Events at Physics |
Events During the Week of April 13th through April 20th, 2008
Monday, April 14th, 2008
- Plasma Physics (Physics/ECE/NE 922) Seminar
- D retentions in a Tokamak with High-Z Plasma Facing Components--Implications for ITER and Reactors
- Time: 12:05 pm
- Place: 2241 Chamberlin Hall
- Speaker: Bruce Lipschultz, Massachusetts Institute of Technology
- Medical Physics Seminar
- Title to be announced
- Time: 4:00 pm
- Place: 1345 Health Science Learning Center (refreshments will be served)
- Speaker: A. Sam Bedder, Ph.D. Associate Professor, Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas
- High Energy Seminar
- Single Top at CDF
- Time: 4:00 pm
- Place: 4274 Chamberlin (Coffee and Cookies at 3:30 pm)
- Speaker: Kevin Lannon, The Ohio State University
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.
Wednesday, April 16th, 2008
- No events scheduled
Thursday, April 17th, 2008
- R. G. Herb Condensed Matter Seminar
- Dynamic Nuclear Polarization in Double Quantum Dots
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Jason Petta, Princeton University
- Abstract: Trapped electrons in GaAs quantum dots are coupled to approximately one million lattice nuclei through the contact hyperfine interaction. Random hyperfine fields drive rotations from the singlet state (S) to the triplet state (T_O ), leading to an ensemble averaged spin dephasing time T_2 * of 10 ns [1]. In this talk, I will describe how fast electrical control of two-electron spin states near the anti-crossing of the singlet (S) and triplet (T_+ ) can be used to polarize the nuclear spin bath. An initialized S state is cyclically brought into resonance with the T_+ state, where hyperfine fields drive rapid rotations between S and T_+ , `flipping' an electron spin and `flopping' a nuclear spin [2]. The resulting Overhauser field approaches 80 mT, in agreement with a simple rate-equation model. A self-limiting pulse sequence is developed that allows the steady-state nuclear polarization to be set using a gate voltage. Lastly, I will describe efforts at Princeton to fabricate semiconductor nanowire double quantum dots. These devices will limit nuclear spin diffusion, resulting in increased nuclear polarization.
[1] J. R. Petta /et al./, Science *309*, 2180 (2005).
[2] J. R. Petta, J. M. Taylor /et al./, Phys. Rev. Lett. *100*, 067601 (2008). - Host: Vavilov
- Special Joint Nuclear Physics and High Energy Physics Seminar
- Polarized Antiprotons
- Time: 2:45 pm - 3:45 pm
- Place: 5310 Chamberlin
- Speaker: Hans-Otto Meyer, Indiana University
- Abstract: Particle physics has made remarkable advances when stored, cooled beams of antiprotons became available. Soon after, scientists called for polarized antiprotons in order to explore the spin degrees of freedom in antiproton-induced reactions. In the past 20 years, many clever ideas on how to satisfy this request have been produced, however, only recently has there been experimental activity in this field. I will review some of the history, what is going on at present, and where this might possibly lead.
- Host: Haeberli
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Colliders to the Cosmos: Dark Matter and Electroweak Phase Transition
- Time: 4:00 pm - 5:00 pm
- Place: 4274 Chamberlin
- Speaker: Maxim Perelstein, Cornell
- Abstract: Experiments at the Large Hadron Collider (LHC) will begin in the second half of this year. This machine, along with the proposed International Linear Collider (ILC), will directly probe physics at the TeV energy scale. The discoveries and measurements made by these experiments can have interesting implications for cosmology. I will discuss two examples of this connection. First, if dark matter is composed of weakly interacting massive particles, these particles may be directly produced and studied at the LHC and the ILC. Second, precise measurements of the Higgs boson properties may allow us to understand the dynamics of the electroweak phase transition in the early universe, with important implications for baryogenesis. In both cases, I will stress the aspects of the connection that do not depend on the (presently unknown) details of the fundamental theory at the TeV scale.
Friday, April 18th, 2008
- Phenomenology Seminar
- Title to be announced
- Time: 2:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Antonio Delgado, Univ. of Notre Dame
- Physics Department Colloquium
- H. H. Barschall Lecture
- Recent Developments in Neutron Radiography
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: Hans Otto Meyer, Indiana University
- Abstract: Neutron radiography is a method to reveal the internal structure of objects without destroying them. The same can be done with X-rays, but the two types of penetrating radiation have different properties and are thus complementary. I will explain what is required in order to generate a neutron radiograph, and I will show examples of current applications of this technique in science and industry. I will also try to illustrate how recent progress in neutron source and detector technology has enhanced the capabilities of neutron radiography.
- Host: Haeberli