52 research outputs found
Illusions of general relativity in Brans-Dicke gravity
Contrary to common belief, the standard tenet of Brans-Dicke theory reducing
to general relativity when omega tends to infinity is false if the trace of the
matter energy-momentum tensor vanishes. The issue is clarified in a new
approach using conformal transformations. The otherwise unaccountable limiting
behavior of Brans-Dicke gravity is easily understood in terms of the conformal
invariance of the theory when the sources of gravity have radiation-like
properties. The rigorous computation of the asymptotic behavior of the
Brans-Dicke scalar field is straightforward in this new approach.Comment: 16 pages, LaTeX, to appear in Physical Review
An inverse approach to Einstein's equations for non-conducting fluids
We show that a flow (timelike congruence) in any type warped product
spacetime is uniquely and algorithmically determined by the condition of zero
flux. (Though restricted, these spaces include many cases of interest.) The
flow is written out explicitly for canonical representations of the spacetimes.
With the flow determined, we explore an inverse approach to Einstein's
equations where a phenomenological fluid interpretation of a spacetime follows
directly from the metric irrespective of the choice of coordinates. This
approach is pursued for fluids with anisotropic pressure and shear viscosity.
In certain degenerate cases this interpretation is shown to be generically not
unique. The framework developed allows the study of exact solutions in any
frame without transformations. We provide a number of examples, in various
coordinates, including spacetimes with and without unique interpretations. The
results and algorithmic procedure developed are implemented as a computer
algebra program called GRSource.Comment: 9 pages revtex4. Final form to appear in Phys Rev
Valor nutricional do mel e pólen de abelhas sem ferrão da região Amazônica
Avaliou-se os constituintes nutricionais de amostras do mel e pólen das espécies Melipona seminigra merrillae (jandaíra), Melipona compressipes manaosensis (jupará), Melipona rufiventris paraensis (uruçu boca de ralo), provenientes do meliponário da Fazenda Poranga no município de Itacoatiara - AM e Meliponário Abelhudo em Manaus - AM. Os resultados demonstraram o potencial do mel como fonte de energia, particularmente a M. rufiventris com 305,3±2,4 kcal em 100g. O pólen da espécie M. compressipes apresentou a maior concentração de proteína 15,7±0,0% e energia 309,8±0,8 kcal. Tais constatações sugerem a implementação de novos estudos visando à incorporação destes produtos na dieta dos amazônidas, possibilitando uma nova fonte alternativa de alimento potencialmente nutritivo e saudável.<br>We evaluated the nutricional constituent of honey and pollen samples of the Melipona species seminigra merrillae (jandaíra) Melipona compressipes manaosensis (jupará), Melipona rufiventris paraensis (uruçu boca de ralo), proceeding from the Poranga Honey Farm in Itacoatiara - AM, and Meliponário Abelhudo in Manaus, AM. The results demonstrated the potencial of honey as a source of energy, particularly the kcal M. rufiventris with 305.3±2.4 kcal in 100g. The compressis pollen of species presented the highest concentration of protein 15.7±0.0 % and energy 309.8±0.8 kcal. Thus we suggest the implementation of new studies aiming at the incorporation of these products in the diet of the Amazon population, making possible a new potentially nutritional and alternative healthful food source
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