La présence de structures filamentaires est souvent rapportée dans plusieurs machines de fusion nucléaire à confinement magnétique, spécialement sur lequel s'appelle Tokamak. Etant porteurs de grandes quantités des particules et chaleur, la présence des filaments dans le bord du tokamak (le scrape-off layer, SOL) pourraient poser des dangers aux superficies solides du tokamak. Pour mieux comprendre leur comportement, dans le cadre de cette thèse doctorale, les filaments sont étudiés par les expériences numériques en utilisant un modèle 3D fluide istherme, TOKAM3X en les considerant comme structures isolées et structures spontanées. Cette manière de les étudier permet de faire divers analyses paramétriques – par exemple la resistivité parallèle du plasma et la présence d'un cisaïllement magnétique, et au même temps les propriétés du filaments (comme sa longeur parallèle, et son intensité de densité). Ces études montrent un impact fort de la resistivité parallèle sur la velocité des filaments et en conséquence peut modifier leur temps de vie dans le bord de la machine. Les résultats des simulations sur le cisaïllement magnétique et la séparatrice indiquent qu'ils sont des ingrédients clés pour la destruction et génération des filaments. En plus, la comparaison entre les filaments initialisés (seeded) et les filaments formés spontanément montre qu'ils ne sont pas parreils dans leur comportement, bien que leurs characteristiques moyennées en temps sont bien conservées. / Filamentary transport has been experimentally observed in a multitude of magnetically confined fusion devices, especially of the tokamak type. Filaments are carriers of large quantities of particles and heat and as such, their presence in the SOL has implications for the target surface design in future fusion reactors. To better understand their nature, this doctoral thesis studies filaments through computer simulations as isolated structures and spontaneously forming structures, using a 3D fluid model called the TOKAM3X. Parametric studies using the model for studying the effect of the plasma's parallel resistivity and magnetic shear, and also the filament's parallel extension and size/density amplitude are performed and analysed. The studies reveal the strong impact of the parallel resistivity on filament velocities and hence their lifetimes in the SOL. The doctoral work also looked at the impact of strong local magnetic shear and the separatrix on the motion and generation of filaments. The results from the simulations performed reveal that strong shear mechanisms may be key to the destruction and formation of filaments. Further, a comparison of spontaneously forming and seeded filaments shows that seeded filaments do not behave completely the same way as spontaneously forming ones. But their mean velocity characteristics are still retained to a good degree.

Environment is known to have a significant impact on the evolution of galaxies. This is most evident in the local Universe, where the oldest and most massive galaxies are found at the of massive galaxy clusters. Current theory predicts that galaxies will form earlier and evolve more rapidly in the densest regions of the Universe. What is not clear is how rapidly the of environment start to have an impact on galaxies, at what stage can we detect physical differences between galaxies in dense regions and those in the field? By the time galaxies are assembled in virialised clusters the effects are clear, but at higher redshift (z ≳ 2), in the unvirialised progenitors of clusters (protoclusters) the effects are harder to detect. In this thesis I study the impact of environment in a z =3.1 protocluster in the SSA22 field. I consider the fraction of mergers in the protocluster, comparing it to the fraction of mergers in field at a similar redshift. My classification is based on the morphology of Lyman break (LBGs), using HST ACS/F814W imaging, which probes the rest frame UV. I find a marginal enhancement of the merger fraction, 48±10 per cent for LBGs in the protocluster compared 30±6 per cent in the field, suggesting that galaxy-galaxy mergers are one of the key driving accelerated star formation and AGN growth in protocluster environments. Having considered the fraction of mergers in the protocluster I then turn my attention to the physical properties of LBGs. I use multiwavelength data and spectral energy distribution fitting to determine the mass of LBGs in the protocluster and in the field. I find no statistical evidence for an enhancement of mass in the protocluster, suggesting that the protocluster environment has not impacted the average mass of LBGs at this redshift. It is possible that the protocluster LBG population may become more massive than LBGs in the field at lower redshift, or the galaxies may cease to be detectable by the Lyman break method before a mass difference between the protocluster galaxies and field is observable. Finally I consider the Lyman-α blobs (LABs) within the protocluster. These are large (~10- 100kpc) scale regions of diffuse Lyman-α emission, thought to be associated with overdense regions. 35 LABs have been detected in the SSA22 protocluster, indicating the presence of large clouds of gas in the circumgalactic medium. A debate has arisen regarding the powering mechanism of the LABs, particularly between star forming processes (e.g. Lyman-α escaping from a star forming galaxy or photoionizing radiation escaping from a star forming galaxy or active galactic nuclei) and a cold accretion model. The latter involves gas gravitationally cooling as it falls into the centre of a dark matter halo to feed a central galaxy. Some of this energy heats the cold gas, which then emits Lyman-α as it cools. The cold gas accretion theory gained popularity because some LABs appear not to contain a luminous galaxy or AGN which could explain the observed emission. One suggestion is that the central galaxy could be hidden by dust and that this could explain the lack of a detection in UV or optical. I therefore use SCUBA2 850μm imaging to search for submm sources (dusty star forming galaxies) in the LABs. I detect submm sources in only two of the LABs at 3.5δ, however, stacking all the LABs gives an average flux density of S850 = 0.6±0.2mJy. This suggests that on average the LABs do contain a submm source which could be a dusty galaxy. However, stacking the LABs by size indicates that only the largest third (area ≳ 1800kpc²) have a mean detection, at 4.5δ, with S850 = 1.4±0.3mJy, suggesting that different mechanisms may dominate the larger and smaller LAB populations. I explore two possible mechanisms for powering the LABs, cold accretion and central star forming galaxies. I find that central star formation is more likely to be the dominant source of emission, with cold accretion playing a secondary role.

NAPL (non-aqueous phase liquid) blob mobilization and solubilization models were developed to predict residual NAPL fate and describe flow dynamics of various displacing phases (water and surfactant foam). The models were achieved by pore-scale mass and force balances and were focused on the understanding of the physico-chemical interactions between NAPL blobs and the displacing phases. The pore-level mass balance indicated changes in NAPL saturation instead of mass reduction occurring with blob solubilization. The force balance was used to explain the complex flow configurations among NAPL blobs and the displacing phases. Some factors such as the wettability and the spreading/entering coefficients were useful in determining flow configurations. From the models developed in this study, dimensional analysis was performed to identify NAPL blob motion during water or surfactant foam flooding. In non-dimensionalized forms, a Trapping number employed as an indicator of blob displacement performance was modified to quantify the onset of blob mobilization. Its value for water flooding was nearly 2-3 orders of magnitude greater than that of surfactant foam flooding. Next, to investigate the blob flow regime in porous media, a blob velocity was computed. Regardless of the displacing phases, a blob’s velocity increased with increasing blob sizes after commencement of blob motion, and the velocity of DNAPL (dense non-aqueous phase liquid) blobs was greater than that of LNAPL (light non-aqueous phase liquid) blobs. From this investigation, it is expected that the pore-scale solubilization and mobilization models would provide better understanding leading to a predictive capability for the flow behavior of NAPL blobs removed by various displacing phases in a porous medium. Additionally, the models based on newly approached concepts and modified governing equations would be useful in conceptualization, as well as the model prediction of other immiscible or miscible fluids flowing through a porous medium. Further, the models developed in our study would be a useful contribution to the study of small-scale contaminants or substances such as particle and bacterial transport in porous media.

NAPL (non-aqueous phase liquid) blob mobilization and solubilization models were developed to predict residual NAPL fate and describe flow dynamics of various displacing phases (water and surfactant foam). The models were achieved by pore-scale mass and force balances and were focused on the understanding of the physico-chemical interactions between NAPL blobs and the displacing phases. The pore-level mass balance indicated changes in NAPL saturation instead of mass reduction occurring with blob solubilization. The force balance was used to explain the complex flow configurations among NAPL blobs and the displacing phases. Some factors such as the wettability and the spreading/entering coefficients were useful in determining flow configurations. From the models developed in this study, dimensional analysis was performed to identify NAPL blob motion during water or surfactant foam flooding. In non-dimensionalized forms, a Trapping number employed as an indicator of blob displacement performance was modified to quantify the onset of blob mobilization. Its value for water flooding was nearly 2-3 orders of magnitude greater than that of surfactant foam flooding. Next, to investigate the blob flow regime in porous media, a blob velocity was computed. Regardless of the displacing phases, a blob’s velocity increased with increasing blob sizes after commencement of blob motion, and the velocity of DNAPL (dense non-aqueous phase liquid) blobs was greater than that of LNAPL (light non-aqueous phase liquid) blobs. From this investigation, it is expected that the pore-scale solubilization and mobilization models would provide better understanding leading to a predictive capability for the flow behavior of NAPL blobs removed by various displacing phases in a porous medium. Additionally, the models based on newly approached concepts and modified governing equations would be useful in conceptualization, as well as the model prediction of other immiscible or miscible fluids flowing through a porous medium. Further, the models developed in our study would be a useful contribution to the study of small-scale contaminants or substances such as particle and bacterial transport in porous media.

Les applications modernes ont des tendances de diverger à la fois le profile I/O et les requiers du stockage. La liaison d'une application scientifique ou commerciale avec un system "general-purpose" produit probablement un résultât sous-optimale. Même sous la présence des systèmes "purpose specific" des application aux classes multiples de workloads ont encore besoin de distribuer du travail de calcul au correct system. Cependant, cette stratégie n'est pas triviale comme des plateformes différentes butent diversifier leur propos et par conséquence elles requièrent que l'application intégrée des chemins multiples de code. Le but de l'implémentation de ces chemins n'est pas trivial, il requiert beaucoup d'effort et des capacités de codage. Le problème devient vaste quand les applications ont besoin de bénéficier de plusieurs data-stores en parallèle. Dans cette dissertation, on va introduire les "storage containers" comme le prochain étape logique, mais révolutionnaire. Un "storage container" est une infrastructure virtuelle qui découple une application de ses data-stores correspondants avec la même manière que Docker découple l'application runtime des servers physiques. En particulier, un "storage container" est un middleware qui sépare des changements fait pour bouts de code des application par des utilisateurs scientifiques, de celui fait pour des actions de I/O par des développeurs ou des administrateurs.Pour faciliter le développement et déploiement d'un "storage container" on va introduire un cadre appelé Tromos. Parmi son filtre, tout qui est nécessaire pour qu'un architecte d'une application construite une solution de stockage est de modéliser l'environnement voulu dans un fichier de définition and laisser le reste au logiciel. Tromos est livré avec un dépôt de plugins parmi les quelles l'architecte peut choisir d'optimiser le conteneur pour l'application activée. Parmi des options disponibles, sont inclus des transformations des données, des politiques de placement des données, des méthodes de reconstruction des données, du management d'espace de noms, et de la gestion de la cohérence à la demande. Comme preuve de concept, on utilisera Tromos pour créer des environnements de stockage personnalisés facilement comparés à Gluster, un système de stockage bien établi et polyvalent. Les résultats vous montrent que les "storage containers" adaptés aux applications, même s'ils sont auto-produits, peuvent surpasser les systèmes "general purpose" les plus sophistiqués en supprimant simplement la surcharge inutile de fonctionnalités factices. / Modern applications tend to diverge both in the I/O profile and storage requirements. Matching a scientific or commercial application with a general-purpose system will most likely yield suboptimal performance. Even in the presence of purpose-specific' systems, applications with multiple classes of workloads are still in need to disseminate the workload to the right system. This strategy, however, is not trivial as different platforms aim at diversified goals and therefore require the application to incorporate multiple codepaths. Implementing such codepaths is non-trivial, requires a lot of effort and programming skills, and is error-prone. The hurdles are getting worse when applications need to leverage multiple data-stores in parallel. In this dissertation, we introduce "storage containers" as the next logical in the storage evolution. A "storage container" is virtual infrastructure that decouples the application from the underlying data-stores in the same way Docker decouples the application runtime from the physical servers. In other words, it is middleware that separate changes made to application codes by science users from changes made to I/O actions by developers or administrators.To facilitate the development and deployment of a "storage container" we introduce a framework called Tromos. Through its lens, all that it takes for an application architect to spin-up a custom storage solution is to model the target environment into a definition file and let the framework handles the rest. Tromos comes with a repository of plugins which the architect can choose as to optimize the container for the application at hand. Available options include data transformations, data placement policies, data reconstruction methods, namespace management, and on-demand consistency handling.As a proof-of-concept we use Tromos to prototype customized storage environments which we compare against Gluster; a well-estalished and versatile storage system. The results have shown that application-tailored "storage containers", even if they are auto-produced, can outperform more mature "general-purpose" systems by merely removing the unnecessary overhead of unused features.

Die Vision dieses Projektes ist es, einen durchgängigen Prozess zu entwickeln, der es erlaubt, den Entwurf, die Berechnung und die Fugenoptimierung von flächigen Strukturen aus Betonfertigteilen sehr einfach und effizient durchzuführen. Damit soll die Herstellung von freien Formen, wie beispielsweise „Blobs“ und Hängeformen aus Beton, unterstützt und gefördert werden. / The vision of this project is to develop a continuous process that allows very easy and efficient design, calculation and joint optimization of surface-like structures made of precast concrete elements. This should support and encourage the production of free forms, such as “blobs” and hanging forms made of concrete.

Controlling the scrape-off layer (SOL) properties in order to limit divertor erosion and extend component lifetime will be crucial to successful operation of ITER and devices that follow, where intermittent thermal loads on the order of GW/m² are expected. Steady state transport in the edge region is generally turbulent with large, order unity, fluctuations and is convection dominated. Owing to the success of the past fifty years of progress in magnetically confining hot plasmas, in this work we examine convective transport phenomena in the SOL that occur in the relatively "slow", drift-ordered fluid limit, most applicable to plasmas near MHD equilibrium. Diamagnetic charge separation in an inhomogeneous magnetic field is the principal energy transfer mechanism powering turbulence and convective transport examined in this work. Two possibilities are explored for controlling SOL conditions. In chapter 2 we review basic physics underlying the equations used to model interchange turbulence in the SOL and use a subset of equations that includes electron temperature and externally applied potential bias to examine the possibility of suppressing interchange driven turbulence in the Texas Helimak. Simulated scans in E₀×B₀ flow shear, driven by changes in the potential bias on the endplates appears to alter turbulence levels as measured by the mean amplitude of fluctuations. In broad agreement with experiment negative biasing generally decreases the fluctuation amplitude. Interaction between flow shear and interchange instability appears to be important, with the interchange rate forming a natural pivot point for observed shear rates. In chapter 3 we examine the possibility of resonant magnetic perturbations (RMPs) or more generally magnetic field-line chaos to decrease the maximum particle flux incident on the divertor. Naturally occurring error fields as well as RMPs applied for stability control are known to cause magnetic field-line chaos in the SOL region of tokamaks. In chapter 3 2D simulations are used to investigate the effect of the field-line chaos on the SOL and in particular on its width and peak particle flux. The chaos enters the SOL dynamics through the connection length, which is evaluated using a Poincaré map. The variation of experimentally relevant quantities, such as the SOL gradient length scale and the intermittency of the particle flux in the SOL, is described as a function of the strength of the magnetic perturbation. It is found that the effect of the chaos is to broaden the profile of the sheath-loss coefficient, which is proportional to the inverse connection length. That is, the SOL transport in a chaotic field is equivalent to that in a model where the sheathloss coefficient is replaced by its average over the unperturbed flux surfaces. Both fully chaotic and the flux-surface averaged approximation of RMP application significantly lower maximum parallel particle flux incident on the divertor. / text