214 research outputs found
Shanidar Cave and the Baradostian, a Zagros Aurignacian industry
Whilst there has been significant interest in the origins and spread of the Aurignacian industry, usually linked with the physical dispersal of anatomically modern humans into Europe, comparatively little attention has been paid to possible origins or movements further east. Recent work at Shanidar Cave, a site better known for the Neanderthal evidence discovered by Ralph Solecki in his 1951–1960 excavations, has recovered new information on the “Baradostian” Upper Palaeolithic in Iraq. This paper reviews the regional evidence for the Baradostian as an example of the Zagros Aurignacian and discusses its place in debates about Neanderthal/Modern Human relations.The financial support of the Leverhulme Trust (Research Grant RPG-2013-105), the Rust Family Foundation, and Natural Environment Research Council's Oxford Radiocarbon Dating Facility (grant NF/2016/2/14) is also gratefully acknowledged
Non-invasive Estimation of Metabolic Uptake Rate of Glucose using F18-FDG PET and Linear Transformation of Outputs
Coronal emission from the shocked circumstellar ring of SN 1987A
High resolution spectra with UVES/VLT of SN 1987A from December 2000 until
November 2005 show a number of high ionization lines from gas with velocities
of roughly 350 km/s, emerging from the shocked gas formed by the ejecta-ring
collision. These include coronal lines from [Fe X], [Fe XI] and [Fe XIV] which
have increased by a factor of about 20 during the observed period. The
evolution of the lines is similar to that of the soft X-rays, indicating that
they arise in the same component. The line ratios are consistent with those
expected from radiative shocks with velocity 310-390 km/s, corresponding to a
shock temperature of (1.6-2.5) x 10^6 K. A fraction of the coronal emission
may, however, originate in higher velocity adiabatic shocks.Comment: 11 pages, 10 figures, accepted for publication in A&
Non-spherical core collapse supernovae III. Evolution towards homology and dependence on the numerical resolution
(abridged) We study the hydrodynamic evolution of a non-spherical
core-collapse supernova in two spatial dimensions. We find that our model
displays a strong tendency to expand toward the pole. We demonstrate that this
expansion is a physical property of the low-mode, SASI instability. The SASI
leaves behind a large lateral velocity gradient in the post shock layer which
affects the evolution for minutes and hours later. This results in a prolate
deformation of the ejecta and a fast advection of Ni-rich material from
moderate latitudes to the polar regions. This effect might actually be
responsible for the global asymmetry of the nickel lines in SN 1987A. The
simulations demonstrate that significant radial and lateral motions in the
post-shock region, produced by convective overturn and the SASI during the
early explosion phase, contribute to the evolution for minutes and hours after
shock revival. They lead to both later clump formation, and a significant
prolate deformation of the ejecta which are observed even as late as one week
after the explosion. As pointed out recently by Kjaer et al., such an ejecta
morphology is in good agreement with the observational data of SN 1987A.
Systematic future studies are needed to investigate how the SASI-induced
late-time lateral expansion depends on the dominant mode of the SASI, and to
which extent it is affected by the dimensionality of the simulations. The
impact on and importance of the SASI for the distribution of iron group nuclei
and the morphology of the young SNR argues for future three-dimensional
explosion and post-explosion studies on singularity-free grids that cover the
entire sphere. Given the results of our 2D resolution study, present 3D
simulations must be regarded as underresolved, and their conclusions must be
verified by a proper numerical convergence analysis in three dimensions.Comment: 16 pages, 20 figures, accepted for publication in Astronomy &
Astrophysic
Introducing WikiPathways as a Data-Source to Support Adverse Outcome Pathways for Regulatory Risk Assessment of Chemicals and Nanomaterials
A paradigm shift is taking place in risk assessment to replace animal models, reduce the number of economic resources, and refine the methodologies to test the growing number of chemicals and nanomaterials. Therefore, approaches such as transcriptomics, proteomics, and metabolomics have become valuable tools in toxicological research, and are finding their way into regulatory toxicity. One promising framework to bridge the gap between the molecular-level measurements and risk assessment is the concept of adverse outcome pathways (AOPs). These pathways comprise mechanistic knowledge and connect biological events from a molecular level toward an adverse effect outcome after exposure to a chemical. However, the implementation of omics-based approaches in the AOPs and their acceptance by the risk assessment community is still a challenge. Because the existing modules in the main repository for AOPs, the AOP Knowledge Base (AOP-KB), do not currently allow the integration of omics technologies, additional tools are required for omics-based data analysis and visualization. Here we show how WikiPathways can serve as a supportive tool to make omics data interoperable with the AOP-Wiki, part of the AOP-KB. Manual matching of key events (KEs) indicated that 67% could be linked with molecular pathways. Automatic connection through linkage of identifiers between the databases showed that only 30% of AOP-Wiki chemicals were found on WikiPathways. More loose linkage through gene names in KE and Key Event Relationships descriptions gave an overlap of 70 and 71%, respectively. This shows many opportunities to create more direct connections, for example with extended ontology annotations, improving its interoperability. This interoperability allows the needed integration of omics data linked to the molecular pathways with AOPs. A new AOP Portal on WikiPathways is presented to allow the community of AOP developers to collaborate and populate the molecular pathways that underlie the KEs of AOP-Wiki. We conclude that the integration of WikiPathways and AOP-Wiki will improve risk assessment because omics data will be linked directly to KEs and therefore allow the comprehensive understanding and description of AOPs. To make this assessment reproducible and valid, major changes are needed in both WikiPathways and AOP-Wiki
Modeling the X-ray emission of SN 1993J
We investigate the effects of radiative shocks on the observed X-ray emission
from the Type II supernova SN 1993J. To this end, the X-ray emission is modeled
as a result of the interaction between the supernova ejecta and a dense
circumstellar medium at an age of 8 years. The circumstances under which the
reverse shock is radiative are discussed and the observed X-ray emission is
analyzed using the numerical code described in Nymark et al. (2006). We argue
that the original analysis of the X-ray observations suffered from the lack of
self-consistent models for cooling shocks with high density and velocity,
leading to questionable conclusions about the temperatures and elemental
abundances. We reanalyze the spectra with our numerical model, and discuss the
expected spectra for different explosion models for the progenitors. We find
that the spectra of SN 1993J are compatible with a CNO-enriched composition and
that the X-ray flux is dominated by the reverse shock.Comment: 12 pages, 7 figures, 3 tables. Accepted for publication in A&
Massive stars as thermonuclear reactors and their explosions following core collapse
Nuclear reactions transform atomic nuclei inside stars. This is the process
of stellar nucleosynthesis. The basic concepts of determining nuclear reaction
rates inside stars are reviewed. How stars manage to burn their fuel so slowly
most of the time are also considered. Stellar thermonuclear reactions involving
protons in hydrostatic burning are discussed first. Then I discuss triple alpha
reactions in the helium burning stage. Carbon and oxygen survive in red giant
stars because of the nuclear structure of oxygen and neon. Further nuclear
burning of carbon, neon, oxygen and silicon in quiescent conditions are
discussed next. In the subsequent core-collapse phase, neutronization due to
electron capture from the top of the Fermi sea in a degenerate core takes
place. The expected signal of neutrinos from a nearby supernova is calculated.
The supernova often explodes inside a dense circumstellar medium, which is
established due to the progenitor star losing its outermost envelope in a
stellar wind or mass transfer in a binary system. The nature of the
circumstellar medium and the ejecta of the supernova and their dynamics are
revealed by observations in the optical, IR, radio, and X-ray bands, and I
discuss some of these observations and their interpretations.Comment: To be published in " Principles and Perspectives in Cosmochemistry"
Lecture Notes on Kodai School on Synthesis of Elements in Stars; ed. by Aruna
Goswami & Eswar Reddy, Springer Verlag, 2009. Contains 21 figure
X-ray emission from radiative shocks in Type II supernovae
The X-ray emission from the circumstellar interaction in Type II supernovae
with a dense circumstellar medium is calculated. In Type IIL and Type IIn
supernovae mass loss rates are generally high enough for the region behind the
reverse shock to be radiative, producing strong radiation, particularly in
X-rays. We present a model for the emission from the cooling region in the case
of a radiative reverse shock. Under the assumption of a stationary flow, a
hydrodynamic model is combined with time dependent ionization balance and
multilevel calculations. The applicability of the steady state approximation is
discussed for various values of the ejecta density gradient and different sets
of chemical composition. We show how the emerging spectrum depends strongly on
the reverse shock velocity and the composition of the shocked gas. We discuss
differences between a spectrum produced by this model and a single-temperature
spectrum. Large differences for especially the line emission are found, which
seriously can affect abundance estimates. We also illustrate the effects of
absorption in the cool shocked ejecta. The applicability of our model for
various types of supernovae is discussed.Comment: 25 pages, 15 figures, 4 tables. Accepted for publication in A&
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