Large volume growth and the topology of open manifolds

In this paper, we study complete noncompact Riemannian manifolds with nonnegative Ricci curvature and large volume growth. We find some reasonable conditions to insure that this kind of manifolds are diffeomorphic to a Euclidean space or have finite topological type. Received: January 4, 2000; in final form: October 31, 2000 / Published online: 19 October 2001     

The scalar curvature problem on S^n: an approach via Morse theory

We prove the existence of positive solutions for the equation on , where is the Laplace-Beltrami operator on is the critical Sobolev exponent, and is a small parameter. The problem can be reduced to a finite dimensional study which is performed via Morse theory. Received: 29 September 1999 / Accepted: 11 May 2001 / Published online: 19 October 2001     

A second order characteristic finite element scheme for convection-diffusion problems

Summary. A new characteristic finite element scheme is presented for It is of second order accuracy in time increment, symmetric, and unconditionally stable. Optimal error estimates are proved in the framework of -theory. Numerical results are presented for two examples, which show the advantage of the scheme. Received November 22, 2000 / Revised version received July 11, 2001 / Published online October 17, 2001     

A sparse finite element method with high accuracy Part I

Summary. In this paper, we develop and analyze a new finite element method called the sparse finite element method for second order elliptic problems. This method involves much fewer degrees of freedom than the standard finite element method. We show nevertheless that such a sparse finite element method still possesses the superconvergence and other high accuracy properties same as those of the standard finite element method. The main technique in our analysis is the use of some integral identities. Received October 1, 1995 / Revised version received August 23, 1999 / Published online February 5, 2001     

Some remarks on the universal cover of an open K3 surface

 We shall give, in an optimal form, a sufficient numerical condition for the finiteness of the fundamental group of the smooth locus of a normal K3 surface. We shall moreover prove that, if the normal K3 surface is elliptic and the above fundamental group is not finite, then there is a finite covering which is a complex torus. Received: 13 April 2001 / Published online: 16 October 2002 RID="⋆" ID="⋆" Supported by Korea Research Foundation Grant(KRF-2001-041-D00025) Mathematics Subject Classification (2000): 14J28     

New projection-type methods for monotone LCP with finite termination

Summary. In this paper we establish two new projection-type methods for the solution of monotone linear complementarity problem (LCP). The methods are a combination of the extragradient method and the Newton method, in which the active set strategy is used and only one linear system of equations with lower dimension is solved at each iteration. It is shown that under the assumption of monotonicity, these two methods are globally and linearly convergent. Furthermore, under a nondegeneracy condition they have a finite termination property. At last, the methods are extended to solving monotone affine variational inequality problem. Received October 10, 2000 / Revised version received May 22, 2001 / Published online October 17, 2001     

Geometric balance of cuspidal points realizing dessins d'enfants on the Riemann sphere

In this paper we give necessary and sufficient conditions for a finite set of points A in to be the set of cuspidal points for a Belyi function of genus zero. The most important one of these conditions is a fundamental relation of geometric balance which must be satisfied by the points of A. Received January 31, 2000 / Accepted October 23, 2000 / Published online March 12, 2001     

Non-topological solutions in the generalized self-dual Chern-Simons-Higgs theory

In this paper we construct a non-topological multivortex solution of a generalized version of the relativistic self-dual Chern-Simons-Higgs system in that makes the energy functional finite. Our method of proof is an extension of the previous argument used by the authors to prove the existence of general type of non-topological multivortex solutions of the relativistic Chern-Simons-Higgs system, using an implicit function theorem argument with features similar to the Liapunov-Schmidt decomposition. Received: 20 January 2001 / Accepted: 25 October 2001 / Published online: 29 April 2002 This research supported partially by BSRI-MOE, KOSEF(2000-2-10200-002-5).     

On the Limit Cycles of Quadratic Differential Systems

In this paper we give the necessary and sufficient conditions for all finite critical points of quadratic differential systems to be weak foci, and solve an open problem proposed by Yanquian Ye. Received January 11, 1999, Revised October 10, 2000, Accepted March 5, 2001     

Upper critical field for superconductors with edges and corners

The effect of non-smoothness of sample surfaces on the value of the upper critical field and on the location of superconductivity nucleation is discussed. It is shown that, superconducting samples with edges and corners have higher value of comparing to samples with smooth surfaces. Superconductivity nucleates first at the top and bottom edges in a cylinder with a finite height, and nucleates first at vertices in a cuboid. Received: 10 September 2000 / Accepted: 11 May 2001 / Published online: 19 October 2001     

Robustness in a posteriori error analysis for FEM flow models

Summary. We derive a residual-based a posteriori error estimator for a stabilized finite element discretization of certain incompressible Oseen-like equations. We focus our attention on the behaviour of the effectivity index and we carry on a numerical study of its sensitiveness to the problem and mesh parameters. We also consider a scalar reaction-convection-diffusion problem and a divergence-free projection problem in order to investigate the effects on the robustness of our a posteriori error estimator of the reaction-convection-diffusion phenomena and, separately, of the incompressibility constraint. Received March 21, 2001 / Revised version received July 30, 2001 / Published online October 17, 2001     

An unusual stabilized finite element method for a generalized Stokes problem

Summary. An unusual stabilized finite element is presented and analyzed herein for a generalized Stokes problem with a dominating zeroth order term. The method consists in subtracting a mesh dependent term from the formulation without compromising consistency. The design of this mesh dependent term, as well as the stabilization parameter involved, are suggested by bubble condensation. Stability is proven for any combination of velocity and pressure spaces, under the hypotheses of continuity for the pressure space. Optimal order error estimates are derived for the velocity and the pressure, using the standard norms for these unknowns. Numerical experiments confirming these theoretical results, and comparisons with previous methods are presented. Received April 26, 2001 / Revised version received July 30, 2001 / Published online October 17, 2001 Correspondence to: Gabriel R. Barrenechea     

Defining Integrality at Prime Sets of High Density over Function Fields

 Let F be a function field of characteristic over a finite field . Then for any finite set of F-primes S and any , there exists a set of F-primes W of density greater than such that and has a Diophantine definition over . (Here and is defined analogously.) Received 5 March 2001; in revised form 4 October 2001     

From compressible to incompressible materials via an asymptotic expansion

Summary. In linear elasticity problems, the pressure is usually introduced for computing the incompressible state. In this paper is presented a technique which is based on a power series expansion of the displacement with respect to the inverse of Lamé's coefficient . It does not require to introduce the pressure as an auxiliary unknown. Moreover, low degree finite elements can be used. The same technique can be applied to Stokes or Navier-Stokes equations, and can be extended to more general parameterized partial differential equations. Discretization error and convergence are analyzed and illustrated by some numerical results. Received April 21, 2000 / Revised version received February 28, 2001 / Published online October 17, 2001     

Actions and irreducible representations of the mapping class group

Let G be a countable discrete group. Call two subgroups and of G commensurable if has finite index in both and . We say that an action of G on a discrete set X has noncommensurable stabilizers if the stabilizers of any two distinct points of X are not commensurable. We prove in this paper that the action of the map ping class group on the complex of curves has noncommensurable stabilizers. Following a method due to Burger and de la Harpe, this action leads to constructions of irreducible unitary representations of the mapping class group. Received: 26 July 1999 / Revised version: 14 May 2001 / Published online: 19 October 2001     

Small sublattices with large dominions

Two examples of finite sublattices with infinite dominions are given. It is proven that this cannot occur in a finitely generated lattice variety. Received May 10, 2001; accepted in final form October 6, 2005.     

Numerical Approximation of the Elastic-Viscoplastic Contact Problem with Non-matching Meshes

Summary.  This work deals with the approximation of a time dependent variational inequality modelling the unilateral contact problem of elastic-viscoplastic bodies in a bidimensional context. The problem is approximated in the space variable with nonconforming finite element methods which allow the handling of nonmatching meshes on the contact zone. Several error estimates are established and the corresponding numerical experiments are achieved. Received Febuary 7, 2001 / Revised version received August 14, 2002 / Published online October 29, 2002 Mathematics Subject Classification (1991): 73T05     

Noncommutative simplicial complexes and the Baum—Connes conjecture

We associate a noncommutative C ^*-algebra with every locally finite simplicial complex.We determine the K-theory of these algebras and show that they can be used to obtain a conceptual explanation for the Baum—Connes conjecture. Our main technical result determines the algebra generated by the coefficients of a universal projection in an algebraic crossed product by a discrete group , in terms of such a noncommutative algebra associated with a simplicial complex defined by . Submitted: May 2001, Revised: October 2001, Revised: April 2002.     

On the Multiplicative Complexity of the Inversion and Division of Hamiltonian Quaternions

The multiplicative complexity of a finite set of rational functions is the number of essential multiplications and divisions that are necessary and sufficient to compute these rational functions. We prove that the multiplicative complexity of inversion in the division algebra \H of Hamiltonian quaternions over the reals, that is, the multiplicative complexity of the coordinates of the inverse of a generic element from \H , is exactly eight. Furthermore, we show that the multiplicative complexity of the left and right division of Hamiltonian quaternions is at least eleven. July 17, 2001. Final version received: October 8, 2001.