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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Morphology of an aluminum alloy eroded by a jet of angular particles impinging at normal incidence

The erosion of an aluminum alloy impinged by crushed glass particles at normal incidence was studied. The erosion patterns were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy, and surface profilometer measurements. From the analysis of specimens tested at various driving gas pressures and time intervals, four distinct erosion regions were identified. A study of pit morphology and its relationship to cumulative erosion was made. Cutting wear is believed to be the predominant material removal mechanism; some evidence of deformation wear was found during the incubation period.

Rao, P. V.↗
NASA NTRS1983

Spherical micro-glass particle impingement studies of thermoplastic materials at normal incidence

Light optical and scanning electron microscope studies were conducted to characterize the erosion resistance of polymethyl methacrylate (PMMA), polycarbonate (PC), polytetrafluoroethylene (PTFE) and ultra-high-molecular-weight-polyethylene (UHMWPE). Erosion was caused by a jet of spherical micro-glass beads at normal impact. During the initial stages of damage, the surfaces of these materials were studied using a profilometer. Material buildup above the original surface was observed on PC and PMMA. As erosion progressed, this buildup disappeared as the pit became deeper. Little or no buildup was observed on PTFE and on UHMWPE. UHMWPE and PTFE are the most resistant materials and PMMA the least. Favorable properties for high erosion resistance seem to be high values of ultimate elongation, and strain energy and a low value of the modulus of elasticity. Erosion-rate-versus-time curves of PC and PTFE exhibit incubation, acceleration and steady state periods. A continuously increasing erosion rate period was observed however for PMMA instead of a steady state period. At early stages of damage and at low impact pressure material removal mechanisms appear to be similar to those for metallic materials.

Rao, P. V.↗
NASA NTRS1982

Study to assess the importance of errors introduced by applying NOAA 6 and NOAA 7 AVHRR data as an estimator of vegetative vigor: Feasibility study of data normalization

The use of NOAA AVHRR data to map and monitor vegetation types and conditions in near real-time can be enhanced by using a portion of each GAC image that is larger than the central 25% now considered. Enlargement of the cloud free image data set can permit development of a series of algorithms for correcting imagery for ground reflectance and for atmospheric scattering anisotropy within certain accuracy limits. Empirical correction algorithms used to normalize digital radiance or VIN data must contain factors for growth stage and for instrument spectral response. While it is not possible to correct for random fluctuations in target radiance, it is possible to estimate the necessary radiance difference between targets in order to provide target discrimination and quantification within predetermined limits of accuracy. A major difficulty lies in the lack of documentation of preprocessing algorithms used on AVHRR digital data.

Duggin, M. J.↗
NASA NTRS1983

An efficient algorithm for generating random number pairs drawn from a bivariate normal distribution

An efficient algorithm for generating random number pairs from a bivariate normal distribution was developed. Any desired value of the two means, two standard deviations, and correlation coefficient can be selected. Theoretically the technique is exact and in practice its accuracy is limited only by the quality of the uniform distribution random number generator, inaccuracies in computer function evaluation, and arithmetic. A FORTRAN routine was written to check the algorithm and good accuracy was obtained. Some small errors in the correlation coefficient were observed to vary in a surprisingly regular manner. A simple model was developed which explained the qualities aspects of the errors.

Campbell, C. W.↗
NASA NTRS1982

Extra-solar astronomy with a 2.4 m normal incidence X-ray telescope at 0.1 arcsec resolution

The advantages and disadvantages for astrophysical observations of a normal incidence X-ray telescope are considered. The baseline configuration is for a 2.4 meter diameter mirror operating at 0.23-0.28 keV with a CCD detector having a pixel size equivalent to 0.1 arcsec. This resolution enables X-ray images to be made comparable to those of Space Telescope in the optical and to those of the Very Large Array in the radio for a large number of sources. Specific examples cover essentially the entire range of astrophysics.

Elvis, M.↗
NASA NTRS1983

Constant-temperature hot-wire anemometer practice in supersonic flows. I - The normal wire

The performance of a constant-temperature normal hot-wire in a supersonic flow is critically examined. It is shown that this instrument is inherently unsuitable for measuring turbulent temperature correlations because of the highly nonlinear response to temperature fluctuations, particularly at low overheat ratios. The instrument is therefore limited to measurements of mean and fluctuating mass-flow rates. Suitable calibration procedures, as well as the limits on spatial and temporal resolution are discussed, and corrections for mean stagnation temperature changes are suggested.

Smits, A. J.↗
NASA NTRS1982

A comparative study of monocot and dicot root development in normal /earth/ and hypogravity /space/ environments

The anatomy and fine structure of roots from oat and mung bean seedlings grown under hypogravity conditions aboard NASA's Space Shuttle were examined and compared to those of roots from ground control plants grown under similar conditions. Oat roots from both sets of plants exhibited normal tissue organization and ultrastructural features, with the exception of cortex cell mitochondria, which characteristically showed a 'swollen' morphology. Flight-grown mung bean roots differed significantly from the controls in that root cap cells were somewhat disorganized and degraded in appearance, especially at the cap periphery. At the EM level, these cells exhibited a loss organelle integrity and a condensed cytoplasm. The potential significance of this finding for the putative gravity-sensing cap cells were noted.

Slocum, R. D.↗
NASA NTRS1983

Morphology of ductile metals eroded by a jet of spherical particles impinging at normal incidence

Scanning electron microscopy and energy-dispersive X-ray spectroscopy are used, together with surface profile measurements, in the present morphological study of the erosion of an aluminum alloy and copper by the normal impact of spherical glass erodent particles. The morphology of the damage pattern is a manifestation of the flow pattern of erodent particles, and yields insight into the mechanisms that may be active at different stages of erosion. The simultaneous appearance of radial cracks and concentric rings is reported, together with wave crests which contain an accumulation of metallic flakes. A preliminary analysis is advanced to explain the formation of the various damage patterns observed.

Veerabhadra Rao, P.↗
NASA NTRS1983

An integral analysis of transonic normal shock wave/turbulent boundary layer interactions in internal flow

An approximate integral viscous-inviscid interaction method is presented for calculating the development of a turbulent boundary layer subjected to a normal shock wave induced adverse pressure gradient in an internal axisymmetric flow. The inflow conditions and the downstream pressure are provided for the computation. In the supersonic region of shock pressure rise, the Prandtl-Meyer function is used to couple the viscous and inviscid flows. An analytical model for the coupling process is postulated and appropriate equations are defined. Downstream of the sonic point, one-dimensional inviscid flow is assumed for coupling with the viscous flow. The turbulent boundary layer is calculated using Green's integral lag-entrainment method. Comparisons of the solutions with the experimental data are made for interactions which are unseparated, near separation and separated. For comparison purposes, solutions to the time-dependent, mass-averaged, Navier-Stokes equations incorporating a two-equation, Wilcox-Rubesin turbulence model are also shown. The computed results from the integral method show good agreement with experimental data for unseparated interactions and reasonable agreement with the trend of the viscous effects when the interaction becomes increasingly separated.

Om, D.↗
NASA NTRS1983

Far infrared absorption in normal H2 from 77 to 298 K

The translational-rotational absorption spectrum of normal H2 has been measured from 80 to 900/cm at seven temperatures from 77.4 to 298 K. These results have been accurately fitted by a three-parameter line-shape function, thereby providing a reliable way of predicting the absorption of H2 anywhere in this frequency and temperature region.

Dore, P.↗
NASA NTRS1983

Discrimination Relative to Measures of Non-Normality

The robustness of discriminant functions to nonnormality is investigated. The performance of procedures relative to measures of the difference between the actual distribution of the observations and the usual assumption of normal densities is assessed. For example, the two population, mixed distributions problem with equal costs of misclassification are considered. The parameters are estimated by maximum likelihood and recently proposed robust methods.

Smith, W. B.↗
NASA NTRS1984

A normal incidence, high resolution X-ray telescope for solar coronal observations

A Normal Incidence high resolution X-ray Telescope is reported. The design of a telescope assembly which, after fabrication, will be integrated with the mirror fabrication process is described. The assembly is engineered to fit into the Black Brant rocket skin to survive sounding rocket launch conditions. A flight ready camera is modified and tested.

Golub, L.↗
NASA NTRS1984

On the identification of normal modes of oscillation from observations of the solar periphery

The decomposition of solar oscillations into their constituent normal modes requires a knowledge of both the spatial and temporal variation of the perturbation to the Sun's surface. The task is especially difficult when only limited spatial information is available. Observations of the limb darkening function, for example, are probably sensitive to too large a number of modes to permit most of the modes to be identified in a power spectrum of measurements at only a few points on the limb, unless the results are combined with other data. A procedure was considered by which the contributions from quite small groups of modes to spatially well resolved data obtained at any instant can be extracted from the remaining modes. Combining these results with frequency information then permits the modes to be identified, at least if their frequencies are low enough to ensure that modes of high degree do not contribute substantially to the signal.

Gough, D. D.↗
NASA NTRS1982

Evaluating the radiance transformation for normalizing Landsat data

A technique is examined for improving the comparability of Landsat multisppectral scanner (MSS) data acquired on different dates. The technique involves conversion of digital brightness counts to relative radiance values measured in energy units (milliwatts per square centimeter-steradian). The statistical data of signature from 23 land cover (or biomass) classifications derived from all three Landsats were compared before and after the radiance normalization. Significant convergence occurred among the data sets for mean spectral values and the variances associated with each of seven major land cover types for MSS bands 4, 5, and 7. Overall, the variance attributed to the sensor component was reduced from 5.39 to 2.69 percent, with the largest decrease occurring in band 4 (14.4 percent to 3.7 percent).

Middleton, E. M.↗
NASA NTRS1984

Wave normal directions of chorus near the equatorial source region

OGO 5 triaxial search coil magnetometer data are used to determine the wave propagation directions of postmidnight chorus in the near-equatorial region at L shells of 6 to 7. The methods used to estimate the wave normal directions involved minimum variance, the imaginary part of the cross-spectral matrix, the eigenvector of the Hermitian cross-spectral matrix, and a fitting of dispersion relations for one-wave and two-wave models to the cross-spectral matrix. Wave propagation at all frequencies within chorus tones is found to occur most frequently along the magnetic field with median and average cone angles of 9.1 deg and 12.2 deg, respectively. It is concluded that for waves propagating parallel to B, wave growth is maximum.

Goldstein, B. E.↗
NASA NTRS1984

The X-ray emission of normal spiral galaxies

Some results of an Einstein Observatory survey of X-ray emitting spiral galaxies are reported. The sources were normally 10-100 times further away than M31. Luminosities of 10 to the 38th to 10 to the 40th erg/sec were calculated and could have been generated by Pop I and Pop II binary systems, supernova remnants and small nuclear sources. Highly positive correlations were found among properties such as the integrated X-ray, optical and radio emissions. The data will also be compared with similar data from star burst and elliptical galaxies.

Fabbiano, G.↗
NASA NTRS1984

On the identification of normal modes of oscillation from observations of the solar periphery

The decomposition of solar oscillations into their constituent normal modes requires a knowledge of both the spatial and temporal variation of the perturbation to the sun's surface. The task can be especially difficult when only limited spatial information is available. Observations of the limb-darkening function, for example, are probably sensitive to too large a number of modes to permit most of the modes to be identified in a power spectrum of measurements at only a few points on the limb, unless the results are combined with other data. In this paper a procedure is considered by which the contributions from quite small groups of modes to spatially well resolved data obtained at any instant can be extracted from the remaining modes. Combining these results with frequency information then permits the modes to be identified, at least if their frequencies are low enough to ensure that modes of high degree do not contribute substantially to the signal.

Gough, D. O.↗
NASA NTRS1984

Maximum Normalized Rate as a Flying Qualities Parameter

Discrete attitude commands have become a standard task for flying qualities evaluation and control system testing. Much pilot opinion data is now available for ground-based and in-flight simulations, but adequate performance measures and prediction methods have not been established. The Step Target Tracking Prediction method, introduced in 1978, correlated time-on-target and rms tracking data with NT-33 in-flight longitudinal simulations, but did not employ parameters easily measured in manned flight and simulation. Recent application of the Step Target Tracking Prediction method to lateral flying qualities analysis has led to a new measure of performance. This quantity, called Maximum Normalized Rate (MNR), reflects the greatest attitude rate a pilot can employ during a discrete maneuver without excessive overshoot and oscillation. MNR correlates NT-33 lateral pilot opinion ratings well, and is easily measured during flight test or simulation. Futhermore, the Step Target MNR method can be used to analyze large amplitude problems concerning rate limiting and nonlinear aerodynamics.

Onstott, E. D.↗