Ronald Mickens (Clark Atlanta University)
The Abel equation, in canonical form, is y' = sin t - y^3 (*) and corresponds to the singular (epsilon -> 0) limit of the nonlinear, forced oscillator epsilon y" + y' + y^3 = sin t, epsilon -> 0. (**) Equation (*) has the property that it has a unique periodic solution defined on (-infty, infty). Further, as t increases, all solutions are attracted into the strip |y| < 1 and any two different solutions y_1(t) and y_2(t) satisfy the condition Lim [y_1(t) - y_2(t)] = 0, (***) t -> infty and for t negatively decreasing, each solution, except for the periodic solution, becomes unbounded. Our purpose is to calculate an approximation to the unique periodic solution of Eq. (*) using the method of harmonic balance. We also determine an estimation for the blow-up time of the non-periodic solutions.  U. Elias, American Mathematical Monthly, vol.115, (Feb. 2008), pps. 147-149.