“…A more recent analytic calculation [24] took the cold ion limit and calculated how PVG can be stabilized by perpendicular shear flow. References [25,26,27] have used fluid equations, rigorously derived from electromagnetic gyrokinetic theory, to understand the interplay between the density gradient, temperature gradient, parallel flow shear, perpendicular flow shear, and magnetic shear. Lastly, several works [28,29] study how perpendicular flow shear enables gyrokinetic simulations to exhibit "subcritical" turbulence, which is a nonlinear instability that is sustained despite the fact that the modes are linearly stable.…”