“…When ␣ -0 -␣ , the uniformly aligned configurations become unstable for sufficiently high shear rates and either tumbling regimes develop in the flow region in the w xŽ shear plane 4, 19, 20 shear plane is defined at the beginning of Sec-. tion 2 or the alignment of nematic liquid crystals takes on a component w x w perpendicular to the shear plane 19,20 . From numerical simulations 15, x 17, 23, 24 , they confirmed that the existence of limit points along the solution branch of planar shear flows and tumbling instability is characterized by the exchange of stability of the planar configuration by another planar configuration with a more distorted director field.…”