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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The kinematics of cool metal-line white dwarfs and accretion in the local interstellar medium

The data base of spectroscopically identified white dwarfs is used to isolate a sample of cool degenerates with trace metals. The spatial distribution and space velocity components of the white dwarfs projected onto and perpendicular to the galactic plane are compared with the distribution of local interstellar hydrogen. The results are consistent with the metals having been accreted during recent encounters with local density enhancements. However, the limited availability of radial velocities, coupled with uncertainties in the derived abundances, the diffusion times, and in the three-dimensional structure of the local medium, prevent a definitive test of the accretion hypothesis at this time.

Aannestad, P. A.↗
NASA NTRS1985

Advanced local area network concepts

Development of a good model of the data traffic requirements for Local Area Networks (LANs) onboard the Space Station is the driving problem in this work. A parameterized workload model is under development. An analysis contract has been started specifically to capture the distributed processing requirements for the Space Station and then to develop a top level model to simulate how various processing scenarios can handle the workload and what data communication patterns result. A summary of the Local Area Network Extendsible Simulator 2 Requirements Specification and excerpts from a grant report on the topological design of fiber optic local area networks with application to Expressnet are given.

Grant, Terry↗
NASA NTRS1987

The localization and crystallographic dependence of Si suboxide species at the SiO2/Si interface

X-ray photoemission spectroscopy has been used to examine the localization and crystallographic dependence of Si(+), Si(2+), and Si(3+) suboxide states at the SiO2/Si interface for (100)and (111)-oriented substrates with gate oxide quality thermal oxides. The Si(+) and Si(2+) states are localized within 6-10 A of the interface while the Si(3+) state extends about 30 A into the bulk SiO2. The distribution of Si(+) and Si(2+) states shows a strong crystallographic dependence with Si(2+) dominating on (100) substrates and Si(+) dominating on (111) substrates. This crystallographic dependence is anticipated from consideration of ideal unreconstructed (100) and (111) Si surfaces, suggesting that (1) the Si(+) and Si(2+) states are localized immediately within the first monolayer at the interface and (2) the first few monolayers of substrate Si atoms are not significantly displaced from the bulk. The total number of suboxide states observed at the SiO2/Si interface corresponds to 94 and 83 percent of a monolayer for these (100) and (111) substrates, respectively.

Grunthaner, P. J.↗
NASA NTRS1986

A local recent supernova - Evidence from X-rays, Al-26 radioactivity and cosmic rays

Possible ways in which cosmic rays could have been contaminated by a local recent supernova are discussed, and ways in which this contamination may be affecting interpretation of Al-26 gamma radiation and locally observed cosmic rays as samples of the average Galactic distribution are considered. Mass spectra of cosmic rays are examined to see whether there is enrichment by a population arising from supernova preacceleration. The reinterpretation of the anomalous component in terms of a local supernova model is addressed.

Clayton, Donald D.↗
NASA NTRS1987

A second catalog of gamma-ray bursts - 1978-1980 localizations from the interplanetary network

A catalog of 84 gamma-ray bursts which occurred between September 14, 1978 and February 13, 1980 is presented. The data presented consist of earth crossing times, given to about the nearest second, and time histories, in the tens of keV to MeV range, for all 84 events, as well as localizations for 80 of the events. The localizations, derived from arrival-time analysis, are given as single error boxes, double error boxes, or annuli of location, and, where possible, have been compared to the Konus localizations. They range in size from less than a square arcminute to over 1000 square degrees. The fluences of the bursts cataloged are in the range 3 x 10 to the -7th ergs/sq cm and above.

Atteia, J.-L.↗
NASA NTRS1987

On local approximations of the pressure-strain term in turbulence models

The results of numerical simulations of turbulent channel flows were used to examine the validity of the local approximation of the pressure-strain term in the Reynolds stress transport equation. Outside of the viscous sublayer the local approximation compares very well with the exact pressure strain. This agreement is due, at least in part, to the high correlation between the rapid pressure and its Laplacian, which suggests that only the near parts of the flow contribute to the rapid pressure at a point. In the viscous sublayer the distance over which the mean shear can be considered constant is comparable to the length scale in the normal direction of the correlations of velocity gradients, leading to failure of the local approximation.

Bradshaw, P.↗
NASA NTRS1988

Global and local Joule heating effects seen by DE 2

In the altitude region between 350 and 550 km, variations in the ion temperature principally reflect similar variations in the local frictional heating produced by a velocity difference between the ions and the neutrals. Here, the distribution of the ion temperature in this altitude region is shown, and its attributes in relation to previous work on local Joule heating rates are discussed. In addition to the ion temperature, instrumentation on the DE 2 satellite also provides a measure of the ion velocity vector representative of the total electric field. From this information, the local Joule heating rate is derived. From an estimate of the height-integrated Pedersen conductivity it is also possible to estimate the global (height-integrated) Joule heating rate. Here, the differences and relationships between these various parameters are described.

Heelis, R. A.↗
NASA NTRS1989

Advanced information processing system: Local system services

The Advanced Information Processing System (AIPS) is a multi-computer architecture composed of hardware and software building blocks that can be configured to meet a broad range of application requirements. The hardware building blocks are fault-tolerant, general-purpose computers, fault-and damage-tolerant networks (both computer and input/output), and interfaces between the networks and the computers. The software building blocks are the major software functions: local system services, input/output, system services, inter-computer system services, and the system manager. The foundation of the local system services is an operating system with the functions required for a traditional real-time multi-tasking computer, such as task scheduling, inter-task communication, memory management, interrupt handling, and time maintenance. Resting on this foundation are the redundancy management functions necessary in a redundant computer and the status reporting functions required for an operator interface. The functional requirements, functional design and detailed specifications for all the local system services are documented.

Burkhardt, Laura↗
NASA NTRS1988

Elastic-plastic crack analysis using a global-local approach on a parallel computer

A global-local finite-element analysis procedure is employed to solve elastoplastic crack problems. This procedure involves a global analysis using a coarse mesh and the subsequent locally refined analysis of a number of subregions. Parallel computation is involved in the local analyses. Numerical examples are performed on a MIMD parallel computer to demonstrate the time-saving capability of the proposed procedure.

Sun, C. T.↗
NASA NTRS1988

The stellar radiation field and the ionization of H and He in the local interstellar medium

Detailed photoionization calculations for the local interstellar medium (LISM) are presented based on constraints imposed by H I column density estimates derived from IUE and Copernicus data toward nearby B stars and hot white dwarfs. It is found that the nearby hot white dwarfs dominate the stellar contributions to the EUV radiation field. Considering stellar contribution to the EUV background alone, the resulting lower limits to the hydrogen and helium fractional ionization in the local diffuse cloud, at the sun, are 0.091 and 0.089, respectively. This result is insensitive to the absorbing geometry of the local cloud. The comparable ionizations of H and He near the sun are due to the lack of absorption from photospheric helium in the hot DA white dwarfs, to the difference in optical depths at wavelengths shortward of the H I and He I ionization edges, and to the fact that the hydrogen ionization controls the electron number density. The derived H and He ionization limits have important implications for the interpretation of the He I and H I backscattering results, for which uncertainties in charge-exchange interactions occurring in or near the heliopause reflect additional significant uncertainties in determining the ionization in the LISM.

Bruhweiler, Frederick C.↗
NASA NTRS1989

Methods and strategies of object localization

An important property of an intelligent robot is to be able to determine the location of an object in 3-D space. A general object localization system structure is proposed, some important issues on localization discussed, and an overview given for current available object localization algorithms and systems. The algorithms reviewed are characterized by their feature extracting and matching strategies; the range finding methods; the types of locatable objects; and the mathematical formulating methods.

Shao, Lejun↗
NASA NTRS1989

A model for the formation of the Local Group

Observational tests of a model for the formation of the Local Group are presented and analyzed in which the mass concentration grows by gravitational accretion of local-pressure matter onto two seed masses in an otherwise homogeneous initial mass distribution. The evolution of the mass distribution is studied in an analytic approximation and a numerical computation. The initial seed mass and separation are adjusted to produce the observed present separation and relative velocity of the Andromeda Nebula and the Galaxy. If H(0) is adjusted to about 80 km/s/Mpc with density parameter Omega = 1, then the model gives a good fit to the motions of the outer members of the Local Group. The same model gives particle orbits at radius of about 100 kpc that reasonably approximate the observed distribution of redshifts of the Galactic satellites.

Peebles, P. J. E.↗
NASA NTRS1990

HII regions in dwarf irregular galaxies of the local group

Deep, narrowband H alpha Charge Coupled Device (CCD) surveys of HII regions were carried out in several dwarf irregular galaxies in and near the local group. Data are now complete for these galaxies: NGC 6822, GR 8, IC 10, IC 1613, Sextans A, Sextans B, and Sag Irr. Observations are complete for DDO 47, 53, 167, 168 and 187. Details of some of the results for the surveys completed so far are discussed. For NGC 6822, CCD survey at H alpha resulted in the detection of 145 HII regions in the local group irregular galaxy NGC 6822. Most of them are newly detected, faint surface-brightness objects. Positions, maps and dimensions are being published elsewhere. For GR 8, a deep narrowband H alpha imaging of the nearby dwarf irregular galaxy GR 8 revealed a total of 32 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies, except for size of sample effects. Most HII regions detected are at the very low luminosity end of the general luminosity function. For IC 10, a deep CCD narrowband H alpha imaging of the local group dwarf irregular galaxy IC 10 revealed a total of 144 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies.

Hodge, Paul↗
NASA NTRS1991

Static Footprint Local Forces, Areas, and Aspect Ratios for Three Type 7 Aircraft Tires

The National Tire Modeling Program (NTMP) is a joint NASA/industry effort to improve the understanding of tire mechanics and develop accurate analytical design tools. This effort includes fundamental analytical and experimental research on the structural mechanics of tires. Footprint local forces, areas, and aspect ratios were measured. Local footprint forces in the vertical, lateral, and drag directions were measured with a special footprint force transducer. Measurements of the local forces in the footprint were obtained by positioning the transducer at specified locations within the footprint and externally loading the tires. Three tires were tested: (1) one representative of those used on the main landing gear of B-737 and DC-9 commercial transport airplanes, (2) a nose landing gear tire for the Space Shuttle Orbiter, and (3) a main landing gear tire for the Space Shuttle Orbiter. Data obtained for various inflation pressures and vertical loads are presented for two aircraft tires. The results are presented in graphical and tabulated forms.

Howell, William E.↗
NASA NTRS1991

Local Synthesis and Tooth Contact Analysis of Face-Milled Spiral Bevel Gears

Computerized simulation of meshing and bearing contact for spiral bevel gears and hypoid gears is a significant achievement that could substantially improve the technology and the quality of the gears. An approach to the synthesis of face-milled spiral bevel gears and their tooth contact analysis is presented. The proposed approach is based on the following ideas: application of the principle of local synthesis that provides optimal conditions of meshing and contact at the mean contact point, M, and in the neighborhood of M; and application of relations between principle directions and curvatures for surfaces being in line contact or in point contact. The developed local synthesis of gears provides the following: (1) the required gear ratio at M; (2) a localized bearing contact with the desired direction of the tangent to the contact path on gear tooth surface and the desired length of the major axis of contact ellipse at M; (3) a predesigned parabolic function of a controlled level for transmission errors which enables absorption of linear functions of transmission errors caused by misalignment and reduces the level of vibrations. The proposed approach does not require either the tilt of the head-cutter for the process of generation or modified roll for the pinion generation. Improved conditions of meshing and contact of the gears can be achieved without the above mentioned parameters. A computer program for determination of basic machine-tool settings and tooth contact analysis for the designed gears is presented. The approach is illustrated with a numerical example.

Litvin, Faydor L.↗
NASA NTRS1990

Synchronizing computer clocks using a local area network

Researchers completed the first tests of a method to synchronize the clocks of networked computers to the National Institute of Standards and Technology (NIST) time scale. The method uses a server computer to disseminate the time to other clients on the same local-area network. The server is synchronized to NIST using the ACTS protocol over a dial-up telephone line. The software in both the server and the parameters of this model are used to adjust the time of the local clock and the interval between calibration requests in a statistically optimum way. The algorithm maximizes the time between calibrations while at the same time keeping the time of the local clock correct within a specific tolerance. The method can be extended to synchronize computers linked over wide-area networks, and an experiment to test the performance of the algorithms over such networks is being planned.

Levine, Judah↗
NASA NTRS1991

Local delamination in laminates with angle ply matrix cracks. Part 2: Delamination fracture analysis and fatigue characterization

Constant amplitude tension-tension fatigue tests were conducted on AS4/3501-6 graphite/epoxy (02/ theta sub 2/ -(theta sub 2))sub s laminates, where theta was 15, 20, 25, or 30 degrees. Fatigue tests were conducted at a frequency of 5 Hz and an R-ratio of 0.1. Dye penetrant enhanced x-radiography was used to document the onset of matrix cracking in the central -(theta) degree plies, and the subsequent onset of local delaminations in the theta/ -(theta) interface at the intersection of the matrix cracks and the free edge, as a function of the number of fatigue cycles. Two strain energy release rate solutions for local delamination from matrix cracks were derived: one for a local delamination growing from an angle ply matrix crack with a uniform delamination growing from an angle ply matrix crack with a triangular shaped delamination area that extended only partially into the laminate width from the free edge. Plots of G(max) vs. N were generated to assess the accuracy of these G solutions. The influence of residual thermal and moisture stresses on G were also quantified. However, a detailed analysis of the G components and a mixed-mode fatigue failure criterion for this material may be needed to predict the fatigue behavior of these laminates.

Obrien, T. Kevin↗
NASA NTRS1991

Residual thermal and moisture influences on the strain energy release rate analysis of local delaminations from matrix cracks

An analysis utilizing laminated plate theory is developed to calculate the strain energy release rate associated with local delaminations originating at off-axis, single ply, matrix cracks in laminates subjected to uniaxial loads. The analysis includes the contribution of residual thermal and moisture stresses to the strain energy released. Examples are calculated for the strain energy release rate associated with local delaminations originating at 90 degrees and angle-ply (non-90 degrees) matrix ply cracks in glass epoxy and graphite epoxy laminates. The solution developed may be used to assess the relative contribution of mechanical, residual thermal, and moisture stresses on the strain energy release rate for local delamination for a variety of layups and materials.

Obrien, T. K.↗