液态Sn-Cu钎料的黏滞性与润湿行为研究

金属熔体的黏度和表面张力都是与液态结构相关的敏感物理性质, 且存在一定的相互关系. 对于微电子封装材料而言, 黏度和表面张力均是影响其工艺性能的重要参量. 本文利用回转振动式高温熔体黏度仪测量了Sn-xCu (x = 0.7, 1.5, 2)钎料熔体在不同温度下的黏度值, 发现在一定温度范围内钎料熔体的黏度值存在突变, 可划分为低温区和高温区. 在各温区内, 黏温关系很好地符合Arrhenius方程, 在此基础上讨论了液态钎料的结构特征和演变规律. 同时, 利用黏度值计算了液态Sn-xCu钎料在相应温度下的表面张力, 并通过Sn-xCu钎料在Cu基板上的润湿铺展实验对计算结果进行验证. 结果显示, 润湿角和扩展率的测试结果与表面张力的计算结果具有很好的一致性, 表明通过熔体黏度值来计算锡基二元无铅钎料合金表面张力并评估其润湿性能的方法是可行的. 关键词： Sn-Cu钎料 黏度 表面张力 润湿性     

黏滞法估算液体的活化能

液体分子要在液体中作一定程度的偏移,需要克服一个高度为W的势垒,这个势垒就是该液体的活化能,活化能是表征液体本身固有性质的一个物理量,它对液体诸多特性参数都有决定性的作用,本文提出一个估算液体活化能的实验方法--黏滞法,其理论依据是液体的黏滞系数n正比于TekT/W[1],通过实验分别测出几个不同温度下液体的黏滞系数反过来即可估算其活化能.     

物理学家江仁寿对金属液体黏滞性和表面张力的贡献

采用文献分析法,研究物理学家江仁寿在金属液体黏滞性和表面张力方面做出的贡献.结论认为:江仁寿从19世纪30年代开始致力于液体黏滞性的研究,改进并发展了亥姆霍兹设计的双线悬挂旋转球法,利用改进的惯性棒双线悬挂球实验装置,测定了水的黏度、液态碱金属钠、钾的黏度以及钠钾合金的黏度,测得的精确数据得到国际公认并被长期沿用.江仁寿后期将研究范围拓展到液态金属表面张力方面,为中国近代流体物理学的发展做出了重要的贡献.     

初速度对测定黏滞系数的影响

利用斯托克斯公式对小球从不同高度h下落进入液体中的初速度v0与达到匀速运动时的平衡时间t0和运动距离s0的关系进行了详细的推导，给出了不同高度h下的平衡时间t0和运动距离s0的公式和曲线．     

利用智能手机磁力计测量液体黏滞系数

利用智能手机搭建了一套可视化的简谐振动系统,通过小球在液体中欠阻尼振动的振幅衰减,测量液体的黏滞系数.实验使用手机Phyphox软件中的磁力计传感器,将小球欠阻尼振动振幅的测量转化为磁感应强度大小的测量,并通过Origin软件对采集的数据进行非线性拟合,得到液体阻尼因数,求出液体的黏滞系数.     

磁场中夸克物质的黏滞系数

研究了磁场中夸克非轻子弱作用过程的反应率和黏滞系数. 改进了在弱磁场情况下的近似计算方法, 给出了非轻子过程的反应率与夸克物质的体黏滞系数的表达式, 显示出在弱磁场情况下, 黏滞系数的温度依赖关系与零磁场情况下一致, 但黏滞系数的大小依赖磁场的强度.     

升球法测量液体黏滞系数

设计制作了一种升球法测量液体黏滞系数的装置。通过砝码拉动待测液体中的小球上升,使用CCD摄像头识别下落砝码从而得到砝码位置与时间的数据,再对数据进行拟合得出液体的黏滞系数。用该方法对蓖麻油进行了测量,结果表明,测得的黏滞系数与蓖麻油黏滞系数标准值的相对偏差为4%,说明该方法测量精度较高。与传统落球法相比,该方法可用于测量非透明、黏滞系数较低的液体。     

关于流体力学黏滞及伯努利方程演示实验

对流体力学演示实验的相关问题进行了分析,指出了理想流体概念的局限性,并深入研究了黏滞及伯努利方程两个演示实验,给出了黏滞演示实验的定量结果;指出伯努利方程演示实验的对象是中心细流管;同时,提出了消除黏滞影响的具体改进方案。     

利用降膜流动测量液体黏滞系数

利用降膜流动设计并搭建了测量液体黏滞系数的实验装置,根据不可压缩液体N-S方程,结合边界条件建模。采取测量液膜表面速度的方法计算液膜厚度。测量了蓖麻油不同流量下的黏滞系数,倾斜板在不同倾角下,黏滞系数测量相对准确的流量区间基本相同,相对误差在8%以下。分析了装置的适用条件和误差来源。并用全内反射法进行了液膜厚度对比验证。该研究丰富了测量液体黏滞系数的教学内容和方法,有助于学生掌握流体力学相关知识,提高综合设计能力。     

黏滞液体表面张力系数的悬滴法测量

开展了悬滴法测量黏滞液体表面张力的实验技术探究。通过微量进样控制技术,结合动态过程的连续图像采集方法,获得了不同液体量时的液滴形态变化。利用液滴表面张力与重力平衡时的临界状态图像,计算得到硅油的表面张力系数。与标准值相比较,测量数据的相对误差为4%左右。     

粘滞性流体动力学

We briefly discuss the phenomenological theory of dissipative fluid. We also present some numerical results for hydrodynamic evolution of QGP fluid with dissipation due to shear viscosity only. Its effect on particle production is also studied.     

Shear Viscosity of Hot QED at Finite Chemical Potential from Kubo Formula

Within the framework of finite temperature field theory this paper discusses the shear viscosity of hot QED plasma through Kubo formula at one-loop skeleton diagram level with a finite chemical potential. The effective widths （damping rates） are introduced to regulate the pinch singularities and then gives a reliable estimation of the shear viscous coefficient. The finite chemical potential contributes positively compared to the pure temperature case. The result agrees with that from the kinetics theory qualitatively.     

求解粘性Hamilton-Jacobi方程的高阶方法

提出了求解具有粘性项的Hamilton-Jacobi方程的二阶、四阶方法.该方法以加权基本无振荡(WENO)格式为基础,通过修正数值通量函数和构造右端粘性项的基于非线性限制器的二阶近似、基于Taylor展开的四阶近似,成功地求解了一维、二维的粘性Hamilton-Jacobi方程.给出的算例说明了本方法具有高分辨率、鲁棒性和无振荡特性.     

A Self-Similar Dynamics in Viscous Spheres

We study the evolution of radiating and viscous fluid spheres assuming an additional homothetic symmetry on the spherically symmetric space-time. We match a very simple solution to the symmetry equations with the exterior one (Vaidya). We then obtain a system of two ordinary differential equations which rule the dynamics, and find a self-similar collapse which is shear-free and with a barotropic equation of state. Considering a huge set of initial self-similar dynamics states, we work out a model with an acceptable physical behavior.     

Shear Viscosity of Hot QED at Finite Chemical Potential from Kubo Formula

Within the framework of finite temperature field theory this paper discusses the shear viscosity of hot QED plasma through Kubo formula at one-loop skeleton diagram level with a finite chemical potential. The effective widths (damping rates) are introduced to regulate the pinch singularities and then gives a reliable estimation of the shear viscous coefficient. The finite chemical potential contributes positively compared to the pure temperature case. The result agrees with that from the kinetics theory qualitatively.     

Simulating 2D Flows with Viscous Vortex Dynamics

Approximate solutions of the two-dimensional Navier–Stokes equation can be constructed as a superposition of viscous Lamb vortices. Requiring minimum deviation from the Navier–Stokes equation, one gets a set of ordinary differential equations for the positions, strength and width of the vortices. We calculate the deviation of the solution from the Navier–Stokes equation in the square norm. The time dependence of this error is determined and discussed.     

Molecular Dynamics Simulations for the Shear Viscosity of the One‐Component Plasma

We discuss two methods for determining the shear viscosity of a fluid of particles with Yukawa interaction potential (a one‐component plasma). Both methods are based on computing the equilibrium dynamics using large‐scale molecular dynamics (MD) simulations. Our MD results illustrate that the hydrodynamic method for computing the shear viscosity is feasible and therefore complements the more widely used method based on the Green‐Kubo relation. We expect that in the future our shear viscosity calculations will be used to assist with the interpretation and analysis of x‐ray scattering experiments, which could in principle measure this fundamental dynamical quantity (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stability of Viscous Shocks in Isentropic Gas Dynamics

In this paper, we examine the stability problem for viscous shock solutions of the isentropic compressible Navier–Stokes equations, or p-system with real viscosity. We first revisit the work of Matsumura and Nishihara, extending the known parameter regime for which small-amplitude viscous shocks are provably spectrally stable by an optimized version of their original argument. Next, using a novel spectral energy estimate, we show that there are no purely real unstable eigenvalues for any shock strength. By related estimates, we show that unstable eigenvalues are confined to a bounded region independent of shock strength. Then through an extensive numerical Evans function study, we show that there are no unstable spectra in the entire right-half plane, thus demonstrating numerically that large-amplitude shocks are spectrally stable up to Mach number M ≈ 3000 for 1 ≤ γ ≤ 3. This strongly suggests that shocks are stable independent of amplitude and the adiabatic constant γ. We complete our study by showing that finite-difference simulations of perturbed large-amplitude shocks converge to a translate of the original shock wave, as expected. This work was supported in part by the National Science Foundation award numbers DMS-0607721 and DMS-0300487.     

Dissipative Dynamics and the Statistics of Energy States of a Hookean Model for Protein Folding

A generic model of a random polypeptide chain, with discrete torsional degrees of freedom and Hookean spring connecting pairs of hydrophobic residues, reproduces the energy probability distribution of real proteins over a very large range of energies. We show that this system with harmonic interactions, under dissipative dynamics driven by random noise, leads to a distribution of energy states obeying a modified one-dimensional Ornstein–Uhlenbeck process and giving rise to the so-called Wigner distribution. A tunably fine- or coarse-grained sampling of the energy landscape yields a family of distributions for the energies and energy spacings.