Fig. 2

a Publication trends in SDF-based research over the past 20 years. b Analysis of the research trends based on types of publication. c Top 10 institutions based on the publications in SDF (1999–2018). d Contour/Heat map showing the publications in SDF (1999–2018). e International collaborations in SDF research. f Analysis of the research trends based on the origin of publications across the globe. g Contour/Heat map showing the top scientist working in the area of SDF. Heat map 2d and 2g shows gradient heat pattern (red, orange, yellow, green and blue) based on the number of publications from journal and author, respectively. The font size of the journal and author names are presented in an ascending manner with respect to an increasing number of publications. Only the names of journals and authors having higher number of publications are visible