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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Geodesy by radio interferometry - Intercontinental distance determinations with subdecimeter precision

Analysis of very-long-baseline interferometer (VLBI) observations yielded estimates of the distances between three radio telescopes in the United States and one in Sweden, with formal standard errors of a few centimeters: Westford, Massachusetts-Onsala, Sweden: 5,599,714.66 + or - 0.03 m; Green Bank, West Virginia-Onsala, Sweden: 6,319,317.75 + or - 0.03 m; and Owens Valley, California-Onsala, Sweden: 7,914,131.19 + or - 0.04 m, where the earth-fixed reference points are defined in each case with respect to the axes of the telescopes. The actual standard errors are difficult to estimate reliably but are probably not greater than twice the formal errors.

Herring, T. A.↗
NASA NTRS1981

Refraction of coastal ocean waves

Refraction of gravity waves in the coastal area off Cape Hatteras, NC as documented by synthetic aperture radar (SAR) imagery from Seasat orbit 974 (collected on September 3, 1978) is discussed. An analysis of optical Fourier transforms (OFTs) from more than 70 geographical positions yields estimates of wavelength and wave direction for each position. In addition, independent estimates of the same two quantities are calculated using two simple theoretical wave-refraction models. The OFT results are then compared with the theoretical results. A statistical analysis shows a significant degree of linear correlation between the data sets. This is considered to indicate that the Seasat SAR produces imagery whose clarity is sufficient to show the refraction of gravity waves in shallow water.

Shuchman, R. A.↗
NASA NTRS1982

Measurements of the lunar induced magnetic moment in the geomagnetic tail - Evidence for a lunar core

Apollo 15 and 16 subsatellite fluxgate magnetometer data have been analyzed for all intervals in which the moon was in the lobes of the geomagnetic tail to obtain an improved estimate of the average magnitude of the induced dipole moment of the moon. The resulting set of estimates yields an induced magnetic moment of -4.23 x 10 to the 22nd Gauss-cu cm per Gauss of applied field, corresponding to a G-factor of -0.008 + or - 0.001. These measurements do not place strong constraints on the conductivity of the lunar core. The observed effects would be detected as long as the core conductivity was greater than about 10 mho/m. If the outer cool layers of the moon that are at temperatures below the effective Curie point contain little or no free iron, then these measurements are consistent with the presence of a conducting core whose radius is slightly larger than 400 km. If these outer layers of the moon contain significant amounts of free iron and hence exhibit the paramagnetism expected in such a situation the core size could be even greater.

Russell, C. T.↗
NASA NTRS1982

Spatial irregularities in Jupiter's upper ionosphere observed by Voyager radio occultations

Radio scintillations (at 3.6 and 13 cm) produced by scattering from ionospheric irregularities during the Voyager occultations are interpreted using a weak-scattering theory. Least squares solutions for ionospheric parameters derived from the observed fluctuation spectra yield estimates of (1) the axial ratio, (2) angular orientation of the anisotropic irregularities, (3) the power law exponent of the spatial spectrum of irregularities, and (4) the magnitude of the spatial variations in electron density. It is shown that the measured angular orientation of the anisotropic irregularities indicates magnetic field direction and may provide a basis for refining Jovian magnetic field models.

Hinson, D. P.↗
NASA NTRS1982

An application of cluster analysis for determining homogeneous subregions: The agroclimatological point of view

A stratification oriented to crop area and yield estimation problems was performed using an algorithm of clustering. The variables used were a set of agroclimatological characteristics measured in each one of the 232 municipalities of the State of Rio Grande do Sul, Brazil. A nonhierarchical cluster analysis was used and the pseudo F-statistics criterion was implemented for determining the "cut point" in the number of strata.

Parada, N. D. J.↗
NASA NTRS1982

Evaluation of the CEAS trend and monthly weather data models for soybean yields in Iowa, Illinois, and Indiana

The CEAS models evaluated use historic trend and meteorological and agroclimatic variables to forecast soybean yields in Iowa, Illinois, and Indiana. Indicators of yield reliability and current measures of modeled yield reliability were obtained from bootstrap tests on the end of season models. Indicators of yield reliability show that the state models are consistently better than the crop reporting district (CRD) models. One CRD model is especially poor. At the state level, the bias of each model is less than one half quintal/hectare. The standard deviation is between one and two quintals/hectare. The models are adequate in terms of coverage and are to a certain extent consistent with scientific knowledge. Timely yield estimates can be made during the growing season using truncated models. The models are easy to understand and use and are not costly to operate. Other than the specification of values used to determine evapotranspiration, the models are objective. Because the method of variable selection used in the model development is adequately documented, no evaluation can be made of the objectivity and cost of redevelopment of the model.

French, V.↗
NASA NTRS1983

Rye Canyon X-ray noise test: One-third octave-band data

Acoustic data were obtained for the 25 ft. diameter X-wing rotor model during performance testing of the rotor system in hover. Data collected at the outdoor whirl tower test facility with a twelve microphone array were taken for approximately 150 test conditions comprised of various combinations of RPM, blade pressure ratio (BPR), and blade angle of attack (collective). The three test parameters had four values of RPM from 404 to 497, twelve values of BPR from 1.0 to 2.1, and six values of collective from 0.0 deg to 8.5 deg. Fifteen to twenty seconds of acoustic data were reduced to obtain an average 1/3 octave band spectrum for each microphone for each test condition. The complete, as measured, 1/3 octave band results for all the acoustic data are listed. Another part of the X-wing noise test was the acoustic calibration of the Rye Canyon whirl tower bowl. Corrections were computed which, when applied to as measured data, yield estimates of the free field X-wing noise. The free field estimates provide a more realistic measure of the rotor system noise levels. Trend analysis of the three test parameters on noise level were performed.

Willshire, W. L., Jr.↗
NASA NTRS1982

The interstellar absorption-line spectrum of Mu Ophiuchi

UV interstellar lines have been measured on high-resolution, long- and short-wavelength IUE spectra of the B8 V star Mu Oph. Column densities for the observed atoms and ions have been determined as well as turbulent velocities. The interstellar spectrum of Mu Oph is similar to the ones for Rho Oph and Zeta Oph. The ionization equilibria of several elements give consistent limits for the electron density. The C I line arising from different fine-structure levels are studied to yield estimates on the physical conditions in the cloud. Relative depletion of elements in the cloud seen in the interstellar spectrum of Mu Oph follows the same pattern as seen in the interstellar spectra of Zeta Oph and six other stars in the Rho Oph cloud complex.

Cardelli, J.↗
NASA NTRS1983

Synthesis maps of ultraviolet observations of neutral interstellar gas

Copernicus and IUE measurements of neutral hydrogen column densities have been taken for about 140 stars distributed between 10 and 3000 pc from the sun and plotted in several maps to directly yield estimates of contours of neutral hydrogen column density in the 5-500 x 10 to the 17th/sq cm range. These maps show that low column density neutral hydrogen is asymmetrically distributed around the sun with a 'hole' in the neutral hydrogen located in the third quadrant. This distribution mirrors that of nearby B stars associated with the Gould belt. The maps clearly show the directions in which observations at wavelengths less than 912 A will be most successful.

Frisch, P. C.↗
NASA NTRS1983

Large-area relation of Landsat MSS and NOAA-6 AVHRR spectral data to wheat yields

Landsat MSS data transformed into Kauth-Thomas greenness were averaged over 5 n.mi x 6 n.mi. sample segments from the U.S. Great Plains winter and spring wheat (Triticum aestivum) regions, and related by regression analysis to yields reported by county, crop reporting district (CRD) and state levels. Evidence of a linear relation between winter- and spring-wheat yields and Landsat spectral data at a broad scale is shown for 1978 and 1979. A common slope of about 1.6 (Bu/A)/unit greenness is discerned for the relation between yield and spectral greenness. Tests at both a smaller scale on sets of field-level spectal data and yield and at a large scale on 25 mi. x 25 mi. gridded spectral data from the NOAA-6 AVHRR sensor support the relation. The implications of these results to yield estimation from satellite spectral data are discussed.

Barnett, T. L.↗
NASA NTRS1984

Aeolian processes on Venus

Many of the questions regarding aeolian processes on Venus and the subsequent implications for surface history involve understanding the physics of particle motion in the venusian environment. The surface environment of Venus is simulated as closely as practicable using the Venus Wind Tunnel and to determine threshold wind speeds, particle flux, particle velocities, and the characteristics of various aeolian bedforms. Despite the relatively low wind speeds on Venus, the flux of windblown material on Venus is potentially high. A high fraction of material is transported as surface creep by rolling, estimates yield rates up to 100 kg per cm lane width per year depending upon the availability of material and wind frequency, suggesting that the formation of lowland plains by aeolian processes and the burial of various landforms such as impact craters could occur on short geological time-scales. Wind tunnel simulations demonstrate that aeolian processes may be very effective in modifying the surface through erosion and deposited and may have an important influence on the composition of the atmosphere.

Greeley, R.↗
NASA NTRS1984

Extragalactic radio sources

The standard model for extragalactic variable radio sources comprises an isotropically expanding plasmoid with frozen magnetic flux and an electron distribution which evolves adiabatically. This model leads to the following relaton between the peak luminosity L (sub nu, m) and the relevant frequency nu(sub m) which are functions of time: L(sub nu,m) is proportional to nu(sub m)(n) where N = (7n + 5)/(4n + 5). In this expression, n is the spectral index in the optically thin part of the spectrum, where L (sub nu) is proportional to nu (-n). For n in the range 0.5 to 1.5, the standard model yields N in the range 1.2 to 1.4. By contrast, analysis of observational data yields estimates of N in a small range about the mean value 0.4, in clear contradiction with the standard model.

Sturrock, P. A.↗
NASA NTRS1984

Time series modeling of human operator dynamics in manual control tasks

A time-series technique is presented for identifying the dynamic characteristics of the human operator in manual control tasks from relatively short records of experimental data. Control of system excitation signals used in the identification is not required. The approach is a multi-channel identification technique for modeling multi-input/multi-output situations. The method presented includes statistical tests for validity, is designed for digital computation, and yields estimates for the frequency responses of the human operator. A comprehensive relative power analysis may also be performed for validated models. This method is applied to several sets of experimental data; the results are discussed and shown to compare favorably with previous research findings. New results are also presented for a multi-input task that has not been previously modeled to demonstrate the strengths of the method.

Biezad, D. J.↗
NASA NTRS1984

Time Series Modeling of Human Operator Dynamics in Manual Control Tasks

A time-series technique is presented for identifying the dynamic characteristics of the human operator in manual control tasks from relatively short records of experimental data. Control of system excitation signals used in the identification is not required. The approach is a multi-channel identification technique for modeling multi-input/multi-output situations. The method presented includes statistical tests for validity, is designed for digital computation, and yields estimates for the frequency response of the human operator. A comprehensive relative power analysis may also be performed for validated models. This method is applied to several sets of experimental data; the results are discussed and shown to compare favorably with previous research findings. New results are also presented for a multi-input task that was previously modeled to demonstrate the strengths of the method.

Biezad, D. J.↗
NASA NTRS1986

Geodesy by radio interferometry - Evidence for contemporary plate motion

Analysis of 211 very long baseline interferometry observing sessions carried out between November 1979 and August 1984 has yielded estimates of the distances between various radio telescopes located in North America and Europe. The average rate of change of the distances between four radio telescopes in North America (Haystack Observatory, Massachusetts; Westford Radio Telescope, Massachusetts; George R. Agassiz Station, Texas; and Owens Valley Radio Observatory, California) and one in Europe (Onsala Space Observatory, Sweden) obtained from the analysis of these data is 19 + or 10 mm/yr, where the (68 percent confidence interval) standard deviation is for the estimate of the rate of change of the Haystack-Onsala baseline length, the one determined most accurately from these data. This estimate of the standard deviation is dominated by the effects of correlated systematic errors due mostly to errors in the model used for the atmospheric delay which introduces errors in each baseline length estimate of 40 mm standard deviation and 60 days correlation time. (By contrast the statistical standard deviation is only 2 mm/yr). The estimated geologic rates of change of these baseline lengths, averaged over 10 to the 6th years, are 15 to 17 + or - 3 mm/yr for the various North American sites to Ondala.

Herring, T. A.↗
NASA NTRS1986

The energy distributions of B supergiants in the Large Magellanic Cloud

It is shown that line-blanketed, LTE, plane-parallel model atmosphere calculations provide excellent fits to the ultraviolet-through-visual energy distributions of B supergiants in the Large Magellanic Cloud. The models were computed using Kurucz's (1979) ATLAS atmosphere program, but with lower gravities than were contained in Kurucz's published model grid. The ultraviolet continua of low gravity stars are found to be sensitive to changes in temperature and gravity. Measurements of Teff and log g for ten LMC B supergiants from model atmosphere fits to the energy distributions yield estimates of their radii, luminosities, and masses. Model atmosphere fits suggest that the late B supergiants have significantly lower masses than the earlier B types of the same luminosity, contrary to stellar evolution theory which predicts that B supergiants are in a post-core hydrogen burning phase and should evolve very quickly and at essentially constant mass.

Fitzpatrick, Edward L.↗
NASA NTRS1987

Subcentimeter-size particle distribution functions in planetary rings from Voyager radio and photopolarimeter occultation data

Analysis of measurements of the scattered and direct components of Voyager 1 radio occultation signals at 3.5 and 13 cm wavelengths yield estimates of the distribution functions of supracentimeter-size particles and thickness of relatively broad regions in Saturn's rings. If mearurements of signal amplitude at a shorter wavelength are combined with the previously analyzed data, the shape of the distribution functions characterizing the smaller particles can be constrained. If size distributions of arbitrary form were considered, many solutions are found that are consistent with the three available observations of signal amplitude. The best-fit power law was calculated to the three observations at three wavelengths for several of the embedded Saturn ringlets. Mie scattering theory predicts that the measured phase of the radio occultation signal is highly sensitive to particles ranging from 0.1 to 1.0 wavelengths in size, thus additional constraints on the subcentimeter-size distribution functions for both the Saturn and Uranus rings can in principle be derived from radio phase measurements.

Zebker, Howard A.↗
NASA NTRS1986

Meteorological data along the Vega 1, 2 float paths

The Vega balloons transmitted in situ measurements of pressure, temperature, vertical wind velocity relative to the balloon craft, cloud-particle backscatter coefficient, and ambient light level in the Venus middle cloud layer. Doppler tracking has yielded estimates for the velocities of atmospheric motion.

Sagdeev, R. Z.↗