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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Substituent and Heteroatom Effects on π–π Interactions: Evidence That Parallel-Displaced π-Stacking is Not Driven by Quadrupolar Electrostatics

Stacking interactions are a recurring motif in supramolecular chemistry and biochemistry, where a persistent theme is a preference for parallel-displaced aromatic rings rather than face-to-face π-stacking. This is usually explained in terms of quadrupole–quadrupole interactions between the arene moieties but that interpretation is inconsistent with accurate calculations, which reveal that the quadrupolar picture is qualitatively wrong. At typical π-stacking distances, quadrupolar electrostatics may differ in sign from an exact calculation based on charge densities of the interacting arenes. We apply symmetry-adapted perturbation theory to dimers composed of substituted benzene and various aromatic heterocycles, which display a wide range of electrostatic interactions, and we investigate the interplay of Pauli repulsion, dispersion, and electrostatics as it pertains to parallel-displaced π-stacking. Profiles of energy components along cofacial slip-stacking coordinates support a prominent role for the “van der Waals model” (dispersion in competition with Pauli repulsion), even for polar monomers where electrostatic interactions are significant. While electrostatic interactions are necessary to explain the optimal face-to-face π-stacking distance and to account for the relative orientation of one polar arene with respect to another, we find no evidence to support continued invocation of quadrupolar electrostatics as a basis for π-stacking. Our results suggest that a driving force for offset-stacking exists even in the absence of electrostatic interactions. Consequently, tuning electrostatics via functionalization does not guarantee that slip-stacking can be avoided. This has implications for rational design of soft materials and other supramolecular architectures.

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

Isospin dependence of Nucleon-Nucleon Short-range Correlations in Inclusive Scattering with Tritium and Helium-3

The nucleon-nucleon (NN) potential has a strong repulsive core. When a two-nucleon (sub)system falls into this range, they will interact strongly at short distance, and move away from each other with momenta above the Fermi level. This is called the NN Short range Correlations (SRCs). Previous experiments reported a neutron-proton pair (isos inglet) dominance in high-momentum nucleons. In inclusive electron scattering, this np dominance will cause a scaling behavior of cross sections at 1.4 < xbj = Q2/2m? < 2 where the high-momentum nucleons dominate. At Je?erson Lab Hall A we checked this hypothesis with electron Quasi-elastic (QE) scattering on A=3 nuclei systems. Our unique gas cell design made electron-tritium scattering possible for the ?rst time in a decade. The 2H, 3H, and 3He inclusive cross sections at 1 < xbj < 3 were measured in two experiments (E12-11-112 and E12-14-011) with a wide Q2 range (0.4 < Q2 < 3 GeV2). This thesis dis cusses the physics goals, experiment setup, and data analysis of the E12-11-112 experiment. Ratios of 3H/2H, 3He/2H and 3H/3He as well as absolute cross sections are presented at 0.4 < Q2 < 1.8 GeV2. NN SRC plateaus are observed in the cross section ratios at high Q2. The 3H/3He ratio of 0.84±0.01 at NN SRC dominant kinematics indicates a np to pp SRC pair ratio of 2.2±0.2 in A=3 nuclei. That implies a preference in T = 0 isospin singlet con?guration. No plateaus are observed at xbj > 2.

Li, Shujie↗
DOE OSTI2018

Laser Synthesis, Processing, and Spectroscopy of Atomically-Thin Two Dimensional Materials

Atomically-thin two-dimensional (2D) materials display widely varying electronic and vibronic properties compared to their bulk counterparts. Laser interactions with 2D materials are central to their development. Here we attempt to overview recent progress and define the current challenges in the broad range of laser interactions involved in the synthesis, processing, and optical characterization of 2D materials as the field has emerged from graphene and h-BN to encompass a multitude of other atomically-thin semiconducting, superconducting, thermoelectric, etc. 2D materials as “building blocks” for future energy applications and devices. Here, we first focus on challenges in the synthesis and processing of mainly semiconducting 2D layers for optoelectronics, and the advantages offered by non-equilibrium laser processing. Then, we review the optical characterization techniques that are being developed to serve as remote probes of their electronic and vibronic properties, as well as their structure, stacking, and atomistic alignment. Together, examples will be shown how these developments are already being merged to fulfill the promise for tailored synthesis and assembly of these exquisite materials with real-time in situ control of structure and optoelectronic properties.

Geohegan, David↗
DOE OSTI2015

PICASSO, COUPP and PICO - Search for dark matter with bubble chambers

The PICASSO and COUPP collaborations use superheated liquid detectors to search for cold dark matter through the direct detection of weakly interacting massive particles (WIMPs). These experiments, located in the underground laboratory of SNOLAB, Canada, detect phase transitions triggered by nuclear recoils in the keV range induced by interactions with WIMPs. We present details of the construction and operation of these detectors as well as the results, obtained by several years of observations. We also introduce PICO, a joint effort of the two collaborations to build a second generation ton-scale bubble chamber with 250 liters of active liquid.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

One-pion production in neutrino-nucleus collisions

We use our model for neutrino pion production on the nucleon to study pion production on a nucleus. The model is conveniently modified to include in-medium corrections and its validity is extended up to 2 GeV neutrino energies by the inclusion of new resonant contributions in the production process. Our results are compared with recent MiniBooNE data measured in mineral oil. Our total cross sections are below data for neutrino energies above ≈ 1 GeV. As with other theoretical calculations, the agreement with data improves if we neglect pion final state interaction. This is also the case for differential cross sections convoluted over the neutrino flux.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Linear growth of structure in massive bigravity

The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction rather than a nonzero cosmological constant. Here the cosmological perturbations are studied in this theory. The full perturbation equations are presented in a general gauge and analyzed, focusing on subhorizon scales in the quasistatic limit during the matter-dominated era. An evolution equation for the matter inhomogeneities and the parameters quantifying the deviations from general relativistic structure formation are expressed in terms of five functions whose forms are determined directly by the coupling parameters in the theory. The evolution equation has a similar structure to Horndeski-type scalar-tensor theories, exhibiting a modified growth rate and scale-dependence at intermediate wavenumbers. Predictions of the theory are confronted with observational data on both background expansion and large-scale structure, although care must be taken to ensure a model is stable. It is found that while the stable models fit the data well, they feature deviations from the standard cosmology that could be detected or ruled out by near-future experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Deformation Mechanisms at Grain Boundaries in Polycrystals (Final Report)

Despite its significance in polycrystalline materials, there have been few experimental investigations of the activity of grain boundary sliding (GBS) and the relationship between GBS and slip transmission at grain boundaries. This work addressed this knowledge gap by an experimental and analytical investigation into the interactions between grain boundary sliding (GBS) and slip transmission plastic deformation mechanisms, and how these are impacted by local microstructure. Polycrystalline columnar aluminum of 99.99% purity was examined as a highly modellable system for characterizing grain boundary-local deformation mechanism interaction. High-resolution, large field-of-view strain fields and grain orientation information were captured and statistically analyzed to identify deformation activity with respect to the local microstructure, using a combination of scanning electron microscopy and digital image correlation (SEM-DIC) with electron backscatter diffraction (EBSD). Alignment between the lower-resolution electron backscatter diffraction (EBSD) data and the higher-resolution strain fields was significantly improved by clustering of strain data within an EBSD-defined boundary mantle. Although this work specifically focuses on characterizing the relationship between grain boundary sliding (GBS) and slip transmission, the developed experimental approach, multimodal data alignment process, and automated displacement discontinuity measurement process can be used to study a variety of mechanism interactions across a broad range of materials. Regarding GBS and slip transmission interaction, significant findings include that (1) grain boundaries that slide easily do not facilitate slip transmission; (2) substantial gradients in GBS magnitude could be found along the length of individual grain boundaries, and these were caused by strain discontinuities across the boundary related to deformation anisotropy between adjacent grains; (3) direct transmission and GBS were anti-compatible and facilitated by opposing boundary types (low misorientation and high energy grain boundaries respectively); (4) increased GBS activity was correlated with decreased indirect transmission behavior; (5) GBS accommodation at triple junctions was enabled by intragranular plasticity; and (6) the local intragranular plastic strain discontinuity between grains determined the magnitude of GBS gradients. The experimental strain fields were compared to that of a tangent crystal plasticity finite element (CPFE) model developed by collaborators (Mr. Ajey Venkataraman and Professor Michael Sangid, Purdue University). Implication of this work for improving CPFE models and deformation prediction are discussed. This work provides insight into the nature of these mechanisms and can be used to identify strain transfer criteria that can lead to improved GBS-sensitive crystal plasticity models.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Meeting the Challenge from Bright and Fast Gamma-Ray Flares of 3C 279

Bright and fast gamma-ray flares with hard spectra have been recently detected from the blazar 3C 279, with apparent GeV luminosities up to 10{sup 49} erg s{sup −1}. The source is observed to flicker on timescales of minutes with no comparable optical–UV counterparts. Such observations challenge current models of high-energy emissions from 3C 279 and similar blazar sources that are dominated by relativistic jets along our line of sight with bulk Lorentz factors up to Γ ∼ 20 launched by supermassive black holes. We compute and discuss a model based on a clumpy jet comprising strings of compact plasmoids as indicated by radio observations. We follow the path of the synchrotron radiations emitted in the optical–UV bands by relativistic electrons accelerated around the plasmoids to isotropic Lorentz factors γ∼10{sup 3}. These primary emissions are partly reflected back by a leading member in the string that acts as a moving mirror for the approaching companions. Around the plasmoids, shrinking gap transient overdensities of seed photons build up. These are upscattered into the GeV range by inverse Compton interactions with the relativistic electrons accelerated in situ. We show that such a combined process produces bright gamma-ray flares with minor optical to X-ray enhancements. Main features of our model include: bright gamma-ray flares with risetimes as short as a few minutes, occurring at distances of order 10{sup 18} cm from the central black hole; Compton dominance at GeV energies by factors up to some 10{sup 2}; minimal reabsorption from local photon–photon interactions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Amino acid interacting network in the receptor-binding domain of SARS-CoV-2 spike protein

The relation between amino acid (AA) sequence and biologically active conformation controls the process of polypeptide chains folding into three-dimensional (3d) protein structures. The recent achievements in the resolution achieved in cryo-electron microscopy coupled with improvements in computational methodologies have accelerated the analysis of structures and properties of proteins. However, the detailed interaction between AAs has not been fully elucidated. Herein, we present a de novo method to evaluate inter-amino acid interactions based on the concept of accurately evaluating the amino acid bond pairs (AABP). The results obtained enabled the identification of complex 3d long-range interconnected AA interacting network in proteins. The method is applied to the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. We show that although nearest-neighbor AAs in the primary sequence have large AABP, other nonlocal AAs make substantial contribution to AABP with significant participation of both covalent and hydrogen bonding. Detailed analysis of AABP in RBD reveals the pivotal role they play in sequence conservation with profound implications on residue mutations and for therapeutic drug design. This approach could be easily applied to many other proteins of biomedical interest in life sciences.

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

Release Timing and Duration Control the Fate of Photolytic Compounds in Stream-Hyporheic Systems

Predicting environmental fate requires an understanding of the underlying, spatiotemporally variable interaction of transport and transformation processes. Photolytic compounds, for example, interact with both time-variable photolysis and the perennially dark hyporheic zone, generating potentially unexpected dynamics that arise from time-variable reactivity. This interaction has been found to significantly impact environmental fate but is commonly oversimplified in predictive models. Our primary objective was to explore how time-variable photolysis and hyporheic storage interact across a range of photolysis rates to control the fate and transport of photolytic solutes in stream-hyporheic systems. In this study, we released a photolytic compound in a natural system at different times of day and simulated variable release timing and durations of photolytic compounds spanning half-lives ranging from about 2 min to 900 hr. To contextualize these results, we simulated five photolytic compounds with varied half-lives to systematically study the interaction between release timing, duration, and reactivity. We found that the environmental fate and transport of photolytic compounds are highly variable as a function of release timing, which controls when, where, and for how long solute is stored in the hyporheic zone or exposed to in-channel photolysis. Finally, this knowledge can be used to improve predictions for photolytic compounds or assess potential impacts for an anticipated discharge or treatment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

MEASUREMENT OF THE EMC EFFECT OF THE TRITIUM NUCLEUS AT JEFFERSON LAB

Experiment E12-10-103 (MARATHON) was conducted in the Hall A Facility of JLab in the winter/spring of 2018 during the initial phase of the 12 GeV energy upgrade of the Lab. One goal of the experiment was the first measurement of the EMC effect of 3H. Four sealed gas targets were used during the experiment, 1H, 2H, 3H, and 3He. All measurements were in the deep inelastic scattering kinematical regime with large Q2 and W2, which are the four-momentum transfer squared and invariant mass squared of the final hadronic state in the inelastic scattering interaction, respectively. The range of Q2 and W2 were 3 < Q2 <12 (GeV/c)2 and 3.2 < W2 < 12.3 GeV/c2, respectively. The measurements spanned a wide range of the Bjorken variable x, between 0.19 and 0.83, where x = Q2/2M(E-E') is the momentum fraction carried by the struck quark in the interaction, with M being the nucleon mass. Knowledge of the EMC effect of light nuclei, such as 3H, will provide an opportunity to better understand the origin of the EMC effect.

Nycz, Michael R.↗
DOE OSTI2020

Antichiral spin order, its soft modes, and their hybridization with phonons in the topological semimetal Mn 3 Ge

Here we report the magnetic structure and spin excitations of Mn 3 Ge , a breathing kagome antiferromagnet with transport anomalies attributed to Weyl nodes. Using polarized neutron diffraction, we show the magnetic order is a k = 0 coplanar state belonging to a Γ 9 irreducible representation, which can be described as a perfect 120 ° antichiral structure with a moment of 2.2(1) μ B /Mn, superimposed with weak collinear ferromagnetism. Inelastic neutron scattering shows three collective Q = 0 excitations at Δ 1 = 2.9 ( 6 ) meV, Δ 2 = 14.6 ( 3 ) meV, and Δ 3 = 17.5 ( 3 ) meV. A field theory of Q ≈ 0 spin waves in triangular antiferromagnets with a 120 ° spin structure was used to classify these modes. The in-plane mode ( α ) is gapless, Δ 1 is the gap to a doublet of out-of-plane spin excitations ( β x , β y ), and Δ 2 , Δ 3 result from hybridization of optical phonons with magnetic excitations. While a phenomenological spin Hamiltonian including exchange interactions, Dzyaloshinskii-Moriya interactions, and single-ion crystal field terms can describe aspects of the Mn-based magnetism, spin-wave damping [ Γ = 25 ( 8 ) meV] and the extended range of magnetic interactions indicate itinerant magnetism consistent with the transport anomalies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Performance of a new coaxial ion–molecule reaction region for low-pressure chemical ionization mass spectrometry with reduced instrument wall interactions

Abstract. Chemical ionization mass spectrometry (CIMS) techniques have become prominent methods for sampling trace gases of relatively low volatility. Such gases are often referred to as being “sticky”, i.e., having measurement artifacts due to interactions between analyte molecules and instrument walls, given their tendency to interact with wall surfaces via absorption or adsorption processes. These surface interactions can impact the precision, accuracy, and detection limits of the measurements. We introduce a low-pressure ion–molecule reaction (IMR) region primarily built for performing iodide-adduct ionization, though other adduct ionization schemes could be employed. The design goals were to improve upon previous low-pressure IMR versions by reducing impacts of wall interactions at low pressure while maintaining sufficient ion–molecule reaction times. Chamber measurements demonstrate that the IMR delay times (i.e., magnitude of wall interactions) for a range of organic molecules spanning 5 orders of magnitude in volatility are 3 to 10 times lower in the new IMR compared to previous versions. Despite these improvements, wall interactions are still present and need to be understood. To that end, we also introduce a conceptual framework for considering instrument wall interactions and a measurement protocol to accurately capture the time dependence of analyte concentrations. This protocol uses short-duration, high-frequency measurements of the total background (i.e., fast zeros) during ambient measurements as well as during calibration factor determinations. This framework and associated terminology applies to any instrument and ionization technique that samples compounds susceptible to wall interactions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2000

Effective Potential Energies and Transport Cross Sections for Interactions of Hydrogen and Nitrogen

The interaction energies for N2-He and N2-H2 are calculated by accurate ab initio methods. The virial coefficient and differential scattering cross section for N2-H2 are calculated; the theoretical results are compared with experimental data. The transport collision integrals for N2-H2 and N2-N2 interactions are calculated and tabulated; the results yield transport coefficients that compare well with measured data. Transport coefficients are found to be determined accurately from the interaction energies for a specific configuration of the molecule formed from the interaction partners. Comparisons with results of measurement and accurate calculations demonstrate that the transport properties of complex molecular interactions can be determined rapidly and fairly accurately from the interaction energies of simpler system using combination rules for the short-range parameters of effective interaction energies and the coefficients for the long-range forces. The coefficients for a two-parameter temperature expansion of diffusion and viscosity are tabulated for a realistic universal potential energy that is based primarily on the results of very accurate calculations of the He-He interaction energy.

Stallcop, James R.↗
DOE OSTI2014

Long Range Debye-Hückel Correction for Computation of Grid-based Electrostatic Forces Between Biomacromolecules

Brownian dynamics (BD) simulations can be used to study very large molecular systems, such as models of the intracellular environment, using atomic-detail structures. Such simulations require strategies to contain the computational costs, especially for the computation of interaction forces and energies. A common approach is to compute interaction forces between macromolecules by precomputing their interaction potentials on three-dimensional discretized grids. For long-range interactions, such as electrostatics, grid-based methods are subject to finite size errors. We describe here the implementation of a Debye-Hückel correction to the grid-based electrostatic potential used in the SDA BD simulation software that was applied to simulate solutions of bovine serum albumin and of hen egg white lysozyme.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2023

Specificity in plant-mycorrhizal fungal relationships: prevalence, parameterization, and prospects

Species interactions exhibit varying degrees of specialization, ranging from generalist to specialist interactions. For many interactions (e.g., plant-microbiome) we lack standardized metrics of specialization, hindering our ability to apply comparative frameworks of specificity across niche axes and organismal groups. Here, we discuss the concept of plant host specificity of arbuscular mycorrhizal (AM) fungi and ectomycorrhizal (EM) fungi, including the predominant theories for their interactions: Passenger, Driver, and Habitat Hypotheses. We focus on five major areas of interest in advancing the field of plant-mycorrhizal fungal host specificity: phylogenetic specificity, host physiology specificity, functional specificity, habitat specificity, and mycorrhizal fungal-mediated plant rarity. Considering the need to elucidate foundational concepts of specificity in this globally important symbiosis, we propose standardized metrics and comparative studies to enhance our understanding. We also emphasize the importance of analyzing global mycorrhizal data holistically to draw meaningful conclusions and suggest a shift toward single-species analyses to unravel the complexities underlying these associations.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Effect of Dipole Interactions on Blocking Temperature and Relaxation Dynamics of Superparamagnetic Iron-Oxide (Fe 3 O 4 ) Nanoparticle Systems

The effects of dipole interactions on magnetic nanoparticle magnetization and relaxation dynamics were investigated using five nanoparticle (NP) systems with different surfactants, carrier liquids, size distributions, inter-particle spacing, and NP confinement. Dipole interactions were found to play a crucial role in modifying the blocking temperature behavior of the superparamagnetic nanoparticles, where stronger interactions were found to increase the blocking temperatures. Consequently, the blocking temperature of a densely packed nanoparticle system with stronger dipolar interactions was found to be substantially higher than those of the discrete nanoparticle systems. The frequencies of the dominant relaxation mechanisms were determined by magnetic susceptibility measurements in the frequency range of 100 Hz–7 GHz. The loss mechanisms were identified in terms of Brownian relaxation (1 kHz–10 kHz) and gyromagnetic resonance of Fe 3 O 4 (~1.12 GHz). It was observed that the microwave absorption of the Fe 3 O 4 nanoparticles depend on the local environment surrounding the NPs, as well as the long-range dipole–dipole interactions. These significant findings will be profoundly important in magnetic hyperthermia medical therapeutics and energy applications.

36 MATERIALS SCIENCE↗