Phase-field simulation of a Fe-Mn alloy under forced flow conditions

In this work a study through numerical simulation of dendritic growth for the system Fe-Mn under the influence of a forced flow field is presented. The investigations are based on an extension of the quantitative phase-field approach developed by Echebarria et. al. Phy. Rev. E 061604 (2004), to simulate the solidification of Fe-Mn under the influence of a forced flow field. The simulations are performed for isothermal conditions and the investigation concentrates on the effects of forced flow on the dendrite morphology during the growth dynamics. The effects of forced flow on microsegregation are also discussed.     

Quasi-two-dimensional solitons in ferroelectrics

The production and dynamics of nonlinear localized acoustic formations in ferroelectrics with the relaxation absorption are investigated. These formations are interpreted as algebraic solitons (lumps). It is shown that they are stable for transverse perturbations. Volgograd State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 14–18, July, 2000.     

Quasi-two-dimensional superfluid fermionic gases

We study a quasi-two-dimensional superfluid Fermi gas where the confinement in the third direction is due to a strong harmonic trapping. We investigate the behavior of such a system when the chemical potential is varied and find strong modifications of the superfluid properties due to the discrete harmonic oscillator states. We show that such quasi-two-dimensional behavior can be created and observed with current experimental capabilities.     

Quasi-two-dimensional Shubnikov-de Haas effect

The theory of the Shubnikov-de Haas effect is generalized to the case of two-dimensional systems with several occupied size-quantization subbands. Possible interlevel scattering is taken into account. It is shown that the relative amplitudes of the Shubnikov-de Haas oscillations are determined not only by the occupancy of the subbands but also by the intensity of intersubband transitions.     

Holographic forced fluid dynamics in non-relativistic limit

We study the thermodynamics and non-relativistic hydrodynamics of the holographic fluid on a finite cutoff surface in the Gauss–Bonnet gravity. It is shown that the isentropic flow of the fluid is equivalent to a radial component of gravitational field equations. We use the non-relativistic fluid expansion method to study the Einstein–Maxwell-dilaton system with a negative cosmological constant, and obtain the holographic incompressible forced Navier–Stokes equations of the dual fluid at AdS boundary and at a finite cutoff surface, respectively. The concrete forms of external forces are given.     

Acoustic force model for the fluid flow under standing waves

An acoustic Strouhal number is introduced to demonstrate that the viscosity of fluid can be ignored in the process of sound propagation and acoustic streaming is independent on the frequency of the acoustic wave. Furthermore, acoustic force based on the periodic velocity fluctuation caused by standing acoustic wave is introduced into Navier–Stokes equation in order to describe the fluid flow in the acoustic boundary layer. The numerical results show that the predicted results are consistent with the analytic solution. And the effect of the nonlinear terms cannot be ignored so the analytic solution derived by boundary-velocity condition is only an approximation for acoustic streaming.     

Irreversible energy flow in forced Vlasov dynamics

Molecular dynamics (MD) simulations are used to investigate the thermodynamic properties and structural changes of KCl spherical nanoparticles at various sizes (1064, 1736, 2800, 3648, 4224 and 5832 ions) upon heating. The melting temperature is dependent on both the size and shape of KCl models, and the behaviour of the first order phase transition is also found in the present work. The surface melting found here is different from the melting phenomena of KCl models or other alkali halides studied in the past. In the premelting stage, a mixed phase containing liquid and solid ions covers the surface of nanoparticles. The only peak of heat capacity spreads out a significant segment of temperature, probably exhibiting both heterogeneous melting on the surface and homogeneous melting in the core. The coexistence of two melting mechanisms, homogeneous and heterogeneous ones, in our model is unlike those considered previously. We also found that the critical Lindemann ratio of the KCl nanoparticle becomes much more stable when the size of the nanoparticle is of the order of thousands of ions. A picture of the structural evolution upon heating is studied in more detail via the radial distribution function (RDF) and coordination numbers. Our results are in a good agreement with previous MD simulations and experimental observations.     

Quasi-two-dimensional organic superconductors: A review

Quasi-two-dimensional organic superconductors are reviewed. These systems exhibit many interesting phenomena, including reduced dimensionality, strong electron - electron and electron - phonon interactions and the proximity of antiferromagnetism, insulator states and superconductivity. Moreover, it has been possible to measure the electronic bands of many of the organics in great detail, in contrast to the situation in other well-known systems in which similar phenomena occur. The crystal structure and normal-state properties of the organics are described before the experimental evidence is presented for and against exotic superconductivity mediated by antiferromagnetic fluctuations. Finally, three instances of field-induced unconventional superconductivity are described.     

Observation of droplet size oscillations in a two-phase fluid under shear flow

Experimental observations of droplet size sustained oscillations are reported in a two-phase flow between a lamellar and a sponge phase. Under shear flow, this system presents two different steady states made of monodisperse multilamellar droplets, separated by a shear-thinning transition. At low and high shear rates, the droplet size results from a balance between surface tension and viscous stress, whereas for intermediate shear rates it becomes a periodic function of time. A possible mechanism for such kinds of oscillations is discussed.     

Quasi-two-dimensional dynamics of plasmas and fluids

In the lowest order of approximation quasi-two-dimensional dynamics of planetary atmospheres and of plasmas in a magnetic field can be described by a common convective vortex equation, the Charney and Hasegawa-Mima (CHM) equation. In contrast to the two-dimensional Navier-Stokes equation, the CHM equation admits "shielded vortex solutions" in a homogeneous limit and linear waves ("Rossby waves" in the planetary atmosphere and "drift waves" in plasmas) in the presence of inhomogeneity. Because of these properties, the nonlinear dynamics described by the CHM equation provide rich solutions which involve turbulent, coherent and wave behaviors. Bringing in nonideal effects such as resistivity makes the plasma equation significantly different from the atmospheric equation with such new effects as instability of the drift wave driven by the resistivity and density gradient. The model equation deviates from the CHM equation and becomes coupled with Maxwell equations. This article reviews the linear and nonlinear dynamics of the quasi-two-dimensional aspect of plasmas and planetary atmosphere starting from the introduction of the ideal model equation (CHM equation) and extending into the most recent progress in plasma turbulence.     

Quasi-two-dimensional hydrodynamics and problems of two-dimensional turbulence

The principal problems of quasi-two-dimensional (Q2-D) hydrodynamics are discussed. Accounting for Q2-D flow vertical structure is shown to eliminate "genetic" defects of the formal 2-D idealization of 3-D Navier-Stokes equations and allows under certain conditions to formulate corrected 2-D motion equations which adequately describe real hydrodynamic processes. The applicability of the approach is directly verified in laboratory experiments. Special attention is paid to the problem of 2-D turbulence. Its simulation on the basis of ordinary 2-D equations is unjustified because of the absence of the external Kolmogorov dissipation scale and reverse spectral energy flux. An alternative approach allows one to introduce the natural external scale of 2-D turbulence which depends only on physical properties of the system under consideration and to formulate the conditions under which the large scale vortex dynamics is expected to be universal at large Reynolds number, i.e., to be independent on the size and form of integration domain and lateral boundary conditions.     

Turbulence in the randomly forced,one-dimensional Burgers flow

The randomly forced, one-dimensional Burgers flow is dealt with by the method of the characteristic functional equation. The time development of the stochastic secondary flow is studied numerically by the Monte Carlo quadrature of the integral representation of solution for two types (white and “red”) of random force fields. A turbulence-like behavior of the flow appears for a supercritical Reynolds number, and its structure is studied in detail.     

Computational modeling of forced flow laser chemical vapor deposition

Laser chemical vapor deposition (LCVD) utilizes a laser to localize a CVD reaction. The process involves complex physical interactions within a very small spatial region. Experimental investigations into the dynamics of the LCVD process are limited by spatial and resolution capabilities of instrumentation. Models are developed herein using the computational fluid dynamics (CFD) code, FLUENT, that incorporate heat transfer, fluid flow, and species transport in a single integrated modeling environment. The models are used to study the carbon deposition process. Insight is gained into the relationships among the process parameters and the deposition rates and deposition rate profiles. Phenomena such as thermal diffusion and the relative importance of mass convection and mass diffusion are explored. A designed set of model cases is executed and the results are used to develop a simple polynomial expression for relating experiment conditions to deposit attributes. PACS 81.10.Bk; 81.05.Uw; 81.15.Gh; 47.50.Cd; 81.16.Mk     

Dynamics of three-tori in a periodically forced navier-stokes flow

Three-tori solutions of the Navier-Stokes equations and their dynamics are elucidated by use of a global Poincare map. The flow is contained in a finite annular gap between two concentric cylinders, driven by the steady rotation and axial harmonic oscillations of the inner cylinder. The three-tori solutions undergo global bifurcations, including a new gluing bifurcation, associated with homoclinic and heteroclinic connections to unstable solutions (two-tori). These unstable two-tori act as organizing centers for the three-tori dynamics. A discrete space-time symmetry influences the dynamics.     

受迫流动下的枝晶生长相场法模拟研究

基于耦合流场和热噪声的相场模型及合理高效的三维动态求解域加速算法,定量模拟了在受迫流动下枝晶的非对称生长及流速对迎流、背流两侧的温度分布和层流层分布的影响.计算结果表明,受迫流动使迎流、背流两侧温度的分布与层流层分布呈现不对称状态,导致迎流侧与背流侧的过冷度不同,而熔体施加于枝晶界面前沿迎流侧的力还不足以抑制过冷度的作用,结果造成枝晶迎流方向优先生长,从而产生倾向于散热方向的倾斜,同时,由于迎流侧的实际过冷度大于背流侧,有利于促进迎流一侧枝晶生长速度以及稳定侧向分枝生长,从而导致了侧向分枝的非对称生长.随