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Events at Physics

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Events During the Week of November 1st through November 7th, 2015

Monday, November 2nd, 2015

Plasma Physics (Physics/ECE/NE 922) Seminar
Enhanced helium exhaust due to resonant magnetic perturbations at the TEXTOR tokamak and the LHD heliotron“
Time: 12:00 pm
Place: 2241 Physics Bldg
Speaker: Oliver Schmitz, Engineering Physics, UW
Abstract:
Helium exhaust is the most generic task for a divertor in magnetically confined fusion plasmas. Without sufficient helium exhaust, it will not be possible to maintain a burning plasma. Measurements and modeling results are presented which demonstrate that resonant magnetic perturbations can be used to improve the helium exhaust features. We compare the dynamic ergodic divertor at the TEXTOR tokamak with the helical divertor in the LHD heliotron. It is shown that a magnetic island in the very plasma edge can be used on both devices as a fine actuator on the helium and main plasma confinement characteristics. Modeling with the EMC3-EIRENE plasma fluid and kinetic neutral transport code supports that the most critical part of the challenge is condensation of the helium which recycles many times on the surfaces outside of the confined volume and close to the exhaust devices is important to generate efficient helium exhaust. The combination of results from modeling and experiment provide consistent evidence that a combination of enhanced outward helium transport with improved coupling to the exhaust devices due to the edge magnetic island induced can yield a substantially enhanced overall helium exhaust.
Host: Paul Terry, UW
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Tuesday, November 3rd, 2015

Chaos & Complex Systems Seminar
The downstream consequences of problem-solving mindsets: How playing with Legos influences creativity
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Page Moreau, UW School of Business
Abstract: Business leaders, governments, and scholars are increasingly recognizing the importance of creativity. Recent trends in technology and education, however, suggest that many individuals are facing fewer opportunities to engage in creative thought as they increasingly solve well-defined (versus ill-defined) problems. Using three studies that involve real problem-solving activities (e.g., putting together a Lego kit), we examine the mindset created by addressing such well-defined problems. The studies demonstrate the negative downstream impact of such a mindset on both creative task performance and the choice to engage in creative tasks. The research has theoretical implications for the creativity and mindset literatures as well as substantive insights for managers and public-policy makers.
Host: Sprott
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Looking for the origin of astrophysical neutrinos
Time: 2:30 pm
Place: 5310 Chamberlin Hall
Speaker: Dmitri Semikoz, APC Paris
Abstract: IceCube neutrino telescope recently discovered astrophysical neutrinos in the energy range from 10 TeV to 3 PeV. This discovery challenged existed theoretical models due to unexpected observation of soft 1/E^{2.5} neutrino spectrum. Together with limits from diffuse gamma-ray flux measured with Fermi LAT this excluded most of existed theoretical predictions. In my talk I'll discuss significance of the galactic component observation in the 4 years IceCube data. Also I'll review theoretical models, which can explain observed data both with Galactic and extra-galactic sources of neutrinos. Finally, I'll present model, which at the same time explain Ultra-High Energy Cosmic Ray protons, astrophysical neutrinos and diffuse gamma-ray background.
Host: Francis Halzen
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Theory Seminar (High Energy/Cosmology)
Effective field theory for spacetime symmetry breaking
Time: 3:30 pm
Place: 5280 Chamberlin Hall
Speaker: Toshifumi Noumi, Hong Kong University of Science and Technology
Abstract: Spacetime symmetry breaking often appears in condensed matter physics and cosmology. In contrast to the internal symmetry case, it is known that the number of broken global spacetime symmetries does not coincide with that of physical Nambu-Goldstone (NG) fields in general. Correspondingly, the coset construction of effective action has to be implemented with the so-called inverse Higgs constraints to compensate such a mismatch. In this talk, I revisit the effective action construction for spacetime symmetry breaking from the local symmetry point of view. Since NG fields are generated by local transformations of order parameters, such a local picture provides a correct identification of physical NG fields. I will illustrate the importance of the local picture and revisit the coset construction. I will also discuss applications to condensed matter physics and cosmology.
Host: Gary Shiu
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Wednesday, November 4th, 2015

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, November 5th, 2015

R. G. Herb Condensed Matter Seminar
Detecting frequency fluctuations in mesoscopic oscillators
Time: 10:00 am
Place: Chamberlin 5310
Speaker: Yaxing Zhang, Michigan State University
Abstract: Mesoscopic oscillators, such as nanomechanical resonators or optomechanical systems, usually experience comparatively large fluctuations due to their small size. An important type of fluctuations is frequency fluctuations, that is, the oscillator eigenfrequency is subject to a random perturbation in time. For nanomechanical resonators, frequency fluctuations can come from tension and mass fluctuations, fluctuating charges in the substrate, or dispersive inter-mode coupling; for electromagnetic cavity modes, they can come from fluctuations of dielectric constant. Frequency fluctuations lead to the broadening of oscillator linewidth. However, this broadening is partly masked by the broadening due to oscillator decay, making the identification of frequency noise difficult. In this talk, I will show that the interplay of a resonant driving and frequency noise can lead to specific features in the oscillator power spectrum that allow sensitive detection and quantitive characterization of frequency noise. I will start with a generic analysis of a harmonic oscillator with frequency noise, corroborated by measurements on a carbon nanotube resonantor [1]. Then I will discuss a particular type of frequency noise that comes from dispersive inter-mode coupling based on microscopic descriptions [2].

[1] Zhang, Y., Moser, J., Güttinger, J., Bachtold, A. & Dykman, M. I. Interplay of driving and frequency noise in the spectra of vibrational systems. Phys. Rev. Lett. 113, 255502 (2014).
[2] Zhang, Y. & Dykman, M. I. Spectral effects of dispersive mode coupling in driven mesoscopic systems. Phys. Rev. B 92, 165419 (2015).

Host: Vavilov
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Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:15 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 Amol Upadhye (aupadhye@wisc.edu).
Host: Amol Upadhye
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Astronomy Colloquium
Dwarf Galaxies, the Local Group, and Cosmology
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee 3:30 pm, Talk 3:45 PM
Speaker: James Bullock, UC Irvine
Abstract: The Local Group and the tiny galaxies that surround the Milky Way provide unique and detailed data sets for testing ideas in cosmology and galaxy formation. In this talk I will discuss how numerical simulations coupled with local "near-field" observations are informing our understanding of dark matter, the formation of the first galaxies, and the physical processes that act at the threshold of galaxy formation.
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Friday, November 6th, 2015

R. G. Herb Condensed Matter Seminar
Meissner qubit - characterization and vortex-probing applications
Time: 11:00 am
Place: 5310 Chamberlin Hall
Speaker: Jaseung Ku , University of Illinois- Urbana Champaign
Abstract: I will present a new type of transmon split-junction qubit which can be tuned by Meissner screening currents in the adjacent superconducting film electrodes. The best detected relaxation time (T1) was of the order of 50 us and the dephasing time (T2) about 40 us. The achieved period of oscillation with magnetic field was much smaller than in usual SQUID-based transmon qubits, thus a strong effective field amplification has been realized. This Meissner qubit allows an efficient coupling to superconducting vortices. I will present a quantitative analysis of the radiation-free energy relaxation in qubits coupled to Abrikosov vortices. The observation of coherent quantum oscillations provides evidence that vortices can exist in coherent quantum superpositions of different position states. According to our suggested model, the wave function collapse is defined by Caldeira-Leggett dissipation associated with viscous motion of the vortex cores.
Host: McDermott
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Physics Department Colloquium
Plasma kinetics in the inner heliosphere and the NASA Solar Probe Plus mission
Time: 3:30 pm
Place: Chamberlin 2241 (Coffee & Cookies at 3:15pm)
Speaker: Stuart D. Bale, UC Berkeley
Abstract: I will describe measurements of the electron velocity distribution function in the solar wind at 1 AU using the 3DP instrument on NASA's WIND spacecraft. Three distinct populations of electrons are observed and the collisional coupling between the cool, dense 'core' electron population and the solar wind protons can be observed directly. This Coulomb coupling relationship can be used probe the electron distribution of the solar corona and suggests that the coronal electron population will be highly nonthermal. I will also describe the NASA Solar Probe Plus mission, which will launch in 2018 and orbit the Sun with a final perihelion altitude of 9.8 solar radii, well within the predicted Alfven surface. Solar Probe Plus will make the first ever in situ measurements of plasma heating processes in the solar corona.
Host: Forest
Poster: https://www.physics.wisc.edu/events/posters/2015/3695.pdf
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