Le choix de la filière SFR (Sodium Fast Reactor : Réacteurs à neutrons rapides refroidis par du sodium liquide), par la France conduit à la réalisation d’un prototype de quatrième génération nommé ASTRID. Le développement de ce type de réacteurs présente plusieurs défis, en particulier du point de vue de l’amélioration de la démonstration de la sûreté et de la surveillance du fonctionnement. Cette dernière passe, entre autres, par la caractérisation de l’engazement du sodium liquide (présence de microbulles de gaz). La caractérisation de l’engazement est l’objet de cette étude, elle implique la détermination du taux de vide (fraction volumique de gaz) et de l’histogramme des rayons des microbulles. Le travail bibliographique réalisé a montré que les techniques acoustiques linéaires de caractérisation des nuages de bulles ne permettaient pas de répondre pleinement à cette problématique, en revanche des pistes prometteuses ont été identifiées en étudiant les techniques acoustiques non linéaires. Cette dernière voie a par conséquent été explorée. Un banc expérimental en eau permettant la génération et le contrôle optique de nuages de microbulles nous a permis de valider finement la reconstruction d’histogrammes des rayons grâce à une technique de mixage nonlinéaire d’une haute fréquence avec une basse fréquence. La potentialité du mixage de deux hautes fréquences, plus intéressante d’un point de vue industriel, a par ailleurs été démontrée. Enfin, les bases de la transposition originale d’une technique de spectroscopie de résonance non linéaire appliquée à un nuage de bulles ont été posées, grâce à la mise en place de résonateurs acoustiques. Les résultats obtenus offrent de nombreuses perspectives, tant du point de vue des applications industrielles que du point de vue plus fondamental de la compréhension du comportement acoustique non linéaire d’une bulle excitée par plusieurs fréquences et d’un nuage de bulles excité à basse fréquence. / The SFR system chosen (Sodium Fast Reactor: fast neutron reactors cooled by liquid sodium) by France led to afourth-generation prototype named ASTRID. The development of this kind of reactors presents several challenges, particularly in terms of improving the safety and monitoring operation. This involves, among other things, characterization of the bubbles presence in liquid sodium. The characterization of the bubbles presence is the subject of this thesis. It involves the determination of void fraction (gas volume fraction) and histogram of the radiiof bubbles. The bibliographic work done has shown that linear acoustic techniques for the characterization of bubble clouds are inadequate to achieve this. However promising leads have been identified by studying nonlinear acoustic techniques. This last idea has therefore been explored. An experimental water bench for the generation and optical control of microbubbles cloudallowed us to validate finely the reconstruction of histograms of radii through a technique of nonlinear mixing of a high frequency with a low frequency. The potential of the mixing of two high frequencies, more interesting for the industrial point of view has also been demonstrated. Finally, the bases of the transposition of an original technique of nonlinear resonance spectroscopy applied to a bubbles cloud were explored through the introduction of acoustic resonators. The results offer many interesting opportunities, both in terms of industrial applications and formore fundamental understanding of non-linear behavior of a bubble excited by multiple frequencies and of bubbles clouds excited at low frequency.

The aim of this study was to investigate the perception of personalization on news applications and to examine to what extent it is seen as an optimal solution for users to receive information. Due to the growth of online news and digital journalism the amount of information that is being published online is significantly higher nowadays than it has previously been. Therefore, a recommendation system called personalization has been introduced to choose content for the reader. Many concerns of personalization have already been brought to light, these concerns are believed to be contributing to filter bubbles and echo chambers. This study will investigate these concerns further in order to understand the users. The methodology used in the study were semi-structured interviews and an analysis based on the concerns brought forward by Borgesius et al. Six interviews were conducted with users and two were conducted with major news organizations in Sweden. The results of the study indicate that users fear personalization will cause filter bubbles and polarization due to them only being subjected to one perspective. The users are unaware as to how personalization works and therefore question why it is being introduced into news applications. Due to personalization being a new phenomenon news applications it is not yet seen as an optimal solution by users or news organizations. There are, however, many factors that can assist in its development such as transparency and awareness of the phenomenon.

L'une des principales missions de l'Ifremer consiste à étudier les ressources sous-marines et les fonds marins via une flotte océanographique importante, employée à travers le globe. Pour ce faire, les navires sont équipés d'équipements acoustiques de type SONAR afin d'obtenir les informations recherchées dans la colonne d'eau. Dans certaines conditions de navigation, la houle et les mouvements du navire génèrent un entraînement d'air conséquent sous la surface. Des nuages de bulles sont ainsi formés et entraînés sous la carène par l'écoulement. L'interaction entre ces bulles et les ondes acoustiques peuvent entraîner des pertes de données, et par conséquent une diminution importante de la productivité du navire. Les outils permettant l'étude du phénomène sont actuellement limités. Les modèles numériques ne sont pas suffisamment performants, pour simuler conjointement les mécanismes d'entraînement d'air à l'étrave puis l'écoulement dysphasique autour de la carène, et les essais classiques en bassin de traction ne donnent pas entière satisfaction. Dans le cadre de cette thèse, une méthode d'essai spécifique, pour l'étude de ce phénomène, a été développée et mise en place au bassin à houle et courant de l'Ifremer. Cette méthode nécessite la synchronisation entre un générateur de houle et un générateur de mouvement (hexapode), permettant d'imposer les mouvements calculés au préalable par simulation numérique à la maquette. Cette configuration permet d'étudier indépendamment les effets de la houle et des mouvements sur la génération des bulles. L'instrumentation employée permet de filmer et de caractériser l'entraînement d'air à l'étrave de la maquette. Deux mécanismes distincts ont été observés : la génération de bulles par entraînement tourbillonnaire ou par le déferlement de la vague d'étrave. Une méthode de traitement d'image a été élaborée pour analyser ces mécanismes pour de nombreuses configurations d'essais. Une étude paramétrique a été réalisée afin de calculer la fréquence de génération de bulles en fonction de chaque paramètre d'essai. Des mesures PIV de l'écoulement permettent de corréler la dynamique des nuages de bulles et de l'écoulement. L'ensemble des résultats obtenus permet d'apporter des éléments nouveaux pour la compréhension et l'étude du phénomène, avec la perspective d'obtenir un outil fiable facilitant la conception des navires océanographiques. / One of the main assignments of Ifremer is to study the seabed and the resources undersea, through a large oceanographic fleet used across the globe. For that purpose, ships are equipped with different kinds of SONAR (SOund Navigation And Ranging) to obtain the information sought in the water column. In some sea conditions, waves and ship motions generate significant air entrainment below the surface. Bubble clouds are then carried under the hull by the flow. The interaction between these bubbles and the acoustic waves may result in data loss, and therefore in a considerable reduction of the vessel’s productivity. The tools used to study this phenomenon are currently limited : the numerical models are not efficient enough to simulate at a time air entrainment at the bow and the two phase flow around the hull. On the other hand conventional towing tank tests are not entirely satisfactory. During this PhD research work, a specific test method to study this phenomenon has been developed and implemented at the Ifremer wave and current tank. This method requires the synchronization between a wave generator and a movement generator (hexapod) that enables to force the model motions, calculated in advance by numerical simulations. With this configuration, the effects of waves or motions characteristics on the bubbles generation can be studied independently. A complete instrumentation allowed to acquire images sequences to characterize the air entrainment at the bow of the model. Two distinct mechanisms have been observed : the generation of bubbles by vortex shedding or by the breaking bow wave. A post-processing method has been developed to analyse these mechanisms, for many test configurations. A parametric study was performed to calculate the frequency of bubbles generation for each test parameter. PIV measurements allowed to correlate the dynamic of bubbles clouds with the own flow dynamic. The overall results provide new elements for the understanding and the study of the phenomenon, with the final objective of obtaining a reliable tool that facilitates the design of research vessels.

The current work has developed a CFD model to characterise a pseudo-annular photocatalytic bubble column reactor. The model development was divided into three stages. Firstly, hydrodynamic assessment of the multiphase fluid flow in the vessel, which incorporated residence time distribution analysis both numerically and experimentally for validation purposes. Secondly, the radiation distribution of the UV source was completed. The final stage incorporated the kinetics for the degradation the model pollutant, sodium oxalate. The hydrodynamics were modelled using an Eulerian-Eulerian approach to the multiphase system with the standard k- turbulence model. This research established that there was significant deviation in the fluid behaviour in the pseudo-annular reactor when compared with traditional cylindrical columns due to the nature of the internal structure. The residence time distribution study showed almost completely mixed flow in the liquid phase, whereas the gas phase more closely represented plug flow behaviour. Whilst there was significant dependence on the superficial gas flow rate the mixing behaviour demonstrated negligible dependence on the liquid superficial velocity or the liquid flow direction, either co- or counter- current with respect to the gas phase. The light distribution was modelled using a conservative variant of the Discrete Ordinate method. The model examined the contribution to the incident radiation within the reactor of both the gas bubbles and titanium dioxide particles. This work has established the importance of the gas phase in evaluating the light distribution and showed that it should be included when examining the light distribution in a gas-liquid-solid three-phase system. An optimal catalyst loading for the vessel was established to be 1g/L. Integration of the kinetics of sodium oxalate degradation was the final step is developing the complete CFD model. Species transport equations were employed to describe the distribution of pollutant concentration within the vessel. Using a response surface methodology it was shown that the reaction rate exhibited a greater dependency on the lamp power that the lamp length, however, the converse was true with the quantum efficiency. This work highlights the complexity of completely modelling a photocatalytic system and has demonstrated the applicability of CFD for this purpose.

<p>To improve the control of a steel casting process ABB has developed an Electro Magnetic Brake (EMBR). This product is designed to improve steel quality, i.e. reduce non-metallic inclusions and blisters as well as risk of surface cracks. There is a demand of increasing the steel quality and in order to optimize the steel casting, simulations and experiments play an important role in achieving this. An advanced CFD simulation model has been created to carry out this task.</p><p>The validation of the simulation model is performed on a water model that has been built for this purpose. This water model also makes experiments possible. One step to the simulation model is to measure the velocity and motion pattern of the seeding particles and the air bubbles in the water model to see if it corresponds to the simulation results. </p><p>Since the water is transparent, seeding particles have been added to the liquid in order to observe the motion of the water. They have the same density as water. Hence the particles will follow the flow accurately. The motions of the air bubbles that are added into the water model need also to be observed since they influence the flow pattern.</p><p>An algorithm - ”Transparent motions” - is thoroughly inspected and implemented. ”Transparent motions” was originally designed to post process x-ray images. However in this thesis, it is investigated whether the algorithm might be applicable to the water model and the image sequences containing seeding particles and air bubbles that are going to be used for motion estimation.</p><p>The result show satisfying results for image sequences of particles only, however with a camera with a faster sampling interval, these results would improve. For image sequences with both bubbles and particles no results have been achieved. </p>

<p><strong>Variations in fertility have caused a problematic situation in Sweden among other European countries. According to </strong>the Council of Europe we are facing an economic and demographic challenge, when the baby boomers of the 1940’s are retiring. <strong>Economists have for a long time studied the connection between economic factors and fertility, and several studies have found a correlation between business cycles and birth rates. This connection is again of current interest 2008, when a financial bubble bursts at the same time as a baby boom occurs. A similar event happened in 1992 when the latest baby boom occurred at the same time as a financial bubble.</strong></p><p><strong> </strong></p><p>This study investigates the correlation between real disposable income, employment among women, the price development of small houses, family policies and fertility during the period 1960-2008. The conclusions are reached by studies of earlier research and literature on economic theory of fertility. In the analysis theories and the results of earlier research are compared to empiric macro data taken from the Swedish Statistical Agency.</p><p> </p><p>The conclusions are that a causal relation between economic factors and fertility exists, but it is not obvious; is fertility affected by variations in economic factors or the opposite? Employment affects both women’s income and their entitlement to parental benefit, which means that fertility and female employment are closely connected. Both financial bubbles and baby booms arise from the same psychological factors, which are rarely explained in economic models. When the Swedish parental benefit was introduced it had two effects; first it made the average age of women having their first baby increase, and secondly fertility became more closely connected to business cycles.<em>  </em></p>

We present methods for incorporating bubbles into a photorealistc fluid simulation. Previous methods of fluid simulation in computer graphics do not include bubbles. Our system automatically creates bubbles, which are simulated on top of the fluid simulation. These bubbles are approximated by spheres and are rendered with the fluid to appear as one continuous surface. This enhances the overall realism of the appearance of a splashing fluid for computer graphics. Our methods leverage the particle level set representation of the fluid surface. We create bubbles from escaped marker particles from the outside to the inside. These marker particles might represent air that has been trapped within the fluid surface. Further, we detect when air is trapped in the fluid and create bubbles within this space. This gives the impression that the air pocket has become bubbles and is an inexpensive way to simulate the air trapped in air pockets. The results of the simulation are rendered with a raytracer that includes caustics. This allows the creation of photorealistic images. These images support our position that the simple addition of bubbles included in a fluid simulation creates results that are much more true to life.

Variations in fertility have caused a problematic situation in Sweden among other European countries. According to the Council of Europe we are facing an economic and demographic challenge, when the baby boomers of the 1940’s are retiring. Economists have for a long time studied the connection between economic factors and fertility, and several studies have found a correlation between business cycles and birth rates. This connection is again of current interest 2008, when a financial bubble bursts at the same time as a baby boom occurs. A similar event happened in 1992 when the latest baby boom occurred at the same time as a financial bubble.   This study investigates the correlation between real disposable income, employment among women, the price development of small houses, family policies and fertility during the period 1960-2008. The conclusions are reached by studies of earlier research and literature on economic theory of fertility. In the analysis theories and the results of earlier research are compared to empiric macro data taken from the Swedish Statistical Agency.   The conclusions are that a causal relation between economic factors and fertility exists, but it is not obvious; is fertility affected by variations in economic factors or the opposite? Employment affects both women’s income and their entitlement to parental benefit, which means that fertility and female employment are closely connected. Both financial bubbles and baby booms arise from the same psychological factors, which are rarely explained in economic models. When the Swedish parental benefit was introduced it had two effects; first it made the average age of women having their first baby increase, and secondly fertility became more closely connected to business cycles.

Financial bubbles are characterized by a large increase in the economic growth on the market as a whole or in specific industries. The change gives rise to an increase in the capital needed to finance this growth. Companies typically have a choice between equity and debt capital to finance its business and the mix of these types of capital is often referred to as the company’s capital structure. There has been a lot of research done in the field of financial bubbles and of capital structure, as of yet no studies seem to address these two areas in combination. The aim of this study is to examine if financial bubbles affect a company’s capital structure and through this also examine if the supposed changes in capital structure can be generalized. The study comprise of two identical time-series which examines the changes in leverage and the choice of financing during the Swedish real estate bubble in the early nineties and the IT-crash at the end of the 2000th century. The study examines changes in leverage, price-to-book ratio and the choice between issuing convertible debt versus issuing equity, of eleven real estate companies and twelve IT-companies respectively. This paper shows that a company’s capital structure is indeed affected by a financial bubble though the way it is affected during different financial bubbles differs. Significant changes in leverage and the choice between different types of financial instruments are identified in both time-series. The study also shows that neither the Pecking Order Hypothesis as presented by Myers (1984) nor the traditional trade-off theory can in whole explain these changes. A significant difference in leverage between the two groups can be identified which is consistent with earlier empirical studies on the difference between capital structures in different industries. The results in this study seem to indicate that the changes in capital structure can be explained either by a supposed disturbance in the cost of different types of capital during the financial bubble or by the assumption that companies in specific industries (as the IT-industry) do not have the possibility to chose the type of financing freely.

This thesis is a statement about a series of paintings based on an invented dollhouse object that conveys the artist’s identity and placement in the world. Through this essay, the artist represents the home as a space that fosters the recovery and rebirth of invisible energy, ki and examines ideas of transience, interconnection, and rebirth in the mysterious flow of ki in the home. Also the artist will explain her own view about being an artist, the methodologies and specific techniques of her paintings, and her artistic direction for the future.