Honors Projects

Showing 201 - 210 of 564 Items

Miniature of Clam shells and sea temperature: Evaluation of the oxygen isotopic climate proxy in <i>Arctica islandica</i> and development of a shell-derived sea temperature reconstruction from Isle au Haut, Maine
Clam shells and sea temperature: Evaluation of the oxygen isotopic climate proxy in Arctica islandica and development of a shell-derived sea temperature reconstruction from Isle au Haut, Maine
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      Date: 2024-01-01

      Creator: Brielle Martin

      Access: Access restricted to the Bowdoin Community



        Basins of Attraction and Metaoptimization for Particle Swarm Optimization Methods

        Date: 2024-01-01

        Creator: David Ma

        Access: Open access

        Particle swarm optimization (PSO) is a metaheuristic optimization method that finds near- optima by spawning particles which explore within a given search space while exploiting the best candidate solutions of the swarm. PSO algorithms emulate the behavior of, say, a flock of birds or a school of fish, and encapsulate the randomness that is present in natural processes. In this paper, we discuss different initialization schemes and meta-optimizations for PSO, its performances on various multi-minima functions, and the unique intricacies and obstacles that the method faces when attempting to produce images for basins of attraction, which are the sets of initial points that are mapped to the same minima by the method. This project compares the relative strengths and weaknesses of the Particle Swarm with other optimization methods, namely gradient-descent, in the context of basin mapping and other metrics. It was found that with proper parameterization, PSO can amply explore the search space regardless of initialization. For all functions, the swarm was capable of finding, within some tolerance, the global minimum or minima in fewer than 60 iterations by having sufficiently well chosen parameters and parameterization schemes. The shortcomings of the Particle Swarm method, however, are that its parameters often require fine-tuning for different search spaces to most efficiently optimize and that the swarm cannot produce the analytical minimum. Overall, the PSO is a highly adaptive and computationally efficient method with few initial restraints that can be readily used as the first step of any optimization task.


        Modulation of the crustacean cardiac neuromuscular system by the SLY neuropeptide family

        Date: 2024-01-01

        Creator: Grant Griesman

        Access: Open access

        Central pattern generators (CPGs) are neuronal networks that produce rhythmic motor output in the absence of sensory stimuli. Invertebrate CPGs are valuable models of neural circuit dynamics and neuromodulation because they continue to generate fictive activity in vitro. For example, the cardiac ganglion (CG) of the Jonah crab (Cancer borealis) and American lobster (Homarus americanus) contains nine electrochemically coupled neurons that fire bursts of action potentials to trigger a heartbeat. The CG is modulated by neuropeptides, amines, small molecule transmitters, gases, and mechanosensory feedback pathways that enable flexibility and constrain output. One such modulator, the SLY neuropeptide family, was previously shown to be expressed in hormonal release sites and within the CG itself and has unusual processing features. However, its physiological effect was unknown. Here, I performed dose-response experiments in the crab and lobster whole heart and isolated CG to determine the threshold concentration of SLY neuropeptides to which these systems respond. The crab isoform had strong, excitatory effects in the crab whole heart and weakly modulated the crab CG. The lobster isoform weakly modulated the lobster whole heart and CG. Surprisingly, the crab isoform exerted large, variable effects on the lobster system, which suggests that SLY neuropeptides, their receptors, and their signaling pathways may be evolutionarily conserved across these two species. This research contributes to our understanding of how neural circuits can generate flexible output in response to modulation. It may also offer insight into processes influenced by peptidergic neurotransmission in the nervous systems of other animals, including mammals.



        ALGOrhythms: Leveraging Markov Chain-Based Generation of Functional Harmonies with User-Defined Musical Corpus as a Compositional Tool

        Date: 2021-01-01

        Creator: Coleman Brockmeier

        Access: Open access

        Music forms the soundtrack to daily life and serves as an important cultural marker for people around the world. As the world becomes digitized and connected via the internet, the opportunity is increasingly accessible for anyone to share music with the world and to create chart-topping music that defines the cultural vernacular. Many prominent producers have little to no formal musical training, especially in Western music theory. As a result, loop-based music dominates the lists of most-played music on the radio and streaming services, often not deviating from basic functional harmony. With this project, I have created a compositional tool in the form of an iOS app which identifies the harmonic “fingerprint” behind a given set of songs. The app then leverages this understanding to create sequences of chords in the style of that fingerprint. To accomplish this, the app employs web scraping to create a corpus of musical information in the form of Markov chains — a transition table which underlies the data set. I introduce the idea of musical “chunks” defining a harmonic “fingerprint” and various methods of traversing the transition table to create chord progressions employing the fingerprint as a guide. The tool allows for specification of corpus, chunk size, traversal method, and the ability to listen to, share, and save generated results. The resulting app is a tool that allows the user to answer the question: “What would happen if Stevie Wonder and Billie Eilish wrote a song together?”



        Miniature of An Analysis of Hezbollah’s Media Platforms, Focusing on Themes, Narratives and Strategy
        An Analysis of Hezbollah’s Media Platforms, Focusing on Themes, Narratives and Strategy
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        • Restriction End Date: 2025-06-01

          Date: 2020-01-01

          Creator: Nichole Irving

          Access: Access restricted to the Bowdoin Community



            Miniature of Noninvasive Memory Modulation Via Targeted Theta TACS Entrainment of the Frontoparietal Network
            Noninvasive Memory Modulation Via Targeted Theta TACS Entrainment of the Frontoparietal Network
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            • Restriction End Date: 2026-06-01

              Date: 2021-01-01

              Creator: Brandon S Lee

              Access: Access restricted to the Bowdoin Community



                Down in arms: Marine climate stress inhibits growth and calcification of regenerating Asterias forbesi (Echinodermata: Asteroidea) arms

                Date: 2021-01-01

                Creator: Hannah L. Randazzo

                Access: Open access

                Anthropogenic CO2 is changing the pCO2, temperature, and carbonate chemistry of seawater. These processes are termed ocean acidification (OA) and ocean warming. Previous studies suggest two opposing hypotheses for the way in which marine climate stress will influence echinoderm calcification, metabolic efficiency, and reproduction: either an additive or synergistic effect. Sea stars have a regenerative capacity, which may be particularly affected while rebuilding calcium carbonate arm structures, leading to changes in arm growth and calcification. In this study, Asterias forbesi were exposed to ocean water of either ambient, high temperature, high pCO2, or high temperature and high pCO2 for 60 days, and the regeneration length of the amputated arm was measured weekly. Ocean acidification conditions (pCO2 ~1180 μatm) had a negative impact on regenerated arm length, and an increase in temperature of +4°C above ambient conditions (Fall, Southern Gulf of Maine) had a positive effect on regenerated arm length, but the additive effects of these two factors resulted in smaller regenerated arms compared to ambient conditions. Sea stars regenerating under high pCO2 exhibited a lower proportion of calcified mass, which could be the result of a more energetically demanding calcification process associated with marine climate stress. These results indicate that A. forbesi calcification is sensitive to increasing pCO2, and that climate change will have an overall net negative effect on sea star arm regeneration. Such effects could translate into lower predation rates by a key consumer in the temperate rocky intertidal of North America.