On the convexity of Relativistic Ideal Magnetohydrodynamics

We analyze the influence of the magnetic field in the convexity properties of the relativistic magnetohydrodynamics system of equations. To this purpose we use the approach of Lax, based on the analysis of the linearly degenerate/genuinely non-linear nature of the characteristic fields. Degenerate and non-degenerate states are discussed separately and the non-relativistic, unmagnetized limits are properly recovered. The characteristic fields corresponding to the material and Alfv\'en waves are linearly degenerate and, then, not affected by the convexity issue. The analysis of the characteristic fields associated with the magnetosonic waves reveals, however, a dependence of the convexity condition on the magnetic field. The result is expressed in the form of a generalized fundamental derivative written as the sum of two terms. The first one is the generalized fundamental derivative in the case of purely hydrodynamical (relativistic) flow. The second one contains the effects of the magnetic field. The analysis of this term shows that it is always positive leading to the remarkable result that the presence of a magnetic field in the fluid reduces the domain of thermodynamical states for which the EOS is non-convex.Comment: 14 pages. Submitted to Classical and Quantum Gravit

Sustainability reporting in Europe: differences in terms of legislation and valuation

Artigo em revista científicaOver the past few years, the number of socially responsible companies has been increasing significantly throughout the world and predominantly in Europe. This trend has accelerated the need to provide credibility, and also to create legislation that supports the information provided. As a result, the Global Reporting Initiative (GRI) was created with the aim of helping organisations to provide information about sustainability, as well as to assist stakeholders in interpreting it. However, the publication of social responsibility reports represents an additional cost and effort for the companies since it is necessary to provide extra resources and, for this reason, not all companies adopt this measure. Moreover, social responsibility can be a mandatory or voluntary requirement, depending on the country and the rules imposed by the government where the companies operate. In this context, the aim of this study is two-fold. Firstly, we provide a deep analysis about the evolution as well as the similarities and differences among European countries in terms of sustainability reporting over the 2001-2013 period following the GRI criteria. Secondly, we provide evidence about the value relevance of this practice for European firms.info:eu-repo/semantics/publishedVersio

Labile carbon in biological soil crusts in the Tabernas desert, SE Spain.

Decomposition processes are extremely important in biological soil crusts (BSCs). Although the effects of temperature and moisture on such processes have been widely studied, little is known about the influence of the readily metabolizable substrate (labile C) and how this substrate varies in different types of BSCs. In the present study, BSCs formed by cyanobacteria (CYANO) and by lichens (DIPLOS and LEPRA) were incubated at 25 °C (optimum temperature) and different moisture levels, for evaluation of the pool of labile C in the crust layers. Labile C was estimated as the sum of CO2-C emitted and the C extracted with hot water (80 °C) at the end of the incubation period. In all crusts, the relationship between emission and moisture fitted a quadratic model. For the different moisture contents, the sum of CO2-C emitted and C extracted with hot water converged to a constant value for each type of crust. This value, considered as the maximum content of labile C in the crust, was extremely high in DIPLOS, reaching up to 40% of the total organic C (TOC) initially present. In all crusts, and independently of the consumption of labile C, simple sugars (sucrose, glucose) remained at the end of the incubation period, which suggests that these sugars may play a protective role in BSCs. The presence of mannitol suggests that the fructose released during hydrolysis of sucrose was reduced to mannitol, thus enabling electron transport during moments of intense respiratory stress. The intense respiration in DIPLOS is partly due to the metabolism of polyphenols, which are possibly derived from the growth and death of free-living fungi that proliferate during incubation of the crusts. These results demonstrate that the metabolic processes in BSCs differ depending on the type of organisms that form the crusts and that there is a high risk of C loss from Diploschistes BSCs after heavy rainfall events.Peer reviewe

Low-Frequency Imaginary Impedance at the Superconducting Transition of 2H-NbSe2

The superconducting transition leads to a sharp resistance drop in a temperature interval that can be a small fraction of the critical temperature Tc. A superconductor exactly at Tc is thus very sensitive to all kinds of thermal perturbation, including the heat dissipated by the measurement current. We show that the interaction between electrical and thermal currents leads to a sizable imaginary impedance at frequencies of the order of tens of hertz at the resistive transition of single crystals of the layered material 2H-NbSe2.We explain the result using models developed for transition-edge sensors. By measuring under magnetic fields and at high currents, we find that the imaginary impedance is strongly influenced by the heat associated with vortex motion and out-of-equilibrium quasiparticles

Portraiture in Early–Childhood education: a didactic proposal about art

El trabajo hace una propuesta didáctica destinada a la etapa de Educación Infantil, en la que se toma como base el género artístico del retrato. El estudio destaca la gran importancia que tiene la educación artística, en sus dos ámbitos —el crítico y el creativo— en la educación de los más pequeños, así como la gran utilidad del género del retrato, que se adapta perfectamente al objetivo de una enseñanza integral en la que los alumnos aprendan desde un punto de vista lúdico y creativo.The work makes a didactic proposal for the Early Childhood Education, based on the artistic genre of portraiture. He study highlights the great importance of the artistic education in its two senses —critical and creative— inside the early childhood education, and moreover the important utility of portraiture adapted properly to the target of an integrated education where students learn with a playful and creative point of view

Hydrolase enzyme activities in a successional gradient of biological soil crusts in arid and semi-arid zones.

In arid and semi-arid regions, pioneer organisms form complex communities that penetrate the upper millimetres of the bare substrate, creating biological soil crusts (BSC). These thin crusts play a vital role in whole ecosystem functioning because they enrich bare surfaces with organic matter, initiate biogeochemical cycling of elements, modify hydrological cycles, etc., thus enabling the ground to be colonized by vascular plants. Various hydrolase enzymes involved in the carbon (cellulase, ß-glucosidase and invertase activities), nitrogen (casein-protease and BAA- protease activities) and phosphorus (alkaline phosphomonoesterase activity) cycles were studied at three levels (crust, middle and deep layers) of three types of BSCs from the Tabernas Desert (SE Spain), representing an ecological gradient ranging from crusts predominated by cyanobacteria to crusts predominated by lichens (Diploschistes diacapsis, Lepraria crassissima). All enzyme activities were higher in all layers of all BSCs than in the bare substrate. The enzymes that hydrolyze low molecular weight substrates were more active than those that hydrolyze high molecular weight substrates (cellulase, casein-protease), highlighting the pioneering characteristics of the BSCs. The hydrolytic capacity developed in parallel to that of ecological succession, and the BSCs in which enzyme activity was highest were those under Lepraria crassissima. The enzyme activity per unit of total organic C was extremely high; the highest values occurred in the BSCs formed by cyanobacteria and the lowest in those formed by lichens, which 2 indicates the fundamental role that the primary colonizers (cyanobacteria) play in enriching the geological substrate with enzymes that enable degradation of organic remains and the establishment of more developed BSCs. The results of the study combine information on different enzyme activities and provide a clear vision of how biogeochemical cycles are established in BSCs, thus confirming the usefulness of enzyme assays as key tools for examining the relationship between biodiversity and ecosystem function in biological soil crusts.Peer reviewe

Diseño, aplicación y evaluación del proyecto “El antiguo Egipto” en educación infantil

Los objetivos de esta investigación son desarrollar conocimientos relacionados con el mundo egipcio, promover en el alumnado de Educación Infantil aprendizajes significativos de ciencias sociales mediante la metodología por proyectos y fomentar la colaboración de las familias en la escuela. Esta investigación semiexperimental está diseñada en tres fases: de exploración, donde se recogen los datos mediante un pretest del mundo egipcio; de intervención, en la que se diseñan las estrategias de actuación, se realizan las sesiones del proyecto y se reflexiona sobre todo lo acontecido en un diario de campo, y conclusiones, donde se emplean como instrumentos de recogida de datos: un cuestionario de valoración por las familias, un postest para el alumnado y una entrevista para la tutora. Los resultados de aprendizaje han sido muy positivos, y se han producido avances importantes en los conocimientos relativos al Antiguo Egipto. Las familias están satisfechas con la metodología empleada. En conclusión, el método de proyectos es idóneo para facilitar al alumnado los conocimientos de ciencias sociales en Educación Infantil.The objectives of this research are to develop knowledge related to the Egyptian world, promoting the kindergarten students meaningful learning through social science methodology for projects and to encourage collaboration of families in the school. This quasi-experimental research is designed in three phases: exploration, where data is collected using a pretest of the Egyptian world; intervention, in which intervention strategies, the sessions of the project are carried out and a reflection on everything that happened is noted on a field journal, and conclusions, which are used as data collection instruments: an evaluation questionnaire for families, a posttest for students and a tutor interview. Learning outcomes have been very positive, and there have been significant advances in the knowledge of the Ancient Egypt. Families are satisfied with the methodology used. In conclusion, the method is suitable for projects to facilitate students of social science knowledge in Early Childhood Education

Basketball training influences shot selection assessment : a multi-attribute decision-making approach1

In spite of the fact that shoot selection is a crucial ingredient of performance in basketball, the judgment and decision making processes involved in it have been largely neglected. In the present work, we explore individuals' strategies to assess the adequateness of shooting (in a simulation laboratory task) in situations varying in the degree of physical defensive pressure, rebound, defensive balance and shooting distance. Our results showed that the four target dimensions have an impact on participants' judgments. More importantly, training influences the degree to which one of the non-obvious dimensions (defensive balance) is taken into account by participants in order to make their judgments. These results stress the necessity to develop measures of shot selection decisional quality beyond scoring rates