共查询到20条相似文献,搜索用时 46 毫秒
1.
H. Maehara 《European Journal of Combinatorics》2002,23(8):1055
Let Ω be a finite subset of the Cartesian productW1 × × Wnof n sets. ForA {1, 2, , n }, denote by ΩAthe projection ofΩ onto the Cartesian product of Wi, i A. Generalizing an inequality given in an article by Shen, we prove that | Ω |2 ≤ |ΩA1 || ΩAk| provided that { A1, , Ak} is a double cover of {1, 2, , n }. This inequality is applied to give some bounds on the numbers of special subgraphs of a graph. 相似文献
2.
Andrs Bir 《Journal of Number Theory》2006,121(2):324-354
In [A. Biró, V.T. Sós, Strong characterizing sequences in simultaneous Diophantine approximation, J. Number Theory 99 (2003) 405–414] we proved that if Γ is a subgroup of the torus R/Z generated by finitely many independent irrationals, then there is an infinite subset AZ which characterizes Γ in the sense that for γR/Z we have ∑aAaγ<∞ if and only if γΓ. Here we consider a general compact metrizable Abelian group G instead of R/Z, and we characterize its finitely generated free subgroups Γ by subsets AG*, where G* is the Pontriagin dual of G. For this case we prove stronger forms of the analogue of the theorem of the above mentioned work, and we find necessary and sufficient conditions for a kind of strengthening of this statement to be true. 相似文献
3.
Konstantin Yu. Osipenko 《Journal of Approximation Theory》1999,97(2):384
LetSβ{z
: |Im z|<β}. For 2π-periodic functions which are analytic inSβwithp-integrable boundary values, we construct an optimal method of recovery off′(ξ), ξSβ, using information about the valuesf(x1), mldr;, f(xn), xj[0, 2π). 相似文献
4.
The following reaction-diffusion system in spatially non-homogeneous almost-periodic media is considered in a bounded domain
: (1) ∂tu=Au−f(u)+g, u|∂Ω=0. Here u=(u1,…,uk) is an unknown vector-valued function, f is a given nonlinear interaction function and the second order elliptic operator A has the following structure: where aijl(y) are given almost-periodic functions. We prove that, under natural assumptions on the nonlinear term f(u), the longtime behavior of solutions of (1) can be described in terms of the global attractor
of the associated dynamical system and that the attractors
, 0<<01, converge to the attractor
of the homogenized problem (1) as →0. Moreover, in the particular case of periodic media, we give explicit estimates for the distance between the non-homogenized
and the homogenized
attractors in terms of the parameter . 相似文献
5.
Hee-Kap Ahn Peter Brass Otfried Cheong Hyeon-Suk Na Chan-Su Shin Antoine Vigneron 《Computational Geometry》2006,33(3):152-164
Given a planar convex set C, we give sublinear approximation algorithms to determine approximations of the largest axially symmetric convex set S contained in C, and the smallest such set S′ that contains C. More precisely, for any >0, we find an axially symmetric convex polygon QC with area |Q|>(1−)|S| and we find an axially symmetric convex polygon Q′ containing C with area |Q′|<(1+)|S′|. We assume that C is given in a data structure that allows to answer the following two types of query in time TC: given a direction u, find an extreme point of C in direction u, and given a line ℓ, find C∩ℓ. For instance, if C is a convex n-gon and its vertices are given in a sorted array, then TC=O(logn). Then we can find Q and Q′ in time O(−1/2TC+−3/2). Using these techniques, we can also find approximations to the perimeter, area, diameter, width, smallest enclosing rectangle and smallest enclosing circle of C in time O(−1/2TC). 相似文献
6.
Let A be an abelian variety of dimension g1 defined over a number field K. We study the size of the torsion group A(F)tors where F/K is a finite extension and more precisely we study the best possible exponent γ in the inequality Card(A(F)tors)[F:K]γ when F is any finite extension of K. In the CM case we give an exact formula for the exponent γ in terms of the characters of the Mumford–Tate group—a torus in this case—and discuss briefly the general case.Finally we give an application of the main result in direction of a generalisation of the Manin–Mumford conjecture. 相似文献
7.
Donglong Li Zhengde Dai Xuhong Liu 《Journal of Mathematical Analysis and Applications》2007,330(2):934-948
In this paper, the two-dimensional generalized complex Ginzburg–Landau equation (CGL)
ut=ρu−Δφ(u)−(1+iγ)Δu−νΔ2u−(1+iμ)|u|2σu+αλ1(|u|2u)+β(λ2)|u|2