Explosion and nucleosynthesis of low redshift pair instability supernovae

Both recent observations and stellar evolution models suggest that pair-instability supernovae (PISNe) could occur in the local Universe, at metallicities below Z_Sun/3. Previous PISN models were mostly produced at very low metallicities in the context of the early Universe. We present new PISNe models at a metallicity of Z=0.001, which are relevant for the local Universe. We take the self-consistent stellar evolutionary models of pair-instability progenitors with initial masses of 150 and 250 solar masses at metallicity of Z=0.001 by Langer et al. (2007) and follow the evolution of these models through the supernova explosions, using a hydrodynamics stellar evolution code with an extensive nuclear network including 200 isotopes. Both models explode as PISNe without leaving a compact stellar remnant. Our models produce a nucleosynthetic pattern that is generally similar to that of Population III PISN models, which is mainly characterized by the production of large amounts of alpha-elements and a strong deficiency of the odd-charged elements. However, the odd-even effect in our models is significantly weaker than that found in Population III models. The comparison with the nucleosynthetic yields from core-collapse supernovae at a similar metallicity (Z=0.002) indicates that PISNe could have strongly influenced the chemical evolution below Z=0.002, assuming a standard initial mass function. The odd-even effect is predicted to be most prominent for the intermediate mass elements between silicon and calcium. With future observations of chemical abundances in Population II stars, our result can be used to constrain the number of PISNe that occurred during the past evolution of our Galaxy.Comment: 10 pages, 13 figures, 3 tables. Accepted by Astronomy & Astrophysic

A DYNAMIC RESPONSE ANALYSIS FOR THE U.S. ROUGH RICE MARKET

This study provides a comparative evaluation of VARs versus structural VARs for policy analysis and simulation via impulse response analysis (IRA). The IRA is valuable information for rice market participants as these results provide an economically intuitive explanation of adjustments that occur as a result of shocks to the market.Marketing,

A Sequential Rationality and Efficiency Test of U.S. Department of Agriculture Program Crop Price Estimates: Rice, Wheat, and Soybeans

This paper examines the USDA price estimates of rice, wheat, and soybeans and whether spot commodity prices reflect price information embodied in USDA estimates. Results indicate that the monthly USDA estimates are failed to meet a rationality condition. Rice and wheat actual prices marginally incorporate the information embodied in USDA past price estimates.Agricultural and Food Policy, Research Methods/ Statistical Methods, Crop Production/Industries,