Crucial Physical Dependencies of the Core-Collapse Supernova Mechanism

We explore with self-consistent 2D F{\sc{ornax}} simulations the dependence of the outcome of collapse on many-body corrections to neutrino-nucleon cross sections, the nucleon-nucleon bremsstrahlung rate, electron capture on heavy nuclei, pre-collapse seed perturbations, and inelastic neutrino-electron and neutrino-nucleon scattering. Importantly, proximity to criticality amplifies the role of even small changes in the neutrino-matter couplings, and such changes can together add to produce outsized effects. When close to the critical condition the cumulative result of a few small effects (including seeds) that individually have only modest consequence can convert an anemic into a robust explosion, or even a dud into a blast. Such sensitivity is not seen in one dimension and may explain the apparent heterogeneity in the outcomes of detailed simulations performed internationally. A natural conclusion is that the different groups collectively are closer to a realistic understanding of the mechanism of core-collapse supernovae than might have seemed apparent.Comment: 25 pages; 10 figure

GYOTO: a new general relativistic ray-tracing code

GYOTO, a general relativistic ray-tracing code, is presented. It aims at computing images of astronomical bodies in the vicinity of compact objects, as well as trajectories of massive bodies in relativistic environments. This code is capable of integrating the null and timelike geodesic equations not only in the Kerr metric, but also in any metric computed numerically within the 3+1 formalism of general relativity. Simulated images and spectra have been computed for a variety of astronomical targets, such as a moving star or a toroidal accretion structure. The underlying code is open source and freely available. It is user-friendly, quickly handled and very modular so that extensions are easy to integrate. Custom analytical metrics and astronomical targets can be implemented in C++ plug-in extensions independent from the main code.Comment: 20 pages, 11 figure

Mutational analysis of the β-subunit of yeast geranylgeranyl transferase I

The gene CAL1 (also known as CDC43 ) of Saccharomyces cerevisiae encodes the β subunit of geranylgeranyl transferase I (GGTase I), which modifies several small GTPases. Biochemical analyses of the mutant-enzymes encoded by cal1 , and cdc43-2 to cdc43-7 , expressed in bacteria, have hown that all of the mutant enzymes possess reduced activity, and that none shows temerature-sensitive enzymatic activities. Nonetheless, all of the cal1/cdc43 mutants show temperature-sensitive growth phenotypes. Increase in soluble pools of the small GTPases was observed in the yeast mutant cells at the restrictive temperature in vivo, suggesting that the yeast prenylation pathway itself is temperative sensitive. The cal-1 mutation, located most proximal to the C-terminus of the protein, differs from the other cdc43 mutations in several respects. An increase in soluble Rholp was observed in the cal-1 strain grown at the restrictive temperature. The temperature-sensitive phenotype of cal-1 is most efficiently suppressed by overproduction of Rholp. Overproduction of the other essential target, Cdc42p, in contrast, is deleterious in cal-1 cells, but not in other cdc43 mutants or the wild-type strains. The cdc43-5 mutant cells accumulate Cdc42p in soluble pools and cdc43-5 is suppressed by overproduction of Cdc42p. Thus, several phenotypic differences are observed among the cal1/cdc43 mutations, possibly due to alterations in substrate specificity caused by the mutations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42258/1/438-252-1-2-1_62520001.pd