My research activity is in the field of general relativity and gravitation. To date, I have published more than 200 research papers in international peer-reviewed journals, with over 3250 citations (self-citations excluded; source: NASA/ADS), and two books as editor. My h-index is currently 39 (source: NASA/ADS). So far, I have received 27 requests by foreign students of international academic institutions as supervisor of their Ph. D. and/or post-Doc research activity.