2,275 research outputs found

    Peri-abelian categories and the universal central extension condition

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    We study the relation between Bourn's notion of peri-abelian category and conditions involving the coincidence of the Smith, Huq and Higgins commutators. In particular we show that a semi-abelian category is peri-abelian if and only if for each normal subobject KXK\leq X, the Higgins commutator of KK with itself coincides with the normalisation of the Smith commutator of the denormalisation of KK with itself. We show that if a category is peri-abelian, then the condition (UCE), which was introduced and studied by Casas and the second author, holds for that category. In addition we show, using amongst other things a result by Cigoli, that all categories of interest in the sense of Orzech are peri-abelian and therefore satisfy the condition (UCE).Comment: 14 pages, final version accepted for publicatio

    Junior Recital: Tim Gray, Euphonium

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    Kemp Recital Hall Saturday Morning April 29, 1995 11:00a.m

    Senior Recital:Tim Gray, Euphonium Patricia Foltz, Piano

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    Kemp Recital Hall Sunday Afternoon April 20, 1997 3:00p.m

    van der Waals dispersion power laws for cleavage, exfoliation and stretching in multi-scale, layered systems

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    Layered and nanotubular systems that are metallic or graphitic are known to exhibit unusual dispersive van der Waals (vdW) power laws under some circumstances. In this letter we investigate the vdW power laws of bulk and finite layered systems and their interactions with other layered systems and atoms in the electromagnetically non-retarded case. The investigation reveals substantial difference between `cleavage' and `exfoliation' of graphite and metals where cleavage obeys a C2D2C_2 D^{-2} vdW power law while exfoliation obeys a C3log(D/D0)D3C_3 \log(D/D_0) D^{-3} law for graphitics and a C5/2D5/2C_{5/2} D^{-5/2} law for layered metals. This leads to questions of relevance in the interpretation of experimental results for these systems which have previously assumed more trival differences. Furthermore we gather further insight into the effect of scale on the vdW power laws of systems that simultaneously exhibit macroscopic and nanoscopic dimensions. We show that, for metallic and graphitic layered systems, the known "unusual" power laws can be reduced to standard or near standard power laws when the effective scale of one or more dimension is changed. This allows better identification of the systems for which the commonly employed `sum of C6D6C_6 D^{-6}' type vdW methods might be valid such as layered bulk to layered bulk and layered bulk to atom

    On the normality of Higgins commutators

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    In a semi-abelian context, we study the condition (NH) asking that Higgins commutators of normal subobjects are normal subobjects. We provide examples of categories that do or do not satisfy this property. We focus on the relationship with the "Smith is Huq" condition (SH) and characterise those semi-abelian categories in which both (NH) and (SH) hold in terms of reflection and preservation properties of the change of base functors of the fibration of points.Comment: 15 pages; final published versio

    CINECITY The Brighton Film Festival 2013 - 2017

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    An ediiton of CINECITY The Brighton Film Festival is presented annually. Industry and curatorial research - and raising public funding - across the year results in the final programme of activity
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