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At least 577 records · Page 32

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NASA NTRS1969

Remote sensing of winds and atmospheric turbulence by cross correlation of passive optical signals

A new method is described for the remote measurement of winds and atmospheric turbulence by the cross-correlation of passive optical signals. If small local variations in atmospheric density, temperature or other parameters cause fluctuations in scattered or thermal radiation detected by a radiometer on the ground, then the cross-correlation of fluctuations detected by two radiometers with crossed fields of view can yield turbulence information pertaining to the region about this intersection point. When the fields of view are not quite crossed turbulent eddies will be convected through the fields of view sequentially, and the transit times of the eddies identified by the correlation procedure will yield wind information. The successful application of this technique, detecting fluctuations in scattered sunlight, has demonstrated both the potential, and the present limitations of the method, which are discussed. Results for the power spectrum of the fluctuations and for winds at an altitude of 61 meters are shown.

Montgomery, A. J.↗

NASA NTRS2000

When is O+ Observed in the High Altitude Polar Cap?

Solar wind and IMF properties are correlated with the properties of O+ and H+ in the polar cap at altitudes greater than 5.5 Re geocentric using the Thermal Ion Dynamics Experiment (TIDE) on the Polar satellite. O+ is of primary interest in this study because the fraction of O+ present in the magnetosphere is commonly used as a measure of the ionospheric contribution to the magnetosphere. O+ is observed to be most abundant at lower latitudes when the solar wind speed is low and across most of the polar cap at high solar winds speeds and Kp. As the solar wind dynamic pressures increases more O+ is present in the polar cap. The O+ density is also shown to be more highly correlated with the solar wind dynamic pressure when IMF Bz is positive. H+ was not as well correlated with solar wind and IMF parameters although some correlation with IMF By is observed. H+ is more plentiful when IMF By is negative than when it is positive. In this data set H+ is very dominate so that if this plasma makes it to the plasma sheet its contribution to the plasma sheet would have a very low O+ to H+ ratio.

Elliott, H. A.↗

NASA NTRS2001

Relationship of Ion Vertical Flows to Topside Electron Temperatures

We present four periods of vertical/field-aligned O(+) flow parameters observed by DMSP12 and DMSP13 at 840 km when they passed the southern polar region near simultaneously during April 1996, together with POLAR observations at 5000 km near the same measurement period. The newest part in this presentation is the inclusion of the electron temperatures measured by DMSP spacecraft and provide us a snapshot of the O(+) vertical flow velocities and O(+) densities as they relate to electron temperatures along distinct satellite tracks passing through both the expected cleft and auroral regions, and the polar cap region. We find some correlation between vertical velocity and electron temperature along the DMSP spacecraft tracks, but only a weak correlation between the vertical velocity and electron temperature was shown in the statistics for the whole period when both flow velocity and electron temperature were measured. Downward O(+) flows occurred only for the lower (less than 4000 K) electron temperature regions. When electron temperatures were lower than 3000 K, the O(+) densities generally increased as the electron temperatures increased. But when electron temperatures were greater than 3500 K, the O(+) densities generally decreased as the electron temperatures increased. Different physical processes may correspond to these different correlation relations between O(+) densities and electron temperatures.

Zeng, W.↗

NASA NTRS1991

Quantum correlation between the junction-voltage fluctuation and the photon-number fluctuation in a semiconductor laser

The photon-number fluctuation of the external field from a semiconductor laser - which was reduced to below the standard quantum limit - is shown to be correlated with the measured junction-voltage noise. The spectral density of the sum of the photon-number fluctuation and junction-voltage fluctuation falls below the squeezed photon-number fluctuation. This confirms the theoretical predictions that this correlation, which originates in the dipole interaction between the internal field and electron-hole pairs, extends into the quantum regime.

Richardson, W. H.↗

NASA NTRS1986

Characterization of vegetation by microwave and optical remote sensing

Two series of carefully controlled experiments were conducted. First, plots of important crops (corn, soybeans, and sorghum), prairie grasses (big bluestem, switchgrass, tal fescue, orchardgrass, bromegrass), and forage legumes (alfalfa, red clover, and crown vetch) were manipulated to produce wide ranges of phytomass, leaf area index, and canopy architecture. Second, coniferous forest canopies were simulated using small balsam fir trees grown in large pots of soil and arranged systematically on a large (5 m) platform. Rotating the platform produced many new canopies for frequency and spatial averaging of the backscatter signal. In both series of experiments, backscatter of 5.0 GHz (C-Band) was measured as a function of view angle and polarization. Biophysical measurements included leaf area index, fresh and dry phytomass, water content of canopy elements, canopy height, and soil roughness and moisture content. For a subset of the above plots, additional measurements were acquired to exercise microwave backscatter models. These measurements included size and shape of leaves, stems, and fruit and the probability density function of leaf and stem angles. The relationships of the backscattering coefficients and the biophysical properties of the canopies were evaluated using statistical correlations, analysis of variance, and regression analysis. Results from the corn density and balsam fir experiments are discussed and analyses of data from the other experiments are summarized.

Daughtry, C. S. T.↗

NASA NTRS1979

Primordial inhomogeneities in the expanding universe. I - Density and velocity distributions of galaxies in the vicinities of rich clusters

The density profiles and Hubble flow deviations in the vicinities of rich galaxy clusters are derived for a variety of models of initial density and velocity perturbations at the recombination epoch. The galaxy correlation function, measured with respect to the Abell clusters, is used to normalize the theoretical models. The angular scales of the required primordial inhomogeneities are calculated. It is found that the resulting density profiles around rich clusters are surprisingly insensitive to the shape of the initial perturbations and also to the cosmological density parameter, Omega. However, it is shown that the distribution of galaxy radial velocities can provide a possible means of deriving Omega.

Silk, J.↗

NASA NTRS1976

Parametric dependence of ion temperature and relative density in the NASA Lewis SUMMA facility

Further hot-ion plasma experiments were conducted in the SUMMA superconducting magnetic mirror facility. A steady-state ExB plasma was formed by applying a strong radially inward dc electric field between cylindrical anodes and hollow cathodes located near the magnetic mirror maxima. Extending the use of water cooling to the hollow cathodes, in addition to the anodes, resulted in higher maximum power input to the plasma. Steady-state hydrogen plasmas with ion kinetic temperatures as high as 830 eV were produced. Functional relations were obtained empirically among the plasma current, voltage, magnetic flux density, ion temperature, and relative ion density. The functional relations were deduced by use of a multiple correlation analysis. Data were obtained for midplane magnetic fields from 0.5 to 3.37 tesla and input power up to 45 kW. Also, initial absolute electron density measurements are reported from a 90 deg Thomson scattering laser system.

Snyder, A.↗

NASA NTRS1976

Parametric dependence of ion temperature and relative density in the NASA Lewis SUMMA facility

Further hot-ion plasma experiments were conducted in the SUMMA superconducting magnetic mirror facility. A steady-state plasma with mutually perpendicular magnetic and electric fields was formed by applying a strong radially inward dc electric field between cylindrical anodes and hollow cathodes located near the magnetic mirror maxima. Extending the use of water cooling to the hollow cathodes, in addition to the anodes, resulted in higher maximum power input to the plasma. Steady-state hydrogen plasmas with ion kinetic temperatures as high as 830 eV were produced. Functional relations were obtained empirically among the plasma current, voltage, magnetic flux density, ion temperature, and relative ion density. The functional relations were deduced by use of a multiple correlation analysis. Data were obtained for midplane magnetic fields from 0.5 to 3.37 tesla and input power up to 45 kW. Also, initial absolute electron density measurements are reported from a 90 deg Thomson scattering laser system.

Snyder, A.↗

NASA NTRS1978

Preliminary design work on a DSN VLBI correlator

The Deep Space Network is in the process of fielding high-density digital instrumentation recorders for support of the Pioneer Venus 1978 entry experiment and other related tasks. It has long been obvious that these recorders would also serve well as the recording medium for very long base interferometry (VLBI) experiments with relatively weak radio sources, provided that a suitable correlation processor for these tape recordings could be established. The overall design and current status of a VLBI correlator designed to mate with these tape recorders are described.

Lushbaugh, W. A.↗

NASA NTRS1979

Association of low-frequency waves with suprathermal ions in the upstream solar wind

Observations obtained upstream of the earth's bowshock with the LASL/MPI plasma instruments and the UCLA magnetometers on ISEE-1 and 2 have revealed a striking relationship between the presence of low-frequency fluctuations in solar wind density and field strength and the different types of distribution functions of upstream ions. Waves are absent when the ions have the beamlike distribution of the 'reflected' ions. Large-amplitude waves are present only in conjunction with the 'diffuse' ions, which are characterized by flat energy spectra and broad angular distributions. The waves are largely compressive, showing very good correlation between oscillations in magnetic field strength and plasma density.

Paschmann, G.↗

NASA NTRS1962

Observations on Cavitation Damage in a Flowing System

Cavitation damage to specimens of stainless steel, carbon steel, aluminum, and plexiglas, placed in a cavitating venturi using water and mercury as test fluids is mostly in the form of irregularly shaped pits which do not change with additional exposure to the cavitating field within the limited durations utilized. The rate of damage is very high initially, decreases for a relatively short period of time, then increases again up to the maximum test durations of 150 hours with water and 270 hours with mercury. Observation of damage effects by several independent techniques, using a variety of specimen materials, with two different fluids under various fluid dynamic conditions, leads to a suggested correlating model in terms of the cavitation bubble density and energy and specimen material strength.

VENTURI TUBE↗

NASA NTRS1972

Low-energy particle radiation environment at synchronous altitude

The degradation of thermal control coatings of satellites due to the effects of low energy charged particles in the space environment is discussed. Data obtained from ATS-5 satellite measurement of proton and electron fluxes are presented. The variations in electron density, proton density, and magnetic activity are presented to show correlations which exist between these space factors.

Shelley, E. G.↗

NASA NTRS1973

Correlation and spectral analysis of daily solar radio flux.

Correlation and spectral analysis of solar radio flux density and sunspot number near the maximum of the sunspot cycle has indicated the existence of several effects. These include (1) long period amplitude modulation of the slowly varying component (SVC) of radio emission, (2) coronal storage over a period of the order of three solar rotations, (3) fast decay (one solar rotation period or less) of gyromagnetic emissions from radio sources, and (4) shift in location of chromospheric sources compared to those of either the upper corona or the photosphere.

El-Raey, M.↗

NASA NTRS1976

Microstructure of hot-pressed Al2O3-Si3N4 mixtures as a function of holding temperature

Powder mixtures of 40 m/o Si3N4-60 m/o Al2O3 were hot-pressed at 4000 psi at various holding temperatures from 1100 C to 1700 C. Scanning Electron Microscopy and Transmission Electro Microscopy results were correlated to X-ray phase analysis and density measurements. The progressively developed microstructure was used to interpret the densification behavior of SiAlON. Photomicrographs of microstructures are shown.

Yeh, H. C.↗

NASA NTRS1976

A description of the mechanical behavior of composite solid propellants based on molecular theory

Both the investigation and the representation of the stress-strain response (including rupture) of gum and filled elastomers can be based on a simple functional statement. Internally consistent experiments are used to sort out the effects of time, temperature, strain and crosslink density on gum rubbers. All effects are readily correlated and shown to be essentially independent of the elastomer when considered in terms of non-dimensionalized stress, strain and time. A semiquantitative molecular theory is developed to explain this result. The introduction of fillers modifies the response, but, guided by the framework thus provided, their effects can be readily accounted for.

Landel, R. F.↗

NASA NTRS1977

Diffuse gamma radiation

An examination of the intensity, energy spectrum, and spatial distribution of the diffuse gamma-radiation observed by SAS-2 satellite away from the galactic plane in the energy range above 35 MeV has shown that it consists of two components. One component is generally correlated with galactic latitudes, the atomic hydrogen column density was deduced from 21 cm measurements, and the continuum radio emission, believed to be synchrotron emission. It has an energy spectrum similar to that in the plane and joins smoothly to the intense radiation from the plane. It is therefore presumed to be of galactic origin. The other component is apparently isotropic, at least on a coarse scale, and has a steep energy spectrum. No evidence is found for a cosmic ray halo surrounding the galaxy in the shape of a sphere or oblate spheroid with galactic dimensions. Constraints for a halo model with significantly larger dimensions are set on the basis of an upper limit to the gamma-ray anisotropy.

Fichtel, C. E.↗

NASA NTRS1977

Microstructure of hot-pressed Al2O3-Si3N4 mixtures as a function of holding temperature

Powder mixtures of 40 m/o Si3N4-60 m/o Al2O3 were hot-pressed at 4000 psi at various holding temperatures from 1100 C to 1700 C. Scanning and transmission electron microscopy results were correlated to X-ray phase analysis and density measurements. The progressively developed microstructure was used to interpret the densification behavior of SiAlON.

Yeh, H. C.↗

NASA NTRS1977

Experimental observations of the chemistry of the SiO2/Si interface

Changes in silicon surface preparation prior to thermal oxidation are shown to leave a signature by altering the final SiO2/Si interface structure. Surface analytical techniques, including XPS, static SIMS, ion milling, and newly developed wet-chemical profiling procedures are used to obtain detailed information on the chemical structure of the interface. The oxides are shown to be essentially SiO2 down to a narrow transitional interface layer (3-7 A). A number of discrete chemical species are observed in this interface layer, including different silicon bonds (e.g., C-, OH-, H-) and a range of oxidation states of silicon (0 to +4). The effect of surface preparation and the observed chemical species are correlated with oxide growth rate, surface-state density, and flatband shifts after irradiation.

Grunthaner, F. J.↗