Multiple time-scale approach for a system of Brownian particles in a non-uniform temperature field

The Smoluchowsky equation for a system of interacting Brownian particles in a temperature gradient is derived from the Kramers equation by means of a multiple time-scale method. The interparticle interactions are assumed to be represented by a mean-field description. We present numerical results that compare well with the theoretical prediction together with an extensive discussion on the prescription of the Langevin equation in overdamped systems.Comment: 8 pages, 2 figure

Monteiroa hatschbachii Krapov.

Cantagalo, PR-170, 13 km S de Biturana.publishedVersio

Extracting Hα\alpha flux from photometric data in the J-PLUS survey

We present the main steps that will be taken to extract H$\alpha$ emission flux from Javalambre Photometric Local Universe Survey (J-PLUS) photometric data. For galaxies with $z\lesssim0.015$, the H$\alpha$+[NII] emission is covered by the J-PLUS narrow-band filter $F660$. We explore three different methods to extract the H$\alpha$ + [NII] flux from J-PLUS photometric data: a combination of a broad-band and a narrow-band filter ($r'$ and $F660$), two broad-band and a narrow-band one ($r'$, $i'$ and $F660$), and a SED-fitting based method using 8 photometric points. To test these methodologies, we simulated J-PLUS data from a sample of 7511 SDSS spectra with measured H$\alpha$ flux. Based on the same sample, we derive two empirical relations to correct the derived H$\alpha$+[NII] flux from dust extinction and [NII] contamination. We find that the only unbiased method is the SED fitting based one. The combination of two filters underestimates the measurements of the H$\alpha$ + [NII] flux by a 28%, while the three filters method by a 9%. We study the error budget of the SED-fitting based method and find that, in addition to the photometric error, our measurements have a systematic uncertainty of a 4.3%. Several sources contribute to this uncertainty: differences between our measurement procedure and the one used to derive the spectroscopic values, the use of simple stellar populations as templates, and the intrinsic errors of the spectra, which were not taken into account. Apart from that, the empirical corrections for dust extinction and [NII] contamination add an extra uncertainty of 14%. Given the J-PLUS photometric system, the best methodology to extract H$\alpha$ + [NII] flux is the SED-fitting based one. Using this method, we are able to recover reliable H$\alpha$ fluxes for thousands of nearby galaxies in a robust and homogeneous way.Comment: 11 pages, 14 figures. Minor changes to match the published versio

Ayenia aprica Cristóbal

Aparicio CuépublishedVersio

Pavonia orientalis Krapov.

Cerro Pan de AzucarAriza 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

Byttneria acalyphifolia (Griseb.) Ariza

Dique San Ignacio, a 10 km de La CochapublishedVersio

Twitter, partisan use and institutional use: Comparative analysis between the profiles of Moncloa, Madrid City Council and their ruling parties

This paper seeks to compare and analyse the differences in the use of Twitter that, Partido Popular, as a traditional political party, and Ahora Madrid, as a new political party, make of the institutional channels for the public institutions that they administer. In addition, the present study analyses three different periods in the electoral process: the pre-campaign, campaign and post-campaign during the Spanish general elections of December 20th, 2015 in order to see if the election periods caused changes in their communications on Twitter. The sample consists of four cases divided into two groups for content analysis. On one hand, the Government’s Twitter profile (@desdelamoncloa) and of its ruling party, Partido Popular (@ppopular), comprise the old political group, while the Madrid City Council (@Madrid) and its ruling party, Ahora Madrid (@AhoraMadrid), are integrated into the new political group. Additionally, word clouds provide a visual representation of the main terms used by each group. The study results show which group uses and better leverages Twitter’s potential, in that Partido Popular and Moncloa have clearer differences between party and institutional channels, while Ahora Madrid and the Madrid City Council do not seem to be as clear about the difference between the two concepts and use the party channel as the city council channel. However, the results demonstrate that the new political profile leverages Twitter’s potential more.El presente trabajo analiza las diferencias de uso de Twitter por parte de dos partidos políticos españoles, Partido Popular, como partido tradicional, y Ahora Madrid, como nuevo partido, así como la utilización de los canales institucionales de los entes públicos que estos partidos presiden a nivel nacional y local, respectivamente. Los resultados muestran usos y aprovechamientos diferentes de las potencialidades de Twitter. El estudio se realizó en tres periodos electorales diferenciados: precampaña, campaña y post-campaña de las elecciones generales del 20 de diciembre de 2015, para examinar también cambios de comportamiento en la comunicación en Twitter en el periodo electoral. La muestra consta de cuatro casos divididos en dos grupos para el análisis de contenido. Por un lado, el perfil en Twitter del Gobierno (@desdelamoncloa) y el del partido gobernante, el Partido Popular (@ppopular) constituyen el grupo de la vieja política. Por otro lado, el Ayuntamiento de Madrid (@madrid) y su partido gobernante, Ahora Madrid (@AhoraMadrid), se integran dentro del grupo de nueva política. Además, unas nubes de palabras presentarán visualmente las principales ideas enviadas por los perfiles. Los resultados indican que Partido Popular y Moncloa mantuvieron un uso diferenciado entre los canales de partido y los institucionales, mientras que en el caso de Ahora Madrid y el Ayuntamiento de Madrid se constataron usos concluyentes y no diferenciados entre el canal del partido y el institucional. Además, se observa que los perfiles de la nueva política aprovechan más las potencialidades de Twitter

Local models-based regression trees for very short-term wind speed prediction

This paper evaluates the performance of different types of Regression Trees (RTs) in a real problem of very short-term wind speed prediction from measuring data in wind farms. RT is a solidly established methodology that, contrary to other soft-computing approaches, has been under-explored in problems of wind speed prediction in wind farms. In this paper we comparatively evaluate eight different types of RTs algorithms, and we show that they are able obtain excellent results in real problems of very short-term wind speed prediction, improving existing classical and soft-computing approaches such as multi-linear regression approaches, different types of neural networks and support vector regression algorithms in this problem.We also show that RTs have a very small computation time, that allows the retraining of the algorithms whenever new wind speed data are collected from the measuring towers.Ministerio de Ciencia y Tecnología ECO2010-22065-C03-02Ministerio de Ciencia y Tecnología TIN2011-28956-C02Junta de Andalucía P12-TIC-1728Universidad Pablo de Olavide APPB81309

Crystallization and melting of bacteria colonies and Brownian Bugs

Motivated by the existence of remarkably ordered cluster arrays of bacteria colonies growing in Petri dishes and related problems, we study the spontaneous emergence of clustering and patterns in a simple nonequilibrium system: the individual-based interacting Brownian bug model. We map this discrete model into a continuous Langevin equation which is the starting point for our extensive numerical analyses. For the two-dimensional case we report on the spontaneous generation of localized clusters of activity as well as a melting/freezing transition from a disordered or isotropic phase to an ordered one characterized by hexagonal patterns. We study in detail the analogies and differences with the well-established Kosterlitz-Thouless-Halperin-Nelson-Young theory of equilibrium melting, as well as with another competing theory. For that, we study translational and orientational correlations and perform a careful defect analysis. We find a non standard one-stage, defect-mediated, transition whose nature is only partially elucidated.Comment: 13 Figures. 14 pages. Submitted to Phys. Rev.