We show that the dynamically selected velocity and tip radius of dendrites in the boundary-layer model of solidification have the special values which permit the existence of steady-state needle-crystal solutions. This result, in conjunction with considerations of stability, provides new insight concerning the validity of the marginal stability hypothesis.

• Received 13 August 1984

DOI:https://doi.org/10.1103/PhysRevLett.53.2110