Uriel Feige, Mohit Singh. Improved Approximation Ratios for Traveling Salesperson Tours and Paths in Directed Graphs. In Moses Charikar, Klaus Jansen, Omer Reingold, José D. P. Rolim, editors, Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques, 10th International Workshop, APPROX 2007, and 11th International Workshop, RANDOM 2007, Princeton, NJ, USA, August 20-22, 2007, Proceedings. Volume 4627 of Lecture Notes in Computer Science, pages 104-118, Springer, 2007. [doi]