HAL Id: hal-00629120
https://hal.archives-ouvertes.fr/hal-00629120
Preprint submitted on 5 Oct 2011
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
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�
❙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 x3∇u
=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:ω→R❢♦r♠❛❧❧② s♦❧✉t✐♦♥ t♦✿
−❞✐✈1 h∇Ψ
=g ✐♥ω, Ψ = 0♦♥∂ω. ✭✷✮
❇❛s✐❝❛❧❧②✱ h ✐s ❛ ♣♦s✐t✐✈❡ ▲✐s♣✐❝❤t③✲❝♦♥t✐♥✉♦✉s ♠❛♣♣✐♥❣✱ ❜❡❤❛✈✐♥❣ ❛s t❤❡ ❞✐st❛♥❝❡
❢✉♥❝t✐♦♥δ(x′) =❞✐st(x′, ∂ω)✱x′∈ω✱ ✐♥ ❛ ♥❡✐❣❤❜♦✉r❤♦♦❞ ♦❢∂ω✳
✶
❚❤❡ ❛✉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
Ψ∈L2(ω)/ h−1/2∇ψ∈L2(ω)2,Ψ = 0♦♥∂ωo ,
❡♥❞♦✇❡❞ ✇✐t❤ t❤❡ ♥♦r♠kΨkH(ω)=
h−1/2∇Ψ L2(ω)2✳
❚❤❡♦r❡♠ ✶✳✶✳ ▲❡tg ❜❡ s✉❝❤ t❤❛tδh1/2g∈L2(ω)✳ ❚❤❡r❡ ❡①✐sts ❛ ✉♥✐q✉❡ s♦❧✉t✐♦♥Ψ
♦❢ ✭✷✮ s✉❝❤ t❤❛t Ψ∈H(ω)❛♥❞✿
kΨkH(ω)6C
δh1/2g L2(ω).
▼♦r❡♦✈❡r✱ ✐❢ h1/2g∈L2(ω),t❤❡♥✿
h1/2∇(1
h∇Ψ)∈L2(ω)4,
h1/2∇(1 h∇Ψ)
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 ∈ W−1,12
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✐♦♥✱√x3g∈L2(R3+),t❤❡♥
√x3∇( 1
x3∇u)∈L2(R3+)9,
√x3∇( 1 x3∇u)
L2(
R3+)9
6Ck√x3gkL2(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✱
✷
❣✐✈❡ ❞❡♥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✿
∇u∈L2(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+)❛♥❞∇u∈L2(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+)/ ρα−1u∈L2(R3+)❛♥❞ρα∇u∈L2(R3+)3 , ✭✹✮
✸
✇❤✐❝❤ ✐s ❛ ❍✐❧❜❡rt s♣❛❝❡ ❢♦r t❤❡ ♥♦r♠✿
kukWα1,2(R3+)= ρα−1u
2
L2(R3+)+kρα∇uk2L2(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✿
∀u∈W˚α1,2(R3+), ρα−1u
L2(R3+)6Hαkρα∇ukL2(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✿
∀u∈W˚α1,2(R3+), ρα−1u
L2(R3+)6 2
(2α+ 1)kρα∇ukL2(R3+)3. ✭✽✮
❆s ❛ ❝♦♥s❡q✉❡♥❝❡ ♦❢ ✭✼✮ ❛♥❞ st✐❧❧ ✐❢ α 6= −1/2✱ t❤❡ ♠❛♣♣✐♥❣ u 7→ kρα∇ukL2(R3+)3
❞❡✜♥❡s ❛ ♥♦r♠ ♦♥W˚α1,2(R3+)✱ ❡q✉✐✈❛❧❡♥t t♦ t❤❡ ♦♥❡ ❞❡✜♥❡❞ ✐♥ ✭✺✮✳ ❙❡❝♦♥❞❧②✱ ✐t ✐s ❛❧s♦
♣r♦✈❡❞ ✐♥ ❬✶✸❪ ♣❛❣❡ ✷✸✽✱ t❤❛t ❢♦r ❛♥②α, β∈Rt❤❡ ♠❛♣♣✐♥❣ ❜❡❧♦✇ ✐s ❛♥ ✐s♦♠♦r♣❤✐s♠✿
Tρ,β:u∈W˚α1,2(R3+)7→ρβu∈W˚α1,−2β(R3+), ✭✾✮
❛♥❞ ♦♥❡ ❤❛s t❤❡ ❡st✐♠❛t❡✿
∀u∈W˚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+) =
u∈Wα1,2(R3+)/ u= 0♦♥Γ .
❲❡ ✜♥✐s❤ t❤✐s ♣❛r❛❣r❛♣❤ ❜② ✐♥tr♦❞✉❝✐♥❣ t❤❡ s♣❛❝❡ ♦❢ ❞✐str✐❜✉t✐♦♥sW−−α1,2(R3+)❛s t❤❡
❞✉❛❧ s♣❛❝❡ ♦❢W˚α1,2(R3+)✳
✹
✷✳✷ ❚❤❡ s♣❛❝❡s W1,2
α, x3(R3+)
❋♦rα∈R✱ ✇❡ ❝♦♥s✐❞❡r t❤❡ ❍✐❧❜❡rt s♣❛❝❡✿
Wα, x1,23(R3+) =
u∈ D′(R3+)/ xα3−1u∈L2(R3+), xα3∇u∈L2(R3+)3 , ✭✶✶✮
❡♥❞♦✇❡❞ ✇✐t❤ t❤❡ ♥♦r♠✿
kukWα, x1,23(R3+)= xα3−1u
2
L2(R3+)+kxα3∇uk2L2(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✐♥❣✿
xα3u∈L2(R3+), xα3∇u∈L2(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
x3→0u(·, 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
v∈L2(α−1)(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 ✇❡❧❧ ❛sγu∈E ❢♦r ❛♥②u∈Wα, x1,23(R3+)✳
❲❡ ❢♦❝✉s ♥♦✇ ♦♥ ❡st❛❜❧✐s❤✐♥❣ t❤✐s ❡♠❜❡❞❞✐♥❣✳ ■t ❢♦❧❧♦✇s ❢r♦♠ t❤❡ ✐♥❡q✉❛❧✐t✐❡s ❜❡❧♦✇✱
❛✈❛✐❧❛❜❧❡ ❢♦r ❛♥②v∈F ❛♥❞T >0✿
✂ T
0 kv(t)kE dt6
✂ +∞
0 kv(t)k2E t2(α−1)dt
1/2 ✂ T 0
t−2(α−1)dt
!1/2
,
✂ T
0 kv′(t)kE dt6
✂ +∞
0 kv(t)k2E t2αdt
1/2 ✂ T 0
t−2αdt
!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 t2αdt <∞.
✺
❚❤❡♦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✿
x∈R3+, ϕε(x) =ψ(x3
ε ),
❛♥❞ s❡tuε=uϕε✳ ❖♥❡ ♣r♦✈❡s ✇✐t❤ ♥♦ ❞✐✣❝✉❧t② t❤❛tuε∈Wα, x1,23(R3+)∩E′(R3+)✳ ◆❡①t✱
♦❜s❡r✈❡ t❤❡ ❢♦❧❧♦✇✐♥❣ ❝♦♠♣✉t❛t✐♦♥s✿
✂ +∞
0 ku(t)ϕε(t)−u(t)k2L2(R2)t2(α−1)dt=
✂ 2ε 0
ψ(t ε)−1
ku(t)k2L2(R2)t2(α−1)dt 6
✂ 2ε
0 ku(t)k2L2(R2)t2(α−1)dt.
❲❡ ❞❡❞✉❝❡ ❢r♦♠ ▲❡❜❡s❣✉❡✬s t❤❡♦r❡♠ t❤❛t uε→ u✐♥ L2α−1(0,+∞, L2(R2))✱ ✇❤❡♥ ε
❣♦❡s t♦ ✵✳ ■t ✐s ❛❧s♦ ❝❧❡❛r t❤❛t ϕε∇u → ∇u✐♥ L2α(0,+∞, L2(R2)3)✳ ❚❤❡r❡❢♦r❡✱ ✐t r❡♠❛✐♥s t♦ ❡st❛❜❧✐s❤ t❤❛tu∇ϕε→0 ✐♥L2α(0,+∞, L2(R2)3)❛♥❞ t❤✐s ❢♦❧❧♦✇s ❢r♦♠✿
✂ +∞
0 ku(t)∇ϕε(t)k2L2(R2)3t2αdt=
✂ 2ε ε
u(t)ψ′(t ε)
2
L2(R2)
t2α ε2 dt
64
✂ 2ε
ε ku(t)k2L2(R2)t2(α−1)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 ϕ∈C1(R3+)s✉❝❤ t❤❛t 0 6ϕ61✱ϕ(x) = 1
✐❢|x|61✱ϕ(x) = 0✐❢|x|>2❛♥❞ ❞❡✜♥❡ ϕk ❜②✿
x∈R3+, ϕk(x) =ϕ(x k).
❚❤❡♥ ❢♦r ❛♥②u∈Wα, x1,23(R3+)✱uk=uϕk❜❡❧♦♥❣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✿
∀u∈Wα, x1,2(R3+), xα3−1u
L2(R3+)6 2
|2α−1|kxα3∇ukL2(R3+)3. ✭✶✸✮
▲❡t ✉s ♥♦✇ ✐♥tr♦❞✉❝❡ ❛♥❞ ❝❤❛r❛❝t❡r✐③❡ t❤❡ ❞✉❛❧ s♣❛❝❡ t♦ Wα, x1,23(R3+)✳
❉❡✜♥✐t✐♦♥ ✷✳✺✳ ▲❡t ✉s ❞❡♥♦t❡ ❜②W−−α, x1,23(R3+)t❤❡ ❞✉❛❧ s♣❛❝❡ ♦❢ Wα, x1,23(R3+)✳
✻