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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Control of chemical reactivity by transition-state and beyond

It has been long established that the transition state for an activated reaction controls the overall reactivity, serving as the bottleneck for reaction flux. However, the role of the transition state in regulating quantum state resolved reactivity has only been addressed more recently, thanks to advances in both experimental and theoretical techniques. Here in this perspective, we discuss some recent advances in understanding mode-specific reaction dynamics in bimolecular reactions, mainly focusing on the X + H 2 O/CH 4 (X = H, F, Cl, and O( 3 P)) systems, extensively studied in our groups. These advances shed valuable light on the importance of the transition state in mode-specific and steric dynamics of these prototypical reactions. It is shown that many mode-specific phenomena can be understood in terms of a transition-state based model, which assumes in the sudden limit that the ability of a reactant mode for promoting the reaction stems from its coupling with the reaction coordinate at the transition state. Yet, in some cases the long-range anisotropic interactions in the entrance (or exit) valley, which govern how the trajectories reach (or leave) the transition state, also come into play, thus modifying the reactive outcomes.

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

Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

Even though the interaction of a <1 mT magnetic field with an electron spin is less than a millionth of the thermal energy at room temperature (k{sub B}T), it still can have a profound effect on the quantum yields of radical pair reactions. We present a study of the effects of sub-millitesla magnetic fields on the photoreaction of flavin mononucleotide with ascorbic acid. Direct control of the reaction pathway is achieved by varying the rate of electron transfer from ascorbic acid to the photo-excited flavin. At pH 7.0, we verify the theoretical prediction that, apart from a sign change, the form of the magnetic field effect is independent of the initial spin configuration of the radical pair. The data agree well with model calculations based on a Green’s function approach that allows multinuclear spin systems to be treated including the diffusive motion of the radicals, their spin-selective recombination reactions, and the effects of the inter-radical exchange interaction. The protonation states of the radicals are uniquely determined from the form of the magnetic field-dependence. At pH 3.0, the effects of two chemically distinct radical pair complexes combine to produce a pronounced response to ∼500 μT magnetic fields. These findings are relevant to the magnetic responses of cryptochromes (flavin-containing proteins proposed as magnetoreceptors in birds) and may aid the evaluation of effects of weak magnetic fields on other biologically relevant electron transfer processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Isolating the Electrocatalytic Activity of a Confined NiFe Motif within Zirconium Phosphate

Unique classes of active-site motifs are needed for improved electrocatalysis. Herein, the activity of a new catalyst motif is engineered and isolated for the oxygen evolution reaction (OER) created by nickel–iron transition metal electrocatalysts confined within a layered zirconium phosphate matrix. It is found that with optimal intercalation, confined NiFe catalysts have an order of magnitude improved mass activity compared to more conventional surface-adsorbed systems in 0.1 m KOH. Interestingly, the confined environments within the layered structure also stabilize Fe-rich compositions (90%) with exceptional mass activity compared to known Fe-rich OER catalysts. Through controls and by grafting inert molecules to the outer surface, it is evidenced that the intercalated Ni/Fe species stay within the interlayer during catalysis and serve as the active site. After determining a possible structure (wycherproofite), density functional theory is shown to correlate with the observed experimental compositional trends. It is further demonstrated that the improved activity of this motif is correlated to the Fe and water content/composition within the confined space. This work highlights the catalytic enhancement possibilities available through zirconium phosphate and isolates the activity from the intercalated species versus surface/edge ones, thus opening new avenues to develop and understand catalysts within unique nanoscale chemical environments.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A bifunctional zeolitic porous liquid with incompatible Lewis pairs for antagonistic cascade catalysis

The emergence of porous liquids (PLs) opened opportunities to form unique antagonistic systems capable of fulfilling cascade reactions promoted by incompatible active sites in one pot, which is a long-term challenging subject in catalysis. Herein, unique bifunctional type III PL-based systems were facilely fabricated via assembly of zeolite nanosheets with ionic liquids. Rational structural design afforded PLs that feature high zeolite concentration, stable dispersion after 2 years, abundant cavity distribution, and involvement of antagonistic groups (acid and base sites) in separated and active form via steric hindrance control and electronic repulsion regulation. These unique properties worked cooperatively to fulfill the cascade deacetalization-Knoevenagel/Aldol condensation in one pot with superior catalytic efficiency outperforming the traditional systems. The key to success lies in the formation of bifunctional composites, transformation of zeolite from heterogeneous to homogeneous via surface modification, as well as rapid mass transfer ensured by the rigid porous architecture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Multiple re-encounter approach to radical pair reactions and the role of nonlinear master equations

We formulate a multiple-encounter model of the radical pair mechanism that is based on a random coupling of the radical pair to a minimal model environment. These occasional pulse-like couplings correspond to the radical encounters and give rise to both dephasing and recombination. While this is in agreement with the original model of Haberkorn and its extensions that assume additional dephasing, we show how a nonlinear master equation may be constructed to describe the conditional evolution of the radical pairs prior to the detection of their recombination. We propose a nonlinear master equation for the evolution of an ensemble of independently evolving radical pairs whose nonlinearity depends on the record of the fluorescence signal. We also reformulate Haberkorn's original argument on the physicality of reaction operators using the terminology of quantum optics/open quantum systems. Our model allows one to describe multiple encounters within the exponential model and connects this with the master equation approach. We include hitherto neglected effects of the encounters, such as a separate dephasing in the triplet subspace, and predict potential new effects, such as Grover reflections of radical spins, that may be observed if the strength and time of the encounters can be experimentally controlled.

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

Redox manipulation of the manganese metal in human manganese superoxide dismutase for neutron diffraction

Human manganese superoxide dismutase (MnSOD) is one of the most significant enzymes in preventing mitochondrial dysfunction and related diseases by combating reactive oxygen species (ROS) in the mitochondrial matrix. Mitochondria are the source of up to 90% of cellular ROS generation, and MnSOD performs its necessary bioprotective role by converting superoxide into oxygen and hydrogen peroxide. This vital catalytic function is conducted via cyclic redox reactions between the substrate and the active-site manganese using proton-coupled electron transfers. Owing to protons being difficult to detect experimentally, the series of proton transfers that compose the catalytic mechanism of MnSOD are unknown. Here, methods are described to discern the proton-based mechanism using chemical treatments to control the redox state of large perdeuterated MnSOD crystals and subsequent neutron diffraction. These methods could be applicable to other crystal systems in which proton information on the molecule in question in specific chemical states is desired.

Azadmanesh, Jahaun↗
DOE OSTI2024

2D-EFICACY: Control of Metastable 2D Carbide[1]Chalcogenide Heterolayers: Strain and Moire Engineering

The experimental isolation of graphene led to the discovery of an entirely new world of two-dimensional (2D) materials in which the 2D nature often leads to emergent behaviors not seen in bulk systems. 2D transition metal dichalcogenides (TMDs) exhibit physico-chemical properties that depend on the transition metal, polymorph, thickness, and presence and type of defects. Recently, a group of thin (10-100nm) transition metal carbides (TMCs), such as Mo2C, has been synthesized that exhibit a thickness-dependent superconducting critical temperature (Tc). These thin TMCs are different from MXenes, another class of 2D materials consisting of few layers of nitrides or carbides (<5nm) produced by chemical etching and delamination. The goal of this renewal proposal is to combine experiment and computation to synthesize and elucidate the guiding principles that control the growth, orientation and strain of heterostacks of thin TMCs and TMDs composed with Nb, Ti and W. We expect to stabilize metastable hybrid phases of TMCs sandwiched between TMDs (H-TMD/Cs) with unprecedented physico-chemical properties. As part of previous DOE-funded work by the Terrones/Sinnott groups, thin (10-100 nm thick) Mo2C flakes were successfully synthesized by chemical vapor deposition (CVD). By subsequently exposing Mo2C to H2S, partial chalcogenization was achieved, resulting in heterostacks of MoCx phases and MoS2. The formation of MoS2 led to a deficiency of Mo atoms in the underlying Mo2C, resulting in an inhomogeneous phase change from α-Mo2C to γ’-MoCx and then to γ-MoC. The γ’-MoCx is a strained metastable phase and the heterostack of all three phases demonstrated an increased Tc relative to that of α-Mo2C, from 4 to 6K; its interleaved layered structure consisting of superconducting and semiconducting phases is ideal for future studies of Josephson junction series arrays. Moiré patterns in these heterostacked systems could result in new phenomena, as moiré patterns in bilayer graphene showed unconventional superconductivity and moiré excitons have been observed in twisted TMD heterobilayers. The scientific hypothesis of the proposed synergistic computational and experimental research is that orientation and strain control within confined thin metastable TMCs, sandwiched by stable phases of TMCs and layered TMDs, will depend on kinetic and thermodynamic “knobs” that include fast temperature changes, chalcogen diffusion through preferred crystallographic planes, reaction times, pressure, reactive atmosphere, precursors, and surfactants, which will also tailor properties such as superconductivity, magnetism, ferroelectricity, piezoelectricity, and catalytic performance. We will develop the guiding principles for the synthesis and stabilization of metastable H-TMD/Cs based on Nb, Ti and W. In order to validate the hypothesis, four tasks are proposed: The first task will synthesize ultra-thin TMCs based on Nb, W and Ti, by: 1) adapting the CVD method used for Mo2C, 2) plasma assisted CVD, 3) defect-mediated CVD processes, and 4) cryo-milling of carbide powders. The second task will accomplish the synthesis and basic physico-chemical characterizations of H-TMD/Cs by chalcogenization of the materials synthesized in task one, and by carbonization of TMDs. H-TMD/Cs will also be investigated for their suitability in energy conversion applications such as supercapacitors, Li and multivalent ion batteries, and electrocatalysts, topics of interest to DoE. These tasks will be carried out in close conjunction with density functional theory (DFT) calculations with insights into energetics, lattice parameters, stability, phase diagrams, band structures, and density of states of H-TMD/Cs. The third task will characterize and evaluate strain and moiré patterns at the interfaces of different H-TMD/Cs by high-resolution scanning transmission electron microscopy (HR-STEM), scanning tunneling microscopy (STM), and conductive tip atomic force microscopy. Nudged elastic band calculations with DFT will be performed to understand the chalcogen diffusion process, which will provide insights into the interfaces between different phases of TMCs and TMDs. The fourth task aims at quantifying the stability and dynamics of H-TMD/Cs by in-situ TEM and Raman studies under heating, strain, and electrical biasing. Phonon calculations using DFT will provide a basis for interpreting Raman spectra. This coherent framework involving synthesis, characterization, and computation will result in a broad scientific impact for energy related applications. The ability to develop new H-TMD/Cs will enhance a range of applications that include batteries, catalysts, switches, sensors, quantum computing components and smart coatings.

2-Dimensional materials↗
DOE OSTI2024

2D-EFICACY: Control of Metastable 2D Carbide Chalcogenide Heterolayers: Strain and Moire Engineering

The experimental isolation of graphene led to the discovery of an entirely new world of two-dimensional (2D) materials in which the 2D nature often leads to emergent behaviors not seen in bulk systems. 2D transition metal dichalcogenides (TMDs) exhibit physico-chemical properties that depend on the transition metal, polymorph, thickness, and presence and type of defects. Recently, a group of thin (10-100nm) transition metal carbides (TMCs), such as Mo 2 C, has been synthesized that exhibit a thickness-dependent superconducting critical temperature (Tc). These thin TMCs are different from MXenes, another class of 2D materials consisting of few layers of nitrides or carbides (<5nm) produced by chemical etching and delamination. The goal of this renewal proposal is to combine experiment and computation to synthesize and elucidate the guiding principles that control the growth, orientation and strain of heterostacks of thin TMCs and TMDs composed with Nb, Ti and W. We expect to stabilize metastable hybrid phases of TMCs sandwiched between TMDs (H-TMD/Cs) with unprecedented physico-chemical properties. As part of previous DOE-funded work by the Terrones/Sinnott groups, thin (10-100 nm thick) Mo 2 C flakes were successfully synthesized by chemical vapor deposition (CVD). By subsequently exposing Mo 2 C to H 2 S, partial chalcogenization was achieved, resulting in heterostacks of MoCx phases and MoS 2 . The formation of MoS 2 led to a deficiency of Mo atoms in the underlying Mo 2 C, resulting in an inhomogeneous phase change from α-Mo 2 C to γ’-MoCx and then to γ-MoC. The γ’-MoCx is a strained metastable phase and the heterostack of all three phases demonstrated an increased Tc relative to that of α-Mo 2 C, from 4 to 6K; its interleaved layered structure consisting of superconducting and semiconducting phases is ideal for future studies of Josephson junction series arrays. Moiré patterns in these heterostacked systems could result in new phenomena, as moiré patterns in bilayer graphene showed unconventional superconductivity and moiré excitons have been observed in twisted TMD heterobilayers. The scientific hypothesis of the proposed synergistic computational and experimental research is that orientation and strain control within confined thin metastable TMCs, sandwiched by stable phases of TMCs and layered TMDs, will depend on kinetic and thermodynamic “knobs” that include fast temperature changes, chalcogen diffusion through preferred crystallographic planes, reaction times, pressure, reactive atmosphere, precursors, and surfactants, which will also tailor properties such as superconductivity, magnetism, ferroelectricity, piezoelectricity, and catalytic performance. We will develop the guiding principles for the synthesis and stabilization of metastable H-TMD/Cs based on Nb, Ti and W. In order to validate the hypothesis, four tasks are proposed: The first task will synthesize ultra-thin TMCs based on Nb, W and Ti, by: 1) adapting the CVD method used for Mo 2 C, 2) plasma assisted CVD, 3) defect-mediated CVD processes, and 4) cryo-milling of carbide powders. The second task will accomplish the synthesis and basic physico-chemical characterizations of H-TMD/Cs by chalcogenization of the materials synthesized in task one, and by carbonization of TMDs. H-TMD/Cs will also be investigated for their suitability in energy conversion applications such as supercapacitors, Li and multivalent ion batteries, and electrocatalysts, topics of interest to DoE. These tasks will be carried out in close conjunction with density functional theory (DFT) calculations with insights into energetics, lattice parameters, stability, phase diagrams, band structures, and density of states of H-TMD/Cs. The third task will characterize and evaluate strain and moiré patterns at the interfaces of different H-TMD/Cs by high-resolution scanning transmission electron microscopy (HR-STEM), scanning tunneling microscopy (STM), and conductive tip atomic force microscopy. Nudged elastic band calculations with DFT will be performed to understand the chalcogen diffusion process, which will provide insights into the interfaces between different phases of TMCs and TMDs. The fourth task aims at quantifying the stability and dynamics of H-TMD/Cs by in-situ TEM and Raman studies under heating, strain, and electrical biasing. Phonon calculations using DFT will provide a basis for interpreting Raman spectra. This coherent framework involving synthesis, characterization, and computation will result in a broad scientific impact for energy related applications. The ability to develop new H-TMD/Cs will enhance a range of applications that include batteries, catalysts, switches, sensors, quantum computing components and smart coatings.

2-Dimensional Materials↗
DOE OSTI2015

Hydrogen-bond Specific Materials Modification in Group IV Semiconductors

Semiconductor dielectric crystals consist of two fundamental components: lattice atoms and electrons. The former component provides a crystalline structure that can be disrupted by various defects or the presence of an interface, or by transient oscillations known as phonons. The latter component produces an energetic structure that is responsible for the optical and electronic properties of the material, and can be perturbed by lattice defects or by photo-excitation. Over the period of this project, August 15, 1999 to March 31, 2015, a persistent theme has been the elucidation of the fundamental role of defects arising from the presence of radiation damage, impurities (in particular, hydrogen), localized strain or some combination of all three. As our research effort developed and evolved, we have experienced a few title changes, which reflected this evolution. Throughout the project, ultrafast lasers usually in a pump-probe configuration provided the ideal means to perturb and study semiconductor crystals by both forms of excitation, vibrational (phonon) and electronic (photon). Moreover, we have found in the course of this research that there are many interesting and relevant scientific questions that may be explored when phonon and photon excitations are controlled separately. Our early goals were to explore the dynamics of bond-selective vibrational excitation of hydrogen from point defects and impurities in crystalline and amorphous solids, initiating an investigation into the behavior of hydrogen isotopes utilizing a variety of ultrafast characterization techniques, principally transient bleaching spectroscopy to experimentally obtain vibrational lifetimes. The initiative could be divided into three related areas: (a) investigation of the change in electronic structure of solids due to the presence of hydrogen defect centers, (b) dynamical studies of hydrogen in materials and (c) characterization and stability of metastable hydrogen impurity states under transient compression. This research focused on the characterization of photon and ion stimulated hydrogen related defect and impurity reactions and migration in solid state matter, which requires a detailed understanding of the rates and pathways of vibrational energy flow, of the transfer channels and of the coupling mechanisms between local vibrational modes (LVMs) and phonon bath as well as the electronic system of the host material. It should be stressed that researchers at Vanderbilt and William and Mary represented a unique group with a research focus and capabilities for low temperature creation and investigation of such material systems. Later in the program, we carried out a vigorous research effort addressing the roles of defects, interfaces, and dopants on the optical and electronic characteristics of semiconductor crystals, using phonon generation by means of ultrafast coherent acoustic phonon (CAP) spectroscopy, nonlinear characterization using second harmonic generation (SHG), and ultrafast pump-and-probe reflectivity and absorption measurements. This program featured research efforts from hydrogen defects in silicon alone to other forms of defects such as interfaces and dopant layers, as well as other important semiconducting systems. Even so, the emphasis remains on phenomena and processes far from equilibrium, such as hot electron effects and travelling localized phonon waves. This program relates directly to the mission of the Department of Energy. Knowledge of the rates and pathways of vibrational energy flow in condensed matter is critical for understanding dynamical processes in solids including electronically, optically and thermally stimulated defect and impurity reactions and migration. The ability to directly probe these pathways and rates allows tests of theory and scaling laws at new levels of precision. Hydrogen embedded in model crystalline semiconductors and metal oxides is of particular interest, since the associated local mode can be excited cleanly, and is usually well-separated in energy from the phonon bath. These basic dynamical studies have provided new insights for example into the fundamental mechanisms that control proton diffusion in these oxides. This area of materials science has largely fulfilled its promise to identify degradation mechanisms in electronic and optoelectronic devices, and to advance solid oxide proton conductors for fuel cells, gas sensors and proton-exchange membrane applications. It also provides the basis for innovations in materials synthesis involving atomic-selective diffusion and desorption.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Ultra-High-Performance Concrete And Advanced Manufacturing Methods For Modular Construction

Small modular reactors (SMR) allow for less onsite construction, increase nuclear material security, and provide a flexible and cost-effective energy alternative. SMR can be factory-built as modular components, and shipped to desired locations for fast assembly. This project successfully developed a new class of ultra-high performance concrete (UHPC), which features a compressive strength greater than 22 ksi (150 MPa) without special treatment and self-consolidating characteristics desired for SMR modular construction. With an ultra-high strength and dense microstructure, it will facilitate rapid construction of steel plate-concrete (SC) beams and walls with thinner and lighter modules, and can withstand harsh environments and mechanical loads anticipated during the service life of nuclear power plants. In addition, the self-consolidating characteristics are crucial for the fast construction and assembly of SC modules with reduced labor costs and improved quality. Following the UHPC material development, the capacity of producing self-consolidating UHPC in mass quantities was investigated and compared to accepted self-consolidating concrete standards. With slightly adjusted mixing procedure using large-scale gravity-based mixers (compared with small-scale force-based mixer), the self-consolidating UHPC has been successfully processed at six cubic yards; the product met both minimum compressive strength requirements and self-consolidating concrete standards. Steel plate-UHPC beams (15 ft. long, 12 in. wide and 16 in. deep) and wall panels (40 in. X 40 in. X 3 in.) were then constructed using the self-consolidating UHPC without any external vibration. Quality control guidelines for producing UHPC in large scale were developed. When the concrete is replaced by UHPC in a steel plate concrete (SC) beam, it is critical to evaluate its structural behavior with both flexure and shear-governed failure modes. In recent years, SC has been widely used for buildings and nuclear containment structures to resist lateral forces induced by severe earthquakes and heavy winds. SC modules have good potential for SMR because of their cost-effectiveness and reduced construction time. However, the minimum shear reinforcement (i.e. cross tie) ratio needs to be determined for the steel plate-UHPC (S-UHPC) beams to exhibit a ductile failure mode. In this project, S-UHPC beams were designed and constructed. The beams were tested to evaluate structural capacity and identify the minimum cross ties ratios. In addition, as the bond between UHPC and steel plate is essential for ensuring structural integrity under shear and flexure, it was measured and examined in this project through digital image correlation system and smart piezoelectric aggregate sensors. Large-scale testing and finite element simulation were also performed on S-UHPC wall panels. New bond slip-based constitutive models of steel plate were developed for S-UHPC, which were used in finite element analysis program to predict S-UHPC behavior under shear. The results were well validated through experimental data. The long-term durability of UHPC were established in this project. UHPC specimens were tested under free shrinkage, restrained shrinkage, elevated temperature, water permeation, chloride diffusion, corrosion, and alkali silica reaction. UHPC has demonstrated significantly improved durability compared with control concrete specimens. This research led to a new generation of steel plate-UHPC modules for SMR that can provide large benefits to the electric power industry. Taking advantage of the high strength and durability of UHPC, their modularity and ease of assembly can address the high cost barriers of typical nuclear power plants.

42 ENGINEERING↗
DOE OSTI2017

High Temperature Chemistry of Aromatic Hydrocarbons. Final Technical Report

The primary goal of this research was to uncover the principal reaction channels available to polycyclic aromatic hydrocarbons (PAHs) at high temperatures in the gas phase and to establish the factors that determine which channels will be followed in varying circumstances. New structure-property relationships for PAHs were also studied. The efficient production of clean energy from fossil fuels will remain a major component of the DOE mission until alternative sources of energy eventually displace coal and petroleum. Hydrocarbons constitute the most basic class of compounds in all of organic chemistry, and as the dominant species in fossil fuels, they figure prominently into the programs of the DOE. Much is already known about the normal chemistry of hydrocarbons under ambient conditions, but far less is known about their intrinsic chemistry at temperatures close to those reached during combustion. An understanding of the fundamental molecular transformations, rearrangements, and interconversions of PAHs at high temperatures in the gas phase, as revealed by careful studies on small, well-designed, molecular systems, provides insights into the underlying chemistry of many important processes that are more complex, such as the generation of energy by the combustion of fossil fuels, the uncatalyzed gasification and liquefaction of coal, the production of fullerenes in fuel-rich flames, and the formation of soot and carcinogenic pollutants in smoke (e.g., benzo[a]pyrene). The rational control of any of these processes, whether it be the optimization of a desirable process or the minimization of an undesirable one, requires a clear knowledge of the basic chemistry that governs the fate of the species involved. Advances in chemistry at the most fundamental level come about primarily from the discovery of new reactions and from new insights into how reactions occur. Harnessing that knowledge is the key to new technologies. The recent commercialization of a combustion synthesis of C 60 and other fullerenes depended critically on a knowledge of hydrocarbon reactions at high temperatures in the gas phase, and the research supported by this project enabled further advances in the realm of carbon-rich materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Bayesian batch optimization for molybdenum versus tungsten inertial confinement fusion double shell target design

Access to reliable, clean energy sources is a major concern for national security. Much research is focused on the “grand challenge” of producing energy via controlled fusion reactions in a laboratory setting. For fusion experiments, specifically inertial confinement fusion (ICF), to produce sufficient energy, the fusion reactions in the ICF fuel need to become self-sustaining and burn deuterium-tritium (DT) fuel efficiently. The recent record-breaking NIF ignition shot was able to achieve this goal as well as produce more energy than used to drive the experiment. This achievement brings self-sustaining fusion-based power systems closer than ever before, capable of providing humans with access to secure, renewable energy. In order to further progress toward the actualization of such power systems, more ICF experiments need to be conducted at large laser facilities such as the United States's National Ignition Facility (NIF) or France's Laser Mega-Joule. The high cost per shot and limited number of shots that are possible per year make it prohibitive to perform large numbers of experiments. As such, experimental design relies heavily on complex predictive physics simulations for high-fidelity “preshot” analysis. These multidimensional, multi-physics, high-fidelity simulations have to account for a variety of input parameters as well as modeling the extreme conditions (pressures and densities) present at ignition. Such simulations (especially in 3D) can become computationally prohibitive to turn around for each ICF experiment. In this work, we explore using Bayesian optimization with Gaussian processes (GPs) to find optimal designs for ICF double shell targets, while keeping computational costs to manageable levels. These double shell targets have an inner shell that grades from beryllium on the outer surface to the higher Z material molybdenum, as opposed to the nominally used tungsten, on the inside in order to trade off between the high performance associated with high density inner shells and capsule stability. We describe our results for “capsule-only” xRAGE simulations to study the physics between different capsule designs, inner shell materials, and potential for future experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Solvents can control solute molecular identity

For solution-phase chemical reactions, the solvent is often considered simply as a medium to allow the reactants to encounter each other by diffusion. Although examples of direct solvent effects on molecular solutes exist, such as the compression of solute bonding electrons due to Pauli repulsion interactions, the solvent is not usually considered a part of the chemical species of interest. We show, using quantum simulations of Na 2 , that when there are local specific interactions between a solute and solvent that are energetically on the same order as a hydrogen bond, the solvent controls not only the bond dynamics but also the chemical identity of the solute. In tetrahydrofuran, dative bonding interactions between the solvent and Na atoms lead to unique coordination states that must cross a free energy barrier of ~8 k B T—undergoing a chemical reaction—to interconvert. In conclusion, each coordination state has its own dynamics and spectroscopic signatures, highlighting the importance of considering the solvent in the identity of condensed-phase chemical systems.

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

Uranium Release from Acidic Weathered Hanford Sediments: Single-Pass Flow-Through and Column Experiments

The reaction of acidic radioactive waste with sediments can induce mineral transformation reactions that, in turn, control contaminant fate. Here, sediment weathering by synthetic uranium-containing acid solutions was investigated using bench-scale experiments to simulate waste disposal conditions at Hanford’s cribs, USA. During acid weathering, the presence of phosphate exerted a strong influence over uranium mineralogy and a rapidly precipitated, crystalline uranium phosphate phase (meta-ankoleite [K(UO2)(PO4)·3H2O]) was identified using spectroscopic and diffraction-based techniques. In phosphate-free system, uranium oxyhydroxide minerals such as K-compreignacite [K2(UO2)6O4(OH)6·7H2O] were formed. Single-pass flow-through (SPFT) and column leaching experiments using synthetic Hanford pore water showed that uranium precipitated as meta-ankoleite during acid weathering was strongly retained in the sediments, with an average release rate of 2.67E-12 mol g-1 s-1. In the absence of phosphate, uranium release was controlled by dissolution of uranium oxyhydroxide (compreignacite-type) mineral with a release rate of 1.05-2.42E-10 mol g-1 s-1. The uranium mineralogy and release rates determined for both systems in this study support the development of accurate U-release models for prediction of contaminant transport. These results suggest that phosphate minerals may be a good candidate for uranium remediation approaches at contaminated sites.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Molecular basis for enantioselective herbicide degradation imparted by aryloxyalkanoate dioxygenases in transgenic plants

The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) is an active ingredient of thousands of commercial herbicides. Multiple species of bacteria degrade 2,4-D via a pathway initiated by the Fe(II) and α-ketoglutarate (Fe/αKG)-dependent aryloxyalkanoate dioxygenases (AADs). Recently, genes encoding 2 AADs have been deployed commercially in herbicide-tolerant crops. Some AADs can also inactivate chiral phenoxypropionate and aryloxyphenoxypropionate (AOPP) herbicides, albeit with varying substrate enantioselectivities. Certain AAD enzymes, such as AAD-1, have expanded utility in weed control systems by enabling the use of diverse modes of action with a single trait. Here, we report 1) the use of a genomic context-based approach to identify 59 additional members of the AAD class, 2) the biochemical characterization of AAD-2 from Bradyrhizobium diazoefficiens USDA 110 as a catalyst to degrade (S)-stereoisomers of chiral synthetic auxins and AOPP herbicides, 3) spectroscopic data that demonstrate the canonical ferryl complex in the AAD-1 reaction, and 4) crystal structures of representatives of the AAD class. Structures of AAD-1, an (R)-enantiomer substrate-specific enzyme, in complexes with a phenoxypropionate synthetic auxin or with AOPP herbicides and of AAD-2, which has the opposite (S)-enantiomeric substrate specificity, reveal the structural basis for stereoselectivity and provide insights into a common catalytic mechanism.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

SU-E-T-245: MR Guided Focused Ultrasound Increased PARP Related Apoptosis On Prostate Cancer in Vivo

Purpose: Our previous study demonstrated that significant tumor growth delay was observed in the mice treated with pulsed high intensity focused ultrasound (pHIFU). The purpose of this study is to understand the cell killing mechanisms of pHIFU. Methods: Prostate cancer cells (LNCaP), were grown orthotopically in 17 nude mice. Tumor-bearing mice were treated using pHIFU with an acoustic power of 25W, pulse width 100msec and 300 pulses in one sonication under MR guidance. Mutiple sonications were used to cover the whole tumor volume. Temperature (less than 40 degree centigrade in the focal spot) was monitored using MR thermometry. Animals were euthanized at pre-determined time points (n=2) after treatment: 0 hours; 6 hrs; 24 hrs; 48 hrs; 4 days and 7 days. Two tumorbearing mice were used as control. Three tumor-bearing mice were treated with radiation (RT, 2 Gy) using 6 MV photon beams. RT treated mice were euthanized at 0 hr, 6 hrs and 24 hrs. The tumors were processed for immunohistochemical (IHC) staining for PARP (a surrogate of apoptosis). A multispectral imaging analysis system was used to quantify the expression of PARP staining. Cell apoptosis was calculated based on the PARP expression level, which is the intensity of the DAB reaction. Results: Our data showed that PARP related apoptosis peaked at 48 hrs and 7 days in pHIFU treated mice, which is comparable to that for the RT group at 24 hrs. The preliminary results from this study were consistent with our previous study on tumor growth delay using pHIFU. Conclusion: Our results demonstrated that non-thermal pHIFU increased apoptotic tumor cell death through the PARP related pathway. MR guided pHIFU may have a great potential as a safe, noninvasive treatment modality for cancer therapy. This treatment modality might be able to synergize with PARP inhibitors to achieve better result.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Installation and Commissioning of the Netzsch Skimmer

The DOE molten salt reactor (MSR) program has been focusing on the thermochemistry and transport properties of fuel, diluent/carrier, coolant, flush, and reprocessing salts proposed for various molten salt reactor technologies. Data from the chemistry project inform models of salt behavior used in dynamic models of nuclear salt reactors, for both high fidelity and systems simulations. Reactor and salt processing systems operate well above salt melting points (>600°C), so salt behavior can be well described by thermodynamics. However, much is not known about salt systems that contain two, three, or even more components. The Netzsch skimmer (commissioned this year) can be used in several configurations to collect data on molten systems. The skimmer uses mass spectrometry coupled with a thermogravimetric analyzer to accurately analyze systems up to 2000°C. Because the mass analyzer is coupled directly to the furnace through two nested orifices, there are no losses due to condensation. As a thermogravimetric analyzer, the skimmer measures weight loss and reaction energies simultaneously with evolved gas analysis. The mass spectrometry identifies gas phase species, and these volatility measurements can be used to derive vapor pressures. The skimmer was purchased in fiscal year 2018, delivered in April, installed in May 2019, and now is fully operational as verified by the analysis of known standards. The skimmer is unique because it will be available for study of salt systems that contain actinides or beryllium, although the additional work control to accommodate these hazards is still under review.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2019

Thermodynamic controls on redox-driven kinetic stable isotope fractionation

Stable isotope fractionation arising from redox reactions has the potential to illuminate the oxygenation of Earth's interior, oceans, and atmosphere. However, reconstruction of past and present redox conditions from stable isotope signatures is complicated by variable fractionations associated with different reduction pathways. Here we demonstrate a linear relationship between redox-driven kinetic fractionation and the standard free energy of reaction for aqueous chromium(VI) reduction by iron(II) species. We also show that the intrinsic kinetic fractionation factor is log-linearly correlated with the rate constant of reaction, which is in turn a function of the free energy of reaction. The linear free energy relationship for kinetic fractionation describes both our experimental results and previous observations of chromium isotope fractionation and allows the magnitude of fractionation to be directly linked to environmental conditions such as pH and oxygen levels. By demonstrating that the magnitude of kinetic fractionation can be thermodynamically controlled, this study systematically explains the large variability in chromium(VI) isotope fractionation and provides a conceptual framework that is likely applicable to other isotope systems.

58 GEOSCIENCES↗