[Jin, Shaojia; Liu, Yanyan] Wuhan Univ, Sch Math & Stat, Wuhan 430072, Peoples R China.
[Jin, Shaojia] Wuhan Text Univ, Sch Math & Phys Sci, Wuhan 430200, Peoples R China.
[Mao, Guangcai] Cent China Normal Univ, Sch Math & Stat, Wuhan 430079, Peoples R China.
[Mao, Guangcai] Cent China Normal Univ, Hubei Key Lab Math Sci, Wuhan 430079, Peoples R China.
[Sun, Jianguo] Univ Missouri, Dept Stat, Columbia, MO USA.