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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Synthèse de formaldéhyde par oxydation directe du méthane en microréacteur / Direct oxidation of methane to formaldehyde in an annular flow microreactor

Zhang, Jie 13 October 2011 (has links)
Le formaldéhyde, un des produits de base de la chimie, est synthétisé industriellement par un procédé multi-étapes, dans lequel l’efficacité énergétique est limitée. Ainsi, une synthèse par oxydation directe du méthane en phase gazeuse, qui pourrait être plus avantageuse, a été étudiée expérimentalement et par une modélisation cinétique, dans le cadre de ce travail. Pour favoriser la production du formaldéhyde, produit intermédiaire de l’oxydation du méthane, des temps de passage faibles (< 100 ms) ont été envisagés. Un microréacteur annulaire (espace annulaire de 0,5 mm) en quartz a été utilisé, dans lequel la réaction a été étudiée en faisant varier les paramètres opératoires suivants : température (600-1000°C), temps de passage (20-80 ms), rapport XO2/XCH4 (0,5-15) et teneur en NO2 ajoutée (0-0,6%). Sans NO2, les sélectivités en HCHO diminuent avec la conversion et le rendement maximal sans recyclage est de 2.4% (950°C, 60 ms et XO2/XCH4 = 8). L’ajout de NO2 permet de diminuer la température requise de 300°C, et d’augmenter le meilleur rendement en HCHO à 9% (700°C, 30 ms et XO2/XCH4 = 7 et 0,5% de NO2). À faible avancement, la réaction sans NO2 peut être modélisée avec le mécanisme Gri-Mech 3.0 sans aucun ajustement. Pour la réaction avec NO2, après quelques corrections et modifications fondées sur une étude bibliographique, le mécanisme de Zalc et al. (2006) permet de rendre correctement compte des résultats expérimentaux. L’analyse de flux a montré que l’inter-conversion entre NO2 et NO joue un rôle important dans le milieu réactionnel. Elle permet de former continuellement les radicaux réactifs OH•, et de convertir les radicaux CH3• et CH3O2• en radicaux CH3O• / Formaldehyde is one of the world’s top organic intermediate chemicals. It is currently produced by a complex three-step process but a one-step process might require less energy. In this work, the direct gas phase partial oxidation of methane to formaldehyde has been studied through experiments and kinetic modeling. As formaldehyde is an intermediate in the sequential oxidation of methane, short residence times (<100 ms) have been considered in order to optimize its production. Thus, a quartz annular flow microreactor (annular space 0.5 mm wide), was chosen. The undertaken experiments consist of a systematic investigation of the effects of temperature (600-1000°C), residence time (20-80 ms), input composition XO2/XCH4 (0.5-15) and initial NO2 concentration (0-0.6%). Without NO2, the HCHO selectivity decreases with the increasing methane conversion. For a single pass operation, the best HCHO yield is 2.4% (950°C, 60 ms, XO2/XCH4 = 8). The addition of NO2 decreases the reaction initiation temperature by 300°C and it remarkably enhances the HCHO yield. The highest HCHO yield attains 9% (700°C, 30 ms, XO2/XCH4 =7) in the presence of NO2 (0.5%). For the reaction without NO2, the mechanism Gri-Mech 3.0 fits well the experimental results. For the reaction with NO2, by using the mechanism of Zalc et al. (2006) with some modifications, we obtained a good agreement between the experimental data and the model. The production and consumption flux analysis shows that the inter-conversion between NO2 and NO plays an important role in the reaction, because it continuously produces the reactive radicals OH• and it converts the radicals CH3• and CH3O2• to radicals CH3O•
102

Towards cybernetic modeling of biological processes in mammalian systems—lipid metabolism in the murine macrophage

Lina M Aboulmouna (9757040) 11 December 2020 (has links)
<p>Regulation of metabolism in mammalian cells is achieved through a complex interplay between cellular signaling, metabolic reactions, and transcriptional changes. The modeling of metabolic fluxes in a cell requires the knowledge of all these mechanisms, some of which may be unknown. A cybernetic approach provides a framework to model these complex interactions through the implicit accounting of such regulatory mechanisms, assuming a biological “goal”. The goal-oriented control policies of cybernetic models have been used to predict metabolic phenomena ranging from complex substrate uptake patterns and dynamic metabolic flux distributions to the behavior of gene knockout strains. The premise underlying the cybernetic framework is that the regulatory processes affecting metabolism can be mathematically formulated as a cybernetic objective through variables that constrain the network to achieve a specified biological “goal”. </p><p>Cybernetic theory builds on the perspective that regulation is organized towards achieving goals relevant to an organism’s survival or displaying a specific phenotype in response to a stimulus. While cybernetic models have been established by prior work carried out in bacterial systems, we show its applicability to more complex biological systems with a predefined goal. We have modeled eicosanoid, a well-characterized set of inflammatory lipids derived from arachidonic acid, metabolism in mouse bone marrow derived macrophage (BMDM) cells stimulated by Kdo2-Lipid A (KLA, a chemical analogue of Lipopolysaccharide found on the surface of bacterial cells) and adenosine triphosphate (ATP, a danger signal released in response to surrounding cell death) using cybernetic control variables. Here, the cybernetic goal is inflammation; the hallmark of inflammation is the expression of cytokines which act as autocrine signals to stimulate a pro-inflammatory response. Tumor necrosis factor (TNF)-α is an exemplary pro-inflammatory marker and can be designated as a cybernetic objective for modeling eicosanoid—prostaglandin (PG) and leukotriene (LK)—metabolism. Transcriptomic and lipidomic data for eicosanoid biosynthesis and conversion were obtained from the LIPID Maps database. We show that the cybernetic model captures the complex regulation of PG metabolism and provides a reliable description of PG formation using the treatment ATP stimulation. We then validated our model by predicting an independent data set, the PG response of KLA primed ATP stimulated BMDM cells.</p><p>The process of inflammation is mediated by the production of multiple cytokines, chemokines, and lipid mediators each of which contribute to specific individual objectives. For such complex processes in mammalian systems, a cybernetic objective based on a single protein/component may not be sufficient to capture all the biological processes thereby necessitating the use of multiple objectives. The choice of the objective function has been made by intuitive considerations in this thesis. If objectives are conjectured, an argument can be made for numerous alternatives. Since regulatory effects are estimated from unregulated kinetics, one encounters the risk of multiplicity in this regard giving rise to multiple models. The best model is of course that which is able to predict a comprehensive set of perturbations. Here, we have extended our above model to also capture the dynamics of LKs. We have used migration as a biological goal for LK using the chemoattractant CCL2 as a key representative molecule describing cell activation leading to an inflammatory response where a goal composed of multiple cybernetic objectives is warranted. Alternative model objectives included relating both branches of the eicosanoid metabolic network to the inflammatory cytokine TNF-α, as well as the simple maximization of all metabolic products such that each equally contributes to the inflammatory system outcome. We were again able to show that all three cybernetic objectives describing the LK and PG branches for eicosanoid metabolism capture the complex regulation and provide a reliable description of eicosanoid formation. We performed simulated drug and gene perturbation analyses on the system to identify differences between the models and propose additional experiments to select the best cybernetic model.</p><p>The advantage to using cybernetic modeling is in its ability to capture system behavior without the same level of detail required for these interactions as standard kinetic modeling. Given the complexity of mammalian systems, the cybernetic goal for mammalian cells may not be based solely on survival or growth but on specific context dependent cellular responses. In this thesis, we have laid the groundwork for the application of cybernetic modeling in complex mammalian systems through a specific example case of eicosanoid metabolism in BMDM cells, illustrated the case for multiple objectives, and highlighted the extensibility of the cybernetic framework to other complex biological systems.</p>
103

[pt] MODELAGEM DA COPOLIMERIZAÇÃO EM SUSPENSÃO DE POLI(ACETATO DE VINILA-CO-METACRILATO DE METILA) APLICADO EM PROCEDIMENTOS DE EMBOLIZAÇÃO VASCULAR / [en] MODELING OF SUSPENSION COPOLYMERIZATION OF POLY(VINYL ACETATE-CO-METHYL METHACRYLATE) FOR VASCULAR EMBOLIZATION PROCEDURES

JOAO GONCALVES NETO 22 December 2020 (has links)
[pt] O processo de tratamento de tumores por embolização vascular é sensível ao conjunto de partículas poliméricas empregado, ditos agentes embólicos, cujos fatores como tamanho e morfologia influenciam no sucesso do procedimento e podem ocasionar complicações quando mal dimensionados. Partículas esféricas de poli(acetato de vinila-co-metacrilato de metila) apresentam a maioria das características desejadas após tratamento por hidrólise alcalina. Este material é relativamente novo, o que significa que há uma lacuna de conhecimento em relação ao estudo dos fenômenos que regem sua cinética. Dessa forma, o presente trabalho investigou a cinética de copolimerização responsável pela sua produção. No desenvolvimento matemático, o método dos momentos foi utilizado assumindo estado quase-estacionário para as espécies radicalares. Além disso, o modelo considera difusão das moléculas no meio para contabilização dos efeitos viscosos, comumente determinados empiricamente. Constatou-se que as características físicas dos monômeros, assim como os parâmetros cinéticos da homopolimerização, puderam ser utilizados na copolimerização. Entretanto, como relatado na literatura para outros sistemas, os efeitos viscosos se comportam de forma consideravelmente diferente na copolimerização, sendo necessário a reestimação de alguns parâmetros relativos aos mesmos. Assim, foi possível reproduzir de forma adequada perfis de conversão, massas molares médias e composição do copolímero. Concluiu-se que o modelo proposto é capaz de representar a cinética da copolimerização em suspensão do poli(acetato de vinila-co-metacrilato de metila), possibilitando um melhor controle das características do copolímero aplicado ao procedimento de embolização vascular. Até onde se tem conhecimento, este é o primeiro trabalho que investiga e implementa com sucesso a modelagem cinética desse sistema. / [en] The treatment of vascularized tumors through vascular embolization is sensible to the polymeric particles used during procedure. These embolic agents have attributes, like size and morphology, which play a significant role on the success of this technique and can promote complications when not well dimensioned. Among the many options available, spherical particles of poly(vinyl acetate-co-methyl methacrylate) present most desired characteristics after alkalyne hydrolysis treatment. Being relatively new, the literature lack studies related to the kinetics of production of this material. Therefore, this research investigated the copolymerization kinetics of poly(vinyl acetate-co-methyl methacrylate) production. In the mathematical development, the method of moments was used assuming quasi-steady state for the free radical species. Additionally, the model includes the viscous effects through the diffusion of the involved molecules, which is usually accounted empirically. It was possible to use the physical properties of the monomers as well as the homopolymerization kinetic parameters in the copolymerization. However, as reported in the literature, some parameters are sensible to the system and some viscous effects affect the copolymerization differently. Therefore, some parameters were reestimated. It was possible to predict the conversion, average molecular weights and composition. Consequently, the model was capable of representing the kinetics of the suspension copolymerization of poly(vinyl acetate-co-methyl methacrylate), meaning it could be used to improve the production of this polymer as an embolic agent for vascular embolization procedure. As far as known by the author, this is the first study to successfully perform the kinetic modeling of this specific system.
104

Development Of A Chemical Kinetic Model For A Fluidized-bed Sewage Sludge Gasifier

Champion, Wyatt 01 January 2013 (has links)
As the need for both sustainable energy production and waste minimization increases, the gasification of biomass becomes an increasingly important process. What would otherwise be considered waste can now be used as fuel, and the benefits of volume reduction through gasification are seen in the increased lifespan of landfills. Fluidized-bed gasification is a particularly robust technology, and allows for the conversion of most types of waste biomass. Within a fluidized-bed gasifier, thermal medium (sand) is heated to operating temperature (around 1350°F) and begins to fluidize due to the rapid expansion of air entering the bottom of the reactor. This fluidization allows for excellent heat transfer and contact between gases and solids, and prevents localized "hot spots" within the gasifier, thereby reducing the occurrence of ash agglomeration within the gasifier. Solids enter the middle of the gasifier and are rapidly dried and devolatilized, and the products of this step are subsequently oxidized and then reduced in the remainder of the gasifier. A syngas composed mainly of N2, H2O, CO2, CO, CH4, and H2 exits the top of the gasifier. A computer model was developed to predict the syngas composition and flow rate, as well as ash composition and mass flow rate from a fluidized-bed gasifier. A review of the literature was performed to determine the most appropriate modeling approach. A chemical kinetic model was chosen, and developed in MATLAB using the Newton-Raphson method to solve sets of 18 simultaneous equations. These equations account for mass and energy balances throughout the gasifier. The chemical kinetic rate expressions for these reactions were sourced from the literature, and some values modified to better fit the predicted gas composition to literature data.
105

Modeling of solution and surface–initiated atom transfer radical polymerization

Mastan, Erlita 01 December 2015 (has links)
Controlled radical polymerization (CRP) can be viewed as the middle ground between living anionic polymerization (LAP) and conventional free radical polymerization (FRP). It combines the precise control over polymer structure offered by LAP, under a tolerant reaction condition similar to FRP. One of the most studied CRP is atom transfer radical polymerization (ATRP), with over 10,000 papers published since its introduction in 1995. Despite the numerous studies, knowledge on its fundamental mechanism is still lacking, as evident from the lack of expression for full MWD and polydispersity that account for termination reaction. Since termination is unavoidable in ATRP, the existing expressions give inaccurate predictions as dead chains accumulate. In this study, we derived expressions for full MWD at low conversion and for polydispersity. These expressions allow us to quantify and gain better understanding on the contribution of termination. In addition, the resulting polydispersity expression shows better agreement than the existing equation when correlated with experiment data. In addition to the aforementioned questions, there are also controversies regarding the kinetics of surface-initiated ATRP, with researchers divided into two schools of theories. We evaluated the validity of these theories by comparing their predictions to experimental trends. Both theories were found to be inadequate in explaining all the experimental observations, thus triggering an investigation of the graft density. Graft density is an important determining property for polymer brushes, yet little is known about what affects its final value. Through simulations, we investigated the effect of experiment factors on the grafting density. A decrease in the amount of deactivator is found to decrease the grafting density, which could be explained by an increase in the number of monomers added per activation cycle. This knowledge allows us to explain the conflicting experiment observations regarding the growth trends of polymer layers reported in the literatures. / Thesis / Doctor of Philosophy (PhD) / Polymer materials are used almost everywhere in our daily life from clothing to water bottle. This wide range of applications owes to the nearly infinite possible properties that polymer can possess. Different polymerization processes to synthesize polymers have their own weaknesses and strengths. Herein we investigated the fundamental mechanism of one of the currently most attractive polymerization systems, atom transfer radical polymerization (ATRP). This process allows the synthesis of polymers with precisely tailored chain microstructures, making it possible to create polymer with sophisticated properties. Using modeling approaches, we derived explicit expressions for determining chain properties, allowing detailed investigation of how various factors affect these properties. Through these investigations, we obtained better understanding on the mechanism of ATRP in solution and on surface. This knowledge is crucial in providing insight and guiding experimental designs for better control over the material properties.
106

A Quantitative Manganese-Enhanced MRI Method For In Vivo Assessment Of L-Type Calcium Channel Activity In Heart

Li, Wen 15 April 2011 (has links)
No description available.
107

Influence des aromatiques sur la stabilité thermique des pétroles dans les gisements / Influence of the aromatic compounds on the thermal stability of oils in oilfields

Lannuzel, Frédéric 05 July 2007 (has links)
Cette étude vise à mieux comprendre les réactions impliquées dans le craquage thermique des huiles en basins sédimentaires. Des pyrolyses d'octane, de toluène et de mélanges octane/toluène ont été effectuées entre 330°C et 450°C et des pressions allant de 1 bar à 700 bar. Le mécanisme radicalaire développé permet de rendre compte de l’influence de la température et de la pression sur la distribution des produits ainsi que sur la conversion jusqu'aux conditions de gisement (200°C, 150-1000 bar). Les pyrolyses du toluène pur et du mélange octane/toluène ont permis de modéliser le rôle inhibiteur des alkylaromatiques sur le craquage des hydrocarbures. Cette étude démontre l'importance des co réactions et donc de la composition des huiles sur la stabilité thermique des pétroles en gisements / This study aims at a better understanding of the reactions involved in the thermal cracking of oil within sedimentary basins. Pyrolysis of octane, toluene and mixtures of octane / toluene were performed between 330°C and 450°C and at pressures going from 1 bar to 700 bar. The constructed radical mechanism allows to report the influence of temperature and pressure on the distribution of products as well as the conversion from laboratory to reservoir conditions (200°C, 150-1000 bar). The pyrolysis of pure toluene and the octane / toluene mixture allowed to model the inhibition effect of alkylaromatics on the cracking of hydrocarbons. This study demonstrates the importance of co reactions and thus the composition of oil on the thermal stability of petroleums in reservoirs
108

Étude structure/fonction des cotransporteurs Na+/glucose

Sasseville, Louis 06 1900 (has links)
Cette thèse porte sur l’étude de la relation entre la structure et la fonction chez les cotransporteurs Na+/glucose (SGLTs). Les SGLTs sont des protéines membranaires qui se servent du gradient électrochimique transmembranaire du Na+ afin d’accumuler leurs substrats dans la cellule. Une mise en contexte présentera d’abord un bref résumé des connaissances actuelles dans le domaine, suivi par un survol des différentes techniques expérimentales utilisées dans le cadre de mes travaux. Ces travaux peuvent être divisés en trois projets. Un premier projet a porté sur les bases structurelles de la perméation de l’eau au travers des SGLTs. En utilisant à la fois des techniques de modélisation moléculaire, mais aussi la volumétrie en voltage imposé, nous avons identifié les bases structurelles de cette perméation. Ainsi, nous avons pu identifier in silico la présence d’une voie de perméation passive à l’eau traversant le cotransporteur, pour ensuite corroborer ces résultats à l’aide de mesures faites sur le cotransporteur Na/glucose humain (hSGLT1) exprimé dans les ovocytes. Un second projet a permis d’élucider certaines caractéristiques structurelles de hSGLT1 de par l’utilisation de la dipicrylamine (DPA), un accepteur de fluorescence dont la répartition dans la membrane lipidique dépend du potentiel membranaire. L’utilisation de la DPA, conjuguée aux techniques de fluorescence en voltage imposé et de FRET (fluorescence resonance energy transfer), a permis de démontrer la position extracellulaire d’une partie de la boucle 12-13 et le fait que hSGLT1 forme des dimères dont les sous-unités sont unies par un pont disulfure. Un dernier projet a eu pour but de caractériser les courants stationnaires et pré-stationaires d’un membre de la famille des SGLTs, soit le cotransporteur Na+/myo-inositol humain hSMIT2 afin de proposer un modèle cinétique qui décrit son fonctionnement. Nous avons démontré que la phlorizine inhibe mal les courants préstationnaires suite à une dépolarisation, et la présence de courants de fuite qui varient en fonction du temps, du potentiel membranaire et des substrats. Un algorithme de recuit simulé a été mis au point afin de permettre la détermination objective de la connectivité et des différents paramètres associés à la modélisation cinétique. / This thesis is about the structure/function relationship in Na+/glucose cotransporters (SGLTs). SGLTs are membrane proteins which use the Na+ transmembrane electrochemical gradient to accumulate their substrates within the cell. As an introduction, a short review of the current state of the field will be followed by a presentation of the different technics used in this work. This work can be divided in three main projects. In the first project, we investigated the structural basis of water permeation through SGLTs. By using molecular modeling technics, we have identified, in silico, a passive permeation pathway used by water to go through the cotransporter across the membrane. Using voltage-clamp volumetric measurement, we were able to corroborate these findings for hSGLT1 expressed in oocytes. A second project allowed elucidation of some of hSGLT1 structural characteristics through the use of dipicrylamine (DPA), a fluorescence acceptor whose repartition in the lipid membrane is voltage-dependant. Use of DPA concomitantly with voltage-clamp fluorescence and FRET (fluorescence resonance energy transfer) has clearly demonstrated the extracellular localisation of part of the 12-13 loop which was previously assumed to be intracellular. In addition, we have shown that hSGLT1 forms a dimeric structure where the subunits are linked by a disulfide bridge. A last project aimed at characterizing the steady-state and pre-steadystate currents of a member of the SGLT family named hSMIT2 (human Na/myo-inositol transporter 2). We showed that phlorizin is a poor inhibitor of pre-steady state currents following depolarisation, and the presence of a time, membrane potential and substrate dependent leak current. A simulated annealing algorithm was developed in order to allow objective determination of both the connectivity and the parameters associated with the optimal kinetic model.
109

Reconstruction 4D intégrant la modélisation pharmacocinétique du radiotraceur en imagerie fonctionnelle combinée TEP/TDM / 4D reconstruction including radiopharmaceutical modeling in PET/CT imaging

Merlin, Thibaut 11 December 2013 (has links)
L'imagerie TEP permet de mesurer et visualiser les changements de la distribution biologique des radiopharmaceutiques au sein des organes d'intérêt au court du temps. Ce suivi temporel offre des informations très utiles concernant les processus métaboliques et physiologiques sous-jacents, qui peuvent être extraites grâce à différentes techniques de modélisation cinétique. De plus, un autre avantage de la prise en compte de l'information temporelle dans les acquisitions TEP pour les examens en oncologie thoracique concerne le suivi des mouvements respiratoires. Ces acquisitions permettent de mettre en place des protocoles et des méthodologies visant à corriger leurs effets néfastes à la quantification, et les artefacts associés. L'objectif de ce projet est de développer une méthode de reconstruction permettant de combiner et mettre en oeuvre d'une part les corrections nécessaires à la quantification des données en TEP, et d'autre part la modélisation de la biodistribution du radiotraceur au cours du temps permettant d'obtenir des images paramétriques pour l'oncologie thoracique. Dans un premier temps, une méthodologie de correction des effets de volume partiel intégrant, dans le processus de reconstruction, une déconvolution de Lucy-Richardson associée à un débruitage dans le domaine des ondelettes, a été proposée. Une seconde étude a été consacrée au développement d'une méthodologie combinant une régularisation temporelle des données par l'intermédiaire d'un ensemble de fonctions de base temporelles, avec une méthode de correction des mouvements respiratoires basée sur un modèle élastique. Enfin, dans une troisième étape, le modèle cinétique de Patlak a été intégré dans un algorithme de reconstruction dynamique, et associé à la correction de mouvement afin de permettre la reconstruction directe d'images paramétriques de données thoraciques soumises au mouvement respiratoire. Les paramètres de transformation élastique pour la correction de mouvement ont été calculés à partir des images TEP d'intervalles synchronisés par rapport à l'amplitude de la respiration du patient. Des simulations Monte-Carlo d'un fantôme 4D géométrique avec plusieurs niveaux de statistiques, et du fantôme anthropomorphique NCAT intégrant des courbes d'activités temporelles réalistes pour les différents tissus, ont été réalisées afin de comparer les performances de la méthode de reconstruction paramétrique développée dans ce travail avec une approche 3D standard d'analyse cinétique. L'algorithme proposé a ensuite été testé sur des données cliniques de patients présentant un cancer bronchique non à petites cellules. Enfin, après la validation indépendante de l'algorithme de correction des effets de volume partiel d'une part, et de la reconstruction 4D incorporant la régularisation temporelle d'autre part, sur données simulées et cliniques, ces deux méthodologies ont été associées afin d'optimiser l'estimation de la fonction d'entrée à partir d'une région sanguine des images reconstruites. Les résultats de ce travail démontrent que l'approche de reconstruction paramétrique proposée permet de conserver un niveau de bruit stable dans les régions tumorales lorsque la statistique d'acquisition diminue, contrairement à l'approche d'estimation 3D pour laquelle le niveau de bruit constaté augmente. Ce résultat est intéressant dans l'optique d'une réduction de la durée des intervalles de la reconstruction 4D, permettant ainsi de réduire la durée totale de l'acquisition 4D. De plus, l'utilisation des fonctions d'entrée estimées avec les méthodes de régularisation temporelle proposées ont conduit à améliorer l'estimation des paramètres de Patlak. Enfin, la correction élastique du mouvement amène à une diminution du biais d'estimation des deux paramètres de Patlak, en particulier sur les tumeurs de petites dimensions situées dans des régions sensibles au mouvement respiratoire. / Positron emission tomography (PET) is now considered as the gold standard and the main tool for the diagnosis and therapeutic monitoring of oncology patients, especially due to its quantitative aspects. With the advent of multimodal imaging in combined PET and X-ray CT systems, many methodological developments have been proposed in both pre-processing and data acquisition, image reconstruction, as well as post-processing in order to improve the quantification in PET imaging. Another important aspect of PET imaging is its high temporal resolution and ability to perform dynamic acquisitions, benefiting from the high sensitivity achieved with current systems. PET imaging allows measuring and visualizing changes in the biological distribution of radiopharmaceuticals within the organ of interest over time. This time tracking provides valuable information to physicians on underlying metabolic and physiological processes, which can be extracted using pharmacokinetic modeling. The objective of this project is, by taking advantage of dynamic data in PET/CT imaging, to develop a reconstruction method combining in a single process all the correction methodology required to accurately quantify PET data and, at the same time, include a pharmacokinetic model within the reconstruction in order to create parametric images for applications in oncology. In a first step, a partial volume effect correction methodology integrating, within the reconstruction process, the Lucy-Richardson deconvolution algorithm associated with a wavelet-based denoising method has been introduced. A second study focused on the development of a 4D reconstruction methodology performing temporal regularization of the dataset through a set of temporal basis functions, associated with a respiratory motion correction method based on an elastic deformation model. Finally, in a third step, the Patlak kinetic model has been integrated in a dynamic image reconstruction algorithm and associated with the respiratory motion correction methodology in order to allow the direct reconstruction of parametric images from dynamic thoracic datasets affected by the respiratory motion. The elastic transformation parameters derived for the motion correction have been estimated from respiratory-gated PET images according to the amplitude of the patient respiratory cycle. Monte-carlo simulations of two phantoms, a 4D geometrical phantom, and the anthropomorphic NCAT phantom integrating realistic time activity curves for the different tissues, have been performed in order to compare the performances of the proposed 4D parametric reconstruction algorithm with a standard 3D kinetic analysis approach. The proposed algorithm has then been assessed on clinical datasets of several patients with non small cell lung carcinoma. Finally, following the prior validation of the partial volume effect correction algorithm on one hand, and the 4D reconstruction incorporating the temporal regularization on the other hand, on simulated and clinical datasets, these two methodologies have been associated within the 4D reconstruction algorithm in order to optimize the estimation of image derived input functions. The results of this work show that the proposed direct parametric approach allows to maintain a similar noise level in the tumor regions when the statistic decreases, contrary to the 3D estimation approach for which the observed noise level increases. This result suggests interesting perspectives for the reduction of frame duration reduction of 4D reconstruction, allowing a reduction of the total 4D acquisition duration. In addition, the use of input function estimated with the developed temporal regularization methods led to the improvement of the Patlak parameters estimation. Finally, the elastic respiratory motion correction led to a diminution of the estimation bias of both Patlak parameters, in particular for small lesions located in regions affected by the respiratory motion.
110

Degradação do antibiótico bacitracina zí­ncica em meio aquoso através de processos oxidativos avançados. / Degradation of antibiotic zinc bacitracin in aqueous medium by advanced oxidation processes.

Metolina, Patrícia 20 June 2018 (has links)
A presença de antibióticos no ecossistema representa um sério risco à saúde humana e animal em virtude do desenvolvimento crescente de resistência bacteriana. Uma vez que a maioria dos antibióticos é persistente à degradação biológica, os processos oxidativos avançados são apontados como uma das tecnologias mais efetivas para decompor esses compostos em águas residuárias. A bacitracina zíncica (Bc-Zn) é um potente antibiótico constituído por uma mistura complexa de peptídeos não-biodegradáveis, conjugados ao zinco. Apesar de ser um antibiótico amplamente consumido na medicina humana e animal, é preocupante a escassez de estudos que investigam sua degradação e destino ambiental. O presente trabalho analisou a degradação da Bc-Zn através dos processos de fotólise direta e UV/H2O2 em diferentes condições de radiação UVC e concentração inicial de H2O2. Os parâmetros cinéticos rendimento quântico da fotólise, constantes cinéticas de pseudo-primeira ordem e constante cinéticas de segunda ordem foram satisfatoriamente estimados pela modelagem do sistema fotoquímico experimental. Os resultados revelaram que a fotólise direta permitiu degradar todos os congêneres da mistura de Bc-Zn nas maiores doses de radiação UVC empregadas. No entanto, não houve remoção de TOC após 120 minutos de irradiação. A adição de H2O2 acelerou substancialmente a fotodegradação do antibiótico, apresentando constantes cinéticas de pseudo-primeira ordem uma ordem de grandeza superiores às obtidas por fotólise direta. Além disso, remoção considerável de até 71% do TOC foi alcançada. A análise estatística demonstrou que a radiação UV foi um fator bem mais significativo para a fotodegradação da Bc-Zn em relação à concentração inicial de H2O2, sendo as melhores condições do processo alcançadas para a maior taxa específica de emissão de fótons (1,11×10-5 Einstein L-1 s-1). Ensaios biológicos com soluções tratadas por fotólise direta e UV/H2O2 indicaram remoção completa da atividade antimicrobiana residual, ainda que os produtos da fotodegradação tenham se mostrado não-biodegradáveis. Análises de toxicidade indicaram que o metal zinco presente no antibiótico é responsável pela a toxicidade no micro-organismo-teste Vibrio fischeri. Estudos adicionais devem ser realizados para identificar os sub-produtos formados, bem como para investigar a degradação da Bc-Zn em efluentes industriais reais. / The presence of antibiotics in ecosystems represents a serious risk to human and animal health, caused by the increase in bacterial resistance. Since most antibiotics resist to biological degradation, advanced oxidation processes are pointed out as the most effective technologies for degrading these compounds in wastewater. Zinc bacitracin (Bc-Zn) is a potent antibiotic with a complex mixture of non-biodegradable peptides conjugated to zinc. Despite being a widely used antibiotic in human and animal medicine, the scarcity of studies dealing with its degradation and environmental fate is a matter of concern. In this work, Bc-Zn degradation by direct photolysis and the UV/H2O2 process was investigated for different UVC radiation conditions and initial H2O2 concentrations. Kinetic parameters, namely the photolysis quantum yield, pseudo-first order kinetic constants and second-order kinetic constants, were satisfactorily estimated from experimental data by modeling the photochemical system. The results showed that all the congeners of the Bc-Zn mixture were photolyzed at the highest UVC doses applied, while no TOC removal was observed after 120 minutes of irradiation. The addition of H2O2 substantially accelerated Bc-Zn photodegradation, with pseudo-first order kinetic constants of one order of magnitude higher than those observed under direct photolysis. In addition, a remarkable removal of up to 71% of TOC was achieved. Statistical analyses showed that UV radiation had a much more important effect on Bc-Zn photodegradation in comparison with initial H2O2 concentration, with the best process conditions achieved for the highest specific photon emission rate (1.11×10-5 Einstein L-1 s-1). Biological assays carried out with the solutions treated by direct photolysis and UV/H2O2 revealed no residual antimicrobial activity, though photodegradation products remained non-biodegradable. In addition, toxicity analyses indicated that the zinc metal present in the antibiotic is responsible for the toxic effect on the test microorganism Vibrio fischeri. Finally, further studies should be performed to identify the by-products formed and to investigate Bc-Zn degradation in real industrial wastewater.

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