Showing 2121 - 2130 of 5713 Items
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.
Date: 2024-01-01
Creator: Athis Osathapan
Access: Access restricted to the Bowdoin Community
Date: 2015-05-01
Creator: Stephen Ligtenberg
Access: Open access
Date: 2008-07-21
Creator: Michael 'Mike' M Hastings, Anita Jensen, Estelle Lavoie, Mary E McAleney
Access: Open access
Biographial Note
Michael M. Hastings, a native of Morrill, Maine, graduated from Tilton School (NH) in 1968 and Bowdoin College in 1972. Following a year of graduate study in Public & International Affairs at George Washington University, he worked for seven years as a foreign and defense policy aide to Senator William S. Cohen (1973-1980) and for four years for Senator George J. Mitchell (1980-1984). In October, 1984, he joined the international staff of Catholic Relief Services (CRS) and moved to Africa. Over a span of eight years, he worked as a CRS development administrator in Kenya, Tanzania, Togo and The Gambia. During the same period, he assisted in the provision of emergency food for people displaced by civil wars in the Southern Sudan and Liberia. In 1992, he returned to Maine to direct a “center for excellence,” focusing on aquaculture and economic development. Since 2004, he has worked for the University of Maine as its Director of Research and Sponsored Programs. Between 1992 and 2008, he also served on several civic boards and institutions including the Maine Fishermen’s Forum, The Maine Oil Spill Advisory Committee (which he chaired), the Maine Indian Tribal State Commission, the Down East Institute, and the Maine Sea Grant Policy Advisory Committee. Between 1996 and 2001 he was elected three times to be a member of the Town Council of Hampden, ME, where he resides with his wife, a middle school teacher. Anita Holst-Jensen was born in Karl-Marx-Stadt (Chemnitz), East Germany, on March 16, 1945, to Rasma Rasmanis and Arvids Lusis. Her mother emigrated from Latvia in September of 1944, and Jensen was born in a displaced persons camp, where she lived until she was four years old. Her family eventually emigrated to Australia in 1949, settling in Victoria. Jensen received all of her schooling in Australia and went to university in Melbourne. She married Henning Holst-Jensen, and in 1966 they moved to Perth. When immigration into the United States became possible in 1968, they relocated to the Washington, D.C. area, and Jensen took a job with Investors Overseas Services, later Equity Funding. In 1970, she went to work in Senator Ed Muskie’s office, where she continued until he became secretary of state. She transitioned to George Mitchell’s staff when he was appointed to Muskie’s vacated Senate seat and remained for his fourteen years of Senate service, becoming increasingly involved with speech writing and research. Estelle Lavoie was born in Lewiston, Maine, on November 23, 1949, and grew up there, the youngest of three children. Her father worked as a building contractor until his death in 1964, after which her mother worked part-time as a bank teller. She attended Lewiston public schools and was graduated from Bates College (class of 1971), spending her junior year studying in Switzerland. At the end of 1972, she went to work for Governor Ken Curtis. By September of 1973, she had been hired as part of Senator Ed Muskie’s staff, working first as a caseworker and eventually as his legislative assistant. She attended law school at American University from 1978 to 1981 and transitioned to Senator Mitchell’s staff when he assumed Muskie’s Senate seat. She left Mitchell’s staff in the fall of 1983 and joined the law firm of Preti, Flaherty, Beliveau & Pachios the following June. Her practice has evolved from health law to other political practice issues. She served on the Democratic State Committee from 1986 to 1990 and was a delegate to the 1988 National Convention. Mary Elizabeth McAleney was born on March 18, 1945, in Tuscaloosa, Alabama. Her mother, Helen Irene (Twombly) McAleney, was a Works Progress Administration worker, and her father, William McAleney, was a U.S. Customs officer. Mary came from a strongly Democratic Maine family and was politically active from a young age. She was sent from her home near Vanceboro, Maine, to St. Joseph’s boarding school in South Portland, and from there she went to Merrimac College. After her graduation, she taught high school in Maine, first at St. Joseph’s and then at Catherine McAuley High School. After eight years of teaching, she went into political work. She quickly rose through the ranks during Senator Muskie’s ‘76 campaign and worked for state Senator Jim Tierney. She served in George Mitchell’s U.S. Senate office for ten years (1984-1994), focusing on Maine issues.
Summary
Interview includes discussion of: how Mary McAleney became Mitchell’s scheduler; the transition from Muskie to Mitchell; how Mitchell’s briefcase would be searched entering the office because initially no one knew who he was; the Elizabeth Taylor story; the cow joke; the 1982 U.S. Senate campaign; anecdotes about when Mitchell accidentally sat in a canoe backwards and when David Emery’s float sank in the Kennebec River; the relationship between Cohen and Mitchell; Mitchell’s gaining the support of one of Estelle Lavoie’s friends because he knew the name spelling; Mitchell’s work ethic; Mitchell’s complimenting Byrd on his history of the Senate; Mitchell eye glasses and the striped belt; visiting Talmadge Plantation after Mitchell’s reelection in 1988; Mitchell’s ability to learn and adapt; Anita Jensen’s experience driving Mitchell to work; Mitchell’s lifestyle in D.C.; Sally Mitchell’s decision to stay in Maine and not become involved in politics; the women’s restroom situation in the Capitol; the machine-gun ban and how Feinstein did not want to come to the Senate floor the day after it passed; Mitchell’s process for examining different points of view; an anecdote about Mitchell’s changing his mind and explaining it to the press; Jensen’s lively discussions with Mitchell; the Rehnquist nomination; the role of the staff in Mitchell’s office; Gayle Cory and her influence in the office and with Mitchell; Buzz Fitzgerald; the dynamics of the Mitchell Senate office and the office organization’s lack of hierarchy; the longevity of the staff; Anita Jensen’s role as the speechwriter; writing updates about China; Larry Benoit’s and David Lemoine’s traveling around Maine to update the voter lists; Larry Benoit; Mitchell’s making sure that there were Mainers working for him; the interns; and the Mitchell Institute.
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.
Date: 2018-05-01
Creator: Angela M Dahl
Access: Open access
Date: 2013-09-01
Creator: Kanokwan Champasa, Scott A. Longwell, Aimee M. Eldridge, Elizabeth A. Stemmler, Danielle H., Dube
Access: Open access
- Virulence of the gastric pathogen Helicobacter pylori (Hp) is directly linked to the pathogen's ability to glycosylate proteins; for example, Hp flagellin proteins are heavily glycosylated with the unusual nine-carbon sugar pseudaminic acid, and this modification is absolutely essential for Hp to synthesize functional flagella and colonize the host's stomach. Although Hp's glycans are linked to pathogenesis, Hp's glycome remains poorly understood; only the two flagellin glycoproteins have been firmly characterized in Hp. Evidence from our laboratory suggests that Hp synthesizes a large number of as-yet unidentified glycoproteins. Here we set out to discover Hp's glycoproteins by coupling glycan metabolic labeling with mass spectrometry analysis. An assessment of the subcellular distribution of azide-labeled proteins by Western blot analysis indicated that glycoproteins are present throughout Hp and may therefore serve diverse functions. To identify these species, Hp's azide-labeled glycoproteins were tagged via Staudinger ligation, enriched by tandem affinity chromatography, and analyzed by multidimensional protein identification technology. Direct comparison of enriched azide-labeled glycoproteins with a mock-enriched control by both SDS-PAGE and mass spectrometry-based analyses confirmed the selective enrichment of azide-labeled glycoproteins. We identified 125 candidate glycoproteins with diverse biological functions, including those linked with pathogenesis. Mass spectrometry analyses of enriched azide-labeled glycoproteins before and after cleavage of O-linked glycans revealed the presence of Staudinger ligation-glycan adducts in samples only after beta-elimination, confirming the synthesis of O-linked glycoproteins in Hp. Finally, the secreted colonization factors urease alpha and urease beta were biochemically validated as glycosylated proteins via Western blot analysis as well as by mass spectrometry analysis of cleaved glycan products. These data set the stage for the development of glycosylation-based therapeutic strategies, such as new vaccines based on natively glycosylated Hp proteins, to eradicate Hp infection. Broadly, this report validates metabolic labeling as an effective and efficient approach for the identification of bacterial glycoproteins. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.
Date: 2018-05-01
Creator: Corinne Alini
Access: Open access
- Computer Vision involves the extraction of data from images that are analyzed in order to provide information crucial to many modern technologies. Object recognition has proven to be a difficult task and programming reliable object recognition remains elusive. Image processing is computationally intensive and this issue is amplified on mobile platforms with processor restrictions. The real-time constraints demanded by robotic soccer in RoboCup competition serve as an ideal format to test programming that seeks to overcome these challenges. This paper presents a method for ball recognition by analyzing the movement of the ball. Major findings include enhanced ball discrimination by replacing the analysis of static images with absolute change in brightness in conjunction with the classification of apparent motion change.
Date: 2014-05-01
Creator: Graham Harper Edwards
Access: Open access
- Morainal and lacustrine sediments in Linnédalen, Spitsbergen, Svalbard, record the fluctuations of a glacier in a currently unglaciated mountain cirque during the Little Ice Age (LIA). This study attempts to reconstruct Late Holocene glacial activity within this cirque from geochemical, physical, and visual stratigraphic variation of the Linnévatnet lacustrine sediment record. A 57 cm lacustrine sediment core (D10.5) from Linnévatnet was analyzed at a high-resolution for variations in X-Ray Fluorescence (XRF)-measured elemental composition, spectral reflectance, and magnetic susceptibility. The visual stratigraphy was observed at a microscopic scale. An age-depth model for D10.5 is developed by extrapolating sedimentation rates from dated horizons, measured by 239+240Pu radionuclide fallout dating and chemostratigraphic enrichment of atmospheric anthropogenic pollutants. Visual stratigraphy of the sediment record indicates two periods of cirque glacier sediment delivery to Linnévatnet during the LIA (1329-1363 CE, 1816 CE-Present) and a third period of sediment delivery during the Medieval Climate Anomaly (MCA; 984-1082 CE). During non-glacial periods, stratigraphic variation in XRF-measured Ti and K appear to be associated with fluctuations in North Atlantic Oscillation (NAO)-regulated precipitation. Within the LIA glacial intervals, decadal-scale variations in sediment Ti and K geochemistry may result from advance and retreat of the cirque glacier ice-margin or fluctuations in precipitation. Stratigraphic variation in Fe content indicates complex erosional and hydrological processes associated with MCA precipitation and glacial meltwater. Stratigraphic and geochemical variations in the lacustrine record of Linnévatnet indicate that both cirque glacier activity and sediment transport in Linnédalen are more sensitive to climatological change than previously thought.
Date: 2019-05-01
Creator: James Little
Access: Open access
- Isolation-Based Scene Generation (IBSG) is a process for creating synthetic datasets made to train machine learning detectors and classifiers. In this project, we formalize the IBSG process and describe the scenarios—object detection and object classification given audio or image input—in which it can be useful. We then look at the Stanford Street View House Number (SVHN) dataset and build several different IBSG training datasets based on existing SVHN data. We try to improve the compositing algorithm used to build the IBSG dataset so that models trained with synthetic data perform as well as models trained with the original SVHN training dataset. We find that the SVHN datasets that perform best are composited from isolations extracted from existing training data, leading us to suggest that IBSG be used in situations where a researcher wants to train a model with only a small amount of real, unlabeled training data.