Digital Commons Network^™

Aspects Of String Compactification, Guoqin Ren

Doctoral Dissertations

This dissertation addresses some interesting problems in string compactification relevant to phenomenology, especially cosmological models derived from string theory Most attention is drawn to stabilizing the moduli and discussing the cosmology solutions given the effective potential obtained from string theory. We first discuss compactification of type IIB string theory in the presence of flux. With the moduli stabilized, we obtain the effective potential in the large volume limit. We then focus on getting the vacua of the potential and solving the cosmology equations. Finally we compare the solutions with observations in cosmology.

Global Structure Of The Nightside Proton Precipitation During Substorms Using Simulations And Observations, Matthew L. Gilson

Doctoral Dissertations

In regions of thin strong current sheets, the first adiabatic invariant of protons can be violated leading to pitch angle diffusion into the loss cone and ultimately auroral precipitation. The central plasma sheet typically provides a stretched enough magnetic field configuration to account for the nightside proton precipitation. During substorms, the outflow from the near earth reconnection line at approximately 20 RE brings magnetic flux from the highly stretched magnetotail into the near earth magnetosphere. Once there, the flux piles up forming an azimuthally localized region where the magnetic field is more dipolar. Current flows into and out of the …

Statistical Study Of Oxygen+ Transport From The Cusp To The Plasmasheet, Jing Liao

Doctoral Dissertations

Using Cluster/CODIF data, we have determined the occurrence frequency of the cusp-source O+ in the magnetotail to determine where and when it is observed. The results show that the probability to observe O+ along the transport path is high even during nonstorm times, although, as expected, the highest probability is found during storm times. In addition to the outflow rate increasing, the transport path itself also changes during storm times, bringing more O+ to the near-earth plasma sheet. Interplanetary magnetic field (IMF) magnitude is the most effective driver for bringing O+ into the near-Earth lobes. It was also found that …

Artifact-Based Reflective Interviews For Identifying Pragmatic Epistemological Resources, Christopher Walden Shubert

Doctoral Dissertations

Physics Education Research studies the science of teaching and learning physics. The process of student learning is complex, and the factors that affect it are numerous. Describing students' understanding of physics knowledge and reasoning is the basis for much productive research; however, such research fails to account for certain types of student learning difficulties. In this dissertation, I explore one source of student difficulty: personal epistemology, students' ideas about knowledge and knowing.

Epistemology traditionally answers three questions: What is knowledge? How is knowledge created? And, how do we know what we know? An individual's responses to these questions can affect …

High Lundquist Number Simulations Of Parker's Model Of Coronal Heating: Scaling And Current Sheet Statistics Using Heterogeneous Computing Architectures, Liwei Lin

Doctoral Dissertations

Parker's model [Parker, Astrophys. J., 174, 499 (1972)] is one of the most discussed mechanisms for coronal heating and has generated much debate. We have recently obtained new scaling results for a 2D version of this problem suggesting that the heating rate becomes independent of resistivity in a statistical steady state [Ng and Bhattacharjee, Astrophys. J., 675, 899 (2008)]. Our numerical work has now been extended to 3D using high resolution MHD numerical simulations. Random photospheric footpoint motion is applied for a time much longer than the correlation time of the motion to obtain converged average coronal heating rates. Simulations …

The Effects Of Weak Collisions On Nonlinear Plasma Kinetics, Carrie E. Black

Doctoral Dissertations

Kinetic plasma behaviors have long been of interest to those studying space and laboratory plasmas. For instance, kinetic plasma instabilities are widely believed to be responsible for the generation of anomalous resistivity in reconnection layers, providing a possible mechanism for fast reconnection. The concept of Landau damping is fundamental to such wave kinetic instabilities in space, and is treated typically within the framework of the collisionless Vlasov equation. It has become clear in recent theoretical and experimental work that weak collisions are a singular perturbation on the collisionless theory, and qualitatively alter the results of the collisionless theory. In particular, …

Observational Aspects Of Imf Draping Around The Magnetosphere, Brendan S. Harris

Master's Theses and Capstones

A key parameter in determining the flow of the solar wind around the magnetosphere is the Alfven Mach number (Ma) because it determines conditions at the bow shock. High Ma approaches the gas dynamic limit of flow around the magnetosphere, while low Ma implies strong magnetic forces on the flow. We study a long interval of high Ma during the recent pronounced solar minimum 2007--2009, and derive the magnetopause and bow shock shapes from data. We compare our results with models of the magnetopause and properties of the bow shock and find that during this period, the subsolar magnetosheath was …