测试双向可控硅输出电压波形对称性的简便方法     

蒋军 《黄山学院学报》2004,6(3):43-43

重点介绍使用万用表测量双向可控硅输出电压波形对称性的简单方法.  相似文献   

基于交-交变频技术实现异步电动机重载起动的研究     

雷慧杰  张艳伟 《安阳工学院学报》2007,(4):18-21

为解决异步电动机重载起动存在的不足,提出了一种以80C196KC DSP为控制技术的交-交变频系统的实现方法.该方法具有起动电流小、启动转矩大、启动平滑、运行稳定、控制效果好的特点,详细阐述系统主电路及控制部分的原理和实现方法.  相似文献   

翻译活动对二语词汇附带习得作用的实证研究     

吴晓萍 《福建工程学院学报》2011,9(2):151-155

运用"投入量假设"的理论,对翻译活动和二语词汇附带习得之间的相关性进行实证研究,考查翻译活动对二语词汇习得的作用与价值。82名高校非英语专业学习者参与了这项实验。在阅读完一篇含有目标词的文章后,他们中的一半做阅读理解和完形填空练习,另一半做英汉互译练习。对受试者进行的即时词汇测试和延时测试的结果表明,翻译练习能够促成二语词汇的附带习得。而且,相对于阅读后做理解题及填空题,翻译练习能够获得更佳的词汇习得效果,尤其在词汇的产出性知识方面。  相似文献   

主应力轴旋转情况下土的各向异性理论研究进展     

董志华  张静 《洛阳工业高等专科学校学报》2011,21(2)

从理论方面,对国内外主应力轴旋转情况下土的各向异性研究进行了对比和总结,并提出了一些研究建议。指出在理论方面,应当对屈服面方程采用应力分量表示的模型在三维空间里进行屈服面性状的描述,同时考虑不同加载方向下屈服面的变化特性以及旋转硬化的问题,并应开展对加载方向变化时土体屈服面变化特性的实验研究及理论验证。  相似文献   

电气化铁路接触网绝缘性能的实践研究     

李丽红  石白云 《雁北师范学院学报》2011,27(3)

结合同煤集团四台沟电气化铁路110 kv牵引变电所及接触网供电设备故障跳闸率对煤矿电气化铁路定量装车点的接触网设备结构及污染情况进行了系统分析,研究出了提高重污区接触网设备绝缘性能的技改方法,并附注实践取得了良好的效果。  相似文献   

Adding immersive virtual reality to a science lab simulation causes more presence but less learning     

《Learning and Instruction》2019

Virtual reality (VR) is predicted to create a paradigm shift in education and training, but there is little empirical evidence of its educational value. The main objectives of this study were to determine the consequences of adding immersive VR to virtual learning simulations, and to investigate whether the principles of multimedia learning generalize to immersive VR. Furthermore, electroencephalogram (EEG) was used to obtain a direct measure of cognitive processing during learning. A sample of 52 university students participated in a 2 × 2 experimental cross-panel design wherein students learned from a science simulation via a desktop display (PC) or a head-mounted display (VR); and the simulations contained on-screen text or on-screen text with narration. Across both text versions, students reported being more present in the VR condition (d = 1.30); but they learned less (d = 0.80), and had significantly higher cognitive load based on the EEG measure (d = 0.59). In spite of its motivating properties (as reflected in presence ratings), learning science in VR may overload and distract the learner (as reflected in EEG measures of cognitive load), resulting in less opportunity to build learning outcomes (as reflected in poorer learning outcome test performance).  相似文献   

IT engagement as a blessing and a curse? Examining its antecedents and outcomes in organizations     

《International Journal of Information Management》2020

Information technology (IT) engagement is defined as a need to spend more time using IT. Practice-based examples show that IT engagement can have adverse effects in organizations. Although users can potentially get more work done through IT engagement, observations show that the users might jeopardize their well-being and hamper their work performance. We aimed to investigate this complexity in the research on IT engagement by examining its potential antecedents and outcomes in organizations. Considering the potentially mixed outcomes, we developed a model to examine the effects of IT engagement on personal productivity and strain. We also aimed to explain the antecedents of IT engagement by drawing on the collective expectations for IT use. In particular, we examined the extent to which normative pressure on IT use drives users’ information load and IT engagement. Finally, we sought to understand whether users’ attempts to avert dependency on IT use reduced their IT engagement. Several hypotheses were developed and tested with survey data of 1091 organizational IT users. The findings help explain the role of normative pressure as a key driver of IT engagement and validate the positive and negative outcomes of IT engagement in organizations.  相似文献   

Genomic consequences of population decline in critically endangered pangolins and their demographic histories     

Jing-Yang Hu  Zi-Qian Hao  Laurent Frantz  Shi-Fang Wu  Wu Chen  Yun-Fang Jiang  Hong Wu  Wei-Min Kuang  Haipeng Li  Ya-Ping Zhang  Li Yu 《国家科学评论(英文版)》2020,7(4):798

Pangolins are among the most critically endangered animals due to heavy poaching and worldwide trafficking. However, their demographic histories and the genomic consequences of their recent population declines remain unknown. We generated high-quality de novo reference genomes for critically endangered Malayan (Manis javanica, MJ) and Chinese (M. pentadactyla, MP) pangolins and re-sequencing population genomic data from 74 MJs and 23 MPs. We recovered the population identities of illegally traded pangolins and previously unrecognized genetic populations that should be protected as evolutionarily distinct conservation units. Demographic reconstruction suggested environmental changes have resulted in a population size fluctuation of pangolins. Additionally, recent population size declines due to human activities have resulted in an increase in inbreeding and genetic load. Deleterious mutations were enriched in genes related to cancer/diseases and cholesterol homeostasis, which may have increased their susceptibility to diseases and decreased their survival potential to adapt to environmental changes and high-cholesterol diets. This comprehensive study provides not only high-quality pangolin reference genomes, but also valuable information concerning the driving factors of long-term population size fluctuations and the genomic impact of recent population size declines due to human activities, which is essential for pangolin conservation management and global action planning.  相似文献   

基于关键资源的水平集成型虚拟企业任务分配研究     

李民  方志梅  李国富 《科技管理研究》2010,30(24)

针对水平集成型虚拟企业的生产特点,通过分析关键资源的作用、负荷状况与生产任务分配的关系,研究水平集成型虚拟企业的生产任务分配问题。以关键资源负荷率均衡和生产成本最低为目标,建立了水平集成型虚拟企业的生产任务分配模型,并通过实例应用验证上述方法的有效性。  相似文献   

100 堂大学女生体育课运动负荷的保健学分析     

董晓虹  姜建华 《首都体育学院学报》1999,(2)

本文测量了普通高校女生１００ 堂９０ ｍ ｉｎ 体育课２００ 人次的运动负荷,显示了课中脉率变化曲线有 ３ 种情况, 其中最高脉率达 １４０～１５０ 次／ｍ ｉｎ, 平均脉率在１１２～１２２ 次／ｍ ｉｎ, 净增脉率在 ３２～４３ 次／ｍ ｉｎ, 此种运动负荷量对 ９６５％ 的女生可能是适宜的, 但对 ３５％ 的女生可能偏大。体育课运动负荷是否适宜可从体育课的脉率变化曲线、运动负荷量等级、机体反应和课后脉率恢复时间等４ 个方面进行综合分析。  相似文献