Dark Energy in vector-tensor theories of gravity

We consider a general class of vector-tensor theories of gravity and show that solutions with accelerated expansion and a future type III singularity are a common feature in these models. We also show that there are only six vector-tensor theories with the same small scales behavior as General Relativity and, in addition, only two of them can be made completely free from instabilities. Finally, two particular models as candidates for dark energy are proposed: on one hand, a cosmic vector that allows to alleviate the usual naturalness and coincidence problems and, on the other hand, the electromagnetic field is shown to give rise to an effective cosmological constant on large scales whose value can be explained in terms of inflation at the electroweak scale.Comment: 4 pages, 1 table. Contribution to the proceedings of Spanish Relativity Meeting 2009, Bilbao, Spain, 7-11 September 200

Cosmic magnetic fields and dark energy in extended electromagnetism

We discuss an extended version of electromagnetism in which the usual gauge fixing term is promoted into a physical contribution that introduces a new scalar state in the theory. This new state can be generated from vacuum quantum fluctuations during an inflationary era and, on super-Hubble scales, gives rise to an effective cosmological constant. The value of such a cosmological constant coincides with the one inferred from observations as long as inflation took place at the electroweak scale. On the other hand, the new state also generates an effective electric charge density on sub-Hubble scales that produces both vorticity and magnetic fields with coherent lengths as large as the present Hubble horizon.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish Relativity Meeting 2010, Granada, Spain, 6-10 September 201

Calibrating the cosmic distance scale ladder: the role of the sound horizon scale and the local expansion rate as distance anchors

We exploit cosmological model-independent measurements of the expansion history of the Universe to provide a cosmic distance ladder. These are supernovae Type Ia used as standard candles (at redshift between 0.01 and 1.3) and baryon acoustic oscillations (at redshifts between 0.1 and 0.8) as standard rulers. We calibrate (anchor) the ladder in two ways: first using the local H0 value as an anchor at z = 0 (effectively calibrating the standard candles) and secondly using the cosmic microwave background-inferred sound-horizon scale as an anchor (giving the standard ruler length) as an inverse distance ladder. Both methods are consistent, but the uncertainty in the expansion history H(z) is smaller if the sound-horizon scale is used. We present inferred values for the sound horizon at radiation drag rd which do not rely on assumptions about the early expansion history nor on cosmic microwave background measurements but on the cosmic distance ladder and baryon acoustic oscillations measurements. We also present derived values of H0 from the inverse distance ladder and we show that they are in very good agreement with the extrapolated value in a Lambda cold dark matter model from Planck cosmic microwave background data

Impacts of sea-level rise-induced erosion on the Catalan coast

The final publication is available at Springer via http://dx.doi.org/10.1007/s10113-016-1052-xThe Catalan coast as most of the developed Mediterranean coastal zone is characterized by the coincidence of stresses and pressures on the natural system with a high exposure and low adaptive capacity. Due to this, climate change-induced effects will increase natural hazards and aggravate their associated impacts and, in consequence, it is necessary to assess their effects for proper long-term management. In this work, we assess the impact of sea-level rise (SLR)-induced shoreline retreat on the Catalan coast for three scenarios ranging from 0.53 to 1.75 m by the year 2100. Implications are analysed in terms of affectation of two main functions provided by beaches, i.e. recreation and protection. Obtained results show that CC will be a serious threat to analysed functions since the expected enhanced shoreline retreat will severely decrease the recreational carrying capacity and the capacity of protection in the near future under tested scenarios. The actual level of development along the coastal zone reduces the natural resilient capacity of beaches to SLR in such a way that the lack of accommodation space can be identified as a main factor for the estimated impacts.Peer ReviewedPostprint (author's final draft

Risk assessment of the spanish national railway system

The principal risks in the railway industry are mainly associated with collisions, derailments and level crossing accidents. An understanding of the nature of previous accidents on the railway network is required to identify potential causes and develop safety systems and deploy safety procedures. Risk assessment is a process for determining the risk magnitude to assist with decision-making. We propose a three-step methodology to predict the mean number of fatalities in railway accidents. The first is to predict the mean number of accidents by analyzing generalized linear models and selecting the one that best fits to the available historical data on the basis of goodness-offit statistics. The second is to compute the mean number of fatalities per accident and the third is to estimate the mean number of fatalities. The methodology is illustrated on the Spanish railway system. Statistical models accounting for annual and grouped data for the 1992-2009 time period have been analyzed. After identifying the models for broad and narrow gauges, we predicted mean number of accidents and the number of fatalities for the 2010-18 time period

Arquitecturas de frontera I: los hijos del muro de Berlín

La frontera Marruecos – España en Ceuta somete al norte marroquí a unas dinámicas globales que adquieren importancia sobre los procesos locales. Estas dinámicas tienen su razón de ser en el carácter productivo de la frontera, que la convierten en centro de un sistema global y multiescalar, y que en su doble condición de límite y nexo, fatigan el territorio provocando un envejecimiento prematuro que altera lógicas, carácter, pobladores y medio físico

Stacking-Fault Energy Measurements in Fe-Mn-Al-Si Austenitic TWIP Steels

This work is sponsored by a grant from the National Science Foundation Division of Materials Research DMR0805295. The support of Prof. Dierk Raabe and the Max-Planck-Institut für Eisenforschung is also gratefully acknowledged.Peer reviewe

La participación de asociaciones de inmigrantes en escuelas multiculturales del sur de España: sugerencias para la cooperación

Educators globally are struggling with how to serve newly arrived immigrant students. This article presents results of a qualitative study in the south of Spain, investigating contributions immigrant associations can make to multicultural schools. We conducted 55 interviews and one focus group with ilntnigrant associations, and 32 interviews with teachers and school directors. We found the teaching staff and immigrant associations willing and interested in cooperating to improving integration of immigrant children and youth. In particular, both groups saw immigrant associations as potential mediators. Afterward, two participating schools began to take significant steps toward collaborating with nearby immigrant associations.Educadores de todo el mundo están preocupados por la forma de enseñar a los alumnos inmigrantes recién llegados. Este artículo presenta los resultados de un estudio cualitativo llevado a cabo en el sur de España. Esta investigaciíin analiza las contribuciones que las asociaciones de inmigrantes pueden aportar a las escuelas mu1ticulturales. Hemos llevado a cabo 55 entrevistas y un grupo de discusión con las asociaciones de inmigrantes, y 32 entrevistas con los maestros y directores de escuela. Encontramos al personal docente y a las asociaciones de inmigrantes dispuestos e interesados en cooperar para mejorar la integración de los niños y jóvenes inmigrantes. En particular, ambos grupos vieron a las asociaciones de inmigrantes como mediadoras potenciales y como una forma de enseñar al nuevo alumnado partiendo de sus fondos de conocimiento. Después, mostramos como dos escuelas participantes comenzaron a tomar medidas significativas hacia la colaboración con asociaciones de inmigrantes de su entorno.Universidad de Granada. Facultad de Educación y Humanidades (Campus de Melilla

A first approach to the optimization of Bogotá's TransMilenio BRT system

Bus rapid transit (BRT) systems are massive transport systems with medium/high capacity, high quality service and low infrastructure and operating costs. TransMilenio is Bogotá's most important mass transportation system and one of the biggest BRT systems in the world, although it only has completed its third construction phase out of a total of eight. In this paper we review the proposals in the literature to optimize BRT system operation, with a special emphasis on TransMilenio, and propose a mathematical model that adapts elements of the above proposals and incorporates novel elements accounting for the features of TransMilenio system

Low molecular weight ϵ-caprolactone-pcoumaric acid copolymers as potential biomaterials for skin regeneration applications

ϵ-caprolactone-p-coumaric acid copolymers at different mole ratios (ϵ-caprolactone:p-coumaric acid 1:0, 10:1, 8:1, 6:1, 4:1, and 2:1) were synthesized by melt-polycondensation and using 4-dodecylbenzene sulfonic acid as catalyst. Chemical analysis by NMR and GPC showed that copolyesters were formed with decreasing molecular weight as p-coumaric acid content was increased. Physical characteristics, such as thermal and mechanical properties, as well as water uptake and water permeability, depended on the mole fraction of pcoumaric acid. The p-coumarate repetitive units increased the antioxidant capacity of the copolymers, showing antibacterial activity against the common pathogen Escherichia coli. In addition, all the synthesized copolyesters, except the one with the highest concentration of the phenolic acid, were cytocompatible and hemocompatible, thus becoming potentially useful for skin regeneration applications