click on all the images in this blog post from Borowski's presentation for a larger version in the same browser window
Borowski explained that he had finished the work 18 months ago and wanted to present the work at last year's joint propulsion conference but had missed that opportunity. He had attended the NASA detection, [asteroid] characteristics and mitigation [mission] conference held in Vail, Colorado in 2006 (here is a paper from that conference) and he was asked by NASA Glenn Research Center to do the study
So if any one tells you that this study is not an "official NASA study" - as one NASA official claimed when asked by a German journalist about Flight's armageddon story at the AIAA SpaceOps 2008 conference in Heidelberg - then you know they don't know what they are talking about
Borowski's study concluded that for deflection of large (~1 km diameter) NEOs on final approach a high energy yield nuclear payload (~1 kT/kg) "appears to be the most viable approach [and] delivery on a high velocity [nuclear engine propelled] intercept stage can also help maximize the intercept range and deflection time"