单相有源AC-DC变换器的统一算法及其应用

1Introduction DuetotheextensiveuseofPWMconverters,elec tricpowerlinesareincreasinglycontaminated.This hascausedmanywidelyrecognizedproblems,leading toseveralelectricregulations[1,2].Itisnoteworthythat inhomeappliances,withincreasingconcernsofenergy savingandreducingoperationloss,manyinverter techniqueshavebeendevelopedandadoptedinpro ductssuchasair conditioners,washingmachinesand refrigerators.Despitetheenergysavingmeritofthe invertersystems,thesesystemshavecriticalproblems ofincreasedpowerf…     

株洲市路桥收费存在的问题及其对策

解决路桥收费问题的关键是整合路桥收费资源及其由资源组成的价格机制.路桥建设＂套牢＂的市场结构导致收费价格扭曲,现行监管体制、法规和监管政策目标难以实现.路桥收费市场需要整合的因素有认识资源整合、收费资源整合、收费条件整合、收费站点整合.     

钢桥面环氧沥青铺装的界面行为

通过引入一个新参数膜劲度,在部分共同作用原理的基础上,建立了描述钢桥面环氧沥青混凝土铺装复合梁在负弯矩作用下的界面行为模型,用以分析钢-环氧沥青混凝土之间的界面滑移与应变.推导了弹性工作状态下复合梁的界面滑移与应变的表达式,编制了数值计算程序并用2根复合梁进行了校核.然后采用该程序分析了界面滑移与应变沿复合梁纵向的分布特征,以及铺装层中的最大拉应力、层间剪应力对材料参数的敏感性.结果表明,界面效应削弱了钢桥面铺装复合梁的整体抗弯刚度;中低温条件下,采用劲度更大的粘结层材料有利于改善沥青铺装层的受力;粘结层的损伤累积将加剧沥青铺装层的破坏.     

在VB6.0上开发偏角法和弧距法计算桥梁工作线的应用程序

结合铁路桥涵课程的教学实践,详细阐述偏角法和弧距法计算桥梁工作线软件的界面设计、算法分析及实现方法等内容。     

几种测电表内阻的方法及误差分析

通过几种测表头内阻方法的讨论和对测量误差的分析比较它们的优越性 ;通过实际测量数据比较它们的测量精度。     

桥梁桩基沉降计算方法研究

阐述了桥梁单桩沉降计算方法和各自的优缺点,并对单桩沉降需要进一步研究的内容提出了建议,分析成果对进一步了解和促进单桩沉降计算方法的发展有一定的借鉴作用。     

陆桥经济带与我国区域协调发展新格局

陆桥经济带在我国区域协调发展总体布局中具有特殊的地位与作用.一方面,我国区域协调发展新内涵对陆桥经济带具有重要的指导意义,另一方面,陆桥经济带涵盖了我国东中西部三大区域,成为衡量我国区域是否协调发展的标志地带.     

基于组态软件的桥式起重机监控系统研究

介绍了应用于实验教学的桥式起重机模型研制过程,将VVVF变频调速和PLC控制技术应用在桥式起重机电气控制系统中,具有减少系统硬件和控制线、节能、减少机械磨损、启动性能好等诸多优点。同时对桥式起重机的保护、报警、故障处理等功能进行了阐述。通过上位机组态王监控软件对设备运行状态进行监控并对参数进行调整,该装置充分模拟工业控制现场,起重机控制系统的理论知识与工程实际得到很好的结合,加强了对学生工程应用能力的培养。     

Engineering design processes in seventh-grade classrooms: bridging the engineering education gap

This paper reports on some findings from the first year of a three-year longitudinal study, in which seventh- to ninth-graders were introduced to engineering education. Specifically, the paper addresses students’ responses to an initial design activity involving bridge construction, which was implemented at the end of seventh grade. This paper also addresses how students created their bridge designs and applied these in their bridge constructions; their reflections on their designs; their reflections on why the bridge failed to support increased weights during the testing process; and their suggestions on ways in which they would improve their bridge designs. The present findings include identification of six, increasingly sophisticated levels of illustrated bridge designs, with designs improving between the classroom and homework activities of two focus groups of students. Students’ responses to the classroom activity revealed a number of iterative design processes, where the problem goals, including constraints, served as monitoring factors for students’ generation of ideas, design thinking and construction of an effective bridge.     

现代电源技术实验平台研制

为构建完整的电力电子技术中使用各种电力电子器件进行功率变换的知识体系,研制了现代电源技术综合实验平台,其包括单端隔离型高频开关电源实验、隔离型桥式DC/DC实验和变频调速实验3个实验。对3个实验的核心控制电路进行了详细介绍,并给出对应的工作波形。该实验平台可满足电气工程高年级本科生、研究生实验的要求,同时也可给相关教师提供功率变换的科研平台。