一类基于Levenberg-Marquardt算法的神经PID控制研究

传统的比例积分控制器具有一定的局限性,尤其是当被控对象会有非线性、不确定性和时变特性,常规的PID控制器往往难以发挥作用,甚至会失稳.利用神经网络进行复杂过程的PID控制可以很好地解决上述问题.Lvenberg-Marquardt(LM)算法是梯度下降法与高斯-牛顿法的结合.就训练次数与精度而言,它明显优于共轭梯度法及变学习率的BP算法,适用于PID控制.得到了在线自适应神经网络PID控制算法,该算法改善了传统BP算法,实现了现有PID控制器控制方法.     

一类基于Levenberg—Marquardt算法的神经PID控制研究

传统的比例积分控制器具有一定的局限性,尤其是当被控对象会有非线性、不确定性和时变特性,常规的PID控制器往往难以发挥作用,甚至会失稳．利用神经网络进行复杂过程的PID控制可以很好地解决上述问题．Levenberg—Marquadt（LM）算法是梯度下降法与高斯一牛顿法的结合,就训练次数与精度而言,它明显优于共轭梯度法及变学习率的BP算法,适用于PID控制．得到了在线自适应神经网络PID控制算法,该算法改善了传统BP算法,实现了现有PID控制器控制方法．     

基于梯度监督学习的理论与应用(Ⅰ)——基本算法

讨论了一类基于梯度的监督训练算法及其用于神经网络的参数优化。文中详细讨论了ＬＭ算法，它是梯度下降法与高斯牛顿法的结合，既有高斯牛顿法的局部收敛性，又有梯度下降法的全局特性。μ很大时，ＬＭ算法近似于梯度下降法；μ为零时，则是高斯牛顿法。由于利用了近似的二阶导数信息，ＬＭ算法比梯度法快得多。就训练次数及准确度而言，ＬＭ算法明显优于共轭梯度法和变学习率的ＢＰ算法。由于主矩阵的正定性，解总是存在的，从这种意义上说，ＬＭ算法优于高斯牛顿法     

发电机励磁与汽门系统的改进神经网络逆控制方法

为提高发电机励磁汽门系统机端电压和转速的控制性能,提出了基于在线学习和扩张状态观测器(ESO)的改进神经网络逆控制方法.首先,将神经网络逆与被控励磁汽门系统组成的复合伪线性系统等效为含有扰动的线性系统.然后,基于自抗扰控制方法,设计了用于在线估计复合伪线性系统状态和扰动的ESO,并在设计的伪控制量中对扰动进行补偿,利用线性系统理论证明了ESO的收敛性和闭环系统的稳定性;同时,在离线训练的基础上设计了基于在线梯度方法的神经网络逆在线学习算法,利用李雅普诺夫稳定性理论证明了神经网络逆在线学习的收敛性.最后,以典型的两区域四机系统为例进行数值仿真,结果表明,与传统的AVR/PSS方法和基于离线训练的神经网络逆控制方法相比,所提方法明显提升了电力系统的暂态性能.     

基于在线学习和ADRC的发电机励磁与汽门系统ANN逆鲁棒控制方法

为提高汽轮发电机组励磁与汽门系统机端电压和功角的控制性能,提出了基于在线学习和自抗扰控制(ADRC)的神经网络逆鲁棒控制方法.首先,将神经网络逆(ANN)与被控励磁汽门系统组成的复合伪线性系统等效为含有扰动的线性系统;然后,基于ADRC,设计了用于在线估计复合伪线性系统状态和扰动的ESO,解决了神经网络逆在线学习时训练样本获取的难题,并在设计的伪控制量中对扰动进行补偿,基于线性系统理论证明了ESO的收敛性并针对励磁子系统和汽门子系统与神经网络逆系统组成的伪线性复合系统分别设计整数阶PID控制器和分数阶PID控制器以实现闭环控制;同时,在离线训练的基础上设计了基于在线梯度方法的神经网络逆在线学习算法,利用李雅普诺夫稳定性理论证明了神经网络逆在线学习的收敛性.最后,以典型的两区域四机系统为例进行数值仿真,与传统的AVR/PSS和基于离线训练的神经网络逆控制方法的比较结果表明所提方法明显提升了电力系统的暂态性能.     

一种具有自适应动量因子的BP算法

为提高神经网络的训练速度,提出一种自适应确定带动量项BP算法中动量因子的方法.在学习率为常数情况下,根据误差函数关于权值向量的梯度变化情况,自适应调节动量因子.数值试验表明,该方法对离线和在线训练均有效,且在收敛速度和算法稳定性上优于常动量因子的BP算法.     

一种基于优化小波神经网络的语音识别

在以往的BP小波神经网络中,最常用的学习算法是BP算法,BP算法实质上就是梯度下降法,是一种局部搜索算法,梯度下降法使得网络极易陷入局部最小值,从而使得网络训练结果不尽人意,搜索成功概率低.取代传统的梯度下降法,利用粒子群算法对小波神经网络中的参数进行优化.然后利用基于粒子群优化(PSO)的小波神经网络进行抗噪声语音识别实验,仿真结果表明,与BP网络相比,PSO算法在迭代次数、函数逼近误差、网络性能方面均优于BP网络,系统的识别率也得到较大的提高.     

一种基于人工神经网络的旋转机械故障监测方法

把神经网络与数字信号处理相结合，提出并实现了一种基于神经网络的旋转机械在线故障监测系统，主要用于识别旋转机械的一些常见故障如转子不平衡振动、转子零部件松动、油膜涡动等等。系统主要由数字信号采集、数字信号预处理和Ｂ－Ｐ神经网络几部分组成。在神经网络中采用批处理加动量项的梯度下降算法学习。仿真结果表明该故障监测系统在故障识别率等各方面性能指标均优于传统的基于知识的工况监测与故障诊断系统。     

基于小波神经网络的自适应控制器设计

针对一类未知非线性系统,设计了一种基于小波神经网络的自适应控制器,并提出了一种适合在线学习的参数混合训练算法。根据离线和在线学习系统的特性,得到小波神经网络控制器的初始参数,使用混合训练算法在线修正控制律,实现了自适应控制。仿真结果验证了该控制方案的有效性。     

基于自构建RBF神经网络的内模控制

针对复杂的非线性被控过程,本文提出一种基于自构建RBF神经网络的内模控制方法。该方法中,神经网络的自构建学习算法包括结构学习和参数学习。结构学习采用最近邻聚类法使网络能够自适应地在线增加和删减神经元以达到理想的网络结构。神经网络的参数学习采用梯度下降法。将该神经网络用于内模控制,使得辨识被控远程内部模型和控制器模型的神经网络的神经元个数可以根据激励强度动态改变,进而改善了控制系统的动态性能和鲁棒性。仿真结果表明了所提方法的有效性。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

英文诗歌中的喻类修辞

为了有助于提高英文爱好者的个人情操、文化素养和学习兴趣,以及专业人员对英语学习和研究进行多途径的探索,本文通过一些精选诗歌的引证和分析,着重论述了喻类修辞法在英文诗歌中的运用其及效果。     

Man Is Unable to Change the Miserable Life——Analysis of the Arrangement of Four Characters in The Glass Menagerie

Tennessee Williams is considered as one of the most important American playwrights since World War II.The Glass Menagerie is his first successful drama,which describes a tragic situation of family and means to say that Man is unable to change the miserable life,no matter whatever means he try,This essay focuses on the analysis of the arrangement of the four main characters:Laura.Amanda,Jim and Tom to reveal the theme.Laura is fragile.Amanda is brave.Jim is vital.Tom is sensible.And all of them develop and try the different means to struggle against life,but fail tragically.With the evidence,the paper comes to conclusion naturally that Man is unable to change the miserable life,and he dooms to fail.     

Characterization of root-nodulating bacteria on Retama raetam in arid Tunisian soils

The aim of this study is to investigate the diversity of Retama raetam root-nodule bacteria isolated from arid regions of Tunisia. Twelve isolates, chosen as representative for different 16S rRNA gene patterns, were characterized by 16S rRNA gene sequencing and phenotypic analysis. Isolates were assigned to Sinorhizobium, Rhizobium and Agrobacterium. Symbiotic properties of Sinorhizobium and Rhizobium isolates showed a large diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Strain RK 22 identified as Rhizobium was the most effective isolate.     

An Affordable Accurate Evaluation of the Binding Conformations Predicted by Molecular Docking Studies in Bio-System

正Recently,docking has been widely used to predict the binding-modes of protein-inhibitors,when the crystal complexes structure was absent.Most docking algorithms are able to generate a large number of probable conformations,it,however,is difficult to effectively evaluate these docking poses and identify the most reasonable bindingmode.In the present study,on the basis of the crystallographic data of human 3-hydroxy-3-methylglutaryl coenzyme     

WIMAX与WI-FI技术分析及联合组网

介绍了WiMAX与Wi-Fi两种无线宽带接入技术,并对两者之间的关系及相互之间的影响做了对比及分析,并对WiMAX的关键技术进行了详细说明,最后对两者的联合组网方式做了简单的探讨。