Density expansion of viscosity coefficient

The formalism developed earlier has been extended to obtain the density expansion of viscosity coefficient. The important role played by the Hartree average energy in obtaining an explicit temperature dependence for the density coefficients of the viscosity is demonstrated. The results obtained are compared with the available experimental data for the first density coefficient. A satisfactory agreement between theory and experiment is found.     

A green function approach to the paramagnetic phase of a Heisenberg ferromagnet

A higher-order decoupling similar to the first-order Bogolyubov-Tyablikov decoupling is used to find various correlation functions in the paramagnetic region for a Heisenberg ferromagnet. Expressions are given for the susceptibility, the nearest-neighbor correlation, and autocorrelation at the critical point as well as at high temperatures.This paper is based on the first author's Oxford University D. Phil, thesis. A preliminary account has been published elsewhere. (¹)     

转筒法测液体黏度关系式比较研究

对文献中转筒法测液体黏度的几个关系式进行了比较研究,指出了其中的问题.     

利用Tracker视频分析软件测量液体黏度

在落球法测量液体黏度中利用Tracker视频分析软件捕捉分析小球下落轨迹,减小了实验中诸多不确定因素带来的测量误差,使数据处理更为直观、准确.结果表明此方法能准确测量小球的收尾速度,而且可以对现有实验内容进行扩展.     

卡西米尔效应的格林函数计算方法

介绍了卡西米尔效应的严格格林函数表达式.作为应用,计算了4种边界条件下两平行板之间的卡西米尔能量.     

A compact artificial viscosity equivalent to a tensor viscosity

We present a compact artificial viscosity for staggered grid Lagrangian hydrodynamics on polygonal cells in two Cartesian dimensions and using a decomposition into triangles we show that this viscosity is equivalent to a tensor viscosity of Campbell and Shashkov for quadrilaterals.     

转筒黏度计测量液体黏度方法研究

用黏性流体力学理论求得测量装置中旋转液体径向速度梯度的理论公式,进而得到转筒法测量黏度的较精确公式.指出了国内的一些教材和文献在推导中使用近似公式的错误,用参数估计的方法求得测量装置的摩擦阻力力矩,使测量结果得到进一步校正.实验研究表明:按照近似公式与精确公式计算求得的径向速度梯度之差可达到13.1%,求得的液体黏度之差可达到28.6%;在蓖麻油的温度为25.5℃时测得测量装置的摩擦阻力力矩为9.482×10-5 N·m,相当于0.540克重物产生的力矩.     

Coefficients of viscosity of a gaseous plasma

We present here an order of magnitude calculation for the coefficients of viscosity with the assumption that the drift velocity introduces asymmetry both in the single-particle distribution functionf ₁ and the correlation functionP(1, 2). These asymmetric parts have been estimated considering the self-relaxation of the system when the cause of drift velocity is suddenly removed. Using these, the kinetic part of the coefficient of electron viscosity has been calculated and the result fairly agrees with similar studies by others. The potential part of shear viscosity coefficient is found to be zero while both parts of the coefficient of bulk viscosity are non-zero.     

用磁铁释放拾取钢球的液体黏度测量仪

研制了一种液体度测量仪.用锥形磁铁吸持和释放钢球使钢球沿量筒中心轴线下落,用磁棒拾取钢球使钢球免清洗重复使用,采用专门设计的量筒盛待测液体.分析了收尾速度计时起点的位置,并用MATLAB计算讨论.实验结果表明,该测量仪测量准确,不产生油污,操作简单方便.     

Long-time behavior of the nonlocal shear viscosity of a one-component plasma: A microscopic approach

The nonlocal shear viscosity(t) of a classical one-component plasma is shown to have anoscillatory long-time tail. This result is obtained on the basis of amicroscopic theory which does not rely on expansions in a small parameter such as the plasma expansion parameter. Our major approximation is the restriction to the coupling oftwo hydrodynamic propagators in the computation of the long-time behavior of the transport matrix. The Coulomb divergence is correctly accounted for, while the nonanalyticities of both the plasma parameter and gradient expansions are discussed at the level of the kinetic as well as the hydrodynamic equations.     

用恒流法自制仪器精确测定液体的黏度

介绍了用恒流法自制仪器精确测定液体的黏度.该自制仪器,能有效地保证底部的密封性、液体水位恒定和可操作性.另外,还增设一个玻璃管连通器,并附加一根标尺和游标,可使液体水位的测量精确度提高.在接毛细管输出液体的量筒处加上光电计时,可使测量液体的流速的精确度提高.再将相关数据送入已编好程序的电子仪器进行计算并显示出黏度.另外该仪器可调换不同管径的毛细管,因此应用本方法能快速准确地测量多种液体的黏度.     

A thermodynamical approach to continued fraction expansions for the shear viscosity

In a thermodynamical framework, evolution equations for the fast (non-conserved) variables are obtained, which in particular cases lead to equations of the Ginzburg-Landau type. The present scheme leads, in a natural way, to a continued fraction expansion for the transport coefficients using thermodynamical assumptions only.     

Radiating gravitational collapse with shear viscosity revisited

A new model is proposed to a collapsing radiating star consisting of an isotropic fluid with shear viscosity undergoing radial heat flow with outgoing radiation. In a previous paper we have introduced a function time dependent into the g _rr , besides the time dependent metric functions and . The aim of this work is to generalize this previous model by introducing shear viscosity and compare it to the non-viscous collapse. The behavior of the density, pressure, mass, luminosity and the effective adiabatic index is analyzed. Our work is compared to the case of a collapsing shearing fluid of a previous model, for a star with 6 . The pressure of the star, at the beginning of the collapse, is isotropic but due to the presence of the shear the pressure becomes more and more anisotropic. The black hole is never formed because the apparent horizon formation condition is never satisfied. An observer at infinity sees a radial point source radiating exponentially until reaches the time of maximum luminosity and suddenly the star turns off. The effective adiabatic index has a very unusual behavior because we have a non-adiabatic regime in the fluid due to the heat flow.     

光吸收介质的吸收系数与介电函数虚部的关系

讨论了相对介电函数虚部和消光系数与光吸收的关系,指出吸收系数与消光系数成正比,而吸收系数与相对介电函数虚部成正比是有条件的.     

一种计算剪切模量温度系数的方法

采用理论计算与动高压实验相结合的方法，提出了一个计算剪切模量温度系数G′T的新方法.首先用理论方法计算一个中间数据G(PS)，然后再与动高压实验数据G(PH)结合在一起计算出G′T,并针对93钨合金材料进行了计算.计算结果表明剪切模量温度系数G′T开始是随温度和压力变化的，但在高温高压下，它趋近于一常数.对于93钨合金，这个常数约为-004GPa／℃.同时，这也是对Steinberg本构模型中的剪切模量温度系数为常数的一个证明.并且，当把这一常数代入剪切模量温度系数的计算式中，将重新计算出的剪切模量与实验测得的剪切模量结果进行了比较，结果表明二者符合得很好，从而证明了本计算的剪切模量温度系数的正确性. 关键词： 有限应变物态方程 剪切模量温度系数 Steinberg本构模型 动高压实验     

Transient time correlation function calculation of the viscosity of a molecular fluid at low shear rates: a comparison of stress tensors

Shear viscosity of n-decane was computed using the molecular stress transient time correlation function (TTCF) formalism for the wide range of shear rates from 1.7 × 10¹⁰ s^?1 to 2.13 × 10⁴ s^?1. In earlier work calculations were presented for the shear viscosity of n-decane using the atomic stress formalism of the TTCF method (G. Pan and C. McCabe, J. Chem. Phys. 125(19), 4527 (2006)) in which we were able to close the gap between the lowest shear rates accessible by direct nonequilibrium molecular dynamics (NEMD) simulations and the highest shear rates possible in experimental studies. Here it is shown that the application of the molecular stress approach within the TTCF formalism, as an alternative to the atomic stress method, significantly reduces the number of NEMD trajectories necessary to obtain the shear viscosity.     

冲击压缩下物质黏性系数与冲击波阵面扰动衰减特性研究

为解决高温高压下物质黏性的测量问题,Sakharov曾提出一种冲击波小扰动实验方法,但人们一直未从理论上给出这类特定冲击波流场中扰动振幅衰减特性与黏性系数之间的量化关联.本文首次针对Mineev等的实验条件采用数值解方法定量地研究了金属铝(Al)中复杂流场演化过程、正弦形波阵面上相对扰动幅度的演化特征和它们的黏性效应,给出了相对扰动幅度衰减曲线的零点相对距离与黏性系数之间的定量关系.与Zaidel的均匀流场模型以及Miller等的非均匀流场模型相比,本文求解的流场演变问题已经接近实验的真实情况.利用本文数     

Molecular dynamics calculations of shear viscosity time-correlation functions for hard spheres

The time-correlation function for shear viscosity is evaluated for hard spheres at volumes of 1.6 and 3 times the close-packed volume by a Monte Carlomolecular dynamics technique. At both densities, the kinetic part of the timecorrelation function is consistent, within its rather large statistical uncertainty, with the long-timet ^–3/2 tail predicted by the mode-coupling theory. However, at the higher density, the time-correlation function is dominated by the cross and potential terms out to 25 mean free times, whereas the mode-coupling theory predicts that these are asymptotically negligible compared to the kinetic part. The total time-correlation function decays roughly ast ^–3/2, with much larger than the mode-coupling value, similar to the recent observations by Evans in his nonequilibrium simulations of argon and methane. The exact value of the exponent is, however, not very precisely determined. By analogy with the case of the velocity autocorrelation function, for which results are also presented at these densities, it is argued that it is quite possible that at high density the asymptotic behavior is not established until times substantially longer than those attainable in the present work. At the lower density, the cross and potential terms are of the same magnitude as the kinetic part, and all are consistent with the mode-coupling predictions within the relatively large statistical uncertainties.Work performed under the auspices of U.S. Department of Energy.     

A green synthetic approach to graphene nanosheets for hydrogen adsorption

A green and facile strategy of preparing graphene by reducing exfoliated graphite oxide (GO) with glucose was developed in this study. The as-prepared samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscopy (AFM). The characterization results indicated that the graphene sheets (GS) were of high quality with smooth surface, rich pore structure and few layer graphene. The samples have a BET specific surface area of 1205.8 m² g⁻¹ measured by N₂ adsorption at 77 K. The hydrogen storage capacity of 2.7 wt.% at 298 K and 25 bar demonstrated that the as-prepared graphene employing glucose as reductant is supposed to be a promising material with outstanding property for hydrogen storage.     

Lecture notes on shear viscosity in heavy ion collisions

These notes are a summary of a lecture delivered at the 30th Erice School in Nuclear Physics and provide an elementary introduction to shear viscosity as it is applied to heavy ion collisions. After a qualitative review of the ideal and viscous space-time evolutions, I calculate the elliptic flow and discuss how viscosity affects the results.