Polyradical character and spin frustration in fullerene molecules: An ab initio non-collinear Hartree--Fock study

Most {\em ab initio} calculations on fullerene molecules have been carried out based on the paradigm of the H\"uckel model. This is consistent with the restricted nature of the independent-particle model underlying such calculations, even in single-reference-based correlated approaches. On the other hand, previous works on some of these molecules using model Hamiltonians have clearly indicated the importance of short-range inter-atomic spin-spin correlations. In this work, we consider {\em ab initio} non-collinear Hartree--Fock (HF) solutions for representative fullerene systems: the bowl, cage, ring, and pentagon isomers of C$_{20}$, and the larger C$_{30}$, C$_{36}$, C$_{60}$, C$_{70}$, and C$_{84}$ fullerene cages. In all cases but the ring we find that the HF minimum corresponds to a truly non-collinear solution with a torsional spin density wave. Optimized geometries at the generalized HF (GHF) level lead to fully symmetric structures, even in those cases where Jahn-Teller distortions have been previously considered. The nature of the GHF solutions is consistent with the $\pi$-electron space becoming polyradical in nature: each $p$-orbital remains effectively singly occupied. The spin frustration, induced by the pentagon rings in an otherwise anti-ferromagnetic background, is minimized at the HF level by aligning the spins in non-collinear arrangements. The long-range magnetic ordering observed is reminiscent of the character of broken symmetry HF solutions in polyacene systems.Comment: 16 figure

Multi-reference symmetry-projected variational approximation for the ground state of the doped one-dimensional Hubbard model

A multi-reference configuration mixing scheme is used to describe the ground state, characterized by well defined spin and space group symmetry quantum numbers as well as doping fractions $N_{e}/N_{sites}$, of one dimensional Hubbard lattices with nearest-neighbor hopping and periodic boundary conditions. Within this scheme, each ground state is expanded in a given number of nonorthogonal and variationally determined symmetry-projected configurations. The results obtained for the ground state and correlation energies of half-filled and doped lattices with 30, 34 and 50 sites, compare well with the exact Lieb-Wu solutions as well as with the ones obtained with other state-of-the-art approximations. The structure of the intrinsic symmetry-broken determinants resulting from the variational procedure is interpreted in terms of solitons whose translational and breathing motions can be regarded as basic units of quantum fluctuations. It is also shown that in the case of doped 1D lattices, a part of such fluctuations can also be interpreted in terms of polarons. In addition to momentum distributions, both spin-spin and density-density correlation functions are studied as functions of doping. The spectral functions and density of states, computed with an ansatz whose quality can be well-controlled by the number of symmetry-projected configurations used to approximate the $N_{e} \pm 1$ electron systems, display features beyond a simple quasiparticle distribution, as well as spin-charge separation trends.Comment: 16 pages, 11 figure

Videojuegos y educación: una visión panorâmica de las investigaciones desarrolladasa nivel internacional

Este artículo presenta los resultados de una investigación más amplia desarrollada entre la Universidad de Cantabria (España) y la Universidad do Minho (Portugal) orientada a conocer las potencialidades educativas de una categoría específica de videojuegos denominada serious games. De forma más concreta, en este artículo se presentan los resultados del análisis de la bibliografía generada a nivel internacional durante los años 2008-2010 sobre los videojuegos elaborados para utilizarse en contextos educativos diversos. En el trabajo se identifican las principales líneas de investigación que en estos momentos está abordando la comunidad internacional sobre la utilización de este tipo de medios en la educación. El estudio revela que la investigación sobre serious games está siendo abordada desde diferentes campos disciplinares y que su utilización no mejora necesariamente los resultados educativos de los estudiantes.This article presents the results of much wider research carried out between the University of Cantabria (Spain) and the University of Minho (Portugal) geared towards discovering the educational possibilities of a specific category of videogames classified as serious games. In more precise terms, this article reproduces the results of the analysis of the bibliography generated on an international scale between 2008 and 2010 on video games created for use in different educational contexts. In the work we identify the main lines of research that are currently being tackled by the international community as to the use of these kinds of tools in education. The study reveals that research on serious games is being considered from a range of academic subjects and that their use does not necessarily improve pupils’ educational results

Teleformación: enfoques pedagógicos críticos frente a modelos de mercado

Este artículo profundiza en la concepción de los procesos de teleformación desde la disciplina didáctica y cuestiona el actual e insuficiente enfoque psicologicista conferido a esta modalidad de formación en línea. La ausencia de un análisis didáctico sobre los componentes que intervienen en estos procesos contrasta con la fabricación de discursos encaminados a sobrevalorar la importancia de otros elementos que integran estas nuevas experiencias educativas (plataformas, estándares, etc.) y que no pueden garantizar el éxito de una acción formativa. Con la intención de entender qué factores intervienen en esta nueva modalidad de formación a distancia, realizamos un proyecto de investigación, empleando la metodología del estudio de caso, sobre un curso de teleformación. Así, recopilamos y analizamos aquellos datos que nos pudieran ofrecer información sobre el comportamiento de docentes y discentes durante ese proceso: correos, chats y foros. En base a los resultados obtenidos intentamos dirimir cuáles son las verdaderas innovaciones y ventajas que, hasta este momento, experimentan los actores y actrices de los procesos de enseñanza-aprendizaje en las experiencias de teleformación. A la luz de las conclusiones extraídas realizamos algunas propuestas encaminadas a introducir mejoras en los cursos de formación en línea.This article analyze the conception of the e‐learning processes from the point of view of didactic discipline and call into question the present and insufficient psychologist approach to this training modality. The lack of a didactical analysis of the components that take part in these processes is in contrasts with the exposition of speeches that overvalue the importance of other elements of these new educative experiences (platforms, standards, etc.) and that can not ensure the success of the training process. With the final aim to understand what are the critical factors that take part in this “new” modality of open learning, we developed an investigation project, leaned against on the case study methodology, in concrete, in an e‐learning course. Thus, we collected and we analyzed those data that could offer information about the behaviour of teachers (etutors) and learners (etrainees) along the process: mails, chats and forums. On the basis of the collected results, we tried to deduce which are the actual innovations and advantages that, until this moment, experiment the process actors and actresses of the e‐learning experience. These conclusions made us able to elaborate some proposals to introduce improvements in the e‐learning courses

Media training for future education professionals: a study of the Spanish context

This article presents the results of research aimed at finding out how training in media education is being developing in Spanish Universities. From a methodological perspective, this work is part of what can be considered a mixed research paradigm. In the first phase, the content of 179 study guides from 83 Spanish universities was analysed using a thematic coding system to analyse the data. In the second phase, 13 in-depth interviews were conducted with university teachers in charge of teaching subjects related to media education in order to understand how they were developing these experiences (methodologies used, systems of assessment, etc.). The results show that the presence of dimensions of media education in curricula is unequal and that teachers are using a wide range of teaching methods and evaluation tools. This study suggests that the education authorities and university teachers should rethink training for future teachers and include contents that facilitate understanding the functioning of the media as a way of accessing diverse cultural representations.This study was funded by: Ministerio de Ciencia e Innovación (Spain). Grant number: EDU2015- 64015-C3-2-R. U. Pompeu Fabr

La figura del tutor de e-learning. Aportaciones de una investigación con estudios de caso

Aquest article recull les conclusions d'una investigació centrada en l'anàlisi del paper del docent-tutor en un parell d'experiències de teleformació desenvolupades en dues institucions públiques a Astúries (Espanya) durant el curs 2007-2008. La finalitat del treball era explorar les diferents formes d'entendre la figura d'aquest professional adoptant un punt de vista diferent però complementari al d'altres investigacions que han subratllat les seves funcions, rols o competències. La metodologia de recerca utilitzada ha estat l'estudi de casos. S'han triat aquests exemples mitjançant un mostreig intencional. L'anàlisi se centra en tres aspectes: a) la concepció de les fases de planificació i desenvolupament de la formació com a fases integrades o separades, i amb això, l'existència d'un o diversos professionals; b) l'avaluació de l'alumnat sobre les tasques del docent-tutor, i c) l'avaluació dels docents-tutors i discents sobre l'ús de les eines de comunicació i el contingut de les interaccions generades a l'aula virtual. Aquesta triple anàlisi ens ha permès concloure que hi ha diferents maneres de concebre i exercir la funció docent-tutorial en la formació en línia («restringida» i «àmplia»). D'altra banda, els resultats d'aquesta investigació apunten la necessitat de fer una lectura crítica dels anomenats avantatges de la modalitat virtual davant de la formació presencial. A la llum dels resultats obtinguts en aquest treball es conclou que és necessari desenvolupar la recerca en aprenentatge virtual a partir de dilemes pedagògics (i no exclusivament tècnics), cosa que implicarà tenir més presents les variables socials, pedagògiques, organitzatives i polítiques que influeixen en l'aprenentatge virtual.This article describes the findings and conclusions drawn from a study analysing the role of the teacher/tutor in two e-learning experiences undertaken at two public institutions in Asturias, Spain, in the 2007/2008 academic year. The aim of the study was to explore the various ways of understanding the teacher/tutor figure from a different yet complementary perspective to that of other studies in which the figure's functions, roles and competencies have already been underscored. A case-study methodology was used for this research project. The cases were selected using intentional sampling. The analysis focused on three aspects: a) The conception of training design and implementation phases as either integrated or separate phases, and, consequently, the existence of one or more professionals; b) The students' assessment of the teacher/tutor's work, and; c) The teacher/tutors' and students' assessment of communication tool use and the content of interaction generated within the virtual classroom. This triple analysis allowed us to conclude that there are several ways of conceiving and carrying out the function of an e-teacher/tutor ("narrow" or "broad"). Furthermore, the results of the study suggest that there is a need to perform a critical reading of the so-called advantages of the e-learning approach over the face-to-face approach. The conclusion drawn from the results of this study is that further research needs to be undertaken into the educational - and not only the technical - dilemmas of e-learning, which would involve taking greater account of the social, educational, organisational and political variables that have an impact on it.Este artículo recoge las conclusiones de una investigación centrada en analizar el papel del docente-tutor en un par de experiencias de teleformación desarrolladas en dos instituciones públicas en Asturias (España) durante el curso 2007-2008. La finalidad del trabajo era explorar las diferentes formas de entender la figura de este profesional adoptando un punto de vista diferente pero complementario al de otras investigaciones que han subrayado sus funciones, roles o competencias. La metodología de investigación utilizada ha sido el estudio de casos. Se han seleccionado estos ejemplos mediante un muestreo intencional. El análisis se centra en tres aspectos: a) la concepción de las fases de diseño y desarrollo de la formación como fases integradas o separadas, y con ello, la existencia de uno o varios profesionales; b) la evaluación del alumnado sobre las tareas del docente-tutor, y c) la evaluación de los docentes-tutores y discentes sobre el uso de las herramientas de comunicación y el contenido de las interacciones generadas en el aula virtual. Este triple análisis nos ha permitido concluir que existen diferentes formas de concebir y ejercer la función docente-tutorial en la formación en línea («restringida» y «amplia»). Por otro lado, los resultados de esta investigación apuntan la necesidad de realizar una lectura crítica de las denominadas ventajas de la modalidad virtual frente a la formación presencial. A la luz de los resultados obtenidos en este trabajo se concluye que es necesario un desarrollo de la investigación en e-learning a partir de dilemas pedagógicos (y no exclusivamente técnicos), lo que supondrá tener más presentes las variables sociales, pedagógicas, organizativas y políticas que influyen en la educación virtual

Numerical solution of an eigenvalue problem for bounded plasma

This article is the result of a research on the propagation of electromagneticwaves in a plasma found confined in a cylindrical metal structure through an intenseaxial magnetic field. The eigenvalue problem resulting from this study is numericallysolved and frequencies of the first electromagnetic modes are obtained. Results ofthis work could be applied to characterize plasmas at the laboratory

Numerical solution of an eigenvalue problem for bounded plasma

This article is the result of a research on the propagation of electromagneticwaves in a plasma found confined in a cylindrical metal structure through an intenseaxial magnetic field. The eigenvalue problem resulting from this study is numericallysolved and frequencies of the first electromagnetic modes are obtained. Results ofthis work could be applied to characterize plasmas at the laboratory