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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 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Process Parameter Optimization in Refill Friction Spot Welding of 6061 Aluminum Alloys Using Response Surface Methodology

6061-T6 aluminum alloy joint was fabricated by refill friction stir spot welding (RFSSW) on which three process parameters of tool rotation speed, sleeve moving rate, and plunge depth make an important effect. The response surface methodology (RSM) was applied to establish a mathematical model to study the effect of process parameters on lap shear fracture load (LSFL) of the RFSSWed joints which were performed in Box–Behnken designs with three factors, three levels and 15 runs. Analysis of variance used to check the adequacy of the developed model indicates that the mathematical model is significant. LSFL increases with the increase in tool rotation speed, sleeve plunge depth, and sleeve moving rate to maximum and then decreases. Sleeve plunge depth makes the most effect on LSFL in all process parameters. The RFSSW process parameters were also optimized using RSM to predict maximize LSFL. The joint produced using a tool rotational speed of 1506 rpm, sleeve moving rate of 1.01 mm/s and sleeve plunge depth of 2.46 mm displays higher LSFL.

36 MATERIALS SCIENCE↗
DOE OSTI2018

LncRNA MALAT1 regulates oxLDL-induced CD36 expression via activating β-catenin

Highlights: • The role of MALAT1 in lipid uptake was explored. • The regulatory mechanism of oxLDL-induced CD36 was also involved. • We first found oxLDL induces MALAT1 transcription by activating the NF-κB pathway. • MALAT1 promotes lipid uptake by promoting CD36 expression via activating β-catenin. The expression of scavenger receptors in macrophages regulating lipid uptake plays an important role in foam cell formation and the subsequent atherosclerotic plaque formation. Long non-coding RNA MALAT1 is abundantly expressed in THP-1-derived macrophages, and oxidized low-density lipoprotein promotes its transcription by qRT-PCR and RNA FISH detection. Through chemical inhibitor treatments and by performing a dual luciferase reporter analysis, we found that oxLDL induces MALAT1 transcription through the NF-κB pathway. The knockdown of MALAT1 using siRNA transfection affects lipid uptake in macrophages. To understand the details, we checked the scavenger receptors, which mainly control lipid uptake, and found that MALAT1 knockdown decreased CD36 expression. Additionally, we also incubated macrophages with actinomycin D, combined with a dual luciferase reporter analysis, and we found that MALAT1 influenced CD36 expression at the transcription level. We aim to investigate the detailed mechanism by which MALAT1 promotes CD36 transcription, and thus, we designed and synthesized biotin-TEG labeled oligonucleotides to precipitate the MALAT1 RNA-DNA-protein complex in vivo. Combined with SDS-PAGE electrophoresis and a subsequent mass spectra analysis, β-catenin, a transcription factor that promotes CD36 transcription, was found in the complex. By performing R-IPs, we validated that β-catenin was bound to MALAT1 under the oxLDL treatment. In addition, using VAX939, a chemical inhibitor of β-catenin, MALAT1 was demonstrated to promote CD36 transcription partly via β-catenin. We also performed chips to detect whether MALAT1 affects β-catenin accumulation in the binding sites of the CD36 promoter and found that MALAT1 knockdown decreases β-catenin binding to the CD36 promoter and vice versa. In conclusion, oxLDL induced MALAT1 transcription and MALAT1 recruits β-catenin to binding sites on the CD36 promoter to induce CD36 expression, which enhances lipid uptake in macrophages.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Biomass pretreatment with distillable ionic liquids for an effective recycling and recovery approach

Ionic liquid (IL) pretreatment methods show incredible promise for the efficient conversion of lignocellulosic feedstocks to fuels and chemicals. Given their low vapor pressures, distillation-based methods of extracting ionic liquids out of biomass post-pretreatment have historically been ignored in favor of alternative methods. We demonstrate a process to distill four acetate-based ionic liquids ([EthA][OAc], [PropA][OAc], [MAEthA][OAc], and [DMAEthA][OAc]) at low pressure and high purity that overcome some disadvantages of “water washing” and “one pot” recovery methods. Out of four tested ILs, ethanolamine acetate ([EthA][OAc]) is shown to have the most agreeable conversion metrics for commercial bioconversion processes achieving 73.6% and 51.4% of theoretical glucose and xylose yields respectively and >85 % recovery rates. Our process metrics are factored into a techno-economic analysis where [EthA][OAc] distillation is compared to other recovery methods as well as ethanolamine pretreatment at both milliliter and liter scales. In conclusion, although our TEA shows [EthA][OAc] distillation underperforming against other processes, we show a step-by-step avenue to reduce sugar production cost below the wholesale dextrose price at scale.

09 BIOMASS FUELS↗
DOE OSTI2021

Hydrological analysis in watersheds with a variable-resolution global climate model (VR-CESM)

Traditionally, watershed-scale hydrology is simulated by distributed hydrological models with offline meteorological forcing data, or by regional regional climate models that link atmospheric and land hydrology interactions. Global climate models (GCMs) are rarely used to study watershed-scale hydrology due to the relatively coarse grid resolution, computationally expensive downscaling, and simplified physical processes. Recently, however, watershed-scale hydrology analysis has become possible in GCMs due to the development of variable-resolution GCMs that dynamically couple the hydrological processes between atmosphere and land systems at fine resolutions in selected regions and coarse resolution elsewhere. In this study, we used the variable-resolution Community Earth System Model (VR-CESM) with refined-resolution (14 km) in the western U.S. and eastern China to evaluate watershed-scale hydrology. Furthermore, we compared the historical VR-CESM outputs with gauge measurements and other hydrological models (e.g., National Water Model in the U.S.) and calibrated the subsurface runoff capacities in four mountainous watersheds. An RCP8.5 projection from 2007 to 2050 is used to estimate the impact of changing precipitation and snow climatology on watershed hydrology. We also analyzed the long-term runoff variability and the possibility of extreme runoff events as simulated by the VR-CESM. Although calibration is not possible in larger-scale watersheds, VR-CESM simulates the long-term annual variability of watersheds and provides insights on climate change impacts on hydrology. We conclude that refined-resolution VR-CESM can be used for watershed-scale hydrology analysis to understand water resources and water balance, in addition to traditional watershed-scale hydrological models. It enables hydrological analysis at multiple watersheds in one simulation and can help understand the two-way dynamics between land surface hydrology and atmospheric processes, and is especially practical for projecting climate change impacts. However, it is challenging to apply VR-CESM for hydrologic analysis in regulated watersheds as human factors (e.g., pumping, irrigation, water diversion) have not been fully addressed in VR-CESM.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Molecular Structure of Sphingomyelin in Fluid Phase Bilayers Determined by the Joint Analysis of Small-Angle Neutron and X-ray Scattering Data

In this work, we have determined the fluid bilayer structure of palmitoyl sphingomyelin (PSM) and stearoyl sphingomyelin (SSM) by simultaneously analyzing small-angle neutron and X-ray scattering data. Using a newly developed scattering density profile (SDP) model for sphingomyelin lipids, we report structural parameters including the area per lipid, total bilayer thickness, and hydrocarbon thickness, in addition to lipid volumes determined by densitometry. Unconstrained all-atom simulations of PSM bilayers at 55 °C using the C36 CHARMM force field produced a lipid area of 56 Å 2 , a value that is 10% lower than the one determined experimentally by SDP analysis (61.9 Å2). Furthermore, scattering form factors calculated from the unconstrained simulations were in poor agreement with experimental form factors, even though segmental order parameter (S CD ) profiles calculated from the simulations were in relatively good agreement with S CD profiles obtained from NMR experiments. Conversely, constrained area simulations at 61.9 Å 2 resulted in good agreement between the simulation and experimental scattering form factors, but not with S CD profiles from NMR. We discuss possible reasons for the discrepancies between these two types of data that are frequently used as validation metrics for molecular dynamics force fields.

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

Polymer, Additives, and Processing Effects on N95 Filter Performance

The current severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) pandemic has highlighted the need for personal protective equipment, specifically filtering facepiece respirators like N95 masks. While it is common knowledge that polypropylene (PP) is the industry standard material for filtration media, trial and error is often required to identify suitable commercial precursors for filtration media production. This work aims to identify differences between several commercial grades of PP and demonstrate the development of N95 filtration media with the intent that the industry partners can pivot and help address N95 shortages. Three commercial grades of high melt flow index PP were melt blown at Oak Ridge National Laboratory and broadly characterized by several methods including differential scanning calorimetry (DSC), X-ray diffraction (XRD), and neutron scattering. Despite the apparent similarities (high melt flow and isotacticity) between PP feedstocks, the application of corona charging and charge enhancing additives improve each material to widely varying degrees. From the analysis performed here, the most differentiating factor appears to be related to crystallization of the polymer and the resulting electret formation. Materials with higher crystallization onset temperatures, slower crystallization rates, and larger number of crystallites form a stronger electret and are more effective at filtration.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Efficiency limits for photoelectrochemical water-splitting

Theoretical limiting efficiencies have a critical role in determining technological viability and expectations for device prototypes, as evidenced by the photovoltaics community’s focus on detailed balance. However, due to their multicomponent nature, photoelectrochemical devices do not have an equivalent analogue to detailed balance, and reported theoretical efficiency limits vary depending on the assumptions made. Here we introduce a unified framework for photoelectrochemical device performance through which all previous limiting efficiencies can be understood and contextualized. Ideal and experimentally realistic limiting efficiencies are presented, and then generalized using five representative parameters—semiconductor absorption fraction, external radiative efficiency, series resistance, shunt resistance and catalytic exchange current density—to account for imperfect light absorption, charge transport and catalysis. Finally, we discuss the origin of deviations between the limits discussed herein and reported water-splitting efficiencies. This analysis provides insight into the primary factors that determine device performance and a powerful handle to improve device efficiency.

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

Integrative genomics reveals paths to sex dimorphism in Salix purpurea L

Sex dimorphism and gene expression were studied in developing catkins in 159 F 2 individuals from the bioenergy crop Salix purpurea , and potential mechanisms and pathways for regulating sex development were explored. Differential expression, eQTL, bisulfite sequencing, and network analysis were used to characterize sex dimorphism, detect candidate master regulator genes, and identify pathways through which the sex determination region (SDR) may mediate sex dimorphism. Eleven genes are presented as candidates for master regulators of sex, supported by gene expression and network analyses. These include genes putatively involved in hormone signaling, epigenetic modification, and regulation of transcription. eQTL analysis revealed a suite of transcription factors and genes involved in secondary metabolism and floral development that were predicted to be under direct control of the sex determination region. Furthermore, data from bisulfite sequencing and small RNA sequencing revealed strong differences in expression between males and females that would implicate both of these processes in sex dimorphism pathways. These data indicate that the mechanism of sex determination in Salix purpurea is likely different from that observed in the related genus Populus . This further demonstrates the dynamic nature of SDRs in plants, which involves a multitude of mechanisms of sex determination and a high rate of turnover.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

High resolution spectral analysis of oxygen. IV. Energy levels, partition sums, band constants, RKR potentials, Franck-Condon factors involving the X{sup 3}Σ{sub g}{sup −}, a{sup 1}Δ{sub g} and b{sup 1}Σ{sub g}{sup +} states

We have updated the isotopically invariant Dunham fit of O{sub 2} with newly reported literature transitions to derive (1) the energy levels, partition sums, band-by-band molecular constants, and RKR potentials for the X{sup 3}Σ{sub g}{sup −}, a{sup 1}Δ{sub g}, and b{sup 1}Σ{sub g}{sup +} states of the six O{sub 2} isotopologues: {sup 16}O{sup 16}O, {sup 16}O{sup 17}O, {sup 16}O{sup 18}O, {sup 17}O{sup 17}O, {sup 17}O{sup 18}O, and {sup 18}O{sup 18}O; (2) Franck-Condon factors for their a{sup 1}Δ{sub g}−X{sup 3}Σ{sub g}{sup −}, b{sup 1}Σ{sub g}{sup +}−X{sup 3}Σ{sub g}{sup −}, and a{sup 1}Δ{sub g}−b{sup 1}Σ{sub g}{sup +} band systems. This new spectroscopic parameterization characterizes all known transitions within and between the X{sup 3}Σ{sub g}{sup −}, a{sup 1}Δ{sub g}, and b{sup 1}Σ{sub g}{sup +} states within experimental uncertainty and can be used for accurate predictions of as yet unmeasured transitions. All of these results are necessary to provide a consistent linelist of all transitions which will be reported in a followup paper.

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

Limiting spectral and angular characteristics of multilayer relief – phase diffraction microstructures

Methods for estimating the parameters of relief – phase diffraction microstructures (local and integral Q-factors) are extended to the case of multilayer double-relief sawtooth microstructures, which makes it possible to select the best combinations of optical materials for multilayer microstructures at a very low computational burden. An approach to the study of multilayer microstructures is proposed, based on the combined use of Q-factors and the method of rigorous analysis of coupled waves, which allows one to estimate the limiting spectral and angular characteristics of multilayer microstructures of various types. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Carbonate-hosted microbial communities are prolific and pervasive methane oxidizers at geologically diverse marine methane seep sites

At marine methane seeps, vast quantities of methane move through the shallow subseafloor, where it is largely consumed by microbial communities. This process plays an important role in global methane dynamics, but we have yet to identify all of the methane sinks in the deep sea. Here, we conducted a continental-scale survey of seven geologically diverse seafloor seeps and found that carbonate rocks from all sites host methane-oxidizing microbial communities with substantial methanotrophic potential. In laboratory-based mesocosm incubations, chimney-like carbonates from the newly described Point Dume seep off the coast of Southern California exhibited the highest rates of anaerobic methane oxidation measured to date. After a thorough analysis of physicochemical, electrical, and biological factors, we attribute this substantial metabolic activity largely to higher cell density, mineral composition, kinetic parameters including an elevated V max , and the presence of specific microbial lineages. Our data also suggest that other features, such as electrical conductance, rock particle size, and microbial community alpha diversity, may influence a sample’s methanotrophic potential, but these factors did not demonstrate clear patterns with respect to methane oxidation rates. Based on the apparent pervasiveness within seep carbonates of microbial communities capable of performing anaerobic oxidation of methane, as well as the frequent occurrence of carbonates at seeps, we suggest that rock-hosted methanotrophy may be an important contributor to marine methane consumption.

58 GEOSCIENCES↗
DOE OSTI2023

Effects of surface vacancy-adatom pair formation on PFC tungsten surface morphological response

Abstract We report a simulation study of the effect of He-irradiation-induced surface vacancy-adatom pair formation on the surface morphological evolution of plasma-facing component (PFC) tungsten and examine a number of factors that impact such evolution. Our analysis is based on self-consistent dynamical simulations according to an atomistically-informed, continuum-scale surface evolution model that has been developed following a hierarchical multiscale modeling strategy and can access the spatiotemporal scales of relevance to fuzz formation. The model accounts for the flux of surface adatoms generated as a result of the surface vacancy-adatom pair formation effect upon He implantation, which contributes to the anisotropic growth of surface nanostructural features due to the different rates of adatom diffusion along and across step edges of islands on the tungsten surface. We have carried out atomic-scale computations of optimal diffusion pathways along and across island step edges on the W(110) surface and calculated Ehrlich–Schwoebel (ES) barriers in adatom diffusion along and across such step edges. This aspect of surface adatom diffusion contributes to anisotropic surface atomic fluxes, terrace and step diffusive currents, and has been incorporated into our PFC surface evolution model, which predicts the formation of preferentially aligned nanoridge stripe patterns on the PFC surface. We establish that these anisotropic diffusive currents accelerate nanotendril growth on the PFC surface and the onset of surface nanostructure pattern formation. We also explore systematically the dependence of the PFC surface morphological response on the surface temperature and He ion incident flux, characterize in detail the resulting surface topographies and growth kinetics, and compare the predicted surface morphologies with experimental observations. Our simulation predictions for the emerging surface nanostructure patterns under certain plasma exposure conditions are consistent with experimental findings in the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Nitrogen fertilization challenges the climate benefit of cellulosic biofuels

Cellulosic biofuels are intended to improve future energy and climate security. Nitrogen (N) fertilizer is commonly recommended to stimulate yields but can increase losses of the greenhouse gas nitrous oxide (N 2 O) and other forms of reactive N, including nitrate. We measured soil N2O emissions and nitrate leaching along a switchgrass ( Panicum virgatum ) high resolution N-fertilizer gradient for three years post-establishment. Results revealed an exponential increase in annual N2O emissions that each year became stronger (R 2 > 0.9, P < 0.001) and deviated further from the fixed percentage assumed for IPCC Tier 1 emission factors. Concomitantly, switchgrass yields became less responsive each year to N fertilizer. Nitrate leaching (and calculated indirect N2O emissions) also increased exponentially in response to N inputs, but neither methane (CH4) uptake nor soil organic carbon changed detectably. Overall, N fertilizer inputs at rates greater than crop need curtailed the climate benefit of ethanol production almost two-fold, from a maximum mitigation capacity of–5.71 ± 0.22 Mg CO 2 e ha –1 yr –1 in switchgrass fertilized at 56 kgNha –1 to only –2.97 ± 0.18 MgCO 2 e ha –1 yr –1 in switchgrass fertilized at 196 kgNha –1 . In conclusion, minimizing N fertilizer use will be an important strategy for fully realizing the climate benefits of cellulosic biofuel production.

09 BIOMASS FUELS↗
DOE OSTI2025

Crust Composition and the Shallow Heat Source in KS 1731–260

The presence of a strong shallow heat source of unknown origin in accreting neutron star crusts has been inferred by analyzing x-ray observations of their cooling in quiescence. Here, we model the cooling of KS 1731–260 using realistic crust compositions and nuclear heating and cooling sources from detailed nuclear reaction network calculations. We find that the required strength of the shallow heat source in KS 1731–260 is reduced by more than a factor of 3 compared to previous analysis, a 5⁢𝜎 difference that alleviates the need for exotic solutions. Our analysis also suggests the existence of an impure nuclear pasta layer in the inner crust of KS 1731–260, though future observations will provide more stringent constraints. In addition, we obtain constraints on the dominant surface burning modes of KS 1731–260 over its history.

neutron star cooling↗
DOE OSTI2020

Low-temperature spin dynamics in the TmFeO 3 orthoferrite with a non-Kramers ion

We investigate the magnetic dynamics of the orthorhombic perovskite TmFeO 3 at low temperatures, below the spin reorientation transition at TSR≈80 K, by means of time-of-flight neutron spectroscopy. We find that the magnetic excitation spectrum combines two emergent collective modes associated with different magnetic sublattices. The Fe subsystem orders below TN~632 K into a canted antiferromagnetic structure and exhibits sharp, high-energy magnon excitations. We describe them using linear spin-wave theory, and reveal a pronounced anisotropy between in- and out-of-plane exchange interactions, which was mainly neglected in previous reports on the spin dynamics in orthoferrites. At lower energies, we find two crystalline electrical field (CEF) excitations of Tm3+ ions at energies of ~2 and 5 meV. In contrast to the sister compound YbFeO 3 , where the Yb 3+ ions form quasi-one-dimensional chains along the c axis, the Tm excitations show dispersion along both directions in the (0KL) scattering plane. Analysis of the neutron scattering polarization factor reveals a longitudinal polarization of the 2 meV excitation. To evaluate the effect of the CEF on the Tm 3+ ions, we perform point-charge model calculations, and their results quantitatively capture the main features of Tm single-ion physics, such as energies, intensities, and polarization of the CEF transitions, and the type of magnetic anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic order and energy-scale hierarchy in artificial spin-ice structures

In order to explain and predict the properties of many physical systems, it is essential to understand the interplay of different energy scales. Here we present investigations of the magnetic order in thermalized artificial spin-ice structures, with different activation energies of the interacting Ising-like elements. We image the thermally equilibrated magnetic states of the nanostructures using synchrotron-based magnetic microscopy. By comparing results obtained from structures with one or two different activation energies, we demonstrate a clear impact on the resulting magnetic order. The differences are obtained by the analysis of the magnetic spin structure factors, in which the role of the activation energies is manifested by distinct short-range order. Furthermore, these results highlight the potential of artificial spin-ice structures to serve as model systems for designing various energy-scale hierarchies and investigating their impact on the collective dynamics and magnetic order.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

How analytic choices can affect the extraction of electromagnetic form factors from elastic electron scattering cross section data

Scientists often try to incorporate prior knowledge into their regression algorithms, such as a particular analytic behavior or a known value at a kinematic endpoint. Unfortunately, there is often no unique way to make use of this prior knowledge, and thus, different analytic choices can lead to very different regression results from the same set of data. In this paper, to illustrate this point in the context of the proton electromagnetic form factors, we use the Mainz elastic data with its 1422 cross section points and 31 normalization parameters. Starting with a complex unbound non-linear regression, we will show how the addition of a single theory-motivated constraint removes an oscillation from the magnetic form factor and shifts the extracted proton charge radius. We then repeat both regressions using the same algorithm, but with a rebinned version of the Mainz dataset. These examples illustrate how analytic choices, such as the function that is being used or even the binning of the data, can dramatically affect the results of a complex regression. These results also demonstrate why it is critical when using regression algorithms to have either a physical model in mind or a firm mathematical basis

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗