排序方式： 共有19条查询结果，搜索用时 15 毫秒
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A new PWM converter based on soft-switching is introduced.The converter uses a minimum number of devices,and requires less switching operations than conventional techniques,Switching is realized solely in a ZVS)zero voltage switching)mode,therefore the loss is reduced and EMI(electromagnetic interference)is suppressed.The paper analyzes the operation of ZVS,and discusses the methods for maintaining a unit power factor and constant DC voltage.Changing the modulation index M and the phase angle θ keeps the input current in phase with the voltage.It also keeps the current sinusoidal,and ensures a constant output voltage. 相似文献
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In this paper, a new soft-switching inverter using a minimum number of devices, and a new PWM (pulse-width modulation) method
suitable for 3-phase soft-switching inverters are proposed. The circuit is used as an interface between the DC supply and
the conventional voltage source of a PWM inverter. The number of switching operations can be reduced by using the PWM strategy.
Increasing the amplitude of the fundamental component contained in the output waveform results in an effective utilization
of the DC supply, a reduction of nominated capacity of the inverter elements, and a reduction of switching loss in the switching
devices.
Supported by National Natural Science Foundation of China (59977012) 相似文献
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Shoichi Taniguchi 《Cataloging & classification quarterly》2017,55(6):387-412
This article examines BIBFRAME 2.0 from the viewpoint of RDA metadata schema, that is, whether the present BIBFRAME is suitable for exchange and sharing of metadata created with RDA. First, an overview of RDA and BIBFRAME models is provided. Second, mapping examples of metadata records and part of the mapping tables from RDA to BIBFRAME are demonstrated. Third, some issues involved in the mapping are investigated: treatment of RDA Expression in BIBFRAME, mapping of RDA elements to BIBFRAME properties, and conversion of extant MARC21 bibliographic records to BIBFRAME metadata. 相似文献
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School management in many sub-Saharan African countries has been enhanced through community participation in an attempt to improve education quality. This study uses field research in a rural district of Malawi to assess how community and parent participation differs between schools, the intentions of communities and parents when carrying out activities in schools, and the mechanism promoting active participation in schools. In high-achieving schools, but not in low-achieving schools, communities and parents were actively involved in events aimed at improving student achievement. Communities and parents considered most highly prioritised activities that directly influenced student achievement, including hiring volunteer teachers, arranging extra classes and holding mock examinations. Community participation did not directly improve student achievement. Instead, when communities and parents actively participated in a school, school management improved, ensuring better student achievement. The implications of this finding are discussed in relation to community participation. 相似文献
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Stacy T. Taniguchi Patti A. Freeman A. LeGrand Richards 《Journal of Adventure Education & Outdoor Learning》2005,5(2):131-144
This phenomenological study sought to identify the attributes of meaningful learning experiences as found in an outdoor education program. Thirteen students in the Wilderness Writing Program at Brigham Young University were the sample of this study. Their participation in outdoor recreational activities and their reflections about their experiences were analyzed. Through written journal entries, group discussions, observations, and writing assignments, a qualitative analysis identified attributes that occurred in their meaningful learning experiences. Meaningful learning was defined as a realization of a person's weaknesses, strengths, and potentials. This realization came through experiences with attributes of a degree of perceived risk, which led to a feeling of awkwardness, followed by a purifying process, or sublimation. A reflective period allowed for reconstruction of a person's view of himself or herself and this was closely tied with feedback from others in the group. 相似文献
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