“…We refer to (Aronson & Weinberger, 1957;Aronson & Weinberger, 1978;Berestycki, Hamel, & Nadirashvili, 2010;Kametaka, 1976;Liang & Zhao, 2007;Liang, Yi, & Zhao, 2006;Sattinger, 1976;Uchiyama, 1978;Weinberger, 1982;etc). for the study of (1.2) in the case that f (x, u) is independent of x and refer to (Berestycki, Hamel, & Nadirashvili, 2005;Berestycki, Hamel, & Roques, 2005;Freidlin & Gärtner, 1979;Hamel, 2008;Hudson & Zinner, 1995;Nadin, 2009;Nolen, Rudd, & Xin, 2005;Weinberger, 2002;etc). for the study of (1.2) in the case that f (x, u) is periodic in x; refer to (Coville & Dupaigne, 2005;Coville, Dávila, & Martínez, 2008;Li, Sun, & Wang, 2010;etc).…”