Showing 881 - 890 of 5701 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.
Collapse of a rotating supermassive star to a supermassive black hole: Post-Newtonian simulations
Date: 2002-01-01
Creator: M. Saijo, T.W. Baumgarte, S.L. Shapiro, M. Shibata
Access: Open access
Sea star inspired crawling and bouncing
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.
David Batchelder: Photographs
Date: 1969-01-01
Creator: Richard V. West
Access: Open access
- Catalog of an exhibition held at the Bowdoin College Museum of Art.
The validity of the kdv approximation in case of resonances arising from periodic media
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.
JUST A BIG MISUNDERSTANDING? BIAS AND BAYESIAN AFFECTIVE POLARIZATION
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.
Reference Points, Prospect Theory, and Momentum on the PGA Tour
Date: 2016-06-01
Creator: Daniel F. Stone, Jeremy Arkes
Access: Open access
- Pope and Schweitzer (2011) study predictions of prospect theory for the reference point of par on the current hole in professional golf. We study prospect-theory predictions of three other plausible reference points: par for recent holes, for the round, and for the tournament. A potentially competing force is momentum in quality of play, that is, the hot or cold hand. While prospect theory predicts negative serial correlation in better (worse)-than-average performance across holes, the hot (cold) hand implies the opposite. We find evidence that, for each of the reference points we study, when scores are better than par, hot-hand effects are dominated by prospect-theory effects. These effects can occur via two mechanisms: greater conservatism or less effort. We find evidence that the former (latter) dominates for scores closer to (further from) the reference point. We also find evidence of prospect theory effects (greater risk seeking) when scores are worse than par for the round in Round 1 and of cold-hand effects for scores worse than par for the tournament in Round 3. The magnitudes of some of the joint effects are comparable to those found by Pope and Schweitzer and other related papers. We conclude by discussing how, rather than compete, prospect-theory and cold-hand forces might also cause one another.
Effects of octopamine and tyramine on the cardiac system of the lobster, Homarus americanus
Date: 2019-05-01
Creator: Casey Breslow
Access: Open access
- Modulation in neural systems is important for regulating physiology and behavior (Wright et al., 2010). Peptides, hormones, and amines are common neural modulators, acting on many neural systems across species. One group of neural networks that can be regulated are central pattern generators (CPGs), which generate rhythmic neural patterns, which drive behaviors (Marder and Bucher, 2001). Octopamine, and its precursor tyramine, are two amines that have been found to regulate (CPGs) across species (Cooke, 2002; Fussnecker et al., 2006). One role of octopamine in the decapod neurogenic heart is regulating the frequency and the duration of heart beats. However, the precise site of octopamine modulation within the cardiac system is not yet known (Kurumoto and Ebara, 1991). One possible site of action is the cardiac ganglion (CG), the CPG in decapod hearts. The transcripts for the enzymes required to synthesize octopamine from tyramine have been identified and localized in the CG (Christie et al., 2018). This would suggest that octopamine is produced in the CG, where it could have a direct action on those neurons, or it could be released peripherally. We have found individual variation in the response to octopamine and its precursor tyramine, and significant effects of frequency and contraction amplitude in the whole heart.
Holocene peatland carbon dynamics in the circum-Arctic region: An introduction
Date: 2014-01-01
Creator: Zicheng Yu, Julie Loisel, Daniel J. Charman, David W. Beilman, Philip, Camill
Access: Open access
- Peatlands represent the largest and most concentrated carbon pool in the terrestrial biosphere, and their dynamics during the Holocene have had significant impacts on the global carbon cycle. In this Introduction paper, we provide an overview of the contributions presented in this Special Issue on Holocene peatland carbon dynamics. We also provide a brief history and current status of peat-core-based research on peatland carbon dynamics. Finally, we identify and discuss some challenges and opportunities that would guide peatland carbon research in the near future. These challenges and opportunities include the need to fill data gaps and increase geographic representations of peat carbon accumulation records, a better understanding of peatland lateral expansion process and improved estimate of peatland area change over time, developing regional carbon accumulation histories and carbon pool estimates, and projecting and quantifying overall peatland net carbon balance in a changing world.