Black string corrections in variable tension braneworld scenarios

Braneworld models with variable tension are investigated, and the corrections on the black string horizon along the extra dimension are provided. Such corrections are encrypted in additional terms involving the covariant derivatives of the variable tension on the brane, providing profound consequences concerning the black string horizon variation along the extra dimension, near the brane. The black string horizon behavior is shown to be drastically modified by the terms corrected by the brane variable tension. In particular, a model motivated by the phenomenological interesting case regarding Eotvos branes is investigated. It forthwith provides further physical features regarding variable tension braneworld scenarios, heretofore concealed in all previous analysis in the literature. All precedent analysis considered uniquely the expansion of the metric up to the second order along the extra dimension, what is able to evince solely the brane variable tension absolute value. Notwithstanding, the expansion terms aftermath, further accomplished in this paper from the third order on, elicits the successive covariant derivatives of the brane variable tension, and their respective coupling with the extrinsic curvature, the Weyl tensor, and the Riemann and Ricci tensors, as well as the scalar curvature. Such additional terms are shown to provide sudden modifications in the black string horizon in a variable tension braneworld scenarioComment: 12 pages, 5 figures, accepted in PR

Notes on the Two-brane Model with Variable Tension

Motivated by possible extensions of the braneworld models with two branes, we investigate some consequences of a variable brane tension using the well established results on consistency conditions. By a slight modification of the usual stress-tensor used in order to derive the braneworld sum rules, we find out some important constraints obeyed by time dependent brane tensions. In particular it is shown that the tensions of two Randall-Sundrum like branes obeying, at the same time, an Eotvos law, aggravate the fine tuning problem. Also, it is shown that if the hidden brane tension obeys an Eotvos law, then the visible brane has a mixed behavior allowing a bouncing-like period at early times while it is dominated by an Eotvos law nowadays. To finalize, we discuss some qualitative characteristics which may arise in the scope of dynamical brane tensions, as anisotropic background and branons production.Comment: 7 pages, 1 figure, accepted for publication in Physical Review

Revisiting Clifford algebras and spinors III: conformal structures and twistors in the paravector model of spacetime

This paper is the third of a series of three, and it is the continuation of math-ph/0412074 and math-ph/0412075. After reviewing the conformal spacetime structure, conformal maps are described in Minkowski spacetime as the twisted adjoint representation of the group Spin_+(2,4), acting on paravectors. Twistors are then presented via the paravector model of Clifford algebras and related to conformal maps in the Clifford algebra over the lorentzian R{4,1}$ spacetime. We construct twistors in Minkowski spacetime as algebraic spinors associated with the Dirac-Clifford algebra Cl(1,3)(C) using one lower spacetime dimension than standard Clifford algebra formulations, since for this purpose the Clifford algebra over R{4,1} is also used to describe conformal maps, instead of R{2,4}. Although some papers have already described twistors using the algebra Cl(1,3)(C), isomorphic to Cl(4,1), the present formulation sheds some new light on the use of the paravector model and generalizations.Comment: 17 page

Com gestionem els recursos pesquers?

Investigadors de la UAB han participat en una sèrie d'estudis que tenien l'objectiu de trobar millors mètodes per gestionar els recursos pesquers. Actualment, els òrgans de gestió de la captura de peixos utilitzen índexs que no tenen en compte les diferents estacions de l'any ni tampoc la indústria pesquera actual, que captura moltes espècies de peixos al mateix temps. Aquesta investigació proposa nous càlculs que tenen en compte tant el moment de l'any en què es pesca com la captura de diferents espècies.Investigadores de la UAB han participado en una serie de estudios que tenían el objetivo de encontrar mejores métodos para gestionar los recursos pesqueros. Actualmente, los órganos de gestión de la captura de peces utilizan indices que no tienen en cuenta las diferentes estaciones del año ni tampoco la industria pesquera actual, que captura muchas especies de peces a la vez. Esta investigación propone nuevos cálculos que tienen en cuenta tanto el momento del año en que se pesca como la captura de diferentes especies

A reconciled version of the cork oak tree genome-scale metabolic model

Quercus suber, commonly known as cork oak tree, is an evergreen tree which produces a thick bark (also known as cork) with multiple (a)biotic stress resistance properties (1). Due to corks natural characteristics, such as the low weight, excellent insulation and low permeability, the cellular structure has a significant economic value as it has multiple applications. For instance, it can be used as a wine bottle sealant and insulation boards (2,3). Additionally, cork is harvested periodically throughout the trees lifetime (4). Nevertheless, the corks quality can only be properly assessed after 40 years of tree growth, which makes the identification of metabolic traits, associated to high-quality cork, of the utmost importance (5). Genome-Scale Metabolic (GSM) models comprise both genomic and metabolic information and can predict the phenotypic behavior of an organism when subjected to distinct environmental conditions (6). Therefore, a reconstructed GSM model of the cork oak tree can point to metabolic properties related to cork quality. Additionally, in silico metabolic engineering strategies could lead to the development of metabolically enhanced trees. The current Quercus suber leaf model, reconstructed within merlin (7), contains 3126 reactions, 2648 metabolites, 7258 genes and was subjected to extensive manual curation, while the biomass and energy requirements were revamped. In silico simulations, using Flux Balance Analysis (8), accurately predict the phenotypic behavior of the leaf cell when exposed to phototrophic and heterotrophic conditions.info:eu-repo/semantics/publishedVersio

FM 047-02: a collisional pair of galaxies with a ring

Aims. We investigate the nature of the galaxy pair FM 047-02, which has been proposed as an archetype of the Solitaire types of peculiar (collisional) ring galaxies. Methods. The study is based on long-slit spectrophotometric data in the range of 3500-9500 angstrons obtained with the Gemini Multi-ObjectComment: 07 pages, 06 figures, 02 tables. arXiv admin note: text overlap with arXiv:1206.071

Gravastars and Black Holes of Anisotropic Dark Energy

Dynamical models of prototype gravastars made of anisotropic dark energy are constructed, in which an infinitely thin spherical shell of a perfect fluid with the equation of state $p = (1-\gamma)\sigma$ divides the whole spacetime into two regions, the internal region filled with a dark energy fluid, and the external Schwarzschild region. The models represent "bounded excursion" stable gravastars, where the thin shell is oscillating between two finite radii, while in other cases they collapse until the formation of black holes. Here we show, for the first time in the literature, a model of gravastar and formation of black hole with both interior and thin shell constituted exclusively of dark energy. Besides, the sign of the parameter of anisotropy ($p_t - p_r$) seems to be relevant to the gravastar formation. The formation is favored when the tangential pressure is greater than the radial pressure, at least in the neighborhood of the isotropic case ($\omega=-1$).Comment: 16 pages, 8 figures. Accepted for publication in Gen. Rel. Gra