Through scaling analysis, Segel went on to show that the RSA determines single-handedly the validity of the asymptotic solutions 2 (16) and . Introducing the dimensionless variables ŝ1 = s 1 /s 0 1 and ĉ1 = c 1 /c 1 , Segel and Slemrod demonstrated that, with respect to the dimensionless timescale 2 Segel did not refer to the condition ε 1 as the RSA [see 17, for more details]. τ = t/t c1 , equations (10a)-(10a) scale as