Interaction between local hydrodynamics and algal community in epilithic biofilm

Interactions between epilithic biofilm and local hydrodynamics were investigated in an experimental flume. Epilithic biofilm from a natural river was grown over a 41 day period in three sections with different flow velocities (0.10, 0.25 and 0.40 m s-¹ noted LV, IV and HV respectively). Friction velocities u* and boundary layer parameters were inferred from PIV measurement in the three sections and related to the biofilm structure. The results show that there were no significant differences in Dry Mass and Ash-Free Dry Mass (g m-²) at the end of experiment, but velocity is a selective factor in algal composition and the biofilms' morphology differed according to differences in water velocity. A hierarchical agglomerative cluster analysis (BrayeCurtis distances) and an Indicator Species Analysis (IndVal) showed that the indicator taxa were Fragilaria capucina var. mesolepta in the lowvelocity (u* = ¼ 0.010e0.012 m s-¹), Navicula atomus, Navicula capitatoradiata and Nitzschia frustulum in the intermediate velocity (u* = ¼ 0.023e0.030 m s-¹) and Amphora pediculus, Cymbella proxima, Fragilaria capucina var. vaucheriae and Surirella angusta in the high-velocity (u* = ¼ 0.033e0.050m s-¹) sections. A sloughing test was performed on 40-day-old biofilms in order to study the resistance of epilithic biofilms to higher hydrodynamic regimes. The results showed an inverse relationship between the proportion of detached biomass and the average value of friction velocity during growth. Therefore, water velocity during epilithic biofilm growth conditioned the structure and algal composition of biofilm, as well as its response (ability to resist) to higher shear stresses. This result should be considered in modelling epilithic biofilm dynamics in streams subject to a variable hydrodynamics regime

The U(1) Lattice Gauge Theory Universally Connects All Classical Models with Continuous Variables, Including Background Gravity

We show that the partition function of many classical models with continuous degrees of freedom, e.g. abelian lattice gauge theories and statistical mechanical models, can be written as the partition function of an (enlarged) four-dimensional lattice gauge theory (LGT) with gauge group U(1). This result is very general that it includes models in different dimensions with different symmetries. In particular, we show that a U(1) LGT defined in a curved spacetime can be mapped to a U(1) LGT with a flat background metric. The result is achieved by expressing the U(1) LGT partition function as an inner product between two quantum states.Comment: Published version, 31 pages, 12 figures; references update

Corrosion effects on hertzian contact fatigue behavior of a WC-Co cemented carbide

The effect of corrosion on the damage induced under cyclic contact loading for a medium-grained WC-6%wtCo hardmetal grade is investigated. Contact fatigue tests are conducted by means of Hertzian indentation techniques. Corrosion damage is introduced in a controlled way by previous immersion of specimens in a stirred acidic medium. Results reveal that corrosion significantly influences the contact fatigue behavior of the material under consideration, in terms of the emergence and evolution of specific failure events: partial/full ring, radial cracks, and grain pull-out, among others. As cycle number increases, damage in the uncorroded condition evolves from partial to full ring cracks. Meanwhile, in the corroded condition, damage evolution is dominated by the appearance of grain pull-out when the number of cycles reaches a certain value. These findings are rationalized on the basis of phase assemblage changes linked to corrosion which are then enhanced by the cyclic nature of the applied loads.Postprint (published version

Small-scale assessment of corrosion-induced damage in hardmetals

In this work, the effect of corrosion-induced damage on the mechanical response of hardmetals was evaluated at small-scale level by means of nanoindentation and nanoscratch. Damage was introduced in a controlled way through immersion in acidic solution. It is found that surface degradation associated with corrosion leads to a strong reduction of hardness and elastic modulus, as compared to non-corroded samples. Similarly, significant differences are observed in nanoscratch response, regarding not only width and depth of tracks but also deformation mechanisms developed as contact load is progressively increased. Damage was already evidenced in corroded surfaces at scratching loads one order of magnitude lower than for virgin specimens. Cracking and fragmentation of individual WC grains, together with chipping of at the track edges were the main deformation and fracture micromechanisms identified. Changes in nanoindentation and nanoscratch response and damage scenario are discussed on the basis of the corrosion-induced changes within the intrinsic microstructural assemblage of hardmetals.Postprint (published version

EU Kids Online : investigación europea sobre riesgos y oportunidades online para los menores

El uso, tanto positivo como negativo, que los menores están haciendo de las nuevas tecnologías y las consecuencias derivadas de este proceso se ha convertido en los últimos años en uno de los principales objetivos a investigar por parte de la Academia. Sin embargo, se ha demostrado que las investigaciones existentes en los diferentes países europeos se han llevado a cabo de manera aislada e inconexa. Esta realidad científica impide, en muchas ocasiones, generar una base sólida y común de conocimiento en este campo para el apoyo de posteriores investigaciones. Es este contexto el que lleva a la Comisión Europea al lanzamiento del programa “Safer Internet”, con el propósito de desarrollar acciones que consigan crear un entorno más seguro para los niños en la Red. Dentro de este programa, la Comisión Europea financió la creación de la red de investigadores: EU Kids Online. El trabajo de esta red se divide en dos fases, en las que España ha participado como miembro activo a través del equipo de investigación de la Universidad del País Vasco. La primera, EU Kids Online I, entre 2006-2009 formada por más de 70 investigadores y expertos de 21 países europeos y la segunda, EU Kids Online II, entre 2009-2011 formada por más 100 investigadores y expertos de 25 países europeos. El objetivo central de EU Kids Online I fue crear esa “base sólida” a partir del análisis de todos los estudios científicos identificados sobre menores e Internet en Europa. Dentro de este marco los objetivos específicos del proyecto han sido cuatro: (i) identificar y evaluar hallazgos sobre el uso que los niños hacen de Internet, así como lagunas en las evidencias base; (ii) examinar cómo el marco en el que se realizan las investigaciones influye en la agenda de investigación e identificar los métodos con mejores prácticas; (iii) comparar hallazgos en toda Europa, contextualizando similitudes y diferencias; y (iv) desarrollar recomendaciones de acciones de políticas públicas que promuevan el uso seguro de Internet basadas en evidencia empíricas. La segunda parte del proyecto, EU Kids Online II, busca completar las lagunas detectadas en EU Kids Online I para mejorar la base de conocimiento relativo a las experiencias y prácticas de menores y padres en el uso arriesgado o seguro de Internet y las nuevas tecnologías online en Europa. Como mejora de la base de conocimiento entendemos: (i) alcanzar conclusiones nuevas, relevantes, sólidas y comparables sobre la incidencia de los riesgos online entre los menores europeos; (ii) señalar con precisión qué menores son los que están en riesgo y por qué, mediante el examen de factores de vulnerabilidad (tanto a nivel individual como de países); y (iii) examinar el funcionamiento y la efectividad de la regulación parental y las estrategias de sensibilización, así como las propias respuestas de los menores a los riesgos, incluyendo su alfabetización digital. Esta comunicación está basada en las conclusiones presentadas por EU Kids Online I, cuya base está constituida por las lagunas de investigación detectadas en los 21 países que formaron parte de este proyecto. Del mismo modo, se expondrán las recomendaciones políticas que EU Kids Online I entregó a la Comisión Europea, fundamentadas en los resultados empíricos obtenidos y que buscan conseguir una regulación de la red acorde a las diferentes necesidades detectadas. Finalmente se presentará el plan de trabajo y la metodología diseñada para llevar a cabo la encuesta de EU Kids Online II

The Welfare State and the demographic dividend: A cross-country comparison

The sustainability of the welfare state is in doubt in many developed countries due to drastic population ageing. The extent of the problem and the margin for reforms depend - among other factors - on the size of the ageing process and the size of the public transfer system. The latter has a crucial impact on the extent to which the first demographic dividend previous to the ageing process turns into a second demographic dividend. The contribution of the different factors driving the demographic dividend is, ultimately, an empirical question. In this paper we contribute to the debate, exploding the cross-country comparison potentialities of the National Transfer Accounts (NTA) database. In particular, we introduce different configurations of the welfare state transfers – Sweden, United States and Spain - into a realistic demography Overlapping Generations, OLG, model and simulate its effects on the second demographic dividend

The welfare state and demographic dividends

The demographic transition experienced by developed countries produces initial positive effects on economic growth ‒ the first demographic dividend ‒ which can be extended into a second demographic dividend if baby boomers' savings increase capital accumulation. Nevertheless, aging might reverse this process if dissaving of elderly baby boomers and the pressure on the pay-as-you-go financed welfare state reduce savings and capital

Linear Gaussian intensity distributions synthesized by reflection on elliptic cylinders: a proposal

A Procedure for obtaining linear (one-dimensional) Gaussian intensity distributions over certain plane regions is proposed. The method is based on the reflection of plane beams on elliptic cylinders