Dozens of world leaders stood and bowed their heads in a moment of silence¬†honoring Polish President¬†Lech Kaczynski and nearly 100¬†others who died on Saturday in a plane crash in western Russia. U.S. President Barack Obama remembered the deaths as losses not just for their own country, “a close friend and ally,” but for the world, before making remarks formally opening a gathering of world leaders to discuss nuclear security issues.