Parsec-Scale Jets and Tori in Seyfert Galaxies
  What causes the dichotomy between very powerful and very weak radio emission from AGNs? Perhaps the engines are the same but the jets get disrupted by dense ISM in radio-quiet objects, or else the engines are intrinsically different with jet power scaling with, say, black hole spin. To distinguish, one can look for interaction between the jets and the NLR and measure the jet speed close to the core using VLBI, before environmental effects become important. We find that in radio-quiet AGN, the jets appear slower and have a greater tendency to bend, and that one-sidedness and flat-spectrum cores are probably due to obscuration. 
A.L. Roy, J.M. Wrobel, A.S. Wilson, J.S. Ulvestad, R.P. Norris, C.G.   Mundell, T.P. Krichbaum, H. Falcke, E.J.M. Colbert