This project continues a long-term program to develop practical radiative transfer methods, and refine them to match the progress of new observations. This program has already had a transformative impact on studies of astronomical masers and dust infrared emission from active galactic nuclei (AGN). The present work will expand and enhance two recently developed techniques, one a new exact method for line emission from multi-level systems and the other for handling radiation from clumpy media. These enhancements will be used for improved matching of dust emission models to forthcoming high-resolution observations, for corrected calculations of line emission from AGN that remove faulty assumptions, for realistic calculations of radiation pressure on dust, and to study the thermal and maser line emission from accretion disks. Close collaboration between this theory program and the observing teams is a major ingredient of the research, because the theory is strongly anchored in observations
Developed modeling codes will continue to be placed in the public domain, and past codes have been used in many unrelated studies. The principal investigator maintains a broad range of international collaborations, and former students all continue active involvement with the program: a major accomplishment of this group has been its continuing educational impact.
