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This Week at Physics

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Events During the Week of April 12th through April 19th, 2015

Monday, April 13th, 2015

Plasma Physics (Physics/ECE/NE 922) Seminar
FNSF: Next Facility to Qualify/Validate Nuclear Technologies for US DEMO
Time: 12:00 pm
Place: 1610 Engineering Hall
Speaker: Dr. Laila El-Guebaly, UW-Madison, Engineering Physics
Host: UW
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Council Meeting
Time: 4:00 pm
Place: 2314 Chamberlin (Chair's Conference Room)
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Tuesday, April 14th, 2015

Chaos & Complex Systems Seminar
How scale-dependent are ecosystem-atmosphere exchanges?
Time: 12:05 pm
Place: 4274 Chamberlin Hall (Refreshments will be served)
Speaker: Ankur Desai, UW Department of Atmospheric and Oceanic Sciences
Abstract: Terrestrial surfaces are a lower boundary condition for exchanges of trace gases ,energy, and momentum with the atmosphere and consist of biologically-active organisms. In terrestrial ecosystems, information relevant to these processes scales upwards from gene to cell to microbe to plant, while for the atmosphere, the relevant modes of interactions with these processes scale downward from climate dynamics to synoptic systems to boundary layer turbulence. Consequently, identifying the appropriate space and time scale over which ecosystems interact with the atmosphere is critical for improving theoretical and numerical simulations of these processes. Further, there is a fundamental spatiotemporal scale mismatch between the terrestrial observations made about these process and the spatial scale over which numerical models of ecosystems, weather systems, and climate operate. I will present a general overview of this problem, a few examples of work in my lab addressing this issue from the perspective of 1) modeling spatial heterogeneity in ecosystem energy balance, 2) data synthesis for terrestrial carbon cycling, and 3) rectification of eddy covariance flux tower observation flux footprint bias. The overview and examples will be used to engage discussion in a general conceptual framework on ecosystem-atmosphere scaling and model-data comparison.
Host: Clint Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Puzzles for Particle Physics
Time: 1:20 pm
Place: 2120 Chamberlin Hall
Speaker: Yang Bai, UW Madison Department of Physics
Host: Smith
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Theory Seminar (High Energy/Cosmology)
Natural Inflation and the Weak Gravity Conjecture
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: William Cottrell, University of Wisconsin
Abstract: Attempts to provide a UV complete model for inflation generically encounter large quantum corrections which spoil the flatness of the inflaton potential. A standard method to work around this, known as 'natural inflation' attempts to use axions as inflatons since they enjoy a perturbative shift symmetry and thus can naturally have very flat potentials. However, we will argue that such theories of inflation are ruled out by the weak gravity conjecture. More precisely, we will show that models with natural inflation are analogous to theories which allow black hole remnants and are thus highly disfavored.
Host: Ran Lu
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Wednesday, April 15th, 2015

"Hubble Clocks the High-Velocity Outflow from the Milky Way's Core"
Time: 12:00 pm
Place: 4421 Sterling Hall
Speaker: Andrew Fox, StSci
Abstract: Like other spiral galaxies, the Milky Way drives a biconical nuclear wind. Outflowing gas is visible in enhanced emission in many parts of the electromagnetic spectrum, including Fermi gamma-ray bubbles and radio lobes extending above and below the Galactic Center. We present early results from a 49-orbit Hubble Space Telescope program to study the kinematics and extent of the nuclear outflow, using UV absorption-line spectroscopy of AGN and halo stars lying close on the sky to the Galactic Center. The variation in absorption properties with Galactic latitude allows us to constrain the physical conditions in the outflowing gas. We present the first constraint on the nuclear outflow velocity (~900-1000 km/s) using kinematic outflow modeling of the absorption components observed in the spectrum of the QSO PDS456, which lies behind the base of the Fermi Bubbles near the Galactic Center (l,b=10.4, +11.2 degrees).
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Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, April 16th, 2015

Astronomy Colloquium
A solar close-up view of physical processes in magnetized plasmas
Time: 3:45 pm
Place: 4421 Sterling Hall
Speaker: Paola Testa, Harvard CfA
Abstract: Observations of the solar outer atmosphere provide us with a close up view of fundamental physical processes that occur in magnetized plasmas in many other astrophysical environments. I will present recent results and discuss the insights we have gained into the mechanisms converting magnetic energy into atmospheric heating and particle acceleration, and other processes relevant to different astrophysical contexts such as accretion on pre-main sequence stars.
I will focus in particular on results from the recently launched Interface Region Imaging Spectrograph (IRIS), which provides us with an unprecedented detailed view of the solar chromosphere and transition region (i.e., the interface region between the gas dominated photosphere and the magnetically dominated corona). IRIS allows detailed diagnostics of the plasma structuring and dynamics through its high resolution NUV and FUV spectroscopic data in combination with high spatial resolution (~0.3") slit-jaw imaging (SJI). I will also discuss the role of state-of-the-art radiative atmospheric models which are necessary forp the interpretation of the emission of plasma from this interface region, because of e.g., optical thickness effects, and partial ionization.
Host: Professor Elena D'Onghia
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Careers for Physicists
Panel with BOV members re: Careers outside academia
Time: 4:30 pm
Place: 5280 Chamberlin Hall
Speaker: Lloyd Hackel & Bob Leach
Abstract: Panel discussion about careers outside academia meant for undergraduate majors, but other students/postdocs are welcome to attend. Panel members will be Physics Board of Visitor members who have worked in industry. Pizza will be served.
Host: Albrecht Karle
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Friday, April 17th, 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:
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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Physics Department Colloquium
Has Compelling Experimental Evidence for Order-by-Disorder at Last Been Found in a Frustrated Magnetic Material?
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Michel Gingras, University of Waterloo
Abstract: In some magnetic systems, known as frustrated magnets, the lattice geometry or the competition between different spin-spin interactions can lead to a sub-exponentially large number of accidentally degenerate classical ground states. Order-by-disorder (ObD) is a concept of central importance in the field of frustrated magnetism. Saddled with large accidental degeneracies, a subset of states, those that support the largest quantum and/or thermal fluctuations, may be selected to form true long-range order. ObD has been discussed extensively on the theoretical front for over 30 years and proposed to be at play in a number of experimental settings. Unfortunately, convincing demonstrations of OBD in real materials have remained scarce. In this talk, I will review the phenomena of thermal and quantum of order-by-disorder and discuss how recent work may have evinced compelling evidence for ObD in some frustrated pyrochlore oxide antiferromagnetic materials.
Host: Sue Coppersmith
Poster: http://www.physics.wisc.edu/twap/posters/2015/3668.pdf
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