The triumvirate of tectonics, lithology, and climate control landscape evolution. This study quantifies how lithologic variation and climate-mediated changes in ecosystems perturb steady state processes in the unglaciated, soil-mantled Oregon Coast Range (OCR). I first demonstrate that minor grain-scale differences in rock properties in a seemingly uniform sandstone control differences in rock strength, biotic bedrock-to-soil production efficacy, and erosion rates and influence relief at the watershed scale. I then build on sedimentology, paleoecology, and isotopic-derived paleoerosion data I collected from a new 50 ka sediment archive at Little Lake, OR to explore climate controls on soil production and erosion rates 21 ka across the OCR and spanning 50 ky within a single watershed. In Chapter III, I combine a mechanistic frost weathering model with a regional Last Glacial Maximum (LGM) climate reconstruction and paleovegetation data to demonstrate that accelerated frost-driven erosion was pervasive across the OCR during the LGM. My findings provide a new framework to quantify how the late Pleistocene affects modern erosion and soil formation rates in unglaciated environments and implies that most landscapes reside in a transient state. In Chapter IV, I document climate-mediated ecosystem influence on erosion rates over 3 climatic intervals. 10Be-derived erosion rates increase 3x (from 0.6 mm/yr to 0.21 mm/yr) as the OCR transitioned from the open forest-dominated marine isotope stage (MIS) climate interval (50-26 ka) into the periglacial subalpine MIS 2 glacial interval (26-13 ka). Measured erosion rates fell by more than half as the subalpine ecosystem gave way to the modern MIS 1 closed canopy Douglas-fir forest. Coupling paleovegetation-derived climate information with core observations I model frost weathering intensity from ~ 43 ka to 21 ka and establish a correspondence with increasing frost weathering intensity and increasing 10Be-derived erosion rates. Utilizing a transient mixing depth and erosion rate model, I am able to broadly replicate measured erosion rates at Little Lake through time. My findings contradict previous work that suggests climate has only weak control on erosion rates. This dissertation includes previously published and unpublished co-authored material.

We study the dynamical behavior of disordered many-particle systems with long-range Coulomb interactions by means of damage-spreading simulations. In this type of Monte-Carlo simulations one investigates the time evolution of the damage, i.e. the difference of the o ccupation numbers of two systems, subjected to the same thermal noise. We analyze the dependence of the damage on temperature and disorder strength. For zero disorder the spreading transition coincides with the equilibrium phase transition, whereas for finite disorder, we find an evidence for a dynamical phase transition well below the transition temperature of the pure system.

L'hadronthérapie joue un rôle de plus en plus important au sein des techniques de radiothérapie grâce aux propriétés balistiques des ions et, dans le cas de ceux plus lourds que les protons, à une augmentation de l'efficacité biologique dans la région tumorale. Ces caractéristiques permettent une meilleure conformation de la dose délivrée au volume tumoral et elles permettent en particulier de traiter des tumeurs radio-résistantes. Elles conduisent cependant à une grande sensibilité du parcours des ions aux incertitudes du traitement. C'est dans ce contexte qu'a été proposée la détection de radiations secondaires émises lors des interactions nucléaires induites par les ions incidents dans le patient. La tomographie par émission de positons et la détection des rayons gamma prompts ont notamment fait l'objet d'une recherche intense ces dernières années. Le réseau de formation européen ENTERVISION, soutenu par la communauté ENLIGHT, a été crée fin 2009 pour développer ce type d'imagerie et, plus généralement, traiter les incertitudes de traitement en hadronthérapie. Le travail présenté dans ce manuscrit et intitulé ≪ Modélisation et simulation des processus physiques pour l'imagerie en ligne de l'hadronthérapie ≫ est l'un des nombreux travaux issus de ce projet. Bien que le sujet soit particulièrement large, le fil conducteur de ce travail a été une étude systématique visant in fine une implémentation d'un dispositif d'imagerie ≪ gamma prompts ≫ utilisable à la fois en faisceau de protons et d'ions carbone / Hadrontherapy is taking an increasingly important role in radiotherapy thanks to the ballistic properties of ions and, for those heavier than protons, an enhancement in the relative biological effectiveness in the tumour region. These features allow for a higher tumour conformality possible and gives the opportunity to tackle the problem of radioresistant tumours. However, they may lead to a great sensitivity of ion range to treatment uncertainties, namely to morphological changes along their path. In view of this, the detection of secondary radiations emitted after nuclear interactions between the incoming ions and the patient have been long proposed as ion range probes and, in this regard, positron emitters and prompt gammas have been the matter of intensive research. The European training network ENTERVISION, supported by the ENLIGHT community, was created in the end of 2009 in order to develop such imaging techniques and more generally to address treatment uncertainties during hadrontherapy. The present work is one of the many resulting from this project, under the subject “Modelling and simulation of physics processes for in-beam imaging in hadrontherapy”. Despite the extensive range of the topic, the purpose was always to make a systematic study towards the clinical implementation of a prompt-gamma imaging device to be used for both proton and carbon ion treatments

The world today has large challenges in order to manage a changing climate and the consequences that the climate change has on the environment and human living standards. This climate change is largely affected by the emissions of greenhouse gases, which come from usage of fossil fuels. This is a global problem that will affect the whole world and cause an increase of mean global temperature, which would lead to drastically changes in the living environment for human beings. A large part of the use of fossil fuels is connected to electric energy production. In EU almost half of the electric energy production is based on combustion of fossil fuels like natural gas and coal. These types of energy production need to be phased out and the energy consumption needs to decrease.   With climate change as a background there is a development towards more sustainable households. Companies around the world today invest in developing products that are more environmentally friendly. Household appliance companies develop products that use less water and energy, and a company like ASKO appliances AB tries to equip their machines with a new type of drying system. This new system would mean that less energy is needed for the drying cycle and humid air would not flow out in the kitchen.   The new drying system uses an air channel mounted on the side of a machine where moist hot air passes through the channel. During the passage the hot air will exchange heat with a cold surface inside of the channel. This work is focused on finding an optimal geometry of the air channel that enhances heat transfer between hot air and a cold surface. Installing obstacles inside of the duct could alter the flow pattern, and therefore enhance heat transfer. The work is mostly computer based with simulations performed in software called COMSOL Multiphysics. The software is used to build a 3-D model, where different geometries of obstacles are placed inside of the air channel. Results from simulations are compared with results from experimental trials, thus validating the computer model. Fluid flow simulations are used to investigate the effects of heat transfer for different types of geometries and sizes of obstacles. Parameters like influence angle and obstacle distance are tested.   The study shows results that obstacles inside of an air channel enhance heat transfer between a fluid and a surface. V-shaped obstacles perform the best results in order to enhance heat exchange, this compared with other tested geometries like W-shaped, wave-shaped obstacles and geometry without obstacles.   Different influence angle and distance between obstacles affects heat transfer, the study indicates that influence angle has larger effects on heat transfer than obstacle distance.

Thanks to the advancement of the modern computer simulation systems, many scientific applications generate, and require manipulation of large volumes of data. Scientific exploration substantially relies on effective and accurate data analysis. The shear size of the generated data, however, imposes big challenges in the process of analyzing the system. In this dissertation we propose novel techniques as well as using some known designs in a novel way in order to improve scientific data analysis. We develop an efficient method to compute an analytical query called spatial distance histogram (SDH). Special heuristics are exploited to process SDH efficiently and accurately. We further develop a mathematical model to analyze the mechanism leading to errors. This gives rise to a new approximate algorithm with improved time/accuracy tradeoff. Known MS analysis systems follow a pull-based design, where the executed queries mandate the data needed on their part. Such a design introduces redundant and high I/O traffic as well as cpu/data latency. To remedy such issues, we design and implement a push-based system, which uses a sequential scan-based I/O framework that pushes the loaded data to a number of pre-programmed queries. The efficiency of the proposed system as well as the approximate SDH algorithms is backed by the results of extensive experiments on MS generated data.

La prédiction des mouvements du sol générés par un séisme est un enjeu majeur pour la prise en compte du risque sismique. C’est l’un des objectifs du projet SIGMA dans le cadre duquel j’ai réalisé ma thèse. Celle-ci se compose de deux parties. La première se concentre sur la dépendance à la magnitude de la décroissance des paramètres des mouvements du sol avec la distance. Celle-ci est un sujet de préoccupation aussi bien pour l’utilisation des relations d’atténuation (GMPEs), que pour les méthodes basées sur l’utilisation de petits évènements en tant que fonctions de Green empiriques. Nous avons démontré qu’aux distances les plus faibles (inférieures à la longueur de la faille), l'effet de saturation dû aux dimensions de la faille est prépondérant. Aux distances plus importantes, l'effet de l’atténuation anélastique devient prépondérant. Nous avons donc montré qu’il pouvait être délicat de mélanger des données de différentes régions dans les GMPEs, et validé l’utilisation des fonctions de Green empiriques à toutes les distances. Dans la deuxième partie sont testées 3 différentes méthodes de simulations dans un contexte complexe : un code combinant une source étendue en k2 et des EGFs, un code point-source EGFs et un code stochastique. Nous avons choisi de travailler sur le séisme de magnitude Mw 5.9 (29 mai 2012) situé dans un bassin sédimentaire profond (la plaine du Po), et qui a engendré des sismogrammes souvent dominés par les ondes de surface. On y démontre que sans connaissance à priori du milieu de propagation, les méthodes basées sur des EGF permettent de reproduire les ondes de surface, les valeurs de PGA, de PGV, ainsi que les durées des signaux générés. / The prediction of ground motion generated by an earthquake is a major issue for the consideration of seismic risk. This is one of the objectives of SIGMA project in which I realized my thesis. It consists of two parts. The first focuses on the magnitude dependence of the ground motion parameters decay with distance. This is a concern both for the use of relation of attenuation (GMPEs) than methods based on the use of small events as empirical Green functions. We have shown that as the shorter distances (less than the length of the fault), the saturation effect due to the fault size is preponderant. For larger distances, it’s the eanelastic attenuation effect which becomes predominant. So we have shown that it can be tricky to mix data from different regions in GMPEs and we validated the use of empirical Green functions at every distance. In the second part are tested three different simulation methods in a complex context: a code combining finite fault source in k2 and EGFs, a point-source code with EGFs and a stochastic code. We chose to work on the Mw 5.9 earthquake (May 29, 2012) which occurs in a deep sedimentary basin (the Po plain), and which has generated seismograms often dominated by surface waves. We show that without a priori knowledge of the propagation medium, methods based on EGFs can reproduce surface waves, the values of PGA, PGV, and the durations of the signals generated.

>Magister Scientiae - MSc / We quantitatively examine the effects of merger and environment within a cosmological hydrodynamic simulation. We show that our simulation model broadly reproduces the observed scatter in H I at a given stellar mass as quantified by the HI mass function in bins of stellar mass, as well as the H I richness versus local galaxy density. The predicted H I fluctuations and environmental effects are roughly consistent with data, though some discrepancies are present at group scales. For satellite galaxies in & 1012Mhalos, the H I richness distribution is bimodal and drops towards the largest halo masses. The depletion rate of H I once a galaxy enters a more massive halo is more rapid at higher halo mass, in contrast to the specific star formation rate which shows much less variation in the attenuation rate versus halo mass. This suggests that, up to halo mass scales probed here (. 1014M), star formation is mainly attenuated by starvation, but H I is additionally removed by stripping once a hot gaseous halo is present. In low mass halos, the H I richness of satellites is independent of radius, while in high mass halos they become gas-poor towards the center, confirming the increasing strength of the stripping with halo mass. By tracking the progenitors of galaxies, we show that the gas fraction of satellite and central galaxiesdecreases from z =5 ! 0, tracking each other until z⇠1 after which the satellites’ H I content drops much more quickly, particularly for the highest halo masses. Mergers somewhat increase the H I richness and its scatter about the mean relation, but these variations are consistent with arising form inflow fluctuations, unlike in the case of star formation where mergers boost it above that expected from inflow fluctuations. In short, our simulations suggest that the H I content in galaxies is determined by their ability to accrete gas from their surroundings, with stripping effects playing a driving role once a hot gaseous halo is present.

The study aims to generate a simulated, ultra high-resolution climatology over the southwestern Cape of South Africa, and in particular the Stellenbosch wine producing region, by the dynamical downscaling of observed synoptic-scale circulation. A variable-resolution global model, the conformal-cubic atmospheric model (CCAM), and a multiple-nudging strategy are applied in order to reach this goal. CCAM is employed in stretched-grid mode as a regional climate model (RCM) to simulate climate for the period 1976-2005 at four different spatial resolutions. Nudging from coarse-resoltion (2.5° in latitude and longitude), the model was first applied at a 60 km resolution over southern Africa in order to obtain a simulation of the synoptic-scale circulation over the region. Two higher resolution simulations, at 8 km and 1 km resolution, were obtained consecutively over the western and southwestern Cape, nudging from the 60 km and 8 km simulations, respectively. Finally, a 200 m simulation was performed over the Stellenbosch region. Because of the high computational requirements of high-resolution runs, each progressively higher resolution simulation is performed over a progressively smaller area of interest over which the spatial resolution is high. The simulations verify well against observed datasets, and generally capture the important climatic features over the area of interest. The 60 km CCAM simulation gives a good representation of the synoptic scale weather over southern Africa, with realistic seasonal circulation patterns and rainfall percentages as well as intra-annual rainfall totals over various regions. The mesoscale climate over the Western Cape of South Africa is captured by the 8 km simulation, especially with respect to seasonal variations in temperature and rainfall percentages - although the actual rainfall over the southwestern tip of the Western Cape is severely underestimated. The ultra high-resolution simulated diurnal cycle of temperature, relative humidity and screen level wind speed compared well against observations for the month of February. The CCAM climate simulations might not be accurate enough for some of the very sensitive studies of the wine industry, but it can have great value for the demarcation of areas which are climatically suited for viticulture and some more general viticultural studies. Ultra high-resolution climate parameter maps are presented for 1976-2005. / Dissertation (MSc)--University of Pretoria, 2009. / Geography, Geoinformatics and Meteorology / Unrestricted

Agricultural production is highly sensitive to climate and weather perturbations. Maize is the main crop cultivated in South Africa and production is predominantly rain-fed. South Africa’s climate, especially rainfall, is extremely variable which influences the water available for agriculture and makes rain-fed cropping very risky. In the aim to reduce the uncertainty in the climate of the forthcoming season, this study investigates whether seasonal climate forecasts can be used to predict maize yields for South Africa with a usable level of skill. Maize yield, under rain-fed conditions, is simulated for each of the magisterial districts in the primary maize producing region of South Africa for the period from 1979 to 1999. The ability of the CERES-Maize model to simulate South African maize yields is established by forcing the CERES-Maize model with observed weather data. The simulated maize yields obtained by forcing the CERES-Maize model with observed weather data set the target skill level for the simulation systems that incorporate Global Circulation Models (GCMs). Two GCMs produced the simulated fields for this study, they are the Conformal Cubic Atmospheric Model (CCAM) and the ECHAM4.5 model. CCAM ran a 5 and ECHAM4.5 a 6- member ensemble of simulations on horizontal grids of 2.1° x 2.1° and 2.8° x 2.8° respectively. Both models were forced with observed sea-surface temperatures for the period 1979 to 2003. The CERES-Maize model is forced with each ensemble member of the CCAM-simulated fields and with each ensemble member of the ECHAM4.5-simulated fields. The CERES-CCAM simulated maize yields and CERES-ECHAM4.5 simulated maize yields are combined to form a Multi-Model maize yield ensemble system. The simulated yields are verified against actual maize yields. The CERES-Maize model shows significant skill in simulating South Africa maize yields. CERES-Maize model simulations using the CCAM-simulated fields produced skill levels comparable to the target skill, while the CERES-ECHAM4.5 simulation system illustrated poor skill. The Multi-Model system presented here could therefore not outscore the skill of the best single-model simulation system (CERES-CCAM). Notwithstanding, the CERES-Maize model has the potential to be used in an operational environment to predict South African maize yields, provided that the GCM forecast fields used to force the model are adequately skilful. Such a yield prediction system does not currently exist in South Africa. / Dissertation (MSc)--University of Pretoria, 2009. / Geography, Geoinformatics and Meteorology / Unrestricted

Numerical simulations of Mach shock reflections have shown that the Mach stem can bifurcate as a result of the slip line jetting forward. Numerical simulations were conducted in this study which determined that these bifurcations occur when the Mach number is high, the ramp angle is high, and specific heat ratio is low. It was clarified that the bifurcation is a result of a sufficiently large velocity difference across the slip line which drives the jet. This bifurcation phenomenon has also been observed after triple point collisions in detonation simulations. A triple point reflection was modelled as an inert shock reflecting off a wedge, and the accuracy of the model at early times after reflection indicates that bifurcations in detonations are a result of the shock reflection process. Further investigations revealed that bifurcations likely contribute to the irregular structure observed in certain detonations.