关于他励直流电动机弱磁调速问题中的疑难分析     

马俊朋  周颍杰 《许昌学院学报》2000,(2)

:根据多年教学实践 ,对直流电动机弱磁调速问题中的疑难问题进行较详细的讨论 .也可算作是对教材的一点补  相似文献   

The effect of mountain bike wheel size on cross-country performance     

Howard Thomas Hurst  Jonathan Sinclair  Stephen Atkins  Lee Rylands  John Metcalfe 《Journal of sports sciences》2017,35(14):1349-1354

ABSTRACT

The purpose of this study was to determine the influence of different wheel size diameters on indicators of cross-country mountain bike time trial performance. Nine competitive male mountain bikers (age 34.7 ± 10.7 years; stature 177.7 ± 5.6 cm; body mass 73.2 ± 8.6 kg) performed 1 lap of a 3.48 km mountain bike (MTB) course as fast as possible on 26″, 27.5″ and 29″ wheeled MTB. Time (s), mean power (W), cadence (revs · min^?1) and velocity (km · h^?1) were recorded for the whole lap and during ascent and descent sections. One-way repeated measure ANOVA was used to determine significant differences. Results revealed no significant main effects for any variables by wheel size during all trials, with the exception of cadence during the descent (F_{(2, 16)} = 8.96; P = .002; P² = .53). Post hoc comparisons revealed differences lay between the 26″ and 29″ wheels (P = .02). The findings indicate that wheel size does not significantly influence performance during cross-country when ridden by trained mountain bikers, and that wheel choice is likely due to personal choice or sponsorship commitments.  相似文献   

表象训练对脑血流速度的影响     

姚宝元  王瑞元 《北京体育大学学报》2007,30(11):1512-1514

目的:探讨表象训练对脑血流速度(cerebral blood flow velocity, CBFV)的影响及性别对CBFV变化的影响.方法:在表象训练时及其先前的休息期,对20名正常大学生用经颅多普勒(TCD)监测其双侧大脑中动脉CBFV的变化.结果:与休息时相比,表象训练的相对变化值左侧为9.40±3.16,右侧为15.86±5.82,表象训练诱导出双侧大脑中动脉CBFV的非常显著增加(P＜0.01).表象训练的偏侧指数(LI)为24.73±14.48(P＜0.01),呈现出显著的右侧半球偏侧化,性别对CBFV偏侧化不产生显著影响,但表象训练诱导的CBFV的增加在两性间有显著的差异(P＜0.05).结论:表象训练能引起双侧大脑中动脉CBFV的非常显著性增加,且可诱导CBFV的右侧偏侧化.  相似文献   

The performance of the ice hockey slap and wrist shots: the effects of stick construction and player skill   总被引：1，自引：0，他引：1  

T.?-C.?Wu  D.?PearsallEmail author  A.?Hodges  R.?Turcotte  R.?Lefebvre  D.?Montgomery  H.?Bateni 《Sports Engineering》2003,6(1):31-39

The purpose of this study was to examine the interaction of players’ skill level, body strength, and sticks of various construction and stiffness on the performance of the slap and wrist shots in ice hockey. Twenty male and twenty female subjects were tested. Ten of each gender group were considered skilled and ten unskilled. In addition to general strength tests, each subject performed the slap and wrist shots with three stick shafts of different construction and stiffness. Shot mechanics were evaluated by simultaneously recording ground reaction forces from a force plate, stick movement and bending from high speed filming and peak puck velocity from a radar gun. Data were analysed with a 4-way repeated measures ANOVA for several dependent variables including peak puck velocity, peak Z (vertical) force, peak bending and stick to ground angles, peak angular deflection of the shaft, and hand placement on the stick. The results indicated that: 1) the slap shot was much faster than the wrist shot corresponding to greater vertical loading force, stick bending, and greater width of the hand placement; 2) the puck velocity was influenced by skill level and body strength but not stick type; and, 3) that skilled players were able to generate more vertical force and bend of the stick, in part, by adjusting their hand positions on the stick. Further studies are needed to address the specific influence of body strength and skill on the techniques of these shots and in relation to stick material and construction properties.  相似文献   

激光淬火硬化层的硬度分布与冷却速度     

戴忠森  吴钢  石娟 《上海海事大学学报》1998,(3)

激光淬火硬化层的硬度分布,无明显的硬度梯度,这与常规淬火方法的结果不太一样。本文对激光淬火相变硬化层硬度分布状态的形成机理进行了研究,分析了无明显硬度下降梯度的硬化层对提高零件耐磨性的重要意义。  相似文献   

对我国优秀女子铅球运动员推铅球技术速度节奏的研究   总被引：5，自引：0，他引：5  

任文君  张斌  张斌南 《体育与科学》1998,(2)

本研究运用高速摄影和影片解析法对我国优秀女子铅球运动员背向滑步推铅球技术进行分析,获得大量有价值的图表和速度曲线。经研究发现：滑步阶段左腿的有效摆动能加大右腿蹬伸力量,提高蹬伸速度,提高滑步速度,加快境速有利于身体重心速度的加快;在过渡阶段,加快右髋的快速前移,不仅有利于保持身体重心速度,同时有利于最后用力姿势的形成;摆动腿快速落地缩短单支撑时间,是尽快形成最后用力姿势的关键。  相似文献   

跳远起跳垂直速度生成机制的运动学和动力学分析     

彭金洲  孙思哲 《湖北体育科技》2007,26(1):60-62

利用世界优秀运动员的跳远技术参数和跳远踏跳阶段踏跳力--时间曲线,剖析助跑速度损失量、起跳快速支撑和蹬伸在跳远起跳垂直速度的生成机制中的运动学和动力学原因,对跳远垂直速度生成提出了新的见解,并为创新跳远训练提供了一条新的思路.  相似文献   

中学生足球训练方式与方法的探讨     

顾民杰 《山东体育科技》2007,29(3):91-92

怎样才能利用有限的训练时间，最大限度地提高训练水平，取得良好的运动成绩。通过对山东师大附中足球队训练方式与方法的实践研究表明；中学生足球训练应重点抓住战术意识的培养、扩展运动协调能力、发展基本力量与反应速度、改善时空感觉和控制平衡能力。  相似文献   

棒球挥击速度的研究   总被引：1，自引：0，他引：1  

孙柏庆  周家颖  王慧  姚康乐  陈学方  曹岳钟 《西安体育学院学报》1995,(1)

应用高速动态分析仪对部分运动员挥击速度现状的解析参数进行了研究．得出从启动──中球的挥击时间：斜碰撞时是在棒速下降时进行的．现要求棒的挥击时间在１００ｍｓ以内，投手球飞行至本垒前３．４ｍ左右时棒开始启挥．  相似文献   

基本体操训练对幼儿某些心理特征的影响   总被引：1，自引：0，他引：1  

褚跃德  韩旭  张冰 《北京体育大学学报》1995,(4)

对“1993年走向2000年全国幼儿基本体操表演大会”的各省市幼儿基本体操运动员的随机抽样测试，发现基本体操训练对幼儿的动作反应速度，平衡能力以及知觉、思维、注意等多项心理品质的发展有促进作用，同时也证实了某些人对幼儿从事基本体操训练可能会破坏幼儿的正常发育，损害儿童的身心健康的疑虑是不必要的。  相似文献