New longitudinal waves in electron-positron-ion quantum plasmas N.L. Tsintsadze, L.N. Tsintsadze, A. Hussain and G. Murtaza Eur. Phys. J. D, 64 2-3 (2011) 447-452 Published online: 11 October 2011 DOI: 10.1140/epjd/e2011-20332-8