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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Wave normal direction and spectral properties of whistler mode hiss observed on the DE 1 satellite

Hiss is represented by a field distribution function in order to investigate magnetospheric hiss as a spatially and temporally enduring phenomenon. The study takes into account the whistler mode relationships and the linear and spin motion of the satellite. Hiss signals received on September 23, 1983 by the DE-1 electric and magnetic field antennas are analyzed. A wave normal angle of 60 + or - 5 deg with respect to the local geomagnetic field is found near the geomagnetic equator, and wave normal directions from 30-80 deg with respect to the local geomagnetic field are found away from the equator.

Sonwalkar, Vikas S.↗
NASA NTRS1989

Improved Algorithm For Finite-Field Normal-Basis Multipliers

Improved algorithm reduces complexity of calculations that must precede design of Massey-Omura finite-field normal-basis multipliers, used in error-correcting-code equipment and cryptographic devices. Algorithm represents an extension of development reported in "Algorithm To Design Finite-Field Normal-Basis Multipliers" (NPO-17109), NASA Tech Briefs, Vol. 12, No. 5, page 82.

Wang, C. C.↗
NASA NTRS1989

An LDA (Laser-Doppler Anemometry) investigation of three-dimensional normal shock wave boundary-layer interactions

Nonintrusive measurements were made of a normal shock wave/boundary layer interaction. Two dimensional measurements were made throughout the interaction region while 3-D measurements were made in the vicinity of the shock wave. The measurements were made in the corner of the test section of a continuous supersonic wind tunnel in which a normal shock wave had been stabilized. Laser Doppler Anemometry, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The results define the flow field structure in detail for each case.

Chriss, R. M.↗
NASA NTRS1990

Low frequency electrical noise across contacts between a normal conductor and superconducting bulk YBa2Cu3O7

Virtually every device that makes use of the new ceramic superconductors will need normal conductor to supercondutor contacts. The current-voltage and electrical noise characteristics of these contacts could be become important design considerations. I-V and low frequency electrical noise measurements are presented on contacts between a normal conductor and superconducting polycrystalline YBa2Cu3O7. The contacts were formed by first sputtering gold palladium pads onto the surface of the bulk superconductor and then using silver epoxy to attach a wire(s) to each pad. Voltage across the contacts was found for small current densities. The voltage spectral density, S sub v(f), a quanity often used to characterize electrical noise, very closely followed an empirical relationship given by, S sub v(f) = C(VR)sq/f, where V is the DC voltage across the contact, R is the contact resistance, F is frequency, and C is a contant found to be 2 x 10(exp -10)/Omega sq at 78 K. This relationship was found to be independent of contact area, contact geometry, sample fabrication technique, and sample density.

Hall, J.↗
NASA NTRS1989

Validation of MCDS by comparison of predicted with experimental velocity distribution functions in rarefied normal shocks

Velocity distribution functions in normal shock waves in argon and helium are calculated using Monte Carlo direct simulation. These are compared with experimental results for argon at M = 7.18 and for helium at M = 1.59 and 20. For both argon and helium, the variable-hard-sphere (VHS) model is used for the elastic scattering cross section, with the velocity dependence derived from a viscosity-temperature power-law relationship in the way normally used by Bird (1976).

Pham-Van-diep, Gerald C.↗
NASA NTRS1990

Normalization of satellite imagery

Sets of Thematic Mapper (TM) imagery taken over the Washington, DC metropolitan area during the months of November, March and May were converted into a form of ground reflectance imagery. This conversion was accomplished by adjusting the incident sunlight and view angles and by applying a pixel-by-pixel correction for atmospheric effects. Seasonal color changes of the area can be better observed when such normalization is applied to space imagery taken in time series. In normalized imagery, the grey scale depicts variations in surface reflectance and tonal signature of multi-band color imagery can be directly interpreted for quantitative information of the target.

Kim, Hongsuk H.↗
NASA NTRS1990

An LDA investigation of the normal shock wave boundary layer interaction

Nonintrusive measurements have been made of two normal shock wave-boundary layer interactions. Two-dimensional measurements were made throughout the interaction region while three-dimensional measurements were made in the vicinity of the shock wave. The measurements were made in the corner of the test section of a continuous flow supersonic wind tunnel in which a normal shock wave had been stabilized. LDA, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The reported results define the flowfield structure in detail for each case.

Chriss, R. M.↗
NASA NTRS1991

A laser velocimeter investigation of the normal shock-wave boundary layer interaction

Nonintrusive 3-D measurements were made of a normal shock wave/turbulent boundary layer interaction. The measurements were made through a quadrant of a square test section of a continuous flow supersonic wind tunnel in which a normal shock wave had been stabilized. Two dimensional measurements were made throughout the interaction region while 3-D measurements were made near the corner in the vicinity of the shock where 3-D flow effects were expected to be significant. Laser Doppler velocimetry, surface static pressure measurements, and flow visualization techniques were used for two freestream nominal Mach number test cases: 1.6 and 1.3. No turbulence information was obtained. The mean velocity measurements were converted to Mach number by recording the wind tunnel total temperature. Some shock oscillation was present during both of the test cases. After startup of the wind tunnel, the shock oscillated with an amplitude of approx. + or - 1 cm, however, after reaching steady condition, the shock oscillation amplitude was greatly reduced, as evidenced by the laser velocimeter results. The Mach 1.3 test case resulted in a nearly uniform flow without secondary shock waves and with no or very isolated corner separation.

Chriss, Randall M.↗
NASA NTRS1989

A restricted signature normal form for Hermitian matrices, quasi-spectral decompositions, and applications

In recent years, a number of results on the relationships between the inertias of Hermitian matrices and the inertias of their principal submatrices appeared in the literature. We study restricted congruence transformation of Hermitian matrices M which, at the same time, induce a congruence transformation of a given principal submatrix A of M. Such transformations lead to concept of the restricted signature normal form of M. In particular, by means of this normal form, we obtain short proofs of most of the known inertia theorems and also derive some new results of this type. For some applications, a special class of almost unitary restricted congruence transformations turns out to be useful. We show that, with such transformations, M can be reduced to a quasi-diagonal form which, in particular, displays the eigenvalues of A. Finally, applications of this quasi-spectral decomposition to generalize inverses and Hermitian matrix pencils are discussed.

Freund, Roland W.↗
NASA NTRS1991

Low frequency electrical noise across contacts between a normal conductor and superconducting bulk YBa2Cu3O7

Virtually every device that makes use of the new ceramic superconductors will need normal conductor to superconductor contacts. The current-voltage and electrical noise characteristics of these contacts could become important design considerations. I-V and low frequency electrical noise measurements are presented on contacts between a normal conductor and superconducting polycrystalline YBa2Cu3O7. The contacts were formed by first sputtering gold palladium pads onto the surface of the bulk superconductor and then using silver epoxy to attach a wire(s) to each pad. Voltage across the contacts was found for small current densities. The voltage spectral density, S sub v(f), a quantity often used to characterize electrical noise, very closely followed an empirical relationship given by S sub v(f) = C(VR)sq/f, where V is the DC voltage across the contact, R is the contact resistance, F is frequency, and C is a contant found to be 2 x 10(exp -10)/Omega sq at 78 K. This relationship was found to be independent of contact area, contact geometry, sample fabrication technique, and sample density.

Hall, J.↗
NASA NTRS1991

Incoherent vs. coherent behavior in the normal state of copper oxide superconductors

The self-consistent quantum fluctuations around the mean-field Hartree-Fock state of the Hubbard model provide a very good description of the ground state and low temperature properties of a 2-D itinerant antiferromagnet. Very good agreement with numerical calculations and experimental data is obtained by including the one- and two-loop spin wave corrections to various physical quantities. In particular, the destruction of the long-range order above the Neel temperature can be understood as a spontaneous generation of a length-scale epsilon(T), which should be identified as the spin correlation length. For finite doping, the question of the Hartree-Fock starting point becomes a more complex one since an extra hole tends to self-trap in antiferromagnetic background. Such quantum defects in an underlying antiferromagnetic state can be spin-bags or vortex-like structures and tend to suppress the long-range order. If motion of the holes occurs on a time-scale shorter than the one associated with the motion of these quantum defects of a spin background, one obtains several important empirical features of the normal state of CuO superconductors like linear T-dependence of resistivity, the cusp in the tunneling density of states, etc. As opposed to a familiar Fermi-liquid behavior, the phenomenology of the above system is dominated by a large incoherent piece of a single hole propagator, resulting in many unusual normal state properties.

Tesanovic, Zlatko↗
NASA NTRS1992

Weighted current sheets supported in normal and inverse configurations - A model for prominence observations

A technique which incorporates both photospheric and prominence magnetic field observations is used to analyze the magnetic support of solar prominences in two dimensions. The prominence is modeled by a mass-loaded current sheet which is supported against gravity by magnetic fields from a bipolar source in the photosphere and a massless line current in the corona. It is found that prominence support can be achieved in three different kinds of configurations: an arcade topology with a normal polarity; a helical topology with a normal polarity; and a helical topology with an inverse polarity. In all cases the important parameter is the variation of the horizontal component of the prominence field with height. Adding a line current external to the prominence eliminates the nonsupport problem which plagues virtually all previous prominence models with inverse polarity.

Demoulin, P.↗
NASA NTRS1992

Energy dependence of normal branch quasi-periodic intensity oscillations in low-mass X-ray binaries

The properties of the approximately 6 Hz quasi-periodic X-ray intensity oscillations observed in the low-mass X-ray binary Cyg X-2 when it is on the normal spectral branch are shown to be consistent with a model in which photons from a central source with a fixed spectrum are Comptonized by an oscillating radial inflow. As the electron scattering optical depth of the flow varies, the spectrum of the escaping X-rays appears to rotate about a pivot energy that depends mainly on the electron temperature in the flow. The temperature derived from the observed energy dependence of the Cyg X-2 normal branch oscillations is approximately 1 keV, in good agreement with the estimated Compton temperature of its X-ray spectrum. The mean optical depth tau of the Comptonizing flow is inferred to be about 10, while the change in tau over an oscillation is estimated to be about 1; both values are in good agreement with radiation hydrodcode simulations of the radial flow.

Miller, Guy S.↗
NASA NTRS1992

Normalization of multidirectional red and NIR reflectances with the SAVI

Directional reflectance measurements were made over a semi-desert gramma grassland at various times of the growing season. View angle measurements from +40 to -40 degrees were made at various solar zenith angles and soil moisture conditions. The sensitivity of the Normalized Difference Vegetation Index (NDVI) and the Soil Adjusted Vegetation Index (SAVI) to bidirectional measurements was assessed for purposes of improving remote temporal monitoring of vegetation dynamics. The SAVI view angle response was found to be symmetric about nadir while the NDVI response was strongly anisotropic. This enabled the view angle behavior of the SAVI to be normalized with a cosine function. In contrast to the NDVI, the SAVI was able to minimize soil moisture and shadow influences for all measurement conditions.

Huete, A. R.↗
NASA NTRS1993

Metals combustion in normal gravity and microgravity

The study of the combustion characteristics of metallic materials has been an ongoing area of research at the NASA White Sands Test Facility (WSTF). This research has been in support of both government and industrial operations and deals not only with the combustion of specific metallic materials but also with the relative flammabilities of these materials under similar conditions. Since many of the metallic materials that are characterized at WSTF for aerospace applications are to be used in microgravity environments, it was apparent that the testing of these materials needed to proceed in a microgravity environment. It was believed that burning metallic materials in a microgravity environment would allow the evaluation of the validity of applying normal gravity combustion tests to characterize metallic materials to be used in microgravity environments. It was also anticipated that microgravity testing would provide insight into the general combustion process of metallic materials. The availability of the NASA Lewis Research Center's (LeRC) 2.2-second drop tower provided the necessary facility to accomplish the microgravity portion of the testing while the normal gravity testing was conducted at NASA WSTF. The tests, both at LeRC and WSTF, were conducted in the same instrumented system and utilized the standard metal flammability test of upward propagation burning of cylindrical rod samples.

Steinberg, Theodore A.↗
NASA NTRS1993

Robust controller design for flexible structures using normalized coprime factor plant descriptions

Stabilization is a fundamental requirement in the design of feedback compensators for flexible structures. The search for the largest neighborhood around a given design plant for which a single controller produces closed-loop stability can be formulated as an H(sub infinity) control problem. The use of normalized coprime factor plant descriptions, in which the plant perturbations are defined as additive modifications to the coprime factors, leads to a closed-form expression for the maximum neighborhood boundary allowing optimal and suboptimal H(sub infinity) compensators to be computed directly without the usual gamma iteration. A summary of the theory on robust stabilization using normalized coprime factor plant descriptions is presented, and the application of the theory to the computation of robustly stable compensators for the phase version of the Control-Structures Interaction (CSI) Evolutionary Model is described. Results from the application indicate that the suboptimal version of the theory has the potential of providing the bases for the computation of low-authority compensators that are robustly stable to expected variations in design model parameters and additive unmodeled dynamics.

Armstrong, Ernest S.↗
NASA NTRS1993

Global normal-mode Rossby waves observed in stratospheric ozone data

Westward-propagating Rossby normal-mode planetary waves are documented in stratospheric ozone data using Solar Backscatter Ultraviolet (SBUV) satellite measurements. These modes are evidenced by enhanced spectral power and near-global coherence for westward-traveling zonal wave 1 oscillations with periods of 5-10 days. The ozone waves have maxima in high latitudes of the middle stratosphere (due to transport) and over midlatitudes in the upper stratosphere (due to photochemistry). These modes are nearly continuous throughout the eight years of SBUV observations, with maximum global coherence during the equinoxes. The upper-stratospheric waves are symmetric (in phase) between hemispheres, even for modes previously identified as antisymmetric in geopotential height. This behavior is due to differing wave vertical structure in each hemisphere; the planetary temperature waves are nearly in phase in the upper stratosphere, even though the height waves are out of phase. The observed ozone waves are furthermore compared to calculations based on linear wave transport and photochemistry, incorporating derived wind and temperature fields. Good agreement is found, showing that normal modes provide an idealized context to study the linear wave behavior of trace constituents in the real atmosphere.

Randel, William J.↗
NASA NTRS1993

On the accurate prediction of the wall-normal velocity in compressible boundary-layer flow

A method for predicting the wall-normal velocity in compressible boundary layer flow is presented which is the extension of the fully implicit, spectral collocation method developed by Pruett and Streett (1991). The spectrally accurate method under consideration is capable of extracting the wall-normal velocity from the transformation from the physical plane to a computational plane, without interpolation, leaving the continuity equation free as a check on the quality of the solution. When used in conjunction with a highly accurate spectral collocation method for the compressible boundary-layer equations, the method gives a discrete solution which satisfies the continuity equation nearly to machine precision.

Pruett, C. D.↗