arXiv subjects

M. Paoluzzi

Publications and source records attributed to M. Paoluzzi.

7 recordsLinked to original sources

arXiv2019

Low-frequency excitations and their localization properties in glasses

Besides the dynamical slowing down signaled by an enormous increase of the viscosity approaching the glass transition, structural glasses show interesting anomalous thermodynamic features at low temperatures that hint at peculiar deviations from Debye's law at low enough frequencies. Theory, numerical simulations, and experiments suggest that deviation from Debye's law is due to soft-localized glassy modes that populate the low-frequency spectrum. We study the localization properties of the low-frequency modes in a three-dimensional supercooled liquid model. The density of states $D(ω)$ is computed considering the inherent structures of configurations well thermalized at parental temperatures close to the dynamical transition $T_\text d$. We observe a crossover in the probability distribution of the inverse of the participation ratio that happens approaching $T_\text d$ from high temperatures. We show that a similar crossover is observed at high parental temperature when the translational invariance of the system is explicitly broken by a random pinning field.

cond-mat.dis-nn↗

arXiv2017

Anomalous glassy dynamics in simple models of dense biological tissue

In order to understand the mechanisms for glassy dynamics in biological tissues and shed light on those in non-biological materials, we study the low-temperature disordered phase of 2D vertex-like models. Recently it has been noted that vertex models have quite unusual behavior in the zero-temperature limit, with rigidity transitions that are controlled by residual stresses and therefore exhibit very different scaling and phenomenology compared to particulate systems. Here we investigate the finite-temperature phase of two-dimensional Voronoi and Vertex models, and show that they have highly unusual, sub-Arrhenius scaling of dynamics with temperature. We connect the anomalous glassy dynamics to features of the potential energy landscape associated with zero-temperature inherent states.

cond-mat.soft↗

arXiv2015

Self-Sustained Density Oscillations of Swimming Bacteria Confined in Microchambers

We numerically study the dynamics of run-and-tumble particles confined in two chambers connected by thin channels. Two dominant dynamical behaviors emerge: (i) an oscillatory pumping state, in which particles periodically fill the two vessels and (ii) a circulating flow state, dynamically maintaining a near constant population level in the containers when connected by two channels. We demonstrate that the oscillatory behaviour arises from the combination of a narrow channel, preventing bacteria reorientation, and a density dependent motility inside the chambers.

cond-mat.soft↗

arXiv2015

First-passage time of run-and-tumble particles

We solve the problem of first-passage time for run-and-tumble particles in one dimension. Exact expression is derived for the mean first-passage time in the general case, considering external force-fields and chemotactic-fields, giving rise to space dependent swim-speed and tumble rate. Agreement between theoretical formulae and numerical simulations is obtained in the analyzed case studies -- constant and sinusoidal force fields, constant gradient chemotactic field. Reported findings can be useful to get insights into very different phenomena involving active particles, such as bacterial motion in external fields, intracellular transport, cell migration, animal foraging.

cond-mat.stat-mech↗

arXiv2014

Run-and-tumble particles in speckle fields

The random energy landscapes developed by speckle fields can be used to confine and manipulate a large number of micro-particles with a single laser beam. By means of molecular dynamics simulations, we investigate the static and dynamic properties of an active suspension of swimming bacteria embedded into speckle patterns. Looking at the correlation of the density fluctuations and the equilibrium density profiles, we observe a crossover phenomenon when the forces exerted by the speckles are equal to the bacteria's propulsion.

cond-mat.stat-mech↗

arXiv2013

Effective run-and-tumble dynamics of bacteria baths

{\it E. coli} bacteria swim in straight runs interrupted by sudden reorientation events called tumbles. The resulting random walks give rise to density fluctuations that can be derived analytically in the limit of non interacting particles or equivalently of very low concentrations. However, in situations of practical interest, the concentration of bacteria is always large enough to make interactions an important factor. Using molecular dynamics simulations, we study the dynamic structure factor of a model bacterial bath for increasing values of densities. We show that it is possible to reproduce the dynamics of density fluctuations in the system using a free run-and-tumble model with effective fitting parameters. We discuss the dependence of these parameters, e.g., the tumbling rate, tumbling time and self-propulsion velocity, on the density of the bath.

cond-mat.stat-mech↗

arXiv2010

The random Blume-Capel model on cubic lattice: first order inverse freezing in a 3D spin-glass system

We present a numerical study of the Blume-Capel model with quenched disorder in 3D. The phase diagram is characterized by spin-glass/paramagnet phase transitions of both first and second order in the thermodynamic sense. Numerical simulations are performed using the Exchange-Monte Carlo algorithm, providing clear evidence for inverse freezing. The main features at criticality and in the phase coexistence region are investigated. The whole inverse freezing transition appears to be first order. The second order transition appears to be in the same universality class of the Edwards-Anderson model. The nature of the spin-glass phase is analyzed by means of the finite size scaling behavior of the overlap distribution functions and the four-spins real-space correlation functions. Evidence for a replica symmetry breaking-like organization of states is provided.

cond-mat.dis-nn↗