在MLIS授予单位迅速扩张的背景下,如何保障人才培养质量是MLIS教育面临的重要问题。文章以课程建设为观察点,调查U. S. News发布的MLIS榜单中的53所美国院校和我国66所MLIS院校的MLIS课程信息,借助BERTopic模型和余弦相似度算法,开展中...在MLIS授予单位迅速扩张的背景下,如何保障人才培养质量是MLIS教育面临的重要问题。文章以课程建设为观察点,调查U. S. News发布的MLIS榜单中的53所美国院校和我国66所MLIS院校的MLIS课程信息,借助BERTopic模型和余弦相似度算法,开展中美课程主题聚类分析及基于扎根理论的课程内容分析。研究发现中美课程均表现出强烈的职业导向性,在以图书馆职业为核心的基础上,MLIS教育出现向健康、政务、商务等多信息工作场景拓展的趋势。除MLIS教育共同发展趋势外,我国MLIS课程还具有重视文化保护的特点。同时,文章也发现我国MLIS课程在内容丰富性、差异性、业务细分等方面尚有提升空间,为此提出立足中国话语体系开发特色MLIS课程,对接区域需求开展差异化课程设计,强化行业合作以细化专业课程等建议。展开更多
根据低温推进剂长时间在轨贮存的要求,设计并搭建了绝热系统地面验证测试装置,对绝热系统的热力学性能进行测试。针对55L贮箱,采用了泡沫绝热(spray on foam insulation,SOFI)和多层绝热(multilayer insulation,MLI)结合的复合绝热系统...根据低温推进剂长时间在轨贮存的要求,设计并搭建了绝热系统地面验证测试装置,对绝热系统的热力学性能进行测试。针对55L贮箱,采用了泡沫绝热(spray on foam insulation,SOFI)和多层绝热(multilayer insulation,MLI)结合的复合绝热系统,分别在高真空(5×10^-3Pa以上)和大气压条件下进行了验证实验(液氮作为替代工质)。贮箱外绝热系统为15m m厚泡沫绝热层和45组多层绝热时,高真空条件下液氮日蒸发率为0.77%,多层绝热层表观热导率为1.29×10^-4W/(m·K),据此折算为液氧时日蒸发率为0.55%。将高真空和大气压条件下的实验结果比较发现,泡沫绝热层所占热阻分别为总热阻的0.19%和45.14%。展开更多
Electric vehicles are in demand in recent days due to depleting conventional energy resources. Electric vehicles which are environmental friendly are set to increase on road in coming days. The Electric vehicles which...Electric vehicles are in demand in recent days due to depleting conventional energy resources. Electric vehicles which are environmental friendly are set to increase on road in coming days. The Electric vehicles which consist of electric drive systems are made up of electric motors, inverters and batteries. There is a need to increase their output quality while decreasing their size and cost. The multilevel inverter plays a vital role in improving the quality of the output voltage of the inverter. This paper presents the implementation of Elliptical Phase Disposition Pulse Width Modulation (EPD PWM) technique for higher level of Cascaded H-Bridge Multi Level Inverter (CHBMLI). The performance of 5, 7 and 9-level CHBMLI with proposed EPD PWM scheme is analyzed for three-phase RL-load. The simulation results prove that the voltage %THD reduces from 28.09 to 12.85 to 9.69 and current %THD reduces from 25.58 to 10.22 to 9.42 as the number of inverter output level increases from 5-7-9 level respectively. The simulation is carried out on MATLAB/ SIMULINK platform and the results were compared with conventional method to validate the proposed scheme. The simulation results prove that the novel EPD-PWM technique can be used to effectively control the CBHMLI.展开更多
文摘在MLIS授予单位迅速扩张的背景下,如何保障人才培养质量是MLIS教育面临的重要问题。文章以课程建设为观察点,调查U. S. News发布的MLIS榜单中的53所美国院校和我国66所MLIS院校的MLIS课程信息,借助BERTopic模型和余弦相似度算法,开展中美课程主题聚类分析及基于扎根理论的课程内容分析。研究发现中美课程均表现出强烈的职业导向性,在以图书馆职业为核心的基础上,MLIS教育出现向健康、政务、商务等多信息工作场景拓展的趋势。除MLIS教育共同发展趋势外,我国MLIS课程还具有重视文化保护的特点。同时,文章也发现我国MLIS课程在内容丰富性、差异性、业务细分等方面尚有提升空间,为此提出立足中国话语体系开发特色MLIS课程,对接区域需求开展差异化课程设计,强化行业合作以细化专业课程等建议。
文摘Electric vehicles are in demand in recent days due to depleting conventional energy resources. Electric vehicles which are environmental friendly are set to increase on road in coming days. The Electric vehicles which consist of electric drive systems are made up of electric motors, inverters and batteries. There is a need to increase their output quality while decreasing their size and cost. The multilevel inverter plays a vital role in improving the quality of the output voltage of the inverter. This paper presents the implementation of Elliptical Phase Disposition Pulse Width Modulation (EPD PWM) technique for higher level of Cascaded H-Bridge Multi Level Inverter (CHBMLI). The performance of 5, 7 and 9-level CHBMLI with proposed EPD PWM scheme is analyzed for three-phase RL-load. The simulation results prove that the voltage %THD reduces from 28.09 to 12.85 to 9.69 and current %THD reduces from 25.58 to 10.22 to 9.42 as the number of inverter output level increases from 5-7-9 level respectively. The simulation is carried out on MATLAB/ SIMULINK platform and the results were compared with conventional method to validate the proposed scheme. The simulation results prove that the novel EPD-PWM technique can be used to effectively control the CBHMLI.
