[1] Univ Fed Minas Gerais UFMG, Dept Math, Belo Horizonte, Brazil
[2] Brown Univ, Dept Math, Providence, RI USA
[3] Florida Int Univ, Dept Math & Statist, Miami, FL USA
[4] Chongqing Univ, Key Lab Nonlinear Anal & Applicat, Minist Educ, Chongqing 401331, Peoples R China
[5] Chongqing Univ, Coll Math & Statist, Chongqing 401331, Peoples R China