Dynamics of a self--gravitating magnetized source

We consider a magnetized degenerate gas of fermions as the matter source of a homogeneous but anisotropic Bianchi I spacetime with a Kasner--like metric. We examine the dynamics of this system by means of a qualitative and numerical study of Einstein-Maxwell field equations which reduce to a non--linear autonomous system. For all initial conditions and combinations of free parameters the gas evolves from an initial anisotropic singularity into an asymptotic state that is completely determined by a stable attractor. Depending on the initial conditions the anisotropic singularity is of the ``cigar'' or ``plate'' types.Comment: 7 pages, 1 figur

Estudio del tiempo de reacción ante estímulos sonoros y visuales.

Tradicionalmente se ha aceptado que el tiempo de reacción (TR) ante estímulos sonoros es menor que ante estímulos visuales. Sin embargo, planteamos la hipótesis de que el TR ante estímulos visuales sea más rápido que ante estímulos sonoros, lo que cobra gran importancia en algunas pruebas deportivas. Se analizaron las diferencias en el TR electivo manual según estímulos sonoros y visuales en una muestra suficiente de sujetos físicamente activos, relacionando factores como el género, el nivel de práctica deportiva y el deporte practicado. El diseño del estudio fue de tipo correlacional, participando 80 voluntarios, con una edad media de 22.6 ±3.7 años. Para la medición del TR se utilizó el programa SuperLab®, comparándose el TR ante estímulos visuales y sonoros por cada sujeto participante. Los resultados obtenidos muestran que el TR medio fue significativamente menor ante estímulos visuales que ante estímulos sonoros. Así mismo, los varones presentaron un TR significativamente más corto que las mujeres para el TR visual, no siendo significativas estas diferencias para el estímulo auditivo. No se registraron diferencias significativas según estímulo para el resto de factores estudiados. Finalmente se presentan sugerencias de futura indagación en base a los hallazgos obtenidos

Woodland loss differently affects seed dispersal by resident and migratory avian frugivores in olive grove-dominated landscapes

Seed dispersal by frugivores is a key ecological process underpinning the functionality of woodland patches and their capacity to maintain biodiversity in agricultural landscapes. Resident and migratory avian frugivores differ in temporal span of their local occurrence, as well as in mobility and territoriality. However, whether landscape homogenization by agriculture affects seed dispersal by avian frugivores differing in migratory strategy remains largely unexplored. We hypothesized a positive role of woodland patches on avian frugivore abundance and seed-dispersal frequency, and a differential impact of woodland loss and landscape simplification on resident and migratory frugivorous birds. We tested these hypotheses in 20 farms distributed along a gradient of woodland loss and olive cropland expansion in south Spain, considering woodland patches and olive fields as two habitats to survey avian frugivore abundance and frequency of seed dispersal. We confirmed that both the abundance and seed-dispersal frequency of avian frugivores were higher in woodland patches than in olive fields, and also that both decayed with decreasing woodland cover. This was largely mediated by a few European (winter) migrants and secondarily by some resident species. However, the woodland patches were unable to intercept sub-Saharan (summer) migrants in sufficient numbers as to make their contribution to dispersal of summer fruits meaningful. Woodland patches with higher seed-dispersal function were located predominantly in landscapes with high woodland cover and/or fruit availability. Moreover, a relatively high woodland cover in the landscape enhanced the seed dispersal function in woodland patches through a balance between high overall frugivore abundance and dispersal frequency, and some increased activity of resident and summer migrants. Our results also inform that the presence of particularly fruit-rich woodland patches can compensate the woodland cover required to maintain the function by enhancing the frequency of seed dispersal of all migratory groups. In contrast, to maintain the function of fruit-poor woodlands their cover at landscape scale should increase. Preserving and restoring woodland patches at landscape scale and enhancing their abundance and diversity of fruits could boost the activity of different disperser groups and their functional complementarity across agricultural landscapes

Automatic image characterization of psoriasis lesions

Psoriasis is a chronic skin disease that affects 125 million people worldwide and, par-ticularly, 2% of the Spanish population, characterized by the appearance of skin lesions due to a growth of the epidermis that is seven times larger than usual. Its diagnosis and monitoring are based on the use of methodologies for measuring the severity and extent of these spots, and this includes a large subjective component. For this reason, this paper presents an automatic method for characterizing psoriasis images that is divided into four parts: image preparation or pre-processing, feature extraction, classification of the lesions, and the obtaining of parameters. The methodology proposed in this work covers different digital-image processing techniques, namely, marker-based image delimitation, hair removal, nipple detection, lesion contour detection, areal-measurement-based lesion classification, as well as lesion characterization by means of red and white intensity. The results obtained were also endorsed by a professional dermatologist. This methodology provides professionals with a common software tool for monitoring the different existing typologies, which proved satisfactory in the cases analyzed for a set of 20 images corresponding to different types of lesions

Noncommutative effective LQC: A (pre-)inflationary dynamics investigation

We conduct a (pre-)inflationary dynamics study within the framework of a simple noncommutative extension of effective loop quantum cosmology -- put forward recently by the authors -- which preserves its key features (in particular, the quantum bounce is maintained). A thorough investigation shows that the (pre-)inflationary scenario associated to the chaotic quadratic potential is in the overall the same as the one featured in standard loop quantum cosmology (which reinforces the conclusion reached by the authors in a preliminary analysis). Hence, this (pre-)inflationary scenario does not easily distinguish between standard loop quantum cosmology and the aforementioned noncommutative scheme. It is argued that a particular tuning of the noncommutativity parameter could accommodate for subtle effects at the level of primordial perturbations (the hybrid quantization framework being a tentative route of analysis).Comment: 22 pages, 18 figures, 1 tabl