Showing 4471 - 4480 of 5713 Items
Identification, physiological actions, and distribution of TPSGFLGMRamide: A novel tachykinin-related peptide from the midgut and stomatogastric nervous system of Cancer crabs
Date: 2007-06-01
Creator: Elizabeth A. Stemmler, Braulio Peguero, Emily A. Bruns, Patsy S. Dickinson, Andrew E., Christie
Access: Open access
- In most invertebrates, multiple species-specific isoforms of tachykinin-related peptide (TRP) are common. In contrast, only a single conserved TRP isoform, APSGFLGMRamide, has been documented in decapod crustaceans, leading to the hypothesis that it is the sole TRP present in this arthropod order. Previous studies of crustacean TRPs have focused on neuronal tissue, but the recent demonstration of TRPs in midgut epithelial cells in Cancer species led us to question whether other TRPs are present in the gut, as is the case in insects. Using direct tissue matrix assisted laser desorption/ionization Fourier transform mass spectrometry, in combination with sustained off-resonance irradiation collision-induced dissociation, we found that at least one additional TRP is present in Cancer irroratus, Cancer borealis, Cancer magister, and Cancer productus. The novel TRP isoform, TPSGFLGMRamide, was present not only in the midgut, but also in the stomatogastric nervous system (STNS). In addition, we identified an unprocessed TRP precursor APSGFLGMRG, which was detected in midgut tissues only. TRP immunohistochemistry, in combination with preadsorption studies, suggests that APSGFLGMRamide and TPSGFLGMRamide are co-localized in the stomatogastric ganglion (STG), which is contained within the STNS. Exogenous application of TPSGFLGMRamide to the STG elicited a pyloric motor pattern that was identical to that elicited by APSGFLGMRamide, whereas APSGFLGMRG did not alter the pyloric motor pattern. © 2007 The Authors.
Retinoic acid expands the evolutionarily reduced dentition of zebrafish
Date: 2012-12-01
Creator: Pawat Seritrakul, Eric Samarut, Tenzing T.S. Lama, Yann Gibert, Vincent, Laudet, William R. Jackman
Access: Open access
- Zebrafish lost anterior teeth during evolution but retain a posterior pharyngeal dentition that requires retinoic acid (RA) cell-cell signaling for its development. The purposes of this study were to test the sufficiency of RA to induce tooth development and to assess its role in evolution. We found that exposure of embryos to exogenous RA induces a dramatic anterior expansion of the number of pharyngeal teeth that later form and shifts anteriorly the expression patterns of genes normally expressed in the posterior tooth-forming region, such as pitx2 and dlx2b. After RA exposure, we also observed a correlation between cartilage malformations and ectopic tooth induction, as well as abnormal cranial neural crest marker gene expression. Additionally, we observed that the RA-induced zebrafish anterior teeth resemble in pattern and number the dentition of fish species that retain anterior pharyngeal teeth such as medaka but that medaka do not express the aldh1a2 RA-synthesizing enzyme in tooth-forming regions. We conclude that RA is sufficient to induce anterior ectopic tooth development in zebrafish where teeth were lost in evolution, potentially by altering neural crest cell development, and that changes in the location of RA synthesis correlate with evolutionary changes in vertebrate dentitions. © FASEB.
GEM-PSO: Particle Swarm Optimization Guided by Enhanced Memory
Date: 2019-05-01
Creator: Kevin Fakai Chen
Access: Open access
- Particle Swarm Optimization (PSO) is a widely-used nature-inspired optimization technique in which a swarm of virtual particles work together with limited communication to find a global minimum or optimum. PSO has has been successfully applied to a wide variety of practical problems, such as optimization in engineering fields, hybridization with other nature-inspired algorithms, or even general optimization problems. However, PSO suffers from a phenomenon known as premature convergence, in which the algorithm's particles all converge on a local optimum instead of the global optimum, and cannot improve their solution any further. We seek to improve upon the standard Particle Swarm PSO algorithm by fixing this premature convergence behavior. We do so by storing and exploiting increased information in the form of past bests, which we deem enhanced memory. We introduce three types of modifications to each new algorithm (which we call a GEM-PSO: Particle Swarm Optimization, Guided by Enhanced Memory, because our modifications all deal with enhancing the memory of each particle). These are procedures for saving a found best, for removing a best from memory when a new one is to be added, and for selecting one (or more) bests to be used from those saved in memory. By using different combinations of these modifications, we can create many different variants of GEM-PSO that have a wide variety of behaviors and qualities. We analyze the performance of GEM-PSO, discuss the impact of PSO's parameters on the algorithms' performances, isolate different modifications in order to closely study their impact on the performance of any given GEM-PSO variant, and finally look at how multiple modifications perform. Finally, we draw conclusions about the efficacy and potential of GEM-PSO variants, and provide ideas for further exploration in this area of study. Many GEM-PSO variants are able to consistently outperform standard PSO on specific functions, and GEM-PSO variants can be shown to be promising, with both general and specific use cases.
Social Media as Technologies of Accountability: Explaining Resistance to Implementation Within Organizations
Date: 2013-04-12
Creator: Jeffrey Treem
Access: Open access
Landscape in Maine 1820-1970: A Sesquicentennial Exhibition
Date: 1970-01-01
Creator: James Morton
Access: Open access
- Catalog of an exhibition held at the Colby College Art Museum, April 4-May 10; the Bowdoin College Museum of Art, May 21-June 28; and the Carnegie Gallery, University of Maine, Orono, July 8-August 30. Sponsored by the Maine Federation of Women's Clubs.
The Effects of Exchange Rates on Employment in Canada
Date: 2013-06-05
Creator: Yao Tang, Haifang Huang, Ke Pang
Access: Open access
- Under the flexible exchange rate regime, the Canadian economy is constantly affected by fluctuations in exchange rates. This paper focuses on employment in Canada. We find that appreciations of the Canadian dollar have significant effects on employment in manufacturing industries; such effects are mostly associated with the export-weighted exchange rate and not the import-weighted exchange rate. The export-weighted exchange rate elasticity of employment is -0.52. However, we also find that exchange rate fluctuations have little impact on Canada’s nonmanufacturing employment. Because the manufacturing sector accounts for only about 10% of the employment in Canada, the overall employment effect of exchange rates is small. In addition, we assess the potential employment impact of a boom in the global commodity market, which often leads to appreciations of the Canadian dollar. We find that a 12.21% increase in commodity prices (one standard deviation in the 1994-2007 data) reduces Canada’s manufacturing employment by 0.98%, less than 0.1% of the total industrial employment.
Reflections questionnaire response by Anonymous on March 31, 2021
Date: 2021-01-01
Creator: Anonymous
Access: Open access
- This is a response to the Documenting Bowdoin & COVID-19 Reflections Questionnaire. The questionnaire was created in March 2021 by staff of Bowdoin's George J. Mitchell Department of Special Collections & Archives. Author is class of 2023.
Emergence of dispersive shocks and rarefaction waves in power-law contact models
Date: 2017-06-16
Creator: H. Yasuda, C. Chong, J. Yang, P. G. Kevrekidis
Access: Open access
- In the present work, motivated by generalized forms of the Hertzian dynamics associated with granular crystals, we consider the possibility of such models to give rise to both dispersive shock and rarefaction waves. Depending on the value p of the nonlinearity exponent, we find that both of these possibilities are realizable. We use a quasicontinuum approximation of a generalized inviscid Burgers model in order to predict the solution profile up to times near the formation of the dispersive shock, as well as to estimate when it will occur. Beyond that time threshold, oscillations associated with the highly dispersive nature of the underlying model emerge, which cannot be captured by the quasicontinuum approximation. Our analytical characterization of the above features is complemented by systematic numerical computations.
Microblogging Practices of Virtual Organizations: Commonalities and Contrasts
Date: 2013-04-12
Creator: Jing Wang
Access: Open access
- Microblogging is becoming increasingly pervasive in computer-supported collaboration, attracting various types of users. Organizations, as one type, are willing to leverage this social media service for their operation, but lack guidance of how to effectively manage their organizational microblogs. However, research on microblogging practices at organizational level, especially in virtual organizations, is very limited. To enhance the understanding of how virtual organizations use microblogs in similar and different ways, we investigate microblogging practices of two virtual organizations by examining the content characteristics of their Twitter posts. We identify eleven categories of microblog themes of three dimensions, consisting of both common and different categories between the two organizations. We further enumerate their potential impacts on organizational context, discuss differences between the two organizations, and compare these organizational practices with personal ones.
Globalizing extraction and indigenous rights in the russian arctic: The enduring role of the state in natural resource governance
Date: 2019-12-01
Creator: Svetlana A. Tulaeva, Maria S. Tysiachniouk, Laura A. Henry, Leah S. Horowitz
Access: Open access
- The governance of extractive industries has become increasingly globalized. International conventions and multi-stakeholder institutions set out rules and standards on a range of issues, such as environmental protection, human rights, and Indigenous rights. Companies' compliance with these global rules may minimize risks for investors and shareholders, while offering people at sites of extraction more leverage. Although the Russian state retains a significant stake in the oil and gas industries, Russian oil and gas companies have globalized as well, receiving foreign investment, participating in global supply chains, and signing on to global agreements. We investigate how this global engagement has affected Nenets Indigenous communities in Yamal, an oil-and gas-rich region in the Russian Arctic, by analyzing Indigenous protests and benefit-sharing arrangements. Contrary to expectations, we find that Nenets Indigenous communities have not been empowered by international governance measures, and also struggle to use domestic laws to resolve problems. In Russia, the state continues to play a significant role in determining outcomes for Indigenous communities, in part by working with Indigenous associations that are state allies. We conclude that governance generating networks in the region are under-developed.