149 research outputs found
Conserved currents in gravitational models with quasi-invariant Lagrangians: Application to teleparallel gravity
Conservation laws in gravitational theories with diffeomorphism and local Lorentz symmetry are studied. Main attention is paid to the construction of conserved currents and charges associated with an arbitrary vector field that generates a diffeomorphism on the spacetime. We further generalize previous results for the case of gravitational models described by quasi-invariant Lagrangians, that is, Lagrangians that change by a total derivative under the action of the local Lorentz group. The general formalism is then applied to the teleparallel models, for which the energy and the angular momentum of a Kerr black hole are calculated. The subsequent analysis of the results obtained demonstrates the importance of the choice of the frame
Dirac fields in f(R)-gravity with torsion
We study f(R)-gravity with torsion in presence of Dirac massive fields. Using
the Bianchi identities, we formulate the conservation laws of the theory and we
check the consistency with the matter field equations. Further, we decompose
the field equations in torsionless and torsional terms: we show that the
non-linearity of the gravitational Lagrangian reduces to the presence of a
scalar field that depends on the spinor field; this additional scalar field
gives rise to an effective stress-energy tensor and plays the role of a scale
factor modifying the normalization of Dirac fields. Problems for fermions
regarding the positivity of energy and the particle-antiparticle duality are
discussed.Comment: 14 page
Massive motion in Brans-Dicke geometry and beyond
Gravity theories that can be viewed as dynamics for area metric manifolds,
for which Brans-Dicke theory presents a recently studied example, require for
their physical interpretation the identification of the distinguished curves
that serve as the trajectories of light and massive matter. Complementing
previous results on the propagation of light, we study effective massive point
particle motion. We show that the relevant geometrical structure is a special
Finsler norm determined by the area metric, and that massive point particles
follow Finsler geodesics.Comment: 12 page
Torsion nonminimally coupled to the electromagnetic field and birefringence
In conventional Maxwell--Lorentz electrodynamics, the propagation of light is
influenced by the metric, not, however, by the possible presence of a torsion
T. Still the light can feel torsion if the latter is coupled nonminimally to
the electromagnetic field F by means of a supplementary Lagrangian of the type
l^2 T^2 F^2 (l = coupling constant). Recently Preuss suggested a specific
nonminimal term of this nature. We evaluate the spacetime relation of Preuss in
the background of a general O(3)-symmetric torsion field and prove by
specifying the optical metric of spacetime that this can yield birefringence in
vacuum. Moreover, we show that the nonminimally coupled homogeneous and
isotropic torsion field in a Friedmann cosmos affects the speed of light.Comment: Revtex, 12 pages, no figure
Carbendazim dissipation in the biomixture of on-farm biopurification systems and its effect on microbial communities
The impact of repeated carbendazim (CARB) applications on the extent of \CARB\ dissipation, the microbial diversity, the community level physiological profile (CLPP), and the enzymatic activity within the biomixture of an on-farm biopurification system was evaluated. After three successive \CARB\ applications, the \CARB\ dissipation efficiency was high; the efficiency of dissipation was 87%, 94% and 96% after each application, respectively. Although microbial enzymatic activity was affected significantly by \CARB\ application, it could recover after each \CARB\ pulse. Likewise, the numbers of cultivable bacteria, fungi and actinomycetes (as measured in CFUs) were slightly affected by the addition of CARB, but the inhibitory effect of the pesticide application was temporary. Denaturing gradient gel electrophoresis (DGGE) and Biolog Ecoplate assays demonstrated that the microbial populations remained relatively stable over time when compared to the control. The results obtained herein therefore demonstrate the high dissipation capacity of this biomixture and highlight the microbiological robustness of this biological system.This work was supported by FONDECYT project No 11100236
The Local Territory as a Resource for Learning Science: A Proposal for the Design of Teaching-learning Sequences in Science Education
The present work arises from the need to reform Science Education, particularly through the contextualization of teaching. It is
proposed to achieve this through the use of local territory as a resource for the design of teaching-learning-sequences (TLS). To
do this, an interdisciplinary group of researchers and teachers from a Secondary School created a Professional Circle for
Reflection on Teaching, which constructed an emerging conceptualization of Territory, analyzed the possibilities of the local area
and established a relationship with the national curriculum. On this basis the TLS were designed, with an interdisciplinary aspect,
and implemented with pupils aged 14 to 17. The results show that the contextualization of teaching through the use of local
territory is possible, and is positive for pupils, and that collaborative work and reflection by teachers are fundamental for this
process
A generalized photon propagator
A covariant gauge independent derivation of the generalized dispersion
relation of electromagnetic waves in a medium with local and linear
constitutive law is presented. A generalized photon propagator is derived. For
Maxwell constitutive tensor, the standard light cone structure and the standard
Feynman propagator are reinstated
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