Antisymmetric tensor propagator with spontaneous Lorentz violation

In this work, we study the spontaneous Lorentz symmetry breaking due to an antisymmetric 2-tensor field in Minkowski spacetime. For a smooth quadratic potential, the spectrum of the theory exhibits massless and massive excitations. We show that the equations of motion for the free field obey some constraints which lead to the massive mode be non-propagating at leading order. Besides, there exists a massless mode in the theory which can be identified with the usual Kalb-Ramond field, carrying only one on-shell degree of freedom. The same conclusion holds when one analyses the pole structure of its Feynman propagator. A new complete set of spin-type operators is found, which was the requirement to evaluate the propagator of the Kalb-Ramond field modified by the presence of a nonzero vacuum expectation value responsible for the Lorentz violation.Comment: 13 pages. Some modifications to match published version in EuroPhysics Letter

Laser frequency combs for astronomical observations

A direct measurement of the universe's expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects. However, this would require measurements of Doppler velocity drifts of about 1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrate the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of approximately 9 meters per second at about 1.5 micrometers - beyond state-of-the-art accuracy. We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universe's putative acceleration.Comment: Science, 5th September 2008. 18 pages, 7 figures (7 JPG files), including Supporting Online Material. Version with higher resolution figures available at http://astronomy.swin.edu.au/~mmurphy/pub.htm

Dynamical reentrance and geometry imposed quantization effects in Nb-AlOx-Nb Josephson junction arrays

In this paper, we report on different phenomena related to the magnetic properties of artificially prepared highly ordered (periodic) two-dimensional Josephson junction arrays (2D-JJA) of both shunted and unshunted Nb-AlOx-Nb tunnel junctions. By employing mutual-inductance measurements and using a high-sensitive bridge, we have thoroughly investigated (both experimentally and theoretically) the temperature and magnetic field dependence of complex AC susceptibility of 2D-JJA. We also demonstrate the use of the scanning SQUID microscope for imaging the local flux distribution within our unshunted arrays

Descrição de sistemas de criação tradicionais de ovinos da Nhecolândia, Pantanal, MS.

Este trabalho tem como objetivo principal resgatar o conhecimento empírico sobre o sistema de criação tradicional de ovinos no Pantanal, caracterizando-o e descrevendo-o a partir de oito fazendas da sub-região da Nhecolândia, Pantanal, MS. Devido a crescente demanda do mercado por carne ovina, os produtores do Pantanal podem diversificar a produção animal. A região apresenta potencial para a produção de ovelhas pantaneiras para cruzamentos no planalto, produção de cordeiros (orgânicos), produção de subsistência da fazenda, entre outros. Para tanto, há a necessidade de desenvolver práticas sustentáveis de manejo da ovinocultura no Pantanalbitstream/item/80589/1/CT94.pd

Group Theory analysis of phonons in two-dimensional Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDCs) have emerged as a new two dimensional materials field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some cases when the bulk material is exfoliated down to a monolayer, an indirect-to-direct band gap in the visible range is observed. The number of layers $N$ ($N$ even or odd) drives changes in space group symmetry that are reflected in the optical properties. The understanding of the space group symmetry as a function of the number of layers is therefore important for the correct interpretation of the experimental data. Here we present a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of TMDCs, i.e. $2Ha$, $2Hc$ and $1T$, as a function of the number of layers. Real space symmetries, the group of the wave vectors, the relevance of inversion symmetry, irreducible representations of the vibrational modes, optical selection rules and Raman tensors are discussed.Comment: 32 pages, 4 figure

Redistribuição de carbono orgânico e fósforo pelo escoamento superficial em sistemas agrícolas convencionais e agroflorestais no semi-árido cearense.

Resumo: O objetivo deste estudo foi avaliar a redistribuição de carbono orgânico e fósforo (P) pelo escoamento superficial, para verificar a hipótese de que os sistemas agroflorestais promovem uma menor redistribuição de carbono orgânico e P no solo. A área experimental localiza-se na Fazenda Crioula, pertencente ao Centro Nacional de Pesquisa de Caprinos da EMBRAPA, no município de Sobral-CE. A partir de projeto desenvolvido desde 1997 foram selecionadas as seguintes áreas: Agrossilvipastoril (AGP), Silvipastoril (SILV), Tradicional (TR), Cultivo Intensivo em Pousio (CIP), Mata Nativa 1 (MN-1) e Mata Nativa 2 (MN-2). A área estudada foi georeferenciada, sendo alocados transectos para coleta de amostras de solo na profundidade de 0-5 cm, a cada 10 m. Em seguida, foi feito o levantamento altimétrico utilizandose o nível topográfico. Os teores de carbono orgânico foram determinados por oxidação úmida e o P disponível por extração com Mehlich I e colorimetria. Os resultados foram avaliados por meio de medidas descritivas e técnicas geoestatísticas. Observou-se a existência de grande variabilidade quantitativa dos teores de C e P entre as áreas estudadas. Entretanto, quando se avaliou a variabilidade espacial em cada uma das áreas estudadas, constatou-se o predomínio de um aspecto uniforme da distribuição de C e P nas áreas TR e CIP, enquanto que isto não ocorreu com as áreas mais conservadoras (AGP e SILV). Tais resultados podem ser explicados pela maior ação dos agentes erosivos no caso específico da área CIP que apresentou uma tendência de redistribuir os nutrientes para outras regiões. O mesmo não acontece com a área AGP, um sistema muito mais conservador: tanto que a variação espacial é muito semelhante à da condição natural. [Redistribution of organic carbon and phosphorus by surface runoff in agroforestry and conventional systems in the semi-arid region of Ceará]. Abstract: The objective of this study was to evaluate the redistribution of organic carbon and phosphorus (P) by surface runoff, in order to verify the hypothesis that agroforestry systems promote lower redistribution of organic carbon and P than conventional systems. The experimental area is located in the Crioula Farm, CNPC – EMBRAPA, in the municipality of Sobral, CE. The following systems were selected: Agrisilvipastoral (AGP), Silvipastoral (SILV), Traditional (TR) Fallow Intense Cropping (FIC), Natural Forest-1 (NF-1) and Natural Forest-2 (NF-2). The studied field was georeferenced and transects were allocated for sampling every 10 m along the area at 0-5 cm depth. An altimetric survey was carried out using topographic leveling. C content was determined by wet oxidation and P was extracted by Mehlich-1 and determined by colorimetry. The results were analyzed using descriptive statistic and geostatistic techniques. Large variability of C and P content was observed, however, when spatial variability was evaluated in each area, it showed a uniform pattern of C and P for TR and FIC systems, but not for the most conservative systems such as AGP and SILV. These results can be explained by the more intense action of erosive agents in FIC that tends to redistribute nutrients to other areas. But the same does not occur in AGP, a much more conservative system, in which spatial variation is very similar to natural condition

Coactivation of the shoulder and arm muscles during closed kinetic chain exercises on an unstable surface

Introduction: The purpose of this study was to compare the electromyography index of muscle coactivation of the following muscle pairs: posterior deltoid and pectoralis major (PD/PM); triceps brachii and biceps brachii (TB/BB); and serratus anterior and upper trapezius (SA/UT) during three different closed kinetic chain exercises (wall-press, bench-press and push-up) on an unstable surface at the maximal load. Methods: A total of 20 healthy sedentary men participated in the study. Integral linear values were obtained from three sustained contractions of six seconds each for the three proposed exercises. Mean coactivation index values were compared using the mixed-effects linear model, with a five percent significance level. Results: Electromyography indexes of muscle coactivation showed significant differences for the PD/PM and TB/BB muscle pairs. No differences were found between exercises for the SA/UT muscle pair. Conclusion: Our results seem to differ from those of previous studies, which reported that the similarity in exercises performed is responsible for the comparable muscle activation levels.Sao Paulo State Research Foundation (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)) [2003/13042-1]National Council of Technological and Scientific Development (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq))[309317/2003-7]National Council of Technological and Scientific Development (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq))[502755/2004-0]Coordination for the Improvement of Higher Education Personnel (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior [CAPES]