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.