84 research outputs found
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
Phytoplankton Size Structure in Association with Mesoscale Eddies off Central-Southern Chile: The Satellite Application of a Phytoplankton Size-Class Model
Understanding the influence of mesoscale and submesoscale features on the structure of phytoplankton is a key aspect in the assessment of their influence on marine biogeochemical cycling and cross-shore exchanges of plankton in Eastern Boundary Current Systems (EBCS). In this study, the spatio-temporal evolution of phytoplankton size classes (PSC) in surface waters associated with mesoscale eddies in the EBCS off central-southern Chile was analyzed. Chlorophyll-a (Chl-a) size-fractionated filtration (SFF) data from in situ samplings in coastal and coastal transition waters were used to tune a three-component (micro-, nano-, and pico-phytoplankton) model, which was then applied to total Chl-a satellite data (ESA OC-CCI product) in order to retrieve the Chl-a concentration of each PSC. A sea surface, height-based eddy-tracking algorithm was used to identify and track one cyclonic (sC) and three anticyclonic (ssAC1, ssAC2, sAC) mesoscale eddies between January 2014 and October 2015. Satellite estimates of PSC and in situ SFF Chl-a data were highly correlated (0.64 < r < 0.87), although uncertainty values for the microplankton fraction were moderate to high (50 to 100% depending on the metric used). The largest changes in size structure took place during the early life of eddies (~2 months), and no major differences in PSC between eddy center and periphery were found. The contribution of the microplankton fraction was ~50% (~30%) in sC and ssAC1 (ssAC2 and sAC) eddies when they were located close to the coast, while nanoplankton was dominant (~60–70%) and picoplankton almost constant (<20%) throughout the lifetime of eddies. These results suggest that the three-component model, which has been mostly applied in oceanic waters, is also applicable to highly productive coastal upwelling systems. Additionally, the PSC changes within mesoscale eddies obtained by this satellite approach are in agreement with results on phytoplankton size distribution in mesoscale and submesoscale features in this region, and are most likely triggered by variations in nutrient concentrations and/or ratios during the eddies’ lifetimes
N=4 superconformal mechanics as a Non linear Realization
An action for a superconformal particle is constructed using the non linear
realization method for the group PSU(1,1|2), without introducing superfields.
The connection between PSU(1,1|2) and black hole physics is discussed. The
lagrangian contains six arbitrary constants and describes a non-BPS
superconformal particle. The BPS case is obtained if a precise relation between
the constants in the lagrangian is verified, which implies that the action
becomes kappa-symmetric.Comment: new subection, references added and new acknowledgment
Hairy planar black holes in higher dimensions
We construct exact hairy planar black holes in D-dimensional AdS gravity.
These solutions are regular except at the singularity and have stress-energy
that satisfies the null energy condition. We present a detailed analysis of
their thermodynamical properties and show that the first law is satisfied. We
also discuss these solutions in the context of AdS/CFT duality and construct
the associated c-function.Comment: 18 pages, no figures; v2: title changed, typos fixe
Sources for Chern-Simons theories
The coupling between Chern-Simons theories and matter sources defined by
branes of different dimensionalities is examined. It is shown that the standard
coupling to membranes, such as the one found in supergravity or in string
theory, does not operate in the same way for CS theories; the only p-branes
that naturally couple seem to be those with p=2n; these p-branes break the
gauge symmetry (and supersymmetry) in a controlled and sensible manner.Comment: 17 pages, Dedicated to Claudio Bunster on the occasion of his 60th
birthday. To appear in Quantum Mechanics of Fundamental Systems: The Quest
for Beauty and Simplicit
Perspectiva del docente de educación superior acerca del proceso de innovación pedagógica a través de la incorporación de tecnología. ESLE, 2013-2014. Una propuesta de investigación – acción.
En las últimas décadas del siglo XX se han producido grandes cambios tecnológicos a nivel global debido a la introducción de las tecnologías de la información y la comunicación (TIC). La educación también se ha visto afectada por este fenómeno. La mayor parte de la literatura pedagógica contemporánea coincide en señalar que las TIC se han convertido en herramientas que potencian y facilitan los procesos de enseñanza y aprendizaje para proveer a las nuevas generaciones habilidades y conocimientos significativos. En este escenario la Escuela de Lenguas Extranjeras de la Universidad del Aconcagua, resolvió incorporar las TIC al aula para el Profesorado en Lengua y Cultura Inglesa.Esta transformación resulta compleja para los docentes de la Institución ya que implica repensar su rol y hacer propio el paradigma de “aprender a aprender” para mejorar las prácticas educativas con la incorporación efectiva de las TIC. Por esta razón se consideró necesario conocer la percepción de estos educadores frente a la adopción de las TIC. El objetivo de la investigación es describir y analizar las posturas de los docentes de educación superior acerca del proceso de innovación pedagógica, a través de la incorporación de tecnología, que está protagonizando la ESLE para poder diseñar acciones que contribuyan al fortalecimiento de la implementación de la nueva modalidad. Esta investigación propone una metodología de investigación – acción que permite obtener esta información y posteriormente, a partir del análisis de los resultados, diseñar acciones a seguir para acompañar y fortalecer la implementación de la nueva modalidad.Esta investigación se encuentra finalizando el segundo ciclo (1er año) de ejecución: se ha realizado el planteamiento del problema, se ha construido el marco teórico, se ha elaborado y aplicado un instrumento de recolección de datos y actualmente se está procesando esta información
Exact Black Holes and Universality in the Backreaction of non-linear Sigma Models with a potential in (A)dS4
The aim of this paper is to construct accelerated, stationary and
axisymmetric exact solutions of the Einstein theory with self interacting
scalar fields in (A)dS4. To warm up, the backreaction of the (non)-minimally
coupled scalar field is solved, the scalar field equations are integrated and
all the potentials compatible with the metric ansatz and Einstein gravity are
found. With these results at hand the non-linear sigma model is tackled. The
scalar field Lagrangian is generic; neither the coupling to the curvature,
neither the metric in the scalar manifold nor the potential, are fixed ab
initio. The unique assumption in the analysis is the metric ansatz: it has the
form of the most general Petrov type D vacuum solution of general relativity;
it is a a cohomogeneity two Weyl rescaling of the Carter metric and therefore
it has the typical Plebanski-Demianski form with two arbitrary functions of one
variable and one arbitrary functions of two variables. It is shown, by an
straightforward manipulation of the field equations, that the metric is
completely integrable without necessity of specifiying anything in the scalar
Lagrangian. This results in that the backreaction of the scalar fields, within
this class of metrics, is universal. The metric functions generically show an
explicit dependence on a dynamical exponent that allows to smoothly connect
this new family of solutions with the actual Plebanski-Demianski spacetime. The
remaining field equations imply that the scalar fields follow geodesics in the
scalar manifold with an affine parameter given by a non-linear function of the
spacetime coordinates and define the on-shell form of the potential plus a
functional equation that it has to satisfy. Finally, a general family of (A)dS4
static hairy black holes is explicitly constructed and its properties are
outlined.Comment: Several typos correcte
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