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This Week at Physics

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Events During the Week of February 7th through February 14th, 2016

Monday, February 8th, 2016

No events scheduled

Tuesday, February 9th, 2016

Chaos & Complex Systems Seminar
Making computer networks work (Part II)
Time: 12:05 pm
Place: 4274 Chamberlin Hall (Refreshments will be served)
Speaker: Aditya Akella, UW Department of Computer Sciences
Abstract: We depend on computer networks for literally every aspect of our daily lives, e.g., work, family, education, socializing, entertainment, and finances. Yet, the quality of experience that we as users derive from these networks is far from satisfactory. We're routinely hit by poor or variable page-load times and download speeds, and even outright unavailability of critical network-accessible services. Researchers and practitioners alike work round the clock to develop fixes, but disruptive applications, protocols, and hardware quickly render them ineffective. <br>
Host: Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Magnetic reconnection, a celestial phenomenon in the laboratory
Time: 1:20 pm
Place: 2241 Chamberlin Hall
Speaker: Jan Egedal, UW Madison Department of Physics
Host: Wesley Smith
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Theory Seminar (High Energy/Cosmology)
TBD
Time: 3:30 pm
Place: 5280 Chamberlin Hall
Speaker: Dr. Jack Kearney , Fermilab
Abstract: TBD
Host: Amol Upadhye
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Wednesday, February 10th, 2016

No events scheduled

Thursday, February 11th, 2016

R. G. Herb Condensed Matter Seminar
Origin of the in-plane resistivity anisotropy of the iron pnictides: scattering rate or plasma frequency?
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Michael Schuett, University of Minnesota
Abstract: In-plane resistivity anisotropy has been the prime tool to probe the electronic nematic state of the iron-based high-temperature superconductors. In these correlated phases, the electronic degrees of freedom spontaneously lower the point-group symmetry of the system from tetragonal to orthorhombic. Thus, the elucidation of the origin of the resistivity anisotropy could provide invaluable information about the microscopic nature of the nematic state of the iron pnictides. In general, an anisotropic resistivity anisotropy can be the result of an anisotropic scattering rate (either elastic or inelastic) and/or an anisotropic plasma frequency. To shed light on this problem, here we investigate the impact of spin fluctuations on the anisotropic ac conductivity of the iron pnictides.

We show that spin fluctuations affect both the scattering rate and the effective plasma frequency. Interestingly, the anisotropy in the effective scattering rate is antagonistic to the anisotropy induced in the effective plasma frequency and can become comparable near the nematic transition temperature. As a result, the ac conductivity may seem to be dominated by an effective plasma frequency anisotropy, although the dc conductivity is actually determined solely by the scattering rate anisotropy. Our results agree qualitatively with recent experiments in detwinned iron pnictides, and reveal an unavoidable entanglement between scattering rate anisotropy and plasma frequency anisotropy caused by spin fluctuations.
Host: Alex Levchenko
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The Atacama B-mode Search: Cosmology at 17,000 Feet
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Sara Simon, Princeton
Abstract: The Atacama B-mode Search (ABS) was a crossed-Dragone telescope located at an elevation of 5200 m in the Atacama Desert in Chile that observed the cosmic microwave background (CMB) from February 2012 until October 2014. ABS was a pathfinder experiment that searched for the primordial B-mode polarization signal at large angular scales from multipole moments of l~40 to l~500, where it is expected to peak. The ABS focal plane consisted of 240 pixels sensitive to 145 GHz, each containing two transition-edge sensor bolometers coupled to orthogonal polarizations. Cold optics and an ambient temperature, rapidly-rotating half-wave plate made the ABS instrument unique. I will discuss the ABS instrument and its contributions to the field of CMB cosmology.
Host: Kam Arnold
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Sub-mm ballooning
Time: 3:00 pm
Place: 5280 Chamberlin Hall
Speaker: Brad Dober, University of Pennsylvania
Abstract: tbd
Host: Kam Arnold
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Astronomy Colloquium
Gas dynamics and star formation in dwarf galaxies
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and Cookies at 3:15 PM
Speaker: Dr. Federico Lelli, Case Western Reserve University
Abstract: Dwarf galaxies are the most common types of galaxies in the Universe. They play a key role in understanding the process of star formation and the effect of stellar feedback on galaxy evolution. I will present recent results from interferometric HI observations, focusing on two key types of low-mass galaxies: starburst dwarfs and tidal dwarfs.

Starburst dwarfs in the nearby Universe represent our best analogues to high-z star-forming galaxies. We find that the inner rotation curves of starburst dwarfs rise more steeply than those of typical dwarf irregulars, pointing to a close link between intense star formation and galaxy dynamics (distribution of baryons and dark matter).

Tidal dwarf galaxies (TDGs) are recycled objects that form within the tidal debris around interacting and merging galaxies. TDGs may represent a new, unexplored channel for the formation of dwarf galaxies. We find that putative TDGs are associated with rotating gas disks and seem to be nearly devoid of dark matter, as predicted by numerical simulations in a LCDM context. I will discuss the implications of these results for the formation and evolution of dwarf galaxies.
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Friday, February 12th, 2016

Physics Department Colloquium
Deciphering IceCube’s High-Energy Neutrinos
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Marek Kowalski, Humboldt University Berlin & DESY Zeuthen
Abstract: The existence of high energy neutrinos of cosmic origin was discovered by IceCube in 2013, opening a new window to the cosmos. Since then much has been learned about their properties, however, the astrophysical sources of the neutrinos remain unresolved so far. In this talk I will summarize the knowns and unknowns concerning IceCube's neutrinos and how advances in multi-messenger astronomy can help solve the puzzle. Plans for a next-generation IceCube detector, named IceCube-Gen2, will be presented.
Host: Albrecht Karle
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Saturday, February 13th, 2016

Wonders of Physics
Physics of Superheros
Time: 1:00 pm
Place: 2103 Chamberlin
Speaker: Sprott and others
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