where the constants lsi2" class="mathmlsrc">lass="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0022247X16303912&_mathId=si2.gif&_user=111111111&_pii=S0022247X16303912&_rdoc=1&_issn=0022247X&md5=22365be02a51d1d203f95f20ca4b56cd" title="Click to view the MathML source">p,q>0lass="mathContainer hidden">lass="mathCode"> and lsi108" class="mathmlsrc">lass="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0022247X16303912&_mathId=si108.gif&_user=111111111&_pii=S0022247X16303912&_rdoc=1&_issn=0022247X&md5=cd69e8a28dcf5f5acdff2c1f01cc19bc" title="Click to view the MathML source">a(x)≩0lass="mathContainer hidden">lass="mathCode"> is on the order lsi4" class="mathmlsrc">lass="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0022247X16303912&_mathId=si4.gif&_user=111111111&_pii=S0022247X16303912&_rdoc=1&_issn=0022247X&md5=bdaf7d5f3d9aac2beefe1bb750f84336" title="Click to view the MathML source">|x|mlass="mathContainer hidden">lass="mathCode"> as lsi249" class="mathmlsrc">lass="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0022247X16303912&_mathId=si249.gif&_user=111111111&_pii=S0022247X16303912&_rdoc=1&_issn=0022247X&md5=c8fc607a5122d30d8b9aeb70e3a4e148" title="Click to view the MathML source">|x|→∞lass="mathContainer hidden">lass="mathCode">, lsi6" class="mathmlsrc">lass="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0022247X16303912&_mathId=si6.gif&_user=111111111&_pii=S0022247X16303912&_rdoc=1&_issn=0022247X&md5=c91e98619d25cfbd8fd7ded54f4f157e" title="Click to view the MathML source">m∈Rlass="mathContainer hidden">lass="mathCode">. The Fujita critical exponent is determined when lsi7" class="mathmlsrc">lass="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0022247X16303912&_mathId=si7.gif&_user=111111111&_pii=S0022247X16303912&_rdoc=1&_issn=0022247X&md5=772718e9553cef8e3a1e0fca211472b5" title="Click to view the MathML source">m≥0lass="mathContainer hidden">lass="mathCode">, and some results of global existence of solution under some assumptions when lsi159" class="mathmlsrc">lass="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0022247X16303912&_mathId=si159.gif&_user=111111111&_pii=S0022247X16303912&_rdoc=1&_issn=0022247X&md5=0b992a5f3cf599561200f2a9a7f63bee" title="Click to view the MathML source">m<0lass="mathContainer hidden">lass="mathCode"> are also obtained. The results extend those in Escobedo and Herrero (1991) [9] and indicate that m affects the Fujita critical exponent.