This Week at Physics

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Events During the Week of February 5th through February 12th, 2012

Monday, February 6th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
High energy density plasmas generated by radial foils on COBRA
Time: 12:05 pm
Place: 2241 Chamberlin
Speaker: Dr. Pierre-Alexandre Gourdain, Cornell University
Abstract: High energy density plasmas turn out to be a wonderful platform to study warm dense matter, high yield fusion energy or astrophysical phenomena. The key ingredient to reach megabars of pressures: geometrical focusing. For instance, a flat metallic foil driven by radial currents, which converge onto a central pin, achieves local densities on the order of 1022 electrons/cm-3 and temperatures in the keV range. More precisely, this foil goes through an ablation phase, characterized by an axial collimated plasma jet, a compression phase, forming a central Z-pinch, and finally an expansion phase, where super-Alfvenic flows carry plasma away. Due to large Reynolds (107 to 109) and magnetic Reynolds numbers (101 to 103), radial foil plasmas reproduce more or less astrophysical jets and outflows. Using these laboratory experiments as intuitive guides, it is possible to highlight the physical mechanisms that might cause such astrophysical formations.
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Condensed Matter Theory Group Seminar
Quantum efficiency of a microwave photon detector based on a current-biased Josephson junction
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Amrit Poudel, UW-Madison
Abstract: We analyze the quantum efficiency of a microwave photon detector based on a current-biased Josephson junction. We consider the Jaynes-Cummings Hamiltonian to describe coupling between the photon field and the junction. We then take into account coupling of the junction and the resonator to the environment. We solve the equation of motion of the density matrix of the resonator-junction system to compute the quantum efficiency of the detector as a function of detection time, bias current, and energy relaxation time. Our results indicate that junctions with modest coherence properties can provide efficient detection of single microwave photons, with quantum efficiency in excess of 80%.
Host: Perkins
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Tuesday, February 7th, 2012

Chaos & Complex Systems Seminar
Social networking sites and adolescent health
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Megan A. Moreno, UW School of Medicine and Public Health
Abstract: Revolutionary advances in biological and biomedical imaging over the last twenty years have brought about the development of improved methods for non-invasively imaging dynamic biological processes. Of particular significance have been optical (photonic) techniques that have allowed for the visualization and manipulation of molecular and cellular structures within living tissue with minimal perturbation. The efforts of the multidisciplinary UW-Madison Laboratory for Optical and Social networking sites are popular among adolescents and college students. References to health behaviors and conditions, such as alcohol and depression, are frequently seen on these sites. The meaning and influence of such displays is currently under investigation and will be explored in this talk.<br>
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Silicon quantum dot spin qubits
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Mark Eriksson, University of Wisconsin Department of Physics
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Theory Seminar (High Energy/Cosmology)
Title to be announced
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Matt Buckley, Fermilab
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Wednesday, February 8th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
The evolution of the edge pedestal structure and turbulence during the edge localized mode (ELM) cycle on NSTX
Time: 12:00 pm
Place: 2241 Chamberlin
Speaker: Dr. Ahmed Diallo, Princeton Plasma Physics Laboatory
Abstract: Fusion performance of the International Thermonuclear Experiment Reactor (ITER) is predicted to be proportional to the square of the pedestal pressure height. The reference scenario for the ITER high confinement mode is projected to be in the Type I edge localized mode (ELMy) regime where the maximum pedestal (edge) pressure is reached leading to an enahcement of the fusion gain. It is also well known that ELMs pose a threat to the plasma facing components. Controlling ELMs is necessary and hence it is vital to understand the underlying physics. In recent years, substantial progress has been made in pedestal research on the National Spherical Torus Experiment (NSTX). Characterizations of the pedestal parameter dynamics and microturbulence in the pedestal region throughout the edge localized modes (ELM) cycles are performed. More specifically, this talk will be describing the current understanding of the inter-ELM evolution, approach to instability of the edge pedestal, and summarize ongoing work aimed at identifying the microturbulence limiting the pedestal gradient. Finally, transition to ELM-free operations enabled by lithiumcoated walls will be discussed as such regime provides larger pedestal pressure than in ELMy cases.
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Department Meeting
CANCELED
Time: 12:15 pm
Place: 5310 Chamberlin Hall
Canceled
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Thursday, February 9th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The Empirical Case For 10 GeV Dark Matter
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Dan Hooper, Fermilab / University of Chicago
Abstract: I will summarize and discuss the body of evidence which has accumulated in favor of dark matter in the form of approximately 10 GeV particles. This evidence includes the spectrum and angular distribution of gamma rays from the Galactic Center, the synchrotron emission from the Milky Way's radio filaments, the diffuse synchrotron emission from the Inner Galaxy (the "WMAP Haze") and low-energy signals from the direct detection experiments DAMA/LIBRA, CoGeNT and CRESST-II. This collection of observations can be explained by a relatively light dark matter particle with an annihilation cross section consistent with that predicted for a simple thermal relic (sigma v ~ 10^-26 cm^3/s) and with a distribution in the halo of the Milky Way consistent with that predicted from simulations. Astrophysical explanations for the gamma ray and synchrotron signals, in contrast, have not been successful in accommodating these observations. Similarly, the phase of the annual modulation observed by DAMA/LIBRA (and now supported by CoGeNT) is inconsistent with all known or postulated modulating backgrounds, but are in good agreement with expectations for dark matter scattering. This scenario is consistent with all existing indirect and collider constraints, as well as the constraints placed by CDMS. Consistency with xenon-based experiments can be achieved if the response of liquid xenon to very low-energy nuclear recoils is somewhat suppressed relative to previous evaluations, or if the dark matter possesses different couplings to protons and neutrons.
Host: Reina Maruyama
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Astronomy Colloquium
"A New Look at Stellar Evolution: Chi-by-Eye Evolves to Bayesian Statistics"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Ted von Hippel, Embry-Riddle Aeronautical University
Abstract: In the 1960's stars were observed with single-channel photometers or worse, stellar evolution codes were run on a computer that barely bested a slide rule, and the results were compared by eye. While the observations and stellar models have improved tremendously in the interim, the methods by which we compare stellar models to data generally have not. I will describe a new Bayesian approach to this problem. Our Bayesian technique yields better precision in the ages, distances, etc. for stars and clusters, provides a fuller understanding of errors and correlations among the derived parameters, and allows us to attack a range of problems in stellar evolution in a consistent manner for the first time.
Host: Robert Mathieu, Chair of Astronomy
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Cosmic Accelerators: Pulsars and Pulsar Wind Nebulae
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Aous Abdo, George Mason University
Abstract: The rapid spins and intense magnetic fields (109 - 1014 Gauss) of pulsars accelerate particles to very high energies, both in their magnetospheres and in relativistic winds, powering emission from radio waves to the highest energy gamma-rays. NASA's Fermi Gamma-Ray Space Telescope, launched in 2008, has proved to be a powerful tool for studying these systems. Fermi observations have increased the population of known gamma-ray pulsars from 6 to more than 100. New classes of gamma-ray pulsars, including millisecond and radio-quiet pulsars, have emerged. With its unprecedented sensitivity, Fermi has transformed our understanding of the energetic particle accelerators in our Galaxy and thereby linked observations of the sky at the highest photon energies (1012 eV) with those at the lower end of the electromagnetic spectrum. In my talk I will discuss some of the new and exciting results from Fermi and focus on how these discoveries integrate with the overall picture of pulsars and their nebulae that covers some 20 decades of energy.
Host: Halzen
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Friday, February 10th, 2012

Theory Seminar (High Energy/Cosmology)
Title to be announced
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Brock Tweedie, Boston University
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Physics Department Colloquium
Reinventing the Accelerator
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Prof. James B. Rosenzweig, UCLA Dept. of Physics and Astronomy
Abstract: The modern accelerator has undeniably served as an essential, workhorse scientific instrument, underpinning progress in fields from high energy physics through colliding beams, to structural biology, condensed matter, ultra-fast science, and and high energy density physics through light sources. The future of these enterprises is threatened, however, by the size and attendant cost of building the next generation instruments. The urgency of providing a new path in accelerators has been recognized for several decades by now, solutions offered, and dramatic progress made. These solutions include use of direct laser acceleration, and new schemes termed "wakefield accelerators", in which one may achieve acceleration in plasma with over 1 TV/m electric fields. Thus one may envision shrinking future accelerators by three-to-four orders of magnitude in size. While the ultimate goal of such research is to provide a path to TeV high energy physics machines, this goal is still years off. In this talk, we will therefore discuss frontier results from the advanced accelerator field, and place them in the context of nearer term application to the next generation X-ray free-electron laser.
Host: Lawler
Poster: http://www.physics.wisc.edu/twap/posters/2012/2336.pdf
Video: http://www.physics.wisc.edu/vod/2012/02/10.html
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Saturday, February 11th, 2012

Wonders of Physics
Physics of the Wisconsin Idea
Time: 1:00 pm
Place: 2103 Chamberlin
Abstract: The twenty-ninth annual presentation of The Wonders of Physics with Professor Clint Sprott and colleagues will show some of the many ways physics has benefited society. This fun-filled educational presentation is suitable for people of all ages.
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Wonders of Physics
Physics of the Wisconsin Idea
Time: 4:00 pm
Place: 2103 Chamberlin
Abstract: The twenty-ninth annual presentation of The Wonders of Physics with Professor Clint Sprott and colleagues will show some of the many ways physics has benefited society. This fun-filled educational presentation is suitable for people of all ages.
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Wonders of Physics
Physics of the Wisconsin Idea
Time: 7:00 pm
Place: 2103 Chamberlin
Abstract: The twenty-ninth annual presentation of The Wonders of Physics with Professor Clint Sprott and colleagues will show some of the many ways physics has benefited society. This fun-filled educational presentation is suitable for people of all ages.
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Sunday, February 12th, 2012

Wonders of Physics
Physics of the Wisconsin Idea
Time: 1:00 pm
Place: 2103 Chamberlin
Abstract: The twenty-ninth annual presentation of The Wonders of Physics with Professor Clint Sprott and colleagues will show some of the many ways physics has benefited society. This fun-filled educational presentation is suitable for people of all ages.
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Wonders of Physics
Physics of the Wisconsin Idea
Time: 4:00 pm
Place: 2103 Chamberlin
Abstract: The twenty-ninth annual presentation of The Wonders of Physics with Professor Clint Sprott and colleagues will show some of the many ways physics has benefited society. This fun-filled educational presentation is suitable for people of all ages.
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-02-06.pdf

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