11,810 research outputs found
Dynamical system analysis of interacting models
We perform a dynamical system analysis of a cosmological model with linear
dependence between the vacuum density and the Hubble parameter, with
constant-rate creation of dark matter. We show that the de Sitter spacetime is
an asymptotically stable critical point, future limit of any expanding
solution. Our analysis also shows that the Minkowski spacetime is an unstable
critical point, which eventually collapses to a singularity. In this way, such
a prescription for the vacuum decay not only predicts the correct future de
Sitter limit, but also forbids the existence of a stable Minkowski universe. We
also study the effect of matter creation on the growth of structures and their
peculiar velocities, showing that it is inside the current errors of redshift
space distortions observations.Comment: 6 pages, 3 figures. A section was added with an analysis of
structures growth rate and peculiar velocities. To appear in General
Relativity and Gravitatio
On dark degeneracy and interacting models
Cosmological background observations cannot fix the dark energy equation of
state, which is related to a degeneracy in the definition of the dark sector
components. Here we show that this degeneracy can be broken at perturbation
level by imposing two observational properties on dark matter. First, dark
matter is defined as the clustering component we observe in large scale
structures. This definition is meaningful only if dark energy is unperturbed,
which is achieved if we additionally assume, as a second condition, that dark
matter is cold, i.e. non-relativistic. As a consequence, dark energy models
with equation-of-state parameter are reduced to two
observationally distinguishable classes with , equally competitive
when tested against observations. The first comprises the CDM model
with constant dark energy density. The second consists of interacting models
with an energy flux from dark energy to dark matter.Comment: Version accepted for publication in JCA
A unified time scale for quantum chaotic regimes
We present a generalised time scale for quantum chaos dynamics, motivated by
nonextensive statistical mechanics. It recovers, as particular cases, the
relaxation (Heisenberg) and the random (Ehrenfest) time scales. Moreover, we
show that the generalised time scale can also be obtained from a nonextensive
version of the Kolmogorov-Sinai entropy by considering the graininess of
quantum phase space and a generalised uncorrelation between subsets of the
phase space. Lyapunov and regular regimes for the fidelity decay are obtained
as a consequence of a nonextensive generalisation of the th point
correlation function for a uniformly distributed perturbation in the classical
limit
Schwarzites for Natural Gas Storage: A Grand-Canonical Monte Carlo Study
The 3D porous carbon-based structures called Schwarzites have been recently a
subject of renewed interest due to the possibility of being synthesized in the
near future. These structures exhibit negatively curvature topologies with
tuneable porous sizes and shapes, which make them natural candidates for
applications such as CO2 capture, gas storage and separation. Nevertheless, the
adsorption properties of these materials have not been fully investigated.
Following this motivation, we have carried out Grand-Canonical Monte Carlo
simulations to study the adsorption of small molecules such as CO2, CO, CH4, N2
and H2, in a series of Schwarzites structures. Here, we present our preliminary
results on natural gas adsorptive capacity in association with analyses of the
guest-host interaction strengths. Our results show that Schwarzites P7par,
P8bal and IWPg are the most promising structures with very high CO2 and CH4
adsorption capacity and low saturation pressure (<1bar) at ambient temperature.
The P688 is interesting for H2 storage due to its exceptional high H2
adsorption enthalpy value of -19kJ/mol
Two loops calculation in chiral perturbation theory and the unitarization program of current algebra
In this paper we compare two loop Chiral Perturbation Theory (ChPT)
calculation of pion-pion scattering with the unitarity second order correction
to the current algebra soft-pion theorem. It is shown that both methods lead to
the same analytic structure for the scattering amplitude.Comment: 13 pages, Revtex 3.0, no figures, submitted to Phys. Lett.
Network induces burst synchronisation in cat brain
The brain of mammals are divided into different cortical areas that are
anatomically connected forming larger networks which perform cognitive tasks.
The cat cerebral cortex is composed of 65 areas organised into the visual,
auditory, somatosensory-motor and frontolimbic cognitive regions. We have built
a network of networks, in which networks are connected among themselves
according to the connections observed in the cat cortical areas aiming to study
how inputs drive the synchronous behaviour in this cat brain-like network. We
show that without external perturbations it is possible to observe high level
of bursting synchronisation between neurons within almost all areas, except for
the auditory area. Bursting synchronisation appears between neurons in the
auditory region when an external perturbation is applied in another cognitive
area. This is a clear evidence that pattern formation and collective behaviour
in the brain might be a process mediated by other brain areas under
stimulation
Subcovers and codes on the curves
In this work, subcovers of the curve
are constructed, the Weierstrass semigroup at
the point is determined and the
corresponding one-point AG codes are investigated. Codes establishing new
records on the parameters with respect to the previously known ones are
discovered, and improvements on MinT tables are obtained
Fisher metric from relative entropy group
In this work we consider the Fisher metric which results from the Hessian of
the relative entropy group, that we called Fisher metric group, and we obtain
the corresponding ones to the Boltzmann-Gibbs, Tsallis, Kaniadakis and
Abe-Borges-Roditi classes. We prove that the scalar curvature of the Fisher
metric group results a multiple of the standard Fisher one, with the factor of
proportionality given by the local properties of the entropy group. For the
Tsallis class, the softening and strengthening of the scalar curvature is
illustrated with the correlated model, from which their associated indexes
for the canonical ensemble of a pair of interacting harmonic oscillators, are
obtained
Self-Dual Codes over Z_2xZ_4
Self-dual codes over are subgroups of that are equal to their orthogonal under an inner-product
that relates to the binary Hamming scheme. Three types of self-dual codes are
defined. For each type, the possible values such that there
exist a code \C\subseteq \Z_2^\alpha \times\Z_4^\beta are established.
Moreover, the construction of a \add-linear code for each type and possible
pair is given. Finally, the standard techniques of invariant
theory are applied to describe the weight enumerators for each type.Comment: Submitted to Designs, Codes and Cryptograph
Number Counts and Dynamical Vacuum Cosmologies
We study non-linear structure formation in an interacting model of the dark
sector of the Universe in which the dark energy density decays linearly with
the Hubble parameter, , leading to a constant-rate
creation of cold dark matter. We derive all relevant expressions to calculate
the mass function and the cluster number density using the Sheth-Torman
formalism and show that the effect of the interaction process is to increase
the number of bound structures of large masses () when compared to the standard CDM model. Since these
models are not reducible to each other, this number counts signature can in
principle be tested in future surveys.Comment: 6 pages, 3 figures. Accepted for publication in MNRA
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