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  • Other Sources  (123)
  • 2015-2019  (18)
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  • 1
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    Laboratory multiple-crystal X-ray topography and reciprocal-space mapping of protein crystals: influence of impurities on crystal perfection (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Double-axis multiple-crystal X-ray topography, rocking-curve measurements and triple-axis reciprocal-space mapping have been combined to characterize protein crystals using a laboratory source. Crystals of lysozyme and lysozyme crystals doped with acetylated lysozyme impurities were examined. It was shown that the incorporation of acetylated lysozyme into crystals of lysozyme induces mosaic domains that are responsible for the broadening and/or splitting of rocking curves and diffraction-space maps along the direction normal to the reciprocal-lattice vector, while the overall elastic lattice strain of the impurity-doped crystals does not appear to be appreciable in high angular resolution reciprocal-space maps. Multiple-crystal monochromatic X-ray topography, which is highly sensitive to lattice distortions, was used to reveal the spatial distribution of mosaic domains in crystals which correlates with the diffraction features in reciprocal space. Discussions of the influence of acetylated lysozyme on crystal perfection are given in terms of our observations.
    Keywords: Life Sciences (General)
    Type: Acta crystallographica. Section D, Biological crystallography (ISSN 0907-4449); Volume 57; Pt 6; 840-6
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  • 2
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    Galileo infrared imaging spectrometry measurements at the Moon (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Imaging spectrometer observations were made of the surface of the Moon during the December 1990 flyby of the Earth-Moon system by the Galileo spacecraft. This article documents this data set and presents analyses of some of the data. The near infrared mapping spectrometer (NIMS) investigation obtained 17 separate mosaics of the Moon in 408 spectral channels between about 0.7 and 5.2 micrometers. The instrument was originally designed to operate in orbit about Jupiter and therefore saturates at many spectral channels for most measurement situations at 1 AU. However, sufficient measurements were made of the Moon to verify the proper operation of the instrument and to demonstrate its capabilities. Analysis of these data show that the NIMS worked as expected and produced measurements consistent with previous ground-based telescopic studies. These are the first imaging spectrometer measurements of this type from space for the Moon, and they illustrate several major points concerning this type of observation and about the NIMS capabilities specifically. Of major importance are the difference between framing and scanning instruments and the effects of the spacecraft and the scan platform on the performance of such and experiment. The science return of subsequent NIMS and other investigation measurements will be significantly enhanced by the experience and results gained.
    Keywords: ASTRONOMY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; E3; p. 5,587-5,600
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  • 3
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    Concept for a lunar array for very low frequency radio astronomy (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We discuss the design considerations relevant to a very low frequency array, to be deployed on the lunar near side during an early expedition. Such an array would operate in the frequency range 1-10 MHz, and would consist nominally of 20 antennas distributed over a region approximately 40 km in extent. Each antenna station would consist of a crossed-dipole antenna, together with a receiver, digitizer, solar cells, and batteries. In addition, the station will contain a UHF transmitter for relaying the digitized signal to a central station where it will be transmitted to Earth for subsequent processing, including cross-correlation with signals from other antennas. Each antenna station (including the central station) would be deployed as a self-contained unit, mounted on a miniature robotic vehicle. No fixed structures are required for the array.
    Keywords: GROUND SUPPORT SYSTEMS AND FACILITIES (SPACE)
    Type: In: Engineering, construction, and operations in space - III: Space '92; Proceedings of the 3rd International Conference, Denver, CO, May 31-June 4, 1992. Vol. 2 (A93-41976 17-12); p. 1935-1940.
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  • 4
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    A miniature high-resolution accelerometer utilizing electron tunneling (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: New methods have been developed to implement high-resolution position sensors based on electron tunneling. These methods allow miniaturization while utilizing the position sensitivity of electron tunneling to give high resolution. A single-element tunneling accelerometer giving a displacement resolution of 0.002 A/sq rt Hz at 10 Hz, corresponding to an acceleration resolution of 5 x 10 exp -8 g/sq rt Hz, is described. A new dual-element tunneling structure which overcomes the narrow bandwidth limitations of a single-element structure is described. A sensor with an operating range of 5 Hz to 10 kHz, which can have applications as an acoustic sensor, is discussed. Noise is analyzed for fundamental thermal vibration of the suspended masses and is compared to electronic noise. It is shown that miniature tunnel accelerometers can achieve resolution such that thermal noise in the suspended masses is the dominant cause of the resolution limit. With a proof mass of order 100 mg, noise analysis predicts limiting resolutions approaching 10 exp -9 g/sq rt Hz in a 300 Hz band and 10 exp -8 g/sq rt Hz at 1 kHz.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ; : International Conf
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  • 5
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    Diffraction and imaging study of imperfections of crystallized lysozyme with coherent X-rays (2004)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Phase-contrast X-ray diffraction imaging and high-angular-resolution diffraction combined with phase-contrast radiographic imaging were employed to characterize defects and perfection of a uniformly grown tetragonal lysozyme crystal in the symmetric Laue case. The full-width at half-maximum (FWHM) of a 4 4 0 rocking curve measured from the original crystal was approximately 16.7 arcsec and imperfections including line defects, inclusions and other microdefects were observed in the diffraction images of the crystal. The observed line defects carry distinct dislocation features running approximately along the 〈1 1 0〉 growth front and have been found to originate mostly in a central growth area and occasionally in outer growth regions. Inclusions of impurities or formations of foreign particles in the central growth region are resolved in the images with high sensitivity to defects. Slow dehydration led to the broadening of a fairly symmetric 4 4 0 rocking curve by a factor of approximately 2.6, which was primarily attributed to the dehydration-induced microscopic effects that are clearly shown in X-ray diffraction images. The details of the observed defects and the significant change in the revealed microstructures with drying provide insight into the nature of imperfections, nucleation and growth, and the properties of protein crystals.
    Keywords: Life Sciences (General)
    Type: Acta crystallographica. Section D, Biological crystallography (ISSN 0907-4449); Volume 60; Pt 4; 621-9
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  • 6
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    Phase sensitive x-ray diffraction imaging of defects in biological macromolecular crystals (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Conventional x-ray diffraction topography is currently used to map defects in the bulk of protein crystals, but the lack of sufficient contrast is frequently a limiting factor. We experimentally demonstrate that this barrier can be circumvented using a method that combines phase sensitive and diffraction imaging principles. Details of defects revealed in tetragonal lysozyme and cubic ferritin crystals are presented and discussed. The approach enabling the detection of the phase changes of diffracted x rays should prove to be useful in the study of defect structures in a broad range of biological macromolecular crystals.
    Keywords: Life Sciences (General)
    Type: Physical review letters (ISSN 0031-9007); Volume 87; 14; 148101
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  • 7
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    Low-frequency scattering from cylindrical structures at oblique incidence (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Classical Rayleigh scattering theory is extended to the case of a homogeneous dielectric cylinder of arbitrary cross section whose transverse dimensions are much smaller than the wavelength. By assuming that the surface fields can be approximated by those of the infinite cylinder, the far zone scattered field is expressed in terms of polarizability tensors, whose properties are discussed. Numerical results are presented for circular, semicircular, triangular, and square cylinders. The results are applicable to the remote sensing of twigs, stalks, and vegetation needles at centimeter and millimeter wavelengths.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 28; 879-885
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  • 8
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    Quality factors for alpha particles emitted in tissue (2002)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A concept of a mean or dose averaged quality factor was defined in ICRP Publication 26 using relationships for quality factor as a function of LET. The concept of radiation weighting factors, wR, was introduced in ICRP Publication 60 in 1990. These are meant to be generalized factors that modify absorbed dose to reflect the risk of stochastic effects as a function of the quality of the radiation incident on the body or emitted by radioactivity within the body. The values of wr are equal to 20 for all alpha particles externally or internally emitted. This note compares the dose averaged quality factor for alpha particles originating in tissue using the old and revised recommendations for quality factor as a function of LET. The dose averaged quality factor never exceeds 20 using the old recommendations and is never less than 20 with the revised recommendations.
    Keywords: Life Sciences (General)
    Type: Health physics (ISSN 0017-9078); Volume 82; 1; 102-4
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  • 9
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    Frequency stability of GPS NAVSTAR block 1 and block 2 on-orbit clocks (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Analysis of the frequency stability of the on-orbit NAVSTAR clocks os performed by the Naval Research Laboratory. The frequency stability is presented for sample times of one day to 30 days. Composite frequency stability profiles are presented for Block 1 and Block 2 NAVSTAR clocks. Several NAVSTAR cesium clocks show frequency stabilities of a few parts in 1 x 10(exp 14) for long sample times. Time-domain noise-process analysis shows the dominant noise type to be white frequency noise for sample times of one to ten days. The non-stationary stochastic behavior of one of the cesium clocks, illustrated by its frequency stability history, shows that the frequency stability is not always time-invariant.
    Keywords: PHYSICS (GENERAL)
    Type: NASA. Goddard Space Flight Center, Proceedings of the 23rd Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; p 307-31
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  • 10
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    Human factors issues in telerobotic systems for Space Station Freedom servicing (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Requirements for Space Station Freedom servicing are described and the state-of-the-art for telerobotic system on-orbit servicing of spacecraft is defined. The projected requirements for the Space Station Flight Telerobotic Servicer (FTS) are identified. Finally, the human factors issues in telerobotic servicing are discussed. The human factors issues are basically three: the definition of the role of the human versus automation in system control; the identification of operator-device interface design requirements; and the requirements for development of an operator-machine interface simulation capability.
    Keywords: MAN/SYSTEM TECHNOLOGY AND LIFE SUPPORT
    Type: NASA, Lyndon B. Johnson Space Center, Third Annual Workshop on Space Operations Automation and Robotics (SOAR 1989); p 485-492
    Format: application/pdf
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