Novel mechanisms to enhance the capacitance beyond the classical limits in capacitors with free-electron-like electrodes

The so-called negative electron compressibility refers to the lowering of the chemical potential of a metallic system when the carrier density increases. This effect has often been invoked in the past to explain the enhancement of the capacitance beyond the classical limits in capacitors with two-dimensional electron gases as electrodes. Based on experiments on strongly confined semiconductor quantum wells (QWs), it has been traditionally ascribed to the electron exchange energy as the main driving force. Recent research, however, has revealed that analogous effects can occur in other classes of materials systems, such as polar oxide interfaces, whose characteristics drastically depart from those of the previously considered cases. To rationalize these new results, it is necessary to revisit the established theory of confined electron gases, and test whether its conclusions are valid beyond the specifics of semiconductor-based QWs. Here we find, based on first-principles calculations of jellium slabs, that one must indeed be very careful when extrapolating existing results to other realistic physical systems. In particular, we identify a number of additional, previously overlooked mechanisms (e.g., related to the displacement of the electronic cloud and to the multiband structure of the delocalized gas), that enter into play and become new sources of negative capacitance in the weak-confinement regime. Our detailed analysis of these emerging contributions, supported by analytic models and multiple test cases, will provide a useful guidance in the ongoing quest for nanometric capacitors with enhanced performance.Comment: 24 pages, 19 figure

Debates—Stochastic subsurface hydrology from theory to practice: why stochastic modeling has not yet permeated into practitioners?

This is the peer reviewed version of the following article: [Sanchez-Vila, X., and D. Fernàndez-Garcia (2016), Debates—Stochastic subsurface hydrology from theory to practice: Why stochastic modeling has not yet permeated into practitioners?, Water Resour. Res., 52, 9246–9258, doi:10.1002/2016WR019302], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/2016WR019302/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingWe address modern topics of stochastic hydrogeology from their potential relevance to real modeling efforts at the field scale. While the topics of stochastic hydrogeology and numerical modeling have become routine in hydrogeological studies, nondeterministic models have not yet permeated into practitioners. We point out a number of limitations of stochastic modeling when applied to real applications and comment on the reasons why stochastic models fail to become an attractive alternative for practitioners. We specifically separate issues corresponding to flow, conservative transport, and reactive transport. The different topics addressed are emphasis on process modeling, need for upscaling parameters and governing equations, relevance of properly accounting for detailed geological architecture in hydrogeological modeling, and specific challenges of reactive transport. We end up by concluding that the main responsible for nondeterministic models having not yet permeated in industry can be fully attributed to researchers in stochastic hydrogeology.Peer ReviewedPostprint (author's final draft

La UNESCO y la protección del Patrimonio Histórico Universal

La UNESCO contribuye desde 1946 a proteger el patrimonio histórico universal mediante diversas Convenciones y recomendaciones. En las tres últimas Conferencias Generales de la UNESCO se ha producido un hecho que no ha ocurrido nunca y que sólo tiene un antecedente en el trienio 1970-1972: la aprobación en cada reunión de una Convención dirigida a proteger un campo específico del Patrimonio Histórico. ¿Ha cambiado la función protectora de la UNESCO y desde hace unos pocos años ha optado por elaborar grandes Tratados internacionales, acentuando una dirección normativa? ¿O, por el contrario, la aprobación de Convenciones se limita a seguir las orientaciones iniciales desde 1946 que combinan medidas singulares de protección y grandes normas convencionales

Stochastic estimation of hydraulic transmissivity fields using flow connectivity indicator data

This is the peer reviewed version of the following article: [Freixas, G., D. Fernàndez-Garcia, and X. Sanchez-Vila (2017), Stochastic estimation of hydraulic transmissivity fields using flow connectivity indicator data, Water Resour. Res., 53, 602–618, doi:10.1002/2015WR018507], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/2015WR018507/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Most methods for hydraulic test interpretation rely on a number of simplified assumptions regarding the homogeneity and isotropy of the underlying porous media. This way, the actual heterogeneity of any natural parameter, such as transmissivity ( math formula), is transferred to the corresponding estimates in a way heavily dependent on the interpretation method used. An example is a long-term pumping test interpreted by means of the Cooper-Jacob method, which implicitly assumes a homogeneous isotropic confined aquifer. The estimates obtained from this method are not local values, but still have a clear physical meaning; the estimated math formula represents a regional-scale effective value, while the log-ratio of the normalized estimated storage coefficient, indicated by math formula, is an indicator of flow connectivity, representative of the scale given by the distance between the pumping and the observation wells. In this work we propose a methodology to use math formula, together with sampled local measurements of transmissivity at selected points, to map the expected value of local math formula values using a technique based on cokriging. Since the interpolation involves two variables measured at different support scales, a critical point is the estimation of the covariance and crosscovariance matrices. The method is applied to a synthetic field displaying statistical anisotropy, showing that the inclusion of connectivity indicators in the estimation method provide maps that effectively display preferential flow pathways, with direct consequences in solute transport.Peer ReviewedPostprint (published version

Binary RDF for Scalable Publishing, Exchanging and Consumption in the Web of Data

El actual diluvio de datos está inundando la web con grandes volúmenes de datos representados en RDF, dando lugar a la denominada 'Web de Datos'. En esta tesis proponemos, en primer lugar, un estudio profundo de aquellos textos que nos permitan abordar un conocimiento global de la estructura real de los conjuntos de datos RDF, HDT, que afronta la representación eficiente de grandes volúmenes de datos RDF a través de estructuras optimizadas para su almacenamiento y transmisión en red. HDT representa efizcamente un conjunto de datos RDF a través de su división en tres componentes: la cabecera (Header), el diccionario (Dictionary) y la estructura de sentencias RDF (Triples). A continuación, nos centramos en proveer estructuras eficientes de dichos componentes, ocupando un espacio comprimido al tiempo que se permite el acceso directo a cualquier dat

Supuestos de Contabilidad II. Enunciados. Curso 2014-2015

Este documento contiene enunciados de ejercicios sobre los temas que componen el Plan Docente de la asignatura COMPTABILITAT II del Grau en Administració i Direcció d’Empreses que se imparte en la Facultat Economia i Empresa de la Universitat de Barcelona. Estos enunciados servirán como material docente para el desarrollo de las clases y serán resueltos durante las sesiones

Skiagrafías y otros desvelos gráficos. Averiguaciones para un nuevo espacio creativo

[EN] The X-rays calmed the hurtful desire experienced by many artists to probe the visible and the invisible, endowing the vision with an unsuspected depth. Those first veiled skiagraphs in the old hospital San Vicente de Paul in Chile in 18961, began the definitive discredit of the old paradigm of the positivist reality, unique and univocal, to incorporate a new substance that in the long run would be definitive in the artistic and creative development of the twentieth century: the other, its hidden face. This essay places value on X-rays, as a photographic (artistic) technique, understood as a beautiful tool for the exploration and analysis of reality hidden behind the appearance of the visible world, and as an “unknown light” applied to the architectural project reveals a suggestive world of possibilities with which to find spaces and invent places. The research analyzes the potential of this suggestive tool, contributing as a result, the personal experience maintained with Nick Veasey in Radar Studio (London, 2015). Unpublished documentation that reveals an exciting world with infinite creative possibilities. A new reality unveiled that surprises us with the discovery of new spaces for art and architecture.[ES] Los rayos X calmaron el deseo hiriente experimentado por muchos artistas de sondear lo visible y lo invisible, dotando a la visión de una profundidad insospechada. Aquellas primeras skiagrafías veladas en el laboratorio del profesor W. C. Rontgen en la Universidad de Würzburg, iniciaron el descrédito definitivo del viejo paradigma de la realidad positivista, única y unívoca, para incorporar una nueva sustancia que a la larga sería definitiva en el desarrollo artístico y creativo del siglo XX: lo otro, lo que el ojo no ve, la cara oculta.Este ensayo pone en valor los rayos X como dibujo sobreexpuesto a un cuerpo ajeno, como técnica gráfica (artística) entendida como hermosa herramienta de exploración y análisis de la realidad que se oculta tras la apariencia del mundo visible. Luz incógnita que aplicada al proyecto arquitectónico desvela un sugerente mundo de posibilidades con las que averiguar espacios e inventar nuevos lugares.La investigación analiza el potencial de esta sugerente herramienta gráfica, aportando como resultado, la experiencia personal mantenida con Nick Veasey en Radar Studio (Londres, 2015). Una documentación inédita, que desvela un mundo apasionante, con unas posibilidades creativas infinitas. Una nueva realidad desvelada que nos sorprende con el descubrimiento de nuevos espacios para el arte y la arquitectura.García García, T.; Montero Fernández, FJ. (2020). Skiagraph and other grafic uncoverings. Inquiries for a new creative Space. EGA Expresión Gráfica Arquitectónica. 25(39):120-131. https://doi.org/10.4995/ega.2020.13005OJS1201312539AA. VV. 1999. Arquitectura y Fotografía. Madrid: Ministerio de Fomento.AA. VV. 2010. La subversión de las imágenes. Surrealismo, Fotografía, Cine, cat. de la Exposición. Madrid: Fundación Mapfre Instituto de Cultura y TF Editores.AA. VV. 2012. Picasso visto por Otero. Madrid: La Fábrica y Museo Picasso Málaga.BAUDELAIRE, C. 1898. Curiosités esthétiques, en Œuvres complètes, vol.II. París: Michel Lévy Frères.BARTHES, R. 2004. La cámara lúcida. Notas sobre la fotografía. Barcelona: Paidós.DE CHIRICO, G. 1919. Sull'arte metafísica. Milan: Valori Plastici.FUKU, N. 2007. Man Ray: despreocupado, pero no indiferente, cat. de la Exposición. Madrid: La Fábrica Editorial y Man Ray Trust.GARCIA, T. 2018. Cartografías del espacio oculto. Sevilla: Universidad de Sevilla.LAHUERTA, J. 1990. Sobre el arte metafísico y otros escritos, Murcia: Colegio Oficial de Aparejadores y Arquitectos Técnicos.LAMATA, A. 2010. Superrealistas. La contribución de los Rayos. Madrid: Universidad Complutense de Madrid.LAMPREAVE, R. 2011. Jornada de Arquitectura y Fotografía 2011. Zaragoza: Institución Fernándo el Católico, Excma. Diputación de Zaragoza.LAMPREAVE, R. 2012. La ilusión de la luz. Arquitecturas y fotografías del siglo xx. Madrid: Lampreave.MANN, T. 1990. La Montaña Mágica, capítulo V, sección «¡Dios mío, lo veo!», Der Zauberberg. Berlin: S.Fischer.OPPENHEIM, J. 1985. The Other World: Spiritualism and Psychical Research in England, 1850-1914. Cambridge: Cambridge University Press.PICABIA, F. 1919. Pensamientos sin lenguaje. Paris: Eugène Figuière.PICABIA, F. 1919. Pensées sans langage. Paris: Eug. ne Figuière.RAMIREZ, J. 1993. Duchamp. El amor y la muerte, incluso. Madrid: Ediciones Siruela.PICASSO, P. 1989. Escritos (1935-1959). Paris: Réunion des Musées Nationaux-Gallimard.SHAKESPEARE, W. 1980. Hamlet. Londres: Penguin Books, Londres.STREMMEL, K. 2011. Conmigo, yo mismo, yo. Retratos fotográficos de Picasso, cat. de la Exposición. Málaga: Museo Ludwig y Museo Picasso Málaga.VEASEY, N. 2015. Nick Veasey. Catalogue of works. Londres: Radar Studio