11,434 research outputs found
Lessons of spin and torsion: Reply to ``Consistent coupling to Dirac fields in teleparallelism"
In reply to the criticism made by Mielke in the pereceding Comment [Phys.
Rev. D69 (2004) 128501] on our recent paper, we once again explicitly
demonstrate the inconsistency of the coupling of a Dirac field to gravitation
in the teleparallel equivalent of general relativity. Moreover, we stress that
the mentioned inconsistency is generic for {\it all} sources with spin and is
by no means restricted to the Dirac field. In this sense the
-covariant generalization of the spinor fields in the teleparallel
gravity theory is irrelevant to the inconsistency problem.Comment: Revtex, 4 pages, no figure
Development of a molecular method for the identification of clone varieties of Coffea canephora via PCR.
Conilon coffee belongs to the Coffea canephora species, which is a diploid (2n = 2 Ă— = 22), perennial, allogamous plant with a high genetic variability. Consequently, a plantation established from seeds will likely have plants with highly diversified characteristics. Accordingly, the production of cuttings is of great value for the success of crop implementation. Using clones produced from superior genotypes instead of seeds has some advantages such as lower implementation costs, higher productivity, higher uniformity of maturation, better grain quality, differentiated cycle of maturation and staggered harvest scheduling. Brazil is an important coffee producer, and the development of new varieties is important to maintain or even increase its production
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.
Teleparallel origin of the Fierz picture for spin-2 particle
A new approach to the description of spin-2 particle in flat and curved
spacetime is developed on the basis of the teleparallel gravity theory. We show
that such an approach is in fact a true and natural framework for the Fierz
representation proposed recently by Novello and Neves. More specifically, we
demonstrate how the teleparallel theory fixes uniquely the structure of the
Fierz tensor, discover the transparent origin of the gauge symmetry of the spin
2 model, and derive the linearized Einstein operator from the fundamental
identity of the teleparallel gravity. In order to cope with the consistency
problem on the curved spacetime, similarly to the usual Riemannian approach,
one needs to include the non-minimal (torsion dependent) coupling terms.Comment: 5 pages, Revtex4, no figures. Accepted for publication in Phys. Rev.
Model for erosion-deposition patterns
We investigate through computational simulations with a pore network model
the formation of patterns caused by erosion-deposition mechanisms. In this
model, the geometry of the pore space changes dynamically as a consequence of
the coupling between the fluid flow and the movement of particles due to local
drag forces. Our results for this irreversible process show that the model is
capable to reproduce typical natural patterns caused by well known erosion
processes. Moreover, we observe that, within a certain range of porosity
values, the grains form clusters that are tilted with respect to the horizontal
with a characteristic angle. We compare our results to recent experiments for
granular material in flowing water and show that they present a satisfactory
agreement.Comment: 8 pages, 12 figures, submitted to Phys. Rev.
Estimativa dos valores de saldo de radiação e fluxo de calor no solo em diferentes condições antrópicas na bacia do rio Ji-Paraná, Rondônia.
Use change and land cover has significant influence on energy flows. Thus, this study aimed to compare the net radiation and soil heat flux on two dates, 19/07/1984 and 25/06/2010 from a locality of river basin Ji-Paraná, Rondônia. To develop the study, an algorithm Surface Energy Balance Algorithm for Land (SEBAL) allowing the estimation of energy flows according to the cover. The model was applied in the study area in a sequence of steps, where the outcome of interest was the net radiation at the surface and the flow of heat in the soil. The results show that on average the net radiation was greater in the scene where the predominant areas of forest, 19/07/1984, since the albedo of the vegetation is lower than in surface of bare ground or with less dense vegetation as observed in the scene 25/06/2010. The values of soil heat flux are larger at the scene of 25/06/2010 and occupy a larger surface due to human action. This shows that the replacement of forest for agriculture, grazing and urbanization are causing decrease the net radiation and increase the flow of heat in the soil, thereby increasing the emission of long wave radiation that affect the surface temperature, air temperature and the hydrological cycle
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