The scope of this work is the theoretical and computational modeling of the interaction between a Newtonian fluid and a cellular biological medium attached on the surface of a vessel. First and foremost, an extensive and comprehensive review is presented with regard to the available approaches for modeling momentum transfer within cellular biological media, including single-scale-single-phase approaches, Biot's poroelasticity, mixture theory, upscaling methods and multiscale computational equation free methods. Thereafter, at the cellular biological medium level, a theoretical model is developed for the description of momentum transfer within a poroelastic biomaterial, taking into account the interaction between the extracellular fluid and the solid skeleton that consists of cells and extracellular matrix (ECM). A continuum based formulation of momentum transport in a fluid-solid system at the finer spatial scale is used as starting point, and then the method of local spatial averaging with a weight function is implemented in order to establish the partial differential equations that describe the dynamics of fluid flow and matrix deformation at the coarser (macroscopic) spatial scale. In the special case of a homogeneous medium and under certain other conditions, the derived equations become similar to those which are postulated in the theory of interacting continua (mixture theory) and Biot's theory of poroelasticity. At the vessel level, the contribution of this work is twofold. First, a benchmark problem is developed for the validation of numerical methods used to solve problems that involve interactions between a fluid and a poroelastic material. Specifically, an analytical solution is developed for the problem of plane Couette-Poiseuille flow past a poroelastic layer. Second, a computational study is performed for plane Poiseuille flow past and through a semi-elliptical poroelastic biomaterial, which is attached to the surface of a straight vessel. Fluid flow in the clear fluid region is described by the Navier-Stokes equations, and momentum transfer within the biomaterial is described by the upscaled biphasic equations established in this work. The effect of the Reynolds and Darcy number that characterize the flow past and through the biomaterial, respectively, is investigated for obstacles with different configuration with respect to flow (semicircle, oblate semi-ellipse, prolate semi-ellipse). The distribution of the von Mises stress within the biomaterial is determined and, also, the drag and lift forces exerted by the fluid on the biomaterial are calculated. / Στόχος της παρούσας εργασίας είναι η θεωρητική και υπολογιστική μοντελοποίηση της αλληλεπίδρασης μεταξύ ενός Νευτώνειου ρευστού και ενός κυτταρικού βιολογικού υλικού το οποίο βρίσκεται προσκολημμένο στην επιφάνεια ενός αγγείου. Αρχικά παρουσιάζεται μια εκτεταμένη και περιεκτική ανασκόπηση των διαθέσιμων προσεγγίσεων για τη μοντελοποίηση της μεταφοράς ορμής σε κυτταρικά βιολογικά υλικά, συμπεριλαμβανομένων των προσεγγίσεων μιας κλίμακας και μιας φάσης, της θεωρίας ποροελαστικότητας του Biot, της θεωρίας αλληλεπιδρώντων συνεχών, των τεχνικών αλλαγής κλίμακας προς τα άνω, και τέλος, των υπολογιστικών τεχνικών πολλαπλών κλιμάκων χωρις τον ορισμό καταστατικών εξισώσεων. Στην συνέχεια, στο επίπεδο του κυτταρικού βιολογικού υλικού, αναπτύσεται ένα θεωρητικό μοντέλο για την περιγραφή της μεταφοράς ορμής εντός ενός ποροελαστικού υλικού, λαμβάνοντας υπόψη την αλληλεπίδραση μεταξύ του εξωκυτταρικού ρευστού και της στερεής μήτρας που αποτελείται από τα κύτταρα και το δίκτυο εξωκυτταρικών πολυμερών. Ως σημείο εκκίνησης στην μικρότερη κλίμακα παρατήρησης, χρησιμοποιείται μια περιγραφή της μεταφοράς ορμής που βασίζεται σε ένα συνεχές μοντέλο και έπειτα εφαρμόζεται η μέθοδος χωρικής στάθμισης μέσω συνάρτησης βάρους προκειμένου να εξαχθούν οι μερικές διαφορικές εξισώσεις που περιγράφουν την δυναμική της ροής του εξωκυτταρικού ρευστού και της παραμόρφωσης της στερεής μήτρας στην μακροσκοπική κλίμακα. Για την ειδική περίπτωση ενός ομογενούς μέσου και υπό την ισχύ ορισμένων πρόσθετων συνθηκών, οι εξαχθείσες εξισώσεις λαμβάνουν μορφή παρόμοια με αυτή των αντίστοιχων εξισώσεων οι οποίες ισχύουν στην θεωρία αλληλεπιδρώντων συνεχών καθώς και στην θεωρία ποροελαστικότητας του Biot. Στο επίπεδο του αγγείου, η συνεισφορά της παρούσας εργασίας λαμβάνει χώρα σε δύο άξονες. Κατά πρώτον, αναπτύσσεται ένα πρότυπο πρόβλημα το οποίο μπορεί να χρησιμεύσει για την επαλήθευση αριθμητικών μεθόδων που χρησιμοποιούνται για την επίλυση προβλημάτων στα οποία ενέχεται η αλληλεπίδραση ενός ρευστού με ένα ποροελαστικό υλικό. Συγκεκριμένα, εξάγεται μια αναλυτική λύση σε κλειστή μορφή για το πρόβλημα της επίπεδης ροής Couette-Poiseuille μέσα και γύρω από ένα ποροελαστικό στρώμα. Κατά δεύτερον, διεξάγεται μια υπολογιστική μελέτη της επίπεδης ροής Poiseuille μέσα και γύρω από ένα ημιελλειπτικό ποροελαστικό βιολογικό υλικό, το οποίο βρίσκεται προσκολημμένο στην επιφάνεια ενός ευθύγραμμου αγγείου. Στην περιοχή καθαρού ρευστού, η ροή περιγράφεται από τις εξισώσεις Navier-Stokes , ενώ η μεταφορά ορμής εντός του βιολογικού υλικού περιγράφεται με τις εξισώσεις που εξήχθησαν σε αυτή την εργασία μέσω της μεθόδου χωρικής στάθμισης. Η επίδραση των αριθμών Reynolds και Darcy, οι οποίοι χαρακτηρίζουν τη ροή γύρω και μέσα από το βιολογικό υλικό αντίστοιχα, διερευνάται για εμπόδια με διάφορες γωμετρικές διαμορφώσεις (ημικύκλιο, και ημιέλλειψη). Προσδιορίζεται η χωρική κατανομή της τάσης von Mises εντός του βιολογικού υλικού και, επιπρόσθετα, υπολογίζονται η οπισθέλκουσα και η ανυψωτική δύναμη που ασκούνται από το ρευστό στο υλικό.

In this thesis, two studies of the diffractive phenomena in the electron proton collisions with the H1 detector at HERA are presented.<p>The first is the study of the inclusive elastic diffractive events $ep \ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

La première partie décrit trois expériences réalisées avec l'interféromètre atomique à jet de lithium supersonique développé à Toulouse. La seconde partie présente le nouvel interféromètre atomique à condensats de Bose-Einstein (CBE) développé dans le but de tester la neutralité de la matière. Les trois premières expériences exploitent l'interaction entre un atome de lithium et différents champs électromagnétiques. Une différence de potentiel électrique dépendant du temps a servi à moduler la phase des deux bras de notre interféromètre à des fréquences différentes, ce qui a permis une détection homodyne et hétérodyne d'ondes de matière. Une phase géométrique de la lumière (la phase de Pancharatnam) a été transférée à notre signal interférométrique par les réseaux de diffraction de Bragg ce qui a ajouté un nouvel outil à la panoplie permettant le contrôle d'ondes de matières. Enfin, un faisceau laser focalisé sur un seul des deux bras nous a permis de mesurer avec exactitude une des longueurs d'onde d'extinction du lithium (correspondant à une valeur de polarisabilité dynamique nulle). L'objectif du nouvel interféromètre à CBE est de réaliser une nouvelle mesure de la charge électrique résiduelle de la matière et en particulier des isotopes du rubidium 85Rb et 87Rb. Cette mesure nous permettra de connaître avec une plus grande sensibilité la différence de charge entre le proton et l'électron ainsi que la charge du neutron. Le principe de cette mesure repose sur une séparation spatiale importante entre les deux bras d'un interféromètre en fontaine ainsi que sur un temps de cycle de 5 s. Ces caractéristiques ont nécessité un travail de conception à la fois au niveau de la source (une puce à atome) et au niveau du phénomène de diffraction (séparation en impulsion importante) qui sera exposé dans un premier temps. Dans un second temps, les choix techniques en matière de chambre à vide, système laser et sources de champs magnétiques seront décrits et caractérisés. Enfin, les performances actuelles de cette source d'atomes froids seront présentées et comparées à nos attentes. / This thesis's first part describes the realization of three experiments using an atom interferometer operated with a lithium supersonic beam. The second part presents the development of a new BEC interferometer designed to test matter neutrality. The first three experiments rely on the interactions of lithium atom with different electromagnetic fields. A time dependent electric potential difference was used to produce phase modulation of both interferometer arms at different frequencies, leading to homodyne and heterodyne detection of atom waves. A geometric phase of light (the Pancharatnam phase) was successfully transferred to our interferometer signal during Bragg diffraction, enlarging the atom optics toolbox for phase control in an atom interferometer. Finally, a focused laser beam was used to measure accurately the value of one lithium tune-out wavelength (for which its dynamic polarizability is zero). The new BEC interferometer was designed to measure a possible non-zero electric charge of rubidium isotopes 85Rb and 87Rb with enhanced sensitivity to the electron-proton charge difference and neutron neutrality. This setup relies on a large spatial separation between the two interferometer arms in a fountain configuration aiming at a cycle time of 5s. These features required particular design work both on the atomic source (atom-chip) and the diffraction process (Large Momentum Transfer). The technical choices on the vacuum chambers, laser system and magnetic sources are described and characterized. Finally, the up-to-date cold-atom source performances is shown and compared to our expectations.

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No description available.

The performance of solid oxide fuel cells (SOFCs) at the cell and system levels is studied using computer simulation. At the cell level, a new model combining the cell micro and macro models is developed. Using this model, the microstructural variables of porous composite electrodes can be linked to the cell performance. In this approach, the electrochemical performance of porous composite electrodes is predicted using a micro-model. In the micro-model, the random-packing sphere method is used to estimate the microstructural properties of porous composite electrodes from the independent microstructural variables. These variables are the electrode porosity, thickness, particle size ratio, and size and volume fraction of electron-conducting particles. Then, the complex interdependency among the multi-component mass transport, electron and ion transports, and the electrochemical and chemical reactions in the microstructure of electrodes is taken into account to predict the electrochemical performance of electrodes. The temperature distribution in the solid structure of the cell and the temperature and species partial pressure distributions in the bulk fuel and air streams are predicted using the cell macro-model. In the macro-model, the energy transport is considered for the cell solid structure and the mass and energy transports are considered for the fuel and air streams. To demonstrate the application of the cell level model developed, entitled the combined micro- and micro-model, several anode-supported co-flow planar cells with a range of microstructures of porous composite electrodes are simulated. The mean total polarization resistance, the mean total power density, and the temperature distribution in the cells are predicted. The results of this study reveal that there is an optimum value for most of the microstructural variables of the electrodes at which the mean total polarization resistance of the cell is minimized. There is also an optimum value for most of the microstructural variables of the electrodes at which the mean total power density of the cell is maximized. The microstructure of porous composite electrodes also plays a significant role in the mean temperature, the temperature difference between the hottest and coldest spots, and the maximum temperature gradient in the solid structure of the cell. Overall, using the combined micro- and micro-model, an appropriate microstructure for porous composite electrodes to enhance the cell performance can be designed. At the system level, the full load operation of two SOFC systems is studied. To model these systems, the basic cell model is used for SOFCs at the cell level, the repeated-cell stack model is used for SOFCs at the stack level, and the thermodynamic model is used for the balance of plant components of the system. In addition to these models, a carbon deposition model based on the thermodynamic equilibrium assumption is employed. For the system level model, the first SOFC system considered is a combined heat and power (CHP) system that operates with biogas fuel. The performance of this system at three different configurations is evaluated. These configurations are different in the fuel processing method to prevent carbon deposition on the anode catalyst. The fuel processing methods considered in these configurations are the anode gas recirculation (AGR), steam reforming (SR), and partial oxidation reformer (POX) methods. The application of this system is studied for operation in a wastewater treatment plant (WWTP) and in single-family detached dwellings. The evaluation of this system for operation in a WWTP indicates that if the entire biogas produced in the WWTP is used in the system with AGR or SR fuel processors, the electric power and heat required to operate the plant can be completely supplied and the extra electric power generated can be sold to the electrical grid. The evaluation of this system for operation in single-family detached dwellings indicates that, depending on the size, location, and building type and design, this system with all configurations studied is suitable to provide the domestic hot water and electric power demands. The second SOFC system is a novel portable electric power generation system that operates with liquid ammonia fuel. Size, simplicity, and high electrical efficiency are the main advantages of this environmentally friendly system. Using a sensitivity analysis, the effects of the cell voltage at several fuel utilization ratios on the number of cells required for the SOFC stack, system efficiency and voltage, and excess air required for thermal management of the SOFC stack are studied.

The performance of solid oxide fuel cells (SOFCs) at the cell and system levels is studied using computer simulation. At the cell level, a new model combining the cell micro and macro models is developed. Using this model, the microstructural variables of porous composite electrodes can be linked to the cell performance. In this approach, the electrochemical performance of porous composite electrodes is predicted using a micro-model. In the micro-model, the random-packing sphere method is used to estimate the microstructural properties of porous composite electrodes from the independent microstructural variables. These variables are the electrode porosity, thickness, particle size ratio, and size and volume fraction of electron-conducting particles. Then, the complex interdependency among the multi-component mass transport, electron and ion transports, and the electrochemical and chemical reactions in the microstructure of electrodes is taken into account to predict the electrochemical performance of electrodes. The temperature distribution in the solid structure of the cell and the temperature and species partial pressure distributions in the bulk fuel and air streams are predicted using the cell macro-model. In the macro-model, the energy transport is considered for the cell solid structure and the mass and energy transports are considered for the fuel and air streams. To demonstrate the application of the cell level model developed, entitled the combined micro- and micro-model, several anode-supported co-flow planar cells with a range of microstructures of porous composite electrodes are simulated. The mean total polarization resistance, the mean total power density, and the temperature distribution in the cells are predicted. The results of this study reveal that there is an optimum value for most of the microstructural variables of the electrodes at which the mean total polarization resistance of the cell is minimized. There is also an optimum value for most of the microstructural variables of the electrodes at which the mean total power density of the cell is maximized. The microstructure of porous composite electrodes also plays a significant role in the mean temperature, the temperature difference between the hottest and coldest spots, and the maximum temperature gradient in the solid structure of the cell. Overall, using the combined micro- and micro-model, an appropriate microstructure for porous composite electrodes to enhance the cell performance can be designed. At the system level, the full load operation of two SOFC systems is studied. To model these systems, the basic cell model is used for SOFCs at the cell level, the repeated-cell stack model is used for SOFCs at the stack level, and the thermodynamic model is used for the balance of plant components of the system. In addition to these models, a carbon deposition model based on the thermodynamic equilibrium assumption is employed. For the system level model, the first SOFC system considered is a combined heat and power (CHP) system that operates with biogas fuel. The performance of this system at three different configurations is evaluated. These configurations are different in the fuel processing method to prevent carbon deposition on the anode catalyst. The fuel processing methods considered in these configurations are the anode gas recirculation (AGR), steam reforming (SR), and partial oxidation reformer (POX) methods. The application of this system is studied for operation in a wastewater treatment plant (WWTP) and in single-family detached dwellings. The evaluation of this system for operation in a WWTP indicates that if the entire biogas produced in the WWTP is used in the system with AGR or SR fuel processors, the electric power and heat required to operate the plant can be completely supplied and the extra electric power generated can be sold to the electrical grid. The evaluation of this system for operation in single-family detached dwellings indicates that, depending on the size, location, and building type and design, this system with all configurations studied is suitable to provide the domestic hot water and electric power demands. The second SOFC system is a novel portable electric power generation system that operates with liquid ammonia fuel. Size, simplicity, and high electrical efficiency are the main advantages of this environmentally friendly system. Using a sensitivity analysis, the effects of the cell voltage at several fuel utilization ratios on the number of cells required for the SOFC stack, system efficiency and voltage, and excess air required for thermal management of the SOFC stack are studied.