Neurotecnología para el ciudadano

Nadie duda de la extraordinaria importancia que las neurociencias tendrán en un futuro cercano, tanto por su impacto sobre la salud y la calidad de vida de la población, como por sus implicaciones económicas, políticas, sociales y culturales

THE DISTANCE THAT BRINGS NEAR: RECTIFICATION OF THE CHRIST OF ANDREA MANTEGNA

[EN] The Death Christ of Andrea Mantegna was a leap forward in the evolution of art and painting of the Renaissance because of its innovative and transgressive perspective. This paper presents a new enhancement of the work based on geometric analysis and culminating with a perspective correction; attending primarily on the change of the observation distance between the artist and his model.[ES] El Cristo yacente de Andrea Mantegna supuso un salto hacia delante en la evolución del arte y la pintura del Renacimiento debido a su innovador y transgresor punto de vista. Se presenta en este escrito una nueva puesta en valor de dicha obra partiendo de su análisis geométrico y culminando con su rectificación perspectiva; atendiendo principalmente a la variación de la distancia de observación entre el artista y su modelo.Álvaro Tordesillas, A.; Linares García, F. (2011). LA DISTANCIA QUE ACERCA: RECTIFICACIÓN DEL CRISTO YACENTE DE ANDREA MANTEGNA. EGA. Revista de Expresión Gráfica Arquitectónica. 16(17). doi:10.4995/ega.2011.923SWORD184197161

Raising the Efficiency Limit of the GaAs-based Intermediate Band Solar Cell Through the Implementation of a Mololithic Tandem with an AlGaAs top Cell.

The high efficiency limit of the intermediate band solar cell (IBSC) corresponds to the case of using as intermediate band (IB) host material a semiconductor with gap in the range of 2 eV. Traditional photovoltaic materials, such as Si and GaAs, are not appropriate to produce IB devices because their gaps are too narrow. To overcome this problem, we propose the implementation of a multi-junction device consisting of an IBSC combined with a single gap cell. We calculate the efficiency limits using the detailed balance model and conclude that they are very high (> 60% under maximum concentration) for any fundamental bandgap from 0.7 to 3.6 eV in the IBSC inserted in the tandem. In particular, the two-terminal tandem of a GaAs-based IBSC current matched to an optimized AlGaAs top cell has an efficiency limit as high as 64%

Radiative thermal escape in intermediate band solar cells

To achieve high efficiency, the intermediate band (IB) solar cell must generate photocurrent from sub-bandgap photons at a voltage higher than that of a single contributing sub-bandgap photon. To achieve the latter, it is necessary that the IB levels be properly isolated from the valence and conduction bands. We prove that this is not the case for IB cells formed with the confined levels of InAs quantum dots (QDs) in GaAs grown so far due to the strong density of internal thermal photons at the transition energies involved. To counteract this, the QD must be smaller

Predicted photoreflectance signatures on QD selective contacts for hot carrier solar cells

The CO2 emission of our present energy transformation processes, based mainly on burning fossil fuels, is possibly the main cause of global climatic change. The photovoltaic conversion of solar energy is a clean way of producing which for sustainability should (and most probably will) become a major source of electricity. The sun is a huge resource but relatively diluted and it is reasonable to expect that only high efficiency extraction can be cost effective for mass exploitation. New concepts are neccessary such as hot carrier solar cells

Understanding experimental characterization of intermediate band solar cell

An intermediate band solar cell is a novel photovoltaic device with the potential to exceed the efficiency of single gap solar cells. In the last few years, several prototypes of these cells, based on different technologies, have been reported. Since these devices do not yet perform ideally, it is sometimes difficult to determine to what extent they operate as actual intermediate band solar cells. In this article we provide the essential guidelines to interpret conventional experimental results (current-voltage plots, quantum efficiency, etc.) associated with their characterization. A correct interpretation of these results is essential in order not to mislead the research efforts directed towards the improvement of the efficiency of these devices

Intraband absorption for normal illumination in quantum dot intermediate band solar cells

In the current intermediate band solar cells made with InAs quantum dots (QDs) in GaAs, the transitions by absorption of photons between the intermediate band and the conduction band for illumination normal to the cell surface is very weak or, more often, undetectable. We model the QD as a parallelepiped potential well and calculate the envelope function of the electron wavefunctions. By obtaining the dipolar matrix elements we find that, with the present shapes, this absorption is forbidden or very weak. Deeper QDs with smaller base dimensions should be made to permit this absorption

Effect of concentration on the performance of quantum dot intermediate-band solar cells

Implementation of a high-efficiency quantum dot intermediate-band solar cell (QD-IBSC) must accompany a sufficient photocurrent generation via IB states. The demonstration of a QD-IBSC is presently undergoing two stages. The first is to develop a technology to fabricate high-density QD stacks or a superlattice of low defect density placed within the active region of a p-i-n SC, and the second is to realize half-filled IB states to maximize the photocurrent generation by two-step absorption of sub-bandgap photons. For this, we have investigated the effect of light concentration on the characteristics of QDSCs comprised of multi-layer stacks of self-organized InAs/GaNAs QDs grown with and without impurity doping in molecular beam epitaxy

Relaciones Suelo-Planta en Bosques de Abies pinsapo Boiss. Disponibilidad de Nutrientes y Estatus Nutricional

Relaciones Suelo-Planta en Bosques de Abies pinsapo Boiss. Disponibilidad de Nutrientes y Estatus Nutricional. Se han evaluado las relaciones entre las propiedades del suelo y el estado nutricional de los árboles en pinsapares del Paraje Natural Los Reales de Sierra Bermeja y del Parque Natural Sierra de las Nieves (Málaga-España). Se seleccionaron pinsapares que difieren en cuanto a su estado sucesional (masas agradativas versus maduras) y sustrato litológico (serpentinas versus calizas), en los que se evaluaron variables morfoedáficas de perfiles de suelo, y se analizaron las concentraciones de nutrientes en muestras de suelo, hojarasca y acículas. Los suelos de pinsapares calcáreos en fase agradativa (Yunquera) mostraron las menores concentraciones de macro y micronutrientes totales. Esto se correspondía con contenidos también mínimos de N y P en tejidos foliares, indicando la existencia de un estrés nutricional general, como es habitual en masas forestales en fase de exclusión de tallos (máxima competencia intraespecífica). No obstante, la presencia de relaciones N/P foliares normales implica que dicho estrés nutricional no ha desencadenado desbalances internos entre dichos nutrientes en los árboles. En pinsapares calcícolas maduros (Ronda), la mayor acumulación de materia orgánica en la hojarasca y el suelo superficial se relaciona con un aumento de la disponibilidad de nutrientes en el suelo, y una reducción en el estrés nutricional de los árboles. El pinsapar serpentinícola de Los Reales de Sierra Bermeja mostró niveles anormalmente elevados de N, y de las relaciones N/P, tanto en el suelo como en los tejidos foliares. Estos síntomas son característicos de ecosistemas forestales en una fase temprana del denominado síndrome de saturación de nitrógeno, asociado a disfunciones en el ciclo del N