Nicola Tosi, a PhD student from GeoForschungsZentrum Potsdam, visited us for 12 weeks, starting October 1, 2005. His stay was oriented towards two issues. First, he continued his PhD work on present-time mantle convection with a laterally-varying viscosity distribution. His discussions with J. Velimsky resulted in significant improvements in the numerical coding of the problem. He managed to model the effect of an elastic lithosphere on mantle flow in 2-D spherical geometry. His results demonstrate a possible mechanism for the creation of continental shelves near large lithospheric cratons. Second, Nicola took part in the course "Weak formulations of partial differential equations", taught for invited PhD students by C. Matyska (WP9). He appreciated the high theoretical level of the course, which helped him to understand details of the formulation of present-time mantle convection, originally developed at our department.