NGC 4151 - A unified active galactic nucleus
  We present a unified picture of active galactic nuclei which we construct from a detailed model of line emission in the active source in NGC 4151. In this scheme NGC 4151 can be regarded as a typical active nucleus, special only in its orientation. This alleviates a number of problems with a unified picture based on a dusty molecular torus with a fixed structure (to which NGC 4151 appears as an anomaly) 
I Cassidy, D.J.Raine (Department of Physics & Astronomy, University of   Leicester, UK)