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P. Viot

Publications and source records attributed to P. Viot.

29 records · Page 2Linked to original sources
arXiv2002

Langevin dynamics of the Coulomb frustrated ferromagnet: a mode-coupling analysis

We study the Langevin dynamics of the soft-spin, continuum version of the Coulomb frustrated Ising ferromagnet. By using the dynamical mode-coupling approximation, supplemented by reasonable approximations for describing the equilibrium static correlation function, and the somewhat improved dynamical self-consistent screening approximation, we find that the system displays a transition from an ergodic to a non-ergodic behavior. This transition is similar to that obtained in the idealized mode-coupling theory of glassforming liquids and in the mean-field generalized spin glasses with one-step replica symmetry breaking. The significance of this result and the relation to the appearance of a complex free-energy landscape are also discussed.

cond-mat.dis-nn↗
arXiv2002

Locally Preferred Structure and Frustration in Glassforming Liquids: A Clue to Polyamorphism?

We propose that the concept of liquids characterized by a given locally preferred structure (LPS) could help in understanding the observed phenomenon of polyamorphism. ``True polyamorphism'' would involve the competition between two (or more) distinct LPS, one favored at low pressure because of its low energy and one favored at high pressure because of its small specific volume, as in tetrahedrally coordinated systems. ``Apparent polyamorphism'' could be associated with the existence of a poorly crystallized defect-ordered phase with a large unit cell and small crystallites, which may be illustrated by the metastable glacial phase of the fragile glassformer triphenylphosphite; the apparent polyamorphism might result from structural frustration, i. e., a competition between the tendency to extend the LPS and a global constraint that prevents tiling of the whole space by the LPS.

cond-mat.stat-mech↗
arXiv2001

Wall-Enhanced Convection in Vibrofluidized Granular Systems

An event-driven molecular dynamics simulation of inelastic hard spheres contained in a cylinder and subject to strong vibration reproduces accurately experimental results[1] for a system of vibrofluidized glass beads. In particular, we are able to obtain the velocity field and the density and temperature profiles observed experimentally. In addition, we show that the appearance of convection rolls is strongly influenced by the value of the sidewall-particle restitution coefficient. Suggestions for observing more complex convection patterns are proposed.

cond-mat.stat-mech↗
arXiv2001

Aging and response properties in the parking-lot model

An adsorption-desorption (or parking-lot) model can reproduce qualitatively the densification kinetics and other features of a weakly vibrated granular material. Here we study the the two-time correlation and response functions of the model and demonstrate that their behavior is consistent with recently observed memory effects in granular materials. Although the densification kinetics and hysteresis are robust properties, we show that the aging behavior of the adsorption-desorption model is different from other models of granular compaction. We propose an experimental test to distinguish the possible aging behaviors.

cond-mat.stat-mech↗
arXiv2001

A Monte Carlo study of the three-dimensional Coulomb frustrated Ising ferromagnet

We have investigated by Monte-Carlo simulation the phase diagram of a three-dimensional Ising model with nearest-neighbor ferromagnetic interactions and small, but long-range (Coulombic) antiferromagnetic interactions. We have developed an efficient cluster algorithm and used different lattice sizes and geometries, which allows us to obtain the main characteristics of the temperature-frustration phase diagram. Our finite-size scaling analysis confirms that the melting of the lamellar phases into the paramgnetic phase is driven first-order by the fluctuations. Transitions between ordered phases with different modulation patterns is observed in some regions of the diagram, in agreement with a recent mean-field analysis.

cond-mat.stat-mech↗
arXiv2000

Phase diagram of an Ising model with long-range frustrating interactions: a theoretical analysis

We present a theoretical study of the phase diagram of a frustrated Ising model with nearest-neighbor ferromagnetic interactions and long-range (Coulombic) antiferromagnetic interactions. For nonzero frustration, long-range ferromagnetic order is forbidden, and the ground-state of the system consists of phases characterized by periodically modulated structures. At finite temperatures, the phase diagram is calculated within the mean-field approximation. Below the transition line that separates the disordered and the ordered phases, the frustration-temperature phase diagram displays an infinite number of ``flowers'', each flower being made by an infinite number of modulated phases generated by structure combination branching processes. The specificities introduced by the long-range nature of the frustrating interaction and the limitation of the mean-field approach are finally discussed.

cond-mat.stat-mech↗
arXiv1999

The adsorption-desorption model and its application to vibrated granular materials

We investigate both analytically and by numerical simulation the kinetics of a microscopic model of hard rods adsorbing on a linear substrate, a model which is relevant for compaction of granular materials. The computer simulations use an event-driven algorithm which is particularly efficient at very long times. For a small, but finite desorption rate, the system reaches an equilibrium state very slowly, and the long-time kinetics display three successive regimes: an algebraic one where the density varies as $1/t$, a logarithmic one where the density varies as $1/\ln(t)$, followed by a terminal exponential approach. The characteristic relaxation time of the final regime, though incorrectly predicted by a mean field arguments, can be obtained with a systematic gap-distribution approach. The density fluctuations at equilibrium are also investigated, and the associated time-dependent correlation function exhibits a power law regime followed by a final exponential decay. Finally, we show that denser particle packings can be obtained by varying the desorption rate during the process.

cond-mat.stat-mech↗
arXiv1999

From Car Parking to Protein Adsorption: An Overview of Sequential Adsorption Processes

The adsorption or adhesion of large particles (proteins, colloids, cells, >...) at the liquid-solid interface plays an important role in many diverse applications. Despite the apparent complexity of the process, two features are particularly important: 1) the adsorption is often irreversible on experimental time scales and 2) the adsorption rate is limited by geometric blockage from previously adsorbed particles. A coarse-grained description that encompasses these two properties is provided by sequential adsorption models whose simplest example is the random sequential adsorption (RSA) process. In this article, we review the theoretical formalism and tools that allow the systematic study of kinetic and structural aspects of these sequential adsorption models. We also show how the reference RSA model may be generalized to account for a variety of experimental features including particle anisotropy, polydispersity, bulk diffusive transport, gravitational effects, surface-induced conformational and orientational change, desorption, and multilayer formation. In all cases, the significant theoretical results are presented and their accuracy (compared to computer simulation) and applicability (compared to experiment) are discussed.

cond-mat.stat-mech↗
arXiv1998

Sluggish Kinetics in the Parking Lot Model

We investigate, both analytically and by computer simulation, the kinetics of a microscopic model of hard rods adsorbing on a linear substrate. For a small, but finite desorption rate, the system reaches the equilibrium state very slowly, and the long-time kinetics display three successive regimes: an algebraic one where the density varies as $1/t$, a logarithmic one where the density varies as $1/ln(t)$, followed by a terminal exponential approach. A mean-field approach fails to predict the relaxation rate associated with the latter. We show that the correct answer can only be provided by using a systematic description based on a gap-distribution approach.

cond-mat.stat-mech↗
arXiv1998

Microphase Separation and modulated phases in a Coulomb frustrated Ising ferromagnet

We study a 3-dimensional Ising model in which the tendency to order due to short-range ferromagnetic interactions is frustrated by competing long-range (Coulombic) interactions. Complete ferromagnetic ordering is impossible for any nonzero value of the frustration parameter, but the system displays a variety of phases characterized by periodically modulated structures. We have performed extensive Monte-Carlo simulations which provide strong evidence that the microphase separation transition between paramagnetic and modulated phases is a fluctuation-induced first-order transition. Additional transitions to various commensurate phases may also occur when further lowering the temperature.

cond-mat.stat-mech↗