Can life survive Gamma-Ray Bursts in the high-redshift universe?

Nearby Gamma-Ray Bursts (GRBs) have been proposed as a possible cause of mass extinctions on Earth. Due to the higher event rate of GRBs at higher redshifts, it has been speculated that life as we know it may not survive above a certain redshift (e.g. $z>0.5$). We examine the duty cycle of lethal (life-threatening) GRBs in the solar neighborhood, in the Sloan Digital Sky Survey (SDSS) galaxies and GRB host galaxies, with the dependence of the long GRB rate on star formation and metallicity properly taken into account. We find that the number of lethal GRBs attacking Earth within the past 500 Myr ($\sim$ epoch of the Ordovician mass extinction) is $0.93$. The number of lethal GRBs hitting a certain planet increases with redshift, thanks to the increasing star formation rate and decreasing metallicity in high-$z$ galaxies. Taking 1 per 500 Myr as a conservative duty cycle for life to survive, as evidenced by our existence, we find that there are still a good fraction of SDSS galaxies beyond $z=0.5$ where the GRB rate at half-mass radius is lower than this value. We derive the fraction of such benign galaxies as a function of redshift through Monte Carlo simulations, and find that the fraction is $\sim 50\%$ at $z\sim 1.5$ and $\sim 10\%$ even at $z \sim 3$. The mass distribution of benign galaxies is dominated by Milky-Way-like ones, thanks to their commonness, relatively large mass, and low star formation rate. GRB host galaxies are among the most dangerous ones.Comment: Accepted for publication in The Astrophysical Journal, 7 pages, 4 figures, 1 tabl

Simultaneous tolerance synthesis for manufacturing and quality.

Tolerance synthesis attempts to minimize the manufacturing cost of a product by specifying an optimal set of tolerances without compromising product performance. Concurrent engineering is a new approach in product design. Tolerancing is a bridge among design, manufacturing and quality engineers and plays a key role in concurrent engineering. Since cost and quality are fundamental product issues, simultaneous tolerance synthesis for manufacturing and quality is an excellent way to implement concurrent engineering. In this thesis, a new tolerance synthesis method, Simultaneous Tolerance Synthesis for Manufacturing and Quality (STSMQ), is presented. A nonlinear optimization model is constructed to implement this method. In this model, the manufacturing cost and quality loss are combined together into a single objective function. Both process tolerance and design tolerance are chosen as decision variables. The manufacturing cost decreases as tolerance is loosened while the quality loss increases as tolerance is loosened. The purpose of this model is to balance both manufacturing cost and quality loss to achieve optimum design tolerances and process tolerances under the minimum total cost of manufacturing and quality loss. A procedure of implementation of this model is also included. The proposed method is tested by some examples. The results show that a significant reduction in total cost in manufacturing and quality loss is obtained compared to other techniques.Dept. of Industrial and Manufacturing Systems Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1998 .Y4. Source: Masters Abstracts International, Volume: 43-05, page: 1791. Adviser: F. Salustri. Thesis (M.A.Sc.)--University of Windsor (Canada), 1999

The FRB 121102 Host Is Atypical among Nearby Fast Radio Bursts

We search for host galaxy candidates of nearby fast radio bursts (FRBs), FRB 180729.J1316+55, FRB 171020, FRB 171213, FRB 180810.J1159+83, and FRB 180814.J0422+73 (the second repeating FRB). We compare the absolute magnitudes and the expected host dispersion measure DMhost of these candidates with that of the first repeating FRB, FRB 121102, as well as those of long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe), the proposed progenitor systems of FRB 121102. We find that while the FRB 121102 host is consistent with those of LGRBs and SLSNe, the nearby FRB host candidates, at least for FRB 180729.J1316+55, FRB 171020, and FRB 180814.J0422+73, either have a smaller DMhost or are fainter than FRB 121102 host, as well as the hosts of LGRBs and SLSNe. In order to avoid the uncertainty in estimating DMhost due to the line-of-sight effect, we propose a galaxy-group-based method to estimate the electron density in the intergalactic regions, and hence, DMIGM. The result strengthens our conclusion. We conclude that the host galaxy of FRB 121102 is atypical, and LGRBs and SLSNe are likely not the progenitor systems of at least most nearby FRB sources. The recently reported two FRB hosts differ from the host of FRB 121102 and also the host candidates suggested in this paper. This is consistent with the conclusion of our paper and suggests that the FRB hosts are very diverse