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Francesco Ginelli

Publications and source records attributed to Francesco Ginelli.

42 records · Page 3Linked to original sources
arXiv2007

Collective motion of self-propelled particles interacting without cohesion

We present a comprehensive study of Vicsek-style self-propelled particle models in two and three space dimensions. The onset of collective motion in such stochastic models with only local alignment interactions is studied in detail and shown to be discontinuous (first-order like). The properties of the ordered, collectively moving phase are investigated. In a large domain of parameter space including the transition region, well-defined high-density and high-order propagating solitary structures are shown to dominate the dynamics. Far enough from the transition region, on the other hand, these objects are not present. A statistically-homogeneous ordered phase is then observed, which is characterized by anomalously-strong density fluctuations, superdiffusion, and strong intermittency.

cond-mat.stat-mech↗
arXiv2006

From synchronization to Lyapunov exponents and back

The goal of this paper is twofold. In the first part we discuss a general approach to determine Lyapunov exponents from ensemble- rather than time-averages. The approach passes through the identification of locally stable and unstable manifolds (the Lyapunov vectors), thereby revealing an analogy with generalized synchronization. The method is then applied to a periodically forced chaotic oscillator to show that the modulus of the Lyapunov exponent associated to the phase dynamics increases quadratically with the coupling strength and it is therefore different from zero already below the onset of phase-synchronization. The analytical calculations are carried out for a model, the generalized special flow, that we construct as a simplified version of the periodically forced Rossler oscillator.

nlin.CD↗
arXiv2006

Nonequilibrium wetting of finite samples

As a canonical model for wetting far from thermal equilibrium we study a Kardar-Parisi-Zhang interface growing on top of a hard-core substrate. Depending on the average growth velocity the model exhibits a non-equilibrium wetting transition which is characterized by an additional surface critical exponent theta. Simulating the single-step model in one spatial dimension we provide accurate numerical estimates for theta and investigate the distribution of contact points between the substrate and the interface as a function of time. Moreover, we study the influence of finite-size effects, in particular the time needed until a finite substrate is completely covered by the wetting layer for the first time.

cond-mat.stat-mech↗
arXiv2006

Minimal model for active nematics: quasi-long-range order and giant fluctuations

We propose a minimal microscopic model for active nematic particles similar in spirit to the Vicsek model for self-propelled polar particles. In two dimensions, we show that this model exhibits a Kosterlitz-Thouless-like transition to quasi-long-range orientational order and that in this non-equilibrium context, the ordered phase is characterized by giant density fluctuations, in agreement with the predictions of Ramaswamy {\it et al.} [Europhys. Lett. {\bf 62}, 196 (2003)].

cond-mat.stat-mech↗
arXiv2004

Mean field theory for skewed height profiles in KPZ growth processes

We propose a mean field theory for interfaces growing according to the Kardar-Parisi-Zhang (KPZ) equation in 1+1 dimensions. The mean field equations are formulated in terms of densities at different heights, taking surface tension and the influence of the nonlinear term in the KPZ equation into account. Although spatial correlations are neglected, the mean field equations still reflect the spatial dimensionality of the system. In the special case of Edwards-Wilkinson growth,our mean field theory correctly reproduces all features. In the presence of a nonlinear term one observes a crossover to a KPZ-like behavior with the correct dynamical exponent $z=3/2$. In particular we compute the skewed interface profile during roughening, and we study the influence of a co-moving reflecting wall, which has been discussed recently in the context of nonequilibrium wetting and synchronization transitions. Also here the mean field approximation reproduces all qualitative features of the full KPZ equation, although with different values of the surface exponents.

cond-mat.stat-mech↗