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Results for “Reproducibility”

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 1,117 records · Page 62

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NASA NTRS1979

Evaluation of a vortex model of turbulent cavity flow

A two dimensional discrete vortex model is applied to turbulent flow over a cavity at a Reynolds number based on cavity half length of approximately 500,000. These model predictions are compared with experimental data on a time average and on a spectral basis. The comparisons indicate that the vortex model reproduces the mean velocity profiles of this complex flow, while the turbulent intensity and Reynolds stress profiles are overpredicted in magnitude. Spectral analyses show that the vortex model introduces unrealistic low frequency power which becomes less dominant as the model becomes more disordered. The spectral power distribution of the model in this state is nearly in agreement with that of the data, somewhat too low at the higher frequencies and too high at the lower frequencies. The model is shown to be capable of reproducing the cavity feedback oscillation phenomenon.

Hardin, J. C.↗

NASA NTRS1980

Steady-state wear and friction in boundary lubrication studies

A friction and wear study was made at 20 C to obtain improved reproducibility and reliability in boundary lubrication testing. Ester-base and C-ether-base fluids were used to lubricate a pure iron rider in sliding contact with a rotating M-50 steel disk in a friction and wear apparatus. Conditions included loads of 1/2 and 1 kg and sliding velocities of 3.6 to 18.2 m/min in a dry air atmosphere and stepwise time intervals from 1 to 250 min for wear measurements. The wear rate results were compared with those from previous studies where a single 25 min test period was used. Satisfactory test conditions for studying friction and wear in boundary lubrication for this apparatus were found to be 1 kg load; sliding velocities of 7.1 to 9.1 m/min (50 rpm disk speed); and use of a time stepwise test procedure. Highly reproducible steady-state wear rates and steady-state friction coefficients were determined under boundary conditions. Wear rates and coefficients of friction were constant following initially high values during run-in periods.

Loomis, W. R.↗

NASA NTRS1980

Analysis of the solar magnesium lines

The observed quiet-sun profiles for a number of Mg I and II lines are compared with theoretical spectra computed for two upper-photosphere lower-chromosphere models published by Ayres and Linsky (1976). Both the Mg I and the Mg II resonance line wings, observed with the University of Hawaii Echelle Rocket Spectrographs, favor a model with a higher temperature in the upper photosphere than required to match the visible region lines 4571 and 5172. Neither model atmosphere reproduces the observed shapes in the cores of the strong lines or the limb darkening of the 4571 A intercombination line. The wings of the ultraviolet lines in plages can be reproduced either with a mean one-component atmosphere or by a two-component model with an ad hoc filling factor.

Heasley, J. N.↗

NASA NTRS1979

July simulation by the UCLA general circulation model

Results of a July simulation produced by the UCLA general circulation model are analyzed with a view to improving the model. It is shown that while many features of the July climatology are well reproduced, others, such as the intensity of the jet streams in the upper troposphere, the frequency of cyclogenesis, the structure of the subtropical pressure belt in the Southern Hemisphere, and the precipitation are not well reproduced. It is suggested that the sources of error are related to inadequate vertical and horizontal resolutions, to the choice of upper boundary at 50 mb, to poor representation of topographically forced motions, and to the indirect coupling between the general circulation model and the planetary boundary model. The analysis has led to the introduction of major design changes in the model.

Mechoso, C. R.↗

NASA NTRS1980

Properties of various silicon oxide phases in thin films

Layers of SiO2 with reproducible properties can be manufactured relatively easily today. In the case of SiO and Si2O3 layers, it is necessary to carefully check all of the manufacturing parameters for producing layers with reproducible properties. The properties of the layers in the case of SiO2 do conform to expectations. In the case of Si2O3 and SiO, they can be understood at least qualitatively. Additional interesting models are available for a quantitative understanding.

Ritter, E.↗

NASA NTRS1981

Evaluation of boundary lubricants using steady-state wear and friction

A friction and wear study was made at 20 C to establish operating limits and procedures for obtaining improved reproducibility and reliability in boundary lubrication testing. Ester base and C-other base fluids were used to lubricate a pure iron rider in sliding contact with a rotating M-50 steel disk in a pin-on-disk apparatus. Results of a parametric study with varying loads and speeds slowed that satisfactory test conditions for studying the direction and wear characteristics in the boundary lubrication regime with this test device were found to be 1 kilogram load; 7 to 9 meters-per-minute (50 rpm) surface speed; dry air test atmosphere (less than 100 ppm H2O); and use of a time stepwise procedure for measuring wear. Highly reproducible steady-state wear rates resulted from the two fluid studies which had a linearity of about 99 percent after initially higher wear rates and friction coefficients during run-in periods of 20 to 40 minutes.

Loomis, W. R.↗

NASA NTRS1981

Fluorescence equilibrium in the ultraviolet spectra of Comets Seargent (1978 m) and Bradfield (1979 l)

Detailed fluorescence calculations for OH including the Swings effect were performed. These calculations were used to reproduce the high resolution spectra of Comets Seargent and Bradfield taken with IUE. The calculations also provide the OH fluorescence efficiencies (g factors), as a function of heliocentric radial velocity, which are needed to derive OH abundances from measured fluxes. A close examination of the spectra shows no sign of the corresponding emission bands of OD allowing upper limits to be placed on the ratio N(OD)/N(OH). Preliminary attempts to reproduce the CO+ band structure by fluorescence are discussed.

Donn, B.↗

NASA NTRS1981

The Mars water cycle

A model has been developed to test the hypothesis that the observed seasonal and latitudinal distribution of water on Mars is controlled by the sublimation and condensation of surface ice deposits in the Arctic and Antarctic, and the meridional transport of water vapor. Besides reproducing the observed water vapor distribution, the model correctly reproduces the presence of a large permanent ice cap in the Arctic and not in the Antarctic. No permanent ice reservoirs are predicted in the temperate or equatorial zones. Wintertime ice deposits in the Arctic are shown to be the source of the large water vapor abundances observed in the Arctic summertime, and the moderate water vapor abundances in the northern temperate region. Model calculations suggest that a year without dust storms results in very little change in the water vapor distribution. The current water distribution appears to be the equilibrium distribution for present atmospheric conditions.

Davies, D. W.↗

NASA NTRS1982

Programable Plasma-Spray System

NASA-funded research led to development of automated plasma-spray system programable and reproducible. System utilizes standard plasma-spray equipment with noncoherent light-measuring system and microprocessor. System monitors and controls surface contours and coating thickness. Other advantages of system are consistant coating reproducibility, exact blending and feathering operations, ability to handle complex shapes and ease of changing spray parameters.

Fetheroff, C. W.↗

NASA NTRS1981

Surface tension of natural silicate melts from 1,200-1,500 C and implications for melt structure

The surface tension between silicate liquid and gas is measured for four lava compositions (limburgite to andesite) from 1,200 to 1,500 C. It is noted that the magnitude of surface tension (gamma) is in the range 350-370 dynes/cm. Variations found in gamma as a function of liquid composition are small and have no obvious relation to liquid composition. Gamma is also found to vary little with furnace atmosphere - air, Ar, CO2, H2, CO and their mixtures. It is found that a relaxation time of hours to days, depending on temperature, is required before reproducible results can be obtained from originally crystalline starting material. The reproducible temperature dependence of gamma for complex silicate liquid solution is found to be small, positive, and a relatively simple function of liquid composition.

Walker, D.↗

NASA NTRS1982

OH fluorescence in comets - Fluorescence efficiency of the ultraviolet bands

The present investigation is concerned with the calculation of the fluorescence efficiency of OH over a wide range of heliocentric radial velocities. Three vibrational states in each of the two lowest electronic states are included in these calculations, producing a total of nine vibrational bands in the ultraviolet. The attempt is made to reproduce observed, ultraviolet, cometary spectra of OH by utilizing the Swings fluorescence mechanism. The inclusion of four rotational states within each of the three vibrational states and a detailed solar atlas make it possible to match observations very well, although there remain some discrepancies. This ability to reproduce observations provides confidence that the more general results obtained for the fluorescence efficiency as a function of heliocentric radial velocity can be used in interpreting both previous and future observations of OH in comets.

Schleicher, D. G.↗

NASA NTRS1982

Compensation mechanism in liquid encapsulated Czochralski GaAs Importance of melt stoichiometry

It is shown that the key to reproducible growth of undoped semi-insulating GaAs by the liquid encapsulated Czochralski (LEC) technique is the control over the melt stoichiometry. Twelve crystals were grown from stoichiometric and nonstoichiometric melts. The material was characterized by secondary ion mass spectrometry, localized vibrational mode far infrared spectroscopy, Hall-effect measurements, optical absorption, and photoluminescence. A quantitative model for the compensation mechanism in the semi-insulating material was developed based on these measurements. The free carrier concentration is controlled by the balance between EL2 deep donors and carbon acceptors; furthermore, the incorporation of EL2 is controlled by the melt stoichiometry, increasing as the As atom fraction in the melt increases. As a result, semi-insulating material can be grown only from melts above a critical As composition. The practical significance of these results is discussed in terms of achieving high yield and reproducibility in the crystal growth process.

Holmes, D. E.↗

NASA NTRS1982

Vomiting Center reanalyzed: An electrical stimulation study

Electrical stimulation of the brainstem of 15 decerebrate cats produced stimulus-bound vomiting in only 4 animals. Vomiting was reproducible in only one cat. Effective stimulating sites were located in the solitary tract and reticular formation. Restricted localization of a vomiting center, stimulation of which evoked readily reproducible results, could not be obtained.

Miller, A. D.↗

NASA NTRS1983

A study of the stress wave factor technique for the characterization of composite materials

A testing program was undertaken to provide an independent investigation and evaluation of the stress wave factor for characterizing the mechanical behavior of composite laminates. Some of the data which was obtained after performing a very large number of tests to determine the reproducibility of the SWF measurement is presented. It was determined that, with some optimizing of experimental parameters, the SWF value can be reproduced to within + or - 10%. Results are also given which show that, after careful calibration procedures, the lowest SWF value along the length of a specimen will correlate very closely to the site of final failure when the specimen is loaded in tension. Finally, using a moire interferometry technique, it was found that local regions having the highest in plane strains under tensile loading also had the lowest SWF values.

Henneke, E. G., II↗

NASA NTRS1983

Fluid inclusions in stony meteorites

The fluid inclusions presently described for five stony meteorites brings to seven the number of such meteorites confirmed. Homogenization temperatures are reproducible in each inclusion, and range from 25 C to over 225 C, with some vapor plus liquid inclusions remaining at 225 C, the highest temperature in these microthermometric experiments. Upon cooling, the fluid in some inclusions appears to freeze, as indicated by deformation and immobilization of the vapor bubble at low temperatures. Melting temperatures are by contrast difficult to observe and are not reproducible. Microthermometric data for the fluid in diogenite ALPHA 77256 and inclusions in four chondrites suggest that the fluid is aqueous, with a high solute content.

Warner, J. L.↗

NASA NTRS1982

Improved uniformity of multiphase ceramic-metal plasma-sprayed coats

Processing-technology development of a multiphase, self-lubricating, plasma-spray powder resulted in greater uniformity and reproducibility of plasma-sprayed coats. The effect of particle-size variation, binder concentration, and reproducible processing parameters are reported. Greater adhesive strengths of coats to substrates were achieved by particle-size variation, use of an intermediate bond coat such as Ni-Cr, or heat treatment. Quantitative analyses of polished, coated specimens are also given.

Nakamura, H. H.↗

NASA NTRS1983

Experimental investigations of trace element fractionation in iron meteorites. II - The influence of sulfur

The partitioning of Ir, Ge, Ga, W, Cr, Au, P, and Ni between solid metal and metallic liquid is investigated as a function of temperature and the S-concentration of the metallic liquid. The partition coefficients for siderophile elements, such as Ir, W, Ga, and Ge, are found to increase by factors of 10-100 as the S-concentration of the metallic liquid increases from 0-30 wt percent. Partition coefficients for other siderophile elements, such as Ni, Au, and P, increase by factors of only 2-3. In contrast, a decrease is seen in the partition coefficients for the more chalcophile element Cr. These experimentally determined coefficients are used in conjunction with a fractional crystallization model to reproduce the geochemical behavior of Ni, P, Au, and Ir during the magmatic evolution of groups IIAB, IIIAB, IVA and IVB iron meteorites. The mean S-concentration for each group increases in the order IVB, IVA, IIIAB, IIAB, which is in accordance with cosmochemical prediction. However, the geochemical behavior of Ge, Ga, W, and Cr cannot be reproduced in an internally consistent way. It is concluded that the magmatic histories of these iron meteorite groups are more complex than has been generally assumed.

Jones, J. H.↗

NASA NTRS1983

Effects of vegetation canopy on the radar backscattering coefficient

Airborne L- and C-band scatterometer data, taken over both vegetation-covered and bare fields, were systematically analyzed and theoretically reproduced, using a recently developed model for calculating radar backscattering coefficients of rough soil surfaces. The results show that the model can reproduce the observed angular variations of radar backscattering coefficient quite well via a least-squares fit method. Best fits to the data provide estimates of the statistical properties of the surface roughness, which is characterized by two parameters: the standard deviation of surface height, and the surface correlation length. In addition, the processes of vegetation attenuation and volume scattering require two canopy parameters, the canopy optical thickness and a volume scattering factor. Canopy parameter values for individual vegetation types, including alfalfa, milo and corn, were also determined from the best-fit results. The uncertainties in the scatterometer data were also explored.

Mo, T.↗