Events at Physics |
Events on Tuesday, April 15th, 2008
- Chaos & Complex Systems Seminar
- Chaotic dynamics on large networks
- Time: 12:05 pm
- Place: 4274 Chamberlin Hall
- Speaker: Clint Sprott, UW Department of Physics
- Abstract: Many systems in nature are governed by a large number of agents that interact nonlinearly through complex feedback loops. When the networks are sufficiently large and interconnected, they typically exhibit self-organization and chaos. This talk describes the results of computer simulations of such large networks and shows the conditions under which chaos can be expected for an unweighted network of ordinary differential equations with sigmoidal nonlinearities and unit coupling. The largest Lyapunov exponent is used as the signature and measure of chaos, and the study includes the effects of damping, asymmetries in the distribution of coupling strengths, network symmetry, and sparseness of connections. Minimum conditions and optimal network architectures are determined for the existence of chaos. The results have implications to the design of social and other networks in the real world in which weak chaos is desired or as a way of understanding why certain networks might exist on the edge of chaos.
- Astronomy Colloquium
- Globular Clusters, Galaxy Formation, Dark Matter, and Black Holes
- Time: 3:45 pm
- Place: 6515 Sterling Hall (coffee at 3:30 pm in 6521 Sterling)
- Speaker: Kathy Rhode, University of Indiana
- Abstract: Globular clusters (GCs) serve as valuable tracers of the origins and star formation histories of galaxies. I will present selected results from a wide-field optical imaging survey of the GC systems of elliptical and spiral galaxies beyond the Local Group. Quantifying the global properties of the galaxies' GC systems provides an important test of specific models for the formation of giant galaxies. The survey results are generally consistent with a hierarchical galaxy formation scenario in which metal-poor GCs form at high redshift in protogalactic building blocks and metal-rich GC populations are built up over time in gas-rich mergers. I will also summarize our ongoing efforts to measure the radial velocities of the GCs found in the survey, and show how this allows us to trace the structure of the host galaxies' outer halos. Finally, I will briefly describe the discovery of a black hole X-ray source in one of the globular clusters we identified in the Virgo elliptical galaxy NGC 4472.