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This Week at Physics

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Events During the Week of January 20th through January 27th, 2013

Monday, January 21st, 2013

No events scheduled

Tuesday, January 22nd, 2013

Chaos & Complex Systems Seminar
The Minus-1st Law: The conservation of information and how it leads to chaos
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: George Hrabovsky, Madison Area Science and Technology
Abstract: The conservation of information is central to all of physics. It also seems so obvious to us physicists that we don't talk about it much in courses. It is a simple idea, the quantity of information in a closed system never changes. This simple idea requires us to think deeply about the nature of dynamical systems. The ramifications are dramatic; it leads to the second law of thermodynamics and to chaos.
Host: Sprott
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Wednesday, January 23rd, 2013

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Dark Matter Results from XENON100 and Scintillation Response of LXe to Low Energy Particles
Time: 1:00 pm
Place: 4274 Chamberlin
Speaker: Kyungeun Lim, Columbia University
Abstract: XENON100 is a dual-phase (liquid-gas) time projection chamber (TPC) containing a total of 161 kg of LXe with a 62 kg WIMP target mass, built with radiopure materials to achieve an ultra-low electromagnetic background and operated at the Laboratori Nazionali del Gran Sasso in Italy. Data from the XENON100 experiment have resulted in the most stringent limits on the spin-independent elastic WIMP-nucleon cross sections for WIMP masses above 8 GeV/c^2.

I will present the experiment and its latest dark matter search results. I will also discuss a dedicated test facility built and operated at Columbia University to measure with high precision the scintillation response of LXe to low-energy electrons and nuclear recoils of interest to dark matter direct detection experiments like XENON.
Host: Reina Maruyama
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Thursday, January 24th, 2013

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
AGN as Multi-Messenger Probes of the High-Energy Universe: Observations with the HAWC Observatory
Time: 2:00 pm
Place: 4274 Chamberlin Hall
Speaker: Asif Imran, Los Alamos National Lab
Abstract: Ground-based gamma-ray observatories have opened up a new window into the high-energy universe. To date, exciting results reported by experiments such as VERITAS, H.E.S.S., and Milagro include the the detection of photons from nearly 50 relativistic AGN jets at TeV energies. However, the picture of the universe beyond 1 TeV is far from complete. The origin and composition of the extra-galactic ultrahigh energy cosmic rays (UHECR) remains a central problems in astrophysics. Based on energy considerations, recent studies have argued that highly relativistic jets in AGNs are the best candidates for the sites of UHECR acceleration. Consequently, we may be able to observe >20 TeV emission from nearby AGN contrary to conventional models that predict significant attenuations of the source gamma-ray photons via the diffuse extragalactic background light. The High Altitude Water Cherenkov (HAWC) observatory, a next-generation ground-based particle shower detector will be sensitive to photon energies from 50 GeV to 100 TeV with angular resolution of 0.3 degrees at E> 1 TeV. HAWC's high duty cycle (~100%) and wide field of view (~2 sr) is ideal to test AGN as possible sites for the acceleration of UHECR. Furthermore, HAWC's observations of an orphan flare from AGN coupled with the detection of coincident neutrinos by the IceCube observatory with allow us to independently probe the acceleration of UHECR in AGN.

In this talk, I will give an overview of the mechanism for the production of high energy photons from UHECR-induced cascade emission along with an update on the current status of the HAWC observatory. I'll also present the sensitivity of the HAWC detector to TeV emission from AGN.
Host: Westerhoff
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WIPAC Seminar
Exploring Fundamental Physics with the Cosmic Microwave Background: New Results from the South Pole Telescope
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Bradford Benson, University of Chicago
Abstract: The cosmic microwave background (CMB) is revolutionizing our understanding of the Universe. The CMB is the most powerful piece of evidence that we live in a geometrically flat Universe, dominated by non-baryonic cold dark matter and dark energy. Even with this basic cosmological model established, there are still many outstanding questions: What is dark energy? What are the neutrino masses? Are there missing standard model particles that we can detect cosmologically? Did Inflation happen, and what physics was responsible for it? The CMB remarkably is imprinted with information regarding each of these questions. In addition, the mm-wave CMB data is opening a new window into the extragalactic sky, simultaneously providing large catalogs of massive galaxy clusters, high-redshift lensed galaxies, and other mm-wave bright sources. I will present recent results from the South Pole Telescope, a 10-meter mm-wavelength telescope which recently completed a survey of 2500 sq. deg. of the sky with unprecedented depth and angular resolution. In particular, I will highlight SPT measurements of the CMB power spectrum, the Sunyaev-Zel'dovich galaxy cluster catalog, and the cosmological implications of the SPT data, including its constraints on dark energy, the sum of the neutrino masses, and the number of relativistic particle species.

Note: this is a joint WIPAC Seminar - Astronomy Colloquium.

Host: Naoko Kurahashi Neilson
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Friday, January 25th, 2013

Physics Department Colloquium
Quantum Coherence in Biology
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: K. Birgitta Whaley, University of California, Berkeley
Abstract: Recent years have seen mounting evidence for the existence of dynamical phenomena in biological systems that involve coherent quantum motion, requiring us to revise the long standing view of quantum effects in biology being restricted to understanding of molecular energetics, stability and kinetics. I shall describe the considerable evidence that quantum coherent electronic dynamics contributes to the extremely efficient light-harvesting stage of photosynthesis, then present theoretical studies that analyze the nature of this coherence, its relation to the non-local quantum correlations characteristic of entanglement, and a possible functional role for long range unidirectional energy transport.
Host: Gilbert
Poster: http://www.physics.wisc.edu/twap/posters/2013/2709.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2013/2013-01-21.pdf

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