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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

A 14-day ground-based hypokinesia study in nonhuman primates: A compilation of results

A 14 day ground based hypokinesia study with rhesus monkeys was conducted to determine if a spaceflight of similar duration might affect bone remodeling and calcium homeostatis. The monkeys were placed in total body casts and sacrificed either immediately upon decasting or 14 days after decasting. Changes in vertebral strength were noted and further deterioration of bone strength continued during the recovery phase. Resorption in the vertebrae increased dramatically while formation decreased. Cortical bone formation was impaired in the long bones. The immobilized animals showed a progressive decrease in total serum calcium which rebounded upon remobilization. Most mandibular parameters remained unchanged during casting except for retardation of osteon birth or maturation rate and density distribution of matrix and mineral moieties.

Kazarian, L.↗
NASA NTRS1981

Response of large cavity ion chambers to space protons

The assumption that spherical-shell ion chamber rssponse is equal to the dose in the center of the cavity is found to be a poor approximation for ion chambers used for area monitoring in the space program. The dose response is calculated using the appropriate areal density distribution function. Effects of nuclear reaction are evaluated using proton buildup factors. Errors of up to 100% are found for some components of the space radiation environments.

Wilson, J. W.↗
NASA NTRS1981

Sunspot dynamics - Gravitational draining - A cooling mechanism

The inward and downward flow of cooled material below sunspots is considered as a possible explanation of the stability, temperature and heat flow characteristics of sunspots. It is suggested that the flow of material inwards towards the center of the sunspot and then downwards towards the center of the sun through magnetic field conduits plays a role in the cooling of sunspots as it does in pores and magnetic knots, although due to the larger size of a sunspot the downflow takes place below the photosphere. In this view, the inflow and cooling of sunspots are sustained by the release of energy by the convecting gas, which then becomes cooler and denser as it returns to the heat source. The lack of a bright ring around sunspots is explained by the entrainment of upward moving heat flux by the downward moving gases. The temperature and density distributions predicted by the present model are shown to be satisfactory agreement with the empirical model of Van't Veer (Tandberg-Hansen, 1966).

Schatten, K. H.↗
NASA NTRS1981

Characteristics of rain and rain systems

The description and measurement of the macroscopic and microscopic characteristics of rain and rain systems are discussed. The statistical relationships of these characteristics and their effect on polarization and attenuation are considered. Macroscopic characteristics include the size, distribution, and movements of rain cells, the height of melting layers, and the presence of ice crystals. Microscopic characteristics include the size distribution, density, and oblateness of rain drops and ice crystals. The estimation of a major propagation effect, specific attenuation, is described.

Source record↗
NASA NTRS1981

Boundary layer thermal stresses in angle-ply composite laminates, part 1

Thermal boundary-layer stresses (near free edges) and displacements were determined by a an eigenfunction expansion technique and the establishment of an appropriate particular solution. Current solutions in the region away from the singular domain (free edge) are found to be excellent agreement with existing approximate numerical results. As the edge is approached, the singular term controls the near field behavior of the boundary layer. Results are presented for cases of various angle-ply graphite/epoxy laminates with (theta/-theta/theta/theta) configurations. These results show high interlaminar (through-the-thickness) stresses. Thermal boundary-layer thicknesses of different composite systems are determined by examining the strain energy density distribution in composites. It is shown that the boundary-layer thickness depends on the degree of anisotropy of each individual lamina, thermomechanical properties of each ply, and the relative thickness of adjacent layers. The interlaminar thermal stresses are compressive with increasing temperature. The corresponding residual stresses are tensile and may enhance interply delaminations.

Wang, S. S.↗
NASA NTRS1982

Holographic interferometry and tomography at Ames Research Center

A YAG laser holographic interferometer system and reconstruction laboratory for the Ames 2- by 2-Foot Transonic Wind Tunnel are discussed. This system provides dual plate and double pulse holography for quantitative and qualitative measurements, respectively. Interferometric measurements of two-dimensional airfoils and three-dimensional bodies of revolution for a tomography feasibility study were made. The two-dimensional work included supercritical airfoils, an oscillating airfoil undergoing dynamic stall, and a circulation control airfoil. The tomography experiments centered around hemispherical nose and tangent ogive models. In addition, the tomography work covered the development of a Fourier transform code for the retrieval of the three dimensional density distributions from the interferograms.

Lee, G.↗
NASA NTRS1981

High-latitude ionospheric model - First step towards a predictive capability

In order to study the plasma density features associated with both weak and strong convection in the winter high-latitude F-region, a simple plasma convection model was combined with an ionospheric-atmospheric composition model. In a model calculation, a field tube of plasma is followed as it moves along a convection trajectory through a moving, neutral atmosphere. The altitude profiles of the ion densities are obtained by solving the appropriate continuity, momentum and energy equations, including many high-latitude processes. The result of following many such plasma field tubes is a time-dependent, three-dimensional ion density distribution for the ions NO(+), O2(+), O(+), N(+), and He(+). The high-latitude ionosphere is covered over one complete day above 42 deg N magnetic latitude, at altitudes of 160-800 km.

Schunk, R. W.↗
NASA NTRS1982

Hydrogen outgassing considerations for an orbiting aluminum molecular shield

A molecular shield and associated hardware made of pure aluminum is shown to have an outgassing rate sufficiently low so that operations in orbit would undergo less density contributions than that present from the upper atmospheric atomic hydrogen contribution. Measurements of the atomic hydrogen outgassing from baked-out 6061 aluminum cylindrical samples 3 mm thick are demonstrated to be less than 1/100 trillion l/sec per sq cm, comparable to that of austenitic stainless steels. Calculations of the density distribution with a hemispherical molecular shield are presented, and the elimination of porosity in the aluminum shells is recommended by means of vacuum melting.

Outlaw, R. A.↗
NASA NTRS1982

Ionospheric hot spot at high latitudes

Schunk and Raitt (1980) and Sojka et al. (1981) have developed a model of the convecting high-latitude ionosphere in order to determine the extent to which various chemical and transport processes affect the ion composition and electron density at F-region altitudes. The numerical model produces time-dependent, three-dimensional ion density distributions for the ions NO(+), O2(+), N2(+), O(+), N(+), and He(+). Recently, the high-latitude ionospheric model has been improved by including thermal conduction and diffusion-thermal heat flow terms. Schunk and Sojka (1982) have studied the ion temperature variations in the daytime high-latitude F-region. In the present study, a time-dependent three-dimensional ion temperature distribution is obtained for the high-latitude ionosphere for an asymmetric convection electric field pattern with enhanced flow in the dusk sector of the polar region. It is shown that such a convection pattern produces a hot spot in the ion temperature distribution which coincides with the location of the strong convection cell.

Schunk, R. W.↗
NASA NTRS1982

Flight and wind-tunnel correlation of boundary-layer transition on the AEDC transition cone

Transition and fluctuating surface pressure data were acquired on a 10 deg included angle cone, using the same instrumentation and technique over a wide range of Mach and Reynolds numbers in 23 wind tunnels and in flight. Transition was detected with a traversing pitot-pressure probe in contact with the surface. The surface pressure fluctuations were measured with microphones set flush in the cone surface. Good correlation of end of transition Reynolds number RE(T) was obtained between data from the lower disturbance wind tunnels and flight up to a boundary layer edge Mach number, M(e) = 1.2. Above M(e) = 1.2, however, this correlation deteriorates, with the flight Re(T) being 25 to 30% higher than the wind tunnel Re(T) at M(e) = 1.6. The end of transition Reynolds number correlated within + or - 20% with the surface pressure fluctuations, according to the equation used. Broad peaks in the power spectral density distributions indicated that Tollmien-Schlichting waves were the probable cause of transition in flight and in some of the wind tunnels.

Fisher, D. L.↗
NASA NTRS1983

Flight and wind-tunnel correlation of boundary-layer transition on the AEDC transition cone

Transition and fluctuating surface pressure data were acquired on a 10 degree included angle cone, using the same instrumentation and technique over a wide range of Mach and Reynolds numbers in 23 wind tunnels and in flight. Transition was detected with a traversing pitot pressure probe in contact with the surface. The surface pressure fluctuations were measured with microphones set flush in the cone surface. Good correlation of end of transition Reynolds number Re (sub T) was obtained between data from the lower disturbance wind tunnels and flight up to a boundary layer edge Mach number, M (sub e) = 1.2. Above M (sub e) = 1.2, however, this correlation deteriorates, with the flight Re (sub T) being 25 to 30% higher than the wind tunnel Re (sub T) at M (sub e) = 1.6. The end of transition Reynolds number correlated within + or - 20% with the surface pressure fluctuations. Broad peaks in the power spectral density distributions indicated that Tollmien-Schlichting waves were the probable cause of transition in flight and in some of the wind tunnels.

Fisher, D. F.↗
NASA NTRS1983

Computed tomographic analysis of meteorite inclusions

The feasibility of obtaining nondestructively a cross-sectional display of very dense heterogeneous rocky specimens, whether lunar, terrestrial or meteoritic, by using a fourth generation computed tomographic (CT) scanner, with modifications to the software only, is discussed. A description of the scanner, and of the experimental and analytical procedures is given. Using this technique, the interior of heterogeneous materials such as Allende can be probed nondestructively. The regions of material with high and low atomic numbers are displayed quickly; the object can then be cut to obtain for analysis just the areas of interest. A comparison of this technique with conventional industrial and medical techniques is made in terms of image resolution and density distribution display precision.

Arnold, J. R.↗
NASA NTRS1983

Abrasion cross sections for Ne-20 projectiles at 2.1 GeV/nucleon

Utilizing eikonal scattering theory, an optical model potential approximation to the exact nucleus-nucleus multiple scattering series is used in an abrasion-ablation collision formalism to predict abrasion cross sections for relativistic Ne-20 projectile nuclei. Excellent agreement with recent experimental abrasion results is obtained. The sensitivity of the abrasion predictions to Pauli exclusion principle correlation effects and to the assumed shape of the nuclear single-particle density distribution is also demonstrated.

Townsend, L. W.↗
NASA NTRS1983

Space radiation interaction mechanisms in materials

Models of charged-particle impact under conditions typical of the space environment are reported, with a focus on impact excitation and nuclear reactions, especially for heavy ions. Impact excitation is studied by using a global model for electronic excitation based on formal relations through the classical dielectric function to derive an approximation related to the local plasma (electron density distribution) within the atoms and molecules; and corrections to the model resulting from the nonfluid nature of this plasma are discussed. Nuclear reactions are studied by reducing quantum-mechanical treatment of this general N-body problem to an equivalent two-body problem that is solvable, and by comparing the results with experimental data. The equations for heavy-charged-particle transport are derived and solution techniques demonstrated. Finally, these methods of analysis are applied to study the change in the electrical properties of a GaAs semiconductor for photovoltaic applications; proton damage to GaAs crystals is found to arise from stable replacement defects and to be nonannealable, in contrast to electron-induced damage.

Wilson, J. W.↗
NASA NTRS1983

Statistical analysis of turbulence data from the NASA Marshall Space Flight Center atmospheric boundary layer tower array facility

Statistical properties of atmospheric turbulence near the Earth's surface are presented. Emphasis is placed on the probability density distribution two point spatial correlation, length scale, and two point and single point spectrum. Comparison of the data with isotropic homogeneous models is made. In general, agreement with the models is poor. For the design of aircraft during operations in the lower levels associated with approach, takeoff, and terrain following, it appears necessary to improve existing models or develop new nonisotropic turbulence models.

Frost, W.↗
NASA NTRS1983

Stellar number densities for magnitudes 0.0-9.0 from SKYMAP

Statistical information regarding the stellar number density distribution brighter than 9.0 mag in B and V of the Johnson magnitude system is presented. Data are extracted from SKYMAP Master Catalog Version 3.1 using computer techniques. The distribution as a function of (B - V) color, galactic latitude, and nearest-neighbor separation is examined. Comparisons of the SKYMAP data are made to four other sources of similar types of data.

Mclaughlin, S. F.↗
NASA NTRS1983

Turbulence measurements in two shock-wave/shear-layer interactions

Measurements of the longitudinal component of the mass-flow fluctuations have been made in an 8-deg compression corner flow and a reattaching shear layer at a Mach number of approximately 2.9 and unit Reynolds number of about 7 x 10 to the 7th per m. The data include turbulence intensities and probability density distributions. Significant turbulence amplification occurs in both interactions. A qualitative explanation in terms of direct shock effects, extra strain rates, and their relative contribution, is suggested.

Hayakawa, K.↗
NASA NTRS1984

A magnetohydrodynamic model of whistler duct structure in the magnetosphere

In this study, the physical structure for the propagation of whistler waves within a duct in the earth's magnetosphere is investigated by means of magnetohydrodynamic (MHD) theory. Expressions for the current density and induced magnetic field are determined analytically and evaluated in terms of two models for the duct plasma density distribution. It is found that once the duct is formed, forces associated with the current structure will maintain it. MHD instabilities are examined briefly and found to be unlikely to threaten duct maintenance in regions where whistlers are typically observed. Examination of some effects of field-aligned currents suggest that this may be a viable mechanism for duct formation.

Wang, S.↗