非线性MIMO系统的降维状态观测器

研究一类多输入多输出（ＭＩＭＯ）非线性时变系统的降维状态观测器设计问题,提出了一种非线性降维状态观测器设计方案,并从理论上证明了状态观测误差的指数收敛性,其中设计的降维状态观测器具有收敛速度可调的特性,最后给出了数值算例,仿真结果表明了本文方法的有效性。     

一个预测路堤沉降的新经验公式模型

大量工程实践验证表明，无论是一级荷载还是多级荷载下的指数曲线模型，均可对地基沉降进行较好地预测，但也存在不足之处。先基于绝对时间坐标系下的软土次压缩计算修正式子，提出耦合软土流变项的新型指数曲线模型，并采用数学中最优化技术，根据前期沉降实测资料对模型中参数进行反演。实例计算表明：该模型对沉降预测精度高，能较合理地反应出土颗粒骨架的蠕变过程，且能给出不同时刻的次压缩量，在实际工程上具有一定的参考价值。     

On the integration schemes for Drucker–Prager's elastoplastic models based on exponential maps

Rate plasticity equations for the case of Drucker–Prager's model in small strain regime are considered. By defining an augmented stress vector, the formulations convert the original problem into a quasi‐linear differential equation system. Two new exponential mapping schemes for integrating model equations are proposed. In addition, two traditional schemes for solving the dynamical system in an explicit manner are discussed. The two semi‐implicit schemes developed pose higher accuracy and better convergency. Error contours are provided for all four methods to display the accuracy of each scheme. In order to compare the results, these contours for the classical one‐step backward Euler integration method are also displayed. Accuracy and efficiency along with the rate of convergency of the existing and the proposed methods are examined by numerical examples. Copyright © 2007 John Wiley & Sons, Ltd.     

幂指关系粘滞流体阻尼器的力学性能研究

从工程应用的角度出发,对采用不同幂指流体时粘滞流体阻尼器的输出力计算公式进行推导,分析了流体的幂指关系对粘滞流体阻尼器力学性能的影响规律。通过对影响阻尼器系数的其他因素进行分析,给出了幂指关系的粘滞流体阻尼器的阻尼孔面积组合原则。推导的理论公式的计算结果和试验结果符合,误差在10%,为粘滞流体阻尼器的实际工程应用提供了依据。     

CMOS Differential-Mode Exponential Voltage-To-Current Converter

A CMOS differential-mode exponential voltage-to-current converter is presented which is based on the approximated Taylor's series expansion. The proposed circuit has been fabricated in a 0.5μm N-well CMOS process. Experimental results show that the output dynamic range of the proposed differential-mode exponential voltage-to-current converter can be 15dB while the nonlinear error is less than 1.35%. The experimental results are given to demonstrate the proposed circuits.     

On the new results of global attractive set and positive invariant set of the Lorenz chaotic system and the applications to chaos control and synchronization

Copyright by Science in China Press 2005 1 Introduction In the 1960s, American scientist E. N. Lorenz discovered the first chaotic attractorwhen he worked on some numerical experiments of meteorology. Since then, studies of chaos have been greatly developed in many areas[1?4]. Professor J. Ford, a famous physi-cist, named the discovery of chaos “the third revolution of physics”. As the first chaotic system, the Lorenz system indicates the essential phenomenon of the complexity of non-li…     

Residual Empirical Processes and Weighted Sums for Time‐Varying Processes with Applications to Testing for Homoscedasticity

In the context of heteroscedastic time‐varying autoregressive (AR)‐process we study the estimation of the error/innovation distributions. Our study reveals that the non‐parametric estimation of the AR parameter functions has a negligible asymptotic effect on the estimation of the empirical distribution of the residuals even though the AR parameter functions are estimated non‐parametrically. The derivation of these results involves the study of both function‐indexed sequential residual empirical processes and weighted sum processes. Exponential inequalities and weak convergence results are derived. As an application of our results we discuss testing for the constancy of the variance function, which in special cases corresponds to testing for stationarity.     

Detecting changes in a multiparameter exponential family by using adaptive CUSUM procedure

An adaptive cumulative sum (CUSUM) procedure is proposed to monitor parameter changes in a multiparameter exponential family where the change-point and postchange parameters are estimated adaptively. Approximations for average run lengths are derived. Monitoring changes in both mean and variance in the normal case is considered as an illustration. The conditional biases of the estimations for the change-point and postchange mean and variance is studied by simulation comparison with several other CUSUM procedures. An adaptive dam process by modifying the adaptive CUSUM process is used to detect and identify change points and change segments by using Citibank stock prices from 30 Dow Jones Industry Index.     

混杂型离散时间脉冲时滞Hopfield神经网络的多稳定性分析

研究一类混杂型离散时间脉冲时滞Hopfield神经网络的多稳定性问题。首先,运用Brouwer不动点定理,证明所考虑的脉冲时滞神经网络具有多个平衡点。然后,引入Lyapunov函数,运用不等式分析技术,建立脉冲离散时滞Hopfield神经网络多稳定性判别准则,并给出平衡点吸引域的估计。最后,通过数值实例仿真验证结果的有效性。     

基于指数平均模型的无线传感器网络动态功耗管理

能耗一直是制约无线传感器网络WSN(Wireless Sensor Networks)发展的关键因素。为了降低节点的功耗,延长WSN的寿命,一种改进指数平均模型的动态功耗管理DPM(Dynamic Power Management)方法被提出。该方法利用历史空闲时间来对未来空闲时间进行预测,预测结果作为节点是否转换为低功耗状态的依据。理论分析和实验仿真表明,本文提出的DPM在突发情况时能够快速自适应地调整,提高了预测的准确性,降低了WSN的功耗。