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This Week at Physics

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Events During the Week of October 28th through November 4th, 2012

Monday, October 29th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
No seminar
Time: 12:00 pm
Place: 1310 Sterling Hall
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Special Lunch Astronomy Talk
"Star Formation in N-Body Dwarf Galaxy Simulations"
Time: 12:00 pm
Place: 4421 Sterling Hall
Speaker: Ferah Munshi, University of Washington
Abstract: In this talk, we examine the total stellar-to-halo mass ratio as a function of halo mass for a new sample of simulated field galaxies using fully cosmological, I>CDM, high resolution SPH + N-Body simulations carried to the present time. These simulations include explicit H2 and metal cooling, star formation (SF) and supernovae (SN) driven gas outflows. We find extremely good agreement between the simulations and predictions from the statistical Halo Occupation Distribution model presented in Moster et al. (2012). This is due to a combination of systematic factors: a) gas outflows that reduce the overall SF efficiency b) estimating the stellar masses of simulated galaxies using artificial observations and photometric techniques similar to those used in observations. Our analysis provides an excellent match to previous observational estimates and suggests that stellar mass estimates based on photometric magnitudes underestimate the contribution of old stellar populations to the total stellar mass, leading to stellar mass errors of up to 50% for individual galaxies. These results highlight the importance of using proper techniques to compare simulations with observations and reduce the perceived tension between the star formation efficiency in galaxy formation models and in real galaxies.
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Condensed Matter Theory Group Seminar
Progress in Superconducting Quantum Circuits
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Robert McDermott
Abstract: Superconducting integrated circuits incorporating Josephson junctions are an attractive candidate for scalable quantum computing in the solid state. Currently, fidelity of multiqubit operations is limited by decoherence and by added noise of the qubit measurement. In this talk I describe work to improve qubit coherence and measurement fidelity. First, I describe the incorporation of crystalline silicon into phase qubit circuits; the improved qubits display energy relaxation times that are a factor 2-3 greater than those achieved with the best available amorphous materials. Next, I will describe efforts to understand and eliminate pure dephasing. We have shown that the dephasing is due to flux noise induced by surface magnetic states at the superconductor-insulator interface; in recent work we have demonstrated a fabrication process that has led to a noise suppression by more than an order of magnitude. Finally (and if time permits), I will discuss development of a novel microwave amplifier based on a variant of the dc Superconducting QUantum Interference Device (dc SQUID). With these devices we have achieved noise performance within a factor of 2 of the standard quantum limit at 8 GHz. Preliminary measurements show a significant improvement in single-shot quantum nondemolition measurement fidelity.
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Tuesday, October 30th, 2012

Chaos & Complex Systems Seminar
The role of the lunar cycles in human evolution
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Art Schmaltz, Prairie State College
Abstract: The moon and lunar cycles are connected to Earth's biological life in diverse and innumerably ways. In all human societies, the moon as "symbol" is deeply entwined in mythology. Recent archaeological discoveries now reveal that the moon and lunar cycles played a crucial role in human and physical and cognitive evolution.
Host: Sprott
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High Energy Seminar
The Search for the Higgs Boson Produced in Association with a Top Quark Pair
Time: 3:00 pm
Place: 4274 Chamberlin
Speaker: Kevin Lannon, University of Notre Dame
Abstract: With the recent observation at ATLAS and CMS of a new particle, consistent with the Standard Model Higgs, with a mass of 125 GeV, the focus of the Higgs search has turned to testing whether the properties of this new particle are consistent with Standard Model expectations. A critical element of this test is verifying that this new particle couples with the expected strengths to the known bosons and fermions. An interesting channel for testing fermion couplings is Higgs production in association with a top quark pair. This channel allows an explicit check of the couplings of the Higgs to the two most massive fermions, the top quark and the bottom quark. However, first, the analysis must overcome challenging backgrounds, in particular, involving top pair production. In this talk, I will present the status of the search for Higgs produced in association with top quarks at the CMS experiment.
Host: Matthew Herndon
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Theory Seminar (High Energy/Cosmology)
Indirect detection of dark matter at GeV and TeV scales
Time: 4:00 pm
Place: 5280 Chamberlin
Speaker: Alexander Belikov, Institut d'Astrophysics, Paris
Abstract: In my talk I will revise the recent interpretations of the isotropic gamma-ray and radio backgrounds, unidentified gamma-ray sources and BBN abundances of light elements in terms of GeV scale dark matter. In the second part of the talk I will focus on multi-TeV dark matter in the perspective of gamma-rays from the galactic center and cosmic ray electrons and positrons in Fermi+HESS data. The spectra of both of gamma rays from the galactic center as well as the spectrum of cosmic ray electrons exhibit a cutoff at TeV energies that can be interpreted as a signature of annihilating dark matter. I present the updated constraints in the parameter space of thermal cross-section vs. dark matter mass and study the best fits to the data in the parameter space defined by the branching ratio to a particular annihilation channel and the mass of the dark matter particle.
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Special Undergraduate Seminar
Fun Facts about the Higgs Boson and Graduate School at Notre Dame
Time: 5:00 pm
Place: 4274 Chamberlin Hall
Speaker: Kevin Lannon, University of Notre Dame
Host: Herndon
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Wednesday, October 31st, 2012

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, November 1st, 2012

R. G. Herb Condensed Matter Seminar
Nonlinear and nonreciprocal effects in magnetic garnet films
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Pradeep Kumar, Michigan Technological University
Abstract: The talk consists of two parts. In the first part, the lattice-imperfection and compositional origins of the nonlinear optical response in RF sputter deposited magnetic garnet thin films are discussed based on experimental findings. The experimental results establish that lattice mismatch strain drives the second harmonic signal in bismuth-substituted yttrium iron garnet (Bi:YIG) films, in agreement with theoretical predictions. This study also elaborates on the influence of the filmaEuroTMs constitutive elements and finds the nonlinear response to increase with yttrium concentration.

The second part of the talk addresses a novel effect, namely nonreciprocal optical Bloch oscillation, recently proposed and developed by us [1, 2]. Our work has established a comprehensive theoretical basis for the implementation of nonreciprocal and unidirectional optical Bloch oscillations. The model system we developed consists of one-dimensional waveguide arrays in silicon-on-insulator platforms with magnetic garnet cover layers. An optical force is introduced into the array through geometrical design, pushing the beam sideways. Laterally displaced photons are periodically returned to a central guide by photonic-crystal action, producing beam revival in the central guide. The unidirectional Bloch oscillation effect allows the implementation of on-chip optical isolation, a technologically important function in photonic integrated circuits [3].

[1] M. Levy and P. Kumar, Optics Letters Vol. 35, Issue 18, page 3147-3149 (2010)
[2] P. Kumar and M. Levy, Optics Letters Vol. 36, Issue 22, page 4359-4361 (2011)
[3] P. Kumar and M. Levy, Optics Letters Vol. 37, Issue 18, page 3762-3764 (2012)
Host: McDermott
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Careers for Physicists
Time: 3:30 pm
Place: 4274 Chamberlin
Speaker: Jim Haugen, IceCube
Abstract: Jim Haugen received his B.S. in applied math, engineering, and physics at UW-Madison in 1983. He worked in the semiconductor industry in several locations including California and Thailand before coming back to Wisconsin to work at IceCube as a project manager. He will discuss his career path, and there will be plenty of time for Q&A.
Host: Reina Maruyama
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Graduate Introductory Seminar
Neutrinos, Dark Matter, and Fundamental Interactions
Time: 5:45 pm
Place: 2223 Chamberlin Hall
Speaker: Balantekin, Heeger, Maruyama, Ramsey-­Musolf, UW Madison
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Friday, November 2nd, 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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Physics Department Colloquium
Anticipating sudden transitions in biological populations: Cooperation, cheating, and collapse
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Jeff Gore, Massachusetts Institute of Technology
Abstract: Natural populations can suffer catastrophic collapse in response to small changes in environmental conditions, and recovery after such a collapse can be exceedingly difficult. We have used laboratory microbial ecosystems to study early warning signals of impending population collapse. Yeast cooperatively breakdown the sugar sucrose, meaning that below a critical size the population cannot sustain itself. We have demonstrated experimentally that changes in the fluctuations of the population size can serve as an early warning signal that the population is close to collapse. The cooperative nature of yeast growth on sucrose suggests that the population may be susceptible to cheater cells, which do not contribute to the public good and instead merely take advantage of the cooperative cells. We confirm this possibility experimentally and explore how such social parasitism can lead to population extinction.
Host: Gilbert
Poster: http://www.physics.wisc.edu/twap/posters/2012/2710.pdf
Video: http://www.physics.wisc.edu/vod/2012/11/02.html
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-10-29.pdf

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