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Qualititative Analysis of Interface Behavior under First Phase Transition  [PDF]
Alex Guskov
Journal of Crystallization Process and Technology (JCPT) , 2012, DOI: 10.4236/jcpt.2012.21005
Abstract: At present there is no explanation of the nature of interface instability upon first order phase transitions. The well-known theory of concentration overcooling under directed crystallization of solutions and Mullins-Sekerka instability cannot account for the diversified liquid component redistribution during solid state transition. In [1-3], within the framework of the nonequilibrium mass transfer problem, it has been shown that there are regimes of the interface instability, which differ from the known ones [4-6]. Moreover, the instability theory of works [1-3] demonstrates a complete experimental agreement of the dependence of eutectic pattern period on interface velocity. However, it is difficult to explain interface instability within the framework of a general setting of the mass-transfer problem. This paper is de-voted to qualitative analysis of the phenomena that are responsible for interface instability. The phenomena are connected by a single equation. Qualitative analysis revealed a variety of different conditions responsible for instability of flat interface stationary movement upon phase transition. The type of instability depends on system parameters. It is important that interface instability in the asymptotic case of quasi-equilibrium problem setting is qualitatively different from interface instability in the case of nonequilibrium problem setting.
On Setting of Heat-and-Mass Transfer Problems under Directed Crystallization  [PDF]
Alex Guskov
Physics , 2011,
Abstract: So far the problem of interface behavior upon phase transition has not yet acquired a satisfactory mathematical formulation due to a variety of the physical phenomena involved. Analytical solutions exist only for elementary problems describing the free interface behavior in directed crystallization conditions, for instance, for those implying a clearly shaped isothermal interface. Numerical calculations of the interface behavior also present significant difficulties since the instability of moving interface does not enable calculations by means of known algorithms. The general solution of this problem does not seem possible now, so quantitative analysis of phase transition is made after significant simplifications of the problem commonly reduced to the so-called quasi-equilibrium problem setting. It was used to study the reasons for the interface instability during phase transition. However, the solutions of the quasi-equilibrium problem are, as a rule, inherently qualitative. In this paper we present a detailed discussion of the boundary conditions of the directed crystallization problem, a formulation of the model considering temperature fields of external sources, the mechanism of attachment of particles to the growing solid surface, the influence of interphase component absorption on the phase distribution ratio of the components as well as the calculation of the period of the morphological interface instability which is made with due regard of all the aforementioned conditions.
Human Movement Is Both Diffusive and Directed  [PDF]
Mark Padgham
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0037754
Abstract: Understanding the influence of the built environment on human movement requires quantifying spatial structure in a general sense. Because of the difficulty of this task, studies of movement dynamics often ignore spatial heterogeneity and treat movement through journey lengths or distances alone. This study analyses public bicycle data from central London to reveal that, although journey distances, directions, and frequencies of occurrence are spatially variable, their relative spatial patterns remain largely constant, suggesting the influence of a fixed spatial template. A method is presented to describe this underlying space in terms of the relative orientation of movements toward, away from, and around locations of geographical or cultural significance. This produces two fields: one of convergence and one of divergence, which are able to accurately reconstruct the observed spatial variations in movement. These two fields also reveal categorical distinctions between shorter journeys merely serving diffusion away from significant locations, and longer journeys intentionally serving transport between spatially distinct centres of collective importance. Collective patterns of human movement are thus revealed to arise from a combination of both diffusive and directed movement, with aggregate statistics such as mean travel distances primarily determined by relative numbers of these two kinds of journeys.
An Interface View of Directed Sandpile Dynamics  [PDF]
Chun-Chung Chen,Marcel den Nijs
Physics , 2001, DOI: 10.1103/PhysRevE.65.031309
Abstract: We present a directed unloading sand box type avalanche model, driven by slowly lowering the retaining wall at the bottom of the slope. The avalanche propagation in the two dimensional surface is related to the space-time configurations of one dimensional Kardar-Parisi-Zhang (KPZ) type interface growth dynamics. We express the scaling exponents for the avalanche cluster distributions into that framework. The numerical results agree closely with KPZ scaling, but not perfectly.
Mathematical Modelling of Particle Movement Ahead of the Solid-liquid Interface in Continuous Casting
Mathematical Modelling of Particle Movement Ahead of the Solid—liquid Interface in Continuous Casting

Hong LEI,Yongli JIN,Miaoyong ZHU,Jicheng HE,
HongLEI
,YongliJIN

材料科学技术学报 , 2002,
Abstract: Whether the particle will be trapped by the solid-liquid interface or not is dependent on its moving behavior ahead of the interface, so a mathematical model has been developed to investigate the movement of the particle ahead of the solid-liquid interface. Based on the theory for the boundary layer, the fluid velocity field near the solid-liquid interface was obtained, and the trajectories of particles were calculated by the equations of motion for particles. In this model, the drag force, the added mass force, the buoyance force, the gravitational force, the Saffman force and the Basset history force are considered. The results show that the behavior of the particle ahead of the solid-liquid interface is affected by the physical property of the particle and fluid flow. And in the continuous casting process, if it moves in the stream directed upward or downward near vertical solid-liquid interface or in the horizontal flow under the solid-liquid interface, the particle with the diameter from 5 um to 60um can reach the solid-liquid interface. But if it moves in horizontal flow above the solid-liquid interface, only the particle with the diameter from 5 um to 10 um can reach the solid-liquid interface.
Decomposition of Solutions in Front of the Interface Induced by Directional Crystallization  [PDF]
A. Guskov, L. Nekrasova
Journal of Crystallization Process and Technology (JCPT) , 2013, DOI: 10.4236/jcpt.2013.34026
Abstract:

Here we show the results of experimental observation of decomposition of the solution components into the neighboring cells. The liquid solution under crystallization first gets into the unstable state and then decomposes. The decomposition result is fixed in the solid phase as inhomogeneous component distribution. Our experimental results enable to argue that the eutectic pattern forms due to interface instability and spinodal decomposition of non-equilibrium solution forming in front of the interface.

The Linear KdV Equation with an Interface  [PDF]
Bernard Deconinck,Natalie E. Sheils,David A. Smith
Mathematics , 2015,
Abstract: The interface problem for the linear Korteweg-de Vries (KdV) equation in one-dimensional piecewise homogeneous domains is examined by constructing an explicit solution in each domain. The location of the interface is known and a number of compatibility conditions at the boundary are imposed. We provide an explicit characterization of sufficient interface conditions for the construction of a solution using Fokas's Unified Transform Method. The problem and the method considered here extend that of earlier papers to problems with more than two spatial derivatives.
Directed avalanche processes with underlying interface dynamics  [PDF]
Chun-Chung Chen,Marcel den Nijs
Physics , 2002, DOI: 10.1103/PhysRevE.66.011306
Abstract: We describe a directed avalanche model; a slowly unloading sandbox driven by lowering a retaining wall. The directness of the dynamics allows us to interpret the stable sand surfaces as world sheets of fluctuating interfaces in one lower dimension. In our specific case, the interface growth dynamics belongs to the Kardar-Parisi-Zhang (KPZ) universality class. We formulate relations between the critical exponents of the various avalanche distributions and those of the roughness of the growing interface. The nonlinear nature of the underlying KPZ dynamics provides a nontrivial test of such generic exponent relations. The numerical values of the avalanche exponents are close to the conventional KPZ values, but differ sufficiently to warrant a detailed study of whether avalanche correlated Monte Carlo sampling changes the scaling exponents of KPZ interfaces. We demonstrate that the exponents remain unchanged, but that the traces left on the surface by previous avalanches give rise to unusually strong finite-size corrections to scaling. This type of slow convergence seems intrinsic to avalanche dynamics.
The Low-Temperature Crystallization and Interface Characteristics of ZnInSnO/In Films Using a Bias-Crystallization Mechanism
K. J. Chen,F. Y. Hung,T. S. Lui,S. J. Chang,Z. S. Hu
Journal of Nanomaterials , 2012, DOI: 10.1155/2012/272387
Abstract: This study presents a successful bias crystallization mechanism (BCM) based on an indium/glass substrate and applies it to fabrication of ZnInSnO (ZITO) transparent conductive oxide (TCO) films. The effects of bias-crystallization on electrical and structural properties of ZITO/In structure indicate that the current-induced Joule heating and interface diffusion were critical factors for low-temperature crystallization. With biases of 4 V and 0.1 A, the resistivity of the ZITO film was reduced from 3.08×10?4 Ω?cm to 6.3×10?5 Ω?cm. This reduction was attributed to the bias-induced energy, which caused indium atoms to diffuse into the ZITO matrix. This effectuated crystallizing the amorphous ZITO (a-ZITO) matrix at a lower temperature (approximately 170°C) for a short period (≤20 min) during a bias test. The low-temperature BCM developed for this study obtained an efficient conventional annealed treatment (higher temperature), possessed energy-saving and speed advantages, and can be considered a candidate for application in photoelectric industries.
Rayleigh-Taylor instability of crystallization waves at the superfluid-solid 4He interface  [PDF]
S. N. Burmistrov,L. B. Dubovskii,V. L. Tsymbalenko
Physics , 2010, DOI: 10.1103/PhysRevE.79.051606
Abstract: At the superfluid-solid 4He interface there exist crystallization waves having much in common with gravitational-capillary waves at the interface between two normal fluids. The Rayleigh-Taylor instability is an instability of the interface which can be realized when the lighter fluid is propelling the heavier one. We investigate here the analogues of the Rayleigh-Taylor instability for the superfluid-solid 4He interface. In the case of a uniformly accelerated interface the instability occurs only for a growing solid phase when the magnitude of the acceleration exceeds some critical value independent of the surface stiffness. For the Richtmyer-Meshkov limiting case of an impulsively accelerated interface, the onset of instability does not depend on the sign of the interface acceleration. In both cases the effect of crystallization wave damping is to reduce the perturbation growth-rate of the Taylor unstable interface.
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