The RNA World : piecing together the historical development of a hypothesis

The concept of an RNA world is a hypothesis firmly rooted in empirical data and is part of a long and complex scientific perspective that goes back more than fifty years to the discovery of the central role RNA and ribonucleotides play in protein synthesis and biochemical reactions took place. As the understanding of RNA biology progressed, several independent proposals of protein-free primordial life forms were suggested. Although this possibility was strongly reinforced with the discovery of ribozymes, there are many definitions of the RNA world, including several contradictory ones. One could say that it was an early, perhaps primordial, stage during which RNA molecules played a much more conspicuous role in heredity and metabolism and, particularly, in the origin and early evolution of protein biosynthesis. The overwhelming evidence for the catalytic, regulatory, and structural properties of RNA molecules, combined with their ubiquity in cellular processes, can only be explained with the proposal that they played a key role in early evolution and perhaps in the origin of life itself

La previa como fenómeno mediático en la información deportiva: evolución del derbi sevillano de fútbol en ABC entre 1975-2010

Los medios de comunicación de masas han encontrado en el deporte una fuente incesante de ingresos debido a las altas audiencias que éste genera. La evolución de la cobertura informativa otorgada a una competición puede ser un claro ejemplo de cómo el periodismo deportivo no sólo informa sobre un determinado acontecimiento, sino que también lo promociona. Por tanto, la previa se ha ido configurando como una poderosa estrategia persuasiva y un recurso mediático donde se dan cita intereses comunicativos, económicos y empresariales. El fútbol y el encuentro Sevilla-Betis pueden ser buenos ejemplos para iniciar el estudio de este tipo de fenómeno.Media have found the sport a constant source of income due to high audience it generates. News coverage evolution given to a competition could be clear example of how sports journalism doesn`t only report about a particular event but also promotes it. Therefore, ‘previa’ has become a powerful persuasive strategy and a media resource which brings together communication, economic and business interests. Football and Sevilla-Betis´s match can be good examples to start the study of this kind of phenomenon

Efficient Computation of Multiple Density-Based Clustering Hierarchies

HDBSCAN*, a state-of-the-art density-based hierarchical clustering method, produces a hierarchical organization of clusters in a dataset w.r.t. a parameter mpts. While the performance of HDBSCAN* is robust w.r.t. mpts in the sense that a small change in mpts typically leads to only a small or no change in the clustering structure, choosing a "good" mpts value can be challenging: depending on the data distribution, a high or low value for mpts may be more appropriate, and certain data clusters may reveal themselves at different values of mpts. To explore results for a range of mpts values, however, one has to run HDBSCAN* for each value in the range independently, which is computationally inefficient. In this paper, we propose an efficient approach to compute all HDBSCAN* hierarchies for a range of mpts values by replacing the graph used by HDBSCAN* with a much smaller graph that is guaranteed to contain the required information. An extensive experimental evaluation shows that with our approach one can obtain over one hundred hierarchies for the computational cost equivalent to running HDBSCAN* about 2 times.Comment: A short version of this paper appears at IEEE ICDM 2017. Corrected typos. Revised abstrac

Limiting efficiencies of GaAs solar cells

The limiting efficiencies of GaAs solar cells when used under concentrated sunlight are calculated. The benefits to be expected from applying techniques which restrict the angle of acceptance of the cell are determined. It is concluded that when the acceptance angle is restricted the emission of the luminescent photons and therefore the associated current loss are reduced. A limiting efficiency close to 39% results for concentration ratios of about 1000 suns AM1.5 direct. For lower concentration ratios, the limiting efficiency decreases if Auger recombination is also taken into accoun