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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The search for extraterrestrial life: Recent developments; Proceedings of the Symposium, Boston University, MA, June 18-21, 1984

The conference presents papers on the history of the search for extraterrestrial life, the scientific rationale and methods used in the search for other planetary systems, the detection of distant planets with the Space Telescope, planetary searches using optical astrometric interferometers, and infrared spectral identification of complex organic molecules in interstellar grains. Also considered are universal protein ancestors from hydrogen cyanide and water, astronomical sources of polarized light and their role in determining molecular chirality on earth, the universal diagrams and life in the universe, the precambrian evolution of terrestrial life and a thermodynamic approach to the occurrance and appearance of galactic life forms. Papers are also presented on the Ohio Seti program, lunar reflections of terrestrial radio leakage, the multichannel spectrum analyzer, software implementation of detection algorithms for the MCSA, the Serendip II design, galactic colonization and competition in a young galactic disk, implications of ancient and future migrations, extraterrestrial intelligence, the ineviability and the possible structures of supercivilizations, planetary, interplanetary and interstellar organic matter, and universal aspects of biological evolution.

Papagiannis, M. D.↗
NASA NTRS1986

International Halley Watch: Discipline specialists for radio science

Some 34 radio observatories in 18 countries are participating in the Radio Science Net of the International Halley Watch. Approximately 100 radio astronomers are contributing to this effort, which has included observations of comets P/Crommelin and P/Giacobini-Zinner as well as P/Halley. It is clear that the record of data for the 18 cm OH ground state lambda doublet, which provides fundamental information on the gas production rate, kinematics, and potentially the magnetic field in the coma, will be vastly more complete and of higher accuracy than has even been obtained on any previous comet. The coverage by a number of radio observatories will enable short period variations to be studied and correlated with simultaneous data obtained at other wavelengths. Likewise, the first definitive detection of the important parent molecule hydrogen cyanide in a comet was obtained and is being studied by groups in the United States, Sweden, and France. The first detection of the comet with the Very Large Array telescope operated by NRAO was achieved and has produced exciting results for the distribution of emission at high angular resolution from the OH radical. At this writing data are still being obtained and being processed, and there are still strong indications that exciting information will be obtained from radar studies of P/Halley and from searches for additional parent molecules.

Irvine, W. M.↗
NASA NTRS1985

Chemistry of the outer planets: Investigations of the chemical nature of the atmosphere of Titan

It is clear from the experiments that a variety of complex organic models can be produced by lightning in a Titan-like gas mixture. The dominant products were found to be acetylene and hydrogen cyanide, with smaller amounts of many other species. Any aerosol produced by lightning inititated process will consist of a complex mixture of organic compounds, many of which should easily be identified by pyrolytic gas chromatography. Work will continue to expand the data base of molecules produced by lightning and other processes in order to assist in the design of appropriate analytical instruments for the upcoming Saturn/Titan mission and any other planetary probes.

Scattergood, Thomas W.↗
NASA NTRS1988

Rocket- and aircraft-borne trace gas measurements in the winter polar stratosphere

In January and February 1987 stratospheric rocket- and aircraft-borne trace gas measurements were done in the North Polar region using ACIMS (Active Chemical Ionization Mass Spectrometry) and PACIMS (PAssive Chemical Ionization Mass Spectrometry) instruments. The rocket was launched at ESRANGE (European Sounding Rocket Launching Range) (68 N, 21 E, Northern Sweden) and the twin-jet research aircraft operated by the DFVLR (Deutsche Forschungs- und Versuchs-anstalt fuer Luft- und Raumfahrt), and equipped with a mass spectrometer laboratory was stationed at Kiruna airport. Various stratospheric trace gases were measured including nitric acid, sulfuric acid, non-methane hydrocarbons (acetone, hydrogen cyanide, acetonitrile, methanol etc.), and ambient cluster ions. The experimental data is presented and possible implications for polar stratospheric ozone discussed.

Arnold, F.↗
NASA NTRS1988

Lightning production of hydrocarbons and HCN on Titan - Laboratory measurements

Experimental measurements have been obtained for the chemical yields of hydrogen cyanide, acetylene, ethylene, ethane, and propane from simulated lightning discharges, in order to ascertain whether lightning in the troposphere of Titan may be contributing to the hydrocarbon inventory. A comparison of these results with those obtained on the basis of thermodynamic equilibrium considerations shows substantial discrepancies and implies that thermodynamic equilibrium theories are inadequate. The production of ethylene by lightning and its subsequent stratospheric diffusion nevertheless appears to be one reasonable mechanism.

Borucki, W. J.↗
NASA NTRS1989

Halley's polymeric organic molecules

The detection of polymeric organic compounds in the mass spectrum of Comet Halley obtained with the Positive Ion Cluster Composition analyzer on Giotto are examined. It is found that, in addition to polyoxymethylene, other polymers and complex molecules may exist in the comet. It is suggested that polymerized hydrogen cyanide may be a source for the observed CN and NH2 jets.

Huebner, W. F.↗
NASA NTRS1990

XANES and EXAFS study of Au-substituted YBa2Cu3O(7-delta)

The near-edge structure (XANES) of the Au L3 and Cu K edges of YBa2Au(0.3)Cu(2.7)O(7-delta) was studied. X ray diffraction suggests that Au goes on the Cu(1) site and XANES shows that this has little effect on the oxidation state of the remaining copper. The gold L3 edge develops a white line feature whose position lies between that of trivalent gold oxide (Au2O3) and monovalent potassium gold cyanide (KAu(CN)2) and whose intensity relative to the edge step is smaller than in the two reference compounds. The L3 EXAFS for Au in the superconductor resembles that of Au2O3. However, differences in the envelope of the Fourier filtered component for the first shell suggest that the local structure of the Au in the superconductor is not equivalent to Au2O3.

Ruckman, Mark W.↗
NASA NTRS1989

Carbon use efficiency in optimal environments

The short- and long-term effects of environmental changes on plant productivity are studied using a model in which yield is determined by four factors: absorption of photosynthetic photon flux, photosynthetic efficiency, respiratory carbon use efficiency, and harvest index. The characteristics of the model are reviewed. Emphasis is given to the relationship between carbon use efficiency and yield. The biochemical pathways resulting in CO2 efflux are examined, including photorespiration, cyanide-resistant respiration, and dark respiration. The possibility of measuring photosynthesis and respiration in a CELSS is discussed.

Bugbee, Bruce↗
NASA NTRS1989

Elevated temperature crack growth

Alloy 718 crack growth experiments were conducted to assess the ability of the selected path-independent (P-I) integrals to describe the elevated temperature crack growth behavior. These tests were performed on single edge notch (SEN) specimens under displacement control with multiple extensometers to monitor the specimen and crack mouth opening displacement (CMOD). The displacements in these tests were sufficiently high to induce bulk cyclic inelastic deformation of the specimen. Under these conditions, the linear elastic fracture mechanics (LEFM) parameter K does not correlate the crack growth data. The experimentally measured displacement gradients at the end of specimen gage length were used as the boundary conditions in elastic-plastic finite element method (FEM) analyses. These analyses were performed with a node release approach using CYANIDE, a GEAE FEM code, which included a gap element which is capable of efficiently simulating crack closure. Excellent correlation was obtained between the experimentally measured and predicted variation of stress and CMOD with crack length and the stress-CMOD loops for Alloy 718 tests conducted at 538 C. This confirmed the accuracy of the FEM crack growth simulation approach. The experimentally measured crack growth rate data correlated well the selected P-I integrals. These investigations have produced significant progress in developing P-I integrals as non-linear fracture mechanics parameters. The results suggest that this methodology has the potential of accurately describing elevated temperature crack growth behavior under the combined influence of thermal cycling and bulk elastic-inelastic deformation states.

Kim, K. S.↗
NASA NTRS1989

Low temperature measurement of the vapor pressures of planetary molecules

Interpretation of planetary observations and proper modeling of planetary atmospheres are critically upon accurate laboratory data for the chemical and physical properties of the constitutes of the atmospheres. It is important that these data are taken over the appropriate range of parameters such as temperature, pressure, and composition. Availability of accurate, laboratory data for vapor pressures and equilibrium constants of condensed species at low temperatures is essential for photochemical and cloud models of the atmospheres of the outer planets. In the absence of such data, modelers have no choice but to assume values based on an educated guess. In those cases where higher temperature data are available, a standard procedure is to extrapolate these points to the lower temperatures using the Clausius-Clapeyron equation. Last summer the vapor pressures of acetylene (C2H2) hydrogen cyanide (HCN), and cyanoacetylene (HC3N) was measured using two different methods. At the higher temperatures 1 torr and 10 torr capacitance manometers were used. To measure very low pressures, a technique was used which is based on the infrared absorption of thin film (TFIR). This summer the vapor pressure of acetylene was measured the TFIR method. The vapor pressure of hydrogen sulfide (H2S) was measured using capacitance manometers. Results for H2O agree with literature data over the common range of temperature. At the lower temperatures the data lie slightly below the values predicted by extrapolation of the Clausius-Clapeyron equation. Thin film infrared (TFIR) data for acetylene lie significantly below the values predicted by extrapolation. It is hoped to bridge the gap between the low end of the CM data and the upper end of the TFIR data in the future using a new spinning rotor gauge.

Kraus, George F.↗
NASA NTRS1991

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using x-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Ruckman, Mark W.↗
NASA NTRS1991

The relative importance of prebiotic synthesis on the Earth and input from comets and meteorites

The prebiotic synthesis of hydrogen cyanide and formaldehyde was studied by the action of electric discharges on various model primitive atmospheres containing CH4, CO, and CO2. Photochemical production rates would also have been important and were calculated for HCN and H2CO. A reasonable rate of synthesis of amino acids from these sources is about 10 n moles/(sq cm yr) or 0.10 moles/sq cm in 10(exp 7) yrs. This would give a concentration of 3 x 10(exp -4) M in an ocean of the present size (300 liters/sq cm). The amino acids cannot accumulate over a longer period because the entire ocean passes through the 350 C submarine vents in 10(exp 7) yrs, which decomposes all the organic compounds. A number of workers have calculated the influx of comets and meteorites on the primitive earth, both as a destructive process for organic compounds and for any life that was present, as well as a source of organic compounds. Some of the amino acids from the meteorite proposed to have hit the earth 65 x 10(exp 6) yrs ago were detected at the Cretaceous/Tertiary boundary sediments. The problem with proposing a large scale input of organic compounds from meteorites and comets is that they must survive passage through the atmosphere and impact. There are some processes that would allow survival such as showers of centimeter to meter sized meteorites and various aerodynamic braking processes for larger objects. Even if a significant amount of the organic material survived impact, the destructive processes in the hydrothermal vents would remove these compounds on the average in 10(exp 7) yrs or less. If it is assumed that the input rate was sufficient to overcome these destructive processes, then too much carbon and water, especially from comets, would have been added to the surface of the earth. It was concluded that while some organic material was added to the earth from comets and meteorites, the amount available from these sources at a given time was only a few percent of that from earth based syntheses.

Miller, S. L.↗
NASA NTRS1991

Near-edge study of gold-substituted YBa2Cu3O(7-delta)

The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using X-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

Ruckman, Mark W.↗
NASA NTRS1991

A Combustion Products Analyzer for contingency use during thermodegradation events on spacecraft

This paper will describe the Combustion Products Analyzer (CPA), which is being developed under the direction of the Toxicology Laboratory at Johnson Space Center to provide necessary data on air quality in the Shuttle following a thermodegradation incident. Using separate electrochemical sensors, the CPA monitors four gases (hydrogen fluoride/carbonyl fluoride, hydrogen chloride, hydrogen cyanide, and carbon monoxide), which were selected as the most hazardous compounds likely to be released during thermodegradation of synthetic materials. Electrochemical sensors have been available for several years; the CPA sensors, which are unique because of their small size and zero-gravity compatibility, will be described in detail.

Limero, Thomas↗
NASA NTRS1992

Comets and the origins and evolution of life; Proceedings of the Conference, Univ. of Wisconsin, Eau Claire, Sept. 30-Oct. 2, 1991

Papers are presented on comets and the formation of biochemical compounds on the primitive earth; the cometary origin of carbon, nitrogen, and water on the earth; comets as a possible source of prebiotic molecules; comet impacts and chemical evolution on the bombarded earth; and cometary supply of terrestrial organics (lessons from the K/T and the present epoch). Other papers are on a computational study of radiation chemical processing in comet nuclei, the origin of the polycyclic aromatic hydrocarbons in meteorites, the fate of organic matter during planetary accretion (preliminary studies of the organic chemistry of experimentally shocked Murchison meteorite), recent observations of interstellar molecules (detection of CCO and a limit on H2C3O), terrestrial and extraterrestrial sources of molecular monochirality, and dark matter in the solar system (hydrogen cyanide polymers).

Thomas, Paul J.↗
NASA NTRS1993

A combustion products analyzer for contingency use during thermodegradation events on spacecraft

The Toxicology Laboratory at JSC and Exidyne Instrumentation Technologies (EIT) have developed a prototype Combustion Products Analyzer (CPA) to monitor, in real time, combustion products from a thermodegradation event on board spacecraft. The CPA monitors the four gases that are the most hazardous compounds (based on the toxicity potential and quantity produced) likely to be released during thermodegradation of synthetic materials: hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen cyanide (HCN), and carbon monoxide (CO). The levels of these compounds serve as markers to assist toxicologists in determining when the cabin atmosphere is safe for the crew to breathe following the contingency event. The CPA is a hand-held, battery-operated instrument containing four electrochemical sensors, one for each target gas, and a pump for drawing air across the sensors. The sensors are unique in their small size and zero-g compatibility. The immobilized electrolytes in each sensor permit the instrument to function in space and eliminate the possibility of electrolye leaks. The sample inlet system is equipped with a particulate filter that prevents clogging from airborne particulate matter. The CPA has a large digital display for gas concentrations and warming signals for low flow and low battery conditions. The CPA has flown on 13 missions beginning with STS 41 in Oct. 1990. Current efforts include the development of a microprocessor, an improved carbon monoxide sensor, and a ground-based test program to evaluate the CPA during actual thermodegradation of selected materials.

Wilson, Steve↗
NASA NTRS1993

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

In observations with the NRAO 12m telescope at Kitt Peak, Arizona, Irvine, a new interstellar radical, CH2N, has been detected. This identification is important for the study of hydrogenation processes in the interstellar medium. In particular, although the abundance of hydrogen is some four orders of magnitude higher than that of other reactive elements in this environment, many organic molecules in quiescent clouds are very unsaturated. This is a consequence of activation barriers which cannot be overcome at the temperatures of cold clouds, even when such reactions are energetically allowed. The hydrogenation series based on the cyanide radical (HnCN) has had four members previously detected in the interstellar medium: CN (n equals O), HCN (n equals l), CH2CN (n equals 3), and CH3NH2 (n equals 5). The recent determination of the rotational spectrum of the CH2N radical through microwave spectroscopy in Japan has made possible a search for this species. In addition to its potential importance for interstellar chemistry, the CH2N radical has been proposed as a reaction intermediate for HCN production in the atmosphere of Jupiter, and as a possible species in the expanding envelopes of oxygen--rich evolved stars. We detected CH2N in the cold cloud TMC--1 where the abundance seems to be some three orders of magnitude lower than that of HCN. A tentative detection was made in the Galactic Center molecular cloud Sgr B2. To our knowledge, there are no predicted abundances of CH2N from models of interstellar chemistry.

Irvine, William M.↗
NASA NTRS1994

The submillimeter-wave spectrum of propionitrile (C2H5CN)

The laboratory millimeter-wave and submillimeter-wave rotational spectrum of propionitrile (ethyl cyanide, C2H5CN) in its ground vibrational state has been extended through J = 70 and K(sub a) = 36. Transitions measured in this study are in the frequency range 250-610 GHz. A fit of 952 transitions including 732 new measurements to a Watson A-reduced Hamiltonian has yielded a complete set of quartic and sextic distortion constants, in addition to six octic distortion constants. Internal rotation and hyperfine splittings have not been resolved, so they are not included in the analysis. Predicted transition frequencies for a large number of additional transitions of interest to radioastronomers are provided.

Pearson, J. C.↗