Development of new asphalt technologies to reduce both energy consumption and CO2 production has attracted great interest in recent years. The use of foam bitumen, as one of them, is attractive due to the low investment and production cost. Formation and decay of foam bitumen is a highly dynamic temperature dependent process which makes characterization difficult. In this thesis, new experimental tools were developed and applied for characterizing the foam bitumen during the hot foaming process.  One of the main goals of this study was to improve understanding and characterization of the foam bitumen formation and decay. X-ray radiography was used to study the formation and decay of foam bitumen in 2D representation. The results demonstrate that the morphology of bubble formation depends on the types of bitumen used. Moreover, theoretical investigation based on the 3D X-ray computed tomography scan dataset of bubble merging showed that the disjoining pressure increased as the gap between the bubbles in the surface layer (foam film) decreased with time and finally was ruptured.   Examining the foam bitumen stream right at the nozzle revealed that foam bitumen at a very early stage contains fragmented pieces of irregular size rather resembling a liquid than foam. The result from thermogravimetric analysis demonstrated that residual water content depends on the initial water content, and was found to be between 38 wt% and 48 wt% of the initial water content of 4 wt% to 6 wt%. Moreover the influence of viscosity and surface tension on bubble shape and rise velocity of the bubbles using level-set method was implemented in finite element method. The modeling results were compared with bubble shape correlation map from literature. The results indicated that the bubble shapes are more dependent on the surface tension parameters than to the viscosity of the bitumen, whereas the bitumen viscosity is dominant for bubble rising velocity. / <p>QC 20160303</p>

When designing modern engines it is important to construct a cooling system that cools the engine structure efficiently. Within the cooling system there is always a certain amount of air which can accumulate and form air pockets in critical areas, such as the water jacket, which can lead to wall degradation. A Computational Fluid Dynamics (CFD) method in STAR-CCM+ from CD-adapco, was derived at Volvo Cars in order to study the accumulation of air bubbles in the water jacket. The method was derived by investigating and evaluating already existing methods. The method initially considered as the best suited was the Eulerian-Eulerian approach. The method was validated against three simpler geometries where experimental data was available. The Eulerian-Eulerian approach treats both phases, liquid and gas, as continuous phases. The idea with the method is to solve the Navier-Stokes equation, the continuity equation and the energy equation for both phases using the Eulerian approach, therefore called Eulerian-Eulerian. The interaction between the two phases was important to model properly which was done by including several interaction models within STAR-CCM+. By tuning different coefficients, which were investigated by a thorough parameter study, the method resembled the experimental data in a satisfying way. The best suited mesh for these simpler geometries was a directed mesh. However, the mesh in the water jacket was automatically generated by STAR-CCM+ and the simpler cases were therefore validated with an automated mesh as well. To capture the experimental data the convection scheme for volume fraction had to be of second order when simulating with automated mesh. This resulted in convergence issues when implementing the method on the water jacket. Instead first order convection scheme, which did not present as satisfying results as second order, had to be implemented. Simulations of the water jacket were performed with two different velocities, that were 10 m/s and 19 m/s, and different flow split ratios for the three outlets. Air with volume fraction 0.1 was injected at the inlet during the first 0.5 s followed by 0.5-1.1 s of further simulation without injecting air. Increased velocity resulted in increased flow through of gas, whereas no big difference could be seen between the different outlet flow split ratios. At two different zones lower pressure was found which resulted in gas holdup. To be able to validate the results from the water jacket, experiments would be necessary to perform in order to provide experimental data for comparison. Velocity profiles from the derived two-phase method resemble the velocity profiles from the one-phase simulation from Volvo, which indicated that the two-phase method did not affect the solution in a remarkable way. Granted that the zones of lower pressure and gas holdup normally coincides, the pressure field from the one-phase simulation could be directly studied, which would lower the computational costs significantly.

<p>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</p><p>capital structure, as of yet no studies seem to address these two areas in combination.</p><p>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.</p><p>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.</p><p>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.</p><p>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.</p>

We present in this thesis three distinct models in Financial Economics. In the first chapter we present a pure exchange economy model with collateral constraints in the spirit of Kiyotaki and Moore (1997). As a first result in this chapter we prove the existence of an equilibrium for this type of economies. We show that in this type of models bubbles can exist and provide a bubble example in which the asset containing the bubble pays positive dividends. We also show for the case of high interest rates the equivalence between this type of models and the Arrow-Debreu market structure. In the second chapter we present a model with limited commitment and one-side exclusion from financial markets in case of default. For this type of models we prove a no-trade theorem in the spirit of Bulow and Rogoff (1989). This is done for an economy with and without bounded investment in a productive activity. The third chapter presents a 2 period economy with complete markets, and 250 states of the world and assets. For this economies we generate a sequence of observed returns, and we show that a market proxy containing only 80% of the assets in the economy provides similar results as the true market portfolio when estimating the CAPM. We also show that for the examples we present a vast amount of observations is required in order to reject the CAPM. This raises the question what the driving force behind the bad empirical performance of the CAPM is.

Approved for public release, distribution is unlimited / When a burst of air is produced in water, the result can be a toroidal bubble. This thesis is concerned with experimental investigations of three acoustical properties of toroidal bubbles: (i) propagation through high-intensity noise, (ii) emission, and (iii) scattering. In (i), an attempt to observe a recent prediction of the acoustic drag on a bubble is described, which is analogous to the Einstein-Hopf effect for an oscillating electric dipole in a fluctuating electromagnetic field. No effect was observed, which may be due to insufficient amplitude of the noise. In (ii), observations of acoustic emissions of volume oscillations of toroidal bubbles are reported. Surprisingly, the emission occurs primarily during the formation of a bubble, and is weak in the case of very smooth toroidal bubbles. In (iii), we describe an experiment to observe the effect of a toroidal bubble on an incident sound field. In addition to the acoustical investigations, we describe the construction of a large hallway apparatus for further investigations and for hands-on use by the public. The tank has cross section 2 feet by 2 feet and height 6 feet, and the parameters of reservoir pressure and time between air bursts are adjustable by the observer. / Lieutenant, United States Navy

Le palladium est couramment utilisé pour le stockage du tritium, isotope radioactif de l’hydrogène, car il forme un tritiure réversible, à basse pression d’équilibre. La décroissance du tritium en hélium-3 provoque un vieillissement du tritiure, caractérisé notamment par l’apparition de bulles d’hélium-3, qui est étudié ici. De précédents travaux de modélisation du vieillissement avaient abouti à la création de deux modèles traitant, d’une part, de la germination des bulles d’hélium-3 (utilisation d’un automate cellulaire) et, d’autre part, de la croissance des bulles (mécanique des milieux continus). Ces modèles étaient fonctionnels, mais leur utilisation était limitée par le manque de données expérimentales d’entrée et de recalage. Ce travail de thèse a donc consisté à acquérir les données expérimentales les plus pertinentes pour améliorer la modélisation du vieillissement du tritiure de palladium. La première partie de ce travail a consisté à estimer les propriétés mécaniques du tritiure de palladium (limite d’élasticité, contrainte maximale, loi de comportement…), déduites de celles de l’hydrure et du deutérure de palladium, mesurées à l’aide d’essais de traction in situ. En seconde partie, la caractérisation du vieillissement a été entreprise, focalisée sur des observations de bulles dans le tritiure de palladium par microscopie électronique en transmission, des mesures de pression à l’intérieur des bulles par résonance magnétique nucléaire et des mesures de gonflement macroscopique du matériau par pycnométrie. Ces travaux ont conduit à des avancées significatives quant à la compréhension du vieillissement et ont permis d’améliorer considérablement sa modélisation. / Palladium is commonly used for the storage of tritium (the hydrogen radioactive isotope), since it forms a low-equilibrium-pressure and reversible tritide. Tritium decay into helium-3 is responsible for the ageing of the tritide, leading to the apparition of helium-3 bubbles for instance. Both experimental and theoretical aspects of this phenomenon are studied here.Previous works on ageing modelling led to two main models, dealing with:- Helium-3 bubbles nucleation (using a cellular automaton),- Bubbles growth (using continuum mechanics).These models were quite efficient, but their use was limited by the lack of input data and fitting experimental parameters.To get through these limitations, this work has consisted in studying the most relevant experimental data to improve the modelling of the palladium tritide ageing.The first part of this work was focused on the assessment of the mechanical properties of the palladium tritide (yield strength, ultimate strength, mechanical behaviour…). They were deduced from the in situ tensile tests performed on palladium hydride and deuteride.In the second part, ageing characterization was undertaken, mainly focusing on:- Bubbles observations in palladium tritide using transmission electron microscopy,- Internal bubble pressure measurements using nuclear magnetic resonance,- Macroscopic swelling measurements using pycnometry.The present work has led to significant progress in ageing understanding and has brought very valuable improvements to the modelling of such a phenomenon.

En plongée, lors d’une décompression, une partie des gaz dissous dans l’organisme est éliminée sous formede bulles qui peuvent être à l’origine d’accidents parfois sévères. Des modèles mathématiques permettentde déterminer des procédures de décompression par paliers fiables mais ne s’appliquent que pour certainesconfigurations de plongée (profondeur, durée, gaz respirés). Une extrapolation de ces modèles à denouveaux types d’exposition comme la plongée profonde aux mélanges est actuellement hasardeuse. Onsuppose ici qu’une modélisation biophysique des mécanismes de la décompression doit apporter dessolutions préventives plus sures, même pour des expositions moins explorées combinant azote et hélium.Deux modèles ont été élaborés pour la prévention des accidents articulaires et neurologiques, formesd’accident les plus fréquentes. Ils ont été corrélés à partir de bases de données et d’analyses de risqueexistantes. Tous deux permettent de représenter l’apparition de symptômes tardifs. Pour l’accidentarticulaire, on montre 1/ l’impact de la diffusion intra-tissulaire (entre un tendon et son voisinage) de gazinerte sur la dynamique d’amplification de la phase gazeuse générée 2/ une augmentation quantifiable durisque d’accident avec le volume de gaz généré 3/ une faible efficacité des paliers 4/ une efficacité modéréede la respiration d’oxygène pur aux paliers proches de la surface. Pour les accidents neurologiques, lemodèle global proposé permet d’estimer le volume instantané des microbulles formées dans les tissus(muscles et graisses) et transférées (via le système lymphatique par ex) dans le sang veineux de retour. Lasurcharge du filtre pulmonaire par les bulles est supposée être un événement précurseur dans la genèse del’accident. La méthode de corrélation du modèle, originale, utilise notamment des campagnes d’écoutes debulles circulantes par système Doppler après plongées, dont une dédiée à cette thèse. Il ressort de cesinvestigations que I/ le risque d’accident peut être relié au volume des bulles transféré dans le sang sur unepériode donnée II/ l’introduction de paliers profonds ne diminue pas le risque III/ la respiration d’oxygènepur aux paliers est très efficace pour réduire ce risque. Un deuxième modèle neurologique dédié à laprévention des accidents médullaires se produisant rapidement après la décompression et à la déterminationdes premiers paliers requis est aussi proposé. L’ensemble de ces trois modélisations offre des perspectivesde prévention intéressantes. / During a scuba diving decompression, a part of the gas that is dissolved in the body is eliminated throughbubbles that can generate potentially severe forms of decompression sickness (DCS). Known mathematicalmodels allow the determination of safe decompression procedures by stages but can only be applied for alimited range of diving configurations (pressure, duration, breathing gas). An extrapolation of these modelsto new expositions such as deep/short dives using mixtures is currently hazardous. In the presented work itis deemed that a biophysical modeling of the decompression mechanisms can produce safer preventivesolutions even for less explored expositions combining nitrogen and helium. Two models have beendeveloped for the prevention of articular and neurological DCS, which are the most frequent forms ofinjury. Existing database and risk analyses have been used to correlate the models. Both predict potentialdelays for the occurrence of DCS symptoms after a decompression. For the articular model it is shown that1/ the intratissular diffusion of inert gases between a target tendon and its neighborhood impacts theamplification dynamics of the generated gas phase 2/ the more the generated gas volume, the bigger theDCS risk 3/ stages of short and moderate durations have a low efficiency 4/ the efficiency of pure oxygenbreathing in order to reduce the risk during the shallow stages is moderated. For neurological DCS, theproposed global model allows estimation of the instantaneous volume of microbubbles that are formed intissues (muscles and adipose tissues) and that are transferred via the lymphatic system for instance in thevenous blood. The overload of the pulmonary filter by bubbles is assumed to be a primary event in the DCSpathogenesis. The original model correlation method uses in particular the recording of circulating bubblessignals through Doppler detections campaigns. One of these campaigns is dedicated to the presented thesiswork. The analysis leads to the following conclusions: I/ the DCS risk is linked to the total bubbles volumethat is transferred into the blood over a given period II/ the introduction of deep stages does not decreasethe risk III/ the breathing of pure oxygen during the shallow stages is very efficient in reducing this risk. Asecond neurological model is proposed: it is dedicated to the prevention of spinal cord DCS forms whichoccur early after the decompression and to the determination of the first required stops. The threedeveloped models give interesting prevention perspectives.

L'objet de cette étude est de mieux formaliser et modéliser de façon générique le processus de structuration d'un produit par le procédé de foisonnement, en reliant les paramètres opératoires aux propriétés des mousses formées et de contribuer ainsi à un meilleur pilotage de l'opération. Une ligne de foisonnement par battage en continu a été instrumentée et l'évolution du diamètre des bulles en fonction des paramètres du produit et du procédé a été suivie pour des milieux modèles newtoniens et rhéofluidifiants. L'analyse dimensionnelle à l'échelle du procédé a permis d'aboutir à un modèle physique de l'opération, et donc d'avoir une compréhension des phénomènes en présence. Elle a aussi permis d'intégrer les paramètres du produit et du procédé et de simplifier la représentation des résultats expérimentaux. Enfin, la cohérence de ce modèle avec d'autres issus de la littérature et une première approche de validation avec un produit réel, semble justifier son caractère générique. / The aim of this study is to better formalize and model in a generic way the structuring of a product by the foaming operation process, by linking the operating parameters to the foams properties and contribute to a better steering of the operation. A continuous whipping line was instrumented and the evolution of bubble diameter depending on both product and process parameters was characterized for Newtonian and shear-thinning model fluids. Dimensional analysis of the process has lead to a physical model of the operation, and therefore makes possible the understanding of the phenomena involved. It also helped to integrate the product and the process parameters and simplify the representation of experimental results. Finally, the consistency of this model with others from the literature and a first validation with a real product seems to justify his relevance.

Surfactant coated microbubbles are widely used as contrast agents (UCA) in medical ultrasound imaging, due to their high echogenicity and non-linear response to acoustic excitation. Controlling the stability of microbubbles in vivo represents a considerable challenge. Understanding the characteristics of the bubble surface and how they change with production method, composition and environment is key to addressing this problem. The aim of this thesis is to investigate viscosity, bubble dissolution, and acoustic response as functions of their composition, manufacturing method and environment. Bubbles were made using combinations of phospholipid and an emulsifier in different molar ratios. Adding the emulsifier decreased both the size and the surface viscosity of the bubbles and caused changes in the scattered pressure amplitude of bubbles under ultrasound. To increase microbubble stability, solid inorganic nanoparticles were adsorbed on to the microbubble surface. These particles behaved as Pickering stabilisers, and deterred Ostwald ripening. The nanoparticles also enhanced the nonlinear behaviour of bubbles at low acoustic pressures. Three manufacturing methods (sonication, cross-flow and flow focusing) were investigated in order to verify stability differences. Sonication produced bubbles with surface viscosities hundreds of centipoise greater than those produced by microfluidics. Both pressure amplitude and harmonic content for sonicated bubbles were found to be much larger due to a higher liposomal adhesion rate at the surface. Solution temperature and bubble age were also investigated. When the solutions were heated above the phospholipid gelling temperature, microfluidic bubbles showed an increased surface viscosity, due to increased liposome adhesion caused by the increased temperature. Bubble composition, manufacturing method and environment were found to vary the surface characteristics of the microbubbles. Further investigations into the affects of the filling gas, in vitro studies, and low temperature TEM characterisation should be conducted to produce a microbubble with the full range of desired characteristics.

The objective of the thesis is to find out whether expansionary monetary policy creates an upward pressure on asset prices and can thus create asset price bubbles, or more precisely significantly contribute to their creation. In doing so, we test the significance and the sign of coefficient on monetary policy stance indicator as a determinant of real estate and stock prices on 19 OECD countries quarterly panel data since 1980. Further we assess periods of real estate and stock price bubbles and periods of expansionary monetary policy and examine their relationship. The asset price bubbles are assessed on the basis of relevant price indices developments without examining the underlying fundamentals. Based on our results it appears that expansionary monetary policy has a positive effect on real estate prices and can thus contribute to formation of real estate bubbles. The effect on stock prices is ambiguous and mostly statistically insignificant. By examining the relationship between assessed asset price bubbles and periods of expansionary monetary policy we found out that monetary expansion is neither sufficient nor necessary condition for formation of asset price bubbles but also that there is a relatively strong relationship between these events. JEL Classification C23, E43, E52, E58, G12, N10, N20...