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This Week at Physics

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Events on Thursday, November 15th, 2018

R. G. Herb Condensed Matter Seminar
Optically-pumped dynamic nuclear polarization under ambient conditions via nitrogen-vacancy centers in diamond
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Prof. Carlos Meriles, City College of New York
Abstract: A broad effort is underway to improve the sensitivity of nuclear magnetic resonance through the use of dynamic nuclear polarization. Nitrogen-vacancy (NV) centers in diamond offer an appealing platform because these paramagnetic defects can be optically polarized efficiently at room temperature. This presentation surveys alternative NV-based 13C spin polarization protocols, with emphasis on recent schemes designed for powder geometries. Through experimental, analytical, and numerical work, we show that 13C spins polarize efficiently for virtually all orientations of the NV axis relative to the applied magnetic field and over a broad range of hyperfine couplings. We will also discuss the mechanics of the polarization of 13C spins through the interaction of the NV with other ‘proxy’ paramagnetic defects, with attention to the interplay that emerges between spin cross-relaxation and mechanical rotation of the crystal as a whole.
Host: McDermott
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Cosmology Journal Club
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
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 Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).
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Astronomy Colloquium
"The Journey or the Destination: Isolating the Origin of the Physics Driving Gas Conditions in Galaxy Nuclei"
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and Cookies 3:30 PM, Talk begins at 3:45 PM
Speaker: Elisabeth Mills, Brandeis University
Abstract: Centers of galaxies are some of the most extreme objects in our universe: hosting starbursts and active supermassive black holes that can launch jets and winds far outside the compact galaxy nucleus. While there are relics of an active past in the center of our own Milky Way, at present it does not exhibit any of this activity. However, the central 300 parsecs of our Galaxy does contain a sizable reservoir of molecular gas that is the fuel for future star formation and black hole accretion. Constraining the physical conditions of this gas is critical for understanding how this reservoir will evolve to influence future activity in the Milky Way’s nucleus. Determining the origin of these conditions is also key to determining whether the same physics that govern gas conditions in this region can help us interpret more distant and active galaxy nuclei. I will present the results of my recent work following the changes in physical properties of this gas as it approaches the black hole; increasing in temperature, density, and turbulence, while largely resisting the onset of star formation. This work provides evidence that the extreme gas conditions in this region are driven largely by infall processes: the journey it takes to reach the central parsecs, rather than the energetic phenomena (supernovae, cosmic rays, massive star winds, UV radiation, and occasional X-ray flaring) encountered at its destination. However, as our Galactic center is relatively inactive, the next challenge is determining the extent to which the understanding gained from a detailed study of this region can be applied to more active systems. I will discuss early results from my ALMA program to make parsec-scale observations of the ionized and molecular gas in the center of NGC 253, a nearby galaxy with an order of magnitude more star formation and molecular gas that hosts a massive molecular outflow. Comparison of these two galaxy centers will isolate the gas conditions that both govern and are influenced by a nuclear starburst, and allow the definition of local templates for understanding the physics of this feedback process.
Host: Professor Snezana Stanimirovic
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Special Joint Condensed Matter - Atomic Molecular Optical Physics Seminar
Time-varying shear strain as an ultrafast symmetry switch in a Weyl semimetal
Time: 4:30 pm
Place: 5310 Chamberlin Hall
Speaker: Aaron Lindenberg, Standford University
Host: Jim Lawler
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