new bounds on distance estrada index of graphs

For a connected graph $g$ with vertex set ${v_1,ldots,v_n}$, the distance matrix of $g$, denoted by $d(g)$, is an $ntimes n$ matrix with zero main diagonal, such that its $(i,j)$-entry is $d(v_i,v_j)$, where $ineq j$ and $d(v_i,v_j)$ is the distance between $v_i$ and $v_j$. let $theta_1,ldots,theta_n$ be the eigenvalues of $d(g)$. the distance estrada index of $g$ is defined as $dee(g)=sum_{i=1}^ne^{theta_i}$. in this paper we find some new sharp bounds for the distance estrada index of graphs. our results improve the previous bounds on the distance estrada index of graphs.