Spherically symmetric static spacetimes in vacuum f(T) gravity

We show that Schwarzschild geometry remains as a vacuum solution for those four-dimensional f(T) gravitational theories behaving as ultraviolet deformations of general relativity. In the gentler context of three-dimensional gravity, we also find that the infrared-deformed f(T) gravities, like the ones used to describe the late cosmic speed up of the Universe, have as the circularly symmetric vacuum solution a Deser-de Sitter or a BTZ-like spacetime with an effective cosmological constant depending on the infrared scale present in the function f(T).Comment: 8 pages. Some typos corrected and references updated. One additional typo corrected in Eq. (33). Accepted for publication in Physical Review D. Final versio

Born-Infeld Determinantal gravity and the taming of the conical singularity in 3-dimensional spacetime

In the context of Born-Infeld \emph{determinantal} gravity formulated in a n-dimensional spacetime with absolute parallelism, we found an exact 3-dimensional \emph{vacuum} circular symmetric solution without cosmological constant consisting in a rotating spacetime with non singular behavior. The space behaves at infinity as the conical geometry typical of 3-dimensional General Relativity without cosmological constant. However, the solution has no conical singularity because the space ends at a minimal circle that no freely falling particle can ever reach in a finite proper time. The space is curved, but no divergences happen since the curvature invariants vanish at both asymptotic limits. Remarkably, this very mechanism also forbids the existence of closed timelike curves in such a spacetime.Comment: 6 pages, 2 figures. References added, some discussions improved. Version accepted in Phys. Lett.

A type of Born-Infeld regular gravity and its cosmological consequences

Born-Infeld deformation strategy to smooth theories having divergent solutions is applied to the teleparallel equivalent of General Relativity. The equivalence between teleparallelism and General Relativity is exploited to obtain a deformed theory of gravity based on second order differential equations, since teleparallel Lagrangian is built just from first derivatives of the vierbein. We show that Born-Infeld teleparallelism cures the initial singularity in a spatially flat FRW universe; moreover, it provides a natural inflationary stage without resorting to an inflaton field. The Born-Infeld parameter bounds the dynamics of Hubble parameter H(t) and establishes a maximum attainable spacetime curvature.Comment: 3 pages. Talk given at the 7th Alexander Friedmann International Seminar on Gravitation and Cosmology, Joao Pessoa, Brazil, July 200

Remnant group of local Lorentz transformations in f(T) theories

It is shown that the extended teleparallel gravitational theories, known as f(T) theories, inherit some on shell local Lorentz invariance associated with the tetrad field defining the spacetime structure. We discuss some enlightening examples, such as Minkowski spacetime and cosmological (Friedmann-Robertson-Walker and Bianchi type I) manifolds. In the first case, we show that the absence of gravity reveals itself as an incapability in the selection of a preferred parallelization at a local level, due to the fact that the infinitesimal local Lorentz subgroup acts as a symmetry group of the frame characterizing Minkowski spacetime. Finite transformations are also discussed in these examples and, contrary to the common lore on the subject, we conclude that the set of tetrads responsible for the parallelization of these manifolds is quite vast and that the remnant group of local Lorentz transformations includes one and two dimensional Abelian subgroups of the Lorentz group.Comment: 10 pages. Minor changes. To appear in PR

Non trivial frames for f(T) theories of gravity and beyond

Some conceptual issues concerning $f(T)$ theories --a family of modified gravity theories based on absolute parallelism-- are analyzed. Due to the lack of local Lorentz invariance, the autoparallel frames satisfying the field equations are evasive to an \emph{a priori} physical understanding. We exemplify this point by working out the vierbein (tetrad) fields for closed and open Friedmann-Robertson-Walker cosmologies.Comment: 7 pages, 3 figures, some references added. Accepted for publication in Phys. Lett. B. Final Versio

Assessment of the cooling potential of an indoor living wall using different substrates in a warm climate

The use of vertical greenery systems in buildings is becoming very popular as they provide several benefits. In this work, the influence of an indoor living wall on the temperature and humidity in a hall inside the School of Agricultural Engineering (University of Seville) was studied. Four different substrates, Geotextile, Epiweb, Xaxim and coconut fibre, were used to grow the plants in order to assess their performance. Several parameters such as temperature, humidity, plant growth or water consumption were monitored and analyzed during a 4-month period. The cooling effect of the living wall was proven, with an average reduction of 4°C over the room temperature though maximum decrements of 6°C have been observed in warmer conditions. Higher air humidity levels were experienced near the living wall, increasing the overall humidity in the room. All the substrates tested were suitable for plant growing and their behaviour was similar. Geotextile showed the best cooling capacity but higher water consumption, coconut fibre presented degradation problems and Epiweb performance was the poorest. Therefore, these systems have been proven to be very useful and interesting for warm indoor environments due to the cooling effect observed in addition to their bio-filtration capacity and the aesthetic component

Algumas notas sobre a historia do cinema documentario etnográfico

Este texto pretende ofrecer una breve historia de documentales etnográfico, desde sus inicios hasta la actualidad. Además, vamos a incursionar en el cine etnográfico en Brasil, el aumento de las producciones más influyentes. Desde este punto de vista histórico, hay una reflexión sobre el lenguaje audiovisual, estudiar conceptos como el documentales y la ficción, ethnofiction, la improvisación, funciones de la cámara, profilm y finalmente sus relaciones con la antropología y el método etnográfico.This text aims to provide a brief history of ethnographic documentary, from its beginning until today. In addition, will make a incursion into the ethnographic film in Brazil, raising the most influential productions. From this historical view, there is a reflection on the audiovisual language, discussing concepts such as documentary and fiction, ethnofiction, acting, improvisation, camera functions, profilm and finally its relations with anthropology and ethnographic method