Incremental learning of skills in a task-parameterized Gaussian Mixture Model

The final publication is available at link.springer.comProgramming by demonstration techniques facilitate the programming of robots. Some of them allow the generalization of tasks through parameters, although they require new training when trajectories different from the ones used to estimate the model need to be added. One of the ways to re-train a robot is by incremental learning, which supplies additional information of the task and does not require teaching the whole task again. The present study proposes three techniques to add trajectories to a previously estimated task-parameterized Gaussian mixture model. The first technique estimates a new model by accumulating the new trajectory and the set of trajectories generated using the previous model. The second technique permits adding to the parameters of the existent model those obtained for the new trajectories. The third one updates the model parameters by running a modified version of the Expectation-Maximization algorithm, with the information of the new trajectories. The techniques were evaluated in a simulated task and a real one, and they showed better performance than that of the existent model.Peer ReviewedPostprint (author's final draft

Social vulnerability to floods in two coastal megacities: New York City and Mumbai

In this paper we assess differential exposure to flooding in two coastal megacities, New York and Mumbai, both of which suffered major flood-related disasters in the past decade. Specifically, we examine whether the most exposed populations are also the most socially vulnerable. First, we developed Social Vulnerability Indices (SoVIs) for each city with census data. We then overlaid the SoVI scores onto flood extent maps for Hurricane Sandy (New York, October 2012) and the Mumbai flash floods (July 2005), as well as for the evacuation zones for New York, to examine patterns of differential exposure. Our results suggest a degree of differential exposure in New York, especially in the highest flood risk areas, and provide fairly clear evidence for differential exposure in Mumbai. However, differences in the input resolution and confidence in the datasets for Mumbai make the results more uncertain. The paper concludes with a discussion of the policy implications and the data needs for urban spatial vulnerability assessments

First data available for the population of scorpions (Buthus occitanus) in the Columbretes Islands (Mediterranean, Spain)

Abstract not availabl

Seguimiento de una invasión de arañas del género Argiope (Arachnida, Araneidae) en las islas Columbretes

Las invasiones de especies foráneas constituyen una de las causas que originan cambios importantes en la biodiversidad global. Hemos realizado un estudio descriptivo para documentar la fluctuación anual de la densidad de arañas del género Argiope (A. lobata y A. bruennichi) después de que en verano de 2004 se detectara una invasión de estas especies en el Parque Natural de las Islas Columbretes (Mediterráneo, España). Desde entonces, ambas especies han estado presentes en la isla hasta 2008, con la excepción de 2007 en que no se observó ningún ejemplar de A. bruennichi durante el mes de agosto en el que se realizaron los censos anuales. El porcentaje de arañas A. lobata ha sido mayor que el de A. bruennichi durante los 5 años de seguimiento. Los resultados sugieren que las condiciones bióticas y abióticas de la isla deben ser más favorables para A. lobata que para A. bruennichi, o bien que debe existir competencia entre ellas. La densidad de ambas especies ha disminuido a lo largo de los años, lo que sugiere que las condiciones de la isla no deben constituir un hábitat adecuado para especies de arañas de este género. Nuestras observaciones parecen indicar que la presencia de Argiope en Columbretes no debería representar una amenaza para las especies endémicas de artrópodos ni para la lagartija endémica Podarcis atrata. No obstante, esto es algo que habría que confirmar con datos empíricos. Por ello sería muy recomendable proceder con el seguimiento de la densidad de Argiope a largo plazo, también con el seguimiento de su dieta y de las interacciones con otras especies. También sería muy recomendable dirigir futuros estudios hacia el examen de los patrones y mecanismos que favorecen el éxito o fracaso de las invasiones de arañas en ecosistemas insulares

Preliminary results on the 233U capture cross section and alpha ratio measured at n_TOF (CERN) with the fission tagging technique

233U is of key importance among the fissile nuclei in the Th-U fuel cycle. A particularity of 233U is its small neutron capture cross-section, which is on average about one order of magnitude lower than the fission cross-section.The accuracy in the measurement of the 233U capture cross-section depends crucially onan efficient capture-fission discrimination, thus a combined set-up of fission and ¿-detectors is needed. A measurement of the 233U capture cross-section and capture-to-fissionratio was performed at the CERN n_TOF facility. The Total Absorption Calorimeter (TAC) of n_TOF was employed as ¿-detector coupled with a novel compact ionization chamber as fission detector. A brief description of the experimental set-up will be given, and essential parts of the analysis procedure as well as the preliminary response of the set-up to capture are presented and discussedPostprint (published version