Amherst, Mass. ONE HUNDRED years ago, on Feb. 12, 1912, the 6-year-old child emperor of the Qing Dynasty abdicated, ending more than 2,000 years of imperial rule in China. But this watershed moment for modern China will not be widely celebrated in the People's Republic. The political climate in Beijing is tense as the ruling Communist Party prepares for a secretive transition to the next generation of leaders, with the untested vice president, Xi Jinping, expected to become president. Reminders of past regime change and the end of dynasties are not welcome. [ABSTRACT FROM AUTHOR]