September 2012 : Professor Zenghu Li (Beijing Normal University) visited J.-F. Delmas from 02/09/2012 to 01/10/2012. He gave a talk at the ANR A3 (PI J.-F. Delmas) workshop at CIRM (Marseille) during the first week of september. Then, he worked with J.-F. Delmas on the research programm of his PhD student Hongwei Bi on branching processes, who spent one year (09/2012-08/2013) at Cermics. The research with H. Bi has led to a submitted paper on the total length of genealogical trees for quadratic stationary continuous-state branching processes and an article at Elect. Journ. of Probab. on population model with non-neutral mutations using branching processes with immigration. We can also mention the development of the collaboration with Hui He (Beijing Normal University) on related themes.