Showing 5031 - 5040 of 5701 Items
Spatial heterogeneity and environmental predictors of permafrost region soil organic carbon stocks
Date: 2021-02-24
Creator: Umakant Mishra, Gustaf Hugelius, Eitan Shelef, Yuanhe Yang, Jens, Strauss, Alexey Lupachev, Jennifer W. Harden, Julie D. Jastrow, Chien Lu Ping, William J. Riley, Edward A.G. Schuur, Roser Matamala, Matthias Siewert, Lucas E. Nave, Charles D. Koven, Matthias Fuchs
Access: Open access
- Large stocks of soil organic carbon (SOC) have accumulated in the Northern Hemisphere permafrost region, but their current amounts and future fate remain uncertain. By analyzing dataset combining >2700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated that Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate.
Effects of permafrost aggradation on peat properties as determined from a pan-Arctic synthesis of plant macrofossils
Date: 2016-01-01
Creator: C. C. Treat, M. C. Jones, P. Camill, A. Gallego-Sala, M., Garneau, J. W. Harden, G. Hugelius, E. S. Klein, U. Kokfelt, P. Kuhry, J. Loisel, P. J.H. Mathijssen, J. A. O'Donnell, P. O. Oksanen, T. M. Ronkainen, A. B.K. Sannel
Access: Open access
- Permafrost dynamics play an important role in high-latitude peatland carbon balance and are key to understanding the future response of soil carbon stocks. Permafrost aggradation can control the magnitude of the carbon feedback in peatlands through effects on peat properties. We compiled peatland plant macrofossil records for the northern permafrost zone (515 cores from 280 sites) and classified samples by vegetation type and environmental class (fen, bog, tundra and boreal permafrost, and thawed permafrost). We examined differences in peat properties (bulk density, carbon (C), nitrogen (N) and organic matter content, and C/N ratio) and C accumulation rates among vegetation types and environmental classes. Consequences of permafrost aggradation differed between boreal and tundra biomes, including differences in vegetation composition, C/N ratios, and N content. The vegetation composition of tundra permafrost peatlands was similar to permafrost-free fens, while boreal permafrost peatlands more closely resembled permafrost-free bogs. Nitrogen content in boreal permafrost and thawed permafrost peatlands was significantly lower than in permafrost-free bogs despite similar vegetation types (0.9% versus 1.5% N). Median long-term C accumulation rates were higher in fens (23 g C m yr ) than in permafrost-free bogs (18 g C m yr ) and were lowest in boreal permafrost peatlands (14 g C m yr ). The plant macrofossil record demonstrated transitions from fens to bogs to permafrost peatlands, bogs to fens, permafrost aggradation within fens, and permafrost thaw and reaggradation. Using data synthesis, we have identified predominant peatland successional pathways, changes in vegetation type, peat properties, and C accumulation rates associated with permafrost aggradation. -2 -1 -2 -1 -2 -1
Genomic plasticity of the human fungal pathogen Candida albicans
Date: 2010-07-01
Creator: Anna Selmecki, Anja Forche, Judith Berman
Access: Open access
- The genomic plasticity of Candida albicans, a commensal and common opportunistic fungal pathogen, continues to reveal unexpected surprises. Once thought to be asexual, we now know that the organism can generate genetic diversity through several mechanisms, including mating between cells of the opposite or of the same mating type and by a parasexual reduction in chromosome number that can be accompanied by recombination events (2, 12, 14, 53, 77, 115). In addition, dramatic genome changes can appear quite rapidly in mitotic cells propagated in vitro as well as in vivo. The detection of aneuploidy in other fungal pathogens isolated directly from patients (145) and from environmental samples (71) suggests that variations in chromosome organization and copy number are a common mechanism used by pathogenic fungi to rapidly generate diversity in response to stressful growth conditions, including, but not limited to, antifungal drug exposure. Since cancer cells often become polyploid and/or aneuploid, some of the lessons learned from studies of genome plasticity in C. albicans may provide important insights into how these processes occur in higher-eukaryotic cells exposed to stresses such as anticancer drugs. © 2010, American Society for Microbiology.
Parterre: An Installation by Lauren Fensterstock
Date: 2008-01-01
Creator: Alison Ferris
Access: Open access
- Catalog of an exhibition held at the Bowdoin College Museum of Art from Oct. 3, 2008 through Jan.11, 2009. Essay by Alison Ferris.
Receptors and Neuropeptides in the Cardiac Ganglion of the American Lobster, Homarus americanus: A Bioinformatics and Mass Spectrometric Investigation
Date: 2019-01-01
Creator: Louis Mendez
Access: Open access
- Central pattern generators (CPGs) are neural networks that generate rhythmic motor patterns to allow organisms to perform stereotypical tasks, such as breathing, scratching, flying, and walking. The American lobster, Homarus americanus, is a simple model system whose CPGs are functionally analogous to those in vertebrate models and model complex rhythmic behaviors. CPGs in many Crustacea, including the American lobster, have been studied because of their ability to maintain biological function after isolation in physiologically relevant conditions. The cardiac ganglion (CG) is a CPG consisting of five larger motor neurons and four smaller pacemaker neurons that innervate the cardiac neuromuscular system and generate electrical bursts that drive patterned behaviors. Neuromodulators, such as neuropeptides, are known to modulate neural output in the CPGs of the American lobster. Currently, neuromodulators affecting the cardiac ganglia are thought to be mainly expressed and secreted outside of the cardiac ganglia, acting as extrinsic neuromodulators. However, there is current evidence to support the idea that neuromodulators can be intrinsically expressed within the cardiac ganglion of the American lobster. Preliminary studies using transcriptomic techniques on genomic and transcriptomic information indicate that neuropeptides are likely expressed within the cardiac ganglion. However, little research has been done to determine whether these neuropeptides are expressed in the cardiac ganglion of the American lobster. Therefore, the purpose of this study is to combine bioinformatics and mass spectrometric techniques to determine whether select neuropeptides are present in the cardiac ganglion within the cardiac neuromuscular system of the American lobster, Homarus americanus. Our data mining techniques using protein query sequences obtained from previously annotated brain and eyestalk transcriptomes resulted in the identification of 22 putative neuropeptides preprohormones from 17 neuropeptide families and 20 putative neuropeptide receptors from 17 neuropeptide receptor families in the CG transcriptome. Additionally, 9 putative neuropeptide receptors from 7 neuropeptide receptor families were detected in the cardiac muscle transcriptome. Of the 17 neuropeptide families detected, receptors for 9 of these neuropeptide families were detected in the CG transcriptome. Receptors for 6 of the neuropeptide families were also present in the cardiac muscle transcriptome. Interestingly, receptors for 6 of neuropeptide families detected were not found in either the CG or cardiac muscle transcriptomes, and receptors for 4 neuropeptide families that weren’t detected in the CG transcriptome were found in the cardiac muscle transcriptome. Therefore, our research suggests that neuropeptides are able to modulate CPG activity extrinsically, either though hormonal or local delivery, or intrinsically. Additionally, neuropeptides were extracted from the stomatogastric ganglion and the commissural ganglion using a scaled-down neuropeptide extraction protocol to estimate the number of tissues required to obtain sufficiently strong mass spectrometry signals. Pooled samples with two commissural ganglia and single samples of a commissural ganglion and a stomatogastric ganglion displayed little signal and an increase in larger peptides and impurities relative to single-tissue samples. Therefore, further optimization of the scaled-down neuropeptide extraction protocol must be done prior to analysis of a cardiac ganglion in the American lobster.
A "Peculiarly American" Enthusiasm: George Bellows, Traditional Masculinity, and The Big Dory
Date: 2014-01-01
Creator: James W. Denison, IV
Access: Open access
- A “Peculiarly American” Enthusiasm: George Bellows, Traditional Masculinity, and The Big Dory investigates the portrayal of masculinity in the oeuvre of the much-lauded yet enigmatic American painter George Bellows (1882-1925). Rather than relying on Bellows’ urban works for source material, a significant portion of this investigation is conducted via a case study of Bellows’ 1913 panel The Big Dory, a scene of fishermen pushing a boat into the North Atlantic off Monhegan Island, Maine that the artist painted during a sojourn on the island in the months after his involvement in the landmark Armory Show in New York. The paper situates The Big Dory within the greater context of the history of the depiction of Maine through the lens of the heroic fisherman. Bellows achieved a heroic effect by forcing the viewer to focus on the labor of the fishermen via their positioning in the near middleground and by echoing the hues and forms of the men elsewhere in the painting, giving the work a sense of visual unity. I argue that these strategies highlight Bellows’ interest in tradition rather than modernism. Armed with this knowledge, Bellows’ other works come more sharply into focus. I reveal that the traditional heterosexual mode of white male identity Bellows represented in The Big Dory was not simply echoed in Bellows’ personal comportment, but in fact pervaded his oeuvre; such masculinity was a reaction by patriarchal American society against the perceived growth of other influences in the early twentieth century. The portrayal of such masculinity is then established as the key underlying feature of the sense of “Americanism” which has traditionally dominated reception of Bellows’ art.
“I’m Going to Help You Become a Better You”: Teacher-Student Dynamics in Special Education
Date: 2019-05-01
Creator: Sophie Sadovnikoff
Access: Open access
- This study explores teachers’ roles in special education in terms of how they interact with students with disabilities. In the struggle against oppression and disempowerment, teachers can play a crucial role in employing education as the great equalizer, or else not. The question this research seeks to answer is: how do special education teachers interact with their students with disabilities, and how does this teacher role fit within a society that seeks to marginalize these students? I argue that special education teachers reproduce ableism by disciplining, normalizing, and controlling their students, but teachers express a deep sense of caring for and about their students, and understand their work as being their best effort at helping their students. The ableist actions that they perform are, ironically, an effort to help their students create fulfilling lives within an ableist society.
Perception is key? Does perceptual sensitivity and parenting behavior predict children's reactivity to others’ emotions?
Date: 2017-11-01
Creator: Joyce Weeland, Alithe Van den Akker, Meike Slagt, Samuel Putnam
Access: Open access
- When interacting with other people, both children's biological predispositions and past experiences play a role in how they will process and respond to social–emotional cues. Children may partly differ in their reactions to such cues because they differ in the threshold for perceiving such cues in general. Theoretically, perceptual sensitivity (i.e., the amount of detection of slight, low-intensity stimuli from the external environment independent of visual and auditory ability) might, therefore, provide us with specific information on individual differences in susceptibility to the environment. However, the temperament trait of perceptual sensitivity is highly understudied. In an experiment, we tested whether school-aged children's (N = 521, 52.5% boys, Mage = 9.72 years, SD = 1.51) motor (facial electromyography) and affective (self-report) reactivities to dynamic facial expressions and vocalizations is predicted by their (parent-reported) perceptual sensitivity. Our results indicate that children's perceptual sensitivity predicts their motor reactivity to both happy and angry expressions and vocalizations. In addition, perceptual sensitivity interacted with positive (but not negative) parenting behavior in predicting children's motor reactivity to these emotions. Our findings suggest that perceptual sensitivity might indeed provide us with information on individual differences in reactivity to social–emotional cues, both alone and in interaction with parenting behavior. Because perceptual sensitivity focuses specifically on whether children perceive cues from their environment, and not on whether these cues cause arousal and/or whether children are able to regulate this arousal, it should be considered that perceptual sensitivity lies at the root of such individual differences.
Effects of Arabidopsis wall associated kinase mutations on ESMERALDA1 and elicitor induced ROS
Date: 2021-05-01
Creator: Bruce D. Kohorn, Bridgid E. Greed, Gregory Mouille, Stéphane Verger, Susan L., Kohorn
Access: Open access
- Angiosperm cell adhesion is dependent on interactions between pectin polysaccharides which make up a significant portion of the plant cell wall. Cell adhesion in Arabidopsis may also be regulated through a pectin-related signaling cascade mediated by a putative O-fucosyltransferase ESMERALDA1 (ESMD1), and the Epidermal Growth Factor (EGF) domains of the pectin binding Wall associated Kinases (WAKs) are a primary candidate substrate for ESMD1 activity. Genetic interactions between WAKs and ESMD1 were examined using a dominant hyperactive allele of WAK2, WAK2cTAP, and a mutant of the putative O-fucosyltransferase ESMD1. WAK2cTAP expression results in a dwarf phenotype and activation of the stress response and reactive oxygen species (ROS) production, while esmd1 is a suppressor of a pectin deficiency induced loss of adhesion. Here we find that esmd1 suppresses the WAK2cTAP dwarf and stress response phenotype, including ROS accumulation and gene expression. Additional analysis suggests that mutations of the potential WAK EGF O-fucosylation site also abate the WAK2cTAP phenotype, yet only evidence for an N-linked but not O-linked sugar addition can be found. Moreover, a WAK locus deletion allele has no effect on the ability of esmd1 to suppress an adhesion deficiency, indicating WAKs and their modification are not a required component of the potential ESMD1 signaling mechanism involved in the control of cell adhesion. The WAK locus deletion does however affect the induction of ROS but not the transcriptional response induced by the elicitors Flagellin, Chitin and oligogalacturonides (OGs).