4,383 research outputs found
Tachyonic Quintessential Inflation
We study the possibility to construct an observationally viable scenario
where both early Inflation and the recently detected accelerated expansion of
the universe can be explained by using a single scalar field associated with
the Tachyon. The Reheating phase becomes crucial to enable us to have a
consistent cosmology and also to get a second accelerated expansion period. A
discussion using an exponential potential is presented.Comment: 5 pages, Revtex4. Added some references. To be published in Physical
Review
Percolation study for the capillary ascent of a liquid through a granular soil
Capillary rise plays a crucial role in the construction of road embankments
in flood zones, where hydrophobic compounds are added to the soil to suppress
the rising of water and avoid possible damage of the pavement. Water rises
through liquid bridges, menisci and trimers, whose width and connectivity
depends on the maximal half-length {\lambda} of the capillary bridges among
grains. Low {\lambda} generate a disconnect structure, with small clusters
everywhere. On the contrary, for high {\lambda}, create a percolating cluster
of trimers and enclosed volumes that form a natural path for capillary rise.
Hereby, we study the percolation transition of this geometric structure as a
function of {\lambda} on a granular media of monodisperse spheres in a random
close packing. We determine both the percolating threshold {\lambda}_{c} =
(0.049 \pm 0.004)R (with R the radius of the granular spheres), and the
critical exponent of the correlation length {\nu} = (0.830 \pm 0.051),
suggesting that the percolation transition falls into the universality class of
ordinary percolation
Effect of support redox character on catalytic performance in the gas phase hydrogenation of benzaldehyde and nitrobenzene over supported gold
The authors are grateful to Dr. N. Perret for her involvement in this work. EPSRC support for free access to the TEM facility at the University of St. Andrews and financial support to Dr. M. Li and Dr. X. Wang through the Overseas Research Students Award Scheme (ORSAS) are also acknowledged.Peer reviewedPostprin
R^2-corrections to Chaotic Inflation
Scalar density cosmological perturbations, spectral indices and reheating in
a chaotic inflationary universe model, in which a higher derivative term is
added, are investigated. This term is supposed to play an important role in the
early evolution of the Universe, specifically at times closer to the Planck
era.Comment: 14 pages, accepted for publication in MPL
Contact forces distribution for a granular material from a Monte Carlo study on a single grain
The force network ensemble is one of the most promising statistical
descriptions of granular media, with an entropy accounting for all force
configurations at mechanical equilibrium consistent with some external stress.
It is possible to define a temperature-like parameter, the angoricity
{\alpha}^{-1}, which under isotropic compression is a scalar variable. This
ensemble is frequently studied on whole packings of grains; however, previous
works have shown that spatial correlations can be neglected in many cases,
opening the door to studies on a single grain. Our work develops a Monte Carlo
method to sample the force ensemble on a single grain at constant angoricity on
two and three-dimensional mono-disperse granular systems, both with or without
static friction. The results show that, despite the steric exclusions and the
constrictions of Coulomb's limit and repulsive normal forces, the pressure per
grain always show a gamma distribution with scale parameter {\nu} =
{\alpha}^{-1} and shape parameter k close to k', the number of degrees of
freedom in the system. Moreover, the average pressure per grain fulfills an
equipartition theorem =k'{\alpha}^{-1} in all cases (in close parallelism
with the one for an ideal gas). These results suggest the existence of k'
independent random variables (i.e. elementary forces) with identical
exponential distributions as the basic elements for describing the force
network ensemble at low angoricities under isotropic compression, in analogy
with the volume ensemble of granular materials
The Higgs decay rate to two photons in a model with two fermiophobic-Higgs doublets
We consider a three Higgs doublet model with an symmetry in which
beside the SM-like doublet there are two fermiophobic doublets. Due to the new
charged scalars there is an enhancement in the two-photon decay while the other
channels have the same decay widths that the SM neutral Higgs. The fermiophobic
scalars are mass degenerated unless soft terms breaking the symmetry are
added.Comment: typos were corrected, the figures have been modified and the
conclusions were increased. Still contains 15 pages, 2 figure
Aprendizaje basado en problemas y en comparación de soluciones en un contexto semipresencial
Este trabajo propone un método de evaluación
continua, no presencial e implementable a través
de entornos de aprendizaje en línea. En una
primera fase, el profesor propone un problema y
define una fecha de entrega, antes de la cual los
alumnos deberán enviar sus soluciones (resultado
A). Cumplido este plazo, el profesor publica una
solución correcta. En una segunda fase, los
alumnos comparan sus soluciones con la del
profesor, y elaboran un informe de autoevaluación
(resultado B). De la entrega A se evalúa corrección
y optimalidad, mientras que de B se valora la
capacidad del alumno para realizar un análisis
crítico de los errores y singularidades de su
solución. Como evaluación global del ejercicio se
propone una media ponderada de las notas de
ambos resultados, A y B.SUMMARY -- This paper proposes a method of continuous
assessment that can be implemented through
online learning environments. In a first phase, the
teacher poses a problem and sets a deadline for
students to submit their individual solutions
(outcome A), after which a correct solution is
published. In a second phase, students will
compare their solutions with that of the teacher,
and write a self-assessment report (outcome B).
The outcome A is evaluated based on its
correctness and optimality, while B is assessed
considering students' ability to detect their errors
and to make a reasoned defense of their solutions.
The overall evaluation is intended as a weighted
average of the notes of both deliverables, A and B.Peer Reviewe
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