1,086 research outputs found
Regolith production and transport at the Susquehanna Shale Hills Critical Zone Observatory, Part 2: Insights from meteoric 10Be
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
Promoting Physical Activity in Low Income African Americans: Project LAPS
Low income African Americans are at increased risk for physical inactivity and related chronic illnesses. Thus, effective interventions are needed to address these health disparities. The current study examined the efficacy of a home-based physical activity intervention among a low income African American sample with high rates of chronic illnesses (obesity, hypertension, diabetes, high cholesterol). Participants (n=214) were randomly assigned to either the home-based physical activity intervention (self-help print materials, five monthly newsletters, two telephone counseling sessions) or an attention control condition, which promoted healthy diet. Results indicated that the intervention did not produce significantly greater increases in physical activity from baseline to six months than the control group. Lessons learned from the current study include the importance of using proactive retention strategies with low income African American participants and taking into consideration the cultural relevance of the intervention
Solving the mystery of booming sand dunes
Desert booming can be heard after a natural slumping
event or during a sand avalanche generated by humans
sliding down the slip face of a large dune. The sound is
remarkable because it is composed of one dominant audible
frequency (70 to 105 Hz) plus several higher harmonics.
This study challenges earlier reports that the dunes’
frequency is a function of average grain size by
demonstrating through extensive field measurements that
the booming frequency results from a natural waveguide
associated with the dune. The booming frequency is fixed
by the depth of the surficial layer of dry loose sand that is
sandwiched between two regions of higher compressional
body wave velocity. This letter presents measurements of
the booming frequencies, compressional wave velocities,
depth of surficial layer, along with an analytical prediction
of the frequency based on constructive interference of
propagating waves generated by avalanching along the dune
surface
Reply to comment by B. Andreotti et al. on "Solving the mystery of booming sand dunes"
This reply addresses three main issues raised in the
comment of Andreotti et al. [2008]. First, the turning of
ray paths in a granular material does not preclude the
propagation of body waves and the resonance condition
described by Vriend et al. [2007]. The waveguide model
still holds in the dune for the observed velocities, even
with a velocity increase with depth as implied by Andreotti
et al. [2008]. Secondly, the method of initiation of
spontaneous avalanching does not influence the booming
frequency. The frequency is independent of the source
once sustained booming starts; it depends on the subsurface
structure of the dune. Thirdly, if all data points from Vriend
et al. [2007] are included in the analysis (and not an
average or selection), no correlation is observed between
the sustained booming frequency and average particle
diameter
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Asymptotic Analysis of Time-Dependent Neutron Transport Coupled with Isotopic Depletion and Radioactive Decay
We describe an asymptotic analysis of the coupled nonlinear system of equations describing time-dependent three-dimensional monoenergetic neutron transport and isotopic depletion and radioactive decay. The classic asymptotic diffusion scaling of Larsen and Keller [1], along with a consistent small scaling of the terms describing the radioactive decay of isotopes, is applied to this coupled nonlinear system of equations in a medium of specified initial isotopic composition. The analysis demonstrates that to leading order the neutron transport equation limits to the standard time-dependent neutron diffusion equation with macroscopic cross sections whose number densities are determined by the standard system of ordinary differential equations, the so-called Bateman equations, describing the temporal evolution of the nuclide number densities
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Angularly Adaptive P1--Double P0 Diffusion Solutions of Non-Equilibrium Grey Radiative Transfer Problems in Planar Geometry
The double spherical harmonics angular approximation in the lowest order, i.e. double P{sub 0} (DP{sub 0}), is developed for the solution of time-dependent non-equilibrium grey radiative transfer problems in planar geometry. The standard P{sub 1} angular approximation represents the angular dependence of the radiation specific intensity using a linear function in the angular domain -1 {le} {mu} {le} 1. In contrast, the DP{sub 0} angular approximation represents the angular dependence as isotropic in each half angular range -1 {le} {mu} < 0 and 0 < {mu} {le} 1. Neglecting the time derivative of the radiation flux, both the P{sub 1} and DP{sub 0} equations can be written as a single diffusion equation for the radiation energy density. Although the DP{sub 0} diffusion approximation is expected to be less accurate than the P{sub 1} diffusion approximation at and near thermodynamic equilibrium, the DP{sub 0} angular approximation can more accurately capture the complicated angular dependence near the non-equilibrium wave front. We develop an adaptive angular technique that locally uses either the DP{sub 0} or the P{sub 1} diffusion approximation depending on the degree to which the radiation and material fields are in thermodynamic equilibrium. Numerical results are presented for a test problem due to Su and Olson for which a semi-analytic transport solution exists. The numerical results demonstrate that the adaptive P{sub 1}-DP{sub 0} diffusion approximation can yield improvements in accuracy over the standard P{sub 1} diffusion approximation for non-equilibrium grey radiative transfer
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Angularly Adaptive P1 - Double P0 Flux-Limited Diffusion Solutions of Non-Equilibrium Grey Radiative Transfer Problems
The double spherical harmonics angular approximation in the lowest order, i.e. double P{sub 0} (DP{sub 0}), is developed for the solution of time-dependent non-equilibrium grey radiative transfer problems in planar geometry. Although the DP{sub 0} diffusion approximation is expected to be less accurate than the P{sub 1} diffusion approximation at and near thermodynamic equilibrium, the DP{sub 0} angular approximation can more accurately capture the complicated angular dependence near a non-equilibrium radiation wave front. In addition, the DP{sub 0} approximation should be more accurate in non-equilibrium optically thin regions where the positive and negative angular domains are largely decoupled. We develop an adaptive angular technique that locally uses either the DP{sub 0} or P{sub 1} flux-limited diffusion approximation depending on the degree to which the radiation and material fields are in thermodynamic equilibrium. Numerical results are presented for two test problems due to Su and Olson and to Ganapol and Pomraning for which semi-analytic transport solutions exist. These numerical results demonstrate that the adaptive P{sub 1}-DP{sub 0} diffusion approximation can yield improvements in accuracy over the standard P{sub 1} diffusion approximation, both without and with flux-limiting, for non-equilibrium grey radiative transfer
A Perspective on the Recent Progress in Solution-processed Methods for Highly Efficient Perovskite Solar Cells
Perovskite solar cells (PSCs) were developed in 2009 and have led to a number of significant improvements in clean energy technology. The power conversion efficiency (PCE) of PSCs has increased exponentially and currently stands at 22%. PSCs are transforming photovoltaic (PV) technology, outpacing many established PV technologies through their versatility and roll-to-roll manufacturing compatibility. The viability of low-temperature and solution-processed manufacturing has further improved their viability. This article provides a brief overview of the stoichiometry of perovskite materials, the engineering behind various modes of manufacturing by solution processing methods, and recommendations for future research to achieve large-scale manufacturing of high efficienc
Mobile air monitoring data-processing strategies and effects on spatial air pollution trends
The collection of real-time air quality measurements while in motion (i.e.,
mobile monitoring) is currently conducted worldwide to evaluate in situ
emissions, local air quality trends, and air pollutant exposure. This
measurement strategy pushes the limits of traditional data analysis with
complex second-by-second multipollutant data varying as a function of time
and location. Data reduction and filtering techniques are often applied to
deduce trends, such as pollutant spatial gradients downwind of a highway.
However, rarely do mobile monitoring studies report the sensitivity of their
results to the chosen data-processing approaches. The study being reported
here utilized 40 h (> 140 000 observations) of mobile monitoring data
collected on a roadway network in central North Carolina to explore common
data-processing strategies including local emission plume detection,
background estimation, and averaging techniques for spatial trend analyses.
One-second time resolution measurements of ultrafine particles (UFPs), black
carbon (BC), particulate matter (PM), carbon monoxide (CO), and nitrogen
dioxide (NO<sub>2</sub>) were collected on 12 unique driving routes that were
each sampled repeatedly. The route with the highest number of repetitions was
used to compare local exhaust plume detection and averaging methods. Analyses
demonstrate that the multiple local exhaust plume detection strategies
reported produce generally similar results and that utilizing a median of
measurements taken within a specified route segment (as opposed to a mean)
may be sufficient to avoid bias in near-source spatial trends. A time-series-based method of estimating background concentrations was shown to produce
similar but slightly lower estimates than a location-based method. For the
complete data set the estimated contributions of the background to the mean
pollutant concentrations were as follows: BC (15%), UFPs (26%), CO (41%),
PM<sub>2.5-10</sub> (45%), NO<sub>2</sub> (57%), PM<sub>10</sub> (60%), PM<sub>2.5</sub>
(68%). Lastly, while temporal smoothing (e.g., 5 s averages) results
in weak pair-wise correlation and the blurring of spatial trends, spatial
averaging (e.g., 10 m) is demonstrated to increase correlation and refine
spatial trends
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