Ascertaining the Core Collapse Supernova Mechanism: An Emerging Picture?

Here we present the results from two sets of simulations, in two and three spatial dimensions. In two dimensions, the simulations include multifrequency flux-limited diffusion neutrino transport in the "ray-by-ray-plus" approximation, two-dimensional self gravity in the Newtonian limit, and nuclear burning through a 14-isotope alpha network. The three-dimensional simulations are model simulations constructed to reflect the post stellar core bounce conditions during neutrino shock reheating at the onset of explosion. They are hydrodynamics-only models that focus on critical aspects of the shock stability and dynamics and their impact on the supernova mechanism and explosion. In two dimensions, we obtain explosions (although in one case weak) for two progenitors (11 and 15 Solar mass models). Moreover, in both cases the explosion is initiated when the inner edge of the oxygen layer accretes through the shock. Thus, the shock is not revived while in the iron core, as previously discussed in the literature. The three-dimensional studies of the development of the stationary accretion shock instability (SASI) demonstrate the fundamentally new dynamics allowed when simulations are performed in three spatial dimensions. The predominant l=1 SASI mode gives way to a stable m=1 mode, which in turn has significant ramifications for the distribution of angular momentum in the region between the shock and proto-neutron star and, ultimately, for the spin of the remnant neutron star. Moreover, the three-dimensional simulations make clear, given the increased number of degrees of freedom, that two-dimensional models are severely limited by artificially imposed symmetries.Comment: 9 pages, 3 figure

Neutrino-driven supernovae: Boltzmann neutrino transport and the explosion mechanism

Core-collapse supernovae are, despite their spectacular visual display, neutrino events. Virtually all of the 10^53 ergs of gravitational binding energy released in the formation of the nascent neutron star is carried away in the form of neutrinos and antineutrinos of all three flavors, and these neutrinos are primarily responsible for powering the explosion. This mechanism depends sensitively on the neutrino transport between the neutrinospheres and the shock. In light of this, we have performed a comparison of multigroup Boltzmann neutrino transport (MGBT) and multigroup flux-limited diffusion (MGFLD) in post-core bounce environments. Differences in the mean inverse flux factors, luminosities, and RMS energies translate to heating rates that are up to 2 times larger for Boltzmann transport, with net cooling rates below the gain radius that are typically 0.8 times the MGFLD rates. These differences are greatest at earlier postbounce times for a given progenitor mass, and for a given postbounce time, greater for greater progenitor mass. The increased differences with increased progenitor mass suggest that the net heating enhancement from MGBT is potentially robust and self-regulated.Comment: 7 pages, 2 figures, 1 table; LaTex using iopconf.sty; To appear in: Proceedings of The Second Oak Ridge Symposium on Atomic & Nuclear Astrophysic

Measurement of the two-photon absorption cross-section of liquid argon with a time projection chamber

This paper reports on laser-induced multiphoton ionization at 266 nm of liquid argon in a time projection chamber (LAr TPC) detector. The electron signal produced by the laser beam is a formidable tool for the calibration and monitoring of next-generation large-mass LAr TPCs. The detector that we designed and tested allowed us to measure the two-photon absorption cross-section of LAr with unprecedented accuracy and precision: sigma_ex=(1.24\pm 0.10stat \pm 0.30syst) 10^{-56} cm^4s{-1}.Comment: 15 pages, 9 figure

Effects of Cadmium on Streams and Irrigated Agriculture in the Presence and Absence of Oil Shale Leachate

Artificial streams, soil perfusion columns, and potted plants were exposed to 20 ug Cd/l in the presence and absence of unretorted oil shale leachate. High cadmium accumulations occurred in the stream biota, but did not measurably affect community structure or function. The presence of oil shale leachate had no effect on bioaccumulation or ecosystem structure or function. Nitrification in soil columns was enhanced by the presence of the organic fraction of oil shale leachate, but this effect was not observed when cadmium was present. Crop accumulation of cadmium was somewhat higher in alfalfa and radishes irrigated with leachate, but did not cause plant concentrations that would be hazardous to livestock or human consumers

2D and 3D Core-Collapse Supernovae Simulation Results Obtained with the CHIMERA Code

Much progress in realistic modeling of core-collapse supernovae has occurred recently through the availability of multi-teraflop machines and the increasing sophistication of supernova codes. These improvements are enabling simulations with enough realism that the explosion mechanism, long a mystery, may soon be delineated. We briefly describe the CHIMERA code, a supernova code we have developed to simulate core-collapse supernovae in 1, 2, and 3 spatial dimensions. We then describe the results of an ongoing suite of 2D simulations initiated from a 12, 15, 20, and 25 solar mass progenitor. These have all exhibited explosions and are currently in the expanding phase with the shock at between 5,000 and 20,000 km. We also briefly describe an ongoing simulation in 3 spatial dimensions initiated from the 15 solar mass progenitor.Comment: 5 pages, 3 figure

Phototesting and photoprotection in LE

Photosensitivity and induction of skin lesions following UV radiation is a common problem of patients with cutaneous and systemic forms of lupus erythematosus. The detrimental effect of UV radiation to patients with lupus erythematosus was already recognized in the last century. Skin lesions can now be provoked under standardized conditions allowing the diagnosis and classification of patients with photosensitive disorders. The aim of this review is to give an overview on the history, test procedure and test results in patients with lupus erythematosus