The nature of correlations in the insulating states of twisted bilayer graphene

The recently observed superconductivity in twisted bilayer graphene emerges from insulating states believed to arise from electronic correlations. While there have been many proposals to explain the insulating behaviour, the commensurability at which these states appear suggests that they are Mott insulators. Here we focus on the insulating states with $\pm 2$ electrons or holes with respect to the charge neutrality point. We show that the theoretical expectations for the Mott insulating states are not compatible with the experimentally observed dependence on temperature and magnetic field if, as frequently assumed, only the correlations between electrons on the same site are included. We argue that the inclusion of non-local (inter-site) correlations in the treatment of the Hubbard model can bring the predictions for the magnetic and temperature dependencies of the Mott transition to an agreement with experiments and have consequences for the critical interactions, the size of the gap, and possible pseudogap physics. The importance of the inter-site correlations to explain the experimental observations indicates that the observed insulating gap is not the one between the Hubbard bands and that antiferromagnetic-like correlations play a key role in the Mott transition.Comment: 8 pages (including appendix), 5 figure

Sustainable planning for poor communities: urban design studios as a catalyst for development in Colombia

This chapter addresses the potential role of sustainable urban design studios as catalysts for development in slum communities of the developing world. Understanding urbanisation processes in the developing world is important to our sustainability challenge because most of the world’s population will live in these places. oreover, world urbanisation patterns are both a key problem as well as a primary resource. Urban proximity makes sustainability with density possible, however urbanisation is both energy intensive and destructive to natural resources

Inclusion of [H3PW12O40] and [H4SiW12O40] into a silica gel matrix via "sol-gel" methodology

Indexación: Web of Science; Scopus.Here we report the inclusion of two Keggin Polyoxometalates (POMs), [H3PW12O40] and [H4SiW12O40], into silica gels by integrating them during the preparation of the SiO2 matrix via "sol-gel" methods. Aerogels were produced by supercritical drying of the wet gels impregnated with the POMs, and lyogels were obtained by means of a lyophilization process. These materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR) spectroscopy and thermoanalytical techniques (TGA-DSC). We found that a large fraction of POMs are lost during the aging time, and solvent exchange for lyophilization. However the thermal stability of the bare matrix is modified by the inclusion of POMs. Some aggregates with a high content of POMs were found via SEM-EDX.http://ref.scielo.org/3fg9t

Experiencia sobre una propuesta metodológica y didáctica para la capacitación de profesores de EGB 3 y polimodal

En este trabajo presentamos los resultados obtenidos como consecuencia del dictado de un Curso de Capacitación para Profesores de EGB 3 y Polimodal, llevado a cabo en la Facultad de Ciencias Exactas y Naturales de la Universidad Nacional de La Pampa. Aprovechando las alternativas que ofrece la evolución tecnológica para propiciar cambios en el enfoque de enseñar y aprender matemática, teniendo en cuenta que la informática ocupa un lugar cada vez más importante en nuestra sociedad y resulta de gran utilidad en el campo educativo, les presentamos a los profesores una propuesta metodológica y didáctica complementaria para la enseñanza del tema Resolución Numérica de Ecuaciones Polinómicas. Esta propuesta consiste, básicamente, en utilizar métodos que usualmente no se enseñan en la Escuela de Nivel Polimodal, con el complemento de la computadora como herramienta colaboradora. Estos métodos permitirán que el alumno analice expresiones polinómicas que no tienen solución exacta, que son de orden elevado y, por consiguiente, son difíciles de tratar por medio de los métodos convencionales. Este tipo de expresiones provienen, por lo general, de problemas técnicos o de situaciones problemáticas de la vida real cuyo tratamiento puede motivar al alumno, facilitando de esta manera el proceso de enseñanza-aprendizaje relativo a la Resolución Numérica de Ecuaciones Polinómicas de cualquier orden. La motivación especial que nos condujo a la elaboración y dictado de este Curso fue la de intentar mejorar el proceso de enseñanza-aprendizaje referido a esta temática en los niveles educativos citados anteriormente. Los participantes respondieron activamente a las distintas propuestas de trabajo que se presentaron a lo largo del desarrollo del Curso. Es por ello que podemos concluir que esta experiencia resultó positiva

Software educativo en línea para la enseñanza y el aprendizaje de temas de Cálculo Numérico

En un proyecto de investigación finalizado, se diseñó un software de escritorio para la enseñanza y el aprendizaje del tema Resolución Numérica de Ecuaciones no Lineales, usando el paquete MatLab

Phytoplankton patchiness in two shallow waterbodies

The hydrodynamic behaviour in lentic ecosystems is closely related with the spatial and temporal evolution of their physical, chemical and biological characteristics. Because of this, and in order to improve our present knowledge on the limnological dynamics of such ecosystems, a coupled analysis on the relationship between the biological patterns and the governing hydrodynamics mechanisms it is necessary. This paper uses both field analysis and numerical simulation to describe the links between the water movements and the phytoplankton spatial distribution on two shallow waterbodies in the South of Spain: Alhama de Granada Reservoir (Granada) and Laguna Nueva de la Albufera de Adra (Almería). In both systems the observed phytoplankton spatial distribution exhibited dynamic patterns forced by hydrodynamical transport processes. The knowledge of this physical-biological coupling could be useful to outline the basic guidelines for water quality management.Los ecosistemas acuáticos leníticos se caracterizan por un intenso acoplamiento entre los mecanismos de transporte hidrodinámico que en ellos ocurren y la evolución espacial y temporal de sus principales variables físico-químicas y biológicas. En consecuencia y con el objetivo de mejorar nuestro entendimiento sobre la dinámica limnológica de este tipo de sistemas, resulta necesario el desarrollo de análisis interdisciplinares que profundicen en esta estrecha relación hidrodinámica-biología. En este trabajo se analiza, a partir de estudios de campo y simulaciones numéricas, el acoplamiento entre el movimiento de la masa fluida a nivel de macroescala y la distribución espacial del fitoplancton en dos ecosistemas acuáticos someros del Sur de España : el embalse de Alhama de Granada (Granada) y la Laguna Nueva de la Albufera de Adra (Almería). En ambos sistemas se han encontrado patrones dinámicos de distribución espacial de las microalgas, íntimamente relacionados con la dinámica de la masa de agua. El conocimiento de este acoplamiento resulta útil en la definición de líneas básicas para la adecuada gestión de la calidad del agua

Effect of addition of an ammonium source in UASB and EGSB reactors when treating low concentrated wastewater: granules morphology

In this work the effect on granules morphology by adding a supplementary nitrogen-ammonium source to UASB and EGSB reactors, treating a low concentrated wastewater is studied. Previously, a complex-synthetic-medium-concentratedwastewater (C/N ratio, 100:4) was fed for granule development and maturation, achieving similar removal performances (higher than 95 % in terms of COD) in both reactors. A subsequent period of 88 days treating low concentrated wastewater (C/N ratio, 100:0.5) led to the destabilisation of granules properties and operational performance in general in both reactors (COD removal efficiencies of approximately 50 %). Ammonium was subsequently supplemented to the low concentrated wastewater, in order to balance the nutrient content (C/N ratio, 100:10) and to study its effect on destabilised granules. After 28 days operating under these conditions, COD removal efficiencies recovered values of 82 and 90 % in UASB and EGSB, respectively. It was also observed, an improvement in granule appearance as given by microscopic observation.CONICYT (Chile); GRICES (Portugal)