20,580 research outputs found

    So Are We Keynesians or Not?

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    There is plenty of room for empirical debate with respect to the efficacy of fiscal policy in general, whether monetary policy is a better tool, or what constitutes spending that will make us more productive in the future.Martin Kennedy, Keynes, Keynesianism, ARRA, stimulus, fiscal policy, Tennessee

    Bott periodicity for Z2Z_2 symmetric ground states of gapped free-fermion systems

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    Building on the symmetry classification of disordered fermions, we give a proof of the proposal by Kitaev, and others, for a "Bott clock" topological classification of free-fermion ground states of gapped systems with symmetries. Our approach differs from previous ones in that (i) we work in the standard framework of Hermitian quantum mechanics over the complex numbers, (ii) we directly formulate a mathematical model for ground states rather than spectrally flattened Hamiltonians, and (iii) we use homotopy-theoretic tools rather than K-theory. Key to our proof is a natural transformation that squares to the standard Bott map and relates the ground state of a d-dimensional system in symmetry class s to the ground state of a (d+1)-dimensional system in symmetry class s+1. This relation gives a new vantage point on topological insulators and superconductors.Comment: 55 pages; one figure added; corrections in Section 8; proofs in Section 6 expande

    A New Approach to the Problem of Dynamical Quarks in Numerical Simulations of Lattice QCD

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    Lattice QCD with an even number of degenerate quark flavours is shown to be a limit of a local bosonic field theory. The action of the bosonic theory is real and bounded from below so that standard simulation algorithms can be expected to apply. The feasibility of such calculations is discussed, but no practical tests have yet been made.Comment: pages 0-15, ps-file 147KB, preprint DESY 93-14

    Arkansas Cotton Variety Test 2013

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    The primary goal of the Arkansas Cotton Variety Test is to provide unbiased data regarding the agronomic performance of cotton varieties and advanced breeding lines in the major cotton-growing areas of Arkansas. This information helps seed companies establish marketing strategies and assists producers in choosing varieties to plant. These annual evaluations will then facilitate the inclusion of new, improved genetic material in Arkansas cotton production

    A Biological Comparison of Two Sites: an Ecological Approach Using Community Ecology Metrics Based on Insect Faunal Composition

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    Two natural sites in the Portland urban area, River View Natural Area (RVNA) and Powers Marine Park (PMP), were sampled to assess their insect faunal composition with the intention of determining whether the areas are sufficiently similar ecologically that they could potentially be managed as a single unit. The two areas were compared using community ecology metrics based on their respective invertebrate fauna. The results suggested that RVNA and PMP had statistically different ecological communities. The Shannon Diversity Index for PMP was 0.303, and 0.819 for RVNA. The Horn Index of Community Overlap suggested a 93.46% overlap based on these data; however, a Hutcheson’s t-test for community ecology data suggested significant differences (P \u3c\u3c\u3c 0.0001) between PMP and RVNA’s insect faunal compositions
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