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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Origin, Bulk Chemical Composition and Physical Structure of the Galilean Satellites of Jupiter: A Post-Galileo Analysis

The origin of Jupiter and the Galilean satellite system is examined in the light of the new data that has been obtained by the NASA Galileo Project. In particular, special attention is given to a theory of satellite origin which was put forward at the start of the Galileo Mission and on the basis of which several predictions have now been proven successful. These predictions concern the chemical composition of Jupiter's atmosphere and the physical structure of the satellites. According to the proposed theory of satellite origin, each of the Galilean satellites formed by chemical condensation and gravitational accumulation of solid grains within a concentric family of orbiting gas rings. These rings were cast off equatorially by the rotating proto-Jovian cloud (PJC which contracted gravitationally to form Jupiter some 4 1/2 billion years ago. The PJC formed from the gas and grains left over from the gas ring that had been shed at Jupiter's orbit by the contracting proto-solar cloud (PSC Supersonic turbulent convection provides the means for shedding discrete gas rings. The temperatures T (sub n) of the system of gas rings shed by the PSC and PJC vary with their respective mean orbital radii R (sub n) (n = 0, 1,2,...) according as T (sub n) proportional to R (sub n) (exp -0.9). If the planet Mercury condenses at 1640 K, so accounting for the high density of that planet via a process of chemical fractionation between iron and silicates, then T (sub n) at Jupiter's orbit is 158 K. Only 35% of the water vapour condenses out. Thus fractionation between rock and ice, together with an enhancement in the abundance of solids relative to gas which takes place through gravitational sedimentation of solids onto the mean orbit of the gas ring, ensures nearly equal proportions of rock and ice in each of Ganymede and Callisto. Io and Europa condense above the H20 ice point and consist solely of hydrated rock (h-rock). The Ganymedan condensate consists of h-rock and H20 ice. For Callisto, NH3 ice makes up -5% of the condensate mass next to h-rock (approximately 50%) and H2O ice (approximately 45%). Detailed thermal and structural models for each of Europa, Ganymede and Callisto are constructed on the basis of the above initial bulk chemical compositions. For Europa (E), a predicted 2-zone model consisting of a dehydrated rock core of mass 0.912 M (sub E) and a 150 km thick frozen mantle of salty H2O yields a moment-of-inertia coefficient which matches the Galileo Orbiter gravity measurement. For Ganymede (G), a 3-zone model possessing an inner core of solid FeS and mass approximately 0.116 M (sub G), and an outer H2O ice mantle of mass approximately 0.502 M (sub G) is needed to explain the gravity data. Ganymede's native magnetic field was formed by thermoremanent magnetization of Fe3O4. A new Callisto (C) model is proposed consisting of a core of mass 0.826 M (sub C) containing a uniform mixture of h-rock (60% by mass) and H2O and NH3 ices, and capped by a mantle of pure ice. This model may have the capacity to yield a thin layer of liquid NH3 (raised dot) 2H2O at the core boundary, in line with Galileo's discovery of an induced magnetic field.

Prentice, A. J. R.↗
NASA NTRS1985

Shock tube study of the fuel structure effects on the chemical kinetic mechanisms responsible for soot formation, part 2

Soot formation in oxidation of allene, 1,3-butadiene, vinylacetylene and chlorobenzene and in pyrolysis of ethylene, vinylacetylene, 1-butene, chlorobenzene, acetylen-hydrogen, benzene-acetylene, benzene-butadiene and chlorobenzene-acetylene argon-diluted mixtures was studied behind reflected shock waves. The results are rationalized within the framework of the conceptual models. It is shown that vinylacetylene is much less sooty than allene, which indicates that conjugation by itself is not a sufficient factor for determining the sooting tendency of a molecule. Structural reactivity in the context of the chemical kinetics is the dominant factor in soot formation. Detailed chemical kinetic modeling of soot formation in pyrolysis of acetylene is reported. The main mass growth was found to proceed through a single dominant route composed of conventional radical reactions. The practically irreversible formation reactions of the fused polycyclic aromatics and the overshoot by hydrogen atom over its equilibrium concentration are the g-driving kinetic forces for soot formation.

Frenklach, M.↗
NASA NTRS1990

The structure of carbon in chemically vapor deposited SiC monofilaments

Electron diffraction and high resolution TEM have been used to study the microstructures of C-rich regions in CVD SCS-6 SiC fibers. The reciprocal lattice of such structures, and their diffraction patterns, have been ascertained on the basis of geometrical considerations. While the C microstructures in the substrate filament and the outer coating layers of the fabric are consistent with different distributions of Oberlin's (1989) 'basic structural units', the microstructure of the inner substrate coating is consistent with turbostratic C.

Ning, X. J.↗
NASA NTRS1993

Terrestrial bitumen analogue of orgueil organic material demonstrates high sensitivity to usual HF-HCl treatment

The relationship between the chemical composition and the interlayer spacing (d002) of organic materials (OM's) is known for various terrestrial OM's. We improved this general trend by correlation with corresponding trend of natural solid bitumens (asphaltite-kerite-anthraxolite) up to graphite. Using the improved trend we identified bitumen analogs of carbonaceous chondrite OM's residued after HF-HCl treatment. Our laboratory experiment revealed that these analogs and, hence, structure and chemical composition of carbonaceous chondrite OM's are very sensitive to the HF-HCl treatment. So, usual extraction of OM from carbonaceous chondrites may change significantly structural and chemical composition of extracted OM.

Korochantsev, A. V.↗
NASA NTRS2005

Probabilisitc Geobiological Classification Using Elemental Abundance Distributions and Lossless Image Compression in Recent and Modern Organisms

Last year we presented techniques for the detection of fossils during robotic missions to Mars using both structural and chemical signatures[Storrie-Lombardi and Hoover, 2004]. Analyses included lossless compression of photographic images to estimate the relative complexity of a putative fossil compared to the rock matrix [Corsetti and Storrie-Lombardi, 2003] and elemental abundance distributions to provide mineralogical classification of the rock matrix [Storrie-Lombardi and Fisk, 2004]. We presented a classification strategy employing two exploratory classification algorithms (Principal Component Analysis and Hierarchical Cluster Analysis) and non-linear stochastic neural network to produce a Bayesian estimate of classification accuracy. We now present an extension of our previous experiments exploring putative fossil forms morphologically resembling cyanobacteria discovered in the Orgueil meteorite. Elemental abundances (C6, N7, O8, Na11, Mg12, Ai13, Si14, P15, S16, Cl17, K19, Ca20, Fe26) obtained for both extant cyanobacteria and fossil trilobites produce signatures readily distinguishing them from meteorite targets. When compared to elemental abundance signatures for extant cyanobacteria Orgueil structures exhibit decreased abundances for C6, N7, Na11, All3, P15, Cl17, K19, Ca20 and increases in Mg12, S16, Fe26. Diatoms and silicified portions of cyanobacterial sheaths exhibiting high levels of silicon and correspondingly low levels of carbon cluster more closely with terrestrial fossils than with extant cyanobacteria. Compression indices verify that variations in random and redundant textural patterns between perceived forms and the background matrix contribute significantly to morphological visual identification. The results provide a quantitative probabilistic methodology for discriminating putatitive fossils from the surrounding rock matrix and &om extant organisms using both structural and chemical information. The techniques described appear applicable to the geobiological analysis of meteoritic samples or in situ exploration of the Mars regolith. Keywords: cyanobacteria, microfossils, Mars, elemental abundances, complexity analysis, multifactor analysis, principal component analysis, hierarchical cluster analysis, artificial neural networks, paleo-biosignatures

Storrie-Lombardi, Michael C.↗
NASA NTRS1983

Shock tube study of the fuel structure effects on the chemical kinetic mechanisms responsible for soot formation

Soot formation in toluene-, benzene-, and acetylene-oxygen-argon mixtures was investigated to study soot formation in a combustion environment. High concentrations of oxygen completely suppress soot formation. The addition of oxygen at relatively low concentrations uniformly suppresses soot formation at high pressures, while at relatively lower pressures it suppresses soot formation at higher temperatures while promoting soot production at lower temperatures. The observed behavior indicates that oxidation reactions compete with ring fragmentation. The main conclusion to be drawn from the results is that the soot formation mechanism is probably the same for the pyrolysis and oxidation of hydrocarbons. That is, the addition of oxygen does not alter the soot route but rather promotes or inhibits this route by means of competitive reactions. An approach to empirical modeling of soot formation during pyrolysis of aromatic hydrocarbons is also presented.

Frenklach, M.↗
NASA NTRS2005

Bulk Velocities, Chemical Composition and Ionization Structure of the X-ray Shocks in WR140 near Periastron as Revealed by the Chandra Gratings

The Wolf-Rayet WC7+O4.5 binary WR140 went through the periastron passage of its 8-year eccentric binary orbit in early 2001 as the two stars made their closest approach. Both stars have powerful supersonic stellar winds which crash into each other between the stars to produce X-rays. Chandra grating observations were made when the X-rays were at their brightest making WR140 the brightest hot-star X-ray source in the sky and giving the opportunity to study the velocity profiles of lines, all of which were resolved and blue-shifted. In the general context of shock physics, the measurements constrain the flow of hot gas and where different ions were made. The lower velocity widths of cool ions imply a plasma that was not in equilibrium. The brightness of lines relative to the strong continuum in conjunction with plasma models gives interim abundance estimates for eight different elements in WC-type material including an Ne/S ratio in good agreement with earlier long-wavelength measurements.

Pollock, A. M. T.↗
NASA NTRS1982

AGT 100 automotive gas turbine system development

General Motors is developing an automotive gas turbine system that can be an alternate powerplant for future automobiles. Work sponsored by DOE and administered by NASA Lewis Research Center is emphasizing small component aerodynamics and high-temperature structural ceramics. Reliability requirements of the AGT 100 turbine system include chemical and structural ceramic component stability in the gas turbine environment. The power train system, its configuration and schedule are presented, and its performance tested. The aerodynamic component development is reviewed with discussions on the compressor, turbine, regenerator, interturbine duct and scroll, and combustor. Ceramic component development is also reviewed, and production cost and required capital investment are taken into consideration.

Helms, H. E. G.↗
NASA NTRS2003

Common 5S rRNA variants are likely to be accepted in many sequence contexts

Over evolutionary time RNA sequences which are successfully fixed in a population are selected from among those that satisfy the structural and chemical requirements imposed by the function of the RNA. These sequences together comprise the structure space of the RNA. In principle, a comprehensive understanding of RNA structure and function would make it possible to enumerate which specific RNA sequences belong to a particular structure space and which do not. We are using bacterial 5S rRNA as a model system to attempt to identify principles that can be used to predict which sequences do or do not belong to the 5S rRNA structure space. One promising idea is the very intuitive notion that frequently seen sequence changes in an aligned data set of naturally occurring 5S rRNAs would be widely accepted in many other 5S rRNA sequence contexts. To test this hypothesis, we first developed well-defined operational definitions for a Vibrio region of the 5S rRNA structure space and what is meant by a highly variable position. Fourteen sequence variants (10 point changes and 4 base-pair changes) were identified in this way, which, by the hypothesis, would be expected to incorporate successfully in any of the known sequences in the Vibrio region. All 14 of these changes were constructed and separately introduced into the Vibrio proteolyticus 5S rRNA sequence where they are not normally found. Each variant was evaluated for its ability to function as a valid 5S rRNA in an E. coli cellular context. It was found that 93% (13/14) of the variants tested are likely valid 5S rRNAs in this context. In addition, seven variants were constructed that, although present in the Vibrio region, did not meet the stringent criteria for a highly variable position. In this case, 86% (6/7) are likely valid. As a control we also examined seven variants that are seldom or never seen in the Vibrio region of 5S rRNA sequence space. In this case only two of seven were found to be potentially valid. The results demonstrate that changes that occur multiple times in a local region of RNA sequence space in fact usually will be accepted in any sequence context in that same local region.

NASA Discipline Exobiology↗
NASA NTRS1981

Quantum chemical calculation of the equilibrium structures of small metal atom clusters

A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.

Kahn, L. R.↗
NASA NTRS1993

Enhancement of photoluminescence intensity of GaAs with cubic GaS chemical vapor deposited using a structurally designed single-source precursor

A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster /(t-Bu)GaS/4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron and Rutherford backscattering spectroscopies.

Macinnes, Andrew N.↗
NASA NTRS1992

Phase transformations in 40-60-GPa shocked gneisses from the Haughton Crater (Canada): An Analytical Transmission Electron Microscopy (ATEM) study

In order to better understand phase transformations, chemical migration, and isotopic disequilibrium in highly shocked rocks, we have performed a microprobe and an ATEM study on gneisses shocked up to 60 GPa from the Haughton Crater. This study reveals the following chemical and structural characteristics: (1) SiO2 dominant areas are formed by a mixture of pure SiO2 polycrystalline quartz identified by electron diffraction pattern and chemical analysis and a silica-rich amorphous phase containing minor amounts of aluminium, potassium, and iron; (2) Areas with biotitelike composition are formed by less than 200-nm grains of iron-rich spinels embedded in a silica-rich amorphous phase that is very similar to the one described above; (3) Layers with feldsparlike composition are constituted by 100-200-nm-sized alumina-rich grains (the indexation of the crystalline structure is under progress) and the silica-rich amorphous phase; (4) Zones characterized by the unusual Al/Si ratio close to 1 are formed by spinel grains (200-nm-sized) embedded in the same silica-rich amorphous phase; and (5) The fracturated sillimanites contain domains with a lamellar structure, defined by the intercalation of 100-nm-wide lamellae of mullite crystals and of a silica-rich amorphous phase. These mullite crystals preserved the crystallographical orientation of the preshock sillimanite. All compositional domains, identified at the microprobe scale, can thus be explained by a mixture in different proportion between the following phases: (1) a silica-rich amorphous phase, with minor Al and K; (2) quartz crystals; (3) spinel crystals and alumina-rich crystals; (4) sillimanite; and (5) mullite. Such mixtures of amorphous phases and crystals in different proportions explain disturbed isotope systems in these rocks and chemical heterogeneities observed on the microprobe.

Martinez, I.↗
NASA NTRS2005

Structure and Bonding of Carbon in Clays from CI Carbonaceous Chondrites

Carbonaceous chondrites (CC) contain a diverse suite of C-rich materials. Acid dissolution of these meteorites leaves a C-rich residue with chemical and structural affinities to kerogen. This material has primarily been analyzed in bulk, and much information has been provided regarding functional groups and elemental and isotopic compositions. However, comparatively little work has been done on C in unprocessed meteorites. Studies of CCs suggest a spatial relationship of some C-rich materials with products of aqueous alteration. Recent studies revealed discrete submicronsized, C-rich particles in Tagish Lake and a range of CM2 meteorites. A challenge is to correlate the findings from the bulk acid-residue studies with those of high-spatial resolution-mineralogical and spectroscopic observations of unprocessed meteorites. Hence, the relationship between the C-rich materials in the acid residues and its form and locations in the unprocessed meteorite remains unclear. Here we provide information on the structure and bonding of C associated with clays in CI carbonaceous chondrites. Additional information is included in the original extended abstract.

Garview, Laurence a. J.↗
NASA NTRS1993

Lamellar olivine in the Divnoe achondrite: Evidence for high-pressure exsolution?

The olivine-rich Divnoe achondrite contains numerous large olivine grains which have a lamellar or banded appearance in back-scattered electron images, caused by minor compositional differences. One such grain, viewed in transmitted light, displays a system of lamellae with the same orientation and scale as the compositional banding. The only process known to produce such structure and chemical variability in olivine grains is high-pressure transformations between alpha-, beta- and gamma-olivines, but in other meteorites and in experimental products the structure is approximately 100 times finer than the Divnoe lamella.

Petaev, M. I.↗
NASA NTRSDate not supplied

Europa Luminescence Microscope

The Europa Luminescence Microscope (ELM) is an automated fluorescence and dark-field mi-croscope designed to meet key objectives defined in the NASA Europa Lander Study Report, includ-ing the identification and characterization of morphological biosignatures. ELM’s heritage stems from a 2U cubesat fluorescence microscope, the Fluorescence Analysis for In-situ Research (FLAIR) im-ager, designed and built at NASA Ames Research Center, for the autonomous study of microbial bi-ology in low Earth orbit. For the ELM implementation, a sample is autonomously manipulated with a microfluidic system using in-line filter sets to capture successively smaller particles on 10, 1.0, and 0.1 µm pore-size filters for imaging. For darkfield imaging, ELM uses ultraviolet and visible light to image organic and inorganic structures with submicron resolution. The ability to detect structural and chemical biosignatures as small as 0.2 µm in size is achieved by imaging native fluorescence and us-ing fluorescence microscopy stains to identify key molecular and structural indicators of microbial life (proteins, lipids, nucleic acids). To excite fluorescence, ELM uses LEDs with wavelengths centered near 265, 370, 470, and 530 nm and five emission bands. The use of multiple excitation and emission wavelengths for native fluorescence imaging not only enables the detection of different molecular species, but also their rough classification. Excitation at 265 nm allows for the detection of smaller polyaromatic hydrocarbons (PAHs; 1-5 rings), aromatic amino acids, and proteins with little to no interference from mineral fluorescence, given proper emission band selection. 370 and 470 nm light excites increasingly larger PAH structures (e.g., coronene) and larger aromatic biomolecules that may be present (e.g., protective pigments). Similarly, inorganic fluorescence can be characterized and sep-arated from organic fluorescence, allowing the recognition and in some cases classification, of miner-als and other abiotic particles. ELM is based upon work supported by the NASA COLDTech and ICEE-2 programs.

Microscope↗