Curvature estimates for irreducible symmetric spaces
  By making use of the classification of real simple Lie algebra, we get the maximum of the squared length of restricted roots case by case, thus we get the upper bounds of sectional curvature for irreducible Riemannian symmetric spaces of compact type. As an application, we verify Sampson's conjecture in all cases for irreducible Riemannian symmetric spaces of noncompact type. 
Xusheng Liu