Geometric ferroelectricity in fluoroperovskites

We used first-principles calculations to investigate the existence and origin of the ferroelectric in- stability in the ABF3 fluoro-perovskites. We find that many fluoro-perovskites have a ferroelectric instability in their high symmetry cubic structure, which is of similar amplitude to that commonly found in oxide perovskites. In contrast to the oxides, however, the fluorides have nominal Born effective charges, indicating a different mechanism for the instability. We show that the instability originates from ionic size effects, and is therefore in most cases largely insensitive to pressure and strain, again in contrast to the oxide perovskites. An exception is NaMnF3, where coherent epitaxial strain matching to a substrate with equal in-plane lattice constants destabilizes the bulk Pnma structure leading to a ferroelectric, and indeed multiferroic, ground state with an unusual polarization/strain response

Spin texture induced by oxygen vacancies in strontium perovskite (001) surfaces: A theoretical comparison between SrTiO 3 and SrHfO 3

The electronic structure of SrTiO3 and SrHfO3 (001) surfaces with oxygen vacancies is studied by means o

Tecnologías para el manejo de metadatos en artículos científicos

(Eng) The use of Semantic Web technologies has been increasing, so it is common using them in different ways. This article evaluates how these technologies can contribute to improve the indexing in articles in scientific journals. Initially, there is a conceptual review about metadata. Later, studying the most important technologies for the use of metadata in Web and, this way, choosing one of them to apply it in the case of study of scientific articles indexing, in order to determine the metadata based in those used in impact research journals, and building a model for indexing scientific articles using Semantic Web technologies.(Spa) El uso de tecnologías de la Web Semántica ha venido acrecentándose, por lo que es común usarlo en diferentes aspectos. Este trabajo evalúa como estas tecnologías pueden contribuir a mejorar la indexación de artículos en revistas científicas. Inicialmente, se hace una revisión conceptual de los metadatos, para posteriormente estudiar las tecnologías más importantes para el uso de metadatos en la Web y, de esta manera, escoger una para aplicarla en el caso de estudio de indexación de artículos científicos, determinando los metadatos con bases en los usados por las revistas de investigación de impacto y construir un modelo para la indexación de artículos científicos usando una tecnología de Web Semántica

Herramienta autor Indesahc para la creación de cursos hipermedia adaptativos

Un elemento fundamental dentro de una plataforma de gestión del aprendizaje (Learning Management Systems, LMS) es la herramienta autor para la producción del material didáctico. En este artículo presentamos un sistema de desarrollo integrado para la creación y evaluación de cursos hipermedia adaptativos accesibles, basados en páginas Web. INDESAHC (Integrated Development System for Adaptive Hypermedia Courses), facilita la introducción del mapa de contenidos del curso, según un modelo del dominio basado en temas, lecciones, conceptos y escenarios tipos, en los cuales se realiza la integración de los archivos de media mediante un entorno visual intuitivo basado en plantillas. Una vez definidas las relaciones entre los temas y los niveles de dificultad de cada lección, se genera el curso hipermedia adaptativo, cuyo diseño final puede ser evaluado a través de una herramienta accesorio llamada EPRules (Educational Prediction Rules). Esta herramienta utiliza algoritmos de minería de datos, para el descubrimiento de información útil para facilitar un proceso de retroalimentación. Se describe además, el modelo didáctico en que se basa INDESAHC y se presenta una metodología eficaz, para evitar los problemas de desorientación y sobrecarga de contenidos en la navegación.In this paper we present an integrated development system for Web Based Adaptive Hypermedia Courses. We have developed an authoring tool called INDESAHC (Integrated Development System for Adaptive Hypermedia Courses) for this purpose. This tool facilitates to the course designer introducing the conceptual map, according to a domain model based on topics, lessons, concepts and learning components. Furthermore, the program allows the integration of media files in the course by means of an intuitive visual environment based on templates. Once defined the relationship among the topics and the difficulty level of each lesson, the user can generate the hypermedia adaptive course. The final design could be evaluated with an accessory tool called EPRules (Educational Prediction Rules). This tool is based on data mining algorithms in order to discover useful information for feedback. We also discuss on how our methodology can avoid the problems of disorientation and cognitive overload

Rational exploitation of a granite outcrop

[Abstract] This piece analizes the possibilities of mining exploitation in a little outcrop of rOSfl granite. The zone has been researched, recognizing the main structural discontinuities, and characterizing the rock mass by the geomechanic classificationofBARTON. Two core drilling have been made to study the evolution ofthe deeper bed. The volume ofthe bed has been calculated by geometric calculation in the researched area. The theories ofCASTAING and RABU have been developed to estimate the useful volume of the bed for a minimum block size of 1 m3. We have implerríented a computer program in base ofEXCEL 4.0. The result is a useful volume of 51.67 %. By the application of the reduction coefficients ofsterility and irregularity, the maximum estimated efficiency of the exploitation is 33 %