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At least 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Ion and electron energy dispersion features detected by ISEE 1

An energy dispersion feature observed by the ISEE 1 medium energy particle instrument is reported. This feature is characterized by enhancements in both electron and ion fluxes which occur in the 20-200 keV energy range and at radial distances from 5 to 13.5 earth radii. There is a strong energy dependence in the onset times of the enhancements. The time period between the first appearance of an enhancement at high energy to its eventual disappearance in the 20 keV channel can be as much as an hour. The duration of the enhancement in a given energy channel decreases with increasing energy. The species and pitch angle of particles in which the feature is most marked depend on local time. It is shown that the feature is a new manifestation of an old phenomenon, the drift dispersion that frequently produces signatures in particle data from geosynchronous satellites.

Greenspan, M. E.↗
NASA NTRS1985

Constraints on short-term mantle rheology from the J2 observation and the dispersion of the 18.6 y tidal Love number

Information derived from data recently acquired from the LAGEOS satellite is used to place some constraints on the rheological parameters of short-term mantle rheology. The validity of Lambeck and Nakiboglu's (1983) rheological model is assessed by formally developing an expression for the transformed shear modulus using a truncated retardation spectrum. This analytical formula is used to show that the parameters of the above mentioned model are not consistent at all with the amount of anelastic dispersion expected in the Chandler wobble and with the attenuation of seismic normal modes. The feasibility of a standard linear solid (SLS) rheology operating over intermediate timescales between 1 and 100 yr is investigated to determine whether the tidal dispersion at 18.6 yr can be explained by this model. An attempt is made to place some constraints on the parameters of the SLS model and the nature of short-term mantle rheology for timescales of less than 100 yr is discussed.

Sabadini, R.↗
NASA NTRS1985

Quantitative study on dispersion relations of TIDs observed by an HF Doppler array

A quantitative study on the dispersion relation of traveling ionospheric disturbances (TIDs) was performed by using data obtained by an HF Doppler array. Observed data at three stations are digitized continuously with a sampling period of 10 sec. A schematic illustration of a running analysis method is given. Fourier components omega's and their wave vectors k's of the TIDs are calculated from these subset data from three stations by means of the cross-spectrum analysis. Diagrams of horizontal trace velocity V sub ph versus wave period T were also obtained. From these diagrams one can see clear cutoff periods of the internal mode of the atmospheric gravity waves. A morphological classification of the mode of the omega - k and V sub ph - T obtained through one year was performed. The estimation of the horizontal velocity vectors of the thermospheric wind form their dispersion relations was performed also. A key point of the method of obtaining the vectors is to estimate the tilt, in azimuthally different omega - k diagrams, of a resonant branch ascribed to the Brunt oscillations.

Tsutsui, M.↗
NASA NTRS1986

Parametric instabilities of the circularly polarized Alfven waves including dispersion

A class of parametric instabilities of large-amplitude, circularly polarized Alfven waves is considered in which finite frequency (dispersive) effects are included. The dispersion equation governing the instabilities is a sixth-order polynomial which is solved numerically. As a function of K identically equal to k/k-sub-0 (where k-sub-0 and k are the wave number of the 'pump' wave and unstable sound wave, respectively), there are three regionals of instability: a modulation instability at K less than 1, a decay instability at K greater than 1, and a relatively weak and narrow instability at K close to squared divided by v-sub-A squared (where c-sub-s and v-sub-A are the sound and Alfven speeds respectively), the modulational instability occurs when beta is less than 1 (more than 1) for left-hand (right-hand) pump waves, in agreement with the previous results of Sakai and Sonnerup (1983). The growth rate of the decay instability of left-hand waves is greater than the modulational instability at all values of beta. Applications to large-amplitude wave observed in the solar wind, in computer simulations, and in the vicinity of planetary and interplanetary collisionless shocks are discussed.

Wong, H. K.↗
NASA NTRS1985

Demonstration of a new method for dispersing warm fogs

Low visibility due to warm fog has caused costly disruptions in the case of aircraft schedules, and fog-related difficulties can arise in connection with Space Shuttle flights. As current methods of fog elimination are not entirely satisfactory, Kelley (1983) has proposed a new brute force procedure for warm fog dispersal. This procedure makes use of recycled water sprays. Fog droplets are removed by coalescence/rainout. Details regarding the involved approaches are described, and a demonstration of the method is discussed. Attention is given to tests conducted in October 1984, visual range improvement in response of water spray fog dispersal, a systematic investigation concerning a selection of firefighting nozzles, and histograms of fog droplet number concentration measured in the spray curtain outflow with a forward scattering spectrometer probe.

Keller, V. W.↗
NASA NTRS1986

Development testing of large volume water sprays for warm fog dispersal

A new brute-force method of warm fog dispersal is described. The method uses large volume recycled water sprays to create curtains of falling drops through which the fog is processed by the ambient wind and spray induced air flow. Fog droplets are removed by coalescence/rainout. The efficiency of the technique depends upon the drop size spectra in the spray, the height to which the spray can be projected, the efficiency with which fog laden air is processed through the curtain of spray, and the rate at which new fog may be formed due to temperature differences between the air and spray water. Results of a field test program, implemented to develop the data base necessary to assess the proposed method, are presented. Analytical calculations based upon the field test results indicate that this proposed method of warm fog dispersal is feasible. Even more convincingly, the technique was successfully demonstrated in the one natural fog event which occurred during the test program. Energy requirements for this technique are an order of magnitude less than those to operate a thermokinetic system. An important side benefit is the considerable emergency fire extinguishing capability it provides along the runway.

Keller, V. W.↗
NASA NTRS1986

Large volume water sprays for dispersing warm fogs

A new method for dispersing of warm fogs which impede visibility and alter schedules is described. The method uses large volume recycled water sprays to create curtains of falling drops through which the fog is processed by the ambient wind and spray-induced air flow; the fog droplets are removed by coalescence/rainout. The efficiency of this fog droplet removal process depends on the size spectra of the spray drops and optimum spray drop size is calculated as between 0.3-1.0 mm in diameter. Water spray tests were conducted in order to determine the drop size spectra and temperature response of sprays produced by commercially available fire-fighting nozzles, and nozzle array tests were utilized to study air flow patterns and the thermal properties of the overall system. The initial test data reveal that the fog-dispersal procedure is effective.

Keller, V. W.↗
NASA NTRS1986

The radial velocity, velocity dispersion, and mass-to-light ratio of the Sculptor dwarf galaxy

The radial velocity, velocity dispersion, and mass-to-light ratio for 16 K giants in the Sculptor dwarf galaxy are calculated. Spectra at the Ca II triplet are analyzed using cross-correlation techniques in order to obtain the mean velocity of + 107.4 + or - 2.0 km/s. The dimensional velocity dispersion estimated as 6.3 (+1.1, -1.3) km/s is combined with the calculated core radius and observed central surface brightness to produce a mass-to-light ratio of 6.0 in solar units. It is noted that the data indicate that the Sculptor contains a large amount of mass not found in globular clusters, and the mass is either in the form of remnant stars or low-mass dwarfs.

Armandroff, T. E.↗
NASA NTRS1988

Weakly relativistic dispersion of Bernstein waves

Weakly relativistic effects on the dispersion of Bernstein waves are investigated for waves propagating nearly perpendicular to a uniform magnetic field in a Maxwellian plasma. Attention is focused on those large-wave-vector branches that are either weakly damped or join continuously onto weakly damped branches since these are the modes of most interest in applications. The transition between dispersion at perpendicular and oblique propagation is examined and major weakly relativistic effects can dominate even in low-temperature plasmas. A number of simple analytic criteria are obtained which delimit the ranges of harmonic number and propagation angle within which various types of weakly damped Bernstein modes can exist.

Robinson, P. A.↗
NASA NTRS1989

Higher order dispersion in the propagation of a gravity wave packet

To the first order of approximation, the complex amplitude of a wave packet in an anisotropic and dispersive medium is convected with the group of velocity. However, a gravity wave is a vector wave. Its wave packet must be formed by superposition of various wave numbers with corresponding frequencies, as is the case for scalar waves, and additionally by superposing many eigenmodes which also depend on the wave number. To represent the vector wave packet self-consistently, it is found that a gradient term must be included in the expansion. For a Guassian wave packet, this gradient term is shown to have important implications on the velocity vector as represented by its hodograph. Numerical results show that the hodograph is influenced by the location of the relative position of interest from the center of a Gaussian pulse. Higher order expansion shows that an initial Gaussian wave packet will retain its Gaussian shape as it propagates, but the pulse will spread in all directions with its major axis undergoing a rotation. Numerical results indicate that these higher order dispersive effects may be marginally observable in the atmosphere.

Yeh, K. C.↗
NASA NTRS1988

Influence of gravity level and interfacial energies on dispersion-forming tendencies in hypermonotectic Cu-Pb-Al alloys

Results on the nondirectional solidification of several hypermonotectic Cu-Pb-Al alloys were obtained aboard NASA's KC-135 zero-gravity aircraft in order to determine the influence of interfacial energies and gravity levels on dispersion-forming tendencies. The Al content was systematially varied in the alloys. The dispersion-forming ability is correlated with gravity level during solidification, the interfacial energy between the immiscible phases, and the tendency for the minority immiscible phase to wet the walls of the crucible.

Andrews, J. B.↗
NASA NTRS1990

Electrostatic Dispersion Of Drops In Clusters

Electrical charging speeds evaporation. Report presents theoretical study of evaporation and dispersion of electrostatically charged clusters of drops in liquid fuel sprays. Represents extension of studies described in article, "More About Evaporation of Drops in Clusters" (NPO-17594). Undertaken in effort to learn how electrostatic atomization used to disperse fuel better in order to reduce formation of soot in diesel engines and other power and combustion systems.

Bellan, Josette↗
NASA NTRS1988

MATE (Materials for Advanced Turbine Engines) Program, Project 3. Volume 2: Design, fabrication and evaluation of an oxide dispersion strengthened sheet alloy combustor liner

The suitability of wrought oxide dispersion strengthened (ODS) superalloy sheet for gas turbine engine combustor applications was evaluated. Two yttria (Y2O3) dispersion strengthened alloys were evaluated; Incoloy MA956 and Haynes Development Alloy (HDA) 8077 (NiCrAl base). Preliminary tests showed both alloys to be potentially viable combustor materials, with neither alloy exhibiting a significant advantage over the other. MA956 was selected as the final alloy based on manufacturing reproducibility for evaluation as a burner liner. A hybrid PW2037 inner burner liner containing MA956 and Hastelloy X components and using a louvered configuration was designed and constructed. The louvered configuration was chosen because of field experience and compatibility with the bill of material PW2037 design. The simulated flight cycle for the ground based engine tests consisted of 4.5 min idle, 1.5 min takeoff and intermediate conditions in a PW2037 engine with average uncorrected combustor exit temperature of 1527 C. Post test evaluation consisting of visual observations and fluorescent penetrant inspections was conducted after 500 cycles of testing. No loss of integrity in the burner liner was shown.

Bose, S.↗
NASA NTRS1989

The internal velocity dispersions of three young star clusters in the Large Magellanic Cloud

The radial velocities of 11 to 37 stars have been measured in each of three rich young star clusters in the LMC: NGC 1866, NGC 2164, and NGC 2214. A thorough analysis of the observational errors and contamination by field stars is presented along with a new method to assign confidence limits to the velocity dispersions. Limits are set to the central densities, total masses, and mass-to-light ratios of the clusters, and the question of whether they have unbound halos is addressed. From the small velocity dispersion and large radial extent of NGC 1866, it is inferred that the cluster is not yet tidally limited by the LMC.

Lupton, Robert H.↗
NASA NTRS1990

Matrix effects for reflectivity spectra of dispersed nanophase (superparamagnetic) hematite with application to Martian spectral data

The effect of the matrix on the reflectivity spectra of nanophase (superparamagnetic) hematite (np-Hm) dispersed within the matrix was investigated in four series of powder samples containing np-Hm dispersed within discrete powder particles (of two size ranges) of silica gel and activated alumina. The spectral data show that matrix effects are large. Samples with the same Fe2O3 content can have np-Hm absorption edges characterized by very different positions and curvature and slope indices, while samples with equivalent absorption edges can have very different Fe2O3 concentrations. Thus, quantitative relationships between the positions of ferric absorption edges and Fe2O3 concentrations are unreliable without knowledge of matrix properties of the system. It is shown that it was possible to match the Fe2O3 concentration, magnetic properties, and spectral data for Martian surface material with a laboratory mixture whose only ferric-bearing phase was hematite.

Morris, Richard V.↗
NASA NTRS1990

Dispersive and viscous scale lengths in the two-stage ion heating at quasi-parallel collisionless shocks

A simulation of quasi-parallel (QP) collisionless shock waves is used to deduce the dispersive and viscous scale lengths of QP shocks. The findings were found to be consistent with the observational results obtained by Scudder et al. (1984) and Kennel et al. (1984). It is shown that the upstream wavelength is the dispersive scale length which governs the magnetic-field structure of the shock. It is also shown that the two-stage ion heating obtained by Mandt and Kan (1988) is an intrinsic characteristic of the ion heating process in QP shocks.

Mandt, M. E.↗
NASA NTRS1990

A computationally efficient model for turbulent droplet dispersion in spray combustion

A novel model for turbulent droplet dispersion is formulated having significantly improved computational efficiency in comparison to the conventional point source stochastic sampling methodology. In the proposed model, a computational parcel representing a group of physical particles is considered to have a normal (Gaussian) probability density function (PDF) in three-dimensional space. The mean of each PDF is determined by Lagrangian tracking of each computational parcel, either deterministically or stochastically. The variance is represented by a turbulence-induced mean squared dispersion which is based on statistical inferences from the linearized direct modeling formulation for particle/eddy interactions. Convolution of the computational parcel PDF's produces a single PDF for the physical particle distribution profile. The validity of the new model is established by comparison with the conventional stochastic sampling method, where in each parcel is represented by a delta function distribution, for non-evaporating particles injected into simple turbulent air flows.

Litchford, Ron J.↗
NASA NTRS1990

Velocity dispersion and the stellar population in the central 1.2 parsecs of the Galaxy

New observations of the 2.3 micron absorption band head of CO in integrated stellar light in the central 1.2 pc of the Galaxy are presented. These data confirm that the velocity dispersion of the stars increases toward the Galactic center and totally dominates their systematic rotation at small radii. The velocity dispersion is constant an average value of 125 km/s within about 30 arcsec projected diameter central region. The strength of the CO features decreases in the integrated faint light within the same region. These observations are all consistent with the hypothesis that both the diffuse 2 micron light and the bright 2 micron point sources in the central region are dominated by sources that have little or no CO absorption feature. The observed CO feature at projected distances less than 0.6 pc thus actually arises in stars that are at true radii greater than 0.6 pc. The mass distribution at radius between 3.7 and 0.6 pc from IRS 16 is strong evidence for an increasing mass/2 micron radiation ratio toward the Galactic center.

Sellgren, K.↗