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Published online by Cambridge University Press: 07 August 2017
Bipolar outflows or polar knots are rather ubiquitous phenomena. A wealth of observational data is now available on bipolar flows associated with young stellar objects or stellar formation regions (Snell, Proc. I. A. U. Symp. Nr. 115, 1987), or nuclei of active galaxies (Asseo and Sol, 1987, Phys. Rep. 148, 307).