Biomedical subjects

L M Pismen

Publications and source records attributed to L M Pismen.

7 recordsLinked to original sources

PubMed2004

A realistic kinetic Monte Carlo simulation of the faceting of a Pt(110) surface under reaction conditions.

The faceting process on Pt(110) is studied with the help of a kinetic Monte Carlo model taking into account realistic Pt-Pt, Pt-CO, and Pt-O interactions. The activation energies of the allowed atomic steps are estimated using available computational and experimental data. The model well reproduces the region in the parameter space where faceting occurs. Under kinetic instability conditions, the simulated faceted pattern forms a periodic hill and valley structure with a lateral periodicity of approximately 140-170 A, which is comparable with experimental data. The simulations reproduce the development of faceting on a realistic time scale.

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PubMed2004

Diffuse-interface effects near a cusp singularity on a free surface.

Cusp singularity on a free surface of a viscous fluid driven by a vortex dipole is resolved through nanoscale molecular interactions. The cusp is formed at finite capillary number due to a decrease of surface tension caused by conjoining interaction near the cusp. The related effects of cusp geometry are weak Marangoni flow, vapor condensation, and a slight decrease of liquid density near the cusp creating a depletion tail downstream.

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PubMed2004

Realistic kinetic Monte Carlo study of the surface phase reconstruction.

Reversible 1 x 1 <==> 1 x 2 reconstruction of Pt(110) surface is studied with the help of a kinetic Monte Carlo model. Activation energies of the allowed atomic steps are estimated using available computational and experimental data, and some discrepancies are reconciled to fit macroscopic data on surface reconstruction. Both energies of the various atomic configurations and activation energies depend on CO coverage and are estimated with the account of Pt-CO binding energies and repulsive interactions on adjacent sites. The model well reproduces both scanning tunneling microscopy results obtained for a clean 1 x 2 surface and available macroscopic data on 1 x 1 <==> 1 x 2 reconstruction.

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PubMed2004

Dynamic phase separation: from coarsening to turbulence via structure formation.

We investigate some new two-dimensional evolution models belonging to the class of convective Cahn-Hilliard models: (i) a local model with a scalar order parameter, (ii) a nonlocal model with a scalar order parameter, and (iii) a model with a vector order parameter. These models are applicable to phase-separating system where concentration gradients cause hydrodynamic motion due to buoyancy or Marangoni effect. The numerical study of the models shows transition from coarsening, typical of Cahn-Hilliard systems, to spatiotemporally irregular behavior (turbulence), typical of the Kuramoto-Sivashinsky equation, which is obtained in the limit of very strong driving. The transition occurs not in a straightforward way, but through the formation of spatial patterns that emerge for intermediate values of the driving intensity. As in driven one-dimensional models studied before, the mere presence of the driving force, however small, breaks the symmetry between the two separating phases, as well as increases the coarsening rate. With increasing driving, coarsening stops. The dynamics is generally irregular at strong driving, but exhibits specific structural features.

Algorithms↗

PubMed2002

Fingering instability of thin evaporating liquid films.

The fingering instability of growing dry patches in an evaporating film of a polar liquid placed on a solid substrate is investigated. The instability manifests itself as fingering of mobile fronts between growing "dry" (thin) and shrinking "wet" (thick) regions of the film corresponding to two stable states of the evaporating film in contact with its vapor. The boundaries of the fingering instability are found through linear stability analysis of numerical solutions of the nonlinear evolution equation defining the film profile, and the influence of the evaporation rate, polar intermolecular forces, and chemical heterogeneity of the substrate is investigated.

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PubMed2001

Nonlocal diffuse interface theory of thin films and the moving contact line.

A nonlocal diffuse interface model is explored using the "lubrication approximation" applicable to thin films. We show the inconsistency of the expansion leading to a nonlinear diffusion model, and solve an untruncated integro-differential mean field equation to compute the equilibrium density profile across the fluid-vapor interface. The disjoining potential and effect of interfacial curvature are computed using approximations compatible with the lubrication approximation. We explore the thick film asymptotics, and find it coinciding with the sharp interface limit. These results are further used for computation of the static contact angle and derivation of an evolution equation for flowing films of dynamic menisci in the lubrication approximation. The structure of the evolution equation is identical to that of the sharp interface theory, but it is free from troublesome divergences near the three-phase contact line.

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PubMed2001

Nonlocal boundary dynamics of traveling spots in a reaction-diffusion system.

The boundary integral method is extended to derive a closed integro-differential equation applicable to computation of the shape and propagation speed of a steadily moving spot and to the analysis of dynamic instabilities in the sharp boundary limit. Expansion of the boundary integral near the locus of traveling instability in a standard reaction-diffusion model proves that the bifurcation is supercritical whenever the spot is stable to splitting. Thus, stable propagating spots do already exist in the basic activator-inhibitor model, without additional long-range variables.

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