A Moment of Perfect Clarity II: Consequences of Sparse Sets Hard for NP   with Respect to Weak Reductions
  This paper discusses advances, due to the work of Cai, Naik, and Sivakumar and Glasser, in the complexity class collapses that follow if NP has sparse hard sets under reductions weaker than (full) truth-table reductions. 
Christian Glasser and Lane A. Hemaspaandra