Letf(u) be twice continuously differentiable on [0, c) for some constant c such thatf(0) > 0,f' 0,f" 2 0, and lim.+cf(u) = 0 0 . Also, let x(S) be the characteristic function of the set S. This article studies all solutions u with non-negative u, in the region where u < c and with continuous u, for the problem: u,,ut = -f(u)x({u < c}), 0 < x < a, 0 c f < 0 0 , subject to zero initial and first boundary conditions. For any length a larger than the critical length, it is shown that if f',f(u) du < to, then as t tends to infinity, all solutions tend to the unique steady-state profile U(x), which can be computed by a derived formula; furthermore, increasing the length a increases the interval where V ( x ) = c by the same amount. For illustration, examples are given.