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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Application of an atmospheric pressure sampling mass spectrometer to chlorination reactions

An atmospheric pressure mass spectrometric sampling system, based on a free jet expansion was used to study certain M-Cl-O reactions at high temperatures. The apparatus enables the volatile species from a 1-atm chemical process to be directly identified with a mass spectrometer which operates at approx. 10 to the minus 8th power torr. Studies for both pure metals and alloys are discussed. It is shown that this mass spectrometer system aids in identifying the volatile species, and provides fundamental information on the reaction mechanism.

Jacobson, N. S.↗
NASA NTRS1986

Numerical studies of collapsing interstellar clouds

Numerical simulation of the structure and evolution of interstellar clouds was initiated. Steps were taken toward an integrated treatment of the dynamical, thermal, and chemical processes entering model calculations. A detailed study was made of radiative transfer in molecular lines to allow model predictions to be tested against empirical data. The calculations have successfully reproduced and explained several observed cloud properties, including abundances of complex molecular species and the apparent depletion of CO in dense cores.

Bodenheimer, P. H.↗
NASA NTRS1985

A striking nitrogen isotope anomaly in the Bencubbin and Weatherford meteorites

The stony-iron meteorites Bencubbin and Weatherford contain nitrogen with a ratio of nitrogen-15 to nitrogen-14 larger than normal by as much as a factor of 2. The excess nitrogen-15 may be due either to a nucleosynthetic origin or to extreme isotopic fractionation. In the former case, it may reflect failure to homogenize nitrogen-15 produced in nova explosions. In the latter case, it may reflect chemical processing at temperatures below 40 K in a presolar molecular cloud.

Prombo, C. A.↗
NASA NTRS1985

The photochemistry of the early atmosphere

The composition of the earth's present atmosphere is described. The formation of the earth from the coalescence and accretion of the refractory elements of the solar nebula is examined. Two possible compositions of the prebiological paleoatmosphere, which are a reducing atmosphere of CH4, NH3, and H2 or a mildly reducing atmosphere of H2O, CO2, and N2, and their photochemistry are analyzed. General photochemical and chemical processes are reviewed. The use of the coupled continuity-transport equation to calculate the vertical distribution of each species is discussed. A study of the photochemical process of CH4 and NH3 reveals that the reducing atmosphere could not possibly exist. An analysis of the photochemistry and chemistry of the H2O, CO2, and N2 atmosphere reveals that the photodissociation of H2O and CO2 results in a prebiotic source of O2, H2CO, and HCN, which are the components for the evolution of photosynthetic organisms and a strongly oxidizing atmosphere. The reactions which produce O2 and H2CO from H2O and CO2, and the relation between H2O and CO2 concentrations and O2 levels are investigated. The formation of O3 photochemically from O2 is explained.

Levine, J. S.↗
NASA NTRS1985

Ice in cometary grains

The presence of icy grains has important consequences for the physical and chemical processes which take place in the comae of comets. The search for the infrared signature of these icy grains is outlined. The absorption feature near 3 microns found in the coma grains of Comets Bowell and Cernis is interpreted as being due to water ice.

Campins, H.↗
NASA NTRS1986

Vertical distribution of dimethylsulphide in the marine atmosphere

The first data on the vertical distribution of dimethylsulfide (DMS) in the marine troposphere are presented. The observations agree well with the distributions predicted by a two dimensional model calculation which includes convective transport and chemical processes. This agreement supports the validity of a previous estimate of about 40 Tg-S/yr for the input of DMS from the oceans to the atmosphere, and suggests that the oxidation of DMS can contribute significantly to the SO2 levels observed in the free troposphere.

Ferek, R. J.↗
NASA NTRS1986

Toxicological safeguards in the manned Mars missions

Safeguards against toxic chemical exposures during manned Mars missions (MMMs) will be important for the maintenance of crew health and the accomplishment of mission objectives. Potential sources include offgassing, thermodegradation or combustion of materials, metabolic products of crew members, and escape of chemical from containment. Spacecraft maximum allowable concentration (SMAC) limits will have to be established for potential contaminants during the MMMs. The following factors will be used in establishing these limits: duration of mission, simultaneous exposure to other contaminants, deconditioning of crew members after long periods of reduced gravity, and simultaneous exposure to ionizing radiation. Atmospheric contaminant levels in all compartments of the transit spacecraft and Manned Mars Station (MMS) will be monitored at frequent intervals with a real time analyzer. This analyzer will be highly automated, requiring minimal crew time and expertise. The atmospheric analyzer will find other usages during the MMMs such as analyzing Martian atmospheres and soils, exhaled breath and body fluids of crew members, and reaction products in chemical processing facilities.

Coleman, Martin E.↗
NASA NTRS1987

Validation of SAM 2 and SAGE satellite

Presented are the results of a validation study of data obtained by the Stratospheric Aerosol and Gas Experiment I (SAGE I) and Stratospheric Aerosol Measurement II (SAM II) satellite experiments. The study includes the entire SAGE I data set (February 1979 - November 1981) and the first four and one-half years of SAM II data (October 1978 - February 1983). These data sets have been validated by their use in the analysis of dynamical, physical and chemical processes in the stratosphere. They have been compared with other existing data sets and the SAGE I and SAM II data sets intercompared where possible. The study has shown the data to be of great value in the study of the climatological behavior of stratospheric aerosols and ozone. Several scientific publications and user-oriented data summaries have appeared as a result of the work carried out under this contract.

Kent, G. S.↗
NASA NTRS1986

Dust and neutral gas modeling of the inner atmospheres of comets

This paper summarizes the present, preencounter understanding of the physical and chemical processes controlling the inner (r less than 1000 km) region of cometary atmospheres. Special emphasis was attached to compiling a self-consistent set of governing equations. This review is aimed at readers who want to understand the present status of the mantle and coma regions and/or who want to develop new, next generation models which will be needed as the large volume of new observational data will become available in the near future.

Gombosi, T. I.↗
NASA NTRS1986

Further interpretation of satellite measurements of Antarctic total ozone

Both dynamical and chemical mechanisms have been advanced to explain the decrease in total ozone in the Antarctic spring. Further analysis of satellite measurements show that during any one year, the September decline in total ozone near the South Pole is compensated by an increase at midlatitudes. The total ozone amount from 44 deg S to the pole remains almost unchanged from August through November even though both the polar and midlatitude values reach extremes during this period. These observations suggest that the variations within the spring season in south polar total ozone are governed by dynamical redistribution rather than chemical processes.

Stolarski, Richard S.↗
NASA NTRS1986

The dayglow of the O2 atmospheric band system

The dayglow of the O2 atmospheric O2(1Sigma) band system has been simulated by taking into account the three main production mechanisms of the O2(1Sigma) state resonance fluorescence, a photochemical term due to quenching of O(1D), and a pure chemical process. Values of the emission rate, which are involved in the resonant scattering of the O2 atmospheric bands (A, B, and gamma), have been obtained as a function of altitude (0-120 km) and solar zenith angle using a line-by-line calculation. The values of the emission rate, along with updated rate coefficients, have been used in the calculation of the production rate of O2(1Sigma) and the volume emission rate of the (O2 1Sigma, v prime = 0)-(O2 3Sigma, v double prime = 0) transition. The results of these calculations are compared to observational measurements and are found to be in excellent agreement.

Bucholtz, A.↗
NASA NTRS1986

Current program to investigate phenomena in a microgravity environment

Current NASA Microgravity Science and Applications Division Shuttle and terrestrial experiments to acquire basic data for space-based materials processing activities are summarized. The research is carried out to increase the understanding and to improve ground-based and space-based processing, to enhance the understanding of basic physical phenomena, and to characterize the forces which effect low-gravity processing. The main areas of research are crystal growth, metallic alloy solidification, bioseparation processes, blood rheology, containerless processing, and studies of combustion processes, chemical and transport phenomena, cloud microphysics and fluid behavior and surface phenomena in microgravity. Specific experiments, which exemplify the research goals and were performed on KC-135 flights along Keplerian trajectories and on Shuttle missions, are described.

Oran, William A.↗
NASA NTRS1987

Far-infrared and submillimeter observations of interstellar clouds

Research in the use of FIR and sub-mm lines to provide data relevant to astrochemistry is examined. Spectroscopic features in the FIR and sub-mm are dominated by transitions from species of atoms and atomic ions, metal hydrides, and heavy molecules. The data of Lester et al.(1983) and Dinerstein et al. (1984) on the N/O abundance ratio are discussed. The N/O abundance ratio is analyzed as a function of the galactic radius, and the procedure for determining the N/O abundance ratio from the FIR and sub-mm lines is given. The conditions at the surface of molecular clouds and the chemical profile of molecular clouds are studied in the forbidden lines O I 63.18 and 145.53 microns and the forbidden line C II 157.74 microns. Results of recent FIR/sub-mm observations of post-shocked gas which relate to modeling the chemical processing that occurs in the wake of shock waves are considered.

Melnick, Gary↗
NASA NTRS1986

Atmospheres and ionospheres of the outer planets and their satellites

Essential aspects of physical and chemical processes in the atmospheres and ionospheres of the outer planets are examined in an introductory overview of current knowledge, intended both for graduate students of planetary science and for practicing scientists. Chapters are devoted to bulk atmospheric compositions, thermal structures, cloud structures, vertical mixing, photochemistry, the ionospheres, and the satellites. Measurement data are compiled in tables, and extensive graphs and diagrams are provided.

Atreya, Sushil K.↗
NASA NTRS1987

Steady state flow/field model of solar wind interaction with Venus - Global implications of local effects

Physical and chemical processes in the Venus ionosphere driven by the interaction of the solar wind with the atmosphere of Venus are described, and a model describing the interrelationships of these processes in a self-consistent manner is formulated. It is shown that the magnetic field configuration of the ionosphere is a steady state global structure which results from a combination of a large-scale 'open' current system connecting through the ionopause to the postshock solar wind and two small-scale 'closed' current systems entirely confined within the ionosphere and generated by ionospheric flows and shears. A previously detected ionospheric layer in O2(+) near 170 km altitude is shown to be a new type of ionospheric layer resulting from transition of solar-wind-driven vertical flow to velocities approaching Mach 1.

Cloutier, P. A.↗
NASA NTRS1986

Vacuum pumps and systems: A review of current practice

A review of the fundamental characteristics of the many types of vacuum pumps and vacuum pumping systems is given. The optimum pumping range, relative cost, performance limitations, maintenance problems, system operating costs and similar subjects are discussed. Experiences from the thin film deposition, chemical processing, material handling, food processing and other industries, as well as space simulation are used to support conclusions and recommendations.

Giles, Stuart↗
NASA NTRS1987

Theory and observations of cometary ionospheres

The basic physical and chemical processes responsible for the makeup of cometary ionospheres are discussed in the framework of relevant in situ measurements on the Halley and Giacobini-Zinner comets, as well as recent theoretical models of cometary ionospheres. Special attention is given to physical processes responsible for the formation of the contact surface (CS), which is that surface where the magnetic field becomes zero or extremely small and which separates the field-free ionosphere and the magnetized plasma on the outside. Results of in situ observations indicate that the plasma just outside the CS is just as ionospheric in nature as the 'classical' ionospheric plasma residing within this surface. An expression for the magnetic field in this region is derived.

Cravens, T. E.↗