arXiv subjects

Bo-Tao Li

Publications and source records attributed to Bo-Tao Li.

3 recordsLinked to original sources

arXiv2026

Particle Acceleration in Cassiopeia A Revealed by Broadband High-Energy Spectrum

Recently, the GeV--sub-PeV spectrum of supernova remnant (SNR) Cassiopeia A (Cas A), one of the youngest and most well-studied SNRs in our Galaxy, has been updated by observations of Fermi-LAT and LHAASO. We revisit Cas A with our previous shell-plus-jet asymmetric model and investigate its particle acceleration ability. The broadband fitting results suggest that the double-peaked gamma-ray spectrum can be well attributed to proton-proton (PP) collisions and inverse Compton scattering within the SNR shell, while the synchrotron emission from a jet component with velocity of $\sim0.1c$ can account for the hard X-ray emission up to 220 keV. Furthermore, the PP collisions in the jet can produce a sub-PeV emission, but constrained by the LHAASO-KM2A limit to a flux below $\sim 1\times10^{-14}\rm erg/(cm^2s)$ at 100 TeV. The energy of accelerated protons in the jet of Cas A could be up to $5\times10^{47}$ erg, which, assuming that the PeV cosmic ray distribution is clumpy in the Galaxy with the clump size comparable to the thickness of the Galactic plane, derives a proton flux consistent with the observed one at 1 PeV, implying that the Cas A-like SNRs can still be PeVatrons in the Galaxy. It is encouraging for LHAASO and future telescopes to detect or constrain Cas A spectrum above 100-TeV more precisely.

astro-ph.HE↗

arXiv2023

Particle-resolved thermal lattice Boltzmann simulation using OpenACC on multi-GPUs

We utilize the Open Accelerator (OpenACC) approach for graphics processing unit (GPU) accelerated particle-resolved thermal lattice Boltzmann (LB) simulation. We adopt the momentum-exchange method to calculate fluid-particle interactions to preserve the simplicity of the LB method. To address load imbalance issues, we extend the indirect addressing method to collect fluid-particle link information at each timestep and store indices of fluid-particle link in a fixed index array. We simulate the sedimentation of 4,800 hot particles in cold fluids with a domain size of $4000^{2}$, and the simulation achieves 1750 million lattice updates per second (MLUPS) on a single GPU. Furthermore, we implement a hybrid OpenACC and message passing interface (MPI) approach for multi-GPU accelerated simulation. This approach incorporates four optimization strategies, including building domain lists, utilizing request-answer communication, overlapping communications with computations, and executing computation tasks concurrently. By reducing data communication between GPUs, hiding communication latency through overlapping computation, and increasing the utilization of GPU resources, we achieve improved performance, reaching 10846 MLUPS using 8 GPUs. Our results demonstrate that the OpenACC-based GPU acceleration is promising for particle-resolved thermal lattice Boltzmann simulation.

physics.flu-dyn↗

arXiv2022

Multi-GPU thermal lattice Boltzmann simulations using OpenACC and MPI

We assess the performance of the hybrid Open Accelerator (OpenACC) and Message Passing Interface (MPI) approach for multi-graphics processing units (GPUs) accelerated thermal lattice Boltzmann (LB) simulation. The OpenACC accelerates computation on a single GPU, and the MPI synchronizes the information between multiple GPUs. With a single GPU, the two-dimension (2D) simulation achieved 1.93 billion lattice updates per second (GLUPS) with a grid number of $8193^{2}$, and the three-dimension (3D) simulation achieved 1.04 GLUPS with a grid number of $385^{3}$, which is more than 76% of the theoretical maximum performance. On multi-GPUs, we adopt block partitioning, overlapping communications with computations, and concurrent computation to optimize parallel efficiency. We show that in the strong scaling test, using 16 GPUs, the 2D simulation achieved 30.42 GLUPS and the 3D simulation achieved 14.52 GLUPS. In the weak scaling test, the parallel efficiency remains above 99% up to 16 GPUs. Our results demonstrated that, with improved data and task management, the hybrid OpenACC and MPI technique is promising for thermal LB simulation on multi-GPUs.

physics.flu-dyn↗