13,904 research outputs found
Bulk viscosity, interaction and the viability of phantom solutions
We study the dynamics of a bulk viscosity model in the Eckart approach for a
spatially flat Friedmann-Robertson-Walker (FRW) universe. We have included
radiation and dark energy, assumed as perfect fluids, and dark matter treated
as an imperfect fluid having bulk viscosity. We also introduce an interaction
term between the dark matter and dark energy components. Considering that the
bulk viscosity is proportional to the dark matter energy density and imposing a
complete cosmological dynamics, we find bounds on the bulk viscosity in order
to reproduce a matter-dominated era (MDE). This constraint is independent of
the interaction term. Some late time phantom solutions are mathematically
possible. However, the constraint imposed by a MDE restricts the interaction
parameter, in the phantom solutions, to a region consistent with a null value,
eliminating the possibility of late time stable solutions with . From the
different cases that we study, the only possible scenario, with bulk viscosity
and interaction term, belongs to the quintessence region. In this latter case,
we find bounds on the interaction parameter compatible with latest
observational data.Comment: 8 pages, 5 figure
Wetting Transitions Displayed by Persistent Active Particles
A lattice model for active matter is studied numerically, showing that it
displays wettings transitions between three distinctive phases when in contact
with an impenetrable wall. The particles in the model move persistently,
tumbling with a small rate , and interact via exclusion volume only.
When increasing the tumbling rates , the system transits from total
wetting to partial wetting and unwetting phases. In the first phase, a wetting
film covers the wall, with increasing heights when is reduced. The
second phase is characterized by wetting droplets on the wall with a periodic
spacing between them. Finally, the wall dries with few particles in contact
with it. These phases present nonequilibrium transitions. The first transition,
from partial to total wetting, is continuous and the fraction of dry sites
vanishes continuously when decreasing the tumbling rate . For the
second transition, from partial wetting to dry, the mean droplet distance
diverges logarithmically when approaching the critical tumbling rate, with
saturation due to finite-size effects
Implementation of a Human-Computer Interface for Computer Assisted Translation and Handwritten Text Recognition
A human-computer interface is developed to provide services of computer assisted machine translation (CAT) and computer assisted transcription of handwritten text images (CATTI). The back-end machine translation (MT) and handwritten text recognition (HTR) systems are provided by the Pattern Recognition and Human Language Technology (PRHLT) research group. The idea is to provide users with easy to use tools to convert interactive translation and transcription feasible tasks. The assisted service is provided by remote servers with CAT or CATTI capabilities. The interface supplies the user with tools for efficient local edition: deletion, insertion and substitution.Ocampo Sepúlveda, JC. (2009). Implementation of a Human-Computer Interface for Computer Assisted Translation and Handwritten Text Recognition. http://hdl.handle.net/10251/14318Archivo delegad
Regional trends and controlling factors of fatal landslides in Latin America and the Caribbean
A new data set of landslides that caused loss of life in Latin America and the
Caribbean in the 10-year period from 2004 and 2013 inclusive has been
compiled, providing new insight into the impact of landslides in this key
part of the world. This data set indicates that in the 10-year period a total
of 11 631 people lost their lives across the region in 611 landslides. The
geographical distribution of the landslides is highly heterogeneous, with
areas of high incidence in parts of the Caribbean (most notably Haiti),
Central America, Colombia, and southeast Brazil. There is significant interannual
variation in the number of landslides, with the El Niño/La Niña cycle
emerging as a key control. Our analysis suggests that on a continental scale
the mapped factors that best explain the observed distribution are
topography, annual precipitation and population density. On a national basis
we have compared the occurrence of fatality-inducing landslide occurrence
with the production of locally authored research articles, demonstrating that
there is a landslide research deficit in Latin America and the Caribbean.
Understanding better the mechanisms, distribution causes and triggers of
landslides in Latin America and the Caribbean must be an essential first step
towards managing the hazard
On bounded-type thin local sets of the two-dimensional Gaussian free field
We study certain classes of local sets of the two-dimensional Gaussian free
field (GFF) in a simply-connected domain, and their relation to the conformal
loop ensemble CLE(4) and its variants. More specifically, we consider
bounded-type thin local sets (BTLS), where thin means that the local set is
small in size, and bounded-type means that the harmonic function describing the
mean value of the field away from the local set is bounded by some
deterministic constant. We show that a local set is a BTLS if and only if it is
contained in some nested version of the CLE(4) carpet, and prove that all BTLS
are necessarily connected to the boundary of the domain. We also construct all
possible BTLS for which the corresponding harmonic function takes only two
prescribed values and show that all these sets (and this includes the case of
CLE(4)) are in fact measurable functions of the GFF.Comment: 24 pages, to appear in J. Inst. Math. Jussie
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