On the invariant causal characterization of singularities in spherically symmetric spacetimes

The causal character of singularities is often studied in relation to the existence of naked singularities and the subsequent possible violation of the cosmic censorship conjecture. Generally one constructs a model in the framework of General Relativity described in some specific coordinates and finds an ad hoc procedure to analyze the character of the singularity. In this article we show that the causal character of the zero-areal-radius (R=0) singularity in spherically symmetric models is related with some specific invariants. In this way, if some assumptions are satisfied, one can ascertain the causal character of the singularity algorithmically through the computation of these invariants and, therefore, independently of the coordinates used in the model.Comment: A misprint corrected in Theor. 4.1 /Cor. 4.

On the Papapetrou field in vacuum

In this paper we study the electromagnetic fields generated by a Killing vector field in vacuum space-times (Papapetrou fields). The motivation of this work is to provide new tools for the resolution of Maxwell's equations as well as for the search, characterization, and study of exact solutions of Einstein's equations. The first part of this paper is devoted to an algebraic study in which we give an explicit and covariant procedure to construct the principal null directions of a Papapetrou field. In the second part, we focus on the main differential properties of the principal directions, studying when they are geodesic, and in that case we compute their associated optical scalars. With this information we get the conditions that a principal direction of the Papapetrou field must satisfy in order to be aligned with a multiple principal direction of the Weyl tensor in the case of algebraically special vacuum space-times. Finally, we illustrate this study using the Kerr, Kasner and pp waves space-times.Comment: 24 pages, LaTeX2e, IOP style. To appear in Classical and Quantum Gravit

Millora d'algorismes de predicció de propagció del Dengue amb eines d'inteligència artificial

It is well known that Dengue is a virus mainly spread by mosquito, the Aedes Aegypty, that is common in the area of Brazil. This country had been very affected by dengue disease, as well as ZiKa and chicunguña. This mosquito was originated in Africa, but now is found in tropical, subtropical and temperate regions throughout the world. Climatological conditions are very related with the number of mosquitoes and the viruses spread. The availability of Earth Observation mission that periodically and globally provide of climatological variables such as temperature and precipitations, may help to develop dengue prevention algorithms. The passive remote sensing group at Signal theory and propagation group lately had started to work in the development of such algorithms. The main objective of this thesis has been the improvement of artificial intelligence algorithms for dengue risk detection in Brazil. For achieving such objective, the original database has been upgraded adding new years of information, with all the information: monthly dengues cases in in Brazil, as well as all the climatologic and socioeconomic variables associated and necessary for the dengue risk prediction. In addition, the predictive algorithms based in Machine Learning and Deep Learning already developed in a previous project had been adapted with the new information in the database, as well as analyzed and improved. This document details the information of the database, its analysis and explains the different statistical models that have been used to make prediction of the epidemiological risk of dengue in a month ahead. Moreover, an analysis of the performances of each model and a comparative study among them is presented.Es bien conocido que el Dengue es un virus principalmente transmitido por el mosquito, Aedes Aegypty, que es común en la zona de Brasil. Este país ha sido muy afectado por esta enfermedad, juntamente con el Zika i la Chikunguña. El mosquito era originario del África, pero ahora se encuentra en áreas tropicales, subtropicales y temperadas de todo el mundo. Las condiciones meteorológicas están muy relacionadas con el número de mosquitos, y por tanto con la propagación de Dengue. El fácil acceso a la misión "Earth Observation" que periódicamente proporciona a nivel mundial variables meteorológicas como la temperatura i las precipitaciones, ha ayudado al desarrollo de algoritmos de prevención del Dengue. El grupo de obtención de datos pasivos al grupo de teoría de señal i propagación del virus ha empezado a trabajar en la implementación de este. El principal objetivo de este proyecto ha estado la mejora de los algoritmos de inteligencia artificial encargados de la predicción de dengue en Brasil. Para cumplir este objetivo se ha mejorado la base de datos original añadiendo más años de información, con toda esta información: el número de casos mensuales de dengue en Brasil, también datos climatológicos i socioeconómicos relacionados i necesarios para la predicción de dengue. A más a más, los algoritmos predictivos basados en Machine Learning i Deep Learning que ya han sido implementados en proyectos anteriores han sido adaptados con la nueva información de la base de datos, también analizados y mejorados. Este documento detalla la información de la base de datos, analiza esta y explica los diferentes modelos estadísticos utilizados para hacer una predicción futura del riesgo epidemiológico del dengue. Adicionalmente, para cada modelo se ha hecho un análisis de su rendimiento y se ha hecho un estudio para comparar los modelos.És ben conegut que el Dengue és un virus principalment transmès per el mosquit, l’Aedes Aegypty, que és comú a la zona de Brasil. Aquest país ha estat molt afectat per aquesta malaltia, juntament amb el Zika i la chicuguña. El mosquit era originari de l’Africa, però ara es troba en àrees tropicals, subtropicals i temperades de tot el món. Les condicions meteorològiques estan molt relacionades amb el nombre de mosquits, i per tant amb la propagació del dengue. El fàcil accés a la missió “Earth Observation” que periòdicament proporciona a nivell mundial variables meteorològiques com la temperatura i les precipitacions, ha ajudat a desenvolupar algorismes de prevenció del Dengue. El grup de obtenció de dades passives al grup de teoria de senyal i propagació del virus ha començat a treballar en la implementació d’aquests. El principal objectiu d’aquest projecte ha estat la millora dels algorismes d’intel·ligència artificial encarregats de la predicció de dengue al Brasil. Per tal d’assolir aquest objectiu s’ha millorat la base de dades original afegint més anys d’informació, amb tota la informació: els casos mensuals de dengue a Brasil, també dades climatològiques i socioeconòmiques relacionades i necessàries per la predicció de dengue. A més a més, els algorismes predictius basats en Machine Learning i Deep Learning que ja han estat implementats en projectes anteriors han estat adaptats amb la nova informació de la base de dades, també com analitzats i millorats. Aquest document detalla la informació de la base de dades, l’anàlisi d’aquesta i explica els diferents models estadístics utilitzats per fer una predicció a un mes vista del risc epidemiològic del dengue. Addicionalment, per cada model s’ha fet un anàlisi del seu rendiment i s’ha fet un estudi per comparar els diferents models

General approach to the study of vacuum space-times with an isometry

In vacuum space-times the exterior derivative of a Killing vector field is a 2-form (named here as the Papapetrou field) that satisfies Maxwell's equations without electromagnetic sources. In this paper, using the algebraic structure of the Papapetrou field, we will set up a new formalism for the study of vacuum space-times with an isometry, which is suitable to investigate the connections between the isometry and the Petrov type of the space-time. This approach has some advantages, among them, it leads to a new classification of these space-times and the integrability conditions provide expressions that determine completely the Weyl curvature. These facts make the formalism useful for application to any problem or situation with an isometry and requiring the knowledge of the curvature.Comment: 24 pages, LaTeX2e, IOP style. To appear in Classical and Quantum Gravit

Quasinormal modes for the charged Vaidya metric

The scalar wave equation is considered in the background of a charged Vaidya metric in double null coordinates $(u,v)$ describing a non-stationary charged black hole with varying mass $m(v)$ and charge $q(v)$. The resulting time-dependent quasinormal modes are presented and analyzed. We show, in particular, that it is possible to identify some signatures in the quasinormal frequencies from the creation of a naked singularity.Comment: 4 pages. Prepared for the proceedings of the Spanish Relativity meeting (ERE2010), Granada, Spain, September 6-10, 201

Dynamic model of a railway wheelset for corrugation problem analysis

[EN] In the present work a model of flexible shafts is adapted for modelling the railway wheelset. The dynamic properties of the solid are obtained from a solid finite element model of a real wheelset. The model adopts an Eulerian coordinate set for numerical efficiency. Results of the crossed-receptance and mobility functions are presented, where the excitation is the vertical wheel-rail contact force and the displacement (or velocity) is measured in the wheel-rail contact plane. These results let us know that the gyroscopic effect may contribute to define the wavelength-fixing mechanism in some corrugation problems, even if the train speed is low.This work was sponsored by Projects T79/2006 (Ministerio de Fomento - Metro de Madrid- CDM) and TRA2007-67167 (Ministerio de Educación y Ciencia - FEDER).Vila Tortosa, MP.; Rovira, A.; Fayos Sancho, J.; Baeza González, LM. (2009). Dynamic model of a railway wheelset for corrugation problem analysis. Noise & Vibration Worldwide. 40(11):10-18. https://doi.org/10.1260/095745609790251579S1018401

Consequences of a Killing symmetry in spacetime's local structure

In this paper we discuss the consequences of a Killing symmetry on the local geometrical structure of four-dimensional spacetimes. We have adopted the point of view introduced in recent works where the exterior derivative of the Killing plays a fundamental role. Then, we study some issues related with this approach and clarify why in many circumstances its use has advantages with respect to other approaches. We also extend the formalism developed in the case of vacuum spacetimes to the general case of an arbitrary energy-momentum content. Finally, we illustrate our framework with the case of spacetimes with a gravitating electromagnetic field.Comment: 20 pages, LaTeX2e, IOP style. Revised version accepted for publication in Classical and Quantum Gravit