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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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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.↗
NASA NTRS1988

Contraction-free, fume-fixed longitudinal sections of fresh frozen muscle

Contraction damage occurring when longitudinal frozen sections of fresh unfixed muscles are thawed on microscope slides has limited histological examination of this tissue mainly to cross sections. Longitudinally oriented sections are advantageous for investigating properties that vary along the length of the muscle fibers. A fume fixation technique has been developed for preventing contraction of thick longitudinal frozen sections. The technique is compatible with histochemical staining of enzymes.

Riley, Danny A.↗
NASA NTRS1990

Dependence of the microwave radar cross section on ocean surface variables - Comparison of measurements and theory using data from the Frontal Air-Sea Interaction Experiment

The purpose of this investigation was to study the ability of theoretical radar cross section (RCS) models to predict the absolute magnitude of the ocean radar cross section under a wide variety of sea and atmospheric conditions. The dependence of the RCS on wind stress (as opposed to wind speed) was also studied. An extensive amount of experimental data was acquired during the Frontal Air-Sea Interaction Experiment. Measurements across an ocean front demonstrated that the vertical polarization and horizontal polarization radar cross section were more strongly dependent on wind stress than on wind magnitude. Current theoretical models for the RCS, based on stress, were tested with this data. In situations where the Bragg scattering theory does not agree with the measured radar cross section (magnitude and angle dependence), revisions are hypothesized and evaluated.

Weissman, David E.↗
NASA NTRS1990

Single- and double-photoionization cross sections of atomic nitrogen from threshold to 31 A

The relative photoionization cross section of atomic nitrogen for the production of singly and doubly charged ions has been measured from 44.3 to 275 A and from 520 to 852 A. The results have been made absolute by normalization to one-half of the molecular nitrogen cross section at short wavelengths. The smoothed atomic nitrogen cross sections sigma can be accurately represented, at short wavelengths, by the equation sigma(Mb) = 36,700 x (E exp-2.3) as a function of the photon energy E (eV), thereby allowing the cross sections to be extrapolated to the nitrogen K edge at 31 A.

Samson, James A. R.↗
NASA NTRS1991

Cross sections for production of H(2p, 2s, 1s) by electron collisional dissociation of H2

The excitation function of H Ly-alpha from the astrophysically important dissociation of electron-excited H2 over the range 10-700 eV has been measured. The analysis predicts the cross section to energies higher than the present experimental limit, and it is found that the predicted shape is in close agreement with measured results. At 6 eV the cross section is dominated by the electric dipole first Born component, while at 100 eV the electric dipole component constitutes 73 percent of the total H(2p) cross section. The cross sections of the H(2s) and H(1s) components are calculated.

Ajello, J. M.↗
NASA NTRS1991

Cross sections and rate coefficients for inelastic interactions of heavy particles

The existing analytical inelastic cross-sections for direct atom-atom ionizing collisions of Firsov (1959), Fleischmann et al. (1972), and Drawin (1968) are discussed. General analytical expressions for direct ionization cross-sections in atom-atom collisions are derived. The main advantage of the present cross-sections is their generality, simplicity, and overall accuracy, which is acceptable in most applications and is better than the overall accuracy of the cross-sections of Firsov, Fleischmann et al., and Drawin. The atom-atom interaction is considered as a superposition of all the pairwise interactions between the test particle and all the electrons of the outer nl shell of the target atom. Such a picture of atom-atom collision is acceptable at low- and medium-impact energies because then the electrons of the outer shell of the target atom are most likely the ones that get ionized. At high-impact energy, the picture becomes inaccurate because of strong overlapping of the atomic shells.

Kunc, J. A.↗
NASA NTRS1991

Unified nonlinear analysis for nonhomogeneous anisotropic beams with closed cross sections

A unified methodology for geometrically nonlinear analysis of nonhomogeneous, anisotropic beams is presented. A 2D cross-sectional analysis and a nonlinear 1D global deformation analysis are derived from the common framework of a 3D, geometrically nonlinear theory of elasticity. The only restrictions are that the strain and local rotation are small compared to unity and that warping displacements are small relative to the cross-sectional dimensions. It is concluded that the warping solutions can be affected by large deformation and that this could alter the incremental stiffnes of the section. It is shown that sectional constants derived from the published, linear analysis can be used in the present nonlinear, 1D analysis governing the global deformation of the beam, which is based on intrinsic equations for nonlinear beam behavior. Excellent correlation is obtained with published experimental results for both isotropic and anisotropic beams undergoing large deflections.

Atilgan, Ali R.↗
NASA NTRS1992

Magnetic-sublevel cross sections for excitation of the n 1P levels of helium by electron impact

First-order many-body theory has been used to calculate collision-frame magnetic-sublevel differential cross sections for electron-impact excitation of the n 1P (n = 2,3,4,5,6) levels of helium for electrons with incident energy in the 25-500-eV range. By combining results from electron-impact differential-cross-section measurements and electron-photon coincidence measurements, experimental magnetic-sublevel cross sections have also been derived for the excitation of the 2 1P and 3 1P levels. The theory predicts a pronounced minimum for the M = 0 magnetic-sublevel differential cross section for incident electron energies around 30 eV. The theoretical results are compared to the experimental data and some other theoretical results.

Csanak, George↗
NASA NTRS1992

Coupled elastic response of open section laminated composite beams subject to generalized beam loading

A generalized beam theory for arbitrary open section laminated composite beams subjected to generalized beam loading is developed using a strength of materials approach. At present, the theory is limited to statistically determinate beams. Solution of the general system of equations yields strain and curvature distributions as functions of the axial coordinate x and the contour coordinate s. Average stresses on a given cross section or ply stresses in a local coordinate system are determined using these distributions. Data obtained for thin-walled open section composite beams reveal that elastic coupling occurs among curvatures, shearing strains, and axial strain, depending on the laminate stiffness parameters. Laminate ply layup does not affect the location of the shear center in the thin-wall approximation, but may have a significant impact for thicker walled open sections. The average axial stress distribution is found to be distinctly different from the isotropic distribution, but the average shear stress distribution is the same as that in the isotropic case.

Zvarick, Albert G.↗
NASA NTRS1992

Flexure-torsion behavior of sheat-deformable beams with applications to aircraft wing sections

The flexure-torsion behavior of a tip-loaded cantilever beam with an arbitrary cross-section is studied using Saint-Venant's semi-inverse method along with a power series solution for the out-of-plane flexure and torsion warping functions. The power series coefficients are determined by solving a set of variationally derived linear algebraic equations. For complex cross-sections, the calculated coefficients represent a 'best-fit approximation' to the exact warping function. The resulting warping functions are used to determine the cross-section properties including: the torsion constant, shear deformation coefficients, shear correction factors, and the shear center location. A new linear relation is developed for locating the shear center using the Saint-Venant flexure and torsion solutions, where the twist rate is zero about the line of shear centers (not the centroidal axis). Numerical results are presented for a triangular cross-section and different NACA airfoils.

Kosmatka, J. B.↗
NASA NTRS1992

Absolute absorption cross sections of ozone at 300 K, 228 K and 195 K in the wavelength region 185-240 nm

An account is given of progress of work on absorption cross section measurements of ozone at 300 K, 228 K and 195 K in the wavelength region 185-240 nm. In this wavelength region, the penetration of solar radiation into the Earth's atmosphere is controlled by O2 and O3. The transmitted radiation is available to dissociate trace species such as halocarbons and nitrous oxide. We have recently measured absolute absorption cross sections of O3 in the wavelength region 240-350 nm (Freeman et al., 1985; Yoshino et al., 1988). We apply these proven techniques to the determination of the absorption cross section of O3 at 300 K, 228 K and 195 K throughout the wavelength region 185-240 nm. A paper titled 'Absolute Absorption Cross Section Measurements of Ozone in the Wavelength Region 185-254 nm and the Temperature Dependence' has been submitted for publication in the Journal of Geophysical Research.

Yoshino, K.↗