Carla Braitenberg (*) & C.K. Shum (**,***)
(*) Dept. of Mathematics and Geosciences, University of Trieste, Via Weiss 1, 34100 Trieste, Italy. Corresponding author e-mail: berg@units.it.
(**) Division of Geodetic Science, School of Earth Sciences, Ohio State University, Columbus, Ohio 43210, USA., e-mail: ckshum@osu.edu
(***) State Key Laboratory of Geodesy and Earth's Dynamics. Institute of Geodesy & Geophysics, Chinese Academy of Sciences, Wuhan 430077, China.