报告人：Nils Dencker 教授

单位：瑞典隆德大学

时间：2016年10月15日（星期六）上午10：00

地点：太白校区 非线性科学研究中心学术报告厅（312）

报告题目：It was a great surprise Hans Lewy in 1957 showed that the tangential Cauchy-Riemann operator on the boundary of a strictly pseudoconvex domain is not locally solvable. Hormander then proved in 1960 that almost all linear partial differential equations are not locallysolvable. Nirenberg and Treves formulated their famous conjecture in 1970: that condition (PSI) is necessary and sufficient for the localsolvability of differential equations of principal type. Principal type means simple characteristics, and condition (PSI) only involves the sign changes of the imaginary part of the principal symbol along the bicharacteristics of the real part. The Nirenberg-Treves conjecture was finally proved in 2006.

In this talk, we shall present some necessary condition for the solvability of differential operators that are not of principal type, instead the principal symbol vanishes of at least second order at the characteristics. Then the solvability may depend on the lower order terms, and one can define a condition corresponding to (PSI) on the subprincipal symbol. We show that this condition is necessary forsolvability in some cases. The condition is not always necessary, for example effectively hyperbolic operators are always solvable with anylower order terms.

报告人简介：Prof. Dencker ，瑞典隆德大学博士毕业，现任隆德大学教授。1983年获得由瑞典皇家科学院颁发的“Stromer-Ferrner Award”奖,2003年获得隆德皇家地理学会颁发的“Grarding Prize”奖，2005年获得克莱数学研究所颁发的“克莱研究奖”，现任欧洲数学会会议委员会主席，瑞典皇家科学院数理部主席。

欢迎广大师生的参加！