An a-contrario approach to quasi-periodic noise removal

International audienceImages can be affected by quasi-periodic noise. This undesirable feature manifests itself by spurious repetitive patterns covering the whole image, well localized in the Fourier domain. While notch filtering permits to get rid of this phenomenon , this however requires to first detect the resulting Fourier spikes, and, in particular, to discriminate between noise spikes and spectrum patterns caused by spatially localized textures or repetitive structures. This paper proposes a statistical a-contrario detection of noise spikes in the Fourier domain. A Matlab code is also provided

A non-local dual-domain approach to cartoon and texture decomposition

International audienceThis paper addresses the problem of cartoon and texture decomposition. Microtextures being characterized by their power spectrum, we propose to extract cartoon and texture components from the information provided by the power spectrum of image patches. Thecontribution of texture to the spectrum of a patch is detected as statistically significant spectral components with respect to a nullhypothesis modeling the power spectrum of a non-textured patch. The null-hypothesis model is built upon a coarse cartoon representationobtained by a basic yet fast filtering algorithm of the literature. Hence the term ``dual domain'': the coarse decomposition is obtained in thespatial domain and is an input of the proposed spectral approach. The statistical model is also built upon the power spectrum of patches with similar textures across the image. The proposed approach therefore falls within the family of non-local methods. Experimental results are shown in various application areas, including canvas pattern removal in fine arts painting, or periodic noise removal in remote sensing imaging

Determining displacement and strain maps immune from aliasing effect with the grid method

International audienceSpatial aliasing may affect methods based on grid image processing to retrieve displacement and strain maps in experimental mechanics. Such methods aim at estimating these maps on the surface of a specimen subjected to a loading test. Aliasing, which is often not noticeable to the naked eye in the grid images, may give spurious fringes in the strain maps. This paper presents an analysis of aliasing in this context and provides the reader with simple guidelines to minimize the effect of aliasing on strain maps extracted from grid images

Suspended Waveguide Platforms for Mid-Infrared Group IV Photonics

Fecha de lectura de Tesis Doctoral: 4 de noviembre 2019En las últimas décadas, la banda del infrarrojo medio (2-20 µm) ha despertado un gran interés en la comunidad científica dedicada a la fotónica del Grupo IV. Este auge se debe a las múltiples aplicaciones que pueden desarrollarse en este rango del espectro electromagnético, entre las que sobresalen las comunicaciones ópticas por espacio libre y, sobre todo, la espectroscopia infrarroja, que permite identificar inequívocamente las sustancias disueltas en una muestra y cuantificar su concentración. La plataforma de guiado más usada en la banda de comunicaciones, la de silicio sobre aislante, no puede utilizarse fácilmente a longitudes de onda mayores de 4 µm a causa de las elevadas pérdidas que presenta el dióxido de silicio (aislante). Por ello, es necesario encontrar nuevas estructuras que puedan operar por encima de los límites de transparencia impuestos por los materiales de las estructuras tradicionales. Así, en esta tesis se expone el desarrollo de nuevas plataformas fotónicas integradas para la banda del infrarrojo medio. En concreto, se han propuesto las plataformas de guiado de silicio suspendido y de germanio suspendido con rejillas laterales en régimen sublongitud de onda, en las que el dióxido de silicio se elimina con una solución ácida. Entre otros dispositivos, se han diseñado, fabricado y demostrado experimentalmente guías de onda a diferentes longitudes de onda, entre las que destaca la de 7.67 μm, consiguiéndose pérdidas de propagación bajas en torno a 3 dB/cm (silicio suspendido) y 5 dB/cm (germanio suspendido). Asimismo, el problema del acoplo chip-fibra, cuya resolución es imprescindible para la utilización práctica de cualquier plataforma integrada competitiva, se ha abordado mediante el diseño de acopladores chip-fibra superficiales de alta eficiencia y banda ancha, a saber: una microantena de germanio suspendido y un acoplador de rejilla de orden cero

Patologie rare dell'orecchio

After fifty years of experience, mostly spent in ENT surgery at the University of Palermo, I have pleasure in presenting this Atlas of rare diseases of the ear, including clinical cases observed and documented during this long period from 1958 to 2006. We would prefer to divide all the case studies into three chapters: the outer ear, middle ear and inner ear

Detectando agrupamientos y contornos: un estudio doble sobre representación de formas

Las formas juegan un rol clave en nuestro sistema cognitivo: en la percepción de las formas yace el principio de la formación de conceptos. Siguiendo esta línea de pensamiento, la escuela de la Gestalt ha estudiado extensivamente la percep- ción de formas como el proceso de asir características estructurales encontradas o impuestas sobre el material de estímulo.En resumen, tenemos dos modelos de formas: pueden existir físicamente o ser un producto de nuestros procesos cogni- tivos. El primer grupo está compuesto por formas que pueden ser definidas extra- yendo los contornos de objetos sólidos. En este trabajo nos restringiremos al caso bidimensional. Decimos entonces que las formas del primer tipo son formas planares. Atacamos el problema de detectar y reconocer formas planares. Cier- tas restricciones teóricas y prácticas nos llevan a definir una forma planar como cualquier pedazo de línea de nivel de una imagen. Comenzamos por establecer que los métodos a contrario existentes para de- tectar líneas de nivel son usualmente muy restrictivos: una curva debe ser enter- amente saliente para ser detectada. Esto se encuentra en clara contradicción con la observación de que pedazos de líneas de nivel coinciden con los contornos de los objetos. Por lo tanto proponemos una modificación en la que el algoritmo de detección es relajado, permitiendo la detección de curvas parcialmente salientes. En un segundo acercamiento, estudiamos la interacción entre dos maneras diferentes de determinar la prominencia de una línea de nivel. Proponemos un esquema para competición de características donde el contraste y la regularidad compiten entre ellos, resultando en que solamente las líneas de nivel contrastadas y regulares son consderedas salientes. Una tercera contribución es un algoritmo de limpieza que analiza líneas de nivel salientes, descartando los pedazos no salientes y conservando los salientes. Está basado en un algoritmo para detección de multisegmentos que fue extendido para trabajar con entradas periódicas. Finalmente, proponemos un descriptor de formas para codificar las formas detectadas, basado en el Shape Context global. Cada línea de nivel es codificada usando shape contexts, generando así un nuevo descriptor semi-local. A contin- uación adaptamos un algoritmShape plays a key role in our cognitive system: in the perception of shape lies the beginning of concept formation. Following this lines of thought, the Gestalt school has extensively studied shape perception as the grasping of structural fea- tures found in or imposed upon the stimulus material. In summary, we have two models for shapes: they can exist physically or be a product of our cognitive pro- cesses. The first group is formed by shapes that can be defined by extracting contours from solid objects. In this work we will restrict ourselves to the two dimensional case. Therefore we say that these shapes of the first type are planar shapes. We ad- dress the problem of detecting and recognizing planar shapes. A few theoretical and practical restrictions lead us to define a planar shape as any piece of mean- ingful level line of an image. We begin by stating that previous a contrario methods to detect level lines are often too restrictive: a curve must be entirely salient to be detected. This is clearly in contradiction with the observation that pieces to level lines coincide with object boundaries. Therefore we propose a modification in which the detection criterion is relaxed by permitting the detection of partially salient level lines. As a second approach, we study the interaction between two different ways of determining level line saliency: contrast and regularity. We propose a scheme for feature competition where contrast and regularity contend with each other, resulting in that only contrasted and regular level lines are considered salient. A third contribution is a clean-up algorithm that analyses salient level lines, discarding the non-salient pieces and returning the salient ones. It is based on an algorithm for multisegment detection, which was extended to work with periodic inputs. Finally, we propose a shape descriptor to encode the detected shapes, based on the global Shape Context. Each level line is encoded using shape contexts, thus generating a new semi-local descriptor. We then adapt an existing a contrario shape matching algorithm to our particular case. The second group is composed by shapes that do not correspond to a solid object but are formed by integrating several solid objects. The simplest shapes in this group are arrangements of points in two dimensions. Clustering techniques might be helpful in these situations. In a seminal work from 1971, Zahn faced the problem of finding perceptual clusters according to the proximity gestalt and proposed three basic principles for clustering algorithms: (1) only inter-point distances matter, (2) stable results across executions and (3) independence from the exploration strategy. A last implicit requirement is crucial: clusters may have arbitrary shapes and detection algorithms must be capable of dealing with this. In this part we will focus on designing clustering methods that completely fulfils the aforementioned requirements and that impose minimal assumptions on the data to be clustered. We begin by assessing the problem of validating clusters in a hierarchical struc- ture. Based on nonparametric density estimation methods, we propose to com- pute the saliency of a given cluster. Then, it is possible to select the most salient clusters in the hierarchy. In practice, the method shows a preference toward com- pact clusters and we propose a simple heuristic to correct this issue. In general, graph-based hierarchical methods require to first compute the com- plete graph of interpoint distances. For this reason, hierarchical methods are often considered slow. The most usually used, and the fastest hierarchical clustering al- gorithm is based on the Minimum Spanning Tree (MST). We therefore propose an algorithm to compute the MST while avoiding the intermediate step of computing the complete set of interpoint distances. Moreover, the algorithm can be fully par- allelized with ease. The algorithm exhibits good performance for low-dimensional datasets and allows for an approximate but robust solution for higher dimensions. Finally we propose a method to select clustered subtrees from the MST, by computing simple edge statistics. The method allows naturally to retrieve clus- ters with arbitrary shapes. It also works well in noisy situations, where noise is regarded as unclustered data, allowing to separate it from clustered data. We also show that the iterative application of the algorithm allows to solve a phenomenon called masking, where highly populated clusters avoid the detection less popu- lated ones.Fil:Tepper, Mariano. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Convective heat transfer control in turbulent boundary layers

Mención Internacional en el título de doctorThe sustainable development of our society opens up concerns in several fields of engineering, including energy management, production, and the impact of our technology, being thermal management a common issue to be addressed. The investigation reported in this manuscript focuses on understanding, controlling and optimizing the physical processes involving convective heat transfer in turbulent wall-bounded flows. The content is divided into two main blocks, namely the investigation of classic open-loop active-control techniques to control heat transfer, and the technological development of machine-learning strategies to enhance the performance of flow control in the field of convective heat transfer. The first block focuses on actuator technology, applying dielectric-barrier discharge (DBD) plasma actuators and a pulsed slot jet in crossflow (JICF), respectively, to control the convective heat transfer in a turbulent boundary layer (TBL) over a flat plate. In the former, an array of DBD plasma actuators is employed to induce pairs of counter-rotating, streamwise-aligned vortices embedded in the TBL to reduce heat transfer downstream of the actuation. The whole three-dimensional mean flow field downstream of the plasma actuator is reconstructed from stereoscopic particle image velocimetry (PIV). Infrared thermography (IR) measurements coupled with a heated thin foil provide ensemble-averaged convective heat transfer distributions downstream of the actuators. The combination of the flow field and heat transfer measurements provides a complete picture of the fluid-dynamic interaction of plasma-induced flow with local turbulent transport effects. The plasmainduced streamwise vortices are stationary and confined across the spanwise direction due to the action of the plasma discharge. The opposing plasma discharge causes a mass- and momentum-flux deficit within the boundary layer, leading to a low-velocity region that grows in the streamwise direction and which is characterised by an increase in displacement and momentum thicknesses. This low-velocity ribbon travels downstream, promoting streak-alike patterns of reduction in the convective heat transfer distribution. Near the wall, the plasma-induced jets divert the main flow due to the DBD-actuator momentum injection and the suction on the surrounding fluid by the emerging jets. The stationarity of the plasma-induced vortices makes them persistent far downstream, reducing the convective heat transfer. Conversely, the target of the second paper in this first block is to enhance convective heat transfer rather than reduce it. A fully modulated, pulsed, slot JICF is used to perturb the TBL. The slot-jet actuator, flush-mounted and aligned in the spanwise direction, is controlled based on two design parameters, namely the duty cycle (DC) and the pulsation frequency (f). Heat transfer and flow-field measurements are performed to characterise the control performance using IR thermography and planar PIV, respectively. A parametric study on f and DC is carried out to assess their effect on the heat transfer distribution. The vorticity fields are reconstructed from the Proper Orthogonal Decomposition (POD) modes, retrieving phase information. The flow topology is considerably altered by the jet pulsation, even compared to the case of a steady jet. The results show that both the jet penetration in the streamwise direction and the overall Nusselt number increase with increasing DC. However, the frequency at which the Nusselt number is maximised is independent of the duty cycle. A wall-attached jet rises from the slot accompanied by a pair of counter-rotating vortices that promote flow entrainment and mixing. Eventually, a simplified model is proposed which decouples the effect of f and DC in the overall heat transfer enhancement, with a good agreement with experimental data. The cost of actuation is also quantified in terms of the amount of injected fluid during the actuation, leading to conclude that the lowest duty cycle is the most efficient for heat transfer enhancement among the tested set. The second block of the thesis splits into a comparative assessment of machine learning (ML) methods for active feedback flow control and an application of linear genetic algorithms to an experimental convective heat transfer enhancement problem. First, the comparative study is carried out numerically based on a well-established benchmark problem, the drag reduction of a two-dimensional Kármán vortex street past a circular cylinder at a low Reynolds number (Re = 100). The flow is manipulated with two blowing/suction actuators on the upper and lower side of a cylinder. The feedback employs several velocity sensors. Two probe configurations are evaluated: 5 and 11 velocity probes located at different points around the cylinder and in the wake. The control laws are optimized with Deep Reinforcement Learning (DRL) and Linear Genetic Programming Control (LGPC). Both methods successfully stabilize the vortex alley and effectively reduce drag while using small mass flow rates for the actuation. DRL features higher robustness with respect to variable initial conditions and noise contamination of the sensor data; on the other hand, LGPC can identify compact and interpretable control laws, which only use a subset of sensors, thus allowing reducing the system complexity with reasonably good results. The gained experience and knowledge of machine-learning methods motivated the last study enclosed in this thesis, which utilises linear genetic algorithm control (LGAC) to identify the best actuation parameters in an experimental application. The actuator is a set of six slot jets in crossflow aligned with the freestream. An open-loop optimal periodic forcing is defined by the carrier frequency (f), the duty cycle (DC) and the phase between actuators (ϕ) as control parameters. The control laws are optimised with respect to the unperturbed TBL and the steady-jet actuation. The cost function includes wall convective heat transfer and the cost of the actuation, thus leading to a multi-objective optimisation problem. Surprisingly, the LGAC algorithm converges to the same frequency and duty cycle for all the actuators. This frequency is equivalent to the optimal frequency reported in the second study of the first block of this thesis. The performance of the controller is characterised by IR thermography and PIV measurements. The action of the jets considerably alters the flow topology compared to the steady-jet actuation, yielding a slightly asymmetric flow field. The phase difference between multiple jet actuation has shown to be very relevant and the main driver of flow asymmetry. A POD analysis concludes the shedding phenomena characterising the steady-jet actuation, while the optimised controller exhibits an elongated large-scale structure just downstream of the actuator. The investigation carried out in this thesis sheds some light on the application of different flow control strategies to the field of convective heat transfer. From the utilisation of plasma actuators and a single jet in cross flow to the development of sophisticated control logic, the results point to the exceptional potential of machine learning control in unravelling unexplored controllers within the actuation space. Ultimately, this work demonstrates the viability of employing sophisticated measurement techniques together with advanced algorithms in an experimental investigation, paving the way towards more complex applications involving feedback information.El desarrollo sostenible de nuestra sociedad abre preocupaciones en varios campos de la ingeniería, incluyendo la gestión de la energía, la producción y el impacto de nuestra tecnología, siendo la gestión térmica un tema común a tratar. La investigación que se presenta en este manuscrito se centra en la comprensión, el control y la optimización de los procesos físicos que implican la transferencia de calor por convección en flujos turbulentos de pared. El contenido se divide en dos bloques principales: la investigación de las técnicas clásicas de control activo de lazo abierto para controlar la transferencia de calor, y el desarrollo tecnológico de estrategias de aprendizaje automático para mejorar el rendimiento del control del flujo en el campo de la transferencia de calor por convección. El primer bloque se centra en la tecnología de los actuadores, aplicando actuadores de plasma de descarga de barrera dieléctrica (dielectric barrier dicharge, DBD) y un chorro con forma de ranura pulsado en flujo cruzado (jet in crossflow, JICF), respectivamente, para controlar la transferencia de calor por convección en una capa límite turbulenta (turbulent boundary layer, TBL) sobre una placa plana. En el primero, se emplea un conjunto de actuadores de plasma DBD para inducir pares de vórtices contra-rotativos, alineados con la corriente e incrustados en la TBL para reducir la transferencia de calor aguas abajo de la actuación. El campo de flujo medio tridimensional completo aguas abajo del actuador de plasma se reconstruye a partir de la velocimetría de imagen de partículas estereoscópica (particle image velocimetry, PIV). Las mediciones de termografía infrarroja (IR) junto a una fina lámina calentada proporcionan distribuciones de transferencia de calor convectiva promediadas aguas abajo de los actuadores. La combinación de las mediciones del campo de flujo y de la transferencia de calor proporciona una imagen completa de la interacción fluido-dinámica del flujo inducido por el plasma con los efectos locales de transporte turbulento. Los vórtices en el sentido de la corriente inducidos por plasma son estacionarios y están confinados transversalmente debido a la acción de la descarga de plasma. La descarga de plasma en oposición causa un déficit de flujo de masa y de momento dentro de la capa límite, lo que conduce a una región de baja velocidad que crece en la dirección de la corriente y que se caracteriza por un aumento de los espesores de desplazamiento y de momento. Esta zona de baja velocidad se desplaza corriente abajo, promoviendo patrones de reducción similares a rayas en los que se reduce la transferencia de calor por convección. Cerca de la pared, los chorros inducidos por el plasma desvían el flujo principal debido a la inyección de momento del actuador DBD y a la succión sobre el fluido circundante por parte de los chorros emergentes. La estacionariedad de los vórtices inducidos por el plasma los hace persistentes aguas abajo, reduciendo la transferencia de calor por convección. Por el contrario, el objetivo del segundo trabajo de este primer bloque es mejorar la transferencia de calor por convección en lugar de reducirla. Se utiliza un JICF, pulsado y con forma de ranura, totalmente modulado para perturbar la TBL. El actuador de chorro, montado a ras y alineado en la dirección transversal, se controla en base a dos parámetros de diseño, a saber, el ciclo de trabajo (DC) y la frecuencia de pulsación (f). Se realizan mediciones de la transferencia de calor y del campo de flujo para caracterizar el rendimiento del control mediante termografía IR y PIV planar, respectivamente. Se lleva a cabo un estudio paramétrico de f y DC para evaluar su efecto en la distribución de la transferencia de calor. Los campos de vorticidad se reconstruyen a partir de los modos de descomposición ortogonal adecuada (POD), recuperando la información de fase. La topología del flujo se ve considerablemente alterada por la pulsación del chorro, incluso en comparación con el caso de un chorro estacionario. Los resultados muestran que tanto la penetración del chorro en la dirección de la corriente como el número Nusselt global aumentan con el incremento de DC. Sin embargo, la frecuencia a la que se maximiza el número Nusselt es independiente del ciclo de trabajo. Un chorro adherido a la pared sale de la ranura acompañado de un par de vórtices contrarrotantes que promueven el arrastre y la mezcla del flujo. Finalmente, se propone un modelo simplificado que desacopla el efecto de f y DC en la mejora global de la transferencia de calor, con un buen acuerdo con los datos experimentales. También se cuantifica el coste de la actuación en términos de la cantidad de fluido inyectado durante la actuación, llegando a la conclusión de que el ciclo de trabajo más bajo es el más eficiente para la mejora de la transferencia de calor entre el conjunto probado. El segundo bloque de la tesis se divide en una evaluación comparativa de los métodos de aprendizaje automático (machine learning, ML) para el control activo del flujo por retroalimentación y una aplicación de algoritmos genéticos lineales a un problema experimental de mejora de la transferencia de calor por convección. En primer lugar, el estudio comparativo se realiza numéricamente a partir de un problema de referencia bien establecido: la reducción de la resistencia aerodinámica de una calle de vórtices de Kármán bidimensional tras un cilindro circular a un número de Reynolds bajo (Re = 100). El flujo se manipula con dos actuadores de soplado/succión en la parte superior e inferior de un cilindro. La retroalimentación emplea varios sensores de velocidad. Se evalúan dos configuraciones de sondas: 5 y 11 sondas de velocidad situadas en diferentes puntos alrededor del cilindro y en la estela. Las leyes de control se optimizan con el aprendizaje profundo por refuerzo (Deep Reinforcement Learning, DRL) y el control por programación genética lineal (Linear Genetic Programming Control, LGPC). Ambos métodos estabilizan con éxito la calle de vórtices y reducen de manera efectiva la resistencia al tiempo que usan caudales másicos pequeños para la actuación. El DRL se caracteriza por una mayor robustez con respecto a la variación de la condición inicial y a la contaminación por ruido de los datos de los sensores; por otro lado, el LGPC puede identificar leyes de control compactas e interpretables, que sólo utilizan un subconjunto de sensores, lo que permite reducir la complejidad del sistema con resultados razonablemente buenos. La experiencia adquirida y el conocimiento de los métodos de aprendizaje automático motivaron el último estudio incluido en esta tesis, que utiliza el control por algoritmo genético lineal (Linear Genetic Algorithm Control, LGAC) para identificar los mejores parámetros de actuación en una aplicación experimental. El actuador es un conjunto de seis chorros con forma de ranura en flujo cruzado y alineados con la corriente principal. Se define una ley de forzado periódica en lazo abierto mediante la frecuencia portadora (f), el ciclo de trabajo (DC) y la fase entre actuadores (ϕ) como parámetros de control. Las leyes de control se optimizan con respecto a la TBL no perturbada y la actuación de chorro constante. La función de coste incluye la transferencia de calor por convección de la pared y el coste de la actuación, lo que da lugar a un problema de optimización multiobjetivo. Sorprendentemente, el algoritmo LGAC converge a la misma frecuencia y ciclo de trabajo para todos los actuadores. Esta frecuencia es equivalente a la frecuencia óptima reportada en el segundo estudio del primer bloque de esta tesis. El rendimiento del controlador se caracteriza mediante termografía IR y mediciones PIV. La acción de los chorros altera considerablemente la topología del flujo en comparación con la actuación de los chorros constantes, dando lugar a un campo de flujo ligeramente asimétrico. La diferencia de fase entre la actuación de múltiples chorros ha demostrado ser muy relevante y el principal impulsor de la asimetría del flujo. Un análisis POD concluye los fenómenos de desprendimiento de vórtices que caracterizan la actuación de chorro constante, mientras que el controlador optimizado muestra una estructura alargada a gran escala justo aguas abajo del actuador. La investigación llevada a cabo en esta tesis arroja algo de luz sobre la aplicación de diferentes estrategias de control de flujo en el campo de la transferencia de calor por convección. Desde la utilización de actuadores de plasma y un único chorro en flujo cruzado hasta el desarrollo de una sofisticada lógica de control, los resultados apuntan al excepcional potencial del control por aprendizaje automático para desentrañar controladores inexplorados dentro del espacio de actuación. En última instancia, este trabajo demuestra la viabilidad de emplear sofisticadas técnicas de medición junto con algoritmos avanzados en una investigación experimental, allanando el camino hacia aplicaciones más complejas que implican información de retroalimentación.The work enclosed in this thesis has been partially supported by the Universidad Carlos III de Madrid through a PIPF scholarship awarded on a competitive basis, and by the following research projects: ARTURO (Active contRol of Turbulence for sUstainable aiRcraft propulsiOn), ref. PID2019-109717RB-I00/AEI/10.13039/501100011033, funded by the Spanish State Research Agency (SRA); the 2020 Leonardo Grant for Researchers and Cultural Creators AEROMATIC (Active flow control of aerodynamic flows with machine learning), funded by the BBVA Foundation with grant number IN[20]_ING_ING_0163; and GloWing Starting Grant, funded by the European Research Council (ERC), under grant agreement ERC-2018.StG-803082.Programa de Doctorado en Mecánica de Fluidos por la Universidad Carlos III de Madrid; la Universidad de Jaén; la Universidad de Zaragoza; la Universidad Nacional de Educación a Distancia; la Universidad Politécnica de Madrid y la Universidad Rovira i VirgiliPresidente: Octavio Armas Vergel.- Secretario: Manuel García-Villalba Navaridas.- Vocal: Gioacchino Cafier

Automated OMA and Damage Detection: an Opportunity for Smart SHM Systems

Il monitoraggio strutturale si propone di sviluppare sistemi che siano in grado di monitorare un’opera permettendone l’ispezione ed il rilevamento dei danni con il minimo intervento antropico. Esso rappresenta dunque un processo di implementazione di una strategia di identificazione dei danni attraverso la quale, osservando una struttura con una determinata periodicità, è possibile pervenire alla valutazione di alcune caratteristiche del sistema, in modo tale da definirne il suo stato attuale di salute. La sua prima applicazione ha interessato campi differenti da quello dell’ingegneria civile. Infatti, era una tecnica impiegata prevalentemente in ambito meccanico, aeronautico e nell’ingegneria aerospaziale. Successivamente è risultato evidente come fosse una strategia che, se correttamente adattata, poteva essere di grande aiuto per il controllo di tutte le strutture civili presenti sul territorio. Può essere sviluppata come un sistema autonomo integrato su grandi infrastrutture (come ponti, dighe, ecc.) con l’obiettivo di monitorare la risposta della struttura sotto delle sollecitazioni durante la costruzione per modificare i progetti se necessario. Sempre su questo tipo di strutture, può mantenere costante il controllo durante il suo arco di vita per attuare tempestivamente interventi prima che possano crearsi situazioni irreversibili e pericolose. Inoltre, il monitoraggio strutturale può essere impiegato, come verrà mostrato in questa tesi, per il monitoraggio della salute strutturale di edifici storici, appartenenti al patrimonio culturale. Questo patrimonio è diffuso in Europa ed in particolare in Italia. Si parla di edifici anche di notevole entità (come grandi chiese), costruite in epoche molto lontane, la cui conservazione è oggi il focus di molti ricercatori. Il caso studio oggetto del presente lavoro è la torre campanaria di una chiesa nelle Marche, in Italia, le cui tracce storiche risalgono a circa il 1330, con numerosi interventi e rimaneggiamenti successivi fino ad arrivare ai giorni nostri. Con la tecnica del monitoraggio strutturale è possibile valutare il comportamento dinamico della struttura (monitorata) attraverso l’identificazione dei suoi principali parametri modali a partire dall’analisi dei dati acquisiti. Con l’espressione “identificazione dinamica” di una struttura si intendono tutte quelle tecniche, sia analitiche che sperimentali, attraverso le quali è possibile appunto individuare la risposta dinamica della struttura stessa andando ad estrapolare frequenze naturali, corrispondenti forme modali e coefficienti di smorzamento. Soffermandoci su questo concetto, il lavoro è stato inizialmente impostato implementando un processo automatico per l’elaborazione dei dati in uscita dal monitoraggio e quindi per la definizione dei parametri modali della struttura sotto esame depurandoli dagli effetti delle azioni ambientali quali temperatura, velocità media del vento ed umidità. Rimuovere questi fattori esterni dai risultati, permette di ottenere una previsione dell’evoluzione delle caratteristiche modali. Dal loro confronto con il comportamento reale della struttura si possono evidenziare eventuali anomalie. In riferimento a quanto appena detto, risulta oggigiorno di importanza fondamentale riuscire a riconoscere e prevedere il progressivo deterioramento di una struttura. Questo può avvenire per naturale degrado dei materiali, o dopo aver subito vibrazioni impreviste (terremoti, esplosioni, ecc). Focalizzandosi su questo concetto, l’identificazione del danno basata sulla valutazione delle variazioni dei parametri modali, depurati dell’influenza di agenti esterni, può essere un processo lungo. Al contrario, poter conoscere quasi istantaneamente il "nuovo" comportamento della costruzione, è un aspetto da tenere bene in considerazione sia per salvaguardare la vita delle persone, sia per attuare in maniera precisa e puntuale interventi di miglioramento. Essere tempestivi in caso di situazioni critiche, permette di evitare di arrivare a condizioni tali per cui è necessario interrompere l’operatività della struttura per molto tempo pur di poterla recuperare, se possibile. Nel presente lavoro si sono utilizzati metodi basati sull’elaborazione diretta dei dati acquisiti dal sistema di monitoraggio in continuo. In questo modo l’onere computazionale è stato notevolmente ridotto. Non è stato necessario elaborare i dati acquisiti per estrarre le caratteristiche modali del sistema e si è ottenuto un feedback quasi istantaneo di variazioni nel comportamento dinamico. Tali aspetti, risultano significativi quando l’obiettivo è di sviluppare un "monitoraggio sostenibile" sia da un punto di vista economico che di tempistiche.Structural monitoring aims to develop systems that can monitor a structure by allowing its inspection and detection of damage with minimal human intervention. It therefore represents a process of implementing a damage identification strategy through which, by observing a structure with a certain periodicity, it is possible to arrive at an evaluation of specific characteristics of the system, to define its current state of health. Its first application was in fields other than civil engineering. It later became evident that it was a strategy that could be of great help in the control of all civil structures in the area. It can be developed as an autonomous integrated system on big infrastructures with the aim of monitoring the response of the structure under stress during construction to modify designs if necessary. Also, on these types of structures, it can maintain constant control during its life cycle to implement timely interventions. In addition, structural monitoring can be used to monitor the structural health of historical buildings belonging to cultural heritage. We are talking about buildings even of considerable size, built in very distant epochs, the conservation of which is now the focus of many researchers. The case study that is the subject of the present work is the bell tower of a church in the Marche region, Italy, whose historical traces date back to around 1330, with numerous subsequent interventions and remodelling up to the present day. With the technique of structural monitoring, it is possible to assess the dynamic behaviour of the structure through the identification of its main modal. The term 'dynamic identification' of a structure means all those techniques, both analytical and experimental, through which it is possible to identify the dynamic response of the structure itself by extrapolating natural frequencies, corresponding modal shapes and damping coefficients. The work was initially set up by implementing an automatic procedure for processing the output data from the monitoring and thus defining the modal parameters of the structure under examination purifying them from the effects of environmental actions. By removing these external factors from the results, a prediction of the evolution of the modal characteristics can be obtained. Comparing them with the actual behaviour of the structure, any anomalies can be highlighted. Regarding the above, it is nowadays of fundamental importance, to be able to recognise and predict the progressive failure of a structure. This may occur due to natural degradation of materials, or because of unexpected vibrations. Focusing on this concept, the identification of damage based on the evaluation of changes in modal parameters, purified of the influence of external agents, can be a time-consuming process. On the contrary, being able to know almost instantaneously the "new" behaviour of the construction, is an aspect that must be taken into well consideration both for safeguarding people's lives and for the accurate and timely implementation of improvements. In the present work, methods based on the direct processing of data acquired from the continuous monitoring system were used. In this way, the computational burden was reduced. It was not necessary to elaborate the acquired data to extract the modal characteristics of the system, and almost instantaneous feedback of changes in dynamic behaviour was obtained. These aspects are significant when the purpose is to develop "sustainable monitoring" from both an economic and timing perspective

Lasing action in dye-doped thin films coupled with 2D plasmonic nanoarrays

In the last few years, due to the great advances in nanotechnology the peculiar properties of the matter at the nanometric scale have been widely investigated. These properties can be exploited for many innovative applications involving several fields, and, in particular, in nanophotonics, where plasmonic nanolasers gather growing interest. These devices are coherent light sources that can support ultrafast dynamics and ultrasmall mode volume below the diffraction limit. Nowadays, the photonic band-edge lasers that are widely used for many applications have various drawbacks, such as low modulation speeds and diffraction-limited mode confinement. Plasmonic nanolasers can potentially overcome these limits and replace the actual light source technology in many fields from integrated photonic circuits and optical communications to high-performance biosensors. The purpose of the present Master thesis is the synthesis and characterisation of a novel plasmonic-based nanolaser device operating in the near infrared-region. In particular, the attention has been focused on plasmonic nanostructures composed of an array of 2D nanoparticles that act as field enhancer for the lasing of the gain medium. The fabrication of the plasmonic nanoarray was substantially different from the usual approach based on electron beam lithography (EBL). On the contrary, the NanoSphere Lithography (NSL) technique adopted in the present thesis is a highthroughput and cost-effective way to manufacture nanoparticle arrays with a highquality order, obtaining defectless domains of several hundreds of square micrometers. The nanostructure adopted in a this work is two-dimensional hexagonal lattice of nanodomes which is fabricated by gold deposition (carried out by magnetron sputtering) over an ordered array of polystyrene (PS) nanospheres (NSs) obtained using NSL. A gain medium layer was then deposited over the metallic array, and it consists of an organic dye, specifically Styryl 9M (LDS 821), embedded in a polymeric matrix. In order to maximise the efficiency and the throughput of the nanolaser, a match between the uorescence emission of the selected dye and the plasmonic resonance of the nanostructure is needed. To this aim, the domes geometry has been optimised by varying metal thickness and the PS nanosphere radius (while keeping the array lattice parameter) by reactive ion etching (RIE). The deposition process for the gain medium has been achieved by embedding the dye molecules in a PMMA matrix, which is then deposited upon the nanodome array to form a solid film of a hundred of micrometers. The nanostructures have been characterised morphologically by atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques and optically by re ection measurements. The absorption and uorescence spectra that characterise the dye were measured by a UV-VIS-NIR spectrophotometry. As a result, samples supporting lasing action were fabricated and characterised: the emission features of the obtained device were investigated by photoluminescence (PL) measurements to determine the main properties of the laser, including the lasing wavelength, linewidth, threshold, beam divergence and emission angle, showing how, when a coupling between the plasmonic resonance of the nanodome array and the dye emission wavelength is obtained, interesting lasing properties arise and the lasing threshold can be decreased by at least one order of magnitude

Applications of Blind Source Separation to the Magnetoencephalogram Background Activity in Alzheimer’s Disease

En esta Tesis Doctoral se ha analizado actividad basal de magnetoencefalograma (MEG) de 36 pacientes con la Enfermedad de Alzheimer (Alzheimer’s Disease, AD) y 26 sujetos de control de edad avanzada con técnicas de separación ciega de fuentes (Blind Source Separation, BSS). El objetivo era aplicar los métodos de BSS para ayudar en el análisis e interpretación de este tipo de actividad cerebral, prestando especial atención a la AD. El término BSS denota un conjunto de técnicas útiles para descomponer registros multicanal en las componentes que los dieron lugar. Cuatro diferentes aplicaciones han sido desarrolladas. Los resultados de esta Tesis Doctoral sugieren la utilidad de la BSS para ayudar en el procesado de la actividad basal de MEG y para identificar y caracterizar la AD.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería Telemátic