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Events on Thursday, February 1st, 2024

R. G. Herb Condensed Matter Seminar
Dissipative mechanisms in SNS junctions and magnetic vortex lattices
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Tony Liu, U Washington
Abstract: In superconductors there is a mechanism of dissipation which is related to the motion of quasiparticle energy levels and is similar to the Debye mechanism of microwave absorption in gases. The dissipation rate associated with this Debye-like mechanism is controlled by the inelastic relaxation time, and in some cases, it can dominate conventional dissipation mechanisms which are controlled by the elastic relaxation time. To illustrate this effect, I will discuss the role of this Debye-like mechanism in the I-V characteristics of SNS junctions as well as the microwave absorption of disordered magnetic vortex lattices. In the former, I will show that there is a new regime at small voltages/currents where the I-V characteristics are controlled entirely by the density of states in the SNS junction and are characterized by a large conductance proportional to the inelastic relaxation time. In the latter, I will show that the microwave absorption coefficient at small frequencies is similarly controlled by the inelastic relaxation time, and that it is significantly larger than the value obtained in the conventional Bardeen-Stephen picture.
Host: Alex Levchenko
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Low-energy Atmospheric Neutrino Oscillations
Time: 2:30 pm - 3:30 pm
Speaker: Kevin Kelly , Texas A&M University
Abstract: Neutrino oscillation physics is a rich phenomenon, especially when any of the following is true: the neutrinos have low energy, the travel distance is large, and interactions with matter are significant along the path of propagation. All three of these criteria are met in low-energy atmospheric neutrino oscillations. I will demonstrate how this class of oscillations is exciting for several applications, and discuss which next-generations are best suited to exploit such measurements.
Host: Sanjib Kumar Agarwalla
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Astronomy Colloquium
Bursty star formation: physical drivers and implications for JWST observations of high-redshift galaxies
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Chris Hayward, CCA
Abstract: A complete theory of galaxy formation requires understanding the details of how gas is converted into stars over cosmic time, which is affected by gas supply, star formation, and feedback-driven outflows. Based on the results of state-of-the-art cosmological zoom simulations, I will argue that galaxy formation is a violent process: at high redshift, stellar feedback causes all star-forming galaxies to undergo rapid fluctuations in their star formation rates on ~10-Myr timescales. Bursts of star formation are followed by strong outflows, which cause the star formation rate to drop precipitously. Fresh gas supply from galactic fountains rejuvenates star formation and restarts the cycle. At z ~ 1, simulations of massive galaxies exhibit a qualitative transition: outflows are no longer driven effectively, and the galaxies transition to steadily star-forming, well-order disk galaxies. I will discuss the physical causes of bursty star formation and the aforementioned transition to time-steady star formation, in addition to some implications for JWST observations of high-redshift galaxies.
Host: Ke Zhang
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Theory Seminar (High Energy/Cosmology)
Novel Methods for the Detection of Dark Matter
Time: 4:00 pm - 5:00 pm
Place: 5280 Chamberlin Hall
Speaker: Carlos Blanco, Princeton University
Host: Lisa Everett
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