Remote measurement of electric field generated by lightning has played a major role in understanding the lightning phenomenon. Even though other measurements such as photographic and channel base current have contributed to this research field, due to practical reasons remote measurements of electric field is considered as the most useful tool in lightning research. This thesis discusses the remotely measured radiation field component of electric field generated by cloud flashes (ICs) and narrow bipolar pulses (NBPs). The associated HF radiation of these events at 3 MHz and 30 MHz are also discussed. To understand the initiation process of these discharges, a comparative study of the initial pulse of cloud flashes against the initial pulse of cloud to ground flashes was conducted. The result suggests that both discharges might have been initiated by similar physical processes inside the thunderclouds. Comparing the features of initial pulse of cloud and ground flashes with that of pulses that appeared in the later stages of cloud flashes suggests that the initiation process involved in both flashes are not very much different from the initiation of cloud flashes at the later stage. The average spectral amplitudes of electric field of full duration cloud flashes (180 ms) showed f  -1 frequency dependence within the interval of 10 kHz to approximately 10 MHz. This is in contrast to the standard f  -2 decrement (or even steeper ) at high frequency region for other lightning processes such as return strokes. It was suggested that small pulses which repeatedly appeared at the later stage of cloud flashes might have contributed to enhance the spectral amplitude at higher frequencies. Electric fields generated by Narrow Bipolar Pulses (NBPs), which are considered as one of the strongest sources of HF radiation, were measured in the tropics of Malaysia and Sri Lanka.  Their features were also studied and show a good agreement with previously published observations of NBPs from other geographical regions. Thorough analyses and observations of these pulses found previously unreported sharp, fine peaks embedded in the rising and decaying edge of the electric field change of NBPs. Therefore it was suggested that these fine peaks are mostly responsible for the intense HF radiation at 30 MHz.

This thesis addresses sound production in bowed-string instruments from two perspectives: the physics of the bowed string, and bow control in performance. Violin performance is characterized by an intimate connection between the player and the instrument, allowing for a continuous control of the sound via the main bowing parameters (bow velocity, bow force and bow-bridge distance), but imposing constraints as well. In the four included studies the focus is gradually shifted from the physics of bow-string interaction to the control exerted by the player. In the first two studies the available bowing parameter space was explored using a bowing machine, by systematically probing combinations of bow velocity, bow force and bow-bridge distance. This allowed for an empirical evaluation of the maximum and minimum bow force required for the production of a regular string tone, characterized by Helmholtz motion. Comparison of the found bow-force limits with theoretical predictions by Schelleng revealed a number of striking discrepancies, in particular regarding minimum bow force. The observations, in combination with bowed-string simulations, provided new insights in the mechanism of breakdown of Helmholtz motion at low bow forces. In the second study the influence of the main bowing parameters on aspects of sound quality was analyzed in detail. It was found that bow force was totally dominating the control of the spectral centroid, which is related to the perceived brightness of the tone. Pitch flattening could be clearly observed when approaching the upper bow-force limit, confirming its role as a practical limit in performance. The last two studies were focused on the measurement of bowing gestures in violin and viola performance. A method was developed for accurate and complete measurement of the main bowing parameters, as well as the bow angles skewness, inclination and tilt. The setup was used in a large performance study. The analyses revealed clear strategies in the use of the main bowing parameters, which could be related to the constraints imposed by the upper and lower bow-force limits and pitch flattening. Further, it was shown that two bow angles (skewness and tilt) were systematically used for controlling dynamic level; skewness played an important role in changing bow-bridge distance in crescendo and diminuendo notes, and tilt was used to control the gradation of bow force. Visualizations and animations of the collected bowing gestures revealed significant features of sophisticated bow control in complex bowing patterns. / QC 20100809

<p>Vid analys av fluider med akustisk spektroskopi finns ett behov av att finna multivariata metoder för att utifrån akustiska spektra prediktera storheter såsom viskositet och densitet. Användning av artificiella neurala nätverk och bayesiska nätverk för detta syfte utreds genom teoretiska och praktiska undersökningar. Förbehandling och uppdelning av data samt en handfull linjära och olinjära multivariata analysmetoder beskrivs och implementeras. Prediktionsfelen för de olika metoderna jämförs och PLS (Partial Least Squares) framstår som den starkaste kandidaten för att prediktera de sökta storheterna.</p> / <p>When analyzing fluids using acoustic spectrometry there is a need of finding multivariate methods for predicting properties such as viscosity and density from acoustic spectra. The utilization of artificial neural networks and Bayesian networks for this purpose is analyzed through theoretical and practical investigations. Preprocessing and division of data along with a handful of linear and non-linear multivariate methods of analysis are described and implemented. The errors of prediction for the different methods are compared and PLS (Partial Least Squares) appear to be the strongest candidate for predicting the sought-after properties.</p>

Vid analys av fluider med akustisk spektroskopi finns ett behov av att finna multivariata metoder för att utifrån akustiska spektra prediktera storheter såsom viskositet och densitet. Användning av artificiella neurala nätverk och bayesiska nätverk för detta syfte utreds genom teoretiska och praktiska undersökningar. Förbehandling och uppdelning av data samt en handfull linjära och olinjära multivariata analysmetoder beskrivs och implementeras. Prediktionsfelen för de olika metoderna jämförs och PLS (Partial Least Squares) framstår som den starkaste kandidaten för att prediktera de sökta storheterna. / When analyzing fluids using acoustic spectrometry there is a need of finding multivariate methods for predicting properties such as viscosity and density from acoustic spectra. The utilization of artificial neural networks and Bayesian networks for this purpose is analyzed through theoretical and practical investigations. Preprocessing and division of data along with a handful of linear and non-linear multivariate methods of analysis are described and implemented. The errors of prediction for the different methods are compared and PLS (Partial Least Squares) appear to be the strongest candidate for predicting the sought-after properties.

<p>In this thesis, two applications of dimensional deconstruction are studied. The first application is a model for neutrino oscillations in the presence of a large decon- structed extra dimension. In the second application, Kaluza{Klein dark matter from a latticized universal extra dimension is studied. The goal of these projects have been twofold. First, to see whether it is possible to reproduce the relevant features of the higher-dimensional continuum theory, and second, to examine the effect of the latticization in experiments. In addition, an introduction to the the- ory of dimensional deconstruction as well as to the theory of continuous extra dimensions is given. Furthermore, the various higher-dimensional models, such as Arkani-Hamed{Dvali{Dimopolous (ADD) models and models with universal extra dimensions, that have been intensively studied in recent years, are discussed.</p>

This thesis treats the control of sound synthesis of bowed string instruments based on physical modelling. The work followed two approaches: (a) a systematic exploration of the influence of control parameters (bow force, bow velocity, and bow-bridge distance) on the output of a physical model of the violin, and (b) measurements and analyses of the bowing parameters in real violin playing in order to model and parameterize basic classes of bowing patterns for synthesis control.First a bowed-string model based on modal solutions of the string equation is described and implemented for synthesis of violin sounds. The behaviour of the model is examined through simulations focusing on playability, i.e. the control parameter space in which a periodic Helmholtz motion is obtained, and the variations of the properties of the simulated sound (sound level and spectral centroid) within this parameter space. The response of the model corresponded well with theoretical predictions and empirical expectations based on observations of real performances. The exploration of the model allowed to define optimal parameter regions for the synthesis, and to map sound properties on the control parameters.A second part covers the development of a sensor for measuring the bow force in real violin performance. The force sensor was later combined with an optical motion capture system for measurement of complete sets of bowing parameters in violin performance.In a last part, measurements of the control parameters for basic classes of bowing patterns (sautillé, spiccato, martelé, tremolo) are analyzed in order to propose a realistic control of the sound synthesis. The time evolution of the bowing parameters were modelled by analytical functions, which allowed to describe and control simulated bowing patterns by a limited set of control parameters. For sustained bowing patterns such as détaché, control strategies for basic elements in playing (variations in dynamic level, bow changes) were extracted from exemplary measurements, and simple rules deduced, which allowed extrapolation of parameters to modified bow strokes with other durations and at different dynamic levels. / Denna avhandling behandlar styrning av syntes av stråkinstrument med tillämpningar inom fysikalisk modellering av musikinstrument. Problemet har angripits i två steg, först genom en systematisk undersökning av inflytandet av styrparametrarna i violinspel (stråkkraft, stråkhastighet, och avstånd stråke-stall) på utsignalen från en fysikalisk modell, följt av mätningar och analyser av stråkningsparametrarna i normalt violinspel med syfte att modellera och parameterisera grundläggande klasser av stråkarter för styrning av syntesen. En modell av interaktionen mellan stråke-sträng har utvecklats baserad på modal syntes och modellen har implementerats för syntes av violintoner. Modellen har utforskats genom simuleringar inriktade dels på spelbarheten, dvs. gränserna för den parameterrymd inom vilken en periodisk Helmholtz-rörelse erhålls, och dels på variationerna hos det syntetiserade ljudets egenskaper (ljudnivå och spektral centroid) inom detta parameterområde. Modellens egenskaper motsvarade väl de teoretiska prediktionerna och förväntade resultat från observationer av violinster. Utforskningen av modellen gjorde det möjligt att definiera optimala parameterområden för styrning av syntesen, och även avbilda ljudens egenskaper på styrparametrarna. En sensor för mätning av stråkkraften utvecklades för att kunna genomföra mätningar under normalt spel. Sensorn kombinerades senare med ett optiskt system för rörelseanalys vilket gjorde det möjligt att mäta kompletta uppsättningar av stråkparametrar under spel. Uppmätta styrparametrar för grundläggande klasser av stråkarter (sautillé, spiccato, martelé, tremolo) analyserades för att ge tillgång till realistiska styrförlopp av syntesen. Stråkningsparametrarna modellerades med analytiska funktioner, för att kunna beskriva och styra simulerade stråkningsförlopp med ett begränsat antal modellparametrar. För stråkarter med uthållna toner som détaché utvecklades styrstrategier för grundläggande element i spelet, som ändringar i styrkegrad och stråkväxlingar, utifrån mätningar på typfall. Enkla regler formulerades för att kunna extrapolera parametrarna till modifierade stråk med andra durationer och styrkegrader. / Cette thèse porte sur le contrôle de la synthèse sonore par modélisation physique des instruments à corde frottée. Il se base, d’une part, sur l’exploration systématique de l’influence des paramètres de contrôle (pression d’archet, vitesse de l’archet et distance au chevalet) sur le comportement du modèle, et d’autre part, sur la mesure et l’analyse du contrôle effectif qu’exerce l’instrumentiste afin de modéliser et paramétriser des modes de jeu typiques pour le contrôle de la synthèse. Un modèle de corde frottée basé sur la résolution modale de l’équation de la corde est d’abord présenté et implémenté pour la synthèse sonore du violon. Le comportement du modèle physique est ensuite examiné en effectuant un grand nombre de simulations et se concentre sur deux aspects : la “jouabilité", c’est-à-dire l’espace des paramètres de contrôle dans lequel un mouvement de Helmholtz périodique est obtenu, et les variations des propriétés du son synthétisé (niveau sonore et centroïde spectral) à l’intérieur de cet espace de paramètres. Un très bon accord a été trouvé entre, d’une part, le résultat des simulations et, d’autre part, les prédictions théoriques ou empiriques basées sur l’expérience des instrumentistes. Cette exploration systématique a permis de définir des régions optimales pour le jeu dans l’espace des paramètres de contrôle et de décrire quantitativement la correspondance entre les propriétés sonores pertinentes et les paramètres de contrôle. La deuxième partie de ce travail concerne la mise au point d’un capteur pour mesurer la force d’appui de l’archet sur la corde dans un contexte de jeu réel. Le capteur est ensuite combiné avec un système optique de capture du mouvement afin de mesurer les paramètres de jeu du violoniste. La dernière partie présente l’analyse des mesures de ces paramètres de contrôle pour des modes de jeu typiques (sautillé, spiccato, martelé, tremolo), afin de proposer un contrôle réaliste de la synthèse sonore. L’évolution temporelle des paramètres de jeu est modélisée par des fonctions analytiques, ce qui permet de décrire et de simuler différents modes de jeu par un nombre limité de paramètres. Pour les modes de jeu soutenus tels que le détaché, les mesures permettent de décrire des stratégies de contrôle pour des tâches typiques (variation de niveau sonore, changement de direction d’archet), et des procédures simples ont été déduites, permettant d’extrapoler les paramètres de contrôle afin de changer le niveau sonore ou la durée des coups d’archet. / QC 20100714. Gemensam forskarutbildning KTH och Universite Pierre et Marie Curie (Paris VI).

<p>Severe accidents in a Light Water Reactor (LWR) have been a subject of the research for the last three decades. The research in this area aims to further understanding of the inherent physical phenomena and reduce the uncertainties surrounding their quantification, with the ultimate goal of developing models that can be applied to safety analysis of nuclear reactors. The research is also focusing on evaluation of the proposed accident management schemes for mitigating the consequences of such accidents.</p><p>During a hypothetical severe accident, whatever the scenario, there is likelihood that the core material will be relocated and accumulated in the lower plenum in the form of a debris bed or a melt pool. Physical phenomena involved in a severe accident progression are complex. The interactions of core debris or melt with the reactor structures depend very much on the debris bed or melt pool thermal hydraulics. That is why predictions of heat transfer during melt pool formation in the reactor lower head are important for the safety assessment.</p><p>The main purpose of the present study is to advance a method for describing turbulent natural convection heat transfer of a melt pool, and to develop a computational platform for cost-effective, sufficiently-accurate numerical simulations and analyses of Core Melt-Structure-Water Interactions in the LWR lower head during a postulated severe core-melting accident.</p><p>Given the insights gained from Computational Fluid Dynamics (CFD) simulations, a physics-based model and computationally-efficient tools are developed for multi-dimensional simulations of transient thermal-hydraulic phenomena in the lower plenum of a Boiling Water Reactor (BWR) during the late phase of an in-vessel core melt progression. A model is developed for the core debris bed heat up and formation of a melt pool in the lower head of the reactor vessel, and implemented in a commercial CFD code. To describe the natural convection heat transfer inside the volumetrically decay-heated melt pool, we advanced the Effective Convectivity Conductivity Model (ECCM), which was previously developed and implemented in the MVITA code. In the present study, natural convection heat transfer is accounted for by only the Effective Convectivity Model (ECM). The heat transport and interactions are represented through an energy-conservation formulation. The ECM then enables simulations of heat transfer of a high Rayleigh melt pool in 3D large dimension geometry.</p><p>In order to describe the phase-change heat transfer associated with core debris, a temperature-based enthalpy formulation is employed in the ECM (the phase-change ECM or so called the PECM). The PECM is capable to represent possible convection heat transfer in a mushy zone. The simple approach of the PECM method allows implementing different models of the fluid velocity in a mushy zone for a non-eutectic mixture. The developed models are validated by a dual approach, i.e., against the existing experimental data and the CFD simulation results.</p><p>The ECM and PECM methods are applied to predict thermal loads to the vessel wall and Control Rod Guide Tubes (CRGTs) during core debris heat up and melting in the BWR lower plenum. Applying the ECM and PECM to simulations of reactor-scale melt pool heat transfer, the results of the ECM and PECM calculations show an apparent effectiveness of the developed methods that enables simulations of long term accident transients. It is also found that during severe accident progression, the cooling by water flowing inside the CRGTs plays a very important role in reducing the thermal load on the reactor vessel wall. The results of the CFD, ECM and PECM simulations suggest a potential of the CRGT cooling as an effective mitigative measure during a severe accident progression.</p>