混凝土梁抗扭性能分析及承载力修正公式

采用ABAQUS有限元软件对各种强度等级下各龄期钢筋混凝土梁的受扭性能进行分析。各龄期混凝土的本构关系采用塑性损伤模型,受拉指标采用断裂能。有限元分析结果表明:各龄期混凝土的抗扭承载力随龄期的增长而增长,开裂前早龄期混凝土梁的抗扭承载力主要由混凝土承担,钢筋的贡献很小;前3d是混凝土扭矩增长最快的主要时间段,开裂扭矩和极限扭矩达到28 d的60%左右。最后,根据有限元参数分析结果,在现行规范的基础上提出了早龄期混凝土梁开裂扭矩和极限扭矩的修正公式。     

异步电动机的交流传动试验平台

为满足港航交流传动与变频电源的试验研究需要,设计异步电动机模拟负载能量回馈方式的交流传动试验平台.该试验平台由电源子系统、传动子系统和测试子系统等3部分组成,结合高精度转矩传感器和转矩控制策略,可为被试系统提供6种电压等级,能进行船舶与港口电气传动控制系统试验、交流传动系统电能质量试验、中小船舶电力推进系统陆上联调、变频电源综合试验等研究.结果表明,该试验平台电能消耗少;功能、性能方面能满足港航传动系统的需求;可为港航领域大功率交流传动系统的研制开发提供试验环境和技术支撑.     

每个非空正则简单图都包含两个不相交的极大独立集

以极大独立集定义为基础,从连通简单图的邻接矩阵入手,寻求邻接矩阵的极高阶零子方阵,以极高阶零子方阵确定极大独立集,从而证明本定理     

基于动态专利有向网络的核心技术集群演化分析

[目的/意义]技术集群因对属性相同的技术集聚进行研究,能够识别新技术,发现技术发展规律,提前感知市场技术变化,引起学者和企业管理者越来越高的关注。[方法/过程]以文本挖掘和复杂网络技术方法对专利文本数据进行分析,进而构建动态专利有向网络,并从网络中基于Python程序提取巨片,通过巨片拓扑性质分析核心技术集群的演化历程。[结果/结论]以美国电商数据处理技术为例的实证研究表明:通过构建动态有向网络,并从网络中提取巨片分析技术演化,能够有效的识别出美国电商数据处理技术中"数据设备技术、数据信息技术、数据系统技术、数据应用技术和数据融合技术"5个核心技术集群,并进一步发现核心技术集群之间很好的更新替换机制。实证研究证明了基于动态专利有向网络的核心技术集群演化分析方法的有效性。     

Comparison of lower limb kinetics during vertical jumps in turnout and neutral foot positions by classical ballet dancers

The purpose of this study was to investigate the effect of hip external rotation (turnout) on lower limb kinetics during vertical jumps by classical ballet dancers. Vertical jumps in a turnout (TJ) and a neutral hip position (NJ) performed by 12 classical female ballet dancers were analysed through motion capture, recording of the ground reaction forces, and inverse dynamics analysis. At push-off, the lower trunk leaned forward 18.2° and 20.1° in the TJ and NJ, respectively. The dancers jumped lower in the TJ than in the NJ. The knee extensor and hip abductor torques were smaller, whereas the hip external rotator torque was larger in the TJ than in the NJ. The work done by the hip joint moments in the sagittal plane was 0.28 J/(Body mass*Height) and 0.33 J/(Body mass*Height) in the TJ and NJ, respectively. The joint work done by the lower limbs were not different between the two jumps. These differences resulted from different planes in which the lower limb flexion–extension occurred, i.e. in the sagittal or frontal plane. This would prevent the forward lean of the trunk by decreasing the hip joint work in the sagittal plane and reduce the knee extensor torque in the jump.     

Differences in take-off leg kinetics between horizontal and vertical single-leg rebound jumps

This study aimed to clarify the differences between the horizontal single-leg rebound jump (HJ) and vertical single-leg rebound jump (VJ) in terms of three-dimensional joint kinetics for the take-off leg, while focusing on frontal and transverse plane movements. Eleven male track and field athletes performed HJ and VJ. Kinematic and kinetic data were calculated using data recorded with a motion capture system and force platforms. The hip abduction torque, trunk lateral flexion torque (flexion for the swing-leg side), hip external and internal torque, trunk rotational torque, and the powers associated with these torques were larger when performing HJ because of resistance to the impact ground reaction force and because of pelvic and posture control. Pelvic rotation was noted in HJ, and this was controlled not only by the hip and trunk joint torque from the transverse plane but also by the hip abduction torque. Therefore, hip and trunk joint kinetics in the frontal and transverse plane play an important role in a single-leg jump, regardless of the jumping direction, and may also play a more important role in HJ than in VJ.     

优秀男子举重运动员专项成绩与下肢等速肌力相关回归分析

采用德国IsoMed 2000等速肌力测试仪,对17名健将（健将组）和18名一级（一级组）男子举重运动员进行双侧髋、膝和踝关节60°/s、120°/s、180°/s和240°/s向心、离心（每种角速度5次）测试。探讨优秀男子举重运动员下肢关节不同角速度等速肌力的特征,比较健将与一级组间差异,对健将组下肢关节相对峰力矩与相对专项成绩进行Pearson相关分析,并建立抓、挺举与峰力矩多元线性回归方程。结果显示,优秀男子举重运动员的髋关节相对伸爆发力与相对抓举呈高度显著正相关,髋关节中速（120°/s）、膝踝关节相对伸爆发力与相对抓举呈中度显著正相关,而踝关节相对屈绝对力呈中度显著负相关;髋关节相对伸爆发力与相对挺举呈高度显著正相关,左膝（挺举弓步腿）相对中速（120°/s）、爆发力和踝关节相对爆发力与相对挺举呈中度显著正相关。     

不同起始力矩设计重力式力量训练器械性能比较

采用实验法和图解法对不同设计的重力式力量训练器械的阻力矩和肌力矩进行比较,结果显示,小起始力矩设计的器械其阻力矩更适应人体肌力矩,其性能优于大起始力矩设计的器械.     

力量训练提升马拉松跑者耐力运动表现的研究进展及训练策略

有氧能力的高低是马拉松跑者能否取得优异成绩的关键。最大摄氧量、乳酸阈和跑步经济性是衡量运动员有氧能力和耐力运动表现的关键指标,也是长跑训练效果的核心考量。由于力量和耐力训练对机体产生不同的训练刺激,教练员和运动员很少将力量训练作为提升耐力运动表现的手段,以防止有氧能力受到负面影响。通过对大量文献梳理发现,力量训练可以在不影响机体最大摄氧量和乳酸阈值的前提下,通过改善神经肌肉功能、转换肌纤维类型以及增强肌肉肌腱刚度和利用弹性势能的能力,提高跑步经济性和无氧能力,改善运动员耐力运动表现。本文基于对力量、耐力训练的生理学适应的探讨,总结不同形式力量训练对耐力运动表现的影响与作用机制,并为马拉松选手科学安排力量训练提出建议,从而优化其耐力运动表现。