98 research outputs found
N-body decomposition of bipartite networks
In this paper, we present a method to project co-authorship networks, that
accounts in detail for the geometrical structure of scientists collaborations.
By restricting the scope to 3-body interactions, we focus on the number of
triangles in the system, and show the importance of multi-scientists (more than
2) collaborations in the social network. This motivates the introduction of
generalized networks, where basic connections are not binary, but involve
arbitrary number of components. We focus on the 3-body case, and study
numerically the percolation transition.Comment: 5 pages, submitted to PR
Strong Shock Waves and Nonequilibrium Response in a One-dimensional Gas: a Boltzmann Equation Approach
We investigate the nonequilibrium behavior of a one-dimensional binary fluid
on the basis of Boltzmann equation, using an infinitely strong shock wave as
probe. Density, velocity and temperature profiles are obtained as a function of
the mixture mass ratio \mu. We show that temperature overshoots near the shock
layer, and that heavy particles are denser, slower and cooler than light
particles in the strong nonequilibrium region around the shock. The shock width
w(\mu), which characterizes the size of this region, decreases as w(\mu) ~
\mu^{1/3} for \mu-->0. In this limit, two very different length scales control
the fluid structure, with heavy particles equilibrating much faster than light
ones. Hydrodynamic fields relax exponentially toward equilibrium, \phi(x) ~
exp[-x/\lambda]. The scale separation is also apparent here, with two typical
scales, \lambda_1 and \lambda_2, such that \lambda_1 ~ \mu^{1/2} as \mu-->0$,
while \lambda_2, which is the slow scale controlling the fluid's asymptotic
relaxation, increases to a constant value in this limit. These results are
discussed at the light of recent numerical studies on the nonequilibrium
behavior of similar 1d binary fluids.Comment: 9 pages, 8 figs, published versio
Singular forces and point-like colloids in lattice Boltzmann hydrodynamics
We present a second-order accurate method to include arbitrary distributions
of force densities in the lattice Boltzmann formulation of hydrodynamics. Our
method may be used to represent singular force densities arising either from
momentum-conserving internal forces or from external forces which do not
conserve momentum. We validate our method with several examples involving point
forces and find excellent agreement with analytical results. A minimal model
for dilute sedimenting particles is presented using the method which promises a
substantial gain in computational efficiency.Comment: 22 pages, 9 figures. Submitted to Phys. Rev.
Coupling of thermal and mass diffusion in regular binary thermal lattice-gases
We have constructed a regular binary thermal lattice-gas in which the thermal
diffusion and mass diffusion are coupled and form two nonpropagating diffusive
modes. The power spectrum is shown to be similar in structure as for the one in
real fluids, in which the central peak becomes a combination of coupled entropy
and concentration contributions. Our theoretical findings for the power spectra
are confirmed by computer simulations performed on this model.Comment: 5 pages including 3 figures in RevTex
Field induced stationary state for an accelerated tracer in a bath
Our interest goes to the behavior of a tracer particle, accelerated by a
constant and uniform external field, when the energy injected by the field is
redistributed through collision to a bath of unaccelerated particles. A non
equilibrium steady state is thereby reached. Solutions of a generalized
Boltzmann-Lorentz equation are analyzed analytically, in a versatile framework
that embeds the majority of tracer-bath interactions discussed in the
literature. These results --mostly derived for a one dimensional system-- are
successfully confronted to those of three independent numerical simulation
methods: a direct iterative solution, Gillespie algorithm, and the Direct
Simulation Monte Carlo technique. We work out the diffusion properties as well
as the velocity tails: large v, and either large -v, or v in the vicinity of
its lower cutoff whenever the velocity distribution is bounded from below.
Particular emphasis is put on the cold bath limit, with scatterers at rest,
which plays a special role in our model.Comment: 20 pages, 6 figures v3:minor corrections in sec.III and added
reference
Generalized dynamical density functional theory for classical fluids and the significance of inertia and hydrodynamic interactions
We study the dynamics of a colloidal fluid including inertia and hydrodynamic
interactions, two effects which strongly influence the non-equilibrium
properties of the system. We derive a general dynamical density functional
theory (DDFT) which shows very good agreement with full Langevin dynamics. In
suitable limits, we recover existing DDFTs and a Navier-Stokes-like equation
with additional non-local terms.Comment: 5 pages, 4 figures, 4 supplementary movie files, I supplementary pd
On the velocity distributions of the one-dimensional inelastic gas
We consider the single-particle velocity distribution of a one-dimensional
fluid of inelastic particles. Both the freely evolving (cooling) system and the
non-equilibrium stationary state obtained in the presence of random forcing are
investigated, and special emphasis is paid to the small inelasticity limit. The
results are obtained from analytical arguments applied to the Boltzmann
equation along with three complementary numerical techniques (Molecular
Dynamics, Direct Monte Carlo Simulation Methods and iterative solutions of
integro-differential kinetic equations). For the freely cooling fluid, we
investigate in detail the scaling properties of the bimodal velocity
distribution emerging close to elasticity and calculate the scaling function
associated with the distribution function. In the heated steady state, we find
that, depending on the inelasticity, the distribution function may display two
different stretched exponential tails at large velocities. The inelasticity
dependence of the crossover velocity is determined and it is found that the
extremely high velocity tail may not be observable at ``experimentally
relevant'' inelasticities.Comment: Latex, 14 pages, 12 eps figure
Kinetics and scaling in ballistic annihilation
We study the simplest irreversible ballistically-controlled reaction, whereby
particles having an initial continuous velocity distribution annihilate upon
colliding. In the framework of the Boltzmann equation, expressions for the
exponents characterizing the density and typical velocity decay are explicitly
worked out in arbitrary dimension. These predictions are in excellent agreement
with the complementary results of extensive Monte Carlo and Molecular Dynamics
simulations. We finally discuss the definition of universality classes indexed
by a continuous parameter for this far from equilibrium dynamics with no
conservation laws
Kinetic Theory of Response Functions for the Hard Sphere Granular Fluid
The response functions for small spatial perturbations of a homogeneous
granular fluid have been described recently. In appropriate dimensionless
variables, they have the form of stationary state time correlation functions.
Here, these functions are expressed in terms of reduced single particle
functions that are expected to obey a linear kinetic equation. The functional
assumption required for such a kinetic equation, and a Markov approximation for
its implementation are discussed. If, in addition, static velocity correlations
are neglected, a granular fluid version of the linearized Enskog kinetic theory
is obtained. The derivation makes no a priori limitation on the density, space
and time scale, nor degree of inelasticity. As an illustration, recently
derived Helfand and Green-Kubo expressions for the Navier-Stokes order
transport coefficients are evaluated with this kinetic theory. The results are
in agreement with those obtained from the Chapman-Enskog solution to the
nonlinear Enskog kinetic equation.Comment: Submitted to J. Stat. Mec
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