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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 217 records · Page 12

Equivariant Graph Attention Network - 3D Conformers & Feature Fusion

EGAN-3F (Equivariant Graph Attention Network - 3D Conformers & Feature Fusion) presents an innovative approach for predicting binding affinity between small molecules and protein targets, a fundamental task in drug discovery. Traditional structure-based methods often depend on protein-ligand complex structures obtained from crystallography or molecular docking. In contrast, ligand-only machine learning models using 1D or 2D representations such as SMILES have been developed to predict binding affinity without structural information about the target; however, their accuracy is often limited due to the lack of 3D ligand information. EGAN-3F addresses this limitation by integrating spatially aware graph learning with traditional descriptor-based features. We systematically investigate how combining 2D and 3D molecular representations enhances binding affinity prediction from SMILES strings. This approach underscores the importance of modeling conformational diversity and incorporating chemically meaningful descriptors to improve predictive accuracy. The key innovation of EGAN-3F lies in its ability to achieve robust ligand-based binding affinity predictions without requiring protein-ligand complex structures, effectively bridging the gap between purely structural and ligand-only modeling paradigms.

Shim, Heesung [Lawrence Livermore National Laborat↗

A Mono-cuboctahedral Series of Gold Nanoclusters: Photoluminescence Origin, Large Enhancement, Wide Tunability, and Structure–Property Correlation

The origin of the near-infrared photoluminescence (PL) from thiolate-protected gold nanoclusters (Au NCs, <2 nm) has long been controversial, and the exact mechanism for the enhancement of quantum yield (QY) in many works remains elusive. Meanwhile, based upon the sole steady-state PL analysis, it is still a major challenge for researchers to map out a definitive relationship between the atomic structure and the PL property and understand how the Au(0) kernel and Au(I)–S surface contribute to the PL of Au NCs. Herein, we provide a paradigm study to address the above critical issues. By using a correlated series of “mono-cuboctahedral kernel” Au NCs and combined analyses of steady-state, temperature-dependence, femtosecond transient absorption, and Stark spectroscopy measurements, we have explicitly mapped out a kernel-origin mechanism and clearly elucidate the surface–structure effect, which establishes a definitive atomic-level structure–emission relationship. A ~100-fold enhancement of QY is realized via suppression of two effects: (i) the ultrafast kernel relaxation and (ii) the surface vibrations. Furthermore the new insights into the PL origin, QY enhancement, wavelength tunability, and structure–property relationship constitute a major step toward the fundamental understanding and structural-tailoring-based modulation and enhancement of PL from Au NCs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Effects of ball milling on the structure of cotton cellulose

Cellulose is typically characterized as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model’s paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.

59 BASIC BIOLOGICAL SCIENCES↗

Temperature-Independent Nuclear Quantum Effects on the Structure of Water

Nuclear quantum effects (NQEs) have a significant influence on the hydrogen bonds in water and aqueous solutions and have thus been the topic of extensive studies. However, the microscopic origin and the corresponding temperature dependence of NQEs have been elusive and still remain the subject of ongoing discussion. Previous x-ray scattering investigations indicate that NQEs on the structure of water exhibit significant temperature dependence. Here, by performing wide-angle x-ray scattering of H 2 O and D 2 O droplets at temperatures from 275 K down to 240 K, we determine the temperature dependence of NQEs on the structure of water down to the deeply supercooled regime. The data reveal that the magnitude of NQEs on the structure of water is temperature independent, as the structure factor of D 2 O is similar to H 2 O if the temperature is shifted by a constant 5 K, valid from ambient conditions to the deeply supercooled regime. Analysis of the accelerated growth of tetrahedral structures in supercooled H 2 O and D 2 O also shows similar behavior with a clear 5 K shift. The results indicate a constant compensation between NQEs delocalizing the proton in the librational motion away from the bond and in the OH stretch vibrational modes along the bond. In conclusion, this is consistent with the fact that only the vibrational ground state is populated at ambient and supercooled conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

The modification of BaCe{sub 0.5}Zr{sub 0.3}Y{sub 0.2}O{sub 3–δ} with copper oxide: Effect on the structural and transport properties

The effect of the content of CuO additive on the sinterability, phase composition, microstructure, and electrical properties of BaCe{sub 0.5}Zr{sub 0.3}Y{sub 0.2}O{sub 3–δ} proton-conducting material is studied. Ceramic samples were produced by the citrate–nitrate synthesis method with the addition of 0, 0.25, 0.5, and 1% CuO. It is shown that the relative density of the samples containing 0.5 and 1% CuO is higher than 94% at a sintering temperature of 1450°C, whereas the relative density of the material is no higher than 85% at a lower content of the sintering additive. From the data of X-ray diffraction analysis and scanning electron microscopy, it is established that the introduction of a small CuO content (0.25%) is inadequate for single-phase and high-dense ceramics to be formed. The conductivity and scanning electron microscopy data show that the sample with BaCe{sub 0.5}Zr{sub 0.3}Y{sub 0.2}O{sub 3–δ} + 0.5% CuO composition possesses high total and ionic conductivities as well as a high degree of microstructural stability after hydrogen reduction of the ceramics. The citrate–nitrate method modified by the introduction of a small CuO content can be recommended for the production of single-phase, gas-tight, and high-conductivity electrolytes based on both BaCeO{sub 3} and BaZrO{sub 3}.

36 MATERIALS SCIENCE↗

An Effect of Internal Structure of Bimetallic Nanoparticles on Optical Properties for AuAg/Glass Material

Optical extinction spectra calculated via multisphere T-matrices for nanoparticles with different concentrations of metals and different architectures (core–shell, inverse core–shell, or alloy) are considered. A method is proposed for determination of architecture of nanoparticles (core–shell or alloy) from only data on the position of plasmon resonance and composition of components. The use of an optical spectrum fitting technique to the spectra of monodisperse noninteracting bimetallic nanoparticles with a predetermined structure appeared to be effective for the determination of the internal structure of nanoparticles, except large nanoparticles with a radius of more than 60 nm containing less than ∼25% silver atoms.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Elucidating the Structural and Electronic Effects of Ni and Mn Cationic Incorporation on CoOOH for Efficient Benzyl Alcohol Electrooxidation

Transition-metal oxyhydroxides such as CoOOH are promising low-cost electrocatalysts for the selective electrooxidation of organic molecules, yet the influence of ubiquitous transition-metal impurities on their performance and durability remains poorly understood. Here, we experimentally probed the individual and synergistic electrochemical and structural effects of Ni and Mn incorporations into model CoOOH electrocatalysts toward an efficient benzyl alcohol oxidation reaction (BAOR). Comprehensive electrochemical, microscopic, and spectroscopic analyses reveal that Ni incorporation enhances charge-transfer kinetics and overall activity through the formation of catalytically active Ni 3+ sites, whereas Mn exhibited a more complex but interesting role. At the early stages of operation, Mn 4+ acts as a stabilizing surface layer that mitigates catalyst degradation but partially blocks Co sites before they undergo gradual leaching. The concurrent incorporation of both Ni and Mn yields a trimetallic 2NMC@NF electrocatalyst that integrates the activity benefits of Ni with the stability conferred by Mn, achieving 92.9% benzyl alcohol conversion and 91.4% Faradaic efficiency after 24 h at 1.5 V vs RHE. These findings elucidate how trace Ni and Mn impurities, often introduced from electrolytes or external sources, can modulate the lattice and electronic structure of CoOOH, offering a design strategy for enhancing both activity and long-term stability in electrocatalytic organic oxidation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

On the bispectra of very massive tracers in the Effective Field Theory of Large-Scale Structure

The Effective Field Theory of Large-Scale Structure (EFTofLSS) provides a consistent perturbative framework for describing the statistical distribution of cosmological large-scale structure. In a previous EFTofLSS calculation that involved the one-loop power spectra and tree-level bispectra, it was shown that the k-reach of the prediction for biased tracers is comparable for all investigated masses if suitable higher-derivative biases, which are less suppressed for more massive tracers, are added. However, it is possible that the non-linear biases grow faster with tracer mass than the linear bias, implying that loop contributions could be the leading correction to the bispectra. To check this, we include the one-loop contributions in a fit to numerical data in the limit of strongly enhanced higher-order biases. Here, we show that the resulting one-loop power spectra and higher-derivative plus leading one-loop bispectra fit the two- and three-point functions respectively up to k≃0.19 h Mpc -1 and ksime 0.14 h Mpc -1 at the percent level. We find that the higher-order bias coefficients are not strongly enhanced, and we argue that the gain in perturbative reach due to the leading one-loop contributions to the bispectra is relatively small. Thus, we conclude that higher-derivative biases provide the leading correction to the bispectra for tracers of a very wide range of masses.

79 ASTRONOMY AND ASTROPHYSICS↗

The cosmological analysis of the SDSS/BOSS data from the Effective Field Theory of Large-Scale Structure

The Effective Field Theory of Large-Scale Structure is a formalism that allows us to predict the clustering of Cosmological Large-Scale Structure in the mildly non-linear regime in an accurate and reliable way. In this paper, after validating our technique against several sets of numerical simulations, we perform the analysis for the cosmological parameters of the DR12 BOSS data. We assume Λ CDM, a fixed value of the baryon/dark-matter ratio, Ω b /Ω c , and of the tilt of the primordial power spectrum, n s , and no significant input from numerical simulations. By using the one-loop power spectrum multipoles, we measure the primordial amplitude of the power spectrum, A s , the abundance of matter, Ω m , and the Hubble parameter, H 0 , {to about 13% , 3.2% and 3.2% respectively, obtaining ln (10 10 A s )=2.72± 0.13 , 0Ω m =0.309± 0.01 , H 0 =68.5± 2.2 km/(s Mpc) at 68% confidence level. If we then add a CMB prior on the sound horizon, the error bar on H 0 is reduced to 1.6% .} These results are a substantial qualitative and quantitative improvement with respect to former analyses, and suggest that the EFTofLSS is a powerful instrument to extract cosmological information from Large-Scale Structure.

79 ASTRONOMY AND ASTROPHYSICS↗

Exposing structural variations in SARS-CoV-2 evolution

The mutation of SARS-CoV-2 influences viral function as residue replacements affect both physiochemical properties and folding conformations. Although a large amount of data on SARS-CoV-2 is available, the investigation of how viral functions change in response to mutations is hampered by a lack of effective structural analysis. Here, we exploit the advances of protein structure fingerprint technology to study the folding conformational changes induced by mutations. With integration of both protein sequences and folding conformations, the structures are aligned for SARS-CoV to SARS-CoV-2, including Alpha variant (lineage B.1.1.7) and Delta variant (lineage B.1.617.2). The results showed that the virus evolution with change in mutational positions and physicochemical properties increased the affinity between spike protein and ACE2, which plays a critical role in coronavirus entry into human cells. Additionally, these structural variations impact vaccine effectiveness and drug function over the course of SARS-CoV-2 evolution. The analysis of structural variations revealed how the coronavirus has gradually evolved in both structure and function and how the SARS-CoV-2 variants have contributed to more severe acute disease worldwide.

59 BASIC BIOLOGICAL SCIENCES↗

Solvent Effect on the Photoinduced Structural Change of a Phosphorescent Molecular Butterfly

Abstract Photoinduced structural changes (PSC) is one of the fundamental excited‐state dynamic processes, and yet often very challenging to distinguish from competing electronic excited‐state relaxation channels having similar or even comparable timescales. Here, we report a detailed study on the PSC of a pyrazolate bridged platinum(II) binuclear complex, BFPtPZ (C^NPt(μ‐pz′) 2 PtC^N, C^N=2‐(2,4‐difluorophenyl)pyridine, pz′=pyrazolate), a molecular butterfly, using time‐correlated single photon counting measurements at different wavelengths and sample temperatures. Analysis of the results obtained using dichloromethane (DCM) and ethylene carbonate (EC) as solvents enabled us to reveal an unexpected, strong solvent effect on the PSC processes. We show that a rapid PSC process with a characteristic timescale of 323 ps is observed in DCM, which leads to an excitation equilibrium between the ligand center/metal‐to‐ligand charge transfer ( 3 LC/MLCT) and metal‐metal‐to‐ligand charge transfer ( 3 MMLCT) triplet states. The subsequent relaxation from these electronic states to the ground state takes place in several nanoseconds. In contrast, the corresponding PSC process in EC appears slow at all temperatures studied in our experiments and showed no sign of such excitation equilibrium. The observed solvent effect is found to arise from distinct solvent properties including their viscosities and polarities as well as the peculiar electronic excited‐states of the butterfly‐like molecules with charge transfer character.

Ma, Ying‐Zhong↗

Electron Beam Longitudinal Tracking (EBLT) v1.0

It is a serial/parallel code for fast electron beam longitudinal forward or backward tracking through an electron linear accelerator. This codes includes longitudinal space-charge effect, structure and resistive wall wakefields, and longitudinal coherent synchrotron radiation effect. To use it as a parallel code, please comment out the "use mpistub" in BeamBunch.f90, rename mpif.h as mpif.hh, and use the Makefile_parallel as Makefile.

Qiang, Ji↗

Hole effective masses and subband splitting in type-II superlattice infrared detectors

We explore band structure effects to help determine the suitability of n-type type-II superlattice (T2SL) absorbers for infrared detectors. It is often assumed that the exceedingly large growth-direction band-edge curvature hole effective mass in n-type long wavelength infrared (LWIR) T2SL would lead to low hole mobility and therefore low detector collection quantum efficiency. We computed the thermally averaged conductivity effective mass and show that the LWIR T2SL hole conductivity effective mass along the growth direction can be orders of magnitude smaller than the corresponding band-edge effective mass. LWIR InAs/GaSb T2SL can have significantly smaller growth-direction hole conductivity effective mass than its InAs/InAsSb counterpart. For the InAs/InAsSb T2SL, higher Sb fraction is more favorable for hole transport. Achieving long hole diffusion length becomes progressively more difficult for the InAs/InAsSb T2SL as the cutoff wavelength increases, since its growth-direction hole conductivity effective mass increases significantly with decreasing band gap. However, this is mitigated by the fact that the splitting between the top valence subbands also increases with the cutoff wavelength, leading to reduced inter-subband scattering and increased relaxation time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Ion irradiation-induced crystal structure changes in inverse spinel MgIn 2 O 4

We performed 400 keV Ne and 200 keV He ion irradiations on fully inverse MgIn 2 O 4 samples at cryogenic temperature (~ 77 K), in order to examine the influence of radiation-induced cation disordering on crystal structure. In the case of MgIn 2 O 4 samples irradiated with Ne ions to a peak displacement damage dose of 4 displacements per atom (dpa), a spinel-to-rocksalt phase transformation was observed. Conversely, for MgIn 2 O 4 samples irradiated with He ions to a peak displacement damage dose of 5 dpa, the only observed structural effect involved cation rearrangements from an inverse to a “random” spinel structure.

36 MATERIALS SCIENCE↗

Electron transfer in polysaccharide monooxygenase catalysis

Polysaccharide monooxygenase (PMO) catalysis involves the chemically difficult hydroxylation of unactivated C–H bonds in carbohydrates. The reaction requires reducing equivalents and will utilize either oxygen or hydrogen peroxide as a cosubstrate. Two key mechanistic questions are addressed here: 1) How does the enzyme regulate the timely and tightly controlled electron delivery to the mononuclear copper active site, especially when bound substrate occludes the active site? and 2) How does this electron delivery differ when utilizing oxygen or hydrogen peroxide as a cosubstrate? Using a computational approach, potential paths of electron transfer (ET) to the active site copper ion were identified in a representative AA9 family PMO from Myceliophthora thermophila ( Mt PMO9E). When Y62, a buried residue 12 Å from the active site, is mutated to F, lower activity is observed with O 2 . However, a WT-level activity is observed with H 2 O 2 as a cosubstrate indicating an important role in ET for O 2 activation. To better understand the structural effects of mutations to Y62 and axial copper ligand Y168, crystal structures were solved of the wild type Mt PMO9E and the variants Y62W, Y62F, and Y168F. A bioinformatic analysis revealed that position 62 is conserved as either Y or W in the AA9 family. The Mt PMO9E Y62W variant has restored activity with O 2 . Overall, the use of redox-active residues to supply electrons for the reaction with O 2 appears to be widespread in the AA9 family. Furthermore, the results provide a molecular framework to understand catalysis with O 2 versus H 2 O 2 .

Sayler, Richard I. (ORCID:000000017252707X)↗

Nuclear Structure Studies for Schiff Moment Enhancement

One of the major open questions in modern physics is the origin of the matter-antimatter asymmetry observed in the universe. While the Standard Model contains sources of charge-parity (CP) violation, they appear insufficient to explain the observed dominance of matter over antimatter. As a result, searches for additional sources of CP violation are an important area of contemporary nuclear and particle physics. Atomic electric dipole moments (EDMs) provide sensitive probes of CP-violating interactions. In heavy nuclei, the observable atomic EDM can be enhanced through the presence of a nuclear Schiff moment, which arises from CP-violating nuclear forces and nuclear structure effects. The review paper Nuclear Schiff Moments and CP Violation by Jonathan Engel provides an overview of the theoretical framework connecting CP violation, nuclear structure, and Schiff moments. The long-term goal of this project is to contribute to the identification and characterization of nuclei that may exhibit enhanced Schiff moments. Such nuclei are often associated with strong octupole correlations or low-energy parity-doublet structures that can amplify CP-violating effects. This report summarizes progress made during the initial phase of the project, including a survey of candidate isotopes and preparation for nuclear-structure calculations using the HFODD code.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗