@unpublished{TUW-196694, author = {B{\"o}hm, Johannes and Spicakova, Hana and Urquhart, Landon and Steigenberger, Peter and Schuh, Harald}, title = {Impact of a priori gradients on VLBI- and GNSS derived reference frames}, year = {2011}, note = {talk: 20th EVGA Meeting, Bonn, Germany; 2011-03-29 -- 2011-03-30} }