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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Deuterium incorporation into cellulose: a mini-review of biological and chemical methods

Isotopic enrichment offers structural insights that are not easily accessible with natural abundance isotopic composition. Deuterated cellulose has attracted considerable attention in the field of neutron scattering studies, providing information about the dynamics, structure of cellulose and its interactions with other plant cell wall components. The deuteration of cellulose also allows the analysis of cellulose hydrogen bonds by FTIR or NMR techniques. The chemical structure of cellulose contains both exchangeable hydroxyl and non-exchangeable alkyl hydrogens. Deuterium incorporation can be divided into two classifications: biological route which incorporates both alkyl and hydroxyl bound deuterium, and chemical route which typically replaces hydroxyl-bound exchangeable hydrogen. Additionally, the biological route involves cultivating plants or microorganisms in a deuterium-enriched medium. The chemical route typically involves an exchange reaction between hydroxyl-bound hydrogen and D 2 O, often facilitating with an alkaline reagent. This review provides an overview of recent advances in deuteration methods and characterization as well as the application of deuterated cellulose.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

On the Relaxation Dynamics of Lohe Oscillators on Some Riemannian Manifolds

We study the collective relaxation dynamics appearing in weakly coupled Lohe oscillators in a large coupling regime. The Lohe models on the unit sphere and unitary group were proposed as a nonabelian generalization of the Kuramoto model on the unit circle and their emergent dynamics has been extensively studied in previous literature for some restricted class of initial data based on the Lyapunov functional approach and order parameter approach. In this paper, we extend the previous partial results to cover a generic initial configuration via the detailed analysis on the order parameter measuring the modulus of the centroid. In particular, we present a detailed relaxation dynamics and structure of the resulting asymptotic states for the Lohe sphere model. We also present new gradient flow formulations for the Lohe matrix models with the same one-body Hamiltonians on some group manifolds. As a direct application of this new formulation, we show that every bounded Lohe flow which originated from any initial configuration converges asymptotically.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Odor mitigation and bacterial community dynamics in on-site biocovers at a sanitary landfill in South Korea

Highlights: • On-site biocovers were evaluated to mitigate odors at a Korean sanitary landfill. • The biocover systems achieved above 80% removal of complex odor. • Removal efficiency of sulfur odor as significant contributor was greater than 90%. • The most abundant bacteria had little correlation with odor removability. • Bacteria increased in relative abundance contributed highly to odor removal. Unpleasant odors emitted from landfills have been caused environmental and societal problems. For odor abatement, two pilot-scale biocovers were installed at a sanitary landfill site in South Korea. Biocovers PBC1 and PBC2 comprised a soil mixture with different ratios of earthworm casts as an inoculum source and were operated for 240 days. Their odor removal efficiencies were evaluated, and their bacterial community structures were characterized using pyrosequencing. In addition, the correlation between odor removability and bacterial community dynamics was assessed using network analysis. The removal efficiency of complex odor intensity in the two biocovers ranged from 81.1% to 97.8%. Removal efficiencies of sulfur-containing odors (hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide), which contributed most to complex odor intensity, were greater than 91% in both biocovers. Despite the fluctuations in ambient temperature (−8.2 to 31.3 °C) and inlet complex odor intensity (10,000–42,748 of odor dilution ratio), biocovers PBC1 and PBC2 displayed stable deodorizing performance. A high ratio of earthworm casts as an inoculum source led to high odor removability during the first 25 days of operation, but different mixing ratios of earthworm casts did not significantly affect overall odor removability. A bacterial community analysis showed that Methylobacter, Arthrobacter, Acinetobacter, Rhodanobacter, and Pedobacter were the dominant genera in both biocovers. Network analysis results indicated that Steroidobacter, Cystobacter, Methylosarcina, Solirubrobacter, and Pseudoxanthomonas increased in relative abundance with time and were major contributors to odor removal, although these bacteria had a relatively low abundance compared to the overall bacterial community. These data contribute to a more comprehensive understanding of the relationship between bacterial community dynamics and deodorizing performance in biocovers.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Thermo-mechanical deterioration and molecular degradation of 3D-printed methacrylate-based polymer in various chemical environments

The advancement of additive manufacturing (AM) has accelerated the development of stereolithographic (SLA) photo-curable resins, particularly methacrylate-based polymers, due to the ability to their high-resolution, robust mechanical properties, and suitability. However, their long-term performance in chemical environments remains poorly understood. This study investigates the extent and mechanisms of degradation on an SLA-printed methacrylate-based polymer subjected to various chemicals, including polar and non-polar solvents, as well as strongly acidic aqueous solutions over a 12-week accelerated aging period. A comprehensive analytical approach incorporating swelling kinetics, surface morphology, tensile and dynamic mechanical analysis (DMA), Fourier-transform infrared (FTIR) spectroscopy, and mass spectrometry (MS) was employed to characterize chemical absorption, structural integrity, and leached products. Results reveal that degradation severity is governed by both the polarity and reactivity of the chemical environment. Notably, exposure to 6 mol L -1 HNO₃ induced the most severe deterioration, with over threefold higher swelling compared to other media, and significant reductions in tensile strength, tensile modulus, and glass transition temperature (T g ). In contrast, specimens aged in non-polar solvents (xylene and dodecane) exhibited negligible chemical interaction and retained mechanical performance. FTIR and MS analyses identified acid-catalyzed hydrolysis of ester groups as prominent degradation pathways in acidic media, while diffusion-controlled plasticization prevailed in polar solvents. Furthermore, this study provides valuable insights into the chemical stability of SLA-printed polymers and develops predictive degradation profiles that are crucial for designing durable polymer systems for advanced industrial use.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Addition of Short Polymer Chains Mechanically Reinforces Glassy Poly(2-vinylpyridine)–Silica Nanoparticle Nanocomposites

The addition of hard fillers to a polymer matrix is a well-known process for achieving mechanical reinforcement. With a decrease in the size of the fillers, the contribution from polymer–particle nanometer-sized interfaces become significant, and these interfaces affect the mechanical performance of polymer nanocomposites (PNCs) beyond the limits established for conventional composites. However, the molecular mechanisms underlying the improvement in the mechanical performance of glassy PNCs remain unresolved, necessitating a deeper understanding of the structure–property relationships in these intrinsically heterogeneous systems. In this effort, by using Brillouin light scattering (BLS) and dynamic mechanical analysis (DMA), we demonstrated that adding shorter chains to a PNC prepared with high molecular weight polymers significantly improved the mechanical properties of the PNC in the glassy state. The strongest enhancement of mechanical properties occurred at an optimum concentration of short chains. This is in contrast to behavior of the glass transition temperature of PNCs which shows a monotonic decrease with an increase in the concentration of shorter chains. Using experimental data and coarse-grained molecular dynamics (MD) simulations, we have identified the molecular mechanism leading to the observed non-monotonic changes in mechanical reinforcement. Here, this mechanism includes changes in the nanoscale organization at the interface, combined with chain stretching amplified by the addition of the short chains. Overall, our approach paves a simple, cost-effective pathway to fabricating glassy PNCs with significantly improved mechanical properties that will fill various practical needs.

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

Chromate Effect on Iodate Incorporation into Calcite

Incorporation of iodate into calcite (CaCO3) may be used as an in situ treatment strategy for radioiodine in contaminated soils and groundwater, but the presence of other contaminants can inhibit its efficiency. To this end, the potential for chromate to interfere with iodate incorporation into CaCO3 was investigated as an example of how co-located contaminants can impact in situ remediation efficacy. Here, batch precipitation experiments were periodically sub-sampled over 21 days to determine the kinetic effects of chromate on iodate removal and incorporation into calcite. From these experiments, a decrease in iodate removal from >60% to <40% was observed upon chromate addition (1 - 100 ppm chromate) and =11% of chromate was removed with a minor dependence on the initial chromate concentration. Analysis of the solid phase using extended X-ray absorption fine structure (EXAFS) spectroscopy informed by ab initio molecular dynamics simulations revealed that the iodate incorporation mode remains unchanged by the presence of chromate. Iodate readily substitutes for carbonate (CO32-) and the calcite structure is charge balanced primarily by substituting H+ for Ca2+. Furthermore, chromate incorporated as a nearest neighbor to iodate did not contribute to the EXAFS fit, therefore, iodate and chromate clustering is unlikely when co-incorporated into calcite.

Saslow, Sarah A.↗
DOE OSTI2017

Conformational Selection as the Mechanism of Guest Binding in a Flexible Supramolecular Host

This work offers a detailed mechanistic investigation of host-guest encapsulation behavior in a new enzyme-mimetic metal-ligand host and provides the first observation of a conformational selection mechanism (as opposed to induced fit) in a supramolecular system. The Ga 4 L 4 host described features a C 3 -symmetric ligand motif with meta-substituted phenyl spacers, which enables the host to initially self-assemble into an S 4 -symmetric structure and then subsequently isomerize to a T -symmetric tetrahedron for better accommodation of a sufficiently large guest. Selective inversion recovery 1 H NMR studies provide structural insights into the self-exchange behaviors of the host and the guest individually in this dynamic system. Kinetic analysis of the encapsulation-isomerization event revealed that increasing the concentration of guest inhibits the rate of host-guest relaxation, a key distinguishing feature of conformational selection. A comprehensive study of this simple enzyme mimic provides insight into analogous behavior in biophysics and enzymology and aims to inform the design of efficient self-assembled microenvironment catalysts.

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

Beyond nothingness in the formation and functional relevance of voids in polymer films

Abstract Voids—the nothingness—broadly exist within nanomaterials and impact properties ranging from catalysis to mechanical response. However, understanding nanovoids is challenging due to lack of imaging methods with the needed penetration depth and spatial resolution. Here, we integrate electron tomography, morphometry, graph theory and coarse-grained molecular dynamics simulation to study the formation of interconnected nanovoids in polymer films and their impacts on permeance and nanomechanical behaviour. Using polyamide membranes for molecular separation as a representative system, three-dimensional electron tomography at nanometre resolution reveals nanovoid formation from coalescence of oligomers, supported by coarse-grained molecular dynamics simulations. Void analysis provides otherwise inaccessible inputs for accurate fittings of methanol permeance for polyamide membranes. Three-dimensional structural graphs accounting for the tortuous nanovoids within, measure higher apparent moduli with polyamide membranes of higher graph rigidity. Our study elucidates the significance of nanovoids beyond the nothingness, impacting the synthesis‒morphology‒function relationships of complex nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Distinguishing artificial and essential symmetry breaking in a single determinant: approach and application to the C 60 , C 36 , and C 20 fullerenes

We present a thorough analysis of symmetry breaking observed in Hartree–Fock (HF) solutions of the C 60 , C 36 , and C 20 fullerenes in order to characterize the nature of electron correlation in them. Our analysis is based on (1) the critical regularization strength to restore symmetry breaking in the recently developed regularized orbital optimized second-order Møller–Plesset perturbation theory (κ-OOMP2), (2) singlet–triplet gaps from various MP2 methods, and (3) natural orbital occupation numbers from restricted coupled-cluster with singles and doubles (RCCSD) and coupled-cluster valence bond with singles and doubles (CCVB-SD). Based on these three independent probes, we conclude that C 36 (D6h) exhibits genuine strong correlation and symmetry breaking whereas C 60 exhibits artificial HF symmetry breaking and is not strongly correlated. Investigating the critical regularization strength, we discuss strong correlation in C 20 at the Jahn–Teller distorted geometries (C 2h , D 2h , C i , and D 3h ) and the Ih geometry. Only C 20 (I h ) was found to be strongly correlated while others exhibit artificial HF symmetry breaking. This analysis highlights a useful feature of the recommended κ-OOMP2 method. It is an electronic structure method that describes dynamic correlation, and attenuates strong correlation in MP2 towards zero by regularization. Therefore, κ-OOMP2 will exhibit symmetry breaking in its reference determinant only when correlation is strong (i.e., essential symmetry breaking). Furthermore, artificial symmetry breaking (arising in HF due to neglect of dynamic correlation) thus appears to be removed in κ-OOMP2.

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

First-principles modeling of plasmons in aluminum under ambient and extreme conditions

The theoretical understanding of plasmon behavior is crucial for an accurate interpretation of inelastic scattering diagnostics in many experiments. In this work, we highlight the utility of linear response time-dependent density functional theory (LR-TDDFT) as a first-principles framework for consistently modeling plasmon properties. We provide a comprehensive analysis of plasmons in aluminum from ambient to warm dense matter conditions and assess typical properties such as the dynamical structure factor, the plasmon dispersion, and the plasmon lifetime. We compare our results with scattering measurements and with other TDDFT results as well as models such as the random phase approximation, the Mermin approach, and the dielectric function obtained using static local field corrections of the uniform electron gas parametrized from path-integral Monte Carlo simulations. We conclude that results for the plasmon dispersion and lifetime are inconsistent between experiment and theories and that the common practice of extracting and studying plasmon dispersion relations is an insufficient procedure to capture the complicated physics contained in the dynamic structure factor in its full breadth.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Understanding the lattice thermal conductivity of SrTiO 3 from an ab initio perspective

Here, we present a detailed analysis of the structure dependence of the lattice thermal conductivity of SrTiO 3 . We have used both ab initio molecular dynamic simulations and density functional theory calculations to decouple the effect of different structural distortions on the thermal conductivity. We have identified two main mechanisms for tuning the thermal conductivity when a distortion is applied. First, the modification of the acoustic-modes energy dispersion when a change in the lattice parameters is imposed and second, the low energy polar modes. In particular and counterintuitively, we have found that an increase in the angle of the oxygen octahedral rotations increases the thermal conductivity due to its coupling to these polar modes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Theoretical Investigation of Equilibrium Properties of the Yukawa Fluid in a Wide Range of Parameters

The static properties of the Yukawa fluids are investigated in a wide range of parameters: the value of the effective nonideality parameter Γ* ranged from 0 to 155, and the value of the screening parameter κ ranged from 1 to 5. Investigations are carried out by the Brownian dynamics method and by solving the Ornstein–Zernike (OZ) equation in the hypernetted chain (HNC) approximation. The analysis of the structure of the fluids shows that they are locally ordered for large values of Γ*; however, no translationally ordered structures are observed. Isothermal compressibility exhibits nonmonotonic behavior as a function of Γ*. The possibility of a phase transition of the fluid to a vitreous state is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Foundational Dataset for Developing Large-Sample Stream Temperature Models in the Conterminous United States

This dataset provides inputs, evaluation results, and trained weights from a large-sample Long Short-Term Memory (LSTM) model designed to predict daily stream temperatures across unregulated river reaches in the conterminous United States (CONUS). It includes dynamic meteorological and hydrologic forcings, static physiographic attributes, and model outputs from cross-validation experiments spanning 300 basins. It supports reproducible modeling, direct application for new basins, and provides data suitable for integration with reservoir and river simulations under current and future climates. It contains two .zip files described below · RQ-AI_runs.zip: Model outputs from 10-fold cross-validation experiments, including observed and predicted daily stream temperatures, along with test performance metrics for water years 2017–2019. Two versions are included: 1. Model trained and validated using subbasin-area weighted dynamic features. 2. Model trained and validated using whole-basin area weighted dynamic features. · RQ-AI_inputs.zip: Collection of all formatted dynamic and static predictor datasets (meteorological, hydrologic, and physiographic features) used in model training and analysis. Detailed instructions and data structure is held at the following GitLab repository: https://code.ornl.gov/tempwise/training.

Gomez-Velez, Jesus [Oak Ridge National Laboratory ↗
DOE OSTI2021

Toward Decoding the Relationship between Domain Structure and Functionality in Ferroelectrics via Hidden Latent Variables

Polarization switching mechanisms in ferroelectric materials are fundamentally linked to local domain structure and the presence of the structural defects, which both can act as nucleation and pinning centers and create local electrostatic and mechanical depolarization fields affecting wall dynamics. However, the general correlative mechanisms between domain structure and polarization dynamics are only weakly explored, precluding insight into the associated physical mechanisms. In this work, the correlation between local domain structures and switching behavior in ferroelectric materials is explored using convolutional encoder–decoder networks, enabling image to spectral (im2spec) and spectral to image (spec2im) translations via encoding of latent variables. The latter reflect the assumption that the relationship between domain structure and polarization switching is parsimonious, i.e., is based upon a small number of local mechanisms. The analysis of latent variables distributions and their real-space representations provides insight into the predictability of the local switching behavior and hence associated physical mechanisms. We further pose that the regions where these correlative relationships are violated, i.e., predictability of the polarization dynamics from domain structure is reduced, represent the obvious target for detailed studies, e.g., in the context of automated experiments. This approach provides a workflow to establish the presence of correlation between local spectral responses and local structure and can be universally applied to spectral imaging techniques such as piezoresponse force microscopy (PFM), scanning tunneling microscopy (STM) and spectroscopy, and electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Resilience Analysis of DC Microgrids under Denial of Service Threats

This paper develops a resilience analysis framework to study the fault ride-through capability of direct current (DC) microgrids in unknown denial of service (DoS) cyber incidents. DoS can be a frequent threat to DC microgrids with advanced controllers that hinge on active information exchanges: it can paralyze data communications and cause control ineptness or even system instability. Furthermore, we show that temporal DoS incidents render the DC microgrid cyber-physical topology and parameters time-varying and cause them to jump between faulty conditions. As existing DC microgrid stability analysis results are primarily developed from time-invariant systems, they might not be valid for the DoS interrupted systems. In this paper, we seek to study whether a DC microgrid is resilient against time-varying unknown DoS incidents. The problem is formulated as a stability analysis problem for a system with randomly switching dynamics. Scalable conditions are developed to provide provable resilience guarantees. In addition, we exploit the special structure of the conditions to yield quantified resilience measure by convex optimization techniques. As a result, the measure can be used for the evaluation of the resilience of different DC microgrid design against DoS incidents. We demonstrate the effectiveness of the proposed work using simulation case studies.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2014

Impact of pulse poling on static and dynamic ferroelastic-domain contributions in tetragonal Pb(Ti, Zr)O{sub 3} films determined by in-situ x–ray diffraction analysis

The effects of bipolar pulse poling on the ferroelastic domain structure and their contribution to the electrical and piezoelectric properties of Pb(Ti{sub 0.7}Zr{sub 0.3})O{sub 3} films are investigated. Micro x-ray diffraction measurements clearly show that the volume fraction of the c-domain increases irreversibly as the poling field is increased, leading to changes in the remanent polarization, dielectric constant, and piezoelectric coefficient. Theoretical estimations well explain the changes of remanent polarization and dielectric constant, but the increase in piezoelectric coefficient is much larger than the theoretical estimation. In-situ x-ray diffraction analysis under an electric field reveals that this disagreement is due to the unexpected activation of the ferroelastic domain wall motion. Our results provide new insight into the poling effect on the electric and piezoelectric properties of ferroelectric films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The origin of the conductivity maximum in molten salts. II. SnCl{sub 2} and HgBr{sub 2}

The phenomenon of electrical conductivity maxima of molten salts versus temperature during orthobaric (closed-vessel) conditions is further examined via ab initio simulations. Previously, in a study of molten BiCl{sub 3}, a new theory was offered in which the conductivity falloff at high temperatures is due not to traditional ion association, but to a rise in the activation energy for atomic ions hopping from counterion to counterion. Here this theory is further tested on two more inorganic melts which exhibit conductivity maxima: another high-conducting melt (SnCl{sub 2}, σ{sub max} = 2.81 Ω{sup −1} cm{sup −1}) and a low-conducting one (HgBr{sub 2}, σ{sub max} = 4.06 × 10{sup −4} Ω{sup −1} cm{sup −1}). First, ab initio molecular dynamics simulations were performed and again appear successful in reproducing the maxima for both these liquids. Second, analysis of the simulated liquid structure (radial distributions, species concentrations) was performed. In the HgBr{sub 2} case, a very molecular liquid like water, a clear Grotthuss chain of bromide transfers was observed in simulation when seeding the system with a HgBr{sup +} cation and HgBr{sub 3}{sup −} anion. The first conclusion is that the hopping mechanism offered for molten BiCl{sub 3} is simply the Grotthuss mechanism for conduction, applicable not just to H{sup +} ions, but also to halide ions in post-transition-metal halide melts. Second, it is conjectured that the conductivity maximum is due to rising activation energy in network-covalent (halide-bridging) melts (BiCl{sub 3}, SnCl{sub 2}, PbCl{sub 2}), but possibly a falling Arrhenius prefactor (collision frequency) for molecular melts (HgBr{sub 2}).

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

Evidence of long-range ferromagnetic order and spin frustration effects in the double perovskite La 2 CoMnO 6

We present a comprehensive study on the magnetic structure, dynamics, and phase evolution in the single phase double perovskite La 2 CoMnO 6 . The mixed valence state due to oxygen deficiency is verified by x-ray photoelectron spectroscopy and confirms a double ferromagnetic transition observed in dc magnetization. Neutron diffraction reveals that the magnetic structure is dominated by long-range ferromagnetic ordering, which is further corroborated by a critical exponents analysis of the paramagnetic to ferromagnetic phase transition. An analysis of the magnetization dynamics by means of linear and nonlinear ac magnetic susceptibilities marks the presence of two distinct cluster-glass-like states that emerge at low temperatures. The isothermal entropy change as a function of temperature and magnetic field (H) is exploited to investigate the mechanism of stabilization of the magnetic phases across the H – T phase diagram. In the regime of the phase diagram where thermal energy is sufficiently low, regions of competing interactions due to local disorder become stabilized and display glasslike dynamics. The freezing mechanism of clusters is illustrated using a unique probe of transverse susceptibility that isolates the effects of the local anisotropy of the spin clusters. Here, the results are summarized in a H – T phase diagram of La 2 CoMnO 6 from these data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗