Thesis/Capstone Archive

Year:
Advisor:
Keir Ashby (Senior Thesis, April 2018, Advisor: Darin Ragozzine )

Abstract

Discovering and understanding the properties of exoplanets, or planets orbiting other stars, is one of the great scientific quests of the 21st century. Since launching in 2009, NASA’s Kepler space telescope has returned measurements for 200,000 stars along with the exoplanet candidates orbiting them. To correct for Kepler’s bias against small and/or long-period planets, we are developing an advanced computer model capable of inferring the true underlying architectures of exoplanetary systems. This Exoplanetary System Simulator, “SysSim”, generates simulated catalogs of exoplanet systems and uses Approximate Bayesian Computation over several generations to produce several estimations of the actual exoplanet population. I have produced a flowchart to help users navigate the complex code structures of SysSim. To improve the accuracy of our MES (Multiple Event Statistic) calculations, I wrote and integrated code to interpolate MES values for individual exoplanets. I have produced several plots to analyze and interpret the results of SysSim. These figures revealed that SysSim works well in determining a good estimate for exoplanet occurrence rates but we also found that individual bins have “leaking” Simulated Observed planets and that the Simulated Observed Catalog and Kepler Catalog are significantly out of balance with each other. Further work will be undergone to examine and correct these problems.

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

Jonathan Bassett (Senior Thesis, April 2018, Advisor: David Neilsen )

Abstract

We study the effects of spinning bodies on the chaotic properties of the three-body problem in general relativity. We use the post-Newtonian Hamiltonian to order 2 with the leading-order spin-orbit Hamiltonian. We study a system composed of a binary star system in a circular orbit and an incoming star. We generalize previous work by adding spin to each of the objects. The parameter space includes both regions with predictable behavior and regions with chaotic behavior, but the spin of the stars does not significantly alter the size of chaotic regions. Spin does not appear to have a significant effect on chaos in the relativistic three-body problem for this system.

William Black (Senior Thesis, April 2018, Advisor: David Neilsen )

Abstract

Supermassive black holes (SMBHs) are orphans—since no known progenitors exist, their origins are mysterious. They are so massive that even if the first stars collapsed into black holes, they would struggle to even come close to supermassive sizes. I investigate whether primordial black holes (PBHs), formed by overdensities in the Big Bang, could be the progenitors of SMBH. I use the cosmology code Enzo to simulate the growth of single solar mass PBHs over the course of ~325 Myr to see if the PBHs can reach supermassive sizes. Additionally, I compare Bondi accretion to viscous accretion. I use two methods to test whether PBHs could grow fast enough to become SMBHs. First: comparison to the growth of their surrounding halos—if a PBH is roughly 10^3 M⊙ by the time its halo is 10^8 M⊙, PBH–SMBH evolution is possible. Second: comparison to observed early SMBHs. If our PBHs reach similar sizes by similar times, PBH–SMBH evolution could be a viable pathway for those early observed SMBHs. Aside from the main results, I discovered that Bondi accretion and viscous accretion result in drastically different accretion rates. While black holes growing with Bondi accretion grew on order 10^-4, black holes with viscous accretion grew on order 10^+4. This is likely due to the dependence of Bondi accretion on simulation resolution. Given sufficiently dense seeding points, I found that the growth of PBHs does match the growth needed to reach supermassive sizes. The PBHs reached 10^3 M⊙ by the time their halos were 10^8 M⊙, so they do have the potential to reach the sizes of many observed SMBHs. Their extrapolated growth barely fell short of observed early SMBHs, but if 10–100 M⊙ PBHs were seeded, their growth trajectory would be on track to reach the sizes of early SMBHs.

Michael Carlson (Senior Thesis, April 2018, Advisor: Ross Spencer )

Abstract

The shock structure near the skimmer cone of the plasma/vacuum interface of an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) is computationally modeled using a Direct Simulation Monte Carlo (DSMC) code, FENIX. These shocks are caused by a hypersonic, rarefied gas flow hitting a metal surface. To determine the most accurate simulation of the shocks, three different gas--surface interaction models are tested against existing experimental data. The three interaction models used in this study are the specular, thermal and Cercignani-Lampis-Lord (CLL) models. The specular and thermal models are simpler to implement, but do not result in the correct shock structure. Namely, the specular model conserves too much energy in the reflected particles and does not scatter the particles enough. The thermal model does not conserve enough energy and scatters particles too much. The CLL model requires more time to set up, but results in a more accurate representation of the shock. This additional set up time comes from accommodation coefficients in the CLL model that can be set to approximately represent any surface, with its accompanying roughness and temperature. To find these accommodation coefficients, the simulated shocks need to be matched with experimental data. We found that the specular gas--surface interaction model gave the most accurate shock structure.

Joseph Chandler (Senior Thesis, April 2018, Advisor: Ross Spencer )

Abstract

Between the skimmer cone and the mass analyzer of an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) lies an electrostatic ion lens. The lens uses a large negative potential to remove the electrons from the plasma and to collimate the ions forming a plasma sheath. By using Boltzmann electrons and collisionless ions to computationally model this interaction, we can calculate the electrostatic potential and ion density near the skimmer cone. Doing this calculation on a cylindrically symmetric grid gives a version of Poisson's equation, which is a second order nonlinear partial differential equation that we try to solve using a successive overrelaxation technique. In this plasma sheath calculation, no pre-sheath is required due to the supersonic velocities of the ions. By calculating the position of the plasma sheath based on different initial conditions we are developing an understanding of how and where this sheath forms in both one and two dimensions.

Scott Crossen (Senior Thesis, April 2018, Advisor: John Colton )

Abstract

Electron spin resonance (ESR) is an important tool in understanding the quantum-mechanical properties of condensed matter. Its applications range from studying lattice defects in solids to studying spin coherence in qubit candidate materials used for quantum computing. When coupled with a photoluminescence measuring component, it is possible to optically record ESR information contained in the resulting induced light. This unique form of ESR is called optically detected magnetic resonance (ODMR). In this thesis we compare experimental ODMR data with ESR predictions generated from a computational modeling system. To investigate the differences between these two methods we will study one spin-system in particular: irradiated 4H silicon carbide. This specimen will serve as the primary means to connect the two very different forms of computational and practical ESR spectroscopy commonly used today. Methods and theory for both methods will be described and resulting spectra will be presented for comparison. Though there will always be some differences, results show that computational ESR predictions match experimental results to the same extent that the underlying Hamiltonian for that particular system is understood.

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.

Carson Evans (Senior Thesis, April 2018, Advisor: Ross Spencer )

Abstract

The plasma torch of the Inductively Coupled Plasma Mass Spectrometer (ICP) is powered by a 3-turn coil attached to a radio-frequency generator running at 40 MHz. The discharge is started by a Tesla coil that briefly ionizes a small fraction of the argon gas flowing through the coil. After the initial ionization pulse, the RF field produces the electric field that gives the electrons enough energy to heat the argon gas. As the electrons gain energy from the RF field they reach an energy capable of either exciting or ionizing the argon atoms. We are modeling the effect of the RF field on the electrons as well as the effect of collisions between electrons with neutral, excited, and ionized argon and with other electrons. We are also including the possibility of de-excitation argon. Our goal is to see an electron avalanche, a chain reaction where electrons ionizing argon neutrals create more free electrons which in turn ionize more argon.

Andy Hernandez (Senior Thesis, April 2018, Advisor: Eric Hintz )

Abstract

Magnitudes of stars are measured from the energy we measure (apparent) and the total energy output over the entire surface of the star (absolute). In this work we find apparent magnitudes for specified wavelengths of the double cluster h and χ Persei. Apparent magnitudes are attained using point spread function photometry, which is utilized in order to help separate closely spaced stars existing in the clusters. Color-color diagrams are shown detailing the physical properties of h and χ Persei. These are done using the Hα index, described herein, with the Hα magnitude. From these diagrams we can recreate a Hertzsprung-Russel diagram with the addition of Be type stars being easily identifiable. A second, unknown group is discussed. An analysis of the Hα index with the Hβ index shows how Hα emission continues beyond Hβ emission for emission type objects. Using this Hα Hβ index plot emission objects are easily identifiable.

Lauren Hindman (Senior Thesis, May 2018, Advisor: Joseph Moody )

Abstract

Blazars, a subclass of Active Galactic Nuclei (AGN), are characterized by a jet of particles accelerated by magnetic fields around supermassive black holes. For blazars, these jets are angled toward Earth. These objects are known to change magnitude, or flare, often and sometimes rapidly. It is thought that two mechalisms are mainly responsible for flaring: geometric instabilities in the jetswhichoccurstochastically,andperiodicchangesinjetoraccretiondiskactivityaddoriendation from orbital perturbations. Using our Remote Observatory for Variable Object Research (ROVOR), we monitored 192 of these objects using both V and R Johnson broadband spectral filters over the course of a year. We comment on the variability observed and which mechanism may be most responsible.

Heather Hogg (Senior Thesis, April 2018, Advisor: John Colton )

Abstract

Determining the relationship between temperature and photoluminescence lifetime is central to creating temperature probes for microfluidic devices and laser surgery. Rhodamine B, a highly photoluminescent organic dye, is a particularly good candidate for temperature probes. This thesis discusses the use of time-correlated single photon counting to determine photoluminescence lifetimes of rhodamine B at temperatures from 16 K to 296.5 K. The instrument response function is separated from the true photoluminescence lifetime data with deconvolution data analysis techniques. The relationship between temperature and photoluminescence lifetime for rhodamine B is shown to be most accurately represented by a sigmoidal function, with very little variation at low temperature ranges. It is concluded that the behavior of the lifetime follows theoretical quenching regions over different temperature ranges.

Stefan Lehnardt (Capstone, April 2018, Advisor: Robert Davis )

Abstract

Single-layer graphene consists of a single layer of sp2-bonded carbon atoms and exhibits many remarkable properties. It is the strongest material ever measured with a tensile strength of 90 GPa. As a single layer of atoms, however, single-layer graphene cannot cope with macroscopic forces and its applications are limited. Multi-layer graphene combines many layers of graphene and may be able to withstand forces that single-layer graphene cannot. To determine whether or not multi-layer graphene, (MLG) is suitable for a given application, it is important to know its mechanical properties and how they compare to those of single-layer graphene. This report focuses on the burst pressure of MLG membranes as grown on modified nickel substrates suspended over openings in silicon.

Steven Maggard (Senior Thesis, April 2018, Advisor: Darin Ragozzine )

Abstract

Thousands of asteroid-like objects reside in the Kuiper Belt Region. For accurate dynamical classification, the precision of their orbits needs rigorously tested. Using an analysis pipeline we created, we generated 30 statistically-weighted orbital clones for over 2000 Kuiper Belt Objects(KBOs). These orbits are integrated backwards in time 50 Myr. We created a database from the propagated orbits, from which we calculated the proper orbital elements for each KBO. We used the method established by Ragozzine and Brown (2007) to determine each KBOs relation to the dwarf planet Haumea. Currently, we have more than tripled the number of Haumea Family Members established by Ragozzine and Brown (2007). We conclude that other collisional families can befound using similar methods applied to Haumea and the orbital database we created.

Brittni Newbold (Senior Thesis, April 2018, Advisor: Karine Chesnel )

Abstract

Magnetite nanoparticles have great potential for use in medical and other applications, so understanding their properties is crucial. A property still left to be understood is the magnetic ordering of assemblies of nanoparticles at the nanoscale. This paper addresses how the magnetic ordering in magnetite nanoparticle assemblies changes as a function of nanoparticle size and external magnetic field at high temperature. Nanoparticle assemblies were fabricated using organic methods and placed on membranes. These samples were put through x-ray resonant magnetic scattering (XRMS) which produced scattering images that provided information about the magnetic ordering of the particles. Various images were obtained using XRMS for different field values and temperatures. These images were reduced to one-dimensional scattering profiles. By fitting these scattering profiles with a model, we found the percentages of ferromagnetic contribution, antiferromagnetic contribution, and the random contribution. There is a large random contribution as the field value approaches 0 Oe for Sample 9, the sample with the smallest particles, at 300 K. For Sample 3, the sample with the largest particles, at 280 K and at 300 K, there is a slight increase in the antiferromagnetic contribution and large random contribution at low field value. The larger particles are thus demonstrating more antiferromagnetic ordering at low magnetic field values than the smaller particles when placed in high temperature. Therefore, our methods yield information about the magnetic ordering of magnetite nanoparticles and the possibility to control the magnetic ordering through particle size.

Felicity Nielson (Senior Thesis, April 2018, Advisor: Gus Hart )

Abstract

Steel is an incredibly valuable, versatile material. Unfortunately, high-strength steels are vulnerable to hydrogen embrittlement, a process that describes the degradation of a crystalline- structured material when too much hydrogen is absorbed. When enough hydrogen builds up, it can lead to early and unexpected failure of the material, which is both costly and dangerous. Recent decades have seen a surge of efforts to solve this problem, but a general, viable solution has yet to be found. In this paper, we continue a new method using machine learning techniques in conjunction with atomic environment representations to predict global properties based on local atomic positions. Steel is comprised mostly of the base element iron. The defects in the iron crystal structure are where hydrogen prefers to adsorb. By developing a technique that will allow us to understand the global properties in these areas, future research will lead to predicting where the hydrogen will adsorb so that we can find another element that will non-deleteriously adsorb to those same sites, thus blocking the hydrogen and preventing hydrogen embrittlement. This methodology can further be applied to any crystalline material, allowing engineers to understand the basic building blocks of what gives a material its properties. Its application will help improve the versatility of materials manufacturing, allowing manufacturers to precisely design a material with whatever properties a customer desires, enhance the properties of existing materials, and stabilize materials that so far only exist in theory.

Will Oldroyd (Senior Thesis, April 2018, Advisor: Darin Ragozzine )

Abstract

Meteorites with high specific gravities, such as irons, appear to be underrepresented in Antarctic collections over the last 40 years. This underrepresentation is in comparison with observed meteorite falls, which are believed to represent the actual population of meteorites striking Earth. Meteorites in the Antarctic ice sheet absorb solar flux, possibly leading to downward tunneling into the ice. This descent is counteracted by ice sheet flow supporting the meteorites coupled with ablation near mountain margins, which helps to force meteorites toward the surface. Meteorites that both absorb adequate thermal energy and have a high enough thermal conductivity may instead reach a shallow equilibrium depth as downward melting overcomes upward forces during the Antarctic summer. Using a pyranometer, the incoming solar flux was measured at multiple depths in two deep field sites in Antarctica, the Miller Range (2013-14) and Elephant Moraine (2016-17). Thermal and physical interactions between a variety of meteorites and their surroundings were modeled, incorporating constraints derived from the pyranometer data. We find that a typical iron meteorite traveling upward through the ice during the Antarctic summer reaches an equilibrium depth of approximately 30 cm beneath the surface. This is slightly less deep than previous estimations. The effect of snowfall on equilibrium depth in our model is minimal. The recovery of an additional population of heavy meteorites would increase our knowledge of the formation and composition of the solar system by further constraining the number of differentiated planetesimals forming in the early inner solar system.

Sean Pearce (Senior Thesis, April 2018, Advisor: Mike Joner )

Abstract

To better understand the effects of high metallicity on white dwarf cooling processes, especially the white dwarf cooling age, we have analyzed images of the metal-rich open cluster NGC 6253, from the 8 m Gemini-South Observatory. To standardize the Gemini photometry of the cluster, we have also secured imaging data of both the cluster and standard star fields using the 0.6 m SARA Observatory at Cerro Tololo Inter-American Observatory. By comparing the photometric magnitudes and colors of additional stars in standard star fields of both the SARA data and the published Gemini zero-points of the standard star fields, we calibrated the data obtained for the cluster. These calibrations are an important part of the project to obtain a standardized deep color magnitude diagram and white dwarf luminosity function to analyze the cluster. With the standardized color magnitude diagram, we determined the cluster’s main sequence turnoff age to be 4.6±0.2 Gyr., much older than the earlier results showing an age ∼ 3.6 Gyr. Because the cluster is much older than expected, the white dwarfs have cooled and dimmed beyond our limits of detection. Since we were unable to detect the coolest white dwarfs, we could not make a white dwarf luminosity function with the current data set.

J. Ryan Peterson (Senior Thesis, April 2018, Advisor: John Colton )

Abstract

Zinc oxide is a promising wide band gap semiconductor with applications in high-temperature, radiation-hard devices and ultraviolet optoelectronics. The p-type material, however, has historically been difficult to produce. In this work, p-type zinc oxide films are grown by rf magnetron sputtering on c-sapphire substrates. Arsenic doping is provided by a Zn3As2 intermediate layer. Electrical characterization shows that while the conductivity correlates strongly with substrate temperature while sputtering, carrier type is inconsistent for samples grown in similar conditions. Photoluminescence measurements reveal poor optical performance related to deep defects. These defects may explain the n-type conductivity and comparison with previous work suggests future improvements to the growth process.

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.

David Van Komen (Senior Thesis, April 2018, Advisor: Traci Neilsen )

Abstract

An improved understanding of the sound generation of high-performance military aircraft is studied through beamforming. Conventional methods of beamforming, while powerful for localizing equivalent acoustics sources, are inadequate due to the complexities of jet noise. These complexities arise from the large, partially correlated source region, which violates the uncorrelated monopole assumption of conventional beamforming, and multiple types of noise sources, including directional and omnidirectional sources that vary with the aircraft’s operating power. These complexities require the utilization of advanced beamforming methods, such as the Hybrid Method and the Generalized Inverse method. The aim of this research is to apply advanced beamforming methods to the high-performance military aircraft jet noise to create frequency-dependent equivalent acoustic source distributions. These methods are applied to a ground-based array of 71 microphones that recorded noise from an F-35 aircraft. To investigate the multiple types of noise sources, the array is split into several subarrays that cover the sideline, maximum, and downstream regions of the noise. The advanced beamforming methods are applied to each of the subarrays at two different operating powers to investigate the different noise sources and how they change with operating powers. Subarray analysis on the F-35 engine noise yields equivalent sources for the different types of noise in overlapping regions.

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

Ethan Welch (Senior Thesis, April 2018, Advisor: Dallin Durfee )

Abstract

I seek to make injection locking a more reliable tool in atomic physics by active stabilization. An injection-locked diode laser can be actively stabilized by monitoring either the laser's frequency spectrum or the overall intensity. I used the transmission of a Fabry-Perot cavity to measure the frequency spectrum of an injection-locked laser. When the injection lock is about to break, the intensity of the dominant spectral mode decreases while the overall intensity increases. Similarly, a photodiode measures the overall intensity of the laser. Under certain conditions, the injection-locked laser's intensity corresponds to how strong the injection-lock is. To prevent the injection-lock from breaking, an Arduino Uno measures either the amplitude of the main spectral peak or the overall intensity while simultaneously adjusting the current of the injection-locked laser. By so doing, an injection-lock that has an average lifetime of a few minutes can be stabilized to have a lifetime of several hours.