By Max Larkin | Harvard Staff Writer | Harvard Gazette From a bicycle seat, Harvard postdoc sees roadblocks facing rural medicine George Usmanov did some unforgettable sightseeing this summer. Over 25 days in June and July, he passed by ghost towns from both the 19th and 20th centuries and acres of forest, “completely charred.” He saw a river run yellow out of a Superfund site and the sun rise purple, thanks to a mix of “desert dust, mist from t…