Teleparallel Spin Connection

A new expression for the spin connection of teleparallel gravity is proposed, given by minus the contorsion tensor plus a zero connection. The corresponding minimal coupling is covariant under local Lorentz transformation, and equivalent to the minimal coupling prescription of general relativity. With this coupling prescription, therefore, teleparallel gravity turns out to be fully equivalent to general relativity, even in the presence of spinor fields.Comment: 2 pages, RevTeX, to appear in Phys. Rev D (Brief Report

Gravitation and Duality Symmetry

By generalizing the Hodge dual operator to the case of soldered bundles, and working in the context of the teleparallel equivalent of general relativity, an analysis of the duality symmetry in gravitation is performed. Although the basic conclusion is that, at least in the general case, gravitation is not dual symmetric, there is a particular theory in which this symmetry shows up. It is a self dual (or anti-self dual) teleparallel gravity in which, due to the fact that it does not contribute to the interaction of fermions with gravitation, the purely tensor part of torsion is assumed to vanish. The ensuing fermionic gravitational interaction is found to be chiral. Since duality is intimately related to renormalizability, this theory may eventually be more amenable to renormalization than teleparallel gravity or general relativity.Comment: 7 pages, no figures. Version 2: minor presentation changes, references added. Accepted for publication in Int. J. Mod. Phys.

Primordial magnetic fields constrained by CMB anisotropies and dynamo cosmology

Magneto-curvature stresses could deform magnetic field lines and this would give rise to back reaction and restoring magnetic stresses [Tsagas, PRL (2001)]. Barrow et al [PRD (2008)] have shown in Friedman universe the expansion to be slow down in spatial section of negative Riemann curvatures. From Chicone et al [CMP (1997)] paper, proved that fast dynamos in compact 2D manifold implies negatively constant Riemannian curvature, here one applies the Barrow-Tsagas ideas to cosmic dynamos. Fast dynamo covariant stretching of Riemann slices of cosmic Lobachevsky plane is given. Inclusion of advection term on dynamo equations [Clarkson et al, MNRAS (2005)] is considered. In absence of advection a fast dynamo is also obtained. Viscous and restoring forces on stretching particles decrease, as magnetic rates increase. From COBE data ($\frac{{\delta}B}{B}\approx{10^{-5}}$), one computes stretching $\frac{{\delta}V^{y}}{V^{y}}=1.5\frac{{\delta}B}{B}\approx{1.5{\times}10^{-5}}$. Zeldovich et al has computed the maximum magnetic growth rate as ${\gamma}_{max}\approx{8.0{\times}10^{-1}t^{-1}}$. From COBE data one computes a lower growth rate for the magnetic field as ${\gamma}_{COBE}\approx{6.0{\times}10^{-6}t^{-1}}$, well-within Zeldovich et al estimate. Instead of the Harrison value $B\approx{t^{{4/3}}}$ one obtains the lower primordial field $B\approx{10^{-6}t}$ which yields the $B\approx{10^{-6}G}$ at the $1s$ Big Bang time.Comment: Dept of theoretical physics-UERJ-Brasi

Épocas de colheita, produção e qualidade de sementes de capim gordura.

Durante tres anos (1978 a 1980) foram realizados experimentos de producao de sementes de capim-gordura (Melinis minutiflora, Beauv), utilizando-se uma pastagem natural, estabelecida em solo de topografia inclinada representativo da Zona da Mata do Estado de Minas Gerais. O objetivo dos experimentos foi avaliar o potencial de producao, a melhor epoca de colheita de sementes desta especie e a sua viabilidade apos o armazenamento por um ano em condicoes ambientais. As melhores producoes foram obtidas quando as sementes colhidas apresentavam de 36 a 43% de umidade. O periodo mais favoravel para a realizacao da colheita, variou consideravelmente nos tres anos, numa amplitude de 20 a 35 dias apos a antese. Em cada ano, o período otimo de colheita foi de aproximadamente sete dias. Colheitas efetuadas quatro dias apos esse periodo ocasionaram uma perda media de 54% na producao de sementes puras viaveis. Sementes desta graminea apresentaram-se ligeiramente dormentes durante os primeiros meses de armazenamento. Nos tres anos, os maiores indices de germinacao foram 40, 79 e 45% e, valor cultural de 19, 43 e 37%, respectivamente, obtidos no sexto mes de armazenamento, declinando apos o nono mes