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This Week at Physics

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Events During the Week of March 25th through April 1st, 2012

Monday, March 26th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The search for direct detection of Dark Matter with MiniCLEAN
Time: 1:00 pm
Place: 4274 Chamberlin Hall
Speaker: Raul Hennings-Yeomans, Los Alamos National Laboratory
Abstract: The particle nature of dark matter remains one of the biggest challenges in Astroparticle physics today. The use of liquid noble elements as scintillators for direct detection of dark matter insingle and dual phase configurations are one of the most promising techniques to reach sensitivities beyond 10$^{-44}$cm$^2$ in spin-independent WIMP-nucleon cross section. MiniCLEAN (CLEAN- Cryogenic Low Energy Astrophysics with Noble Gases) is an approximately spherical ~500~kg liquid argon or neon vessel that encloses 92 optical cassettes (modular photo-detectors) pointing at the center of the sphere through a TPB (Tetraphenyl Butadine) evaporated window that converts VUV light from the argon or neon scintillation into the visible. The modular spherical design allows both for a viable radon-mitigated assembly and for position reconstruction. Furthermore, the use of Pulse-Shape discrimination techniques between nuclear and electronic recoils that are particularly good for these two condensed noble gases will test the single-phase approach as a viable instrument for direct detection of dark matter at the multi-tonne scale with a projected sensitivity of 10$^{-46}$~cm$^2$ for a $sim$100~GeV/c$^2$ WIMP mass in terms of spin-independent WIMP-nucleon cross section. I will be presenting a review and status of the MiniCLEAN research program as well as new developments in the mitigation of depth-dependent and radiogenic neutron backgrounds.
Host: Reina Maruyama
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Condensed Matter Theory Group Seminar
Superconducting Instabilities in Cuprates Mediated by Spin Density Wave Order at Quantum Criticality
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Yuxuan Wang, UW-Madison
Abstract: I will start with the introduction of the model and its uniqueness near quantum criticality, especially, its distinction with BCS-type theories. I will use a solved example in a specific temperature scale to show how in this case perturbation theory fails to account for the critical temperature of the system. Next I will demonstrate that in another temperature scale the superconducting vertex shows a log2 (Λ/T) behavior up to leading contributions, which would seem to give Tc ~ exp (−1/√g), g being the coupling. I will then present how this problem again cannot be properly addressed by counting leading contributions in each order of perturbation theory. Theoretical and numerical investigations are then used to show the actual exp (−1/g) behavior of the critical temperature. Finally by looking at the full problem, I will talk about the conditions at which each temperature scale takes dominance, and what one can learn from studying the models at these specific temperature scales.
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Tuesday, March 27th, 2012

Chaos & Complex Systems Seminar
The anatomy of economics
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Jim Blair, Milton and Edgewood College
Abstract: A- The 3 Levels of economic analysis: Macro, Micro, and Nano B- Conflicting schools of Macro Economics: Demand Side, Supply Side and Marxist: John Maynard Keynes, Frederick Hayek, and Karl C- Different views of Money and Inflation: Or &quot;What is Your Position on Bimetallism?&quot; D- Throwing us Curves: Arthur Laffer and William Phillips E- Wealth Distribution and Income Mobility: or the "race to the bottom".
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Chaos
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Clint Sprott, University of Wisconsin Department of Physics
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Wednesday, March 28th, 2012

Department Meeting
CANCELED
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, March 29th, 2012

R. G. Herb Condensed Matter Seminar
Atomic-Layer Engineering and Topological insulators
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Seongshik Oh, Dept. of Physics & Astronomy, Rutgers University
Abstract: Atomic-layer engineering was first made possible in III-V semiconductors in 1980s by MBE (Molecular Beam Epitaxy), and later in complex oxides in 1990s by MBE and in 2000s by PLD (Pulsed Laser Deposition). The challenges of atomic-layer engineering in complex-oxides compared to those in semiconductors will be discussed. Then I will describe how we apply this technique to a new family of materials called topological insulators (TIs). Topological insulators are predicted to have metallic surface states with polarized spins while inside of the material is insulating. These unique properties pose TIs as promising candidates for spintronics and quantum computation. However, material problems in the current-generation TIs are a major hurdle to implementing real TI devices. I will discuss how we utilize the atomic-engineering schemes to overcome this hurdle and navigate through the vastly unexplored territory of topological insulators.
Host: Rzchowski
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Probing TeV scale physics in ultra-cold neutron decays
Time: 2:30 pm
Place: 4274 Chamberlin
Speaker: Rajan Gupta, Los Alamos National Laboratory
Abstract: This talk will describe the possibility of probing scalar and tensor interactions
arising from new physics at the TeV scale at the two experiments, UCNb
and UCNB, being developed at the ultra-cold neutron source at Los Alamos.
I will show that the largest uncertainty is connecting theory to experiments
(with measurements at the 10^{-3} level), comes from estimates of the
scalar and tensor charges of a nucleon. I will then discuss the status of our lattice
QCD calculations of these matrix elements and plans for the future. As summary, a
discussion of current bounds on these novel interactions will be presented.
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Astronomy Colloquium
"X-ray Spectroscopy of Massive Stars: Constraints on Stellar Wind Mass-Loss Rates, Clumping, and Shock Physics"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: David Cohen, Swarthmore College
Abstract: Hot, luminous, massive stars are strong sources of soft X-ray emission, despite their general lack of surface magnetic fields and the associated dynamo activity and MHD processes that heat a corona and explain the X-ray emission of solar-type stars. Since massive stars' surprising discovery as X-ray sources in the late 1970s, a consensus has emerged that the X-rays are produced in their strong radiation-driven winds. I will show how high-resolution X-ray spectroscopy carried out over the past decade with the Chandra and XMM-Newton satellite observatories has confirmed the basic wind-shock scenario of X-ray production in massive stars and enabled the testing of theoretical models by providing quantitative constraints on the temperature, spatial distribution, and kinematics of the X-ray emitting plasma embedded in the stellar wind. I will also discuss how absorption signatures in the X-ray spectra can be used to measure the mass-loss rates of these winds, and present some initial results that indicate lower mass-loss rates than have been traditionally assumed. When combined with observations in the optical and radio, these X-ray absorption measurements also provide information about the clumping properties of massive star winds.
Host: Richard Townsend
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Friday, March 30th, 2012

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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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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Physics Department Colloquium
Canceled
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Michael Corradini, Engineering Physics, University of Wisconsin-Madison
Host: Himpsel
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-03-26.pdf

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