Investigating the reasons of variability in Si IV and C IV broad absorption line troughs of quasars Dimitrios Stathopoulos, Evangelia Lyratzi, Emmanuel Danezis, Antonios Antoniou and Dimitrios Tzimeas Eur. Phys. J. D, 71 9 (2017) 224 Published online: 05 September 2017 DOI: 10.1140/epjd/e2017-70749-x