Sign-Changing Solutions to Equations of Elliptic Type

1 Department of Mathematical Sciences, Tsinghua University, Beijing 100084, China 2 Mathematisches Institut, University Giessen, Arndtstr. 2, 35392 Giessen, Germany 3 Graduate School of Environment and Information Science, Yokohama National University, Tokiwadai, Yokohama 240-8501, Japan 4 Mathematics Department, University of California, Irvine, CA 92697-3875, USA 5 Department of Mathematics and Statistics, Utah State University, Logan, UT 84322-4205, USA