Showing 21 - 30 of 2039 Items
Dendrites of Cardiac Ganglion Regulate Heartbeat of American Lobster, Homarus americanus, Through Stretch Feedback
Date: 2014-05-01
Creator: Mara R Chin-Purcell
Access: Open access
- Central pattern generators are neuronal networks that produce reliable rhythmic motor output. A simple pattern generator, known as the cardiac ganglion (CG), controls the heart of the American lobster, Homarus americanus. Previous studies have suggested that stretch feedback relays information to the cardiac ganglion about the degree of filling in the heart, and that this feedback is mediated by stretch-sensitive dendrites extending from CG neurons. I sought to determine the mechanisms behind this stretch feedback pathway. One hundred second extension pyramids were applied to each heart while amplitude and frequency of contractions were recorded; 87% of hearts responded to stretch with a significant increase in frequency of contractions. To ascertain the role of dendrites in this feedback pathway, the accessible branches along the trunk of the CG were severed, de-afferenting the CG. In de-afferented hearts, stretch sensitivity was significantly less than in intact hearts, suggesting that the dendrites extending from the CG are essential for carrying stretch feedback information. To separate the effects of active and passive forces of heart contraction on stretch sensitivity, the CG was de-efferented by severing the motor nerves that induce muscle contraction. Hearts with only anterolateral nerves cut or with all four efferents cut were significantly less stretch sensitive than controls. These results indicate that the CG is sensitive to active stretch of each contraction. Hearts with reduced stretch feedback had more irregular frequency of contractions, indicating that a role of stretch feedback in the cardiac system may be to maintain a regular heart rate.
Divinity School: A Novel
Date: 2022-01-01
Creator: Ella Marie Schmidt
Access: Open access
- I wrote Divinity School, an Honors Project for the Department of English, under the auspices of my project advisor, Professor Anthony Walton, and my readers, Professors Marilyn Reizbaum, Ann Kibbie, and Aaron Kitch. Divinity School is a novel whose conflicts are religious, generational, and familial. Set mostly in Hoboken, New Jersey with vignettes in Manhattan, Vienna, the west coast of Ireland, and an anonymous New England college town, it is the story of one family and the open secrets that keep them apart. Hal Macpherson is a Divinity School professor uged into premature retirement by allegations of misconduct; his wife, Annie Price, is a withdrawn would-be actress. They are parents to Amelia Macpherson, a woman in her twenties who rejects her father’s righteous claims of innocence and her mother’s exhausted but unwavering devotion to him. This project is concerned with sex and pedagogy, youth, want-it-all politcs, parenthood, getting old, Protestantism, and domestic life. Using third-person free indirect style, I traverse the public-private planes of literature. As an undergraduate at Bowdoin College, I have enjoyed the privilege of a great English education in literature, creative writing, and independent work. Divinity School is the culmination of these studies.
Transforming the Humane: Human/Animal Relationships in Marlen Haushofer’s Die Wand and Franz Kafka’s Die Verwandlung
Date: 2022-01-01
Creator: Joosep R. Vorno
Access: Open access
- In this project, I investigate Franz Kafka’s Die Verwandlung (1915) and Marlen Haushofer’s Die Wand (1963) through a magic realist interpretive strategy. I identify how, as a result of a mysterious opening premise, the two texts accomplish a human/animal transformation in the protagonists. While the transformations differ in several aspects, even at times being direct opposites, the way in which the characters navigate their new nonhuman selves poses many important questions about care and humaneness, the human condition, and social and familial structures. By drawing on discussions of magic realism – from its roots in Weimar German art criticism, its contemporary features in literature, and the inherently subversive nature of the narrative mode – I discuss how the lens of magic realism becomes a helpful tool in recognizing, exploring, and appreciating the human/animal transformations as a defamiliarization of the familiar.
The experience of crunch in the video games industry amongst current and aspiring developers
Date: 2022-01-01
Creator: Radu Ioan Stochita
Access: Open access
- The video games industry relies on crunch - overworking the developers, usually towards the end of the project in order to meet a required deadline. In this paper, I analyze the different relationships that aspiring and current game developers have with the games industry and how they position themselves when it comes to crunch. Passion is a major component of people's desire to join the games' industry, later being used to justify one's need of staying overtime: "Since I am passionate about video games, it did not feel like work at all." Other aspiring or current developers are more skeptical when it comes to crunch and are developing secondary plans, either to quit the industry, join labor unions or push for better working conditions.
Urban Pastures: A Computational Approach to Identify the Barriers of Segregation
Date: 2022-01-01
Creator: Noah Gans
Access: Open access
- Urban Sociology is concerned with identifying the relationship between the built environment and the organization of residents. In recent years, computational methods have offered new techniques to measure segregation, including using road networks to measure marginalized communities' institutional and social isolation. This paper contributes to existing computational and urban inequality scholarship by exploring how the ease of mobility along city roads determines community barriers in Atlanta, GA. I use graph partitioning to separate Atlanta’s road network into isolated chunks of intersections and residential roads, which I call urban pastures. Urban pastures are social communities contained to residential road networks because movement outside of a pasture requires the need to use larger roads. Urban pastures fences citizens into homogenous communities. The urban pastures of atlanta have little (
"Know-Nothingism, Abolitionism, and Fanaticism:" An Analysis of the Collapse of the Second Party System in Maine
Date: 2023-01-01
Creator: Justis Dixon
Access: Open access
- The 1850s were a tumultuous period in American politics, with a complete partisan realignment fundamentally shifting the balance of power away from the status quo and toward possibilities for change. This paper focuses on the collapse of the Second Party System in Maine, and understanding how we can explain this stunning and rapid shift. The varying factors can be placed into two broad categories First, ethnocultural issues were primarily responsible for much of the growing turmoil within and between the major parties throughout the 1840s, and accelerating greatly in the early 1850s with rising levels of immigration and the increasing draw of the temperance movement, which was then followed by the passage of highly controversial legislation concerning these issues. Second, national-level issues such as the Fugitive Slave Act and detailed reports of the violence out West in local newspapers brought the consequences of the unfettered expansion of slavery closer to home for many Mainers. Scholars of this period have expressed varying opinions as to the relative importance of local and national level issues in generating a change to the political system. Using Maine as a case study due to its position as a leader in the temperance movement and its geographical distance from the battlegrounds of national politics at the time, I conduct an in-depth examination of the political history of the state and conclude that rising tensions on both local and national levels were necessary to cause such transformational change.
Student Activism and Malaysian Politics, 1955-74: Revising the History of the Malay Language Society (PBMUM)
Date: 2023-01-01
Creator: Song Eraou
Access: Open access
- In the literature on student activism in Malaysia, the years from 1967 to 1974 are emphasized as vibrant years—students organized large-scale demonstrations, regularly asserted their opinions in the political arena, and even participated in electoral politics. This period was followed, however, with the imposition of strict laws in 1975 limiting freedom of speech and expression. Such laws were part of the broader containment policy pursued by the state after the May 13, 1969, racial riots, which allowed the state to stifle any form of political dissidence to ensure peace between different ethnic groups. One particularly active organization in this period was the Malay Language Society (PBMUM) of the University of Malaya. While PBMUM began with a dream of using language as a mode to foster national unity, after the riots it would be remembered as a race-based organization oriented toward Malays. This thesis offers a historical analysis and reinterpretation of the PBMUM, characterizing it as a platform for students at the University of Malaya to meet, discuss, and mobilize around the most important issues concerning Malaysian society. Importantly, members exhibited a continued devotion towards changing the fate of the rakyat (the people). In revising the history of PBMUM, this thesis also offers a deeper understanding of the Malaysian political landscape in the ‘60s and ‘70s, focusing on political discussions around nation-building in the lead up to the May 13 riots and its aftermath.
An Alternative Perspective on Special Purpose Acquisition Companies (SPACs): Underpricing in the “No Target" Phase
Date: 2023-01-01
Creator: Anna G Constantine
Access: Open access
- Special Purpose Acquisition Companies marked a restructuring of the often-fraudulent 1980s blank check company, an entity gathering funds to merge or acquire another business entity. Based on the Special Purpose Acquisition Company structure, “the stock price should be greater than or equal to the pro-rata trust value, discounted from the SPAC’s expiration date, at all times prior to the shareholder vote date.” In this study, I research the “no target” phase of the Special Purpose Acquisition Company’s lifecycle to evaluate whether there is a difference between their trust value and their market capitalization. Based on previous research, we know that there is a discount to trust value prior to 2009; however, I postulate the decoupling of the SPAC merger approval vote and the vote for investors to redeem may eliminate this discount. Using a first difference regression to establish the premium to the average trust value of 1,057 Special Purpose Acquisition Companies traded between 2005 and 2022, we find that both the period before 2010 and after 2010 trades at a negative premium, or discount. Because the decoupling of the merger vote and the redemption vote did not eliminate the negative premium to trust value, I postulate that the structure of SPAC redemptions, modeled as a call option with decaying time value, may be responsible for this mispricing. I also draw opportunities for future research to investigate if the embedding of a call option into the SPAC redemption structure discourages shareholders from desiring merger outcomes early in the SPAC lifecycle.
The Current Hunt for Nitric Oxide's Effects on the Homarus americanus Cardiac Ganglion
Date: 2022-01-01
Creator: Joanna Lin
Access: Open access
- The crustacean heartbeat is produced and modulated by the cardiac ganglion (CG), a central pattern generator. In the American lobster, Homarus americanus, the CG consists of 4 small premotor cells (SCs) that electrically and chemically synapse onto 5 large motor cells (LCs). Rhythmic driver potentials in the SCs generate bursting in the LCs, which elicit downstream cardiac muscle contractions that are essential for physiological functions. Endogenous neuromodulators mediate changes in the CG to meet homeostatic demands caused by environmental stressors. Nitric oxide (NO), a gaseous neuromodulator, inhibits the lobster CG. Heart contractions release NO, which directly decreases the CG burst frequency and indirectly decreases the heartbeat amplitude, to mediate negative feedback. I investigated NO’s inhibitory effects on the CG to further understand the mechanisms underlying intrinsic feedback. Using extracellular recordings, I examined NO modulation of the SCs and LCs when coupled in the intact circuit and when firing independently in the ligatured preparation. Using two-electrode voltage clamp, I additionally analyzed the modulation of channel kinetics. Based on previous studies, I hypothesized that NO decreases the burst frequency of the LCs and SCs by modulating conductance properties of the voltage-gated A-type potassium current (IA). My data showed that NO decreased the burst frequency in the LCs and the burst duration in the SCs in a state-dependent manner. Furthermore, NO increased the IA inactivation time constant to decrease the LCs’ burst frequency. Thus, NO mediated inhibitory effects on cardiac output by differentially targeting both cell types and altering the IA current kinetics.
To hum or not to hum: analyzing and provoking sound production in the American lobster (Homarus americanus)
Date: 2024-01-01
Creator: Renske Kerkhofs
Access: Open access
- American lobsters (Homarus americanus) produce humming sounds by vibrating their carapace. These sounds have a fundamental frequency on the order of 100 Hz, with multiple higher harmonics. Though I found no relationship between lobster carapace length and hum frequency, I observed sounds similarly structured to hums but with frequencies an order of magnitude higher, suggesting that lobsters may use a wider range of sounds than previously thought. Using laser vibrometry, I was able to pick up high frequencies of carapace vibration that were similar to those I observed on sound recordings. Lobsters seem to hum most readily when approached from above, but many studies have found it difficult to reliably find soniferous lobsters. To find a way to reliably evoke sound production in American lobsters without contributing to the sound environment, lobsters were exposed to overhead abstract visual stimuli on a screen, after which their behavioral reactions were recorded, as well as any sound production in response to the stimulus. Lobsters responded to the screen stimulus with the same types of behaviors with which they responded to general overhead physical stimuli. This study demonstrates that American lobsters may produce high-pitched sounds and that abstract visual cues can be used as a silent tool to elicit lobster behaviors, but not sound production.