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This Week at Physics

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Events During the Week of March 31st through April 7th, 2019

Monday, April 1st, 2019

Plasma Physics (Physics/ECE/NE 922) Seminar
Electrostatically driven helical plasma state
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: John Finn, Tibbar Plasma Technologies
Abstract: I will describe a novel plasma state found in resistive MHD simulations. This state starts with a uniform applied axial magnetic field in a periodic cylinder and is driven electrostatically by helical electrodes. We focus on m=n=1. For sufficiently strong helical drive the mean field of the state has field line field line safety factor q(r) just above the pitch of the electrodes m/n=1 except near the edge, where q increases monotonically. This state is characterized as a single helicity Ohmic equilibrium with the helical symmetry of the applied field. This state is analyzed in terms of Pfirsch-Schlueter currents, flux conversion in helical geometry, and magnetic helicity. Possible applications to current drive in toroidal confinement devices and to DC-DC electrical transformers are discussed.

Collaborators: C. Akcay, R. Nebel and D. Barnes
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Tuesday, April 2nd, 2019

Chaos & Complex Systems Seminar
Disruptive technologies in the transition to renewable energy: The future of energy production and storage
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Michael Winokur, UW Department of Physics
Abstract: Many forms of renewable energy are based on mature technologies (e.g. single layer solar cells, wind, hydro) and while now economically competitive there are clear limitations for each. This talk will focus on a number of complimentary developing technologies that, if successful, will both reduce and/or displace the consumption of fossil fuels and thereby accelerate the transition to an energy portfolio centered around renewable energy. Specific examples include supercritical CO2 turbines, hydrogen production and tandem solar cells. Novel energy storage systems, such as those based on chemical redox reactions and solid state chemistry, will also be discussed.
Host: Clint Sprott
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Council Meeting
Time: 3:30 pm
Place: 2314 Chamberlin Hall
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Wednesday, April 3rd, 2019

Department Meeting
Time: 12:15 pm
Place: b343 Sterling Hall
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Thursday, April 4th, 2019

R. G. Herb Condensed Matter Seminar
Quantum Advantage for Annealing
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Dr. David Ferguson, Northrop Grumman
Abstract: Analog annealing using superconducting circuits is a leading candidate to establish a quantum advantage for computing problems of application interest. This seminar will discuss some recent research thrusts in quantum annealing. The first topic will delve into new methods to extract Pauli Hamiltonians using a variant of Bravyi’s Schrieffer-Wolff technique. While this method has many compelling advantages, it also generates non-trivial holonomy of the Hilbert space over the control parameter manifold. This path dependence of the effective Hamiltonian presents both challenges and opportunities for analog control of annealing systems. The next topic builds on this framework to facilitate a direct comparison between quantum and classical models of superconducting circuits using phase space techniques which enable a clear definition of a “Quantum Advantage for Annealing.” Finally, looking to future capabilities, a definition of non-stoquasticity will be presented along with an explanation of why it is relevant for quantum annealing, why typical superconducting qubits don’t have it, and what sort of design changes are necessary to engineer qubits that are simultaneously capable of annealing and generating strong non-stoquastic interactions.
Host: Vavilov
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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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Astronomy Colloquium
"Science with a Complete Catalog of Galactic HII Regions"
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Speaker: Loren Anderson, West Virginia University
Abstract: HII regions are the signature of ongoing high-mass star formation, and are key to understanding star formation and feedback. Modern mid-infrared surveys have for the first time enabled a complete census of Galactic HII regions, and with such a census we can get a global view of high-mass star formation in the Milky Way. We found that all HII regions have the same mid-infrared morphology of ~20um emission surrounded by ~10um emission. The former is largely due to small grains scholastically heated in the HII region plasma and the latter is mostly caused by emission from polycyclic aromatic hydrocarbons. We used mid-infrared survey data to create a catalog of all objects sharing this morphology in the Galaxy, the "WISE Catalog of Galactic HII Regions." This catalog has over 8000 entries, ~2000 of which are known to be HII regions, ~2000 of which are HII region candidates with radio continuum emission from ionized gas, and ~4000 of which are radio-quiet candidates. Radio recombination line observations can turn HII region candidates into known regions, and radio continuum observations can turn radio quiet candidates into candidates. I will detail our efforts on these two fronts, which together have allowed us to determine the Galactic locations of a large number of HII regions and to estimate the overall HII region population.

Over large portions of the Milky Way, the WISE catalog is now statistically complete for all HII regions ionized by single O-stars. With such a catalog, we can begin to examine the overall Galactic HII region population, and to compare massive star formation in the Milky Way with that of external galaxies. Our current investigations include the z-distribution of massive star formation regions and the Sun's height above the midplane, the form Galactic HII region luminosity function, massive star formation in the far outer Galaxy, the Galactic electron temperature gradient, a strange cluster of HII regions near to the Galactic center, the distribution of ionized gas in the inner Galaxy, and the luminosity and star formation rate of the Milky Way.
Host: Robert Benjamin
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Friday, April 5th, 2019

Theory Seminar (High Energy/Cosmology)
Large Field Ranges from Aligned and Misaligned Winding
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Andreas Schachner, Heidelberg University
Abstract: One of the most prominent aspects of the landscape-swampland program is the quest for large field ranges in string compactifications. One reason for this is the interest in large-field inflation. Another is the hope for a deeper understanding of general quantum gravity constraints and therefore of quantum gravity itself. In the present talk, I focus on large axionic field ranges summarizing work done in collaboration with A. Hebecker and D. Junghans (arXiv: 1812.05626). More specifically, I explain our attempt to construct effective axions with parametrically large decay constants in type IIB string models. I argue that such axions can be realised as long winding trajectories in complex-structure moduli space by an appropriate flux choice. The main findings are: The simplest models with aligned winding in a 2-axion field space fail due to a general no-go theorem. However, equally simple models with misaligned winding, where the effective axion is not close to any of the fundamental axions, appear to work to the best of the present understanding. These models have large decay constants but no large monotonic regions in the potential, making them unsuitable for large-field inflation. I also show that the no-go theorem can be avoided by aligning three or more axions. Contrary to misaligned models, such models can in principle have both large decay constants and large monotonic regions in the potential. These results may be used to argue against the refined Swampland Distance Conjecture and strong forms of the axionic Weak Gravity Conjecture. After stabilizing Kähler moduli, it becomes apparent, however, that realizing inflation is by far harder than just producing a light field with large periodicity.
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Physics Department Colloquium
Special Event: Stefan Westerhoff Memorial Colloquium
Exploring Nature's Extreme Accelerators
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Julie McEnery, NASA
Abstract: Cosmic rays, neutrinos and gamma rays provide three different ways to identify and explore locations of the most efficient astrophysical particle accelerators in the universe. In the past decade we have transformed our understanding of the extreme universe. Ground-breaking gamma-ray observations with Fermi, HAWC and IACTs have uncovered many new classes of sources and provided detailed information on these objects; IceCube has broken new ground by observing astrophysical neutrinos; and we have refined our understanding of the origin of cosmic rays. In this talk, I will discuss some of the recent breakthroughs in the study of cosmic accelerators.

A reception and a concert will follow the colloquium
Host: Sridhara Dasu
Video: https://vod.physics.wisc.edu/media/2019_04_05.m4v
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Stefan Westerhoff Memorial Concert
Chamber Music
Time: 5:00 pm
Place: 2241 Chamberlin Hall
Speaker: Solano Quartet, UW-Madison
Abstract: In remembrance of Stefan Westerhoff's great love of music, we will have chamber music following the colloquium.
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