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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Cross sections for electron impact excitation of the b 3Sigma(+)u state of H2 - An application of the Schwinger multichannel variational method

In this and the two accompanying letters, the results of calculations of the cross sections for electron impact excitation of the b 3Sigma(+)u state of H2, for collision energies from near threshold to 30 eV, are presented. These results are obtained using a multichannel extension of the Schwinger variational principle at the two-state level. The quantitative agreement between the integral cross sections of these three studies is very good. Inclusion of correlation terms in the scattering wavefunctions, which relax the orthogonality between bound and continuum orbitals, is seen to affect the cross sections substantially. Although a comparison of these calculated cross sections with available experimental data is encouraging, some seious discrepancies exist.

Lima, M. A. P.↗
NASA NTRS1986

Influence of forebody cross-sectional shape on wing vortex burst location

A water tunnel study examining the influence of forebody cross section on the position of the wing vortex burst was carried out in the NASA Ames-Dryden water tunnel for a 55-deg cropped delta-wing model. Two of three cross sections investigated were chine-shaped, where the included angle of the chine was either 7.5-deg, representing a rather small side-edge angle, or 90 deg, representing a more moderate design. The third cross section was circular and served as a baseline for comparison. It is found that the 7.5 deg chine cross section generated the strongest forebody vortices of the three configurations and that these strong forebody vortices interacted with the main wing vortices in such a manner as to dramatically delay wing vortex burst position at zero sideslip. If the configuration is sideslipped, large asymmetries in wing vortex burst location may result.

Hall, R. M.↗
NASA NTRS1985

The ultraviolet cross-sections of ozone. I. The measurements. II - Results and temperature dependence

Absorption cross-sections of ozone have been measured over the range 230 nm to 350 nm, and for temperatures 200 K to 300 K, with improved photometric accuracy and spectral resolution. These measurements are referred to the cross-section at the 253.65 nm mercury line by the Hearn value (1961), 1147 x 10 to the -20th/sq cm, and show an internal consistency of + or - 1 percent. Tables of ozone absorption cross-section in the ultraviolet have been prepared for intervals of 0.05 nm over the range 245 to 340 nm. at each wavelength entry in the table a set of coefficients has been derived that permits the cross-section to be computed as a function of temperature, between 200 K and 300 K, with an accuracy of 1 percent.

Bass, A. M.↗
NASA NTRS1986

Differential electron scattering cross sections for the first optically forbidden and resonance transitions in Mg II, Zn II and Cd II

Differential electron scattering cross sections have been measured for dipole-forbidden and resonance transitions in Mg II, Zn II and Cd II in the angular range theta = 4-17 deg at 50 eV. These provide the first recorded angular distributions for an optically forbidden transition. It is found that while the cross section for excitation of the 4s (2)S-3d(9)4s(2) (2)D transition in Zn II is small, those for the 3s (2)S-3d (2)D, 4s (2)S (unresolved lines) in Mg II, and the 5s (2)S-4d(9)5s(2) D in Cd II are comparable in magnitude with the cross sections for resonance excitation. In addition, for Cd II it is found that the allowed and forbidden transitions have very similar angular distributions, and it is proposed that excitation to the 2D state may be dominated by a virtual 'double-dipole' transition via the 2P state. Also, the total excitation cross section of the resonance 2P state in Cd II is a factor of four higher than that predicted by the Gaunt factor approximation, suggesting that the accepted value for the oscillator strength may be too low.

Williams, I. D.↗
NASA NTRS1987

SO2 absorption cross sections in the near U.V.

In order to understand data measured by the TOMS instrument on Nimbus 7 after the eruption of El Chichon, absorption cross sections are measured in SO2 between 3000 and 3240 A at 295 and 210 K. Errors for these measurements range from less than 2 percent to about 10 percent. Measurements in the 3175 + or 5 A spectral region observed by TOMS indicate that there is a 9 percent reduction in the average cross section at 210 K compared to room-temperature data. Peak cross sections measured at low temperature show increases up to 20 percent over room-temperature data, while cross-section decreases are measured at low temperatures in the areas between the strong features.

Mcgee, Thomas J.↗
NASA NTRS1987

Electron-impact excitation cross sections for the b 3Sigma(+)nu state of H2

Differential and integral cross sections for electron-impact excitation of the b 3Sigma(+)nu state of H2 have been determined in the 20-100-eV impact energy region. The calibration of the cross sections was achieved through the H2 elastic scattering cross sections, which in turn were normalized to absolute He elastic scattering cross sections. Comparison is made with available experimental data and with theoretical results applying Born-Ochkur-Rudge, distorted-wave, and close-coupling approximations.

Khakoo, M. A.↗
NASA NTRS1988

Sectioning Coated Specimens Without Edge Rounding

New method devised for preparation of cross sections of coated specimens for scanning electron microscopy or energy-dispersive analysis without rounding edges of coatings. After cutting and polishing, specimen section remains smooth and flat so it can be examined under high magnification out to edge of coating. Sectioned blade first electroplated with hard nickel 0.003 in., then encapsulated in two layers of material: soft conductive material at bottom and 0.25 in. of hard diallyl phthalate at top. Nickel plate provides electrical path from surface of section to conductive material below.

Mckechnie, Timothy N.↗
NASA NTRS1987

High resolution absorption cross-sections and band oscillator strengths of the Schumann-Runge bands of oxygen at 79 K

Cross sections of O2 at 79 K have been obtained from photoabsorption measurements at various pressures throughout the wavelength region 179.3-198.0 nm with a 6.65-m photoelectric scanning spectrometer equipped with a 2400-lines/mm grating and having an instrumental width (FWHM) of 0.0013 nm. The measured absorption cross sections of the Schumann-Runge bands (12,0) through (2,0) are independent of the instrumental width. The measured cross-sections are presented graphically here and are available at wavenumber intervals of about 0.1/cm as numerical compilations stored on magnetic tape from the National Space Science Data Center, NASA/Goddard. Band oscillator strengths of these bands have been determined by direct numerical integration of the measured cross sections.

Yoshino, K.↗
NASA NTRS1987

Measuring and modeling the backscattering cross section of a leaf

Leaves are a significant feature of any vegetation canopy, and for remote sensing purposes it is important to develop an effective model for predicting the scattering from a leaf. From measurements of the X band backscattering cross section of a coleus leaf in varying stages of dryness, it is shown that a uniform resistive sheet constitutes such a model for a planar leaf. The scattering is determined by the (complex) resistivity which is, in turn, entirely specified by the gravimetric moisture content of the leaf. Using an available asymptotic expression for the scattering from a rectangular resistive plate which includes, as a special case, a metallic plate whose resistivity is zero, the computed backscattering cross sections for both principal polarizations are found to be in excellent agreement with data measured for rectangular sections of leaves with different moisture contents. If the resistivity is sufficiently large, the asymptotic expressions do not differ significantly from the physical optics ones, and for naturally shaped leaves as well as rectangular sections, the physical optics approximation in conjunction with the resistive sheet model faithfully reproduces the dominant feataures of the scattering patterns under all moisture conditions.

Senior, T. B. A.↗
NASA NTRS1988

Aerodynamic flow quality and acoustic characteristics of the 40- by 80-foot test section circuit of the National Full-Scale Aerodynamic Complex

The 40- by 80-foot wind tunnel circuit of the National Full-Scale Aerodynamic Complex (NFAC) has recently undergone major modifications and subsequently completed final acceptance testing. The initial testing and calibration of the wind tunnel are described and in many cases these results are compared with predictions derived from model tests and theoretical analyses. The wind tunnel meets or exceeds essentially all performance objectives. The facility runs smoothly and routinely at its maximum test-section velocity of 300 knots (Mach number = 0.45). An effective cooling air exchange system enables the wind tunnel to operate indefinitely at this maximum power condition. Throughout the operating envelope of the wind tunnel the test-section dynamic pressure is uniform to within + or - 0.5 deg, and the axial component of turbulence is generally less than 0.5 percent. Acoustic measurements indicate that, due to the low noise fans and acoustic treatment in the wind-tunnel circuit and test section, the background noise level in the test section is comparable to other large-scale acoustic wind tunnels in the United States and abroad.

Olson, Lawrence E.↗
NASA NTRS1988

Measurement of electron-attachment line shapes, cross sections, and rate constants in HI and DI at ultralow electron energies

Electron-attachment cross sections are reported in the electron energy range 0-150 MeV, at an energy resolution of 6.5 MeV (full width at half maximum) for the molecules HI and DI. Use is made of the Kr photoionization method to obtain cross sections for HI, and a signal intercomparison technique to obtain cross sections and the thermal-attachment rate constant for DI. Attachment properties of the two molecules are very similar. The ratio of attachment cross sections is discussed in terms of the reduced-mass dependence of the dissociation width and the survival probability, and in terms of spectroscopic thresholds and rotational populations for attachment at 300 K. Approximate potential-energy curves for the lowest states of the neutral molecule and negative ion are given.

Alajajian, S. H.↗
NASA NTRS1988

Toward improved durability in advanced aircraft engine hot sections; Proceedings of the Thirty-third ASME International Gas Turbine and Aeroengine Congress and Exposition, Amsterdam, Netherlands, June 5-9, 1988

The present conference on durability improvement methods for advanced aircraft gas turbine hot-section components discusses NASA's 'HOST' project, advanced high-temperature instrumentation for hot-section research, the development and application of combustor aerothermal models, and the evaluation of a data base and numerical model for turbine heat transfer. Also discussed are structural analysis methods for gas turbine hot section components, fatigue life-prediction modeling for turbine hot section materials, and the service life modeling of thermal barrier coatings for aircraft gas turbine engines.

Sokolowski, Daniel E.↗
NASA NTRS1988

Determination of spectroscopic properties of atmospheric molecules from high resolution vacuum ultraviolet cross section and wavelength measurements

Progress is given on work on: cross section measurements in the transmission window regions of the Schumann-Runge bands of oxygen; the determinations of predissociation linewidths; the theoretical calculation of band oscillator strengths of the Schumann-Runge absorption bands of O-16O-18; the determination of molecular spectroscopic constants; and the combined Herzberg continuum cross sections. The experimental investigations relevant to the cross section measurements, predissociation linewidths, and molecular spectroscopic constants are effected at high resolution with a 6.65 m scanning spectrometer which is, by virtue of its small instrumental width (FWHM = 0.0013 nm), suitable for cross section measurements of molecular bands with discrete rotational structure. Such measurements are needed for accurate calculations of the stratospheric production of atomic oxygen and heavy ozone formed following the photo-predissociation of O-16O-18 by solar radiation penetrating between the absorption lines of O-16(sub 2).

Parkinson, W. H.↗
NASA NTRS1988

Macrofossil extinction patterns at Bay of Biscay Cretaceous-Tertiary boundary sections

Researchers examined several K-T boundary cores at Deep Sea Drilling Project (DSDP) core repositories to document biostratigraphic ranges of inoceramid shell fragments and prisms. As in land-based sections, prisms in the deep sea cores disappear well before the K-T boundary. Ammonites show a very different extinction pattern than do the inoceramids. A minimum of seven ammonite species have been collected from the last meter of Cretaceous strata in the Bay of Biscay basin. In three of the sections there is no marked drop in either species numbers or abundance prior to the K-T boundary Cretaceous strata; at the Zumaya section, however, both species richness and abundance drop in the last 20 m of the Cretaceous, with only a single ammonite specimen recovered to date from the uppermost 12 m of Cretaceous strata in this section. Researchers conclude that inoceramid bivalves and ammonites showed two different times and patterns of extinction, at least in the Bay of Biscay region. The inoceramids disappeared gradually during the Early Maestrichtian, and survived only into the earliest Late Maestrichtian. Ammonites, on the other hand, maintained relatively high species richness throughout the Maestrichtian, and then disappeared suddenly, either coincident with, or immediately before the microfossil extinction event marking the very end of the Cretaceous.

Ward, Peter D.↗
NASA NTRS1988

High resolution absorption cross-sections and band oscillator strengths of the Schumann-Runge absorption bands of isotopic oxygen, (O-18)2, at 79 K

Cross-sections of (O-18)2 at 79 K have been obtained from photoabsorption measurements at various pressures throughout the wavelength region 177.8-197.8 nm with a 6.65 m photoelectric scanning spectrometer equipped with a 2400 lines/mm grating and having an instrumental width (FWHM) of 0.0013 nm. The measured absorption cross-sections of the Schumann-Runge bands (14,0) through (2,0) are, with the exception of the (12,0) band, independent of the instrumental width. The measured cross-sections are presented graphically here and are available at wavenumber intervals of about 0.1/cm as numerical compilations stored on magnetic tape. Band oscillator strengths of those bands have been determined by direct numerical integration of the measured absolute cross-sections and are in excellent agreement with these theoretically calculated values.

Yoshino, K.↗
NASA NTRS1989

The abundance of N-14 at the cosmic-ray source - A study using new fragmentation cross sections

The abundance of N-14 at the Galactic cosmic ray source was examined using new fragmentation cross sections measured by the University of New Hampshire group for 12 different source nuclei (ranging from C-12 to Ni-58) which cover about 70 percent of all cosmic-ray nuclei arriving at earth. A new cross-section program was used to estimate unmeasured cross sections. These cross sections were then incorporated into a Galactic propagation program to calculate the interstellar production of B and N. Results indicate that atomic selection effects alone cannot explain adequately the observed depletion of N-14 relative to O-16 in the cosmic-ray source with respect to the solar corona, indicating that some part of this depletion must have a nuclear/nucleosynthetic origin.

Gupta, M.↗
NASA NTRS1989

Impact evaluation of composite floor sections

Graphite-epoxy floor sections representative of aircraft fuselage construction were statically and dynamically tested to evaluate their response to crash loadings. These floor sections were fabricated using a frame-stringer design typical of present aluminum aircraft without features to enhance crashworthiness. The floor sections were tested as part of a systematic research program developed to study the impact response of composite components of increasing complexity. The ultimate goal of the research program is to develop crashworthy design features for future composite aircraft. Initially, individual frames of six-foot diameter were tested both statically and dynamically. The frames were then used to construct built-up floor sections for dynamic tests at impact velocities of approximately 20 feet/sec to simulate survivable crash velocities. In addition, static tests were conducted to gain a better understanding of the failure mechanisms seen in the dynamic tests.

Boitnott, Richard L.↗
NASA NTRS1989

Precision measurements of photoabsorption cross sections of Ar, Kr, Xe, and selected molecules at 58.4, 73.6, and 74.4 nm

Absolute absorption cross sections have been measured for the rare gases at 58.43, 73.59, and 74.37 nm with an accuracy of + or - 0.8 percent. For the molecules H2, N2, O2, CO, N2O, CO2, and CH4, precision measurements were made at 58.43 nm with an accuracy of + or - 0.8 percent. Molecular absorption cross sections are also reported at 73.59 and 74.37 nm. However, in the vicinity of these wavelengths most molecules exhibit considerable structure, and cross sections measured at these wavelengths may depend on the widths and the amounts of self-reversal of these resonance lines. A detailed discussion is given of the systematic errors encountered with the double-ion chamber used in the cross-sectional measurements. Details are also given of precision pressure measurements.

Samson, James A. R.↗