数字化电源功率因数校正器的设计

本文以单相功率因数校正器（PFC）为对象讨论了如何设计数字电源,重要的是讨论了单相PFC的小信号模型,在这个基础上阐明了电源双环控制的组成,详细讨论了设计控制器的方法,完善了从小信号建模等理论直到完成整个数字化电源控制的过程,并对具体的工程技术问题给出了具体的分析手段和可操作的解决方法。     

“李森科”事件再思考

随着前苏联国内部分档案材料的解密和最新研究,＂李森科＂事件的来龙去脉变得越来越清晰。从表面上看,整个事件的发生是由于国家权力的滥用所致,实质上这一事件的产生除了由于李森科本人趁机利用当时的国内政治形势和意识形态状况达到个人目的外,科学家自身立场的摇摆不定和前苏联国内科技管理的纷乱,是李森科事件发生和兴起的根本原因。     

Temporal specificity of training: intra-day effects on biochemical responses and Olympic-Weightlifting performances

The aim of this study was to investigate the performance of an Olympic-Weightlifting session training at three times of the day on the performance related to biochemical responses. Nine weightlifters (21 ± 0.5 years) performed, in randomised order, on three Olympic-Weightlifting training (snatch, clean and jerk) sessions (08:00 a.m., 02:00 p. m., 06:00 p. m.). Blood samples were collected: before, 3 min and 48 h after each training session. Haematological parameters and markers of muscle injury were assessed. Resting oral temperature and rating of perceived exertion (RPE) were also assessed during each session. ANOVA showed that the performance was better (P < 0.001) at 02:00 p. m. with a less RPE (P < 0.01) compared to the morning and the evening sessions while there was higher (P < 0.05) oral temperature at 06:00 p. m. versus 08:00 a.m. and 02:00 p. m. Muscle damage changed immediately (without significant effect after 48 h) after the training sessions with lower values ??in the evening compared to the morning. In conclusion, the afternoon training is more effective than morning or evening sessions for weightlifters. Therefore, coaches and weightlifters should be advised to schedule their training session in the afternoon hour.     

Lifesource XL-18 pedometer for measuring steps under controlled and free-living conditions

The primary aim was to examine the criterion and construct validity and test–retest reliability of the Lifesource XL-18 pedometer (A&D Medical, Toronto, ON, Canada) for measuring steps under controlled and free-living activities. The influence of body mass index, waist size and walking speed on the criterion validity of XL-18 was also explored. Forty adults (35–74 years) performed a 6-min walk test in the controlled condition, and the criterion validity of XL-18 was assessed by comparing it to steps counted manually. Thirty-five adults participated in the free-living condition and the construct validity of XL-18 was assessed by comparing it to Yamax SW-200 (YAMAX Health & Sports, Inc., San Antonio, TX, USA). During the controlled condition, XL-18 did not significantly differ from criterion (P > 0.05) and no systematic error was found using Bland–Altman analysis. The accuracy of XL-18 decreased with slower walking speed (P = 0.001). During the free-living condition, Bland–Altman analysis revealed that XL-18 overestimated daily steps by 327 ± 118 than Yamax (P = 0.004). However, the absolute percent error (APE) (6.5 ± 0.58%) was still within an acceptable range. XL-18 did not differ statistically between pant pockets. XL-18 is suitable for measuring steps in controlled and free-living conditions. However, caution may be required when interpreting the steps recorded under slower speeds and free-living conditions.     

公司重整管理人的法律地位与权责研究——从公司控制权的角度展开

公司重整时期对公司事务的控制权从董事会向重整管理人转移,明确重整管理人的法律地位和权责对正确适用相关法律规则具有积极意义。由于重整制度价值目标的多元性,管理人不是对债权人会议负责的机构,也不是债权人的利益代表,而应当是一个中立的机构。在债务人自行管理和管理人管理的不同情形下,重整管理人具有不同的角色和职权,但总体上管理人都应承担起信息披露义务、中立义务、忠实义务和勤勉义务,对违反义务者可参照董事责任进行追究。     

深圳市城市道路汽车行驶工况调查分析

通过对深圳城市道路交通流量以及道路状况的调查分析,对道路状况进行了分类,采用GPS定位技术,实时记录了深圳市实际道路状况下汽车行驶的运行状况．通过对从GPS监测平台获取的大量速度数据的归纳分析,合成了深圳市道路的综合行驶工况,并与标准测试工况、主要城市工况进行了对比分析,指出了深圳城市道路汽车运行的特点．     

FTU技术在公路建设供电电网中的应用分析

在对公路建设用电供电电网负荷变化情况调查的基础上,基于柔性输电理论,分析在供电电网中适时采用FTU技术,提高供电质量和供电可靠性的必要性及可行性,提出解决公路建设用电的具体实施方案,为公路建设供电改造提出决策依据.     

数字化实验系统在实验教学中的应用

实现实验教学的信息化对培养学生的实践动手能力、激发学生的学习兴趣、提高综合素质和培养创新思维起着重要作用。数字仿真实验系统和数字化真实实验系统作为实验教学信息化建设的重要内容,应优势互补,共同在实验教学中发挥作用。     

Effect of gear ratio on peak power and time to peak power in BMX cyclists

The aim of this study was to ascertain if gear ratio selection would have an effect on peak power and time to peak power production in elite Bicycle Motocross (BMX) cyclists. Eight male elite BMX riders volunteered for the study. Each rider performed three, 10-s maximal sprints on an Olympic standard indoor BMX track. The riders’ bicycles were fitted with a portable SRM power meter. Each rider performed the three sprints using gear ratios of 41/16, 43/16 and 45/16 tooth. The results from the 41/16 and 45/16 gear ratios were compared to the current standard 43/16 gear ratio. Statistically, significant differences were found between the gear ratios for peak power (F(2,14)?=?6.448; p?=?.010) and peak torque (F(2,14)?=?4.777; p?=?.026), but no significant difference was found for time to peak power (F(2,14)?=?0.200; p?=?.821). When comparing gear ratios, the results showed a 45/16 gear ratio elicited the highest peak power,1658?±?221?W, compared to 1436?±?129?W and 1380?±?56?W, for the 43/16 and 41/16 ratios, respectively. The time to peak power showed a 41/16 tooth gear ratio attained peak power in ?0.01?s and a 45/16 in 0.22?s compared to the 43/16. The findings of this study suggest that gear ratio choice has a significant effect on peak power production, though time to peak power output is not significantly affected. Therefore, selecting a higher gear ratio results in riders attaining higher power outputs without reducing their start time.     

Assessment of leg muscles mechanical capacities: Which jump,loading, and variable type provide the most reliable outcomes?

This study aimed to explore the strength of the force–velocity (F–V) relationship of lower limb muscles and the reliability of its parameters (maximum force [F₀], slope [a], maximum velocity [V₀], and maximum power [P₀]). Twenty-three men were tested in two different jump types (squat and countermovement jump: SJ and CMJ), performed under two different loading conditions (free weight and Smith machine: Free and Smith) with 0, 17, 30, 45, 60, and 75?kg loads. The maximum and averaged values of F and V were obtained for the F–V relationship modelling. All F–V relationships were strong and linear independently whether observed from the averaged across the participants (r?≥?0.98) or individual data (r?=?0.94–0.98), while their parameters were generally highly reliable (F₀ [CV: 4.85%, ICC: 0.87], V₀ [CV: 6.10%, ICC: 0.82], a [CV: 10.5%, ICC: 0.81], and P₀ [CV: 3.5%, ICC: 0.93]). Both the strength of the F–V relationships and the reliability of their parameters were significantly higher for (1) the CMJ over the SJ, (2) the Free over the Smith loading type, and (3) the maximum over the averaged F and V variables. In conclusion, although the F–V relationships obtained from all the jumps tested were linear and generally highly reliable, the less appropriate choice for testing the F–V relationship could be through the averaged F and V data obtained from the SJ performed either in a Free weight or in a Smith machine. Insubstantial differences exist among the other combinations tested.