This Week at Physics

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Events During the Week of January 26th through February 2nd, 2014

Monday, January 27th, 2014

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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R. G. Herb Condensed Matter Seminar
Topological insulators driven by an electron spin
Time: 4:30 pm
Place: Chamberlin 5310
Speaker: Maxim Dzero, Kent State University
Abstract: The application of ideas developed in topology to the electronic band structure led to an intriguing discovery: materials can conduct electricity at the surface while remaining insulating at the bulk. These materials, called topological insulators, will have transformative impact on spintronics, low-power transport, and quantum computing. The search for a true topological insulator took years because even best candidates exhibited significant bulk conductivity. Only recently, literally in the past few months, several experimental groups established that samarium hexaboride, discovered in 1969 in Bell Labs, is a first topological insulator in its bulk form. In my talk, I review the theory which paved the way for this discovery. I will explain how crystalline symmetry, electron-electron interactions, and orbital degeneracy contribute to protecting the topological states in SmB6. In addition, I will discuss the experimental signatures of metallic surface states. Finally, I formulate the theoretical principles for discovering new topological insulators with designable properties.
Host: Vavilov
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Tuesday, January 28th, 2014

Chaos & Complex Systems Seminar
Fractals for kids
Time: 12:05 pm
Place: 4274 Chamberlin Hall (refreshments will be served)
Speaker: Clint Sprott, UW Department of Physics
Abstract: This is a tale of how a physics professor at a major research university came to write a coloring book for children. What better way to learn about fractals than to actually try to draw one by hand? I will explain what fractals are, survey some of the many ways of making fractal images, and show lots of pretty (colored) pictures. Suitable for all ages.
Host: Clint Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
High Energy Neutrinos with Ice Cube
Time: 1:20 pm
Place: 2223 Chamberlin
Speaker: Albrecht Karle, UW Madison Department of Physics
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Wednesday, January 29th, 2014

Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, January 30th, 2014

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Understanding Nature's Particle Accelerators Using Multi-wavelength Signatures
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Udara Abeysekara, Michigan State
Abstract: Nature's particle accelerators, such as Pulsars, Pulsar Wind Nebulae, Active Galactic Nuclei and Supernova Remnants accelerate charged particles to very high energies that then produce high energy photons. The particle acceleration mechanisms and the high energy photon emission mechanisms are poorly understood phenomena. These mechanisms can be understood either by studying individual sources in detail or, alternatively, using the collective properties of a sample of sources. Recent development of GeV survey instruments, such as Fermi-LAT, and TeV survey instruments, such as Milagro and HAWC, provides a large sample of high energy gamma-ray flux measurements from galactic and extra-galactic sources. In this talk, I will present a new multi-wavelength technique, developed to study the collective properties of a given GeV pulsar sample, using the GeV-TeV correlation between pulsars and their associated pulsar wind nebulae. This method is able to measure the beaming factor vs. pulsar spin-down luminosity distribution of a Fermi-LAT GeV pulsar sample. Interestingly, it appears that pulsar acceleration model simulations may be distinguishable by their beaming factor predictions. I will also compare the simulated beaming factor vs. pulsar spin-down luminosity distributions with the experimental results and present the future phase of this technique.
Host: Vandenbroucke
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Astronomy Colloquium
"Baryonic physics in galaxy evolution as seen by the CALIFA survey"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Jakob Walcher, Astrophysical Institute Potsdam
Abstract: Ironically, while the predictions on the dark side of the cosmological &quot;concordance&quot; model LambdaCDM are well understood theoretically, many open questions in cosmology and galaxy evolution revolve around the difficult physics of the luminous, baryonic matter. The Calar Alto Legacy Integral Field Area Survey (CALIFA) is designed to study the baryonic physics of nearby galaxies by providing integral field spectroscopic data cubes in the optical wavelength domain of 600 galaxies of all morphological types. I will present the survey, show the current status, describe the science potential and advertise recent science results. Science results to be shown address a number of topics, among them 1) the powering mechanism of so-called LINER galaxies, 2) the origin of the mas-metallicity relationship, 3) baryonic vs. total matter content, 4) mass build-up of stars over the history of the univers
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Friday, January 31st, 2014

Physics Department Colloquium
Circinus X-1 - A puzzle solved
Time: 3:30 pm
Place: 2441 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Sebastian Heinz, University of Wisconsin-Madison
Abstract: Neutron stars are nature's strongest magnets. At birth their fields are thought to exceed 1e8 Tesla and can reach up to 1e11 Tesla. Over time, these strong fields are believed to decay, but this process is expected to take millions of years. When a neutron star is born in a supernova explosion, it may stay bound to a stellar companion it was in orbit with before. In such a case, the companion can transfer mass to the neutron star and make it shine - we call this an X-ray binary. The nature of the accretion transport of matter can tell us a lot about the properties of a neutron star. For example, we can use X-ray binaries to probe whether the simple picture of young strong magnetized and old weakly magnetized neutron stars hold in nature. I will present results from an ongoing study of the neutron star X-ray binary Circinus X-1 that solve a number of outstanding puzzles about this source and show that even young neutron stars can be weakly magnetized.
Host: Justin Vandenbroucke
Poster: http://www.physics.wisc.edu/twap/posters/2014/3253.pdf
Video: http://www.physics.wisc.edu/vod/2014/01/31.html
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2014/2014-01-27.pdf

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