Oxygen photo-adsorption related quenching of photoluminescence in group-III nitride nanocolumns

GaN and InGaN nanocolumns of various compositions are studied by room-temperature photoluminescence (PL) under different ambient conditions. GaN nanocolumns exhibit a reversible quenching upon exposure to air under constant UV excitation, following a t−1/2 time dependence and resulting in a total reduction of intensity by 85–90%, as compared to PL measured in vacuum, with no spectral change. This effect is not observed when exposing the samples to pure nitrogen. We attribute this effect to photoabsorption and photodesorption of oxygen that modifies the surface potential bending. InGaN nanocolumns, under the same experimental conditions do not show the same quenching features: The high-energy part of the broad PL line is not modified by exposure to air, whereas a lower-energy part, which does quench by 80–90%, can now be distinguished. We discuss the different behaviors in terms of carrier localization and possible composition or strain gradients in the InGaN nanocolumns.

Estudio comparativo en el dimensionamiento de cimentaciones

El presente documento es el resultado de la participación de forma activa del autor en el equipo de la oficina de proyectos IDEAM S.A. encargada de realizar en U.T.E. con F.H.E.C.O.R. un manual de aplicación del Eurocódigo 7 a petición de la Dirección General de Carreteras del Ministerio de Fomento. El trabajo se ha centrado en la comparación entre las diversas formulaciones existentes para obtener la carga de hundimiento en cimentaciones superficiales, comparando los resultados de los distintos factores que participan en la formulación de los diferentes autores. De este modo el estudio ha servido para detectar algunas incongruencias entre las formulaciones clásicas de Brinch-Hansen y la formulación propuesta en el anexo D del Eurocódigo 7 (UNE-EN 1997-1) A sí mismo la investigación también se centra en las implicaciones que supone realizar el diseño de las cimentaciones superficiales utilizando para ello el método de los coeficientes parciales de seguridad y combinaciones de acciones mayoradas tal y como plantea el Eurocódigo 7 en lugar de realizar dicho diseño mediante el método de los coeficientes globales de seguridad y combinaciones características de acciones en la forma en que la tradición geotécnica española ha venido haciendo hasta la fecha. This document is the result of the active participation of the author in IDEAM SA, responsible for compiling a guide for the Eurocode 7 as a request by General Director of Hihways of the Fomento Ministry The work primarily focuses on the comparison between the different theories used to obtain the bearing capacity of shallow foundations and comparing the results of the multpile factors involved in the formulas designed by different authors Thereby, the present study has helped identify inconsistencies between the classical formulations of Brinch-Hansen and the proposed formulation in the Annex D of the Eurocode 7 (UNE- EN 1997-1) The investigation additionally focuses on the implications of shallow foundations desing by using the method of partial safety factors and the ULS combinations of actions instead of employing the design by the global safety factor method and SLS combinations of the actions.

Análisis del comportamiento en servicio de los puentes de fábrica ante las nuevas condiciones de explotación

Los puentes arco de fábrica representan una parte importante del inventario de puentes en España y en Europa. De aquí, la importancia cuantitativa de estas estructuras y el interés que representa tanto para las Administraciones, organismos públicos y privados como para la sociedad en general, mantener estos puentes en servicio. Para poder alargar su vida útil, aún más si cabe, se plantea imprescindible llevar a cabo una labor de conservación y mantenimiento adecuada. La importancia de la evaluación estructural de los puentes de fábrica se basa en la conveniencia de conocer el comportamiento estructural tanto en condiciones de servicio como en agotamiento. El comportamiento en Estado Límite Último ha sido estudiado en profundidad y como resultado, la seguridad frente a agotamiento ha quedado definida con cierta confianza. Sin embargo, el comportamiento en Estado Límite de Servicio no es tan conocido. Se considera necesaria una revisión del concepto de ELS en puentes arco de fábrica puesto que muchos de ellos, cumpliendo las comprobaciones establecidas para ELU, presentan daños asociados a las actuales condiciones de explotación existentes actuales. El presente trabajo se enmarca dentro de un proyecto que está llevando a cabo la UIC (Union Internationale de Chemins de Fer) desde 2004. El objetivo general del mismo es conocer el comportamiento de los puentes arco de fábrica y mejorar los métodos de evaluación, mantenimiento y reparación existentes. Con este estudio, se pretende contribuir a mejorar la caracterización del comportamiento en servicio de estas estructuras. Para ello se ha realizado un análisis del estado tensional de la bóveda y el relleno estudiando la influencia de la configuración geométrica de los puentes y las propiedades de los materiales que los componen. Entender el funcionamiento de estas estructuras y conocer sus peculiares características ha sido el paso previo al desarrollo del estudio. Para ello, se ha acudido al minucioso trabajo desarrollado por diversos autores, desde los primeros análisis mediante la línea de presiones hasta los actuales métodos basados en elementos finitos. En primer lugar, se ha realizado un estudio paramétrico de diferentes configuraciones geométricas. El objetivo es comprobar la influencia de las dimensiones absolutas y las relaciones existentes entre las mismas en el comportamiento en servicio de los puentes. A continuación, se ha estudiado la influencia de las propiedades mecánicas de los rellenos rígido y granular (modificando su módulo de deformabilidad) en el estado tensional de la bóveda y el propio relleno. Para las dos etapas anteriores se emplea un modelo simplificado de puente arco de fábrica. A continuación, se crea un modelo más completo del mismo, para estudiar la influencia de las propiedades mecánicas del substrato de cimentación en el comportamiento estructural en servicio de la estructura. El objetivo final de este trabajo fin de máster, es conocer el comportamiento en servicio de los puentes arco de fábrica, para poder establecer las variables que condicionan el mismo. El siguiente paso en este campo de estudio, consiste en fijar unos valores límite para las mismas. Como síntesis de las conclusiones obtenidas, se menciona que el comportamiento estructural de los puente arco de fábrica, en mayor o menor medida, está influenciado por su geometría y las propiedades de los rellenos y substrato de cimentación que forman parte del mismo. Masonry arch bridges represent an important part of the total bridges, both in Spain and Europe. For this reason, these structures are so important in terms of quantity. They play an essential role for public administration and people in general. In order to remain those bridges serviceable, suitable inspections and repairs are required. It is necessary to have knowledge of the bridge condition so that an assessment can be made with confidence. It is therefore necessary to check that bridges behave properly under Ultimate Limit State criterion and Serviceability Limit State criterion. ULS has been studied thoroughly and as result, requirements under collapse are well described. However, structural behaviour under conditions of serviceability is not well evaluated. Serviceability Limit State criterion should be redefined for masonry arch bridges assessment. This is because many bridges that fulfil SLS criterion have damages. The purpose of this work is to take part in the improvement of assessment under serviceability. A vault and fill structural behaviour analysis has been performed from two points of view: geometry of the bridge and materials’ properties. The starting point was learning about masonry arch bridges behaviour and their special features. For this task, a revision of several authors’ thorough study has been made, from the line of thrust analysis to the current finite element analysis. Firstly, a parametric study of typologies of bridge has been made. The aim is to know how vault and fill behaviour changes modifying both absolute dimensions and relation between them. In the next step, a study of both surface fill and backfill properties has been done. The aim is to know how vault and fill behaviour changes modifying Young’s modulus. The principal conclusion achieved along this work is that the structural behaviour of masonry bridges depends of the bridge geometry and its material properties.

Memoria geognostico-agrícola sobre la provincia de Castellón

Premiada por la Real Academia de Ciencias en concurso público con arreglo al programa presentado por la misma para el año 1858

Voltage limitation analysis in strain-balanced InAs/GaAsN quantum dot solar cells applied to the intermediate band concept

Several attempts have been carried out to manufacture intermediate band solar cells (IBSC) by means of quantum dot (QD) superlattices. This novel photovoltaic concept allows the collection of a wider range of the sunlight spectrum in order to provide higher cell photocurrent while maintaining the open-circuit voltage (VOC) of the cell. In this work, we analyze InAs/GaAsN QD-IBSCs. In these cells, the dilute nitrogen in the barrier plays an important role for the strain-balance (SB) of the QD layer region that would otherwise create dislocations under the effect of the accumulated strain. The introduction of GaAsN SB layers allows increasing the light absorption in the QD region by multi-stacking more than 100 QD layers. The photo-generated current density (JL) versus VOC was measured under varied concentrated light intensity and temperature. We found that the VOC of the cell at 20 K is limited by the bandgap of the GaAsN barriers, which has important consequences regarding IBSC bandgap engineering that are also discussed in this work.

Sistemas de comunicación por satélite: utilización en los sistemas de navegación aeronáuticos

Este Proyecto Fin de Carrera tiene como principal objetivo analizar la evolución de los Sistemas de Comunicación por Satélite, así como dar a conocer al lector la tecnología EGNOS y su aplicabilidad como ayuda a la navegación Aeronáutica. Este trabajo comenzará con una primera parte, la cual está dedicada a conocer qué es un satélite y como ha sido su evolución a lo largo de la historia, desde la aparición del primer satélite hasta nuestros días, así como mostrar las partes que lo componen y su proceso de lanzamiento. Todo este capítulo, sirve de base para poder entender mejor las siguientes partes del proyecto. En la segunda parte de esta memoria, se entra más en detalle y se desarrollan los temas principales de este documento. Podríamos decir que este segundo capítulo se divide a su vez en dos subpartes claramente diferenciadas: En la primera, se analiza la estructura de un sistema de comunicaciones por satélite, los diferentes tipos de satélites según su órbita o según su finalidad, viendo unos claros ejemplos de cada uno de ellos, así como las bandas de frecuencias en las que trabajan. Para concluir esta sección se habla de los diferentes tipos de servicios que ofrecen las comunicaciones por satélite para centrarnos más adelante en los servicios aeronáuticos. En la segunda parte, se habla de la aplicación de la tecnología EGNOS como ayuda a la navegación aeronáutica. Para ello, primero se explican los diferentes sistemas de navegación que usan las aeronaves, entre los que se encuentran los sistemas VOR, DME, ADF y TACAN, y después se introduce al usuario a la tecnología EGNOS, viendo su arquitectura y explicando su funcionamiento. Como ejemplo de aplicabilidad de esta tecnología se explica el novedoso sistema SLS que llevan las aeronaves. Toda esta segunda parte constituye el cuerpo del proyecto y el punto más importante de esta memoria. Para finalizar, en la última parte del Proyecto Fin de Carrera, se habla del presente y futuro del sistema EGNOS evaluando sus principales ventajas y las conclusiones que se han sacado al hacer esta memoria. ABSTRACT. This thesis has as main objective to analyze the evolution of satellite communication systems, as well as to inform the reader about EGNOS technology and its applicability as an aid to aeronautical navigation. This document will begin with a first part, which is dedicated to know what a satellite is and how has its evolution been throughout history, from the appearance of the first satellite until nowadays, as well as showing the parts that it is composed of and different launch processes. This chapter serves as a base to a better understanding of these parts of the project. In the second part of this report, more detail is introduced and it is developed the main themes of this document. We could say that this second chapter is divided in two clearly differentiated subparts: The first, analyzes the structure of a communications system by satellite, different types of satellites according to its orbit or according to their purpose, seeing some clear examples of each of them, as well as the frequency bands in which they work. To conclude, this section refers to different types of services offered by satellite communications to focus later in the aeronautical services. In the second part, application of EGNOS technology is referred as an aid to the aeronautical navigation. To do this, first they are explained the different navigation systems that the aircraft uses, which include VOR, DME, ADF and TACAN systems, and then EGNOS technology is introduced to the user, seeing its architecture and explaining its operation. As an example of applicability of this technology, the new system SLS carried by the aircraft is explained. Throughout this second part it is constituted the body of the project and the most important point of this report. Finally, in the last part of the thesis, the present and future of the EGNOS system are analyzed evaluating the main advantages and conclusions that have been obtained to make this memory.

Trans-spliced leader addition to mRNAs in a cnidarian

A search of databases with the sequence from the 5′ untranslated region of a Hydra cDNA clone encoding a receptor protein-tyrosine kinase revealed that a number of Hydra cDNAs contain one of two different sequences at their 5′ ends. This finding suggested the possibility that mRNAs in Hydra receive leader sequences by trans-splicing. This hypothesis was confirmed by the finding that the leader sequences are transcribed as parts of small RNAs encoded by genes located in the 5S rRNA clusters of Hydra. The two spliced leader (SL) RNAs (SL-A and -B) contain splice donor dinucleotides at the predicted positions, and genes that receive SLs contain splice acceptor dinucleotides at the predicted positions. Both of the SL RNAs are bound by antibody against trimethylguanosine, suggesting that they contain a trimethylguanosine cap. The predicted secondary structures of the Hydra SL RNAs show significant differences from the structures predicted for the SLs of other organisms. Messenger RNAs have been identified that can receive either SL-A or -B, although the impact of the two different SLs on the function of the mRNA is unknown. The presence and features of SL addition in the phylum Cnidaria raise interesting questions regarding the evolution of this process.

Modelització de Sistemes Ecològics. Manual de pràctiques de laboratori

Manual de pràctiques de laboratori de l'assignatura Modelització de Sistemes Ecològics.

Substantial enlargement of angular existence range for Dyakonov-like surface waves at semi-infinite metal-dielectric superlattice

We investigated surface waves guided by the boundary of a semi-infinite layered metal-dielectric nanostructure cut normally to the layers and a semi-infinite dielectric material. Using the Floquet-Bloch formalism, we found that Dyakonov-like surface waves with hybrid polarization can propagate in dramatically enhanced angular range compared to conventional birefringent materials. Our numerical simulations for an Ag-GaAs stack in contact with glass show a low to moderate influence of losses.

Magnetic Edge Anisotropy in Graphenelike Honeycomb Crystals

The independent predictions of edge ferromagnetism and the quantum spin Hall phase in graphene have inspired the quest of other two-dimensional honeycomb systems, such as silicene, germanene, stanene, iridates, and organometallic lattices, as well as artificial superlattices, all of them with electronic properties analogous to those of graphene, but a larger spin-orbit coupling. Here, we study the interplay of ferromagnetic order and spin-orbit interactions at the zigzag edges of these graphenelike systems. We find an in-plane magnetic anisotropy that opens a gap in the otherwise conducting edge channels that should result in large changes of electronic properties upon rotation of the magnetization.

Topological spin waves in the atomic-scale magnetic skyrmion crystal

We study the spin waves of the triangular skyrmion crystal that emerges in a two-dimensional spin lattice model as a result of the competition between Heisenberg exchange, Dzyalonshinkii–Moriya interactions, Zeeman coupling and uniaxial anisotropy. The calculated spin wave bands have a finite Berry curvature that, in some cases, leads to non-zero Chern numbers, making this system topologically distinct from conventional magnonic systems. We compute the edge spin-waves, expected from the bulk-boundary correspondence principle, and show that they are chiral, which makes them immune to elastic backscattering. Our results illustrate how topological phases can occur in self-generated emergent superlattices at the mesoscale.

Human naïve regulatory T-cells feature high steady-state turnover and are maintained by IL-7

Naïve FoxP3-expressing regulatory T-cells (Tregs) are essential to control immune responses via continuous replenishment of the activated-Treg pool with thymus-committed suppressor cells. The mechanisms underlying naïve-Treg maintenance throughout life in face of the age-associated thymic involution remain unclear. We found that in adults thymectomized early in infancy the naïve-Treg pool is remarkably well preserved, in contrast to conventional naïve CD4 T-cells. Naïve-Tregs featured high levels of cycling and pro-survival markers, even in healthy individuals, and contrasted with other circulating naïve/memory CD4 T-cell subsets in terms of their strong γc-cytokine-dependent signaling, particularly in response to IL-7. Accordingly, ex-vivo stimulation of naïve-Tregs with IL-7 induced robust cytokine-dependent signaling, Bcl-2 expression, and phosphatidylinositol 3-kinase (PI3K)-dependent proliferation, whilst preserving naïve phenotype and suppressive capacity. Altogether, our data strongly implicate IL-7 in the thymus-independent long-term survival of functional naïve-Tregs, and highlight the potential of targeting the IL-7 pathway to modulate Tregs in different clinical settings.

Middle East respiratory syndrome coronavirus neutralising serum antibodies in dromedary camels: a comparative serological study

A new betacoronavirus-Middle East respiratory syndrome coronavirus (MERS-CoV)-has been identified in patients with severe acute respiratory infection. Although related viruses infect bats, molecular clock analyses have been unable to identify direct ancestors of MERS-CoV. Anecdotal exposure histories suggest that patients had been in contact with dromedary camels or goats. We investigated possible animal reservoirs of MERS-CoV by assessing specific serum antibodies in livestock. METHODS: We took sera from animals in the Middle East (Oman) and from elsewhere (Spain, Netherlands, Chile). Cattle (n=80), sheep (n=40), goats (n=40), dromedary camels (n=155), and various other camelid species (n=34) were tested for specific serum IgG by protein microarray using the receptor-binding S1 subunits of spike proteins of MERS-CoV, severe acute respiratory syndrome coronavirus, and human coronavirus OC43. Results were confirmed by virus neutralisation tests for MERS-CoV and bovine coronavirus. FINDINGS: 50 of 50 (100%) sera from Omani camels and 15 of 105 (14%) from Spanish camels had protein-specific antibodies against MERS-CoV spike. Sera from European sheep, goats, cattle, and other camelids had no such antibodies. MERS-CoV neutralising antibody titres varied between 1/320 and 1/2560 for the Omani camel sera and between 1/20 and 1/320 for the Spanish camel sera. There was no evidence for cross-neutralisation by bovine coronavirus antibodies. INTERPRETATION: MERS-CoV or a related virus has infected camel populations. Both titres and seroprevalences in sera from different locations in Oman suggest widespread infection. FUNDING: European Union, European Centre For Disease Prevention and Control, Deutsche Forschungsgemeinschaft.