1,135 research outputs found

    Regolith production and transport at the Susquehanna Shale Hills Critical Zone Observatory, Part 2: Insights from meteoric 10Be

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    Regolith-mantled hillslopes are ubiquitous features of most temperate landscapes, and their morphology reflects the climatically, biologically, and tectonically mediated interplay between regolith production and downslope transport. Despite intensive research, few studies have quantified both of these mass fluxes in the same field site. Here we present an analysis of 87 meteoric 10Be measurements from regolith and bedrock within the Susquehanna Shale Hills Critical Zone Observatory (SSHO), in central Pennsylvania. Meteoric 10Be concentrations in bulk regolith samples (n=73) decrease with regolith depth. Comparison of hillslope meteoric 10Be inventories with analyses of rock chip samples (n=14) from a 24 m bedrock core confirms that >80% of the total inventory is retained in the regolith. The systematic downslope increase of meteoric 10Be inventories observed at SSHO is consistent with 10Be accumulation in slowly creeping regolith (∼ 0.2 cm yr-1). Regolith flux inferred from meteoric 10Be varies linearly with topographic gradient (determined from high-resolution light detection and ranging-based topography) along the upper portions of hillslopes at SSHO. However, regolith flux appears to depend on the product of gradient and regolith depth where regolith is thick, near the base of hillslopes. Meteoric 10Be inventories at the north and south ridgetops indicate minimum regolith residence times of 10.5 ± 3.7 and 9.1 ± 2.9 ky, respectively, similar to residence times inferred from U-series isotopes in Ma et al. (2013). The combination of our results with U-series-derived regolith production rates implies that regolith production and erosion rates are similar to within a factor of two on SSHO hillcrests. ©2013. American Geophysical Union. All Rights Reserved

    Luminous Intensity for Traffic Signals: A Scientific Basis for Performance Specifications

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    Humnan factors experiments on visual responses to simulated traffic signals using incandescent lamps and light-emitting diodes are described

    Pace and Process of Active Folding and Fluvial Incision Across the Kantishna Hills Anticline, Central Alaska

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    Rates of northern Alaska Range thrust system deformation are poorly constrained. Shortening at the system\u27s west end is focused on the Kantishna Hills anticline. Where the McKinley River cuts across the anticline, the landscape records both Late Pleistocene deformation and climatic change. New optically stimulated luminescence and cosmogenic 10Be depth profile dates of three McKinley River terrace levels (~22, ~18, and ~14–9 ka) match independently determined ages of local glacial maxima, consistent with climate-driven terrace formation. Terrace ages quantify rates of differential bedrock incision, uplift, and shortening based on fault depth inferred from microseismicity. Differential rock uplift and incision (≤1.4 m/kyr) drive significant channel width narrowing in response to ongoing folding at a shortening rate of ~1.2 m/kyr. Our results constrain northern Alaska Range thrust system deformation rates, and elucidate superimposed landscape responses to Late Pleistocene climate change and active folding with broad geomorphic implications

    C1: Applying the Cosmogenic Nuclide Dipstick Model for Deglaciation of Mt. Washington

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    Guidebook for field trips in Western Maine and Northern New Hampshire: New England Intercollegiate Geological Conference, p. 247-272

    Nonlinear Semi-Analytic Methods for Trajectory Estimation

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76298/1/AIAA-29106-621.pd

    Fusion of radioactive 132^{132}Sn with 64^{64}Ni

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    Evaporation residue and fission cross sections of radioactive 132^{132}Sn on 64^{64}Ni were measured near the Coulomb barrier. A large sub-barrier fusion enhancement was observed. Coupled-channel calculations including inelastic excitation of the projectile and target, and neutron transfer are in good agreement with the measured fusion excitation function. When the change in nuclear size and shift in barrier height are accounted for, there is no extra fusion enhancement in 132^{132}Sn+64^{64}Ni with respect to stable Sn+64^{64}Ni. A systematic comparison of evaporation residue cross sections for the fusion of even 112124^{112-124}Sn and 132^{132}Sn with 64^{64}Ni is presented.Comment: 9 pages, 11 figure

    Fusion versus Breakup: Observation of Large Fusion Suppression for ^9Be + ^{208}Pb

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    Complete fusion excitation functions for 9^{9}Be + 208^{208}Pb have been measured to high precision at near barrier energies. The experimental fusion barrier distribution extracted from these data allows reliable prediction of the expected complete fusion cross-sections. However, the measured cross-sections are only 68% of those predicted. The large cross-sections observed for incomplete fusion products support the interpretation that this suppression of fusion is caused by 9^{9}Be breaking up into charged fragments before reaching the fusion barrier. Implications for the fusion of radioactive nuclei are discussed.Comment: RevTex, 11 pages, 2 postscript figures, to appear in PR

    Coupled-channels analysis of the 16^{{\bf 16}}O+208^{{\bf 208}}Pb fusion barrier distribution

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    Analyses using simplified coupled-channels models have been unable to describe the shape of the previously measured fusion barrier distribution for the doubly magic 16^{16}O+208^{208}Pb system. This problem was investigated by re-measuring the fission excitation function for 16^{16}O+208^{208}Pb with improved accuracy and performing more exact coupled-channels calculations, avoiding the constant-coupling and first-order coupling approximations often used in simplified analyses. Couplings to the single- and 2-phonon states of 208^{208}Pb, correctly taking into account the excitation energy and the phonon character of these states, particle transfers, and the effects of varying the diffuseness of the nuclear potential, were all explored. However, in contrast to other recent analyses of precise fusion data, no satisfactory simultaneous description of the shape of the experimental barrier distribution and the fusion cross-sections for 16^{16}O+208^{208}Pb was obtained.Comment: RevTex, 29 pages, 7 postscript figures, to appear in PR

    Regolith production and transport at the Susquehanna Shale Hills Critical Zone Observatory, part 2: Insights from meteoric10Be

    Get PDF
    Regolith-mantled hillslopes are ubiquitous features of most temperate landscapes, and their morphology reflects the climatically, biologically, and tectonically mediated interplay between regolith production and downslope transport. Despite intensive research, few studies have quantified both of these mass fluxes in the same field site. Here we present an analysis of 87 meteoric 10Be measurements from regolith and bedrock within the Susquehanna Shale Hills Critical Zone Observatory (SSHO), in central Pennsylvania. Meteoric 10Be concentrations in bulk regolith samples (n=73) decrease with regolith depth. Comparison of hillslope meteoric 10Be inventories with analyses of rock chip samples (n=14) from a 24 m bedrock core confirms that >80% of the total inventory is retained in the regolith. The systematic downslope increase of meteoric 10Be inventories observed at SSHO is consistent with 10Be accumulation in slowly creeping regolith (∼ 0.2 cm yr-1). Regolith flux inferred from meteoric 10Be varies linearly with topographic gradient (determined from high-resolution light detection and ranging-based topography) along the upper portions of hillslopes at SSHO. However, regolith flux appears to depend on the product of gradient and regolith depth where regolith is thick, near the base of hillslopes. Meteoric 10Be inventories at the north and south ridgetops indicate minimum regolith residence times of 10.5 ± 3.7 and 9.1 ± 2.9 ky, respectively, similar to residence times inferred from U-series isotopes in Ma et al. (2013). The combination of our results with U-series-derived regolith production rates implies that regolith production and erosion rates are similar to within a factor of two on SSHO hillcrests
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