I get this a lot in my current role already, so it wasn't that hard to answer. It was just a little harder in that the "customers" in this role would be PhD level people. One would expect all these smart people would understand. While they do high energy physics and nuclear chemistry, they may not know the project development lifecycle. My job as a project manager would be to manage their expectations and help educate and delineate their actual needs and deliverables. The project manager would hold them accountable for their part; likewise they would also hold the project manager accountable to complete the task on time and on budget while meeting all the written and unstated objectives.