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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Nanoparticles modified with multiple organic acids

Surface-modified nanoparticles of boehmite, and methods for preparing the same. Aluminum oxyhydroxide nanoparticles are surface modified by reaction with selected amounts of organic acids. In particular, the nanoparticle surface is modified by reactions with two or more different carboxylic acids, at least one of which is an organic carboxylic acid. The product is a surface modified boehmite nanoparticle that has an inorganic aluminum oxyhydroxide core, or part aluminum oxyhydroxide core and a surface-bonded organic shell. Organic carboxylic acids of this invention contain at least one carboxylic acid group and one carbon-hydrogen bond. One embodiment of this invention provides boehmite nanoparticles that have been surface modified with two or more acids one of which additional carries at least one reactive functional group. Another embodiment of this invention provides boehmite nanoparticles that have been surface modified with multiple acids one of which has molecular weight or average molecular weight greater than or equal to 500 Daltons. Yet, another embodiment of this invention provides boehmite nanoparticles that are surface modified with two or more acids one of which is hydrophobic in nature and has solubility in water of less than 15 by weight. The products of the methods of this invention have specific useful properties when used in mixture with liquids, as filler in solids, or as stand-alone entities.

Cook, Ronald Lee↗
DOE OSTI2023

Oxygen carrying materials with surface modification for redox-based catalysis and methods of making and uses thereof

Redox catalysts having surface medication, methods of making redox catalysts with surface modification, and uses of the surface modified redox catalysts are provided. In some aspects, the redox catalysts include a core oxygen carrier region such as CaMnO 3 , BaMnO 3−δ , SrMnO 3−δ , Mn 2 SiO 4 , Mn 2 MgO 4−δ , La 0.8 Sr 0.2 O 3−δ , La 0.8 Sr 0.2 FeO 3−δ , Ca 9 Ti 0.1 Mn 0.9 O 3−δ , Pr 6 O 11−δ , manganese ore, or a combination thereof; and an outer shell having an average thickness of about 1-100 monolayers surrounding the outer surface of the core region. The outer shell can include, for example a salt selected such as Li 2 WO 4 , Na 2 WO 4 , K 2 WO 4 , SrWO 4 , Li 2 MoO 4 , Na 2 MoO 4 , K 2 MoO 4 , CsMoO 4 , Li 2 CO 3 , Na 2 CO 3 , K 2 CO 3 , or a combination thereof.

Li, Fanxing↗
NASA NTRS1975

Preliminary results on detailed helium shell flash calculations

Preliminary results are reported for detailed calculations of ten successive helium flashes in Population I stars of 3 and 3.3 solar masses. The calculations have been conducted to determine whether an inner-shell convection zone that is driven outward from the center of the helium-burning shell by the flashes can penetrate into the hydrogen-rich zones of a star. Based on the present incomplete calculations, the process of flash evolution is outlined, the relationship between core mass and interflash period is described together with the relationship between core mass and intershell mass, and nucleosynthesis during helium-shell flash burning is considered. The results thus far indicate that the flashes increase in strength and consist of up to five subcomponents, the mass of the degenerate carbon-oxygen core may determine the interflash period as well as the intershell mass, and that helium flash burning produces mostly C-12 and a small amount of O-16.

Christy-Sackmann, I.-J.↗
DOE OSTI2026

Strong Effect of Nonpolar Solvent Molecular Structure on CdSe Nanoplatelet Stacking

We report a drastic difference in stacking behavior of oleic acid-stabilized 4-monolayer (4 ML) CdSe nanoplatelets (NPLs) in toluene and methylcyclohexane (MCH), two nonpolar solvents that differ in the conformational flexibility of their molecules. Using liquid cell transmission electron microscopy (TEM) and small angle scattering (SAXS) techniques, we show that NPLs form microns-long ribbons consisting of 4 ML CdSe NPLs in toluene, the solvent widely used to form stable colloidal solutions of a broad range of quasi-spherical nanoparticles. In contrast, 4 ML CdSe NPLs are well dispersed in MCH. The difference in stacking behavior of NPLs in toluene and MCH suggests that the conformational flexibility of the solvent molecules, such as the ability to adopt multiple chair conformations, modulates nanoplatelet interactions. Molecular dynamics (MD) simulations reveal that solvent molecules subtly alter the structure of the organic ligand shell. These solvent-dependent changes propagate to the inorganic core, modulating the degree of CdSe nanoplatelet (NPL) twisting and, consequently, the properties of the nanoparticles. We show that toluene better solvates oleate ligands while MCH induces a bimodal oleate span distribution, which can lead to increased solubility of CdSe NPLs. In addition, the solvent can also influence the inorganic core, which, in turn, can modify the nanoparticle properties. We demonstrate that destabilization of toluene solution containing ribbons of 4 ML CdSe NPLs without CdS shells results in the formation of NPL assemblies with amplified spontaneous emission (ASE) with a low threshold of 14 µJ cm−2 that is comparable with that of CdSe/CdS core/shell NPLs. Our results emphasize that the solvent plays a major role in mediating interactions between NPLs and hence their processability for fabrication of functional structures.

CdSe↗
NASA NTRS1986

Candidate solar-type protostars in nearby molecular cloud cores

IRAS data have been used to examine the vicinity of nearly 100 dense clumps of molecular gas observed in lines of CO and NH3. More than one-third of these molecular cloud 'cores' contain infrared sources that appear to be newly formed, or forming, low mass stars. While about one-third of the infrared sources are associated with visible stars and have properties that resemble T Tauri stars, the remainder of the infrared sources have no optical counterparts and are probably embedded within the molecular cloud itself. These invisible sources lie close to the molecular cloud peaks and have cold, massive shells of material around them. Some of the cores without infrared sources have gas properties similar to those with embedded sources and so may be on the verge of gravitational collapse. The selection of the IRAS sample and its properties are described. The spectral energy distributions of the sources and their nature are discussed along with their physical properties, the properties of cores with and without infrared sources, and the time scale for the evolution of the sources.

Beichman, C. A.↗
DOE OSTI2025

Size-dependent second-order-like phase transitions in Fe nanocluster melting from low-temperature structural isomerization

Here, in this work, the melting phase transitions of Fe n nanoclusters with 10 ≤ n ≤ 100 atoms are investigated using classical many-body molecular dynamics simulations. For many cluster sizes, surface melting occurs at much lower temperatures than core melting. Surface and core melting points and energetic melting points (temperatures of maximum heat capacity, C v ) are calculated for all cluster sizes. Melting properties are found to be strong functions of cluster structure. Cluster sizes with closed-shell structures always have first-order-like phase transitions. Almost one-third of cluster sizes in the analyzed range exhibit second-order-like phase transitions due to the presence of multiple structural configurations close in energy. 1-shell clusters with one to a few more atoms than a neighboring closed-shell structure have very low surface melting points and very high energetic melting points compared to their closed-shell counterparts. In clusters above 50 atoms with certain core structures, melting of the surface before the core was observed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2001

Physical and Electronic Isolation of Carbon Nanotube Conductors

Multi-walled nanotubes are proposed as a method to electrically and physically isolate nanoscale conductors from their surroundings. We use tight binding (TB) and density functional theory (DFT) to simulate the effects of an external electric field on multi-wall nanotubes. Two categories of multi-wall nanotube are investigated, those with metallic and semiconducting outer shells. In the metallic case, simulations show that the outer wall effectively screens the inner core from an applied electric field. This offers the ability to reduce crosstalk between nanotube conductors. A semiconducting outer shell is found not to perturb an electric field incident on the inner core, thereby providing physical isolation while allowing the tube to remain electrically coupled to its surroundings.

OKeeffe, James↗
DOE OSTI2023

Large two-photon cross sections and low-threshold multiphoton lasing of CdS/CdSe/CdS quantum shells

Colloidal quantum shells are spherical semiconductor quantum wells, which have shown strong promise as optical materials, particularly in classes of experiments requiring multiple excitons. The two-photon properties of CdS/CdSe/CdS quantum shell samples are studied here to demonstrate large non-linear absorption cross-sections while retaining advantageous multiexciton physics conferred by the geometrical structure. The quantum shells have large two-phonon cross sections (0.4–7.9 × 10 6 GM), which highlights their potential use in upconversion imaging in which large per particle two-photon absorption is critical. Time-resolved measurements confirmed that the quantum shells have long biexciton lifetime (>10 ns in the largest core samples reported here) and large gain bandwidth (>300 meV). The combination of these attributes with large two-photon cross sections makes the CdS/CdSe/CdS quantum shells excellent gain media for two-photon excitation. With a broad gain bandwidth and long gain lifetime, quantum shell solids support multimodal amplified spontaneous emission from excitons, biexcitons, and higher excited states. In conclusion, thresholds for amplified spontaneous emission and lasing, which are as low as 1 mJ cm −2 , are comparable to, or lower than, the thresholds reported for other colloidal materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2016

Buckling Design and Imperfection Sensitivity of Sandwich Composite Launch-Vehicle Shell Structures

Composite materials are increasingly being considered and used for launch-vehicle structures. For shell structures, such as interstages, skirts, and shrouds, honeycomb-core sandwich composites are often selected for their structural efficiency. Therefore, it is becoming increasingly important to understand the structural response, including buckling, of sandwich composite shell structures. Additionally, small geometric imperfections can significantly influence the buckling response, including considerably reducing the buckling load, of shell structures. Thus, both the response of the theoretically perfect structure and the buckling imperfection sensitivity must be considered during the design of such structures. To address the latter, empirically derived design factors, called buckling knockdown factors (KDFs), were developed by NASA in the 1960s to account for this buckling imperfection sensitivity during design. However, most of the test-article designs used in the development of these recommendations are not relevant to modern launch-vehicle constructions and material systems, and in particular, no composite test articles were considered. Herein, a two-part study on composite sandwich shells to (1) examine the relationship between the buckling knockdown factor and the areal mass of optimized designs, and (2) to interrogate the imperfection sensitivity of those optimized designs is presented. Four structures from recent NASA launch-vehicle development activities are considered. First, designs optimized for both strength and stability were generated for each of these structures using design optimization software and a range of buckling knockdown factors; it was found that the designed areal masses varied by between 6.1% and 19.6% over knockdown factors ranging from 0.6 to 0.9. Next, the buckling imperfection sensitivity of the optimized designs is explored using nonlinear finite-element analysis and the as-measured shape of a large-scale composite cylindrical shell. When compared with the current buckling design recommendations, the results suggest that the current recommendations are overly conservative and that the development of new recommendations could reduce the acreage areal mass of many composite sandwich shell designs by between 4% and 19%, depending on the structure.

Schultz, Marc R.↗
DOE OSTI2020

Superconducting air core inductor systems and methods

Provided is a low-weight, high-efficiency inductor design for use with or in electrical power equipment, such as inverters. A toroidal power inductor includes a support structure comprising an outer shell, an inner shell, and one or more coolant channels formed therebetween, a plurality of conductors wrapped around and supported by an exterior surface of the outer shell, and an interior cavity substantially enclosed by the inner shell of the toroidal support structure. The plurality of conductors are configured to provide an inductance for the toroidal power inductor, and the one or more coolant channels are distributed beneath the exterior surface of the outer shell to cool the plurality of conductors. An air-core power inductor may implement the conductors using high-temperature superconducting (HTS) tapes cooled by cryogenic fluid flowing within the coolant channels.

42 ENGINEERING↗
DOE OSTI2024

A universal and constant rate of gene content change traces pangenome flux to LUCA

Abstract Prokaryotic genomes constantly undergo gene flux via lateral gene transfer, generating a pangenome structure consisting of a conserved core genome surrounded by a more variable accessory genome shell. Over time, flux generates change in genome content. Here, we measure and compare the rate of genome flux for 5655 prokaryotic genomes as a function of amino acid sequence divergence in 36 universally distributed proteins of the informational core (IC). We find a clock of gene content change. The long-term average rate of gene content flux is remarkably constant across all higher prokaryotic taxa sampled, whereby the size of the accessory genome—the proportion of the genome harboring gene content difference for genome pairs—varies across taxa. The proportion of species-level accessory genes per genome, varies from 0% (Chlamydia) to 30%–33% (Alphaproteobacteria, Gammaproteobacteria, and Clostridia). A clock-like rate of gene content change across all prokaryotic taxa sampled suggest that pangenome structure is a general feature of prokaryotic genomes and that it has been in existence since the divergence of bacteria and archaea.

Microbiology↗
DOE OSTI2026

𝑁 = 8 Shell Breaking in 12 Be from a Single-Particle Perspective

Experimental observations of the low-lying states in 12 Be and their accurate modeling play an essential role in understanding the disappearance of the 𝑁 = 8 magic number. Long-standing experimental ambiguities have been clarified using an one-neutron adding (𝑑, 𝑝) reaction on 11 Be using the ISOLDE Solenoidal Spectrometer at CERN’s HIE-ISOLDE facility. The single-particle energies of 1⁢𝑠 1/2 , 0⁢𝑑 5/2 , and 0⁢𝑝 1/2 orbitals in 12 Be have been determined from the extracted spectroscopic factors. A significant reduction between the separation of 1⁢𝑠 1/2 and 0⁢𝑝 1/2 orbitals is found in comparison with the carbon isotones, highlighting the breakdown of the 𝑁 = 8 shell. These observations serve as an important test of different effects incorporated in theoretical models. It is found that two synergistic mechanisms, core deformation and weak binding, are responsible for the 𝑁 = 8 shell breaking and the exotic near-threshold phenomena observed in 12 Be, including the narrow unnatural-parity resonance $0^{-}_1$ and the possible halolike nature of the $0^+_2$ isomer.

Chen, Jie [Southern University of Science and Tech↗
DOE OSTI2024

Efficient Oxidative Decomposition of Jet-Fuel exo -Tetrahydrodicyclopentadiene (JP-10) by Aluminum Nanoparticles in a Catalytic Microreactor: An Online Vacuum Ultraviolet Photoionization Study

The oxidation of gas-phase exo-tetrahydrodicyclopentadiene (JP-10, C 10 H 16 ) over aluminum nanoparticles (AlNP) has been explored between a temperature range of 300 and 1250 K with a novel chemical microreactor. The results are compared with those obtained from chemical microreactor studies of helium-seeded JP-10 and of helium–oxygen-seeded JP-10 without AlNP to gauge the effects of molecular oxygen and AlNP, respectively. Vacuum ultraviolet (VUV) photoionization mass spectrometry reveals that oxidative decomposition of JP-10 in the presence of AlNP is lowered by 350 and 200 K with and without AlNP, respectively, in comparison with pyrolysis of the fuel. Overall, 63 nascent gas-phase products are identified through photoionization efficiency (PIE) curves; these can be categorized as oxygenated molecules and their radicals as well as closed-shell hydrocarbons along with hydrocarbon radicals. Quantitative branching ratios of the products reveal diminishing yields of oxidized species and enhanced branching ratios of hydrocarbon species with the increase in temperature. While in the low-temperature regime (300–1000 K), AlNP solely acts as an efficient heat transfer medium, in the higher-temperature regime (1000–1250 K), chemical reactivity is triggered, facilitating the primary decomposition of the parent JP-10 molecule. Furthermore, this enhanced reactivity of AlNP could plausibly be linked to the exposed reactive surface of the aluminum (Al) core generated upon the rupture of the alumina shell material above the melting point of the metal (Al).

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

High Fidelity CFD Simulations Supporting the KP-FHR

Kairos Power, LLC, is developing its version of the Fluoride-cooled High-temperature Reactor, the KP-FHR. The design uses a pebble bed core with fluoride salt as a coolant. The pebbles used in the KP-FHR have a diameter of 4 cm, with a shell fuel region where TRISO particles are embedded. A Pebble bed core design is adopted by several Gen IV reactors, They boast many benefits, such as fuel integrity, highly efficient heat transfer, and passive safety. However, it is challenging to accurately predict temperature and flow inside a pebble bed. Traditional approaches use the porous media model, which regards the pebble bed as a continuous medium, but with different temperature fields representing different levels, such as the fluid temperature, pebble surface temperature, and pebble center temperature. Empirical heat transfer correlations are adopted to calculate the heat transfer coefficient between different phases. However, empirical correlations are usually validated with experimental data, which usually lacks detail inside the pebble bed. The available experimental data is also generally at a high Reynolds number, which falls outside of the conditions of KP-FHR. Explicit computational fluid dynamics (CFD) simulations of randomly packed pebble beds have only become feasible recently. This is thanks to the rapid development of computational power and scalable algorithms. In this work, we used the Spectral Element Method (SEM) CFD code NekRS to simulate the randomly packed pebble bed in a cylindrical container. NekRS, which is the GPU variant of Nek5000, but refactored to utilize the computational power of GPUs using the OCCA library to run on hybrid architecture high performance computing systems. It was initially developed with the libParamunal library, but truncated and tuned for large-scale turbulence simulation. As a result, the SEM reaches higher precision with the same degrees of freedom by using a high-order Lagrange polynomial basis distributed on Gauss-Lobatto-Legendre quadrature inside each element, compared to lower-order methods, such the Finite Volume Method and Finite Element Method. The report is divided into five parts. We start with a general discussion of the pebble bed reactor, along with a specific investigation into the KP-FHR. The second part presents the numerical methodology. In the third part, we study a modular pebble bed with 1741 pebbles in a container of 7 pebble-diameter radius. Beyond LES simulations done by NekRS, we also leveraged the thermal radiation model in OpenFOAM to study heat transfer under no-forced-flow scenarios. Then, in the fourth part we simulated a pebble bed similar to the size of the Hermes Test Reactor. The total number of pebbles is in these simulations is 34,374. The container radius is 14 pebble-diameters. Finally, the report concludes in part five, with a discussion of future work.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2026

Impact of atomic substitution on core-hole relaxation dynamics: A study of Br 2 and IBr

Understanding inner-shell decay processes in heavy-element molecules is essential for unraveling x-ray-induced photodynamics and advancing molecular imaging techniques. Here, in this study, we investigate the influence of atomic substitution on core-hole relaxation dynamics and molecular fragmentation in Br 2 and IBr, initiated by x-ray ionization absorption at the Br K-edge. Using a combination of x-ray/ion coincidence measurements and Monte Carlo/molecular dynamics simulations, we track the charge distribution and the kinetic energy release (KER) of fragment ions with a total charge from 2+ to 8+. For both molecules, the simulated KER values show good agreement with experiment across different fragmentation channels. Our comparison reveals that substituting Br with the heavier I atom in IBr has a minimal impact on the inner-shell electronic decay process but significantly influences nuclear motion, leading to slower dissociation and thus a KER close to the Coulomb limit—an effect attributed to the atomic mass. These findings highlight the interplay between electronic and nuclear effects in molecular fragmentation, particularly in heavy-element species, and provide new insights into medical therapies, structural biology, and astrophysics.

Bhat, Nivedita [Argonne National Laboratory (ANL),↗
NASA NTRS2002

On Magnetic Spectra of Earth and Mars

The spectral method for distinguishing crustal from core-source magnetic fields is reexamined, modified, and applied to both a comprehensive geomagnetic field model and an altitude normalized magnetic map of Mars. The observational spectra are fairly fitted by theoretical forms expected from certain elementary classes of magnetic sources. For Earth we find fields from a core of radius 3512 +/- 64 km, in accord with the seismologic core radius of 3480 km, and a crust represented by a shell of random dipolar sources at radius 6367 +/- 14 km, near the planetary mean radius of 6371.2 km. For Mars we find no sign of a core-source field, only a field from a crust represented in same way, but at radius 3344 +/- 10 km, about 46 km below the planetary mean radius of 3389.5 km, and with sources about 9.6 +/- 3.2 times stronger.

Voorhies, C. V.↗
NASA NTRS1993

Phase transitions and 2D spherical convection in a large icy satellite

Three ice phase transitions, based on experimental and theoretical results, were incorporated into a 2D spherical convection model. These phase transitions are the exothermic Ice 1-2, the endothermic Ice 2-6, and the exothermic Ice 6-8 phase transitions. The fluid is assumed isoviscous and the anelastic liquid formulation was used. The object is an icy satellite whose physical characteristics resemble those of Ganymede or Callisto. Structural models, similar to those of Mueller and McKinnon, with different core sizes, i.e. with different degree of differentiation were studied. The shells, i.e. the mantle of the satellite, is heated both internally and from below to account for the decaying radiogenic heating and the heat flow from the solid core. The lower boundary of the mantle is rigid and isothermal, the upper boundary is isothermal. Calculations with rigid and shear stress free upper boundary are carried out in order to assess the role of the different boundary conditions. Two different Rayleigh numbers, depending on the assumed value of the viscosity, were used in the calculations and the thermal evolution of the satellite was studied. The suit of calculations presented demonstrates that phase transition cannot be ignored when the thermal evolution of a large icy satellite has to be studied. The importance of the construction of the realistic phase diagram for ice was also documented. On the other hand the degree of differentiation, simulated with the structures with different core's radius does not seem to drastically influence the overall behavior of the convective activity. Within the limits of our simulations, the post-accretional evolution seems to be independent on the degree of primordial differentiation.

Forni, O.↗
DOE OSTI2022

The effect of micro-encapsulation on thermal characteristics of metallic phase change materials

Micro-encapsulated phase change material with metallic core can work under high temperature for energy storage purpose, making it an appealing candidate for renewable energy technologies, such as thermal energy storage for concentrating solar power plants. Here, the objective of this work is to study the impact of encapsulation on the thermal performance of the micro-encapsulated phase change materials under various operating conditions. To evaluate the thermal performance of the micro-encapsulated phase change material particles, the governing equation of transient heat conduction with phase change in spheres with composite walls is solved numerically. The impact of encapsulation shell on the convective heat transfer rate, total energy absorption, latent heat ratio, energy density, and duration of phase change is presented and analyzed under different operating conditions. Three different core materials including tin, aluminum and copper with distinct Stephan numbers are investigated. In addition to the encapsulation shell effect, this model can be used to study micro-encapsulated phase change materials with different material compositions, core to shell ratios, and it can be used to analyze the impact of air gaps in between materials. Understanding the thermal performance at particle level is essential, and the results of this study could potentially be used as input for thermal energy storage system level analysis, such as the charging and discharging processes.

42 ENGINEERING↗