共查询到20条相似文献，搜索用时 31 毫秒
1.
D. Junghenn 《Semigroup Forum》2008,66(2):328-336
Abstract. Let
be a semidirect product of semitopological semigroups S and T . If S and T act on topological spaces X and Y , respectively, then under suitable conditions there is a natural action of
on X × Y . In this paper we characterize the almost periodic and strongly almost periodic compactification of the flow
,
in terms of related compactifications of (S,X) and (T,Y) . 相似文献
2.
Lewin 《Semigroup Forum》2008,66(1):43-62
Abstract. Given a set A and a function
, we study the set of all functions
that are continuous for all topologies for which f continuous.
We prove that in a sense to be made precise in the text, for any essentially infinitary function f , any non-constant such g equals f
n
, for some n∈ N. We also prove a similar result for the clone of n -ary functions from
. 相似文献
3.
Micciancio 《Discrete and Computational Geometry》2003,29(1):133-138
Abstract. We prove that the best way to reduce the volume of the n -dimensional unit cube by a linear transformation that maps each of the main vertices
to a point within distance ɛ <
from
is to shorten all edges by a factor (1-ɛ) . In particular, the minimal volume of such an almost cubic parallelepiped is (1-ɛ)
n
. This problem naturally arises in the construction of lattice-based one-way functions with worst-case/ average-case connection. 相似文献
4.
Abstract. Given a finite set A and a distinguished function
, we study the set of all functions
that are continuous for all topologies for which f is continuous. The main result is a characterization of the functions f such that this set is trivial, that is, contains only the constant functions and the iterates of f . 相似文献
5.
Viorel Barbu Aurel Răşcanu Gianmario Tessitore 《Applied Mathematics and Optimization》2003,47(2):97-120
Abstract. This work is concerned with Carleman inequalities and controllability properties for the following stochastic linear heat
equation (with Dirichlet boundary conditions in the bounded domain D
⊂ R
d
and multiplicative noise):
and for the corresponding backward dual equation:
We prove the null controllability of the backward equation and obtain partial results for the controllability of the forward
equation.
\par 相似文献
6.
Schöbel 《Discrete and Computational Geometry》2003,29(2):229-238
Abstract. The anchored hyperplane location problem is to locate a hyperplane passing through some given points P
R
n
and minimizing either the sum of weighted distances (median problem ), or the maximum weighted distance (center problem ) to some other points Q
R
n
.
This problem of computational geometry is analyzed by using nonlinear programming techniques. If the distances are measured
by a norm, it will be shown that in the median case there exists an optimal hyperplane that passes through at least n - k affinely independent points of Q , if k is the maximum number of affinely independent points of P . In the center case, there exists an optimal hyperplane which is at maximum distance to at least n- k +1 affinely independent points of Q . Furthermore, if the norm is a smooth norm, all optimal hyperplanes satisfy these criteria. These results generalize known results about unrestricted hyperplane location
problems. 相似文献
7.
Abstract. Weakly left ample semigroups are a class of semigroups that are (2,1) -subalgebras of semigroups of partial transformations, where the unary operation takes a transformation α to the identity map in the domain of α . It is known that there is a class of proper weakly left ample semigroups whose structure is determined by unipotent monoids acting on semilattices or categories. In
this paper we show that for every finite weakly left ample semigroup S , there is a finite proper weakly left ample semigroup
and an onto morphism from
to S which separates idempotents. In fact,
is actually a (2,1) -subalgebra of a symmetric inverse semigroup, that is, it is a left ample semigroup (formerly, left type A). 相似文献
8.
Abstract. Subdivision with finitely supported masks is an efficient method to create discrete multiscale representations of smooth
surfaces for CAGD applications. Recently a new subdivision scheme for triangular meshes, called
-subdivision , has been studied. In comparison to dyadic subdivision, which is based on the dilation matrix 2I ,
-subdivision is based on a dilation M with det M=3 . This has certain advantages, for example, a slower growth for the number of control points.
This paper concerns the problem of achieving maximal sum rule orders for stationary
-subdivision schemes with given mask support, which is important because the sum rule order characterizes the order of the
polynomial reproduction, and provides an upper bound on the Sobolev smoothness of the surface. We study both interpolating
and approximating schemes for a natural family of symmetric mask support sets related to squares of sidelength 2n in Z
2
, and obtain exact formulas for the maximal sum rule order for arbitrary n . For approximating schemes, the solution is simple, and schemes with maximal sum rule order are realized by an explicit
family of schemes based on repeated averaging [15].
In the interpolating case, we use properties of multivariate Lagrange polynomial interpolation to prove the existence of
interpolating schemes with maximal sum rule orders. These can be found by solving a linear system which can be reduced in
size by using symmetries. From this, we construct some new examples of smooth (C
2
,C
3
) interpolating
-subdivision schemes with maximal sum rule order and symmetric masks. The construction of associated dual schemes is also
discussed. 相似文献
9.
Chang 《Semigroup Forum》2008,66(1):68-80
Abstract. For the generator A of a C
0
-semigroup on a Banach space (X, ||⋅||) , we apply the perturbation of Desch-Schappacher type to solve the Volterra integordifferential equation
which can be applied to treat boundary value problems and inhomogeneous retarded differential equations. 相似文献
10.
Abstract. We study the approximation complexity of certain kinetic variants of the Traveling Salesman Problem (TSP) where we consider
instances in which each point moves with a fixed constant speed in a fixed direction. We prove the following results:
• If the points all move with the same velocity, then there is a polynomial time approximation scheme for the Kinetic TSP.
• The Kinetic TSP cannot be approximated better than by a factor of 2 by a polynomial time algorithm unless P = NP, even if
there are only two moving points in the instance.
• The Kinetic TSP cannot be approximated better than by a factor of
by a polynomial time algorithm unless P = NP, even if the maximum velocity is bounded. n denotes the size of the input instance.
The last result is especially surprising in the light of existing polynomial time approximation schemes for the static version
of the problem. 相似文献
11.
Abstract. Given an m × n rectangular mesh, its adjacency matrix A , having only integer entries, may be interpreted as a map between vector spaces over an arbitrary field K . We describe the kernel of A : it is a direct sum of two natural subspaces whose dimensions are equal to
and
, where c = gcd (m+1,n+1) - 1 . We show that there are bases to both vector spaces, with entries equal to 0,1 and -1 . When K = Z/(2), the kernel elements of these subspaces are described by rectangular tilings of a special kind. As a corollary, we count
the number of tilings of a rectangle of integer sides with a specified set of tiles. 相似文献
12.
Abstract. Bourgain [1] showed that every embedding of the complete binary tree of depth n into l
2
has metric distortion ≥
. An alternative proof was later given by Matousek [3]. This note contains a short proof for this fact. 相似文献
13.
Hui Yin Shuyue Chen Jing Jin 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2008,59(6):969-1001
This paper is concerned with the large time behavior of traveling wave solutions to the Cauchy problem of generalized Benjamin–Bona–Mahony–Burgers
equations
with prescribed initial data
Here v( > 0), β are constants, u
± are two given constants satisfying u
+ ≠ u
− and the nonlinear function f(u) ∈C
2(R) is assumed to be either convex or concave. An algebraic time decay rate to traveling waves of the solutions of the Cauchy
problem of generalized Benjamin-Bona-Mahony-Burgers equation is obtained by employing the weighted energy method developed
by Kawashima and Matsumura in [6] to discuss the asymptotic behavior of traveling wave solutions to the Burgers equation.
revised: May 23 and August 8, 2007 相似文献
14.
Heppes 《Discrete and Computational Geometry》2003,29(3):477-481
Abstract. Kershner proved in 1939 that the density of a covering of the plane by congruent circles is at least 2π/
[3]. In 1950 L. Fejes Tóth [2] extended this result showing that the same density bound holds for coverings with congruent
ellipses which do not ``cross'. In the present paper we prove that the non-crossing assumption is not necessary if the ellipses
are sufficiently ``fat'. 相似文献
15.
We establish a new bound for the exponential sum
where λ is an element of the residue ring modulo a large prime number
and
are arbitrary subsets of the residue ring modulo p − 1 and γ (n) are any complex numbers with | γ (n)| ≦ 1.
Received: 15 June 2005 相似文献
16.
Abstract. Let Ω and Π be two simply connected domains in the complex plane C which are not equal to the whole plane C and let λ
Ω
and λ
Π
denote the densities of the Poincare metric in Ω and Π , respectively. For f: Ω → Π analytic in Ω , inequalities of the type
are considered where M
n
(z,Ω, Π) does not depend on f and represents the smallest value possible at this place. We prove that
if Δ is the unit disk and Π is a convex domain. This generalizes a result of St. Ruscheweyh.
Furthermore, we show that
holds for arbitrary simply connected domains whereas the inequality 2
n-1
≤ C
n
(Ω,Π) is proved only under some technical restrictions upon Ω and Π . 相似文献
17.
The aim of this note is to prove the following theorem. Let
where P(ix) is a nonnegative homogeneous elliptic polynomial on R
d
and V is a nonnegative polynomial potential. Then for every 1 < p < ∞ and every α > 0 there exist constants C
1, C
2 > 0 such that
and
for f in the Schwartz class . We take advantage of the Christ inversion theorem for singular integral operators with a small amount of smoothness on
nilpotent Lie groups, the maximal subelliptic L
2-estimates for the generators of stable semi-groups of measures, and the principle of transference of Coifman–Weiss.
In memory of Tadek Pytlik, our teacher and friend.
Research supported by the European Commission Marie Curie Host Fellowship for the Transfer of Knowledge “Harmonic Analysis,
Nonlinear Analysis and Probability” MTKD-CT-2004-013389 and by Polish funds for science in years 2005–2008 (research project
1P03A03029). 相似文献
18.
E.G. Coffman Jr. George S. Lueker Joel Spencer Peter M. Winkler 《Probability Theory and Related Fields》2001,120(4):585-599
A random rectangle is the product of two independent random intervals, each being the interval between two random points
drawn independently and uniformly from [0,1]. We prove that te number C
n
of items in a maximum cardinality disjoint subset of n random rectangles satisfies
where K is an absolute constant. Although tight bounds for the problem generalized to d > 2 dimensions remain an open problem, we are able to show that, for some absolute constat K,
Finally, for a certain distribution of random cubes we show that for some absolute constant K, the number Q
n
of items in a maximum cardinality disjoint subset of the cubes satisies
Received: 1 September 1999 / Revised version: 3 November 2000 / Published online: 14 June 2001 相似文献
19.
Let and be the von Mangoldt function and M?bius function, respectively, x real and y“small” compared with x. This paper gives, for the first time, a non-trivial estimate of the sum
for all whenever . Correspondingly, it is also proved that
相似文献
20.