Events at Physics |
Events During the Week of September 20th through September 27th, 2009
Monday, September 21st, 2009
- Plasma Physics (Physics/ECE/NE 922) Seminar
- "Recent Progress in Validating Simulations of Plasma Turbulence
- Time: 12:05 pm
- Place: 4274 Chamberlin Hall
- Speaker: Christopher Holland, University of California/San Diego
- Special Theory/Phenomenology Seminar
- LHC Physics Simulation on a Graphic Card
- Time: 1:20 pm
- Place: 4274 Chamberlin Hall - Note special location
- Speaker: Kaoru Hagiwara, KEK, Tsukuba
- Host: V. Barger
Tuesday, September 22nd, 2009
- Chaos & Complex Systems Seminar
- Anti-Newtonian dynamics
- Time: 12:05 pm
- Place: 4274 Chamberlin (Refreshments will be served)
- Speaker: Clint Sprott, UW Department of Physics
- Abstract: This talk describes a world in which Newton's first and second laws hold, but Newton's third law takes the form that the forces between any two objects are equal in magnitude and direction. The dynamics for such a system exhibit curious and unfamiliar features including chaos for two bodies in two spatial dimensions. This talk is an introduction to a more detailed talk to be given on October 6th by Vladimir Zhdankin.
Ref: J. C. Sprott, Am. J. Phys. 77, 783-787 (2009)(http://sprott.physics.wisc.edu/pubs/paper339.pdf)
Wednesday, September 23rd, 2009
- No events scheduled
Thursday, September 24th, 2009
- R. G. Herb Condensed Matter Seminar
- Biot-Savart correlations in layered superconductors
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Kumar Raman, University of California - Riverside
- Abstract: We discuss the superconductor to normal phase transition in an infinite-layered type-II superconductor in the limit where the Josephson coupling between layers is negligible. We model each layer as a neutral gas of thermally excited pancake vortices. We assume the dominant interaction between vortices in the same and in different layers is the electromagnetic interaction between the screening currents induced by these vortices. Our main result, obtained by exactly solving the leading order renormalization group flow, is that the phase transition in this model is a Kosterlitz-Thouless transition despite being a three-dimensional system. While the transition itself is driven by the unbinding of two-dimensional pancake vortices, an RG analysis of the low temperature phase and a mean-field theory of the high temperature phase reveal that both phases possess three-dimensional correlations. An experimental consequence of this is that the jump in the measured in-plane superfluid stiffness, which is a universal quantity in 2d Kosterlitz-Thouless theory, will receive a small non--universal correction (of order 1% in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$). This overall picture places some claims expressed in the literature on a more secure analytical footing and also resolves some conflicting views.
Reference: Phys. Rev. B 79, 174528 (2009), arXiv:0902.1547 - Host: Natalia Perkins
- Special Interest Presentation
- Intersections Between Physics and the Movement Arts
- Time: 10:30 am
- Place: Grainger Hall Plenary Room
- Speaker: Elizabeth Streb, MacArthur Genius Award winner and world-renowned choreographer
- Abstract: Elizabeth Streb is a MacArthur "Genius" Award winner and world-renowned choreographer and has been celebrated as the "Evel Knievel of dance" for her muscular, daredevil approach to movement. Streb holds an honorary doctorate from Rhode Island College and a master of arts in time and space from New York University's Draper Program. Streb's choreography, which she calls "PopAction," intertwines the disciplines of dance, athletics, boxing, rodeo, the circus and Hollywood stunt-work. The result is a bristling, muscle-and-motion vocabulary that combines daring with strict precision in pursuit of the public display of "pure movement". Come to this special presentation for Physics students and faculty, where Streb will discuss the intersections between physics and the movement arts.
Elizabeth Steb, Founder/Action Architect, Streb Lab for Action Mechanics (SLAM), Brooklyn, New York www.streb.org
(Enter Grainger Hall at Park and University-into the new addition of Grainger Hall-and the Plenary room will be directly to your right).
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Special Colloquium
- Time-lapse seismic monitoring of reservoir deformation
- Time: 4:00 pm
- Place: 2103 Chamberlin (tentative) (coffee & cookies at 3:30)
- Speaker: Paul Hatchell, Shell International E&P, Research and Development, Houston, TX
- Abstract: Seismic imaging is a technology used worldwide by the oil industry to look into the subsurface and determine underground structures and their potential for oil and gas production. Time-lapse seismic monitoring is a relatively new technology that consists of carefully repeating a seismic image months to years after production starts and looking for changes that indicate where production did or did not occur to help guide future operations. <br>
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Production of oil and gas is often accompanied by a large reduction in the reservoir fluid pressure that in some cases leads to compaction as large as several meters. The deformation of the reservoir layers is coupled to the adjacent rocks and leads to changes in the stress and strain fields that extend a great distance away from the reservoir. Time-lapse seismic measurements through these rocks show large variations that are useful for monitoring the distribution of deformation within the reservoir.<br>
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The compaction induces seismic velocity changes that are observed on many different wave types including conventional P-P reflection seismic, P-S mode converted seismic, and surface waves such as the Scholte wave and refracted compressional waves. Using geomechanical models that predict changes in stress and strain fields within the earth we can start to understand the factors that control the changes in seismic velocities. We find that simple non-linear relationships between velocity and strain produce forward models that match many of our observations. <br>
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- Host: Balantekin
- Introductory Graduate Seminar
- Plasma
- Time: 5:30 pm
- Place: 2223 Chamberlin Hall
- Speaker: Boldyrev, Forest, Sarff, Schnack, Terry, Zweibel, University of Wisconsin Department of Physics
Friday, September 25th, 2009
- Physics Department Colloquium
- New Phenomena at Oxide Interfaces
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee and cookies at 3:30 pm)
- Speaker: Jean-Marc Triscone, University of Geneva
- Abstract: At interfaces between complex oxides, electronic systems with unusual properties can be generated [see for instance 1,2]. A striking example is the interface between LaAlO3 and SrTiO3, two good insulating perovskite oxides, which was found in 2004 to be conducting with a high mobility [3]. We discovered that the ground state of this system is a superconducting condensate, with a critical temperature of about 200 mK [4]. The characteristics observed for the superconducting transitions are consistent with a two-dimensional superconducting sheet a few nanometers thick. Recent field effect experiments revealed the sensitivity of the normal and superconducting states to the carrier density. In particular, the electric field allows the tuning of the critical temperature between 200 mK and 0 K and thus the on-off switching of superconductivity, revealing a complex phase diagram and a superconductor to insulator transition[5]. Recent results suggest that this phase diagram is linked to the large interfacially generated spin-orbit coupling. I will discuss the perspectives opened by this new field of research sometimes called "oxide interface engineering".
[1] "When oxides meet face to face." E. Dagotto, Science 318, 1076 (2007).
[2] "Enter the oxides." J. Heber, Nature 459, 28 (2009).
[3] "A high mobility electron gas at the LaAlO3/SrTiO3 heterointerface." A. Ohtomo, H. Y. Hwang, Nature 427, 423 (2004).
[4] "Superconducting interfaces between insulating oxides." N. Reyren, S. Thiel, A. D. Caviglia, L. Fitting Kourkoutis, G. Hammerl, C. Richter, C. W. Schneider, T. Kopp, A.-S. Ruetschi, D. Jaccard, M. Gabay, D. A. Muller, J.-M. Triscone and J. Mannhart, Science 317, 1196 (2007).
[5] "Electric field control of the LaAlO3/SrTiO3 interface ground state." A. Caviglia, S. Gariglio, N. Reyren, D. Jaccard, T. Schneider, M. Gabay, S. Thiel, G. Hammerl, J. Mannhart, and J.-M. Triscone, Nature 456, 624 (2008).
- Host: Rzchowski
- Math Colloquia
- Complexity Theory --- The World of P and NP
- Time: 4:00 pm
- Place: B239 Van Vleck
- Speaker: Jin-Yi Cai, UW Madison CS Dept.
- Abstract: The study of computational complexity presents challenging mathematical problems. In Complexity Theory computational problems are classified into complexity classes, the best known include P, NP and Valiant's class #P for counting problems. A central problem in Valiant's theory is the permanent vs. determinant problem. We will report some latest progress on this problem. Graph homomorphism was introduced by Lovasz over 40 years ago, and it is also called the partition functions in Statistical Physics, and can encode a rich class of counting problems: Given an $m imes m$ symmetric matrix $A$ over the complex numbers, compute the function $Z_A(cdot)$, where for an arbitrary input graph $G$, [ Z_A(G) = sum_{xi:V(G)
ightarrow [m]} prod_{(u,v)in E(G)} A_{xi(u),xi(v)}.] Our foucs is the computational complexity of $Z_A(cdot)$. With Xi Chen and Pinyan Lu, we have achieved a complete classification theorem for the complexity of $Z_A(cdot)$. The classification proof is too complicated to present, but we will present the proof of a lemma. It states that in order to be computable in polynomial time, the matrix $A$ must possess a group structure. Another component of the proof uses Gauss sums. (In a subsequent Number Theory Seminar I will present some related work.) No prior knowledge of complexity theory is assumed. <br>