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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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A prediction model of foreign language reading proficiency based on reading time and text complexity
In textbooks, foreign （second） language reading proficiency is often evaluated through comprehension questions. In case, authentic texts are used as reading material, such questions should be prepared by teachers. However, preparing appropriate questions may be a very demanding task for teachers. This paper introduces a method for automatically evaluating proficiency, wherein comprehension questions are not required. This method assesses a learner＇s reading proficiency on the basis of the linguistic features of the text and the learner＇s reading time. A reading model following this method predicted reading proficiency with an ER （error rate） of 18.2%. This ER is lower than those of models proposed in previous studies. Furthermore, the ER of the authors＇ reading model for various learner groups classified by their RS （reading speeds） was examined. The result of this examination showed that the error rate was the lowest for the group of learners with fast RS. 相似文献
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Mariko Kotani 《Journal of Intercultural Communication Research》2016,45(2):126-144
This study describes speech codes used by Japanese and English speakers in remedying problematic situations. By analyzing in-depth interviews, the study reveals the Japanese-speaking participants’ use of a code in which offering detailed explanations can be a way to deny having caused another person discomfort, thus being incompatible with their meaning of “apology.” The English-speaking participants used a code in which offering and listening to explanations is a way to show that they care about the relationship and to seek forgiveness. The analysis illustrates how the participants used these codes as a resource to draw a boundary between two speech communities. 相似文献
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Taishi Tsuji Satoru Kanamori Masashige Saito Ryota Watanabe Yasuhiro Miyaguni Katsunori Kondo 《Journal of sports sciences》2020,38(4):422-429
ABSTRACTOlder people who engage in sports and exercise in a group render greater benefits for socio-psychological aspects compared to exercising alone. The aim of this study was to identify the prevalence of specific types of sports and exercise groups and the association with self-rated health, depressive symptoms, and frequency of laughter among community-dwelling older people. We used cross-sectional data from the 2016 Japan Gerontological Evaluation Study and analysed 63,465 males and 68,497 females aged ≥65 years. The top three most popular types among males were golf (11.3%), walking (8.4%), and ground golf (6.3%). Among females, the top three were fitness exercises (13.8%), walking (8.3%), and weight exercises (6.2%). After adjusting for potential confounders, engaging in golf with a group was significantly related with excellent self-rated health (prevalence ratio, PR, 1.31 in male and 1.78 in female), low depressive symptoms (PR, 0.70 and 0.71), and a high frequency of laughter (PR, 1.12 and 1.13). Among females, walking displayed a significant relationship with all three characteristics (PR, 1.23, 0.79, and 1.06, respectively). Golf in older males and walking in older females might be the first choice for an effective programme to spread sports and exercise groups within the older Japanese community. 相似文献
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Mariko Kotani 《Journal of Intercultural Communication Research》2017,46(5):463-477
Using the ethnography of communication and speech codes theory, this study aims to capture instances in which individuals’ views of appropriate conduct and cultural boundaries are undergoing change in intercultural interactions. The paper proposes a way of describing such instances by illustrating Japanese speakers’ experiences of encountering unfamiliar codes in problematic situations with English speakers in the United States, recognizing boundaries, negotiating contrasting codes, and revising their perceptions of codes and boundaries as a result of engaging in remedial episodes. The study illuminates the dynamic nature of the boundaries of speech communities and adds an ethnographic exploration of intercultural communication. 相似文献
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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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