University of Extremadura

About: University of Extremadura is a education organization based out in Badajoz, Spain. It is known for research contribution in the topics: Population & Hyperspectral imaging. The organization has 7856 authors who have published 18299 publications receiving 396126 citations. The organization is also known as: Universidad de Extremadura.

Testosterone and sexual signalling in male house sparrows (Passer domesticus)

Abstract: Female preference for mates with elaborated ornaments has often been explained on the basis that exaggerated secondary sexual traits might reflect individual quality and females might gather direct and indirect benefits in mating with such males. Sexual signals must however also entail costs to be reliable indicators of male quality. Androgens have been suggested as a physiological link between sexual signals and individual quality for several reasons, including their immunosuppressive effect. In this study, we tested two hypotheses linked to the hormonal basis of sexual signal expression. First, we investigated whether testosterone is correlated with the size of the black feather bib on the throat of male house sparrows (Passer domesticus) – a trait involved in intra- and inter-sexual selection. Second, we tested whether testosterone affects the seasonal exposure of the trait. Observational work conducted in 1998 showed that the testosterone level was positively correlated with badge size both in spring and in the subsequent fall, after molt. In 1999, we experimentally reduced spring testosterone levels using silastic implants filled with cyproterone acetate, an antiandrogen. Male house sparrows implanted with cyproterone acetate showed reduced exposure of the badge, because the white tips of the black feathers of the badge wore off later than in control males implanted with empty silastic tubes. This result suggests that testosterone can be causally involved in the expression of a secondary sexual trait in house sparrows, at least in terms of its seasonal exposure.

The anatomical arrangement of the myocardial cells making up the ventricular mass.

Abstract: The architectural arrangement of the myocytes within the ventricular mass remains a highly contentious topic. It has recently been suggested by several distinguished surgeons that the overall myocardial structure is disposed in the form of a 'ventricular myocardial band'. There are, however, major anatomic deficiencies in this hypothesis, because the heart is formed on the basis of a modified blood vessel, rather than a collection of discrete muscular entities resembling the skeletal musculature. There is ample alternative evidence, nonetheless, already existing to provide a suitable explanation for the 'forceful reciprocal twisting' of the ventricular mass that is seen by cardiac surgeons during operative procedures. We provide here, therefore, a review of the anatomical studies we have performed separately and conjointly over a period of nearly 30 years. As before, we show that there is no anatomic evidence to support the concept of the 'ventricular myocardial band'. The overall arrangement is for the myocytes to be supported as the muscular components of a continuous and complex mass, the supporting collagenous fibrous matrix possessing epimysial, perimysial, and endomysial components. It had already been discussed at length during the previous century why there was no anatomic evidence to support the existence of separate 'muscles' within the ventricular continuum. There are no fibrous sheaths within the ventricular walls that permit the myofibres to be dissected on the basis of muscle bundles having a discrete origin and insertion, as is the case with the arrangement of the skeletal muscles. We have never sought ourselves, however, to deny the central helical nature of the overall architecture of the ventricular walls. The anatomic evidence supporting an overall helical nature for the ventricular myocardium has existed for over 150 years. All the available evidence, nonetheless, shows that these helical patterns are to be found throughout the walls, and in no way constitute a unique myocardial band.

Robust Collaborative Nonnegative Matrix Factorization for Hyperspectral Unmixing

Abstract: Spectral unmixing is an important technique for remotely sensed hyperspectral data exploitation. It amounts to identifying a set of pure spectral signatures, which are called endmembers, and their corresponding fractional, draftrulesabun-dances in each pixel of the hyperspectral image. Over the last years, different algorithms have been developed for each of the three main steps of the spectral unmixing chain: 1) estimation of the number of endmembers in a scene; 2) identification of the spectral signatures of the endmembers; and 3) estimation of the fractional abundance of each endmember in each pixel of the scene. However, few algorithms can perform all the stages involved in the hyperspectral unmixing process. Such algorithms are highly desirable to avoid the propagation of errors within the chain. In this paper, we develop a new algorithm, which is termed robust collaborative nonnegative matrix factorization (R-CoNMF), that can perform the three steps of the hyperspectral unmixing chain. In comparison with other conventional methods, R-CoNMF starts with an overestimated number of endmembers and removes the redundant endmembers by means of collaborative regularization. Our experimental results indicate that the proposed method provides better or competitive performance when compared with other widely used methods.

The Impact of Heavy Grazing on Soil Quality and Pasture Production in Rangelands of SW Spain

Abstract: Soil degradation phenomena, including water erosion and physical and biological processes, have already been reported in rangelands of southwestern Spain. The increasing numbers of livestock since 1986 have been highlighted as one of the key causes. The main goal of this work is to analyse the effects of the excessive number of animals on soil quality and pasture production on privately owned farms dedicated to extensive ranching. Soil properties and surface cover, pasture production, rainfall and land management variables such as livestock density were analysed during a period of 3 years (2008–2011). The study was carried out in 22 livestock enclosures selected from ten farms distributed throughout the Spanish region of Extremadura. The occurrence of bare soil patches and water erosion processes, as well as an increase of mean bulk density in the soil layer from 5 to 10 cm in depth, was observed in the enclosures with animal stocking rates exceeding 1 AU ha−1. Indications that confirm the negative effects of increased bulk density on pasture production and quality were also found. Copyright © 2016 John Wiley & Sons, Ltd.