In this study, a mathematical model is developed for investigating the discrete sound propagation in viscoelastic medium to identify its viscoelastic properties. The outcome of the model suggests that pulse repetition frequency is a very important parameter for the determination of relaxation time. Adjusting the order of magnitude of the pulse repetition frequency, the corresponding relaxation time which has similar magnitude with pulse repetition frequency is filtered while the others in the spectrum are discarded. Discrete relaxation spectrum can be obtained by changing the magnitude of the pulse repetition frequency. Therefore, the model enables to characterize the relaxation times by ultrasonic measurements.

Hemodynamic monitoring is extremely important in the accurate measurement of vital parameters. Current methods are highly invasive or noncontinuous, and require direct access to the patient’s skin. This study intends to explore the modulated magnetic signature of blood method (MMSB) to attain blood flow information. This method uses an applied magnetic field to magnetize the iron in the red blood cells and measures the disturbance to the field with a magnetic sensor [1]. Exploration will be done by experimentally studying in-vitro, as well as simulating in COMSOL the alteration of magnetic fields induced by the flow of a magnetic solution. It was found that the variation in magnetic field is due to a high magnetization of blood during slow flow and low magnetization during rapid flow. The understanding of this phenomenon can be used in order to create a portable, non-invasive, continuous, and accurate sensor to monitor the cardiovascular system.

abstract: The non-quasi-static (NQS) description of device behavior is useful in fast switching and high frequency circuit applications. Hence, it is necessary to develop a fast and accurate compact NQS model for both large-signal and small-signal simulations. A new relaxation-time-approximation based NQS MOSFET model, consistent between transient and small-signal simulations, has been developed for surface-potential-based MOSFET compact models. The new model is valid for all regions of operation and is compatible with, and at low frequencies recovers, the quasi-static (QS) description of the MOSFET. The model is implemented in two widely used circuit simulators and tested for speed and convergence. It is verified by comparison with technology computer aided design (TCAD) simulations and experimental data, and by application of a recently developed benchmark test for NQS MOSFET models. In addition, a new and simple technique to characterize NQS and gate resistance, Rgate, MOS model parameters from measured data has been presented. In the process of experimental model verification, the effects of bulk resistance on MOSFET characteristics is investigated both theoretically and experimentally to separate it from the NQS effects. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

Since a decade, spintronics and related physics have attracted considerable attention due to the massive research conducted in these areas. The main reason for growing interest in these fields is the expectation to use the electrons spin instead of or in addition to the charge for the applications in spin-based electronics, quantum information, and quantum computation. A prime concern for these spins to be possible candidates for carrying information is the ability to coherently control them on the time scales much faster than the decoherence times. This thesis reports on the spin dynamics in two-dimensional electron gases hosted in artificially grown III-V semiconductor quantum wells. Here we present a series of experiments utilizing the techniques to optically control the spin polarization triggered by either optical or electrical methods i.e. well known pump-probe technique and current-induced spin polarization. We investigated the spin coherence in high mobility dense two-dimensional electron gas confined in GaAs/AlGaAs double and triple quantum wells, and, it\'s dephasing on the experimental parameters like applied magnetic field, optical power, pump-probe delay and excitation wavelength. We have also studied the large spin relaxation anisotropy and the influence of sample temperature on the long-lived spin coherence in triple quantum well structure. The anisotropy was studied as a function sample temperature, pump-probe delay time, and excitation power, where, the coherent spin dynamics was measured in a broad range of temperature from 5 K up to 250 K using time-resolved Kerr rotation and resonant spin amplification. Additionally, the influence of Al concentration on the spin dynamics of AlGaAs/AlAs QWs was studied. Where, the composition engineering in the studied structures allows tuning of the spin dephasing time and electron g-factor. Finally, we studied the macroscopic transverse drift of long current-induced spin coherence using non-local Kerr rotation measurements, based on the optical resonant amplification of the electrically-induced polarization. Significant spatial variation of the electron g-factor and the coherence times in the nanosecond scale transported away half-millimeter distances in a direction transverse to the applied electric field was observed. / Há uma década, a spintrônica e outras áreas relacionadas vêm atraindo considerável atenção, devido a enorme quantidade de pesquisa conduzidas por elas. A principal razão para o crescente interesse neste campo é a expectativa da aplicação do controle do spin do elétron no lugar ou em adição à carga, em dispositivos eletrônicos e informação e computação quânticas. A possibilidade destes spins carregarem informação depende, primeiramente, da habilidade de controlá-los coerentemente, em uma escala de tempo muito mais rápida do que o tempo de decoerência. Esta tese trata da dinâmica de spins em gases de elétrons bidimensionais, em poços quânticos de semicondutores III-V, crescidos artificialmente. Nós apresentamos uma série de experimentos, utilizando técnicas para o controle ótico da polarização de spin, desencadeadas por métodos óticos ou eletrônicos, ou seja, técnicas conhecidas de bombeio e prova e polarização de spin induzida por corrente. Nós investigamos a coerência de spin em gases bidimensionais, confinados em poços quânticos duplos e triplos de GaAs/AlGaAs e a dependência da defasagem com parâmetros experimentais, como campo magnético externo, potência ótica, tempo entre os pulsos de bombeio e prova e comprimento de onda da excitação. Também estudamos a grande anisotropia de relaxação de spin como função da temperatura da amostra, potência de excitação e defasagem entre bombeio e prova, medidos para uma vasta gama de temperatura, entre 5K e 250K, usando Rotação de Kerr com Resolução Temporal (TRKR) e Amplificação Ressonante de Spin (RSA). Além disso estudamos a influência da concentração de Al na dinâmica dos poços de AlGaAs/AlAs, para o qual a engenharia da composição da estrutura permite sintonizar o tempo de defasagem de spin e o fator $ g $ do elétron. Por fim, estudamos a deriva transversal macroscópica da longa coerência de spin induzida por corrente, através de medidas de Rotação de Kerr não-locais, baseadas na amplificação ressonante ótica da polarização eletricamente induzida. Observamos uma variação espacial significante do fator $ g $ e do tempo de vida da coerência, na escala de nanosegundos, deslocada distâncias de meio milímetro na direção transversa ao campo magnético aplicado.

Abstract Cartilage-related diseases such as osteoarthritis (OA) are a major cause of disability and decrease in the quality of life. Moreover OA causes a heavy economical burden on the social welfare and health care systems. Conventional magnetic resonance imaging (MRI) provides accurate noninvasive method of morphological evaluation of the articular cartilage. However, there are early degenerative changes in the articular cartilage that can be evaluated with modern quantitative MRI methods prior to the signs of cartilage loss. In this study, T2 relaxation time of the articular cartilage was further evaluated in 1.5T in vivo using clinical patients and asymptomatic volunteers. The detection of focal patellar cartilage lesions in T2 mapping as compared to standard clinical MRI was evaluated. T2 mapping showed more lesions than the clinical MRI, and in T2 maps the lesions appeared generally wider. This suggests that T2-mapping is feasible in the clinical setting and may reveal cartilage lesions not seen in the standard knee MRI. The normal topographical variation of T2 relaxation time of articular cartilage in different compartments of the knee joint and at different zones of cartilage in young healthy adults was assessed. T2 values were significantly higher in the superficial zone as compared to the deep tissue at all locations and there was remarkable variation in T2 relaxation between different locations. The normal variation in cartilage T2 within a joint is significant and should be acknowledged when pathology-related T2 changes are investigated. The short- and long-term repeatability of T2 relaxation time measurements of articular cartilage in the knee joint was assessed. The results showed mostly good repeatability, and with careful patient positioning T2 relaxation time at the different cartilage surfaces of the knee can be accurately determined. / Tiivistelmä Nivelrikko, joka usein liittyy nivelruston vaurioitumiseen, aiheuttaa merkittävää toimintakyvyn ja elämänlaadun heikentymistä ikääntyvässä väestössä. Lisäksi nivelrikosta aiheutuu merkittäviä kustannuksia sosiaali- ja terveydenhuollolle. Magneettikuvaus on tarkka kajoamaton menetelmä rustovaurioiden arvioimiseksi. Kuitenkin rustovaurion alkuvaiheessa tapahtuu ruston sisäisiä rakenteellisia ja biokemiallisia muutoksia, joita on mahdollista arvioida uusilla kvantitatiivisilla magneettikuvausmenetelmillä ennen varsinaisten rustopuutosten kehittymistä. Tässä tutkimuksessa tutkittiin ruston T2-relaksaatioaikamittausta 1.5T magneettikuvauslaitteella sekä potilasaineistossa että vapaaehtoisilla. Tutkimuksessa verrattiin paikallisten rustomuutosten havaitsemisen herk¬kyyttä T2-relaksaatioaikakartoituksen ja tavanomaisen kliinisen magneetti¬kuvauksen välillä kliinisessä potilasaineistossa. T2-relaksaatiomittaus osoitti useampia muutoksia kuin kliininen magneettikuvaus ja muutokset olivat yleensä laajempia. Voidaan olettaa, että T2-relaksaatioaikamittaus soveltuu kliiniseen käyttöön ja voi osoittaa tavanomaisessa magneettikuvauksessa näkymättömiä rustomuutoksia. Tutkimuksessa arvioitiin ruston T2-relaksaatioajan paikkakohtaista ja kerroksittaista vaihtelua polven nivelpintojen eri alueilla nuorten vapaaehtoisten aineistossa. T2-relaksaatioaika oli merkitsevästi pidempi ruston pinnallisessa kuin syvässä kerroksessa kaikilla nivelpintojen alueilla. Lisäksi T2-relaksaatioajassa oli merkittävää normaalia vaihtelua eri alueiden välillä ja tämä tulisi huomioida ruston patologisia muutoksia arvioitaessa. Tutkimuksessa arvioitiin polven ruston T2-relaksaatioajan lyhyen ja pitkän aikavälin toistettavuutta vapaaehtoisaineistossa. Tulokset osoittivat enimmäkseen hyvää toistettavuutta ja huolellisella asettelulla voidaan ruston T2-relaksaatioaika mitata luotettavasti polven nivelpintojen eri alueilla.

Analyses of heat and mass transfer between different materials and phases are essential in numerous fundamental scientific problems and practical engineering applications, such as thermal and chemical transport in porous media, design of heat exchangers, dendritic growth during solidification, and thermal/mechanical analysis of additive manufacturing processes. In the numerical simulation, interface treatment can be further divided into sharp interface schemes and diffuse interface schemes according to the morphological features of the interface. This work focuses on the following subjects through computational studies: (1) critical evaluation of the various sharp interface schemes in the literature for conjugate heat and mass transfer modeling with the lattice Boltzmann method (LBM), (2) development of a novel sharp interface scheme in the LBM for conjugate heat and mass transfer between materials/phases with very high transport property ratios, and (3) development of a new diffuse-interface phase-field-lattice Boltzmann method (PFM/LBM) for dendritic growth and solidification modeling. For comparison of the previous sharp interface schemes in the LBM, the numerical accuracy and convergence orders are scrutinized with representative test cases involving both straight and curved geometries. The proposed novel sharp interface scheme in the LBM is validated with both published results in the literature as well as in-house experimental measurements for the effective thermal conductivity (ETC) of porous lattice structures. Furthermore, analytical correlations for the normalized ETC are proposed for various material pairs and over the entire range of porosity based on the detailed LBM simulations. In addition, we provide a modified correlation based on the SS420-air and SS316L-air metal pairs and the high porosity range for specific application. The present PFM/LBM model has several improved features compared to those in the literature and is capable of modeling dendritic growth with fully coupled melt flow and thermosolutal convection-diffusion. The applicability and accuracy of the PFM/LBM model is verified with numerical tests including isothermal, iso-solutal and thermosolutal convection-diffusion problems in both 2D and 3D. Furthermore, the effects of natural convection on the growth of multiple crystals are numerically investigated.

In this work the relationships between penetrant structure, its transport properties, and its effects on the mechanical properties of a polymer matrix were investigated. Although there is a vast amount of data on the diffusion of low molecular weight molecules into polymeric materials and on the mechanical properties of various polymer-penetrant systems, no attempts have been made to inter-relate the two properties with respect to the chemical structure of the diffusant. Therefore, two series of penetrants - n-alkanes and esters - were examined in this context, with the goal of correlating molecular size, shape, and chemical nature of the penetrant to its final transport and matrix mechanical properties. These correlations have been demonstrated to allow quantitative prediction of one property, given a reasonable set of data on the other parameters. A series of n-alkanes (C6-C17) and esters (C5-C17) have been used to separate the effects of penetrant size and shape, from those due to polymer-penetrant interactions, in the diffusion through a polyamide polymeric adhesive. These effects have been taken into account in order to yield a qualitative relationship that allows for prediction of diffusivity based upon penetrant structural information. Transport properties have been analyzed using mass uptake experiments as well as an in-situ FTIR-ATR technique to provide detailed kinetic as well as thermodynamic information on this process. The phenomenon of diffusion and its effects on the resulting dynamic mechanical response of a matrix polymeric adhesive have been studied in great detail using the method of reduced variables. The concept of a diffusion-time shift factor (log aDt) has been introduced to create doubly-reduced master curves, taking into account the effects of temperature and the variations in the polymer mechanical response due to the existence of a low molecular weight penetrant. / Ph. D.

La cartographie du temps de relaxation longitudinale T1 est une technique d'IRM quantitative pour caractériser les tissus myocardiques. Plusieurs études ont déjà montré la corrélation entre la mesure de T1 et la présence de fibrose. Celle-ci est souvent observée dans les pathologies cardiaques telles que les cardiomyopathies ou l'infarctus du myocarde. Cependant, l'acquisition d'une carte T1 du coeur reste techniquement difficile. Actuellement, la quantification T1 du myocarde humain est réalisée en apnée à l'aide de séquences 2D qui sont spécifiques aux constructeurs et donc peu disponibles. Afin de pallier aux limitations de ces séquences, nous proposons une méthode basée sur une séquence 3D clinique. Cette technique, utilisant la variation des angles de bascule avec intégration d'une correction B1, a été adaptée pour une utilisation en imagerie cardiaque. Des essais sur fantôme ont permis de sélectionner les paramètres optimaux et de montrer la reproductibilité de la méthode. Puis, une étude sur volontaires sains a permis de valider la méthode en double synchronisation (cardiaque et respiratoire). Enfin, une méthode de reconstruction intégrant des signaux physiologiques de mouvement a également été utilisée afin de faire de la quantification T1 en respiration libre et de diminuer le temps d'acquisition. Les valeurs de T1 myocardique sur volontaires sont comprises entre 1289 ± 66 ms et 1376 ± 43 ms, correspondant aux valeurs de la littérature. Ces travaux ouvrent la voie à l'utilisation de la cartographie T1 chez les patients avec pour objectifs une meilleure caractérisation des pathologies et une meilleure adaptation des stratégies thérapeutiques / T1 mapping is a useful quantitative MR technique for cardiac tissue characterization. Several studies have shown that T1 measurements are correlated with fibrosis, which is observed in cardiac diseases such as cardiomyopathy or myocardial infarction. However, cardiac T1 mapping remains challenging, mainly because of long acquisition times and interference from cardiac and respiratory motions. T1 quantification on the human myocardium is generally performed on breath-hold with 2D specific sequences. Unfortunately these sequences are scanner specific and poorly available for clinical use. To overcome these limitations, we propose a new method based on a 3D clinical sequence. This technique, using a variable flip angle approach that integrates B1 correction, was adapted in cardiac imaging. Phantom tests were used to select the optimal parameters and to show the method reproducibility. Then, the method was validated with a volunteer study using double synchronization (cardiac and respiratory). Moreover, a reconstruction method integrating physiological signals of motion was also used to perform T1 quantification in free breathing and to reduce the total acquisition time. The myocardial T1 values on volunteers ranged between 1289 ± 66 ms and 1376 ± 43 ms, which was in good agreement with previously published works. These studies allow the use of T1 mapping in patients with better characterization of pathologies and a better adaptation to therapeutic strategies

Dans cette thèse, une solution de caoutchouc de styrène-butadiène (SBR) réticulé avec du peroxyde organique, a été transformé en un gel autodégradable par l’ajout d’hydropéroxyde comme agent de dégradation. La formulation a été caractérisée en rhéologie dynamique. Les spectres de temps de relaxation ont été calculés à partir des modules dynamiques de cisaillement, par une nouvelle méthode développée dans ces travaux présentée avec une revue complète de méthodes pour le calcul des spectres de relaxation à partir de données de rhéométrie de cisaillement. Des expériences in-situ et ex-situ ont été réalisées afin d’évaluer l’évolution de les réactions de réticulation et dégradation. Les changements de la structure du réseau polymérique sont mises en évidence dans les spectres de temps de relaxation. La cinétique de la dégradation de la solution de SBR a été étudiée dans des conditions anaérobies et caractérisée par diffusion de la lumière multi-angles couplée à la chromatographie d’exclusion stérique (SEC-MALS). En utilisant des équations de bilan de populations, nous avons pu calculer les constantes cinétiques de dégradation thermique et thermo-oxydative. Différentes formulations de ces gels auto-dégradables à base d’huile ont été évaluées en tant que potentiels agents de dérivation pour des opérations de traitement de puits. Le comportement rhéologique de ces gels a été mesuré en fonction du temps, pour vérifier la réticulation du polymère, la force de gel, et la dégradation ; ces variables peuvent être ajustées aux nécessités de l’opération de traitement en jouant sur la formulation. Des tests d’écoulement dans carotte simples ont été réalisés pour évaluer la résistance à la pression en fonction de la force du gel et de sa dégradation. Des tests d’écoulement dans carottes parallèles ont également été menés, afin d’évaluer l’efficacité de la dérivation et la restauration de mobilité. / In this work, a solution of peroxide crosslinked styrene-butadiene rubber (SBR) has been transformed to a self-degradable gel system by adding hydroperoxide as a degradation agent to the formulation. Dynamic rheometry was employed to calculate the relaxation time with a new method presented along with a full review of methods for calculation of the relaxation time spectrum from oscillatory rheometry. In-situ and ex-situ experiments were performed to evaluate the evolution of crosslinking and degradation reactions. Structural changes in the polymer network were visible within the relaxation time spectra. The degradation kinetics of styrene butadiene rubber (SBR) in solution was studied in anaerobic conditions and the characterization was performed by multiangle light scattering coupled to size exclusion chromatography (SEC-MALS). Using population balance equations, it was possible to calculate the kinetic constants for thermal and thermooxidative degradation. Different formulations of these oil-based self-degradable gels have been evaluated as possible diverting agents during oil wells operations. The time dependent rheological behavior of the gels was measured to verify polymer crosslinking, maximum gel strength and gel degradation, all of which can be adjusted by varying formulation depending on operation needs. Single core tests were performed to evaluate pressure resistance as a function of gel strength and gel degradation. Parallel cores tests were also carried out to validate diversion efficiency and mobility restoration.

Echocardiography is a well established technique when evaluating the size and function of the heart. One of the most common ways to measure the size of the right ventricle (RV) is to measure the RV outflow tract 1(RVOT1). Several ways to measure RVOT1 are described in the literature.These ways were compared with echocardiography on 27 healthy subjects.The result showed significant differences in RVOT1, depending on the way it was measured, concluding that the same site, method and body positionshould be used when comparing RVOT1 in the same subject over time.One parameter to evaluate the RV diastolic function (RVDF) is to measure the RV isovolumetric relaxation time (RV-IVRT), a sensitive marker ofRV dysfunction. There are different ways to measure this. In this thesis two ways of measuring RV-IVRT and their time intervals were compared in 20 patients examined with echocardiography. There was a significant difference between the two methods indicating that they are not measuring the same interval.Another way to assess the RVDF is to measure the maximal early diastolicvelocity (MDV) in the long-axis direction. MDV can be measured bydifferent methods, hence 29 patients were examined and MDV was measured according to two methods. There was a good correlation but a poor agreement between the two methods meaning that reference values cannot be used interchangeably.Takotsubo cardiomyopathy is characterized by apical wall motion abnormalities without coronary stenosis. The pathology of this condition remains unclear. To evaluate biventricular changes in systolic long-axisfunction and diastolic parameters in the acute phase and after recovery, 13 patients were included and examined with echocardiography at admission and after recovery. The results showed significant biventricular improvementof systolic long-axis function while most diastolic parameters remainedunchanged.