Thesis/Capstone Archive

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Tyler Bahr (Senior Thesis, April 2018, Advisor: Mark Transtrum )

Abstract

In 1952 Hodgkin and Huxley formulated the fundamental biophysical model of how neurons integrate input and fire electric spikes. With 25 parameters and 4 dynamical variables, the model is quite complex. Using information theory, we analyze the model complexity and demonstrate that it is unnecessarily complex for many neural modeling tasks. Using the manifold boundary approximation method of model reduction, we perform a series of parameter reductions on the original 25-parameter model and create a series of spiking Hodgin-Huxley models, each with decreasing parameter number. We analyze the physical meaning of some key approximations uncovered by our systematic reduction methods, which are "blind" to the real physical processes the model is intended to capture. We then evaluate the behavior of the most greatly reduced 14-parameter model under different experimental conditions, including networks of neurons. We also discuss new questions that have arisen as a result of our work

Adam Dodson (Senior Thesis, April 2018, Advisor: Scott Bergeson )

Abstract

Emission spectra from atoms with hyperfine structure typically show closely-spaced atomic transitions. This happens because the hyperfine interaction splits and shifts the fine-structure energy levels in both the ground and excited state by a small amount. In laser-induced fluorescence measurements, the atoms are driven into a superposition of excited hyperfine states which then decay into a range of ground hyperfine states. Interference in different quantum pathways for this process influences the probability of excitation. Unless this is properly accounted for, this interference effect systematically shifts the apparent center of the fluorescence lineshape. We report measurements of this quantum interference (QI) effect in Yb-171 and Yb-173 and show that QI shifts the line centers by up to 5 MHz. We extend and verify a published QI model for Yb-171. We show that optical pumping complicates a straightfoward application of the model to the experiment for Yb-173. We then demonstrate that optical pumping-induced variations in the distribution of magnetic sub-levels in the hyperfine structure are insufficient to explain observed shifts in Yb-173.

Jesse Richmond (Senior Thesis, April 2018, Advisor: David Allred )

Abstract

The Labeled Release experiment of the Viking landers led to the hypothesis that martian soil is highly oxidized. Hydrogen peroxide has been suggested as the primary oxidant, but no definitive theory exists as to how it forms in the martian environment. We propose that ultraviolet radiation interacts with carbon dioxide, water, and other trace substances in the martian atmosphere to form this hydrogen peroxide. We tested this theory by constucting a Mars-like atmosphere within a vacuum system and then exposing it to ultraviolet radiation from a UV lamp. The resulting products were then collected into a cold trap and analyzed by a mass spectrometer. Initial results do seem to indicate that hydrogen peroxide was generated by the interaction, as well as other substances. If correct, this data further expands our knowledge of the martian environment and explains why no martian organics have been discovered thus far.

Aaron Vaughn (Senior Thesis, April 2018, Advisor: Traci Neilsen )

Abstract

Jet noise has primarily been examined for laboratory-scale jets and only recently for full-scale jets. In this thesis, jet noise from a laboratory-scale Mach 1.8 jet and an F-35B high-performance military aircraft are observed and compared. Both contain turbulent mixing noise while only the full-scale jet contains broadband shock-associated noise (BBSAN). Previously developed empirical models for turbulent mixing noise were used to perform spectral decompositions. Similar angular trends for similarity spectra decompositions of the turbulent mixing noise exist across both sets of measurements. Full-scale BBSAN spatial trends are similar to laboratory-scale results from the literature for peak frequency but differ for peak level and spectral width. Similarity spectra decomposition is sufficient to match the spectra from the laboratory-scale jet while a three-way spectral decomposition including BBSAN is needed to fit the F-35B spectra. Discrepancies between fits and measured spectra exist for both jets at small inlet angles for high frequencies and at the region of maximum radiation for the F-35B. However, overall, the empirical models produce realistic representations of the measured spectra