Showing 851 - 860 of 2039 Items
Statistically Principled Deep Learning for SAR Image Segmentation
Date: 2024-01-01
Creator: Cassandra Goldberg
Access: Open access
- This project explores novel approaches for Synthetic Aperture Radar (SAR) image segmentation that integrate established statistical properties of SAR into deep learning models. First, Perlin Noise and Generalized Gamma distribution sampling methods were utilized to generate a synthetic dataset that effectively captures the statistical attributes of SAR data. Subsequently, deep learning segmentation architectures were developed that utilize average pooling and 1x1 convolutions to perform statistical moment computations. Finally, supervised and unsupervised disparity-based losses were incorporated into model training. The experimental outcomes yielded promising results: the synthetic dataset effectively trained deep learning models for real SAR data segmentation, the statistically-informed architectures demonstrated comparable or superior performance to benchmark models, and the unsupervised disparity-based loss facilitated the delineation of regions within the SAR data. These findings indicate that employing statistically-informed deep learning methodologies could enhance SAR image analysis, with broader implications for various remote sensing applications and the general field of computer vision. The code developed for this project can be found here: https://github.com/cgoldber/Statistically-Principled-SAR-Segmentation.git.
Investigating the Impacts of Drought on Turfgrass (Festuca arundinacea) Chlorophyll-a Fluorescence Emission
Date: 2024-01-01
Creator: Ayanna S Hatton
Access: Open access
- When photons from sunlight are absorbed by plants, they can take paths of photosynthesis, fluorescence, or energy dissipation. Instruments to quantify fluorescence have expanded in scale to allow measurements from satellites and flux towers using Solar-Induced Chlorophyll Fluorescence (SIF). Studies have found a positive correlation between SIF and gross primary productivity (GPP; representative of photosynthesis), suggesting SIF is a proxy for GPP. This conclusion encourages the use of SIF to inform decisions about carbon budgets and responding to climate change. Studies of fluorescence on the single-leaf scale have revealed that SIF measurements do not account for all variables nor is there an understanding of the impact of environmental factors, such as drought, on these measurements. In this project, tall fescue turfgrass was placed in one of four differing drought severities for 19 days. Leaf-level measurements of photosynthesis and pulse-amplitude modulated fluorescence were made, demonstrating stomatal closure and inhibition of photosynthesis. This physiological change caused greater photon allocation to energy dissipation. Changes in greenness and the utilization of photoprotective mechanisms such as senescence and anthocyanin accumulation were observed. This study has provided an understanding of the temporal, physiological, and visible impacts of drought on turfgrass to inform interpretations of SIF in future experiments. Caution is crucial in utilizing SIF as a proxy for GPP before further research into the impact of drought on SIF is completed.
Physiological responses of the American lobster cardiovascular system to neuropeptide SGRNFLRFamide (SGRN)
Date: 2024-01-01
Creator: Andre Eden
Access: Open access
- During every second of a human’s life, the cardiovascular system is modulated by factors both intrinsic and extrinsic to the physiology of the heart. We can uncover new insights regarding the nature of our system through investigations of similar systems in other model species. One example materializes itself in the form of the American Lobster (Homarus americanus) whose single-chambered heart finds resemblance to the function and anatomy to that of humans. The lobster heart is powered by the cardiac ganglion (CG), a group of neurons that drive contractions of surrounding heart muscles, known as the myocardium. Both the CG and myocardium work in a feedback loop, with both intrinsic (afterload and preload) and extrinsic (temperature and neuropeptides) factors affecting cardiac output (CO) or the overall ability of the heart to carry out its primary function of nutrient distribution. In this paper, we examine how the addition of these factors into in vitro whole heart preparations affect CO and other associated variables. From experimentation, we conclude that the neuropeptide SGRNFLRFamide (SGRN) increases the heartbeat frequency and the active force exerted by the heart. We also conclude that increases in temperature decrease CO as higher temperatures decrease heartbeat frequency and the active force exerted by the heart. Lastly, we conclude that the effect of preload and afterload combined produce more robust effects on the CO and active force of the heart, potentially painting a better picture of what may happen in vivo.
A histological investigation of Arceuthobium pusillum infections in Picea rubens and Picea glauca
Date: 2024-01-01
Creator: Sade K. McClean
Access: Open access
- Arceuthobium pusillum is a hemiparasite that infects select Picea species. The hosts of A. pusillum do not experience the same symptoms of infection. A. pusillum infections are more fatal to P. marinara, and P. glauca. P. rubens, on the other hand, can survive longer with sustained infection. This presents itself as a contemporary issue because P. glauca, one of the parasite’s most vulnerable hosts, was untethered from ecological competition when old growth forests were subjected to large scale anthropogenic disturbances. These disturbances allowed P. glauca to proliferate, with A. pusillum following. A deeper understanding of the host-species specific responses to A. pusillum infection can broaden general knowledge of parasitic growth and development while also potentially inspiring conservation techniques. This study took advantage of the intrinsic differences between host and parasite to visualize infections in P. rubens and P. glauca, highlighting differences in infection outcome. By illuminating lignin and callose within cross sections of infected P. rubens and P. glauca branches, it was revealed that P. rubens forms dense bands of cells around the cortical strands of infection. These bands form more frequently in P. rubens than in P. glauca and are of a significantly larger area in P. rubens than in P. glauca (t(8), p=0.003, p=0.005). The discovery of the exterior bands is novel and exciting, as the bands are possibly made of callose and potentially facilitate P. rubens survival against A. pusillum infection. The foundational discoveries and results of this study should inspire, and warrant, further analysis.
Poverty Ends with a 12 Year Old Girl: Empowerment and the Contradictions of International Development
Date: 2017-05-01
Creator: Meghan Elizabeth Bellerose
Access: Open access
- This thesis argues that international development programs focused on adolescent girls reproduce problematic and contradictory depictions of girls in the global South. Using Girl Effect marketing materials and interviews with INGO staff, I demonstrate that present-day international aid programs center on the neoliberal notion that an empowered adolescent girl holds the unique potential to end global poverty. Through empowerment programs, girls are encouraged to recognize their agency and take personal responsibility for improving the wellbeing of their communities. However, I argue that even as development leaders claim that an empowered adolescent girl is a source of indefatigable strength who can transform her community, they carry a deep conviction that such a feat is not possible without significant Western aid. Despite the empowerment rhetoric that The Girl Effect and related international initiatives espouse, their programs depict adolescent girls in the developing world as vulnerable and oppressed by poverty, local men, and their cultures. Thus, Western donors are called upon to save “Third World” adolescent girls. I argue that these contradictions in the language of international development contribute to the perception of girls in the global South as weak, inferior, and homogenous and lead to the establishment of programs that strengthen inequitable structures and sideline girls’ sexual rights.
Hybridization dynamics of a newly discovered parrotfish swarm in the Tropical Eastern Pacific
Date: 2017-05-01
Creator: Robert Barron
Access: Open access
- Hybrid zones and their dynamics are important in the understanding of the genetic basis of reproductive isolation and speciation. This study seeks to investigate the hybridization dynamics of a Scarus hybrid swarm within the Tropical Eastern Pacific (TEP) that includes four phenotypically distinct species: S. perrico, S. ghobban, S. rubroviolaceus, and S. compressus. Genetic and population structure analyses of four nuclear loci and a mitochondrial locus revealed that one of the four species, S. compressus, was the result of two different hybrid crosses: S. perrico ✕ S. rubroviolaceus and S. perrico ✕ S. ghobban. A NewHybrids model indicated that most of the S. compressus samples were F1 hybrids, but 21% of the S. compressus sample was classified as “parentals” which could also be explained by the presence of either F2 hybrids or backcrosses with S. compressus phenotypes, given the relatively low power of the nuclear data set (4 loci) to resolve complex hybrid genotypes. Significant mito-nuclear discordance in all three non-hybrid species is consistent with an evolutionary effect of backcrossing between F1 hybrids and “pure” species. This study reveals a relative ease of hybridization between parrotfish taxa separated by an estimated 4.5 million years of isolation and opens the door to further studies on the potential effects of gene flow across old species boundaries and perhaps the formation of new species by hybrid speciation in a diverse clade of tropical reef fish. Elucidating the nature of potentially “deep” F2 crosses and backcrosses within the TEP Scarus hybrid system will allow us to better understand the effects of hybridization on evolution and speciation on both a micro- and macro-ecological scale.
Some like it cold: the relationship between thermal tolerance and mitochondrial genotype in an invasive population of the European green crab, Carcinus maenas
Date: 2017-05-01
Creator: Aidan Fisher Coyle
Access: Open access
- Hybrid zones provide natural laboratories to study how specific genes, and interactions among genes, may influence fitness. On the east coast of North America, two separate populations of the European green crab (Carcinus maenas) have been introduced in the last two centuries. An early invasion from Southern Europe colonized New England around 1800, and was followed by a second invasion from Northern Europe to Nova Scotia in the early 1980s (Roman 2006). As these populations hybridize, new combinations of genes potentially adapted to different ends of a thermal spectrum are created in a hybrid zone. To test the hypothesis that mitochondrial and nuclear genes have effects on thermal tolerance, I measured response to cold stress in crabs collected from locations between southern Maine and northern Nova Scotia, and then genotyped the mitochondrial CO1 gene and two nuclear SNPs. Three mitochondrial haplotypes, originally from Northern Europe, had a strong effect on the ability of crabs to right themselves at a temperature of 4.5ºC. Crabs carrying these three haplotypes were 20% more likely to right compared to crabs carrying the haplotype from Southern Europe. The two nuclear SNPs, which were derived from transcriptome sequencing and were strong outliers between Northern and Southern European C. maenas populations, had no effect on righting response at low temperature. These results add C. maenas to the short list of ectotherms in which mitochondrial variation affects thermal tolerance, and suggests that natural selection is shaping the structure of the hybrid zone between the northern and southern populations This discovery of linkage between mitochondrial genotype and thermal tolerance also provides potential insight into the patterns of expansion for invasive populations of C. maenas around the world.
Damned If You Do, Damned If You Don't: A Logical Analysis of Moral Dilemmas
Date: 2018-05-01
Creator: Samuel Monkman
Access: Open access
- This project explores the logical structure of moral dilemmas. I introduce the notion of genuine contingent moral dilemmas, as well as basic topics in deontic logic. I then examine two formal arguments claiming that dilemmas are logically impossible. Each argument relies on certain principles of normative reasoning sometimes accepted as axioms of deontic logic. I argue that the principle of agglomeration and a statement of entailment of obligations are both not basic to ethical reasoning, concluding that dilemmas will be admissible under some logically consistent ethical theories. In the final chapter, I examine some consequences of admitting dilemmas into a theory, in particular how doing so complicates assignment of blame.
Shaping Canons and Building Legacies: Collectors and the History of African American Art
Date: 2019-01-01
Creator: Kinaya Hassane
Access: Open access