Achieving Extreme Resolution in Numerical Cosmology Using Adaptive Mesh Refinement: Resolving Primordial Star Formation

As an entry for the 2001 Gordon Bell Award in the "special" category, we describe our 3-d, hybrid, adaptive mesh refinement (AMR) code, Enzo, designed for high-resolution, multiphysics, cosmological structure formation simulations. Our parallel implementation places no limit on the depth or complexity of the adaptive grid hierarchy, allowing us to achieve unprecedented spatial and temporal dynamic range. We report on a simulation of primordial star formation which develops over 8000 subgrids at 34 levels of refinement to achieve a local refinement of a factor of 10^12 in space and time. This allows us to resolve the properties of the first stars which form in the universe assuming standard physics and a standard cosmological model. Achieving extreme resolution requires the use of 128-bit extended precision arithmetic (EPA) to accurately specify the subgrid positions. We describe our EPA AMR implementation on the IBM SP2 Blue Horizon system at the San Diego Supercomputer Center.Comment: 23 pages, 5 figures. Peer reviewed technical paper accepted to the proceedings of Supercomputing 2001. This entry was a Gordon Bell Prize finalist. For more information visit http://www.TomAbel.com/GB

The Formation of the First Star in the Universe

We describe results from a fully self-consistent three dimensional hydrodynamical simulation of the formation of one of the first stars in the Universe. Dark matter dominated pre-galactic objects form because of gravitational instability from small initidal density perturbations. As they assemble via hierarchical merging, primordial gas cools through ro-vibrational lines of hydrogen molecules and sinks to the center of the dark matter potential well. The high redshift analog of a molecular cloud is formed. When the dense, central parts of the cold gas cloud become self-gravitating, a dense core of approximately 100 solar mass undergoes rapid contraction. At densities n>10^9 cm^-3 a one solar mass proto-stellar core becomes fully molecular due to three-body H_2 formation. Contrary to analytical expectations this process does not lead to renewed fragmentation and only one star is formed. The calculation is stopped when optical depth effects become important, leaving the final mass of the fully formed star somewhat uncertain. At this stage the protostar is acreting material very rapidly (~0.01 solar masses per year). Radiative feedback from the star will not only halt its growth but also inhibit the formation of other stars in the same pre-galactic object (at least until the first star ends its life, presumably as a supernova). We conclude that at most one massive (M >> 1 solar mass) metal free star forms per pre-galactic halo, consistent with recent abundance measurements of metal poor galactic halo stars.Comment: 8 pages, 5 figures. Science. Published in Science Express online on 11/15/2001. More information can be found at http://www.TomAbel.com/GB

A COMPARISON OF NONINVASIVE SURVEY METHODS FOR MONITORING MESOCARNIVORE POPULATIONS IN KENTUCKY

Harvest data are typically used to evaluate mesocarnivore population dynamics in many states, including Kentucky. While relatively easy to collect, these data are subject to reporting biases, and inferences about population trends can often only be made at coarse spatial scales. Gray fox (Urocyon cinereoargenteus), bobcat (Lynx rufus), and coyote (Canis latrans) populations in Kentucky are managed primarily through harvest data used to establish future harvest quotas. Increasingly, noninvasive survey methods have been used to characterize a number of population parameters for a variety of species; however, successful use of these methods is often site-specific. We assessed the efficacy and cost-effectiveness of two noninvasive survey methods, scat detection dogs and rub-pad hair snares, for surveying mesocarnivore species at two sites in the mixed-mesophytic forest of northeastern Kentucky. We sampled 100 hair snares covering approximately 100km2 and 27 transects covering approximately 27km2 from which 7 hair samples and 261 scat samples were collected respectively. Hair snares cost $397/sample at 6.4 hours/day, while scat detection dogs cost$47/sample at 4.9 hours/day. Genetic methods were used to identify biological samples to species and individual. Our findings should prove useful to state wildlife managers in comparatively evaluating methods for future mesocarnivore monitoring

Improved Ball-and-Socket Docking Mechanism

A proposed docking mechanism would form a ball-and-socket joint in the docked condition. The mechanism could tolerate significant initial misalignment because it would include an alignment cone that would guide the ball into the socket. Like other ball-and-socket joints, the joint would have three rotational degrees of freedom. This docking mechanism would be a successor to the one described in Passive Capture Joint With Three Degrees of Freedom (MFS-31146), NASA Tech Briefs, Vol. 22, No. 7 (July 1998), page 65. It would contain most of the components of the prior mechanism, plus some additional components that would expand its capabilities