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Study of a singular equation set in the half-space

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HAL Id: hal-00629120

https://hal.archives-ouvertes.fr/hal-00629120

Preprint submitted on 5 Oct 2011

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Study of a singular equation set in the half-space

Chérif Amrouche, Fabien Dahoumane, Guy Vallet

To cite this version:

Chérif Amrouche, Fabien Dahoumane, Guy Vallet. Study of a singular equation set in the half-space.

2010. �hal-00629120�

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❙t✉❞② ♦❢ ❛ s✐♥❣✉❧❛r ❡q✉❛t✐♦♥ s❡t ✐♥ t❤❡

❤❛❧❢✲s♣❛❝❡

❈✳ ❆♠r♦✉❝❤❡✱ ❋✳ ❉❛❤♦✉♠❛♥❡✱ ●✳ ❱❛❧❧❡t

❏✉❧② ✶✻✱ ✷✵✶✵

▲❛❜♦r❛t♦✐r❡ ❞❡ ▼❛t❤é♠❛t✐q✉❡s ❆♣♣❧✐q✉é❡s ❯▼❘✲❈◆❘❙ ◆➦ ✺✶✹✷

■P❘❆ ❇P ✶✶✺✺

✻✹✵✶✸ P❛✉ ❝❡❞❡①

❝❤❡r✐❢✳❛♠r♦✉❝❤❡❅✉♥✐✈✲♣❛✉✳❢r✱ ❢❛❜✐❡♥✳❞❛❤♦✉♠❛♥❡❅✉♥✐✈✲♣❛✉✳❢r✱ ❣✉②✳✈❛❧❧❡t❅✉♥✐✈✲♣❛✉✳❢r

❆❜str❛❝t✳ ❚❤✐s ✇♦r❦ ✐s ❞❡❞✐❝❛t❡❞ t♦ t❤❡ r❡s♦❧✉t✐♦♥ ♦❢ ❛ s✐♥❣✉❧❛r ❡q✉❛t✐♦♥ s❡t

✐♥ t❤❡ ❤❛❧❢✲s♣❛❝❡✱ ✇✐t❤ ❛ ❞✐✛✉s✐♦♥ ❝♦❡✣❝✐❡♥t t❤❛t ❜❧♦✇s ✉♣ ♦♥ t❤❡ ❜♦✉♥❞❛r②✳ ▼♦r❡

♣r❡❝✐s❡❧②✱ ❢♦r ❛ ❞❛t✉♠g :R3+ R✱ ♦✉r ♣r♦❜❧❡♠ ❝♦♥s✐sts ✐♥ s❡❡❦✐♥❣ u:R3+ R

❢♦r♠❛❧❧② s♦❧✉t✐♦♥ t♦✿

−❞✐✈

1

x3

∇u

«

=g✐♥R3+, u= 0♦♥Γ =R2× {0}.

❲❡ ❣✐✈❡ ❡①✐st❡♥❝❡ ❛♥❞ ✉♥✐q✉❡♥❡ss r❡s✉❧ts ♦❢ ✇❡❛❦ ❛♥❞ str♦♥❣ s♦❧✉t✐♦♥s ✐♥ s✉✐t❛❜❧❡

✇❡✐❣❤t❡❞ s♣❛❝❡s✱ ✇❤❡r❡ t❤❡ ✇❡✐❣❤t ❞❡♣❡♥❞s ♦♥x3

❑❡② ✇♦r❞s✳ ❊❧❧✐♣t✐❝ ❡q✉❛t✐♦♥✱ s✐♥❣✉❧❛r ❡q✉❛t✐♦♥✱ ❤❛❧❢✲s♣❛❝❡✱ ✇❡✐❣❤t❡❞ s♣❛❝❡s✱

✇❡❛❦ s♦❧✉t✐♦♥s✱ str♦♥❣ s♦❧✉t✐♦♥s✱ ❍❛r❞②✬s ✐♥❡q✉❛❧✐t②✳

❆▼❙ s✉❜❥❡❝t ❝❧❛ss✐❢✐❝❛t✐♦♥s✳ ✸✺◗✸✵✱ ✸✺❇✹✵✱ ✼✻❉✵✺✱ ✸✹❈✸✺

✶ ■♥tr♦❞✉❝t✐♦♥

❚❤✐s ✇♦r❦ ✐s ❞❡✈♦t❡❞ t♦ t❤❡ st✉❞② ♦❢ ❛ s✐♥❣✉❧❛r ❡❧❧✐♣t✐❝ ❡q✉❛t✐♦♥ s❡t ✐♥ t❤❡ ❤❛❧❢✲s♣❛❝❡

R3+✳ ▼♦r❡ ♣r❡❝✐s❡❧②✱ ❢♦r ❛ ❞❛t✉♠g : R3+ R✱ ♦✉r ♣r♦❜❧❡♠ ❝♦♥s✐sts ✐♥ ❧♦♦❦✐♥❣ ❢♦r u:R3+R❢♦r♠❛❧❧② s♦❧✉t✐♦♥ t♦✿

−❞✐✈

1 x3u

=g ✐♥ R3+, u= 0♦♥Γ =R2× {0}. ✭✶✮

❚♦ ✉♥❞❡rst❛♥❞ t❤❡ ♦r✐❣✐♥s ♦❢ t❤✐s ❡q✉❛t✐♦♥✱ ✇❡ t✉r♥ t♦ t❤❡ ✇♦r❦ ♦❢ ❇r❡s❝❤✱ ●✉✐❧❧é♥✲

●♦♥③á❧❡③ ❛♥❞ ▲❡♠♦✐♥❡ ✐♥ ❬✼❪✱ ✇❤♦ st✉❞② ❛♥ ❛♥❛❧♦❣♦✉s ❡q✉❛t✐♦♥ s❡t ✐♥ r❡❣✉❧❛r ❜♦✉♥❞❡❞

❞♦♠❛✐♥ ω R2✳ ●✐✈❡♥ h : ω R ❛♥❞ g : ω R✱ t❤❡ ❛✉t❤♦rs ❛r❡ ❧♦♦❦✐♥❣ ❢♦r ψ:ωR❢♦r♠❛❧❧② s♦❧✉t✐♦♥ t♦✿

−❞✐✈1 hΨ

=g ✐♥ω, Ψ = 0♦♥∂ω. ✭✷✮

❇❛s✐❝❛❧❧②✱ h ✐s ❛ ♣♦s✐t✐✈❡ ▲✐s♣✐❝❤t③✲❝♦♥t✐♥✉♦✉s ♠❛♣♣✐♥❣✱ ❜❡❤❛✈✐♥❣ ❛s t❤❡ ❞✐st❛♥❝❡

❢✉♥❝t✐♦♥δ(x) =❞✐st(x, ∂ω)✱xω✱ ✐♥ ❛ ♥❡✐❣❤❜♦✉r❤♦♦❞ ♦❢∂ω✳

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❚❤❡ ❛✉t❤♦rs ✐♥ ❬✼❪ ❡①♣❧❛✐♥ ❤♦✇ s✉❝❤ s✐♥❣✉❧❛r ❡q✉❛t✐♦♥ ✭✷✮ ♥❛t✉r❛❧❧② ❛♣♣❡❛rs ✐♥ t❤❡

st✉❞② ♦❢ ♠♦❞❡❧s ✐ss✉❡❞ ❢r♦♠ ♦❝❡❛♥♦❣r❛♣❤②✱ ✉♥❞❡r ❛ ❤②❞r♦st❛t✐❝ ♣r❡ss✉r❡ ❛ss✉♠♣t✐♦♥

❛♥❞ s❡t ✐♥ ❞♦♠❛✐♥s ✇✐t❤ ✈❛♥✐s❤✐♥❣ ❞❡♣t❤✳ ■t ✐s t❤❡ ❝❛s❡ ❢♦r ❡①❛♠♣❧❡ ♦❢ t❤❡ ♣❧❛♥❡t❛r②

❣❡♦str♦♣❤✐❝ ❡q✉❛t✐♦♥ ❬✾❪✱ t❤❡ ✈❡rt✐❝❛❧✲❣❡♦str♦♣❤✐❝ ❡q✉❛t✐♦♥s ❬✽❪✱ ❛♥❞ t❤❡ ❤②❞r♦st❛t✐❝

❙t♦❦❡s ♦r ◆❛✈✐❡r✲❙t♦❦❡s ❡q✉❛t✐♦♥s ❬✶✱ ✸✱ ✺✱ ✶✶✱ ✶✺❪✳ ❇❡❢♦r❡ st❛t✐♥❣ t❤❡✐r ♠❛✐♥ r❡s✉❧t✱

✇❡ ❞❡✜♥❡ t❤❡ s♣❛❝❡

H(ω) =n

ΨL2(ω)/ h1/2ψL2(ω)2,Ψ = 0♦♥∂ωo ,

❡♥❞♦✇❡❞ ✇✐t❤ t❤❡ ♥♦r♠kΨkH(ω)=

h1/2Ψ L2(ω)2

❚❤❡♦r❡♠ ✶✳✶✳ ▲❡tg ❜❡ s✉❝❤ t❤❛tδh1/2gL2(ω)✳ ❚❤❡r❡ ❡①✐sts ❛ ✉♥✐q✉❡ s♦❧✉t✐♦♥Ψ

♦❢ ✭✷✮ s✉❝❤ t❤❛t ΨH(ω)❛♥❞✿

kΨkH(ω)6C

δh1/2g L2(ω).

▼♦r❡♦✈❡r✱ ✐❢ h1/2gL2(ω),t❤❡♥✿

h1/2(1

hΨ)L2(ω)4,

h1/2(1 hΨ)

L2(ω)4

6C h1/2g

L2(ω).

❚♦ ♦✉r ❦♥♦✇❧❡❞❣❡✱ ♥♦ t❤❡♦r❡t✐❝❛❧ st✉❞② ✇❛s ♠❛❞❡ ✐♥ t❤❡ ❝❛s❡ ♦❢ t❤❡ ❤❛❧❢✲s♣❛❝❡

R2+✱ ❤♦✇❡✈❡r ✉s❡❢✉❧❧ t♦ ♦❜t❛✐♥ ❛ ❣♦♦❞ ❝♦♠♣r❡❤❡♥s✐♦♥ ♦❢ t❤❡ ❣❡♥❡r❛❧ ❝❛s❡ ♦❢ ❛ ❜♦✉♥❞❡❞

❞♦♠❛✐♥✳ ❚❤✐s ♣❛♣❡r ✐s t❤❡r❡❢♦r❡ ❞❡✈♦t❡❞ t♦ t❤❡ st✉❞② ♦❢ s✉❝❤ ❛ ❝❛s❡✱ s❡❡ ✭✶✮✳ ❲❡

♣r❡s❡♥t t❤❡ ❝❛s❡ ♦❢ t❤❡ ❞✐♠❡♥s✐♦♥ ✸ ♦♥❧② ❢♦r t❡❝❤♥✐❝❛❧ r❡❛s♦♥s✱ ❡①♣❧❛✐♥❡❞ ❧❛t❡r✳

❖♥ t❤❡ ♦♥❡ ❤❛♥❞✱ ♦✉r ✇♦r❦ ❡♥❛❜❧❡s t♦ ❛❝❤✐❡✈❡ t❤❡ ❢♦❧❧♦✇✐♥❣ r❡s✉❧t s✐♠✐❧❛r t♦ ❚❤❡♦r❡♠

✶✳✶✱ ✐♥ ❛ ❝♦♥t❡①t ♦❢ ✇❡✐❣❤t❡❞ s♣❛❝❡s✱ ✇❤❡r❡ t❤❡ ✇❡✐❣❤t ❞❡♣❡♥❞s ♦♥ x3✳ ❇❡❢♦r❡❤❛♥❞✱

✇❡ ✐♥tr♦❞✉❝❡ ♣r❡♠❛t✉r❡❧② t❤❡ s♣❛❝❡ W1,2

12, x3(R3+)✱ s❡❡ ✭✶✶✮✱ ❡♥❞♦✇❡❞ ✇✐t❤ t❤❡ ♥♦r♠

❣✐✈❡♥ ❜② ✭✶✷✮✳

❚❤❡♦r❡♠ ✶✳✷✳ ▲❡t g ∈ D(R3+) s✉❝❤ t❤❛t x3/23 g L2(R3+)✳ ❚❤❡♥✱ t❤❡r❡ ❡①✐sts ❛

✉♥✐q✉❡ s♦❧✉t✐♦♥ u W1,12

2, x3(R3+) ♦❢ ✭✶✮✳ ▼♦r❡♦✈❡r✱ t❤❡r❡ ✐s ❛ ♣♦s✐t✐✈❡ ❝♦♥st❛♥t C s✉❝❤ t❤❛t✿

kukW1,2

1 2, x3

(R3+)6C x3/23 g

L2(R3+).

■❢ ✐♥ ❛❞❞✐t✐♦♥✱x3gL2(R3+),t❤❡♥

x3( 1

x3u)L2(R3+)9,

x3( 1 x3u)

L2(

R3+)9

6Ckx3gkL2(R3+).

❖♥ t❤❡ ♦t❤❡r ❤❛♥❞✱ ✇❡ ❝♦♥s✐❞❡r ❛ ❧❛r❣❡r ❝❧❛ss ♦❢ ❞❛t❛ g ✐♥ s✉✐t❛❜❧❡ ✇❡✐❣❤t❡❞ s♣❛❝❡s✱

❛♥❞ ❣✐✈❡ r❡s✉❧ts ♦❢ ❡①✐st❡♥❝❡ ❛♥❞ ✉♥✐q✉❡♥❡ss ♦❢ ✇❡❛❦ ❛♥❞ str♦♥❣ s♦❧✉t✐♦♥s t♦ ✭✶✮✱ t❤❛t

✐♥❝❧✉❞❡ ❚❤❡♦r❡♠ ✶✳✷✳

◆♦t❡ t❤❛t t❤❡ ✐❞❡❛s ❝♦♥t❛✐♥❡❞ ✐♥ t❤✐s ✇♦r❦✱ ❝❛♥ ❜❡ ❛❞❛♣t❡❞ t♦ t❤❡ RN+✲❝❛s❡ ✇❤❡r❡

N >3✳ ■♥ t❤❡R2+✲❝❛s❡✱ ✐t ✐s ♥❡❝❡ss❛r② t♦ ✐♥tr♦❞✉❝❡ ❛♥ ❛❞❞✐t✐♦♥❛❧ ❧♦❣❛r✐t❤♠✐❝ ✇❡✐❣❤t✱

✇❤✐❝❤ ❝♦♠♣❧✐❝❛t❡s ❛ ❜✐t ♠♦r❡ t❤❡ ♣r❡s❡♥t❛t✐♦♥ ♦❢ t❤❡ r❡s✉❧ts✳ ❚❤✐s ✐s ✇❤② ✇❡ ❧✐♠✐t

♦✉r st✉❞② t♦ t❤❡ ❝❛s❡ ♦❢ t❤❡ ❞✐♠❡♥s✐♦♥ ✸✳

❆♥ ♦✉t❧✐♥❡ ♦❢ t❤✐s ♣❛♣❡r ✐s ❛s ❢♦❧❧♦✇s✳ ■♥ ❙❡❝t✐♦♥ ✷✱ ✇❡ s❡t t❤❡ ❢✉♥❝t✐♦♥❛❧ ❢r❛♠❡✇♦r❦✱

❜② ✐♥tr♦❞✉❝t✐♥❣ t✇♦ ❦✐♥❞s ♦❢ ✇❡✐❣❤t❡❞ s♣❛❝❡s✳ ❋✐rst❧②✱ ✇❡ ❣✐✈❡ ❛♥ ♦✈❡r✈✐❡✇ ♦❢ t❤❡

✇❡✐❣❤t❡❞ s♣❛❝❡s Wα1,2(R3+)✱ s❡❡ ✭✹✮✱ ❡♥❝♦✉♥t❡r❡❞ ✐♥ ✇♦r❦s ❝♦♥❝❡r♥✐♥❣ ❢♦r ❡①❛♠♣❧❡

▲❛♣❧❛❝❡ ❡q✉❛t✐♦♥ st✉❞✐❡❞ ✐♥ R3+✳ ❙❡❝♦♥❞❧②✱ ✇❡ ✇✐❧❧ ❜✉✐❧❞ ❛♥♦t❤❡r ❢❛♠✐❧② ♦❢ ✇❡✐❣❤t❡❞

s♣❛❝❡sWα, x1,23(R3+)✱ s❡❡ ✭✶✶✮✱ ✇❤❡r❡ t❤❡ ✇❡✐❣❤t ❞❡♣❡♥❞s ♦♥x3✱ ❛♥❞ ❡s♣❡❝✐❛❧❧② ❛❞❛♣t❡❞

t♦ t❤❡ st✉❞② ♦❢ ✭✶✮✳ ❋♦❧❧♦✇✐♥❣ t❤❡ ✇♦r❦ ♦❢ ●r✐s✈❛r❞ ❬✶✷❪✱ ✇❡ ✇✐❧❧ ❞❡✜♥❡ ❛ tr❛❝❡ ♦♣❡r❛t♦r✱

(4)

❣✐✈❡ ❞❡♥s✐t② r❡s✉❧ts ❛♥❞ ❣❡♥❡r❛❧✐③❡❞ ❍❛r❞②✬s ✐♥❡q✉❛❧✐t✐❡s✳ ❲❡ ✇✐❧❧ ✜♥✐s❤ t❤✐s s❡❝t✐♦♥

✇✐t❤ ❛ ❝♦♠♣❛r❛✐s♦♥ ❜❡t✇❡❡♥ t❤❡s❡ t✇♦ ❢❛♠✐❧✐❡s ♦❢ ✇❡✐❣❤t❡❞ s♣❛❝❡s✱ ♣r♦✈✐♥❣ ❝♦♥t✐♥✉♦✉s

❛♥❞ ❞❡♥s❡ ❡♠❜❡❞❞✐♥❣s ❜❡t✇❡❡♥ t❤❡♠✳

■♥ ❙❡❝t✐♦♥ ✸✱ ✇❡ st✉❞② t❤❡ ❡①✐st❡♥❝❡ ❛♥❞ ✉♥✐q✉❡♥❡ss ♦❢ ✇❡❛❦ s♦❧✉t✐♦♥s t♦ ✭✶✮✱ ❜②

❝♦♥s✐❞❡r✐♥❣ ❛ ❧❛r❣❡ ❝❧❛ss ♦❢ ❞❛t❛ g✳ ▼♦r❡ ♣r❡❝✐s❡❧②✱ ✇❡ ♣r♦✈❡ ✐♥ ❚❤❡♦r❡♠ ✸✳✷ t❤❡

❡①✐st❡♥❝❡ ❛♥❞ ✉♥✐q✉❡♥❡ss ♦❢ ❛ ✇❡❛❦ s♦❧✉t✐♦♥ t♦ ✭✶✮ ✐♥ Wα, x1,23(R3+)✱ ✇❤✐❧❡ ✐♥ ❚❤❡♦r❡♠

✸✳✹✱ ❡①✐st❡♥❝❡ ❛♥❞ ✉♥✐q✉❡♥❡ss ♦❢ ❛ ✇❡❛❦ s♦❧✉t✐♦♥ t♦ ✭✶✮ ✐s ♦❜t❛✐♥❡❞ ✐♥Wα1,2(R3+)✳

❚❤❡ ❧❛st s❡❝t✐♦♥ ♦❢ t❤✐s ♣❛♣❡r ✐s ❞❡✈♦t❡❞ t♦ t❤❡ st✉❞② ♦❢ str♦♥❣ s♦❧✉t✐♦♥s t♦ ✭✶✮✱

❝♦♠♣❧❡t✐♥❣ t❤❡ t❤❡♦r❡t✐❝❛❧ st✉❞② ♦❢ Pr♦❜❧❡♠ ✭✶✮✳ ▼♦r❡ ♣r❡❝✐s❡❧②✱ ✇❡ ❣✐✈❡ t✇♦ s✐t✉❛t✐♦♥s

✇❤❡r❡ t❤❡ ✇❡❛❦ s♦❧✉t✐♦♥ ♦❢ ❚❤❡♦r❡♠ ✸✳✷ ✐s ✐♥ ❢❛❝t ❛ str♦♥❣ s♦❧✉t✐♦♥✱ s❡❡ ❚❤❡♦r❡♠ ✹✳✶

❛♥❞ ❚❤❡♦r❡♠ ✹✳✺✳

✷ ❋✉♥❝t✐♦♥❛❧ ❢r❛♠❡✇♦r❦

❚❤✐s ✜rst s❡❝t✐♦♥ ✐s ❛✐♠❡❞ t♦ s❡t t❤❡ ❢✉♥❝t✐♦♥❛❧ ❢r❛♠❡✇♦r❦ ❛❞♣❛t❡❞ t♦ t❤❡ st✉❞② ♦❢

Pr♦❜❧❡♠ ✭✶✮✳ ■♥ ♣❛rt✐❝✉❧❛r✱ ✇❡ ❞❡✜♥❡ ❛♥❞ st✉❞② ❤❡r❡ t❤❡ ❛♣♣r♦♣r✐❛t❡ s♣❛❝❡ ❢♦r ✇❡❛❦

s♦❧✉t✐♦♥s t♦ ✭✶✮✳

▲❡t ✉s ♠❛❦❡ t❤❡ ❢♦❧❧♦✇✐♥❣ ♦❜s❡r✈❛t✐♦♥✳ ▲❡t ✉s ❝♦♥s✐❞❡r ❛ ❞❛t✉♠ g s✉❝❤ t❤❛tx3g L2(R3+)✳ ❋♦r♠❛❧❧②✱ ❧❡t ✉s ♠✉❧t✐♣❧② ✭✶✮ ❜② x3u ❛♥❞ ✐♥t❡❣r❛t❡ ♦✈❡r R3+✳ ❚❤❡♥✱ ✉s✐♥❣

●r❡❡♥✬s ❢♦r♠✉❧❛ ❛♥❞ t❛❦✐♥❣ ✐♥t♦ ❛❝❝♦✉♥t t❤❡ ❜♦✉♥❞❛r② ❝♦♥❞✐t✐♦♥ ♦✈❡r u✱ ✇❡ ❞❡❞✉❝❡

t❤❡ ❢♦❧❧♦✇✐♥❣ ❡♥❡r❣② ❡q✉❛❧✐t②✿

R3+

|∇u|2 dx+1 2

R3+

u x3

2

dx=

R3+

x3gu dx.

❚❤❡r❡❢♦r❡✱ ✇❡ ❛r❡ ♥❛t✉r❛❧❧② ❧❡❛❞ t♦ ❧♦♦❦ ❢♦r ✇❡❛❦ s♦❧✉t✐♦♥sus✉❝❤ t❤❛t✿

uL2(R3+)3, u

x3 L2(R3+), u= 0♦♥Γ. ✭✸✮

❚❤✐s ✜rst s✐t✉❛t✐♦♥ ✐s ❝♦♥s✐❞❡r❡❞ ✐♥ Pr♦♣♦s✐t✐♦♥ ✸✳✶✱ ✇❤❡r❡ ✇❡ ❡st❛❜❧✐s❤ t❤❡ ❡①✐st❡♥❝❡

❛♥❞ ✉♥✐q✉❡♥❡ss ♦❢ s✉❝❤ ❛ ✇❡❛❦ s♦❧✉t✐♦♥✳ ❚❤❡♥✱ s✐♥❝❡ |x3| 6(1 +|x|2)1/2✱ ❛♥② ✇❡❛❦

s♦❧✉t✐♦♥ s❛t✐s❢②✐♥❣ ✭✸✮ ✐s ✐♥ ❢❛❝t ✐♥ t❤❡ ✇❡✐❣❤t❡❞ ❙♦❜♦❧❡✈ s♣❛❝❡W01,2(R3+)✱ ✇❤❡r❡✿

W01,2(R3+) = (

u∈ D(R3+)/ u

(1 +|x|2)1/2 L2(R3+)❛♥❞uL2(R3+)3 )

.

❆♥❞ t❤❡r❡❢♦r❡✱ t❤❡ ❜♦✉♥❞❛r② ❝♦♥❞✐t✐♦♥u= 0♦♥Γ✐s ♠❡❛♥✐♥❣❢✉❧❧✳

▲❡t ✉s r❡❝❛❧❧ ♣r♦♣❡rt✐❡s ♦❢ t❤❡ ✇❡✐❣❤t❡❞ ❙♦❜♦❧❡✈ s♣❛❝❡s Wα1,2(R3+)✱ ✉s❡❢✉❧❧ ✐♥ t❤❡

s❡q✉❡❧✱ ❛♥❞ st✉❞② ❛ ♥❡✇ ❢❛♠✐❧❧② ♦❢ ✇❡✐❣❤t❡❞ s♣❛❝❡s✱ ✇❤❡r❡ t❤❡ ✇❡✐❣❤t ❞❡♣❡♥❞s ♦♥x3 s❡❡ ✭✶✶✮✳

✷✳✶ ❆♥ ♦✈❡r✈✐❡✇ ♦❢ t❤❡ ✇❡✐❣❤t❡❞ ❙♦❜♦❧❡✈ s♣❛❝❡s Wα1,2(R3+)

■♥ ❛ ❣❡♥❡r❛❧ ✇❛②✱ t❤❡ s♣❛❝❡s Wα1,2(R3+)✱ α R✱ ❤❛✈❡ ❜❡❡♥ ✐♥tr♦❞✉❝❡❞ s✐♥❝❡ t❤❡②

❛r❡ ❛❞❛♣t❡❞ t♦ t❤❡ st✉❞② ♦❢ s♦♠❡ s❡❝♦♥❞ ♦r❞❡r ❡❧❧✐♣t✐❝ ❡q✉❛t✐♦♥s s❡t ✐♥R3+✱ ❛♥❞ ♠♦r❡

♣r❡❝✐s❡❧②✱ t♦ t❤❡ ▲❛♣❧❛❝❡ ❡q✉❛t✐♦♥ ✇✐t❤ ✐♥❤♦♠♦❣❡♥❡♦✉s ❉✐r✐❝❤❧❡t ♦r ◆❡✉♠❛♥ ❜♦✉♥❞❛r②

❝♦♥❞✐t✐♦♥s✳ ❲❡ r❡❢❡r ❤❡r❡ t♦ t❤❡ ✇♦r❦ ♦❢ ❆♠r♦✉❝❤❡ ❛♥❞ ◆❡ˇc❛s♦✈❛ ❬✷❪✱ ❇♦✉❧♠❡③❛♦✉❞

❬✻❪✱ ♦r t❤❡ ♦♥❡ ♦❢ ❍❛♥♦✉③❡t ❬✶✸❪✳

▲❡t α R ❛♥❞ s❡t ❢♦r ❛♥② x R3+ ρ(x) = q

1 +|x|2✱ ✇❤❡r❡ |x| ❞❡♥♦t❡s t❤❡

❡✉❝❧✐❞❡❛♥ ♥♦r♠ ♦❢x✳ ❚❤❡♥✱ ✇❡ ✐♥tr♦❞✉❝❡ t❤❡ ✇❡✐❣❤t❡❞ ❙♦❜♦❧❡✈ s♣❛❝❡✿

Wα1,2(R3+) =

u∈ D(R3+)/ ρα1uL2(R3+)❛♥❞ραuL2(R3+)3 , ✭✹✮

(5)

✇❤✐❝❤ ✐s ❛ ❍✐❧❜❡rt s♣❛❝❡ ❢♦r t❤❡ ♥♦r♠✿

kukWα1,2(R3+)= ρα1u

2

L2(R3+)+kραuk2L2(R3+)3

1/2

. ✭✺✮

❚❤❡ ✇❡✐❣❤t ρ✐s ❝❤♦s❡♥ s✉❝❤ t❤❛t t❤❡ s♣❛❝❡ Wα1,2(R3+) s❛t✐s✜❡s t✇♦ ❢✉♥❞❛♠❡♥t❛❧

♣r♦♣❡rt✐❡s✳ ❖♥ t❤❡ ♦♥❡ ❤❛♥❞✱ D(R3+)✐s ❞❡♥s❡ ✐♥Wα1,2(R3+) ✭s❡❡ ❬✶✸❪✮✳ ❖♥ t❤❡ ♦t❤❡r

❤❛♥❞✱ ✐❢ α6= 1/2✱ ❛♥② ❢✉♥❝t✐♦♥s ♦❢ Wα1,2(R3+) s❛t✐s✜❡s ❛ P♦✐♥❝❛ré t②♣❡ ✐♥❡q✉❛❧✐t②

✭s❡❡ ❬✷❪✮✳

❆s 1ρ ✐s ❜♦✉♥❞❡❞✱ ♥♦t❡ t❤❛t ❢♦r ❛♥② α>β✱ t❤❡ ❢♦❧❧♦✇✐♥❣ ❝♦♥t✐♥✉♦✉s ❡♠❜❡❞❞✐♥❣

❤♦❧❞s✿

Wα1,2(R3+)֒Wβ1,2(R3+), ✭✻✮

❚❤❡♥✱ ❛♥② ❢✉♥❝t✐♦♥u✐♥Wα1,2(R3+)❤❛s ❛ tr❛❝❡ ♦♥Γ✱ ❛♥❞u|Γ ❜❡❧♦♥❣s t♦ t❤❡ ✇❡✐❣❤t❡❞

s♣❛❝❡Wα1/2,2(Γ)✳ ❋♦r ♠♦r❡ ♣r❡❝✐s✐♦♥✱ ✇❡ r❡❢❡r t♦ ❬✶✸❪✳

❚❤❡♦r❡♠ ✷✳✶✳ ❚❤❡ ♠❛♣♣✐♥❣γ:u7→u(x,0) ❞❡✜♥❡❞ ♦♥D(R3+)✱ ❝❛♥ ❜❡ ❡①t❡♥❞❡❞ ✐♥

❛ ✉♥✐q✉❡ ✇❛② t♦ ❛ ❧✐♥❡❛r ❛♥❞ ❝♦♥t✐♥✉♦✉s ♠❛♣♣✐♥❣✱ st✐❧❧ ❞❡♥♦t❡❞ ❜②γ✱ ❢r♦♠Wα1,2(R3+)

✐♥t♦Wα1/2,2(Γ)✳

❚❤❡ ❢♦❧❧♦✇✐♥❣ s❤♦rt ♣❛r❛❣r❛♣❤ ✐s ❞❡❞✐❝❛t❡❞ t♦ ❜❛s✐❝ ♣r♦♣❡rt✐❡s ♦❢ t❤❡ s♣❛❝❡W˚α1,2(R3+)✱

t❤❡ ❝❧♦s✉r❡ ♦❢D(R3+)✐♥Wα1,2(R3+)✳ ❋✐rst❧②✱ ✇❤❡♥α6=1/2❛♥❞ ❛❝❝♦r❞✐♥❣ ❢♦r ❡①❛♠♣❧❡

t♦ ❬✻❪✱ ✇❡ ❤❛✈❡ t❤❡ ❢♦❧❧♦✇✐♥❣ ❍❛r❞② t②♣❡ ✐♥❡q✉❛❧✐t②✿

uW˚α1,2(R3+), ρα1u

L2(R3+)6HαkραukL2(R3+)3, ✭✼✮

✇❤❡r❡Hα✐s ❛ ♣♦s✐t✐✈❡ ❝♦♥st❛♥t✱ ❞❡♣❡♥❞✐♥❣ ♦♥❧② ♦♥α✳ ❆♥❞ ❢♦❧❧♦✇✐♥❣ ❢♦r ❡①❛♠♣❧❡ t❤❡

♣r♦♦❢ ♦❢ ❚❤❡♦r❡♠ ■✳✷ ♦❢ ❬✶✸❪✱ ✇❡ ❝❛♥ ❝❤♦♦s❡ Hα = (2α+1)2 ✇❤❡♥0 6α61✱ ②✐❡❧❞✐♥❣

✜♥❛❧❧②✿

uW˚α1,2(R3+), ρα1u

L2(R3+)6 2

(2α+ 1)kραukL2(R3+)3. ✭✽✮

❆s ❛ ❝♦♥s❡q✉❡♥❝❡ ♦❢ ✭✼✮ ❛♥❞ st✐❧❧ ✐❢ α 6= 1/2✱ t❤❡ ♠❛♣♣✐♥❣ u 7→ kραukL2(R3+)3

❞❡✜♥❡s ❛ ♥♦r♠ ♦♥W˚α1,2(R3+)✱ ❡q✉✐✈❛❧❡♥t t♦ t❤❡ ♦♥❡ ❞❡✜♥❡❞ ✐♥ ✭✺✮✳ ❙❡❝♦♥❞❧②✱ ✐t ✐s ❛❧s♦

♣r♦✈❡❞ ✐♥ ❬✶✸❪ ♣❛❣❡ ✷✸✽✱ t❤❛t ❢♦r ❛♥②α, βRt❤❡ ♠❛♣♣✐♥❣ ❜❡❧♦✇ ✐s ❛♥ ✐s♦♠♦r♣❤✐s♠✿

Tρ,β:uW˚α1,2(R3+)7→ρβuW˚α1,2β(R3+), ✭✾✮

❛♥❞ ♦♥❡ ❤❛s t❤❡ ❡st✐♠❛t❡✿

uW˚α1,2(R3+), kTρ, βukWα−β1,2(R3+)6p

1 +β2kukWα1,2(R3+). ✭✶✵✮

❋✐♥❛❧❧②✱ ❛♥❞ ❛❝❝♦r❞✐♥❣ t♦ ❬✶✸❪ ♣❛❣❡ ✷✺✽ ❚❤❡♦r❡♠ ■■✳ ✸✱ t❤❡ s♣❛❝❡ W˚α1,2(R3+) ❝❛♥ ❜❡

❝❤❛r❛❝t❡r✐③❡❞ ❛s t❤❡ ❦❡r♥❡❧ ♦❢γ✿

W˚α1,2(R3+) =

uWα1,2(R3+)/ u= 0♦♥Γ .

❲❡ ✜♥✐s❤ t❤✐s ♣❛r❛❣r❛♣❤ ❜② ✐♥tr♦❞✉❝✐♥❣ t❤❡ s♣❛❝❡ ♦❢ ❞✐str✐❜✉t✐♦♥sWα1,2(R3+)❛s t❤❡

❞✉❛❧ s♣❛❝❡ ♦❢W˚α1,2(R3+)✳

(6)

✷✳✷ ❚❤❡ s♣❛❝❡s W1,2

α, x3(R3+)

❋♦rαR✱ ✇❡ ❝♦♥s✐❞❡r t❤❡ ❍✐❧❜❡rt s♣❛❝❡✿

Wα, x1,23(R3+) =

u∈ D(R3+)/ xα31uL2(R3+), xα3uL2(R3+)3 , ✭✶✶✮

❡♥❞♦✇❡❞ ✇✐t❤ t❤❡ ♥♦r♠✿

kukWα, x1,23(R3+)= xα31u

2

L2(R3+)+kxα3uk2L2(R3+)3

1/2

. ✭✶✷✮

■♥ t❤❡ ❡❛r❧② ✶✾✻✵s✱ ❛ s✐♠✐❧❛r s♣❛❝❡ ❤❛s ❜❡❡♥ st✉❞✐❡❞ ❜② ●r✐s✈❛r❞✱ s❡❡ ❬✶✷❪✳ ■♥ ❤✐s

✇♦r❦✱ ●r✐s✈❛r❞ ❝♦♥s✐❞❡rs t❤❡ ❝❛s❡ ♦❢ ❢✉♥❝t✐♦♥sus❛t✐s❢②✐♥❣✿

xα3uL2(R3+), xα3uL2(R3+)3.

❍❡ ❡st❛❜❧✐s❤❡s ❝r✉❝✐❛❧ ♣r♦♣❡rt✐❡s✱ s✉❝❤ ❛s t❤❡ ❡①✐st❡♥❝❡ ♦❢ ❛ tr❛❝❡ ♦♣❡r❛t♦r ❛♥❞ ❞❡♥s✐t② r❡s✉❧ts✳ ❋♦❧❧♦✇✐♥❣ ❤✐s ✐❞❡❛s✱ ✇❡ ❜❡❣✐♥ t❤✐s s❡❝t✐♦♥ ❜② ❡st❛❜❧✐s❤✐♥❣ t❤❛t ✇❤❡♥α <1/2✱

❛♥② ❢✉♥❝t✐♦♥su♦❢Wα, x1,23(R3+)♣♦ss❡ss❡s ❛ tr❛❝❡ ✐♥ L2(R2)✳ ❚❤❡ ✐❞❡❛ ✐s t♦ ♣r♦✈❡ t❤❛t

❛♥② ❢✉♥❝t✐♦♥u♦❢Wα, x1,23(R3+)✐s ❝♦♥t✐♥✉♦✉s ✐♥ t❤❡ ✈❡rt✐❝❛❧ ❞✐r❡❝t✐♦♥✱ ❡♥s✉r✐♥❣ t❤❡r❡❢♦r❡

t❤❡ ❡①✐st❡♥❝❡ ♦❢ t❤❡ ❡①♣❡❝t❡❞ tr❛❝❡✳

Pr♦♣♦s✐t✐♦♥ ✷✳✷✳ ▲❡tα <1/2✳ ❚❤❡ ♠❛♣♣✐♥❣u7→γu ❞❡✜♥❡❞ ❜②✿

γu= lim

x30u(·, x3),

✐s ❧✐♥❡❛r ❛♥❞ ❝♦♥t✐♥✉♦✉s ❢r♦♠ Wα, x1,23(R3+)✐♥t♦L2(R2)✳

Pr♦♦❢✳ ❋♦r ❝♦♥✈❡♥✐❡♥❝❡✱ ✇❡ s❡tE=L2(R2)✳ ❚❤❡♥✱ ❧❡t ✉s ✐♥tr♦❞✉❝❡ t❤❡ s♣❛❝❡ ✭✮✿

F =n

vL21)(0, +;E)/ v L2α(0,+;E)o ,

❛♥❞ ♥♦t❡ t❤❛tWα, x1,23(R3+)❝❛♥ ❜❡ ✐❞❡♥t✐✜❡❞ ❛s ❛ s✉❜s♣❛❝❡ ♦❢F✱ ❛s ❛ ❝♦♥s❡q✉❡♥❝❡ ♦❢

t❤❡ t❤❡♦r❡♠ ♦❢ ❋✉❜✐♥✐✳ ❚❤❡r❡❢♦r❡✱ ✐❢ ✇❡ ♣r♦✈❡ t❤❛t F ✐s ❝♦♥t✐♥✉♦✉s❧② ❡♠❜❡❞❞❡❞ ✐♥

C0([0,+[;E)✱ ✇❡ ❛r❡ ❛❜❧❡ t♦ ❞❡✜♥❡u(0)❛s ✇❡❧❧ ❛sγuE ❢♦r ❛♥②uWα, x1,23(R3+)✳

❲❡ ❢♦❝✉s ♥♦✇ ♦♥ ❡st❛❜❧✐s❤✐♥❣ t❤✐s ❡♠❜❡❞❞✐♥❣✳ ■t ❢♦❧❧♦✇s ❢r♦♠ t❤❡ ✐♥❡q✉❛❧✐t✐❡s ❜❡❧♦✇✱

❛✈❛✐❧❛❜❧❡ ❢♦r ❛♥②vF ❛♥❞T >0✿

T

0 kv(t)kE dt6

+

0 kv(t)k2E t2(α1)dt

1/2 T 0

t2(α1)dt

!1/2

,

T

0 kv(t)kE dt6

+

0 kv(t)k2E tdt

1/2 T 0

tdt

!1/2

,

t❤❛t t❤❡ ♠❛♣♣✐♥❣ v 7→ (v, v) ✐s ❝♦♥t✐♥✉♦✉s ❢r♦♠ F ✐♥t♦ L1❧♦❝([0,+[; E)2 ✳ ❆s ❛

❝♦♥s❡q✉❡♥❝❡✱ ♦♥❡ ❤❛s ♣r♦✈❡❞ t❤❛t✿

F ֒C0([0,+[;E),

❛♥❞ t❤❡ ♣r♦♦❢ ✐s ✜♥✐s❤❡❞✳

❲❡ ❢♦❧❧♦✇ t❤✐s s❡❝t✐♦♥ ❜② ❡st❛❜❧✐s❤✐♥❣ ❛ ❞❡♥s✐t② r❡s✉❧t✱ ❛❞❛♣t❡❞ ❢r♦♠ ❬✶✷❪✳

L2α(0,+∞;E)❞❡♥♦t❡s t❤❡ s❡t ♦❢ ♠❡❛s✉r❛❜❧❡ ❢✉♥❝t✐♦♥sv: ]0,+∞[→Es✉❝❤ t❤❛t✿

+ 0

kvk2E tdt <∞.

(7)

❚❤❡♦r❡♠ ✷✳✸✳ ❋♦r ❛♥② α R✱ t❤❡ s♣❛❝❡ D(R3+) ✐s ❞❡♥s❡ ✐♥ Wα, x1,23(R3+)✳ ❆s ❛

❝♦♥s❡q✉❡♥❝❡✱ ✐❢α <1/2t❤❡ ❢✉♥❝t✐♦♥s ♦❢ Wα, x1,23(R3+)❤❛s ♥✉❧❧ tr❛❝❡ ♦♥ R2

Pr♦♦❢✳ ■❢ ✇❡ ♣r♦✈❡ t❤❛tD(R3+)✐s ❞❡♥s❡ ✐♥Wα, x1,23(R3+)✱ t❤❡♥ ✐t ❢♦❧❧♦✇s ❢r♦♠ Pr♦♣♦s✐t✐♦♥

✷✳✷ t❤❛t ✇❤❡♥❡✈❡r t❤❡ tr❛❝❡ ♦❢u✐s ❞❡✜♥❡❞✱ ✐t ✐s ♥❡❝❡ss❛r✐❧② ❡q✉❛❧ t♦ ✵✳

❊①❝❡♣t✐♦♥❛❧❧② ✐♥ t❤✐s ♣r♦♦❢✱ ✇❡ ❞❡♥♦t❡ ❜②E(R3+)t❤❡ s❡t ♦❢ ❞✐str✐❜✉t✐♦♥s ✇✐t❤ ❝♦♠♣❛❝t s✉♣♣♦rt ✐♥R3+✱ ❛♥❞E(R3+)t❤❡ s❡t ♦❢ ❞✐str✐❜✉t✐♦♥s ✇✐t❤ ❝♦♠♣❛❝t s✉♣♣♦rt ✐♥R3+✳ ❚❤❡

♣r♦♦❢ ✐s t❤❡♥ ❞✐✈✐❞❡❞ ✐♥t♦ t❤r❡❡ st❡♣s✳

❙t❡♣ ♦♥❡✳ ■t ✐s ❝❧❡❛r t❤❛tD(R3+)✐s ❞❡♥s❡ ✐♥Wα, x1,23(R3+)∩ E(R3+)✱ s✐♥❝❡ ❛♥② ❢✉♥❝t✐♦♥

✐♥ Wα, x1,23(R3+)∩ E(R3+)❜❡❧♦♥❣s t♦H01(R3+)∩ E(R3+)✳

❙t❡♣ t✇♦✳ ❲❡ ♣r♦✈❡ t❤❛tWα, x1,23(R3+)∩ E(R3+)✐s ❞❡♥s❡ ✐♥Wα, x1,23(R3+)∩ E(R3+)✳ ▲❡t u ✐♥ Wα, x1,23(R3+)∩ E(R3+) ❛♥❞ ψ C1([0,+[)✱ s✉❝❤ t❤❛t 0 6 ψ 61✱ ψ(t) = 0✐❢

t61✱ψ(t) = 1 ✐❢t>2✳ ❚❤❡♥✱ ❧❡t ✉s ❞❡✜♥❡ϕε❜②✿

xR3+, ϕε(x) =ψ(x3

ε ),

❛♥❞ s❡tuε=ε✳ ❖♥❡ ♣r♦✈❡s ✇✐t❤ ♥♦ ❞✐✣❝✉❧t② t❤❛tuεWα, x1,23(R3+)∩E(R3+)✳ ◆❡①t✱

♦❜s❡r✈❡ t❤❡ ❢♦❧❧♦✇✐♥❣ ❝♦♠♣✉t❛t✐♦♥s✿

+

0 ku(t)ϕε(t)u(t)k2L2(R2)t2(α1)dt=

0

ψ(t ε)1

ku(t)k2L2(R2)t2(α1)dt 6

0 ku(t)k2L2(R2)t2(α1)dt.

❲❡ ❞❡❞✉❝❡ ❢r♦♠ ▲❡❜❡s❣✉❡✬s t❤❡♦r❡♠ t❤❛t uε u✐♥ L2α1(0,+, L2(R2))✱ ✇❤❡♥ ε

❣♦❡s t♦ ✵✳ ■t ✐s ❛❧s♦ ❝❧❡❛r t❤❛t ϕεu → ∇u✐♥ L2α(0,+, L2(R2)3)✳ ❚❤❡r❡❢♦r❡✱ ✐t r❡♠❛✐♥s t♦ ❡st❛❜❧✐s❤ t❤❛tuϕε0 ✐♥L2α(0,+, L2(R2)3)❛♥❞ t❤✐s ❢♦❧❧♦✇s ❢r♦♠✿

+

0 ku(t)ϕε(t)k2L2(R2)3tdt=

ε

u(t)ψ(t ε)

2

L2(R2)

t ε2 dt

64

ε ku(t)k2L2(R2)t2(α1)dt.

❙t❡♣ t❤r❡❡✳ ❲❡ ❝❤❡❦ t❤❛t Wα, x1,23(R3+)∩ E(R3+) ✐s ❞❡♥s❡ ✐♥ Wα, x1,23(R3+)✱ ✉s✐♥❣ t❤❡

✉s✉❛❧ ♣r♦❝❡ss ♦❢ tr✉♥❝❛t✐♦♥✳ ■♥❞❡❡❞✱ ❧❡t ϕC1(R3+)s✉❝❤ t❤❛t 0 6ϕ61✱ϕ(x) = 1

✐❢|x|61✱ϕ(x) = 0✐❢|x|>2❛♥❞ ❞❡✜♥❡ ϕk ❜②✿

xR3+, ϕk(x) =ϕ(x k).

❚❤❡♥ ❢♦r ❛♥②uWα, x1,23(R3+)✱uk=k❜❡❧♦♥❣s t♦Wα, x1,23(R3+)∩E(R3+)✱ ❛♥❞ ❢♦❧❧♦✇✐♥❣

❙t❡♣ t✇♦✱ ✇❡ ❞❡❞✉❝❡ t❤❛tuk ❝♦♥✈❡r❣❡s str♦♥❣❧② t♦u✐♥ Wα, x1,23(R3+)✳

❘❡♠❛r❦ ✷✳✹✳ ❆❝❝♦r❞✐♥❣ ❢♦r ❡①❛♠♣❧❡ t♦ ❬✶✷❪✱ s❡❡ ❚❤❡♦r❡♠ ✶✳✷ ❛♥❞ ❚❤❡♦r❡♠ ✶✳✸✱

♦❜s❡r✈❡ t❤❛t ❢♦r ❛♥②α6= 1/2 t❤❡ ❢♦❧❧♦✇✐♥❣ ❍❛r❞②✬s ✐♥❡q✉❛❧✐t② ❤♦❧❞s✿

uWα, x1,2(R3+), xα31u

L2(R3+)6 2

|1|kxα3ukL2(R3+)3. ✭✶✸✮

▲❡t ✉s ♥♦✇ ✐♥tr♦❞✉❝❡ ❛♥❞ ❝❤❛r❛❝t❡r✐③❡ t❤❡ ❞✉❛❧ s♣❛❝❡ t♦ Wα, x1,23(R3+)✳

❉❡✜♥✐t✐♦♥ ✷✳✺✳ ▲❡t ✉s ❞❡♥♦t❡ ❜②Wα, x1,23(R3+)t❤❡ ❞✉❛❧ s♣❛❝❡ ♦❢ Wα, x1,23(R3+)✳

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