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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 595 records · Page 33
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NASA NTRS1985

The cosmic ray differential diurnal variation dependences on the zenith angle and the geomagnetic disturbance

Simultaneous and continuous muon measurements in two opposite azimuthal directions under equal zenith angles demonstrated the importance of this method for cosmic ray diurnal variation investigations. Lately these measurements were extended by means of improved telescopes. The obtained cosmic ray diurnal variations were presented as intensity differential curves. Theoretical investigations connected the properties of these curves with some interplanetary spece parameters. The harmonics of these curves were interpreted physically. Some order difference curves were introduced. In earlier works some dependences between the parameters characterizing the first and the second harmonics of the differential intensity curves and the geomagnetic activity were found. Then all measurements were carried out under only one zenith angle. The results of investigations of similar dependences using data of simultaneous measurements under three different zenith angles are presented.

Kavlakov, S.↗
NASA NTRS1983

Evidence for an energy dependence in the short pathlengths of the cosmic ray pathlength distribution

The energy dependence of the short pathlengths in the cosmic ray pathlength distribution is investigated in a galactic propagation plus solar modulation calculation. In order to reproduce, simultaneously, the compiled B/C and sub-Fe/Fe measurements, an energy dependent deficiency of short pathlengths is required which is largest at low energies and becomes negligible above a few GeV/nucleon. Such behavior could imply a significant contribution from matter in the vicinity of the cosmic ray source or the acceleration site.

Garcia-Munoz, M.↗
NASA NTRS1983

The energy dependence of the secondary to primary ratio

The energy dependence of the secondary to primary ratios in the Cosmic Rays can be explained by a model accounting for the scattering of the particles by self-generated Alfven waves. This model predicts an energy-dependent truncation of the pathlength distribution.

Margolis, S. H.↗
NASA NTRS1985

IMF By-dependent plasma flow and Birkeland currents in the dayside magnetosphere. I - Dynamics Explorer observations

Plasma, magnetic-field, and dc electric-field observations from Dynamics Explorers 1 and 2 are used to investigate the morphology of solar-wind ion injection, Birkeland currents, and plasma convection in the morning sector for both positive and negative interplanetary magnetic field (IMF) By components. The results of the study are used to construct a By-dependent global convection model for southward IMF. A significant element of the model is the coexistence of three types of convection cells ('merging cells', 'viscous cells', and 'lobe cells'). This model can account for observations of a nearly stationary (in local time) convection 'throat', a sunward-antisunward convection reversal zone at the polar-cap boundary in both the morning and afternoon quadrants, the morphology of solar-wind ion injection and transport in the mid-altitude polar cusp, and the By-dependent dawn-dusk asymmetry of polar-cap electron fluxes.

Burch, J. L.↗
NASA NTRS1985

A time-dependent theoretical model of the polar wind Preliminary results

The coupled, time-dependent continuity, momentum, and energy equations of a two-ion O(+) and H(+) quasi-neutral plasma were solved in order to extend understanding of polar wind behavior. This numerical code allows studies of the time dependent behavior of polar wind-type flows into and out of the ionosphere. Initial studies indicate that the typical time constants for electron and ion temperature changes are of the order of minutes and tens of minutes, respectively. The response time of the minor high altitude ion O(+) is less than an hour, whereas that of the major ion, H(+), is many hours. The initial test runs also demonstrate the fact that temporary supersonic flows of both O(+) and H(+) are possible, especially in the presence of significant ion heating.

Gombosi, T. I.↗
NASA NTRS1985

The gravity dependence of the H-alpha width in late-type stars

A theoretical gravity-scaling law for the H-alpha absorption width in late-type stars is developed. The derivation is based upon (1) the hydrostatic thickening of stellar chromospheres with decreasing surface gravity, and (2) a dependence of the H-alpha width upon opacity and Doppler width in a region subject to a chromospheric temperature rise. The scaling relation is approximately consistent with the mean gravity dependence deduced from the empirical correlation between H-alpha and Ca II K Wilson-Bappu widths. The calculations suggest that gravity variations in chromospheric-mass column density may, in addition to Doppler velocity enhancements, control the width-luminosity broadening of the H-alpha profile in late-type stars.

Zarro, D. M.↗
NASA NTRS1985

Enhancement of intensity-dependent absorption in InP and GaAs at 1.9 microns by doping

It is pointed out that the study of intensity-dependent absorption (IDA) in general, and two-photon absorption (TPA), in particular, has suffered from experimental difficulties and inadequate theoretical models. Bass et al. (1979) could improve the experimental situation by making use of laser calorimetry to obtain directly the TPA coefficient of a medium with a high degree of sensitivity. In the present investigation, the employed technique has been used to study the effect of deep level dopants on IDA in InP and GaAs. It is found that the coefficient for IDA is strongly dependent on the presence of Fe in InP and Cr in GaAs. The conducted investigation had the objective to examine the effect of deep level impurities on IDA processes in InP and GaAs. Fe-doped InP and Cr-doped GaAs were compared with undoped crystals.

Li, N.-L.↗
NASA NTRS1985

Pressure dependence of the absolute rate constant for the reaction Cl + C2H2 from 210-361 K

In recent years, considerable attention has been given to the role of chlorine compounds in the catalytic destruction of stratospheric ozone. However, while some reactions have been studied extensively, the kinetic data for the reaction of Cl with C2H2 is sparse with only three known determinations of the rate constant k3. The reactions involved are Cl + C2H2 yields reversibly ClC2H2(asterisk) (3a) and ClC2H2(asterisk) + M yields ClC2H2 + M (3b). In the present study, flash photolysis coupled with chlorine atomic resonance fluorescence have been employed to determine the pressure and temperature dependence of k3 with the third body M = Ar. Room temperature values are also reported for M = N2. The pressure dependence observed in the experiments confirms the expectation that the reaction involves addition of Cl to the unsaturated C2H2 molecule followed by collisional stabilization of the resulting adduct radical.

Brunning, J.↗
NASA NTRS1985

Utilizing remote sensing of Thematic Mapper data to improve our understanding of estuarine processes and their influence on the productivity of estuarine-dependent fisheries

The purpose of the project is to refine and validate a probabilistic spatial computer model through the analyses of thematic mapper imagery. The model is designed to determine how the interface between marshland and water changes as marshland is converted to water in a disintegrating marsh. Coastal marshland in Louisiana is disintegrating at the rate of approximately 40 sq mi a year, and an evaluation of the potential impact of this loss on the landings of estuarine-dependent fisheries is needed by fisheries managers. Understanding how marshland-water interface changes as coastal marshland is lost is essential to the process of evaluating fisheries effects, because several studies suggest that the production of estuarine-dependent fish and shellfish may be more closely related to the interface between marshland and water than to acreage of marshland. The need to address this practical problem has provided an opportunity to apply some scientifically interesting new techniques to the analyses of satellite imagery. Progress with the development of these techniques is the subject of this report.

Browder, Joan A.↗
NASA NTRS1986

Inference of stress and texture from angular dependence of ultrasonic plate mode velocities

The theory for the angular dependence of the ultrasonic wave velocity in a symmetry plane of an orthorhombic, stressed material is presented. The two waves having polarizations in this plane are shown to have velocities which can be estimated from measurements of the SH sub 0 and S sub 0 guided modes of a thin plate: the relationship being exact for the SH sub 0 mode and requiring a 10% correction for the S sub 0 mode at long wavelength. It is then shown how stress and texture can be independently inferred from various features of the angular dependence of these two velocities. From the SH sub 0 data, the ability to determine the directions and differences in magnitudes of principal stresses is described and supported by experimental data on several materials. From a combination of the SH sub 0 and S sub 0 data, a procedure is proposed for determining the coefficients W sub 400, W sub 420 and W sub 440 of an expansion of the crystallite orientation distribution function in terms of generalized Legendre functions. Possible applications in process control are indicated.

Thompson, R. B.↗
NASA NTRS1986

Variation of cosmic rays and solar wind properties with respect to the heliospheric current sheet. II - Rigidity dependence of the latitudinal gradient of cosmic rays at 1 AU

The role which empirical determinations of the latitudinal variation of cosmic rays with respect to the current sheet may have in illuminating the importance of the cross-field drift of particles in the large-scale heliospheric magnetic field is discussed. Using K coronameter observations and measured solar wind speeds, the latitudinal gradients have been determined with respect to the current sheet for cosmic rays in four rigidity ranges. Gradients vary between approximately -2 and -50 pct/AU. The rigidity dependence of the decrease of cosmic ray flux with distance from the current sheet lies between the -0.72 to -0.86 power of the rigidity, with the exact dependence being determined by the definition used for the median rigidity of each monitor.

Newkirk, G., Jr.↗
NASA NTRS1986

The SIR-B observations of microwave backscatter dependence on soil moisture, surface roughness, and vegetation covers

An experiment was conducted from an L-band SAR aboard Space Shuttle Challenger in October 1984 to study the microwave backscatter dependence on soil moisture, surface roughness, and vegetation cover. The results based on the analyses of an image obtained at 21-deg incidence angle show a positive correlatlion between scattering coefficient and soil moisture content, with a sensitivity comparable to that derived from the ground radar measurements reported by Ulaby et al. (1978). The surface roughness strongly affects the microwave backscatter. A factor of two change in the standard deviation of surface roughness height gives a corresponding change of about 8 dB in the scattering coefficient. The microwave backscatter also depends on the vegetation types. Under the dry soil conditions, the scattering coefficient is observed to change from about -24 dB for an alfalfa or lettuce field to about -17 dB for a mature corn field. These results suggest that observations with a SAR system of multiple frequencies and polarizations are required to unravel the effects of soil moisture, surface roughness, and vegetation cover.

Wang, J. R.↗
NASA NTRS1986

Wavelength dependence of position angle in polarization standards

Eleven of the 15 stars on Serkowski's (1974) list of 'Standard Stars with Large Interstellar Polarization' were investigated to determine whether the orientation of the plane of their linear polarization showed any dependence on wavelength. Nine of the eleven stars exhibited a statistically significant wavelength dependence of position angle when measured with an accuracy of about 0.1 deg standard deviation. For the majority of these stars, the effect is caused primarily by intrinsic polarization. The calibration of polarimeter position angles in a celestial coordinate frame must evidently be done at the 0.1 deg level of accuracy by using only carefully selected standard stars or by using other astronomical or laboratory methods.

Dolan, J. F.↗
NASA NTRS1986

Temperature dependence of association of diatomic ions in diatomic gases

The present study compares the experimental rate coefficient temperature dependences for the association of diatomic ions in diatomic gases with the results of model calculations in which it is assumed that the stabilization of the initially formed unstable association complex occurs through the formation of a 'supercomplex'. The acceptable degree of agreement obtained between model and experimental data for the cases of four sample reactions, on the basis of a minimum of plausible assumptions, indicates that earlier theoretical models furnishing an accurate description of the formation and destruction of the association complex, but failing to reproduce experimental data, inadequately treated the temperature dependence of the stabilization step.

Johnsen, R.↗
NASA NTRS1986

Theoretical temperature dependence of solar cell parameters

A simple formulation has been derived for the temperature dependence of cell parameters for any solar cell material. Detailed calculations have been performed for high-quality monocrystalline GaAs, Si and Ge cells. Preliminary experimental data for GaAs and Si cells are close to the calculated values. In general, the higher the energy gap of a material, the small is the temperature dependence of its solar cell parameters.

Fan, John C. C.↗
NASA NTRS1986

The Shane-Wirtanen counts - Observer and time-dependent effects

In a recent paper, de Lapparent, Kurtz, and Geller (1986) announce the discovery of possible observer and time-dependent effects in the counts of galaxies in the Lick catalog and suggest that these effects may have distorted the galaxy correlation function calculated by Groth and Peebles (1986) from the Lick counts. In particular, they suggest that these effects may have introduced a break where none exists or may have diluted a break stronger than that seen by Groth and Peebles. The Lick counts have been reexamined and it is found that the observer and time-dependent effects are marginal and that they can have had only a negligible effect on the estimates of the correlation functions. Correlation functions have been calculated for each observer and time period separately and it is found that they all depart from the small-angle power law at about the expected scale. Further, the average of these correlation functions agrees extremely well with the average correlation function published by Groth and Peebles.

Groth, Edward J.↗
NASA NTRS1987

On time-dependent radiative transfer

An integral equation is developed for application to time-dependent laboratory experiments in which partial redistribution effects are important. The equation of transport with the Heasly-Kneer (1976) emission coefficient and the equation of statistical equilibrium lead to a time-dependent redistribution function containing an absorption - reemission term which decays exponentially in time and a scattering term which is instantaneous. This integral equation does not agree with an equation written by Payne et al. (1974) that has been used to compare theory with experiments. The difference between the Payne equation and the equation developed here needs to be examined in detail, since it might under some circumstances be on the same order as the difference between partial and complete redistribution.

Streater, A.↗
NASA NTRS1986

Time-dependent numerical simulation of hot ion outflow from the polar ionosphere

The time-dependent hydrodynamic model of Gombosi et al. (1985) was used to investigate the effects of bulk plasma heating on ion flows in the polar ionosphere. In the analysis, coupled time-dependent continuity, momentum, and energy equations of a two-ion (H/+/ and O/+/) quasi-neutral plasma were solved between 200 and 8000 km for polar wind conditions. In spite of its several limitations, the model can serve to indicate the gross behavior of polar region plasma flows. Two specific cases, ion heating and electron heating, were considered. The calculated temperature and flow profiles suggest that ion heating, rather than electron heating, generates the upwelling ion events, for which large transient O(+) outflows accompanied by elevated ion temperatures were observed.

Gombosi, T. I.↗