Ahlers, Anna L. External, Max Planck Institute for the History of Science, Max Planck Society;
https://caod.oriprobe.com/issues/1636653/toc.htm (Table of contents)
Ahlers, A. L. (2015). Lu'er qu <bianhui lantian> dui Beijing de qishi 鲁尔区《变回蓝天》对北京的启示 [How the Sky Over the Ruhr Became Blue Again: A Vision for Beijing]. Xiaokang, (21), 24-26.