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This Week at Physics

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Events During the Week of February 22nd through March 1st, 2015

Monday, February 23rd, 2015

Plasma Physics (Physics/ECE/NE 922) Seminar
"Rossby Waves - The Good, The Bad, and The Ugly"
Time: 12:00 pm
Place: 1610 Engineering Hall
Speaker: Prof. Matthew Hitchman, , Atmospheric and Oceanic Sciences, UW-Madison
Abstract: The mathematical and physical basis for Rossby waves in neutral fluids is described. Conservation of potential vorticity creates an elastic restoring mechanism for an upstream-propagating transverse wave on a rotating sphere. This Beta effect is due to the meridional gradient of planetary vorticity. Manifestations include "Alberta Clippers" and the "Polar Vortex of 2013-14". Violations of the non-acceleration theorem during Rossby wave breaking (RWB) couple the Rossby wave activity conservation relation to the mean flow equations. Consideration of 3D RWB provides insight into stratosphere - troposphere
exchange and the distribution of tropopause folds.
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Faculty Candidate Seminar
Benchtop Particle Astrophysics
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Gray Rybka, University of Washington
Abstract: Advances in low noise cryogenic amplifiers and the commercialization of microwave technology have not only improved astrophysical measurements, but also enabled exquisitely sensitive laboratory experiments. I will discuss a number of benchtop experiments that utilize radio astronomy techniques and technology to make measurements that are important for astroparticle physics. The experiments I cover will include searches for dark matter axions using electronics with noise limited only by quantum mechanical effects, searches for light exotic beyond-the-standard-model particles, and a precision measurement of beta decay energies that could be used to determine the neutrino mass scale.
Host: Dasu
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Tuesday, February 24th, 2015

Chaos & Complex Systems Seminar
Sweet talks and trade deals in symbiotic associations
Time: 12:05 pm
Place: 4274 Chamberlin Hall (Refreshments will be served)
Speaker: Jean-Michel Ané, UW Department of Agronomy
Abstract: Living organisms, such as plants, animals and humans in particular, interact constantly with microbes present in their environment to form symbioses. These symbioses are very dynamic and can range all along a continuum between mutually beneficial interactions to parasitic ones. Sometimes, these associations are necessary for the survival of one or both partners, but they can also be facultative. These associations can be lost or acquired over time depending on environmental constraints. We will discuss how plants and microbes communicate (sweet talks) to initiate and maintain symbiotic associations, how these mechanisms evolved or have been lost sometimes, but also how nutrients exchanges between partners are regulated with interesting similarities to economic markets (trade deals).
Host: Clint Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Direct Search for Dark Matter
Time: 1:20 pm
Place: 2120 Chamberlin Hall
Speaker: Duncan Carlsmith, UW Madison Department of Physis
Host: Smith
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Faculty Candidate Seminar
The Discovery of Fermi Bubbles and Future Gamma-ray Telescopes
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Meng Su, MIT, Joint MIT Pappalardo and NASA Einstein Fellow
Abstract: The Fermi Bubbles are a pair of giant lobes at the heart of the Milky Way, extending roughly 50 degrees north and south of the Galactic Center, and emitting photons with energies up to 100 GeV. This previously unknown structure could be evidence for past activity of the central supermassive black hole. I will first summarize what we have learned about the bubbles through multi-wavelength observations and numerical simulations. We discovered the bubbles while searching for potential signal of dark matter particle annihilation toward the Galactic Center, using data from the Fermi Gamma-ray Space Telescope. More than six years successful operation of Fermi has proved the great potential of studying astrophysics, cosmology, and fundamental physics through gamma-ray sky. I will highlight the search of dark matter particles using gamma-ray and cosmic-ray observations, which motivated three future space telescopes: DAMPE, HERD, and PANGU. Together with the next generation ground-based Cherenkov telescopes e.g. CTA and LHAASO, we will be able to measure gamma-ray photons with energies from MeV to above PeV with much improved sensitivity. Finally, I will comment on a future plan to search for primordial gravitational waves produced from inflation in the very beginning of the Universe.
Host: Dasu
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Wednesday, February 25th, 2015

No events scheduled

Thursday, February 26th, 2015

Astronomy Colloquium
"Cosmic ray feedback in Galaxies and Cool Core Clusters"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: CHristopher Pfrommer, HITS Heidelberg
Abstract: Understanding the physics of galaxy formation is arguably among the greatest problems in modern astrophysics. Recent cosmological simulations have demonstrated that "feedback" by star formation, supernovae and active galactic nuclei appears to be critical in obtaining realistic disk galaxies, to slow down star formation to the small observed rates, to move gas and metals out of galaxies into the intergalactic medium, and to balance radiative cooling of the low-entropy gas at the centers of galaxy clusters. However the particular physical processes underlying this "feedback" still remain elusive. In particular, these simulations neglected cosmic rays and magnetic fields, which provide a comparable pressure support in comparison to turbulence in our Galaxy, and are known to couple dynamically and thermally to the gas. Using hydrodynamic simulations of galaxy formation, I will show how cosmic rays are able to drive powerful galactic winds in low-mass galaxies. This reduces the available amount of gas for star formation and implies a shallower slope of the faint-end of the galaxy luminosity function as required by observations. In the second part of the talk I demonstrate that cosmic-ray heating can balance radiative cooling of the low-entropy gas at the centers of galaxy clusters and helps in mitigating the star formation of the brightest cluster galaxies. New data on the low-frequency radio and gamma-ray emission of M87, the closest active galaxy interacting with the cooling cluster plasma, enable us to put forward a comprehensive, physics-based model of feedback by active galactic nuclei.
Host: Prof Jay Gallagher and Chair Ellen Zweibel
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R. G. Herb Condensed Matter Seminar
Faculty Candidate Seminar
Many body localization: a new frontier for quantum statistical physics
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Rahul Nandkishore, Princeton Center for Theoretical Science
Abstract: The existing theory of quantum statistical mechanics describes open systems in contact with large reservoirs. However, experimental advances in the construction and control of isolated quantum systems have highlighted the need for an analogous theory of isolated quantum systems. It has been realized that isolated many body quantum systems can support behavior which has no analog in traditional statistical mechanics. A prominent example is the phenomenon of many body localization.

Many body localization occurs in isolated quantum systems, usually with strong disorder, and is marked by absence of dissipation, absence of thermal equilibration, and a memory of the initial conditions that survives in local observables for arbitrarily long times. The many body localized regime is a far from equilibrium, strongly disordered regime that constitutes a new frontier for quantum statistical mechanics. Recently, my co-workers and I have demonstrated that many body localization opens the door to new states of matter which cannot exist in thermal equilibrium, such as topologically ordered states without a bulk gap, and broken symmetry states at high energy densities in one dimension. We have also uncovered a host of unexpected properties, such as a set of universal spectral features and a non-local charge response, that have striking implications for fields as diverse as quantum Hall based quantum computation and quantum control. In this talk, I review the essential features of the many body localization phenomenon, and present some of the recent progress that has been made in this field. I also discuss the implications of these results for both theory and experiment, and the connections with diverse areas of theoretical physics. I conclude with a discussion of future directions.

Reference: Rahul Nandkishore and David A. Huse, arXiv: 1404.0686 [Annual Reviews of Condensed Matter Physics, 2015]
Host: Coppersmith
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Friday, February 27th, 2015

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:15 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
    http://cmb.physics.wisc.edu/journal/index.html
Please 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 Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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NPAC Faculty Search Committee Meeting
NPAC Faculty Search Committee Meeting
Time: 1:30 pm
Place: 4272 Chamberlin
Speaker: Dasu, UW - Madison
Host: Dasu
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Physics Department Colloquium
Detection of B-mode polarization at 150GHz and degree angular scales by BICEP2 and Keck Array
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Dr. Clem Pryke, University of Minnesota
Abstract: The theory of Cosmic Inflation postulates that our entire observable universe was spawned from a quantum fluctuation in an incredibly brief burst of hyper expansion. Inflation makes several predictions which appear to match features of the actual Universe in which we find ourselves, and, in addition, predicts that a background of gravitational waves will exist which may produce a specific observable feature in the polarization pattern of the Cosmic Microwave Background - the long sought B-mode polarization. Using data from a specialized radio telescope called BICEP2 operating from the South Pole in Antarctica our collaboration reported last year a highly significant detection of B-modes at 150GHz and few degree angular scales. However in a recently submitted joint analysis with the Planck space mission we find that, once an unexpectedly high level of polarized emission from dust grains in our own galaxy is taken into account, there is not currently significant evidence for a gravitational wave signal. I will describe the background, the results, and the ongoing BICEP/Keck-Array experimental program.
Host: Halzen
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