430 research outputs found
Breaking of scale-invariance symmetry in adsorption processes
Standard models of sequential adsorption are implicitly formulated in a {\em
scale invariant} form, by assuming adsorption on an infinite surface, with no
characteristic length scales. In real situations, however, involving complex
surfaces, intrinsic length scales may be relevant. We present an analytic model
of continuous random sequential adsorption, in which the scale invariance
symmetry is explicitly broken. The characteristic length is imposed by a set of
scattered obstacles, previously adsorbed onto the surface. We show, by means of
analytic solutions and numerical simulations, the profound effects of the
symmetry breaking on both the jamming limit and the correlation function of the
adsorbed layer.Comment: 7 pages, 2 eps figures, EPL style. Europhys. Lett. (in press
Dipolar interactions induced order in assemblies of magnetic particles
We discuss the appareance of ordered structures in assemblies of magnetic
particles. The phenomenon occurs when dipolar interactions and the thermal
motion of the particles compete, and is mediated by screening and excluded
volume effects. It is observed irrespective of the dimensionality of the system
and the resulting structures, which may be regular or fractal, indicate that
new ordered phases may emerge in these system when dipolar interactions play a
significant role.Comment: 7 pages, 6 EPS figures. Journal of Magnetism and Magnetic Materials
(in press
Entropy production and rectification efficiency in colloids transport along a pulsating channel
We study the current rectification of particles moving in a pulsating channel
under the in uence of an applied force. We have shown the existence of diferent
rectification scenarios in which entropic and energetic effects compete. The
effect can be quantified by means of a rectification coefficient that is
analyzed in terms of the force, the frequency and the diffusion coefficient.
The energetic cost of the motion of the particles expressed in terms of the
entropy production depends on the importance of the entropic contribution to
the total force. Rectification is more important at low values of the applied
force when entropic effects become dominant. In this regime, the entropy
production is not invariant under reversal of the applied force. The phenomenon
observed could be used to optimize transport in microfluidic devices or in
biological channels
Nonequilibrium translational effects in evaporation and condensation
This paper shows how mesoscopic nonequilibrium thermodynamics can be applied
to condensation and evaporation. By extending the normal set of thermodynamic
variables with two internal variables, we are able to give a new theoretical
foundation for a mechanism of condensation that has been proposed from
molecular simulation results. The flux does not follow a simple Arrhenius
formula for small activation energies which are relevant here.Comment: To appear in J. Chem. Phy
Stochastic population dynamics in turbulent fields
The behavior of interacting populations typically displays irregular temporal
and spatial patterns that are difficult to reconcile with an underlying
deterministic dynamics. A classical example is the heterogeneous distribution
of plankton communities, which has been observed to be patchy over a wide range
of spatial and temporal scales. Here, we use plankton communities as prototype
systems to present theoretical approaches for the analysis of the combined
effects of turbulent advection and stochastic growth in the spatiotemporal
dynamics of the population. Incorporation of these two factors into
mathematical models brings an extra level of realism to the description and
leads to better agreement with experimental data than that of previously
proposed models based on reaction-diffusion equations.Comment: 11 pages, 9 figures. Submitted to EPJ Special Topic
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