Peter Hogan is Emeritus Professor at University College Dublin. He received his B.Sc., M.Sc., Ph.D. and D.Sc. degrees from The National University of Ireland and is a member of the Royal Irish Academy. He was a postdoctoral fellow in the School of Theoretical Physics, Dublin Institute for Advanced Studies, the Centre for Relativity, University of Texas at Austin and the School of Mathematics, Trinity College Dublin. His publications of more than 90 papers and three monographs are in Electrodynamics, Yang-Mills gauge theory from the fibre bundle point of view and general relativity (equations of motion, gravitational waves, exact solutions of Einstein's equations and cosmology). He has published research carried out in Japan, South Africa, France, Poland and the U.S.Dirk Puetzfeld is a researcher at Bremen University (Germany). He received his Dipl. Phys. and Dr. rer. nat. degrees from University of Cologne (Germany), both in theoretical physics. He was an assistant professor at Tohoku University (Japan), and a postdoctoral fellow at the Max-Planck-Institute for Gravitational Physics (Germany), University of Oslo (Norway), Iowa State University (USA). His main research interests include gravitational physics, cosmology, relativistic geodesy, as well as computational methods. His publication record encompasses over 50 scientific papers in international journals as well as two books.