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  • Departmental Colloquium May 5, 2022

    A New Approach to the Cosmic Lithium Problem

    Guest: J. Christopher Howk, Department of Physics, University of Notre Dame
    Thursday, May 5, 2022 3:55 pm - 4:55 pm
    Location: Zoom Meeting

    The predictions of light element abundances in standard Big Bang Nucleosynthesis agree very well with astrophysical probes of primordial material, with the exception of lithium. Most of the observational constraints we have on the primordial abundance and cosmic evolution of Li comes by way of the Li abundance in stellar atmospheres, which are four times lower than BBN predictions in the Planck era. A broad range of potential solutions to this "lithium problem" have been suggested, from stellar astrophysics solutions (depletion of the surface Li abundances in stars) to physics beyond the Standard Model (annihilating or decaying dark matter in the epoch of BBN). We have adopted a new approach to this problem, using observations of Li in interstellar gas of low-metallicity galaxies to probe the cosmic evolution of Li. I will summarize our results using this approach, including new estimates of the 7Li/6Li ratio that show no evidence for non-standard model approaches.

  • Departmental Colloquium Jul 21, 2022

    Connecting Hydrodynamic Simulations of Planet Formation with Observations

    Guest: Prof. Dr. Judit Szulagyi, Department of Physics Inst. f. Teilchen- und Astrophysik Zürich, Switzerland
    Thursday, July 21, 2022 3:55 pm - 4:55 pm
    Location: Physics Auditorium (202) and Zoom

    Planets born in circumstellar disks create various disk substructures, such as gaps, rings, spirals, vortices. Similar structures are observed widely with ALMA, SPHERE and similar instruments. At least some of these disk features are likely due to forming planets, however there are also other mechanisms to explain them.

    Carrying out high resolution, 3D hydrodynamic simulations with radiative transfer already included, allow us to create realistic “mock observations” or “synthetic images” for a given instrument & telescope combination. These mock observations can be compared with already existing real data, or prepare for future observational proposals. We use them to understand how massive forming planets could be observed with the different instruments, how the planet- disk interactions look like on various wavelengths and what planet-generated features we can observe with the current & near-future instrumentation. I review our findings for near- and mid- infrared, sub-millimeter and radio wavelengths, and identify what are the best wavelengths and instruments for hunting for forming planets.

  • Departmental Colloquium Aug 17, 2022

    Gravitational Instabilities in Protoplanetary Discs: A Vanishing Act

    Guest: Sahl Rowther, Dept. of Physics and Astronomy University of Leicester England
    Wednesday, August 17, 2022 3:55 pm - 4:55 pm
    Location: Physics Auditorium (202) and Zoom

    In their youth, protoplanetary discs are expected to be massive and self-gravitating, which results in non-axisymmetric spiral structures. However recent observations of young protoplanetary discs with ALMA have revealed that discs with large-scale spiral structure are rarely observed in the midplane. Instead, axisymmetric discs with some also having ring & gap structures are more commonly observed. In the first part of the talk I will present our results of planet-disc interactions in gravitationally unstable (GI) discs. In the second half I will show our recent results of warped GI discs. Consideration of complex processes such as these has important implications on observations of protoplanetary as it shows how evolution of GI discs can be altered, potentially resolving the discrepancy between theory and observations.

  • CSP Lunch Seminar Aug 30, 2022

    CSP Computing Resources

    Guest: Michael Caplinger and Jeff Deroshia(1), Shan-Ho Tsai(2), (1) Center for Simulational Physics, University of Georgia, (2) GACRC, University of Georgia
    Tuesday, August 30, 2022 12:45 pm - 1:45 pm
    Location: Zoom Meeting

  • Departmental Colloquium Sep 1, 2022

    Random Language Model

    Guest: Dr. Eric DeGiuli, Assistant Professor, Department of Physics Toronto Metropolitan University (formerly Ryerson)
    Thursday, September 1, 2022 3:55 pm - 4:55 pm
    Location: Zoom Meeting

    Many complex generative systems use languages to create structured objects. We consider a model of random languages, defined by weighted context-free grammars. As the distribution of grammar weights broadens, a transition is found from a random phase, in which sentences are indistinguishable from noise, to an organized phase in which nontrivial information is carried. This marks the emergence of deep structure in the language, and can be understood by a competition between energy and entropy.

    Note: no background in linguistics will be assumed.

  • CSP Lunch Seminar Sep 6, 2022

    Compile and Run HPC code on Sapelo2

    Guest: Zhuofei Hou, GACRC
    Tuesday, September 6, 2022 12:45 pm - 1:45 pm
    Location: Zoom Meeting

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