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This Week at Physics

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Events During the Week of November 25th through December 1st, 2012

Monday, November 26th, 2012

Plasma Physics (Physics/ECE/NE 922) Seminar
Observing the acceleration of suprathermal electrons by Alfven waves using the diagnostic of whistler-mode wave absorption
Time: 12:00 pm
Place: 1310 Sterling Hall
Speaker: Fred Skiff, University of Iowa
Abstract: Shear Alfven waves are believed to accelerate plasma electrons through both linear and nonlinear wave-particle interactions. In the LAPD plasma device wave packets of nearly-periodic plane waves with dB/B~10E-5 are generated using an arbitrary spatial waveform antenna in the central region of the plasma. When the perpendicular wavelength is shortened to a few times the collisionless skin depth a parallel electric field is produced that should be able to accelerate plasma electrons. The difficulty in observing these electrons is that the change to the distribution function is small and should be greatest at high velocity where the total number of particles is small. Preliminary results of using whistler-mode wave absorption as a diagnostic of the suprathermal electrons indicate that it is indeed possible to observe the effects produced by electron acceleration. We will discuss the problems of separating out the effect of changes in the bulk plasma density (including ducting) from the effects of wave damping (of the whistler-mode wave) that enable us to measure the perturbed electron velocity distribution to high resolution.
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Tuesday, November 27th, 2012

Chaos & Complex Systems Seminar
The prospects for extraterrestrial life
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Jim Blair, Milton and Edgewood College
Abstract: The betting odds for discovering ET life have increased dramatically recently because of discoveries in astronomy, oceanography and extremophile biology.

A--The Drake Equation

B--Is There Humanoid Life on Other Planets?
(An update of my 1970's lecture given at Milton College, the UW Madison, and Wisconsin Public Radio.)

C--Stellar Evolution and Galactic Geopolitics

D--Are Planets necessary for Life?
Life on Moons?
Life in Space?
Life inside Stars?
Aliens
Host: Sprott
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Special ASTRONOMY TALK
"The Cosmological Challenges of Dwarf Galaxies"
Time: 3:45 pm
Place: 4421 Sterling Hall
Speaker: Julio Navarro, University of Victoria
Abstract: A prime challenge to our understanding of galaxy formation concerns the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in the current LCDM paradigm. This is usually accounted for by assuming that energetic feedback from evolving stars confines dwarf galaxy formation to relatively massive halos spanning a narrow mass range. I will highlight a number of observations that may be used to test this assumption and discuss the puzzles and challenges that arise from this analysis.
Host: Prof Elena D'onghia
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Wednesday, November 28th, 2012

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Astronomy Colloquium
Special Colloquium
A screening of "Hubble's Diverse Universe"
Time: 4:30 pm
Place: 2241 Chamberlin Hall
Speaker: Dr. Jarita Holbrook
Abstract: A different kind of science documentary, the scientific research and experiences of six African American and three Hispanic American astronomers and astrophysicists are explored. aEuro~HubbleaEuroTM is short for the Hubble Space Telescope (HST). 'Diverse' refers to both the ethnic diversity of the scientists who appear in the film and the diverse set of astronomy topics discussed. Science (14A1/2 minutes): Beautiful images of celestial bodies taken by the Hubble Space Telescope are interspersed with the astrophysicistsaEuroTM descriptions of the images and the importance of HST to their research. HST discoveries, unexpected astronomy results, and the continually changing theories within astronomy are all examined. Pulsars, planetary nebulae, gamma-ray bursts, active galactic nuclei, black holes, and star formation are covered. Diversity (7A1/2 minutes): The astrophysicists talk about what life is like as a minority within this scientific discipline. They share some of the daily experiences of being less than 8% of the astronomy population in the United States. Mentoring and Outreach (8 minutes): All of the astrophysicists agree that having mentors is important to succeed as a scientist. In order to become an astrophysicist people helped them and now they try to help others. They talk about the good mentors that they have and focus on specific things that make them good mentors. They also give warnings about how to steer clear of pitfalls. NASAaEuroTMs Contributions (10 minutes): NASA has played a significant role in the lives of these nine minority scientists. The astrophysicists are young, vibrant, funny, and generally engaging making this an exceptional astronomy documentary in which the people are as engaging as the science. Hubble's Diverse Universe is a tribute to the Hubble Space Telescope now in its 20th year given eloquently by these underrepresented minority scientists.
Host: The Holtz Center for Science and Technology
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Thursday, November 29th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Microwave Detection of Cosmic Ray Air Showers
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Christopher Williams, Kavli Institute for Cosmological Physics, The University of Chicago
Abstract: I will present the design and implementation of the Microwave Detection of Air Showers (MIDAS) experiment, a pathfinder for detection of Extensive Air Showers (EAS) induced by Ultra High Energy Cosmic Rays (UHECRs). The MIDAS experiment uses a multi-pixel imaging telescope instrumented with commercially sourced GHz receivers and custom fast-detection electronics to search for EAS. The microwave detection technique is analogous to the already successful fluorescence technique, but with nearly 100% duty cycle. If successful, the microwave technique will provide an attractive method for instrumenting the extremely large areas required by future UHECR observatories. The first science phase of the MIDAS experiment gathered 61 days of livetime data operating on the University of Chicago campus. I will present the current limits on EAS microwave emission from this data set. The second science phase is underway with installation of the MIDAS detector at the Pierre Auger Observatory in MalargA1/4e, Argentina. Operating in coincidence with the Auger surface detector will greatly increase the sensitivity of the MIDAS experiment.
Host: Peter Timbie
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Astronomy Colloquium
"Revealing the origins and environments of Mg II absorbers with the SDSS and 3D-HST"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Britt Lundgren, Astronomy Department
Abstract: Foreground absorption features in the spectra of distant quasars provide largely unbiased probes of the baryon content of galaxies and the intergalactic medium to high redshift. Absorption features from singly-ionized magnesium (Mg II) are particularly prolific in optical spectra within the range 0.3 < z < 2.0, and are expected to trace a wide range of galaxy environments and halo-disk processes, though detecting the individual host galaxies of these absorbers presents an observational challenge. The extraction of ~100,000 quasar absorption line systems from the Sloan Digital Sky Survey -I/II and -III has begun to revolutionize our understanding of the host galaxies and environments of Mg II absorbers. I will present highlights from my work examining the statistical properties of Mg II host galaxies from stacking and clustering measurements using the largest absorption line data set ever compiled. I will also present new direct observations of Mg II host galaxies at z > 1 from the 3D-HST Survey. These analyses reveal compelling links between high equivalent width Mg II absorbers and large-scale star formation-driven outflows, which I will discuss in the context of other recent findings from the literature.
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Graduate Introductory Seminar
Astrophysics III: HAWC/CTA/Fermi
Time: 5:45 pm
Place: 2223 Chamberlin Hall
Speaker: Westerhoff, Vandenbrouke, UW Madison
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Friday, November 30th, 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
Emergent phases of correlated electrons in materials with spin-orbit coupling and magnetic frustration.
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Natalia Perkins, UW-Madison
Abstract: Recently spin-orbit coupling (SOC) effects have become a subject of intensive research across many different disciplines in condensed matter physics. In particular, SOC has been appreciated in correlated electron systems with orbital degrees of freedom for its role in creating a new class of electronic states that allow crossed-responses of the electrons to electric and magnetic fields. The effects of SOC are especially pronounced in 4d and 5d transition-metal compounds, which have large intrinsic atomic SOC due to their high atomic weight. In these materials electrons are more delocalized than in the 3d systems, the Coulomb interaction is effectively screened, and SOC often becomes a dominant interaction, which makes the hierarchy of energy scales very unusual. This unusual hierarchy of interactions and strong entanglement between spin and orbital degrees of freedom in 5d-systems lead to a variety of interesting ground states but also to novel types of elementary excitations which carry both spin and orbital characteristics and also strongly depend on lattice and bonding geometries. Because of these properties 5dsystems might be considered as promising materials for the realization of various emergent quantum phases, such as spin liquids, topological insulators, Weyl semimetals, and novel magnetically ordered Mott insulators. 3d transition metals may also exhibit important SOC if competing interactions such as crystal fields and exchange interactions are suppressed by geometrical frustration of the underlying crystal structures. Examples of this type have been observed in various 3d-based spinels, in which the SOC is responsible for the orthogonal magnetic structure in the V-based spinel MnV2O4, multiferroic behavior of FeV2O4, and the spin-orbital liquid state in the Fe-based spinel FeSc2S4.
Host: Chung
Poster: http://www.physics.wisc.edu/twap/posters/2012/2767.pdf
Video: http://www.physics.wisc.edu/vod/2012/11/30.html
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2012/2012-11-26.pdf

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