Acoustic emission during the formation and breakdown of a dislocation cluster

We construct a model for the formation of a dislocation cluster and its evolution after the detachment of the head dislocation. The results obtained with the help of this model are used for calculating the acoustic emission signal accompanying the stages of cluster formation and breakdown. The elastic stresses in the signal under investigation are estimated. The data on relaxation of elastic stresses in the sample containing the cluster are reported.     

Interface dynamics under nonequilibrium conditions: From a self-propelled droplet to dynamic pattern evolution

In this article, we describe the instability of a contact line under nonequilibrium conditions mainly based on the results of our recent studies. Two experimental examples are presented: the self-propelled motion of a liquid droplet and spontaneous dynamic pattern formation. For the self-propelled motion of a droplet, we introduce an experiment in which a droplet of aniline sitting on an aqueous layer moves spontaneously at an air-water interface. The spontaneous symmetry breaking of Marangoni-driven spreading causes regular motion. In a circular Petri dish, the droplet exhibits either beeline motion or circular motion. On the other hand, we show the emergence of a dynamic labyrinthine pattern caused by dewetting of a metastable thin film from the air-water interface. The contact line between the organic phase and the aqueous phase forms a unique spatio-temporal pattern characterized as a dynamic labyrinth. Motion of the contact line is controlled by diffusion processes. We propose a theoretical model to interpret essential aspects of the observed dynamic behavior.     

Decaying quasi-two-dimensional turbulence in a thin liquid layer

The results of laboratory measurements of decaying quasi-two-dimensional turbulence in a thin liquid layer are considered. It is shown that the enstrophy-to-energy ratio decreases according to a power law on a certain decay interval. The exponent in the power law is a function of the Reynolds number. The enstrophy decay is found to be anomalously slow as predicted in a number of numerical studies. It is shown that the anomalous decay in the quasi-two-dimensional flow under investigation is not due to intense vortex formation as in the numerical decaying turbulence, but due to the limited range of scales on which a flow can be regarded as two-dimensional.     

Crown evolution kinematics of a camellia oil droplet impacting on a liquid layer

The phenomenon of droplet impact on an immiscible liquid is encountered in a variety of scenarios in nature and industrial production. Despite exhaustive research, it is not fully clear how the immiscibility of the liquid on which a droplet impacts affects the crown evolution. The present work experimentally investigates the evolution kinematics of a crown formed by the normal impact of a camellia oil droplet on an immiscible water layer. Based on discussion of dynamic impact behaviors for three critical Weber numbers (We), the radius of the crown and its average spreading velocity are compared with those of previous theoretical models to discuss their applicability to the immiscible liquid. The evolution kinematics (morphology and velocity) are analyzed by considering the effects of the We and layer thickness. Furthermore, the ability of crown expansion in radial and vertical directions is characterized by a velocity ratio. The results show that our experimental crown radius still follows a square-root function of evolution time, which agrees with the theoretical predictions. The dimensionless average spreading velocity decreases with We and follows a multivariate power law, while the dimensionless average rising velocity remains constant. The velocity ratio is shown to linearly increase with We, demonstrating that the rising movement in crown evolution gradually enhances with We. These results are helpful for further investigation on the droplet impact on an immiscible liquid layer.     

Second-harmonic generation from a thin spherical layer and No-generation conditions

The dispersion of the electro-optical effect in polydisperse hydrosols of diamond is studied in the external field frequency ranging from 10 Hz to 2.5 MHz. The conservative dichroism, which is determined by the difference in the turbidity constants for light polarized along and perpendicular to the particle-orienting field, is chosen as the electro-optic effect. The dispersion dependences of the dichroism are determined and used to calculate the dispersion of the average values of the polarizability anisotropy of the diamond particles. The influence of the concentration of monovalent ions in an aqueous KCl solution on these dispersion dependences is studied. The experimental dependences of the dispersion are compared with the theoretical ones within the model of the polarizability of the colloidal particles which takes into account the polarizability of the diffuse part of their double electric layer.     

On the cryogenic layer formation under conditions of high-frequency mechanical action

The results of a series of experiments using a piezovibration formation module for producing cryogenic targets with a given fuel layer structure are presented.     

Laser-induced jet formation and droplet ejection from thin metal films

An experimental study of femtosecond laser-induced jet formation and droplet ejection from thin metal films is presented. These processes are compared to liquid jet formation during laser-induced forward transfer of viscous liquids. As a result of this comparison, a mechanism explaining the main features of laser processing of thin metal films is proposed. According to this mechanism, laser-induced generation of a molten bump and its collapse are similar to the collapse of cavitation bubbles on a liquid?Cair interface. Material criteria required for realization of the jetting process are discussed and supported by experimental observations.     

Parametric instabilities of a viscous liquid layer covered by a thin elastic plate under vertical periodic motion

Parametric instabilities of a horizontal liquid layer with a finite depth covered by a thin elastic plate under a vertical periodic motion are investigated with account taken of the viscosity of the liquid layer. The primary regions and the secondary ones of dynamic instabilities are determined by using the equation of a thin elastic plate including the normal component of the viscous stress, but not the tangential component of it. The critical amplitude of the imposed oscillation, beyond which a parametric instability occurs (that is, the neutral stability curves) is found in the space of the frequency and amplitude of the imposed vertical oscillation. These results are confirmed by experimental ones for a liquid layer of glycerine covered with a thin rubber plate.     

液滴在梯度微结构表面上的铺展动力学分析

本文通过改变肋柱宽度和间距, 构造了二级和多级梯度微结构表面, 采用格子-Boltzmann方法对液滴在两种梯度表面上的铺展过程进行了研究, 探析液滴运动的机理和调控方法. 结果表明, 在改变肋柱间距的二级梯度表面上, 当液滴处于Cassie态时, 接触角滞后大小与粗糙度梯度成正比关系; 当液滴从Cassie态转换为Wenzel态或介于两者之间的不稳定态时, 这一正比关系不再遵循. 在改变肋柱宽度的二级梯度表面上, 接触角滞后大小与粗糙度梯度始终成正比关系. 在多级梯度表面上, 随液滴初始半径增大, 接触角滞后减小, 但液滴平衡位置相较于初始位置偏离增大. 对梯度微结构表面上液滴运动和接触角滞后的定量分析, 可为实现梯度微结构表面液滴运动调控提供理论依据.     

Thermocapillary deformation of a thin locally heated horizontal liquid layer

In this paper, steady thermocapillary flow in a thin horizontal layer of a viscous incompressible liquid with a free surface is considered. An axially symmetric steady problem with a localized thermal action on a horizontal liquid layer with a deformable free surface is solved in a thin-layer approximation. In addition to the thermocapillary effect, the model takes into account the capillary pressure caused by the free surface variable curvature and the convective mechanism of heat transfer in the liquid. Analytical expressions for the velocity vector components as functions of the liquid layer thickness and surface temperature are obtained. The free surface and velocity profiles caused by various kinds of heating are calculated. The influence of convective heat transfer on the flow pattern is analyzed.     

Memory effect and redistribution of cavitation nuclei in a thin liquid layer

Temporal evolution and spatial distribution of acoustic cavitation structures in a thin liquid layer were investigated experimentally with high-speed photography. The inception and disappearance processes of cavitation bubble cloud revealed that the metastable cavitaton structures formed in the thin liquid layer caused a long-term “memory effect”. A factor which weakens the memory effect was identified. The distribution of cavitation nuclei was investigated by changing the temporal decay of the memory effect.     

Instability and dynamics of thin viscoelastic liquid films

The instability, rupture, and subsequent growth of holes in a thin Jeffreys-type viscoelastic film under the influence of long-range van der Waals force are investigated using both linear stability analysis and nonlinear numerical solutions. The linear stability analysis of full governing equations valid for arbitrary wave numbers shows that although fluid rheology does not influence the dominant length scale of the instability, it significantly affects the growth rate. It is shown that neglect of inertia and solvent dynamics results in a nonphysical singularity in the growth rate beyond a critical value of relaxation time. We further carry out numerical simulations of a set of long-wave, nonlinear differential equations (also derived in Rauscher et al., Eur. Phys. J. E 17, 373 (2005)) governing the evolution of the free surface. The nonlinear simulations, in their domain of validity, confirm the results of the linear analysis. Interestingly, results from nonlinear simulations further show that both for Newtonian and viscoelastic liquids, the shape and the dewetting dynamics of a hole are identical when examined in terms of a rescaled time which depends on rheological parameters. Thus, viscoelasticity of Jeffreys type merely accelerates the growth rate, without however affecting the important morphological characteristics.     

Three-dimensional nonlinear dynamics of thin liquid films

Using a general two-body exponential parametrization for the wave function, the Nakatsuji two-particle density equation [Phys. Rev. A 14, 41 (1976)] is transformed into a set of nonlinear algebraic equations in which the number of unknowns precisely equals the number of equations. Since the Nakatsuji two-particle density equation is equivalent to the time-independent Schrodinger equation for Hamiltonians containing up to two-body interactions, the answer to the title question is affirmative, provided the equations have solutions. Practical implications of the parametrization and possible approximation schemes are briefly discussed.     

Voltage self-sustained oscillation and phase separation dynamics in a thin layer of a weakly conducting ferromagnetic liquid with periodically emerging electrohydrodynamic flows

It is shown that voltage self-sustained oscillations, which are determined by the properties of the near-electrode layer and electrohydrodynamic flows that are periodically formed in the colloid layer, emerge for a preset direct current at the electrodes of a plane-parallel cell filled with a colloid system consisting of stabilized magnetic nanoparticles dispersed in a weakly conducting liquid. The effect of self-sustained oscillations and periodic electrohydrodynamic flows in phase separation in the colloid system is analyzed. It is found that new dynamic formations are generated, which are regions of elevated concentration of magnetite particles having the shape of labyrinths of millimeter size. The emergence of a negative real part of the permittivity of the colloid layer is detected and attributed to the fact that the normal component of the internal electric field produced by volume charges becomes codirectional with the applied field when steady-state electrohydrodynamic flows appear in the system.     

Simulation of the ignition of liquid fuel with a local source of heating under conditions of fuel burnout

The processes of heat and mass transfer with phase transitions and chemical reactions in the ignition of liquid fuel by a local source of heating, a hot metal particle, under conditions of fuel burnout are studied. The influence of liquid fuel burnout on the ignition characteristics is analyzed, and the results of investigation of the extent of influence of this factor for solid and liquid condensed materials under conditions of local heating are compared.     

Cu87团簇在升温与急冷过程中结构变化的原子尺度模拟

本文采用基于嵌入原子法的正则系综分子动力学方法在原子尺度上计算了包含87个原子的Cu87金属团簇在连续升温和急冷降温时的结构演化过程。根据原子平均势能、对分布函数、原子堆积结构和主要原子键对数目随温度的变化表明,温度的不同极大地影响团簇内的原子堆积结构。在升温过程中,随着温度的升高,团簇内原子堆积结构出现由密排六方、二十面体直到无序堆积的变化。在急冷降温过程中,随着急冷温度的降低,团簇内由出现的一定数量的二十面体和面心立方的局域结构、数量不一的HCP,FCC和二十面体局域结构,直到急冷温度较低时的一定数量的二十面体局域结构。     

Mechanism of energy dissipation in a droplet cluster

It has been shown that thermocapillary processes on the surface of the drops in a drop cluster that appears above a locally heated liquid ensure additional energy transfer. Thus, the drop cluster is a typical dissipative structure. The energy dissipated by an individual drop of the cluster has been estimated.     

Post-deposition dynamics of multiple cluster aggregation on liquid surfaces

A comprehensive simulation model---deposition, diffusion, rotation and aggregation---is presented to demonstrate the post-deposition phenomena of multiple cluster growth on liquid surfaces, such as post-deposition nucleation, post-deposition growth and post-deposition coalescence. Emphasis is placed on the relaxations of monomer density, dimer density and cluster density as well as combined cluster-plus-monomer density with time after deposition ending. It is shown that post-deposition coalescence largely takes place after deposition due to the large mobility of clusters on liquid surfaces, while the post-deposition nucleation is only possible before the saturation cluster density is reached at the end of the deposition. The deposition flux and the moment of deposition ending play important roles in the post-deposition dynamics.