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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Topological kagome magnets and superconductors

A kagome lattice naturally features Dirac fermions, flat bands and van Hove singularities in its electronic structure. The Dirac fermions encode topology, flat bands favour correlated phenomena such as magnetism, and van Hove singularities can lead to instabilities towards long-range many-body orders, altogether allowing for the realization and discovery of a series of topological kagome magnets and superconductors with exotic properties. Recent progress in exploring kagome materials has revealed rich emergent phenomena resulting from the quantum interactions between geometry, topology, spin and correlation. Here we review these key developments in this field, starting from the fundamental concepts of a kagome lattice, to the realizations of Chern and Weyl topological magnetism, to various flat-band many-body correlations, and then to the puzzles of unconventional charge-density waves and superconductivity. We highlight the connection between theoretical ideas and experimental observations, and the bond between quantum interactions within kagome magnets and kagome superconductors, as well as their relation to the concepts in topological insulators, topological superconductors, Weyl semimetals and high-temperature superconductors. In conclusion, these developments broadly bridge topological quantum physics and correlated many-body physics in a wide range of bulk materials and substantially advance the frontier of topological quantum matter.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Probing the state of hydrogen in δ − AlOOH at mantle conditions with machine learning potential

Hydrous and nominally anhydrous minerals are a fundamental class of solids of enormous significance to geophysics. They are the water carriers in the deep geological water cycle and impact structural, elastic, plastic, and thermodynamic properties and phase relations in Earth's forming aggregates (rocks). They play a critical role in the geochemical and geophysical processes that shape the planet. Their complexity has prevented predictive calculations of their properties, but progress in materials simulations ushered by machine-learning potentials is transforming this state of affairs. Here, we adopt a hybrid approach that combines deep learning potentials (DPs) with the strongly constrained and appropriately normed meta-generalized gradient approximation functional to simulate a prototypical hydrous system. We illustrate the success of this approach to simulate δ − AlOOH ( δ ) , a phase capable of transporting water down to near the core-mantle boundary of the Earth ( ∼ 2900 km depth and ∼ 135 GPa ) in subducting slabs. A high-throughput sampling of phase space using molecular dynamics simulations with DPs sheds light on the hydrogen-bond behavior and proton diffusion at geophysical conditions. These simulations provide a pathway for a deeper understanding of these crucial components that shape Earth's internal state. Published by the American Physical Society 2024

Luo, Chenxing (ORCID:0000000341166851)↗
DOE OSTI2018

Effects of Local Environment on the Ultra-Fast Carrier Dynamics of Photo-Excited 2D Transition Metal Dichalcogenides

Layered transition metal dichalcogenides (TMDs) represent a diverse, emerging source of two-dimensional (2D) nanostructures with broad application in optoelectronics and energy. In particular, tungsten disulfide (WS2) is an efficient visible light absorber with relatively high carrier mobilities and catalytic activity towards hydrogen evolution. While explanation of the quantum confinement and excitonic effects governing TMD optoelectronic properties has progressed in recent years, less is known about the ultra-fast photoresponse and carrier dynamics following light excitation. This work utilizes transient absorption spectroscopy, with pump tunability and broadband visible probing, to monitor the carrier dynamics of both CVD-grown monolayer and solution exfoliated WS2. Picosecond-scale features include simultaneous bleaching of excitonic states and a red-shifted absorption spectrum attributed to bandgap renormalization, while free carriers, defect trapped carriers, and recombination signatures are apparent at increasing pico- to nanosecond lifetimes. Features associated with excitons, trions, and photo-excited carriers exhibit strong dependence on local environmental factors. Moisture, oxygen, chemical dopants, and dielectric environment strongly affect the strength and decay lifetimes of these photo-excited species. These results highlight the importance of understanding and controlling these local environmental factors to the rational design and implementation of 2D TMDs optoelectronic device platforms.

2D materials↗
DOE OSTI2016

Are Lock-Free Concurrent Algorithms Practically Wait-Free?

Lock-free concurrent algorithms guarantee that some concurrent operation will always make progress in a finite number of steps. Yet programmers prefer to treat concurrent code as if it were wait-free, guaranteeing that all operations always make progress. Unfortunately, designing wait-free algorithms is generally a very complex task, and the resulting algorithms are not always efficient. Although obtaining efficient wait-free algorithms has been a long-time goal for the theory community, most nonblocking commercial code is only lock-free. This article suggests a simple solution to this problem. We show that for a large class of lock-free algorithms, under scheduling conditions that approximate those found in commercial hardware architectures, lock-free algorithms behave as if they are wait-free. In other words, programmers can continue to design simple lock-free algorithms instead of complex wait-free ones, and in practice, they will get wait-free progress. Our main contribution is a new way of analyzing a general class of lock-free algorithms under a stochastic scheduler. Our analysis relates the individual performance of processes to the global performance of the system using Markov chain lifting between a complex per-process chain and a simpler system progress chain. We show that lock-free algorithms are not only wait-free with probability 1 but that in fact a general subset of lock-free algorithms can be closely bounded in terms of the average number of steps required until an operation completes. Here, to the best of our knowledge, this is the first attempt to analyze progress conditions, typically stated in relation to a worst-case adversary, in a stochastic model capturing their expected asymptotic behavior.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

FY24 progress report on A709 mechanical properties data development and A709 thermal aging status

The report provides the status of the creep, fatigue, and creep-fatigue testing to date conducted at Idaho National Laboratory to generate the data package. This data package evaluates the material performance from three commercial heats to support the Alloy 709 qualification in American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section III, Division 5. First procured heat was manufactured by G.O. Carlson with heat number 58776. Second and third heats were fabricated by ATI Specialty Rolled Products with heat numbers 529900 and 530843, respectively. A series of creep and cyclic specimens were fabricated from these three heats and tests were performed. A list of finished, ongoing, and planned test are presented for creep, fatigue, and creep-fatigue tests. Cyclic properties of three commercial heats are compared.

36 MATERIALS SCIENCE↗
DOE OSTI2025

FY24 progress report on A709 mechanical properties data development and A709 thermal aging status

The report provides the status of the creep, fatigue, and creep-fatigue testing to date conducted at Idaho National Laboratory to generate the data package. This data package evaluates the material performance from three commercial heats to support the Alloy 709 qualification in American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section III, Division 5. First procured heat was manufactured by G.O. Carlson with heat number 58776. Second and third heats were fabricated by ATI Specialty Rolled Products with heat numbers 529900 and 530843, respectively. A series of creep and cyclic specimens were fabricated from these three heats and tests were performed. A list of finished, ongoing, and planned test are presented for creep, fatigue, and creep-fatigue tests. Cyclic properties of three commercial heats are compared.

36 - MATERIALS SCIENCE↗
DOE OSTI2015

Temperature dependence of Raman shifts in layered ReSe{sub 2} and SnSe{sub 2} semiconductor nanosheets

Transition metal dichalcogenides (TMDCs) are attractive for variety of nanoscale electronics and optoelectronics devices due to their unique properties. Despite growing progress in the research field of TMDCs, many of their properties are still unknown. In this letter, we report measurements of Raman spectra of rhenium diselenide (ReSe{sub 2}) and tin diselenide (SnSe{sub 2}) layered semiconductor nanosheets as a function of temperature (70–400 K). We analyze the temperature dependence of the positions of eight ReSe{sub 2} modes and SnSe{sub 2} A{sub 1g} mode. All observed Raman mode shifts exhibit nonlinear temperature dependence at low temperatures which is explained by optical phonon decay process into two or three acoustics phonons. The first order temperature coefficients (χ), determined for high temperatures, of rhenium diselenide Raman modes are in the range between −0.0033 and −0.0118 cm{sup −1}/K, whereas χ of tin diselenide A{sub 1g} mode was −0.0129 cm{sup −1}/K. Our findings are useful for further analysis of phonon and thermal properties of these dichalcogenide layered semiconductors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Studying the effect of phenyl group content on the physical properties of un-crosslinked PDMS (Progress Summary)

Over the last couple of years, the emphasis on our A&L efforts has been on developing a thermal-age-aware constitutive model for foam cushions. From our studies so far, it appears that an $N = 2$ Ogden hyperfoam model within the framework of a two-network Tobolsky scheme is appropriate to describe the age-aware stress-strain response of both stochastic and additively manufactured (AM) foams. The models have so far been fitted only to a limited number of silicone-based materials systems, i.e., M97 and M9763 stochastic foams and AM foams made of SE1700 rubber. As we explore new and different rubber formulations for improved structural as well as A&L properties, we find it important to develop a deeper understanding of the effect of functional groups on the physical, mechanical, and flow properties of the constituent elastomer. To this end, in Q2 FY19, we have begun a project on multiscale modeling of polymers that realistically incorporates from bond-level dynamics to terminal dynamics of whole chains (e.g., tube dynamics). In such mesoscale simulations the polymer tube dynamics is modeled through coarse-graining of monomers to mesoscale “beads”, with the bead-bead potential being systematically fitted to accurate atomic-level forcefields. The aim of this collaboration is to develop a fully physical constitutive model that predicts the mechanical response of polymers of our interest based on structure and modeled dynamics alone.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterizing cellular mechanical phenotypes with mechano-node-pore sensing

The mechanical properties of cells change with their differentiation, chronological age, and malignant progression. Consequently, these properties may be useful label-free biomarkers of various functional or clinically relevant cell states. Here, we demonstrate mechano-node-pore sensing (mechano-NPS), a multi-parametric single-cell-analysis method that utilizes a four-terminal measurement of the current across a microfluidic channel to quantify simultaneously cell diameter, resistance to compressive deformation, transverse deformation under constant strain, and recovery time after deformation. We define a new parameter, the whole-cell deformability index (wCDI), which provides a quantitative mechanical metric of the resistance to compressive deformation that can be used to discriminate among different cell types. The wCDI and the transverse deformation under constant strain show malignant MCF-7 and A549 cell lines are mechanically distinct from non-malignant, MCF-10A and BEAS-2B cell lines, and distinguishes between cells treated or untreated with cytoskeleton-perturbing small molecules. We categorize cell recovery time, ΔTr, as instantaneous (ΔTr ~ 0 ms), transient (ΔTr≤40 ms), or prolonged (ΔTr440 ms), and show that the composition of recovery types, which is a consequence of changes in cytoskeletal organization, correlates with cellular transformation. Through the wCDI and cell-recovery time, mechano-NPS discriminates between sub-lineages of normal primary human mammary epithelial cells with accuracy comparable to flow cytometry, but without antibody labeling. Mechano-NPS identifies mechanical phenotypes that distinguishes lineage, chronological age, and stage of malignant progression in human epithelial cells.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Sub-5 nm, globally aligned graphene nanoribbons on Ge(001)

Graphene nanoribbons (GNRs) hold great promise for future electronics because of their edge and width dependent electronic bandgaps and exceptional transport properties. While significant progress toward GNR devices has been made, the field has been limited by difficulties achieving narrow widths, global alignment, and atomically pristine GNR edges on technologically relevant substrates. A recent advance has challenged these limits by using Ge(001) substrates to direct the bottom-up growth of GNRs with nearly pristine armchair edges and widths near ∼10 nm via atmospheric pressure chemical vapor deposition. In this work, the growth of GNRs on Ge(001) is extended to ultra-high vacuum conditions, resulting in the realization of GNRs with widths narrower than 5 nm. Armchair graphene nanoribbons oriented along Ge 〈110〉 surface directions are achieved with excellent width control and relatively large bandgaps. The bandgap magnitude and electronic uniformity of these sub-5 nm GNRs are well-suited for emerging nanoelectronic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Involvement of LPA signaling via LPA receptor-2 in the promotion of malignant properties in osteosarcoma cells

Highlights: • LPA receptor expressions were changed by the long-term CDDP treatment in MG-63 cells. • The cell motile and invasive activities of MG-63 cells were stimulated by the long-term CDDP treatment. • LPAR2 expression was markedly elevated in highly migratory MG-63 cells. • Cellular functions induced by CDDP were suppressed by LPA{sub 2} knockdown. • LPA{sub 2} plays an important role in the acquisition of malignant properties during tumor progression in MG-63 cells. Lysophosphatidic acid (LPA) signaling via G protein-coupled LPA receptors mediates various biological effects in cancer cells. This study aimed to investigate the roles of LPA receptors in the regulation of cellular functions during tumor progression in osteosarcoma cells. Long-term cisplatin (CDDP)-treated MG63-C and MG63-R7-C cells were generated from osteosarcoma MG-63 and highly-migratory MG63-R7 cells, respectively. LPAR2 and LPAR3 expression levels were significantly higher in MG63-C cells than in MG-63 cells, while LPAR1 expression was reduced. MG63-C cells were highly motile, compared with MG-63 cells. MG63-C cell motility was suppressed by LPA{sub 2} knockdown and enhanced by the LPA{sub 1}/LPA{sub 3} antagonist, dioctanoylglycerol pyrophosphate. LPAR2 and LPAR3 expression levels were significantly elevated in MG63-R7-C cells in comparison with MG63-R7 cells. MG63-R7-C cells were found to be highly invasive, correlating with metalloproteinase-2 activation. MG63-R7-C cells formed large colonies, whereas colony formation was absent from MG63-R7 cells. Notably, MG63-R7-C cell activities were inhibited by LPA{sub 2} knockdown. These results suggest that LPA signaling via LPA{sub 2} plays an important role in the acquisition of malignant properties during tumor progression in MG-63 cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Theoretical studies of chemical reactions related to the formation and growth of polycyclic aromatic hydrocarbons (PAH) and molecular properties of their key intermediates (Final Progress Report)

The formation mechanisms of polycyclic aromatic hydrocarbons, (PAHs) – organic molecules carrying fused benzene rings – are of great interest to scientists and engineers due to their importance in combustion chemistry and astrochemistry. On Earth, PAHs are largely produced in incomplete combustion of fossil fuel and are considered as critical precursors to unwanted soot particles leading to combustion inefficiency and causing air pollution along with detrimental health effects. Simple PAH molecules initially formed in the gas phase, are further involved in a build-up process in combustion flames leading to larger PAH, bowl-shaped nanostructures, fullerenes, and solid-phase species including carbonaceous dust, graphene particles, and soot. In deep space, PAH and their derivatives are potential key intermediates and nucleation sites leading eventually to carbonaceous nanoparticles (“interstellar grains”). Therefore, the understanding of the key processes in the synthesis of PAHs along with their precursors and their degradation mechanisms in combustion systems and in interstellar, circumstellar, and planetary atmospheric environments will provide critical insights into how complex aromatic structures, carbonaceous nanoparticles, and fullerenes are formed and destroyed. Achieving this understanding is an important step in the development of the efficient combustion processes and of the ecofriendly devices with reduced environmental pollution as well as technological strategies for the production of hydrogen and solid carbon through thermal or plasma-assisted pyrolysis of natural gas and biomass. Also, the understanding of the key processes of PAH and soot growth will help in our comprehension of chemical evolution in the universe. Detailed information on the mechanisms and reliable rate constants of the key elementary chemical reactions involved in PAH formation and destruction processes and in inception of soot particles is often missing, with the main deficiencies being the absence of temperature- and pressure-dependent rate constants for the broad range of conditions occurring in various terrestrial and interstellar processes and the lack of data on the reaction products and their branching ratios. Complementary to experimental studies, these gaps in knowledge can be filled by using quantum chemical calculations of reaction potential energy surfaces providing us with accurate energies of reaction products, intermediates, and transition states, revealing the reaction mechanism, and giving the molecular properties required to compute rate constants for relevant reaction steps and product branching ratios using the RRKM-Master Equation (ME) method. Molecular dynamics (MD) simulations can be used in cases when a reaction rate cannot be properly described by statistical theories. During the terminal renewal project period we employed these ab initio/RRKM-ME and MD approaches to complete our studies on several key reactions relevant to the formation/growth of PAH and inception of soot particles including (1) the reaction mechanism and kinetics of the resonance stabilized fulvenallenyl radical with propargyl and C 3 H 4 isomers; (2) the reaction mechanism and kinetics for the C + indene and C 2 + styrene reactions producing naphthyl or azulenyl radicals in low-temperature environments; (3) the MD study of non-equilibrium dimerization of acepyrene and coronene and its radical. The information derived from our theoretical calculations contributed to a better fundamental understanding of the reaction mechanisms and provide missing critical kinetic data to improve combustion models of hydrocarbon fuels and astrochemical models of the growth of carbonaceous molecules and particles in cold molecular clouds, circumstellar envelopes, and planetary atmospheres.

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

Incipient Melting in AA7075

Incipient melting is a phenomenon that can occur in aluminum alloys where solute rich areas, such as grain boundaries, can melt before the rest of the material; incipient melting can degrade mechanical and corrosion properties and is irreversible, resulting in material scrapping. After detecting indications of incipient melting as the cause of failure in 7075 aluminum alloy parts (AA7075), a study was launched to determine threshold temperature for incipient melting. Samples of AA7075 were solution annealed using temperatures ranging from 870-1090F. A hardness profile was developed to demonstrate the loss of mechanical properties through the progression of incipient melting. Additionally, Zeiss software Zen Core Intellesis was utilized to more accurately quantify the changes in microstructural properties as AA7075 surpassed the onset of incipient melting. The results from this study were compared with previous AA7075 material that demonstrated incipient melting.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Brush-Modified Materials: Control of Molecular Architecture, Assembly Behavior, Properties and Applications

Recent progress in surface-initiated polymerization enables the deliberate polymer modification of nanoscopic surfaces with high levels of precision. This has given rise to the development of brush particle-based materials (sometimes referred to as ‘hairy nanoparticles’) that are formed by tethering of polymer chains to the surface of nanoparticle-like objects. Brush particles have attracted interest as model systems to understand the effect of surface modification on the structure and interactions in polymer modified colloidal systems (which play a role across fields as diverse as functional coatings, cosmetics, foods or pharmaceuticals) but also as building blocks for the assembly of ‘one-component hybrid materials’ that exhibit unprecedented property combinations, not realizable in classical composite materials. This review presents a summary and analysis of the developments in the field of ‘particle brush materials’. The evolution of synthetic methodologies from the original pioneering work to emerging trends and opportunities in the field of brush synthesis is presented first. Subsequently, the effect of brush architecture on the structure, interaction and assembly of brush particles both with and without a matrix is discussed. Lastly, recent advances in the development of functional hybrid materials with applications in energy, catalysis, sensing and other areas is presented.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Development of Potent and Selective Pyrazolopyrimidine IRAK4 Inhibitors

In this work, a series of pyrazolopyrimidine inhibitors of IRAK4 were developed from a high-throughput screen (HTS). Modification of an HTS hit led to a series of bicyclic heterocycles with improved potency and kinase selectivity but lacking sufficient solubility to progress in vivo. Structure-based drug design, informed by cocrystal structures with the protein and small-molecule crystal structures, yielded a series of dihydrobenzofurans. This semisaturated bicycle provided superior druglike properties while maintaining excellent potency and selectivity. Improved physicochemical properties allowed for progression into in vivo experiments, where lead molecules exhibited low clearance and showed target-based inhibition of IRAK4 signaling in an inflammation-mediated PK/PD mouse model.

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

Dimensional Evolution Guides Property Control in the A n Cu 4– n TiS 4 Semiconductor Series

Through progressive reduction of the three-dimensional (3D) covalent network of Cu 4 TiS 4 , we isolate seven new members of the A n Cu 4–n TiS 4 family (A = alkali metal; n = 0–4), spanning 3D, 2D, 1D, and 0D structural fragments. The dimensional reduction is rational, as it preserves the edge-sharing connectivity between [CuS 4 ] 7– and [TiS 4 ] 4– tetrahedra across the series. This structural evolution is driven by the stepwise substitution of Cu with alkali metals, guiding the formation of fragments with reduced dimensionality. The effects of “n” and “A” on the crystal structures, stabilities, electronic structures, and optoelectronic properties are profound, demonstrating that the manipulation of alkali metal size and A n Cu 4–n TiS 4 stoichiometry enables predictable variations in structure and properties. For example, the n = 0 and n = 4 end members of the A n Cu 4–n TiS 4 family set the range of achievable band gaps with 2.00 eV for Cu 4 TiS 4 , 2.60 eV for Na 4 TiS 4 , and intermediate values for the n = 1–3 members. Notably, CsCu 3 TiS 4 exhibits exceptional air stability and congruent melting, with density functional theory (DFT) calculating moderate hole and electron effective masses in specific crystallographic directions (mh = 1.24m 0 , me = 0.87m 0 ). Additionally, A 3 CuTiS 4 (A = Na, K, Rb) displays direct band gap behavior and long photoluminescence lifetimes of 2.3–8.6 μs, and K 3 CuTiS 4 has a PLQY of 5.19%. These findings underscore the potential of the A n Cu 4–n TiS 4 family for applications in optoelectronics and demonstrate widely applicable design concepts that unveil rational stoichiometries within a given composition space to generate a series of crystal structures related through an evolving covalent dimensionality that corresponds to a predictable electronic structure and property progression.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗