310 research outputs found
Kinetics of Fragmenting Freely Evolving Granular Gases
We investigate the effect of fragmentation on the homogeneous free cooling of
inelastic hard spheres, using Boltzmann kinetic theory and Direct Monte Carlo
simulations. We analyze in detail a model where dissipative collisions may
subsequently lead to a break-up of the grains. With a given probability, two
off-springs are then created from one of the two colliding partners, with
conservation of mass, momentum and kinetic energy. We observe a scaling regime
characterized by a single collisional average, that quantifies the deviations
from Gaussian behaviour for the joint size and velocity distribution function.
We also discuss the possibility of a catastrophe whereby the number of
particles diverges in a finite time. This phenomenon appears correlated to a
``shattering'' transition marked by a delta singularity at vanishingly small
grains for the rescaled size distribution.Comment: 22 pages, 8 figure
Discrete solution of the electrokinetic equations
We present a robust scheme for solving the electrokinetic equations. This
goal is achieved by combining the lattice-Boltzmann method (LB) with a discrete
solution of the convection-diffusion equation for the different charged and
neutral species that compose the fluid. The method is based on identifying the
elementary fluxes between nodes, which ensures the absence of spurious fluxes
in equilibrium. We show how the model is suitable to study electro-osmotic
flows. As an illustration, we show that, by introducing appropriate dynamic
rules in the presence of solid interfaces, we can compute the sedimentation
velocity (and hence the sedimentation potential) of a charged sphere. Our
approach does not assume linearization of the Poisson-Boltzmann equation and
allows us for a wide variation of the Peclet number.Comment: 24 pages, 7 figure
Geometrically-tuned channel permeability
We characterize the motion of charged as well as neutral tracers, in an
electrolyte embedded in a varying section channel. We exploit a set of
systematic approximations that allows us to simplify the problem, yet capturing
the essential of the interplay between the geometrical confinement provided by
the corrugated channel walls and the electrolyte properties. Our simplified
approach allows us to characterize the transport properties of corrugated
channels when a net flux of tracers is obtained by keeping the extrema of the
channel at different chemical potentials. For highly diluted tracer
suspensions, we have characterized tracers currents and we have estimated the
net electric current which occurs when both positively and negatively charged
tracers are considered.Comment: Fixed reference
Synchronization in dynamical networks of locally coupled self-propelled oscillators
Systems of mobile physical entities exchanging information with their
neighborhood can be found in many different situations. The understanding of
their emergent cooperative behaviour has become an important issue across
disciplines, requiring a general conceptual framework in order to harvest the
potential of these systems. We study the synchronization of coupled oscillators
in time-evolving networks defined by the positions of self-propelled agents
interacting in real space. In order to understand the impact of mobility in the
synchronization process on general grounds, we introduce a simple model of
self-propelled hard disks performing persistent random walks in 2 space and
carrying an internal Kuramoto phase oscillator. For non-interacting particles,
self-propulsion accelerates synchronization. The competition between agent
mobility and excluded volume interactions gives rise to a richer scenario,
leading to an optimal self-propulsion speed. We identify two extreme dynamic
regimes where synchronization can be understood from theoretical
considerations. A systematic analysis of our model quantifies the departure
from the latter ideal situations and characterizes the different mechanisms
leading the evolution of the system. We show that the synchronization of
locally coupled mobile oscillators generically proceeds through coarsening
verifying dynamic scaling and sharing strong similarities with the phase
ordering dynamics of the 2 XY model following a quench. Our results shed
light into the generic mechanisms leading the synchronization of mobile agents,
providing a efficient way to understand more complex or specific situations
involving time-dependent networks where synchronization, mobility and excluded
volume are at play
Velocity alignment promotes motility-induced phase separation
We study the phase behavior of polar Active Brownian Particles moving in
two-spatial dimensions and interacting through volume exclusion and velocity
alignment. We combine particle-based simulations of the microscopic model with
a simple mean-field kinetic model to understand the impact of velocity
alignment on the motility-induced phase separation of self-propelled disks. We
show that, as the alignment strength is increased, approaching the onset of
collective motion from below, orientational correlations grow, rendering the
diffusive reorientation dynamics slower. As a consequence, the tendency of
particles to aggregate into isotropic clusters is enhanced, favoring the
complete de-mixing of the system into a low and high-density phase.Comment: 7 pages, 5 figure
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