Events at Physics

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Events During the Week of October 22nd through October 29th, 2017

Monday, October 23rd, 2017

Plasma Physics (Physics/ECE/NE 922) Seminar
No Seminar - APS DPP Meeting
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Graduate Introductory Seminar
Time: 12:00 pm - 1:00 pm
Place: 4274 Chamberlin Hall
Speaker: McCammon, Timbie
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Tuesday, October 24th, 2017

Chaos & Complex Systems Seminar
How an important Supreme Court case was created
Time: 12:05 pm - 1:00 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Bill Whitford, UW Law School
Abstract: Whitford is the lead plaintiff in Gill v. Whitford, which will be heard by the U.S. Supreme Court on Oct. 3, 2018 The case raises the question whether the federal courts should interpret the U.S. Constitution to place some limits on the extent of partisan bias in legislative districting. If Whitford and the other plaintiffs win, as they did in the trial court, it will be the first time the federal courts have placed any limits of the extent of partisan bias, and hence create a new precedent. Whitford will explain the context in which case arose and how he and others were able to obtain the services of a team of lawyers and experts that have gotten the case to its present position.
Host: Clint Sprott
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Wednesday, October 25th, 2017

No events scheduled

Thursday, October 26th, 2017

R. G. Herb Condensed Matter Seminar
Watching a quantum system: How to continuously measure a superconducting qubit
Time: 10:00 am - 11:00 am
Place: Chamberlin 53100
Speaker: Justin Dressel, Chapman University
Abstract: It has recently become experimentally possible to monitor the energy levels of a superconducting transmon qubit continuously in time using microwave fields. Such measurements weakly perturb the qubit per unit time, lead to a competition between unitary Hamiltonian dynamics and non-unitary collapse dynamics. I review several subtleties about modeling this measurement process, and discuss several recent achievements made in collaboration with the Siddiqi laboratory at UC Berkeley. Topics include simultaneous measurements of multiple non-commuting observables, the active use of the quantum Zeno effect with a moving measurement basis for qubit control, and subtle aspects about the information content contained in the collected stochastic readout.
Host: Vavilov
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Astronomy Colloquium
The Plasma Physics of TeV Blazars
Time: 3:30 pm - 5:00 pm
Place: 4421 Sterling Hall, Coffee and Cookies at 3:30 PM. Talk begins at 3:45 PM
Speaker: Phil Chang, UW - Milwaukee
Abstract: Constraints on the primordial intergalactic magnetic field from the non-observation of inverse Compton cascades around extragalactic very high energy sources, i.e., the TeV blazars, assume that inverse Compton scattering is the dominant physical mechanism by which dilute ultrarelativistic pair beams lose their energy. Over the last few years, we have considered the effect of plasma instabilities on these ultrarelativistic beams. We argue that the linear growth rate of these instabilities, and in particular the oblique instability, are so fast that these instabilites may dominate the cooling of these pair beams leading to an order of magnitude or more suppression in the inverse Compton cascade. We review the relevant physics of these
plasma instabilities and discuss the linear instability of these pair beams. We also discuss recent work on the various nonlinear aspects of this instability and the effect of density gradients on the instability. We highlight the effect of this instability on the constraints of the intergalactic magnetic field, arguing that these constraints are precluded in the presences of these instabilities. We also discuss the implication of these instabilities on the population of TeV blazars, and the intergalactic gamma ray background. Finally, we close with a discussion on the effect of these extra blazar heating on cosmological structure formation, in particular, the<br>
temperature-overdensity profile and the Lyman-alpha forest.<br><br>
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Friday, October 27th, 2017

Physics Department Colloquium
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Raluca Scarlat, Engineering Physics, UW-Madison
Abstract: Molten salt technology that has the possibility of being a sustainable source of energy that does not produce atmospheric pollution and that is competitive with energy from fossil fuels. There are more than a dozen start-up companies pursuing molten salt technology, both U.S. and internationally. Some are driven by sustainability characteristics of molten salt reactors, which can recycle spent fuel from conventional nuclear reactors. Other companies are driven by the economic advantages that arise from the inherent safety features of molten salts as coolants for nuclear reactors. For example, molten salt mixtures have low vapor pressure and can operate at atmospheric pressure without boiling up to very high temperature (1000 oC and above). The atmospheric pressure operation significantly reduces costs and material testing timelines for advanced nuclear reactors. The high temperature operation enables coupling to high-efficiency modern gas turbines (open air Brayton cycles with combined cycle efficiencies of >60%), compared to steam turbines that are used by conventional, water-cooled nuclear power plants that operate below 350 oC (with efficiencies of ~35%). The high temperature operation also enables a broader market for process heat applications, and the use of gas turbines enables the production of rapidly-deployable peaking power by the use of gas co-firing.

Development of advanced nuclear reactors that use molten salts requires an understanding of the physics and chemistry of the molten salts as coolants, as solvents, as containment barriers for radioactive isotopes, as optically-transparent media through which in-service inspection of components is to be performed. In my research, I investigate the interaction of molten 2LiF-BeF2 with graphite and transport of tritium between the two, the heat transfer behavior of the fluids with liquid-solid phase change, and the physical chemistry of molten fluoride salts. The talk will provide an overview of advanced nuclear reactors and a discussion of the fundamental unknowns and the experimental challenges of studying high temperature molten fluoride salts.
Host: Pupa Gilbert
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