Structure in the classical knot concordance group
  We provide new information about the structure of the abelian group of topological concordance classes of knots in $S^3$. One consequence is that there is a subgroup of infinite rank consisting entirely of knots with vanishing Casson-Gordon invariants but whose non-triviality is detected by $L^{(2)}$ signatures. 
Tim D. Cochran, Kent E. Orr, Peter Teichner