Periodic and fractal (chaotic) precipitation in gels. Insights concerning precipitation during gallstone growth: L-B Wang, R.D. Soloway, J-G Wu, S-F Weng, W-D Huang, D-F Xu, N. Shi, G-X Xu. Institute of Chemistry and Molecular Engineering, Peking University, Beijing, China and the Gastroenterology Division, University of Texas Medical Branch, Galveston TX1995