Kerr-Schild ansatz in Einstein-Gauss-Bonnet gravity: An exact vacuum solution in five dimensions

As is well-known, Kerr-Schild metrics linearize the Einstein tensor. We shall see here that they also simplify the Gauss-Bonnet tensor, which turns out to be only quadratic in the arbitrary Kerr-Schild function f when the seed metric is maximally symmetric. This property allows us to give a simple analytical expression for its trace, when the seed metric is a five dimensional maximally symmetric spacetime in spheroidal coordinates with arbitrary parameters a and b. We also write in a (fairly) simple form the full Einstein-Gauss-Bonnet tensor (with a cosmological term) when the seed metric is flat and the oblateness parameters are equal, a=b. Armed with these results we give in a compact form the solution of the trace of the Einstein-Gauss-Bonnet field equations with a cosmological term and a different than b. We then examine whether this solution for the trace does solve the remaining field equations. We find that it does not in general, unless the Gauss-Bonnet coupling is such that the field equations have a unique maximally symmetric solution.Comment: 10 pages, no figures, references added. Last version for CQ

Degenerate Dynamical Systems

Dynamical systems whose symplectic structure degenerates, becoming noninvertible at some points along the orbits are analyzed. It is shown that for systems with a finite number of degrees of freedom, like in classical mechanics, the degeneracy occurs on domain walls that divide phase space into nonoverlapping regions each one describing a nondegenerate system, causally disconnected from each other. These surfaces are characterized by the sign of the Liouville's flux density on them, behaving as sources or sinks of orbits. In this latter case, once the system reaches the domain wall, it acquires a new gauge invariance and one degree of freedom is dynamically frozen, while the remaining degrees of freedom evolve regularly thereafter.Comment: 6 pages, 1 figure, two columns, revtex. Minor changes. Final version for J. Math. Phy

de Sitter black hole with a conformally coupled scalar field in four dimensions

A four-dimensional black hole solution of the Einstein equations with a positive cosmological constant, coupled to a conformal scalar field, is given. There is a curvature singularity at the origin, and scalar field diverges inside the event horizon. The electrically charged solution, which has a fixed charge-to-mass ratio is also found. The quartic self-interacting coupling becomes bounded in terms of Newton's and the cosmological constants.Comment: 5 pages, no figures, CECS style, energy conditions are discussed and some references were added. To appear in Phys. Rev.

Las Vacunas Y La Inmunidad Un Estudio Didáctico A Partir De Las Percepciones De Los Estudiantes De Secundaria En Mendoza, Argentina

Los Diseños Curriculares para la Educación Secundaria señalan como objeto de estudio las acciones de protección y promoción de la salud tanto como los conceptos sobre inmunidad, en el marco de la regulación y control en el organismo humano. Los objetivos del trabajo fueron: detectar la solidez de conocimientos sobre inmunidad y vacunas en estudiantes de secundaria y evaluar el constructo posicionamiento ante la vacunación. El estudio se desarrolló sobre una muestra poblacional de N=89 estudiantes de Tercer Año de Educación Secundaria en la ciudad de Mendoza, a los cuales se les aplicó instrumentos en momentos de pre y post-test, desarrollando entre ambos una intervención didáctico-disciplinar. El análisis de los resultados se resolvió desde una dimensión cuali-cuantitativa, siendo el índice de fiabilidad siempre superior a 0,8. Luego de la intervención didáctica, los porcentajes de superior a 0,8. Luego de la intervención didáctica, los porcentajes de respuestas correctas sobre las nociones básicas de inmunidad y las diferentes dimensiones del concepto vacuna se incrementaron, con excepción de la proyección de protección ante una campaña de vacunación preventiva. Los resultados en general y la significatividad estadística en diferentes momentos del estudio, señalan ciertas debilidades y conflictos en el proceso de construcción de esta competencia. The Curricular Designs for Secondary Education indicate as an object of study the actions of protection and promotion of health as well as the concepts of immunity, within the framework of regulation and control in the human organism. The goals of the present study were: to detect the accuracy of knowledge about immunity and vaccines in secondary school students and to evaluate the construct positioning before vaccination. The study was carried out on a population sample of N=89 students of Third Year of Secondary Education in the city of Mendoza. The instruments were applied at moments of pre and post-test, carrying out between them a didactic-disciplinary intervention. The analysis of the results was determined from a qualiquantitative dimension, with a reliability index always being greater than 0.8. After the didactic intervention, the percentages of correct answers on the basic ideas of immunity and the different dimensions of the vaccine concept increased, with the exception of the projection of defense against a preventive vaccination campaign. The overall results and the statistical significance at different stages of the study, indicate certain weaknesses and conflicts in the process of developing this competence

Platforming Equality: Policy Challenges for the Digital Economy

This is the final version. Available from Autonomy via the link in this recordWelcome to Autonomy’s ‘Platforming Equality’ document: a collection of papers on the challenges that the digital economy poses to policymakers, activists and researchers. We’ve invited a range of contributors to probe deeper into under-examined topics in the digital economy and to shed light on how they operate. Another aim of the collection is to explore policy options for alleviating a range of new challenges that have emerged within the digital economy. Contributors move beyond theoretical discussion of the problems themselves and turn towards an analysis of responses that are open to activists, municipal authorities and government policy makers. Articles suggest a range of policy recommendations and discuss the strengths and weaknesses of different approaches. Each contributor examines a specific issue based on their own research and an analysis of the existing literature. They then provide their own perspective on the policies and approaches that would be most suitable to tackling the issue

Young Galaxy Candidates in the Hubble Frontier Fields - III. MACSJ0717.5+3745

In this paper we present the results of our search for and study of $z \gtrsim 6$ galaxy candidates behind the third Frontier Fields (FF) cluster, MACSJ0717.5+3745, and its parallel field, combining data from Hubble and Spitzer. We select 39 candidates using the Lyman Break technique, for which the clear non-detection in optical make the extreme mid-$z$ interlopers hypothesis unlikely. We also take benefit from $z \gtrsim 6$ samples selected using previous Frontier Fields datasets of Abell 2744 and MACS0416 to improve the constraints on the properties of very high-redshift objects. We compute the redshift and the physical properties, such emission lines properties, star formation rate, reddening, and stellar mass for all Frontier Fields objects from their spectral energy distribution using templates including nebular emission lines. We study the relationship between several physical properties and confirm the trend already observed in previous surveys for evolution of star formation rate with galaxy mass, and between the size and the UV luminosity of our candidates. The analysis of the evolution of the UV Luminosity Function with redshift seems more compatible with an evolution of density. Moreover, no robust $z\ge$8.5 object is selected behind the cluster field, and few $z$$\sim$9 candidates have been selected in the two previous datasets from this legacy survey, suggesting a strong evolution in the number density of galaxies between $z$$\sim$8 and 9. Thanks to the use of the lensing cluster, we study the evolution of the star formation rate density produced by galaxies with L$>$0.03L$^{\star}$, and confirm the strong decrease observed between $z$$\sim$8 and 9.Comment: 21 pages - Accepted for publication in ApJ - v2: small correction

The evolution of Balmer jump selected galaxies in the ALHAMBRA survey

We present a new color-selection technique, based on the Bruzual & Charlot models convolved with the bands of the ALHAMBRA survey, and the redshifted position of the Balmer jump to select star-forming galaxies in the redshift range 0.5 < z < 1.5. These galaxies are dubbed Balmer jump Galaxies BJGs. We apply the iSEDfit Bayesian approach to fit each detailed SED and determine star-formation rate (SFR), stellar mass, age and absolute magnitudes. The mass of the haloes where these samples reside are found via a clustering analysis. Five volume-limited BJG sub-samples with different mean redshifts are found to reside in haloes of median masses $\sim 10^{12.5 \pm 0.2} M_\odot$ slightly increasing toward z=0.5. This increment is similar to numerical simulations results which suggests that we are tracing the evolution of an evolving population of haloes as they grow to reach a mass of $\sim 10^{12.7 \pm 0.1} M_\odot$ at z=0.5. The likely progenitors of our samples at z$\sim$3 are Lyman Break Galaxies, which at z$\sim$2 would evolve into star-forming BzK galaxies, and their descendants in the local Universe are elliptical galaxies.Hence, this allows us to follow the putative evolution of the SFR, stellar mass and age of these galaxies. From z$\sim$1.0 to z$\sim$0.5, the stellar mass of the volume limited BJG samples nearly does not change with redshift, suggesting that major mergers play a minor role on the evolution of these galaxies. The SFR evolution accounts for the small variations of stellar mass, suggesting that star formation and possible minor mergers are the main channels of mass assembly.Comment: 14 pages, 10 figures. Submitted to A&A. It includes first referee's comments. Abstract abridged due to arXiv requirement

Parodianthus ilicifolius (Mold.) Tronc.

Ulapes, Estancia La DianaFil: Ariza Espinar. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto Multidisciplinario de Biología Vegetal; Argentin

On creating mass/matter by extra dimensions in the Einstein-Gauss-Bonnet gravity

Kaluza-Klein (KK) black hole solutions in the Einstein-Gauss-Bonnet (EGB) gravity in $D$ dimensions obtained in the current series of the works by Maeda, Dadhich and Molina are examined. Interpreting their solutions, the authors claim that the mass/matter is created by the extra dimensions. To support this claim, one needs to show that such objects have classically defined masses. We calculate the mass and mass flux for 3D KK black holes in 6D EGB gravity whose properties are sufficiently physically interesting. Superpotentials for arbitrary types of perturbations on arbitrary curved backgrounds, recently obtained by the author, are used, and acceptable mass and mass flux are obtained. A possibility of considering the KK created matter as dark matter in the Universe is discussed.Comment: 15 pages, no figures, minor changes related to the Journal publication with adding two references in footnote

Cuscuta microstyla Engelm. var. bicolor (Hunz.) Hunz.

Valle del SosneadopublishedVersio