Events at Physics
Events on Tuesday, March 9th, 2010
- R. G. Herb Condensed Matter Seminar
- Ultrafast physics in photosynthesis: Mapping sub-nanometer energy flow
- Time: 11:00 am
- Place: 5310 Chamberlin
- Speaker: Naomi Ginsberg, Lawrence Berkeley National Laboratory
- Abstract: In the first picoseconds of photosynthesis, photoexcitations of chlorophyll molecules are passed through a network of chlorophyll-binding proteins to a charge transfer site, initiating the conversion of absorbed energy to chemical fuels. The remarkably high quantum efficiency of this energy transfer relies on near-field coupling between adjacent chlorophyll molecules and their interaction with protein phonon modes. Using two-dimensional electronic spectroscopy, we track the time-evolution of energy flow in a chlorophyll-protein complex, CP29, found in green plants. The results from these nonlinear four-wave mixing experiments elucidate the role of CP29 as a light harvester and energy conduit by drawing causal relationships between the spatial and electronic configurations of its chlorophyll molecules. Through independent control of experimental light pulse polarizations, we have furthermore developed a technique to determine the relative angles between the transition dipole moments responsible for energy transfer. This work not only yields tools for structural and spectral molecular characterization, but also deepens our understanding of how photosynthetic systems have evolved to optimize the conversion of light to biomass.
- Host: Pupa Gilbert
- Chaos & Complex Systems Seminar
- "Why We Need to Conserve Crop Diversity and What We Need to Know-An Example from the Andes"
- Time: 12:05 pm
- Place: 4274 Chamberlin Hall
- Speaker: Eve Emshwiller, UW-Madison, Dept of Botany
- Abstract: Dr Emshwiller will provide an overview of the value of crop genetic diversity and the kinds of information needed to conserve the diversity of crop plants and their wild relatives. An ongoing project in the Andes Mountains provides an example of research designed to provide information for conservation. The tuber crop "oca," Oxalis tuberosa, is second to potatoes in the diet and farming systems of traditional agriculturists in rural highland communities of Peru and Bolivia. The crop is a polyploid, with eight sets of chromosomes. Dr. Emshwiller's research has focused on finding out which wild Oxalis species may have hybridized to contribute oca's several genomes, and studying how the exchange of planting material among farming families has affected the distributions of varieties of the crop.
- Astronomy Colloquium
- "The Role of Gas Bearing Dwarfs in Near Field Cosmology"
- Time: 3:30 pm
- Place: 3425 Sterling Hall
- Speaker: Dr. Sabrina Stierwalt, CALTECH
- Abstract: Dwarf galaxies constitute the most numerous extragalactic population in the local universe and can thus place constraints galaxy formation. Gas-deficient dwarfs with little to no recent star formation dominate the Local Group but a few faint, HI-bearing dwarfs like Leo T have been discovered in the outskirts of the Milky Way's influence. ALFALFA, an ongoing blind HI survey, has found a significant population of low surface brightness dwarfs missed by previous optical surveys suggesting that these systems may represent a so far poorly studied population of widely distributed, optically faint yet gas-bearing dwarf. In this talk I will present our current understanding of the contribution of gas-bearin dwarfs to cosmology at z=0. Can they solve the substructure problem? How significant is the role of environment in their formation? What fraction of dwarfs have been formed from tidal debris?<br>