Showing 1201 - 1250 of 5831 Items

Date: 2011-06-01

Creator: David K. Hecht

Access: Open access

This article uses the voluminous public discourse around Rachel Carson and her controversial bestseller Silent Spring to explore Americans' views on science and scientists. Carson provides a particularly interesting case study because of intense and public debates over whether she was a scientist at all, and therefore whether her book should be granted legitimacy as science. Her career defied easy classification, as she acted variously as writer, activist, and environmentalist in addition to scientist. Defending her work as legitimate science, which many though not all commentators did, therefore became an act of defining what both science and scientists could and should be. This article traces the variety of nonscientific images and narratives readers and writers assigned to Carson, such as "reluctant crusader" and "scientist-poet." It argues that nonscientific attributes were central to legitimating her as both admirable person and admirable scientist. It explores how debates over Silent Spring can be usefully read as debates over the desirability of putatively nonscientific attributes in the professional work of a scientist. And it examines the nature of Carson's very democratized image for changing notions of science and scientists in 1960s United States politics and culture. © 2011 by the Regents of the University of California. All rights reserved.

Date: 2007-12-01

Creator: Michael M. Franz, Travis N. Ridout

Access: Open access

Well over $1 billion was spent on televised political advertising in the U.S. in 2004. Given the ubiquity of the 30 second spot, one might presume that ads must affect viewers' vote choices. Somewhat surprisingly, though, scholars have yet to make much progress in confirming this claim. In this paper, we leverage a comprehensive dataset that tracks political ads in the nation's top media markets and a survey of presidential and U.S. Senate voters in 2004. We ask whether exposure to presidential and Senate advertising influences voters' evaluations of candidates and the choices that they make at the ballot box. In the end, we find considerable evidence that advertising persuades-and that its impact varies depending on the characteristics of the viewer. © 2007 Springer Science+Business Media, LLC.

Date: 2004-09-01

Creator: Travis N. Ridout, Dhavan V. Shah, Kenneth M. Goldstein, Michael M. Franz

Access: Open access

Scholars employ various methods to measure exposure to televised political advertising but often arrive at conflicting conclusions about its impact on the thoughts and actions of citizens. We attempt to clarify one of these debates while validating a parsimonious measure of political advertising exposure. To do so, we assess the predictive power of six different measurement approaches - from the simple to the complex - on learning about political candidates. Two datasets are used in this inquiry: (1) geo-coded political advertising time-buy data, and (2) a national panel study concerning patterns of media consumption and levels of political knowledge. We conclude that many traditional methods of assessing exposure are flawed. Fortunately, there is a relatively simple measure that predicts knowledge about information featured in ads. This measure involves combining a tally of the volume of advertisements aired in a market with a small number of survey questions about the television viewing habits of geo-coded respondents.

Date: 2013-03-01

Creator: William R. Jackman, Shelby H. Davies, David B. Lyons, Caitlin K. Stauder, Benjamin R., Denton-Schneider, Andrea Jowdry, Sharon R. Aigler, Scott A. Vogel, David W. Stock

Access: Open access

Teeth with two or more cusps have arisen independently from an ancestral unicuspid condition in a variety of vertebrate lineages, including sharks, teleost fishes, amphibians, lizards, and mammals. One potential explanation for the repeated origins of multicuspid teeth is the existence of multiple adaptive pathways leading to them, as suggested by their different uses in these lineages. Another is that the addition of cusps required only minor changes in genetic pathways regulating tooth development. Here we provide support for the latter hypothesis by demonstrating that manipulation of the levels of Fibroblast growth factor (Fgf) or Bone morphogenetic protein (Bmp) signaling produces bicuspid teeth in the zebrafish (Danio rerio), a species lacking multicuspid teeth in its ancestry. The generality of these results for teleosts is suggested by the conversion of unicuspid pharyngeal teeth into bicuspid teeth by similar manipulations of the Mexican Tetra (Astyanax mexicanus). That these manipulations also produced supernumerary teeth in both species supports previous suggestions of similarities in the molecular control of tooth and cusp number. We conclude that despite their apparent complexity, the evolutionary origin of multicuspid teeth is positively constrained, likely requiring only slight modifications of a pre-existing mechanism for patterning the number and spacing of individual teeth. © 2013 Wiley Periodicals, Inc.

Date: 2013-01-01

Creator: Collin S. Roesler, Andrew H. Barnard

Access: Open access

The pigment absorption peak in the red waveband observed in phytoplankton and particulate absorption spectra is primarily associated with chlorophyll-a and exhibits much lower pigment packaging compared to the blue peak. The minor contributions to the signature by accessory pigments can be largely removed by computing the line height absorption at 676 nm above a linear background between approximately 650 nm and 715 nm. The line height determination is also effective in removing the contributions to total or particulate absorption by colored dissolved organic matter and non-algal particles, and is relatively independent of the effects of biofouling. The line height absorption is shown to be significantly related to the extracted chlorophyll concentration over a large range of natural optical regimes and diverse phytoplankton cultures. Unlike the in situ fluorometric method for estimating chlorophyll, the absorption line height is not sensitive to incident irradiance, in particular non-photochemical quenching. The combination of the two methods provides a combination of robust phytoplankton biomass estimates, pigment based taxonomic information and a means to estimate the photosynthetic parameter, , the irradiance at which photosynthesis transitions from light limitation to light saturation. © 2013 The Authors. E K

Date: 2020-01-01

Creator: Mac Brower

Access: Open access

This is a poem I composed while stay-at-home orders were being issued nationwide. I wrote it shortly after leaving my home in Washington, DC to live with my parents in North Carolina. The author is an alumnus from the class of 2018.

Date: 2019-11-09

Creator: Saira Toppin

Access: Open access

Saira Toppin ’09 discusses her upbringing in Brooklyn, New York, and how that made for a challenging transition to Brunswick, Maine. She shares how a few juniors mentored her during her first year, which helped Toppin adjust to Bowdoin. She credits this mentorship with encouraging her to carve out space for herself on campus as an Afro-Latina and also to look out for others once she became an upperclassman. She shares stories from her time on the boards of both the African American Society and the Latin American Students Organization (LASO). As co-president of LASO during her junior and senior year, Toppin helped the organization have an impact on campus by organizing Latin American Heritage Month event Fall. She made sure to mentor underclassman so that they could run the club in her absence and considers LASO to be her legacy.

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. The author is a member of Bowdoin's faculty.

Date: 2004-01-01

Creator: Paul Freedman, Michael Franz, Kenneth Goldstein

Access: Open access

Concern about the state of American democracy is a staple of political science and popular commentary. Critics warn that levels of citizen participation and political knowledge are disturbingly low and that seemingly ubiquitous political advertising is contributing to the problem. We argue that political advertising is rife with both informational and emotional content and actually contributes to a more informed, more engaged, and more participatory citizenry. With detailed advertising data from the 2000 election, we show that exposure to campaign advertising produces citizens who are more interested in the election, have more to say about the candidates, are more familiar with who is running, and ultimately are more likely to vote. Importantly, these effects are concentrated among those citizens who need it most: those with the lowest pre-existing levels of political information.

Date: 2009-06-01

Creator: Yoshiyuki Yamamoto, Mardi S. Byerly, William R. Jackman, William R. Jeffery

Access: Open access

This study addresses the role of sonic hedgehog (shh) in increasing oral-pharyngeal constructive traits (jaws and taste buds) at the expense of eyes in the blind cavefish Astyanax mexicanus. In cavefish embryos, eye primordia degenerate under the influence of hyperactive Shh signaling. In concert, cavefish show amplified jaw size and taste bud numbers as part of a change in feeding behavior. To determine whether pleiotropic effects of hyperactive Shh signaling link these regressive and constructive traits, shh expression was compared during late development of the surface-dwelling (surface fish) and cave-dwelling (cavefish) forms of Astyanax. After an initial expansion along the midline of early embryos, shh was elevated in the oral-pharyngeal region in cavefish and later was confined to taste buds. The results of shh inhibition and overexpression experiments indicate that Shh signaling has an important role in oral and taste bud development. Conditional overexpression of an injected shh transgene at specific times in development showed that taste bud amplification and eye degeneration are sensitive to shh overexpression during the same early developmental period, although taste buds are not formed until much later. Genetic crosses between cavefish and surface fish revealed an inverse relationship between eye size and jaw size/taste bud number, supporting a link between oral-pharyngeal constructive traits and eye degeneration. The results suggest that hyperactive Shh signaling increases oral and taste bud amplification in cavefish at the expense of eyes. Therefore, selection for constructive oral-pharyngeal traits may be responsible for eye loss during cavefish evolution via pleiotropic function of the Shh signaling pathway. © 2009 Elsevier Inc. All rights reserved.

Date: 1880-01-01

Access: Open access

Date: 2013-06-11

Creator: Kent Kovacs, Stephen Polasky, Erik Nelson, Bonnie L. Keeler, Derric, Pennington, Andrew J. Plantinga, Steven J. Taff

Access: Open access

We evaluate the return on investment (ROI) from public land conservation in the state of Minnesota, USA. We use a spatially-explicit modeling tool, the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST), to estimate how changes in land use and land cover (LULC), including public land acquisitions for conservation, influence the joint provision and value of multiple ecosystem services. We calculate the ROI of a public conservation acquisition as the ratio of the present value of ecosystem services generated by the conservation to the cost of the conservation. For the land scenarios analyzed, carbon sequestration services generated the greatest benefits followed by water quality improvements and recreation opportunities. We found ROI values ranged from 0.21 to 5.28 depending on assumptions about future land use change, service values, and discount rate. Our study suggests conservation is a good investment as long as investments are targeted to areas with low land costs and high service values. © 2013 Kovacs et al.

Date: 2019-05-01

Creator: Connor Rockett

Access: Open access

Focusing on sub-Saharan Africa, this study tests the hypothesis that state intervention in agrarian economies causes peasant movements to engage in broad-based contention, on regional and national levels. The study traces the connections between government land and agricultural institutions and the characteristics of rural movements that make claims on them. Case studies of regions of Tanzania, Senegal, Côte d’Ivoire, and Ethiopia show the ways in which rural movements are constructed in response to the political and social environments in which they arise. That is, the comparisons demonstrate that the character of political authority and social organization are important determinants of the form taken by peasant movements.

Date: 1997-01-01

Access: Open access

Date: 2011-12-01

Creator: Guido Grosse, Jennifer Harden, Merritt Turetsky, A. David McGuire, Philip, Camill, Charles Tarnocai, Steve Frolking, Edward A.G. Schuur, Torre Jorgenson, Sergei Marchenko, Vladimir Romanovsky, Kimberly P. Wickland, Nancy French, Mark Waldrop, Laura Bourgeau-Chavez, Robert G. Striegl

Access: Open access

This synthesis addresses the vulnerability of the North American high-latitude soil organic carbon (SOC) pool to climate change. Disturbances caused by climate warming in arctic, subarctic, and boreal environments can result in significant redistribution of C among major reservoirs with potential global impacts. We divide the current northern high-latitude SOC pools into (1) near-surface soils where SOC is affected by seasonal freeze-thaw processes and changes in moisture status, and (2) deeper permafrost and peatland strata down to several tens of meters depth where SOC is usually not affected by short-term changes. We address key factors (permafrost, vegetation, hydrology, paleoenvironmental history) and processes (C input, storage, decomposition, and output) responsible for the formation of the large high-latitude SOC pool in North America and highlight how climate-related disturbances could alter this pool's character and size. Press disturbances of relatively slow but persistent nature such as top-down thawing of permafrost, and changes in hydrology, microbiological communities, pedological processes, and vegetation types, as well as pulse disturbances of relatively rapid and local nature such as wildfires and thermokarst, could substantially impact SOC stocks. Ongoing climate warming in the North American high-latitude region could result in crossing environmental thresholds, thereby accelerating press disturbances and increasingly triggering pulse disturbances and eventually affecting the C source/sink net character of northern high-latitude soils. Finally, we assess postdisturbance feedbacks, models, and predictions for the northern high-latitude SOC pool, and discuss data and research gaps to be addressed by future research. Copyright 2011 by the American Geophysical Union.

Date: 1891-01-01

Access: Open access

Date: 2001-01-01

Creator: A. S. Johnson

Access: Open access

Dense algal canopies, which are common in the lower intertidal and shallow subtidal along rocky coastlines, can alter flow-induced forces in their vicinity. Alteration of flow-induced forces on algal thalli may ameliorate risk of dislodgement and will affect important physiological processes, such as rates of photosynthesis. This study found that the force experienced by a thallus of the red alga Chondrus crispus (Stackhouse) at a given flow speed within a flow tank depended upon (1) the density of the canopy surrounding the thallus, (2) the position of the thallus within the canopy, and (3) the length of the stipe of the thallus relative to the height of the canopy. At all flow speeds, a solitary thallus experienced higher forces than a thallus with neighbors. A greater than 65% reduction in force occurred when the thallus drafted in the region of slower velocities that occurs in the wake region of even a single upstream neighbor, similar to the way racing bicyclists draft one behind the other. Mechanical interactions between thalli were important to forces experienced within canopies. A thallus on the upstream edge of a canopy experienced 6% less force than it did when solitary, because the canopy physically supported it. A thallus in the middle of a canopy experienced up to 83% less force than a solitary thallus, and forces decreased with increasing canopy density. Thus, a bushy morphology that increases drag on a solitary thallus may function to decrease forces experienced by that thallus when it is surrounded by a canopy, because that morphology increases physical support provided by neighbors.

Date: 1977-01-01

Creator: William H. Barker

Access: Open access

This paper is motivated by the observation that Noether’s theorem for quadratic differentials fails for hyperelliptic Riemann surfaces. In this paper we provide an appropriate substitute for Noether’s theorem which is valid for plane domains with hyperelliptic double. Our result is somewhat more explicit than Noether’s, and, in contrast with the case of nonhyperelliptic surfaces, it provides a basis for the (even) quadratic differentials which holds globally for all domains with hyperelliptic double. An important fact which plays a significant role in these considerations is that no two normal differentials of the first kind can have a common zero on a domain with hyperelliptic double. © 1977 Pacific Journal of Mathematics. All rights reserved.

Date: 1930-01-01

Access: Open access

Date: 2015-09-01

Creator: Kate R. Farnham, Danielle H. Dube

Access: Open access

Here we present the development of a 13 week project-oriented biochemistry laboratory designed to introduce students to foundational biochemical techniques and then enable students to perform original research projects once they have mastered these techniques. In particular, we describe a semester-long laboratory that focuses on a biomedically relevant enzyme-Helicobacter pylori (Hp) urease-the activity of which is absolutely required for the gastric pathogen Hp to colonize the human stomach. Over the course of the semester, students undertake a biochemical purification of Hp urease, assess the success of their purification, and investigate the activity of their purified enzyme. In the final weeks of the semester, students design and implement their own experiments to study Hp urease. This laboratory provides students with an understanding of the importance of biochemistry in human health while empowering them to engage in an active area of research.

Date: 2014-08-01

Creator: Christine Walder

Access: Open access

Ascophyllum nodosum, the dominant intertidal macroalgal species from Maine to Canada, plays an important role in buffering intertidal stresses and supports a variety of organisms such as molluscs, crustaceans, fish and birds. A. nodosum is harvested commercially for use in fertilizers and food additives, and landings have been increasing in Maine in recent years. The ecological impact of removing the rockweed canopy was assessed in a comparative study between Kent Island in the Bay of Fundy, New Brunswick, Canada and Orr’s Island in Harpswell, ME, USA. Paired 2x2m control and experimental plots were set up, harvested, and surveyed monthly during the summers of 2013 (15 plots on Kent Island) and 2014 (an additional 9 plots on Kent Island and 20 on Orr’s Island) in a BACI design (Before, After, Control, Impact). One square meter surveys were conducted to determine algal species richness, algal percent secondary cover, and megafauna abundance and diversity. Surveys were designed to assess the overall diversity within plots and count/identify all present species. Initial t-tests of Kent Island data show a short-term reduction in amphipods and isopods, Carcinus maenas (green crabs), and Littorina obtusata (smooth periwinkles) and a short-term increase in Littorina littorea (common periwinkles) (p Final Report of research funded by the Rusack Coastal Studies Fellowship (2014).

Date: 2019-05-01

Creator: Matthew Maguire

Access: Access restricted to the Bowdoin Community

Date: 2001-06-09

Creator: D. J. Sutton, Z. J. Kabala, A. Francisco, D. Vasudevan

Access: Open access

We conducted chemical characterization, batch, column, and modeling studies to elucidate the sorption and transport of rhodamine WT (RWT) in the subsurface. The sand-pack material from the Lizzie field site near Greenville, North Carolina, served as our porous media. Our study confirms earlier results that RWT consists of two isomers with different sorption properties. It also shows that the two isomers have distinct emission spectra and are equally distributed in the RWT solution. The presence of the two isomers with different sorption properties and distinct emission spectra introduces an error in measuring the RWT concentration with fluorometers during porous media tracer studies. The two isomers become chromatographically separated during transport and thus arrive in a different concentration ratio than that of the RWT solutions used for fluorometer calibration and test injection. We found that this groundwater tracer chromatographic error could be as high as 7.8%. We fit six different reactive-solute transport models of varying complexity to our four column experiments. A two-solute, two-site sorption transport model that accounts for nonequilibrium sorption accurately describes the breakthrough curves of the shorter-timescale column experiments. However, possibly due to the groundwater tracer chromatographic error we discovered, this model, or a similar one that accounts for a Freundlich isotherm for one of the solutes, fails to describe the RWT transport in the longer-timescale column experiments. The presence of the two RWT isomers may complicate the interpretation of field tracer tests because a shoulder, or any two peaks in a breakthrough curve, could result from either aquifer heterogeneity or the different arrival times of the two isomers. In cases where isomer 2 sorbs to such an extent that its breakthrough is not recorded during a test, only isomer 1 is measured, and therefore only 50% of the injected mass is recorded. Isomer 1 of RWT can be accurately modeled with a one-solute, two-site, nonequilibrium sorption model. This conclusion and the results from our batch studies suggest that RWT isomer 1 is an effective groundwater tracer but that the presence of isomer 2 hampers its effectiveness.

Date: 2018-05-11

Creator: H. Kim, E. Kim, C. Chong, P. G. Kevrekidis, J., Yang

Access: Open access

We report an experimental and numerical demonstration of dispersive rarefaction shocks (DRS) in a 3D-printed soft chain of hollow elliptical cylinders. We find that, in contrast to conventional nonlinear waves, these DRS have their lower amplitude components travel faster, while the higher amplitude ones propagate slower. This results in the backward-tilted shape of the front of the wave (the rarefaction segment) and the breakage of wave tails into a modulated waveform (the dispersive shock segment). Examining the DRS under various impact conditions, we find the counterintuitive feature that the higher striker velocity causes the slower propagation of the DRS. These unique features can be useful for mitigating impact controllably and efficiently without relying on material damping or plasticity effects.

Date: 2014-08-01

Creator: Jenna Watling

Access: Open access

Since early July, I’ve been working on three projects. I’ve been studying parrotfish speciation, dissecting green crabs, and collecting samples of muscle tissue from blue mussels. My primary occupation is the study of parrotfish speciation with Dr. Carlon. He has found evidence of speciation through hybridization, which is has not been commonly observed. During the 2013-2014 academic year, he and I extracted DNA from fin or scale samples from Pacific parrotfish. Throughout the year and during this summer, we have been amplifying specific genes—nuclear and mitochondrial—using a polymerase chain reaction, confirming the amplification via gel electrophoresis, and preparing the samples for Sanger sequencing, which is done by the Nevada Genomics Center. Once we receive the sequencing results electronically, I use the program Geneious to check the quality of the individual sequences and resolve ambiguous calls (e.g., whether a specific base pair is an arginine or a cytosine) and align the sequences so we can compare them base pair by base pair. By examining both nuclear and mitochondrial genes, which evolve at different rates, we can hypothesize about the way in which different species arise. Green crab (Carcinus maenas) dissection is an early step in Aidan Short’s analysis of their diet. I assist in collecting tissue samples. We collect muscle tissue from the crabs’ claws. These samples will allow Aiden to differentiate between the crabs’ food and the crabs themselves. Then their carapaces are cut open and their entire stomachs are collected. In the near future, Aidan will use next-generation sequencing to identify any species present in the crab stomachs and quantify the abundance of these species’ DNA. Sequencing the crabs’ stomach contents is more precise and more complete than the older method of hard part analysis. The green crabs’ diet is of interest because green crabs are an invasive species and have been implicated in loss of sea grass beds and decreasing soft shell clam populations. Collection of tissue from blue mussels (Mytilus edulis) and bay mussels (M. trossulus) is a preliminary step for Dr. Sarah Kingston’s investigation of the genetic basis of variation in shell calcification rate under environmental conditions possible due to ocean acidification. She collects mussels from various sites along the Maine coast, marks each with a color and number, and records their buoyant weight. The buoyant weight allows Dr. Kingston to determine the mass of the shells without having to kill the mussels. In the first round of experiments, Dr. Kingston determined which of three experimental schemes (involving the manipulation of food levels, temperature, and pH) resulted in the greatest variation of shell calcification after two weeks. The harshest scheme—no food, high temperature, and low pH—resulted in the greatest variation, and this scheme will be used in the experiment going forward. After the experimental period, the mussels are re-weighed and tissue samples are collected. I assist in tissue sample collection; we cut open the mussels and remove the foot and the adductor muscle. In the next round of experiments, I will further assist by participating in mussel collection, monitoring tank conditions during the experimental period, and labeling and weighing the specimens. The DNA libraries obtained from the tissue samples will be sent away for next generation sequencing, and Dr. Kingston will begin looking for genetic variation associated with calcification rates. Final Report, summer 2014 student-faculty research.

Date: 1991-01-01

Access: Open access

Date: 1961-01-01

Access: Open access

Catalogue of an exhibition held Jan. 29-Feb. 28, 1961 at the Bowdoin College Museum of Art, Brunswick, Maine.

Date: 2019-01-01

Creator: Caroline Rice

Access: Open access

Previous studies show that active exploration of an environment contributes to spatial learning more than passive visual exposure (Chrastil & Warren, 2013; Chrastil & Warren, 2015). Active navigation and cognitive decision-making in a novel environment leads to increased spatial knowledge and memory of location compared to a passive exploration that removes the decision-making component. There is evidence of theta oscillations present in electroencephalography (EEG) recordings from the hippocampus and pre-frontal cortex (PFC). These low-frequency waves could reflect spatial navigation and memory performance, suggested by their involvement in communication between the formerly named brain regions. Through communication with the hippocampus, theta oscillations could be involved in the integration of new spatial information into memory. While undergoing EEG, subjects in this study either actively or passively explored a virtual maze, identified as the “Free” or “Guided” groups, respectively. After exploring, subjects’ spatial memory of the maze was tested through a task that required navigation from a starting object to a target object. Behavioral data show increased spatial memory for the Free group, indicated by significantly greater navigation to the correct target object in the memory task. EEG results indicate significantly greater theta oscillations in frontal regions for the Free group during the exploration phase. These results support those found in previous studies and could indicate a correlation between frontal theta oscillations during learning of novel environments and spatial memory.

Date: 2014-12-16

Creator: Michael F. Palopoli, Samuel Minot, Dorothy Pei, Alicia Satterly, Julie, Endrizzi

Access: Open access

Background: Follicle mites of the genus Demodex are found on a wide diversity of mammals, including humans. surprisingly little is known, however, about the evolution of this association. Additional sequence information promises to facilitate studies of Demodex variation within and between host species. Here we report the complete mitochondrial genome sequences of two species of Demodex known to live on humans-Demodex brevis and D. folliculorum-which are the first such genomes available for any member of the genus. We analyzed these sequences to gain insight into the evolution of mitochondrial genomes within the Acariformes. We also used relaxed molecular clock analyses, based on alignments of mitochondrial proteins, to estimate the time of divergence between these two species. Results: Both Demodex genomes shared a novel gene order that differs substantially from the ancestral chelicerate pattern, with transfer RNA (tRNA) genes apparently having moved much more often than other genes. Mitochondrial tRNA genes of both species were unusually short, with most of them unable to encode tRNAs that could fold into the canonical cloverleaf structure. indeed, several examples lacked both D- and T-arms. Finally, the high level of sequence divergence observed between these species suggests that these two lineages last shared a common ancestor no more recently than about 87 mya. Conclusions: Among Acariformes, rearrangements involving tRNA genes tend to occur much more often than those involving other genes. The truncated tRNA genes observed in both Demodex species would seem to require the evolution of extensive tRNA editing capabilities and/or coevolved interacting factors. The molecular machinery necessary for these unusual tRNAs to function might provide an avenue for developing treatments of skin disorders caused by Demodex. The deep divergence time estimated between these two species sets a lower bound on the time that Demodex have been coevolving with their mammalian hosts, and supports the hypothesis that there was an early split within the genus Demodex into species that dwell in different skin microhabitats.

Date: 2014-08-01

Creator: Lloyd Anderson

Access: Open access

Increased atmospheric CO2 due to the combustion of fossil fuels and subsequent oceanic uptake has led to a phenomenon known as ocean acidification: CO2 gas dissolved in the ocean lowers surface ocean pH and acidifies ocean waters, a process which has raised global concern. The purpose of my research was to investigate why a particular clam flat in Phippsburg, ME is not as productive as it used to be. This clam flat, located on “The Branch” in Phippsburg adjacent to Head Beach, has decreased to approximately a sixth of its former productivity in just over a decade. A possible explanation for this drop in clam bed productivity is acidification. I worked in a partnership with Bailey Moritz ’16, with the goal to measure indicators of ocean acidification in the clam flat and see if there was a difference in those indicators between productive and unproductive areas of the flat. Bailey’s focus was alkalinity, a quantification of the buffering capacity of seawater, where my specific research focus was on the effective collection of pH measurements. We were ultimately able to combine our alkalinity and pH measurements to calculate saturation state, an indicator of the susceptibility of clam shells to dissolution. I measured pH, a direct indicator of water acidity, from the top centimeter of the mudflat, the region where clam spat (juvenile clams) are seeded. The first few weeks of my fellowship time I spent researching the most accurate and precise way to measure pH in the field, and ultimately decided to measure pH on site using glass electrode probes. Sites 1 and 2 were located in a productive region of the flat, sites 4 and 5 were located in an unproductive region, and site 3 was located on the boundary between the two zones. Average pH values within the clam flat ranged from 6.9-7.5, and there was no significant difference in pH between productive and unproductive sites across the flat (Figure 1). The wide variations in pH across this clam flat could potentially be attributed to daily shifts in temperature, freshwater input, and biological productivity in the sediments. Low average pH values seen across all sites contribute to a low saturation state across the flat: our average calculated saturation state was 0.47, lower than similar data measured by Green et al. on a clam flat in South Portland in 2013, where average saturation state was 0.9. Our data indicate that the soft-shell clams at the productive sites in this particular Phippsburg clam flat are managing to survive in undersaturated (saturation state < 1) conditions. Since saturation state was low across both productive and unproductive sites, ocean acidification seems not to be the cause for the clams’ decline. However, other factors such as dissolved oxygen or sediment type may have combined with low saturation states to create a difference in productivity across the flat. In further research I would be interested to see how average pH at these same sites varies over a year-long period, which would give a better representation of the environment that the soft-shell clams are exposed to through yearly cycles. Final Report of research funded by the Rusack Coastal Studies Fellowship.

Date: 1885-01-01

Access: Open access

Date: 2014-08-01

Creator: Nora Hefner

Access: Open access

Gulf of Maine cod fisheries, once essential to Maine’s economy and culture, are currently in a state of collapse. Following a long decline throughout the 1800s and two collapses in the 1900s – one in the middle of the century and one in the 1990s, cod populations along the coast exist now as small fractions of their former bounty. Though the connection was largely forgotten in the twentieth century, fishermen in the nineteenth century attributed the decline of the cod fishery to the loss of alewives, an anadromous river herring upon which cod prey. Alewives have been cut off from their spawning and nursery habitat along much of the Gulf of Maine due to the damming of rivers that empty into the Gulf. My research is a part of an ongoing study that aims to establish the historical relationship between cod and other gadoid groundfish fisheries, their ecosystems, and anadromous alewives using spatial data from geographic information systems (GIS). GIS maps were created with the positions of 466 historical Gulf of Maine cod fishing grounds, identified using a database developed by fisheries scientist Ted Ames (whose work is largely responsible for fisheries scientists’ renewed interest in the groundfish-alewife connection). The spatial database generated from these data will be analyzed using a logistical regression to identify characteristics of fishing grounds that define them as fishing grounds, as well as characteristics that determine the relative quality of individual fishing grounds. The Ames database contains data in two main categories: biophysical (ecosystem characteristics) and socioeconomic (infrastructure). The focus of my research was on generating two specific data sets from historical literature, government reports, and experts in the field, and on mapping that data using GIS software (see Figure 1). The first was a list of rivers that supported annual alewife runs before the mid-twentieth century cod groundfish fishery collapse. Using GIS software, I mapped the locations at which these rivers enter the ocean, creating spatial data that show the point at which cod in the Gulf and alewives in the rivers would meet. The second data set was a list of ports and harbors that supported the groundfish industry, also before the mid-twentieth century collapse. These locations were mapped as the areas from which fishing boats would set out in pursuit of groundfish, again creating a set of spatial data points. Both of these data sets were added to the existing spatial database. My data and Ames’ data will be used to calculate distances between individual groundfish fishing grounds and historic alewife runs and between fishing grounds and ports and harbors. Statistical analyses will determine both whether those two factors have any significant relationship with fishing ground quality and the nature of their effects, if any. Ultimately, the results of these analyses will contribute to an increasingly detailed picture of the Gulf of Maine as it existed – physically, ecologically, and economically – when it still supported astoundingly large populations of cod and other groundfish. With a better idea of what the system looked like when it worked properly, we can make a more informed and focused attempt to rebuild it. This research provided me with opportunities to develop practical skills like use of GIS software, contacting and collaborating with scientists, researchers, and government agencies in my field, and data management. I also gained a greater understanding of and appreciation for the complexity and challenge of trying to bring research from the science level to management policy and action. Final Report of research funded by the Cooke Environmental Research Fellowship

Date: 2018-11-01

Creator: Sasha J. Kramer, Collin S. Roesler, Heidi M. Sosik

Access: Open access

Diatoms dominate global silica production and export production in the ocean; they form the base of productive food webs and fisheries. Thus, a remote sensing algorithm to identify diatoms has great potential to describe ecological and biogeochemical trends and fluctuations in the surface ocean. Despite the importance of detecting diatoms from remote sensing and the demand for reliable methods of diatom identification, there has not been a systematic evaluation of algorithms that are being applied to this end. The efficacy of these models remains difficult to constrain in part due to limited datasets for validation. In this study, we test a bio-optical algorithm developed by Sathyendranath et al. (2004) to identify diatom dominance from the relationship between ratios of remote sensing reflectance and chlorophyll concentration. We evaluate and refine the original model with data collected at the Martha's Vineyard Coastal Observatory (MVCO), a near-shore location on the New England shelf. We then validated the refined model with data collected in Harpswell Sound, Maine, a site with greater optical complexity than MVCO. At both sites, despite relatively large changes in diatom fraction (0.8–82% of chlorophyll concentration), the magnitude of variability in optical properties due to the dominance or non-dominance of diatoms is less than the variability induced by other absorbing and scattering constituents of the water. While the original model performance was improved through successive re-parameterizations and re-formulations of the absorption and backscattering coefficients, we show that even a model originally parameterized for the Northwest Atlantic and re-parameterized for sites such as MVCO and Harpswell Sound performs poorly in discriminating diatom-dominance from optical properties.

Date: 2015-05-22

Creator: Michael F. Palopoli, Colin Peden, Caitlin Woo, Ken Akiha, Megan, Ary, Lori Cruze, Jennifer L. Anderson, Patrick C. Phillips

Access: Open access

Background: Although males and females need one another in order to reproduce, they often have different reproductive interests, which can lead to conflict between the sexes. The intensity and frequency of male-male competition for fertilization opportunities is thought to be an important contributor to this conflict. The nematode genus Caenorhabditis provides an opportunity to test this hypothesis because the frequency of males varies widely among species with different mating systems. Results: We find evidence that there is strong inter- and intra-sexual conflict within C. remanei, a dioecious species composed of equal frequencies of males and females. In particular, some C. remanei males greatly reduce female lifespan following mating, and their sperm have a strong competitive advantage over the sperm of other males. In contrast, our results suggest that both types of conflict have been greatly reduced within C. elegans, which is an androdioecious species that is composed of self-fertilizing hermaphrodites and rare males. Using experimental evolution in mutant C. elegans populations in which sperm production is blocked in hermaphrodites (effectively converting them to females), we find that the consequences of sexual conflict observed within C. remanei evolve rapidly within C. elegans populations experiencing high levels of male-male competition. Conclusions: Together, these complementary data sets support the hypothesis that the intensity of intersexual conflict varies with the intensity of competition among males, and that male-induced collateral damage to mates can evolve very rapidly within populations.

Date: 2010-06-18

Creator: M. Aydin, S. A. Montzka, M. O. Battle, M. B. Williams, W. J., De Bruyn, J. H. Butler, K. R. Verhulst, C. Tatum, B. K. Gun, D. A. Plotkin, B. D. Hall, E. S. Saltzman

Access: Open access

In this study, we report measurements of CFC-12 (CCl2F2) in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for the presence of modern air entrapped in the shallow ice core samples that likely contained open pores at the time of collection. We propose that this is due to closure of the open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our results reveal that open porosity can exist below the maximum depth at which firn air samples can be collected, particularly at sites with lower accumulation rates. CFC-12 measurements demonstrate that post-drilling closure of open pores can lead to a change in the composition of bubble air in shallow ice cores through purely physical processes. The results have implications for investigations involving trace gas composition of bubbles in shallow ice cores collected near the firn-ice transition. © Author(s) 2010.

Date: 2020-02-01

Creator: Daniel F. Stone

Access: Open access

I present a model of affective polarization—growth in hostility over time between two parties—via quasi-Bayesian inference. In the model, two agents repeatedly choose actions. Each choice is based on a balance of concerns for private interests and the social good. More weight is put on private interests when an agent's character is intrinsically more self-serving and when the other agent is believed to be more self-serving. Each agent Bayesian updates about the other's character, and dislikes the other more when she is perceived as more self-serving. I characterize the effects on growth in dislike of three biases: a prior bias against the other agent's character, the false consensus bias, and limited strategic thinking. Prior bias against the other's character remains constant or declines over time, and actions do not diverge. The other two biases cause actions to become more extreme over time and repeatedly be “worse” than expected, causing mutual growth in dislike, that is, affective polarization. The magnitude of dislike can become arbitrarily large—even when both players are arbitrarily “good” (unselfish). The results imply that seemingly irrelevant cognitive biases can be an important cause of the devolution of relationships, in politics and beyond, and that subtlety and unawareness of bias can be key factors driving the degree of polarization.

Date: 2008-07-01

Creator: Samuel P. Putnam, Mary K. Rothbart, Maria A. Gartstein

Access: Open access

Longitudinal continuity was investigated for fine-grained and factor-level aspects of temperament measured with the Infant Behaviour Questionnaire-Revised (IBQ-R), Early Childhood Behaviour Questionnaire (ECBQ), and Children's Behaviour Questionnaire (CBQ). Considerable homotypic continuity was found. Convergent and discriminant validity of the measures was supported, as all fine-grained dimensions exhibited stability across adjacent measurement periods, and all scales found on both the ECBQ and CBQ were most highly correlated with their equivalent scales. At the factor level, Surgency and Negative Affect factors were stable across all time points, and Effortful Control/Regulatory Capacity was stable across adjacent time periods. High-Intensity Pleasure, Activity Level, and Impulsivity contributed strongly to continuity of Surgency, and Sadness, Frustration, and Falling Reactivity played strong roles in the continuity of Negative Affect. Heterotypic continuity was also found. High levels of Infant Surgency predicted high toddler Effortful Control, whereas high toddler Surgency predicted low Effortful Control in preschoolers. Infant Surgency dimensions especially predicted Toddler Attention Shifting and Low-Intensity Pleasure, and toddler Activity Level was most closely associated with later deficits in Effortful Control. Inverse relations were also obtained between Negative Affect and Effortful Control, with substantial negative connections between toddler Negative Affect and preschool Attention Focusing and Inhibitory Control. Copyright © 2008 John Wiley & Sons, Ltd.

Date: 2014-11-04

Creator: F. Li, C. Chong, J. Yang, P. G. Kevrekidis, C., Daraio

Access: Open access

We present a dynamically tunable mechanism of wave transmission in one-dimensional helicoidal phononic crystals in a shape similar to DNA structures. These helicoidal architectures allow slanted nonlinear contact among cylindrical constituents, and the relative torsional movements can dynamically tune the contact stiffness between neighboring cylinders. This results in cross-talking between in-plane torsional and out-of-plane longitudinal waves. We numerically demonstrate their versatile wave mixing and controllable dispersion behavior in both wavenumber and frequency domains. Based on this principle, a suggestion toward an acoustic configuration bearing parallels to a transistor is further proposed, in which longitudinal waves can be switched on and off through torsional waves.

Date: 2014-08-01

Creator: Xuan Qu

Access: Open access

Central pattern generators are networks of neurons that produce rhythmic and repetitiveoutputs. These outputs control behaviors such as walking, breathing and digestion. In the Americanlobster, central pattern generators control the behavior of muscles in its foregut, which allows thedigestion of a variety of food types. The stomatogastric ganglion (STG) is a bundle of about thirtyneurons in the foregut of American lobsters. It has been studied extensively since each one of theneurons in it is both identifiable and produces simple patterned outputs. The analysis of American lobster’s stomach behaviors and the neural mechanisms controlling them could provide general insights into how rhythmic motor patterns for locomotion are produced. A large number of the neurons in the STG are modulatory neurons that use neuromodulators for at least part of their synaptic receptions. These neuromodulators are released by neurons and cause long-lasting changes in the synaptic efficacies of the targets. At present, many types of neuropeptides have been identified within the crustacean stomatogastric nervous system. The pyrokinins are members of one peptide family, PBAN. PBAN peptides all share the common Cterminalpentapeptide FXPRL-amide, in which X can be S, T, G, N, or V. Previous studies, using immunohistochemistry, have found that there are pyrokinin peptides present in both the STG and the cardiac ganglion (CG) of American lobsters. My research tests five different kinds of pyrokinin peptides, including PevPK1 (DFAFSPRLamide) and PevPK2 (ADFAFNPRLamide) from the shrimp L.vannamei (Torfs et al., 2001; Ma et al., 2010), CabPK1 (TNFAFSPRLamide) and CabPK2(SGGFAFSPRLamide from the crab C.borealis (Saideman et al., 2007;Ma et al., 2009) and Conserved Sequence (FSPRLamide) from the lobster, H.americanus (Ma, et al, 2008). ConservedSequence, the only pyrokinin identified in the American lobster so far, is highly conserved among many other pyrokinin peptides. Therefore, it is believed to be just a fragment with the complete sequence yet to be identified. Thus, we predicted that it might produce a weaker effect on the STG. Previous studies on the pyrokinin peptides have shown that in crabs, CabPK1, CabPK2 and LeucoPK (identified in an insect), all had a virtually identical effect on the CG, suggesting that the differences among these pyrokinin peptides are not important and the receptors for these peptides are the same. However, research done by Bowdoin students in 2011-2012 showed that among PevPK1,PevPK2, CabPK1, CabPK2, and Conserved Sequence, all but Conserved Sequence (not yet tested) had strong effects on the STG. However, only PevPK2 had an effect on the CG. My goal for this summer research was to determine whether or not there are differences between the responses of the STG to the different peptides in order to further determine the cause for the differences between the responses of the CG and those of the STG. The results from the extracellular recordings from the identified neurons in my research have shown that none of the five kinds of pyrokinin peptides affect the pyloric rhythm, which controls the pumping and filtering of food through the pylorus in Americanlobsters. They all, however, excite the gastric mill rhythm, which controls the movements of the teeth that grind up the food before it is transferred into the pylorus. Moreover, there is no significant difference among the effects of these five kinds of pyrokinin peptides. Conserved Sequence, which was predicted to produce a relatively weaker effect, proved to produce virtually identical effect asfour other kinds of pyrokinin peptides. Future research will focus on studying the differences between the STG and CG to determine the cause of the varied responses between them. Final Report of research funded by the Doherty Coastal Studies Research Fellowship.

Date: 2014-04-01

Creator: Andrew Rudalevige

Access: Open access

In his 2014 State of the Union address Barack Obama pledged to act without Congress on a variety of fronts, following up his "we can't wait" campaign of unilateralism before the 2012 election. The partisan furor this engendered tended to obscure the longstanding efforts of presidents to "faithfully execute" the law in a manner that aligns with their policy preferences. This paper examines the broad logic of those efforts, and delineates five areas where the Obama administration has been particularly aggressive: in its (1) recess appointments; (2) refusal to defend federal law (notably, the Defense of Marriage Act) in court; (3) use of prosecutorial discretion in declining to pursue violations of immigration and drug laws; (4) use of waivers; and (5) its utilization of the regulatory process to interpret the meaning of statutes, as with the Clean Air Act and the Affordable Care Act. Presidents do have flexibility in many cases; but this ends where they seek to alter the plain "letter of the law.".

Date: 2020-01-01

Creator: Sina Heydari, Amy Johnson, Olaf Ellers, Matthew J. McHenry, Eva, Kanso

Access: Open access

The oral surface of sea stars is lined with arrays of tube feet that enable them to achieve highly controlled locomotion on various terrains. The activity of the tube feet is orchestrated by a nervous system that is distributed throughout the body without a central brain. How such a distributed nervous system produces a coordinated locomotion is yet to be understood. We develop mathematical models of the biomechanics of the tube feet and the sea star body. In the model, the feet are coupled mechanically through their structural connection to a rigid body. We formulate hierarchical control laws that capture salient features of the sea star nervous system. Namely, at the tube foot level, the power and recovery strokes follow a state-dependent feedback controller. At the system level, a directionality command is communicated through the nervous system to all tube feet. We study the locomotion gaits afforded by this hierarchical control model. We find that these minimally coupled tube feet coordinate to generate robust forward locomotion, reminiscent of the crawling motion of sea stars, on various terrains and for heterogeneous tube feet parameters and initial conditions. Our model also predicts a transition from crawling to bouncing consistently with recent experiments. We conclude by commenting on the implications of these findings for understanding the neuromechanics of sea stars and their potential application to autonomous robotic systems.

Date: 2001-01-01

Creator: Olivia C. Vitale

Access: Open access

Catalog of an exhibition held at the Bowdoin College Museum of Art, Apr. 12-June 17, 2001.

Date: 1889-01-01

Access: Open access

Date: 2011-11-15

Creator: Christopher Chong, Guido Schneider

Access: Open access

It is the purpose of this short note to discuss some aspects of the validity question concerning the Korteweg-de Vries (KdV) approximation for periodic media. For a homogeneous model possessing the same resonance structure as it arises in periodic media we prove the validity of the KdV approximation with the help of energy estimates. © 2011 Elsevier Inc.

Date: 1982-01-01

Access: Open access

Date: 2020-01-01

Creator: Joseph Campbell Hilleary

Access: Open access

This thesis explores changes in and challenges to Moroccan political authority in the region of the Sous during the late nineteenth century. It attempts to show how the phenomenon of British informal empire created a crisis over Moroccan sovereignty that caused the sultan to both materially and discursively change the way he wielded power in southern Morocco. It further connects these changes and the narrative contestation that accompanied them to the construction of the Bilad al-Siba/Bilad al-Makhzan dichotomy found in Western academic literature on Morocco starting in the colonial period. It begins with an examination of letters between Sultan Hassan I and local leaders in the Sous that show a shift toward a more bureaucratic form of governance in response to repeated openings of black-market ports by British trading companies. It then investigates the textual debate over the framing of Hassan I’s military expeditions to southern Morocco in the 1880s and 90s by drawing on a collection of European travel accounts, American consular reports, and a royal Moroccan history. Finally, it ties the illegal trade in the Sous to the broader theory of informal empire through a close examination of the Tourmaline Incident of 1897, using documents from the British Foreign Office as well as published accounts by crew members aboard the Tourmaline, itself.

Date: 2017-06-01

Creator: Collin Roesler, Julia Uitz, Hervé Claustre, Emmanuel Boss, Xiaogang, Xing, Emanuele Organelli, Nathan Briggs, Annick Bricaud, Catherine Schmechtig, Antoine Poteau, Fabrizio D'Ortenzio, Josephine Ras, Susan Drapeau, Nils Haëntjens, Marie Barbieux

Access: Open access

Chlorophyll fluorometers provide the largest in situ global data set for estimating phytoplankton biomass because of their ease of use, size, power consumption, and relatively low price. While in situ chlorophyll a (Chl) fluorescence is proxy for Chl a concentration, and hence phytoplankton biomass, there exist large natural variations in the relationship between in situ fluorescence and extracted Chl a concentration. Despite this large natural variability, we present here a global validation data set for the WET Labs Environmental Characterization Optics (ECO) series chlorophyll fluorometers that suggests a factor of 2 overestimation in the factory calibrated Chl a estimates for this specific manufacturer and series of sensors. We base these results on paired High Pressure Liquid Chromatography (HPLC) and in situ fluorescence match ups for which non-photochemically quenched fluorescence observations were removed. Additionally, we examined matchups between the factory-calibrated in situ fluorescence and estimates of chlorophyll concentration determined from in situ radiometry, absorption line height, NASA's standard ocean color algorithm as well as laboratory calibrations with phytoplankton monocultures spanning diverse species that support the factor of 2 bias. We therefore recommend the factor of 2 global bias correction be applied for the WET Labs ECO sensors, at the user level, to improve the global accuracy of chlorophyll concentration estimates and products derived from them. We recommend that other fluorometer makes and models should likewise undergo global analyses to identify potential bias in factory calibration.

Date: 2002-01-01

Creator: Katy Kline

Access: Open access

Catalog accompanies the exhibition of the same name held April 5-June 9, 2002 at the Bowdoin College Museum of Art. Essay by Katy Kline.

Date: 1897-01-01

Access: Open access

Date: 1895-01-01

Access: Open access