Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Data fitting”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Determination of the rate constant for the reaction O + NO yields N + O2

A shock-tube technique was used to determine the rate constant for the reaction O + NO yields N + O2 in the 2500-4100 K range. Mixtures of NO, N2O, and an inert gas (Ar or Kr) were shock-heated, and the decay of infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was monitored. The N2O dissociates quickly to provide a source of O atoms for the above reaction. An expression for the rate constant is derived which fits these data and previous data at higher and lower temperatures.

Hanson, R. K.↗
NASA NTRS1975

Shock wave relations in lunar ash flow

A detailed analysis of steady normal shock waves in a layer of lunar ash by the theory of two phase flow of a mixture of a gas and small solid particles is presented. New terms of pressure gradient and virtual mass forces in the particle momentum equation and the particle kinetic energy and work done in the particle energy equation are included in the fundamental equations and their influences are investigated. The flow variables as functions of the free stream Mach number, initial particle volume fraction and the density ratio G are presented. The thickness of the relaxation zone is found to increase with decreasing initial particle volume fraction and almost independent of G for any given values of free stream Mach number. A new empirical relation of the drag coefficient for the spherical particles in the mixture is proposed to fit experimental data.

Pai, S. I.↗
NASA NTRS1976

Global atomic hydrogen density derived from OGO-6 Lyman-alpha measurements

The paper analyzes a one-year set of Lyman-alpha airglow data measured in the local zenith at altitudes from 400 to 1100 km by a UV photometer aboard OGO-6. The zenith-intensity data are fitted to theoretical airglow calculations in four spherically symmetric models of the hydrogen geocorona to determine both the Ly-alpha solar flux at line center and the average atomic hydrogen column density. After correcting for a loss of instrument sensitivity, the Ly-alpha flux is found to be linearly correlated with daily Zurich sunspot number. It is also found that the hydrogen density is inversely correlated with Jacchia exospheric temperature, but the dependence is not that predicted by steady-state models with Jeans evaporative escape as the only loss mechanism. It is suggested that charge-exchange production of fast hydrogen atoms from 'hot' ionospheric protons might provide the additional loss this result requires.

Thomas, G. E.↗
NASA NTRS1975

Rb-Sr ages and initial Sr-87/Sr-86 for Apollo 17 basalts and KREEP basalt 15386

The Rb-Sr data reported for Apollo 17 mare basalts and for KREEP basalt 15386 is used to determine mineral isochrons. The weighted average age of four Apollo 17 basalts is 3.76 + or - 0.06 AE, while the age determined for 15386 is 3.94 + or - 0.04 AE. The isotopic data for the Apollo 17 basalts are discussed in the context of Sm and Eu data for the same samples. The Sr-isotopic data are fit best by a three-stage model evolution involving evolution of Sr-87/Sr-86 in an environment with Rb/Sr greater than in the basalts, production of mare basalt source regions of lower but variable Rb/Sr sometime in the interval 4.6 to 3.75 AE ago, and extraction of lavas from these sources 3.75 AE ago. Other possibilities are considered.

Nyquist, L. E.↗
NASA NTRS1978

The X-ray source Serpens X-1 - Ariel 5 observations and discussion of models for the spectrum and time variability

Experimental data from Ariel 5 on the spectral shape and time variability of Ser X-1 are presented, and possible explanations for the observations are discussed in terms of current theoretical suggestions for source emission. The observations are summarized in the form of a light curve for 3-7.6-keV photons. The data are fitted with a power law of index -2.3, which yields a hydrogen column density of (1.1 + or - 0.4) x 10 to the 22nd power atoms/sq cm. No persistent periodicity of amplitude greater than 5% of the steady flux is found, but evidence of statistically significant burst activity is obtained. Various emission mechanisms are considered for the time-averaged spectrum and the X-ray bursts. It is suggested that the inverse Compton mechanism is a likely cause for the emission from this source and that the source is radiating near the Eddington limit.

Coe, M. J.↗
NASA NTRS1979

HEAO-A2 observations of the X-ray spectra of the Centaurus and A1060 clusters of galaxies

The X-ray spectral observations of two low luminosity clusters of galaxies, Centaurus and A1060, are presented. An emission feature of the Centaurus cluster at 7.9 keV is detected at about one third of the strength of the 6.7 keV line. This higher energy line represents K sub beta emission from highly ionized iron. An isothermal model with an Fe emission line is discussed and it is shown that the model cannot fit the data of the Centaurus or the A1060 clusters. The implications of the two component nature of the continuum on the Fe abundance and the X-ray surface brightness distribution are discussed.

Mitchell, R.↗
NASA NTRS1978

Silicon X-ray line emission from solar flares and active regions

New observations of solar flare and active region X-ray spectra obtained with the Columbia University instrument on OSO-8 are presented and discussed. The high sensitivity of the graphite crystal panel has allowed both line and continuum spectra to be served with moderate spectral resolution. Observations with higher spectral resolution have been made with a panel of pentaerythritol crystals. Twenty-nine lines between 1.5 and 7.0 A have been resolved and identified, including several dielectronic recombination satellite lines to Si XIV and Si XIII lines which have been observed for the first time. It has been found that thermal continuum models specified by single values of temperature and emission measure have fitted the data adequately, there being good agreement with the values of these parameters derived from line intensity ratios.

Parkinson, J. H.↗
NASA NTRS1979

Further observational support for the lossy radial diffusion model of the inner Jovian magnetosphere

A mathematical model describing radial diffusion, with violation of the third adiabatic invariant and with local losses, is applied to the Pioneer 10 and 11 observations of omnidirectional integral intensities of electrons with energy exceeding 21 MeV. Local losses outside L = 3 are much stronger than synchrotron losses but weaker than the losses one would expect for strong pitch angle diffusion. If radial diffusion is driven by ionospheric winds, as was suggested by Brice and McDonough (1973), it is found that the theoretical solution which best fits the data requires that the radial diffusion coefficient equals 3 x 10 to the -9th L-cubed/s and the lifetime against local losses is approximately a few million seconds.

Goertz, C. K.↗
NASA NTRS1979

On the nature of the blue and ultraviolet absorption in the Jovian atmosphere

Spatially resolved reflectivities from 3000 to 6600 A of three positions from the center to the limb of the Jovian Equator, North Equatorial Belt, and North Tropical Zone are analyzed to determine the vertical distribution and wavelength dependence of various sources of blue and uv absorption. Six different models of the distribution of absorbing dust particles are examined. In each model, the variation of dust optical depth and cloud single-scattering albedo are determined. Only those models having dust above the upper NH3 cloud layer will fit the data. The high altitude dust distribution is approximately uniform over the three regions examined. The contrast in reflectivity of the belts and zones may be modeled by a different cloud single-scattering albedo in the different regions.

Cochran, W. D.↗
NASA NTRS1979

Determination of polar motion and earth rotation from laser tracking of satellites

Laser tracking of the Lageos spacecraft has been used to derive the position of the earth's pole of rotation at intervals during October, November and December 1976. The estimated precision of the results is 0.01 to 0.02 arcseconds in both x and y components, although the formal uncertainty is an order of magnitude better, and there is general agreement with the Bureau International de l'Heure smoothed pole path to about 0.02 arcseconds. Present orbit determination capability of Lageos is limited to about 25 cm rms fit to data over periods of 5 days and about 50 cm over 50 days. The present major sources of error in the perturbations of Lageos are earth and ocean tides followed by the earth's gravity field, and solar and earth reflected radiation pressure. Ultimate accuracy for polar motion and earth rotation from Lageos after improved modeling of the perturbing forces appears to be of order + or - 5 cm for polar motion over a period of about one day and about + or - 0.2 to + or - 0.3 milliseconds in UT for periods up to 2 or 3 months.

Smith, D. E.↗
NASA NTRS1980

Soft X-ray observations of the supernova remnants HB 3 and 3C 58

The HEAO 1 A-2 low energy detectors have discovered soft X-ray emission from a source positionally coincident with the supernova remnant HB 3. The flux in the energy range 0.3-2.2 keV is about 6 x 10 to the -11th ergs per sq cm s. The spectral data are fitted to a hydrogen thermal bremsstrahlung model, and the physical parameters of the supernova remnant are estimated. The age derived is about 21,000 years, and the initial blast energy is about 3.1 x 10 to the 50th ergs. Upper limits to the soft X-ray flux and the luminosity of the supernova remnant 3 C 58 are also derived.

Galas, C. M. F.↗
NASA NTRS1980

Time-dependent radio fine structure of the compact sources NRAO 150 and 4C 39.25

Very long baseline interferometer observations at 7.85 GHz have been used to probe the milliarcsecond structure of the unidentified, very compact radio source NRAO 150 and QSO 4 C 39.25. NRAO 150 exhibited no structural variations from 1972 to the end of 1974. A model with two circular Gaussian components fits the data well. NRAO 150 had a flux density of 7.6 plus or minus 0.5 Jy in the compact component; 4 C 39.25 showed a two-component structure, the components having a separation of (2.02 plus or minus 0.05 arc sec) x 10 to the -3rd power. The upper bound on the speed of transverse separation is 0.0001 arc sec per year or less than 2.7 c. From the spectrum there are also indications of a third, larger component.

Baath, L. B.↗
NASA NTRS1981

Low-energy X-ray line emission from IC 443

HEAO 1 observations of the spectrum of the supernova remnant IC 443 in the energy range of 0.4-3 keV reveal the presence of a complex structure suggestive of emission from Fe XVIII-XX, S XV-XVI, and Si XIII-XIV ions. The best electron temperature in the band for simple model fits is about (6-11) x 10 to the 6th K. Raymond and Smith collisional equilibrium emission models do not adequately fit the data. These results are discussed in terms of possible nonequilibrium effects in the remnant.

Charles, P. A.↗
NASA NTRS1981

Far-infrared observations of shocked CO in Orion

The J = 27-26 and J = 30-29 transitions of CO have been detected in the Orion molecular cloud. These detections, together with an improved measurement of the J = 21-20 transition, allow estimation of the temperature and density of the shocked material and the fractional abundance of CO. By solving the equations of detailed balance for J less than or equal to 50 and fitting the data to a two-component model consistent with earlier 2-micron and 12-micron H2 observations, it is shown that the hot (2000 K) component has a density of approximately 1.0 x 10 to the 6th/cu cm, while the cooler component lies in the range of 400-1000 K and is 2-5 times more dense. Approximately 25% of the carbon is in the form of CO. The spatial extent of the hot CO has also been examined by observing the J = 21-20 transition at a number of positions, and it is found to be distributed similarly to the H2 lines. In addition, a search for J = 21-20 and J = 22-21 CO emission from six other sources has resulted in 3-standard-deviation upper limits of a factor of 10 below the intensity of the Orion lines.

Storey, J. W. V.↗
NASA NTRS1981

The libration of the Saturnian satellite Dione B

Previously published positions of Dione B are combined with new observations reported in this paper to determine its motion. The data are fit to the analytic solution of Erdi (1978) to derive the parameters of the libratory motion. The satellite oscillates about the leading equilateral libration point (L4) of Dione with a period of 785.0 + or - 0.5 days. The maximum separation in orbital longitude from Dione of 76.7 deg was reached on UT 1980 April 20.3 + or - 1 day; the minimum separation is 46.7 deg.

Reitsema, H. J.↗
NASA NTRS1982

Photopolarimetry from Voyager 2 - Preliminary results on Saturn, Titan, and the rings

The Voyager 2 photopolarimeter was reprogrammed prior to the August 1981 Saturn encounter to perform orthogonal-polarization, two-color measurements on Saturn, Titan, and the rings. Saturn's atmosphere has ultraviolet limb brightening in the mid-latitudes and pronounced polar darkening north of 65 deg N. Titan's opaque atmosphere shows strong positive polarization at all phase angles (2.7 deg to 154 deg), and no single-size spherical particle model appears to fit the data. A single radial stellar occultation of the darkened, shadowed rings indicated a ring thickness of less than 200 meters at several locations and clear evidence for density waves caused by satellite resonances. Multiple, very narrow strands of material were found in the Encke division and within the brightest single strand of the F ring.

Lane, A. L.↗
NASA NTRS1982

Compressional wave velocities of a lunar regolith sample in a simulated lunar environment

Ultrasonic compressional wave velocities have been measured in the laboratory for an Apollo 15 soil sample (15301, 38) under very low uniaxial stress and high vacuum conditions. The velocities measured range from 125 to 522 m/sec. The velocities of the soil are stress dependent and are strongly affected by compaction history. Hertzian contact theory does not appear to fit the data adequately for the pressure range of the experiment. Moderate increases in temperature do not have a significant effect on the compressional wave velocities.

Johnson, D. M.↗
NASA NTRS1982

Sensitivity of constrained linear inversions to the selection of the Lagrange multiplier

The influence of the choice of the Lagrange multiplier on constrained linear inversions is explored, with reference made to applications in inferring the columnar aerosol size distributions from spectral aerosol optical depth measurements. A range of the Lagrange multiplier is examined to find all positive solutions for the solution vector, which represents modifying factors to the assumed form of the size distribution. An iterative method is devised to constrain the calculations to consideration of only positive quantities and a requirement that the regression fit to data be consistent with measurement errors. The determination of the variances and covariances is formulated and applied to existing data sets for optical depth. Variances in the solution are found to be large for particle radii when the information content of the data is small.

King, M. D.↗