On the global uniqueness for the Einstein-Maxwell-scalar field system with a cosmological constant. Part 3: Mass inflation and extendibility of the solutions

This paper is the third part of a trilogy dedicated to the following problem: given spherically symmetric characteristic initial data for the Einstein-Maxwell-scalar field system with a cosmological constant $\Lambda$, with the data on the outgoing initial null hypersurface given by a subextremal Reissner-Nordstrom black hole event horizon, study the future extendibility of the corresponding maximal globally hyperbolic development as a "suitably regular" Lorentzian manifold. In the first part of this series we established the well posedness of the characteristic problem, whereas in the second part we studied the stability of the radius function at the Cauchy horizon. In this third and final paper we show that, depending on the decay rate of the initial data, mass inflation may or may not occur. When the mass is controlled, it is possible to obtain continuous extensions of the metric across the Cauchy horizon with square integrable Christoffel symbols. Under slightly stronger conditions, we can bound the gradient of the scalar field. This allows the construction of (non-isometric) extensions of the maximal development which are classical solutions of the Einstein equations. Our results provide evidence against the validity of the strong cosmic censorship conjecture when $\Lambda>0$.Comment: 48 pages, 5 figures; v2: some presentation changes, mostly in the Introduction; v3: substantial changes in Section 5; v4: expanded Introduction; some presentation changes; matches final published versio

On the global uniqueness for the Einstein-Maxwell-scalar field system with a cosmological constant. Part 2: Structure of the solutions and stability of the Cauchy horizon

This paper is the second part of a trilogy dedicated to the following problem: given spherically symmetric characteristic initial data for the Einstein-Maxwell-scalar field system with a cosmological constant $\Lambda$, with the data on the outgoing initial null hypersurface given by a subextremal Reissner-Nordstrom black hole event horizon, study the future extendibility of the corresponding maximal globally hyperbolic development as a "suitably regular" Lorentzian manifold. In the first paper of this sequence, we established well posedness of the characteristic problem with general initial data. In this second paper, we generalize the results of Dafermos on the stability of the radius function at the Cauchy horizon by including a cosmological constant. This requires a considerable deviation from the strategy followed by Dafermos, focusing on the level sets of the radius function instead of the red-shift and blue-shift regions. We also present new results on the global structure of the solution when the free data is not identically zero in a neighborhood of the origin. In the third and final paper, we will consider the issue of mass inflation and extendibility of solutions beyond the Cauchy horizon.Comment: 44 pages, 13 figures; v2: a few small changes; v3: a paragraph was added in the Introduction, minor clarifications were made thoughout, the list of references was expanded, matches final published versio

Magnetic monopole and string excitations in a two-dimensional spin ice

We study the magnetic excitations of a square lattice spin-ice recently produced in an artificial form, as an array of nanoscale magnets. Our analysis, based upon the dipolar interaction between the nanomagnetic islands, correctly reproduces the ground-state observed experimentally. In addition, we find magnetic monopole-like excitations effectively interacting by means of the usual Coulombic plus a linear confining potential, the latter being related to a string-like excitation binding the monopoles pairs, what indicates that the fractionalization of magnetic dipoles may not be so easy in two dimensions. These findings contrast this material with the three-dimensional analogue, where such monopoles experience only the Coulombic interaction. We discuss, however, two entropic effects that affect the monopole interactions: firstly, the string configurational entropy may loose the string tension and then, free magnetic monopoles should also be found in lower dimensional spin ices; secondly, in contrast to the string configurational entropy, an entropically driven Coulomb force, which increases with temperature, has the opposite effect of confining the magnetic defects.Comment: 8 pages. Accepted by Journal of Applied Physics (2009

Cursos superiores de tecnologia do IFRN – uma análise epistemológica do currículo

Atas do XI Colóquio sobre Questões Curriculares, VII Colóquio Luso-Brasileiro & I Colóquio Luso-Afro-Brasileiro de Questões CurricularesO presente trabalho enquadra-se numa pesquisa em curso no âmbito do doutoramento em Ciências da Educação, na especialidade de Desenvolvimento Curricular. Um dos objetivos da pesquisa é sistematizar e ampliar conhecimentos sobre as bases curriculares dos cursos de tecnologia e problematizar o currículo do ensino superior, considerando o atual contexto social demarcado por complexidades, incertezas e permanentes mudanças. Trata-se de um estudo de natureza qualitativa em que a pesquisa documental é uma das fontes para a recolha de dados. Nesta comunicação incide-se nalguns resultados de uma investigação bibliográfica acerca do currículo dos cursos de tecnologia do IFRN, enfocando o estudo das bases epistemológicas do desenho curricular dos cursos de graduação tecnológica reformulados a partir de 2009 e implementados, na Instituição, em 2012. A primeira parte trata da caracterização e contextualização dos cursos tecnológicos no IFRN, situando-os historicamente e acerca das bases conceituais e metodológicas orientadoras das revisões curriculares do atual contexto institucional. A segunda parte apresenta uma descrição e análise dos princípios organizadores da proposta curricular desses cursos no IFRN, as implicações didáticas e suas articulações com as necessidades formativas dos docentes do ensino superior. Desse modo, espera-se refletir a respeito da proposta curricular dos cursos de graduação tecnológica, a partir da compreensão de uma formação superior integral e produtora de sentidos no âmbito da formação humana, pessoal e profissional, tanto na perspectiva de docentes, quanto de discentes. Visa ainda, ampliar o conhecimento a respeito da concepção e do desenvolvimento curricular nos cursos de graduação tecnológica e contribuir com sistematizações teórico metodológicas que venham a fortalecer o ensino superior e a atuação docente nesse campo de formação. Em síntese, ao se estabelecer relações entre a epistemologia dos conhecimentos teóricos e a epistemologia dos saberes da prática, o estudo busca sistematizar contributos para a construção de uma nova pedagogia universitária.Fundação para a Ciência e a Tecnologia (FCT

Quantifying the interdisciplinarity of scientific journals and fields

There is an overall perception of increased interdisciplinarity in science, but this is difficult to confirm quantitatively owing to the lack of adequate methods to evaluate subjective phenomena. This is no different from the difficulties in establishing quantitative relationships in human and social sciences. In this paper we quantified the interdisciplinarity of scientific journals and science fields by using an entropy measurement based on the diversity of the subject categories of journals citing a specific journal. The methodology consisted in building citation networks using the Journal Citation Reports database, in which the nodes were journals and edges were established based on citations among journals. The overall network for the 11-year period (1999-2009) studied was small-world and scale free with regard to the in-strength. Upon visualizing the network topology an overall structure of the various science fields could be inferred, especially their interconnections. We confirmed quantitatively that science fields are becoming increasingly interdisciplinary, with the degree of interdisplinarity (i.e. entropy) correlating strongly with the in-strength of journals and with the impact factor.Comment: 23 pages, 6 figure

Tuned liquid dampers simulation for earthquake response control of buildings

This paper is focused on the study of an earthquake protection system, the Tuned Liquid Damper (TLD), which can, if adequately designed, reduce earthquake demands on buildings. This positive effect is accomplished taking into account the oscillation of the free surface of a fluid inside a tank (sloshing). The behaviour of an isolated Tuned Liquid Damper, subjected to a sinusoidal excitation at its base, with different displacement amplitudes, was studied by finite element analysis. The efficiency of the TLD in improving the seismic response of an existing building, representative of modern architecture buildings in southern European countries was also evaluated based on linear dynamic analyses

Sensitivity analysis of a crawl gait multi-objective optimization system

This paper describes the analysis of a crawl gait multi-objective optimization system that combines bio-inspired Central Patterns Generators (CPGs) and a multi-objective evolutionary algorithm. In order to optimize the crawl gait, a multiobjective problem, an optimization system based on NSGAII allows to find a set of non-dominated solutions that correspond to different motor solutions The experimental results highlight the effectiveness of this multi-objective approach.(undefined