1,511 research outputs found
XMM-Newton observations of HESS J1813-178 reveal a composite Supernova remnant
We present X-ray and 12CO(J=1-0) observations of the very-high-energy (VHE)
gamma-ray source HESS J1813-178 with the aim of understanding the origin of the
gamma-ray emission. Using this dataset we are able to undertake spectral and
morphological studies of the X-ray emission from this object with greater
precision than previous studies. NANTEN 12CO(J=1-0) data are used to search for
correlations of the gamma-ray emission with molecular clouds which could act as
target material for gamma-ray production in a hadronic scenario. The NANTEN
12CO(J=1-0) observations show a giant molecular cloud of mass 2.5 10^5
M_{\sun} at a distance of 4 kpc in the vicinity of HESS J1813-178. Even
though there is no direct positional coincidence, this giant cloud might have
influenced the evolution of the gamma-ray source and its surroundings. The
X-ray data show a highly absorbed non-thermal X-ray emitting object coincident
with the previously known ASCA source AX J1813-178 showing a compact core and
an extended tail towards the north-east, located in the centre of the radio
shell-type Supernova remnant (SNR) G12.82-0.2. This central object shows
morphological and spectral resemblance to a Pulsar Wind Nebula (PWN) and we
therefore consider that the object is very likely to be a composite SNR. We
discuss the scenario in which the gamma-rays originate in the shell of the SNR
and the one in which they originate in the central object. We demonstrate, that
in order to connect the core X-ray emission to the VHE gamma-ray emission
electrons have to be accelerated to energies of at least 1 PeV.Comment: Submitted to A&
Transcriptional control of glyoxalase 1 by Nrf2 provides a stress-responsive defence against dicarbonyl glycation
Abnormal cellular accumulation of the dicarbonyl metabolite MG (methylglyoxal) occurs on exposure to high glucose concentrations, inflammation, cell aging and senescence. It is associated with increased MG-adduct content of protein and DNA linked to increased DNA strand breaks and mutagenesis, mitochondrial dysfunction and ROS (reactive oxygen species) formation and cell detachment from the extracellular matrix. MG-mediated damage is countered by glutathione-dependent metabolism by Glo1 (glyoxalase 1). It is not known, however, whether Glo1 has stress-responsive up-regulation to counter periods of high MG concentration or dicarbonyl stress. We identified a functional ARE (antioxidant-response element) in the 5'-untranslated region of exon 1 of the mammalian Glo1 gene. Transcription factor Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2) binds to this ARE, increasing basal and inducible expression of Glo1. Activators of Nrf2 induced increased Glo1 mRNA, protein and activity. Increased expression of Glo1 decreased cellular and extracellular concentrations of MG, MG-derived protein adducts, mutagenesis and cell detachment. Hepatic, brain, heart, kidney and lung Glo1 mRNA and protein were decreased in Nrf2-/- mice, and urinary excretion of MG protein and nucleotide adducts were increased approximately 2-fold. We conclude that dicarbonyl stress is countered by up-regulation of Glo1 in the Nrf2 stress-responsive system, protecting protein and DNA from increased damage and preserving cell function
Nonthermal X-radiation of SNR RX J1713.7-3946: The Relations to a Nearby Molecular Cloud
The recent X-ray and CO observations of RX J1713.7-3946 show that a
significant fraction of the nonthermal X-ray emission of this unique supernova
remnant associates, in one way or another, with a molecular cloud interacting
with the west part of the shell. This adds a new puzzle in the origin of X-ray
emission which cannot be easily explained within the standard model in
accordance of which X-rays are result of synchrotron radiation of multi-TeV
electrons accelerated by supernova shock waves. We explore an alternative
origin of the X-ray emission assuming that it is produced by secondary
electrons resulting from high energy hadronic interactions in the molecular
gas. Such a scenario could explain in a quite natural way the apparent
correlation between the X-ray and CO morphologies. However, the TeV gamma-ray
emission recently reported by H.E.S.S. significantly constrains the parameter
space of this model. Namely, this mechanism cannot reproduce the bulk of the
observed X-ray flux unless one postulates existence of a PeV cosmic-ray
component penetrating with an unusually hard spectrum into the dense cloud.Comment: 6 pages, 3 figures, to appear in Proc. of Int. Symp. on High Energy
Gamma-ray Astronomy, Heidelberg (July 2004
The multi-band nonthermal emission from the supernova remnant RX J1713.7-3946
Nonthermal X-rays and very high-energy (VHE) -rays have been detected
from the supernova remnant (SNR) RX J1713.7-3946, and especially the recent
observations with the \textit{Suzaku} satellite clearly reveal a spectral
cutoff in the X-ray spectrum, which directly relates to the cutoff of the
energy spectrum of the parent electrons. However, whether the origin of the VHE
-rays from the SNR is hadronic or leptonic is still in debate. We
studied the multi-band nonthermal emission from RX J1713.7-3946 based on a
semi-analytical approach to the nonlinear shock acceleration process by
including the contribution of the accelerated electrons to the nonthermal
radiation. The results show that the multi-band observations on RX J1713.7-3946
can be well explained in the model with appropriate parameters and the TeV
-rays have hadronic origin, i.e., they are produced via proton-proton
(p-p) interactions as the relativistic protons accelerated at the shock collide
with the ambient matter.Comment: 6 pages, 5 figures, accepted by MNRA
Life-cycle assessment of domestic and transboundary recycling of post-consumer PET bottles
Abstract Background, aim, and scope In recent years, besides being recycled domestically, a part of Japanese post-consumer polyethylene terephthalate (PET) bottles have been exported to and recycled in mainland China. In this study, life-cycle assessment (LCA) was applied to compare domestic and transboundary recycling scenarios between Japan and China and disposal scenarios from the viewpoints of greenhouse gases (GHG) emission and fossil resource consumption. Methods The following 10 scenarios based on our field surveys were evaluated: Japanese post-consumer PET bottles are (i) recycled into polyester staple in Japan, (ii) recycled into polyester filaments in Japan, (iii) recycled into polyester clothes in Japan, (iv) chemically decomposed and recycled into bottle-grade PET resin in Japan, (v) chemically decomposed and recycled into polyester filaments in Japan, (vi)-(vii) recycled into polyester staple via two different flows in China, (viii) recycled into polyester clothes in China, (ix) incinerated and partly recovered as electricity in Japan, and (x) directly landfilled in Japan. In all the evaluated scenarios, the functional unit is the recycling or disposal of 1 kg of Japanese post-consumer PET bottles. The system boundaries range from waste collection by municipalities to the manufacture of recycled products that can be regarded as substitutes for virgin products, and a credit for the avoided production of equivalent virgin products is given to each scenario. The inventories of both foreground and background processes in Japan were quoted from published reports and databases. The actual conditions of PET bottle recycling that were obtained through field surveys in China were reflected to some inventories of foreground processes in China. The inventories of public electricity supplies in China were based on the national statistics, and the inventories of petroleum products, industrial water supply, and waste treatment are based on our field surveys in China. Other unknown inventories in China were substituted by corresponding inventories in Japan. Results and discussion The results showed that all the domestic and transboundary recycling scenarios had smaller GHG emissions and fossil resource consumptions than the incineration scenario and that the chemical recycling scenarios had larger GHG emissions and fossil resource consumptions than the other recycling scenarios. The landfilling scenario had the largest fossil resource consumption, while it was better than the incineration scenario and slightly better than the chemical recycling scenarios from the viewpoint of GHG emission. The robustness of the results was examined, and it was found that the differences in GHG emission and fossil resource consumption between the domestic and transboundary recycling scenarios, other than the scenarios including cloth-manufacturing processes in system boundaries, were sufficiently large to be robust against the variability of background parameters for electricity supplies. As for the Responsible editor: Shabbir Gheewala Electronic supplementary material The online version of this articl
Comparison between classical potentials and ab initio for silicon under large shear
The homogeneous shear of the {111} planes along the direction of bulk
silicon has been investigated using ab initio techniques, to better understand
the strain properties of both shuffle and glide set planes. Similar
calculations have been done with three empirical potentials, Stillinger-Weber,
Tersoff and EDIP, in order to find the one giving the best results under large
shear strains. The generalized stacking fault energies have also been
calculated with these potentials to complement this study. It turns out that
the Stillinger-Weber potential better reproduces the ab initio results, for the
smoothness and the amplitude of the energy variation as well as the
localization of shear in the shuffle set
Electronic structure of periodic curved surfaces -- topological band structure
Electronic band structure for electrons bound on periodic minimal surfaces is
differential-geometrically formulated and numerically calculated. We focus on
minimal surfaces because they are not only mathematically elegant (with the
surface characterized completely in terms of "navels") but represent the
topology of real systems such as zeolites and negative-curvature fullerene. The
band structure turns out to be primarily determined by the topology of the
surface, i.e., how the wavefunction interferes on a multiply-connected surface,
so that the bands are little affected by the way in which we confine the
electrons on the surface (thin-slab limit or zero thickness from the outset).
Another curiosity is that different minimal surfaces connected by the Bonnet
transformation (such as Schwarz's P- and D-surfaces) possess one-to-one
correspondence in their band energies at Brillouin zone boundaries.Comment: 6 pages, 8 figures, eps files will be sent on request to
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