The mayor of Nagasaki sent a letter of protest to U.S. President Barack Obama on Wednesday after the United States revealed it had conducted an experiment using a small amount of plutonium to examine the capabilities of its nuclear weapons between July and September.The mayor of Nagasaki sent a letter of protest to U.S. President Barack Obama on Wednesday after the United States revealed it had conducted an experiment using a small amount of plutonium to examine the capabilities of its nuclear weapons between July and September.