6,081 research outputs found

    Distribution of Aromatic Compounds in Coastal Bermudagrass Cell Walls Using Ultraviolet Absorption Scanning Microspectrophotometry

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    The distribution of aromatic constituents, including lignin , in the leaf cell walls of Coastal hermudagrass (Cynodon dacrylon (L.) Pers.) was investigated using scanning ultraviolet (UV) microspectrophotometry. Leaf blade sections and individual tissue types were scanned at three wavelengths representing the absorbance maxima (318, 287 and 250 nm) of aromatic constituents present in bermudagrass leaves. The measured absorbance data were printed in a geometric arrangement to produce an image of the distribution and amount of aromatic constituents among and within cell wall types which vary in digestibility . Differences in absorbance were observed among cell wall types, among walls of the same cell type, and at different sites in individual cell walls. Scans of the mid vein at lOX magnification showed that various tissues and cells could be distinguished on the basis of U V absorbance. The abaxial sclerenchyma and mestome sheath gave the highest absorbance followed by those of the epidermis and parenchyma bundle sheath . The lowest levels of absorbance were observed in the mesophyll, parenchyma tissue and xylem tissue. Images produced from scanning individual cell walls at lOOx magnification showed the heterogeneous nature of aromatic constituents within a cell wall. Varying the wavelength resulted in similar but not identical images, indicating that variations in the chemical structures of aromatic constituents in the cell wall can he detected using this technique

    An On-Line Survey Process for Assessing Impact of an Email-Delivered Pest Advisory

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    IPM specialists simplified the entry, collection, editing, and distribution of pest alerts by creating a new Web site, the Virginia Ag Pest Advisory. A simple on-line survey was used to assess the usefulness of the advisory. The on-line survey was low-cost and required less effort than conventional surveys. Such a system provides feedback from users, which can be used to improve Extension programs and generates results to be used in reporting impact data

    Role of material properties and mesostructure on dynamic deformation and shear instability in Al-W granular composites

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    Dynamic experiments with Al-W granular/porous composites revealed qualitatively different behavior with respect to shear localization depending on bonding between Al particles. Two-dimensional numerical modeling was used to explore the mesomechanics of the large strain dynamic deformation in Al-W granular/porous composites and explain the experimentally observed differences in shear localization between composites with various mesostructures. Specifically, the bonding between the Al particles, the porosity, the roles of the relative particle sizes of Al and W, the arrangements of the W particles, and the material properties of Al were investigated using numerical calculations. It was demonstrated in simulations that the bonding between the "soft" Al particles facilitated shear localization as seen in the experiments. Numerical calculations and experiments revealed that the mechanism of the shear localization in granular composites is mainly due to the local high strain flow of "soft" Al around the "rigid" W particles causing localized damage accumulation and subsequent growth of the meso/macro shear bands/cracks. The "rigid" W particles were the major geometrical factor determining the initiation and propagation of "kinked" shear bands in the matrix of "soft" Al particles, leaving some areas free of extensive plastic deformation as observed in experiments and numerical calculations.Comment: 10 pages, 14 figures, submitted to Journal of Applied Physic

    Non-classical symmetries and the singular manifold method: A further two examples

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    This paper discusses two equations with the conditional Painleve property. The usefulness of the singular manifold method as a tool for determining the non-classical symmetries that reduce the equations to ordinary differential equations with the Painleve property is confirmed once moreComment: 9 pages (latex), to appear in Journal of Physics

    Nonlinear transport of Bose-Einstein condensates through mesoscopic waveguides

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    We study the coherent flow of interacting Bose-condensed atoms in mesoscopic waveguide geometries. Analytical and numerical methods, based on the mean-field description of the condensate, are developed to study both stationary as well as time-dependent propagation processes. We apply these methods to the propagation of a condensate through an atomic quantum dot in a waveguide, discuss the nonlinear transmission spectrum and show that resonant transport is generally suppressed due to an interaction-induced bistability phenomenon. Finally, we establish a link between the nonlinear features of the transmission spectrum and the self-consistent quasi-bound states of the quantum dot.Comment: 23 pages, 16 figure

    First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li

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    In this letter, we report a new mass for 11^{11}Li using the trapping experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived nuclide, t1/2=8.8mst_{1/2} = 8.8 \rm{ms}, for which a mass measurement has ever been performed with a Penning trap. Combined with our mass measurements of 8,9^{8,9}Li we derive a new two-neutron separation energy of 369.15(65) keV: a factor of seven more precise than the best previous value. This new value is a critical ingredient for the determination of the halo charge radius from isotope-shift measurements. We also report results from state-of-the-art atomic-physics calculations using the new mass and extract a new charge radius for 11^{11}Li. This result is a remarkable confluence of nuclear and atomic physics.Comment: Formatted for submission to PR

    MUSTANG: 90 GHz Science with the Green Bank Telescope

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    MUSTANG is a 90 GHz bolometer camera built for use as a facility instrument on the 100 m Robert C. Byrd Green Bank radio telescope (GBT). MUSTANG has an 8 by 8 focal plane array of transition edge sensor bolometers read out using time-domain multiplexed SQUID electronics. As a continuum instrument on a large single dish MUSTANG has a combination of high resolution (8") and good sensitivity to extended emission which make it very competitive for a wide range of galactic and extragalactic science. Commissioning finished in January 2008 and some of the first science data have been collected.Comment: 9 Pages, 5 figures, Presented at the SPIE conference on astronomical instrumentation in 200
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