Study on inverter fault-tolerant operation of PMSM DTC

This paper presents an investigation of inverter fault-tolerant operation for a permanent magnet synchronous motor （PMSM） direct torque control （DTC） system under various inverter faults. The performance of a faulty standard 6-switch inverter driven PMSM DTC system is analyzed. To avoid the loss or even disaster caused by the inverter faults, a topology-modified inverter with fault-tolerant capability is introduced, which is reconfigured as a 3-phase 4-switch inverter. The modeling of the 4-switch inverter is then analyzed and a novel DTC strategy with a unique nonlinear perpendicular flux observer and feedback compensation scheme is proposed for obtaining a continuous, disturbance-flee drive system. The simulation and experimental results demonstrate that the proposed inverter fault-tolerant PMSM DTC system is able to operate stably and continuously with acceptable static and pretty good dynamic performance.     

An examination of the Counting Talk Test’s ability to discern individual variability in exercise-induced metabolic stress

The purpose of this study was to determine if the counting talk test can be used to discern whether an individual is exercising above or at/below maximal lactate steady state. Twenty-two participants completed VO₂peak and counting talk test incremental step tests followed by an endurance test at 65% of work rate at VO₂peak (WR_VO2peak). The change in relative count time during endurance exercise decreased in those exercising above maximal lactate steady state only (p < .01); however, this change was less than 1 second. Despite a significant correlation during the incremental step test, large changes in counting talk test performance and blood lactate concentration occurred at different points and there was considerable inter-individual variability in counting talk test performance at a given blood lactate concentration. These results suggest that the counting talk test cannot discern whether an individual is exercising above maximal lactate steady state and that it cannot be used to accurately prescribe intensities targeting specific blood lactate concentrations.     

地震动混沌特性判别及影响因素分析

采用主成分分析法与混沌时间序列分析方法对地震动的非线性特性进行分析,分别从定性与定量的角度考察地震动的非线性特性;探讨了地震动的要素对其混沌特性的影响。结果表明:地震动最大幅值的变化对混沌特性没有影响,而持时、频谱特性、采样频率等要素对混沌的定量指标均产生了影响。     

Elite status maintained: a 12-year physiological and performance follow-up of two Olympic champion rowers

This case study reports the results of a 12-year (2005–2016) follow-up study of two Olympic champion rowers. The rowers were prospective athletes at the junior level when the study began, and we monitored their relevant physiological and performance data annually. Our findings indicated that their V?O_2max gradually increased up to about 22 years of age and leveled off at a value of approximately 7 l·min^?1 with minimal fluctuations thereafter. However, the variables that directly influence the V?O_2max changed. There was an age-related decline in maximal heart rate of about 0.5 beats·year^?1, while oxygen pulse, which serves as an indirect measure of stroke volume, correspondingly increased by about 1 ml O₂·beat^?1 per year, allowing the athletes to maintain exceptional V?O_2max values. Maximal minute power of the studied rowers, derived each year from their ramp-wise tests, closely resembled the mean power output sustained during the 2000-m all-out tests on a rowing ergometer. A 12-year improvement of 28% and 33% occurred for the mean power output sustained over 2000 and 6000-m on a rowing ergometer, respectively. The findings contribute to the body of knowledge on athletes representing the true elites of their respective sports.     

How does buoyancy affect performance during a 200m maximum front crawl swim?

We investigated the rotational effect of buoyant force around the body’s transverse axis, termed buoyant torque, during a 200m front crawl maximal swim. Eleven male swimmers of national or international level participated. One stroke cycle (SC) for each 50m was recorded with two above and four below water cameras. The following variables were analysed: swimming velocity; absolute and normalised buoyant force; minimum, average and maximum buoyant torque; SC and arm recovery times. The average value of buoyant torque was higher in the first 50m (14.2 ± 4.5Nm) than in the following 150m (9.3 ± 4.1Nm~10.9 ± 4.5Nm) and was directed to raise the legs and lower the head throughout the race. The change in its magnitude seemed to be linked to the shorter time spent proportionally in arm recovery (first 50m: 27.6% of SC time; next 150m: 23.3–24.4% of SC time). Most swimmers had periods of the SC where buoyant torque was directed to sink the legs, which accounted to 10% of SC time in the first 50m and about twice this duration in the next 150m. These periods were observed exclusively at some instances when the recovering arm had entered the water while the opposite arm was still underwater.     

关于Riesz代数中的极大不相交系和表示(英)

设E是具有弱单位元素e的ArchimedeanRiesz代数,｛ei∶∈I｝是一个极大不相交系,其中每一个ei都是投影元素．由ei生成的主带记为B（ei）．此文的主要结果是：若存在一个完全正则Hausdorff空间X使得E是Riesz代数同构于C（X）,则对每一个i∈I皆存在一个完全正则Hausdorff空间Xi使得B（ei）是Riesz代数同构于C（Xi）．在一个附加条件下其逆成立．     

青年男子举重运动员肘关节屈伸肌群等速肌力特征

通过分析青年男子举重运动员肘关节屈伸肌群的力量参数,探讨肘关节屈伸肌群在举重专项训练中的作用,为预防肘关节损伤及科学训练提供理论依据。采用Cybex—Norm型等速测力与康复系统,在预定角速度90°／s．180°／s和300°／s下对上海举重队9名青年男子举重运动员肘关节进行等速向心屈伸肌力测试。结果发现举重运动员肘关节屈伸肌群相对峰力矩、相对总劝和相对平均功率随着运动速度的增大而减小,屈伸肌群峰力矩比值接近1．0。表明举重项目中肘关节屈伸肌群主要功能是维持运动中关节的稳定性,而两侧肘关节同名肌群肌力素质的不均衡性可能是阻碍专项能力韦黾高的重要因素和诱发运动性伤病的潜在因素。     

我国青少年网球运动员盂肱关节旋转等速肌力研究

应用Cybex-6000等速仪器分别对136名青少年网球运动员盂肱关节内、外旋转肌力进行等速向心肌力测试与评价,分析网球运动员优势臂盂肱关节等速向心肌力特征,比较双侧盂肱关节等速向心肌力差异,探索双侧盂肱关节外旋肌力/内旋肌力比值特征,从而完善网球运动员肩部运动生物力学及有关参数,以期能为探讨网球运动员肩关节损伤的生物力学因素、机制,进而为预防网球运动员肩关节损伤以及指导网球运动员肩关节伤后进行科学的康复训练提供理论依据.     

一种二用户协作HARQ通信方案

针对协作通信(cooperative communication)的重传问题,提出了在2个用户和基站之间的通信过程中,用户之间如何协作进行混合ARQ(hybrid ARQ)的方案. 通过分时发送机制,每个用户都保存对方上一次发送的数据,在收到基站的ACK/NACK后,根据基站的指示,从存储的上一次发送数据包中,寻找需要重传的数据包,并插入自己需要传送的新数据包,在下一个发送时隙中进行传输. 通过协作通信系统所实现的空间分集增益,提高了HARQ的性能. 比较2个用户分别独立与基站通信和相互协作与基站通信的HARQ方案,并通过理论分析和仿真,比较不同信噪比(SNR)下的吞吐量(throughput)和误包率(PER)以及平均时延,证实了本系统在可提高系统传输时延的前提下,具有更高的吞吐量和更低的PER.     

可换矩阵空间的最大维数

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