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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Dependence of growth rate of quartz in fused silica on pressure and impurity content

The effects of pressure, temperature, and some variations in impurity content on the growth rate u of quartz into fused silica were measured. Under all conditions the growth rate was interface controlled and increased exponentially with pressure with an activation volume averaging -21.2 cu cm/mole. The activation enthalpy for all specimens is extrapolated to a zero pressure value of 64 kcal/mole, within the experimental uncertainty. At a given stoichiometry the effect of hydroxyl content on growth rate is described entirely by a linear term C(OH) in the prefactor of the equation for the growth rate. The effect of chlorine impurity can be described similarly. Also u is increased as the ideal stoichiometry is approached from the partially reduced state.

Fratello, V. J.↗
NASA NTRS1981

An analytical study of the longitudinal response of airplanes to positive wind shear

The longitudinal response of jet transport aircraft to vertical variation of the horizontal winds is analyzed. Specific reference is given to the role of the speed (u) stability derivatives in the interaction of the airplane and its environment. The relative importance of the u stability derivatives is determined. The wind shear tolerance factor is found which can be used to determine, in a qualitative manner, the stability (tolerance) of an airplane to wind shear. A further study of the control problem shows that the criteria for good control could be reduced from two to one automatic control systems. Only a speed control system is necessary for good control in wind shear.

Sherman, W. L.↗
NASA NTRS1981

Coordinated IUE, Einstein and optical observations of accreting degenerate dwarfs

Three binary systems believed to be composed of a white dwarf and a late type star, AM Her, SS Cyg, and U Gem were observed simultaneously in the IV X-ray and optical wavelengths. The system AM Her was in its customary high state at the time of the observations, while SS Cyg and U Gem were in a low state. In all three cases, a significant UV black body component with KT approximately greater than 10 eV was found. The flux in this component is in excess of the amount predicted by current scenarios of gravitational energy release.

Fabbiano, B.↗
NASA NTRS1980

Thunderstorm Overflight Program

The Thunderstorm Overflight Program is being conducted by NASA, NOAA, and universities to evaluate the feasibility of making meaningful measurements of lightning parameters from an orbiting platform above thunderstorms. A NASA instrumented U-2 high-altitude research aircraft was used during the summer of 1979 and spring of 1980 to collect data over the tops of the thunderstorms while ground-based measurements were being made simultaneously. Test sites at Langmuir Laboratory, Socorro, N. Mex., and the National Severe Storms Laboratory, Norman, Okla. were used for this program. Additional flights are planned for the spring and summer of 1981. Data from the NASA U-2 flights will also be used to interpret measurements made during the Nighttime/Daytime Optical Survey Lightning Experiment to be flown on the Space Shuttle in late 1981.

Vaughan, O. H., Jr.↗
NASA NTRS1980

UDU/T/ covariance factorization for Kalman filtering

There has been strong motivation to produce numerically stable formulations of the Kalman filter algorithms because it has long been known that the original discrete-time Kalman formulas are numerically unreliable. Numerical instability can be avoided by propagating certain factors of the estimate error covariance matrix rather than the covariance matrix itself. This paper documents filter algorithms that correspond to the covariance factorization P = UDU(T), where U is a unit upper triangular matrix and D is diagonal. Emphasis is on computational efficiency and numerical stability, since these properties are of key importance in real-time filter applications. The history of square-root and U-D covariance filters is reviewed. Simple examples are given to illustrate the numerical inadequacy of the Kalman covariance filter algorithms; these examples show how factorization techniques can give improved computational reliability.

Thornton, C. L.↗
NASA NTRS1979

Hard X-ray properties of cataclysmic variables

A brief summary is presented of results for AM Her, EX Hya, SS Cyg, and U Gem obtained with the high-energy detectors of the HEAO A2 experiment from 2-60 keV and the Solid State Spectrometer Experiment with the Monitor Proportional Control on the Einstein Observatory. It is found that the magnetic variable AM Her and the dwarf novae are similar in having bremsstrahlung of similar luminosity with temperatures for the dwarf novae that can approach that for AM Her and in flickering on a time scale of 5-15 min. But in general these dwarf novae temperatures are about 2-10 times lower. Only in Am Her is there evidence in the spectrum and eclipses for a small spot very close to the white dwarf surface. Most of the hard X-rays in SS Cyg, EX Hya, and U Gem are not pulsed, and the hard X-ray fluxes observed have never been significantly absorbed or degraded.

Swank, J. H.↗
NASA NTRS1979

Analysis of the soft X-ray pulsations of dwarf novae

Both SS Cyg and U Gem show enhanced soft X-ray emission (0.1 to 0.5 keV) during optical outbursts. The fact that a large fraction of this emission is pulsed confirms the general expectation that high energy pulsations are the ultimate source of the optical pulsations observed during outbursts of dwarf novae. The present analysis leads to the conclusion that coherent optical oscillations, of the type exhibited by SS Cyg, can be explained by intrinsic phase instability. The quasi-coherent optical pulsations observed for several dwarf novae on the decline from maximum brightness have a behavior similar to the X-ray pulsation in U Gem. It is suggested that all of the optical and X-ray oscillations are produced by the same mechanism.

Cordova, F. A.↗
NASA NTRS1981

Algol - A further study of the optical polarization

Results of a study of the phase-locked optical polarization of the Algol triple star system are presented. Polarimetry was obtained in the B filter during 75 nights from 1979 to 1980, and results were folded on the AB orbital period for the equatorial Stokes parameters Q and U. As expected for a nearly edge-on system, the polarization variations are predominantly in one direction of the Stokes-vector plane, and are mainly second-harmonic in character. The variable polarization indicates an eigendirection for the AB system at an angle of 137 + or - 4 deg, and a projected major axis of the third star at 133 + or - 3 deg with respect to the AB system. Considerations of the lowest-order theories of polarizing mechanisms, including limb polarization and reflection, indicate that the AB and AB-C orbital planes are almost normal to each other, rather than coplanar. An angular splitting in the Q-U curve between the two quadrature phases 0.25 and 0.75 is also found which can be explained by centrifugal flattening of the secondary's Roche lobe, or reflection from an optically thick, flattened gas cloud near the L1 point.

Kemp, J. C.↗
NASA NTRS1981

Lead isotopic studies of the Samail ophiolite, Oman

The isotopic composition of Pb and the concentrations of U, Th, and Pb are determined for samples from massive sulfides and lithologic units of the Samail ophiolite. It is shown that the magma that formed the ophiolite was probably derived from a depleted mantle, similar in Pb isotopic composition to the source area of mid-ocean ridge basalt. The gross geochemical characteristics of the mantle sources have remained almost unchanged for the last 100 million years. It is also shown that the U-Th-Pb systematics of the Samail formation indicate that local vertical heterogeneity in the oceanic crust can result from crystal fractionation and metasomatism at, and near, an oceanic spreading center.

Chen, J. H.↗
NASA NTRS1981

Enhanced skeletal muscle insulin sensitivity in year-old rats adapted to hypergravity

Rats induced into a hypermetabolic state by exposure to chronic (7 mo) centrifugation at 4.15 g exhibited increased glucose uptake at lower plasma insulin levels than weight-matched control animals following oral glucose administration. In order to determine the insulin sensitivity of specific tissues, the effect of exogenous insulin on glucose uptake by isolated perfused livers and hindlim skeletal muscle from rats adapted to chronic centrifugation for one year was compared with perfused tissue from 2.5 mo-old noncentrifuged control animals of equal body weight. Metabolic glucose clearance by skeletal muscle from hypergravic rats did not prove significantly greater than control muscle when perfused in the absence of insulin (10.6 vs 8.1 microliters/min-g-muscle), but was twice as fast (23.0 vs 9.5) at perfusate insulin levels of 35 micro-U/ml. Conversely, glucose uptake by hypergravic livers was significantly decreased (P is less than 0.001) compared with control livers (10.3 vs 27.8) at perfusate insulin levels of 40 micro-U/ml. Results suggest that skeletal muscle rather than liver is primarily responsible for the enhanced sensitivity to insulin and the increased energy expenditure observed in rats subjected to hypergravity.

Mondon, C. E.↗
NASA NTRS1981

Effect of polynucleotides on the dimerization of glycine

Results from experiments to determine the effect of polynucleotides on abiological formation of peptide bonds are reported. The reaction between glycine molecules in an aqueous phase in the presence of a condensing agent was chosen as a model, with polyphosphates being selected as the condensing agent for biologically relevant peptide formation. Four types of polynucleotides were used: polygluanic acid (G), polyuridic acid (U), polyadenylic acid (A), and polycytidylic acid (C); the effects of small anions, acetate, chloride, and phosphate, were also studied. Procedures are given, including concentrations, pH, and incubation time, and the type of amino acid analyzer. The diglycine yields were, in order of most to least: G, C, A, U, and are diagrammed as a function of time; rate of formation followed the same order of magnitude as the final yields. Anion presence displayed no discernible effect. The results are taken to indicate that polynucleotides do have an effect on the formation of peptide bonds, an effect significant in the understanding of chemical evolution.

Mizutani, H.↗
NASA NTRS1982

Numerical comparisons of nonlinear convergence accelerators

As part of a continuing program of numerical tests of convergence accelerators, the iterated Aitken's Delta-squared method, Wynn's epsilon algorithm, Brezinski's theta algorithm, and Levin's u transform are compared on a broad range of test problems: linearly convergence alternating, monotone, and irregular-sign series, logarithmically convergent series, power method and Bernoulli method sequences, alternating and monotone asymptotic series, and some perturbation series arising in applications. In each category either the epsilon algorithm or the u transform gives the best results of the four methods tested. In some cases differences among methods are slight, and in others they are quite striking.

Smith, D. A.↗
NASA NTRS1982

Broad band airborne water vapor radiometry

An infrared radiometer with a pass band of 280 to 520/cm (35.7 to 19.2 microns) is employed on the NASA Ames Research Center U-2 and C-141A aircraft in the measurement of water vapor burden in the upper troposphere and stratosphere. Coincidentally with altitude changes the water vapor mass mixing ratio is also inferred by observing the change in optical depth over a known vertical distance. Data from the December 1980 U-2 Water Vapor Exchange Experiment over the Panama Canal Zone add to the concept that overshooting cumulonimbus towers 'moisten' the lower stratosphere. The average mass mixing ratio in close proximity to or above such towers ranges from 3.5 to 5.0 parts per million above 18 km while the average background mass mixing ratio is only 2.9 parts per million. Generally the lowest background mixing ratios, averaging 2.6 parts per million occurred in the 18 to 21 km layer. For the same levels background Panama mass mixing ratios averaged from 1.0 to 3.0 parts per million higher than in middle latitudes.

Kuhn, P. M.↗
NASA NTRS1983

Higher modes of the Orr-Sommerfeld problem for boundary layer flows

The discrete spectrum of the Orr-Sommerfeld problem of hydrodynamic stability for boundary layer flows in semi-infinite regions is examined. Related questions concerning the continuous spectrum are also addressed. Emphasis is placed on the stability problem for the Blasius boundary layer profile. A general theoretical result is given which proves that the discrete spectrum of the Orr-Sommerfeld problem for boundary layer profiles (U(y), 0,0) has only a finite number of discrete modes when U(y) has derivatives of all orders. Details are given of a highly accurate numerical technique based on collocation with splines for the calculation of stability characteristics. The technique includes replacement of 'outer' boundary conditions by asymptotic forms based on the proper large parameter in the stability problem. Implementation of the asymptotic boundary conditions is such that there is no need to make apriori distinctions between subcases of the discrete spectrum or between the discrete and continuous spectrums. Typical calculations for the usual Blasius problem are presented.

Lakin, W. D.↗
NASA NTRS1983

Elastohydrodynamics of elliptical contacts for materials of low elastic modulus

The influence of the ellipticity parameter k and the dimensionless speed U, load W, and materials G parameters on minimum film thickness for materials of low elastic modulus was investigated. The ellipticity parameter was varied from 1 (a ball-on-plane configuration) to 12 (a configuration approaching a line contact); U and W were each varied by one order of magnitude. Seventeen cases were used to generate the minimum- and central-film-thickness relations. The influence of lubricant starvation on minimum film thickness in starved elliptical, elastohydrodynamic configurations was also investigated for materials of low elastic modulus. Lubricant starvation was studied simply by moving the inlet boundary closer to the center of the conjunction in the numerical solutions. Contour plots of pressure and film thickness in and around the contact were presented for both fully flooded and starved lubrication conditions. It is evident from these figures that the inlet pressure contours become less circular and closer to the edge of the Hertzian contact zone and that the film thickness decreases substantially as the serverity of starvation increases. The results presented reveal the essential features of both fully flooded and starved, elliptical, elastohydrodynamic conjunctions for materials of low elastic modulus.

Hamrock, B. J.↗
NASA NTRS1983

The doubly excited autoionizing states of H2

Neutral doubly excited states of H2 lie in the Franck-Condon region at energies beyound 23 eV above the ground state of H2. These repulsive resonance states may autoionize yielding H2(+) + e(-), H + H(+) + e(-) or dissociate to neutral ground and excited H atoms or H(+) + H(-). These processes are important in determining the thermal balance of interstellar clouds and the chemistry of the Jovian atmosphere. The present investigation is concerned with ab initio calculations of 24 autoionizing states of H2 which have mostly the 2 Sigma u + and first excited 2 Pi u states of H2(+) as the core orbital near R = 1. 4a(0). Of the 24 states reported, 14 have not appeared previously in the literature. For four of the remaining ten states an energy at only a single internuclear distance has been previously reported.

Guberman, S. L.↗
NASA NTRS1983

Worldwide photometry and lightcurve observations of 1 Ceres during the 1975-1976 apparition

Lightcurves and UBV photometry of Ceres from the 1975-1976 apparition are presented. The synodic period is 0.37812 + or 0.00004 day, the mean absolute V magnitude is 3.61 + or 0.03, and the phase coefficient is 0.040 + or - 0.001 mag/deg. The U-B and B-V phase coefficients are +0.0015 + or - 0.0007 and +0.0006 + or - 0.0003 mag/deg, respectively. The colors at zero phase are B-V = +0.70 + or - 0.01 and U-B = +0.41 + or 0.01.

Tedesco, E. F.↗
NASA NTRS1983

Transport properties of ground state nitrogen atoms

In view of the dependence of the transport properties of dilute monatomic gases on the two-body, atom-atom interaction potential, any one of four potential energy curves corresponding to the N2 molecule can be followed when two ground state N atoms interact. Transport collision integrals for the 1Sigma(+)g and 3Sigma(+)u states have been calculated by representing their potentials with the Hulburt-Hirschfelder (1941, 1961) potential. The 5Sigma(+)g state has a large local maximum requiring changes in a previously used computational procedure, and its potential has also been represented by a Hulburt-Hirschfelder potential. Collision integrals for the 7Sigma(+)u state have been obtained through the direct use of a recently proposed theoretical potential for this state. The collision integrals are compared with results gathered from previous studies.

Rainwater, J. C.↗