HONG KONG — Chinese President Xi Jinping’s purges of senior military officials run far deeper than previously thought, researchers say, threatening the effectiveness of his People’s Liberation Army. The crackdown, documented in two new studies released Tuesday, includes the recent ouster of Xi's top two generals. Purges have been a regular occurrence under Xi, but observers were still shocked last month when it was announced that Gen. Zhang Youxia , the military’s No. 2 official after Xi