From generalized Fourier transforms to spectral curves for the Manakov hierarchy. I. Generalized Fourier transformsV. S. Gerdjikov, A. O. Smirnov and V. B. MatveevEur. Phys. J. Plus, 135 8 (2020) 659DOI: https://doi.org/10.1140/epjp/s13360-020-00668-2