Showing 1001 - 1010 of 2595 Items
"A Doula Can Only Do So Much": Birth Doulas and Stratification in United States Maternity Care
Date: 2015-05-01
Creator: Kaylee S Wolfe
Access: Open access
Robot Detection Using Gradient and Color Signatures
Date: 2016-05-01
Creator: Megan Marie Maher
Access: Open access
- Tasks which are simple for a human can be some of the most challenging for a robot. Finding and classifying objects in an image is a complex computer vision problem that computer scientists are constantly working to solve. In the context of the RoboCup Standard Platform League (SPL) Competition, in which humanoid robots are programmed to autonomously play soccer, identifying other robots on the field is an example of this difficult computer vision problem. Without obstacle detection in RoboCup, the robotic soccer players are unable to smoothly move around the field and can be penalized for walking into another robot. This project aims to use gradient and color signatures to identify robots in an image as a novel approach to visual robot detection. The method, "Fastgrad", is presented and analyzed in the context of the Bowdoin College Northern Bites codebase and then compared to other common methods of robot detection in RoboCup SPL.
Mitigation of Negative Effects of Ocean Change on Oysters by Eelgrass and its Implications for Aquaculture in Midcoast Maine
Date: 2022-01-01
Creator: Fiona G Ralph
Access: Open access
- Species interactions are important to organisms and to the ecosystems they inhabit. These interactions, sometimes facilitations, can result in increased resiliency for both species. When facilitation occurs, organisms co-assist with physiological and environmental stressors. As anthropogenic impacts become more stressful for modern organisms, these interactions could offer a solution for many species. Ocean acidification has been shown to be detrimental to many calcifying organisms including oysters. More acidic conditions can slow the process of shell calcification, which can slow growth rates. This effect could directly impact the robust oyster farming business in Midcoast Maine. Because of its possible importance to oyster crops, we assessed the potential of Zostera marina, or eelgrass, to ameliorate the stresses of ocean acidification on farmed Eastern Oysters (Crassotrea virginica). Photosynthesizing organisms such as seagrasses have been shown to locally raise pH, which could create growth refugia for calcifying organisms. While eelgrass has the potential to enhance oyster growth rates, its meadows could also be influencing food availability. To better understand these dynamics, we grew C. virginica in two locations in Harpswell, ME. Crassostrea virginica were split into three habitats at each location: seagrass, fringe, and mudflat, and placed on surface or benthic arrays. We found that seagrass presence and depth interacted to increase shell growth rate. Similarly, Z. marina improved condition index of C. virginica. As ocean acidification worsens, oyster farmers might have to turn to mitigation strategies to ensure profit yield from their labors. Zostera marina could be the solution to their future problems.
Alexander the Great and the Rise of Christianity
Date: 2021-01-01
Creator: Stephen M. Girard
Access: Open access
- Alexander the Great and the Rise of Christianity focuses on the political, mythical, and philosophical connection between Alexander the Great's life and the beginnings of early Christianity. The first chapter of the text focuses on an analysis of mythical conceptions of Alexander the Great as “Son of God” as well as cultural perceptions of him as “Philosopher King” and cosmopolitan, and how these portraits of Alexander were influential for Christianity. The second chapter analyzes Alexander’s relationship with the Jewish people, and his appearances in the Old Testament apocalyptic Book of Daniel. The last chapter discusses Alexander’s relationship with Christianity itself, seen through a study of the life of Jesus, Alexandrian Judaism, and the early Christian apologists.
The Role of the Golgi ELMO Proteins in Cell Adhesion in Arabidopsis thaliana
Date: 2021-01-01
Creator: Wesley James Hudson
Access: Open access
- Proper growth and development of plant cells is dependent upon successful cell adhesion between cells, and this is mostly mediated by pectin in the plant cell wall. Previously, the Kohorn Laboratory identified a non-enzymatic Golgi protein named ELMO1 as it is required for cell adhesion, likely acting as a scaffold for cell wall polymer synthesis. Plants with mutant ELMO1 demonstrate a weak defective cellular adhesion phenotype as well as reduced mannose content in the cell wall. ELMO1 has homologous proteins in at least 29 different vascular plants. These homologues have 2 possible deletions in their amino acid sequence, but protein modeling determined that these variations will not affect protein structure. There are 5 homologous ELMO1 proteins in Arabidopsis thaliana that have been aptly named ELMO2, ELMO3, ELMO4, ELMO5. elmo2-/-mutants revealed no mutant adhesion phenotypes, while elmo1-/-elmo2-/-double mutants revealed strong defects in adhesion. Confocal microscopy of propidium iodide-stained seedlings confirmed the lack of a phenotype for elmo2-/-mutants and showed disorganized gapping cells for the elmo1-/-elmo2-/-mutant. Additionally, while elmo2-/-did not have any change to root or hypocotyl length, elmo1-/-elmo2-/- mutants were significantly shorter in both regards. Taken together, these data support that ELMO2 and ELMO1 are partially redundant.
The Effects of Temperature on the Cardiac System of the American Lobster, Homarus americanus
Date: 2014-05-01
Creator: Elizabeth A Owens
Access: Open access
- The American lobster, Homarus americanus, inhabits a large oceanic range spanning from Labrador, Canada to North Carolina, USA. This geographic range varies in temperature by as much as 25ºC, and daily temperature fluctuations of up to 12ºC may occur at a single location depending on season, water depth, and tides. The cardiac system of the lobster is sensitive to these temperature changes, and has been shown to adjust its functioning over a large temperature range. A previous study showed that various functional parameters respond differently to temperature changes, but a stable cardiac output can be maintained over the range of 2-20ºC. The current study showed that the effects of temperature were exerted primarily through changes in the lobster heart central pattern generator, the cardiac ganglion. Similar patterns of change were seen in both semi-intact hearts and isolated cardiac ganglion preparations in response to increasing temperature. Specifically, with increasing temperature, the burst frequency showed a biphasic pattern in which frequency initially increased, then decreased rapidly at high temperatures. The burst duration, duty cycle, and number of spikes per burst generally decreased with increasing temperature, and spike frequency increased over the entire temperature range. Semi-intact hearts and isolated cardiac ganglia showed similar “crash” patterns, characterized by complete loss of function at high temperatures and complete recovery of function when temperature was returned to baseline. Feedback in the semi-intact heart provided some stabilization of bursting activity, but it did not provide the expected protection from high temperatures. The isolated CG had a significantly higher crash temperature than did the semi-intact system. This discrepancy in crash temperatures may be explained by considering factors at the level of the muscle and neuromuscular junction (NMJ), such as stretch and nitric oxide (NO) feedback and the balance of facilitation and depression at the NMJ. Stimulated preparations showed defacilitation of contraction amplitude at high temperatures despite the maintenance of constant burst parameters of stimulation. Therefore, several factors contributing to the relatively low crash temperature of the intact system may be a shift in the balance of facilitation and depression at the NMJ, a depression in ganglion function due to the release of NO by the muscle, or a combination of the two mechanisms.
A Moderated-Mediation Model of Emerging Adult and Parent Religiosity, Externalizing Behavior, and Parenting Style
Date: 2021-01-01
Creator: Benjamin M. Simonds
Access: Open access
- The present study investigated whether emerging adult religiosity mediated the relationship between high parental religiosity and low levels of offspring externalizing, and whether these pathways are moderated by aspects of authoritative parenting (i.e., acceptance, firm control, and psychological autonomy). Surveys were completed by 275 emerging adults aged 18-25, including scales assessing their religiosity, the religiosity of their parents, the style of parenting in which they were raised, and their own engagement in externalizing behaviors. Results indicated a correlation between high levels of parental and emerging adult religiosity, and a marginal relationship between high parental religiosity and reduced offspring externalizing. However, emerging adult religiosity was not related to externalizing, such that no mediation model could be tested. Psychological autonomy granting moderated the relationship between parental religiosity and emerging adult externalizing: low parental religiosity was associated with high levels of emerging adult externalizing only in parents who exhibited low levels of psychological autonomy granting, while high parental religiosity was related to low emerging adult externalizing regardless of psychological autonomy granting. The results indicate a complex relationship between parenting, externalizing, and religiosity.
Aortic pressure and heart rate in the lobster Homarus americanus are modulated by mechanical feedback and neuropeptides
Date: 2021-01-01
Creator: Grace Marie Hambelton
Access: Open access
- Baroreceptors are stretch receptors located in the aorta of mammals; in response to increased afterload, they elicit a decrease in heart rate, creating a negative feedback loop that lowers blood pressure. Although lobsters (Homarus americanus) do not have baroreceptors like mammals, closely related land crabs have been shown to have baroreceptor-like responses. Heart contraction is also regulated by the Frank-Starling response, where increasing stretch or preload increases the contractile force of the heart. In addition to these types of biomechanical modulations, lobsters use a central pattern generator, the cardiac ganglion, to maintain synchronicity of the heartbeat. The heart is also controlled by the central nervous system via neuromodulators, such as myosuppressin, which has been shown to increase active force and decrease frequency in isolated lobster hearts. We performed experiments on a lobster heart with the main arteries still intact, and varied the preload by stretching anterior arteries, and the afterload by elevating the dorsal abdominal artery. We added myosuppressin to modulate the cardiac ganglion output and muscle contraction. We found that the baroreceptor-like response is most directly modulated by active force, whereas frequency could be a secondary control. Increasing preload does increase active force, but that does not correlate to a higher cardiac output, which shows that how hard the heart pumps is not what determines how effectively it is pumping. Additionally, we found that myosuppressin has a much stronger effect on frequency than active force, and so with myosuppressin, frequency becomes the main determinant of cardiac output.
Extreme Value Theory and Backtest Overfitting in Finance
Date: 2015-05-01
Creator: Daniel C Byrnes
Access: Open access
- In order to identify potentially profitable investment strategies, hedge funds and asset managers can use historical market data to simulate a strategy's performance, a process known as backtesting. While the abundance of historical stock price data and powerful computing technologies has made it feasible to run millions of simulations in a short period of time, this process may produce statistically insignificant results in the form of false positives. As the number of configurations of a strategy increases, it becomes more likely that some of the configurations will perform well by chance alone. The phenomenon of backtest overfitting occurs when a model interprets market idiosyncrasies as signal rather than noise, and is often not taken into account in the strategy selection process. As a result, the finance industry and academic literature are rife with skill-less strategies that have no capability of beating the market. This paper explores the development of a minimum criterion that managers and investors can use during the backtesting process in order to increase confidence that a strategy's performance is not the result of pure chance. To do this we will use extreme value theory to determine the probability of observing a specific result, or something more extreme than this result, given that multiple configurations of a strategy were tested.
Stuck in Limbo: Temporary Protected Status, Climate Migrants and the Expanding Definition of Refugees in the United States
Date: 2021-01-01
Creator: Noelia Calcaño
Access: Open access
- There will be 1.2 billion climate refugees by 2050 as ecological disasters precipitate mass migrations around the world. The U.S. does not legally recognize climate migrants as refugees, instead adhering to the 1951 UN Refugee Convention that limits the definition of a refugee to individuals facing political persecution. Despite failing to expand the definition of a refugee, the U.S. has accommodated migrants displaced by natural disasters through a series of ad hoc fixes, most notably “Temporary Protected Status.” In Central American countries that were granted TPS, we encounter the paradox of the U.S. employing environmental disasters to justify continued extensions of this temporary protection, while addressing chronic conditions in the region. The central question of this thesis is, has employing the environment as a catch-all tool for Temporary Protected Status protection expanded the de facto definition of a “refugee,” for Central American migrants impacted by climate catastrophes and if so, how? Though TPS fills a gap in US law by providing de facto protections to migrants fleeing environmental disasters, the environment is being used as a catch-all tool for more systemic economic and political vulnerabilities in Central America. The environment is a catch-all tool for continued protection only insofar as it is not recognized as political, yet it is getting harder to employ the environment as an apolitical driver of migration. The precarious foundation of TPS threatens the hundreds of thousands of Central Americans that depend on this program to live and work legally in the United States.