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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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NASA NTRS2008

Benchmark Comparison of Dual- and Quad-Core Processor Linux Clusters with Two Global Climate Modeling Workloads

This viewgraph presentation details the science and systems environments that NASA High End computing program serves. Included is a discussion of the workload that is involved in the processing for the Global Climate Modeling. The Goddard Earth Observing System Model, Version 5 (GEOS-5) is a system of models integrated using the Earth System Modeling Framework (ESMF). The GEOS-5 system was used for the Benchmark tests, and the results of the tests are shown and discussed. Tests were also run for the Cubed Sphere system, results for these test are also shown.

McGalliard, James↗
NASA NTRS2010

Quad-Chip Double-Balanced Frequency Tripler

Solid-state frequency multipliers are used to produce tunable broadband sources at millimeter and submillimeter wavelengths. The maximum power produced by a single chip is limited by the electrical breakdown of the semiconductor and by the thermal management properties of the chip. The solution is to split the drive power to a frequency tripler using waveguides to divide the power among four chips, then recombine the output power from the four chips back into a single waveguide. To achieve this, a waveguide branchline quadrature hybrid coupler splits a 100-GHz input signal into two paths with a 90 relative phase shift. These two paths are split again by a pair of waveguide Y-junctions. The signals from the four outputs of the Y-junctions are tripled in frequency using balanced Schottky diode frequency triplers before being recombined with another pair of Y-junctions. A final waveguide branchline quadrature hybrid coupler completes the combination. Using four chips instead of one enables using four-times higher power input, and produces a nearly four-fold power output as compared to using a single chip. The phase shifts introduced by the quadrature hybrid couplers provide isolation for the input and output waveguides, effectively eliminating standing waves between it and surrounding components. This is accomplished without introducing the high losses and expense of ferrite isolators. A practical use of this technology is to drive local oscillators as was demonstrated around 300 GHz for a heterodyne spectrometer operating in the 2-3-THz band. Heterodyne spectroscopy in this frequency band is especially valuable for astrophysics due to the presence of a very large number of molecular spectral lines. Besides high-resolution radar and spectrographic screening applications, this technology could also be useful for laboratory spectroscopy.

Lin, Robert H.↗
NASA NTRS2003

Quad-Tree Visual-Calculus Analysis of Satellite Coverage

An improved method of analysis of coverage of areas of the Earth by a constellation of radio-communication or scientific-observation satellites has been developed. This method is intended to supplant an older method in which the global-coverage-analysis problem is solved from a ground-to-satellite perspective. The present method provides for rapid and efficient analysis. This method is derived from a satellite-to-ground perspective and involves a unique combination of two techniques for multiresolution representation of map features on the surface of a sphere.

Lo, Martin W.↗
NASA NTRS1975

Conservation and the industry sector

The following six highly energy intensive industries were studied as targets of energy conservation opportunity: food and kindred products, paper and allied products, chemicals and allied products, petroleum and coal products, stone, glass and clay products, and primary manufacturing. After studying conservation actions within each industry the actions were grouped under three broad categories: increased combustion efficiency, process improvement, and good housekeeping. Some of the results were: (1) approximately 2.18 quads could be saved in 1980 and 2.57 quads in 1985 by installing cogenerative facilities in 50% of the industries, (2) regenerative air-preheaters could result in a 10-15% increase in furnace efficiency representing a 15-25% fuel savings (2.3 to 3.9 quads in 1980 and 2.7 to 4.5 quads in 1985), (3) several major industries have potential for energy savings by recycling-aluminum (0.2 quads), steel (1 quad), glass (0.006 quads), paper and cement (0.08 quads).

Source record↗
NASA NTRS1994

Theoretical investigation of wave-vector-dependent analytical and numerical formulations of the interband impact-ionization transition rate for electrons in bulk silicon and GaAs

The electron interband impact-ionization rate for both silicon and gallium arsenide is calculated using an ensemble Monte Carlo simulation with the expressed purpose of comparing different formulations of the interband ionization transition rate. Specifically, three different treatments of the transition rate are examined: the traditional Keldysh formula, a new k-dependent analytical formulation first derived by W. Quade, E. Scholl, and M. Rudan (1993), and a more exact, numerical method of Y. Wang and K. F. Brennan (1994). Although the completely numerical formulation contains no adjustable parameters and as such provides a very reliable result, it is highly computationally intensive. Alternatively, the Keldysh formular, although inherently simple and computationally efficient, fails to include the k dependence as well as the details of the energy band structure. The k-dependent analytical formulation of Quade and co-workers overcomes the limitations of both of these models but at the expense of some new parameterization. It is found that the k-dependent analytical method of Quade and co-workers produces very similar results to those obtained with the completely numerical model for some quantities. Specifically, both models predict that the effective threshold for impact ionization in GaAs and silicon is quite soft, that the majority of ionization events originate from the second conduction band in both materials, and that the transition rate is k dependent. Therefore, it is concluded that the k-dependent analytical model can qualitatively reproduce results similar to those obtained with the numerical model yet with far greater computational efficiency. Nevertheless, there exist some important drawbacks to the k-dependent analytical model of Quade and co-workers: These are that it does not accurately reproduce the quantum yield data for bulk silicon, it requires determination of a new parameter, related physically to the overlap intergrals of the Bloch state which can only be adjusted by comparison to experiment, and fails to account for any wave-vector dependence of the overlap integrals. As such the transition rate may be overestimated at those points for which 'near vertical,' small change in k, transitions occur.

Kolnik, Jan↗
NASA NTRS1994

Theoretical Investigation of Wave-Vector-Dependent Analytical and Numerical Formulations of the Interband Impact-Ionization Transition Rate for Electron in Bulk Silicon and GaAs

The electron interband impact-ionization rate for both silicon and gallium arsenide is calculated using an ensemble Monte Carlo simulation with the expressed purpose of comparing different formulations of the interband ionization transition rate. Specifically, three different treatments of the transition rate are examined: the traditional Keldysh formula, a new k-dependent analytical formulation first derived by W. Quade, E Scholl, and M. Rudan, and a more exact, numerical method of Y. Wang and K. F. Brennan. Although the completely numerical formulation contains no adjustable parameters and as such provides a very reliable result, it is highly computationally intensive. Alternatively, the Keldysh formula, although inherently simple and computationally efficient, fails to include the k dependence as well as the details of the energy band structure. The k-dependent analytical formulation of Quade and co-workers overcomes the limitations of both of these models but at the expense of some new parameterization. It is found that the k-dependent analytical method of Quade and co-workers produces very similar results to those obtained with (he completely numerical model for some quantities. Specifically, both models predict that the effective threshold for impact ionization in GaAs and silicon is quite soft, that the majority of ionization events originate from the second conduction band in both materials, and that the transition rate is k dependent. Therefore, it is concluded that the k-dependent analytical model can qualitatively reproduce results similar to those obtained with the numerical model yet with far greater computational efficiency. Nevertheless, there exist some important drawbacks to the k-dependent analytical model of Quade and co-workers: These are that it does not accurately reproduce the quantum yield data for bulk silicon, it requires determination of a new parameter, related physically to (he overlap integrals of the Bloch state which can only be adjusted by comparison to experiment, and fails to account for any wave-vector dependence of the overlap integrals. As such [he transition rate may be overestimated at those points for which "near vertical," small change in k, transitions occur.

Kolnik, Jan↗
NASA NTRS1971

Apollo 11 Mission Report, Supplement 5: Performance of Lunar Module Reaction Control Systems

Spacecraft velocity data and crew reports indicated that RCS engine performance was nominal. It is estimated that the RCS engines accumulated a total of 1060 seconds on-time and 12,000 firings during the mission. The quad temperatures ranged from 132 to 232 F during the period when the heaters were active, within predicated ranges. The total propellant consumption from the RCS tanks was about 319 pounds, compared to a predicted value of 253 pounds. An additional 69 pounds of propellant were used from the ascent propulsion system tanks during interconnect feed operations associated with APS lift-off, following periods of rapid propellant usage. The only problems noted were two thrust chamber pressure switch failures on the quad one down-firing engine and on the quad 2 aft-firing engine. Engine performance was nominal on both engines, and the switch failures had no effect on the mission.

Blevins, D. R.↗
NASA NTRS1984

Hoop/column antenna RF verification model. Volume 2: Analysis and correlation

As part of the Large Space System Technology Program, the theoretical and experimental results of the RF characteristic of a hoop/column, quad aperture antenna using an RF verification model are presented. To satisfy the primary purposes of the model, experimental pattern data is provided for the quad aperture configuration at different reflector edge illumination levels, from which the geometry and edge effects can be assessed, and experimental data which can be compared with calculations using various theoretical reflector scattering formulae are provided. It also experimentally determines the effects upon secondary patterns of scale model quartz cables, as used in the hoop/column design, upon secondary patterns in order to assess the importance of developing a scattering theory to predict such effects. In addition, a comprehensive theoretical study and the experimental pattern results of quad aperture antenna feeds, a discussion of the fundamental affect of parasitic side lobes, their amplitude, and location in space.

Croswell, W. F.↗