This Week at Physics

 
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This Week at Physics

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Events During the Week of October 28th through November 4th, 2018

Monday, October 29th, 2018

Plasma Physics (Physics/ECE/NE 922) Seminar
Wave Conversion from Stellar Magnetic Fields
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Daniel Lecoanet, Princeton University
Abstract: Stars have global oscillation modes, which can be observed by looking for periodic brightness variations. If many modes of oscillation have been identified, one can infer the properties of the deep interiors of stars. This was first applied to observations of the Sun, but recently space-based telescopes have measured oscillations in many other stars, leading to new mysteries in stellar structure and evolution. Recent work has suggested that low dipole oscillation amplitudes in red giant branch stars may indicate strong core magnetic fields. Here we present both numerical simulations and analytic calculations of the interactions of waves with a strong magnetic field. We can solve the problem very accurately by using the WKB approximation to reduce the 2D PDE into an ODE for each height. We find that magnetic fields convert the buoyancy-driven waves observable at the surface of the star to magnetic waves, which are not present at the surface, in agreement with observations.
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Vector Boson Fusion Production of WZ at CMS
Time: 12:30 pm
Place: 4272 Chamberlin
Speaker: Kenneth Long, University of Wisconsin
Host: Sridhara Dasu
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Tuesday, October 30th, 2018

Chaos & Complex Systems Seminar
Jevons paradox, economic EROI and r- and K-selection
Time: 12:05 pm
Place: 4274 Chamberlin (Refreshments will be served)
Speaker: Tim Allen, UW Department of Botany
Abstract: Complexity demands more than one level of analysis. Rate-dependent and rate-independent descriptions yield contradictory accounts of resource use. In termites we see flipping between prudent frugal consumption and profligate waste depending how the analyst addresses poses the system at more than one level of analysis. All this can be expressed as a fractal response surface of increasing frugality. Wood dwelling cockroaches, wood dwelling termites, twig gathering termites and soil eating cockroaches. Most of the biomass is in twig gathering but 60% of species are soil eating.
Host: Clint Sprott
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Wednesday, October 31st, 2018

No events scheduled

Thursday, November 1st, 2018

R. G. Herb Condensed Matter Seminar
Localization at the Edge of 2D Topological Insulator by Kondo Impurities
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Boris Altshuler, Columbia University
Host: Lev Ioffe
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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
Survey of the Large-Scale Flows of Baryons Around Galaxies
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and Cookies 3:30 PM, Talk begins at 3:45 PM
Speaker: Nicholas Lehner, University of Notre Dame
Abstract: It has become clear that the level of activity in a galaxy is affected by phenomena occurring in its disk, but also in its halo, known as the circumgalactic medium (CGM) -- the gas at the interface of a galaxy and the intergalactic medium. Gas flows through the CGM directly influence the baryon distribution and metal content of their host galaxies as well as the level of stellar activity in the disk, and hence the evolution of galaxies. The metallicity is a key parameter that allows us to directly determine the level and type of enrichment of the CGM gas and its possible origin(s). I will present an HI-selected absorption-line survey of the gas at low and high redshift where we estimated the metallicity of the gas for several hundreds of CGM absorbers. I will show that there is a a significant fraction of the CGM that is metal rich at any z. I will show that there is surprisingly also a large reservoir of metal-poor gas at any z, some of this gas showing little chemical enrichment over several billions of years. I will argue that this metal-poor gas might be the long-sought cold flow accretion that provides a source of gas for ongoing star-formation over billions of years in cosmological simulations. I will finally discuss these observational results in the context of recent cosmological simulations and future radio 21-cm HI emission surveys.
Host: Bart Wakker
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Friday, November 2nd, 2018

Theory Seminar (High Energy/Cosmology)
Weak Gravity Conjecture from Unitarity and Causality
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Toshifumi Noumi, Kobe University
Abstract: The Weak Gravity Conjecture, motivated by string theory and black hole thought experiments, states that gravity is the weakest force. In particular, it claims that there exist theoretical bounds on the charge-to-mass ratio and the axion decay constant in quantum gravity, which provides theoretical constraints on models of inflation and dark matter for example. In this talk, I will first review the Weak Gravity Conjecture and its phenomenological implications. I will then introduce our recent work providing its strong evidence based on unitarity and causality.
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Physics Department Colloquium
Bose condensation of excitons in TiSe2
Time: 3:30 pm
Place: 2241 chamberlin hall
Speaker: Peter Abbamonte, UIUC
Host: Mark Eriksson
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