Matching Items (188)
Description
The standard theory of indirect gap optical absorption in semiconductors predicts an unphysical divergence when the photon energy reaches the direct band gap. Current theoretical efforts to eliminate this divergence require experimental validation with measurements covering a spectral region that exceeds the direct band gap. For transmittance and reflectance measurements needed in examining the absorption in a material like Ge, the needed film thicknesses are too small for the samples to be mechanically stable. On the other hand, very thin films can be grown epitaxially on silicon.
This thesis focuses on testing a novel technique for examining absorption in these thin films. Spectrophotometry was used to measure the reflection and transmission over a spectral range of 0.54 eV to 1.38 eV for various epitaxial thin film Ge on Si samples. The resultant data was then renormalized and used in a custom spline fitting procedure to extract the dielectric/optical constants over the established spectral range.
Analysis of the extracted dielectric function spectra indicates an apparent bias towards thinner films (less than 1000 nm) in producing spectra having good agreement with new theoretical models. Dielectric function spectra from thick samples (over 2000 nm) show well matched general behavior but fail to accurately predict regions of absorption around the band gap.
ContributorsBoone, David (Author) / Menéndez, Jose (Thesis director) / Kouvetakis, John (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Department of Physics (Contributor) / School of Sustainability (Contributor)
Created2025-05
Description
Keresan languages feature complex verbal morphology with a staggering degree of allomorphy. Previous work on Santa Ana Keres in the 1960s did a good job of describing the language, but it did not come with a robust analysis; this has brought difficulty in teaching the language as part of a revitalization program, so in-depth analysis is necessary. Here I lay the foundations for future work on Santa Ana Keres by analyzing the existing data. I identified some correlations evident therein, corroborated by similar observations in later research on other Keresan languages: these include a possible split-intransitive alignment and a palatalization process in the pronominal prefixes. I mentioned certain points of contention, like the shape of the verb stem and laryngeal allophony in the prefixes, and offer my hypotheses. I finish with some remarks on what work needs to be done to definitively resolve these problems.
ContributorsVandian, David (Author) / Peterson, Tyler (Thesis director) / Shirtz, Shahar (Committee member) / Barrett, The Honors College (Contributor) / Department of English (Contributor) / School of Life Sciences (Contributor) / Department of Physics (Contributor)
Created2025-05
Description
In this work, we analyze the nearby, spiral galaxy, NGC 3344. This particular galaxy is
interesting due to its extended UV disk (Padave et al. 2021). NGC 3344 was observed
using broadband optical imaging from the Large Binocular Telescope. We begin with a
photometric analysis of the stellar populations in the inner versus outer disk of the galaxy.
We then present the color as a function of galactocentric distance to infer the age gradient
in NGC 3344. We find a higher ratio of younger stars to older stars in the outer disk,
which indicates that NGC 3344 grows from the inside-out. Then, we use Code Investigating
GALaxy Emission (CIGALE) to model the star formation history of the galaxy. After testing
over 1,469,664 combinations of models, we conclude that NGC 3344 matches the pattern of
a constant star forming galaxy with a delayed burst episode. Based on the modeled star
formation rate, NGC 3344 experienced a 5% increase in star formation 50 million years ago.
This finding corroborates the presence of an extended UV (XUV) disk in the galaxy, which
could be tied to an accretion event of a spiral density wave. These results are very exciting,
and will be explored further in Padave et al. 2025 (in prep).
ContributorsCarl, Naomi (Author) / Borthakur, Sanchayeeta (Thesis director) / Jansen, Rolf (Committee member) / Padave, Mansi (Committee member) / Barrett, The Honors College (Contributor) / School of Music, Dance and Theatre (Contributor) / School of Earth and Space Exploration (Contributor) / Department of Physics (Contributor)
Created2025-05
Description
Both a classical and a semiclassical analysis of a worldline with an impulse acceleration coupled to a Yang-Mills field were analyzed. The semiclassical derivation demonstrates the resultant radiation is a sum of coherent states, and therefore has a rather simple structure. In the case of a $U(1)$ gauge symmetry, the standard double log form of the Sudakov form factor pops out, providing credit to the derivation technique. In the classical limit, surprisingly the results match with the QED results, suggesting that in some sense, the Sudakov form factor is a field theoretic effect rather than a quantum effect. Finally when the Yang-Mills theory uses any gauge group $G$, the resultant form factor, at first order, gets modified by a factor of the quadratic Casimir operator $C_F$ in both the quantum and semiclassical cases.
ContributorsGrumskiFlores, Joshua (Author) / Baumgart, Matthew (Thesis director) / Yildirim, Tuna (Committee member) / Barrett, The Honors College (Contributor) / Department of Physics (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2025-05
Description
The goal of this project was to develop an affordable, functional, and reliable automated pill sorting system using Raspberry Pi and computer vision. The prototype was designed to assist individuals with physical or cognitive impairments in managing their daily medications more efficiently. For demonstration and testing purposes, candies with different shapes and colors were used to simulate pills. The system uses a Raspberry Pi 5, a camera module, and servo motors controlled through a PCA9685 driver to identify and sort candies based on their color and shape. A conveyor belt moves each candy under the camera where images are captured, processed in real time using OpenCV, and classified using HSV color filtering and contour analysis. Classified items are then routed to the correct compartments using servos. Testing was conducted under both bright and dim lighting conditions to evaluate system robustness, yielding classification accuracies of 95.9% and 100% respectively. The total build cost was $264.03, significantly less than commercial alternatives. The system proved effective in demonstrating low-cost, high-accuracy automated sorting. Future improvements include adding a feeder mechanism, enhancing the user interface, integrating a pill database, and potentially training a custom machine learning model for improved classification and real-world deployment.
ContributorsGarcia, David (Author) / Menees, Jodi (Thesis director) / Li, Cindy (Xiangjia) (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor) / Department of Physics (Contributor)
Created2025-05
Description
Bright electron beams with photo injectors are used for XFELS, UEM, UED, and accelerators for fundamental physics research. Essential to a photocathode’s use in a photoinjector system is the minimum MTE achievable for a beam generated with it. Atomically ordered, single-crystalline photocathodes are ideal, and multiple materials have been identified for their potential as photocathodes, but not properly tested. At the Arizona State University Photoemission and Bright Beams Laboratory, we have developed a 200 kV crycooled electron gun and vacuum beamline with widely available parts to test a variety of photocathode candidates for bright electron beams, as well as programs to process this data to obtain MTE and emittance measurements.
ContributorsMama, Jo (Author) / Karkare, Siddharth (Thesis director) / Owusu, Peter (Committee member) / Barrett, The Honors College (Contributor) / Department of Physics (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2025-05
Description
Rubisco activase is a chaperone-like AAA+ ATPase essential for maintaining
photosynthetic activity by releasing inhibitory sugar phosphates from Rubisco’s active site. In
higher plants, including spinach, Rca exists in α and β isoforms and is believed to function
primarily as a nucleotide-dependent hexamer. Despite recent structural insights, questions remain
about the full-length assembly of Rca and its interaction with Rubisco under physiological
conditions.
Here, we present a detailed biochemical and structural analysis of spinach β-Rca,
including an improved purification protocol, oligomerization behavior under defined nucleotide
conditions, and structural characterization using negative stain electron microscopy. Both
SoβRca and Rubisco were purified to homogeneity, with SoβRca consistently forming hexamers
in the presence of ATPγS. When mixed under activating conditions, SoβRca and Rubisco
produced a reproducible early-eluting peak in SEC, distinct from either protein alone. Negative
stain imaging of these fractions revealed large, asymmetric assemblies containing multiple
Rubisco-like particles–raising the possibility of higher-order interactions. However, no strong
conclusion can be drawn due to the low abundance of SoβRca in these fractions and the
uncertainty surrounding the identity and stoichiometry of the observed complexes.
Higher-resolution work, and further trials are required to resolve the structure and determine the
relevance of these complexes.
ContributorsCarsten, Alexander (Author) / Chiu, Po-Lin (Thesis director) / Klein-Seetharaman, Judith (Committee member) / Sarkar, Susanta (Committee member) / Barrett, The Honors College (Contributor) / School of Molecular Sciences (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Department of Physics (Contributor)
Created2025-05
Description
Cadmium Telluride (CdTe) is a promising II–VI photovoltaic material, offering a detailed-balance efficiency limit around 30%. However, achieving this potential in practice requires minimizing non-radiative losses. This thesis examines the effects of black-body radiation of a CdTe/InSb solar cell absorber layer. Here, both experimental and theoretical approaches are used to understand how black-body emission and recombination losses influence solar cell device performance. Key topics include black-body radiation fundamentals, calibration of a black-body source, optical absorption in monocrystalline vs. polycrystalline CdTe absorbers, the Shockley–Queisser limit under radiative recombination, and photoluminescence quantum efficiency (PLQE) measurements. The goal was to understand how intrinsic thermal radiation and device design limit open-circuit voltage and efficiency, and how advanced structural engineering such as heterostructure barrier layers can mitigate these limits. In fact, the PLQE of the measured sample appeared to be extremely low: 6×10^(-7)%, which indicated a very large non-radiative recombination. Transmission Electron Microscopy and Solar Cell Modelling were utilized to explain this result. By using modified Shockley–Queisser approach to account for large non-radiative recombination, a more realistic maximum efficiency of 9.28% was calculated.
ContributorsVoinkov, Ky (Author) / Zhang, Yong-Hang (Thesis director) / Smith, David (Committee member) / Ju, Zheng (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor) / Department of Physics (Contributor) / School of Mathematical and Statistical Sciences (Contributor)
Created2025-05