《电机与电气控制技术》课程教学改革与实践

本文从培养满足社会需求的实用型、技能型人才出发,笔者根据自己的实践教学经验对《电机与电气控制技术》课程从教学模式、教学内容、教学方法与手段、实验教学等方面进行了教学改革。课程改革实施后,学生的综合能力及教学质量得到了明显提高。     

新型双桥路三相交流逆变器的研究

逆变器的谐波问题一直是困扰电气工程师的一大难题，也是衡量交流逆变器的一个重要指标．利用电气相角的偏差和电磁效应的叠加原理来实现控制策略，可以有效地消除或抑制谐波，使三相逆变器输出电压的质量得到提高．仿真结果表明，双桥路逆变器的电压输出波形比常规的三相逆变器的电压输出波形好．     

体操教学中运用迁移法效果的研究

体操是一项动作结构复杂多样化而非同期性的运动项目,在体操教学和训练中,运动技能的迁移现象普遍存在。通过分析体操动作技术的内在联系,掌握技能迁移的原理和规律,合理运用一系列手段来促进技能间的积极性迁移,防止或减少消极性迁移的影响,提高体操教学效果。     

基于MRAS磁链观测、转速估计的无速度传感器异步电机矢量控制系统

针对传统矢量控制系统磁链观测不准,且需要速度传感器的问题,提出了一种基于MRAS磁链观测、转速估计的无速度传感器异步电机矢量控制系统。介绍了磁链观测、转速估计的MRAS结构,并运用Popov超稳定理论推导出了其对应自适应律,建立了实验系统。实验结果表明,该矢量控制系统在启动、调速、稳态运行时具有良好的静、动态性能,是一种高性能的交流调速系统。     

迷宫电脑鼠电机控制系统设计

本文介绍以IEEE标准电脑鼠走迷宫竞赛为背景,以专用控制芯片MC33035、MC33039为核心构成的永磁无刷直流电机控制器,主要涉及核心控制电路的构成、功率开关元件的驱动、转速显示电路的实现、保证系统运行可靠性的抗干扰及EMC防治措施。     

Fundamental motor skills,nutritional status,perceived competence,and school performance of Brazilian children in social vulnerability: Gender comparison

Being at risk or in social vulnerability situations can affect important aspects of child development. The aim of this study was to investigate fundamental motor skills (locomotor and object control) and school (writing, arithmetic, reading) performances, the perceived competence and the nutritional status of girls and boys living in social vulnerability in the poorest regions of Brazil. Two hundred eleven (211) children (87 girls, 41%), 7–10-year-old (M = 8.3, SD = 0.9), from public schools in Ceará (Brazil), living in social vulnerability, participated in the study. Children were assessed using the Test of Gross Motor Development – 2, the Body Mass Index (BMI), the Self-Perception Profile for Children, and the School Performance Test. Multivariate analysis of covariance (MANCOVA), adjusted for age, did not show any significant effect for locomotion. There was an effect of gender on the object control. Boys showed higher scores in striking, kicking, throwing, and rolling a ball. Quade's nonparametric analysis showed no difference in BMI between the genders. Most children presented healthy weight. The MANCOVA showed no effect of gender on children’s scores on perceived competence on the subscales; moderate scores were found for most children. There were no gender effects on school performance; both boys and girls demonstrated inferior performance. Boys and girls in social vulnerability showed inferior performance in most motor skills, moderate perceived competence and inferior school performance. These results reveal that the appropriate development of these children is at risk and that intervention strategies should be implemented to compensate the difficulties presented.     

The association between fundamental athletic movements and physical fitness in elite junior Australian footballers

This study investigated the associations between fundamental athletic movement and physical fitness in junior Australian football (AF). Forty-four under 18 players performed a fundamental athletic movement assessment consisting of an overhead squat, double lunge, single leg Romanian deadlift and a push up. Movements were scored on three assessment criterions using a three-point scale. Additionally, participants performed five physical fitness tests commonly used for talent identification in AF. A Spearman’s nonparametric correlation matrix was built, with correlation coefficients being visualised using a circularly rendered correlogram. Score on the overhead squat was moderately positively associated with dynamic vertical jump height on left (r_s = 0.40; P ≤ 0.05) and right (r_s = 0.30; P ≤ 0.05) leg take-off, stationary vertical jump (r_s = 0.32; P ≤ 0.05) and negatively associated with 20-m sprint time (r_s = ?0.35; P ≤ 0.05). Score on the double lunge (left/right side) was moderately positively associated with the same physical fitness tests as well as score on the multistage fitness test. Results suggest that improvements in physical fitness qualities may occur through concurrent increases in fundamental athletic movement skill, namely the overhead squat and double lunge movements. These findings may assist with the identification and development of talent.     

Choose your primary outcome variables with care

The changes in postural tremor of the hand and the subsequent effect on shooting performance produced by moderate cooling and heating of the forearm were studied in six subjects. Cooling produced a large decrease in tremor size of the ipsilateral hand, whereas warming the limb produced an increase in tremor size. Cooling or warming the forearm did not change the peak frequency of tremor significantly, which was quite stable for each subject. The improvement in shooting performance after cooling the forearm, as measured by grouping pattern of the shots, reached statistical significance and warming caused a significant worsening. This measure of performance was shown to correlate (r = 0.776) inversely with tremor size. The causes and implications of these changes are discussed. It is suggested that local cooling may be useful for people who wish temporarily to reduce tremor in order to improve dexterity for shooting and for other purposes.     

Identifying and developing rugby talent among 10-year-old boys: A practical model

The re-entry of South Africa into the international sporting arena and the resultant need for the identification and development of talent, especially among formerly deprived groups of people, provided the incentive for this study. Its aim was to identify the physical, motor and anthropometric variables that will enable coaches to identify 10-year-old boys, based on their abilities, who could become successful rugby players. Altogether, 173 ten-year-old boys with no rugby experience from a cross-section of the population were selected at random and subjected to 14 physical and motor tests and 14 anthropometric measurements. From 22 schools which participated in the Western Transvaal primary schools under-11 rugby league, the three top teams (n = 45 individuals) were selected and also tested. The results from these three teams were used as the criteria for rugby talent among 10-year-old boys. To establish the best predictors of talent, a stepwise discriminant analysis was conducted: this indicated eight variables (four motor and four anthropometric) that discriminated maximally between the talented and the rest of the players of this age. With classification functions based on these eight variables, 93.8% of all the subjects were classified correctly, indicating good validity. A canonical analysis, based on the selected variables, was then conducted on all the under-11 teams that played in the league in the region (n = 330), and they were ranked according to the scores of the first canonical variable from the most to the least talented. By comparing these results with the players who were chosen for the region's primary schools team, a success rate of 88% in prediction of talent was established. We conclude that this is a successful and practical method to aid the teacher and the coach in selecting and developing talent among 10-year-old rugby players in South Africa.