2,469 research outputs found
On aether terms in a space-time with a compact extra dimension
In this paper, for the CPT-even and CPT-odd extensions of the QED, we
explicitly obtain the aether-like corrections for the electromagnetic field in
the case when the space-time involves an extra compact spatial dimension
besides of usual four dimensions. Our methodology is based on an explicit
summation over the Kaluza-Klein tower of fields which is no more difficult than
the finite-temperature calculations. The quantum corrections turn out to be
large as the extra dimension is small. We demonstrate that in the CPT-even
case, the extra dimension manifests itself through a new scalar particle.Comment: 9 page
The Godel metric in the Chern-Simons modified gravity
We discuss the consistency of the Godel metric within the Chern-Simons
modified gravity, both for external and dynamical Chern-Simons coefficients.Comment: 6 pages; to be published in the Proceedings of 5th International
Workshop on Astronomy and Relativistic Astrophysics (IWARA 2011), matches the
accepted versio
Recent Findings and Open Issues concerning the Seismic Behaviour of Masonry Infill Walls in RC Buildings
The extension of the damages observed after the last major earthquakes shows that the seismic risk mitigation of infilled reinforced concrete structures is a paramount topic in seismic prone regions. In the assessment of existing structures and the design of new ones, the infill walls are considered as nonstructural elements by most of the seismic codes and, generally, comprehensive provisions for practitioners are missing. However, nowadays, it is well recognized by the community the importance of the infills in the seismic behaviour of the reinforced concrete structures. Accurate modelling strategies and appropriate seismic assessment methodologies are crucial to understand the behaviour of existing buildings and to develop efficient and appropriate mitigation measures to prevent high level of damages, casualties, and economic losses. The development of effective strengthening solutions to improve the infill seismic behaviour and proper analytical formulations that could help design engineers are still open issues, among others, on this topic. The main aim of this paper is to provide a state-of-the-art review concerning the typologies of damages observed in the last earthquakes where the causes and possible solutions are discussed. After that, a review of in-plane and out-of-plane testing campaigns from the literature on infilled reinforced concrete frames are presented as well as their relevant findings. The most common strengthening solutions to improve the seismic behaviour are presented, and some examples are discussed. Finally, a brief summary of the modelling strategies available in the literature is presented
Collaboration networks from a large CV database: dynamics, topology and bonus impact
Understanding the dynamics of research production and collaboration may
reveal better strategies for scientific careers, academic institutions and
funding agencies. Here we propose the use of a large and multidisciplinar
database of scientific curricula in Brazil, namely, the Lattes Platform, to
study patterns of scientific production and collaboration. In this database,
detailed information about publications and researchers are made available by
themselves so that coauthorship is unambiguous and individuals can be evaluated
by scientific productivity, geographical location and field of expertise. Our
results show that the collaboration network is growing exponentially for the
last three decades, with a distribution of number of collaborators per
researcher that approaches a power-law as the network gets older. Moreover,
both the distributions of number of collaborators and production per researcher
obey power-law behaviors, regardless of the geographical location or field,
suggesting that the same universal mechanism might be responsible for network
growth and productivity.We also show that the collaboration network under
investigation displays a typical assortative mixing behavior, where teeming
researchers (i.e., with high degree) tend to collaborate with others alike.
Finally, our analysis reveals that the distinctive collaboration profile of
researchers awarded with governmental scholarships suggests a strong bonus
impact on their productivity.Comment: 8 pages, 8 figure
Redes observação e a evolução tecnológica contribuindo para o desenvolvimento de modelos matemáticos na Meteorologia no século XX.
O objetivo deste trabalho é promover uma reflexão relacionada às características da evolução científica e institucional do campo científico da Meteorologia que possibilitaram, a partir de meados do século XX, a utilização de modelos matemáticos para fins de previsão do tempo. A Meteorologia é uma ciência relativamente jovem, se comparada à Matemática ou à Física, e que tem ganhado destaque desde a última metade do século XX. Alguns historiadores apontam que, antes do advento dos computadores e da ameaça do aquecimento global, a Meteorologia não possuia um carisma e uma velocidade de progresso que pudesse atrair eventuais historiadores. No entanto, a própria significância das preocupações sociais com o clima e suas alterações que marcaram a segunda metade do século XX, acabaram por gerar interesse pelas análises históricas relacionadas à Meteorologia. Estas análises apontam a especial relevância da evolução/ revolução tecnológica ocorrida no século XVII, com a invenção de vários instrumentos de medição como o barômetro e ou termômetro que permitiram que a Meteorologia passasse a ser uma ciência de bases quantitativas. No século XIX, a Meteorologia teve novo impulso com a invenção de instrumentos mais modernos para medição e do telégrafo aliada à sua ampla utilização por redes de observação meteorológica. Estas condições tornaram possível a geração de mapas sinópticos de previsão e a criação de sistemas de monitoramento e alarmes. Com isto, os serviços meteorológicos passaram a chamar a atenção dos Estados Nacionais. A evolução tecnológica e as formas institucionais criadas para o fornecimento de serviços meteorológicos - notadamente marcadas pelas redes de observação apoiadas pelo telégrafo - fornecem elementos para entender a evolução das técnicas utilizadas para atividades de previsão do tempo nos séculos XIX e XX. No século XX, a evolução tecnológica, calcada no desenvolvimento de tecnologias de informação e comunicação, permitiu o desenvolvimento de modelos matemáticos de previsão do tempo. O desenvolvimento do computador ENIAC, na década de 1950, possibilitou o cálculo da primeira previsão numérica do tempo. Este trabalho apresenta, sob uma forma revisional, o contexto tecnológico, organizacional e histórico que criou condições para a consolidação dos modelos de previsão numérica no campo da Meteorologia.Simpósio temático "Ciência&Tecnologia-Sociedade-História: Abordagens construtivistas"
Bound states in the dynamics of a dipole in the presence of a conical defect
In this work we investigate the quantum dynamics of an electric dipole in a
-dimensional conical spacetime. For specific conditions, the
Schr\"odinger equation is solved and bound states are found with the energy
spectrum and eigenfunctions determined. We find that the bound states spectrum
extends from minus infinity to zero with a point of accumulation at zero. This
unphysical result is fixed when a finite radius for the defect is introduced.Comment: 4 page
On the dual equivalence between self-dual and Maxwell-Chern-Simons models with Lorentz symmetry breaking
In this paper, we use gauge embedding procedure and master action approach to
establish the equivalence between the self-dual and Maxwell-Chern-Simons models
with Lorentz symmetry breaking. As a result, new kinds of Lorentz-breaking
terms arise.Comment: 14 pages, minor corrections, version accepted to Physical Review
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