The U.S. government said Thursday that its data collectors have not seen any significant progress on the cooling of the Japanese nuclear reactors. The data was collected by the Aerial Measurement System, considered one of the most sophisticated nuclear reading devices in use and rushed to Japan by the White House. U.S. aircraft usually used to monitor North Korean nuclear-weapon activity were dispatched to fly over the reactor, as the U.S. pressured the Japanese to stop relying on numbers from the operator of the plant, the Tokyo Electric Power Co. But the right for anyone other than the Japanese measuring the radioactivity has been a bitter battle, as the U.S. government called Wednesday for a 50-mile evacuation around the Fukushima Daiichi plant rather than the 12 miles suggested by Japanese officials. The numbers released Thursday indicated no contamination had spread beyond the 18-mile range established by Japanese authorities.