质点组内力的功改变质心动能的条件

讨论了质点组内力的功是可以改变质心动能的，以及所满足的条件．     

Hip and upper extremity kinematics in youth baseball pitchers

The purpose of this study was to examine the relationship between dynamic hip rotational range of motion and upper extremity kinematics during baseball pitching. Thirty-one youth baseball pitchers (10.87 ± 0.92 years; 150.03 ± 5.48 cm; 44.83 ± 8.04 kg) participated. A strong correlation was found between stance hip rotation and scapular upward rotation at maximum shoulder external rotation (r = 0.531, P = 0.002) and at ball release (r = 0.536, P = 0.002). No statistically significant correlations were found between dynamic hip rotational range of motion and passive hip range of motion. Hip range of motion deficits can constrain pelvis rotation and limit energy generation in the lower extremities. Shoulder pathomechanics can then develop as greater responsibility is placed on the shoulder to generate the energy lost from the proximal segments, increasing risk of upper extremity injury. Additionally, it appears that passive seated measurements of hip range of motion may not accurately reflect the dynamic range of motion of the hips through the progression of the pitch cycle.     

卢瑟福模型中电子运动分析

关于卢瑟福模型中电子的运动是加速还是减速,不同文献给出不同描述,甚至是截然相反的描述.本文分别从能量和力的角度定量、定性地分析了卢瑟福模型中电子的运动情况,得出了卢瑟福模型中电子绕原子核旋转、辐射能量时作加速运动的结论.     

Validation of the Microsoft Kinect® camera system for measurement of lower extremity jump landing and squatting kinematics

Cost effective, quantifiable assessment of lower extremity movement represents potential improvement over standard tools for evaluation of injury risk. Ten healthy participants completed three trials of a drop jump, overhead squat, and single leg squat task. Peak hip and knee kinematics were assessed using an 8 camera BTS Smart 7000DX motion analysis system and the Microsoft Kinect® camera system. The agreement and consistency between both uncorrected and correct Kinect kinematic variables and the BTS camera system were assessed using interclass correlations coefficients. Peak sagittal plane kinematics measured using the Microsoft Kinect® camera system explained a significant amount of variance [Range_hip = 43.5–62.8%; Range_knee = 67.5–89.6%] in peak kinematics measured using the BTS camera system. Across tasks, peak knee flexion angle and peak hip flexion were found to be consistent and in agreement when the Microsoft Kinect® camera system was directly compared to the BTS camera system but these values were improved following application of a corrective factor. The Microsoft Kinect® may not be an appropriate surrogate for traditional motion analysis technology, but it may have potential applications as a real-time feedback tool in pathological or high injury risk populations.     

可编程控制器系统设计分析

可编程序控制器(Programmable Logic Controller简称PLC),在工业生产过程自动控制领域得到广泛的应用,而可编程序控制器的实际应用,需要符号要求的系统设计。探讨系统采用PLC控制的一般本条件和系统设计的基本原则,能很好地寻求PLC最适合的控制对象。基于系统设计内容与步骤的分析,有助于结合实际问题进行PLC控制系统的设计。     

数字电视信号地面发射机整机控制器的实现

控制器是确保发射机实现不间断播出和安全运转的重要部件.本文针对发射机的整机集成,简述了数字电视信号地面发射机的基本组成,重点介绍了发射机整机控制器的原理及所实现的功能.     

轴瓦自激振动的诊断及几点消除措施

该文分析了轴瓦自激振动的原因，并提出了怎样对该故障现象进行诊断及一些消除措施。     

解析法在机构运动分析中的应用

解析法适用于精度机构的运动分析。只要将解析结果编程上机，就可完成计算机辅助分析和设计。随着计算机的日益普及，解析法日遂受到人们的重视。     

牛顿第二定律对变质量问题的应用

从经典力学范围和相对论力学两方面,分别讨论了牛顿第二定律的应用条件,并从所导出的牛顿第二定律解决变质量问题的公式,通过具体举例说明了如何应用变质量公式来解决实际问题.