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Events During the Week of February 21st through February 28th, 2021

Monday, February 22nd, 2021

Plasma Physics (Physics/ECE/NE 922) Seminar
DIII-D and The Advanced Tokamak Path to Fusion Energy
Time: 12:00 pm
Place: Zoom
Speaker: Richard Buttery, GA
Abstract: The Advanced Tokamak represents a concept for fusion energy in which a magnetically confined plasma sustains itself in a stationary state. It is found that at high pressure, ion orbit affects can drive the necessary current in the plasma, while the fusion process keeps the plasma hot. Such pressures can be reached by shaping the plasma's physical geometry and current distribution to improve underlying stability and turbulent heat fluxes. The benefits of this more efficient approach is that it can reduce the current needed to be carried by the plasma, which greatly improves stability, heat and neutron fluxes. This talk will discuss the scientific principles behind the advanced tokamak approach to a fusion power plant, going on to present what such a device might look like and what research challenges it poses. We will then discuss these challenges and consider how DIII-D can address the critical plasma physics questions with research programs and new capabilities.

Chris Hegna is inviting you to a scheduled Zoom meeting.

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Meeting ID: 918 3541 9103
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Host: Chris Hegna
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Plasma Theory Seminar
Automated Normal Mode Analysis in Reduced Models of Turbulence for Stellarator Optimization
Time: 4:00 pm
Place: Zoom meeting
Speaker: Ben Faber, UW-Madison
Abstract: Chris Hegna is inviting you to a scheduled Zoom meeting.

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Meeting ID: 954 878 7359
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Host: Chris Hegna
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Tuesday, February 23rd, 2021

Council Meeting
Physics Council
Time: 4:00 pm - 5:00 pm
Place:
Host: Sridhara Dasu
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Wednesday, February 24th, 2021

Plasma Theory Seminar
Special Plasma Seminar
Plasma rotation: from mass separation applications to light manipulation
Time: 9:00 am
Place: Zoom Meeting
Speaker: Renaud Gueroult, Laplace, Université de Toulouse, CNRS, Toulouse, France
Abstract: Rotation phenomena in plasmas are found everywhere, from plasma technologies to laboratory experiments and all the way to astrophysics, and can lead to peculiar effects. In this talk, I will first discuss how the mass differential confinement properties found in a rotating plasma could enable developing mass separation technologies [1] with high upside potential for societal applications including nuclear waste cleanup and rare earth recycling. I will then show how the problem of crossed-field rotation control is intimately tied to the question of what cross-field conductivity is in a rotating plasma, and how answering this basic question is also crucial to certain alternative magnetic confinement fusion concepts [2]. Finally, as a further illustration of the peculiar effects of rotation, I will briefly touch on the basic effect of rotation on wave polarization, and how this may be of importance for pulsars' physics [3] and light manipulation applications.

[1] Gueroult R., Rax J.-M., Zweben S. J. and Fisch, N. J., Plasma Phys. Control. Fusion, 2018, 60, 014018

[2] Rax J. M., Gueroult, R. and Fisch, N. J., Phys. Plasmas, 2017, 24, 032504

[3] Gueroult R., Shi Y., Rax J.-M. and Fisch N. J., Nat. Commun., 2019, 10, 3232



Cary Forest is inviting you to a scheduled Zoom meeting

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Host: Cary Forest
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Physics ∩ ML Seminar
Neural Mechanics: Symmetry and Broken Conservation Laws in Deep Learning Dynamics
Time: 11:00 am - 12:15 pm
Place: Online Seminar: Please sign up for our mailing list at www.physicsmeetsml.org for zoom link
Speaker: Daniel Kunin and Hidenori Tanaka, Stanford University
Abstract: Understanding the dynamics of neural network parameters during training is one of the key challenges in building a theoretical foundation for deep learning. A central obstacle is that the motion of a network in high-dimensional parameter space undergoes discrete finite steps along complex stochastic gradients derived from real-world datasets. We circumvent this obstacle through a unifying theoretical framework based on intrinsic symmetries embedded in a network’s architecture that are present for any dataset. We show that any such symmetry imposes stringent geometric constraints on gradients and Hessians, leading to an associated conservation law in the continuous-time limit of stochastic gradient descent (SGD), akin to Noether’s theorem in physics. We further show that finite learning rates used in practice can actually break these symmetry induced conservation laws. We apply tools from finite difference methods to derive modified gradient flow, a differential equation that better approximates the numerical trajectory taken by SGD at finite learning rates. We combine modified gradient flow with our framework of symmetries to derive exact integral expressions for the dynamics of certain parameter combinations. We empirically validate our analytic expressions for learning dynamics on VGG-16 trained on Tiny ImageNet. Overall, by exploiting symmetry, our work demonstrates that we can analytically describe the learning dynamics of various parameter combinations at finite learning rates and batch sizes for state of the art architectures trained on any dataset.
Host: Gary Shiu
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Department Meeting
Time: 12:15 pm - 1:15 pm
Place: Virtual see "abstract" for connection info
Speaker: Sridhara Dasu, Department Chair
AIMEE N LEFKOW is inviting you to a scheduled Zoom meeting.

Topic: Department Meeting
Time: Jan 13, 2021 12:15 PM Central Time (US and Canada)
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Host: Sridhara Dasu
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Thursday, February 25th, 2021

Cosmology Journal Club
Time: 12:00 pm - 1:00 pm
Abstract: Cosmology Journal Club is back! We will be having virtual meetings this semester.

Each week, we start with a couple scheduled 15 minute talks about one's research, or an arXiv paper. The last 30 minutes will typically be open to the group for anyone to discuss an arXiv paper.

All are welcome and all fields of cosmology are appropriate.

Contact Ross Cawthon, cawthon@wisc, for more information.

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Meeting ID: 93592708053, passcode: cmbadger

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Astronomy Colloquium
PHANGS Results: Connecting the Small Scale ISM Physics to the Galaxy Structures
Time: 3:30 pm - 5:00 pm
Place: Zoom meeting(see Abstract ) Coffee and tea 3:30pm, Talk 3:45pm
Speaker: Dyas Otomo, NRAO
Abstract: The physical and dynamical states of molecular gas are closely tied to the location and amount of star formation in galaxies. This interaction between molecular gas and star formation occurs in small scale (< 100pc), therefore, high resolution observations are needed. PHANGS-ALMA mapped CO line emission in 90 nearby galaxies at 1’’ (~100 pc) resolution to quantify the physics of star formation and feedback at the scale of individual giant molecular clouds (GMCs) and connecting these measurements to the galaxy-scale properties. In this talk, I will present recent results from the PHANGS collaboration. First, I will show that the molecular gas in roughly in viral equilibrium, but their properties vary between regions inside galaxies. Second, I will present recent measurement of the star formation efficiency per free fall time at the GMC scale. Third, I will explain how we can estimate the stellar feedback and GMCs lifetime though statistical analysis. Finally, I will conclude by showing that the star formation process is self regulated.

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Host: Professor Ellen Zweibel
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Friday, February 26th, 2021

Thesis Defense
Thermal Transport Across Interfaces, Two-Dimensional Materials, and III-V Ternary-Alloy Superlattice
Time: 12:00 pm
Place:
Speaker: Gabriel Jaffe, Physics PhD Graduate Student
Abstract: Time: Feb 26, 2021 12:00 PM Central Time (US and Canada)

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Host: Mark Eriksson, Faculty Advisor
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Theory Seminar (High Energy/Cosmology)
Decoding and bootstrapping cosmological fluctuations
Time: 2:00 pm - 3:00 pm
Place: For zoom link, sign up at:
Speaker: Guilherme Pimentel, Leiden University & University of Amsterdam
Abstract: I will review our current understanding of the initial conditions of the universe, and describe what information is available from current and future measurements of cosmological correlation functions. Then I will describe a new method to compute and constrain the possible shapes of those correlation functions, assuming they were generated during inflation. This ``cosmological bootstrap” draws inspiration from the modern scattering amplitudes program in flat space, as well as the conformal bootstrap of phase transitions. After discussing primordial scalar fluctuations, I will also explain how the consistent propagation of gravitational waves imposes further constraints on the structure of spinning primordial correlators.
Host: Lars Aalsma
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Department Coffee Hour
Department Coffee Hour (Virtual)
Time: 3:30 pm - 4:30 pm
Place: Virtual (see abstract for connection info)
Abstract: AIMEE N LEFKOW is inviting you to a scheduled Zoom meeting.

Topic: Department Coffee Hour
Time: Jan 29, 2021 03:30 PM Central Time (US and Canada)
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Meeting ID: 979 8528 1970
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Host: Climate and Diversity Committee
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