高压共轨喷油系统中的电磁阀

研究了电磁材料和线圈结构等因素对高速电磁阀的影响，并采用有限单元法对电磁阀的特性进行了分析计算．结果表明：影响电磁阀性能的主要参数有驱动电压、初始气隙、预紧力、运动部件的质量等．通过降低驱动电压，减小初始气隙，降低弹簧预肾力，减轻电磁阀运动部件的质量，均可以提高电磁阀的性能．     

自动变速器脉宽调制开关电磁阀工作频率研究

脉宽调制开关式电磁阀是汽车自动变速器中常用的一种换档执行元件,其控制信号分为低频信号和高频信号,低频信号用于离合器调压控制,高频信号则用于离合器油压保持控制.针对电磁阀工作频率的选择方法进行了理论分析和试验研究.对于低频信号频率需要考虑电磁阀本身的固有频率、开启和关断的响应时间及控制系统采样频率等因素影响,并尽可能采用较高的值,以获得较高的调压精度.对于高频信号频率,则要考虑到保持电流的波动、电磁干扰、磁损及驱动元件的驱动特性等因素,再选择尽可能低的占空比,以获得理想的保持电流及关断的响应速度.     

共轨喷油器电磁阀双电压式驱动模块设计

设计了电磁阀双电压式驱动方法的硬件电路和驱动程序．硬件电路由驱动电压产生电路和控制电路组成，驱动电压产生电路用它激式极性反转型开关电源产生可调的高压和中压，控制电路控制高压和中压的开启和关闭时刻．驱动程序通过设置定时器匹配中断的方式实现高压和中压持续时间的控制．试验结果表明，电磁阀开启电流大。保持电流较低且保持平稳，电流特性符合电磁阀的驱动要求，可通过微调电压来调制保持电流．     

基于PWM控制模式的高速开关阀开关特性分析及优化

高速开关电磁阀作为自动变速器电液控制系统的核心控制元件,其开关响应特性直接影响自动变速换挡执行机构的响应速度和作动品质。文章在分析高速开关电磁阀结构及工作原理的基础上,建立了基于Matlab/Simulink平台上PWM维持占空比方式控制下的仿真模型,并通过仿真分析研究开关特性及关键参数对维持占空比及关闭时延的影响。结果表明,与定压信号控制方式相比,采用PWM维持占空比的控制方式以及结构参数优化调节,有效提高了阀开关动作的整体响应速度。     

一种用于PWM变换器的斜坡补偿电路设计

针对传统斜坡补偿的PWM变换器的电流输出能力会随着补偿电流的增加而下降的缺点,设计了一种用于峰值电流模式PWM变换器的斜坡补偿电路.通过改进系统箝位电路,使箝位电压能够随着补偿电流动态变化,从而保持系统的输出电流能力恒定,减小输出电压纹波.仿真采用CSMC 0.6 μm工艺,结果表明:在输入电压大于1 V、占空比大于50 %时,输出电压纹波在10 mV左右,大大提高了负载能力和系统稳定性.     

磁性源电磁法发射电流分段控制方法

针对磁性源发射系统中脉冲宽度调制(PWM)控制方法电磁干扰强及上升沿、下降沿拖尾严重的问题,提出一种磁性源电磁法发射电流分段控制的方法。将发射电流分为4段精确控制,即通过引进高压辅助电源的方法控制发射电流的上升沿、平顶段与下降沿,并利用软硬件相结合的方法消除下降沿过冲。讨论供电电压与波形线性度、延迟时间的关系,给出具体设计方案及电路参数计算,采用仿真和实验的方法与PWM控制方法所得电流波形进行对比分析。研究结果表明:通过输出电流分段控制方法得到的输出电流波形的上升沿时间小于1.5 ms;下降沿时间小于0.5 ms,过冲电流小于3 A,线性度大于0.875,与PWM控制方法所得波形相比,其上升沿提升速度快,下降沿延迟时间短,线性度高,反向过冲电流小。     

电压型PWM整流器电流控制策略的研究

电压型PWM整流器通过对整流器直流侧电压PWM调制，不但能使直流电压在一定范围内可调，而且使整流器的交流侧电流正弦化，并能够实现单位功率因数运行，实现高功率因数的整流装置．而控制PWM整流器交流侧的方法有多种，从电压型PWM整流器的静态模型入手，详细分析了电压型PWM整流器交流侧电流电流的控制规律，得出了一种间接电流控制模型，并阐述了间接电流控制的PWM整流器系统的设计，最后对该方法进行仿真，结果表明，采用这种电流控制，能够实现PWM整流器高功率因数运行．     

三相PWM整流器不平衡电网下的功率波动抑制控制

在电网电压不平衡下三相电压型整流器会产生负序电流致使有功功率和无功功率波动,而功率的波动又会导致网侧电流的畸变和直流侧电压的波动,从而影响整流器的工作性能。为了解决这些问题,本文利用不平衡电网下无功功率的新定义在α-β两相静止坐标系下建立了三相PWM整流器的数学模型,推导出有功和无功的功率表达式,得到了更为简单的参考电流计算表达式,并提出了相应的控制方案。通过功率平衡控制,可以使电网电流总谐波畸变率降低并且有效抑制直流侧电压的二倍频波动。对所建议的方法通过实验进行了验证,实验结果表明该策略的有效性。     

高速电磁开关阀开关特性的机理研究

为改善高速电磁阀的开关特性,从电磁阀的数学模型着手,用实验仿真的方法,分析了高速电磁阀的开关特性机理,提出了高速开关阀的设计准则,探讨了阀芯质量、阀芯行程、线圈匝数、线圈电阻、驱动电压与电流等各参数对开关特性的影响．提供了寻找电磁阀快速开关的有效方法．     

一种基于半自动弧焊发电机外部电流/电压的控制方法

半自动弧焊发电机通常工作在平特性或降特性状态,工作于平特性时要求电压基本恒定,工作于降特性时要求电流基本恒定。数据采集模块采集焊接电流/电压,并送单片机分析处理,利用模糊控制理论,通过计算隶属度把电流/电压信号分成过强、强、中、弱和微弱5类,不同类型采用不同的控制策略来控制PWM信号的占空比,PWM信号调节发电机励磁回路电流,以达到对发电机输出电流和电压的控制,从而实现对半自动弧焊发电机的焊接电流/电压进行控制。     

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.     

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     

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.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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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.     

Features of Women''s language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

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