness. With the assistance of a unique nonlinear decoupling method, a feasible controller design method is presented in terms of linear matrix inequality. Compared with the existing literatures, the proposed control principle is more practical, and it can be conveniently implemented into the Internet routers while introduces less computational burden. Finally, the proposed result is embedded into Network Simulator 2 and compared with the other schemes in the literature. Numerical experiments illustrate the effectiveness of the proposed method. Copyright © 2015 John Wiley & Sons, Ltd.     

Stochastic consensus control with finite frequency specification for Markov jump networks

A stochastic finite frequency consensus protocol for directed networks with Markov jump topologies and external disturbances is proposed in this paper. By introducing the frequency band information into consensus control design, the disagreement dynamics of interconnected networks asymptotically converge to zero with an improved level of disturbance attenuation in the specific frequency band. In addition, the new model transformation approach is presented by exploring certain features of Laplacian matrix in real Jordan form, which leads to more generality of the designed protocol. A numerical example validates the potential of the developed results. Copyright © 2015 John Wiley & Sons, Ltd.     

H∞ Control with Transients for Singular Systems

In this paper, the problem of a generalized type of H_∞ control is investigated for continuous‐time singular systems, which treats a mixed attenuation of exogenous inputs and initial conditions. First, a performance measure that is essentially the worst‐case norm of the regulated outputs over all exogenous inputs and initial conditions is introduced. A necessary and sufficient condition is obtained to ensure the singular system to be admissible and the performance measure to be less than a prescribed scalar. Based on the criterion a sufficient condition for the existence of a state‐feedback controller is established in terms of linear matrix inequalities. Moreover, the relationship between the performance measure and the standard H_∞ norm of the system is provided. Two numerical examples are given to demonstrate the properties of the obtained results.     

Robust H∞ Tracking Control of Uncertain Robotic Systems with Periodic Disturbances

This paper addresses the problem of designing robust tracking control for a large class of uncertain robotic systems. A more general model of the external disturbance is employed in the sense that the external disturbance can be expressed as the sum of a modeled disturbance and an unmodeled disturbance, for example, any periodic disturbance can be expressed in this general form. An adaptive neural network system is constructed to approximate the behavior of unknown robot dynamics. An adaptive control algorithm is designed to estimate the behavior of the modeled disturbance, and in turn the robust H_∞ control algorithm is required to attenuate the effects of the unmodeled disturbance only. Consequently, an intelligent adaptive/robust tracking control scheme is constructed such that an H_∞ tracking control is achieved in the sense that all the states and signals of the closed‐loop system are bounded and the effect due to the unmodeled disturbance on the tracking error can be attenuated to any preassigned level. Finally, simulations are provided to demonstrate the effectiveness and performance of the proposed control algorithm.     

Some results on disturbance attenuation for Hamiltonian systems via direct discrete‐time design

The disturbance attenuation and robust disturbance attenuation problems for Hamiltonian systems in the discrete‐time setting are considered and some new results are presented. The new results are derived utilizing the recently presented dissipativity equality obtained by adding the dissipation rate function to the classical dissipativity inequality. A selection of the dissipation rate function yields new results. These results include a condition on the dissipation structure of the system to achieve the desired disturbance attenuation level and gives direct construction of optimal control laws for any desired disturbance attenuation level. The results remove the need to solve Hamilton–Jacobi–Isaacs inequalities. Copyright © 2014 John Wiley & Sons, Ltd.