Figure 1.

Contours of $\mathcal{Q}$ showing intense, rotational, vortex tubes (red, $\mathcal{Q}=+5\sqrt{⟨{\mathcal{Q}}^2⟩}$) enveloped by strong straining sheets (blue, $\mathcal{Q}=-2\sqrt{⟨{\mathcal{Q}}^2⟩}$), in three-dimensional homogeneous isotropic turbulence. The black scale bar at the top-left corner corresponds to a length of 35η. (Online version in colour.)