FPGA-based PWM Control for DC Motors

应用PWM实现直流电机转速的控制,可用可编程序控制器PlC、单片机等方案来实现。但是这些控制方法的功能修改及调试都需要硬件电路的支持,在一定程度上增加了功能修改及系统调试的困难。因此,在设计中采用EdA技术,应用目前广泛应用的VHdl硬件电路描述语言,实现直流电机转向的控制设计,利用QuArTuSⅡ集成开发环境进行综合、仿真。仿真结果表明,应用VHdl硬件电路描述语言实现直流电机控制具有良好的控制效果。For PWM DC motor speed control,one can use the programmable logic controller( PLC),SCM,and other programs.However,modifying these functions and debuging control methods all need the support of hardware circuit.To a certain extent,it increases the difficulty of functional changes and system debugging.Therefore,this paper uses EDA technologies and hardware circuit description language VHDL which are now widely applied to complete the DC motor steering control.Quartus Ⅱ is used to integrate the development environment for synthesis,simulation.Simulation results show that the application description language VHDL is effective for hardware circuit DC motor control

Regional coordination control for optimization of urban traffic

针对目前我国城市交通区域控制的研究现状,应用群决策理论和模糊控制理论,对整个城市区域交通建立协调二级模糊控制模型。以相邻交叉口之间的车流量信息和预测剩余时间周期为模糊控制器输入,由二级模糊控制器的输出控制下一时刻的绿灯相位,从而调整控制子区内相邻交叉口上下游之间的交通流和集散程度,最终实现对控制子区的宏观区域协调控制.In view of the present research status of urban traffic zone control in our country, by using the group decision theory and fuzzy control theory, to the whole city area, the secondary fuzzy control model is established.The adjacent intersections traffic information and predict remaining time period are used as the input of the fuzzy controller, the secondary fuzzy controller's outputs control the green light phase of the next moment, to adjust the control zone between upstream and downstream adjacent intersection traffic flow and distribution.Finally the macro regional coordination's control can be realized

中国城市化进程中农村劳动力转移问题研究

本文从以下几个角度进行分析的:首先,阐述了我国农村劳动力转移的现状,进而对农村劳动力转移现象的原因进行分析,然后分析农民工返乡潮对城市化的影响,最后对于促进返乡农民工就业提出具有实践性的对策

Experimental Study on Tip-Induced Electrospinning

针尖诱导电纺技术(TIE)利用针尖阵列插入聚合物溶液表面后快速抽离,由于高压强电场和黏性力作用在液面抽离处诱导形成泰勒锥,进而在收集板上得到大量纳米纤维,实现纳米纤维的批量制造.实验结果表明在不同电极间距下,电纺阈值电压随着溶液浓度的增加而增大.当工作电压为63 kV,溶液槽尺寸为142 MMx50 MM时,电纺聚氧化乙烯(PEO)溶液的纤维产量达1.961 2 g/H.当工作电压从45 kV增加到63 kV时,纤维沉积均匀性变化范围为31.08%~43.23%.Tip-induced electrospinning(TIE) is demonstrated to produce nanofibers with high throughput.Probe array was plunged into the plane polymer solution and then withdrawn quickly,and due to the effects of viscous force and the electric force,Taylor cones were generated from the position where the probes left,and then mass nanofibers were obtained on the collector.The experimental results show that the threshold voltage under different electrode distances increases with the increase of the concentration,and the mean throughput of polyethylene oxide(PEO) nanofibers is up to 1.961 2 g / h when the solution tank size is 142 mm × 50 mm and the applied voltage is 63 kV.And the maximum deposition error of nanofibers is within the range of 31.08% —43.23% on the condition that the applied voltage changes from 45 kV to 63 kV.国家自然科学基金重点资助项目(51035002); 国家自然科学基金资助项目(51205334); 福建省自然科学基金资助项目(2011J05139

Study and Design of the Track Vibration Monitoring System

在轨道振动研究的基础上,设计完成了基于uSb2.0接口的监测系统.该系统以891-2型拾振器作为测振传感器,以lPC1768作为核心控制芯片,以uSb串行接口总线作为数据传输通道,实现了对轨道表面振动信号的采集、时域分析、频域分析以及实时显示等功能.经过试验测试,该系统性能稳定,试验结果符合预期设想,适合于工程现场监测,具有很好的实用性和借鉴性.On the basis of the study of track vibration,a monitoring system is completed based on USB2.0 interface.The system,with 891-2vibration pickup as vibration sensor,LPC1768as central control chip, USB serial interface bus as the transport channel of data,realizes the acquisition of track surface vibration signal,analysis of time domain,frequency domain and function of real-time display.After testing,the system performance is stable and the result is in line with expectation.It is suitable for monitoring of construction site with good practicality and usability

念珠藻属植物的应用研究

念珠藻属是一类富有经济价值的陆生蓝藻;其中的 Nostoc flagelliforme、Nostocmuscorum、Nostoc commume三个种因具有较高的营养价值;在中国民间被广泛食用。现代生物技术分析结果表明;念珠藻含有人体必需的氨基酸及多种天然色素;和高比例的多糖成分;具有十分广阔的开发应用前景。同时还发现念珠藻多个种的水提物都含有广谱抗菌、抗病毒的成分;如Nostoc muscorum中提取的多酚类物质对多种病原微生物有高效的抑制

念珠藻的研究进展及其应用前景

干燥环境中的念珠藻受到多种环境因素的胁迫(如水分、紫外线、电离辐射等)，其细胞如何保持稳定性、完整性并对各种损伤进行修复是一个十分值得研究的问题。本文将综述近年来在念珠藻抗逆生物学的进展以及念珠藻在工业、农业、食品及制药业的广泛用途

念珠藻的研究进展及其应用前景

干燥环境中的念珠藻受到多种环境因素的胁迫(如水分、紫外线、电离辐射等)，其细胞如何保持稳定性、完整性并对各种损伤进行修复是一个十分值得研究的问题。本文将综述近年来在念珠藻抗逆生物学的进展以及念珠藻在工业、农业、食品及制药业的广泛用途

Fabrication of high performance thin film composite forward osmosis membranes and its application for juice concentration

The conventional technology for juice concentration often leads to severe nutrition loss and high costs.Recently,forward osmosis(FO)shows great potential for juice concentration.However,the lack of efficient FO membranes is one of the critical challenges for the development of FO technology.Thus, high performance thin film composite(TFC)forward osmosis membrane was fabricated by depositing carbon nanotubes on the back surface of PSf support to shrink the surface pores and synthesizing the polyamide on top surface of the PSf support.The impacts of CNT deposition on the performance of TFC polyamide membranes were investigated,and the results showed that the TFC membrane with CNT (TFCCNT20) achieved the best performance.After 4 200min FO operation for juice concentration,the TFC membrane with CNT exhibited a lower flux decline percentage and a higher recovery percentage,compare with control membranes without the CNT

design and implementation of paas-oriented performance modeling system for web applications

按需供给是PaaS平台面临的一个核心挑战。传统以局部优化为目标的反馈控制方法难以实现全局资源供给最优,为了更合理分配资源,利用性能模型预测Web系统的资源需求就变得至关重要。随着平台服务化的发展,其部署方式由封闭环境转为开放的服务形式,为模型的构造提出了新的挑战:由于应用和平台分属不同组织,大大增加了解系统全貌的难度,所以传统手工建模方法除了建模难度大之外,更难以在开放的环境下实施;在开放和动态的环境下,用户的使用难以预期,而用户行为的改变又会极大的影响系统行为,因而也有必要使模型适应用户行为的变化。针对上述问题,给出了一种动态性能建模工具的设计与实现。该工具在Web系统中插入必要的探针收集系统运行时状态,并输出为日志。通过周期性的对这些日志进行分析,从大量数据中提取出性能模型,使其与实际用户使用情况相符。文中以TPC-W基准测试为例,验证了该系统的有效性。国家973重点基础研究发展计划基金项目(2009CB320704)|国家自然科学基金项目(61173003)|国家科技重大专项“核高基”基金项目(2011ZX03002-002-01)On-demand provision is a core challenge for PaaS platform. Traditional feedback method solves the problem of local optimization and is hard to realize global optimization of resources provision. In order to allocate resources reasonably, performa-nce model plays an important role in predicting resources demand of Web applications. However, with the development of the service platform, the way of deployment is changed from closed environment to an opened one, such as PaaS. New challenges are broughr for performance modeling of such systems. First, it is difficult to build a performance model in advance, because applications and platforms belong to different organizations. Second, in the opening and dynamic environment, the user behaviors is unexpected, which makes it is necessary to let the model adapt to the change of the mixed workload mode. To solve above problems, a dynamic performance modeling tool is designed and implemented. The tool is used to collect the running condition of Web systems at first step by inserting necessary probes into those Web systems and writing to log files. And then through periodically analyzing these log files, the tool extracts a performance model from the mass data which is in coincidence with the use condition of Web users. At last, our work is evaluated with TPC-W bench mark, whose results can demonstrate the effectiveness of our approach