NASA Scientific and Technical Aerospace Reports

20040112060 National Space Science and Technology Center, Huntsville, AL, USA
Potential Application of Anaerobic Extremophiles for Hydrogen Production
Pikuta, Elena V.; Hoover, Richard B.; 49th Annual Meeting Proceedings: Insruments, Methods, and Missions for Astrobiology
VIII; [2004]; Volume 5555; 1 pp.; In English; International Society for Optical Science and Technology: Insruments,
Methods, and Missions for Astrobiology VIII, 2-6 Aug. 2004, Denver, CO, USA; Original contains black and white
illustrations; No Copyright; Avail: Other Sources; Abstract Only
During substrate fermentation many anaerobes produce the hydrogen as a waste product, which often regulates the growth
of the cultures as an inhibitor. In nature the hydrogen is usually removed from the ecosystem due to its physical properties
or by consumption of hydrogen by secondary anaerobes, which sometimes behave as competitors for electron donors as is seen
in the classical example in anaerobic microbial communities via the interaction between methanogens and sulfate- or sulfurreducers.
It was demonstrated previously on mixed cultures of anaerobes at neutral pH that bacterial hydrogen production
could provide an alternative energy source. But at neutral pH the original cultures can easily be contaminated by methanogens,
a most unpleasant side effect of these conditions is the development of pathogenic bacteria. In both cases the rate of hydrogen
production was dramatically decreased since some part of the hydrogen was transformed to methane, and the cultivation of
human pathogens on a global scale is very dangerous. In our laboratory, experiments with obligately alkaliphilic bacteria that
excrete hydrogen as the end metabolic product were performed at different temperature regimes. Mesophilic and moderately
thermophilic bacterial cultures have been studied and compared for the most effective hydrogen production. For
high-mineralized media with pH 9.5-10.0 not many methanogens are known to exist. Furthermore, the development of
pathogenic contaminant microorganisms is virtually impossible: carbonate-saturated solutions are used as antiseptics in
medicine. Therefore the cultivation of alkaliphilic hydrogen producing bacteria could be considered as most safe process for
global Scale industry in future. Here we present experimental data on the rates of hydrogen productivity for mesophilic,
alkaliphilic, obligately anaerobic bacterium Spirocheta americana ASpG1 and moderately thermophilic, alkaliphilic,
facultative anaerobe Anoxybacillus pushchinoensis K1 and discuss the potential implications for alternative energy sources.
Author
Hydrogen Production; Anaerobes; Fermentation; Sulfates; Electron Transfer; Energy Technology
20040120904 NASA Marshall Space Flight Center, Huntsville, AL, USA
High Efficiency Microwave Power Amplifier (HEMPA) Design
Sims, W. Herbert; [2004]; 7 pp.; In English; International IPSI-2004, 28 Jul. - 2 Aug. 2004, Pescara, Italy; Original contains
black and white illustrations; No Copyright; Avail: CASI; A02, Hardcopy
This paper will focus on developing an exotic switching technique that enhances the DC-to-RF conversion efficiency of
microwave power amplifiers. For years, switching techniques implemented in the 10 kHz to 30 MHz region have resulted in
DC-to-RF conversion efficiencies of 90-95-percent. Currently amplifier conversion efficiency, in the 2-3 GHz region
approaches, 10-20-percent. Using a combination of analytical modeling and hardware testing, a High Efficiency Microwave
Power Amplifier was built that demonstrated conversion efficiencies four to five times higher than current state of the art.
Author
Microwave Amplifiers; Power Amplifiers; Energy Conversion Effıciency; Amplifier Design
20040120909 National Renewable Energy Lab., Golden, CO
Analysis of the GaInP/GaAs/1-eV/Ge Cell and Related Structures for Terrestrial Concentrator Application
Friedman, D. J.; Kurtz, S. R.; Geisz, J. F.; May 2002; 12 pp.; In English
Report No.(s): DE2004-15007049; NREL/CP-520-32188; No Copyright; Avail: Department of Energy Information Bridge
This conference paper describes the analysis of the potential of GaInP/GaAs/1-eV/Ge four-junction solar cell to improve
on the efficiency of the state-of-the-art GaInP/GaAs/Ge benchmark. We emphasize three factors: (1) The newly proposed
terrestrial concentrator spectrum has a lower ratio of red to blue light than does the old AM1.5 direct standard spectrum. (2)
Standard two-layer antireflection coatings do not provide near-zero reflectance over the full spectral range of interest for these
devices. (3) GaInNAs junctions used to date for the 1-eV junction have quantum efficiencies less than(approx)75%. These
factors all limit the device current, adversely affecting the four-junction efficiency. We discuss strategies for ameliorating this
problem, including going to alternate structures such as a GaInP/GaAs/0. 9-eV three-junction device.
NTIS
Solar Cells; Concentrators
145