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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Molecular-Beam Chopper and Four-Channel Amplifier

Molecular-beam chopper phase controller and timing interface is subsystem of four-stage, differentially pumped, modulated molecular-beam/mass spectrometer. Subsystem maintains accurate phase control and timing for repetitive signal averaging over several hours of operation. Chopper phase controller/ timing interface and four-channel programable time-multiplexed amplifier provide substantial improvements in attainable signal-to-noise ratio, detection limit, and accuracy of molecular-beam/mass-spectrometer system.

Adams, B. R.↗
NASA NTRS1984

Observations of Highly-ionized Interstellar Iron

The spectra of 24 stars, including 5 at distances d 200 pc, have been observed in the regions of the coronal Fe X lambda 6375 and Fe X lambda 5303 lines at detection limits near an equivalent width of 1 mA in the best cases. In general agreement with predictions based on a multi-phase model of the interstellar medium, no absorption which can be attributed to Fe X or Fe X4 ions in hot interstellar gas emitting the soft X-ray background is seen in any of these spectra, except for two. Toward lambda Cephei an absorption line near lambda 6375 is measured with an equivalent width of 8.1 + or - 2 mA, a width corresponding to 20 + or - 5 km/sec or a temperature T or = (0.5 + or - 0.25) x 10 to the 6th power K, and, if it is caused by Fe X ions, a radial velocity of -355 km/sec. On that hypothesis, the interstellar gas constitutes at least 63% of the column density of gas along this light path.

Hobbs, L. M.↗
NASA NTRS1984

Extreme incompatibility of Pb during the crystallization of magmatic iron meteorites

The partitioning behavior of Pb in the three-phase system metal-troilite-sulfide liquid was investigated. Microscopic examination and electron microprobe analysis of a polished section showed three phases--Fe metal, troilite and an Fe-S-Pb-O metallic liquid. The Pb concentration of the metallic liquid was 1.4 wt.%; the Pb contents of both the troilite and the Fe metal were below the detection limit of the electron probe. To better define the Pb concentrations of the solid phases, the same sample was analyzed for Pb and Fe using the M.I.T., Harvard and Brown ion microprobe. Even at this level of precision, some conclusions and speculations are possible: (1) The D(Pb) (troilite/metallic liquid) is low (.01 to .001) and, contrary to expectation, troilite, like metal, excludes Pb very effectively during the crystallization of metallic liquids; (2) Pb in iron meteorites is conceivably concentrated in trace phases which are less susceptible to contamination than metal and troilite; and (3) taken at face value D(Pb)(metal/troilite) is 0.1, but given the Pb and Fe ion yields from simple endmember phases (Fe, FeS, Pb, PbS), this D is more likely to be 0.05 to 0.03.

Jones, J. H.↗
NASA NTRS1985

History, design and performance of the space shuttle hazardous gas detection system

The Hazardous Gas Detection System (HGDS) is designed to detect leaks hich could result in pre-launch or in-flight fires or explosions resulting from the presence of cryogenic rocket propellants. The historical development, design, and performance of the HGDS is discussed. Data for response time, detection limits, accuracy, and drift are presented. Finally, present and future applications are discussed, and some general conclusions are drawn.

Helms, W. R.↗
NASA NTRS1984

Absolute OH absorption cross sections (for lidar measurements)

Experimental data are employed to calculate absorption cross sections for several rotational lines in the OH A-X system. The cross sections are computed as functions of the spectral and line widths and temperature of a laser beam, and account for lifetimes and branching ratios. Detection limits for the P1(2) transition of the (1,0) band were examined. The oscillator strengths and cross-sections obtained are important for quantifying OH concentrations in the stratosphere from lidar return signals.

Mcgee, T. J.↗
NASA NTRS1984

Optical interstellar absorption lines toward 29 stars

Observations of optical interstellar absorption lines of Ti II, Ca II, and/or Na I acquired at an instrumental resolution typically of 5.6 km/s are reported for 29 stars. The data were recorded primarily with a Digicon detector and achieve 2 sigma detection limits generally near an equivalent width of 1 mA. The primary purpose of the observations is, in combination with previously published data, to provide a comprehensive, high-sensitivity survey of Ti II, Ca II, and Na I absorption at all velocities, toward 41 stars for which a correspondingly complete survey of certain ultraviolet interstellar lines also is available. New high-velocity optical interstellar lines at /v(LSR)/ greater than about 25 km/s are found toward four of the 29 stars.

Hobbs, L. M.↗
NASA NTRS1984

Measuring spectra of arid lands

The principles, instrumentation and data acquisition and interpretation techniques employed in multispectral remote sensing for geological applications are surveyed. Sensing is based on exact measurements of electromagnetic radiation interacting with atoms and molecules in the sensed scene. Absorbed radiation can be used to identify elements in the near-IR bands and emitted or reflected energy can be sensed in the mid- and far-IR. Sunlight normally serves as the exciting source. Wavelength absorptance and emittance characteristics are distinct for the various elements and molecules such as transition metal ions, water, carbonates, etc. The bands for identifying different materials are determined in the laboratory, followed by ground truth field tests. Several hand-held radiometers and spectrometers have been developed for the field trials. Each instrument usually has a limited detection range and serves for developing a data base for subtle distinctions among contiguous minerals with similar radiometric signatures. The data serve for calibrating first airborne and then satellite sensors, e.g., the Landsat MSS and Thematic Mapper. Instruments are also being tested using the Orbiter as the test platform.

Kahle, A. B.↗
NASA NTRS1986

multiplex gas chromatography: A novel analytical technique for future planetary studies

Determination of molecular species comprised of the biogenic elements in the atmospheres of planets and moons of the solar system is one the foremost requirements of the exobiologist studying chemical evolution and the origin of life. Multiplex chromatography is a technique where many samples are pseudo-randomly introduced to the chromatograph without regard to elution of preceding components. The resulting data are then reduced using mathematical techniques such as cross correlation or Fourier Transforms. To demonstrate the utility of this technique for future solar system exploration, chemical modulators were developed. Several advantages were realized from this technique in combination with these modulators: improvement in detection limits of several orders of magnitude, improvement in the analysis of complex mixtures by selectively modulating some of the components present in the sample, increase in the number of analyses that can be conducted in a given period of time, and reduction in the amount of expendables needed to run an analysis. In order to apply this technique in a real application, methane in ambient air was monitored continuously over a period of one week. By using ambient air as its own carrier all expendables beyond power were eliminated.

Valentin, J. R.↗
NASA NTRS1985

Nitric oxide measurements at a nonurban eastern United States site - Wallops instrument results from July 1983 GTE/CITE mission

The NASA Goddard Space Flight Center/Wallops Flight Facility nitric oxide detector used in the July 1983 GTE/CITE 1 instrument intercomparison is a chemiluminescence system which, at that time, had a detection limit of about 2 pptv (S/N = 1) for 60-s integrations. A substantial amount of NO concentration data was taken with this system at Wallops Island, VA, a site that should be typical of numerous nonurban coastal areas of the eastern United States and for which little other data are available. Midday concentrations under conditions of northwest winds averaged about 200 pptv, a value low enough to imply lower NO(x) amounts than are generally thought to exist in the eastern United States. During a 2-day period when the sampled air had spent 1-2 days over the Atlantic Ocean, average NO concentrations of 70 and 33 ptv were observed. Measurements at night indicated an average NO concentration of 16 pptv under wind conditions making contamination of the sampled air by local anthropogenic sources unlikely.

Torres, A. L.↗
NASA NTRS1986

The discovery of dust trails in the orbits of periodic comets

Analysis of data from the Infrared Astronomical Satellite has yielded evidence for narrow trails of dust coincident with the orbits of periodic comets Tempel 2, Encke, and Gunn. Dust was found both ahead of and behind the orbital positions of these comets. This dust was produced by the low-velocity ejection of large particles during perihelion passage. More than 100 additional dust trails are suggested by the data, almost all near the detection limits of the satellite. Many of these dust trails may be derived from previously unobserved comets.

Sykes, M. V.↗
NASA NTRS1987

Radio continuum observations of early- and late-type spiral galaxies

Two complete subsamples of early and late type spiral galaxies were mapped with the VLA in order to explore their radio and optical properties. The choice of the samples is explained, and the observational procedure and data reduction are described. The detection rate was 97 percent, with a detection limit of the order of 1-2 mJy. Total intensity data at 20 cm are presented for the whole sample, and 6 cm data for 11 galaxies. The results are presented in the form of tables and radio contour maps, and are discussed in comparison with previous work.

Gioia, Isabella M.↗
NASA NTRS1987

In situ ozone instrumentation for 10-Hz measurements - Development and evaluation

The development of the fast-response ozone detector for the Electra aircraft is described. The selection of a technique to meet the design goal of 10-Hz detection is examined in terms of detection principles, instrument sampling parameters, signal conditioning, and aircraft and sampling environment. An instrument which employs a NO technique for detection of ozone with a reaction chamber volume of 16 cu cm, a pressure of 60 torr, and a sample flow of 1000 standard cu cm/min was developed. Laboratory and flight testings of the detector were conducted in order to evaluate its performance. The data reveal that the fast-response ozone detector is highly reliable with a response of 0.1 sec to 90 percent of reading, has a lower detection limit of 1 ppbv, and an S/N of 20 at 20 ppbv ozone.

Gregory, G. L.↗
NASA NTRS1988

Room-temperature codeposition growth technique for pinhole reduction in epitaxial CoSi2 on Si (111)

A solid-phase epitaxy has been developed for the growth of CoSi2 films on Si (111) with no observable pinholes (1000/sq cm detection limit). The technique utilizes room-temperature codeposition of Co and Si in stoichiometric ratio, followed by the deposition of an amorphous Si capping layer and subsequent in situ annealing at 550-600 C. CoSi2 films grown without the Si cap are found to have pinhole densities of (1-10) x 10 to the 7th/sq cm when annealed at similar temperatures. A CF4 plasma-etching technique was used to increase the visibility of the pinholes in the silicide layer.

Lin, T. L.↗
NASA NTRS1988

A white dwarf companion to the main-sequence star 4 Omicron(1) Orionis and the binary hypothesis for the origin of peculiar red giants

Ultraviolet spectra of the peculiar red giants (PRGs) called MS stars are investigated, and the discovery of a white dwarf (WD) companion to the MS star 4 Omicron(1) Orionis is reported. The observations and data analysis are discussed and compared with those for field WDs in order to derive parameters for the WD and the luminosity of the primary. Detection limits for the other MS stars investigated are derived, and the binary hypothesis for PRGs is reviewed.

Ake, Thomas B.↗
NASA NTRS1988

Application of the V/V(max) test to gamma-ray bursts

The V/V(max) test applied to a well-defined sample of objects provides a quantitative test for the uniformity of the space distribution of the parent population of the objects. The application of this test to gamma-ray bursts is discussed. In contrast to tests involving size-frequency distributions, the V/V(max) test is independent of variations in sensitivity. The use of the V/V(max) test on a small sample of bursts from the HEAO A-4 experiment is illustrated. It is urged that experimenters publish the detection limit for each recorded gamma-ray burst.

Schmidt, Maarten↗
NASA NTRS1988

Characterization of a turbomolecular-pumped magnetic sector mass spectrometer

A Perkin Elmer MGA-1200, turbomolecular-pumped, magnetic sector, multiple gas analyzer mass spectrometer with modified inlet for fast response was characterized for the analysis of hydrogen, helium, oxygen and argon in nitrogen and helium background gases. This instrument was specially modified for the Vanderberg AFB SLC-6 Hydrogen Disposal Test Program, as a part of the Hydrogen Sampling System (H2S2). Linearity, precision, drift, detection limits and accuracy among other analytical parameters for each of the background gas were studied to evaluate the performance of the instrument. The result demonstrates that H2S2 mass spectrometer is a stable instrument and can be utilized for the quantitative analytical determination of hydrogen, helium, oxygen and argon in nitrogen and helium background gases.

Mehta, Narinder K.↗
NASA NTRS1988

Search for the Tunguska event in the Antarctic snow

The Tunguska explosion in 1908 is supposed to have been produced by the impact of a small celestial body. The absence of any identifiable crater together with the huge energy released by the event suggest that the impactor exploded in midair and that its material was widely spread over the Earth. The short term contribution of such exceptional events to the total accretion rate of extraterrestrial material by the Earth could be significant. Samples were chosen in a core electromechanically drilled in 1984 near South Pole Station. There, the low temperatures, preventing melting all year long, and the nearly regular snow fall rate provide good conditions for a reliable continuous record of any infalling material. In many samples Ir was below the detection limit of the instrumentation. The iridium infall averaged over 45 samples is given. In a few samples the iridium content is significantly higher than the average: the frequency and amplitude of such fluctuations can be explained by the presence on some filters of finite size cosmic particles. No significant systematic increase above the average level is observed in the part of the core corresponding to the Tunguska event. The two major results of this study are: (1) The presence of Tunguska explosion debris in the Antarctic snow is not confirmed; and (2) The estimate of the average iridium infall, is an order of magnitude lower than the Ganapathy's background but is close to the values measured in Antarctic snow and atmospheric samples by Takahashi et al. The results are also consistent with the flux of micrometeoroids deduced from optical and radar observations or derived from the study of Greenland cosmic dust collection but are lower than the flux at mid-latitude measured in paleocene-oligocene sediments from the central part of the Pacific Ocean.

Rocchia, R.↗
NASA NTRS1988

Metal with anomalously low Ni and Ge concentrations in the Allan Hills A77081 winonaite

The Ge content of metal in the Allan Hills A77081 winonaite was determined by high-sensitivity electron microprobe analysis. By optimizing analytical conditions for Ge determination, a detection limit of about 75 ppm could be achieved. In A77081 some small kamacite grains contain less Ni and Ge and more Co than coarse-grained metal. These small grains are always associated with sulfide, raising the possibility that anomalous metal is related to eutectic melting. However, when published partition coefficients for Ni and Ge in the Fe-Ni-S system are used to model fractionation of these elements during eutectic melting, one finds that secondary metal should be enriched in Ni and depleted in Ge. Thus, the positive Ni-Ge correlation found in this study is the opposite of the expected trend. No explanation for this discrepancy has yet been found. Nonetheless, the existence of anomalous metal is an indication that A77081, and probably other winonaites as well, have undergone some fractionation. This supports the notion that the high-temperature history of winonaites is related to the formation of IAB iron meteorites, whose silicate inclusions are very similar to winonaites.

Kracher, Alfred↗