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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Off-shell pion properties: Electromagnetic form factors and light-front wave functions

The off-shell pion electromagnetic form factors are explored with corresponding off-shell light-front wave functions modeled by constituent quark and antiquark. We apply the Mandelstam approach for the microscopic computation of the form factors relating the model parameters with the pion decay constant and charge radius. Analyzing the existing data on the cross sections for the Sullivan process, 1 H(e,e',π + )⁢n, Charged pion form factor between Q 2 = 0.60, and 2.45 GeV 2 . I. Measurements of the cross section for the 1 H⁡(e,e'⁢π + )⁢n reaction, we extract the off-shell pion form factor using the relation derived from the generalized Ward-Takahashi identity for the pion electromagnetic current. They are compared with our previous results from exactly solvable manifestly covariant model of a (3+1)-dimensional fermion field theory. We find that the adopted constituent quark model reproduces the extracted off-shell form factor F 1 ⁡(Q 2 ,t) from the experimental data within a few percent difference and matches well with our previous theoretical simulation which exhibits a variation of about 10% for the extracted off-shell pion form factor g(Q 2 ,t). We also identify the pion valence parton distribution function (PDF) and transverse momentum distribution (TMD) in terms of the light-front wave function and discuss their off-shell properties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Shell Timeout Scripts

Automatic shell timeout configuration scripts for POSIX shells (bash/zsh) and C shells (csh/tcsh). These scripts automatically set shell timeout values based on User ID (UID) or Group ID (GID) membership (including secondary groups). When a matching user logs in, their shell will automatically terminate after a configured period of inactivity. NOTE: Not all shells implement this feature. Features UID and/or GID-based timeout configuration Additive and subtractive list management Validation of timeout values (positive integers only) Can set timeout to readonly (bash/zsh).

Riehecky, Pat [Fermilab]↗
DOE OSTI2020

Dynamics of Subsiding Shells in Actively Growing Clouds with Vertical Updrafts

The dynamics of a subsiding shell at the edges of actively growing shallow cumulus clouds with updrafts is analyzed using direct numerical simulation. The actively growing clouds have a fixed in-cloud buoyancy and velocity. Turbulent mixing and evaporative cooling at the cloud edges generate a subsiding shell that grows with time. A self-similar regime is observed for first- and second-order moments when normalized with respective maximum values. Internal scales derived from integral properties of the flow problem are identified. A self-similarity analysis using these scales reveals that contrary to classical self-similar flows, the turbulent kinetic energy budget terms and velocity moments scale according to the buoyancy and not with the mean velocity. The shell thickness is observed to increase linearly with time. The buoyancy scale remains time invariant and is set by the initial cloud–environment thermodynamics. The shell accelerates ballistically with a magnitude set by the saturation value of the buoyancy of the cloud–environment mixture. In this regime, the shell is buoyancy driven and independent of the in-cloud velocity. Relations are obtained for predicting the shell thickness and minimum velocities by linking the internal scales with external flow parameters. The values thus calculated are consistent with the thickness and velocities observed in typical shallow cumulus clouds. The entrainment coefficient is a function of the initial state of the cloud and the environment, and is shown to be on the same order of magnitude as fractional entrainment rates calculated for large-scale models.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Soot-particle core-shell and fractal structures from small-angle X-ray scattering measurements in a flame

We have characterized soot particles measured in situ in a laminar co-flow ethylene-air diffusion flame using small-angle X-ray scattering (SAXS). The analysis includes temperature measurements made with coherent anti-Stokes Raman spectroscopy (CARS) and complements soot volume-fraction and maturity measurements made with laser-induced incandescence (LII). We compared the results of fits to the SAXS measurements using a unified model and a fractal core-shell model. Power-law parameters yielded by the unified model indicate that aggregates of primary particles are in the mass-fractal regime, whereas the primary particles are in the surface-fractal regime in the middle of the flame. Higher and lower in the flame, the primary-particle power-law parameter approaches 4, suggesting smooth primary particles. Furthermore, these trends are consistent with fits using the fractal core-shell model, which indicate that particles have an established core-shell structure in the middle of the flame and are internally homogeneous at higher and lower heights in the flame. Primary-particle size distributions derived using the fractal core-shell model demonstrate excellent agreement with distributions inferred from transmission electron microscopy (TEM) images in the middle of the flame. Higher in the flame, a second small mode appears in the size distributions, suggesting particle fragmentation during oxidation. Surface oxidation would explain (1) aggregate fragmentation and (2) loss of core-shell structure leading to smoother primary-particle surfaces by removal of carbon overlayers. SAXS measurements are much more sensitive to incipient and young soot particles than LII and demonstrate significant volume fraction from particles low in the flame where the LII signal is negligible.

42 ENGINEERING↗
DOE OSTI2025

Electromagnetic moments of 215,217 Bi: Probing shell evolution beyond N = 126

The nuclear properties of bismuth isotopes (Z = 83) , with just one valence proton above the closed spherical shell at (Z = 82) , are expected to be governed by a single unpaired proton. However, already in semimagic 209 Bi (Z = 83, N = 126) , , the magnetic moment (μ) strongly deviates from the single-particle Schmidt value. A near linear decrease in μ with the increase of N after the N = 126 magic number was observed up to N = 130 . In order to test whether this trend is kept at N > 130 and to reveal the underlying mechanisms, an investigation of 215,217 Bi (N = 132, 134) has been undertaken. The magnetic dipole and electric quadrupole moments of the I π = 9/2 - nuclear ground states in these isotopes have been measured for the first time using the in-source resonance-ionization spectroscopy technique at ISOLDE (CERN). It has been shown that the linearly decreasing trend of μ( 209,211,213 Bi g ) is broken in 215,217 Bi with a nearly constant value of μ observed. Experimental data have been compared to calculations in the framework of the configuration-interaction shell model with the monopole-based universal V MU +LS interaction. The peculiarities in the behavior of μ(Bi, 9/2 - ) with increasing neutron number are explained as being due to the shell evolution, change of the neutron orbitals occupancies and strong configuration mixing beyond N = 130 . Also, the difference in the μ trends for bismuth (Z = 83) and astatine (Z = 85) isotopes with N > 126 are reproduced by the shell-model calculations. It is shown that monopole interaction plays noticeable role in the description of the peculiarities of the μ behaviour. Additionally, the extension of the application of the V MU interaction to the μ isotopic trends for heavy nuclei is important for further study of the capabilities of this promising version of the shell-model calculations.

Dipole magnetic moments↗
DOE OSTI2025

Implications of a weakening N = 126 shell closure away from stability for r -process astrophysical conditions

The formation of the third r-process abundance peak near A ∼ 195 is highly sensitive to both nuclear structure far from stability and the astrophysical conditions that produce the heaviest elements. In particular, the N = 126 shell closure plays a crucial role in shaping this peak. Experimental data hints that the shell weakens as proton number departs from Z = 82, a trend largely missed by global mass models. To investigate its impact on r-process nucleosynthesis, we employ both standard global models with strong closures and modified Duflo-Zuker (DZ) models that reproduce the weakening, combined with three sets of β − -decay rates. Strong shell closures generate sharply peaked abundances, whereas weakened closures consistent with the experimental trend produce broader, flatter patterns. Accurately reproducing the solar third peak under weakened shell strength requires sufficiently neutron-rich conditions that significant fission occurs, and slower decay rates. These results demonstrate that a weakening N = 126 shell closure away from stability imposes significant constraints on the astrophysical environments of the r-process and underscores the need for precise mass measurements and improved characterization of β − -decay properties in this region.

N = 126 closed shells↗
DOE OSTI2020

Oxide-Free Three-Dimensional Germanium/Silicon Core–Shell Metalattice Made by High-Pressure Confined Chemical Vapor Deposition

Metalattices are crystalline arrays of uniform particles in which the period of the crystal is close to some characteristic physical length scale of the material. In this work, we explore the synthesis and properties of a germanium metalattice in which the similar to 70 nm periodicity of a silica colloidal crystal template is close to the similar to 24 nm Bohr exciton radius of the nanocrystalline Ge replica. The problem of Ge surface oxidation can be significant when exploring quantum confinement effects or designing electronically coupled nanostructures because of the high surface area to volume ratio at the nanoscale. To eliminate surface oxidation, we developed a coreshell synthesis in which the Ge metalattice is protected by an oxide-free Si interfacial layer, and we explore its properties by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The interstices of a colloidal crystal film grown from 69 nm diameter spherical silica particles were filled with polycrystalline Ge by high-pressure confined chemical vapor deposition (HPcCVD) from GeH4. After the SiO2 template was etched away with aqueous HF, the Ge replica was uniformly coated with an amorphous Si shell by HPcCVD as confirmed by TEM-EDS (energy-dispersive X-ray spectroscopy) and Raman spectroscopy. Formation of the shell prevents oxidation of the Ge core within the detection limit of XPS. The electronic properties of the core-shell structure were studied by accessing the Ge 3d edge onset using STEM-EELS. A blue shift in the edge onset with decreasing size of Ge sites in the metalattices suggests quantum confinement of the Ge core. The degree of quantum confinement of the Ge core depends on the void sizes in the template, which is tunable by using silica particles of varying size. The edge onset also shows a shift to higher energy near the shell in comparison with the Ge core. This shift along with the observation of Ge-Si vibrational modes in the Raman spectrum indicate interdiffusion of Ge and Si. Both the size of the voids in the template and core-shell interdiffusion of Si and Ge can in principle be tuned to modify the electronic properties of the Ge metalattice.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Design of Zn Chalcogenide Shells for Emissive Ga-Rich In 1– X Ga X As Quantum Dots Synthesized in Molten Salts

Colloidal quantum dots (QDs) have seen expanded applications in optoelectronics from visible to near-infrared (NIR) wavelengths. However, the options for QDs with bright and size-tunable emission in the NIR region are mostly limited to heavy-metal-based (Pb, Cd, Hg) semiconductors. Here, Ga-rich In 1–X Ga X As QDs with zinc chalcogenide shells are demonstrated as candidates for NIR emitters. Based on new developments in inorganic molten salt chemistry, we synthesized colloidal In 1–X Ga X As QDs containing up to 85% gallium with high crystallinity based on Raman and XRD analyses. Zinc selenide and sulfide shells with different morphologies were grown on In 1–X Ga X As QDs by controlling the Zn precursor chemistry. Despite the nominally reduced lattice mismatch in the In 1–X Ga X As/ZnSe heterostructure, a ZnS shell was found to be a much more effective passivation material: In 1–X Ga X As/ZnS core–shell QDs show a photoluminescence quantum yield (PL QY) of about 30% versus 11% for ZnSe shells. In conclusion, based on the analysis of PL decay and transient absorption (TA) dynamics, we surmise that electron trapping is the major reason for efficiency loss, providing a clear heterostructure design principle for realizing efficient NIR-emitting In 1–X Ga X As QDs.

Electron trapping↗
DOE OSTI2023

Los Alamos National Laboratory Double Shell Program Target Development

The Double Shell Program at Los Alamos National Laboratory is studying an alternative platform for achieving robust alpha-particle heating at the National Ignition Facility. Double shells benefit from having a low convergence ratio and lower predicted temperature for achieving volume ignition. The joint required to assemble a double shell has an imperfection in the outer shell that seeds instabilities that can greatly impact the inner capsule’s implosion at bang time. Furthermore, different variations of the shape and placement of the joint were implemented with improvements in the quality of the machining leading to measurable improvements in yield. High-Z coatings on the outer joint mitigated the impact of the 1- to 2-μm gap sometimes found in double shell assemblies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

ABLE direct drive multi-shell NIF campaign [Slides]

The ABLE campaign is validating design and fabrication capabilities for multi-shell high-yield NIF targets. PDD double shell of outer two shells validates both hydroefficiency and shell collision efficiency for innovative NIF ignition concept. The goal is to obtain design hydro-efficiency and collision efficiency with predictive shell symmetry. The results will be used to determine if further development of this ICF concept is warranted.

42 ENGINEERING↗
DOE OSTI2023

Calcite Twinning in Mollusk Shells and Carrara Marble

Mollusk shells protect the animals that form and inhabit them. They are composites of minerals and organics, with diverse mesostructures, including nacre, prismatic calcite, crossed-lamellar aragonite, and foliated calcite. Twins, that is, crystals mirror symmetric with respect to their coherent interface, occurring as formation or deformation twins, are observed in all mollusk shell mesostructures but never within calcite prisms. Here, nanotwins and microwins within single calcite prisms are observed in different shells. Using Polarization-dependent Imaging Contrast (PIC) mapping with 20–60 nm resolution, twins are observed to be 0.2–3 µm thick layers of differently oriented and colored crystals with respect to the main prism crystal. Multiple twins are interspersed with the prism crystal, parallel to one another, and similarly oriented. When comparing images of calcite prisms and twins obtained by PIC mapping and by Electron Back-Scattered Diffraction (EBSD), the images correspond precisely. All twins are e-twin types, with 127° angular distance between c-axes. E-twins are the most common deformation twins in geologic calcite, as also observed here in Carrara marble. Location of all twins near the outer surface of all shells and e-twin type both suggest that twins within calcite prisms in mollusk shells result from deformation twinning.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Dual material fused filament fabrication of composite core‐shell structures with improved impact resistance and interfacial adhesion

The mechanical performance of parts produced by fused filament fabrication (FFF) has been limited due to the presence of voids and poor interlayer welding. Recent advancements in FFF have enabled the fabrication of void-free objects with strong interlayer welding through the use of semicrystalline polymer shells such as high-density polyethylene (HDPE) along with a high viscosity core polymer like acrylonitrile-butadiene-styrene (ABS). Furthermore, the zero-shear viscosity (η0) of ABS is three orders of magnitude higher than HDPE making the ABS-HDPE core-shell configuration preferable. ABS holds the shape by preventing bulk flow and part bending while HDPE promotes full surface contact across the layers. Most polymers, however, are immiscible which causes a weak weld line along the core-shell interface. Herein, maleic anhydride (MAH) is grafted to the butadiene segment of the ABS core thereby compatibilizing the interface with HDPE, improving the interfacial adhesion. Attenuated total reflectance-Fourier transform infrared spectroscopy was employed to confirm successful grafting. Using a custom-made die affording the core-shell structure, the ABS-g-MAH is shown to improve the impact resistance by 253% and 16% compared to neat HDPE and ABS specimens, respectively. Additionally, a 10% increase compared to the unmodified ABS-HDPE core-shell configuration is observed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Comparison of δ 13 C analyses of individual foraminifer ( Orbulina universa ) shells by secondary ion mass spectrometry and gas source mass spectrometry

Rationale: The use of secondary ion mass spectrometry (SIMS) to perform micrometer-scale in situ carbon isotope (δ 13 C) analyses of shells of marine microfossils called planktic foraminifers holds promise to explore calcification and ecological processes. The potential of this technique, however, cannot be realized without comparison to traditional whole-shell δ 13 C values measured by gas source mass spectrometry (GSMS). Methods: Paired SIMS and GSMS δ 13 C values measured from final chamber fragments of the same shell of the planktic foraminifer Orbulina universa are compared. The SIMS–GSMS δ 13 C differences (Δ 13 C SIMS-GSMS ) were determined via paired analysis of hydrogen peroxide-cleaned fragments of modern cultured specimens and of fossil specimens from deep-sea sediments that were either untreated, sonicated, and cleaned with hydrogen peroxide or vacuum roasted. After treatment, fragments were analyzed by a CAMECA IMS 1280 SIMS instrument and either a ThermoScientific MAT-253 or a Fisons Optima isotope ratio mass spectrometer (GSMS). Results: Paired analyses of cleaned fragments of cultured specimens (n = 7) yield no SIMS–GSMS δ 13 C difference. However, paired analyses of untreated (n = 18) and cleaned (n = 12) fragments of fossil shells yield average Δ 13 C SIMS-GSMS values of 0.8‰ and 0.6‰ (±0.2‰, 2 SE), respectively, while vacuum roasting of fossil shell fragments (n = 11) removes the SIMS–GSMS δ 13 C difference. Conclusions: The noted Δ 13 C SIMS-GSMS values are most likely due to matrix effects causing sample–standard mismatch for SIMS analyses but may also be a combination of other factors such as SIMS measurement of chemically bound water. The volume of material analyzed via SIMS is ~10 5 times smaller than that analyzed by GSMS; hence, the extent to which these Δ 13 C SIMS-GSMS values represent differences in analyte or instrument factors remains unclear.

58 GEOSCIENCES↗
DOE OSTI2024

Bayesian batch optimization for molybdenum versus tungsten inertial confinement fusion double shell target design

Access to reliable, clean energy sources is a major concern for national security. Much research is focused on the “grand challenge” of producing energy via controlled fusion reactions in a laboratory setting. For fusion experiments, specifically inertial confinement fusion (ICF), to produce sufficient energy, the fusion reactions in the ICF fuel need to become self-sustaining and burn deuterium-tritium (DT) fuel efficiently. The recent record-breaking NIF ignition shot was able to achieve this goal as well as produce more energy than used to drive the experiment. This achievement brings self-sustaining fusion-based power systems closer than ever before, capable of providing humans with access to secure, renewable energy. In order to further progress toward the actualization of such power systems, more ICF experiments need to be conducted at large laser facilities such as the United States's National Ignition Facility (NIF) or France's Laser Mega-Joule. The high cost per shot and limited number of shots that are possible per year make it prohibitive to perform large numbers of experiments. As such, experimental design relies heavily on complex predictive physics simulations for high-fidelity “preshot” analysis. These multidimensional, multi-physics, high-fidelity simulations have to account for a variety of input parameters as well as modeling the extreme conditions (pressures and densities) present at ignition. Such simulations (especially in 3D) can become computationally prohibitive to turn around for each ICF experiment. In this work, we explore using Bayesian optimization with Gaussian processes (GPs) to find optimal designs for ICF double shell targets, while keeping computational costs to manageable levels. These double shell targets have an inner shell that grades from beryllium on the outer surface to the higher Z material molybdenum, as opposed to the nominally used tungsten, on the inside in order to trade off between the high performance associated with high density inner shells and capsule stability. We describe our results for “capsule-only” xRAGE simulations to study the physics between different capsule designs, inner shell materials, and potential for future experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Evolutionary relationships among shell proteins of carboxysomes and metabolosomes

Bacterial microcompartments (BMCs) are self-assembling prokaryotic organelles which encapsulate enzymes within a polyhedral protein shell. Additionally, the shells are comprised of only two structural modules, distinct domains that form pentagonal and hexagonal building blocks, which occupy the vertices and facets, respectively. As all BMC loci encode at least one hexamer-forming and one pentamer-forming protein, the evolutionary history of BMCs can be interrogated from the perspective of their shells. Here, we discuss how structures of intact shells and detailed phylogenies of their building blocks from a recent phylogenomic survey distinguish families of these domains and reveal clade-specific structural features. These features suggest distinct functional roles that recur across diverse BMCs. For example, it is clear that carboxysomes independently arose twice from metabolosomes, yet the principles of shell assembly are remarkably conserved.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Nonadiabatic Excited-State Molecular Dynamics for Open-Shell Systems

Nonadiabatic Molecular Dynamics (NAMD) of excited states has been widely used in the simulation of photoinduced phenomena. However, the inability to treat bond breaking and forming processes with single-reference electronic structure methods limits their application in photochemistry for extended molecular systems. In this work, the extension of excited-state NAMD for open-shell systems is developed and implemented in the NEXMD software. We present the spin-unrestricted CIS and TDSCF formalism for the ground and excited states, analytical derivatives, and nonadiabatic derivative couplings for the respective potential energy surfaces. Next, this methodology is employed to study the photochemical reaction of three model molecules. The results demonstrate the advantage of the open-shell approach in modeling photochemical reactions, especially involving bond breaking processes. We find that the open-shell method lowers the reaction barrier at the bond-breaking limits resulting in larger calculated photochemical quantum yields compared to the respective closed-shell results. We also address problems related to spin contamination in the open-shell method, especially when molecular geometries are far from equilibrium.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Auger Dynamics in InP/ZnSe/ZnS Quantum Dots Having Pure and Doped Shells

In this study, we report the negative trion and biexciton Auger dynamics in very high-quality InP/ZnSe/ZnS quantum dots (QDs) having varying amounts of indium-based traps in the ZnSe shell. Negative trion times are determined by time-correlated photon-counting measurements on QDs that have been photoreduced with lithium triethylborohydride. We find that the Auger times vary from 280 to 425 ps and scale linearly with the total particle volume. Excess indium in the ZnSe shell gives rise to hole traps that are transiently populated following photoexcitation. Comparing stoichiometric and nonstoichiometric particles, we find that the negative trion lifetimes are independent of the presence of indium in the ZnSe shell. Biexciton dynamics are determined from transient absorption (TA) bleach recovery measurements. Absorption of two photons results in the formation of two types of biexcitons: those having both holes in the InP core (XX state) and those having one hole trapped in the ZnSe shell (XT state). XX state Auger times are measured in stoichiometric QDs, and for these particles, the Auger times are ~80 ps. Nonstoichiometric QDs show an additional long TA decay component, assigned to Auger recombination of the XT state. Here, a previous study (J. Phys. Chem. C 2021, 125, 4110–4118) found that hole trapping at indium-based shell traps results in a slow photoluminescence (PL) rise component. We find that the fraction of the XT state formed by the absorption of two photons correlates with the product of the fraction of slow PL rise and the rise time constant following one-photon excitation.

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

Synthesis and Evaluation of Cu@ZnO Core@Shell Nanowires for Use in the Carbon Dioxide Thermal Reduction Reaction

Copper-based core@shell nanomaterials are of interest for the catalytic hydrogenation of carbon dioxide toward value-added products. In this context, we have developed a facile, microwave-based procedure for the reliable and reproducible synthesis of Cu@ZnO core@shell nanowires. A systematic assessment of the effect of rationally varying various reaction conditions on this protocol was completed in order to better evaluate the growth process of these core–shell motifs. We determined that among different reaction parameters, it was the critical role of reaction time which enabled the quantitatively reliable growth of external shells with tunable thicknesses of up to 20 nm. As a demonstration of the material’s practical viability, catalytic testing was subsequently performed for the reverse water–gas shift reaction (CO 2 + H 2 → CO + H 2 O), with the evolution of the process followed with in situ X-ray diffraction and X-ray absorption spectroscopy in order to probe structural changes and gauge stability. These tests found the catalysts to be effective at converting CO 2 to CO, with notable stability detected in the shell layer and no observed alloying between copper and zinc. Furthermore, our studies support the idea that the Cu–ZnO and CuO x –ZnO interfaces are essential for the effective activation of CO 2 and H 2 .

36 MATERIALS SCIENCE↗