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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Oxidation of C/SiC Composites at Reduced Oxygen Partial Pressures

T-300 carbon fibers and T-300 carbon fiber reinforced silicon carbide composites (C/SiC) were oxidized in flowing reduced oxygen partial pressure environments at a total pressure of one atmosphere (0.5 atm O2, 0.05 atm O2 and 0.005 atm O2, balance argon). Experiments were conducted at four temperatures (816deg, 1149deg, 1343deg, and 1538 C). The oxidation kinetics were monitored using thermogravimetric analysis. T-300 fibers were oxidized to completion for times between 0.6 and 90 h. Results indicated that fiber oxidation kinetics were gas phase diffusion controlled. Oxidation rates had an oxygen partial pressure dependence with a power law exponent close to one. In addition, oxidation rates were only weakly dependent on temperature. The C/SiC coupon oxidation kinetics showed some variability, attributed to differences in the number and width of cracks in the SiC seal coat. In general, weight losses were observed indicating oxidation of the carbon fibers dominated the oxidation behavior. Low temperatures and high oxygen pressures resulted in the most rapid consumption of the carbon fibers. At higher temperatures, the lower oxidation rates were primarily attributed to crack closure due to SiC thermal expansion, rather than oxidation of SiC since these reduced rates were observed even at the lowest oxygen partial pressures where SiC oxidation is minimal.

Opila, E. J.↗
DOE OSTI2020

Mapping the Temperature-dependent and network site-specific onset of spectral diffusion at the surface of a water cluster cage

We explore the kinetic processes that sustain equilibrium in a microscopic, finite system. This is accomplished by monitoring the spontaneous, time-dependent frequency evolution (the frequency autocorrelation) of a single OH oscillator, embedded in a water cluster held in a temperature-controlled ion trap. The measurements are carried out by applying two-color, IR-IR photodissociation mass spectrometry to the D3O+?(HDO)(D2O)19 isotopologue of the “magic number” protonated water cluster, H+?(H2O)21. The OH group can occupy any one of the five spectroscopically distinct sites in the distorted pentagonal dodecahedron cage structure. The OH frequency is observed to evolve over tens of milliseconds in the temperature range (90-120 K). Starting at 100 K, large “jumps” are observed between two OH frequencies separated by ~300 cm-1 indicating migration of the OH group from the bound OH site at 3350 cm-1 to the free position at 3686 cm-1. Increasing the temperature to 110 K leads to partial interconversion among many sites. All sites are observed to interconvert at 120 K such that the distribution of the unique OH group among them adopts the form one would expect for a canonical ensemble. The spectral dynamics displayed by the clusters thus offer an unprecedented view into the molecular-level processes that drive spectral diffusion in an extended network of water molecules.

Yang, Nan↗
DOE OSTI2014

Tri-peptide reference structures for the calculation of relative solvent accessible surface area in protein amino acid residues

Relative amino acid residue solvent accessibility values allow the quantitative comparison of atomic solvent-accessible surface areas in different residue types and physical environments in proteins and in protein structural alignments. Geometry-optimised tri-peptide structures in extended solvent-exposed reference conformations have been obtained for 43 amino acid residue types at a high level of quantum chemical theory. Significant increases in side-chain solvent accessibility, offset by reductions in main-chain atom solvent exposure, were observed for standard residue types in partially geometry-optimised structures when compared to non-minimised models built from identical sets of proper dihedral angles abstracted from the literature. Optimisation of proper dihedral angles led most notably to marked increases of up to 54% in proline main-chain atom solvent accessibility compared to literature values. Similar effects were observed for fully-optimised tri-peptides in implicit solvent. The relief of internal strain energy was associated with systematic variation in N, C α and C β atom solvent accessibility across all standard residue types. The results underline the importance of optimisation of ‘hard’ degrees of freedom (bond lengths and valence bond angles) and improper dihedral angle values from force field or other context-independent reference values, and impact on the use of standardised fixed internal co-ordinate geometry in sampling approaches to the determination of absolute values of protein amino acid residue solvent accessibility. Finally, quantum chemical methods provide a useful and accurate alternative to molecular mechanics methods to perform energy minimisation of peptides containing non-standard (chemically modified) amino acid residues frequently present in experimental protein structure data sets, for which force field parameters may not be available. Reference tri-peptide atomic co-ordinate sets including hydrogen atoms are made freely available.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1992

Chemical differentiation on one-plate planets: Predictions and geologic observations for Venus

Recent studies have examined the partial melting of planetary interiors on one-plate planets and the implications for the formation and evolution of basaltic crust and the complementary residual mantle layer. In contrast to the Earth, where the crust and residual layer move laterally and are returned to the interior following subduction, one-plate planets such as Venus are characterized by vertical accretion of the crust and residual layer. The residual mantle layer is depleted and compositionally buoyant, being less dense than undepleted mantle due to its reduced Fe/Mg and dense Al-bearing minerals; its melting temperature is also increased. As the crust and depleted mantle layer grow vertically during the thermal evolution of the planet, several stages develop. As a step in the investigation and testing of these theoretical treatments of crustal development on Venus, we investigate the predictions deriving from two of these stages (a stable thick crust and depleted layer, and a thick unstable depleted layer) and compare these to geologic and geophysical observations, speculating on how these might be interpreted in the context of the vertical crustal accretion models. In each case, we conclude with an outline of further tests and observations of these models.

Head, James W., III↗
DOE OSTI2016

Analysis of the SPS Long Term Orbit Drifts

The Super Proton Synchrotron (SPS) is the last accelerator in the Large Hadron Collider (LHC) injector chain, and has to deliver the two high-intensity 450 GeV proton beams to the LHC. The transport from SPS to LHC is done through the two Transfer Lines (TL), TI2 and TI8, for Beam 1 (B1) and Beam 2 (B2) respectively. During the first LHC operation period Run 1, a long term drift of the SPS orbit was observed, causing changes in the LHC injection due to the resulting changes in the TL trajectories. This translated into longer LHC turnaround because of the necessity to periodically correct the TL trajectories in order to preserve the beam quality at injection into the LHC. Different sources for the SPS orbit drifts have been investigated: each of them can account only partially for the total orbit drift observed. In this paper, the possible sources of such drift are described, together with the simulated and measured effect they cause. Possible solutions and countermeasures are also discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

R Coronae Borealis Star Evolution: Simulating 3D Merger Events to 1D Stellar Evolution Including Large-scale Nucleosynthesis

R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich variable supergiants thought to be the result of dynamically unstable white dwarf mergers. In this article, we attempt to model RCB stars through all the relevant timescales by simulating a merger event in Octo-tiger, a 3D adaptive mesh refinement (AMR) hydrodynamics code, and mapping the post-merger object into MESA, a 1D stellar evolution code. We then post-process the nucleosynthesis on a much larger nuclear reaction network to study the enhancement of s-process elements. We present models that match observations or previous studies in most surface abundances, isotopic ratios, early evolution, and lifetimes. We also observe similar mixing behavior to previous modeling attempts that result in the partial He-burning products visible on the surface in observations. However, we do note that our subsolar models lack any enhancement in s-process elements, which we attribute to a lack of hydrogen in the envelope. We also find that the 16 O/ 18 O isotopic ratio is very sensitive to initial hydrogen abundance and increases outside of the acceptable range with a hydrogen mass fraction greater than 10 -4 .

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Temperature minima in the average thermal structure of the middle mesosphere (70 - 80 km) from analysis of 40- to 92-km SME global temperature profiles

Global temperatures have been derived for the upper stratosphere and mesosphere from analysis of Solar Mesosphere Explorer (SME) limb radiance profiles. The SME temperature represent fixed local time observations at 1400 - 1500 LT, with partial zonal coverage of 3 - 5 longitudes per day over the 1982-1986 period. These new SME temperatures are compared to the COSPAR International Ionosphere Reference Atmosphere 86 (CIRA 86) climatology (Fleming et al., 1990) as well as stratospheric and mesospheric sounder (SAMS); Barnett and Corney, 1984), National Meteorological Center (NMC); (Gelman et al., 1986), and individual lidar and rocket observations. Significant areas of disagreement between the SME and CIRA 86 mesospheric temperatures are 10 K warmer SME temperatures at altitudes above 80 km. The 1981-1982 SAMS temperatures are in much closer agreement with the SME temperatures between 40 and 75 km. Although much of the SME-CIRA 86 disagreement probably stems from the poor vertical resolution of the observations comprising the CIRA 86 modelm, some portion of the differences may reflect 5- to 10-year temporal variations in mesospheric temperatures. The CIRA 86 climatology is based on 1973-1978 measurements. Relatively large (1 K/yr) 5- to 10-year trends in temperatures as functions of longitude, latitude, and altitude have been observed for both the upper stratosphere (Clancy and Rusch, 1989a) and mesosphere (Clancy and Rusch, 1989b; Hauchecorne et al., 1991). The SME temperatures also exhibit enhanced amplitudes for the semiannual oscillation (SAO) of upper mesospheric temperatures at low latitudes, which are not evident in the CIRA 86 climatology. The so-called mesospheric `temperature inversions' at wintertime midlatitudes, which have been observed by ground-based lidar (Hauschecorne et al., 1987) and rocket in situ measurements (Schmidlin, 1976), are shown to be a climatological aspect of the mesosphere, based on the SME observations.

Clancy, R. Todd↗
NASA NTRS2005

Coordinated Polar Spacecraft, Geosynchronous Spacecraft, and Ground-based Observations of Magnetopause Oscillations and Pc5 Waves in the Magnetosphere

In this paper, we present in situ observations of surface waves at the magnetopause and oscillatory magnetospheric field lines, and coordinated observations Pc5 waves at geosynchronous orbit by the GOES spacecraft, and on the ground by CANOPUS and 210 Degree Magnetic Meridian (210MMJ magnetometer arrays. On February 7,2002 during a highspeed solar wind stream, the Polar spacecraft was skimming the magnetopause in a post-noon meridian plane for approximately 3 hours. During this interval, it made two short excursions and a few partial crossings into the magnetosheath and observed quasi-periodic cold ion bursts in the region adjacent to the magnetopause current layer. The multiple magnetopause crossings as well as the velocity of the cold ion bursts indicate that the magnetopause was oscillating with about 6 minute period. Simultaneous observations of Pc5 waves at geosynchronous orbit by the GOES spacecraft and on the ground by the CANOPUS magnetometer array reveal that these magnetospheric pulsations were forced oscillations of magnetic field lines directly driven by the magnetopause oscillations. The magnetospheric pulsations occurred only in a limited longitudinal region in the post-noon dayside sector, and were not a global phenomenon as one would expect for global field line resonance. Thus, the magnetopause oscillations at the source were also limited to a localized region spanning about 4 hours in local time.

Le, G.↗
NASA NTRS2011

Improved Surface and Tropospheric Temperatures Determined Using Only Shortwave Channels: The AIRS Science Team Version-6 Retrieval Algorithm

The Goddard DISC has generated products derived from AIRS/AMSU-A observations, starting from September 2002 when the AIRS instrument became stable, using the AIRS Science Team Version-5 retrieval algorithm. The AIRS Science Team Version-6 retrieval algorithm will be finalized in September 2011. This paper describes some of the significant improvements contained in the Version-6 retrieval algorithm, compared to that used in Version-5, with an emphasis on the improvement of atmospheric temperature profiles, ocean and land surface skin temperatures, and ocean and land surface spectral emissivities. AIRS contains 2378 spectral channels covering portions of the spectral region 650 cm(sup -1) (15.38 micrometers) - 2665 cm(sup -1) (3.752 micrometers). These spectral regions contain significant absorption features from two CO2 absorption bands, the 15 micrometers (longwave) CO2 band, and the 4.3 micrometers (shortwave) CO2 absorption band. There are also two atmospheric window regions, the 12 micrometer - 8 micrometer (longwave) window, and the 4.17 micrometer - 3.75 micrometer (shortwave) window. Historically, determination of surface and atmospheric temperatures from satellite observations was performed using primarily observations in the longwave window and CO2 absorption regions. According to cloud clearing theory, more accurate soundings of both surface skin and atmospheric temperatures can be obtained under partial cloud cover conditions if one uses observations in longwave channels to determine coefficients which generate cloud cleared radiances R(sup ^)(sub i) for all channels, and uses R(sup ^)(sub i) only from shortwave channels in the determination of surface and atmospheric temperatures. This procedure is now being used in the AIRS Version-6 Retrieval Algorithm. Results are presented for both daytime and nighttime conditions showing improved Version-6 surface and atmospheric soundings under partial cloud cover.

Susskind, Joel↗
DOE OSTI2022

Stream and ocean hydrodynamics mediate partial migration strategies in an amphidromous Hawaiian goby

Abstract Partial migration strategies, in which some individuals migrate but others do not, are widely observed in populations of migratory animals. Such patterns could arise via variation in migratory behaviors made by individual animals, via genetic variation in migratory predisposition, or simply by variation in migration opportunities mediated by environmental conditions. Here we use spatiotemporal variation in partial migration across populations of an amphidromous Hawaiian goby to test whether stream or ocean conditions favor completing its life cycle entirely within freshwater streams rather than undergoing an oceanic larval migration. Across 35 watersheds, microchemical analysis of otoliths revealed that most adult Awaous stamineus were freshwater residents (62% of n = 316 in 2009, 83% of n = 274 in 2011), but we found considerable variation among watersheds. We then tested the hypothesis that the prevalence of freshwater residency increases with the stability of stream flows and decreases with the availability of dispersal pathways arising from ocean hydrodynamics. We found that streams with low variation of daily discharge were home to a higher incidence of freshwater residents in each survey year. The magnitude of the shift in freshwater residency between survey years was positively associated with predicted interannual variability in the success of larval settlement in streams on each island based on passive drift in ocean currents. We built on these findings by developing a theoretical model of goby life history to further evaluate whether mediation of migration outcomes by stream and ocean hydrodynamics could be sufficient to explain the range of partial migration frequency observed across populations. The model illustrates that the proportion of larvae entering the ocean and differential survival of freshwater‐resident versus ocean‐going larvae are plausible mechanisms for range‐wide shifts in migration strategies. Thus, we propose that hydrologic variation in both ocean and stream environments contributes to spatiotemporal variation in the prevalence of migration phenotypes in A. stamineus . Our empirical and theoretical results suggest that the capacity for partial migration could enhance the persistence of metapopulations of diadromous fish when confronted with variable ocean and stream conditions.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2003

Experimental Hypersonic Aerodynamic Characteristics of the Space Shuttle Orbiter for a Range of Damage Scenarios

Aerodynamic tests in support of the Columbia accident investigation were conducted in two hypersonic wind tunnels at the NASA Langley Research Center, the 20-Inch Mach 6 Air Tunnel and the 20-Inch Mach 6 CF4 Tunnel. The primary purpose of these tests was to measure the forces and moments generated by a variety of outer mold line alterations (damage scenarios) using 0.0075-scale models of the Space Shuttle Orbiter (approximately 10 inches in length). Simultaneously acquired global heat transfer mappings were obtained for a majority of the configurations tested. Test parameters include angles of attack from 38 to 42 deg, unit Reynolds numbers from 0.26 to 3.0 x10^6 per foot, and normal shock density ratios of 5 (Mach 6 air) and 12 (Mach 6 CF4). The damage scenarios evaluated included asymmetric boundary layer transition, gouges in the windward surface acreage thermal protection system tiles, wing leading edge damage (partially and fully missing reinforced carbon-carbon (RCC) panels), holes through the wing from the windward surface to the leeside, deformation of the wing windward surface, and main landing gear door and/or gear deployment. The aerodynamic data were compared to the magnitudes and directions observed in flight, and the heating images were evaluated in terms of the location of the generated disturbances and how these disturbance might relate to the response of discrete gages on the Columbia Orbiter vehicle during entry. The measured aerodynamic increments were generally small in magnitude, as were the flight-derived values during most of the entry. Asymmetric boundary layer transition (ABLT) results were consistent with the flight-derived Shuttle ABLT model, but not with the observed flight trends for STS-107. The partially missing leading edge panel results best matched both the early aerodynamic and heating trends observed in flight. A progressive damage scenario is presented that qualitatively matches the flight observations for the full entry.

Brauckman, Gregory J.↗
DOE OSTI2019

Influence of Chemical Structure of Petrochemical Polyol on Properties of Bio-polyurethane Foams

In this study, the influence of the chemical structures of petrochemical polyols on the foaming process of polyurethane compositions as well as on selected properties of the foams obtained has been investigated. Two types of petrochemical polyols were used—polyester and polyether polyols as well as their blends with a rapeseed oil-based polyol. Dielectric polarization, temperature and expansion velocity were determined during the foaming process of the polyurethane systems with different polyol components. The results show the highest reactivity of the polyester polyol and a decrease of the polyurethane system’s reactivity as a result of a partial replacement of the petrochemical polyol with the bio-based polyol. The content of the closed cells in the materials obtained strongly depends on the petrochemical polyol used. The results indicate that the chemical structure of the petrochemical polyol had a significant effect on the cellular structure as well as the physical–mechanical properties of the final products. A significant worsening of the foams’ mechanical properties was observed as an effect of a partial replacement of the polyester polyol with the rapeseed oil-based polyol. In contrast, a partial replacement of the polyether polyol caused an improvement of the cell structure keeping the mechanical properties of the modified foams at the same level.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Extended defects in GaAs/GaAs 1-x Sb x /GaAs (001) heterostructures

The atomic-scale structure of extended defects in GaAs/GaAs 1-x Sb x /GaAs (001) heterostructures has been characterized using aberration-corrected scanning transmission electron microscopy. The defect located at the tensile-strained GaAs(cap)/GaAs 0.34 Sb 0.66 interface had no edge component in the projection plane and is identified as either a dissociated screw dislocation or a partial dislocation dipole. The associated intrinsic stacking fault is bounded by two 30° Shockley partial dislocations of opposite sign. Another defect, located at the compressively-strained GaAs 0.91 Sb 0.09 /GaAs(substrate) interface, is identified as a dissociated 90° dislocation. The associated intrinsic stacking fault is bounded by a 30° Shockley partial dislocation and a partial dislocation with a Burgers vector of either or , where a is the lattice constant. Unpaired atomic columns observed at the cores of the 30° Shockley partial dislocations indicate that both defects belong primarily to the glide set.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Comparison of the Distribution of the In Situ Ring Current Density Based on Magnetic Field Observations From THEMIS, MMS and Cluster

Abstract We review and extend previous work on the ring current density distribution by applying the curlometer technique to multi‐spacecraft magnetic field data on different spatial scales, directly comparing the results of three space missions: Time History of Events and Macroscale Interactions during Substorms (THEMIS), The Magnetospheric Multiscale (MMS) and Cluster, that have so far accrued decades of data on a range of spatial separation scales. We suggest that the statistical results of Cluster data over two decades can illustrate well the overall form of the ring current (in the ring plane), but can underestimate the current density, while THEMIS (partially) and MMS are able to observe the detailed structure of the ring current and indeed show different behavior on some (smaller) spatial scales. These results suggest that, in addition to the local time and radial form, reported previously, the morphology of the ring current may also depend on magnetic latitude, as influenced by the tilt angle between the inner and outer magnetic fields.

Tan, X. [School of Space and Earth Sciences Beihan↗
NASA NTRS1994

Chronology of chrondrule and CAI formation: Mg-Al isotopic evidence

Details of the chondrule and Ca-Al-rich inclusion (CAI) formation during the earliest history of the solar system are imperfectly known. Because CAI's are more 'refractory' than ferromagnesian chondrules and have the lowest recorded initial Sr-87/Sr-86 ratios of any solar system materials, the expectation is that CAI's formed earlier than chondrules. But it is not known, for example, if CAI formation had stopped by the time chondrule formation began. Conventional (absolute) age-dating techniques cannot adequately resolve small age differences (less than 10(exp 6) years) between objects of such antiquity. One approach has been to look at systematic differences in the daughter products of short-lived radionuclides such as Al-26 and I-129. Unfortunately, neither system appears to be 'well-behaved.' One possible reason for this circumstance is that later secondary events have partially reset the isotopic systems, but a viable alternative continues to be large-scale (nebular) heterogeneity in initial isotopic abundances, which would of course render the systems nearly useless as chronometers. In the past two years the nature of this problem has been redefined somewhat. Examination of the Al-Mg isotopic database for all CAI's suggests that the vast majority of inclusions originally had the same initial Al-26/Al-27 abundance ratio, and that the ill-behaved isotopic systematics now observed are the results of later partial reequilibration due to thermal processing. Isotopic heterogeneities did exist in the nebula, as demonstrated by the existence of so-called FUN inclusions in CV3 chondrites and isotopically anomalous hibonite grains in CM2 chondrites, which had little or no live Al-26 at the time of their formation. But, among the population of CV3 inclusions at least, FUN inclusions appear to have been a relatively minor nebular component.

Macpherson, G. J.↗
NASA NTRS2008

Current Leakage Evolution in Partially Gate Raptured Power MOSFETs

It has been observed that power MOSFETs can experience an SEGR and continue to function with altered parameters. We propose that there are three different types of SEGR modes; the micro-break, the thermal runaway, and the avalanche breakdown. Data that demonstrates these stages of device failure are presented as well as a proposed model for the micro-break. Brief discussions of the other modes, based on analysis combined with our interpretations of the older literature, are also given.

metal oxide semiconductor field-effect transistors↗
NASA NTRS1992

Very Large Array-RATAN 600 observations of a solar active region

VLA-RATAN-600 observations of the sun around the partial solar eclipse in July 1990 are discussed. The relatively flat spectrum of the extended emission is attributed to the optically thin thermal bremsstrahlung of electrons trapped in a magnetic loop at coronal temperatures. Step-spectrum sunspot-associated emission is attributed to thermal gyroresonance radiation at different heights along the leg of a loop joining regions of positive magnetic polarity. Comparisons with predicted distributions of gyroresonance radio indicate that compact sunspot-associated sources lie at heights of 2500-17,500 km above the photosphere. Differences in the observed and predicted microwave emission suggest an inhomogeneous distribution of thermal plasma in the corona above the sunspot or the presence of localized flux tubes containing higher density plasma or nonpotential fields.

Bogod, V. M.↗
DOE OSTI2016

Protein–Mineral Interactions: Molecular Dynamics Simulations Capture Importance of Variations in Mineral Surface Composition and Structure

Molecular dynamics simulations, conventional and metadynamics, were performed to determine the interaction of model protein Gb1 over kaolinite (001), Na+-montmorillonite (001), Ca2+-montmorillonite (001), goethite (100), and Na+-birnessite (001) mineral surfaces. Gb1, a small (56 residue) protein with a well-characterized solution-state nuclear magnetic resonance (NMR) structure and having α-helix, four-fold β-sheet, and hydrophobic core features, is used as a model protein to study protein soil mineral interactions and gain insights on structural changes and potential degradation of protein. From our simulations, we observe little change to the hydrated Gb1 structure over the kaolinite, montmorillonite, and goethite surfaces relative to its solvated structure without these mineral surfaces present. Over the Na+-birnessite basal surface, however, the Gb1 structure is highly disturbed as a result of interaction with this birnessite surface. Unraveling of the Gb1 β-sheet at specific turns and a partial unraveling of the α-helix is observed over birnessite, which suggests specific vulnerable residue sites for oxidation or hydrolysis possibly leading to fragmentation.

Environmental Molecular Sciences Laboratory↗