Nullspace embeddings for outerplanar graphs
  We study relations between geometric embeddings of graphs and the spectrum of associated matrices, focusing on outerplanar embeddings of graphs. For a simple connected graph $G=(V,E)$, we define a "good" $G$-matrix as a $V\times V$ matrix with negative entries corresponding to adjacent nodes, zero entries corresponding to distinct nonadjacent nodes, and exactly one negative eigenvalue. We give an algorithmic proof of the fact that it $G$ is a 2-connected graph, then either the nullspace representation defined by any "good" $G$-matrix with corank 2 is an outerplanar embedding of $G$, or else there exists a "good" $G$-matrix with corank 3. 
L\'aszl\'o Lov\'asz and Alexander Schrijver
math.CO