套管和油管螺纹密封性在油田使用中的重要性

套管、油管在使用时,通常对其强度的承载能力考虑较多,而对它的密封性考虑较少,如何解决这一难题,是今后研究的新课题。     

Biomechanics of increased spin velocity of flying discs during forehand throws by skilled and unskilled throwers

We aimed to assess the relationship between throwing distance and kinematic release parameters of the flying disc in unskilled throwers, and to assess the relationship between kinetic variables acting on flying discs and the change in spin velocity during long forehand throws by skilled and unskilled throwers. Ten skilled and eleven unskilled throwers performed throws at maximum effort. Reflective marker positions on the disc and body were recorded with a 3D motion capture system during the throws to derive kinematic variables of a disc and kinetic variables acting on the disc. The analysis interval was from maximum external shoulder rotation to disc release. Significant correlations were observed between the throwing distance and spin velocity in skilled (r = 0.722, P < 0.05) and unskilled throwers (r = 0.794, P < 0.01), between the change in spin velocity and the angular impulse of moments of force, in unskilled throwers (r = 0.703, P < 0.05), and between the change in spin velocity and the angular impulse of torque among skilled throwers (r = 0.680, P < 0.01). Therefore, a strategy for increasing spin velocity in unskilled throwers could be used to generate a larger torque, similar to that observed in skilled throwers.     

Neural mechanisms of strength increase after one-week motor imagery training

The neural mechanisms explaining strength increase following mental training by motor imagery (MI) are not clearly understood. While gains are mostly attributed to cortical reorganization, the sub-cortical adaptations have never been investigated. The present study investigated the effects of MI training on muscle force capacity and the related spinal and supraspinal mechanisms. Eighteen young healthy participants (mean age: 22.5?±?2.6) took part in the experiment. They were distributed into two groups: a control group (n?=?9) and an MI training group (n?=?9). The MI group performed seven consecutive sessions (one per day) of imagined maximal isometric plantar flexion (4 blocks of 25 trials per session). The control group did not engage in any physical or mental training. Both groups were tested for the isometric maximal plantar flexion torque (MVC) and the rate of torque development (RTD) before and after the training session. In addition, soleus and medial gastrocnemius spinal and supraspinal adaptations were assessed through the recording of H-reflexes and V-waves, with electrical stimulations of the posterior tibial nerve evoked at rest and during MVC, respectively. After one week, only the MI training group increased both plantar flexion MVC and RTD. The enhancement of muscle torque capacity was accompanied by significant increase of electromyographic activity and V-wave during MVC and of H-reflex at rest. The increased cortical descending neural drive and the excitability of spinal networks at rest could explain the greater RTD and MVC after one week of MI training.     

永磁无刷直流电机换相转矩分析

介绍了人工心脏轴流式血泵永磁无刷直流电机换相转矩脉动变化过程．根据影响电机换相转矩脉动的因素,给出了减小电机转矩脉动的解决方案,以使电机运行更加平稳．通过实验波形证实本结论分析正确,可以为电机减小转矩脉动作为参考．     

女子举重运动员抓挺举发力阶段等动肌力的特征

采用高速摄影与等动测试相结合的研究方法,对女子举重运动员抓挺举时的等动肌力特征进行探讨。结果显示,抓举发力阶段,提肘动作发生在伸髋结束时,不同关节等动肌力的比值反映了举重发力动作的先后顺序;抓举与挺举上挺发力阶段的最大相关速度与上肢等动测试的峰力矩,平均功率相关指标有显著性相关,而最大速度与等动测试的峰力矩、平均功率指标无相关性。     

CybexⅡ~+测试中膝关节腘绳肌与股四头肌力矩峰值比率问题初探

对不同运动项目的男女青少年运动员84人进行CybexⅡ~+等速膝关节屈伸测试,发现随着测试速度的提高,腘绳肌与股四头肌力矩峰值比率也相应上升。各项目上升幅度有所不同:以膝关节伸屈动作为主、腿部动作负荷愈大、动作速度愈快的项目,该比率上升幅度愈大。     

由电流型逆变器供电的感应电动机的稳态和稳定性分析

用等效的两相对称电机的方法建立由电流型逆变器供电的感应电动机的数学模型，并进行稳态特性和稳定性分析，从而为实际设计提供了理论依据。     

液力变矩器液黏零速加载试验系统的研制

介绍一种可以实现液力变矩器零速加载的试验系统。为完成液力变矩器的性能试验,特别是液力变矩器零速工况试验,应用液体黏性传动技术设计了液黏零速加载试验系统。试验系统由动力及其控制系统、液黏测功加载及其辅助系统和测控系统组成。试验系统利用电液比例控制技术实现液黏测功机加载转矩控制,应用虚拟仪器思想实现试验数据采集与处理。液黏零速加载试验系统具有广阔的应用前景。     

功能性力量训练对男子自由式摔跤运动员膝关节等速肌力影响的研究

目的:分析功能性力量训练对男子自由式摔跤运动员膝关节等速肌力的影响。对象与方法:运用实验法,以16名广东省男子自由式摔跤队运动员为研究对象,随机分为对照组和实验组并将其分别进行为期8周的训练干预,其中对照组进行常规力量训练,实验组进行功能性力量训练,实验前后分别测试所有运动员的膝关节等速肌力,选取峰值力矩(PT)、异侧同名肌比值(PTR)和同侧屈伸肌比值(H/Q)指标比较分析功能性训练在提高男子自由式摔跤运动员下肢力量素质的影响。结果:实验组运动员经过功能性力量训练,等速肌力测试在角速度60°/s和240°/s状态下,下肢双侧屈肌PT和伸肌PT较实验前均有非常显著性提高(P<0.01),屈伸肌PTR及左右侧H/Q也均有非常显著性提高(P<0.01)。对照组运动员经过传统力量训练,等速肌力测试在角速度60°/s和240°/s状态下,下肢双侧屈肌和伸肌PT值较实验前均有显著性提高(P<0.01),但是左右侧H/Q及屈伸肌PTR均无显著性变化(P>0.05)。实验后在角速度60°/s状态下,实验组运动员膝关节两侧伸肌PT与对照组相比均无显著性差异(P>0.05),但是两侧屈肌PT值均显著高于对照组(P<0.05);在角速度240°/s状态下实验组左侧伸肌PT值显著高于对照组(P<0.05),右侧伸肌PT值虽高于对照组,但是差异不显著(P>0.05),左右侧的屈肌PT值均非常显著高于对照组(P<0.01);实验组运动员的屈伸肌PTR及左右侧的H/Q均非常显著高于对照组(P<0.01)。结论:功能性训练可以显著提高男子自由式摔跤运动员的下肢肌肉最大力量和快速力量素质,在最大力量训练效果方面与传统力量训练相比差异不大,但是在快速力量方面提高效果要更好;功能性力量训练能够有效提高自由式摔跤运动员的异侧同名肌比值和屈伸肌比值,对改善运动员两侧肌肉力量不对称和同侧屈伸肌力量不对称方面效果也比传统力量训练效果更好,对运动员膝关节肌群肌力的平衡有着重要作用。     

万有引力常数G值的确定

自从牛顿提出万有引力理论以后,科学家们就开始了用实验的方法测定万有引力常数G值的努力.介绍了几个著名的G值测定实验,其中英国物理学家和化学家亨利·卡文迪许的实验具有开创性的重要意义.该项实验设计精巧,具有相当高的精确度,在历史上影响很深,至今对学习者仍有较强的指导作用.