SGEM 2019 : 19th international multidisciplinary scientific geoconference SGEM 2019, 30 June - 6 July, 2019, Albena, Bulgaria. 19, Energy and clean technology. Nuclear technologies renewable energy sources and clean technologies recycling air pollution and climate change . Sofia :  STEP92 Technology , 2019 . 1150 s . ISBN 978-619-7408-83-6 .