Events at Physics |
Events on Tuesday, February 19th, 2008
- Chaos & Complex Systems Seminar
- Acceleration of human evolution: interactions of genes with culture and geography
- Time: 12:05 pm
- Place: 4274 Chamberlin Hall
- Speaker: John Hawks, Anthropology
- Abstract: Recent surveys of the human genome have shown that thousands of recent mutations have strong advantages and have increased greatly in frequency since their origins during the last 40,000 years. The rate of such changes appears to have increased by a factor of 100 times over the rate that characterized most of human evolution. Natural selection, as Darwin recognized, is fundamentally a demographic phenomenon: individuals with one allele have a higher intrinsic rate of growth than those having alternative alleles, resulting in the replacement of such alleles over time. When this process occurs across a population spread over geographic space, a wave of population growth and migration tends to disperse a selected allele outward from its source. This process is well understood when modeled for a single gene. However, the introduction of many (perhaps thousands) of simultaneously selected alleles may lead interactions between genes to outweigh the fitness consequences of individual genes.
- Astronomy Colloquium
- Illuminating the Glowing Magnetospheres of Massive, Luminous Stars
- Time: 3:45 pm
- Place: 6515 Sterling Hall (coffee at 3:30 pm in 6521 Sterling)
- Speaker: Richard Townsend, University of Delaware- Bartol Research Institute
- Abstract: Massive, luminous stars are not expected to harbor magnetic fields, owing to their lack of envelope convection zones and associated field-generating dynamos. Puzzlingly, however, it has been known since the 1970s that a small yet growing subset of massive stars possess strong, global-scale fields. These fields channel and confine the stars' supersonic, radioactively driven winds, leading to the formation of glowing, co-rotating magnetospheres that can be observed across the electromagnetic spectrum, from X-rays through to radio.My interest in massive-star magnetospheres stems from the challenge of understanding the rich variety of phenomena they manifest, at a detailed, quantitative level. In my presentation, I aim to illuminate the basic physical processes responsible for the existence of these magnetospheres. Then, with the aid of extensive animations, I willintroduce the new 'Rigidly Rotating Magnetosphere' and 'Rigid Field Hydrodynamics' models that I have developed for understanding magnetospheric signatures at optical, UV and X-ray wavelengths.