1,475 research outputs found

    Cohomology and profinite topologies for solvable groups of finite rank

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    Assume GG is a solvable group whose elementary abelian sections are all finite. Suppose, further, that pp is a prime such that GG fails to contain any subgroups isomorphic to Cp∞C_{p^\infty}. We show that if GG is nilpotent, then the pro-pp completion map G→G^pG\to \hat{G}_p induces an isomorphism H∗(G^p,M)→H∗(G,M)H^\ast(\hat{G}_p,M)\to H^\ast(G,M) for any discrete G^p\hat{G}_p-module MM of finite pp-power order. For the general case, we prove that GG contains a normal subgroup NN of finite index such that the map H∗(N^p,M)→H∗(N,M)H^\ast(\hat{N}_p,M)\to H^\ast(N,M) is an isomorphism for any discrete N^p\hat{N}_p-module MM of finite pp-power order. Moreover, if GG lacks any Cp∞C_{p^\infty}-sections, the subgroup NN enjoys some additional special properties with respect to its pro-pp topology.Comment: This paper supersedes arXiv:1009.2645v5: the two theorems in the introduction to the latter paper are both corollaries to Theorem 1.1 in the present paper. In the second version, Theorem 1.1 is expressed in a slightly more general form than in the first versio

    Groups with the same cohomology as their pro-pp completions

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    For any prime pp and group GG, denote the pro-pp completion of GG by G^p\hat{G}^p. Let C\mathcal{C} be the class of all groups GG such that, for each natural number nn and prime number pp, Hn(Gp^,Z/p)≅Hn(G,Z/p)H^n(\hat{G^p},\mathbb Z/p)\cong H^n(G, \mathbb Z/p), where Z/p\mathbb Z/p is viewed as a discrete, trivial G^p\hat{G}^p-module. In this article we identify certain kinds of groups that lie in C\mathcal{C}. In particular, we show that right-angled Artin groups are in C\mathcal{C} and that this class also contains some special types of free products with amalgamation.Comment: The revisions in the second version pertain to the exposition: the proof of Prop. 1.1, in particular, now includes more details. The third version includes a proof that right-angled Artin groups are residually pp-finite for every prime $p

    The quarter-point quadratic isoparametric element as a singular element for crack problems

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    The quadratic isoparametric elements which embody the inverse square root singularity are used for calculating the stress intensity factors at tips of cracks. The strain singularity at a point or an edge is obtained in a simple manner by placing the mid-side nodes at quarter points in the vicinity of the crack tip or an edge. These elements are implemented in NASTRAN as dummy elements. The method eliminates the use of special crack tip elements and in addition, these elements satisfy the constant strain and rigid body modes required for convergence
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