AREMARK ON A PAPER OF J・M・GRE餌BERG・
‘R.C. MACCAMY AND V. J. MIZEL*
BYKENJI NISHIHARA**
1.Intr①duction..In this paper we give a remaτk on a paper[1]by J. M. G,㏄。b。,g, R. C M・・C・my・nd V.」. M泣・1, i・whi・h・n i・iti・1−b・und・・y・・lue problem fbr the equation σ’似)Uxx+u。tx =Utt was treated. They showed the solution d㏄ays to zgro in the max㎞um norm with it、 d。,ivati。。、 up t・th・・㏄・nd・・d・・a・’→。。・We sh・n Sh・w・m・・e p・eciS・1y・ the solution with the derivatives up to the second order decays exponentially in the same norm, applying the method of P. H. Rabinowitz[3]. The author should like to express his sincere gratitude to Professor T. Kakita fbr his kind advices and constant encouragement. 2.Notations an己resロ1ts. For C2−function u on ST≡{(x,’)iO≦x≦1,0≦t≦T} (Tis an a正bitrary positive fixed numbCr).we put l・(t)1・一Σ}、蒜、〃(・)・t∈[…コ 0≦α1+α2≦2where
lh(t)H乃ω1・−max lh(X,’)1・ 0≦x≦1 Then the fbllowing theorem has been pToved hl[1]by J. M. Gr㏄nberg, R. C. MacCamy and V. J. M▲ze1. THEoREM.([1;Theorems l and 2 and Lemma 5・6]) Assumptions: (。.1)1。t。b・a㎞・ti・n C・(一。。,。。)・u・h th・t・(0)−0・nd・’>0 (。.2)∫・nd g, gi・・nゴ㎞・ti・n・, are・C‘・and・C2・n[0・1コ・e・p㏄ti・・1y・nd vanish together wi血their second derivatives at x=O and 1. Then there exists one and Only one solution u(x,’)∈C2(S。。)of the equation (E)Lu≡Utt−d(u。)Uxx−u・・…o satisfシ麺g the following.collditions: * R.㏄eived September 4,1974. **D。p。rtm。nt・f m・th・m・ti・・, S・h・・1・f S・i・n・e・and・E・gi・ee血g・Wa・eda University・ [37]38 K.NISHIHARA (c.1)u(0,’)=〃(1,’)−0 (c.2)u(x,0)=ノてX),Ut(x,0)−9(x),0≦x≦1 (c・3)μ擁ヲ埠一4xxt onぷ、. (c.4) there exists a constant M==M(f,.g), which tends to zero as lfl 2十Igl 2 tends to zero, such that lu(t)1・≦M, Iu、,x(釧≦MO’≧o (c・5)lm [u(t)1・−0,1im lu。、。(t)1−0. t→。. t→o。 Now we assert that the solution u(x, t)also satis丘es the condition: (c・5)’.there. exist positive constantsγand C i皿dependent of t such that lu(釧・≦Ce−rt,’ ’ lu#x(t)1≦Ce−rt. 3. Pmof of our assertion. F丘st we note that fbr any O(x,’)∈C2(5。。)with ψ(0,t)=の(1,t)・−O IIe(釧1≦lo(t)|≦llψ。ωll≦1¢。(t)1≦ll¢xx(t)II≦1のxx(t)l
w・er・H・ll・−1:1・・(・)1・嚥・・∈L・(・,1). . ・
Now fbr a丘xedλ,0<λ<1/2, we can rewrite (Ut+λu)ム=O in divergence fbrm: £(S:’・(・)吻+丁〃∼+ZUUt+争・2) 竜@’・ω+〃tU.・+・u・ω+・〃u.t)+(・.∼+・・ω〃.−Zu∼)一・.(・.1) t Integrating both sides of(3.1)from O to 1 and takng the vanished boundary condi− tions into consideration we obtain 昔∫:・(x・t)dx+1:e(x,鋤一・, (・.・)where
P(xの弍’・(・)吻+Tu∼+・・〃・+丁・〃∼, ρ(x,t)=Ut.2+λ o(u。)Ux→u、2、 ・・(・・1)・1:・(カ)両≧・f・・anyξ∈(一・・,・・)・nd !,’p(・・ ・)dx≧Tl:(〃∼一・・〃・2一丁・・+…z)此 ≧9(1−・・)1:〃∼dx+才1:〃・・dx, (・.・) …ce∫:・・dx≦1:u・2dx・ By the mean value theoremAREMARK ON A PAPER OF GREENBERG, MACCAMY AND MIZEL 39
1:・(切dx≦1:(・触)・汁丁・’・+i・・2+iu・+i・・2)dx ≦∼:(・’(・・θ・u・)・・u・2+1−ltl・1−Z u∼熾2)dx ≦1>λ1:〃∼dx+(E・(M)+・)1:u∼dx (…) where Iθi(x, t)1≦1@=1,2)and E1(a)=sup{σ’(’);ltl≦α}.・i・ce∼:磁≦1:口
1:・(・・’)dx≧1:(Ux∼一…∼+・・’(・・U・)U・・)dx ≧(1−・)∼:・鍋品(M)∼:蹴・ ≧(1−・)1:u・物+醐)∼:典 (…)
where lθ3(x,’)1≦1 and Eoω=inf{σ’ω;Itl≦a}.. Combining(3.4)and(3.5)we have lle(・・ t)dx≧m翠諜(呈)1:P( )dx≡・・∼:・(抽砒・, (…)
From(3.2) θ一・・’昔・…∼:P(抽dx+∼:(ρ(”一・・P(・・’))dx−・・ Hence by(3.6) 昔…’ll・(・…)dx≦・ ・h・・・・・…’P:・(・・’)d・・iS・卿・…9・・n・n一血・・6・Sin・血丘・…n・・’・nd ∼:P(鋤dx≦・一…∼:・(…)dx・ Thus we obtain丘om(3.3) ll〃,(t)ll≦CI exp(一γ1’/2), ll〃x(t)11≦C1‘exp(一γ1’/2). (3.7) N・xt w・q・・ th・Ni・enbe・g’・桓・q・・晦亡2コ llD∫〃ll・・≦・・P・t・ll功〃ll習II〃ll脇∫/傷・1≦ノ≦〃・1<〆。。・ Ta㎞9 P→m=2,ノ=1,〃=Ut we get 1]Ust(’)il≦const・llUxtx(’)ll1’211〃’(’)H112and
l〃t(t)1≦llUxt(’)ll≦C2 exp(一γit/4). (3.8) 、 If we multiply Lμ=O by ・xp(∼:、・’(Ux(…))吻) and integrate the resulting fbrm in’over(’1, t2), we’№? ■,