Worse than a big rip?

We show that a generalised phantom Chaplygin gas can present a future singularity in a finite future cosmic time. Unlike the big rip singularity, this singularity happens for a finite scale factor, but like the big rip singularity, it would also take place at a finite future cosmic time. In addition, we define a dual of the generalised phantom Chaplygin gas which satisfies the null energy condition. Then, in a Randall-Sundrum 1 brane-world scenario, we show that the same kind of singularity at a finite scale factor arises for a brane filled with a dual of the generalised phantom Chaplygin gas.Comment: 6 pages, 4 figures, RevTeX 4. Discussion expanded and references added. Version to appear in PL

An improved discrete bat algorithm for symmetric and asymmetric traveling salesman problems

Bat algorithm is a population metaheuristic proposed in 2010 which is based on the echolocation or bio-sonar characteristics of microbats. Since its first implementation, the bat algorithm has been used in a wide range of fields. In this paper, we present a discrete version of the bat algorithm to solve the well-known symmetric and asymmetric traveling salesman problems. In addition, we propose an improvement in the basic structure of the classic bat algorithm. To prove that our proposal is a promising approximation method, we have compared its performance in 37 instances with the results obtained by five different techniques: evolutionary simulated annealing, genetic algorithm, an island based distributed genetic algorithm, a discrete firefly algorithm and an imperialist competitive algorithm. In order to obtain fair and rigorous comparisons, we have conducted three different statistical tests along the paper: the Student's $t$-test, the Holm's test, and the Friedman test. We have also compared the convergence behaviour shown by our proposal with the ones shown by the evolutionary simulated annealing, and the discrete firefly algorithm. The experimentation carried out in this study has shown that the presented improved bat algorithm outperforms significantly all the other alternatives in most of the cases

Combined frequency-amplitude nonlinear modulation: theory and applications

In this work we formulate a generalized theoretical model to describe the nonlinear dynamics observed in combined frequency-amplitude modulators whose characteristic parameters exhibit a nonlinear dependence on the input modulating signal. The derived analytical solution may give a satisfactory explanation of recent laboratory observations on magnetic spin-transfer oscillators and fully agrees with results of micromagnetic calculations. Since the theory has been developed independently of the mechanism causing the nonlinearities, it may encompass the description of modulation processes of any physical nature, a promising feature for potential applications in the field of communication systems.Comment: 8 pages, 4 figures, to be published on IEEE Transactions on Magnetic

Effects of interdot dipole coupling in mesoscopic epitaxial Fe(100) dot arrays

The domain structure and the coercivity of epitaxial Fe(100) circular dot arrays of different diameters and separations have been studied using magnetic force microscopy (MFM) and focused magneto-optical Kerr effect (MOKE). The MFM images of the 1 µm diameter single domain dot arrays show direct evidence of strong interdot dipole coupling when the separation is reduced down to 0.1 µm. The coercivity of the dots is also found to be dependent on the separation, indicating the effect of the interdot dipole coupling on the magnetization reversal process

The role of scattered trees and habitat diversity for biodiversity of Iberian dehesas

PosterWe studied 10 dehesas of CW Spain (40º 00’-10’ N, 06º 10’-20’ W), mapping every habitat according to a standardized protocol developed by the European BioBio project. We defined 35 habitat types, with 19 habitat types (split in 85 plots) per dehesa, on average. In one randomly selected plot per habitat type diversity of the four taxa, plants, bees, spiders and earthworms, were assessed. In total, 450 plant species (average of 189 per farm and 36 per habitat), 63 bee species (17.6 and 3.2), 130 spider species (43.8 and 7.4), and 17 earthworm species ( 7.8 and 2.5) were recorded. In each taxa, only some species were very abundant, while most of the species were found only in few farms/habitats. A high proportion of species (ca. 40%) were observed only in just one habitat per farm, indicating that farm biodiversity strongly depends on the habitat diversity. The analysis of unique and shared species among habitats revealed that every habitat contribute significantly to farm biodiversity. By contrast, species richness was poorly explained by the presence of scattered trees, whereas the combination of wood pastures and open pastures was a significant predictor. Summarizing, our extensive survey showed that diversity of the four taxa was strongly related to the existence of a wide mosaic of habitats, including non-productive habitats and linear elements, which harbor a disproportionate number of species compared to the low area occupied. Moreover, these habitats harbor a high number of exclusive species. As a next step, the importance of the spatial arrangement of main and non-productive habitats for biodiversity at the farm and landscape levels, need to be checked

Polymorphic ventricular arrhythmia triggered by temporary epicardial right ventricular stimulation after cardiac surgery

Temporary epicardial pacing is commonly used for rhythmic support in the acute postoperative period after cardiac surgery. Clinical studies suggest that pacing in the left ventricular epicardium during resynchronization therapy may be proarrhythmic in a minority of patients. The epicardial pacing increases transmural heterogeneity of repolarization. This could prolong the QT and JT intervals on the electrocardiogram (ECG), with subsequent proarrhythmic effects. The following case describes polymorphic ventricular arrhythmias after temporary epicardial ventricular stimulation

Darwin y el mar

Además de sus conocidos aportes a la geología, la paleontología y la biogeografía de ecosistemas terrestres de la región pampeana y la Patagonia (Argentina), Darwin realizó notables y poco difundidas contribuciones al conocimiento de los ambientes marinos costeros del actual territorio argentino y de los organismos que habitan en ellos. La intimidad de Darwin con el mar se advierte en toda su obra: en el Viaje y en el Origen igual que en numerosos trabajos de investigación realizados y publicados a su regreso a Inglaterra. Entre 1846 y 1854 dio a conocer una extensa obra sobre cirrípedos o cirripedios, que sentó las bases del estudio de esos crustáceos y, aún hoy, es bibliografía obligada de los taxónomos. Su trabajo sobre la estructura y distribución de los arrecifes coralinos de 1842, es considerado un documento fundacional del conocimiento sobre el origen de los atolones. Los moluscos fueron igualmente objeto de publicaciones y cartas entre 1848 y 1871. La difundida imagen de Darwin sentado ante un escritorio escribiendo sus libros lleva a olvidar que pasaba también mucho tiempo con el microscopio. En el Viaje del Beagle incluyó párrafos sobre aves marinas, lo mismo que sobre briozoos o briozoarios, y en El origen, explicó sus pensamientos acerca de la migración de los ojos en los lenguados. Dedicó especial atención a las algas gigantes o sargazos marinos de Tierra del Fuego (donde se los conoce por cachiyuyos). Se incluyen los siguientes trabajos de divulgación científica -Darwin y los briozoos; -Darwin y el desarrollo larval de crustáceos; -Sobre Cirripedios; De Darwin a los acelerómetros; -Los peces de cara torcida; -La incursión en la costa sur de Buenos Aires