# Thesis/Capstone Archive

Abstract

Physics 108 is a one-credit hour, non-majors physics lab course centered on investigating topics related to electricity, magnetism, and optics. My research involved the addition of model building and observation to the circuits lab. Modeling as defined by the American Association of Physics Teachers (AAPT) "entails developing an abstract representation of a real system.” The goal is to use models to teach students how to construct knowledge of circuits. We wrote the lab so that the students would have opportunities to make predictions, measure the voltage and current in various circuits, and evaluate what was happening within the circuit. We included multiple models of both voltage and current to allow students to confront topics that are commonly misunderstood. Through observation, quizzes, and surveys, we were able to find that many students struggle to build circuits from a schematic and measure current. One solution would be to include information about how multi-meters work in the pre-reading. Another solution is to include more questions that will cause students to self-evaluate to discover their mistakes and find the answer. Further research is necessary to better evaluate the growth in student understanding after performing the circuits lab. This can be done with observations of every section's misconceptions and notebook checks to read student predictions and conclusions to assess critical thinking. Standardized pre and post lab quizzes would help pinpoint where growth and misconceptions occurred.

Abstract

Many-parameter models of complex systems are ubiquitous, yet often difficult to interpret. To gain insight, these models are often simplified, sacrificing some of their global considerations as well as versatility. The task of finding a model that balances these features is of particular interest in statistical mechanics. Our group addresses the problem through a novel approach—the Manifold Boundary Approximation Method (MBAM). As the central step to this approach, we interpret models geometrically as manifolds. Many model manifolds have a set of boundary cells arranged in a hierarchy of dimension. Each of these boundary cells is itself a manifold which corresponds to a simpler version of the original model, with fewer parameters. Thus, a complete picture of all the manifold’s boundary cells—the boundary complex—yields a corresponding family of simplified models. It also characterizes the relationships among the extreme behaviors of the original model, as well as relationships among minimal models that relate subsets of these extreme behaviors. This global picture of the boundary complex for a model is termed the model’s manifold topology. Beginning in the context of statistical mechanics, this thesis defines a class of models— Superficially Determined Lattice (SDL) models—whose manifold topologies can be ascertained algorithmically. This thesis presents two algorithms. Given an SDL model, the Reconstruction Algorithm determines its manifold topology from minimal information. Given a model and desired extreme behaviors, the Minimal Model Algorithm finds the simplified model (with fewest parameters) that interpolates between all of the behaviors.

Abstract

Hα and Hβ indexes are used in astronomy to compare prominent spectral features for celestial objects. By plotting these two particular indexes against each other, astronomers are able to easily differentiate between spectral types of stars. An extensive amount of research has been carried out to create a list of standard stars that appear in a line on the Hα vs Hβ plot. It has long been wondered if different types of objects occupy a different location on such a plot. For example, where do Seyfert galaxies appear on an Hα vs Hβ plot? There is a vast database of spectra from various Seyfert galaxies that can be used to obtain Ha and Hβ indexes. Before expending the time and resources to extract and manipulate these spectra, it is important to test one specific Seyfert galaxy and see if the location of the data on the final plot deems further research in this direction. Data, in the form of spectra, were obtained from the Dominion Astrophysical Observatory (DAO) in Canada for the Seyfert galaxy NGC 4151. This galaxy was studied for 11 nights over the span of two years. This data was reduced and analyzed to obtain the strength of the Hα and Hβ lines for the spectra at varying redshift values (ranging from a redshift of 0 km/s to 3000 km/s). An Hα vs Hβ plot was created for each redshifted spectrum. The results were compared to Ha vs Hβ plots of standard stars, and it was discovered that NGC 4151 occupies a unique location of the plot. Other active galactic nuclei (AGN) may provide information to other regions of this plot, and using this plot may assist astronomers in detecting Seyfert galaxies in a field of observation.

Abstract

Many different teachers teach the Physics 127 (intro to astronomy) class at Brigham Young University (BYU). Each teacher has their own tests for their own students and these tests between teachers are so different from one another that there has arisen a need for some unity between them all. It was determined to create 10 multiple-choice questions that could be included in all of the tests some time in the future. To do this, research was done on what makes a good test question, then each teacher’s exams were analyzed for similarities and differences, and finally 10 questions were created based on this research.

Abstract

With homeland security applications in mind, I constructed and tested a gamma ray and neutron detector designed to detect spontaneous fission events from highly shielded sources. The detector consisted primarily of a 25.4 cm $\times$ 25.4 cm $\times$ 15.2 cm block of Eljen EJ-200 plastic scintillator coupled to four Adit 5-inch photomultiplier tubes. The signals from all the tubes were added following gain matching with a $^{60}$Co gamma source. Using a $^{252}$Cf source, I measured the efficiency of the detector for various shielding types and thicknesses. Data were acquired both with a Cd foil placed on the front of the detector and with the Cd foil removed. The difference of the pulse-height histograms for these two configurations was shown to be a good measure of the neutron source strength. Neutron detection efficiency per fission neutron in a 4$\pi$ detector peaked at 13.5\%, corresponding to a shielding diameter of 20.4 cm. Through single and double pulse analysis, we were able to confidently determine if a fission source was present and also if boron was being used in the shielding.

Abstract

The complexity and pattern found in animal aggregations, such as starling murmurations, reveals emergent phenomena which arise from the simple, individual interactions of its members. Simulated in a two-dimensional algorithmic model, self-driven particles (boids) group together and display emergent flocking characteristics. The model is based on the ideas of consensus and frustration, where consensus is a nonlinear topological averaging that drives the boids toward one of three unique phases, and frustration is a perturbation that pushes the boids beyond these simple phases and toward disordered behavior. The nonlinearity merged with the perturbation produces characteristics which go beyond the dynamic interplay of global and local phase transitions. The emergent results are interpreted in terms of global and local order parameters, and correlation functions. The results also strongly agree with observational data and empirical analysis.

Abstract

Metal electroplating of carbon nanotube (CNT) forests is viable method for fabricating metal microelectromechanical systems (MEMS). Recent work has demonstrated that electroplating an interconnected carbon nanotube structure is possible through direct electrical contact to the CNT structure. However, this is not ideal since features in MEMS fabrication often need to be both electrically and mechanically isolated from each other. Current efforts have been directed toward electroplating CNT patterns through electrical contacts on the substrate. In this case contacting to CNTs through metallic leads that sit between the substrate and the grown CNT forests. Since the CNT forest catalyst layer involves an insulating, alumina diffusion barrier between the iron catalyst layer and the metallic substrate, this is not as simple as it sounds. Results on the measured resistance of this structure are presented in this thesis.

Abstract

The most common challenge faced in architectural acoustics is designing a room with a proper reverberation time that will suit the purposes of the space. At the Center for Change located at 1790 N State St in Orem, Utah, a room known as the Dance Room exhibits an extraordinarily high reverberation time, making communication in the room extremely difficult. Using the EASERA system (Electronic and Acoustic System Evaluation and Response Analysis), as well as a starter pistol with multiple Larson Davis 824 sound level meters, measurements of the reverberation time were made in the room at the Center for Change on March 26th, 2016. Several possible solutions designed to lower the reverberation time were investigated and tested by constructing a computational model of the room using the Sabine equation as well as EASE software (Enhanced Acoustic Simulator for Engineers). Two solutions were chosen, and proposed in a written report to the Physical Facilities Manager at the center, Glenn Klemetson.

Abstract

Brown dwarf binary systems are typically too small and cold to be visually resolved, making the study of their spectral features the next best method to determine the general nature of these particu- lar systems. I obtained data from the Spitzer Heritage Archive in the near to mid-infrared spectrum for several brown dwarf binary candidates. Using a least-squares approach and over a thousand synthetic spectral models, I performed a statistical analysis to determine which models best fit the original data. From these models, I determined the most likely parameter values for each com- ponent of either the single or binary system which include the temperature, surface gravity, cloud density, and the amount of atmospheric convection for each star. A binary system, or combination of two models, was found to better fit the following dwarfs: Kelu-1, 2MASSW J0036159+182110, 2MASSW J2224438-015852, SDSS J080531.83+481233.1, SDSS J105213.51+442255.7AB, and 2MASS J05591914-1404488. Kelu-1 and SD1052 are visually confirmed binary systems. The results of the statistical fitting match the known temperatures of each component for both stars, implying that this is a reliable method. The next step will be to identify and perform the statistical spectral analysis on additional brown dwarf binary candidates.

Abstract

Acoustic beamforming uses recordings from a microphone array to find sound source locations. The response of a beamformer is limited by two requirements–the spatial Nyquist frequency on the high-frequency end and aperture requirements on the low-frequency end, which correspond respectively to the spacing of the microphones and the total length of the array. These limitations cause any array with a finite number of microphones to have a limited frequency bandwidth over which beamforming results are useful. This paper presents a method for overcoming the high-frequency limitation using phase unwrapping and array interpolation. This process can approximate the response of an array with many more microphones than are present by adding virtual microphone signals determined by interpolation. Experimental and numerical verifications of the method are presented. The method is found to octuple the bandwidth of the array when the source of interest is broadband.

Abstract

We are building a volumetric display that depends on photophoretic trapping to draw out images in free space. Because our display requires the particle to move very fast, we need to optimize the strength of our trap so the particle will not fall out. We studied the effect of angle-dependent aberration patterns on trapping strength so we can hold a particle and draw images at very high speeds. We mounted a lens on a rotation stage allowing for coarse control of lens angle relative to the incoming beam. By conducting 50 measurements on the maximum trapping time, velocity, and acceleration vs lens angle, we could determine at what angle the trap was strongest. Measurements showed the strongest trapping occurs within a degree of normal incidence but not at normal incidence.

Abstract

Reverberation mapping is a technique used to determine the mass of the supermassive black hole at the center of an active galaxy. The technique uses both photometry and spectroscopy. This project focuses on the photometry aspect of reverberation mapping and seeks to determine if the photometric method used will significantly affect the results. The light curves of NGC 4151 produced using AstroImageJ, IRAF, and ISIS are compared. IRAF and AstroImageJ use differential aperture photometry with comparison stars, while ISIS uses image subtraction photometry. ISIS yielded light curves different to those created from AstroImageJ and IRAF. Furthermore, due to errors from comparison stars, it is concluded that image subtraction photometry may be more accurate than differential aperture photometry for this galaxy.

Abstract

This thesis presents a new synthesis method for PbSe and MoS$_2$ semiconductor nanoparticles inside the protein ferritin. It also presents a simplified synthesis method for PbS, based on the work of Hennequin, et al. To our knowledge, PbSe and MoS$_2$ nanoparticles have not been synthesised inside ferritin before. All three materials could potentially have several applications outside photovoltaics, e.g. as biological markers and cancer therapies; however, this thesis focuses on their application to photovoltaics. PbS-ferritin is used to replace dye molecules in a dye-sensitized solar cell and the device shows an efficiency of $0.28\%$.

Abstract

The dynamics of a coupled ground and coherent state are explored. The approach is focused on solving for the time evolution operator and then applying it to a tensor product of a ground and coherent state representing a physical system and environment respectively. The coherent state is then partially traced to extract the dynamics of the ground state. The time evolution operator is found by solving a series of eleven coupled differential equations. The results demonstrate that a change in coupling results in a change in the evolution of the ground state.

Abstract

A Brown Dwarf is a celestial object that forms like a star, but is not massive enough to undergo hydrogen fusion in its core. Due to a lack of an internal energy source, brown dwarf temperatures are not stable with age, making mass and age estimates difficult. Recent evidence suggests that models of brown dwarf evolution are inaccurate; to improve these models, direct mass measurements are required. One of the best methods to empirically measure mass is through observations of the orbital parameters of a binary pair. Angular separation between binary brown dwarfs is often small enough that they are unresolved in images. Due to the great distances from Earth, these brown dwarfs appear as point sources of light and spread out in images in a predictable pattern, due to diffraction, known as the point spread function (PSF). I have developed a Python script based on an older FORTRAN program to find binary systems which are unresolved by creating models of PSFs and testing those models against images taken from the Hubble Space Telescope archive.

Abstract

Blazars are believed to be supermassive black holes in galactic nuclei, emitting high-energy radiation. Despite much theoretical and observational research performed on these enormous masses, the mysteries of their inner dynamics remain unsolved. BYU-owned telescopes (ROVOR and WMO) have monitored the prototypical blazar, Mrk 501, from 2009–2016 at optical wavelengths, searching for any obvious periodicity to its variations in brightness. We performed differential photometry on this data set using Mira and VPhot. The photometric calibration of these data is used to construct a low-noise light curve. Frequency analysis is performed using Period04. The light curve analysis unveils an obvious long-term periodicity of ∼2300 days. Further frequency analysis shows other possible simultaneous periods of lesser duration. These results match expectations for a multibody black hole system.

Abstract

Transiting planets can be discovered through the method of photometry. The Kilodegree Extremely Little Telescope (KELT) Transit Survey team is a collaborative effort to discover more transiting planets. Image Reduction and Analysis Facility (IRAF) has been used to create a script to efficiently pipeline the night sky's raw images into processed ones to prepare them for photometric measurements. The details to the structure and reliability of the data reduction script are outlined. The photometric results are sent back to the KELT team. Discussion of the significance of the light curve is also detailed.

Abstract

High-resolution speech directivity data has been measured in the BYU anechoic chamber. The data was taken at 2,522 discrete points in a spherical measurement surface. While speech directivity data have been taken in the past, the current increased-resolution data are more useful in speech and architectural acoustic studies. This capstone report presents the results of the measurements in the forms of balloon plots and polar plots with interesting frequency-dependent trends. The directivity is nearly omnidirectional at lower frequencies such as 200 Hz. Higher levels below the mouth axis are present at mid-range frequencies such as 800 Hz. Higher radiation levels above the head are present at higher frequencies such as 1,600 Hz. In order to resample the balloon plots or begin the process of modeling directivity patterns at other radii, a spherical harmonic expansion method was developed so the discrete measurement data could be described in terms of continuous functions.

Abstract

Blazar light curves are studied to deepen our understanding of super massive black hole systems. Sinusoidal variations in a light curve are generally a signature of orbital dynamics. We have made and analyzed optical observations of Markarian 501, using Johnson BVR filters, from 2010--2016. In the optical light curve, we find significant evidence for a sinusoidal variation with a period of $\sim2300$ days, or about 6--6.5 years, along with smaller, quasi-periodic variations. In 2000, Rieger \& Mannheim calculated a binary black hole orbital period of 6--14 years, based on the 23-day period found in gamma ray observations, by assuming a bulk Lorentz factor $\Gamma=$10--15 for a helical, relativistic jet, as seen in radio observations. We propose that optical observations reflect the intrinsic orbital period predicted by Rieger \& Mannheim and constrain $\Gamma$ to $\sim10.3$. Further investigation could lead to a gravitational wave profile for Mrk 501 and reveal signature characteristics of future candidates for similar gravity wave sources.

Abstract

Existing wavefront sensing technologies, like those used in various adaptive optics systems, often have problems dealing with high turbulence conditions. Holographic interferometry could function as a more robust wavefront sensor in high turbulence conditions if the procedure can successfully be taken from theory to practice. To make that step, I built a Mach-Zehnder-style holographic interferometer that measured turbulent phase shifts accumulated in a signal beam over 80 m. To convert holographic interferograms into wavefront-sensing phase profiles, I converted the interferogram into the Fourier plane and isolated features of interest. The experimental results were inconclusive due to design problems and equipment issues.

Abstract

EBID allows metals to be directly written to a substrate in order to connect to randomly oriented devices. When depositing with the precursor Trimethyl(Methylcyclopentadienyl)Platinum(IV), the deposited metal has a resistivity a few orders of magnitude higher than pure platinum. Therefore, the leads are highly resistive and present problems in experimental electrical measurements. By introducing an anneal with an alumina coating, the resistivity can be lowered to 1.32E−6 Ω𝑚, which is only 12 times above the resistivity of bulk platinum.

Abstract

If the scale of surface roughness is on the order of the wavelength of incident light, traditional optics methods like ray tracing and physical optics fail to adequately model reflectance. In this project, boundary integral techniques were chosen because they provide direct solutions only limited by computer memory. Discretizing Maxwell's equations across a surface yields an $Ax=b$ matrix equation relating the surface current to electric field over a net of points. Reflectance calculations for transverse-magnetic (TM) waves on a perfect conductor in two dimensions are analyzed in depth to model the effects of scattering from surface roughness. Root mean square (rms) furface roughness more than a hundredth the wavelength of the incident beam is noticeable and anything larger than a tenth the wavelength dominates the reflectance. These calculations allow for comparison with previous approaches --such as the scalar correction factors of Debye-Waller -- at various spatial frequencies. The Debye-Waller models the smaller roughness but loses precision as roughness increases. The effects of spatial frequencies are also analyzed are compared to the current work of Stearn in showing additional surface parameters affecting roughness. The results of altering spatial frequency supports the work of stern suggesting additional parameters like spatial frequency are factors that affect overall reflectance. Optimizing the calculation through generating and solving the matrix equation are analyzed. Nonsingular, off-diagonal elements of the relation matrix are relatively slow to calculate in the generation process. A method using the multipole expansion is theorized to combat this inefficiency.

Abstract

Pure aluminum mirrors optimize the reflectance of broadband mirrors for space-based telescopes; however, they oxidize instantly in atmospheric conditions, decreasing reflectance in the far-UV from 90% to 20%. The largely untried method of Removable Volatile Aluminum Protection (REVAP) overcoats freshly deposited Al mirrors with a barrier layer of cadmium or zinc intended for removal in vacuum. I use ellipsometry and energy dispersive x-ray spectroscopy (EDS) periodically to observe how the barrier layers interact with the Al and how the composition of the mirrors changes with time. Preliminary EDS results show Cd may have prevented aluminum oxidation in some samples. Cd and Zn exhibit low adhesion to Al, making REVAP with them unfavorable. EDS measurements on samples after attempting re-evaporation shows uneven removal of Cd and Zn.