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

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

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

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

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

Monte Carlo Particle Transport Capability for Inertial Confinement Fusion Applications

A time-dependent massively-parallel Monte Carlo particle transport calculational module (ParticleMC) for inertial confinement fusion (ICF) applications is described. The ParticleMC package is designed with the long-term goal of transporting neutrons, charged particles, and gamma rays created during the simulation of ICF targets and surrounding materials, although currently the package treats neutrons and gamma rays. Neutrons created during thermonuclear burn provide a source of neutrons to the ParticleMC package. Other user-defined sources of particles are also available. The module is used within the context of a hydrodynamics client code, and the particle tracking is performed on the same computational mesh as used in the broader simulation. The module uses domain-decomposition and the MPI message passing interface to achieve parallel scaling for large numbers of computational cells. The Doppler effects of bulk hydrodynamic motion and the thermal effects due to the high temperatures encountered in ICF plasmas are directly included in the simulation. Numerical results for a three-dimensional benchmark test problem are presented in 3D XYZ geometry as a verification of the basic transport capability. In the full paper, additional numerical results including a prototype ICF simulation will be presented

Biotic controls on solute distribution and transport in headwater catchments

Solute concentrations in stream water vary with discharge in patterns that record complex feedbacks between hydrologic and biogeochemical processes. In a comparison of headwater catchments underlain by shale in Pennsylvania, USA (Shale Hills) 5 and Wales, UK (Plynlimon), dissimilar concentration-discharge behaviors are best explained by contrasting landscape distributions of soil solution chemistry – especially dissolved organic carbon (DOC) – that have been established by patterns of vegetation. Specifically, elements that are concentrated in organic-rich soils due to biotic cycling (Mn, Ca, K) or that form strong complexes with DOC (Fe, Al) are spatially heteroge- 10 neous in pore waters because organic matter is heterogeneously distributed across the catchments. These solutes exhibit non-chemostatic “bioactive” behavior in the streams, and solute concentrations either decrease (Shale Hills) or increase (Plynlimon) with increasing discharge. In contrast, solutes that are concentrated in soil minerals and form only weak complexes with DOC (Na, Mg, Si) are spatially homogeneous in pore waters 15 across each catchment. These solutes are chemostatic in that their stream concentrations vary little with stream discharge, likely because these solutes are released quickly from exchange sites in the soils during rainfall events. Differences in the hydrologic connectivity of organic-rich soils to the stream drive differences in concentration behavior between catchments. As such, in catchments where soil organic matter (SOM) is dom- 20 inantly in lowlands (e.g., Shale Hills), bioactive elements are released to the stream early during rainfall events, whereas in catchments where SOM is dominantly in uplands (e.g., Plynlimon), bioactive elements are released later during rainfall events. The distribution of vegetation and SOM across the landscape is thus a key component for predictive models of solute transport in headwater catchments