Le dioxyde d'uranium UO2 est utilisé en tant que combustible standard dans les réacteurs à eau pressurisée (REP). Pour cette raison il est très important de bien connaître ses propriétés mécaniques, thermiques et physico-chimiques dans les conditions de fonctionnement normales ou accidentelles (600K - 2000K). Lors des réactions de fission de l'uranium, des gaz rares tels que le Xe et Kr sont générés. Ces atomes présentent une très faible solubilité dans la matrice combustible et vont donc soit être relâchés, soit former des bulles de gaz (intra ou intergranulaires) au sein de l'UO2. La présence de ces bulles modifie les propriétés thermomécaniques du combustible. Les enjeux en terme de sûreté, liés à la présence de ces bulles, ont donné lieu à d'importants travaux, tant sur le plan expérimental que théorique, afin d'accroître la compréhension de l'ensemble des propriétés physiques et du comportement du combustible. L'objectif de nos travaux est de mieux comprendre l'impact de bulles de gaz intragranulaires sur le comportement du combustible au moyen de modélisations atomistiques. Dans un premier temps, l'impact de cavités intragranulaires sur les propriétés thermomécaniques (comportement élastique, dilatation thermique et conductivité thermique) ont été étudiées par des approches semi-empiriques. Un soin particulier a été porté à l'étude des effets d'interfaces pour ces cavités nanométriques. Dans un deuxième temps, nous avons procédé à un remplissage physique de ces cavités par du xénon et nous avons étudié la microstructure et les pressions régnant au sein des bulles. / ...

We  are increasingly turn to social media for our news consumption two related media phenomenon that influence media consumption are the “Echo chamber” and “Filter Bubble”. Echo chamber this the phenomenon that we tend to have conversation only with those that has the same likeminded as we do while Filter bubble is created by Social media and information retrieval technology that tends to priorities showing us things it already know we like. The aim of this thesis is to suggest design solution for social media that may counter the effect of “Echo chamber” and “Filter Bubble”. The precise method used on this thesis is play centric design method and both intermediate and final evaluations were done through qualitative evaluation. At the end a design solution of Viewlette game were presented. It can be concluded that the suggested design solution may have the tendency to counter the effect of Filter bubble and Echo chamber on social networking site by enabling people that has conflicting points of view to still listen to each other and understand an argument from different perspective. / Som vi i allt högre grad vänder  oss till sociala medier för vår nyhetskonsumtion, två besläktade medier fenomen som påverkar mediekonsumtion är "Ekokammare" och "Filter Bubble". Ekokammare är fenomen där vi tenderar att ha samtal endast med dem som har samma intresse som vi själva, medan Filter bubbla skapas av sociala medier och informationssöknings teknik som tenderar att prioriteringar och visar oss saker man redan vet att vi gillar. Syftet med denna avhandling är att föreslå konstruktionslösningen för sociala medier som kan motverka effekten av "Echo kammare" och "Filter Bubble". Den exakta metod som används på denna avhandling är att spela centrerade designmetod och både den mellanliggande och slutliga utvärderingen som görs genom kvalitativ bedömning. I slutet presenterades en designlösning av ”Viewlette”- spelet. Man kan dra slutsatsen att den föreslagna designlösningen kan ha en tendens att motverka effekten av “Filter bubble” och “Echo chamber” på nätgemenskap, genom att människor som har motstridiga synpunkter fortfarande lyssna på varandra och förstå ett argument från olika perspektiv.

La connaissance du comportement hydrodynamique et du transfert de matière de la bulle est importante car elle fournira des indications pour la sélection des conditions de fonctionnement et la conception du réacteur dans de tels processus. Cette thèse a réalisé une étude expérimentale pour les bulles d’air isolées en ascension dans diverses solutions de polymères (Breox, Polyacrylamide (PAAm) and Xanthan gum) qui peuvent simuler les propriétés des eaux usées. Les travaux sont divisés en trois parties: Tout d’abord, en dressant l’état de l'art sur les techniques de visualisation pour le transfert de matière, trois techniques ont été testées pour les bulles d’air (diamètre équivalent ≈ 1 mm) en ascension dans l'eau, notamment la fluorescence induite par plan laser (PLIF, fluorophore: résorufine fluorescente), la PLIF avec inhibition (fluorophore: complexe de ruthénium) et techniques colorimétriques (colorant: résorufine rose), respectivement. Par la suite, sur la base des images capturées par une caméra haute vitesse, le comportement hydrodynamique des bulles d'air (diamètres équivalents: 0,7 à 7 mm) s'élevant dans les solutions de polymères (PAAm et Xanthan) a été étudiée, notamment la vitesse, la trajectoire et la forme de la bulle. Enfin, appliquant la technique PLIF-I, les phénomènes de transfert de matière et de diffusion dans le sillage de bulles d'air (diamètre équivalent 1 ≈ mm) dans différentes solutions aqueuses de polymères (PAAm et Breox) ont été étudiés. / The knowledge on the hydrodynamic property and mass transfer of bubbles is important since it will give guidelines for selecting the operation condition and for reactor design in such processes. For this purpose, this PhD manuscript has implemented an experimental investigation of single air bubbles rising in various polymer solutions (Breox, Polyacrylamide (PAAm) and Xanthan gum) which can simulate the property of the sewage. The works can divided into three parts: Firstly, with a review of the current visualization techniques for mass transfer, three techniques have been tested for air bubble (equivalent diameter ≈ 1 mm) rising in water including traditional Planar Laser Induced Fluorescent (PLIF, dye: fluorescent resorufin), Fluorescent quenching technique (PLIF with Inhibition, dye: ruthenium complex) and colorimetric techniques (dye: pink resorufin), respectively. Secondly, based on images captured by a high speed camera, the hydrodynamics of the bubble single air bubbles (equivalent diameters: 0.7-7 mm) rising in the polymer solutions (PAAm and Xanthan) have been investigated including the bubble velocity, trajectory and bubble shape. Finally, based on PLIF-I technique, the mass transfer and diffusion phenomena in the wake of single air bubbles (equivalent diameter ≈ 1 mm) rising in various aqueous polymer solutions (PAAm and Breox) are investigated.

The two-phase flow displacement of a viscous fluid by a less viscous one in a confined environment leads to a viscous fingering instability commonly encountered in natural systems, for example, in flows through porous media or pulmonary airways. The classical study of viscous fingering has been conducted in rectangular channels of high aspect ratio (large channel width/height), known as Hele-Shaw channels where a unique, steady symmetric, semi-infinite bubble (finger) emerges. In this Journal Format thesis, the propagation of semi-infinite (open) and finite (closed) air bubbles is considered in Hele-Shaw channels where thin, axially-uniform occlusions are introduced. This configuration is known to generate symmetric, asymmetric and oscillatory modes with complex interactions and rich behaviour. Numerical results of finger propagation using a depth-averaged model in these constricted channels are found to be in quantitative agreement with experimental results once the aspect ratio reaches a value of $\alpha\geq40$ and capillary numbers below $Ca\leq 0.012$. The same evolution of the bifurcation scenario between multiple modes is found, however, it occurs for decreasing values of occlusion height as the value of aspect ratio is increased that the system exhibits sensitivity to small but finite depth-variations. The numerical simulations reveal multiple-tipped unstable symmetric solutions which interact with the single symmetric mode at vanishing occlusion heights resulting in stabilisation of the asymmetric and oscillatory modes. Moreover, deviations from the single symmetric mode are predicted when depth-variations of order of the roughness of the channel walls ($\sim 1$ $\mu$m) are introduced for larger aspect ratios of $\alpha\geq 155$. The propagation of finite bubbles is studied in a channel with constant aspect ratio of $\alpha=30$ and where the height of the occlusion, termed rail, is $1/40$ of the channel height. For bubble diameters of the order of the rail width, a tongue-shaped stability boundary for symmetric (on-rail) propagation is encountered so that for flow rates marginally larger than a critical value, a narrow band of bubble sizes can propagate (stably) over the rail while bubbles of other sizes segregate to the side of the rail. The numerical depth-averaged model is adapted for bubble propagation and captures in qualitative agreement the experimental observations. Time-dependent calculations are additionally performed, showing that on-rail bubble propagation is the result of a non-trivial dynamical interaction between capillary and viscous forces.

Light intensity distribution studies in the heterogeneous photocatalytic reactors were carried out successfully with potassium ferrioxalate chemical actinometry, reproducible light intensity estimates of the irradiation source were obtained. The increased light intensity in the reactor system increased the absorption as determined by actinometry. It was found that reflectivity was a dependent variable but mesh opening area was an independent variable. The photocatalytic mineralization of dichoroacetic acid DCAA, in the presence of TiO2 immobilized on a plate in an externally irradiated bubble column photoreactor had been investigated. The mass transfer and activity evaluation were measured. It was found that increasing the catalyst thickness, increased the photoactivity until it reaches the optimum loading, further loading increase caused the reaction rate to remain constant. This phenomenon was observed with increased lamp power (intensity) and initial solute concentration. However, the catalyst activity was not influenced by the increasing concentration of dissolved oxygen. The reaction rate for DCAA photomineralization was expressed using the Langmuir-Hinsheldwood model.

In bubble dynamics, an underwater bubble may evolve from being singly-connected to being toroidal. Furthermore, two or more individual bubbles may merge to form a single large bubble. These dynamics involve significant topological changes such as merging and breaking, which may not be handled well by front-tracking boundary element methods. In the level set method, topological changes are handled naturally through a higher-dimensional level set function. This makes it an attractive method for bubble simulation. In this paper, we present a method that combines the level set method and the boundary element method for the simulation of bubble dynamics. We propose a formulation for the update of a potential function in the level set context. This potential function is non-physical off the bubble surface but consistent with the physics on the bubble surface. We consider only axisymmetric cavitation bubbles in this paper. Included in the paper are some preliminary results and findings. / Singapore-MIT Alliance (SMA)

In this paper, a new methodology for predicting fluid free surface shape using Model Order Reduction (MOR) is presented. Proper Orthogonal Decomposition combined with a linear interpolation procedure for its coefficient is applied to a problem involving bubble dynamics near to a free surface. A model is developed to accurately and efficiently capture the variation of the free surface shape with different bubble parameters. In addition, a systematic approach is developed within the MOR framework to find the best initial locations and pressures for a set of bubbles beneath the quiescent free surface such that the resultant free surface attained is close to a desired shape. Predictions of the free surface in two-dimensions and three-dimensions are presented. / Singapore-MIT Alliance (SMA)

Multiple scattering effects from bubble clouds are investigated in this study. A high performance, general purpose numerical tool for multiple scattering calculations is developed. This numerical tool is applied in three computational scenarios in this study. The total scattering cross section of a bubble cloud is investigated. Numerical results indicate that the resonant frequency of the bubble cloud is much lower than that of a single bubble. The variation of resonant frequency of multiple scattering is also studied. It is found that the resonant frequency decreases as the number of bubbles increases, or as the void fraction of the bubble cloud decreases. Phase distributions of bubble oscillations in various multiple scattering scenarios are presented. It is found that, at resonance, the bubbles synchronize to the same phase, which is indicative of the lowest mode of collective oscillation. At wave localization, half of the bubbles oscillate at phase 0 while the other half oscillate at phase Pi. An intuitive interpretation of this behavior is given.

Bubbles are often present in the natural ocean. Bubbly liquid will have the significant influence the sound propagation, and creates a significant disturbance to under water target's detection. Therefore, it is an important research subject of bubble influence to the sound wave propagation. This study used the sonar training system which developed by British's iTP corporation, through suitable additional design discuss the attenuation of sound propagating through a bubble screen. At first this study collects and infers the formula by the literature review. Secondly, the experimental design of measuring the attenuation of sound wave. The experiment process by using two parallel iron boards to carry on the measurement of gas-volume fraction. Then correlate with the sound pressure from the measurement of hydrophone. After curve fitting, we can clearly know the each other correlation. Finally taking the result compare with the attenuation coefficient formula. The experimental consists of two parts. The first part is to measure the gas-volume fraction of the bubbly liquid contained in the screen; while the second part is to measure the sound attenuation of the bubble screen. The result display that the bubble screen can attenuate about 8 dB per centimeter as the gas-volume fraction stay at 1 percent. At high gas-volume fraction the coefficient of attenuation has increased, and is different from theoretical value. This is because the bubble's correlation has not been considered. In addition, the low frequency sound wave is close to theoretical value, but the high frequency sound wave has big different to theoretical value. Because the high frequency sound wave's wavelength is too small to satisfy the condition. At experiment I suggest to use more appropriate transducers and precise bubble's tube. Thus the experimental result will be better.

Bubble CPAP (BCPAP) is used in the neonatal intensive care unit (NICU) as a form of non-invasive ventilation and is commonly employed in neonates demonstrating respiratory distress. BCPAP may be used to avoid the need for intubation and mechanical ventilation thereby reducing lung injury and other morbidities as well as decrease hospital stay. PURPOSE: The purpose of this study is to retrospectively investigate the length of stay on bubble CPAP (BCPAP) considering gestational age, birth weight, and surfactant delivery in the neonatal population born at an urban tertiary high load level three (NICU). METHODS: A retrospective study using existing data from an urban tertiary high load level three NICU was completed. DATA ANALYSIS: Data analysis was performed using SPSS 16.0. Descriptive statistics were run for each variable. Contingency tables were run to determine if gestational age at birth, birth weight, and length of time on BCPAP had significance compared to surfactant delivery. Intercorrelations were run to determine if gestational age at birth, birth weight, and length of time on BCPAP had an effect on each other. Davis conventions were used to analyze the results. RESULTS: Descriptive statistics indicated the mean gestational age at birth to be 32.263 weeks, SD = +2.978, mean neonatal weight to be 1.899 kg, SD = +0.728, and mean length of time on BCPAP to be 124.430 hours, SD = +185.474. Contingency statistics showed a substantial association (reta = 0.562) between the gestational age at birth and surfactant delivery, a very strong association (reta = 1.000) between the birth weight and surfactant delivery, and a very strong association (reta = 0.914) between the length of time the neonate was on BCPAP and surfactant delivery. Pearson product-moment correlation coefficients showed gestational age at birth had a very strong positive association with birth weight (r = 0.811, p < 0.01) and a moderate negative association with length of time on BCPAP (r = -0.439, p < 0.01). Intercorrelations also showed birth weight had a moderate negative association with length of time on BCPAP (r = -0.306, p < 0.01). CONCLUSIONS: The neonate was less likely to receive surfactant if, their gestational age was older at birth, they had a heavier birth weight, and their length of time on BCPCP was shorter. The data also demonstrated that the older the neonate’s gestational age at birth and the heavier the neonatal birth weight equated to a shorter length of time on BCPAP. Lastly the data demonstrated that the heavier the neonate’s birth weight, the shorter length of time on BCPAP.