“…Therefore, it is clear that (1) considered here contains (4) and (5) as special cases. Moreover, with various boundary conditions, the particular forms of (1) have been extensively studied by many authors; for example, we refer to [3][4][5][6][7][8][9][10][11][12][13][14][15] and the references given therein. In these works, many interesting results about existence, regularity, asymptotic behavior, asymptotic expansion, and decay of solutions were obtained.…”