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At least 919 records · Page 51

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NASA NTRS1971

Absorbing ice model of interstellar grains.

Extinction curves have been calculated for Mie scattering by grains with a refractive index m equals to n - ik, where n was between 1.3 and 2.0 and k varied from 0 to 0.5. A good fit for the observed interstellar extinction in the wavelength region of 0.1 to 2.0 microns was obtained for particles with a radius of 0.1 micron and m equal to 1.3 - 0.2i. Inclusion of the changes in the refractive index in the vacuum ultraviolet region due to the strong absorptions of methane, ammonia and water does not appreciably alter these results. Theoretical extinction curves for the composite medium of H2O, NH3, CH4, and graphite show a general agreement with the observed interstellar reddening curve over the whole spectral range, in addition to producing kinks in the far-ultraviolet region.

Swamy, K. S. K.↗

NASA NTRS1971

Magnetic stress anisotropy field in plated cylindrical Permalloy films.

An analysis is made of the magnetic stress anisotropy field (Hks) arising from internal and external stress sources in plated-wire memory elements. The analysis takes into consideration circumferential composition variation and cylindrical geometry of the Permalloy film. Expressions are derived relating Hks to uniaxial film stress, average composition, and amplitude of composition variation. A result of particular importance is that even for average zeromagnetostrictive composition (ZMC) films, Hks may still make an appreciable contribution to the total anisotropy field if the composition is not uniform. Calculated Hks characteristics are shown to correlate with anisotropy field changes observed in annealing experiments. Examples are given to show the importance of composition uniformity in determining the stability of the anisotropy field. The utility of the analysis is extended by the inclusion of data expressing the inverse relation between anisotropy field and easy-axis dispersion in the film.

Lutes, O. S.↗

NASA NTRS1972

Calculation of compressible adverse pressure gradient turbulent boundary layers.

Difficulties encountered in computing profile shapes in supersonic turbulent boundary layers with large pressure gradients, which result from a disagreement between data and theory, are investigated. Possible reasons given by various authors for this disagreement are discussed. Initial results seem to indicate that conventional reasons do not account for the observed difficulties. However, inclusion of the effect of curvature upon turbulent mixing has brought an improvement in calculations. Possible three-dimensional effects are also examined.

Bushnell, D. M.↗

NASA NTRS1972

Effect of core polarizability on photoionization cross-section calculations.

Demonstration of the importance of core polarizability in a case where cancellation is only moderate, with suggestion of an improvement to the scaled Thomas-Fermi (STF) wave functions of Stewart and Rotenberg (1965). The inclusion of dipole polarizability of the core for argon is shown to substantially improve the agreement between the theoretical and experimental photoionization cross sections for the ground-state configuration.

Kirkpatrick, R. C.↗

NASA NTRS1972

High-frequency electromagnetic response of the moon.

It is shown that the contribution of higher harmonics to the lunar transfer functions for the tangential components of the surface magnetic field is significant at frequencies greater than 0.01 Hz. The inclusion of the higher harmonics shows that there are two distinct transfer functions corresponding to the components of the tangential surface magnetic field perpendicular and parallel to the direction of the wave vector of the external disturbance forcing the lunar induction. The dependences of these transfer functions on frequency and location are determined. The effects of the higher harmonics can (1) account for a hitherto unexplained feature in the Apollo 12 and Explorer 35 transfer functions, namely the rolloff at high frequencies, and (2) offer a possible explanation for the frequency dependence of the difference between the transfer functions for the two orthogonal components of the surface magnetic field.

Schubert, G.↗

NASA NTRS1972

A two dimensional theory for two phase detonation of liquid films.

A theory for the propagation of detonations through tubes coated with a thin fuel film is developed. Vaporization is assumed as the rate limiting process dominating the detonation structure. Inclusion of the boundary layer displacement effect resulted in better agreement between computed and measured propagation speed, pressure ratio, and reaction zone length than was obtained in an earlier theory in which this effect was neglected. New film detonation data is presented covering a wide range of fuel air ratios. A general Chapman-Jouguet condition is formulated for film detonations, and use of the plane of complete film vaporization as the Chapman-Jouguet plane is justified in the case of thin films.

Rao, C. S. R.↗

NASA NTRS1972

Sources, losses, and transport of magnetospherically trapped particles.

Trapping, pseudo-trapping, and non-trapping regions within an observed magnetospheric configuration are described. Time averaged proton and electron distributions and available data concerning the alpha particle distribution within the trapping and pseudo-trapping regions are presented. A review of the observational evidence leading to the identification of major sources, losses, and transport of magnetospherically trapped particles is given. Conclusions are summarized and additional suggestions offered on these factors for inner and outer zone protons and electrons. One general result of this review is that much is now known of source, loss, and transport processes, although specific experiments and calculations must still be done. It is shown that the inclusion of pitch angle diffusion processes within the magnetosphere significantly alters the concept of stable trapping and allows a consistent quiescent description of outer zone electrons to be formulated from energies of a few tens of kilovolts to several MeV.

Williams, D. J.↗

NASA NTRS1972

Stability of plane Poiseuille flow with heat transfer.

Investigation of the influence of heat transfer on the stability of a plane Poiseuille flow iahnnl. The liquid flow is affected by the heat transfer through the variation in viscosity with temperature. Additional viscosity gradient terms are included in a modified Orr-Sommerfeld equation, and it is the presence of these terms which leads to a prediction of more unstable flows, for without the inclusion of these extra terms, the flow is stabilized. The results show that a temperature difference between the walls is always destabilizing and, in particular, a temperature difference between the walls of 100 F leads to a reduction in the critical Reynolds number from 7800 to 4600.

Potter, M. C.↗

NASA NTRS1972

Unsteady radiant heating of conical foil receptors.

The time dependent thermal equations of two types of conical radiation detectors are discussed and solved for a step function application of radiation parallel to the axis of the cases. The first type has a heat sink at the base and the second has the vertex buried in a heat sink to a variable proportion of its total height. It is found that the first case has the lower sensitivity and better time response. The time response of the second case is improved by more deeply burying the vertex, but to the detriment of sensitivity. At no value of this inclusion can both a superior sensitivity and time response be achieved for the second case.

Saunders, R. C., Jr.↗

NASA NTRS1972

Composition of the upper clouds of Venus.

Recent developments have shed new light on the composition of the upper Venus clouds. An analysis of the Mariner 5 occultation data has led to improved temperature and pressure profiles. When these are combined with transit data, it is concluded that there is an optically thin cloud layer with a top at 81-km altitude where the temperature and pressure are, respectively, 175 K and 3 mb. The inclusion of temperatures derived from the near-infrared CO2 bands leads to the postulate of a second cloud deck with a top at 61-km altitude, where temperature and pressure are 260 K and 240 mb. Additional important constraints on cloud models are imposed by the measured abundances of HCl and H2O, by the polarization data, and by the reflection and emission spectra. It is concluded that the leading candidate for the uppermost clouds is liquid drops of HCl-H2O, that there is no recommended candidate for the second cloud deck, and that H2O ice is at most a minor component of these cloud systems.

Rea, D. G.↗

NASA NTRS1972

The Martian bow wave - Theory and observation.

Refinement of the relationship between the trajectory of Mariner 4 in its fly-by of Mars and the calculated location of a proposed Martian bow arising from interaction of the solar wind and the ionosphere by inclusion of aberration effects of the planet's motion about the sun. The modified theory indicates that the bow wave was crossed twice during a three-hour interval following the time of closest approach of Mariner 4 to Mars, instead of being missed slightly by the spacecraft as indicated in a previous paper in which the theory of this interaction was presented, and the solar wind was considered, for simplicity, to flow along the sun-Mars line. It is shown that the observed magnetic field changed abruptly at virtually the precise times of the shock crossings indicated by the theory. Although malfunction of the plasma probe prevents observational confirmation of these as shock crossings, this coincidence supports the recent suggestion of the magnetometer experimenters that a bow wave may have been traversed. It also supports the interpretation that the bow wave results from interaction of the solar wind with the ionosphere, and not with a weak planetary magnetic field.

Spreiter, J. R.↗

NASA NTRS1972

Correcting for nonlinear effects in fracture toughness testing.

Expressions for fracture toughness, which include nonlinear effects due to crack front plastic yield and possible small crack extension prior to fracture instability, are obtained for several test specimen configurations. Inclusion of such effects is based on a simple compliance type determination of the total energy rate at onset of fast fracture.

Liebowitz, H.↗

NASA NTRS1972

Experimental and theoretical investigation of stress wave attenuation in fiber reinforced composites.

The propagation of an initialrcidrical pressure pulse through a linear elastic fiber reinforced composite medium is analysed, both experimentally and analytically. In the experiment, tests were performed on plates with single and multiple circular inclusions embedded in a matrix of lower characteristic impedance. Sharp compression pulses were generated at an edge of the plate. Strain gages were mounted on various positions of the plate to determine the attenuation of the transient stress in the fiber reinforced composite. The qualitative analytical treatment is based on the methods of propagating stress discontinuities. Computer programs were written to numerically determine the changes in the shape of the leading wave front and the stresses immediately behind it. Experimental results for the attenuation of stress wave on steel-aluminum and steel-brass fiber-matrix composites compared very well with the computed analytical results when the applied pressure is generated by small explosive charges. The results did not compare well when the applied pressure is generated by projectile impact.

Yang, J. C. S.↗

NASA NTRS1972

Model atmosphere for engineering applications.

A model has been developed which can be used to determine system responses to nominal profiles of atmospheric parameters from orbital altitudes down to 25 km altitude. At the present time perturbations can be added to the model on an individual basis. However, future plans are for the inclusion of identified perturbations on a routine basis so that system sensitivities can be identified, evaluated, and minimized by design and operational constraints.

Smith, R. E.↗

NASA NTRS1972

Convective envelopes and radial pulsation of massive red supergiants.

A grid of convective envelope models covering a wide range of astrophysical parameters has been constructed for M-type supergiants with the help of theoretical evolutionary tracks, mixing-length theory, and the inclusion of hydrogen and helium ionization zones. Linear adiabatic pulsation theory has been used to obtain the first four normal modes of radial pulsation for all the models. All the convective envelopes are found to be dynamically stable. The theoretical pulsation calculations confirm that the primary observed period in variable M-type supergiants is probably due to the fundamental mode of radial pulsation.

Stothers, R.↗

NASA NTRS1972

The Nimbus 4 infrared spectroscopy experiment. I - Calibrated thermal emission spectra.

Measurement of the infrared spectrum of the earth and atmosphere between 400 and 1600/cm. In an effort to obtain spectra with high absolute accuracy, it was necessary to incorporate many factors into the calibration, including small departures from unity in the emissivity of the on-board calibration source, imbalance between cold and warm calibration ports, and effects due to orbital variations in instrument temperature. The inclusion of such higher order corrections, along with careful data screening processes, has ensured a high quality data set that can be used in a variety of geophysical and meteorological investigations. Representative samples of data are presented that illustrate the behavior of the thermal emission spectra under a variety of conditions encountered in a typical orbit, including extremes in temperature, surface reststrahlung (or residual ray) effects, and various types of cloud conditions.

Hanel, R. A.↗

NASA NTRS1972

Some aspects of the thermal history of lunar glass.

Electron microprobe examination revealed that glassy lunar fragments had inclusions as well as boundaries between mineral glasses of different compositions. Glassy lunar spherules showed detectable heterogeneity less marked than that of the fragments. The room-temperature refractive indices and densities of the spherules are changed by heat-treating them at 500 to 700 C. The large increases (as much as 2% in density and 0.7% in index of refraction) are difficult to explain on the basis of classical glass-transition phenomena alone unless extremely rapid cooling rates are assumed. Further, the spherules darkened significantly when they were heated in air or a medium vacuum above 625 C.

Cooper, A. R.↗

NASA NTRS1972

Fluctuation-induced conductivity of superconductors above the transition temperature - Regularization of the Maki diagram.

The Maki contribution to the conductivity above the superconducting transition temperature is regularized within the framework of the BCS theory. This is achieved through the renormalization of the impurity-scattering vertex by inclusion of the effects of pair fluctuations. The conductivity is evaluated for a thin film. It depends only on the reduced temperature and the normal resistance per square. Fair agreement is found with Al films over a wide temperature range. Agreement is not found with experiments on Bi, Pb, and Ga films, which apparently contain a strong additional pair-breaking effect. The temperature range in which interactions among fluctuations become important in the Maki conductivity is generally larger than that given by the Ginzburg criterion.

Keller, J.↗