.Ehsan Roohi is a Lecturer in the Department of Mechanical and Industrial Engineering at the University of Massachusetts Amherst. His expertise spans rarefied gas dynamics, multiscale transport, and high-fidelity computational modeling for aerospace and micro/nano-scale applications, with an emphasis on physics-based, verifiable, and experimentally grounded simulation tools. He received his Ph.D. in Aerospace Engineering from Sharif University of Technology (2010), his M.S. from Ferdowsi University of Mashhad (2006), and his B.S. from Sharif University of Technology (2004). He has academic and research experience across the United States, China, and Iran, and has collaborated with or held roles involving institutions such as Embry-Riddle Aeronautical University, Johns Hopkins University, Xi’an Jiaotong University, and Ferdowsi University of Mashhad. He is particularly known for advancing the Direct Simulation Monte Carlo (DSMC) method—especially collision modeling and strategies that improve both accuracy and computational efficiency—and for applying these developments to hypersonic rarefaction, microflows, and gas–surface interactions. He has authored numerous scientific publications and books, including Advances in Direct Simulation Monte Carlo: From Micro-Scale to Rarefied Flow Phenomena (Springer Nature, 2025). He also works on physics-constrained machine-learning surrogate models and mentors students in reproducible scientific computing.