Showing 2181 - 2190 of 5708 Items
The pyloric neural circuit of the herbivorous crab Pugettia producta shows limited sensitivity to several neuromodulators that elicit robust effects in more opportunistically feeding decapods
Date: 2008-05-01
Creator: Patsy S. Dickinson, Elizabeth A. Stemmler, Andrew E. Christie
Access: Open access
- Modulation of neural circuits in the crustacean stomatogastric nervous system (STNS) allows flexibility in the movements of the foregut musculature. The extensive repertoire of such resulting motor patterns in dietary generalists is hypothesized to permit these animals to process varied foods. The foregut and STNS of Pugettia producta are similar to those of other decapods, but its diet is more uniform, consisting primarily of kelp. We investigated the distribution of highly conserved neuromodulators in the stomatogastric ganglion (STG) and neuroendocrine organs of Pugettia, and documented their effects on its pyloric rhythm. Using immunohistochemistry, we found that the distributions of Cancer borealis tachykinin-related peptide I (CabTRP I), crustacean cardioactive peptide (CCAP), proctolin, red pigment concentrating hormone (RPCH) and tyrosine hydroxylase (dopamine) were similar to those of other decapods. For all peptides except proctolin, the isoforms responsible for the immunoreactivity were confirmed by mass spectrometry to be the authentic peptides. Only two modulators had physiological effects on the pyloric circuit similar to those seen in other species. In non-rhythmic preparations, proctolin and the muscarinic acetylcholine agonist oxotremorine consistently initiated a full pyloric rhythm. Dopamine usually activated a pyloric rhythm, but this pattern was highly variable. In only about 25% of preparations, RPCH activated a pyloric rhythm similar to that seen in other species. CCAP and CabTRP I had no effect on the pyloric rhythm. Thus, whereas Pugettia possesses all the neuromodulators investigated, its pyloric rhythm, when compared with other decapods, appears less sensitive to many of them, perhaps because of its limited diet.
Effects of differential rotation on the maximum mass of neutron stars
Date: 2003-01-01
Creator: N.D. Lyford, T.W. Baumgarte, S.L. Shapiro
Access: Open access
Extreme Value Theory and Backtest Overfitting in Finance
Date: 2015-05-01
Creator: Daniel C Byrnes
Access: Open access
- In order to identify potentially profitable investment strategies, hedge funds and asset managers can use historical market data to simulate a strategy's performance, a process known as backtesting. While the abundance of historical stock price data and powerful computing technologies has made it feasible to run millions of simulations in a short period of time, this process may produce statistically insignificant results in the form of false positives. As the number of configurations of a strategy increases, it becomes more likely that some of the configurations will perform well by chance alone. The phenomenon of backtest overfitting occurs when a model interprets market idiosyncrasies as signal rather than noise, and is often not taken into account in the strategy selection process. As a result, the finance industry and academic literature are rife with skill-less strategies that have no capability of beating the market. This paper explores the development of a minimum criterion that managers and investors can use during the backtesting process in order to increase confidence that a strategy's performance is not the result of pure chance. To do this we will use extreme value theory to determine the probability of observing a specific result, or something more extreme than this result, given that multiple configurations of a strategy were tested.
Mass spectrometric identification of pEGFYSQRYamide: A crustacean peptide hormone possessing a vertebrate neuropeptide Y (NPY)-like carboxy-terminus
Date: 2007-05-15
Creator: Elizabeth A. Stemmler, Emily A. Bruns, Noah P. Gardner, Patsy S. Dickinson, Andrew E., Christie
Access: Open access
- In invertebrates, peptides possessing the carboxy (C)-terminal motif -RXRFamide have been proposed as the homologs of vertebrate neuropeptide Y (NPY). Using matrix assisted laser desorption/ionization mass spectrometry, in combination with sustained off-resonance irradiation collision-induced dissociation and chemical and enzymatic reactions, we have identified the peptide pEGFYSQRYamide from the neuroendocrine pericardial organ (PO) of the crab Pugettia producta. This peptide is likely the same as that previously reported, but misidentified, as PAFYSQRYamide in several earlier reports (e.g. [Li, L., Kelley, W.P., Billimoria, C.P., Christie, A.E., Pulver, S.R., Sweedler, J.V., Marder, E. 2003. Mass spectrometric investigation of the neuropeptide complement and release in the pericardial organs of the crab, Cancer borealis. J. Neurochem. 87, 642-656; Fu, Q., Kutz, K.K., Schmidt, J.J., Hsu, Y.W., Messinger, D.I., Cain, S.D., de la Iglesia, H.O., Christie, A.E., Li, L. 2005. Hormone complement of the Cancer productus sinus gland and pericardial organ: an anatomical and mass spectrometric investigation. J. Comp. Neurol. 493, 607-626.]). The -QRYamide motif contained in pEGFYSQRYamide is identical to that present in many vertebrate members of the NPY superfamily. Mass spectrometric analysis conducted on the POs of several other decapods showed that pEGFYSQRYamide is present in three other brachyurans (Cancer borealis, Cancer irroratus and Cancer productus) as well as in one species from another decapod infraorder (Lithodes maja, an anomuran). Thus, our findings show that at least some invertebrates possess NPY-like peptides in addition to those exhibiting an -RXRFamide C-terminus, and raise the question as to whether the invertebrate -QRYamides are functionally and/or evolutionarily related to the NPY superfamily. © 2007 Elsevier Inc. All rights reserved.
Aortic pressure and heart rate in the lobster Homarus americanus are modulated by mechanical feedback and neuropeptides
Date: 2021-01-01
Creator: Grace Marie Hambelton
Access: Open access
- Baroreceptors are stretch receptors located in the aorta of mammals; in response to increased afterload, they elicit a decrease in heart rate, creating a negative feedback loop that lowers blood pressure. Although lobsters (Homarus americanus) do not have baroreceptors like mammals, closely related land crabs have been shown to have baroreceptor-like responses. Heart contraction is also regulated by the Frank-Starling response, where increasing stretch or preload increases the contractile force of the heart. In addition to these types of biomechanical modulations, lobsters use a central pattern generator, the cardiac ganglion, to maintain synchronicity of the heartbeat. The heart is also controlled by the central nervous system via neuromodulators, such as myosuppressin, which has been shown to increase active force and decrease frequency in isolated lobster hearts. We performed experiments on a lobster heart with the main arteries still intact, and varied the preload by stretching anterior arteries, and the afterload by elevating the dorsal abdominal artery. We added myosuppressin to modulate the cardiac ganglion output and muscle contraction. We found that the baroreceptor-like response is most directly modulated by active force, whereas frequency could be a secondary control. Increasing preload does increase active force, but that does not correlate to a higher cardiac output, which shows that how hard the heart pumps is not what determines how effectively it is pumping. Additionally, we found that myosuppressin has a much stronger effect on frequency than active force, and so with myosuppressin, frequency becomes the main determinant of cardiac output.
Molecular characterization of putative neuropeptide, amine, diffusible gas and small molecule transmitter biosynthetic enzymes in the eyestalk ganglia of the American lobster, Homarus americanus
Date: 2018-12-01
Creator: Andrew E. Christie, Meredith E. Stanhope, Helen I. Gandler, Tess J. Lameyer, Micah G., Pascual, Devlin N. Shea, Andy Yu, Patsy S. Dickinson, J. Joe Hull
Access: Open access
- The American lobster, Homarus americanus, is a model for investigating the neuromodulatory control of physiology and behavior. Prior studies have shown that multiple classes of chemicals serve as locally released/circulating neuromodulators/neurotransmitters in this species. Interestingly, while many neuroactive compounds are known from Homarus, little work has focused on identifying/characterizing the enzymes responsible for their biosynthesis, despite the fact that these enzymes are key components for regulating neuromodulation/neurotransmission. Here, an eyestalk ganglia-specific transcriptome was mined for transcripts encoding enzymes involved in neuropeptide, amine, diffusible gas and small molecule transmitter biosynthesis. Using known Drosophila melanogaster proteins as templates, transcripts encoding putative Homarus homologs of peptide precursor processing (signal peptide peptidase, prohormone processing protease and carboxypeptidase) and immature peptide modifying (glutaminyl cyclase, tyrosylprotein sulfotransferase, protein disulfide isomerase, peptidylglycine-α-hydroxylating monooxygenase and peptidyl-α-hydroxyglycine-α-amidating lyase) enzymes were identified in the eyestalk assembly. Similarly, transcripts encoding full complements of the enzymes responsible for dopamine [tryptophan-phenylalanine hydroxylase (TPH), tyrosine hydroxylase and DOPA decarboxylase (DDC)], octopamine (TPH, tyrosine decarboxylase and tyramine β-hydroxylase), serotonin (TPH or tryptophan hydroxylase and DDC) and histamine (histidine decarboxylase) biosynthesis were identified from the eyestalk ganglia, as were those responsible for the generation of the gases nitric oxide (nitric oxide synthase) and carbon monoxide (heme oxygenase), and the small molecule transmitters acetylcholine (choline acetyltransferase), glutamate (glutaminase) and GABA (glutamic acid decarboxylase). The presence and identity of the transcriptome-derived transcripts were confirmed using RT-PCR. The data presented here provide a foundation for future gene-based studies of neuromodulatory control at the level of neurotransmitter/modulator biosynthesis in Homarus.
Isospin mass splittings from precision measurements of D*-D mass differences
Date: 1992-01-01
Creator: D. Bortoletto, D. N. Brown, J. Dominick, R. L. Mcilwain, T., Miao, D. H. Miller, M. Modesitt, S. F. Schaffner, E. I. Shibata, I. P.J. Shipsey, M. Battle, J. Ernst, H. Kroha, S. Roberts, K. Sparks, E. H. Thorndike, C. H. Wang, S. Sanghera, T. Skwarnicki, R. Stroynowski, M. Artuso, M. Goldberg, N. Horwitz, R. Kennett, G. C. Moneti, F. Muheim, S. Playfer, Y. Rozen, P. Rubin, S. Stone, M. Thulasidas
Access: Open access
- Using the decay modes, D*+→D+π0 and D*0→D0π0, we have measured the D*+-D+ and D*0-D0 mass differences to be 140±0.08±0.06 and 142.12±0.05±0.05 MeV, respectively. Combining these measurements with the Particle Data Group average for the D*+-D0 mass difference, we obtain isospin mass splittings for D*+-Dusp*0 and D+-D0 of 3.32±0.08±0.05 and 4.80±0.10 ±0.06 MeV. We discuss the implications of these measurements for models of isospin mass differences and model-dependent estimates of fD. © 1992 The American Physical Society.
Alexander the Great and the Rise of Christianity
Date: 2021-01-01
Creator: Stephen M. Girard
Access: Open access
- Alexander the Great and the Rise of Christianity focuses on the political, mythical, and philosophical connection between Alexander the Great's life and the beginnings of early Christianity. The first chapter of the text focuses on an analysis of mythical conceptions of Alexander the Great as “Son of God” as well as cultural perceptions of him as “Philosopher King” and cosmopolitan, and how these portraits of Alexander were influential for Christianity. The second chapter analyzes Alexander’s relationship with the Jewish people, and his appearances in the Old Testament apocalyptic Book of Daniel. The last chapter discusses Alexander’s relationship with Christianity itself, seen through a study of the life of Jesus, Alexandrian Judaism, and the early Christian apologists.
A revised 1000 year atmospheric δ13 C-CO2 record from Law Dome and South Pole, Antarctica
Date: 2013-08-16
Creator: M. Rubino, D. M. Etheridge, C. M. Trudinger, C. E. Allison, M. O., Battle, R. L. Langenfelds, L. P. Steele, M. Curran, M. Bender, J. W.C. White, T. M. Jenk, T. Blunier, R. J. Francey
Access: Open access
- We present new measurements of δ13C of CO2 extracted from a high-resolution ice core from Law Dome (East Antarctica), together with firn measurements performed at Law Dome and South Pole, covering the last 150 years. Our analysis is motivated by the need to better understand the role and feedback of the carbon (C) cycle in climate change, by advances in measurement methods, and by apparent anomalies when comparing ice core and firn air δ13C records from Law Dome and South Pole. We demonstrate improved consistency between Law Dome ice, South Pole firn, and the Cape Grim (Tasmania) atmospheric δ13C data, providing evidence that our new record reliably extends direct atmospheric measurements back in time. We also show a revised version of early δ13C measurements covering the last 1000 years, with a mean preindustrial level of -6.50‰. Finally, we use a Kalman Filter Double Deconvolution to infer net natural CO2 fluxes between atmosphere, ocean, and land, which cause small δ13C deviations from the predominant anthropogenically induced δ13C decrease. The main features found from the previous δ13C record are confirmed, including the ocean as the dominant cause for the 1940 A.D. CO2 leveling. Our new record provides a solid basis for future investigation of the causes of decadal to centennial variations of the preindustrial atmospheric CO2 concentration. Those causes are of potential significance for predicting future CO2 levels and when attempting atmospheric verification of recent and future global carbon emission mitigation measures through Coupled Climate Carbon Cycle Models. Key Points New and revised, firn and ice δ13C-CO2 measurements from Antarctica Improve consistency between ice and firn δ13C-CO2 measurements Net natural CO2 fluxes between atmosphere, ocean and land inferred ©2013. American Geophysical Union. All Rights Reserved.
The Effects of Temperature on the Cardiac System of the American Lobster, Homarus americanus
Date: 2014-05-01
Creator: Elizabeth A Owens
Access: Open access
- The American lobster, Homarus americanus, inhabits a large oceanic range spanning from Labrador, Canada to North Carolina, USA. This geographic range varies in temperature by as much as 25ºC, and daily temperature fluctuations of up to 12ºC may occur at a single location depending on season, water depth, and tides. The cardiac system of the lobster is sensitive to these temperature changes, and has been shown to adjust its functioning over a large temperature range. A previous study showed that various functional parameters respond differently to temperature changes, but a stable cardiac output can be maintained over the range of 2-20ºC. The current study showed that the effects of temperature were exerted primarily through changes in the lobster heart central pattern generator, the cardiac ganglion. Similar patterns of change were seen in both semi-intact hearts and isolated cardiac ganglion preparations in response to increasing temperature. Specifically, with increasing temperature, the burst frequency showed a biphasic pattern in which frequency initially increased, then decreased rapidly at high temperatures. The burst duration, duty cycle, and number of spikes per burst generally decreased with increasing temperature, and spike frequency increased over the entire temperature range. Semi-intact hearts and isolated cardiac ganglia showed similar “crash” patterns, characterized by complete loss of function at high temperatures and complete recovery of function when temperature was returned to baseline. Feedback in the semi-intact heart provided some stabilization of bursting activity, but it did not provide the expected protection from high temperatures. The isolated CG had a significantly higher crash temperature than did the semi-intact system. This discrepancy in crash temperatures may be explained by considering factors at the level of the muscle and neuromuscular junction (NMJ), such as stretch and nitric oxide (NO) feedback and the balance of facilitation and depression at the NMJ. Stimulated preparations showed defacilitation of contraction amplitude at high temperatures despite the maintenance of constant burst parameters of stimulation. Therefore, several factors contributing to the relatively low crash temperature of the intact system may be a shift in the balance of facilitation and depression at the NMJ, a depression in ganglion function due to the release of NO by the muscle, or a combination of the two mechanisms.