Slow vector optical solitons in a cold four-level inverted-Y atomic system L. G. Si, W. X. Yang, X. Y. Lü, J. H. Li and X. X. Yang Eur. Phys. J. D, 55 1 (2009) 161-166 Published online: 17 July 2009 DOI: 10.1140/epjd/e2009-00205-7