先进材料疑固实验室 Dendrite arm spacing Laboratory of Advanced Materials Solidification Secondary arms start very close to the tips.The appear initially as a sinusoidal perturbation of the paraboloid.These perturbations grow become cell-like,are sometimes eliminated by their neighbors,and a number of them finally become real secondary dendrites growing perpendicularly to the primary trunk. t2>t1 2R 2r 上浒充通大学 SHANGHAI JIAO TONG UNIVERSITYDendrite arm spacing Secondary arms start very close to the tips. The appear initially as a sinusoidal perturbation of the paraboloid. These perturbations grow become cell-like, are sometimes eliminated by their neighbors, and a number of them finally become real secondary dendrites growing perpendicularly to the primary trunk