Showing 761 - 770 of 4695 Items
Gravity darkening and brightening in binaries
Date: 2012-01-01
Creator: H.E. White
T.W. Baumgarte
S.L. Shapiro
Access: Open access
The peptide hormone pQDLDHVFLRFamide (crustacean myosuppressin) modulates the Homarus americanus cardiac neuromuscular system at multiple sites
Date: 2009-12-15
Creator: J. S. Stevens
C. R. Cashman
C. M. Smith
K. M. Beale
D. W., Towle
A. E. Christie
P. S. Dickinson
Access: Open access
- pQDLDHVFLRFamide is a highly conserved crustacean neuropeptide with a structure that places it within the myosuppressin subfamily of the FMRFamide-like peptides. Despite its apparent ubiquitous conservation in decapod crustaceans, the paracrine and/or endocrine roles played by pQDLDHVFLRFamide remain largely unknown. We have examined the actions of this peptide on the cardiac neuromuscular system of the American lobster Homarus americanus using four preparations: the intact animal, the heart in vitro, the isolated cardiac ganglion (CG), and a stimulated heart muscle preparation. In the intact animal, injection of myosuppressin caused a decrease in heartbeat frequency. Perfusion of the in vitro heart with pQDLDHVFLRFamide elicited a decrease in the frequency and an increase in the amplitude of heart contractions. In the isolated CG, myosuppressin induced a hyperpolarization of the resting membrane potential of cardiac motor neurons and a decrease in the cycle frequency of their bursting. In the stimulated heart muscle preparation, pQDLDHVFLRFamide increased the amplitude of the induced contractions, suggesting that myosuppressin modulates not only the CG, but also peripheral sites. For at least the in vitro heart and the isolated CG, the effects of myosuppressin were dose-dependent (10 -9 to 10-6mol l-1 tested), with threshold concentrations (10-8-10-7 mol l-1) consistent with the peptide serving as a circulating hormone. Although cycle frequency, a parameter directly determined by the CG, consistently decreased when pQDLDHVFLRFamide was applied to all preparation types, the magnitudes of this decrease differed, suggesting the possibility that, because myosuppressin modulates the CG and the periphery, it also alters peripheral feedback to the CG.
Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide
Date: 2011-11-14
Creator: M. O. Battle
J. P. Severinghaus
E. D. Sofen
D. Plotkin
A. J., Orsi
M. Aydin
S. A. Montzka
T. Sowers
P. P. Tans
Access: Open access
- We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4-5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ∼10 m thick lock-in zone beginning at ∼67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO2 at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr-1 ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of Δage (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process. © 2011 Author(s).
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
A simple family of analytical trumpet slices of the Schwarzschild spacetime
Date: 2014-06-07
Creator: Kenneth A. Dennison
Thomas W. Baumgarte
Access: Open access
- We describe a simple family of analytical coordinate systems for the Schwarzschild spacetime. The coordinates penetrate the horizon smoothly and are spatially isotropic. Spatial slices of constant coordinate time t feature a trumpet geometry with an asymptotically cylindrical end inside the horizon at a prescribed areal radius R0 (with 0 < R0 M) that serves as the free parameter for the family. The slices also have an asymptotically flat end at spatial infinity. In the limit R0 = 0 the spatial slices lose their trumpet geometry and become flat - in this limit, our coordinates reduce to Painlevé- Gullstrand coordinates. © 2014 IOP Publishing Ltd.
Invariants for tendex and vortex fields
Date: 2012-11-08
Creator: Kenneth A. Dennison
Thomas W. Baumgarte
Access: Open access
- Tendex and vortex fields, defined by the eigenvectors and eigenvalues of the electric and magnetic parts of the Weyl curvature tensor, form the basis of a recently developed approach to visualizing spacetime curvature. In analogy to electric and magnetic fields, these fields are coordinate-dependent. However, in a further analogy, we can form invariants from the tendex and vortex fields that are invariant under coordinate transformations, just as certain combinations of the electric and magnetic fields are invariant under coordinate transformations. We derive these invariants, and provide a simple, analytical demonstration for nonspherically symmetric slices of a Schwarzschild spacetime. © 2012 American Physical Society.
Interview with Larry Pope by Andrea L’Hommedieu
Date: 2008-05-14
Creator: Laurence 'Larry' E Pope
Access: Open access
- Biographical NoteLaurence E. “Larry” Pope was born on September 24, 1945, in New Haven, Connecticut, and grew up in Braintree, Massachusetts. He attended Bowdoin College; upon graduating in 1967, he entered the Peace Corps and then the foreign service in 1969. He spent thirty-one years as a diplomat, serving as ambassador to Chad and as a political advisor to General Tony Zinni. He was the original staff director for the Sharm el-Sheikh International Fact-Finding Committee chaired by Senator George J. Mitchell. SummaryInterview includes discussion of: Braintree, Massachusetts, during the 1950s; interest in the Foreign Service; Bowdoin College; events surrounding the Iraq Liberation Act and Pope’s nomination to become ambassador to Kuwait; the Sharm el-Sheikh International Fact-Finding Committee; the fact-finding process with Israelis and Palestinians; Pope’s resignation from the commission; selecting Fred Hof as deputy staff director and later director; Senator Warren Rudman; and appointment of Khai Eide as Czar of International Reconstruction Efforts in Afghanistan.
Interview with Chuck Robb by Brien Williams
Date: 2009-08-04
Creator: Charles 'Chuck' S Robb
Access: Open access
- Biographical NoteCharles “Chuck” Robb was born on July 26, 1939, in Phoenix, Arizona, and grew up near Mount Vernon in Alexandria, Virginia. He completed his undergraduate studies at the University of Wisconsin-Madison in 1961. He joined the United States Marine Corps and was graduated with honors from Quantico. He met Lynda Bird Johnson, daughter of President Lyndon B. Johnson, when he became a White House social aide; they were married there in 1967. He served two years of combat duty in Vietnam leading a rifle company, for which he was awarded a Bronze Star. Upon his military discharge, he earned a doctor of law degree from the University of Virginia Law School in 1973. Following a clerkship with a federal appeals judge, he entered private practice as a lawyer. He served as lieutenant governor of Virginia from 1978 to 1982 and as governor of Virginia from 1982 to 1986. He was elected to the U.S. Senate and served from 1989 until 2001, was instrumental in creating the Super Tuesday primary, and co-founded the Democratic Leadership Council. In 2004, he chaired the Iraq Intelligence Commission. Since 2001, he has held the position of distinguished professor of law and public policy at George Mason University. SummaryInterview includes discussion of: Robb’s political family history; comparison of serving as governor and as senator; the work accomplished as governor; running for U.S. Senate; the CODEL to Kuwait; the founding of and involvement with the Democratic Leadership Council; the process of electing Mitchell as majority leader; Mitchell’s leadership; conflict with the Budget Committee; partisanship in the Senate; Mitchell’s position with the party spectrum; the continued growth of the DLC and recruiting Bill Clinton; Mitchell and the DLC; success as chairman of the Democratic Senatorial Campaign Committee (DSCC); Mitchell’s retirement from the Senate; Robb’s last term; the Vietnam group of six in the Senate; and George Mitchell’s legacy.
Interview with Gerry Petruccelli by Mike Hastings
Date: 2009-07-26
Creator: Gerald 'Gerry' F Petruccelli
Access: Open access
- Biographical NoteGerald F. Petruccelli was born on February 24, 1943, in Boston, Massachusetts, to Mary Rita (Madden) and Gerald F. Petruccelli, Sr. Gerry went to Archbishop Williams in Quincy, Massachusetts, and then to Boston College. He attended law school at the University of Toledo and then the University of Maine, receiving his degree from Boston College, where he was involved in Boston College’s Law Review. He served as professor of law at the University of Maine Law School from 1968-1975, lecturer from 1975-1979, and adjunct professor from 1979 to the the time of this interview. In 1971 he was a special assistant attorney general in Maine, and from 1973 to 1980 he practiced law at Preti Flaherty. Since 1980, Petruccelli has worked for Petruccelli, Martin, and Haddow, LLP in Portland, Maine. SummaryInterview includes discussion of: childhood and educational background; background in politics; description of Boston College Law School Dean Bob Dryden; becoming a member of the faculty at the University of Maine Law School; the change in Uniform Commercial Code; how Petruccelli met George Mitchell through Joe Brennan; working for Mitchell as a lawyer; the Muskie reelection in 1970; working at the district attorney’s office with Mitchell when Joe Brennan was elected; interaction with Mitchell in the Democratic primary election of 1974; working on a major marijuana importation case with Mitchell as U.S. attorney; and meeting with managers of TV stations on behalf of Mitchell in the 1982 campaign.