“…A conceptual phenomenon of classical adiabatic theory is destruction of adiabatic invariance at separatrix crossings which is encountered, in particular, in plasma physics and hydrodynamics, classical and celestial mechanics [10,11,12,13,14,15,16,17,18,19,20,21,22]. The phenomenon is very important for BEC physics: we consider here nonlinear two-mode models related to tunnelling between coupled BEC in a double well [23], nonlinear Landau-Zener tunnelling [24,25], Feshbach resonance passage in atom-molecule systems [26,27,28].…”