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This Week at Physics

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Events During the Week of January 22nd through January 29th, 2012

Monday, January 23rd, 2012

First Day of Class

Plasma Physics (Physics/ECE/NE 922) Seminar
Understanding and predicting turbulence in laboratory plasmas
Time: 12:05 pm
Place: 2535 Engineering Hall
Speaker: Prof. Frank Jenko, Max Planck Institute for Plasma Physics, Garching
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Tuesday, January 24th, 2012

Chaos & Complex Systems Seminar
Linear social interactions models
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Steven Durlauf, UW Department of Economics
Abstract: This talk will provide an overview of recent efforts by economists to understand social influences on economic behavior. The talk will emphasize the difficulties involved in uncovering evidence of social forces from observational data. Links to the growing literature on social networks will be made.
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
The Higgs Boson
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Sridhara Dasu, University of Wisconsin Department of Physics
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Wednesday, January 25th, 2012

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
Agenda: http://www.physics.wisc.edu/twap/agendas/2283.pdf
Minutes: http://www.physics.wisc.edu/twap/minutes/2283.pdf
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Thursday, January 26th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Measuring the Extragalactic Magnetic Field Via Gamma-Ray Blazar Observations
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Tom Weisgarber, University of Chicago
Abstract: Despite many efforts, the extragalactic magnetic field (EGMF), presumed to exist in the voids of the large scale structure, remains undetected. Since the EGMF may be generated either by processes in the early universe or by outflows from galaxies, and it could supply the seed fields required by many models of galactic and cluster field formation, its properties are of interest from both cosmological and astrophysical viewpoints. I will review a recently developed technique for measuring the EGMF strength using combined gamma-ray observations from the Fermi Gamma-Ray Space Telescope and ground-based instruments such as VERITAS. The technique relies on modeling the electromagnetic cascade that develops in extragalactic space due to gamma-ray interactions with the extragalactic background light and CMB and for the first time permits the placement of a lower limit on the EGMF strength. I will describe two approaches to characterizing the cascade and discuss the interpretation of gamma-ray observations of the blazar RGB J0710+591 as limits on the existence of an EGMF-induced "halo."
Host: Stefan Westerhoff
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Astronomy Colloquium
Probing the dark hearts of dusty galaxies - molecules as diagnostic tools
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Susanne Aalto, Chalmers University of Technology
Abstract: Spectacular starburst and AGN activity occurs when mergers of gas-rich systems funnel massive amounts of molecular gas and dust
into the remnant centers of ultraluminous infrared galaxies (ULIRGs). In these compact regions molecular gas rotating in the cores obscures and feeds the activity. Much of the ongoing research into initial phases of galaxy building, however, also focuses on the pre-ULIRG phases of starbursts, QSOs and assembly of galaxies via major mergers. These phases parallel conditions in lower luminosity starbursts (LIRGs) with spatially extended starburst regions. Detailed studies of LIRGS, ULIRGs, and AGN in the near-field are therefore essential both for defining the evolution of present day galaxies and sorting out key astrophysical processes in their more distant predecessors.

I will present how we can probe the nature and evolution of the dense interstellar medium (ISM), a primary evolutionary vector in starburst and AGN activity, using molecular tracers that penetrate the vast columns of dust - and also enable unique investigations of chemical and physical conditions in the molecular gas and dust. The most compact obscured nuclei, for example, need to be studied with radiatively excited molecular emission to get past the optically thick barrier.
With the emerging unprecedented capacities of ALMA we can address the nature of AGNs and starbursts, their associated molecular outflows in the context of their evolution and the starburst-AGN connection near and far.
Host: Professor John S Gallagher
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Friday, January 27th, 2012

Atomic Physics Seminar
Preparation and stabilisation of a non-classical field in cavity by quantum feedback
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Clément Sayrin, Laboratoire Kastler Brossel, l'Ecole Normale Supérieure
Abstract: Feedback loops are central in most classical control procedures. A controller compares the signal measured by a sensor with the target value. It then adjusts an actuator to bring the signal close to the target value. Generalizing this scheme to the quantum world must overcome a fundamental difficulty: the sensor measurement causes a random back-action on the system. I will present how we have been able to continuously operate a quantum feedback loop stabilizing photon number states in a very high finesse Fabry-Perot cavity. Circular Rydberg atoms repeatedly achieve weak quantum non-demolition measurements of the photon number. A classical computer estimates in real-time the density matrix of the field, based on the outcome of these measurements, and taking into account all known experimental imperfections. It then calculates the amplitude of small classical microwave fields injected into the cavity to bring the field into the target state. We have been able to prepare on demand and stabilize Fock states containing from 1 to 4 photons. This achievement opens interesting perspectives for the production and control of non-classical states for quantum information processing.
Host: Mark Saffman
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Physics Department Colloquium
Atom Trap, Krypton-81, and Global Groundwater
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Zheng-Tian Lu, Argonne National Laboratory & the University of Chicago
Abstract: The long-lived noble-gas isotope 81Kr is the ideal tracer for old water and ice in the age range of 10^5 - 10^6 years, a range beyond the reach of 14C. 81Kr-dating, a concept pursued over the past four decades by numerous laboratories employing a variety of techniques, is now available for the first time to the earth science community at large. This is made possible by the development of an atom counter based on the Atom Trap Trace Analysis (ATTA) method, in which individual atoms of the desired isotope are selectively captured and detected with a laser-based atom trap. ATTA possesses superior selectivity, and is thus far used to analyze the environmental radioactive isotopes 81Kr, 85Kr, and 39Ar, These three isotopes have extremely low isotopic abundances in the range of 10^-16 to 10^-11, and cover a wide range of ages and applications. In collaboration with earth scientists, we are dating groundwater and mapping its flow in major aquifers around the world.
Host: Heeger
Poster: http://www.physics.wisc.edu/twap/posters/2012/2244.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-01-23.pdf

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