This study proposed a novel hybrid resolved framework coupling computational fluid dynamics (CFD) with discrete element method (DEM) to investigate internal erosion in gap-graded soils. In this framework, a fictitious domain (FD) method for clump was developed to solve the fluid flow around realistic-shaped coarse particles, while a semi-resolved method based on a Gaussian-weighted function was adopted to describe the interactions between fine particles and fluid. Firstly, the accuracy of the proposed CFD-DEM was rigorously validated through simulations of flow past a fixed sphere and single ellipsoid particle settling, compared with experimental results. Subsequently, the samples of gap-graded soil considering realistic shape of coarse particles were established, using spherical harmonic (SH) analysis and clump method. Finally, the hybrid resolved CFD-DEM model was applied to simulate internal erosion in gap-graded soils. Detailed numerical analyses concentrated on macro- -micro mechanics during internal erosion, including the critical hydraulic gradient, structure deformation, as well as particle migration, pore flow, and fabric evolution. The findings from this study provide novel insights into the multi-scale mechanisms underlying the internal erosion in gap-graded soils.

This study proposes a resolved framework coupling computational fluid dynamics (CFD) with discrete element method (DEM) to simulate the sedimentation of granular sand. Realistic sand particles were reconstructed by spherical harmonic representation combined with the multi-sphere clump method, and a fictitious domain method for irregular clumps was further developed to solve the fluid-particle interaction. This resolved CFD-DEM offers a direct and robust approach for computing real fluid forces on irregular-shaped granular sands, without relying on any empirical drag force models. Initially, the effectiveness and accuracy of the proposed CFD-DEM were validated through a series of single-particle free settling simulations for various ideal-shaped particles. Critical fluid-particle interacting behaviors in terms of drag force and wake structure were mainly investigated and corroborated with experimental data. The study subsequently progressed to simulate the sedimentation processes of various granular sand assemblies composed of realistic-shaped sand particles, utilizing the proposed CFD-DEM. Detailed numerical analyses concentrated on particle-scale mechanics during sedimentation, including settling trajectories and velocities of particles, as well as the coordination and anisotropy of inter-particle contacts. The results and findings gained from this study provide a novel insight into the micro-mechanisms underlying the sedimentation and accumulation process of granular soils in geological environments.

Recent observational studies suggest that nucleation-scavenging is the principal path to removing black carbon-containing aerosol from the atmosphere, thus affecting black carbon's lifetime and radiative forcing. Modeling the process of nucleation-scavenging is challenging, since black carbon (BC) forms complex internal mixtures with other aerosol species. Here, we examined the impacts of black carbon mixing state on nucleation scavenging using the particle-resolved aerosol model PartMC-MOSAIC. This modeling approach has the unique advantage that complex aerosol mixing states can be represented on a per-particle level. For a scenario library that comprised hundreds of diverse aerosol populations, we quantified nucleation-scavenged BC mass fractions. Consistent with measurements, these vary widely, depending on the amount of BC, the amount of coating and coating material, as well as the environmental supersaturation. We quantified the error in the nucleation-scavenged black carbon mass fraction introduced when assuming an internally mixed distribution, and determined its bounds depending on environmental supersaturation and on the aerosol mixing state index chi. For a given chi value, the error decreased at higher supersaturations. For more externally mixed populations (chi 75%), the error was below 100% for the range of supersaturations (from 0.02% to 1%) investigated here. Accounting for black carbon mixing state and knowledge of the supersaturation of the environment are crucial when determining the amount of black carbon that can be incorporated into clouds.

The climate effects of black carbon (BC) aerosols are sensitive to BC size distributions and this sensitivity over China is studied using a regional climate model, namely RIEMS2.0. A new size-resolved scheme is developed based on observational data. The simulated BC concentrations with the new scheme are better compared with the observation than the previous uniform scheme, which is likely to overestimate BC concentrations, radiative forcings, and warming effects in many regions of China due to its simple assumption on BC size. The simulation with the size-resolved scheme suggests a reduction of the all-sky radiative forcing of BC at the top of atmosphere (TOA) by 0-0.25 W m(-2) over the most study domain. Correspondingly, the warming effect of BC is weakened by -0.04 to -0.16 K over most parts of South China and North China. The difference in BC-induced precipitation between the two schemes varies irregularly from region to region, ranging from -2.8 to 2.8 mm d(-1). With the size-resolved scheme, the BC radiative properties and the climate effects are reassessed and the means (ranges) over the study domain are summarized as follows. The annual mean surface concentration of BC is 0.88 mu g/m(3), ranging from 1 to 8 mu g/m(3) over North China and Central China. The all-sky and clear-sky radiative forcings of BC at the TOA are 0.43 and 0.39 W/m(2), respectively. Over most parts of Southwest China, Central China, and North China, the BC warming effect prevails, with enhanced temperature of 0.04-028 K. BC aerosols usually enhance precipitation in South China and North China, ranging from 0.40 to 2.8 mm d(-1). (C) 2016 Elsevier B.V. All rights reserved.

The ability of a particle to uptake water and form a cloud droplet depends on its hygroscopicity. To understand its impact on cloud properties and ultimately radiative forcing, knowledge of chemically resolved mixing state information or the one based on hygroscopic growth is crucial. Typically, global models assume either pure internal or external mixing state which might not be true for all conditions and sampling locations. To investigate into this, the current study employed an indirect approach to infer the probable mixing state. The hygroscopic parameters derived from kappa-Kohler theory using size-resolved CCN measurements (kappa(CCN)) and bulk/size-resolved aerosol mass spectrometer (AMS) measurements (kappa(Ams)) were compared. The accumulation mode particles were found to be more hygroscopic (kappa(CCN) = 0.24) than Aitken mode (kappa(CCN) = 0.13), perhaps due to increased ratio of inorganic to organic mass fraction. The activation diameter calculated from size-resolved CCN activity measurements at 5 different supersaturation (SS) levels varied in the range of 115 nm-42 nm with kappa(CCN) = 0.13-0.23 (avg = 0.18 +/- 0.10 (+/- 1 sigma)). Further, kappa(AMS)> kappa(CCN) was observed possibly due to the fact that organic and inorganic mass present in the Aitken mode was not correctly represented by bulk chemical composition and size-resolved fractional contribution of oxidized OA was not accurately accounted. Better correlation of organic fraction (f(org)) and kappa(CCN) at lower SS explained this behaviour. The decrease in kappa(CCN) with the time of the day was more pronounced at lower SS because of the relative mass reduction of soluble inorganic species by similar to 17%. Despite the large differences between kappa measured from two approaches, less over-prediction (up to 18%) between measured and predicted CCN concentration suggested lower impact of chemical composition and mixing state at higher SS. However, at lower SS, presences of externally mixed CCN-inactive aerosols lead to CCN over-prediction reflecting the significance of aerosol mixing state information. Further examination of the effect of biomass burning aerosols (similar to 35% in least oxidized biomass burning organic aerosol (BBOA-2 fraction) on hygroscopicity and CCN activity showed increase in the concentration of all AMS measured species (except NH4+ and SO42-), less O:C ratio, and organic mass fraction (f(org)) peak shift to lower diameter range caused similar to 13% change in critical diameter (Da) and similar to 40% change in kappa(CCN). Increased deviation of similar to 100% between kappa(CCN) and kappa(AMS) due to sudden influx of internally mixed BBOA caused suppressed hygroscopic growth. This study finally suggests the assumption of pure internally mixed aerosol does not completely hold true for this anthropogenically polluted site. (C) 2016 Elsevier Ltd. All rights reserved.

In-Situ Resource Utilization (ISRU) is a key NASA initiative to exploit resources at the site of planetary exploration for mission-critical consumables, propellants, and other supplies. The Resource Prospector mission, part of ISRU, is scheduled to launch in 2020 and will include a rover and lander hosting the Regolith & Environment Science and Oxygen & Lunar Volatile Extraction (RESOLVE) payload for extracting and analyzing lunar resources, particularly low molecular weight volatiles for fuel, air, and water. RESOLVE contains the Lunar Advanced Volatile Analysis (LAVA) subsystem with a Gas Chromatograph-Mass Spectrometer (GC-MS). RESOLVE subsystems, including the RP'15 rover and LAVA, are in NASA's Engineering Test Unit (ETU) phase to assure that all vital components of the payload are space-flight rated and will perform as expected during the mission. Integration and testing of LAVA mass spectrometry verified reproducibility and accuracy of the candidate MS for detecting nitrogen, oxygen, and carbon dioxide. The RP'15 testing comprised volatile analysis of water-doped simulant regolith to enhance integration of the RESOLVE payload with the rover. Multiple tests show the efficacy of the GC to detect 2% and 5% water-doped samples.

The Regolith and Environment Science and Oxygen and Lunar Volatiles Extraction (RESOLVE) project aims to verify the presence of water and other volatiles on the Moon, and to serve as a precursor for future prospecting missions. The Artemis Jr. rover was developed as the surface mobility component of the RESOLVE project, and was specifically designed to accommodate the RESOLVE payload in a sixday NASA-CSA mission simulation carried out on Mauna Kea, Hawaii in July 2012. This paper describes the preparation, results, and lessons learned as they apply to the Artemis Jr. rover. Areas of focus include the operations as well as the rover software and hardware. Key results include support for the skid-steer configuration of the rover and the success of the absolute and relative localization functions of the rover. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

The RESOLVE project requires an analytical system to identify and quantitate the volatiles released from a lunar drill core sample as it is crushed and heated to 150 degrees C. The expected gases and their range of concentrations were used to assess Gas Chromatography (GC) and Mass Spectrometry (MS), along with specific analyzers for use on this potential lunar lander. The ability of these systems to accurately quantitate water and hydrogen in an unknown matrix led to the selection of a small MEMS commercial process GC for use in this project. The modification, development and testing of this instrument for the specific needs of the project is covered.

Resource investigation in the lunar poles is important to the potential impact of in-situ resource utilization (ISRU). The Regolith and Environment Science and Oxygen and Lunar Volatile Extraction (RESOLVE) project aims to develop a payload that will investigate the permanently shadowed areas of the lunar poles and demonstrate ISRU technology. As a part of the RESOLVE project, the regolith volatile characterization (RVC) subsystem will examine the release of volatiles from sample cores. The volatile sample will be introduced into the lunar water resource demonstration (LWRD) subsystem where the released hydrogen and water will be selectively captured. The water will be condensed to form a droplet and electrolyzed to produce hydrogen and oxygen. This process will demonstrate small scale ISRU techniques. This paper will present the challenges, characteristics, and development of the RVC and LWRD. The experiments performed to evaluate adsorption methods will be discussed. Based on these experiments, it has been decided that a salt hydride will be used to capture water vapor and a metal hydride will be used to capture hydrogen from the sample.