On stimulated emission processes in gravitational fields - Ruffini, R.; Stella, L. (Elsevier)
We here introduce necessary conditions to be fulfilled in order to have stimulated emission processes in a gravitational field. We also define ''regions of constant shift'' with respect to an asymptotic observer.
http://linkinghub.elsevier.com/retrieve/pii/0370-2693(80)90105-7
Keywords: U