2,380 research outputs found
Ni abundance in the core of the Perseus Cluster: an answer to the significance of resonant scattering
Using an XMM-Newton observation of the Perseus cluster we show that the
excess in the flux of the 7-8 keV line complex previously detected by ASCA and
BeppoSAX is due to an overabundance of Nickel rather than to an anomalously
high Fe He/Fe He ratio. This observational fact leads to the
main result that resonant scattering, which was assumed to be responsible for
the supposed anomalous Fe He/Fe He ratio, is no longer required.
The absence of resonant scattering points towards the presence of significant
gas motions (either turbulent or laminar) in the core of the Perseus cluster.Comment: 29 pages, 10 bw figures, accepted for publication in the
Astrophysical Journa
PILOT: a balloon-borne experiment to measure the polarized FIR emission of dust grains in the interstellar medium
Future cosmology space missions will concentrate on measuring the
polarization of the Cosmic Microwave Background, which potentially carries
invaluable information about the earliest phases of the evolution of our
universe. Such ambitious projects will ultimately be limited by the sensitivity
of the instrument and by the accuracy at which polarized foreground emission
from our own Galaxy can be subtracted out. We present the PILOT balloon project
which will aim at characterizing one of these foreground sources, the
polarization of the dust continuum emission in the diffuse interstellar medium.
The PILOT experiment will also constitute a test-bed for using multiplexed
bolometer arrays for polarization measurements. We present the results of
ground tests obtained just before the first flight of the instrument.Comment: 17 pages, 13 figures. Presented at SPIE, Millimeter, Submillimeter,
and Far-Infrared Detectors and Instrumentation for Astronomy VII. To be
published in Proc. SPIE volume 915
Computational Docking Simulations of Nitroanisole and Nitrophenol with CYP2E1
Studies have shown that CYP2E1, a cytochrome P450 enzyme containing two primary binding sites, plays a substantial role in the oxidative metabolism of many foreign substances, including the detoxification reaction of 4-nitroanisole to 4-nitrophenol. Through the advancements of the computational docking software Tripos Sybyl7.2, it has been possible to investigate the mechanism of oxidation of 4-nitroanisole. Docking modules of Sybyl7.2 software, including Surflext and molecular dynamics, have created the ability to ascertain the likely binding configurations of 4-nitranisole and its constitutional isomers in either the distal or proximal binding sites of CYP2E1. Knowing the relative binding relationships of 4-nitroanisole to the heme of the CYP2E1 plays in human oxidative metabolism of xenobiotic substances. The goal in this research was to observe the configuration of nitroanisole and its derivatives in relation to the heme of the enzyme and possibly determine a cause for the unconventional reaction kinetics of CYP2E1
Switchgrass Biomass Simulation at Diverse Sites in the Northern Great Plains of the U.S.
The Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) model, originally developed and tested in Texas, needs to be tested for switchgrass (Panicum virgatum L.) simulation in more northerly locations. The Northern Great Plains of the U.S. has regionally adapted native populations of switchgrass and has excellent potential for growing switchgrass as a biofuel crop. The objective of this study was to adjust switchgrass parameters (potential leaf area index (DMLA) and degree days to maturity (PHU)) for northern sites and populations and to validate the model against switchgrass data from diverse sites in this region. Three or 4 years of measured yield data were used from a ten field sites in North Dakota (ND), South Dakota (SD), and Nebraska (NE). ALMANAC realistically simulated mean annual switchgrass yields ranging from means of 4.75 to 9.13 Mg ha−1. Mean simulated yields were within 3%, 15%, and 9% of mean measured yields for NE, SD, and ND, respectively. Sensitivity analysis with temperature and rainfall demonstrated variable responses of potential yields depending on whether season duration, soil water, or soil nitrogen was the limiting factor at a site. ALMANAC shows promise as a useful tool for switchgrass evaluation and management in the northern Great Plains and in similar latitudes with low rainfall such as the East European Plain
Soil Carbon Storage by Switchgrass Grown for Bioenergy
Life-cycle assessments (LCAs) of switchgrass (Panicum virgatum L.) grown for bioenergy production require data on soil organic carbon (SOC) change and harvested C yields to accurately estimate net greenhouse gas (GHG) emissions. To date, nearly all information on SOC change under switchgrass has been based on modeled assumptions or small plot research, both of which do not take into account spatial variability within or across sites for an agro-ecoregion. To address this need, we measured change in SOC and harvested C yield for switchgrass fields on ten farms in the central and northern Great Plains, USA (930 km latitudinal range). Change in SOC was determined by collecting multiple soil samples in transects across the fields prior to planting switchgrass and again 5 years later after switchgrass had been grown and managed as a bioenergy crop. Harvested aboveground C averaged 2.5± 0.7 Mg C ha−1 over the 5 year study. Across sites, SOC increased significantly at 0–30 cm (P=0.03) and 0–120 cm (P=0.07), with accrual rates of 1.1 and 2.9 Mg C ha−1 year−1 (4.0 and 10.6 Mg CO2 ha−1 year−1), respectively. Change in SOC across sites varied considerably, however, ranging from −0.6 to 4.3 Mg C ha−1 year−1 for the 0–30 cm depth. Such variation in SOC change must be taken into consideration in LCAs. Net GHG emissions from bioenergy crops vary in space and time. Such variation, coupled with an increased reliance on agriculture for energy production, underscores the need for long-term environmental monitoring sites in major agro-ecoregions
Field-Scale Soil Property Changes under Switchgrass Managed for Bioenergy
The capacity of perennial grasses to affect change in soil properties is well documented but information on switchgrass (Panicum virgatum L.) managed for bioenergy is limited. An on-farm study (10 fields) in North Dakota, South Dakota, and Nebraska was sampled before switchgrass establishment and after 5 years to determine changes in soil bulk density (SBD), pH, soil phosphorus (P), and equivalent mass soil organic carbon (SOC). Changes in SBD were largely constrained to near-surface depths (0–0.05 m). SBD increased (0–0.05 m) at the Nebraska locations (mean=0.16 Mgm-3), while most South Dakota and North Dakota locations showed declines in SBD (mean=-0.18 Mgm-3; range=-0.42–0.07 Mgm-3). Soil pH change was significant at five of the 10 locations at near surface depths (0–0.05 m), but absolute changes were modest (range=-0.67–0.44 pH units). Available P declined at all sites where it was measured (North Dakota and South Dakota locations). When summed across the surface 0.3 m depth, annual decreases in available P averaged 1.5 kg P ha-1 yr-1 (range=0.5–2.8 kg P ha-1 yr-1). Averaged across locations, equivalent mass SOC increased by 0.5 and 2.4 Mg Cha-1 yr-1 for the 2500 and 10 000 Mg ha-1 soil masses, respectively. Results from this study underscore the contribution of switchgrass to affect soil property changes, though considerable variation in soil properties exists within and across locations
A protosolar nebula origin for the ices agglomerated by Comet 67P/Churyumov-Gerasimenko
The nature of the icy material accreted by comets during their formation in
the outer regions of the protosolar nebula is a major open question in
planetary science. Some scenarios of comet formation predict that these bodies
agglomerated from crystalline ices condensed in the protosolar nebula.
Concurrently, alternative scenarios suggest that comets accreted amorphous ice
originating from the interstellar cloud or from the very distant regions of the
protosolar nebula. On the basis of existing laboratory and modeling data, we
find that the N/CO and Ar/CO ratios measured in the coma of the Jupiter
family comet 67P/Churyumov-Gerasimenko by the ROSINA instrument aboard the
European Space Agency's Rosetta spacecraft match those predicted for gases
trapped in clathrates. If these measurements are representative of the bulk
N/CO and Ar/CO ratios in 67P/Churyumov-Gerasimenko, it implies that the
ices accreted by the comet formed in the nebula and do not originate from the
interstellar medium, supporting the idea that the building blocks of outer
solar system bodies have been formed from clathrates and possibly from pure
crystalline ices. Moreover, because 67P/Churyumov-Gerasimenko is impoverished
in Ar and N, the volatile enrichments observed in Jupiter's atmosphere
cannot be explained solely via the accretion of building blocks with similar
compositions and require an additional delivery source. A potential source may
be the accretion of gas from the nebula that has been progressively enriched in
heavy elements due to photoevaporation.Comment: The Astrophysical Journal Letters, in pres
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In Search of the Solar Wind Nitrogen Isotope Composition: Analysis of a Gold Plate from the Genesis Spacecraft Concentrator
We report N isotope analysis of a gold plate from the Genesis spacecraft concentrator. We did not find evidence for a light N component in the solar wind
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