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This Week at Physics

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Events During the Week of December 2nd through December 9th, 2012

Monday, December 3rd, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
Gyrokinetic Simulations of Solar Wind Turbulence and Dissipation
Time: 12:00 pm
Place: 1310 Sterling Hall
Speaker: Jason TenBarge, University of Iowa
Abstract: Turbulence plays an important role in space and astrophysical plasmas by mediating the transfer of energy from large-scale motions to the small scales at which the turbulence can be dissipated. Recent advances in solar wind data extending to sub-electron scales have increased the focus on turbulence and dissipation at kinetic scales. Due to the nature of plasma turbulence, gyrokinetics is well suited to study weakly collisional kinetic plasmas, such as the solar wind. We present nonlinear gyrokinetic simulation results in- cluding: (1) energy spectra spanning the entire dissipation range from ion to sub-electron scales that show striking agreement with in situ solar wind data, (2) identification of a dissipation range anisotropic cascade of energy in agreement with predictions of critical balance, and (3) constraints on the physical origin of energy dissipation at kinetic scales.
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Special Lunch Astronomy Talk
"H-alpha Dots: A Catalog of Faint Emission-line Objects Discovered in Narrowband Images"
Time: 12:00 pm
Place: 4421 Sterling Hall
Speaker: Jessica Kellar, Darthmouth College
Abstract: I discovered a number of isolated and compact sources of emission (aEurooeH-alpha dotsaEuro) in a narrow-band H-alpha survey. These H-alpha dots could be (1) isolated extra-galactic HII regions associated with a nearby larger galaxy, (2) dwarf star-forming galaxies, or (3) background galaxies, where another strong emission-line such as [OIII]5007 has redshifted into the H-alpha filter. Based on follow-up spectra taken at the MDM 2.4 meter telescope and HET, I determined that the H-alpha dots are a combination of nearby (z~0.01) dwarf star-forming galaxies and intermediate-redshift (mostly at z~0.3) starforming galaxies and AGN. I will discuss the star-formation properties, environments, and metallicities of the dwarf galaxies. The star-forming galaxies at z~0.3 are very metal-poor, which suggests that they may be recently formed. I will discuss the insights this diverse sample of galaxies from the H-alpha dot survey can give us about galaxy evolution.
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Tuesday, December 4th, 2012

Atomic Physics Seminar
Towards Precision Spectroscopy of Single Trapped Molecular Ions
Time: 11:00 am
Place: 5280 Chamberlin
Speaker: Brian Odom, Northwestern University
Abstract: Precision of the best molecular spectroscopy is currently orders of magnitude behind atomic ion spectroscopy, owing primarily to challenges in molecular state preparation and readout. Applications of improved molecular spectroscopy would include searches for time-variation of fundamental constants, parity violation studies, and searches for fundamental electric dipole moments. Our group at Northwestern University is developing the necessary tools to perform clock-quality spectroscopy on single trapped molecular ions. We are currently working with species having semi-closed electronic cycling transitions, so that optical pumping into the rotational ground state can be achieved by pulse-shaping of a resonant femtosecond laser. I will also describe a simple readout technique we are developing to map the internal molecular state onto a co-trapped atomic ion, using a pulsed radiation pressure force to excite secular motion.
Host: Saffman
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Chaos & Complex Systems Seminar
Cognitive functions of language and their implications for language evolution
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Gary Lupyan, UW Department of Psychology
Abstract: Language is a defining trait of our species. A standard assumption shared by many in the cognitive sciences is that language simply allows for public expression of ideas that are themselves represented in a language-independent aEuro~mentaleseaEuroTM. Similarly, capacities on which humans appear to differ markedly from other animalsaEuro"relational reasoning, theory of mind, categorization, and executive functionaEuro"are often viewed as developments largely unrelated to language. In contrast, recent empirical evidence suggests that normal human cognition is actually language-augmented cognition. Exploring the role that language learning and language use exerts on human cognition leads to a better understanding of the evolutionary trajectory of language and offers a partial solution to the puzzle of how humans have come to possess intellectual capacities that could not have evolved through natural selection (aEurooeWallaceaEuroTMs problemaEuro). A computational framework for exploring the role language exerts on cognition is also discussed.
Host: Sprott
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High Energy Seminar
What can a W boson and some jets reveal at CMS?
Time: 3:00 pm
Place: 4274 Chamberlin
Speaker: Jake Anderson, Fermilab
Abstract: The final state with the leptonic decay of a W boson and a few high pt jets is a fertile area to probe important physics questions at the LHC. Starting with the known standard model, I explore WW and WZ production in the semi-leptonic final state and anomalous triple-gauge coupling. Moving to a search for the enhancement reported by CDF near 150 GeV, I detail the CMS result of a search for this final state. Finally I'll report the latest high-mass Higgs boson searches in decays H > WW > lnujj. All of these topics have made important contributions to our understanding of the electroweak physics and beyond.
Host: Matthew Herndon
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Wednesday, December 5th, 2012

No events scheduled

Thursday, December 6th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Searching for Pulsars and Radio Transients with the Murchison Widefield Array
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: David Kaplan, UW Milwaukee, Department of Physics
Abstract: As one of a new generation of widefield, low-frequency radio
telescopes, the Murchison Widefield Array has enormous potential to
conduct blind searches for radio transients and probe the nearby
pulsar population. We are working to develop a common framework
with the Australian Square Kilometer Array Pathfinder (ASKAP)
Variables and Slow Transients (VAST) survey to allow real-time
transient detection and characterization. I will discuss the expected
types of sources that we hope to discover with the full array and
review some of the initial results from our 32-element testbed.
Host: Peter Timbie
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Astronomy Colloquium
Adaptive Mesh Refinement Dimulations of Cosmic Rays in Clusters of Galaxies
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Samuel Skillman, University of Colorado
Abstract: The observed properties of galaxy clusters are the result of a non-linear interaction between many physical processes including gravity, hydrodynamics, magnetic fields, turbulence, radiation, galaxy formation and feedback, and cosmology. This provides a unique "cosmic laboratory" with which we can learn about our Universe. In particular, galaxy clusters are hosts to cosmic shocks, which propagate through the intracluster medium as a signature of structure formation. It is believed that at these shock fronts, magnetic field inhomogeneities in a compressing flow may lead to the acceleration of cosmic ray electrons and ions. These relativistic particles decay and radiate through a variety of mechanisms, and have observational signatures in radio, hard X-ray, and Gamma-ray wavelengths. The construction of several new low frequency radio telescopes have begun observations of aEurooeradio relicsaEuro, which are thought to be the result of synchrotron emission from shock accelerated electrons. I will present recent work using adaptive mesh refinement MHD simulations of galaxy clusters using Enzo and analyzed with yt, that explain many of the observed properties of these radio relics including polarization fraction and direction of the radiation. I will also present preliminary work of combining a numerical library for momentum-space transport of cosmic rays with Enzo, where we can follow the spectral evolution of these high energy particles along with their spatial transport.
Host: Prof Sebastian Heinz
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Graduate Introductory Seminar
Quantum Computing & Information
Time: 5:45 pm
Place: 2223 Chamberlin Hall
Speaker: , UW Madison
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Friday, December 7th, 2012

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
    http://cmb.physics.wisc.edu/journal/index.html
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
Testing Landauer’s Principle in a feedback trap
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: John Bechhoefer, Simon Fraser University
Abstract: Landauer's principle, formulated in 1961, postulates that irreversible logical or computational operations such as memory erasure require work, no matter how slowly they are performed. For example, to "reset to one" a one-bit memory requires a work of at least kT ln2, which is dissipated as heat. In 1982, Bennett pointed out a link to Maxwell's Demon: Were Landauer's principle to fail, it would be possible to repeatedly extract work from a heat bath.

We report tests of Landauer's principle in an experimental system, where a "virtual" double-well potential is created via a feedback loop. We observe the position of a charged, fluorescent, colloidal particle in water and calculate and then apply the appropriate force using an electric field. In a first experiment, the probability of "erasure" (resetting to one) is unity, and at long cycle times, we observe that the work is compatible with kT ln2. In a second, the probability of erasure is zero; the system may end up in two states; and, at long cycle times, the measured work tends to zero.
Host: Coppersmith
Poster: http://www.physics.wisc.edu/twap/posters/2012/2588.pdf
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-12-03.pdf

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