F. ). Alpes, K. G. Larsen-belgium-), and E. Pimentel, Our thanks go also to the anonymous referees who kindly agreed to help us with the selection and reviewing of the papers in this special section and carried out an excellent job during this lengthy and laborious process, Jaco van de Pol Marco Roveri (FBK-IRST, Italy), John Rushby (SRI International , USA)