Nonuniform dichotomy spectrum and reducibility for nonautonomous   equations
  For nonautonomous linear differential equations with nonuniform hyperbolicity, we introduce a definition for nonuniform dichotomy spectrum, which can be seen as a generalization of Sacker-Sell spectrum. We prove a spectral theorem and use the spectral theorem to prove a reducibility result. 
Jifeng Chu, Fang-Fang Liao, Stefan Siegmund, Yonghui Xia, Weinian   Zhang
math.DS