Sharp pointwise estimates for functions in the Sobolev spaces Hs(Rn)
  We obtain the optimal value of the constant K(n,s) in the Sobolev-Nirenberg-Gagliardo inequality $ \|\,u\,\|_{L^{\infty}(\mathbb{R}^{n})} \leq K(n,s) \,\|\, u \,\|_{L^{2}(\mathbb{R}^{n})}^{1 - n/(2s)} \|\, u \,\|_{\dot{H}^{s}(\mathbb{R}^{n})}^{n/(2s)} $ where $ s > n/2 $. 
Lineia Schutz, Juliana S. Ziebel, Janaina P. Zingano and Paulo R.   Zingano
math.FA