Lower Bound of Concurrence Based on Generalized Positive Maps
  We study the concurrence of arbitrary dimensional bipartite quantum systems. By using a positive but not completely positive map, we present an analytical lower bound of concurrence. Detailed examples are used to show that our bound can detect entanglement better and can improve the well known existing lower bounds. 
Hui-hui Qin and Shao-Ming Fei
quant-ph