JinHyun Kim

Sun Jo, Seok Young Hong, JinHyun Kim et al.

4D flow magnetic resonance imaging (MRI) is a reliable, non-invasive approach for estimating blood flow velocities, vital for cardiovascular diagnostics. Unlike conventional MRI focused on anatomical structures, 4D flow MRI requires high spatiotemporal resolution for early detection of critical conditions such as stenosis or aneurysms. However, achieving such resolution typically results in prolonged scan times, creating a trade-off between acquisition speed and prediction accuracy. Recent studies have leveraged physics-informed neural networks (PINNs) for super-resolution of MRI data, but their practical applicability is limited as the prohibitively slow training process must be performed for each patient. To overcome this limitation, we propose PINGS-X, a novel framework modeling high-resolution flow velocities using axes-aligned spatiotemporal Gaussian representations. Inspired by the effectiveness of 3D Gaussian splatting (3DGS) in novel view synthesis, PINGS-X extends this concept through several non-trivial novel innovations: (i) normalized Gaussian splatting with a formal convergence guarantee, (ii) axes-aligned Gaussians that simplify training for high-dimensional data while preserving accuracy and the convergence guarantee, and (iii) a Gaussian merging procedure to prevent degenerate solutions and boost computational efficiency. Experimental results on computational fluid dynamics (CFD) and real 4D flow MRI datasets demonstrate that PINGS-X substantially reduces training time while achieving superior super-resolution accuracy. Our code and datasets are available at https://github.com/SpatialAILab/PINGS-X.

Juyeong Hwang, Seong-Eun Hong, Jinhyun Kim et al.

Crowds do not merely move; they decide. Human navigation is inherently contextual: people interpret the meaning of space, social norms, and potential consequences before acting. Sidewalks invite walking, crosswalks invite crossing, and deviations are weighed against urgency and safety. Yet most crowd simulation methods reduce navigation to geometry and collision avoidance, producing motion that is plausible but rarely intentional. We introduce CrowdVLA, a new formulation of crowd simulation that models each pedestrian as a Vision-Language-Action (VLA) agent. Instead of replaying recorded trajectories, CrowdVLA enables agents to interpret scene semantics and social norms from visual observations and language instructions, and to select actions through consequence-aware reasoning. CrowdVLA addresses three key challenges-limited agent-centric supervision in crowd datasets, unstable per-frame control, and success-biased datasets-through: (i) agent-centric visual supervision via semantically reconstructed environments and Low-Rank Adaptation (LoRA) fine-tuning of a pretrained vision-language model, (ii) a motion skill action space that bridges symbolic decision making and continuous locomotion, and (iii) exploration-based question answering that exposes agents to counterfactual actions and their outcomes through simulation rollouts. Our results shift crowd simulation from motion-centric synthesis toward perception-driven, consequence-aware decision making, enabling crowds that move not just realistically, but meaningfully.