I am a postdoctoral researcher in Applied Mathematics at Harvard, working with Prof. L. Mahadevan. Previously, I completed my Ph.D. in Mechanical Engineering at Seoul National University under the supervision of Prof. Ho-Young Kim.

I develop physics-based computational tools for soft and active matter that combine reduced-order modeling and optimization with tightly coupled experiments. A central theme of my research is using computation to close the loop between experiment, model, and inverse design, so that simulations are not just descriptive but actively guide what we build and measure, while interfacing naturally with emerging data-driven approaches in the longer term. Earlier in my PhD, my work focused on optimal principles discovered in natural transport systems (e.g., the lungs and plant roots) and stable structures (e.g., bird nests made of mud). Below are some of my recent works.

Entanglement transition

• Rod Dynamics Simulation in 3D — C++ simulation of rod ensembles with contact and friction
• Entanglement Optimization — Maximize linking number in rod configurations (C++ and JAX)
• Random Sequential Adsorption of 3D Rods — RSA packings and the entanglement transition

Control and inverse design

• Snake Control — Topology-guided trajectory optimization for hyper-redundant robots
• Snake Lattice — Inverse design of elastic curve networks

Simulation infrastructure

• DER Python — Discrete Elastic Rods in Python/JAX with inextensibility plugin
• 3D Segmentation of Rods from X-Ray Scans — MATLAB pipeline for CT-based rod reconstruction

Active matter

• Active Billiards — Work extraction from active AR(1) particles via a ratcheted wheel

Publications

*: Co-first authors

Emergent cohesion via self-caging in maximally entangled rod packings
YJ and L. Mahadevan
(In preparation)

Boundary-driven active matter and stochastic rectification via Leidenfrost impulses
Minseong Cho, YJ and Jonghyun Ha
(In preparation)

Rotational 3D printing of active-passive filaments and lattices with programmable shape morphing
Mustafa K. Abdelrahman, Jackson K. Wilt, YJ, Rodrigo Telles, Gurminder K. Paink, Natalie M. Larson, Joanna Aizenberg, L. Mahadevan, and Jennifer A. Lewis
(Under review)

Morphogenesis and morphometry of brain folding patterns across species
Sifan Yin, Chunzi Liu, Gary PT Choi, YJ, Katja Heuer, Roberto Toro, L. Mahadevan eLife 14, RP107138 (2025)

Phase transitions in rolling of irregular cylinders and spheres
Daoyuan Qian, YJ, L. Mahadevan
Proceedings of the National Academy of Sciences 122, e2417161122 (2025)

Entanglement transition in rod packings
YJ, Thomas Plumb-Reyes, Hao-Yu Greg Lin, L. Mahadevan
Proceedings of the National Academy of Sciences 122, e2401868122 (2025)

Active entanglement enables stochastic, topological grasping
Kaitlyn Becker, Clark Teeple, Nicholas Charles, YJ, Daniel Baum,
James C. Weaver, L. Mahadevan, Robert Wood
Proceedings of the National Academy of Sciences 119, e2209819119 (2022)

Thermodynamics of hygroresponsive soft engines: Cycle analysis and work ratio
Beomjune Shin, YJ, Munkyeong Choi, Ho-Young Kim
Physical Review Applied 18, 044061 (2022)

Evaporative capillary rise
Jungtaek Kim, YJ, Ho-Young Kim
Physical Review Fluids 7, L032001 (2022)

Soft artificial electroreceptors for non-contact spatial perception
W. J. Song, Y. Lee, YJ *, Y.-W. Kang, J. Kim, J.-M. Park, Y.-L. Park, H.-Y. Kim, J.-Y. Sun
Science Advances 7, sciadv.abg9203 (2021)

Avian mud nest architecture by self-secreted saliva
YJ, Sohyun Jung, Sang-im Lee, Wongjung Kim, Ho-Young Kim
Proceedings of the National Academy of Sciences 118, e2018509118 (2021)

Ionic spiderwebs
Y. Lee, W. J. Song, YJ, H. You, M.-Y. Kim, H.-Y. Kim, J.-Y. Sun
Science Robotics 5, eaaz5405 (2020)

Optimal diameter reduction ratio of acinar airways in human lungs
K. Park*, YJ *, T. Son, Y.-J. Cho, N. L. Jeon, W. Kim, H.-Y. Kim
PLOS ONE 14, e0218947 (2019)

Poro-elasto-capillary wicking of cellulose sponges
J. Ha, J. Kim, YJ, G. Yun, D.-N. Kim, H.-Y. Kim
Science Advances 4, eaao7051 (2018)

Capillarity ion concentration polarization as spontaneous desalting mechanism
S. Park*, YJ *, S. Y. Son, I. Cho, Y. Cho, H. Lee, H.-Y. Kim, S. J. Kim
Nature Communications 7, 11223 (2016)

Three-dimensional point spread function of surface plasmon-coupled emission microscopy
YJ, Euiheon Chung
Proceedings of SPIE, Nano-Bio Sensing, Imaging, and Spectroscopy, 88790D (2013)

Media

🪺 How do bird nests stay together?
🏀 Getting the ball rolling.
🦑 This robotic tentacle gripper is gentle, practical, and terrifying.
🦑 Bizarre Tentacle Robot Looks Like It Emerged From ‘The Matrix’.
🦑 This spooky robot uses inflatable tentacles to grab delicate items.
🌲 New Models Expand Thermodynamics to Humidity-Driven Engines That Mimic Plants.
🐟 가오리 피부가 ‘힌트’… 눈 감고도 사물 감지하는 센서 개발
🛖 제비 무게 100배 견디는 제비집의 비밀은 ‘침’
🕸️ Artificial spider web gets an ionic boost
🧽 An absorbing study on the maths of sponges

Experience

2021-Present. Postdoctoral Fellow.
Harvard School of Engineering and Applied sciences, Cambridge, MA, USA.
Research: Control/design of soft matter under topological/frictional constraints.
Supervisor: Prof. Lakshminarayanan Mahadevan

2020-2021. Postdoctoral Fellow.
Rowland institute, Harvard University, Cambridge, MA, USA.
Research: Fluid dynamics of textured surfaces (e.g., shark skin) for drag reduction.
Supervisor: Dr. Shabnam Raayai-Ardakani

2019-2020. Postdoctoral Fellow.
Department of Mechanical Engineering, Seoul National University, Seoul, South Korea.
Research: Structural optimization in animal architectures.
Supervisor: Prof. Ho-Young Kim

Education

2014-2019 PhD in Mechanical Engineering.
Seoul National University, Seoul, South Korea.
Thesis: Optimal control/design principles in biological transport systems. Supervisor: Prof. Ho-Young Kim

2012-2014 MS in Biomedical Engineering.
Gwangju Institute of Science and Technology, Gwangju, South Korea.
Thesis: Statistical optics for biomedical applications.
Supervisor: Prof. Euiheon Chung

2008-2012 BS in Mechanical engineering.
Pohang university of Science and Technology, Pohang, South Korea.