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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
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.↗
NASA NTRS1951

Contributions to the theory of the spreading of a free jet issuing from a nozzle

For the flow field of a free jet leaving a nozzle of circular cross section in a medium with a straight uniform flow field, approximate formulas are presented for the calculation of the velocity distribution and the dimensions of the core region. The agreement with measured results is satisfactory.

FLOW, TURBULENT - JETS↗
NASA NTRS1994

Self-Locking Spreading Pliers

Tool is modified pair of commercial self-locking pliers. Jaws of modified pliers face outward instead of inward. Applies force opposite to that of conventional pliers. Used to force surfaces apart and hold them at fixed separation or to grip a tube from inside.

Bickler, Donald B.↗
NASA NTRS1994

Multipath noise reduction spread spectrum signals

The concepts of early-prompt delay tracking, multipath correction of early-prompt delay tracking from correlation shape, and carrier phase multipath correction are addressed. In early-prompt delay tracking, since multipath is always delayed with respect to the direct signals, the system derives phase and pseudorange observables from earlier correlation lags. In multipath correction of early-prompt delay tracking from correlation shape, the system looks for relative variations of amplitude across the code correlation function that do not match the predicted multipath-free code cross-correlation shape. The system then uses deviations from the multipath-free shape to infer the magnitude of multipath, and to generate corrections pseudorange observables. In carrier phase multipath correction, the system looks for variations of phase among plural early and prompt lags. The system uses the measured phase variations, along with the general principle that the multipath errors are larger for later lags, to infer the presence of multipath, and to generate corrections for carrier-phase observables.

Meehan, Thomas K.↗
NASA NTRS1994

Axis switching and spreading of an asymmetric jet: Role of vorticity dynamics

The effects of vortex generators and periodic excitation on vorticity dynamics and the phenomenon of axis switching in a free asymmetric jet are studied experimentally. Most of the data reported are for a 3:1 rectangular jet at a Reynolds number of 450,000 and a Mach number of 0.31. The vortex generators are in the form of 'delta tabs', triangular shaped protrusions into the flow, placed at the nozzle exit. With suitable placement of the tabs, axis switching could be either stopped or augmented. Two mechanisms are identified governing the phenomenon. One, as described by previous researchers and referred to here as the omega(sub theta)-induced dynamics, is due to difference in induced velocities for different segments of a rolled up azimuthal vortical structure. The other, omega(sub x)-induced dynamics, is due to the induced velocities of streamwise vortex pairs in the flow. Both dynamics can be active in a natural asymmetric jet; the tendency for axis switching caused by the omega(sub theta)-induced dynamics may be, depending on the streamwise vorticity distribution, either resisted or enhanced by the omega(sub x)-induced dynamics. While this simple framework qualitatively explains the various observations made on axis switching, mechanisms actually in play may be much more complex. The two dynamics are not independent as the flow field is replete with both azimuthal and streamwise vortical structures which continually interact. Phase averaged flow field data for a periodically forced case, over a volume of the flow field, are presented and discussed in an effort to gain insight into the dynamics of these vortical structures.

Zaman, K. B. M. Q.↗
NASA NTRS1994

Spread of denitrification from 1987 Antarctic and 1988-1989 Arctic stratospheric vortices

Vertical profiles of N2O and NO(y) taken by the ER-2 outside the vortex are used to construct average vertical profiles of F(NO(y)) = NO(y)/(A-N2O), where A is the tropospheric content of N2O three years prior to the measurements. The southern hemisphere had less nitrous oxide in the range 400 less than Theta less than 470 K, by up to 25% relative to the northern hemisphere. F(NO(y)) is the ratio of NOy produced to N2O lost in a stratospheric air mass since entry from the troposphere. The profiles of F(NO(y)) have the following characteristics: (1) Relative to 1991-1992, a year without denitrification inside or outside the vortex, the northern hemisphere in 1988-1989 showed denitrification outside the vortex ranging up to 25% and averaging 17% above Theta = 425 K. (2) Relative to the northern hemisphere in 1991-1992, the southern hemisphere in 1987 showed denitrification outside the vortex ranging up to 32% and averaging 20% above Theta = 400 K. (3) Below Theta = 400 K the southern hemisphere showed enhancements of F(NO(y)) relative to the northern hemisphere in 1991-1992 ranging up to 200% at Theta = 375 K, outside the vortex. Corresponding profiles of residual water, R(H2O) = H2O - 2(1.6 - CH4), are considered and shown to be consistent with those of F(NO(y)) in the sense that they show deficits outside the Antarctic vortex, which was both dehydrated and denitrified, but not outside the 1988-1989 Arctic vortex, which was denitrified but not dehydrated. R(H2O) is the water content of stratospheric air with the contribution from methane oxidation subtracted. Comparison of F(NO(y)) and R(H2O) below 400 K outside the Antarctic vortex leads to the suggetion that dehydration in the Antarctic vortex occurs by the sedimentation of ice crystals large enough to fall out of the stratosphere, whereas denitrification occurs mainly on mixed nitric acid-water crystals which evaporate below the base of the vortex at Theta = 400 K but above the tropopause.

Tuck, A. F.↗