He held long-term positions at the University of Wuppertal and at the Forschungszentrum Jülich (Germany). Other positions that lasted between 2 years and 3 months were at CERN, at the Universities of Kabul, Nice, Calgary, Rome and Utrecht, the Weizmann Institute, the Max Planck Institute for the Physics of Complex Systems in Dresden, the Istituto nazionale di ottica [ it ] in Florence, and at the Institute for Advanced Studies in Basic Sciences in Zanjan, Iran.