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  • 1
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    Supersonic-nitrogen flow-field measurements with the resonant Doppler velocimeter (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The application of the resonant Doppler velocimeter (RDV) for obtaining the mean velocity, temperature, and pressure measurements and flow-field visualization in a supersonic free nitrogen jet is reported. This method utilizes laser-induced fluorescence to determine the spectral absorption of an atomic or molecular species seeded into the flow. A narrow linewidth tunable laser is directed into the flow and the total fluorescence from any point is obtained as the laser is tuned. The velocity of the flow is obtained from the Doppler shifted absorption frequency, and the temperature and pressure of the gas are determined from line broadening measurements. Results are presented for the use of this technique to determine the velocity, temperature, and pressure of the flow of sodium atoms seeded into a supersonic nitrogen jet. It is concluded that the visible signal is sufficiently intense for spatially resolved flow visualization purposes.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Physics Letters (ISSN 0003-6951); 43; July 15
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  • 2
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    Total Dose Effects (TDE) of heavy ionizing radiation in fungus spores and plant seeds: Preliminary investigations (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The opportunity to compare cosmic radiation effects caused during long and short duration exposure flights in biological objects are limited until now, and data obtained so far are very rare and insufficient. Because of the very long exposure of the experiment during the Long Duration Exposure Facility (LDEF) mission (approximately 2000 days) structural changes of the hardware material can be expected which will influence its biocompatibility and, thus, will interact with the radiobiological effects. The aim of the experiment flown on LDEF was a detailed investigation of biological effects caused by cosmic radiation especially of particles of high atomic number Z and high energy. The flight hardware consisted of standard BIOSTACK containers; in these containers a special sandwich construction consisted of visual plastic detectors with seed rsp. spore layers interlocked.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. First Post-Retrieval Symposium, Part 3; p 1651-1660
    Format: text
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  • 3
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    Separation of time-averaged turbulence components by laser-induced fluorescence (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A resonant Doppler velocimeter technique is introduced for time averaged gas flow turbulence fluctuation measurements. A monochrome laser beam is shone through a flow seeded with an atomic or molecular species that has an absorption frequency to which the laser is tuned. The resulting fluorescence is recorded by a detector, and the Doppler shift of the absorption frequency yields the velocity component of the flow in the direction of the beam. Static temperature and pressure data are available from the spectroscopic absoption line broadening. An analytical formulation of the laser-induced fluorescence intensity is defined and related to the velocity, temperature, and pressure. Comparison with data from a Na-seeded laminar supersonic jet demonstrates the accuracy of both the technique and model. Varying the pump laser frequency allows determination of the mean square velocity, temperature, and pressure fluctuations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 26; April 19
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  • 4
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    Low-temperature He-Na collision rate measurements (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The foreign-gas collision broadening of the Na D2 line by He at a temperature of 8 K is measured. These data combined with those of other investigators provide an empirical scaling of the collision rates and cross sections over a wide range of temperatures and relative velocities, respectively.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Journal of Physics B - Atomic and Molecular Physics; 14; Feb. 14
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  • 5
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    Gravitational waves from rotating and precessing rigid bodies - Simple models and applications to pulsars (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: An axially symmetric, torque-free rigid body, rotating and precessing, emits gravitational quadrupole radiation at two frequencies, omega and 2 omega, corresponding to the l = 2, m = 1,2 spherical harmonics. The paper presents explicitly the waveforms of the two polarizations at both frequencies. From observations of gravitational waves, one can derive information about the body's orientation and its precession amplitude. Electromagnetic radiation emitted by a spot fixed on the surface of the body arrives in pulses at a mean frequency Omega which is typically different from omega. If the body is not axially symmetric but the amplitude of the precession is small, the gravitational radiation at the lower frequency omega is split into two frequencies on either side of the electromagnetic pulse frequency. Explicit waveforms for the two polarizations in this case are also presented.
    Keywords: ASTROPHYSICS
    Type: Physical Review D - Particles and Fields; vol. 20
    Format: text
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  • 6
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    Gravitational waves from rotating and precessing rigid bodies. II - General solutions and computationally useful formulas (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A rigid, freely precessing Newtonian body emits gravitational radiation. In this paper the classical-mechanics results for free precession which are needed in order to calculate the weak-field slow-motion quadrupole-moment gravitational waves are reviewed. Within that formalism, algorithms for computing the exact gravitational power radiated and waveforms produced by arbitrary rigid-body freely precessing source are given. Also presented are the dominant terms in series expansions of the waveforms for the case of an almost-spherical object precessing with a small wobble angle. These series expansions, which retain the precise frequency dependence of the waves, may be useful for gravitational astronomers when freely precessing sources begin to be observed.
    Keywords: ASTROPHYSICS
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  • 7
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    Resonant Doppler velocimeter (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A technique is presented for visualizing and quantitatively measuring velocity, temperature, and pressure by shining a single frequency laser beam into a gaseous flow which is seeded with an atomic species. The laser is tuned through the absorption frequencies of the seeded species and the absorption profile is detected by observing fluorescence as the atoms relax back to the ground state. The flow velocity is determined by observing the Doppler shift in the absorption frequency. Spectroscopic absorption line broadening mechanisms furnish information regarding the static temperature and pressure of the moving gas. Results of experiments conducted in the free stream and in the bow shock of a conical model mounted in a hypersonic wind tunnel indicate that the experimental uncertainties in the measurement of average values for the velocity, temperature and pressure of the flow are 0.1, 5 and 10 percent respectively.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-162815 , MAE-T-1465
    Format: application/pdf
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  • 8
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    Hypersonic-helium-flow-field measurements with the resonant Doppler velocimeter (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A low density of sodium atoms seeded into a hypersonic helium flow is used to quantitatively determine flow-field properties. By observing fluorescence from a point as a single-mode dye laser is tuned through the sodium D2 line, the absorption profile may be found. This profile is fitted to a properly weighted sum of Voigt functions to yield the velocity, temperature, and pressure at the observation point. The fluorescence is strong enough to use this technique for qualitative flow-field visualization.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Physics Letters; 37; Nov. 15
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  • 9
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    Quantum nondemolition measurements of harmonic oscillators (1978)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Measuring systems to determine the real component of the complex amplitude of a harmonic oscillator are described. This amplitude is constant in the absence of driving forces, and the uncertainty principle accounts for the fact that only the real component can be measured precisely and continuously ('quantum nondemolition measurement'). Application of the measuring systems to the detection of gravitational waves is considered.
    Keywords: NUCLEAR AND HIGH-ENERGY PHYSICS
    Type: Physical Review Letters; 40; Mar. 13
    Format: text
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  • 10
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    Velocity selective flow visualization in a free supersonic nitrogen jet with the resonant Doppler velocimeter (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The use of the resonant Doppler velocimeter for flow visualization in a free supersonic nitrogen jet is demonstrated experimentally. In the experiment reported here, room-temperature nitrogen at 12.7 psi expands through a Mach 3.4 converging diverging nozzle into a plenum chamber; small amount of sodium is injected through a heated needle centered 0.5-in. upstream of the nozzle throat. The beam of a single frequency dye laser is expanded into a sheet of light with a cylindrical beam expander and directed counter to the jet to spatially resolve any slice across the core of the flow. By tuning the laser to different frequencies, particular velocity and density fields can be highlighted.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Flow visualization III; Sep 06, 1983 - Sep 09, 1983; Ann Arbor, MI
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