Consistency of performances in the Tkatchev release and re-grasp on high bar

The Tkatchev on the high bar is a release and re-grasp skill in which the gymnast rotates in a direction during flight opposite to that of the preceding swing. Since the release window is defined as the time during which the gymnast has appropriate linear and angular momentum to ensure the bar can be re-grasped, it was speculated that the release windows for this skill would be smaller than for dismounts that are less constrained. One senior male gymnast competing at national standard performed 60 Tkatchev trials. A four-segment planar simulation model of the gymnast and high bar was used to determine the release windows in 10 successful and 10 unsuccessful performances of the Tkatchev recorded using a Vicon motion analysis system. Model parameters were optimized to obtain a close match between simulations and recorded performances in terms of rotation angle (1°), bar displacements (0.01 m), and release velocities (1%). Each matched simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the Tkatchev successfully. The release windows for the successful trials were small compared with those of dismounts. The unsuccessful trials were associated with later release and later timing of the actions at the shoulders and hips.     

从一个佯谬对电磁场动量守恒的理论推证

从一个佯谬问题出发,利用数学计算的方法,得出了稳态电磁场动量守恒的结论.目的是加深对电磁场具有物质属性概念的理解.     

电磁场波动性和物质性的三维描述及统一

在Maxwell方程组的基础上,推证三维空间中电磁场的波动方程.给出三维空间中电磁场的能量密度、能流密度、动量密度、动量流密度、角动量和角动量流,还给出了运动带电体与电磁场组成系统的能量、动量、角动量守恒律.并通过实例计算电磁场的辐射压强.     

Improving the accuracy of heart disease diagnosis with an augmented back propagation algorithm

1. Introduction Statistics has consistently shown that heart disease is one of the leading causes of death all over the world [1]. Every year, millions of people suffer from various types of heart diseases, among which coronary heart disease, rheumatic valvular heart disease, hypertension, chronic cor pulmonale and congenital heart disease are the commonest. Significant life saving can be achieved if an accurate diagnosis decision, which is the prerequisite of a proper and timely treatment, ca…     

自旋为整数的粒子的投影算符

以自旋为任意整数的粒子的Bargmann-Wigner方程的解为基础。在运动系中直接导出自旋为任意整数的投影算符的表达式，将低自旋投影算符理论推广到了自旋为任意整数的高自旋情形，验证了Behrends和Fronsdal所构造的投影算符的正确性。     

刚体平面运动的研究

从角动量的定义出发,计论了刚体平面运动时对任一定轴的角动量,推出了刚体平面运动时对质心轴、瞬心轴的转动定理.     

对核反应阈能的讨论

在实验室坐标系下，给出吸能核反应所要求的阈能，其结果与质心系下得到的结果完全一致。     

静电场、稳恒磁场、交变电磁场的物质属性

从“场”与“实物”的区别和联系出发,给出了物质概念较为本质的定义,指出物质的最本质属性是具有能量、动量。     

再谈一维无限深势阱内粒子动量几率分布

本文通过对自由粒子系统和一线无限深势阱中粒子系统各种性质的比较,论证计算一维无限深势阱内粒子的动量分布的两种方法中,泡利方法是正确的,朗道方法是不对的。并由改进后的朗道方法求出了泡利正确的结果。     

关于绝对角动量定理

导出了质点系对动点的绝对角动量定理,并应用它简捷地求解了一些力学问题