Spatial clustering of interacting bugs: Levy flights versus Gaussian jumps

A biological competition model where the individuals of the same species perform a two-dimensional Markovian continuous-time random walk and undergo reproduction and death is studied. The competition is introduced through the assumption that the reproduction rate depends on the crowding in the neighborhood. The spatial dynamics corresponds either to normal diffusion characterized by Gaussian jumps or to superdiffusion characterized by L\'evy flights. It is observed that in both cases periodic patterns occur for appropriate parameters of the model, indicating that the general macroscopic collective behavior of the system is more strongly influenced by the competition for the resources than by the type of spatial dynamics. However, some differences arise that are discussed.Comment: This version incorporates in the text the correction published as an Erratum in Europhysics Letters (EPL) 95, 69902 (2011) [doi: 10.1209/0295-5075/95/69902

Fabrication and Characterization of Multiband Solar Cells Based on Highly Mismatched Alloys

Multiband solar cells are one type of third generation photovoltaic devices in which an increase of the power conversion efficiency is achieved through the absorption of low energy photons while preserving a large band gap that determines the open circuit voltage. The ability to absorb photons from different parts of the solar spectrum originates from the presence of an intermediate energy band located within the band gap of the material. This intermediate band, acting as a stepping stone allows the absorption of low energy photons to transfer electrons from the valence band to the conduction band by a sequential two photons absorption process. It has been demonstrated that highly mismatched alloys offer a potential to be used as a model material system for practical realization of multiband solar cells. Dilute nitride GaAs1-xNx highly mismatched alloy with low mole fraction of N is a prototypical multiband semiconductor with a well-defined intermediate band. Currently, we are using chemical beam epitaxy to synthesize dilute nitride highly mismatched alloys. The materials are characterized by a variety of structural and optical methods to optimize their properties for multiband photovoltaic devices

Obtaining preforms by additive fused deposition modelling (FDM) extrusion technology for the manufacture of high-performance composites

The composites industry is present in practically all industrial sectors with an annual growth rate of 5%. Its contribution to the priority "light-weighting" driver in the transport sector is key. The efficiency of the industry is made possible by the evolution of manufacturing processes that also improve the performance of the products obtained. For example, out-of-autoclave (OOA) processes can obtain high-performance composites such as those obtained by the autoclave process at lower costs. A key aspect in the development of this type of process is the preforming of continuous fibre reinforcements, which can achieve high fibre percentages while facilitating processing. Manufacturing these preforms currently requires multiple steps, equipment and tooling. TECNALIA's work developing the ADDICOMP technology, an alternative preform manufacturing method using an additive process based on Fused Deposition Modelling (FDM) is detailed in this article. This development is patented by Tecnalia and was conducted in 2 phases: (a) development of continuous fibre filaments coated with polymeric material and printable by FDM and (b) fine-tuning of FDM technology to print filaments with a very high content of continuous fibre

Motivations of the University s tudents in the physical and sports practice of free time. The nautical activities

El estudio de los perfiles motivacionales proporciona información detallada sobre los hábitos de los grupos de personas hacia la práctica de la actividad física, permitiendo poder fomentar una motivación más positiva y conseguir una mayor adherencia a la práctica. Así el objetivo de este estudio ha sido clarificar cuáles son las motivaciones frente a la práctica de actividad físico -deportiva de una muestra de jóvenes universitarios, incidiendo especialmente en las actividades náuticas. La muestra estuvo compuesta por 1011 estudiantes de la Universidad de Almería (España). El instrumento utilizado fue el cuestionario de hábitos físicos -deportivos y de práctica de deportes náuticos . Los resultados obtenidos apuntan que los principales motivos para desarrollar la práctica deportiva fueron la flexibilidad horaria y una adecuada a la disponibilidad de su tiempo libre, seguido de la cercanía a su domicilio de las instalaciones. Otros motivos son por diversión, o estar con su grupo de amigos. Respecto a las actividades náuticas, se decide practicar o no sólo porque les gustan, seguido del interés por estar en contacto con el medio natural y acuático. Las modalidades náuticas más practicadas son el piragüismo y la natación. En relación al abandono de la práctica deportiva, claramente se produce por la falta de tiempo por el estudio o el trabajo. Es evidente que la falta de tiempo por los estudios o por el trabajo, perjudica gravemente la adherencia a la actividad física, pero existen porcentajes muy altos de personas (62%) que admiten no practicar por pereza y desgana, por lo que se deben buscar nuevas estra tegias de motivación para que aumente la adherencia a la actividad físico deportiva

Climate Change-induced Effects on Beach Degradation and Tourist Behaviour: A review of previous studies with potential in an island tourism context

This article conducts a qualitative meta-analysis of papers addressing the topic of climate change impacts on beach loss and degradation, and its relation to tourist behaviour (destination choice, willingness to re-visit, expenditure and willingness to pay). The main aim is to identify values that can be used in future research works in the context of island tourism. We found that the strong specialisation and fragmentation of data and methods limit the transferability potential of previous research analysing climate-induced effects on beaches and tourist behaviour. Researchers from different fields bring their own conceptual models which often address similar problems but use different lenses and measurement units. Among the available studies, the ones with usable potential in a value transfer context are related to willingness to pay for adaptation measures. Overall, findings confirm that a greater transparency in the methodologies used to elicit values and a multidisciplinary approach are needed to ensure a more sustainable use of the information in order to fill knowledge gaps that still hinder the study of climate change

The Role of Sphingolipids Metabolism in Cancer Drug Resistance

Acid ceramidase (AC); Glucosylceramide synthase (GCS); ShingolipidsCeramidasa ácida (AC); Glucosilceramida sintasa (GCS); EsfingolípidosCeramidasa àcida (AC); Glucosilceramida sintasa (GCS); EsfingolípidsDrug resistance continues to be one of the major challenges to cure cancer. As research in this field evolves, it has been proposed that numerous bioactive molecules might be involved in the resistance of cancer cells to certain chemotherapeutics. One well-known group of lipids that play a major role in drug resistance are the sphingolipids. Sphingolipids are essential components of the lipid raft domains of the plasma membrane and this structural function is important for apoptosis and/or cell proliferation. Dysregulation of sphingolipids, including ceramide, sphingomyelin or sphingosine 1-phosphate, has been linked to drug resistance in different types of cancer, including breast, melanoma or colon cancer. Sphingolipid metabolism is complex, involving several lipid catabolism with the participation of key enzymes such as glucosylceramide synthase (GCS) and sphingosine kinase 1 (SPHK1). With an overview of the latest available data on this topic and its implications in cancer therapy, this review focuses on the main enzymes implicated in sphingolipids metabolism and their intermediate metabolites involved in cancer drug resistance.We thank Teresa Moline and Rosa Somoza from the VHIR. This work was supported by grants from the Instituto de Salud Carlos III (ISCIII; PI20/00556 and CP03/00101 [ML]) and CIBERONC (ML). This work was also co-financed by the European Regional Fund (ERDF) and AECC (Spanish Association of Cancer Research) (Founding Ref. GC16173720CARR [ML]). YG-M, CM, and AS-G were supported by the VHIR, iP-FIS (ISCIII) and VHIR fellowships, respectively

Pulsed interactions unify reaction-diffusion and spatial nonlocal models for biological pattern formation

The emergence of a spatially-organized population distribution depends on the dynamics of the population and mediators of interaction (activators and inhibitors). Two broad classes of models have been used to investigate when and how self-organization is triggered, namely, reaction-diffusion and spatially nonlocal models. Nevertheless, these models implicitly assume smooth propagation scenarios, neglecting that individuals many times interact by exchanging short and abrupt pulses of the mediating substance. A recently proposed framework advances in the direction of properly accounting for these short-scale fluctuations by applying a coarse-graining procedure on the pulse dynamics. In this paper, we generalize the coarse-graining procedure and apply the extended formalism to new scenarios in which mediators influence individuals' reproductive success or their motility. We show that, in the slow- and fast-mediator limits, pulsed interactions recover, respectively, the reaction-diffusion and nonlocal models, providing a mechanistic connection between them. Furthermore, at each limit, the spatial stability condition is qualitatively different, leading to a timescale-induced transition where spatial patterns emerge as mediator dynamics becomes sufficiently fast

Bounds on the Wilson Dirac Operator

New exact upper and lower bounds are derived on the spectrum of the square of the hermitian Wilson Dirac operator. It is hoped that the derivations and the results will be of help in the search for ways to reduce the cost of simulations using the overlap Dirac operator. The bounds also apply to the Wilson Dirac operator in odd dimensions and are therefore relevant to domain wall fermions as well.Comment: 16 pages, TeX, 3 eps figures, small corrections and improvement