Six year program of French as a solution to the problem of the better attainment of objectives

Thesis (Ed. M.)--Boston University, 193

Perceptions and Experiences of African American AmeriCorps Program Participants

AmeriCorps, a voluntary public service program founded in 1993, has largely consisted of a nonminority middle-class group, generally 20 to 29 years old, who had the financial assistance of family while serving. African American participants may be experiencing AmeriCorps-based programs differently, in areas such as financial solvency, job readiness skills, and the ability to begin or return to college. This qualitative study was designed to reveal the perceptions and experiences of African American participants who have completed AmeriCorps service in a Midwest metropolis. Using the lens of critical race theory, which explored African American Corps members through a historical position of disadvantage. This study was conducted using group characteristics sampling of nine participants. In-depth interviews were transcribed, and data were coded and assessed for trends related to Corps-member experiences. The data revealed that AmeriCorps-based programs have been designed for a nonminority middle class that can sustain the financial hardships of serving in communities of need, which was revealed in part by most participants receiving public assistance and the underutilization of the participant’s Education Award. The results of this study may provide a better understanding of the effectiveness of AmeriCorps-based programs for African American participants. Although limited in scope, the results of the study support positive social change through the need for AmeriCorps leadership to recognize that African American AmeriCorps members may need to be supported differently from their nonminority Corps members in service

Stability issues of entropy-stable and/or split-form high-order schemes -- Analysis of local linear stability

The focus of the present research is on the analysis of local linear stability of high-order (including split-form) summation-by-parts methods, with e.g. two-point entropy-conserving fluxes, approximating non-linear conservation laws. Our main finding is that local linear stability is not guaranteed even when the scheme is non-linearly stable and that this has grave implications for simulation results. We show that entropy-conserving two-point fluxes are inherently locally linearly unstable, as they can be dissipative or anti-dissipative. Unfortunately, these fluxes are at the core of many commonly used high-order entropy-stable extensions, including split-form summation-by-parts discontinuous Galerkin spectral element methods (or spectral collocation methods). For the non-linear Burgers equation, we demonstrate numerically that such schemes cause exponential growth of errors. Furthermore, we demonstrate a similar abnormal behaviour for the compressible Euler equations. Finally, we demonstrate numerically that other commonly used split-forms, such as the Kennedy and Gruber splitting, are also locally linearly unstable

Global gyrokinetic simulations of ITG turbulence in the configuration space of the Wendelstein 7-X stellarator

We study the effect of turbulent transport in different magnetic configurations of the Weldenstein 7-X stellarator. In particular, we performed direct numerical simulations with the global gyrokinetic code GENE-3D, modeling the behavior of Ion Temperature Gradient turbulence in the Standard, High-Mirror, and Low-Mirror configurations of W7-X. We found that the Low-Mirror configuration produces more transport than both the High-Mirror and the Standard configurations. By comparison with radially local simulations, we have demonstrated the importance of performing global nonlinear simulations to predict the turbulent fluxes quantitatively

Genetic Effect of Transportation Infrastructure on Roe Deer Populations (Capreolus capreolus)

Anthropogenic transportation infrastructure is a major factor of habitat fragmentation leading to genetic population fragmentation in wildlife. Assessing and understanding the impact of this deterministic factor on genetic diversity and divergence of populations is crucial to appraise the viability of wildlife populations in fragmented landscapes. In this study, the roe deer is used as an example species for the assessment of genetic differentiation of populations separated by an anthropogenic barrier. In order to detect genetic discontinuities, we screened 12 polymorphic microsatellites on 222 individuals out of 11 roe deer populations that were sampled on the east and the westside of a fenced motorway in Central Switzerland. The interaction between landscape structure and microevolutionary processes such as gene flow and drift were assessed and evaluated by different population genetic methods like F-statistics, Mantel test, spatial autocorrelation analyses, Monmonier algorithm, and principal component analysis in conjunction with geographic information system data (synthesis map). We revealed an influence of the transportation infrastructure on genetic divergence of the roe deer population examined, but no impact on genetic diversity was detected. Based on the achieved genetic findings, recommendations for management implementation were mad

Nano-Material Aspects of Shock Absorption in Bone Joints

This theoretical study is based on a nano-technological evaluation of the effect of pressure on the composite bone fine structure. It turned out, that the well known macroscopic mechano-elastic performance of bones in combination with muscles and tendons is just one functional aspect which is critically supported by additional micro- and nano- shock damping technology aimed at minimising local bone material damage within the joints and supporting spongy bone material. The identified mechanisms comprise essentially three phenomena localised within the three–dimensional spongy structure with channels and so called perforated flexible tensulae membranes of different dimensions intersecting and linking them. Kinetic energy of a mechanical shock may be dissipated within the solid-liquid composite bone structure into heat via the generation of quasi-chaotic hydromechanic micro-turbulence. It may generate electro-kinetic energy in terms of electric currents and potentials. And the resulting specific structural and surface electrochemical changes may induce the compressible intra-osseal liquid to build up pressure dependent free chemical energy. Innovative bone joint prostheses will have to consider and to be adapted to the nano-material aspects of shock absorption in the operated bones

An Entropy Stable Nodal Discontinuous Galerkin Method for the resistive MHD Equations. Part II: Subcell Finite Volume Shock Capturing

The second paper of this series presents two robust entropy stable shock-capturing methods for discontinuous Galerkin spectral element(DGSEM)discretizations of the compressible magneto-hydrodynamics (MHD) equations. Specifically, we use the resistive GLM-MHD equations, which include a divergence cleaning mechanism that is based on a generalized Lagrange multiplier (GLM). For the continuous entropy analysis to hold, and due to the divergence-free constraint on the magnetic field, the GLM-MHD system requires the use of non-conservative terms, which need special treatment. Hennemann et al. ["A provably entropy stable subcell shock capturing approach for high order split form DG for the compressible Euler equations". JCP, 2020] recently presented an entropy stable shock-capturing strategy for DGSEM discretizations of the Euler equations that blends the DGSEM scheme with a subcell first-order finite volume (FV) method. Our first contribution is the extension of the method of Hennemann et al. to systems with non-conservative terms, such as the GLM-MHD equations. In our approach, the advective and non-conservative terms of the equations are discretized with a hybrid FV/DGSEM scheme, whereas the visco-resistive terms are discretized only with the high-order DGSEM method. We prove that the extended method is entropy stable on three-dimensional unstructured curvilinear meshes. Our second contribution is the derivation and analysis of a second entropy stable shock-capturing method that provides enhanced resolution by using a subcell reconstruction procedure that is carefully built to ensure entropy stability. We provide a numerical verification of the properties of the hybrid FV/DGSEM schemes on curvilinear meshes and show their robustness and accuracy with common benchmark cases, such as the Orszag-Tang vortex and the GEM (Geospace Environmental Modeling) reconnection challenge. Finally, we simulate a space physics application: the interaction of Jupiter's magnetic field with the plasma torus generated by the moon Io

A matrix-free high-order discontinuous Galerkin compressible Navier-Stokes solver: A performance comparison of compressible and incompressible formulations for turbulent incompressible flows

Both compressible and incompressible Navier-Stokes solvers can be used and are used to solve incompressible turbulent flow problems. In the compressible case, the Mach number is then considered as a solver parameter that is set to a small value, $\mathrm{M}\approx 0.1$, in order to mimic incompressible flows. This strategy is widely used for high-order discontinuous Galerkin discretizations of the compressible Navier-Stokes equations. The present work raises the question regarding the computational efficiency of compressible DG solvers as compared to a genuinely incompressible formulation. Our contributions to the state-of-the-art are twofold: Firstly, we present a high-performance discontinuous Galerkin solver for the compressible Navier-Stokes equations based on a highly efficient matrix-free implementation that targets modern cache-based multicore architectures. The performance results presented in this work focus on the node-level performance and our results suggest that there is great potential for further performance improvements for current state-of-the-art discontinuous Galerkin implementations of the compressible Navier-Stokes equations. Secondly, this compressible Navier-Stokes solver is put into perspective by comparing it to an incompressible DG solver that uses the same matrix-free implementation. We discuss algorithmic differences between both solution strategies and present an in-depth numerical investigation of the performance. The considered benchmark test cases are the three-dimensional Taylor-Green vortex problem as a representative of transitional flows and the turbulent channel flow problem as a representative of wall-bounded turbulent flows