Randall-Sundrum brane cosmology: modification of late-time cosmic dynamics by exotic matter

In this paper we show, through the study of concrete examples, that, depending on the cosmic dynamics of the energy density of matter degrees of freedom living in the brane, Randall-Sundrum (RS) brane effects can be important not only at short distances (UV regime), but also at large cosmological scales (IR regime). Our first example relies on the study, by means of the dynamical systems tools, of a toy model based in a non-linear electrodynamics (NLED) Lagrangian. Then we show that other, less elaborated models, such as the inclusion of a scalar phantom field, and of a tachyon phantom field -- trapped in the brane -- produce similar results. The form of the RS correction seems to convert what would have been future attractors in general relativity into saddle points. The above "mixing of scales" effect is distinctive only of theories that modify the right-hand-side (matter part) of the Friedmann equation, so that, for instance, DGP-brane models do not show this feature.Comment: Latex, 12 pages, 9 eps figures. Title changed, discussion improved. Version that matches the one published in CQ

Asymptotic Properties of a Supposedly Regular (Dirac-Born-Infeld) Modification of General Relativity

We apply the dynamical systems tools to study the asymptotic properties of a cosmological model based on a non-linear modification of General Relativity in which the standard Einstein-Hilbert action is replaced by one of Dirac-Born-Infeld type. It is shown that the dynamics of this model is extremely rich: there are found equilibrium points in the phase space that can be associated with matter-dominated, matter-curvature scaling, de Sitter, and even phantom-like solutions. Depending on the value of the overall parameters the dynamics in phase space can show multi-attractor structure into the future (multiple future attractors may co-exist). This is a consequence of bifurcations in control parameter space, showing strong dependence of the model's dynamical properties on the free parameters. Contrary to what is expected from non-linear modifications of general relativity of this kind, removal of the initial spacetime singularity is not a generic feature of the corresponding cosmological model. Instead, the starting point of the cosmic dynamics -- the past attractor in the phase space -- is a state of infinitely large value of the Hubble rate squared, usually associated with the big bang singularity.Comment: 12 pages, Revtex, 12 eps figures. Several new references added. Minor changes in the main text. Discussion improve

Determinar la vulnerabilidad al desabastecimiento hídrico del Páramo Guerrero y establecer las posibles medidas de adaptación y mitigación

Saneamiento de comunidadesEl propósito del trabajo fue el de determinar la vulnerabilidad al desabastecimiento hídrico de diez (10) veredas de Páramo Guerrero utilizando la metodología del IDEAM y con base en sus resultados recomendar medidas de adaptación y mitigación encaminadas a proteger y regular el Recurso Hídrico. La importancia del trabajo realizado fue la de mostrar la fragilidad de mantener la oferta de agua para el abastecimiento de las veredas evaluadas.EspecializaciónEspecialista en Recursos Hídrico

La medición retrospectiva del bienestar mediante indicadores antropométricos: Zamora, 1840-1935

En este trabajo analizamos la altura de la población de una ciudad castellana, Zamora, en el largo plazo, con el propósito de estimar la evolución de su nivel de vida. Nuestro objetivo es probar que el capitalismo agrario como estrategia de crecimiento provocó un incremento del nivel de vida menor que el que indujo la industrialización plena. Por otra parte, constatamos la existencia de una "penalización" urbana en Castilla. Los niveles de vida de la población rural fueron más altos que los calculados para la urbana, al menos, hasta comienzos del siglo XX.In this paper we analyse the population height of a Castilian town, Zamora, in the long term in order to estimate the evolution of standard of living. Our aim is to prove that the agrarian capitalism a economic development strategy provoked and improvement of the standard of living smaller that the industrialization. On the other hand, we reveal the existence of an "urban penalty" in Castile. Rural inhabitants' standard of living, were higher than those calculated for the urban population, at least, until the beginnings of the 20 century

An anthropometric study of inequality and social segregation in a castilian city. Zamora, 1840-1936

this paper proposes several indicators for income distribution derived from the height of individuals. From the study of these indicators, we can conclude that the economic backwardness that zamora suffered led a further deterioration of living standards compared to other more economically advanced areas in the region, but less drastic changes in income distribution. Even so, anthropometric indicators show the strong bias and discrimination suffered by unskilled workers as well as the social segregation of the needy, who were isolated in the marginal areas of the city. (paper in Spanish)Living standards, Income distribution, Anthropometry, Urban history, Castille, Zamora

Exchanges and Money from a Liberal Perspective

En tanto una sociedad libre debe fundamentarse en intercambios voluntarios, veremos en qué consisten estos y los definiremos, desarrollando sus dos tipos: el directo, con sus limitaciones, y el indirecto, con los beneficios que conlleva. Los indirectos necesitan de un medio para su ejecución, el dinero, que definiremos, estudiando su origen y las características que han de cumplirse para que un medio de intercambio pueda ser efectivamente considerado como dinero. Señalaremos los tipos de dinero, y la importancia que tienen en la formación de los precios, y estudiaremos la determinación del poder adquisitivo del propio dinero. Se señalará por qué pensamos que las criptomonedas no pueden ser consideradas como dinero, y se terminará el artículo con las características que debería poseer el dinero en una sociedad libre.As a free society must be based on voluntary exchanges, we will see what they consist of and define them, developing their two types: direct voluntary exchanges, with their limitations, and the indirect ones, with the benefits they entail. Indirect ones need a means for their execution, money, which we will define, studying its origin and the characteristics that must be accomplished so that a means of exchange can be considered as money. We will point out the types of money, and the importance they have in the formation of prices, and also observe the determination of the purchasing power of money itself. It will be pointed out why we think that cryptocurrencies cannot be considered as money, and the work will be finished with the characteristics that money should have in a free society

How to interweave accessibility with didactic and technological quality of digital educational materials

Accessibility is a quality requirement for digital educational materials (or contents) in interactive learning environments. It ensures that students with disabilities do not face barriers when using such content. However, guaranteeing the accessibility of these materials is no easy task, at least for a significant part of the producers, evaluators, and users of educational materials, such as teachers. Proof of this can be found in the results of the case studies on the usability and reliability of technological accessibility evaluation standards conducted by Spanish Association for Standardisation (UNE) during the development of the Spanish Standard for the Quality of Digital Educational Materials UNE 71362. The results obtained show the difficulty of ensuring a good level of accessibility to digital educational materials, concluding that most creators and evaluators did not apply the guidelines due to either ignorance or difficulties. In order to minimise this problem, a new research approach has been taken based on unifying and abstracting the technology accessibility indicators from the regulations in force and integrating them, according to their applicability, transversally in the teaching and technological criteria of the new standard. This paper presents, explains and justifies this new approach in which the accessibility criteria are not isolated.Peer Reviewe

Planificación de trabajos en intervalos.

La planificación de trabajos en intervalos aparece en los sistemas en los que cada tarea tiene que ser realizada dentro de un intervalo de tiempo. La planificación de la capacidad en estos sistemas trata tanto de la asignación de los recursos a las tareas atendiendo a un criterio de optimización (planificación operacional), como del cálculo de la capacidad necesaria para realizar todas las tareas (planificación táctica). En este trabajo se establece una clasificación de toda esta clase de problemas, realizando una revisión bibliográfica de los principales trabajos y describiendo las aplicaciones prácticas más relevantes