Second-order nonlinear optical properties of mexylaminotriazine-functionalized glass-forming azobenzene derivatives

The second-order nonlinear optical coefficients of thin films of mexylaminotriazine-functionalized azobenzene molecular glass derivatives were measured using second harmonic generation. The thin films were poled using a custom corona poling set-up and the second harmonic light from a pulsed 1064-nm laser was detected. Four out of the six tested compounds showed optical nonlinearity and a maximum coefficient of 75 pm/V was obtained. The time dependence of the nonlinear coefficients was studied under ambient light and under dark; the second harmonic generation intensity stayed constant for thiazole-containing derivatives while a significant decay was measured for the other compounds.     

半导体光放大器(SOA)皮秒增益和折射率非线性的数值模拟

从速率方程出发 ,采用分段模型对半导体光放大器 (SOA)的皮秒增益和折射率非线性进行了数值模拟 ,具体分析了注入光脉冲引起的载流子浓度的变化、输出光脉冲时域波形的畸变、注入光脉冲引起的增益和位相变化 ,以及输出光脉冲上的频率啁啾。     

A new method for solving kinematic tasks for robots

The main difficulties in solving inverse kinematic tasks for robots are singularities and nonlinearities. In the first part of this paper practical conditions regarding singularities of 6 df wrist-joint structure robots are presented. These considerations are based on a simple iterative inversion method by the use of which introduction and characterization of the concepts of “essential” and “procedural” singularities are realized. The second part of the paper deals with the question of nonlinearities. It is pointed out that in robotics there are two different kinds of nonlinearities. The first type is present because the sine and cosine functions of the joint coordinates appear in the formulae of direct kinematic tasks. The second type is of finite polynomial nature, and originates from the quadratic functions of the unit vectors parallel to the rotation axes of the joints of the arm. The authors point out that an appropriate quaternion representation of the robot kinematics offers a convenient possibility to get rid of sine- and cosine-type nonlinearities. Those nonlinearities which remain are the results of simple quadratic operations (mainly multiplications and additions, subtractions and divisions); therefore the proposed method seems to be especially appropriate for realizations based on neural networks or particular hardwares using RISC processors. The advantages and disadvantages of this new method are compared to those of another solution recently published by the authors.     

基于径向基函数神经网络的多级离心压缩机混合模型

大型离心压缩机作为多影响因素和强非线性的复杂系统,其性能的准确预测难以实现.针对这一问题,结合径向基函数(RBF)神经网络,本文建立了多级离心压缩机性能预测的混合模型.首先基于热力学第一定律和压缩机能量损失机理建立了多级离心压缩机性能预测的机理模型.该模型无需任何实验确定的性能曲线,完全由压缩机的几何结构参数预测出压缩机在设计工况和非设计工况下的性能.然后利用RBF神经网络修正机理模型的误差,并通过对RBF神经网络的不断更新,进一步提高了模型的预测精度和适用性.将所建立的混合模型应用于实际的离心压缩机,结果表明该方法具有良好的预测性能.     

H∞ filtering for uncertain time‐varying systems with multiple randomly occurred nonlinearities and successive packet dropouts

This paper is concerned with the robust H_∞ finite‐horizon filtering problem for discrete time‐varying stochastic systems with multiple randomly occurred sector‐nonlinearities (MROSNs) and successive packet dropouts. MROSNs are proposed to model a class of sector‐like nonlinearities that occur according to the multiple Bernoulli distributed white sequences with a known conditional probability. Different from traditional approaches, in this paper, a time‐varying filter is designed directly for the addressed system without resorting to the augmentation of system states and measurement, which helps reduce the filter order. A new H_∞ filtering technique is developed by means of a set of recursive linear matrix inequalities that depend on not only the current available state estimate but also the previous measurement, therefore ensuring a better accuracy. Finally, two illustrative examples are used to demonstrate the effectiveness and applicability of the proposed filter design scheme. Copyright © 2010 John Wiley & Sons, Ltd.     

浅谈某单层球面网壳设计分析要点

通过一个具体工程实例,总结了单层球面网壳型式的选择、结构薄弱区域的处理以及杆件应力比的控制、结构的非线性稳定极限承载力与设计荷载的比值等设计分析要点。     

二阶混合非线性椭圆方程的强迫振动性质

本文对含有阻尼项二阶混合非线性椭圆方程,建立了其所有解振动的判定定理,这些定理包含和改进了其对应的常微分方程和超线性椭圆方程相应的结果.     

Adaptive control for nonlinear uncertain systems with actuator amplitude and rate saturation constraints

A direct adaptive nonlinear tracking control framework for multivariable nonlinear uncertain systems with actuator amplitude and rate saturation constraints is developed. To guarantee asymptotic stability of the closed‐loop tracking error dynamics in the face of amplitude and rate saturation constraints, the control signal to a given reference (governor or supervisor) system is modified to effectively robustify the error dynamics to the saturation constraints. Illustrative numerical examples are provided to demonstrate the efficacy of the proposed approach. Copyright © 2008 John Wiley & Sons, Ltd.     

Numerical and experimental studies of the Braga Sports Stadium suspended roof

This paper describes a set of dynamic numerical and experimental studies conducted on the suspended roof of the Braga Municipal Sports Stadium. Modal parameters, calculated from a numerical model of the constructed structure that takes into account the geometrically nonlinear structural behaviour and the progressive application of loads, are compared with the corresponding parameters identified on the basis of an ambient vibration test. Particular attention is given to modal damping identification due to the necessity of analysing the susceptibility of the suspended roof to buffeting effects.