Finite-time decentralized adaptive neural constrained control for interconnected nonlinear time-delay systems with dynamics couplings among subsystems

The problem of finite-time decentralized neural adaptive constrained control is studied for large-scale nonlinear time-delay systems in the non-affine form. The main features of the considered system are that 1) unknown unmatched time-delay interactions are considered, 2) the couplings among the nested subsystems are involved in uncertain nonlinear systems, 3) based on finite-time stability approach, asymmetric saturation actuators and output constraints are studied in large-scale systems. First, the smooth asymmetric saturation nonlinearity and barrier Lyapunov functions are used to achieve the input and output constraints. Second, the appropriately designed Lyapunov-Krasovskii functional and the property of hyperbolic tangent functions are used to deal with the unknown unmatched time-delay interactions, and the neural networks are employed to approximate the unknown nonlinearities. Note that, due to unknown time-delay interactions and the couplings among subsystems, the controller design is more meaningful and challenging. At last, based on finite-time stability theory and Lyapunov stability theory, a decentralized adaptive controller is proposed, which decreases the number of learning parameters. It is shown that the designed controller can ensure that all closed-loop signals are bounded and the tracking error converges to a small neighborhood of the origin. The simulation studies are presented to show the effectiveness of the proposed method.     

弱激光—DNA分子相互作用方程时空混沌特性分析

对描述弱激光与ＤＮＡ分子相互作用的动力学方程进行了数值研究，通过改变方程中４个参量的值，由时空演变图象、相空间中的分布状态，频谱分析以及最大Ｌｙａｐｕｎｏｖ指数演变曲线获得了时空非线性特征和发生突变的临界参数。     

基于小波模极大值的信号奇异性检测

小波分析近乎完美的数学特性受到各领域科学家和工程技术人员的青睐.文中讨论了基于小波模极大值的信号奇异性检测方法,该方法突破了傅立叶分析在时域和频域方面的局部化能力,信号的局部正则性可由其小波变换模随尺度参数的衰减特性来刻画,通过确定小波变换在细尺度下的局部模极大值来检测信号奇异性.实验表明,该方法能有效的、实用的.     

基于Lyapunov指数谱的转子-机匣系统故障诊断研究

发展了基于Lyapunov指数谱的航空发动机转子-机匣系统故障诊断方法。基于实测的航空发动机机匣振动时间序列求解了系统不同状态的Lyapunov指数谱;基于Lyapunov指数谱,应用最大Lyapunov指数和Lyapunov指数谱图对航空发动机转子-机匣系统进行了故障诊断。研究结果表明:航空发动机机匣振动时间序列在不同状态下具有不同的Lyapunov指数谱,即可以Lyapunov指数谱作为故障诊断的特征量。     

Robust non-fragile LQ controllers: The static state feedback case

This paper describes the synthesis of non-fragile or resilient regulators for linear systems. A general framework for fragility is described using state-space methodologies, and the LQ/H₂ static state-feedback problem is examined in detail. We discuss the multiplicative structured uncertainties case, and propose remedies of the fragility problem using an optimization programming framework via matrix inequalities. A special case that leads to a convex optimization framework via linear matrix inequalities (LMIs) will be considered. The benchmark problem is taken as an example to show how special controller gain variations can affect the performance of the closed-loop system.     

Nanoscale periodic and faceted structures formation on Si(1 0 0) by oblique angle oxygen ion sputtering

The dynamics of ripple topography on silicon surfaces generated by oxygen ion bombardment with increasing fluences have been investigated by atomic force microscopy (AFM). At the early stages of sputtering, periodic ripples with the wave vector parallel to ion beam direction are developed. At the late stages of sputtering, the ripple structure tends to break down and the surface becomes faceted. The growth rate of the ripples and the scaling exponents of the faceted surface have been determined. The results are discussed with reference to the Bradley–Harper theory and its nonlinear extension. Finally, the ripple wavelength is found to be a linear function of the bombarding energy.     

多变量线性时延系统的稳定性分析及应用

基于Lyapunov稳定性理论，推导出多变量线性时滞系统的时滞独立稳定充分条件方程式，并给出了定理的另一种表述形式．在此基础上，给出了几个判定线性时滞系统独立稳定的简单判据．还讨论了时滞系统的指数稳定性，给出了系统具有任意指定收敛速度指数稳定的充分条件及相应的推论．在使用这些条件时，只需选取一组合适的参数即可降低条件的保守性．通过实例计算和对文中方法与文献中的方法进行比较表明，文中方法具有较小的保守性。     

Time dependent properties of thermoreversible gels

Rheological properties of the system gelatin + water at a polymer concentration of 5.0% by wt at a temperature of 301 K and an angular frequency of 0.628 rads^–1 are presented and evaluated by use of the percolation theory. A frequency power law has been found close to the gel point from which a critical time range could be deduced in which the powers of the loss and storage modulus are the same. The times needed for the gelation from the percolation relations are close to the range where the exponents of the frequency power law relations are identical. The scaling coefficient Δ for physical gelation agrees very well with that found for chemical gelation by Durand and coworkers. Received: 9 October 2000 / Reviewed and accepted: 10 October 2000     

一种新的鲁棒自适应控制律

本文提出了一神新的称为θ-δ修正法的鲁棒自适应控制律.与其它修正法比较,θ-δ修 正法不会使系统性能退化.即在无摄动的理想情况下,这种自适应律可以保证跟踪误差以及 自适应回路里的其它信号为渐近稳定.当系统受到摄动时,该自适应律是鲁棒的且无论设计 常数γ是大是小,输出误差的漂移都很小,因而γ可以取大于零的任意值.     

Gas-Condensate Reservoir Pseudo-relative Permeability Derived by Pressure-Transient Analysis. Incorporation of Near-Wellbore Effects

Gas-condensate reservoirs exhibit a near-wellbore complex behavior due to the existence of a two-phase system when pressure drops below dew point. In analyzing well-testing data, a single-phase approach is only valid for well condition above dew point, whereas a multi-phase pseudo-pressure approach is widely adopted for a gas reservoir operating below dew-point. This article utilizes the pseudo-pressure approach, for analyzing well-test data in gas-condensate reservoirs producing below the dew-point pressure, to generate Corey exponents for relative permeability in order to determine near-wellbore representative relative permeability that history matches the actual well-testing data.