New Directions for Contact Integrators

Contact integrators are a family of geometric numerical schemes which guarantee the conservation of the contact structure. In this work we review the construction of both the variational and Hamiltonian versions of these methods. We illustrate some of the advantages of geometric integration in the dissipative setting by focusing on models inspired by recent studies in celestial mechanics and cosmology.Comment: To appear as Chapter 24 in GSI 2021, Springer LNCS 1282

Blind dereverberation of speech from moving and stationary speakers using sequential Monte Carlo methods

Speech signals radiated in confined spaces are subject to reverberation due to reflections of surrounding walls and obstacles. Reverberation leads to severe degradation of speech intelligibility and can be prohibitive for applications where speech is digitally recorded, such as audio conferencing or hearing aids. Dereverberation of speech is therefore an important field in speech enhancement. Driven by consumer demand, blind speech dereverberation has become a popular field in the research community and has led to many interesting approaches in the literature. However, most existing methods are dictated by their underlying models and hence suffer from assumptions that constrain the approaches to specific subproblems of blind speech dereverberation. For example, many approaches limit the dereverberation to voiced speech sounds, leading to poor results for unvoiced speech. Few approaches tackle single-sensor blind speech dereverberation, and only a very limited subset allows for dereverberation of speech from moving speakers. Therefore, the aim of this dissertation is the development of a flexible and extendible framework for blind speech dereverberation accommodating different speech sound types, single- or multiple sensor as well as stationary and moving speakers. Bayesian methods benefit from – rather than being dictated by – appropriate model choices. Therefore, the problem of blind speech dereverberation is considered from a Bayesian perspective in this thesis. A generic sequential Monte Carlo approach accommodating a multitude of models for the speech production mechanism and room transfer function is consequently derived. In this approach both the anechoic source signal and reverberant channel are estimated using their optimal estimators by means of Rao-Blackwellisation of the state-space of unknown variables. The remaining model parameters are estimated using sequential importance resampling. The proposed approach is implemented for two different speech production models for stationary speakers, demonstrating substantial reduction in reverberation for both unvoiced and voiced speech sounds. Furthermore, the channel model is extended to facilitate blind dereverberation of speech from moving speakers. Due to the structure of measurement model, single- as well as multi-microphone processing is facilitated, accommodating physically constrained scenarios where only a single sensor can be used as well as allowing for the exploitation of spatial diversity in scenarios where the physical size of microphone arrays is of no concern. This dissertation is concluded with a survey of possible directions for future research, including the use of switching Markov source models, joint target tracking and enhancement, as well as an extension to subband processing for improved computational efficiency

The negatively charged tin vacancy centre in diamond : a good quantum bit?

The rapidly developing field of quantum information processing demands for qubit and quantum network node systems exhibiting outstanding characteristics such as exceptional spin and optical coherence. This thesis investigates the recently emerged negatively charged tin vacancy (SnV) centre in diamond as a promising candidate addressing those needs. On that account we conduct a detailed spectroscopic study revealing its single photon and zero-phonon line emission properties, the centre-phonon interactions impacting the phonon sideband and Debye-Waller factor as well as the energetic position of a higher lying excited state. Furthermore, we unveil the charge cycle of the SnV centre based upon which we realise highly efficient and rapid initialisation of the desired negative charge state. This charge control enables studying the optical and spin coherence of single centres, which we show to outperform other group IV vacancy emitters in diamond at temperatures of 1.7K. The close to ideal optical coherence is preserved for hours, while the spin life- and dephasing times amount to T1~20ms and T2* ~5µs, respectively, even for large angles between magnetic field and the centre's symmetry axis. Furthermore, we demonstrate single-shot readout of spin states enabled by highly cycling spin-conserving transitions with a fidelity of F=74%. Eventually, we explore the possibility of two-photon interference as a crucial prerequisite of remote entanglement and many quantum communication protocols.Das sich rapide entwickelnde Themengebiet der Quanteninformationsverarbeitung bedarf Qubit- und Quantennetzwerkknotensystemen, welche herausragende Eigenschaften wie bspw. exzeptionelle optische sowie Spinkohärenz aufweisen. Diese Arbeit untersucht das kürzlich entdeckte Zinn-Fehlstellen (SnV) Zentrum in Diamant als einen vielversprechenden Kandidaten. Dazu führen wir detaillierte spektroskopische Untersuchungen der Eigenschaften seiner Einzelphotonen- und Null-Phononen-Linienemission, des Einflusses der Zentrum-Phonon Wechselwirkungen auf phononisches Seitenband und Debye-Waller Faktor sowie der energetischen Lage eines höher liegenden angeregten Zustandes durch. Basierend auf unserem experimentell verifizierten Modell des Ladungszyklusses des SnV Zentrums initialisieren wir den negativen Ladungszustand schnell und hocheffizient. Diese Ladungskontrolle erlaubt die Untersuchung der optischen und Spinkohärenz bei einer Temperatur von 1.7K, welche anderen Gruppe IV Zentren überlegen sind. Die nahezu perfekte optische Kohärenz ist über Stunden erhalten, während die Spinlebens- bzw. Dephasierungsdauer selbst für große Winkle zwischen Magnetfeld und Symmetrieachse des Zentrums T1~20ms bzw. T2*~5µs beträgt. Weiterhin demonstrieren wir Spinzustandsauslese mit nur einem optischen Puls und Fidelity von F=74%. Abschließend untersuchen wir die Möglichkeit der Zwei-Photonen Interferenz, welche Grundlage für die Verschränkung entfernter Zentren sowie vielen Quantenkommunikationsprotokollen ist

Untangling hotel industry’s inefficiency: An SFA approach applied to a renowned Portuguese hotel chain

The present paper explores the technical efficiency of four hotels from Teixeira Duarte Group - a renowned Portuguese hotel chain. An efficiency ranking is established from these four hotel units located in Portugal using Stochastic Frontier Analysis. This methodology allows to discriminate between measurement error and systematic inefficiencies in the estimation process enabling to investigate the main inefficiency causes. Several suggestions concerning efficiency improvement are undertaken for each hotel studied.info:eu-repo/semantics/publishedVersio

Controlling Cavity Magnon Polariton Properties in Frequency and Time Domain

The cavity-magnon-polariton (CMP) is the quasi-particle of a hybrid system that connects photonic excitations to magnonic ones. With this connection, the CMP is an ideal candidate to build a bridge between the promising fields of quantum computing and magnonics. However, for the CMP to fulfill its role as an effective interface, a robust control of its underlying physical properties is imperative. Here, we show how the coupling strength can be manipulated within the experiment by a second continuous drive tone applied directly to the magnon system. Furthermore, switching into the time-domain, we demonstrate a coherent control over the different CMP modes based on ns-short pulses to both oscillating systems. At last, frequency fluctuations are investigated with the future goal of improving magnon coherence times

5 European & African Conference on Wind Engineering

The 5th European-African Conference of Wind Engineering is hosted in Florence, Tuscany, the city and the region where, in the early 15th century, pioneers moved the first steps, laying down the foundation stones of Mechanics and Applied Sciences (including fluid mechanics). These origins are well reflected by the astonishing visionary and revolutionary studies of Leonardo Da Vinci, whose kaleidoscopic genius intended the human being to become able to fly even 500 years ago… This is why the Organising Committee has decided to pay tribute to such a Genius by choosing Leonardo's "flying sphere" as the brand of 5th EACWE

Técnicas de filtrado adaptativo aplicadas al rechazo selectivo de perturbaciones en inversores fotovoltaicos trifásicos

La conexión de paneles solares fotovoltaicos a la red eléctrica puede llevarse a cabo mediante el empleo de inversores de potencia tipo VSI (Voltage Source Inverter). Los inversores pueden ser controlados en un marco de referencia estacionario (StRF, Stationary Reference Frame) mediante reguladores resonantes (PR) sintonizados tanto a la frecuencia de la red como a determinados armónicos habituales de la misma, de manera que permitan obtener un factor de potencia próximo a la unidad con una tasa de distorsión armónica (THD) en corriente dentro de los límites establecidos en las normativas de conexión a red. Para ello, es habitual estimar la fase de la red eléctrica mediante el empleo de un PLL en un marco de referencia síncrono (SRF-PLL, Synchronous Reference Frame-Phase Locked Loop). En la presente tesis se ha realizado un estudio sobre el efecto que las perturbaciones en la red eléctrica trifásica tienen sobre el SRF-PLL y los reguladores PR, y su repercusión en el deterioro del factor de potencia y en el THD en corriente del inversor, demostrando que dicho deterioro no permite, en determinados supuestos, cumplir las normativas anteriormente citadas, sobre todo si existe variación en la frecuencia de la red eléctrica de acuerdo a la tolerancia definida en distintas normativas, o bien cuando el inversor se encuentra conectado a redes de generación distribuida en situación de isla. Teniendo en cuenta que las perturbaciones más habituales son desequilibrio y distorsión armónica, para mejorar el rechazo de las mismas pueden emplearse diversas técnicas de filtrado convencional para el diseño de los reguladores PR y del SRF-PLL. No obstante, dichas técnicas se muestran poco eficientes cuando existe variación en la frecuencia de la red eléctrica. En la presente tesis se ha propuesto el empleo de técnicas de filtrado adaptativo, capaces de adaptar sus coeficientes de manera automática en función de la variación de la frecuencia de la red eléctrica.González Espín, FJ. (2010). Técnicas de filtrado adaptativo aplicadas al rechazo selectivo de perturbaciones en inversores fotovoltaicos trifásicos [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/10082Palanci

Discrete Event Simulations

Considered by many authors as a technique for modelling stochastic, dynamic and discretely evolving systems, this technique has gained widespread acceptance among the practitioners who want to represent and improve complex systems. Since DES is a technique applied in incredibly different areas, this book reflects many different points of view about DES, thus, all authors describe how it is understood and applied within their context of work, providing an extensive understanding of what DES is. It can be said that the name of the book itself reflects the plurality that these points of view represent. The book embraces a number of topics covering theory, methods and applications to a wide range of sectors and problem areas that have been categorised into five groups. As well as the previously explained variety of points of view concerning DES, there is one additional thing to remark about this book: its richness when talking about actual data or actual data based analysis. When most academic areas are lacking application cases, roughly the half part of the chapters included in this book deal with actual problems or at least are based on actual data. Thus, the editor firmly believes that this book will be interesting for both beginners and practitioners in the area of DES