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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Preliminary results of ultraviolet photometry of shell stars

Photometry of 40 B stars acquired by the OAO-2 has been examined for systematic differences between the 25 standard stars and 15 program objects. The latter include shell and Be stars and a few objects with at least a modest infrared excess. Although individual deviations did occur, no definite distinction between the program and comparison stars was found. A possible, but very weak, tendency for the program objects to lie somewhat below the standards in color-color plots is discussed, especially with reference to errors of misclassification and variability of the ultraviolet reddening law.

Bottemiller, R. L.↗
NASA NTRS1972

Large spacecraft antennas: Conical ring-membrane reflectors

A 1.83-m diameter furlable conical Gregorian antenna based on a novel spoke-supported ring-membrane concept has been successfully demonstrated. Mechanical measurements of the conical reflecting surface, as well as BE gain measurements at Ku-band, show an rms surface deviation from the proper conical surface of 0.3 mm and a repeatability after multiple furling-unfurling cycles of + or - 0.05 mm. Design features and performance characteristics of this antenna indicate that the spoke-supported ring-membrane concept is a promising approach for producing large, furlable, lightweight, conical reflectors for spacecraft high-gain antennas.

Oliver, R. E.↗
NASA NTRS1972

Mars gravitational field estimation error

The error covariance matrices associated with a weighted least-squares differential correction process have been analyzed for accuracy in determining the gravitational coefficients through degree and order five in the Mars gravitational potential junction. The results are presented in terms of standard deviations for the assumed estimated parameters. The covariance matrices were calculated by assuming Doppler tracking data from a Mars orbiter, a priori statistics for the estimated parameters, and model error uncertainties for tracking-station locations, the Mars ephemeris, the astronomical unit, the Mars gravitational constant (G sub M), and the gravitational coefficients of degrees six and seven. Model errors were treated by using the concept of consider parameters.

Compton, H. R.↗
NASA NTRS1972

Wind sensitivity studies of a non-return wind tunnel, with a 216- by 432-mm (8.5- by 17.0-inch) test section, phase 1

The study to develop inlet and exit treatments which would minimize the effect of external wind on the test-section flow quality of a nonreturn wind tunnel is reported. The investigation was conducted in the Ames Research Center 40- by 80-Foot Wind Tunnel which served as the wind source. Several inlets and two exits were tested at wind directions ranging from 0 to 180 degrees and at wind-to-test-section velocity ratios between zero and one. For the best inlet configuration the flow quality was good, with a velocity deviation in each of the three directions generally less than 1/2 knot (0.26 m/sec) for wind velocities of 15 knots (7.7 m/sec) or less. The loss in total pressure due to the inlet treatment was low: about 0.03 of the test-section dynamic pressure.

Eckert, W. T.↗
NASA NTRS1972

Laboratory and field evaluation of an underwater sand height gage

An underwater sand height gage was investigated. This instrument consisted of two transducers, one screened and one unscreened. Laboratory experimentation included static and dynamic tests with three test sands--fine, medium, and coarse. Field tests were conducted at Rudee Inlet, Virginia Beach, Virginia. Test results showed a linear response to up to 10 inches of sand loading. Deviation observed in identical tests appeared to be due to variation in the density of sand. Density differences reflected varying packing styles which, in turn, were a consequence of grain size and flow regime. Further evaluations of the sand height gage reflect this instrument's potential.

Swift, D. J. P.↗
NASA NTRS1971

On nonlinear effects in fracture mechanics.

Linear elastic treatment of fracture is considered applicable for net section stress up to about 0.8 the uniaxial tensile yield stress. Crack front plastic yield is still small enough to be viewed and treated as a small perturbation to the local crack front elastic stress field. Assuming these same circumstances and adopting the same point of view, an approach is presented for incorporating the nonlinear effects of small scale crack front plastic yield and slow crack extension in determination of the energy release rate and fracture toughness. Deviation from linearity of the load-displacement record in a fracture toughness test offers a quantifiable measure of these effects and is used to calculate the energy release rate. Fracture toughness values for one-eight inch thick 7075-T6 center cracked aluminum sheet are compared with uncorrected values and with values obtained by the Irwin method of plasticity correction.

Liebowitz, H.↗
NASA NTRS1971

The spectrum of steady state turbulent convection.

Based on Heisenberg's statistical theory of turbulence, a model for steady state turbulent convection is herein proposed, and on the basis of this model, equations for the energy spectrum for steady state turbulent convection are derived. The spectrum is obtained from the solution of a nonlinear integral equation. After the integral equation is brought into a universally valid nondimensional form, it is transformed into a nonlinear first order differential equation to be solved numerically, with the Rayleigh number appearing as the only parameter. The energy spectrum has a substantial deviation from the Kolmogoroff law, as a result of the buoyancy force acting on the rising and falling eddies. The presented theory may be applicable to convection in planetary and stellar atmospheres wherein the radiative heat transport is small.

Winterberg, F.↗
NASA NTRS1971

Theoretical N2 vibrational distribution in an aurora.

The N2 vibrational distribution in an aurora is investigated. During the auroral bombardment, the vibrational distribution is non-Boltzmann. The deviation from the Boltzmann distribution increases with increasing altitude. Above 200 km, the loss rate of O(+) due to the reaction O(+) + N2 leading to NO(+) + N is increased by a factor of 1.5 when allowance is made for the non-Boltzmann character of the N2 distribution. This increased loss rate persists for 1000-2000 sec after auroral bombardment commences.

Schunk, R. W.↗
NASA NTRS1971

Time dependent shear stress and temperature distribution over an insulated flat plate moving at hypersonic speed.

The laminar two-dimensional flow over a stepwise accelerated flat plate moving with hypersonic speed at zero angle of attack is analysed. The governing equations in the self-similar form are linearized and solved numerically for small times. The solutions obtained are the deviations of the velocity and the temperature profiles from those of steady state. The presented results may be used to find the first order boundary layer induced pressure on the plate.

Rodkiewicz, C. M.↗
NASA NTRS1971

The relation of QRS amplitude to the frontal QRS axis and the heart-electrode distance.

The relation between QRS amplitude, QRS axis deviation and heart position was studied in 360 subjects, using the 12-lead EKG. The height of the V sub 6 R wave was used as the measure of QRS amplitude. The distance from the left lateral border of the heart was used to indicate heart position. The frontal and horizontal QRS axes were determined by noting the isoelectric limb and precordial leads, measured according to Schmitt's values.

Dougherty, J. D.↗
NASA NTRS1971

Irradiation of linear polyethylene - Partitioning between sol and gel.

Molecular weight fractions of linear polyethylene were irradiated at 133 C, in the completely molten and highly crystalline states, for the purpose of assessing the importance of chain-scission processes and establishing the critical conditions for gelation. The partitioning between sol and gel in either state was found to adhere to the theory for the intermolecular cross-linking of monodisperse species for dosages just beyond the gel point. Deviations from theory occurred as the dosage was increased further. It was concluded that main-chain scission, at these temperatures, is not a significant process. High molecular weight samples in the completely molten state obeyed the Flory-Stockmayer condition for critical gelation.

Rijke, A. M.↗
NASA NTRS1972

Gamma-ray observations of the galactic center and some possible point sources.

A 0.5 x 0.5-m digitized spark-chamber gamma-ray telescope was flown on three balloon flights to look at the galactic center region, Virgo, and the Crab Nebula. An excess flux above atmospheric background of over 4 standard deviations was found for gamma-rays exceeding 100 MeV coming from the galactic center region, but there was no statistically significant excess in the 50-100 MeV interval. As a result, there is only a 6% chance that Compton or synchrotron radiation from electrons with a power-law spectrum having an exponent of 2.6 could make as much as a 50% contribution to the gamma-radiation in this energy range.

Fitchtel, C. E.↗
NASA NTRS1972

A theoretical and experimental investigation of the hypersonic turbulent boundary layer subject to normal and longitudinal pressure gradients and cross flow along a windward plane of symmetry.

A theoretical and experimental investigation for the hypersonic turbulent boundary layer undergoing both normal and longitudinal pressure gradients and cross flow along the plane of symmetry on the windward side of a body of revolution is presented. The purpose of this investigation is to provide a method for calculating boundary layers that occur on the centerline of symmetry of an inlet. The three-dimensional compressible integral equations are written along the symmetry plane and integrated numerically, and the effect of the cross flow on the behavior of the boundary layer is also studied. The experiments were performed at Mach number 6 and Reynolds number of 44,000,000/ft for the axisymmetric case and for the case with cross flow. The velocity profiles and the boundary layer parameters agree relatively well with theoretical values with and without cross flow effects. The presence of the cross flow alters significantly the value of the profiles. Total temperature-velocity correlations deviate from the linear Crocco distribution. Heat transfer rates agree with theoretical values and values obtained by the flat plate reference enthalpy method. Cross flow influence on the heat transfer rates is of minor relevance.

Zakkay, V.↗
NASA NTRS1972

Experimental investigation of two-phase heat transfer in a porous matrix.

One-dimensional two-phase flow transpiration cooling through porous metal is studied experimentally. The experimental data is compared with a previous one-dimensional analysis. Good agreement with calculated temperature distribution is obtained as long as the basic assumptions of the analytical model are satisfied. Deviations from the basic assumptions are caused by nonhomogeneous and oscillating flow conditions. Preliminary derivation of nondimensional parameters which characterize the stable and unstable flow conditions is given. Superheated liquid droplets observed sputtering from the heated surface indicated incomplete evaporation at heat fluxes well in access of the latent energy transport. A parameter is developed to account for the nonequilibrium thermodynamic effects. Measured and calculated pressure drops show contradicting trends which are attributed to capillary forces.

Von Reth, R.↗
NASA NTRS1972

Guidance technique for automated air traffic control.

A guidance technique has been developed for flying an aircraft automatically along curved trajectories. The technique consists of a set of algorithms for automatically synthesizing flight profiles, i.e., the horizontal trajectory, the altitude and speed profiles, and a time sequence of commands. The flyability of the synthesized profile under wind disturbances and initial conditions error is verified by closing the loop around the synthesized trajectory and flying it in a computer-simulated jet aircraft. A control law having longitudinal, lateral, and heading deviation from the synthesized profile in the feedback loops is used for the simulated flight. The performance of the system is excellent, errors that are initially zero never exceed 230 ft, and large initial errors are reduced rapidly. The system also behaves quite well under wind disturbance.

Lee, H. Q.↗
NASA NTRS1972

Mariner 9 celestial mechanics experiment - Gravity field and pole direction of Mars.

Analysis of the Mariner 9 radio-tracking data shows that the Martian gravity field is rougher than that of earth or the moon, and that the accepted direction of the Mars rotation axis is in error by about 0.5 deg. Contours of equivalent surface heights deduced from a sixth-degree solution for the Martian gravity field are presented. These contours represent the deviations from sphericity of a uniformly dense body with an external potential which is given by the first sixth-degree solution. In addition to Doppler observations, ranging or group-delay measurements have been made regularly since orbit insertion.

Lorell, J.↗
NASA NTRS1972

Radio-auroral aspect sensitivity and the two-stream instability.

The possibility is explored that the auroral electrojet current motions may be sufficiently great not only to introduce some distortion in the magnetic field, but also to substantially increase the maximum deviation from orthogonality permitted by Farley's mechanism. These two effects are then combined to give an approximate indication of how the aspect sensitivity should vary with current strength and direction.

Moorcroft, D. R.↗
NASA NTRS1972

The configuration of the geomagnetic field.

Spherical harmonic representations of the geomagnetic field based on ground-based and low-altitude spacecraft measurements adequately describe the field within several earth radii of the earth's surface. As the internal field decreases with increasing distance from the earth, external field sources become relatively more important. In the region of 3 to 6 earth radii, magnetospheric plasma inflates the field lines and decreases the field strength by an amount which is typically 10's of gammas and occasionally 100's of gammas. At greater distances on the day side of the earth, the solar wind compresses the field and produces equatorial field strengths of approximately 60 gammas at 10 earth radii. Field lines near the magnetopause intersect the earth at approximately 78 deg latitude in the sunward hemisphere. The solar wind drags high latitude field lines away from the earth in the night hemisphere forming the geomagnetic tail and neutral sheet. Asymmetric field inflation in the magnetosphere occurs during magnetic disturbances with the largest effects concentrated in the evening quadrant. The tail configuration can deviate substantially from the average configuration during magnetic disturbances.

Fairfield, D. H.↗