Probing the Large Magellanic Cloud's recent chemical enrichment history through its star clusters

We present Washington system colour-magnitude diagrams (CMDs) for 17 practically unstudied star clusters located in the bar as well as in the inner disc and outer regions of the Large Magellanic Cloud (LMC). Cluster sizes were estimated from star counts distributed throughout the entire observed fields. Based on the best fits of theoretical isochrones to the cleaned $(C-T_1,T_1)$ CMDs, as well as on the $\delta T_1$ parameter and the standard giant branch method, we derive ages and metallicities for the cluster sample. Four objects are found to be intermediate-age clusters (1.8-2.5 Gyr), with [Fe/H] ranging from -0.66 to -0.84. With the exception of SL263, a very young cluster ($\sim$ 16 Myr), the remaining 12 objects are aged between 0.32 and 0.89 Gyr, with their [Fe/H] values ranging from -0.19 to -0.50. We combined our results with those for other 231 clusters studied in a similar way using the Washington system. The resulting age-metallicity relationship shows a significant dispersion in metallicities, whatever age is considered. Although there is a clear tendency for the younger clusters to be more metal-rich than the intermediate ones, we believe that none of the chemical evolution models currently available in the literature reasonably well represents the recent chemical enrichment processes in the LMC clusters. The present sample of 17 clusters is part of our ongoing project of generating a database of LMC clusters homogeneously studied using the Washington photometric system and applying the same analysis procedureComment: 11 pages, 20 figures, 3 tables, Accepted for publication in MNRA

Ca II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. IV. ABUNDANCES FOR A LARGE SAMPLE OF FIELD STARS AND COMPARISON WITH THE CLUSTER SAMPLE

This paper represents a major step forward in the systematic and homogeneous study of Small Magellanic Cloud (SMC) star clusters and field stars carried out by applying the calcium triplet technique. We present in this work the radial velocity and metallicity of approximately 400 red giant stars in 15 SMC fields, with typical errors of about 7 km s-1 and 0.16 dex, respectively. We added to this information our previously determined metallicity values for 29 clusters and approximately 350 field stars using the identical techniques. Using this enlarged sample, we analyze the metallicity distribution and gradient in this galaxy. We also compare the chemical properties of the clusters and of their surrounding fields. We find a number of surprising results. While the clusters, taken as a whole, show no strong evidence for a metallicity gradient (MG), the field stars exhibit a clear negative gradient in the inner region of the SMC, consistent with the recent results of Dobbie et al. For distances to the center of the galaxy less than 4\ub0, field stars show a considerably smaller metallicity dispersion than that of the clusters. However, in the external SMC regions, clusters and field stars exhibit similar metallicity dispersions. Moreover, in the inner region of the SMC, clusters appear to be concentrated in two groups: one more metal-poor and another more metal-rich than field stars. Individually considered, neither cluster group presents an MG. Most surprisingly, the MG for both stellar populations (clusters and field stars) appears to reverse sign in the outer regions of the SMC. The difference between the cluster metallicity and the mean metallicity of the surrounding field stars turns out to be a strong function of the cluster metallicity. These results could be indicating different chemical evolution histories for these two SMC stellar populations. They could also indicate variations in the chemical behavior of the SMC in its internal and external regions

New variable stars discovered in the fields of three Galactic open clusters using the VVV Survey

This project is a massive near-infrared (NIR) search for variable stars in highly reddened and obscured open cluster (OC) fields projected on regions of the Galactic bulge and disk. The search is performed using photometric NIR data in the $J$-, $H$- and $K_s$- bands obtained from the Vista Variables in the V\'ia L\'actea (VVV) Survey. We performed in each cluster field a variability search using Stetson's variability statistics to select the variable candidates. Later, those candidates were subjected to a frequency analysis using the Generalized Lomb-Scargle and the Phase Dispersion Minimization algorithms. The number of independent observations range between 63 and 73. The newly discovered variables in this study, 157 in total in three different known OCs, are classified based on their light curve shapes, periods, amplitudes and their location in the corresponding color-magnitude $(J-K_s,K_s)$ and color-color $(H-K_s,J-H)$ diagrams. We found 5 possible Cepheid stars which, based on the period-luminosity relation, are very likely type II Cepheids located behind the bulge. Among the newly discovered variables, there are eclipsing binaries, $\delta$ Scuti, as well as background RR Lyrae stars. Using the new version of the Wilson & Devinney code as well as the "Physics Of Eclipsing Binaries" (PHOEBE) code, we analyzed some of the best eclipsing binaries we discovered. Our results show that these studied systems turn out to be ranging from detached to double-contact binaries, with low eccentricities and high inclinations of approximately $80^{\circ}$. Their surface temperatures range between $3500$K and $8000$K.Comment: 34 pages, 10 figures, 7 tables. Accepted for publication in New Astronom

Using combination of actions in reinforcement learning

Software agents are programs that can observe their environment and act in an attempt to reach their design goals. In most cases the selection of particular agent architecture determines the behaviour in response to the different problem states However, there are some problem domains in which it is desirable that the agent learns a good action execution policy by interacting with its environment. This kind of learning is called Reinforcement Learning and it is useful in the process control area. Given a problem state, the agent selects the adequate action to do and receives an immediate reward, then estimations about every action are updated and, after a certain period of time, the agent learns which the best action to be executed is. Most reinforcement learning algorithms perform simple actions while two or more are capable of being used. This work involves the use of RL algorithms to find an optimal policy in a gridworld problem and proposes a mechanism to combine actions of different types.Facultad de Informátic

Pueblos de indios Postconquista de la jurisdicción de Santiago del Estero : Investigación en las fuentes

Se analizaron fuentes editas e inéditas para localizar “pueblos indios” con los cuales los españoles hicieron contacto en los primeros años de la conquista del territorio de Santiago del Estero.Prime and late sources were analyzed in search of the indian peoples with which the Spaniards were in touch in the first years of the conquest of the territory of Santiago del Estero.Sociedad Argentina de Antropologí

Pueblos de indios Postconquista de la jurisdicción de Santiago del Estero : Investigación en las fuentes

Se analizaron fuentes editas e inéditas para localizar “pueblos indios” con los cuales los españoles hicieron contacto en los primeros años de la conquista del territorio de Santiago del Estero.Prime and late sources were analyzed in search of the indian peoples with which the Spaniards were in touch in the first years of the conquest of the territory of Santiago del Estero.Sociedad Argentina de Antropologí

Delayed Corneal Epithelial Healing after Intravitreal Bevacizumab: A Clinical and Experimental Study

Purpose: To report corneal epithelial defects (CEDs) and delayed epithelial healing after intravitreal bevacizumab (IVB) injection and to describe delayed corneal epithelial healing with topical administration of bevacizumab in an experimental rabbit model. Methods: A retrospective chart review was performed on 850 eyes of 850 patients with neovascular eye disease and diabetic macular edema who had received 1.25 to 2.5 mg IVB. In the experimental arm of the study, photorefractive keratectomy was used to create a 3 mm CED in the right eyes of 18 New Zealand rabbits which were then randomized to three equal groups. All rabbits received topical antibiotics, additionally those in group A received topical bevacizumab and animals in group B were treated with topical corticosteroids. The rate of epithelial healing was assessed at different time points using slitlamp photography. Results: In the clinical study, seven eyes of seven subjects developed CEDs the day after IVB injection. All of these eyes had preexisting corneal edema. The healing period ranged from 3 to 38 days (average 11 days) despite appropriate medical management. In the experimental study, topical bevacizumab and corticosteroids both significantly hindered corneal epithelial healing at 12 and 24 hours. Conclusion: Bevacizumab was demonstrated to cause CEDs in clinical settings. Moreover, corneal epithelial healing was delayed by topical application of bevacizumab, in the experimental model. These short-term results suggest that corneal edema may be considered as a risk factor for epithelial defects after IVB

Modelo de apoyo para la Toma de Decisiones en QoS

El proceso de Toma de Decisiones es fundamental en todos los niveles de una organización y consiste en seleccionar la mejor alternativa entre todas las disponibles para resolver una situación problemática. Si bien las decisiones son tomadas por personas especializadas, existen herramientas (los Sistemas de Soporte de Decisiones) que pueden ser utilizadas para dar apoyo durante el proceso de decisión. En este artículo se presenta un modelo de soporte de decisiones para administradores de redes de computadoras que determina la configuración adecuada de los parámetros de la red con el objetivo de mejorar la calidad del servicio. El modelo utiliza el Proceso Jerárquico Analítico basado en los criterios y alternativas de tráfico definidos por el administrador. Se ejemplifica la utilización en un entorno académico y finalmente se presenta una extensión del modelo para añadir opiniones de múltiples expertos (administradores).Presentado en el XII Workshop Agentes y Sistemas Inteligentes (WASI)Red de Universidades con Carreras en Informática (RedUNCI

Multi-Criteria Decision Model based on AHP and Linguistic Information

Multi-Criteria Decision Analysis (MCDA) is a usual activity among organisations and decisions related to people’s activities. Due to the complexity of considering multiple criteria, to select an alternative is a non-trivial task. From operative levels to managerial ones, MCDA is implemented by using several (formal and informal) techniques. Two useful techniques that help to make a decision are the Analytic Hierarchy Process (AHP) and MCDA models based on Linguistic Information (LI). This work describes a MCDA framework that combines the mentioned techniques in order to provide more confidence in the decision making process. To test the proposed model, framework was used to select the adequate network configuration to improve quality of service (QoS). Finally, the framework’s outputs were compared to real experts’ opinions obtaining satisfactory results. Keywords: IPv6 deployment, IPv6 transition solutions, performance analysis, DNS64, TOTD, security, cache poisoning attack, random permutation.Facultad de Informátic