Energy estimates of harmonic maps between Riemannian manifolds

Let $\Omega \subset {R}^n,$ $n \geq 3,$ be a bounded open set, $x=(x_1,x_2,\ldots,x_n)$ a generic point which belongs to $\Omega,$ $u \colon \Omega \to {R}^N ,$ $N>1,$ and $Du=(D_\alpha u^i)$, $D_\alpha = \partial/\partial x_\alpha,$ $\alpha =1,\ldots,n,\,$ $i=1,\ldots,N .\,$ Main goal is the study of regularity of the minima of nondifferentiable functionals $${\cal F} \,=\, \int_\Omega F(x,u,Du) dx.$$ having the integrand function different shapes of smoothness. The method is based on the use some majorizations for the functional, rather than the well known Euler equation associated to it.