Department of Statistics, Chonnam National University, Gwangju 500-757, South Korea. jbaek@chonnam.ac.kr|Department of Statistics, Chonnam National University, Gwangju 500-757, South Korea. jbaek@chonnam.ac.kr|Department of Statistics, Chonnam National University, Gwangju 500-757, South Korea. jbaek@chonnam.ac.kr