共查询到20条相似文献,搜索用时 31 毫秒
1.
Fang Gensun 《中国科学A辑(英文版)》2001,44(9):1126-1131
The main result of this paper asserts that if a function f is in the class Bπ,p, 1 <p < ∞; that is, those p-integrable functions whose Fourier transforms are supported in the interval [ - π, π], then f and its
derivatives f(j) j = 1, 2, …, can be recovered from its sampling sequence{f(k)} via the cardinal interpolating spline of degree m in the metric
ofL
q(ℝ)), 1 <p=q < ∞, or 11 <p=q < ⩽ ∞. 相似文献
2.
The Marcinkiewicz-Zygmund inequality and the Bernstein inequality are established on ∮2m(T,R)∩L2(R) which is the space of polynomial splines with irregularly distributed nodes T={tj}j∈Z, where {tj}j∈Z is a real sequence such that {eitξ}j∈Z constitutes a Riesz basis for L2([-π,π]). From these results, the asymptotic relation E(f,Bπ,2)2=lim E(f,∮2m(T,R)∩L2(R))2 is proved, where Bπ,2 denotes the set of all functions from L2(R) which can be continued to entire functions of exponential type ≤π, i.e. the classical Paley-Wiener class. 相似文献
3.
R. Norvaiša 《Lithuanian Mathematical Journal》2008,48(4):418-426
Let B
H,K
= {B
H,K
(t)}
t⩾0 be a bifractional Brownian motion with parameters H ∈ (0, 1) and K ∈ (0, 1]. For a function Φ: [0, ∞) → [0, ∞) and for a partition κ = {t
i
}n
i=0 of an interval [0, T] with T > 0, let {ie418-01}. We prove that, for a suitable Φ depending on H and K, {ie418-02} almost surely.
The research was partially supported by the Lithuanian State Science and Studies Foundation, grant No. T-16/08 相似文献
4.
G. Lepsveridze 《Georgian Mathematical Journal》1998,5(2):157-176
It is proved that for any given sequence (σ
n
,n ∈ ℕ)=Γ0 ⊂ Γ, where Γ is the set of all directions in ℝ2 (i.e., pairs of orthogonal straight lines) there exists a locally integrable functionf on ℝ2 such that: (1) for almost all directionsσ ∈ Γ\Γ0 the integral ∫f is differentiable with respect to the familyB
2σ
of open rectangles with sides parallel to the straight lines fromσ: (2) for every directionσ
n
∈ Γ0 the upper derivative of ∫f with respect toB
2σ
n
equals +∞; (3) for every directionσ ∈ Γ the upper derivative of ∫ |f| with respect toB
2σ
equals +∞. 相似文献
5.
Robert S. Strichartz 《Journal of Geometric Analysis》1991,1(3):269-289
Let μ be a measure on ℝn that satisfies the estimate μ(B
r(x))≤cr
α for allx ∈ ℝn and allr ≤ 1 (B
r(x) denotes the ball of radius r centered atx. Let ϕ
j,k
(ɛ)
(x)=2
nj2ϕ(ɛ)(2
j
x-k) be a wavelet basis forj ∈ ℤ, κ ∈ ℤn, and ∈ ∈E, a finite set, and letP
j
(T)=Σɛ,k
<T,ϕ
j,k
(ɛ)
>ϕ
j,k
(ɛ)
denote the associated projection operators at levelj (T is a suitable measure or distribution). Iff ∈Ls
p(dμ) for 1 ≤p ≤ ∞, we show thatP
j(f dμ) ∈ Lp(dx) and ||P
j
(fdμ)||L
p(dx)≤c2
j((n-α)/p′))||f||L
p(dμ) for allj ≥ 0. We also obtain estimates for the limsup and liminf of ||P
j
(fdμ)||L
p(dx) under more restrictive hypotheses.
Communicated by Guido Weiss 相似文献
6.
Let Bσ,p,1 <-p<-∞, be the set of all functions from L8(R) which can be continued to entire functions of exponential type <-σ. The well known Shannon sampling theorem and its generalization [1] state that every f∈Bσ,p, 1<p<∞, can be represented as
$f(x) = \mathop \Sigma \limits_{j \in z} f(j\pi /\sigma )\tfrac{{sin\sigma (x - j\pi /\sigma )}}{{\sigma (x - j\pi /\sigma )}}, \sigma > 0$f(x) = \mathop \Sigma \limits_{j \in z} f(j\pi /\sigma )\tfrac{{sin\sigma (x - j\pi /\sigma )}}{{\sigma (x - j\pi /\sigma )}}, \sigma > 0 相似文献
7.
Let L
p
(S), 0 < p < +∞, be a Lebesgue space of measurable functions on S with ordinary quasinorm ∥·∥
p
. For a system of sets {B
t
|t ∈ [0, +∞)
n
} and a given function ψ: [0, +∞)
n
↦ [ 0, +∞), we establish necessary and sufficient conditions for the existence of a function f ∈ L
p
(S) such that inf {∥f − g∥
p
p
g ∈ L
p
(S), g = 0 almost everywhere on S\B
t
} = ψ (t), t ∈ [0, +∞)
n
. As a consequence, we obtain a generalization and improvement of the Dzhrbashyan theorem on the inverse problem of approximation
by functions of the exponential type in L
2.
__________
Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 8, pp. 1116–1127, August, 2006. 相似文献
8.
Let ℤ2N={0, ..., 2N-1} denote the group of integers modulo 2N, and let L be the space of all real functions of ℤ2N which are supported on {0,...N−1}. The spectral phase of a function f:ℤ2N→ℝ is given by φf(k)=arg
for k ∈ ℤ2N, where
denotes the discrete Fourier transforms of f.
For a fixed s∈L let Ks denote the cone of all f:ℤ2N→ℝ which satisfy φf ≡ φs and let Ms be its linear span. The angle αs between Ms and L determines the convergence rate of the signal restoration from phase algorithm of Levi and Stark [3]. Here we prove
the following conjectures of Urieli et al. [7] who verified them for the N≤3 case:
9.
Joaquim Ortega-Cerdà 《Arkiv f?r Matematik》1998,36(1):103-117
We characterize in geometric terms the zero sets of holomorphic functionsf in the bidisk such that log |f|∈L
p
(D
2) for 1<p<∞.
Partially supported by the DGCYT grant PB95-0956-C02-02 and grant 1996-SGR-26. 相似文献
10.
Let 𝔄 denote the C*-algebra of bounded operators on L
2 ℝ generated by: (i) all multiplications a(M) by functions a∈C[ − ∞, + ∞], (ii) all multiplications by 2π-periodic continuous functions, and (iii) all operator of the form F
−1
b(M)F, where F denotes the Fourier transform and b∈C[ − ∞, + ∞]. A given A ∈ 𝔄 is a Fredholm operator if and only if σ(A) and γ(A) are invertible, where σ denotes the continuous extension of the usual principal symbol, while γ denotes an operator-valued “boundary principal symbol” (the “boundary” here consists of two copies of the circle, one at
each end of the real line). We give two proofs of the fact that K
0(𝔄) is isomorphic to ℤ and that K
1(𝔄) is isomorphic to ℤ ⊕ ℤ . We do it first by computing the connecting mappings in the six-term exact sequence associated
to σ. For the second proof, we show that the image of γ is isomorphic to the direct sum of two copies of the crossed product
, where α denotes the translation-by-one automorphism. Its K-theory can be computed using the Pimsner–Voiculescu exact sequence,
and that information suffices for the analysis of the standard cyclic exact sequence associated to γ.
Received: February 2006 相似文献
11.
Jerome A. Goldstein 《Semigroup Forum》1996,52(1):37-47
Of concern are semigroups of linear norm one operators on Hilbert space of the form (discrete case)T={T
n
/n=0,1,2,...} or (continuous case)T={T(t)/t=≥0}. Using ergodic theory and Hilbert-Schmidt operators, the Cesàro limits (asn→∞) of |〈T
n
f,f〉|2, |〈T
(n)f,f〉|2 are computed (withn∈ℤ+ orn∈ℤ+). Specializing the Hilbert space to beL
2(T,μ) (discrete case) orL
2(ℝ,μ) (continuous case) where μ is a Borel probability measure on the circle group or the line, the Cesàro limit of
(asn→±∞, with,n∈ℤ orn∈ℝ) is obtained and interpreted. Extensions toT
M
, and ℝ
M
are given. Finally, we discuss recent operator theoretic extensions from a Hilbert to a Banach space context.
Partially supported by an NSF grant 相似文献
12.
In this paper, we present the conditions on dilation parameter {s
j}j that ensure a discrete irregular wavelet system {s
j
n/2ψ(s
j
·−bk)}
j∈ℤ,k∈ℤ
n
to be a frame on L2(ℝn), and for the wavelet frame we consider the perturbations of translation parameter b and frame function ψ respectively. 相似文献
13.
Sofiya Ostrovska 《Archiv der Mathematik》2006,86(3):282-288
Let Bn (f, q; x), n=1, 2, ... , 0 < q < ∞, be the q-Bernstein polynomials of a function f, Bn (f, 1; x) being the classical Bernstein polynomials. It is proved that, in general, {Bn (f, qn; x)} with qn ↓ 1 is not an approximating sequence for f ∈C[0, 1], in contrast to the standard case qn ↓ 1. At the same time, there exists a sequence 0 < δn ↓ 0 such that the condition
implies the approximation of f by {Bn (f, qn; x)} for all f ∈C[0, 1].
Received: 15 March 2005 相似文献
14.
Song Li 《中国科学A辑(英文版)》2003,46(3):364-375
The purpose of this paper is to investigate the refinement equations of the form
15.
For the Jacobi-type Bernstein–Durrmeyer operator M
n,κ
on the simplex T
d
of ℝ
d
, we proved that for f∈L
p
(W
κ
;T
d
) with 1<p<∞,
|
设为首页 | 免责声明 | 关于勤云 | 加入收藏 |
Copyright©北京勤云科技发展有限公司 京ICP备09084417号 |