Doctor of Philosophy

dissertationThis dissertation focuses initially on development of a nanoparticle mass spectrometer (NPMS) for single particle analysis utilizing a split ring electrode trap (SRET). Electrospray ionization generates nanoparticle ions that are guided and trapped in the SRET. Detection of single particles occurs by observing light scattered or fluorescence emitted from the particle. Three methods are used to determine the secular frequency (®z) of a single trapped particle: Fourier transform analysis of scattered light intensity, frequency sweep of the laser force, or frequency sweep of a constant AC voltage. From ©z, the mass-to-charge ratio may be ascertained. The AC frequency sweep method results in a peak width nearing 10 ppm. By averaging the peak position of multiple AC frequency sweep measurements, precision approaches 1 ppm. This method is then applied to single core-shell CdSe/ZnS quantum dots by activating their fluorescence with a CO2 laser. The secular frequency, mass, charge, and fluorescence intensity are tracked for a single QD over multiple days. Heating the QD sublimates the particle and causes it to eventually go dark. Once dark, the QD remains in the trap and begins to fluoresce intermittently. The focus of the later half is on reactions of vibrationally state-selected HOD+. Each of the fundamental vibrational states of HOD+ was investigated. Cross sections and product velocity distributions were obtained for every product for each reaction and each vibrational state investigated. Reactions of HOD+ with CO, N2O, CO2, and N2 were investigated. These reactions were chosen because proton transfer is endoergic for each reaction or thermoneutral. Mode- and bond-selective enhancement was observed for the cross sections of H+ and D+ transfer for the OH and OD stretch, respectively. The bend vibration also enhances reactivity; in some cases, the total enhancement for the bend is greater than that of the OH or OD stretches. Velocity distributions indicated that the mechanism for H+ and D+ transfer near threshold might be complex mediated, but it is difficult to tell because there is little energy available to the system near threshold. However, with increasing collision energy (Ecol), the reaction becomes increasingly direct and backward scattered

A Numerical Study of Methods for Moist Atmospheric Flows: Compressible Equations

We investigate two common numerical techniques for integrating reversible moist processes in atmospheric flows in the context of solving the fully compressible Euler equations. The first is a one-step, coupled technique based on using appropriate invariant variables such that terms resulting from phase change are eliminated in the governing equations. In the second approach, which is a two-step scheme, separate transport equations for liquid water and vapor water are used, and no conversion between water vapor and liquid water is allowed in the first step, while in the second step a saturation adjustment procedure is performed that correctly allocates the water into its two phases based on the Clausius-Clapeyron formula. The numerical techniques we describe are first validated by comparing to a well-established benchmark problem. Particular attention is then paid to the effect of changing the time scale at which the moist variables are adjusted to the saturation requirements in two different variations of the two-step scheme. This study is motivated by the fact that when acoustic modes are integrated separately in time (neglecting phase change related phenomena), or when sound-proof equations are integrated, the time scale for imposing saturation adjustment is typically much larger than the numerical one related to the acoustics

Unitarisation of EFT Amplitudes for Dark Matter Searches at the LHC

We propose a new approach to the LHC dark matter search analysis within the effective field theory (EFT) framework by utilising the K-matrix unitarisation formalism. This approach provides a reasonable estimate of the dark matter production cross section at high energies, and hence allows reliable bounds to be placed on the cut-off scale of relevant operators without running into the problem of perturbative unitarity violation. We exemplify this procedure for the effective operator D5 in monojet dark matter searches in the collinear approximation. We compare our bounds to those obtained using the truncation method and identify a parameter region where the unitarisation prescription leads to more stringent bounds.Comment: 20 pages, 7 figures. References added and minor corrections made to match published versio

Final Report: Lake Vostok: A Curiosity or a Focus for Interdisciplinary Study?

The goal of the NSF-sponsored workshop, held in held in Washington, D.C., on November 7-8, 1998, was to stimulate discussion within the U.S. science community on Lake Vostok, specifically addressing the question: "Is Lake Vostok a natural curiosity or an opportunity for uniquely posed interdisciplinary scientific programs?" The workshop was designed to outline an interdisciplinary science plan for studies of the lake

Evolutionary Processes a Focus of Decade-Long Ecosystem Study of Antarctic's Lake Vostok

As scientists probe for life in new habitats and try to understand the processes that triggered the origin and guided the evolution of life on Earth, environments beneath large ice sheets are beginning to emerge as key ecosystems. Modern subglacial environments are analogues both for the icy moons of Jupiter and the environmental stresses that led to widespread evolutionary radiation following the Neoproterozoic "snowball" Earth. The largest modern analogue to these distant systems is Lake Vostok, a great Antarctic subglacial lake, and the international science community is developing a plan to systematically survey and explore this complex system over the next decade. Approximately the size of Lake Ontario, Lake Vostok lies beneath the 4 km thick East Antarctic ice sheet (Figure 1). The lake is much deeper than Lake Ontario—remotely measured water depths reach 670 m

Trends and Regional Variation in Hip, Knee and Shoulder Replacement

Analyzes patterns in underuse or overuse of joint replacements among Medicare beneficiaries by geographic regions and race/ethnicity. Explores underlying factors and highlights the need for physician and patient education and shared decision making

Assessing intra- and inter-regional climate effects on Douglas-fir biomass dynamics in Oregon and Washington, USA

While ecological succession shapes contemporary forest structure and dynamics, other factors like forest structure (dense vs. sparse canopies) and climate may alter structural trajectories. To assess potential sources of variation in structural trajectories, we examined proportional biomass change for a regionally dominant tree species, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), across vegetation zones representing broad gradients in precipitation and temperature with 3510 forest inventory plots in Oregon and Washington, USA. We found that P. menziesii biomass change decreased with P. menziesii biomass stocks and increased with P. menziesii density, remaining positive in older stands only in the wet and warm vegetation zone. Within two of the vegetation zones, biomass change was greatest in warm and wet environments. In dry vegetation zones, positive P. menziesii biomass change responses to initial canopy cover and canopy cover change (i.e., increases with cover loss and decreases with cover gain) indicated shifts in forest structure. Variation in P. menziesii biomass dynamics within and between vegetation zones imply multi-scale climatic controls on forest structural trajectories for P. menziesii and highlight the potential for continued atmospheric carbon sequestration in warm and wet forests of the Pacific Northwest for both young and old forests, given that future climatic conditions support similar forest dynamics

Assessing intra- and inter-regional climate effects on Douglas-fir biomass dynamics in Oregon and Washington, USA

While ecological succession shapes contemporary forest structure and dynamics, other factors like forest structure (dense vs. sparse canopies) and climate may alter structural trajectories. To assess potential sources of variation in structural trajectories, we examined proportional biomass change for a regionally dominant tree species, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), across vegetation zones representing broad gradients in precipitation and temperature with 3510 forest inventory plots in Oregon and Washington, USA. We found that P. menziesii biomass change decreased with P. menziesii biomass stocks and increased with P. menziesii density, remaining positive in older stands only in the wet and warm vegetation zone. Within two of the vegetation zones, biomass change was greatest in warm and wet environments. In dry vegetation zones, positive P. menziesii biomass change responses to initial canopy cover and canopy cover change (i.e., increases with cover loss and decreases with cover gain) indicated shifts in forest structure. Variation in P. menziesii biomass dynamics within and between vegetation zones imply multi-scale climatic controls on forest structural trajectories for P. menziesii and highlight the potential for continued atmospheric carbon sequestration in warm and wet forests of the Pacific Northwest for both young and old forests, given that future climatic conditions support similar forest dynamics