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This Week at Physics

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Events on 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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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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