Function Spaces as Dirichlet Spaces (About a Paper by Maz'ya and ...
Function Spaces as Dirichlet Spaces (About a Paper by Maz'ya and ...
Function Spaces as Dirichlet Spaces (About a Paper by Maz'ya and ...
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10 N. Jacob <strong>and</strong> R. L. Schilling<br />
<strong>and</strong> the convolution theorem for the (one-sided) Laplace transform,<br />
where Lu(x) = ∫ ∞<br />
e −xy u(y) dy <strong>and</strong><br />
0<br />
u ⋆ w(x) =<br />
L(u ⋆ w) = Lu · Lw,<br />
∫ x<br />
0<br />
u(x − r)w(r) dr.<br />
Setting u(r) := ∫ ∞<br />
0+ e−r/s /s ρ(ds) <strong>and</strong> w(r) := Γ ( )<br />
n −1r n/2−1 we find<br />
2<br />
Finally,<br />
<strong>and</strong> (21) follows.<br />
( 1<br />
)<br />
r −n/2 g =<br />
r<br />
∫ ∞<br />
0<br />
e −rx u ⋆ w(x) dx.<br />
∫ x<br />
( ∫<br />
1<br />
∞<br />
)<br />
u ⋆ w(x) =<br />
0 Γ ( ) t n/2−1 −(x−t)/s ρ(ds)<br />
e dt<br />
n<br />
2<br />
0+<br />
s<br />
= 1 ∫ ∞<br />
( ∫ x<br />
)<br />
Γ ( ) e −x/s t n/2 t/s dt ρ(ds)<br />
e<br />
n<br />
2 0+<br />
0 t s<br />
= 1 ∫ ∞<br />
( ∫ x/s<br />
)<br />
Γ ( ) s n/2−1 e −x/s y n/2−1 e y dy ρ(ds),<br />
n<br />
2 0+<br />
0<br />
Lemma 3.5. Let g : [0, ∞) → [0, ∞) be a monotone incre<strong>as</strong>ing function with<br />
g(0) = 0. If<br />
∫ 1<br />
G := g(s) ds ∫ ∞<br />
s + g(s) ds<br />
s s < ∞,<br />
0<br />
then the function µ(t) defined in Lemma 3.3 is finitely valued <strong>and</strong><br />
µ(t) =<br />
∫ t<br />
Conversely, if µ(1) < ∞, then G < ∞.<br />
Proof. By definition, µ(t) := ∫ t<br />
0<br />
∫ 1<br />
( ∫ ∞<br />
µ(1) =<br />
0<br />
r<br />
0<br />
g(s) ds<br />
s 2 )<br />
dr <br />
1<br />
g(s) ds<br />
s + t ∫ ∞<br />
t<br />
g(s)<br />
s<br />
ds<br />
s .<br />
∫ ∞<br />
g(s)/s 2 ds dr so that<br />
r<br />
∫ 1<br />
( ∫ ∞<br />
0<br />
1<br />
g(s) ds ) ∫ ∞<br />
g(s) ds<br />
dr =<br />
s 2 1 s s<br />
<strong>and</strong><br />
µ(1) =<br />
∫ 1<br />
0<br />
( ∫ ∞<br />
r<br />
g(s) ds<br />
s 2 )<br />
dr <br />
∫ 1<br />
0<br />
( ∫ ∞<br />
)<br />
ds<br />
g(r) dr =<br />
r s 2<br />
∫ 1<br />
0<br />
g(r) dr<br />
r .