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Events During the Week of March 7th through March 14th, 2010

Monday, March 8th, 2010

Plasma Physics (Physics/ECE/NE 922) Seminar
Varying Stochasticity in the Core of the MST RFP
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Joshua Reusch, UW-Madison Dept of Physics/Plasma
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Plasma Theory Seminar
Magnetic Barriers as Possible q95-Dependence Inhibitors of ELM Control by Resonant Magnetic Perturbations at DII-D
Time: 4:00 pm
Place: 514 ERB
Speaker: Jonathan Kessler, Southeast Missouri State
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String Theory Seminar
On the existence of meta-stable vacua in the Klebanov-Strassler Background
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Nick Halmagyi, Saclay
Host: Shiu
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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
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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.

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Astronomy Colloquium
The Role of Gas Bearing Dwarfs in Near Field Cosmology
Time: 3:30 pm - 5:00 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>
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Wednesday, March 10th, 2010

No events scheduled

Thursday, March 11th, 2010

R. G. Herb Condensed Matter Seminar
Theory of nonequilibrium magnetooscillations in 2D electron transport in high Landau levels
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Ivan Dmitriev, Institute for Theoretical Physics, Karlsruhe University, Germany
Abstract: We propose a unified quantum kinetic description of a family of nonequilibrium magnetooscillations recently discovered in high-mobility quantum Hall structures, including the microwave induced resistance oscillations (MIRO), Hall-field induced RO (HIRO), and phonon induced RO (PIRO). The magnetoresistivity is due to quantum oscillations in the density of states in high Landau levels and is governed by spectral and spatial resonances set by the cyclotron frequency and the cyclotron diameter in various combinations with the parameters of the external fields and phonons. External ac or dc driving leads to local population inversion in the energy distribution of electrons and modifies the scattering off impurities and phonons. In particular, PIRO are shown to be very sensitive to the applied direct current. In the supersonic regime, where the Hall velocity exceeds the sound velocity, the phonon-assisted conductivity remains finite at zero temperature, while below the supersonic transition the oscillations get exponentially suppressed at low temperature. Quite interestingly, in the microwave-illuminated inhomogeneous 2D electron gas, the photocurrent and photovoltage oscillations arise in the absence of the external dc driving, due to nonequilibrium violation of the Einstein relation between electrical current and diffusion.

[ I.A. Dmitriev et al., PRL 91, 226802 (2003); 99, 206805 (2007); JETP Lett. 85, 86 (2007); PRB 70, 165305 (2004); 71, 115316 (2005); 75, 245320 (2007); 80, 125418 (2009); 80, 165327 (2009).]
Host: Maxim Vavilov
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Physics with ultra-cold and very cold neutrons at the Institut Laue-Langevin in Grenoble, France
Time: 4:00 pm
Place: 4274 Chamberlin
Speaker: Peter Geltenbort, Institute Laue-Langevin, Grenoble
Abstract: Due to their outstanding property to be storable and hence observable for long periods of time (several hundreds of seconds) in suitable material or magnetic traps, ultra-cold neutrons (UCN)with energies around 100 neV are an unique tool to study fundamental properties of the free neutron. Their properties and production are described in detail. Selected experiments with ultra-cold neutrons (UCN) - the measurement of its lifetime and the search for an electric dipole moment - performed at the instrument &amp;quot;Physique Fondamentale 2 (PF2)&amp;quot; of the Institut Laue-Langevinn (ILL) are highlighted. For particles to have electric dipole moments, the forces concerned in their structure must be asymmetric with regard to space-parity (P) and time reversal (T). P violation is a well-known intrinsic feature of the weak interaction which is responsible for the beta-decay of the free neutron. T violation turns out to be necessary to explain the survival of matter at the expense of antimatter after the Big Bang. By searching for an EDM of the free neutron hypothetical new channels of T-violation can be investigated. The experiments at the ILL will be compared to competing EDM projects worldwide. The measurement of the lifetime of the free neutron together with the determination of one of the correlation parameters characterizing neutron decay allows tests of the Standard Model. Furthermore, the neutron lifetime plays an important role in Big-Bang Nucleosynthesis cosmology. Up to 180 s after the big-bang nuclei with more than one nucleon are unstable. The neutron lifetime determines how many neutrons have decayed up to this moment and hence the relative helium abundance in the universe. The different methods to measure the lifetime of the free neutron are reviewed and the latest experiments using storage of UCN at the ILL are described in detail. A brief outlook on future projects worldwide will be given.
Host: Michael Ramsey-Musolf
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Friday, March 12th, 2010

Physics Department Colloquium
Richards Lecture
Probing Early Universe Particle Physics with Neutrons at the Institut Laue-Langevin
Time: 4:00 pm
Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
Speaker: Peter Geltenbort, ILL Grenoble
Abstract: Low energy experiments at the "precision frontier" provide a powerful probe of early universe. A brief introduction to the Institute Laue-Langevin (ILL) in Grenoble, France, which is a world leader in academic research with neutrons will be given. The scope of fundamental physics studies with neutrons is outlined. The main instruments provided for such studies are described and some past and current flagship experiments with ultra-cold neutrons (UCN) in this field (lifetime, electric dipole moment, quantum states) are highlighted. A brief outlook on future projects is given. About the speaker Peter W.H. Geltenbort received a Ph D from the University of Tuebingen, Germany, in 1983. He joined the Nuclear and Particle Physics (NPP) College at the ILL in 1983 responsible for a fission fragment spectrometer. From 1989 to 1993 he held the position of Head of the Detector Group. In 1993 he reintegrated into the NPP College responsible for the Ultra-Cold Neutron/Very Cold Neutron facilities at the ILL. His current research interests are the fundamental properties of the neutron.
Host: Ramsey-Musolf
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