Migración de los colorantes dispersos en triacetato.

Entre toda la literatura técnica publicada sobre la tintura del triacetato, que nos ha sido posible examinar, no hemos encontrado ningún estudio referente a la migración de los colorantes dispersos en la tintura del triacetato de celulosa y por ello hemos creído que podría ser interesante, al menos desde un punto de vista teórico, el conocer dicho fenómeno y los factores que pueden tener influencia sobre él, ya que con ello se complementan los estudios efectuados por otros investigadores en el campo de la físico-química de este sistema tintóreo.Peer Reviewe

Competencia financiera y modelación matemática en bachillerato: un acercamiento cualitativo desde la investigación basada en diseño (DBR)

La competencia matemática se articula como un conjunto de habilidades y capacidades que van permitir a los individuos analizar, resolver e interpretar problemas matemáticos en diferentes situaciones, y su importancia para mejorar el bienestar de los ciudadanos se recoge en informes como PISA o leyes como la LOMCE. El estudio del proceso de adquisición de la competencia financiera al trabajar dicha competencia con las competencias matemática y de modelación, es uno de los objetivos centrales de nuestra investigación, que se desarrolla en un contexto de enseñanza de Economía en Bachillerato

The paradox of the Long-Term positive effects of a north american crayfish on a european community of predators

Invasions of non-native species are one of the major causes of losses of native species. In some cases, however, non-natives may also have positive effects on native species. We investigated the potential facilitative effects of the North American red swamp crayfish (Procambarus clarkii) on the community of predators in southwestern Spain. To do so, we examined the diets of predators in the area and their population trends since introduction of the crayfish. Most predator species consumed red swamp crayfish, which sometimes occurred in over 50% of their diet samples. Moreover, the abundance of species preying on crayfish increased significantly in the area as opposed to the abundance of herbivores and to predator populations in other areas of Europe, where those predators are even considered threatened. Thus, we report the first case in which one non-native species is both beneficial because it provides prey for threatened species and detrimental because it can drive species at lower trophic levels to extinction. Increases in predator numbers that are associated with non-native species of prey, especially when some of these predators are also invasive non-natives, may increase levels of predation on other species and produce cascading effects that threaten native biota at longer temporal and larger spatial scales. Future management plans should include the complexity of interactions between invasive non-natives and the entire native community, the feasibility of successful removal of non-native species, and the potential social and economic interests in the area. © 2010 Society for Conservation Biology.Peer Reviewe

Hyperbolic reflections as fundamental building blocks for multilayer optics

We reelaborate on the basic properties of lossless multilayers by using bilinear transformations. We study some interesting properties of the multilayer transfer function in the unit disk, showing that hyperbolic geometry turns out to be an essential tool for understanding multilayer action. We use a simple trace criterion to classify multilayers into three classes that represent rotations, translations, or parallel displacements. Moreover, we show that these three actions can be decomposed as a product of two reflections in hyperbolic lines. Therefore, we conclude that hyperbolic reflections can be considered as the basic pieces for a deeper understanding of multilayer optics.Comment: 7 pages, 7 figures, accepted for publication in J. Opt. Soc. Am.

El hidrógeno como vector energético: Mucho hecho pero casi todo por hacer

Los autores desarrollan, muy brevemente, los aspectos esenciales de lo que globalmente se denomina “Sistema Energético Solar-Hidrógeno” o a veces “Economía del hidrógeno”. El hidrógeno, obtenido por descomposición del agua mediante energías primarias renovables (solar, eólica…) se convierte en transportador de energía (vector energético) y en combustible limpio. Se discute la conveniencia del uso del hidrógeno en el contexto energético actual, así como los tres pilares fundamentales del uso del hidrógeno como vector energético: su producción usando fuentes renovables, su acumulación mediante diferentes métodos y, finalmente, su combustió

Hipoplasia de la valva posterior de la válvula mitral y válvula aórtica bicúspide. Una muy rara asociación para encontrar en un paciente adulto

The congenital heart diseases are a diagnostic challenge for the clinician, particularly when they are presented in an adult. These types of anomalies that are observed in the mitral valve can be presented in isolated form or together with other heart defects. The case is presented of a patient with severe hypoplasia of the posterior mitral valve leaflet. This anomaly is, under normal conditions, fatal before birth or very symptomatic during childhood, and its delayed presentation is extremely rare and difficult to find in the adult. This the first case reported, not only in this country, but in the whole of South America. © 2018 Sociedad Colombiana de Cardiología y Cirugía Cardiovascula

Universal temporal features of rankings in competitive sports and games

Many complex phenomena, from the selection of traits in biological systems to hierarchy formation in social and economic entities, show signs of competition and heterogeneous performance in the temporal evolution of their components, which may eventually lead to stratified structures such as the wealth distribution worldwide. However, it is still unclear whether the road to hierarchical complexity is determined by the particularities of each phenomena, or if there are universal mechanisms of stratification common to many systems. Human sports and games, with their (varied but simplified) rules of competition and measures of performance, serve as an ideal test bed to look for universal features of hierarchy formation. With this goal in mind, we analyse here the behaviour of players and team rankings over time for several sports and games. Even though, for a given time, the distribution of performance ranks varies across activities, we find statistical regularities in the dynamics of ranks. Specifically the rank diversity, a measure of the number of elements occupying a given rank over a length of time, has the same functional form in sports and games as in languages, another system where competition is determined by the use or disuse of grammatical structures. Our results support the notion that hierarchical phenomena may be driven by the same underlying mechanisms of rank formation, regardless of the nature of their components. Moreover, such regularities can in principle be used to predict lifetimes of rank occupancy, thus increasing our ability to forecast stratification in the presence of competition