UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

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2010 - 20112

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    Measurements of Coronal Rotation and Small Coronal Ejections Using the STEREO COR1 Coronagraphs
    (2011) Jones, Shaela I; Davila, Joseph M; Hamilton, Douglas C; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    I present results of two studies conducted using the STEREO COR1 coronagraph: single- and dual-spacecraft measurements of white-light coronal rotation rates in 2007 and 2008 as a function of latitude and altitude, and trajectory characteristics of small, upward-moving coronal density enhancements. Single-spacecraft coronal rotation measurements indicate that the rotation rate of the corona in the COR1 field of view is independent of latitude and altitude, consistent with previous studies that showed rotation in the corona is very rigid compared with rotation in the photosphere. The equatorial rotation rate for this study was found to be 27.06 ± 0.08 days in 2007 and 26.97 ± 0.10 days in 2008. Using the measured rotation periods, I extract the average coronal intensity as a function of longitude at each latitude at 1.8 solar radii, and compare them to reconstructions of the coronal electron density. The longitudinal structure derived from the rotation measurements is very similar to the electron density measurements, indicating that the observed rigidity of the coronal rotation does not seem to be due to projection of low-latitude features onto higher latitudes as some authors have speculated. It has been suggested that the relative rigidity of the coronal rotation may be at least in part a measurement effect, due to the selective measurement of large and/or long-lived features in coronagraph rotation studies. Following the measurements of coronal rotation in the STEREO COR1 field of view using standard coronagraph rotation measurement techniques, I present for the first time short time lag coronagraph rotation measurements, using the unique capabilities of the STEREO dual-spacecraft mission. Finally, I present results of a systematic search of nineteen days' worth of COR1 data for small, faint, outward-moving density enhancements, sometimes referred to in the literature as plasma blobs. In the past these plasma blobs have been studied in the LASCO C2 and C3 fields of view, which extend only as low as 2 - 2.5 solar radii, and it was believed that their origin was in pointed cusps at the top of the streamer belt. Using the COR1 coronagraph I was able to observe many such features between 1.5 - 2.0 solar radii, a height below what would normally be expected if these features originate at the top of the streamer belt as suggested by the earlier observations.
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    Visualization of the Vortex Lattice Dynamics in Superfluid Helium
    (2010) Gaff, Kristina Teresa; Lathrop, Daniel P; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    We study the lattice structure and dynamics of the quantized vortices in superfluid helium-4 using a new rotating experiment. This setup includes control of the entire apparatus from the rotating frame, installation of a new EMCCD camera that allows for imaging of nanoscale tracer particles, and the development and implementation of a new isolation cell, which permits investigation into new phenomena such as differential rotation in helium-II. We have observed the vortex lattice dynamics in the (r, &phi) plane (i.e. transverse to the vortices) and present here the first real-time visualization of Tkachenko waves in helium-II from this cross section. Additionally, we present evidence of differential rotation with distinct Stewartson layer boundaries, possible Kelvin-Helmholtz instabilities, and the formation and propagation of superfluid collective vortex eddies. We show that the angular velocity is a function of radius and may be driven by the geometry of the isolation cell. We also document the observation and analysis of gravity-capillary surface waves that demonstrate an interaction between the liquid helium free surface and the bulk of the fluid.