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  • Other Sources  (304)
  • INSTRUMENTATION AND PHOTOGRAPHY  (304)
  • 1990-1994  (304)
  • 1970-1974
  • 1990  (304)
  • 1
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    Instantaneous velocity field measurement of objects in coaxial rotation using digital image velocimetry (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The instantaneous velocity fields of time-dependent flows, or of a collection of objects moving with spatially varying velocities, can be measured by means of digital image velocimetry (DIV). DIV overcomes several shortcomings of such existing techniques as laser-speckle or particle-image velocimetry. Attention is presently given to numerically generated images representing objects in uniform motion which are then used for the experimental validation of DIV.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ; : Mechanical behavio
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  • 2
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    Design criteria for small coded aperture masks in gamma-ray astronomy (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Most theoretical work on coded aperture masks in X-ray and low-energy gamma-ray astronomy has concentrated on masks with large numbers of elements. For gamma-ray spectrometers in the MeV range, the detector plane usually has only a few discrete elements, so that masks with small numbers of elements are called for. For this case it is feasible to analyze by computer all the possible mask patterns of given dimension to find the ones that best satisfy the desired performance criteria. A particular set of performance criteria for comparing the flux sensitivities, source positioning accuracies and transparencies of different mask patterns is developed. The results of such a computer analysis for masks up to dimension 5 x 5 unit cell are presented and it is concluded that there is a great deal of flexibility in the choice of mask pattern for each dimension.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Nuclear Instruments and Methods in Physics Research, Section A - Accelerators, Spectrometers, Detectors, and Associated Equipment (ISSN 0168-9002); A295; 477-488
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  • 3
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    Isotopically enriched germanium detectors for astrophysical gamma-ray spectroscopy (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A study is presented of the instrumental background in astrophysical gamma-ray spectrometers using isotopically enriched germanium detectors. Calculations show that the beta-decay background, which is the largest component between approximately 0.1 and 1.0 MeV in balloonborne and satellite spectrometers, is dominated by the activation of Ge-74. This component can be reduced by an order of magnitude using detectors enriched to more than 80 percent in (Ge-70). The predicted reduction in the total background for current balloonborne instruments is more than a factor of 1.7 between 0.2 and 1.0 MeV. For future satellite instruments, the reduction in this energy range is by more than a factor of 5.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Nuclear Instruments and Methods in Physics Research, Section A - Accelerators, Spectrometers, Detectors, and Associated Equipment (ISSN 0168-9002); 292; 505-516
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  • 4
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    Method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O2 fluorescence (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations owing to turbulence can be measured in air flows associated with high-speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainties in the temperature and density measurements can be less than 2 percent, if the signal uncertainties are dominated by photon statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 4873-488
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  • 5
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    Advanced CCD imager technology for use from 1 to 10,000 A (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A low-noise, high-sensitivity charge-coupled-device (CCD) technology for imaging applications extending from the soft X-ray (1 A) to the near-infrared (10,000 A) regimes was developed together with a fabrication technology for making back-illuminated versions of these devices with quantum efficiencies as high as 90 percent from 5000 to 7000 A. The efforts have focused on two devices, a 64 x 64 pixel back-illuminated imager with two output ports that operates at 2000 frames per second with 23 electrons read noise, and a larger device, with 420 x 420 pixel format, designed for lower frame rates with noise as low as 1.5 electrons and used at visible, UV, and X-ray wavelengths. Applications to plasma diagnostics include Thomson scattering and high-frame-rate imaging in the visible, as well as X-ray imaging and bolometry.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 2744-274
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  • 6
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    A novel sample-positioning system for microgravity application (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper proposes a novel method for sample positioning in containerless processing at microgravity, using a system based on pulsed lasers. The method has two attributes. First, by generating beams that cancel out vectorially, the suspended material can be heated without being accelerated, a feature that can be used in melting and heat-treatment applications. Second, the specimen can be positioned within a fairly large work space. It is emphasized that this method can service a regime unfulfilled by the other levitation methods, such as electromagnetic levitation, active magnetic suspension, acoustic levitation, of electrostatic suspension.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 2251-225
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  • 7
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    Simultaneous multivelocity component laser Doppler velocimetry using one digital frequency processor (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Digital frequency processing used in conjunction with optical frequency shifting is an ideal way to achieve simultaneous multivelocity component measurements in laser Doppler velocimetry. This becomes obvious once realized that multivelocity component information at different frequency offsets can be obtained directly from the composite frequency spectrum of a single-channel digital frequency processor. The approach has numerous advantages over the very popular approach of using a different laser wavelength, photodetector, and signal processor for each velocity component.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 1989
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  • 8
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    Measurement of Allan variance and phase noise at fractions of a millihertz (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Although the measurement of Allan variance of oscillators is well documented, there is a need for a simplified system for finding the degradation of phase noise and Allan variance step-by-step through a system. This article describes an instrumentation system for simultaneous measurement of additive phase noise and degradation in Allan variance through a transmitter system. Also included are measurements of a 20-kW X-band transmitter showing the effect of adding a pass tube regulator.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 61; 1720-172
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  • 9
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    Electrooptic modulation methods for high sensitivity tunable diode laser spectroscopy (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A CdTe phase modulator and low power RF sources have been used with Pb-salt tunable diode lasers operating near 8 microns to generate optical sidebands for high sensitivity absorption spectroscopy. Sweep averaged, first-derivative sample spectra of CH4 were acquired by wideband phase sensitive detection of the electrooptically (EO) generated carrier-sideband beat signal. EO generated beat signals were also used to frequency lock the TDL to spectral lines. This eliminates low frequency diode jitter, and avoids the excess laser linewidth broadening that accompanies TDL current modulation frequency locking methods.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 2282-228
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  • 10
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    Image recovery from edge primitives (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A method for extracting edge primitives from Mach-band patterns is presented together with a method for recovering image representations of features outlined by the edge boundaries. The accuracy, stability, and resolution of these representations are assessed. Since these representations are most commonly used in characterizing targets, this method of low-level processing offers new opportunities for computer vision and high data-compressing coding. Two bandpass filters are considered, the spatially invariant Laplacian of Gaussian filter and spatially variant intensity-dependent spatial (IDS) summation. It is shown that the recovery from the IDS bandpass data is particularly advantageous in applications for which robustness to local and temporal variations in illumination is important. It is concluded that the edge primitives extracted from bandpassed images can be an efficient way to store, transmit, and represent images.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Optical Society of America, Journal, A: Optics and Image Science (ISSN 0740-3232); 7; 898-911
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