Who May Serve as PI:Doctoral Dissertation Research Improvement Awards: DDRI proposals must be submitted with a principal investigator (PI) and a co-principal investigator (co-PI). The PI must be the advisor of the doctoral student or another faculty member at the U.S. institution where the doctoral student is enrolled. The co-PI must be the doctoral student whose dissertation research will be supported. For all other types of awards, there are no restrictions or limits.