Stellar Open Clusters' Membership Probabilities: an N-Dimensional Geometrical Approach

We present a new geometrical method aimed at determining the members of open clusters. The methodology estimates, in an N-dimensional space, the membership probabilities by means of the distances between every star and the cluster central overdensity. It can handle different sets of variables, which have to satisfy the simple condition of being more densely distributed for the cluster members than for the field stars (as positions, proper motions, radial velocities and/or parallaxes are). Unlike other existing techniques, this fact makes the method more flexible and so can be easily applied to different datasets. To quantify how the method identifies the clus- ter members, we design series of realistic simulations recreating sky regions in both position and proper motion subspaces populated by clusters and field stars. The re- sults, using different simulated datasets (N = 1, 2 and 4 variables), show that the method properly recovers a very high fraction of simulated cluster members, with a low number of misclassified stars. To compare the goodness of our methodology, we also run other existing algorithms on the same simulated data. The results show that our method has a similar or even better performance than the other techniques. We study the robustness of the new methodology from different subsamplings of the ini- tial sample, showing a progressive deterioration of the capability of our method as the fraction of missing objects increases. Finally, we apply all the methodologies to the real cluster NGC 2682, indicating that our methodology is again in good agreement with preceding studies.Comment: 15 pages, 9 figures, 6 tables, accepted for publication in MNRA

Entropy stabilizes floppy crystals of mobile DNA-coated colloids

Grafting linkers with open ends of complementary single-stranded DNA makes a flexible tool to tune interactions between colloids,which facilitates the design of complex self-assembly structures. Recently, it has been proposed to coat colloids with mobile DNA linkers, which alleviates kinetic barriers without high-density grafting, and also allows the design of valency without patches.However, the self-assembly mechanism of this novel system is poorly understood.Using a combination of theory and simulation, we obtain phase diagrams forthe system in both two and three dimensional spaces, and find stable floppy squareand CsCl crystals when the binding strength is strong, even in the infinite bindingstrength limit. We demonstrate that these floppy phases are stabilized by vibrational entropy, and "floppy" modes play an important role in stabilizing the floppy phases for the infinite binding strength limit. This special entropic effect in the self-assembly of mobile DNA-coated colloids is very different from conventional molecular self-assembly, and it offers new axis to help design novel functional materials using mobile DNA-coated colloids.Comment: Accepted in Physical Review Letter

Activismo ciudadano y acontecimientos políticos en la transformación de la esfera pública digital en españa: del sms ¡pásalo! a Podemos

This paper discusses digital communication, activism and political system in Spain from a critical-historical perspective. The results of combined empirical and analytical research indicate that a critical digital public sphere emerged in 2004 affecting the evolution of the political sphere to this day. Traditional parties had a slow and instrumental approach to the digital realm. Conversely, cyber-activism unfolded new options of political action, both in the short and long term, transforming the bipartisan system.El artículo aborda la comunicación digital, el activismo y el sistema político en España desde una perspectiva crítica-histórica. Los resultados de una investigación empírica y analítica indican que en 2004 surgió una esfera pública digital crítica que afectó la evolución de la esfera política hasta hoy. Los partidos tradicionales se acercaron al entorno digital de manera lenta e instrumental. En cambio, el ciberactivismo abrió nuevas opciones de acción política, a corto y largo plazo, transformando el sistema bipartidista

Highly dynamically evolved intermediate-age open clusters

We present a comprehensive UBVRI and Washington CT1T2 photometric analysis of seven catalogued open clusters, namely: Ruprecht 3, 9, 37, 74, 150, ESO 324-15 and 436-2. The multiband photometric data sets in combination with 2MASS photometry and Gaia astrometry for the brighter stars were used to estimate their structural parameters and fundamental astrophysical properties.We found that Ruprecht 3 and ESO 436-2 do not show self-consistent evidence of being physical systems. The remained studied objects are open clusters of intermediate age (9.0 ≤ log(t yr-1) ≤ 9.6), of relatively small size (rcls ~ 0.4-1.3 pc) and placed between 0.6 and 2.9 kpc from the Sun.We analysed the relationships between core, half-mass, tidal and Jacoby radii as well as half-mass relaxation times to conclude that the studied clusters are in an evolved dynamical stage. The total cluster masses obtained by summing those of the observed cluster stars resulted to be ~10-15 per cent of the masses of open clusters of similar age located closer than 2 kpc from the Sun. We found that cluster stars occupy volumes as large as those for tidally filled clusters.Fil: Piatti, Andres Eduardo. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Dias, Wilton S.. Universidade Federal de Itajuba; BrasilFil: Sampedro, Laura M.. Instituto de Astrofísica de Andalucía; España. Universidade de Sao Paulo; Brasi

Estimular la demanda

The public today has within its grasp an offer of scientific knowledge without the remotest historical precedent. And while it is true that technology demands ever more specialists, what is it important is that we also have ever better theories, ideas which are worth a thousand jargons and a million data. While the specialists are solving the technical problems, this impedes their results and ideas from reaching —not to speak of the wider public, that is, 10 million spectators— but the general educated audience, which of course represents far more than the 3000 typical buyers of each book in a science collection. One hundred thousand people would already by an ambitious target. And we will not reach them without launching attractive offers which narrate the exciting intellectual adventure of scientific discovery. KEY WORDS: scientific content; scientific communicator; media; public; culture. PALABRAS CLAVE: contenidos científicos; comunicador científico; medios de comunicación; público; cultura

Assessments of the "Acceptance of Virtual Training Technology" by University Teachers Attending to a Virtual Training Course

En esta investigación se describe la experiencia desarrollada con 24 profesores y profesoras universitarios de la Universidad Apec, en Santo Domingo (República Dominicana), con la finalidad de conocer el grado de aceptación de la formación virtual como metodología, después de participar en una acción formativa sobre dicha temática, a través del modelo TAM de Davis (Davis, F. (1989), "Perceived usefulness, perceived ease of use, and user acceptance of information technology", MIS Quarterly 13(3), 319–340.). Entre los resultados más relevantes destacamos que la percepción que tienen sobre la facilidad de uso y utilidad, la actitud hacia el uso y la relevancia de la misma en el desarrollo de su trabajo como docentes es muy positiva.In this investigation there are described the experience developed with 24 university teachers of the University Apec, in Santo Domingo (Dominican Republic), by the purpose of knowing the degree of acceptance of the virtual formation as methodology, after taking part in a formative action on the above mentioned subject matter, across the model Davis's TAM (Davis, F. (1989), "Perceived usefulness, perceived ease of use, and user acceptance of information technology", MIS Quarterly 13(3), 319–340). Between the most relevant results we emphasize that the perception that they have on the facility of use and usefulness, the attitude towards the use and the relevancy of the same one in the development of his work like teachers is very positive