Magnification by Galaxy Group Dark Matter Halos

We report on the detection of gravitational lensing magnification by a population of galaxy groups, at a significance level of 4.9 sigma. Using X-ray selected groups in the COSMOS 1.64 deg^2 field, and high-redshift Lyman break galaxies as sources, we measure a lensing-induced angular cross-correlation between the samples. After satisfying consistency checks that demonstrate we have indeed detected a magnification signal, and are not suffering from contamination by physical overlap of samples, we proceed to implement an optimally weighted cross-correlation function to further boost the signal to noise of the measurement. Interpreting this optimally weighted measurement allows us to study properties of the lensing groups. We model the full distribution of group masses using a composite-halo approach, considering both the singular isothermal sphere and Navarro-Frenk-White profiles, and find our best fit values to be consistent with those recovered using the weak-lensing shear technique. We argue that future weak-lensing studies will need to incorporate magnification along with shear, both to reduce residual systematics and to make full use of all available source information, in an effort to maximize scientific yield of the observations.Comment: 6 pages, 3 figures, Accepted by Ap

Weak lensing peak count as a probe of f(R) theories

Weak gravitational lensing by galaxy clusters on faint higher redshift galaxies has been traditionally used to study the cluster mass distribution and as a tool to identify clusters as peaks in the shear maps. However, it becomes soon clear that peaks statistics can also be used as a way to constrain the underlying cosmological model due to its dependence on both the cosmic expansion rate and the growth rate of structures. This feature makes peak statistics particularly interesting from the point of view of discriminating between General Relativity and modified gravity. Here we consider a general class of $f(R)$ theories and compute the observable mass function based on the aperture mass statistics. We complement our theoretical analysis with a Fisher matrix forecast of the constraints that an Euclid\,-\,like survey can impose on the $f(R)$ model parameters. We show that peak statistics alone can in principle discriminate between General Relativity and $f(R)$ models and strongly constrain the $f(R)$ parameters that are sensitive to the non-linear growth of structure. However, further analysis is needed in order to include possible selection function in the peaks redshift determination.Comment: 17 pages, 9 figures, 1 table, accepted for publication on MNRAS on Jan 14, 2013; updated to match the published versio

Galaxy cluster mass reconstruction project - I. Methods and first results on galaxy-based techniques

This paper is the first in a series in which we perform an extensive comparison of various galaxy-based cluster mass estimation techniques that utilize the positions, velocities and colours of galaxies. Our primary aim is to test the performance of these cluster mass estimation techniques on a diverse set of models that will increase in complexity. We begin by providing participating methods with data from a simple model that delivers idealized clusters, enabling us to quantify the underlying scatter intrinsic to these mass estimation techniques. The mock catalogue is based on a Halo Occupation Distribution (HOD) model that assumes spherical Navarro, Frenk and White (NFW) haloes truncated at R₂₀₀, with no substructure nor colour segregation, and with isotropic, isothermal Maxwellian velocities. We find that, above 1014Mʘ, recovered cluster masses are correlated with the true underlying cluster mass with an intrinsic scatter of typically a factor of 2. Below 1014Mʘ, the scatter rises as the number of member galaxies drops and rapidly approaches an order of magnitude. We find that richness-based methods deliver the lowest scatter, but it is not clear whether such accuracy may simply be the result of using an over-simplistic model to populate the galaxies in their haloes. Even when given the true cluster membership, large scatter is observed for the majority non-richness-based approaches, suggesting that mass reconstruction with a low number of dynamical tracers is inherently problematic

Multivariate index of use and appropriation of ICT in schools

The present study proposes and validates empirically a multivariate index to assess the use and appropriation of ICT in school teachers, using a quantitative scale based on the UbiTAG model. Data is collected from 121 schools in Colombia, where 24 schools where intervened by a program that integrates ICT in learning environments in a local town in Colombia since 2013. The rest of the schools are located in 5 departments in Colombia, and are used as a control group in this analysis. Our findings provide empirical evidence that the theoretical model and its corresponding ntervention improves the use and appropriation of ICT with educational purposes by teachers. Using exploratory factor analysis we also validate statistically our instrument, and the usefulness of the proposed metric for ICT use in an education environment

Germán Espinosa y la lección del maestro

The philosophical interest related language has in Germán Espinosa’s writing one solution: the pertinence between things and ideas which assure the logic comprehension. It is precisely in this point, where the present article proposes to develop a dialoguEl lenguaje relacionado con el interés filosófico tiene en la escritura de Germán Espinosa una solución: la pertinencia entre las cosas y las ideas que aseguran la comprensión lógica. Es precisamente en este punto, donde el presente artículo propone desa

(IN)VERSIONES EN EL PROYECTO DE LA INTELIGENCIA ARTIFICIAL

Las siguientes líneas hablan del ‘proyecto de la inteligencia artificial (IA)’, no en lostérminos de un proyecto concreto, como lo harían los ingenieros de lacomputación, sino desde la perspectiva estrictamente teórica. ¿Qué comprometepropiamente el proyecto de la IA? El artículo da a este respecto los pasos quepodrían llevarnos desde las imposibles versiones de la literatura, hasta lasexigencias de una ‘filosofía de la IA’, como los problemas estructurales de lainducción, del marco, de la simulación, de la implicación

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We return to Andrés Bello's work to integrate his deliberations to the history of philosophy. In 1829, at the request of Simón Bolivar, Bello brought back to America not one but many revolutions: he organized "public instruction" in Chile, was principal of the new Universidad de Chile, redacted the Código civil chileno, oriented foreign policy, redacted Tratado de derecho internacional, and lastly, happily culminated his Gramática de la lengua castellana destinada al uso de los americanos (1847). Among these revolutionary tasks, it is worth exploring the aspect of one of them, represented in Filosofia del entendimiento. The task thus proposed, however, is not that simple, because the revolution in this work is strong in relation to outdated philosophical systems oriented to the prescription of behavioural canons and to the observation of dogmas.Volvemos a la obra de Andrés Bello para integrar su deliberación en la historia de la filosofía. Bello trajo de regreso a América en 1829 a instancias de Simón Bolívar, no una, sino muchas revoluciones; organizó en Chile la "instrucción pública", fue Rector de la nueva Universidad de Chile, redactó el Código civil chileno, orientó la política exterior, y el Tratado de derecho internacional, llevó a feliz término su Gramática de la lengua castellana destinada al uso de los americanos (1847). Entre estas tareas de desprendimiento revolucionario, conviene explorar el cariz de una de ellas, representada en la Filosofía del entendimiento. La tarea así propuesta no resulta sin embargo sencilla, puesto que la revolución es en esta obra contundente en relación con sistemas filosóficos caducos orientados a la prescripción de cánones de comportamiento y a la observancia de dogmas.

En el nombre de Edmund Husserl: el caso Gadamer, o la escalera al vacío

The thesis I’m looking to advance is related to Wittgestein’s “Stairway to emptiness”, applied to the intellectual relationship between Edmund Husserl and Hans-Georg Gadamer. An event that is not self evident if we consider that in philosophical discussioLa tesis que estoy buscando avanzar está relacionada con la "Escalera al vacío" de Wittgestein, aplicada a la relación intelectual entre Edmund Husserl y Hans-Georg Gadamer. Un evento que no es evidente si consideramos que en las discusiones filosóficas