Effects of fourth-order dispersion on modulational instability in metamaterials with exponential saturable nonlinearity and self-steepening coefficientsAboukar, A. D. Aboubakar, S. Mohammadou, Alim, S. Abdoulkary, A. Mohamadou and S. Y. DokaEur. Phys. J. Plus, 129 12 (2014) 279DOI: https://doi.org/10.1140/epjp/i2014-14279-7