arXiv subjects

Julien Cividini

Publications and source records attributed to Julien Cividini.

7 recordsLinked to original sources

arXiv2018

Derivation of fluctuating hydrodynamics and crossover from diffusive to anomalous transport in a hard-particle gas

A recently developed non-linear fluctuating hydrodynamics theory has been quite successful in describing various features of anomalous energy transport. However the diffusion and the noise terms present in this theory are not derived from microscopic descriptions but rather added phenomenologically. We here derive these hydrodynamic equations with explicit calculation of the diffusion and noise terms in a one-dimensional model. We show that in this model the energy current scales anomalously with system size $L$ as $\sim L^{-2/3}$ in the leading order with a diffusive correction of order $\sim L^{-1}$. The crossover length $\ell_{c}$ from diffusive to anomalous transport is expressed in terms of microscopic parameters. Our theoretical predictions are verified numerically.

cond-mat.stat-mech↗

arXiv2017

Zone clearance in an infinite TASEP with a step initial condition

The TASEP is a paradigmatic model of out-of-equilibrium statistical physics, for which many quantities have been computed, either exactly or by approximate methods. In this work we study two new kinds of observables that have some relevance in biological or traffic models. They represent the probability for a given clearance zone of the lattice to be empty (for the first time) at a given time, starting from a step density profile. Exact expressions are obtained for single-time quantities, while more involved history-dependent observables are studied by Monte Carlo simulation, and partially predicted by a phenomenological approach.

cond-mat.stat-mech↗

arXiv2017

Tagged particle in single-file diffusion with arbitrary initial conditions

We compute the full probability distribution of the positions of a tagged particle exactly for given arbitrary initial positions of the particles and for general single-particle propagators. We consider the thermodynamic limit of our exact expressions in quenched and annealed settings. For a particular class of single-particle propagators, the exact formula is expressed in a simple integral form in the quenched case whereas in the annealed case, it is expressed as a simple combination of Bessel functions. In particular, we focus on the step and the power-law initial configurations. In the former case, a drift is induced even when the one-particle propagators are symmetric. On the other hand, in the later case the scaling of the cumulants of the position of the tracer becomes different than the uniform case. We provide numerical verifications of our results.

cond-mat.stat-mech↗

arXiv2015

Two dimensional outflows for cellular automata with shuffle updates

In this paper, we explore the two-dimensional behavior of cellular automata with shuffle updates. As a test case, we consider the evacuation of a square room by pedestrians modeled by a cellular automaton model with a static floor field. Shuffle updates are characterized by a variable associated to each particle and called phase, that can be interpreted as the phase in the step cycle in the frame of pedestrian flows. Here we also introduce a dynamics for these phases, in order to modify the properties of the model. We investigate in particular the crossover between low- and high-density regimes that occurs when the density of pedestrians increases, the dependency of the outflow in the strength of the floor field, and the shape of the queue in front of the exit. Eventually we discuss the relevance of these results for pedestrians.

nlin.CG↗

arXiv2015

Exact gap statistics for the random average process on a ring with a tracer

We study statistics of the gaps in Random Average Process (RAP) on a ring with particles hopping symmetrically, except one tracer particle which could be driven. These particles hop either to the left or to the right by a random fraction $η$ of the space available till next particle in the respective directions. The random fraction $η\in [0,~1)$ is chosen from a distribution $R(η)$. For non-driven tracer, when $R(η)$ satisfies a necessary and sufficient condition, the stationary joint distribution of the gaps between successive particles takes an universal form that is factorized except for a global constraint. Some interesting explicit forms of $R(η)$ are found which satisfy this condition. In case of driven tracer, the system reaches a current-carrying steady state where such factorization does not hold. Analytical progress has been made in the thermodynamic limit, where we computed the single site mass distribution inside the bulk. We have also computed the two point gap-gap correlation exactly in that limit. Numerical simulations support our analytical results.

cond-mat.stat-mech↗

arXiv2013

Diagonal patterns and chevron effect in intersecting traffic flows

We study a lattice model of two perpendicular intersecting flows of pedestrians represented by hard core particles of two types, eastbound (`$\pE$') and northbound (`$\pN$'). Each flow takes place on a strip of width $M$ so that the intersection is an $M\times M$ square lattice. In experiment and simulation there occurs on this square spontaneous formation of a diagonal pattern of alternating $\pE$ and $\pN$ particles. We show that this pattern formation may be understood in terms of a linear instability of the corresponding mean field equations. A refined investigation reveals that the pattern actually consists of chevrons rather than straight diagonals. We explain this effect as the consequence of the existence of a nonlinear mode sustained by the interaction between the two types of particles.

cond-mat.stat-mech↗

arXiv2013

Wake-mediated interaction between driven particles crossing a perpendicular flow

Diagonal or chevron patterns are known to spontaneously emerge at the intersection of two perpendicular flows of self-propelled particles, e.g. pedestrians. The instability responsible for this pattern formation has been studied in previous work in the context of a mean-field approach. Here we investigate the microscopic mechanism yielding to this pattern. We present a lattice model study of the wake created by a particle crossing a perpendicular flow and show how this wake can localize other particles traveling in the same direction as a result of an effective interaction mediated by the perpendicular flow. The use of a semi-deterministic model allows us to characterize analytically the effective interaction between two particles.

cond-mat.stat-mech↗