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Events During the Week of September 19th through September 26th, 2021

Monday, September 20th, 2021

Plasma Physics (Physics/ECE/NE 922) Seminar
Pegasus
Time: 12:00 pm
Place: 2241 Chamberlin Hall
Speaker: Stephanie Diem , UW
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Plasma Theory Seminar
New MHD equilibrium tools for stellarators
Time: 4:00 pm
Place: 514 ERB
Speaker: Sanket Patil, UW
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Tuesday, September 21st, 2021

Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
Transport in Neutron Star Mergers
Time: 2:00 pm
Place: https://berkeley.zoom.us/j/99464252867
Speaker: Alexander Haber, Washington University in St. Louis
Abstract: Transport processes in hot and dense matter are an important way to improve our understanding of fundamental interactions and might be accessible via gravitational wave observations. In this talk I will especially focus on modified and direct Urca processes in nuclear matter under conditions that we expect in binary neutron star mergers. Nuclear Urca processes have shown to be a potential significant source of bulk viscosity under merger conditions. I will explain how a correct relativistic treatment can alter the rates and the true beta equilibrium significantly.
Host: Baha Balantekin
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Thesis Defense
Correlated Charge Noise and Relaxation Errors in Superconducting Qubits
Time: 2:00 pm
Place: Zoom: https://uwmadison.zoom.us/j/92504329607?pwd=MGtOVm1NZEhUVW1TZ09RYUlCS0NEUT09
Speaker: Chris Wilen, Physics PhD Graduate Student
Abstract: A crucial requirement to the surface code is that errors cannot be correlated. Here, we characterize a superconducting multiqubit circuit and find that charge fluctuations are highly correlated on a length scale over 600~μm; moreover, discrete charge jumps are accompanied by a strong transient suppression of qubit energy relaxation time across the millimeter-scale chip. The resulting correlated errors are explained in terms of the charging event and phonon-mediated quasiparticle poisoning associated with absorption of gamma rays and cosmic-ray muons in the qubit substrate. Robust quantum error correction will require the development of mitigation strategies to protect multiqubit arrays from correlated errors due to particle impacts.
Host: Robert McDermott, faculty advisor
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Theory Seminar (High Energy/Cosmology)
Computation of Gravitational Particle Production Using Adiabatic Invariants
Time: 4:00 pm
Place: Chamberlin 5280
Speaker: Edward Basso, University of Wisconsin-Madison
Abstract: Analytic and numerical techniques are presented for computing gravitational production of scalar particles in the limit that the inflaton mass is much larger than the Hubble expansion rate at the end of inflation. These techniques rely upon adiabatic invariants and time modeling of a typical inflaton field which has slow and fast time variation components. A faster computation time for numerical integration is achieved via subtraction of slowly varying components that are ultimately exponentially suppressed. The fast oscillatory remnant results in production of scalar particles with a mass larger than the inflationary Hubble expansion rate through a mechanism analogous to perturbative particle scattering. An improved effective Boltzmann collision equation description of this particle production mechanism is developed. This model allows computation of the spectrum using only adiabatic invariants, avoiding the need to explicitly solve the inflaton equations of motion. Note: This is a hybrid event. A zoom link will be distributed via the seminar mailing list. To join, email the organizer.
Host: Lars Aalsma
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Wednesday, September 22nd, 2021

Physics ∩ ML Seminar
Differentiable Physics Simulations for Deep Learning
Time: 11:00 am
Place: Online Seminar: Please sign up for our mailing list at www.physicsmeetsml.org for zoom link
Speaker: Nils Thuerey, TU Munich
Abstract: In this talk I will focus on the possibilities that arise from recent advances in the area of deep learning for physical simulations. In this context, especially the Navier-Stokes equations represent an interesting and challenging advection-diffusion PDE that poses a variety of challenges for deep learning methods. In particular, I will focus on differentiable physics solvers from the larger field of differentiable programming. Differentiable solvers are very powerful tools to integrate into deep learning processes. The existing numerical methods for efficient solvers can be leveraged within learning tasks to provide crucial information in the form of reliable gradients to update the weights of a neural networks. Interestingly, it turns out to be beneficial to combine supervised and physics-based approaches. The former poses a much simpler learning task by providing explicit reference data that is typically pre-computed. Physics-based learning on the other hand can provide gradients for a larger space of states that are only encountered at training time. Here, differentiable solvers are particularly powerful to, e.g., provide neural networks with feedback about how inferred solutions influence the long-term behavior of a physical model. I will demonstrate this concept with several examples from learning to reduce numerical errors, over long-term planning and control, to generalization. I will conclude by discussing current limitations and by giving an outlook about promising future directions.
Host: Gary Shiu
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Thursday, September 23rd, 2021

Astronomy Colloquium
Sizing up Protoplanetary Disks
Time: 3:30 pm
Place: Coffee and Tea 3:30 pm, Talk begins 3:45 pm
Speaker: Leon Trapman, UW Madison
Abstract: Although we are certain that planets can be formed, there are still large gaps in our understanding of how they formed. Observations show that exoplanets are found in a large variety of planetary systems, from multiple terrestrial planets packed inside the central ~1 AU to several gas giants spread over tens of AU from the central star. The diverse outcomes of planet formation are intimately linked to the disks of gas and dust around young stars, called protoplanetary disks, in which these planets have formed and grown. How much material do these disks contain for planet formation? Is this material concentrated close to the star or spread over a large area? And how do the gas and dust that make up the disk evolve over time? In my talk I will show how studying bulk properties of protoplanetary disks, especially their size, can answer these questions and help us solve the riddle of planet formation.
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Friday, September 24th, 2021

Graduate Introductory Seminar (Physics 701)
Biomineralization: past, present, and future climate change
Time: 12:05 pm
Place: 2241 Chamberlin
Speaker: Pupa Gilbert, UW Madison Department of Physics
Host: Sridhara Dasu
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Physics Department Colloquium
Wonders of Electronic Hydrodynamics
Time: 3:30 pm
Place: 2103 Chamberlin Hall
Speaker: Alex Levchenko, UW-Madison
Host: tbd
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