24,630 research outputs found

    Measured and calculated steady aerodynamic loads on a large-scale upper-surface blown model

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    Static aerodynamic loads measurements from wind tunnel tests of a full-scale upper surface blown jet flap configuration are presented. The measured loads are compared with calculations using a method for predicting longitudinal aerodynamic characteristics of upper surface blown jet flap configurations

    Hulme: Ten years on

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    Making the HESP work: choices and challenges in Trent

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    HABITAT UTILIZATION BY THE TEXAS HORNED LIZARD (PHRYNOSOMA CORNUTUM) FROM TWO SITES IN CENTRAL TEXAS

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    The Texas Horned Lizard (Phrynosoma cornutum) is found in a variety of habitats. Although several studies have been conducted on habitat use by this species, none have been performed in central Texas, a more mesic habitat than most of those previously studied. This area is of special interest because horned lizard populations have been experiencing sharp declines in central Texas over the last approximately 50 years. We collected habitat data at two sites in central Texas, Camp Bowie and Blue Mountain Peak Ranch. Microhabitat data included canopy cover and ground cover from digitized photographs of Daubenmire quadrats; macrohabitat variables included vegetation height and length, cactus height, soil penetrability, woody plant species richness, tree density, tree diameter at breast height (DBH), and density of ant mounds collected along 100-m by 2-m transects. Similar patterns of habitat use were observed between the two sites. At Blue Mountain Peak Ranch, lizards appeared to be located in areas with a diversity of ground cover types, as observed in previous studies. At Camp Bowie, vegetation encroachment limited lizards in some areas to the use of roads and road margins. Implementation of prescribed burns or other vegetation management could create the preferred ground cover mosaic at such sites

    Analytic Treatment of Positronium Spin Splittings in Light-Front QED

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    We study the QED bound-state problem in a light-front hamiltonian approach. Starting with a bare cutoff QED Hamiltonian, HBH_{_{B}}, with matrix elements between free states of drastically different energies removed, we perform a similarity transformation that removes the matrix elements between free states with energy differences between the bare cutoff, Λ\Lambda, and effective cutoff, \lam (\lam < \Lam). This generates effective interactions in the renormalized Hamiltonian, HRH_{_{R}}. These effective interactions are derived to order α\alpha in this work, with αâ‰Ș1\alpha \ll 1. HRH_{_{R}} is renormalized by requiring it to satisfy coupling coherence. A nonrelativistic limit of the theory is taken, and the resulting Hamiltonian is studied using bound-state perturbation theory (BSPT). The effective cutoff, \lam^2, is fixed, and the limit, 0 \longleftarrow m^2 \alpha^2\ll \lam^2 \ll m^2 \alpha \longrightarrow \infty, is taken. This upper bound on \lam^2 places the effects of low-energy (energy transfer below \lam) emission in the effective interactions in the ∣ee‟>| e {\overline e} > sector. This lower bound on \lam^2 insures that the nonperturbative scale of interest is not removed by the similarity transformation. As an explicit example of the general formalism introduced, we show that the Hamiltonian renormalized to O(α)O(\alpha) reproduces the exact spectrum of spin splittings, with degeneracies dictated by rotational symmetry, for the ground state through O(α4)O(\alpha^4). The entire calculation is performed analytically, and gives the well known singlet-triplet ground state spin splitting of positronium, 7/6α2Ryd7/6 \alpha^2 Ryd. We discuss remaining corrections other than the spin splittings and how they can be treated in calculating the spectrum with higher precision.Comment: 46 pages, latex, 3 Postscript figures included, section on remaining corrections added, title changed, error in older version corrected, cutoff placed in a windo
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