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At least 145 records · Page 8

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NASA NTRS2010

Metal/Silicate Partitioning at High Pressures and Temperatures

The behavior of siderophile elements during metal-silicate segregation, and their resulting distributions provide insight into core formation processes. Determination of partition coefficients allows the calculation of element distributions that can be compared to established values of element abundances in the silicate (mantle) and metallic (core) portions of the Earth. Moderately siderophile elements, including W, are particularly useful in constraining core formation conditions because they are sensitive to variations in T, P, oxygen fugacity (fO2), and silicate composition. To constrain the effect of pressure on W metal/silicate partitioning, we performed experiments at high pressures and temperatures using a multi anvil press (MAP) at NASA Johnson Space Center and laser-heated diamond anvil cells (LHDAC) at the University of Maryland. Starting materials consisted of natural peridotite mixed with Fe and W metals. Pressure conditions in the MAP experiments ranged from 10 to 16 GPa at 2400 K. Pressures in the LHDAC experiments ranged from 26 to 58 GPa, and peak temperatures ranged up to 5000 K. LHDAC experimental run products were sectioned by focused ion beam (FIB) at NASA JSC. Run products were analyzed by electron microprobe using wavelength dispersive spectroscopy. Liquid metal/liquid silicate partition coefficients for W were calculated from element abundances determined by microprobe analyses, and corrected to a common fO2 condition of IW-2 assuming +4 valence for W. Within analytical uncertainties, W partitioning shows a flat trend with increasing pressure from 10 to 16 GPa. At higher pressures, W becomes more siderophile, with an increase in partition coefficient of approximately 0.5 log units.

Shofner, G.↗

NASA NTRSDate not supplied

Probing Sensitivity of Discharge Characteristics to Model Selection using Uncertainty Quantification in an aprotic Li-Oxygen Battery

Currently, there are several models in the literature, such as kinetic models, microstructural models, and mass transport models that describe a Li-air battery's discharge behavior. Many of these models are calibrated and tested at low current densities and cannot be easily transferred to high current densities. Even at low current densities, there is no quantitative method for a researcher to choose a reaction kinetic model such as classical Butler-Volmer and its derivatives, and modified Marcus-Hush-Chidsey, a resistance model for lithium peroxide such as electron transport via tunneling or linear resistivity, a surface coverage model (lithium peroxide growth) such as partial coverage or full coverage, and mass transport model (discussed in Ref. [1]). Also, it is time-consuming to test different models at high current density (1C) due to a lack of well-tested models and well-calibrated model parameters. For this presentation, we will develop an analytical model, which acts as a surrogate model for a sophisticated finite element model to predict discharge time and discharge voltage. Next, we use an uncertainty quantifying technique called reduced-order stochastic optimization [2, 3] to determine the uncertainty in model parameters for rate kinetics, lithium peroxide resistivity, and parasitic resistance. Finally, a finite element simulation is performed to determine the error introduced by the surrogate model and its influence on the uncertainty in the model parameters.

M Mehta↗

NASA NTRS2022

Clumped-Isotope Constraint on Upper-Tropospheric Cooling During the Last Glacial Maximum

Ice cores and other paleotemperature proxies, together with general circulation models, have provided information on past surface temperatures and the atmosphere's composition in different climates. Little is known, however, about past temperatures at high altitudes, which play a crucial role in Earth's radiative energy budget. Paleoclimate records at high-altitude sites are sparse, and the few that are available show poor agreement with climate model predictions. These disagreements could be due to insufficient spatial coverage, spatiotemporal biases, or model physics; new records that can mitigate or avoid these uncertainties are needed. Here, we constrain the change in upper-tropospheric temperature at the global scale during the Last Glacial Maximum (LGM) using the clumped-isotope composition of molecular oxygen trapped in polar ice cores. Aided by global three-dimensional chemical transport modeling, we exploit the intrinsic temperature sensitivity of the clumped-isotope composition of atmospheric oxygen to infer that the upper troposphere (effective mean altitude 10–11 km) was 6–9°C cooler during the LGM than during the late preindustrial Holocene. A complementary energy balance approach supports a minor or negligible steepening of atmospheric lapse rates during the LGM, which is consistent with a range of climate model simulations. Proxy-model disagreements with other high-altitude records may stem from inaccuracies in regional hydroclimate simulation, possibly related to land-atmosphere feedbacks.

clumped isotope↗

NASA NTRS1994

Preparation and Dielectric Measurements of the Rare Earth Green Phases R2BaCuO(5-x) (R = Y, Sm, Gd, Dy, Ho, Er, Yb)

It has been demonstrated that R2BaCuO(5-x) (R = Y, Sm, Gd, Dy, Ho, Er, Yb) does not undergo significant densification unless the sintering temperatures are near the incongruent melting point or the sintering times are long. Good quality powders of Y2BaCuO(5-x) have been synthesized by using oxide raw materials or precursors such as acetates and nitrates. The acetates- and the nitrates-derived yttrium green phase resulted in finer particle sizes, acceptable dielectric properties and lower melting temperatures than those processed via oxide raw materials. The hot pressing technique has been employed to produce a dense R2BaCuO(5-x) (R=Y,Gd) substrate with satisfactory dielectric properties. Reactivity to reducing conditions, i.e. graphite die, limited the optimization of the properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO,.,,. Oxygen treatment at 950 OC has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO(5-x). Oxygen treatment at 950 C has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. The dielectric constants of the rare earth green phases R2BaCuO(5-x) were found to be low. Relaxation peaks were detected at low temperatures (T less than 150 K) and at high temperatures (150 less than T greater than 420 K). The dielectric losses and conductivities at 77 K were measured to be in the range of 10(exp -4) and 10(exp -12) (Omega-cm)(exp -1), respectively. Many parameters were found to exhibit dependencies on the rare earth cation sizes.

Gonzalez-Titman, Carlos↗

NASA NTRS1967

Study of thermal effects on nickel-cadmium batteries

Isothermal continuous flow calorimeter is designed to test a nickel-cadmium battery under numerous orbital conditions. This sensitive calorimeter collects cell data such as oxygen pressure and rate of heat generation, and calculates changes in enthalpy.

Foley, R. T.↗

NASA NTRS1978

Theory for charge states of energetic oxygen ions in the earth's radiation belts

Fluxes of geomagnetically trapped energetic oxygen ions have been studied in detail. Ion distributions in radial locations below the geostationary orbit, energy spectra between 1 keV and 100 MeV, and the distribution over charge states have been computed for equatorially mirroring ions. Both ionospheric and solar wind oxygen ion sources have been considered, and it is found that the charge state distributions in the interior of the radiation belts are largely independent of the charge state characteristics of the sources. In the MeV range, oxygen ions prove to be a more sensitive probe for radiation belt dynamics than helium ions and protons.

Spjeldvik, W. N.↗

NASA NTRS1991

The vibrational spectrum of H2O3: An ab initio investigation

Theoretically determined frequencies and absorption intensities are reported for the vibrational spectrum of the covalent HOOOH and hydrogen bonded HO---HOO intermediates that may form in the reaction of the hydroxyl and hydroperoxyl radicals. Basis sets of DZP quality, augmented by diffuse and second sets of polarization functions have been used with CASSCF wave functions. The calculated harmonic vibrational frequencies of HOOOH have been corrected with empirical factors and presented in the form of a 'stick' spectrum. The oxygen backbone vibrations, predicted to occur at 519, 760, and 870 cm(exp -1), are well separated from most interferences, and may be the most useful for the species' identification. In the case of the hydrogen bonded isomer, emphasis has been placed upon prediction of the shifts in the intramolecular vibrational frequencies that take place upon formation of the complex. In particular, the HO stretch and HOO bend of HO2 are predicted to have shifts of -59 and 53 cm(exp -1), respectively, which should facilitate their identification. It is also noted that the antisymmetric stretching frequency of the oxygen backbone in HOOOH exhibits a strong sensitivity to the degree of electron correlation, such as has been previously observed for the same mode in ozone.

Jackels, Charles F.↗

NASA NTRS1992

The orbital record in stratigraphy

Orbital signals are being discovered in pre-Pleistocene sediments. Due to their hierarchical nature these cycle patterns are complex, and the imprecision of geochronology generally makes the assignment of stratigraphic cycles to specific orbital cycles uncertain, but in sequences such as the limnic Newark Group under study by Olsen and pelagic Cretaceous sequence worked on by our Italo-American group the relative frequencies yield a definitive match to the Milankovitch hierarchy. Due to the multiple ways in which climate impinges on depositional systems, the orbital signals are recorded in a multiplicity of parameters, and affect different sedimentary facies in different ways. In platform carbonates, for example, the chief effect is via sea-level variations (possibly tied to fluctuating ice volume), resulting in cycles of emergence and submergence. In limnic systems it finds its most dramatic expression in alternations of lake and playa conditions. Biogenic pelagic oozes such as chalks and the limestones derived from them display variations in the carbonate supplied by planktonic organisms such as coccolithophores and foraminifera, and also record variations in the aeration of bottom waters. Whereas early studies of stratigraphic cyclicity relied mainly on bedding variations visible in the field, present studies are supplementing these with instrumental scans of geochemical, paleontological, and geophysical parameters which yield quantitative curves amenable to time-series analysis; such analysis is, however, limited by problems of distorted time-scales. My own work has been largely concentrated on pelagic systems. In these, the sensitivity of pelagic organisms to climatic-oceanic changes, combined with the sensitivity of botton life to changes in oxygen availability (commonly much more restricted in the Past than now) has left cyclic patterns related to orbital forcing. These systems are further attractive because (1) they tend to offer depositional continuity, and (2) presence of abundant microfossils yields close ties to geochronology. A tantalizing possibility that stratigraphy may yield a record of orbital signals unrelated to climate has turned up in magnetic studies of our Cretaceous core. Magnetic secular variations here carry a strong 39 ka periodicity, corresponding to the theoretical obliquity period of that time - Does the obliquity cycle perhaps have some direct influence on the magnetic field?

Fischer, Alfred G.↗

NASA NTRS1993

Temperature sensitivity of an atmospheric Raman lidar system based on a XeF excimer laser

The temperature sensitivity of Raman backscattering from atmospheric nitrogen, oxygen, and water vapor is considered over the range of temperatures expected in the troposphere. These results are applied to the Raman spectrum induced by a XeF excimer laser, which produces three line groups centered at approximately 349, 351, and 353 nm. Bandpass filter characteristics are determined for this case.

Whiteman, David N.↗

NASA NTRS1994

Implementation of and measurement with the LIPA technique in a subsonic jet

LIPA (Laser Induced Photochemical Anemometry) was used to measure velocity, vorticity, Reynolds stress, and turbulent intensity distributions in a subsonic jet. The jet region of interest was the area close to the jet-orifice. The LIPA-technique is a nonintrusive quantitative flow visualization technique, consisting of tracking a phosphorescing grid of fluid particles, which is impressed by laser-beams directed into the flow. The phosphorescence of biacetyl gas was used to enable tracking of the impressed light grid. In order to perform measurements in a jet, LIPA was developed and implemented for the specific flow requirements. Nitrogen was used as the carrier gas to avoid quenching of the phosphorescent radiation of the tracer gas biacetyl by ambient oxygen. The use of sulfur dioxide to sensitize phosphorescent emission of biacetyl was examined. Preliminary data was used in a discussion of the potential of the LIPA technique.

Falco, R. E.↗

NASA NTRS1995

Analysis of Aerothermal Heating Over Reusable Single-Stage to Orbit Vehicles

Using the General Aerodynamic Simulation Program (GASP) with finite-rate surface catalysis and radiative equilibrium surface temperature conditions, a computational study has been conducted to predict three-dimensional aero-convective heating over the proposed reusable single-stage to orbit vehicles. The solutions for three basic classes of usable single-stage-to-orbit vehicles, including wing body, lifting body and vertical lander, are presented and compared to provide information for vehicle design. The free stream conditions used in this study occur at an altitude of 57.5 km, ambient density of 4.129e-4 kg/cubic m, and velocity of 4,849 m/s. The convective heating over the vehicle surface in both laminar and turbulent flow regimes were computed. The Baldwin-Lomax algebraic model with a modified van Driest damping factor was applied in the turbulent flow calculations. A bifurcation model which guarantees the conservation of mass diffusive fluxes was adopted to account for the multi-species mass diffusion. The effects of turbulence and surface catalysis on the surface heating are discussed in detail The solutions indicate the degree of oxygen dissociation over the leeward side is sensitive to the shape of vehicle body. Predicted convective heating over the entire surface of lifting body is strongly affected by the presence of surface catalysis. For wing body and vertical lander, the surface catalysis effect does not appear to be important in the far downstream region, and turbulence is the dominant effect on the heating prediction in this region.

Chen, Y. K.↗

NASA NTRS2001

Endothelial NOS-dependent activation of c-Jun NH(2)- terminal kinase by oxidized low-density lipoprotein

Oxidized low-density lipoprotein (oxLDL) is known to activate a number of signal transduction pathways in endothelial cells. Among these are the c-Jun NH(2)-terminal kinase (JNK), also known as stress-activated protein kinase, and extracellular signal-regulated kinase (ERK). These mitogen-activated protein kinases (MAP kinase) determine cell survival in response to environmental stress. Interestingly, JNK signaling involves redox-sensitive mechanisms and is activated by reactive oxygen and nitrogen species derived from both NADPH oxidases, nitric oxide synthases (NOS), peroxides, and oxidized low-density lipoprotein (oxLDL). The role of endothelial NOS (eNOS) in the activation of JNK in response to oxLDL has not been examined. Herein, we show that on exposure of endothelial cells to oxLDL, both ERK and JNK are activated through independent signal transduction pathways. A key role of eNOS activation through a phosphatidylinositol-3-kinase-dependent mechanism leading to phosphorylation of eNOS is demonstrated for oxLDL-dependent activation of JNK. Moreover, we show that activation of ERK by oxLDL is critical in protection against the cytotoxicity of oxLDL.

Non-NASA Center↗

NASA NTRSDate not supplied

Liquefaction of Cryogenic Fluids for Production and Storage of Commodities on Extra-Terrestrial Surfaces

The Cryogenic Fluid In-situ Liquefaction for Landers (CryoFILL) activity has been investigating concepts for the liquefaction of cryogenic fluids produced on the surface of the Moon and Mars. CryoFILL consists of four activities: liquid nitrogen liquefaction testing that was completed in 2019, liquid oxygen liquefaction testing planned to begin in early 2022, fiber-optic sensor temperature measurement system development, and lightweight vacuum jacketed systems designed for the atmosphere of Mars. Additional activities include the development and validation of numerical modeling systems at three stages: thermodynamic models of the liquefaction process for basic energy/mass estimates, nodal models to predict liquefaction tank system level performance, and computational fluid dynamics to assess fluid phenomena occurring within the tank, specifically condensation and stratification within the ullage. These developments form a combined liquefaction and storage solution to support Lunar and Martian exploration. Key testing results from liquid nitrogen testing as well as plans for liquid oxygen testing will be discussed including key sensitivities from analytical evaluation of completed test results. Progress on the development and improvements on fiber optic sensor testing and developments will also be provided. Finally, work on the progress of the lightweight vacuum jacketed systems being co-developed by NASA and industry will be summarized.

Liquefaction↗

NASA NTRSDate not supplied

Energy and Momentum in Mechanical Impact Testing

The ASTM G86 method is used to determine the ignition sensitivity of materials to mechanical impact in oxygen. It has long been known that different systems built to the standard produce different results. Given the current push towards direct comparison of numerical results from different systems rather than just material rankings, it is desirable to normalize the systems to some performance-based metric. Normalization is complicated by the fact that the energy and momentum of a particular impact scale differently with plummet mass and drop height, and therefore adjusting the mass and height to account for system differences would result in a different impact. The standard uses dent blocks to assess impacts. However, it was unknown if the differences in momentum could be identified during dent block impacts. To determine this, dent blocks were impacted with constant energy and different momentums, using instrumented and non-instrumented plummets. The dent blocks showed statistically significant differences in the penetration function when subjected to impacts with the same energy but different momentum. Further, the instrumented plummet showed drastic differences in the power delivery with different momentums. System configuration was also shown to have an effect on the response of the penetration function to different momentums.

Energy↗

NASA NTRS2024

Energy and Momentum in Mechanical Impact Testing

Energy↗

NASA NTRS1971

A Quantitative Evaluation of Dissolved Oxygen Instrumentation

The implications of the presence of dissolved oxygen in water are discussed in terms of its deleterious or beneficial effects, depending on the functional consequences to those affected, e.g., the industrialist, the oceanographer, and the ecologist. The paper is devoted primarily to an examination of the performance of five commercially available dissolved oxygen meters. The design of each is briefly reviewed and ease or difficulty of use in the field described. Specifically, the evaluation program treated a number of parameters and user considerations including an initial check and trial calibration for each instrument and a discussion of the measurement methodology employed. Detailed test results are given relating to the effects of primary power variation, water-flow sensitivity, response time, relative accuracy of dissolved-oxygen readout, temperature accuracy (for those instruments which included this feature), error and repeatability, stability, pressure and other environmental effects, and test results obtained in the field. Overall instrument performance is summarized comparatively by chart.

Pijanowski, Barbara S.↗

NASA NTRS2000

Testing and Selection of Fire-Resistant Materials for Spacecraft Use

Spacecraft fire-safety strategy emphasizes prevention, mostly through the selection of onboard items classified accord- ing to their fire resistance. The principal NASA acceptance tests described in this paper assess the flammability of materials and components under "worst-case" normal-gravity conditions of upward flame spread in controlled-oxygen atmospheres. Tests conducted on the ground, however, cannot duplicate the unique fire characteristics in the nonbuoyant low-gravity environment of orbiting spacecraft. Research shows that flammability an fire-spread rates in low gravity are sensitive to forced convection (ventilation flows) and atmospheric-oxygen concentration. These research results are helping to define new material-screening test methods that will better evaluate material performance in spacecraft.

Friedman, Robert↗

NASA NTRS1986

Ragland - An LL3.4 chondrite find from New Mexico

The Ragland, New Mexico, chondrite was found in 1978. It consists of a single stone of 12.16 kg that broke into three pieces. The stone is moderately weathered and has a pronounced chondritic texture. Bulk composition favors an LL classification, and modal analysis and oxygen isotopic composition are consistent with this. The thermoluminescence sensitivity of 0.056 + or - 0.020 normalized to Dhajala, compositional variability of olivine (mean Fa 18.3, sigma = 10.1) and low-Ca pyroxene (mean Fs 14.6, sigma = 6.7), and Ca concentrations in olivine indicate metamorphic subtype 3.4 + or - 0.1. The isotopically heavy oxygen composition, which is characteristic of subtypes 3.0-3.1, may be a primary characteristic and not a result of weathering. Low concentrations of radiogenic Ar-40 and planetary Ar-36 suggest noble gas loss.

Recca, S. I.↗