HJJ

Papers & Reports

Research publications and technical reports.

Publications

SHIFT: Sigmoid-Based Heuristic Invertible Fitness-Landscape Transformation

Jeongjin Han, Seunghoon Sim, Jian Lee, Seongyoon Park

arXiv preprint2025

A sigmoid-based invertible fitness-landscape transformation for search-based software testing (SBST), enabling hill climbing to escape plateaus. Applies compiler techniques (AST-based instrumentation, constant folding, SSA-like variable-shading) to Python source transformation, with parallel time-budgeted evaluation infrastructure.

SBSTSearch-Based TestingCompiler TechniquesHill Climbing

VRAIL: Vectorized Reward-based Attribution for Interpretable Learning

Jeongjin Han, et al.

arXiv preprint2025

A bi-level RL framework that learns interpretable linear/quadratic value estimators as potential-based reward shaping functions, improving DQN convergence stability in Taxi-v3. Includes reward transfer experiments and α-scheduling trials.

Reinforcement LearningReward ShapingInterpretability

Technical Reports

Transient Thermal-Hydraulic Analysis of an Overcooling Accident in a Pressurized Water Reactor

Jeongjin Han

NQE625: Computational Analysis in Nuclear Systems, KAIST2025

A multi-channel 1-D nuclear system code implemented from scratch in MATLAB, modeling coupled fluid dynamics, point kinetics with delayed neutrons, fuel heat conduction (FVM), and steam generator primary–secondary coupling. Steady-state and transient analyses validated against the industry-standard MARS code across 10 physical quantities.

Thermal-HydraulicsFVMNuclear System CodeMATLAB

Steady-State Thermal-Hydraulic Analysis of a Multi-Channel PWR Core

Jeongjin Han

NQE625: Computational Analysis in Nuclear Systems, KAIST2025

Multi-channel steady-state analysis of a PWR core implementing finite-difference and finite-volume methods for coupled heat conduction and fluid flow. Covers constitutive relations (HTC, friction factor, CHF), channel mass flux distribution, and thermal margin evaluation with 2-D core map visualization.

Thermal-HydraulicsFDMFVMPWRMATLAB