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31.
Oleg Bogopolski 《Geometriae Dedicata》2002,94(1):63-89
Let T be a closed surface. It is proven that any decomposition of 1(T,x) into an amalgamated product (or, more generally, into the fundamental group of a finite graph of groups) with f.g. edge group(s) is almost geometric. A problem of H. Zieschang is solved and the edge rigidity property is investigated. 相似文献
32.
In this paper we prove the smoothness of solutions of a class of elliptic-parabolic nonlinear Levi type equations, represented as a sum of squares plus a vector field. By means of a freezing method the study of the operator is reduced to the analysis of a family of left invariant operators on a free nilpotent Lie group. The fundamental solution of the operator is used as a parametrix of the fundamental solution of the Levi operator, and provides an explicit representation formula for the solution of the given equation. Differentiating this formula and applying a bootstrap method, we prove that the solution is .
33.
J M Landsberg 《Compositio Mathematica》1999,118(2):189-201
Let XP be a variety (respectively an open subset of an analytic submanifold) and let xX be a point where all integer valued differential invariants are locally constant. We show that if the projective second fundamental form of X at x is isomorphic to the second fundamental form of a point of a Segre P× P, n,m2, a Grassmaniann G(2,n+2), n4, or the Cayley plane OP2, then X is the corresponding homogeneous variety (resp. an open subset of the corresponding homogeneous variety). The case of the Segre P2×P2 had been conjectured by Griffiths and Harris in [GH]. If the projective second fundamental form of X at x is isomorphic to the second fundamental form of a point of a Veronese v2(P) and the Fubini cubic form of X at x is zero, then X=v2 (P) (resp. an open subset of v2(P)). All these results are valid in the real or complex analytic categories and locally in the C category if one assumes the hypotheses hold in a neighborhood of any point x. As a byproduct, we show that the systems of quadrics I2(P P) S2C, I2(P1× P) S2C and I2(S5) S2C16 are stable in the sense that if A S* is an analytic family such that for t0,AA, then A0A. We also make some observations related to the Fulton–:Hansen connectedness theorem. 相似文献
34.
This paper presents the integral representations of the displacement and rotation fields of the micropolar continuum, and the regularized integral representations of the traction and couple vector. Thus the boundary integral equations and the boundary integro-differential equations are derived. In addition, the formulation for crack problems is given by both the boundary integral equations and the boundary integro-differential equations. 相似文献
35.
We show that every finite subgroup of U(2) is contained with index two in a group generated by involutions fixing Lagrangian planes. We describe fundamental domains for their action on
related to the configuration of these Lagrangian planes. 相似文献
36.
In the early 1960s of the 20th century de Broglie was able to explain the cosmological observable red shift, without ad hoc assumptions. Starting from basic quantum considerations he developed his tired light model for the photon. This model explains in a single and beautiful causal way the cosmological redshift without need of assuming the Big Bang and consequently a beginning for the universe. Evidence coming from Earth sciences seems also to confirm these ideas and furthermore concrete proposal of laboratorial scale experiments that can test the model are reviewed. 相似文献
37.
It is shown that the class of perturbations of the semigroup of shifts on by unitary cocycles with the property (where is the Hilbert-Schmidt class) contains strongly continuous semigroups of isometric operators, whose unitary parts possess spectral decompositions with the measure being singular with respect to the Lebesgue measure. Thus, we describe also the subclass of strongly continuous groups of unitary operators that are perturbations of the group of shifts on by Markovian cocycles with the property .
38.
Andrea Bonfiglioli Ermanno Lanconelli Francesco Uguzzoni 《Transactions of the American Mathematical Society》2004,356(7):2709-2737
We construct the fundamental solutions and for the non-divergence form operators and , where the 's are Hörmander vector fields generating a stratified group and is a positive-definite matrix with Hölder continuous entries. We also provide Gaussian estimates of and its derivatives and some results for the relevant Cauchy problem. Suitable long-time estimates of allow us to construct using both -saturation and approximation arguments.
39.
For two covariant differential *-calculi, the twisted cyclic cocycle associated with the volume form is represented in terms of commutators
for some self-adjoint operator
and some *-representation of the underlying *-algebra. 相似文献
40.
We study the class of cyclically presented groups which contain Fibonacci groups and Sieradski groups. Conditions are specified for these groups to be finite, pairwise isomorphic, or aspherical. As a partial answer to the question of Cavicchioli, Hegenbarth, and Repov, it is stated that there exists a wide subclass of groups with an odd number of generators cannot appear as fundamental groups of hyperbolic three-dimensional manifolds of finite volume. 相似文献