673 research outputs found

    Restoring Prosperity: The State Role in Revitalizing America's Older Industrial Cities

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    Presents a five-part agenda and organizing plan to reinvigorate the nation's older industrial cities, and aims to mobilize governors, legislative leaders, and local constituencies toward advancing urban reform

    A force balance system for the measurement of skin friction drag force in the presence of large vibrations and temperatures

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    Design of counterbalance system for skin friction drag measurements on hypersonic vehicle

    Multi-component Force Balance Control Systems Final Report

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    Technique and apparatus for drag, lift, and pitch force measurements in hypersonic wind tunnel

    Cohomology of groups of diffeomorphims related to the modules of differential operators on a smooth manifold

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    Let MM be a manifold and TMT^*M be the cotangent bundle. We introduce a 1-cocycle on the group of diffeomorphisms of MM with values in the space of linear differential operators acting on C(TM).C^{\infty} (T^*M). When MM is the nn-dimensional sphere, SnS^n, we use this 1-cocycle to compute the first-cohomology group of the group of diffeomorphisms of SnS^n, with coefficients in the space of linear differential operators acting on contravariant tensor fields.Comment: arxiv version is already officia

    The definability criterions for convex projective polyhedral reflection groups

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    Following Vinberg, we find the criterions for a subgroup generated by reflections \Gamma \subset \SL^{\pm}(n+1,\mathbb{R}) and its finite-index subgroups to be definable over A\mathbb{A} where A\mathbb{A} is an integrally closed Noetherian ring in the field R\mathbb{R}. We apply the criterions for groups generated by reflections that act cocompactly on irreducible properly convex open subdomains of the nn-dimensional projective sphere. This gives a method for constructing injective group homomorphisms from such Coxeter groups to \SL^{\pm}(n+1,\mathbb{Z}). Finally we provide some examples of \SL^{\pm}(n+1,\mathbb{Z})-representations of such Coxeter groups. In particular, we consider simplicial reflection groups that are isomorphic to hyperbolic simplicial groups and classify all the conjugacy classes of the reflection subgroups in \SL^{\pm}(n+1,\mathbb{R}) that are definable over Z\mathbb{Z}. These were known by Goldman, Benoist, and so on previously.Comment: 31 pages, 8 figure

    Consistent Anisotropic Repulsions for Simple Molecules

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    We extract atom-atom potentials from the effective spherical potentials that suc cessfully model Hugoniot experiments on molecular fluids, e.g., O2O_2 and N2N_2. In the case of O2O_2 the resulting potentials compare very well with the atom-atom potentials used in studies of solid-state propertie s, while for N2N_2 they are considerably softer at short distances. Ground state (T=0K) and room temperatu re calculations performed with the new NNN-N potential resolve the previous discrepancy between experimental and theoretical results.Comment: RevTeX, 5 figure

    Turing instabilities in a mathematical model for signaling networks

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    GTPase molecules are important regulators in cells that continuously run through an activation/deactivation and membrane-attachment/membrane-detachment cycle. Activated GTPase is able to localize in parts of the membranes and to induce cell polarity. As feedback loops contribute to the GTPase cycle and as the coupling between membrane-bound and cytoplasmic processes introduces different diffusion coefficients a Turing mechanism is a natural candidate for this symmetry breaking. We formulate a mathematical model that couples a reaction-diffusion system in the inner volume to a reaction-diffusion system on the membrane via a flux condition and an attachment/detachment law at the membrane. We present a reduction to a simpler non-local reaction-diffusion model and perform a stability analysis and numerical simulations for this reduction. Our model in principle does support Turing instabilities but only if the lateral diffusion of inactivated GTPase is much faster than the diffusion of activated GTPase.Comment: 23 pages, 5 figures; The final publication is available at http://www.springerlink.com http://dx.doi.org/10.1007/s00285-011-0495-
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