sentences:  He was elected as the President of the Cosmology Commission (2009-2012) of the International Astronomical Union (IAU) and was providing advice to IAU activities in this field.He was elected in 2011 as the Chairman of the Astrophysics Commission (2011-2014) of the International Union of Pure and Applied Physics (IUPAP)  and co-ordinated the activities of IUPAP in this area.He has also been a Visiting Faculty at many institutes including the California Institute of Technology, Princeton University, and a Sackler Distinguished Astronomer of the Institute of Astronomy, Cambridge.