On the spectral dynamics of the deformation tensor and new a priori   estimates for the 3D Euler equations
  In this paper we study the dynamics of eigenvalues of the deformation tensor for solutions of the 3D incompressible Euler equations. Using the evolution equation of the $L^2$ norm of spectra, we deduce new a priori estimates of the $L^2$ norm of vorticity. As an immediate corollary of the estimate we obtain a new sufficient condition of $L^2$ norm control of vorticity. We also obtain decay in time estimates of the ratios of the eigenvalues. In the remarks we discuss what these estimates suggest in the study of searching initial data leading to a possible finite time singularities. We find that the dynamical behaviors of $L^2$ norm of vorticity are controlled completely by the second largest eigenvalue of the deformation tensor. 
Dongho Chae