Events at Physics |
Events During the Week of October 5th through October 12th, 2008
Monday, October 6th, 2008
- Plasma Physics (Physics/ECE/NE 922) Seminar
- Multi-probe Measurements and Simulation of Global Edge-Turbulence Properties in the Torsatron TJ-K
- Time: 12:05 pm
- Place: 1227 Engineering Hall
- Speaker: Dr. Mirko Ramisch, UW-Madison, Dept. of ECE
- Plasma Theory Seminar
- Electron Density Structures in Decaying Kinetic Alfven Wave Turbulence
- Time: 4:00 pm
- Place: 514 ERB
- Speaker: Kurt Smith, UW-Madison, Dept of Physics/Plasma
Tuesday, October 7th, 2008
- Chaos & Complex Systems Seminar
- Molecular mechanisms of synaptic growth: insights from the Drosophila neuromuscular junction
- Time: 12:05 pm
- Place: 4274 Chamberlin (Refreshments will be served)
- Speaker: Kate O'Connor-Giles, UW Department of Genetics
- Abstract: Neural function requires effective communication between neurons and their targets at synapses. Thus, the proper formation, growth and plasticity of synapses are critical to behavior. Despite this, the mechanisms that determine synapse size and complexity remain poorly understood. The Drosophila larval neuromuscular junction (NMJ) has become a powerful model system for dissecting the molecular mechanisms that regulate synaptic growth. Drosophila NMJs are dynamic structures that coordinate their size and strength with muscle growth and undergo changes in morphology and physiology in response to environmental stimuli and altered levels of activity. These processes depend on intercellular communication between neurons and their muscle targets. A retrograde (muscle to neuron) transforming growth factor (TGF-b/BMP) signal is required to promote synaptic growth, homeostasis and stability at NMJs. We have recently found that neuronal responsiveness to this signal is modulated by a presynaptic endocytic mechanism. This additional level of regulation underscores the high degree of molecular control over synaptic growth and highlights the importance to the organism of getting it right. I will present recent insights from studies at the Drosophila NMJ that have increased our understanding of how this complex task is achieved.
- Astronomy Colloquium
- Dark Energy and The Hubble Constant
- Time: 3:30 pm
- Place: 6515 Sterling Hall
- Speaker: Jim Condon, NRAO
- Abstract: Dark energy (DE) dominates the energy density and future expansion of the universe, and its nature is a major unsolved problem for theoretical physics. The equation-of-state and energy density of DE can be constrained observationally by comparing an accurate (< 3% rms) value of the Hubble constant with the known distance to the last-scattering surface of the cosmic microwave background. The Megamaser Cosmology Project (MCP) is now measuring geometric distances to water masers in the nuclei of distant Seyfert galaxies in order to obtain an accurate value of H0 free from the systematic errors associated with "standard candles." I will review the effect of DE on the Hubble constant and present the latest MCP results.
- Host: Professor Amy Barger
Wednesday, October 8th, 2008
- No events scheduled
Thursday, October 9th, 2008
- Yum Kippur
- R. G. Herb Condensed Matter Seminar
- Magnetotransport in Microwave-irradiated Quantum Hall Systems
- Time: 10:00 am
- Place: Chamberlin 5310
- Speaker: Michael Zudov, University of Minnesota
- Abstract: When a high quality two-dimensional electron system is irradiated by microwaves, its magnetoresistance exhibits microwave-induced resistance oscillations (MIRO) and zero-resistance states. MIRO were discussed in terms of the aEurooedisplacementaEuro model, which is based on microwave-assisted impurity scattering, and the aEurooeinelasticaEuro model, stepping from the oscillatory electron distribution function. It is believed that the aEurooeinelasticaEuro contribution greatly exceeds the aEurooedisplacementaEuro contribution and can also account for MIRO temperature dependence.
This talk will discuss our recent experiments focusing on non-linear response and temperature dependence of MIRO. First, we show that the aEuro~aEuroTMdisplacementaEuroTMaEuroTM mechanism cannot be ignored and might even dominate the response under typical experimental conditions. Further, we find that the MIRO temperature dependence originates primarily from the temperature-dependent quantum lifetime entering the Dingle factor. We suggest that the main source of the modification of the quantum scattering rate is the contribution from electron-electron scattering, a quantity hardly available from other experiments. - Host: Vavilov
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Neutron beta-decay with Ultra-Cold Neutrons
- Time: 4:00 pm
- Place: 4274 Chamberlin
- Speaker: Brad Filippone, Caltech
- Abstract: Ultra-Cold Neutrons - UCN - (E < 350 neV) can be trapped in material bottles and with magnetic fields. The UCNA collaboration has recently measured the beta-decay electron distribution from polarized neutron decay for the first time using UCN. The use of UCN suppresses a variety of systematic experimental effects compared to previous experiments using cold neutron beams. This allows for precision measurements of some Standard Model electroweak observables as well as searches for new physics. Results from this new experiment will be discussed along with prospects for future measurements.
- Host: Michael J Ramsey-Musolf
Friday, October 10th, 2008
- Physics Department Colloquium
- Nuclear Forensics: Preparing for the Experiment One Hopes Never to Do
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: Dr. Jay Davis, Lawrence Livermore National Laboratory (Retired) and The Hertz Foundation
- Abstract: Applying the tools of nuclear physics and nuclear chemistry to determine the origin of nuclear materials is a matter of growing concern, investment and practice in the current environment. The Government asserts that the unexpected detonation of a nuclear weapon on US soil is the largest threat facing the United States at present. Nuclear forensics techniques contribute to the increased safety of weapons useable materials, the discouragement of trafficking in them to deny them to would-be bomb makers, and, after a detonation, to the possible identification of sources and perpetrators.
Jay Davis, who established the national program in post detonation forensics while Director of the Defense Threat Reduction Agency at DoD from 1998 to 2001, will describe the, technical, operational and policy challenges of the program to create an effective, rapid, and credible forensics capability. He had on-the-job training in nuclear forensics as an UNSCOM inspector in Iraq after the first Gulf War.
- Host: Coppersmith