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  • 1
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    Development of a piezopolymer pressure sensor for a portable fetal heart rate monitor (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A piezopolymer pressure sensor has been developed for service in a portable fetal heart rate monitor, which will permit an expectant mother to perform the fetal nonstress test, a standard predelivery test, in her home. Several sensors are mounted in an array on a belt worn by the mother. The sensor design conforms to the distinctive features of the fetal heart tone, namely, the acoustic signature, frequency spectrum, signal amplitude, and localization. The components of a sensor serve to fulfill five functions: signal detection, acceleration cancellation, acoustical isolation, electrical shielding, and electrical isolation of the mother. A theoretical analysis of the sensor response yields a numerical value for the sensor sensitivity, which is compared to experiment in an in vitro sensor calibration. Finally, an in vivo test on patients within the last six weeks of term reveals that nonstress test recordings from the acoustic monitor compare well with those obtained from conventional ultrasound.
    Keywords: Life Sciences (General)
    Type: IEEE transactions on bio-medical engineering (ISSN 0018-9294); Volume 40; 9; 963-9
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  • 2
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    Atmospheric absorption of sound - Update (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Best current expressions for the vibrational relaxation times of oxygen and nitrogen in the atmosphere are used to compute total absorption. The resulting graphs of total absorption as a function of frequency for different humidities should be used in lieu of the graph published earlier by Evans et al (1972).
    Keywords: ACOUSTICS
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 88; 2019-202
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  • 3
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    Ultrasonic level sensors for liquids under high pressure (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An ultrasonic level sensor of novel design continuously measures the level of a liquid subjected to a high pressure (up to about 40 MPa), as is sometimes required for the effective transfer of the liquid. The sensor operates as a composite resonator fabricated from a standard high-pressure plug. A flat-bottom hole is machined into the plug along its center line. An ultrasonic transducer is bonded rigidly to the interior surface of the bottom wall, while the exterior surface is in contact with the liquid. Although the bottom wall is designed to satisfy the pressure code, it is still sufficiently thin to permit ready excitation of the axisymmetric plate modes of vibration. The liquid level is measured by a conventional pulse-echo technique. A prototype sensor was tested successfully in a 2300-l water vessel at pressures up to about 37 MPa. A spectral analysis of the transmitted pulse reveals that the flexural, extensional, thickness-shear, and radial plate modes are excited into vibration, but none of these appears to be significantly affected by the pressurization of the liquid.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 57; 2318-232
    Format: text
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  • 4
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    Self-deactivation of water vapor - Role of the dimer (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A phenomenological multiple-relaxation theory of the deactivation rate constant for the nu-2 (1 - 0) bending mode of water vapor is presented which incorporates the role not only of the excited monomer but also of the bound molecular complex, in particular the dimer. The deactivation takes place by means of three parallel processes: (1) collisional deexcitation of the excited monomer, (2) a two-step reaction involving association and spontaneous redissociation of an H2O collision complex, and (3) spontaneous dissociation of the stably bound H2O dimer. Oxygen, but not nitrogen or argon, serves as an effective chaperon for the formation of the activated complex. This observation explains the impurity dependence of the self-deactivation rate constant of water vapor. Analysis of an ultrasonic absorption peak based on the third process yields values for the standard entropy and enthalpy of dissociation of the stably bound H2O dimer.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 76; 178-183
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  • 5
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    Acoustical measurements of vibrational relaxation in moist N2 at elevated temperatures (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Sound absorption measurements are conducted by the resonant tube technique to study vibrational relaxation in moist N2 at 301, 343, and 387 K. Analysis of the data shows that improved measurement accuracy at the higher temperatures establishes vibrational-vibrational energy transfer as the operative relaxation path for the de-excitation of N2 by H2O beyond the uncertainty of experimental error. The best-fitted temperature dependence of the vibrational-vibrational rate constant is given, noting that the expression is consistent with seven independent sets of both acoustical and nonacoustical data.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Acoustical Society of America; vol. 71
    Format: text
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  • 6
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    Acoustic ground impedance meter (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A compact, portable instrument was developed to measure the acoustic impedance of the ground, or other surfaces, by direct pressure-volume velocity measurement. A Helmholtz resonator, constructed of heavy-walled stainless steel but open at the bottom, is positioned over the surface having the unknown impedance. The sound source, a cam-driven piston of known stroke and thus known volume velocity, is located in the neck of the resonator. The cam speed is a variable up to a maximum 3600 rpm. The sound pressure at the test surface is measured by means of a microphone flush-mounted in the wall of the chamber. An optical monitor of the piston displacement permits measurement of the phase angle between the volume velocity and the sound pressure, from which the real and imaginary parts of the impedance can be evaluated. Measurements using a 5-lobed cam can be made up to 300 Hz. Detailed design criteria and results on a soil sample are presented. Previously announced in STAR as N82-17476
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 73; June 198
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  • 7
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    Airflow resistivity instrument for in situ measurement on the earth's ground surface (1983)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An airflow resistivity instrument features a novel specimen holder, especially designed for in situ measurement on the earth's ground surface. This capability eliminates the disadvantages of prior intrusive instruments, which necessitate the removal of a test specimen from the ground. A prototype instrument can measure airflow resistivities in the range 10-5000 cgs rayl/cm, at specimen depths up to 15.24 cm (6 in.), and at differential pressures up to 2490.8 dyn sq cm (1 in. H2O) across the specimen. Because of the close relationship between flow resistivity and acoustic impedance, this instrument should prove useful in acoustical studies of the earth's ground surface. Results of airflow resistivity measurements on an uncultivated grass field for varying values of moisture content are presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 54; May 1983
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  • 8
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    Digital data-acquisition system for measuring the free decay of acoustical standing waves in a resonant tube (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A low-cost digital system based on an 8-bit Apple II microcomputer has been designed to provide on-line control, data acquisition, and evaluation of sound absorption measurements in gases. The measurements are conducted in a resonant tube, in which an acoustical standing wave is excited, the excitation removed, and the sound absorption evaluated from the free decay envelope. The free decay is initiated from the computer keyboard after the standing wave is established, and the microphone response signal is the source of the analog signal for the A/D converter. The acquisition software is written in ASSEMBLY language and the evaluation software in BASIC. This paper describes the acoustical measurement, hardware, software, and system performance and presents measurements of sound absorption in air as an example.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Review of Scientific Instruments (ISSN 0034-6748); 55; 116-118
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  • 9
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    Infrasonic emissions from local meteorological events: A summary of data taken throughout 1984 (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Records of infrasonic signals, propagating through the Earth's atmosphere in the frequency band 2 to 16 Hz, were gathered on a three microphone array at Langley Research Center throughout the year 1984. Digital processing of these records fulfilled three functions: time delay estimation, based on an adaptive filter; source location, determined from the time delay estimates; and source identification, based on spectral analysis. Meteorological support was provided by significant meteorological advisories, lightning locator plots, and daily reports from the Air Weather Service. The infrasonic data are organized into four characteristic signatures, one of which is believed to contain emissions from local meteorological sources. This class of signature prevailed only on those days when major global meteorological events appeared in or near to eastern United States. Eleven case histories are examined. Practical application of the infrasonic array in a low level wing shear alert system is discussed.
    Keywords: ACOUSTICS
    Type: NASA-TM-87686 , NAS 1.15:87686
    Format: application/pdf
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  • 10
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    Preliminary study of gaseous nitrogen-liquid oxygen mixing and self cleaning (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The penetration of gaseous nitrogen into liquid oxygen at a pressure of 150 psi was determined by monitoring the composition of the evaporating liquid in a nitrogen analyzer. For pressurization times of about 1 hr the penetration depth varies between 0.0024 and 0.018 in. at an evaporation rate of about 1 gal/day. These are small compared to the penetration depth of 22.2 in. measured in the 7-inch high temperature tunnel at a pressure of 1500 psi, pressurization time of 5 min, and evaporation rate of 121 gal/day.
    Keywords: THERMODYNAMICS AND STATISTICAL PHYSICS
    Type: NASA-TM-87658 , NAS 1.15:87658
    Format: application/pdf
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