1,721 research outputs found
Atherosclerosis and calcium signalling in endothelial cells
The link between atherosclerosis and regions of disturbed flow and low wall shear
stress is now firmly established, but the causal mechanisms underlying the link are not
yet understood. It is now recognised that the endothelium is not simply a passive barrier
between the blood and the vessel wall, but plays an active role in maintaining vascular
homeostasis and participates in the onset of atherosclerosis. Calcium signalling is one of
the principal intracellular signalling mechanisms by which endothelial cells (EC) respond
to external stimuli, such as fluid shear stress and ligand binding. Previous studies have
separately modelled mass transport of chemical species in the bloodstream and calcium
dynamics in EC via the inositol triphosphate (IPâ) signalling pathway. In this study, we
integrate these two important components to provide an inclusive model for the calcium
response of the endothelium in an arbitrary vessel geometry. This enables the combined
effects of fluid flow and biochemical stimulation on EC to be investigated. Model results
show that low endothelial calcium levels in the area of disturbed flow at an arterial
widening may be one contributing factor to the onset of vascular disease
FADI: a fault-tolerant environment for open distributed computing
FADI is a complete programming environment that serves the reliable execution of distributed application programs. FADI encompasses all aspects of modern fault-tolerant distributed computing. The built-in user-transparent error detection mechanism covers processor node crashes and hardware transient failures. The mechanism also integrates user-assisted error checks into the system failure model. The nucleus non-blocking checkpointing mechanism combined with a novel selective message logging technique delivers an efficient, low-overhead backup and recovery mechanism for distributed processes. FADI also provides means for remote automatic process allocation on the distributed system nodes
A mantle melting profile across the Basin and Range, SW USA
This is the published version. Copyright 2002 American Geophysical Union. All Rights Reserved.The major and trace element composition of late Cenozoic basalts (0â10 Ma) across the Basin and Range province (B&R) preserve a clear signal of mantle melting depth variations. FeO, Fe8.0, and Tb/Yb increase, whereas Si8.0 and Al8.0 decrease, from west to east across the B&R along a profile at 36°â37°N. These variations are qualitatively consistent with shallower melting beneath the Western Great Basin (WGB) than in the central B&R. In order to quantify the depth range and percent of decompression melting, we invert primary Na2O and FeO contents of basalts using a melting model based on the partitioning of FeO and MgO in olivine and Na2O in clinopyroxene. An independent inversion, using the rare earth elements (REE), corroborates the melting depths obtained from the major element model and places most of the melting beneath the central B&R in the garnet-peridotite stability field. We find that the shape of the melting region across the B&R closely mimics the shape of the mantle lithosphere, as inferred from geological and geophysical observations. Melting across the study area occurs largely within the asthenosphere and generally stops at the base of the mantle lithosphere. In the WGB, melting paths are shallow, from 75 to 50 km, and in some cases extend almost to the base of the crust. These melting paths are consistent with adiabatic melting in normal-temperature asthenosphere, beneath an extensively thinned (or absent) mantle lithosphere. Shallow melting is consistent with geobarometry and isotopic compositions of local mantle xenoliths. Lithospheric thinning was caused by thermal erosion during Mesozoic subduction and/or simple shear or foundering during Cenozoic extension. In contrast, melting beneath the central B&R occurs beneath thick mantle lithosphere and requires mantle potential temperatures 200°C hotter than normal (melting paths from 140 to 100 km). The excess temperature beneath the central B&R is consistent with active upwelling of hot mantle in this region
Volcanic activity and gas emissions along the South Sandwich Arc
The South Sandwich Volcanic Arc is one of the most remote and enigmatic arcs on Earth. Sporadic observations from rare cloud-free satellite imagesâand even rarer in situ reportsâprovide glimpses into a dynamic arc system characterised by persistent gas emissions and frequent eruptive activity. Our understanding of the state of volcanic activity along this arc is incomplete compared to arcs globally. To fill this gap, we present here detailed geological and volcanological observations made during an expedition to the South Sandwich Islands in January 2020. We report the first in situ measurements of gas chemistry, emission rate and carbon isotope composition from along the arc. We show that Mt. Michael on Saunders Island is a persistent source of gas emissions, releasing 145â±â59 t dayâ1 SO2 in a plume characterised by a CO2/SO2 molar ratio of 1.8â±â0.2. Combining this CO2/SO2 ratio with our independent SO2 emission rate measured near simultaneously, we derive a CO2 flux of 179â±â76 t dayâ1. Outgassing from low temperature (90â100 °C) fumaroles is pervasive at the active centres of Candlemas and Bellingshausen, with measured gas compositions indicative of interaction between magmatic fluids and hydrothermal systems. Carbon isotope measurements of dilute plume and fumarole gases from along the arc indicate a magmatic ÎŽ13C of ââ4.5â±â2.0â°. Interpreted most simply, this result suggests a carbon source dominated by mantle-derived carbon. However, based on a carbon mass balance from sediment core ODP 701, we show that mixing between depleted upper mantle and a subduction component composed of sediment and altered crust is also permissible. We conclude that, although remote, the South Sandwich Volcanic Arc is an ideal tectonic setting in which to explore geochemical processes in a young, developing arc
Morphometric analyses of the visual pathways in macular degeneration
Introduction. Macular degeneration (MD) causes central visual field loss.
When field defects occur in both eyes and overlap, parts of the visual pathways
are no longer stimulated. Previous reports have shown that this affects the
grey matter of the primary visual cortex, but possible effects on the preceding
visual pathway structures have not been fully established. Method. In this
multicentre study, we used high-resolution anatomical magnetic resonance
imaging and voxel-based morphometry to investigate the visual pathway
structures up to the primary visual cortex of patients with age-related macular
degeneration (AMD) and juvenile macular degeneration (JMD). Results. Compared
to age-matched healthy controls, in patients with JMD we found volumetric
reductions in the optic nerves, the chiasm, the lateral geniculate bodies, the
optic radiations and the visual cortex. In patients with AMD we found
volumetric reductions in the lateral geniculate bodies, the optic radiations
and the visual cortex. An unexpected finding was that AMD, but not JMD, was
associated with a reduction in frontal white matter volume. Conclusion. MD is
associated with degeneration of structures along the visual pathways. A
reduction in frontal white matter volume only present in the AMD patients may
constitute a neural correlate of previously reported association between AMD
and mild cognitive impairment.
Keywords: macular degeneration - visual pathway - visual field - voxel-based
morphometryComment: appears in Cortex (2013
Central American Subduction System
Workshop to Integrate Subduction Factory and Seismogenic Zone Studies in Central America, Heredia, Costa Rica, 18â22 June 2007 The driving force for great earthquakes and the cycling of water and climate-influencing volatiles (carbon dioxide, sulfur, halogens) across the convergent margin of Central America have been a focus of international efforts for over 8 years, as part of the MARGINS program of the U.S. National Science Foundation, the Collaborative Research Center (SFB 574) of the German Science Foundation, and the Central American science community. Over 120 scientists and students from 10 countries met in Costa Rica to synthesize this intense effort spanning from land to marine geological and geophysical studies
Magma decompression rates during explosive eruptions of KiÌlauea volcano, Hawai'i, recorded by melt embayments
The decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behaviour. In this study we quantify decompression rates for basaltic magmas using volatile diffusion in olivine-hosted melt tubes (embayments) for three contrasting eruptions of KÄ«lauea volcano, Hawai'i. Incomplete exsolution of HâO, COâ and S from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques, and then modelled to infer the average decompression rate. We obtain average rates of ~0.05-0.45 MPa s-1 for eruptions ranging from Hawaiian style fountains to basaltic subplinian, with the more intense eruptions having higher rates. The ascent timescales for these magmas vary from around ~5 to ~36 minutes from depths of ~2 to ~4 km respectively. Decompression-exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre-existing exsolved volatiles within the magma body. In the eruptions studied this varies from 0.1-3.2 wt%, but does not appear to be the key control on eruptive intensity. Our results do not support a direct link between the concentration of pre-eruptive volatiles and eruptive intensity; rather they suggest that for these eruptions decompression rates are proportional to independent estimates of mass discharge rate. Although the intensity of eruptions is defined by the discharge rate, based on the currently available dataset of embayment analyses it does not appear to scale linearly with average decompression rate. This study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions
Reduced model for H-mode sustainment in unfavorable drift configuration in ASDEX Upgrade
A recently developed reduced model of H-mode sustainment based on
interchange-drift-Alfv\'en turbulence description in the vicinity of the
separatrix matching experimental observations in ASDEX Upgrade has been
extended to experiments with the unfavorable drift. The combination
with the theory of the magnetic-shear-induced Reynolds stress offers a
possibility to quantitatively explain the phenomena. The extension of the
Reynolds stress estimate in the reduced model via the magnetic shear
contribution is able to reproduce the strong asymmetry in the access conditions
depending on the ion drift orientation in agreement with
experimental observations. The Reynolds stress profile asymmetry predicted by
the magnetic shear model is further extended by comparison with GRILLIX and
GENE-X simulations matched with comparable experiments in realistic X-point
geometry. The predictions of the radial electric field well depth and its
difference between the favorable and unfavorable configurations at the same
heating power from the extended model also show consistency with experimental
measurements.Comment: Submitted to Nuclear Fusio
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