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Volumes of unit balls of Lorentz spaces
Doležalová, Anna ; Vybíral, Jan (advisor)
This thesis studies the volume of the unit ball of finite-dimensional Lorentz sequence spaces p,q n . Lorentz spaces are a generalisation of Lebesgue spaces with a quasinorm described by two parameters 0 < p, q ≤ ∞. The volume of the unit ball Bp,q n of a general finite-dimensional Lorentz space was so far an unknown quantity, even though for the Lebesgue spaces it has been well-known for many years. We present the explicit formula for Vol(Bp,∞ n ) and Vol(Bp,1 n ). We also describe the asymptotic behaviour of the n-th root of Vol(Bp,q n ) with respect to the dimension n and show that [Vol(Bp,q n )]1/n ≈ n−1/p for all 0 < p < ∞, 0 < q ≤ ∞. Furthermore, we study the ratio of Vol(Bp,∞ n ) and Vol(Bp n). We conclude by examining the decay of entropy numbers of embeddings of the Lorentz spaces.
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Characterization of functions with zero traces via the distance function
Turčinová, Hana ; Nekvinda, Aleš (advisor) ; Edmunds, David Eric (referee)
Consider a domain Ω ⊂ RN with Lipschitz boundary and let d(x) = dist(x, ∂Ω). It is well known for p ∈ (1, ∞) that u ∈ W1,p 0 (Ω) if and only if u/d ∈ Lp (Ω) and ∇u ∈ Lp (Ω). Recently a new characterization appeared: it was proved that u ∈ W1,p 0 (Ω) if and only if u/d ∈ L1 (Ω) and ∇u ∈ Lp (Ω). In the author's bachelor thesis the condition u/d ∈ L1 (Ω) was weakened to the condition u/d ∈ L1,p (Ω), but only in the case N = 1. In this master thesis we prove that for N ≥ 1, p ∈ (1, ∞) and q ∈ [1, ∞) we have u ∈ W1,p 0 (Ω) if and only if u/d ∈ L1,q (Ω) and ∇u ∈ Lp (Ω). Moreover, we present a counterexample to this equivalence in the case q = ∞. 1
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Laplaceova transformace na prostorech funkcí
Buriánková, Eva ; Pick, Luboš (advisor) ; Nekvinda, Aleš (referee)
In this manuscript we study the action of the Laplace transform on rearrangement-invariant Banach function spaces. Our principal goal is to characterize the optimal range space corresponding to a given domain space within the category of rearrangement-invariant Banach function spaces. We first prove a key pointwise estimate of the non-increasing rearrangement of the image under the Laplace transform of a given function. Then we use this inequality to carry out the construction of the optimal range space. We apply this general result to establish an optimality relation between the Lebesgue and Lorentz spaces under the Laplace transform.
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Skorokompaktní vnoření prostorů funkcí
Křepela, Martin ; Pick, Luboš (advisor) ; Spurný, Jiří (referee)
This work is dealing with almost-compact embeddings of function spaces, in particular, the class of classical and weak Lorentz spaces with a norm given by a general weight fuction is studied. These spaces are not Banach function spaces in general, thus the almost-compact em- bedding is defined for more general sturctures of rearrangement-invariant lattices. A general characterization of when an r.i. lattice is almost-compactly embedded into a Lorentz space, involving an optimal constant of a certain continuous embedding, is proved. Based on this the- orem and appropriate known results about continuous embeddings, explicit characterizations of mutual almost-compact embeddings of all subtypes of Lorentz spaces are obtained. 1
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Properties of weakly differentiable functions and mappings
Kleprlík, Luděk
We study the optimal conditions on a homeomorphism f : Ω → Rn which guarantee that the composition u◦f is weakly differentiable and its weak derivative belongs to the some function space. We show that if f has finite distortion and q-distortion Kq = |Df|q /Jf is integrable enough, then the composition operator Tf (u) = u ◦ f maps functions from W1,q loc into space W1,p loc and the well-known chain rule holds. To prove it we characterize when the inverse mapping f−1 maps sets of measure zero onto sets of measure zero (satisfies the Luzin (N−1 ) con- dition). We also fully characterize conditions for Sobolev-Lorentz space WLn,q for arbitrary q and for Sobolev Orlicz space WLq log L for q ≥ n and α > 0 or 1 < q ≤ n and α < 0. We find a necessary condition on f for Sobolev rearrangement invariant function space WX close to WLq , i.e. X has q-scaling property. 1
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Inequalities for discrete and continuous supremum operators
Oľhava, Rastislav ; Pick, Luboš (advisor) ; Cianchi, Andrea (referee) ; Nekvinda, Aleš (referee)
Inequalities for discrete and continuous supremum operators Rastislav O , lhava In this thesis we study continuous and discrete supremum operators. In the first part we investigate general properties of Hardy-type operators involving suprema. The boundedness of supremum operators is used for characterization of interpo- lation spaces between two Marcinkiewicz spaces. In the second part we provide equivalent conditions for boundedness of supremum operators in the situation when the domain space in one of the classical Lorentz spaces Λp w1 or Γp w1 and the target space Λq w2 or Γq w2 . In the case p ≤ q we use inserting technique obtaining continuous conditions. In the setting of coefficients p > q we provide only partial results obtaining discrete conditions using discretization method. In the third part we deal with a three-weight inequality for an iterated discrete Hardy-type operator. We find its characterization which enables us to reduce the problematic case when the domain space is a weighted ℓp with p ∈ (0, 1) into the one with p = 1. This leads to a continuous analogue of investigated discrete inequality. The work consists of author's published and unpublished results along with material appearing in the literature.
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Volumes of unit balls of Lorentz spaces
Doležalová, Anna ; Vybíral, Jan (advisor) ; Lang, Jan (referee)
This thesis studies the volume of the unit ball of finite-dimensional Lorentz sequence spaces p,q n . Lorentz spaces are a generalisation of Lebesgue spaces with a quasinorm described by two parameters 0 < p, q ≤ ∞. The volume of the unit ball Bp,q n of a general finite-dimensional Lorentz space was so far an unknown quantity, even though for the Lebesgue spaces it has been well-known for many years. We present the explicit formula for Vol(Bp,∞ n ) and Vol(Bp,1 n ). We also describe the asymptotic behaviour of the n-th root of Vol(Bp,q n ) with respect to the dimension n and show that [Vol(Bp,q n )]1/n ≈ n−1/p for all 0 < p < ∞, 0 < q ≤ ∞. Furthermore, we study the ratio of Vol(Bp,∞ n ) and Vol(Bp n). We conclude by examining the decay of entropy numbers of embeddings of the Lorentz spaces.
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Inequalities for discrete and continuous supremum operators
Oľhava, Rastislav ; Pick, Luboš (advisor) ; Nekvinda, Aleš (referee)
Inequalities for discrete and continuous supremum operators Rastislav O , lhava In this thesis we study continuous and discrete supremum operators. In the first part we investigate general properties of Hardy-type operators involving suprema. The boundedness of supremum operators is used for characterization of interpo- lation spaces between two Marcinkiewicz spaces. In the second part we provide equivalent conditions for boundedness of supremum operators in the situation when the domain space in one of the classical Lorentz spaces Λp w1 or Γp w1 and the target space Λq w2 or Γq w2 . In the case p ≤ q we use inserting technique obtaining continuous conditions. In the setting of coefficients p > q we provide only partial results obtaining discrete conditions using discretization method. In the third part we deal with a three-weight inequality for an iterated discrete Hardy-type operator. We find its characterization which enables us to reduce the problematic case when the domain space is a weighted ℓp with p ∈ (0, 1) into the one with p = 1. This leads to a continuous analogue of investigated discrete inequality. The work consists of author's published and unpublished results along with material appearing in the literature.
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Characterization of functions with zero traces via the distance function
Turčinová, Hana ; Nekvinda, Aleš (advisor) ; Edmunds, David Eric (referee)
Consider a domain Ω ⊂ RN with Lipschitz boundary and let d(x) = dist(x, ∂Ω). It is well known for p ∈ (1, ∞) that u ∈ W1,p 0 (Ω) if and only if u/d ∈ Lp (Ω) and ∇u ∈ Lp (Ω). Recently a new characterization appeared: it was proved that u ∈ W1,p 0 (Ω) if and only if u/d ∈ L1 (Ω) and ∇u ∈ Lp (Ω). In the author's bachelor thesis the condition u/d ∈ L1 (Ω) was weakened to the condition u/d ∈ L1,p (Ω), but only in the case N = 1. In this master thesis we prove that for N ≥ 1, p ∈ (1, ∞) and q ∈ [1, ∞) we have u ∈ W1,p 0 (Ω) if and only if u/d ∈ L1,q (Ω) and ∇u ∈ Lp (Ω). Moreover, we present a counterexample to this equivalence in the case q = ∞. 1
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Characterization of functions vanishing at the boundary
Turčinová, Hana ; Nekvinda, Aleš (advisor) ; Edmunds, David Eric (referee)
Let Ω ⊂ Rn be a domain with a moderate boundary regularity, p ∈ (1, ∞) and let d be the distance function defined by d(t) = dist(t, ∂Ω), t ∈ Rn . Assume that u belongs to the Sobolev space W1,p (Ω). A classical result states that u ∈ W1,p 0 (Ω) if and only if u d ∈ Lp (Ω) and ∇u ∈ Lp (Ω). This fact has been several times consecutively refined, and each time the required condition u d ∈ Lp (Ω) was relaxed to a weaker one. The first such improvement shows that the condition u d ∈ Lp,∞ (Ω) is sufficient. In the next such result the condition u d ∈ L1 (Ω) was considered. Moreover, this result was extended to Sobolev spaces of higher order. In this thesis we improve the previous results in the case when n = 1 and Ω is an open interval I. In our principal result we prove that u ∈ W1,p 0 (I) if and only if u d ∈ L1,p (I) and u′ ∈ Lp (I). 1
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