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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Confining Liquids inside Carbon Nanotubes: Accelerated Molecular Dynamics with Spliced, Soft-Core Potentials and Simulated Annealing

Understanding emergent phenomena of fluids under physical confinement requires the development of advanced tools for rapid and accurate simulation of their physiochemical properties. Simulating liquid molecules commensurate in size with the nanoscale enclosures that confine them is a key challenge. In this work, we demonstrate an accelerated molecular dynamics simulation technique that combines soft-core potentials (SCP) and simulated annealing (SA) to analyze confined liquids. This integrated SCP/SA method relies on a new spliced soft-core potential (SSCP), which enables tunable accuracy with respect to the target hard-core potential (HCP). SCP/SA enables the packing of enclosures with bulk material in a controlled, thermodynamically consistent manner. The enhanced SSCP accuracy is a critical feature of SCP/SA, enabling a smooth transition between the SCP and the HCP at a desired SCP hardness. We applied SCP/SA to the problem of filling a carbon nanotube (CNT) in periodic boundary conditions with a popular ionic liquid (IL), 1- butyl-3-methylimidazolium hexafluorophosphate $[\text{BMIM}^+][\text{PF}^–_6]$. We performed a series of triplicate simulations on systems with varying CNT diameter and charge to demonstrate SCP/SA’s versatility. Beyond this IL/CNT system, the SCP/SA simulation framework has a broad range of potential applications, not limited to nanoscale enclosures and interfaces, including both solid-state and biological systems.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser

Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H 2 O 2+ , D 2 O 2+ , and HDO 2+ , such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Core hole processes in x-ray absorption and photoemission by resonant Auger-electron spectroscopy and first-principles theory

Electron–core hole interactions are critical for proper interpretation of core-level spectroscopies commonly used as analytical tools in materials science. Here we utilize resonant Auger-electron spectroscopy to uniquely identify exciton, shake, and charge-transfer processes that result from the sudden creation of the core hole in both x-ray-absorption and photoemission spectra. These effects are captured for the transition-metal compounds SrTiO 3 and MoS 2 by fully ab initio, combined real-time cumulant, and Bethe-Salpeter equation approaches to account for core hole dynamics and screening. Atomic charges and excited-state electron-density fluctuations reflect materials’ solid-state electronic structure, loss of translational symmetry around the core hole, and breakdown of the sudden approximation. They also demonstrate competition between long- and short-range screening in a solid.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

The core metabolome and root exudation dynamics of three phylogenetically distinct plant species

Abstract Root exudates are plant-derived, exported metabolites likely shaping root-associated microbiomes by acting as nutrients and signals. However, root exudation dynamics are unclear and thus also, if changes in exudation are reflected in changes in microbiome structure. Here, we assess commonalities and differences between exudates of different plant species, diurnal exudation dynamics, as well as the accompanying methodological aspects of exudate sampling. We find that exudates should be collected for hours rather than days as many metabolite abundances saturate over time. Plant growth in sterile, nonsterile, or sugar-supplemented environments significantly alters exudate profiles. A comparison of Arabidopsis thaliana , Brachypodium distachyon , and Medicago truncatula shoot, root, and root exudate metabolite profiles reveals clear differences between these species, but also a core metabolome for tissues and exudates. Exudate profiles also exhibit a diurnal signature. These findings add to the methodological and conceptual groundwork for future exudate studies to improve understanding of plant-microbe interactions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Coupling to short linear motifs creates versatile PME-1 activities in PP2A holoenzyme demethylation and inhibition

Protein phosphatase 2A (PP2A) holoenzymes target broad substrates by recognizing short motifs via regulatory subunits. PP2A methylesterase 1 (PME-1) is a cancer-promoting enzyme and undergoes methylesterase activation upon binding to the PP2A core enzyme. Here, we showed that PME-1 readily demethylates different families of PP2A holoenzymes and blocks substrate recognition in vitro. The high-resolution cryoelectron microscopy structure of a PP2A-B56 holoenzyme–PME-1 complex reveals that PME-1 disordered regions, including a substrate-mimicking motif, tether to the B56 regulatory subunit at remote sites. They occupy the holoenzyme substrate-binding groove and allow large structural shifts in both holoenzyme and PME-1 to enable multipartite contacts at structured cores to activate the methylesterase. B56 interface mutations selectively block PME-1 activity toward PP2A-B56 holoenzymes and affect the methylation of a fraction of total cellular PP2A. The B56 interface mutations allow us to uncover B56-specific PME-1 functions in p53 signaling. Our studies reveal multiple mechanisms of PME-1 in suppressing holoenzyme functions and versatile PME-1 activities derived from coupling substrate-mimicking motifs to dynamic structured cores.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Monitoring the growth dynamics of colloidal gold-silver core-shell nanoparticles using in situ second harmonic generation and extinction spectroscopy

The growth dynamics of gold-silver core-shell (Au@Ag) nanoparticles are studied using in situ time-dependent second harmonic generation (SHG) and extinction spectroscopy to investigate the nanoparticle shell formation. The silver shell is grown by reduction of silver cations onto a 14 nm gold core using ascorbic acid in colloidal aqueous solution under varying reaction concentrations producing Au@Ag nanoparticles of final sizes ranging from 51 to 78 nm in diameter. The in situ extinction spectra show a rapid increase in intensity on the timescale of 5–6 s with blue shifting and narrowing of the plasmonic peak during the silver shell formation. The in situ SHG signals show an abrupt rise at early times of the reaction, followed by a time-dependent biexponential decrease, where the faster SHG lifetime corresponds to the timescale of the shell growth, and where the slower SHG lifetime is attributed to changes in the nanoparticle surface charge density. A large enhancement in the SHG signal at early stages of the reaction is caused by plasmonic hot spots due to the nanoparticle surface morphology, which becomes smoother as the reaction proceeds. The final extinction spectra are compared to finite-difference time-domain (FDTD) calculations, showing general agreement with experiment, where the plasmon peak red shifts and increases in spectral width as the silver shell thickness increases. These in situ SHG and extinction spectroscopy results, combined with FDTD calculations, help characterize the complicated processes involved in colloidal nanoparticle shell formation in real time for developing potential plasmon-enhanced nanomaterial applications.

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

An Energy Consistent Discretization of the Nonhydrostatic Equations in Primitive Variables

We derive a formulation of the nonhydrostatic equations in spherical geometry with a Lorenz staggered vertical discretization. The combination conserves a discrete energy in exact time integration when coupled with a mimetic horizontal discretization. The formulation is a version of Dubos and Tort (2014, https://doi.org/10.1175/MWR-D-14-00069.1) rewritten in terms of primitive variables. It is valid for terrain following mass or height coordinates and for both Eulerian or vertically Lagrangian discretizations. The discretization relies on an extension to Simmons and Burridge (1981, https://doi.org/10.1175/1520-0493(1981)109<0758:AEAAMC>2.0.CO;2) vertical differencing, which we show obeys a discrete derivative product rule. This product rule allows us to simplify the treatment of the vertical transport terms. Energy conservation is obtained via a term-by-term balance in the kinetic, internal, and potential energy budgets, ensuring an energy-consistent discretization up to time truncation error with no spurious sources of energy. We demonstrate convergence with respect to time truncation error in a spectral element code with a horizontal explicit vertically implicit implicit-explicit time stepping algorithm.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Attosecond pulse shaping using a seeded free-electron laser

Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters, multilayer mirrors and manipulation of the driving field. However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free-electron lasers, by contrast, deliver femtosecond, extreme-ultraviolet and X-ray pulses with energies ranging from tens of microjoules to a few millijoules. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot. In this paper we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time-resolved experiments with free-electron lasers.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Structure and assembly of the diiron cofactor in the heme-oxygenase–like domain of the N-nitrosourea–producing enzyme SznF

In biosynthesis of the pancreatic cancer drug streptozotocin, the tridomain nonheme-iron oxygenase SznF hydroxylates N δ and N ω ' of N ω -methyl- L -arginine before oxidatively rearranging the triply modified guanidine to the N-methyl-N-nitrosourea pharmacophore. A previously published structure visualized the monoiron cofactor in the enzyme’s C-terminal cupin domain, which promotes the final rearrangement, but exhibited disorder and minimal metal occupancy in the site of the proposed diiron cofactor in the N-hydroxylating heme-oxygenase–like (HO-like) central domain. We leveraged our recent observation that the N-oxygenating µ-peroxodiiron(III/III) intermediate can form in the HO-like domain after the apo protein self-assembles its diiron(II/II) cofactor to solve structures of SznF with both of its iron cofactors bound. These structures of a biochemically validated member of the emerging heme-oxygenase–like diiron oxidase and oxygenase (HDO) superfamily with intact diiron cofactor reveal both the large-scale conformational change required to assemble the O 2 -reactive Fe 2 (II/II) complex and the structural basis for cofactor instability—a trait shared by the other validated HDOs. During cofactor (dis)assembly, a ligand-harboring core helix dynamically (un)folds. The diiron cofactor also coordinates an unanticipated Glu ligand contributed by an auxiliary helix implicated in substrate binding by docking and molecular dynamics simulations. The additional carboxylate ligand is conserved in another N-oxygenating HDO but not in two HDOs that cleave carbon–hydrogen and carbon–carbon bonds to install olefins. Among ~9,600 sequences identified bioinformatically as members of the emerging HDO superfamily, ~25% conserve this additional carboxylate residue and are thus tentatively assigned as N-oxygenases.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

DOE National Laboratories: Vital to U.S. science and technology [Slides]

DOE has extremely challenging and diverse missions, each born out of national need. The national labs serve as the science and technology engine for DOE missions. Each Lab stewards distinctive capabilities which DOE leverages through networks of labs address core missions, dynamic programs and rapid response needs. National lab networks have transformative impact.

96 KNOWLEDGE MANAGEMENT AND PRESERVATION↗
DOE OSTI2026

Dynamics and observational signatures of core-collapse supernovae with central engines: hydrodynamics simulations with Monte Carlo post-processing

A long-lived central engine embedded in expanding supernova ejecta can alter the dynamics and observational signatures of the event, producing an unusually luminous, energetic, and/or rapidly evolving transient. We use 2D hydrodynamics simulations to study the effect of a central energy source, varying the amount, rate, and isotropy of the energy deposition. We post-process the results with a time-dependent Monte Carlo radiation transport code to extract observational signatures. The engine excavates a bubble at the centre of the ejecta, which becomes Rayleigh–Taylor unstable. Sufficiently powerful engines are able to break through the edge of the bubble and accelerate, shred, and compositionally mix the entire ejecta. The breakout of the engine-driven wind occurs at distinct rupture points, and the outflowing high-velocity gas may eventually give rise to radio emission. The dynamical impact of the engine leads to faster rising optical light curves, with photon escape facilitated by the faster expansion of the ejecta and the opening of low-density channels. For models with strong engines, the spectra are initially hot and featureless, but later evolve to resemble those of broad-line Ic supernovae. Under certain conditions, line emission from ionized, low-velocity material near the centre of the ejecta may be able to escape and produce narrow emission similar to that seen in interacting supernovae. We discuss how variability in the engine energy reservoir and injection rate could give rise to a heterogeneous set of events spanning multiple observational classes, including the fast blue optical transients, broad-line Ic supernovae, and superluminous supernovae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Physics of Edge-Core Coupling by Inward Turbulence Propagation

The dynamics of edge-core coupling is critically important to the optimization of magnetically confined fusion plasmas. Since early proposals, there has been persistent speculation that inward propagation of turbulence from the boundary is a possible means to energize the edge-core coupling region. However, the detailed mechanism of this process has remained a mystery until recent experiments observed that regular, intense gradient relaxation events generated blob-void pairs very close to the last closed flux surface. Blobs ($\tilde{n}$ >0) propagate outward and detach from the bulk plasma, while voids ($\tilde{n}$ <0) propagate inward, and so stir the core plasma. Here, in this work, we demonstrate that this heretofore ignored process of void emission can drive a broad turbulent layer of width ∼100 𝜌 𝑠 , for typical parameters. The mechanism is the Cherenkov emission of drift waves from inward-propagating voids. The model shows promise to resolve several questions surrounding the shortfall problem and the strong turbulence in the edge-core coupling region.

drift waves↗
DOE OSTI2020

Origin of core-to-core x-ray emission spectroscopy sensitivity to structural dynamics

Recently, coherent structural dynamics in the excited state of an iron photosensitizer was observed through oscillations in the intensity of Kα x-ray emission spectroscopy (XES). Understanding the origin of the unexpected sensitivity of core-to-core transitions to structural dynamics is important for further development of femtosecond time-resolved XES methods and, we believe, generally necessary for interpretation of XES signals from highly non-equilibrium structures that are ubiquitous in photophysics and photochemistry. Here, we use multiconfigurational wavefunction calculations combined with atomic theory to analyze the emission process in detail. The sensitivity of core-to-core transitions to structural dynamics is due to a shift of the minimum energy metal–ligand bond distance between 1s and 2p core-hole states. A key effect is the additional contraction of the non-bonding 3s and 3p orbitals in 1s core-hole states, which decreases electron– electron repulsion and increases overlap in the metal–ligand bonds. The effect is believed to be general and especially pronounced for systems with strong bonds. The important role of 3s and 3p orbitals is consistent with the analysis of radial charge and spin densities and can be connected to the negative chemical shift observed for many transition metal complexes. The XES sensitivity to structural dynamics can be optimized by tuning the emission energy spectrometer, with oscillations up to ±4% of the maximum intensity for the current system. The theoretical predictions can be used to design experiments that separate electronic and nuclear degrees of freedom in ultrafast excited state dynamics.

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

Strength, plasticity, and spin transition of Fe-N compounds in planetary cores

Elastic and plastic properties of Fe-light element alloys and compounds are needed to determine the compositions and dynamics of planetary cores. Elastic strength and plastic deformation mechanisms and their relationship to electronic properties of ε-Fe 7 N 3 and γ’-Fe 4 N mixture were investigated by x-ray diffraction and x-ray emission spectroscopy in the diamond anvil cell from 1 bar up to 60 GPa. X-ray diffraction shows that ε-Fe 7 N 3 reaches a pressure of 15–20 GPa before undergoing bulk plasticity at a differential stress of 4.4–10.4 GPa. ε-Fe 7 N 3 is stronger than γ’-Fe 4 N and hcp-Fe which achieve a flow stress of 1.5–3.6 GPa at 10–15 GPa and 2–3 GPa at ~20 GPa, respectively. X-ray emission spectroscopy shows that a decrease in electronic spin moment begins before and completes after plastic flow onset for each nitride, suggesting that pressure-driven changes in electronic arrangement do not trigger a plastic response although they may modify the strength and plastic behavior of Fe-N compounds. Plastic deformation in ε-Fe 7 N 3 and hcp-Fe results in a preferred orientation of (0001) normal to maximum compression, while γ’-Fe 4 N develops a maximum in the (110). Furthermore, these observations may be combined with measurements of elasticity to model seismic properties of cores of small planetary bodies such as Mars, Mercury, and the Moon.

58 GEOSCIENCES↗
DOE OSTI2021

Carrier-Specific Hot Phonon Bottleneck in CH 3 NH 3 PbI 3 Revealed by Femtosecond XUV Absorption

Femtosecond carrier cooling in the organohalide perovskite semiconductor CH 3 NH 3 PbI 3 is measured using extreme ultraviolet (XUV) and optical transient absorption spectroscopy. XUV absorption between 44 and 58 eV measures transitions from the I 4d core to the valence and conduction bands and gives distinct signals for hole and electron dynamics. The core-to-valence-band signal directly maps the photoexcited hole distribution and provides a quantitative measurement of the hole temperature. The combination of XUV and optical probes reveals that upon excitation at 400 nm, the initial hole distribution is 3.5 times hotter than the electron distribution. At an initial carrier density of 1.4 × 10 20 cm –3 both carriers are subject to a hot phonon bottleneck, but at 4.2 × 10 19 cm –3 the holes cool to less than 1000 K within 400 fs. Finally, this result places significant constraints on the use of organohalide perovskites in hot-carrier photovoltaics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Tree-based solvers for adaptive mesh refinement code FLASH – III: a novel scheme for radiation pressure on dust and gas and radiative transfer from diffuse sources

Radiation is an important contributor to the energetics of the interstellar medium, yet its transport is difficult to solve numerically. We present a novel approach towards solving radiative transfer of diffuse sources via backwards ray tracing. Here, we focus on the radiative transfer of infrared radiation and the radiation pressure on dust. The new module, TREERAY/RADPRESSURE, is an extension to the novel radiative transfer method TREERAY implemented in the grid-based Magneto-Hydrodynamics code FLASH. In TREERAY/RADPRESSURE, every cell and every star particle is a source of infrared radiation. We also describe how gas, dust, and radiation are coupled via a chemical network. This allows us to compute the local dust temperature in thermal equilibrium, leading to a significantly improvement over the classical grey approximation. In several tests, we demonstrate that the scheme produces the correct radiative intensities as well as the correct momentum input by radiation pressure. Subsequently, we apply our new scheme to model massive star formation from a collapsing, turbulent core of 150 M ⊙ . We include the effects of both, ionizing and infrared radiation on the dynamics of the core. We find that the newborn massive star prevents fragmentation in its proximity due to radiative heating. Over time, dust and radiation temperature equalize, while the gas temperature can be either warmer due to shock heating or colder due to insufficient dust–gas coupling. Compared to gravity, the effects of radiation pressure are insignificant for the stellar mass on the simulated time-scale in this work.

(ISM:) HII regions↗