Multi-layer metasurfaces for manipulating the propagation of microwaves along surfaces and edges

This thesis comprises original experimental studies on surface waves propagating on metasurfaces at microwave frequencies. These studies are supported by matching simulation data, obtained by means of Finite Element Method modelling. The structures studied throughout this thesis are comprised of more than one layer of sub-wavelength elements arranged in different periodic lattices. However, these layers are very thin compared to the size of the elements comprising the arrays, resulting in structures that are extremely sub-wavelength in the (out-of-plane) dimension. The work carried out as part of this thesis is divided in three main blocks, each of them looking at different features of metasurfaces, aiming to maximise different properties. The first type of structure presented in this thesis are designed and engineered to maximise three main properties. These are the mode index of the modes bound to the structures, its in-plane isotropy and the bandwidth of operation of prospective devices based on such metasurfaces. Whereas previous work in this field has considered single layers, the novelty here is the introduction of additional layers in order to increase the effective mode index of the modes supported by the structures. These extra layers create a capacitive effect between the overlapping areas of metal, therefore increasing the confinement of the waves. This is increased even further by minimising the separation between such layers. The second main goal in the design of the metasurfaces was to create a frequency independent mode index, aiming for the prospective development of broadband devices. For this, higher symmetries between the layers comprising the structures were introduced. Following the studies of the infinitely periodic metasurfaces and its properties, the suitability for their implementation as graded index devices is proven. Such devices are based on a graded mode index or surface impedance profile across the structure, which modifies the propagation of the wave. In the case of metasurfaces, the grading of the mode index is achieved by gradually varying the size or shape of the elements comprising the structure. This technique is used to design and manufacture two working planar Luneburg lenses, which are characterised experimentally and their performance compared with simulation data. The Luneburg lenses designed and manufactured as part of the work contained in this thesis have the novelty of a higher fractional bandwidth of operation compared to similar metasurface devices, reaching $73\%$. Another piece of work contained in this thesis involves a structure that guides microwaves with very high phase and group indices compared to similar metasurfaces. Its design is a simple two-layer discontinuous crossed metal-strip array. However, the novelty of this structure resides in the length of the metal strips, which extend to several unit cells. This work focuses on the isotropic wave dispersion shown at the lower frequencies. However, in addition to this, two of the higher frequency bands give rise to very strong negative dispersion, and also strong beaming occurs, which can be tailored easily by modifying the relative orientation of the layers. The third piece of work included in this thesis focuses on the propagation of edge modes along the termination of a particular metasurface structure with hexagonal symmetry. Our metasurface is comprised of two layers of hexagonal arrays of circular metal patches. This structure, in addition to supporting a bound wave that propagates isotropically across the two-dimensional structure, also supports an edge mode that propagates only along its termination. Here, the propagation of the mentioned edge mode has been extensively studied. Firstly, its propagation along finite strips is considered, followed by its use to guide the electromagnetic field around different shapes. Finally, the coupling of two of these edge modes across small gaps between two terminated structures is explored, with different symmetries between them. In all cases, samples are designed, fabricated and experiments have been carried out and the original results obtained have been compared with simulation data calculated with a finite element method modelling software.Engineering and Physical Sciences Research Council (EPSRC

Localization of algebras over coloured operads

We give sufficient conditions for homotopical localization functors to preserve algebras over coloured operads in monoidal model categories. Our approach encompasses a number of previous results about preservation of structures under localizations, such as loop spaces or infinite loop spaces, and provides new results of the same kind. For instance, under suitable assumptions, homotopical localizations preserve ring spectra (in the strict sense, not only up to homotopy), modules over ring spectra, and algebras over commutative ring spectra, as well as ring maps, module maps, and algebra maps. It is principally the treatment of module spectra and their maps that led us to the use of coloured operads (also called enriched multicategories) in this context.Comment: 34 page

On the asymptotic optimality of a low-complexity coding strategy for WSS, MA, and AR vector sources

In this paper, we study the asymptotic optimality of a low-complexity coding strategy for Gaussian vector sources. Specifically, we study the convergence speed of the rate of such a coding strategy when it is used to encode the most relevant vector sources, namely wide sense stationary (WSS), moving average (MA), and autoregressive (AR) vector sources. We also study how the coding strategy considered performs when it is used to encode perturbed versions of those relevant sources. More precisely, we give a sufficient condition for such perturbed versions so that the convergence speed of the rate remains unaltered

TP30 210. Tratamiento de la fibrilación auricular mediante ablación con ultrasonidos concomitante a otra cirugía cardíaca. Resultados a largo plazo en nuestro centro

Introducción y objetivosActualmente la ablación quirúrgica de la fibrilación auricular (FA) es un procedimiento simple que puede realizarse en la mayoría de los pacientes durante la cirugía cardíaca. Presentamos nuestros resultados a largo plazo en ablación con ultrasonidos.Pacientes y métodosEn 23 pacientes con diferentes afecciones quirúrgicas cardíacas y FA (12 pacientes con FA permanente, 2 con FA persistente, 7 con FA paroxística, 1 paciente con fibrilo-flutter y un paciente con flutter auricular aislado), se asoció la ablación con ultrasonidos con el dispositivo UltraCinch™ Epicor, durante 2007–2008. El tamaño preoperatorio por ecocardiografía (ECO) de la aurícula izquierda (AI) fue de 45mm (rango 34–55). En un paciente no pudo realizarse por fallo de la consola.ResultadosNo hubo mortalidad intrahospitalaria. Un paciente precisó un marcapasos definitivo. Dos casos registrados de accidente cerebrovascular (ACV). Tras el procedimiento el 63,6% de los pacientes recuperó el ritmo sinusal, bajando al 54% de los pacientes en el momento del alta. A los 6 meses el 63% de los pacientes se encontraban en ritmo sinusal (RS) y a los 12 meses el 68%. Tras un seguimiento de 4 años obtenemos que sólo el 45% de los pacientes mantiene el RS, de los cuales el 20% tiene episodios de FA paroxística.ConclusiónLa ablación mediante ultrasonidos (US) de la FA es un procedimiento sencillo, reproducible y seguro, siendo su efectividad a corto y medio plazo similar a la de otros procedimientos de ablación. En nuestra corta serie, su eficacia a largo plazo disminuye significativamente

Injuries in Physical Education of High School. A Problem?

El control de la incidencia de lesiones en la clase de Educación Física debe ser un factor prioritario para la salud pública. El objetivo de este estudio es analizar la incidencia de lesiones en las clases de Educación Física (EF) y cómo se relacionan con la falta de participación de los estudiantes. Estudio de cohortes prospectivo. Conglomerado de muestreo bi-etapa para un total de 637 estudiantes. Las ausencias y las lesiones se registraron durante el curso escolar. De 1.463 sesiones, solo el 4,58% registró ausencias causadas por lesión (0,33% de la participación total esperada). La tasa de lesiones producidas en las clases de Educación Física fue de 1,90 por cada 1.000 horas de participación. La frecuencia de ausencia en las clases de Educación Física debido a una lesión es muy baja en comparación con la participación general esperada; por lo tanto, no es un factor que influya significativamente en la tasa de participación de los estudiantesThe incidence of injuries in physical education class should be a priority factor for public health. The aim of this study is to analyze the incidence of injuries in Physical Education (PE) lessons and how they relate to lack of full student participation. Prospective cohort study. Conglomerate bi-stage sampling for a total of 637 students. Absence and injuries were recorded for the school year. Of 1463 lessons, only 4.58% were documented with identification of the causal incident (0.33% of the total participation expected). The rate of injuries produced in PE lessons was of 1.90 for every 1000 hours of participation. The frequency of absence of in PE lessons due to injury is very low compared to the overall expected participation; therefore it is not a factor that influences the rate of student participation significantl

Comparación de los elementos estructurales de los modelos actuales de gestión de la calidad

En la actualidad, la implantación de los principios de la Gestión de la Calidad en las empresas, se puede llevar a cabo a través de diferentes modelos como el EFQM, Seis Sigma, Normas ISO, o el Malcom Baldrige. Sin embargo estos modelos, se fundamentan en elementos de la GC, que pueden ser comunes, o específicos de cada uno de ellos. En la organización puede que ya se practiquen algunos de estos elementos. Así, parte de la dificultad de implantación del modelo, vendrá dada en función de que los elementos necesarios para su implantación fueran conocidos o no por la organización. En este artículo, descomponemos los modelos en los elementos sobre los que se apoyan, para concluir que existe una base común a todos, y elementos específicos de cada uno. Además, se puede construir una evolución de los modelos en función de su cercanía a la implantación máxima de la GC

La flexibilidad estratégica como opción de cambio estratégico

En estas fechas, un nuevo horizonte se está planteando en el mundo de los negocios, motivado por los cambios tecnológicos, el desarrollo del conocimiento y la evidente globalización. Un modo de combatir esas situaciones de incertidumbre generadas por estos cambios puede ser a través del desarrollo y la utilización de la flexibilidad estratégica. Las empresas deben ser flexibles para manejar los cambios impredecibles y discontinuos del entorno. En este artículo se desarrolla teóricamente el concepto de flexibilidad, revisando sus tipos, pasando a analizar más detenidamente el concepto de flexibilidad estratégica, sus componentes, sus dimensiones y las fuentes para obtenerla. Posteriormente se justifica su presencia en las organizaciones entendiéndola como una actividad susceptible de planificarse desde la organización, como una capacidad que puede ayudar a modificar rápidamente la estrategia actual si es necesario, como una fuente de ventaja competitiva directamente con el desempeño y principalmente como una opción estratégica de cambio