# Article

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Keywords:
$k$-connected graph; non-regular graph; algebraic connectivity; Laplacian spectral radius; maximum degree
Summary:
Let $\mu _{n-1}(G)$ be the algebraic connectivity, and let $\mu _{1}(G)$ be the Laplacian spectral radius of a $k$-connected graph $G$ with $n$ vertices and $m$ edges. In this paper, we prove that \begin {equation*} \mu _{n-1}(G)\geq \frac {2nk^2}{(n(n-1)-2m)(n+k-2)+2k^2}, \end {equation*} with equality if and only if $G$ is the complete graph $K_n$ or $K_{n}-e$. Moreover, if $G$ is non-regular, then \begin {equation*} \mu _1(G)<2\Delta -\frac {2(n\Delta -2m)k^2}{2(n\Delta -2m)(n^2-2n+2k)+nk^2}, \end {equation*} where $\Delta$ stands for the maximum degree of $G$. Remark that in some cases, these two inequalities improve some previously known results.
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