This Week at Physics

 
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This Week at Physics

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Events During the Week of September 15th through September 22nd, 2019

Monday, September 16th, 2019

Plasma Physics (Physics/ECE/NE 922) Seminar
Computational approaches for nuclear design analyses of the stellarator power reactor HELIAS
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: A. Haeussler, KIT
Abstract: The Helical-Axis Advanced Stellarator (HELIAS) is the leading stellarator concept in Europe and developed at the Max-Planck-Institute for Plasma Physics (IPP), Greifswald, Germany. Based on the 5-field-period symmetry, the HELIAS-5B engineering design study emerged which aims at a stellarator power reactor designed for 3000 MW fusion power. The stellarator confines hot plasma only by external superconducting field coils, which are very sensitive for the neutron flux, leading to a complex 3D topology of the magnetic configuration. These coils define the shape of the device and limit the space available outside the plasma chamber for the vacuum vessel and the in-vessel components required for breeding, shielding and heat removal. The neutronic performance of the HELIAS fusion reactor needs to be assessed. This requires a suitable computational approach to simulate the generation of source neutrons in the plasma chamber and the neutron transport through the complex HELIAS geometry. The approach is based on the Monte Carlo (MC) particle transport technique applied with the Direct Accelerated Geometry Monte Carlo (DAGMC) method. Beside the neutron source is a suitable geometry description important to represent a simplified HELIAS geometry as good as possible in the simulation. For the first neutronic design analyses, like neutron wall loading, tritium breeding ratio, neutron flux distribution and shielding performance, a simplified HELIAS model with homogenized material for each functional layer is used. The talk will present the development of the stellarator neutron source based on plasma physics simulation, challenges in CAD to MC geometry translation including different translation approaches, first neutronic design analyses and the shielding performance in comparison to the design values specified as limits for the radiation loads to the superconducting toroidal field coils of the DEMO tokamak.
Host: John Sarff
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Theory Seminar (High Energy/Cosmology)
Parity and the origin of (neutrino) mass
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Speaker Goran Senjanovic, The Abdus Salam International Centre for Theoretical Physics ITALY
Host: Orlofsky
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Tuesday, September 17th, 2019

Chaos & Complex Systems Seminar
Data and computational advances in the fight against floods
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Dan Wright, UW Department of Civil and Environmental Engineering
Abstract: Recent decades have seen a substantial increase in the number and severity of rainstorms in Wisconsin and elsewhere. This increase is driven by global warming, and is likely to continue into the foreseeable future. Many logically assume that floods are also becoming worse as a result. In this seminar, we’ll see that the story is more complicated. Some human actions have had clear impacts on floods—urbanization, for example, significantly exacerbates flooding, while dams and reservoirs are able to mitigate these risks to some extent. Advances in weather forecasting have reduced flood-related fatalities, but economic growth has greatly increased the overall economic risks from flooding. When it comes to climate change impacts on floods, the story is complex and not well understood. The reason for this is that floods are “recipes” that consist of multiple ingredients—not just rain but also land cover, soil moisture, snow, and river properties. We will discuss what we know and don’t know about how these ingredients are changing, and see several recent examples of how new data and tools can be brought to bear to understand the complex relationships between rainfall, floods, and how they are co-evolving in a changing Wisconsin.
Host: Clint Sprott
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Wednesday, September 18th, 2019

No events scheduled

Thursday, September 19th, 2019

R. G. Herb Condensed Matter Seminar
Optical control of free-electron decoherence
Time: 11:00 am
Place: 5310 Chamberlin Hall
Speaker: Wayne Huang, Northwestern University
Abstract: In electron grating diffraction, the peak width in the diffraction pattern is a direct measure of the free electron transverse coherence length. A broadened peak indicates decoherence of the free electron wavepacket. Using the above band-gap photoexcitation, we created a charge pattern on a GaAs surface that interacts with the diffracted electron matter wave through a dipole field. We observed a significant broadening of the diffraction peak as electrons flew over certain regions of the charge structure. The decoherence strength can be controlled through the excitation laser that is applied to the GaAs plate. As only one electron is present in the chamber at any time, such a system is suitable for studying decoherence of single electrons. In this talk, I will present some recent experimental results and discuss a possible decoherence model.
Host: Saffman
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Cosmology Journal Club
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
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 Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).
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PGSC Professional Development Seminar
Building a Free Professional Website for Your Research in 10 Minutes!
Time: 2:30 pm
Place: 5310 Chamberlin Hall
Speaker: Rob Morgan, Physics PhD Graduate Student
Abstract: The first Physics Graduate Student Council Professional Development Seminar! We will briefly outline the topics for the semester as an introduction to the seminar series. This session will focus on the importance of making yourself and your work accessible to collaborators and potential employers. Personal websites are the perfect tools for this purpose. There will be a step-by-step walkthrough to create a free, easy-to-use personal website. By the end, everyone will be online! Visit https://rmorgan10.github.io/UWMadisonPGSC-PD/ for more information.
Host: Rob Morgan, graduate student
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Astronomy Colloquium
The Geometry, Energetics, and Environment of the Binary Neutron Star Merger GW170817: The Radio View
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Speaker: David Kaplan, UW Milwaukee Physics Department
Abstract: I will discuss the major uncertainties regarding the geometry, energetics, and environment of the first EM/GW binary neutron star merger GW170817. In particular I will look at the origin of the radio emission, how it differs from the early-time optical/infrared emission, and what that tells us about how the explosion proceeded. I will show how constraints from the radio lightcurve, polarization, and Very Long Baseline Interferometry helped provide evidence for a broad, mildly relativistic "cocoon" along with a narrow jet. This broke degeneracies in the gravitational wave data analysis to provide inclination constraints and improved measurements of the Hubble Constant. Finally, I will talk about new events from LIGO's latest observing run.
Host: UW Astronomy Department
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Friday, September 20th, 2019

Thesis Defense
Ethan Peterson Thesis Defense
Time: 12:00 pm
Place: B343 Sterling Hall
Speaker: Ethan Peterson, Physics Graduate Student
Abstract: A Laboratory Model for Magnetized Stellar Winds
Host: Cary Forest, Faculty Advisor
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Plasma Physics (Physics/ECE/NE 922) Seminar
Engineering Solutions for Fusion Energy: Control and Liquid Metals
Time: 12:00 pm
Place: 2241 Chamberlin Hall
Speaker: Egemen Kolemen, Princeton University
Host: John Sarff
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Physics Department Colloquium
Work and Dissipation in the Cell Cytoskeleton
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Michael Murrell, Yale
Abstract: Living cells generate and transmit mechanical forces over diverse time-scales and length-scales to determine the dynamics of cell and tissue shape during both homeostatic and pathological processes, from early embryonic development to cancer metastasis. These forces arise from the cell cytoskeleton, a scaffolding network of entangled protein polymers driven out-of-equilibrium by enzymes that convert chemical energy into mechanical work. However, how molecular interactions within the cytoskeleton lead to the accumulation of mechanical stresses that determine the dynamics of cell shape is unknown. Furthermore, how cellular interactions are subsequently modulated to determine the shape of the tissue is also unclear. To bridge these scales, our group in collaboration with others, uses a combination of experimental, computational and theoretical approaches. On the molecular scale, we use active gels as a framework to understand how mechanical work is produced and dissipated within the cell cytoskeleton. On the scale of cells and tissues, we abstract mechanical stresses to surface tension in a liquid film and draw analogies between the dynamics of wetting and the dynamics of simple tissues. Together, we attempt to develop comprehensive description for how cytoskeletal stresses translate to the physical behaviors of cells and tissues with significant phenotypic outcomes such as epithelial wound healing.
Host: Pupa Gilbert
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