实验验证肥皂膜与肥皂泡的两个物理特性

为了验证对称双漏斗肥皂膜实验在肥皂膜腰部半径自动变细之前的整个过程中肥皂膜的形状始终满足最小表面能原理,采用了四对半径不同的漏斗分别进行验证,利用FastStone Capture[1]软件对每种情况下的腰部半径随漏斗间距变化关系进行测量。通过拟合理论曲线与构建四种情况下分别对应的离散点,从而验证了这样一个结论：肥皂膜的形状在稳定区以内均满足最小表面能原理。此外,为了验证大小肥皂泡连通前后的半径关系,使用简易三通管,并使用FastStone Capture软件,测量了五次独立重复实验的数据。最后得到与理论计算相比较低误差的实验结果,从而验证了大小肥皂泡连通前后满足体积相加性。     

肥皂膜破裂速度的高速摄影实验

由高速摄像机拍摄的肥皂膜破裂图片,得到了圆形和球形肥皂膜破裂时半径和时间数据. 数据拟合表 明,肥皂膜以匀速收缩破裂, 并简要理论说明这个实验现象     

基于颜色仿真与匹配的肥皂膜厚度测量

肥皂膜在日常生活和物理学中经常会遇到.在薄膜干涉中也常会作为例子使用.人们总是关心,各种不同肥皂膜的厚度及其变化情况如何.本文以宽光谱LED为光源,观察并用相机拍摄了肥皂膜上的干涉图样,用颜色仿真和匹配法测量了肥皂膜的厚度.并且采用已知波长的单色光重复测量了肥皂膜厚度,同时用等厚干涉公式验证了测量结果.结果显示,与宽光谱光源相比,用单色光源做此类实验更具优势.     

肥皂水的新配方

演示液体的表面张力和光的薄膜干涉需要肥皂水，我们往往就用一般的洗衣粉配制肥皂水，其肥皂膜的持续时间不过几秒钟，影响实验效果，为了使肥皂膜的时间延长，笔者通过反复实验，发现一种新的配方，用这种配方配制的肥皂水可以保存较长的时间，所成的肥皂膜能延续几分钟。     

肥皂膜过滤性能研究

通过构建平面肥皂膜及正曲率肥皂膜，结合相图、高速摄像系统研究肥皂膜过滤性及玻璃颗粒贯穿肥皂膜动力学过程。由颗粒下落高度、肥皂膜直径构建的相图表明，随着颗粒直径增加，肥皂膜承重质量较大的区域而逐渐缩减且最大承重质量骤降。若颗粒下落高度、肥皂膜直径恒定，颗粒直径增加导致肥皂膜承重减少。在颗粒贯穿肥皂膜过程中，肥皂膜呈现漏斗状，逐渐收缩于颈点，最后与颗粒分离，并伴随卫星气泡产生。肥皂膜形变与韦伯数正相关，当韦伯数大于9000时，正曲率肥皂膜较易破裂。     

薄膜干涉实验的改进

肥皂膜干涉实验是高中物理光学部分一个重要的演示实验.做好这个演示,对于学生理解光的干涉现象和干涉条件有着重要的作用.但是由于常规实验方法自身的限制,干涉条纹可见范围很小,大多数学生看不到烛焰的像,就更谈不上看到干涉现象了.于是大多数教师在此只好口头介绍实验现象,其实验效果当然只能是事倍功半.鉴于此,笔者改变了原来用眼直接观察烛焰像的惯例,改用入射光照射肥皂膜,反射到屏上进行观察,大大提高了实验的可见度、成功率.     

泡泡形成的理论和实验探究

通过改变气体密度、喷口尺寸以及泡泡环和气体喷口之间的距离,探究了泡泡形成的速度阈值以及吹出泡泡的异同,建立了简单的理论模型,对泡泡的形成进行了解释,即比较了肥皂膜处气体流动所产生的动压强和由表面弯曲而产生的拉普拉斯压强,理论结果与实验数据相吻合.     

用迈克耳孙干涉仪测肥皂膜厚度实验的分析

利用白光干涉原理,借助迈克耳孙干涉仪对肥皂膜的厚度进行了非接触测量.在干涉条纹宽窄相同的条件下,对不同层数的肥皂膜进行对比测量;在干涉条纹宽窄不同的条件下,对相同层数的肥皂膜进行对比测量;通过计算给出了膜的中心厚度和不确定度,对比分析了各种条件下测量时误差产生的原因.结果表明:单层、双层膜适合在宽条纹下测量,四层膜适合在窄条纹下测量.     

肥皂泡破裂现象及产生小液滴分布研究

肥皂泡破裂产生液滴的大小和数目受破裂过程影响.本文研究了肥皂泡大小和高度对破裂产生液滴的影响,以及所产生液滴的分布规律.实验发现肥皂泡破裂产生的液滴在破裂高度较低时存在放射性线状分布现象;随着高度增加放射性线状分布消失;同时分析了肥皂泡破裂产生液滴的数目及肥皂膜的厚度随肥皂泡体积的变化规律.结果表明,肥皂泡体积和液滴数目之间存在幂函数关系,理想情况下肥皂膜厚度与碎片数目之间也存在幂函数关系.肥皂泡破裂过程中产生的液滴可以按照拟合结果大致分为小碎片,中等碎片和大碎片,它们分别对应于肥皂泡破裂过程的3个变化阶段.     

三维漏斗中颗粒物质堵塞问题的数值实验研究

对于工程和实验中使用漏斗颗粒流而言,连续稳定的流量是必要的.当漏斗口较小时,很容易发生堵塞行为.堵塞现象对于交通流、疏散问题等也具有重要的意义.前人主要使用扰动的方法破坏漏斗中已有的堵塞,以便引起下一次堵塞,加快实验进程.本文利用自主开发的基于GPU(graphics processing unit)的密集颗粒流模拟程序,主要研究当三维漏斗开口打开后的第一次堵塞行为,不再引入扰动.详细讨论了漏斗开口尺寸、漏斗锥角等几何参数对坍塌规模的影响.发现对于坍塌规模的概率分布符合前人的研究结果,可以分为两部分:峰的左边呈幂函数上升形式,峰的右边呈指数衰减趋势.对于漏斗开口尺寸和漏斗锥角而言,均存在一个临界值使得堵塞不再发生.     

Dynamics of density waves in a two dimensional funnel on an inclined plane

We report here experiments on two-dimensional funnel flow of diameter glass beads on an inclined plane. We have investigated the properties of the flow according to the outlet size D of the funnel and the gravity. We have identified three different regimes. For small funnel outlet sizes, there is no significant change in flow density: the flow is rather steady and homogeneous. For intermediate outlet sizes (), the flow is intermittent, consisting of spatially ordered density waves propagating upwards. At bigger outlet sizes, density waves do not exhibit any ordering and the flow dynamics becomes chaotic. In addition, we find that the flow dynamics is independent of the funnel opening angle except close to the channel flow configuration. Finally, it is stressed that the interactions between the beads and the inclined plane play a crucial role in the mechanism of formation of density waves. Received: 9 July 1998 / Received in final form and Accepted: 18 September 1998     

Statistics of shock waves in a two-dimensional granular flow

We have investigated the dynamics of shock waves in a single layer of uniform balls in a small-angle two-dimensional funnel. When the funnel half-angle 0 degrees < or approximately beta < or approximately 2 degrees, the flow is intermittent and kinematic shock waves are observed to propagate against the flow. We have used fast video equipment and image analysis methods to study the statistics of the shock waves. It is found that their speed and frequency increase with the distance from the outlet. In particular, the shock speed scales as the ratio of the local funnel width to the width of the funnel outlet. Various kinds of interactions between shock waves are observed, including repulsion. New shock waves are only created at those sites where a close-packed triangular packing of the monodisperse balls fits across the funnel.     

A cold cesium atomic beam produced out of a pyramidal funnel

We have built an atomic funnel which produces a slow and cold cesium atomic beam. The atomic funnel is based on a pyramidal Magneto Optical Trap (MOT) with a small hole at its apex. Characterization of the funnel operation has been carried out by fluorescence emission and absorption spectroscopy, and optical time of flight (TOF) methods. The atomic beam has a longitudinal velocity in the range 8–12 m/s and a spread less than 1.5 m/s. The transverse temperature is close to the Doppler limit. Typically, an atom flux 4×10⁹ atoms/s is attained. These features, combined with the compactness and simplicity of the experimental arrangement, make this system an ideal source for experiments in atom lithography and atom optics.     

Resonance Chains and Geometric Limits on Schottky Surfaces

Resonance chains have been observed in many different physical and mathematical scattering problems. Recently, numerical studies linked the phenomenon of resonances chains to an approximate clustering of the length spectrum on integer multiples of a base length. A canonical example of such a scattering system is provided by 3-funneled hyperbolic surfaces where the lengths of the three geodesics around the funnels have rational ratios. In this article we present a mathematically rigorous study of the resonance chains for these systems. We prove the analyticity of the generalized zeta function, which provides the central mathematical tool for understanding the resonance chains. Furthermore, we prove for a fixed ratio between the funnel lengths and in the limit of large lengths that after a suitable rescaling, the resonances in a bounded domain align equidistantly along certain lines. The position of these lines is given by the zeros of an explicit polynomial that only depends on the ratio of the funnel lengths.     

基于PS-InSAR技术的北京地面沉降特征及成因初探

地下水持续超量开采是导致北京地面沉降快速发展的主要原因。目前已形成南北两大沉降中心,在快速沉降区域,地表仍以每年30～60 mm的速度持续发展,对城市基础设施和人员安全造成危害。文中采用永久散射体干涉测量(PS-InSAR)技术获取北京平原区2003年—2009年地面沉降时间序列形变信息;综合气象数据、地下水监测网数据,SAR干涉测量数据和区域基底构造,建立地面沉降综合分析模型,阐明北京地面沉降空间分布特征,并对其成因机制进行初探。研究发现： (1)北京区域地面沉降不均匀性明显,多个沉降漏斗连成一片,沉降量受降雨入渗补给影响较大,表现出季节性波动变化特征;(2)沉降中心与地下水降落漏斗中心并非完全一致,第二承压含水层(底板埋深100～180 m)漏斗区与地面沉降中心在空间展布上较为吻合。(3)地面沉降多发生于粘性土层厚度50～70m地区。(4)地面沉降受区域基底构造控制作用明显,在断裂带两侧形变梯度较大。     

Microfabricated evanescent-light funnel with high-intensity cold atom flux

We process a silicon-on-insulator substrate into a funnel with a 25-μm-side square-shaped outlet by photolithography and anisotropic chemical etching. The funnel is utilized to form a cold atomic beam by means of reflection and cooling on repulsive evanescent light. Monte Carlo simulations show that the flux intensity of emitted cold Rb atoms reaches 10¹² cm⁻² s⁻¹. The mean horizontal velocity is estimated to be below 10 cm/s, while the mean vertical velocity decreases in proportion to the outlet side. The evanescent-light funnel can be developed to concentrate 80% of Rb atoms falling from a standard magneto-optical trap.     

一种新颖的全光型表面原子(分子)漏斗

提出了一种产生全光型表面原子(分子)漏斗的新方案.采用红失谐高斯激光束照明由柱面透镜组成的光学系统，可在透镜焦平面附近产生横向漏斗形光强分布，以构成一表面光波导型原子漏斗.计算了漏斗的光强分布及其光学偶极势与偶极力分布.研究结果表明：该原子漏斗可用于冷原子(分子)的表面光波导、分束器和干涉仪以及微阱囚禁的有效装载，因而在集成原子光学及其原子芯片的研究中有着重要的应用. 关键词： 原子漏斗 分子漏斗 光学偶极势 原子芯片     

Study of dynamical behaviour and fermionization of a bosonic gas in funnel potential

This paper presents a funnel external potential model to investigate dynamic properties of ultracold Bose gas. By using variational method, we obtain the ground-state energy and density properties of ultracold Bose atoms. The results show that the ultracold Bose gas confined in a funnel potential experiences the transition from three-dimensional regime to quasi-one-dimensional regime in a small aspect ratio, and undergoes fermionization process as the aspect ratio increases.     

任意夹角的双色偏振激光作用下孤立阿秒脉冲的产生

本文选取脉宽为12 fs波长为2000 nm和800 nm的两束线性偏振激光, 适当调节两束激光的偏振方向的夹角θ, 发现当θ=π/2时, 高次谐波谱的第二级平台出现了“漏斗形”凹槽.当θ为π/6时, 得到了290 eV的超宽连续谱的高次谐波发射, 利用小波变换合理的解释了高次谐波形状及截止位置. 在该段连续谱上任意截取70 eV宽度的频率, 都可以得到脉宽约为60 as的孤立阿秒脉冲. 适当减小截取范围可以得到线性偏振的脉宽94 as的孤立阿秒脉冲. 这为实验中产生能灵活调节的孤立阿秒脉冲提供了一种方案.