14,696 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
Adsorption of Self-Assembled Rigid Rods on Two-Dimensional Lattices
Monte Carlo (MC) simulations have been carried out to study the adsorption on
square and triangular lattices of particles with two bonding sites that, by
decreasing temperature or increasing density, polymerize reversibly into chains
with a discrete number of allowed directions and, at the same time, undergo a
continuous isotropic-nematic (IN) transition. The process has been monitored by
following the behavior of the adsorption isotherms for different values of
lateral interaction energy/temperature. The numerical data were compared with
mean-field analytical predictions and exact functions for noninteracting and 1D
systems. The obtained results revealed the existence of three adsorption
regimes in temperature. (1) At high temperatures, above the critical one
characterizing the IN transition at full coverage Tc(\theta=1), the particles
are distributed at random on the surface and the adlayer behaves as a
noninteracting 2D system. (2) At very low temperatures, the asymmetric monomers
adsorb forming chains over almost the entire range of coverage, and the
adsorption process behaves as a 1D problem. (3) In the intermediate regime, the
system exhibits a mixed regime and the filling of the lattice proceeds
according to two different processes. In the first stage, the monomers adsorb
isotropically on the lattice until the IN transition occurs in the system and,
from this point, particles adsorb forming chains so that the adlayer behaves as
a 1D fluid. The two adsorption processes are present in the adsorption
isotherms, and a marked singularity can be observed that separates both
regimes. Thus, the adsorption isotherms appear as sensitive quantities with
respect to the IN phase transition, allowing us (i) to reproduce the phase
diagram of the system for square lattices and (ii) to obtain an accurate
determination of the phase diagram for triangular lattices.Comment: Langmuir, 201
The Maximum Entropy principle and the nature of fractals
We apply the Principle of Maximum Entropy to the study of a general class of
deterministic fractal sets. The scaling laws peculiar to these objects are
accounted for by means of a constraint concerning the average content of
information in those patterns. This constraint allows for a new statistical
characterization of fractal objects and fractal dimension.Comment: 7 pages, RevTex, includes 2 PS figure
Transportation of hazardous materials via pipeline. A historical overview
The transportation of hazardous materials via pipelines is often considered a safer alternative to other transportation modalities such as railway, road and ship. However, pipelines often cross industrial and highly populated areas, so that their failure can pose a significant risk to the surrounding environment and the exposed population: the possible release of flammable and/or toxic materials in such areas can generate catastrophic events with very severe consequences. A number of accidents have actually occurred in the past years, and even when no deaths or injured are reported, significant damages to the surrounding environment often occur. This suggests that, given the extremely wide extension of the network worldwide, and the very high amounts of transported materials, a careful analysis is still required. In addition, the construction of pipelines also involves the contribution of expertise from a range of technical areas. As a consequence, the occurrence of accidents and the impact of their consequences, depend on the combination of a large number of parameters. In the present paper, an analysis of data relative to pipelines transporting hazardous materials has been carried out, and the influence of specific issues connected with their type and operation, has been assessed
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