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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

A Rb-Sr and Sm-Nd Isotope Geochronology and Trace Element Study of Lunar Meteorite LaPaz Icefield 02205

Rubidium-strontium and samarium-neodymium isotopes of lunar meteorite LaPaz Icefield (LAP) 02205 are consistent with derivation of the parent magma from a source region similar to that which produced the Apollo 12 low-Ti olivine basalts followed by mixing of the magma with small amounts (1 to 2 wt%) of trace element-enriched material similar to lunar KREEP-rich sample SaU 169. The crystallization age of LAP 02205 is most precisely dated by an internal Rb-Sr isochron of 2991+/-14 Ma, with an initial Sr-87/Sr-88 at the time of crystallization of 0.699836+/-0.000010. Leachable REE-rich phosphate phases of LAP 02205 do not plot on a Sm-Nd mineral isochron, indicating contamination or open system behavior of the phosphates. Excluding anomalous phases from the calculation of a Sm-Nd isochron yields a crystallization age of 2992+/-85 (initial Epsilon Nd-143 = +2.9+/-0.8) that is within error of the Rb-Sr age, and in agreement with other independent age determinations for LAP 02205 from Ar-Ar and U-Pb methods. The calculated Sm-147/Nd-144 source ratios for LAP 02205, various Apollo 12 and 15 basalts, and samples with strong affinities to KREEP (SaU 169, NWA 773, 15386) are uncorrelated with their crystallization ages. This finding does not support the involvement of a common KREEP component as a heat source for lunar melting events that occurred after crystallization of the lunar magma ocean.

Rankenburg, K.↗
NASA NTRS2013

Update on Development of the Potassium-Argon Laser Experiment (KArLE) Instrument for In Situ Geochronology

Absolute dating of planetary samples is an essential tool to establish the chronology of geological events, including crystallization history, magmatic evolution, and alteration. We are addressing this challenge by developing the Potassium (K) -- Argon Laser Experiment (KArLE), building on previous work to develop a K-Ar in situ instrument. KArLE ablates a rock sample, determines the K in the plasma state using laser-induced breakdown spectroscopy (LIBS), measures the liberated Ar using quadrupole mass spectrometry (QMS), and relates the two by the volume of the ablated pit using laser confocal microscopy (LCM). Our goal is for the KArLE instrument to be capable of determining the age of several kinds of planetary samples to address a wide range of geochronolgy problems in planetary science.

Cohen, Barbara A.↗
NASA NTRS2015

The Structure, Anharmonic Vibrational Frequencies, and Intensities of NNHNN+

A semi-global potential energy surface (PES) and quartic force field (QFF) based on fitting high-level electronic structure energies are presented to describe the structures and spectroscopic properties of NNHNN+. The equilibrium structure of NNHNN+ is linear with the proton equidistant between the two nitrogen groups and thus of D(sub ∞h) symmetry. Vibrational second-order perturbation theory (VPT2) calculations based on the QFF fails to describe the proton “rattle” motion, i.e., the antisymmetric proton stretch, due to the very flat nature of PES around the global minimum, but performs properly for other modes with sharper potential wells. Vibrational self-consistent field/virtual state configuration interaction (VSCF/VCI) calculations using a version of MULTIMODE without angular momentum terms successfully describe this motion and predict the fundamental to be at 759 cm(exp -1). This is in good agreement with the value of 746 cm(exp -1) from a fixed-node diffusion Monte Carlo calculation and the experimental Ar-tagged result of 743 cm(exp -1). Other VSCF/VCI energies are in good agreement with other experimentally reported ones. Both double-harmonic intensity and rigorous MULTIMODE intensity calculations show the proton transfer fundamental has a very strong intensity.

Astrochemistry↗
DOE OSTI2022

Proton decay spectroscopy of S 28 and Cl 30

States in 28 S and 30 Cl have been studied using one- and two-proton decay spectroscopy. In the first spectrometer setting, states in 28 S were populated following one-neutron knockout from a fast 29 S beam. Three new states are observed in 28 S from one- and two-proton decay. For the two-proton case the nature of the decay was investigated and found to proceed via sequential two-proton emission. For the second setting, states in 30 Cl were populated via one-proton knockout from a fast 31 Ar beam. The decay energy of the ground and first excited state were measured, with the ground-state decay energy found to be in disagreement with a previous measurement. Here, the spin and parity of these two 30 Cl states were inferred from shell-model calculations.

20 ≤ A ≤ 38↗
NASA NTRS1985

Optical properties of hydrogenated amorphous carbon films grown from methane plasma

A 30 kHz ac glow discharge formed from methane gas was used to grow carbon films on InP substrates. Both the growth rate, and the realitive Ar ion sputtering rate at 3 keV varied monotonically with deposition power. Results from the N-15 nuclear reaction profile experiments indicated a slight drop in the hydrogen concentration as more energy was dissipated in the ac discharge. Values for the index of refraction and extinction coefficient ranged from 1.721 to 1.910 and 0 to -0.188, respectively. Optical bandgaps as high as 2.34 eV were determined.

Pouch, J. J.↗
NASA NTRS1988

On the origin of Venus' atmosphere - Possible contributions from simple component mixtures and fractionated solar wind

It is suggested that while an origin of the volatiles of the Venus atmosphere as a single, fractionated component derivable from the solar wind can account for Ar, Kr, and Xe relative abundances, it does so only with an excess of C, and perhaps of N. A similarity is noted in relative abundances between Venus volatiles and fractionated solar wind gases in the lunar regolith which implies that such a lunar-type component is a major contributor to Venus' volatiles. A variety of Venus atmosphere models is considered; these fail to explain the low Ne/Ar ratio on Venus.

Bogard, Donald D.↗
NASA NTRS1990

Role of the methylene amidogen (H2CN) radical in the atmospheres of Titan and Jupiter

The methylene amidogen (H2CN) radical can be shown to be an important intermediate in models for the formation of HCN (via N + CH3) and the recombination of H to H2 (via H + HCN) on Titan as well as in models for the formation of HCN (via NH2 + C2H3) in the atmosphere of Jupiter. Experiments in our laboratory in a discharge flow system with mass spectrometric detection of both reactants and products have established that the major product channel (90 percent for the reaction N + CH3 is that leading to H2CN + H. The same result was obtained for N + CD3 yields D2CN + D. The rate constant for the reaction D + D2CN yields DCN + D2 was measured for the first time and k(298 K) greater than 7 x 10(exp -11) cu cm/s was found. The same result was obtained for the H atom reaction. This is the final step in the reaction sequence leading to HCN on both Titan and Jupiter and to formation of H2 from H on Titan. The first measurement of the ionization potentials for H2CN and D2CN was also made. From electron impact studies I.P. = (9.6 + or - 1.0) eV was obtained for both radicals. An upperlimit of I.P. less than 11.6 eV came from observations of the H2CN radical by photoionization mass spectrometry using an Ar resonance lamp (106.7 nm). Further photoionization experiments are planned using synchrotron radiation plus monochromator as a tunable vacuum UV light source.

Nesbitt, F. L.↗
NASA NTRS2010

Re-Evaluation of Ar-39 - Ar-40 Ages for Apollo Lunar Rocks 15415 and 60015

We re-analyzed 39Ar-40Ar ages of Apollo lunar highland samples 15415 and 60015, two ferroan anorthosites analyzed previously in the 1970 s, with a more detailed approach and with revised decay constants. From these samples we carefully prepared 100-200 mesh mineral separates for analysis at the Noble Gas Laboratory at NASA-Johnson Space Center. The Ar-39-Ar-40 age spectra for 15415 yielded an age of 3851 +/- 38 Ma with 33-99% of Ar39 release, roughly in agreement with previously reported Ar-Ar ages. For 60015, we obtained an age of 3584 +/- 152 Ma in 23-98% of Ar39 release, also in agreement with previously reported Ar-Ar ages of approximately 3.5 Ga. Highland anorthosites like these are believed by many to be the original crust of the moon, formed by plagioclase floatation atop a magma ocean, however the Ar-Ar ages of 15415 and 60015 are considerably younger than lunar crust formation. By contrast, recently recovered lunar anorthosites such as Dhofar 489, Dhofar 908, and Yamato 86032 yield older Ar-Ar ages, up to 4.35 Ga, much closer to time of formation of the lunar crust. It follows that the Ar-Ar ages of the Apollo samples must have been reset by secondary heating, and that this heating affected highland anorthosites at both the Apollo 15 and Apollo 16 landing sites but did not affect lunar highland meteorites. One obvious consideration is that while the Apollo samples were collected from the near side of the moon, these lunar meteorites are thought to have originated from the lunar far side

Park, J.↗
NASA NTRS1988

A rapid method for the computation of equilibrium chemical composition of air to 15000 K

A rapid computational method has been developed to determine the chemical composition of equilibrium air to 15000 K. Eleven chemically reacting species, i.e., O2, N2, O, NO, N, NO+, e-, N+, O+, Ar, and Ar+ are included. The method involves combining algebraically seven nonlinear equilibrium equations and four linear elemental mass balance and charge neutrality equations. Computational speeds for determining the equilibrium chemical composition are significantly faster than the often used free energy minimization procedure. Data are also included from which the thermodynamic properties of air can be computed. A listing of the computer program together with a set of sample results are included.

Prabhu, Ramadas K.↗
DOE OSTI2021

Bright, single helicity, high harmonics driven by mid-infrared bicircular laser fields

High-harmonic generation (HHG) is a unique tabletop light source with femtosecond-to-attosecond pulse duration and tailorable polarization and beam shape. Here, we use counter-rotating femtosecond laser pulses of 0.8 µm and 2.0 μm to extend the photon energy range of circularly polarized high-harmonics and also generate single-helicity HHG spectra. By driving HHG in helium, we produce circularly polarized soft x-ray harmonics beyond 170 eV—the highest photon energy of circularly polarized HHG achieved to date. In an Ar medium, dense spectra at photon energies well beyond the Cooper minimum are generated, with regions composed of a single helicity—consistent with the generation of a train of circularly polarized attosecond pulses. Finally, we show theoretically that circularly polarized HHG photon energies can extend beyond the carbon K edge, extending the range of molecular and materials systems that can be accessed using dynamic HHG chiral spectro-microscopies.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1980

Electrostatic bonding of thin (approximately 3 mil) 7070 cover glass to Ta2O5 AR-coated thin (approximately 2 mil) silicon wafers and solar cells

Electrostatic bonding (ESB) of thin (3 mil) Corning 7070 cover glasses to Ta2O5 AR-coated thin (2 mil) silicon wafers and solar cells is investigated. An experimental program was conducted to establish the effects of variations in pressure, voltage, temperature, time, Ta2O5 thickness, and various prebond glass treatments. Flat wafers without contact grids were used to study the basic effects for bonding to semiconductor surfaces typical of solar cells. Solar cells with three different grid patterns were used to determine additional requirements caused by the raised metallic contacts.

Egelkrout, D. W.↗
NASA NTRS1995

Coarsening strategies for unstructured multigrid techniques with application to anisotropic problems

Over the years, multigrid has been demonstrated as an efficient technique for solving inviscid flow problems. However, for viscous flows, convergence rates often degrade. This is generally due to the required use of stretched meshes (i.e., the aspect-ratio AR = delta y/delta x is much less than 1) in order to capture the boundary layer near the body. Usual techniques for generating a sequence of grids that produce proper convergence rates on isotopic meshes are not adequate for stretched meshes. This work focuses on the solution of Laplace's equation, discretized through a Galerkin finite-element formulation on unstructured stretched triangular meshes. A coarsening strategy is proposed and results are discussed.

Morano, E.↗
NASA NTRS1996

Coarsening Strategies for Unstructured Multigrid Techniques with Application to Anisotropic Problems

Over the years, multigrid has been demonstrated as an efficient technique for solving inviscid flow problems. However, for viscous flows, convergence rates often degrade. This is generally due to the required use of stretched meshes (i.e. the aspect-ratio AR = (delta)y/(delta)x much less than 1) in order to capture the boundary layer near the body. Usual techniques for generating a sequence of grids that produce proper convergence rates on isotropic meshes are not adequate for stretched meshes. This work focuses on the solution of Laplace's equation, discretized through a Galerkin finite-element formulation on unstructured stretched triangular meshes. A coarsening strategy is proposed and results are discussed.

Morano, E.↗
NASA NTRS1987

Physical parameters for 12 planetary nebulae and their central stars in the Magellanic Clouds

Nebular and central star parameters and elemental abundances of C, N, O, Ne, S, and Ar are presented for the planetary nebulae N2, N5, N43, N54, and N67 in the SMC and P2, P7, P9, P25, P33, and P40 in the LMC. The nebular chemical compositions are affected by nuclear processes in the precursor stars, which may not have been sufficiently massive to synthesize Ne, S, or Ar, which appear to be deficient with respect to their solar abundances by factors of roughly four and five for the LMC and SMC, respectively. Even after excluding nebulae formed by stars in which O apparently was destroyed by nuclear processes, O depletion in the LMC and SMC nebulae is significantly greater than in galactic planetaries. The estimated masses of the 12 remnant central stars range from 0.58 to 0.71 solar mass.

Aller, Lawrence H.↗
NASA NTRS1992

Solidification processing of intermetallic Nb-Al alloys

Several Nb-Al alloys, including single-phase NbAl3 and the eutectic of Nb2Al and NbAl3, were prepared either by nonconsumable arc melting in Ar or by zone processing in He following initial induction melting and rod casting, and the effect of the solidification route on the microstructure and room-temperature mechanical properties of these alloys was investigated. Automated control procedures and melt conditions for directional solidification of NbAl3 and the Nb2Al/Nb3Al eutectic were developed; high purity and stoichiometry were obtained. The effects of ternary additions of Ti and Ni are described.

Smith, Preston P.↗
NASA NTRS1996

Reactions of CH3(+) with C2N2, CH2CHCN, and HC3N: A Low-Pressure/High-Pressure Study

The association of CH3(+) with the three molecules C2N2, CH2CHCN, and HCCCN has been examined using ion cyclotron resonance (ICR) and selected ion flow tube (SIFT) techniques at room temperature. In each reaction, the mean lifetime of the complex (CH3 x N-=C-R(+))(sup *) formed in the association has a major influence on the outcome of the reaction and the product channels that are observed using ICR and SIFT. Termolecular rate coefficients are reported for the association of CH3(+) + C2N2 for the bath gases M = He, Ar, N2, and C2N2. k(sub 3) = 8.2 x 10(exp-24) cm(sup 6)/s (M = C2N2). In each system the association product channel occurs in competition with exothermic bimolecular channels. The complex lifetimes in all three systems are in the range 30-70 microsec. Very rapid ion-molecule association reactions have been observed in several systems of hydrocarbons and nitriles, and the implications for Titan ion chemistry are discussed briefly.

McEwan, M. J.↗
DOE OSTI2026

First Measurement of Sub-GeV $ν_μ$ Charged-Current Coherent Pion Production on Argon in MicroBooNE

We report a measurement of the charged-current coherent pion production cross section on argon using the MicroBooNE liquid argon time projection chamber exposed to the Booster Neutrino Beam at Fermilab. The measurement uses the MicroBooNE data set corresponding to $1.26 \times 10^{21}$ protons on target with a mean neutrino energy of $0.8$~GeV. The flux-averaged cross section is measured to be $(9.1 \pm 1.2_{\text{stat}} \pm 1.2_\text{syst}) \times 10^{-40}\,\text{cm}^2/\text{Ar}$. This result represents the first measurement of charged-current coherent pion production on argon at sub-GeV neutrino energies. Due to its clean two-body kinematics, where the neutrino interacts coherently with the entire nucleus producing a forward muon and pion with no nuclear breakup, this process provides a useful tool for constraining neutrino flux uncertainties in current and future oscillation experiments such as DUNE.

Abratenko, P. [Tufts U.] (ORCID:0000000169455941)↗
DOE OSTI2021

Galvanic Transformation Dynamics in Heterostructured Nanoparticles

Corrosion is a significant problem for the stability of structural metals and potentially for functional nanomaterials in operating environments. When two metals with different electrochemical potentials form a junction, galvanic corrosion occurs, resulting in the sacrificial dissolution of the metal with a higher oxidation potential (lower electrode potential). In this report it is shown that bimetallic hetero-nanostructures composed of phase-segregated metals undergo galvanic corrosion in aqueous environments. Such selective etching of the sacrificial metal in heterojunction particles leads to the formation of unusual and kinetically stabilized half-spheroid particles. By using a fluid cell and in situ scanning transmission electron microscopy, a two-stage corrosion process can be observed where the Cu experiences a fractal breakdown before the Ag corrodes due to the lack of a protective oxide layer. However, when treated with a mild Ar plasma, the stability of these structures against corrosion is enhanced due to the conversion of the amorphous native oxide to a denser, thin layer of CuO on the Cu surface. Taken together, this work highlights the importance of considering the effects of galvanic corrosion on the stability of multicomponent nanoparticles, and it shows how mass transport in a nanoscale system is influenced by redox processes.

36 MATERIALS SCIENCE↗