65 research outputs found

    Les pavages, les quasi-cristaux et le 18th problème de Hilbert

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    Le 18e problème de Hilbert est constitué de trois questions vaguement liées : Le nombre de groupes a région fondamentale (bornée) dans E mest-il fini ? Existet-il un pavage sur les paves duquel aucun groupe n’agisse de façon transitive ? Quels sont les juxtapositions les plus denses de corps congruents dans E3 ? Ces questions ont orienté la cristallographie mathématique vers de nouvell es directions et ont été excessivement efficaces: de nos jours, les quasicristaux posent des problèmes mathématiques qui se situent précisément dans les champs indiqués par Hilbert. En effet, plusieurs des nouveaux problèmes sont des reformulations de ceux de Hilbert. On a fait de considérables progrès dans les demières années, mais une question clé - comment les parties du problème sont liées entre elles - n’e st pas encore complètement comprise.Hilbert’s 18th problem consisted of three loosely related questions: Is the number of groups in En with (bounded) fundamental region finite? Does there exist a tiling on whose tiles no group acts transitively? What are the densest packings of congruent bodies in E3? These questions pointed mathematical crystallography in new directions and have been unreasonably effective: in our time quasicrystals pose mathematical problems in precisely the areas indicated by Hilbert. Indeed, many of the new problems are reformulations of Hilbert’s. Considerable progress has been made in the last few years, but a key issue-how the parts of the problem are related to one another-is still not completely understood.Peer Reviewe

    Computing layouts with deformable templates

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    On the Hausdorff Dimension of the Boundary of a Self-Similar Tile

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    In our everyday experiences, we have developed a concept of dimension, neatly expressed as integers, i.e. a point, line, square and cube as 0-, 1-, 2-, and 3-dimensional, respectively. Less intuitive are dimensions of sets such as the Koch Curve and Cantor Set. The formal definition of toplogical dimension in a metric space conforms to our intuitive concept of dimension, but it is inadequate to describe the dimension of fractals. The purpose of this thesis is to develop notions of fractal dimension and in particular, to explore Hausdorff dimension with regard to self-similar tiles in detail. Methods of calculation of Hausdorff dimension will be discussed

    Lattice setup for quantum field theory in AdS2

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    Holographic conformal field theories (CFTs) are usually studied in a limit where the gravity description is weakly coupled. By contrast, lattice quantum field theory can be used as a tool for doing computations in a wider class of holographic CFTs where nongravitational interactions in AdS become strong, and gravity is decoupled. We take preliminary steps for studying such theories on the lattice by constructing the discretized theory of a scalar field in AdS 2 and investigating its approach to the continuum limit in the free and perturbative regimes. Our main focus is on finite sublattices of maximally symmetric tilings of hyperbolic space. Up to boundary effects, these tilings preserve the triangle group as a large discrete subgroup of AdS 2 , but have a minimum lattice spacing that is comparable to the radius of curvature of the underlying spacetime. We quantify the effects of the lattice spacing as well as the boundary effects, and find that they can be accurately modeled by modifications within the framework of the continuum limit description. We also show how to do refinements of the lattice that shrink the lattice spacing at the cost of breaking the triangle group symmetry of the maximally symmetric tilings.Published versio
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