Nucleosynthesis in Metal-Free and Metal-Poor Stars

There have been a number of important recent developments in theoretical and observational studies of nucleosynthesis, especially regarding nucleosynthetic sources at low metallicities. Those selected for discussion here include the origin of Li6, the primary production of N, the s-process, and the supernova sources for three groups of metals: (1) C to Zn with mass numbers A<70, (2) Sr to Ag with A~90-110, and (3) r-process nuclei with A~130 and above.Comment: 8 pages, no figures, published in "Proceedings of First Stars III," Eds. Brian W. O'Shea, Alexander Heger & Tom Abe

Astrophysical Models of r-Process Nucleosynthesis: An Update

An update on astrophysical models for nucleosynthesis via rapid neutron capture, the r process, is given. A neutrino-induced r process in supernova helium shells may have operated up to metallicities of ~10^-3 times the solar value. Another r-process source, possibly neutron star mergers, is required for higher metallicities.Comment: 8 pages, invited talk given at 11th International Symposium on Origin of Matter and Evolution of Galaxies (OMEG11), Wako, Japa

Recent Progress in Understanding Nucleosynthesis via Rapid Neutron Capture

I discuss the recent progress in our understanding of nucleosynthesis via rapid neutron capture, the r-process, based on meteoritic data for the early solar system and observations of stars at low metallicities. At present, all data require that there be two distinct kinds of r-process events and suggest that supernovae are associated with these events. The diversity of supernova sources for the r-process may depend on whether a neutron star or black hole is formed in an individual supernova. This dependence, if substantiated by future observations discussed here, has important implications for properties of nuclear matter.Comment: 7 pages including 2 figures, to appear in the Proceedings of the 7th Conference on the Intersections of Particle and Nuclear Physic

Neutrino Processes in Strong Magnetic Fields

The processes of electron neutrino capture on neutron and electron anti-neutrino capture on proton, and their reverse processes provide the dominant mechanisms for heating and cooling the material below the stalled shock in a core-collapse supernova. We summarize the major effects of strong magnetic fields on the rates of the above reactions and illustrate these effects with a simple supernova model. Due to parity violation of weak interaction the heating rates are asymmetric even for a uniform magnetic field. The cooling rates are also asymmetric for nonuniform fields. The most dramatic effect of strong magnetic fields of 10^16 G is suppression of the cooling rates by changing the equations of state through the phase space of electrons and positrons.Comment: 10 pages, 4 figures, talk given at INT workshop "Open Issues in Understanding Core Collapse Supernovae," Seattle, June 200

Privacy-preserving Cross-domain Routing Optimization -- A Cryptographic Approach

Today's large-scale enterprise networks, data center networks, and wide area networks can be decomposed into multiple administrative or geographical domains. Domains may be owned by different administrative units or organizations. Hence protecting domain information is an important concern. Existing general-purpose Secure Multi-Party Computation (SMPC) methods that preserves privacy for domains are extremely slow for cross-domain routing problems. In this paper we present PYCRO, a cryptographic protocol specifically designed for privacy-preserving cross-domain routing optimization in Software Defined Networking (SDN) environments. PYCRO provides two fundamental routing functions, policy-compliant shortest path computing and bandwidth allocation, while ensuring strong protection for the private information of domains. We rigorously prove the privacy guarantee of our protocol. We have implemented a prototype system that runs PYCRO on servers in a campus network. Experimental results using real ISP network topologies show that PYCRO is very efficient in computation and communication costs