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This Week at Physics

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Events During the Week of April 27th through May 4th, 2014

Monday, April 28th, 2014

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
    http://cmb.physics.wisc.edu/journal/index.html
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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Plasma Physics (Physics/ECE/NE 922) Seminar
Influence of energetic ions on resistive wall mode in reversed field pinch".
Time: 12:00 pm
Place: 2241 Chamberlin
Speaker: Hui Shan Cai, University of Science and Technology, China
Abstract: A stability analysis of the circulating energetic ions (CEIs) on resistive wall mode is carried out in the reversed field pinch (RFP). In contrast to the minor resonant effects of CEI on resistive wall mode (RWM) in tokamak, the resonant interaction between RWM and CEI is important for high toroidal mode number in RFP with high beta value. The resonance provides an energy dissipation channel of free energy, and stabilizes RWM. As the fraction of CEI is large enough, the RWM is fully suppressed by CEI in the low plasma rotation, even vanishing rotation. Further, a possibility to suppress the RWM by CEI is suggested.
Host: Weixing Ding
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Condensed Matter Theory Group Seminar
R.G. Herb Condensed Matter Seminar
"Coupled electricity and magnetism in Mott insulators: currents, dipoles and monopoles
Time: 4:30 pm
Place: Chamberlin 5310
Speaker: Daniel Khomskii , University of Cologne, Germany
Abstract: The standard point of view is that at low energies Mott insulators exhibit only magnetic properties, while charge degrees of freedom are frozen out, because electrons are localized. I demonstrate that in general this is not true [1, 2]: for certain spin textures there exist quite nontrivial effects in the ground and lowest excited states, connected with charge degrees of freedom. In particular this may happen in frustrated systems, e.g. containing triangles or tetrahedra as building blocks. I will show that in some cases there may exist spontaneous circular currents in the ground state of insulators, proportional to the scalar chirality; this clarifies the meaning of the latter and opens the ways to directly experimentally access it. For other spin structures there may exist spontaneous charge redistribution, so that average charge at a site may be different from 1. This can lead to the appearance of dipole moments and possibly of the net spontaneous polarization. This is a novel, purely electronic mechanism of multiferroic behaviour. In particular I show [3] that such electric dipoles should exist in spin ice materials at every tetrahedra with three-in/one-out or one-in /three-out spin configurations, which are equivalent to magnetic monopoles [4]. Thus there should be an electric dipole attached to each magnetic monopole in spin ice. This leads to electric activity of magnetic monopoles, and opens the possibility to control magnetic monopoles by electric field. I will also discuss unconventional dynamics of magnetoelectric materials, in which there should be magnetic monopole attached to each electric charge [5]. The possibility to use chirality as qubits will be also discussed. [1] L.N.Bulaevskii, C.D.Batista, M.V.Mostovoy and D.I.Khomskii, Phys.Rev.B 78, 028402 (2008) [2] D.I.Khomskii, JPCM 22, 164209 (2010) [3] D.I.Khomskii, Nature Communications 3, Article 904 (2012) [4] C.Castelnovo, R.Moessner and S.L.Sondhi, Nature 451, 42 (2008) [5] D.I.Khomskii, arXiv:1307.2327 (2013)
Host: Perkins
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Tuesday, April 29th, 2014

Chaos & Complex Systems Seminar
Event detection in the Twittersphere
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Adel Ardalan, UW Department of Computer Science
Abstract: Twitter has gone viral over the past few years, both in terms of the volume of posted messages and the number of users. People talk about real-world events on Twitter before events start, during the events and after they are finished. In many applications, it is desirable to monitor the Twitter stream and detect the interesting events people are discussing. In this talk, we define and motivate the event detection problem and suggest a model for detecting emerging, dynamic, interesting events. We discuss the challenges we have faced in building a system to generate candidate events based on the aforementioned model in a timely manner and how we have addressed them. Our experiments show promising results both in terms of accuracy of our detection and also the response time of the system.<br>
Host: Clint Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
LHC Dark Matter Searches
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Sridhara Dasu, UW Madison Department of Physics
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Wednesday, April 30th, 2014

Physics Education Innovation Seminar
Social Bookmarking II and new Collaborative Learning Spaces: Experiments in Physics 241 and 207 (Kyriaki Chatzikyriakidou); Learning Assistants in Introductory Physics Courses (Bethany Reilly)
Time: 11:00 am
Place: 5310 Chamberlin Hall
Abstract: Social Bookmarking II and new Collaborative Learning Spaces: Experiments in Physics 241 and 207 (Kyriaki Chatzikyriakidou); Learning Assistants in Introductory Physics Courses (Bethany Reilly)
Poster: http://www.physics.wisc.edu/twap/posters/2014/3312.pdf
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Thursday, May 1st, 2014

Astronomy Colloquium
Gas Flows in Galaxy Clusters
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Brian McNamara, University of Waterloo
Abstract: Galaxies and clusters are embedded in gaseous hot atmospheres that serve as repositories of unused fuel for galaxy formation, ejecta from evolved stars, and mechanical energy released by supermassive black holes. The hot gas located within the central galaxy is expected to cool and fuel star formation. Yet most giant elliptical galaxies are "red and dead." Instead, cooling is suppressed by powerful radio jets that periodically heat the gas in a self-regulating feedback loop. Radio-mechanical feedback may explain the the dearth of luminous, blue galaxies predicted by standard Lambda-CDM models and the excess of hot baryons in the Universe. I will discuss recent studies showing that radio-mechanical feedback also drives hot outflows at rates of tens of solar masses per year from central cluster galaxies. I will highlight new results from the Atacama Large Millimeter Array (ALMA) showing that the hot gas that has cooled resides in nascent molecular gas disks and plumes of molecular gas clouds flying in and out of the galaxy. The ALMA data for the Abell 1835 BCG indicate a molecular outflow at a rate of ~200 solar masses per year behind a pair of buoyantly rising radio/X-ray bubbles. Apparently, X-ray bubbles couple efficiently to molecular clouds, and this may have broader implication for the evolution of galaxies and supermassive black holes.
Host: Brian Morsony
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Friday, May 2nd, 2014

Theory Seminar (High Energy/Cosmology)
A MSSM scenario with a light stau and a bino DM
Time: 2:15 pm
Place: 5280
Speaker: Kaoru Hagiwara, KEK Theory Center, Japan
Abstract: We study signals of pair produced scalar-tau's that decay into a tau and a light bino at the LHC, for a specific MSSM scenario which could explain the observed gamma ray spectrum in the low-latitudes of Fermi Bubble in the Galactic center.
The scenario is consistent with the observation only when the dark matter is almost pure bino and the light stau of mass around 100 GeV is a maximally mixed state. The higgsino component of the dark matter is constrained by the Higgs invisible width and the direct DM search experiments, while the large stau mixing enhances the Higgs to two gamma rate and breaks lepton universality of electroweak observables.
At the LHC, both the stau pair production cross section and the produced tau polarization depends strongly on the stau mixing. We show that there is a possibility of observing the signal in tau-pair production events with large missing transverse momentum at LHC8 with 20/fb of integrated luminosity.
Host: Jordi Salvado
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Physics Department Colloquium
Annual Awards Banquet Speaker
The 1991 UN Inspections of Iraq: A Look Back Across Two Decades
Time: 4:00 pm
Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
Speaker: Jay Davis, President of Hertz Foundation and Chair of the Physics Department Board of Visitors
Abstract: In the summer of 1991, Jay Davis was asked on five days notice to join a UN inspection team for Iraqi nuclear facilities to determine whether or not the Iraqis had an active nuclear weapons program. He played leadership, operational, and technical roles in assessing what proved to be an excellent and well-advanced weapons program. There were technical surprises, obvious intelligence lapses, occasional incidents of gunfire, and other experiences somewhat off the norm for physics research. In consequence, Davis ended up briefing the UN Security Council, being asked to form a defense agency at DoD, and ending his physics career in a rather different manner than he had planned. This talk is a reprise of the first public talk he gave on the subject, a Physics Colloquium in Madison in September 1991. A student of Heinz Barschall, he is currently President of the Hertz Foundation and chairs the Board of Visitors for Physics at Wisconsin. This September will be fifty years since he came to Wisconsin as a graduate student.
Host: Department of Physics
Poster: http://www.physics.wisc.edu/twap/posters/2014/3178.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2014/2014-04-28.pdf

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