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  • 1
    Publication Date: 2011-08-24
    Description: We demonstrate a compact real-time optical image correlator using diode lasers and a semi-insulating GaAs/AlGaAs multiple-quantum-well (SI-MQW) device as the holographic element. With only 3 mW of power incident upon the SI-MQW device, the correlation is obtained in 1 microsec and can be erased in as fast as 2 microsec, which presents the possibility of a system capable of 3 x 10 exp 5 correlations/s. We also show that images can be stored for a controllable length of time (2-25 microsec), which presents possibilities for the use of the SI-MQW device as a data or image buffer memory.
    Keywords: OPTICS
    Type: Optics Letters (ISSN 0146-9592); 18; 11; p. 906-908.
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  • 2
    Publication Date: 2006-10-26
    Description: Positron annihilation in condensed gases - helium, hydrogen, nitrogen, & oxygen
    Keywords: FACILITIES, RESEARCH, AND SUPPORT
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  • 3
    Publication Date: 2006-10-26
    Description: Positronium lifetime in condensed hydrogen
    Keywords: PHYSICS, GENERAL
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  • 4
    Publication Date: 2011-08-19
    Description: A low-frequency plasma deposition system was used to prepare amorphous hydrogenated carbon (a-C:H) films. The growth energy was varied by changing the power and/or pressure of the plasma. Ellipsometry and optical absorption were used to obtain the optical energy gap, the density of states, and the refractive index. Ion sputtering was used in conjunction with ellipsometry and Auger electron spectroscopy to get absolute sputtering rates. The plasma deposited a-C:H is amorphous with an optical energy gap of approximately 2.0-2.4 eV. These a-C:H films have higher density and/or hardness, higher refractive index, and lower optical energy gaps with increasing energy of the particles in the plasma, while the density of states remains unchanged. These results are in agreement with, and give a fine-tuned positive confirmation to, an existing conjecture on the nature of the a-C:H films (Kaplan et al., 1985).
    Keywords: SOLID-STATE PHYSICS
    Type: Electrochemical Society, Journal (ISSN 0013-4651); 133; 2339-234
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  • 5
    Publication Date: 2011-08-16
    Description: Chromium ions isothermal annealing kinetics in X ray irradiated ruby crystals, using EPR method
    Keywords: PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Type: ; ADEMIE DES SCIENCES
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  • 6
    Publication Date: 2011-08-11
    Description: Three quantum decay of super 1S sub zero state positronium determined via measurement of three quantum coincidence events in Al and oxygen with energy sum of 1.02 Mev
    Keywords: PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Type: PHYSICAL REVIEW LETTERS
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  • 7
    Publication Date: 2011-08-10
    Description: Free-positron annihilation mean life in diatomic and rare gases as a function of first electron ionization potential and outermost electron density
    Keywords: PHYSICS, GENERAL
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  • 8
    Publication Date: 2013-08-29
    Description: Scintillation response of alkali iodides to alpha particles and protons
    Keywords: NAVIGATION
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  • 9
    Publication Date: 2013-08-31
    Description: A case study of a spacecraft having flexible solar arrays is presented. A stationkeeping attitude control mode using both earth and rate gyro reference signals and a flexible vehicle dynamics modeling and implementation is discussed. The control system is designed to achieve both pointing accuracy and structural mode stability during stationkeeping maneuvers. Reduction of structural mode interactions over the entire mode duration is presented. The control mode using a discrete time observer structure is described to show the convergence of the spacecraft attitude transients during Delta-V thrusting maneuvers without preloading thrusting bias to the onboard control processor. The simulation performance using the three axis, body stabilized nonlinear dynamics is provided. The details of a five body dynamics model are discussed. The spacecraft is modeled as a central rigid body having cantilevered flexible antennas, a pair of flexible articulated solar arrays, and to gimballed momentum wheels. The vehicle is free to undergo unrestricted rotations and translations relative to inertial space. A direct implementation of the equations of motion is compared to an indirect implementation that uses a symbolic manipulation software to generate rigid body equations.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center, Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems, Part 1; p 291-330
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  • 10
    Publication Date: 2013-08-31
    Description: Very high-efficiency GaAs Cassegrainian solar cells have been fabricated in both the n-p and p-n configurations. The n-p configuration exhibits the highest efficiency at concentration, the best cells having an efficiency eta of 24.5 percent (100X, AM0, temperature T = 28 C). Although the cells are designed for operation at this concentration, peak efficiency is observed near 300 suns (eta = 25.1 percent). To our knowledge, this is the highest reported solar cell efficiency for space applications. The improvement in efficiency over that reported at the previous SPRAT conference is attributed primarily to lower series resistance and improved grid-line plating procedures. Using previously measured temperature coefficients, researchers estimate that the n-p GaAs cells should deliver approximately 22.5 percent efficiency at the operating conditions of 100 suns and T = 80 C. This performance exceeds the NASA program goal of 22 percent for the Cassegrainian cell. One hundred Cassegrainian cells have been sent to NASA as deliverables, sixty-eight in the n-p configuration and thirty-two in the p-n configuration.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA, Lewis Research Center, Space Photovoltaic Research and Technology, 1988. High Efficiency. Space Environment, and Array Technology; p 292-297
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