6,200 research outputs found
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
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