2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/130086We give an extended review of recent work on the extended weak coupling limit. Background material on completely positive semigroups and their unitary dilations is given, as well as a particularly easy construction of `quadratic noises'.39 pages, review article for the conference "Noncommutative harmonic analysis" in Bedlewo, Poland, 2006. v1-->v2, corrections in Section 5 and changes in notationMathematical Physicstext