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Events at Physics

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Events on Thursday, February 11th, 2016

Special LIGO Press Conference
LIGO Online Press Conference
Time: 9:30 am
Place: 5280 Chamberlin Hall
Speaker: LIGO online press conference
Abstract: This year marks the 100th anniversary of the first publication of Albert Einstein's prediction of the existence of gravitational waves. With interest in this topic piqued by the centennial, the LIGO group will discuss their ongoing efforts to observe gravitational waves.

LIGO, a system of two identical detectors carefully constructed to detect incredibly tiny vibrations from passing gravitational waves, was conceived and built by MIT and Caltech researchers, funded by the National Science Foundation, with significant contributions from other U.S. and international partners. The twin detectors are located in Livingston, Louisiana, and Hanford, Washington. Research and analysis of data from the detectors is carried out by a global group of scientists, including the LSC, which includes the GEO600 Collaboration, and the VIRGO Collaboration.

The LIGO team will host an online press conference from Washington DC at 9:30 AM central time.
Host: Peter Timbie
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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
The Next Generation Balloon-borne Large Aperture Submillimeter Telescope (BLAST-TNG)
Time: 3:00 pm
Place: 5280 Chamberlin Hall
Speaker: Brad Dober, University of Pennsylvania
Abstract: After decades of study, the physical processes regulating star formation remain poorly understood. In particular, the role played by magnetic fields in both the formation of molecular cloud structure and the regulation of core collapse is unclear. In many simulations, magnetic fields dramatically affect both the star formation efficiency and lifetime of molecular clouds. However, observationally the strength and morphology of magnetic fields in molecular clouds remain poorly constrained. Submillimeter polarimetry provides an important observational window on magnetic fields in star forming regions. By mapping polarized emission from dust grains aligned with respect to their local magnetic field, the field orientation (projected on the sky) can be traced. The Next-Generation Balloon-borne Large Aperture Submillimeter Telescope (BLAST-TNG) is a 2.5 meter submillimeter polarimeter designed to map magnetic fields. BLAST-TNG utilizes three polarization-sensitive arrays of over 4000 microwave kinetic inductance detectors, centered at 250, 350, and 500 microns. BLAST-TNG will provide an unprecedented number of magnetic field vectors, and will enable a rigorous statistical analysis of the role that magnetic fields play in star formation. I will present the overall design and progress towards deployment of both the detector arrays and readout hardware in anticipation for a December 2016 BLAST-TNG Antarctic flight.
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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