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Wyświetlanie 1-10 z 10
Tytuł:
Complementation in spaces of symmetric tensor products and polynomials
Autorzy:
Blasco, Fernando
Powiązania:
https://bibliotekanauki.pl/articles/1220111.pdf
Data publikacji:
1997
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
symmetric tensor
polynomial
complementation
Opis:
For a locally convex space E we prove that the space of n-symmetric tensors is complemented in the space of (n+1)-symmetric tensors endowed with the projective topology. Applications and related results are also given.
Źródło:
Studia Mathematica; 1997, 123, 2; 165-173
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On the invertibility of isometric semigroup representations
Autorzy:
Batty, C. J. K.
Greenfield, D.
Powiązania:
https://bibliotekanauki.pl/articles/1290204.pdf
Data publikacji:
1994
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
semigroup
isometric representation
spectrum
polynomial convexity
Opis:
Let T be a representation of a suitable abelian semigroup S by isometries on a Banach space. We study the spectral conditions which will imply that T(s) is invertible for each s in S. On the way we analyse the relationship between the spectrum of T, Sp(T,S), and its unitary spectrum $Sp_{u}(T,S)$. For $S = ℤ^{n}_{+}$ or $ℝ^{n}_{+}$, we establish connections with polynomial convexity.
Źródło:
Studia Mathematica; 1994, 110, 3; 235-250
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Pointwise inequalities for Sobolev functions and some applications
Autorzy:
Bojarski, Bogdan
Hajłasz, Piotr
Powiązania:
https://bibliotekanauki.pl/articles/1292626.pdf
Data publikacji:
1993
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Sobolev function
Taylor polynomial
approximation
integral representation
Bessel capacity
Opis:
We get a class of pointwise inequalities for Sobolev functions. As a corollary we obtain a short proof of Michael-Ziemer's theorem which states that Sobolev functions can be approximated by $C^m$ functions both in norm and capacity.
Źródło:
Studia Mathematica; 1993, 106, 1; 77-92
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Factorization of weakly continuous holomorphic mappings
Autorzy:
González, Manuel
Gutiérrez, Joaqín
Powiązania:
https://bibliotekanauki.pl/articles/1287688.pdf
Data publikacji:
1996
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
weakly continuous holomorphic mapping
factorization of holomorphic mappings
polynomial
weakly continuous multilinear mapping
Opis:
We prove a basic property of continuous multilinear mappings between topological vector spaces, from which we derive an easy proof of the fact that a multilinear mapping (and a polynomial) between topological vector spaces is weakly continuous on weakly bounded sets if and only if it is weakly uniformly} continuous on weakly bounded sets. This result was obtained in 1983 by Aron, Hervés and Valdivia for polynomials between Banach spaces, and it also holds if the weak topology is replaced by a coarser one. However, we show that it need not be true for a stronger topology, thus answering a question raised by Aron. As an application of the first result, we prove that a holomorphic mapping ƒ between complex Banach spaces is weakly uniformly continuous on bounded subsets if and only if it admits a factorization of the form f = g∘S, where S is a compact operator and g a holomorphic mapping.
Źródło:
Studia Mathematica; 1996, 118, 2; 117-133
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Polynomial asymptotics and approximation of Sobolev functions
Autorzy:
Hajłasz, Piotr
Kałamajska, Agnieszka
Powiązania:
https://bibliotekanauki.pl/articles/1289688.pdf
Data publikacji:
1995
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Sobolev space
Beppo Levi space
approximation
polynomial asymptotics
density of $C_0^∞$ functions
Opis:
We prove several results concerning density of $C_{0}^{∞}$, behaviour at infinity and integral representations for elements of the space $L^{m,p} = {⨍ | ∇^{m}⨍ ∈ L^p}$.
Źródło:
Studia Mathematica; 1995, 113, 1; 55-64
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An uncertainty principle related to the Poisson summation formula
Autorzy:
Gröchenig, K.
Powiązania:
https://bibliotekanauki.pl/articles/1221102.pdf
Data publikacji:
1996
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
uncertainty principle
Poisson summation formula
unimodular polynomial
modulation space
time-frequency analysis
phase space
Opis:
We prove a class of uncertainty principles of the form $∥S_{g}f∥_{1} ≤ C(∥x^{a}f∥_{p} + ∥ω^{b}f̂∥_{q})$, where $S_{g}f$ is the short time Fourier transform of f. We obtain a characterization of the range of parameters a,b,p,q for which such an uncertainty principle holds. Counter-examples are constructed using Gabor expansions and unimodular polynomials. These uncertainty principles relate the decay of f and f̂ to their behaviour in phase space. Two applications are given: (a) If such an inequality holds, then the Poisson summation formula is valid with absolute convergence of both sums. (b) The validity of an uncertainty principle implies sufficient conditions on a symbol σ such that the corresponding pseudodifferential operator is of trace class.
Źródło:
Studia Mathematica; 1996, 121, 1; 87-104
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A weighted Plancherel formula II. The case of the ball
Autorzy:
Zhang, Genkai
Powiązania:
https://bibliotekanauki.pl/articles/1293186.pdf
Data publikacji:
1992
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Plancherel formula
Harish-Chandra c-function
reproducing kernel
orthogonal polynomial
invariant Cauchy-Riemann operator
Opis:
The group SU(1,d) acts naturally on the Hilbert space $L²(B dμ_α) (α > -1)$, where B is the unit ball of $ℂ^d$ and $dμ_α$ the weighted measure $(1-|z|²)^α dm(z)$. It is proved that the irreducible decomposition of the space has finitely many discrete parts and a continuous part. Each discrete part corresponds to a zero of the generalized Harish-Chandra c-function in the lower half plane. The discrete parts are studied via invariant Cauchy-Riemann operators. The representations on the discrete parts are equivalent to actions on some holomorphic tensor fields.
Źródło:
Studia Mathematica; 1992, 102, 2; 103-120
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Linear extension operators for restrictions of function spaces to irregular open sets
Autorzy:
Rychkov, V. S.
Powiązania:
https://bibliotekanauki.pl/articles/1206076.pdf
Data publikacji:
2000
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Sobolev spaces
Besov-Triebel-Lizorkin spaces
restrictions
extension operators
irregular domains
Hausdorff content
local polynomial approximation
complemented subspaces
Opis:
Let an open set $Ω ⊂ ℝ^n$ satisfy for some 0≤d≤n and ε > 0 the condition: the $d$-Hausdorff content $H_d(Ω∩B) ≥ ε|B|^{d/n}$ for any ball B centered in Ω of volume |B|≤1. Let $H_p^s$ denote the Bessel potential space on $ℝ^n$ 1 < p < ∞,s > 0, and let $H_p^s[Ω]$ be the linear space of restrictions of elements of $H_p^s$ to Ω endowed with the quotient space norm. We find sufficient conditions for the existence of a linear extension operator for $H_p^s[Ω]$, i.e., a bounded linear operator $H_p^s[Ω]→H_p^s$ such that $ext⨍|_Ω}=⨍$ for all ⨍. The main result is that such an operator exists if (i) d > n-1 and s > (n-d)/min(p,2), or (ii) d≤n-1 and s-[s] > (n-d)/min(p,2). It is an open problem whether these assumptions are sharp.
Źródło:
Studia Mathematica; 2000, 140, 2; 141-162
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Polynomial selections and separation by polynomials
Autorzy:
Wąsowicz, Szymon
Powiązania:
https://bibliotekanauki.pl/articles/1287380.pdf
Data publikacji:
1996
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
separation theorem
set-valued function
selection
n-convex function
n-concave function
affine function
Helly's theorem
Lagrange interpolating polynomial
Opis:
K. Nikodem and the present author proved in [3] a theorem concerning separation by affine functions. Our purpose is to generalize that result for polynomials. As a consequence we obtain two theorems on separation of an n-convex function from an n-concave function by a polynomial of degree at most n and a stability result of Hyers-Ulam type for polynomials.
Źródło:
Studia Mathematica; 1996, 120, 1; 75-82
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
On the exponential Orlicz norms of stopped Brownian motion
Autorzy:
Peškir, Goran
Powiązania:
https://bibliotekanauki.pl/articles/1288072.pdf
Data publikacji:
1996
Wydawca:
Polska Akademia Nauk. Instytut Matematyczny PAN
Tematy:
Brownian motion (Wiener process)
stopping time
exponential Young function
exponential Orlicz norm
Doob's maximal inequality for martingales
Burkholder-Gundy's inequality
Davis' best constants
Hermite polynomial
continuous (local) martingale
Ito's integral
the quadratic variation process
time change (of Brownian motion)
Kahane-Khinchin's inequalities
Opis:
Necessary and sufficient conditions are found for the exponential Orlicz norm (generated by $ψ_p(x) = exp(|x|^p)-1$ with 0 < p ≤ 2) of $max_{0≤t≤τ}|B_t|$ or $|B_τ|$ to be finite, where $B = (B_t)_{t≥0}$ is a standard Brownian motion and τ is a stopping time for B. The conditions are in terms of the moments of the stopping time τ. For instance, we find that $∥max_{0≤t≤τ}|B_t|∥_{ψ_1} < ∞$ as soon as $E(τ^{k}) = O(C^{k}k^{k})$ for some constant C > 0 as k → ∞ (or equivalently $∥τ∥_{ψ_1} < ∞$). In particular, if τ ∼ Exp(λ) or $|N(0,σ^2)|$ then the last condition is satisfied, and we obtain $∥max_{0≤t≤τ}|B_t|∥_{ψ_1} ≤ K √{E(τ)}$ with some universal constant K > 0. Moreover, this inequality remains valid for any class of stopping times τ for B satisfying $E(τ^{k}) ≤ C(Eτ)^{k}k^{k}$ for all k ≥ 1 with some fixed constant C > 0. The method of proof relies upon Taylor expansion, Burkholder-Gundy's inequality, best constants in Doob's maximal inequality, Davis' best constants in the $L^p$-inequalities for stopped Brownian motion, and estimates of the smallest and largest positive zero of Hermite polynomials. The results extend to the case of any continuous local martingale (by applying the time change method of Dubins and Schwarz).
Źródło:
Studia Mathematica; 1995-1996, 117, 3; 253-273
0039-3223
Pojawia się w:
Studia Mathematica
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-10 z 10

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