Non-collapsing condition and Sobolev embeddings for Haj{\l}asz-Besov spaces (original) (raw)

Compact embeddings in Besov-type and Triebel–Lizorkin-type spaces on bounded domains

Revista Matemática Complutense, 2020

We study embeddings of Besov-type and Triebel–Lizorkin-type spaces,$${\text {id}}_\tau {:}\,{B}_{p_1,q_1}^{s_1,\tau _1}(\varOmega )\,\hookrightarrow \,{B}_{p_2,q_2}^{s_2,\tau _2}(\varOmega )idτ:Bp1,q1s1,τ1(Ω)↪Bp2,q2s2,τ2(Ω)andid τ : B p 1 , q 1 s 1 , τ 1 ( Ω ) ↪ B p 2 , q 2 s 2 , τ 2 ( Ω ) andidτ:Bp1,q1s1,τ1(Ω)Bp2,q2s2,τ2(Ω)and{\text {id}}_\tau {:}\,{F}_{p_1,q_1}^{s_1,\tau _1}(\varOmega ) \hookrightarrow {F}_{p_2,q_2}^{s_2,\tau _2}(\varOmega ) idτ:Fp1,q1s1,τ1(Ω)↪Fp2,q2s2,τ2(Ω),whereid τ : F p 1 , q 1 s 1 , τ 1 ( Ω ) ↪ F p 2 , q 2 s 2 , τ 2 ( Ω ) , whereidτ:Fp1,q1s1,τ1(Ω)Fp2,q2s2,τ2(Ω),where\varOmega \subset {{\mathbb R}^d}Ω⊂Rdisaboundeddomain,andobtainnecessaryandsufficientconditionsforthecompactnessofΩ ⊂ R d is a bounded domain, and obtain necessary and sufficient conditions for the compactness ofΩRdisaboundeddomain,andobtainnecessaryandsufficientconditionsforthecompactnessof{\text {id}}_\tau id τ . Moreover, we characterize its entropy and approximation numbers. Surprisingly, these results are completely obtained via embeddings and the application of the corresponding results for classical Besov and Triebel–Lizorkin spaces as well as for Besov–Morrey and Triebel–Lizorkin–Morrey spaces.

Sobolev embeddings in metric measure spaces with variable dimension

Mathematische Zeitschrift, 2006

In this article we study metric measure spaces with variable dimension. We consider Lebesgue spaces on these sets, and embeddings of the Riesz potential in these spaces. We also investigate Hajłasz-type Sobolev spaces, and prove Sobolev and Trudinger inequalities with optimal exponents. All of these questions lead naturally to function spaces with variable exponents.

Embeddings of Besov–Morrey spaces on bounded domains

Studia Mathematica, 2013

We study embeddings of spaces of Besov-Morrey type, idΩ : N s 1 p 1 ,u 1 ,q 1 (Ω) → N s 2 p 2 ,u 2 ,q 2 (Ω), where Ω ⊂ R d is a bounded domain, and obtain necessary and sufficient conditions for the continuity and compactness of idΩ. This continues our earlier studies relating to the case of R d. Moreover, we also characterise embeddings into the scale of Lp spaces or into the space of bounded continuous functions. 1. Introduction. In recent years smoothness spaces related to Morrey spaces, in particular Besov-Morrey and Triebel-Lizorkin-Morrey spaces, attracted some attention. The classical Morrey spaces M p,u (R d), 0 < u ≤ p < ∞, were introduced by Ch. B. Morrey [Mo] and are part of the wider class of Morrey-Campanato spaces (cf. [Pe]). They can be considered as a complement to L p spaces, since M p,p (R d) = L p (R d). However, on the one hand the Morrey spaces with u < p consist of locally u-integrable functions, but on the other hand the spaces scale with d/p instead of d/u, that is, f (λ •) | M p,u (R d) = λ −d/p f | M p,u (R d) , λ > 0. This property is very useful for some partial differential equations. Built upon this basic family M p,u (R d), different spaces of Besov-Triebel-Lizorkin type were defined in the last years. H. Kozono and M. Yamazaki [KY] and A. Mazzucato [Ma] introduced the Besov-Morrey N s p,u,q spaces and used them in the theory of Navier-Stokes equations. As before, if u = p, then these spaces coincide with the classical ones, i.e., N s p,p,q (R d) = B s p,q (R d). Some of their properties including wavelet characterisations were proved by Y. Sawano [S1, S4, S3], Y. Sawano and H. Tanaka [ST2, ST1] and L. Tang and J. Xu [TX]. The most systematic and general approach to spaces of this type can be found in the recent book [YSY] of W. Yuan, W. Sickel and D. Yang or in the very recent survey papers by W. Sickel [Si1, Si2]. We recommend the monograph and the survey for further up-to-date references 2010 Mathematics Subject Classification: Primary 46E35.

Sobolev embeddings, extensions and measure density condition

Journal of Functional Analysis, 2008

There are two main results in the paper. In the first one, Theorem 1, we prove that if the Sobolev embedding theorem holds in Ω, in any of all the possible cases, then Ω satisfies the measure density condition. The second main result, Theorem 5, provides several characterizations of the W m,p -extension domains for 1 < p < ∞. As a corollary we prove that the property of being a W 1,p -extension domain, 1 < p ∞, is invariant under bi-Lipschitz mappings, Theorem 8.

Compactness of Sobolev embeddings and decay of norms

arXiv: Functional Analysis, 2020

We investigate the relationship between the compactness of embeddings of Sobolev spaces built upon rearrangement-invariant spaces into rearrangement-invariant spaces endowed with ddd-Ahlfors measures under certain restriction on the speed of its decay on balls. We show that the gateway to compactness of such embeddings, while formally describable by means of optimal embeddings and almost-compact embeddings, is quite elusive. It is known that such a Sobolev embedding is not compact when its target space has the optimal fundamental function. We show that, quite surprisingly, such a target space can actually be "fundamentally enlarged", and yet the resulting embedding remains noncompact. In order to do that, we develop two different approaches. One is based on enlarging the optimal target space itself, and the other is based on enlarging the Marcinkiewicz space corresponding to the optimal fundamental function.

Compactness in quasi-Banach function spaces and applications to compact embeddings of Besov-type spaces

Proceedings of the Royal Society of Edinburgh: Section A Mathematics, 2016

There are two main aims of the paper. The first is to extend the criterion for the precompactness of sets in Banach function spaces to the setting of quasi-Banach function spaces. The second is to extend the criterion for the precompactness of sets in the Lebesgue spacesLp(ℝn), 1 ⩽p< ∞, to the so-called power quasi-Banach function spaces. These criteria are applied to establish compact embeddings of abstract Besov spaces into quasi-Banach function spaces. The results are illustrated on embeddings of Besov spaces, into Lorentz-type spaces.