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Events at Physics

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Events on Thursday, February 13th, 2020

R. G. Herb Condensed Matter Seminar
The fall and rise of the mass on a spring
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Prof. Benjamin Aleman , University of Oregon
Abstract: Since antiquity, the mass on a spring and other simple mechanical systems have been used in everyday applications, like time-keeping clocks. But at one time, they were also employed in smarter information technologies such as calculators and computers, technologies now ruled by silicon-based microelectronics. In recent years, thanks largely to the nanometer-scale miniaturization of mechanical systems and the discovery of atomic-scale materials like graphene, the mass on a spring has been rising in scientific and technological prominence, and is once again knocking on the door of more sophisticated uses. The next step in this mechanical evolution—as occurred with electronic microchips—is to form large programmable networks of interacting nanomechanical resonators, but such networks demand unprecedented, scalable control over the resonance frequencies and coupling of the constituent resonators. Here, I will detail recent projects in my lab that advance the quest to realize these networks, projects enabled by optically addressable graphene nanoelectromechanical resonators. By harnessing several unique properties of graphene, we develop an optoelectronic non-volatile mechanical strain memory and a means for fast, photothermally mediated strain modulation, which together enable local static and dynamic frequency and coupling control of resonators in large arrays. I will discuss several applications already enabled by our work, such as a new light detector that "hears" light, as well as some wilder, yet promising aspirations.
Host: Brar
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Cosmology Journal Club
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: We discuss papers from arxiv.org related to cosmology each week. All are welcome and feel free to bring your lunch. If there is a paper you would like to present, or have questions or comments, please email Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).
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Astronomy Colloquium
Diffusion and dispersion in anisotropic magnetohydrodynamic turbulence
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Speaker: Professor Jane Pratt, Georgia State University, Physics and Astronomy Deparment
Abstract: Diffusion and transport processes in turbulent plasmas constitute fundamental astrophysical problems; a clear understanding of these processes is needed in order to produce improved theoretical models for the diffusion and transport of energetic particles, including cosmic rays.
Magnetohydrodynamic (MHD) turbulence structured by a large-scale magnetic field is an essential aspect of interstellar or interplanetary plasmas. Here we investigate how turbulent diffusion and dispersion differ in the directions parallel and perpendicular to the magnetic field. We adopt the Lagrangian viewpoint, the natural point of view to study diffusion, and construct statistics based on the trajectories of Lagrangian tracer particles. From the motions of these tracer particles, we evaluate Lagrangian statistics for single-particle diffusion, two-particle dispersion, and velocity autocorrelations. We also demonstrate new Lagrangian statistics developed to understand anisotropic turbulent dispersion. Results will be presented from simulations with grid sizes up to 2048^3.

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Host: Professor Ellen Zweibel
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