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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1958

Statistical Study of Turbulence: Spectral Functions and Correlation Coefficients

In reading the publications on turbulence of different authors, one often runs the risk of confusing the various correlation coefficients and turbulence spectra. We have made a point of defining, by appropriate concepts, the differences which exist between these functions. Besides, we introduce in the symbols a few new characteristics of turbulence. In the first chapter, we study some relations between the correlation coefficients and the different turbulence spectra. Certain relations are given by means of demonstrations which could be called intuitive rather than mathematical. In this way we demonstrate that the correlation coefficients between the simultaneous turbulent velocities at two points are identical, whether studied in Lagrange's or in Euler's systems. We then consider new spectra of turbulence, obtained by study of the simultaneous velocities along a straight line of given direction. We determine some relations between these spectra and the correlation coefficients. Examining the relation between the spectrum of the turbulence measured at a fixed point and the longitudinal-correlation curve given by G. I. Taylor, we find that this equation is exact only when the coefficient is very small.

Frenkiel, Francois N.↗
NASA NTRS2008

ART: Surveying the Local Universe at 2-11 keV

The Astronomical Rontgen Telescope (ART) is a medium-energy x-ray telescope system proposed for the Russian-led mission Spectrum Rontgen-Gamma (SRG). Optimized for performance over the 2-11-keV band, ART complements the softer response of the SRG prime instrument-the German eROSITA x-ray telescope system. The anticipated number of ART detections is 50,000-with 1,000 heavily-obscured (N(sub H)> 3x10(exp 23)/sq cm) AGN-in the SRG 4-year all-sky survey, plus a comparable number in deeper wide-field (500 deg(sup 2) total) surveys. ART's surveys will provide a minimally-biased, nearly-complete census of the local Universe in the medium-energy x-ray band (including Fe-K lines), at CCD spectral resolution. During long (approx.100-ks) pointed observations, ART can obtain statistically significant spectral data up to about 15 keY for bright sources and medium-energy x-ray continuum and Fe-K-line spectra of AGN detected with the contemporaneous NuSTAR hard-x-ray mission.

O'Dell, S. L.↗
NASA NTRS2002

The spectral correlation of functional clouds: a statistical test for theoretical models

We compute the spectral correlation function (SCF) of CO J=1-0 maps of moleculary cloud complexes. The SCF is a power law over approximately an order of magnitude in spatial separation in every map. The power law slope of the SCF, its normalization, and the spectral line width averaged over the whole map, are computed for all the observational maps.

turbulence kinematics↗
NASA NTRS1988

Moored surface wind observations at four sites along the Pacific equator between 140 and 95 deg W

Moored surface wind measurements were recorded along the Pacific equator at 140, 124, 110, and 95 deg W during portions of 1980-1985. Minimum record length is one year. The annual mean and monthly mean westward speeds at 110 deg W were about 1.5 m/s higher during the year preceding the 1982-1983 El Nino than in the year following this event. The annual cycle, which moved westward at about 0.8 m/s, consisted of weak westward and northward speeds in February-April and vice versa in September-October. The spectral slope between 5-day and 0.05-day periods was -1.5. The rms amplitude of the 95-percent statistically significant diurnal period oscillation was 0.3 m/s, and the meridional component was nearly twice as large as the zonal component. The diurnal period wave was coherent (at the 95-percent confidence level) between 95 and 124 deg W, with westward phase propagation of about 138 m/s. No statistically significant spectral peak was found in the 40- to 50-day intraseasonal period band. The surface zonal ocean current component, which reached approximately 0.5 and -0.5 m/s in April and October, respectively at 110 deg W, influenced the surface wind stress computed from the quadratic bulk aerodynamic formulation by 10-20 percent.

Halpern, David↗
NASA NTRS1981

Simulation of atmospheric turbulent gusts and gust gradients

An improved three-dimensional, nonrecursive model for atmospheric turbulence has been developed which provides for simulation of both instantaneous gusts and gust gradients along the flight path of the Space Shuttle. The one-dimensional gust and gust gradient spectral models, which form the basis for the simulation scheme, are developed from three-dimensional, von Karman spectra, integrated over finite limits based on the characteristic dimensions (length, width, and thickness) of the flight vehicle. By means of the simulation process nondimensional time series for both gusts and gust gradients have been generated and stored on a series of magnetic tapes for four altitude bands ranging from 0 to 10,000 meters. These Shuttle Simulated Turbulence Tapes (SSTT) have been validated by means of spectral and statistical analyses with satisfactory results. The dimensionless form of the time series coupled with the use of a von Karman spectral model (as opposed to a Dryden model) distinguish the SSTT from earlier turbulence simulation concepts.

Tatom, F. B.↗
NASA NTRS1989

Atmospheric velocity spectral width measurements using the statistical distribution of pulsed CO2 lidar return signal intensities

A pulsed CO2 lidar with coherent detection has been used to measure the correlation time of backscatter from an ensemble of atmospheric aerosol particles which are illuminated by the pulsed radiation. The correlation time of the backscatter of the return signal, which is directly related to the velocity spectral width, can be used to study the velocity structure constant of atmospheric turbulence and wind shear. Various techniques for correlation time measurement are discussed, and several measurement results are presented for the technique using the information contained in the statistical distribution of a set of lidar return signal intensities.

Ancellet, Gerard M.↗
NASA NTRS1975

Calculations of the heights, periods, profile parameters, and energy spectra of wind waves

Sea wave behavior calculations require the precalculation of wave elements as well as consideration of the spectral functions of ocean wave formation. The spectrum of the random wave process is largely determined by the distribution of energy in the actual wind waves observed on the surface of the sea as expressed in statistical and spectral characteristics of the sea swell.

Korneva, L. A.↗
NASA NTRS1979

A search for gamma-ray spectral lines from the Galactic Center by HEAO-1

Preliminary results are reported for a search by HEAO 1 for gamma-ray lines from the Galactic Center in the energy range from 1.5 to 8 MeV. The hard X-ray/low-energy gamma-ray instrument aboard HEAO 1 is briefly described, and results are examined which indicate no obvious statistically significant spectral lines from the Galactic Center. It is concluded that the present observations fail to confirm the previously reported 4.4-MeV flux from the Galactic Center but that the existence of the reported 4.4-MeV feature cannot be strongly rejected on the basis of these results.

Matteson, J. L.↗
NASA NTRS1983

Spectral reflectance of surface soils - A statistical analysis

The relationship of the physical and chemical properties of soils to their spectral reflectance as measured at six wavebands of Thematic Mapper (TM) aboard NASA's Landsat-4 satellite was examined. The results of performing regressions of over 20 soil properties on the six TM bands indicated that organic matter, water, clay, cation exchange capacity, and calcium were the properties most readily predicted from TM data. The middle infrared bands, bands 5 and 7, were the best bands for predicting soil properties, and the near infrared band, band 4, was nearly as good. Clustering 234 soil samples on the TM bands and characterizing the clusters on the basis of soil properties revealed several clear relationships between properties and reflectance. Discriminant analysis found organic matter, fine sand, base saturation, sand, extractable acidity, and water to be significant in discriminating among clusters.

Crouse, K. R.↗
NASA NTRS1989

An Investigation of the Overlap Between the Statistical Discrete Gust and the Power Spectral Density Analysis Methods

The results of a NASA investigation of a claimed Overlap between two gust response analysis methods: the Statistical Discrete Gust (SDG) Method and the Power Spectral Density (PSD) Method are presented. The claim is that the ratio of an SDG response to the corresponding PSD response is 10.4. Analytical results presented for several different airplanes at several different flight conditions indicate that such an Overlap does appear to exist. However, the claim was not met precisely: a scatter of up to about 10 percent about the 10.4 factor can be expected.

Perry, Boyd, III↗
NASA NTRS1973

Preparation of urban land use inventories by machine-processing of ERTS MSS data

Spectral classes of urban phenomena identified from ERTS multispectral scanner data in Milwaukee included Surburban, Inner City, Industry, Grassy (open area), Road, Wooded Suburb, Water, Cloud, and Shadow. The Milwaukee spectral class statistics were used to classify the Chicago area, within the same ERTS frame, and similar results were achieved. In another ERTS frame, Marion County (Indianapolis) data were classified into similar classes. The Marion County ERTS study was supported by a land use classification of an area near downtown Indianapolis that utilized 12-band MSS data collected by aircraft from 3000 feet. The results of the ERTS analyses suggest that satellite data will be a useful tool for the urban planner for monitoring urban land use.

Todd, W.↗
NASA NTRS1973

Preparation of urban land use inventories by machine processing of ERTS MSS data

Spectral classes of urban phenomena identified from Earth Resources Technology Satellite (ERTS) multispectral scanner data in Milwaukee included suburban inner city, industry, grassy (open area), road, wooded suburb, water cloud, and shadow. The Milwaukee spectral class statistics were used to classify the Chicago area, within the same ERTS frame, and similar results were achieved. In another ERTS frame, Marion County (Indianapolis) data were classified into similar classes. The Marion County ERTS study was supported by a land use classification of an area near downtown Indianapolis that utilized 12-band MSS data collected by aircraft from 3000 feet. The results of the ERTS analyses suggest that satellite data will be a useful tool for the urban planner for monitoring urban land use.

Todd, W.↗
NASA NTRS1973

The distribution of redshifts of radio galaxies with different optical spectra and forms

The distribution of redshifts of 222 radio galaxies has been subjected to a power-spectrum analysis. No statistically significant spectral peaks are present for galaxies showing normal absorption-line characteristics; on the other hand, significant spectral peaks are present for those exhibiting strong emission features. Of these spectral peaks, the most significant, at a wavelength of 0.031 in redshift, occurs for those strong-emission radio galaxies which are also compact. The result is consistent with the proposal suggested earlier by Burbidge that the nonrandom features, which may suggest intrinsic redshifts, are confined to those objects - QSOs, N systems, etc. - in which radiation from stars does not dominate. Possible explanations of the apparently nonrandom features are briefly discussed. Finally, a table of the most recently published small-redshift QSOs and compact emission-line galaxies is presented. The redshifts appear to conform to the 0.061 (or 0.031) periodicity found earlier.

Burbidge, G. R.↗
NASA NTRS1974

Investigation of Northrop F-5A wing buffet intensity in transonic flight

A flight test and data processing program utilizing a Northrop F-5A aircraft instrumented to acquire buffet pressures and response data during transonic maneuvers is discussed. The data are presented in real-time format followed by spectral and statistical analyses. Also covered is a comparison of the aircraft response data with computed responses based on the measured buffet pressures.

Chintsun, H.↗