Mikael R?rdam教授是華東師范大學榮譽教授、丹麥皇家科學院院士、哥本哈根大學教授,國際算子代數研究領域的領軍人物。R?rdam教授長期致力于算子代數、動力系統、幾何群論、K-理論等領域的研究,其研究成果發表在Annals of Mathematics、Acta Mathematica等頂尖的數學雜志上,文章總引用率達2800多次。由于在C*-代數的結構和分類理論中的卓越工作,2006年,他應邀在馬德里召開的第25屆國際數學家大會(ICM)上作特邀報告。
In his study of the relative Dixmier property for von Neumann algebras and C*-algebras, Popa introduced a property of an automorphism, which can be thought of as a twisted Dixmier averaging property. We give an almost complete characterization of when an automorphism has this property. We further show how one can use this property to give much easier and more transparent proofs of a number of results on the inclusion of a C*-algebra into its crossed product C*-algebra by a group of automorphisms, assuming the automorphisms have averaging property.