Publications

2026

1. In prep.

   Physics-Informed Neural Networks and Conventional Numerical Modelling for Real-Time Atrial Fibrillation Mapping from High-Density 6×6 Grid Electrograms: A Comparative Study

   Yoogeun Song, David Colling, Alexander J. Richards, and Nicholas Linton

   IEEE Transactions on Biomedical Engineering. Imperial College London, with clinical data from Hammersmith Hospital. , 2026

   Draft in preparation

   Abs Bib

   Real-time activation mapping during catheter ablation requires reconstruction that is both fast enough for use in theatre and physically consistent on sparse electrode grids. We compare a physics-informed neural network (ATRIPINN), which imposes wave, eikonal and monodomain (Aliev–Panfilov) dynamics as soft constraints, against conventional numerical modelling of the same governing equations, on electrograms recorded from a 6x6 high-density grid catheter in normal sinus rhythm and atrial fibrillation. We assess localisation error, end-to-end latency and channel-wise fidelity, and characterise the data-efficiency and physical-plausibility trade-off that the soft-constraint formulation buys.

   @article{song2026atripinn,
     title = {Physics-Informed Neural Networks and Conventional Numerical Modelling for Real-Time Atrial Fibrillation Mapping from High-Density 6×6 Grid Electrograms: A Comparative Study},
     author = {Song, Yoogeun and Colling, David and Richards, Alexander J. and Linton, Nicholas},
     journal = {IEEE Transactions on Biomedical Engineering},
     year = {2026},
     note = {Draft in preparation},
   }

2. In prep.

   Multi-wavelength variability of Sagittarius A* from GRMHD simulations with electron heating

   Yoogeun Song, Ziri Younsi, Yosuke Mizuno, Kinwah Wu, and 1 more author

   Monthly Notices of the Royal Astronomical Society. Work carried out at UCL/MSSL with Dr Ziri Younsi and Prof Kinwah Wu. , 2026

   Draft in preparation

   Abs Bib

   General-relativistic magnetohydrodynamic (BHAC) simulations of magnetically arrested discs, post-processed with general-relativistic radiative transfer (BHOSS), are used to model the multi-wavelength variability of Sgr A*. We compare electron-heating prescriptions (R-beta, turbulent, and magnetic-reconnection heating) across black hole spins a = -0.94 to +0.94 and assess their observational signatures.

   @article{song2026sgra,
     title = {Multi-wavelength variability of {Sagittarius A*} from {GRMHD} simulations with electron heating},
     author = {Song, Yoogeun and Younsi, Ziri and Mizuno, Yosuke and Wu, Kinwah and Fromm, Christian M.},
     journal = {Monthly Notices of the Royal Astronomical Society},
     year = {2026},
     note = {Draft in preparation},
   }

2024

1. arXiv

   Electromagnetic Energy Extraction in Kerr Black Holes through Frame-Dragging Magnetospheres

   Isao Okamoto, Toshio Uchida, and Yoogeun Song

   arXiv preprint, 2024

   Abs arXiv Bib HTML

   A zero-angular-momentum-observer (ZAMO) treatment of Blandford-Znajek energy extraction from rotating black holes, in which the frame-dragging force-free magnetosphere mediates the outward transport of electromagnetic energy.

   @article{okamoto2024kerr,
     title = {Electromagnetic Energy Extraction in {Kerr} Black Holes through Frame-Dragging Magnetospheres},
     author = {Okamoto, Isao and Uchida, Toshio and Song, Yoogeun},
     journal = {arXiv preprint},
     year = {2024},
   }

2023

1. arXiv

   Energy self-extraction of a Kerr black hole through its frame-dragged force-free magnetosphere

   Isao Okamoto and Yoogeun Song

   arXiv preprint, 2023

   v7

   Abs arXiv Bib HTML

   The force-free magnetosphere of a Kerr black hole is divided at the null surface, and electromagnetic energy is shown to be self-extracted across it – a reformulation of the Blandford-Znajek process in terms of frame dragging.

   @article{okamoto2019selfextraction,
     title = {Energy self-extraction of a {Kerr} black hole through its frame-dragged force-free magnetosphere},
     author = {Okamoto, Isao and Song, Yoogeun},
     journal = {arXiv preprint},
     year = {2023},
     note = {v7},
   }

2018

1. ApJ

   High-energy and Very High Energy Emission from Stellar-mass Black Holes Moving in Gaseous Clouds

   Kouichi Hirotani, Hung-Yi Pu, S. Outmani, H. Huang, and 4 more authors

   The Astrophysical Journal, 2018

   Abs DOI arXiv Bib HTML

   Frame dragging near a rapidly rotating black hole reverses the sign of the Goldreich-Julian charge density, producing a magnetic-field-aligned electric field that accelerates electrons and positrons in opposite directions and drives a pair cascade. We show that a stellar-mass black hole moving through a gaseous cloud can emit a detectable very-high-energy flux if it is extremely rotating and within roughly 1 kpc.

   @article{hirotani2018stellar,
     title = {High-energy and Very High Energy Emission from Stellar-mass Black Holes Moving in Gaseous Clouds},
     author = {Hirotani, Kouichi and Pu, Hung-Yi and Outmani, S. and Huang, H. and Kim, D. and Song, Yoogeun and Matsushita, Satoki and Kong, Albert K. H.},
     journal = {The Astrophysical Journal},
     volume = {867},
     number = {2},
     pages = {120},
     year = {2018},
     doi = {10.3847/1538-4357/aae47a},
   }

2017

1. MNRAS-L

   Enhanced gamma radiation towards the rotation axis from the immediate vicinity of extremely rotating black holes

   Yoogeun Song, Hung-Yi Pu, Kouichi Hirotani, Satoki Matsushita, and 2 more authors

   Monthly Notices of the Royal Astronomical Society: Letters, Oct 2017

   Abs DOI arXiv Bib HTML

   Applying pulsar outer-gap theory to black hole magnetospheres, we show that a lepton accelerator arises near the event horizon as a consequence of frame dragging. The resulting gamma-ray flux is beamed towards the rotation axis and is enhanced by more than an order of magnitude as the spin increases from a = 0.90M to a = 0.9999M, with implications for Fermi-LAT and CTA detectability.

   @article{song2017gamma,
     title = {Enhanced gamma radiation towards the rotation axis from the immediate vicinity of extremely rotating black holes},
     author = {Song, Yoogeun and Pu, Hung-Yi and Hirotani, Kouichi and Matsushita, Satoki and Kong, Albert K. H. and Chang, Hsiang-Kuang},
     journal = {Monthly Notices of the Royal Astronomical Society: Letters},
     volume = {471},
     number = {1},
     pages = {L135--L139},
     year = {2017},
     month = oct,
     doi = {10.1093/mnrasl/slx119},
   }

2016

1. arXiv

   The Influence of the Shear on the Gravitational Waves in the Early Anisotropic Universe

   Yoo Geun Song and Seok Jae Park

   arXiv preprint, 2016

   Abs arXiv Bib HTML

   Raychaudhuri-type and shear-evolution equations are derived for geodesic congruences in a Bianchi-I universe, and used to study how anisotropic shear imprints itself on primordial gravitational waves.

   @article{song2016shear,
     title = {The Influence of the Shear on the Gravitational Waves in the Early Anisotropic Universe},
     author = {Song, Yoo Geun and Park, Seok Jae},
     journal = {arXiv preprint},
     year = {2016},
   }