This Week at Physics

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This Week at Physics

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Events During the Week of November 12th through November 18th, 2017

Monday, November 13th, 2017

Plasma Physics (Physics/ECE/NE 922) Seminar
Schnack Memorial Seminar: Nonlinear Modeling of Mode Locked States Induced by Transient Magnetic Perturbations
Time: 12:00 pm
Place: Chamberlin 2241
Speaker: Dr. Matthew Beidler, Department of Engineering Physics, UW Madison
Abstract: Externally applied 3D magnetic fields in tokamaks can penetrate into the plasma and lead to forced magnetic reconnection, and hence magnetic islands, on resonant surfaces. Analytic theory has been reasonably successful in describing many aspects of this paradigm with regard to describing the time asymptotic-steady state [1]. However, understanding the nonlinear evolution into a low-slip, field-penetrated state, especially how MHD events such as sawteeth and ELMs precipitate this transition, is in its early development. We present nonlinear computations employing the extended-MHD code NIMROD, building on previous work [2] by incorporating a temporally varying external perturbation as a simple model for an MHD event that produces resonant magnetic signals. A parametric series of proof-of-principle computations and accompanying analytical theory characterize the transition into a mode-locked state with an emphasis on detailing the temporal evolution properties.

[1] R. Fitzpatrick, Nucl. Fusion 33, 1049 (1993)
[2] M.T. Beidler, J.D. Callen, C.C. Hegna, and C.R. Sovinec, Phys. Plasmas 24, 052508 (2017)
Host: Carl Sovinec
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Tuesday, November 14th, 2017

Chaos & Complex Systems Seminar
Inference for high-dimensional self-exciting point processes
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Becca Willett, UW Department of Electrical and Computer Engineering
Abstract: In a variety of settings, our only glimpse at a network’s structure is through observations of a corresponding dynamical system. For instance, in a social network, we may observe a time series of members’ activities, such as posts on social media. In biological neural networks, firing neurons can trigger or inhibit the firing of their neighbors, so that information about the network structure is embedded within spike train observations. These processes are “self-exciting” in that the likelihood of future events depends on past events. In these and other settings, a network’s structure corresponds to the extent to which one node’s activity stimulates or inhibits activity in another node. In this talk, I will describe sparsity-regularized inference methods and theoretical guarantees that reflect the role of the network’s degree distribution and other network properties in determining the complexity of the inference problem for large-scale networks. In addition, we will see how these techniques can be used in applications ranging from criminology to predicting adverse drug reactions.
Host: Clint Sprott
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Council Meeting
Council Meeting
Time: 3:30 pm
Place: 2314 Chamberlin Hall
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Theory Seminar (High Energy/Cosmology)
A New Dark Matter (in)Direct Search Strategy
Time: 3:30 pm
Place: 5280 Chamberlin Hall
Speaker: Doo Jin Kim, CERN
Abstract: I propose a new dark matter (DM) detection strategy for models with a non-minimal dark sector. The strategy is to seach for relativistic, inelastic scattering signatures of DM at large-volume neutrino detectors and/or conventional DM direct detection experiments via a DM interaction with target material inside the detector. The signal process is characterized by an inelastic scattering of relativistic/boosted DM, which may arise in multi-component DM scenarios, into a heavier unstable dark-sector state which subsequently decays back into DM along with visible particles. I will argue that the presence of the secondary (visible) decay signature along with an energetic target recoil is very unique, hence allow to unambiguously separate signal events from associated background ones. I will then dicuss some interesting phenomenology including detection prospects at the above-mentioned experiments, taking the dark photon scenario as a benchmark model.
Presentation: Presentation_UW_DoojinKim.pdf
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Wednesday, November 15th, 2017

Department Meeting
Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, November 16th, 2017

Astronomy Department Whitford Lecturer
CHILES, the COSMOS HI Large Extragalactic Survey
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 pm, Talk begins at 3:45 pm
Speaker: Jacqueline VanGorkom, Columbia University
Abstract: Our understanding of the growth of large scale structure has advanced enormously over the last decade, thanks to an impressive synergy between theoretical and observational efforts. The formation and evolution of galaxies within these structures is less well understood and especially the details of the gas physics during accretion and outflow are still controversial.

Neutral hydrogen images can help distinguish between growth by mergers and accretion of gas, and between inflow and outflow. While these images have taught us a lot about galaxy evolution in the local universe very few HI imaging observations have been done beyond z=0.1. The recent upgrade of the VLA has now made it possible to go as far as z=0.5. CHILES the COSMOS HI Large Extragalactic Survey, is an ongoing pencil beam survey of one pointing in the COSMOS field covering the range of 0<z<0.5. I will discuss the goals, challenges and the very first results of this survey.
Host: Professor Eric Wilcots
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Friday, November 17th, 2017

Physics Department Colloquium
Assembly and eco-evolutionary dynamics of communities of antibiotic producing bacteria
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Kalin Vetsigian, UW-Madison Bacteriology and Wisconsin Institute for Discovery
Host: Pupa Gilbert
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