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At least 721 records · Page 40

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NASA NTRS1975

The accelerations of the earth and moon from early astronomical observations

An investigation has compiled a very large amount of data on central or near central solar eclipses as recorded in four principal ancient sources (Greek and Roman classics, medieval European chronicles, Chinese annals and astronomical treatises, and Late Babylonian astronomical texts) and applied careful data selectivity criteria and statistical methods to obtain reliable dates, magnitudes, and places of observation of the events, and thereby made estimates of the earth acceleration and lunar acceleration. The basic conclusion is that the lunar acceleration and both tidal and nontidal earth accelerations have been essentially constant during the period from 1375 B.C. to the present.

Muller, P. M.↗

NASA NTRS1976

Time-dependent MOS breakdown

A general model for time-dependent breakdown in metal-oxide-silicon (MOS) structures is developed and related to experimental measurements on samples deliberately contaminated with Na. A statistical method is used for measuring the breakdown probability as a function of log time and applied field. It is shown that three time regions of breakdown can be explained respectively in terms of silicon surface defects, ion emission from the metal interface, and lateral ion diffusion at the silicon interface.

Li, S. P.↗

NASA NTRS1976

Correlation between multispectral photography and near-surface turbidities

Four-band multispectral photography obtained from an aerial platform at an altitude of about 10,000 feet has been utilized to measure near-surface turbidity at numerous sampling sites in the Ross Barnett Reservoir, Mississippi. Correlation of the photographs with turbidity measurements has been accomplished via an empirical mathematical model which depends upon visual color recognition when the composited photographs are examined on either an I squared S model 600 or a Spectral Data model 65 color-additive viewer. The mathematical model was developed utilizing least-squares, iterative, and standard statistical methods and includes a time-dependent term related to sun angle. This model is consistent with information obtained from two overflights of the target area - July 30, 1973 and October 30, 1973 - and now is being evaluated with regard to information obtained from a third overflight on November 8, 1974.

Wertz, D. L.↗

NASA NTRS1976

Retrieval of atmospheric temperature profiles by a scanning microwave spectrometer

The Nimbus-6 satellite carries a scanning microwave spectrometer (SCAMS) experiment. The five frequency bands observed are near 22.2, 31.6, 52.8, 53.8, and 55.4 GHz. The calibration system permitted preflight calibration to an accuracy of about 1 K. In orbit, small empirical corrections were made to the calibration constants to obtain agreement in the mean of SCAMS measurements with computations based on conventional data analyzed by the National Meteorological Center (NMC). Global maps of temperature profiles were retrieved from the SCAMS measurements by a statistical method. Using the NMC analysis as the verification, RMS errors in level temperatures range of about 2-4 K, depending on altitude. Errors for layers of octave extent in pressure are uniformly about 2 K. Theoretical computations show that additional spectrometer channels would improve temperature sensing performance

Rosenkranz, P. W.↗

NASA NTRS1978

Verification of redundancy management design

Statistical method checks designs by simulating system operating conditions and adding error factors. Method has potential applicability to commercial and industrial situations where redundancy management system is used to detect and isolate failed components.

Gelderloos, H. C.↗

NASA NTRS1977

Statistical principles of inversion theory

Statistical methods are used to deal with the inverse problem of radiative transfer. All the available information about an unknown profile can be expressed in the form of values of functions of that profile and error estimates of these values. Estimation theory shows how these values are combined to give an estimate of the unknown profile and its error covariance. Many inversion methods are expressed in this form, although the error estimate is not usually carried out. Practical applications are described, both for inversion of individual profiles, and the global analysis of satellite data.

Rodgers, C. D.↗

NASA NTRS1978

Gamma ray spectroscopy in astrophysics: An observational overview (50 keV-20 MeV)

The observational status of gamma ray astronomy based on results reported prior to April 1978 is discussed. Specific line observations are reviewed from the Sun, the galactic plane, the Galactic Center region, the active Galaxy NGC 5128 (Cen A), the Crab Nebula region, and a transient source in the general direction of the anti-Galactic Center region. A statistical method is described which determines the relative probability that a given, reported observation is due to an external source as compared to a random fluctuation in the experimental background counting rate. Only a few of the many reported observations can be considered likely extraterrestrial observations of an extraterrestrial source made with a confidence level of 99%.

Chupp, E. L.↗

NASA NTRS1977

Estimation of regional heat flux from scanning radiometer measurements

The paper presents a statistical method for extracting regional information on the radiative heat flux at the top of the atmosphere from a satellite-borne scanning radiometer. The radiative heat flux distribution is denoted by a double Fourier series with coefficients to be determined from measurements. The method determines, in the sense of minimum variance, the best linear estimator of the total flux over a region. The heat flux distribution is represented by a truncated series which is unbiased.

Bess, T. D.↗

NASA NTRS1979

Problems with the interpretation of paleomagnetic measurements due to studies of basalts from the Paleovolcano Vogelsberg in Hessen

The palaeomagnetic parameters of more than 5,000 samples of cores taken from 33 drilling holes through innumerable basalt units of the Vogelsberg Paleovolcano in Hessen were measured. Measurements of specimens of thin and thick layers without any gap proved that inclination, natural remanence, susceptibility and Konigsberger factor were dependent on their distance from the surface of units, layers, lamelles, etc. Therefore, representative data for the evaluation of palaeomagnetic measurements can be expected only in the interior part of lava flows and intrusions. The statistic method which enclosed all values of measurements gave significant data which was not appropriate for the interpretation of palaeomagnetic and geological events.

Schenk, E.↗

NASA NTRS1978

Climate diagnostics

Diagnoses of climate fluctuations is examined emphasizing the assemblage of a host of observations, to develop a clearer physical picture of the nature and causal interrelationships of the climate events. Development of better statistical methods for making predictions of climate fluctuations and improving numerical climate prediction models is considered along with obtaining data for areas for which meager records exist such as the tropics and the southern hemisphere. The major circulation systems in the tropics, energy transports by the oceans and atmosphere, and the reflected or absorbed solar radiation values from the earth's surface are among the phenomena to be studied.

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NASA NTRS1978

Five micron limb-darkening and the structure of the Jovian atmosphere

A combined radiative, dynamical, and chemical model of the Jovian atmosphere is presented which reproduces the observed IR limb-darkening curves for several regions on the disk of Jupiter. Two approaches are used to perform the inversion required for determination of the source function, and a power-series-expansion model is examined, along with a convective-equilibrium model, cloud and intermediate-zone models, and a thin-shell model. The statistical methods used in the analysis are outlined, and model fits to the observations are discussed. The chemistry of phase transitions in the hot spots of Jupiter's equatorial belt is briefly investigated.

Newman, W. I.↗

NASA NTRS1978

Efficiency degradation due to tracking errors for point focusing solar collectors

An important parameter in the design of point focusing solar collectors is the intercept factor which is a measure of efficiency and of energy available for use in the receiver. Using statistical methods, an expression of the expected value of the intercept factor is derived for various configurations and control law implementations. The analysis assumes that a radially symmetric flux distribution (not necessarily Gaussian) is generated at the focal plane due to the sun's finite image and various reflector errors. The time-varying tracking errors are assumed to be uniformly distributed within the threshold limits and allows the expected value calculation.

Hughes, R. O.↗

NASA NTRS1979

The effect of variety and maturity on the quality of freeze-dried carrots. The effect of microwave blanching on the nutritional and textural quality of freeze-dried spinach

Using carrots, the quality of freeze-dried products was studied to determine the optimum varieties and maturation stages for quality attributes such as appearance, flavor, texture, and nutritive value. The quality of freeze-dried carrots is discussed in terms of Gardner color, alcohol insoluble solids, viscosity, and core/cortex ratio. Also, microwave blanching of freeze-dried spinach was studied to determine vitamin interrelationships, anatomical changes, and oxidative deteriorations in terms of preprocessing microwave treatments. Statistical methods were employed in the gathering of data and interpretation of results in both studies.

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NASA NTRS1980

Long-time predictions in nonlinear dynamics

It is known that nonintegrable dynamical systems do not allow precise predictions concerning their behavior for arbitrary long times. The available series solutions are not uniformly convergent according to Poincare's theorem and numerical integrations lose their meaningfulness after the elapse of arbitrary long times. Two approaches are the use of existing global integrals and statistical methods. This paper presents a generalized method along the first approach. As examples long-time predictions in the classical gravitational satellite and planetary problems are treated.

Szebehely, V.↗

NASA NTRS1981

Assessment of variations in thermal cycle life data of thermal barrier coated rods

An analysis of thermal cycle life data for 22 thermal barrier coated (TBC) specimens was conducted. The Zr02-8Y203/NiCrAlY plasma spray coated Rene 41 rods were tested in a Mach 0.3 Jet A/air burner flame. All specimens were subjected to the same coating and subsequent test procedures in an effort to control three parametric groups; material properties, geometry and heat flux. Statistically, the data sample space had a mean of 1330 cycles with a standard deviation of 520 cycles. The data were described by normal or log-normal distributions, but other models could also apply; the sample size must be increased to clearly delineate a statistical failure model. The statistical methods were also applied to adhesive/cohesive strength data for 20 TBC discs of the same composition, with similar results. The sample space had a mean of 9 MPa with a standard deviation of 4.2 MPa.

Hendricks, R. C.↗

NASA NTRS1981

Forum for discussion and debate

The application of statistical methods to meteorological data for which there are long, compatible series, and where known trend changes took place were suggested. The effects of optical wedge deterioration, atmospheric aerosol variation, solar irradiance variations, etc., are evaluated. It is recommended that coupled satellite ground based observational system is required to determine global long term trends.

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NASA NTRS1984

Least-Squares Prediction of Solar Activity

Studies of statistical methods for predicting future solar activity described in report containing extensive graphical and tabular presentations of analyses. Lagrangian-least-squares method, which gives best predictions presented in detail. FORTRAN source code for method given.

Holland, R. L.↗

NASA NTRS1984

Predicting Solar Deficits

Statistical method uses available long term solar irradiance data at selected sites in United States to predict probable deviations from long term monthly averages. Technique useful in sizing solar collectors and backup storage systems to cover solar deficits.

Ross, R. G., Jr.↗