2022 Honors Thesis Submissions

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    Chaucer’s Missing Manuscripts
    (2021-09) Green, Adrienne
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    Thermal Quenching of Luminescence in YAG:Ce.
    (Wheaton College. (Norton, Mass.), 2022-05-16) Osborn, Benjamin M.
    Yttrium aluminum garnet doped with cerium (YAG:Ce) is currently the phosphor of choice for LED lighting applications, due to its broad spectrum emission and relatively high efficiency at common LED operating temperatures. For applications where higher temperatures are reached, such as high-powered LED lighting, a decline in the luminescent efficiency of this phosphor is observed. This phenomenon is referred to as thermal quenching and can be explained by several nonradiative decay processes within the phosphor. This research investigated the luminescent properties of a sample of YAG:Ce with a 2.1% cerium concentration at various temperatures in order to better understand the relationship between temperature and luminescence in this material. Through measurements of continuous luminescence, excitation, and response to pulsed excitation, the properties of this material were determined and compared to previous findings as well as computer models. After fitting this data to various models, and considering previously published research, it was determined that the primary mechanism of thermal quenching in this sample is concentration quenching. By comparing the model for concentration quenching to the experimental data, it was found that, on average, energy transferred between 2.2 cerium ions before ending up in a killer center.
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    The 2821 Star Southern Hemisphere Optical SETI Survey: An Archival Search for Candidate Laser Signals in ESO’s HARPS Spectroscope Database
    (2022-05-16) Fields, Benjamin
    I conducted a survey of archived observations taken from 2821 stellar targets by the HARPS spectroscope for potential signatures of lasers from extraterrestrial civilizations. The HARPS instrument examines light across a spectral range of 378-691 nanometers down to a resolution of .01 angstroms–allowing for high wavelength range and sensitivity across the optical spectrum which makes it an ideal instrument for optical SETI surveys. This search operates under the premise that such lasers would be distinct from their stellar spectral background and appear as anomalously narrow emission lines. We develop an algorithm designed to search for statistically significant spikes at least 3.5 standard deviations above the median flux in each wavelength window. Using an initial sample set of 100 stars, we established a classification system as well as methodologies for ruling out a number of types of false positives, including cosmic rays, bleedthrough from the calibration lamp, night sky airglow lines from the Earth’s own atmosphere, and large clusters of emission lines which are likely the product of natural stellar activity and flaring. Our project split into two separate approaches–The Broad Search of one observation of each star in the 2821 star target list designed to detect constant lighthouse-like beacons, and a Deep Search of all observations of each star for more intermittent sources. The Deep Search is ongoing. The Broad Search is complete, and we investigated all 294 candidates our algorithm detected in all 2821 spectra, covering the entire range of stars. Of all 294 all candidates, 29.3% appeared to be in clusters indicative of natural emission lines, possibly from flaring activity. Cosmic rays were the most common type of false positives, accounting for 47.6% of all candidates. Bleedthrough from the calibration lamp accounted for 2.4% of all candidates and 3.1% of candidates were night sky atmospheric airglow lines which evaded the algorithm’s filters. Finally, 17.7% of all candidates remain unexplained and warrant further investigation as potential signatures of extraterrestrial lasers.
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    Derivation and meaning: a computer-assisted investigation into etymological and semantic connections in English
    (Wheaton College. (Norton, Mass.), 2022-05-16)
    An important subfield within philology is etymology, the study of words and their origins. This thesis combines philology and etymology with computational techniques to quantify the large-scale relationships between words in the English language. Specifically, using English headwords, definitions, and etymology data from Wiktionary, graphs were constructed of English words and their relationships in etymology and meaning. These graphs were then examined to test for any correlation between etymological and semantic associations in the graphs. No clear correlation was found, meaning relationships in etymology are not a reliable guide to relationships in meaning in the English language.