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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Effects of Simulated Microgravity and LINC-Complex on Chromosome 8 of Human Mammary Cells

Previously, human breast epithelial cells were studied under simulated microgravity to determine the role of the LINC-complex in maintaining nuclear morphology and gene expression. Data from that study was used in this project to understand how the LINC-complex influences gene expression at chromosome 8 under simulated microgravity. Differentially expressed genes found in clusters typically indicate a molecular relationship amongst them. Visual and data analyses (GO, pathways) identified 51 genes within clusters on chromosome 8 across various simulated microgravity conditions that did not share any molecular relationship. Additional results also determined that cells with a disrupted LINC-complex experienced more differential gene expression than the control, and that extended periods of simulated microgravity exacerbated differential gene expression in chromosome 8 of LINC-disrupted cells. These results suggest that the stressful simulated microgravity environment coupled with disrupted biological processes, such as in the case of the LINC-complex, can increase differential gene expression in chromosomes. Future studies where additional analyses are performed to further analyze gene expression of clusters under simulated microgravity could potentially elucidate the molecular relationship amongst affected genes.

Simulated microgravity↗
NASA NTRS1996

Enhancing Adhesion: Relative Merits of Different Approaches

Adhesive performance is improved mainly by manipulation of the bimaterials interface zone, which is only a few molecules thick. There are three approaches to enhancement of interfacial adhesion at the molecular level. They are 1) changing the nonchemically bonded interactions across the interface from weak ones to strong ones, 2) making the true interfacial area much larger than the simple geometric area, and 3) inducing chemical bonding between the two materials forming the interface. Our goal this summer was to question some of the built-in assumptions contained within these approaches and to determine the most promising approach, both theoretically and practically, for enhancing adhesion in NASA structures. Our computations revealed that all three of these approaches have, in theory, the potential to enhance molecular adhesion approximately ten-fold. Experiments, however, revealed that this excellent level of enhancement is not likely to be reached in practice. Each approach was found to be severely limited by practical problems. In addition, some of the built-in assumptions associated with these approaches were found to be insufficient or inadequate. The first approach, changing the nonchemically bonded interactions from weak to strong, Is an example of one containing inadequate assumptions. The extensive literature on intermolecular interactions, based on solution studies, shows that certain functional group pairs interact much more strongly than others. It has always been assumed that these data can be reliably extended to systems where only one member of the pair is in solution and the other Is contained in a solid surface. Our experiments this summer demonstrated that solution data do not adequately predict the strength of functional group interaction at the solid-liquid interface. Furthermore, the strong solvents needed to dissolve the monomers or polymers to which the functional groups of interest are attached compete successfully with the solid surface for the functional group. As a result, functional groups in solution cannot pair with the complementary groups in the solid surface, and the expected enhancement of nonchemically bonded interactions is not realized. The second approach, increasing the true interfacial area, is an example of one containing inadequate assumptions and suffering from numerous practical problems. First, practitioners have assumed that material removal, such as bead blasting or etching, increases true surface area (and therefore interfacial area) in a meaningful way. Our geometric analysis demonstrated that removal methods increase area by a factor of two at most. To increase interfacial area by an order of magnitude or more. a thin layer of high porosity must be added to the substrate surface prior to application of the adhesive phase. Consistent with this finding, we attempted to create a thin layer of rigid, highly porous glass on the surface of our smooth glass substrate by means of sol-gel technology. We were unable to surmount a wide variety of practical problems and obtained only collapsed, nonporous layers. Thus this approach, appealing in principle, would require long term development and is not promising in the near term. The third approach, inducing chemical bonding at the interface, is an example of one having neither inadequate assumptions nor insurmountable practical problems. When silicate glass is the substrate, there are only a few chemical reactions that can be successfully conducted to create these chemical bonds, and these reactions usually involve silicon-containing reagents. We compared the silazane reagents to the silane reagents and found through experiment that the silazanes react with the glass surface much more readily, and under milder conditions, than the silanes. The functional groups attached to the glass surface by silazane reactions were not able to be removed by solvent extraction, elevated temperature exposure, or mechanical action. This clearly indicates that the formation of chemical bonds at the interface is the most effective approach for enhancing molecular adhesion.

Penn, L. S.↗
NASA NTRS1977

Atomic and molecular fluorescence as a stratospheric species monitor

The results of an investigation are presented evaluating the potential of atomic and molecular fluorescence as a stratospheric monitor of the concentrations of any one of 18 minor species: Cl, Cl2, ClO, ClO2, CO, H2, HCHO, HCl, HNO2, HNO3, H2S, NH3, NO, NO2, N2O, O, OH, and SO2. All spectral regions from the vacuum ultraviolet through the infrared were included. It was found that suitable systems can be constructed for the stratospheric monitoring of CO (5 ppb), NO2 (less than 1 ppb), OH (0.2 ppt), and O (50-200 ppt). The fluorescence sensitivities for Cl (0.5-1.0 ppt), H2 (0.2 ppm at 10 torr) and SO2 (1-10 ppb) are marginally insufficient with current technology.

Schofield, K.↗
NASA NTRS2005

Improved Charge-Transfer Fluorescent Dyes

Improved charge-transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combinations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods. These dyes exhibit high fluorescence quantum yields -- ranging from 0.2 to 0.98, depending upon solvents and chemical structures. The wavelengths, quantum yields, intensities, and lifetimes of the fluorescence emitted by these dyes vary with (and, hence, can be used as indicators of) the polarities of solvents in which they are dissolved: In solvents of increasing polarity, fluorescence spectra shift to longer wavelengths, fluorescence quantum yields decrease, and fluorescence lifetimes increase. The wavelengths, quantum yields, intensities, and lifetimes are also expected to be sensitive to viscosities and/or glass-transition temperatures. Some chemical species -- especially amines, amino acids, and metal ions -- quench the fluorescence of these dyes, with consequent reductions in intensities, quantum yields, and lifetimes. As a result, the dyes can be used to detect these species. Another useful characteristic of these dyes is a capability for both two-photon and one-photon absorption. Typically, these dyes absorb single photons in the ultraviolet region of the spectrum (wavelengths < 400 nm) and emit photons in the long-wavelength ultraviolet, visible, and, when dissolved in some solvents, near-infrared regions. In addition, these dyes can be excited by two-photon absorption at near-infrared wavelengths (600 to 800 nm) to produce fluorescence spectra identical to those obtained in response to excitation by single photons at half the corresponding wavelengths (300 to 400 nm). While many prior fluorescent dyes exhibit high quantum yields, solvent-polarity- dependent fluorescence behavior, susceptibility to quenching by certain chemical species, and/or two-photon fluorescence, none of them has the combination of all of these attributes. Because the present dyes do have all of these attributes, they have potential utility as molecular probes in a variety of applications. Examples include (1) monitoring curing and deterioration of polymers; (2) monitoring protein expression; (3) high-throughput screening of drugs; (4) monitoring such chemical species as glucose, amines, amino acids, and metal ions; and (5) photodynamic therapy of cancers and other diseases.

Meador, Michael↗
DOE OSTI2025

Parameterizing empirical interatomic potentials for predicting thermophysical properties via an irreducible derivative approach: the case of ThO 2 and UO 2

The accuracy of classical physical property predictions using molecular dynamics simulations is determined by the quality of the interatomic potentials. Here we introduce a training approach for empirical interatomic potentials (EIPs) which is well suited for capturing phonons and phonon-related properties. Our approach is based on direct comparisons of the second- and third-order irreducible derivatives (IDs) between an EIP and the Born–Oppenheimer potential within density functional theory (DFT) calculations. IDs fully exploit space group symmetry and allow for training without redundant information. We demonstrate the fidelity of our approach in the context of ThO 2 and UO 2 , where we optimize parameters of an embedded-atom method potential in addition to core–shell interactions. Our EIPs provide thermophysical properties in good agreement with DFT and outperform widely utilized EIPs for phonon dispersion and thermal conductivity predictions. Reasonable estimates of thermal expansion and formation energies of Frenkel pairs are also obtained.

empirical interatomic potential↗
DOE OSTI2026

Frontiers in divalent $f$-block chemistry

Divalent f-block chemistry has undergone rapid expansion in recent years, driven by advances in the stabilization of low-valent lanthanide and actinide complexes. Although f-elements were historically accessed in the +3 or higher oxidation states, the isolation of +2 species has revealed unusual spectroscopic signatures, distinct bonding motifs, and multiple accessible electronic configurations that influence their chemical and physical properties. These developments have generated opportunities in areas including quantum information science, molecular magnetism, catalysis, and luminescence. Computational chemistry has played a pivotal role in interpreting the electronic structure and reactivity of these systems. However, accurately modeling divalent f-block complexes remains challenging because of strong electronic correlation, multiconfigurational character, and the presence of close-in-energy competing electronic states. As experimental capabilities and theoretical methodologies continue to advance, a comprehensive assessment of divalent chemistry is both timely and needed. In this Review, we integrate experimental and theoretical perspectives to provide a systematic analysis of divalent lanthanide and actinide complexes across the f-block series. We critically assess the role of ligands in determining competing ground-state configurations (f n d 1 vs. f n+1 ) resulting in their distinct spectroscopic, magnetic, and bonding properties. Finally, we discuss emerging strategies for predictive modeling and rational design of low-valent f-block molecular systems, with potential applications ranging from dinitrogen reduction to quantum technologies.

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

Elucidating the Mechanism of Helium Evaporation from Liquid Water

Here, we investigate the evaporation of trace amounts of helium solvated in liquid water using molecular dynamics simulations and theory. Consistent with experimental observations, we find a super-Maxwellian distribution of kinetic energies of evaporated helium. This excess of kinetic energy over typical thermal expectations is explained by an effective continuum theory of evaporation based on a Fokker–Planck equation, parametrized molecularly by a potential of mean force and position-dependent friction. Using this description, we find that helium evaporation is strongly influenced by the friction near the interface, which is anomalously small near the Gibbs dividing surface due to the ability of the liquid–vapor interface to deform around the gas particle. Our reduced description provides a mechanistic interpretation of trace gas evaporation as the motion of an underdamped particle in a potential subject to a viscous environment that varies rapidly across the air–water interface. From it we predict the temperature dependence of the excess kinetic energy of evaporation, which is yet to be measured.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Ultrasonic-Assisted Extrusion Processing for Enhancing Physical Properties of High-Density Polyethylene by Flow-Induced Crystallization

The evolution of crystallinity resulting from stress imposed on a melt, known as flow-induced crystallinity, can strongly influence the mechanical and physical properties of semicrystalline polymers. This study investigates shear-induced crystallization by applying an ultrasonic field to the melt flow as it passes through dies with various geometries. A custom-built sonication die is employed for controlling the dynamic temperature and shear environment, resulting in molecular alignment and potential for flow-induced crystallization. Application of both conventional and ultrasonic shear rates at the equilibrium melt temperature of high-density polyethylene (HDPE) was investigated to accelerate crystallinity and manipulate the crystal morphology across the film in pursuit of improved mechanical and gas barrier properties without the need for additives or other polymer layers. The relationships among ultrasonic-assisted extrusion processing, polymer structure, and performance were analyzed using wide- and small-angle X-ray scattering (WAXS and SAXS), tensile testing, and oxygen transmission rate (OTR) analysis. Multiple linear regression models were implemented to predict the correlation among HDPE structure, process, and properties. Structural analysis revealed that both conventional and ultrasonic shear rates had the most significant influence on lamellar spacing and redistribution of rigid and soft amorphous fractions within the crystalline domains, ultimately dictating the mechanical and physical properties of the films. The goal is to explore the potential of the ultrasonic-assisted high crystallinity monolayer that can replace some of the functionality of complex, heterogeneous multilayer packaging with a single-material film having enhanced oxygen barrier properties.

crystallinity↗
DOE OSTI2026

Direct Ab Initio Simulation of the Synthesis of BaZrO 3 and the Microstructure Impacts on Proton Transport

Controlling and predicting the processing-structure-performance relationship in functional materials is a grand challenge in materials science, with important implications for a wide range of emerging applications; a high fidelity understanding of the performance impact of microstructures formed under synthesis conditions is required to develop advanced materials, such as solid-state fuel cells and electrolyzers. Using the ceramic BaZrO 3 as a case study, we directly simulate the synthesis and investigate how proton transport is dictated by microstructures. We develop a framework that couples density functional theory (DFT), machine-learning interatomic potential (MLIP) driven molecular dynamics, and grand canonical Monte Carlo to perform large-scale, microstructure-resolved, atomistic simulations of proton transport in experimentally representative polycrystalline structures. Our fully ab initio approach, using a MLIP as a proxy for DFT, allows us to quantify the competition between two distinct diffusion mechanisms: one associated with grain-boundary regions and another within grains. When the impacts of grain boundaries are taken into account, proton transport exhibits substantial deviation from the bulk oxide limit. This addresses long-standing discrepancies between theory and experiments. Our integrated approach provides atomistic insight into microstructure-dependent proton pathways in BaZrO 3 and establishes a general protocol for predicting processing-structure-performance relationships.

organic↗
DOE OSTI2024

Cyclically conjugated porphyrin trimers linked through benzo[4,5]imidazo[2,1- a ]isoindole bridges

Cyclically conjugated porphyrin trimers were prepared via a concise synthetic method. Zn-Trimer-1 displayed strong exciton coupling, suggesting the presence of effective electronic interactions. UV-Vis absorption and fluorescence spectra obtained through titration studies on the donor–acceptor adduct (Zn-Trimer-1–C60Im) indicate the occurrence of excited state photo-events. Inspired by nature's photosynthetic process of plants and bacteria, electronically interacting multiporphyrinic systems have long been investigated as synthetic models of natural photosynthetic systems. Remarkable successes have been achieved with cyclic porphyrin arrays, where porphyrins are arranged in a wheel-like structure or nanoring as photosynthetic antennae. Considerable efforts have also been devoted to constructing other porphyrin arrays such as molecular wires for potential applications in sensors, solar energy conversion, non-linear optical (NLO) materials, and more. Due to synthetic difficulties, cyclically conjugated porphyrin arrays in which porphyrins are arranged in planar geometry are very rare. Very recently, Anderson and coworkers have reported unprecedented β,β-directly linked porphyrin trimers and tetramers with different geometries, propeller and saddle, respectively, which result in distinct photophysical and electrochemical properties (Fig. 1a). In this paper, we present novel cyclically conjugated porphyrin trimers, which feature planar geometry with porphyrins assembled around the aromatic triphenylene at the center (Fig. 1b).

Han, Ting↗
DOE OSTI2026

Extended Rice–Thomson analysis and atomistic simulations revealing grain boundary effects on fracture in refractory high-entropy alloys

Significance This work serves to extend the fundamental ductile vs. brittle fracture theory, specifically the Rice–Thomson criterion, by introducing a grain boundary ahead of an initiating crack which propagates at an oblique angle to impinge the boundary. Atomistic fracture simulations on two refractory complex concentrated alloys, the brittle NbMoTaW and the ductile Nb 45 Ta 25 Ti 15 Hf 15 , demonstrate qualitative correspondence with the extended Rice–Thomson criterion and experimental observations. Abstract Understanding how grain boundaries mediate fracture remains a critical challenge in designing ductile, high-performance refractory alloys. Here, we extend the Rice–Thomson criterion to account for the angle between cracks and the impinging grain boundaries (GBs), capturing the competition between intergranular fracture and dislocation-mediated plasticity. Using machine learning interatomic potentials, we performed molecular statics simulations to probe fracture mechanisms in nanocrystalline NbMoTaW and Nb 45 Ta 25 Ti 15 Hf 15 , each with two different grain sizes, revealing trends consistent with experimental observations and the extended Rice model. Comparison with averaged R-curves for bulk samples demonstrates that GBs enhance ductility in Nb 45 Ta 25 Ti 15 Hf 15 in both grain sizes investigated. In contrast, GBs only locally improve fracture resistance in NbMoTaW when cracks are temporarily pinned at GBs inclined at high angles from the crack, but generally promote brittle intergranular fracture. These contrasting behaviors are attributed to differences in GB cohesion, reflecting clear alloying trends that align with ab-initio calculations and trends observed experimentally. Our results bridge classical fracture theory, atomistic simulations, and experimental observations, providing a comprehensive understanding of the fracture mechanisms in nanocrystalline refractory complex concentrated alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Simulated structure and thermodynamics of decagonal Al-Co-Cu quasicrystals

Atomic structures of Al-Co-Cu decagonal quasicrystals (dQCs) are investigated using empirical oscillating pair potentials (EOPP) in molecular dynamic (MD) simulations that we enhance by Monte Carlo (MC) swapping of chemical species and replica exchange. Predicted structures exhibit planar decagonal tiling patterns and are periodic along the perpendicular direction. We then recalculate the energies of promising structures using first-principles density functional theory (DFT), along with energies of competing phases. We find that our τ -inflated sequence of QC approximants (QCAs) are energetically unstable at low temperature by at least 3 meV/atom. Extending our study to finite temperatures by calculating harmonic vibrational entropy, as well as anharmonic contributions that include chemical species swaps and tile flips, our results suggest that the quasicrystal phase is entropically stabilized at temperatures in the range 600-800 K and above. It decomposes into ordinary (though complex) crystal phases at low temperatures, including a partially disordered B2-type phase. We discuss the influence of density and composition on QC phase stability; we compare the structural differences between Co-rich and Cu-rich quasicrystals; and we analyze the role of entropy in stabilizing the quasicrystal, concluding with a discussion of the possible existence of “high entropy” quasicrystals. Published by the American Physical Society 2024

Huang, Yang (ORCID:0009000045917347)↗
DOE OSTI2026

Gauging the Impact of Cosmic-ray Feedback on the Stellar Initial Mass Function

Cosmic rays (CRs) drive ionization and influence gas dynamics in molecular clouds (MCs), potentially impacting the resulting star formation outcomes. Although previous simulations of individual star formation have included methods for CR transport (CRT), none have been large enough to resolve the stellar initial mass function (IMF). We conduct numerical simulations following the collapse of a 20,000 M ⊙ MC and the subsequent star formation including CRT, both with and without CRs accelerated by winds from the young massive stars, and compare against a non-CRT simulation. We show that after the first massive stars form, the cavity produced by feedback is more pronounced in the CRT simulations because the external CRs are able to propagate inward and compress the gas into higher-density structures. This increases the subsequent star formation in the cloud; by the end of the simulation, the star formation efficiency (SFE) in the CRT simulation including stellar wind CRs is 43% higher than the non-CRT simulation. The IMF is also top-heavy in comparison, with a slope above 1 M ⊙ that is shallower by ∼20%. These effects are also present in the simulation without wind-accelerated CRs, but they are not as pronounced; the SFE is only 16% higher than the non-CRT simulation, and the IMF high-mass slope is shallower by ∼10%. These results may explain some of the observed top-heavy IMFs, which typically occur in high-CR environments such as the Galactic center.

Fitz Axen, Margot [Oak Ridge National Laboratory (↗
NASA NTRS1981

Effect of laser frequency on a collision-induced radiative process

A review is presented of the principles of collision induced radiative processes, followed by an examination of the effects of laser frequencies on these processes. A one-dimensional problem involving two electron states is considered, and it is found that the Hamiltonian of the radiation field is dominated by electric-dipole interaction which couples states of different parity. Transitions are noted to be dependent on collisions, and the complexities of three-dimensional systems are expressed as considerations of the angular momentum of the photon, the necessity of treating different states simultaneously, and the fact that a radiation field destroys rotational invariance. Changing the radiation frequency alters the crossing point and offers opportunities to study the interplay of potential surfaces with molecular dynamics. Experiments on Na+A systems are outlined for several collision energies and various laser frequencies. Multiple crossings were obtained, although the total cross-section, at all energies, decreased at 18,350/cm.

Devries, P. L.↗
NASA NTRS1985

Pulsed Excimer Laser Processing for Cost-Effective Solar Cells

Residual lattice damage by 5 keV ion implantation and surface flaws induced by wafer cleaning are proven to affect the V sub oc more adversely for laser annealed cells than conventional thermal diffusion. However, an alternative, molecular implantation of molecular species holds potential. The first experimental results are encouraging. The lack of a commercially available mass analyzed implantation with low energy, high fluence ions is constraining.

Wong, D.↗
NASA NTRS1991

Middle atmosphere heating by exothermic chemical reactions involving odd-hydrogen species

The rate of heating which occurs in the middle atmosphere due to four exothermic reactions involving members of the odd-hydrogen family is calculated. The following reactions are considered: O + OH yields O2 + H; H + O2 + M yields HO2 + M; H + O3 yields OH + O2; and O + HO2 yields OH + O2. It is shown that the heating rates due to these reactions rival the oxygen-related heating rates conventionally considered in middle-atmosphere models. The conversion of chemical potential energy into molecular translational energy (heat) by these odd-hydrogen reactions is shown to be a significant energy source in the middle atmosphere that has not been previously considered.

Mlynczak, Martin G.↗
NASA NTRS1992

Development of nontoxic heat transport fluids for habitat two-phase thermal control systems

A computational chemistry approach based on pattern recognition techniques is used to correlate molecules thermodynamic and chemical properties with its molecular structure. The potential to develop a suitable two-phase nontoxic heat transport working fluid for the spacecraft habitat environment is discussed. It is concluded that the perfluorocarbons represent a potentially useful class to consider as a source of the working fluids because of their low toxicity, thermal stability, and chemical inertness. The ADAPT software program is considered to be adequate to make structural and property predictions.

Parrish, Clyde F.↗
NASA NTRS2002

In Situ Poling and Imidization of Amorphous Piezoelectric Polyimides

An amorphous piezoelectric polyimide containing polar functional groups has been developed using a combination of experimental and molecular modeling for potential use in high temperature applications. This amorphous polyimide, (Beta-CN)APB/ODPA, has exhibited good thermal stability and piezoelectric response at temperatures up to 150C. Density functional calculations predicted that a partially cured amic acid (open imide ring) possesses a dipole moment four times larger than the fully imidized closed ring. In situ poling and imidization of the partially cured (Beta-CN)APB/ODPA, was studied in an attempt to maximize the degree of dipolar orientation and the resultant piezoelectric response. A positive corona poling was used to minimize localized arcing during poling and to allow use of higher poling fields without dielectric breakdown. The dielectric relaxation strength, remanent polarization, and piezoelectric response were evaluated as a function of the poling profile. The partially cured, corona poled polymers exhibited higher dielectric relaxation strength (delta varepsilon), remanent polarization (Pr) and piezoelectric strain coefficient (d33) than the fully cured, conventionally poled ones.

Park, Cheol↗