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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Molecular clouds and galactic spiral structure

Galactic CO line emission at 115 GHz was surveyed in order to study the distribution of molecular clouds in the inner galaxy. Comparison of this survey with similar H1 data reveals a detailed correlation with the most intense 21 cm features. To each of the classical 21 cm H1 spiral arms of the inner galaxy there corresponds a CO molecular arm which is generally more clearly defined and of higher contrast. A simple model is devised for the galactic distribution of molecular clouds. The modeling results suggest that molecular clouds are essentially transient objects, existing for 15 to 40 million years after their formation in a spiral arm, and are largely confined to spiral features about 300 pc wide.

Dame, T. M.↗
NASA NTRS1979

The spectrum of the Becklin-Neugebauer source in Orion from 3.3 to 5.5 microns

Spectra of the Becklin-Neugebauer source in Orion and the associated nebula are presented covering the complete range from 3.3-5.5 microns with a resolution of 1.2 kaysers. The data were taken in December 1976 and February 1978. Atomic hydrogen emission lines of Brackett-alpha and Pfund-beta are seen, as well as molecular CO absorptions. No other features intrinsic to BN were detected. The December 1976 data show an anomalously high intensity for Pfund-beta line. Theoretical considerations are presented which suggest that Pfund-beta radiation arises in a small dense region, with the transition possibly lasing.

Smith, H. A.↗
NASA NTRS1990

Molecular clouds without detectable CO

The clouds identified by Desert, Bazell, and Boulanger (DBB clouds) in their search for high-latitude molecular clouds were observed in the CO (J = 1-0) line, but only 13 percent of the sample was detected. The remaining 87 percent are diffuse molecular clouds with CO abundances of about 10 to the -6th, a typical value for diffuse clouds. This hypothesis is shown to be consistent with Copernicus data. The DBB clouds are shown to ben an essentially complete catalog of diffuse molecular clouds in the solar vicinity. The total molecular surface density in the vicinity of the sun is then only about 20 percent greater than the 1.3 solar masses/sq pc determined by Dame et al. (1987). Analysis of the CO detections indicates that there is a sharp threshold in extinction of 0.25 mag before CO is detectable and is derived from the IRAS I(100) micron threshold of 4 MJy/sr. This threshold is presumably where the CO abundance exhibits a sharp increase

Blitz, Leo↗
NASA NTRS1991

Theoretical studies of important processes in planetary and comet atmospheres

The dissociative recombination (DR) of the AB(+) molecular ion with an electron has been shown to be an important component in the detailed interpretation of planetary ionosphere data. A first principles theoretical approach is developed for calculating the DR cross sections and rates for AB(+) molecular ions. The calculations focus on O2(+) and N2(+) DR, and are the first to include the indirect DR mechanism (Ryberg vibrational levels below v = 0 level of ion) for a molecule larger than H2(+). The importance of electron capture width in calculating the cross sections and rates is also examined. Electron capture widths are given for all states of O2 that are of importance to DR (lowest 10 vibrational levels of ion). Knowledge of the details of dissociative recombination will be needed for interpretation of data from future interplanetary and comet atmospheric studies.

Guberman, Steven L.↗
NASA NTRS1973

Role of gas-surface interactions in the reduction of OGO 6 neutral-particle mass spectrometer data

Data obtained with the quadrupole mass spectrometer aboard the OGO 6 satellite show the effects of significant surface interaction processes, including nearly complete recombination of incoming atomic oxygen on the walls of the instrument antechamber plus absorption and desorption of oxygen and carbon monoxide. The observed data are fit by solving the time-dependent continuity equations accounting for production and loss of atomic oxygen, molecular oxygen, and (in the case of mass 28) carbon monoxide. The surface parameters that best fit the data are selected and applied to the determination of ambient densities and their estimated errors.

Hedin, A. E.↗
NASA NTRS1973

Role of gas-surface interactions in the reduction of Ogo 6 neutral particle mass spectrometer data.

Data obtained with the quadrupole mass spectrometer aboard the Ogo 6 satellite show the effects of significant surface interaction processes, including nearly complete recombination of incoming atomic oxygen on the walls of the instrument antechamber plus adsorption and desorption of oxygen and carbon monoxide. The observed data are fit by solving the time-dependent continuity equations accounting for production and loss of atomic oxygen, molecular oxygen, and (in the case of mass 28) carbon monoxide. The surface parameters that best fit the data are selected and applied to the determination of ambient densities and their estimated errors.

Hedin, A. E.↗
NASA NTRS1975

A study of molecular contamination

Contamination kinetics of typical space materials were studied using several techniques, including ellipsometry. Data were obtained on contaminant deposition rates, sticking coefficients, and reevaporation of the contamination. Materials studied included silicone sealants, a thermal control paint, and a graphite laminate as contaminant sources, and gold coated surfaces, a thermal control paint and a second surface mirror material as the contaminees. Both deposition and reevaporation rates were found to be nonlinear with time, and followed an exponential decay. A hypothesis is presented that the nonlinear behavior was a result of disproportionation of the molecular weight fractions of the polymers. The measured sticking coefficients were found to vary substantially with temperature over narrow ranges. Simulated space radiation was found to reduce the evaporation rates of contaminants by several orders of magnitude.

Allen, T. H.↗
NASA NTRS2003

Bacillus nealsonii sp. nov., isolated from a spacecraft-assembly facility, whose spores are gamma-radiation resistant

One of the spore-formers isolated from a spacecraft-assembly facility, belonging to the genus Bacillus, is described on the basis of phenotypic characterization, 16S rDNA sequence analysis and DNA-DNA hybridization studies. It is a Gram-positive, facultatively anaerobic, rod-shaped eubacterium that produces endospores. The spores of this novel bacterial species exhibited resistance to UV, gamma-radiation, H2O2 and desiccation. The 18S rDNA sequence analysis revealed a clear affiliation between this strain and members of the low G+C Firmicutes. High 16S rDNA sequence similarity values were found with members of the genus Bacillus and this was supported by fatty acid profiles. The 16S rDNA sequence similarity between strain FO-92T and Bacillus benzoevorans DSM 5391T was very high. However, molecular characterizations employing small-subunit 16S rDNA sequences were at the limits of resolution for the differentiation of species in this genus, but DNA-DNA hybridization data support the proposal of FO-92T as Bacillus nealsonii sp. nov. (type strain is FO-92T =ATCC BAAM-519T =DSM 15077T).

Non-programmatic↗
NASA NTRS1990

The effect of thermal damage on the mechanical properties of polymer regrinds

Reprocessed polymers are subjected to high processing temperatures that result in the breakdown of molecular chains and changes in the molecular structures. These phenomena are reflected in the mechanical properties of materials. Practically every regrind is seen as a new material. These experiments deal with the molding, regrinding, and reprocessing of test specimens for the study of their mechanical properties. The comparative test data from each recycled material would give students an insight of the molecular structures and property degradation. Three important rheological and mechanical properties such as melt flow, impact strength, and flexural strength are to be determined. These properties play key roles in the selection of engineering materials. The material selected for demonstration was Makrolon 3000L, a polycarbonate thermoplastic from Bayer AG. The thermal degradation due to repeated processing is reflected in the decrease in molecular weight and breakdown of molecular chains causing increase in melt flow. The Izod-impact resistance and the flexural strength deteriorate gradually.

Kundu, Nikhil K.↗
NASA NTRS1992

Model for oxygen recombination on silicon-dioxide surfaces. II - Implications toward reentry heating

This paper briefly reviews the model for recombination of oxygen on a silicon-dioxide surface presented in detail in a previous paper. New data supporting the model is also presented. The ramifications of the model toward the production of excited molecular oxygen is examined as it pertains to surface heating. A reentry simulation is given and compared to STS-2 reentry data, and conclusions are drawn as to the implications of the recombination model toward reentry heating. A possible buffering of the heating above a critical temperature associated with the physics of the model is also discussed.

Jumper, E. J.↗
NASA NTRS1995

Vibrational and Electronic Energy Transfer and Dissociation of Diatomic Molecules by Electron Collisions

At high altitudes and velocities equal to or greater than the geosynchronous return velocity (10 kilometers per second), the shock layer of a hypersonic flight will be in thermochemical nonequilibrium and partially ionized. The amount of ionization is determined by the velocity. For a trans atmospheric flight of 10 kilometers per second and at an altitude of 80 kilometers, a maximum of 1% ionization is expected. At a velocity of 12 - 17 kilometer per second, such as a Mars return mission, up to 30% of the atoms and molecules in the flow field will be ionized. Under those circumstances, electrons play an important role in determining the internal states of atoms and molecules in the flow field and hence the amount of radiative heat load and the distance it takes for the flow field to re-establish equilibrium. Electron collisions provide an effective means of transferring energy even when the electron number density is as low as 1%. Because the mass of an electron is 12,760 times smaller than the reduced mass of N2, its average speed, and hence its average collision frequency, is more than 100 times larger. Even in the slightly ionized regime with only 1% electrons, the frequency of electron-molecule collisions is equal to or larger than that of molecule-molecule collisions, an important consideration in the low density part of the atmosphere. Three electron-molecule collision processes relevant to hypersonic flows will be considered: (1) vibrational excitation/de-excitation of a diatomic molecule by electron impact, (2) electronic excitation/de-excitation, and (3) dissociative recombination in electron-diatomic ion collisions. A review of available data, both theory and experiment, will be given. Particular attention will be paid to tailoring the molecular physics to the condition of hypersonic flows. For example, the high rotational temperatures in a hypersonic flow field means that most experimental data carried out under room temperatures are not applicable. Also, the average electron temperature is expected to be between 10,000 and 20,000 K. Thus only data for low energy electrons are relevant to the model.

Huo, Winifred M.↗
NASA NTRS2013

Compound Specific Hydrogen Isotope Composition of Type II and III Kerogen Extracted by Pyrolysis-GC-MS-IRMS

The use of Hydrogen (H) isotopes in understanding oil and gas resource plays is in its infancy. Described here is a technique for H isotope analysis of organic compounds pyrolyzed from oil and gas shale-derived kerogen. Application of this technique will progress our understanding. This work complements that of Pernia et al. (2013, this meeting) by providing a novel method for the H isotope analysis of specific compounds in the characterization of kerogen extracted by analytically diverse techniques. Hydrogen isotope analyses were carried out entirely "on-line" utilizing a CDS 5000 Pyroprobe connected to a Thermo Trace GC Ultra interfaced with a Thermo MAT 253 IRMS. Also, a split of GC-separated products was sent to a DSQ II quadrupole MS to make semi-quantitative compositional measurements of the extracted compounds. Kerogen samples from five different basins (type II and III) were dehydrated (heated to 80 C overnight in vacuum) and analyzed for their H isotope compositions by Pyrolysis-GC-MS-TC-IRMS. This technique takes pyrolysis products separated via GC and reacts them in a high temperature conversion furnace (1450 C) which quantitatively forms H2, following a modified method of Burgoyne and Hayes, (1998, Anal. Chem., 70, 5136-5141). Samples ranging from approximately 0.5 to 1.0mg in size, were pyrolyzed at 800 C for 30s. Compounds were separated on a Poraplot Q GC column. Hydrogen isotope data from all kerogen samples typically show enrichment in D from low to high molecular weight compounds. Water (H2O) average deltaD = -215.2 (V-SMOW), ranging from -271.8 for the Marcellus Shale to -51.9 for the Polish Shale. Higher molecular weight compounds like toluene (C7H8) have an average deltaD of -89.7 0/00, ranging from -156.0 for the Barnett Shale to -50.0 for the Monterey Shale. We interpret these data as representative of potential H isotope exchange between hydrocarbons and sediment pore water during formation within each basin. Since hydrocarbon H isotopes readily exchange with water, these data may provide some useful information on gas-water or oil-water interaction in resource plays, and further as a possible indicator of paleo-environmental conditions. Alternatively, our data may be an indication of H isotope exchange with water and/or acid during the kerogen isolation process. Either of these interpretations will prove useful when deciphering H isotope data derived from kerogen analysis. More experiments are planned to discern these two or other possible scenarios.

Socki, Richard A.↗
NASA NTRS1993

Validation of multi-temperature nozzle flow code NOZNT

A computer code NOZNT (Nozzle in n-Temperatures), which calculates one-dimensional flows of partially dissociated and ionized air in an expanding nozzle, is tested against five existing sets of experimental data. The code accounts for: a) the differences among various temperatures, i.e., translational-rotational temperature, vibrational temperatures of individual molecular species, and electron-electronic temperature, b) radiative cooling, and c) the effects of impurities. The experimental data considered are: 1) the sodium line reversal and 2) the electron temperature and density data, both obtained in a shock tunnel, and 3) the spectroscopic emission data, 4) electron beam data on vibrational temperature, and 5) mass-spectrometric species concentration data, all obtained in arc-jet wind tunnels. It is shown that the impurities are most likely responsible for the observed phenomena in shock tunnels. For the arc-jet flows, impurities are inconsequential and the NOZNT code is validated by numerically reproducing the experimental data.

Park, Chul↗
NASA NTRS1982

Science support for the atmospheric trace molecule spectroscopy (ATMOS) experiment

The experiment is a satellite solar occultation interferometer spectrometer experiment under development for flight on Spacelab 3. Launch is expected in March 1985. ATMOS will provide high spectral resolution (0.02/cm) and high spatial resolution (2 km from Shuttle altitude) data over the spectral range from 2 micrometers to 16 micrometers. This region of the spectrum is rich in absorption features of major and minor trace gases which are critical to the understanding of the chemistry and physics of the Earth's upper atmosphere. The broad objectives of the ATMOS experiment are to: identify and measure, on a global scale, the volume mixing ratios of known and newly discovered molecular species; determine vertical profiles for these species; and provide spectral data on the atmosphere for use in optimizing the design of future instruments to monitor specific gases.

Rinsland, C. P.↗
NASA NTRS2004

QCM Thermo-Gravimetric Analysis (QTGA) Comparisons

The ASTM E-1559 apparatus has been used for years at NASA/Goddard Space Flight Center (GSFC) to determine in situ outgassing rate information, as well as pertinent in situ TML and multiple VCM values. The apparatus also affords the opportunity to experimentally compute the evaporation rates of molecular species that are reemitted as the Quartz Crystal Microbalances (QCMs) are gradually warmed up at some controlled temperature. Typically the molecular mass that accumulates onto the test QCMs are a compilation of species that are outgassing from the sample due to their respective activation energies and the desorption processes that the sample undergoes at various tested temperatures. It has been speculated that if there is too much molecular buildup of condensed water vapor (ice) onto the QCM crystal that a significantly higher temperature would be needed to break these "ice" bonds. ASTM E-1559 data plots will be used to demonstrate the thermogravimetric effects of water and other miscible molecular species with various water/ice thicknesses and at different evaporation rates.

Rosecrans, Glenn↗
NASA NTRS1996

A mutation in protein phosphatase 2A regulatory subunit A affects auxin transport in Arabidopsis

The phytohormone auxin controls processes such as cell elongation, root hair development and root branching. Tropisms, growth curvatures triggered by gravity, light and touch, are also auxin-mediated responses. Auxin is synthesized in the shoot apex and transported through the stem, but the molecular mechanism of auxin transport is not well understood. Naphthylphthalamic acid (NPA) and other inhibitors of auxin transport block tropic curvature responses and inhibit root and shoot elongation. We have isolated a novel Arabidopsis thaliana mutant designated roots curl in NPA (rcn1). Mutant seedlings exhibit altered responses to NPA in root curling and hypocotyl elongation. Auxin efflux in mutant seedlings displays increased sensitivity to NPA. The rcn1 mutation was transferred-DNA (T-DNA) tagged and sequences flanking the T-DNA insert were cloned. Analysis of the RCN1 cDNA reveals that the T-DNA insertion disrupts a gene for the regulatory A subunit of protein phosphatase 2A (PP2A-A). The RCN1 gene rescues the rcn1 mutant phenotype and also complements the temperature-sensitive phenotype of the Saccharomyces cerevisiae PP2A-A mutation, tpd3-1. These data implicate protein phosphatase 2A in the regulation of auxin transport in Arabidopsis.

Non-NASA Center↗
NASA NTRS1985

A wide latitude CO survey of molecular clouds in the III galactic quadrant

Molecular clouds in the third galactic quadrant from 180-280 galactic longitude were surveyed in the 115.271 GHz line of CO at an angular resolution of 0.5 deg. In galactic latitude the survey covers from b = -5 to +5 deg, with a few extensions to higher latitudes. A preliminary analysis of the data allowed the determination of distances and masses of at least 30 molecular clouds related to the Perseus arm and to the Cygnus, or outer, arm. The studied clouds are located between 2.5 kpc and 10.7 kpc from the sun with most of the masses between 30,000-700,000 solar masses, and only three up to two million solar masses. The most interesting result comes from the distribution of the clouds distance from the galactic plane that indicates a warp in the arms to which these clouds belong.

May, J.↗