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Filamentary structures have been found at almost all size scales (~0.03 to 300 pc) in the Galaxy. Massive filamentary dark clouds of a few parsecs to more than 10 parsec long are commonly found inside giant molecular clouds (e.g., Bergin & Tafalla 2007, Andre et al. 2014, Hacar et al. 2023). High resolution observations reveal large number of thinner (≤ 0.1 pc) and shorter (≤ 1 pc) filamentary substructures (dense fibers) inside molecular clouds, even in long and slender filamentary dark clouds (e.g., Hacar et al. 2013). Dense cores are found located along or at the intersection of these filamentary substructures (e.g., Tafalla and Hacar 2015, Könyves et al. 2015). Chain-of-cores and clumpy appearances of some filamentary molecular clouds indicate that these structures probably are gravitational unstable and are undergoing fragmentation. Observationally, it is unclear on the details of formation of filamentary substructures and how exactly these substructures fragment into cores. What are the roles of magnetic fields in the formation processes? For molecular clouds crowded with filamentary substructures, frequent collisions and merging of filaments can induce fragmentation to the marginally stable filamentary substructures. On the other hand, magnetic field that is usually found to be perpendicular to the filaments can suppress the fragmentation. In the presentation, I shall summarize the recent observational results on filamentary clouds and use my high-resolution 3D simulations on filamentary cloud formation to compare with observational implications. My talk will focus on the size scales from a few to ~ 0.01 pc to cover the formation of filamentary clouds, filamentary sub-structures, and dense cloud cores observed in the simulations. I shall discuss the evolution and stability of the fiber-like substructures in the highly supersonic turbulent and magnetized environment inside molecular clouds and the possible mechanisms of the formation of dense cloud cores
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Biographical Sketch
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Education
University of Wyoming Physics Ph.D. 1999
University of Calgary Astrophysics MSc 1993
Hong Kong Polytechnic University Mathematics and Physics BSc 1990
Hong Kong Polytechnic University Civil and Structural Engineering Associateship 1983
Hong Kong Polytechnic University Structural Engineering Higher Diploma 1982
Hong Kong Polytechnic University Structural Engineering Diploma 1980
Appointments and Synergistic Activities
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Researcher: Shanghai Astronomical Observatory, 2023 – now
· Studied the formation of filamentary molecular clouds, their structures, and magnetic
properties.
· Develop a new radiation transfer module for ORION2 using M1 method.
· Develop a new star formation code for GPU machines.
· Study on formation of filamentary molecular clouds, their structures, and magnetic properties.
· Study on stellar cluster formation.
Research Specialist: Astronomy Department, University of California at Berkeley, 2004 – 2023
· Managed and assisted the development of the second-generation multi-physics, massively parallel, adaptive mesh refinement code ORION2, which is widely used by different groups working on star formation. My contribution to the code includes the overall code structure design, the implementation of ideal MHD using Constrained Transport scheme, and a multigrid poison solver for self-gravity.
· Conducted comprehensive studies of the formation of magnetized turbulent molecular clouds using ideal MHD and non-ideal MHD simulations with ambipolar diffusion and compare with observation.
· Studied the formation of filamentary molecular clouds, their structures, and magnetic properties.
· Studied stellar cluster formation in filamentary dark clouds and super star cluster formation with different metallicity and their feedback to the environment using numerical simulations.
· Principal investigator of two polarization observation projects using the polarimeter HAWC+ onboard SOFIA on filamentary clouds in Taurus and Orion A regions.
Postdoctorate Research Associate: Astronomy Department, University of California at Berkeley, 2003 – 2004
· Developed a new 2-fluid semi-implicit algorithm for non-ideal MHD with ambipolar diffusion for ZEUS-MP code
Postdoctorate Research Associate: Physics Department, University of California at San Diego, 2002 – 2003
· Studied super-Alfvénic, self-gravitating turbulent molecular clouds using ideal MHD simulations.
Postdoctorate Research Associate: National Center for Supercomputing Applications, 1999 – 2002
· Developed CactusZeus and AMRZeus as thorns for Cactus as an application for nonrelativistic MHD simulations. It was part of the NSF funded Knowledge Distribution Interface (KDI) project over 10 centers in Europe/USA. Cactus is a Grid-aware application.
· Developed and maintained the public released ZEUS-MP code.
Other Professional Experience
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· Resident Engineer of P & T Architects & Engineers HK Ltd., 1987-1990
· Engineer of China Overseas Building Development Co., Ltd., 1984-1987
Previous Projects Involved as co-I or PI
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Theory projects:
· Co-Investigator of NASA Astrophysics Theory Program project “The Formation of Star Clusters in the Era of JWST”, 2020 – 2023
· Co-Investigator of NASA Astrophysics Theory Program project “Massive Stars and Star Clusters in the Era of JWST”, 2017 – 2019
· Co-Investigator of NASA TCAN project “From the ISM to the IMF: Multi-Scale, MultiPhysics Modeling of Star Formation”, 2014 – 2017 (TCAN is a joint project among Princeton University, UC Santa Cruz, and UC Berkeley)
· Co-Investigator of NASA Astrophysics Theory Program project “The Effect of Feedback on the Formation of High Mass Stars: From High Mass Cores to Massive Star Clusters”, 2012 -2016
· Co-Investigator of NASA Astrophysics Theory Program project “The Formation of High Mass Stars and their Feedback Effects”, 2009 – 2012
Observation projects:
· Principle investigator of SOFIA project “The Role of Magnetic Fields in the Formation of Starless Cores in Filamentary Molecular Clouds”, 2021 – 2022
· Principle investigator of SOFIA project “Understanding the Dynamical State Inside Filamentary Molecular Cloud L1495 Through Magnetic Field Morphology”, 2019 – 2020
Membership in Professional Affiliation
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· American Astronomical Society, 1993 – present
· American Physical Society, 1993 – present
· International Astronomical Union, 2018 – present
Five Publications Closely Related to the Seminar Talk:
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· Li, P. S., Lopez-Rodriguez, E., Soam, A., Klein, R. I. “The Role of magnetic fields in the stability and fragmentation of filamentary molecular clouds: two case studies at OMC-3 and OMC-4”, 2022, MNRAS, 514, 3024
· Li, P. S., Lopez-Rodriguez, E., Ajeddig, H., et al. “Mapping the magnetic field in the Taurus/B211 filamentary cloud with SOFIA HAWC+ and comparing with simulation”, MNRAS, 2022, MNRAS, 510, 6085
· Li, P. S., Cunningham, A., Gaches, B., et at. “ORION2: A magnetohydrodynamics codes for star formation”, 2021, JOSS, 6, 3771
· Li, P. S., McKee, C. F., & Klein, R. I. “Magnetized Interstellar Molecular Clouds - II. The Structure and Formation of Filamentary Dark Clouds”, 2019, MNRAS, 485, 4509
· Li, P. S., McKee, C. F., & Klein, R. I. “Magnetic Fields in Interstellar Molecular Clouds: I. Comparison Between Simulations and Zeeman Observations”, 2015, MNRAS, 452, 2500