- Karl-Heinz Foerster; Bela Nagy
*On Spectra of Expansion Graphs and Matrix Polynomials, II,*

Electron. J. Linear Algebra 9 (2002), 158-170. - Michael Neumann; Nic Ormes
*Bounds for graph expansions via elasticity,*

Electron. J. Linear Algebra 10 (2003), 163-178.