Hidden attractors in a chaotic system with an exponential nonlinear term V.-T. Pham, S. Vaidyanathan, C.K. Volos and S. Jafari Eur. Phys. J. Special Topics, 224 8 (2015) 1507-1517 Published online: 27 July 2015 DOI: 10.1140/epjst/e2015-02476-9