Stochastic motion of the untrapped particle in electrostatic mode

The stochastic energy diffusion of the untrapped particle in the electrostatic mode is investigated analytically. We find that the equilibrium electrostatic field of periodical structure plays the same role as the usual focusing magnetic field to lead the test particle to stochastic motion. The resonance overlapping criterion for the random state is given, and also the Fokker-Planek-Kohnogorov approach to diffusion is considered for our system.     

Late-Stage Vortical Structures and Eddy Motions in a Transitional Boundary Layer

A high-order direct numerical simulation of flow transition over a flat-plate at a free stream Mach number 0.5 is carried out. Formation and development of three-dimensional vortical structures, typically shown as λ-vortices, hairpin vortices and ring-like vortices, are observed. Numerical results show that there is a strong downdraft motion of fluid excited by every ring-like vortex in the late-stage of the transition process. At two sides of the vortical structure centerline, the downdraft motions induced by the ring-like vortex and the rotating legs superimpose. This is responsible for the appearance of a high-speed streak associated with the positive spike observed in a previous investigation and the appearance of a high-shear layer in the near wall region.     

Observation of Influence of Nucleons＇ Motion on Kaons Collective Flow in Dense Medium

In order to extract the information of the momentum-dependent interaction of kaons under the extreme condition, the properties of the positively charged kaons produced in a heavy ion collision are studied via a simple model which has an invariable nucleon＇s velocity. Our special attention is focused on the observation of the dependence of the kaon＇s properties on the motion of nucleons in a hot and dense nuclear environment. Starting from two kinds of kaon quasiparticle models defined in transport theories for simulating heavy ion collisions, we calculate the effective mass and potential of the K＋＇s produced in the collisions and find that these properties not only depend closely on the velocity of nucleons but the dependence varies with kaon＇s quasiparticle model. It is clearly shown that the motion of nucleons reduces the momentum of K＋＇s at a given rapidity and thus weakens the rapidity distribution of K＋＇s directed flow in realistic nuclear collisions.     

对第26届物理竞赛一道“角动量”题目的解读

第26届全国中学生物理竞赛复赛第一大题的第5题原题如下．如图1,给静止在水平粗糙地面上的木块一初速度,使之开始运动．一学生利用角动量定理来考查此木块以后的运动过程：“把参考点设于如图所示的地面上一点O,此时摩擦力f的力矩为零,从而地面上木块的角动量将守恒,这样木块将不减速而做匀速运动．”请指出上述推理的错误,并给出正确的解释．     

2009年全国各地高考试题赏析——带电粒子在磁场中运动问题

带电粒子在磁场中的运动是历年高考中的重点内容之一.在2009年的全国各地高考试卷中,涉及带电粒子在磁场中运动的问题很多,题型新颖,构思巧妙、灵活,题材也较丰富,并且以计算题为主.纵观这类题目,所涉及的情景基本相同,都是带电粒子在洛仑兹力作用下在磁场中做匀速圆周运动,但题目往往拟定不同的题设条件,从多角度提出问题,多层次考查知识和能力.     

小球转动对平抛实验结果的影响探讨

高中物理探究平抛物体的运动,大多采用使小球从一定高度释放沿轨道滚动后做平抛运动的装置进行相关实验.那么小球的滚动在多大程度上影响实验的结果,在什么条件下可以不考虑小球的滚动.     

巧用已知图形突破作图难关

高中物理中有两个作图的难关,一个是根据两点振动情况,画简谐波波形求解波长的问题;另一个是根据带电粒子在两个点的运动情况,画出带电粒子在有界磁场中运动轨迹,确定带电粒子运动轨迹圆的半径,进而求解粒子速度和运动时间的问题.完整的简谐波的波形是一个正弦或余弦函数的图像;带电粒子在磁场中的运动轨迹是一个圆.但是在受到两个点的限制下,需要画的不是完整的图形或图像.如果先画出完整的图形或图像,再在图像上取满足题目条件的点,作图就显得很容易,问题解决起来就比较轻松.     

运动双原子与光场依赖强度耦合系统中的纠缠操纵与量子态制备

将Tavis-Cummings模型推广到同时考虑原子运动及与光场依赖强度耦合的情况.运用原子约化熵和Concurrence操纵了该系统在真空场、弱相干场和强相干场条件下,双原子-场之间以及双原子之间纠缠演化特性.以此为依据,选择双原子与场相互作用时间、选取双原子纠缠因子、调节场模结构参数,控制系统纯态概率幅和选择测量,制备了双原子-场W类态、双原子Bell态、Bell态原子保真态、光场的单光子态、双光子态及稳定的数态.实现了双原子Bell态突然产生及有限时间内的保持、Bell态原子周期量子回声的形成及其信息(态)持续保真.结果表明,该系统具有强大的量子信息功能,为量子信息处理的实验实现提供了物理载体和理论参数.     

基于最小关节力矩优化的自由浮动空间刚柔耦合机械臂混沌动力学建模与控制

采用拉格朗日法、假设模态法和系统动量守恒原理,推导了一种平面内三连杆的自由浮动刚柔耦合冗余度空间机械臂的动力学模型.基于最小关节驱动力矩优化,建立了自由浮动刚柔耦合冗余度空间机械臂的混沌运动状态方程,采用混沌数值方法分析机械臂运动中的混沌现象,分别在工作空间、关节空间和模态空间,设计鲁棒Proportional-Derivtive(PD)补偿控制、延迟反馈控制和模态力最优控制,实现了轨迹跟踪、混沌运动抑制和振动控制.通过数值仿真验证了建模与控制方法的有效性.     

走向统一的自然力——天上力与地上力的统一(Ⅲ)

 在前人工作的基础上, 牛顿对天上星星运动和地上物体运动的规律进行了总结, 提出了运动三定律, 建立了经典力学, 并在开普勒三定律的启发下发现了万有引力定律, 指出星星的圆周运动起因于相互吸引;物体自由下落也是因为物体与地球相互吸引, 从而统一了天上力和地上力。