Solid-state traveling-wave amplifiers and oscillators in the THz range: effect of electron collisions O. Sydoruk, E. Shamonina and L. Solymar Eur. Phys. J. D, 59 2 (2010) 233-240 Published online: 11 June 2010 DOI: 10.1140/epjd/e2010-00158-8