Generation of vertical angular momentum in single,double, and triple-turn pirouette en dehors in ballet

The purpose of this study was to investigate the vertical angular momentum generation strategies used by skilled ballet dancers in pirouette en dehors. Select kinematic parameters of the pirouette preparation (stance depth, vertical center-of-mass motion range, initial shoulder line position, shoulder line angular displacement, and maximum trunk twist angle) along with vertical angular momentum parameters during the turn (maximum momentums of the whole body and body parts, and duration and rate of generation) were obtained from nine skilled collegiate ballet dancers through a three-dimensional motion analysis and compared among three turn conditions (single, double, and triple). A one-way (‘turn’) multivariate analysis of variance of the kinematic parameters and angular momentum parameters of the whole body and a two-way analysis of variance (‘turn’ × ‘body’) of the maximum angular momentums of the body parts were conducted. Significant ‘turn’ effects were observed in the kinematic/angular momentum parameters (both the preparation and the turn) (p < 0.05). As the number of turns increased, skilled dancers generated larger vertical angular momentums by predominantly increasing the rate of momentum generation using rotation of the upper trunk and arms. The trail (closing) arm showed the largest contribution to whole-body angular momentum followed by the lead arm.     

The means of managing momentum: Bridging technological paths and organisational fields

This paper examines how technological and organisational changes are mediated through different means of mutually monitoring and collectively coordinating technological developments in the field of semiconductor manufacturing. As collective practices, both monitoring and coordinating aim at generating momentum in order to stabilise or redirect technological paths in organisational fields. The empirical analysis of innovation practices in the field of semiconductor manufacturing technology shows that the means of managing momentum, above all roadmaps, conferences, and R&D consortia, influence and transform the development of new technologies as well as the social relations within the organisational field. The transformative capacity of these means is elaborated conceptually using Giddens’ theory of structuration.     

广义相对论的角动量守恒与广义守恒

根据最小作用量原理,另辟蹊径,系统推导了广义相对论的广义守恒定理、能量守恒定理与角动量守恒定理,特别是简明扼要和较完整地推出带有自旋角动量守恒的角动量守恒定理这一新的表述结果,在广义相对论理论中还是第一次．     

ENSO形成机制与变化趋势预测

El Nino是从南美西海岸延伸至赤道东太平洋向西至日界线大范围的海面温度异常增暖现象.Southern Oscillation是太平洋东西两侧海平面气压的反相关关系.El Nino/Southern Oscillation合称为ENSO.信风强弱关系到赤道西太平洋暖池的维持与El Nino的爆发,而人类活动所引起的地球变暖将是今后气候变化总的趋势,气候变暖将使全球海面上升,地球的自转半径增加,从角动量守恒的角度考虑,地球自转的速度将减慢,赤道两侧的信风相对于海面的速度也相应减小,维持赤道西太平洋暖池及海面东低西高形势的支柱被破坏.因此,我们将面临更频繁的El Nino和更多的极端天气.     

再议“诗豪”刘禹锡

白居易称刘禹锡为"诗豪",但对于何者为"豪",刘禹锡为何被称为"豪"等问题,学界一直未给出一个相对清晰的界定。文章从具体语境及"豪"等的字源分析入手,对"诗豪"的内涵进行解读。认为刘禹锡诗歌的主要风格是"豪劲"。     

The Central Eurasian Interactive Atlas Project: A Progress Report

SUMMARY

Since 2000, researchers and staff at the University of Washington have been developing a unified Geographic Information Systems database of Russian Federation socioeconomic, demographic, and political information at the raion and city (gorsovet) level. The Central Eurasian Interactive Atlas (CEIA) that has grown from this effort serves both to archive and to provide access to annual progressions of standardized geographic and tabular data covering the entire Russian Federation at a level of geographic detail not readily available elsewhere. As the CEIA grows, it will serve as a curricular and research focus of the UW's Russian, East European, and Central Asian Studies program.     

Contributions of the non-kicking-side arm to rugby place-kicking technique

To investigate non-kicking-side arm motion during rugby place kicking, five experienced male kickers performed trials under two conditions, both with an accuracy requirement but one with an additional maximal distance demand. Joint centre coordinates were obtained at 120 Hz during kicking trials and a three-dimensional model was created to enable the determination of segmental contributions to whole-body angular momentum. All kickers possessed minimal non-kicking-side arm angular momentum about the global medio-lateral axis. The more accurate kickers exhibited greater non-kicking-side arm angular momentum about the global antero-posterior axis. This augmented the whole-body antero-posterior angular momentum, and altered the whole-body lateral lean at ball contact. The accurate kickers also exhibited greater non-kicking-side arm angular momentum about the global longitudinal axis, which opposed the kicking leg longitudinal angular momentum and attenuated the whole-body longitudinal angular momentum. All participants increased the longitudinal angular momentum of the non-kicking-side arm in the additional distance demand condition, except for one participant whose accuracy decreased, suggesting that the longitudinal angular momentum of the non-kicking-side arm assists maintenance of accuracy in maximum distance kicking. Goal kickers should be encouraged to produce non-kicking-side arm rotations about both the antero-posterior and longitudinal axes, as these appear important for both the initial achievement of accuracy, and for maintaining accuracy during distance kicking.     

铅球投掷滑步技术的力学分析

铅球投掷滑步的作用不仅使铅球获得一定的预先运行速度，而且将人体处于推铅球前最良好的准备状态(精神高度集中，超越器械和拉紧有关肌群)，从而使投掷在利用滑步惯性的基础上充分发挥机体的能力对铅球进行最后的加速。     

对定轴转动刚体角动量的教学讨论

文章以例分析，澄清了一些物理学教材的不明确的角动量概念，建议物理教师在教学中注意强调角动量概念的准确性。     

关于变质量物体运动方程的讨论

通过引入变质量物体运动方程，讨论力学中的变质量问题．为了更好的理解与应用变质量物体动力学方程。对其导出、物理意义及应用条件作了详细论述．