V. A. Srećković, D. M. Šulić, V. Vujčić, D. Jevremović, and Y. Vyklyuk, “THE EFFECTS OF SOLAR ACTIVITY: ELECTRONS IN THE TERRESTRIAL LOWER IONOSPHERE”, J. Geogr. Inst. Cvijic, vol. 67, no. 3, pp. 221–233, Dec. 2017.