Soliton-like molecular deformations in a nematic liquid crystal film

We study the nature of molecular deformations in a nematic liquid crystal film with elastic energy under homeotropic boundary conditions. The deformation in terms of splay, twist and bend fields of the director axis is found to be governed by the completely integrable Davey-Stewartson-I (DS-I) equation in (2+1) dimensions. Using the line soliton and breather solutions of the DS-I equation, the director axis is constructed, the components of which exhibit damped spatial oscillations. However, the splay and bend fields of the director axis exhibit localized structures of deformation.     

非平整基底上受热液膜流动稳定性研究

本文研究了二维黏性流体薄膜沿非平整不均匀加热基底流动时非线性表面波的演化及其流动稳定性.利用长波摄动法推导出非平整线性加热基底上非线性表面波的零阶和一阶演化方程,基于所得演化方程,绘制出正弦波纹基底上液膜的表面波形图,并研究液膜流动的线性稳定性,分析了各无量纲参数对液膜线性稳定性的影响.分析结果表明:在正弦波纹基底上,液膜自由表面随同壁面作相同频率的正弦型波动,且液膜厚度沿流动方向逐渐变小;Marangoni数为稳定影响因素,随Marangoni数的增大,液膜稳定区域增大;Peclet数和倾角θ均为不稳定影响因素,随Peclet数和倾角θ的增大,液膜稳定区域减小;在非平整基底的波峰和波谷处,Peclet数、Marangoni数和倾角θ对稳定性的影响趋势一致,但基底波谷处的液膜稳定区域小于波峰处区域,流动更易失稳.     

Formation of thermocapillary structures in a heated liquid film

The conditions of formation of a three-dimensional thermocapillary structure on the surface of a liquid film flowing along a heater with the constant temperature were studied numerically based on the derived system of equations. Formation of the thermocapillary structure was modeled by periodic perturbations in the transverse direction superimposed on the two-dimensional flow. It is shown in calculations that transversal perturbations can develop into periodic rivulet structures on the film surface if the Marangoni number exceeds some threshold value. It is revealed that the rivulet structure develops when the period belongs to a certain range, which is determined by the value of Marangoni number. The results of calculations are in a good agreement with experimental data.     

Influence of thermocapillary effects on wave characteristics of the heated liquid film

Wave characteristics of the water film flow over a vertical plate with a heater were studied. Without a heat flux, data obtained perfectly coincide with results of other authors obtained for an isothermal liquid film. When heating the falling liquid, thermocapillary forces form the rivulets and thin film between them. It was found out that an increase in the heat flux causes a rise of the phase velocity and decreases the frequency of 3D waves. It is shown that in contrast to the known data for an isothermal liquid film, the average relative wave amplitude increases with a rise of dimensionless complex Re_loc/Ka _loc ^1/11 at relatively high heat flux densities in the interrivulet. The growth of wave amplitude under the action of thermocapillary forces was revealed in the interrivulet, what corresponds to calculations. The work was financially supported by the Russian Foundation for Basic Research (Grants Nos. 05-08-33325-a and 06-01-00360-a), Federal Target R&D Program (State contracts Nos. 02.438.11.7002 and NSh-6749.2006.8), and SB RAS (International interdisciplinary project No. 111).     

Stability of the heated liquid film in the presence of the thermocapillary effect

Stability of the flow of the heated liquid film is studied in the presence of the thermocapillary effect. To describe the waves in the film, the integral model is used. According to results of linear analysis of stability, the thermocapillary effect expands the area of instability only at low values of Peclet number Pe, and at high values of Pe, the instability area narrows. Wave evolution in the film on a substrate with the fixed temperature was simulated numerically. Results of numerical simulations agree with the linear theory of stability.     

Stability of inertialess liquid film flowing down a heated inclined plane

This paper investigates the stability of inertialess falling film down an uniformly heated inclined plane. Normal mode analysis is performed to study the linear stability of the falling film.     

Stability of liquid film falling down a vertical non-uniformly heated wall

The main object in this paper is to study the stability of a viscous film flowing down a vertical non-uniformly heated wall under gravity. The wall temperature is assumed linearly distributed along the wall and the free surface is taken to be adiabatic. A long wave perturbation method is used to derive the nonlinear evolution equation for the falling film. Using the method of multiple scale, the nonlinear stability analysis is studied for travelling wave solution of the evolution equation. The complex Ginzburg-Landau equation is determined to discuss the bifurcation analysis of the evolution equation. The results indicate that the supercritical unstable region increases and the subcritical stable region decreases with the increase of Peclet number. It has been also shown that the spatial uniform solution corresponding to the sideband disturbance may be stable in the unstable region.     

X射线透射法测量膜厚

薄膜厚度不仅与薄膜的电导率有关,而且与薄膜的光学性能甚至表面结构密切相关. 薄膜厚度的测量精确有助于研究薄膜的物理性能. 本文利用X射线在材料中传播的特征设计了大学物理实验室测量薄膜厚度的方法.     

Analysis of explosive boiling of a liquid film on an impulsively heated substrate

Explosive boiling of a thin liquid film on a substrate heated by nanosecond laser pulse, which results in film peeling from a substrate, is considered. It was shown that, to explain the experimental data [1] on the maximum film peeling velocity, the features of evaporation kinetics in the appearing cavity and the shaking effect associated with the nonlinear thermal expansion of the film immediately before its detachment from the substrate should be taken into account.     

干涉法测量铝薄膜的轴向应力

将干涉法测量圆薄膜应力的方法推广到椭圆形铝薄膜,利用Stoney公式和牛顿环原理测量了常温下铝薄膜长轴和短轴方向上轴向应力的大小,给出了应力分布图像.     

Thermalization time of thin metal film heated by short pulse laser

Based on the hyperbolic two-step heat conduction model, using the Laplace transform and numerical inverse transform method (Riemann-sum approximation method), the thermal behaviour of thin metal films has been studied during femtosecond pulse laser heating. Also the thermalization time, which is the time for the electron gas and solid lattice to reach thermal balance, has been studied in detail. The values of thermalization time for silver (Ag), gold (Au), copper (Cu) and lead (Pb) are obtained. The effects of material parameters of the thin metal film on the thermalization time are considered for the four kinds of metals by changing one of the parameters and regarding the other parameters as constant. For a typical metal material, the order of the thermalization time is of the order of hundreds of picoseconds. The thermalization time decays exponentially with the increase of phonon－electron coupling factor or electron gas thermal conductivity, and it increases linearly with the increase of the ratio of lattice heat capacity to electron gas heat capacity. However, the relaxation time of the electron gas has very little effect on the thermalization time.     

Effect of the shape of a particle heated to a high temperature on the gas-phase ignition of a liquid film

The process of gas-phase ignition of a liquid fuel film with incandescent small metal particles in the form of a parallelepiped, disk, or hemisphere was numerically simulated. The magnitude of influence of the particle shape on the delay time of ignition of a liquid fuel was determined. The range of parameters of the particle at which the effect of its shape on the ignition delay time is unimportant was established.     

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.     

A liquid film or droplet of miscible binary fuel burning on a heated surface at elevated pressures

An experimental study has been made of the combustion and evaporation of miscible binary fuels on a heated surface at elevated pressures. Photographic observation was made for elucidating how the binary fuel droplets or films behaved on the heated surface and for obtaining the characteristic lifetime as a function of the surface temperature, the ambient pressure and the initial concentration of highly volatile component of the fuels. The binary fuels tested were mixtures of n-hexane and n-decane. The results showed that the lifetime curve both for the combustion and for the evaporation of n-hexane/n-decane on the heated surface had two peaks at lower pressures, the first peak in the film-type evaporation region and the second peak in the spheroid-type evaporation region. The preferential evaporation of the highly volatile component was responsible for the appearance of the first peak in the film-type evaporation region. The second peak corresponded to Leidenfrost point. The increase in the ambient pressure caused a shift of the lifetime curve toward higher surface temperature and a decrease in the lifetime at two peaks. The lifetime curve decreased monotonically with increasing the surface temperature and the spheroid-type evaporation was not observed at higher pressures. The increase in the initial concentration of highly volatile component caused a shift of the first peak toward higher surface temperature, a decrease in its lifetime and a slight shift of the second peak toward lower surface temperature. The combustion caused a remarkable decrease in the lifetimes around the first peak and in the spheroid-type evaporation region and a slight increase in the surface temperature at the first peak, while the surface temperature at the second peak remained almost unchanged.     

Holographic study of laser-induced liquid surface deformations

Laser-induced liquid surface deformations are studied by means of holographic real-time interferometry. It is shown that for the two-dimensional case the experimental results are in good agreement with theoretical predictions by Landau. Possible applications of the phenomenon are discussed.     

超声光栅测声速的方法运用到液体表面波波速的测量

理论上分析了超声光栅衍射和液体表面波光栅衍射,得到了表面波光栅衍射图样与表面波参数的解析关系.实验上得到清晰的衍射图样,利用表面波光栅衍射法测量了液体表面波波速,实验结果与理论值误差不超过1%.     

Simulation of arbitrary deformations of polycrystals by the method of cellular atomata

A computer model for the deformation of polycrystals is developed, based on the concept of cellular automata. The model is used to investigate a polycrystal by treating it as a multilevel hierarchical system, and to study the peculiarities in the behavior of this system as a function of the material structure, mechanisms of low-level deformation, history of loading and/or deformation at the top hierarchical level, the temperature, and other parameters. Zh. Tekh. Fiz. 68, 130–132 (November 1998)