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71.
The main objective of this short note is to give a sufficient condition for a non constant function k to be Q curvature candidate for a conformal metric on a closed Riemannian manifold with the null Q-curvature. In contrast to the prescribed scalar curvature on the two-dimensional flat tori, the condition we provided is
not necessary as some examples show.
The second author would like to thank Department of Mathematics, University of Paris XII for their invitation, hospitality
and financial support during his visit. His research is partially supported by NUS research grant: R-146-000-077-112. 相似文献
72.
Thomas Strömberg 《Indagationes Mathematicae》2009,20(4):619-629
The subject of this paper is the generation of singularities of solutions of Hamilton-Jacobi equations set in (0, ∞) × ? fordataofclass C∞. Shockwaves originate from conjugate points. To show sharpness of a known Hausdorff estimate, an example is given in which the set of conjugate, regular points includes uncountably many affine subspaces of dimension n − 1. 相似文献
73.
We discuss the identification problem for current dipoles in a spherically symmetric conductor. This mathematical model is used for a biomedical inverse problem such as the source current identification for the human brain activity. We have already proposed a direct identification method for this inverse source problem using observations of the magnetic fields outside of the conductor. One of the difficulties of current dipole identification using the magnetic fields is caused by the fact that magnetic field does not include any information about the radial component of dipole moments. In this paper, we consider an improvement of the direct method to identify both radial and tangential components of current dipole moments by combining electric and magnetic observation data. Furthermore, our approach is effective in the case where the number of dipoles is unknown. 相似文献
74.
The key equations of BiCGStab are summarised to show its connections with Padé and vector-Padé approximation. These considerations lead naturally to stabilised vector-Padé approximation of a vector-valued function (VPAStab), and an algorithm for the acceleration of convergence of a linearly generated sequence of vectors. A generalisation of this algorithm for the acceleration of convergence of a nonlinearly generated system is proposed here, and comparative numerical results are given. 相似文献
75.
T. Arias-Marco 《Differential Geometry and its Applications》2007,25(1):29-34
In this short note we correct the (incomplete) classification theorem from [F. Podestà, A. Spiro, Four-dimensional Einstein-like manifolds and curvature homogeneity, Geom. Dedicata 54 (1995) 225-243], we improve a result from [P. Bueken, L. Vanhecke, Three- and four-dimensional Einstein-like manifolds and homogeneity, Geom. Dedicata 75 (1999) 123-136] and we announce the final solution of the classification problem for 4-dimensional homogeneous D'Atri spaces. 相似文献
76.
Masatoshi Enomoto 《Advances in Mathematics》2006,201(2):263-317
We study the relative position of several subspaces in a separable infinite-dimensional Hilbert space. In finite-dimensional case, Gelfand and Ponomarev gave a complete classification of indecomposable systems of four subspaces. We construct exotic examples of indecomposable systems of four subspaces in infinite-dimensional Hilbert spaces. We extend their Coxeter functors and defect using Fredholm index. The relative position of subspaces has close connections with strongly irreducible operators and transitive lattices. There exists a relation between the defect and the Jones index in a type II1 factor setting. 相似文献
77.
Manfred Peter 《Monatshefte für Mathematik》2002,135(1):37-57
An asymptotic formula is proved for the number of lattice points in large threedimensional convex bodies. In contrast to
the usual assumption the Gaussian curvature of the boundary may vanish at non-isolated points. It is only assumed that the
second fundamental form vanishes at isolated points where the tangent plane is rational and some ellipticity condition holds.
Received 25 April 2001 相似文献
78.
Felix Finster Oliver C. Schnürer 《Calculus of Variations and Partial Differential Equations》2002,15(1):67-80
We prove an existence theorem for convex hypersurfaces of prescribed Gau? curvature in the complement of a compact set in
Euclidean space which are close to a cone.
Received: 23 February 2001 / Accepted: 11 May 2001 / Published online: 19 October 2001 相似文献
79.
This work is part of a doctoral thesis, written under the supervision of Prof. A. Berman. It was supported by the Fund for Promotion of Research at the Technion. 相似文献
80.
D. S. Lubinsky 《Constructive Approximation》2002,18(2):285-308
Let a≥ 0 , ɛ >0 . We use potential theory to obtain a sharp lower bound for the linear Lebesgue measure of the set Here P is an arbitrary polynomial of degree ≤ n . We then apply this to diagonal and ray Padé sequences for functions analytic (or meromorphic) in the unit ball. For example,
we show that the diagonal \left{ [n/n]\right}
n=1
∞
sequence provides good approximation on almost one-eighth of the circles centre 0 , and the \left{ [2n/n]\right}
n=1
∞
sequence on almost one-quarter of such circles.
July 18, 2000. Date revised: . Date accepted: April 19, 2001. 相似文献