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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Plant reproduction in spaceflight environments

Because plant reproduction is a complex developmental process there are many possible sites of perturbation by the unusual environments of orbital spacecraft. Previous long-duration experiments on Soviet platforms shared features of slowed development through the vegetative stage of plant growth and aborted reproductive function. Our goal has been to understand how special features of the spaceflight environment impact physiological function and reproductive development. In a series of short-duration experiments in the Shuttle mid-deck we studied early reproductive development in Arabidopsis thaliana. Pollen and ovule development aborted at an early stage in the first experiment on STS-54 which utilized closed plant growth chambers. Post-flight analysis suggested that the plants may have been carbon dioxide limited. Subsequent experiments utilized carbon dioxide enrichment (on STS-51) and cabin air flow-through with an air exchange system (on STS-68). Both modifications allowed pollen and ovule development to occur normally on orbit, and full reproductive development up to the stage of an immature seed occurred on STS-68. However, analysis of plant roots from these experiments demonstrated a limitation in rootzone aeration in the spaceflight material that was not mitigated by these procedures. In the future, additional resources (crew time, upgraded flight hardware, and special platforms) will invite more elaborate, long-duration experimentation. On the ISS, a variable speed centrifuge and upgraded plant habitats will permit detailed experiments on the role of gravity in shaping the plant micro-environment, and what influence this plays during reproduction.

Review, Tutorial↗
NASA NTRS1992

Studies on the reactive melt infiltration of silicon and silicon-molybdenum alloys in porous carbon

Investigations on the reactive melt infiltration of silicon and silicon-1.7 and 3.2 at percent molybdenum alloys into porous carbon preforms have been carried out by process modeling, differential thermal analysis (DTA) and melt infiltration experiments. These results indicate that the initial pore volume fraction of the porous carbon preform is a critical parameter in determining the final composition of the raction-formed silicon carbide and other residual phases. The pore size of the carbon preform is very detrimental to the exotherm temperatures due to liquid silicon-carbon reactions encountered during the reactive melt infiltration process. A possible mechanism for the liquid silicon-porous (glassy) carbon reaction has been proposed. The composition and microstructure of the reaction-formed silicon carbide has been discussed in terms of carbon preform microstructures, infiltration materials, and temperatures.

Singh, M.↗
NASA NTRS2021

Classifying Forest Type in the National Forest Inventory Context with Airborne Hyperspectral and Lidar Data

Forest structure and composition regulate a range of ecosystem services, including biodiversity, water and nutrient cycling, and wood volume for resource extraction. Forest type is an important metric measured in the US Forest Service Forest Inventory and Analysis (FIA) program, the national forest inventory of the USA. Forest type information can be used to quantify carbon and other forest resources within specific domains to support ecological analysis and forest management decisions, such as managing for disease and pests. In this study, we developed a methodology that uses a combination of airborne hyperspectral and lidar data to map FIA-defined forest type between sparsely sampled FIA plot data collected in interior Alaska. To determine the best classification algorithm and remote sensing data for this task, five classification algorithms were tested with six different combinations of raw hyperspectral data, hyperspectral vegetation indices, and lidar-derived canopy and topography metrics. Models were trained using forest type information from 632 FIA subplots collected in interior Alaska. Of the thirty model and input combinations tested, the random forest classification algorithm with hyperspectral vegetation indices and lidar-derived topography and canopy height metrics had the highest accuracy (78% overall accuracy). This study supports random forest as a powerful classifier for natural resource data. It also demonstrates the benefits from combining both structural (lidar) and spectral (imagery) data for forest type classification.

random forest↗
NASA NTRS2000

Abrupt Changes at the Permian/Triassic Boundary: Tempo of Events from High-Resolution Cyclostratigraphy

The Permian/Triassic (P/Tr) boundary (251.4 +/- 3 Myr) is marked by the most severe mass extinction in the geologic record. Recently, precise absolute dating has bracketed the marine extinctions and associated carbon-isotope anomaly within less than 1 Myr. We improve this resolution through high-resolution stratigraphy across the P/Tr boundary in the 331-m Gartnerkofel-1 core and nearby Reppwand outcrop section (Carnic Alps, Austria) utilizing FFT and wavelet timeseries analyses of cyclic components in down-hole core logs of density and natural gamma-ray intensity, and carbon-isotopic ratios of bulk samples. The wavelet analysis indicates continuity of deposition across the P/Tr boundary interval, and the timeseries analyses show evidence for persistent cycles in the ratio of approximately 40: 10: 4.7: 2.3 meters, correlated with Milankovitch-band orbital cycles of approximately 412: 100: 40: 20 kyr (eccentricity 1 and 2, obliquity, and precession), and giving a consistent average sedimentation rate of approximately 10 cm/1,000 yr. Milankovitch periods in delta C-13 and density in these shallow-water carbonates were most likely the result of climatically induced oscillations of sea level and climate, coupled with changes in ocean circulation and productivity, that affected sedimentation. Fluctuations in gamma radiation reflect varying input of clay minerals and the presence of shaly interbeds. Throughout the P/Tr boundary interval in the core, the 100,000-year eccentricity cycle seems to be dominant. Weaker obliquity and precession cycles are in line with the location of the Austrian section in the latest Permian, close to the Equator in the western bight of the Tethys, where obliquity and precessional effects on seasonal contrast might be subdued. Using the improved resolution provided by cycle analysis in the GK-1 core, we find that the dramatic change in the faunal record that marks the P/Tr boundary takes place over less than 6m, or less than 60,000 years. In the nearby Reppwand outcrop section, the same faunal changes occurs over only 0.8 m or about 8,000 years, close to the limit of time-resolution induced by bioturbation and reworking in these sediments. The sharp negative global carbon-isotope shift took place within less than or equal to 40,000 yr, and the isotope excursions persisted for approximately 480,000 yr into the Early Triassic. The results indicate that the severe marine faunal event that marks the P/Tr boundary was very sudden, perhaps less than the resolution window in the GK-1 core, and suggest a catastrophic cause. The wavelet-analysis approach to high-resolution cyclostratigraphy can be applied to other P/Tr boundary sections, and when combined with precise absolute dating and magnetostratigraphic methods promises a significant increase in resolution in determining the correlation and tempo of the end-Permian extinctions and related events worldwide.

Rampino, M. R.↗
NASA NTRS1979

Transport properties of monatomic carbon. II - Contributions from excited electronic states

The aim of the present analysis is to verify the conventional assumption that the transport properties of atoms and molecules in excited electronic states are nearly the same as in the ground state. Reasonably exact calculations of the transport properties of excited-state carbon atoms are obtained on the basis of available experimental and theoretical data on the interactions between carbon atoms in excited electronic states. A comparison with results obtained with several models that have been used to estimate the transport properties of excited species indicates that the assumption under consideration is correct, but that the models do not predict very accurately the transport properties of excited species.

Biolsi, L.↗
NASA NTRS1979

Measurements of carbon monoxide, condensation nuclei, and ozone on a B 747SP aircraft flight around the world

Measurements of carbon monoxide, condensation nuclei, and ozone concentrations were obtained during a 54 hour polar flight around the world by an automated instrument package carried by a B-747SP commercial aircraft. These and other data were obtained as part of the NASA Global Atmospheric Sampling Program. All data exhibited longitudinal and hemispheric differences. Analysis of the data indicate increased concentrations of carbon monoxide and condensation nuclei at flight levels in the troposphere over tropical land masses. A background concentration for condensation nuclei was found to be 200 per cu cm for tropical tropospheric maritime air.

Gauntner, D. J.↗
NASA NTRS1976

Hydrogen-fueled scramjets: Potential for detailed combustor analysis

Combustion research related to hypersonic scramjet (supersonic combustion ramjet) propulsion is discussed from the analytical point of view. Because the fuel is gaseous hydrogen, mixing is single phase and the chemical kinetics are well known; therefore, the potential for analysis is good relative to hydro-carbon fueled engines. Recent progress in applying two and three dimensional analytical techniques to mixing and reacting flows indicates cause for optimism, and identifies several areas for continuing effort.

Beach, H. L., Jr.↗
NASA NTRS1986

Observational constraints on circumstellar dust

There is an enormous range in the properties of stars that are losing mass. The red giants responsible for injecting roughly half or more of the material into the interstellar medium are reviewed. The physical properties are described for the out flowing gases. Broadband observation constaints on the dust are described by use of spectrum analysis. Circumstellar dust is identified by carbon-carbon and carbon-hydrogen bonds.

Jura, M.↗
NASA NTRS1988

Infrared spectroscopy of Jupiter and Saturn

High resolution infrared spectoscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn. The 5 micrometer spectral region, which is transparent to deep levels, is particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. These are tracers of convective and strongly non-equilibrium processes in the atmosphere. High resolution ground-based spectroscopy complements Voyager and Galileo measurements. Spectroscopy is sensitive to lower mixing levels for selected molecules, while the on-board mass spectrometers probe molecules that are spectroscopically inaccessible. Analysis and modeling of the 4.7 micrometer carbon monoxide in Jupiter was completed. CO is present at a mole fraction of 1.6 plus or minus 0.3 x 10 to the 9th power and concentrated in the troposphere. At this abundance, it must be convected upward from much deeper levels in Jupiter where the temperature is near 1100 K. Thus CO is a tracer of the deep atmosphere which is otherwise unobservable. The oxygen abundance in Jupiter (as measured by the CO abundance) is near solar. Chemical or physical process must deplete the major oxygen carrier, water. Germane, GeH4, was discovered on Saturn at amole fraction of 4 plus or minus 2 x 10 to the 10th power.

Knacke, Roger↗
NASA NTRS1999

C/SiC Component & Material Analysis, Attachment Verification, & Blisk Turbopump Testing

Ceramic composite blisk components constructed of carbon fibers & silicon carbide ceramic matrix have been fabricated and tested. Room and cryogenic torque testing have verified the attachment configuration. The polar and quasi-isotropic blisks have been proof spun, balanced, and tested in the Simplex turbopump. Foreign particle impact analysis was conducted for C/SiC. Data and manufacturing lessons learned are significantly benefiting the development of the Reusable Launch Vehicle's ceramic matrix composite integrally bladed disk.

Effinger, Michael R.↗
NASA NTRS2005

Graphite Sheet Coating for Improved Thermal Oxidative Stability of Carbon Fiber Reinforced/PMR-15 Composites

Expanded graphite was compressed into graphite sheets and used as a coating for carbon fiber reinforced PMR-15 composites. BET analysis of the graphite indicated an increase in graphite pore size on compression, however the material was proven to be an effective barrier to oxygen when prepegged with PMR-15 resin. Oxygen permeability of the PMR-15/graphite was an order of magnitude lower than the compressed graphite sheet. By providing a barrier to oxygen permeation, the rate of oxidative degradation of PMR-15 was decreased. As a result, the composite thermo-oxidative stability increased by up to 25%. The addition of a graphite sheet as a top ply on the composites yielded little change in the material's flexural strength or interlaminar shear strength.

Campbell, Sandi↗
NASA NTRS2008

Reliability of Semiconductor Laser Packaging in Space Applications

A typical set up used to perform lifetime tests of packaged, fiber pigtailed semiconductor lasers is described, as well as tests performed on a set of four pump lasers. It was found that two lasers failed after 3200, and 6100 hours under device specified bias conditions at elevated temperatures. Failure analysis of the lasers indicates imperfections and carbon contamination of the laser metallization, possibly from improperly cleaned photo resist. SEM imaging of the front facet of one of the lasers, although of poor quality due to the optical fiber charging effects, shows evidence of catastrophic damage at the facet. More stringent manufacturing controls with 100% visual inspection of laser chips are needed to prevent imperfect lasers from proceeding to packaging and ending up in space applications, where failure can result in the loss of a space flight mission.

Gontijo, Ivair↗
NASA NTRS2018

Understanding Climate-Vegetation Interactions in Global Rainforests Through a GP-Tree Analysis

The tropical rainforests are the largest reserves of terrestrial carbon and, therefore, the future of these rainforests is a question that is of immense importance in the geoscience research community. With the recent severe Amazonian droughts in 2005 and 2010 and on-going drought in the Congo region for more than two decades, there is growing concern that these forests could succumb to precipitation reduction, causing extensive carbon release and feedback to the carbon cycle. However, there is no single ecosystem model that quantifies the relationship between vegetation health in these rainforests and climatic factors. Small scale studies have used statistical correlation measure and simple linear regression to model climate-vegetation interactions, but suffer from the lack of comprehensive data representation as well as simplistic assumptions about dependency of the target on the covariates. In this paper we use genetic programming (GP) based symbolic regression for discovering equations that govern the vegetation climate dynamics in the rainforests. Expecting micro-regions within the rainforests to have unique characteristics compared to the overall general characteristics, we use a modified regression-tree based hierarchical partitioning of the space to build individual models for each partition. The discovery of these equations reveal very interesting characteristics about the Amazon and the Congo rainforests. Our method GP-tree shows that the rainforests exhibit tremendous resiliency in the face of extreme climatic events by adapting to changing conditions.

genetic programming↗
NASA NTRS1982

Origin of SiC impurities in silicon crystals grown from the melt in vacuums

A main source of high carbon levels in silicon crystals grown from melt under reduced pressures and contained in silica crucibles supported by graphite retainer/susceptor was identified by thermodynamic analysis. The calculations were verified by experimental results and the carbon level is reduced by approximately 50% with the use of molybdenum retainers.

Schmid, F.↗
NASA NTRS2006

Lab-Scale Study of the Calcium Carbonate Dissolution and Deposition by Marine Cyanobacterium Phormidium subcapitatum

Suggestions that calcification in marine organisms changes in response to global variations in seawater chemistry continue to be advanced (Wilkinson, 1979; Degens et al. 1985; Kazmierczak et al. 1986; R. Riding 1992). However, the effect of [Na+] on calcification in marine cyanobacteria has not been discussed in detail although [Na+] fluctuations reflect both temperature and sea-level fluctuations. The goal of these lab-scale studies therefore was to study the effect of environmental pH and [Na+] on CaCO3 deposition and dissolution by marine cyanobacterium Phormidium subcapitatum. Marine cyanobacterium P. subcapitatum has been cultivated in ASN-III medium. [Ca2+] fluctuations were monitored with Ca(2+) probe. Na(+) concentrations were determined by the initial solution chemistry. It was found that the balance between CaCO3 dissolution and precipitation induced by P. subcapitatum grown in neutral ASN III medium is very close to zero. No CaCO3 precipitation induced by cyanobacterial growth occurred. Growth of P. subcapitatum in alkaline ASN III medium, however, was accompanied by significant oscillations in free Ca(2+) concentration within a Na(+) concentration range of 50-400 mM. Calcium carbonate precipitation occurred during the log phase of P. subcapitatum growth while carbonate dissolution was typical for the stationary phase of P. subcapitatum growth. The highest CaCO3 deposition was observed in the range of Na(+) concentrations between 200-400 mM. Alkaline pH also induced the clamping of P. subcapitatum filaments, which appeared to have a strong affinity to envelop particles of chemically deposited CaCO3 followed by enlargement of those particles size. EDS analysis revealed the presence of Mg-rich carbonate (or magnesium calcite) in the solution containing 10-100 mM Na(+); calcite in the solution containing 200 mM Na(+); and aragonite in the solution containing with 400 mM Na(+). Typical present-day seawater contains xxmM Na(+). Early (Archean) seawater was likely less saline. The division of marine cyanobacterium P. subcapitatum is associated with periodic deposition and dissolution of CaCO3, the rhythms and intensity of which are dependent on concentrations of both OH(-) and Na(+). Thus, the role of present-day marine cyanobacteria in the global carbonate cycle might be reduced to aggregation and recrystallization of available CaCO3 particles in marine water rather than long-term precipitation and accumulation of CaCO3 deposits. For lower Na(+) concentrations, precipitation of carbonates by cyanobacteria would be even less significant. These results suggest that the lack of calcified cyanobacteria in stromatalite-bearing Precambrian sequences can be explained not only by high dissolved inorganic carbon concentrations but also by lower salinity, as well as possible lower pH compared to present-day oceans.

Karakis, S. G.↗
NASA NTRS2000

Thermal and Evolved Gas Analysis of Hydromagnesite and Nesquehonite: Implications for Remote Thermal Analysis on Mars

Volatile-bearing minerals (e.g., Fe-oxyhydroxides, phyllosilicates, carbonates, and sulfates) may be important phases on the surface of Mars. In order to characterize these potential phases the Thermal Evolved-Gas Analyzer (TEGA), which was onboard the Mars Polar Lander, was to have performed differential scanning calorimetry (DSC) and evolved-gas analysis of soil samples collected from the surface. The sample chamber in TEGA operates at about 100 mbar (approximately 76 torr) with a N2, carrier gas flow of 0.4 seem. Essentially, no information exists on the effects of reduced pressure on the thermal properties of volatile-bearing minerals. In support of TEGA, we have constructed a laboratory analog for TEGA from commercial instrumentation. We connected together a commercial differential scanning calorimeter, a quadruple mass spectrometer, a vacuum pump, digital pressure gauge, electronic mass flow meter, gas "K" bottles, gas dryers, and high and low pressure regulators using a collection of shut off and needle valves. Our arrangement allows us to vary and control the pressure and carrier gas flow rate inside the calorimeter oven chamber.

Lauer, H. V., Jr.↗