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At least 865 records · Page 48

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NASA NTRS1987

The nature of the meteoritic components of Apollo 16 soil, as inferred from correlations of iron, cobalt, iridium, and gold with nickel

The Apollo 16 soil concentrations of Ni, Fe, Co, Ir, and Au were studied to determine the correlations with Ni. The correlations obtained indicate that the variation in the siderophile element concentrations in Apollo 16 soils result from the variation in the concentration of a Fe-Ni metal (with the mean composition of 5.6 pct Ni and 0.36 pct Co) that contributes about 0.4-0.5 pct to a typical soil from Apollo 16. It is shown that the siderophile elements of the 'ancient meteorite component' of Anders et al. (1973) and Hertogen et al. (1977) are located in the grains of Fe-Ni metal that in turn are contained in noritic impact melt breccias produced about 3.9 Ga ago. The ancient Fe-Ni is different from the metal of ordinary chondrites by having lower Ni/Co, Ir/Ni, and Ir/Au ratios. It is shown that Ni in the Apollo 16 soil is contributed approximately equally by the 'ancient meteorite component' and the 'micrometeorite component' (dominated by carbonaceous chondrites); however, most of the variation in Ni concentration results from the variation of the ancient Fe-Ni metal among samples of Apollo 16 soil.

Korotev, Randy L.↗

NASA NTRS1987

Experimental data correlations for the effects of rotation on impingement cooling of turbine blades

The effects of rotation on impingement cooling have been experimentally studied under simulated gas turbine operating conditions. A large scale model of a blade is spun in vacuum. External heating is simulated by resistve dissipation in the thin wall of the model, which is impingement cooled. The local internal Nu is measured by an IR radiometric technique with high spatial resolution. At low rotational speeds the data agree well with published measurements taken under stationary conditions. At higher speeds, a decrease in the average Nu by up to 20-30 percent is observed. Severe gradients are generated near the hub region. Empirical correlations, which fit the data well and render it more useful for design purposes, are presented. Measurements and correlations suggest that rotational effects are very important and can cause premature blade failure.

Kreatsoulas, J. C.↗

NASA NTRS1987

Correlations and Ostwald ripening

A previously developed model (Weins and Cahn, 1973) describing the growth of spheres of a second phase in metal alloys (Ostwald coarsening) is slightly modified to make it possible to study the complete time evolution of the system rather than simply the late-stage scaling behavior. Closed equations are obtained which describe the time evolution of two-particle correlations in the system. The development of the correlations is analyzed, and simpler expressions are found and solved numerically. The results are compared with experimental data for different systems (e.g., Ni-Al, Ni-Cr-Al, Co-Ni-Cr-Ti, Cu-Co, and MgO-Fe), alternate methods, and existing theories.

Marder, M.↗

NASA NTRS1987

Small Al clusters. I - The effect of basis set and correlation on the geometry of small Al clusters

A detailed study is presented of the basis set requirements and effects of correlation on the geometry and structure of small Al(n) clusters n = 2, 4, and 13. An effective core potential (ECP) is developed from the Huzinaga basis which accurately reproduces the all-electron results. It is found that depolarization functions are very important in computing the bond length, and that the bond contraction obtained is about as large for a 13-atom cluster as for the Al(4) rhombus structure. With d functions on each center in Al(13), a bond distance shorter than the bulk is obtained, as expected. The inclusion of correlation in Al(4) is found to be less important than the addition of polarization functions for determining the bond length, but increases substantially the calculated atomization energy. These calibration calculations allow an accurate treatment for Al(n) clusters to be designed.

Bauschlicher, Charles W., Jr.↗

NASA NTRS1986

Correlated isotopic effects near the Fe abundance peak

A special class of refractory inclusions in carbonaceous meteorites show large isotopic anomalies in Ca, Ti, and Cr that are correlated by virtue of having been measured on the same samples. Large excesses in the neutron-rich isotopes Ca-48, Ti-50, and Cr-54 are comparable and consistent with theoretical calculations of the composition of materials produced during neutron-rich nuclear statistical equilibrium nucleosynthesis. This correlation suggests that materials from very near the core of an expoloding massive star may be injected into the interstellar medium.

Papanastassiou, D. A.↗

NASA NTRS1987

Correlation between aircraft MSS and LIDAR remotely sensed data on a forested wetland in South Carolina

Wetlands in a portion of the Savannah River swamp forest, the Steel Creek Delta, were mapped using April 26, 1985 high-resolution aircraft multispectral scanner (MSS) data. Due to the complex spectral characteristics of the wetland vegetation, it was necessary to implement several techniques in the classification of the MSS imagery of the Steel Creek Delta. In particular, when performing unsupervised classification, an iterative cluster busting technique was used which simplified the cluster labeling process. In addition to the MSS data, light detecting and ranging (LIDAR) data were acquired by National Aeronautics and Space Administration (NASA) personnel along two flightlines over the Steel Creek Delta. These data were registered with the wetland classification map and correlated. Statistical analyses demonstrated that the laser derived canopy height information was significantly correlated with the Steel Creek Delta wetland classes encountered along the profiling transect of the LIDAR data.

Jensen, John R.↗

NASA NTRS1988

A simplified, general-purpose deep-space ranging correlator design

A much-simplified, yet more general-purpose multi-channel deep-space ranging system correlator design that was used in past JPL spacecraft ranging systems is described. The method applies to detection of both single-component and multiple-component ranging codes, in either sequential (mu) or composite (pi) transmitted forms, and using either pseudonoise or square-wave components. Using this design, the Phobos Probe ranging system correlator computational complexity was reduced by over three orders of magnitude in multiply-and-add circuits and 45,000 bits of accumulator storage.

Tausworthe, R. C.↗

NASA NTRS1988

Improvement of the Reynolds-stress model by a new pressure-strain correlation

A study is made to improve the predictions of Reynolds stresses in backward facing step flows, through modifications of the pressure-strain correlation. The mean-strain term of the pressure-strain correlation is formulated only in terms of nonisotropic turbulence in order to take the severe nonisotropic effect caused by a separating flow. This model is compared with other models and results are verified with experimental results.

Amano, Ryoichi S.↗

NASA NTRS1987

Relations between two-point correlations and pressure strain terms

The structure of the two-point spatial correlations (velocity-velocity, velocity-scalar, and scalar-scalar) were studied with a view to improve turbulence closure models. The linear model for the two-point correlations proposed by Naot provides a method of including the information about the turbulence structure in the turbulence models. The assumptions and adequacy of this model were tested against the homogeneous shear flow simulation data base. The model performs poorly in some details and it is suggested how it may be improved. The models were also tested for rapid pressure-strain terms in a variety of flows including axisymmetric expansion and contraction flows, homogeneous shear flow, channel flow, and boundary layer.

Wolfshtein, Micha↗

NASA NTRS1988

Periodically correlated processes and their stationary dilations

An explicit form for a stationary dilation for periodically correlated random processes is obtained. This is then used to give spectral conditions for a periodically correlated process to be non-deterministic, purely deterministic, minimal, and to have a positive angle between its past and future.

Miamee, A. G.↗

NASA NTRS1988

Loran-C monitor correlation over a 92-mile baseline in Ohio

Two Loran C monitors, at Galion and Athens, Ohio, were operated over a one-year period, measuring chain 9960 Time Delay (TD) and Signal to Noise Ratio (SNR). Analysis of data concentrated on correlation of short term TD variations during the winter months of 1985 to 86, over the 92 nm baseline. Excellent correlation was found, with slight additional improvement possible if local temperature is also included in the analysis. Although SNR and TD effects were suspected during the presence of thunderstorms near the monitors, the scope of the study did not permit storm by storm analysis. A computer tape data base of all measurements was produced, with measurements at both sites included. Data recording and analysis concentrated on the fall and winter months of September 1985 to February 1986.

Lilley, Robert W.↗

NASA NTRS1988

Correlations of velocity and temperature fluctuations in the stagnation-point flow of circular cylinder in turbulent flow

Boundary layer flow and turbulence transport analyses to study the influence of the free-stream turbulence on the surface heat transfer rate and the skin friction around the stagnation point of a circular cylinder in a turbulent flow are presented. The analyses are formulated with the turbulent boundary layer equations, the Reynolds stress transport equations and the k - epsilon two-equation turbulence modeling. The analyses are used to calculate the time-averaged turbulence double correlations, the mean flow properties, the surface heat transfer rate and the skin friction with an isotropic turbulence in the freestream. The analytical results are described and compared with the existing experimental measurements. Depending on the free-stream turbulence properties, the turbulence kinetic energy can increase or decrease as the flow moves toward the surface. However, the turbulence kinetic energy induces large Reynolds normal stresses at the boundary layer edge. The Reynolds normal stresses change the boundary layer profiles of the time-averaged double correlations of the velocity and temperature fluctuations, the surface heat transfer rate and the skin friction. The free-stream turbulence dissipation rate can affect the stagnation-point heat transfer rate but the influence of the free-stream temperature fluctuation on the heat transfer rate is insignificant.

Wang, Chi R.↗

NASA NTRS1987

Correlation between aircraft MSS and lidar remotely sensed data on a forested wetland

Inland wetland in a portion of the Savannah River swamp forest were mapped with an overall accuracy of 88.5 percent on April 26,l985 using high resolution aircraft Daedalus AADS-1268 MSS data. In addition, data were acquired using a NASA sensor system flown along two flight lines over the Steel Creek Delta. The data were significantly correlated with in situ tree height measurements. The data were registered to the wetland classification map and correlated. Statistical analyses demonstrated that the laser derived canopy height information was significantly associated with the Steel Creek Delta wetland classes encountered along the transect (an F-value of 58.46 at the 0.0001 level of confidence). The relationship between vegetation height and vegetation type was then used to produce a three-dimensional model of the landscape which can be of value when computing biomass or canopy density in this forested wetland environment.

Jensen, John R.↗

NASA NTRS1988

A five-band study of spiral galaxies - X-ray, optical, near- and far-infrared, and radio continuum correlations

A statistical analysis is given of the relationships between global emission properties of spiral galaxies, including the radio continuum, far-infared, near-infrared H-band, optical (B), and X-ray emission. Different properties are observed in early-type and in late-type spiral galaxies, which can be ascribed to the presence of prominent bulges in the former. In late-type spirals, the statistical properties of the emission at different wavelengths are consistent with a common disk/arm origin. The power-law exponents of the correlations are consistent with a steeper IMF in low-luminosity galaxies and with the presence of an obscured starburst component in high-luminosity galaxies. The strongest correlation of the radio continuum luminosity with any other variable is with the far-infrared, suggesting that the radio emission is disjoint from the older low-mass stellar component.

Fabbiano, G.↗

NASA NTRS1988

Growth of correlation in compressible two-dimensional magnetofluid turbulence

Spectral transfer has been proposed as the primary mechanism for generating outward-propagating Alfven waves in the solar wind. This process has been investigated extensively for imcompressible magnetofluids, but the issue of whether it occurs in compressible magnetofluids such as the solar wind remains unresolved. The results of direct numerical simulations of nonisentropic-compressible two-dimensional MHD turbulence indicate that, for systems with finite initial cross helicity, the correlation between the fluctuating velocity field and the fluctuating magnetic field grows as a function of time. This growth of correlation can be interpreted as a turbulent process, as shown by examination of modal wavenumber spectra.

Dahlburg, R. B.↗

NASA NTRS1988

Clustering correlations and limits on cosmological gravitational waves

A cosmological background of gravitational waves induces angular deviations in the propagation of light traversing it. All observed astrophysical sources might therefore have varying apparent positions, with the time dependence set by the wave period. Wavelengths greater than a kiloparsec are examined, so the positions are frozen but in general correlated. Comparison with observed galaxy-galaxy n-point correlation functions provide a spectrum-independent limit on the energy density of gravitational waves with wavelengths between a few tens of kiloparsecs and a few hundred megaparsecs of Omega(GW) less than 0.001.

Linder, Eric V.↗

NASA NTRS1987

Correlation between aircraft MSS and LIDAR remotely sensed data on a forested wetland in South Carolina

Jensen, John R.↗

NASA NTRS1988

Aircraft on-board SAR processing using a frequency-domain fast correlation technique

The design of a frequency-domain fast correlation processor for aircraft onboard synthetic-aperture radar (SAR) applications is described. The design uses the fast Fourier transform (FFT) fast correlation technique to perform both range and azimuth pulse compression functions for the NASA/JPL L-band, quad-polarization airborne SAR. The subject processor is computationally efficient and requires a simple control unit. It is capable of producing single-look, 8-m (slant range) by 10-m (azimuth) resolution, SAR images of a selected polarization over a swath width of up to 15 km in real time onboard the aircraft.

Liu, Kuang Y.↗