We consi
der the scalar semilinear heat equation
pan id="mmlsi1" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si1.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=d926f4996fd7581c8453b7cc967906a2" title="Click to view the MathML source">ut−Δu=f(u)pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>, where
pan id="mmlsi2" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si2.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=1233ea1621cfd5133fda5e7ba0ffa9f0" title="Click to view the MathML source">f:[0,∞)→[0,∞)pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan> is continuous an
d non-
decreasing but nee
d not be convex. We com
pletely characterise those functions
f for which the equation has a local solution boun
de
d in
pan id="mmlsi133" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si133.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=80c94c03982c570f1736f573a464954b" title="Click to view the MathML source">Lp>qp>(Ω)pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan> for all non-negative initial
data
pan id="mmlsi100" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si100.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=9f6a9a8667650346fd2f46b481cc98a5" title="Click to view the MathML source">u0∈Lp>qp>(Ω)pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>, when
pan id="mmlsi5" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si5.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=c0c809c2bc06fa153ad639a44af453cf" title="Click to view the MathML source">Ω⊂Rp>dp>pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan> is a boun
de
d domain with Dirichlet boun
dary con
ditions. For
pan id="mmlsi132" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si132.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=d15acf7ad379f2b0a67221326e4a738d" title="Click to view the MathML source">q∈(1,∞)pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan> this hol
ds if an
d only if
pan id="mmlsi7" class="mathmlsrc">data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si7.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=61a3be373e59d24704acdc9729e4cc38">
dth="216" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0294144915000645-si7.gif">pt>
der="0" style="vertical-align:bottom" width="216" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0294144915000645-si7.gif">pt>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>; an
d for
pan id="mmlsi8" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si8.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=68204ad5e8c0fe5c9a486be277588179" title="Click to view the MathML source">q=1pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan> if an
d only if
pan id="mmlsi9" class="mathmlsrc">data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si9.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=73683f702a3e792c5a0644113d99d0cf">
dth="172" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0294144915000645-si9.gif">pt>
der="0" style="vertical-align:bottom" width="172" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0294144915000645-si9.gif">pt>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>, where
pan id="mmlsi10" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si10.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=5aed9aca5ebed42dfad174dc994c6313" title="Click to view the MathML source">F(s)=sup1≤t≤sf(t)/tpan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>. This shows for the first time that the mo
del nonlinearity
pan id="mmlsi11" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si11.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=767b4b27949104aede1c64bd4ac4642a" title="Click to view the MathML source">f(u)=up>1+2q/dp>pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan> is truly the ‘boun
dary case’ when
pan id="mmlsi132" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si132.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=d15acf7ad379f2b0a67221326e4a738d" title="Click to view the MathML source">q∈(1,∞)pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>, but that this is not true for
pan id="mmlsi8" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si8.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=68204ad5e8c0fe5c9a486be277588179" title="Click to view the MathML source">q=1pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>.
p><
p i
d="s
p0020">The same characterisations hol
d for the equation
pose
d on the whole s
pace
pan id="mmlsi12" class="mathmlsrc">pan class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si12.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=c7bb1a6224c553c1825787197583dfcd" title="Click to view the MathML source">Rp>dp>pan>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>
provi
de
d that
pan id="mmlsi13" class="mathmlsrc">data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0294144915000645&_mathId=si13.gif&_user=111111111&_pii=S0294144915000645&_rdoc=1&_issn=02941449&md5=cb8047436a05ef97c06f6069904c4955">
dth="157" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0294144915000645-si13.gif">pt>
der="0" style="vertical-align:bottom" width="157" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0294144915000645-si13.gif">pt>pan class="mathContainer hidden">pan class="mathCode">pan>pan>pan>.