abstract: Quantum Monte Carlo is one of the most accurate ab initio methods used to study nuclear physics. The accuracy and efficiency depend heavily on the trial wave function, especially in Auxiliary Field Diffusion Monte Carlo (AFDMC), where a simplified wave function is often used to allow calculations of larger systems. The simple wave functions used with AFDMC contain short range correlations that come from an expansion of the full correlations truncated to linear order. I have extended that expansion to quadratic order in the pair correlations. I have investigated this expansion by keeping the full set of quadratic correlations as well an expansion that keeps only independent pair quadratic correlations. To test these new wave functions I have calculated ground state energies of 4He, 16O, 40Ca and symmetric nuclear matter at saturation density ρ = 0.16 fm−3 with 28 particles in a periodic box. The ground state energies calculated with both wave functions decrease with respect to the simpler wave function with linear correlations only for all systems except 4He for both variational and AFDMC calculations. It was not expected that the ground state energy of 4He would decrease due to the simplicity of the alpha particle wave function. These correlations have also been applied to study alpha particle formation in neutron rich matter, with applications to neutron star crusts and neutron rich nuclei. I have been able to show that this method can be used to study small clusters as well as the effect of external nucleons on these clusters. / Dissertation/Thesis / Doctoral Dissertation Physics 2019

Le but de cette thèse a été de construire un modèle haute résolutionde la vitesse des ondes Sau sein la croûte et du manteau supérieur de l'arc alpin et del'Europe, à partir de corrélations de bruit. Dans ce cadre, nous avonsconstruit plusieurs modèle tomographiques à partir d'un jeu de donnéecomposé de 4 années de bruit ambiant enregistré par 1293 stationsréparties à travers l'Europe.Nous avons tout d'abord réalisé une tomographie par corrélation debruit "classique". Desmesures de vitesse de groupe des ondes de Rayleigh entre 5 et 150s depériode ont été inversées pour construire des cartes de vitesse degroupe. Elles ont été inversées avec une approche bayésienne afind'établir un modèle probabiliste de la vitesse des onde S et d'évaluerla probabilité d'avoir une interface en chaque point du modèle. Ceci apermis d'établir un modèle tomographique haute résolution del'ensemble de l'Europe en bon accord avec des études antérieursciblées sur des zones spécifiques.La forte densité de station au niveau de l'arc alpin nous a permisd'établir des cartes de vitesse de phase avec la méthode Eikonal entre7 et 25s de période. Celles-ci sont en accord avec les cartes devitesse de groupe précédemment établies. De plus nous avons pu aveccette méthode étudier l'anisotropie de la croûte à l'échelle desAlpes.Nous avons continué à affiner notre modèle de la lithosphère alpine enréalisant une tomographie basée sur l'équation d'onde ("wave equationtomography", WET) s'appuyant sur des simulationsnumériques de la propagation des ondes elastiques en 3D.Nous avons ainsi itérativement amélioré le modèle en minimisant ladifférence de vitesse de phase des ondes de Rayleigh mesurée sur descorrélations observées et simulées numériquement entre 10 et 55s depériode. Le modèle final a été obtenu après 15 itérations avec uneréduction du misift de ~65%. Au sein de la croûte, et àl'interface croûte/manteau, ce modèle présente de nouvelles structureset des contraste de vitesse plus important. Ceci illustre que cetteapproche permet d’améliorer significativement les modèlestomographiques obtenus par corrélations de bruit. / The primary goal of the thesis is to build high-resolution shear-wave velocity models of the Alpine crust and uppermost mantle using ambient noise based tomography.In this framework, we performed a series of tomographic applications using a large cross-correlation dataset computed from 4 years of noise recorded at 1293 broadband seismic stations across Europe.We first applied a 'classical' ambient noise group velocity tomography.Rayleigh wave group velocity measurements in the period band 5-150 s were inverted to construct group velocity maps.With a Bayesian 1-D depth inversion approach, we determined both the shear-wave velocity and probability of interfaces at each cell of the model.This has allowed to finally establish a high-resolution model of the European crust and uppermost mantle in good agreement with previous localized geophysical studies.Taking advantage of the dense seismic array in the Alpine region, we performed ambient noise Eikonal tomography using Rayleigh wave phase velocity measurements in the period band 7-25 s.With this method, we were able to study the anisotropy of the Alpine crust.We refined the shear wave velocity model of the Alpine crust and uppermost mantle using wave-equation tomography (WET) based on the numerical simulation of 3-D elastic wave propagation.We iteratively improved the initial model by minimizing the phase traveltime differences between the observed and synthetic Rayleigh waves in the period band 10-55 s.We obtained the final model after 15 iterations with a reduction of total misfit ~65%.At crustal and Moho depths, the final model displays several new features and much stronger velocity contrasts, which indicates that this approach can significantly improves the model obtained by classical ambient noise tomography.

The directional correlation of the 346-136 Kev gamma-gamma cascade in Ta¹⁸¹ was measured using the delayed coincidence method with a source of Hf¹⁸¹ in 27 N HF. The contributions to the composite delayed coincidence spectrum of the interfering 133-482 Kev and 133 - 346 Kev cascades were removed by the subtraction from this spectrum of appropriate 133-482 Kev pure delayed coincidence data. The extracted 346 -136 Kev coincidence data then yielded the correlation coefficients A₂₂ = o.190 土0.011 and A₄₄. = -0.025 土O. 024 that are consistent with the established spin sequence 5/ 2(E2)9 / 2(Ml +E2)7 / 2 and with an admixture of 16.20/0土1. 2% E2 radiation in the 136 Kev mixed transition. The results of the experiment are in excellent agreement with those obtained from conversion electron measurements and resolve the discrepancy apparent in earlier work on the 346-136 Kev cascade

Concurrency bugs are extremely hard to detect due to huge interleaving space. They are happening in the real world more often because of the prevalence of multi-threaded programs taking advantage of multi-core hardware, and microservice based distributed systems moving more and more applications to the cloud. As the most common non-deadlock concurrency bugs, atomicity violations are studied in many recent works, however, those methods are applicable only to single-variable atomicity violation, and don't consider the specific challenge in distributed systems that have both pessimistic and optimistic concurrency control. This dissertation presents a tool using model checking to predict atomicity violation concurrency bugs involving two shared variables or shared resources. We developed a unique method inferring correlation between shared variables in multi-threaded programs and shared resources in microservice based distributed systems, that is based on dynamic analysis and is able to detect the correlation that would be missed by static analysis. For multi-threaded programs, we use a binary instrumentation tool to capture runtime information about shared variables and synchronization events, and for microservice based distributed systems, we use a web proxy to capture HTTP based traffic about API calls and the shared resources they access including distributed locks. Based on the detected correlation and runtime trace, the tool is powerful and can explore a vast interleaving space of a multi-threaded program or a microservice based distributed system given a small set of captured test runs. It is applicable to large real-world systems and can predict atomicity violations missed by other related works for multi-threaded programs and a couple of previous unknown atomicity violation in real world open source microservice based systems. A limitation is that redundant model checking may be performed if two recorded interleaved traces yield the same partial order model.

With growing awareness and necessity for the world to move towards more sustainable (energy saving) forms of power generation, focus on the commercial use of Organic Rankine Cycle (ORC) turbine systems has subsequently increased in turn. ORC systems with their modular design can thus help in recovering heat, obtained as a byproduct from a variety of industrial processes, and thereby increase their overall system efficiency. As with conventional turbine systems, methods to improve their performance is an avenue that is still being actively researched on today. The various sources of losses in a turbine have thus been looked into, while prioritizing the literature study to factors that result in losses associated with the leakage flow over the blade tip. The purpose of this study is to develop a working methodology to investigate factors that affect the tip leakage loss in a small scale ORC turbine. The model and associated data used for comparison is based on an existing system, whose design has been provided by Againity AB, with the subsequent simulations carried out using Ansys CFX.

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This study presents an in-depth analysis of spatial voting behavior in Finland at the municipality level, using electoral data from 1983 to 2019. The primary objective is to investigate if the cultural field hypothesis holds true for Finland. If this hypothesis holds, distinct cultural domains should emerge within Finland. Furthermore, we hypothesized that if the cultural field hypothesis holds true, a distinct community would appear along the Russian border, leading to an east-west partition of Finland. To test the cultural field hypothesis, we do a spatial correlation analysis, and we use community detection to find distinct communities within Finland. The spatial correlation analysis suggested the existence of distinct communities in Finland that span approximately 400 km in length. The community detection then confirms this, revealing two main communities: The northern and the southern communities, and in 6 out of 10 elections, three communities emerged. Hence, the cultural field hypothesis holds true for Finland. However, the distribution of these communities did not support the hypothesis that a distinct community would emerge along the Russian border creating an east-west partition of Finland. Instead, we observed a north-south and a “west/south coastal” partition.

It has been shown in many studies that turbulent flows are highly dependent on their initial conditions. This thesis explores turbulent flow using direct numerical simulation (DNS) in a variety of situations, and culminates in the development of physically realizable initial conditions. The reaction of isotropic homogeneous turbulent flow to the instantaneous insertion of a wall is investigated using two-point correlations. A model with which to predict the behavior of the two-point correlations is also proposed. The proposed model utilizes a reflection technique that with a linear operation, it accurately predicts the behavior of the non-linear two point correlations. The model works exceedingly well for correlations involving wall-perpendicular velocities, but does not predict correlations involving only wall-parallel velocities as well. A vorticity approach is covered, in an effort to highlight which parts of the correlation decomposition are important to the prediction of the correlations after wall imposition. The vorticity study also helps highlight why the proposed linear model predicts the flow. The impact of the initial conditions on axisymmetric contraction flow of turbulent flow is examined, and as a consequence new initial conditions are developed based off of a physically realizable flow condition. The development of the new-initial conditions and the resulting fields are covered, as well as a study on the value of the turbulent decay exponent associated with decay of isotropic turbulent velocity fields.

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No description available.