The original paper reference is cited below:
A pharmacodynamic model for the time course of tumor shrinkage by gemcitabine + carboplatin in non-small cell lung cancer patients, Lai-San Tham, Lingzhi Wang, Ross A Soo, Soo-Chin Lee, How-Sung Lee, Wei-Peng Yong, Boon-Cher Goh and Nicholas H.G. Holford, 2008, Clin Cancer Res, volume 14, 4213-4218. PubMed ID: 18594002
Approximate model of cooperative activation and crossbridge cycling in cardiac muscle using ordinary differentialequations.