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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

Impact and extinction signatures in complete Cretaceous-Tertiary (K-T) boundary sections

The Zumaya, Caravaca and Agost sections in Spain, the El Kef section in Tunisia and the Negev (Nahal Avdat) sections in Israel are among the most continuous, expanded and complete K-T boundary sections. The distribution patterns of the planktic faunas were quantitatively analyzed in closely spaced samples across the K-T boundary in these sections, in conjuction with the geochemistry, stable isotopes, mineralogy and magnetostratigraphy. Three hundred foraminiferal specimens were randomly selected and determined. Reliable estimates for the foraminiferal productivity changes across the K-T boundary and for the 1 to 2 Ma interval preceding the K-T boundary were made from the numbers of individuals/gram of sediment corrected for the sedimentation rates (calculated from magnetic reversals and lithology). No gradual or stepwise extinction is seen below the K-T boundary nor any productivity decrease. Stable isotope analyses show a warming just after deposition of the ejecta layer, not cooling as predicted by nuclear winter scenarios, although the duration of such cooling may be too short to be observed even in these complete sections. Low REE values and cpx spherules with quench textures idential to quench-textures in diagenetically altered spherules, strongly indicate an oceanic site of (one of) the impactor(s).

Smit, J.↗

NASA NTRS1989

New results concerning the use of kinematically redundant manipulators in microgravity environments

This paper is concerned with the development of control strategies for kinematically redundant manipulators to be used in Space Station laboratories. These robots must be able to conduct experiments and manufacturing processes without disturbing the microgravity environment, and thus their dynamic base reactions/motions must be nearly eliminated. Redundant degrees of freedom permit the inverse kinematics problem to be solved in conjuction with the minimization of a cost function defined as a weighted sum of the base reactions. It is shown that the weights in the cost function should be used as an additional set of parameters in the minimization problem. The actual performance of the local optimal trajectory approach is demonstrated to be not as good as was previously reported.

Quinn, R. D.↗

NASA NTRS1989

Analysis of reactively loaded microstrip disk antenna

The moment method solution to the problem of a reactively loaded circular patch is presented. Using the reaction integral equation in conjuction with the method of moments, parameters of the Thevenin's equivalent network for the loaded patch are obtained. From the equivalent network parameters an expression for the imput impedance of the loaded patch is derived. A design procedure for a circularly polarized disk antenna is presented. Computed results are compared with the experimental data.

Deshpande, M. D.↗

NASA NTRS1989

Electromagnetic instabilities in the plasma sheet boundary layer

Plasma and magnetic field data observed during two ISEE crossing of the plasma sheet boundary layer are studied in conjuction with a linear theory analysis. The plasma distribution functions exhibit three distinct potential sources of free energy: ion/ion relative drifts, electron/ion relative drifts corresponding to nonzero field-aligned current, and large ion temperature anistropies. These observed distributions are used as source functions in a linear Vlasov theory of electromagnetic instabilities at propagation parallel or antiparallel to the average magnetic field. The theory shows that the field-aligned current gives rise to the low frequency kinklike instability, and anisotropies of the flowing ion components give rise to two distinct branches of the ion cyclotron anisotropy instability with spacecraft frame frequencies both below and above the proton cyclotron frequency Omega (p). Analysis of the magnetic field data demonstrates that the appearence of two fast, counterstreaming, anisotropic ion components corresponds to a significant increase in the magnetic fluctuation energy density both below and above Omega(p), in full agreement with the theoretical predictions.

Angelopoulos, Vassilis↗

NASA NTRS1989

Experiments in swept-wing transition

Stability and transition experiments are conducted on a 45 degree sweep airfoil in the ASU Unsteady Wind Tunnel. Combined flow-visualization techniques and hot-wire measurements are used in conjuction with stability-code calculations to map out transition behavior for this flow geometry. Both steady and unsteady crossflow vortices are observed and at this time there is no contradiction with the theoretical predictions.

Saric, William S.↗

NASA NTRS1989

The dissociation energy of He2(+)

Ab initio potential energy curves for He2(+) are computed using full CI wavefunctions in conjuction with large Gaussian and Slater basis sets. The computed curves yield rotational-vibrational transitions with errors of less than 1/cm. They also yield quasi-bound levels with energies and lifetimes in reasonable agreement with translational spectroscopy measurements. The best D(e) is estimated to be 2.470 eV. Green's function Monte Carlo calculations yield a very similar value, 2.466 + or - 0.005.

Bauschlicher, Charles W., Jr.↗

NASA NTRS1990

Mariner 9 observations of the south polar cap of Mars - Evidence for residual CO2 frost

The first spacecraft observations of the south residual polar cap of Mars were obtained by the Mariner 9 orbiter during the Martian southern summer season, 1971-1972. Analyses of Viking orbiter observations obtained 3 Mars years later have shown that residual carbon dioxide frost was present at the south polar cap in 1977. In this study, Mariner 9 infrared interferometer spectrometer spectra and television camera images are used in conjuction with multispectral thermal emission models to constrain the temperatures of dark bare ground and bright frost regions within the south residual cap. The results provide strong evidence that carbon dioxide frost was present throughout the summer season despite the fact that the residual frost deposits observed by Mariner 9 were less extensive than those observed by Viking.

Paige, D. A.↗

NASA NTRS1989

Large-scale transport of a CO-enhanced air mass from Europe to the Middle East

On November 14, 1981, the shuttle-borne Measurement of Air Pollution from Satellites (MAPS) experiment observed a carbon monoxide (CO) enhanced air mass in the middle troposphere over the Middle East. The primary source of this polluted air was estimated by constructing adiabatic isentropic trajectories backwards from the MAPS measurement location over a 36 h period. The isentropic diagnostics indicate that CO-enhanced air was transported southeastward over the Mediterranean from an organized synoptic-scale weather regime, albeit of moderate intensity, influencing central Europe on November 12. Examination of the evolving synoptic scale vertical velocity and precipitation patterns during this period, in conjuction with Meteosat visible, infrared, and water vapor imagery, suggests that the presence of this disturbed weather system over Europe may have created upward transport of CO-enhanced air between the boundary-layer and midtropospheric levels, and subsequent entrainment in the large-scale northwesterly jet stream flow over Europe and the Mediterranean.

Connors, V. S.↗

NASA NTRS1990

Numerical simulation of an F-16A at angle of attack

The transonic flowfield around an F-16A fighter configuration at a moderate incidence angle is simulated by solving the Navier-Stokes equations on a single-block grid. The numerical solution matches experimental freestream conditions with a mach number of 0.85, 16 degrees angle of attack, and a characteristic Reynolds number of 12.75 million. MacCormack's explicit algorithm is used in conjuction with a local time step and consecutive mesh refinement procedure to accelerate numerical convergence. The Baldwin-Lomax algebraic model provides turbulent closure. Computed surface pressure distributions and the aircraft lift coefficient compare favorably with wind tunnel data. The drag coefficient in the simulation overpredicts the experimental value by 8 percent.

Huband, G. W.↗

NASA NTRS1990

In situ measurements of BrO in the Arctic stratosphere

Mixing ratios of BrO have been measured in the Arctic lower statosphere with an instrument mounted on the NASA ER-2 aircraft. Observations from fourteen flights above the Arctic Circle in January and February of 1989 defined mixing ratios within the vortex of 4 + or - 2 parts per trillion by volume (pptv) at a potential temperature of 400 K, rising to 8 + or - 2 pptv at 470 K. These values are twice as large as values found at equivalent potential temperatures at lower latitudes, and are comparable to the mixing ratios found inside the antarctic polar vortex. Within the statistical uncertainty of the measurements, no BrO was observed in darkness at any time either inside or outside of the vortex, indicating that active bromine was sequestered in long-lived reservoirs, probably BrONO2 and BrCl. These measurements, in conjuction with measurements of ClO, demonstrate that the interaction of bromine and chlorine could represent a major sink for ozone in the presence of sunlight.

Toohey, D. W.↗

NASA NTRS1990

Numerical and experimental simulations of the postbuckling response of laminated anisotropic panels

Numerical simulations are used in conjuction with experiments to study the buckling and postbuckling responses and failure initiation of flat unstiffened composite panels. The numerical simulations are conducted using two-dimensional shear-flexible finite elements. The effect of the laminate stacking sequence on the buckling and postbuckling responses is studied. Correlation between numerical and experimental results is good through buckling, but the numerical models overestimate the postbuckling stiffness of the panels. To explain the discrepancies in the postbuckling stiffnesses, analytic sensitivity derivatives are calculated and are used to study the sensitivity of the buckling and postbuckling responses to variations in different material and lamination parameters of the panel. Experimental results indicate that failure occurs along a nodal line. Numerical results show that the location of failure initiation corresponds to that of the maximum transverse shear strain energy density in the panel, which occurs at the edge of the panel at a nodal line.

Noor, Ahmed K.↗

NASA NTRS1990

The impedance of a tubular electrode - A model for a porous electrode

A cylindrical tube is used as the basis for a two-dimensional mathematical model to calculate the impedance of a flooded porous electrode. The model incorporates charge-transfer, mass-transfer, and ohmic resistances to obtain the axial and radial dependencies of the concentration and potential profiles. A linearized Butler-Volmer kinetic expression for a simple redox reaction O + e yielding R is used, in conjuction with analytical expressions for the surface concentration and overpotential, to compute the open-circuit impedance. The results of the two-dimensional model, which omits double-layer charging, are compared with the results of a more standardly applied one-dimensional model in which radial variations are neglected, with and without double-layer charging. The simpler-to-apply one-dimensional model is found to be satisfactory when mass-transfer and ohmic resistances are small with respect to charge-transfer resistance. The omission of double-layer charging does not introduce error into the two-dimensional model in the frequency range in which capacitive-like effects are caused by mass-transfer limitations.

Viner, Andrew S.↗

NASA NTRS1990

Algebraic turbulence modeling for unstructured and adaptive meshes

An algebraic turbulence model based on the Baldwin-Lomax model, has been implemented for use on unstructured grids. The implementation is based on the use of local background structured turbulence meshes. At each time-step, flow variables are interpolated from the unstructured mesh onto the background structured meshes, the turbulence model is executed on these meshes, and the resulting eddy viscosity values are interpolated back to the unstructured mesh. Modifications to the algebraic model were required to enable the treatment of more complicated flows, such as confluent boundary layers and wakes. The model is used in conjuction with an efficient unstructured multigrid finite-element Navier-Stokes solver in order to compute compressible turbulent flows on fully unstructured meshes. Solutions about single and multiple element airfoils are obtained and compared with experimental data.

Mavriplis, Dimitri J.↗

NASA NTRS1990

Theoretical study of the A 3Sigma(-)-X 3Pi transition in SiC

A theoretical study of the A 3Sigma(-)-X 3Pi infrared transition in SiC is presented using atomic natural orbital Gaussian basis sets in conjuction with multireference configuration interaction calculations. Dipole moment functions have been computed for both states as well as the A-X electronic transition moment function. The calculations predict that T(00) is 3700 + or - 200/cm, so that the transition recently observed in emission near 4500/cm and assigned to the 0-0 band of the A 3Sigma(-)-X 3Pi system of SiC is actually the 1-0 band.

Langhoff, Stephen R.↗

NASA NTRS1990

Mission profiles for human Mars missions

Strategies for round-trip missions to Mars with stopover are reviewed. The significant characteristics of the two main classes of stopover mission, whose midpiont corresponds either to the date of earth-Mars conjuction or opposition, are described. Strategies for round-trip flybys, fast round trips, and split missions are also considered. The latter involves a separate, prior mission in which cargo is sent to Mars.

Lineberry, Edgar C.↗

NASA NTRS1994

X-ray clusters from a high-resolution hydrodynamic PPM simulation of the cold dark matter universe

A new three-dimensional hydrodynamic code based on the piecewise parabolic method (PPM) is utilized to compute the distribution of hot gas in the standard Cosmic Background Explorer (COBE)-normalized cold dark matter (CDM) universe. Utilizing periodic boundary conditions, a box with size 85 h(exp-1) Mpc, having cell size 0.31 h(exp-1) Mpc, is followed in a simulation with 270(exp 3)=10(exp 7.3) cells. Adopting standard parameters determined from COBE and light-element nucleosynthesis, Sigma(sub 8)=1.05, Omega(sub b)=0.06, we find the X-ray-emitting clusters, compute the luminosity function at several wavelengths, the temperature distribution, and estimated sizes, as well as the evolution of these quantities with redshift. The results, which are compared with those obtained in the preceding paper (Kang et al. 1994a), may be used in conjuction with ROSAT and other observational data sets. Overall, the results of the two computations are qualitatively very similar with regard to the trends of cluster properties, i.e., how the number density, radius, and temeprature depend on luminosity and redshift. The total luminosity from clusters is approximately a factor of 2 higher using the PPM code (as compared to the 'total variation diminishing' (TVD) code used in the previous paper) with the number of bright clusters higher by a similar factor. The primary conclusions of the prior paper, with regard to the power spectrum of the primeval density perturbations, are strengthened: the standard CDM model, normalized to the COBE microwave detection, predicts too many bright X-ray emitting clusters, by a factor probably in excess of 5. The comparison between observations and theoretical predictions for the evolution of cluster properties, luminosity functions, and size and temperature distributions should provide an important discriminator among competing scenarios for the development of structure in the universe.

Bryan, Greg L.↗

NASA NTRS1994

HD 129333: The Sun in its infancy

HD 129333 is a remarkable young, nearby solar-type G star which offers a unique opportunity of studying the properties of the Sun at a time very shortly after in arrived on the main sequence. Its space motion suggest that it is a member of the Pleiades moving group, with an age of approximately 70 Myr; its lithium abundance is consistent with this. HD 129333 has the highest level of Ca II emission of any G star which is not a member of a close binary. Our observations in 1983 showed it to have low-amplitude (5%) light variations implying a rotation period of about 2.7 days, or about 10 times faster than the Sun. Modeling of the photometric variations on the assumption that they are due to starspots yields a spot temperature about 500 K cooler than the photosphere, and a coverage of about 6% of the stellar surface area. ROSAT observations in 1990 revealed the star to be an X-ray source, with an X-ray luminosity in the 0.2 to 2.4 keV range about 300 times that of the Sun. We have used International Ultraviolet Explorer (IUE) observations in conjuction with ground-based photometry to examine the magnetic activity of this star. The IUE emission-line fluxes reveal a level of chromospheric activity 3 to 20 times greater than the Sun's. The transition-region activity is 20 to 100 times that of the Sun. The activity level of HD 129333 is consistent with the Skumanich law relating activity to age, and with the rotation-activity relation, although it may be near saturation level. This star can yield valuable information about the magnetic dynamo of the young Sun, as well as about stellar dynamos in general. The 1988 IUE observations covered four phases of its rotational cycle. A phase dependence of the Mg II h and k emission flux suggests a close association of chromospheric plages with starspot regions at that time. Systematic variations in the mean brightness of HD 129333 between 1983 and 1993, and in the UV emission fluxes, indicate the presence of an activity cycle of an estimated 12 years' duration. HD 129333 is the first solar-type star other than RS CVn binaries for which luminosity variations provide evidence for a spot cycle. Unlike the Sun, which is brighter at activity maximum HD 129333 appears to be fainter when more heavily spotted. Although evolutionary models for the Sun suggest that it was about 30% less luminous at age 70 Myr, they give no information about the UV flux. Accordingly, we have used the 1988 IUE observations of HD 129333 to construct a model spectrum of the infant Sun, which can be used to provide a quantitative estimate of the UV flux in the early solar system.

Dorren, J. David↗

NASA NTRS1994

Protein crystal growth in microgravity: Temperature induced large scale crystallization of insulin

One of the major stumbling blocks that prevents rapid structure determination using x-ray crystallography is macro-molecular crystal growth. There are many examples where crystallization takes longer than structure determination. In some cases, it is impossible to grow useful crystals on earth. Recent experiments conducted in conjuction with NASA on various Space Shuttle missions have demonstrated that protein crystals often grow larger and display better internal molecular order than their earth-grown counterparts. This paper reports results from three Shuttle flights using the Protein Crystallization Facility (PCF). The PCF hardware produced large, high-quality insulin crystals by using a temperature change as the sole means to affect protein solubility and thus, crystallization. The facility consists of cylinders/containers with volumes of 500, 200, 100, and 50 ml. Data from the three Shuttle flights demonstrated that larger, higher resolution crystals (as evidenced by x-ray diffraction data) were obtained from the microgravity experiments when compared to earth-grown crystals.

Long, Marianna M.↗