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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Black Carbon in Estuarine (Coastal) High-molecular-weight Dissolved Organic Matter

Dissolved organic matter (DOM) in the ocean constitutes one of the largest pools of organic carbon in the biosphere, yet much of its composition is uncharacterized. Observations of black carbon (BC) particles (by-products of fossil fuel combustion and biomass burning) in the atmosphere, ice, rivers, soils and marine sediments suggest that this material is ubiquitous, yet the contribution of BC to the ocean s DOM pool remains unknown. Analysis of high-molecular-weight DOM isolated from surface waters of two estuaries in the northwest Atlantic Ocean finds that BC is a significant component of DOM, suggesting that river-estuary systems are important exporters of BC to the ocean through DOM. We show that BC comprises 4-7% of the dissolved organic carbon (DOC) at coastal ocean sites, which supports the hypothesis that the DOC pool is the intermediate reservoir in which BC ages prior to sedimentary deposition. Flux calculations suggest that BC could be as important as vascular plant-derived lignin in terms of carbon inputs to the ocean. Production of BC sequesters fossil fuel- and biomass-derived carbon into a refractory carbon pool. Hence, BC may represent a significant sink for carbon to the ocean.

Mannino, Antonio↗
NASA NTRS2012

Hypervelocity Impact Experiments on Epoxy/Ultra-High Molecular Weight Polyethylene Composite Panels Reinforced with Nanotubes

Advanced composites with multi-functional capabilities are of great interest to the designers of aerospace structures. Polymer matrix composites (PMCs) reinforced with high strength fibers provide a lightweight and high strength alternative to metals and metal alloys conventionally used in aerospace architectures. Novel reinforcements such as nanofillers offer potential to improve the mechanical properties and add multi-functionality such as radiation resistance and sensing capabilities to the PMCs. This paper reports the hypervelocity impact (HVI) test results on ultra-high molecular weight polyethylene (UHMWPE) fiber composites reinforced with single-walled carbon nanotubes (SWCNT) and boron nitride nanotubes (BNNT). Woven UHMWPE fabrics, in addition to providing excellent impact properties and high strength, also offer radiation resistance due to inherent high hydrogen content. SWCNT have exceptional mechanical and electrical properties. BNNT (figure 1) have high neutron cross section and good mechanical properties that add multi-functionality to this system. In this project, epoxy based UHMWPE composites containing SWCNT and BNNT are assessed for their use as bumper shields and as intermediate plates in a Whipple Shield for HVI resistance. Three composite systems are prepared to compare against one another: (I) Epoxy/UHMWPE, (II) Epoxy/UHMWPE/SWCNT and (III) Epoxy/UHMWPE/SWCNT/BNNT. Each composite is a 10.0 by 10.0 by 0.11 cm3 panel, consisting of 4 layers of fabrics arranged in cross-ply orientation. Both SWCNT and BNNT are 0.5 weight % of the fabric preform. Hypervelocity impact tests are performed using a two-stage light gas gun at Rice University

Khatiwada, Suman↗
NASA NTRS2001

Microbial detection with low molecular weight RNA

The need to monitor microorganisms in the environment has increased interest in assays based on hybridization probes that target nucleic acids (e.g., rRNA). We report the development of liquid-phase assays for specific bacterial 5S rRNA sequences or similarly sized artificial RNAs (aRNAs) using molecular beacon technology. These beacons fluoresce only in the presence of specific target sequences, rendering as much as a 27-fold fluorescence enhancement. The assays can be used with both crude cell lysates and purified total RNA preparations. Minimal sample preparation (e.g., heating to promote leakage from cells) is sufficient to detect many Gram-negative bacteria. Using this approach it was possible to detect an aRNA-labeled Escherichia coli strain in the presence of a large background of an otherwise identical E. coli strain. Finally, by using a longer wavelength carboxytetramethylrhodamine beacon it was possible to reduce the fraction of the signal due to cellular autofluorescence to below 0.5%.

NASA Discipline Life Sciences Technologies↗
NASA NTRS1983

Polyfunctional epoxies - Different molecular weights of brominated polymeric additives as flame retardants in graphite composites

The imparting of flame retardancy to graphite-reinforced composites without incurring mechanical property deterioration is investigated for the case of an experimental, trifunctional epoxy resin incorporating brominated polymeric additives (BPAs) of the diglycidyl type. Such mechanical properties as flexural strength and modulus, and short beam shear strength, were measured in dry and in hot/wet conditions, and the glass transition temperature, flammability, and water absorption were measured and compared with nonbromilated systems. Another comparison was made with a tetrafunctional epoxy system. The results obtained are explained in terms of differences in the polymeric backbone length of the bromine carrier polymer. BPAs are found to be a reliable bromine source for fire inhibition in carbon-reinforced composites without compromise of mechanical properties.

Nir, Z.↗
NASA NTRS1984

Carbon isotope composition of low molecular weight hydrocarbons and monocarboxylic acids from Murchison meteorite

Carbon isotopic compositions have been measured for individual hydrocarbons and monocarboxylic acids from the Murchison meteorite, a C2 carbonaceous chondrite which fell in Australia in 1969. With few exceptions, notably benzene, the volatile products are substantially isotopically heavier than their terrestrial counterparts, signifying their extraterrestrial origin. For both classes of compounds, the ratio of C-13 to C-12 decreases with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic ratio than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with the kinetically controlled synthesis of higher homologues from lower ones. The results suggest the possibility that the production mechanisms for hydrocarbons and carboxylic acids may be similar, and impose constraints on the identity of the reactant species.

Yuen, G.↗
NASA NTRS1983

Occurrence of low molecular weight thiols in biological systems

Bromobimane labeling and high performance chromatography analysis were applied to various species of bacteria, plant tissues, and animal tissues. The reaction between thiols and monobromobimane is studied. Chromatograms revealing peaks produced by nonthiols and thiols are analyzed and compared. It is observed that all the bacteria species contain hydrogen sulfide, and glutathione is contained in facultative and aerobic gram-negative bacteria. For the plant tissues, the data reveal that mung bean sprouts contain homoglutathione and no glutathione; alfalfa sprouts contain homoglutathione and glutathione; the pea seed, nonlegumes, and fungi contain glutathione and no homoglutathione. It is detected that the main thiol in the animal tissues is glutathione. Based on the data, it is suggested that glutathione has an essential function in higher organisms.

Fahey, Robert C.↗
NASA NTRS1990

Characterization of LaRC-TPI 1500 powders - A new version with controlled molecular weight

The crystallization behavior and the melt flow properties of two batches of 1500 series LaRC-TPI polymers have been investigated. The characterization methods include DSC, XRD, and melt rheology. The as-received materials posses initial crystalline melting peak temperatures of 295 and 305 C, respectively. These materials are less readily recrystallizable at elevated temperatures when compared to other semicrystalline thermoplastics. For the samples annealed at temperatures below 330 C, a semicrystalline polymer can be obtained. On the other hand, a purely amorphous structure is realized in samples annealed at temperatures above 330 C. The viscoelastic properties at elevated temperatures below and above T(g)s of the polymers were measured. Information with regard to the molecule sizes and distributions in these polymers were also extracted from melt rheology.

Hou, T. H.↗
NASA NTRS1993

Extraction and isotopic analysis of medium molecular weight hydrocarbons from Murchison using supercritical carbon dioxide

The large variety of organic compounds present in carbonaceous chondrites poses particular problems in their analysis not the least of which is terrestrial contamination. Conventional analytical approaches employ simple chromatographic techniques to fractionate the extractable compounds into broad classes of similar chemical structure. However, the use of organic solvents and their subsequent removal by evaporation results in the depletion or loss of semi-volatile compounds as well as requiring considerable preparative work to assure solvent purity. Supercritical fluids have been shown to provide a powerful alternative to conventional liquid organic solvents used for analytical extractions. A sample of Murchison from the Field Museum was analyzed. Two interior fragments were used; the first (2.85 g) was crushed in an agate pestel and mortar to a grain size of ca. 50-100 micron, the second (1.80 g) was broken into chips 3-8 mm in size. Each sample was loaded into a stainless steel bomb and placed in the extraction chamber of an Isco supercritical fluid extractor maintained at 35 C. High purity (99.9995 percent) carbon dioxide was used and was pressurized using an Isco syringe pump. The samples were extracted dynamically by flowing CO2 under pressure through the bomb and venting via a 50 micron fused filica capillary into 5 mls of hexane used as a collection solvent. The hexane was maintained at a temperature of 0.5 C. A series of extractions were done on each sample using CO2 of increasing density. The principal components extracted in each fraction are summarized.

Gilmour, Iain↗
NASA NTRS2004

Chemistry, Adhesive and Composite Properties of Low Molecular Weight Phenylethynyl Terminated Oligomers

PETI-5 (1250 and 2500 g/mole) were prepared and characterized. Neat resin, adhesive and composite properties were determined and compared with those of PETI-5 (5000 g/mole). Relative to PETI-5 (5000 g/mole), PETI-5 (2500 g/mole) exhibited improved processability and equivalency in the adhesive and composite properties measured thus far. This resin, in both adhesive film and prepreg form, has the potential to offer significant improvements in the processing of complex structural composite parts.

Connell, John W.↗