An improved upper bound for critical value of the contact process on $mathbb{Z}^d$ with $dgeq 3$

In this paper we give an improved upper bound for critical value $lambda_c$ of the basic contact process on the lattice $mathbb{Z}^d$ with $dgeq 3$. As a direct corollary of out result, [ lambda_cleq 0.384. ] when $d=3$.