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Events During the Week of April 9th through April 16th, 2017

Monday, April 10th, 2017

Plasma Physics (Physics/ECE/NE 922) Seminar
Laboratory Investigation of the Dynamics of Jets and Spheromaks in a Background Magnetized Plasma
Time: 12:00 pm - 12:55 pm
Place: 2317 Engineering Hall
Speaker: Dr. Mark Gilmore, University of New Mexico, USA
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Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:15 pm - 1:15 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:<br>
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Please feel free to bring your lunch!<br>
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 (
Host: Amol Upadhye
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Tuesday, April 11th, 2017

Chaos & Complex Systems Seminar
The influence of spatial connectivity on landscape regime shifts and pattern formation after external pulses
Time: 12:05 am - 1:00 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Zak Ratajczak, UW Department of Zoology
Abstract: Ecosystems are often exposed to driver pulses, such as climate oscillations or consumer outbreaks. We currently lack robust theoretical predictions for when a driver pulse will elicit regime shifts, which are instances when an ecosystem no longer recovers to its essential form, functions, and feedbacks. We used a spatially extended vegetation model where increases in grazing pressure can force patches of the landscape to undergo a regime shift from a high productivity state to a self-reinforcing low-productivity state. We considered a factorial combination of driver pulses that increase grazing pressure by differing intensities and for differing durations. These pulses were applied to simulated landscapes with high underlying spatial heterogeneity and differing levels of spatial connectivity between adjacent patches. We considered two scales of resistance to regime shifts: landscape integrity, defined as when >95% of the landscape returned to a high biomass state and refugia potential, defined as the ability to keep >5% of the landscape in the high biomass state. High connectivity landscapes had greater landscape integrity, meaning that they could withstand more intense and longer pulses, and still have a majority of the landscape return to a high biomass state. Low connectivity systems, in contrast, had greater refugia potential, meaning that at least a small portion of the landscape was able to return to a high biomass state, even after more intense or longer pulses. Systems with intermediate connectivity had a more balanced combination of landscape integrity and refugia potential. These landscapes also tended to form coherent spatial patterns after driver pulses that nearly forced a landscape-scale regime shift. Such pattern formation could potentially be used as a warning sign for adaptive management. Ensemble, these simulations suggest that underlying landscape characteristics can greatly alter the landscape and patch-scale potential for regime shifts in response to various external pulses.
Host: Clint Sprott
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Council Meeting
Time: 12:00 pm
Place: 2314 Chamberlin hall
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Theory Seminar (High Energy/Cosmology)
Dark Matter Interpretations of the AMS Positron Excess
Time: 3:30 pm
Place: 5280 Chamberlin
Speaker: Ian Low, Northwestern
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Wednesday, April 12th, 2017

Department Meeting
Time: 12:15 pm - 1:00 pm
Place: 5310 Chamberlin Hall
Speaker: Albrecht Karle, UW-Madison
Host: Albrecht Karle
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Thursday, April 13th, 2017

Theory Seminar (High Energy/Cosmology)
A new top-down model of inflation
Time: 3:30 pm - 4:30 am
Place: 5280 Chamberlin Hall
Speaker: Marjorie Schillo, K.U. Leuven
Abstract: I will present recent work that has succeeded in embedding the mechanism of Unwinding Inflation in string theory. I will review Unwinding Inflation and the process of brane-flux annihilation, in which D-branes lower flux numbers and therefore the 4D vacuum energy. A dynamical brane mediates the brane-flux annihilation as it moves across a compact internal cycle. This mechanism has recently been extended such that many units of flux can be discharged in a “flux cascade.” The flux cascade can be used to substantially reduce vacuum energy and give rise to 60 efolds of inflation.
Presentation: Madison13417.pdf
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Friday, April 14th, 2017

Physics Department Colloquium
New Dark Matter Search Results from PICO 60
Time: 3:30 pm
Place: 2241 Chamberlin hall
Speaker: Carsten Krauss, University of Alberta
Abstract: Bubble chambers have long been a tool for discovery in particle physics. Since the nature of dark matter within the standard model is still unknown, a broad search with many target materials and techniques is currently underway. The PICO collaboration, which formed as the merger of the PICASSO and COUPP collaborations in 2012 is currently operating the world’s largest bubble chamber filled with 52kg of superheated octaflouropropane (C3F8). Between November 2016 and January 2017 a blind run with an exposure of 1.5 ton days was taken. This run had no events in the dark matter search area. This allows us to set world leading limits on the interaction between WIMPs and protons. This remarkable progress promises to enable the coming generations of dark matter bubble chambers. These chambers are expected to have an excellent sensitivity now that confidence has been gained that the backgrounds we observed in previous bubble chambers can be controlled. I will report on the status of both the PICO 40L experiment, planned for operation in later 2017 and PICO 500, proposed for 2017/2019 at SNOLAB.
Host: Kim Palladino
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