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NASA NTRS1983

NASA interdisciplinary collaboration in tribology. A review of oxidational wear

An in-depth review of oxidational wear of metals is presented. Special emphasis is given to a description of the concept of oxidational wear and the formulation of an Oxidational Wear Theory. The parallelism between the formation of an oxide film for dry contact conditions and the formation of other surface films for a lubricated contact is discussed. The description of oxidational wear is prefaced with a unification of wear modes into two major classes of mild and severe wear including both lubricated and dry contacts. Oxidational wear of metals is a class of mild wear where protective oxide films are formed at real areas of contact and during the time of contact at temperataure T sub c. When the oxide reaches a critical thickness, frequently in the range of 1 to 3 microns, the oxide breaks up and eventually appears as a wear particle. These oxides are preferentially formed on plateaux which alternately carry the load as they reach their critical thickness and are removed. If the system is operated at elevated temperatures, thick oxides can form both out of contact and between the plateaux. Temperature is important in determining the structure of the oxide film present. Spinel oxide (Fe3O4) which forms above 300 C is more protective than the lower temperature rhomobohedral (alpha-Fe2O3) oxide which is abrasive. An Oxidational Wear Theory is derived using a modified Archard wear law expressed in terms of activation energy (Qp) and Arrhenius constant (Ap).

Quinn, T. F. J.↗

NASA NTRS1981

The promise of remote sensing in the atmospheric sciences

The applications and advances in remote sensing technology for weather prediction, mesoscale meteorology, severe storms, and climate studies are discussed. Doppler radar permits tracking of the three-dimensional field of motion within storms, thereby increasing the accuracy of convective storm modeling. Single Doppler units are also employed for detecting mesoscale storm vortices and tornado vortex signatures with lead times of 30 min. Clear air radar in pulsed and high resolution FM-CW forms reveals boundary layer convection, Kelvin-Helmoltz waves, shear layer turbulence, and wave motions. Lidar is successfully employed for stratospheric aerosol measurements, while Doppler lidar provides data on winds from the ground and can be based in space. Sodar is useful for determining the structure of the PBL. Details and techniques of satellite-based remote sensing are presented, and results from the GWE and FGGE experiments are discussed.

Atlas, D.↗

NASA NTRS1982

X-ray nebular models

Theoretical models are presented for the temperature and ionization structure of spherically symmetric, constant density, gaseous nebulae surrounding compact X-ray sources and for the optical, UV, and X-ray spectra emerging from the nebulae. The structure is determined by assuming a local balance between heating and cooling in the gas, and the radiation field is found by solving a simplified equation of transfer. The calculations include an accurate and comprehensive treatment of the atomic processes affecting the state of the gas and the radiation field. The destruction of line radiation during resonance scattering causes models to be significantly hotter and more highly ionized than previous models of the same type. Model results are presented for a wide variety of gas densities and X-ray source spectra, scaling laws which allow these results to be generalized to a wide variety of astrophysical solutions are discussed, and column densities of multiply charged species are tabulated.

Kallman, T. R.↗

NASA NTRS1983

The shape of cooling filaments in old supernova remnants

The evolution of a filament in an old supernova remnant is investigated in two dimensions using analytical methods to determine its structure and stability and to show whether it collapses into a sheet or a cylinder. All parameters are assumed constant along the length of the feature. The cross section of the filament is found to flatten as it cools, and to degenerate into a thin sheet which is unstable to asymmetric warping disturbances. This probably leads to a number of parallel striations as the filament splits up, consistent with observations in the Cygnus Loop. The ratio of depth to width is typically 10:1, and so the feature may appear to be tubelike or a sheet, depending on perspective. The application to Vela and Puppis, IC 443, S 147, and CTB 1 is pointed out.

Smith, M. D.↗

NASA NTRS1983

Chromospheric heating by electron and proton bombardment in the solar flare of June 7, 1980

Using observations of both hard X rays and gamma rays in the large solar flare on June 7, 1980, the amount of chromospheric heating due to bombardment both by nonthermal electrons and by protons, respectively, are inferred. If a thick-target model for the X ray bremsstrahlung is adopted, then proton heating is shown to be important only in the lower chromosphere: however, if the hard X rays are substantially thermal in origin, then proton heating may play an important or indeed dominant role in determining the structure of the entire flaring chromosphere.

Emslie, A. G.↗

NASA NTRS1983

Electron impact excitation from a 1 Delta g state of molecular oxygen

First measurements of electron impact excitation on the O2 a delta-one sub g metastable state to a higher bound state, pi-one sub u, is reported. The data were taken at an incident electron energy of 500 eV and scattering angles of 0 deg to 15 deg. A superelastic electron scattering experiment was performed on the pure oxygen target gas in order to establish the composition of the discharged oxygen and to confirm the existence of delta-one sub g molecules in the interaction region. The electron-impact energy loss spectrum obtained is shown. The electronic assignment of the upper state which produces the vibrational structure was determined to be pi-one sub u by examining the potential energy curves of O2 and applying the electric dipole selection rules. The relative line intensities were obtained and used to determine the Morse potential for the pi-one sub u state.

Khakoo, M. A.↗

NASA NTRS1983

Progress research of non-Cz silicon material

The simultaneous diffusion of liquid boron and liquid phosphorus dopants into N-type dendritic silicon web for solar cells was investigated. It is planned that the diffusion parameters required to achieve the desired P(+)NN(+) cell structure be determined and the resultant cell properties be compared to cells produced in a sequential differential process. A cost analysis of the simultaneous junction formation process is proposed.

Campbell, R. B.↗

NASA NTRS1983

Observations of a loop current frontal eddy intrusion onto the west Florida shelf

Data were examined to determine the structure of this intrusion (April 1-7, 1982) and to investigate its effects on water masses in the outer shelf region. A frontal eddy, made up of a warm filament separated from the main current by a region of cooler water, propagated southeastward at 30 cm/s, intruding onto the shelf near 26 deg N between April 4 and 6. It was found from temperature-salinity (T-S) properties that water in the filament was Loop Current water that had been contiguous with Loop Current water 80 m deeper in the main body of the current. It is noted that water in the cold region was Continental Edge water, a transitional water mass with cooler, fresher T-S characteristics. Under this region, upwelling of deeper Loop Current water occurred, and elevated nutrient concentrations were found in the upwelled dome under the cold region.

Paluszkiewicz, T.↗

NASA NTRS1984

EVA-glass interface bond stability

The ethylene vinyl acetate/glass interface bond stability was investigated. Special methods to determine the structure of polymer/glass interface were developed. Structural changes related to hydrothermal degradation of polymer/glass interface are examined. Methods to inhibit the degradation reaction which occur at polymer/glass interface are developed.

Koenig, J. L.↗

NASA NTRS1984

Uniformly spaced field-aligned ionization ducts

A number of interesting cases of combination mode ducted echoes for mid- and low-latitude regions are presented that show nearly uniformly spaced multiple combination mode traces on the ionograms in the frequency range above 1 MHz. These traces suggest that a parallel system of field-aligned ducts is present. Ray tracing studies are made to determine the structure that would explain the observations using the electron density profile derivable from the vertical trace and assuming field-aligned ducts. Spacing perpendicular to the ducts is found to be as much as 70 km. Some of these parallel duct structures are found to extend to the conjugate hemisphere, possibly to the F peak.

Gross, S. H.↗

NASA NTRS1984

Energetics of the protonation of CO - Implications for the observation of HOC(+) in dense interstellar clouds

A number of molecular species on the H3CO(+) energy hypersurface is examined. Ab initio molecular orbital theory is used to determine the structures and relative energetics of the two isomers of HCO(+) and HOC(+) together with the affinity of CO for protonation at either end. The proton affinities of H2 and H2CO are also examined. The calculations are performed using large basis sets and include the effects of electron correlation. The calculated vibrational frequencies are used to correct for zero point energy differences. The results show that the proton affinities of H2 and CO to form HOC(+) are within 1 kcal of each other. The calculations demonstrate that there is no thermodynamic driving force to form HOC(+) in collisions of H3(+) with CO, and that the formation of HCO(+) in such collisions is very exoergic. A plausible mechanism is suggested to explain the differences observed between the laboratory and the interstellar medium.

Dixon, D.↗

NASA NTRS1985

Neurophysiological model of the normal and abnormal human pupil

Anatomical, experimental, and computer simulation studies were used to determine the structure of the neurophysiological model of the pupil size control system. The computer simulation of this model demonstrates the role played by each of the elements in the neurological pathways influencing the size of the pupil. Simulations of the effect of drugs and common abnormalities in the system help to illustrate the workings of the pathways and processes involved. The simulation program allows the user to select pupil condition (normal or an abnormality), specific site along the neurological pathway (retina, hypothalamus, etc.) drug class input (barbiturate, narcotic, etc.), stimulus/response mode, display mode, stimulus type and input waveform, stimulus or background intensity and frequency, the input and output conditions, and the response at the neuroanatomical site. The model can be used as a teaching aid or as a tool for testing hypotheses regarding the system.

Krenz, W.↗

NASA NTRS1985

Load-deflection tests and computer analyses of a high-precision adhesive-bonded antenna reflector panel

New adhesive-bonded panels are being investigated as a part of an effort to extend and upgrade the 64-m to a 70-m antenna network. Load-deflection tests were conducted on a sample high-precision adhesive-bonded panel for comparison with design criteria. Two computerized structural models were developed in order to predict the deformation patterns under different types of distributed and concentrated loadings. The main purpose was to obtain empirical stiffness factors for the slit beams and girders in the panel structure. With determination and use of the empirical stiffness factors, there is a good agreement between the theoretically predicted deflections and the test measurements. It was also found that the new bonded panels satisfy the stringent design specifications and surface tolerance bounds.

Chian, C. T.↗

NASA NTRS1985

The next generation geophysical investigation of the moon

Planetary geophysics has mainly the objective to determine the structure, composition, and state of a given body and the relationship between internal processes and surface tectonic features. The moon represents an obvious initial case for application of geophysical techniques to bodies other than the earth. As a result of the Apollo program and associated scientific investigations, some initial progress was made toward geophysical exploration of the moon. The obtained results are briefly discussed, and some major unresolved issues are pointed out. The present status of lunar geophysical data sets is evaluated, taking into account the issues cited and the extent to which future orbital surveys and surface measurements may resolve the remaining problems. Attention is given to seismic data, electromagnetic sounding data, heat-flow data, gravity/topography data, and paleomagnetic data.

Hood, L. L.↗

NASA NTRS1986

The structure, energetics and evolution of the dominant frequency-dependent three-dimensional atmospheric modes

The three-dimensional structure of the dominant modes of wintertime variability are examined, and the mode structures are determined by an EOF analysis of the coupled vertical mean and shear streamfunction fields for a wide range of time-scale classes. The time mean energy conversions are determined from a two-layer quasigeostrophic model. Lag-cross correlations between the dominant low-frequency modes tend to be small and/or symmetric about zero, the high frequency modes are found to show highly asymmetric sinusoidal cross correlation functions similar to traveling waves, and some intermediate and short-time scale modes exhibit correlations indicating an association with the decaying phases of blocking in the Pacific. It is suggested that the mean flow barotropic (baroclinic) instabilities are an important source of variance for some of the lowest (highest) fluctuations considered.

Schubert, S. D.↗

NASA NTRS1986

The 15 meter hoop-column antenna dynamics: Test and analysis

A 15 meter model of the hoop-column antenna concept has been vibration tested for model characterization and analytical model verification. Linear finite element analysis predicted the global vibration frequencies accurately. Good agreement between analysis and test data was obtained only after the analytical model was refined using static test data. As structures become more flexible, structural properties determined from static data become more accurate and should be used to update analytical models. Global vibration modes are not significantly affected by the surface mesh which permits simplified analytical models to be used for prediction of global behavior. These reduced models are believed sufficient for preliminary design and controls simulations where only global behavior is desired. The mesh modes were highly damped due to the knit mesh used for the reflector surface. These modes were also highly coupled and very difficult to measure in the laboratory. The inability to fully characterize the antenna mesh modes in the laboratory indicates robust methods for active surface vibration suppression will be needed. Fortunately, the surface mesh exhibits high passive damping which should be beneficial to active control systems.

Belvin, W. Keith↗

NASA NTRS1986

Magnetic configurations of planetary obstacles

The interaction between planetary magnetospheres and solar wind flow is discussed. A proper planetary magnetosphere results from the interaction of a flowing plasma with a planet having an intrinsic, global, magnetic field of sufficient strength to stand off the impinging plasma. Upstream of such an obstacle a bow shock usually exists. The known magnetospheres have severely asymmetric shapes, being elongated approximately along the solar wind flow direction. Conditions which fundamentally determine the structure of a proper planetary magnetosphere are the state of the externally flowing plasma, the planet's magnetic moment, its vector spin, and the presence and nature of internal plasma sources and any plasma sinks. Planets known to have proper magnetospheres are Earth, Mercury, Jupiter, and Saturn. Uranus and Neptune may also have magnetospheres, with that of Uranus promising to have an exotic field configuration, because the planet's magnetic moment is expected to be nearly aligned with the solar wind flow direction. Venus and Mars are also discussed. Magnetopause surface waves are mentioned.

Lepping, R. P.↗

NASA NTRS1986

Preflare magnetic and velocity fields

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

Hagyard, M. J.↗