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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

The asymptotic distribution of maxima in bivariate samples

The joint distribution (as n tends to infinity) of the maxima of a sample of n independent observations of a bivariate random variable (X,Y) is studied. A method is developed for deriving the asymptotic distribution of the maxima, assuming that X and Y possess asymptotic extreme-value distributions and that the probability element dF(x,y) can be expanded in a canonical series. Applied both to the bivariate normal distribution and to the bivariate gamma and compound correlated bivariate Poisson distributions, the method shows that maxima from all these distributions are asymptotically uncorrelated.

Campbell, J. W.↗
NASA NTRS1974

Monte Carlo calculations of the surface brightness profiles of spherical dark nebulae

Theoretical surface brightness profiles of spherical dark nebulae of both uniform density and a density proportional to 1/r squared are being discussed. The albedo and asymmetry factor of the dust grains and the optical radius measured from the cloud center were the variable parameters in this study, which further assumed an isotropically incident radiation field. The occurrence of dark cores in the surface brightness profiles is examined, and their frequent existence in galactic dark nebulae is interpreted as resulting from a strongly forward scattering phase function and a high optical depth of the associated objects. The shape and depth of the profiles of the dark cores is closely related to the internal density distribution of the clouds, and it is suggested that detailed observations of the surface brightness profiles of dark nebulae will reveal important information on the type of their internal density distribution and, thus, their evolutionary status.

Witt, A. N.↗
NASA NTRS1974

Mariner Mars 1971 television picture catalog. Volume 1: Experiment design and picture data

A compilation of Mariner 9 television data is presented for the study of the planet Mars and of its two satellites, Phobos and Deimos. The concept of the basic mission, camera characteristics, and various processing techniques of the raw television data recovered from the spacecraft are discussed. Data are arranged into the following disciplines; (1) mapping and geology, (2) polar studies, (3) geodesy, (4) variable surface features, (5) atmospheric phenomena, and (6) satellites. Reproduction and arrangements of approximately 3000 individual pictures and photomosaics are provided.

Cutts, J. A.↗
NASA NTRS1976

Variable-cycle engines for supersonic cruise aircraft

Progress and the current status of the Variable Cycle Engine (VCE) study are reviewed with emphasis placed on the impact of technology advancements and design specifications. A large variety of VCE concepts are also examined.

Willis, E.↗
NASA NTRS1976

Variable-cycle engines for supersonic cruising aircraft

The paper reviews the evolution and current status of selected recent variable-cycle engine (VCE) studies and describes how the results are influenced by airplane requirements. The engine/airplane studies are intended to identify promising VCE concepts, simplify their designs and identify the potential benefits in terms of aircraft performance. This includes range, noise, emissions, and the time and effort it may require to ensure technical readiness of sufficient depth to satisfy reasonable economic, performance, and environmental constraints. A brief overview of closely-related, on-going technology programs in acoustics and exhaust emissions is presented. It is shown that realistic technology advancements in critical areas combined with well matched aircraft and selected VCE concepts can lead to significantly improved economic and environmental performance relative to first-generation SST predictions.

Willis, E. A.↗
NASA NTRS1976

Supersonic variable-cycle engines

The evolution and current status of selected recent variable cycle engine (VCE) studies are reviewed, and how the results were influenced by airplane requirements is described. Promising VCE concepts are described, their designs are simplified and the potential benefits in terms of aircraft performance are identified. This includes range, noise, emissions, and the time and effort it may require to ensure technical readiness of sufficient depth to satisfy reasonable economic, performance, and environmental constraints. A brief overview of closely related, ongoing technology programs in acoustics and exhaust emissions is also presented. Realistic technology advancements in critical areas combined with well matched aircraft and selected VCE concepts can lead to significantly improved economic and environmental performance relative to first generation SST predictions.

Willis, E. A.↗
NASA NTRS1977

Temporal variations in atmospheric water vapor and aerosol optical depth determined by remote sensing

By automatically tracking the sun, a four-channel solar radiometer was used to continuously measure optical depth and atmospheric water vapor. The design of this simple autotracking solar radiometer is presented. A technique for calculating the precipitable water from the ratio of a water band to a nearby nonabsorbing band is discussed. Studies of the temporal variability of precipitable water and atmospheric optical depth at 0.610, 0.8730 and 1.04 microns are presented. There was good correlation between the optical depth measured using the autotracker and visibility determined from National Weather Service Station data. However, much more temporal structure was evident in the autotracker data than in the visibility data. Cirrus clouds caused large changes in optical depth over short time periods. They appear to be the largest deleterious atmospheric effect over agricultural areas that are remote from urban pollution sources.

Pitts, D. E.↗
NASA NTRS1978

Transmission of sound through high subsonic flows in non-uniform ducts

The transmission of sound through a near-sonic throat in a variable area duct is studied using the method of matched asymptotic expansions applied to a quasi-one-dimensional model. Nonlinear interactions between the mean flow and the acoustic perturbation in the throat region are shown to cause significant effects on the sound field upstream and downstream of the throat. Numerical results are presented for several special applications of the general nonlinear theory.

Myers, M. K.↗
NASA NTRS1979

Magnetic field and shock effects and remanent magnetization in a hypervelocity impact experiment

The impact of aluminum projectiles onto high-alumina terrestrial basalt blocks at 13-15 km/s in the presence of a variable magnetic field is studied. Plasma production but not field production was detected, and characteristics of the remanence and the shocked basalt are reported. Mineralogical data suggest that the magnetization acquired in the material near the craters is shock remanence. The experimental results might indicate that shock effects or possibly thermoremanence in ejecta fragments, may be responsible for part of the magnetization of the lunar surface.

Srnka, L. J.↗
NASA NTRS1979

Sound transmission in ducts containing nearly choked flows

The nonlinear theory previously developed by the authors (1977, 1978) is used to obtain numerical results for sound transmission through a nearly choked throat in a variable-area duct. Parametric studies are performed for different source locations, strengths and frequencies. It is shown that the nonlinear interactions in the throat region generate superharmonics of the fundamental (source) frequency throughout the duct. The amplitudes of these superharmonics increase as the source parameters (frequency and strength) are increased toward values leading to acoustic shocks. For a downstream source, superharmonics carry about 20% of the total acoustic power as shocking conditions are approached. For the source strength levels and frequencies considered, streaming effects are negligible.

Callegari, A. J.↗
NASA NTRS1979

A fast-reacting and versatile optokinetic stimulus pattern by computer graphics with application examples

A computer graphics method for the generation of horizontally moving vertical stripes which serve as stimuli for optokinetic nystagmus is presented. The pattern is generated by the successive addition of a constant in a digital register, leading to its periodic overflow. Digital to analog conversion of the register contents results in a staircase waveform, which is converted into a pattern of vertical lines on a CRT. The addition of any number to the reference buffer shifts all lines uniformly, so that the group velocity of the pattern is easily controlled. The computer controlled display allows an accurate realization of a commanded velocity profile with practically no time delay and facilitates study under conditions of variable feedback. The display software can be easily modified to limit stimulation to a selected area of the moving retina, and the method has been used to simulate central scotomata. It is pointed out that the technique, while more accurate, versatile and responsive than a rotating drum device, may be less useful in experiments requiring a wide field display.

Yasui, S.↗
NASA NTRS1981

Studies conducted as a search for physical mechanisms relating solar variability and the troposphere

Chains of causative mechanisms that are hypothesized to relate solar variability to the behavior of the Earth's lower atmosphere were assessed. Solar variations believed most likely to constitute the forcing functions in hypothesized solar terrestrial atmosphere chain, changes in the Earth's atmospheric electrical characteristics due to solar variability, and the observed variations in atmospheric behavior that are influenced by solar variability were also examined.

Wu, S. T.↗
NASA NTRS1981

Experimental evaluation of a perspective tunnel display for three-dimensional helicopter approaches

A computer-generated perspective tunnel display for a steep and strongly curved three-dimensional helicopter approach is studied. The necessary control variables for following a curved trajectory are analyzed, the effectiveness of superimposed predictor symbology is investigated, and a suitable predictor law is formulated. The theoretical considerations are validated by an extensive fixed-base simulator program. The tunnel display with a superimposed predictor symbol is shown to outperform conventional-type displays in its abilities to follow a curved trajectory in the presence of gust disturbances, to enter the trajectory from an unknown position outside this trajectory, as well as to monitor automatic approaches. The feasibility of the tunnel display for operation in actual flight has been demonstrated in an exploratory flight test.

Grunwald, A. J.↗
NASA NTRS1982

Solar calibration of stellar rotation tracers

A study of the time variability of the disk-integrated solar magnetic flux, with a view to the behavior of emission-line intensity variations observed in lower main sequence stars, has determined that solar rotation modulation of the integrated flux is present in 75% of all rotations. For observing intervals of more than twice the lifetime of the features causing rotational modulation, the correct rotation period is identified in more than 90% of all cases. The optimum time for measuring rotational modulation is the decay phase of the activity cycle, and the solar rotation period is measured with an accuracy of a few percent. The lifetime of a rotational modulation period is approximately five rotations, and a sensitivity limit of Delta S= 0.005 is found for the Vaughan et al (1981) stellar rotation measures.

Labonte, B. J.↗
NASA NTRS1982

Combining remotely sensed and other measurements for hydrologic areal averages

A method is described for combining measurements of hydrologic variables of various sampling geometries and measurement accuracies to produce an estimated mean areal value over a watershed and a measure of the accuracy of the mean areal value. The method provides a means to integrate measurements from conventional hydrological networks and remote sensing. The resulting areal averages can be used to enhance a wide variety of hydrological applications including basin modeling. The correlation area method assigns weights to each available measurement (point, line, or areal) based on the area of the basin most accurately represented by the measurement. The statistical characteristics of the accuracy of the various measurement technologies and of the random fields of the hydrologic variables used in the study (water equivalent of the snow cover and soil moisture) required to implement the method are discussed.

Johnson, E. R.↗
NASA NTRS1982

Polarization studies of the Venus UV contrasts - Cloud height and haze variability

The present investigation is concerned with the measurement of differences in the polarization of bright and dark areas on Venus. The differential polarization is matched by simple models in which the cloud height, amount of submicron haze above the clouds, and absorber amount in the clouds are varied. Physical and chemical models consistent with the findings are proposed. The differences in polarization between bright and dark ultraviolet features on Venus are found to have a straightforward interpretation in terms of known constituents of the atmosphere near the cloud tops. The observations of the polarization in four colors over 2 1/2 Venus years imply that the submicron haze and UV absorbers are anticorrelated, and that the clouds lie slightly (approximately 1 km) lower in the dark regions. These findings pose strong constraints on any model for the brightness variations in the UV.

Esposito, L. W.↗
NASA NTRS1985

Probabilistic Structural Analysis of SSME Turbopump Blades: Probabilistic Geometry Effects

A probabilistic study was initiated to evaluate the precisions of the geometric and material properties tolerances on the structural response of turbopump blades. To complete this study, a number of important probabilistic variables were identified which are conceived to affect the structural response of the blade. In addition, a methodology was developed to statistically quantify the influence of these probabilistic variables in an optimized way. The identified variables include random geometric and material properties perturbations, different loadings and a probabilistic combination of these loadings. Influences of these probabilistic variables are planned to be quantified by evaluating the blade structural response. Studies of the geometric perturbations were conducted for a flat plate geometry as well as for a space shuttle main engine blade geometry using a special purpose code which uses the finite element approach. Analyses indicate that the variances of the perturbations about given mean values have significant influence on the response.

Nagpal, V. K.↗
NASA NTRS1985

Galactic gamma-ray sources, SNOBs, and giant H2 regions

Progress towards understanding the nature of the COS-B galactic gamma-ray sources was made by two recent developments. The developments are: (1) the existence of extensive wide-latitude CO surveys, from the Northern Hemisphere, and from the Southern Hemisphere which give more precise information on molecular cloud population of the Perseus, Sagittarius, and Carina spiral arms; (2) the study of the time variability of gamma-ray sources in gamma-rays but also at other wavelengths, leading to the discovery of four new variable sources in addition to the already known Crab and Vela pulsars. Three classes of gamma-ray sources are found; invariable sources, active sources, and passive sources.

Montmerle, T.↗