对乒乓球运动中球拍与球摩擦作用的新认识

应用物理学的基本知识，通过对乒乓球的受力分析，指出球拍对球的摩擦力不但能制造旋转，同时还能使球产生平动初速度。在制造上旋时，有利于回球顺利过网，提高回球的稳健性，在制造下旋时，有利于降低回球的高度，提高回球的质量。     

STUDY OF THE PERFORMANCE ON THE WEAR AND FRICTION OF THE C/Cu COMPOSITE MATERIAL

研究了Ｃ／Ｃｕ复合材料的摩擦磨损性能．通过在块－环型摩擦试验机上进行试验，得出在轻微磨损状态下，复合材料的摩擦系数和磨损率随压强增大而缓慢增大．电子显微镜观察和电子探针分析表明，摩擦面间形成了一层表面膜，这层膜具有一定的自润滑性和阻碍粘附发生的作用，这是使摩擦系数和磨损率保持较低水平的根本原因．     

摩擦促进沉淀产生的原因

在阐述沉淀形成的基础上，从晶核的形成、晶核的成长、固体表面作用、界面层(润湿)作用及化学反应速度等方面分析了摩擦产生沉淀的原因．     

内燃机活塞环-缸套摩擦磨损性能的实验研究

利用自行研制的往复式摩擦磨损实验机对内燃机活塞环-缸套进行了摩擦磨损实验,主要测试载荷、转速以及润滑方式对摩擦副磨损的影响,应用称重法测量活塞环的磨损量,结果表明：在极限载荷下,活塞环的磨损量随着载荷的增大而加剧;若转速较低,难以形成润滑油膜,磨损加剧;必须使摩擦副处于一种弹性流体动力润滑状态,才能降低磨损量。     

蒋桂之争与渡江战役发起时间的确定

渡江战役是一场结束国民党政府统治中国大陆的重大战役。其发起时间的确定,与蒋桂之争和蒋介石的军事部署变化有着密切的关系。桂系幻想防守长江,"划江而治"。蒋介石则撤退台湾,竭力搞垮桂系,并依此调整军事部署。根据蒋桂矛盾的演变,中共中央采取灵活的措施,调整和确定了渡江战役的发起时间,一举取得了渡江战役的伟大胜利。     

黄河三角洲纺织企业国际化进程中的问题及对策——以滨州纺织企业为例

金融危机后,黄河三角洲的纺织企业受宏观环境变化及自身因素的影响,放慢了其国际化的发展步伐。以滨州市纺织企业发展为例,从国际上各类繁多的贸易摩擦和贸易壁垒、原料价格上涨、劳动成本增加、人民币升值以及该地区企业自身发展水平的局限等方面分析了纺织企业国际化进程受到的影响,在新的环境条件下,黄河三角洲纺织企业应以建立黄河三角洲高效生态经济区为契机,以打造"世界纺织物流之都"的理念为基础,为纺织企业向国际化发展,提高自身在国际市场上竞争力。     

一类永磁同步电动机的TSM控制器设计

基于永磁同步电动机精确的数学模型,针对永磁同步电动机绕组相电流和转速强耦合特性,依据中继切换控制机制和有限时间收敛的终端滑动模态控制机制,考虑了永磁同步电动机的有限时间跟踪问题。给出了其终端滑模控制器的设计方案。在所设计的控制作用下,闭环系统将在有限时间内达到平衡状态。并且保证了闭环系统所有信号的有界性和平衡点的全局稳定性,以及系统在有限时间内精确地跟踪给定的参考信号。最后对一具体的永磁同步电动机模型进行了数值仿真,仿真结果表明在所设计的终端滑模控制器作用下,系统的跟踪误差在有限时间内达到零,验证了所提算法的正确有效性。     

The effects of surface traction characteristics on frictional demand and kinematics in tennis

The interaction between footwear and surfaces influences the forces experienced by tennis players. The purpose of this study was to investigate traction demand and kinematic adaptation during tennis-specific movements with changes in traction characteristics of surfaces. We hypothesised that players would increase the utilised coefficient of friction (horizontal to vertical ground reaction force ratio) when the shoe surface combination had a high coefficient of friction and flex their knee after contact to facilitate braking. Eight participants performed two separate movements, side jump out of stance and running forehand. Ground reaction force was measured and three-dimensional kinematic data were recorded. Clay surface and cushioned acrylic hard court (low vs. high shoe–surface friction) were used. The peak utilised coefficient of friction was greater on clay than the hard court. The knee was less flexed at impact on clay ( ? 5.6 ± 10.2°) and at peak flexion ( ? 13.1 ± 12.0°) during the running forehand. Our results indicate that tennis players adapt the level of utilised friction according to the characteristics of the surface, and this adaptation favours sliding on the low friction surface. Less knee flexion facilitates sliding on clay, whereas greater knee flexion contributes to braking on the hard court.     

Adaptive backstepping sliding mode control for nonlinear systems with input saturation

An adaptive backstepping sliding mode control is proposed for a class of uncertain nonlinear systems with input saturation.A command filtered approach is used to prevent input saturation from destroying the adaptive capabilities of neural networks (NNs).The control law and adaptive updating laws of NNs are derived in the sense of Lyapunov function,so the stability can be guaranteed even under the input saturation.The proposed control law is robust against the disturbance,and it can also eliminate the impact of input saturation.Simulation results indicate that the proposed controller has a good performance.