高频串联谐振逆变器频率跟踪控制电路的仿真与应用     

郭红 《宁波职业技术学院学报》2008,12(5):22-26

为了解决高频逆变电源负载参数变化引起固有谐振频率变化,导致逆变器效率降低及开关器件应力增加的问题,提出了一种以集成高速锁相环74HC4046为核心的、应用于功率MOSFET为主开关器件的高频串联谐振逆变电源的无相差频率跟踪控制系统,对电源的输出频率进行实时控制,并用Pspiee进行了仿真分析。结果证明,该系统具有较好的应用前景和推广价值。  相似文献   

Dynamic Wave Pressures on Deeply Embedded Large Cylindrical Structures due to Random Waves     

刘海笑  唐云  周锡礽 《天津大学学报(英文版)》2003,9(1):21-28

The response of dynamic wave pressures on structures would be more complicated and bring about new phenomena under the dynamic interaction between soil asnd structure.In order to better understand the response characteristics on deeply embedded large cylindrical structures under random waves,and accordingly to offer valuable findings for engineering ,the authors designed wave flume experiments to investigate comparatively dynamic wave pressures on a single and on continuous cylinders with two different cembedment depths in response to two wave spectra ,The time histories of the water surface elevation and the corresponding dynamic wave pressures exerted on the cylinder were analyzed in the frequency domain,By calculating the transfer function and spectral density for dynamic wave pressures along the height and around the circumference of the cylinder,experimental results of the single cylinder were compared with the theoretical results based on the linear diffraction theory ,and detailed comparisons were also carried out between the single and continuous cylinders ,Some new findings and the corresponding analysis are reported in present paoer,The investigation on continuous cylinders will be used in particular for reference in engineering applications becaus information is scarce on studying such kind of problem both analytically and experimentally.  相似文献   

锁相环在频率合成技术中的应用研究     

邹道生  李铭 《赣南师范学院学报》2002,(6):39-40

本文重点分析了锁相环在频率合成技术中存在的问题,利用前置分频、混频及双模分频器来提高频率合成器的输出频率,运用多环构成频率合成器以减小频率间隔.  相似文献   

无线传感器网络节点的物理层设计   总被引：3，自引：0，他引：3  

钟子果  胡爱群  王丹 《东南大学学报》2006,22(1):21-25

比较和分析了无线传感器网络节点物理层设计的各种无线通信技术、现有的成熟标准、重要的射频参数以及不同的处理器方案,对节点物理层设计的各个主要方面进行了较为全面的研究.介绍了无线传感器网络节点的一种实现,给出了相关的测试数据以及一种“单处理器双工作频率”的新节能策略.分析了符合传感器网络MAC算法中节点周期性侦听要求的节点寿命估算问题.指出无线传感器网络节点物理层设计的关键考虑因素为:RF启动时间(决定MAC协议可以实现的最佳节点睡眠时间比例和最小的退避时间颗粒)、RF载波频率和调制方式(决定射频收发功耗)以及处理器工作在2个频率的片上系统的总体功耗.  相似文献   

多层框架结构自振周期一种简便计算方法 ——相当刚度相当质量法     

董卫华  陈林文 《福建工程学院学报》2006,4(6):763-774

推导证明了计算多层刚架体系自振频率、自振周期的一种新的近似计算方法——相当刚度相当质量法，并通过算例分析讨论了相当刚度相当质量法的计算精度和适用范围，增加了ω2的改进算法，推证了4种特殊情况下系统自振频率和主振型的解析解。算例和误差分析表明：相当刚度相当质量法所得的计算结果可靠，计算精度完全可以满足一般的工程需要，且方法简单明了，与其它常用近似计算方法比较可节省大量计算工作量。  相似文献   

Frequency of Six Early Childhood Education Approaches: A 10-Year Content Analysis of Early Childhood Education Journal     

Bridget A. Walsh  Karen Petty 《Early Childhood Education Journal》2007,34(5):301-305

The frequency of early childhood education approaches spanning 10 years of publications was investigated. A content analysis of publications (N = 492) from Early Childhood Education Journal was conducted. From a previous content analysis six approaches or search words were identified: Bank Street, Head Start, High/Scope, Montessori, Reggio Emilia, and Waldorf. Overall, the current content analysis demonstrated that the Head Start approach most frequently appeared. The results indicate that approaches vary as to their frequency of appearance and that contributors of Early Childhood Education Journal have investigated, reflected upon, and expanded upon approaches to educating young children to different degrees. This finding may be beneficial to future contributors of Early Childhood Education Journal. In addition, we have provided a brief overview of each approach that early childhood professionals may use to aid parents with their early childhood education enrollment decisions.  相似文献   

医疗体操、中频电疗法等治疗腰椎间盘突出症138例疗效观察     

严亚军 《牡丹江教育学院学报》2005,(4):91-92

医疗体操、中频电疗法等治疗腰椎间盘突出症的对象分A、B、C 3组,共138例患者.A组:中频电疗加医疗体操;B组:按摩加牵引;C组:按摩加中频电疗法.比较A、B组显效率,经统计学处理0.01＜P＜0.05,有显著性差异;比较A、C组显效率,经统计学分析处理P＜0.01,有极显著性差异.医疗体操、中频电疗法是治疗腰椎间盘突出症的较好选择.  相似文献   

A novel cell search scheme for OFDM cellular systems     

DING Ming LUO Han-wen WU Yun 《浙江大学学报(A卷英文版)》2007,8(1):10-17

INTRODUCTION Owing to its inherent ability to combat the multi-path fading channel, the modulation technology of orthogonal frequency division multiplexing (OFDM) has been widely used in many high-rate data transmissions such as digital video broadcasting (DVB-T), wireless local area network (IEEE 802.11a) and broadband wireless access (IEEE 802.16e). Re-cently, it is accepted as the most promising candidate for E-UTRA downlink (3GPP TSG-RAN-1, 2006a), which is a super 3G cell…  相似文献   

模拟式超低频信号发生器的研制     

王卫林  肖建辉 《宜春学院学报》2001,(2)

采用RC振荡器产生 0 1～ 0 0 0 1Hz的超低频正弦波信号 ,经分频电路产生二分频及四分频方波和三角波 ,用同步记录仪记录的输出波形表明 :研制的超低频信号发生器满足实验测量的技术要求。  相似文献   

机床主轴的动刚性评估     

崔勇俊 《大连大学学报》2003,24(2):12-15

本文提出了一种评估机床主轴的动刚性的一种新方法,此方法以机床主轴的固有频率为基础,在安装在机床主轴上的实验棒的半径方向上加振动脉冲,测出其固有频率,然后用固有频率算出主轴的刚度,另外对被测的机床又进行了主铣刀切削实验,得出了表面粗糙度与刚度的相关性.  相似文献