The dynamic evolution of a protoplanetary nebula is investigated using analytical solutions of the surface density transport equations. Constant- and so-called β-viscosity turbulence models are compared with a functional analytical model and the well-known α-viscosity formulation. The model presented here is related to a number of simplified disk evolution models but is also associated with β-viscosity models based on hydrodynamic generation of turbulence. The β-viscosity model, heretofore used for steady state disks, is shown to be a useful approximation for disk evolution problems.
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