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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Observations of the 157.7 micron (C II) emission from the galactic H II regions W3 and W51

The 157.7 micron ground-state fine-structure transition of singly ionized carbon was detected from three positions, each in galactic H II region W3 and W51. These findings show that this emission goes beyond the H II regions and the carbon recombination region in each source. In addition these observations establish a lower limit to the luminosity in the 157.7 micron (C II) line of 360 solar luminosity from W3 and 41 solar luminosity from W51. Mechanisms for 157.7 micron-line excitation are discussed, and it is noted that a substantial part of the observed emission originates in the thin carbon recombination line-emitting region which borders on the H II regions and the warm atomic and molecular gas at the surface of neighboring molecular clouds. It is proposed that excitation by electrons present in the diffuse gas surrounding W51 contributes to the extended 157.7 micron (C II) line emission from this region. It was found that the (C II)FIR continuum ratios for W3 and W51 are in agreement with those of other galactic H II regions.

Melnick, G.↗
NASA NTRS1986

C II forbidden-line 158 micron mapping in Sagittarius A Rotation curve and mass distribution in the galactic center

Based on data obtained with the NASA Kuiper Airborne Observatory 91.4 cm telescope, the 158-micron fine structure line emission of C(+) is mapped near the galactic center. The strongest emission comes from a 10-pc FWHM diameter disk centered on Sgr A West whose dominant motion is rotation. Extended C(+) emission is also found from the +50 km/s galactic center molecular cloud, and a second cloud at v(LSR) of about -35 km/s. The rotation curve and mass distribution within 10 pc of the galactic center are derived, and the C(+) profiles show a drop-off of rotation velocity between 2 and 10 pc. A mass model is suggested with 2-4 million solar masses in a central point mass, and a M/L ratio of the central stellar cluster of 0.5 solar masses/solar luminosities, suggesting a large abundance of giants and relatively recent star formation in the center.

Lugten, J. B.↗
NASA NTRS1986

The SIR-C ground data system: Digital processor, data products, information flow

The SIR-C (Shuttle Imaging Radar) instrument will collect both C-Band and L-Band data with each frequency band consisting of direct (HH or VV) and cross-polarized (HV or VH) data. Considering all possible combinations as many as eight different data channels will be available for any given target area. This data will be digitized and formatted on-board for direct downlink via the Tracking and Data Relay Satellite System (TDRSS), or it will be buffered through on-board high density digital recorders for storage or transmission when TDRSS is available. The data is received by the TDRSS ground station at White Sands and is nominally relayed via DOMSAT to the high data rate recording facility at GSFC. The tapes are then shipped to JPL for processing into imagery and eventual distribution to the SIR-C investigators.

Curlander, John C.↗
NASA NTRS1986

NASA C-141/KAO Comet Halley observations

As part of NASA's Airborne Astronomy Program, research teams studied the infrared emissions of comet Halley before and after perihelion from NASA's C-141 Kuiper Airborne Observatory (KAO) and from NASA's Lear Jet Observatory (LJO). The objectives were to determine the presence of water vapor and other molecules and the composition of dust in the coma and nucleus. The C-141/KAO, the LJO, the detecting instruments, and the observational flight plans are described. The observed spectral range extended from 2 to 800 microns, plus wide-field, visible photography. The C-141/KAO's flights occurred in December 1985 from California and in March and April 1986 from New Zealand. The LJO's observations were made from Kwajalein Island in April 1986.

Haughney, L. C.↗
NASA NTRS1987

C-13/C-12 ratio in methane from the flooded Amazon forest

The C1-C4 hydrocarbon concentrations and the C-13/C-12 ratio in CH4 detected in air samples collected in the Amazon region (3.5 deg S latitude and 5.9 deg W longitude) are analyzed. It is observed that the CH4 concentrations of each sample are enhanced over the background concentration for remote locations, and the C-13/C-12 ratio in this biogenic methane is depleted in C-13 relative to atmospheric CH4. It is concluded, from the C2-C4 hydrocarbon data, that minor yields of C2-C4 hyrocarbons are released coincident with CH4; however, the minor yields do not contribute to the regionally enhanced concentrations of hydrocarbons found in Amazonia and the global atmosphere release of C2-C4 compounds.

Tyler, Stanley C.↗
NASA NTRS1987

C-type transitions in methyl formate

Based on previously determined spectral constants for methyl formate in its ground torsional degenerate substate, the frequencies and intensities of forbidden c-type transitions in this molecule, which is represented by a large number of lines in OMC-1, are calculated along with other 'forbidden' transitions labeled x-type. The stronger c-type transitions below 300 GHz with angular momentum quantum number of 30 or less and with upper state rotational energy of 350/cm or less are included in a list of spectral frequencies presented in this paper. Because the c-type transitions borrow intensity from the b-type transitions, the intensities of strongly affected b-type spectra are recalculated and presented.

Plummer, Grant M.↗
NASA NTRS1988

Systematic variation of magnetic-field penetration depth in high-T(c) superconductors studied by muon spin relaxation

The muon relaxation rate (sigma) was measured in the high critical temperature superconductors YBa2Cu3O(x) for x = 6.66, 6.95, 7.0, and La1.85 Sr0.15 CuO4 in transverse external magnetic fields 1 is approximately 4kG. A simple relation is found which connects the transition temperature T(c), the magnetic field penetration depth lambda(L), the carrier concentration n(s) and the effective mass m* as T(c) varies as sigma which varies as 1/lambda(L) squared which varies as n(s)/m*. The linear dependence T(c) varies as n(s)/m* suggests a high energy scale for the coupling between superconducting carriers.

Uemura, Y. J.↗
NASA NTRS1988

Nature and origin of C-rich ordinary chondrites and chondritic clasts

The abundance and the isotopic compositions of C, O, and noble gases were investigated together with the petrologic characteristics of four carbon-rich ordinary chondrites (Sharps and Allan Hills A77011, A78119, and A81024) and three C-rich chondritic clasts. The results of the analyses suggest that all of the chondrites and clasts analyzed belong to petrologic type 3 and contain abundant carbon-rich aggregates, which, in at least two of these samples, consist of poorly graphitized carbon commonly associated with metallic Fe,Ni. The data also suggest that the four C-rich chondrites originated on the H, L, and LL parental bodies, but that clasts in Dimmitt and Plainview and other regolith breccias may come from different bodies. The results obtained are consistent with the view that graphite is not a common nebular phase.

Scott, E. R. D.↗
NASA NTRS1989

Characterizations of electrical properties of highT(sub c) superconducting materials

The automated data acquisition system developed in the Space Science Laboratory at Marshall Space Flight Center for measuring electrical properties of high temperature superconductors is described. The acquisition system, consisting of a computer and computer-controlled hardware, allows large numbers of voltage, current, temperature, and magnetic measurements to be performed on bulk and thin film samples. Typical results are shown characterizing transition temperature (T sub c), critical current density (J sub c), and magnetic properties of bulk high T(sub c) materials as a function of temperature.

Sisk, R. C.↗
NASA NTRS1990

Magnetic forces in high-T(sub c) superconducting bearings

In September 1987 research at Cornell levitated a small rotor on superconducting bearing at 10,000 rpm. In April 1989 a speed of 120,000 rpm was achieved in a passive bearing with no active control. The bearing material used was YBa2Cu3O7. There is no evidence that the rotation speed has any significant effect on the lift force. Magnetic force measurements between a permanent rare-earth magnet and high T(sub c) superconducting material versus vertical and lateral displacements were made. A large hysteresis loop results for large displacements, while minor loops result for small displacements. These minor loops seem to give a slope proportional to the magnetic stiffness, and are probably indicative of flux pinning forces. Experiments of rotary speed versus time show a linear decay in a vacuum. Measurements of magnetic drag forces of a magnetic dipole over a high-T(sub c) superconducting disc of YBCO show that the drag force reaches a constant value, independent of the speed. Dampling of lateral vibrations of levitated rotors were measured which indicates that transverse flux motion in the superconductor will create dissipation. As a result of these force measurements, an optimum shape for the superconductor bearing pads which gives good lateral and axial stability was designed. Recent force measurements on melt-quench processed superconductors indicate a substantial increase in levitation force and magnetic stiffness over free sintered materials. As a result, application of high-T(sub c) superconducting bearings are beginning to show great promise at this time.

Moon, F. C.↗
NASA NTRS1991

C-130 Automated Digital Data System (CADDS)

Real time airborne data acquisition, archiving and distribution on the NASA/Ames Research Center (ARC) C-130 has been improved over the past three years due to the implementation of the C-130 Automated Digital Data System (CADDS). CADDS is a real time, multitasking, multiprocessing ROM-based system. CADDS acquires data from both avionics and environmental sensors inflight for all C-130 data lines. The system also displays the data on video monitors throughout the aircraft.

Scofield, C. P.↗
NASA NTRS1991

Sliding wear of self-mated Al2O3-SiC whisker reinforced composites at 23-1200 C

Microstructural changes occurring during sliding wear of self-mated Al2O3-SiC whisker reinforced composites were studied using optical, scanning electron microscopy, and transmission electron microscopy. Pin-on-disk specimens were slid in air at 2.7 m/sec sliding velocity under a 26.5 N load for 1 hr. Wear tests were conducted at 23, 600, 800, and 1200 C. Mild wear with a wear factor of 2.4 times 10(exp -7) to 1.5 times 10(exp -6) cu mm/Nm was experienced at all test temperatures. The composite shows evidence of wear by fatigue mechanisms at 800 C and below. Tribochemical reaction (SiC oxidation and reaction of SiO2 and Al2O3) leads to intergranular failure at 1200 C. Distinct microstructural differences existing at each test temperature are reported.

Farmer, Serene C.↗
NASA NTRS1991

First results from Goddard High-Resolution Spectrograph - C I, S I, and CO toward Xi Persei and the physical conditions in diffuse clouds

Observations made by the Goddard High Resolution Spectrograph of the cool, neutral interstellar gas in the line of sight to Xi Per are reported. Heliocentric velocities and equivalent widths were measured for absorption lines of C I and S I. Synthetic spectra were computed and fitted to the observed CO(2-0) and (3-0) bands in the A IPi - X 1Sigma(+) system. Derived populations of the C I ground-state fine-structure levels and the CO ground-state rotational levels were used to derive densities of two of the three, and possibly four, detected cloud components. The velocity component displaying the strongest C I absorption reveals extraordinarily high pressure.

Smith, Andrew M.↗
NASA NTRS1991

Laboratory spectra of C-13 ethane

The laboratory infrared spectrum of C-13 monosubstituted ethane has been obtained at high resolution (0.0025/cm) using the McMath Fourier transform spectrometer at Kitt Peak National Observatory in May 1990. A preliminary analysis of the nu12 rQ0 branch (substituted species) suggests that its intensity is 1.15 + or - 0.05 times stronger than the equivalent nu9 branch in the normal (C-12)2H6 species. This result leads to a correction of a previously published estimate for the C-12/C-13 ratio in the atmosphere of Jupiter from about 94 to about 106.

Kurtz, Joe↗
NASA NTRS1991

Crystal-field-driven redox reactions: How common minerals split H2O and CO2 into reduced H2 and C plus oxygen

It is difficult to prove the presence of molecular H2 and reduced C in minerals containing dissolved H2 and CO2. A technique was developed which unambiguously shows that minerals grown in viciously reducing environments contain peroxy in their crystal structures. The peroxy represent interstitial oxygen atoms left behind when the solute H2O and/or CO2 split off H2 and C as a result of internal redox reactions, driven by the crystal field. The observation of peroxy affirms the presence of H2 and reduced C. It shows that the solid state is indeed an unusual reaction medium.

Freund, F.↗
NASA NTRS1992

Recent progress towards developing a high field, high-T(sub c) superconducting magnet for magnetic suspension and balance systems

This paper reviews superconducting magnets and high T(sub c) superconducting oxide ceramic materials technology to identify areas of fundamental impasse to the fabrication of components and devices that tap what are believed to be the true potential of these new materials. High T(sub c) ceramics pose problems in fundamentally different areas which need to be solved unlike low T(sub c) materials. The authors map out an experimental plan designed to research process technologies which, if suitably implemented, should allow these deficiencies to be solved. Finally, assessments are made of where and on what regimes magnetic system designers should focus their attention to advance the practical development of systems based on these new materials.

Derochemont, L. Pierre↗
NASA NTRS1988

Measurement of C-12, O-16, and Fe-56 charge changing cross sections in helium at high energy, comparison with cross sections in hydrogen, and application to cosmic-ray propagation

We present measurements of the spallation cross sections of carbon, oxygen, and iron in helium and hydrogen, at beam energies from 540 to 1600 MeV/nucleon, performed by exposing liquid helium, CH2, and C targets. Charge changing cross sections are reported for fragments down to Ne for Fe + alpha and Fe + p reactions, and down to B for O + alpha, O + p, C + alpha, and C + p reactions. Alpha- to p-induced cross section ratios (sigma(sub alpha)/sigma(sub p)) are determined at the same energy per nucleon. From these measurements an empirical formula for the (sigma(sub alpha)/sigma(sub p)) ratios is derived and is found in good agreement with available isotopic cross sections data from radioactivity and radiochemical techniques. These results are applied to the propagation of heavy charged cosmic rays in an interstellar medium with a helium to hydrogen abundance ratio of 0.10. It is shown that the Sc-Mn/Fe ratio prediction is decreased relative to the B/C ratio when compared to propagation calculations in a pure hydrogen interstellar medium.

Ferrando, P.↗
NASA NTRS1992

H Ly-alpha transmittance of thin foils of C, Si/C, and Al/C for keV particle detectors

A class of instruments designed for remote sensing of space plasmas by measuring energetic neutral atoms (ENA) uses a thin foil as both a signal generator and a light shield. An ENA imager must look directly at the ENA source region, which is also usually an intense source of H Ly-alpha (1216 A) photons. It is desirable to minimize the energy threshold for ENA detectors, at the same time maximizing the blocking of H Ly-alpha. Optimizing filter design to meet these two contrary requirements has led us to measure the transmittance of thin C, Si/C, and Al/C foils at H Ly-alpha. Our results indicate that (1) transmittance of less than 0.0007 can be achieved with 7 micro-g/sq cm Si on 1.7 micro-g/sq cm C; (2) an Si/C composite foil with a thin carbon layer is more effective in blocking UV radiation while having the lowest energy threshold of all the foils measured; and (3) transmittance of Si/C foils of known Si and C thicknesses cannot be accurately predicted, but must be measured.

Drake, V. A.↗