Randall-Sundrum brane cosmology: modification of late-time cosmic dynamics by exotic matter

In this paper we show, through the study of concrete examples, that, depending on the cosmic dynamics of the energy density of matter degrees of freedom living in the brane, Randall-Sundrum (RS) brane effects can be important not only at short distances (UV regime), but also at large cosmological scales (IR regime). Our first example relies on the study, by means of the dynamical systems tools, of a toy model based in a non-linear electrodynamics (NLED) Lagrangian. Then we show that other, less elaborated models, such as the inclusion of a scalar phantom field, and of a tachyon phantom field -- trapped in the brane -- produce similar results. The form of the RS correction seems to convert what would have been future attractors in general relativity into saddle points. The above "mixing of scales" effect is distinctive only of theories that modify the right-hand-side (matter part) of the Friedmann equation, so that, for instance, DGP-brane models do not show this feature.Comment: Latex, 12 pages, 9 eps figures. Title changed, discussion improved. Version that matches the one published in CQ

Self accelerating solutions in a DGP brane with a scalar field trapped on it: the dynamical systems perspective

We apply the dynamical systems tools to study the linear dynamics of a self-interacting scalar field trapped on a DGP brane. The simplest kinds of self-interaction potentials are investigated: a) constant potential, and b) exponential potential. It is shown that the dynamics of DGP models can be very rich and complex. One of the most interesting results of this study shows that dynamical screening of the scalar field self-interaction potential, occuring within the Minkowski cosmological phase of the DGP model and mimetizing 4D phantom behaviour, is an attractor solution for a constant self-interaction potential but not for the exponential one. In the latter case gravitational screening is not even a critical point of the corresponding autonomous system of ordinary differential equations.Comment: 9 pages, 8 figures. Version that matches the one published by PL

La investigación internacional en seres humanos: de la justicia distributiva a la justicia social

La investigación internacional en seres humanos patrocinada por la industria farmacéutica ha sido objeto de múltiples pronunciamientos bioéticos. Sin embargo ha hecho falta una reflexión desde la justicia social, que tome en cuenta los determinantes sociales de la salud en cada lugar. En este artículo se ofrecen algunos aportes para la bioética de la investigación internacional en seres humanos a partir de la justicia social. Many bioethical papers have been written about the international research in humans sponsored by the pharmaceutical industry. The perspective of social justice, which takes into account the social determinants of health in each place, however, has been lacking in most of these papers. This article offers some contributions to the bioethics of international human-subjects research based on social justice

Present accelerated expansion of the universe from new Weyl-Integrable gravity approach

We investigate if a recently introduced formulation of general relativity on a Weyl-integrable geometry, contains cosmological solutions exhibiting acceleration in the present cosmic expansion. We derive the general conditions to have acceleration in the expansion of the universe and obtain a particular solution for the Weyl scalar field describing a cosmological model for the present time in concordance with the data combination Planck + WP + BAO + SN.Comment: Version to be published in Eur. Phys. J.

Application of aircraft's flight testing techniques to the aerodynamic characterization of power kites

This thesis has developed an experimental methodology for the flight testing and data analysis of power kites applied to Airborne Wind Energy Systems (AWES). In particular, the Estimation Before Modeling technique, a well-known method in the aerospace industry for the aerodynamic characterization of an aircraft using real flight data, has been adapted for tethered aircraft. The developed methodology has two main building blocks: (i) an experimental setup to record experimental data during the flight testing, and (ii) a Flight Path Reconstruction algorithm to estimate the state of the system from the experimental data. From them, the aerodynamic characteristics of two types of kites were investigated. The proposed experimental setup was designed to be low cost, portable and easily adaptable to both, rigid and semi-rigid kites. It is composed of an instrumented kite representative of the ones used in AWES, an instrumented control bar, a ground computer and a wind station. Whenever it was possible, commercial off the shelf components have been used, including low cost openhardware sensors based on the PixHawk platform. However, after the first flight tests were conducted and the obtained results were discussed, high precision sensors were also included. The Flight Path Reconstruction (FPR) algorithm for tethered aircraft is based on an Extended Kalman Filter (EKF). In addition to the standard set of estimated state variables (ie. Euler angles, position or ground speed), the algorithm also provides the aerodynamic torque and forces upon the kite as well as the tether tensions and wind velocity vector. The EBM technique, and the FPR algorithm have been used to identify the aerodynamic characteristics of both, four-line Leading Edge Inflatable (LEI) kites and two-line Rigid Frame Delta (RFD) kites. Quantitative and qualitative results have been obtained. Albeit both types of kites exhibited very high AoA during the flight, some significant differences were found. In particular, the estimated lift coefficient of the LEI kite showed a behavior identified with a post-stall condition, while the RFD showed a pre-stall behavior with a lower AoA and a positive relation between the lift coefficient and the kite AoA. The presented experimental methodology can be of great interest for AWE industry as it helps to improve modeling of tethered aircraft, leading to more accurate performance figures which may increase investors interest in the technology. Moreover, flight testing methodologies and experimental data analysis are of great interest for benchmarking AWES performances, contributing to de-risk their development process and providing better tools for AWE "best concept" identification. Finally, as a sub-product of the presented methodology, the FPR algorithm can be used as a validated state estimator of the tethered aircraft, which is a key element of a closed loop flight control system.Programa de Doctorado en Mecánica de Fluidos por la Universidad Carlos III de Madrid; la Universidad de Jaén; la Universidad de Zaragoza; la Universidad Nacional de Educación a Distancia; la Universidad Politécnica de Madrid y la Universidad Rovira i VirgiliPresidente: Marco Fontana.- Secretario: Manuel García-Villalba Navaridas.- Vocal: Félix Terroba Ramíre