Interior regularity criteria in weak spaces for the Navier-Stokes equations

We study the interior regularity of weak solutions of the incompressible Navier-Stokes equations in ×(0,T), where and 0<T<. The local boundedness of a weak solution u is proved under the assumption that is sufficiently small for some (r,s) with and 3r<. Our result extends the well-known criteria of Serrin (1962), Struwe (1988) and Takahashi (1990) to the weak space-time spaces.Mathematics Subject Classification (2000): 35Q30, 76N10     

Restriction of the cotangent bundle to elliptic curves and Hilbert-Kunz functions

We describe the possible restrictions of the cotangent bundle to an elliptic curve . We apply this in positive characteristic to the computation of the Hilbert-Kunz function of a homogeneous R₊-primary ideal in the graded section ring .     

Infinitely many solutions of a semilinear problem for the Heisenberg Laplacian on the Heisenberg group

We study the semilinear equationwhere is the Heisenberg Laplacian and is the Heisenberg group. The function f C²(×, ) is supposed to satisfy some (subcritical) growth conditions and to be left invariant under the action of the subgroup of consisting of points with integer coordinates.. We show the existence of infinitely many solutions in the space S₁²(), which is the Heisenberg analogue of the Sobolev space W^1,2(^N).Mathematics Subject Classification (2000): 22E30, 22E27     

Diophantine inequalities involving several power sums

Let denote the ring of power sums, i.e. complex functions of the form for some and _iA, where is a multiplicative semigroup. Moreover, let We consider Diophantine inequalities of the form where >1 is a quantity depending on the dominant roots of the power sums appearing as coefficients in F(n,y), and show that all its solutions have y parametrized by some power sums from a finite set. This is a continuation of the work of Corvaja and Zannier [4–6] and of the authors [10, 18] on such problems.Mathematics Subject Classification (2000):11D45,11D61Revised version: 6 May 2004     

On the commutativity of <Emphasis Type="Italic">C</Emphasis>* -algebras

Let be a C* -algebra. Let f be a non-constant complex-valued continuous function defined on a closed interval I. We shall show that f densely spans As an application, is commutative if f(x)f(y)=f(y)f(x) for all self-adjoint elements x and y in with spectrums contained in I.Mathematics Subject Classification (1991):Primary 46L05     

Analysis of nonsmooth vector-valued functions associated with second-order cones

Let be the Lorentz/second-order cone in . For any function f from to , one can define a corresponding function f^soc(x) on by applying f to the spectral values of the spectral decomposition of x with respect to . We show that this vector-valued function inherits from f the properties of continuity, (local) Lipschitz continuity, directional differentiability, Fréchet differentiability, continuous differentiability, as well as (-order) semismoothness. These results are useful for designing and analyzing smoothing methods and nonsmooth methods for solving second-order cone programs and complementarity problems.Mathematics Subject Classification (1991): 26A27, 26B05, 26B35, 49J52, 90C33, 65K05     

L p -Estimates for the Navier–Stokes Equations for Steady Compressible Flow

We consider the Navier–Stokes equations for compressible isentropic flow in the steady three-dimensional case. The pressure and the kinetic energy are estimated uniformly in L^q with being the density. This is an improvement of known estimates in the case Mathematics Subject Classification (2000): 35Q30, 76N10     

The Rees algebra of a positive normal affine semigroup ring

Let R be a positive normal affine semigroup ring of dimension d and let be the maximal homogeneous ideal of R. We show that the integral closure of is equal to for all n ∈ℕ with n ≥ d − 2. From this we derive that the Rees algebra R[t] is normal in case that d ≤ 3. If emb dim(R) = d + 1, we can give a necessary and sufficient condition for R[t] to be normal.     

2-universal -lattices over real quadratic fields

Let be a real quadratic field with m a square-free positive rational integer, and be the ring of integers in F. An -lattice L on a totally positive definite quadratic space V over F is called r-universal if L represents all totally positive definite -lattices l with rank r over . We prove that there exists no 2-universal -lattice over F with rank less than 6, and there exists a 2-universal -lattice over F with rank 6 if and only if m=2, 5. Moreover there exists only one 2-universal -lattice with rank 6, up to isometry, over .     

Inducing W-graphs II

Let be the Hecke algebra associated with a Coxeter group W, and the Hecke algebra associated with W_J, a parabolic subgroup of W. In [5] an algorithm was described for the construction of a W-graph for an induced module where V is an -module derived from a W_J-graph. This note is a continuation of [5], and involves the following results:[] inducing ordered and bipartite W-graphs;[] the relationship between the cell decomposition of a W_J-graph and the cell decomposition of the corresponding induced W-graph;[] a Mackey-type formula for the restriction of an induced W-graph;[] a formula relating the polynomials used in the construction of induced W-graphs to Kazhdan-Lusztig polynomials.The result on cells is a version of a Theorem of M. Geck [4], dealing with cells in W (allowing unequal parameters).Mathematics Subject Classification (2000): Primary 20C     

Fast convolution with radial kernels at nonequispaced knots

Summary. We develop a new algorithm for the fast evaluation of linear combinations of radial functions based on the recently developed fast Fourier transform at nonequispaced knots. For smooth kernels, e.g. the Gaussian, our algorithm requires arithmetic operations. In case of singular kernels an additional regularization procedure must be incorporated and the algorithm has the arithmetic complexity if either the points y_j or the points x_k are reasonably uniformly distributed. We prove error estimates to obtain clues about the choice of the involved parameters and present numerical examples for various singular and smooth kernels in two dimensions.Mathematics Subject Classification (2000): 65T40, 65T50, 65F30Revised version received December 3, 2003     

On the exact Hausdorff dimension of the set of Liouville numbers

Let denote the set of Liouville numbers. For a dimension function h, we write () for the h-dimensional Hausdorff measure of . In this paper we locate the exact cut-point at which the Hausdorff measure of drops from infinity to zero. Namely, if h is a dimension function that increases faster than any power function near 0, then ()=, and if h is a dimension function that increases slower than some power function near 0, then ()=0. This answers a question asked by R. D. Mauldin.Mathematics Subject Classification (2000): 28A80     

Tannaka duality on quotient stacks

Let = [X/G] be the quotient stack of a scheme X by an affine group scheme G over a field k. Assume that there is a line bundle on whose underlying line bundle on X is very ample. Let VB() be the category of vector bundles on .We show that is canonically isomorphic to the stack of fiber functors on VB(). This is an analogue of the Tannaka duality for affine groups. Partially supported by CNCSIS contract no. 33079/2004     

Conjugacy classes of affine automorphisms of and linear automorphisms of ℙ n in the Cremona groups

We describe the conjugacy classes of affine automorphisms in the group Aut(n,) (respectively Bir()) of automorphisms (respectively of birational maps) of . From this we deduce also the classification of conjugacy classes of automorphisms of ℙⁿ in the Cremona group Bir().     

Eilenberg-Moore spectral sequence calculation of function space cohomology

The purpose of this article is to introduce an Eilenberg-Moore spectral sequence converging to the cohomology algebra of a function space with an adjunction space as its source. Computability of the spectral sequence is shown by determining explicitly the mod p cohomology algebra of the function space of maps from a non-orientable surface S to the classifying space of a simply-connected Lie group G whose homology is p-torsion free. Let M be a closed orientable 3-dimensional manifold. Applying the spectral sequence obtained from a Heegaard splitting of the manifold M, we also prove that is a direct summand of .Mathematics Subject Classification (2000):55T20, 57T35This research was partially supported by a Grant-in-Aid for Scientific Research (C)14540095 from Japan Society for the Promotion of Science.     

The theory of energy for sub-Laplacians with an application to quasi-continuity

In this paper, we provide a suitable theory for the energy where μ is a Radon measure and Γ is the fundamental solution of a sub-Laplacian on a stratified group As a significant application, we prove the quasi-continuity of superharmonic functions related to . The proofs are elementary and mostly rely on the use of appropriate mean-value formulas and mean-integral operators relevant to the Potential Theory for .     

Estimates for stable hypersurfaces of prescribed F-mean curvature

We consider immersed hypersurfaces :Mⁿ→ℝⁿ⁺¹ with prescribed anisotropic mean curvature . Such hypersurfaces can be characterized as critical points of parametric functionals of the type with an elliptic Lagrangian F depending on normal directions and a smooth vectorfield Q satisfying . We establish curvature estimates for stable hypersurfaces of dimension n≤5, provided F is C³-close to the area integrand.     

Manifolds of infinite topological type with integrable geodesic flows

Let (M,k) be a complete surface of constant negative curvature (resp. an -geometric 3-manifold). This paper constructs a complete riemannian 8-manifold (resp. 9-manifold) (,h) such that is homotopy equivalent to M, the geodesic flow of h is completely integrable and there is a riemannian embedding (M,k)(,h). This embeds the geodesic flow of (M,k) as a subsystem of an integrable geodesic flow. Amongst the manifolds is an 8-dimensional manifold whose fundamental group is the free group on countably many generators.Thanks to Keith Burns and Leo Jonker for comments. Research partially supported by the Natural Sciences and Engineering Research Council of Canada.Mathematics Subject Classification (2000): 58F17, 53D25, 37D40     

Heat kernels on metric spaces and a characterisation of constant functions

Using the Dirichlet forms theory, we prove that when the locally compact measure metric space (X,,m) is the state space of a Markov process with transition density p(t,x,y) bounded from the above by where is a function satisfying certain integrability condition, then the following statement holds: when u L²(X) and then u is a constant function.This work is partially supported by a KBN grant no. 2-PO3A-028-22.Mathematics Subject Classification (2000): primary 60J35, secondary 46E35     

On the logarithmic plurigenera of complements of plane curves

Let B be a (not necessarily irreducible) plane curve in ². In the present article, we prove that if and only if Moreover, we determine the curve B when and Mathematics Subject Classification (2000): 14R05, 14H50, 14J26