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Events on Thursday, May 12th, 2016

R. G. Herb Condensed Matter Seminar
Measurement of resistance induced by a single potassium atom on chiral-angle known nanotubes: understanding the impact of a model scatterer for nanoscale sensors
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Prof. Masa Ishigami, U. Central Florida
Abstract: Even atomic impurities are expected to impact device properties of carbon nanotubes. Such sensitivity makes them ultimately useful for sensor technologies. Rational design for nanotube-based sensors requires precise understanding of how impurities impact transport properties of nanotubes. Such impurity-induced carrier scattering is expected to be dependent on the chirality of nanotubes and the nature of scattering potentials imposed by impurities. Yet until our recent measurements, it has been impossible to measure the impact of impurities on resistance of carbon nanotubes with known chirality. We have developed arrays of experimental techniques to control experiments down to atomic scale to measure the scattering strength of charged impurities on semiconducting single-walled carbon nanotubes with known chirality. The resistivity of nanotubes is measured as a function of the density of adsorbed potassium atoms, enabling the determination of the resistance added by an individual potassium atom. Holes are scattered 37 times more efficiently than electrons by an adsorbed potassium atom. The determined scattering strength is used to reveal the spatial extent and depth of the scattering potential for potassium, a model Coulomb adsorbate, paving way for rational design of nanotube-based sensors.
Host: Robert McDermott
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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 Amol Upadhye (aupadhye@wisc.edu).
Host: Amol Upadhye
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
A Fast Radio Burst Host Galaxy
Time: 12:15 pm
Place: 5248 Chamberlin Hall
Speaker: David Kaplan, UW - Milwaukee
Abstract: This talk has been rescheduled to occur at the time and located of the Cosmology Journal Club, 12:15-1:15
in 5248 Chamberlin Hall.
Host: Peter Timbie
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Astronomy Colloquium
"The role of cosmic rays in stellar and supermassive black hole feedback"
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and Cookies 3:30 PM, Talk at 3:45 PM
Speaker: Mateusz Ruszkowski, University of Michigan, Department of Astronomy
Abstract: I will discuss the role of cosmic rays in stellar and supermassive black hole feedback. I will argue that cosmic rays are likely to play a very important role across a large range of distance scales -- from the scales of individual galaxies to the scales comparable to those of cool cores of galaxy clusters. Regarding the galactic scale feedback, I will focus on supernova and cosmic ray driven winds but will also briefly discuss black hole feedback model for the Fermi bubbles. Galactic outflows play an important role in galaxy evolution and, despite their importance, a detailed understanding of the physical mechanisms responsible for the driving of these winds is lacking. Although cosmic rays comprise only a tiny fraction of interstellar particles by number, they carry energy comparable to that in the thermal gas. I will describe a suite of global 3D MHD numerical simulations that focus on the dynamical role of cosmic rays injected by supernovae, and specifically on the impact of cosmic ray streaming along the magnetic fields. Our results show that this microphysical effect can have a significant impact on the wind launching depending on the details of the plasma physics. Regarding the feedback on galaxy cluster scales, I will briefly discuss preliminary results from our simulations of black hole jets in cool cores of galaxy clusters including the effects of cosmic rays. I will argue that cosmic ray heating of the intracluster medium (ICM) may be an important heating mechanism both in the tenuous and cold phases of the ICM. While largely an unexplored territory in the context of galactic winds and AGN feedback, cosmic ray feedback is an important process facilitating launching and efficient driving of galactic-scale winds in starburst galaxies and heating of the ICM and remains the subject of intense research.
Host: Professor Robert Mathieu
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