Breaking of vortex lines - a new mechanism of collapse in hydrodynamics
  A new mechanism of the collapse in hydrodynamics is suggested, due to breaking of continuously distributed vortex lines. Collapse results in formation of the point singularities of the vorticity field $|{\bf\Omega}|$. At the collapse point, the value of the vorticity blows up as $(t_0-t)^{-1}$ where $t_0$ is a collapse time. The spatial structure of the collapsing distribution approaches a pancake form: contraction occurs by the law $l_1\sim(t_0-t)^{3/2}$ along the "soft" direction, the characteristic scales vanish like $l_2\sim(t_0-t)^{1/2}$ along two other ("hard") directions. This scenario of the collapse is shown to take place in the integrable three-dimensional hydrodynamics with the Hamiltonian ${\cal H}=\int|{\bf\Omega}|d{\bf r}$. Most numerical studies of collapse in the Euler equation are in a good agreement with the proposed theory. 
E.A.Kuznetsov and V.P.Ruban (L.D.Landau Institute, Russia)