Doctor of Philosophy

dissertationThe research presented in this dissertation focuses on the use of platinum-based catalysts to enhance endothermic fuel cooling. Chapter 1 gives a brief introduction to the motivation for this work. Chapter 2 presents fundamental studies on the catalytic dehydrogenation of ethylene by size-selected Ptn (n = 4, 7, 8) clusters deposited onto thin film alumina supports. The model catalysts were probed by a combination of experimental and theoretical techniques including; temperature-programmed desorption and reaction (TPD/R), low energy ion scattering spectroscopy (ISS), X-ray photoelectron spectroscopy (XPS), plane wave density-functional theory (PW-DFT), and statistical mechanical theory. It is shown that the Pt clusters dehydrogenated approximately half of the initially adsorbed ethylene, leading to deactivation of the catalyst via (coking) carbon deposition. The catalytic activity was observed to be size-dependent and strongly correlated to the cluster structure, with Pt7 demonstrating the highest activity. In Chapter 3 the focus turns to selectively doping Pt7 clusters with boron. A combination of experiment and theory were used investigate the alkene-binding affinity of the bimetallic (PtnBm/alumina) model catalysts. A comparison of the theoretical and experimental results show that doping the Pt clusters with boron modifies the alkene-binding affinity and thus the tendency toward dehydrogenation to coke precursors. Chapter 4 describes a way to produce bimetallic (PtnBm/alumina) model catalysts by exposing prepared Ptn/alumina samples to diborane and heating. It is shown that the diborane exposure/hearting procedure results in the preferential binding of B to the Pt clusters

Non-Gaussianity and Excursion Set Theory: Halo Bias

We study the impact of primordial non-Gaussianity generated during inflation on the bias of halos using excursion set theory. We recapture the familiar result that the bias scales as $k^{-2}$ on large scales for local type non-Gaussianity but explicitly identify the approximations that go into this conclusion and the corrections to it. We solve the more complicated problem of non-spherical halos, for which the collapse threshold is scale dependent.Comment: 13 pages, 3 figures. v2 references added. Matches published versio

Constraining the Mass-Richness Relationship of redMaPPer Clusters with Angular Clustering

The potential of using cluster clustering for calibrating the mass-observable relation of galaxy clusters has been recognized theoretically for over a decade. Here, we demonstrate the feasibility of this technique to achieve high precision mass calibration using redMaPPer clusters in the Sloan Digital Sky Survey North Galactic Cap. By including cross-correlations between several richness bins in our analysis we significantly improve the statistical precision of our mass constraints. The amplitude of the mass-richness relation is constrained to 7% statistical precision. However, the error budget is systematics dominated, reaching an 18% total error that is dominated by theoretical uncertainty in the bias-mass relation for dark matter halos. We perform a detailed treatment of the effects of assembly bias on our analysis, finding that the contribution of such effects to our parameter uncertainties is somewhat greater than that of measurement noise. We confirm the results from Miyatake et al. (2015) that the clustering amplitude of redMaPPer clusters depends on galaxy concentration, and provide additional evidence in support of this effect being due to some form of assembly bias. The results presented here demonstrate the power of cluster clustering for mass calibration and cosmology provided the current theoretical systematics can be ameliorated.Comment: 18 pages, 9 figure

Testing Classical Interactions Between Finite Particles as a Model of Nuclear Structure

A finite dimensional model for the electron and proton has been used to compute nuclear properties such as: structure, binding energies, energies and rates of decay of radioactive isotopes. Computations were conducted within the frame of classical electromagnetic interactions between toroidal electrons and protons of finite, fixed dimensions. Positions and orientations of each particle were allowed to vary using the variational method, until the minimum energy configuration was attained. Nucleon shell structures were found to build from outer levels toward inner ones, with occupancies following the magic numbers so well known in nuclear physics. Neutrons were found to be formed via toroidal protons binding electronically and magnetically within toroidal electrons, which are significantly larger than the former. Details are presented for 40K as a model test case. Additional results are provided for several select radio nuclides having a diversity of nuclear structures. These calculations, although admittedly of questionable accuracy, do none the less appear to yield results which are in some 90% agreement with the experimental values, over the very limited number of examples tested