Authorities struggle to avert full meltdowns and to cool fuel rods at the earthquake-crippled Fukushima Daiichi plant as U.S. and Japanese authorities appear to disagree over the magnitude of the nuclear crisis. Public anger mounts over lagging quake relief efforts.Japanese authorities took desperate new measures to avert full-scale meltdowns at a quake-battered nuclear plant Thursday, dispatching helicopters to drop tons of water on the reactors and using water cannons to cool a spent-fuel pool that an American official said was responsible for "very significant radiation levels."