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1.
Let be a local complete ring. For an -module the canonical ring map is in general neither injective nor surjective; we show that it is bijective for every local cohomology module if for every ( an ideal of ); furthermore the same holds for the Matlis dual of such a module. As an application we prove new criteria for an ideal to be a set-theoretic complete intersection.
2.
Christopher B. Croke 《Proceedings of the American Mathematical Society》2008,136(2):715-717
We consider Riemannian metrics on the -sphere for such that the distance between any pair of antipodal points is bounded below by 1. We show that the volume can be arbitrarily small. This is in contrast to the -dimensional case where Berger has shown that .
3.
It is an observation due to J. J. Kohn that for a smooth bounded pseudoconvex domain in there exists such that the -Neumann operator on maps (the space of -forms with coefficient functions in -Sobolev space of order ) into itself continuously. We show that this conclusion does not hold without the smoothness assumption by constructing a bounded pseudoconvex domain in , smooth except at one point, whose -Neumann operator is not bounded on for any .
4.
Alexander S. Kechris Todor Tsankov 《Proceedings of the American Mathematical Society》2008,136(2):687-697
In this paper, we study the connections between properties of the action of a countable group on a countable set and the ergodic theoretic properties of the corresponding generalized Bernoulli shift, i.e., the corresponding shift action of on , where is a measure space. In particular, we show that the action of on is amenable iff the shift has almost invariant sets.
5.
W. Kucharz 《Proceedings of the American Mathematical Society》2008,136(1):55-60
By the Nash-Tognoli theorem, each compact smooth manifold is diffeomorphic to a nonsingular real algebraic set, called an algebraic model of . We construct algebraic models of with controlled behavior of the group of cohomology classes represented by algebraic subsets of .
6.
We refine our earlier work on the existence and uniqueness of structures on -theoretic spectra to show that the connective versions of real and complex -theory as well as the connective Adams summand at each prime have unique structures as commutative -algebras. For the -completion we show that the McClure-Staffeldt model for is equivalent as an ring spectrum to the connective cover of the periodic Adams summand . We establish a Bousfield equivalence between the connective cover of the Lubin-Tate spectrum and .
7.
We show that there is an abelian group structure on the orbit set of ``squares' of unimodular rows of length over a commutative ring of stable dimension when , odd and also an abelian group structure on the orbit set of ``fourth powers' of unimodular rows of length over a commutative ring of stable dimension when , even.
8.
Paola Bonacini 《Proceedings of the American Mathematical Society》2008,136(7):2289-2297
If is an integral curve and an algebraically closed field of characteristic 0, it is known that the points of the general plane section of are in uniform position. From this it follows easily that the general minimal curve containing is irreducible. If char, the points of may not be in uniform position. However, we prove that the general minimal curve containing is still irreducible.
9.
This paper presents a property of geometric and topological nature of Gateaux differentiability points and Fréchet differentiability points of almost CL-spaces. More precisely, if we denote by a maximal convex set of the unit sphere of a CL-space , and by the cone generated by , then all Gateaux differentiability points of are just n-s, and all Fréchet differentiability points of are (where n-s denotes the non-support points set of ).
10.
M. Hellus 《Proceedings of the American Mathematical Society》2008,136(7):2313-2321
For a Noetherian ring we call an -module cofinite if there exists an ideal of such that is -cofinite; we show that every cofinite module satisfies . As an application we study the question which local cohomology modules satisfy . There are two situations where the answer is positive. On the other hand, we present two counterexamples, the failure in these two examples coming from different reasons.
11.
Vincenzo Di Gennaro 《Proceedings of the American Mathematical Society》2008,136(3):791-799
Fix integers such that and , and let be the set of all integral, projective and nondegenerate curves of degree in the projective space , such that, for all , does not lie on any integral, projective and nondegenerate variety of dimension and degree . We say that a curve satisfies the flag condition if belongs to . Define where denotes the arithmetic genus of . In the present paper, under the hypothesis , we prove that a curve satisfying the flag condition and of maximal arithmetic genus must lie on a unique flag such as , where, for any , denotes an integral projective subvariety of of degree and dimension , such that its general linear curve section satisfies the flag condition and has maximal arithmetic genus . This proves the existence of a sort of a hierarchical structure of the family of curves with maximal genus verifying flag conditions.
12.
Stephen J. Gardiner Mary Hanley 《Proceedings of the American Mathematical Society》2003,131(3):773-779
Let denote a relatively closed subset of the unit ball of . The purpose of this paper is to characterize those sets which have the following property: any harmonic function on which satisfies on (where 0$">) can be locally uniformly approximated on by a sequence of harmonic polynomials which satisfy the same inequality on . This answers a question posed by Stray, who had earlier solved the corresponding problem for holomorphic functions on the unit disc.
13.
Yasuhiro Yabuki 《Proceedings of the American Mathematical Society》2008,136(1):301-310
According to Schoen and Yau (1988), an extensive class of conformally flat manifolds is realized as Kleinian manifolds. Nayatani (1997) constructed a metric on a Kleinian manifold which is compatible with the canonical flat conformal structure. He showed that this metric has a large symmetry if is a complete metric. Under certain assumptions including the completeness of , the isometry group of coincides with the conformal transformation group of . In this paper, we show that may have a large symmetry even if is not complete. In particular, every conformal transformation is an isometry when corresponds to a geometrically finite Kleinian group.
14.
Paul J. Szeptycki 《Proceedings of the American Mathematical Society》2007,135(7):2273-2282
For a family of sets , and a set , is said to be a transversal of if and for each . is said to be a Bernstein set for if for each . Erdos and Hajnal first studied when an almost disjoint family admits a set such as a transversal or Bernstein set. In this note we introduce the following notion: a family of sets is said to admit a -transversal if can be written as such that each admits a transversal. We study the question of when an almost disjoint family admits a -transversal and related questions.
15.
Anders J. Frankild Sean Sather-Wagstaff 《Proceedings of the American Mathematical Society》2008,136(7):2303-2312
Motivated by work of C. U. Jensen, R.-O. Buchweitz, and H. Flenner, we prove the following result. Let be a commutative noetherian ring and an ideal in the Jacobson radical of . Let be the -adic completion of . If is a finitely generated -module such that for all , then is -adically complete.
16.
Radu Miculescu Alexandru Mihail 《Proceedings of the American Mathematical Society》2008,136(2):587-592
It is known that Lipscomb's space can be imbedded in Hilbert's space . Let be the imbedded version of endowed with the -induced topology. We show how to construct as the attractor of an iterated function system containing an infinite number of affine transformations of . In this way we answer an open question of J.C. Perry.
17.
Hamidreza Rahmati 《Proceedings of the American Mathematical Society》2008,136(2):467-474
Let be a -dimensional local ring, with maximal ideal , containing a field and let be a system of parameters for . If and the local cohomology module is finitely generated, then there exists an integer such that the modules have the same Betti numbers, for all .
18.
A. Lazarev 《Proceedings of the American Mathematical Society》2008,136(2):735-745
We revisit Stasheff's construction of a minimal Lie-Quillen model of a simply-connected closed manifold using the language of infinity-algebras. This model is then used to construct a graded Lie bracket on the equivariant homology of the free loop space of minus a point similar to the Chas-Sullivan string bracket.
19.
Lisa Orloff Clark Astrid an Huef 《Proceedings of the American Mathematical Society》2008,136(2):623-634
Suppose is a second countable, locally compact, Hausdorff, principal groupoid with a fixed left Haar system. We define a notion of integrability for groupoids and show is integrable if and only if the groupoid -algebra has bounded trace.
20.
Sé rgio Mendonç a Heudson Mirandola 《Proceedings of the American Mathematical Society》2008,136(3):1065-1070
Let be an immersion of an -dimensional connected manifold in an -dimensional connected complete Riemannian manifold without conjugate points. Assume that the union of geodesics tangent to does not cover . Under these hypotheses we have two results. The first one states that is simply connected provided that the universal covering of is compact. The second result says that if is a proper embedding and is simply connected, then is a normal graph over an open subset of a geodesic sphere. Furthermore, there exists an open star-shaped set such that is a manifold with the boundary .