+ ω y -ω y Figure 2: Left: Velocity shearing and scaling reverse non-equilibrium molecular dynamics (VSS-RNEMD) imposes a momentum flux, j z (p x ) between two regions (orange and yellow). This is equivalent to a shear stress, τ zx . Right: the fluid responds by creating a velocity profile along the zaxis. At low flux, the regions between the orange and yellow slabs (colorless regions) experience a constant velocity gradient, and therefore a constant vorticity, +ω y or -ω y , which points in opposite directions on either side of the simulation cell.