Showing 3501 - 3510 of 5713 Items
Bowdoin College Catalogue (1968-1969)
Date: 1969-01-01
Access: Open access
- Bowdoin College Bulletin no. 370
Characterization of plexinA and two distinct semaphorin1a transcripts in the developing and adult cricket Gryllus bimaculatus
Date: 2020-03-01
Creator: Hadley W. Horch, Sara B. Spicer, Isabel I.C. Low, Colby T. Joncas, Eleanor D., Quenzer, Hikmah Okoya, Lisa M. Ledwidge, Harrison P. Fisher
Access: Open access
- Guidance cues act during development to guide growth cones to their proper targets in both the central and peripheral nervous systems. Experiments in many species indicate that guidance molecules also play important roles after development, though less is understood about their functions in the adult. The Semaphorin family of guidance cues, signaling through Plexin receptors, influences the development of both axons and dendrites in invertebrates. Semaphorin functions have been extensively explored in Drosophila melanogaster and some other Dipteran species, but little is known about their function in hemimetabolous insects. Here, we characterize sema1a and plexA in the cricket Gryllus bimaculatus. In fact, we found two distinct predicted Sema1a proteins in this species, Sema1a.1 and Sema1a.2, which shared only 48% identity at the amino acid level. We include a phylogenetic analysis that predicted that many other insect species, both holometabolous and hemimetabolous, express two Sema1a proteins as well. Finally, we used in situ hybridization to show that sema1a.1 and sema1a.2 expression patterns were spatially distinct in the embryo, and both roughly overlap with plexA. All three transcripts were also expressed in the adult brain, mainly in the mushroom bodies, though sema1a.2 was expressed most robustly. sema1a.2 was also expressed strongly in the adult thoracic ganglia while sema1a.1 was only weakly expressed and plexA was undetectable.
The Mérida Initiative and the Violence of Transnational Criminal Organizations in Mexico
Date: 2021-01-01
Creator: Brianna Madison Canning
Access: Open access
- Organized crime related violence in Mexico remains at unprecedented levels despite decades of effort and billions of dollars spent attempting to weaken Transnational Criminal Organizations (TCOs) through the Mérida Initiative (MI): a bilateral security partnership established in October 2007 between US President George W. Bush and Mexican President Felipe Calderón. The MI sought to combat TCOs (often called cartels), their drug trafficking operations, and their networks of corruption. However, since then TCOs have expanded their businesses beyond drug trafficking, and they have adopted violent practices that target civilians. Extortion, torture, murder, and human trafficking have become common as TCOs look to other illicit markets to make up for losses in drug profits, and to signal strength to their opponents. More specifically, the homicide rate in Mexico increased by more than 100% between 2007 and 2008, aligning with the creation of the initiative designed to have the opposite effect. However, case study research into the violence in Ciudad Juárez and Tijuana determined that the MI was not actually implemented until mid-2009 because of bureaucratic delays, meaning it did not impact the initial spike in homicides in Mexico in 2008. Instead, the violence starting in 2008 is a result of changing dynamics between and within TCOs, as they adapted to survive and maintain control of resources. By supporting the Mexican government’s drug war efforts over the next several years, the Mérida Initiative became one of many complex domestic and international factors that ultimately contributed to extreme levels of violence in Mexico.
Photochemistry of Cyano-Substituted 8-Amino-2-Naphthol This record is embargoed.
- Embargo End Date: 2026-05-20
Date: 2021-01-01
Creator: Jialin Xie
Access: Embargoed
Can Small Donations Have Big Consequences? Candidate Ideology, Small Donations, and Election Results in the 2016 and 2018 Congressional Cycles
Date: 2021-01-01
Creator: Michael Borecki
Access: Open access
- Small donors have provided an increased share of total campaign contributions in the 2016, 2018, and 2020 U.S. federal election cycles, including about $3 billion of the $14.4 billion raised in 2020. Campaign funding is still dominated by an influential set of large donors, but small donations may be the basis for an effective response to the disproportionate amount of “big money” in politics. This study investigates whether candidates who are more extreme perform better with small donors, and then examines the impact of small donations and overall funding on election results. These analyses were performed using linear sum-of-squares regression models. The results in Chapter 2 show that candidates who are more politically-extreme receive more of their funding from small donations, but perform worse in general elections when fundraising is equal. Chapter 3 shows that small donations do not have an impact on candidate performance in general elections more generally, but candidates who outraise their opponent also outperform relative to the district’s partisan lean. However, that effect disappears when looking only at elections decided by less than 10 percent of the vote. These results suggest that small donors are more likely to support candidates who are more politically polarized, but the effects of small donors on the makeup of Congress is marginal at best, at least as far as general election outcomes are concerned. The project concludes by considering reform proposals that seek to broaden the pool of Americans who donate small sums to political candidates.
How do long-term above-ground biomass dynamics vary between different forest stand types at Harvard Forest?
Date: 2023-01-01
Creator: Maya Y. Chandar-Kouba
Access: Open access
- Monitoring forest carbon storage is necessary in accurately modelling the global carbon cycle. In the Northeast, terrestrial forests represent a major carbon sink with above-ground biomass (AGB) accounting for 40% of stored forest carbon. Therefore, understanding how AGB varies spatiotemporally is essential in predicting future carbon storage. Repeated measurements in permanent, long-term plots provide an opportunity to examine how carbon stored in AGB is changing over time. I used 29 years of data from the Harvard Forest Environmental Monitoring Systems (HF EMS) Site to determine how stand composition, intrinsic factors, and extrinsic environmental factors influenced rates of carbon storage in AGB over time. Using a partition around medoids (PAM) clustering method, I separated the 34 ground plots at the EMS stand into their respective stand types. I found that each stand type at the HF EMS plots accumulates carbon at consistent rates throughout the study period, although rates of carbon accumulation between stands were significantly different. Red Pine stands experience a rapid decline in biomass in 2018 due to the introduction of the Southern Pine Beetle. Across all stand types, sporadic mortality events determine variations in yearly rates of carbon accumulation, although this has little significant influence on total AGB accumulation. Leaf area index (LAI) and foliar N contents have no effect on growth increments. Extrinsic environmental variables had mixed effects on growth and mortality, highlighting the complexities of predicting forest carbon storage under changing climate conditions.
Rhythmic behaviors: Understanding neuromodulation at the neuromuscular level
Date: 2023-01-01
Creator: Kenneth Garcia
Access: Open access
- Neuromodulation allows for the flexibility of neural circuit dynamics and the outputs they produce. Studies of the stomatogastric nervous system (STNS) have expanded our knowledge on the actions of neuromodulators, small molecules that most often activate G-protein coupled receptors and reconfigure circuit activity and composition. In these systems, modulation has been found to occur at every level, from sensory-motor coupling to neuromuscular transmission (Harris-Warrick and Marder 1991). Neuromodulators have complex effects on motor output; they can alter the firing of individual neurons while also modulating muscle properties, neuromuscular transmission, and sensory neuron response to muscle activity (Fort et al. 2004). We investigated this further by recording the motor output produced by the gastric mill rhythm of the lobster STNS under neuromodulator conditions. How is this neuromuscular system as a whole modulated to produce motor flexibility? We hypothesized that these neuromodulators act on individual receptors of component neurons of central pattern generator (CPG)-effector system themselves and at the periphery, coordinately altering muscle contraction by altering all levels of the crustacean neuromuscular system. Application of NRNFLRFamide, RPCH, oxotremorine, and proctolin to the gastric mill 4 (gm4) muscles of the Cancer crab showed that neuromodulators that have been found to have variable, yet significant effects on the activity of the neurons of the STNS directly alter the activity of the gm4 muscles as well, suggesting that coordination of peripheral actions and direct neuronal modulation regulates patterned motor output.
Neptune City This record is embargoed.
- Embargo End Date: 2026-05-18
Date: 2023-01-01
Creator: Lily Randall
Access: Embargoed