de Broglie-Proca and Bopp-Podolsky massive photon gases in cosmology

We investigate the influence of massive photons on the evolution of the expanding universe. Two particular models for generalized electrodynamics are considered, namely de Broglie-Proca and Bopp-Podolsky electrodynamics. We obtain the equation of state (EOS) $P=P(\varepsilon)$ for each case using dispersion relations derived from both theories. The EOS are inputted into the Friedmann equations of a homogeneous and isotropic space-time to determine the cosmic scale factor $a(t)$. It is shown that the photon non-null mass does not significantly alter the result $a\propto t^{1/2}$ valid for a massless photon gas; this is true either in de Broglie-Proca's case (where the photon mass $m$ is extremely small) or in Bopp-Podolsky theory (for which $m$ is extremely large).Comment: 8 pages, 2 figures; v2 matches the published versio

The silicon stable isotope distribution along the GEOVIDE section (GEOTRACES GA-01) of the North Atlantic Ocean

The stable isotope composition of dissolved silicon in seawater (δ30SiDSi) was examined at 10 stations along the GEOVIDE section (GEOTRACES GA-01), spanning the North Atlantic Ocean (40–60∘ N) and Labrador Sea. Variations in δ30SiDSi below 500 m were closely tied to the distribution of water masses. Higher δ30SiDSi values are associated with intermediate and deep water masses of northern Atlantic or Arctic Ocean origin, whilst lower δ30SiDSi values are associated with DSi-rich waters sourced ultimately from the Southern Ocean. Correspondingly, the lowest δ30SiDSi values were observed in the deep and abyssal eastern North Atlantic, where dense southern-sourced waters dominate. The extent to which the spreading of water masses influences the δ30SiDSi distribution is marked clearly by Labrador Sea Water (LSW), whose high δ30SiDSi signature is visible not only within its region of formation within the Labrador and Irminger seas, but also throughout the mid-depth western and eastern North Atlantic Ocean. Both δ30SiDSi and hydrographic parameters document the circulation of LSW into the eastern North Atlantic, where it overlies southern-sourced Lower Deep Water. The GEOVIDE δ30SiDSi distribution thus provides a clear view of the direct interaction between subpolar/polar water masses of northern and southern origin, and allow examination of the extent to which these far-field signals influence the local δ30SiDSi distribution

Chitosan and poly(Methyl methacrylate-co-butyl methacrylate) bioclends: a compatibility study.

Made available in DSpace on 2015-04-15T05:43:44Z (GMT). No. of bitstreams: 1 souza2014.pdf: 1629099 bytes, checksum: 2211f33daee6bb1d462adff4937e5ac3 (MD5) Previous issue date: 2015-04-14201

Noether symmetry for non-minimally coupled fermion fields

A cosmological model where a fermion field is non-minimally coupled with the gravitational field is studied. By applying Noether symmetry the possible functions for the potential density of the fermion field and for the coupling are determined. Cosmological solutions are found showing that the non-minimally coupled fermion field behaves as an inflaton describing an accelerated inflationary scenario, whereas the minimally coupled fermion field describes a decelerated period being identified as dark matter.Comment: Revised version accepted for publication in Classical and Quantum Gravit

Constraining non-minimally coupled tachyon fields by Noether symmetry

A model for a spatially flat homogeneous and isotropic Universe whose gravitational sources are a pressureless matter field and a tachyon field non-minimally coupled to the gravitational field is analyzed. Noether symmetry is used to find the expressions for the potential density and for the coupling function, and it is shown that both must be exponential functions of the tachyon field. Two cosmological solutions are investigated: (i) for the early Universe whose only source of the gravitational field is a non-minimally coupled tachyon field which behaves as an inflaton and leads to an exponential accelerated expansion and (ii) for the late Universe whose gravitational sources are a pressureless matter field and a non-minimally coupled tachyon field which plays the role of dark energy and is the responsible of the decelerated-accelerated transition period.Comment: 11 pages, 5 figures. Version accepted for publication in Classical and Quantum Gravit

Relação espaço temporal da cafeicultura com as áreas de preservação permanente na Região de Três Pontas, Minas Gerais.

As Áreas de Preservação Permanente são espaços protegidos cobertos ou não por vegetação nativa, com a função ambiental de preservar os recursos hídricos, a paisagem, a estabilidade geográfica, a biodiversidade, o fluxo gênico de fauna e flora, proteger o solo e assegurar o bem-estar das populações humanas. Desde a década de 70, com a expansão da cafeicultura em Minas Gerais, ocorreram inúmeras mudanças no uso e ocupação da terra. No cenário atual a cafeicultura corresponde a 70% da renda das propriedades rurais da região Sul do estado e região de Três Pontas tem sua economia baseada na produção de café. A expansão das fronteiras agrícolas devido à pressão econômica foi uma das grandes motivadoras da mudança no uso da terra e da substituição da vegetação natural, o que acarretou na supressão das áreas destinadas a preservação permanente. Neste intuito, este estudo objetivou delimitar e caracterizar as Áreas de Preservação Permanente de uma área piloto na região de Três Pontas, entre os anos de 1987 a 2010, utilizando geotecnologias, de forma a avaliar o impacto da cafeicultura sobre o ambiente da região. Para delimitar as áreas de preservação permanente, foi utilizada uma carta topográfica do IBGE e imagens do satélite Landsat 5, sensor TM. Foram utilizados os mapas de uso da terra de 1987 a 2010. A hidrografia da região foi obtida por meio da digitalização da carta topográfica. Foi realizado, na rede de drenagem, o levantamento espacial das áreas que deveriam estar preservadas, utilizando a relação de proximidade (buffer). Foi realizado o cruzamento da hidrografia com os mapas de uso da terra, para obtenção das áreas preservadas e não preservadas. Os resultados mostraram que o município apresentou um parque cafeeiro diversificado para todos os anos estudados. Em todos os anos de estudo foi observada uma preservação de mais de 50% das Áreas de Preservação Permanente, com exceção do ano de 2000 que apresentou 75% de áreas não preservadas. Da percentagem das Áreas de Preservação Permanente não preservadas, a cafeicultura ocupa cerca de 10%, o que mostra que esta cultura não é a grande responsável pela ocupação indevida dessas áreas. De qualquer forma, a avaliação mostra que a região não se adéqua às exigências do Código Florestal, uma vez que estas áreas deveriam ser integralmente preservadas

Experimental investigation of linear-optics-based quantum target detection

The development of new techniques to improve measurements is crucial for all sciences. By employing quantum systems as sensors to probe some physical property of interest allows the application of quantum resources, such as coherent superpositions and quantum correlations, to increase measurement precision. Here we experimentally investigate a scheme for quantum target detection based on linear optical measurment devices, when the object is immersed in unpolarized background light. By comparing the quantum (polarization-entangled photon pairs) and the classical (separable polarization states), we found that the quantum strategy provides us an improvement over the classical one in our experiment when the signal to noise ratio is greater than 1/40, or about 16dB of noise. This is in constrast to quantum target detection considering non-linear optical detection schemes, which have shown resilience to extreme amounts of noise. A theoretical model is developed which shows that, in this linear-optics context, the quantum strategy suffers from the contribution of multiple background photons. This effect does not appear in our classical scheme. By improving the two-photon detection electronics, it should be possible to achieve a polarization-based quantum advantage for a signal to noise ratio that is close to 1/400 for current technology.Comment: comments are welcome, submitted to PR

Comparação da seleção genômica e fenotípica utilizando indices de seleção em milho.

O objetivo deste estudo foi comparar a seleção genômica com a seleção fenotípica, quando esta é realizada utilizando índices de seleção