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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

CdS and CdS/CdSe sensitized ZnO nanorod array solar cells prepared by a solution ions exchange process

Graphical abstract: - Highlights: • CdS and CdS/CdSe quantum dots are assembled on ZnO nanorods by ion exchange process. • The CdS/CdSe sensitization of ZnO effectively extends the absorption spectrum. • The performance of ZnO/CdS/CdSe cell is improved by extending absorption spectrum. - Abstract: In this paper, cadmium sulfide (CdS) and cadmium sulfide/cadmium selenide (CdS/CdSe) quantum dots (QDs) are assembled onto ZnO nanorod arrays by a solution ion exchange process for QD-sensitized solar cell application. The morphology, composition and absorption properties of different photoanodes were characterized with scanning electron microscope, transmission electron microscope, energy-dispersive X-ray spectrum and Raman spectrum in detail. It is shown that conformal and uniform CdS and CdS/CdSe shells can grow on ZnO nanorod cores. Quantum dot sensitized solar cells based on ZnO/CdS and ZnO/CdS/CdSe nanocable arrays were assembled with gold counter electrode and polysulfide electrolyte solution. The CdS/CdSe sensitization of ZnO can effectively extend the absorption spectrum up to 650 nm, which has a remarkable impact on the performance of a photovoltaic device by extending the absorption spectrum. Preliminary results show one fourth improvement in solar cell efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Electrochemically decorated gold nanoparticles on CVD graphene ChemFET sensor for the highly sensitive detection of As(III)

Here, in this paper, we report a novel reusable receptor-free chemically sensitive field-effect transistor (ChemFET) sensor for the sensitive detection of As(III) using electrochemical doping of Au nanoparticles (AuNPs)-chemical vapour deposition (CVD) graphene (Gr) sensing film (AuNPs-Gr). The sensor consists of a single-gap gold electrode and a single layer of CVD graphene as a conducting/sensing channel decorated with a thin layer of electrochemically deposited AuNPs to catalyze the electroreduction of As(III) ions onto the sensing channel. A new detection strategy was proposed by measuring the resistance change rate of the AuNPs-Gr sensing channel modified between the source electrode and drain electrode, wherein the resistance change was caused by the electrochemical doping of As(0). The results indicated that the electrochemical doping of As(0) onto the sensing channel led to an increase in resistance through the doping interaction among As(0), AuNPs and graphene, enabling the proposed sensor to have an extraordinary detection performance with a high sensitivity. Moreover, the proposed sensor can be recycled by removing the As(0) deposited on the sensing film with the aid of a simple electrochemical oxidization process. Additionally, the mechanism of the sensing strategy based on the electrochemical n-doping of As(0) into the AuNPs-Gr sensing film was investigated using a top liquid gate electrode. The As(III) concentration detected by the AuNPs-Gr ChemFET sensor was as low as 0.001 μg/L, demonstrating that such sensors with a compatible sensing strategy can be used to detect As(III) with high sensitivity, easy fabrication, fast response and can be recycled.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Suppression of NRF2–ARE activity sensitizes chemotherapeutic agent-induced cytotoxicity in human acute monocytic leukemia cells

Nuclear factor erythroid 2-related factor 2 (NRF2), a master regulator of the antioxidant response element (ARE)-dependent transcription, plays a pivotal role in chemical detoxification in normal and tumor cells. Consistent with previous findings that NRF2–ARE contributes to chemotherapeutic resistance of cancer cells, we found that stable knockdown of NRF2 by lentiviral shRNA in human acute monocytic leukemia (AML) THP-1 cells enhanced the cytotoxicity of several chemotherapeutic agents, including arsenic trioxide (As{sub 2}O{sub 3}), etoposide and doxorubicin. Using an ARE-luciferase reporter expressed in several human and mouse cells, we identified a set of compounds, including isonicotinic acid amides, isoniazid and ethionamide, that inhibited NRF2–ARE activity. Treatment of THP-1 cells with ethionamide, for instance, significantly reduced mRNA expression of multiple ARE-driven genes under either basal or As{sub 2}O{sub 3}-challenged conditions. As determined by cell viability and cell cycle, suppression of NRF2–ARE by ethionamide also significantly enhanced susceptibility of THP-1 and U937 cells to As{sub 2}O{sub 3}-induced cytotoxicity. In THP-1 cells, the sensitizing effect of ethionamide on As{sub 2}O{sub 3}-induced cytotoxicity was highly dependent on NRF2. To our knowledge, the present study is the first to demonstrate that ethionamide suppresses NRF2–ARE signaling and disrupts the transcriptional network of the antioxidant response in AML cells, leading to sensitization to chemotherapeutic agents. - Highlights: • Identification of novel inhibitors of ARE-dependent transcription • Suppression of NRF2–ARE sensitizes THP-1 cells to chemotherapy. • Ethionamide suppresses ARE-dependent transcriptional activity. • Ethionamide and isoniazid increase the cytotoxicity of As{sub 2}O{sub 3} in AML cells. • Sensitization of THP-1 cells to As{sub 2}O{sub 3} toxicity by ethionamide is NRF2-dependent.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

ATM inhibition induces synthetic lethality and enhances sensitivity of PTEN-deficient breast cancer cells to cisplatin

Highlights: • ATM is a synthetically lethal target in breast cancer cells with PTEN defects. • ATM inhibitor KU-60019 preferentially sensitizes PTEN-deficient breast cancer cells to cisplatin. • The selective cytotoxicity results from the increase of DNA damage accumulation and the decreased capability of DNA repair. • PTEN-deficient MDA-MB-468 cells have lower level of Rad51, higher ATM kinase activity than PTEN wild-type MDA-MB-231 cells. PTEN deficiency often causes defects in DNA damage repair. Currently, effective therapies for breast cancer are lacking. ATM is an attractive target for cancer treatment. Previous studies suggested a synthetic lethality between PTEN and PARP. However, the synthetically lethal interaction between PTEN and ATM in breast cancer has not been reported. Moreover, the mechanism remains elusive. Here, using KU-60019, an ATM kinase inhibitor, we investigated ATM inhibition as a synthetically lethal strategy to target breast cancer cells with PTEN defects. We found that KU-60019 preferentially sensitizes PTEN-deficient MDA-MB-468 breast cancer cells to cisplatin, though it also slightly enhances sensitivity of PTEN wild-type breast cancer cells. The increased cytotoxic sensitivity is associated with apoptosis, as evidenced by flow cytometry and PARP cleavage. Additionally, the increase of DNA damage accumulation due to the decreased capability of DNA repair, as indicated by γ-H2AX and Rad51 foci, also contributed to this selective cytotoxicity. Mechanistically, compared with PTEN wild-type MDA-MB-231 cells, PTEN-deficient MDA-MB-468 cells have lower level of Rad51, higher ATM kinase activity, and display the elevated level of DNA damage. Moreover, these differences could be further enlarged by cisplatin. Our findings suggest that ATM is a promising target for PTEN-defective breast cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Global Sensitivity Analysis with Small Sample Sizes: Ordinary Least Squares Approach

A new version of global sensitivity analysis is developed in this paper. This new version coupled with tools from statistics, machine learning, and optimization can devise small sample sizes that allow for the accurate ordering of sensitivity coefficients for the first 10-30 most sensitive chemical reactions in complex chemical-kinetic mechanisms, and is particularly useful for studying the chemistry in realistic devices. A key part of the paper is calibration of these small samples. Because these small sample sizes are developed for use in realistic combustion devices, the calibration is done over the ranges of conditions in such devices, with a test case being the operating conditions of a compression ignition engine studied earlier. Compression ignition engines operate under low-temperature combustion conditions with quite complicated chemistry making this calibration difficult, leading to the possibility of false positives and false negatives in the ordering of the reactions. So an important aspect of the paper is showing how to handle the trade-off between false positives and false negatives using ideas from the multiobjective optimization literature. The combination of the new global sensitivity method and the calibration are sample sizes a factor of approximately 10 times smaller than were available with our previous algorithm.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Enhancing the Sensitivity of Solid-State NMR Experiments with Very Low Gyromagnetic Ratio Nuclei with Fast Magic Angle Spinning and Proton Detection

Many transition metals commonly encountered in inorganic materials and organometallic compounds possess NMR-active nuclei with very low gyromagnetic ratios (γ) such as 89 Y, 103 Rh, 109 Ag, and 183 W. A low-γ leads to poor NMR sensitivity and other experimental challenges. Consequently, nuclei with low-γ are often impossible to study with conventional solid-state NMR methods. In this paper, we combine fast magic angle spinning (MAS) and proton detection to enhance the sensitivity of solid-state NMR experiments with very low-γ nuclei by 1–2 orders of magnitude. Coherence transfer between 1 H and low-γ nuclei was performed with low-power double quantum (DQ) or zero quantum (ZQ) cross-polarization (CP) or dipolar refocused insensitive nuclei enhanced by polarization transfer (D-RINEPT). Comparison of the absolute sensitivity of CP NMR experiments performed with proton detection with 1.3 mm rotors and direct detection with 4 mm rotors shows that proton detection with a 1.3 mm rotor provides a significant boost in absolute sensitivity, while requiring approximately 1/40 th of the material required to fill a 4 mm rotor. Fast MAS and proton detection were applied to obtain 89 Y and 103 Rh solid-state NMR spectra of organometallic complexes. Finally, these results demonstrate that proton detection and fast MAS represents a general approach to enable and accelerate solid-state NMR experiments with very low-γ nuclei.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Perovskite-Sensitized Upconversion under Operando Conditions

Perovskite-sensitized upconversion (UC) has resulted in near-infrared-to-visible UC at solar-relevant fluxes. However, the successful implementation of UC devices into operating solar cells will result in exposure to similar environmental stressors as for the commercial photovoltaics (PVs), mainly elevated temperatures, and continuous irradiation. In this article, we investigated the effects of these two stressors, heat and light, on the triplet generation process at the perovskite/rubrene interface. Following exposure to both stressors, local discrepancies across the upconversion device were discovered. Here, the first region showed changes to the morphology, and no detectable upconverted emission was observed. Through the combination of optical microscopy and spectroscopy, crystallization of the organic semiconductor layer, degradation of dibenzotetraphenylperiflanthene, and concurrent degradation of the perovskite sensitizer were found. These effects culminate in a reduction in both triplet generation and triplet–triplet annihilation. In the second region, no changes to the morphology were present and visible UC emission was observed following exposure to both stressors. To probe the triplet sensitization process at elevated temperatures, transient absorption spectroscopy was performed. The presence of the excited spin-triplet state of rubrene at 60 °C highlighted successful triplet generation even at elevated temperatures. This work emphasizes the challenges and continued potential for the integration of perovskite-sensitized UC into commercial photovoltaic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Charge Recombination Dynamics in Sensitized SnO 2 /TiO 2 Core/Shell Photoanodes

Studies have been conducted to examine the mechanisms of charge recombination in dye-sensitized SnO 2 /TiO 2 core/shell films. Nanostructured SnO 2 /TiO 2 core/shell films varying in TiO 2 shell thicknesses were prepared via atomic layer deposition and sensitized with a phosphonate-derivatized ruthenium chromophore [Ru(bpy) 2 (4,4$'$-(PO 3 H 2 ) 2 bpy)] 2+ . Transient absorption spectroscopy was used to study the interfacial charge recombination dynamics for these core/shell materials. Charge recombination for sensitized, as-deposited SnO 2 /TiO 2 core/shell systems is dominated by a tunneling mechanism for shell thicknesses between 0 and 3.2 nm, with $β$ = 0.25 Å–1. For shell thicknesses greater than 3.2 nm, recombination primarily proceeds directly via electrons localized in the relatively thick TiO 2 shell. Annealing the SnO 2 /TiO 2 core/shell structure at 450°C affects the recombination dynamics substantially; charge recombination dynamics for the annealed films do not show a dependence on shell thickness and are comparable to ZrO 2 /TiO 2 control samples, suggesting the annealing process perturbs the core/shell interface. This analysis of charge recombination dynamics indicates that there is an optimum shell thickness to maximize charge separation lifetimes in dye-sensitized core/shell photoanodes and that the nature of the core/shell interface influences the efficacy of these materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

MOF-Sensitized Solar Cells Enabled by a Pillared Porphyrin Framework

Metal–organic frameworks (MOFs) are highly ordered, functionally tunable supramolecular materials with the potential to improve dye-sensitized solar cells (DSSCs). Several recent reports have indicated that photocurrent can be generated in Grätzel-type DSSC devices when MOFs are used as the sensitizer. However, the specific role(s) of the incorporated MOFs and the potential influence of residual MOF precursor species on device performance are unclear. Herein, we describe the assembly and characterization of a simplified DSSC platform in which isolated MOF crystals are used as the sensitizer in a planar device architecture. We selected a pillared porphyrin framework (PPF) as the MOF sensitizer, taking particular care to avoid contamination from light-absorbing MOF precursors. Photovoltaic and electrochemical characterization under simulated 1-sun and wavelength-selective illumination revealed photocurrent generation that is clearly ascribable to the PPF MOF. In conclusion, continued refinement of highly versatile MOF structure and chemistry holds promise for dramatic improvements in emerging photovoltaic technologies.

14 SOLAR ENERGY↗
DOE OSTI2016

Hundreds-fold Sensitivity Enhancement of Photothermal Microscopy in Near-Critical Xenon

Photothermal absorption microscopy of single Au nanoparticles was conducted at temperatures and pressures near the critical point of Xenon ( T c = 16.583 °C, P c = 5.842 MPa). The divergence of the thermal expansion coefficient at the critical point makes the refractive index highly sensitive to changes in temperature, which directly translates to a large enhancement of the photothermal signal. We determine that measurements taken near the critical point of Xe give a signal enhancement factor of up to 440 ± 130 over those taken in glycerol. The highest sensitivity recorded here corresponds to power dissipation of 64 pW, achieving a signal-to-noise ratio of 9.4 for 5 nm Au nanoparticles with an integration time of 50 ms, making this the most sensitive of any absorption microscopy technique reported to date. Enhancing the sensitivity of absorption microscopy lowers the operating heating power, enabling the method to be more compatible with absorbers with absorption coefficient and photochemical stability lower than that of Au.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Modification of Carbon Nitride/Reduced Graphene Oxide van der Waals Heterostructure with Copper Nanoparticles To Improve CO 2 Sensitivity

Carbon nitride/reduced graphene oxide (rGO) van der Waals heterostructures (vdWH) have previously shown exceptional oxygen sensitivity via a photoredox mechanism, making it a potential material candidate for various applications such as oxygen reduction reaction catalysis and oxygen sensing. In this work, the electronic structure of a carbon nitride/rGO composite is modified through the introduction of copper nanoparticles (NPs). When incorporated into a chemiresistor device, this vdWH displayed a newfound CO 2 sensitivity. The effects of humidity and light were investigated and found to be crucial components for the CO 2 sensitivity. Density functional theory calculations performed on a carbon nitride/copper NP@rGO model system found an enhanced stabilization of CO 2 caused by H-bonds between the carbon nitride layer and chemisorbed CO 2 on copper, pointing to the important role played by humidity. The synergetic effect between the carbon nitride layer interfaced with CuNP@rGO, in combination with humidity and light (395 nm) irradiation, is found to be responsible for the newfound sensitivity toward CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Excited Carrier Dynamics in a Dye-Sensitized Niobate Nanosheet Photocatalyst for Visible-Light Hydrogen Evolution

Dye-sensitized photocatalysts that consist of a light-absorbing dye and a wide gap oxide semiconductor have been studied extensively as components of solar energy conversion systems. Although surface modification by a metal and/or metal oxide has a significant impact on the photocatalytic efficiency, the mechanism by which these modifications increase the activity has not been fully understood. Here a dye-sensitized H 2 evolution system was constructed by using Pt-intercalated HCa 2 Nb 3 O 10 nanosheets, Ru(II) complex photosensitizers ([Ru(4,4’-(CH 3 ) 2- bpy) 2 (4,4’-(PO 3 H 2 ) 2- bpy)] 2+ and [Ru(4,4’-(CH 3 ) 2- bpy) 2 (4,4’-(CH 2 PO 3 H 2 ) 2- bpy)] 2+ , abbreviated as RuP 2+ and RuCP 2+ ; bpy = 2,2'-bipyridine), and amorphous Al 2 O 3 as building blocks. In the presence of iodide as the electron donor, the H 2 evolution rate from Pt/HCa 2 Nb 3 O 10 nanosheets sensitized by RuP 2+ was increased by modification of the nanosheets with Al 2 O 3 . On the other hand, Al 2 O 3 had a negative impact on the H 2 evolution rate when RuCP 2+ was employed. These hybrid materials were studied by transient diffuse reflectance spectroscopy and steady-state emission spectroscopy. A detailed analysis of the transient absorption profiles of the adsorbed Ru(II) complexes revealed that there are at least three states of the complexes on the nanosheet surface. The transient bleaching of the ground state absorbance had different lifetime components ranging from a few μs to several hundred μs, which mainly reflect back electron transfer rates from HCa 2 Nb 3 O 10 to the oxidized Ru(II) complexes. Here, the Al 2 O 3 modifier could inhibit not only the back electron transfer events but also electron injection from the excited state photosensitizer. Interestingly, the negative effect of Al 2 O 3 on the electron injection rate was negligible in the case of RuP 2+ , which also had a higher H 2 evolution rate. This work highlights that suppressing fast back electron transfer from Pt/HCa 2 Nb 3 O 10 to the oxidized Ru(II) complex, which occurs on a time scale of a few μs, and maximizing the electron injection efficiency are both necessary for improving dye-sensitized H 2 evolution.

14 SOLAR ENERGY↗
DOE OSTI2025

An Integral Activity-Based Protein Profiling Method for Higher Throughput Determination of Protein Target Sensitivity to Small Molecules

Activity-based protein profiling (ABPP) is a chemoproteomic technique that uses small molecule probes to label active enzymes selectively and covalently in complex proteomes. Competitive ABPP, which involves treatment of the active proteome with an analyte of interest, is especially powerful for profiling how small molecules impact specific protein activities. Advances in higher throughput workflows have made it possible to generate extensive competitive ABPP data across diverse biological samples, making this approach highly appealing for characterizing shared and unique proteins affected by perturbations such as drug or chemical exposures. To use the competitive ABPP approach effectively to understand potential adverse effects of chemicals of concern (CoC), a wide range of concentrations may be needed, particularly for chemicals that lack potency or toxicity data. In this work, we present an integral competitive ABPP method that enables target sensitivity determination for different organophosphate (OP) pesticides as model toxicants. Using previously developed OP-ABPs, we optimized conditions for tandem mass tag (TMT) multiplexing of ABPP samples and compared conventional competitive ABPP involving samples at discrete paraoxon concentrations to pooled samples across that same concentration range. We then expanded our approach to compare protein target sensitivities toward two additional OP pesticides, chlorpyrifos oxon and malaoxon. The results showed that differences in integral intensities for the pooled competition sample can be used to evaluate the relative sensitivity of specific proteins without increasing the overall number of samples. For 8 CoC concentrations of interest, this strategy reduced the number of TMT plexes and the corresponding number of LC–MS/MS analyses 3-fold. In conclusion, we envision the integral ABPP (IABPP) method will provide a means to screen diverse chemicals more rapidly to identify both high and low sensitivity protein targets.

activity-based probes↗
DOE OSTI2018

Sensitivities of Simulated Satellite Views of Clouds to Subgrid-Scale Overlap and Condensate Heterogeneity

Satellite simulators are often used to account for limitations in satellite retrievals of cloud properties in comparisons between models and satellite observations. The purpose of this framework is to enable more robust evaluation of model cloud properties, so that differences between models and observations can more confidently be attributed to model errors. A critical step in this process is accounting for the difference between the spatial scales at which cloud properties are retrieved with those at which clouds are simulated in global models. In this study, we create a series of sensitivity tests using 4-km global model output from the multiscale modeling framework to evaluate the sensitivity of simulated satellite retrievals to common assumptions about cloud and precipitation overlap and condensate variability used in climate models whose grid spacing is many tens to hundreds of kilometers. We find the simulated retrievals are sensitive to these assumptions. Using maximum-random overlap with homogeneous cloud and precipitation condensate leads to errors in Multiangle Imaging Spectroradiometer and International Satellite Cloud Climatology Project-simulated cloud cover and in CloudSat-simulated radar reflectivity that are significant compared to typical differences between the model simulations and observations. A more realistic treatment of unresolved clouds and precipitation is shown to substantially reduce these errors. The sensitivity to these assumptions underscores the need for the adoption of more realistic subcolumn treatments in models and the need for consistency among subcolumn assumptions between models and simulators to ensure that simulator-diagnosed errors are consistent with the model formulation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

The Role of Subsurface Flow on Evapotranspiration: A Global Sensitivity Analysis

Abstract Water resources are impacted by water‐energy balance fluxes at the land surface, most notably evapotranspiration ( ET ), the largest component of surface energy balance. While integrated hydrologic models show promise in quantifying the nonlinear dynamics at this interface, the model results are plagued by parametric uncertainties. Given the high computational demand of running multiple parameter spaces of these models, little is known about how these uncertainties propagate into land surface processes. In this work, we perform a global sensitivity analysis by computing Sobol and AMAE indices using a surrogate model constructed with a polynomial chaos expansion to assess the impacts of the subsurface physical properties on ET . We do so by modeling a semisynthetic test case. Our results show that the effects of vertical hydraulic conductivity, porosity, and the water retention curve parameter Van Genuchten α mainly control ET . However, we note that while evaporation ( E ) shows behavior similar to the ET with high sensitivity to the parameters controlling the flow in the unsaturated zone, transpiration ( T ) is very sensitive to the saturated zone parameters and groundwater flow, especially during periods without rain. Our results also show that heterogeneities in land cover impact the flow in the saturated zone. Furthermore, our work demonstrates that reduced‐order models can be developed to make integrated models more accessible for rigorous sensitivity analyses and calibration purposes.

Maina, Fadji Zaouna↗
DOE OSTI2021

Sensitivity of Grass Fires Burning in Marginal Conditions to Atmospheric Turbulence

Abstract Atmospheric forcing and interactions between the fire and atmosphere are primary drivers of wildland fire behavior. The atmosphere is known to be a chaotic system that, although deterministic, is very sensitive to small perturbations to initial conditions. We assume that as a result of the tight coupling between fire and atmosphere; wildland fire behavior, in turn, should also be sensitive to perturbations in atmospheric initial conditions. Observations suggest that low intensity prescribed fire, in particular, is susceptible to small perturbations in the wind field, which can significantly alter fire spread. Here, we employ a computational fluid dynamics model of coupled fire‐atmosphere interactions to answer the question: How sensitive is fire behavior to small variations in atmospheric turbulence? We perform ensemble simulations of fires in homogenous grass fuels. The only difference between ensemble members is the state of the turbulent atmosphere provided to the model throughout the simulation. The atmospheric state is a function of the initial conditions applied at the start of the simulation and boundary conditions applied throughout the simulation. We find a wide range of outcomes, with area burned ranging from 2,212 to 11,236 m 2 (>400% change), driven primarily by sensitivity to initial conditions, with nonnegligible contributions from boundary condition variability during the initial 30 s of simulation. Our results highlight the need for ensemble simulations, especially when considering fire behavior in marginal burning conditions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Understanding the eco-geomorphologic feedback of coastal marsh under sea level rise: vegetation dynamic representations, processes interaction, and parametric sensitivity

A growing number of coastal eco-geomorphologic modeling studies have been conducted to understand coastal marsh evolution under sea-level rise (SLR). Although these models quantify marsh topographic change as a function of sedimentation and erosion, their representations of vegetation dynamics that control organic sedimentation differ. How vegetation dynamic schemes contribute to simulation outcomes is not well quantified. Additionally, the sensitivity of modeling outcomes to parameter selection in the available formulations has not been rigorously tested to date, especially under the influence of an accelerating SLR. In this paper, we used a coastal eco-geomorphologic model with different vegetation dynamic schemes to investigate the eco-geomorphologic feedbacks of coastal marshes and parametric sensitivity under SLR scenarios. We found that marsh platform relief increased with sea level rise rate. The simulations with different vegetation schemes exhibited different spatial-temporal variations in elevation and biomass. The nonlinear Spartina scheme presented the most resilient prediction with generally the highest marsh accretion and vegetation biomass, and the least elevation relief under SLR. But the linear Spartina scheme predicts the lowest unvegetated-vegetated ratio. We also found that vegetation-related parameters and sediment diffusivity, which were not well measured or discussed in previous studies, were identified as some of the most critical parameters. Additionally, the model sensitivity to vegetation-related parameters increased with SLR rates. The identified most sensitive parameters may inform how to appropriately choose modeling representations of key processes and parameters for different coastal marsh landscapes under SLR, and demonstrate the importance of future field measurements of these key parameters.

58 GEOSCIENCES↗
DOE OSTI2021

Local and Global Sensitivity Analysis of a Reactive Transport Model Simulating Floodplain Redox Cycling

Reactive transport models (RTMs) are essential tools that simulate the coupling of advective, diffusive, and reactive processes in the subsurface, but their complexity makes them difficult to understand, develop and improve without accompanying statistical analyses. Although global sensitivity analysis (SA) can address these issues, the computational cost associated with most global SA techniques limits their use with RTMs. In this study, we apply distance-based generalized sensitivity analysis (DGSA), a novel and computationally efficient method of global SA, to a floodplain-scale RTM and compare DGSA results to those from local SA. Our test case focuses on the impact of 17 uncertain environmental parameters on spatially and temporally variable redox conditions within a floodplain aquifer. The input parameters considered include flow and diffusion rates, geochemical reaction rates, and the spatial distribution of sediment facies. Sensitivity was evaluated for three distinct components of the model response, encompassing both multidimensional and categorical output. Parameter rankings differ between local SA and DGSA, due to nonlinear effects of individual parameters and interaction effects between parameters. DGSA results show that fluid residence time, which is controlled by aquifer permeability, generally exerts a stronger control on redox conditions than do geochemical reaction rates. Sensitivity indices also demonstrate that sulfate reduction is key for establishing and maintaining reducing conditions throughout the aquifer. Furthermore, these results provide insights into the key drivers of heterogeneous redox processes within floodplain aquifers, as well as the main sources of uncertainty when modeling complex subsurface systems.

54 ENVIRONMENTAL SCIENCES↗