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ZVS（zero voltage switching） PWM（pulse width modulation） inverters have attracted much attention recently. The basic idea is to use ZVS circuit as the main circuit of inverter resonance at the beginning of every carrier period so that each power device can commutate when voltage of the main circuit＇s DC bus line is zero. To ensure the resonant circuit to operate properly, sawtooth with alternate slope （positive or negative） is used as carrier. But the time of zero voltage vectors with such PWM pattern is greatly different from traditional hard-switching PWM pattern. This paper discusses the locus of flux linkage under soft-switching PWM pattern by using space voltage vector. It is pointed out that, under the hard-switching PWM pattern, speed of flux linkage is adjusted by zero space voltage vector. When soft-switching PWM pattern is used, however, effective time of space voltage vector varies considerably, sometimes even without zero space voltage vector. Therefore non-zero space voltage vector has been used to make the speed of flux linkage locus equal to that of hard-switching PWM pattern. The cause of current distortion in soft-switching PWM inverters is also discussed. Based on the flux linkage locus circle, corresponding compensation methods are proposed. Experimental results show that the described method can effectively improve output current waveform of inverter. 相似文献
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日本大学图书馆期刊价格上涨对策研究 总被引：11，自引：0，他引：11
通过分析日本大学图书馆面对期刊价格上涨所采取的一系列措施,希望对中国的图书馆应对期刊价格上涨问题起到参考作用。 相似文献
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Marine Cotte Emilie Checroun Wout De Nolf Yoko Taniguchi Laurence De Viguerie Manfred Burghammer 《文物保护研究》2017,62(1):2-23
The origin(s) and role(s) of metal soaps in paints are a worldwide concern today. These hybrid compounds, containing both fatty acid chains and metals associated with a carboxylate function, are increasingly identified in paints. As reviewed in the first part of this work, the presence of metal soaps in paints is differently interpreted in scientific publications: metal soaps are sometimes considered to play a positive role as anchor points, during paint drying processes; they can also be considered as responsible for many degradation processes (protrusions, efflorescences, darkening, etc.). Their origins are also interpreted in various ways. In some paintings (in particular from the twentieth century), they have sometimes introduced on purpose, as additives, to modify the physical properties of the painting materials. In older paintings, metal soaps are usually thought to result from an uncontrolled reaction of oil with lead-based pigments, in particular lead white, red lead, and lead tin yellow. In the second part of this work, the review of historical recipes of lead-based paint shows an important number of recipes based on controlled mixing of oil with lead driers. In the third part, the experimental reproduction of such traditional recipes using walnut oil and litharge (PbO) shows that lead soaps can be formed, both in about one hour at ～100°C, or in about one month at room temperature. It shows as well that after a few years, litharge is no longer detected in the paint medium, while different lead carbonates are. Finally, the micro-infrared spectroscopy and micro-X-ray diffraction re-analysis of protrusions from a nine-year model painting shows together with lead soaps, the presence of Pb5(CO3)3(OH)2O (‘synthetic plumbonacrite’), an unusual phase recently observed in a protrusion from a painting by Vincent Van Gogh. This work highlights (i) the multiple origins and roles of metal soaps in paints and (ii) the importance of combining the analysis of fragments from historical paintings with the analysis and reproduction of historical recipes. In particular, we show that the components detected today in historical paintings may severely differ from those originally used or prepared by the painter, complicating the assessment of the painter's intentions. More than the presence of metal soaps, the key questions to be tackled should be about their origins and (re)mobilization. 相似文献
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Eiichi Tomiura 《Research Policy》2007,36(5):758-767
This paper examines how internal R&D intensity and external networking channels are related with the firm's export decision, based on a large firm-level data set covering all manufacturing industries in Japan without any firm-size threshold. Internal R&D is not the only determinant of exporting, while it is strongly related with exports in the science-based sector. Collaborations with other firms on joint projects and operations of subsidiaries overseas are significantly linked to exports of large-sized firms, while affiliations with business associations and R&D intensity are critical for small-sized firms to export. Connections with computer networks have a weaker impact. 相似文献
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Edward P. Armstrong Eiichi Akaho James W. Tysinger 《Education and Information Technologies》1997,2(2):155-163
The purpose of this study was to evaluate the computer experiences and attitudes of first- and fourth-year Japanese pharmacy students. An existing questionnaire that asked questions about computer hardware and software owned, reported level of expertise with software applications, attitudes and concerns about computers, and demographic information was translated into Japanese. After ensuring the accuracy of the translation, first- and fourth-year pharmacy students completed the survey. This study found that most of these Japanese pharmacy students did not frequently use computers. About one-quarter of the students owned a home computer. Slightly more than 10% of the students reported that they could use word processing programs. Their attitudes about computers were positive. Most stated that they should possess basic computer skills when graduating from pharmacy school. The students also indicated that they would rather learn from computers than attend lectures or read texts or journals. However, 63 first-year (32%) and 45 fourth-year (43.7%) students said that microcomputers were too complicated for them to use 相似文献