Nature of the axial-vector mesons from their Nc behavior within the chiral unitary approach L. S. Geng, E. Oset, J. R. Peláez and L. Roca Eur. Phys. J. A, 39 1 (2009) 81-87 Published online: 15 December 2008 DOI: 10.1140/epja/i2008-10689-y