Search results for "FEL"
showing 10 items of 774 documents
Nonsingular black holes, wormholes, and de Sitter cores from anisotropic fluids
2017
We study Born-Infeld gravity coupled to an anisotropic fluid in a static, spherically symmetric background. The free function characterizing the fluid is selected on the following grounds: i) recovery of the Reissner-Nordstr\"om solution of GR at large distances, ii) fulfillment of classical energy conditions and iii) inclusion of models of nonlinear electrodynamics as particular examples. Four branches of solutions are obtained, depending on the signs of two parameters on the gravity and matter sectors. On each branch, we discuss in detail the modifications on the innermost region of the corresponding solutions, which provides a plethora of configurations, including nonsingular black holes…
Born-Infeld gravity and its functional extensions
2014
We investigate the dynamics of a family of functional extensions of the (Eddington-inspired) Born-Infeld gravity theory, constructed with the inverse of the metric and the Ricci tensor. We provide a generic formal solution for the connection and an Einstein-like representation for the metric field equations of this family of theories. For particular cases we consider applications to the early-time cosmology and find that non-singular universes with a cosmic bounce are very generic and robust solutions.
Q7-branes and their coupling to IIB supergravity
2007
We show how, by making use of a new basis of the IIB supergravity axion-dilaton coset, SL(2,R)/SO(2), 7-branes that belong to different conjugacy classes of the duality group SL(2,R) naturally couple to IIB supergravity with appropriate source terms characterized by an SL(2,R) charge matrix Q. The conjugacy classes are determined by the value of the determinant of Q. The (p,q) 7-branes are the branes in the conjugacy class detQ = 0. The 7-branes in the conjugacy class detQ > 0 are labelled by three numbers (p,q,r) which parameterize the matrix Q and will be called Q7-branes. We construct the full bosonic Wess--Zumino term for the Q7-branes. In order to realize a gauge invariant coupling …
Geodesically complete BTZ-type solutions of $2+1$ Born-Infeld gravity
2016
We study Born-Infeld gravity coupled to a static, nonrotating electric field in $2+1$ dimensions and find exact analytical solutions. Two families of such solutions represent geodesically complete, and hence nonsingular, spacetimes. Another family represents a point-like charge with a singularity at the center. Despite the absence of rotation, these solutions resemble the charged, rotating BTZ solution of General Relativity but with a richer structure in terms of horizons. The nonsingular character of the first two families turn out to be attached to the emergence of a wormhole structure on their innermost region. This seems to be a generic prediction of extensions of General Relativity for…
On gravitational waves in Born-Infeld inspired non-singular cosmologies
2017
We study the evolution of gravitational waves for non-singular cosmological solutions within the framework of Born-Infeld inspired gravity theories, with special emphasis on the Eddington-inspired Born-Infeld theory. We review the existence of two types of non-singular cosmologies, namely bouncing and asymptotically Minkowski solutions, from a perspective that makes their features more apparent. We study in detail the propagation of gravitational waves near these non-singular solutions and carefully discuss the origin and severity of the instabilities and strong coupling problems that appear. We also investigate the role of the adiabatic sound speed of the matter sector in the regularisatio…
Born–Infeld inspired modifications of gravity
2017
General Relativity has shown an outstanding observational success in the scales where it has been directly tested. However, modifications have been intensively explored in the regimes where it seems either incomplete or signals its own limit of validity. In particular, the breakdown of unitarity near the Planck scale strongly suggests that General Relativity needs to be modified at high energies and quantum gravity effects are expected to be important. This is related to the existence of spacetime singularities when the solutions of General Relativity are extrapolated to regimes where curvatures are large. In this sense, Born-Infeld inspired modifications of gravity have shown an extraordin…
Clustering Analysis of Questionnaire for Ph.D. studies in Electrical and Information Engineering in Europe
2013
The ELLEIEC ERASMUS thematic network was running from October 2008 to September 2011. This project deals with several aspects linked to Lifelong Learning in Electrical and Information Engineering in Europe. Within this project, Task 4 is dedicated to “Implementation issues across EIE”. The idea of this task was to see how we can, thanks to implementation using Programs available from the European Commission, and associates (ERASMUS, CD, ERASMUS-MUNDUS, ATLANTIS, IP) to emphasize and develop mobility and cross-recognition. Another aspect, strongly connected, was to analyze the existing and possible interactions of Higher Education Institutions and Lifelong Learning. The European consortium o…
Synthesis and X-ray Crystal Structure Analysis of Substituted 1,2,4-Triazolo [4’,3’:2,3]pyridazino[4,5-b]indole and Its Precursor
2023
The hit compound 1,2,4-triazolo[4’,3’:2,3]pyridazino[4,5-b]indole 3 was synthesized from the reflux of 4-amino-5-indolyl-1,2,4-triazole-3-thione 1 with 4′-bromoacetophenone 2 in methanol catalyzed by concentrated HCl and the desired final molecule was obtained by recrystallization from methanol. The suggested structures of compounds 1 and 3 based on the spectral characterizations were confirmed by X-ray single crystal diffraction analysis. Compound 3 crystallized in the triclinic crystal system and P-1 space group with a = 5.9308(2) Å, b = 10.9695(3) Å, c = 14.7966(4) Å, α = 100.5010(10)°, β = 98.6180(10)°, and γ = 103.8180(10)°. On the other hand, the crystal system of 1 is monoclinic, whe…
La tapicería de la expulsión de los moriscos : un proyecto frustrado de Rodrigo Calderón
2018
espanolEl articulo pone en relacion la serie ya conocida de pinturas titulada «La expulsion de los moriscos del Reino de Valencia» con una documentacion inedita de un encargo realizado por Rodrigo Calderon al virrey de Valencia, marques de Caracena, que incluia, ademas de la narracion de la expulsion, una vista de la ciudad de Valencia y retratos de los protagonistas, y que debia convertirse en una coleccion de tapices nunca realizada. EnglishThis paper deals with an already known series of paintings titled The Expulsion of the Moriscos from the Kingdom of Valencia and provides unpublished documentation of a commission made by Rodrigo Calderon to the viceroy of Valencia, Marquis of Caracena…
El poderoso y su doble. Amis y Amiles en el teatro clásico español
2017
El propósito de este artículo es doble. Por un lado, se pretende estudiar dos muestras de la versión teatral española de la leyenda de Amis y Amiles, representada por La sutil maraña de los dos fieles y parescidos amigos Luis y Alejandro y los sucesos de Alejandro y cómo por su saber vino a ser rey de Egipto (BNE, mss. 15049) y Los pronósticos de Alejandre (BNE, mss. 16064) y su conexión con el capítulo 21 de los Siete Sabios de Roma. El análisis de la estructura métrica de estos dramas pone de manifiesto que debieron componerse durante las dos últimas décadas del siglo XVI. Por otro lado, se intenta profundizar en el contexto educativo del futuro Felipe III para explorar los significados q…