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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

the P-wave upper mantle structure beneath an active spreading center: The Gulf of California

Detailed analysis of short period travel time, and waveform data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km. More than 1400 digital seismograms from earthquakes in Mexico and central America recorded at SCARLET yield 1753 travel times and 58 direct measurements of short period travel time as well as high quality, stable waveforms. The 29 events combine to form a continuous record section from 9 deg to 40 deg with an average station spacing of less than 5 km. First the travel times are inverted. Further constraints arise from the observed relative amplitudes of mantle phases, which are modeled by trial and error.

Walck, M. C.↗
NASA NTRS1983

Influence of the E region dynamo on equatorial spread F

The integrated E region Pedersen conductivity can be an important parameter in determining whether the bottomside of the equatorial F layer will be stable against the Rayleigh-Taylor gravitational instability. The F layer is observed to become unstable when it rises to great heights after sunset. One effect of this height rise is to decrease the stabilizing influence of ion-neutral collisions at F region heights. It is shown here that the same eastward electric field that raises the F layer also decreases the Pedersen conductivity of the E region, which further destabilizes convective overturning. Because the conductivity of magnetic tubes that penetrate the main F layer is large compared to the E layer contribution, these effects are important only for the bottomside of the equatorial F layer.

Hanson, W. B.↗
NASA NTRS1983

High frequency green function for aerodynamic noise in moving media. I - General theory. II - Noise from a spreading jet

It is shown how a high frequency analysis can be made for general problems involving flow-generated noise. In the parallel shear flow problem treated by Balsa (1976) and Goldstein (1982), the equation governing sound propagation in the moving medium could be transformed into a wave equation for a stationary medium with an inhomogeneous index of refraction. It is noted that the procedure of Avila and Keller (1963) was then used to construct a high frequency Green function. This procedure involves matching a solution valid in an inner region around the point source to an outer, ray-acoustics solution. This same procedure is used here to construct the Green function for a source in an arbitrary mean flow. In view of the fact that there is no restriction to parallel flow, the governing equations cannot be transformed into a wave equation; the analysis therefore proceeds from the equations of motion themselves.

Durbin, P. A.↗
NASA NTRS1982

Error correction coding for frequency-hopping multiple-access spread spectrum communication systems

A communication system which would effect channel coding for frequency-hopped multiple-access is described. It is shown that in theory coding can increase the spectrum utilization efficiency of a system with mutual interference to 100 percent. Various coding strategies are discussed and some initial comparisons are given. Some of the problems associated with implementing the type of system described here are discussed.

Healy, T. J.↗
NASA NTRS1984

The p-wave upper mantle structure beneath an active spreading centre - The Gulf of California

Over 1400 seismograms of earthquakes in Mexico are analyzed and data sets for the travel time, apparent phase velocity, and relative amplitude information are utilized to produce a tightly constrained, detailed model for depths to 900 km beneath an active oceanic ridge region, the Gulf of California. The data are combined by first inverting the travel times, perturbing that model to fit the p-delta data, and then performing trial and error synthetic seismogram modelling to fit the short-period waveforms. The final model satisfies all three data sets. The ridge model is similar to existing upper mantle models for shield, tectonic-continental, and arc-trench regimes below 400 km, but differs significantly in the upper 350 km. Ridge model velocities are very low in this depth range; the model 'catches up' with the others with a very large velocity gradient from 225 to 390 km.

Walck, M. C.↗
NASA NTRS1984

Photovoltaic module spread-of-flame testing

Photovoltaic modules used in solar energy conversion are tested for flammability. Class B burning brand tests were conducted with the following results: module glass shattered and hydrocarbon encapsulants ignited. Penetration of back surface material was the prime cause of failure. Materials with greater flame and heat resistance are under consideration to increase back surface integrity up to Class A burning brand standard. The most promising is stainless steel foil.

Sugimura, R. S.↗
NASA NTRS1985

Electrodynamic interaction of Ganymede with the Jovian magnetosphere and the radial spread of wake-associated disturbances

An investigation is conducted of the electrostatics of the interaction of Jupiter's satellite Ganymede with the Jovian plasma and the MHD stability of the resulting downstream cavity, taking into account an evaluation of the effect of distorted magnetic field models on the radial extent of the disturbances. The objective of the investigation is an understanding of the data which have been provided by Voyager 2 during its approach to Jupiter, giving attention to the Voyager 2 magnetometer experiment. It is concluded that the magnetic field distortion by itself is insufficient to explain the large radial extent of the observed wake encounters. Linear treatment of MHD equations showed that the Kelvin-Helmholtz instability is initiated at the plasma-cavity interface.

Tariq, G. F.↗
NASA NTRS1988

Microplate and shear zone models for oceanic spreading center reorganizations

The kinematics of rift propagation and the resulting goemetries of various tectonic elements for two plates is reviewed with no overlap zone. The formation and evolution of overlap regions using schematic models is discussed. The models are scaled in space and time to approximate the Easter plate, but are simplified to emphasize key elements. The tectonic evolution of overlap regions which act as rigid microplates and shear zones is discussed, and the use of relative motion and structural data to discriminate between the two types of models is investigated. The effect of propagation rate and rise time on the size, shape, and deformation of the overlap region is demonstrated.

Engeln, Joseph F.↗
NASA NTRS1988

Time scales for formation and spreading of velocity shells of pickup ions in the solar wind

This paper discusses the process of assimilation (pickup) by the solar wind of newly ionized atoms and molecules. Generally, the pickup process is considered to evolve in three stages: (1) the initial interaction of newly created ions with the interplanetary magnetic field to form the ring-beam distribution; (2) pitch angle scattering of the ring beam to form a hollow shell; and (3) slower velocity diffusion to form a partially filled-in shell distribution. Using numerical simulations of turbulence such as would occur naturally in the solar wind and such as would be encountered near cometary bow shocks, the processes of shell formation and evolution are studied, and the results are used to estimate the time scales for shell formation and diffusion in several situations of recent observational interest, the interstellar He data obtained by AMPTE and cometary ion pickup distributions obtained by various spacecraft at comets Giacobini-Zinner and Halley.

Gaffey, J. D., Jr.↗
NASA NTRS1989

Spread Of Charge From Ion Tracks In Integrated Circuits

Single-event upsets (SEU's) propagate to adjacent cells in integrated memory circuits. Findings of experiments in lateral transport of electrical-charge carriers from ion tracks in 256K dynamic randon-access memories (DRAM's). As dimensions of integrated circuits decrease, vulnerability to SEU's increases. Understanding gained enables design of less vulnerable circuits.

Zoutendyk, John A.↗
NASA NTRS1990

A phase-space fluid simulation of a two-component narrow planetary ring - Particle size segregation, edge formation, and spreading rates

The Krook kinetic equation for identical planetary ring particles is presently generalized for the case of two-component systems, and the equations are numerically solved on the basis of Brophy and Esposito's (1989) phase-space CFD method. Attention is given to the simulation results obtained for a two-component narrow ring, in which the large particles are eight times as massive as the small particles. This ring's unconstrained edge dynamics are resolved by the simulation, and are found to exhibit a sharpening that would not have been expected in single-component rings.

Brophy, Thomas G.↗
NASA NTRS1990

Prediction of heat transfer to a thin liquid film in plane and radially spreading flows

The energy equation is incorporated in the solution algorithm of Rahman et al. (1990) to compute the heat transfer to a thin film in the presence or absence of gravity. For a plane flow under zero gravity, it is found that, for both isothermal and uniformly heated walls, the heat transfer coefficient gradually decreases downstream, with Nu-asterisk (the Nusselt number in terms of film height) remaining approximately constant except for regions very close to the entrance. In the case of radial flow under zero gravity, Nu-asterisk is found to decrease monotonically when the plane is uniformly heated. Two different flow regimes are identified in the presence of gravity for both plane and radial flows. The results of the study may be applicable to the design of space-based cooling systems.

Rahman, M. M.↗
NASA NTRS1991

Direct sequence spread spectrum CDMA in shared spectrum applications

Personal Communication Network (PCN) is an entirely wireless communication system with the capability of assessing the wired telephone system to reach anyone processing only a wired telephone. It is expected to compete with the existing mobile cellular system which connects directly to the wired telephone system. While many PCN systems employ TDMA technology, the PCN system described here uses Broadband CDMA (BCDMA(sup SM)) which is capable of sharing the spectrum with other users and which is extremely resistant to fading caused by multipath.

Schilling, Donald L.↗
NASA NTRS1992

Lateral spread of sonic boom measurements from US Air Force boomfile flight tests

A series of sonic boom flight tests were conducted by the US Air Force at Edwards AFB in 1987 with current supersonic DOD aircraft. These tests involved 43 flights by various aircraft at different Mach number and altitude combinations. The measured peak overpressures to predicted values as a function of lateral distance are compared. Some of the flights are combined into five groups because of the varying profiles and the limited number of sonic booms obtained during this study. The peak overpressures and the lateral distances are normalized with respect to the Carlson method predicted centerline overpressures and lateral cutoff distances, respectively, to facilitate comparisons between sonic boom data from similar flight profiles. It is demonstrated that the data agrees with sonic boom theory and previous studies and adds to the existing sonic boom database by including sonic boom signatures, tracking, and weather data in a digital format.

Downing, J. Micah↗
NASA NTRS1992

Nonlinear numerical simulation of equatorial spread-F - Effects of winds and electric fields

Recent investigations by means of linear theory revealed the importance of the vertical winds on Rayleigh-Taylor (R-T) instability in the bottomside F-region, along with other driving agencies like the zonal electric field and winds. In the present paper, the nonlinear effects of vertical winds and zonal electric fields on the R-T instability are investigated. The results reveal that the effects of downward wind or/and eastward electric field on the evolutionary process of R-T are significant even beyond 350-km altitude where their effects are considered to be less important according to linear theory.

Raghavarao, R.↗
NASA NTRS1992

Phase-Scrambler Plate Spreads Point Image

Array of small prisms retrofit to imaging lens. Phase-scrambler plate essentially planar array of small prisms partitioning aperture of lens into many subapertures, and prism at each subaperture designed to divert relatively large diffraction spot formed by that subaperture to different, specific point on focal plane.

Edwards, Oliver J.↗
NASA NTRS1993

Tectonics and volcanism of Eastern Aphrodite Terra, Venus - No subduction, no spreading

Eastern Aphrodite Terra, a deformed region with high topographic relief on Venus, has been interpreted as analogous to a terrestrial extensional or convergent plate boundary. However, analysis of geological and structural relations indicates that the tectonics of eastern Aphrodite Terra is dominated by blistering of the crust by magma diapirs. The findings imply that, within this region, vertical tectonism dominates over horizontal tectonism and, consequently, that this region is neither a divergent nor a convergent plate boundary.

Hansen, Vicki L.↗
NASA NTRS1993

A semi-empirical model for heat transfer and flame spreading in slotted rocket motors

This paper presents analytical and experimental results for the cold-flow aerothermodynamics of the head-end star slot region of the Space Shuttle solid rocket motor (SRM). Particular attention is paid to the determination of the heat transfer from the developing igniter flow to the propellant grain (slot wall). Igniter geometries considered include a single port configuration with flow along the axis of the motor (present Shuttle configuration) and a multiport 45-deg canted nozzle configuration which is similar (but not identical) to the proposed ASRM igniter geometry.

Jenkins, R. M.↗