共查询到20条相似文献,搜索用时 15 毫秒
1.
Franki Dillen Johan Fastenakels Joeri Van der Veken Luc Vrancken 《Monatshefte für Mathematik》2007,152(2):89-96
In this article we study surfaces in
for which the unit normal makes a constant angle with the
-direction. We give a complete classification for surfaces satisfying this simple geometric condition. 相似文献
2.
R.V. Gurjar 《Mathematische Zeitschrift》2002,240(1):83-94
We give a new proof of the Cancellation Theorem for which says that if V is a smooth complex affine surface such that is isomorphic to then V is isomorphic to The proof is based on the topological method of Mumford-Ramanujam.
Received: 2 November 2000 / in final form: 10 September 2001 / Published online: 1 February 2002 相似文献
3.
Let be a mapping in the Sobolev space . We assume that the cofactors of the differential matrix Df(x) belong to . Then, among other things, we prove that the Jacobian determinant detDf lies in the Hardy space .
Received: 20 November 2000 / Revised version: 17 December 2001 / Published online: 5 September 2002
Iwaniec was supported by NSF grant DMS-0070807. This research was done while Onninen was visiting Mathematics Department at
Syracuse University. He wishes to thank SU for the support and hospitality. 相似文献
4.
Given a finite subset
of an additive group
such as
or
, we are interested in efficient covering of
by translates of
, and efficient packing of translates of
in
. A set
provides a covering if the translates
with
cover
(i.e., their union is
), and the covering will be efficient if
has small density in
. On the other hand, a set
will provide a packing if the translated sets
with
are mutually disjoint, and the packing is efficient if
has large density.
In the present part (I) we will derive some facts on these concepts when
, and give estimates for the minimal covering densities and maximal packing densities of finite sets
. In part (II) we will again deal with
, and study the behaviour of such densities under linear transformations. In part (III) we will turn to
.
Authors’ address: Department of Mathematics, University of Colorado at Boulder, Campus Box 395, Boulder, Colorado 80309-0395,
USA
The first author was partially supported by NSF DMS 0074531. 相似文献
5.
In this paper, we establish several decidability results for pseudovariety joins of the form
, where
is a subpseudovariety of
or the pseudovariety
. Here,
(resp.
) denotes the pseudovariety of all
-trivial (resp.
-trivial) semigroups. In particular, we show that the pseudovariety
is (completely) κ-tame when
is a subpseudovariety of
with decidable κ-word problem and
is (completely) κ-tame. Moreover, if
is a κ-tame pseudovariety which satisfies the pseudoidentity x1 ⋯ xryω+1ztω = x1 ⋯ xryztω, then we prove that
is also κ-tame. In particular the joins
,
,
, and
are decidable.
Partial support by FCT, through the Centro de Matemática da Universidade do Porto, is also gratefully acknowledged.
Partial support by FCT, through the Centro de Matemática da Universidade do Minho, is also gratefully acknowledged. 相似文献
6.
Summary. We combine a primal mixed finite element approach with a Dirichlet-to-Neumann mapping (arising from the boundary integral
equation method) to study the weak solvability and Galerkin approximations of a class of linear exterior transmission problems
in potential theory. Our results are mainly based on the Babuska-Brezzi theory for variational problems with constraints.
We establish the uniqueness of solution for the continuous and discrete formulations, and show that finite element subspac
es of Lagrange type satisfy the discrete compatibility conditions. In addition, we provide the error analysis, including polygonal
approximations of the domain, and prove strong convergence of the Galerkin solutions. Moreover, under additional regularity
assumptions on the solution of the continuous formulation, we obtain the asymptotic rate of convergence O(h).
Received August 25, 1998 / Revised version received March 8, 2000 / Published online October 16, 2000 相似文献
7.
Alexandru Dimca Fayçal Maaref Claude Sabbah Morihiko Saito 《Mathematische Annalen》2000,318(1):107-125
Using local cohomology and algebraic -Modules, we generalize a comparison theorem between relative de Rham cohomology and Dwork cohomology due to N. Katz, P. Monsky,
A. Adolphson and S. Sperber.
Received June 10, 1999 / Published online July 20, 2000 相似文献
8.
Summary. In this paper we describe and analyse a class of spectral methods, based on spherical polynomial approximation, for second-kind
weakly singular boundary integral equations arising from the Helmholtz equation on smooth closed 3D surfaces diffeomorphic
to the sphere. Our methods are fully discrete Galerkin methods, based on the application of special quadrature rules for computing
the outer and inner integrals arising in the Galerkin matrix entries. For the outer integrals we use, for example, product-Gauss
rules. For the inner integrals, a variant of the classical product integration procedure is employed to remove the singularity
arising in the kernel. The key to the analysis is a recent result of Sloan and Womersley on the norm of discrete orthogonal
projection operators on the sphere. We prove that our methods are stable for continuous data and superalgebraically convergent
for smooth data. Our theory includes as a special case a method closely related to one of those proposed by Wienert (1990)
for the fast computation of direct and inverse acoustic scattering in 3D.
Received May 29, 2000 / Revised version received March 26, 2001/ Published online December 18, 2001 相似文献
9.
J. P. Moreno 《Monatshefte für Mathematik》2007,152(3):255-263
This paper is motivated by recent attempts to investigate classical notions from finite-dimensional convex geometry in spaces
of continuous functions. Let
be the family of all closed, convex and bounded subsets of C(K) endowed with the Hausdorff metric. A completion of
is a diametrically maximal set
satisfying A ⊂ D and diam A = diam D. Using properties of semicontinuous functions and an earlier result by Papini, Phelps and the author [12], we characterize
the family γ(A) of all possible completions of
. We give also a formula which calculates diam γ(A) and prove finally that, if K is a Hausdorff compact space with card K > 1, then the family of those elements of
having a unique completion is uniformly very porous in
with a constant of lower porosity greater than or equal to 1/3. 相似文献
10.
11.
By estimating the subgroup numbers associated with various classes of large groups, we exhibit a number of new phenomena in the theory of subgroup growth. 相似文献
12.
P. A. Zalesskii 《Monatshefte für Mathematik》2002,135(2):167-171
A profinite group is said to be just infinite if each of its proper quotients is finite. We address the question which profinite
groups admit just infinite quotients. It is proved that any profinite group whose order (as a supernatural number) is divisible
only by finitely many primes admits just infinite quotients. It is shown that if a profinite group G possesses the property in question then so does every open subgroup and every finite extension of G.
Received 20 July 2001 相似文献
13.
Todd Eisworth 《Archive for Mathematical Logic》2001,40(3):235-242
We investigate a two-player game involving pairs of filters on ω. Our results generalize a result of Shelah ([7] Chapter VI) dealing with applications of game theory in the study of ultrafilters. Received: 28 September 1998 / Published online: 25 January 2001 相似文献
14.
Let Ω and Π be two finitely connected hyperbolic domains in the complex plane
and let R(z, Ω) denote the hyperbolic radius of Ω at z and R(w, Π) the hyperbolic radius of Π at w. We consider functions f that are analytic in Ω and such that all values f(z) lie in the domain Π. This set of analytic functions is denoted by A(Ω, Π). We prove among other things that the quantities
are finite for all
if and only if ∂Ω and ∂Π do not contain isolated points.
This work was supported by a grant of the Deutsche Forschungsgemeinschaft for F. G. Avkhadiev. 相似文献
15.
Sijong Kwak 《Mathematische Annalen》2001,320(4):649-664
For a projective variety X of codimension 2 in defined over the complex number field , it is traditionally said that X has no apparent -ple points if the -secant lines of X do not fill up the ambient projective space , equivalently, the locus of -ple points of a generic projection of X to ${\Bbb P}^{n+1}$ is empty. We show that a smooth threefold in has no apparent triple points if and only if it is contained in a quadric hypersurface. We also obtain an enumerative formula
counting the quadrisecant lines of X passing through a general point of and give necessary cohomological conditions for smooth threefolds in without apparent quadruple points. This work is intended to generalize the work of F. Severi [fSe] and A. Aure [Au], where
it was shown that a smooth surface in has no triple points if and only if it is either a quintic elliptic scroll or contained in a hyperquadric. Furthermore we
give open questions along these lines.
Received: 24 January 2000 / Published online: 18 June 2001 相似文献
16.
Carlo Toffalori 《Archive for Mathematical Logic》1998,37(2):127-142
We show undecidability for lattices over a group ring where has a cyclic subgroup of order for some odd prime . Then we discuss the decision problem for -lattices where is a cyclic group of order 8, and we point out that a positive answer implies – in some sense – the solution of the “wild
undecidable” conjecture.
Received November 15, 1995 相似文献
17.
It is known that for any finite group G given by a finite group presentation there exists a finite semigroup presentation for G of the same deficiency, i.e. satisfying . It is also known that the analogous statement does not hold for all finite monoids. In this paper we give a necessary and
sufficient condition for a finite monoid M, given by a finite monoid presentation, to have a finite semigroup presentation of the same deficiency.
(Received 17 April 2001; in revised form 15 September 2001) 相似文献
18.
Dan Coman 《Mathematische Zeitschrift》2000,235(1):111-122
We consider (pluricomplex) Green functions defined on , with logarithmic poles in a finite set and with logarithmic growth at infinity. For certain sets, we describe all the corresponding
Green functions. The set of these functions is large and it carries a certain algebraic structure. We also show that for some
sets no such Green functions exist. Our results indicate the fact that the set of poles should have certain algebro-geometric
properties in order for these Green functions to exist.
Received November 24, 1998; in final form April 19, 1999 / Published online July 3, 2000 相似文献
19.
Let be a compact hypersurface in bounding a convex set with non-empty interior. In this paper it is proved that there always exist at least n geometrically distinct closed characteristics on if is symmetric with respect to the origin.
Received: 18 May 1999 / Published online: 4 April 2002 相似文献
20.
Yasuyuki Nagatomo 《Mathematische Zeitschrift》2003,243(2):243-261
We prove the completeness of an instanton moduli space on quaternion-K?hler manifold . A point in the boundary of the moduli represents an ASD bundle with a particular singular set. It is shown that the singular
set is a quaternion submanifold of and the Poincaré dual of the homology class represented by is the second Chern class o f the instanton bundle.
Received: 4 July 2000 / Published online: 2 December 2002
Current Address: Faculty of Mathematics, Kyushu University, Ropponmatsu, Fukuoka, 810-8560, Japan (e-mail: nagatomo@math.kyushu-u.ac.jp) 相似文献