1,680 research outputs found
Naturalness and stability of the generalized Chaplygin gas in the seesaw cosmon scenario
The seesaw mechanism is conceived on the basis that a mass scale, , and
a dimensionless scale, , can be fine-tuned in order to control the dynamics
of active and sterile neutrinos through cosmon-type equations of motion: the
seesaw cosmon equations. This allows for sterile neutrinos to be a dark matter
candidate. In this scenario, the dynamical masses and energy densities of
active and sterile neutrinos can be consistently embedded into the generalized
Chaplygin gas (GCG), the unified dark sector model. In addition, dark matter
adiabatically coupled to dark energy allows for a natural decoupling of the
(active) mass varying neutrino (MaVaN) component from the dark sector. Thus
MaVaN's turn into a secondary effect. Through the scale parameters, and
, the proposed scenario allows for a convergence among three distinct
frameworks: the cosmon scenario, the seesaw mechanism for mass generation and
the GCG model. It is found that the equation of state of the perturbations is
the very one of the GCG background cosmology so that all the results from this
approach are maintained, being smoothly modified by active neutrinos.
Constrained by the seesaw relations, it is shown that the mass varying
mechanism is responsible for the stability against linear perturbations and is
indirectly related to the late time cosmological acceleration.Comment: 24 pages, 6 figure
Mass varying dark matter in effective GCG scenarios
A unified treatment of mass varying dark matter coupled to cosmon-{\em like}
dark energy is shown to result in {\em effective} generalized Chaplygin gas
(GCG) scenarios. The mass varying mechanism is treated as a cosmon field
inherent effect. Coupling dark matter with dark energy allows for reproducing
the conditions for the present cosmic acceleration and for recovering the
stability resulted from a positive squared speed of sound c_{s}^{\2}, as in
the GCG scenario. The scalar field mediates the nontrivial coupling between the
dark matter sector and the sector responsible for the accelerated expansion of
the universe. The equation of state of perturbations is the same as that of the
background cosmology so that all the effective results from the GCG paradigm
are maintained. Our results suggest the mass varying mechanism, when obtained
from an exactly soluble field theory, as the right responsible for the
stability issue and for the cosmic acceleration of the universe.Comment: 17 pages, 3 figure
Towards Loop Quantization of Plane Gravitational Waves
The polarized Gowdy model in terms of Ashtekar-Barbero variables is further
reduced by including the Killing equations for plane-fronted parallel
gravitational waves with parallel rays. The resulting constraint algebra,
including one constraint derived from the Killing equations in addition to the
standard ones of General Relativity, are shown to form a set of first-class
constraints. Using earlier work by Banerjee and Date the constraints are
expressed in terms of classical quantities that have an operator equivalent in
Loop Quantum Gravity, making space-times with pp-waves accessible to loop
quantization techniques.Comment: 14 page
Tailoring the frictional properties of granular media
A method of modifying the roughness of soda-lime glass spheres is presented,
with the purpose of tuning inter-particle friction. The effect of chemical
etching on the surface topography and the bulk frictional properties of grains
is systematically investigated. The surface roughness of the grains is measured
using white light interferometry and characterised by the lateral and vertical
roughness length scales. The underwater angle of repose is measured to
characterise the bulk frictional behaviour. We observe that the co-efficient of
friction depends on the vertical roughness length scale. We also demonstrate a
bulk surface roughness measurement using a carbonated soft drink.Comment: 10 pages, 17 figures, submitted to Phys. Rev.
Stereo Computation for a Single Mixture Image
This paper proposes an original problem of \emph{stereo computation from a
single mixture image}-- a challenging problem that had not been researched
before. The goal is to separate (\ie, unmix) a single mixture image into two
constitute image layers, such that the two layers form a left-right stereo
image pair, from which a valid disparity map can be recovered. This is a
severely illposed problem, from one input image one effectively aims to recover
three (\ie, left image, right image and a disparity map). In this work we give
a novel deep-learning based solution, by jointly solving the two subtasks of
image layer separation as well as stereo matching. Training our deep net is a
simple task, as it does not need to have disparity maps. Extensive experiments
demonstrate the efficacy of our method.Comment: Accepted by European Conference on Computer Vision (ECCV) 201
The Revival of the Unified Dark Energy-Dark Matter Model ?
We consider the generalized Chaplygin gas (GCG) proposal for unification of
dark energy and dark matter and show that it admits an unique decomposition
into dark energy and dark matter components once phantom-like dark energy is
excluded. Within this framework, we study structure formation and show that
difficulties associated to unphysical oscillations or blow-up in the matter
power spectrum can be circumvented. Furthermore, we show that the dominance of
dark energy is related to the time when energy density fluctuations start
deviating from the linear behaviour.Comment: 6 pages, 4 eps figures, Revtex4 style. New References are added. Some
typos are corrected. Conclusions remain the sam
Women, ethnicity and nationalisms in Latin America
Gutierrez Chong, Natividad (ed. lit.) "Women, ethnicity and nationalisms in Latin America". Aldershot : Ashgate, 2007. 235 p. ISBN
978-075-464-925-0Nationalism is a multifaceted phenomenon that has recently become a focus of redefinition through new multidisciplinary and multi-method approaches. The complex links among gender, ethnicity and nationalism, neglected for a long time in academic research, are increasingly receiving coverage in the scholarly literature. The book "Women, Ethnicity and Nationalisms in Latin America”, edited by Natividad Gutiérrez Chong, systematically explores these links in the context of Latin America, with case studies covering Argentina, Ecuador, Bolivia and Mexico. Contributions are by leading Latin American scholars from diverse academic fields who share the aim of overcoming the limitations of the Eurocentric and androcentric framework that characterizes the main approaches to nationalism
Progressive ataxia with oculo-palatal tremor and optic atrophy
The final publication is available at Springer via doi: 10.1007/s00415-013-7136-
A Graph Theoretic Approach for Object Shape Representation in Compositional Hierarchies Using a Hybrid Generative-Descriptive Model
A graph theoretic approach is proposed for object shape representation in a
hierarchical compositional architecture called Compositional Hierarchy of Parts
(CHOP). In the proposed approach, vocabulary learning is performed using a
hybrid generative-descriptive model. First, statistical relationships between
parts are learned using a Minimum Conditional Entropy Clustering algorithm.
Then, selection of descriptive parts is defined as a frequent subgraph
discovery problem, and solved using a Minimum Description Length (MDL)
principle. Finally, part compositions are constructed by compressing the
internal data representation with discovered substructures. Shape
representation and computational complexity properties of the proposed approach
and algorithms are examined using six benchmark two-dimensional shape image
datasets. Experiments show that CHOP can employ part shareability and indexing
mechanisms for fast inference of part compositions using learned shape
vocabularies. Additionally, CHOP provides better shape retrieval performance
than the state-of-the-art shape retrieval methods.Comment: Paper : 17 pages. 13th European Conference on Computer Vision (ECCV
2014), Zurich, Switzerland, September 6-12, 2014, Proceedings, Part III, pp
566-581. Supplementary material can be downloaded from
http://link.springer.com/content/esm/chp:10.1007/978-3-319-10578-9_37/file/MediaObjects/978-3-319-10578-9_37_MOESM1_ESM.pd
Cosmology as a search for overall equilibrium
In this letter we will revise the steps followed by A. Einstein when he first
wrote on cosmology from the point of view of the general theory of relativity.
We will argue that his insightful line of thought leading to the introduction
of the cosmological constant in the equations of motion has only one weakness:
The constancy of the cosmological term, or what is the same, its independence
of the matter content of the universe. Eliminating this feature, I will propose
what I see as a simple and reasonable modification of the cosmological
equations of motion. The solutions of the new cosmological equations give place
to a cosmological model that tries to approach the Einstein static solution.
This model shows very appealing features in terms of fitting current
observations.Comment: 9 pages, 1 figur
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