5,572 research outputs found
Cosmological parameter inference with Bayesian statistics
Bayesian statistics and Markov Chain Monte Carlo (MCMC) algorithms have found
their place in the field of Cosmology. They have become important mathematical
and numerical tools, especially in parameter estimation and model comparison.
In this paper, we review some fundamental concepts to understand Bayesian
statistics and then introduce MCMC algorithms and samplers that allow us to
perform the parameter inference procedure. We also introduce a general
description of the standard cosmological model, known as the CDM
model, along with several alternatives, and current datasets coming from
astrophysical and cosmological observations. Finally, with the tools acquired,
we use an MCMC algorithm implemented in python to test several cosmological
models and find out the combination of parameters that best describes the
Universe.Comment: 30 pages, 17 figures, 5 tables; accepted for publication in Universe;
references adde
Peak characteristics of F2 region over Tucumán: Predictions and measurements
Ionosonde measurements obtained at Tucuman are used to check the validity of the International Reference Ionosphere model to predict the maximum electron density of F2 region (NmF2) and its height (hmF2) over this station. Data corresponding to different months and solar activity conditions are considered. CCIR and URSI options are used to model calculations. The results show that, generally, the predictions of hmF2 are better than those of NmF2. Disagreements between predicted and measured NmF2 values are observed and the consequence in the vertical total electron content modeling are stressed.Fil: Ezquer, Rodolfo Gerardo. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Ionósfera; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mosert, Marta Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Scida, Luis Alberto. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Ionósfera; ArgentinaFil: López, J.. Universidad Tecnológica Nacional; Argentin
Multiplicative structures of hypercyclic functions for convolution operators
In this note, it is proved the existence of an infinitely generated
multiplicative group consisting of entire functions that are, except for the
constant function 1, hypercyclic with respect to the convolution operator
associated to a given entire function of subexponential type. A certain
stability under multiplication is also shown for compositional hypercyclicity
on complex domains.Comment: 12 page
Model selection applied to non-parametric reconstructions of the Dark Energy
The main aim of this paper is to perform a model comparison for
non-parametric reconstructions of the key properties that describe the dark
energy of the Universe i.e. energy density and the equation of state (EoS). We
carry out this process by using a binning and a linear interpolation
methodologies, and on the top of that, we incorporate a correlation function
mechanism. An extension of the two of them was also introduced, where internal
amplitudes are allowed to vary in height as well as in position. The
reconstructions were made with data from the Hubble parameter, Supernovae Type
Ia and Baryon Acoustic Oscillations (H+SN+BAO), all of which span a range from
to . First we perform the parameter estimation for each of the
reconstructions to then provide a model selection through the Bayesian
Evidence. Throughout our process we found a better fit to the data, up to
compared to CDM, and the presence of some interesting
features, i.e. an oscillatory behaviour at late times, a decrease in the dark
energy density component at early times and a transition to the phantom
divide-line in the EoS. To discern these features from noisy contributions, we
include a principal component analysis and found that some of these
characteristics should be taken into account to satisfy observations.Comment: 14 pages, 7 figure
Compositional uniformity, domain patterning and the mechanism underlying nano-chessboard arrays
We propose that systems exhibiting compositional patterning at the nanoscale,
so far assumed to be due to some kind of ordered phase segregation, can be
understood instead in terms of coherent, single phase ordering of minority
motifs, caused by some constrained drive for uniformity. The essential features
of this type of arrangements can be reproduced using a superspace construction
typical of uniformity-driven orderings, which only requires the knowledge of
the modulation vectors observed in the diffraction patterns. The idea is
discussed in terms of a simple two dimensional lattice-gas model that simulates
a binary system in which the dilution of the minority component is favored.
This simple model already exhibits a hierarchy of arrangements similar to the
experimentally observed nano-chessboard and nano-diamond patterns, which are
described as occupational modulated structures with two independent modulation
wave vectors and simple step-like occupation modulation functions.Comment: Preprint. 11 pages, 11 figure
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