text: Elliptic regularization of the Hamilton-Jacobi equation led to the development of solutions named after this quantity for nonlinear degenerate elliptic equations.
full_question: Elliptic regularization of the Hamilton-Jacobi equation led to the development of solutions named after this quantity for nonlinear degenerate elliptic equations. When Burgers' equation is solved in the limit where this quantity approaches zero, the solution possesses a shock discontinuity. This quantity is the central variable to the transport equation in the Spalart-Allmaras model. The dynamic response caused by a material possessing this property is quantified by the loss modulus. One form of this quantity serves as a diffusion coefficient for linear momentum. The length scale over which this quantity is significant can be calculated with the Blasius formula. This quantity acquires time dependence in rheopectic and thixotropic materials. The effects of this quantity are significant only inside the boundary layer. This quantity is equal to the ratio of shear stress to shear rate, and it comes in dynamic and kinematic types. For 10 points, name this quantity which is constant for Newtonian fluids.
first_sentence: Elliptic regularization of the Hamilton-Jacobi equation led to the development of solutions named after this quantity for nonlinear degenerate elliptic equations.
raw_answer: viscosity [or kinematic viscosity; or dynamic viscosity; or eddy viscosity]