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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Vortex rings and the solar granulation

Observations indicate that solar granules have the flow topology of updraft vortex loops. We interpret granule behavior in terms of the mutual and self-interactions of such loops. In particular, the expansion phase that granules commonly undergo is explained by the self-expansion of a vortex ring in a stratified fluid. For a range of granular parameters, we find that the expansion velocity of a vortex ring varies from 0.7 to 1.5 times the maximum surface flow velocity, in agreement with granule observations. We also present speculation on the nature of granule fragmentation.

Arendt, Steve↗
NASA NTRS1992

Continual expansion of the active-region corona observed by the Yohkoh Soft X-ray Telescope

We have found from the observations of the Yohkoh Soft X-ray Telescope (SXT) that the corona above active regions expands occasionally, and almost continually in the cases of 'active' active regions. The key to this discovery has been a movie representation of the Yohkoh SXT data, which, for the first time, provides adequate sampling and continuity for this purpose. The movies show ubiquitous expansions above the active regions, with velocities in the range of a few to a few tens km/s. The expansion appears to preserve the overall structure of the active-region corona. This finding of almost continual expansion of the active-region corona may affect some of the basic ideas concerning active regions, as well as those of the mass-loss from the Sun and Sunlike stars.

Uchida, Yutaka↗
NASA NTRS1997

A new look at age and area: the geographic and environmental expansion of genera during the Ordovician Radiation

Although available paleobiological data indicate that the geographic ranges of marine species are maintained throughout their entire observable durations, other evidence suggests, by contrast, that the ranges of higher taxa expand as they age, perhaps in association with increased species richness. Here, I utilize a database of Ordovician genus occurrences collected from the literature for several paleocontinents to demonstrate that a significant aging of the global biota during the Ordovician Radiation was accompanied by a geographic and environmental expansion of genus ranges. The proportion of genera occurring in two or more paleocontinents in the database, and two or more environmental zones within a six-zone onshore-offshore framework, increased significantly in the Caradocian and Ashgillian. Moreover, widespread genera tended to be significantly older than their endemic counterparts, suggesting a direct link between their ages and their environmental and geographic extents. Expansion in association with aging was corroborated further by demonstrating this pattern directly among genera that ranged from the Tremadocian through the Ashgillian. Taken together, these results are significant not only for what they reveal about the kinetics of a major, global-scale diversification, but also for what they suggest about the interpretation of relationships between diversity trends at the alpha (within-community) and beta (between-community) levels.

NASA Discipline Exobiology↗
NASA NTRS1988

A fast and accurate method for evaluating the nonrelativistic free-free Gaunt factor for hydrogenic ions

A fast method for obtaining a two-dimensional Chebyshev expansion of the nonrelativistic hydrogenic free-free Gaunt factor is presented which gives a maximum relative error of 0.7 percent over a wide range of temperatures and frequencies. The expansion derived by Karzas and Latter (1961) is used to derive primary values of the free-free Gaunt factor as a function of the initial and final electron energies. Thermal averages have been numerically computed and are presented in tabular form in intervals of 0.25 dex.

Hummer, D. G.↗
NASA NTRS1977

Pauli correlations in heavy-ion collisions at high energies

We calculate the effects of short-range correlations on the Glauber expansion for nucleus-nucleus collisions using the Fermi gas model for nuclei. When we neglect the Pauli principle for collisions between heavy nuclei, calculation of the optical phase-shift function leads to non-unitary results and we cannot obtain cross sections. When we include Pauli correlations we find important cancellations in the optical phase-shift function, which make possible the calculation of total and differential cross sections for heavy nuclei.

Franco, V.↗
NASA NTRS1985

Optical Mounts for Cryogenic Beam Splitters

Spring-loaded optical mounts maintain flatness and alinement of rigid, framed, or pellicle beam splitters over wide temperature range, despite differences in thermal expansion amoung materials. Mounts permit optical adjustments at ambient temperature even though optical system operated subsequently within few degrees of absolute zero. Mounts useful as holders for integrated-circuit master patterns, survey targets, vibrating membranes, noise- or pressure-sensing membranes, osmosis filters, and fuel-cell elements.

Rudman, A. A.↗
NASA NTRS1985

Swirling flows in typical combustor geometries

The results of experimental attempts and subsequent computational efforts targeted at improving numerical models for swirling recirculating confined turbulent combustion flows are reported. Attention was focused on the mean flow patterns, scales and shapes of the recirculation zones, mapping the flowfield time-mean velocity, normal and Re shear stresses, and producing a predictive computer code based on the TEACH-T program. The work was performed mainly by graduate students. The studies covered swirl strengths, swirler performance, the effects of downstream contraction nozzle size and placement, expansion ratios, and inlet side-wall angles. The STARPIC program was developed in FORTRAN 4 for computing air flow through expansions and over a wide range of inlet swirl vane angles.

Lilley, D. G.↗
NASA NTRS1985

Simulation and modeling of homogeneous, compressed turbulence

Low Reynolds number homogeneous turbulence undergoing low Mach number isotropic and one-dimensional compression was simulated by numerically solving the Navier-Stokes equations. The numerical simulations were performed on a CYBER 205 computer using a 64 x 64 x 64 mesh. A spectral method was used for spatial differencing and the second-order Runge-Kutta method for time advancement. A variety of statistical information was extracted from the computed flow fields. These include three-dimensional energy and dissipation spectra, two-point velocity correlations, one-dimensional energy spectra, turbulent kinetic energy and its dissipation rate, integral length scales, Taylor microscales, and Kolmogorov length scale. Results from the simulated flow fields were used to test one-point closure, two-equation models. A new one-point-closure, three-equation turbulence model which accounts for the effect of compression is proposed. The new model accurately calculates four types of flows (isotropic decay, isotropic compression, one-dimensional compression, and axisymmetric expansion flows) for a wide range of strain rates.

Wu, C. T.↗
NASA NTRS1985

Effect of R(3+) ions on the structure and properties of lanthanum borate glasses

The present investigation of glass formation in the (mole percent) systems 25La2O3 (x)R2O3 (75-x)B2O3, where R = Al, Ga, and (25-x)La2O3 (x)Ln2O3 75B2O3, where Ln = Gd, Er, Y, notes that up to 25 mol pct Al2O3 or Ga2O3 can be substituted for B2O3, while no more than about 5 mol pct Ln2O3, substituted for La2O3, caused macro-phase separation. The substitution of either R2O3 or Ln2O3 in the lanthanum borate system changes the separation distance between adjacent B3O6 chains. The effect of this structural change on the molar volume, transformation temperature, thermal expansion coefficient, and transformation-range viscosity is discussed.

Chakraborty, I. N.↗
NASA NTRS1990

Visual-Inspection Probe For Cryogenic Chamber

Visual-inspection probe that resembles borescope enables observer at ambient temperature to view objects immersed in turbulent flow of liquid oxygen, liquid nitrogen, or other cryogenic fluid. Design of probe fairly conventional, except special consideration given to selection of materials and to thermal expansion to provide for expected range of operating temperatures. Penetrates wall of cryogenic chamber to provide view of interior. Similar probe illuminates scene. View displayed on video monitor.

Friend, Steve↗
NASA NTRS2005

Linear Thermal Expansion Measurements of Lead Magnesium Niobate (PMN) Electroceramic Material for the Terrestrial Planet Finder Coronagraph

Linear thermal expansion measurements of nine samples of Lead Magnesium Niobate (PMN) electroceramic material were recently performed in support of NASA's Terrestrial Planet Finder Coronagraph (TPF-C) mission. The TPF-C mission is a visible light coronagraph designed to look at roughly 50 stars pre- selected as good candidates for possessing earth-like planets. Upon detection of an earth-like planet, TPF-C will analyze the visible-light signature of the planet's atmosphere for specific spectroscopic indicators that life may exist there. With this focus, the project's primary interest in PMN material is for use as a solid-state actuator for deformable mirrors or compensating optics. The nine test samples were machined from three distinct boules of PMN ceramic manufactured by Xinetics Inc. Thermal expansion measurements were performed in 2005 at NASA Jet Propulsion Laboratory (JPL) in their Cryogenic Dilatometer Facility. All measurements were performed in vacuum with sample temperature actively controlled over the range of 270K to 3 10K. Expansion and contraction of the test samples with temperature was measured using a JPL developed interferometric system capable of sub-nanometer accuracy. Presented in this paper is a discussion of the sample configuration, test facilities, test method, data analysis, test results, and future plans.

Terrestrial Planet Finder (TPF)↗
NASA NTRS2013

Nickel-Graphite Composite Compliant Interface and/or Hot Shoe Material

Next-generation high-temperature thermoelectric-power-generating devices will employ segmented architectures and will have to reliably withstand thermally induced mechanical stresses produced during component fabrication, device assembly, and operation. Thermoelectric materials have typically poor mechanical strength, exhibit brittle behavior, and possess a wide range of coefficient of thermal expansion (CTE) values. As a result, the direct bonding at elevated temperatures of these materials to each other to produce segmented leg components is difficult, and often results in localized microcracking at interfaces and mec hanical failure due to the stresses that arise from the CTE mismatch between the various materials. Even in the absence of full mechanical failure, degraded interfaces can lead to increased electrical and thermal resistances, which adversely impact conversion efficiency and power output. The proposed solution is the insertion of a mechanically compliant layer, with high electrical and thermal conductivity, between the low- and high-temperature segments to relieve thermomechanical stresses during device fabrication and operation. This composite material can be used as a stress-relieving layer between the thermoelectric segments and/or between a thermoelectric segment and a hot- or cold-side interconnect material. The material also can be used as a compliant hot shoe. Nickel-coated graphite powders were hot-pressed to form a nickel-graphite composite material. A freestanding thermoelectric segmented leg was fabricated by brazing the compliant pad layer between the high-temperature p- Zintl and low-temperature p-SKD TE segments using Cu-Ag braze foils. The segmented leg stack was heated in vacuum under a compressive load to achieve bonding. The novelty of the innovation is the use of composite material that re duces the thermomechanical stresses en - countered in the construction of high-efficiency, high-temperature therm - o-electric devices. The compliant pad enables the bonding of dissimilar thermoelectric materials while maintaining the desired electrical and thermal properties essential for efficient device operation. The modulus, CTE, electrical, and thermal conductances of the composite can be controlled by varying the ratio of nickel to graphite.

Firdosy, Samad A.↗
NASA NTRS2019

ZERODUR Substrates for Application of High-Temperature Protected-Aluminum Far Ultraviolet Coatings

Recent development in coating deposition processes for aluminum mirrors that are protected with a metal-fluoride overcoat (such as LiF, MgF2, or LiF) have improved reflectance performance particularly in the far-ultraviolet (FUV) part of the optical spectrum. The active research in this area is motivated by the fact that these gains in reflectance are expected to significantly increase the throughput of any future FUV-sensitive NASA missions into the Lyman Ultraviolet. These reflectance improvements are attributed, in part, by performing the metal-fluoride overcoat depositions with the substrates at an elevated temperature as high as 220-250 degrees Celsius. ZERODUR® is a widely used material as a mirror substrate because, among other things, it exhibits a low coefficient of thermal expansion (CTE) over a wide range of temperatures. Moreover, ZERODUR® has recently been proposed for several future NASA concept missions where this improved FUV mirror coating may be used. Given the elevated temperature at which these improved FUV coatings are produced, it is imperative to make sure that heating of the substrate will not significantly impact the final figure of the coated mirror. In this paper, we will study and report the effects of heating ZERODUR® up to the highest temperature mentioned above (250 degrees Celsius) during a simulated coating process. These studies are relevant since it has been reported the CTE will change slightly if ZERODUR® is cooled down from application temperatures between 130 degrees Celsius and 320 degrees Celsius with rates that differ from the initial production annealing rate of 3 degrees Celsius per hour.

Engineering↗
NASA NTRS1994

The 1992/93 eclipse of 31 Cygni

Extensive new ultraviolet and optical spectra of an atmospheric eclipse define the physical properties throughout the wind and chromosphere of 31 Cyg. These data require mass loss of approximately 3 x 10(exp -8) solar masses/yr in a wind that may merge smoothly into the chromosphere. Considerations of how energy is injected into the wind, however, suggest that the chromosphere and wind are separate structures. Most, if not all, of the velocity structure in metallic lines, which we have heretofore simulated with Doppler widths in the range 15-25 km/s, results from differential expansion of the atmosphere. Electron densities in the inner R(sub star) of the chromosphere are in the range 1.5 x 10(exp 9) - 2 x 10(exp 8)/cu cm, which implies clumping of the gas. The ionization of oxygen and nitrogen is consistent with clumping by factors of 3-30 in the outer chromosphere, roughly the amount required to give enough gas pressure to support the chromosphere. Chromospheric gas in 31 Cyg becomes hotter with increasing height, thus with decreasing optical depth, in a way that seems similar for all the zeta Aur binaries. Excitation temperature for Fe II in 1992/93 rises from about 5000 K at the deepest points sampled to about 12,500 K high in the wind. Strengths of violet Balmer lines give an excitation temperature for hydrogen of 6200-6500 K above a radial mass column density of approximately 0.01 g/sq cm. This amount of excitation implies that Lyman-alpha is thermalized beneath about 4 x 10(exp -3) g/sq cm. The outer atmosphere was symmetrical to within a factor of 2 in 1992/93, although it was clearly variable at this level, and it had similar mass column densities as in 1982. One manifestation of the variability was a flow toward the B star at phases 0.013-0.022 spanning velocities 45-100 km/s. Several lines of evidence point to a complicated and variable ionization in the wind: At large distance from the K star, measured mass column densities are less by up to a factor of 3 than required by a smoothly flowing wind. Also, much of the gas beyond r = 350 solar radii = 1.75 R(sub star) has a negative radial velocity. Radial velocities of the shell lines imply the outer atmosphere rotates in the direction of orbital motion, possibly through the deflection of wind flow lines in this direction.

Eaton, Joel A.↗
NASA NTRS2016

Threats to North American Forests from Southern Pine Beetle with Warming Winters

In coming decades, warmer winters are likely to lift range constraints on many cold-limited forest insects. Recent unprecedented expansion of the southern pine beetle (SPB, Dendroctonus frontalis) into New Jersey, New York, Connecticut, and Massachusetts in concert with warming annual temperature minima highlights the risk that this insect pest poses to the pine forests of the northern United States and Canada under continued climate change. Here we present the first projections of northward expansion in SPB-suitable climates using a statistical bioclimatic range modeling approach and current-generation general circulation model (GCM) output under the RCP 4.5 and 8.5 emissions scenarios. Our results show that by the middle of the 21st century, the climate is likely to be suitable for SPB expansion into vast areas of previously unaffected forests throughout the northeastern United States and into southeastern Canada. This scenario would pose a significant economic and ecological risk to the affected regions, including disruption oflocal ecosystem services, dramatic shifts in forest structure, and threats to native biodiversity.

risk↗
NASA NTRS1994

An error covariance model for sea surface topography and velocity derived from TOPEX/POSEIDON altimetry

In order to facilitate the use of satellite-derived sea surface topography and velocity oceanographic models, methodology is presented for deriving the total error covariance and its geographic distribution from TOPEX/POSEIDON measurements. The model is formulated using a parametric model fit to the altimeter range observations. The topography and velocity modeled with spherical harmonic expansions whose coefficients are found through optimal adjustment to the altimeter range residuals using Bayesian statistics. All other parameters, including the orbit, geoid, surface models, and range corrections are provided as unadjusted parameters. The maximum likelihood estimates and errors are derived from the probability density function of the altimeter range residuals conditioned with a priori information. Estimates of model errors for the unadjusted parameters are obtained from the TOPEX/POSEIDON postlaunch verification results and the error covariances for the orbit and the geoid, except for the ocean tides. The error in the ocean tides is modeled, first, as the difference between two global tide models and, second, as the correction to the present tide model, the correction derived from the TOPEX/POSEIDON data. A formal error covariance propagation scheme is used to derive the total error. Our global total error estimate for the TOPEX/POSEIDON topography relative to the geoid for one 10-day period is found tio be 11 cm RMS. When the error in the geoid is removed, thereby providing an estimate of the time dependent error, the uncertainty in the topography is 3.5 cm root mean square (RMS). This level of accuracy is consistent with direct comparisons of TOPEX/POSEIDON altimeter heights with tide gauge measurements at 28 stations. In addition, the error correlation length scales are derived globally in both east-west and north-south directions, which should prove useful for data assimilation. The largest error correlation length scales are found in the tropics. Errors in the velocity field are smallest in midlatitude regions. For both variables the largest errors caused by uncertainty in the geoid. More accurate representations of the geoid await a dedicated geopotential satellite mission. Substantial improvements in the accuracy of ocean tide models are expected in the very near future from research with TOPEX/POSEIDON data.

Tsaoussi, Lucia S.↗
NASA NTRS1978

A critical examination of expansion tunnel performance

An experimental study of the performance of the expansion tunnel for various test gases and range of quiescent acceleration section and nozzle pressure, nozzle geometric area ratio, and nozzle axial station has been performed. Flow diagnostics used to examine expansion tunnel flow characteristics were time histories and profiles of pitot pressure and axial component of flow velocity. The purpose of this study was to determine experimentally what limitations might restrict predicted operational flexibility and the advantages and disadvantages of this mode of operation as compared to the expansion tube. Results are presented which demonstrate the expansion tunnel offers several advantages over the expansion tube, but the severity of the disadvantages of the tunnel makes the expansion tube mode of operation the more desirable for performing hypersonic-hypervelocity aerothermodynamic studies of proposed entry configurations.

Miller, C. G.↗