Mathematical models that involve a combination of convective and diffusive processes are among the most widespread in all of science, engineering and other fields where mathematical modelling is important.Water quality problems, convective heat transfer problems, simulation of the semiconductor devices can be given as an example of these models. Also, the Linearization of the Navier-Stokes equation and drift-diffusion equation of semiconductor device modelling are important instances. The dimensionless parameter that measures the relative strenght of diffusion is generally quite small; so one...