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  • American Institute of Physics  (158,094)
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  • 1
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    American Institute of Physics
    Publication Date: 2022-05-26
    Description: Author Posting. © American Institute of Physics, 2017. This article is posted here by permission of American Institute of Physics for personal use, not for redistribution. The definitive version was published in Physics Today 70, no. 11 (2017): 78, doi:10.1063/PT.3.3773.
    Description: With only a minimal flapping, the wandering albatross can circumnavigate the globe. During its peregrinations over the Southern Ocean, the seabird exploits wind shear—the gradient of wind speed—to extract energy for its sustained flight. That same maneuver, called dynamic soaring, is used by pilots of radio-controlled gliders. In flights that take advantage of the shear associated with wind blowing over mountain ridges, the gliders reach air speeds of an astonishing 500 mph. Engineers are currently developing autonomous unmanned vehicles that can use the technique to supplement different sources of energy for sustained flight over the oceans. Possible applications include environmental monitoring, surveillance, and search and rescue.
    Description: 2018-11-01
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    American Institute of Physics
    In:  Review of Scientific Instruments, 90 (12). p. 124504.
    Publication Date: 2021-01-08
    Description: Understanding mechanical interactions between hydrate and hosting sediments is critical for evaluating formation stability and associated environmental impacts of hydrate-bearing sediments during gas production. While core-scale studies of hydrate-bearing sediments are readily available and some explanations of observed results rely on pore-scale behavior of hydrate, actual pore-scale observations supporting the larger-scale phenomena are rarely available for hydrate-bearing sediments, especially with methane as guest molecules. The primary reasons for the scarcity include the challenge of developing tools for small-scale testing apparatus and pore-scale visualization capability. We present a testing assembly that combines pore-scale visualization and triaxial test capability of methane hydrate-bearing sediments. This testing assembly allows temperature regulation and independent control of four pressures: influent and effluent pore pressure, confining pressure, and axial pressure. Axial and lateral effective stresses can be applied independently to a 9.5 mm diameter and 19 mm long specimen while the pore pressure and temperature are controlled to maintain the stability of methane hydrate. The testing assembly also includes an X-ray transparent beryllium core holder so that 3D computed tomography scanning can be conducted during the triaxial loading. This testing assembly permits pore-scale exploration of hydrate-sediment interaction in addition to the traditional stress-strain relationship. Exemplary outcomes are presented to demonstrate applications of the testing assembly on geomechanical property estimations of methane-hydrate bearing sediments.
    Type: Article , PeerReviewed
    Format: text
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  • 3
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    American Institute of Physics
    In:  Journal of the Acoustical Society of America, 66 (4). pp. 1093-1101.
    Publication Date: 2020-07-16
    Description: The ratio of compressional wavevelocityV p to shear wavevelocityV s , and Poisson’s ratio in marine sediments and rocks are important in modeling the sea floor for underwater acoustics,geophysics, and foundation engineering. V p and V s versus depth information was linked at common depths in terrigenous sediments (to 1000 m) and in sands (to 20 m) to yield data on V p vs V s , and V p /V s and Poisson’s ratios versus depth. Soft, terrigenous sediments usually grade with depth into mudstones and shales; V p /V s ratios vary from about 13 or more at the sea floor to about 2.6 at 1000 m. Poisson’s ratios vary from above 0.49 at the sea floor to about 0.41 at 1000 m. In sands, V p , V s , and V p /V s have very high gradients in the first few meters; below about 5 m, V p /V s ratios decrease from about 9 to about 6 at 20 m; Poisson’s ratios vary from above 0.49 at the surface to above 0.48 at 20 m. The mean value of V p /V s in 30 laboratory samples of chalk and limestone is 1.90 (standard error: 0.03); mean Poisson’s ratio is 0.31. Literature data on basalts from the sea floor are reviewed. Equations relating V p to V s are given for terrigenous sediments, sands, and basalts.
    Type: Article , PeerReviewed
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  • 4
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    American Institute of Physics
    In:  Journal of the Acoustical Society of America, 63 (2). pp. 366-377.
    Publication Date: 2020-07-16
    Description: In studies in underwater acoustics,geophysics, and geology, the relations between soundvelocity and density allow assignment of approximate values of density to sediment and rock layers of the earth’s crust and mantle, given a seismicmeasurement of velocity. In the past, single curves of velocity versus density represented all sediment and rock types. A large amount of recent data from the Deep Sea Drilling Project (DSDP), and reflection and refraction measurements of soundvelocity, allow construction of separate velocity–density curves for the principal marine sediment and rock types. The paper uses carefully selected data from laboratory and i n s i t umeasurements to present empirical sound velocity–density relations (in the form of regression curves and equations) in terrigenous silt clays, turbidites, and shale, in calcareous materials (sediments, chalk, and limestone), and in siliceous materials (sediments, porcelanite, and chert); a published curve for DSDP basalts is included. Speculative curves are presented for composite sections of basalt and sediments. These velocity–density relations, with seismicmeasurements of velocity, should be useful in assigning approximate densities to sea‐floor sediment and rock layers for studies in marine geophysics, and in forming geoacoustic models of the sea floor for underwater acoustic studies.
    Type: Article , PeerReviewed
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  • 5
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    American Institute of Physics
    In:  Journal of the Acoustical Society of America, 140 (4). pp. 2695-2702.
    Publication Date: 2020-07-16
    Description: The Green's function (GF) for the scalar wave equation is numerically constructed by an advanced geometric ray-tracing method based on the eikonal approximation related to the semiclassical propagator. The underlying theory is first briefly introduced, and then it is applied to acoustics and implemented in a ray-tracing-type numerical simulation. The so constructed numerical method is systematically used to calculate the sound field in a rectangular (cuboid) room, yielding also the acoustic modes of the room. The simulated GF is rigorously compared to its analytic approximation. Good agreement is found, which proves the devised numerical approach potentially useful also for low frequency acoustic modeling, which is in practice not covered by geometrical methods.
    Type: Article , PeerReviewed
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  • 6
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    American Institute of Physics
    In:  The Journal of the Acoustical Society of America, 138 (3). pp. 1253-1267.
    Publication Date: 2020-05-11
    Description: Responses obtained in consonant perception experiments typically show a large variability across stimuli of the same phonetic identity. The present study investigated the influence of different potential sources of this response variability. It was distinguished between source-induced variability, referring to perceptual differences caused by acoustical differences in the speech tokens and/or the masking noise tokens, and receiver-related variability, referring to perceptual differences caused by within- and across-listener uncertainty. Consonant-vowel combinations consisting of 15 consonants followed by the vowel /i/ were spoken by two talkers and presented to eight normal-hearing listeners both in quiet and in white noise at six different signal-to-noise ratios. The obtained responses were analyzed with respect to the different sources of variability using a measure of the perceptual distance between responses. The speech-induced variability across and within talkers and the across-listener variability were substantial and of similar magnitude. The noise-induced variability, obtained with time-shifted realizations of the same random process, was smaller but significantly larger than the amount of within-listener variability, which represented the smallest effect. The results have implications for the design of consonant perception experiments and provide constraints for future models of consonant perception.
    Type: Article , PeerReviewed
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  • 7
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    American Institute of Physics
    In:  The Journal of the Acoustical Society of America, 58 (6). pp. 1318-1319.
    Publication Date: 2020-05-11
    Description: A simple equation is presented for the dependence of sound speed on temperature, salinity, and depth of water. The comparison with Del Grosso’s NRL II shows discrepancies of the order of tenths of m/sec for realistic values of the parameters.
    Type: Article , PeerReviewed
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  • 8
    Publication Date: 2019-12-28
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 9
  • 10
    Publication Date: 2019-12-28
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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