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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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Supercritical Carbon Dioxide Power Cycle Design and Configuration Optimization to Minimize Levelized Cost of Energy of Molten Salt Power Towers Operating at 650 °C
This analysis investigates the design, cost, and performance of the simple, recompression, and partial-cooling configurations of the supercritical carbon dioxide power cycle integrated with a molten salt power tower concentrating solar power system. This paper uses a steady-state model to design each cycle with varying amounts of recuperator conductance to understand performance and cost trade-offs. The recompression cycle can achieve a higher thermal efficiency than the partial-cooling cycle, and the partial-cooling cycle achieves a higher thermal efficiency than the simple cycle. The partial-cooling cycle is the most expensive cycle because it requires more total turbomachinery capacity. However, the partial-cooling cycle has the largest temperature range of heat input. This feature leads to cheaper two-tank thermal energy storage, higher receiver efficiencies, and lower mass flow rates in the power tower. Crucially, the lower mass flow rates significantly reduce pump electricity consumption relative to the recompression-cycle system. Consequently, this study finds that the power tower system integrated with the partial-cooling cycle is both cheaper and generates more net electricity than systems integrated with the other two cycles. Finally, this paper presents a parametric study on the air-cooler approach temperature and shows that small approach temperatures can improve cycle efficiency and increase the temperature range of heat input, which can lead to smaller optimal approach temperatures than may be expected.
Evaluation of conditions to minimize mercury losses from leaching test eluates
Not Available
Development of a human live attenuated West Nile infectious DNA vaccine: Identification of a minimal mutation set conferring the attenuation level acceptable for a human vaccine
ABSTRACT: For the development of a human West Nile (WN) infectious DNA (iDNA) vaccine, we created highly attenuated chimeric virus W1806 with the serological identity of highly virulent WN-NY99. Earlier, we attempted to utilize mutations found in the E protein of the SA14-14-2 vaccine to bring safety of W1806 to the level acceptable for human use (). Here, we analyzed effects of the SA14-14-2 changes on growth properties and neurovirulence of W1806. A set including the E138K, K279M, K439R and G447D changes was identified as the perspective subset for satisfying the target safety profile without compromising immunogenicity of the vaccine candidate. The genetic stability of the attenuated phenotype was found to be unsatisfactory being dependent on a subset of attenuating changes incorporated in W1806. Elucidation of underlying mechanisms influencing selection of pathways for restoration of the envelope protein functionality will facilitate resolution of the emerged genetic stability issue. - Highlights: •Effect of mutations in E on properties of WN1806 is determined. •A subset of attenuating mutations suitable for a human vaccine is defined. •Mechanism of attenuation is proposed and illustrated. •Underlying mechanisms of neurovirulence reversion are suggested.
Balancing Technological Innovation with Waste Burden Minimization: An Examination of the Global Lighting Industry
This paper examines the waste burden associated with an evolving waste stream: residential lighting. To understand the impact of lighting we used life cycle assessment analysis of LED products. We developed several personas representing different pats of the product adoption curve to quantify the volume and change rate of lighting products. The personas have also been used to estimate the waste impact for larger populations. The results indicate that the waste burden of high performance lighting still requires recycling programs and policies to prevent significant levels of waste to landfills. The results also confirm that attention must be paid to how to reduce the waste burden of LED lighting products through improved design.
Predicting novel substrates for enzymes with minimal experimental effort with active learning
Enzymatic substrate promiscuity is more ubiquitous than previously thought, with significant consequences for understanding metabolism and its application to biocatalysis. This realization has given rise to the need for efficient characterization of enzyme promiscuity. Enzyme promiscuity is currently characterized with a limited number of human-selected compounds that may not be representative of the enzyme's versatility. While testing large numbers of compounds may be impractical, computational approaches can exploit existing data to determine the most informative substrates to test next, thereby more thoroughly exploring an enzyme's versatility. Here, to demonstrate this, we used existing studies and tested compounds for four different enzymes, developed support vector machine (SVM) models using these datasets, and selected additional compounds for experiments using an active learning approach. SVMs trained on a chemically diverse set of compounds were discovered to achieve maximum accuracies of similar to 80% using similar to 33% fewer compounds than datasets based on all compounds tested in existing studies. Active learning-selected compounds for testing resolved apparent conflicts in the existing training data, while adding diversity to the dataset. Finally, the application of these algorithms to wide arrays of metabolic enzymes would result in a library of SVMs that can predict high-probability promiscuous enzymatic reactions and could prove a valuable resource for the design of novel metabolic pathways.
A Method for Plan-View FIB Liftout of Near Surface Defects with Minimal Beam-Induced Damage.
Abstract not provided.
Minimizing Crinkling of Soft Specimens Using Holey Gold Films on Molybdenum Grids for Cryogenic Electron Microscopy
We introduce a novel composite holey gold support that prevents cryo-crinkling and reduces beam-induced motion of soft specimens, building on the previously introduced all-gold support. The composite holey gold support for high-resolution cryogenic electron microscopy of soft crystalline membranes was fabricated in two steps. In the first step, a holey gold film was transferred on top of a molybdenum grid. In the second step, a continuous thin carbon film was transferred onto the holey gold film. This support (Au/Mo grid) was used to image crystalline synthetic polymer membranes. The low thermal expansion of Mo is not only expected to avoid cryo-crinkling of the membrane when the grids are cooled to cryogenic temperatures, but it may also act to reduce whatever crinkling existed even before cooling. Here, the Au/Mo grid exhibits excellent performance with specimens tilted to 45°. This is demonstrated by quantifying beam-induced motion and differences in local defocus values. In addition, images of specimens on the Au/Mo grids that are tilted at 45° show high-resolution information of the crystalline membranes that, after lattice-unbending, extends beyond 1.5 Å in the direction perpendicular to the tilt axis.
Application of Dislocation Theory to Minimize Defects in Artificial Solids Built with Nanocrystal Building Blocks
Conspectus. Oriented atomic attachment of colloidal inorganic nanocrystals represents a powerful synthetic method for preparing complex inorganic superstructures. Examples include fusion of nanocrystals into dimer and superlattice structures. If the attachment were perfect throughout, then the resulting materials would have single crystal-like alignment of the individual nanocrystals' atomic lattices. While individual colloidal nanocrystals typically are free of many defects, there are a multitude of pathways that can generate defects upon nanocrystal attachment. These attachment generated defects are typically undesirable, and thus developing strategies to favor defect-free attachment or heal defective interfaces are essential. There may also be some cases where attachment-derived defects are desirable. In this Account, we summarize our current understanding of how these defects arise, in order to offer guidance to those who are designing nanocrystal derived solids. The small size of inorganic nanocrystals means short diffusion lengths to the surface, which favor the formation of nanocrystal building blocks with pristine atomic structures. Upon attachment, however, there are numerous pathways that can lead to atomic scale defects, and bulk crystal dislocation theory provides an invaluable guide to understanding these phenomena. As an example, an atomic step edge can be incorporated into the interface leading to an extra half-plane of atoms, known as an edge dislocation. These dislocations can be well described by the Burgers vector description of dislocations, which geometrically identifies planes in which a dislocation can move. Our in situ measurements have verified that bulk dislocation theory predictions for 1D defects hold true at few-nanometer length scales in PbTe and CdSe nanocrystal interfaces. Ultimately, the applicability of dislocation theory to nanocrystal attachment enables the predictive design of attachment to prevent or facilitate healing of defects upon nanocrystal attachment. We applied similar logic to understand formation of planar (2D) defects such as stacking faults upon nanocrystal attachment. Again concepts from bulk crystal defect crystallography can identify attachment pathways that can prevent or deterministically form planar defects upon nanocrystal attachment. The concepts we discuss work well for identifying favorable attachment geometries for nanocrystal pairs ; however it is currently unclear how to translate these ideas to near-simultaneous multiparticle attachment. Geometric frustration, which prevents nanocrystal rotation, and yet-to-be considered defect generation pathways unique to multiparticle attachment complicate defect-free superlattice attachment. New imaging methods now allow for the direct observation of local attachment trajectories and may enable improved understanding of such multiparticle phenomena. With further refinement, a unified framework for understanding and ultimately eliminating structural defects in fused nanocrystal superstructures may well be achievable in coming years.
Structures of Class Id Ribonucleotide Reductase Catalytic Subunits Reveal a Minimal Architecture for Deoxynucleotide Biosynthesis
Class I ribonucleotide reductases (RNRs) share a common mechanism of nucleotide reduction in a catalytic α subunit. All RNRs initiate catalysis with a thiyl radical, generated in class I enzymes by a metallocofactor in a separate β subunit. Class Id RNRs use a simple mechanism of cofactor activation involving oxidation of a Mn II 2 cluster by free superoxide to yield a metal-based Mn III Mn IV oxidant. This simple cofactor assembly pathway suggests that class Id RNRs may be representative of the evolutionary precursors to more complex class Ia–c enzymes. X-ray crystal structures of two class Id α proteins from Flavobacterium johnsoniae (Fj) and Actinobacillus ureae (Au) reveal that this subunit is distinctly small. The enzyme completely lacks common N-terminal ATP-cone allosteric motifs that regulate overall activity, a process that normally occurs by dATP-induced formation of inhibitory quaternary structures to prevent productive β subunit association. Class Id RNR activity is insensitive to dATP in the Fj and Au enzymes evaluated here, as expected. However, the class Id α protein from Fj adopts higher-order structures, detected crystallographically and in solution. The Au enzyme does not exhibit these quaternary forms. Our study reveals structural similarity between bacterial class Id and eukaryotic class Ia α subunits in conservation of an internal auxiliary domain. Overall, our findings with the Fj enzyme illustrate that nucleotide-independent higher-order quaternary structures can form in simple RNRs with truncated or missing allosteric motifs.
Minimal Impacts of Microplastics on Soil Physical Properties under Environmentally Relevant Concentrations
Agricultural soils are a major reservoir of microplastics, and concerns have arisen about the impacts of microplastics on soil properties and functioning. In this report we measured the physical properties of a silt loam in response to the incorporation of polyester fibers and polypropylene granules over a wide range of concentrations. We further elucidated the underlying mechanisms through determining the role of microplastic shape and the baseline effects from the amendment of soil particles. The incorporation of microplastics into soil tended to increase contact angle and saturated hydraulic conductivity, decrease bulk density and water holding capacity, while did not affect aggregate stability. Polyester fibers affected soil physical properties more profoundly than polypropylene granules, due to the vastly different shape of fibers from that of soil particles. However, changes in soil properties were gradual, and significant changes did not occur until a high concentration of microplastics was reached (i.e., 0.5% w/w for polyester fibers and 2% w/w for polypropylene granules). Currently, microplastic concentrations in soils not heavily polluted with plastics are far below these concentrations, and results from this study suggest that microplastics at environmentally relevant concentrations have no significant effects on soil physical properties.
Minimal Kinetic Model of Direct Air Capture of CO 2 by Supported Amine Sorbents in Dry and Humid Conditions
Not Available
Utilizing Charge Effects and Minimizing Intramolecular Proton Rearrangement to Improve the Overpotential of a Thiosemicarbazonato Zinc HER Catalyst
The zinc(II) complex of diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-hydrazonepyridine), ZnL 1 (1), was prepared and evaluated as a precatalyst for the hydrogen evolution reaction (HER) under homogeneous conditions in acetonitrile. Complex 1 is protonated on the noncoordinating nitrogen of the hydrazonepyridine moiety to yield the active catalyst Zn(HL 1 )OAc (2) upon addition of acetic acid. Addition of methyl iodide to 1 yields the corresponding methylated derivative ZnL 2 I (3). In solution, partial dissociation of the coordinated iodide yields the cationic derivative 3'. Complexes 1–3 were characterized by 1 H NMR, FT-IR, and UV–visible spectroscopies. The solid-state structures of 2 and 3 were determined by single crystal X-ray diffraction. HER studies conducted in acetonitrile with acetic acid as the proton source yield a turnover frequency (TOF) of 7700 s –1 for solutions of 1 at an overpotential of 1.27 V and a TOF of 6700 s –1 for solutions of 3 at an overpotential of 0.56 V. For both complexes, the required potential for catalysis, E cat/2 , is larger than the thermodynamic reduction potential, E 1/2 , indicative of a kinetic barrier attributed to intramolecular proton rearrangement. The effect is larger for solutions of 1 (+440 mV) than for solutions of 3 (+160 mV). Controlled potential coulometry studies were used to determine faradaic efficiencies of 71 and 89% for solutions of 1 and 3, respectively. For both catalysts, extensive cycling of potential under catalytic conditions results in the deposition of a film on the glassy carbon electrode surface that is active as an HER catalyst. Analysis of the film of 3 by X-ray photoelectron spectroscopy indicates the complex remains intact upon deposition. A proposed ligand-centered HER mechanism with 1 as a precatalyst to 2 is supported computationally using density functional theory (DFT). All catalytic intermediates in the mechanism were structurally and energetically characterized with the DFT/B3LYP/6-311g(d,p) in solution phase using a polarizable continuum model (PCM). Finally, the thermodynamic feasibility of the mechanism is supported by calculation of equilibrium constants or reduction potentials for each proposed step.
Discovery of 1-(3,3-Dimethylbutyl)-3-(2-fluoro-4-methyl-5-(7-methyl-2-(methylamino)pyrido[2,3- d ]pyrimidin-6-yl)phenyl)urea (LY3009120) as a Pan-RAF Inhibitor with Minimal Paradoxical Activation and Activity against BRAF or RAS Mutant Tumor Cells
The RAS-RAF-MEK-MAPK cascade is an essential signaling pathway, with activation typically mediated through cell surface receptors. The kinase inhibitors vemurafenib and dabrafenib, which target oncogenic BRAF V600E, have demonstrated significant clinical efficacy in melanoma patients harboring this mutation. Because of paradoxical pathway activation, both agents were demonstrated to promote growth and metastasis of tumor cells with RAS mutations in preclinical models and are contraindicated for treatment of cancer patients with BRAF WT background, including patients with KRAS or NRAS mutations. In order to eliminate the issues associated with paradoxical MAPK pathway activation and to provide therapeutic benefit to patients with RAS mutant cancers, we sought to identify a compound not only active against BRAF V600E but also wild type BRAF and CRAF. On the basis of its superior in vitro and in vivo profile, compound 13 was selected for further development and is currently being evaluated in phase I clinical studies.
Removal of Ca 2+ from the Oxygen-Evolving Complex in Photosystem II Has Minimal Effect on the Mn 4 O 5 Core Structure: A Polarized Mn X-ray Absorption Spectroscopy Study
We studied Ca 2+ -depleted and Ca 2+ -reconstituted spinach photosystem II using polarized X-ray absorption spectroscopy of oriented PS II preparations to investigate the structural and functional role of the Ca 2+ ion in the Mn 4 O 5 Ca cluster of the oxygen-evolving complex (OEC). Samples were prepared by low pH/citrate treatment as one-dimensionally ordered membrane layers and poised in the Ca 2+ -depleted S 1 (S 1 ') and S 2 (S 2 ') states, the S 2 'Y Z • state, at which point the catalytic cycle of water oxidation is inhibited, and the Ca 2+ -reconstituted S 1 state. Polarized Mn K-edge XANES and EXAFS spectra exhibit pronounced dichroism. Polarized EXAFS data of all states of Ca 2+ -depleted PS II investigated show only minor changes in distances and orientations of the Mn-Mn vectors compared to the Ca 2+ -containing OEC, which may be attributed to some loss of rigidity of the core structure. Thus, removal of the Ca 2+ ion does not lead to fundamental distortion or rearrangement of the tetranuclear Mn cluster, which indicates that the Ca 2+ ion in the OEC is not critical for structural maintenance of the cluster, at least in the S 1 and S 2 states, but fulfills a crucial catalytic function in the mechanism of the water oxidation reaction. On the basis of this structural information, reasons for the inhibitory effect of Ca 2+ removal are discussed, attributing to the Ca 2+ ion a fundamental role in organizing the surrounding (substrate) water framework and in proton-coupled electron transfer to Y Z • (D1-Tyr161).