曲面的主曲率中心曲面的相关性质

阐述了曲面的主曲率中心曲面及其性质,通过计算得到曲面与其主曲率中心曲面的关系.     

The effect of track geometry on 200- and 400-m sprint running performance

Abstract

This study looked at how the geometry of the running track affects performances in the 200- and 400 m sprint running events. Although an athletics track must be designed with two parallel straights and two curved bends, the lengths of the straights and bends are not fixed and may vary within an approved set of limits. The bend can be semi-circular or a double-curve consisting of arcs of two different radii. A mathematical model was used to calculate the effect of track geometry on race times for six different track designs; three with semi-circular bends (encompassing the extremes of the permitted designs), and the three permitted double-curve designs. The calculations revealed substantial differences among the track designs. The time difference (in the inside lane) between the fastest and slowest tracks is about 0.1 s in the 200-m race and 0.2 s in the 400-m race. The time differential between the outside and inside lanes for a double-curve track can be up to 0.08 s greater than for a standard track with semi-circular bends.     

复G(k,n)流形中三维SU(2)轨道的几何

利用Cartan嵌入和活动标架法研究复格拉斯曼流形G(k,n)中三维SU(2)轨道的几何.     

冷弯薄壁型钢梁的滞回性能非线性有限元分析

在确定冷弯薄壁型简支钢梁应力-应变模型的基础上,采用有限元软件ANSYS对冷弯薄壁型简支钢梁荷载-位移关系进行非线性有限元计算分析。对冷弯薄壁型简支钢梁荷载-位移关系骨架线、弯矩-曲率关系骨架线进行比较分析,主要比较了跨高比、宽厚比对其的影响。     

各种微小物体的相平衡温度

本文根据热力学基本原理,导出各种微小物体的相平衡温度(如微小晶体的熔点、微小液滴的沸点、液体沸腾时微小气泡的气液平衡温度、固体熔化时微小液滴的液固平衡温度等)与其曲率半径之间的关系.     

局部对称共形平坦黎曼流形的伪脐点子流形

本文研究局部对称共形平坦黎曼流形的具有平行非零中曲率向量的焦脐点子流形的截面曲率和数量曲率的拼挤问题。     

剪力和弯矩的计算规律

总结出梁发生平面弯曲时,用截面法计算梁中指定截面的剪力和弯矩的一些规律．     

The geometric curvature of the spine during the sirshasana,the yoga’s headstand

This study analysed the behaviour of the geometric curvature of the spine during sirshasana. The position of dorsal retroreflective markers was computed via stereophotogrammetric analysis in six males and five females (29.4 ± 8.8 years, 63.0 ± 11.4 kg, 1.66 ± 0.08 m [average ± standard deviation]). The spinal points were projected onto the sagittal and frontal planes of the trunk, a polynomial was fitted to the data and the two-dimensional geometric curvature was quantified. The inferior lumbar lordosis decreased compared to the orthostatic position and gait, which may favour the posterior protrusion of the lumbar spinal nucleus pulposus in people with posterior herniation. The lateral deviation at the middle of the thoracic spine increases during sirshasana, which may reflect increased difficulties for postural control and spinal loads. It could be useful for promoting positive spinal structural and functional chronic adaptations for healthy participants, if the yoga programme is carefully planned and the spinal alignment is carefully monitored during a headstand. However, it may aggravate some spinal diseases, especially scoliosis.     

有某种对应关系的两条曲线

有一一对应关系的 2曲线在对应点处的切线、主法线、副法线中某 2条平行或重合时 ,研究了曲线在该点处的基本向量、曲率、挠率满足的条件     

曲面的曲率线解法数例

本文不但给出了旋转曲面的曲率线的解法,而且给出了由隐函数所确定的曲率线的解法,最后给出了二次曲率线的解法。