337 research outputs found
Atmospheric Pco2 Perturbations Associated with the Central Atlantic Magmatic Province
The effects of a large igneous province on the concentration of atmospheric carbon dioxide (Pco2) are mostly unknown. In this study, we estimate Pco2 from stable isotopic values of pedogenic carbonates interbedded with volcanics of the Central Atlantic Magmatic Province (CAMP) in the Newark Basin, eastern North America. We find pre-CAMP Pco2 values of ~2000 parts per million (ppm), increasing to ~4400 ppm immediately after the first volcanic unit, followed by a steady decrease toward pre-eruptive levels over the subsequent 300 thousand years, a pattern that is repeated after the second and third flow units. We interpret each Pco2 increase as a direct response to magmatic activity (primary outgassing or contact metamorphism). The systematic decreases in Pco2 after each magmatic episode probably reflect consumption of atmospheric CO2 by weathering of silicates, stimulated by fresh CAMP volcanics
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A 30 Myr record of Late Triassic atmospheric pCO2 variation reflects a fundamental control of the carbon cycle by changes in continental weathering.
We generate a detailed âź30 Myr record of pCO2 spanning most of the Late Triassic (Carnian-Norian-Rhaetian) to earliest Jurassic (Hettangian), based on stable carbon isotope ratios of soil carbonate and preserved organic matter from paleosols in the eastern North American Newark rift basin. Atmospheric pCO2 was near 4500 ppm in the late Carnian, decreasing to below âź2000 ppm by the late Rhaetian just before the earliest Jurassic eruption of the Central Atlantic Magmatic Province, which triggered measurable pulses of CO2 outgassing. These data are consistent with published modeling results using the GEOCLIM model, which predict a decrease in pCO2 over the Late Triassic as a result of the progressive increase in continental area subject to the intense weathering regime of the tropical humid belt due to Pangeaâs northward motion. The finer-scale pCO2 changes we observe may be dependent on the lithology introduced to the tropics, such as the dip to âź2000 ppm around 212 Ma and its rebound to âź4000 ppm at 209 Ma, which can be accomplished by introducing a more weatherable subaerial basaltic terrain. These observations indicate that the consumption of CO2 by continental silicate weathering can force long-term changes in pCO2 comparable to those driven by presumed changes in mantle degassing
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Rampino and Caldeira argue that the first pulse of the Central Atlantic Magmatic Province would increase the concentration of atmospheric carbon dioxide (PCO2) by only 400 parts per million if erupted over 20,000 years, whereas we observed a doubling within this interval. In the absence of any data to the contrary, we suggest that a more rapid (â¤1000-year) eruption is sufficient to explain this observation without relying on thermogenic degassing
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Rapid emplacement of the Central Atlantic Magmatic Province as a net sink for CO2
Recent evidence from the ~ 201.5 Ma Central Atlantic Magmatic Province (CAMP) in the Newark rift basin demonstrates that this Large Igneous Province produced a transient doubling of atmospheric pCO2, followed by a falloff to pre-eruptive concentrations over ~ 300 kyr. This paper confirms the short-term findings from the Newark basin, and tests the million-year effects of the CAMP volcanism on Early Jurassic pCO2 from strata in the corollary Hartford basin of Eastern North America (ENA) also using the pedogenic carbonate paleobarometer. We find pCO2 levels for pre-CAMP background of 2000 Âą 700 ppm (at S(z) = 3000 Âą 1000 ppm), increasing to ~ 5000 Âą 1700 ppm immediately above the first lava flow unit, consistent with observations from the Newark. The longer post-extrusive Portland Formation of the Hartford basin records a fourth pulse of pCO2 to ~ 4500 Âą 1200 ppm, about 240 kyr after the last lava recorded in the ENA section. We interpret this fourth increase as due to a major episode of volcanism, and revise the main CAMP duration to 840 Âą 60 kyr. The Portland also records a post-eruptive decrease in pCO2 reaching pre-eruptive background concentrations of ~ 2000 ppm in only ~ 300 kyr, and continuing to levels below pre-CAMP background over the subsequent 1.5 Myr following the final episode of eruptions. Geochemical modeling (using modified COPSE code) demonstrates that the rapidity of the pCO2 decreases, and fall to concentrations below background can be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the CAMP basalts themselves. These results demonstrate that a continental flood basalt capable of producing a short-term perturbation of the carbon system may actually have an overall net-cooling effect on global climates due to a long-term net-decrease in pCO2 to below pre-eruptive levels, as previous models have suggested followed the emplacement of the Deccan Traps
Does facial soft tissue protect against zygomatic fractures?: results of a finite element analysis
Introduction: Zygomatic fractures form a major entity in craniomaxillofacial traumatology. Few studies have dealt with biomechanical basics and none with the role of the facial soft tissues. Therefore this study should investigate, whether facial soft tissue plays a protecting role in lateral midfacial trauma
On the nature of the galactic early-B hypergiants
Despite their importance to a number of astrophysical fields, the lifecycles
of very massive stars are still poorly defined. In order to address this
shortcoming, we present a detailed quantitative study of the physical
properties of four early-B hypergiants (BHGs); Cyg OB2 #12, zeta Sco, HD190603
and BP Cru. These are combined with an analysis of their long-term
spectroscopic and photometric behaviour in order to determine their
evolutionary status. The long-term datasets revealed that they are remarkably
stable over long periods (>40yr), with the possible exception of zeta Sco prior
to the 20th century, in contrast to the typical excursions that characterise
luminous blue variables (LBVs). Zeta Sco, HD190603 and BP Cru possess physical
properties intermediate between B supergiants and LBVs; we therefore suggest
that BHGs are the immediate descendants and progenitors (respectively) of such
stars (for initial masses in the range ~30-60Msun). In contrast, while the wind
properties of Cyg OB2 #12 are consistent with this hypothesis, the combination
of extreme luminosity and spectroscopic mass (~110Msun) and comparatively low
temperature means it cannot be accommodated in such a scheme. Likewise, despite
its co-location with several LBVs above the Humphreys-Davidson (HD) limit, the
lack of long term variability and its unevolved chemistry apparently excludes
such an identification. Since such massive stars are not expected to evolve to
such cool temperatures, the properties of Cyg OB2 #12 are difficult to
understand under current evolutionary paradigms. [ABRIDGED]Comment: 36 pages, 19 figures (of which 17 pages are online supplemental
material). Accepted for publication in Astronomy and Astrophysic
Histamine H4 receptor antagonism diminishes existing airway inflammation and dysfunction via modulation of Th2 cytokines
<p>Abstract</p> <p>Background</p> <p>Airway remodeling and dysfunction are characteristic features of asthma thought to be caused by aberrant production of Th2 cytokines. Histamine H<sub>4 </sub>receptor (H<sub>4</sub>R) perturbation has previously been shown to modify acute inflammation and Th2 cytokine production in a murine model of asthma. We examined the ability of H<sub>4</sub>R antagonists to therapeutically modify the effects of Th2 cytokine production such as goblet cell hyperplasia (GCH), and collagen deposition in a sub-chronic model of asthma. In addition, effects on Th2 mediated lung dysfunction were also determined.</p> <p>Methods</p> <p>Mice were sensitized to ovalbumin (OVA) followed by repeated airway challenge with OVA. After inflammation was established mice were dosed with the H<sub>4</sub>R antagonist, JNJ 7777120, or anti-IL-13 antibody for comparison. Airway hyperreactivity (AHR) was measured, lungs lavaged and tissues collected for analysis.</p> <p>Results</p> <p>Therapeutic H<sub>4</sub>R antagonism inhibited T cell infiltration in to the lung and decreased Th2 cytokines IL-13 and IL-5. IL-13 dependent remodeling parameters such as GCH and lung collagen were reduced. Intervention with H<sub>4</sub>R antagonist also improved measures of central and peripheral airway dysfunction.</p> <p>Conclusions</p> <p>These data demonstrate that therapeutic H<sub>4</sub>R antagonism can significantly ameliorate allergen induced, Th2 cytokine driven pathologies such as lung remodeling and airway dysfunction. The ability of H<sub>4</sub>R antagonists to affect these key manifestations of asthma suggests their potential as novel human therapeutics.</p
Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC
Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H âÎł Îł, H â Z Zâ â4l and H âW Wâ âlνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of âs = 7 TeV and âs = 8 TeV, corresponding to an integrated luminosity of about 25 fbâ1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined ďŹts probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson
Standalone vertex ďŹnding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at âs = 7 TeV collected with the ATLAS detector at the LHC during 2011
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