Let $D$ be a bounded domain in ${\bb R}^n$ . For a function $f$ on the boundary $\partial D$ , the Dirichlet solution of $f$ over $D$ is denoted by $H_D f$ , provided that such a solution exists. Conditions on $D$ for $H_D$ to transform a Hölder continuous function on $\partial D$ to a Hölder continuous function on $D$ with the same Hölder exponent are studied. In particular, it is demonstrated here that there is no bounded domain that preserves the Hölder continuity with exponent 1. It is also also proved that a bounded regular domain $D$ preserves the Hölder continuity with some exponent $\alpha$ , $0 < \alpha < 1$ , if and only if $\partial D$ satisfies the capacity density condition, which is equivalent to the uniform perfectness of $\partial D$ if $n = 2$ .

In this paper we point out how some recent developments in the theory of constant scalar curvature Kähler metrics can be used to clarify the existence issue for such metrics in the special case of (geometrically) ruled complex surfaces.

It is proved that the existence of zero modes of Weyl–Dirac operators is a rare phenomenon. An estimate of the multiplicity is given in term of the magnetic potential.

Let $X$ be a non-singular algebraic curve of genus $g\ge 2,\;n\ge 2$ an integer, $\xi$ a line bundle over $X$ of degree $d>2n(g-1)$ with $(n,d)=1$ and ${\cal M}_\xi$ the moduli space of stable bundles of rank $n$ and determinant $\xi$ over $X$ . It is proved that the Picard bundle ${\cal W}_\xi$ is stable with respect to the unique polarisation of ${\cal M}_\xi$ .

Let F be a field, and let Σn be the symmetric group on n letters. In this paper we address the following question: given two irreducible FΣn-modules D1 and D2 of dimensions greater than 1, can it happen that D1 [otimes ] D2 is irreducible? The answer is known to be ‘no’ if char F = 0 [12] (see also [2] for some generalizations). So we assume from now on that F has positive characteristic p. The following conjecture was made in [4].

CONJECTURE. Let D1and D2be two irreducible FΣn-modules of dimensions greater than 1. Then D1 [otimes ] D2 is irreducible if and only if p = 2, n = 2 + 4l for some positive integer l; one of the modules corresponds to the partition (2l + 2, 2l) and the other corresponds to a partition of the form (n − 2j − 1, 2j + 1), 0 [les ] j < l. Moreover, in the exceptional cases, one has

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The main result of this paper is the following theorem, which establishes a big part of the conjecture.

This paper proves bounds for the commutator width of a wreath product of two groups. As a corollary, it is shown that the commutator width of finite perfect linear groups of dimension 15 is unbounded. It follows that the covering number of these groups is unbounded. On the other hand, the commutator width of iterated wreath products of nonabelian finite simple groups is bounded by an absolute constant.

The classical Mikhlin–Hörmander multiplier theorem is generalised to the context of discrete groups of polynomial volume growth.

the degree defined by p. benevieri and m. furi (see ‘a simple notion of orientability for fredholm maps of index zero between banach manifolds and degree theory’, ann. sci. math. québec 22 (1998) 131–148) is used here to obtain some sharp lower bounds for the number of solutions of the $\lambda$-sections of the compact components of the set of non-trivial solutions of $\mf{f}(\lambda,x)=0$, where $\mf{f}$ is a $\cal{c}^1$ fredholm map of index 1 such that $\mf{f}(\lambda,0)=0$ for all $\lambda\in\mathbb{r}$. these bounds are given in terms of the parity of the linearized fredholm family $d_2\mf{f}(\cdot,0)$. the parity is a local invariant measuring the change of the orientation of $d_2\mf{f}(\lambda,0)$ as $\lambda$ crosses an interval. the set of eigenvalues of $d_2\mf{f}(\cdot,0)$ is not assumed to be discrete. therefore, even in the classical situation when $\mf{f}$ is a compact perturbation of the identity, the results presented here are completely new.

For the classical groups, Kraft and Procesi have resolved the question of which nilpotent orbits have closures that are normal and which do not, with the exception of the very even orbits in $D_{2l}$ that have partitions of the form $(a^{2k}, b^2)$ for $a\,{>}\,b$ even natural numbers satisfying $a k\,{+}\,b\,{=}\,2 l$.

In this paper, these orbits are shown to have normal closure.

Global convergence is established in this paper for monotone and subhomogeneous discrete dynamical systems on product Banach spaces. This result is then used to obtain the asymptotic periodicity of solutions to a class of periodic and cooperative reaction-diffusion systems.

In this paper, we give some complete characterizations of the primitive of a Henstock integrable function in Euclidean space.

Upper bounds are obtained for the heat content and the torsional rigidity of a complete Riemannian manifold $M$, assuming a Hardy inequality for the Dirichlet Laplacian on $M$.

In his book Abelian groups, L. Fuchs raised the question as to whether, in general, in the factorization of a finite (cyclic) abelian group one factor may always be replaced by some subgroup. The answer turned out to be negative in general, but positive in certain cases. In this paper the complete answer for cyclic groups is given. In all previously unsolved cases, the answer turns out to be positive. It is shown that a cyclic group has the property that in every factorization, one factor may be replaced by a subgroup if and only if the group has order equal to the product of a prime and a square-free integer. Certain results are also given in non-cyclic cases.

It is shown that the method of estimation of exponential sums with nonlinear recurring sequences, invented by the authors in a recent series of works, can be applied to estimating sums of multiplicative characters as well. As a consequence, results are obtained about the distribution of power residues and primitive elements in such sequences.

Let $E$ be an elliptic curve over a finitely generated infinite field $K$. Let $K^{\rm s}$ denote a separable closure of $K$, $\sigma$ an element of the Galois group $G_{K}\,{=}\,\hbox{Gal}(K^{\rm s}/K)$, and $K^{\rm s}(\sigma)$ the invariant subfield of $K^{\rm s}$. If the characteristic of $K$ is not 2 and $\sigma$ belongs to a suitable open subgroup of $G_K$, then $E(K^{\rm s}(\sigma))$ has infinite rank.Partially supported by the Sloan Foundation and by NSF Grant DMS 97-27553.

This paper proves the rationality of Poincaré series whose coefficients are defined using the number of conjugacy classes in a system of finite groups defined as finite images of linear groups over $\Bbb{Z}_{p}$ modulo natural congruence subgroups.

We prove that each interval of the lattice [Escr ] of c.e. sets under inclusion is either a boolean algebra or has an undecidable theory. This solves an open problem of Maass and Stob [11]. We develop a method to prove undecidability by interpreting ideal lattices, which can also be applied to degree structures from complexity theory. We also answer a question left open in [7] by giving an example of a non-definable subclass of [Escr ]* which has an arithmetical index set and is invariant under automorphisms.

Let $2\le p <\infty$, and let $X$ be a complex Banach space. It is shown that $X$ is $p$-uniformly PL-convex if and only if there exists $\lambda >0$ such that $ \|f\|_{H^p(X)}\,{\ge}\, (\|f(0)\|^p+\lambda\int_{\mathbb D} (1-|z|^2)^{p-1}\|f^{\prime}(z)\|^p\,dA(z))^{1/p}$, for all $f\in H^p(X)$. Applications to embeddings between vector-valued BMOA spaces defined via Poisson integral or Carleson measures are provided.

Given a field k and a finite group G acting on the rational function field k(X1, . . ., Xn) as a group of k-automorphisms, an important Noether's problem asks whether the invariant subfieldformula here is purely transcendental over k.

In [1], Hirano gives a method for constructing families of curves with a large number of singularities. The idea is to consider an abelian covering of ℙ2 ramified along three lines in general position, and to take the pull-back of a curve C intersecting the lines non-generically. Similar constructions are used by Shimada in [10] and Oka in [8]. We apply this method for the case where C is a conic, constructing a family of curves with the following asymptotic behaviour (see [9]):

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The goal of this paper is to calculate the fundamental group for the curves in this family as well as their Alexander polynomial.