  Stretching in continuum mechanics is naturally described using the
Cauchy-Green strain tensors. These tensors quantify the Lagrangian stretching
experienced by a material element, and provide a powerful way to study
processes in turbulent fluid flows that involve stretching such as vortex
stretching and alignment of anisotropic particles. Analyzing data from a
simulation of isotropic turbulence, we observe preferential alignment between
anisotropic particles and vorticity. We show that this alignment arises because
both of these quantities independently tend to align with the strongest
Lagrangian stretching direction, as defined by the maximum eigenvector of the
left Cauchy-Green strain tensor. In particular, anisotropic particles approach
almost perfect alignment with the strongest stretching direction. The alignment
of vorticity with stretching is weaker, but still much stronger than previously
observed alignment of vorticity with the eigenvectors of the Eulerian strain
rate tensor. The alignment of strong vorticity is almost the same as that of
rods that have experienced the same stretching.
