OMAHA, Neb. (AP) — Federal inspectors said they found an alarming number of defects in the locomotives and railcars Union Pacific was using at the world's largest railyard in western Nebraska this summer, and the railroad was reluctant to fix the problems. Federal Railroad Administrator Amit Bose wrote a letter to UP's top three executives Friday expressing his concern that the defects represent a “significant risk to rail safety " on the Union Pacific railroad.