Papers by Annalisa Fierro
New Kinds of Phase Transitions: Transformations in Disordered Substances, 2002
Encyclopedia of Complexity and Systems Science, 2009
In the framework of schematic hard spheres lattice models we discuss Edwards' Statistical Mechani... more In the framework of schematic hard spheres lattice models we discuss Edwards' Statistical Mechanics approach to granular media. As this approach appears to hold here to a very good approximation, by analytical calculations of Edwards' partition function at a mean field level we derive the system phase diagram and show that ``jamming'' corresponds to a phase transition from a ``fluid'' to a ``glassy'' phase, observed when crystallization is avoided. The nature of such a ``glassy'' phase turns out to be the same found in mean field models for glass formers. In the same context, we also briefly discuss mixing/segregation phenomena of binary mixtures: the presence of fluid-crystal phase transitions drives segregation as a form of phase separation and, within a given phase, gravity can also induce a kind of ``vertical'' segregation, usually not associated to phase transitions.
The European Physical Journal E Soft Matter, Feb 1, 2011
We construct a very simple epidemic model for influenza spreading in an age-class-distributed pop... more We construct a very simple epidemic model for influenza spreading in an age-class-distributed population, by coupling a lattice gas model for the population dynamics with a SIR stochastic model for susceptible, infected and removed/immune individuals. We use as a test case the age-distributed Italian epidemiological data for the novel influenza A(H1N1). The most valuable features of this model are its country-independent and virus-independent structure (few demographic, social and virological data are used to fix some parameters), its large statistic due to a very short run-time machine, and its easy generalizability to include mitigation strategies. In spite of its simplicity, the model presented reproduces the epidemiological Italian data, with sensible predictions for the reproduction number and theoretically interesting results for the generation time distribution.
We discuss mixing/segregation phenomena in a schematic hard spheres lattice model for binary mixt... more We discuss mixing/segregation phenomena in a schematic hard spheres lattice model for binary mixtures of granular media, by analytical evaluation, within Bethe-Peierls approximation, of Edwards' partition function. The presence of fluid-crystal phase transitions in the system drives segregation as a form of phase separation. Within a pure phase, gravity can also induce a kind of vertical segregation not associated to phase transitions.
The structural arrest of a polymeric suspension might be driven by an increase of the cross-linke... more The structural arrest of a polymeric suspension might be driven by an increase of the cross-linker concentration, which drives the gel transition, as well as by an increase of the polymer density, which induces a glass transition. These dynamical continuous (gel) and discontinuous (glass) transitions might interfere, since the glass transition might occur within the gel phase, and the gel transition might be induced in a polymer suspension with glassy features. Here we study the interplay of these transitions by investigating via event-driven molecular dynamics simulation the relaxation dynamics of a polymeric suspension as a function of the cross-linker concentration and the monomer volume fraction. We show that the slow dynamics within the gel phase is characterized by a long sub-diffusive regime, which is due both to the crowding as well as to the presence of a percolating cluster. In this regime, the transition of structural arrest is found to occur either along the gel or along the glass line, depending on the length scale at which the dynamics is probed. Where the two lines meet there is no apparent sign of higher order dynamical singularity. Logarithmic behavior typical of A 3 singularity appears inside the gel phase along the glass transition line. These findings seem to be related to the results of the mode coupling theory for the F 13 schematic model.
We discuss some recent results on Statistical Mechanics approach to dense granular media. In part... more We discuss some recent results on Statistical Mechanics approach to dense granular media. In particular, by analytical mean field investigation we derive the phase diagram of monodisperse and bydisperse granular assemblies. We show that "jamming" corresponds to a phase ...
EPL (Europhysics Letters)
We study segregation patterns in a hard sphere binary model under gravity subject to sequences of... more We study segregation patterns in a hard sphere binary model under gravity subject to sequences of taps. We discuss the appearance of the "Brazil nut" effect (where large particles move up) and the "reverse Brazil nut" effects in the stationary states reached by "tap" dynamics. In particular, we show that the stationary state depends only on two thermodynamical quantities: the gravitational energy of the first and of the second species and not on the sample history. To describe the properties of the system, we generalize Edwards' approach by introducing a canonical distribution characterized by two configurational temperatures, conjugate to the energies of the two species. This is supported by Monte Carlo calculations showing that the average of several quantities over the tap dynamics and over such distribution coincide. The segregation problem can then be understood as an equilibrium statistical mechanics problem with two control parameters.
Complexity, Metastability and Nonextensivity - 31st Workshop of the International School of Solid State Physics, 2005
We discuss some recent results on Statistical Mechanics approach to dense granular media. In part... more We discuss some recent results on Statistical Mechanics approach to dense granular media. In particular, by analytical mean field investigation we derive the phase diagram of monodisperse and bydisperse granular assemblies. We show that "jamming" corresponds to a phase transition from a "fluid" to a "glassy" phase, observed when crystallization is avoided. The nature of such a "glassy" phase turns
Physica A: Statistical Mechanics and its Applications, 2001
We review the results of a statistical mechanics approach to granular materials and its extension... more We review the results of a statistical mechanics approach to granular materials and its extension to non-thermal systems in their "inherent states". We introduce a "tapping" dynamics, based on a dynamics used for real granular matter, which allows to visit the space of the inherent states. It is assumed that under stationarity or quasi-stationarity the distribution among the inherent states satisÿes the principle of maximum entropy. This leads to a distribution characterised by a conÿgurational temperature related to Edwards compactivity. The prediction from such an approach are checked on a standard Hamiltonian lattice model and, in the present unifying framework, it is possible to explain a variety of properties of granular materials, ranging from their logarithmic compaction to typical "memory" phenomena. c 2001 Published by Elsevier Science B.V.
Lecture Notes in Physics, 2006
We review some recent results on Statistical Mechanics approach to dense granular media. In parti... more We review some recent results on Statistical Mechanics approach to dense granular media. In particular, by analytical mean field investigation we derive the phase diagram of a monodisperse system. We show that "jamming" corresponds to a phase transition from a "fluid" to a "glassy" phase. The nature of such a "glassy" phase turns out to be the same found in mean field models for glass formers. This gives quantitative evidence to the idea of a unified description of the "jamming" transition in granular media and thermal systems, such as glasses.
The European Physical Journal Special Topics, 2014
ABSTRACT A long standing problem in glassy dynamics is the geometrical interpretation of clusters... more ABSTRACT A long standing problem in glassy dynamics is the geometrical interpretation of clusters and the role they play in the observed scaling laws. In this context, the mode-coupling theory (MCT) of type-A transition and the sol-gel transition are both characterized by a structural arrest to a disordered state in which the long-time limit of the correlator continuously approaches zero at the transition point. In this paper, we describe a cluster approach to the sol-gel transition and explore its predictions, including universal scaling laws and a new stretched relaxation regime close to criticality. We show that while MCT consistently describes gelation at mean-field level, the percolation approach elucidates the geometrical character underlying MCT scaling laws.
The Journal of Physical Chemistry B, 2011
We study the dynamical behavior in chemical gelation, as the gelation threshold is approached fro... more We study the dynamical behavior in chemical gelation, as the gelation threshold is approached from the sol phase. On the basis of the heterogeneous diffusion due to the cluster size distribution, as expected by the percolation theory, we predict the long time decay of the self-overlap as a power law in time t(-3/2). Moreover, under the hypothesis that the cluster diffusion coefficient decreases in size as a power law, s(-x), the fluctuation of the self-overlap, χ(4)(t), exhibits growth at short time as t((3-τ)/x), where τ is the cluster size distribution critical exponent. At longer times, χ(4)(t) decays as t(-3/2) while, at intermediate times, it reaches a maximum at time t*, which scales as s*(x), where s* is the size of the critical cluster. Finally, the value of the maximum χ(4)(t*) scales as the mean cluster size. The theoretical predictions are in agreement with molecular dynamic calculations in a model system, where spherical monomers are bonded by a finite extendable nonlinear elastic (FENE) potential.
Physical Review E, 2000
In this paper we study the 3d frustrated lattice gas model in the annealed version, where the dis... more In this paper we study the 3d frustrated lattice gas model in the annealed version, where the disorder is allowed to evolve in time with a suitable kinetic constraint. Although the model does not exhibit any thermodynamic transition it shows a diverging peak at some characteristic time in the dynamical non-linear susceptibility, similar to the results on the pspin model in mean field and Lennard-Jones mixture recently found by ]. Comparing these results to those obtained in the model with quenched interactions, we conclude that the critical behavior of the dynamical susceptibility is reminiscent of the thermodynamic transition present in the quenched model, and signaled by the divergence of the static non-linear susceptibility, suggesting therefore a similar mechanism also in supercooled glassforming liquids.
... Author(s): MASSIMO PICA CIAMARRA CNISM, Second University of Naples, 81031 Aversa (CE), Italy... more ... Author(s): MASSIMO PICA CIAMARRA CNISM, Second University of Naples, 81031 Aversa (CE), Italy ANTONIO DE CANDIA Dip. ... di Scienze Fisiche and Coherentia, Universitá di Napoli Federico II, via Cintia, 80129, Napoli, Italy MARIO NICODEMI Complexity Science Centre ...
Physical Review E, 2006
In colloidal suspensions, at low volume fraction and temperature, dynamical arrest occurs via the... more In colloidal suspensions, at low volume fraction and temperature, dynamical arrest occurs via the growth of elongated structures, that aggregate to form a connected network at gelation. Here we show that, in the region of parameter space where gelation occurs, the stable thermodynamical phase is a crystalline columnar one. Near and above the gelation threshold, the disordered spanning network slowly evolves and finally orders to form the crystalline structure. At higher volume fractions the stable phase is a lamellar one, that seems to have a still longer ordering time.
The Journal of Physical Chemistry B, 2011
We study the dynamical properties of a model for charged colloidal particles, performing molecula... more We study the dynamical properties of a model for charged colloidal particles, performing molecular dynamics simulations and observing the behavior of bond persistence functions, self-intermediate scattering functions at different wave vectors, and mean-square displacements of the particles, in three different regimes of the volume fraction. At the lowest volume fraction the system displays properties very similar to those of a gelling system, which can be interpreted in terms of the distribution of cluster sizes, with a peak in the dynamical susceptibility at the lowest wave vector. At the highest volume fraction, a percolating network of bonds is always present, and the system is strongly reminiscent of strong glasses, with the maximum in the dynamical susceptibility increasing when the temperature is lowered, and an Arrhenius dependence of the relaxation times. At intermediate volume fractions, a complex behavior is found, where both the distribution of cluster sizes and the intercluster correlations due to crowding are important.
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Papers by Annalisa Fierro