After several days of meetings with senior Chinese officials covering major issues like national security, technology and trade, Treasury Secretary Janet Yellen said her trip to Beijing was "successful" in that it laid a foundation for ongoing diplomacy with the United States. "We have a new team on the economic side in Beijing, and it's important to establish person-to-person relationships and to open ongoing channels of communication, where concerns can be aired and discussed," Yellen told "Face the Nation" moderator Margaret Brennan during a "Face the Nation" interview that aired on Sunday morning. "And I do think my trip has…