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Sample records for 3-d shear wave

  1. 3D mapping of elastic modulus using shear wave optical micro-elastography

    NASA Astrophysics Data System (ADS)

    Zhu, Jiang; Qi, Li; Miao, Yusi; Ma, Teng; Dai, Cuixia; Qu, Yueqiao; He, Youmin; Gao, Yiwei; Zhou, Qifa; Chen, Zhongping

    2016-10-01

    Elastography provides a powerful tool for histopathological identification and clinical diagnosis based on information from tissue stiffness. Benefiting from high resolution, three-dimensional (3D), and noninvasive optical coherence tomography (OCT), optical micro-elastography has the ability to determine elastic properties with a resolution of ~10 μm in a 3D specimen. The shear wave velocity measurement can be used to quantify the elastic modulus. However, in current methods, shear waves are measured near the surface with an interference of surface waves. In this study, we developed acoustic radiation force (ARF) orthogonal excitation optical coherence elastography (ARFOE-OCE) to visualize shear waves in 3D. This method uses acoustic force perpendicular to the OCT beam to excite shear waves in internal specimens and uses Doppler variance method to visualize shear wave propagation in 3D. The measured propagation of shear waves agrees well with the simulation results obtained from finite element analysis (FEA). Orthogonal acoustic excitation allows this method to measure the shear modulus in a deeper specimen which extends the elasticity measurement range beyond the OCT imaging depth. The results show that the ARFOE-OCE system has the ability to noninvasively determine the 3D elastic map.

  2. 3D mapping of elastic modulus using shear wave optical micro-elastography

    PubMed Central

    Zhu, Jiang; Qi, Li; Miao, Yusi; Ma, Teng; Dai, Cuixia; Qu, Yueqiao; He, Youmin; Gao, Yiwei; Zhou, Qifa; Chen, Zhongping

    2016-01-01

    Elastography provides a powerful tool for histopathological identification and clinical diagnosis based on information from tissue stiffness. Benefiting from high resolution, three-dimensional (3D), and noninvasive optical coherence tomography (OCT), optical micro-elastography has the ability to determine elastic properties with a resolution of ~10 μm in a 3D specimen. The shear wave velocity measurement can be used to quantify the elastic modulus. However, in current methods, shear waves are measured near the surface with an interference of surface waves. In this study, we developed acoustic radiation force (ARF) orthogonal excitation optical coherence elastography (ARFOE-OCE) to visualize shear waves in 3D. This method uses acoustic force perpendicular to the OCT beam to excite shear waves in internal specimens and uses Doppler variance method to visualize shear wave propagation in 3D. The measured propagation of shear waves agrees well with the simulation results obtained from finite element analysis (FEA). Orthogonal acoustic excitation allows this method to measure the shear modulus in a deeper specimen which extends the elasticity measurement range beyond the OCT imaging depth. The results show that the ARFOE-OCE system has the ability to noninvasively determine the 3D elastic map. PMID:27762276

  3. 3-D FDTD simulation of shear waves for evaluation of complex modulus imaging.

    PubMed

    Orescanin, Marko; Wang, Yue; Insana, Michael

    2011-02-01

    The Navier equation describing shear wave propagation in 3-D viscoelastic media is solved numerically with a finite differences time domain (FDTD) method. Solutions are formed in terms of transverse scatterer velocity waves and then verified via comparison to measured wave fields in heterogeneous hydrogel phantoms. The numerical algorithm is used as a tool to study the effects on complex shear modulus estimation from wave propagation in heterogeneous viscoelastic media. We used an algebraic Helmholtz inversion (AHI) technique to solve for the complex shear modulus from simulated and experimental velocity data acquired in 2-D and 3-D. Although 3-D velocity estimates are required in general, there are object geometries for which 2-D inversions provide accurate estimations of the material properties. Through simulations and experiments, we explored artifacts generated in elastic and dynamic-viscous shear modulus images related to the shear wavelength and average viscosity.

  4. Radially anisotropic 3-D shear wave structure of the Australian lithosphere and asthenosphere from multi-mode surface waves

    NASA Astrophysics Data System (ADS)

    Yoshizawa, K.

    2014-10-01

    A new radially anisotropic shear wave speed model for the Australasian region is constructed from multi-mode phase dispersion of Love and Rayleigh waves. An automated waveform fitting technique based on a global optimization with the Neighbourhood Algorithm allows the exploitation of large numbers of three-component broad-band seismograms to extract path-specific dispersion curves covering the entire continent. A 3-D shear wave model is constructed including radial anisotropy from a set of multi-mode phase speed maps for both Love and Rayleigh waves. These maps are derived from an iterative inversion scheme incorporating the effects of ray-path bending due to lateral heterogeneity, as well as the finite frequency of the surface waves for each mode. The new S wave speed model exhibits major tectonic features of this region that are in good agreement with earlier shear wave models derived primarily from Rayleigh waves. The lateral variations of depth and thickness of the lithosphere-asthenosphere transition (LAT) are estimated from the isotropic (Voigt average) S wave speed model and its vertical gradient, which reveals correlations between the lateral variations of the LAT and radial anisotropy. The thickness of the LAT is very large beneath the Archean cratons in western Australia, whereas that in south Australia is thinner. The radial anisotropy model shows faster SH wave speed than SV beneath eastern Australia and the Coral Sea at the lithospheric depth. The faster SH anomaly in the lithosphere is also seen in the suture zone between the three cratonic blocks of Australia. One of the most conspicuous features of fast SH anisotropy is found in the asthenosphere beneath the central Australia, suggesting anisotropy induced by shear flow in the asthenosphere beneath the fast drifting Australian continent.

  5. 3-D shear wave radially and azimuthally anisotropic velocity model of the North American upper mantle

    NASA Astrophysics Data System (ADS)

    Yuan, Huaiyu; Romanowicz, Barbara; Fischer, Karen M.; Abt, David

    2011-03-01

    Using a combination of long period seismic waveforms and SKS splitting measurements, we have developed a 3-D upper-mantle model (SAWum_NA2) of North America that includes isotropic shear velocity, with a lateral resolution of ˜250 km, as well as radial and azimuthal anisotropy, with a lateral resolution of ˜500 km. Combining these results, we infer several key features of lithosphere and asthenosphere structure. A rapid change from thin (˜70-80 km) lithosphere in the western United States (WUS) to thick lithosphere (˜200 km) in the central, cratonic part of the continent closely follows the Rocky Mountain Front (RMF). Changes with depth of the fast axis direction of azimuthal anisotropy reveal the presence of two layers in the cratonic lithosphere, corresponding to the fast-to-slow discontinuity found in receiver functions. Below the lithosphere, azimuthal anisotropy manifests a maximum, stronger in the WUS than under the craton, and the fast axis of anisotropy aligns with the absolute plate motion, as described in the hotspot reference frame (HS3-NUVEL 1A). In the WUS, this zone is confined between 70 and 150 km, decreasing in strength with depth from the top, from the RMF to the San Andreas Fault system and the Juan de Fuca/Gorda ridges. This result suggests that shear associated with lithosphere-asthenosphere coupling dominates mantle deformation down to this depth in the western part of the continent. The depth extent of the zone of increased azimuthal anisotropy below the cratonic lithosphere is not well resolved in our study, although it is peaked around 270 km, a robust result. Radial anisotropy is such that, predominantly, ξ > 1, where ξ= (Vsh/Vsv)2, under the continent and its borders down to ˜200 km, with stronger ξ in the bordering oceanic regions. Across the continent and below 200 km, alternating zones of weaker and stronger radial anisotropy, with predominantly ξ < 1, correlate with zones of small lateral changes in the fast axis direction of

  6. Application of 3D and 2D quantitative shear wave elastography (SWE) to differentiate between benign and malignant breast masses

    PubMed Central

    Tian, Jie; Liu, Qianqi; Wang, Xi; Xing, Ping; Yang, Zhuowen; Wu, Changjun

    2017-01-01

    As breast cancer tissues are stiffer than normal tissues, shear wave elastography (SWE) can locally quantify tissue stiffness and provide histological information. Moreover, tissue stiffness can be observed on three-dimensional (3D) colour-coded elasticity maps. Our objective was to evaluate the diagnostic performances of quantitative features in differentiating breast masses by two-dimensional (2D) and 3D SWE. Two hundred ten consecutive women with 210 breast masses were examined with B-mode ultrasound (US) and SWE. Quantitative features of 3D and 2D SWE were assessed, including elastic modulus standard deviation (ESDE) measured on SWE mode images and ESDU measured on B-mode images, as well as maximum elasticity (Emax). Adding quantitative features to B-mode US improved the diagnostic performance (p < 0.05) and reduced false-positive biopsies (p < 0.0001). The area under the receiver operating characteristic curve (AUC) of 3D SWE was similar to that of 2D SWE for ESDE (p = 0.026) and ESDU (p = 0.159) but inferior to that of 2D SWE for Emax (p = 0.002). Compared with ESDU, ESDE showed a higher AUC on 2D (p = 0.0038) and 3D SWE (p = 0.0057). Our study indicates that quantitative features of 3D and 2D SWE can significantly improve the diagnostic performance of B-mode US, especially 3D SWE ESDE, which shows considerable clinical value. PMID:28106134

  7. 3-D upper mantle shear wave speed structure beneath the South Pacific Superswell by a BBOBS array

    NASA Astrophysics Data System (ADS)

    Isse, T.; Suetsugu, D.; Shiobara, H.; Sugioka, H.; Yoshizawa, K.; Kanazawa, T.; Fukao, Y.

    2005-12-01

    Previous seismic tomography studies show a broad low velocity anomaly in the lower mantle, so-called superplume, beneath the South Pacific and there are hotspot chains and large scale topographic high at surface of this region. However, the resolution of seismic tomography is poor, especially in the upper mantle, because of limited spatial distribution of seismic stations. To improve the station coverage, we deployed an array of long-term broadband ocean bottom seismometers (BBOBS) in this region. The quality of the vertical component of seismograms recorded by the BBOBS array is comparable with those by island seismic stations. This observation has enabled us to obtain a more precise 3-D shear wave speed structure in the upper mantle of this region by analyzing Rayleigh waves. We employed a two-station method to determine phase velocity of fundamental mode Rayleigh wave recorded by the BBOBS array and island stations in the Pacific Ocean. We obtained 1025 path-average phase velocity dispersion curves including 188 dispersion curves using the BBOBS data in a period range between 40 and 140 seconds. We then inverted them to a 3-D shear wave speed structure down to a depth of 200 km. At shallow depths the eastern part of the French Polynesia region is in general slower than the western part, which indicates an age-dependence of seismic structure of the uppermost mantle. Slow speed anomalies corresponding to the hotspots are apparently superposed on this age-dependence: Slow speed anomalies can be seen from the surface to a depth of 200 km beneath the Society, Pitcairn, and Macdonald hotspots, but they are limited only to the deep part beneath the Samoa hotspot. The slow speed anomalies beneath the Pitcairn and Society hotspots apparently coalesce at a depth of 100 km, where a single anomaly extending upward from below seems to branch into two directions. A resolution analysis indicates that the BBOBS array data has improved the spatial resolution substantially.

  8. SHEAR WAVE SEISMIC STUDY COMPARING 9C3D SV AND SH IMAGES WITH 3C3D C-WAVE IMAGES

    SciTech Connect

    John Beecherl; Bob A. Hardage

    2004-07-01

    The objective of this study was to compare the relative merits of shear-wave (S-wave) seismic data acquired with nine-component (9-C) technology and with three-component (3-C) technology. The original proposal was written as if the investigation would be restricted to a single 9-C seismic survey in southwest Kansas (the Ashland survey), on the basis of the assumption that both 9-C and 3-C S-wave images could be created from that one data set. The Ashland survey was designed as a 9-C seismic program. We found that although the acquisition geometry was adequate for 9-C data analysis, the source-receiver geometry did not allow 3-C data to be extracted on an equitable and competitive basis with 9-C data. To do a fair assessment of the relative value of 9-C and 3-C seismic S-wave data, we expanded the study beyond the Ashland survey and included multicomponent seismic data from surveys done in a variety of basins. These additional data were made available through the Bureau of Economic Geology, our research subcontractor. Bureau scientists have added theoretical analyses to this report that provide valuable insights into several key distinctions between 9-C and 3-C seismic data. These theoretical considerations about distinctions between 3-C and 9-C S-wave data are presented first, followed by a discussion of differences between processing 9-C common-midpoint data and 3-C common-conversion-point data. Examples of 9-C and 3-C data are illustrated and discussed in the last part of the report. The key findings of this study are that each S-wave mode (SH-SH, SV-SV, or PSV) involves a different subsurface illumination pattern and a different reflectivity behavior and that each mode senses a different Earth fabric along its propagation path because of the unique orientation of its particle-displacement vector. As a result of the distinct orientation of each mode's particle-displacement vector, one mode may react to a critical geologic condition in a more optimal way than do

  9. Conducting a 3D Converted Shear Wave Project to Reduce Exploration Risk at Wister, CA

    SciTech Connect

    Matlick, Skip; Walsh, Patrick; Rhodes, Greg; Fercho, Steven

    2015-06-30

    Ormat sited 2 full-size exploration wells based on 3D seismic interpretation of fractures, prior drilling results, and temperature anomaly. The wells indicated commercial temperatures (>300 F), but almost no permeability, despite one of the wells being drilled within 820 ft of an older exploration well with reported indications of permeability. Following completion of the second well in 2012, Ormat undertook a lengthy program to 1) evaluate the lack of observed permeability, 2) estimate the likelihood of finding permeability with additional drilling, and 3) estimate resource size based on an anticipated extent of permeability.

  10. Verification of Long Period Surface Waves from Ambient Noise and Its Application in Constructing 3D Shear Wave Structure of Lithosphere in United States

    NASA Astrophysics Data System (ADS)

    Xie, J.; Yang, Y.; Ni, S.; Zhao, K.

    2015-12-01

    In the past decade, ambient noise tomography (ANT) has become an estimated method to construct the earth's interior structures thanks to its advantage in extracting surface waves from cross-correlations of ambient noise without using earthquake data. However, most of previous ambient noise tomography studies concentrate on short and intermediate periods (<50sec) due to the dominant energy of the microseism at these periods. Studies of long period surface waves from cross-correlation of ambient noise are limited. In this study, we verify the accuracy of the long period (50-250sec) surface wave (Rayleigh wave) from ambient noise by comparing both dispersion curves and seismic waveforms from ambient noise with those from earthquake records quantitatively. After that, we calculate vertical-vertical cross-correlation functions among more than1800 USArray Transportable Array stations and extract high quality interstation phase velocity dispersion curves from them at 10-200 sec periods. Then, we adopt a finite frequency ambient noise tomography method based on Born approximation to obtain high resolution phase velocity maps using the obtained dispersion measurements at 10-150 sec periods. Afterward, we extract local dispersion curves from these dispersion maps and invert them for 1D shear wave velocity profiles at individual grids using a Bayesian Monte Carlo method. Finally, a 3D shear velocity model is constructed by assembling all the 1D Vs profiles. Our 3D model is overall similar to other models constructed using earthquake surface waves and body waves. In summary, we demonstrate that the long period surface waves can be extracted from ambient noise, and the long period dispersion measurements from ambient noise are as accurate as those from earthquake data and can be used to construct 3D lithospheric structure from surface down to lithosphere/asthenosphere depths.

  11. 3D linear dispersion relation for arbitrary shear currents

    NASA Astrophysics Data System (ADS)

    Ellingsen, Simen; Smeltzer, Benjamin

    2016-11-01

    Dispesion properties of waves can be strongly affected by the presence of a sub-surface shear current. A number of approximation techniques exist to calculate dispersion properties of waves on shear currents, most relying on assumptions such as long wavelength, weak vorticity or near-potentiality. Another approach has been to approximate the shear current by a piecewise linear function, corresponding to dividing the fluid phase into a sequence of layers with constant vorticity in each layer. We discuss the practical implementation of this scheme in 3D for arbitrary wavelengths, and how how it may be applied to 3D linear surface waves problems where the full Fourier spectrum in the horizontal plane is required. Solutions to particular implementation challenges such as optimal choice of layer distribution and the nature and removal of spurious solutions are presented, as are several validation cases and tests of convergence. Applications to ring waves and ship waves are provided as examples. Norwegian Research Council (FRINATEK).

  12. Investigating Global 3-D Shear-Wave Anisotropy in the Earth's Mantle from Free Oscillations, Body Waves, Surface Waves and Long-period Waveforms

    NASA Astrophysics Data System (ADS)

    Moulik, P.; Ekstrom, G.

    2012-12-01

    We have developed a framework that can be used to investigate anisotropic velocity, density and anelastic heterogeneity in the Earth's mantle using a wide spectrum (0.3-50 mHz) of seismological observables. We start with the extensive dataset of surface-wave phase anomalies, long-period waveforms, and body-wave travel times collected by Kustowski et al. (2008) for the development of the global model S362ANI. The additional data included in our analysis are splitting functions of spheroidal and toroidal modes, which are analogous to phase velocity maps at low frequencies. We include in this set of observations a new dataset containing the splitting functions of 56 spheroidal fundamental modes and overtones, measured by Deuss et al. (2011, 2012) using data from large recent earthquakes. Apart from providing unique constraints on the long-wavelength elastic and density structure in the mantle, the overtone splitting data are especially sensitive to the velocity (and anisotropic) structure in the transition zone and in the deeper mantle. The detection of anisotropy, a marker of flow, in the transition zone has implications for our understanding of mantle convection. Our forward modeling of the splitting functions, like the other types of data, includes the effects of radial anisotropy (Mochizuki, 1986). We show that the upper-mantle shear-wave anisotropy of S362ANI generates a clear contribution to the splitting functions of the modes that are sensitive to the upper-mantle structure. We explore the tradeoffs between fitting the mode splitting functions and the travel-times of body waves that turn in the transition zone or in the lower mantle (e.g. SS), while observing that the waveforms and the surface wave phase-anomalies provide complementary information about the mantle. Our experiments suggest that the splitting data are sufficiently sensitive to the anisotropy in the mantle such that their inclusion may provide a better depth resolution of the anisotropic shear

  13. New constraints on the 3D shear wave velocity structure of the upper mantle underneath Southern Scandinavia revealed from non-linear tomography

    NASA Astrophysics Data System (ADS)

    Wawerzinek, B.; Ritter, J. R. R.; Roy, C.

    2013-08-01

    We analyse travel times of shear waves, which were recorded at the MAGNUS network, to determine the 3D shear wave velocity (vS) structure underneath Southern Scandinavia. The travel time residuals are corrected for the known crustal structure of Southern Norway and weighted to account for data quality and pick uncertainties. The resulting residual pattern of subvertically incident waves is very uniform and simple. It shows delayed arrivals underneath Southern Norway compared to fast arrivals underneath the Oslo Graben and the Baltic Shield. The 3D upper mantle vS structure underneath the station network is determined by performing non-linear travel time tomography. As expected from the residual pattern the resulting tomographic model shows a simple and continuous vS perturbation pattern: a negative vS anomaly is visible underneath Southern Norway relative to the Baltic Shield in the east with a contrast of up to 4% vS and a sharp W-E dipping transition zone. Reconstruction tests reveal besides vertical smearing a good lateral reconstruction of the dipping vS transition zone and suggest that a deep-seated anomaly at 330-410 km depth is real and not an inversion artefact. The upper part of the reduced vS anomaly underneath Southern Norway (down to 250 km depth) might be due to an increase in lithospheric thickness from the Caledonian Southern Scandes in the west towards the Proterozoic Baltic Shield in Sweden in the east. The deeper-seated negative vS anomaly (330-410 km depth) could be caused by a temperature anomaly possibly combined with effects due to fluids or hydrous minerals. The determined simple 3D vS structure underneath Southern Scandinavia indicates that mantle processes might influence and contribute to a Neogene uplift of Southern Norway.

  14. Crustal and upper mantle 3D shear wave velocity structure of the High Lava Plains, Oregon, determined from ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Hanson-Hedgecock, S.; Wagner, L.; Fouch, M. J.; James, D. E.

    2011-12-01

    We present the results of inversions for 3D shear velocity structure of the crust and uppermost mantle beneath the High Lava Plains, Oregon using data from ~300 broadband stations of the High Lava Plains seismic experiment and the EarthScope/USArray Transportable Array (TA). The High Lava Plains (HLP) is a WNW progressive silicic volcanism, initiated ~14.5 Ma near the Owyhee Plateau and is currently active at the Newberry caldera. The Yellowstone Snake River Plain (YSRP) volcanic track is temporally contemporaneous with the HLP, but trends to the northeast, parallel to North American plate motion. The cause of volcanism along the HLP is debated and has been variously attributed to Basin and Range extension, back-arc extension, rollback of the subducting Juan de Fuca plate, and an intra-continental hotspot/plume source. Additionally the relationship between the HLP, YSRP, and Columbia River Basalts (CRB), the three major post-17Ma intracontinental volcanic provinces of the Pacific Northwest, is not well understood. The 3D shear velocity structure of the crust and uppermost mantle to ~65km depth is determined from fundamental mode Rayleigh wave ambient noise phase velocity maps at periods up to 40s. The use of ambient noise tomography with the dense station spacing of the combined High Lava Plains seismic experiment and the EarthScope/USArray Transportable Array (TA) datasets allows the shallow structure of the High Lava Plains to be imaged in finer detail than previous ANT studies that focused on the entire western United States. In the crust, low velocities in central Oregon are observed in association with the Brothers Fault Zone, Jordan and Diamond Craters and Steens Mountain regions in addition to the strong low velocity zone associated with the Cascades to the west. To the east of the HLP, low velocities are observed to about 10km depth in the western SRP. In the eastern SRP we observe a shallow veneer of low velocities underlain by a ~10km thick high velocity

  15. A new approach to obtaining a 3D shear wave velocity model of the crust and upper mantle: An application to eastern Turkey

    NASA Astrophysics Data System (ADS)

    Delph, Jonathan R.; Zandt, George; Beck, Susan L.

    2015-12-01

    We present a new approach to the joint inversion of surface wave dispersion data and receiver functions by utilizing Common Conversion Point (CCP) stacking to reconcile the different sampling domains of the two datasets. Utilizing CCP stacking allows us to suppress noise in the data by waveform stacking, and correct for backazimuthal variations and complex crustal structure by mapping receiver functions back to their theoretical location. When applied to eastern Turkey, this approach leads to a higher resolution image of the subsurface and clearly delineates different tectonic features in eastern Turkey that were not apparent using other approaches. We observe that the slow seismic velocities near the Karliova Triple Junction correlate to moderate strain rates and high heat flow, which leads to a rheologically weak crust that has allowed for the upward propagation of Miocene and younger volcanics near the triple junction. We find seismically fast, presumably rigid blocks located in the southeastern Anatolian Plate and Arabian Plate are separated by a band of low shear wave velocities that correspond to the East Anatolian Fault Zone, which is consistent with the presence of fluids in the fault zone. We observe that the Arabian Plate has underthrust the Eurasian Plate as far as the northern boundary of the Bitlis Massif, which can explain the high exhumation rates in the Bitlis Massif as a result of slab break-off of the Arabian oceanic lithosphere. We also find a shallow ( 33 km) anomaly beneath eastern Turkey that we interpret as a localized wedge of mantle that was underthrust by a crustal fragment during the collision of Arabia and Eurasia. These observations are possible because of the high-resolution images obtained by combining common conversion point receiver function stacks with ambient noise dispersion data to create a data-driven three-dimensional shear wave velocity model.

  16. Application of the H/V and SPAC Method to Estimate a 3D Shear Wave Velocity Model, in the City of Coatzacoalcos, Veracruz.

    NASA Astrophysics Data System (ADS)

    Morales, L. E. A. P.; Aguirre, J.; Vazquez Rosas, R.; Suarez, G.; Contreras Ruiz-Esparza, M. G.; Farraz, I.

    2014-12-01

    Methods that use seismic noise or microtremors have become very useful tools worldwide due to its low costs, the relative simplicity in collecting data, the fact that these are non-invasive methods hence there is no need to alter or even perforate the study site, and also these methods require a relatively simple analysis procedure. Nevertheless the geological structures estimated by this methods are assumed to be parallel, isotropic and homogeneous layers. Consequently precision of the estimated structure is lower than that from conventional seismic methods. In the light of these facts this study aimed towards searching a new way to interpret the results obtained from seismic noise methods. In this study, seven triangular SPAC (Aki, 1957) arrays were performed in the city of Coatzacoalcos, Veracruz, varying in sizes from 10 to 100 meters. From the autocorrelation between the stations of each array, a Rayleigh wave phase velocity dispersion curve was calculated. Such dispersion curve was used to obtain a S wave parallel layers velocity (VS) structure for the study site. Subsequently the horizontal to vertical ratio of the spectrum of microtremors H/V (Nogoshi and Igarashi, 1971; Nakamura, 1989, 2000) was calculated for each vertex of the SPAC triangular arrays, and from the H/V spectrum the fundamental frequency was estimated for each vertex. By using the H/V spectral ratio curves interpreted as a proxy to the Rayleigh wave ellipticity curve, a series of VS structures were inverted for each vertex of the SPAC array. Lastly each VS structure was employed to calculate a 3D velocity model, in which the exploration depth was approximately 100 meters, and had a velocity range in between 206 (m/s) to 920 (m/s). The 3D model revealed a thinning of the low velocity layers. This proved to be in good agreement with the variation of the fundamental frequencies observed at each vertex. With the previous kind of analysis a preliminary model can be obtained as a first

  17. 3D Zombie Vortices in Rotating Stratified Shear

    NASA Astrophysics Data System (ADS)

    Marcus, Philip; Pei, Suyang; Jiang, Chung-Hsiang; Hassanzadeh, Pedram; Barranco, Joseph; Lecoanet, Daniel

    2013-11-01

    We have shown that there is a finite-amplitude instability in linearly-stable, rotating, vertically-stratified, horizontally-shearing flows. The instability is due to excitations of baroclinic critical layers in which the vertical velocity of a neutrally-stable eigenmode is singular in the inviscid limit. This singularity coupled with the Coriolis and stretching terms in the vertical vorticity equation create intense vortex layers. Those layers roll-up into 3D vortices, which then de-stabilize other critical layers. These vortices, which we call zombie vortices, can fill the dead zone of a protoplanetary disk around a forming star. The vortices, either by themselves or by exciting inertio-gravity waves or acoustic waves, can transport angular momentum in a protoplanetary disk and thereby allow a protostar to form into a star. We find that the zombie vortices are similar in flows with Boussinesq, anelastic, and fully compressible equations of state. However, the rates of angular momentum transport and the mechanisms by which it is transported vary significantly in flows with different equations of state.

  18. 3-D shear wave velocity model of Mexico and South US: bridging seismic networks with ambient noise cross-correlations (C1) and correlation of coda of correlations (C3)

    NASA Astrophysics Data System (ADS)

    Spica, Zack; Perton, Mathieu; Calò, Marco; Legrand, Denis; Córdoba-Montiel, Francisco; Iglesias, Arturo

    2016-09-01

    This work presents an innovative strategy to enhance the resolution of surface wave tomography obtained from ambient noise cross-correlation (C1) by bridging asynchronous seismic networks through the correlation of coda of correlations (C3). Rayleigh wave group dispersion curves show consistent results between synchronous and asynchronous stations. Rayleigh wave group traveltimes are inverted to construct velocity-period maps with unprecedented resolution for a region covering Mexico and the southern United States. The resulting period maps are then used to regionalize dispersion curves in order to obtain local 1-D shear velocity models (VS) of the crust and uppermost mantle in every cell of a grid of 0.4°. The 1-D structures are obtained by iteratively adding layers until reaching a given misfit, and a global tomography model is considered as an input for depths below 150 km. Finally, a high-resolution 3-D VS model is obtained from these inversions. The major structures observed in the 3-D model are in agreement with the tectonic-geodynamic features and with previous regional and local studies. It also offers new insights to understand the present and past tectonic evolution of the region.

  19. Ultrasonic shear wave couplant

    DOEpatents

    Kupperman, David S.; Lanham, Ronald N.

    1985-01-01

    Ultrasonically testing of an article at high temperatures is accomplished by the use of a compact layer of a dry ceramic powder as a couplant in a method which involves providing an ultrasonic transducer as a probe capable of transmitting shear waves, coupling the probe to the article through a thin compact layer of a dry ceramic powder, propagating a shear wave from the probe through the ceramic powder and into the article to develop echo signals, and analyzing the echo signals to determine at least one physical characteristic of the article.

  20. Shear wave transmissivity measurement by color Doppler shear wave imaging

    NASA Astrophysics Data System (ADS)

    Yamakoshi, Yoshiki; Yamazaki, Mayuko; Kasahara, Toshihiro; Sunaguchi, Naoki; Yuminaka, Yasushi

    2016-07-01

    Shear wave elastography is a useful method for evaluating tissue stiffness. We have proposed a novel shear wave imaging method (color Doppler shear wave imaging: CD SWI), which utilizes a signal processing unit in ultrasound color flow imaging in order to detect the shear wave wavefront in real time. Shear wave velocity is adopted to characterize tissue stiffness; however, it is difficult to measure tissue stiffness with high spatial resolution because of the artifact produced by shear wave diffraction. Spatial average processing in the image reconstruction method also degrades the spatial resolution. In this paper, we propose a novel measurement method for the shear wave transmissivity of a tissue boundary. Shear wave wavefront maps are acquired by changing the displacement amplitude of the shear wave and the transmissivity of the shear wave, which gives the difference in shear wave velocity between two mediums separated by the boundary, is measured from the ratio of two threshold voltages required to form the shear wave wavefronts in the two mediums. From this method, a high-resolution shear wave amplitude imaging method that reconstructs a tissue boundary is proposed.

  1. Direct ambient noise tomography for 3-D near surface shear velocity structure: methodology and applications

    NASA Astrophysics Data System (ADS)

    Yao, H.; Fang, H.; Li, C.; Liu, Y.; Zhang, H.; van der Hilst, R. D.; Huang, Y. C.

    2014-12-01

    Ambient noise tomography has provided essential constraints on crustal and uppermost mantle shear velocity structure in global seismology. Recent studies demonstrate that high frequency (e.g., ~ 1 Hz) surface waves between receivers at short distances can be successfully retrieved from ambient noise cross-correlation and then be used for imaging near surface or shallow crustal shear velocity structures. This approach provides important information for strong ground motion prediction in seismically active area and overburden structure characterization in oil and gas fields. Here we propose a new tomographic method to invert all surface wave dispersion data for 3-D variations of shear wavespeed without the intermediate step of phase or group velocity maps.The method uses frequency-dependent propagation paths and a wavelet-based sparsity-constrained tomographic inversion. A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. This avoids the assumption of great-circle propagation that is used in most surface wave tomographic studies, but which is not appropriate in complex media. The wavelet coefficients of the velocity model are estimated with an iteratively reweighted least squares (IRLS) algorithm, and upon iterations the surface wave ray paths and the data sensitivity matrix are updated from the newly obtained velocity model. We apply this new method to determine the 3-D near surface wavespeed variations in the Taipei basin of Taiwan, Hefei urban area and a shale and gas production field in China using the high-frequency interstation Rayleigh wave dispersion data extracted from ambient noisecross-correlation. The results reveal strong effects of off-great-circle propagation of high-frequency surface waves in these regions with above 30% shear wavespeed variations. The proposed approach is more efficient and robust than the traditional two-step surface wave tomography for imaging complex

  2. Simulation of 3D Chaotic Electroconvection in Shear Flow

    NASA Astrophysics Data System (ADS)

    Davidson, Scott; Mani, Ali

    2016-11-01

    Electroconvection, a microscale electrohydrodynamic phenomenon with chaotic features reminiscent of turbulence, provides the dominant transport mechanism in many electrochemical processes where ions are driven through ion-selective surfaces under large applied voltages. Electrodialysis, for example, desalinates water by flowing it between layers of ion-selective membranes with alternating selectivity while an electric field is applied normal to the membranes. This process leads to alternating channels becoming enriched and depleted of ions. Despite its key importance, much about how electroconvection enhances ion transport, particularly in the presence of crossflow, remains a mystery. We present results of 3D direct numerical simulations of electroconvection in a canonical geometry of an electrolyte between an ion-selective membrane and a reservoir with periodic sides subject to applied shear flow. We analyze the effects of crossflow on both flow statistics and qualitative structures in the fully chaotic regime. Stanford Graduate Fellowship, NSF GRFP.

  3. 3D dynamic simulation of crack propagation in extracorporeal shock wave lithotripsy

    NASA Astrophysics Data System (ADS)

    Wijerathne, M. L. L.; Hori, Muneo; Sakaguchi, Hide; Oguni, Kenji

    2010-06-01

    Some experimental observations of Shock Wave Lithotripsy(SWL), which include 3D dynamic crack propagation, are simulated with the aim of reproducing fragmentation of kidney stones with SWL. Extracorporeal shock wave lithotripsy (ESWL) is the fragmentation of kidney stones by focusing an ultrasonic pressure pulse onto the stones. 3D models with fine discretization are used to accurately capture the high amplitude shear shock waves. For solving the resulting large scale dynamic crack propagation problem, PDS-FEM is used; it provides numerically efficient failure treatments. With a distributed memory parallel code of PDS-FEM, experimentally observed 3D photoelastic images of transient stress waves and crack patterns in cylindrical samples are successfully reproduced. The numerical crack patterns are in good agreement with the experimental ones, quantitatively. The results shows that the high amplitude shear waves induced in solid, by the lithotriptor generated shock wave, play a dominant role in stone fragmentation.

  4. 3D-PTV measurement of the phototactic movement of algae in shear flow

    NASA Astrophysics Data System (ADS)

    Maeda, Tatsuyuki; Ishikawa, Takuji; Ueno, Hironori; Numayama-Tsuruta, Keiko; Imai, Yosuke; Yamaguchi, Takami

    2012-11-01

    Recently, swimming motion of algae cells is researched actively, because algae fuel is one of the hottest topic in engineering. It is known that algae swim toward the light for photosynthesis however, the effect of a background flow on the unidirectional swimming is unclear. In this study, we used Volvox as a model alga and placed them in a simple shear flow with or without light stimulus. The shear flow was generated by moving two flat sheets in the opposite direction tangentially. A red LED light (wave length 660 nm) was used as an observation light source, and a white LED light was used to stimulate cells for the phototaxis. The trajectories of individual cells were measured by a 3D-PTV system, consists of a pair of high-speed camera with macro lenses. The results were analyzed to understand the effect of the background shear flow on the phototaxis of cells.

  5. Investigation of surface wave amplitudes in 3-D velocity and 3-D Q models

    NASA Astrophysics Data System (ADS)

    Ruan, Y.; Zhou, Y.

    2010-12-01

    It has been long recognized that seismic amplitudes depend on both wave speed structures and anelasticity (Q) structures. However, the effects of lateral heterogeneities in wave speed and Q structures on seismic amplitudes has not been well understood. We investigate the effects of 3-D wave speed and 3-D anelasticity (Q) structures on surface-wave amplitudes based upon wave propagation simulations of twelve globally-distributed earthquakes and 801 stations in Earth models with and without lateral heterogeneities in wave speed and anelasticity using a Spectral Element Method (SEM). Our tomographic-like 3-D Q models are converted from a velocity model S20RTS using a set of reasonable mineralogical parameters, assuming lateral perturbations in both velocity and Q are due to temperature perturbations. Surface-wave amplitude variations of SEM seismograms are measured in the period range of 50--200 s using boxcar taper, cosine taper and Slepian multi-tapers. We calculate ray-theoretical predictions of surface-wave amplitude perturbations due to elastic focusing, attenuation, and anelastic focusing which respectively depend upon the second spatial derivative (''roughness'') of perturbations in phase velocity, 1/Q, and the roughness of perturbations in 1/Q. Both numerical experiments and theoretical calculations show that (1) for short-period (~ 50 s) surface waves, the effects of amplitude attenuation due to 3-D Q structures are comparable with elastic focusing effects due to 3-D wave speed structures; and (2) for long-period (> 100 s) surface waves, the effects of attenuation become much weaker than elastic focusing; and (3) elastic focusing effects are correlated with anelastic focusing at all periods due to the correlation between velocity and Q models; and (4) amplitude perturbations are depend on measurement techniques and therefore cannot be directly compared with ray-theoretical predictions because ray theory does not account for the effects of measurement

  6. Stratified shear flow in an inclined duct: near-instantaneous 3D velocity and density measurements

    NASA Astrophysics Data System (ADS)

    Partridge, Jamie; Lefauve, Adrien; Dalziel, Stuart; Linden, Paul

    2016-11-01

    We present results from a new experimental setup to study the exchange flow in an inclined square duct between two reservoirs containing fluids of different densities. This system can exhibit stratified shear wave motions, and has a distinct parameter threshold above which turbulence is triggered and progressively fills a larger fraction of the duct. To probe these intrinsically 3D flows, we introduce a new setup in which a traversing laser sheet allows us to obtain near-instantaneous 3D velocity and density fields. Three components of velocity are measured on successive 2D planes using stereo particle image velocimetry (PIV) with density information obtained simultaneously using laser induced fluorescence (LIF). Supported by EPSRC Programme Grant EP/K034529/1 entitled "Mathematical Underpinnings of Stratified Turbulence".

  7. 3D Ultrasonic Wave Simulations for Structural Health Monitoring

    NASA Technical Reports Server (NTRS)

    Campbell, Leckey Cara A/; Miler, Corey A.; Hinders, Mark K.

    2011-01-01

    Structural health monitoring (SHM) for the detection of damage in aerospace materials is an important area of research at NASA. Ultrasonic guided Lamb waves are a promising SHM damage detection technique since the waves can propagate long distances. For complicated flaw geometries experimental signals can be difficult to interpret. High performance computing can now handle full 3-dimensional (3D) simulations of elastic wave propagation in materials. We have developed and implemented parallel 3D elastodynamic finite integration technique (3D EFIT) code to investigate ultrasound scattering from flaws in materials. EFIT results have been compared to experimental data and the simulations provide unique insight into details of the wave behavior. This type of insight is useful for developing optimized experimental SHM techniques. 3D EFIT can also be expanded to model wave propagation and scattering in anisotropic composite materials.

  8. On the shear viscosity of 3D Yukawa liquids

    SciTech Connect

    Donko, Z.; Hartmann, P.

    2008-09-07

    We report calculations of the shear viscosity of three-dimensional strongly-coupled Yukawa liquids, based on two different non-equilibrium molecular dynamics methods. The present simulations intend to improve the accuracy of shear viscosity data, compared to those obtained in earlier studies.

  9. Elastic wave modelling in 3D heterogeneous media: 3D grid method

    NASA Astrophysics Data System (ADS)

    Jianfeng, Zhang; Tielin, Liu

    2002-09-01

    We present a new numerical technique for elastic wave modelling in 3D heterogeneous media with surface topography, which is called the 3D grid method in this paper. This work is an extension of the 2D grid method that models P-SV wave propagation in 2D heterogeneous media. Similar to the finite-element method in the discretization of a numerical mesh, the proposed scheme is flexible in incorporating surface topography and curved interfaces; moreover it satisfies the free-surface boundary conditions of 3D topography naturally. The algorithm, developed from a parsimonious staggered-grid scheme, solves the problem using integral equilibrium around each node, instead of satisfying elastodynamic differential equations at each node as in the conventional finite-difference method. The computational cost and memory requirements for the proposed scheme are approximately the same as those used by the same order finite-difference method. In this paper, a mixed tetrahedral and parallelepiped grid method is presented; and the numerical dispersion and stability criteria on the tetrahedral grid method and parallelepiped grid method are discussed in detail. The proposed scheme is successfully tested against an analytical solution for the 3D Lamb problem and a solution of the boundary method for the diffraction of a hemispherical crater. Moreover, examples of surface-wave propagation in an elastic half-space with a semi-cylindrical trench on the surface and 3D plane-layered model are presented.

  10. Excited waves in shear layers

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.

    1982-01-01

    The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.

  11. The cross-correlation between 3D cosmic shear and the integrated Sachs-Wolfe effect

    NASA Astrophysics Data System (ADS)

    Zieser, Britta; Merkel, Philipp M.

    2016-06-01

    We present the first calculation of the cross-correlation between 3D cosmic shear and the integrated Sachs-Wolfe (iSW) effect. Both signals are combined in a single formalism, which permits the computation of the full covariance matrix. In order to avoid the uncertainties presented by the non-linear evolution of the matter power spectrum and intrinsic alignments of galaxies, our analysis is restricted to large scales, i.e. multipoles below ℓ = 1000. We demonstrate in a Fisher analysis that this reduction compared to other studies of 3D weak lensing extending to smaller scales is compensated by the information that is gained if the additional iSW signal and in particular its cross-correlation with lensing data are considered. Given the observational standards of upcoming weak-lensing surveys like Euclid, marginal errors on cosmological parameters decrease by 10 per cent compared to a cosmic shear experiment if both types of information are combined without a cosmic wave background (CMB) prior. Once the constraining power of CMB data is added, the improvement becomes marginal.

  12. Turbulent Shear and Internal Waves

    NASA Astrophysics Data System (ADS)

    Munroe, James; Sutherland, Bruce

    2008-11-01

    A series of experiments is presented that model the generation of non-hydrostatic internal gravity waves in upper ocean by the forcing of wind driven turbulent eddies in the surface mixed layer. A turbulent shear layer is forced by a conveyor belt with affixed flat plates near the surface of a stratified fluid and downward propagating internal waves are generated. The turbulence in the shear layer is characterized using particle image velocimetry to measure the kinetic energy as well as length and time scales. The internal waves are measured using synthetic schlieren to determine the amplitudes, frequencies, momentum fluxes, and the energy of the generated waves. The fraction of energy that leaks from the mixed layer to the internal wave field is presented. Consistent with other studies, it is found that the frequencies of internal waves generated by turbulence are an approximate constant fraction of the buoyancy frequency. Implications to internal waves propagating into the deep ocean will be discussed.

  13. 3D Guided Wave Motion Analysis on Laminated Composites

    NASA Technical Reports Server (NTRS)

    Tian, Zhenhua; Leckey, Cara; Yu, Lingyu

    2013-01-01

    Ultrasonic guided waves have proved useful for structural health monitoring (SHM) and nondestructive evaluation (NDE) due to their ability to propagate long distances with less energy loss compared to bulk waves and due to their sensitivity to small defects in the structure. Analysis of actively transmitted ultrasonic signals has long been used to detect and assess damage. However, there remain many challenging tasks for guided wave based SHM due to the complexity involved with propagating guided waves, especially in the case of composite materials. The multimodal nature of the ultrasonic guided waves complicates the related damage analysis. This paper presents results from parallel 3D elastodynamic finite integration technique (EFIT) simulations used to acquire 3D wave motion in the subject laminated carbon fiber reinforced polymer composites. The acquired 3D wave motion is then analyzed by frequency-wavenumber analysis to study the wave propagation and interaction in the composite laminate. The frequency-wavenumber analysis enables the study of individual modes and visualization of mode conversion. Delamination damage has been incorporated into the EFIT model to generate "damaged" data. The potential for damage detection in laminated composites is discussed in the end.

  14. Gravity waves on shear flows

    NASA Astrophysics Data System (ADS)

    Miles, John

    2001-09-01

    The eigenvalue problem for gravity waves on a shear flow of depth h and non-inflected velocity profile U(y) (typically parabolic) is revisited, following Burns (1953) and Yih (1972). Complementary variational formulations that provide upper and lower bounds to the Froude number F as a function of the wave speed c and wavenumber k are constructed. These formulations are used to improve Burns's long-wave approximation and to determine Yih's critical wavenumber k[low asterisk], for which the wave is stationary (c = 0) and to which k must be inferior for the existence of an upstream running wave.

  15. 3D volumetric radar using 94-GHz millimeter waves

    NASA Astrophysics Data System (ADS)

    Takács, Barnabás

    2006-05-01

    This article describes a novel approach to the real-time visualization of 3D imagery obtained from a 3D millimeter wave scanning radar. The MMW radar system employs a spinning antenna to generate a fan-shaped scanning pattern of the entire scene. The beams formed this way provide all weather 3D distance measurements (range/azimuth display) of objects as they appear on the ground. The beam width of the antenna and its side lobes are optimized to produce the best possible resolution even at distances of up to 15 Kms. To create a full 3D data set the fan-pattern is tilted up and down with the help of a controlled stepper motor. For our experiments we collected data at 0.1 degrees increments while using both bi-static as well as a mono-static antennas in our arrangement. The data collected formed a stack of range-azimuth images in the shape of a cone. This information is displayed using our high-end 3D visualization engine capable of displaying high-resolution volumetric models with 30 frames per second. The resulting 3D scenes can then be viewed from any angle and subsequently processed to integrate, fuse or match them against real-life sensor imagery or 3D model data stored in a synthetic database.

  16. Frozen Gaussian approximation for 3-D seismic wave propagation

    NASA Astrophysics Data System (ADS)

    Chai, Lihui; Tong, Ping; Yang, Xu

    2017-01-01

    We present a systematic introduction on applying frozen Gaussian approximation (FGA) to compute synthetic seismograms in 3-D earth models. In this method, seismic wavefield is decomposed into frozen (fixed-width) Gaussian functions, which propagate along ray paths. Rather than the coherent state solution to the wave equation, this method is rigorously derived by asymptotic expansion on phase plane, with analysis of its accuracy determined by the ratio of short wavelength over large domain size. Similar to other ray-based beam methods (e.g. Gaussian beam methods), one can use relatively small number of Gaussians to get accurate approximations of high-frequency wavefield. The algorithm is embarrassingly parallel, which can drastically speed up the computation with a multicore-processor computer station. We illustrate the accuracy and efficiency of the method by comparing it to the spectral element method for a 3-D seismic wave propagation in homogeneous media, where one has the analytical solution as a benchmark. As another proof of methodology, simulations of high-frequency seismic wave propagation in heterogeneous media are performed for 3-D waveguide model and smoothed Marmousi model, respectively. The second contribution of this paper is that, we incorporate the Snell's law into the FGA formulation, and asymptotically derive reflection, transmission and free surface conditions for FGA to compute high-frequency seismic wave propagation in high contrast media. We numerically test these conditions by computing traveltime kernels of different phases in the 3-D crust-over-mantle model.

  17. Shear Behavior of 3D Woven Hollow Integrated Sandwich Composites: Experimental, Theoretical and Numerical Study

    NASA Astrophysics Data System (ADS)

    Zhou, Guangming; Liu, Chang; Cai, Deng'an; Li, Wenlong; Wang, Xiaopei

    2016-11-01

    An experimental, theoretical and numerical investigation on the shear behavior of 3D woven hollow integrated sandwich composites was presented in this paper. The microstructure of the composites was studied, then the shear modulus and load-deflection curves were obtained by double lap shear tests on the specimens in two principal directions of the sandwich panels, called warp and weft. The experimental results showed that the shear modulus of the warp was higher than that of the weft and the failure occurred in the roots of piles. A finite element model was established to predict the shear behavior of the composites. The simulated results agreed well with the experimental data. Simultaneously, a theoretical method was developed to predict the shear modulus. By comparing with the experimental data, the accuracy of the theoretical method was verified. The influence of structural parameters on shear modulus was also discussed. The higher yarn number, yarn density and dip angle of the piles could all improve the shear modulus of 3D woven hollow integrated sandwich composites at different levels, while the increasing height would decrease the shear modulus.

  18. Fast wave current drive antenna performance on D3-D

    NASA Astrophysics Data System (ADS)

    Mayberry, M. J.; Pinsker, R. I.; Petty, C. C.; Chiu, S. C.; Jackson, G. L.; Lippmann, S. I.; Prater, R.; Porkolab, M.

    1991-10-01

    Fast wave current drive (FWCD) experiments at 60 MHz are being performed on the D3-D tokamak for the first time in high electron temperature, high (beta) target plasmas. A four-element phased-array antenna is used to launch a directional wave spectrum with the peak n(sub parallel) value (approximately = 7) optimized for strong single-pass electron absorption due to electron Landau damping. For this experiment, high power FW injection (2 MW) must be accomplished without voltage breakdown in the transmission lines or antenna, and without significant impurity influx. In addition, there is the technological challenge of impedance matching a four-element antenna while maintaining equal currents and the correct phasing (90 degrees) in each of the straps for a directional spectrum. We describe the performance of the D3-D FWCD antenna during initial FW electron heating and current drive experiments in terms of these requirements.

  19. Instability and Wave Propagation in Structured 3D Composites

    NASA Astrophysics Data System (ADS)

    Kaynia, Narges; Fang, Nicholas X.; Boyce, Mary C.

    2014-03-01

    Many structured composites found in nature possess undulating and wrinkled interfacial layers that regulate mechanical, chemical, acoustic, adhesive, thermal, electrical and optical functions of the material. This research focused on the complex instability and wrinkling pattern arising in 3D structured composites and the effect of the buckling pattern on the overall structural response. The 3D structured composites consisted of stiffer plates supported by soft matrix on both sides. Compression beyond the critical strain led to complex buckling patterns in the initially straight plates. The motivation of our work is to elaborate the formation of a system of prescribed periodic scatterers (metamaterials) due to buckling, and their effect to interfere wave propagation through the metamaterial structures. Such metamaterials made from elastomers enable large reversible deformation and, as a result, significant changes of the wave propagation properties. We developed analytical and finite element models to capture various aspects of the instability mechanism. Mechanical experiments were designed to further explore the modeling results. The ability to actively alter the 3D composite structure can enable on-demand tunability of many different functions, such as active control of wave propagation to create band-gaps and waveguides.

  20. Modeling shear wave splitting observations from Iceland

    NASA Astrophysics Data System (ADS)

    Fu, Y. V.; Li, A.; Ito, G.; Hung, S.

    2010-12-01

    The goal of this research is to investigate the sources of shear-wave splitting in Iceland using synthetic waveforms generated from a variety of models. We employ a pseudospectral method in waveform modeling that allows 3-D heterogeneity and anisotropy. Several 1-D and 2-D models have been tested for a vertically propagating plane shear wave. For the two-layer models with horizontal symmetry axes, our results show that the apparent fast direction is towards the fast orientation in the upper layer. This experiment may explain why shear wave splitting measurements tend to be correlated with surface geology. We have also tested models with lateral anisotropic variations including a dike and a plume. The anisotropic boundary can be well resolved based on the change of fast directions and delay times. The splitting parameters near the boundary are affected by the laterally varied structure and the affected distance depends on wavelength, which is about 40 km for periods of 4-6 s and 50 km for periods of 8-10 s. We are currently performing experiments on a radial flow model from a plume stem. Synthetic shear-wave splitting measurements will be conducted from two more realistic geodynamic models. The first one is the “radial flow” model with low Rayleigh number. The pounding plume material is much thicker than the lithosphere and therefore does not strongly “feel” the lithosphere thickening away from the axis. Thus the plume spreads as fast away from the axis as it does along it. The other one is the “channel flow” model with high Rayleigh number. In this model the plume stem is much narrower and the thickness of the pounding plume material beneath the lithosphere much thinner. Thus the very low viscosity plume material is channeled more along axis by the thickening lithosphere. Combing the synthetic with the observed splitting results, we expect to determine the best geodynamic models for Iceland that fit seismic constraints.

  1. Protrusive waves guide 3D cell migration along nanofibers

    PubMed Central

    Guetta-Terrier, Charlotte; Monzo, Pascale; Zhu, Jie; Long, Hongyan; Venkatraman, Lakshmi; Zhou, Yue; Wang, PeiPei; Chew, Sing Yian; Mogilner, Alexander

    2015-01-01

    In vivo, cells migrate on complex three-dimensional (3D) fibrous matrices, which has made investigation of the key molecular and physical mechanisms that drive cell migration difficult. Using reductionist approaches based on 3D electrospun fibers, we report for various cell types that single-cell migration along fibronectin-coated nanofibers is associated with lateral actin-based waves. These cyclical waves have a fin-like shape and propagate up to several hundred micrometers from the cell body, extending the leading edge and promoting highly persistent directional movement. Cells generate these waves through balanced activation of the Rac1/N-WASP/Arp2/3 and Rho/formins pathways. The waves originate from one major adhesion site at leading end of the cell body, which is linked through actomyosin contractility to another site at the back of the cell, allowing force generation, matrix deformation and cell translocation. By combining experimental and modeling data, we demonstrate that cell migration in a fibrous environment requires the formation and propagation of dynamic, actin based fin-like protrusions. PMID:26553933

  2. Protrusive waves guide 3D cell migration along nanofibers.

    PubMed

    Guetta-Terrier, Charlotte; Monzo, Pascale; Zhu, Jie; Long, Hongyan; Venkatraman, Lakshmi; Zhou, Yue; Wang, PeiPei; Chew, Sing Yian; Mogilner, Alexander; Ladoux, Benoit; Gauthier, Nils C

    2015-11-09

    In vivo, cells migrate on complex three-dimensional (3D) fibrous matrices, which has made investigation of the key molecular and physical mechanisms that drive cell migration difficult. Using reductionist approaches based on 3D electrospun fibers, we report for various cell types that single-cell migration along fibronectin-coated nanofibers is associated with lateral actin-based waves. These cyclical waves have a fin-like shape and propagate up to several hundred micrometers from the cell body, extending the leading edge and promoting highly persistent directional movement. Cells generate these waves through balanced activation of the Rac1/N-WASP/Arp2/3 and Rho/formins pathways. The waves originate from one major adhesion site at leading end of the cell body, which is linked through actomyosin contractility to another site at the back of the cell, allowing force generation, matrix deformation and cell translocation. By combining experimental and modeling data, we demonstrate that cell migration in a fibrous environment requires the formation and propagation of dynamic, actin based fin-like protrusions.

  3. Mach-wave coherence in 3D media with random heterogeneities

    NASA Astrophysics Data System (ADS)

    Vyas, Jagdish C.; Mai, P. Martin; Galis, Martin; Dunham, Eric M.; Imperatori, Walter

    2016-04-01

    We investigate Mach-waves coherence for complex super-shear ruptures embedded in 3D random media that lead to seismic scattering. We simulate Mach-wave using kinematic earthquake sources that include fault-regions over which the rupture propagates at super-shear speed. The local slip rate is modeled with the regularized Yoffe function. The medium heterogeneities are characterized by Von Karman correlation function. We consider various realizations of 3D random media from combinations of different values of correlation length (0.5 km, 2 km, 5 km), standard deviation (5%, 10%, 15%) and Hurst exponent (0.2). Simulations in a homogeneous medium serve as a reference case. The ground-motion simulations (maximum resolved frequency of 5 Hz) are conducted by solving the elasto-dynamic equations of motions using a generalized finite-difference method, assuming a vertical strike-slip fault. The seismic wavefield is sampled at numerous locations within the Mach-cone region to study the properties and evolution of the Mach-waves in scattering media. We find that the medium scattering from random heterogeneities significantly diminishes the coherence of Mach-wave in terms of both amplitude and frequencies. We observe that Mach-waves are considerably scattered at distances RJB > 20 km (and beyond) for random media with standard deviation 10%. The scattering efficiency of the medium for small Hurst exponents (H <= 0.2) is mainly controlled by the standard deviation of the velocity heterogeneities, rather than their correlation length, as both theoretical considerations and numerical experiments indicate. Based on our simulations, we propose that local super-shear ruptures may be more common in nature then reported, but are very difficult to detect due to the strong seismic scattering. We suggest that if an earthquake is recorded within 10-15 km fault perpendicular distance and has high PGA, then inversion should be carried out by allowing rupture speed variations from sub

  4. Generation Of 3d Periodic Internal Wave Beams:

    NASA Astrophysics Data System (ADS)

    Chashechkin, Yuli D.; Vasiliev, Alexey Yu.

    We study generation of 2D and 3D periodic internal wave beams in continuously strat- ified viscous liquid basing on a complete set of governing equations and exact bound- ary conditions that is no-slip for velocity and attenuation of all disturbances at infinite distance from the source. The linearized governing equations are solved by an integral transform method. A total set of dispersion equation roots contains terms correspond- ing to internal waves and additional roots describing two kinds of periodic boundary layers. The first one is a viscous boundary layer and has an analogue that is a periodic or Stokes' layer in a homogeneous fluid. Its thickness is defined by a kinematic viscos- ity coefficient and a buoyancy frequency. The second one, that is an internal boundary layer, is a specific feature of stratified flows. Its thickness besides the Stokes' scale contains additional factor depending on relative wave frequency and geometry of the problem that is on the local slope of emitting surface and a direction of the waves propagation. We have constructed exact solutions of linear problems describing gen- eration of 2D waves by a strip and 3D by a rectangular with an arbitrary ratio of sides moving along or normally to a sloping plane. We also calculated the wave pattern gen- erated by a part of a vertical cylinder surface with different ratios of intrinsic scales that is of cylinder radius, thickness of the boundary layer and internal viscous scale. All solutions are regularly matched between themselves in limiting cases. The spatial decay of the waves depends on dimension and geometry of the problem. Non-linear generation of internal waves by the Stokes' boundary layer on a periodically rotating horizontal disk or by interacting boundary layers on an arbitrary moving strip is in- vestigated. We found conditions of generation of the main frequency and its second harmonic. In experiments periodic waves beams from different sources are visualised by the

  5. Simulation of 3D Global Wave Propagation Through Geodynamic Models

    NASA Astrophysics Data System (ADS)

    Schuberth, B.; Piazzoni, A.; Bunge, H.; Igel, H.; Steinle-Neumann, G.

    2005-12-01

    This project aims at a better understanding of the forward problem of global 3D wave propagation. We use the spectral element program "SPECFEM3D" (Komatitsch and Tromp, 2002a,b) with varying input models of seismic velocities derived from mantle convection simulations (Bunge et al., 2002). The purpose of this approach is to obtain seismic velocity models independently from seismological studies. In this way one can test the effects of varying parameters of the mantle convection models on the seismic wave field. In order to obtain the seismic velocities from the temperature field of the geodynamical simulations we follow a mineral physics approach. Assuming a certain mantle composition (e.g. pyrolite with CMASF composition) we compute the stable phases for each depth (i.e. pressure) and temperature by system Gibbs free energy minimization. Elastic moduli and density are calculated from the equations of state of the stable mineral phases. For this we use a mineral physics database derived from calorimetric experiments (enthalphy and entropy of formation, heat capacity) and EOS parameters.

  6. 3D Numerical Study of the Shear Rheology of a Semi-dilute Viscoelastic Suspension

    NASA Astrophysics Data System (ADS)

    Yang, Mengfei; Krishnan, Sreenath; Shaqfeh, Eric

    2016-11-01

    The stress in suspensions of rigid particles in polymer solutions is of considerable interest in applications such as manufacturing processes and fracturing technologies. Deriving an analytic expression for the material functions of a viscoelastic suspension under shear is difficult due to the nonlinear particle-fluid and particle-particle interactions, and theoretical studies have been limited to dilute suspensions at low shear Weissenberg number (Wi) or low polymer concentrations. Previously, we performed 3D single-particle simulations and showed that the results agreed well with the existing theories in the appropriate parameter regimes. We found that suspensions in constant-viscosity elastic fluids shear-thicken over a range of Wi and their material properties plateau at higher Wi. However, discrepancies between simulation and existing experimental measurements for volume fractions as low as 2.5% suggested that interparticle hydrodynamic interactions could not be neglected. We now present 3D high fidelity numerical simulations of multiple spheres freely suspended in a sheared viscoelastic fluid using an immersed boundary framework to study the relationship between hydrodynamic interactions, particle structure formation, and the bulk rheology of viscoelastic suspensions. We observe that in a non-shear thinning elastic fluid, particles do not "chain", but their interactions induce additional polymer stresses in the fluid which contribute to a stronger particle effect than predicted in the dilute limit.

  7. Rail Shear and Short Beam Shear Properties of Various 3-Dimensional (3-D) Woven Composites

    DTIC Science & Technology

    2016-01-01

    from stress-strain response. A 0.2% plastic strain offset method was used to calculate the yield of the material. Table 4 compares the maximum... plastic region where the progressive damages began to form in the samples. Based on the stress-strain curves, it was notable that the 12° configuration...outperformed the other architectures in terms of shear strength and moduli. Another observation made from the curvatures was that the plastic portion

  8. Shear induced alignment of short nanofibers in 3D printed polymer composites

    NASA Astrophysics Data System (ADS)

    Erdem Yunus, Doruk; Shi, Wentao; Sohrabi, Salman; Liu, Yaling

    2016-12-01

    3D printing of composite materials offers an opportunity to combine the desired properties of composite materials with the flexibility of additive manufacturing in geometric shape and complexity. In this paper, the shear-induced alignment of aluminum oxide nanowires during stereolithography printing was utilized to fabricate a nanowire reinforced polymer composite. To align the fibers, a lateral oscillation mechanism was implemented and combined with wall pattern printing technique to generate shear flow in both vertical and horizontal directions. A series of specimens were fabricated for testing the composite material’s tensile strength. The results showed that mechanical properties of the composite were improved by reinforcement of nanofibers through shear induced alignment. The improvement of tensile strength was approximately ∼28% by aligning the nanowires at 5 wt% (∼1.5% volume fraction) loading of aluminum oxide nanowires.

  9. Shear induced alignment of short nanofibers in 3D printed polymer composites.

    PubMed

    Yunus, Doruk Erdem; Shi, Wentao; Sohrabi, Salman; Liu, Yaling

    2016-12-09

    3D printing of composite materials offers an opportunity to combine the desired properties of composite materials with the flexibility of additive manufacturing in geometric shape and complexity. In this paper, the shear-induced alignment of aluminum oxide nanowires during stereolithography printing was utilized to fabricate a nanowire reinforced polymer composite. To align the fibers, a lateral oscillation mechanism was implemented and combined with wall pattern printing technique to generate shear flow in both vertical and horizontal directions. A series of specimens were fabricated for testing the composite material's tensile strength. The results showed that mechanical properties of the composite were improved by reinforcement of nanofibers through shear induced alignment. The improvement of tensile strength was approximately ∼28% by aligning the nanowires at 5 wt% (∼1.5% volume fraction) loading of aluminum oxide nanowires.

  10. An octahedral shear strain-based measure of SNR for 3D MR elastography

    NASA Astrophysics Data System (ADS)

    McGarry, M. D. J.; Van Houten, E. E. W.; Perriñez, P. R.; Pattison, A. J.; Weaver, J. B.; Paulsen, K. D.

    2011-07-01

    A signal-to-noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for magnetic resonance elastography (MRE), where motion-based SNR measures are commonly used. The shear strain, γ, is directly related to the shear modulus, μ, through the definition of shear stress, τ = μγ. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and the human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects.

  11. An Octahedral Shear Strain Based measure of SNR for 3D MR Elastography

    PubMed Central

    McGarry, MDJ; Van Houten, EEW; Perriñez, PR; Pattison, AJ; Weaver, JB; Paulsen, KD

    2011-01-01

    A signal to noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for MR elastography, where motion-based SNR measures are commonly used. The shear strain, γ, is directly related to the shear modulus, μ, through the definition of shear stress, τ = μγ. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects. PMID:21654044

  12. An octahedral shear strain-based measure of SNR for 3D MR elastography.

    PubMed

    McGarry, M D J; Van Houten, E E W; Perriñez, P R; Pattison, A J; Weaver, J B; Paulsen, K D

    2011-07-07

    A signal-to-noise ratio (SNR) measure based on the octahedral shear strain (the maximum shear strain in any plane for a 3D state of strain) is presented for magnetic resonance elastography (MRE), where motion-based SNR measures are commonly used. The shear strain, γ, is directly related to the shear modulus, μ, through the definition of shear stress, τ = μγ. Therefore, noise in the strain is the important factor in determining the quality of motion data, rather than the noise in the motion. Motion and strain SNR measures were found to be correlated for MRE of gelatin phantoms and the human breast. Analysis of the stiffness distributions of phantoms reconstructed from the measured motion data revealed a threshold for both strain and motion SNR where MRE stiffness estimates match independent mechanical testing. MRE of the feline brain showed significantly less correlation between the two SNR measures. The strain SNR measure had a threshold above which the reconstructed stiffness values were consistent between cases, whereas the motion SNR measure did not provide a useful threshold, primarily due to rigid body motion effects.

  13. Shear wave splitting and shear wave splitting tomography of the southern Puna plateau

    NASA Astrophysics Data System (ADS)

    Calixto, Frank J.; Robinson, Danielle; Sandvol, Eric; Kay, Suzanne; Abt, David; Fischer, Karen; Heit, Ben; Yuan, Xiaohui; Comte, Diana; Alvarado, Patricia

    2014-11-01

    We have investigated the seismic anisotropy beneath the Central Andean southern Puna plateau by applying shear wave splitting analysis and shear wave splitting tomography to local S waves and teleseismic SKS, SKKS and PKS phases. Overall, a very complex pattern of fast directions throughout the southern Puna plateau region and a circular pattern of fast directions around the region of the giant Cerro Galan ignimbrite complex are observed. In general, teleseismic lag times are much greater than those for local events which are interpreted to reflect a significant amount of sub and inner slab anisotropy. The complex pattern observed from shear wave splitting analysis alone is the result of a complex 3-D anisotropic structure under the southern Puna plateau. Our application of shear wave splitting tomography provides a 3-D model of anisotropy in the southern Puna plateau that shows different patterns depending on the driving mechanism of upper-mantle flow and seismic anisotropy. The trench parallel a-axes in the continental lithosphere above the slab east of 68W may be related to deformation of the overriding continental lithosphere since it is under compressive stresses which are orthogonal to the trench. The more complex pattern below the Cerro Galan ignimbrite complex and above the slab is interpreted to reflect delamination of continental lithosphere and upwelling of hot asthenosphere. The a-axes beneath the Cerro Galan, Cerro Blanco and Carachi Pampa volcanic centres at 100 km depth show some weak evidence for vertically orientated fast directions, which could be due to vertical asthenospheric flow around a delaminated block. Additionally, our splitting tomographic model shows that there is a significant amount of seismic anisotropy beneath the slab. The subslab mantle west of 68W shows roughly trench parallel horizontal a-axes that are probably driven by slab roll back and the relatively small coupling between the Nazca slab and the underlying mantle. In

  14. Effects of extracellular fiber architecture on cell membrane shear stress in a 3D fibrous matrix.

    PubMed

    Pedersen, John A; Boschetti, Federica; Swartz, Melody A

    2007-01-01

    Interstitial fluid flow has been shown to affect the organization and behavior of cells in 3D environments in vivo and in vitro, yet the forces driving such responses are not clear. Due to the complex architecture of the extracellular matrix (ECM) and the difficulty of measuring fluid flow near cells embedded in it, the levels of shear stress experienced by cells in this environment are typically estimated using bulk-averaged matrix parameters such as hydraulic permeability. While this is useful for estimating average stresses, it cannot yield insight into how local matrix fiber architecture-which is cell-controlled in the immediate pericellular environment-affects the local stresses imposed on the cell surface. To address this, we used computational fluid dynamics to study flow through an idealized mesh constructed of a cubic lattice of fibers simulating a typical in vitro collagen gel. We found that, in such high porosity matrices, the fibers strongly affect the flow fields near the cell, with peak shear stresses up to five times higher than those predicted by the Brinkman equation. We also found that minor remodeling of the fibers near the cell surface had major effects on the shear stress profile on the cell. These findings demonstrate the importance of fiber architecture to the fluid forces on a cell embedded in a 3D matrix, and also show how small modifications in the local ECM can lead to large changes in the mechanical environment of the cell.

  15. Coded excitation plane wave imaging for shear wave motion detection.

    PubMed

    Song, Pengfei; Urban, Matthew W; Manduca, Armando; Greenleaf, James F; Chen, Shigao

    2015-07-01

    Plane wave imaging has greatly advanced the field of shear wave elastography thanks to its ultrafast imaging frame rate and the large field-of-view (FOV). However, plane wave imaging also has decreased penetration due to lack of transmit focusing, which makes it challenging to use plane waves for shear wave detection in deep tissues and in obese patients. This study investigated the feasibility of implementing coded excitation in plane wave imaging for shear wave detection, with the hypothesis that coded ultrasound signals can provide superior detection penetration and shear wave SNR compared with conventional ultrasound signals. Both phase encoding (Barker code) and frequency encoding (chirp code) methods were studied. A first phantom experiment showed an approximate penetration gain of 2 to 4 cm for the coded pulses. Two subsequent phantom studies showed that all coded pulses outperformed the conventional short imaging pulse by providing superior sensitivity to small motion and robustness to weak ultrasound signals. Finally, an in vivo liver case study on an obese subject (body mass index = 40) demonstrated the feasibility of using the proposed method for in vivo applications, and showed that all coded pulses could provide higher SNR shear wave signals than the conventional short pulse. These findings indicate that by using coded excitation shear wave detection, one can benefit from the ultrafast imaging frame rate and large FOV provided by plane wave imaging while preserving good penetration and shear wave signal quality, which is essential for obtaining robust shear elasticity measurements of tissue.

  16. Effects of obliquely opposing and following currents on wave propagation in a new 3D wave-current basin

    NASA Astrophysics Data System (ADS)

    Lieske, Mike; Schlurmann, Torsten

    2016-04-01

    INTRODUCTION & MOTIVATION The design of structures in coastal and offshore areas and their maintenance are key components of coastal protection. Usually, assessments of processes and loads on coastal structures are derived from experiments with flow and wave parameters in separate physical models. However, Peregrin (1976) already points out that processes in natural shallow coastal waters flow and sea state processes do not occur separately, but influence each other nonlinearly. Kemp & Simons (1982) perform 2D laboratory tests and study the interactions between a turbulent flow and following waves. They highlight the significance of wave-induced changes in the current properties, especially in the mean flow profiles, and draw attention to turbulent fluctuations and bottom shear stresses. Kemp & Simons (1983) also study these processes and features with opposing waves. Studies on the wave-current interaction in three-dimensional space for a certain wave height, wave period and water depth were conducted by MacIver et al. (2006). The research focus is set on the investigation of long-crested waves on obliquely opposing and following currents in the new 3D wave-current basin. METHODOLOGY In a first step the flow analysis without waves is carried out and includes measurements of flow profiles in the sweet spot of the basin at predefined measurement positions. Five measuring points in the water column have been delineated in different water depths in order to obtain vertical flow profiles. For the characterization of the undisturbed flow properties in the basin, an uniformly distributed flow was generated in the wave basin. In the second step wave analysis without current, the unidirectional wave propagation and wave height were investigated for long-crested waves in intermediate wave conditions. In the sweet spot of the wave basin waves with three different wave directions, three wave periods and uniform wave steepness were examined. For evaluation, we applied a common

  17. Controlling Shear Stress in 3D Bioprinting is a Key Factor to Balance Printing Resolution and Stem Cell Integrity.

    PubMed

    Blaeser, Andreas; Duarte Campos, Daniela Filipa; Puster, Uta; Richtering, Walter; Stevens, Molly M; Fischer, Horst

    2016-02-04

    A microvalve-based bioprinting system for the manufacturing of high-resolution, multimaterial 3D-structures is reported. Applying a straightforward fluid-dynamics model, the shear stress at the nozzle site can precisely be controlled. Using this system, a broad study on how cell viability and proliferation potential are affected by different levels of shear stress is conducted. Complex, multimaterial 3D structures are printed with high resolution. This work pioneers the investigation of shear stress-induced cell damage in 3D bioprinting and might help to comprehend and improve the outcome of cell-printing studies in the future.

  18. Squire's transformation and 3D Optimal Perturbations in Bounded Parallel Shear Flows

    NASA Astrophysics Data System (ADS)

    Chomaz, Jean-Marc; Soundar Jerome, J. John

    2011-11-01

    The aim of this short communication is to present the implication of Squire's transformation on the optimal transient growth of arbitrary 3D disturbances in parallel shear flow bounded in the cross-stream direction. To our best knowledge this simple property has never been discussed before. In particular it allows to express the long-time optimal growth for perturbations of arbitrary wavenumbers as the product of the gains from the 2D optimal at a lower Reynolds number itself due to the Orr-mechanism by a term that may be identified as due to the lift-up mechanism. This property predict scalings for the 3D optimal perturbation well verified by direct computation. It may be extended to take into account buoyancy effect.

  19. 3D resolution tests of two-plane wave approach using synthetic seismograms

    NASA Astrophysics Data System (ADS)

    Ceylan, S.; Larmat, C. S.; Sandvol, E. A.

    2012-12-01

    Two-plane wave tomography (TPWT) is becoming a standard approach to obtain fundamental mode Rayleigh wave phase velocities for a variety of tectonic settings. A recent study by Ceylan et al. (2012) has applied this method to eastern Tibet, using data from INDEPTH-IV and Namche-Barwa seismic experiments. The TPWT assumes that distortion of wavefronts at each station can be expressed as the sum of two plane waves. However, there is currently no robust or complete resolution test for TPWT, to address its limitations such as wavefront healing. In this study, we test the capabilities of TPWT and resolution of INDEPTH-IV seismic experiment, by performing 3D resolution tests using synthetic seismograms. Utilizing SPECFEM3D software, we compute synthetic data sets resolving periods down to ~30 s. We implement a checkerboard upper mantle (for depths between 50 and 650 km) with variable cell sizes, superimposed to PREM as the background model. We then calculate fundamental mode surface wave phase velocities using TPWT for periods between 33-143 seconds, using synthetic seismograms computed from our three dimensional hypothetical model. Assuming a constant Poisson's ratio, we use partial derivatives from Saito (1988) to invert for shear wave velocities. We show that the combination of TPWT and Saito (1988) methods is capable of retrieving anomalies down to depths of ~200 km for Rayleigh waves. Below these depths, we observe evidence of both lateral and vertical smearing. We also find that the traditional method for estimating the resolution of TPWT consistently overestimates phase velocity resolutions. Love waves exhibit adequate resolution down to depths of ~100 km. At depths greater than 100 km, smearing is more evident in SH wave results than those of SV waves. Increased smearing of SH waves is most probably due to propagation characteristics and shallower sensitivity of Love waves. Our results imply that TPWT can be applied to Love waves, making future investigations of

  20. Converted-Wave Processing of a 3D-3C Refection Seismic Survey of Soda Lake Geothermal Field

    NASA Astrophysics Data System (ADS)

    Louie, J. N.; Kent, T.; Echols, J.

    2012-12-01

    This 3D-3C seismic survey greatly improves the structural model of the Soda Lake, Nevada geothermal system. The picked top of a mudstone interval above reservoir levels reveals a detailed fault map. The geothermal reservoir is within a complex of nested grabens. Determining a "geothermal indicator" for the deeper reservoir in the seismic signal, and processing of the 3D converted-wave data, have been unsuccessful to date. Due to a high near-surface Vp/Vs ratio the shear-wave energy is under-sampled with 220 ft receiver spacing and 550 ft (168 m) line spacing. The 2D converted-wave data that we can image shows encouraging similarity to the deep structural features in the P-wave sections, but have little resolution of shallow structures. Higher-density receivers and a better shallow shear-wave model are needed in conjunction with this deep reflection study to effectively image the 3D converted waves.

  1. Numerical simulation of suspended sediment concentration by 3D coupled wave-current model in the Oujiang River Estuary, China

    NASA Astrophysics Data System (ADS)

    Xu, Ting; You, Xue-yi

    2017-04-01

    A 3D sediment transport model based on the modified environmental fluid dynamics code (EFDC) and the nearshore waves simulation model (SWAN) is developed to study the change of suspended sediment concentration and bottom shear stress under the actions of pure current and wave-current. After being validated by the field measured data, the proposed sediment transport model is applied in the Oujiang River Estuary, China. The results show that the ratios of both bottom shear stress and suspended sediment concentration of pure current to those of wave-current show a gradually increase from shallow nearshore water to deep open sea. The results also show that the proportion of wave contributions on bottom shear stress and sediment concentration are above 60%, approximately 20-30% and less than 10% for the water depth of less than 5 m, 5-10 m and more than 20 m, respectively. For the waters among islands, the proportion of wave contribution to bottom shear stress and sediment concentration is reduced to 10-20% for -5 m water depth and this is more obvious for the waves of large amplitude. The bottom stress and suspended sediment concentration between islands are mainly controlled by tidal current, and the effect of wave is not significant.

  2. The application of low shear modeled microgravity to 3-D cell biology and tissue engineering.

    PubMed

    Navran, Stephen

    2008-01-01

    The practice of cell culture has been virtually unchanged for 100 years. Until recently, life scientists have had to content themselves with two-dimensional cell culture technology. Clearly, living creatures are not constructed in two dimensions and thus it has become widely recognized that in vitro culture systems must become three dimensional to correctly model in vivo biology. Attempts to modify conventional 2-D culture technology to accommodate 3-D cell growth such as embedding cells in extracellular matrix have demonstrated the superiority of concept. Nevertheless, there are serious drawbacks to this approach including limited mass transport and lack of scalability. Recently, a new cell culture technology developed at NASA to study the effects of microgravity on cells has emerged to solve many of the problems of 3-D cell culture. The technology, the Rotating Wall Vessel (RWV) is a single axis clinostat consisting of a fluid-filled, cylindrical, horizontally rotating culture vessel. Cells placed in this environment are suspended by the resolution of the gravitational, centrifugal and Coriolis forces with extremely low mechanical shear. These conditions, which have been called "low shear modeled microgravity", enable cells to assemble into tissue-like aggregates with high mass transport of nutrients, oxygen and wastes. Examples of the use of the RWV for basic cell biology research and tissue engineering applications are discussed.

  3. Continuous wave laser for wind shear detection

    NASA Technical Reports Server (NTRS)

    Nelson, Loren

    1991-01-01

    Details of the design and development of a continuous-wave heterodyne carbon dioxide laser which has wind shear detection capabilities are given in viewgraph form. The goal of the development was to investigate the lower cost CW (rather than pulsed) lidar option for look-ahead wind shear detection from aircraft. The device has potential utility for ground based wind shear detection at secondary airports where the high cost of a Terminal Doppler Weather Radar system is not justifiable.

  4. Shear wave velocity measurements in marine sediments

    NASA Astrophysics Data System (ADS)

    Matthews, J. E.

    1982-09-01

    Pulsed ultrasonic techniques for the measurement of sound speed are reliable and well documented. Extension of these techniques to the measurement of shear wave velocities in marine sediments, generally was unsuccessful. Recently developed shear wave transducers, based upon piezoelectric benders operated at sonic frequencies, provide significantly improved transducer-sample mechanical coupling. This improved coupling allows the application of pulsed techniques to the measurement of shear wave velocities in marine sediments, and the rapid determination of sediment dynamic elastic properties. Two types of bender-based shear wave transducer and preliminary data are described: 1) a probe configuration for box core samples, and 2) a modification to the Hamilton Frame Velocimeter for cut samples.

  5. Longitudinal shear wave and transverse dilatational wave in solids.

    PubMed

    Catheline, S; Benech, N

    2015-02-01

    Dilatation wave involves compression and extension and is known as the curl-free solution of the elastodynamic equation. Shear wave on the contrary does not involve any change in volume and is the divergence-free solution. This letter seeks to examine the elastodynamic Green's function through this definition. By separating the Green's function in divergence-free and curl-free terms, it appears first that, strictly speaking, the longitudinal wave is not a pure dilatation wave and the transverse wave is neither a pure shear wave. Second, not only a longitudinal shear wave but also a transverse dilatational wave exists. These waves are shown to be a part of the solution known as coupling terms. Their special motion is carefully described and illustrated.

  6. Coherence holography by achromatic 3-D field correlation of generic thermal light with an imaging Sagnac shearing interferometer.

    PubMed

    Naik, Dinesh N; Ezawa, Takahiro; Singh, Rakesh Kumar; Miyamoto, Yoko; Takeda, Mitsuo

    2012-08-27

    We propose a new technique for achromatic 3-D field correlation that makes use of the characteristics of both axial and lateral magnifications of imaging through a common-path Sagnac shearing interferometer. With this technique, we experimentally demonstrate, for the first time to our knowledge, 3-D image reconstruction of coherence holography with generic thermal light. By virtue of the achromatic axial shearing implemented by the difference in axial magnifications in imaging, the technique enables coherence holography to reconstruct a 3-D object with an axial depth beyond the short coherence length of the thermal light.

  7. Magnetized stratified rotating shear waves.

    PubMed

    Salhi, A; Lehner, T; Godeferd, F; Cambon, C

    2012-02-01

    We present a spectral linear analysis in terms of advected Fourier modes to describe the behavior of a fluid submitted to four constraints: shear (with rate S), rotation (with angular velocity Ω), stratification, and magnetic field within the linear spectral theory or the shearing box model in astrophysics. As a consequence of the fact that the base flow must be a solution of the Euler-Boussinesq equations, only radial and/or vertical density gradients can be taken into account. Ertel's theorem no longer is valid to show the conservation of potential vorticity, in the presence of the Lorentz force, but a similar theorem can be applied to a potential magnetic induction: The scalar product of the density gradient by the magnetic field is a Lagrangian invariant for an inviscid and nondiffusive fluid. The linear system with a minimal number of solenoidal components, two for both velocity and magnetic disturbance fields, is eventually expressed as a four-component inhomogeneous linear differential system in which the buoyancy scalar is a combination of solenoidal components (variables) and the (constant) potential magnetic induction. We study the stability of such a system for both an infinite streamwise wavelength (k(1) = 0, axisymmetric disturbances) and a finite one (k(1) ≠ 0, nonaxisymmetric disturbances). In the former case (k(1) = 0), we recover and extend previous results characterizing the magnetorotational instability (MRI) for combined effects of radial and vertical magnetic fields and combined effects of radial and vertical density gradients. We derive an expression for the MRI growth rate in terms of the stratification strength, which indicates that purely radial stratification can inhibit the MRI instability, while purely vertical stratification cannot completely suppress the MRI instability. In the case of nonaxisymmetric disturbances (k(1) ≠ 0), we only consider the effect of vertical stratification, and we use Levinson's theorem to demonstrate the

  8. Coded Excitation Plane Wave Imaging for Shear Wave Motion Detection

    PubMed Central

    Song, Pengfei; Urban, Matthew W.; Manduca, Armando; Greenleaf, James F.; Chen, Shigao

    2015-01-01

    Plane wave imaging has greatly advanced the field of shear wave elastography thanks to its ultrafast imaging frame rate and the large field-of-view (FOV). However, plane wave imaging also has decreased penetration due to lack of transmit focusing, which makes it challenging to use plane waves for shear wave detection in deep tissues and in obese patients. This study investigated the feasibility of implementing coded excitation in plane wave imaging for shear wave detection, with the hypothesis that coded ultrasound signals can provide superior detection penetration and shear wave signal-to-noise-ratio (SNR) compared to conventional ultrasound signals. Both phase encoding (Barker code) and frequency encoding (chirp code) methods were studied. A first phantom experiment showed an approximate penetration gain of 2-4 cm for the coded pulses. Two subsequent phantom studies showed that all coded pulses outperformed the conventional short imaging pulse by providing superior sensitivity to small motion and robustness to weak ultrasound signals. Finally, an in vivo liver case study on an obese subject (Body Mass Index = 40) demonstrated the feasibility of using the proposed method for in vivo applications, and showed that all coded pulses could provide higher SNR shear wave signals than the conventional short pulse. These findings indicate that by using coded excitation shear wave detection, one can benefit from the ultrafast imaging frame rate and large FOV provided by plane wave imaging while preserving good penetration and shear wave signal quality, which is essential for obtaining robust shear elasticity measurements of tissue. PMID:26168181

  9. Shear Alfv'en spectrum and mode structures for 3D configurations

    NASA Astrophysics Data System (ADS)

    Spong, D. A.; Todo, Y.

    2007-11-01

    Energetic particle destabilized Alfv'en modes are observed in a wide range of stellarator experiments. We have developed a code (AE3D) to calculate the full shear Alfv'en frequency spectrum and associated mode structures for arbitrary stellarator equilibria. This is based on a Galerkin approach using a combined Fourier mode (poloidal/toroidal angle) finite element (radial) representation. It has been applied to an LHD case where Alfv'en activity and enhanced ion losses were seen. Applications also are underway to other experiments, such as HSX, where ECH-driven Alfv'en modes were observed. This model can form the basis for stellarator optimization targets, synthetic diagnostics, and reduced linear/nonlinear stability models. It is also applicable to tokamaks with symmetry-breaking effects. By matching observed frequencies with calculated mode structures, improved understanding of the physics mechanisms of AE modes, such as sideband coupling, damping, and enhanced fast particle losses can be developed.

  10. Stiffener bond line monitoring using ultrasonic shear guided waves

    NASA Astrophysics Data System (ADS)

    Fan, Z.; Castaings, M.; Lowe, M. J. S.; Fromme, P.; Biateau, C.

    2012-05-01

    Adhesively bonded stiffeners are employed in aerospace applications to increase structural stiffness. The potential of shear guided wave modes for the verification of adhesion and bond line thickness in difficult to access regions has been investigated. The properties of guided wave modes propagating along a T-shaped stiffener bonded to an aluminium plate were calculated using the Semi-Analytical Finite Element (SAFE) method. Shear modes were identified as well suited with energy concentrated at the stiffener and bond line, limiting energy radiation into the plate and thus achieving increased inspection length. The influence of bond line properties and thickness was investigated from SAFE and 3D Finite Element calculations and a significant influence of the epoxy shear (Coulomb) modulus on the phase velocity found. Experiments were conducted during the curing of an epoxy adhesive, bonding a stiffener to the plate with bond strength and stiffness increasing over time. The excited shear mode was measured using a laser interferometer. The measured phase velocity changed significantly during curing. The frequency dependency matches well with the SAFE calculations for a variation of the Coulomb's modulus of the adhesive layer. The potential of the shear guided wave mode for bond line inspection and monitoring has been shown.

  11. DNS of Sheared Particulate Flows with a 3D Explicit Finite-Difference Scheme

    NASA Astrophysics Data System (ADS)

    Perrin, Andrew; Hu, Howard

    2007-11-01

    A 3D explicit finite-difference code for direct simulation of the motion of solid particulates in fluids has been developed, and a periodic boundary condition implemented to study the effective viscosity of suspensions in shear. The code enforces the no-slip condition on the surface of spherical particles in a uniform Cartesian grid with a special particle boundary condition based on matching the Stokes flow solutions next to the particle surface with a numerical solution away from it. The method proceeds by approximating the flow next to the particle surface as a Stokes flow in the particle's local coordinates, which is then matched to the finite difference update in the bulk fluid on a ``cage'' of grid points near the particle surface. (The boundary condition is related to the PHYSALIS method (2003), but modified for explicit schemes and with an iterative process removed.) Advantages of the method include superior accuracy of the scheme on a relatively coarse grid for intermediate particle Reynolds numbers, ease of implementation, and the elimination of the need to track the particle surface. For the sheared suspension, the effects of fluid and solid inertia and solid volume fraction on effective viscosity at moderate particle Reynolds numbers and concentrated suspensions will be discussed.

  12. Shear wave speed recovery in sonoelastography using crawling wave data.

    PubMed

    Lin, Kui; McLaughlin, Joyce; Renzi, Daniel; Thomas, Ashley

    2010-07-01

    The crawling wave experiment, in which two harmonic sources oscillate at different but nearby frequencies, is a development in sonoelastography that allows real-time imaging of propagating shear wave interference patterns. Previously the crawling wave speed was recovered and used as an indicator of shear stiffness; however, it is shown in this paper that the crawling wave speed image can have artifacts that do not represent a change in stiffness. In this paper, the locations and shapes of some of the artifacts are exhibited. In addition, a differential equation is established that enables imaging of the shear wave speed, which is a quantity strongly correlated with shear stiffness change. The full algorithm is as follows: (1) extract the crawling wave phase from the spectral variance data; (2) calculate the crawling wave phase wave speed; (3) solve a first-order PDE for the phase of the wave emanating from one of the sources; and (4) compute and image the shear wave speed on a grid in the image plane.

  13. Seismic shear waves as Foucault pendulum

    NASA Astrophysics Data System (ADS)

    Snieder, Roel; Sens-Schönfelder, Christoph; Ruigrok, Elmer; Shiomi, Katsuhiko

    2016-03-01

    Earth's rotation causes splitting of normal modes. Wave fronts and rays are, however, not affected by Earth's rotation, as we show theoretically and with observations made with USArray. We derive that the Coriolis force causes a small transverse component for P waves and a small longitudinal component for S waves. More importantly, Earth's rotation leads to a slow rotation of the transverse polarization of S waves; during the propagation of S waves the particle motion behaves just like a Foucault pendulum. The polarization plane of shear waves counteracts Earth's rotation and rotates clockwise in the Northern Hemisphere. The rotation rate is independent of the wave frequency and is purely geometric, like the Berry phase. Using the polarization of ScS and ScS2 waves, we show that the Foucault-like rotation of the S wave polarization can be observed. This can affect the determination of source mechanisms and the interpretation of observed SKS splitting.

  14. Finite-difference modeling of SH-wave conversions in shallow shear-wave refraction surveying

    NASA Astrophysics Data System (ADS)

    Mi, Binbin; Xia, Jianghai; Xu, Yixian

    2015-08-01

    The shallow shear-wave refraction method works successfully in an area with a series of horizontal layers. Complex near-surface geology, however, may not fit into the assumption of a series of horizontal layers. It is theoretically inevitable that a plane SH-wave undergoes wave-type conversions along an interface in an area of non-horizontal layers. One real example has shown that the shallow SH-wave refraction method provides velocities of a converted wave rather than SH-wave. Moreover, it is impossible to identify the converted wave by refraction data itself. In this paper, we implement numerical simulation for conversion of SH- to P-wave in 3D heterogeneous medium with the finite-difference method. An SH-wave source excitation method that we give in the numerical simulation is testified, which can only generate SH-wave without P-wave. The numerical modeling results demonstrate that the conversion of the SH-wave to other wave-types will occur in an area of non-horizontal layers. All the converted P-wave arrivals are shown reversed polarity like S-wave arrivals in the modeling of reverse of the source and we have clarified the peculiar properties of converted P-waves from the S-wave. Our numerical simulation results confirm that velocities calculated from an SH-wave refraction survey are velocities of converted waves. Therefore, special attention should be paid to this pitfall in the real world.

  15. A new method for shear wave speed estimation in shear wave elastography.

    PubMed

    Engel, Aaron J; Bashford, Gregory R

    2015-12-01

    Visualization of mechanical properties of tissue can aid in noninvasive pathology diagnosis. Shear wave elastography (SWE) measures the elastic properties of soft tissues by estimation of local shear wave propagation speed. In this paper, a new robust method for estimation of shear wave speed is introduced which has the potential for simplifying continuous filtering and real-time elasticity processing. Shear waves were generated by external mechanical excitation and imaged at a high frame rate. Three homogeneous phantoms of varying elastic moduli and one inclusion phantom were imaged. Waves propagating in separate directions were filtered and shear wave speed was estimated by inversion of the 1-D first-order wave equation. Final 2-D shear wave speed maps were constructed by weighted averaging of estimates from opposite traveling directions. Shear wave speed results for phantoms with gelatin concentrations of 5%, 7%, and 9% were 1.52 ± 0.10 m/s, 1.86 ± 0.10 m/s, and 2.37 ± 0.15 m/s, respectively, which were consistent with estimates computed from three other conventional methods, as well as compression tests done with a commercial texture analyzer. The method was shown to be able to reconstruct a 2-D speed map of an inclusion phantom with good image quality and variance comparable to conventional methods. Suggestions for further work are given.

  16. A 3-D shear velocity model of the southern North American and Caribbean plates from ambient noise and earthquake tomography

    NASA Astrophysics Data System (ADS)

    Gaite, B.; Villaseñor, A.; Iglesias, A.; Herraiz, M.; Jiménez-Munt, I.

    2015-02-01

    We use group velocities from earthquake tomography together with group and phase velocities from ambient noise tomography (ANT) of Rayleigh waves to invert for the 3-D shear-wave velocity structure (5-70 km) of the Caribbean (CAR) and southern North American (NAM) plates. The lithospheric model proposed offers a complete image of the crust and uppermost-mantle with imprints of the tectonic evolution. One of the most striking features inferred is the main role of the Ouachita-Marathon-Sonora orogeny front on the crustal seismic structure of the NAM plate. A new imaged feature is the low crustal velocities along the USA-Mexico border. The model also shows a break of the east-west mantle velocity dichotomy of the NAM and CAR plates beneath the Isthmus of the Tehuantepec and the Yucatan Block. High upper-mantle velocities along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest velocities correspond to active volcanic arcs and thin lithospheric mantle regions.

  17. 3D Full-Wave Simulations of Reflectometry

    SciTech Connect

    Valeo, E. J.; Kramer, G. J.; Nazikian, R.

    2009-11-26

    The characterization of fluctuation amplitudes, spatial correlation lengths, and wave vectors through measurement of the correlation properties of reflected microwave diagnostic signals depends on a quantitative knowledge of propagation in toroidal, magnetized plasma. The disparity between the radiation wavelength (mm) and the plasma size makes full wave computations challenging. We extend a two dimensional model which computes propagation in a poloidal plane to include toroidal variation. The model reduces the computational burden compared to that of solving the full-wave equation everywhere-but retains both diffraction and refraction-by merging a description appropriate to the under dense plasma (paraxial) with the required full-wave description near the reflection layer. Initial results for ITER-like profiles demonstrate the utility of the tool as an aid in specifying antenna positioning and setting sensitivity requirements.

  18. Analysis of wave propagation in periodic 3D waveguides

    NASA Astrophysics Data System (ADS)

    Schaal, Christoph; Bischoff, Stefan; Gaul, Lothar

    2013-11-01

    Structural Health Monitoring (SHM) is a growing research field in the realm of civil engineering. SHM concepts are implemented using integrated sensors and actuators to evaluate the state of a structure. Within this work, wave-based techniques are addressed. Dispersion effects for propagating waves in waveguides of different materials are analyzed for various different cross-sections. Since analytical theory is limited, a general approach based on the Waveguide Finite Element Method is applied. Numerical results are verified experimentally.

  19. Shear waves in acoustic anisotropic media

    SciTech Connect

    Grechka, Vladimir; Zhang, Linbin; Rector, James W.

    2003-01-02

    Acoustic transversely isotropic (TI) media are defined by artificially setting the shear-wave velocity in the direction of symmetry axis, VS0, to zero. Contrary to conventional wisdom that equating VS0 = 0 eliminates shear waves, we demonstrate their presence and examine their properties. Specifically, we show that SV-waves generally have finite nonzero phase and group velocities in acoustic TI media. In fact, these waves have been observed in full waveform modeling, but apparently they were not understood and labeled as numerical artifacts. Acoustic TI media are characterized by extreme, in some sense infinite strength of anisotropy. It makes the following unusual wave phenomena possible: (1) there are propagation directions, where the SV-ray is orthogonal to the corresponding wavefront normal, (2) the SV-wave whose ray propagates along the symmetry axis is polarized parallel to the P-wave propagating in the same direction, (3) P-wave singularities, that is, directions where P- and SV -wave phase velocities coincide might exist in acoustic TI media. We also briefly discuss some aspects of wave propagation in low-symmetry acoustic anisotropic models. Extreme anisotropy in those media creates bizarre phase- and group-velocity surfaces that might bring intellectual delight to an anisotropic guru.

  20. Shear surface waves in phononic crystals.

    PubMed

    Kutsenko, A A; Shuvalov, A L

    2013-02-01

    The existence of shear horizontal (SH) surface waves in two-dimensional periodic phononic crystals with an asymmetric depth-dependent profile is theoretically reported. Examples of dispersion spectra with bandgaps for subsonic and supersonic SH surface waves are demonstrated. The link between the effective (quasistatic) speeds of the SH bulk and surface waves is established. Calculation and analysis is based on the integral form of a projector on the subspace of evanescent modes which means no need for their explicit finding. This method can be extended to the vector waves and the three-dimensional case.

  1. Shear wave speed and dispersion measurements using crawling wave chirps.

    PubMed

    Hah, Zaegyoo; Partin, Alexander; Parker, Kevin J

    2014-10-01

    This article demonstrates the measurement of shear wave speed and shear speed dispersion of biomaterials using a chirp signal that launches waves over a range of frequencies. A biomaterial is vibrated by two vibration sources that generate shear waves inside the medium, which is scanned by an ultrasound imaging system. Doppler processing of the acquired signal produces an image of the square of vibration amplitude that shows repetitive constructive and destructive interference patterns called "crawling waves." With a chirp vibration signal, successive Doppler frames are generated from different source frequencies. Collected frames generate a distinctive pattern which is used to calculate the shear speed and shear speed dispersion. A special reciprocal chirp is designed such that the equi-phase lines of a motion slice image are straight lines. Detailed analysis is provided to generate a closed-form solution for calculating the shear wave speed and the dispersion. Also several phantoms and an ex vivo human liver sample are scanned and the estimation results are presented.

  2. High Resolution WENO Simulation of 3D Detonation Waves

    DTIC Science & Technology

    2012-02-27

    pocket behind the detonation front was not observed in their results because the rotating transverse detonation completely consumed the unburned gas. Dou...three-dimensional detonations We add source terms (functions of x, y, z and t) to the PDE system so that the following functions are exact solutions to... detonation rotates counter-clockwise, opposite to that in [48]. It can be seen that, the triple lines and transverse waves collide with the walls, and strong

  3. Anomalously low amplitude of S waves produced by the 3D structures in the lower mantle

    NASA Astrophysics Data System (ADS)

    To, Akiko; Capdeville, Yann; Romanowicz, Barbara

    2016-07-01

    Direct S and Sdiff phases with anomalously low amplitudes are recorded for the earthquakes in Papua New Guinea by seismographs in northern America. According to the prediction by a standard 1D model, the amplitudes are the lowest at stations in southern California, at a distance and azimuth of around 95° and 55°, respectively, from the earthquake. The amplitude anomaly is more prominent at frequencies higher than 0.03 Hz. We checked and ruled out the possibility of the anomalies appearing because of the errors in the focal mechanism used in the reference synthetic waveform calculations. The observed anomaly distribution changes drastically with a relatively small shift in the location of the earthquake. The observations indicate that the amplitude reduction is likely due to the 3D shear velocity (Vs) structure, which deflects the wave energy away from the original ray paths. Moreover, some previous studies suggested that some of the S and Sdiff phases in our dataset are followed by a prominent postcursor and show a large travel time delay, which was explained by placing a large ultra-low velocity zone (ULVZ) located on the core-mantle boundary southwest of Hawaii. In this study, we evaluated the extent of amplitude anomalies that can be explained by the lower mantle structures in the existing models, including the previously proposed ULVZ. In addition, we modified and tested some models and searched for the possible causes of low amplitudes. Full 3D synthetic waveforms were calculated and compared with the observations. Our results show that while the existing models explain the trends of the observed amplitude anomalies, the size of such anomalies remain under-predicted especially at large distances. Adding a low velocity zone, which is spatially larger and has less Vs reduction than ULVZ, on the southwest side of ULVZ, contributes to explain the low amplitudes observed at distances larger than 100° from the earthquake. The newly proposed low velocity zone

  4. 3D Hall MHD Reconnection Dynamics in a Strongly Sheared System

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Rudakov, L. I.

    2002-12-01

    A 3D Hall MHD simulation code (VooDoo) has recently been developed at the Naval Research Laboratory. Recent results have demonstrated that magnetic shock-like structures [Rudakov and Huba, 2002] and a `reconnection wave' [Huba and Rudakov, 2002] can propagate in three dimensional, reversed field plasma layers. In this talk we present preliminary results of a fully 3D magnetic reconnection process in a reversed field plasma that includes a strong guide field, i.e., no magnetic nulls. The initial configuration of the plasma system is as follows. The ambient, reversed magnetic field is in the x-direction with Bx = B0 tanh(y/Ly) where Ly is the scale length of the current sheet. The ambient guide field is in the z-direction with Bz = B0. Perturbation fields δ Bx and δ By are introduced to initiate the reconnection process. This initial configuration is similar to that used in the 2D GEM reconnection study. However, the perturbation fields are localized in the z-direction. We find that the magnetic topology of the system is reconfigured via a process akin to `magnetic flipping' described by Priest and Forbes (1992). A high-density, magnetic flux-rope forms in the center of the plasma sheet. Magnetic flipping occurs between the center of the flux-tube and the boundaries in the x-direction. Associated with this magnetic flipping geometry, the reconnected magnetic field component By reverses sign 3 times in the x-direction, in contrast to only once in the no-guide field case. As in previous Hall MHD reconnection simulation studies, the system evolves asymmetrically along the current. Huba, J.D. and L.I. Rudakov, to be published in Phys. Plasmas, 2002. Priest, E.R. and T.G. Forbes, J. Geophys. Res. 97, 1521, 1992. Rudakov, L.I. and J.D. Huba, Phys. Rev. Lett. 89, 095002, 2002. Research supported by NASA and ONR.

  5. Modeling of flow-induced shear stress applied on 3D cellular scaffolds: Implications for vascular tissue engineering.

    PubMed

    Lesman, Ayelet; Blinder, Yaron; Levenberg, Shulamit

    2010-02-15

    Novel tissue-culture bioreactors employ flow-induced shear stress as a means of mechanical stimulation of cells. We developed a computational fluid dynamics model of the complex three-dimensional (3D) microstructure of a porous scaffold incubated in a direct perfusion bioreactor. Our model was designed to predict high shear-stress values within the physiological range of those naturally sensed by vascular cells (1-10 dyne/cm(2)), and will thereby provide suitable conditions for vascular tissue-engineering experiments. The model also accounts for cellular growth, which was designed as an added cell layer grown on all scaffold walls. Five model variants were designed, with geometric differences corresponding to cell-layer thicknesses of 0, 50, 75, 100, and 125 microm. Four inlet velocities (0.5, 1, 1.5, and 2 cm/s) were applied to each model. Wall shear-stress distribution and overall pressure drop calculations were then used to characterize the relation between flow rate, shear stress, cell-layer thickness, and pressure drop. The simulations showed that cellular growth within 3D scaffolds exposes cells to elevated shear stress, with considerably increasing average values in correlation to cell growth and inflow velocity. Our results provide in-depth analysis of the microdynamic environment of cells cultured within 3D environments, and thus provide advanced control over tissue development in vitro.

  6. Fan-structure waves in shear ruptures

    NASA Astrophysics Data System (ADS)

    Tarasov, Boris

    2016-04-01

    This presentation introduces a recently identified shear rupture mechanism providing a paradoxical feature of hard rocks - the possibility of shear rupture propagation through the highly confined intact rock mass at shear stress levels significantly less than frictional strength. According to the fan-mechanism the shear rupture propagation is associated with consecutive creation of small slabs in the fracture tip which, due to rotation caused by shear displacement of the fracture interfaces, form a fan-structure representing the fracture head. The fan-head combines such unique features as: extremely low shear resistance (below the frictional strength), self-sustaining stress intensification in the rupture tip (providing easy formation of new slabs), and self-unbalancing conditions in the fan-head (making the failure process inevitably spontaneous and violent). An important feature of the fan-mechanism is the fact that for the initial formation of the fan-structure an enhanced local shear stress is required, however, after completion of the fan-structure it can propagate as a dynamic wave through intact rock mass at shear stresses below the frictional strength. Paradoxically low shear strength of pristine rocks provided by the fan-mechanism determines the correspondingly low transient strength of the lithosphere, which favours generation of new earthquake faults in the intact rock mass adjoining pre-existing faults in preference to frictional stick-slip instability along these faults. The new approach reveals an alternative role of pre-existing faults in earthquake activity: they represent local stress concentrates in pristine rock adjoining the fault where special conditions for the fan-mechanism nucleation are created, while further dynamic propagation of the new fault (earthquake) occurs at low field stresses even below the frictional strength.

  7. High speed all optical shear wave imaging optical coherence elastography (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Song, Shaozhen; Hsieh, Bao-Yu; Wei, Wei; Shen, Tueng; O'Donnell, Matthew; Wang, Ruikang K.

    2016-03-01

    Optical Coherence Elastography (OCE) is a non-invasive testing modality that maps the mechanical property of soft tissues with high sensitivity and spatial resolution using phase-sensitive optical coherence tomography (PhS-OCT). Shear wave OCE (SW-OCE) is a leading technique that relies on the speed of propagating shear waves to provide a quantitative elastography. Previous shear wave imaging OCT techniques are based on repeated M-B scans, which have several drawbacks such as long acquisition time and repeated wave stimulations. Recent developments of Fourier domain mode-locked high-speed swept-source OCT system has enabled enough speed to perform KHz B-scan rate OCT imaging. Here we propose ultra-high speed, single shot shear wave imaging to capture single-shot transient shear wave propagation to perform SW-OCE. The frame rate of shear wave imaging is 16 kHz, at A-line rate of ~1.62 MHz, which allows the detection of high-frequency shear wave of up to 8 kHz. The shear wave is generated photothermal-acoustically, by ultra-violet pulsed laser, which requires no contact to OCE subjects, while launching high frequency shear waves that carries rich localized elasticity information. The image acquisition and processing can be performed at video-rate, which enables real-time 3D elastography. SW-OCE measurements are demonstrated on tissue-mimicking phantoms and porcine ocular tissue. This approach opens up the feasibility to perform real-time 3D SW-OCE in clinical applications, to obtain high-resolution localized quantitative measurement of tissue biomechanical property.

  8. Modelling the impulse diffraction field of shear waves in transverse isotropic viscoelastic medium

    NASA Astrophysics Data System (ADS)

    Chatelin, Simon; Gennisson, Jean-Luc; Bernal, Miguel; Tanter, Mickael; Pernot, Mathieu

    2015-05-01

    The generation of shear waves from an ultrasound focused beam has been developed as a major concept for remote palpation using shear wave elastography (SWE). For muscular diagnostic applications, characteristics of the shear wave profile will strongly depend on characteristics of the transducer as well as the orientation of muscular fibers and the tissue viscoelastic properties. The numerical simulation of shear waves generated from a specific probe in an anisotropic viscoelastic medium is a key issue for further developments of SWE in fibrous soft tissues. In this study we propose a complete numerical tool allowing 3D simulation of a shear wave front in anisotropic viscoelastic media. From the description of an ultrasonic transducer, the shear wave source is simulated by using Field’s II software and shear wave propagation described by using the Green’s formalism. Finally, the comparison between simulations and experiments are successively performed for both shear wave velocity and dispersion profile in a transverse isotropic hydrogel phantom, in vivo forearm muscle and in vivo biceps brachii.

  9. Cells in 3D matrices under interstitial flow: effects of extracellular matrix alignment on cell shear stress and drag forces.

    PubMed

    Pedersen, John A; Lichter, Seth; Swartz, Melody A

    2010-03-22

    Interstitial flow is an important regulator of various cell behaviors both in vitro and in vivo, yet the forces that fluid flow imposes on cells embedded in a 3D extracellular matrix (ECM), and the effects of matrix architecture on those forces, are not well understood. Here, we demonstrate how fiber alignment can affect the shear and pressure forces on the cell and ECM. Using computational fluid dynamics simulations, we show that while the solutions of the Brinkman equation accurately estimate the average fluid shear stress and the drag forces on a cell within a 3D fibrous medium, the distribution of shear stress on the cellular surface as well as the peak shear stresses remain intimately related to the pericellular fiber architecture and cannot be estimated using bulk-averaged properties. We demonstrate that perpendicular fiber alignment of the ECM yields lower shear stress and pressure forces on the cells and higher stresses on the ECM, leading to decreased permeability, while parallel fiber alignment leads to higher stresses on cells and increased permeability, as compared to a cubic lattice arrangement. The Spielman-Goren permeability relationships for fibrous media agreed well with CFD simulations of flow with explicitly considered fibers. These results suggest that the experimentally observed active remodeling of ECM fibers by fibroblasts under interstitial flow to a perpendicular alignment could serve to decrease the shear and drag forces on the cell.

  10. Tailored complex 3D vortex lattice structures by perturbed multiples of three-plane waves.

    PubMed

    Xavier, Jolly; Vyas, Sunil; Senthilkumaran, Paramasivam; Joseph, Joby

    2012-04-20

    As three-plane waves are the minimum number required for the formation of vortex-embedded lattice structures by plane wave interference, we present our experimental investigation on the formation of complex 3D photonic vortex lattice structures by a designed superposition of multiples of phase-engineered three-plane waves. The unfolding of the generated complex photonic lattice structures with higher order helical phase is realized by perturbing the superposition of a relatively phase-encoded, axially equidistant multiple of three noncoplanar plane waves. Through a programmable spatial light modulator assisted single step fabrication approach, the unfolded 3D vortex lattice structures are experimentally realized, well matched to our computer simulations. The formation of higher order intertwined helices embedded in these 3D spiraling vortex lattice structures by the superposition of the multiples of phase-engineered three-plane waves interference is also studied.

  11. A 3D staggered-grid finite difference scheme for poroelastic wave equation

    NASA Astrophysics Data System (ADS)

    Zhang, Yijie; Gao, Jinghuai

    2014-10-01

    Three dimensional numerical modeling has been a viable tool for understanding wave propagation in real media. The poroelastic media can better describe the phenomena of hydrocarbon reservoirs than acoustic and elastic media. However, the numerical modeling in 3D poroelastic media demands significantly more computational capacity, including both computational time and memory. In this paper, we present a 3D poroelastic staggered-grid finite difference (SFD) scheme. During the procedure, parallel computing is implemented to reduce the computational time. Parallelization is based on domain decomposition, and communication between processors is performed using message passing interface (MPI). Parallel analysis shows that the parallelized SFD scheme significantly improves the simulation efficiency and 3D decomposition in domain is the most efficient. We also analyze the numerical dispersion and stability condition of the 3D poroelastic SFD method. Numerical results show that the 3D numerical simulation can provide a real description of wave propagation.

  12. Wave propagation analysis of quasi-3D FG nanobeams in thermal environment based on nonlocal strain gradient theory

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Farzad; Barati, Mohammad Reza

    2016-09-01

    This article examines the application of nonlocal strain gradient elasticity theory to wave dispersion behavior of a size-dependent functionally graded (FG) nanobeam in thermal environment. The theory contains two scale parameters corresponding to both nonlocal and strain gradient effects. A quasi-3D sinusoidal beam theory considering shear and normal deformations is employed to present the formulation. Mori-Tanaka micromechanical model is used to describe functionally graded material properties. Hamilton's principle is employed to obtain the governing equations of nanobeam accounting for thickness stretching effect. These equations are solved analytically to find the wave frequencies and phase velocities of the FG nanobeam. It is indicated that wave dispersion behavior of FG nanobeams is significantly affected by temperature rise, nonlocality, length scale parameter and material composition.

  13. Demonstration of Shear Waves, Lamb Waves, and Rayleigh Waves by Mode Conversion.

    ERIC Educational Resources Information Center

    Leung, W. P.

    1980-01-01

    Introduces an experiment that can be demonstrated in the classroom to show that shear waves, Rayleigh waves, and Lamb waves can be easily generated and observed by means of mode conversion. (Author/CS)

  14. AE3D

    SciTech Connect

    Spong, Donald A

    2016-06-20

    AE3D solves for the shear Alfven eigenmodes and eigenfrequencies in a torodal magnetic fusion confinement device. The configuration can be either 2D (e.g. tokamak, reversed field pinch) or 3D (e.g. stellarator, helical reversed field pinch, tokamak with ripple). The equations solved are based on a reduced MHD model and sound wave coupling effects are not currently included.

  15. Seismic waves in 3-D: from mantle asymmetries to reliable seismic hazard assessment

    NASA Astrophysics Data System (ADS)

    Panza, Giuliano F.; Romanelli, Fabio

    2014-10-01

    A global cross-section of the Earth parallel to the tectonic equator (TE) path, the great circle representing the equator of net lithosphere rotation, shows a difference in shear wave velocities between the western and eastern flanks of the three major oceanic rift basins. The low-velocity layer in the upper asthenosphere, at a depth range of 120 to 200 km, is assumed to represent the decoupling between the lithosphere and the underlying mantle. Along the TE-perturbed (TE-pert) path, a ubiquitous LVZ, about 1,000-km-wide and 100-km-thick, occurs in the asthenosphere. The existence of the TE-pert is a necessary prerequisite for the existence of a continuous global flow within the Earth. Ground-shaking scenarios were constructed using a scenario-based method for seismic hazard analysis (NDSHA), using realistic and duly validated synthetic time series, and generating a data bank of several thousands of seismograms that account for source, propagation, and site effects. Accordingly, with basic self-organized criticality concepts, NDSHA permits the integration of available information provided by the most updated seismological, geological, geophysical, and geotechnical databases for the site of interest, as well as advanced physical modeling techniques, to provide a reliable and robust background for the development of a design basis for cultural heritage and civil infrastructures. Estimates of seismic hazard obtained using the NDSHA and standard probabilistic approaches are compared for the Italian territory, and a case-study is discussed. In order to enable a reliable estimation of the ground motion response to an earthquake, three-dimensional velocity models have to be considered, resulting in a new, very efficient, analytical procedure for computing the broadband seismic wave-field in a 3-D anelastic Earth model.

  16. Shear Wave Attenuation in Unconsolidated Laboratory Sediments.

    DTIC Science & Technology

    1983-06-01

    pressure) exponent of one-fourth for prediction of shear wave velocities in sands. This recommendation is based upon both in situ and laboratory...measurements. However, as we have seen from the data presented, there is consider- able scatter in the pressure exponent with values varying from...standard deviation of 0.98. Hamilton 5 4 takes % . -. ... .... . ...... .. ............ ...... 21 exception to this frequency exponent , pointing out

  17. Waves in Turbulent Stably Stratified Shear Flow

    NASA Technical Reports Server (NTRS)

    Jacobitz, F. G.; Rogers, M. M.; Ferziger, J. H.; Parks, John W. (Technical Monitor)

    2002-01-01

    Two approaches for the identification of internal gravity waves in sheared and unsheared homogeneous stratified turbulence are investigated. First, the phase angle between the vertical velocity and density fluctuations is considered. It was found, however, that a continuous distribution of the phase angle is present in weakly and strongly stratified flow. Second, a projection onto the solution of the linearized inviscid equations of motion of unsheared stratified flow is investigated. It was found that a solution of the fully nonlinear viscous Navier-Stokes equations can be represented by the linearized inviscid solution. The projection yields a decomposition into vertical wave modes and horizontal vortical modes.

  18. Horizontal Shear Wave Imaging of Large Optics

    SciTech Connect

    Quarry, M J

    2007-09-05

    When complete the National Ignition Facility (NIF) will be the world's largest and most energetic laser and will be capable of achieving for the first time fusion ignition in the laboratory. Detecting optics features within the laser beamlines and sizing them at diameters of 0.1 mm to 10 mm allows timely decisions concerning refurbishment and will help with the routine operation of the system. Horizontally polarized shear waves at 10 MHz were shown to accurately detect, locate, and size features created by laser operations from 0.5 mm to 8 mm by placing sensors at the edge of the optic. The shear wave technique utilizes highly directed beams. The outer edge of an optic can be covered with shear wave transducers on four sides. Each transducer sends a pulse into the optic and any damage reflects the pulse back to the transmitter. The transducers are multiplexed, and the collected time waveforms are enveloped and replicated across the width of the element. Multiplying the data sets from four directions produces a map of reflected amplitude to the fourth power, which images the surface of the optic. Surface area can be measured directly from the image, and maximum depth was shown to be correlated to maximum amplitude of the reflected waveform.

  19. 3D Modeling of Ultrasonic Wave Interaction with Disbonds and Weak Bonds

    NASA Technical Reports Server (NTRS)

    Leckey, C.; Hinders, M.

    2011-01-01

    Ultrasonic techniques, such as the use of guided waves, can be ideal for finding damage in the plate and pipe-like structures used in aerospace applications. However, the interaction of waves with real flaw types and geometries can lead to experimental signals that are difficult to interpret. 3-dimensional (3D) elastic wave simulations can be a powerful tool in understanding the complicated wave scattering involved in flaw detection and for optimizing experimental techniques. We have developed and implemented parallel 3D elastodynamic finite integration technique (3D EFIT) code to investigate Lamb wave scattering from realistic flaws. This paper discusses simulation results for an aluminum-aluminum diffusion disbond and an aluminum-epoxy disbond and compares results from the disbond case to the common artificial flaw type of a flat-bottom hole. The paper also discusses the potential for extending the 3D EFIT equations to incorporate physics-based weak bond models for simulating wave scattering from weak adhesive bonds.

  20. Efficient global wave propagation adapted to 3-D structural complexity: a pseudospectral/spectral-element approach

    NASA Astrophysics Data System (ADS)

    Leng, Kuangdai; Nissen-Meyer, Tarje; van Driel, Martin

    2016-12-01

    We present a new, computationally efficient numerical method to simulate global seismic wave propagation in realistic 3-D Earth models. We characterize the azimuthal dependence of 3-D wavefields in terms of Fourier series, such that the 3-D equations of motion reduce to an algebraic system of coupled 2-D meridian equations, which is then solved by a 2-D spectral element method (SEM). Computational efficiency of such a hybrid method stems from lateral smoothness of 3-D Earth models and axial singularity of seismic point sources, which jointly confine the Fourier modes of wavefields to a few lower orders. We show novel benchmarks for global wave solutions in 3-D structures between our method and an independent, fully discretized 3-D SEM with remarkable agreement. Performance comparisons are carried out on three state-of-the-art tomography models, with seismic period ranging from 34 s down to 11 s. It turns out that our method has run up to two orders of magnitude faster than the 3-D SEM, featured by a computational advantage expanding with seismic frequency.

  1. FGG-NUFFT-Based Method for Near-Field 3-D Imaging Using Millimeter Waves

    PubMed Central

    Kan, Yingzhi; Zhu, Yongfeng; Tang, Liang; Fu, Qiang; Pei, Hucheng

    2016-01-01

    In this paper, to deal with the concealed target detection problem, an accurate and efficient algorithm for near-field millimeter wave three-dimensional (3-D) imaging is proposed that uses a two-dimensional (2-D) plane antenna array. First, a two-dimensional fast Fourier transform (FFT) is performed on the scattered data along the antenna array plane. Then, a phase shift is performed to compensate for the spherical wave effect. Finally, fast Gaussian gridding based nonuniform FFT (FGG-NUFFT) combined with 2-D inverse FFT (IFFT) is performed on the nonuniform 3-D spatial spectrum in the frequency wavenumber domain to achieve 3-D imaging. The conventional method for near-field 3-D imaging uses Stolt interpolation to obtain uniform spatial spectrum samples and performs 3-D IFFT to reconstruct a 3-D image. Compared with the conventional method, our FGG-NUFFT based method is comparable in both efficiency and accuracy in the full sampled case and can obtain more accurate images with less clutter and fewer noisy artifacts in the down-sampled case, which are good properties for practical applications. Both simulation and experimental results demonstrate that the FGG-NUFFT-based near-field 3-D imaging algorithm can have better imaging performance than the conventional method for down-sampled measurements. PMID:27657066

  2. FGG-NUFFT-Based Method for Near-Field 3-D Imaging Using Millimeter Waves.

    PubMed

    Kan, Yingzhi; Zhu, Yongfeng; Tang, Liang; Fu, Qiang; Pei, Hucheng

    2016-09-19

    In this paper, to deal with the concealed target detection problem, an accurate and efficient algorithm for near-field millimeter wave three-dimensional (3-D) imaging is proposed that uses a two-dimensional (2-D) plane antenna array. First, a two-dimensional fast Fourier transform (FFT) is performed on the scattered data along the antenna array plane. Then, a phase shift is performed to compensate for the spherical wave effect. Finally, fast Gaussian gridding based nonuniform FFT (FGG-NUFFT) combined with 2-D inverse FFT (IFFT) is performed on the nonuniform 3-D spatial spectrum in the frequency wavenumber domain to achieve 3-D imaging. The conventional method for near-field 3-D imaging uses Stolt interpolation to obtain uniform spatial spectrum samples and performs 3-D IFFT to reconstruct a 3-D image. Compared with the conventional method, our FGG-NUFFT based method is comparable in both efficiency and accuracy in the full sampled case and can obtain more accurate images with less clutter and fewer noisy artifacts in the down-sampled case, which are good properties for practical applications. Both simulation and experimental results demonstrate that the FGG-NUFFT-based near-field 3-D imaging algorithm can have better imaging performance than the conventional method for down-sampled measurements.

  3. Numerical Investigation of 3D multichannel analysis of surface wave method

    NASA Astrophysics Data System (ADS)

    Wang, Limin; Xu, Yixian; Luo, Yinhe

    2015-08-01

    Multichannel analysis of surface wave (MASW) method is an efficient tool to obtain near-surface S-wave velocity, and it has gained popularity in engineering practice. Up to now, most examples of using the MASW technique are focused on 2D models or data from a 1D linear receiver spread. We propose a 3D MASW scheme. A finite-difference (FD) method is used to investigate the method using linear and fan-shaped receiver spreads. Results show that the 3D topography strongly affects propagation of Rayleigh waves. The energy concentration of dispersion image is distorted and bifurcated because of the influence of free-surface topography. These effects are reduced with the 3D MASW method. Lastly we investigate the relation between the array size and the resolution of dispersion measurement.

  4. Plane shear flows of frictionless spheres: Kinetic theory and 3D soft-sphere discrete element method simulations

    SciTech Connect

    Vescovi, D.; Berzi, D.; Richard, P.

    2014-05-15

    We use existing 3D Discrete Element simulations of simple shear flows of spheres to evaluate the radial distribution function at contact that enables kinetic theory to correctly predict the pressure and the shear stress, for different values of the collisional coefficient of restitution. Then, we perform 3D Discrete Element simulations of plane flows of frictionless, inelastic spheres, sheared between walls made bumpy by gluing particles in a regular array, at fixed average volume fraction and distance between the walls. The results of the numerical simulations are used to derive boundary conditions appropriated in the cases of large and small bumpiness. Those boundary conditions are, then, employed to numerically integrate the differential equations of Extended Kinetic Theory, where the breaking of the molecular chaos assumption at volume fraction larger than 0.49 is taken into account in the expression of the dissipation rate. We show that the Extended Kinetic Theory is in very good agreement with the numerical simulations, even for coefficients of restitution as low as 0.50. When the bumpiness is increased, we observe that some of the flowing particles are stuck in the gaps between the wall spheres. As a consequence, the walls are more dissipative than expected, and the flows resemble simple shear flows, i.e., flows of rather constant volume fraction and granular temperature.

  5. Shear waves in inhomogeneous, compressible fluids in a gravity field.

    PubMed

    Godin, Oleg A

    2014-03-01

    While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. These shear waves are described by an exact analytic solution of linearized hydrodynamics equations in inhomogeneous, quiescent, inviscid, compressible fluids with piecewise continuous parameters in a uniform gravity field. It is demonstrated that the shear acoustic-gravity waves also can be supported by moving fluids as well as quiescent, viscous fluids with and without thermal conductivity. Excitation of a shear-wave normal mode by a point source and the normal mode distortion in realistic environmental models are considered. The shear acoustic-gravity waves are likely to play a significant role in coupling wave processes in the ocean and atmosphere.

  6. Extensions of 1d Bgk Electron Solitary Wave Solutions To 3d Magnetized and Unmagnetized Plasmas

    NASA Astrophysics Data System (ADS)

    Chen, Li-Jen; Parks, George K.

    This paper will compare the key results for BGK electron solitary waves in 3D mag- netized and unmagnetized plasmas. For 3D magnetized plasmas with highly magnetic field-aligned electrons, our results predict that the parallel widths of the solitary waves can be smaller than one Debye length, the solitary waves can be large scale features of the magnetosphere, and the parallel width-amplitude relation has a dependence on the perpendicular size. We can thus obtain an estimate on the typical perpendicular size of the observed solitary waves assuming a series of consecutive solitary waves are in the same flux tude with a particular perpendicular span. In 3D unmagnetized plasma systems such as the neutral sheet and magnetic reconnection sites, our theory indi- cates that although mathematical solutions can be constructed as the time-stationary solutions for the nonlinear Vlasov-Poisson equations, there does not exist a param- eter range for the solutions to be physical. We conclude that single-humped solitary potential pulses cannot be self-consistently supported by charged particles in 3D un- magnetized plasmas.

  7. 3-Dimensional shear wave elastography of breast lesions

    PubMed Central

    Chen, Ya-ling; Chang, Cai; Zeng, Wei; Wang, Fen; Chen, Jia-jian; Qu, Ning

    2016-01-01

    Abstract Color patterns of 3-dimensional (3D) shear wave elastography (SWE) is a promising method in differentiating tumoral nodules recently. This study was to evaluate the diagnostic accuracy of color patterns of 3D SWE in breast lesions, with special emphasis on coronal planes. A total of 198 consecutive women with 198 breast lesions (125 malignant and 73 benign) were included, who underwent conventional ultrasound (US), 3D B-mode, and 3D SWE before surgical excision. SWE color patterns of Views A (transverse), T (sagittal), and C (coronal) were determined. Sensitivity, specificity, and the area under the receiver operating characteristic curve (AUC) were calculated. Distribution of SWE color patterns was significantly different between malignant and benign lesions (P = 0.001). In malignant lesions, “Stiff Rim” was significantly more frequent in View C (crater sign, 60.8%) than in View A (51.2%, P = 0.013) and View T (54.1%, P = 0.035). AUC for combination of “Crater Sign” and conventional US was significantly higher than View A (0.929 vs 0.902, P = 0.004) and View T (0.929 vs 0.907, P = 0.009), and specificity significantly increased (90.4% vs 78.1%, P = 0.013) without significant change in sensitivity (85.6% vs 88.0%, P = 0.664) as compared with conventional US. In conclusion, combination of conventional US with 3D SWE color patterns significantly increased diagnostic accuracy, with “Crater Sign” in coronal plane of the highest value. PMID:27684820

  8. Numerical simulations of full-wave fields and analysis of channel wave characteristics in 3-D coal mine roadway models

    NASA Astrophysics Data System (ADS)

    Yang, Si-Tong; Wei, Jiu-Chuan; Cheng, Jiu-Long; Shi, Long-Qing; Wen, Zhi-Jie

    2016-12-01

    Currently, numerical simulations of seismic channel waves for the advance detection of geological structures in coal mine roadways focus mainly on modeling twodimensional wave fields and therefore cannot accurately simulate three-dimensional (3-D) full-wave fields or seismic records in a full-space observation system. In this study, we use the first-order velocity-stress staggered-grid finite difference algorithm to simulate 3-D full-wave fields with P-wave sources in front of coal mine roadways. We determine the three components of velocity V x, V y, and V z for the same node in 3-D staggered-grid finite difference models by calculating the average value of V y, and V z of the nodes around the same node. We ascertain the wave patterns and their propagation characteristics in both symmetrical and asymmetric coal mine roadway models. Our simulation results indicate that the Rayleigh channel wave is stronger than the Love channel wave in front of the roadway face. The reflected Rayleigh waves from the roadway face are concentrated in the coal seam, release less energy to the roof and floor, and propagate for a longer distance. There are surface waves and refraction head waves around the roadway. In the seismic records, the Rayleigh wave energy is stronger than that of the Love channel wave along coal walls of the roadway, and the interference of the head waves and surface waves with the Rayleigh channel wave is weaker than with the Love channel wave. It is thus difficult to identify the Love channel wave in the seismic records. Increasing the depth of the receivers in the coal walls can effectively weaken the interference of surface waves with the Rayleigh channel wave, but cannot weaken the interference of surface waves with the Love channel wave. Our research results also suggest that the Love channel wave, which is often used to detect geological structures in coal mine stopes, is not suitable for detecting geological structures in front of coal mine roadways

  9. Efficient methods to model the scattering of ultrasonic guided waves in 3D

    NASA Astrophysics Data System (ADS)

    Moreau, L.; Velichko, A.; Wilcox, P. D.

    2010-03-01

    The propagation of ultrasonic guided waves and their interaction with a defect is of interest to the nondestructive testing community. There is no general solution to the scattering problem and it is still an ongoing research topic. Due to the complexity of guided wave scattering problems, most existing models are related to the 2D case. However, thanks to the increase in computer calculation power, specific 3D problems can also be studied, with the help of numerical or semi-analytical methods. This paper describes two efficient methods aimed at modeling 3D scattering problems. The first method is the use of the Huygens' principle to reduce the size of finite element models. This principle allows the area of interest to be restricted to the very near field of the defect, for both the generation of the incident field and the modal decomposition of the scattered field. The second method consists of separating the 3D problem into two 2D problems for which the solutions are calculated and used to approximate the 3D solution. This can be used at low frequency-thickness products, where Lamb waves have a similar behavior to bulk waves. These two methods are presented briefly and compared on simple scattering cases.

  10. Moving past normal force: capturing and classifying shear motion using 3D sensors.

    PubMed

    Kwan, Calvin; Salud, Lawrence; Ononye, Chiagozie; Zhao, Shenshen; Pugh, Carla

    2012-01-01

    In our previous research, we used clinical breast examination models instrumented with direct (normal) force sensors for training and assessment. A weakness of the normal force sensors is the ability to delineate, in detail, all of the performance measures we wish to understand. This study incorporated the use of newly developed shear force sensors to extend a framework for quantifying hands-on performance.

  11. From supersonic shear wave imaging to full-field optical coherence shear wave elastography

    NASA Astrophysics Data System (ADS)

    Nahas, Amir; Tanter, Mickaël; Nguyen, Thu-Mai; Chassot, Jean-Marie; Fink, Mathias; Claude Boccara, A.

    2013-12-01

    Elasticity maps of tissue have proved to be particularly useful in providing complementary contrast to ultrasonic imaging, e.g., for cancer diagnosis at the millimeter scale. Optical coherence tomography (OCT) offers an endogenous contrast based on singly backscattered optical waves. Adding complementary contrast to OCT images by recording elasticity maps could also be valuable in improving OCT-based diagnosis at the microscopic scale. Static elastography has been successfully coupled with full-field OCT (FF-OCT) in order to realize both micrometer-scale sectioning and elasticity maps. Nevertheless, static elastography presents a number of drawbacks, mainly when stiffness quantification is required. Here, we describe the combination of two methods: transient elastography, based on speed measurements of shear waves induced by ultrasonic radiation forces, and FF-OCT, an en face OCT approach using an incoherent light source. The use of an ultrafast ultrasonic scanner and an ultrafast camera working at 10,000 to 30,000 images/s made it possible to follow shear wave propagation with both modalities. As expected, FF-OCT is found to be much more sensitive than ultrafast ultrasound to tiny shear vibrations (a few nanometers and micrometers, respectively). Stiffness assessed in gel phantoms and an ex vivo rat brain by FF-OCT is found to be in good agreement with ultrasound shear wave elastography.

  12. From supersonic shear wave imaging to full-field optical coherence shear wave elastography.

    PubMed

    Nahas, Amir; Tanter, Mickaël; Nguyen, Thu-Mai; Chassot, Jean-Marie; Fink, Mathias; Claude Boccara, A

    2013-12-01

    Elasticity maps of tissue have proved to be particularly useful in providing complementary contrast to ultrasonic imaging, e.g., for cancer diagnosis at the millimeter scale. Optical coherence tomography (OCT) offers an endogenous contrast based on singly backscattered optical waves. Adding complementary contrast to OCT images by recording elasticity maps could also be valuable in improving OCT-based diagnosis at the microscopic scale. Static elastography has been successfully coupled with full-field OCT (FF-OCT) in order to realize both micrometer-scale sectioning and elasticity maps. Nevertheless, static elastography presents a number of drawbacks, mainly when stiffness quantification is required. Here, we describe the combination of two methods: transient elastography, based on speed measurements of shear waves induced by ultrasonic radiation forces, and FF-OCT, an en face OCT approach using an incoherent light source. The use of an ultrafast ultrasonic scanner and an ultrafast camera working at 10,000 to 30,000 images/s made it possible to follow shear wave propagation with both modalities. As expected, FF-OCT is found to be much more sensitive than ultrafast ultrasound to tiny shear vibrations (a few nanometers and micrometers, respectively). Stiffness assessed in gel phantoms and an ex vivo rat brain by FF-OCT is found to be in good agreement with ultrasound shear wave elastography.

  13. Shear wave elastography with a new reliability indicator.

    PubMed

    Dietrich, Christoph F; Dong, Yi

    2016-09-01

    Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

  14. A unifying fractional wave equation for compressional and shear waves.

    PubMed

    Holm, Sverre; Sinkus, Ralph

    2010-01-01

    This study has been motivated by the observed difference in the range of the power-law attenuation exponent for compressional and shear waves. Usually compressional attenuation increases with frequency to a power between 1 and 2, while shear wave attenuation often is described with powers less than 1. Another motivation is the apparent lack of partial differential equations with desirable properties such as causality that describe such wave propagation. Starting with a constitutive equation which is a generalized Hooke's law with a loss term containing a fractional derivative, one can derive a causal fractional wave equation previously given by Caputo [Geophys J. R. Astron. Soc. 13, 529-539 (1967)] and Wismer [J. Acoust. Soc. Am. 120, 3493-3502 (2006)]. In the low omegatau (low-frequency) case, this equation has an attenuation with a power-law in the range from 1 to 2. This is consistent with, e.g., attenuation in tissue. In the often neglected high omegatau (high-frequency) case, it describes attenuation with a power-law between 0 and 1, consistent with what is observed in, e.g., dynamic elastography. Thus a unifying wave equation derived properly from constitutive equations can describe both cases.

  15. Surface Acoustic Waves (SAW)-Based Biosensing for Quantification of Cell Growth in 2D and 3D Cultures

    PubMed Central

    Wang, Tao; Green, Ryan; Nair, Rajesh Ramakrishnan; Howell, Mark; Mohapatra, Subhra; Guldiken, Rasim; Mohapatra, Shyam Sundar

    2015-01-01

    Detection and quantification of cell viability and growth in two-dimensional (2D) and three-dimensional (3D) cell cultures commonly involve harvesting of cells and therefore requires a parallel set-up of several replicates for time-lapse or dose–response studies. Thus, developing a non-invasive and touch-free detection of cell growth in longitudinal studies of 3D tumor spheroid cultures or of stem cell regeneration remains a major unmet need. Since surface acoustic waves (SAWs) permit mass loading-based biosensing and have been touted due to their many advantages including low cost, small size and ease of assembly, we examined the potential of SAW-biosensing to detect and quantify cell growth. Herein, we demonstrate that a shear horizontal-surface acoustic waves (SH-SAW) device comprising two pairs of resonators consisting of interdigital transducers and reflecting fingers can be used to quantify mass loading by the cells in suspension as well as within a 3D cell culture platform. A 3D COMSOL model was built to simulate the mass loading response of increasing concentrations of cells in suspension in the polydimethylsiloxane (PDMS) well in order to predict the characteristics and optimize the design of the SH-SAW biosensor. The simulated relative frequency shift from the two oscillatory circuit systems (one of which functions as control) were found to be concordant to experimental data generated with RAW264.7 macrophage and A549 cancer cells. In addition, results showed that SAW measurements per se did not affect viability of cells. Further, SH-SAW biosensing was applied to A549 cells cultured on a 3D electrospun nanofiber scaffold that generate tumor spheroids (tumoroids) and the results showed the device's ability to detect changes in tumor spheroid growth over the course of eight days. Taken together, these results demonstrate the use of SH-SAW device for detection and quantification of cell growth changes over time in 2D suspension cultures and in 3D cell

  16. Surface Acoustic Waves (SAW)-Based Biosensing for Quantification of Cell Growth in 2D and 3D Cultures.

    PubMed

    Wang, Tao; Green, Ryan; Nair, Rajesh Ramakrishnan; Howell, Mark; Mohapatra, Subhra; Guldiken, Rasim; Mohapatra, Shyam Sundar

    2015-12-19

    Detection and quantification of cell viability and growth in two-dimensional (2D) and three-dimensional (3D) cell cultures commonly involve harvesting of cells and therefore requires a parallel set-up of several replicates for time-lapse or dose-response studies. Thus, developing a non-invasive and touch-free detection of cell growth in longitudinal studies of 3D tumor spheroid cultures or of stem cell regeneration remains a major unmet need. Since surface acoustic waves (SAWs) permit mass loading-based biosensing and have been touted due to their many advantages including low cost, small size and ease of assembly, we examined the potential of SAW-biosensing to detect and quantify cell growth. Herein, we demonstrate that a shear horizontal-surface acoustic waves (SH-SAW) device comprising two pairs of resonators consisting of interdigital transducers and reflecting fingers can be used to quantify mass loading by the cells in suspension as well as within a 3D cell culture platform. A 3D COMSOL model was built to simulate the mass loading response of increasing concentrations of cells in suspension in the polydimethylsiloxane (PDMS) well in order to predict the characteristics and optimize the design of the SH-SAW biosensor. The simulated relative frequency shift from the two oscillatory circuit systems (one of which functions as control) were found to be concordant to experimental data generated with RAW264.7 macrophage and A549 cancer cells. In addition, results showed that SAW measurements per se did not affect viability of cells. Further, SH-SAW biosensing was applied to A549 cells cultured on a 3D electrospun nanofiber scaffold that generate tumor spheroids (tumoroids) and the results showed the device's ability to detect changes in tumor spheroid growth over the course of eight days. Taken together, these results demonstrate the use of SH-SAW device for detection and quantification of cell growth changes over time in 2D suspension cultures and in 3D cell

  17. Standing shear waves in anisotropic viscoelastic media

    NASA Astrophysics Data System (ADS)

    Krit, T.; Golubkova, I.; Andreev, V.

    2015-10-01

    We studied standing shear waves in anisotropic resonator represented by a rectangular parallelepiped (layer) fixed without slipping between two wooden plates of finite mass. The viscoelastic layer with edges of 70 mm × 40 mm × 15 mm was made of a rubber-like polymer plastisol with rubber bands inside. The bands were placed vertical between the top and the bottom plate. Mechanical properties of the plastisol itself were carefully measured previously. It was found that plastisol shows a cubic nonlinear behavior, i.e. the stress-strain curve could be represented as: σ = μɛ + βμɛ3, where ɛ stands for shear strain and σ is an applied shear stress. The value of shear modulus μ depends on frequency and was found to be several kilopascals which is common for such soft solids. Nonlinear parameter β is frequency dependent too and varies in range from tenths to unity at 1-100 Hz frequency range, decreasing with frequency growth. Stretching the rubber bands inside the layer leads to change of elastic properties in resonator. Such effect could be noticed due to frequency response of the resonator. The numerical model of the resonator was based on finite elements method (FEM) and performed in MatLab. The resonator was cut in hundreds of right triangular prisms. Each prism was provided with viscoelastic properties of the layer except for the top prisms provided with the wooden plate properties and the prisms at the site of the rubber bands provided with the rubber properties. The boundary conditions on each prism satisfied the requirements that resonator is inseparable and all its boundaries but bottom are free. The bottom boundary was set to move horizontally with constant acceleration amplitude. It was shown numerically that the resonator shows anisotropic behavior expressed in different frequency response to oscillations applied to a bottom boundary in different directions.

  18. Origin of crustal anisotropy: Shear wave splitting studies in Japan

    SciTech Connect

    Kaneshima, Satoshi )

    1990-07-10

    Shear wave splitting manifested as leading shear wave polarization, that is, parallel alignment of leading shear wave particle motions from a variety of sources, has been observed at a number of seismograph stations in Japan. Detected on shear wave seismograms from crustal earthquakes over a wide range of source zones and source-receiver azimuths, the shear wave splitting can be attributed to crustal anisotropy. This paper discusses the relation between leading shear wave polarization directions and tectonic features of Japan. To explain the observed shear wave splitting, the author proposes that at least three phenomena should be taken into account: stress-induced microcracks primarily aligned in vertical or subvertical planes; cracks or fractures in the vicinity of active faults having their orientation parallel to the fault planes; and intrinsic rock anisotropy resulting from preferred orientation of minerals. Travel time differences between leading and slower split shear waves from crustal and upper mantle earthquakes analyzed for about one third of the stations suggest that the crustal anisotropy which causes the observed shear wave splitting may be limited to the upper 15-25 km. This implies that the density of nonhorizontally aligned cracks or fractures below 15-25 km and into the upper mantle is much smaller than that in the crust above 15-25 km.

  19. Shear Wave Splitting Beneath the Galapagos Archipelago

    NASA Astrophysics Data System (ADS)

    Fontaine, F. R.; Burkett, P. G.; Hooft, E. E.; Toomey, D. R.; Solomon, S. C.; Silver, P. G.

    2004-12-01

    We report measurements of teleseismic shear wave splitting in the Galápagos Archipelago. The inferred lateral variations in azimuthal anisotropy allow us to examine the dynamics of an evolving hotspot-ridge system. The data are from SKS and SKKS phases, as well as S waves from deep sources, recorded by a relatively dense network of 10 portable broadband seismometers deployed from 1999 to 2003 for the IGUANA (Imaging Galápagos Upwelling and Neotectonics of the Archipelago) experiment and from the GSN broadband station in Santa Cruz (PAYG). We find a delay time between fast and slow shear waves of 0.4 to 0.9 s and fast polarization directions of N85-90° E beneath five stations at the leading and southern edge of the archipelago. Despite clear seismic signals, we did not find any anisotropy at the six stations located in the interior of the archipelago. For those stations that show shear wave splitting, there is an increase in the delay time toward the expected location of the Galápagos hotspot at the western edge of the archipelago. With the exception of Española, fast polarization directions (N85-90° E) are close to the current direction of absolute plate motion of the overlying Nazca plate (N91° E). The lack of azimuthal anisotropy in the interior of the archipelago is interpreted as an absence of strongly oriented mantle fabric beneath these stations. The apparent isotropy in this dynamic region, where we expect considerable mantle strain, is surprising. It is not likely that the olivine a-axis is oriented vertically beneath the interior of the archipelago as the Galápagos plume is thought to lie at the western edge. It is also unlikely that there are two layers of perpendicularly-oriented anisotropy which are solely confined to the center of the archipelago. However, there appears to be some correlation between the region of apparent isotropy and a zone of anomalously low upper mantle velocities imaged beneath Santiago and Marchena from surface waves by

  20. Importance of a 3D forward modeling tool for surface wave analysis methods

    NASA Astrophysics Data System (ADS)

    Pageot, Damien; Le Feuvre, Mathieu; Donatienne, Leparoux; Philippe, Côte; Yann, Capdeville

    2016-04-01

    Since a few years, seismic surface waves analysis methods (SWM) have been widely developed and tested in the context of subsurface characterization and have demonstrated their effectiveness for sounding and monitoring purposes, e.g., high-resolution tomography of the principal geological units of California or real time monitoring of the Piton de la Fournaise volcano. Historically, these methods are mostly developed under the assumption of semi-infinite 1D layered medium without topography. The forward modeling is generally based on Thomson-Haskell matrix based modeling algorithm and the inversion is driven by Monte-Carlo sampling. Given their efficiency, SWM have been transfered to several scale of which civil engineering structures in order to, e.g., determine the so-called V s30 parameter or assess other critical constructional parameters in pavement engineering. However, at this scale, many structures may often exhibit 3D surface variations which drastically limit the efficiency of SWM application. Indeed, even in the case of an homogeneous structure, 3D geometry can bias the dispersion diagram of Rayleigh waves up to obtain discontinuous phase velocity curves which drastically impact the 1D mean velocity model obtained from dispersion inversion. Taking advantages of high-performance computing center accessibility and wave propagation modeling algorithm development, it is now possible to consider the use of a 3D elastic forward modeling algorithm instead of Thomson-Haskell method in the SWM inversion process. We use a parallelized 3D elastic modeling code based on the spectral element method which allows to obtain accurate synthetic data with very low numerical dispersion and a reasonable numerical cost. In this study, we choose dike embankments as an illustrative example. We first show that their longitudinal geometry may have a significant effect on dispersion diagrams of Rayleigh waves. Then, we demonstrate the necessity of 3D elastic modeling as a forward

  1. A Novel Method for Dynamic Short-Beam Shear Testing of 3D Woven Composites

    DTIC Science & Technology

    2011-08-11

    Yip MC, Lin JL (1998) Effects of low-energy impact on the fatigue behavior of carbon /epoxy composites. Composites Science and Technology 58(1):1–8 5...Compos- ite Materials 42(20):2111–2122 12. Davis DC, Whelan BD (2012) An experimental study of interlam- inar shear fracture toughness of a nanotube ...delamination toughness of stitched graphite/epoxy textile composites. Composites Science and Technology 57(7):729–737 15. Chen L, Ifju PG, Sankar BV (2001) A

  2. 3D analysis of interaction of Lamb waves with defects in loaded steel plates.

    PubMed

    Kazys, R; Mazeika, L; Barauskas, R; Raisutis, R; Cicenas, V; Demcenko, A

    2006-12-22

    The objective of the research presented here is the investigation of the interaction of guided waves with welds, defects and other non-uniformities in steel plates loaded by liquid. The investigation has been performed using numerical simulation for 2D and 3D cases by the finite differences method, finite element method and measurement of 3D distributions of acoustic fields. Propagation of the S(0) mode in a steel plate and its interaction with non-uniformities was investigated. It was shown that using the measured leaky wave signals in the water loading of the steel plate and by application of signal processing, the 3D ultrasonic field structure inside and outside of the plate can be reconstructed. The presence of leaky wave signals over the defect caused by the mode conversion of Lamb waves has been proved using the numerical modelling and experimental investigations. The developed signal and data processing enables to visualise dynamics of ultrasonic fields over the plate, and also to estimate spatial positions of defects inside the steel plates.

  3. Multi-Channel Optical Coherence Elastography Using Relative and Absolute Shear-Wave Time of Flight

    PubMed Central

    Elyas, Eli; Grimwood, Alex; Erler, Janine T.; Robinson, Simon P.; Cox, Thomas R.; Woods, Daniel; Clowes, Peter; De Luca, Ramona; Marinozzi, Franco; Fromageau, Jérémie; Bamber, Jeffrey C.

    2017-01-01

    Elastography, the imaging of elastic properties of soft tissues, is well developed for macroscopic clinical imaging of soft tissues and can provide useful information about various pathological processes which is complementary to that provided by the original modality. Scaling down of this technique should ply the field of cellular biology with valuable information with regard to elastic properties of cells and their environment. This paper evaluates the potential to develop such a tool by modifying a commercial optical coherence tomography (OCT) device to measure the speed of shear waves propagating in a three-dimensional (3D) medium. A needle, embedded in the gel, was excited to vibrate along its long axis and the displacement as a function of time and distance from the needle associated with the resulting shear waves was detected using four M-mode images acquired simultaneously using a commercial four-channel swept-source OCT system. Shear-wave time of arrival (TOA) was detected by tracking the axial OCT-speckle motion using cross-correlation methods. Shear-wave speed was then calculated from inter-channel differences of TOA for a single burst (the relative TOA method) and compared with the shear-wave speed determined from positional differences of TOA for a single channel over multiple bursts (the absolute TOA method). For homogeneous gels the relative method provided shear-wave speed with acceptable precision and accuracy when judged against the expected linear dependence of shear modulus on gelatine concentration (R2 = 0.95) and ultimate resolution capabilities limited by 184μm inter-channel distance. This overall approach shows promise for its eventual provision as a research tool in cancer cell biology. Further work is required to optimize parameters such as vibration frequency, burst length and amplitude, and to assess the lateral and axial resolutions of this type of device as well as to create 3D elastograms. PMID:28107368

  4. Multi-Channel Optical Coherence Elastography Using Relative and Absolute Shear-Wave Time of Flight.

    PubMed

    Elyas, Eli; Grimwood, Alex; Erler, Janine T; Robinson, Simon P; Cox, Thomas R; Woods, Daniel; Clowes, Peter; De Luca, Ramona; Marinozzi, Franco; Fromageau, Jérémie; Bamber, Jeffrey C

    2017-01-01

    Elastography, the imaging of elastic properties of soft tissues, is well developed for macroscopic clinical imaging of soft tissues and can provide useful information about various pathological processes which is complementary to that provided by the original modality. Scaling down of this technique should ply the field of cellular biology with valuable information with regard to elastic properties of cells and their environment. This paper evaluates the potential to develop such a tool by modifying a commercial optical coherence tomography (OCT) device to measure the speed of shear waves propagating in a three-dimensional (3D) medium. A needle, embedded in the gel, was excited to vibrate along its long axis and the displacement as a function of time and distance from the needle associated with the resulting shear waves was detected using four M-mode images acquired simultaneously using a commercial four-channel swept-source OCT system. Shear-wave time of arrival (TOA) was detected by tracking the axial OCT-speckle motion using cross-correlation methods. Shear-wave speed was then calculated from inter-channel differences of TOA for a single burst (the relative TOA method) and compared with the shear-wave speed determined from positional differences of TOA for a single channel over multiple bursts (the absolute TOA method). For homogeneous gels the relative method provided shear-wave speed with acceptable precision and accuracy when judged against the expected linear dependence of shear modulus on gelatine concentration (R2 = 0.95) and ultimate resolution capabilities limited by 184μm inter-channel distance. This overall approach shows promise for its eventual provision as a research tool in cancer cell biology. Further work is required to optimize parameters such as vibration frequency, burst length and amplitude, and to assess the lateral and axial resolutions of this type of device as well as to create 3D elastograms.

  5. Opportunities for shear energy scaling in bulk acoustic wave resonators.

    PubMed

    Jose, Sumy; Hueting, Raymond J E

    2014-10-01

    An important energy loss contribution in bulk acoustic wave resonators is formed by so-called shear waves, which are transversal waves that propagate vertically through the devices with a horizontal motion. In this work, we report for the first time scaling of the shear-confined spots, i.e., spots containing a high concentration of shear wave displacement, controlled by the frame region width at the edge of the resonator. We also demonstrate a novel methodology to arrive at an optimum frame region width for spurious mode suppression and shear wave confinement. This methodology makes use of dispersion curves obtained from finite-element method (FEM) eigenfrequency simulations for arriving at an optimum frame region width. The frame region optimization is demonstrated for solidly mounted resonators employing several shear wave optimized reflector stacks. Finally, the FEM simulation results are compared with measurements for resonators with Ta2O5/ SiO2 stacks showing suppression of the spurious modes.

  6. Gravitational Wave Signals from 2D and 3D Core Collapse Supernova Explosions

    NASA Astrophysics Data System (ADS)

    Yakunin, Konstantin; Mezzacappa, Anthony; Marronetti, Pedro; Bruenn, Stephen; Hix, W. Raphael; Lentz, Eric J.; Messer, O. E. Bronson; Harris, J. Austin; Endeve, Eirik; Blondin, John

    2016-03-01

    We study two- and three-dimensional (2D and 3D) core-collapse supernovae (CCSN) using our first-principles CCSN simulations performed with the neutrino hydrodynamics code CHIMERA. The following physics is included: Newtonian hydrodynamics with a nuclear equation of state capable of describing matter in both NSE and non-NSE, MGFLD neutrino transport with realistic neutrino interactions, an effective GR gravitational potential, and a nuclear reaction network. Both our 2D and 3D models achieve explosion, which in turn enables us to determine their complete gravitational wave signals. In this talk, we present them, and we analyze the similarities and differences between the 2D and 3D signals.

  7. Non-Newtonian models for molecular viscosity and wall shear stress in a 3D reconstructed human left coronary artery.

    PubMed

    Soulis, Johannes V; Giannoglou, George D; Chatzizisis, Yiannis S; Seralidou, Kypriani V; Parcharidis, George E; Louridas, George E

    2008-01-01

    The capabilities and limitations of various molecular viscosity models, in the left coronary arterial tree, were analyzed via: molecular viscosity, local and global non-Newtonian importance factors, wall shear stress (WSS) and wall shear stress gradient (WSSG). The vessel geometry was acquired using geometrically correct 3D intravascular ultrasound (3D IVUS). Seven non-Newtonian molecular viscosity models, plus the Newtonian one, were compared. The WSS distribution yielded a consistent LCA pattern for nearly all non-Newtonian models. High molecular viscosity, low WSS and low WSSG values occurred at the outer walls of the major bifurcation in proximal LCA regions. The Newtonian blood flow was found to be a good approximation at mid- and high-strain rates. The non-Newtonian Power Law, Generalized Power Law, Carreau and Casson and Modified Cross blood viscosity models gave comparable molecular viscosity, WSS and WSSG values. The Power Law and Walburn-Schneck models over-estimated the non-Newtonian global importance factor I(G) and under-estimated the area averaged WSS and WSSG values. The non-Newtonian Power Law and the Generalized Power Law blood viscosity models were found to approximate the molecular viscosity and WSS calculations in a more satisfactory way.

  8. 3D numerical simulation of the long range propagation of acoustical shock waves through a heterogeneous and moving medium

    SciTech Connect

    Luquet, David; Marchiano, Régis; Coulouvrat, François

    2015-10-28

    Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D

  9. 3D numerical simulation of the long range propagation of acoustical shock waves through a heterogeneous and moving medium

    NASA Astrophysics Data System (ADS)

    Luquet, David; Marchiano, Régis; Coulouvrat, François

    2015-10-01

    Many situations involve the propagation of acoustical shock waves through flows. Natural sources such as lightning, volcano explosions, or meteoroid atmospheric entries, emit loud, low frequency, and impulsive sound that is influenced by atmospheric wind and turbulence. The sonic boom produced by a supersonic aircraft and explosion noises are examples of intense anthropogenic sources in the atmosphere. The Buzz-Saw-Noise produced by turbo-engine fan blades rotating at supersonic speed also propagates in a fast flow within the engine nacelle. Simulating these situations is challenging, given the 3D nature of the problem, the long range propagation distances relative to the central wavelength, the strongly nonlinear behavior of shocks associated to a wide-band spectrum, and finally the key role of the flow motion. With this in view, the so-called FLHOWARD (acronym for FLow and Heterogeneous One-Way Approximation for Resolution of Diffraction) method is presented with three-dimensional applications. A scalar nonlinear wave equation is established in the framework of atmospheric applications, assuming weak heterogeneities and a slow wind. It takes into account diffraction, absorption and relaxation properties of the atmosphere, quadratic nonlinearities including weak shock waves, heterogeneities of the medium in sound speed and density, and presence of a flow (assuming a mean stratified wind and 3D turbulent ? flow fluctuations of smaller amplitude). This equation is solved in the framework of the one-way method. A split-step technique allows the splitting of the non-linear wave equation into simpler equations, each corresponding to a physical effect. Each sub-equation is solved using an analytical method if possible, and finite-differences otherwise. Nonlinear effects are solved in the time domain, and others in the frequency domain. Homogeneous diffraction is handled by means of the angular spectrum method. Ground is assumed perfectly flat and rigid. Due to the 3D

  10. Shear wavelength estimation based on inverse filtering and multiple-point shear wave generation

    NASA Astrophysics Data System (ADS)

    Kitazaki, Tomoaki; Kondo, Kengo; Yamakawa, Makoto; Shiina, Tsuyoshi

    2016-07-01

    Elastography provides important diagnostic information because tissue elasticity is related to pathological conditions. For example, in a mammary gland, higher grade malignancies yield harder tumors. Estimating shear wave speed enables the quantification of tissue elasticity imaging using time-of-flight. However, time-of-flight measurement is based on an assumption about the propagation direction of a shear wave which is highly affected by reflection and refraction, and thus might cause an artifact. An alternative elasticity estimation approach based on shear wavelength was proposed and applied to passive configurations. To determine the elasticity of tissue more quickly and more accurately, we proposed a new method for shear wave elasticity imaging that combines the shear wavelength approach and inverse filtering with multiple shear wave sources induced by acoustic radiation force (ARF). The feasibility of the proposed method was verified using an elasticity phantom with a hard inclusion.

  11. The Vajont disaster: a 3D numerical simulation for the slide and the waves

    NASA Astrophysics Data System (ADS)

    Rubino, Angelo; Androsov, Alexey; Vacondio, Renato; Zanchettin, Davide; Voltzinger, Naum

    2016-04-01

    A very high resolution O(5 m), 3D hydrostatic nonlinear numerical model was used to simulate the dynamics of both the slide and the surface waves produced during the Vajont disaster (north Italy, 1963), one of the major landslide-induced tsunamis ever documented. Different simulated wave phenomena like, e.g., maximum run-up on the opposite shore, maximum height, and water velocity were analyzed and compared with data available in literature, including the results of a fully 3D simulation obtained with a Smoothed Particle Hydrodynamic code. The difference between measured and simulated after-slide bathymetries was calculated and used in an attempt to quantify the relative magnitude and extension of rigid and fluid motion components during the event.

  12. Reverberant shear wave fields and estimation of tissue properties

    NASA Astrophysics Data System (ADS)

    Parker, Kevin J.; Ormachea, Juvenal; Zvietcovich, Fernando; Castaneda, Benjamin

    2017-02-01

    The determination of shear wave speed is an important subject in the field of elastography, since elevated shear wave speeds can be directly linked to increased stiffness of tissues. MRI and ultrasound scanners are frequently used to detect shear waves and a variety of estimators are applied to calculate the underlying shear wave speed. The estimators can be relatively simple if plane wave behavior is assumed with a known direction of propagation. However, multiple reflections from organ boundaries and internal inhomogeneities and mode conversions can create a complicated field in time and space. Thus, we explore the mathematics of multiple component shear wave fields and derive the basic properties, from which efficient estimators can be obtained. We approach this problem from the historic perspective of reverberant fields, a conceptual framework used in architectural acoustics and related fields. The framework can be recast for the alternative case of shear waves in a bounded elastic media, and the expected value of displacement patterns in shear reverberant fields are derived, along with some practical estimators of shear wave speed. These are applied to finite element models and phantoms to illustrate the characteristics of reverberant fields and provide preliminary confirmation of the overall framework.

  13. Full-wave Moment Tensor and Tomographic Inversions Based on 3D Strain Green Tensor

    DTIC Science & Technology

    2010-01-31

    G. Jahnke, Wave propagation in 3D spherical sections: effects of subduction zones , Phys. Earth Planet. Inter., 132, 219-234, 2002. Komastitsch, D...is at scales smaller than the Fresnel zone . For example, a 1-Hz P/Pn wave recorded by a receiver ~1000 km from the source has a Fresnel zone width...approach, Eos Trans. AGU, 89(53), Fall Meet. Suppl., abstract T11E-06 Invited, 2008b. Sigloch, K., N. McQuarrie, G. Nolet, Two-stage subduction

  14. 3D tomographic reconstruction of the internal velocity field of an immiscible drop in a shear flow

    NASA Astrophysics Data System (ADS)

    Kerdraon, Paul; Dalziel, Stuart B.; Goldstein, Raymond E.; Landel, Julien R.; Peaudecerf, Francois J.

    2015-11-01

    We study experimentally the internal flow of a drop attached to a flat substrate and immersed in an immiscible shear flow. Transport inside the drop can play a crucial role in cleaning applications. Internal advection can enhance the mass transfer across the drop surface, thus increasing the cleaning rate. We used microlitre water-glycerol drops on a hydrophobic substrate. The drops were spherical and did not deform significantly under the shear flow. An oil phase of relative viscosity 0.01 to 1 was flowed over the drop. Typical Reynolds numbers inside the drops were of the order of 0.1 to 10. Using confocal microscopy, we performed 3D tomographic reconstruction of the flow field in the drop. The in-plane velocity field was measured using micro-PIV, and the third velocity component was computed from incompressibility. To our knowledge, this study gives the first experimental measurement of the three-dimensional internal velocity field of a drop in a shear flow. Numerical simulations and theoretical models published in the past 30 years predict a toroidal internal recirculation flow, for which the entire surface flows streamwise. However, our measurements reveal a qualitatively different picture with a two-lobed recirculation, featuring two stagnation points at the surface and a reverse surface flow closer to the substrate. This finding appears to be independent of Reynolds number and viscosity ratio in the ranges studied; we conjecture that the observed flow is due to the effect of surfactants at the drop surface.

  15. 3D Modeling of Antenna Driven Slow Waves Excited by Antennas Near the Plasma Edge

    NASA Astrophysics Data System (ADS)

    Smithe, David; Jenkins, Thomas

    2016-10-01

    Prior work with the 3D finite-difference time-domain (FDTD) plasma and sheath model used to model ICRF antennas in fusion plasmas has highlighted the possibility of slow wave excitation at the very low end of the SOL density range, and thus the prudent need for a slow-time evolution model to treat SOL density modifications due to the RF itself. At higher frequency, the DIII-D helicon antenna has much easier access to a parasitic slow wave excitation, and in this case the Faraday screen provides the dominant means of controlling the content of the launched mode, with antenna end-effects remaining a concern. In both cases, the danger is the same, with the slow-wave propagating into a lower-hybrid resonance layer a short distance ( cm) away from the antenna, which would parasitically absorb power, transferring energy to the SOL edge plasma, primarily through electron-neutral collisions. We will present 3D modeling of antennas at both ICRF and helicon frequencies. We've added a slow-time evolution capability for the SOL plasma density to include ponderomotive force driven rarefaction from the strong fields in the vicinity of the antenna, and show initial application to NSTX antenna geometry and plasma configurations. The model is based on a Scalar Ponderomotive Potential method, using self-consistently computed local field amplitudes from the 3D simulation.

  16. Moored Observations of Internal Waves in Luzon Strait: 3-D Structure, Dissipation, and Evolution

    DTIC Science & Technology

    2014-09-30

    the performance of operational and climate models, as well as for understanding local problems such as pollutant dispersal and biological productivity...substantially improves both our understanding and predictive ability of linear internal tides and NLIWs in Luzon Strait and the South China Sea...westward into the northeastern South China Sea (SCS). • To better understand generation and propagation of internal waves in a strongly sheared

  17. Noise and Turbulence Generate 3D Zombie Vortices in Stably Stratified Rotating Shear Flows

    NASA Astrophysics Data System (ADS)

    Pei, Suyang; Marcus, Philip S.; Jiang, Chung-Hsiang; Hassanzadeh, Pedram; Lecoanet, Daniel; Barranco, Joseph A.

    2013-11-01

    We showed previously that a linearly stable shearing, rotating, stably stratified flow has a finite-amplitude instability creating ``zombie vortices'' that self-replicate and fill the domain. Our flows were initialized with perturbations of one or two vortices. Our motivation was to determine whether ``dead zones'' in protoplanetary disks were stable, or whether they could be de-stabilized to produce vortices necessary for the final part of star formation and for planet formation. To be more relevant to astrophysics, we choose the initial conditions to be noise or turbulence with a Kolmogorov spectrum with small kinetic energy and Mach number. In a Kolmogorov spectrum, the largest eddies determine the kinetic energy and Mach number, while the smallest determine the vorticity and Rossby number Ro ≡ ω / f , where ω is the vertical vorticity and f is the Coriolis parameter. The protoplanetary disks (which have large inertial ranges due to their large Reynolds numbers), can have large Rossby numbers, but weak Mach numbers and kinetic energies. It is important to know whether the triggering of the finite-amplitude instability that creates zombie vortices depends on threshold values of Mach number, kinetic energy, or the Rossby number. Here, we show it is the latter.

  18. Piezoelectric shear wave resonator and method of making same

    DOEpatents

    Wang, J.S.; Lakin, K.M.; Landin, A.R.

    1983-10-25

    An acoustic shear wave resonator comprising a piezoelectric film having its C-axis substantially inclined from the film normal such that the shear wave coupling coefficient significantly exceeds the longitudinal wave coupling coefficient, whereby the film is capable of shear wave resonance, and means for exciting said film to resonate. The film is prepared by deposition in a dc planar magnetron sputtering system to which a supplemental electric field is applied. The resonator structure may also include a semiconductor material having a positive temperature coefficient of resonance such that the resonator has a temperature coefficient of resonance approaching 0 ppM//sup 0/C.

  19. Piezoelectric shear wave resonator and method of making same

    DOEpatents

    Wang, J.S.; Lakin, K.M.; Landin, A.R.

    1985-05-20

    An acoustic shear wave resonator comprising a piezoelectric film having its C-axis substantially inclined from the film normal such that the shear wave coupling coefficient significantly exceeds the longitudinal wave coupling coefficient, whereby the film is capable of shear wave resonance, and means for exciting said film to resonate. The film is prepared by deposition in a dc planar magnetron sputtering system to which a supplemental electric field is applied. The resonator structure may also include a semiconductor material having a positive temperature coefficient of resonance such that the resonator has a temperature coefficient of resonance approaching 0 ppM//sup 0/C.

  20. Method of making a piezoelectric shear wave resonator

    DOEpatents

    Wang, Jin S.; Lakin, Kenneth M.; Landin, Allen R.

    1987-02-03

    An acoustic shear wave resonator comprising a piezoelectric film having its C-axis substantially inclined from the film normal such that the shear wave coupling coefficient significantly exceeds the longitudinal wave coupling coefficient, whereby the film is capable of shear wave resonance, and means for exciting said film to resonate. The film is prepared by deposition in a dc planar magnetron sputtering system to which a supplemental electric field is applied. The resonator structure may also include a semiconductor material having a positive temperature coefficient of resonance such that the resonator has a temperature coefficient of resonance approaching 0 ppm/.degree.C.

  1. Piezoelectric shear wave resonator and method of making same

    DOEpatents

    Wang, Jin S.; Lakin, Kenneth M.; Landin, Allen R.

    1988-01-01

    An acoustic shear wave resonator comprising a piezoelectric film having its C-axis substantially inclined from the film normal such that the shear wave coupling coefficient significantly exceeds the longitudinal wave coupling coefficient, whereby the film is capable of shear wave resonance, and means for exciting said film to resonate. The film is prepared by deposition in a dc planar magnetron sputtering system to which a supplemental electric field is applied. The resonator structure may also include a semiconductor material having a positive temperature coefficient of resonance such that the resonator has a temperature coefficient of resonance approaching 0 ppm/.degree.C.

  2. Shear wave splitting survey of Western Tibet

    NASA Astrophysics Data System (ADS)

    Shakhnovich, M.; Levin, V. L.; Cao, Z.

    2011-12-01

    The goal of our study is to investigate the distribution of seismic anisotropy beneath the western part of the Tibetan plateau to better understand the tectonic processes dominating it. We used new data from 29 portable seismic stations in the Western Tibet that operated from 2007 to 2011. The network covered an approximately triangular area between the Karakorum fault (KF) in the south and the Banggong-Nujiang Suture (BNS) in the north, between longitudes of 79.5 and 83.5 east. In our study we used the data covering approximately two and a half years, from July 2007 to December 2009. Ten stations were operating from 2007, and additional 19 were introduced in 2009. We used earthquakes with magnitudes over 5.5, and picked and analyzed 130 well-recorded SKS phases. We employed three different algorithms of shear wave splitting estimation (cross-correlation, minimization of transverse component and an eigenvalue minimization technique) and used agreement in their respective results to assess the relative quality of our measurements. Observations that yielded radical disagreement in results from different algorithms were designated as NULLs. For a subset of NULLs we verified the absence of shear wave birefringence by visual inspection of particle motion. We report a set of 231 nulls and 310 splitting measurements, of which 128 we deem to be good (i.e., three techniques yield consistent results), and 182 are fair (two out of three methods agree). The delay time in good splitting observation varied from as little as 0.3s to 2.2s, with majority of measurements falling below 1 s. Fast polarizations display directional variability at individual observing sites, and also change laterally. We can identify four regions with distinct patterns of splitting. In the area between the KF and the BNS, fast direction of 40-65SE dominates, and most good splitting measurements yield delays ~1s. At most sites here we also see minor changes in fast direction with backazimuth. Two sites

  3. Multiscale modeling of mechanosensing channels on vesicles and cell membranes in 3D constricted flows and shear flows

    NASA Astrophysics Data System (ADS)

    Peng, Zhangli; Pak, On Shun; Young, Yuan-Nan; Liu, Allen; Stone, Howard

    2015-11-01

    We investigate the gating of mechanosensing channels (Mscls) on vesicles and cell membranes under different flow conditions using a multiscale approach. At the cell level (microns), the membrane tension is calculated using a 3D two-component whole-cell membrane model based on dissipative particle dynamics (DPD), including the cortex cytoskeleton and its interactions with the lipid bilayer. At the Mscl level (nanometers), we predict the relation between channel gating and the membrane tension obtained from a cell-level model using a semi-analytical model based on the bilayer hydrophobic mismatch energy. We systematically study the gating of Mscls of vesicles and cell membranes in constricted channel flows and shear flows, and explore the dependence of the gating on flow rate, cell shape and size. The results provide guidance for future experiments in inducing Mscl opening for various purposes such as drug delivery.

  4. Enhancement of USM3D Unstructured Flow Solver for High-Speed High-Temperature Shear Flows

    NASA Technical Reports Server (NTRS)

    Pandya, Mohagna J.; Abdol-Hamid, Khaled S.; Frink, Neal T.

    2009-01-01

    Large temperature and pressure fluctuations have a profound effect on turbulence development in transonic and supersonic jets. For high-speed, high-temperature jet flows, standard turbulence models lack the ability to predict the observed mixing rate of a shear layer. Several proposals to address this deficiency have been advanced in the literature to modify the turbulence transport equations in a variety of ways. In the present study, some of the most proven and simple modifications to two-equation turbulence models have been selected and implemented in NASA's USM3D tetrahedral Navier-Stokes flow solver. The modifications include the addition of compressibility correction and pressure dilatation terms in the turbulence transport equations for high-speed flows, and the addition of a simple modification to the Boussinesq's closure model coefficient for high-temperature jets. The efficacy of the extended models is demonstrated by comparison with experimental data for two supersonic axisymmetric jet test cases at design pressure ratio.

  5. Ultra wide band millimeter wave holographic ``3-D`` imaging of concealed targets on mannequins

    SciTech Connect

    Collins, H.D.; Hall, T.E.; Gribble, R.P.

    1994-08-01

    Ultra wide band (chirp frequency) millimeter wave ``3-D`` holography is a unique technique for imaging concealed targets on human subjects with extremely high lateral and depth resolution. Recent ``3-D`` holographic images of full size mannequins with concealed weapons illustrate the efficacy of this technique for airport security. A chirp frequency (24 GHz to 40 GHz) holographic system was used to construct extremely high resolution images (optical quality) using polyrod antenna in a bi-static configuration using an x-y scanner. Millimeter wave chirp frequency holography can be simply described as a multi-frequency detection and imaging technique where the target`s reflected signals are decomposed into discrete frequency holograms and reconstructed into a single composite ``3-D`` image. The implementation of this technology for security at airports, government installations, etc., will require real-time (video rate) data acquisition and computer image reconstruction of large volumetric data sets. This implies rapid scanning techniques or large, complex ``2-D`` arrays and high speed computing for successful commercialization of this technology.

  6. A global 3-D MHD model of the solar wind with Alfven waves

    NASA Technical Reports Server (NTRS)

    Usmanov, A. V.

    1995-01-01

    A fully three-dimensional solar wind model that incorporates momentum and heat addition from Alfven waves is developed. The proposed model upgrades the previous one by considering self-consistently the total system consisting of Alfven waves propagating outward from the Sun and the mean polytropic solar wind flow. The simulation region extends from the coronal base (1 R(sub s) out to beyond 1 AU. The fully 3-D MHD equations written in spherical coordinates are solved in the frame of reference corotating with the Sun. At the inner boundary, the photospheric magnetic field observations are taken as boundary condition and wave energy influx is prescribed to be proportional to the magnetic field strength. The results of the model application for several time intervals are presented.

  7. 3D P-Wave Velocity Structure of the Deep Galicia Rifted Margin

    NASA Astrophysics Data System (ADS)

    Bayrakci, Gaye; Minshull, Timothy; Davy, Richard; Sawyer, Dale; Klaeschen, Dirk; Papenberg, Cord; Reston, Timothy; Shillington, Donna; Ranero, Cesar

    2015-04-01

    The combined wide-angle reflection-refraction and multi-channel seismic (MCS) experiment, Galicia 3D, was carried out in 2013 at the Galicia rifted margin in the northeast Atlantic Ocean, west of Spain. The main geological features within the 64 by 20 km (1280 km²) 3D box investigated by the survey are the peridotite ridge (PR), the fault bounded, rotated basement blocks and the S reflector, which has been interpreted to be a low angle detachment fault. 44 short period four-component ocean bottom seismometers and 28 ocean bottom hydrophones were deployed in the 3D box. 3D MCS profiles sampling the whole box were acquired with two airgun arrays of 3300 cu.in. fired alternately every 37.5 m. We present the results from 3D first-arrival time tomography that constrains the P-wave velocity in the 3D box, for the entire depth sampled by reflection data. Results are validated by synthetic tests and by the comparison with Galicia 3D MCS lines. The main outcomes are as follows: 1- The 3.5 km/s iso-velocity contour mimics the top of the acoustic basement observed on MCS profiles. Block bounding faults are imaged as velocity contrasts and basement blocks exhibit 3D topographic variations. 2- On the southern profiles, the top of the PR rises up to 5.5 km depth whereas, 20 km northward, its basement expression (at 6.5 km depth) nearly disappears. 3- The 6.5 km/s iso-velocity contour matches the topography of the S reflector where the latter is visible on MCS profiles. Within a depth interval of 0.6 km (in average), velocities beneath the S reflector increase from 6.5 km/s to 7 km/s, which would correspond to a decrease in the degree of serpentinization from ~45 % to ~30 % if these velocity variations are caused solely by variations in hydration. At the intersections between the block bounding normal faults and the S reflector, this decrease happens over a larger depth interval (> 1 km), suggesting that faults act as conduit for the water flow in the upper mantle.

  8. 3D P-Wave Velocity Structure of the Deep Galicia Rifted Margin

    NASA Astrophysics Data System (ADS)

    Bayrakci, G.; Minshull, T. A.; Davy, R. G.; Sawyer, D. S.; Klaeschen, D.; Papenberg, C. A.; Reston, T. J.; Shillington, D. J.; Ranero, C. R.

    2014-12-01

    The combined wide-angle reflection-refraction and multi-channel seismic (MCS) experiment, Galicia 3D, was carried out in 2013 at the Galicia rifted margin in the northeast Atlantic Ocean, west of Spain. The main geological features within the 64 by 20 km (1280 km²) 3D box investigated by the survey are the peridotite ridge (PR), the fault bounded, rotated basement blocks and the S reflector, which has been interpreted to be a low angle detachment fault. 44 short period four-component ocean bottom seismometers and 28 ocean bottom hydrophones were deployed in the 3D box. 3D MCS profiles sampling the whole box were acquired with two airgun arrays of 3300 cu.in. fired alternately every 37.5 m. We present the results from 3D first-arrival time tomography that constrains the P-wave velocity in the 3D box, for the entire depth sampled by reflection data. Results are validated by synthetic tests and by the comparison with Galicia 3D MCS lines. The main outcomes are as follows: 1- The 3.5 km/s iso-velocity contour mimics the top of the acoustic basement observed on MCS profiles. Block bounding faults are imaged as velocity contrasts and basement blocks exhibit 3D topographic variations. 2- On the southern profiles, the top of the PR rises up to 5.5 km depth whereas, 20 km northward, its basement expression (at 6.5 km depth) nearly disappears. 3- The 6.5 km/s iso-velocity contour matches the topography of the S reflector where the latter is visible on MCS profiles. Within a depth interval of 0.6 km (in average), velocities beneath the S reflector increase from 6.5 km/s to 7 km/s, which would correspond to a decrease in the degree of serpentinization from ~45 % to ~30 % if these velocity variations are caused solely by variations in hydration. At the intersections between the block bounding normal faults and the S reflector, this decrease happens over a larger depth interval (> 1 km), suggesting that faults act as conduit for the water flow in the upper mantle.

  9. Charactrisation of particle assemblies by 3D cross correlation light scattering and diffusing wave spectroscopy

    NASA Astrophysics Data System (ADS)

    Scheffold, Frank

    2014-08-01

    To characterize the structural and dynamic properties of soft materials and small particles, information on the relevant mesoscopic length scales is required. Such information is often obtained from traditional static and dynamic light scattering (SLS/DLS) experiments in the single scattering regime. In many dense systems, however, these powerful techniques frequently fail due to strong multiple scattering of light. Here I will discuss some experimental innovations that have emerged over the last decade. New methods such as 3D static and dynamic light scattering (3D LS) as well as diffusing wave spectroscopy (DWS) can cover a much extended range of experimental parameters ranging from dilute polymer solutions, colloidal suspensions to extremely opaque viscoelastic emulsions.

  10. The effect of interface microstructure on interfacial shear strength for osteochondral scaffolds based on biomimetic design and 3D printing.

    PubMed

    Zhang, Weijie; Lian, Qin; Li, Dichen; Wang, Kunzheng; Hao, Dingjun; Bian, Weiguo; Jin, Zhongmin

    2015-01-01

    Interface integration between chondral phase and osseous phase is crucial in engineered osteochondral scaffolds. However, the integration was poorly understood and commonly failed to meet the need of osteochondral scaffolds. In this paper, a biphasic polyethylene glycol (PEG)/β-tricalcium phosphate (β-TCP) scaffold with enhanced interfacial integration was developed. The chondral phase was a PEG hydrogel. The osseous phase was a β-TCP ceramic scaffold. The PEG hydrogel was directly cured on the ceramic interface layer by layer to fabricate osteochondral scaffolds by 3D printing technology. Meanwhile, a series of interface structure were designed with different interface pore area percentages (0/10/20/30/40/50/60%), and interfacial shear test was applied for interface structure optimization (n=6 samples/group). The interfacial shear strength of 30% pore area group was nearly three folds improved compared with that of 0% pore area percentage group, and more than fifty folds improved compared with that of traditional integration (5.91±0.59 kPa). In conclusion, the biomimetic PEG/β-TCP scaffolds with interface structure enhanced integration show promising potential application for osteochondral tissue engineering.

  11. Total-Field Technique for 3-D Modeling of Short Period Teleseismic Waves

    NASA Astrophysics Data System (ADS)

    Monteiller, V.; Beller, S.; Operto, S.; Nissen-Meyer, T.; Tago Pacheco, J.; Virieux, J.

    2014-12-01

    The massive development of dense seismic arrays and the rapid increase in computing capacity allow today to consider application of full waveform inversion of teleseismic data for high-resolution lithospheric imaging. We present an hybrid numerical method that allows for the modellingof short period teleseismic waves in 3D lithospheric target with both the discontinuous Galerkin finite elements method and finite difference method, opening the possibility to perform waveform inversion of seismograms recorded by dense regional broadband arrays. However, despite the supercomputer ability, the forward-problem remains expensive at global scale for teleseismic configuration especially when 3D numerical methods are considered. In order to perform the forward problem in a reasonable amount of time, we reduce the computational domain in which full waveform modelling is performed. We define a 3D regional domain located below the seismological network that is embedded in a homogeneous background or axisymmetric model, in which the seismic wavefield can be computed efficiently. The background wavefield is used to compute the full wavefield in the 3D regional domain using the so-called total-field/scattered-field technique. This method relies on the decomposition of the wavefield into a background and a scattered wavefields. The computational domain is subdivided into three sub-domains: an outer domain formed by the perfectly-matched absorbing layers, an intermediate domain in which only the outgoing wavefield scattered by the lithospheric heterogeneities is computed, and the inner domain formed by the lithospheric target in which the full wavefield is computed. In this study, we shall present simulations in realistic lithospheric target when the axisymetric background wavefield is computed with the AxiSEM softwave and the 3D simulation in lithospheric target model is performed with the discontinuous Galerkin or finite difference method.

  12. Shear waves in vegetal tissues at ultrasonic frequencies

    NASA Astrophysics Data System (ADS)

    Fariñas, M. D.; Sancho-Knapik, D.; Peguero-Pina, J. J.; Gil-Pelegrín, E.; Gómez Álvarez-Arenas, T. E.

    2013-03-01

    Shear waves are investigated in leaves of two plant species using air-coupled ultrasound. Magnitude and phase spectra of the transmission coefficient around the first two orders of the thickness resonances (normal and oblique incidence) have been measured. A bilayer acoustic model for plant leaves (comprising the palisade parenchyma and the spongy mesophyll) is proposed to extract, from measured spectra, properties of these tissues like: velocity and attenuation of longitudinal and shear waves and hence Young modulus, rigidity modulus, and Poisson's ratio. Elastic moduli values are typical of cellular solids and both, shear and longitudinal waves exhibit classical viscoelastic losses. Influence of leaf water content is also analyzed.

  13. 3D frequency-domain finite-difference modeling of acoustic wave propagation

    NASA Astrophysics Data System (ADS)

    Operto, S.; Virieux, J.

    2006-12-01

    We present a 3D frequency-domain finite-difference method for acoustic wave propagation modeling. This method is developed as a tool to perform 3D frequency-domain full-waveform inversion of wide-angle seismic data. For wide-angle data, frequency-domain full-waveform inversion can be applied only to few discrete frequencies to develop reliable velocity model. Frequency-domain finite-difference (FD) modeling of wave propagation requires resolution of a huge sparse system of linear equations. If this system can be solved with a direct method, solutions for multiple sources can be computed efficiently once the underlying matrix has been factorized. The drawback of the direct method is the memory requirement resulting from the fill-in of the matrix during factorization. We assess in this study whether representative problems can be addressed in 3D geometry with such approach. We start from the velocity-stress formulation of the 3D acoustic wave equation. The spatial derivatives are discretized with second-order accurate staggered-grid stencil on different coordinate systems such that the axis span over as many directions as possible. Once the discrete equations were developed on each coordinate system, the particle velocity fields are eliminated from the first-order hyperbolic system (following the so-called parsimonious staggered-grid method) leading to second-order elliptic wave equations in pressure. The second-order wave equations discretized on each coordinate system are combined linearly to mitigate the numerical anisotropy. Secondly, grid dispersion is minimized by replacing the mass term at the collocation point by its weighted averaging over all the grid points of the stencil. Use of second-order accurate staggered- grid stencil allows to reduce the bandwidth of the matrix to be factorized. The final stencil incorporates 27 points. Absorbing conditions are PML. The system is solved using the parallel direct solver MUMPS developed for distributed

  14. 3D Numerical Simulation on the Sloshing Waves Excited by the Seismic Shacking

    NASA Astrophysics Data System (ADS)

    Zhang, Lin; Wu, Tso-Ren

    2016-04-01

    In the event of 2015 Nepal earthquake, a video clip broadcasted worldwide showed a violent water spilling in a hotel swimming pool. This sloshing phenomenon indicates a potential water loss in the sensitive facilities, e.g. the spent fuel pools in nuclear power plant, has to be taken into account carefully under the consideration of seismic-induced ground acceleration. In the previous studies, the simulation of sloshing mainly focused on the pressure force on the structure by using a simplified Spring-Mass Method developed in the field of solid mechanics. However, restricted by the assumptions of plane water surface and limited wave height, significant error will be made in evaluating the amount of water loss in the tank. In this paper, the computational fluid dynamical model, Splash3D, was adopted for studying the sloshing problem accurately. Splash3D solved 3D Navier-Stokes Equation directly with Large-Eddy Simulation (LES) turbulent closure. The Volume-of-fluid (VOF) method with piecewise linear interface calculation (PLIC) was used to track the complex breaking water surface. The time series acceleration of a design seismic was loaded to excite the water. With few restrictions from the assumptions, the accuracy of the simulation results were improved dramatically. A series model validations were conducted by compared to a 2D theoretical solution, and a 3D experimental data. Good comparisons can be seen. After the validation, we performed the simulation for considering a sloshing case in a rectangular water tank with a dimension of 12 m long, 8 m wide, 8 m deep, which contained water with 7 m in depth. The seismic movement was imported by considering time-series acceleration in three dimensions, which were about 0.5 g to 1.2 g in the horizontal directions, and 0.3 g to 1 g in the vertical direction. We focused the discussions on the kinematics of the water surface, wave breaking, velocity field, pressure field, water force on the side walls, and, most

  15. Constructing a starting 3D shear velocity model with sharp interfaces for SEM-based upper mantle tomography in North America

    NASA Astrophysics Data System (ADS)

    Calo, M.; Bodin, T.; Yuan, H.; Romanowicz, B. A.; Larmat, C. S.; Maceira, M.

    2013-12-01

    this work we propose instead to directly tackle the non-linearity of the inverse problem by using stochastic methods to construct a 3D starting model with a good estimate of the depths of the main layering interfaces. We present preliminary results of the construction of such a starting 3D model based on: (1) Regionalizing the study area to define provinces within which lateral variations are smooth; (2) Applying trans-dimensional stochastic inversion (Bodin et al., 2012) to obtain accurate 1D models in each province as well as the corresponding error distribution, constrained by receiver function and surface wave dispersion data as well as the previously constructed 3D model (name), and (3) connecting these models laterally using data-driven smoothing operators to obtain a starting 3D model with errors. References Bodin, T.,et al. 2012, Transdimensional inversion of receiver functions and surface wave dispersion, J. Geophys. Res., 117, B02301, doi:10.1029/2011JB008560. Yuan and Romanowicz, 2013, in revison. Yuan, H., et al. 2011, 3-D shear wave radially and azimuthally anisotropic velocity model of the North American upper mantle. Geophysical Journal International, 184: 1237-1260. doi: 10.1111/j.1365-246X.2010.04901.x Yuan, H. & Romanowicz, B., 2010. Lithospheric layering in the North American Craton, Nature, 466, 1063-1068.

  16. 3D Simulation of an Audible Ultrasonic Electrolarynx Using Difference Waves

    PubMed Central

    Mills, Patrick; Zara, Jason

    2014-01-01

    A total laryngectomy removes the vocal folds which are fundamental in forming voiced sounds that make speech possible. Although implanted prosthetics are commonly used in developed countries, simple handheld vibrating electrolarynxes are still common worldwide. These devices are easy to use but suffer from many drawbacks including dedication of a hand, mechanical sounding voice, and sound leakage. To address some of these drawbacks, we introduce a novel electrolarynx that uses vibro-acoustic interference of dual ultrasonic waves to generate an audible fundamental frequency. A 3D simulation of the principles of the device is presented in this paper. PMID:25401965

  17. Multiple-frequency tomography with shear waves and Love waves

    NASA Astrophysics Data System (ADS)

    Tian, Yue

    In this thesis I study the velocity and attenuation structure of the North American mantle using multiple-frequency shear-wave and Love-wave measurements, together with finite-frequency sensitivity kernels. The software for dynamic ray tracing and fast computation of body-wave finite-frequency sensitivity kernels is described and extensively validated and tested for accuracy. The program works for arbitrarily defined phases and one-dimensional background models. In kinematic and dynamic ray tracing, an integration step size of about 20 km is needed to produce travel-time errors under 0.1 s for the most common seismic phases. In kernel computation, a minimum integration step size of 10--30 km is sufficient to obtain numerical errors of the kernel's spatial quadrature below observational uncertainties. Larger errors may occur for long-period minimax phases such as SS . The paraxial approximation fails and errors become intolerable at epicentral distances larger than 140°. A global data set is built to contain multiple-frequency SH-wave travel-time and amplitude anomalies and SS-wave differential delays, estimated by band-pass filtering and cross-correlation. Most of the data are recorded at USArray stations. Frequency dependence is observed for all three types of data, and is strongest for amplitudes. The shallow structure is constrained by the addition of Love-wave phase delays. Velocity and attenuation heterogeneities are simultaneously estimated by allowing for focusing. The velocity model shows evidence of heavy fragmentation of the Farallon slab, including two separate subduction systems under western and eastern North America respectively, trench-perpendicular slab tears, and blob-like slab fragments in the lower mantle. The velocity model reveals a lower-mantle plume originating at about 1500 km depth beneath the Yellowstone area and tilting about 40° from vertical. Complex interaction between the plume and slab fragments is observed. High correlation

  18. 3D dynamic rupture with anelastic wave propagation using an hp-adaptive Discontinuous Galerkin method

    NASA Astrophysics Data System (ADS)

    Tago, J.; Cruz-Atienza, V. M.; Etienne, V.; Virieux, J.; Benjemaa, M.; Sanchez-Sesma, F. J.

    2010-12-01

    Simulating any realistic seismic scenario requires incorporating physical basis into the model. Considering both the dynamics of the rupture process and the anelastic attenuation of seismic waves is essential to this purpose and, therefore, we choose to extend the hp-adaptive Discontinuous Galerkin finite-element method to integrate these physical aspects. The 3D elastodynamic equations in an unstructured tetrahedral mesh are solved with a second-order time marching approach in a high-performance computing environment. The first extension incorporates the viscoelastic rheology so that the intrinsic attenuation of the medium is considered in terms of frequency dependent quality factors (Q). On the other hand, the extension related to dynamic rupture is integrated through explicit boundary conditions over the crack surface. For this visco-elastodynamic formulation, we introduce an original discrete scheme that preserves the optimal code performance of the elastodynamic equations. A set of relaxation mechanisms describes the behavior of a generalized Maxwell body. We approximate almost constant Q in a wide frequency range by selecting both suitable relaxation frequencies and anelastic coefficients characterizing these mechanisms. In order to do so, we solve an optimization problem which is critical to minimize the amount of relaxation mechanisms. Two strategies are explored: 1) a least squares method and 2) a genetic algorithm (GA). We found that the improvement provided by the heuristic GA method is negligible. Both optimization strategies yield Q values within the 5% of the target constant Q mechanism. Anelastic functions (i.e. memory variables) are introduced to efficiently evaluate the time convolution terms involved in the constitutive equations and thus to minimize the computational cost. The incorporation of anelastic functions implies new terms with ordinary differential equations in the mathematical formulation. We solve these equations using the same order

  19. A 3D unstructured non-hydrostatic ocean model for internal waves

    NASA Astrophysics Data System (ADS)

    Ai, Congfang; Ding, Weiye

    2016-10-01

    A 3D non-hydrostatic model is developed to compute internal waves. A novel grid arrangement is incorporated in the model. This not only ensures the homogenous Dirichlet boundary condition for the non-hydrostatic pressure can be precisely and easily imposed but also renders the model relatively simple in its discretized form. The Perot scheme is employed to discretize horizontal advection terms in the horizontal momentum equations, which is based on staggered grids and has the conservative property. Based on previous water wave models, the main works of the present paper are to (1) utilize a semi-implicit, fractional step algorithm to solve the Navier-Stokes equations (NSE); (2) develop a second-order flux-limiter method satisfying the max-min property; (3) incorporate a density equation, which is solved by a high-resolution finite volume method ensuring mass conservation and max-min property based on a vertical boundary-fitted coordinate system; and (4) validate the developed model by using four tests including two internal seiche waves, lock-exchange flow, and internal solitary wave breaking. Comparisons of numerical results with analytical solutions or experimental data or other model results show reasonably good agreement, demonstrating the model's capability to resolve internal waves relating to complex non-hydrostatic phenomena.

  20. Image reconstruction with acoustic radiation force induced shear waves

    NASA Astrophysics Data System (ADS)

    McAleavey, Stephen A.; Nightingale, Kathryn R.; Stutz, Deborah L.; Hsu, Stephen J.; Trahey, Gregg E.

    2003-05-01

    Acoustic radiation force may be used to induce localized displacements within tissue. This phenomenon is used in Acoustic Radiation Force Impulse Imaging (ARFI), where short bursts of ultrasound deliver an impulsive force to a small region. The application of this transient force launches shear waves which propagate normally to the ultrasound beam axis. Measurements of the displacements induced by the propagating shear wave allow reconstruction of the local shear modulus, by wave tracking and inversion techniques. Here we present in vitro, ex vivo and in vivo measurements and images of shear modulus. Data were obtained with a single transducer, a conventional ultrasound scanner and specialized pulse sequences. Young's modulus values of 4 kPa, 13 kPa and 14 kPa were observed for fat, breast fibroadenoma, and skin. Shear modulus anisotropy in beef muscle was observed.

  1. Effect of shear on failure waves in soda lime glass

    NASA Astrophysics Data System (ADS)

    Clifton, R. J.; Mello, M.; Brar, N. S.

    1998-07-01

    By means of in-material stress gauges, failure waves in shock-compressed soda lime glass have been shown to be distinguished by a marked reduction in shear stress. To explore further the relation between failure waves and shearing resistance, a series of pressure-shear impact experiments have been performed involving the impact of a glass plate by a steel flyer plate and vice versa. The latter configuration is designed to allow direct measurements of the shearing resistance of the failed material. In both configurations, the normal and transverse motion of the free surface of the target is monitored using laser interferometry. The transverse velocity-time profiles show a pronounced loss in shearing resistance of the glass at impact velocities above the threshold for failure waves to occur.

  2. Optimized shear wave generation using hybrid beamforming methods.

    PubMed

    Nabavizadeh, Alireza; Greenleaf, James F; Fatemi, Mostafa; Urban, Matthew W

    2014-01-01

    Elasticity imaging is a medical imaging modality that measures tissue elasticity as an aid in the diagnosis of certain diseases. Shear wave-based methods have been developed to perform elasticity measurements in soft tissue. These methods often use the radiation force mechanism of focused ultrasound to induce shear waves in soft tissue such as liver, kidney, breast, thyroid and skeletal muscle. The efficiency of the ultrasound beam in producing broadband extended shear waves in soft tissue is very important to the widespread use of this modality. Hybrid beamforming combines two types of focusing, conventional spherical focusing and axicon focusing, to produce a beam for generating a shear wave that has increased depth-of-field (DOF) so that measurements can be made with a shear wave with a consistent wave front. Spherical focusing is used in many applications to achieve high lateral resolution, but has low DOF. Axicon focusing, with a cone-shaped transducer, can provide good lateral resolution with large DOF. We describe our linear aperture design and beam optimization performed using angular spectrum simulations. We performed a large parametric simulation study in which we varied the focal depth for the spherical focusing portion of the aperture, the numbers of elements devoted to the spherical and axicon focusing portions of the aperture and the opening angle used for axicon focusing. The hybrid beamforming method was experimentally tested in two phantoms, and shear wave speed measurement accuracy and DOF for each hybrid beam were evaluated. We compared our results with those for shear waves generated using only spherical focusing. The results of this study indicate that hybrid beamforming is capable of producing a beam with increased DOF over which accurate shear wave speed measurements can be made for different-size apertures and at different focal depths.

  3. Ultrasound shear wave simulation based on nonlinear wave propagation and Wigner-Ville Distribution analysis

    NASA Astrophysics Data System (ADS)

    Bidari, Pooya Sobhe; Alirezaie, Javad; Tavakkoli, Jahan

    2017-03-01

    This paper presents a method for modeling and simulation of shear wave generation from a nonlinear Acoustic Radiation Force Impulse (ARFI) that is considered as a distributed force applied at the focal region of a HIFU transducer radiating in nonlinear regime. The shear wave propagation is simulated by solving the Navier's equation from the distributed nonlinear ARFI as the source of the shear wave. Then, the Wigner-Ville Distribution (WVD) as a time-frequency analysis method is used to detect the shear wave at different local points in the region of interest. The WVD results in an estimation of the shear wave time of arrival, its mean frequency and local attenuation which can be utilized to estimate medium's shear modulus and shear viscosity using the Voigt model.

  4. Investigation of 3D surface acoustic waves in granular media with 3-color digital holography

    NASA Astrophysics Data System (ADS)

    Leclercq, Mathieu; Picart, Pascal; Penelet, Guillaume; Tournat, Vincent

    2017-01-01

    This paper reports the implementation of digital color holography to investigate elastic waves propagating along a layer of a granular medium. The holographic set-up provides simultaneous recording and measurement of the 3D dynamic displacement at the surface. Full-field measurements of the acoustic amplitude and phase at different excitation frequencies are obtained. It is shown that the experimental data can be used to obtain the dispersion curve of the modes propagating in this granular medium layer. The experimental dispersion curve and that obtained from a finite element modeling of the problem are found to be in good agreement. In addition, full-field images of the interaction of an acoustic wave guided in the granular layer with a buried object are also shown.

  5. Wave optics theory and 3-D deconvolution for the light field microscope.

    PubMed

    Broxton, Michael; Grosenick, Logan; Yang, Samuel; Cohen, Noy; Andalman, Aaron; Deisseroth, Karl; Levoy, Marc

    2013-10-21

    Light field microscopy is a new technique for high-speed volumetric imaging of weakly scattering or fluorescent specimens. It employs an array of microlenses to trade off spatial resolution against angular resolution, thereby allowing a 4-D light field to be captured using a single photographic exposure without the need for scanning. The recorded light field can then be used to computationally reconstruct a full volume. In this paper, we present an optical model for light field microscopy based on wave optics, instead of previously reported ray optics models. We also present a 3-D deconvolution method for light field microscopy that is able to reconstruct volumes at higher spatial resolution, and with better optical sectioning, than previously reported. To accomplish this, we take advantage of the dense spatio-angular sampling provided by a microlens array at axial positions away from the native object plane. This dense sampling permits us to decode aliasing present in the light field to reconstruct high-frequency information. We formulate our method as an inverse problem for reconstructing the 3-D volume, which we solve using a GPU-accelerated iterative algorithm. Theoretical limits on the depth-dependent lateral resolution of the reconstructed volumes are derived. We show that these limits are in good agreement with experimental results on a standard USAF 1951 resolution target. Finally, we present 3-D reconstructions of pollen grains that demonstrate the improvements in fidelity made possible by our method.

  6. Wave optics theory and 3-D deconvolution for the light field microscope

    PubMed Central

    Broxton, Michael; Grosenick, Logan; Yang, Samuel; Cohen, Noy; Andalman, Aaron; Deisseroth, Karl; Levoy, Marc

    2013-01-01

    Light field microscopy is a new technique for high-speed volumetric imaging of weakly scattering or fluorescent specimens. It employs an array of microlenses to trade off spatial resolution against angular resolution, thereby allowing a 4-D light field to be captured using a single photographic exposure without the need for scanning. The recorded light field can then be used to computationally reconstruct a full volume. In this paper, we present an optical model for light field microscopy based on wave optics, instead of previously reported ray optics models. We also present a 3-D deconvolution method for light field microscopy that is able to reconstruct volumes at higher spatial resolution, and with better optical sectioning, than previously reported. To accomplish this, we take advantage of the dense spatio-angular sampling provided by a microlens array at axial positions away from the native object plane. This dense sampling permits us to decode aliasing present in the light field to reconstruct high-frequency information. We formulate our method as an inverse problem for reconstructing the 3-D volume, which we solve using a GPU-accelerated iterative algorithm. Theoretical limits on the depth-dependent lateral resolution of the reconstructed volumes are derived. We show that these limits are in good agreement with experimental results on a standard USAF 1951 resolution target. Finally, we present 3-D reconstructions of pollen grains that demonstrate the improvements in fidelity made possible by our method. PMID:24150383

  7. Effect of background rotation on the evolution of 3D internal gravity wave beams

    NASA Astrophysics Data System (ADS)

    Fan, Boyu; Akylas, T. R.

    2016-11-01

    The effect of background rotation on the 3D propagation of internal gravity wave beams (IGWB) is studied, assuming that variations in the along-beam and transverse directions are of long length scale relative to the beam width. The present study generalizes the asymptotic model of KA (Kataoka & Akylas 2015) who considered the analogous problem in the absence of rotation. It is shown that the role of mean vertical vorticity in the earlier analysis is now taken by the flow mean potential vorticity (MPV). Specifically, 3D variations enable resonant transfer of energy to the flow MPV, resulting in strong nonlinear coupling between a 3D IGWB and its induced mean flow. This coupling mechanism is governed by a system of two nonlinear equations of the same form as those derived in KA. Accordingly, the induced mean flow features a purely inviscid modulational component, as well as a viscous one akin to acoustic streaming; the latter grows linearly with time for a quasi-steady IGWB. On the other hand, owing to background rotation, the induced mean flow in the vicinity of the IGWB is no longer purely horizontal and develops an asymmetric behavior. Supported by NSF.

  8. 3D Plenoptic PIV Measurements of a Shock Wave Boundary Layer Interaction

    NASA Astrophysics Data System (ADS)

    Thurow, Brian; Bolton, Johnathan; Arora, Nishul; Alvi, Farrukh

    2016-11-01

    Plenoptic particle image velocimetry (PIV) is a relatively new technique that uses the computational refocusing capability of a single plenoptic camera and volume illumination with a double-pulsed light source to measure the instantaneous 3D/3C velocity field of a flow field seeded with particles. In this work, plenoptic PIV is used to perform volumetric velocity field measurements of a shock-wave turbulent boundary layer interaction (SBLI). Experiments were performed in a Mach 2.0 flow with the SBLI produced by an unswept fin at 15°angle of attack. The measurement volume was 38 x 25 x 32 mm3 and illuminated with a 400 mJ/pulse Nd:YAG laser with 1.7 microsecond inter-pulse time. Conventional planar PIV measurements along two planes within the volume are used for comparison. 3D visualizations of the fin generated shock and subsequent SBLI are presented. The growth of the shock foot and separation region with increasing distance from the fin tip is observed and agrees with observations made using planar PIV. Instantaneous images depict 3D fluctuations in the position of the shock foot from one image to the next. The authors acknowledge the support of the Air Force Office of Scientific Research.

  9. Shear Wave Propagation Across Filled Joints with the Effect of Interfacial Shear Strength

    NASA Astrophysics Data System (ADS)

    Li, J. C.; Liu, T. T.; Li, H. B.; Liu, Y. Q.; Liu, B.; Xia, X.

    2015-07-01

    The thin-layer interface model for filled joints is extended to analyze shear wave propagation across filled rock joints when the interfacial shear strength between the filling material and the rocks is taken into account. During the wave propagation process, the two sides of the filled joint are welded with the adjacent rocks first and slide on each other when the shear stress on the joint is greater than the interfacial shear strength. By back analysis, the relation between the shear stress and the relative tangential deformation of the filled joints is obtained from the present approach, which is shown as a cycle parallelogram. Comparison between the present approach and the existing method based on the zero-thickness interface model indicates that the present approach is efficient to analyze shear wave propagation across rock joints with slippery behavior. The calculation results show that the slippery behavior of joints is related to the interfacial failure. In addition, the interaction between the shear stress wave and the two sides of the filling joint influences not only the wave propagation process but also the dynamic response of the filled joint.

  10. 3D P-wave Velocity Structure Beneath the Eastern Canadian Shield and Northern Appalachian Region

    NASA Astrophysics Data System (ADS)

    Villemaire, M.; Darbyshire, F. A.; Bastow, I. D.

    2010-12-01

    Previous seismic studies of the upper mantle of the Canadian Shield have indicated some low-velocity anomalies within the cratonic lithosphere in the Abitibi-Grenville region. The lack of seismograph station coverage to the east and south-east of the studied area prevented definition of the 3D geometry of these anomalies. Adding new stations from the province of Quebec and from the northeastern United States allows us to carry out new studies of the P-wave velocity structure of the upper mantle, in order to better understand the complexity of the region and the interaction of the lithosphere with possible thermal anomalies in the underlying mantle. We analysed teleseismic P wave arrivals from almost 200 earthquakes, recorded at 45 stations deployed across the provinces of Quebec and Ontario and across the northeastern US. The relative arrival times of teleseismic P waves across the array were measured using the cross-correlation method of VanDecar & Crosson (1990). The travel time data were then inverted to estimate the 3D P-wave velocity structure beneath the region, using the least-squares tomographic inversion code of VanDecar (1991). The model shows some interesting features. We see a diffuse low-velocity structure beneath New-England that extends to at least 500 km depth, and that may be related to the Appalachian Mountain belt. There is also a linear low-velocity structure, flanked by higher velocities, perpendicular to the Grenville Front, and along the Ottawa Valley. We interpret this feature as a mantle signature of the Great Meteor Hotspot track. We have looked for systematic differences between the mantle underlying the Archean Superior craton and the Proterozoic Grenville Province but did not find a significant difference in the upper mantle. We investigate the role of thermal and compositional effects to interpret the velocity models and to relate the patterns of the anomalies to past and present tectonic structures.

  11. A 3-D shear velocity model of the southern North America and the Caribbean plates from ambient noise and earthquake tomography

    NASA Astrophysics Data System (ADS)

    Gaite, B.; Villaseñor, A.; Iglesias, A.; Herraiz, M.; Jiménez-Munt, I.

    2014-10-01

    We use group velocities from earthquake tomography together with group and phase velocities from ambient noise tomography (ANT) of Rayleigh-waves to invert for the 3-D shear-wave velocity structure (5-70 km) of the Caribbean (CAR) and southern North American (NAM) plates. The lithospheric model proposed offers a complete image of the crust and uppermost-mantle with imprints of the tectonic evolution. One of the most striking features inferred is the main role of the Ouachita-Marathon-Sonora orogeny front on the crustal seismic structure of NAM plate. A new imaged feature is the low crustal velocities along USA-Mexico border. The model also shows a break of the E-W mantle velocity dichotomy of the NAM and CAR plates beneath the Isthmus of Tehuantepec and Yucatan Block. High upper-mantle velocities along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest velocities correspond to active volcanic arcs and thin lithospheric mantle regions.

  12. Poroelastic Wave Propagation With a 3D Velocity-Stress-Pressure Finite-Difference Algorithm

    NASA Astrophysics Data System (ADS)

    Aldridge, D. F.; Symons, N. P.; Bartel, L. C.

    2004-12-01

    Seismic wave propagation within a three-dimensional, heterogeneous, isotropic poroelastic medium is numerically simulated with an explicit, time-domain, finite-difference algorithm. A system of thirteen, coupled, first-order, partial differential equations is solved for the particle velocity vector components, the stress tensor components, and the pressure associated with solid and fluid constituents of the two-phase continuum. These thirteen dependent variables are stored on staggered temporal and spatial grids, analogous to the scheme utilized for solution of the conventional velocity-stress system of isotropic elastodynamics. Centered finite-difference operators possess 2nd-order accuracy in time and 4th-order accuracy in space. Seismological utility is enhanced by an optional stress-free boundary condition applied on a horizontal plane representing the earth's surface. Absorbing boundary conditions are imposed on the flanks of the 3D spatial grid via a simple wavefield amplitude taper approach. A massively parallel computational implementation, utilizing the spatial domain decomposition strategy, allows investigation of large-scale earth models and/or broadband wave propagation within reasonable execution times. Initial algorithm testing indicates that a point force density and/or moment density source activated within a poroelastic medium generates diverging fast and slow P waves (and possibly an S-wave)in accord with Biot theory. Solid and fluid particle velocities are in-phase for the fast P-wave, whereas they are out-of-phase for the slow P-wave. Conversions between all wave types occur during reflection and transmission at interfaces. Thus, although the slow P-wave is regarded as difficult to detect experimentally, its presence is strongly manifest within the complex of waves generated at a lithologic or fluid boundary. Very fine spatial and temporal gridding are required for high-fidelity representation of the slow P-wave, without inducing excessive

  13. 3D reconstruction and particle acceleration properties of Coronal Shock Waves During Powerful Solar Particle Events

    NASA Astrophysics Data System (ADS)

    Plotnikov, Illya; Vourlidas, Angelos; Tylka, Allan J.; Pinto, Rui; Rouillard, Alexis; Tirole, Margot

    2016-07-01

    Identifying the physical mechanisms that produce the most energetic particles is a long-standing observational and theoretical challenge in astrophysics. Strong pressure waves have been proposed as efficient accelerators both in the solar and astrophysical contexts via various mechanisms such as diffusive-shock/shock-drift acceleration and betatron effects. In diffusive-shock acceleration, the efficacy of the process relies on shock waves being super-critical or moving several times faster than the characteristic speed of the medium they propagate through (a high Alfven Mach number) and on the orientation of the magnetic field upstream of the shock front. High-cadence, multipoint imaging using the NASA STEREO, SOHO and SDO spacecrafts now permits the 3-D reconstruction of pressure waves formed during the eruption of coronal mass ejections. Using these unprecedented capabilities, some recent studies have provided new insights on the timing and longitudinal extent of solar energetic particles, including the first derivations of the time-dependent 3-dimensional distribution of the expansion speed and Mach numbers of coronal shock waves. We will review these recent developments by focusing on particle events that occurred between 2011 and 2015. These new techniques also provide the opportunity to investigate the enigmatic long-duration gamma ray events.

  14. Shear horizontal guided wave modes to infer the shear stiffness of adhesive bond layers.

    PubMed

    Le Crom, Bénédicte; Castaings, Michel

    2010-04-01

    This paper presents a non-destructive, ultrasonic technique to evaluate the quality of bonds between substrates. Shear-horizontally polarized (SH) wave modes are investigated to infer the shear stiffness of bonds, which is necessarily linked to the shear resistance that is a critical parameter for bonded structures. Numerical simulations are run for selecting the most appropriate SH wave modes, i.e., with higher sensitivity to the bond than to other components, and experiments are made for generating-detecting pre-selected SH wave modes and for measuring their phase velocities. An inverse problem is finally solved, consisting of the evaluation of the shear stiffness modulus of a bond layer at different curing times between a metallic plate and a composite patch, such assembly being investigated in the context of repair of aeronautical structures.

  15. Drift Wave Test Particle Transport in Reversed Shear Profile

    SciTech Connect

    Horton, W.; Park, H.B.; Kwon, J.M.; Stronzzi, D.; Morrison, P.J.; Choi, D.I.

    1998-06-01

    Drift wave maps, area preserving maps that describe the motion of charged particles in drift waves, are derived. The maps allow the integration of particle orbits on the long time scale needed to describe transport. Calculations using the drift wave maps show that dramatic improvement in the particle confinement, in the presence of a given level and spectrum of E x B turbulence, can occur for q(r)-profiles with reversed shear. A similar reduction in the transport, i.e. one that is independent of the turbulence, is observed in the presence of an equilibrium radial electric field with shear. The transport reduction, caused by the combined effects of radial electric field shear and both monotonic and reversed shear magnetic q-profiles, is also investigated.

  16. Cardiac Shear Wave Velocity Detection in the Porcine Heart.

    PubMed

    Vos, Hendrik J; van Dalen, Bas M; Heinonen, Ilkka; Bosch, Johan G; Sorop, Oana; Duncker, Dirk J; van der Steen, Antonius F W; de Jong, Nico

    2017-04-01

    Cardiac muscle stiffness can potentially be estimated non-invasively with shear wave elastography. Shear waves are present on the septal wall after mitral and aortic valve closure, thus providing an opportunity to assess stiffness in early systole and early diastole. We report on the shear wave recordings of 22 minipigs with high-frame-rate echocardiography. The waves were captured with 4000 frames/s using a programmable commercial ultrasound machine. The wave pattern was extracted from the data through a local tissue velocity estimator based on one-lag autocorrelation. The wave propagation velocity was determined with a normalized Radon transform, resulting in median wave propagation velocities of 2.2 m/s after mitral valve closure and 4.2 m/s after aortic valve closure. Overall the velocities ranged between 0.8 and 6.3 m/s in a 95% confidence interval. By dispersion analysis we found that the propagation velocity only mildly increased with shear wave frequency.

  17. Measurement of Oblique Impact-generated Shear Waves

    NASA Technical Reports Server (NTRS)

    Dahl, J. M.; Schultz, P. H.

    2001-01-01

    Experimental strain measurements reveal that oblique impacts can generate shear waves with displacements as large as those in the P-wave. Large oblique impacts may thus be more efficient sources of surface disruption than vertical impacts. Additional information is contained in the original extended abstract.

  18. Acoustomicrofluidic application of quasi-shear surface waves.

    PubMed

    Darinskii, A N; Weihnacht, M; Schmidt, H

    2017-02-20

    The paper analyzes the possibility of using predominantly boundary polarized surface acoustic waves for actuating fluidic effects in microchannels fabricated inside containers made of PDMS. The aim is to remove a shortcoming peculiar to conventionally utilized predominantly vertically polarized waves. Such waves strongly attenuate while they propagate under container side walls because of the leakage into them. Due to a specific feature of PDMS - extremely small shear elastic modulus - losses of boundary polarized modes should be far smaller. The amplitude of vertical mechanical displacements can be increased right inside the channel owing to the scattering of acoustic fields. As an example, the predominantly vertically polarized surface wave on 128YX LiNbO3 is compared with the quasi-shear leaky wave on 64YX LiNbO3. Our computations predict that, given the electric power supplied to the launching transducer, the quasi-shear wave will drive the fluid more efficiently than the surface wave on 128YX LiNbO3 when the container wall thickness is larger than 25-30 wavelengths, if there are no additional scatterers inside the channel. In the presence of a scatterer, such as a thin gold strip, the quasi-shear wave can be more efficient when the wall thickness exceeds 10-15 wavelengths.

  19. Optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling

    NASA Astrophysics Data System (ADS)

    Li, Y.; Han, B.; Métivier, L.; Brossier, R.

    2016-09-01

    We investigate an optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. An anti-lumped mass strategy is incorporated to minimize the numerical dispersion. The optimal finite-difference coefficients and the mass weighting coefficients are obtained by minimizing the misfit between the normalized phase velocities and the unity. An iterative damped least-squares method, the Levenberg-Marquardt algorithm, is utilized for the optimization. Dispersion analysis shows that the optimal fourth-order scheme presents less grid dispersion and anisotropy than the conventional fourth-order scheme with respect to different Poisson's ratios. Moreover, only 3.7 grid-points per minimum shear wavelength are required to keep the error of the group velocities below 1%. The memory cost is then greatly reduced due to a coarser sampling. A parallel iterative method named CARP-CG is used to solve the large ill-conditioned linear system for the frequency-domain modeling. Validations are conducted with respect to both the analytic viscoacoustic and viscoelastic solutions. Compared with the conventional fourth-order scheme, the optimal scheme generates wavefields having smaller error under the same discretization setups. Profiles of the wavefields are presented to confirm better agreement between the optimal results and the analytic solutions.

  20. Can we trace the eastern Gondwanan margin in Australia? New perspectives from transdimensional inversion of ambient noise for 3D shear velocity structure

    NASA Astrophysics Data System (ADS)

    Pilia, S.; Rawlinson, N.; Direen, N. G.

    2013-12-01

    Although the notion of Rodinia is quite well accepted in the geoscience community, the location and nature of the eastern continental margin of the Gondwana fragment in Australia is still vague and remains one of the most hotly debated topics in Australian geology. Moreover, most post-Rodinian reconstructions models choose not to tackle the ';Tasmanian challenge', and focus only on the tectonic evolution of mainland southeast Australia, thereby conveniently ignoring the wider tectonic implications of Tasmania's complex geological history. One of the chief limitations of the tectonic reconstructions in this region is a lack of information on Paleozoic (possibly Proterozoic) basement structures. Vast Mesozoic-Cainozoic sedimentary and volcanic cover sequences obscure older outcrops and limit the power of direct observational techniques. In response to these challenges, our effort is focused on ambient seismic noise for imaging 3D crustal shear velocity structure using surface waves, which is capable of illuminating basement structure beneath younger cover. The data used in this study is sourced from the WOMBAT transportable seismic array, which is compounded by around 650 stations spanning the majority of southeastern Australia, including Tasmania and several islands in Bass Strait. To produce the highest quality Green's functions, careful processing of the data has been performed, after which group velocity dispersion measurements have been carried out using a frequency-time analysis method on the symmetric component of the empirical Green's functions (EGFs). Group dispersion measurements from the EGFs have been inverted using a novel hierarchical, transdimensional, Bayesian algorithm to obtain Rayleigh-wave group velocity maps at different periods from 2 to 30 s. The new approach has several advantages in that the number and distribution of model parameters are implicitly controlled by the data, in which the noise is treated as unknown in the inversion. This

  1. 3D P and S Wave Velocity Structure and Tremor Locations in the Parkfield Region

    NASA Astrophysics Data System (ADS)

    Zeng, X.; Thurber, C. H.; Shelly, D. R.; Bennington, N. L.; Cochran, E. S.; Harrington, R. M.

    2014-12-01

    We have assembled a new dataset to refine the 3D seismic velocity model in the Parkfield region. The S arrivals from 184 earthquakes recorded by the Parkfield Experiment to Record MIcroseismicity and Tremor array (PERMIT) during 2010-2011 were picked by a new S wave picker, which is based on machine learning. 74 blasts have been assigned to four quarries, whose locations were identified with Google Earth. About 1000 P and S wave arrivals from these blasts at permanent seismic network were also incorporated. Low frequency earthquakes (LFEs) occurring within non-volcanic tremor (NVT) are valuable for improving the precision of NVT location and the seismic velocity model at greater depths. Based on previous work (Shelley and Hardebeck, 2010), waveforms of hundreds of LFEs in same family were stacked to improve signal qualify. In a previous study (McClement et al., 2013), stacked traces of more than 30 LFE families at the Parkfileld Array Seismic Observatory (PASO) have been picked. We expanded our work to include LFEs recorded by the PERMIT array. The time-frequency Phase Weight Stacking (tf-PWS) method was introduced to improve the stack quality, as direct stacking does not produce clear S-wave arrivals on the PERMIT stations. This technique uses the coherence of the instantaneous phase among the stacked signals to enhance the signal-to-noise ratio (SNR) of the stack. We found that it is extremely effective for picking LFE arrivals (Thurber et al., 2014). More than 500 P and about 1000 S arrivals from 58 LFE families were picked at the PERMIT and PASO arrays. Since the depths of LFEs are much deeper than earthquakes, we are able to extend model resolution to lower crustal depths. Both P and S wave velocity structure have been obtained with the tomoDD method. The result suggests that there is a low velocity zone (LVZ) in the lower crust and the location of the LVZ is consistent with the high conductivity zone beneath the southern segment of the Rinconada fault that

  2. Explicit wave action conservation for water waves on vertically sheared flows

    NASA Astrophysics Data System (ADS)

    Quinn, B. E.; Toledo, Y.; Shrira, V. I.

    2017-04-01

    This paper addresses a major shortcoming of the current generation of wave models, namely their inability to describe wave propagation upon ambient currents with vertical shear. The wave action conservation equation (WAE) for linear waves propagating in horizontally inhomogeneous vertically-sheared currents is derived following Voronovich (1976). The resulting WAE specifies conservation of a certain depth-averaged quantity, the wave action, a product of the wave amplitude squared, eigenfunctions and functions of the eigenvalues of the boundary value problem for water waves upon a vertically sheared current. The formulation of the WAE is made explicit using known asymptotic solutions of the boundary value problem which exploit the smallness of the current magnitude compared to the wave phase velocity and/or its vertical shear and curvature; the adopted approximations are shown to be sufficient for most of the conceivable applications. In the limit of vanishing current shear, the new formulation reduces to that of Bretherton and Garrett (1968) without shear and the invariant is calculated with the current magnitude taken at the free surface. It is shown that in realistic oceanic conditions, the neglect of the vertical structure of the currents in wave modelling which is currently universal might lead to significant errors in wave amplitude. The new WAE which takes into account the vertical shear can be better coupled to modern circulation models which resolve the three-dimensional structure of the uppermost layer of the ocean.

  3. 3D P-wave velocity structure of the deep Galicia rifted margin: A first analysis of the Galicia 3D wide-angle seismic dataset

    NASA Astrophysics Data System (ADS)

    Bayrakci, Gaye; Minshull, Timothy A.; Davy, Richard G.; Karplus, Marianne S.; Kaeschen, Dirk; Papenberg, Cord; Krabbenhoeft, Anne; Sawyer, Dale; Reston, Timothy J.; Shillington, Donna J.; Ranero, César R.

    2014-05-01

    Galicia 3D, a reflection-refraction and long offset seismic experiment was carried out from May through September 2013, at the Galicia rifted margin (in the northeast Atlantic Ocean, west of Spain) as a collaboration between US, UK, German and Spanish groups. The 3D multichannel seismic acquisition conducted by R/V Marcus Langseth covered a 64 km by 20 km (1280 km2) zone where the main geological features are the Peridotite Ridge (PR), composed of serpentinized peridotite and thought be upper mantle exhumed to the seafloor during rifting, and the S reflector which has been interpreted to be a low angle detachment fault overlain by fault bounded, rotated, continental crustal blocks. In the 3D box, two airgun arrays of 3300 cu.in. were fired alternately (in flip-flop configuration) every 37.5 m. All shots are recorded by 44 short period four component ocean bottom seismometers (OBS) and 26 ocean bottom hydrophones (OBH) deployed and recovered by R/V Poseidon, as well as four 6 km hydrophone streamers with 12.5 m channel spacing towed by R/V Marcus Langseth. We present the preliminary results of the first arrival time tomography study which is carried out with a subset of the wide-angle dataset, in order to generate a 3D P-wave velocity volume for the entire depth sampled by the reflection data. After the relocation of OBSs and OBHs, an automatic first-arrival time picking approach is applied to a subset of the dataset, which comprises more than 5.5 million source-receiver pairs. Then, the first-arrival times are checked visually, in 3-dimensions. The a priori model used for the first-arrival time tomography is built up using information from previous seismic surveys carried out at the Galicia margin (e.g. ISE, 1997). The FAST algorithm of Zelt and Barton (1998) is used for the first-arrival time inversion. The 3D P-wave velocity volume can be used in interpreting the reflection dataset, as a starting point for migration, to quantify the thinning of the crustal layers

  4. Magnetic resonance imaging of shear wave propagation in excised tissue.

    PubMed

    Bishop, J; Poole, G; Leitch, M; Plewes, D B

    1998-01-01

    The propagation of shear waves in ex vivo tissue samples, agar/gel phantoms, and human volunteers was investigated. A moving coil apparatus was constructed to generate low acoustic frequency shear perturbations of 50 to 400 Hz. Oscillating gradients phase-locked with the shear stimulus were used to generate a series of phase contrast images of the shear waves at different time-points throughout the wave cycle. Quantitative measurements of wave velocity and attenuation were obtained to evaluate the effects of temperature, frequency, and tissue anisotropy. Results of these experiments demonstrate significant variation in shear wave behavior with tissue type, whereas frequency and anisotropic behavior was mixed. Temperature-dependent behavior related mainly to the presence of fat. Propagation velocities ranged from 1 to 5 m/sec, and attenuation coefficients of from 1 to 3 nepers/unit wavelength, depending on tissue type. These results confirm the potential of elastic imaging attributable to the intrinsic variability of elastic properties observed in normal tissue, although some difficulty may be experienced in clinical implementation because of viscous attenuation in fat.

  5. Monitoring of thermal therapy based on shear modulus changes: II. Shear wave imaging of thermal lesions.

    PubMed

    Arnal, Bastien; Pernot, Mathieu; Tanter, Mickael

    2011-08-01

    The clinical applicability of high-intensity focused ultrasound (HIFU) for noninvasive therapy is currently hampered by the lack of robust and real-time monitoring of tissue damage during treatment. The goal of this study is to show that the estimation of local tissue elasticity from shear wave imaging (SWI) can lead to a precise mapping of the lesion. HIFU treatment and monitoring were respectively performed using a confocal setup consisting of a 2.5-MHz single element transducer focused at 34 mm on ex vivo samples and an 8-MHz ultrasound diagnostic probe. Ultrasound-based strain imaging was combined with shear wave imaging on the same device. The SWI sequences consisted of 2 successive shear waves induced at different lateral positions. Each wave was created with pushing beams of 100 μs at 3 depths. The shear wave propagation was acquired at 17,000 frames/s, from which the elasticity map was recovered. HIFU sonications were interleaved with fast imaging acquisitions, allowing a duty cycle of more than 90%. Thus, elasticity and strain mapping was achieved every 3 s, leading to real-time monitoring of the treatment. When thermal damage occurs, tissue stiffness was found to increase up to 4-fold and strain imaging showed strong shrinkages that blur the temperature information. We show that strain imaging elastograms are not easy to interpret for accurate lesion characterization, but SWI provides a quantitative mapping of the thermal lesion. Moreover, the concept of shear wave thermometry (SWT) developed in the companion paper allows mapping temperature with the same method. Combined SWT and shear wave imaging can map the lesion stiffening and temperature outside the lesion, which could be used to predict the eventual lesion growth by thermal dose calculation. Finally, SWI is shown to be robust to motion and reliable in vivo on sheep muscle.

  6. Intersymbol Interference Investigations Using a 3D Time-Dependent Traveling Wave Tube Model

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Andro, Monty

    2002-01-01

    For the first time, a time-dependent, physics-based computational model has been used to provide a direct description of the effects of the traveling wave tube amplifier (TWTA) on modulated digital signals. The TWT model comprehensively takes into account the effects of frequency dependent AM/AM and AM/PM conversion; gain and phase ripple; drive-induced oscillations; harmonic generation; intermodulation products; and backward waves. Thus, signal integrity can be investigated in the presence of these sources of potential distortion as a function of the physical geometry and operating characteristics of the high power amplifier and the operational digital signal. This method promises superior predictive fidelity compared to methods using TWT models based on swept- amplitude and/or swept-frequency data. First, the TWT model using the three dimensional (3D) electromagnetic code MAFIA is presented. Then, this comprehensive model is used to investigate approximations made in conventional TWT black-box models used in communication system level simulations. To quantitatively demonstrate the effects these approximations have on digital signal performance predictions, including intersymbol interference (ISI), the MAFIA results are compared to the system level analysis tool, Signal Processing Workstation (SPW), using high order modulation schemes including 16 and 64-QAM.

  7. Intersymbol Interference Investigations Using a 3D Time-Dependent Traveling Wave Tube Model

    NASA Technical Reports Server (NTRS)

    Kory, Carol L.; Andro, Monty; Downey, Alan (Technical Monitor)

    2001-01-01

    For the first time, a physics based computational model has been used to provide a direct description of the effects of the TWT (Traveling Wave Tube) on modulated digital signals. The TWT model comprehensively takes into account the effects of frequency dependent AM/AM and AM/PM conversion; gain and phase ripple; drive-induced oscillations; harmonic generation; intermodulation products; and backward waves. Thus, signal integrity can be investigated in the presence of these sources of potential distortion as a function of the physical geometry of the high power amplifier and the operational digital signal. This method promises superior predictive fidelity compared to methods using TWT models based on swept amplitude and/or swept frequency data. The fully three-dimensional (3D), time-dependent, TWT interaction model using the electromagnetic code MAFIA is presented. This model is used to investigate assumptions made in TWT black box models used in communication system level simulations. In addition, digital signal performance, including intersymbol interference (ISI), is compared using direct data input into the MAFIA model and using the system level analysis tool, SPW (Signal Processing Worksystem).

  8. A new omnidirectional shear horizontal wave transducer using face-shear (d24) piezoelectric ring array.

    PubMed

    Miao, Hongchen; Huan, Qiang; Wang, Qiangzhong; Li, Faxin

    2017-02-01

    The non-dispersive fundamental shear horizontal (SH0) wave in plate-like structures is of practical importance in non-destructive testing (NDT) and structural health monitoring (SHM). Theoretically, an omnidirectional SH0 transducer phased array system can be used to inspect defects in a large plate in the similar manner to the phased array transducers used in medical B-scan ultrasonics. However, very few omnidirectional SH0 transducers have been proposed so far. In this work, an omnidirectional SH0 wave piezoelectric transducer (OSH-PT) was proposed, which consists of a ring array of twelve face-shear (d24) trapezoidal PZT elements. Each PZT element can produce face-shear deformation under applied voltage, resulting in circumferential shear deformation in the OSH-PT and omnidirectional SH0 waves in the hosting plate. Both finite element simulations and experiments were conducted to examine the performance of the proposed OSH-PT. Experimental testing shows that the OSH-PT exhibits good omnidirectional properties, no matter it is used as a SH0 wave transmitter or a SH0 wave receiver. This work may greatly promote the applications of SH0 waves in NDT and SHM.

  9. Wave-current interaction, experiments with controlled uniform shear

    NASA Astrophysics Data System (ADS)

    Simon, Bruno; Touboul, Julien; Rey, Vincent

    2016-04-01

    Vertically varying currents have a non negligible impact on the propagation of waves. Even though the analytical aspect of the interaction between wave and sheared current is being an active subject of research, experimental data remain rare. Here, the effects of a uniformly shear were investigated in the 10 m long by 0.3 m wide wave flume of the Université de Toulon, France. The main difficulty of the study was to produce several conditions of current with constant shear (du/dz = cst) that would persist along the channel. This was achieved by using curved wire screens upstream the channel (Dunn and Tavoularis, 2007). The geometry and properties of the screens were adjusted to deflect the streamline towards the channel bed or the free surface in order to change the velocity profile. The study focused on regular wave propagating against the current for several wave frequencies and amplitudes. Properties of the free surface and flow velocity are discussed for current with positive and negative shear in order to quantify the influence of the current on the waves. ACKNOWLEDGEMENTS The DGA (Direction Générale de l'Armement, France) is acknowledged for its financial support through the ANR grant N° ANR-13-ASTR-0007.

  10. Wave propagation in carbon nanotubes under shear deformation

    NASA Astrophysics Data System (ADS)

    Dong, K.; Wang, X.

    2006-06-01

    This paper reports the results of an investigation on the effect of shear deformations on wave propagation in carbon nanotubes embedded in an elastic matrix. A multi-walled carbon nanotube is considered as a multiple shell coupled together through van der Waals forces between two adjacent tubes. The surrounding matrix is considered as a spring element defined by the Winkler model. Using the variational calculus of Hamilton's principle, dynamic governing equations considering the shear deformation and rotary inertia terms are derived. Numerical examples describe the effects of shear deformation, rotary inertia and elastic matrix on the velocity, the critical frequency, the cut-off frequency and the amplitude ratio of wave propagation in multi-walled carbon nanotubes embedded in an elastic matrix, respectively. The results obtained show that wave propagation in carbon nanotubes appears in a critical frequency or a cut-off frequency for different wave modes; the effect of shear deformation decreases the value of critical frequency; the critical frequency increases as the matrix stiffness increases; the inertia rotary has an obvious influence on the wave velocity for some wave modes in the higher frequency region.

  11. The uppermost mantle shear wave velocity structure of eastern Africa from Rayleigh wave tomography: constraints on rift evolution

    NASA Astrophysics Data System (ADS)

    O'Donnell, J. P.; Adams, A.; Nyblade, A. A.; Mulibo, G. D.; Tugume, F.

    2013-08-01

    An expanded model of the 3-D shear wave velocity structure of the uppermost mantle beneath eastern Africa has been developed using earthquakes recorded by the AfricaArray East African Seismic Experiment in conjunction with data from permanent stations and previously deployed temporary stations. The combined data set comprises 331 earthquakes recorded on a total of 95 seismic stations spanning Kenya, Uganda, Tanzania, Zambia and Malawi. In this study, data from 149 earthquakes were used to determine fundamental-mode Rayleigh wave phase velocities at periods ranging from 20 to 182 s using the two-plane wave method, and then combined with the similarly processed published measurements and inverted for a 3-D shear wave velocity model of the uppermost mantle. New features in the model include (1) a low-velocity region in western Zambia, (2) a high-velocity region in eastern Zambia, (3) a low-velocity region in eastern Tanzania and (4) low-velocity regions beneath the Lake Malawi rift. When considered in conjunction with mapped seismicity, these results support a secondary western rift branch striking southwestwards from Lake Tanganyika, likely exploiting the relatively weak lithosphere of the southern Kibaran Belt between the Bangweulu Block and the Congo Craton. We estimate a lithospheric thickness of ˜150-200 km for the substantial fast shear wave anomaly imaged in eastern Zambia, which may be a southward subsurface extension of the Bangweulu Block. The low-velocity region in eastern Tanzania suggests that the eastern rift branch trends southeastwards offshore eastern Tanzania coincident with the purported location of the northern margin of the proposed Ruvuma microplate. Pronounced velocity lows along the Lake Malawi rift are found beneath the northern and southern ends of the lake, but not beneath the central portion of the lake.

  12. Could linear hysteresis contribute to shear wave losses in tissues?

    PubMed

    Parker, Kevin J

    2015-04-01

    For nearly 100 y in the study of cyclical motion in materials, a particular phenomenon called "linear hysteresis" or "ideal hysteretic damping" has been widely observed. More recently in the field of shear wave elastography, the basic mechanisms underlying shear wave losses in soft tissues are in question. Could linear hysteresis play a role? An underlying theoretical question must be answered: Is there a real and causal physical model that is capable of producing linear hysteresis over a band of shear wave frequencies used in diagnostic imaging schemes? One model that can approximately produce classic linear hysteresis behavior, by examining a generalized Maxwell model with a specific power law relaxation spectrum, is described here. This provides a theoretical plausibility for the phenomenon as a candidate for models of tissue behavior.

  13. A new shear wave imaging system for ultrasound elastography.

    PubMed

    Qiu, Weibao; Wang, Congzhi; Xiao, Yang; Qian, Ming; Zheng, Hairong

    2015-08-01

    Ultrasound elastography is able to provide a non-invasive measurement of tissue elasticity properties. Shear wave imaging (SWI) technique is a quantitative method for tissue stiffness assessment. However, traditional SWI implementations cannot acquire 2D quantitative images of tissue elasticity distribution. In this study, a new shear wave imaging system is proposed and evaluated. Detailed delineation of hardware and image processing algorithms are presented. Programmable devices are selected to support flexible control of the system and the image processing algorithms. Analytic signal based cross-correlation method and a Radon transform based shear wave speed determination method are proposed with parallel computation ability. Tissue mimicking phantom imaging, and in vitro imaging measurements are conducted to demonstrate the performance of the proposed system. The system has the ability to provide a new choice for quantitative mapping of the tissue elasticity, and has good potential to be implemented into commercial ultrasound scanner.

  14. Terrane-controlled crustal shear wave splitting in Taiwan

    NASA Astrophysics Data System (ADS)

    Okaya, David; Christensen, Nikolas I.; Ross, Zachary E.; Wu, Francis T.

    2016-01-01

    Taiwan is the result of arc-continent collision associated with the convergence of the Philippine Sea plate with the eastern Eurasian plate continental margin. The locus of deformation is found in eastern Taiwan in the form of mountain building (Central Range) with underlying thickened lithosphere. Rapid tectonic exhumation in the Central Range has uncovered low-to-high-grade metamorphic rocks marked by steep cleavage. We carried out a crustal seismic anisotropy study across Taiwan, producing a database of over 27,000 local earthquake shear wave splitting measurements. Additionally, we carried out rock physics measurements of metamorphic outcrop samples to quantify shear wave rock anisotropy. We produced a map of station-averaged splitting measurements across Taiwan. Patterns of fast shear wave directions correlate with tectonic terranes produced by plate convergence. Deformation-related mineral-preferred orientation in the metamorphic rocks produces a significant amount of the crustal anisotropy in the Taiwan collision zone.

  15. Lithology and shear-wave velocity in Memphis, Tennessee

    USGS Publications Warehouse

    Gomberg, J.; Waldron, B.; Schweig, E.; Hwang, H.; Webbers, A.; Van Arsdale, R.; Tucker, K.; Williams, R.; Street, R.; Mayne, P.; Stephenson, W.; Odum, J.; Cramer, C.; Updike, R.; Hutson, S.; Bradley, M.

    2003-01-01

    We have derived a new three-dimensional model of the lithologic structure beneath the city of Memphis, Tennessee, and examined its correlation with measured shear-wave velocity profiles. The correlation is sufficiently high that the better-constrained lithologic model may be used as a proxy for shear-wave velocities, which are required to calculate site-amplification for new seismic hazard maps for Memphis. The lithologic model and its uncertainties are derived from over 1200 newly compiled well and boring logs, some sampling to 500 m depth, and a moving-least-squares algorithm. Seventy-six new shear-wave velocity profiles have been measured and used for this study, most sampling to 30 m depth or less. All log and velocity observations are publicly available via new web sites.

  16. Shear wave velocity structures of the Arabian Peninsula

    NASA Astrophysics Data System (ADS)

    Mokhtar, Talal A.; Al-Saeed, Mohammed M.

    1994-02-01

    The shear velocity structures of the different tectonic provinces of the Arabian Peninsula has been studied using surface wave data recorded by the RYD (Riyadh) station. The inversion of Rayleigh wave group velocities indicates that the Arabian shield can be modeled by two layers, each of which is 20 km thick with a shear velocity of 3.61 km/s in the upper crust and 3.88 km/s in the lower crust. The underlying upper mantle velocity is 4.61 km/s. Inversion of both Love and Rayleigh waves group velocities shows that the Arabian platform upper and lower crusts are comparable in their thicknesses to those of the shield, but with shear velocities of 3.4 and 4 km/s, respectively. The upper mantle velocity beneath the platform is 4.4 km/s and the average total thickness of the crust is 45 km.

  17. Two-dimensional shear wave speed and crawling wave speed recoveries from in vitro prostate data

    PubMed Central

    Lin, Kui; McLaughlin, Joyce R.; Thomas, Ashley; Parker, Kevin; Castaneda, Benjamin; Rubens, Deborah J.

    2011-01-01

    The crawling wave experiment was developed to capture a shear wave induced moving interference pattern that is created by two harmonic vibration sources oscillating at different but almost the same frequencies. Using the vibration sonoelastography technique, the spectral variance image reveals a moving interference pattern. It has been shown that the speed of the moving interference pattern, i.e., the crawling wave speed, is proportional to the shear wave speed with a nonlinear factor. This factor can generate high-speed artifacts in the crawling wave speed images that do not actually correspond to increased stiffness. In this paper, an inverse algorithm is developed to reconstruct both the crawling wave speed and the shear wave speed using the phases of the crawling wave and the shear wave. The feature for the data is the application to in vitro prostate data, while the features for the algorithm include the following: (1) A directional filter is implemented to obtain a wave moving in only one direction; and (2) an L1 minimization technique with physics inspired constraints is employed to calculate the phase of the crawling wave and to eliminate jump discontinuities from the phase of the shear wave. The algorithm is tested on in vitro prostate data measured at the Rochester Center for Biomedical Ultrasound and University of Rochester. Each aspect of the algorithm is shown to yield image improvement. The results demonstrate that the shear wave speed images can have less artifacts than the crawling wave images. Examples are presented where the shear wave speed recoveries have excellent agreement with histology results on the size, shape, and location of cancerous tissues in the glands. PMID:21786924

  18. Two-dimensional shear wave speed and crawling wave speed recoveries from in vitro prostate data.

    PubMed

    Lin, Kui; McLaughlin, Joyce R; Thomas, Ashley; Parker, Kevin; Castaneda, Benjamin; Rubens, Deborah J

    2011-07-01

    The crawling wave experiment was developed to capture a shear wave induced moving interference pattern that is created by two harmonic vibration sources oscillating at different but almost the same frequencies. Using the vibration sonoelastography technique, the spectral variance image reveals a moving interference pattern. It has been shown that the speed of the moving interference pattern, i.e., the crawling wave speed, is proportional to the shear wave speed with a nonlinear factor. This factor can generate high-speed artifacts in the crawling wave speed images that do not actually correspond to increased stiffness. In this paper, an inverse algorithm is developed to reconstruct both the crawling wave speed and the shear wave speed using the phases of the crawling wave and the shear wave. The feature for the data is the application to in vitro prostate data, while the features for the algorithm include the following: (1) A directional filter is implemented to obtain a wave moving in only one direction; and (2) an L(1) minimization technique with physics inspired constraints is employed to calculate the phase of the crawling wave and to eliminate jump discontinuities from the phase of the shear wave. The algorithm is tested on in vitro prostate data measured at the Rochester Center for Biomedical Ultrasound and University of Rochester. Each aspect of the algorithm is shown to yield image improvement. The results demonstrate that the shear wave speed images can have less artifacts than the crawling wave images. Examples are presented where the shear wave speed recoveries have excellent agreement with histology results on the size, shape, and location of cancerous tissues in the glands.

  19. Shear-Alfv'en Waves in Gyrokinetic Particle Simulation

    NASA Astrophysics Data System (ADS)

    Dickerson, Thomas D.; Startsev, Edward A.; Lee, W. W.

    2012-10-01

    Numerical properties of shear-Alfv'en waves in slab geometry have been studied using a Particle-in-Cell code implementing the recently developed double split-weight scheme [1]. This scheme separates the non-adiabatic response of the particles from both their adiabatic responses and the field-line bending effects arising from the background density and temperature gradients of both the electrons and the ions. This scheme is an improvement over the original split-weight scheme [2] in the presence of the zeroth-order inhomogeneities. The present studies consist of testing numerical restrictions on temporal resolution in the simulation of these waves in one and two dimensions, and on spatial resolutions on the formation of shear Alfv'en eigenmodes in two dimensional sheared slab simulations. For example, it is found that the correct behavior of ion temperature gradient modes in terms of frequencies and growth rates can be maintained with time steps larger than the limit imposed by the shear-Alfven waves. Details will be reported.[4pt] [1] E. A. Startsev and W. W. Lee, ``Finite-Beta Simulation of Microinstabilities,'' manuscript in preparation (2012). [0pt] [2] W. W. Lee, J. L. V. Lewandowski, T. S. Hahm and Z. Lin, ``Shear-Alf'en Waves in Gyrokinetic Plasmas,'' Phys. Plasmas 10, 4435 (2001).

  20. Shear wave elastography quantification of blood elasticity during clotting.

    PubMed

    Bernal, Miguel; Gennisson, Jean-Luc; Flaud, Patrice; Tanter, Mickael

    2012-12-01

    Deep venous thrombosis (DVT) affects millions of people worldwide. A fatal complication occurs when the thrombi detach and create a pulmonary embolism. The diagnosis and treatment of DVT depends on clot's age. The elasticity of thrombi is closely related to its age. Blood was collected from pigs and anticoagulated using ethylenediaminetetraacetic acid (EDTA). Coagulation was initiated using calcium ions. Supersonic shear wave imaging was used to generate shear waves using 100 μs tone bursts of 8 MHz. Tracking of the shear waves was done by ultrafast imaging. Postprocessing of the data was done using Matlab(®). Two-dimensional (2-D) maps of elasticity were obtained by calculating the speed of shear wave propagation. Elasticity varied with time from around 50 Pa at coagulation to 1600 Pa at 120 min after which the elasticity showed a natural decreased (17%) because of thrombolytic action of plasmin. Ejection of the serum from the clot showed a significant decrease in the elasticity of the clot next to the liquid pool (65% decrease), corresponding to the detachment of the clot from the beaker wall. The use of a thrombolytic agent (Urokinase) on the coagulated blood decreased the shear elasticity close to the point of injection, which varied with time and distance. Supersonic imaging proved to be useful mapping the 2-D clot's elasticity. It allowed the visualization of the heterogeneity of mechanical properties of thrombi and has potential use in predicting thrombi breakage as well as in monitoring thrombolytic therapy.

  1. The parametric decay of Alfven waves into shear Alfven waves and dust lower hybrid waves

    SciTech Connect

    Jamil, M.; Shah, H. A.; Zubia, K.; Zeba, I.; Uzma, Ch.; Salimullah, M.

    2010-07-15

    The parametric decay instability of Alfven wave into low-frequency electrostatic dust-lower-hybrid and electromagnetic shear Alfven waves has been investigated in detail in a dusty plasma in the presence of external/ambient uniform magnetic field. Magnetohydrodynamic fluid equations of plasmas have been employed to find the linear and nonlinear response of the plasma particles for this three-wave nonlinear coupling in a dusty magnetoplasma. Here, relatively high frequency electromagnetic Alfven wave has been taken as the pump wave. It couples with other two low-frequency internal possible modes of the dusty magnetoplasma, viz., the dust-lower-hybrid and shear Alfven waves. The nonlinear dispersion relation of the dust-lower-hybrid wave has been solved to obtain the growth rate of the parametric decay instability. The growth rate is maximum for small value of external magnetic field B{sub s}. It is noticed that the growth rate is proportional to the unperturbed electron number density n{sub oe}.

  2. The origin of shear wave splitting beneath Iceland

    NASA Astrophysics Data System (ADS)

    Ito, Garrett; Dunn, Robert; Li, Aibing

    2015-06-01

    The origin of shear wave splitting (SWS) in the mantle beneath Iceland is examined using numerical models that simulate 3-D mantle flow and the development of seismic anisotropy due to lattice-preferred orientation (LPO). Using the simulated anisotropy structure, we compute synthetic SKS waveforms, invert them for fast polarization directions and split times, and then compare the predictions with the results from three observational studies of Iceland. Models that simulate a mantle plume interacting with the Mid-Atlantic Ridge in which the shallow-most mantle has a high viscosity due to the extraction of water with partial melting, or in which C-type olivine LPO fabric is present due to high water content in the plume, produce the largest chi-squared misfits to the SWS observations and are thus rejected. Models of a low-viscosity mantle plume with A-type olivine fabric everywhere, or with the added effects of E-type fabric in the plume below the solidus produce lower misfits. The lowest misfits are produced by models that include a rapid (˜50 km Myr-1) northward regional flow (NRF) in the mid-upper mantle, either with or without a plume. NRF was previously indicated by a receiver function study and a regional tomography study, and is shown here to be a major cause of the azimuthal anisotropy beneath Iceland. The smallest misfits for the models with both a plume and NRF are produced when LPO forms above depths of 300-400 km, which, by implication, also mark the depths above which dislocation creep dominates over diffusion creep. This depth of transition between dislocation and diffusion creep is greater than expected beneath normal oceanic seafloor, and is attributed to the unusually rapid strain rates associated with an Iceland plume and the NRF.

  3. The effect of subducting slabs in global shear wave tomography

    NASA Astrophysics Data System (ADS)

    Lu, Chang; Grand, Stephen P.

    2016-05-01

    Subducting slabs create strong short wavelength seismic anomalies in the upper mantle where much of Earth's seismicity is located. As such, they have the potential to bias longer wavelength seismic tomography models. To evaluate the effect of subducting slabs in global tomography, we performed a series of inversions using a global synthetic shear wave traveltime data set for a theoretical slab model based on predicted thermal anomalies within slabs. The spectral element method was applied to predict the traveltime anomalies produced by the 3-D slab model for paths corresponding to our current data used in actual tomography models. Inversion tests have been conducted first using the raw traveltime anomalies to check how well the slabs can be imaged in global tomography without the effect of earthquake mislocation. Our results indicate that most of the slabs can be identified in the inversion result but with smoothed and reduced amplitude. The recovery of the total mass anomaly in slab regions is about 88 per cent. We then performed another inversion test to investigate the effect of mislocation caused by subducting slabs. We found that source mislocation largely removes slab signal and significantly degrades the imaging of subducting slabs-potentially reducing the recovery of mass anomalies in slab regions to only 41 per cent. We tested two source relocation procedures-an iterative relocation inversion and joint relocation inversion. Both methods partially recover the true source locations and improve the inversion results, but the joint inversion method worked significantly better than the iterative method. In all of our inversion tests, the amplitudes of artefact structures in the lower mantle caused by the incorrect imaging of slabs (up to ˜0.5 per cent S velocity anomalies) are comparable to some large-scale lower-mantle heterogeneities seen in global tomography studies. Based on our inversion tests, we suggest including a-priori subducting slabs in the

  4. Dispersion relations of short surface gravity waves over vertically sheared currents from stereo-video measurements

    NASA Astrophysics Data System (ADS)

    Peureux, Charles; Ardhuin, Fabrice

    2016-04-01

    The stereo-video reconstuction method [Leckler et al. 2015] allows now for the full reconstruction of 3D frequency-wavenumber spectra of short waves. A new field campaign in 2013 on the Katsiveli platform (Black Sea) provided such spectra in various wind and waves conditions, and particularly a stormy event, after which very mature waves had been generated. The short waves energies are found to be mostly located around a dispersion relation of the form, () ° ----------- ω ⃗k = gktanh(kH)+ ⃗kṡ ⃗Ueff The effective advection velocity [Kirby and Chen 1989] ⃗Ueff(k) integrates contributions from both the Stokes drift and quasi-eulerian current [Groeneweg and Klopman 1998]. We find that the effective drift velocity has a very weak wavenumber dependancy, as a result the eulerian current must be vertically sheared. This shear is relevant to the breaking of small scale waves [Banner and Phillips 1974]. It is possible that in field conditions the wind drift is much less important than in the laboratory. Bibliography Banner, M. L. and Phillips, O. M., On the incipient breaking of small scale waves, J. Fluid Mech., 1974, 65, 647. Groeneweg, J. and Klopman, G., Changes of the mean velocity profiles in the combined wave-current motion described in a GLM formulation, J. Fluid Mech., 1998, 370, 271-296. Kirby, J. T. and Chen, T. M., Surface waves on vertically sheared flows : Approximate dispersion relations, J. Geophys. Res., 1989, 94, 1013. Leckler, F., Ardhuin, F., Peureux, C.,Benetazzo, A., Bergamasco, F. and Dulov, V., Analysis and interpretation of frequency-wavenumber spectra of young wind-waves, J. Phys. Oceanogr., 2015, 45, 2484-2496.

  5. A goal-oriented adaptive finite-element approach for plane wave 3-D electromagnetic modelling

    NASA Astrophysics Data System (ADS)

    Ren, Zhengyong; Kalscheuer, Thomas; Greenhalgh, Stewart; Maurer, Hansruedi

    2013-08-01

    We have developed a novel goal-oriented adaptive mesh refinement approach for finite-element methods to model plane wave electromagnetic (EM) fields in 3-D earth models based on the electric field differential equation. To handle complicated models of arbitrary conductivity, magnetic permeability and dielectric permittivity involving curved boundaries and surface topography, we employ an unstructured grid approach. The electric field is approximated by linear curl-conforming shape functions which guarantee the divergence-free condition of the electric field within each tetrahedron and continuity of the tangential component of the electric field across the interior boundaries. Based on the non-zero residuals of the approximated electric field and the yet to be satisfied boundary conditions of continuity of both the normal component of the total current density and the tangential component of the magnetic field strength across the interior interfaces, three a-posterior error estimators are proposed as a means to drive the goal-oriented adaptive refinement procedure. The first a-posterior error estimator relies on a combination of the residual of the electric field, the discontinuity of the normal component of the total current density and the discontinuity of the tangential component of the magnetic field strength across the interior faces shared by tetrahedra. The second a-posterior error estimator is expressed in terms of the discontinuity of the normal component of the total current density (conduction plus displacement current). The discontinuity of the tangential component of the magnetic field forms the third a-posterior error estimator. Analytical solutions for magnetotelluric (MT) and radiomagnetotelluric (RMT) fields impinging on a homogeneous half-space model are used to test the performances of the newly developed goal-oriented algorithms using the above three a-posterior error estimators. A trapezoidal topographical model, using normally incident EM waves

  6. A Multiresolution Approach to Shear Wave Image Reconstruction

    PubMed Central

    Hollender, Peter; Bottenus, Nick; Trahey, Gregg

    2015-01-01

    Shear wave imaging techniques build maps of local elasticity estimating the local group velocity of induced mechanical waves. Velocity estimates are formed using the time delay in the motion profile of the medium at two or more points offset from the shear wave source. Because the absolute time-of-flight between any pair of locations scales with the distance between them, there is an inherent trade-off between robustness to time-of-flight errors and lateral spatial resolution based on the number and spacing of the receive points used for each estimate. This work proposes a method of using the time delays measured between all combinations of locations to estimate a noise-robust, high-resolution image. The time-of-flight problem is presented as an overdetermined system of linear equations that can be directly solved with and without spatial regularization terms. Finite element method simulations of acoustic radiation force-induced shear waves are used to illustrate the method, demonstrating superior contrast-to-noise ratio and lateral edge resolution characteristics compared to linear regression of arrival times. This technique may improve shear wave imaging in situations where time-of-flight noise is a limiting factor. PMID:26276953

  7. 3D Anisotropic structure of the south-central Mongolia from Rayleigh and Love wave tomography

    NASA Astrophysics Data System (ADS)

    Yu, D.; Wu, Q.; Montagner, J. P.

    2014-12-01

    A better understanding of the geodynamics of the crust and mantle below Baikal-Mongolia is required to identify the role of mantle processes versus that of far-field tectonic effects from India-Asia collision. Anisotropy tomography can provide new perspective to the continental growth mechanism. In order to study the 3D anisotropic structure of the upper mantle in the south-central Mongolia, we collected the vertical and transverse components of seismograms recorded at 69 broadband seismic stations. We have measured inter-station phase velocities of 7181 Rayleigh waves and 901 Love waves using the frequency-time analysis of wavelet transformation method for the fundamental mode at period range 10~80s. The lateral phase velocity variations are computed by using a regionalization method. These phase velocities have been inverted to obtain the first anisotropic model including Sv velocities, azimuthal and radial anisotropy. The Middle Gobi is associated with low velocity. Based on the distribution of the Cenozoic basalts in the Middle Gobi, it refers that the low velocity anomaly is related to the Cenozoic volcanism. In the northern domain, near to Baikal zone, the azimuthal anisotropy is normal to the Baikal rift and consistent with the fast direction of previous SKS splitting measurements. In the South Gobi, north to Main Mongolian Lineament, the azimuthal anisotropy is NEE-SWW in the crust and NW-SE in the mantle. It indicates that the crust and mantle are decoupled. We propose that the crustal deformation is related to the far-field effects of India-Asia collision and that the mantle flow is correlated with the Baikal rift activity. Further study in process will provide more evidence and insight to better understand the geodynamics in this region.

  8. On the initiation of surface waves by turbulent shear flow

    NASA Astrophysics Data System (ADS)

    Teixeira, M. A. C.; Belcher, S. E.

    2006-02-01

    An analytical model is developed for the initial stage of surface wave generation at an air-water interface by a turbulent shear flow in either the air or in the water. The model treats the problem of wave growth departing from a flat interface and is relevant for small waves whose forcing is dominated by turbulent pressure fluctuations. The wave growth is predicted using the linearised and inviscid equations of motion, essentially following Phillips [Phillips, O.M., 1957. On the generation of waves by turbulent wind. J. Fluid Mech. 2, 417-445], but the pressure fluctuations that generate the waves are treated as unsteady and related to the turbulent velocity field using the rapid-distortion treatment of Durbin [Durbin, P.A., 1978. Rapid distortion theory of turbulent flows. PhD thesis, University of Cambridge]. This model, which assumes a constant mean shear rate Γ, can be viewed as the simplest representation of an oceanic or atmospheric boundary layer. For turbulent flows in the air and in the water producing pressure fluctuations of similar magnitude, the waves generated by turbulence in the water are found to be considerably steeper than those generated by turbulence in the air. For resonant waves, this is shown to be due to the shorter decorrelation time of turbulent pressure in the air (estimated as ∝ 1/ Γ), because of the higher shear rate existing in the air flow, and due to the smaller length scale of the turbulence in the water. Non-resonant waves generated by turbulence in the water, although being somewhat gentler, are still steeper than resonant waves generated by turbulence in the air. Hence, it is suggested that turbulence in the water may have a more important role than previously thought in the initiation of the surface waves that are subsequently amplified by feedback instability mechanisms.

  9. Threshold response using modulated continuous wave illumination for multilayer 3D optical data storage

    NASA Astrophysics Data System (ADS)

    Saini, A.; Christenson, C. W.; Khattab, T. A.; Wang, R.; Twieg, R. J.; Singer, K. D.

    2017-01-01

    In order to achieve a high capacity 3D optical data storage medium, a nonlinear or threshold writing process is necessary to localize data in the axial dimension. To this end, commercial multilayer discs use thermal ablation of metal films or phase change materials to realize such a threshold process. This paper addresses a threshold writing mechanism relevant to recently reported fluorescence-based data storage in dye-doped co-extruded multilayer films. To gain understanding of the essential physics, single layer spun coat films were used so that the data is easily accessible by analytical techniques. Data were written by attenuating the fluorescence using nanosecond-range exposure times from a 488 nm continuous wave laser overlapping with the single photon absorption spectrum. The threshold writing process was studied over a range of exposure times and intensities, and with different fluorescent dyes. It was found that all of the dyes have a common temperature threshold where fluorescence begins to attenuate, and the physical nature of the thermal process was investigated.

  10. Nonhydrostatic granular flow over 3-D terrain: New Boussinesq-type gravity waves?

    NASA Astrophysics Data System (ADS)

    Castro-Orgaz, Oscar; Hutter, Kolumban; Giraldez, Juan V.; Hager, Willi H.

    2015-01-01

    granular mass flow is a basic step in the prediction and control of natural or man-made disasters related to avalanches on the Earth. Savage and Hutter (1989) pioneered the mathematical modeling of these geophysical flows introducing Saint-Venant-type mass and momentum depth-averaged hydrostatic equations using the continuum mechanics approach. However, Denlinger and Iverson (2004) found that vertical accelerations in granular mass flows are of the same order as the gravity acceleration, requiring the consideration of nonhydrostatic modeling of granular mass flows. Although free surface water flow simulations based on nonhydrostatic depth-averaged models are commonly used since the works of Boussinesq (1872, 1877), they have not yet been applied to the modeling of debris flow. Can granular mass flow be described by Boussinesq-type gravity waves? This is a fundamental question to which an answer is required, given the potential to expand the successful Boussinesq-type water theory to granular flow over 3-D terrain. This issue is explored in this work by generalizing the basic Boussinesq-type theory used in civil and coastal engineering for more than a century to an arbitrary granular mass flow using the continuum mechanics approach. Using simple test cases, it is demonstrated that the above question can be answered in the affirmative way, thereby opening a new framework for the physical and mathematical modeling of granular mass flow in geophysics, whereby the effect of vertical motion is mathematically included without the need of ad hoc assumptions.

  11. Characterization of an SRF gun: a 3D full wave simulation

    SciTech Connect

    Wang, E.; Ben-Zvi, I.; Wang, J.

    2011-03-28

    We characterized a BNL 1.3GHz half-cell SRF gun is tested for GaAs photocathode. The gun already was simulated several years ago via two-dimensional (2D) numerical codes (i.e., Superfish and Parmela) with and without the beam. In this paper, we discuss our investigation of its characteristics using a three dimensional (3D) full-wave code (CST STUDIO SUITE{trademark}).The input/pickup couplers are sited symmetrically on the same side of the gun at an angle of 180{sup o}. In particular, the inner conductor of the pickup coupler is considerably shorter than that of the input coupler. We evaluated the cross-talk between the beam (trajectory) and the signal on the input coupler compared our findings with published results based on analytical models. The CST STUDIO SUITE{trademark} also was used to predict the field within the cavity; particularly, a combination of transient/eigenmode solvers was employed to accurately construct the RF field for the particles, which also includes the effects of the couplers. Finally, we explored the beam's dynamics with a particle in cell (PIC) simulation, validated the results and compare them with 2D code result.

  12. On the interaction between shear dusty currents and buildings in vertical collapse: Theoretical aspects, experimental observations, and 3D numerical simulation

    NASA Astrophysics Data System (ADS)

    Doronzo, Domenico M.; de Tullio, Marco D.; Pascazio, Giuseppe; Dellino, Pierfrancesco; Liu, Guilin

    2015-09-01

    We investigate the behavior of vertical building collapses that, at impact on the ground, can generate shear dusty currents. These currents macroscopically resemble natural currents like dust storms and pyroclastic density currents, which may heavily interact with the surroundings while propagating. In particular, shear dusty currents are generated because of building collapse after pulverization, whereas pyroclastic density currents can be generated because of eruptive column or volcano collapse after fragmentation. Pyroclastic density currents can move for kilometers, and then load the surroundings by flow dynamic pressure; a similar dynamical behavior occurs in shear dusty currents that load buildings. We employed 3D engineering fluid dynamics to simulate the generation (by vertical collapse), and the propagation and building interaction of shear dusty currents. We used an Eulerian-Lagrangian multiphase approach to model the gas-particle flow, and an immersed boundary technique to mesh the domain, in order to account for sedimentary processes and complex 3D urban geometry in the computation. Results show that the local dynamic pressure of the shear current is amplified up to a factor ~ 10 because of flow-building interaction. Also, the surroundings consisting of multiple buildings and empty spaces make walls and streets as surfaces of particle accumulation, which from the collapse zone on can get thinner by exponential law. These results can help better assessing the intricate interaction between pyroclastic density currents and urban surroundings, as well as better link fragmentation, collapse and density current to each other.

  13. Lamellipodin promotes invasive 3D cancer cell migration via regulated interactions with Ena/VASP and SCAR/WAVE

    PubMed Central

    Carmona, Guillaume; Perera, Upamali; Gillett, Cheryl; Naba, Alexandra; Law, Ah-Lai; Sharma, Ved P.; Wang, Jian; Wyckoff, Jeffrey; Balsamo, Michele; Mosis, Fuad; De Piano, Mario; Monypenny, James; Woodman, Natalie; McConnell, Russell E.; Mouneimne, Ghassan; Van Hemelrijck, Mieke; Cao, Yihai; Condeelis, John; Hynes, Richard O.; Gertler, Frank B.; Krause, Matthias

    2016-01-01

    Cancer invasion is a hallmark of metastasis. The mesenchymal mode of cancer cell invasion is mediated by elongated membrane protrusions driven by the assembly of branched F-actin networks. How deregulation of actin regulators promotes cancer cell invasion is still enigmatic. We report that increased expression and membrane localization of the actin regulator Lamellipodin correlates with reduced metastasis-free survival and poor prognosis in breast cancer patients. In agreement we find that Lamellipodin depletion reduced lung metastasis in an orthotopic mouse breast cancer model. Invasive 3D cancer cell migration as well as invadopodia formation, and matrix degradation were impaired upon Lamellipodin depletion. Mechanistically, we show that Lamellipodin promotes invasive 3D cancer cell migration via both actin-elongating Ena/VASP proteins and the Scar/WAVE complex, which stimulates actin branching. In contrast, Lamellipodin interaction with Scar/WAVE but not Ena/VASP is required for random 2D cell migration. We identify a phosphorylation-dependent mechanism that regulates selective recruitment of these effectors to Lamellipodin: Abl-mediated Lamellipodin phosphorylation promotes its association with both Scar/WAVE and Ena/VASP, while Src-dependent phosphorylation enhances binding to Scar/WAVE but not Ena/VASP. Through these selective, regulated interactions Lamellipodin mediates directional sensing of EGF gradients and invasive 3D migration of breast cancer cells. Our findings imply that increased Lamellipodin levels enhance Ena/VASP and Scar/WAVE activities at the plasma membrane to promote 3D invasion and metastasis. PMID:26996666

  14. Transverse instability and viscous dissipation of forced 3-D gravity-capillary solitary waves on deep water

    NASA Astrophysics Data System (ADS)

    Cho, Yeunwoo

    2014-11-01

    The shedding phenomena of 3-D viscous gravity-capillary solitary waves generated by a moving air-forcing on the surface of deep water are investigated. Near the resonance where the forcing speed is close to 23 cm/s, two kinds of shedding modes are possible; Anti-symmetric and symmetric modes. A relevant theoretical model equation is numerically solved for the identification of shedding of solitary waves, and is analytically studied in terms of their linear stability to transverse perturbations. Furthermore, by tracing trajectories of shed solitary waves, the decay rate of a 3-D solitary wave due to viscous dissipation is estimated. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2014R1A1A1002441).

  15. Nonlinear evolution of 3D-inertial Alfvén wave and turbulent spectra in Auroral region

    NASA Astrophysics Data System (ADS)

    Rinawa, M. L.; Modi, K. V.; Sharma, R. P.

    2014-10-01

    In the present paper, we have investigated nonlinear interaction of three dimensional (3D) inertial Alfvén wave and perpendicularly propagating magnetosonic wave for low β-plasma ( β≪ m e / m i ). We have developed the set of dimensionless equations in the presence of ponderomotive nonlinearity due to 3D-inertial Alfvén wave in the dynamics of perpendicularly propagating magnetosonic wave. Stability analysis and numerical simulation has been carried out to study the effect of nonlinear coupling on the formation of localized structures and turbulent spectra, applicable to auroral region. The results reveal that the localized structures become more and more complex as the nonlinear interaction progresses. Further, we have studied the turbulent spectrum which follows spectral index (˜ k -3.57) at smaller scales. Relevance of the obtained results has been shown with the observations received by various spacecrafts like FAST, Hawkeye and Heos 2.

  16. Shear Wave Speed Measurements Using Crawling Wave Sonoelastography and Single Tracking Location Shear Wave Elasticity Imaging for Tissue Characterization.

    PubMed

    Ormachea, Juvenal; Lavarello, Roberto J; McAleavey, Stephen A; Parker, Kevin J; Castaneda, Benjamin

    2016-09-01

    Elastography provides tissue stiffness information that attempts to characterize the elastic properties of tissue. However, there is still limited literature comparing elastographic modalities for tissue characterization. This study focuses on two quantitative techniques using different vibration sources that have not been compared to date: crawling wave sonoelastography (CWS) and single tracking location shear wave elasticity imaging (STL-SWEI). To understand each technique's performance, shear wave speed (SWS) was measured in homogeneous phantoms and ex vivo beef liver tissue. Then, the contrast, contrast-to-noise ratio (CNR), and lateral resolution were measured in an inclusion and two-layer phantoms. The SWS values obtained with both modalities were validated with mechanical measurements (MM) which serve as ground truth. The SWS results for the three different homogeneous phantoms (10%, 13%, and 16% gelatin concentrations) and ex vivo beef liver tissue showed good agreement between CWS, STL-SWEI, and MM as a function of frequency. For all gelatin phantoms, the maximum accuracy errors were 2.52% and 2.35% using CWS and STL-SWEI, respectively. For the ex vivo beef liver, the maximum accuracy errors were 9.40% and 7.93% using CWS and STL-SWEI, respectively. For lateral resolution, contrast, and CNR, both techniques obtained comparable measurements for vibration frequencies less than 300 Hz (CWS) and distances between the push beams ( ∆x ) between 3 mm and 5.31 mm (STL-SWEI). The results obtained in this study agree over an SWS range of 1-6 m/s. They are expected to agree in perfectly linear, homogeneous, and isotropic materials, but the SWS overlap is not guaranteed in all materials because each of the three methods have unique features.

  17. Shear horizontal (SH) ultrasound wave propagation around smooth corners.

    PubMed

    Petcher, P A; Burrows, S E; Dixon, S

    2014-04-01

    Shear horizontal (SH) ultrasound guided waves are being used in an increasing number of non-destructive testing (NDT) applications. One advantage SH waves have over some wave types, is their ability to propagate around curved surfaces with little energy loss; to understand the geometries around which they could propagate, the wave reflection must be quantified. A 0.83mm thick aluminium sheet was placed in a bending machine, and a shallow bend was introduced. Periodically-poled magnet (PPM) electromagnetic acoustic transducers (EMATs), for emission and reception of SH waves, were placed on the same side of the bend, so that reflected waves were received. Additional bending of the sheet demonstrated a clear relationship between bend angles and the reflected signal. Models suggest that the reflection is a linear superposition of the reflections from each bend segment, such that sharp turns lead to a larger peak-to-peak amplitude, in part due to increased phase coherence.

  18. Influence of 3D Teleseismic Body Waves in the Finite-Fault Source Inversion of Subduction Earthquakes

    NASA Astrophysics Data System (ADS)

    Sladen, A.; Monteiller, V.

    2014-12-01

    Most large earthquakes are generated in subduction zones. To study the complexity of these events, teleseismic body waves offer many advantages over other types of data: they allow to study both the temporal and spatial evolution of slip during the rupture, they don't depend on the presence of nearby land and they allow to study earthquakes regardless of their location. Since the development of teleseismic finite-fault inversion in the 1980th, teleseismic body waves have been simulated using 1D velocity models to take into account propagation effects at the source. Yet, subduction zones are known to be highly heterogeneous: they are characterized by curved and dipping structures, strong seismic velocity contrasts, strong variations of topography and height of the water column. The main reason for relying on a 1D approximation is the computational cost of 3D simulations. And while forward simulations of teleseismic waves in a 3D Earth are only starting to be tractable on modern computers at the frequency range of interest (0.1Hz or shorter), finite-fault source studies require a large number of these simulations. In this work, we present a new and efficient approach to compute 3D teleseismic body waves, in which the full 3D propagation is only computed in a regional domain using discontinuous Galerkin finite-element method, while the rest of the seismic wave field is propagated in a background axisymmetric Earth. The regional and global wave fields are matched using the so-called Total-Field/Scattered-Field technique. This new simulation approach allows us to study the waveform complexities resulting from 3D propagation and investigate how they could improve the resolution and reduce the non-uniqueness of finite-fault inversions.

  19. Constraints on the 3D shape of the ultra low shear velocity zone at the base of the mantle beneath the central Pacific

    NASA Astrophysics Data System (ADS)

    To, A.; Capdeville, Y.

    2011-12-01

    Prominent postcursors to S/Sdiff waves with delays as large as 26 s are observed in Northern America for Papua New Guinea events (To et al., 2011). The emergence of the postcursor is explained by placing a laterally localized ultra low shear velocity zone (ULSVZ, dVs/Vs<-25%) on the CMB, which is fully or partially covered by a broad and weak anomaly region (dVs/Vs~-5%). The ULSVZ is located approximately 900 km southwest of the projection of the Hawaiian hotspot onto the CMB. In the previous study, we limited our focus to an azimuthal range around 60 degrees from the source in Papua New Guinea, where the records show a relatively small azimuthal variation, suggesting a relatively small 3D effect there. The modelling was limited to 2D structure along the great circle plane, partly because of the sparse station distribution in Midwestern US at the time. In this study, we investigated data from USArray and further constrained the 3D shape of the ULSVZ. The postcursors to S/Sdiff waves are observed at 240 USArray stations for an event, which occurred near Papua New Guinea in 2010. The records from the large number of stations enabled us to conduct array analysis. First, we mapped the variation of incident azimuth and slowness of the secondary arrivals to the stations. In southern stations, which are located along the azimuth of approximately 60 degrees from the source, the postcursors arrive from the direction of the source. On the other hand, in northern stations, which are located at the azimuth of approximately 52 degrees from the source, the postcursors arrive from the azimuth of 5 to 10 degrees to the south with respect to the direction toward the source. Second, we compared the observed amplitude of the main S/Sdiff phase with synthetic waveforms created by Direct solution method (Kawai et al., 2006). The comparison shows that the amplitude of the main phase become very small at stations which are located approximately at the distance of 100 degrees and the

  20. Shear velocity structure of the crust and upper mantle of Madagascar derived from surface wave tomography

    NASA Astrophysics Data System (ADS)

    Pratt, Martin J.; Wysession, Michael E.; Aleqabi, Ghassan; Wiens, Douglas A.; Nyblade, Andrew A.; Shore, Patrick; Rambolamanana, Gérard; Andriampenomanana, Fenitra; Rakotondraibe, Tsiriandrimanana; Tucker, Robert D.; Barruol, Guilhem; Rindraharisaona, Elisa

    2017-01-01

    The crust and upper mantle of the Madagascar continental fragment remained largely unexplored until a series of recent broadband seismic experiments. An island-wide deployment of broadband seismic instruments has allowed the first study of phase velocity variations, derived from surface waves, across the entire island. Late Cenozoic alkaline intraplate volcanism has occurred in three separate regions of Madagascar (north, central and southwest), with the north and central volcanism active until <1 Ma, but the sources of which remains uncertain. Combined analysis of three complementary surface wave methods (ambient noise, Rayleigh wave cross-correlations, and two-plane-wave) illuminate the upper mantle down to depths of 150 km. The phase-velocity measurements from the three methods for periods of 8-182 s are combined at each node and interpolated to generate the first 3-D shear-velocity model for sub-Madagascar velocity structure. Shallow (upper 10 km) low-shear-velocity regions correlate well with sedimentary basins along the west coast. Upper mantle low-shear-velocity zones that extend to at least 150 km deep underlie the north and central regions of recent alkali magmatism. These anomalies appear distinct at depths <100 km, suggesting that any connection between the zones lies at depths greater than the resolution of surface-wave tomography. An additional low-shear velocity anomaly is also identified at depths 50-150 km beneath the southwest region of intraplate volcanism. We interpret these three low-velocity regions as upwelling asthenosphere beneath the island, producing high-elevation topography and relatively low-volume magmatism.

  1. Nonlinear dynamics of 3D beams of fast magnetosonic waves propagating in the ionospheric and magnetospheric plasma

    NASA Astrophysics Data System (ADS)

    Belashov, V. Yu.; Belashova, E. S.

    2016-11-01

    On the basis of the model of the three-dimensional (3D) generalized Kadomtsev-Petviashvili equation for magnetic field h = B / B the formation, stability, and dynamics of 3D soliton-like structures, such as the beams of fast magnetosonic (FMS) waves generated in ionospheric and magnetospheric plasma at a low-frequency branch of oscillations when β = 4 πnT/ B 2 ≪ 1 and β > 1, are studied. The study takes into account the highest dispersion correction determined by values of the plasma parameters and the angle θ = ( B, k), which plays a key role in the FMS beam propagation at those angles to the magnetic field that are close to π/2. The stability of multidimensional solutions is studied by an investigation of the Hamiltonian boundness under its deformations on the basis of solving of the corresponding variational problem. The evolution and dynamics of the 3D FMS wave beam are studied by the numerical integration of equations with the use of specially developed methods. The results can be interpreted in terms of the self-focusing phenomenon, as the formation of a stationary beam and the scattering and self-focusing of the solitary beam of FMS waves. These cases were studied with a detailed investigation of all evolutionary stages of the 3D FMS wave beams in the ionospheric and magnetospheric plasma.

  2. A time-space domain stereo finite difference method for 3D scalar wave propagation

    NASA Astrophysics Data System (ADS)

    Chen, Yushu; Yang, Guangwen; Ma, Xiao; He, Conghui; Song, Guojie

    2016-11-01

    The time-space domain finite difference methods reduce numerical dispersion effectively by minimizing the error in the joint time-space domain. However, their interpolating coefficients are related with the Courant numbers, leading to significantly extra time costs for loading the coefficients consecutively according to velocity in heterogeneous models. In the present study, we develop a time-space domain stereo finite difference (TSSFD) method for 3D scalar wave equation. The method propagates both the displacements and their gradients simultaneously to keep more information of the wavefields, and minimizes the maximum phase velocity error directly using constant interpolation coefficients for different Courant numbers. We obtain the optimal constant coefficients by combining the truncated Taylor series approximation and the time-space domain optimization, and adjust the coefficients to improve the stability condition. Subsequent investigation shows that the TSSFD can suppress numerical dispersion effectively with high computational efficiency. The maximum phase velocity error of the TSSFD is just 3.09% even with only 2 sampling points per minimum wavelength when the Courant number is 0.4. Numerical experiments show that to generate wavefields with no visible numerical dispersion, the computational efficiency of the TSSFD is 576.9%, 193.5%, 699.0%, and 191.6% of those of the 4th-order and 8th-order Lax-Wendroff correction (LWC) method, the 4th-order staggered grid method (SG), and the 8th-order optimal finite difference method (OFD), respectively. Meanwhile, the TSSFD is compatible to the unsplit convolutional perfectly matched layer (CPML) boundary condition for absorbing artificial boundaries. The efficiency and capability to handle complex velocity models make it an attractive tool in imaging methods such as acoustic reverse time migration (RTM).

  3. Probe Oscillation Shear Elastography (PROSE): A High Frame-Rate Method for Two-Dimensional Ultrasound Shear Wave Elastography.

    PubMed

    Mellema, Daniel C; Song, Pengfei; Kinnick, Randall R; Urban, Matthew W; Greenleaf, James F; Manduca, Armando; Chen, Shigao

    2016-09-01

    Ultrasound shear wave elastography (SWE) utilizes the propagation of induced shear waves to characterize the shear modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) "push beam" to generate shear waves. However, specialized hardware is required to generate the push beams, and the thermal stress that is placed upon the ultrasound system, transducer, and tissue by the push beams currently limits the frame-rate to about 1 Hz. These constraints have limited the implementation of ARF to high-end clinical systems. This paper presents Probe Oscillation Shear Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates shear waves using a harmonic mechanical vibration of an ultrasound transducer, while simultaneously detecting motion with the same transducer under pulse-echo mode. Motion of the transducer during detection produces a "strain-like" compression artifact that is coupled with the observed shear waves. A novel symmetric sampling scheme is proposed such that pulse-echo detection events are acquired when the ultrasound transducer returns to the same physical position, allowing the shear waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) shear wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of shear wave motion. The shear wave imaging frame rate of PROSE is comparable to the vibration frequency, which can be an order of magnitude higher than ARF based techniques. PROSE was able to produce smooth and accurate shear wave images from three homogeneous phantoms with different moduli, with an effective frame rate of 300 Hz. An inclusion phantom study showed that increased vibration frequencies improved the accuracy of inclusion imaging, and allowed targets as small as 6.5 mm to be resolved with good contrast (contrast-to-noise ratio ≥ 19 dB) between the target and

  4. Constructing a 3D Crustal Model Across the Entire Contiguous US Using Broadband Rayleigh Wave Phase Velocity and Ellipticity Measurements

    NASA Astrophysics Data System (ADS)

    Lin, F. C.; Schmandt, B.

    2015-12-01

    Imaging the crust and lithosphere structure beneath North America is one of the primary targets for the NSF-funded EarthScope project. In this study, we apply the recently developed ambient noise and surface wave tomography methods to construct a detailed 3D crustal model across the entire contiguous US using USArray data between January 2007 and May 2015. By using both Rayleigh wave phase velocity and ellipticity measurements between 8 and 100 sec period, the shear velocity structure can be well resolved within the five crustal layers we modeled: three upper crust, one middle crust, and one lower crust. Clear correlations are observed between the resolved velocity anomalies and known geological features at all depths. In the uppermost crust, slow Vs anomalies are observed within major sedimentary environments such as the Williston Basin, Denver Basin, and Mississippi embayment, and fast Vs anomalies are observed in environments with deeply exhumed bedrock outcrops at the surface including the Laurentian Highlands, Ouachita-Ozark Interior Highlands, and Appalachian Highlands. In the deeper upper crust, slow anomalies are observed in deep sedimentary basins such as the Green River Basin, Appalachian Basin, Southern Oklahoma Aulacogen, and areas surrounding the Gulf of Mexico. Fast anomalies, on the other hand, are observed in the Colorado Plateau, within the Great Plains between the Front Ranges and Midcontinental Rift, and east of the Appalachian Mountains. At this depth, the Midcontinental Rift and Grenville Front clearly correlate well with various velocity structure boundaries. In the middle crust, slow anomalies are mostly observed in the tectonically active areas in the western US, but relatively slow anomalies are also observed southeast of the Precambrian Rift Margins. At this depth, fast anomalies are observed beneath various deep sedimentary basins such as the Southern Oklahoma Aulacogen, Appalachian Basin, and Central Valley. In the lower crust, a clear

  5. High-frequency shear-horizontal surface acoustic wave sensor

    DOEpatents

    Branch, Darren W

    2013-05-07

    A Love wave sensor uses a single-phase unidirectional interdigital transducer (IDT) on a piezoelectric substrate for leaky surface acoustic wave generation. The IDT design minimizes propagation losses, bulk wave interferences, provides a highly linear phase response, and eliminates the need for impedance matching. As an example, a high frequency (.about.300-400 MHz) surface acoustic wave (SAW) transducer enables efficient excitation of shear-horizontal waves on 36.degree. Y-cut lithium tantalate (LTO) giving a highly linear phase response (2.8.degree. P-P). The sensor has the ability to detect at the pg/mm.sup.2 level and can perform multi-analyte detection in real-time. The sensor can be used for rapid autonomous detection of pathogenic microorganisms and bioagents by field deployable platforms.

  6. High-frequency shear-horizontal surface acoustic wave sensor

    DOEpatents

    Branch, Darren W

    2014-03-11

    A Love wave sensor uses a single-phase unidirectional interdigital transducer (IDT) on a piezoelectric substrate for leaky surface acoustic wave generation. The IDT design minimizes propagation losses, bulk wave interferences, provides a highly linear phase response, and eliminates the need for impedance matching. As an example, a high frequency (.about.300-400 MHz) surface acoustic wave (SAW) transducer enables efficient excitation of shear-horizontal waves on 36.degree. Y-cut lithium tantalate (LTO) giving a highly linear phase response (2.8.degree. P-P). The sensor has the ability to detect at the pg/mm.sup.2 level and can perform multi-analyte detection in real-time. The sensor can be used for rapid autonomous detection of pathogenic microorganisms and bioagents by field deployable platforms.

  7. Excitation and reception of pure shear horizontal waves by using face-shear d24 mode piezoelectric wafers

    NASA Astrophysics Data System (ADS)

    Miao, Hongchen; Huan, Qiang; Li, Faxin

    2016-11-01

    The fundamental shear horizontal (SH0) wave in plate-like structures is of great importance in non-destructive testing (NDT) and structural health monitoring (SHM) as it is non-dispersive, while excitation or reception of SH0 waves using piezoelectrics is always a challenge. In this work, we firstly demonstrate via finite element simulations that face-shear piezoelectrics is superior to thickness-shear piezoelectrics in driving SH waves. Next, by using a newly defined face-shear d24 PZT wafer as an actuator and face-shear d36 PMN-PT wafers as sensors, pure SH0 wave was successfully excited in an aluminum plate from 130 to 180 kHz. Then, it was shown that the face-shear d24 PZT wafer could receive the SH0 wave only and filter the Lamb waves over a wide frequency range (120-230 kHz). The directionality of the excited SH0 wave was also investigated using face-shear d24 PZT wafers as both actuators and sensors. Results show that pure SH0 wave can be excited symmetrically along two orthogonal directions (0° and 90°) and the amplitude of the excited SH0 wave can keep over 90% of the maximum amplitude when the deviate angle is within 30°. This work could greatly promote the applications of SH0 wave in NDT and SHM.

  8. The limits of ray theory when measuring shear wave splitting in the lowermost mantle with ScS waves

    NASA Astrophysics Data System (ADS)

    Nowacki, Andy; Wookey, James

    2016-12-01

    Observations of shear wave splitting provide unambiguous evidence of the presence of anisotropy in the Earth's lowermost mantle, a region known as D″. Much recent work has attempted to use these observations to place constraints on strain above the core-mantle boundary (CMB), as this may help map flow throughout the mantle. Previously, this interpretation has relied on the assumption that waves can be modelled as infinite-frequency rays, or that the Earth is radially symmetric. Due to computational constraints it has not been possible to test these approximations until now. We use fully 3-D, generally anisotropic simulations of ScS waves at the frequencies of the observations to show that ray methods are sometimes inadequate to interpret the signals seen. We test simple, uniform models, and for a D″ layer as thin as 50 km, significant splitting may be produced, and we find that recovered fast orientations usually reflect the imposed fast orientation above the CMB. Ray theory in these cases provides useful results, though there are occasional, notable differences between forward methods. Isotropic models do not generate apparent splitting. We also test more complex models, including ones based on our current understanding of mineral plasticity and elasticity in D″. The results show that variations of anisotropy over even several hundred kilometres cause the ray-theoretical and finite-frequency calculations to differ greatly. Importantly, models with extreme mineral alignment in D″ yield splitting times not dissimilar to observations (δt ≤ 3 s), suggesting that anisotropy in the lowermost mantle is probably much stronger than previously thought-potentially ˜10 per cent shear wave anisotropy or more. We show that if the base of the mantle is as complicated as we believe, future studies of lowermost mantle anisotropy will have to incorporate finite-frequency effects to fully interpret observations of shear wave splitting.

  9. Instability of subharmonic resonances in magnetogravity shear waves.

    PubMed

    Salhi, A; Nasraoui, S

    2013-12-01

    We study analytically the instability of the subharmonic resonances in magnetogravity waves excited by a (vertical) time-periodic shear for an inviscid and nondiffusive unbounded conducting fluid. Due to the fact that the magnetic potential induction is a Lagrangian invariant for magnetohydrodynamic Euler-Boussinesq equations, we show that plane-wave disturbances are governed by a four-dimensional Floquet system in which appears, among others, the parameter ɛ representing the ratio of the periodic shear amplitude to the vertical Brunt-Väisälä frequency N(3). For sufficiently small ɛ and when the magnetic field is horizontal, we perform an asymptotic analysis of the Floquet system following the method of Lebovitz and Zweibel [Astrophys. J. 609, 301 (2004)]. We determine the width and the maximal growth rate of the instability bands associated with subharmonic resonances. We show that the instability of subharmonic resonance occurring in gravity shear waves has a maximal growth rate of the form Δ(m)=(3√[3]/16)ɛ. This instability persists in the presence of magnetic fields, but its growth rate decreases as the magnetic strength increases. We also find a second instability involving a mixing of hydrodynamic and magnetic modes that occurs for all magnetic field strengths. We also elucidate the similarity between the effect of a vertical magnetic field and the effect of a vertical Coriolis force on the gravity shear waves considering axisymmetric disturbances. For both cases, plane waves are governed by a Hill equation, and, when ɛ is sufficiently small, the subharmonic instability band is determined by a Mathieu equation. We find that, when the Coriolis parameter (or the magnetic strength) exceeds N(3)/2, the instability of the subharmonic resonance vanishes.

  10. Moored Observations of Internal Waves in Luzon Strait: 3-D Structure, Dissipation, and Evolution

    DTIC Science & Technology

    2013-09-30

    variability, it may be due to waves propagating into Luzon strait from remote sources. Lee Waves and Dissipation on Supercritical Slopes A profiling...variability of the internal wave field in the upper 1000 m of the water column. The phase progression of internal waves as they propagate away from their

  11. Validation and Comparison of 2D and 3D Codes for Nearshore Motion of Long Waves Using Benchmark Problems

    NASA Astrophysics Data System (ADS)

    Velioǧlu, Deniz; Cevdet Yalçıner, Ahmet; Zaytsev, Andrey

    2016-04-01

    Tsunamis are huge waves with long wave periods and wave lengths that can cause great devastation and loss of life when they strike a coast. The interest in experimental and numerical modeling of tsunami propagation and inundation increased considerably after the 2011 Great East Japan earthquake. In this study, two numerical codes, FLOW 3D and NAMI DANCE, that analyze tsunami propagation and inundation patterns are considered. Flow 3D simulates linear and nonlinear propagating surface waves as well as long waves by solving three-dimensional Navier-Stokes (3D-NS) equations. NAMI DANCE uses finite difference computational method to solve 2D depth-averaged linear and nonlinear forms of shallow water equations (NSWE) in long wave problems, specifically tsunamis. In order to validate these two codes and analyze the differences between 3D-NS and 2D depth-averaged NSWE equations, two benchmark problems are applied. One benchmark problem investigates the runup of long waves over a complex 3D beach. The experimental setup is a 1:400 scale model of Monai Valley located on the west coast of Okushiri Island, Japan. Other benchmark problem is discussed in 2015 National Tsunami Hazard Mitigation Program (NTHMP) Annual meeting in Portland, USA. It is a field dataset, recording the Japan 2011 tsunami in Hilo Harbor, Hawaii. The computed water surface elevation and velocity data are compared with the measured data. The comparisons showed that both codes are in fairly good agreement with each other and benchmark data. The differences between 3D-NS and 2D depth-averaged NSWE equations are highlighted. All results are presented with discussions and comparisons. Acknowledgements: Partial support by Japan-Turkey Joint Research Project by JICA on earthquakes and tsunamis in Marmara Region (JICA SATREPS - MarDiM Project), 603839 ASTARTE Project of EU, UDAP-C-12-14 project of AFAD Turkey, 108Y227, 113M556 and 213M534 projects of TUBITAK Turkey, RAPSODI (CONCERT_Dis-021) of CONCERT

  12. Relation Between the 3D-Geometry of the Coronal Wave and Associated CME During the 26 April 2008 Event

    NASA Astrophysics Data System (ADS)

    Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.

    We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the 26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) with a mean speed of ˜ 240 km s-1. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations. We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed of ˜ 750±50 km s-1, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying the forward fitting model developed by Thernisien, Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding flanks of the CME most likely drive and shape the coronal wave.

  13. Relation Between the 3D-Geometry of the Coronal Wave and Associated CME During the 26 April 2008 Event

    NASA Astrophysics Data System (ADS)

    Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.

    2011-11-01

    We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the 26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) with a mean speed of ˜ 240 km s-1. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations. We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed of ˜ 750±50 km s-1, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying the forward fitting model developed by Thernisien, Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding flanks of the CME most likely drive and shape the coronal wave.

  14. Relation Between the 3D-Geometry of the Coronal Wave and Associated CME During the 26 April 2008 Event

    NASA Technical Reports Server (NTRS)

    Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.

    2011-01-01

    We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the 26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) with a mean speed of approx 240 km/s. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations. We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed of approx 750 +/- 50 km/s, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying the forward fitting model developed by Thernisien, Howard, and Vourlidas we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding flanks of the CME most likely drive and shape the coronal wave.

  15. Bond slip detection of concrete-encased composite structure using shear wave based active sensing approach

    NASA Astrophysics Data System (ADS)

    Zeng, Lei; Parvasi, Seyed Mohammad; Kong, Qingzhao; Huo, Linsheng; Lim, Ing; Li, Mo; Song, Gangbing

    2015-12-01

    Concrete-encased composite structure exhibits improved strength, ductility and fire resistance compared to traditional reinforced concrete, by incorporating the advantages of both steel and concrete materials. A major drawback of this type of structure is the bond slip introduced between steel and concrete, which directly reduces the load capacity of the structure. In this paper, an active sensing approach using shear waves to provide monitoring and early warning of the development of bond slip in the concrete-encased composite structure is proposed. A specimen of concrete-encased composite structure was investigated. In this active sensing approach, shear mode smart aggregates (SAs) embedded in the concrete act as actuators and generate desired shear stress waves. Distributed piezoceramic transducers installed in the cavities of steel plates act as sensors and detect the wave response from shear mode SAs. Bond slip acts as a form of stress relief and attenuates the wave propagation energy. Experimental results from the time domain analysis clearly indicate that the amplitudes of received signal by lead zirconate titanate sensors decreased when bond slip occurred. In addition, a wavelet packet-based analysis was developed to compute the received signal energy values, which can be used to determine the initiation and development of bond slip in concrete-encased composite structure. In order to establish the validity of the proposed method, a 3D finite element analysis of the concrete-steel bond model is further performed with the aid of the commercial finite element package, Abaqus, and the numerical results are compared with the results obtained in experimental study.

  16. Anisotropic Shear-wave Velocity Structure of East Asian Upper Mantle from Waveform Tomography

    NASA Astrophysics Data System (ADS)

    Chong, J.; Yuan, H.; French, S. W.; Romanowicz, B. A.; Ni, S.

    2012-12-01

    East Asia is a seismically active region featuring active tectonic belts, such as the Himalaya collision zone, western Pacific subduction zones and the Tianshan- Baikal tectonic belt. In this study, we applied full waveform time domain tomography to image 3D isotropic, radially and azimuthally anisotropic upper mantle shear velocity structure of East Asia. High quality teleseismic waveforms were collected for both permanent and temporary stations in the target and its adjacent regions, providing good ray path coverage of the study region. Fundamental and overtone wave packets, filtered down to 60 sec, were inverted for isotropic and radially anisotropic shear wave structure using normal mode asymptotic coupling theory (NACT: Li and Romanowicz, 1995). Joint inversion of SKS measurements and seismic waveforms was then carried out following the methodology described in (Marone and Romanowicz, 2007). The 3D velocity model shows strong lateral heterogeneities in the target region, which correlate well with the surface geology in East Asia. Our model shows that Indian lithosphere has subducted beneath Tibet with a different northern reach from western to eastern Tibet,. We also find variations of the slab geometry in Western Pacific subduction zones. Old and stable regions, such as, Indian shield, Siberia platform, Tarim and Yangtze blocks are found to have higher shear wave velocity in the upper mantle. Lower velocity anomalies are found in regions like Baikal rift, Tienshan, Indochina block, and the regions along Japan island-Ryukyu Trench and Izu-bonin Trench. The dominant fast and slow velocity boundaries in the study region are well correlated with tectonic belts, such as the central Asian orogenic belt and Alty/Qilian-Qinling/Dabie orogenic belt. Our radially anisotropic model shows Vsh> Vsv in oceanic regions and at larger depths(>300km), and Vsv > Vsh in some orogenic zones.. We'll show preliminary results of azimuthally anisotropic joint inversion of SKS

  17. 3D Discontinuous Galerkin elastic seismic wave modeling based upon a grid injection method

    NASA Astrophysics Data System (ADS)

    Monteiller, V.

    2015-12-01

    Full waveform inversion (FWI) is a seismic imaging method that estimates thesub-surface physical properties with a spatial resolution of the order of thewavelength. FWI is generally recast as the iterative optimization of anobjective function that measures the distance between modeled and recordeddata. In the framework of local descent methods, FWI requires to perform atleast two seismic modelings per source and per FWI iteration.Due to the resulting computational burden, applications of elastic FWI have been usuallyrestricted to 2D geometries. Despite the continuous growth of high-performancecomputing facilities, application of 3D elastic FWI to real-scale problemsremain computationally too expensive. To perform elastic seismic modeling with a reasonable amount of time, weconsider a reduced computational domain embedded in a larger background modelin which seismic sources are located. Our aim is to compute repeatedly thefull wavefield in the targeted domain after model alteration, once theincident wavefield has been computed once for all in the background model. Toachieve this goal, we use a grid injection method referred to as the Total-Field/Scattered-Field (TF/SF) technique in theelectromagnetic community. We implemented the Total-Field/Scattered-Field approach in theDiscontinuous Galerkin Finite Element method (DG-FEM) that is used to performmodeling in the local domain. We show how to interface the DG-FEM with any modeling engine (analytical solution, finite difference or finite elements methods) that is suitable for the background simulation. One advantage of the Total-Field/Scattered-Field approach is related to thefact that the scattered wavefield instead of the full wavefield enter thePMLs, hence making more efficient the absorption of the outgoing waves at theouter edges of the computational domain. The domain reduction in which theDG-FEM is applied allows us to use modest computational resources opening theway for high-resolution imaging by full

  18. Probing the shear-band formation in granular media with sound waves

    NASA Astrophysics Data System (ADS)

    Khidas, Y.; Jia, X.

    2012-05-01

    We investigate the mechanical responses of dense granular materials, using a direct shear box combined with simultaneous acoustic measurements. Measured shear wave speeds evidence the structural change of the material under shear, from the jammed state to the flowing state. There is a clear acoustic signature when the shear band is formed. Subjected to cyclic shear, both shear stress and wave speed show the strong hysteretic dependence on the shear strain, likely associated with the geometry change in the packing structure. Moreover, the correlation function of configuration-specific multiply scattered waves reveals an intermittent behavior before the failure of material.

  19. Shear waves in a resonator with cubic nonlinearity

    NASA Astrophysics Data System (ADS)

    Andreev, V. G.; Krit, T. B.; Sapozhnikov, O. A.

    2011-11-01

    Shear waves with finite amplitude in a one-dimensional resonator in the form of a layer of a rubber-like medium with a rigid plate of finite mass at the upper surface of the layer are investigated. The lower boundary of the layer oscillates according to a harmonic law with a preset acceleration. The equation of motion for particles in a resonator is determined using a model of a medium with a single relaxation time and cubical dependence of the shear modulus on deformation. The amplitude and form of shear waves in a resonator are calculated numerically by the finite difference method at shifted grids. Resonance curves are obtained at different acceleration amplitudes at the lower boundary of a layer. It is demonstrated that, as the oscillation amplitude in the resonator grows, the value of the resonance frequency increases and the shape of the resonance curve becomes asymmetrical. At sufficiently large amplitudes, a bistability region is observed. Measurements were conducted with a resonator, where a layer with the thickness of 15 mm was manufactured of a rubber-like polymer called plastisol. The shear modulus of the polymer at small deformations and the nonlinearity coefficient were determined according to the experimental dependence of mechanical stress on shear deformation. Oscillation amplitudes in the resonator attained values when the maximum shear deformations in the layer were 0.4-0.6, which provided an opportunity to observe nonlinear effects. Measured dependences of the resonance frequency on the oscillation amplitude corresponded to the calculated ones that were obtained at a smaller value of the nonlinear coefficient.

  20. Shear Alfvén waves in turbulent plasmas.

    PubMed

    Núñez, Manuel

    2002-03-01

    The rate of decay of shear Alfvén waves along a magnetic field line of a diffusive plasma grows with the number of nodes of the initial perturbation. It is reasonable to think that the energy dissipation produced by this decay will be small if the perturbation was localized in a small set. This does not happen in turbulent plasmas: transport of the oscillation by the flow involves the whole domain. A general relation is obtained proving that the global energy dissipation is bounded below by an exponential of the number of nodes of any shear Alfvén wave along a segment of any field line of the average magnetic field.

  1. Phase Aberration and Attenuation Effects on Acoustic Radiation Force-Based Shear Wave Generation.

    PubMed

    Carrascal, Carolina Amador; Aristizabal, Sara; Greenleaf, James F; Urban, Matthew W

    2016-02-01

    Elasticity is measured by shear wave elasticity imaging (SWEI) methods using acoustic radiation force to create the shear waves. Phase aberration and tissue attenuation can hamper the generation of shear waves for in vivo applications. In this study, the effects of phase aberration and attenuation in ultrasound focusing for creating shear waves were explored. This includes the effects of phase shifts and amplitude attenuation on shear wave characteristics such as shear wave amplitude, shear wave speed, shear wave center frequency, and bandwidth. Two samples of swine belly tissue were used to create phase aberration and attenuation experimentally. To explore the phase aberration and attenuation effects individually, tissue experiments were complemented with ultrasound beam simulations using fast object-oriented C++ ultrasound simulator (FOCUS) and shear wave simulations using finite-element-model (FEM) analysis. The ultrasound frequency used to generate shear waves was varied from 3.0 to 4.5 MHz. Results: The measured acoustic pressure and resulting shear wave amplitude decreased approximately 40%-90% with the introduction of the tissue samples. Acoustic intensity and shear wave displacement were correlated for both tissue samples, and the resulting Pearson's correlation coefficients were 0.99 and 0.97. Analysis of shear wave generation with tissue samples (phase aberration and attenuation case), measured phase screen, (only phase aberration case), and FOCUS/FEM model (only attenuation case) showed that tissue attenuation affected the shear wave generation more than tissue aberration. Decreasing the ultrasound frequency helped maintain a focused beam for creation of shear waves in the presence of both phase aberration and attenuation.

  2. Phase Aberration and Attenuation Effects on Acoustic Radiation Force-Based Shear Wave Generation

    PubMed Central

    Amador, Carolina; Aristizabal, Sara; Greenleaf, James F.; Urban, Matthew W.

    2016-01-01

    Tissue elasticity is measured by shear wave elasticity imaging methods using acoustic radiation force to create the shear waves. Phase aberration and tissue attenuation can hamper the generation of shear waves for in vivo applications. In this study effects of phase aberration and attenuation in ultrasound focusing for creating shear waves were explored. This includes the effects of phase shifts and amplitude attenuation on shear wave characteristics such as shear wave amplitude, shear wave speed, shear wave center frequency and bandwidth. Two samples of swine belly tissue were used to create phase aberration and attenuation experimentally. To explore the phase aberration and attenuation effects individually, tissue experiments were complemented with ultrasound beam simulations using FOCUS and shear wave simulations using Finite Element Model (FEM) analysis. The ultrasound frequency used to generate shear waves was varied from 3.0 to 4.5 MHz. Results The measured acoustic pressure and resulting shear wave amplitude decreased approximately 40% to 90% with the introduction of the tissue samples. Acoustic intensity and shear wave displacement were correlated for both tissue samples, the resulting Pearson’s correlation coefficients were 0.99 and 0.97. Analysis of shear wave generation with tissue samples (Phase Aberration and Attenuation case), measured phase screen (Only Phase Aberration case) and FOCUS/FEM model (Only Attenuation case) showed that tissue attenuation affected the shear wave generation more than tissue aberration. Decreasing the ultrasound frequency helped maintain a focused beam for creation of shear waves in the presence of both phase aberration and attenuation. PMID:26742131

  3. Lamellipodin promotes invasive 3D cancer cell migration via regulated interactions with Ena/VASP and SCAR/WAVE.

    PubMed

    Carmona, G; Perera, U; Gillett, C; Naba, A; Law, A-L; Sharma, V P; Wang, J; Wyckoff, J; Balsamo, M; Mosis, F; De Piano, M; Monypenny, J; Woodman, N; McConnell, R E; Mouneimne, G; Van Hemelrijck, M; Cao, Y; Condeelis, J; Hynes, R O; Gertler, F B; Krause, M

    2016-09-29

    Cancer invasion is a hallmark of metastasis. The mesenchymal mode of cancer cell invasion is mediated by elongated membrane protrusions driven by the assembly of branched F-actin networks. How deregulation of actin regulators promotes cancer cell invasion is still enigmatic. We report that increased expression and membrane localization of the actin regulator Lamellipodin correlate with reduced metastasis-free survival and poor prognosis in breast cancer patients. In agreement, we find that Lamellipodin depletion reduced lung metastasis in an orthotopic mouse breast cancer model. Invasive 3D cancer cell migration as well as invadopodia formation and matrix degradation was impaired upon Lamellipodin depletion. Mechanistically, we show that Lamellipodin promotes invasive 3D cancer cell migration via both actin-elongating Ena/VASP proteins and the Scar/WAVE complex, which stimulates actin branching. In contrast, Lamellipodin interaction with Scar/WAVE but not with Ena/VASP is required for random 2D cell migration. We identified a phosphorylation-dependent mechanism that regulates selective recruitment of these effectors to Lamellipodin: Abl-mediated Lamellipodin phosphorylation promotes its association with both Scar/WAVE and Ena/VASP, whereas Src-dependent phosphorylation enhances binding to Scar/WAVE but not to Ena/VASP. Through these selective, regulated interactions Lamellipodin mediates directional sensing of epidermal growth factor (EGF) gradients and invasive 3D migration of breast cancer cells. Our findings imply that increased Lamellipodin levels enhance Ena/VASP and Scar/WAVE activities at the plasma membrane to promote 3D invasion and metastasis.

  4. Laboratory measurements of compressional and shear wave speeds through methane hydrate

    USGS Publications Warehouse

    Waite, W.F.; Helgerud, M.B.; Nur, A.; Pinkston, J.C.; Stern, L.A.; Kirby, S.H.; Durham, W.B.

    2000-01-01

    Simultaneous measurements of compressional and shear wave speeds through polycrystalline methane hydrate have been made. Methane hydrate, grown directly in a wave speed measurement chamber, was uniaxially compacted to a final porosity below 2%. At 277 K, the compacted material had a compressional wave speed of 3650 ?? 50 m/s. The shear wave speed, measured simultaneously, was 1890 ?? 30 m/s. From these wave speed measurements, we derive V(p)/V(s), Poisson's ratio, bulk, shear, and Young's moduli.

  5. Spatial Statistics of Deep-Water Ambient Noise; Dispersion Relations for Sound Waves and Shear Waves

    DTIC Science & Technology

    2015-09-30

    Environmental and system data will also be depth-profiled, including temperature , salinity, pressure and (directly measured) sound speed, along...configurations, and an environmental sensor package [Conductivity- Temperature - Depth sensor (CTD) plus sound speed sensor (SVX)]. The system is untethered...Dispersion Relations for Sound Waves and Shear Waves Michael J. Buckingham Marine Physical Laboratory, Scripps Institution of Oceanography University

  6. Ultrasonic tracking of shear waves using a particle filter

    PubMed Central

    Ingle, Atul N.; Ma, Chi; Varghese, Tomy

    2015-01-01

    Purpose: This paper discusses an application of particle filtering for estimating shear wave velocity in tissue using ultrasound elastography data. Shear wave velocity estimates are of significant clinical value as they help differentiate stiffer areas from softer areas which is an indicator of potential pathology. Methods: Radio-frequency ultrasound echo signals are used for tracking axial displacements and obtaining the time-to-peak displacement at different lateral locations. These time-to-peak data are usually very noisy and cannot be used directly for computing velocity. In this paper, the denoising problem is tackled using a hidden Markov model with the hidden states being the unknown (noiseless) time-to-peak values. A particle filter is then used for smoothing out the time-to-peak curve to obtain a fit that is optimal in a minimum mean squared error sense. Results: Simulation results from synthetic data and finite element modeling suggest that the particle filter provides lower mean squared reconstruction error with smaller variance as compared to standard filtering methods, while preserving sharp boundary detail. Results from phantom experiments show that the shear wave velocity estimates in the stiff regions of the phantoms were within 20% of those obtained from a commercial ultrasound scanner and agree with estimates obtained using a standard method using least-squares fit. Estimates of area obtained from the particle filtered shear wave velocity maps were within 10% of those obtained from B-mode ultrasound images. Conclusions: The particle filtering approach can be used for producing visually appealing SWV reconstructions by effectively delineating various areas of the phantom with good image quality properties comparable to existing techniques. PMID:26520761

  7. Nonlinear evolution of oblique waves on compressible shear layers

    NASA Technical Reports Server (NTRS)

    Goldstein, M. E.; Leib, S. J.

    1989-01-01

    The effects of critical-layer nonlinearity on spatially growing oblique instability waves on compressible shear layers between two parallel streams are considered. The analysis shows that mean temperature nonuniformities cause nonlinearity to occur at much smaller amplitudes than it does when the flow is isothermal. The nonlinear instability wave growth rate effects are described by an integrodifferential equation which bears some resemblance to the Landau equation, in that it involves a cubic-type nonlinearity. The numerical solutions to this equation are worked out and discussed in some detail. Inviscid solutions always end in a singularity at a finite downstream distance, but viscosity can eliminate this singularity for certain parameter ranges.

  8. Heating of ionospheric O(+) ions by shear Alfven waves

    NASA Technical Reports Server (NTRS)

    Winglee, R. M.; Ashour-Abdalla, M.; Sydora, R. D.

    1987-01-01

    Ionospheric ions, in particular O(+) ions, which have been transversely heated, are often observed flowing upward along auroral field lines. A new mechanism, heating by current-driven shear (or kinetic) Alfven waves (SAW), is proposed. An electron current drives oblique SAWs unstable near a wave frequency of about the oxygen cyclotron frequency, and these waves are in turn gyroresonantly absorbed by the ions. The mechanism is similar to ion heating by current-driven electrostatic ion cyclotron waves (EICW). However, the SAW differs from the EICW in that as the perpendicular temperature of the ions increases, growth of the SAW can still occur, whereas growth of the EICW becomes suppressed. As a consequence, the SAW is able to provide sustained perpendicular heating of ions with smaller currents being required for the heating than for heating via EICWs.

  9. Shear flow induced wave couplings in the solar wind

    SciTech Connect

    Poedts, S.; Rogava, A.D. |; Mahajan, S.M. |

    1998-01-01

    A sheared background flow in a plasma induces coupling between different MHD wave modes, resulting in their mutual transformations with corresponding energy redistributing between the modes. In this way, the energy can be transfered from one wave mode to the other, but energy can also be added to or extracted from the background flow. In the present paper it is investigated whether the wave coupling and energy transfer mechanisms can operate under solar wind conditions. It is shown that this is indeed the case. Hence, the long-period waves observed in the solar wind at r > 0.3 AU might be generated by much faster periodic oscillations in the photosphere of the Sun. Other possible consequences for observable beat phenomena in the wind and the acceleration of the solar wind particles are also discussed.

  10. Shear waves in a cubic nonlinear inhomogeneous resonator

    NASA Astrophysics Data System (ADS)

    Krit, Timofey B.; Andreev, Valery G.; Sapozhnikov, Oleg A.

    2012-09-01

    We study finite-amplitude shear waves in one-dimensional resonator represented by a layer of rubber-like medium with inhomogeneities in the form of through holes made on the side face. The holes are parallel to the bases and perpendicular to the direction of vibrations. Two different configurations of the resonator: with holes at the bottom and at the top are studied. A rigid plate of finite mass is fixed on the upper surface. The lower boundary of the layer oscillates harmonically with a given acceleration. The equation of motion of particles in the resonator was found using the model of medium with one relaxation time, and a cubic dependence of the shear modulus of deformation. The measurements were performed in a resonator in the form of a rectangular parallelepiped of 15 mm thickness made of a rubber-like polymer plastisol. The linear shear modulus and shear viscosity of the polymer at the first resonant frequency were determined using the finite element method. The amplitudes of the oscillations in the resonator reached a point where the maximum shear strain in the resonator is 0.4 - 0.6, making it possible to observe nonlinear effects. The evolution of the resonance curves at different amplitudes of acceleration was investigated. A harmonic analysis of the acceleration profiles of the upper boundary was performed. The dependence of nonlinear effects on the holes position was studied.

  11. Three-dimensional two-fluid investigation of 3D-localized magnetic reconnection and its relation to whistler waves

    NASA Astrophysics Data System (ADS)

    Yoon, Young Dae; Bellan, Paul M.

    2016-10-01

    A full three-dimensional computer code was developed in order to simulate a 3D-localized magnetic reconnection. We assume an incompressible two-fluid regime where the ions are stationary, and electron inertia and Hall effects are present. We solve a single dimensionless differential equation for perturbed magnetic fields with arbitrary background fields. The code has successfully reproduced both experimental and analytic solutions to resonance and Gendrin mode whistler waves in a uniform background field. The code was then modified to model 3D-localized magnetic reconnection as a 3D-localized perturbation on a hyperbolic-tangent background field. Three-dimensional properties that are asymmetric in the out-of-plane direction have been observed. These properties pertained to magnetic field lines, electron currents and their convection. Helicity and energy have also been examined, as well as the addition of a guide field.

  12. A 3D algorithm based on the combined inversion of Rayleigh and Love waves for imaging and monitoring of shallow structures

    NASA Astrophysics Data System (ADS)

    Pilz, Marco; Parolai, Stefano; Woith, Heiko

    2017-01-01

    SUMMARYIn recent years there has been increasing interest in the study of seismic noise interferometry as it can provide a complementary approach to active source or earthquake based methods for imaging and continuous monitoring the shallow structure of the Earth. This meaningful information is extracted from wavefields propagating between those receiver positions at which seismic noise was recorded. Until recently, noise-based imaging relied mostly on Rayleigh <span class="hlt">waves</span>. However, considering similar wavelengths, a combined use of Rayleigh and Love <span class="hlt">wave</span> tomography can succeed in retrieving velocity heterogeneities at depth due to their different sensitivity kernels. Here we present a novel one-step algorithm for simultaneously inverting Rayleigh and Love <span class="hlt">wave</span> dispersion data aiming at identifying and describing complex <span class="hlt">3</span><span class="hlt">D</span> velocity structures. The algorithm may help to accurately and efficiently map the <span class="hlt">shear-wave</span> velocities and the Poisson ratio of the surficial soil layers. In the high-frequency range, the scattered part of the correlation functions stabilizes sufficiently fast to provide a reliable estimate of the velocity structure not only for imaging purposes but also allows for changes in the medium properties to be monitored. Such monitoring can be achieved with a high spatial resolution in <span class="hlt">3</span><span class="hlt">D</span> and with a time resolution as small as a few hours. In this article, we describe a recent array experiment in a volcanic environment in Solfatara (Italy) and we show that this novel approach has identified strong velocity variations at the interface between liquids and gas-dominated reservoirs, allowing localizing a region which is highly dynamic due to the interaction between the deep convection and its surroundings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EML...tmp...50S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EML...tmp...50S"><span>Fabrication and <span class="hlt">shear</span> strength analysis of Sn-3.5Ag/Cu-filled TSV for <span class="hlt">3</span><span class="hlt">D</span> microelectronic packaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharma, Ashutosh; Jung, Do-Hyun; Roh, Myong-Hoon; Jung, Jae Pil</p> <p>2016-09-01</p> <p>In this study, lead free Sn-3.5Ag solder bumps have been deposited on Cu-filled through-silicon via (TSV) by electroplating method. The solder bumps are plated using an acidic solution composed of SnSO4, H2SO4, Ag2SO4, thiourea and an additive. The current density is varied from -30 to -60 mA/cm2 to obtain the eutectic Sn-3.5Ag solder. The copper is electroplated in TSV using an acidic solution of CuSO4·5H2O, H2SO4, HCl, and an inhibitor. The bottom-up Cu-filling in TSV is achieved by a 3-step pulse periodic reverse (PPR) electroplating. It has been observed that the eutectic Sn-3.5Ag solder is achieved at a current density of -55 mA/cm2. The solder bumps are further reflowed onto TSV at 260 °C for 20 seconds, and <span class="hlt">shear</span> strength of the formed Sn-3.5Ag/Cu-filled TSV joint is investigated. The results indicate the formation of Cu6Sn5 and Ag3Sn intermetallic compounds (IMCs) at the joint interface. It is found that with an increase of <span class="hlt">shear</span> speed from 0.5-10 mm/s, the <span class="hlt">shear</span> stress initially increases to a maximum, and then decreases beyond <span class="hlt">shear</span> speed of 10 mm/s through 500 mm/s. It is shown that the ductile fracture mode gradually decreases beyond <span class="hlt">shear</span> speed of 10 mm/s and disappears completely at 500 mm/s.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25207828','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25207828"><span><span class="hlt">3</span><span class="hlt">D</span> ultrafast ultrasound imaging in vivo.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Provost, Jean; Papadacci, Clement; Arango, Juan Esteban; Imbault, Marion; Fink, Mathias; Gennisson, Jean-Luc; Tanter, Mickael; Pernot, Mathieu</p> <p>2014-10-07</p> <p>Very high frame rate ultrasound imaging has recently allowed for the extension of the applications of echography to new fields of study such as the functional imaging of the brain, cardiac electrophysiology, and the quantitative imaging of the intrinsic mechanical properties of tumors, to name a few, non-invasively and in real time. In this study, we present the first implementation of Ultrafast Ultrasound Imaging in <span class="hlt">3</span><span class="hlt">D</span> based on the use of either diverging or plane <span class="hlt">waves</span> emanating from a sparse virtual array located behind the probe. It achieves high contrast and resolution while maintaining imaging rates of thousands of volumes per second. A customized portable ultrasound system was developed to sample 1024 independent channels and to drive a 32  ×  32 matrix-array probe. Its ability to track in <span class="hlt">3</span><span class="hlt">D</span> transient phenomena occurring in the millisecond range within a single ultrafast acquisition was demonstrated for <span class="hlt">3</span><span class="hlt">D</span> <span class="hlt">Shear-Wave</span> Imaging, <span class="hlt">3</span><span class="hlt">D</span> Ultrafast Doppler Imaging, and, finally, <span class="hlt">3</span><span class="hlt">D</span> Ultrafast combined Tissue and Flow Doppler Imaging. The propagation of <span class="hlt">shear</span> <span class="hlt">waves</span> was tracked in a phantom and used to characterize its stiffness. <span class="hlt">3</span><span class="hlt">D</span> Ultrafast Doppler was used to obtain <span class="hlt">3</span><span class="hlt">D</span> maps of Pulsed Doppler, Color Doppler, and Power Doppler quantities in a single acquisition and revealed, at thousands of volumes per second, the complex <span class="hlt">3</span><span class="hlt">D</span> flow patterns occurring in the ventricles of the human heart during an entire cardiac cycle, as well as the <span class="hlt">3</span><span class="hlt">D</span> in vivo interaction of blood flow and wall motion during the pulse <span class="hlt">wave</span> in the carotid at the bifurcation. This study demonstrates the potential of <span class="hlt">3</span><span class="hlt">D</span> Ultrafast Ultrasound Imaging for the <span class="hlt">3</span><span class="hlt">D</span> mapping of stiffness, tissue motion, and flow in humans in vivo and promises new clinical applications of ultrasound with reduced intra--and inter-observer variability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PMB....59L...1P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PMB....59L...1P"><span><span class="hlt">3</span><span class="hlt">D</span> ultrafast ultrasound imaging in vivo</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Provost, Jean; Papadacci, Clement; Esteban Arango, Juan; Imbault, Marion; Fink, Mathias; Gennisson, Jean-Luc; Tanter, Mickael; Pernot, Mathieu</p> <p>2014-10-01</p> <p>Very high frame rate ultrasound imaging has recently allowed for the extension of the applications of echography to new fields of study such as the functional imaging of the brain, cardiac electrophysiology, and the quantitative imaging of the intrinsic mechanical properties of tumors, to name a few, non-invasively and in real time. In this study, we present the first implementation of Ultrafast Ultrasound Imaging in <span class="hlt">3</span><span class="hlt">D</span> based on the use of either diverging or plane <span class="hlt">waves</span> emanating from a sparse virtual array located behind the probe. It achieves high contrast and resolution while maintaining imaging rates of thousands of volumes per second. A customized portable ultrasound system was developed to sample 1024 independent channels and to drive a 32  ×  32 matrix-array probe. Its ability to track in <span class="hlt">3</span><span class="hlt">D</span> transient phenomena occurring in the millisecond range within a single ultrafast acquisition was demonstrated for <span class="hlt">3</span><span class="hlt">D</span> <span class="hlt">Shear-Wave</span> Imaging, <span class="hlt">3</span><span class="hlt">D</span> Ultrafast Doppler Imaging, and, finally, <span class="hlt">3</span><span class="hlt">D</span> Ultrafast combined Tissue and Flow Doppler Imaging. The propagation of <span class="hlt">shear</span> <span class="hlt">waves</span> was tracked in a phantom and used to characterize its stiffness. <span class="hlt">3</span><span class="hlt">D</span> Ultrafast Doppler was used to obtain <span class="hlt">3</span><span class="hlt">D</span> maps of Pulsed Doppler, Color Doppler, and Power Doppler quantities in a single acquisition and revealed, at thousands of volumes per second, the complex <span class="hlt">3</span><span class="hlt">D</span> flow patterns occurring in the ventricles of the human heart during an entire cardiac cycle, as well as the <span class="hlt">3</span><span class="hlt">D</span> in vivo interaction of blood flow and wall motion during the pulse <span class="hlt">wave</span> in the carotid at the bifurcation. This study demonstrates the potential of <span class="hlt">3</span><span class="hlt">D</span> Ultrafast Ultrasound Imaging for the <span class="hlt">3</span><span class="hlt">D</span> mapping of stiffness, tissue motion, and flow in humans in vivo and promises new clinical applications of ultrasound with reduced intra—and inter-observer variability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25927794','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25927794"><span>Imaging and characterizing <span class="hlt">shear</span> <span class="hlt">wave</span> and <span class="hlt">shear</span> modulus under orthogonal acoustic radiation force excitation using OCT Doppler variance method.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zhu, Jiang; Qu, Yueqiao; Ma, Teng; Li, Rui; Du, Yongzhao; Huang, Shenghai; Shung, K Kirk; Zhou, Qifa; Chen, Zhongping</p> <p>2015-05-01</p> <p>We report on a novel acoustic radiation force orthogonal excitation optical coherence elastography (ARFOE-OCE) technique for imaging <span class="hlt">shear</span> <span class="hlt">wave</span> and quantifying <span class="hlt">shear</span> modulus under orthogonal acoustic radiation force (ARF) excitation using the optical coherence tomography (OCT) Doppler variance method. The ARF perpendicular to the OCT beam is produced by a remote ultrasonic transducer. A <span class="hlt">shear</span> <span class="hlt">wave</span> induced by ARF excitation propagates parallel to the OCT beam. The OCT Doppler variance method, which is sensitive to the transverse vibration, is used to measure the ARF-induced vibration. For analysis of the <span class="hlt">shear</span> modulus, the Doppler variance method is utilized to visualize <span class="hlt">shear</span> <span class="hlt">wave</span> propagation instead of Doppler OCT method, and the propagation velocity of the <span class="hlt">shear</span> <span class="hlt">wave</span> is measured at different depths of one location with the M scan. In order to quantify <span class="hlt">shear</span> modulus beyond the OCT imaging depth, we move ARF to a deeper layer at a known step and measure the time delay of the <span class="hlt">shear</span> <span class="hlt">wave</span> propagating to the same OCT imaging depth. We also quantitatively map the <span class="hlt">shear</span> modulus of a cross-section in a tissue-equivalent phantom after employing the B scan.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26520346','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26520346"><span>Modeling explosion generated Scholte <span class="hlt">waves</span> in sandy sediments with power law dependent <span class="hlt">shear</span> <span class="hlt">wave</span> speed.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Soloway, Alexander G; Dahl, Peter H; Odom, Robert I</p> <p>2015-10-01</p> <p>Experimental measurements of Scholte <span class="hlt">waves</span> from underwater explosions collected off the coast of Virginia Beach, VA in shallow water are presented. It is shown here that the dispersion of these explosion-generated Scholte <span class="hlt">waves</span> traveling in the sandy seabed can be modeled using a power-law dependent <span class="hlt">shear</span> <span class="hlt">wave</span> speed profile and an empirical source model that determines the pressure time-series at 1 m from the source as a function of TNT-equivalent charge weight.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22711412','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22711412"><span>Imaging feedback of histotripsy treatments using ultrasound <span class="hlt">shear</span> <span class="hlt">wave</span> elastography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Tzu-Yin; Hall, Timothy L; Xu, Zhen; Fowlkes, J Brian; Cain, Charles A</p> <p>2012-06-01</p> <p>Histotripsy is a cavitation-based ultrasound therapy that mechanically fractionates soft solid tissues into fluid-like homogenates. This paper investigates the feasibility of imaging the tissue elasticity change during the histotripsy process as a tool to provide feedback for the treatments. The treatments were performed on agar tissue phantoms and ex vivo kidneys using 3-cycle ultrasound pulses delivered by a 750-kHz therapeutic array at peak negative/positive pressure of 17/108 MPa and a repetition rate of 50 Hz. Lesions with different degrees of damage were created with increasing numbers of therapy pulses from 0 to 2000 pulses per treatment location. The elasticity of the lesions was measured with ultrasound <span class="hlt">shear</span> <span class="hlt">wave</span> elastography, in which a quasi-planar <span class="hlt">shear</span> <span class="hlt">wave</span> was induced by acoustic radiation force generated by the therapeutic array, and tracked with ultrasound imaging at 3000 frames per second. Based on the <span class="hlt">shear</span> <span class="hlt">wave</span> velocity calculated from the sequentially captured frames, the Young's modulus was reconstructed. Results showed that the lesions were more easily identified on the <span class="hlt">shear</span> <span class="hlt">wave</span> velocity images than on B-mode images. As the number of therapy pulses increased from 0 to 2000 pulses/location, the Young's modulus decreased exponentially from 22.1 ± 2.7 to 2.1 ± 1.1 kPa in the tissue phantoms (R2 = 0.99, N = 9 each), and from 33.0 ± 7.1 to 4.0 ± 2.5 kPa in the ex vivo kidneys (R2 = 0.99, N = 8 each). Correspondingly, the tissues transformed from completely intact to completely fractionated as examined via histology. A good correlation existed between the lesions' Young's modulus and the degree of tissue fractionation as examined with the percentage of remaining structurally intact cell nuclei (R2 = 0.91, N = 8 each). These results indicate that lesions produced by histotripsy can be detected with high sensitivity using <span class="hlt">shear</span> <span class="hlt">wave</span> elastography. Because the decrease in the tissue elasticity corresponded well with the morphological and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4019419','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4019419"><span><span class="hlt">Shear</span> modulus imaging by direct visualization of propagating <span class="hlt">shear</span> <span class="hlt">waves</span> with phase-sensitive optical coherence tomography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Song, Shaozhen; Huang, Zhihong; Nguyen, Thu-Mai; Wong, Emily Y.; Arnal, Bastien; O’Donnell, Matthew</p> <p>2013-01-01</p> <p>Abstract. We propose an integrated method combining low-frequency mechanics with optical imaging to map the <span class="hlt">shear</span> modulus within the biological tissue. Induced <span class="hlt">shear</span> <span class="hlt">wave</span> propagating in tissue is tracked in space and time using phase-sensitive optical coherence tomography (PhS-OCT). Local estimates of the <span class="hlt">shear-wave</span> speed obtained from tracking results can image the local <span class="hlt">shear</span> modulus. A PhS-OCT system remotely records depth-resolved, dynamic mechanical <span class="hlt">waves</span> at an equivalent frame rate of ∼47  kHz with the high spatial resolution. The proposed method was validated by examining tissue-mimicking phantoms made of agar and light scattering material. Results demonstrate that the <span class="hlt">shear</span> <span class="hlt">wave</span> imaging can accurately map the elastic moduli of these phantoms. PMID:24213539</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21097242','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21097242"><span><span class="hlt">3</span>-<span class="hlt">D</span> flow characterization and <span class="hlt">shear</span> stress in a stenosed carotid artery bifurcation model using stereoscopic PIV technique.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kefayati, Sarah; Poepping, Tamie L</p> <p>2010-01-01</p> <p>The carotid artery bifurcation is a common site of atherosclerosis which is a major leading cause of ischemic stroke. The impact of stenosis in the atherosclerotic carotid artery is to disturb the flow pattern and produce regions with high <span class="hlt">shear</span> rate, turbulence, and recirculation, which are key hemodynamic factors associated with plaque rupture, clot formation, and embolism. In order to characterize the disturbed flow in the stenosed carotid artery, stereoscopic PIV measurements were performed in a transparent model with 50% stenosis under pulsatile flow conditions. Simulated ECG gating of the flowrate waveform provides external triggering required for volumetric reconstruction of the complex flow patterns. Based on the three-component velocity data in the lumen region, volumetric <span class="hlt">shear</span>-stress patterns were derived.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4594487','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4594487"><span>Flow <span class="hlt">shear</span> stress regulates endothelial barrier function and expression of angiogenic factors in a <span class="hlt">3</span><span class="hlt">D</span> microfluidic tumor vascular model</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Buchanan, Cara F; Verbridge, Scott S; Vlachos, Pavlos P; Rylander, Marissa Nichole</p> <p>2014-01-01</p> <p>Endothelial cells lining blood vessels are exposed to various hemodynamic forces associated with blood flow. These include fluid <span class="hlt">shear</span>, the tangential force derived from the friction of blood flowing across the luminal cell surface, tensile stress due to deformation of the vessel wall by transvascular flow, and normal stress caused by the hydrodynamic pressure differential across the vessel wall. While it is well known that these fluid forces induce changes in endothelial morphology, cytoskeletal remodeling, and altered gene expression, the effect of flow on endothelial organization within the context of the tumor microenvironment is largely unknown. Using a previously established microfluidic tumor vascular model, the objective of this study was to investigate the effect of normal (4 dyn/cm2), low (1 dyn/cm2), and high (10 dyn/cm2) microvascular wall <span class="hlt">shear</span> stress (WSS) on tumor-endothelial paracrine signaling associated with angiogenesis. It is hypothesized that high WSS will alter the endothelial phenotype such that vascular permeability and tumor-expressed angiogenic factors are reduced. Results demonstrate that endothelial permeability decreases as a function of increasing WSS, while co-culture with tumor cells increases permeability relative to mono-cultures. This response is likely due to <span class="hlt">shear</span> stress-mediated endothelial cell alignment and tumor-VEGF-induced permeability. In addition, gene expression analysis revealed that high WSS (10 dyn/cm2) significantly down-regulates tumor-expressed MMP9, HIF1, VEGFA, ANG1, and ANG2, all of which are important factors implicated in tumor angiogenesis. This result was not observed in tumor mono-cultures or static conditioned media experiments, suggesting a flow-mediated paracrine signaling mechanism exists with surrounding tumor cells that elicits a change in expression of angiogenic factors. Findings from this work have significant implications regarding low blood velocities commonly seen in the tumor vasculature</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.207...59O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.207...59O"><span>Lapse-time-dependent coda-<span class="hlt">wave</span> depth sensitivity to local velocity perturbations in <span class="hlt">3</span>-<span class="hlt">D</span> heterogeneous elastic media</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Obermann, Anne; Planès, Thomas; Hadziioannou, Céline; Campillo, Michel</p> <p>2016-10-01</p> <p>In the context of seismic monitoring, recent studies made successful use of seismic coda <span class="hlt">waves</span> to locate medium changes on the horizontal plane. Locating the depth of the changes, however, remains a challenge. In this paper, we use <span class="hlt">3</span>-<span class="hlt">D</span> wavefield simulations to address two problems: first, we evaluate the contribution of surface- and body-<span class="hlt">wave</span> sensitivity to a change at depth. We introduce a thin layer with a perturbed velocity at different depths and measure the apparent relative velocity changes due to this layer at different times in the coda and for different degrees of heterogeneity of the model. We show that the depth sensitivity can be modelled as a linear combination of body- and surface-<span class="hlt">wave</span> sensitivity. The lapse-time-dependent sensitivity ratio of body <span class="hlt">waves</span> and surface <span class="hlt">waves</span> can be used to build <span class="hlt">3</span>-<span class="hlt">D</span> sensitivity kernels for imaging purposes. Second, we compare the lapse-time behaviour in the presence of a perturbation in horizontal and vertical slabs to address, for instance, the origin of the velocity changes detected after large earthquakes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3818126','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3818126"><span>Validation of <span class="hlt">Shear</span> <span class="hlt">Wave</span> Elastography in Skeletal Muscle</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Eby, Sarah F.; Song, Pengfei; Chen, Shigao; Chen, Qingshan; Greenleaf, James F.; An, Kai-Nan</p> <p>2013-01-01</p> <p>Skeletal muscle is a very dynamic tissue, thus accurate quantification of skeletal muscle stiffness throughout its functional range is crucial to improve the physical functioning and independence following pathology. <span class="hlt">Shear</span> <span class="hlt">wave</span> elastography (SWE) is an ultrasound-based technique that characterizes tissue mechanical properties based on the propagation of remotely induced <span class="hlt">shear</span> <span class="hlt">waves</span>. The objective of this study is to validate SWE throughout the functional range of motion of skeletal muscle for three ultrasound transducer orientations. We hypothesized that combining traditional materials testing (MTS) techniques with SWE measurements will show increased stiffness measures with increasing tensile load, and will correlate well with each other for trials in which the transducer is parallel to underlying muscle fibers. To evaluate this hypothesis, we monitored the deformation throughout tensile loading of four porcine brachialis whole-muscle tissue specimens, while simultaneously making SWE measurements of the same specimen. We used regression to examine the correlation between Young's modulus from MTS and <span class="hlt">shear</span> modulus from SWE for each of the transducer orientations. We applied a generalized linear model to account for repeated testing. Model parameters were estimated via generalized estimating equations. The regression coefficient was 0.1944, with a 95% confidence interval of (0.1463 – 0.2425) for parallel transducer trials. <span class="hlt">Shear</span> <span class="hlt">waves</span> did not propagate well for both the 45° and perpendicular transducer orientations. Both parallel SWE and MTS showed increased stiffness with increasing tensile load. This study provides the necessary first step for additional studies that can evaluate the distribution of stiffness throughout muscle. PMID:23953670</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFMOS53B1315M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFMOS53B1315M"><span>Prediction of Tsunami <span class="hlt">Waves</span> and Runup Generated by <span class="hlt">3</span><span class="hlt">d</span> Granular Landslides</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mohammed, F.; Fritz, H. M.</p> <p>2008-12-01</p> <p>Subaerial and submarine landslides can trigger tsunamis with locally high amplitudes and runup, which can cause devastating effects in the near field region. The 50th anniversary of the Lituya Bay 1958 landslide impact generated mega tsunami recalls the largest tsunami runup of 524m in recorded history. In contrast to earthquake generated tsunamis, landslide generated tsunami sources are not confined to active tectonic regions and therefore are of particular importance for the Atlantic Ocean. Landslide generated tsunamis were studied in the three dimensional NEES tsunami <span class="hlt">wave</span> basin TWB at OSU based on the generalized Froude similarity. A novel pneumatic landslide generator was deployed to control the landslide geometry and kinematics. Granular materials were used to model deformable landslides. Measurement techniques such as particle image velocimetry (PIV), multiple above and underwater video cameras, multiple acoustic transducer arrays (MTA), as well as resistance <span class="hlt">wave</span> and runup gauges were applied. The <span class="hlt">wave</span> generation was characterized by an extremely unsteady three phase flow consisting of the slide granulate, water and air entrained into the flow. The underwater cameras and the MTA provide data on the landslide deformation as it impacts the water surface, penetrates the water and finally deposits on the bottom of the basin. The influence of the landslide volume, shape and the impact speed on the generated tsunami <span class="hlt">wave</span> characteristics were extensively studied. The experimental data provides prediction models for the generated tsunami <span class="hlt">wave</span> characteristics based on the initial landslide characteristics and the final slide deposits. PIV provided instantaneous surface velocity vector fields, which gave insight into the kinematics of the landslide and <span class="hlt">wave</span> generation process. At high impact velocities flow separation occurred on the slide shoulder resulting in a hydrodynamic impact crater. The recorded <span class="hlt">wave</span> profiles yielded information on the <span class="hlt">wave</span> propagation and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1413083L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1413083L"><span><span class="hlt">3</span>-<span class="hlt">D</span> Inverse Teleseismic Scattered <span class="hlt">Wave</span> Imaging using the Kirchhoff Approximation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, K.; Levander, A.</p> <p>2012-04-01</p> <p>We have developed a <span class="hlt">3</span>-<span class="hlt">D</span> teleseismic imaging technique for scattered elastic wavefields using the Kirchhoff approximation. Kirchhoff migration/inversion have been well developed in exploration seismology within the inverse scattering framework (e.g. Miller et al., 1987; Beylkin and Burridge, 1990) to image subsurface structure that generates secondary wavefields caused by localized heterogeneities. Application of this method in global seismology has been largely limited to 2-D images made with 1-D reference models due to high computational cost and the lack of adequately dense receiver arrays (Bostock, 2002, Poppeliers and Pavlis, 2003; Frederiksen and Revenaugh, 2004; Cao et al., 2010). The deployment of the USArray Transportable and Flexible arrays in the United States and dense array recordings in other countries motivate developing teleseismic scattered wavefield imaging with the Kirchhoff approximation for <span class="hlt">3</span>-<span class="hlt">D</span> velocity models for both scalar and vector wavefields to improve upper mantle imaging. Following Bostock's development of the 2-D problem (2002), we derive the <span class="hlt">3</span>-<span class="hlt">D</span> P-to-S scattering inversion formula by phrasing the inverse problem in terms of the generalized Radon transform (GRT) and singular functions of discontinuity surfaces. In the forward scattering modeling, we extend the method to utilize a <span class="hlt">3</span>-<span class="hlt">D</span> migration velocity model by calculating <span class="hlt">3</span>-<span class="hlt">D</span> finite-difference traveltimes, backprojected from the receivers using an eikonal solver. To demonstrate the relative accuracy of the inversion, we examine several synthetic cases with a variety of discontinuity surfaces (sinuous, dipping, dome- and crater-shaped discontinuity interfaces, point scatterers, etc.). The Kirchhoff GRT imaging can successfully recover the shapes of these structures very well. We compare our Kirchhoff approximation imaging with the Born-approximate results, as well as the common-conversion point (CCP) stacked receiver function imaging for the various synthetic cases, and show a field</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AIPC.1706l0013M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AIPC.1706l0013M"><span><span class="hlt">3</span><span class="hlt">D</span> finite element modelling of guided <span class="hlt">wave</span> scattering at delaminations in composites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Murat, Bibi Intan Suraya; Fromme, Paul</p> <p>2016-02-01</p> <p>Carbon fiber laminate composites are increasingly used for aerospace structures as they offer a number of advantages including a good strength to weight ratio. However, impact during the operation and servicing of the aircraft can lead to barely visible and difficult to detect damage. Depending on the severity of the impact, delaminations can occur, reducing the load carrying capacity of the structure. Efficient nondestructive testing of composite panels can be achieved using guided ultrasonic <span class="hlt">waves</span> propagating along the structure. The guided <span class="hlt">wave</span> (A0 Lamb <span class="hlt">wave</span> mode) scattering at delaminations was modeled using full three-dimensional Finite Element (FE) simulations. The influence of the delamination size was systematically investigated from a parameter study. A significant influence of the delamination width on the guided <span class="hlt">wave</span> scattering was found, especially on the angular dependency of the scattered guided <span class="hlt">wave</span> amplitude. The sensitivity of guided ultrasonic <span class="hlt">waves</span> for the detection of delamination damage in composite panels is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA505433','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA505433"><span><span class="hlt">Wave</span> Propagation from Complex <span class="hlt">3</span><span class="hlt">D</span> Sources using the Representation Theorem</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2009-09-30</p> <p>wavenumber integration. The equations for the Green’s functions for surface <span class="hlt">waves</span> are given by Bache et al. (1982). The Green’s functions for the...Green’s functions for body <span class="hlt">waves</span> are generated by a procedure similar to that described by Bache and Harkrider (1976) using a saddle point...931 951. Bache , T. C. and D. G Harkrider (1976). The Body <span class="hlt">Waves</span> Due to a General Seismic source in a Layered Earth Model, Bull. Seism. Soc. Am. 66</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993JaJAP..32.2376K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993JaJAP..32.2376K"><span>New Biosensor Using <span class="hlt">Shear</span> Horizontal Surface Acoustic <span class="hlt">Wave</span> Device</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kondoh, Jun; Matsui, Yoshikazu; Shiokawa, Showko</p> <p>1993-05-01</p> <p>This paper describes a new biosensor to detect an enzyme reaction in liquid using surface acoustic <span class="hlt">wave</span> (SAW) devices fabricated on 36°-rotated Y-cut, X-propagating LiTaO3. The sensing <span class="hlt">wave</span> on the substrate is a predominantly <span class="hlt">shear</span>-horizontal-mode SAW (SH-SAW) and is affected by a strong acoustoelectric interaction between the piezoelectric potential and electrical properties of the materials in the adjacent liquid. As an example of an electrical property, pH change associated with an enzyme reaction leads to measurable perturbation in the <span class="hlt">wave</span>-propagation characteristic. Taking advantage of this phenomenon we realized a SAW biosensor which consists of an immobilized urease membrane on the surface. Also, highly sensitive detection for the urea solution was obtained in our preliminary experiments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhFl...23a6604C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhFl...23a6604C"><span>Generation of intermediately long sea <span class="hlt">waves</span> by weakly <span class="hlt">sheared</span> winds</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chernyavski, V. M.; Shtemler, Y. M.; Golbraikh, E.; Mond, M.</p> <p>2011-01-01</p> <p>The present study is concerned with the numerical modeling of sea-<span class="hlt">wave</span> instability under the effect of logarithmic-wind profile in hurricane conditions. The central point of the study is the calculation of the <span class="hlt">wave</span> growth rate, which is proportional to the fractional input energy from the weakly <span class="hlt">sheared</span> (logarithmic) wind to the <span class="hlt">wave</span> exponentially varying with time. It is shown for hurricane conditions that the Miles-type stability model based on the Charnock's formula with the standard constant coefficient underestimates the growth rate ˜5-50 times as compared with the model that employs the roughness adopted from the experimental data for hurricane winds. The drag reduction with wind speed at hurricane conditions coupled with the similar behavior of the dimensionless gravity acceleration leads to the minimum in the maximal growth rate and the maximum in the most unstable wavelength.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUSM.U42A..02L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUSM.U42A..02L"><span>3C<span class="hlt">3</span><span class="hlt">D</span> VSP Imaging of Salt Flanks Using Converted <span class="hlt">Waves</span> in the Gulf of Mexico</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Y.; Doherty, F.; Jackson, J.</p> <p>2005-05-01</p> <p>Locating salt boundary and imaging updip sediment structures flanking the salt domes are very important tasks for exploration in the Gulf of Mexico since major petroleum reserves are often trapped underneath overhangs of diapiric salt domes. Although the top of salt and less steep structures can be well imaged using current surface seismic methods, the steep sides of a salt dome with irregularly shapes are hard to image with adequate accuracy. Thus, Vertical Seismic Profiling (VSP) surveys with three-component (3C) receivers in wells are usually requested for improving images of subsurface structures. Conventional multi-offset VSP (OVSP) and refraction salt proximity (SP) surveys are widely applied in the Gulf of Mexico to improve images of slat interfaces, sub-salt and salt flank structures using P <span class="hlt">waves</span>. In this paper, we will focus on using converted <span class="hlt">waves</span> to image the steep salt-sediment boundary. A VSP dataset, including multi-OVSP and a SP survey, acquired in the Gulf of Mexico was used in this study. We analyzed 3C OVSP data to identify and separate converted <span class="hlt">waves</span>, such as PS, P-SP, P-SS, generated at a salt boundary. Then both PP <span class="hlt">wave</span> and converted <span class="hlt">waves</span> were 3C<span class="hlt">3</span><span class="hlt">D</span> depth migrated to generate images of the steep salt-sediment interface. Both transmitted P-P and P-S converted <span class="hlt">waves</span> from the SP survey were used to calculate <span class="hlt">3</span><span class="hlt">D</span> salt exit points which delineate the steep salt face. The VSP results derived from both methods are abundant and a suitable <span class="hlt">3</span><span class="hlt">D</span> visualization tool is required for visual integration and interpretation. The image volumes and other available geophysical and geological data were integrated using a <span class="hlt">3</span><span class="hlt">D</span> visualization tool specially designed for VSP solutions. The migrated images using PP and converted <span class="hlt">waves</span> provides a precise and complete definition of the steep salt face and reservoir sands flanking the salt dome. This study indicates that both reflection and reflection surveys can result in a consistent location of the steep salt flank</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PMB....61.2485H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PMB....61.2485H"><span>In vivo quantification of the <span class="hlt">shear</span> modulus of the human Achilles tendon during passive loading using <span class="hlt">shear</span> <span class="hlt">wave</span> dispersion analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Helfenstein-Didier, C.; Andrade, R. J.; Brum, J.; Hug, F.; Tanter, M.; Nordez, A.; Gennisson, J.-L.</p> <p>2016-03-01</p> <p>The <span class="hlt">shear</span> <span class="hlt">wave</span> velocity dispersion was analyzed in the Achilles tendon (AT) during passive dorsiflexion using a phase velocity method in order to obtain the tendon <span class="hlt">shear</span> modulus (C 55). Based on this analysis, the aims of the present study were (i) to assess the reproducibility of the <span class="hlt">shear</span> modulus for different ankle angles, (ii) to assess the effect of the probe locations, and (iii) to compare results with elasticity values obtained with the supersonic <span class="hlt">shear</span> imaging (SSI) technique. The AT <span class="hlt">shear</span> modulus (C 55) consistently increased with the ankle dorsiflexion (N  =  10, p  <  0.05). Furthermore, the technique showed a very good reproducibility (all standard error of the mean values  <10.7 kPa and all coefficient of variation (CV) values  ⩽0.05%). In addition, independently from the ankle dorsiflexion, the <span class="hlt">shear</span> modulus was significantly higher in the proximal location compared to the more distal one. The <span class="hlt">shear</span> modulus provided by SSI was always lower than C55 and the difference increased with the ankle dorsiflexion. However, <span class="hlt">shear</span> modulus values provided by both methods were highly correlated (R  =  0.84), indicating that the conventional <span class="hlt">shear</span> <span class="hlt">wave</span> elastography technique (SSI technique) can be used to compare tendon mechanical properties across populations. Future studies should determine the clinical relevance of the <span class="hlt">shear</span> <span class="hlt">wave</span> dispersion analysis, for instance in the case of tendinopathy or tendon tear.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4820600','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4820600"><span><span class="hlt">3</span><span class="hlt">D</span> Ultrafast Ultrasound Imaging In Vivo</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Provost, Jean; Papadacci, Clement; Arango, Juan Esteban; Imbault, Marion; Gennisson, Jean-Luc; Tanter, Mickael; Pernot, Mathieu</p> <p>2014-01-01</p> <p>Very high frame rate ultrasound imaging has recently allowed for the extension of the applications of echography to new fields of study such as the functional imaging of the brain, cardiac electrophysiology, and the quantitative real-time imaging of the intrinsic mechanical properties of tumors, to name a few, non-invasively and in real time. In this study, we present the first implementation of Ultrafast Ultrasound Imaging in three dimensions based on the use of either diverging or plane <span class="hlt">waves</span> emanating from a sparse virtual array located behind the probe. It achieves high contrast and resolution while maintaining imaging rates of thousands of volumes per second. A customized portable ultrasound system was developed to sample 1024 independent channels and to drive a 32×32 matrix-array probe. Its capability to track in <span class="hlt">3</span><span class="hlt">D</span> transient phenomena occurring in the millisecond range within a single ultrafast acquisition was demonstrated for <span class="hlt">3</span>-<span class="hlt">D</span> <span class="hlt">Shear-Wave</span> Imaging, <span class="hlt">3</span>-<span class="hlt">D</span> Ultrafast Doppler Imaging and finally <span class="hlt">3</span><span class="hlt">D</span> Ultrafast combined Tissue and Flow Doppler. The propagation of <span class="hlt">shear</span> <span class="hlt">waves</span> was tracked in a phantom and used to characterize its stiffness. <span class="hlt">3</span>-<span class="hlt">D</span> Ultrafast Doppler was used to obtain <span class="hlt">3</span>-<span class="hlt">D</span> maps of Pulsed Doppler, Color Doppler, and Power Doppler quantities in a single acquisition and revealed, for the first time, the complex <span class="hlt">3</span>-<span class="hlt">D</span> flow patterns occurring in the ventricles of the human heart during an entire cardiac cycle, and the <span class="hlt">3</span>-<span class="hlt">D</span> in vivo interaction of blood flow and wall motion during the pulse <span class="hlt">wave</span> in the carotid at the bifurcation. This study demonstrates the potential of <span class="hlt">3</span>-<span class="hlt">D</span> Ultrafast Ultrasound Imaging for the <span class="hlt">3</span>-<span class="hlt">D</span> real-time mapping of stiffness, tissue motion, and flow in humans in vivo and promises new clinical applications of ultrasound with reduced intra- and inter-observer variability. PMID:25207828</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....4952D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....4952D"><span>Analysis of non linear partially standing <span class="hlt">waves</span> from <span class="hlt">3</span><span class="hlt">D</span> velocity measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drevard, D.; Rey, V.; Svendsen, Ib; Fraunie, P.</p> <p>2003-04-01</p> <p>Surface gravity <span class="hlt">waves</span> in the ocean exhibit an energy spectrum distributed in both frequency and direction of propagation. <span class="hlt">Wave</span> data collection is of great importance in coastal zones for engineering and scientific studies. In particular, partially standing <span class="hlt">waves</span> measurements near coastal structures and steep or barred beaches may be a requirement, for instance for morphodynamic studies. The aim of the present study is the analysis of partially standing surface <span class="hlt">waves</span> icluding non-linear effects. According to 1st order Stokes theory, synchronous measurements of horizontal and vertical velocity components allow calculation of rate of standing <span class="hlt">waves</span> (Drevard et al, 2003). In the present study, it is demonstrated that for deep water conditions, partially standing 2nd order Stokes <span class="hlt">waves</span> induced velocity field is still represented by the 1st order solution for the velocity potential contrary to the surface elevation which exhibits harmonic components. For intermediate water depth, harmonic components appear not only in the surface elevation but also in the velocity fields, but their weight remains much smaller, because of the vertical decreasing <span class="hlt">wave</span> induced motion. For irregular <span class="hlt">waves</span>, the influence of the spectrum width on the non-linear effects in the analysis is discussed. Keywords: <span class="hlt">Wave</span> measurements ; reflection ; non-linear effects Acknowledgements: This work was initiated during the stay of Prof. Ib Svendsen, as invited Professor, at LSEET in autumn 2002. This study is carried out in the framework of the Scientific French National Programmes PNEC ART7 and PATOM. Their financial supports are acknowledged References: Drevard, D., Meuret, A., Rey, V. Piazzola, J. And Dolle, A.. (2002). "Partially reflected <span class="hlt">waves</span> measurements using Acoustic Doppler Velocimeter (ADV)", Submitted to ISOPE 03, Honolulu, Hawaii, May 2003.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhDT........21R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhDT........21R"><span><span class="hlt">Wave</span>Q<span class="hlt">3</span><span class="hlt">D</span>: Fast and accurate acoustic transmission loss (TL) eigenrays, in littoral environments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reilly, Sean M.</p> <p></p> <p>This study defines a new <span class="hlt">3</span><span class="hlt">D</span> Gaussian ray bundling acoustic transmission loss model in geodetic coordinates: latitude, longitude, and altitude. This approach is designed to lower the computation burden of computing accurate environmental effects in sonar training application by eliminating the need to transform the ocean environment into a collection of Nx2D Cartesian radials. This approach also improves model accuracy by incorporating real world <span class="hlt">3</span><span class="hlt">D</span> effects, like horizontal refraction, into the model. This study starts with derivations for a <span class="hlt">3</span><span class="hlt">D</span> variant of Gaussian ray bundles in this coordinate system. To verify the accuracy of this approach, acoustic propagation predictions of transmission loss, time of arrival, and propagation direction are compared to analytic solutions and other models. To validate the model's ability to predict real world phenomena, predictions of transmission loss and propagation direction are compared to at-sea measurements, in an environment where strong horizontal refraction effect have been observed. This model has been integrated into U.S. Navy active sonar training system applications, where testing has demonstrated its ability to improve transmission loss calculation speed without sacrificing accuracy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DPPU10060C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DPPU10060C"><span>Investigation of Parametric Excitation of Whistler <span class="hlt">Waves</span> Using <span class="hlt">3</span><span class="hlt">D</span> Particle-In-Cell Simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caplinger, James; Sotnikov, Vladimir; Main, Daniel; Rose, David; Paraschiv, Ioana</p> <p>2016-10-01</p> <p>Previous theoretical work has shown that a parametric interaction between quasi-electrostatic lower oblique resonance (LOR) and lower frequency (ω < ωLH) ion acoustic or extremely low frequency (ELF) <span class="hlt">waves</span> can produce electromagnetic whistler <span class="hlt">waves</span> in a cold magnetized plasma. It was also demonstrated theoretically that this interaction can more efficiently generate electromagnetic whistler <span class="hlt">waves</span> than by direct excitation by a conventional loop antenna, operating at a single frequency. For the purpose of numerically validating the above result, a series of particle-in-cell simulations were carried out. We first demonstrate the ability to accurately model whistler <span class="hlt">wave</span> excitation producing the familiar resonant surfaces which comprise the LOR using a modeled loop antenna. Next we demonstrate the ability to generate ion acoustic <span class="hlt">waves</span> as well as ELF <span class="hlt">waves</span>, both of which are shown to agree with the expected linear dispersion relations. Finally, we investigate the existence of any nonlinear interaction which indicates the desired parametric excitation and attempt to analyze the efficiency of this method of excitation and radiated power going into the whistler part of the VLF <span class="hlt">wave</span> spectrum.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......539S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......539S"><span>The Effects of Realistic Geological Heterogeneity on Seismic Modeling: Applications in <span class="hlt">Shear</span> <span class="hlt">Wave</span> Generation and Near-Surface Tunnel Detection</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sherman, Christopher Scott</p> <p></p> <p>Naturally occurring geologic heterogeneity is an important, but often overlooked, aspect of seismic <span class="hlt">wave</span> propagation. This dissertation presents a strategy for modeling the effects of heterogeneity using a combination of geostatistics and Finite Difference simulation. In the first chapter, I discuss my motivations for studying geologic heterogeneity and seis- mic <span class="hlt">wave</span> propagation. Models based upon fractal statistics are powerful tools in geophysics for modeling heterogeneity. The important features of these fractal models are illustrated using borehole log data from an oil well and geomorphological observations from a site in Death Valley, California. A large part of the computational work presented in this disserta- tion was completed using the Finite Difference Code E<span class="hlt">3</span><span class="hlt">D</span>. I discuss the Python-based user interface for E<span class="hlt">3</span><span class="hlt">D</span> and the computational strategies for working with heterogeneous models developed over the course of this research. The second chapter explores a phenomenon observed for <span class="hlt">wave</span> propagation in heteroge- neous media - the generation of unexpected <span class="hlt">shear</span> <span class="hlt">wave</span> phases in the near-source region. In spite of their popularity amongst seismic researchers, approximate methods for modeling <span class="hlt">wave</span> propagation in these media, such as the Born and Rytov methods or Radiative Trans- fer Theory, are incapable of explaining these <span class="hlt">shear</span> <span class="hlt">waves</span>. This is primarily due to these method's assumptions regarding the coupling of near-source terms with the heterogeneities and mode conversion. To determine the source of these <span class="hlt">shear</span> <span class="hlt">waves</span>, I generate a suite of <span class="hlt">3</span><span class="hlt">D</span> synthetic heterogeneous fractal geologic models and use E<span class="hlt">3</span><span class="hlt">D</span> to simulate the <span class="hlt">wave</span> propaga- tion for a vertical point force on the surface of the models. I also present a methodology for calculating the effective source radiation patterns from the models. The numerical results show that, due to a combination of mode conversion and coupling with near-source hetero- geneity, <span class="hlt">shear</span> <span class="hlt">wave</span> energy on the order of 10% of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.9573M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.9573M"><span><span class="hlt">3</span><span class="hlt">D</span> crustal structure of the Alpine belt and foreland basins as imaged by ambient-noise surface <span class="hlt">wave</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Molinari, Irene; Morelli, Andrea; Cardi, Riccardo; Boschi, Lapo; Poli, Piero; Kissling, Edi</p> <p>2016-04-01</p> <p>We derive a <span class="hlt">3</span>-<span class="hlt">D</span> crustal structure (S <span class="hlt">wave</span> velocity) underneath northern Italy and the wider Alpine region, from an extensive data set of measurements of Rayleigh-<span class="hlt">wave</span> phase- and group-velocities from ambient noise correlation among all seismographic stations available to date in the region, via a constrained tomographic inversion made to honor detailed active source reflection/refraction profiles and other geological information. We first derive a regional-scale surface <span class="hlt">wave</span> tomography from ambient-noise-based phase- and group- surface <span class="hlt">wave</span> velocity observations (Verbeke et al., 2012). Our regional <span class="hlt">3</span><span class="hlt">D</span> model (Molinari et al., 2015) shows the low velocity area beneath the Po Plain and the Molasse basin; the contrast between the low-velocity crust of the Adriatic domain and the high-velocity crust of the Tyrrhenian domain is clearly seen, as well as an almost uniform crystalline crust beneath the Alpine belt. However, higher frequency data can be exploited to achieve higher resolution images of the Po Plain and Alpine foreland <span class="hlt">3</span><span class="hlt">D</span> crustal structure. We collected and analyze one year of noise records (2011) of ~100 North Italy seismic broadband stations, we derive the Green functions between each couple of stations and we measure the phase- and group-Rayleigh <span class="hlt">wave</span> velocity. We conduct a suite of linear least squares inversion of both phase- and group-velocity data, resulting in 2-D maps of Rayleigh-<span class="hlt">wave</span> phase and group velocity at periods between 3 and 40s with a resolution of 0.1x0.1 degrees. The maps are then inverted to get the <span class="hlt">3</span><span class="hlt">D</span> structure with unprecedented details. We present here our results, we compare them with other studies, and we discuss geological/geodynamical implications. We believe that such a model stands for the most up-to-date seismological information on the crustal structure of the Alpine belt and foreland basins, and it can represent a reliable reference for further, more detailed, studies to come, based on the high seismograph station density</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA487585','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA487585"><span><span class="hlt">Wave</span> Propagation from Complex <span class="hlt">3</span><span class="hlt">D</span> Sources Using the Representation Theorem</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2008-09-30</p> <p>functions for surface <span class="hlt">waves</span> are given by Bache et al. (1982). The Green’s functions for the complete seismograms are computed using a ring load source...procedure similar to that described by Bache and Harkrider (1976), using a saddle point approximation to calculate a far-field plane <span class="hlt">wave</span> for a given takeoff...space, Part II, Bull. Seism. Soc. Am. 73: 931-951. Bache , T. C. and D. G. Harkrider (1976). The body <span class="hlt">waves</span> due to a general seismic source in a layered</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014709','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014709"><span>Anomalous <span class="hlt">shear</span> <span class="hlt">wave</span> attenuation in the shallow crust beneath the Coso volcanic regionn, California ( USA).</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Sanders, C.; Ho-Liu, P.; Rinn, D.; Hiroo, Kanamori</p> <p>1988-01-01</p> <p>We use seismograms of local earthquakes to image relative <span class="hlt">shear</span> <span class="hlt">wave</span> attenuation structure in the shallow crust beneath the region containing the Coso volcanic-geothermal area of E California. Seismograms of 16 small earthquakes show SV amplitudes which are greatly diminished at some azimuths and takeoff angles, indicating strong lateral variations in S <span class="hlt">wave</span> attenuation in the area. <span class="hlt">3</span>-<span class="hlt">D</span> images of the relative S <span class="hlt">wave</span> attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data. The results indicate regions within a 20 by 30 by 10 km volume of the shallow crust (one shallower than 5 km) that severely attenuate SV <span class="hlt">waves</span> passing through them. These anomalies lie beneath the Indian Wells Valley, 30 km S of the Coso volcanic field, and are coincident with the epicentral locations of recent earthquake swarms. No anomalous attenuation is seen beneath the Coso volcanic field above about 5 km depth. Geologic relations and the coincidence of anomalously slow P <span class="hlt">wave</span> velocities suggest that the attenuation anomalies may be related to magmatism along the E Sierra front.-from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMOS11B1649M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMOS11B1649M"><span>Evolution of a Directional <span class="hlt">Wave</span> Spectrum in a <span class="hlt">3</span><span class="hlt">D</span> Marginal Ice Zone with Random Floe Size Distribution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Montiel, F.; Squire, V. A.</p> <p>2013-12-01</p> <p>A new ocean <span class="hlt">wave</span>/sea-ice interaction model is proposed that simulates how a directional <span class="hlt">wave</span> spectrum evolves as it travels through a realistic marginal ice zone (MIZ), where <span class="hlt">wave</span>/ice dynamics are entirely governed by coherent conservative <span class="hlt">wave</span> scattering effects. Field experiments conducted by Wadhams et al. (1986) in the Greenland Sea generated important data on <span class="hlt">wave</span> attenuation in the MIZ and, particularly, on whether the <span class="hlt">wave</span> spectrum spreads directionally or collimates with distance from the ice edge. The data suggest that angular isotropy, arising from multiple scattering by ice floes, occurs close to the edge and thenceforth dominates <span class="hlt">wave</span> propagation throughout the MIZ. Although several attempts have been made to replicate this finding theoretically, including by the use of numerical models, none have confronted this problem in a <span class="hlt">3</span><span class="hlt">D</span> MIZ with fully randomised floe distribution properties. We construct such a model by subdividing the discontinuous ice cover into adjacent infinite slabs of finite width parallel to the ice edge. Each slab contains an arbitrary (but finite) number of circular ice floes with randomly distributed properties. Ice floes are modeled as thin elastic plates with uniform thickness and finite draught. We consider a directional <span class="hlt">wave</span> spectrum with harmonic time dependence incident on the MIZ from the open ocean, defined as a continuous superposition of plane <span class="hlt">waves</span> traveling at different angles. The scattering problem within each slab is then solved using Graf's interaction theory for an arbitrary incident directional plane <span class="hlt">wave</span> spectrum. Using an appropriate integral representation of the Hankel function of the first kind (see Cincotti et al., 1993), we map the outgoing circular <span class="hlt">wave</span> field from each floe on the slab boundaries into a directional spectrum of plane <span class="hlt">waves</span>, which characterizes the slab reflected and transmitted fields. Discretizing the angular spectrum, we can obtain a scattering matrix for each slab. Standard recursive</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012ApPhL.100m3702H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012ApPhL.100m3702H"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> induced resonance elastography of spherical masses with polarized torsional <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hadj Henni, Anis; Schmitt, Cédric; Trop, Isabelle; Cloutier, Guy</p> <p>2012-03-01</p> <p><span class="hlt">Shear</span> <span class="hlt">wave</span> induced resonance (SWIR) is a technique for dynamic ultrasound elastography of confined mechanical inclusions. It was developed for breast tumor imaging and tissue characterization. This method relies on the polarization of torsional <span class="hlt">shear</span> <span class="hlt">waves</span> modeled with the Helmholtz equation in spherical coordinates. To validate modeling, an invitro set-up was used to measure and image the first three eigenfrequencies and eigenmodes of a soft sphere. A preliminary invivo SWIR measurement on a breast fibroadenoma is also reported. Results revealed the potential of SWIR elastography to detect and mechanically characterize breast lesions for early cancer detection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/842635','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/842635"><span>Development of Scientific Simulation <span class="hlt">3</span><span class="hlt">D</span> Full <span class="hlt">Wave</span> ICRF Code for Stellarators and Heating/CD Scenarios Development</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Vdovin V.L.</p> <p>2005-08-15</p> <p>In this report we describe theory and <span class="hlt">3</span><span class="hlt">D</span> full <span class="hlt">wave</span> code description for the <span class="hlt">wave</span> excitation, propagation and absorption in 3-dimensional (<span class="hlt">3</span><span class="hlt">D</span>) stellarator equilibrium high beta plasma in ion cyclotron frequency range (ICRF). This theory forms a basis for a <span class="hlt">3</span><span class="hlt">D</span> code creation, urgently needed for the ICRF heating scenarios development for the operated LHD, constructed W7-X, NCSX and projected CSX3 stellarators, as well for re evaluation of ICRF scenarios in operated tokamaks and in the ITER . The theory solves the <span class="hlt">3</span><span class="hlt">D</span> Maxwell-Vlasov antenna-plasma-conducting shell boundary value problem in the non-orthogonal flux coordinates ({Psi}, {theta}, {var_phi}), {Psi} being magnetic flux function, {theta} and {var_phi} being the poloidal and toroidal angles, respectively. All basic physics, like <span class="hlt">wave</span> refraction, reflection and diffraction are self consistently included, along with the fundamental ion and ion minority cyclotron resonances, two ion hybrid resonance, electron Landau and TTMP absorption. Antenna reactive impedance and loading resistance are also calculated and urgently needed for an antenna -generator matching. This is accomplished in a real confining magnetic field being varying in a plasma major radius direction, in toroidal and poloidal directions, through making use of the hot dense plasma <span class="hlt">wave</span> induced currents with account to the finite Larmor radius effects. We expand the solution in Fourier series over the toroidal ({var_phi}) and poloidal ({theta}) angles and solve resulting ordinary differential equations in a radial like {Psi}-coordinate by finite difference method. The constructed discretization scheme is divergent-free one, thus retaining the basic properties of original equations. The Fourier expansion over the angle coordinates has given to us the possibility to correctly construct the ''parallel'' <span class="hlt">wave</span> number k{sub //}, and thereby to correctly describe the ICRF <span class="hlt">waves</span> absorption by a hot plasma. The toroidal harmonics are tightly coupled with each</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S53B2809F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S53B2809F"><span>Hammering Yucca Flat, Part Two: <span class="hlt">Shear-Wave</span> Velocity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Finlay, T. S.; Abbott, R. E.; Knox, H. A.; Tang, D. G.; James, S. R.; Haney, M. M.; Hampshire, J. B., II</p> <p>2015-12-01</p> <p>In preparation for the next phase of the Source Physics Experiment (SPE), we conducted an active-source seismic survey of Yucca Flat, Nevada, on the Nevada National Security Site. Results from this survey will be used to inform the geologic models associated with the SPE project. For this study, we used a novel 13,000 kilogram weight-drop seismic source to interrogate an 18-km North-South transect of Yucca Flat. Source points were spaced every 200 meters and were recorded by 350 to 380 3-component 2-Hz geophones with variable spacings of 10, 20, and 100 meters. We utilized the Refraction-Microtremor (ReMi) technique to create multiple 1D dispersion curves, which were then inverted for <span class="hlt">shear-wave</span> velocity profiles using the Dix inversion method (Tsai and Haney, 2015). Each of these 1D velocity models was subsequently stitched together to create a 2D profile over the survey area. The dispersion results indicate a general decrease in surface-<span class="hlt">wave</span> phase velocity to the south. This result is supported by slower <span class="hlt">shear-wave</span> velocity sediments and increasing basin depth towards the survey's southern extent. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021669','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021669"><span>Estimation of near-surface <span class="hlt">shear-wave</span> velocity by inversion of Rayleigh <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Xia, J.; Miller, R.D.; Park, C.B.</p> <p>1999-01-01</p> <p>The <span class="hlt">shear-wave</span> (S-<span class="hlt">wave</span>) velocity of near-surface materials (soil, rocks, pavement) and its effect on seismic-<span class="hlt">wave</span> propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh-<span class="hlt">wave</span> phase velocity of a layered-earth model is a function of frequency and four groups of earth properties: P-<span class="hlt">wave</span> velocity, S-<span class="hlt">wave</span> velocity, density, and thickness of layers. Analysis of the Jacobian matrix provides a measure of dispersion-curve sensitivity to earth properties. S-<span class="hlt">wave</span> velocities are the dominant influence on a dispersion curve in a high-frequency range (>5 Hz) followed by layer thickness. An iterative solution technique to the weighted equation proved very effective in the high-frequency range when using the Levenberg-Marquardt and singular-value decomposition techniques. Convergence of the weighted solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Synthetic examples demonstrated calculation efficiency and stability of inverse procedures. We verify our method using borehole S-<span class="hlt">wave</span> velocity measurements.Iterative solutions to the weighted equation by the Levenberg-Marquardt and singular-value decomposition techniques are derived to estimate near-surface <span class="hlt">shear-wave</span> velocity. Synthetic and real examples demonstrate the calculation efficiency and stability of the inverse procedure. The inverse results of the real example are verified by borehole S-<span class="hlt">wave</span> velocity measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Ap%26SS.357..110S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Ap%26SS.357..110S"><span>Localization of <span class="hlt">3</span><span class="hlt">D</span> inertial Alfvén <span class="hlt">wave</span> and generation of turbulence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharma, R. P.; Sharma, Prachi; Yadav, N.</p> <p>2015-06-01</p> <p>The present paper deals with the nonlinear interaction of Inertial Alfvén <span class="hlt">wave</span> (IAW) and fast magnetosonic <span class="hlt">wave</span> in the low beta plasma, where beta is the ratio of thermal pressure to the background magnetic pressure. In this paper, the localization and turbulent spectra of IAW along with the density dips correlated with the fast magnetosonic <span class="hlt">wave</span> have been investigated. Variation of parallel electric field along and across the field lines has also been studied. Taking ponderomotive nonlinear effect in the dynamics of fast magnetosonic <span class="hlt">wave</span>, couple of dimensionless equations has been derived. These coupled equations have been simulated numerically using the pseudo-spectral method. The obtained results reveal that the Kolmogorov scaling is followed by a steeper scaling in magnetic power spectrum, which is consistent with the observations by the FAST and Hawkeye spacecraft in auroral region. The relevance of present investigation has been discussed for auroral plasmas.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.205..179M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.205..179M"><span>ML <span class="hlt">shear</span> <span class="hlt">wave</span> velocity tomography for the Iranian Plateau</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maheri-Peyrov, Mehdi; Ghods, Abdolreza; Abbasi, Madjid; Bergman, Eric; Sobouti, Farhad</p> <p>2016-04-01</p> <p>Iranian Plateau reflects several different tectonic styles of collision, and large-scale strike-slip faults. We calculate a high-resolution 2-D ML <span class="hlt">shear</span> velocity map for the Iranian Plateau to detect lateral crustal thickness changes associated with different tectonic boundaries. The ML velocity is very sensitive to strong lateral variations of crustal thickness and varies between the velocity of Lg and Sn phases. Our data set consists of 65 795 ML amplitude velocity measurements from 2531 precisely relocated events recorded by Iranian networks in the period 1996-2014. Using a constrained least-squares inversion scheme, we inverted the ML velocities for a 2-D <span class="hlt">shear</span> velocity map of Iran. Our results show that the Zagros and South Caspian Basin (SCB) have <span class="hlt">shear</span> <span class="hlt">wave</span> velocities close to the Sn phase, and are thus Lg-blocking regions. High velocities in the High Zagros and the Simply Folded Belt imply significant crustal undulations within these zones. We note that in the central and south Zagros, the velocity border between the Zagros and central Iran is not coincident with the Zagros suture line that marks underthrusting of the Arabian plate beneath central Iran. The low plains of Gilan and Gorgan to the south of the Caspian Sea show high <span class="hlt">shear</span> velocities similar to the SCB, implying that they are either underlain by an oceanic type crust or a transitional crust with a strong lateral crustal thickness gradient. The Lut block is an Lg-passing block implying that it is not surrounded by any sudden crustal thickness changes along its borders with central Iran. In the Alborz, NW Iran, Kopeh-Dagh, Binalud and most of the central Iran, low <span class="hlt">shear</span> velocity near the Lg velocity is attributed to smooth or minor Moho undulations within these regions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22220698','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22220698"><span>Observation of <span class="hlt">3</span><span class="hlt">D</span> defect mediated dust acoustic <span class="hlt">wave</span> turbulence with fluctuating defects and amplitude hole filaments</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chang, Mei-Chu; Tsai, Ya-Yi; I, Lin</p> <p>2013-08-15</p> <p>We experimentally demonstrate the direct observation of defect mediated <span class="hlt">wave</span> turbulence with fluctuating defects and low amplitude hole filaments, from a <span class="hlt">3</span><span class="hlt">D</span> self-excited plane dust acoustic <span class="hlt">wave</span> in a dusty plasma by reducing dissipation. The waveform undulation is found to be the origin for the amplitude and the phase modulations of the local dust density oscillation, the broadening of the sharp peaks in the frequency spectrum, and the fluctuating defects. The corrugated <span class="hlt">wave</span> crest surface also causes the observed high and low density patches in the transverse (xy) plane. Low oscillation amplitude spots (holes) share the same positions with the defects. Their trajectories in the xyt space appear in the form of chaotic filaments without long term predictability, through uncertain pair generation, propagation, and pair annihilation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S33A4497Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S33A4497Y"><span><span class="hlt">Shear</span> <span class="hlt">Wave</span> Structure in the Lithosphere of Texas from Ambient Noise Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yao, Y.; Li, A.</p> <p>2014-12-01</p> <p>Texas contains several distinct tectonic provinces, the Laurentia craton, the Ouachita belt, and the Gulf coastal plain. Although numerous geophysical experiments have been conducted in Texas for petroleum exploration, the lithosphere structure of Texas has not been well studied. We present here the Texas-wide <span class="hlt">shear</span> <span class="hlt">wave</span> structure using seismic ambient noise data recorded at 87 stations from the Transportable Array of the USArray between March 2010 and February 2011. Rayleigh <span class="hlt">wave</span> phase velocities between pairs of stations are obtained by cross-correlating long ambient noise sequences and are used to develop phase velocity maps from 6 to 40 s. These measured phase velocities are used to construct 1-D and <span class="hlt">3</span>-<span class="hlt">D</span> <span class="hlt">shear</span> <span class="hlt">wave</span> velocity models, which consist of four crust layers and one upper mantle layer. <span class="hlt">Shear</span> <span class="hlt">wave</span> velocity maps reveal a close correlation with major geological features. From the surface to 25 km depth, Positive anomalies coincide with the Laurentia craton, and negative anomalies coincide with the continental margin. The boundary of positive-negative anomaly perfectly matches the Ouachita belt. The Llano Uplift is imaged as the highest velocity through the mid-crust because the igneous rock forming the uplift has faster seismic velocity than the normal continental crust. Similarly, three small high-velocity areas exist beneath the Waco Uplift, Devils River Uplift, and Benton Uplift, even though surface geological traces are absent in these areas. The lowest velocity at the shallow crust appears in northeastern and southeastern Texas separated by the San Marcos Arch, correlating with thick sediment layers. An exceptional low velocity is imaged in southernmost Texas in the lower crust and upper mantle, probably caused by subducted wet oceanic crust before the rifting in the Gulf of Mexico. In the uppermost mantle, positive <span class="hlt">shear</span> <span class="hlt">wave</span> anomalies extend southeastward from the Ouachita belt to the Gulf coast, likely evidencing the subducted oceanic lithosphere</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/AD1006109','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/AD1006109"><span>Moored Observations of Internal <span class="hlt">Waves</span> in Luzon Strait: <span class="hlt">3</span>-<span class="hlt">D</span> Structure, Dissipation, and Evolution</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2016-03-01</p> <p>advancing the performance of operational and climate models, as well as for understanding local problems such as pollutant dispersal and biological...Y.J. Yang, M.-H. Chang , and Q. Li. 2011. From Luzon Strait to Dongsha Plateau: Stages in the life of an internal <span class="hlt">wave</span>. Oceanography 24(4):64–77...Knowledge of the general problems of internal <span class="hlt">waves</span> and ocean mixing are important for advancing the performance of operational and climate models, as well</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDA15009M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDA15009M"><span>Wall <span class="hlt">Shear</span> Stress Restoration in Dialysis Patient's Venous Stenosis: Elucidation via <span class="hlt">3</span><span class="hlt">D</span> CFD and Shape Optimization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mahmoudzadeh Akherat, S. M. Javid; Cassel, Kevin; Hammes, Mary; Boghosian, Michael; Illinois Institute of Technology Team; University of Chicago Team</p> <p>2016-11-01</p> <p>Venous stenosis developed after the growth of excessive neointimal hyperplasia (NH) in chronic dialysis treatment is a major cause of mortality in renal failure patients. It has been hypothesized that the low wall <span class="hlt">shear</span> stress (WSS) triggers an adaptive response in patients' venous system that through the growth of neointimal hyperplastic lesions restores WSS and transmural pressure, which also regulates the blood flow rate back to physiologically acceptable values which is violated by dialysis treatment. A strong coupling of three-dimensional CFD and shape optimization analyses were exploited to elucidate and forecast this adaptive response which correlates very well topographically with patient-specific clinical data. Based on the framework developed, a medical protocol is suggested to predict and prevent dialysis treatment failure in clinical practice. Supported by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health (R01 DK90769).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8565G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8565G"><span>Propagation of <span class="hlt">3</span><span class="hlt">D</span> nonlinear <span class="hlt">waves</span> over complex bathymetry using a High-Order Spectral method</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gouin, Maïté; Ducrozet, Guillaume; Ferrant, Pierre</p> <p>2016-04-01</p> <p>Scattering of regular and irregular surface gravity <span class="hlt">waves</span> propagating over a region of arbitrary three-dimensional varying bathymetry is considered here. The three-dimensional High-Order Spectral method (HOS) with an extension to account for a variable bathymetry is used. The efficiency of the model has been proved to be conserved even with this extension. The method is first applied to a bathymetry consisting of an elliptical lens, as used in the Vincent and Briggs (1989) experiment. Incident <span class="hlt">waves</span> passing across the lens are transformed and a strong convergence region is observed after the elliptical mound. The <span class="hlt">wave</span> amplification depends on the incident <span class="hlt">wave</span>. Numerical results for regular and irregular <span class="hlt">waves</span> are analysed and compared with other methods and experimental data demonstrating the efficiency and practical applicability of the present approach. Then the method is used to model <span class="hlt">waves</span> propagating over a real bathymetry: the canyons of Scripps/La Jolla in California. The implementation of this complex bathymetry in the model is presented, as well as the first results achieved. They will be compared to the ones obtained with another numerical model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22263913','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22263913"><span>Nonlinear physics of <span class="hlt">shear</span> Alfvén <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zonca, Fulvio; Chen, Liu</p> <p>2014-02-12</p> <p><span class="hlt">Shear</span> Alfvén <span class="hlt">waves</span> (SAW) play fundamental roles in thermonuclear plasmas of fusion interest, since they are readily excited by energetic particles in the MeV range as well as by the thermal plasma components. Thus, understanding fluctuation induced transport in burning plasmas requires understanding nonlinear SAW physics. There exist two possible routes to nonlinear SAW physics: (i) <span class="hlt">wave-wave</span> interactions and the resultant spectral energy transfer; (ii) nonlinear <span class="hlt">wave</span>-particle interactions of SAW instabilities with energetic particles. Within the first route, it is advantageous to understand and describe nonlinear processes in term of proximity of the system to the Alfvénic state, where <span class="hlt">wave-wave</span> interactions are minimized due to the cancellation of Reynolds and Maxwell stresses. Here, various <span class="hlt">wave-wave</span> nonlinear dynamics are elucidated in terms of how they break the Alfvénic state. In particular, we discuss the qualitative and quantitative modification of the SAW parametric decay process due to finite ion compressibility and finite ion Larmor radius. We also show that toroidal geometry plays a crucial role in the nonlinear excitation of zonal structures by Alfvén eigenmodes. Within the second route, the coherent nonlinear dynamics of structures in the energetic particle phase space, by which secular resonant particle transport can occur on meso- and macro-scales, must be addressed and understood. These 'nonlinear equilibria' or 'phase-space zonal structures' dynamically evolve on characteristic (fluctuation induced) turbulent transport time scales, which are generally of the same order of the nonlinear time scale of the underlying fluctuations. In this work, we introduce the general structure of nonlinear Schrödinger equations with complex integro-differential nonlinear terms, which govern these physical processes. To elucidate all these aspects, theoretical analyses are presented together with numerical simulation results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1814109Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1814109Q"><span>Explicit <span class="hlt">wave</span> action conservation for water <span class="hlt">waves</span> on vertically <span class="hlt">sheared</span> flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Quinn, Brenda; Toledo, Yaron; Shrira, Victor</p> <p>2016-04-01</p> <p>Water <span class="hlt">waves</span> almost always propagate on currents with a vertical structure such as currents directed towards the beach accompanied by an under-current directed back toward the deep sea or wind-induced currents which change magnitude with depth due to viscosity effects. On larger scales they also change their direction due to the Coriolis force as described by the Ekman spiral. This implies that the existing <span class="hlt">wave</span> models, which assume vertically-averaged currents, is an approximation which is far from realistic. In recent years, ocean circulation models have significantly improved with the capability to model vertically-<span class="hlt">sheared</span> current profiles in contrast with the earlier vertically-averaged current profiles. Further advancements have coupled <span class="hlt">wave</span> action models to circulation models to relate the mutual effects between the two types of motion. Restricting <span class="hlt">wave</span> models to vertically-averaged non-turbulent current profiles is obviously problematic in these cases and the primary goal of this work is to derive and examine a general <span class="hlt">wave</span> action equation which accounts for these shortcoming. The formulation of the <span class="hlt">wave</span> action conservation equation is made explicit by following the work of Voronovich (1976) and using known asymptotic solutions of the boundary value problem which exploit the smallness of the current magnitude compared to the <span class="hlt">wave</span> phase velocity and/or its vertical <span class="hlt">shear</span> and curvature. The adopted approximations are shown to be sufficient for most of the conceivable applications. This provides correction terms to the group velocity and <span class="hlt">wave</span> action definition accounting for the <span class="hlt">shear</span> effects, which are fitting for application to operational <span class="hlt">wave</span> models. In the limit of vanishing current <span class="hlt">shear</span>, the new formulation reduces to the commonly used Bretherton & Garrett (1968) no-<span class="hlt">shear</span> <span class="hlt">wave</span> action equation where the invariant is calculated with the current magnitude taken at the free surface. It is shown that in realistic oceanic conditions, the neglect of the vertical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T31E2561D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T31E2561D"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> velocity structure of the Anatolian Plate and surrounding regions using Ambient Noise Tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Delph, J. R.; Beck, S. L.; Zandt, G.; Biryol, C. B.; Ward, K. M.</p> <p>2013-12-01</p> <p>The Anatolian Plate consists of various lithospheric terranes amalgamated during the closure of the Tethys Ocean, and is currently extruding to the west in response to a combination of the collision of the Arabian plate in the east and the roll back of the Aegean subduction zone in the west. We used Ambient Noise Tomography (ANT) at periods <= 40s to investigate the crust and uppermost mantle structure of the Anatolian Plate. We computed a total of 13,779 unique cross-correlations using one sample-per-second vertical component broadband seismic data from 215 stations from 8 different networks over a period of 7 years to compute fundamental-mode Rayleigh <span class="hlt">wave</span> dispersion curves following the method of Benson et al. (2007). We then inverted the dispersion data to calculate phase velocity maps for 11 periods from 8 s - 40 s throughout Anatolia and the Aegean regions (Barmin et al. 2001). Using smoothed Moho values derived from Vanacore et al. (2013) in our starting models, we inverted our dispersion curves using a linear least-squares iterative inversion scheme (Herrmann & Ammon 2004) to produce a <span class="hlt">3</span>-<span class="hlt">D</span> <span class="hlt">shear-wave</span> velocity model of the crust and uppermost mantle throughout Anatolia and the Aegean. We find a good correlation between our seismic <span class="hlt">shear</span> <span class="hlt">wave</span> velocities and paleostructures (suture zones) and modern deformation (basin formation and fault deformation). The most prominent crustal velocity contrasts occur across intercontinental sutures zones, resulting from the juxtaposition of the compositionally different basements of the amalgamated terranes. At shallow depths, seismic velocity contrasts correspond closely with surficial features. The Thrace, Cankiri and Tuz Golu basins, and accretionary complexes related to the closure of the Neotethys are characterized by slow <span class="hlt">shear</span> <span class="hlt">wave</span> velocities, while the Menderes and Kirsehir Massifs, Pontides, and Istanbul Zone are characterized by fast velocities. We find that the East Anatolia Plateau has slow <span class="hlt">shear-wave</span> velocities</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/10583949','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/10583949"><span>Complex <span class="hlt">Shear</span> <span class="hlt">Wave</span> Velocity Structure Imaged Beneath Africa and Iceland.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ritsema; van Heijst HJ; Woodhouse</p> <p>1999-12-03</p> <p>A model of three-dimensional <span class="hlt">shear</span> <span class="hlt">wave</span> velocity variations in the mantle reveals a tilted low velocity anomaly extending from the core-mantle boundary (CMB) region beneath the southeastern Atlantic Ocean into the upper mantle beneath eastern Africa. This anomaly suggests that Cenozoic flood basalt volcanism in the Afar region and active rifting beneath the East African Rift is linked to an extensive thermal anomaly at the CMB more than 45 degrees away. In contrast, a low velocity anomaly beneath Iceland is confined to the upper mantle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OptCo.370...68G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OptCo.370...68G"><span>Display depth analyses with the <span class="hlt">wave</span> aberration for the auto-stereoscopic <span class="hlt">3</span><span class="hlt">D</span> display</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gao, Xin; Sang, Xinzhu; Yu, Xunbo; Chen, Duo; Chen, Zhidong; Zhang, Wanlu; Yan, Binbin; Yuan, Jinhui; Wang, Kuiru; Yu, Chongxiu; Dou, Wenhua; Xiao, Liquan</p> <p>2016-07-01</p> <p>Because the aberration severely affects the display performances of the auto-stereoscopic <span class="hlt">3</span><span class="hlt">D</span> display, the diffraction theory is used to analyze the diffraction field distribution and the display depth through aberration analysis. Based on the proposed method, the display depth of central and marginal reconstructed images is discussed. The experimental results agree with the theoretical analyses. Increasing the viewing distance or decreasing the lens aperture can improve the display depth. Different viewing distances and the LCD with two lens-arrays are used to verify the conclusion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/15014005','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/15014005"><span>Seismic <span class="hlt">Waves</span> in Finely Layered VTI Media: Poroelasticity, Thomsen Parameters, and Fluid Effects on <span class="hlt">Shear</span> <span class="hlt">Waves</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Berryman, J G</p> <p>2004-02-24</p> <p>Layered earth models are well justified by experience, and provide a simple means of studying fairly general behavior of the elastic and poroelastic characteristics of seismic <span class="hlt">waves</span> in the earth. Thomsen's anisotropy parameters for weak elastic and poroelastic anisotropy are now commonly used in exploration, and can be conveniently expressed in terms of the layer averages of Backus. Since our main interest is usually in the fluids underground, it would be helpful to have a set of general equations relating the Thomsen parameters as directly as possible to the fluid properties. This end can be achieved in a rather straightforward fashion for these layered earth models, and the present paper develops and then discusses these relations. Furthermore, it is found that, although there are five effective <span class="hlt">shear</span> moduli for any layered VTI medium, one and only one effective <span class="hlt">shear</span> modulus for the layered system contains all the dependence of pore fluids on the elastic or poroelastic constants that can be observed in vertically polarized <span class="hlt">shear</span> <span class="hlt">waves</span> in VTI media. The effects of the pore fluids on this effective <span class="hlt">shear</span> modulus can be substantial - an increase of <span class="hlt">shear</span> <span class="hlt">wave</span> speed on the order of 10% is shown to be possible when circumstances are favorable -when the medium behaves in an undrained fashion, and the <span class="hlt">shear</span> modulus fluctuations are large (resulting in strong anisotropy). These effects are expected to be seen at higher frequencies such as sonic and ultrasonic <span class="hlt">waves</span> for well-logging or laboratory experiments, or at seismic <span class="hlt">wave</span> frequencies for low permeability regions of reservoirs, prior to hydrofracing. Results presented are strictly for velocity analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA609610','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA609610"><span>Seismic <span class="hlt">Wave</span> Generation and Propagation from Complex <span class="hlt">3</span><span class="hlt">D</span> Explosion Sources</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2014-04-28</p> <p>Initial strength corresponded to fractured granite , and strength reduction was modeled using a <span class="hlt">shear</span> strain based shock damage model derived for...Piledriver granite (Stevens et al, 2003). The grid used in the calculation was 2 km x 2 km by 0.8 km deep with 10 meter spacing. The initial cavity was...All waveforms were calculated at a distance of 1000 km in a granite half space and were filtered with a causal low pass filter at 5 Hz. All waveforms</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AIPC.1706b0005R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AIPC.1706b0005R"><span>SAFE-<span class="hlt">3</span><span class="hlt">D</span> analysis of a piezoelectric transducer to excite guided <span class="hlt">waves</span> in a rail web</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ramatlo, Dineo A.; Long, Craig S.; Loveday, Philip W.; Wilke, Daniel N.</p> <p>2016-02-01</p> <p>Our existing Ultrasonic Broken Rail Detection system detects complete breaks and primarily uses a propagating mode with energy concentrated in the head of the rail. Previous experimental studies have demonstrated that a mode with energy concentrated in the head of the rail, is capable of detecting weld reflections at long distances. Exploiting a mode with energy concentrated in the web of the rail would allow us to effectively detect defects in the web of the rail and could also help to distinguish between reflections from welds and cracks. In this paper, we will demonstrate the analysis of a piezoelectric transducer attached to the rail web. The forced response at different frequencies is computed by the Semi-Analytical Finite Element (SAFE) method and compared to a full three-dimensional finite element method using ABAQUS. The SAFE method only requires the rail track cross-section to be meshed using two-dimensional elements. The ABAQUS model in turn requires a full three-dimensional discretisation of the rail track. The SAFE approach can yield poor predictions at cut-on frequencies associated with other modes in the rail. Problematic frequencies are identified and a suitable frequency range identified for transducer design. The forced response results of the two methods were found to be in good agreement with each other. We then use a previously developed SAFE-<span class="hlt">3</span><span class="hlt">D</span> method to analyse a practical transducer over the selected frequency range. The results obtained from the SAFE-<span class="hlt">3</span><span class="hlt">D</span> method are in good agreement with experimental measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5223661','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5223661"><span>Measuring <span class="hlt">shear-wave</span> speed with point <span class="hlt">shear-wave</span> elastography and MR elastography: a phantom study</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kishimoto, Riwa; Suga, Mikio; Koyama, Atsuhisa; Omatsu, Tokuhiko; Tachibana, Yasuhiko; Ebner, Daniel K; Obata, Takayuki</p> <p>2017-01-01</p> <p>Objectives To compare <span class="hlt">shear-wave</span> speed (SWS) measured by ultrasound-based point <span class="hlt">shear-wave</span> elastography (pSWE) and MR elastography (MRE) on phantoms with a known <span class="hlt">shear</span> modulus, and to assess method validity and variability. Methods 5 homogeneous phantoms of different stiffnesses were made. <span class="hlt">Shear</span> modulus was measured by a rheometer, and this value was used as the standard. 10 SWS measurements were obtained at 4 different depths with 1.0–4.5 MHz convex (4C1) and 4.0–9.0 MHz linear (9L4) transducers using pSWE. MRE was carried out once per phantom, and SWSs at 5 different depths were obtained. These SWSs were then compared with those from a rheometer using linear regression analyses. Results SWSs obtained with both pSWE as well as MRE had a strong correlation with those obtained by a rheometer (R2>0.97). The relative difference in SWS between the procedures was from −25.2% to 25.6% for all phantoms, and from −8.1% to 6.9% when the softest and hardest phantoms were excluded. Depth dependency was noted in the 9L4 transducer of pSWE and MRE. Conclusions SWSs from pSWE and MRE showed a good correlation with a rheometer-determined SWS. Although based on phantom studies, SWSs obtained with these methods are not always equivalent, the measurement can be thought of as reliable and these SWSs were reasonably close to each other for the middle range of stiffness within the measurable range. PMID:28057657</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SPIE.9022E..0RL','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SPIE.9022E..0RL"><span>Real-time <span class="hlt">3</span><span class="hlt">D</span> millimeter <span class="hlt">wave</span> imaging based FMCW using GGD focal plane array as detectors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Levanon, Assaf; Rozban, Daniel; Kopeika, Natan S.; Yitzhaky, Yitzhak; Abramovich, Amir</p> <p>2014-03-01</p> <p>Millimeter <span class="hlt">wave</span> (MMW) imaging systems are required for applications in medicine, communications, homeland security, and space technology. This is because there is no known ionization hazard for biological tissue, and atmospheric attenuation in this range of the spectrum is relatively low. The lack of inexpensive room temperature imaging systems makes it difficult to give a suitable MMW system for many of the above applications. <span class="hlt">3</span><span class="hlt">D</span> MMW imaging system based on chirp radar was studied previously using a scanning imaging system of a single detector. The system presented here proposes to employ a chirp radar method with a Glow Discharge Detector (GDD) Focal Plane Array (FPA) of plasma based detectors. Each point on the object corresponds to a point in the image and includes the distance information. This will enable <span class="hlt">3</span><span class="hlt">D</span> MMW imaging. The radar system requires that the millimeter <span class="hlt">wave</span> detector (GDD) will be able to operate as a heterodyne detector. Since the source of radiation is a frequency modulated continuous <span class="hlt">wave</span> (FMCW), the detected signal as a result of heterodyne detection gives the object's depth information according to value of difference frequency, in addition to the reflectance of the image. In this work we experimentally demonstrate the feasibility of implementing an imaging system based on radar principles and FPA of GDD devices. This imaging system is shown to be capable of imaging objects from distances of at least 10 meters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRB..119..409B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRB..119..409B"><span>High-resolution <span class="hlt">3</span>-<span class="hlt">D</span> P <span class="hlt">wave</span> attenuation structure of the New Madrid Seismic Zone using local earthquake tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bisrat, Shishay T.; DeShon, Heather R.; Pesicek, Jeremy; Thurber, Clifford</p> <p>2014-01-01</p> <p>A three-dimensional (<span class="hlt">3</span>-<span class="hlt">D</span>), high-resolution P <span class="hlt">wave</span> seismic attenuation model for the New Madrid Seismic Zone (NMSZ) is determined using P <span class="hlt">wave</span> path attenuation (t*) values of small-magnitude earthquakes (MD < 3.9). Events were recorded at 89 broadband and short-period seismometers of the Cooperative New Madrid Seismic Zone Network and 40 short-period seismometers of the Portable Array for Numerical Data Acquisition experiment. The amplitude spectra of all the earthquakes are simultaneously inverted for source, path (t*), and site parameters. The t* values are inverted for QP using local earthquake tomography methods and a known <span class="hlt">3</span>-<span class="hlt">D</span> P <span class="hlt">wave</span> velocity model for the region. The four major seismicity arms of the NMSZ exhibit reduced QP (higher attenuation) than the surrounding crust. The highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid-rich fractures along the southeast extension of the Reelfoot fault. The QP results are consistent with previous attenuation studies in the region, which showed that active fault zones and fractured crust in the NMSZ are highly attenuating.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AIPC.1511...51A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AIPC.1511...51A"><span>Guided <span class="hlt">wave</span>-based J-integral estimation for dynamic stress intensity factors using <span class="hlt">3</span><span class="hlt">D</span> scanning laser Doppler vibrometry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ayers, J.; Owens, C. T.; Liu, K. C.; Swenson, E.; Ghoshal, A.; Weiss, V.</p> <p>2013-01-01</p> <p>The application of guided <span class="hlt">waves</span> to interrogate remote areas of structural components has been researched extensively in characterizing damage. However, there exists a sparsity of work in using piezoelectric transducer-generated guided <span class="hlt">waves</span> as a method of assessing stress intensity factors (SIF). This quantitative information enables accurate estimation of the remaining life of metallic structures exhibiting cracks, such as military and commercial transport vehicles. The proposed full wavefield approach, based on <span class="hlt">3</span><span class="hlt">D</span> laser vibrometry and piezoelectric transducer-generated guided <span class="hlt">waves</span>, provides a practical means for estimation of dynamic stress intensity factors (DSIF) through local strain energy mapping via the J-integral. Strain energies and traction vectors can be conveniently estimated from wavefield data recorded using <span class="hlt">3</span><span class="hlt">D</span> laser vibrometry, through interpolation and subsequent spatial differentiation of the response field. Upon estimation of the Jintegral, it is possible to obtain the corresponding DSIF terms. For this study, the experimental test matrix consists of aluminum plates with manufactured defects representing canonical elliptical crack geometries under uniaxial tension that are excited by surface mounted piezoelectric actuators. The defects' major to minor axes ratios vary from unity to approximately 133. Finite element simulations are compared to experimental results and the relative magnitudes of the J-integrals are examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3943673','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3943673"><span>The Gaussian <span class="hlt">Shear</span> <span class="hlt">Wave</span> in a Dispersive Medium</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Parker, Kevin J.; Baddour, Natalie</p> <p>2014-01-01</p> <p>Within the field of “imaging the biomechanical properties of tissues,” a number of approaches analyze <span class="hlt">shear</span> <span class="hlt">wave</span> propagation initiated by a short radiation force push. Unfortunately, it is experimentally observed that the displacement vs. time curves in lossy tissues are rapidly damped and distorted in ways that confound any simple tracking approach. This paper addresses the propagation, decay, and distortion of pulses in lossy and dispersive media, in order to derive closed form analytic expressions for the propagating pulses. The theory identifies key terms that drive the distortion and broadening of the pulse. Furthermore, the approach taken is not dependent on any particular viscoelastic model of tissue, but instead takes a general first order approach to dispersion. Examples with a Gaussian beam pattern and realistic dispersion parameters are given along with general guidelines for identifying the features of the distorting <span class="hlt">wave</span> that are the most compact. PMID:24412170</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..DFD.E9006P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..DFD.E9006P"><span>A <span class="hlt">3</span><span class="hlt">D</span> MPI-Parallel GPU-accelerated framework for simulating ocean <span class="hlt">wave</span> energy converters</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pathak, Ashish; Raessi, Mehdi</p> <p>2015-11-01</p> <p>We present an MPI-parallel GPU-accelerated computational framework for studying the interaction between ocean <span class="hlt">waves</span> and <span class="hlt">wave</span> energy converters (WECs). The computational framework captures the viscous effects, nonlinear fluid-structure interaction (FSI), and breaking of <span class="hlt">waves</span> around the structure, which cannot be captured in many potential flow solvers commonly used for WEC simulations. The full Navier-Stokes equations are solved using the two-step projection method, which is accelerated by porting the pressure Poisson equation to GPUs. The FSI is captured using the numerically stable fictitious domain method. A novel three-phase interface reconstruction algorithm is used to resolve three phases in a VOF-PLIC context. A consistent mass and momentum transport approach enables simulations at high density ratios. The accuracy of the overall framework is demonstrated via an array of test cases. Numerical simulations of the interaction between ocean <span class="hlt">waves</span> and WECs are presented. Funding from the National Science Foundation CBET-1236462 grant is gratefully acknowledged.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960047033','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960047033"><span>Summary of work on shock <span class="hlt">wave</span> feature extraction in <span class="hlt">3</span>-<span class="hlt">D</span> datasets</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hesselink, Lambertus (Principal Investigator)</p> <p>1996-01-01</p> <p>A method for extracting and visualizing shock <span class="hlt">waves</span> from three dimensional data-sets is discussed. Issues concerning computation time, robustness to numerical perturbations, and noise introduction are considered and compared with other methods. Finally, results using this method are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3894258','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3894258"><span><span class="hlt">Shear</span> <span class="hlt">Wave</span> Speed Estimation in the Human Uterine Cervix</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Carlson, Lindsey C.; Feltovich, Helen; Palmeri, Mark L.; Dahl, Jeremy J.; del Rio, Alejandro Munoz; Hall, Timothy J.</p> <p>2014-01-01</p> <p>Objectives Our goals were to explore the spatial variability within the cervix and the sensitivity of <span class="hlt">shear</span> <span class="hlt">wave</span> speeds (SWS) to assess softness/stiffness differences in ripened (softened) versus unripened tissue. Methods We obtained SWS estimates from hysterectomy specimens (n=22), a subset of which were ripened (n = 13). Multiple measurements were made longitudinally along the cervical canal on both the anterior and posterior sides of the cervix. Statistical tests of differences in the proximal vs. distal, anterior vs. posterior, and ripened vs. unripened cervix were performed with individual two-sample t-tests and a linear mixed model. Results We discovered that SWS estimates monotonically increase from distal to proximal longitudinally along the cervix, that they also vary in the anterior compared to the posterior cervix, and that they are significantly different in ripened vs. unripened cervical tissue. Specifically, the mid position SWS estimates for the unripened group were 3.45±0.95 m/s (anterior) and 3.56±0.92 m/s (posterior), and 2.11±0.45 m/s (anterior) and 2.68±0.57 m/s (posterior) for the ripened (p<0.001). Conclusions We propose that <span class="hlt">shear</span> <span class="hlt">wave</span> speed estimation may be a valuable research and, ultimately, diagnostic tool for objective quantification of cervical stiffness/softness. PMID:23836486</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010MNRAS.404..858S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010MNRAS.404..858S"><span>Delensing gravitational <span class="hlt">wave</span> standard sirens with <span class="hlt">shear</span> and flexion maps</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shapiro, C.; Bacon, D. J.; Hendry, M.; Hoyle, B.</p> <p>2010-05-01</p> <p>Supermassive black hole binary (SMBHB) systems are standard sirens - the gravitational <span class="hlt">wave</span> analogue of standard candles - and if discovered by gravitational <span class="hlt">wave</span> detectors, they could be used as precise distance indicators. Unfortunately, gravitational lensing will randomly magnify SMBHB signals, seriously degrading any distance measurements. Using a weak lensing map of the SMBHB line of sight, we can estimate its magnification and thereby remove some uncertainty in its distance, a procedure we call `delensing'. We find that delensing is significantly improved when galaxy <span class="hlt">shears</span> are combined with flexion measurements, which reduce small-scale noise in reconstructed magnification maps. Under a Gaussian approximation, we estimate that delensing with a 2D mosaic image from an Extremely Large Telescope could reduce distance errors by about 25-30 per cent for an SMBHB at z = 2. Including an additional wide <span class="hlt">shear</span> map from a space survey telescope could reduce distance errors by nearly a factor of 2. Such improvement would make SMBHBs considerably more valuable as cosmological distance probes or as a fully independent check on existing probes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24021638','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24021638"><span>Improved <span class="hlt">Shear</span> <span class="hlt">Wave</span> Motion Detection Using Pulse-Inversion Harmonic Imaging With a Phased Array Transducer.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pengfei Song; Heng Zhao; Urban, Matthew W; Manduca, Armando; Pislaru, Sorin V; Kinnick, Randall R; Pislaru, Cristina; Greenleaf, James F; Shigao Chen</p> <p>2013-12-01</p> <p>Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound <span class="hlt">shear</span> <span class="hlt">wave</span> elastography (SWE), because the <span class="hlt">shear</span> <span class="hlt">wave</span> motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the <span class="hlt">shear</span> <span class="hlt">wave</span> motion tracking process and consequently result in noisy and biased <span class="hlt">shear</span> <span class="hlt">wave</span> motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in <span class="hlt">shear</span> <span class="hlt">wave</span> tracking, with the hypothesis that harmonic imaging can improve <span class="hlt">shear</span> <span class="hlt">wave</span> motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve <span class="hlt">shear</span> <span class="hlt">wave</span> motion detection by producing less underestimated <span class="hlt">shear</span> <span class="hlt">wave</span> motion and more consistent <span class="hlt">shear</span> <span class="hlt">wave</span> speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the <span class="hlt">shear</span> <span class="hlt">wave</span> motion and give consistent <span class="hlt">shear</span> <span class="hlt">wave</span> speed measurements of the left ventricular myocardium while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve <span class="hlt">shear</span> <span class="hlt">wave</span> motion tracking and thus potentially</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMDI31A2173G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMDI31A2173G"><span>Exploring the resolution capabilities of subduction zone guided <span class="hlt">waves</span>: 2D visco-elastic and <span class="hlt">3</span><span class="hlt">D</span> <span class="hlt">wave</span> simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Garth, T.; Rietbrock, A.</p> <p>2011-12-01</p> <p>Dispersion of body <span class="hlt">wave</span> arrivals observed in the fore-arc have been attributed to high frequency guided <span class="hlt">waves</span> being retained and delayed by a low velocity layer (LVL) in the subducted crust. Lower frequency seismic <span class="hlt">waves</span> travel at higher velocities in the surrounding mantle. These subduction zone guided <span class="hlt">waves</span> have the potential to offer unique insights into subducting oceanic crust. Two and three dimensional finite difference (FD) <span class="hlt">wave</span> propagation models are used to investigate the factors controlling guided <span class="hlt">wave</span> dispersion and to test which features of the subducted crust can be resolved by guided <span class="hlt">waves</span>. Other factors that may affect the frequency content of arrivals in the fore-arc such as elevated attenuation are also investigated. Modeling results are compared to observed guided <span class="hlt">wave</span> dispersion in the Japan, Aleutian and Central American subduction zones. Modeling has shown that trade-offs occur between the velocity contrast and the thickness of the waveguide, with both parameters potentially affecting the frequency content that is delayed. We combine amplitude spectra plots with displacement spectrograms so that the relative amplitudes and relative arrival times of different frequencies can be compared. This allows the specific effects of given parameters to be understood. The effect of elevated attenuation on the frequency content of arrivals in the fore-arc is investigated using a visco-elastic FD <span class="hlt">wave</span> propagation model (Bohlen 2002). The sensitivity of observed dispersion to variations in the Vp/Vs ratio of the waveguide material is also investigated. Understanding the relative dispersion of P and S <span class="hlt">waves</span> as well as the relative importance of attenuation in the subduction system may allow us to understand more about the hydrous conditions in subduction zones. Systematic variations in the contrast between the LVL and the surrounding material are investigated. Modeling is designed to test if guided <span class="hlt">wave</span> dispersion can resolve down dip velocity changes in the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSV...363..545H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSV...363..545H"><span>Full <span class="hlt">3</span><span class="hlt">D</span> dispersion curve solutions for guided <span class="hlt">waves</span> in generally anisotropic media</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hernando Quintanilla, F.; Lowe, M. J. S.; Craster, R. V.</p> <p>2016-02-01</p> <p>Dispersion curves of guided <span class="hlt">waves</span> provide valuable information about the physical and elastic properties of <span class="hlt">waves</span> propagating within a given waveguide structure. Algorithms to accurately compute these curves are an essential tool for engineers working in non-destructive evaluation and for scientists studying <span class="hlt">wave</span> phenomena. Dispersion curves are typically computed for low or zero attenuation and presented in two or three dimensional plots. The former do not always provide a clear and complete picture of the dispersion loci and the latter are very difficult to obtain when high values of attenuation are involved and arbitrary anisotropy is considered in single or multi-layered systems. As a consequence, drawing correct and reliable conclusions is a challenging task in the modern applications that often utilize multi-layered anisotropic viscoelastic materials. These challenges are overcome here by using a spectral collocation method (SCM) to robustly find dispersion curves in the most complicated cases of high attenuation and arbitrary anisotropy. Solutions are then plotted in three-dimensional frequency-complex wavenumber space, thus gaining much deeper insight into the nature of these problems. The cases studied range from classical examples, which validate this approach, to new ones involving materials up to the most general triclinic class for both flat and cylindrical geometry in multi-layered systems. The apparent crossing of modes within the same symmetry family in viscoelastic media is also explained and clarified by the results. Finally, the consequences of the centre of symmetry, present in every crystal class, on the solutions are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/494322','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/494322"><span>Well-posedness of linearized motion for <span class="hlt">3</span>-<span class="hlt">D</span> water <span class="hlt">waves</span> far from equilibrium</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hou, T.Y.; Zhen-huan Teng; Pingwen Zhang</p> <p>1996-12-31</p> <p>In this paper, we study the motion of a free surface separating two different layers of fluid in three dimensions. We assume the flow to be inviscid, irrotational, and incompressible. In this case, one can reduce the entire motion by variables on the surface alone. In general, without additional regularizing effects such as surface alone. In general, without additional regularizing effects such as surface tension or viscosity, the flow can be subject to Rayleigh-Taylor or Kelvin-Helmholtz instabilities which will lead to unbounded growth in high frequency <span class="hlt">wave</span> numbers. In this case, the problem is not well-posed in the Hadamard sense. The problem of water <span class="hlt">wave</span> with no fluid above is a special case. It is well-known that such motion is well-posed when the free surface is sufficiently close to equilibrium. Beale, Hous and Lowengrub derived a general condition which ensures well-posedness of the linearization about a presumed time-dependent motion in two dimensional case. The linearized equations, when formulated in a proper coordinate system are found to have a qualitative structure surprisingly like that for the simple case of linear <span class="hlt">waves</span> near equilbrium. Such an analysis is essential in analyzing stability of boundary integral methods for computing free interface problems. 19 refs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3381031','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3381031"><span>Numerical investigation of the effects of <span class="hlt">shear</span> <span class="hlt">waves</span> in transcranial photoacoustic tomography with a planar geometry</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wang, Lihong V.</p> <p>2012-01-01</p> <p>Abstract. Using a recently developed reconstruction method for photoacoustic tomography (PAT) valid for a planar measurement geometry parallel to a layered medium, we investigate the effects of <span class="hlt">shear</span> <span class="hlt">wave</span> propagation in the solid layer upon the ability to estimate Fourier components of the object. We examine this ability as a function of the thickness of the layer supporting <span class="hlt">shear</span> <span class="hlt">waves</span> as well as of the incidence angle of the field in the planewave representation. Examples are used to demonstrate the importance of accounting for <span class="hlt">shear</span> <span class="hlt">waves</span> in transcranial PAT. Error measures are introduced to quantify the error found when omitting <span class="hlt">shear</span> <span class="hlt">waves</span> from the forward model in PAT. PMID:22734745</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/245166','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/245166"><span>The relationship between ELF-VHF <span class="hlt">waves</span> and magnetic <span class="hlt">shear</span> at the dayside magnetopause</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zhu, Z.; Song, P.</p> <p>1996-04-01</p> <p>ELF-VLF <span class="hlt">waves</span> within the current layer of the dayside magnetopause are studied using ISEE-1 data. The database consists of 272 current layer crossings at the dayside magnetopause from 1977 to 1979. For each crossing, the average intensity of ELF-VLF <span class="hlt">waves</span> inside the current layer is obtained and the magnetic <span class="hlt">shear</span> angle across the current layer is calculated from the magnetometer data. It is found that the <span class="hlt">wave</span> amplitudes (both electric and magnetic fields), after normalization by the average magnetic field strength in the current layer, are proportional to the local magnetic <span class="hlt">shear</span> angle, i.e. large magnetic <span class="hlt">shear</span> corresponds to strong <span class="hlt">wave</span> emission and vice versa. From the dispersion relation of the <span class="hlt">waves</span> for different <span class="hlt">shear</span> angles, the phase velocity of the <span class="hlt">waves</span> increases with the magnetic <span class="hlt">shear</span> and peaks around 700 Hz to 1 kHz. The dispersion curve of the <span class="hlt">waves</span> is consistent with that of whistler modes. 21 refs., 3 fig.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EPJAP..6424512B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EPJAP..6424512B"><span>Localization of metal targets by time reversal of electromagnetic <span class="hlt">waves</span> . <span class="hlt">3</span><span class="hlt">D</span>-numerical and experimental study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Benhamouche, Mehdi; Bernard, Laurent; Serhir, Mohammed; Pichon, Lionel; Lesselier, Dominique</p> <p>2013-11-01</p> <p>This paper proposes a criterion for locating obstacles by time reversal (TR) of electromagnetic (EM) <span class="hlt">waves</span> based on the analysis of the density of EM energy map in time domain. Contrarily to a monochromatic study of the TR, the wide-band approach requires to determine the instant of the <span class="hlt">wave</span> focus. This enables us to locate the focal spots that are indicative of the positions. The criterion proposed is compared to the inverse of the minimum entropy criterion as used in the literature [X. Xu, E.L. Miller, C.M. Rappaport, IEEE Trans. Geosci. Remote Sens. 41, 1804 (2003)]. An application for the localization of <span class="hlt">3</span><span class="hlt">D</span> metal targets is proposed using finite integration technique (FIT) as computational tool at the modeling stage. An experimental validation is presented for canonical three-dimensional configurations with two kinds of metal objects. Contribution to the Topical Issue "Numelec 2012", Edited by Adel Razek.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011GeoJI.184.1327Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011GeoJI.184.1327Z"><span>Fast and accurate <span class="hlt">3</span>-<span class="hlt">D</span> ray tracing using bilinear traveltime interpolation and the <span class="hlt">wave</span> front group marching</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Jianzhong; Huang, Yueqin; Song, Lin-Ping; Liu, Qing-Huo</p> <p>2011-03-01</p> <p>We propose a new ray tracing technique in a <span class="hlt">3</span>-<span class="hlt">D</span> heterogeneous isotropic media based on bilinear traveltime interpolation and the <span class="hlt">wave</span> front group marching. In this technique, the media is discretized into a series of rectangular cells. There are two steps to be carried out: one is a forward step where <span class="hlt">wave</span> front expansion is evolved from sources to whole computational domain and the subsequent one is a backward step where ray paths are calculated for any source-receiver configuration as desired. In the forward step, we derive a closed-form expression to calculate traveltime at an arbitrary point in a cell using a bilinear interpolation of the known traveltimes on the cell's surface. Then the group marching method (GMM), a fast <span class="hlt">wave</span> front advancing method, is applied to expand the <span class="hlt">wave</span> front from the source to all girds. In the backward step, ray paths starting from receivers are traced by finding the intersection points of potential ray propagation vectors with the surfaces of relevant cells. In this step, the same TI scheme is used to compute the candidate intersection points on all surfaces of each relevant cell. In this process, the point with the minimum traveltime is selected as a ray point from which the similar step is continued until sources. A number of numerical experiments demonstrate that our <span class="hlt">3</span>-<span class="hlt">D</span> ray tracing technique is able to achieve very accurate computation of traveltimes and ray paths and meanwhile take much less computer time in comparison with the existing popular ones like the finite-difference-based GMM method, which is combined with the maximum gradient ray tracing, and the shortest path method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.9674C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.9674C"><span>High-resolution <span class="hlt">3</span>-<span class="hlt">D</span> S-<span class="hlt">wave</span> Tomography of upper crust structures in Yilan Plain from Ambient Seismic Noise</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Kai-Xun; Chen, Po-Fei; Liang, Wen-Tzong; Chen, Li-Wei; Gung, YuanCheng</p> <p>2015-04-01</p> <p>The Yilan Plain (YP) in NE Taiwan locates on the western YP of the Okinawa Trough and displays high geothermal gradients with abundant hot springs, likely resulting from magmatism associated with the back-arc spreading as attested by the offshore volcanic island (Kueishantao). YP features NS distinctive characteristics that the South YP exhibits thin top sedimentary layer, high on-land seismicity and significant SE movements, relative those of the northern counterpart. A dense network (~2.5 km station interval) of 89 Texan instruments was deployed in Aug. 2014, covering most of the YP and its vicinity. The ray path coverage density of each 0.015 degree cells are greater than 150 km that could provide the robustness assessment of tomographic results. We analyze ambient noise signals to invert a high-resolution <span class="hlt">3</span><span class="hlt">D</span> S-<span class="hlt">wave</span> model for shallow velocity structures in and around YP. The aim is to investigate the velocity anomalies corresponding to geothermal resources and the NS geological distinctions aforementioned. We apply the Welch's method to generate empirical Rayleigh <span class="hlt">wave</span> Green's functions between two stations records of continuous vertical components. The group velocities of thus derived functions are then obtained by the multiple-filter analysis technique measured at the frequency range between 0.25 and 1 Hz. Finally, we implement a wavelet-based multi-scale parameterization technique to construct <span class="hlt">3</span><span class="hlt">D</span> model of S-<span class="hlt">wave</span> velocity. Our first month results exhibit low velocity in the plain, corresponding existing sediments, those of whole YP show low velocity offshore YP and those of high-resolution south YP reveal stark velocity contrast across the Sanshin fault. Key words: ambient seismic noises, Welch's method, S-<span class="hlt">wave</span>, Yilan Plain</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T21E2623K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T21E2623K"><span>Three-Dimensional <span class="hlt">Shear</span> <span class="hlt">Wave</span> Velocity Structure of the Peru Flat Slab Subduction Segment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Knezevic Antonijevic, S.; Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.</p> <p>2012-12-01</p> <p>Recent studies focused on flat slab subduction segments in central Chile (L. S. Wagner, 2006) and Alaska (B. R. Hacker and G. A. Aber, 2012) suggest significant differences in seismic velocity structures, and hence, composition in the mantle wedge between flat and normal "steep" subducting slabs. Instead of finding the low velocities and high Vp/Vs ratios common in normal subduction zones, these studies find low Vp, high Vs, and very low Vp/Vs above flat slabs. This may indicate the presence of dry, cold material in the mantle wedge. In order to investigate the seismic velocities of the upper mantle above the Peruvian flat segment, we have inverted for 2D Rayleigh <span class="hlt">wave</span> phase velocity maps using data from the currently deployed 40 station PULSE seismic network and some adjacent stations from the CAUGHT seismic network. We then used the sensitivity of surface <span class="hlt">waves</span> to <span class="hlt">shear</span> <span class="hlt">wave</span> velocity structure with depth to develop a <span class="hlt">3</span><span class="hlt">D</span> <span class="hlt">shear</span> <span class="hlt">wave</span> velocity model. This model will allow us to determine the nature of the mantle lithosphere above the flat slab, and how this may have influenced the development of local topography. For example, dry conditions (high Vs velocities) above the flat slab would imply greater strength of this material, possibly making it capable of causing further inland overthrusting, while wet conditions (low Vs) would imply weaker material. This could provide some insight into the ongoing debate over whether the Fitzcarrald arch (along the northern most flank of the Altiplano) could be a topographical response to the subducted Nazca ridge hundred kilometers away from the trench (N. Espurt, 2012, P. Baby, 2005, V. A. Ramos, 2012) or not (J. Martinod, 2005, M. Wipf, 2008, T. Gerya, 2008).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3995Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3995Q"><span>A <span class="hlt">wave</span> action equation for water <span class="hlt">waves</span> propagating on vertically <span class="hlt">sheared</span> flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Quinn, Brenda; Toledo, Yaron; Shrira, Victor</p> <p>2015-04-01</p> <p>The coexistence of motions of different scales in oceans and other natural water basins presents a challenge for their dynamic modeling. For water <span class="hlt">waves</span> on currents, an asymptotic procedure exploiting the separation of scales allows the modeling of two motions of a qualitatively different nature, the fast shortwaves on the surface and the dynamics of the slow, long currents. Most <span class="hlt">wave</span> forecast models are based on the <span class="hlt">wave</span> action equation which is a conservation equation which takes into account the propagation of the <span class="hlt">wave</span> energy in geographic space, shoaling, refraction, diffraction and also source terms which account for generation, <span class="hlt">wave-wave</span> interactions and dissipation of the energy. Water <span class="hlt">waves</span> almost always propagate on currents with a vertical structure such as currents directed towards the beach accompanied by an under-current directed back toward the deep sea or wind-induced currents which change magnitude with depth due to viscosity effects. On larger scales they also change their direction due to the Coriolis force as described by the Ekman spiral. This implies that the existing <span class="hlt">wave</span> models, which assume vertically-averaged currents, is an approximation which is far from realistic. In recent years, ocean circulation models have significantly improved with the capability to model vertically-<span class="hlt">sheared</span> current profiles in contrast with the earlier vertically-averaged current profiles. Further advancements have coupled <span class="hlt">wave</span> action models to circulation models to relate the mutual effects between the two types of motion. Restricting <span class="hlt">wave</span> models to vertically-averaged current profiles is obviously problematic in these cases and the primary goal of this work is to derive and examine a general <span class="hlt">wave</span> action equation which accounts for this shortcoming. Combining two previous theoretical approaches [Voronovich, 1976; Skop, 1987], the developed <span class="hlt">wave</span> action formulation greatly improves the representation of linear <span class="hlt">wave</span>-current interaction in the case of tidal inlets</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.2822M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.2822M"><span>Imaging of <span class="hlt">3</span><span class="hlt">D</span> Ocean Turbulence Microstructure Using Low Frequency Acoustic <span class="hlt">Waves</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Minakov, Alexander; Kolyukhin, Dmitriy; Keers, Henk</p> <p>2015-04-01</p> <p>In the past decade the technique of imaging the ocean structure with low-frequency signal (Hz), produced by air-guns and typically employed during conventional multichannel seismic data acquisition, has emerged. The method is based on extracting and stacking the acoustic energy back-scattered by the ocean temperature and salinity micro- and meso-structure (1 - 100 meters). However, a good understanding of the link between the scattered wavefield utilized by the seismic oceanography and physical processes in the ocean is still lacking. We describe theory and the numerical implementation of a <span class="hlt">3</span><span class="hlt">D</span> time-dependent stochastic model of ocean turbulence. The velocity and temperature are simulated as homogeneous Gaussian isotropic random fields with the Kolmogorov-Obukhov energy spectrum in the inertial subrange. Numerical modeling technique is employed for sampling of realizations of random fields with a given spatial-temporal spectral tensor. The model used is shown to be representative for a wide range of scales. Using this model, we provide a framework to solve the forward and inverse acoustic scattering problem using marine seismic data. Our full-waveform inversion method is based on the ray-Born approximation which is specifically suitable for the modelling of small velocity perturbations in the ocean. This is illustrated by showing a good match between synthetic seismograms computed using ray-Born and synthetic seismograms produced with a more computationally expensive finite-difference method.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016cosp...41E1265M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016cosp...41E1265M"><span>Horizontal structure and propagation characteristics of mesospheric gravity <span class="hlt">waves</span> observed by Antarctic Gravity <span class="hlt">Wave</span> Imaging/Instrument Network (ANGWIN), using a <span class="hlt">3</span>-<span class="hlt">D</span> spectral analysis technique</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matsuda, Takashi S.; Nakamura, Takuji; Murphy, Damian; Tsutsumi, Masaki; Moffat-Griffin, Tracy; Zhao, Yucheng; Pautet, Pierre-Dominique; Ejiri, Mitsumu K.; Taylor, Michael</p> <p>2016-07-01</p> <p>ANGWIN (Antarctic Gravity <span class="hlt">Wave</span> Imaging/Instrument Network) is an international airglow imager/instrument network in the Antarctic, which commenced observations in 2011. It seeks to reveal characteristics of mesospheric gravity <span class="hlt">waves</span>, and to study sources, propagation, breaking of the gravity <span class="hlt">waves</span> over the Antarctic and the effects on general circulation and upper atmosphere. In this study, we compared distributions of horizontal phase velocity of the gravity <span class="hlt">waves</span> at around 90 km altitude observed in the mesospheric airglow imaging over different locations using our new statistical analysis method of <span class="hlt">3</span>-<span class="hlt">D</span> Fourier transform, developed by Matsuda et al. (2014). Results from the airglow imagers at four stations at Syowa (69S, 40E), Halley (76S, 27W), Davis (69S, 78E) and McMurdo (78S, 156E) out of the ANGWIN imagers have been compared, for the observation period between April 6 and May 21 in 2013. In addition to the horizontal distribution of propagation and phase speed, gravity <span class="hlt">wave</span> energies have been quantitatively compared, indicating a smaller GW activity in higher latitude stations. We further investigated frequency dependence of gravity <span class="hlt">wave</span> propagation direction, as well as nightly variation of the gravity <span class="hlt">wave</span> direction and correlation with the background wind variations. We found that variation of propagation direction is partly due to the effect of background wind in the middle atmosphere, but variation of <span class="hlt">wave</span> sources could play important role as well. Secondary <span class="hlt">wave</span> generation is also needed to explain the observed results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011APS..SHK.C1001K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011APS..SHK.C1001K"><span>2D- and <span class="hlt">3</span><span class="hlt">D</span>-explosive experiments for verification of spall and <span class="hlt">shear</span> strengths models for some steels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kozlov, Evgeny</p> <p>2011-06-01</p> <p>Presented are new results on the kinetics of stress relaxation on the elastic and phase precursors in hardened 30KhGSA steel (HRC 35...40), as well as results how parameters of the main plastic <span class="hlt">wave</span> and spall signals change throughout wedge samples and semispherical shells. Comparative study of specificities in the fracture of wedge samples and semispherical shells of 12Kh18N10T and 30KhGSA steels (HRC 35...40) was made using optical lever method, multi-channel laser interferometry, mild recovery and calorimetric measurement of converged shells, their multi-angleshot gamma-tomography; the high-rate and heavily deformed material was investigated using optical, scanning, and transmission electron microscopy. Mechanisms of the high-rate developed deformation including issues on localization of deformation and nocrystallographic flow of crystals are briefly discussed. I'd like to express gratitude and appreciation to my co-workers V.I. Tarzhanov, I.V. Telichko, D.G. Pankratov, S.A. Brichikov, D.S. Boyarnikov, L.P. Brezgina, V.N. Povyshev and collaborators A.V. Dobromyslov, N.I. Taluts for their contribution to experimental research.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26439616','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26439616"><span>Generation of remote adaptive torsional <span class="hlt">shear</span> <span class="hlt">waves</span> with an octagonal phased array to enhance displacements and reduce variability of <span class="hlt">shear</span> <span class="hlt">wave</span> speeds: comparison with quasi-plane <span class="hlt">shear</span> wavefronts.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ouared, Abderrahmane; Montagnon, Emmanuel; Cloutier, Guy</p> <p>2015-10-21</p> <p>A method based on adaptive torsional <span class="hlt">shear</span> <span class="hlt">waves</span> (ATSW) is proposed to overcome the strong attenuation of <span class="hlt">shear</span> <span class="hlt">waves</span> generated by a radiation force in dynamic elastography. During the inward propagation of ATSW, the magnitude of displacements is enhanced due to the convergence of <span class="hlt">shear</span> <span class="hlt">waves</span> and constructive interferences. The proposed method consists in generating ATSW fields from the combination of quasi-plane <span class="hlt">shear</span> wavefronts by considering a linear superposition of displacement maps. Adaptive torsional <span class="hlt">shear</span> <span class="hlt">waves</span> were experimentally generated in homogeneous and heterogeneous tissue mimicking phantoms, and compared to quasi-plane <span class="hlt">shear</span> <span class="hlt">wave</span> propagations. Results demonstrated that displacement magnitudes by ATSW could be up to 3 times higher than those obtained with quasi-plane <span class="hlt">shear</span> <span class="hlt">waves</span>, that the variability of <span class="hlt">shear</span> <span class="hlt">wave</span> speeds was reduced, and that the signal-to-noise ratio of displacements was improved. It was also observed that ATSW could cause mechanical inclusions to resonate in heterogeneous phantoms, which further increased the displacement contrast between the inclusion and the surrounding medium. This method opens a way for the development of new noninvasive tissue characterization strategies based on ATSW in the framework of our previously reported <span class="hlt">shear</span> <span class="hlt">wave</span> induced resonance elastography (SWIRE) method proposed for breast cancer diagnosis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014cosp...40E.246B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014cosp...40E.246B"><span>Nonlinear dynamics of the <span class="hlt">3</span><span class="hlt">D</span> FMS and Alfven <span class="hlt">wave</span> beams propagating in plasma of ionosphere and magnetosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Belashov, Vasily</p> <p></p> <p>We study the formation, structure, stability and dynamics of the multidimensional soliton-like beam structures forming on the low-frequency branch of oscillation in the ionospheric and magnetospheric plasma for cases when beta=4pinT/B(2) <<1 and beta>1. In first case with the conditions omega<omega_B=eB/Mc, kλ_D<<1 the fast magnetosonic (FMS) <span class="hlt">waves</span> are excited. Their dynamics under conditions {k_{x}}(2) >>{k_{yz}}(2,) v_{x}$<<c_{A} near the cone of angles Theta=arctan(M/m)(1/2) is described by the <span class="hlt">3</span><span class="hlt">D</span> Belashov-Karpman (BK) equation [1] for magnetic field h=B_{<span class="hlt">wave</span>}/B with due account of the high order dispersive correction defined by values of plasma parameters and the angle Theta=(B,k) [2]. In another case the dynamics of the finite-amplitude Alfvén <span class="hlt">waves</span> propagating in the ionosphere and magnetosphere near-to-parallel to the field B is described by the <span class="hlt">3</span><span class="hlt">D</span> derivative nonlinear Schrödinger (3-DNLS) equation for the magnetic field of the <span class="hlt">wave</span> h=(B_{y}+iB_{z})/2B/1-beta/ [3]. To study the stability of multidimensional solitons in both cases we use the method developed in [2] and investigated the Hamiltonian bounding with its deformation conserving momentum by solving the corresponding variation problem. To study evolution of solitons and their collision dynamics the proper equations were being integrated numerically using the codes specially developed and described in detail in [3]. As a result, we have obtained that in both cases for a single solitons on a level with <span class="hlt">wave</span> spreading and collapse the formation of multidimensional solitons can be observed. These results may be interpreted in terms of self-focusing phenomenon for the FMS and Alfvén waves’ beam as stationary beam formation, scattering and self-focusing of <span class="hlt">wave</span> beam. The soliton collisions on a level with known elastic interaction can lead to formation of complex structures including the multisoliton bound states. For all cases the problem of multidimensional soliton dynamics in the ionospheric and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP13A1268H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP13A1268H"><span><span class="hlt">3</span><span class="hlt">D</span> transient electromagnetic simulation using a modified correspondence principle for <span class="hlt">wave</span> and diffusion fields</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hu, Y.; Ji, Y.; Egbert, G. D.</p> <p>2015-12-01</p> <p>The fictitious time domain method (FTD), based on the correspondence principle for <span class="hlt">wave</span> and diffusion fields, has been developed and used over the past few years primarily for marine electromagnetic (EM) modeling. Here we present results of our efforts to apply the FTD approach to land and airborne TEM problems which can reduce the computer time several orders of magnitude and preserve high accuracy. In contrast to the marine case, where sources are in the conductive sea water, we must model the EM fields in the air; to allow for topography air layers must be explicitly included in the computational domain. Furthermore, because sources for most TEM applications generally must be modeled as finite loops, it is useful to solve directly for the impulse response appropriate to the problem geometry, instead of the point-source Green functions typically used for marine problems. Our approach can be summarized as follows: (1) The EM diffusion equation is transformed to a fictitious <span class="hlt">wave</span> equation. (2) The FTD <span class="hlt">wave</span> equation is solved with an explicit finite difference time-stepping scheme, with CPML (Convolutional PML) boundary conditions for the whole computational domain including the air and earth , with FTD domain source corresponding to the actual transmitter geometry. Resistivity of the air layers is kept as low as possible, to compromise between efficiency (longer fictitious time step) and accuracy. We have generally found a host/air resistivity contrast of 10-3 is sufficient. (3)A "Modified" Fourier Transform (MFT) allow us recover system's impulse response from the fictitious time domain to the diffusion (frequency) domain. (4) The result is multiplied by the Fourier transformation (FT) of the real source current avoiding time consuming convolutions in the time domain. (5) The inverse FT is employed to get the final full waveform and full time response of the system in the time domain. In general, this method can be used to efficiently solve most time-domain EM</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFMSM11C..10M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFMSM11C..10M"><span><span class="hlt">3</span>-<span class="hlt">D</span> Modelling of Stretched Solitary <span class="hlt">Waves</span> along Magnetic Field Lines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muschietti, L.; Roth, I.; Carlson, C. W.; Berthomier, M.</p> <p>2001-12-01</p> <p>A model is presented for a new type of fast solitary <span class="hlt">waves</span> which is observed by FAST in downward current regions of the auroral zone. The three-dimensional, coherent structures are electrostatic, have a positive potential, and move along the ambient magnetic field lines with speeds on the order of the electron drift. Their potential profile in the parallel direction, which can be directly measured, is flat-top whereby it cannot fit to the Gaussian shape used in previous work. Their potential profile in the perpendicular direction can only be inferred from a measured unipolar electric signal. We develop an extended BGK model which includes a flattened potential and an assumed cylindrical symmetry around a centric magnetic field line. The model envisions concentric shells of trapped electrons slowly drifting azimuthally while bouncing back and forth in the parallel direction. The electron dynamics is analysed in terms of three basic motions that occur on different time scales. These are defined by the cyclotron frequency Ω e, the bounce frequency ω b, and the azimuthal drift frequency ω γ , for which explicit analytical expressions are obtained. Subject to the ordering ω γ <<ωb<< Ωe, we calculate self-consistent distribution functions in terms of approximate constants of motion. Constraints on the parameters characterizing the amplitude and shape of the stretched solitary <span class="hlt">wave</span> are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S53B2816R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S53B2816R"><span><span class="hlt">Shear</span> <span class="hlt">Wave</span> Generation by Explosions in Anisotropic Crystalline Rock</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rogers-Martinez, M. A.; Sammis, C. G.; Stroujkova, A. F.</p> <p>2015-12-01</p> <p>The use of seismic <span class="hlt">waves</span> to discriminate between earthquakes and underground explosions is complicated by the observation that explosions routinely radiate strong S <span class="hlt">waves</span>. Whether these S <span class="hlt">waves</span> are primarily generated by non-linear processes at the source, or by mode conversions and scattering along the path remains an open question. It has been demonstrated that S <span class="hlt">waves</span> are generated at the source by any mechanism that breaks the spherical symmetry of the explosion. Examples of such mechanisms include tectonic <span class="hlt">shear</span> stress, spall, and anisotropy in the emplacement medium. Many crystalline rock massifs are transversely isotropic because they contain aligned fractures over a range of scales from microfractures at the grain scale (called the rift) to regional sets of joints. In this study we use a micromechanical damage mechanics to model the fracture damage patterns and seismic radiation generated by explosions in a material in which the initial distribution of fractures has a preferred direction. Our simulations are compared with a set of field experiments in a granite quarry in Barre, VT conducted by New England Research and Weston Geophysical. Barre granite has a strong rift plane of aligned microfractures. Our model captures two important results of these field studies: 1) the spatial extent of rock fracture and generation of S <span class="hlt">waves</span> depends on the burn-rate of the explosion and 2) the resultant damage is anisotropic with most damage occurring in the preferred direction of the microfractures (the rift plane in the granite). The physical reason damage is enhanced in the rift direction is that the mode I stress intensity factor is large for each fracture in the array of parallel fractures in the rift plane. Tensile opening on the rift plane plus sliding on the preexisting fractures make strong non-spherical contributions to the moment tensor in the far-field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25615301','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25615301"><span>Understanding the core-halo relation of quantum <span class="hlt">wave</span> dark matter from <span class="hlt">3</span><span class="hlt">D</span> simulations.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Schive, Hsi-Yu; Liao, Ming-Hsuan; Woo, Tak-Pong; Wong, Shing-Kwong; Chiueh, Tzihong; Broadhurst, Tom; Hwang, W-Y Pauchy</p> <p>2014-12-31</p> <p>We examine the nonlinear structure of gravitationally collapsed objects that form in our simulations of wavelike cold dark matter, described by the Schrödinger-Poisson (SP) equation with a particle mass ∼10(-22)  eV. A distinct gravitationally self-bound solitonic core is found at the center of every halo, with a profile quite different from cores modeled in the warm or self-interacting dark matter scenarios. Furthermore, we show that each solitonic core is surrounded by an extended halo composed of large fluctuating dark matter granules which modulate the halo density on a scale comparable to the diameter of the solitonic core. The scaling symmetry of the SP equation and the uncertainty principle tightly relate the core mass to the halo specific energy, which, in the context of cosmological structure formation, leads to a simple scaling between core mass (Mc) and halo mass (Mh), Mc∝a(-1/2)Mh(1/3), where a is the cosmic scale factor. We verify this scaling relation by (i) examining the internal structure of a statistical sample of virialized halos that form in our <span class="hlt">3</span><span class="hlt">D</span> cosmological simulations and by (ii) merging multiple solitons to create individual virialized objects. Sufficient simulation resolution is achieved by adaptive mesh refinement and graphic processing units acceleration. From this scaling relation, present dwarf satellite galaxies are predicted to have kiloparsec-sized cores and a minimum mass of ∼10(8)M⊙, capable of solving the small-scale controversies in the cold dark matter model. Moreover, galaxies of 2×10(12)M⊙ at z=8 should have massive solitonic cores of ∼2×10(9)M⊙ within ∼60  pc. Such cores can provide a favorable local environment for funneling the gas that leads to the prompt formation of early stellar spheroids and quasars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MS%26E...96a2060S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MS%26E...96a2060S"><span><span class="hlt">Wave</span> Phase-Sensitive Transformation of <span class="hlt">3</span><span class="hlt">d</span>-Straining of Mechanical Fields</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smirnov, I. N.; Speranskiy, A. A.</p> <p>2015-11-01</p> <p>It is the area of research of oscillatory processes in elastic mechanical systems. Technical result of innovation is creation of spectral set of multidimensional images which reflect time-correlated three-dimensional vector parameters of metrological, and\\or estimated, and\\or design parameters of oscillations in mechanical systems. Reconstructed images of different dimensionality integrated in various combinations depending on their objective function can be used as homeostatic profile or cybernetic image of oscillatory processes in mechanical systems for an objective estimation of current operational conditions in real time. The innovation can be widely used to enhance the efficiency of monitoring and research of oscillation processes in mechanical systems (objects) in construction, mechanical engineering, acoustics, etc. Concept method of vector vibrometry based on application of vector <span class="hlt">3</span><span class="hlt">D</span> phase- sensitive vibro-transducers permits unique evaluation of real stressed-strained states of power aggregates and loaded constructions and opens fundamental innovation opportunities: conduct of continuous (on-line regime) reliable monitoring of turboagregates of electrical machines, compressor installations, bases, supports, pipe-lines and other objects subjected to damaging effect of vibrations; control of operational safety of technical systems at all the stages of life cycle including design, test production, tuning, testing, operational use, repairs and resource enlargement; creation of vibro-diagnostic systems of authentic non-destructive control of anisotropic characteristics of materials resistance of power aggregates and loaded constructions under outer effects and operational flaws. The described technology is revolutionary, universal and common for all branches of engineering industry and construction building objects.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28295027','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28295027"><span>Improved <span class="hlt">shear</span> <span class="hlt">wave</span> motion detection using coded excitation for transient elastography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>He, Xiao-Nian; Diao, Xian-Fen; Lin, Hao-Ming; Zhang, Xin-Yu; Shen, Yuan-Yuan; Chen, Si-Ping; Qin, Zheng-Di; Chen, Xin</p> <p>2017-03-15</p> <p>Transient elastography (TE) is well adapted for use in studying liver elasticity. However, because the <span class="hlt">shear</span> <span class="hlt">wave</span> motion signal is extracted from the ultrasound signal, the weak ultrasound signal can significantly deteriorate the <span class="hlt">shear</span> <span class="hlt">wave</span> motion tracking process and make it challenging to detect the <span class="hlt">shear</span> <span class="hlt">wave</span> motion in a severe noise environment, such as within deep tissues and within obese patients. This paper, therefore, investigated the feasibility of implementing coded excitation in TE for <span class="hlt">shear</span> <span class="hlt">wave</span> detection, with the hypothesis that coded ultrasound signals can provide robustness to weak ultrasound signals compared with traditional short pulse. The Barker 7, Barker 13, and short pulse were used for detecting the <span class="hlt">shear</span> <span class="hlt">wave</span> in the TE application. Two phantom experiments and one in vitro liver experiment were done to explore the performances of the coded excitation in TE measurement. The results show that both coded pulses outperform the short pulse by providing superior <span class="hlt">shear</span> <span class="hlt">wave</span> signal-to-noise ratios (SNR), robust <span class="hlt">shear</span> <span class="hlt">wave</span> speed measurement, and higher penetration intensity. In conclusion, this study proved the feasibility of applying coded excitation in <span class="hlt">shear</span> <span class="hlt">wave</span> detection for TE application. The proposed method has the potential to facilitate robust <span class="hlt">shear</span> elasticity measurements of tissue.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5353590','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5353590"><span>Improved <span class="hlt">shear</span> <span class="hlt">wave</span> motion detection using coded excitation for transient elastography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>He, Xiao-Nian; Diao, Xian-Fen; Lin, Hao-Ming; Zhang, Xin-Yu; Shen, Yuan-Yuan; Chen, Si-Ping; Qin, Zheng-Di; Chen, Xin</p> <p>2017-01-01</p> <p>Transient elastography (TE) is well adapted for use in studying liver elasticity. However, because the <span class="hlt">shear</span> <span class="hlt">wave</span> motion signal is extracted from the ultrasound signal, the weak ultrasound signal can significantly deteriorate the <span class="hlt">shear</span> <span class="hlt">wave</span> motion tracking process and make it challenging to detect the <span class="hlt">shear</span> <span class="hlt">wave</span> motion in a severe noise environment, such as within deep tissues and within obese patients. This paper, therefore, investigated the feasibility of implementing coded excitation in TE for <span class="hlt">shear</span> <span class="hlt">wave</span> detection, with the hypothesis that coded ultrasound signals can provide robustness to weak ultrasound signals compared with traditional short pulse. The Barker 7, Barker 13, and short pulse were used for detecting the <span class="hlt">shear</span> <span class="hlt">wave</span> in the TE application. Two phantom experiments and one in vitro liver experiment were done to explore the performances of the coded excitation in TE measurement. The results show that both coded pulses outperform the short pulse by providing superior <span class="hlt">shear</span> <span class="hlt">wave</span> signal-to-noise ratios (SNR), robust <span class="hlt">shear</span> <span class="hlt">wave</span> speed measurement, and higher penetration intensity. In conclusion, this study proved the feasibility of applying coded excitation in <span class="hlt">shear</span> <span class="hlt">wave</span> detection for TE application. The proposed method has the potential to facilitate robust <span class="hlt">shear</span> elasticity measurements of tissue. PMID:28295027</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDA14007L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDA14007L"><span><span class="hlt">Wave</span>-interference Effects in the Presence of a <span class="hlt">Shear</span> Current</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Yan; Ellingsen, Simen; Noblesse, Francis</p> <p>2016-11-01</p> <p><span class="hlt">Wave</span>-interference effects, based on a 2-point wavemaker model of monohull ships, are analysed when a <span class="hlt">shear</span> current of uniform vorticity is present. Indeed, <span class="hlt">wave</span> interferences in the presence of a <span class="hlt">shear</span> current, similar to the cases in finite water depth, are considerably more complicated than in deep water without vorticity. The effects of a <span class="hlt">shear</span> current on far-field <span class="hlt">waves</span> that are formed by 2-point wavemaker models greatly depend on the <span class="hlt">shear</span> Froude number VS/g, where V is the speed of the ship, S is the uniform vorticity of the <span class="hlt">shear</span>, g is the gravitational acceleration, as well as the angle between the ship's motion direction and the <span class="hlt">shear</span> current. Various circumstances, under which ray angles of the highest <span class="hlt">waves</span> that are associated with constructive interferences between <span class="hlt">waves</span> are much narrower than the wake angles of the cusps or the asymptotes of <span class="hlt">wave</span> patterns formed by Kelvin's classical 1-point wavemaker, are shown. In particular, cusp <span class="hlt">shear</span> Froude numbers Frscusp where ray angles of the highest <span class="hlt">waves</span> are equal to the cusp angles are determined. As for <span class="hlt">shear</span> Froude numbers VS/g that are larger than Frscusp, the apparent angles where highest <span class="hlt">waves</span> are found are significantly smaller than the cusp/asymptote angles. Furthermore, the asymmetry due to the presence of a <span class="hlt">shear</span> current results in remarkable differences between the cases where a ship moves upstream or downstream.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006APS..APR.R1045N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006APS..APR.R1045N"><span>Propagation of global <span class="hlt">shear</span> Alfven <span class="hlt">waves</span> in gyrokinetic tokamak plasmas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nishimura, Y.; Lin, Z.; Holod, I.; Chen, L.; Decyk, V.; Klasky, S.; Ma, K.; Adams, M.; Ethier, S.; Hahm, T.; Lee, W.; Lewandowski, J.; Rewoldt, G.; Wang, W.</p> <p>2006-04-01</p> <p>Employing the electromagnetic gyrokinetic simulation models, Alfven <span class="hlt">wave</span> dynamics in global tokamak geometry is studied. Based on a small parameter expansion by the square-root of the electron-ion mass ratio, the fluid-kinetic hybrid electron model solves the adiabatic response in the lowest order and solves the kinetic response in the higher orders. We verify the propagation of <span class="hlt">shear</span> Alfven <span class="hlt">waves</span> in the absence of drives or damping mechanisms by perturbing the magnetic field lines at t=0 in a global eigenmode structure. The Alfven <span class="hlt">wave</span> experiences continuum damping. In the presence of energetic particles, excitations of toroidal Alfven eigenmode (TAE) is expected within the frequency gap. With the ηi gradient drive, at a critical β value, the kinetic ballooning mode (KBM) is excited below the ideal MHD limit. W.W.Lee et al., Phys. Plasmas 8, 4435 (2001). Z.Lin and L.Chen, Phys. Plasmas 8, 1447 (2001). J.A.Tataronis and W. Grossman, Z. Phys. 14, 203 (1973). C.Z.Cheng, L.Chen, and M.S.Chance, Ann.Phys. 161, 21 (1984). C.Z.Cheng, Nucl. Fusion 22, 773 (1982).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970006988','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970006988"><span>Skin-Friction Measurements in a <span class="hlt">3</span>-<span class="hlt">D</span>, Supersonic Shock-<span class="hlt">Wave</span>/Boundary-Layer Interaction</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wideman, J. K.; Brown, J. L.; Miles, J. B.; Ozcan, O.</p> <p>1994-01-01</p> <p>The experimental documentation of a three-dimensional shock-<span class="hlt">wave</span>/boundary-layer interaction in a nominal Mach 3 cylinder, aligned with the free-stream flow, and 20 deg. half-angle conical flare offset 1.27 cm from the cylinder centerline. Surface oil flow, laser light sheet illumination, and schlieren were used to document the flow topology. The data includes surface-pressure and skin-friction measurements. A laser interferometric skin friction data. Included in the skin-friction data are measurements within separated regions and three-dimensional measurements in highly-swept regions. The skin-friction data will be particularly valuable in turbulence modeling and computational fluid dynamics validation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRF..119..287K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRF..119..287K"><span>Pseudo <span class="hlt">3</span>-<span class="hlt">D</span> P <span class="hlt">wave</span> refraction seismic monitoring of permafrost in steep unstable bedrock</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Krautblatter, Michael; Draebing, Daniel</p> <p>2014-02-01</p> <p>permafrost in steep rock walls can cause hazardous rock creep and rock slope failure. Spatial and temporal patterns of permafrost degradation that operate at the scale of instability are complex and poorly understood. For the first time, we used P <span class="hlt">wave</span> seismic refraction tomography (SRT) to monitor the degradation of permafrost in steep rock walls. A 2.5-D survey with five 80 m long parallel transects was installed across an unstable steep NE-SW facing crestline in the Matter Valley, Switzerland. P <span class="hlt">wave</span> velocity was calibrated in the laboratory for water-saturated low-porosity paragneiss samples between 20°C and -5°C and increases significantly along and perpendicular to the cleavage by 0.55-0.66 km/s (10-13%) and 2.4-2.7 km/s (>100%), respectively, when freezing. Seismic refraction is, thus, technically feasible to detect permafrost in low-porosity rocks that constitute steep rock walls. Ray densities up to 100 and more delimit the boundary between unfrozen and frozen bedrock and facilitate accurate active layer positioning. SRT shows monthly (August and September 2006) and annual active layer dynamics (August 2006 and 2007) and reveals a contiguous permafrost body below the NE face with annual changes of active layer depth from 2 to 10 m. Large ice-filled fractures, lateral onfreezing of glacierets, and a persistent snow cornice cause previously unreported permafrost patterns close to the surface and along the crestline which correspond to active seasonal rock displacements up to several mm/a. SRT provides a geometrically highly resolved subsurface monitoring of active layer dynamics in steep permafrost rocks at the scale of instability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20570268','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20570268"><span>Advanced human carotid plaque progression correlates positively with flow <span class="hlt">shear</span> stress using follow-up scan data: an in vivo MRI multi-patient <span class="hlt">3</span><span class="hlt">D</span> FSI study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yang, Chun; Canton, Gador; Yuan, Chun; Ferguson, Marina; Hatsukami, Thomas S; Tang, Dalin</p> <p>2010-09-17</p> <p>Although it has been well-accepted that atherosclerosis initiation and early progression correlate negatively with flow wall <span class="hlt">shear</span> stresses (FSS), increasing evidence suggests mechanisms governing advanced plaque progression are not well understood. Fourteen patients were scanned 2-4 times at 18 month intervals using a histologically validated multi-contrast magnetic resonance imaging (MRI) protocol to acquire carotid plaque progression data. Thirty-two scan pairs (baseline and follow-up scans) were formed with slices matched for model construction and analysis. <span class="hlt">3</span><span class="hlt">D</span> fluid-structure interaction (FSI) models were constructed and plaque wall stress (PWS) and flow <span class="hlt">shear</span> stress (FSS) were obtained from all matching lumen data points (400-1000 per plaque; 100 points per matched slice) to quantify correlations with plaque progression measured by vessel wall thickness increase (WTI). Using FSS and PWS data from follow-up scan, 21 out of 32 scan pairs showed a significant positive correlation between WTI and FSS (positive/negative/no significance ratio=21/8/3), and 26 out of 32 scan pairs showed a significant negative correlation between WTI and PWS (positive/negative/no significance ratio=2/26/4). The mean FSS value of lipid core nodes (n=5294) from all 47 plaque models was 63.5dyn/cm(2), which was 45% higher than that from all normal vessel nodes (n=27553, p<0.00001). The results from this intensive FSI study indicate that flow <span class="hlt">shear</span> stress from follow-up scan correlates positively with advanced plaque progression which is different from what has been observed in plaque initiation and early-stage progression. It should be noted that the correlation results do not automatically lead to any causality conclusions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22567590','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22567590"><span>Feasibility of optical coherence elastography measurements of <span class="hlt">shear</span> <span class="hlt">wave</span> propagation in homogeneous tissue equivalent phantoms.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Razani, Marjan; Mariampillai, Adrian; Sun, Cuiru; Luk, Timothy W H; Yang, Victor X D; Kolios, Michael C</p> <p>2012-05-01</p> <p>In this work, we explored the potential of measuring <span class="hlt">shear</span> <span class="hlt">wave</span> propagation using optical coherence elastography (OCE) based on a swept-source optical coherence tomography (OCT) system. <span class="hlt">Shear</span> <span class="hlt">waves</span> were generated using a 20 MHz piezoelectric transducer (circular element 8.5 mm diameter) transmitting sine-<span class="hlt">wave</span> bursts of 400 μs, synchronized with the OCT swept source wavelength sweep. The acoustic radiation force (ARF) was applied to two gelatin phantoms (differing in gelatin concentration by weight, 8% vs. 14%). Differential OCT phase maps, measured with and without the ARF, demonstrate microscopic displacement generated by <span class="hlt">shear</span> <span class="hlt">wave</span> propagation in these phantoms of different stiffness. We present preliminary results of OCT derived <span class="hlt">shear</span> <span class="hlt">wave</span> propagation velocity and modulus, and compare these results to rheometer measurements. The results demonstrate the feasibility of <span class="hlt">shear</span> <span class="hlt">wave</span> OCE (SW-OCE) for high-resolution microscopic homogeneous tissue mechanical property characterization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/sir/2013/5141/pdf/SIR13-5141.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/sir/2013/5141/pdf/SIR13-5141.pdf"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> velocities of unconsolidated shallow sediments in the Gulf of Mexico</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lee, Myung W.</p> <p>2013-01-01</p> <p>Accurate <span class="hlt">shear-wave</span> velocities for shallow sediments are important for a variety of seismic applications such as inver-sion and amplitude versus offset analysis. During the U.S. Department of Energy-sponsored Gas Hydrate Joint Industry Project Leg II, <span class="hlt">shear-wave</span> velocities were measured at six wells in the Gulf of Mexico using the logging-while-drilling SonicScope acoustic tool. Because the tool measurement point was only 35 feet from the drill bit, the adverse effect of the borehole condition, which is severe for the shallow unconsolidated sediments in the Gulf of Mexico, was mini-mized and accurate <span class="hlt">shear-wave</span> velocities of unconsolidated sediments were measured. Measured <span class="hlt">shear-wave</span> velocities were compared with the <span class="hlt">shear-wave</span> velocities predicted from the compressional-<span class="hlt">wave</span> velocities using empirical formulas and the rock physics models based on the Biot-Gassmann theory, and the effectiveness of the two prediction methods was evaluated. Although the empirical equation derived from measured <span class="hlt">shear-wave</span> data is accurate for predicting <span class="hlt">shear-wave</span> velocities for depths greater than 500 feet in these wells, the three-phase Biot-Gassmann-theory -based theory appears to be optimum for predicting <span class="hlt">shear-wave</span> velocities for shallow unconsolidated sediments in the Gulf of Mexico.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhPl...23g2504R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhPl...23g2504R"><span>Drift-<span class="hlt">wave</span> transport in the velocity <span class="hlt">shear</span> layer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rosalem, K. C.; Roberto, M.; Caldas, I. L.</p> <p>2016-07-01</p> <p>Particle drift driven by electrostatic <span class="hlt">wave</span> fluctuations is numerically computed to describe the transport in a gradient velocity layer at the tokamak plasma edge. We consider an equilibrium plasma in large aspect ratio approximation with E × B flow and specified toroidal plasma velocity, electric field, and magnetic field profiles. A symplectic map, previously derived for infinite coherent time modes, is used to describe the transport dependence on the electric, magnetic, and plasma velocity <span class="hlt">shears</span>. We also show that resonant perturbations and their correspondent islands in the Poincaré maps are much affected by the toroidal velocity profiles. Moreover, shearless transport barriers, identified by extremum values of the perturbed rotation number profiles of the invariant curves, allow chaotic trajectories trapped into the plasma. We investigate the influence of the toroidal plasma velocity profile on these shearless transport barriers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9833E..0EC','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9833E..0EC"><span>Capturing atmospheric effects on <span class="hlt">3</span><span class="hlt">D</span> millimeter <span class="hlt">wave</span> radar propagation patterns</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cook, Richard D.; Fiorino, Steven T.; Keefer, Kevin J.; Stringer, Jeremy</p> <p>2016-05-01</p> <p>Traditional radar propagation modeling is done using a path transmittance with little to no input for weather and atmospheric conditions. As radar advances into the millimeter <span class="hlt">wave</span> (MMW) regime, atmospheric effects such as attenuation and refraction become more pronounced than at traditional radar wavelengths. The DoD High Energy Laser Joint Technology Offices High Energy Laser End-to-End Operational Simulation (HELEEOS) in combination with the Laser Environmental Effects Definition and Reference (LEEDR) code have shown great promise simulating atmospheric effects on laser propagation. Indeed, the LEEDR radiative transfer code has been validated in the UV through RF. Our research attempts to apply these models to characterize the far field radar pattern in three dimensions as a signal propagates from an antenna towards a point in space. Furthermore, we do so using realistic three dimensional atmospheric profiles. The results from these simulations are compared to those from traditional radar propagation software packages. In summary, a fast running method has been investigated which can be incorporated into computational models to enhance understanding and prediction of MMW propagation through various atmospheric and weather conditions.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20531725','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20531725"><span>Intensity images and statistics from numerical simulation of <span class="hlt">wave</span> propagation in <span class="hlt">3</span>-<span class="hlt">D</span> random media.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Martin, J M; Flatté, S M</p> <p>1988-06-01</p> <p>An extended random medium is modeled by a set of 2-D thin Gaussian phase-changing screens with phase power spectral densities appropriate to the natural medium being modeled. Details of the algorithm and limitations on its application to experimental conditions are discussed, concentrating on power-law spectra describing refractive-index fluctuations of the neutral atmosphere. Inner and outer scale effects on intensity scintillation spectra and intensity variance are also included. Images of single realizations of the intensity field at the observing plane are presented, showing that under weak scattering the small-scale Fresnel length structure of the medium dominates the intensity scattering pattern. As the strength of scattering increases, caustics and interference fringes around focal regions begin to form. Finally, in still stronger scatter, the clustering of bright regions begins to reflect the large-scale structure of the medium. For plane <span class="hlt">waves</span> incident on the medium, physically reasonable inner scales do not produce the large values of intensity variance observed in the focusing region during laser propagation experiments over kilometer paths in the atmosphere. Values as large as experimental observations have been produced in the simulations, but they require inner scales of the order of 10 cm. Inclusion of an outer scale depresses the low-frequency end of the intensity spectrum and reduces the maximum of the intensity variance. Increasing the steepness of the power law also slightly increases the maximum value of intensity variance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OptLT..83..177P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OptLT..83..177P"><span>[INVITED] Laser generation and detection of ultrafast <span class="hlt">shear</span> acoustic <span class="hlt">waves</span> in solids and liquids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pezeril, Thomas</p> <p>2016-09-01</p> <p>The aim of this article is to provide an overview of the up-to-date findings related to ultrafast <span class="hlt">shear</span> acoustic <span class="hlt">waves</span>. Recent progress obtained for the laser generation and detection of picosecond <span class="hlt">shear</span> acoustic <span class="hlt">waves</span> in solids and liquids is reviewed. Examples in which the transverse isotropic symmetry of the sample structure is broken in order to permit <span class="hlt">shear</span> acoustic <span class="hlt">wave</span> generation through sudden laser heating are described in detail. Alternative photo-induced mechanisms for ultrafast <span class="hlt">shear</span> acoustic generation in metals, semiconductors, insulators, magnetostrictive, piezoelectric and electrostrictive materials are reviewed as well. With reference to key experiments, an all-optical technique employed to probe longitudinal and <span class="hlt">shear</span> structural dynamics in the GHz frequency range in ultra-thin liquid films is described. This technique, based on specific ultrafast <span class="hlt">shear</span> acoustic transducers, has opened new perspectives that will be discussed for ultrafast <span class="hlt">shear</span> acoustic probing of viscoelastic liquids at the nanometer scale.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009ZaMP...60..450C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009ZaMP...60..450C"><span>On the interaction of deep water <span class="hlt">waves</span> and exponential <span class="hlt">shear</span> currents</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cheng, Jun; Cang, Jie; Liao, Shi-Jun</p> <p>2009-05-01</p> <p>A train of periodic deep-water <span class="hlt">waves</span> propagating on a steady <span class="hlt">shear</span> current with a vertical distribution of vorticity is investigated by an analytic method, namely the homotopy analysis method (HAM). The magnitude of the vorticity varies exponentially with the magnitude of the stream function, while remaining constant on a particular streamline. The so-called Dubreil-Jacotin transformation is used to transfer the original exponentially nonlinear boundary-value problem in an unknown domain into an algebraically nonlinear boundary-value problem in a known domain. Convergent series solutions are obtained not only for small amplitude water <span class="hlt">waves</span> on a weak current but also for large amplitude <span class="hlt">waves</span> on a strong current. The nonlinear <span class="hlt">wave</span>-current interaction is studied in detail. It is found that an aiding <span class="hlt">shear</span> current tends to enlarge the <span class="hlt">wave</span> phase speed, sharpen the <span class="hlt">wave</span> crest, but shorten the maximum <span class="hlt">wave</span> height, while an opposing <span class="hlt">shear</span> current has the opposite effect. Besides, the amplitude of <span class="hlt">waves</span> and fluid velocity decay over the depth more quickly on an aiding <span class="hlt">shear</span> current but more slowly on an opposing <span class="hlt">shear</span> current than that of <span class="hlt">waves</span> on still water. Furthermore, it is found that Stokes criteria of <span class="hlt">wave</span> breaking is still valid for <span class="hlt">waves</span> on a <span class="hlt">shear</span> current: a train of propagating <span class="hlt">waves</span> on a <span class="hlt">shear</span> current breaks as the fiuid velocity at crest equals the <span class="hlt">wave</span> phase speed. Especially, it is found that the highest <span class="hlt">waves</span> on an opposing <span class="hlt">shear</span> current are even higher and steeper than that of <span class="hlt">waves</span> on still water. Mathematically, this analytic method is rather general in principle and can be employed to solve many types of nonlinear partial differential equations with variable coefficients in science, finance and engineering.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SPIE.9253E..07R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SPIE.9253E..07R"><span>Detection of hidden objects using a real-time <span class="hlt">3</span>-<span class="hlt">D</span> millimeter-<span class="hlt">wave</span> imaging system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rozban, Daniel; Aharon, Avihai; Levanon, Assaf; Abramovich, Amir; Yitzhaky, Yitzhak; Kopeika, N. S.</p> <p>2014-10-01</p> <p>Millimeter (mm)and sub-mm wavelengths or terahertz (THz) band have several properties that motivate their use in imaging for security applications such as recognition of hidden objects, dangerous materials, aerosols, imaging through walls as in hostage situations, and also in bad weather conditions. There is no known ionization hazard for biological tissue, and atmospheric degradation of THz radiation is relatively low for practical imaging distances. We recently developed a new technology for the detection of THz radiation. This technology is based on very inexpensive plasma neon indicator lamps, also known as Glow Discharge Detector (GDD), that can be used as very sensitive THz radiation detectors. Using them, we designed and constructed a Focal Plane Array (FPA) and obtained recognizable2-dimensional THz images of both dielectric and metallic objects. Using THz <span class="hlt">wave</span> it is shown here that even concealed weapons made of dielectric material can be detected. An example is an image of a knife concealed inside a leather bag and also under heavy clothing. Three-dimensional imaging using radar methods can enhance those images since it can allow the isolation of the concealed objects from the body and environmental clutter such as nearby furniture or other people. The GDDs enable direct heterodyning between the electric field of the target signal and the reference signal eliminating the requirement for expensive mixers, sources, and Low Noise Amplifiers (LNAs).We expanded the ability of the FPA so that we are able to obtain recognizable 2-dimensional THz images in real time. We show here that the THz detection of objects in three dimensions, using FMCW principles is also applicable in real time. This imaging system is also shown here to be capable of imaging objects from distances allowing standoff detection of suspicious objects and humans from large distances.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28092532','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28092532"><span>Improved <span class="hlt">Shear</span> <span class="hlt">Wave</span> Group Velocity Estimation Method Based on Spatiotemporal Peak and Thresholding Motion Search.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Amador Carrascal, Carolina; Chen, Shigao; Manduca, Armando; Greenleaf, James F; Urban, Matthew W</p> <p>2017-04-01</p> <p>Quantitative ultrasound elastography is increasingly being used in the assessment of chronic liver disease. Many studies have reported ranges of liver <span class="hlt">shear</span> <span class="hlt">wave</span> velocity values for healthy individuals and patients with different stages of liver fibrosis. Nonetheless, ongoing efforts exist to stabilize quantitative ultrasound elastography measurements by assessing factors that influence tissue <span class="hlt">shear</span> <span class="hlt">wave</span> velocity values, such as food intake, body mass index, ultrasound scanners, scanning protocols, and ultrasound image quality. Time-to-peak (TTP) methods have been routinely used to measure the <span class="hlt">shear</span> <span class="hlt">wave</span> velocity. However, there is still a need for methods that can provide robust <span class="hlt">shear</span> <span class="hlt">wave</span> velocity estimation in the presence of noisy motion data. The conventional TTP algorithm is limited to searching for the maximum motion in time profiles at different spatial locations. In this paper, two modified <span class="hlt">shear</span> <span class="hlt">wave</span> speed estimation algorithms are proposed. The first method searches for the maximum motion in both space and time [spatiotemporal peak (STP)]; the second method applies an amplitude filter [spatiotemporal thresholding (STTH)] to select points with motion amplitude higher than a threshold for <span class="hlt">shear</span> <span class="hlt">wave</span> group velocity estimation. The two proposed methods (STP and STTH) showed higher precision in <span class="hlt">shear</span> <span class="hlt">wave</span> velocity estimates compared with TTP in phantom. Moreover, in a cohort of 14 healthy subjects, STP and STTH methods improved both the <span class="hlt">shear</span> <span class="hlt">wave</span> velocity measurement precision and the success rate of the measurement compared with conventional TTP.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NHESS..16.2071G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NHESS..16.2071G"><span>A coupled <span class="hlt">wave</span>-<span class="hlt">3</span>-<span class="hlt">D</span> hydrodynamics model of the Taranto Sea (Italy): a multiple-nesting approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaeta, Maria Gabriella; Samaras, Achilleas G.; Federico, Ivan; Archetti, Renata; Maicu, Francesco; Lorenzetti, Giuliano</p> <p>2016-09-01</p> <p>The present work describes an operational strategy for the development of a multiscale modeling system, based on a multiple-nesting approach and open-source numerical models. The strategy was applied and validated for the Gulf of Taranto in southern Italy, scaling large-scale oceanographic model results to high-resolution coupled <span class="hlt">wave</span>-<span class="hlt">3</span>-<span class="hlt">D</span> hydrodynamics simulations for the area of Mar Grande in the Taranto Sea. The spatial and temporal high-resolution simulations were performed using the open-source TELEMAC suite, forced by wind data from the COSMO-ME database, boundary <span class="hlt">wave</span> spectra from the RON buoy at Crotone and results from the Southern Adriatic Northern Ionian coastal Forecasting System (SANIFS) regarding sea levels and current fields. Model validation was carried out using data collected in the Mar Grande basin from a fixed monitoring station and during an oceanographic campaign in October 2014. The overall agreement between measurements and model results in terms of <span class="hlt">waves</span>, sea levels, surface currents, circulation patterns and vertical velocity profiles is deemed to be satisfactory, and the methodology followed in the process can constitute a useful tool for both research and operational applications in the same field and as support of decisions for management and design of infrastructures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDG14004F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDG14004F"><span>Computational modeling of pitching cylinder-type ocean <span class="hlt">wave</span> energy converters using <span class="hlt">3</span><span class="hlt">D</span> MPI-parallel simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Freniere, Cole; Pathak, Ashish; Raessi, Mehdi</p> <p>2016-11-01</p> <p>Ocean <span class="hlt">Wave</span> Energy Converters (WECs) are devices that convert energy from ocean <span class="hlt">waves</span> into electricity. To aid in the design of WECs, an advanced computational framework has been developed which has advantages over conventional methods. The computational framework simulates the performance of WECs in a virtual <span class="hlt">wave</span> tank by solving the full Navier-Stokes equations in <span class="hlt">3</span><span class="hlt">D</span>, capturing the fluid-structure interaction, nonlinear and viscous effects. In this work, we present simulations of the performance of pitching cylinder-type WECs and compare against experimental data. WECs are simulated at both model and full scales. The results are used to determine the role of the Keulegan-Carpenter (KC) number. The KC number is representative of viscous drag behavior on a bluff body in an oscillating flow, and is considered an important indicator of the dynamics of a WEC. Studying the effects of the KC number is important for determining the validity of the Froude scaling and the inviscid potential flow theory, which are heavily relied on in the conventional approaches to modeling WECs. Support from the National Science Foundation is gratefully acknowledged.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AIPC.1503..118A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AIPC.1503..118A"><span>Assessment of HIFU lesions by <span class="hlt">shear-wave</span> elastography: Initial in-vivo results</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anquez, Jeremie; Corréas, Jean-Michel; Criton, Aline; Lacoste, François; Yon, Sylvain</p> <p>2012-11-01</p> <p>The aim of this work was to evaluate <span class="hlt">Shear</span> <span class="hlt">Wave</span> Elastography (SWE) as a tool to visualize HIFU lesions in an acute in-vivo setting. Extracorporeal HIFU sonications of liver were performed on 14 rabbits in 19 consecutive, adjacent pulses, with in situ energies between 75 J and 228 J. A set of images of the sonicated area was acquired prior and post HIFU ablation: 2 orthogonal SWE images (transverse and sagittal) and contrast enhanced CT scan. SWE images were acquired with theAixplorer® device (SuperSonic Imagine, Aix, France). Prior to the treatment, the liver elasticity appeared homogeneous, with a elasticity comprised between 5 and 11 kPa. The lesion extents were manually segmented on post-treatment SWE images and their areas A(SWE)T (transverse) and A(SWE)S (sagittal) were computed. On <span class="hlt">3</span><span class="hlt">D</span> CT the lesions were segmented as a hypo intense (devascularized) region on <span class="hlt">3</span><span class="hlt">D</span> CT images, and considered as "ground truth". The transverse and sagittal planes passing by their centers of mass were extracted. The lesion areas were computed for each plane, respectively A(CT)T and A(CT)S. The ratios A(CT)T/A(SWE)T and A(CT)S/A(SWE)S were computed for all the 14 cases. SWE appear to underestimate the lesion extent in the sagittal orientation with respect to CT images, while a good matching is obtained in the transverse orientation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..317...42O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..317...42O"><span><span class="hlt">3</span><span class="hlt">D</span>-ambient noise Rayleigh <span class="hlt">wave</span> tomography of Snæfellsjökull volcano, Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Obermann, Anne; Lupi, Matteo; Mordret, Aurélien; Jakobsdóttir, Steinunn S.; Miller, Stephen A.</p> <p>2016-05-01</p> <p>From May to September 2013, 21 seismic stations were deployed around the Snæfellsjökull volcano, Iceland. We cross-correlate the five months of seismic noise and measure the Rayleigh <span class="hlt">wave</span> group velocity dispersion curves to gain more information about the geological structure of the Snæfellsjökull volcano. In particular, we investigate the occurrence of seismic <span class="hlt">wave</span> anomalies in the first 6 km of crust. We regionalize the group velocity dispersion curves into 2-D velocity maps between 0.9 and 4.8 s. With a neighborhood algorithm we then locally invert the velocity maps to obtain accurate <span class="hlt">shear</span>-velocity models down to 6 km depth. Our study highlights three seismic <span class="hlt">wave</span> anomalies. The deepest, located between approximately 3.3 and 5.5 km depth, is a high velocity anomaly, possibly representing a solidified magma chamber. The second anomaly is also a high velocity anomaly east of the central volcano that starts at the surface and reaches approximately 2.5 km depth. It may represent a gabbroic intrusion or a dense swarm of inclined magmatic sheets (similar to the dike swarms found in the ophiolites), typical of Icelandic volcanic systems. The third anomaly is a low velocity anomaly extending up to 1.5 km depth. This anomaly, located directly below the volcanic edifice, may be interpreted either as a shallow magmatic reservoir (typical of Icelandic central volcanoes), or alternatively as a shallow hydrothermal system developed above the cooling magmatic reservoir.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6807612','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6807612"><span>Anomalous <span class="hlt">shear</span> <span class="hlt">wave</span> delays and surface <span class="hlt">wave</span> velocities at Yellowstone Caldera, Wyoming</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Daniel, R.G.; Boore, D.M.</p> <p>1982-04-10</p> <p>To investigate the effects of a geothermal area on the propagation of intermediate-period (1--30 s) teleseismic body <span class="hlt">waves</span> and surface <span class="hlt">waves</span>, a specially designed portable seismograph system was operated in Yellowstone Caldera, Wyoming. Travel time residuals, relative to a station outside the caldera, of up to 2 s for compressional phases are in agreement with short-period residuals for P phases measured by other investigators. Travel time delays for <span class="hlt">shear</span> arrivals in the intermediate-period band range from 2 to 9 s and decrease with increasing dT/d..delta... Measured Rayleigh <span class="hlt">wave</span> phase velocities are extremely low, ranging from 3.2 km/s at 27-s period to 2.0 km/s at 7-s period; the estimated uncertainty associated with these values is 15%. We propose a model for compressional and <span class="hlt">shear</span> velocities and Poisson's ratio beneath the Yellowstone caldera which fits the teleseismic body and surface <span class="hlt">wave</span> data: it consists of a highly anomalous crust with an average <span class="hlt">shear</span> velocity of 3.0 km/s overlying an upper mantle with average velocity of 4.1 km/s. The high average value of Poisson's ratio in the crust (0.34) suggests the presence of fluids there; Poisson's ratio in the mantle between 40 and approximately 200 km is more nearly normal (0.29) than in the crust. A discrepancy between normal values of Poisson's ratio in the crust calculated from short-period data and high values calculated from teleseismic data can be resolved by postulating a viscoelastic crustal model with frequency-dependent <span class="hlt">shear</span> velocity and attenuation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15..503C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15..503C"><span><span class="hlt">Wave</span> propagation against current : a study of the effects of vertical <span class="hlt">shears</span> of the mean current on the geometrical focusing of water <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Charland, Jenna; Touboul, Julien; Rey, Vincent</p> <p>2013-04-01</p> <p><span class="hlt">Wave</span> propagation against current : a study of the effects of vertical <span class="hlt">shears</span> of the mean current on the geometrical focusing of water <span class="hlt">waves</span> J. Charland * **, J. Touboul **, V. Rey ** jenna.charland@univ-tln.fr * Direction Générale de l'Armement, CNRS Délégation Normandie ** Université de Toulon, 83957 La Garde, France Mediterranean Institute of Oceanography (MIO) Aix Marseille Université, 13288 Marseille, France CNRS/INSU, IRD, MIO, UM 110 In the nearshore area, both <span class="hlt">wave</span> propagation and currents are influenced by the bathymetry. For a better understanding of <span class="hlt">wave</span> - current interactions in the presence of a <span class="hlt">3</span><span class="hlt">D</span> bathymetry, a large scale experiment was carried out in the Ocean Basin FIRST, Toulon, France. The <span class="hlt">3</span><span class="hlt">D</span> bathymetry consisted of two symmetric underwater mounds on both sides in the mean <span class="hlt">wave</span> direction. The water depth at the top the mounds was hm=1,5m, the slopes of the mounds were of about 1:3, the water depth was h=3 m elsewhere. For opposite current conditions (U of order 0.30m/s), a huge focusing of the <span class="hlt">wave</span> up to twice its incident amplitude was observed in the central part of the basin for T=1.4s. Since deep water conditions are verified, the <span class="hlt">wave</span> amplification is ascribed to the current field. The mean velocity fields at a water depth hC=0.25m was measured by the use of an electromagnetic current meter. The results have been published in Rey et al [4]. The elliptic form of the "mild slope" equation including a uniform current on the water column (Chen et al [1]) was then used for the calculations. The calculated <span class="hlt">wave</span> amplification of factor 1.2 is significantly smaller than observed experimentally (factor 2). So, the purpose of this study is to understand the physical processes which explain this gap. As demonstrated by Kharif & Pelinovsky [2], geometrical focusing of <span class="hlt">waves</span> is able to modify significantly the local <span class="hlt">wave</span> amplitude. We consider this process here. Since vertical velocity profiles measured at some locations have shown significant</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6400586','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6400586"><span>A <span class="hlt">shear-wave</span> polarization study in the Wellington region New Zealand</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gledhill, K.R. )</p> <p>1990-08-01</p> <p>A month of digital data from two three component seismograph stations near Wellington, New Zealand, was analyzed as part of a feasibility study for a major project to investigate <span class="hlt">shear-wave</span> splitting. Although the total number of earthquakes studies was small (14), some suggestive results were obtained. Almost all events recorded within the <span class="hlt">shear</span> <span class="hlt">wave</span> window showed a phase reversal of the horizontal components after one or two <span class="hlt">shear</span> <span class="hlt">wave</span> cycles, suggesting that there are actually two <span class="hlt">shear-wave</span> arrivals. The measured polarization of the first <span class="hlt">shear</span> <span class="hlt">wave</span> arrivals was N (31 {plus minus} 11) E. This polarization alignment cannot be explained by focal mechanisms, and it is unlikely to be due to topography because of the station-to-station correlation. The present evidence suggests the most likely cause is crustal anistropy due to the geological structure at shallow depth, rather than stress aligned micro-cracks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70028272','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70028272"><span>Modeling and validation of a <span class="hlt">3</span><span class="hlt">D</span> velocity structure for the Santa Clara Valley, California, for seismic-<span class="hlt">wave</span> simulations</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hartzell, S.; Harmsen, S.; Williams, R.A.; Carver, D.; Frankel, A.; Choy, G.; Liu, P.-C.; Jachens, R.C.; Brocher, T.M.; Wentworth, C.M.</p> <p>2006-01-01</p> <p>A <span class="hlt">3</span><span class="hlt">D</span> seismic velocity and attenuation model is developed for Santa Clara Valley, California, and its surrounding uplands to predict ground motions from scenario earthquakes. The model is developed using a variety of geologic and geophysical data. Our starting point is a <span class="hlt">3</span><span class="hlt">D</span> geologic model developed primarily from geologic mapping and gravity and magnetic surveys. An initial velocity model is constructed by using seismic velocities from boreholes, reflection/refraction lines, and spatial autocorrelation microtremor surveys. This model is further refined and the seismic attenuation is estimated through waveform modeling of weak motions from small local events and strong-ground motion from the 1989 Loma Prieta earthquake. Waveforms are calculated to an upper frequency of 1 Hz using a parallelized finite-difference code that utilizes two regions with a factor of 3 difference in grid spacing to reduce memory requirements. Cenozoic basins trap and strongly amplify ground motions. This effect is particularly strong in the Evergreen Basin on the northeastern side of the Santa Clara Valley, where the steeply dipping Silver Creek fault forms the southwestern boundary of the basin. In comparison, the Cupertino Basin on the southwestern side of the valley has a more moderate response, which is attributed to a greater age and velocity of the Cenozoic fill. Surface <span class="hlt">waves</span> play a major role in the ground motion of sedimentary basins, and they are seen to strongly develop along the western margins of the Santa Clara Valley for our simulation of the Loma Prieta earthquake.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRA..119..431C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRA..119..431C"><span>Modeling ionospheric disturbance features in quasi-vertically incident ionograms using <span class="hlt">3</span>-<span class="hlt">D</span> magnetoionic ray tracing and atmospheric gravity <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cervera, M. A.; Harris, T. J.</p> <p>2014-01-01</p> <p>The Defence Science and Technology Organisation (DSTO) has initiated an experimental program, Spatial Ionospheric Correlation Experiment, utilizing state-of-the-art DSTO-designed high frequency digital receivers. This program seeks to understand ionospheric disturbances at scales < 150 km and temporal resolutions under 1 min through the simultaneous observation and recording of multiple quasi-vertical ionograms (QVI) with closely spaced ionospheric control points. A detailed description of and results from the first campaign conducted in February 2008 were presented by Harris et al. (2012). In this paper we employ a <span class="hlt">3</span>-<span class="hlt">D</span> magnetoionic Hamiltonian ray tracing engine, developed by DSTO, to (1) model the various disturbance features observed on both the O and X polarization modes in our QVI data and (2) understand how they are produced. The ionospheric disturbances which produce the observed features were modeled by perturbing the ionosphere with atmospheric gravity <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25089408','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25089408"><span>Dynamic diffraction-limited light-coupling of <span class="hlt">3</span><span class="hlt">D</span>-maneuvered <span class="hlt">wave</span>-guided optical waveguides.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Villangca, Mark; Bañas, Andrew; Palima, Darwin; Glückstad, Jesper</p> <p>2014-07-28</p> <p>We have previously proposed and demonstrated the targeted-light delivery capability of <span class="hlt">wave</span>-guided optical waveguides (WOWs). As the WOWs are maneuvered in <span class="hlt">3</span><span class="hlt">D</span> space, it is important to maintain efficient light coupling through the waveguides within their operating volume. We propose the use of dynamic diffractive techniques to create diffraction-limited spots that will track and couple to the WOWs during operation. This is done by using a spatial light modulator to encode the necessary diffractive phase patterns to generate the multiple and dynamic coupling spots. The method is initially tested for a single WOW and we have experimentally demonstrated dynamic tracking and coupling for both lateral and axial displacements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/39934','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/39934"><span>How <span class="hlt">3</span>-<span class="hlt">D</span>, 3-C seismic characterized a carbonate reservoir</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Arestad, J.F.; Mattocks, B.W.; Davis, T.L.; Benson, R.D.</p> <p>1995-04-01</p> <p>The Reservoir Characterization Project (RCP) at the Colorado School of Mines has pioneered research into <span class="hlt">3</span>-<span class="hlt">D</span>, 3-C (multicomponent) reflection seismology for nearly a decade utilizing both P-<span class="hlt">wave</span> and S-<span class="hlt">wave</span> sources. Multicomponent-seismic surveys provide significantly more information about petroleum reservoirs than compressional-<span class="hlt">wave</span> surveys. Initial <span class="hlt">3</span>-<span class="hlt">D</span>, 3-C surveys acquired by RCP were targeted at characterizing naturally fractured reservoirs. The current phase of the project is oriented towards utilizing <span class="hlt">shear</span> <span class="hlt">waves</span> to discriminate lithologic and diagenetic changes within stratigraphic reservoirs where compressional-seismic data has not be effective. The Joffre field, Nisku reservoir, is the site of RCP`s ongoing multidisciplinary research effort in Western Canada. The research team is directed by Colorado School of Mines faculty with graduate team members from geology, geophysics and petroleum engineering departments. While this study is still in progress, some key findings and directions of this research are reported here. The following topics will be discussed: Joffre field <span class="hlt">3</span>-<span class="hlt">D</span>, 3-C survey; compressional <span class="hlt">wave</span> <span class="hlt">3</span>-<span class="hlt">D</span> technique; <span class="hlt">shear-wave</span> <span class="hlt">3</span>-<span class="hlt">D</span> technique; converted-<span class="hlt">wave</span> <span class="hlt">3</span>-<span class="hlt">D</span> technique; reservoir characterization, and future directions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003PhyD..179...33L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003PhyD..179...33L"><span>Analogy between a 10D model for nonlinear <span class="hlt">wave-wave</span> interaction in a plasma and the <span class="hlt">3</span><span class="hlt">D</span> Lorenz dynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Letellier, C.; Aguirre, L. A.; Maquet, J.; Lefebvre, B.</p> <p>2003-05-01</p> <p>This paper investigates nonlinear <span class="hlt">wave-wave</span> interactions in a system that describes a modified decay instability and consists of three Langmuir and one ion-sound <span class="hlt">waves</span>. As a means to establish that the underlying dynamics exists in a <span class="hlt">3</span><span class="hlt">D</span> space and that it is of the Lorenz-type, both continuous and discrete-time multivariable global models were obtained from data. These data were obtained from a 10D dynamical system that describes the modified decay instability obtained from Zakharov’s equations which characterise Langmuir turbulence. This 10D model is equivariant under a continuous rotation symmetry and a discrete order-2 rotation symmetry. When the continuous rotation symmetry is modded out, that is, when the dynamics are represented with the continuous rotation symmetry removed under a local diffeomorphism, it is shown that a <span class="hlt">3</span><span class="hlt">D</span> system may describe the underlying dynamics. For certain parameter values, the models, obtained using global modelling techniques from three time series from the 10D dynamics with the continuous rotation symmetry modded out, generate attractors which are topologically equivalent. These models can be simulated easily and, due to their simplicity, are amenable for analysis of the original dynamics after symmetries have been modded out. Moreover, it is shown that all of these attractors are topologically equivalent to an attractor generated by the well-known Lorenz system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024602','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024602"><span>Comparing <span class="hlt">shear-wave</span> velocity profiles inverted from multichannel surface <span class="hlt">wave</span> with borehole measurements</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Xia, J.; Miller, R.D.; Park, C.B.; Hunter, J.A.; Harris, J.B.; Ivanov, J.</p> <p>2002-01-01</p> <p>Recent field tests illustrate the accuracy and consistency of calculating near-surface <span class="hlt">shear</span> (S)-<span class="hlt">wave</span> velocities using multichannel analysis of surface <span class="hlt">waves</span> (MASW). S-<span class="hlt">wave</span> velocity profiles (S-<span class="hlt">wave</span> velocity vs. depth) derived from MASW compared favorably to direct borehole measurements at sites in Kansas, British Columbia, and Wyoming. Effects of changing the total number of recording channels, sampling interval, source offset, and receiver spacing on the inverted S-<span class="hlt">wave</span> velocity were studied at a test site in Lawrence, Kansas. On the average, the difference between MASW calculated Vs and borehole measured Vs in eight wells along the Fraser River in Vancouver, Canada was less than 15%. One of the eight wells was a blind test well with the calculated overall difference between MASW and borehole measurements less than 9%. No systematic differences were observed in derived Vs values from any of the eight test sites. Surface <span class="hlt">wave</span> analysis performed on surface data from Wyoming provided S-<span class="hlt">wave</span> velocities in near-surface materials. Velocity profiles from MASW were confirmed by measurements based on suspension log analysis. ?? 2002 Elsevier Science Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.5461M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.5461M"><span>Implementation and validation of a <span class="hlt">3</span><span class="hlt">D</span> <span class="hlt">wave</span>-induced current model from the surf zone to the inner-shelf</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michaud, H.; Marsaleix, P.; Leredde, Y.; Estournel, C.; Bourrin, F.; Lyard, F.; Mayet, C.; Ardhuin, F.</p> <p>2012-04-01</p> <p> the complex bathymetry and the consideration of wind and non-stationary processes. In the inner shelf, <span class="hlt">wave</span> impacts are less visible since wind and regional circulation seem to be the predominant forcing. Besides, a discrepancy between model and observations is noted at that scale, possibly linked to an underestimation of the wind stress. Lastly, this three-dimensional method allows a good representation of vertical current profiles and permits to calculate the <span class="hlt">shear</span> stress associated with <span class="hlt">wave</span> and current. Future work will focus on the combination with a sediment transport model. Ardhuin, F., Rascle, N. & Belibassakis, K.A., Explicit <span class="hlt">wave</span>-averaged primitive equations using a generalized Lagrangian mean. Ocean Modelling 20, 35-60, 2008. Ardhuin, F. et al., Semiempirical Dissipation Source Functions for Ocean <span class="hlt">Waves</span>. Part I: Definition, Calibration, and Validation. J. Phys. Oceanogr. 40, 1917-194, 2010. Bennis, A.-C., Ardhuin, F. & Dumas, F., On the coupling of <span class="hlt">wave</span> and three-dimensional circulation models: Choice of theoretical framework, practical implementation and adiabatic tests. Ocean Modelling 40, 260-272, 2011. Booij, N., R. C. Ris, and L. H. Holthuijsen, A third generation <span class="hlt">wave</span> model for coastal regions, part I, model description and validation, Journal of Geophysical Research, 104 , 7649-7666, 1999. Haas, K. A., and J. C. Warner, Comparing a quasi-<span class="hlt">3</span><span class="hlt">d</span> to a full <span class="hlt">3</span><span class="hlt">d</span> nearshore circulation model: Shorecirc and roms, Ocean Modelling, 26 , 91-103, 2009. Haller, M. C., R. A. Dalrymple, and I. A. Svendsen, Experimental study of nearshore dynamics on a barred beach with rip channels, Journal of Geophysical Research, 107 (C6-3061), 2002. Marsaleix, P. et al., Energy conservation issues in sigma-coordinate free-surface ocean models. Ocean Modelling 20, 61-89, 2008. Marsaleix, P., Auclair, F. & Estournel, C., Low-order pressure gradient schemes in sigma coordinate models: The seamount test revisited. Ocean Modelling 30, 169-177, 2009. Tolman, H., A mosaic approach to wind</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/983087','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/983087"><span>Measurement of sound speed vs. depth in South Pole ice: pressure <span class="hlt">waves</span> and <span class="hlt">shear</span> <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>IceCube Collaboration; Klein, Spencer</p> <p>2009-06-04</p> <p>We have measured the speed of both pressure <span class="hlt">waves</span> and <span class="hlt">shear</span> <span class="hlt">waves</span> as a function of depth between 80 and 500 m depth in South Pole ice with better than 1% precision. The measurements were made using the South Pole Acoustic Test Setup (SPATS), an array of transmitters and sensors deployed in the ice at the South Pole in order to measure the acoustic properties relevant to acoustic detection of astrophysical neutrinos. The transmitters and sensors use piezoceramics operating at {approx}5-25 kHz. Between 200 m and 500 m depth, the measured profile is consistent with zero variation of the sound speed with depth, resulting in zero refraction, for both pressure and <span class="hlt">shear</span> <span class="hlt">waves</span>. We also performed a complementary study featuring an explosive signal propagating vertically from 50 to 2250 m depth, from which we determined a value for the pressure <span class="hlt">wave</span> speed consistent with that determined for shallower depths, higher frequencies, and horizontal propagation with the SPATS sensors. The sound speed profile presented here can be used to achieve good acoustic source position and emission time reconstruction in general, and neutrino direction and energy reconstruction in particular. The reconstructed quantities could also help separate neutrino signals from background.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1215517','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1215517"><span>Numerical Study of Velocity <span class="hlt">Shear</span> Stabilization of <span class="hlt">3</span><span class="hlt">D</span> and Theoretical Considerations for Centrifugally Confined Plasmas and Other Interchange-Limited Fusion Concepts</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hassam, Adil</p> <p>2015-09-21</p> <p>We studied the feasibility of resonantly driving GAMs in tokamaks. A numerical simulation was carried out and showed the essential features and limitations. It was shown further that GAMs can damp by phase-mixing, from temperature gradients, or nonlinear detuning, thus broadening the resonance. Experimental implications of this were quantified. Theoretical support was provided for the Maryland Centrifugal Experiment, funded in a separate grant by DOE. Plasma diamagnetism from supersonic rotation was established. A theoretical model was built to match the data. Additional support to the experiment in terms of numerical simulation of the interchange turbulence was provided. Spectra from residual turbulence on account of velocity <span class="hlt">shear</span> suppression were obtained and compared favorably to experiment. A new drift <span class="hlt">wave</span>, driven solely by the thermal force, was identified.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24815265','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24815265"><span>Analysis and measurement of the modulation transfer function of harmonic <span class="hlt">shear</span> <span class="hlt">wave</span> induced phase encoding imaging.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>McAleavey, Stephen A</p> <p>2014-05-01</p> <p><span class="hlt">Shear</span> <span class="hlt">wave</span> induced phase encoding (SWIPE) imaging generates ultrasound backscatter images of tissue-like elastic materials by using traveling <span class="hlt">shear</span> <span class="hlt">waves</span> to encode the lateral position of the scatters in the phase of the received echo. In contrast to conventional ultrasound B-scan imaging, SWIPE offers the potential advantages of image formation without beam focusing or steering from a single transducer element, lateral resolution independent of aperture size, and the potential to achieve relatively high lateral resolution with low frequency ultrasound. Here a Fourier series description of the phase modulated echo signal is developed, demonstrating that echo harmonics at multiples of the <span class="hlt">shear</span> <span class="hlt">wave</span> frequency reveal target k-space data at identical multiples of the <span class="hlt">shear</span> wavenumber. Modulation transfer functions of SWIPE imaging systems are calculated for maximum <span class="hlt">shear</span> <span class="hlt">wave</span> acceleration and maximum <span class="hlt">shear</span> constraints, and compared with a conventionally focused aperture. The relative signal-to-noise ratio of the SWIPE method versus a conventionally focused aperture is found through these calculations. Reconstructions of wire targets in a gelatin phantom using 1 and 3.5 MHz ultrasound and a cylindrical <span class="hlt">shear</span> <span class="hlt">wave</span> source are presented, generated from the fundamental and second harmonic of the <span class="hlt">shear</span> <span class="hlt">wave</span> modulation frequency, demonstrating weak dependence of lateral resolution with ultrasound frequency.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6302112','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6302112"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> measurements in shock-induced, high-pressure phases</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Aidun, J.B.</p> <p>1993-01-01</p> <p>Structural phase transformations under shock loading are of considerable interest for understanding the response of solids under nonhydrostatic stresses and at high strain-rates. Examining shock-induced transformations from continuum level measurements is fundamentally constrained by the inability to directly identify microscopic processes, and also by the limited number of material properties that can be directly measured. ne latter limitation can be reduced by measuring both <span class="hlt">shear</span> and compression <span class="hlt">waves</span> using Lagrangian gauges in combined, compression and <span class="hlt">shear</span> loading. The <span class="hlt">shear</span> <span class="hlt">wave</span> serves as an important, real-time probe of the shocked state and unloading response. Using results from a recent study of CaCO[sub 3], the unique information obtained from the <span class="hlt">shear</span> <span class="hlt">wave</span> speed and the detailed structure of the <span class="hlt">shear</span> <span class="hlt">wave</span> are shown to be useful for distinguishing the effects of phase transformations from yielding, as well as in characterizing the high-pressure phases and the yielding process under shock loading.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10166120','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10166120"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> measurements in shock-induced, high-pressure phases</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Aidun, J.B.</p> <p>1993-07-01</p> <p>Structural phase transformations under shock loading are of considerable interest for understanding the response of solids under nonhydrostatic stresses and at high strain-rates. Examining shock-induced transformations from continuum level measurements is fundamentally constrained by the inability to directly identify microscopic processes, and also by the limited number of material properties that can be directly measured. ne latter limitation can be reduced by measuring both <span class="hlt">shear</span> and compression <span class="hlt">waves</span> using Lagrangian gauges in combined, compression and <span class="hlt">shear</span> loading. The <span class="hlt">shear</span> <span class="hlt">wave</span> serves as an important, real-time probe of the shocked state and unloading response. Using results from a recent study of CaCO{sub 3}, the unique information obtained from the <span class="hlt">shear</span> <span class="hlt">wave</span> speed and the detailed structure of the <span class="hlt">shear</span> <span class="hlt">wave</span> are shown to be useful for distinguishing the effects of phase transformations from yielding, as well as in characterizing the high-pressure phases and the yielding process under shock loading.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997APS..SHK..G203B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997APS..SHK..G203B"><span>Effect of <span class="hlt">Shear</span> on Failure <span class="hlt">Waves</span> in Shocked Soda Lime Glass</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brar, N. S.; Mello, M.; Clifton, R. J.</p> <p>1997-07-01</p> <p>Failure <span class="hlt">waves</span> in shock-compressed soda lime glass are thought to involve a loss of <span class="hlt">shearing</span> resistance because in-material stress gauges have shown a marked increase in the transverse stress, and consequent reduction in the <span class="hlt">shear</span> stress on arrival of the failure <span class="hlt">wave</span>. To explore the relation between failure <span class="hlt">waves</span> and <span class="hlt">shearing</span> resistance, a series of pressure-<span class="hlt">shear</span> (oblique impact) are being performed in the 4-inch gas gun at Brown University. These experiments involve the impact of a glass plate by a steel flyer plate or vice versa. The former configuration is designed to relate failure <span class="hlt">wave</span> phenomena in oblique impact to those reported for normal impact, whereas the latter configuration is designed to allow direct measurements of the <span class="hlt">shearing</span> resistance of the failed material. In both configurations, the normal and transverse motion of the free surface of the target is monitored using laser interferometery. Initial results from these experiments will be reported.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRB..121.3686B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRB..121.3686B"><span>Lithospheric <span class="hlt">shear</span> velocity structure of South Island, New Zealand, from amphibious Rayleigh <span class="hlt">wave</span> tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ball, Justin S.; Sheehan, Anne F.; Stachnik, Joshua C.; Lin, Fan-Chi; Yeck, William L.; Collins, John A.</p> <p>2016-05-01</p> <p>We present a crust and mantle <span class="hlt">3</span>-<span class="hlt">D</span> <span class="hlt">shear</span> velocity model extending well offshore of New Zealand's South Island, imaging the lithosphere beneath the South Island as well as the Campbell and Challenger Plateaus. Our model is constructed via linearized inversion of both teleseismic (18-70 s period) and ambient noise-based (8-25 s period) Rayleigh <span class="hlt">wave</span> dispersion measurements. We augment an array of 4 land-based and 29 ocean bottom instruments deployed off the South Island's east and west coasts in 2009-2010 by the Marine Observations of Anisotropy Near Aotearoa experiment with 28 land-based seismometers from New Zealand's permanent GeoNet array. Major features of our <span class="hlt">shear</span> <span class="hlt">wave</span> velocity (Vs) model include a low-velocity (Vs < 4.4 km/s) body extending from near surface to greater than 75 km depth beneath the Banks and Otago Peninsulas and high-velocity (Vs~4.7 km/s) mantle anomalies underlying the Southern Alps and off the northwest coast of the South Island. Using the 4.5 km/s contour as a proxy for the lithosphere-asthenosphere boundary, our model suggests that the lithospheric thickness of Challenger Plateau and central South Island is substantially greater than that of the inner Campbell Plateau. The high-velocity anomaly we resolve at subcrustal depths (>50 km) beneath the central South Island exhibits strong spatial correlation with upper mantle earthquake hypocenters beneath the Alpine Fault. The ~400 km long low-velocity zone we image beneath eastern South Island and the inner Bounty Trough underlies Cenozoic volcanics and the locations of mantle-derived helium measurements, consistent with asthenospheric upwelling in the region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PEPI..231....1L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PEPI..231....1L"><span><span class="hlt">3</span><span class="hlt">D</span> velocity distribution of P- and S-<span class="hlt">waves</span> in a biotite gneiss, measured in oil as the pressure medium: Comparison with velocity measurements in a multi-anvil pressure apparatus and with texture-based calculated data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lokajíček, T.; Kern, H.; Svitek, T.; Ivankina, T.</p> <p>2014-06-01</p> <p>Ultrasonic measurements of the <span class="hlt">3</span><span class="hlt">D</span> velocity distribution of P- and S-<span class="hlt">waves</span> were performed on a spherical sample of a biotite gneiss from the Outokumpu scientific drill hole. Measurements were done at room temperature and pressures up to 400 and 70 MPa, respectively, in a pressure vessel with oil as a pressure medium. A modified transducer/sample assembly and the installation of a new mechanical system allowed simultaneous measurements of P- and S-<span class="hlt">wave</span> velocities in 132 independent directions of the sphere on a net in steps of 15°. Proper signals for P- and S-<span class="hlt">waves</span> could be recorded by coating the sample surface with a high-viscosity <span class="hlt">shear</span> <span class="hlt">wave</span> gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements. The <span class="hlt">3</span><span class="hlt">D</span> seismic measurements revealed a strong foliation-related directional dependence (anisotropy) of P- and S-<span class="hlt">wave</span> velocities, which is confirmed by measurements in a multi-anvil apparatus on a cube-shaped specimen of the same rock. Both experimental approaches show a marked pressure sensitivity of P- and S-<span class="hlt">wave</span> velocities and velocity anisotropies. With increasing pressure, P- and S-<span class="hlt">wave</span> velocities increase non-linearly due to progressive closure of micro-cracks. The reverse is true for velocity anisotropy. <span class="hlt">3</span><span class="hlt">D</span> velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation (CPO) of major minerals show that the intrinsic bulk anisotropy is basically caused by the CPO of biotite constituting about 23 vol.% of the rock. Including the shape of biotite grains and oriented low-aspect ratio microcracks into the modelling increases bulk anisotropy. An important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences, particularly in <span class="hlt">shear</span> <span class="hlt">wave</span> velocities. It is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer-sample assembly</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024212','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024212"><span>Surface and downhole <span class="hlt">shear</span> <span class="hlt">wave</span> seismic methods for thick soil site investigations</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hunter, J.A.; Benjumea, B.; Harris, J.B.; Miller, R.D.; Pullan, S.E.; Burns, R.A.; Good, R.L.</p> <p>2002-01-01</p> <p><span class="hlt">Shear</span> <span class="hlt">wave</span> velocity-depth information is required for predicting the ground motion response to earthquakes in areas where significant soil cover exists over firm bedrock. Rather than estimating this critical parameter, it can be reliably measured using a suite of surface (non-invasive) and downhole (invasive) seismic methods. <span class="hlt">Shear</span> <span class="hlt">wave</span> velocities from surface measurements can be obtained using SH refraction techniques. Array lengths as large as 1000 m and depth of penetration to 250 m have been achieved in some areas. High resolution <span class="hlt">shear</span> <span class="hlt">wave</span> reflection techniques utilizing the common midpoint method can delineate the overburden-bedrock surface as well as reflecting boundaries within the overburden. Reflection data can also be used to obtain direct estimates of fundamental site periods from <span class="hlt">shear</span> <span class="hlt">wave</span> reflections without the requirement of measuring average <span class="hlt">shear</span> <span class="hlt">wave</span> velocity and total thickness of unconsolidated overburden above the bedrock surface. Accurate measurements of vertical <span class="hlt">shear</span> <span class="hlt">wave</span> velocities can be obtained using a seismic cone penetrometer in soft sediments, or with a well-locked geophone array in a borehole. Examples from thick soil sites in Canada demonstrate the type of <span class="hlt">shear</span> <span class="hlt">wave</span> velocity information that can be obtained with these geophysical techniques, and show how these data can be used to provide a first look at predicted ground motion response for thick soil sites. ?? 2002 Published by Elsevier Science Ltd.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JBO....18l1511C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JBO....18l1511C"><span>Viscosity measurement based on <span class="hlt">shear-wave</span> laser speckle contrast analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cheng, Yi; Li, Sinan; Eckersley, Robert J.; Elson, Daniel S.; Tang, Meng-Xing</p> <p>2013-12-01</p> <p>Tissue viscosity is correlated with tissue pathological changes and provides information for tissue characterization. In this study, we report an optical method to track continuous <span class="hlt">shear-wave</span> propagation at centimeter depths in an optically turbid medium. <span class="hlt">Shear-wave</span> attenuation coefficients were measured at multiple frequencies using <span class="hlt">shear-wave</span> laser speckle contrast analysis (SW-LASCA) to quantitatively estimate tissue viscosity using the Voigt model. <span class="hlt">Shear</span> <span class="hlt">waves</span> were generated within tissue-mimicking phantoms by an amplitude-modulated ultrasound (modulation frequency: 100 to 600 Hz) and tracked by time-resolved laser speckle contrast difference received on a charged-coupled device camera. Averaged contrast difference over a selected time window was related to <span class="hlt">shear-wave</span> amplitude and used to calculate the <span class="hlt">shear-wave</span> attenuation coefficient. Phantoms of varying viscosities (0.1 and 0.3 Pa s) were studied. Attenuation coefficients for different <span class="hlt">shear-wave</span> frequencies (100 to 600 Hz) were calculated. Derived viscosity values had a maximum standard deviation of 9%, and these values were consistent with the independent measurements reported in a previous study using nonoptical methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PMB....61.8105C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PMB....61.8105C"><span>Electromechanical <span class="hlt">wave</span> imaging (EWI) validation in all four cardiac chambers with <span class="hlt">3</span><span class="hlt">D</span> electroanatomic mapping in canines in vivo</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Costet, Alexandre; Wan, Elaine; Bunting, Ethan; Grondin, Julien; Garan, Hasan; Konofagou, Elisa</p> <p>2016-11-01</p> <p>Characterization and mapping of arrhythmias is currently performed through invasive insertion and manipulation of cardiac catheters. Electromechanical <span class="hlt">wave</span> imaging (EWI) is a non-invasive ultrasound-based imaging technique, which tracks the electromechanical activation that immediately follows electrical activation. Electrical and electromechanical activations were previously found to be linearly correlated in the left ventricle, but the relationship has not yet been investigated in the three other chambers of the heart. The objective of this study was to investigate the relationship between electrical and electromechanical activations and validate EWI in all four chambers of the heart with conventional <span class="hlt">3</span><span class="hlt">D</span> electroanatomical mapping. Six (n  =  6) normal adult canines were used in this study. The electrical activation sequence was mapped in all four chambers of the heart, both endocardially and epicardially using the St Jude’s EnSite <span class="hlt">3</span><span class="hlt">D</span> mapping system (St. Jude Medical, Secaucus, NJ). EWI acquisitions were performed in all four chambers during normal sinus rhythm, and during pacing in the left ventricle. Isochrones of the electromechanical activation were generated from standard echocardiographic imaging views. Electrical and electromechanical activation maps were co-registered and compared, and electrical and electromechanical activation times were plotted against each other and linear regression was performed for each pair of activation maps. Electromechanical and electrical activations were found to be directly correlated with slopes of the correlation ranging from 0.77 to 1.83, electromechanical delays between 9 and 58 ms and R 2 values from 0.71 to 0.92. The linear correlation between electrical and electromechanical activations and the agreement between the activation maps indicate that the electromechanical activation follows the pattern of propagation of the electrical activation. This suggests that EWI may be used as a novel non-invasive method</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5388157','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5388157"><span>Self-Propagating Combustion Triggered Synthesis of <span class="hlt">3</span><span class="hlt">D</span> Lamellar Graphene/BaFe12O19 Composite and Its Electromagnetic <span class="hlt">Wave</span> Absorption Properties</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zhao, Tingkai; Ji, Xianglin; Jin, Wenbo; Yang, Wenbo; Peng, Xiarong; Duan, Shichang; Dang, Alei; Li, Hao; Li, Tiehu</p> <p>2017-01-01</p> <p>The synthesis of <span class="hlt">3</span><span class="hlt">D</span> lamellar graphene/BaFe12O19 composites was performed by oxidizing graphite and sequentially self-propagating combustion triggered process. The <span class="hlt">3</span><span class="hlt">D</span> lamellar graphene structures were formed due to the synergistic effect of the tremendous heat induced gasification as well as huge volume expansion. The <span class="hlt">3</span><span class="hlt">D</span> lamellar graphene/BaFe12O19 composites bearing 30 wt % graphene present the reflection loss peak at −27.23 dB as well as the frequency bandwidth at 2.28 GHz (< −10 dB). The <span class="hlt">3</span><span class="hlt">D</span> lamellar graphene structures could consume the incident <span class="hlt">waves</span> through multiple reflection and scattering within the layered structures, prolonging the propagation path of electromagnetic <span class="hlt">waves</span> in the absorbers. PMID:28336889</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4245153','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4245153"><span>Statistical Analysis of <span class="hlt">Shear</span> <span class="hlt">Wave</span> Speed in the Uterine Cervix</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Carlson, Lindsey C.; Feltovich, Helen; Palmeri, Mark L.; del Rio, Alejandro Muñoz; Hall, Timothy J.</p> <p>2014-01-01</p> <p>Although cervical softening is critical in pregnancy, there currently is no objective method for assessing the softness of the cervix. <span class="hlt">Shear</span> <span class="hlt">wave</span> speed (SWS) estimation is a noninvasive tool used to measure tissue mechanical properties such as stiffness. The goal of this study was to determine the spatial variability and assess the ability of SWS to classify ripened vs. unripened tissue samples. Ex vivo human hysterectomy samples (n = 22) were collected, a subset (n = 13) were ripened. SWS estimates were made at 4–5 locations along the length of the canal on both anterior and posterior halves. A linear mixed model was used for a robust multivariate analysis. Receiver operating characteristic (ROC) analysis and the area under the ROC curve (AUC) were calculated to describe the utility of SWS to classify ripened vs. unripened tissue samples. Results showed that all variables used in the linear mixed model were significant (p<0.05). Estimates at the mid location for the unripened group were 3.45 ± 0.95 m/s (anterior) and 3.56 ± 0.92 m/s (posterior), and 2.11 ± 0.45 m/s (anterior) and 2.68 ± 0.57 m/s (posterior) for the ripened (p < 0.001). The AUC’s were 0.91 and 0.84 for anterior and posterior respectively suggesting SWS estimates may be useful for quantifying cervical softening. PMID:25392863</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/55866','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/55866"><span><span class="hlt">Shear</span> Alfven <span class="hlt">waves</span> with Landau and collisional effects</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hedrick, C.L.; Leboeuf, J.; Spong, D.A.</p> <p>1995-06-01</p> <p><span class="hlt">Shear</span> Alfven <span class="hlt">waves</span> can be driven unstable by hot particles such as alpha particles in an ignited fusion device or hot ions in existing devices. Motivated by rather collisional Wendelstein 7 Advanced Stellarator (W7-AS) [Phys. Rev. Lett. {bold 72}, 1220 (1994)] beam-driven global Alfven instability experiments, the effect of electron and ion collisions on these modes has been examined. Collisions broaden and suppress the peak associated with Landau effects. This broadening makes ion damping more important, while the electron damping is suppressed. Additional resistive effects provide increased damping for the main part of the spectrum, which can have a rather high phase velocity. Of more general interest is the fact that collisional and collisionless resistivity has a numerically stabilizing effect that is known to be important for nonlinear resistive magnetohydrodynamics (MHD). This can preclude the need for introducing and testing the sensitivity to similar ad hoc effects. Numerical and analytic results for both a particle-conserving Krook collision operator and a Lorentz (pitch angle) collision operator are compared and contrasted.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI22A..06N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI22A..06N"><span><span class="hlt">Shear</span> <span class="hlt">Wave</span> Splitting Across Eastern, Western and Southern Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nyblade, A.; Ramirez, C.; Bagley, B. C.; Mulibo, G. D.; Tugume, F.; Wysession, M. E.; Wiens, D. A.</p> <p>2014-12-01</p> <p>The expansion of the AfricaArray network across eastern, western and southern Africa, in conjunction with seismic data from many PASSCAL deployments over the past 20 years, is helping to fill in major gaps in the global coverage of <span class="hlt">shear</span> <span class="hlt">wave</span> splitting measurements. New results from stations in Ghana, Nigeria, Mozambique, Botswana, Angola, Namibia and South Africa are presented in this study that when combined with previously published measurements help to map the pattern of seismic anisotropy over much of the African continent. A general pattern of fast polarization directions, characterized by NE orientations, is found, and superimposed on this subcontinental-scale pattern is local and regional variability, most notably around the Archean Tanzania craton in eastern Africa. The subcontinental-scale pattern, as well as local and regional variations in this pattern, are interpreted in terms of large-scale mantle flow from the African Superplume, fossil anisotropy in the lithosphere, and shape anisotropy in magmatic regions of the East African rift system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22525164','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22525164"><span>Gravitational, <span class="hlt">shear</span> and matter <span class="hlt">waves</span> in Kantowski-Sachs cosmologies</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Keresztes, Zoltán; Gergely, László Á.; Forsberg, Mats; Bradley, Michael; Dunsby, Peter K.S. E-mail: forsberg.mats.a.b@gmail.com E-mail: peter.dunsby@uct.ac.za</p> <p>2015-11-01</p> <p>A general treatment of vorticity-free, perfect fluid perturbations of Kantowski-Sachs models with a positive cosmological constant are considered within the framework of the 1+1+2 covariant decomposition of spacetime. The dynamics is encompassed in six evolution equations for six harmonic coefficients, describing gravito-magnetic, kinematic and matter perturbations, while a set of algebraic expressions determine the rest of the variables. The six equations further decouple into a set of four equations sourced by the perfect fluid, representing forced oscillations and two uncoupled damped oscillator equations. The two gravitational degrees of freedom are represented by pairs of gravito-magnetic perturbations. In contrast with the Friedmann case one of them is coupled to the matter density perturbations, becoming decoupled only in the geometrical optics limit. In this approximation, the even and odd tensorial perturbations of the Weyl tensor evolve as gravitational <span class="hlt">waves</span> on the anisotropic Kantowski-Sachs background, while the modes describing the <span class="hlt">shear</span> and the matter density gradient are out of phase dephased by π /2 and share the same speed of sound.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JCAP...11..042K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JCAP...11..042K"><span>Gravitational, <span class="hlt">shear</span> and matter <span class="hlt">waves</span> in Kantowski-Sachs cosmologies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keresztes, Zoltán; Forsberg, Mats; Bradley, Michael; Dunsby, Peter K. S.; Gergely, László Á.</p> <p>2015-11-01</p> <p>A general treatment of vorticity-free, perfect fluid perturbations of Kantowski-Sachs models with a positive cosmological constant are considered within the framework of the 1+1+2 covariant decomposition of spacetime. The dynamics is encompassed in six evolution equations for six harmonic coefficients, describing gravito-magnetic, kinematic and matter perturbations, while a set of algebraic expressions determine the rest of the variables. The six equations further decouple into a set of four equations sourced by the perfect fluid, representing forced oscillations and two uncoupled damped oscillator equations. The two gravitational degrees of freedom are represented by pairs of gravito-magnetic perturbations. In contrast with the Friedmann case one of them is coupled to the matter density perturbations, becoming decoupled only in the geometrical optics limit. In this approximation, the even and odd tensorial perturbations of the Weyl tensor evolve as gravitational <span class="hlt">waves</span> on the anisotropic Kantowski-Sachs background, while the modes describing the <span class="hlt">shear</span> and the matter density gradient are out of phase dephased by π /2 and share the same speed of sound.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25714307','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25714307"><span>A comparative study of strain and <span class="hlt">shear-wave</span> elastography in an elasticity phantom.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Carlsen, Jonathan F; Pedersen, Malene R; Ewertsen, Caroline; Săftoiu, Adrian; Lönn, Lars; Rafaelsen, Søren R; Nielsen, Michael B</p> <p>2015-03-01</p> <p>OBJECTIVE. The purpose of this study was to assess the diagnostic accuracy of strain and <span class="hlt">shear-wave</span> elastography for determining targets of varying stiffness in a phantom. The effect of target diameter on elastographic assessments and the effect of depth on <span class="hlt">shear-wave</span> velocity were also investigated. MATERIALS AND METHODS. We examined 20 targets of varying diameters (2.5-16.7 mm) and stiffnesses (8, 14, 45, and 80 kPa) with a 4-9-MHz linear-array transducer. Targets were evaluated 10 times with three different methods-<span class="hlt">shear-wave</span> elastography, strain ratio, and strain histogram analysis-yielding 600 evaluations. AUCs were calculated for data divided between different stiffnesses. A 1.5-6-MHz curved-array transducer was used to assess the effect of depth (3.5 vs 6 cm) on <span class="hlt">shear-wave</span> elastography in 80 scans. Mixed model analysis was performed to assess the effect of target diameter and depth. RESULTS. Strain ratio and strain histogram AUCs were higher than the <span class="hlt">shear-wave</span> velocity AUC (p < 0.001) in data divided as 80 versus 45, 14, and 8 kPa. In data divided as 80 and 45 versus 14 and 8 kPa, the methods were equal (p = 0.959 and p = 1.000, respectively). Strain ratios were superior (p = 0.030), whereas strain histograms were not significantly better (p = 0.083) than <span class="hlt">shear-wave</span> elastography in data divided as 80, 45, and 14 versus 8 kPa. Target diameter had an effect on all three methods (p = 0.001). Depth had an effect on <span class="hlt">shear-wave</span> velocity (p = 0.001). CONCLUSION. The ability to discern different target stiffnesses varies between <span class="hlt">shear-wave</span> and strain elastography. Target diameter affected all methods. <span class="hlt">Shear-wave</span> elastography is affected by target depth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6135937','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6135937"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> reflectivity and physical properties of the southern Appalachian Thorn Hill Paleozoic sequence</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Johnston, J.E.; Christensen, N.I. . Dept. of Earth and Atmospheric Sciences)</p> <p>1992-01-01</p> <p>The physical properties of a sequence of Paleozoic sedimentary rocks have been examined in detail, with an emphasis on laboratory measurements of density, <span class="hlt">shear</span> <span class="hlt">wave</span> velocity, <span class="hlt">shear</span> <span class="hlt">wave</span> splitting, and Vp/Vs ratios. Seismic properties of 147 cores from 49 rock samples collected from the thorn hill sedimentary sequence of eastern Tennessee are examined in terms of implications for future seismic studies in the southern Appalachians. The <span class="hlt">shear</span> <span class="hlt">wave</span> velocities of these rocks are strongly influenced by the relatively high <span class="hlt">shear</span> <span class="hlt">wave</span> velocity of quartz. <span class="hlt">Shear</span> <span class="hlt">wave</span> velocity anisotropy is present in most of the lithologic groups: it is highest in the shales while being almost insignificant in the dolostones. The related phenomenon of <span class="hlt">shear</span> <span class="hlt">wave</span> splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation. Compressional to <span class="hlt">shear</span> velocity (Vp/Vs) ratios of approximately 1.82 (dolostones) and 1.95 (limestones) effectively characterize the carbonates while other lithologies display wider ranges of Vp/Vs, primarily due to the influence of accessory minerals such as quartz. Densities of the sample suite range from 2.34 g/cm[sup 3] (shale) to 2.86 g/cm[sup 3] (dolostone). Normal incidence <span class="hlt">shear</span> and compressional <span class="hlt">wave</span> synthetic seismograms of the entire Thorn Hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3,327 meter thick sequence. differences are seen at some interfaces in the Mississippian-Devonian interval, which are more reflective to <span class="hlt">shear</span> <span class="hlt">waves</span>, and in the Ordovician Martinsburg Formation, which appears more reflective to compressional <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T43B2315P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T43B2315P"><span><span class="hlt">3</span><span class="hlt">D</span> Simulation of Elastic <span class="hlt">Wave</span> Propagation in Heterogeneous Anisotropic Media in Laplace Domain for Electromagnetic-Seismic Inverse Modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petrov, P.; Newman, G. A.</p> <p>2011-12-01</p> <p>Recent developments in high resolution imaging technology of subsurface objects involves a combination of different geophysical measurements (gravity, EM and seismic). A joint image of the subsurface geophysical attributes (velocity, electrical conductivity and density) requires the consistent treatment of the different geophysical data due to their differing physical nature. For example, in conducting media, which is typical of the Earth's interior, EM energy propagation is defined by a diffusive mechanism and may be characterized by two specific length scales: wavelength and skin depth. However, the propagation of seismic signals is a multiwave process and is characterized by a set of wavelengths. Thus, to consistently treat seismic and electromagnetic data an additional length scale is needed for seismic data that does not directly depend on a wavelength and describes a diffusive process, similar to EM <span class="hlt">wave</span> propagation in the subsurface. Works by Brown et al.(2005), Shin and Cha(2008), and Shin and Ha(2008) suggest that an artificial damping of seismic <span class="hlt">wave</span> fields via Laplace-Fourier transformation can be an effective approach to obtain a seismic data that have similar spatial resolution to EM data. The key benefit of such transformation is that diffusive <span class="hlt">wave</span>-field inversion works well for both data sets: seismic (Brown et al.,2005; Shin and Cha,2008) and electromagnetic (Commer and Newman,2008; Newman et al.,2010). With the recent interest in the Laplace-Fourier domain full waveform inversion, <span class="hlt">3</span><span class="hlt">D</span> fourth and second-order finite-difference schemes for modeling of seismic <span class="hlt">wave</span> propagation have been developed (Petrov and Newman, 2010). Incorporation of attenuation and anisotropy into a velocity model is a necessary step for a more realistic description of subsurface media. Here we consider the extension of our method which includes attenuation and VTI anisotropy. Our approach is based on the integro-interpolation technique for velocity-stress formulation. Seven</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21632054','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21632054"><span><span class="hlt">Wave</span> propagation in protein microtubules modeled as orthotropic elastic shells including transverse <span class="hlt">shear</span> deformations.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Daneshmand, Farhang; Ghavanloo, Esmaeal; Amabili, Marco</p> <p>2011-07-07</p> <p><span class="hlt">Wave</span> propagation along the microtubules is one of the issues of major concern in various microtubule cellular functions. In this study, the general <span class="hlt">wave</span> propagation behavior in protein microtubules is investigated based on a first-order <span class="hlt">shear</span> deformation shell theory for orthotropic materials, with particular emphasis on the role of strongly anisotropic elastic properties of microtubules. According to experimental observation, the first-order <span class="hlt">shear</span> deformation theory is used for the modeling of microtubule walls. A general displacement representation is introduced and a type of coupled polynomial eigenvalue problem is developed. Numerical examples describe the effects of <span class="hlt">shear</span> deformation and rotary inertia on <span class="hlt">wave</span> velocities in orthotropic microtubules. Finally, the influences of the microtubule <span class="hlt">shear</span> modulus, axial external force, effective thickness and material temperature dependency on <span class="hlt">wave</span> velocities along the microtubule protofilaments, helical pathway and radial directions are elucidated. Most results presented in the present investigation have been absent from the literature for the <span class="hlt">wave</span> propagation in microtubules.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T21A2140P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T21A2140P"><span>Using <span class="hlt">3</span><span class="hlt">D</span> Simulation of Elastic <span class="hlt">Wave</span> Propagation in Laplace Domain for Electromagnetic-Seismic Inverse Modeling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petrov, P.; Newman, G. A.</p> <p>2010-12-01</p> <p>-Fourier domain we had developed <span class="hlt">3</span><span class="hlt">D</span> code for full-<span class="hlt">wave</span> field simulation in the elastic media which take into account nonlinearity introduced by free-surface effects. Our approach is based on the velocity-stress formulation. In the contrast to conventional formulation we defined the material properties such as density and Lame constants not at nodal points but within cells. This second order finite differences method formulated in the cell-based grid, generate numerical solutions compatible with analytical ones within the range errors determinate by dispersion analysis. Our simulator will be embedded in an inversion scheme for joint seismic- electromagnetic imaging. It also offers possibilities for preconditioning the seismic <span class="hlt">wave</span> propagation problems in the frequency domain. References. Shin, C. & Cha, Y. (2009), Waveform inversion in the Laplace-Fourier domain, Geophys. J. Int. 177(3), 1067- 1079. Shin, C. & Cha, Y. H. (2008), Waveform inversion in the Laplace domain, Geophys. J. Int. 173(3), 922-931. Commer, M. & Newman, G. (2008), New advances in three-dimensional controlled-source electromagnetic inversion, Geophys. J. Int. 172(2), 513-535. Newman, G. A., Commer, M. & Carazzone, J. J. (2010), Imaging CSEM data in the presence of electrical anisotropy, Geophysics, in press.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PMB....61.2582G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PMB....61.2582G"><span>Contactless remote induction of <span class="hlt">shear</span> <span class="hlt">waves</span> in soft tissues using a transcranial magnetic stimulation device</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grasland-Mongrain, Pol; Miller-Jolicoeur, Erika; Tang, An; Catheline, Stefan; Cloutier, Guy</p> <p>2016-03-01</p> <p>This study presents the first observation of <span class="hlt">shear</span> <span class="hlt">waves</span> induced remotely within soft tissues. It was performed through the combination of a transcranial magnetic stimulation device and a permanent magnet. A physical model based on Maxwell and Navier equations was developed. Experiments were performed on a cryogel phantom and a chicken breast sample. Using an ultrafast ultrasound scanner, <span class="hlt">shear</span> <span class="hlt">waves</span> of respective amplitudes of 5 and 0.5 μm were observed. Experimental and numerical results were in good agreement. This study constitutes the framework of an alternative <span class="hlt">shear</span> <span class="hlt">wave</span> elastography method.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70028851','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70028851"><span>Spatial correlation of <span class="hlt">shear-wave</span> velocity within San Francisco Bay Sediments</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Thompson, E.M.; Baise, L.G.; Kayen, R.E.</p> <p>2006-01-01</p> <p>Sediment properties are spatially variable at all scales, and this variability at smaller scales influences high frequency ground motions. We show that surface <span class="hlt">shear-wave</span> velocity is highly correlated within San Francisco Bay Area sediments using <span class="hlt">shear-wave</span> velocity measurements from 210 seismic cone penetration tests. We use this correlation to estimate the surface sediment velocity structure using geostatistics. We find that the variance of the estimated <span class="hlt">shear-wave</span> velocity is reduced using ordinary kriging, and that including this velocity structure in 2D ground motion simulations of a moderate sized earthquake improves the accuracy of the synthetics. Copyright ASCE 2006.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4738718','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4738718"><span>Rescaled Local Interaction Simulation Approach for <span class="hlt">Shear</span> <span class="hlt">Wave</span> Propagation Modelling in Magnetic Resonance Elastography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Packo, P.; Staszewski, W. J.; Uhl, T.</p> <p>2016-01-01</p> <p>Properties of soft biological tissues are increasingly used in medical diagnosis to detect various abnormalities, for example, in liver fibrosis or breast tumors. It is well known that mechanical stiffness of human organs can be obtained from organ responses to <span class="hlt">shear</span> stress <span class="hlt">waves</span> through Magnetic Resonance Elastography. The Local Interaction Simulation Approach is proposed for effective modelling of <span class="hlt">shear</span> <span class="hlt">wave</span> propagation in soft tissues. The results are validated using experimental data from Magnetic Resonance Elastography. These results show the potential of the method for <span class="hlt">shear</span> <span class="hlt">wave</span> propagation modelling in soft tissues. The major advantage of the proposed approach is a significant reduction of computational effort. PMID:26884808</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25643079','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25643079"><span>Two-dimensional <span class="hlt">shear-wave</span> elastography on conventional ultrasound scanners with time-aligned sequential tracking (TAST) and comb-push ultrasound <span class="hlt">shear</span> elastography (CUSE).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Song, Pengfei; Macdonald, Michael; Behler, Russell; Lanning, Justin; Wang, Michael; Urban, Matthew; Manduca, Armando; Zhao, Heng; Callstrom, Matthew; Alizad, Azra; Greenleaf, James; Chen, Shigao</p> <p>2015-02-01</p> <p>Two-dimensional <span class="hlt">shear-wave</span> elastography presents 2-D quantitative <span class="hlt">shear</span> elasticity maps of tissue, which are clinically useful for both focal lesion detection and diffuse disease diagnosis. Realization of 2-D <span class="hlt">shear-wave</span> elastography on conventional ultrasound scanners, however, is challenging because of the low tracking pulse-repetition-frequency (PRF) of these systems. Although some clinical and research platforms support software beamforming and plane-<span class="hlt">wave</span> imaging with high PRF, the majority of current clinical ultrasound systems do not have the software beamforming capability, which presents a critical challenge for translating the 2-D <span class="hlt">shear-wave</span> elastography technique from laboratory to clinical scanners. To address this challenge, this paper presents a time-aligned sequential tracking (TAST) method for <span class="hlt">shear-wave</span> tracking on conventional ultrasound scanners. TAST takes advantage of the parallel beamforming capability of conventional systems and realizes high-PRF <span class="hlt">shear-wave</span> tracking by sequentially firing tracking vectors and aligning <span class="hlt">shear</span> <span class="hlt">wave</span> data in the temporal direction. The comb-push ultrasound <span class="hlt">shear</span> elastography (CUSE) technique was used to simultaneously produce multiple <span class="hlt">shear</span> <span class="hlt">wave</span> sources within the field-of-view (FOV) to enhance <span class="hlt">shear</span> <span class="hlt">wave</span> SNR and facilitate robust reconstructions of 2-D elasticity maps. TAST and CUSE were realized on a conventional ultrasound scanner. A phantom study showed that the <span class="hlt">shear-wave</span> speed measurements from the conventional ultrasound scanner were in good agreement with the values measured from other 2-D <span class="hlt">shear</span> <span class="hlt">wave</span> imaging technologies. An inclusion phantom study showed that the conventional ultrasound scanner had comparable performance to a state-of-the-art <span class="hlt">shear-wave</span> imaging system in terms of bias and precision in measuring different sized inclusions. Finally, in vivo case analysis of a breast with a malignant mass, and a liver from a healthy subject demonstrated the feasibility of using the conventional ultrasound</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ApPhL.103a4101C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ApPhL.103a4101C"><span>Tomography from diffuse <span class="hlt">waves</span>: Passive <span class="hlt">shear</span> <span class="hlt">wave</span> imaging using low frame rate scanners</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Catheline, S.; Souchon, R.; Rupin, M.; Brum, J.; Dinh, A. H.; Chapelon, J.-Y.</p> <p>2013-07-01</p> <p>We present an approach to extract from the local measurement of a complex field a wavelength tomography. In contrast with noise correlation techniques developed in recent years in seismology or ultrasound, field measurement is under-sampled which opens applications to slow imaging devices. Through simulations and experiments, it is demonstrated that the loss of time and/or spatial coherence of the field measurement is not an obstacle for tomography reconstruction. We present an application in <span class="hlt">shear</span> <span class="hlt">wave</span> imaging: a conventional ultrasonic scanner working at 25 Hz is tested in a medical phantom and in the thyroid of a healthy volunteer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24168315','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24168315"><span>Triboelectric nanogenerator built on suspended <span class="hlt">3</span><span class="hlt">D</span> spiral structure as vibration and positioning sensor and <span class="hlt">wave</span> energy harvester.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hu, Youfan; Yang, Jin; Jing, Qingshen; Niu, Simiao; Wu, Wenzhuo; Wang, Zhong Lin</p> <p>2013-11-26</p> <p>An unstable mechanical structure that can self-balance when perturbed is a superior choice for vibration energy harvesting and vibration detection. In this work, a suspended <span class="hlt">3</span><span class="hlt">D</span> spiral structure is integrated with a triboelectric nanogenerator (TENG) for energy harvesting and sensor applications. The newly designed vertical contact-separation mode TENG has a wide working bandwidth of 30 Hz in low-frequency range with a maximum output power density of 2.76 W/m(2) on a load of 6 MΩ. The position of an in-plane vibration source was identified by placing TENGs at multiple positions as multichannel, self-powered active sensors, and the location of the vibration source was determined with an error less than 6%. The magnitude of the vibration is also measured by the output voltage and current signal of the TENG. By integrating the TENG inside a buoy ball, <span class="hlt">wave</span> energy harvesting at water surface has been demonstrated and used for lighting illumination light, which shows great potential applications in marine science and environmental/infrastructure monitoring.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoJI.196.1123M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoJI.196.1123M"><span>Time-stepping stability of continuous and discontinuous finite-element methods for <span class="hlt">3</span>-<span class="hlt">D</span> <span class="hlt">wave</span> propagation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mulder, W. A.; Zhebel, E.; Minisini, S.</p> <p>2014-02-01</p> <p>We analyse the time-stepping stability for the <span class="hlt">3</span>-<span class="hlt">D</span> acoustic <span class="hlt">wave</span> equation, discretized on tetrahedral meshes. Two types of methods are considered: mass-lumped continuous finite elements and the symmetric interior-penalty discontinuous Galerkin method. Combining the spatial discretization with the leap-frog time-stepping scheme, which is second-order accurate and conditionally stable, leads to a fully explicit scheme. We provide estimates of its stability limit for simple cases, namely, the reference element with Neumann boundary conditions, its distorted version of arbitrary shape, the unit cube that can be partitioned into six tetrahedra with periodic boundary conditions and its distortions. The Courant-Friedrichs-Lewy stability limit contains an element diameter for which we considered different options. The one based on the sum of the eigenvalues of the spatial operator for the first-degree mass-lumped element gives the best results. It resembles the diameter of the inscribed sphere but is slightly easier to compute. The stability estimates show that the mass-lumped continuous and the discontinuous Galerkin finite elements of degree 2 have comparable stability conditions, whereas the mass-lumped elements of degree one and three allow for larger time steps.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70033017','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70033017"><span>Spatial correlation of <span class="hlt">shear-wave</span> velocity in the San Francisco Bay Area sediments</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Thompson, E.M.; Baise, L.G.; Kayen, R.E.</p> <p>2007-01-01</p> <p>Ground motions recorded within sedimentary basins are variable over short distances. One important cause of the variability is that local soil properties are variable at all scales. Regional hazard maps developed for predicting site effects are generally derived from maps of surficial geology; however, recent studies have shown that mapped geologic units do not correlate well with the average <span class="hlt">shear-wave</span> velocity of the upper 30 m, Vs(30). We model the horizontal variability of near-surface soil <span class="hlt">shear-wave</span> velocity in the San Francisco Bay Area to estimate values in unsampled locations in order to account for site effects in a continuous manner. Previous geostatistical studies of soil properties have shown horizontal correlations at the scale of meters to tens of meters while the vertical correlations are on the order of centimeters. In this paper we analyze <span class="hlt">shear-wave</span> velocity data over regional distances and find that surface <span class="hlt">shear-wave</span> velocity is correlated at horizontal distances up to 4 km based on data from seismic cone penetration tests and the spectral analysis of surface <span class="hlt">waves</span>. We propose a method to map site effects by using geostatistical methods based on the <span class="hlt">shear-wave</span> velocity correlation structure within a sedimentary basin. If used in conjunction with densely spaced <span class="hlt">shear-wave</span> velocity profiles in regions of high seismic risk, geostatistical methods can produce reliable continuous maps of site effects. ?? 2006 Elsevier Ltd. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70037147','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70037147"><span>Rayleigh-<span class="hlt">wave</span> phase-velocity maps and three-dimensional <span class="hlt">shear</span> velocity structure of the western US from local non-plane surface <span class="hlt">wave</span> tomography</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pollitz, F.F.; Snoke, J. Arthur</p> <p>2010-01-01</p> <p>We utilize two-and-three-quarter years of vertical-component recordings made by the Transportable Array (TA) component of Earthscope to constrain three-dimensional (<span class="hlt">3</span>-<span class="hlt">D</span>) seismic <span class="hlt">shear</span> <span class="hlt">wave</span> velocity structure in the upper 200 km of the western United States. Single-taper spectral estimation is used to compile measurements of complex spectral amplitudes from 44 317 seismograms generated by 123 teleseismic events. In the first step employed to determine the Rayleigh-<span class="hlt">wave</span> phase-velocity structure, we implement a new tomographic method, which is simpler and more robust than scattering-based methods (e.g. multi-plane surface <span class="hlt">wave</span> tomography). The TA is effectively implemented as a large number of local arrays by defining a horizontal Gaussian smoothing distance that weights observations near a given target point. The complex spectral-amplitude measurements are interpreted with the spherical Helmholtz equation using local observations about a succession of target points, resulting in Rayleigh-<span class="hlt">wave</span> phase-velocity maps at periods over the range of 18–125 s. The derived maps depend on the form of local fits to the Helmholtz equation, which generally involve the nonplane-<span class="hlt">wave</span> solutions of Friederich et al. In a second step, the phase-velocity maps are used to derive <span class="hlt">3</span>-<span class="hlt">D</span> <span class="hlt">shear</span> velocity structure. The <span class="hlt">3</span>-<span class="hlt">D</span> velocity images confirm details witnessed in prior body-<span class="hlt">wave</span> and surface-<span class="hlt">wave</span> studies and reveal new structures, including a deep (>100 km deep) high-velocity lineament, of width ∼200 km, stretching from the southern Great Valley to northern Utah that may be a relic of plate subduction or, alternatively, either a remnant of the Mojave Precambrian Province or a mantle downwelling. Mantle seismic velocity is highly correlated with heat flow, Holocene volcanism, elastic plate thickness and seismicity. This suggests that shallow mantle structure provides the heat source for associated magmatism, as well as thinning of the thermal lithosphere, leading to relatively high</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ESASP.709E..10D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ESASP.709E..10D"><span>Airborne & SAR Synergy Reveals the <span class="hlt">3</span><span class="hlt">D</span> Structure of Air Bubble Entrainment in Internal <span class="hlt">Waves</span> and Frontal Zones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>da Silva, J. C. B.; Magalhaes, J. M.; Batista, M.; Gostiaux, L.; Gerkema, T.; New, A. L.</p> <p>2013-03-01</p> <p> spectral range 8-12 μm. With a nominal ground resolution of approximately 1.5 meters (at an altitude of 500 meters) it is capable to detect fine structure associated to turbulence. The LiDAR system that has been used is the Leica ALS50-II (1064nm) with a hit rate greater than 1 hit per square meter and a vertical resolution of approximately 15 cm. Both systems were available simultaneously, together with the hyperspectral system and the RCD105 39Mpx digital camera, integrated with the LiDAR navigation system. We analyse the airborne data together with a comprehensive dataset of satellite Synthetic Aperture Radar (SAR) that includes ENVISAT and TerraSAR-X images. In addition, in situ observations in the near-shore zone were obtained in a previous experiment (Project SPOTIWAVE-II POCI/MAR/57836/2004 funded by the Portuguese FCT) during the summer period in 2006. These included thermistor chain measurements along the water column that captured the vertical structure of shoaling internal (tidal) <span class="hlt">waves</span> and ISWs close to the breaking point. The SAR and airborne images were obtained in light wind conditions, in the near-shore zone, and in the presence of ISWs. The LiDAR images revealed sub-surface structures (some 1-2 m below the sea surface) that were co-located with surface films. These film slicks were induced by the convergent fields of internal <span class="hlt">waves</span> and upwelling fronts. Some of the sub-surface features were located over the front slopes of the internal <span class="hlt">waves</span>, which coincides with the internal <span class="hlt">wave</span> slick band visible in the aerial photos and hyperspectral systems. Our flight measurements revealed thermal features similar to “boils” of cold water within the wake of (admittedly breaking) internal <span class="hlt">waves</span>. These features are consistent with the previous in situ measurements of breaking ISWs. In this paper we will show coincident multi-sensor airborne and satellite SAR observations that reveal the <span class="hlt">3</span><span class="hlt">D</span> structure of air bubble entrainment in the internal <span class="hlt">wave</span> field and frontal</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4000517','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4000517"><span>Point <span class="hlt">shear</span> <span class="hlt">wave</span> elastography method for assessing liver stiffness</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ferraioli, Giovanna; Tinelli, Carmine; Lissandrin, Raffaella; Zicchetti, Mabel; Dal Bello, Barbara; Filice, Gaetano; Filice, Carlo</p> <p>2014-01-01</p> <p>AIM: To estimate the validity of the point <span class="hlt">shear-wave</span> elastography method by evaluating its reproducibility and accuracy for assessing liver stiffness. METHODS: This was a single-center, cross-sectional study. Consecutive patients with chronic viral hepatitis scheduled for liver biopsy (LB) (Group 1) and healthy volunteers (Group 2) were studied. In each subject 10 consecutive point <span class="hlt">shear-wave</span> elastography (PSWE) measurements were performed using the iU22 ultrasound system (Philips Medical Systems, Bothell, WA, United States). Patients in Group 1 underwent PSWE, transient elastography (TE) using FibroScan (Echosens, Paris, France) and ultrasound-assisted LB. For the assessment of PSWE reproducibility two expert raters (rater 1 and rater 2) independently performed the examinations. The performance of PSWE was compared to that of TE using LB as a reference standard. Fibrosis was staged according to the METAVIR scoring system. Receiver operating characteristic curve analyses were performed to calculate the area under the receiver operating characteristic curve (AUC) for F ≥ 2, F ≥ 3 and F = 4. The intraobserver and interobserver reproducibility of PSWE were assessed by calculating Lin’s concordance correlation coefficient. RESULTS: To assess the performance of PSWE, 134 consecutive patients in Group 1 were studied. The median values of PSWE and TE (in kilopascals) were 4.7 (IQR = 3.8-5.4) and 5.5 (IQR = 4.7-6.5), respectively, in patients at the F0-F1 stage and 3.5 (IQR = 3.2-4.0) and 4.4 (IQR = 3.5-4.9), respectively, in the healthy volunteers in Group 2 (P < 10-5). In the univariate analysis, the PSWE and TE values showed a high correlation with the fibrosis stage; low correlations with the degree of necroinflammation, aspartate aminotransferase and gamma-glutamyl transferase (GGT); and a moderate negative correlation with the platelet count. A multiple regression analysis confirmed the correlations of both PSWE and TE with fibrosis stage and GGT but not with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhDT........22J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhDT........22J"><span>Three-dimensional <span class="hlt">shear</span> <span class="hlt">wave</span> velocity structure in the Atlantic upper mantle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>James, Esther Kezia Candace</p> <p></p> <p>Oceanic lithosphere constitutes the upper boundary layer of the Earth's convecting mantle. Its structure and evolution provide a vital window on the dynamics of the mantle and important clues to how the motions of Earth's surface plates are coupled to convection in the mantle below. The three-dimensional <span class="hlt">shear</span>-velocity structure of the upper mantle beneath the Atlantic Ocean is investigated to gain insight into processes that drive formation of oceanic lithosphere. Travel times are measured for approximately 10,000 fundamental-mode Rayleigh <span class="hlt">waves</span>, in the period range 30-130 seconds, traversing the Atlantic basin. Paths with >30% of their length through continental upper mantle are excluded to maximize sensitivity to the oceanic upper mantle. The lateral distribution of Rayleigh <span class="hlt">wave</span> phase velocity in the Atlantic upper mantle is explored with two approaches. One, phase velocity is allowed to vary only as a function of seafloor age. Two, a general two-dimensional parameterization is utilized in order to capture perturbations to age-dependent structure. Phase velocity shows a strong dependence on seafloor age, and removing age-dependent velocity from the 2-D maps highlights areas of anomalously low velocity, almost all of which are proximal to locations of hotspot volcanism. Depth-dependent variations in vertically-polarized <span class="hlt">shear</span> velocity (Vsv) are determined with two sets of <span class="hlt">3</span>-<span class="hlt">D</span> models: a layered model that requires constant VSV in each depth layer, and a splined model that allows VSV to vary continuously with depth. At shallow depths (˜75 km) the seismic structure shows the expected dependence on seafloor age. At greater depths (˜200 km) high-velocity lithosphere is found only beneath the oldest seafloor; velocity variations beneath younger seafloor may result from temperature or compositional variations within the asthenosphere. The age-dependent phase velocities are used to constrain temperature in the mantle and show that, in contrast to previous results for</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhDT........91T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhDT........91T"><span>Investigation of the Maule, Chile rupture zone using seismic attenuation tomography and <span class="hlt">shear</span> <span class="hlt">wave</span> splitting methods</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Torpey, Megan Elizabeth</p> <p></p> <p>The Maule, Chile 2010 Mw 8.8 earthquake afforded the opportunity to study the rupture zone (33°S-38°S) in detail using aftershocks recorded by the rapid-response IRIS CHAMP seismic network. We used measurements of differential S to P seismic attenuation to characterize the attenuation structure of the South American crust and upper mantle wedge. We implemented an evolving time window to determine Qs-1 values using a spectral ratio method and incorporated these measurements into a bounded linear inequality least squares inversion to solve for Qs -1 in a <span class="hlt">3</span><span class="hlt">D</span> volume. On a large-scale, we observe an east-dipping low attenuation feature, consistent with the location of the Nazca oceanic slab, and image progressively greater attenuation as we move towards the surface of our model. A dramatic feature in our model is a large, low-attenuation body in the same location where Hicks et al. (2014) resolved a high P <span class="hlt">wave</span> velocity anomaly in their velocity tomography model. We calculated the <span class="hlt">shear</span> <span class="hlt">wave</span> splitting intensity of the Maule rupture zone by implementing the multichannel method of Chevrot (2000) which calculates the splitting intensity of teleseismic SK(K)S phases and splitting parameters, ϕ and deltat. The results we obtained show an overall fast direction with a strong component of trench parallel splitting and very few trench normal splits. The fast directions do not parallel the Nazca APM, but are instead dominated by splits rotated 40°-50° counter-clockwise from Nazca APM. Based on these data, we see little evidence for sub-slab entrained mantle flow and invoke the trench-parallel retrograde flow model as an explanation for our measurements. We developed an extended splitting intensity method to allow for use of the upgoing S phase from Maule aftershocks, utilizing the initial event polarization. For this local dataset, we observe three dominant fast directions oriented N20°W, N40°E, and N10°W-20°E and a subset of fast directions trending N60°-90°E which</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.9555I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.9555I"><span>The Origin of <span class="hlt">Shear</span> <span class="hlt">Wave</span> Splitting Beneath Iceland</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ito, Garrett; Dunn, Robert; Li, Aibing</p> <p>2016-04-01</p> <p>The origin of <span class="hlt">shear</span> <span class="hlt">wave</span> splitting (SWS) in the mantle beneath Iceland is examined using numerical models that simulate three-dimensional mantle flow and the development of seismic anisotropy due to lattice-preferred orientation (LPO). Using the simulated anisotropy structure, we compute synthetic SKS waveforms, invert them for fast polarization directions and split times, and then compare the predictions with the results from three observational studies of Iceland. Models that simulate a mantle plume interacting with the Mid-Atlantic Ridge in which the shallow-most mantle has a high viscosity due to the extraction of water with partial melting, or in which C-type olivine LPO fabric is present due to high water content in the plume, produce the largest chi-squared misfits to the SWS observations and are thus rejected. Models of a low-viscosity mantle plume with A-type olivine fabric everywhere, or with the added effects of E-type fabric in the plume below the solidus produce lower misfits. The lowest misfits are produced by models that include a rapid (~50 km/Myr) northward regional flow (NRF) in the mid-upper mantle, either with or without a plume. NRF was previously indicated by a receiver function study and a regional tomography study, and is shown here to be a major cause of the azimuthal anisotropy beneath Iceland. The smallest misfits for the models with both a plume and NRF are produced when LPO forms above a depth of 300-400 km, which, by implication, also marks the depth range in which dislocation creep dominates over diffusion creep. This depth of transition between dislocation and diffusion creep is greater than expected beneath normal oceanic seafloor, and is attributed to the unusually rapid strain-rates associated with an Iceland plume and the NRF.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20355876','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20355876"><span>Monitoring polymer properties using <span class="hlt">shear</span> horizontal surface acoustic <span class="hlt">waves</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gallimore, Dana Y; Millard, Paul J; Pereira da Cunha, Mauricio</p> <p>2009-10-01</p> <p>Real-time, nondestructive methods for monitoring polymer film properties are increasingly important in the development and fabrication of modern polymer-containing products. Online testing of industrial polymer films during preparation and conditioning is required to minimize material and energy consumption, improve the product quality, increase the production rate, and reduce the number of product rejects. It is well-known that <span class="hlt">shear</span> horizontal surface acoustic <span class="hlt">wave</span> (SH-SAW) propagation is sensitive to mass changes as well as to the mechanical properties of attached materials. In this work, the SH-SAW was used to monitor polymer property changes primarily dictated by variations in the viscoelasticity. The viscoelastic properties of a negative photoresist film were monitored throughout the ultraviolet (UV) light-induced polymer cross-linking process using SH-SAW delay line devices. Changes in the polymer film mass and viscoelasticity caused by UV exposure produced variations in the phase velocity and attenuation of the SH-SAW propagating in the structure. Based on measured polymer-coated delay line scattering transmission responses (S(21)) and the measured polymer layer thickness and density, the viscoelastic constants c(44) and eta(44) were extracted. The polymer thickness was found to decrease 0.6% during UV curing, while variations in the polymer density were determined to be insignificant. Changes of 6% in c(44) and 22% in eta(44) during the cross-linking process were observed, showing the sensitivity of the SH-SAW phase velocity and attenuation to changes in the polymer film viscoelasticity. These results indicate the potential for SH-SAW devices as online monitoring sensors for polymer film processing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007E%26PSL.259..526B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007E%26PSL.259..526B"><span>Stochastic analysis of <span class="hlt">shear-wave</span> splitting length scales</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Becker, Thorsten W.; Browaeys, Jules T.; Jordan, Thomas H.</p> <p>2007-07-01</p> <p>The coherence of azimuthal seismic anisotropy, as inferred from <span class="hlt">shear-wave</span> splitting measurements, decreases with the relative distance between stations. Stochastic models of a two-dimensional vector field defined by a von Karma'n [T. von Karma'n, Progress in the statistical theory of turbulence, J. Mar. Res., 7 (1948) 252-264.] autocorrelation function with horizontal correlation length L provide a useful means to evaluate this heterogeneity and coherence lengths. We use the compilation of SKS splitting measurements by Fouch [M. Fouch, Upper mantle anisotropy database, accessed in 06/2006, http://geophysics.asu.edu/anisotropy/upper/] and supplement it with additional studies, including automated measurements by Evans et al. [Evans, M.S., Kendall, J.-M., Willemann, R.J., 2006. Automated SKS splitting and upper-mantle anisotropy beneath Canadian seismic stations, Geophys. J. Int. 165, 931-942, Evans, M.S., Kendall, J.-M., Willemann, R.J. Automated splitting project database, Online at http://www.isc.ac.uk/SKS/, accessed 02/2006]. The correlation lengths of this dataset depend on the geologic setting in the continental regions: in young Phanerozoic orogens and magmatic zones L ˜ 600 km, smaller than the smooth L ˜ 1600 km patterns in tectonically more stable regions such as Phanerozoic platforms. Our interpretation is that the relatively large coherence underneath older crust reflects large-scale tectonic processes (e.g. continent-continent collisions) that are frozen into the tectosphere. In younger continental regions, smaller scale flow (e.g. slab anomaly induced) may predominantly affect anisotropy. In this view, remnant anisotropy is dominant in the old continents and deformation-induced anisotropy caused by recent asthenospheric flow is dominant in active continental regions and underneath oceanic plates. Auxiliary analysis of surface-<span class="hlt">wave</span> anisotropy and combined mantle flow and anisotropic texture modeling is consistent with this suggestion. In continental</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26803391','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26803391"><span>Improvement of <span class="hlt">Shear</span> <span class="hlt">Wave</span> Motion Detection Using Harmonic Imaging in Healthy Human Liver.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Amador, Carolina; Song, Pengfei; Meixner, Duane D; Chen, Shigao; Urban, Matthew W</p> <p>2016-05-01</p> <p>Quantification of liver elasticity is a major application of <span class="hlt">shear</span> <span class="hlt">wave</span> elasticity imaging (SWEI) to non-invasive assessment of liver fibrosis stages. SWEI measurements can be highly affected by ultrasound image quality. Ultrasound harmonic imaging has exhibited a significant improvement in ultrasound image quality as well as for SWEI measurements. This was previously illustrated in cardiac SWEI. The purpose of this study was to evaluate liver <span class="hlt">shear</span> <span class="hlt">wave</span> particle displacement detection and <span class="hlt">shear</span> <span class="hlt">wave</span> velocity (SWV) measurements with fundamental and filter-based harmonic ultrasound imaging. In a cohort of 17 patients with no history of liver disease, a 2.9-fold increase in maximum <span class="hlt">shear</span> <span class="hlt">wave</span> displacement, a 0.11 m/s decrease in the overall interquartile range and median SWV and a 17.6% increase in the success rate of SWV measurements were obtained when filter-based harmonic imaging was used instead of fundamental imaging.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JaJAP..49gHF09T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JaJAP..49gHF09T"><span>Measurement of Elastic Properties of Tissue by <span class="hlt">Shear</span> <span class="hlt">Wave</span> Propagation Generated by Acoustic Radiation Force</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tabaru, Marie; Azuma, Takashi; Hashiba, Kunio</p> <p>2010-07-01</p> <p>Acoustic radiation force (ARF) imaging has been developed as a novel elastography technology to diagnose hepatic disease and breast cancer. The accuracy of <span class="hlt">shear</span> <span class="hlt">wave</span> speed estimation, which is one of the applications of ARF elastography, is studied. The Young's moduli of pig liver and foie gras samples estimated from the <span class="hlt">shear</span> <span class="hlt">wave</span> speed were compared with those measured the static Young's modulus measurement. The difference in the two methods was 8%. Distance attenuation characteristics of the <span class="hlt">shear</span> <span class="hlt">wave</span> were also studied using finite element method (FEM) analysis. We found that the differences in the axial and lateral beam widths in pressure and ARF are 16 and 9% at F-number=0.9. We studied the relationship between two branch points in distance attenuation characteristics and the shape of ARF. We found that the maximum measurable length to estimate <span class="hlt">shear</span> <span class="hlt">wave</span> speed for one ARF excitation was 8 mm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JaJAP..49gHF09M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JaJAP..49gHF09M"><span>Measurement of Elastic Properties of Tissue by <span class="hlt">Shear</span> <span class="hlt">Wave</span> Propagation Generated by Acoustic Radiation Force</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marie Tabaru,; Takashi Azuma,; Kunio Hashiba,</p> <p>2010-07-01</p> <p>Acoustic radiation force (ARF) imaging has been developed as a novel elastography technology to diagnose hepatic disease and breast cancer. The accuracy of <span class="hlt">shear</span> <span class="hlt">wave</span> speed estimation, which is one of the applications of ARF elastography, is studied. The Young’s moduli of pig liver and foie gras samples estimated from the <span class="hlt">shear</span> <span class="hlt">wave</span> speed were compared with those measured the static Young’s modulus measurement. The difference in the two methods was 8%. Distance attenuation characteristics of the <span class="hlt">shear</span> <span class="hlt">wave</span> were also studied using finite element method (FEM) analysis. We found that the differences in the axial and lateral beam widths in pressure and ARF are 16 and 9% at F-number=0.9. We studied the relationship between two branch points in distance attenuation characteristics and the shape of ARF. We found that the maximum measurable length to estimate <span class="hlt">shear</span> <span class="hlt">wave</span> speed for one ARF excitation was 8 mm.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25722029','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25722029"><span>What do we know about <span class="hlt">shear</span> <span class="hlt">wave</span> dispersion in normal and steatotic livers?</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Parker, Kevin J; Partin, Alexander; Rubens, Deborah J</p> <p>2015-05-01</p> <p>A number of new approaches to measure the viscoelastic properties of the liver are now available to clinicians, many involving <span class="hlt">shear</span> <span class="hlt">waves</span>. However, we are at an early stage in understanding the physical processes that govern <span class="hlt">shear</span> <span class="hlt">wave</span> propagation in normal liver, with more unknowns added when pathologies such as steatosis are present. This technical note focuses on what is known about the characterization of normal and steatotic (or fatty) livers, with a particular focus on dispersion. Some studies in phantoms and mouse livers support the hypothesis that, starting with a normal liver, increasing accumulations of micro- and macrosteatosis will increase the lossy viscoelastic properties of <span class="hlt">shear</span> <span class="hlt">waves</span> in a medium. This results in an increased dispersion (or slope) of <span class="hlt">shear</span> <span class="hlt">wave</span> speed and attenuation in the steatotic livers. Theoretical and empirical findings across a number of studies are summarized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUSMNS24A..04C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUSMNS24A..04C"><span>Tomography <span class="hlt">3</span><span class="hlt">D</span> models of S <span class="hlt">wave</span> from cross-correlation of seismic noise to explore irregularities of subsoil under the artificial lake of Chapultepec Park</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cárdenas-Soto, M.; Valdes, J. E.; Escobedo-Zenil, D.</p> <p>2013-05-01</p> <p>In June 2006, the base of the artificial lake in Chapultepec Park collapsed. 20 thousand liters of water were filtered to the ground through a crack increasing the dimensions of initial gap. Studies indicated that the collapse was due to saturated material associated with a sudden and massive water filtration process. Geological studies indicates that all the area of this section the subsoil is composed of vulcano-sedimentary materials that were economically exploited in the mid-20th century, leaving a series of underground mines that were rehabilitated for the construction of the Park. Currently, the Lake is rehabilitated and running for recreational activities. In this study we have applied two methods of seismic noise correlation; seismic interferometry (SI) in time domain and the Spatial Power Auto Correlation (SPAC) in frequency domain, in order to explore the <span class="hlt">3</span><span class="hlt">D</span> subsoil velocity structure. The aim is to highlight major variations in velocity that can be associated with irregularities in the subsoil that may pose a risk to the stability of the Lake. For this purpose we use 96 vertical geophones of 4.5 Hz with 5-m spacing that conform a semi-circular array that provide a length of 480 m around the lake zone. For both correlation methods, we extract the phase velocity associated with the dispersion characteristics between each pair of stations in the frequency range from 4 to 12 Hz. In the SPAC method the process was through the dispersion curve, and in SI method we use the time delay of the maximum amplitude in the correlation pulse, which was previously filtered in multiple frequency bands. The results of both processes were captured in <span class="hlt">3</span><span class="hlt">D</span> velocity volumes (in the case SI a process of traveltime tomography was applied). We observed that in the frequency range from 6 to 8 Hz, appear irregular structures, with high velocity contrast in relation with the <span class="hlt">shear</span> <span class="hlt">wave</span> velocity of surface layer (ten thick m of saturated sediments). One of these anomalies is related</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA610268','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA610268"><span>Evaluating Macro and Microscopic Rock Damage from Explosions and the Effects on <span class="hlt">Shear</span> <span class="hlt">Wave</span> Generation</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2014-06-30</p> <p>AFRL-RV-PS- AFRL-RV-PS- TR-2014-0167 TR-2014-0167 EVALUATING MACRO AND MICROSCOPIC ROCK DAMAGE FROM EXPLOSIONS AND THE EFFECTS ON <span class="hlt">SHEAR</span> <span class="hlt">WAVE</span>...Macro and Microscopic Rock Damage from Explosions and the Effects on <span class="hlt">Shear</span> <span class="hlt">Wave</span> Generation 5a. CONTRACT NUMBER FA9453-10-C-0257 5b. GRANT NUMBER...the rock was highly pulverized and granulated. Outward and above the emplacement level, the granite was characterized by high angle fractures</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/1983/0917/report.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/1983/0917/report.pdf"><span>Sketches of a hammer-impact, spiked-base, <span class="hlt">shear-wave</span> source</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hasbrouck, W.P.</p> <p>1983-01-01</p> <p>Generation of <span class="hlt">shear</span> <span class="hlt">waves</span> in shallow seismic investigations (those to depths usually less than 100 m) can be accomplished by horizontally striking with a hammer either the end of a wood plank or metal structure embedded at the ground surface. The dimensioned sketches of this report are of a steel, hammer-impact, spiked-base, <span class="hlt">shear-wave</span> source. It has been used on outcrops and in a desert environment and for conducting experiments on the effect of rotating source direction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA251492','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA251492"><span>Shallow Water Sediment Properties Derived from High-Frequency <span class="hlt">Shear</span> and Interface <span class="hlt">Waves</span></span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1992-04-10</p> <p>FREQUENCY <span class="hlt">SHEAR</span> ONR N00014-88-C-1238 AND INTERFACE <span class="hlt">WAVES</span> 6. AUTHOR(S) JOHN EWING, JERRY A. CARTER, GEORGE H. SUTTON AND NOEL BARSTOW 7. PERFORMING...B4. PAGES 4739--4762. APRIL 10. 1992 Shallow Water Sediment Properties Derived From High-Frequency <span class="hlt">Shear</span> and Interface <span class="hlt">Waves</span> JOHN EWING Woods Hole...calculating thickness. The amplitude falloff with range establishes a Q velocity gradients and penetration depths [ Nettleton . 19401 estimate of 40 in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040172889&hterms=Bone+measurements&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DBone%2Bmeasurements','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040172889&hterms=Bone+measurements&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DBone%2Bmeasurements"><span>Measurement of <span class="hlt">shear-wave</span> velocity by ultrasound critical-angle reflectometry (UCR)</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mehta, S.; Antich, P.; Blomqvist, C. G. (Principal Investigator)</p> <p>1997-01-01</p> <p>There exists a growing body of research that relates the measurement of pressure-<span class="hlt">wave</span> velocity in bone to different physiological conditions and treatment modalities. The <span class="hlt">shear-wave</span> velocity has been less studied, although it is necessary for a more complete understanding of the mechanical properties of bone. Ultrasound critical-angle reflectometry (UCR) is a noninvasive and nondestructive technique previously used to measure pressure-<span class="hlt">wave</span> velocities both in vitro and in vivo. This note describes its application to the measurement of <span class="hlt">shear-wave</span> velocity in bone, whether directly accessible or covered by soft tissue.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MsT..........1C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MsT..........1C"><span>A new method to test <span class="hlt">shear</span> <span class="hlt">wave</span> splitting: Improving statistical assessment of splitting parameters</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corbalan Castejon, Ana</p> <p></p> <p><span class="hlt">Shear</span> <span class="hlt">wave</span> splitting has proved to be a very useful technique to probe for seismic anisotropy in the earth's interior, and measurements of seismic anisotropy are perhaps the best way to constrain the strain history of the lithosphere and asthenosphere. However, existent methods of <span class="hlt">shear</span> <span class="hlt">wave</span> splitting analysis do not estimate uncertainty correctly, and do not allow for careful statistical modeling of anisotropy and uncertainty in complex scenarios. Consequently, the interpretation of <span class="hlt">shear</span> <span class="hlt">wave</span> splitting measurements has an undesirable subjective component. This study illustrates a new method to characterize <span class="hlt">shear</span> <span class="hlt">wave</span> splitting and the associated uncertainty based on the cross-convolution method [Menke and Levin, 2003]. This new method has been tested on synthetic data and benchmarked with data from the Pasadena, California seismic station (PAS). Synthetic tests show that the method can successfully obtain the splitting parameters from observed split <span class="hlt">shear</span> <span class="hlt">waves</span>. PAS results are very reasonable and consistent with previous studies [Liu et al., 1995; Ozalaybey and Savage, 1995; Polet and Kanamori, 2002]. As presented, the Menke and Levin [2003] method does not explicitly model the errors. Our method works on noisy data without any particular need for processing, it fully accounts for correlation structures on the noise, and it models the errors with a proper bootstrapping approach. Hence, the method presented here casts the analysis of <span class="hlt">shear</span> <span class="hlt">wave</span> splitting into a more formal statistical context, allowing for formal hypothesis testing and more nuanced interpretation of seismic anisotropy results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T23F2744P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T23F2744P"><span>PICASSO: <span class="hlt">Shear</span> velocities in the Western Mediterranean from Rayleigh <span class="hlt">Wave</span> tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Palomeras, I.; Thurner, S.; Levander, A.</p> <p>2012-12-01</p> <p>The Western Mediterranean has been affected by complex subduction and slab rollback, simultaneously with compression due to African-European convergence. The deformed region occupies a wide area from the intra-continental Atlas mountain belt in Morocco to the southern Iberian Massif in Spain. Evolutionary models of the Western Mediterranean invoke extensive slab rollback and compression in the Cenozoic, as well as likely upper mantle delamination scenarios during formation of the Alboran domain, the Betics, Rif, and Atlas Mountains. PICASSO (Program to Investigate Convective Alboran Sea System Overturn) is a multidisciplinary, international investigation of the Alboran System and surrounding areas. In this study we have analyzed data from the 95 PICASSO broadband stations with data from the Spanish IberArray and Siberia Array in Spain and Morocco, the University of Muenster array in the Atlas Mountains and the permanent Spanish and Portuguese networks. We present Rayleigh <span class="hlt">wave</span> tomography results made from 168 teleseimic events recorded by 237 stations from April 2009 to April 2011. We measured Rayleigh phase velocities using the two-plane-<span class="hlt">wave</span> method to remove complications due to multi-pathing, and finite-frequency kernels to improve lateral resolution. Phase velocities were then inverted for <span class="hlt">shear</span> velocity structure on a grid of 0.5 by 0.5 degree to form a well-resolved <span class="hlt">3</span><span class="hlt">D</span> <span class="hlt">shear</span> velocity model to 230 km depth. Our results show low S-velocities (2.9 km/s) in the crust beneath the Gibraltar Strait. Low upper mantle S-velocities are mapped beneath the Middle and High Atlas at ~60 km depth suggesting an elevated asthenosphere beneath these young mountain belts, in agreement with receiver functions analysis (Thurner et al, this session). Beneath the Western Alboran Sea, upper-mantle velocities change laterally from high velocities (>4.5 km/s) in the east to lower velocities to the west (~4.3 km/s). The Rayleigh <span class="hlt">wave</span> tomography is consistent with P-tomography that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23947476','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23947476"><span>Identification process based on <span class="hlt">shear</span> <span class="hlt">wave</span> propagation within a phantom using finite element modelling and magnetic resonance elastography.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Leclerc, Gwladys E; Charleux, Fabrice; Ho Ba Tho, Marie-Christine; Bensamoun, Sabine F</p> <p>2015-01-01</p> <p>Magnetic resonance elastography (MRE), based on <span class="hlt">shear</span> <span class="hlt">wave</span> propagation generated by a specific driver, is a non-invasive exam performed in clinical practice to improve the liver diagnosis. The purpose was to develop a finite element (FE) identification method for the mechanical characterisation of phantom mimicking soft tissues investigated with MRE technique. Thus, a <span class="hlt">3</span><span class="hlt">D</span> FE phantom model, composed of the realistic MRE liver boundary conditions, was developed to simulate the <span class="hlt">shear</span> <span class="hlt">wave</span> propagation with the software ABAQUS. The assumptions of homogeneity and elasticity were applied to the FE phantom model. Different ranges of mesh size, density and Poisson's ratio were tested in order to develop the most representative FE phantom model. The simulated <span class="hlt">wave</span> displacement was visualised with a dynamic implicit analysis. Subsequently, an identification process was performed with a cost function and an optimisation loop provided the optimal elastic properties of the phantom. The present identification process was validated on a phantom model, and the perspective will be to apply this method on abdominal tissues for the set-up of new clinical MRE protocols that could be applied for the follow-up of the effects of treatments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMOS32A..07M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMOS32A..07M"><span><span class="hlt">Shear-wave</span> velocity of slope sediments near Hudson Canyon from analysis of ambient noise</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miller, N. C.; Ten Brink, U. S.; Collins, J. A.; McGuire, J. J.; Flores, C. H.</p> <p>2014-12-01</p> <p>We present new ambient noise data that help constrain the <span class="hlt">shear</span> strength of marine sediments on the continental slope north of Hudson Canyon on the U.S. Atlantic margin. Sediment <span class="hlt">shear</span> strength is a key parameter in models of potentially tsunamigenic, submarine slope failures, but <span class="hlt">shear</span> strength is difficult to measure in situ and is expected to evolve in time with changes in pore pressure. The ambient noise data were recorded by 11 short-period, ocean-bottom seismometers and hydrophones deployed in a ~1 by 1.5 km array for ~6 months on the continental slope. These high frequency (~0.1 - 50 Hz), narrow-aperture data are expected to record noise propagating as interface <span class="hlt">waves</span> and/or resonating in the upper ~500 m of sediment. Propagation of interface <span class="hlt">waves</span> is controlled by the <span class="hlt">shear-wave</span> velocity of the sediment, which we measure by calculating lag-times in cross-correlations of waveforms recorded by pairs of receivers. These measurements of <span class="hlt">shear-wave</span> velocity will be used to constrain <span class="hlt">shear</span> strength. The data also appear to record wind-generated noise resonating in layered sediment. We expect this resonance to also be sensitive to <span class="hlt">shear-wave</span> velocity, and spectral analysis and modeling of harmonics may provide a second constraint on sediment <span class="hlt">shear</span> strength. Both the correlogram- and spectral-based measurements can be made using hour- to day-long segments of data, enabling us to constrain temporal evolution of <span class="hlt">shear-wave</span> velocity and potential forcing mechanisms (e.g., tidal and storm loading and submarine groundwater discharge) through the ~6 month deployment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/863745','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/863745"><span>Apparatus for checking the direction of polarization of <span class="hlt">shear-wave</span> ultrasonic transducers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Karplus, Henry H. B.</p> <p>1980-01-01</p> <p>An apparatus for checking the direction of polarization of <span class="hlt">shear-wave</span> ultrasonic transducers comprises a first planar surface for mounting the <span class="hlt">shear-wave</span> transducer, a second planar surface inclined at a predetermined angle to the first surface to generate longitudinal <span class="hlt">waves</span> by mode conversion, and a third planar surface disposed at a second predetermined angle to the first for mounting a longitudinal-<span class="hlt">wave</span> ultrasonic transducer. In an alternate embodiment, two second planar surfaces at the predetermined angle are placed at an angle to each other. The magnitude of the <span class="hlt">shear</span> <span class="hlt">wave</span> is a function of the angle between the direction of polarization of the transducer and the mode-conversion surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5268805','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/biblio/5268805"><span>Apparatus for checking the direction of polarization of <span class="hlt">shear-wave</span> ultrasonic transducers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Karplus, H.H.B.; Forster, G.A.</p> <p></p> <p>An apparatus for checking the direction of polarization of <span class="hlt">shear-wave</span> ultrasonic transducers comprises a first planar surface for mounting the <span class="hlt">shear-wave</span> transducer, a second planar surface inclined at a predetermined angle to the first surface to generate longitudinal <span class="hlt">waves</span> by mode conversion, and a third planar surface disposed at a second predetermined angle to the first for mounting a longitudinal-<span class="hlt">wave</span> ultransonic transducer. In an alternate embodiment, two second planar surfaces at the predetermined angle are placed at an angle to each other. The magnitude of the <span class="hlt">shear</span> <span class="hlt">wave</span> is a function of the angle between the direction of polarization of the transducer and the mode-conversion surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AIPC..820..187A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AIPC..820..187A"><span>Spiral Creeping <span class="hlt">Waves</span> in Ultrasonic Angled-Beam <span class="hlt">Shear</span> <span class="hlt">Wave</span> Inspection of Fastener Holes in Multilayer Structures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aldrin, John C.; Knopp, Jeremy; Judd, Dave; Mandeville, John R.; Lindgren, Eric</p> <p>2006-03-01</p> <p>This paper explores the propagation and scattering of spiral creeping <span class="hlt">waves</span> around a fastener hole. Preliminary experimental data demonstrates the presence of spiral creeping <span class="hlt">waves</span> in angled beam inspection and the benefit for detecting cracks of varying angular location. Analytical models are used to provide insight into the propagation and focusing of spiral creeping <span class="hlt">waves</span> around cylindrical holes. A hybrid numerical method is proposed as a measurement model for <span class="hlt">3</span><span class="hlt">D</span> scattering from holes with cracks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.S31B2236Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.S31B2236Z"><span>High-resolution <span class="hlt">3</span>-<span class="hlt">D</span> P-<span class="hlt">wave</span> tomographic imaging of the shallow magmatic system of Erebus volcano, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zandomeneghi, D.; Aster, R. C.; Barclay, A. H.; Chaput, J. A.; Kyle, P. R.</p> <p>2011-12-01</p> <p>Erebus volcano (Ross Island), the most active volcano in Antarctica, is characterized by a persistent phonolitic lava lake at its summit and a wide range of seismic signals associated with its underlying long-lived magmatic system. The magmatic structure in a 3 by 3 km area around the summit has been imaged using high-quality data from a seismic tomographic experiment carried out during the 2008-2009 austral field season (Zandomeneghi et al., 2010). An array of 78 short period, 14 broadband, and 4 permanent Mount Erebus Volcano Observatory seismic stations and a program of 12 shots were used to model the velocity structure in the uppermost kilometer over the volcano conduit. P-<span class="hlt">wave</span> travel times were inverted for the <span class="hlt">3</span>-<span class="hlt">D</span> velocity structure using the shortest-time ray tracing (50-m grid spacing) and LSQR inversion (100-m node spacing) of a tomography code (Toomey et al., 1994) that allows for the inclusion of topography. Regularization is controlled by damping and smoothing weights and smoothing lengths, and addresses complications that are inherent in a strongly heterogeneous medium featuring rough topography and a dense parameterization and distribution of receivers/sources. The tomography reveals a composite distribution of very high and low P-<span class="hlt">wave</span> velocity anomalies (i.e., exceeding 20% in some regions), indicating a complex sub-lava-lake magmatic geometry immediately beneath the summit region and in surrounding areas, as well as the presence of significant high velocity shallow regions. The strongest and broadest low velocity zone is located W-NW of the crater rim, indicating the presence of an off-axis shallow magma body. This feature spatially corresponds to the inferred centroid source of VLP signals associated with Strombolian eruptions and lava lake refill (Aster et al., 2008). Other resolved structures correlate with the Side Crater and with lineaments of ice cave thermal anomalies extending NE and SW of the rim. High velocities in the summit area possibly</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DPPB10085V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DPPB10085V"><span>Nonlinear interactions of kink-unstable flux ropes and <span class="hlt">shear</span> Alfvén <span class="hlt">waves</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vincena, S.; Gekelman, W.; Dehaas, T.; Tripathi, S. K. P.</p> <p>2016-10-01</p> <p>Magnetic flux ropes and <span class="hlt">shear</span> Alfvén <span class="hlt">waves</span> occur simultaneously in plasmas ranging from solar prominences, the solar wind, and the earth's magnetotail. If the flux ropes evolve to become unstable to the kink mode, interactions between the kink oscillations and the <span class="hlt">shear</span> <span class="hlt">waves</span> can arise, and may even lead to nonlinear phenomena. Experiments aimed at elucidating such interactions are performed in the upgraded Large Plasma Device at UCLA. Flux ropes are generated using a 20 cm × 20 cm LaB6 cathode discharge (with L=18 m and β 0.1 .) The ropes are embedded in a otherwise current-free, cylindrical (r = 30 cm) ambient plasma produced by a second, BaO cathode. <span class="hlt">Shear</span> Alfvén <span class="hlt">waves</span> are launched using either internal antennas, or by modulating the BaO cathode-anode discharge current. In the latter case, kink unstable oscillations and driven <span class="hlt">shear</span> <span class="hlt">waves</span> nonlinearly generate sidebands about the higher <span class="hlt">shear</span> <span class="hlt">wave</span> frequency (evident in power spectra) via three-<span class="hlt">wave</span> coupling; this is demonstrated though bi-coherence calculations and k-matching. Informational complexity and entropy of the time series are also investigated. Future work will focus on antenna-launched <span class="hlt">waves</span> to control amplitude and frequency, as well as a possible evolution to a turbulent state. Work performed at the Basic Plasma Science Facility which is funded by the DoE OFES and the NSF.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4710687','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4710687"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> elastography in medullary thyroid carcinoma diagnostics</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gumińska, Anna; Bakuła-Zalewska, Elwira; Mlosek, Krzysztof; Słapa, Rafał Z.; Wareluk, Paweł; Krauze, Agnieszka; Ziemiecka, Agnieszka; Migda, Bartosz; Jakubowski, Wiesław; Dedecjus, Marek</p> <p>2015-01-01</p> <p><span class="hlt">Shear</span> <span class="hlt">wave</span> elastography (SWE) is a modern method for the assessment of tissue stiffness. There has been a growing interest in the use of this technique for characterizing thyroid focal lesions, including preoperative diagnostics. Aim The aim of the study was to assess the clinical usefulness of SWE in medullary thyroid carcinoma (MTC) diagnostics. Materials and methods A total of 169 focal lesions were identified in the study group (139 patients), including 6 MTCs in 4 patients (mean age: 45 years). B-mode ultrasound and SWE were performed using Aixplorer (SuperSonic, Aix-en-Provence), with a 4–15 MHz linear probe. The ultrasound was performed to assess the echogenicity and echostructure of the lesions, their margin, the halo sign, the height/width ratio (H/W ratio), the presence of calcifications and the vascularization pattern. This was followed by an analysis of maximum and mean Young's (E) modulus values for MTC (EmaxLR, EmeanLR) and the surrounding thyroid tissues (EmaxSR, EmeanSR), as well as mean E-values (EmeanLRz) for 2 mm region of interest in the stiffest zone of the lesion. The lesions were subject to pathological and/or cytological evaluation. Results The B-mode assessment showed that all MTCs were hypoechogenic, with no halo sign, and they contained micro- and/ or macrocalcifications. Ill-defined lesion margin were found in 4 out of 6 cancers; 4 out of 6 cancers had a H/W ratio > 1. Heterogeneous echostructure and type III vascularity were found in 5 out of 6 lesions. In the SWE, the mean value of EmaxLR for all of the MTCs was 89.5 kPa and (the mean value of EmaxSR for all surrounding tissues was) 39.7 kPa Mean values of EmeanLR and EmeanSR were 34.7 kPa and 24.4 kPa, respectively. The mean value of EmeanLRz was 49.2 kPa. Conclusions SWE showed MTCs as stiffer lesions compared to the surrounding tissues. The lesions were qualified for fine needle aspiration biopsy based on B-mode assessment. However, the diagnostic algorithm for MTC is based on the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMSM42A..05O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMSM42A..05O"><span>Observations of Plasma <span class="hlt">Waves</span> in the Colliding Jet Region of a <span class="hlt">3</span><span class="hlt">D</span> Magnetic Flux Rope Flanked by Two Active Reconnection X Lines at the Subsolar Magnetopause</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oieroset, M.; Sundkvist, D. J.; Chaston, C. C.; Phan, T. D.; Mozer, F.; McFadden, J. P.; Angelopoulos, V.; Andersson, L.; Eastwood, J. P.</p> <p>2014-12-01</p> <p>We have performed a detailed analysis of plasma and <span class="hlt">wave</span> observations in a <span class="hlt">3</span><span class="hlt">D</span> magnetic flux rope encountered by the THEMIS spacecraft at the subsolar magnetopause. The extent of the flux rope was ˜270 ion skin depths in the outflow direction, and it was flanked by two active reconnection X lines producing colliding plasma jets in the flux rope core where ion heating and suprathermal electrons were observed. The colliding jet region was highly dynamic and characterized by the presence of high-frequency <span class="hlt">waves</span> such as ion acoustic-like <span class="hlt">waves</span>, electron holes, and whistler mode <span class="hlt">waves</span> near the flux rope center and low-frequency kinetic Alfvén <span class="hlt">waves</span> over a larger region. We will discuss possible links between these <span class="hlt">waves</span> and particle heating.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5269522','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5269522"><span>Inability of <span class="hlt">shear-wave</span> elastography to distinguish malignant from benign prostate tissue – a comparison of biopsy, whole-mount sectioning and <span class="hlt">shear-wave</span> elastography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Görner, Claudia; Wendler, Johann Jakob; Liehr, Uwe-Bernd; Lux, Anke; Siedentopf, Sandra; Schostak, Martin; Pech, Maciej</p> <p>2016-01-01</p> <p>Aim This study was designed to assess the possible usefulness of <span class="hlt">shear-wave</span> elastography in differentiating between benign and malignant tissue in prostate neoplasia. Patients and methods A total of 120 prostate tissue samples were obtained from 10 patients treated by radical prostatectomy and investigated pre-operatively by ultrasound elastography followed by directed biopsy. After resection, whole-mount sectioning and histological examination was performed. The predictions based on <span class="hlt">shear-wave</span> elastography were compared with biopsy and histological results. Results The comparison between the results of <span class="hlt">shear-wave</span> elastography and those of biopsy was performed by receiver operating characteristic analysis, which suggested an optimum cut-off tissue elasticity value of 50 kPa, in agreement with earlier studies aimed at distinguishing between benign and malignant tissue. However, the diagnostic selectivity (and thus the diagnostic power) was poor (area under the curve 0.527, which hardly differs from the value of 0.500 that would correspond to a complete lack of predictive power); furthermore, application of this cut-off value to the samples led to a sensitivity of only 74% and a specificity of only 43%. An analogous comparison between the results of <span class="hlt">shear-wave</span> elastography and those of whole-mount histology, which itself is more reliable than biopsy, gave an even poorer diagnostic selectivity (sensitivity of 62%, specificity of 35%). Meaningful association with Gleason score was not found for D’Amico risk groups (p = 0.35). Conclusions The (negative) findings of this investigation add to the dissonance among results of studies investigating the possible value of <span class="hlt">shear-wave</span> elastography as a diagnostic tool to identify malignant neoplasia. There is a clear need for further research to elucidate the diversity of study results and to identify the usefulness, if any, of the method in question. PMID:28138406</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.5475M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.5475M"><span>Theoretical and numerical comparison of <span class="hlt">3</span><span class="hlt">D</span> numerical schemes for their accuracy with respect to P-<span class="hlt">wave</span> to S-<span class="hlt">wave</span> speed ratio</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moczo, P.; Kristek, J.; Galis, M.; Chaljub, E.; Chen, X.; Zhang, Z.</p> <p>2012-04-01</p> <p>Numerical modeling of earthquake ground motion in sedimentary basins and valleys often has to account for the P-<span class="hlt">wave</span> to S-<span class="hlt">wave</span> speed ratios (VP/VS) as large as five and even larger, mainly in sediments below groundwater level. The ratio can attain values larger than 10 - the unconsolidated lake sediments in Ciudad de México are a good example. At the same time, accuracy of the numerical schemes with respect to VP/VS has not been sufficiently analyzed. The numerical schemes are often applied without adequate check of the accuracy. We present theoretical analysis and numerical comparison of 18 <span class="hlt">3</span><span class="hlt">D</span> numerical time-domain explicit schemes for modeling seismic motion for their accuracy with the varying VP/VS. The schemes are based on the finite-difference, spectral-element, finite-element and discontinuous-Galerkin methods. All schemes are presented in a unified form. Theoretical analysis compares accuracy of the schemes in terms of local errors in amplitude and vector difference. In addition to the analysis we compare numerically simulated seismograms with exact solutions for canonical configurations. We compare accuracy of the schemes in terms of the local errors, grid dispersion and full wavefield simulations with respect to the structure of the numerical schemes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.207..848M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.207..848M"><span>Improving the <span class="hlt">shear</span> <span class="hlt">wave</span> velocity structure beneath Bucharest (Romania) using ambient vibrations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Manea, Elena Florinela; Michel, Clotaire; Poggi, Valerio; Fäh, Donat; Radulian, Mircea; Balan, Florin Stefan</p> <p>2016-11-01</p> <p>. This is essential to explore and resolve the deeper portions of the basin. The horizontal to vertical spectral ratio (H/V) curves provide important additional information about the structure and are here characterized by two major peaks. The first is attributed to the fundamental frequency of the basin, while the second can be interpreted as a mixture of the second higher mode of Rayleigh <span class="hlt">waves</span> and other types of <span class="hlt">waves</span> such as SH <span class="hlt">waves</span>. This hypothesis has been verified by comparing the H/V curves with the SH-<span class="hlt">wave</span> transfer function from the retrieved velocity structure. We could also approximate the SH transfer function with H/V ratios of earthquake recordings, providing additional verification of the robustness of the proposed velocity model. The Cretaceous bedrock depth was then inverted at each URS station from the fundamental frequency of resonance and using this model. A <span class="hlt">3</span>-<span class="hlt">D</span> geophysical model for Bucharest has been constructed based on the integration of the inverted velocity profiles and the available geological information using a geographic information system.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22490111','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22490111"><span>Modified ion-acoustic solitary <span class="hlt">waves</span> in plasmas with field-aligned <span class="hlt">shear</span> flows</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Saleem, H.; Haque, Q.</p> <p>2015-08-15</p> <p>The nonlinear dynamics of ion-acoustic <span class="hlt">waves</span> is investigated in a plasma having field-aligned <span class="hlt">shear</span> flow. A Korteweg-deVries-type nonlinear equation for a modified ion-acoustic <span class="hlt">wave</span> is obtained which admits a single pulse soliton solution. The theoretical result has been applied to solar wind plasma at 1 AU for illustration.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5669225','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5669225"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> polarization anisotropy in the upper mantle beneath Honshu, Japan</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ando, M.; Ishikawa, Y.; Yamazaki, F.</p> <p>1983-07-10</p> <p><span class="hlt">Shear</span> <span class="hlt">wave</span> polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth's surface is investigated using three-component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in Honshu, Japan. Eighty nine high-quality seismograms were selected from a period of 3 years. The data used in this study are restricted such that incidence angles are smaller than the critical angle of 30/sup 0/ to the earth's surface in order to avoid phase shifts in the <span class="hlt">shear</span> <span class="hlt">wave</span> train. To find directions of the maximum and minimum velocities in split <span class="hlt">shear</span> <span class="hlt">waves</span>, where <span class="hlt">shear</span> <span class="hlt">waves</span> are resolved into two phases with the maximum time separation, each set of the two horizontal component seismograms is rotated in the horizontal plane. The split <span class="hlt">shear</span> <span class="hlt">waves</span> thus obtained are again recombined after the correction of anisotropy, and the anisotropy-corrected particle motion is compared with the focal mechanism for a cross-check of the observed anisotropy. Directions of the maximum axes are plotted on azimuth-incidence angle stereograms at each station. The stereograms and the cross sections of seismic ray paths show that (1) the anisotropic material is distributed at intermediate locations between earthquake sources and receiving stations, and (2) the anisotropic region is separated into two parts: one in the north of the present study area with the polarization of the maximum velocity <span class="hlt">shear</span> <span class="hlt">wave</span> trending 0/sup 0/ to 30/sup 0/ from the north (north anisotropy) and the other in the south with it trending 90/sup 0/ to 120/sup 0/ (south anisotropy). The maximum time delays between the two <span class="hlt">shear</span> <span class="hlt">waves</span> along a vertical seismic ray is about 1 s for both the anisotropic regions. The horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km. perhaps prevalent in west Honshu.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.3438G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.3438G"><span><span class="hlt">3</span>-<span class="hlt">D</span> frequency-domain seismic <span class="hlt">wave</span> modelling in heterogeneous, anisotropic media using a Gaussian Quadrature Grid (GQG) approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greenhalgh, Stewart; Zhou, Bing; Maurer, Hansruedi</p> <p>2010-05-01</p> <p>We have developed a modified version of the spectral element method (SEM), called the Gaussian Quadrature Grid (GQG) approach, for frequency domain <span class="hlt">3</span><span class="hlt">D</span> seismic modelling in arbitrary heterogeneous, anisotropic media. The model may incorporate an arbitrary free-surface topography and irregular subsurface interfaces. Unlike the SEM ,it does not require a powerful mesh generator such as the Delauney Triangular or TetGen. Rather, the GQG approach replaces the element mesh with Gaussian quadrature abscissae to directly sample the physical properties of the model parameters and compute the weighted residual or variational integral. This renders the model discretisation simple and easily matched to the model topography, as well as direct control of the model paramterisation for subsequent inversion. In addition, it offers high accuracy in numerical modelling provided that an appropriate density of the Gaussian quadrature abscissae is employed. The second innovation of the GQG is the incorporation of a new implementation of perfectly matched layers to suppress artificial reflections from the domain margins. We employ PML model parameters (specified complex valued density and elastic moduli) rather than explicitly solving the governing <span class="hlt">wave</span> equation with a complex co-ordinate system as in conventional approaches. Such an implementation is simple, general, effective and easily extendable to any class of anisotropy and other numerical modelling methods. The accuracy of the GQG approach is controlled by the number of Gaussian quadrature points per minimum wavelength, the so-called sampling density. The optimal sampling density should be the one which enables high definition of geological characteristics and high precision of the variational integral evaluation and spatial differentiation. Our experiments show that satisfactory results can be obtained using sampling densities of 5 points per minimum wavelength. Efficiency of the GQG approach mainly depends on the linear</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/21537273','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/21537273"><span>Generation of <span class="hlt">shear</span> Alfven <span class="hlt">waves</span> by a rotating magnetic field source: Three-dimensional simulations</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Karavaev, A. V.; Gumerov, N. A.; Papadopoulos, K.; Shao, Xi; Sharma, A. S.; Gekelman, W.; Wang, Y.; Van Compernolle, B.; Pribyl, P.; Vincena, S.</p> <p>2011-03-15</p> <p>The paper discusses the generation of polarized <span class="hlt">shear</span> Alfven <span class="hlt">waves</span> radiated from a rotating magnetic field source created via a phased orthogonal two-loop antenna. A semianalytical three-dimensional cold two-fluid magnetohydrodynamics model was developed and compared with recent experiments in the University of California, Los Angeles large plasma device. Comparison of the simulation results with the experimental measurements and the linear <span class="hlt">shear</span> Alfven <span class="hlt">wave</span> properties, namely, spatiotemporal <span class="hlt">wave</span> structure, a dispersion relation with nonzero transverse <span class="hlt">wave</span> number, the magnitude of the <span class="hlt">wave</span> dependences on the <span class="hlt">wave</span> frequency, show good agreement. From the simulations it was found that the energy of the Alfven <span class="hlt">wave</span> generated by the rotating magnetic field source is distributed between the kinetic energy of ions and electrons and the electromagnetic energy of the <span class="hlt">wave</span> as: {approx}1/2 is the energy of the electromagnetic field, {approx}1/2 is the kinetic energy of the ion fluid, and {approx}2.5% is the kinetic energy of electron fluid for the experiment. The <span class="hlt">wave</span> magnetic field power calculated from the experimental data and using a fluid model differ by {approx}1% and is {approx}250 W for the experimental parameters. In both the experiment and the three-dimensional two-fluid magnetohydrodynamics simulations the rotating magnetic field source was found to be very efficient for generating <span class="hlt">shear</span> Alfven <span class="hlt">waves</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006APS..DPPBP1061I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006APS..DPPBP1061I"><span>Suppression of drift <span class="hlt">wave</span> instability due to <span class="hlt">sheared</span> field-aligned flow and negative ions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ichiki, Ryuta; Hayashi, Kenichiro; Kaneko, Toshiro; Hatakeyama, Rikizo</p> <p>2006-10-01</p> <p><span class="hlt">Sheared</span> field-aligned plasma flow is a significant topic in space/circumterrestrial plasmas. Taking into account negative ions or dust grains will make the space plasma physics more general and accurate. Using the QT-Upgrade Machine, we have conducted laboratory experiments to examine negative ion effects on <span class="hlt">shear</span>-modified drift <span class="hlt">waves</span>. Field-aligned K^+ ion flow and its <span class="hlt">shear</span> strength are controlled with a concentrically segmented W hot plate. Negative ions SF6^- are produced by introducing SF6 gas in the plasma. The drift <span class="hlt">wave</span> shows a gradual monotonic decrease in amplitude as the <span class="hlt">shear</span> strength is increased from zero. However, as the <span class="hlt">shear</span> strength is decreased from zero to negative values, the amplitude increases up to a certain <span class="hlt">shear</span> strength and rapidly decreases after the peaking. The negative ion introduction, in general, suppresses this instability while retaining the dependence of the amplitude on the <span class="hlt">shear</span>. These <span class="hlt">wave</span> characteristics are interpreted using the theories of current-driven (kinetic) and of D’Angelo (fluid) instabilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMNS13A1146P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMNS13A1146P"><span>Urban <span class="hlt">shear-wave</span> reflection seismics: Reconstruction support by combined shallow seismic and engineering geology investigations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Polom, U.; Guenther, A.; Arsyad, I.; Wiyono, P.; Krawczyk, C. M.</p> <p>2009-12-01</p> <p>After the big 2004 Sumatra-Andaman earthquake, the massive reconstruction activities in the Aceh province (Northern Sumatra) were promoted by the Republic of Indonesia and the Federal Ministry of Economic Cooperation and Development. The aims of the project MANGEONAD (Management of Georisk Nanggroe Aceh Darussalam). are to establish geoscientific on the ground support for a sustainable development and management of save building constructions, lifelines, infrastructure and also natural resources. Therefore, shallow <span class="hlt">shear-wave</span> reflection seismics was applied in close combination to engineering geology investigations in the period between 2005-2009 since depth and internal structure of the Krueng Aceh River delta (mainly young alluvial sediments) were widely unknown. Due to the requirements in the densely populated Banda Aceh region, lacking also traffic infrastructure, a small and lightweight engineering seismic setup of high mobility and high subsurface resolution capability was chosen. The S-<span class="hlt">wave</span> land streamer system with 48 channels was applied successfully together with the ELVIS vibratory source using S- and P-<span class="hlt">waves</span> on paved roads within the city of Banda Aceh. The performance of the S-<span class="hlt">wave</span> system enabled the detailed seismic investigation of the shallow subsurface down to 50-150 m depth generating shaking frequencies between 20 Hz to 200 Hz. This also provides depth information extending the maximum depths of boreholes and Standard Penetrometer Testings (SPT), which could only be applied to max. 20 m depth. To integrate the results gained from all three methods, and further to provide a fast statistical analysis tool for engineering use, the Information System Engineering Geology (ISEG, BGR) was developed. This geospatial information tool includes the seismic data, all borehole information, geotechnical SPT and laboratory results from samples available in the investigation area. Thereby, the geotechnical <span class="hlt">3</span><span class="hlt">D</span> analysis of the subsurface units is enabled. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3371183','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3371183"><span>Intracardiac Echocardiography (ICE) Measurement of Dynamic Myocardial Stiffness with <span class="hlt">Shear</span> <span class="hlt">Wave</span> Velocimetry</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hollender, Peter J.; Wolf, Patrick D.; Goswami, Robi; Trahey, Gregg E.</p> <p>2012-01-01</p> <p>Acoustic Radiation Force (ARF)-based methods have been demonstrated to be a viable tool for noninvasively estimating tissue elastic properties, and <span class="hlt">shear</span> <span class="hlt">wave</span> velocimetry has been used to quantitatively measure the stiffening and relaxation of myocardial tissue in open-chest experiments. Dynamic stiffness metrics may prove to be indicators for certain cardiac diseases, but a clinically-viable means of remotely generating and tracking transverse <span class="hlt">wave</span> propagation in myocardium is needed. Intracardiac echocardiography (ICE) catheter-tip transducers are demonstrated here as a viable tool for making this measurement. ICE probes achieve favorable proximity to the myocardium, enabling the use of <span class="hlt">shear</span> <span class="hlt">wave</span> velocimetry from within the right ventricle throughout the cardiac cycle. This work describes the techniques used to overcome the challenges of using a small probe to perform ARF-driven <span class="hlt">shear</span> <span class="hlt">wave</span> velocimetry, and presents in vivo porcine data showing the effectiveness of this method in the interventricular septum. Acoustic Radiation Force (ARF)-based methods have been demonstrated to be a viable tool for noninvasively estimating tissue elastic properties, and <span class="hlt">shear</span> <span class="hlt">wave</span> velocimetry has been used to quantitatively measure the stiffening and relaxation of myocardial tissue in open-chest experiments. Dynamic stiffness metrics may prove to be indicators for certain cardiac diseases, but a clinically-viable means of remotely generating and tracking transverse <span class="hlt">wave</span> propagation in myocardium is needed. Intracardiac echocardiography (ICE) catheter-tip transducers are demonstrated here as a viable tool for making this measurement. ICE probes achieve favorable proximity to the myocardium, enabling the use of <span class="hlt">shear</span> <span class="hlt">wave</span> velocimetry from within the right ventricle throughout the cardiac cycle. This work describes the techniques used to overcome the challenges of using a small probe to perform ARF-driven <span class="hlt">shear</span> <span class="hlt">wave</span> velocimetry, and presents in vivo porcine data showing the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28214750','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28214750"><span>Propagation of thickness <span class="hlt">shear</span> <span class="hlt">waves</span> in a periodically corrugated quartz crystal plate and its application exploration in acoustic <span class="hlt">wave</span> filters.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Peng; Cheng, Li</p> <p>2017-02-07</p> <p>The propagation of thickness <span class="hlt">shear</span> <span class="hlt">waves</span> in a periodically corrugated quartz crystal plate is investigated in the present paper using a power series expansion technique. In the proposed simulation model, an equivalent continuity of <span class="hlt">shear</span> stress moment is introduced as an approximation to handle sectional interfaces with abrupt thickness changes. The Bloch theory is applied to simulate the band structures for three different thickness variation patterns. It is shown that the power series expansion method exhibits good convergence and accuracy, in agreement with results by finite element method (FEM). A broad stop band can be obtained in the power transmission spectra owing to the trapped thickness <span class="hlt">shear</span> modes excited by the thickness variation, whose physical mechanism is totally different from the well-known Bragg scattering effect and is insensitive to the structural periodicity. Based on the observed energy trapping phenomenon, an acoustic <span class="hlt">wave</span> filter is proposed in a quartz plate with sectional decreasing thickness, which inhibits <span class="hlt">wave</span> propagation in different regions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28257065','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28257065"><span>A Guided <span class="hlt">Wave</span> Sensor Enabling Simultaneous Wavenumber-Frequency Analysis for Both Lamb and <span class="hlt">Shear</span>-Horizontal <span class="hlt">Waves</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ren, Baiyang; Cho, Hwanjeong; Lissenden, Cliff J</p> <p>2017-03-01</p> <p>Guided <span class="hlt">waves</span> in plate-like structures have been widely investigated for structural health monitoring. Lamb <span class="hlt">waves</span> and <span class="hlt">shear</span> horizontal (SH) <span class="hlt">waves</span>, two commonly used types of <span class="hlt">waves</span> in plates, provide different benefits for the detection of various types of defects and material degradation. However, there are few sensors that can detect both Lamb and SH <span class="hlt">waves</span> and also resolve their modal content, namely the wavenumber-frequency spectrum. A sensor that can detect both <span class="hlt">waves</span> is desirable to take full advantage of both types of <span class="hlt">waves</span> in order to improve sensitivity to different discontinuity geometries. We demonstrate that polyvinylidene difluoride (PVDF) film provides the basis for a multi-element array sensor that detects both Lamb and SH <span class="hlt">waves</span> and also measures their modal content, i.e., the wavenumber-frequency spectrum.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5375774','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5375774"><span>A Guided <span class="hlt">Wave</span> Sensor Enabling Simultaneous Wavenumber-Frequency Analysis for Both Lamb and <span class="hlt">Shear</span>-Horizontal <span class="hlt">Waves</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ren, Baiyang; Cho, Hwanjeong; Lissenden, Cliff J.</p> <p>2017-01-01</p> <p>Guided <span class="hlt">waves</span> in plate-like structures have been widely investigated for structural health monitoring. Lamb <span class="hlt">waves</span> and <span class="hlt">shear</span> horizontal (SH) <span class="hlt">waves</span>, two commonly used types of <span class="hlt">waves</span> in plates, provide different benefits for the detection of various types of defects and material degradation. However, there are few sensors that can detect both Lamb and SH <span class="hlt">waves</span> and also resolve their modal content, namely the wavenumber-frequency spectrum. A sensor that can detect both <span class="hlt">waves</span> is desirable to take full advantage of both types of <span class="hlt">waves</span> in order to improve sensitivity to different discontinuity geometries. We demonstrate that polyvinylidene difluoride (PVDF) film provides the basis for a multi-element array sensor that detects both Lamb and SH <span class="hlt">waves</span> and also measures their modal content, i.e., the wavenumber-frequency spectrum. PMID:28257065</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JMSA....9..156L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JMSA....9..156L"><span>Using a time-domain higher-order boundary element method to simulate <span class="hlt">wave</span> and current diffraction from a <span class="hlt">3</span>-<span class="hlt">D</span> body</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Zhen; Teng, Bin; Ning, De-Zhi; Sun, Liang</p> <p>2010-06-01</p> <p>To study <span class="hlt">wave</span>-current actions on <span class="hlt">3</span>-<span class="hlt">D</span> bodies a time-domain numerical model was established using a higher-order boundary element method (HOBEM). By assuming small flow velocities, the velocity potential could be expressed for linear and higher order components by perturbation expansion. A 4th-order Runge-Kutta method was applied for time marching. An artificial damping layer was adopted at the outer zone of the free surface mesh to dissipate scattering <span class="hlt">waves</span>. Validation of the numerical method was carried out on run-up, <span class="hlt">wave</span> exciting forces, and mean drift forces for <span class="hlt">wave</span>-currents acting on a bottom-mounted vertical cylinder. The results were in close agreement with the results of a frequency-domain method and a published time-domain method. The model was then applied to compute <span class="hlt">wave</span>-current forces and run-up on a Seastar mini tension-leg platform.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.6106L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.6106L"><span>Changes in <span class="hlt">shear-wave</span> splitting before volcanic eruptions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Sha; Crampin, Stuart</p> <p>2015-04-01</p> <p>We have shown that observations of <span class="hlt">shear-wave</span> splitting (SWS) monitor stress-accumulation and stress-relaxation before earthquakes which allows the time, magnitude, and in some circumstances fault-plane of impending earthquakes to be stress-forecast. (We call this procedure stress-forecasting rather than predicting or forecasting to emphasise the different formalism.) We have stress-forecast these parameters successfully three-days before a 1988 M5 earthquake in SW Iceland, and identified characteristic anomalies retrospectively before ~16 other earthquakes in Iceland and elsewhere. SWS monitors microcrack geometry and shows that microcracks are so closely spaced that they verge on fracturing and earthquakes. Phenomena verging on failure in this way are critical-systems with 'butterfly wings' sensitivity. Such critical-systems are very common. The Earth is an archetypal complex heterogeneous interactive phenomenon and must be expected to be a critical-system. We claim this critical system as a New Geophysics of a critically-microcracked rock mass. Such critical systems impose a range of fundamentally-new properties on conventional sub-critical physics/geophysics, one of which is universality. Consequently it is expected that we observe similar stress-accumulation and stress-relaxation before volcanic eruptions to those before earthquakes. There are three eruptions where appropriate changes in SWS have been observed similar to those observed before earthquakes. These are: the 1996 Gjálp fissure eruption, Vatnajökull, Iceland; a 2001 flank eruption on Mount Etna, Sicily (reported by Francesca Bianco, INGV, Naples); and the 2010 Eyjafjajökull ash-cloud eruption, SW Iceland. These will be presented in the same normalised format as is used before earthquakes. The 1996 Gjálp eruption showed a 2½-month stress-accumulation, and a ~1-year stress-relaxation (attributed to the North Atlantic Ridge adjusting to the magma injection beneath the Vatnajökull Ice Cap). The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JGRB..11711301P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JGRB..11711301P"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> velocities in the Pampean flat-slab region from Rayleigh <span class="hlt">wave</span> tomography: Implications for slab and upper mantle hydration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Porter, Ryan; Gilbert, Hersh; Zandt, George; Beck, Susan; Warren, Linda; Calkins, Josh; Alvarado, Patricia; Anderson, Megan</p> <p>2012-11-01</p> <p>The Pampean flat-slab region, located in central Argentina and Chile between 29° and 34°S, is considered a modern analog for Laramide flat-slab subduction within western North America. Regionally, flat-slab subduction is characterized by the Nazca slab descending to ˜100 km depth, flattening out for ˜300 km laterally before resuming a more "normal" angle of subduction. Flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of deformation and the cessation of volcanism within the region. To better understand flat-slab subduction we combine ambient-noise tomography and earthquake-generated surface <span class="hlt">wave</span> measurements to calculate a regional <span class="hlt">3</span><span class="hlt">D</span> <span class="hlt">shear</span> velocity model for the region. <span class="hlt">Shear</span> <span class="hlt">wave</span> velocity variations largely relate to changes in lithology within the crust, with basins and bedrock exposures clearly defined as low- and high-velocity regions, respectively. We argue that subduction-related hydration plays a significant role in controlling <span class="hlt">shear</span> <span class="hlt">wave</span> velocities within the upper mantle. In the southern part of the study area, where normal-angle subduction is occurring, the slab is visible as a high-velocity body with a low-velocity mantle wedge above it, extending eastward from the active arc. Where flat-slab subduction is occurring, slab velocities increase to the east while velocities in the overlying lithosphere decrease, consistent with the slab dewatering and gradually hydrating the overlying mantle. The hydration of the slab may be contributing to the excess buoyancy of the subducting oceanic lithosphere, helping to drive flat-slab subduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4314720','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4314720"><span>Modeling Transversely Isotropic, Viscoelastic, Incompressible Tissue-like Materials with Application in Ultrasound <span class="hlt">Shear</span> <span class="hlt">Wave</span> Elastography</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Qiang, Bo; Brigham, John C.; Aristizabal, Sara; Greenleaf, James F.; Zhang, Xiaoming; Urban, Matthew W.</p> <p>2015-01-01</p> <p>In this paper, we propose a method to model the <span class="hlt">shear</span> <span class="hlt">wave</span> propagation in transversely isotropic, viscoelastic and incompressible media. The targeted application is ultrasound-based <span class="hlt">shear</span> <span class="hlt">wave</span> elastography for viscoelasticity measurements in anisotropic tissues such as the kidney and skeletal muscles. The proposed model predicts that if the viscoelastic parameters both across and along fiber directions can be characterized as a Voigt material, then the spatial phase velocity at any angle is also governed by a Voigt material model. Further, with the aid of Taylor expansions, it is shown that the spatial group velocity at any angle is close to a Voigt type for weakly attenuative materials within a certain bandwidth. The model is implemented in a finite element code by a time domain explicit integration scheme and <span class="hlt">shear</span> <span class="hlt">wave</span> simulations are conducted. The results of the simulations are analyzed to extract the <span class="hlt">shear</span> <span class="hlt">wave</span> elasticity and viscosity for both the spatial phase and group velocities. The estimated values match well with theoretical predictions. The proposed theory is further verified by an ex vivo tissue experiment measured in a porcine skeletal muscle by an ultrasound <span class="hlt">shear</span> <span class="hlt">wave</span> elastography method. The applicability of the Taylor expansion to analyze the spatial velocities is also discussed. We demonstrate that the approximations from the Taylor expansions are subject to errors when the viscosities across or along the fiber directions are large or the maximum frequency considered is beyond the bandwidth defined by radii of convergence of the Taylor expansions. PMID:25591921</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S53B2807P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S53B2807P"><span>Near Source Structural Effects on Seismic <span class="hlt">Waves</span>: Implication for <span class="hlt">Shear</span> Motion Generation During SPE-4Prime</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pitarka, A.</p> <p>2015-12-01</p> <p>Arben Pitarka, Souheil M. Ezzedine, Oleg Y. Vorobiev, Tarabay H. Antoun, Lew A. Glenn, William R. Walter, Robert J. Mellors, and Evan Hirakawa. We have analyzed effects of <span class="hlt">wave</span> scattering due to near-source structural complexity and sliding joint motion on generation of <span class="hlt">shear</span> <span class="hlt">waves</span> from SPE-4Pprime, a shallow chemical explosion conducted at the Nevada National Security Site. In addition to analyzing far-field ground motion recorded on three-component geophones, we performed high-frequency simulations of the explosion using a finite difference method and heterogeneous media with stochastic variability. The stochastic variations of seismic velocity were modeled using Gaussian correlation functions. Using simulations and recorded waveforms we demonstrate the implication of <span class="hlt">wave</span> scattering on generation of <span class="hlt">shear</span> motion, and show the gradual increase of <span class="hlt">shear</span> motion energy as the <span class="hlt">waves</span> propagate through media with variable scattering. The amplitude and duration of <span class="hlt">shear</span> <span class="hlt">waves</span> resulting from <span class="hlt">wave</span> scattering are found to be dependent on the model complexity and to a lesser extent to source distance. Analysis of <span class="hlt">shear</span>-motion generation due to joint motion were conducted using numerical simulations performed with GEODYN-L, a parallelized Lagrangian hydrocode, while a stochastic approach was used in depicting the properties of joints. Separated effects of source and <span class="hlt">wave</span> scattering on <span class="hlt">shear</span> motion generation will be shown through simulated motion. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 Release Number: LLNL-ABS-675570</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1613974M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1613974M"><span><span class="hlt">3</span><span class="hlt">D</span> geological to geophysical modelling and seismic <span class="hlt">wave</span> propagation simulation: a case study from the Lalor Lake VMS (Volcanogenic Massive Sulphides) mining camp</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miah, Khalid; Bellefleur, Gilles</p> <p>2014-05-01</p> <p>The global demand for base metals, uranium and precious metals has been pushing mineral explorations at greater depth. Seismic techniques and surveys have become essential in finding and extracting mineral rich ore bodies, especially for deep VMS mining camps. Geophysical parameters collected from borehole logs and laboratory measurements of core samples provide preliminary information about the nature and type of subsurface lithologic units. Alteration halos formed during the hydrothermal alteration process contain ore bodies, which are of primary interests among geologists and mining industries. It is known that the alteration halos are easier to detect than the ore bodies itself. Many <span class="hlt">3</span><span class="hlt">D</span> geological models are merely projection of 2D surface geology based on outcrop inspections and geochemical analysis of a small number of core samples collected from the area. Since a large scale <span class="hlt">3</span><span class="hlt">D</span> multicomponent seismic survey can be prohibitively expensive, performance analysis of such geological models can be helpful in reducing exploration costs. In this abstract, we discussed challenges and constraints encountered in geophysical modelling of ore bodies and surrounding geologic structures from the available coarse <span class="hlt">3</span><span class="hlt">D</span> geological models of the Lalor Lake mining camp, located in northern Manitoba, Canada. Ore bodies in the Lalor lake VMS camp are rich in gold, zinc, lead and copper, and have an approximate weight of 27 Mt. For better understanding of physical parameters of these known ore bodies and potentially unknown ones at greater depth, we constructed a fine resolution <span class="hlt">3</span><span class="hlt">D</span> seismic model with dimensions: 2000 m (width), 2000 m (height), and 1500 m (vertical depth). Seismic properties (P-<span class="hlt">wave</span>, S-<span class="hlt">wave</span> velocities, and density) were assigned based on a previous rock properties study of the same mining camp. <span class="hlt">3</span><span class="hlt">D</span> finite-difference elastic <span class="hlt">wave</span> propagation simulation was performed in the model using appropriate parameters. The generated synthetic <span class="hlt">3</span><span class="hlt">D</span> seismic data was then compared to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.4467V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.4467V"><span><span class="hlt">Shear</span> <span class="hlt">wave</span> identification near by shallow seismic source</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vilhelm, Jan; Rudajev, Vladimír.; Živor, Roman</p> <p>2010-05-01</p> <p>Interference of P- and S-<span class="hlt">waves</span> occurs during the first period of P-<span class="hlt">wave</span> when the shallow seismic measurement is realized near the seismic source (the distance is less or equal to one P-<span class="hlt">wave</span> wavelength). Polarization analysis method (particle motion) is suitable for the determination of S-<span class="hlt">wave</span> arrival time in these conditions. Three component geophones are usually used in this case for the registration of seismic <span class="hlt">waves</span> generated by a hammer blow. With regard to P- and S-<span class="hlt">waves</span> polarization it is advantageous to orientate the three component orthogonal system of geophones so that separate components make an angle of 35.26° to horizontal plane (Galperin geophone configuration). Azimuth angle between separate components is 120° in this case. This configuration insures the equivalent gravity force moments affect all the three components in the same way. It is in the contrast to the standard arrangement of the three component geophone with two horizontal and one vertical component. The inclined arrangement results in equal frequency responses for all the three components. Phase and amplitude characteristics between the components should therefore be the same. This facilitates the S-<span class="hlt">wave</span> arrival detection. An example of application of this method to the determination of seismic <span class="hlt">wave</span> propagation velocity anisotropy is presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010061424&hterms=Sound+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DSound%2Bwaves','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010061424&hterms=Sound+waves&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DSound%2Bwaves"><span>Comparison with Analytical Solution: Generation and Radiation of Acoustic <span class="hlt">Waves</span> from a 2-D <span class="hlt">Shear</span> Layer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dahl, Milo D.</p> <p>2000-01-01</p> <p>An acoustic source inside of a 2-D jet excites an instability <span class="hlt">wave</span> in the <span class="hlt">shear</span> layer resulting in sound radiating away from the <span class="hlt">shear</span> layer. Solve the linearized Euler equations to predict the sound radiation outside of the jet. The jet static pressure is assumed to be constant. The jet flow is parallel and symmetric about the x-axis. Use a symmetry boundary condition along the x-axis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70026224','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70026224"><span>Measured temperature and pressure dependence of compressional (Vp) and <span class="hlt">shear</span> (Vs) <span class="hlt">wave</span> speeds in compacted, polycrystalline ice lh</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Helgerud, M.B.; Waite, W.F.; Kirby, S.H.; Nur, A.</p> <p>2003-01-01</p> <p>We report on laboratory measurements of compressional- and <span class="hlt">shear-wave</span> speeds in a compacted, polycrystalline ice-Ih sample. The sample was made from triply distilled water that had been frozen into single crystal ice, ground into small grains, and sieved to extract the 180-250 ??m diameter fraction. Porosity was eliminated from the sample by compacting the granular ice between a hydraulically driven piston and a fixed end plug, both containing <span class="hlt">shear-wave</span> transducers. Based on simultaneous compressional- and <span class="hlt">shear-wave</span>-speed measurements, we calculated Poisson's ratio and compressional-<span class="hlt">wave</span>, bulk, and <span class="hlt">shear</span> moduli from -20 to -5??C and 22 to 33 MPa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22218322','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22218322"><span>Nonlinear electron acoustic <span class="hlt">waves</span> in presence of <span class="hlt">shear</span> magnetic field</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dutta, Manjistha; Khan, Manoranjan; Ghosh, Samiran; Chakrabarti, Nikhil</p> <p>2013-12-15</p> <p>Nonlinear electron acoustic <span class="hlt">waves</span> are studied in a quasineutral plasma in the presence of a variable magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary positively charged ion background. Linear analysis of the governing equations manifests dispersion relation of electron magneto sonic <span class="hlt">wave</span>. Whereas, nonlinear <span class="hlt">wave</span> dynamics is being investigated by introducing Lagrangian variable method in long wavelength limit. It is shown from finite amplitude analysis that the nonlinear <span class="hlt">wave</span> characteristics are well depicted by KdV equation. The <span class="hlt">wave</span> dispersion arising in quasineutral plasma is induced by transverse magnetic field component. The results are discussed in the context of plasma of Earth's magnetosphere.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22243085','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22243085"><span>Large-scale magnetic field generation by randomly forced <span class="hlt">shearing</span> <span class="hlt">waves</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Heinemann, T; McWilliams, J C; Schekochihin, A A</p> <p>2011-12-16</p> <p>A rigorous theory for the generation of a large-scale magnetic field by random nonhelically forced motions of a conducting fluid combined with a linear <span class="hlt">shear</span> is presented in the analytically tractable limit of low magnetic Reynolds number (Rm) and weak <span class="hlt">shear</span>. The dynamo is kinematic and due to fluctuations in the net (volume-averaged) electromotive force. This is a minimal proof-of-concept quasilinear calculation aiming to put the <span class="hlt">shear</span> dynamo, a new effect recently found in numerical experiments, on a firm theoretical footing. Numerically observed scalings of the <span class="hlt">wave</span> number and growth rate of the fastest-growing mode, previously not understood, are derived analytically. The simplicity of the model suggests that <span class="hlt">shear</span> dynamo action may be a generic property of <span class="hlt">sheared</span> magnetohydrodynamic turbulence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813745S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813745S"><span>Water-<span class="hlt">waves</span> on linear <span class="hlt">shear</span> currents. A comparison of experimental and numerical results.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Simon, Bruno; Seez, William; Touboul, Julien; Rey, Vincent; Abid, Malek; Kharif, Christian</p> <p>2016-04-01</p> <p>Propagation of water <span class="hlt">waves</span> can be described for uniformly <span class="hlt">sheared</span> current conditions. Indeed, some mathematical simplifications remain applicable in the study of <span class="hlt">waves</span> whether there is no current or a linearly <span class="hlt">sheared</span> current. However, the widespread use of mathematical <span class="hlt">wave</span> theories including <span class="hlt">shear</span> has rarely been backed by experimental studies of such flows. New experimental and numerical methods were both recently developed to study <span class="hlt">wave</span> current interactions for constant vorticity. On one hand, the numerical code can simulate, in two dimensions, arbitrary non-linear <span class="hlt">waves</span>. On the other hand, the experimental methods can be used to generate <span class="hlt">waves</span> with various <span class="hlt">shear</span> conditions. Taking advantage of the simplicity of the experimental protocol and versatility of the numerical code, comparisons between experimental and numerical data are discussed and compared with linear theory for validation of the methods. ACKNOWLEDGEMENTS The DGA (Direction Générale de l'Armement, France) is acknowledged for its financial support through the ANR grant N° ANR-13-ASTR-0007.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9710E..0YZ','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9710E..0YZ"><span>A comparative study of <span class="hlt">shear</span> <span class="hlt">wave</span> speed estimation techniques in optical coherence elastography applications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zvietcovich, Fernando; Yao, Jianing; Chu, Ying-Ju; Meemon, Panomsak; Rolland, Jannick P.; Parker, Kevin J.</p> <p>2016-03-01</p> <p>Optical Coherence Elastography (OCE) is a widely investigated noninvasive technique for estimating the mechanical properties of tissue. In particular, vibrational OCE methods aim to estimate the <span class="hlt">shear</span> <span class="hlt">wave</span> velocity generated by an external stimulus in order to calculate the elastic modulus of tissue. In this study, we compare the performance of five acquisition and processing techniques for estimating the <span class="hlt">shear</span> <span class="hlt">wave</span> speed in simulations and experiments using tissue-mimicking phantoms. Accuracy, contrast-to-noise ratio, and resolution are measured for all cases. The first two techniques make the use of one piezoelectric actuator for gener