Dark lattice solitons in one-dimensional waveguide arrays with defocusing saturable nonlinearity and alternating couplingsA. Kanshu, C.E. Rüter, D. Kip, J. Cuevas and P.G. KevrekidisEur. Phys. J. D, 66 7 (2012) 182DOI: https://doi.org/10.1140/epjd/e2012-30204-4