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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Solar wind latitudinal variations deduced from Mariner 10 interplanetary H /1216 A/ observations

The Mariner 10 H (1216-A) interplanetary observations are examined by using models that consider anisotropies in the solar fluxes. It is verified that the dominant contribution to asymmetric structure in the Mariner 10 H (1216-A) data is a latitudinal variation of the solar-wind flux and of the solar wind velocity, leading to a hydrogen atom lifetime that is latitude dependent. The average lifetime at 1 AU is found to increase from the solar equator to the solar poles by about 25%. This allows interstellar hydrogen to penetrate closer to the solar poles than to the equator. A general analytic model is constructed for evaluating the neutral hydrogen density distribution in interplanetary space. This model takes into account the latitude-dependent ionization rate. When this model is applied to the Mariner 10 H (1216-A) data, it is shown to be capable of matching the observations with a statistical accuracy of 5%. The effect of this latitudinal variation on H (1216-A) sky background maps is to produce a latitudinal shift in the maximum toward the north ecliptic pole.

Witt, N.↗
NASA NTRS1982

Intense Ly-alpha emission from Uranus

The existence of intense atomic hydrogen Ly-alpha emission from Uranus is demonstrated here by utilizing the monochromatic imaging capabilities of the International Ultraviolet Explorer (IUE) spectrograph. Observations show increased emission in the vicinity of Uranus superimposed on the geocoronal/interplanetary background. If resonant scattering of solar Ly-alpha is the source of the 1.6 + or - 0.4 kR disk averaged brightness, then very high column densities of atomic H above the absorbing methane are required. Precipitation of trapped charged particles, i.e., aurora, could explain the emissions. This would imply a planetary magnetic field.

Durrance, S. T.↗
NASA NTRS1983

Helium on Venus - Implications for uranium and thorium

Helium is removed at an average rate of 10 to the 6th atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on earth, suggesting comparable abundances of crustal uranium and thorium.

Prather, M. J.↗
NASA NTRS1984

Chondrules in the bishunpur L13 chondrite

Twenty-six chondrules, chondrule fragments or clasts were analyzed. An automated wavelength dispersive instrument with a 90 micrometer beam integrated a series of analyses in traverses across each object. Depending on the size of the cross-sectional area, from 1 to 21 analyses were performed for each bulk analysis. Si, Ti, Al, Cr, Fe, Ni, Mn, Mg, Ca, Na, K and S were determined, and an analyzed augite was used as a secondary standard before and after each set of analyses. The work is part of a study of chondrule rims, interchondrule matrix, chondrules and clasts in unequilibrated ordinary chondrites. Only two of the twenty-six objects analyzed have Ca/Al atomic ratios greater than the ordinary chondritic average of 0.74. The bulk meteorite has a normal Ca/Al ratio, so presumably a Ca-rich, Al-poor component must be present to compensate for chondrules and chlasts. This component is unlikely to be rim or matrix, but may be phosphate associated with metal or sulphide. Na/Al ratios range from 1 to almost zero, but there is no hiatus as in a suite of Manych chondrules and glasses.

Hutchison, R.↗
NASA NTRS1985

Preparation and analysis of particulate metal deposits

Small particles and clusters of palladium were grown by deposition from the vapor phase under ultrahigh vacuum conditions. Amorphous and crystalline support films of Al2O3 and ultrathin amorphous carbon films were used as substrate materials. The growth of the metal deposit was monitored in situ by scanning transmission diffraction of energy-filtered 100 kV electrons and high resolution transmission electron microscopy (TEM) analysis was performed in a separate instrument. It was established by in situ TEM, however, that the transfer of specimens in this case did not unduly affect the size and distribution of deposit particles. It was found that the cleanness, stoichiometry, crystallinity and structural perfection of the support surface play an essential role in determining the crystalline perfection and structure of the particles. The smallest palladium clusters reproducibly prepared contained not more than six atoms but size determinations below 1 nm average particle diameter are very problematic with conventional TEM. Palladium particles grown on carbon supports feature an impurity-stabilized mosaic structure.

Poppa, H.↗
NASA NTRS2000

Atomic-Based-Combined-Cycle Analysis

Atomic-based-combined-cycle (ABCC) engine combines an air-breathing ramjet engine with an atomic reactor to increase the mission-averaged specific impulse and thereby increasing the dry-mass ratio. ABCC engine is similar to RBCC engine except that energy needed for the propulsive power is derived from nuclear reaction rather than chemical combustion used in the RBCC engine. The potential performance improvement of an ABCC engine over a RBCC engine comes from two factors. Firstly, the energy density of nuclear reaction is several order of magnitudes higher than the chemical combustion. Secondly, hydrogen can produce much higher nozzle exit velocity because of its small molecular weight. A one-dimensional, transient numerical model was used to analyze a generic scramjet engine and it is used as a baseline to evaluate an imaginary ABCC engine performance. A nuclear reactor is treated as a black box energy source that replaces the role of the primary rocket and the chemical combustion chamber in a RBCC engine. Hydrogen is heated by the reactor and accelerated to produce high-speed ejection velocity. The ejection velocity up 10,000 m/sec is theoretically possible because of high energy density from the reactor and large gas constant of the hydrogen. Oxygen contained in the entrained air reacts with hydrogen and produces propulsive power for ejector mode operation. To provide enough thrust for initial acceleration, relatively large amount of hydrogen must be pumped through the reactor. Amount of oxygen contained in the entrained air may not be sufficient to burn all hydrogen and consequently combustion could occur at the end of exit nozzle. It is assumed that this combustion process is constant-pressure combustion at 1.0 atmospheric pressure and thus not affects the nozzle exit condition.

Han, Sam↗
NASA NTRS1999

Hierarchical Approach to 'Atomistic' 3-D MOSFET Simulation

We present a hierarchical approach to the 'atomistic' simulation of aggressively scaled sub-0.1 micron MOSFET's. These devices are so small that their characteristics depend on the precise location of dopant atoms within them, not just on their average density. A full-scale three-dimensional drift-diffusion atomistic simulation approach is first described and used to verify more economical, but restricted, options. To reduce processor time and memory requirements at high drain voltage, we have developed a self-consistent option based on a solution of the current continuity equation restricted to a thin slab of the channel. This is coupled to the solution of the Poisson equation in the whole simulation domain in the Gummel iteration cycles. The accuracy of this approach is investigated in comparison to the full self-consistent solution. At low drain voltage, a single solution of the nonlinear Poisson equation is sufficient to extract the current with satisfactory accuracy. In this case, the current is calculated by solving the current continuity equation in a drift approximation only, also in a thin slab containing the MOSFET channel. The regions of applicability for the different components of this hierarchical approach are illustrated in example simulations covering the random dopant-induced threshold voltage fluctuations, threshold voltage lowering, threshold voltage asymmetry, and drain current fluctuations.

Asenov, Asen↗
NASA NTRS1999

Atomic-Based-Combined-Cycle Analysis

Atomic-based-combined-cycle (ABCC) engine combines an air-breathing ramjet engine with an atomic reactor to increase the mission-averaged specific impulse and thereby increasing the dry-mass ratio. ABCC engine is similar to RBCC engine except that energy needed for the propulsive power is derived from nuclear reaction rather than chemical combustion used in the RBCC engine. The potential performance improvement of an ABCC engine over a RBCC engine comes from two factors. Firstly, the energy density of nuclear reaction is several order of magnitudes higher than the chemical combustion. Secondly, hydrogen can produce much higher nozzle exit velocity because of its small molecular weight. A one-dimensional, transient numerical model was used to analyze a generic RBCC engine and it is used as a baseline to evaluate an imaginary ABCC engine performance. A nuclear reactor is treated as a black box energy source that replaces the role of the primary rocket and the chemical combustion chamber in a RBCC engine. The performance of a generic ABCC engine along a flight path (q0 =10 (exp 3) lbf per square ft) shows that the mission averaged-specific impulse is about twice larger than RBCC engine and the dry mass-ratio is about 50% larger. Results of the present ABCC engine performance are based on the assumptions that the flow passage of working fluids is identical to that of RBCC engine and that a nuclear reactor is treated as an energy black box. Preliminary heat transfer calculation shows that the rate of heat transfer to the working fluids is within the limit of turbulent convective heat transfer regimes. The flow passage of realistic ABCC engine must be known for a better prediction of ABCC engine performance. Also, critical heat transfer calculations must be performed for the ejector mode and ramjet mode operations. This is possible only when the details of a reactor configuration are available.

Han, Samuel S.↗
NASA NTRS1976

Formation of the 0.511 MeV line in solar flares

The slowing down and annihilation of positrons and the formation of positronium in a solar flare plasma are investigated to determine how the width of the 0.511-MeV line and its strength relative to the three-photon continuum from positronium decay depend on the temperature and density of the medium in which the positron comes to rest. The calculations are limited to the cases of annihilation in a completely ionized plasma, in a partially ionized plasma with an electron/neutron density ratio of 1.0 or 0.1, and in an atomic gas with a very small ion density. Thermally averaged rate coefficients are obtained for the free annihilation of positrons and for positronium formation through radiative recombination in the fully ionized plasma. Positronium formation rates and the resultant energy distributions of the positronium atoms in the partially ionized medium are determined by numerically solving the Fokker-Planck equation in a medium where the ambient free electrons have a Maxwell-Boltzmann distribution of finite temperature but the density of the medium is sufficiently low that positronium atoms decay without further collisions following their formation. A Monte Carlo calculation is performed for the positron energy loss, positronium formation through charge exchange, and positronium breakup in the weakly ionized medium. The energy distributions of decaying positronium atoms and the relative number of triplet to singlet positronium decays are evaluated for ion concentrations and densities characteristic of the solar photosphere.

Crannell, C. J.↗
NASA NTRS1976

Ultraviolet observations of local gas

From satellite measurements of ultraviolet spectra of stars, an average density of approximately 1.1/cu cm for hydrogen atoms, in both atomic and molecular form, is estimated for regions of space along the galactic plane within about 1 kpc of the sun. About 20% of the atoms are bound in molecular form although this figure is uncertain since the ultraviolet measurements avoid the very dense interstellar clouds. Discrete values for this percentage are observed to vary markedly; regions with less than average density seem to have fractional abundances of H2 several orders of magnitude lower than average. A ratio of CO/H is observed for regions in front of stars observed by the Copernicus satellite.

Jenkins, E. B.↗
NASA NTRS1977

Ultraviolet observations of local gas

From satellite measurements of ultraviolet spectra of stars, an average density of approximately 1.1 cu m/sec for hydrogen atoms, in both atomic and molecular form, is estimated for regions of space along the galactic plane within about 1 kpc of the sun. About 20 percent of the atoms are bound in molecular form, although this figure is uncertain because the ultraviolet measurements avoid the very dense interstellar clouds. Discrete values for this percentage are observed to vary markedly; regions with less than average density appear to have fractional abundances of H2 several orders of magnitude lower than average. A ratio of CO/H which ranges from 10 to the minus 9th to 10 to the minus 6th power is observed for regions in front of stars observed by the Copernicus satellite.

Jenkins, E. B.↗
DOE OSTI2023

Size-Dependent Energy and Adhesion of Pd Nanoparticles on Graphene on Ni(111) by Pd Vapor Adsorption Calorimetry

Carbon-supported late transition-metal nanoparticles are promising catalysts and electrocatalysts for wide-ranging applications. However, experimental investigations of the bonding energetics of metal nanoparticles on carbon supports are very limited. Here, in this work, we report heats of adsorption of Pd vapor deposited onto single-layer graphene(0001) supported on Ni(111) at 100 and 300 K as Pd grows particles of well-defined size in the range from three atom clusters to 6 nm diameter. Sizes were determined from He + low-energy ion scattering (LEIS). In this size range, the differential heat of Pd adsorption increases from 228 kJ/mol to within 10 kJ/mol of the heat of sublimation of bulk Pd (377 kJ/mol). The chemical potential of metal atoms in these nanoparticles as a function of average particle size was determined from these results. The adhesion energy at the Pd/graphene(0001)/Ni(111) interface was extracted from these data and found to be 3.5 J/m 2 for the largest Pd particles. For the three metal elements that have now been studied (Pd, Ni, and Ag), we found an increase in metal/graphene(0001)/Ni(111) adhesion energy with metal carbophilicity, which we defined here as the heat of C atom adsorption on that metal’s (111) surface estimated from published density functional theory calculations.

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

Solving complex nanostructures with ptychographic atomic electron tomography

Abstract Transmission electron microscopy (TEM) is essential for determining atomic scale structures in structural biology and materials science. In structural biology, three-dimensional structures of proteins are routinely determined from thousands of identical particles using phase-contrast TEM. In materials science, three-dimensional atomic structures of complex nanomaterials have been determined using atomic electron tomography (AET). However, neither of these methods can determine the three-dimensional atomic structure of heterogeneous nanomaterials containing light elements. Here, we perform ptychographic electron tomography from 34.5 million diffraction patterns to reconstruct an atomic resolution tilt series of a double wall-carbon nanotube (DW-CNT) encapsulating a complex ZrTe sandwich structure. Class averaging the resulting tilt series images and subpixel localization of the atomic peaks reveals a Zr 11 Te 50 structure containing a previously unobserved ZrTe 2 phase in the core. The experimental realization of atomic resolution ptychographic electron tomography will allow for the structural determination of a wide range of beam-sensitive nanomaterials containing light elements.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Using Complementary Methods of Synchrotron Radiation Powder Diffraction and Pair Distribution Function to Refine Crystal Structures with High Quality Parameters—A Review

Determination of the atomic-scale structures of certain fine-grained minerals using single-crystal X-ray diffraction (XRD) has been challenging because they commonly occur as submicron and nanocrystals in the geological environment. Synchrotron powder diffraction and scattering techniques are useful complementary methods for studying this type of minerals. In this review, we discussed three example studies investigated by combined methods of synchrotron radiation XRD and pair distribution function (PDF) techniques: (1) low-temperature cristobalite; (2) kaolinite; and (3) vernadite. Powder XRD is useful to determine the average structure including unit-cell parameters, fractional atomic coordinates, occupancies and isotropic atomic displacement parameters. X-ray/Neutron PDF methods are sensitive to study the local structure with anisotropic atomic displacement parameters (ADP). The results and case studies suggest that the crystal structure and high-quality ADP values can be obtained using the combined methods. The method can be useful to characterize crystals and minerals that are not suitable for single-crystal XRD.

58 GEOSCIENCES↗
DOE OSTI2020

Finite-Temperature Structures of Supported Subnanometer Catalysts Inferred via Statistical Learning and Genetic Algorithm-Based Optimization

Single-atom catalysts (SACs) minimize noble metal utilization and can alter the activity and selectivity of supported metal nanoparticles. However, the morphology of active centers, including single atoms and subnanometer clusters of a few atoms, remains elusive due to experimental challenges. The computational cost to describe numerous cluster shapes and sizes makes direct first-principles calculations impractical. We present a computational framework to enable structure determination for single-atom and subnanometer cluster catalysts. As a case study, we obtained the low energy structures of Pd n (n = 1-21) clusters supported on CeO 2 (111), which are critical components of automobile three-way catalysts. Trained on density functional theory data, a three-dimensional cluster expansion is established using statistical learning to describe the Hamiltonian and predict energies of supported Pdn clusters of any structure. Low energy stable and metastable structures are identified using a Metropolis Monte Carlo-based genetic algorithm in the canonical ensemble at 300 K. We observe that supported single atoms sinter to form bilayer clusters and large cluster isomers share similarities in both shape and energy, and elucidate the significance of the support and microstructure on cluster stability. We discovered a simple surrogate structure-energy model, where the energy per atom scales with the square root of the average first coordination number, which can be used to estimate energies and compare the stability of clusters. Our framework, applicable to any metal/support system, fills an important methodological gap to predict the stability of supported metal catalysts in the subnanometer regime.

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

Development of a wide bandwidth heterodyne dispersion interferometer for electron density measurement of atmospheric pressure plasmas

One of the challenges of electron density measurements of an atmospheric pressure plasma (APP) with a laser interferometer is the significant and unwanted phase shift caused by changes in the neutral gas density. These unwanted phase shifts can be mitigated and plasma density measured using an interferometer architecture called a dispersion interferometer (DI). A DI is composed of two nonlinear orientation patterned GaAs crystals for frequency doubling and measures the phase shift induced by a plasma in the interference signal between two second-harmonic beams. Measurement of plasma dynamics or a short plasma pulse in less than a millisecond is enabled with heterodyne detection in a DI using an acousto-optic cell with a frequency of 40 MHz. This heterodyne DI (HDI) is targeted to measure APPs in an electron density range of 10 20 –10 24 m −3 . Finally, the HDI achieves a line-integrated density resolution of 2 × 10 15 m −2 (a phase resolution of 0.005°) with a time constant of 1 μs using ensemble averaging techniques.

atmospheric pressure plasma↗
NASA NTRS1999

TiCl, TiH and TiH+ Bond Energies, a Test of a Correlation Consistent Ti Basis Set

Correlation consistent basis sets are developed for Ti atom. The polarization functions are optimized for the average of the 3F and 5F states. One series of correlation consistent basis sets is for 3d and 4s correlation, while the second series includes 3s and 3p correlation as well as 3d and 4s correlation. These basis sets are tested using the Ti 3F-5F separation and the dissociation energies of TiCl X4Phi, TiH X4Phi, and TiH(+) X3Phi. The CCSD(T) complete basis set limit values are determined by extrapolation. The Douglas Kroll approach is used to compute the scalar relativistic effect. Spin-orbit effects are taken from experiment and/or computed at the CASSCF level. The Ti 3F-5F separation is in excellent agreement with experiment, while the TiCl, TiH, and TiH(+) bond energies are in good agreement with experiment. Extrapolation with the valence basis set is consistent with other atoms, while including 3s and 3p correlation appears to make extrapolation.

Bauschlicher, Charles W., Jr.↗