I'm happy to report that http://maraca.d.umn.edu has returned to service and is now running the UMLS::Similarity web interface, using UMLS version 2013AA (which is just a few days old).
Our main production server remains http://atlas.ahc.umn.edu, which is running UMLS version 2012AA. So, please feel free to visit either/both sites to use the web interface. Please let us know if any questions arise. Enjoy, ted
