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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Enhanced indirect optical absorption in AlAs and GaP.

Measurement and analysis of indirect interband optical absorption in GaP. Deviations from a simple indirect absorption law are shown to be consistent with those given by a model which takes into account both the variation of the energy denominators with photon energy and indirect absorption to higher-energy conduction-band valleys. The analysis of the GaP data indicates that such an analysis on data of limited absorption-constant range can provide reasonably accurate values of the direct band gap. The value of the direct band gap best fitting this model for AlAs at 6 K is 3.13 eV. In GaP and AlAs there is evidence of a higher set of extrema giving rise to an additional indirect absorption component 0.34 and 0.20 eV, respectively, above that due to the lowest-energy conduction-band minima. The strength of the absorption due to these higher-energy valleys indicates that they contain states of X sub 3 symmetry.

Dumke, W. P.↗
NASA NTRS2013

The Simplified Aircraft-Based Paired Approach With the ALAS Alerting Algorithm

This paper presents the results of an investigation of a proposed concept for closely spaced parallel runways called the Simplified Aircraft-based Paired Approach (SAPA). This procedure depends upon a new alerting algorithm called the Adjacent Landing Alerting System (ALAS). This study used both low fidelity and high fidelity simulations to validate the SAPA procedure and test the performance of the new alerting algorithm. The low fidelity simulation enabled a determination of minimum approach distance for the worst case over millions of scenarios. The high fidelity simulation enabled an accurate determination of timings and minimum approach distance in the presence of realistic trajectories, communication latencies, and total system error for 108 test cases. The SAPA procedure and the ALAS alerting algorithm were applied to the 750-ft parallel spacing (e.g., SFO 28L/28R) approach problem. With the SAPA procedure as defined in this paper, this study concludes that a 750-ft application does not appear to be feasible, but preliminary results for 1000-ft parallel runways look promising.

Perry, Raleigh B.↗
NASA NTRS1970

Thermal expansion of AlAs

Lattice parameter and thermal expansion of AlAs as function of temperature, indicating lattice match at 900 C with GaAs

Ettenberg, M.↗
NASA NTRS1985

Structure variation of the index of refraction of GaAs-AlAs superlattices and multiple quantum wells

A detailed calculation of the index refraction of various GaAs-AlAs superlattices is presented for the first time. The calculation is performed by using a hybrid approach which combines the k-p method with the pseudopotential technique. Appropriate quantization conditions account for the influence of the superstructures on the electronic properties of the systems. The results of the model are in very good agreement with the experimental data. In comparison with the index of refraction of the corresponding AlGaAs alloy, characterized by the same average mole fraction of Al, the results indicate that the superlattice index of refraction values attain maxima at the various quantized transition energies. For certain structures the difference can be as large as 2 percent. These results suggest that the waveguiding and dispersion relation properties of optoelectronic devices can be tailored to design for specific optical application by an appropriate choice of the superlattice structure parameters.

Kahen, K. B.↗
NASA NTRS1988

Atmospheric Lyman-Alpha Emissions (ALAE)

The Atmospheric Lyman-Alpha Emissions (ALAE) experiment which is designed to measure atomic hydrogen and deuterium in the terrestrial atmosphere is described. The development of the instrument is a joint effort of the Service d'Aeronomie du CNRS in France and the Institut d'Aeronomie Spatiale in Belgium. This experiment will be part of the atmospheric science research payload flown on the Atmospheric Laboratory for Applications and Science (ATLAS 1) NASA mission planned for late 1990.

Bertaux, J. L.↗
NASA NTRS1988

Simulation of GaAs cluster formation on GaAs(00-1), AlAs(00-1), Si(001), and As1/Si(001) surfaces

Recently developed semiempirical potential energy functions for the Ga-As-Si and Ga-As-Al systems have been applied here to determine the excess formation energy for GaAs clusters on GaAs(00-1), AlAs(00-1), Si(001), and one atomic layer As-covered Si(001) substrates as a function of cluster size and cluster shape by the Monte Carlo technique. Pyramidal type ledges on the GaAs clusters are found to be the favored ledge for the first three layers while an inverted-pyramidal type ledge is also favored in certain cases for the As1/Si(001) substrate. Cluster formation at ledges is compared with cluster formation on a flat terrace for the Si(001) and the As1/Si(001) substrates.

Choi, D. K.↗
NASA NTRS1975

Application of solar energy; Proceedings of the First Southeastern Conference, Huntsville, Ala., March 24-26, 1975

Topics related to architectural and institutional considerations are discussed along with studies of components and subsystems. Subjects in the area of system design and analysis are also explored. Residential and commercial applications are considered, taking into account hot-water usage in a typical single-family residence, solar heating and cooling of mobile homes, aspects of design and performance in the case of a solar heating system using a reflective pyramid optical condenser, solar heating in a Boston school, a performance analysis of solar service hot water systems, comparative performance analyses of three solar heated and cooled buildings, and the use of solar energy in a soybeam processing operation. Applications related to power generation are also examined, giving attention to solar thermal electric power systems and photovoltaic research. Individual items are announced in this issue.

Wu, S. T.↗