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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Tunable CHA/AEI Zeolite Intergrowths with A Priori Biselective Organic Structure‐Directing Agents: Controlling Enrichment and Implications for Selective Catalytic Reduction of NOx

Abstract A novel ab initio methodology based on high‐throughput simulations has permitted designing unique biselective organic structure‐directing agents (OSDAs) that allow the efficient synthesis of CHA/AEI zeolite intergrowth materials with controlled phase compositions. Distinctive local crystallographic ordering of the CHA/AEI intergrowths was revealed at the nanoscale level using integrated differential phase contrast scanning transmission electron microscopy (iDPC STEM). These novel CHA/AEI materials have been tested for the selective catalytic reduction (SCR) of NOx, presenting an outstanding catalytic performance and hydrothermal stability, even surpassing the performance of the well‐established commercial CHA‐type catalyst. This methodology opens the possibility for synthetizing new zeolite intergrowths with more complex structures and unique catalytic properties.

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

Thermal Transport and Fracture Behavior of Sintered Fuel Pellets: Experimental Validation of NEAMS Tool MARMOT

The project targets at experimental validation of NEAMS tool MARMOT for predicting thermal transport and fuel fracture. The key components of the project include: (1) sintering UO 2 samples with well-controlled microstructures (grain size, pore, fission bubble, porosity and pore distribution either in intra- or inter-granular pores); (2) thermal conductivity measurements of these wellcharacterized polycrystalline samples; (3) indentation testing of sintered UO 2 with various grain size, porosity and stoichiometry to obtain fracture and crack propagation mechanisms (inter or intragranular fracture); and (4) validation and uncertainty quantification of the MARMOT thermal transport and fracture models. The high quality experimental data will be used to validate the predictions of MARMOT for thermal transport and fracture, using average data and local microstructure information. In this work, UO 2 fuels with controlled microstructure (grain size, pore size/structure and fuel chemistry) were successfully prepared by high energy ball milling of the hyper-stoichiometric UO 2+x powders purchased commercially, and consolidated by spark plasma sintering. Dense nano-sized UO 2 fuel pellets with controlled stoichiometry were sintered by SPS. The effects of different SPS sintering parameters on the pore size and distribution were investigated, and the correlation among the SPS parameter – microstructure control – stoichiometry/defect structure was established. To further control the pore structure and fuel chemistry, systematic thermal annealing of the sintered fuels with the controlled pore structure was performed in a reduced. The controlled microstructure and fuel chemistry enable the investigation of the separate effects of pore structure and fuel chemistry on thermal transport behavior. The mechanical properties of the sintered UO 2 fuels were tested by nanoindentation and microindentation testing at different temperatures. The fracture behavior of the sintered fuels as functions of grain structure and temperature was investigated. Nanocrystalline UO 2 display higher hardness than microcrystalline counterpart, consistent with the Hall-Petch strengthening mechanism. Greater Young’s modulus and fracture toughness are also identified for the nanocrystalline UO 2 , and hardness and Young’s modulus decrease with temperature, suggesting better ductility of oxide fuels at greater temperature at small length scale. Hyper-stoichiometric UO 2 specimen displays higher hardness and fracture toughness than stoichiometric UO 2 , due to the impediment of the crack propagation by the oxygen interstitial atoms. These results are useful in understanding the mechanical properties of the high burn-up structure (HBS) formed in nuclear fuels during reactor operation, and also provide critical experimental data as the input for the development and validation of the MARMOT fracture model of nuclear fuels. The thermal properties of the sintered UO 2 fuel pellets with controlled grain structure, fuel chemistry and pore structures are measured by laser flash and the impact of the microstructure characteristics on the thermal transport properties is elucidated. Through a close collaboration with the MARMOT team at Idaho National Laboratory, the thermal properties of the sintered oxide fuel pellets with controlled microstructures are measured experimentally, and modeled using the developed MARMOT thermal transport models for a joint effort of demonstrating high spatial resolution measurements at the microstructural level on as-fabricated nuclear fuels and materials and obtain critical experimental data for model validation and properties predictions. In this work, we also conducted sensitivity analysis and uncertainty quantification (UQ) on a mesoscale simulation that has been applied to understand the effective thermal conductivity of UO 2 reactor fuel using the MARMOT tool. We also conduced UQ on mechanistic macroscale models that have been developed to predict the effective thermal conductivity. The most sensitive parameter is the thermal conductivity of bulk UO 2 for the thermal conductivity models. In the future, the predicted simulation distributions need to be compared to experimental data for validation of the models.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

pH control of the structure, composition, and catalytic activity of sulfated zirconia

We report a detailed study of structural and chemical transformations of amorphous hydrous zirconia into sulfated zirconia-based superacid catalysts. Precipitation pH is shown to be the key factor governing structure, composition and properties of amorphous sulfated zirconia gels and nanocrystalline sulfated zirconia. Increase in precipitation pH leads to substantial increase of surface fractal dimension (up to {approx}2.7) of amorphous sulfated zirconia gels, and consequently to increase in specific surface area (up to {approx}80 m{sup 2}/g) and simultaneously to decrease in sulfate content and total acidity of zirconia catalysts. Complete conversion of hexene-1 over as synthesized sulfated zirconia catalysts was observed even under ambient conditions. - Graphical abstract: Surface fractal dimension of amorphous sulfated zirconia and specific surface area and catalytic activity of crystalline sulfated zirconia as a function of precipitation pH. Highlights: Black-Right-Pointing-Pointer Structural transformation of amorphous hydrous zirconia into sulfated zirconia is studied. Black-Right-Pointing-Pointer Precipitation pH controls surface fractal dimension of amorphous zirconia gels. Black-Right-Pointing-Pointer Precipitation pH is the key factor governing properties of sulfated zirconia.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Compositional Control on Shale Pore Structure Characteristics across a Maturation Gradient: Insights from the Devonian New Albany Shale and Marcellus Shale in the Eastern United States

The pore structure characteristics of shales are controlled by their mineralogical and organic matter (OM) composition. However, the contributions by different components in shales at varying thermal maturities remain poorly understood. In this study, Devonian New Albany Shale and Marcellus Shale samples spanning a thermal maturity from marginally mature (vitrinite reflectance R o 0.55%) to post-mature (R o 2.41 %) were selected to study the control of composition on the pore structure properties of shales at different stages of thermal maturation. Scanning electron microscope (SEM) imaging was used to examine pore types in shales, and low-pressure N 2 and CO 2 adsorption analyses were used to quantitatively characterize the mesopore and micropore characteristics of bulk shales and major components in shales. The results show that matrix-associated pores including interparticle pores between silt-sized mineral grains, phyllosilicate framework pores, and intraparticle pores within mineral grains exist in all samples but become less common with increasing maturity, which is likely caused by elevated compaction, cementation, and occlusion with bitumen. Secondary organic pores were not observed under SEM at marginal maturity but were detected in the condensate–wet gas and dry gas windows, with more organic pores in the dry gas window. At marginal maturity, OM has large amounts of mesopores and micropores as demonstrated by low-pressure N 2 and CO 2 adsorption analyses of OM isolated from shales, even though no OM-hosted pores were observed under SEM. With increasing thermal maturity, the mesopore and micropore specific surface area of OM increase and make greater contributions to the pore structure properties of bulk shales. The mesopore and micropore properties of shales are controlled by OM content and maturity as well as by clay mineral type and content, and they can be estimated from the contribution of each component at different stages of thermal maturation. In conclusion, accurate evaluation of the pore volume and SSA of shales will have important implications for assessing gas adsorption and transport in shales.

03 NATURAL GAS↗
DOE OSTI2015

Technical report on "BES Early Career. Control Graphene Electronic Structure for Energy Technology"

Graphene, a one-atom thick sheet of carbon, exhibits incredible structural flexibility, electrical transport, and optical responses. And remarkably, the graphene electronic structure can be varied through interlayer coupling, nanoscale patterning, and electrical gating. In this project we made significant contribution to better understand and control physical properties of graphene and other novel two-dimensional layered materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ionization-Based Optical Structures for the Control of Short-Pulse Lasers (Full LDRD Report)

High-power lasers require enormous beam sizes to avoid optics damage; without plasma control of light, future higher-power systems will have prohibitive costs. The laser-induced formation of ionization patterns in gases provides an opportunity to manipulate the spatial and temporal properties of femtosecond to picosecond beams with precise control at high intensity, providing a path towards compact multi-petawatt lasers. In this project, we proposed new concepts of diffractive optics elements relying on ionization-based structures, including a holographic lens and a compression grating. The theoretical characterization of these optical elements was supported by particle-in-cell simulations. Experiments have been carried out to achieve reflective elements (i.e., plasma-based gratings) that demonstrated high robustness and efficiencies on the order of 50%, which validates the feasibility of our new concepts and paves the way for future plasma-based high-power laser systems.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Helical Poly(5-alkyl-2,3-thiophene)s: Controlled Synthesis and Structure Characterization

Whereas Poly(3-alkyl-2,5-thiophene)s (P3AT), with many potential applications, have been extensively investigated, their ortho-connected isomers, poly(5-alkyl-2,3-thiophene)s (P5AT), have never been reported because of the difficulty in their syntheses. We herein present the first synthesis of regioregular P5AT via controlled Suzuki cross-coupling polymerization with PEPPSI-IPr as catalyst, affording the polymers with tunable molecular weight, narrow polydispersity (PDI) and well-defined functional end groups at the gram scale. The helical geometry of P5AT was studied by a combination of NMR, small angle x-ray scattering (SAXS) and scanning tunneling microscopy (STM). Particularly, the single polymer chain of poly(5- 2 butyl-2,3-thiophene) (P5BT) on highly oriented pyrolytic graphite (HOPG) substrates with either M or P helical conformation was directly observed by STM. The comparison of UV-vis absorption between poly(5-hexyl-2,3-thiophene) (P5HT) (λ = 345 nm) and poly(3-hexyl-2,5- thiophene) (P3HT) (λ = 450 nm) indicated that the degree of conjugation of the backbone in P5HT is less than in P3HT, which may be a consequence of the helical geometry of the former compared to the more planar geometry of the latter. Moreover, we found that P5HT can emit green fluorescence under UV (λ = 360 nm) irradiation

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Structural switching dynamically controls the doubly pseudoknotted Rous sarcoma virus–programmed ribosomal frameshifting element

A hallmark of retrovirus replication is the translation of two different polyproteins from one RNA through programmed –1 frameshifting. This is a mechanism in which the actively translating ribosome is induced to slip in the 5′ direction at a defined codon and then continues translating in the new reading frame. Programmed frameshifting controls the stoichiometry of viral proteins and is therefore under stringent evolutionary selection. Forty years ago, the first frameshifting stimulatory element was discovered in the Rous sarcoma virus. The ~120 nt RNA segment was predicted to contain a pseudoknot, but its 3D structure has remained elusive. Now, we have determined cryoEM and X-ray crystallographic structures of this classic retroviral element, finding that it adopts a butterfly-like double-pseudoknot fold. One “wing” contains a dynamic pyrimidine-rich helix, observed crystallographically in two conformations and in a third conformation via cryoEM. The other wing encompasses the predicted pseudoknot, which interacts with a second unexpected pseudoknot through a toggle residue, A2546. This key purine switches conformations between structural states and tunes the stability of interacting residues in the two wings. We find that its mutation can modulate frameshifting by as much as 50-fold, likely by altering the relative abundance of different structural states in the conformational ensemble of the RNA. Taken together, our structure–function analyses reveal how a dynamic double pseudoknot junction stimulates frameshifting by taking advantage of conformational heterogeneity, supporting a multistate model in which high Shannon entropy enhances frameshifting efficiency.

Science & Technology - Other Topics↗
DOE OSTI2017

Adjoint-based optimization of mechanical performance in polycrystalline materials and structures through texture control

The texture of a polycrystalline material refers to the preferred orientation of the grains within the material. In metallic materials, texture can significantly affect the mechanical properties such as elastic moduli, yield stress, strain hardening, and fracture toughness. Recent advances in additive manufacturing of metallic materials offer the possibility in the not too distant future of controlling the spatial variation of texture. In this work, we investigate the advantages, in terms of mechanical performance, of allowing the texture to vary spatially. We use an adjoint-based gradient optimization algorithm within a finite element solver (COMSOL) to optimize several engineering quantities of interest in a simple structure (hole in a plate) and loading (uniaxial tension) condition. As a first step to general texture optimization, we consider the idealized case of a pure fiber texture in which the homogenized properties are transversely isotropic. In this special case, the only spatially varying design variables are the three Euler angles that prescribe the orientation of the homogenized material at each point within the structure. This work paves a new way to design metallic materials for tunable mechanical properties at the microstructure level.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural basis of control of inward rectifier Kir2 channel gating by bulk anionic phospholipids

Inward rectifier potassium (Kir) channel activity is controlled by plasma membrane lipids. Phosphatidylinositol-4,5-bisphosphate (PIP 2 ) binding to a primary site is required for opening of classic inward rectifier Kir2.1 and Kir2.2 channels, but interaction of bulk anionic phospholipid (PL - ) with a distinct second site is required for high PIP 2 sensitivity. Here we show that introduction of a lipid-partitioning tryptophan at the second site (K62W) generates high PIP 2 sensitivity, even in the absence of PL - . Furthermore, high-resolution x-ray crystal structures of Kir2.2[K62W], with or without added PIP 2 (2.8- and 2.0-Å resolution, respectively), reveal tight tethering of the C-terminal domain (CTD) to the transmembrane domain (TMD) in each condition. Our results suggest a refined model for phospholipid gating in which PL - binding at the second site pulls the CTD toward the membrane, inducing the formation of the high-affinity primary PIP 2 site and explaining the positive allostery between PL - binding and PIP 2 sensitivity.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Optical control of ultrafast structural dynamics in a fluorescent protein

The photoisomerization reaction of a fluorescent protein chromophore occurs on the ultrafast timescale. The structural dynamics that result from femtosecond optical excitation have contributions from vibrational and electronic processes and from reaction dynamics that involve the crossing through a conical intersection. The creation and progression of the ultrafast structural dynamics strongly depends on optical and molecular parameters. When using X-ray crystallography as a probe of ultrafast dynamics, the origin of the observed nuclear motions is not known. Now, high-resolution pump–probe X-ray crystallography reveals complex sub-ångström, ultrafast motions and hydrogen-bonding rearrangements in the active site of a fluorescent protein. However, we demonstrate that the measured motions are not part of the photoisomerization reaction but instead arise from impulsively driven coherent vibrational processes in the electronic ground state. A coherent-control experiment using a two-colour and two-pulse optical excitation strongly amplifies the X-ray crystallographic difference density, while it fully depletes the photoisomerization process. A coherent control mechanism was tested and confirmed the wave packets assignment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ionization-Based Optical Structures for the Control of Short-Pulse Lasers (Abbreviated LDRD Report)

The intensity of light from the highest-power lasers is limited by the size of the optics required to amplify, compress, transport, and focus a laser beam. Indeed, optics damage puts strict constraints on the laser energy density that solid optics can sustain; this leads to enormous optics sizes and limits the maximum intensity that these lasers can achieve. In this project we investigated new types of diffractive optics based on mixtures of neutral gas and plasmas. The basic idea is to interfere laser beams in a gas near the ionization threshold, so that plasma is created in the constructive interference regions (i.e., the “bright” fringes of the interference pattern) while the destructive interference regions remain a neutral gas. The resulting refractive index modulation, due to the different indices in gas vs. plasma, effectively turns such structures into diffractive optics elements. We proposed several new types of optics based on this general concept: i) reflection gratings, which can act as mirrors of “pulse cleaners” to eliminate laser pre-pulse; ii) transmission gratings, as part of a new type of pulse compression scheme with the potential to achieve laser intensities orders of magnitude above what is currently feasible using solid-state optics; and iii) holographic lenses, to focus high-power lasers. We conducted laboratory experiments which demonstrated high efficiency reflection gratings, paving the way for practical applications of our new concepts.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Prediction of DIII-D Pedestal Structure From Externally Controllable Parameters

The sharp increase of pressure at the edge of a high confinement mode (H-mode) plasma, the pedestal, strongly impacts overall plasma performance. Predicting the pedestal is a necessity to control and optimize tokamak operations. Here, an experimental data-driven machine learning (ML) approach is presented that predicts the pedestal heights and widths of electron density (n e ) and electron temperature (T e ) profiles as well as the separatrix ne from externally controllable parameters such as the plasma shape, heating method and power, and gas puff rate and integrated gas puff. The OMFIT framework was used with DIII-D data to efficiently, robustly, and automatically build a database of pedestal parameters to train machine learning models. Database creation was enabled by the search engine tool for DIII-D data, TokSearch, which parallelizes data fetching, enabling fast searches through basic signals of thousands of DIII-D shots and selection of relevant time intervals. Principal Component Analysis (PCA) separated the database into three clusters that represent classes of plasma shapes that are regularly used in DIII-D. The most important parameters for setting the pedestal structure were plasma current (I p ), toroidal magnetic field (B Φ ), neutral beam heating power (P NBI ) and shaping quantities. The Deep Jointly Informed Neural Networks (DJINN) algorithm was applied to identify suitable neural network (NN) architectures that appropriately capture the features of the pedestal database. Separate NNs were implemented for each pedestal parameter, and ensembling methods were used to improve the prediction accuracy and allowed estimation of the prediction uncertainty. The pedestal predictions of the test dataset lie within the measurement uncertainties of the pedestal parameters. The NN outperformed simple Linear Regression (LR) analysis, indicating non-linear dependencies in the pedestal structure. The presented achievements illustrate a promising path for future research, using feature extraction to infer experimental trends and thereby improve pedestal models as well as deploying NN for a fast pedestal prediction in DIII-D scenario development.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Prediction of DIII-D Pedestal Structure from Externally Controllable Parameters

The sharp increase of pressure at the edge of a high confinement mode (H-mode) plasma, the pedestal, strongly impacts overall plasma performance. Predicting the pedestal is a necessity to control and optimize tokamak operations. An experimental data-driven machine learning (ML) approach is presented that predicts the pedestal heights and widths of electron density (ne) and electron temperature (Te) profiles as well as the separatrix ne from externally controllable parameters such as the plasma shape, heating method and power, and gas puff rate and integrated gas puff. The OMFIT framework was used with DIII-D data to efficiently, robustly, and automatically build a database of pedestal parameters to train machine learning models. Database creation was enabled by the search engine tool for DIII-D data, TokSearch, which parallelizes data fetching, enabling fast searches through basic signals of thousands of DIII-D shots and selection of relevant time intervals. Principal Component Analysis (PCA) separated the database into three clusters that represent classes of plasma shapes that are regularly used in DIII-D. The most important parameters for setting the pedestal structure were plasma current (Ip), toroidal magnetic field (Bφ), neutral beam heating power (PNBI) and shaping quantities. The Deep Jointly Informed Neural Networks (DJINN) algorithm was applied to identify suitable neural network (NN) architectures that appropriately capture the features of the pedestal database. Separate NNs were implemented for each pedestal parameter, and ensembling methods were used to improve the prediction accuracy and allowed estimation of the prediction uncertainty. The pedestal predictions of the test dataset lie within the measurement uncertainties of the pedestal parameters. The NN outperformed simple Linear Regression (LR) analysis, indicating non-linear dependencies in the pedestal structure. The presented achievements illustrate a promising path for future research, using feature extraction to infer experimental trends and thereby improve pedestal models as well as deploying NN for a fast pedestal prediction in DIII-D scenario development.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Controlling the electronic structure of graphene using surface-adsorbate interactions

Hybridization of atomic orbitals in graphene on Ni(111) opens up a large energy gap of ≈2.8eV between nonhybridized states at the K point. Here we use alkali-metal adsorbate to reduce and even eliminate this energy gap, and also identify a new mechanism responsible for decoupling graphene from the Ni substrate without intercalation of atomic species underneath. Using angle-resolved photoemission spectroscopy and density functional theory calculations, we show that the energy gap is reduced to 1.3 eV due to moderate decoupling after adsorption of Na on top of graphene. Calculations confirm that after adsorption of Na, graphene bonding to Ni is much weaker due to a reduced overlap of atomic orbitals, which results from n doping of graphene. Finally, we show that the energy gap is eliminated by strong decoupling resulting in a quasifreestanding graphene, which is achieved by subsequent intercalation of the Na underneath graphene. Furthermore, the ability to partially decouple graphene from a Ni substrate via n doping, with or without intercalation, suggests that the graphene-to-substrate interaction could be controlled dynamically.

36 MATERIALS SCIENCE↗