Showing 311 - 320 of 722 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
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.
Recent decreases in fossil-fuel emissions of ethane and methane derived from firn air
Date: 2011-08-11
Creator: Murat Aydin
Kristal R. Verhulst
Eric S. Saltzman
Mark O. Battle
Stephen A., Montzka
Donald R. Blake
Qi Tang
Michael J. Prather
Access: Open access
- Methane and ethane are the most abundant hydrocarbons in the atmosphere and they affect both atmospheric chemistry and climate. Both gases are emitted from fossil fuels and biomass burning, whereas methane (CH 4) alone has large sources from wetlands, agriculture, landfills and waste water. Here we use measurements in firn (perennial snowpack) air from Greenland and Antarctica to reconstruct the atmospheric variability of ethane (C 2H 6) during the twentieth century. Ethane levels rose from early in the century until the 1980s, when the trend reversed, with a period of decline over the next 20 years. We find that this variability was primarily driven by changes in ethane emissions from fossil fuels; these emissions peaked in the 1960s and 1970s at 14-16 teragrams per year (1 Tg = 10 12 g) and dropped to 8-10 Tg yr -1 by the turn of the century. The reduction in fossil-fuel sources is probably related to changes in light hydrocarbon emissions associated with petroleum production and use. The ethane-based fossil-fuel emission history is strikingly different from bottom-up estimates of methane emissions from fossil-fuel use, and implies that the fossil-fuel source of methane started to decline in the 1980s and probably caused the late twentieth century slow-down in the growth rate of atmospheric methane. © 2011 Macmillan Publishers Limited. All rights reserved.
Approximate initial data for binary black holes
Date: 2006-09-21
Creator: Kenneth A. Dennison
Thomas W. Baumgarte
Harald P. Pfeiffer
Access: Open access
- We construct approximate analytical solutions to the constraint equations of general relativity for binary black holes of arbitrary mass ratio in quasicircular orbit. We adopt the puncture method to solve the constraint equations in the transverse-traceless decomposition and consider perturbations of Schwarzschild black holes caused by boosts and the presence of a binary companion. A superposition of these two perturbations then yields approximate, but fully analytic binary black hole initial data that are accurate to first order in the inverse of the binary separation and the square of the black holes' momenta. © 2006 The American Physical Society.
Animal-to-animal variability in the phasing of the crustacean cardiac motor pattern: An experimental and computational analysis
Date: 2013-01-01
Creator: Alex H. Williams
Molly A. Kwiatkowski
Adam L. Mortimer
Eve Marder
Mary Lou, Zeeman
Patsy S. Dickinson
Access: Open access
- The cardiac ganglion (CG) of Homarus americanus is a central pattern generator that consists of two oscillatory groups of neurons: "small cells" (SCs) and "large cells" (LCs). We have shown that SCs and LCs begin their bursts nearly simultaneously but end their bursts at variable phases. This variability contrasts with many other central pattern generator systems in which phase is well maintained. To determine both the consequences of this variability and how CG phasing is controlled, we modeled the CG as a pair of Morris-Lecar oscillators coupled by electrical and excitatory synapses and constructed a database of 15,000 simulated networks using random parameter sets. These simulations, like our experimental results, displayed variable phase relationships, with the bursts beginning together but ending at variable phases. The model suggests that the variable phasing of the pattern has important implications for the functional role of the excitatory synapses. In networks in which the two oscillators had similar duty cycles, the excitatory coupling functioned to increase cycle frequency. In networks with disparate duty cycles, it functioned to decrease network frequency. Overall, we suggest that the phasing of the CG may vary without compromising appropriate motor output and that this variability may critically determine how the network behaves in response to manipulations. © 2013 the American Physiological Society.
Quantum kinks: Solitons at strong coupling
Date: 1992-01-01
Creator: Stephen G. Naculich
Access: Open access
- We examine solitons in theories with heavy fermions. These "quantum" solitons differ dramatically from semiclassical (perturbative) solitons because fermion loop effects are important when the Yukawa coupling is strong. We focus on kinks in a (1 + 1)-dimensional 4 theory coupled to fermions; a large-N expansion is employed to treat the Yukawa coupling g nonperturbatively. A local expression for the fermion vacuum energy is derived using the WKB approximation for the Dirac eigenvalues. We find that fermion loop corrections increase the energy of the kink and (for large g) decrease its size. For large g, the energy of the quantum kink is proportional to g, and its size scales as 1g, unlike the classical kink; we argue that these features are generic to quantum solitons in theories with strong Yukawa couplings. We also discuss the possible instability of fermions to solitons. © 1992 The American Physical Society.
Atmospheric O2/N2 changes, 1993-2002: Implications for the partitioning of fossil fuel CO2 sequestration
Date: 2005-12-01
Creator: Michael L. Bender
David T. Ho
Melissa B. Hendricks
Robert Mika
Mark O., Battle
Pieter P. Tans
Thomas J. Conway
Blake Sturtevant
Nicolas Cassar
Access: Open access
- Improvements made to an established mass spectrometric method for measuring changes in atmospheric O2/N2 are described. With the improvements in sample handling and analysis, sample throughput and analytical precision have both increased. Aliquots from duplicate flasks are repeatedly measured over a period of 2 weeks, with an overall standard error in each flask of 3-4 per meg, corresponding to 0.6-0.8 ppm O2 in air. Records of changes in O2/N2 from six global sampling stations (Barrow, American Samoa, Cape Grim, Amsterdam Island, Macquarie Island, and Syowa Station) are presented. Combined with measurements Of CO2 from the same sample flasks, land and ocean carbon uptake were calculated from the three sampling stations with the longest records (Barrow, Samoa, and Cape Grim). From 1994-2002, We find the average CO2 uptake by the ocean and the land biosphere was 1.7 ± 0.5 and 1.0 ± 0.6 GtC yr -1 respectively; these numbers include a correction of 0.3 Gt C yr-l due to secular outgassing of ocean O2. Interannual variability calculated from these data shows a strong land carbon source associated with the 1997-1998 El Niño event, supporting many previous studies indicating that high atmospheric growth rates observed during most El Niño events reflect diminished land uptake. Calculations of interannual variability in land and ocean uptake are probably confounded by non-zero annual air sea fluxes of O2. The origin of these fluxes is not yet understood. Copyright 2005 by the American Geophysical Union.
Phononic rogue waves
Date: 2018-09-13
Creator: E. G. Charalampidis
J. Lee
P. G. Kevrekidis
C. Chong
Access: Open access
- We present a theoretical study of extreme events occurring in phononic lattices. In particular, we focus on the formation of rogue or freak waves, which are characterized by their localization in both spatial and temporal domains. We consider two examples. The first one is the prototypical nonlinear mass-spring system in the form of a homogeneous Fermi-Pasta-Ulam-Tsingou (FPUT) lattice with a polynomial potential. By deriving an approximation based on the nonlinear Schrödinger (NLS) equation, we are able to initialize the FPUT model using a suitably transformed Peregrine soliton solution of the NLS equation, obtaining dynamics that resembles a rogue wave on the FPUT lattice. We also show that Gaussian initial data can lead to dynamics featuring a rogue wave for sufficiently wide Gaussians. The second example is a diatomic granular crystal exhibiting rogue-wave-like dynamics, which we also obtain through an NLS reduction and numerical simulations. The granular crystal (a chain of particles that interact elastically) is a widely studied system that lends itself to experimental studies. This study serves to illustrate the potential of such dynamical lattices towards the experimental observation of acoustic rogue waves.
A genomewide survey argues that every zygotic gene product is dispensable for the initiation of somatic homolog pairing in Drosophila
Date: 2008-11-01
Creator: Jack R. Bateman
C. Ting Wu
Access: Open access
- Studies from diverse organisms show that distinct interchromosomal interactions are associated with many developmental events. Despite recent advances in uncovering such phenomena, our understanding of how interchromosomal interactions are initiated and regulated is incomplete. During the maternal-to-zygotic transition (MZT) of Drosophila embryogenesis, stable interchromosomal contacts form between maternal and paternal homologous chromosomes, a phenomenon known as somatic homolog pairing. To better understand the events that initiate pairing, we performed a genomewide assessment of the zygotic contribution to this process. Specifically, we took advantage of the segregational properties of compound chromosomes to generate embryos lacking entire chromosome arms and, thus, all zygotic gene products derived from those arms. Using DNA fluorescence in situ hybridization (FISH) to assess the initiation of pairing at five separate loci, this approach allowed us to survey the entire zygotic genome using just a handful of crosses. Remarkably, we found no defect in pairing in embryos lacking any chromosome arm, indicating that no zygotic gene product is essential for pairing to initiate. From these data, we conclude that the initiation of pairing can occur independently of zygotic control and may therefore be part of the developmental program encoded by the maternal genome. Copyright © 2008 by the Genetics Society of America.