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Sample records for group velocity tomography

  1. Eurasian surface wave tomography: Group velocities

    NASA Astrophysics Data System (ADS)

    Ritzwoller, Michael H.; Levshin, Anatoli L.

    1998-03-01

    This paper presents the results of a study of the dispersion characteristics of broadband fundamental surface waves propagating across Eurasia. The study is broader band, displays denser and more uniform data coverage, and demonstrates higher resolution than previous studies of Eurasia performed on this scale. In addition, the estimated group velocity maps reveal the signatures of geological and tectonic features never before displayed in similar surface wave studies. We present group velocity maps from 20 s to 200 s period for Rayleigh waves and from 20 s to 125 s for Love waves. Broadband waveform data from about 600 events from 1988 through 1995 recorded at 83 individual stations across Eurasia have produced about 9000 paths for which individual dispersion curves have been estimated. Dispersion curves from similar paths are clustered to reduce redundancy, to identify outliers for rejection, and to assign uncertainty estimates. On average, measurement uncertainty is about 0.030-0.040 km/s and is not a strong function of frequency. Resolution is estimated from "checker-board" tests, and we show that average resolutions across Eurasia range from 5° to 7.5° but degrade at periods above about 100 s and near the periphery of the maps. The estimated maps produce a variance reduction relative to the Preliminary Reference Earth Model (PREM) of more than 90% for Rayleigh waves below 60 s period but reduce to about 70% between 80 and 200 s period. For Love waves, variance reductions are similar, being above 90% for most periods below 100 s and falling to 70% at 150 s. Synthetic experiments are presented to estimate the biases that theoretical approximations should impart to the group velocity maps, in particular source group time shifts, azimuthal anisotropy, and systematic event mislocations near subducting slabs. The most significant problems are probably caused by azimuthal anisotropy, but above 100 s the effect of source group time shifts may also be appreciable

  2. Rayleigh Wave Group Velocity Distributions for East Asia from Ambient Seismic Noise Tomography

    NASA Astrophysics Data System (ADS)

    Witek, M.; van der Lee, S.; Kang, T. S.; Chang, S. J.; Ning, S.; Ning, J.

    2014-12-01

    We have collected continuous vertical-component broadband data from 1109 seismic stations in regional networks across China, Korea, and Japan for the year 2011 to perform the largest surface wave tomography study in the region. Using this data set, we have measured over half a million Rayleigh wave group velocity dispersion curves from 1-year stacks of station-pair ambient seismic noise cross-correlations. Quality control is performed by measuring the coherency of the positive and negative lag time sides of the cross-correlations. If the coherency is below an empirically determined threshold, the dispersion curve is measured on the side of the highest SNR. Otherwise, the positive and negative sides of the cross-correlation are averaged before dispersion curve measurement. Group velocity measurements for which the SNR was less than 10 are discarded. The Rayleigh wave group velocity dispersion curves are regionalized on a tessellated spherical shell grid in the period range 10 to 50 s to produce maps of Rayleigh wave group velocity distributions. Preliminary maps at 10 seconds period match well with geologic features at the surface. In particular, we observe low group velocities in the Songliao, Bohai Bay, Sichuan, Ordos, Tarim, and Junggar Basins in China, and the Ulleung and Yamato Basins in the East Sea (Sea of Japan). Higher group velocities are observed in regions with less sediment cover. At periods around 30 s, we observe group velocity decreases going from east to west in China, representing an overall trend of crustal thickening due to the collision between the Indian and Eurasian plates. The Ordos and Sichuan blocks show higher group velocities relative to the eastern margin of the Tibetan Plateau, possibly reflecting low temperatures in these cratons.

  3. Noise directivity and group velocity tomography in a region with small velocity contrasts: the northern Baltic shield

    NASA Astrophysics Data System (ADS)

    Poli, P.; Pedersen, H. A.; Campillo; , M.; Polenet/Lapnet Working Group

    2013-01-01

    Ambient noise tomography (ANT) is widely used to image strong velocity variations within the upper crust. Using careful processing, we obtained a 3-D model of shear velocities in the upper crust beneath northern Finland, where the lateral velocity variations are less than 3 per cent. As part of the tomography, the noise field is analysed. It is strongly heterogeneous but the signal-to-noise ratio is sufficient to obtain stable dispersion curves for all profile azimuths. Our results show that the directions of dominant noise sources of Rayleigh and Love waves are the same, but the amplitude distribution with azimuth is different for the two types of waves. More intriguingly, the high frequency Love waves are dominated by a mixture of higher modes rather than the fundamental mode. The reconstructed 3-D model shows the Lapland Granulite Belt as a high velocity body with a limit at surface in excellent agreement with geological observations at surface. Following this interface at depth, our results are compatible with previous studies suggesting an Archean north oriented subduction.

  4. Group Velocity Tomography for Eastern Mexico and Crustal Structure for Tehuantepec Isthmus

    NASA Astrophysics Data System (ADS)

    Córdoba Montiel, F.; Iglesias, A.; Melgar, D.; Singh, S.; Perez-Campos, X.

    2013-05-01

    We use seismic noise records from the broadband network of the Mexican National Seismological Service (Servicio Sismológico Nacional) and from MASE and VEOX stations (two temporal seismic experiments) to compute the vertical-vertical component of noise cross correlations for station pairs. MASE (Mesoamerican Seismic Experiment) consisted of one hundred stations deployed along a profile perpendicular to the trench and starting in Acapulco,Gro. Mex. This experiment ran from December 2004 until May, 2007. Fifty of these stations were relocated in a N-S profile crossing the Tehuantepec Isthmus from the Gulf of Mexico to the Pacific coast. These stations were operated from July 2007 until February 2009 and this stage of the experiment was called VEOX (Veracruz-Oaxaca). From the cross correlation for each pair of stations, Rayleigh wave dispersion curves were computed which represents the average group velocity between stations pairs. Furthermore, regional earthquakes recorded by the stations, were used to compute Rayleigh wave dispersion curves, which represent the average group velocity between epicenter and station. This mixed set of group velocity measurements was inverted to obtain tomographic images in discrete periods (5-50 s). Resolution tests show that the better-covered regions are surrounding both temporal experiments. Good coverage is also achieved in the large area between both experiments. In order to find details of crustal structure in the Tehuantepec Isthmus we use a set of previously computed receiver functions (Melgar and Pérez-Campos, 2011), to perform a joint inversion together with local dispersion curves reconstructed from the tomographic images. Results show good agreement with previous results by Melgar and Pérez-Campos (2011).

  5. Rayleigh-Wave, Group-Velocity Tomography of the Borborema Province, NE Brazil, from Ambient Seismic Noise

    NASA Astrophysics Data System (ADS)

    Dias, Rafaela Carreiro; Julià, Jordi; Schimmel, Martin

    2015-06-01

    Ambient seismic noise has traditionally been regarded as an unwanted perturbation that "contaminates" earthquake data. Over the last decade, however, it has been shown that consistent information about subsurface structure can be extracted from ambient seismic noise. By cross-correlation of noise simultaneously recorded at two seismic stations, the empirical Green's function for the propagating medium between them can be reconstructed. Moreover, for periods less than 30 s the seismic spectrum of ambient noise is dominated by microseismic energy and, because microseismic energy travels mostly as surface-waves, the reconstruction of the empirical Green's function is usually proportional to the surface-wave portion of the seismic wavefield. In this paper, we present 333 empirical Green's functions obtained from stacked cross-correlations of one month of vertical component ambient seismic noise for different pairs of seismic stations in the Borborema Province of NE Brazil. The empirical Green's functions show that the signal obtained is dominated by Rayleigh waves and that dispersion velocities can be measured reliably for periods between 5 and 20 s. The study includes permanent stations from a monitoring seismic network and temporary stations from past passive experiments in the region, resulting in a combined network of 34 stations separated by distances between approximately 40 and 1,287 km. Fundamental-mode group velocities were obtained for all station pairs and then tomographically inverted to produce maps of group velocity variation. For short periods (5-10 s) the tomographic maps correlate well with surface geology, with slow velocities delineating the main rift basins (Potiguar, Tucano, and Recôncavo) and fast velocities delineating the location of the Precambrian São Francisco craton and the Rio Grande do Norte domain. For longer periods (15-20 s) most of the velocity anomalies fade away, and only those associated with the deep Tucano basin and the S

  6. THE VELOCITY FIELD AROUND GROUPS OF GALAXIES

    SciTech Connect

    Hartwick, F. D. A.

    2011-06-15

    A statistical method is presented for determining the velocity field in the immediate vicinity of groups of galaxies using only positional and redshift information with the goal of studying the perturbation of the Hubble flow around groups more distant than the Local Group. The velocities are assumed to obey a Hubble-like expansion law, i.e., V = H{sub exp} R, where the expansion rate H{sub exp} is to be determined. The method is applied to a large, representative group catalog and evidence is found for a sub-Hubble expansion rate within two well-defined radii beyond the virial radii of the groups. This result is consistent with that of Teerikorpi et al. who found a similar expansion law around three nearby groups and extends it to a more representative volume of space.

  7. Chandra Observations of Low Velocity Dispersion Groups

    NASA Astrophysics Data System (ADS)

    Helsdon, Stephen F.; Ponman, Trevor J.; Mulchaey, J. S.

    2005-01-01

    Deviations of galaxy groups from cluster scaling relations can be understood in terms of an excess of entropy in groups. The main effect of this excess is to reduce the density and thus the luminosity of the intragroup gas. Given this, groups should also show a steep relationship between X-ray luminosity and velocity dispersion. However, previous work suggests that this is not the case, with many measuring slopes flatter than the cluster relation. Examining the group LX-σ relation shows that much of the flattening is caused by a small subset of groups that show very high X-ray luminosities for their velocity dispersions (or vice versa). Detailed Chandra study of two such groups shows that earlier ROSAT results were subject to significant (~30%-40%) point-source contamination but confirm that a significant hot intergalactic medium is present in these groups, although these are two of the coolest systems in which intergalactic X-ray emission has been detected. Their X-ray properties are shown to be broadly consistent with those of other galaxy groups, although the gas entropy in NGC 1587 is unusually low, and its X-ray luminosity is correspondingly high for its temperature when compared with most groups. This leads us to suggest that the velocity dispersion in these systems has been reduced in some way, and we consider how this might have come about.

  8. Raman solitons with group velocity dispersion

    NASA Astrophysics Data System (ADS)

    Skryabin, D. V.; Yulin, A. V.

    2006-10-01

    We consider the coupled propagation of the pump and Stokes waves in a Raman active medium accounting for the group velocity walk off and group velocity dispersion. Interplay of the Raman coherence and the dispersion can lead to the formation of a complete band gap in the spectrum of linear waves consisting of the two consecutive subgaps located at different frequencies. Using an approximate analytic technique, we find exponentially localized solitons residing in the complete gap, and find algebraic solitons when the gap is closed. Feasibility of observation of these structures in hollow fibers is discussed.

  9. Reconstruction of velocity fields in electromagnetic flow tomography.

    PubMed

    Lehtikangas, Ossi; Karhunen, Kimmo; Vauhkonen, Marko

    2016-06-28

    Electromagnetic flow meters (EMFMs) are the gold standard in measuring flow velocity in process industry. The flow meters can measure the mean flow velocity of conductive liquids and slurries. A drawback of this approach is that the velocity field cannot be determined. Asymmetric axial flows, often encountered in multiphase flows, pipe elbows and T-junctions, are problematic and can lead to serious systematic errors. Recently, electromagnetic flow tomography (EMFT) has been proposed for measuring velocity fields using several coils and a set of electrodes attached to the surface of the pipe. In this work, a velocity field reconstruction method for EMFT is proposed. The method uses a previously developed finite-element-based computational forward model for computing boundary voltages and a Bayesian framework for inverse problems. In the approach, the vz-component of the velocity field along the longitudinal axis of the pipe is estimated on the pipe cross section. Different asymmetric velocity fields encountered near pipe elbows, solids-in-water flows in inclined pipes and in stratified or multiphase flows are tested. The results suggest that the proposed reconstruction method could be used to estimate velocity fields in complicated pipe flows in which the conventional EMFMs have limited accuracy. This article is part of the themed issue 'Supersensing through industrial process tomography'. PMID:27185961

  10. Measurement of multidimensional ion velocity distributions by optical tomography

    NASA Astrophysics Data System (ADS)

    Koslover, R.; McWilliams, R.

    1986-10-01

    The development of a new diagnostic capable of measuring plasma ion distributions as a function of all three velocity-space coordinates is reported. The diagnostic makes use of laser-induced fluorescence (LIF) and computer-assisted image reconstruction techniques. LIF yields high-resolution, nonperturbing measurements of one-dimensional distributions that are integrated in two directions through three-dimensional velocity space. Computer tomography allows for the unambiguous determinations of the complete ion velocity distribution. In addition to a description of the diagnostic, examples of recovered distributions obtained from experiments are given, and the effects of the major steps in the data processing are discussed.

  11. Simultaneous inversion for velocity and attenuation by waveform tomography

    NASA Astrophysics Data System (ADS)

    Gao, Fengxia; Wang, Yanghua

    2016-08-01

    Seismic waveform tomography can invert for the velocity and attenuation (Q- 1) variations simultaneously. For this simultaneous inversion, we propose two strategies for waveform tomography. First, we analyze the contributions of the real part and the imaginary part of the gradients, associated with the velocity and attenuation parameters respectively, and determine that the combination of the real part of the gradient subvector for the velocity parameter and the imaginary part of the gradient subvector for the attenuation parameter would produce an optimal inversion result. Second, we attempt to balance the sensitivities of the objective function to the velocity and the attenuation parameters. Considering the magnitude differences between these two-type parameters in the simultaneous inversion, we apply preliminarily a normalization to both the velocity model and the attenuation model. However, for balancing their sensitivities, we further adjust the corresponding model updates using a tuning factor. We determine this tuning parameter adaptively, based on the sensitivities of these two parameters, at each iteration. Numerical tests demonstrate the feasibility and reliability of these two strategies in full waveform inversion.

  12. HALO VELOCITY GROUPS IN THE PISCES OVERDENSITY

    SciTech Connect

    Sesar, Branimir; Ivezic, Zeljko; Vivas, A. Katherina; Duffau, Sonia E-mail: zi@u.washington.ed E-mail: sonia.duffau@gmail.co

    2010-07-01

    We report spectroscopic observations of five faint (V {approx} 20) RR Lyrae stars associated with the Pisces overdensity conducted with the Gemini South Telescope. At a heliocentric and galactocentric distance of {approx}80 kpc, this is the most distant substructure in the Galactic halo known to date. We combined our observations with literature data and confirmed that the substructure is composed of two different kinematic groups. The main group contains eight stars and has (V{sub gsr}) = 50 km s{sup -1}, while the second group contains four stars at a velocity of (V{sub gsr}) = -52 km s{sup -1}, where V{sub gsr} is the radial velocity in the galactocentric standard of rest. The metallicity distribution of RR Lyrae stars in the Pisces overdensity is centered on [Fe/H] = -1.5 dex and has a width of 0.3 dex. The new data allowed us to establish that both groups are spatially extended making it very unlikely that they are bound systems, and are more likely to be debris of a tidally disrupted galaxy or galaxies. Due to small sky coverage, it is still unclear whether these groups have the same or different progenitors.

  13. The circular velocity function of group galaxies

    SciTech Connect

    Abramson, Louis E.; Williams, Rik J.; Benson, Andrew J.; Kollmeier, Juna A.; Mulchaey, John S.

    2014-09-20

    A robust prediction of ΛCDM cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with N-body simulations, but that of the field is distinctly Schechter-like, flattened compared to ΛCDM expectations at circular velocities v {sub c} ≲ 200 km s{sup –1}. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric v {sub c} estimators, we find no transition from field to ΛCDM-shaped CVF above v {sub c} = 50 km s{sup –1} as a function of group halo mass. All groups with 12.4 ≲ log M {sub halo}/M {sub ☉} ≲ 15.1 (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low v {sub c} compared to that of the field. Conversely, some agreement with N-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to ΛCDM predictions. We conclude that the flattening of the low-v {sub c} slope in groups is due to their depressed late-type fractions—environment affecting the CVF only to the extent that it correlates with this quantity—and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.

  14. Demonstration of images with negative group velocities.

    PubMed

    Glasser, Ryan T; Vogl, Ulrich; Lett, Paul D

    2012-06-18

    We report the experimental demonstration of the superluminal propagation of multi-spatial-mode images via four-wave mixing in hot atomic vapor, in which all spatial sub-regions propagate with negative group velocities. We investigate the spatial mode properties and temporal reshaping of the fast light images, and show large relative pulse peak advancements of up to 64 % of the input pulse width. The degree of temporal reshaping is quantified and increases as the relative pulse peak advancement increases. When optimized for image quality or pulse advancement, negative group velocities of up to v(g)=-c/880 and v(g)=-c/2180, respectively, are demonstrated when integrating temporally over the entire image. The present results are applicable to temporal cloaking devices that require strong manipulation of the dispersion relation, where one can envision temporally cloaking various spatial regions of an image for different durations. Additionally, the modes involved in a four-wave mixing process similar to the present experiment have been shown to exhibit quantum correlations and entanglement. The results presented here provide insight into how to tailor experimental tests of the behavior of these quantum correlations and entanglement in the superluminal regime. PMID:22714436

  15. Rogue events in the group velocity horizon

    PubMed Central

    Demircan, Ayhan; Amiranashvili, Shalva; Brée, Carsten; Mahnke, Christoph; Mitschke, Fedor; Steinmeyer, Günter

    2012-01-01

    The concept of rogue waves arises from a mysterious and potentially calamitous phenomenon of oceanic surfaces. There is mounting evidence that they are actually commonplace in a variety of different physical settings. A set of defining criteria has been advanced; this set is of great generality and therefore applicable to a wide class of systems. The question arises naturally whether there are generic mechanisms responsible for extreme events in different systems. Here we argue that under suitable circumstances nonlinear interaction between weak and strong waves results in intermittent giant waves with all the signatures of rogue waves. To obtain these circumstances only a few basic conditions must be met. Then reflection of waves at the so-called group-velocity horizon occurs. The connection between rogue waves and event horizons, seemingly unrelated physical phenomena, is identified as a feature common in many different physical systems. PMID:23152941

  16. Explore Seismic Velocity Change Associated with the 2010 Kaohsiung Earthquake by Ambient Noise Tomography

    NASA Astrophysics Data System (ADS)

    Ku, Chin-Shang; Wu, Yih-Min; Huang, Bor-Shouh; Huang, Win-Gee; Liu, Chun-Chi

    2016-04-01

    A ML 6.4 earthquake occurred on 4 March 2010 in Kaohsiung, the southern part of Taiwan, this shallow earthquake is the largest one of that area in the past few years. Some damages occurred on buildings and bridges after the earthquake, obvious surface deformation up to few cm was observed and the transportation including road and train traffic was also affected near the source area. Some studies about monitoring the velocity change induced by the big earthquake were carried out recently, most of studies used cross-correlation of the ambient noise-based method and indicated velocity drop was observed immediately after the big earthquake. However, this method is not able to constrain the depth of velocity change, and need to assume a homogeneous seismic velocity change during the earthquake. In this study, we selected 25 broadband seismic stations in the southern Taiwan and time period is from 2009/03 to 2011/03. Then we explored the velocity change associated with the 2010 Kaohsiung earthquake by applying ambient noise tomography (ANT) method. ANT is a way of using interferometry to image subsurface seismic velocity variations by using surface wave dispersions extracted from the ambient noise cross-correlation of seismic station-pairs, then the 2-D group velocity map with different periods could be extracted. Compare to ambient noise-based cross-correlation analysis, we estimated sensitivity kernel of dispersion curves and converted 2-D group velocity map from "with the period" to "with the depth" to have more constraints on the depth of velocity change. By subtracting shear velocity between "before" and "after" the earthquake, we could explore velocity change associated with the earthquake. Our result shows velocity reduction about 5-10% around the focal depth after the 2010 Kaohsiung earthquake and the post-seismic velocity recovery was observed with time period increasing, which may suggest a healing process of damaged rocks.

  17. Sleipner CCS site: velocity and attenuation model from seismic tomography

    NASA Astrophysics Data System (ADS)

    Rossi, G.; Chadwick, R. A.; Williams, G. A.

    2012-04-01

    The results of the travel-time and frequency shift tomographic inversion of the seismic data from one of the high-resolution lines acquired in 2006 on the Sleipner CO2 geological storage site are here presented. The work has been performed within the European project CO2ReMoVe, to produce an accurate model in-depth, of both seismic velocities and attenuation, to constrain better the quantification studies of the project's partners. Tomographic techniques have the advantage of not assuming horizontal layering or uniform lateral velocities, and of enabling an easy comparison of models, even if resulting from seismic data acquired with different geometries, unavoidable in a time-lapse data set. Through an iterative process, the differences in travel-times between observed direct, reflected or refracted arrivals and the same, calculated on a discrete model, with a ray-tracing based on the Fermat's principle, are minimized. Other minimization procedures provide the reflector/refractor geometries in -depth. Analogously, in attenuation tomography, the minimization process takes into account the observed and calculated spectral-centroid frequency-shift, due to the loss of the highest frequency of the seismic wave, while crossing an attenuating medium. The result is a seismic quality factor (Q) model in-depth, and hence of the attenuation that is known to be more sensitive to subtle changes in physical properties than seismic velocity. The model is across the center of the CO2 plume, on the in-line 1838, and is constituted by nine layers, four resulting by a preliminary analysis of the pre-injection 1994 data set, i.e. seabed, a strong reflection in the overburden and the top and bottom of the Utsira Sand, plus additional five horizons, four of which within Utsira Sands, and one just above the top of it. The layers within the reservoir are very close to each other and in some cases they merge together laterally. The accumulation of CO2 in the uppermost layer of the

  18. Preliminary Shear Velocity Tomography of Mt St Helens, Washington from iMUSH Array

    NASA Astrophysics Data System (ADS)

    Crosbie, K.; Abers, G. A.; Creager, K. C.; Moran, S. C.; Denlinger, R. P.; Ulberg, C. W.

    2015-12-01

    The imaging Magma Under Mount St Helens (iMUSH) experiment will illuminate the crust beneath Mt St Helens volcano. The ambient noise tomography (ANT) component of this experiment measures shear velocity structure, which is more sensitive than P velocity to the presence of melt and other pore fluids. Seventy passive-source broadband seismometers for iMUSH were deployed in the summer of 2014 in a dense array of 100 Km diameter with a 10 km station spacing. We cross correlated ambient noise in 120 s windows and summed the result over many months for pairs of stations. Then frequency-domain methods on these cross correlations are employed to measure the phase velocities (Ekström et al. Geophys Rev Lett, 2009). Unlike velocities attained by group velocity methods, velocities for path lengths as small as one wavelength can be measured, enabling analysis of higher frequency signals and increasing spatial resolution. The minimum station spacing from which signals can be recovered ranges from 12 km at 0.18 Hz, a frequency that dominantly samples the upper crust to 20 km, to 37 km at 0.04 Hz, a frequency sensitive to structure through the crust and uppermost mantle, with lower spacing at higher frequencies. These phase velocities are tomographically inverted to obtain shear velocity maps for each frequency, assuming ray theory. Initial shear velocity maps for frequencies between 0.04-0.18 Hz reveal low-velocity sediments in the Puget Lowland west of Mount St Helens at 0.16-0.18 Hz, and a low velocity zone near 0.10 Hz between Mt Rainier and Mt Adams, east of Mount St Helens. The latter may reflect large-scale crustal plumbing of the arc between volcanic centers. In subsequent analyses these ANT results will be jointly inverted with receiver functions in order to further resolve crustal and upper mantle structure.

  19. DIFFERENTIAL GROUP-VELOCITY DETECTION OF FLUID PATHS

    SciTech Connect

    Leland Timothy Long

    2005-12-20

    For nearly 50 years, surface waves that propagate through near-surface soils have been utilized in engineering for the determination of the small-strain dynamic properties of soils. These techniques, although useful, have not been sufficiently precise to use in detecting the subtle changes in soil properties that accompany short-term changes in fluid content. The differential techniques developed in this research now make it possible to monitor small changes (less than 3 cm) in the water level of shallow soil aquifers. Using inversion techniques and tomography, differential seismic techniques could track the water level distribution in aquifers with water being pumped in or out. Differential surface wave analysis could lead to new ways to monitor reservoir levels and verify hydrologic models. Field data obtained during this investigation have measured changes in surface-wave phase and group velocity before and after major rain events, and have detected subtle changes associated with pumping water into an aquifer and pumping water out of an aquifer. This research has established analysis techniques for observing these changes. These techniques combine time domain measurements to isolate surface wave arrivals with frequency domain techniques to determine the effects as a function of frequency. Understanding the differences in response as a function of wave frequency facilitates the inversion of this data for soil velocity structure. These techniques have also quantified many aspects of data acquisition and analysis that are important for significant results. These include tight control on the character of the source and proper placement of the geophones. One important application is the possibility that surface waves could be used to monitor and/or track fluid movement during clean-up operations, verifying that the fluid reached all affected areas. Extending this to a larger scale could facilitate monitoring of water resources in basins without having to drill many

  20. Crustal and uppermost mantle velocity structure beneath northwestern China from seismic ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Li, Hongyi; Li, S.; Song, X. D.; Gong, M.; Li, X.; Jia, J.

    2012-01-01

    In this paper, we conduct ambient noise seismic tomography of northwestern China and adjacent regions. The data include 9 months (2009 January to 2009 September) three-component continuous data recorded at 146 seismic stations of newly upgraded China Provincial Digital Seismic Networks and regional Kyrgyzstan and Kazakhstan networks. Empirical Rayleigh and Love wave Green's functions are obtained from interstation cross-correlations. Group velocity dispersion curves for both Rayleigh and Love waves between 7 and 50 s periods were measured for each interstation path by applying the multiple-filter analysis method with phase-matched processing. The group velocity maps show clear lateral variations which correlate well with major geological structures and tectonic units in the study region. Shear wave velocity structures are inverted from Rayleigh wave and love wave dispersion maps. The results show that the Tibetan Plateau has a very thick crust with a low-velocity zone in its mid-lower crust. Along the northern margin of the plateau where a steep topographic gradient is present, the low-velocity zone does not extend to the Tarim basin which may indicate that crustal materials beneath the Tarim basin are colder and stronger than beneath the plateau, therefore inhibit the extension of mid-lower crustal flow and deformation of the Tibetan Plateau, resulting in very sharp topography contrasts. In the northeastern margin with a gentle topographic gradient toward the Ordos platform, the low-velocity zone diminishes around the eastern KunLun fault. Meanwhile, our results reveal obvious lateral velocity changes in the crust beneath the Tarim basin. In the upper crust, the Manjaer depression in the eastern Tarim basin is featured with very low velocities and the Bachu uplift in the western Tarim basin with high velocities; in the mid-lower crust, the northern Tarim basin in general displays lower velocities than the southern part along latitude ˜40° N with an east

  1. 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.

  2. Group-Velocity-Matched Three Wave Mixing in Birefringent Crystals

    SciTech Connect

    SMITH,ARLEE V.

    2000-12-12

    We show that the combination of pulse-front slant, k-vector tilt, and crystal birefringence often permits exact matching of both phase and group velocities in three wave mixing in birefringent crystals. This makes possible more efficient mixing of short light pulses, and it permits efficient mixing of chirped or broad bandwidth light. We analyze this process and present examples. Differences in the group velocities of the three interacting waves in a nonlinear crystal often limits the effective interaction length. For example, in mixing very short pulses, temporal walk off can stretch the pulses in time unless the crystal is very short. Efficient mixing with such short crystals requires high irradiances, but the irradiances are limited by higher order nonlinear effects such as intensity-dependent refractive index and two-photon absorption. Improved matching of the group velocities can alleviate this problem, allowing longer crystal and lower irradiances. Similarly, for high energy pulses, practical limits on crystal apertures mandate temporally stretching the pulses to reduce irradiances. For the resulting chirped pulses, temporal walk off restricts the chirp range unless the group velocities are well matched. In addition to perfectly matching the group velocities of all three waves, it is sometimes useful to match two velocities, such as the signal and idler in parametric amplification, permitting broadband parametric amplification, or to arrange the velocities of two inputs to bracket the generated sum frequency pulse, giving pulse compression under suitable circumstances.

  3. Complex group velocity and energy transport in absorbing media.

    PubMed

    Gerasik, Vladimir; Stastna, Marek

    2010-05-01

    Complex group velocity is common in absorbing and active media, yet its precise physical meaning is unclear. While in the case of a nondissipative medium the group velocity of propagating waves Cg=dω/dk is exactly equal to the observable energy velocity (defined as the ratio between the energy flux and the total energy density) Cg=F/E , in a dissipative medium Cg=dω/dk is in general a complex quantity which cannot be associated with the velocity of energy transport. Nevertheless, we find that the complex group velocity may contain information about the energy transport as well as the energy dissipated in the medium. The presented analysis is intended to expound the connection between the complex group velocity and energy transport characteristics for a class of hyperbolic dissipative dynamical systems. Dissipation mechanisms considered herein include viscous and viscoelastic types of damping. Both cases of spatial and temporal decay are discussed. The presented approach stems from the Lagrangian formulation and is illustrated with identities that relate the complex group velocity and energy transport characteristics for the damped Klein-Gordon equation; Maxwell's equations, governing electromagnetic waves in partially conducting media; and Biot's theory, governing acoustic wave propagation in porous solids. PMID:20866345

  4. Filtering for unwrapping noisy Doppler optical coherence tomography images for extended microscopic fluid velocity measurement range.

    PubMed

    Xu, Yang; Darga, Donald; Smid, Jason; Zysk, Adam M; Teh, Daniel; Boppart, Stephen A; Scott Carney, P

    2016-09-01

    In this Letter, we report the first application of two phase denoising algorithms to Doppler optical coherence tomography (DOCT) velocity maps. When combined with unwrapping algorithms, significantly extended fluid velocity dynamic range is achieved. Instead of the physical upper bound, the fluid velocity dynamic range is now limited by noise level. We show comparisons between physical simulated ideal velocity maps and the experimental results of both algorithms. We demonstrate unwrapped DOCT velocity maps having a peak velocity nearly 10 times the theoretical measurement range. PMID:27607963

  5. Rayleigh-wave group velocity distribution in the Antarctic region

    NASA Astrophysics Data System (ADS)

    Kobayashi, Reiji; Zhao, Dapeng

    2004-03-01

    We determined 2D group velocity distribution of Rayleigh waves at periods of 20-150 s in the Antarctic region using a tomographic inversion technique. The data are recorded by both permanent networks and temporary arrays. In East Antarctica the velocities are high at periods of 90-150 s, suggesting that the root of East Antarctica is very deep. The velocities in West Antarctica are low at all periods, which may be related to the volcanic activity and the West Antarctic Rift System. Low velocity anomalies appear at periods of 40-140 s along the Southeastern Indian Ridge and the western part of the Pacific Antarctic Ridge. The velocities are only slightly low around the Atlantic Indian Ridge, Southwestern Indian Ridge, and the eastern part of the Pacific Antarctic Ridge, where the spreading rates are small. Around two hotspots, the Mount Erebus and Balleny Islands, the velocity is low at periods of 50-150 s.

  6. Inverse characterization of plates using zero group velocity Lamb modes.

    PubMed

    Grünsteidl, Clemens; Murray, Todd W; Berer, Thomas; Veres, István A

    2016-02-01

    In the presented work, the characterization of plates using zero group velocity Lamb modes is discussed. First, analytical expressions are shown for the determination of the k-ω location of the zero group velocity Lamb modes as a function of the Poisson's ratio. The analytical expressions are solved numerically and an inverse problem is formulated to determine the unknown wave velocities in plates of known thickness. The analysis is applied to determine the elastic properties of tungsten and aluminum plates based on the experimentally measured frequency spectra. PMID:26527393

  7. ML shear wave velocity tomography for the Iranian Plateau

    NASA Astrophysics Data System (ADS)

    Maheri-Peyrov, Mehdi; Ghods, Abdolreza; Abbasi, Madjid; Bergman, Eric; Sobouti, Farhad

    2016-04-01

    Iranian Plateau reflects several different tectonic styles of collision, and large-scale strike-slip faults. We calculate a high-resolution 2-D ML shear 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 shear velocity map of Iran. Our results show that the Zagros and South Caspian Basin (SCB) have shear wave 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 shear 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 shear velocity near the Lg velocity is attributed to smooth or minor Moho undulations within these regions.

  8. Negative Group Velocity in the Absence of Absorption Resonance

    PubMed Central

    Ye, Dexin; Zheng, Guoan; Wang, Jingyu; Wang, Zhiyu; Qiao, Shan; Huangfu, Jiangtao; Ran, Lixin

    2013-01-01

    Scientific community has well recognized that a Lorentzian medium exhibits anomalous dispersion behavior in its resonance absorption region. To satisfy the Krammers-Kronig relation, such an anomalous region has to be accompanied with significant loss, and thus, experimental observations of negative group velocity in this region generally require a gain-assisted approach. In this letter, we demonstrate that the negative group velocity can also be observed in the absence of absorption resonance. We show that the k-surface of a passive uniaxial Lorentzian medium undergoes a distortion near the plasma frequency. This process yields an anomalous dispersion bandwidth that is far away from the absorption resonance region, and enables the observation of negative group velocity at the plasma frequency band. Introducing anomalous dispersion in a well-controlled manner would greatly benefit the research of ultrafast photonics and find potential applications in optical delay lines, optical data storage and devices for quantum information processing. PMID:23568139

  9. 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

  10. Ambient noise surface wave tomography to determine the shallow shear velocity structure at Valhall: depth inversion with a Neighbourhood Algorithm

    NASA Astrophysics Data System (ADS)

    Mordret, A.; Landès, M.; Shapiro, N. M.; Singh, S. C.; Roux, P.

    2014-09-01

    This study presents a depth inversion of Scholte wave group and phase velocity maps obtained from cross-correlation of 6.5 hr of noise data from the Valhall Life of Field Seismic network. More than 2 600 000 vertical-vertical component cross-correlations are computed from the 2320 available sensors, turning each sensor into a virtual source emitting Scholte waves. We used a traditional straight-ray surface wave tomography to compute the group velocity map. The phase velocity maps have been computed using the Eikonal tomography method. The inversion of these maps in depth are done with the Neighbourhood Algorithm. To reduce the number of free parameters to invert, geological a priori information are used to propose a power-law 1-D velocity profile parametrization extended with a gaussian high-velocity layer where needed. These parametrizations allowed us to create a high-resolution 3-D S-wave model of the first 600 m of the Valhall subsurface and to precise the locations of geological structures at depth. These results would have important implication for shear wave statics and monitoring of seafloor subsidence due to oil extraction. The 3-D model could also be a good candidate for a starting model used in full-waveform inversions.

  11. Subduction zones beneath Indonesia imaged by Rayleigh wave phase velocity tomography

    NASA Astrophysics Data System (ADS)

    Liu, F.; Yang, T.; Harmon, N.

    2013-12-01

    Situated at the junction of several tectonic plates including Indian-Australia, Eurasia, and Philippine Sea, the Indonesian archipelago is one of the most tectonically complex regions on earth with subductions, collisions and accretions occurring along and within its boundaries. A high-resolution lithospheric and upper mantle model, therefore, is needed to understand these complex processes beneath this region. We present a phase velocity model derived from teleseismic Rayleigh waves recorded at seismic stations in this region. We use the modified version of the two-plane wave tomography, in which the non-planar effects of surface wave propagation such as multipathing and scattering are accounted for by two plane wave interference and using of finite frequency kernels. We measure the amplitudes and phases at 16 individual periods ranging from 20s to 150s for the fundamental mode of Rayleigh waves at over 30 stations. 254 earthquakes are selected from global events greater than Ms 5.5 in the distance range of 25°- 150°. To account for the wavefield inconsistencies among stations for each earthquake due to the large scale of our study region, we divide the seismic array into 4 groups of stations in the two-plane wave parameter inversion. The phase velocity maps from our preliminary results show coherent features between adjacent periods. The most dominant structure in phase velocity maps for all periods is the strong fast-velocity belts beneath Sunda Trench, Java Trench, Timor Trough and the trenches around Celebes Sea, which shift gradually toward the subduction directions. The strength of the high velocity anomaly varies among trenches, likely suggesting the different age of subducting slabs. In addition, a velocity contrast in the middle of Borneo appears to mark the Lupar Line, a boundary between the stable Sundaland continental core and fragments of ophiolitic and Asian continental material accreted to Borneo during the Cretaceous. The 3-D shear wave structure

  12. SPIDER - IX. Classifying galaxy groups according to their velocity distribution

    NASA Astrophysics Data System (ADS)

    Ribeiro, A. L. B.; de Carvalho, R. R.; Trevisan, M.; Capelato, H. V.; La Barbera, F.; Lopes, P. A. A.; Schilling, A. C.

    2013-09-01

    We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD), designed for detecting departures from a Gaussian velocity distribution. Testing different approaches to measure normality of a distribution, we conclude that HD is the least vulnerable method to type I and II statistical errors. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD < 0.05). In this work, we study the Gaussian nature of the velocity distribution of the Berlind group sample, and of the FoF groups from the Millennium simulation. For the Berlind group sample (z < 0.1), 67 per cent of the systems are classified as relaxed, while for the Millennium sample we find 63 per cent (z = 0). We verify that in multi-modal groups the average mass of modes in high-multiplicity (N ≥ 20) systems are significantly larger than in low-multiplicity ones (N < 20), suggesting that groups experience a mass growth at an increasing virialization rate towards z = 0, with larger systems accreting more massive subunits. We also investigate the connection between galaxy properties ([Fe/H], Age, eClass, g - r, Rpetro and <μpetro>) and the Gaussianity of the velocity distribution of the groups. Bright galaxies (Mr ≤ -20.7) residing in the inner and outer regions of groups do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7 < Mr ≤ -17.9). In G groups, there is a remarkable difference between the galaxy properties of the inner and outer galaxy populations, testifying how the environment is affecting the galaxies. Instead, in NG groups there is no segregation between the properties of galaxies in the inner and outer regions, showing that the properties of these galaxies still reflect the physical

  13. Absolute velocity measurement using three-beam spectral-domain Doppler optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Sharma, P.; Verma, Y.; Kumar, S.; Gupta, P. K.

    2015-09-01

    We report the development of a three-beam spectral-domain Doppler optical coherence tomography setup that allows single interferometer-based measurement of absolute flow velocity. The setup makes use of galvo-based phase shifting to remove complex conjugate mirror artifact and a beam displacer in the sample arm to avoid cross talk image. The results show that the developed approach allows efficient utilization of the imaging range of the spectral-domain optical coherence tomography setup for three-beam-based velocity measurement.

  14. Crosswell seismic studies in gas hydrate-bearing sediments: P wave velocity and attenuation tomography

    NASA Astrophysics Data System (ADS)

    Bauer, K.; Haberland, Ch.; Pratt, R. G.; Ryberg, T.; Weber, M. H.; Mallik Working Group

    2003-04-01

    We present crosswell seismic data from the Mallik 2002 Production Research Well Program, an international research project on Gas Hydrates in the Northwest Territories of Canada. The program participants include 8 partners; The Geological Survey of Canada (GSC), The Japan National Oil Corporation (JNOC), GeoForschungsZentrum Potsdam (GFZ), United States Geological Survey (USGS), United States Department of the Energy (USDOE), India Ministry of Petroleum and Natural Gas (MOPNG)/Gas Authority of India (GAIL) and the Chevron-BP-Burlington joint venture group. The crosswell seismic measurements were carried out by making use of two 1160 m deep observation wells (Mallik 3L-38 and 4L-38) both 45 m from and co-planar with the 1188 m deep production research well (5L-38). A high power piezo-ceramic source was used to generate sweeped signals with frequencies between 100 and 2000 Hz recorded with arrays of 8 hydrophones per depth level. A depth range between 800 and 1150 m was covered, with shot and receiver spacings of 0.75 m. High quality data could be collected during the survey which allow for application of a wide range of crosswell seismic methods. The initial data analysis included suppression of tube wave energy and picking of first arrivals. A damped least-squares algorithm was used to derive P-wave velocities from the travel time data. Next, t* values were derived from the decay of the amplitude spectra, which served as input parameters for a damped least-squares attenuation tomography. The initial results of the P-wave velocity and attenuation tomography reveal significant features reflecting the stratigraphic environment and allow for detection and eventually quantification of gas hydrate bearing sediments. A prominent correlation between P velocity and attenuation was found for the gas hydrate layers. This contradicts to the apparently more meaningful inverse correlation as it was determined for the gas hydrates at the Blake Ridge but supports the results from

  15. On electromagnetic waves with a negative group velocity

    NASA Astrophysics Data System (ADS)

    Makarov, V. P.; Rukhadze, A. A.; Samokhin, A. A.

    2010-12-01

    Recent publications devoted to the electrodynamics of media in which waves with a negative group velocity can exist are discussed. The properties of such waves have been studied from the beginning of the past century, and the most important results in this field were obtained by Soviet physicists in the 1940s-1950s. However, in most recent publications, this circumstance has not been taken into account.

  16. On electromagnetic waves with a negative group velocity

    SciTech Connect

    Makarov, V. P.; Rukhadze, A. A.; Samokhin, A. A.

    2010-12-15

    Recent publications devoted to the electrodynamics of media in which waves with a negative group velocity can exist are discussed. The properties of such waves have been studied from the beginning of the past century, and the most important results in this field were obtained by Soviet physicists in the 1940s-1950s. However, in most recent publications, this circumstance has not been taken into account.

  17. Envelope, group and phase velocities in a nested frequency comb

    NASA Astrophysics Data System (ADS)

    Masuda, Koji; Hendrie, James; Diels, Jean-Claude; Arissian, Ladan

    2016-04-01

    Fabry–Pérot etalons have been traditionally used in a laser cavity to tune the optical frequency. In this work we present the generation of interwoven frequency combs with insertion of an intracavity Fabry–Pérot in a mode-locked laser. A high frequency comb is generated by insertion of an uncoated (low finesse) Fabry–Pérot inside the laser cavity. The intracavity Fabry–Pérot acquires a high finesse from the laser cavity and the velocity of the pulses in the Fabry–Pérot is affected by the laser cavity length, gain and losses, with the dielectric group velocity dk/dΩ playing only a minor role. The output characteristics are explained by the condition that the radiation is simultaneously resonant with the etalon and the laser cavity.

  18. Envelope, group and phase velocities in a nested frequency comb

    NASA Astrophysics Data System (ADS)

    Masuda, Koji; Hendrie, James; Diels, Jean-Claude; Arissian, Ladan

    2016-05-01

    Fabry–Pérot etalons have been traditionally used in a laser cavity to tune the optical frequency. In this work we present the generation of interwoven frequency combs with insertion of an intracavity Fabry–Pérot in a mode-locked laser. A high frequency comb is generated by insertion of an uncoated (low finesse) Fabry–Pérot inside the laser cavity. The intracavity Fabry–Pérot acquires a high finesse from the laser cavity and the velocity of the pulses in the Fabry–Pérot is affected by the laser cavity length, gain and losses, with the dielectric group velocity dk/dΩ playing only a minor role. The output characteristics are explained by the condition that the radiation is simultaneously resonant with the etalon and the laser cavity.

  19. Superfluid phase transition with activated velocity fluctuations: Renormalization group approach

    NASA Astrophysics Data System (ADS)

    Dančo, Michal; Hnatič, Michal; Komarova, Marina V.; Lučivjanský, Tomáš; Nalimov, Mikhail Yu.

    2016-01-01

    A quantum field model that incorporates Bose-condensed systems near their phase transition into a superfluid phase and velocity fluctuations is proposed. The stochastic Navier-Stokes equation is used for a generation of the velocity fluctuations. As such this model generalizes model F of critical dynamics. The field-theoretic action is derived using the Martin-Siggia-Rose formalism and path integral approach. The regime of equilibrium fluctuations is analyzed within the perturbative renormalization group method. The double (ɛ ,δ ) -expansion scheme is employed, where ɛ is a deviation from space dimension 4 and δ describes scaling of velocity fluctuations. The renormalization procedure is performed to the leading order. The main corollary gained from the analysis of the thermal equilibrium regime suggests that one-loop calculations of the presented models are not sufficient to make a definite conclusion about the stability of fixed points. We also show that critical exponents are drastically changed as a result of the turbulent background and critical fluctuations are in fact destroyed by the developed turbulence fluctuations. The scaling exponent of effective viscosity is calculated and agrees with expected value 4 /3 .

  20. Superfluid phase transition with activated velocity fluctuations: Renormalization group approach.

    PubMed

    Dančo, Michal; Hnatič, Michal; Komarova, Marina V; Lučivjanský, Tomáš; Nalimov, Mikhail Yu

    2016-01-01

    A quantum field model that incorporates Bose-condensed systems near their phase transition into a superfluid phase and velocity fluctuations is proposed. The stochastic Navier-Stokes equation is used for a generation of the velocity fluctuations. As such this model generalizes model F of critical dynamics. The field-theoretic action is derived using the Martin-Siggia-Rose formalism and path integral approach. The regime of equilibrium fluctuations is analyzed within the perturbative renormalization group method. The double (ε,δ)-expansion scheme is employed, where ε is a deviation from space dimension 4 and δ describes scaling of velocity fluctuations. The renormalization procedure is performed to the leading order. The main corollary gained from the analysis of the thermal equilibrium regime suggests that one-loop calculations of the presented models are not sufficient to make a definite conclusion about the stability of fixed points. We also show that critical exponents are drastically changed as a result of the turbulent background and critical fluctuations are in fact destroyed by the developed turbulence fluctuations. The scaling exponent of effective viscosity is calculated and agrees with expected value 4/3. PMID:26871026

  1. Seismic velocity structure of the Puget Sound Region from three dimensional nonlinear tomography

    NASA Astrophysics Data System (ADS)

    Symons, Neill Philip

    In this dissertation I describe a non-linear seismic tomography experiment in the Greater Puget Sound Region (GPSR). The GPSR contains portions of three distinct geologic provinces: (1) the Coast Range Province---composed of the Olympic Mountains and the Siletzia terrane lying along the Washington Coast (the western edge of the GPSR). (2) The Puget Lowland---an approximately linear depression that stretches from Oregon's Willamette Valley to the Strait of Georgia in Canada. The Puget Lowland lies in the middle of the GPSR. (3) The Cascade Range---lying along the eastern edge of the GPSR and characterized by extensive episodic volcanism since the later Mesozoic. The result of this study is a three-dimensional model of the P-wave velocity within the GPSR. Interpretation of this model provides information about the subsurface geology in the region. The method used to perform the tomography has been developed as part of this research. The method uses a finite-difference algorithm to calculate seismic travel-times to every point in the region using the full 3-d velocity model. The method is capable of using three different types of data: (1) earthquakes with unknown hypocenters. The earthquake hypocenters are found as part of the model during solution of the tomography problem. (2) Explosions or other seismic events with known locations. (3) External data constraining the seismic velocity at known locations within the model. There is a good correlation between the velocity model derived in this experiment and several known geologic structures in the GPSR, including: the core of the Olympic Mountains; high seismic velocity where the basalt that makes up the Siletzia terrane outcrops; and low-velocity regions at basins under the cities of Seattle, Tacoma, Everett, and Chehalis. The data provides sufficient resolution to delineate the geometry of the contacts between these units within a large portion of the GPSR.

  2. Finite-frequency traveltime tomography of San Francisco Bay region crustal velocity structure

    USGS Publications Warehouse

    Pollitz, F.F.

    2007-01-01

    Seismic velocity structure of the San Francisco Bay region crust is derived using measurements of finite-frequency traveltimes. A total of 57 801 relative traveltimes are measured by cross-correlation over the frequency range 0.5-1.5 Hz. From these are derived 4862 'summary' traveltimes, which are used to derive 3-D P-wave velocity structure over a 341 ?? 140 km2 area from the surface to 25 km depth. The seismic tomography is based on sensitivity kernels calculated on a spherically symmetric reference model. Robust elements of the derived P-wave velocity structure are: a pronounced velocity contrast across the San Andreas fault in the south Bay region (west side faster); a moderate velocity contrast across the Hayward fault (west side faster); moderately low velocity crust around the Quien Sabe volcanic field and the Sacramento River delta; very low velocity crust around Lake Berryessa. These features are generally explicable with surface rock types being extrapolated to depth ???10 km in the upper crust. Generally high mid-lower crust velocity and high inferred Poisson's ratio suggest a mafic lower crust. ?? Journal compilation ?? 2007 RAS.

  3. PICASSO: Shear velocities in the Western Mediterranean from Rayleigh Wave tomography

    NASA Astrophysics Data System (ADS)

    Palomeras, I.; Thurner, S.; Levander, A.

    2012-12-01

    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 wave 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-wave method to remove complications due to multi-pathing, and finite-frequency kernels to improve lateral resolution. Phase velocities were then inverted for shear velocity structure on a grid of 0.5 by 0.5 degree to form a well-resolved 3D shear 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 wave tomography is consistent with P-tomography that

  4. The crustal and mantle velocity structure in central Asia from 3D traveltime tomography

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Martin, R. V.; Toksoz, M. N.; Pei, S.

    2010-12-01

    The lithospheric structure in central Asia features large blocks such as the Indian plate, the Afghan block, the Turan plate, and the Tarim block. This geologically and tectonically complicated area is also one of the most seismically active regions in the world. We developed P- and S- wave velocity structures of the central Asia in the crust using the traveltime data from Kyrgyzstan, Tajikistan, Kazakhstan, and Uzbek. We chose the events and stations between 32N65E and 45N85E and focused on the areas of Pamir and western Tianshan. In this data set, there are more than 6000 P and S arrivals received at 80 stations from about 300 events. The double difference tomography is applied to relocate events and to invert for seismic structures simultaneously. Our results provide accurate locations of earthquakes and high resolution crustal structure in this region. To extend the model deeper into the mantle through the upper mantle transition zone, ISC/EHB data for P and PP phases are combined with the ABCE data. To counteract the “smearing effect,” the crust and upper mantle velocity structure, derived from regional travel-times, is used. An adaptive grid method based on ray density is used in the inversion. A P-wave velocity model extending down to a depth of 2000 km is obtained. regional-teleseismic tomography provides a high-resolution, 3-D P-wave velocity model for the crust, upper mantle, and the transition zone. The crustal models correlate well with geologic and tectonic features. The upper mantle tomograms show the images of Tian Shan. The slab geometry is quite complex, reflecting the history of the changes in the plate motions and collision processes. Vp/Vs tomography was also determined in the study region, and an attenuation tomography was obtained as well.

  5. Benchmark and combined velocity-space tomography of fast-ion D-alpha spectroscopy and collective Thomson scattering measurements

    NASA Astrophysics Data System (ADS)

    Jacobsen, A. S.; Salewski, M.; Geiger, B.; Korsholm, S. B.; Leipold, F.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Weiland, M.; the ASDEX Upgrade Team

    2016-04-01

    We demonstrate the combination of fast-ion D-alpha spectroscopy (FIDA) and collective Thomson scattering (CTS) measurements to determine a common best estimate of the fast-ion velocity distribution function by velocity-space tomography. We further demonstrate a benchmark of FIDA tomography and CTS measurements without using a numerical simulation as common reference. Combined velocity-space tomographies from FIDA and CTS measurements confirm that sawtooth crashes reduce the fast-ion phase-space densities in the plasma center and affect ions with pitches close to one more strongly than those with pitches close to zero.

  6. Crustal velocity structure of Central and Eastern Turkey from ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Warren, Linda M.; Beck, Susan L.; Biryol, C. Berk; Zandt, George; Özacar, A. Arda; Yang, Yingjie

    2013-09-01

    In eastern Turkey, the ongoing convergence of the Arabian and African plates with Eurasia has resulted in the westward extrusion of the Anatolian Plate. To better understand the current state and the tectonic history of this region, we image crust and uppermost mantle structure with ambient noise tomography. Our study area extends from longitudes of 32° to 44°E. We use continuous data from two temporary seismic deployments, our 2006-2008 North Anatolian Fault Passive Seismic Experiment and the 1999-2001 Eastern Turkey Seismic Experiment, as well as from additional seismographs in the region. We compute daily cross-correlations of noise records between all station pairs and stack them over the entire time period for which they are available, as well as in seasonal subsets, to obtain interstation empirical Green's functions. After selecting interstation cross-correlations with high signal-to-noise ratios and measuring interstation phase velocities, we compute phase velocity maps at periods ranging from 8 to 40 s. At all periods, the phase velocity maps are similar for winter and summer subsets of the data, indicating that seasonal variations in noise sources do not bias our results. Across the study area, we invert the phase velocity estimates for shear velocity as a function of depth. The shear velocity model, which extends to 50 km depth, highlights tectonic features apparent at the surface: the Eastern Anatolian Plateau is a prominent low-velocity anomaly whereas the Kirşehir Massif has relatively fast velocities. There is a large velocity jump across the Inner Tauride Suture/Central Anataolian Fault Zone throughout the crust whereas the North Anatolian Fault does not have a consistent signature. In addition, in the southeastern part of our study area, we image a high velocity region below 20 km depth which may be the northern tip of the underthrusting Arabian Plate.

  7. Surface wave phase-velocity tomography based on multichannel cross-correlation

    NASA Astrophysics Data System (ADS)

    Jin, Ge; Gaherty, James B.

    2015-06-01

    We have developed a new method to retrieve seismic surface wave phase velocity using dense seismic arrays. The method measures phase variations between nearby stations based on waveform cross-correlation. The coherence in waveforms between adjacent stations results in highly precise relative phase estimates. Frequency-dependent phase variations are then inverted for spatial variations in apparent phase velocity via the Eikonal equation. Frequency-dependent surface wave amplitudes measured on individual stations are used to correct the apparent phase velocity to account for multipathing via the Helmholtz equation. By using coherence and other data selection criteria, we construct an automated system that retrieves structural phase-velocity maps directly from raw seismic waveforms for individual earthquakes without human intervention. The system is applied to broad-band seismic data from over 800 events recorded on EarthScope's USArray from 2006 to 2014, systematically building up Rayleigh-wave phase-velocity maps between the periods of 20 and 100 s for the entire continental United States. At the highest frequencies, the resulting maps are highly correlated with phase-velocity maps derived from ambient noise tomography. At all frequencies, we observe a significant contrast in Rayleigh-wave phase velocity between the tectonically active western US and the stable eastern US, with the phase velocity variations in the western US being 1-2 times greater. The Love wave phase-velocity maps are also calculated. We find that overtone contamination may produce systemic bias for the Love-wave phase-velocity measurements.

  8. Seismic Velocity Anomalies beneath Tatun Volcano Group, Northern Taiwan

    NASA Astrophysics Data System (ADS)

    Lin, Tzu-yu; Lin, Cheng-Horng; Yang, Tsanyao Frank; Chang, Li-Chin

    2015-04-01

    Volcanic eruption has been a natural disaster for human society. Taiwan is located in the Pacific Ring of Fire. Although there is no obvious phenomenon of volcanic activity in Taiwan, some volcanoes need to be monitored, especially the Tatun Volcano Group (TVG), which exhibits very active hydrothermal activity, is located on the tip of southwestern Ryukyu arc. TVG is about 15 km north to Taipei, capital of Taiwan, and is nearby two nuclear power plants along the northern coast of Taiwan. If TVG erupts, there must be a serious impact and damage to Taiwan. Since TVG is located within the Yangmingshan National Park, any artificial seismic source is not allowed to estimate possible eruption site and the degree of volcanic disaster. Instead, we use natural seismic waves generated by earthquakes to image the possible velocity anomaly of magma chamber and/or hydrothermal system beneath TVG. We systematically compare the differences of arrival times generated by some local earthquakes and recorded at 42 seismic stations in 2014 for finding any low-velocity zone within the crust. The results show that the arrival times always appeared significant delay at some particular seismic stations, such as Chi-Hsin-Shan (CHS), Siao-You-Keng (SYK) and some other stations at TVG, no matter where the earthquakes occurred. It implies that possible low-velocity zones, which could be the location of magma chamber and/or active hydrothermal system, exist beneath the CHS and SYK areas. This feature is generally consistent with the clustered micro-earthquakes in the shallow crust beneath the CHS area in the last decade.

  9. Velocity structure of the uppermost mantle beneath East Asia from Pn tomography and its dynamic implications

    NASA Astrophysics Data System (ADS)

    Wang, Suyun; Niu, Fenglin; Zhang, Guomin

    2013-01-01

    AbstractEast Asia is one of the most tectonically active regions on Earth's surface due to the collision from the India plate and the suctions induced by the subduction of the Pacific and Philippine plates. To better understand the complicated deformation and active seismicity of the area, we conducted a Pn traveltime <span class="hlt">tomography</span> to estimate the compressive wave speed of the uppermost mantle beneath East Asia. We collected a total of 296,334 Pn arrivals recorded by 1354 stations from 27,777 earthquakes in a rectangular area from 60°E to 145°E in longitude, 15°N to 60°N in latitude. The data set was carefully integrated from three different catalogs after examining potential systematic biases in the catalogs. The inversion results revealed a large-scale <span class="hlt">velocity</span> perturbation in the study area. Pn <span class="hlt">velocity</span> in the region west to ~108°E is approximately 10% higher than that in the east. In each region, stable blocks tend to have high Pn <span class="hlt">velocity</span> while the boundary regions, which show a high level of seismicity and surface deformation, appear to have low Pn <span class="hlt">velocity</span>. We further computed the Benioff strain rate in the two regions and found it correlates negatively with the averaged Pn <span class="hlt">velocity</span>. Our observations here suggest that Pn <span class="hlt">velocity</span>, which is predominantly determined by Moho temperature, is a good indicator of lithosphere strength.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SPIE.9234E..16P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SPIE.9234E..16P"><span id="translatedtitle">Implementation and characterization of phase-resolved Doppler optical coherence <span class="hlt">tomography</span> method for flow <span class="hlt">velocity</span> measurement</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pongchalee, Pornthep; Palawong, Kunakorn; Meemon, Panomsak</p> <p>2014-06-01</p> <p>In this work, the system implementation and characterization of a Phase-Resolved Doppler Optical Coherence <span class="hlt">Tomography</span> (PR-DOCT) is presented. The phase-resolved Doppler technique was implemented on a custom built Frequency Domain OCT (FD-OCT) that was recently developed at Suranaree University of Technology. Utilizing Doppler phase changed relation in a complex interference signal caused by moving samples, PR-DOCT can produce visualization and characterization of flow activity such as blood flow in biological samples. Here we report the performance of the implemented PR-DOCT system in term of the <span class="hlt">Velocity</span> Dynamic Range (VDR), which is defined by the range from the minimum to the maximum detectable axial <span class="hlt">velocity</span>. The minimum detectable <span class="hlt">velocity</span> was quantified from a histogram distribution of phase difference between consecutive depth-scan signals when performing Doppler imaging of a stationary mirror. By applying a Gaussian curve fitting to the histogram, the Full Width at Half Maximum (FWHM) of the fitted curve was measured to represent the detectable minimum flow <span class="hlt">velocity</span> of the system. The maximum detectable <span class="hlt">velocity</span> was limited by the phase wrapping of the Doppler signal, which is governed by the acquisition speed of the system. We demonstrate the 3D Doppler imaging and <span class="hlt">velocity</span> measurement of feed flow phantom using 100% milk pumped through a microfluidic chip by using a syringe pump system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SolED...6.2971G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SolED...6.2971G"><span id="translatedtitle">A 3-D shear <span class="hlt">velocity</span> model of the southern North America and the Caribbean plates from ambient noise and earthquake <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gaite, B.; Villaseñor, A.; Iglesias, A.; Herraiz, M.; Jiménez-Munt, I.</p> <p>2014-10-01</p> <p>We use <span class="hlt">group</span> <span class="hlt">velocities</span> from earthquake <span class="hlt">tomography</span> together with <span class="hlt">group</span> and phase <span class="hlt">velocities</span> from ambient noise <span class="hlt">tomography</span> (ANT) of Rayleigh-waves to invert for the 3-D shear-wave <span class="hlt">velocity</span> 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 <span class="hlt">velocities</span> along USA-Mexico border. The model also shows a break of the E-W mantle <span class="hlt">velocity</span> dichotomy of the NAM and CAR plates beneath the Isthmus of Tehuantepec and Yucatan Block. High upper-mantle <span class="hlt">velocities</span> along the Mesoamerican Subduction Zone coincide with inactive volcanic areas while the lowest <span class="hlt">velocities</span> correspond to active volcanic arcs and thin lithospheric mantle regions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.T41F..06Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.T41F..06Z"><span id="translatedtitle">Probing the Detailed Seismic <span class="hlt">Velocity</span> Structure of Subduction Zones Using Advanced Seismic <span class="hlt">Tomography</span> Methods</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, H.; Thurber, C. H.</p> <p>2005-12-01</p> <p>Subduction zones are one of the most important components of the Earth's plate tectonic system. Knowing the detailed seismic <span class="hlt">velocity</span> structure within and around subducting slabs is vital to understand the constitution of the slab, the cause of intermediate depth earthquakes inside the slab, the fluid distribution and recycling, and tremor occurrence [Hacker et al., 2001; Obara, 2002].Thanks to the ability of double-difference <span class="hlt">tomography</span> [Zhang and Thurber, 2003] to resolve the fine-scale structure near the source region and the favorable seismicity distribution inside many subducting slabs, it is now possible to characterize the fine details of the <span class="hlt">velocity</span> structure and earthquake locations inside the slab, as shown in the study of the Japan subduction zone [Zhang et al., 2004]. We further develop the double-difference <span class="hlt">tomography</span> method in two aspects: the first improvement is to use an adaptive inversion mesh rather than a regular inversion grid and the second improvement is to determine a reliable Vp/Vs structure using various strategies rather than directly from Vp and Vs [see our abstract ``Strategies to solve for a better Vp/Vs model using P and S arrival time'' at Session T29]. The adaptive mesh seismic <span class="hlt">tomography</span> method is based on tetrahedral diagrams and can automatically adjust the inversion mesh according to the ray distribution so that the inversion mesh nodes are denser where there are more rays and vice versa [Zhang and Thurber, 2005]. As a result, the number of inversion mesh nodes is greatly reduced compared to a regular inversion grid with comparable spatial resolution, and the tomographic system is more stable and better conditioned. This improvement is quite valuable for characterizing the fine structure of the subduction zone considering the highly uneven distribution of earthquakes within and around the subducting slab. The second improvement, to determine a reliable Vp/Vs model, lies in jointly inverting Vp, Vs, and Vp/Vs using P, S, and S</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70030816','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70030816"><span id="translatedtitle">Comparative <span class="hlt">velocity</span> structure of active Hawaiian volcanoes from 3-D onshore-offshore seismic <span class="hlt">tomography</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>Park, J.; Morgan, J.K.; Zelt, C.A.; Okubo, P.G.; Peters, L.; Benesh, N.</p> <p>2007-01-01</p> <p>We present a 3-D P-wave <span class="hlt">velocity</span> model of the combined subaerial and submarine portions of the southeastern part of the Island of Hawaii, based on first-arrival seismic <span class="hlt">tomography</span> of marine airgun shots recorded by the onland seismic network. Our model shows that high-<span class="hlt">velocity</span> materials (6.5-7.0??km/s) lie beneath Kilauea's summit, Koae fault zone, and the upper Southwest Rift Zone (SWRZ) and upper and middle East Rift Zone (ERZ), indicative of magma cumulates within the volcanic edifice. A separate high-<span class="hlt">velocity</span> body of 6.5-6.9??km/s within Kilauea's lower ERZ and upper Puna Ridge suggests a distinct body of magma cumulates, possibly connected to the summit magma cumulates at depth. The two cumulate bodies within Kilauea's ERZ may have undergone separate ductile flow seaward, influencing the submarine morphology of Kilauea's south flank. Low <span class="hlt">velocities</span> (5.0-6.3??km/s) seaward of Kilauea's Hilina fault zone, and along Mauna Loa's seaward facing Kao'iki fault zone, are attributed to thick piles of volcaniclastic sediments deposited on the submarine flanks. Loihi seamount shows high-<span class="hlt">velocity</span> anomalies beneath the summit and along the rift zones, similar to the interpreted magma cumulates below Mauna Loa and Kilauea volcanoes, and a low-<span class="hlt">velocity</span> anomaly beneath the oceanic crust, probably indicative of melt within the upper mantle. Around Kilauea's submarine flank, a high-<span class="hlt">velocity</span> anomaly beneath the outer bench suggests the presence of an ancient seamount that may obstruct outward spreading of the flank. Mauna Loa's southeast flank is also marked by a large, anomalously high-<span class="hlt">velocity</span> feature (7.0-7.4??km/s), interpreted to define an inactive, buried volcanic rift zone, which might provide a new explanation for the westward migration of Mauna Loa's current SWRZ and the growth of Kilauea's SWRZ. ?? 2007 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016JGRB..121.2429F&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016JGRB..121.2429F&link_type=ABSTRACT"><span id="translatedtitle">Tomographic Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocities</span> in the Central Valley, California, centered on the Sacramento/San Joaquin Delta</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fletcher, Jon B.; Erdem, Jemile; Seats, Kevin; Lawrence, Jesse</p> <p>2016-04-01</p> <p>If shaking from a local or regional earthquake in the San Francisco Bay region were to rupture levees in the Sacramento/San Joaquin Delta, then brackish water from San Francisco Bay would contaminate the water in the Delta: the source of freshwater for about half of California. As a prelude to a full shear-wave <span class="hlt">velocity</span> model that can be used in computer simulations and further seismic hazard analysis, we report on the use of ambient noise <span class="hlt">tomography</span> to build a fundamental mode, Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> model for the region around the Sacramento/San Joaquin Delta in the western Central Valley, California. Recordings from the vertical component of about 31 stations were processed to compute the spatial distribution of Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocities</span>. Complex coherency between pairs of stations was stacked over 8 months to more than a year. Dispersion curves were determined from 4 to about 18 s. We calculated average <span class="hlt">group</span> <span class="hlt">velocities</span> for each period and inverted for deviations from the average for a matrix of cells that covered the study area. Smoothing using the first difference is applied. Cells of the model were about 5.6 km in either dimension. Checkerboard tests of resolution, which are dependent on station density, suggest that the resolving ability of the array is reasonably good within the middle of the array with resolution between 0.2 and 0.4°. Overall, low <span class="hlt">velocities</span> in the middle of each image reflect the deeper sedimentary syncline in the Central Valley. In detail, the model shows several centers of low <span class="hlt">velocity</span> that may be associated with gross geologic features such as faulting along the western margin of the Central Valley, oil and gas reservoirs, and large crosscutting features like the Stockton arch. At shorter periods around 5.5 s, the model's western boundary between low and high <span class="hlt">velocities</span> closely follows regional fault geometry and the edge of a residual isostatic gravity low. In the eastern part of the valley, the boundaries of the low-<span class="hlt">velocity</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S53A2787E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S53A2787E"><span id="translatedtitle">Simultaneous Local and Teleseismic P-Wave <span class="hlt">Velocity</span> <span class="hlt">Tomography</span> in Western Mexico</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Escudero, C. R.; Alarcon, E.; Ochoa, J.; Nuñez-Cornu, F. J.</p> <p>2015-12-01</p> <p>In western Mexico, the subduction of the Rivera and Cocos plates beneath the North America plate has deformed and fragmented the overriding plate, forming several structural rifts and crustal blocks. To improve the current tomographic images of the continental crust and uppermost mantle in this complex area, we used P-wave arrivals of local and teleseismic earthquakes along with the Fast Marching Method <span class="hlt">tomography</span> technique. Our traveltime datasets include 2100 local earthquakes P-wave arrival times and 5,062 P-wave relative arrival time residuals of teleseismic earthquakes. The local earthquake phase picking was manually corrected and the relative arrival time residuals were estimated using the Multi-Channel Cross-Correlation method. All earthquakes occurred between 2006 and 2007 and were recorded by seismic stations deployed during the Mapping the Rivera Subduction Zone (MARS) experiment. The temporal seismic network consisted of 50 stations equipped with Streckeisen STS-2 and Quanterra Q330. We use an iterative nonlinear tomographic procedure and the fast marching method to map the residual patterns as P wave <span class="hlt">velocity</span> anomalies. We followed an inversion scheme consisting of: (1) selection of a local and teleseismic earthquake, (2) estimation of improved 1-D reference <span class="hlt">velocity</span> model, and (3) checkerboard testing to determine the optimum configuration of the <span class="hlt">velocity</span> nodes, and inversion parameters, finally (4) perform final <span class="hlt">tomography</span> and results analysis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PPCF...58b5012W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PPCF...58b5012W"><span id="translatedtitle">Enhancement of the FIDA diagnostic at ASDEX Upgrade for <span class="hlt">velocity</span> space <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weiland, M.; Geiger, B.; Jacobsen, A. S.; Reich, M.; Salewski, M.; Odstrčil, T.; the ASDEX Upgrade Team</p> <p>2016-02-01</p> <p>Recent upgrades to the FIDA (fast-ion D-alpha) diagnostic at ASDEX Upgrade are discussed. The diagnostic has been extended from three to five line of sight arrays with different angles to the magnetic field, and a spectrometer redesign allows the simultaneous measurement of red- and blue-shifted parts of the Doppler spectrum. These improvements make it possible to reconstruct the 2D fast-ion <span class="hlt">velocity</span> distribution f≤ft(E,{{v}\\parallel}/v\\right) from the FIDA measurements by tomographic inversion under a wide range of plasma parameters. Two applications of the <span class="hlt">tomography</span> are presented: a comparison between the distributions resulting from 60 keV and 93 keV neutral beam injection and a <span class="hlt">velocity</span>-space resolved study of fast-ion redistribution induced by a sawtooth crash inside and outside the sawtooth inversion radius.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.205...51L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.205...51L"><span id="translatedtitle">Global Rayleigh wave phase-<span class="hlt">velocity</span> maps from finite-frequency <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Kui; Zhou, Ying</p> <p>2016-04-01</p> <p>We report global phase-<span class="hlt">velocity</span> maps of fundamental-mode Rayleigh waves at periods between 25 and 100 s based on finite-frequency <span class="hlt">tomography</span>. Rayleigh wave dispersion measurements are made using a multitaper technique for both minor-arc and major-arc wave trains. The global phase-<span class="hlt">velocity</span> maps confirm many features associated with surface tectonics including the ocean-continent dichotomy and the signature of lithospheric cooling in oceanic plates. In addition, the high-resolution phase-<span class="hlt">velocity</span> maps reveal a major change in the distribution of small-scale anomalies in the Pacific at different wave periods. We calculate the global average of Rayleigh wave phase <span class="hlt">velocity</span> in major tectonic regions and show that large discrepancies exist between our model and global crustal and mantle models: (1) In oceanic regions, short-period (<˜40 s) Rayleigh waves are faster than calculations based on models CRUST2.0 and S40RTS. The discrepancies could be explained by a thinner crust or faster wave speeds in the crust or upper mantle. The implementation of model CRUST1.0 significantly improves the agreement, with phase-<span class="hlt">velocity</span> discrepancies less than 0.5 per cent on average. (2) In Archean cratons, Rayleigh wave phase <span class="hlt">velocities</span> in our model are faster than calculations based on model S40RTS at periods longer than ˜40 s; and the global average in orogenic belts is ˜1-2 per cent slower than CRUST1.0 at periods shorter than ˜50 s.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4771474','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4771474"><span id="translatedtitle">Fully distributed absolute blood flow <span class="hlt">velocity</span> measurement for middle cerebral arteries using Doppler optical coherence <span class="hlt">tomography</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>Qi, Li; Zhu, Jiang; Hancock, Aneeka M.; Dai, Cuixia; Zhang, Xuping; Frostig, Ron D.; Chen, Zhongping</p> <p>2016-01-01</p> <p>Doppler optical coherence <span class="hlt">tomography</span> (DOCT) is considered one of the most promising functional imaging modalities for neuro biology research and has demonstrated the ability to quantify cerebral blood flow <span class="hlt">velocity</span> at a high accuracy. However, the measurement of total absolute blood flow <span class="hlt">velocity</span> (BFV) of major cerebral arteries is still a difficult problem since it is related to vessel geometry. In this paper, we present a volumetric vessel reconstruction approach that is capable of measuring the absolute BFV distributed along the entire middle cerebral artery (MCA) within a large field-of-view. The Doppler angle at each point of the MCA, representing the vessel geometry, is derived analytically by localizing the artery from pure DOCT images through vessel segmentation and skeletonization. Our approach could achieve automatic quantification of the fully distributed absolute BFV across different vessel branches. Experiments on rodents using swept-source optical coherence <span class="hlt">tomography</span> showed that our approach was able to reveal the consequences of permanent MCA occlusion with absolute BFV measurement. PMID:26977365</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PPCF...58d5016J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PPCF...58d5016J"><span id="translatedtitle">Inversion methods for fast-ion <span class="hlt">velocity</span>-space <span class="hlt">tomography</span> in fusion plasmas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jacobsen, A. S.; Stagner, L.; Salewski, M.; Geiger, B.; Heidbrink, W. W.; Korsholm, S. B.; Leipold, F.; Nielsen, S. K.; Rasmussen, J.; Stejner, M.; Thomsen, H.; Weiland, M.; the ASDEX Upgrade Team</p> <p>2016-04-01</p> <p><span class="hlt">Velocity</span>-space <span class="hlt">tomography</span> has been used to infer 2D fast-ion <span class="hlt">velocity</span> distribution functions. Here we compare the performance of five different tomographic inversion methods: truncated singular value decomposition, maximum entropy, minimum Fisher information and zeroth- and first-order Tikhonov regularization. The inversion methods are applied to fast-ion {{\\text{D}}α} measurements taken just before and just after a sawtooth crash in the ASDEX Upgrade tokamak as well as to synthetic measurements from different test distributions. We find that the methods regularizing by penalizing steep gradients or maximizing entropy perform best. We assess the uncertainty of the calculated inversions taking into account photon noise, uncertainties in the forward model as well as uncertainties introduced by the regularization which allows us to distinguish regions of high and low confidence in the <span class="hlt">tomographies</span>. In high confidence regions, all methods agree that ions with pitch values close to zero, as well as ions with large pitch values, are ejected from the plasma center by the sawtooth crash, and that this ejection depletes the ion population with large pitch values more strongly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21156393','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21156393"><span id="translatedtitle">Study on creating hydraulic <span class="hlt">tomography</span> for crystalline rock using frequency dependent elastic wave <span class="hlt">velocity</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yoshimura, K.; Sakashita, S.; Ando, K.; Bruines, P.; Blechschmidt, I.; Kickmaier, W.; Onishi, Y.; Nishiyama, S.</p> <p>2007-07-01</p> <p>The objective of this study is to establish a technique to obtain hydraulic conductivity distribution in granite rock masses using seismic <span class="hlt">tomography</span>. We apply the characteristic that elastic wave <span class="hlt">velocity</span> disperses in fully saturated porous media on frequency and this <span class="hlt">velocity</span> dispersion is governed by the hydraulic conductivity - this characteristic has been confirmed in laboratory experiments. The feasibility and design of the field experiment was demonstrated in a first step with numerical simulations. In a second step we applied the technique to the fractured granite at the Grimsel Test Site in Switzerland. The emphasis of the field campaign was on the evaluation of the range of applicability of this technique. The field campaign was structured in three steps, each one corresponding to a larger spatial scale. First, the seismic <span class="hlt">tomography</span> was applied to a small area - the two boreholes were located at a distance of 1.5 m. In the following step, we selected a larger area, in which the distance of the boreholes amounts to 10 m and the field corresponds to a more complex geology. Finally we applied the testing to a field where the borehole distance was of the order of 75 m. We also drilled a borehole to confirm hydraulic characteristic and reviewed hydraulic model in the 1.5 m cross-hole location area. The results from the field campaign are presented and their application to the various fields are discussed and evaluated. (authors)</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_1");'>1</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li class="active"><span>3</span></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_3 --> <div id="page_4" 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_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="61"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26977365','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26977365"><span id="translatedtitle">Fully distributed absolute blood flow <span class="hlt">velocity</span> measurement for middle cerebral arteries using Doppler optical coherence <span class="hlt">tomography</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Qi, Li; Zhu, Jiang; Hancock, Aneeka M; Dai, Cuixia; Zhang, Xuping; Frostig, Ron D; Chen, Zhongping</p> <p>2016-02-01</p> <p>Doppler optical coherence <span class="hlt">tomography</span> (DOCT) is considered one of the most promising functional imaging modalities for neuro biology research and has demonstrated the ability to quantify cerebral blood flow <span class="hlt">velocity</span> at a high accuracy. However, the measurement of total absolute blood flow <span class="hlt">velocity</span> (BFV) of major cerebral arteries is still a difficult problem since it is related to vessel geometry. In this paper, we present a volumetric vessel reconstruction approach that is capable of measuring the absolute BFV distributed along the entire middle cerebral artery (MCA) within a large field-of-view. The Doppler angle at each point of the MCA, representing the vessel geometry, is derived analytically by localizing the artery from pure DOCT images through vessel segmentation and skeletonization. Our approach could achieve automatic quantification of the fully distributed absolute BFV across different vessel branches. Experiments on rodents using swept-source optical coherence <span class="hlt">tomography</span> showed that our approach was able to reveal the consequences of permanent MCA occlusion with absolute BFV measurement. PMID:26977365</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/24582555','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/24582555"><span id="translatedtitle">Corrosion and erosion monitoring in plates and pipes using constant <span class="hlt">group</span> <span class="hlt">velocity</span> Lamb wave inspection.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Nagy, Peter B; Simonetti, Francesco; Instanes, Geir</p> <p>2014-09-01</p> <p>Recent improvements in tomographic reconstruction techniques generated a renewed interest in short-range ultrasonic guided wave inspection for real-time monitoring of internal corrosion and erosion in pipes and other plate-like structures. Emerging evidence suggests that in most cases the fundamental asymmetric A0 mode holds a distinct advantage over the earlier market leader fundamental symmetric S0 mode. Most existing A0 mode inspections operate at relatively low inspection frequencies where the mode is highly dispersive therefore very sensitive to variations in wall thickness. This paper examines the potential advantages of increasing the inspection frequency to the so-called constant <span class="hlt">group</span> <span class="hlt">velocity</span> (CGV) point where the <span class="hlt">group</span> <span class="hlt">velocity</span> remains essentially constant over a wide range of wall thickness variation, but the phase <span class="hlt">velocity</span> is still dispersive enough to allow accurate wall thickness assessment from phase angle measurements. This paper shows that in the CGV region the crucial issue of temperature correction becomes especially simple, which is particularly beneficial when higher-order helical modes are also exploited for <span class="hlt">tomography</span>. One disadvantage of working at such relatively high inspection frequency is that, as the slower A0 mode becomes faster and less dispersive, the competing faster S0 mode becomes slower and more dispersive. At higher inspection frequencies these modes cannot be separated any longer based on their vibration polarization only, which is mostly tangential for the S0 mode while mostly normal for the A0 at low frequencies, as the two modes become more similar as the frequency increases. Therefore, we propose a novel method for suppressing the unwanted S0 mode based on the Poisson effect of the material by optimizing the angle of inclination of the equivalent transduction force of the Electromagnetic Acoustic Transducers (EMATs) used for generation and detection purposes. PMID:24582555</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007AGUFM.S23B1388T&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007AGUFM.S23B1388T&link_type=ABSTRACT"><span id="translatedtitle">Development of a State-Wide 3-D Seismic <span class="hlt">Tomography</span> <span class="hlt">Velocity</span> Model for California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thurber, C. H.; Lin, G.; Zhang, H.; Hauksson, E.; Shearer, P.; Waldhauser, F.; Hardebeck, J.; Brocher, T.</p> <p>2007-12-01</p> <p>We report on progress towards the development of a state-wide tomographic model of the P-wave <span class="hlt">velocity</span> for the crust and uppermost mantle of California. The dataset combines first arrival times from earthquakes and quarry blasts recorded on regional network stations and travel times of first arrivals from explosions and airguns recorded on profile receivers and network stations. The principal active-source datasets are Geysers-San Pablo Bay, Imperial Valley, Livermore, W. Mojave, Gilroy-Coyote Lake, Shasta region, Great Valley, Morro Bay, Mono Craters-Long Valley, PACE, S. Sierras, LARSE 1 and 2, Loma Prieta, BASIX, San Francisco Peninsula and Parkfield. Our beta-version model is coarse (uniform 30 km horizontal and variable vertical gridding) but is able to image the principal features in previous separate regional models for northern and southern California, such as the high-<span class="hlt">velocity</span> subducting Gorda Plate, upper to middle crustal <span class="hlt">velocity</span> highs beneath the Sierra Nevada and much of the Coast Ranges, the deep low-<span class="hlt">velocity</span> basins of the Great Valley, Ventura, and Los Angeles, and a high- <span class="hlt">velocity</span> body in the lower crust underlying the Great Valley. The new state-wide model has improved areal coverage compared to the previous models, and extends to greater depth due to the data at large epicentral distances. We plan a series of steps to improve the model. We are enlarging and calibrating the active-source dataset as we obtain additional picks from investigators and perform quality control analyses on the existing and new picks. We will also be adding data from more quarry blasts, mainly in northern California, following an identification and calibration procedure similar to Lin et al. (2006). Composite event construction (Lin et al., in press) will be carried out for northern California for use in conventional <span class="hlt">tomography</span>. A major contribution of the state-wide model is the identification of earthquakes yielding arrival times at both the Northern California Seismic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T33E2700C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T33E2700C"><span id="translatedtitle">Anisotropic Shear-wave <span class="hlt">Velocity</span> Structure of East Asian Upper Mantle from Waveform <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chong, J.; Yuan, H.; French, S. W.; Romanowicz, B. A.; Ni, S.</p> <p>2012-12-01</p> <p>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 <span class="hlt">tomography</span> to image 3D isotropic, radially and azimuthally anisotropic upper mantle shear <span class="hlt">velocity</span> 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 <span class="hlt">velocity</span> 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 <span class="hlt">velocity</span> in the upper mantle. Lower <span class="hlt">velocity</span> 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 <span class="hlt">velocity</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T51C..07O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T51C..07O"><span id="translatedtitle">Seismic <span class="hlt">velocity</span> variation along the Izu-Bonin arc estaimated from traveltime <span class="hlt">tomography</span> using OBS data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Obana, K.; Tamura, Y.; Takahashi, T.; Kodaira, S.</p> <p>2014-12-01</p> <p>The Izu-Bonin (Ogasawara) arc is an intra-oceanic island arc along the convergent plate boundary between the subducting Pacific and overriding Philippine Sea plates. Recent active seismic studies in the Izu-Bonin arc reveal significant along-arc variations in crustal structure [Kodaira et al., 2007]. The thickness of the arc crust shows a remarkable change between thicker Izu (~30 km) and thinner Bonin (~10 km) arcs. In addition to this, several geological and geophysical contrasts, such as seafloor topography and chemical composition of volcanic rocks, between Izu and Bonin arc have been reported [e.g., Yuasa 1992]. We have conducted earthquake observations using ocean bottom seismographs (OBSs) to reveal seismic <span class="hlt">velocity</span> structure of the crust and mantle wedge in the Izu-Bonin arc and to investigate origin of the along-arc structure variations. We deployed 40 short-period OBSs in Izu and Bonin area in 2006 and 2009, respectively. The OBS data were processed with seismic data recorded at routine seismic stations on Hachijo-jima, Aoga-shima, and Chichi-jima operated by National Research Institute for Earth Science and Disaster Prevention (NIED). More than 5000 earthquakes were observed during about three-months observation period in each experiment. We conducted three-dimensional seismic <span class="hlt">tomography</span> using manually picked P- and S-wave arrival time data. The obtained image shows a different seismic <span class="hlt">velocity</span> structures in the mantle beneath the volcanic front between Izu and Bonin arcs. Low P-wave <span class="hlt">velocity</span> anomalies in the mantle beneath the volcanic front in the Izu arc are limited at depths deeper than those in the Bonin arc. On the other hand, P-wave <span class="hlt">velocity</span> in the low <span class="hlt">velocity</span> anomalies beneath volcanic front in the Bonin arc is slower than that in the Izu arc. These large-scale along-arc structure variations in the mantle could relate to the geological and geophysical contrasts between Izu and Bonin arcs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUSM.S31B..04Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUSM.S31B..04Y"><span id="translatedtitle">P-Wave <span class="hlt">Velocity</span> Structure beneath Eastern Eurasia from Finite Frequency Seismic <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, T.; Shen, Y.; Yang, X.</p> <p>2006-05-01</p> <p>Despite the recent extensive seismic studies, the detailed lithospheric structure and deep mantle dynamic processes beneath eastern Eurasia remain poorly constrained. In this study, we applied the Finite Frequency Seismic <span class="hlt">Tomography</span> (FFST) method, which utilizes the 3D Fréchet sensitivity kernels of the travel times of finite frequency seismic waves to account for wavefront healing and off-ray scattering, to eastern Eurasia. Taking advantage of the broadband feature of seismic records, we measured P wave relative delays times by waveform cross-correlation in three frequency bands (0.03-0.1Hz, 0.1-0.5 Hz and 0.5 to 2.0 Hz), which were inverted jointly to constrain <span class="hlt">velocity</span> heterogeneities with different distances from the central geometric rays. The effect of strong variations in crustal structure beneath this region on travel time data was removed by conducting a frequency dependent crustal correction. A comprehensive dataset, including waveforms from the publicly accessible sources and other seismic networks in the region, were collected for this study. Our preliminary results are consistent with the <span class="hlt">velocity</span> models obtained in previous tomographic studies. A more complete dataset will further improve the resolution of the <span class="hlt">velocity</span> structure beneath eastern Eurasia.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/7149038','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/7149038"><span id="translatedtitle">High-resolution seismic <span class="hlt">tomography</span> of compressional wave <span class="hlt">velocity</span> structure at Newberry Volcano, Oregon Cascade Range</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Achauer, U.; Evans, J.R.; Stauber, D.A.</p> <p>1988-09-10</p> <p>Compressional wave <span class="hlt">velocity</span> structure is determined for the upper crust beneath Newberry Volcano, central Oregon, using a high-resolution active-source seismic-<span class="hlt">tomography</span> method. Newberry Volcano is a bimodal shield volcano east of the axis of the Cascade Range. It is associated both with the Cascade Range and with northwest migrating silicic volcanism in southeast Oregon. High-frequency (approx.7 Hz) crustal phases, nominally Pg and a midcrustal reflected phase, travel upward through a target volume beneath Newberry Volcano to a dense array of 120 seismographs. This arrangement is limited by station spacing to 1- to 2-km resolution in the upper 5 to 6 km of the crust beneath the volcano's summit caldera. The experiment tests the hypothesis that Cascade Range volcanoes are underlain only by small magma chambers. A small low-<span class="hlt">velocity</span> anomaly delineated abosut 3 km below the summit caldera supports this hypothesis for Newberry Volcano and is interpreted as a possible magma chamber of a few to a few tens of km/sup 3/ in volume. A ring-shaped high-<span class="hlt">velocity</span> anomaly nearer the surface coincides with the inner mapped ring fractures of the caldera. It also coincides with a circular gravity high, and we interpret it as largely subsolidus silicic cone sheets. The presence of this anomaly and of silicic vents along the ring fractures suggests that the fractures are a likely eruption path between the small magma chamber and the surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T43B2644P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T43B2644P"><span id="translatedtitle">Rayleigh wave phase <span class="hlt">velocity</span> maps from the ambient noise <span class="hlt">tomography</span> in central Mongolia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pan, J.; Wu, Q.; Gao, M.; Li, Y.; Demberel, S. G.; Munkhuu, U.</p> <p>2013-12-01</p> <p>The study area (103°E-111°E, 44°N-49°N) located in the Mongolian fold belts and situated at the southeast of Baikal rift zone which is known as one of the most active regions on the Earth due to integrated influence of the India-Asia collision and compression and the subduction of the Pacific Plate. Additionally, it also located in the north of South-North earthquake belts of China. So, it is believed to be an ideal site for understanding intraplate dynamics. Seismic ambient noise <span class="hlt">tomography</span> has been performed all over the world these years, and it has been proved it's a powerful way to image and study the structure of crust and uppermost mantle due to its exclusive capability to extract estimated Green's functions for short period surface waves. Compared with traditional earthquake <span class="hlt">tomography</span> methods of surface waves, ambient noise <span class="hlt">tomography</span> hasn't limitations related to the distribution of earthquakes as well as errors in earthquake locations and source mechanisms. A new scientific project was carried out in 2011 by Institute of Geophysics of China Earthquake Administration (IGP-CEA) and Research center of Astronomy and Geophysics of Mongolian Academy of Science (RCAG-MAS). In the seismic sub-project 60 portable seismic stations were deployed in central Mongolia in August 2011. Continuous time-series of vertical component between August 2011 and July 2012 have been collected and cross-correlated to obtain estimated Green's functions (EGF) of Rayleigh wave. Using the frequency and time analysis technique based on continuous wavelet transformation, 1258 of phase <span class="hlt">velocity</span> dispersion curves of Rayleigh wave were extracted from EGFs. High resolution phase <span class="hlt">velocity</span> maps at periods of 5, 10, 20 and 30 s were reconstructed with grid size 0.5°x0.5° by utilizing a generalized 2-D-linear inversion method developed by Ditmar & Yanovskaya. The <span class="hlt">tomography</span> results reveal lateral heterogeneity of shear wave structure in the crust and upper mantle in the study region. For</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.7382C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.7382C"><span id="translatedtitle">Extraction of the local phase <span class="hlt">velocity</span> and the <span class="hlt">group</span> <span class="hlt">velocity</span> from surface noise source in microseismic monitoring.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chmiel, Malgorzata; Roux, Philippe; Bardainne, Thomas</p> <p>2015-04-01</p> <p>The aim of this work is to demonstrate the extraction of the local phase <span class="hlt">velocity</span> and the <span class="hlt">group</span> <span class="hlt">velocity</span> from surface noise source in microseismic monitoring. One of the biggest challenges in microseismic monitoring is surface seismic noise. Microseismic surface studies are often contaminated with instrumental and ambient seismic noise, originating from both natural (wind, rain) and anthropogenic sources (injection, pumps, infrastructure, traffic). The two primary ways to attenuate the undesired surface noise sources are via processing and acquisition strategies. At the acquisition stage, one solution is through the use of patch array. One patch is a <span class="hlt">group</span> of 48 vertical sensors densely distributed on the area of~150m*150m, and one trace is the array of 12 vertical geophones. In the present work, 44 patches were sparsely distributed on a 41 square kilometer area. Benefitting from continuous recording, we used Matched Field Processing (MFP) methods to extract local phase and <span class="hlt">group</span> <span class="hlt">velocities</span> over the whole area. The aim of this technique is to detect and locate uncoherent noise sources while using array-processing methods. The method is based on the comparison between a recorded wave field per patch (the data vector) and a theoretical (or modeled) wave-field (the replica vector) in the frequency domain. The replica vector is a Green's function at a given frequency, which depends on the following parameters: position (x,y) in 2D-grid and a phase <span class="hlt">velocity</span>. The noise source location is obtained by matching the data vector with the replica vector using a linear "low-resolution" algorithm or a nonlinear "high-resolution" adaptive processor. These algorithms are defined for each point in the 2D - grid and for each phase <span class="hlt">velocity</span>. The phase <span class="hlt">velocity</span> per patch is optimal if it maximizes the processor output. As a result, an ambiguity surface is produced which shows the probability of presence of primary noise sources per patch. The combination of all the maps per patch</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011SPIE.8091E..0LW','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011SPIE.8091E..0LW"><span id="translatedtitle">Enhanced joint spectral and time domain optical coherence <span class="hlt">tomography</span> for quantitative flow <span class="hlt">velocity</span> measurement</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walther, Julia; Koch, Edmund</p> <p>2011-06-01</p> <p>Recently, a new method called joint spectral and time domain optical coherence <span class="hlt">tomography</span> (STdOCT) for flow <span class="hlt">velocity</span> measurement in spectral domain OCT (SD OCT) was presented. This method analyzes the detected timeresolved interference fringe spectra by using a two-dimensional fast Fourier transformation (2D FFT) to determine directly the Doppler frequency shift instead of calculating the phase difference at each depth position of adjacent A-scans. There, it was found that STdOCT is more robust for measurements with low signal to noise ratio than the classic phase-resolved Doppler OCT (DOCT) making it attractive first for imaging fast flow <span class="hlt">velocities</span> at which a strong Doppler angle dependent signal damping occurs due to interference fringe washout and second for investigating large blood vessels with a big diameter and a highly damped signal of blood with increasing depth due to strong scattering and absorption in the near-infrared wavelength range. In the present study, we would like to introduce an enhanced algorithm for STdOCT permitting a more precise flow <span class="hlt">velocity</span> measurement in comparison to the conventional STdOCT. The new method determines the amplitude of the broadened Doppler frequency shift by calculating the center of gravity via the complex analytical signal as a result of the second FFT instead of detecting the maximum intensity signal. Furthermore, the comparison with phase-resolved DOCT was done experimentally by using a flow phantom consisting of a 1% Intralipid emulsion and a 320 μm glass capillary. As a result, the enhanced STdOCT and DOCT processed data are completely equivalent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1610360A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1610360A"><span id="translatedtitle">Surface wave phase <span class="hlt">velocities</span> from 2-D surface wave <span class="hlt">tomography</span> studies in the Anatolian plate</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arif Kutlu, Yusuf; Erduran, Murat; Çakır, Özcan; Vinnik, Lev; Kosarev, Grigoriy; Oreshin, Sergey</p> <p>2014-05-01</p> <p>We study the Rayleigh and Love surface wave fundamental mode propagation beneath the Anatolian plate. To examine the inter-station phase <span class="hlt">velocities</span> a two-station method is used along with the Multiple Filter Technique (MFT) in the Computer Programs in Seismology (Herrmann and Ammon, 2004). The near-station waveform is deconvolved from the far-station waveform removing the propagation effects between the source and the station. This method requires that the near and far stations are aligned with the epicentre on a great circle path. The azimuthal difference of the earthquake to the two-stations and the azimuthal difference between the earthquake and the station are restricted to be smaller than 5o. We selected 3378 teleseismic events (Mw >= 5.7) recorded by 394 broadband local stations with high signal-to-noise ratio within the years 1999-2013. Corrected for the instrument response suitable seismogram pairs are analyzed with the two-station method yielding a collection of phase <span class="hlt">velocity</span> curves in various period ranges (mainly in the range 25-185 sec). Diffraction from lateral heterogeneities, multipathing, interference of Rayleigh and Love waves can alter the dispersion measurements. In order to obtain quality measurements, we select only smooth portions of the phase <span class="hlt">velocity</span> curves, remove outliers and average over many measurements. We discard these average phase <span class="hlt">velocity</span> curves suspected of suffering from phase wrapping errors by comparing them with a reference Earth model (IASP91 by Kennett and Engdahl, 1991). The outlined analysis procedure yields 3035 Rayleigh and 1637 Love individual phase <span class="hlt">velocity</span> curves. To obtain Rayleigh and Love wave travel times for a given region we performed 2-D tomographic inversion for which the Fast Marching Surface <span class="hlt">Tomography</span> (FMST) code developed by N. Rawlinson at the Australian National University was utilized. This software package is based on the multistage fast marching method by Rawlinson and Sambridge (2004a, 2004b). The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1076806','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1076806"><span id="translatedtitle">Derivation of site-specific relationships between hydraulic parameters and p-wave <span class="hlt">velocities</span> based on hydraulic and seismic <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Brauchler, R.; Doetsch, J.; Dietrich, P.; Sauter, M.</p> <p>2012-01-10</p> <p>In this study, hydraulic and seismic tomographic measurements were used to derive a site-specific relationship between the geophysical parameter p-wave <span class="hlt">velocity</span> and the hydraulic parameters, diffusivity and specific storage. Our field study includes diffusivity tomograms derived from hydraulic travel time <span class="hlt">tomography</span>, specific storage tomograms, derived from hydraulic attenuation <span class="hlt">tomography</span>, and p-wave <span class="hlt">velocity</span> tomograms, derived from seismic <span class="hlt">tomography</span>. The tomographic inversion was performed in all three cases with the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm, using a ray tracing technique with curved trajectories. The experimental set-up was designed such that the p-wave <span class="hlt">velocity</span> tomogram overlaps the hydraulic tomograms by half. The experiments were performed at a wellcharacterized sand and gravel aquifer, located in the Leine River valley near Göttingen, Germany. Access to the shallow subsurface was provided by direct-push technology. The high spatial resolution of hydraulic and seismic <span class="hlt">tomography</span> was exploited to derive representative site-specific relationships between the hydraulic and geophysical parameters, based on the area where geophysical and hydraulic tests were performed. The transformation of the p-wave <span class="hlt">velocities</span> into hydraulic properties was undertaken using a k-means cluster analysis. Results demonstrate that the combination of hydraulic and geophysical tomographic data is a promising approach to improve hydrogeophysical site characterization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S41B2744B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S41B2744B"><span id="translatedtitle">Anisotropic 3-D Crustal <span class="hlt">Velocity</span> Structure of Idaho/ Oregon from a Joint Inversion of <span class="hlt">Group</span> and Phase <span class="hlt">Velocities</span> of Love and Rayleigh Waves from Ambient Seismic Noise: Results from the IDOR Project</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bremner, P. M.; Panning, M. P.; Russo, R.; Mocanu, V. I.; Stanciu, A. C.; Torpey, M. E.; Hongsresawat, S.; VanDecar, J. C.</p> <p>2015-12-01</p> <p>We present new 3-D radially anisotropic and isotropic crustal <span class="hlt">velocity</span> models beneath central Idaho and eastern Oregon. We produced the <span class="hlt">velocity</span> models from Love and horizontal component Rayleigh wave <span class="hlt">group</span> and phase <span class="hlt">velocity</span> measurements on the IDaho/ORegon (IDOR) Passive seismic network, 86 broadband seismic stations, dataset using ambient noise <span class="hlt">tomography</span> and the methods of Gallego et. al (2010) and Lin et. al (2008). We calculated inter-station <span class="hlt">group</span>/phase <span class="hlt">velocities</span> in narrow frequency bands from travel-time measurements of the rotated stacked horizontal component cross-correlations (bandpass filtered between 2 and 30 seconds), which we used to invert for <span class="hlt">velocity</span> structure beneath the network. We derived <span class="hlt">group</span> and phase <span class="hlt">velocity</span> maps for each frequency band using the damped least-squares inversion method of Tarantola (2005), and then jointly inverted for <span class="hlt">velocity</span> with depth. Moho depths are prescribed in the joint inversions based on receiver functions, also from the IDOR seismic data, and provides a starting crustal <span class="hlt">velocity</span> model. Goals of our work include refining models of crustal structure in the accreted Blue Mountain terranes in the western study area; determining the depth extent of the Salmon River Suture/West Idaho Shear Zone (WISZ), which crosses north-south through the middle of the network; determining the architecture of the Idaho batholith, an extensive largely crustal-derived pluton; and examining the nature of the autochthonous (?) North American crust and lithosphere beneath and east of the batholith.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.S33A1754S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.S33A1754S"><span id="translatedtitle">Improved Near-surface <span class="hlt">Velocity</span> Models from Waveform <span class="hlt">Tomography</span> Applied to Vibroseis MCS Reflection Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smithyman, B.; Clowes, R. M.</p> <p>2009-12-01</p> <p>Multichannel vibroseis reflection surveys are prevalent in the land exploration seismic industry because of benefits in speed and cost, along with reduced environmental impact when compared to explosive sources. Since the downgoing energy must travel through the shallow subsurface, an improved model of near-surface <span class="hlt">velocity</span> can in theory substantially improve the resolution of deeper reflections. We describe techniques aimed at allowing the use of vibroseis data for long-offset refraction processing of first-arrival traveltimes and waveforms. Refraction processing of surface vibroseis data is typically limited to near-offset refraction statics. <span class="hlt">Velocity</span> models of the shallow subsurface can be built to facilitate CDP stacking and migration, but these models are typically coarse and of limited use for interpretation. Waveform <span class="hlt">tomography</span> combines inversion of first-arrival traveltime data with full waveform inversion of densely-sampled refracted arrivals. Since inversion of the waveform amplitude and phase is not limited by the ray-theory approximation, identification of low-<span class="hlt">velocity</span> zones and small scattering targets is possible. Incorporating a wide range of offsets is critical for a more complete characterization of the near-surface. Because of the use of a non-linear frequency-domain approach to the solution of this inverse problem, low data frequencies are important in comparison with conventional reflection processing. Through the use of waveform <span class="hlt">tomography</span>, we plan to build useful, detailed near-surface <span class="hlt">velocity</span> models for both the reflection work flow and direct interpretation. Several difficulties exist in first-arrival analysis and waveform inversion of vibroseis data. The mixed-phase vibroseis source signature exhibits variations in phase with offset that are difficult to quantify without detailed a priori knowledge of the near-surface. This causes difficulties with picking and initial model building, which is critical for non-linear waveform inversion. A</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.S31E..05W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.S31E..05W"><span id="translatedtitle">Can we go From Tomographically Determined Seismic <span class="hlt">Velocities</span> to Composition? Amplitude Resolution Issues in Local Earthquake <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wagner, L.</p> <p>2007-12-01</p> <p>There have been a number of recent papers (i.e. Lee (2003), James et al. (2004), Hacker and Abers (2004), Schutt and Lesher (2006)) which calculate predicted <span class="hlt">velocities</span> for xenolith compositions at mantle pressures and temperatures. It is tempting, therefore, to attempt to go the other way ... to use tomographically determined absolute <span class="hlt">velocities</span> to constrain mantle composition. However, in order to do this, it is vital that one is able to accurately constrain not only the polarity of the determined <span class="hlt">velocity</span> deviations (i.e. fast vs slow) but also how much faster, how much slower relative to the starting model, if absolute <span class="hlt">velocities</span> are to be so closely analyzed. While much attention has been given to issues concerning spatial resolution in seismic <span class="hlt">tomography</span> (i.e. what areas are fast, what areas are slow), little attention has been directed at the issue of amplitude resolution (how fast, how slow). <span class="hlt">Velocity</span> deviation amplitudes in seismic <span class="hlt">tomography</span> are heavily influenced by the amount of regularization used and the number of iterations performed. Determining these two parameters is a difficult and little discussed problem. I explore the effect of these two parameters on the amplitudes obtained from the tomographic inversion of the Chile Argentina Geophysical Experiment (CHARGE) dataset, and attempt to determine a reasonable solution space for the low Vp, high Vs, low Vp/Vs anomaly found above the flat slab in central Chile. I then compare this solution space to the range in experimentally determined <span class="hlt">velocities</span> for peridotite end-members to evaluate our ability to constrain composition using tomographically determined seismic <span class="hlt">velocities</span>. I find that in general, it will be difficult to constrain the compositions of normal mantle peridotites using tomographically determined <span class="hlt">velocities</span>, but that in the unusual case of the anomaly above the flat slab, the observed <span class="hlt">velocity</span> structure still has an anomalously high S wave <span class="hlt">velocity</span> and low Vp/Vs ratio that is most</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012SPIE.8222E..0HD&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012SPIE.8222E..0HD&link_type=ABSTRACT"><span id="translatedtitle">Dual-beam optical coherence <span class="hlt">tomography</span> system for quantification of flow <span class="hlt">velocity</span> in capillary phantoms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Daly, S. M.; Silien, C.; Leahy, M. J.</p> <p>2012-03-01</p> <p>The quantification of (blood) flow <span class="hlt">velocity</span> within the vasculature has potent diagnostic and prognostic potential. Assessment of flow irregularities in the form of increased permeability (micro haemorrhaging), the presence of avascular areas, or conversely the presence of vessels with enlarged or increased tortuosity in the acral regions of the body may provide a means of non-invasive in vivo assessment. If assessment of dermal flow dynamics were performed in a routine manner, the existence and prevalence of ailments such as diabetes mellitus, psoriatic arthritis and Raynaud's condition may be confirmed prior to clinical suspicion. This may prove advantageous in cases wherein the efficacy of a prescribed treatment is dictated by a prompt diagnosis and to alleviate patient discomfort through early detection. Optical Coherence <span class="hlt">Tomography</span> (OCT) is an imaging modality which utilises the principle of optical interferometry to distinguish between spatial changes in refractive index within the vasculature and thus formulate a multi-dimensional representation of the structure of the epi- and dermal skin layers. The use of the Doppler functionality has been the predominant force for the quantification of moving particles within media, elucidated via estimation of the phase shift in OCT A-scans. However, the theoretical formulation for the assessment of these phase shifts dictates that the angle between the incident light source and the vessel under question be known a priori; this may be achieved via excisional biopsy of the tissue segment in question, but is counter to the non-invasive premise of the OCT technique. To address the issue of angular dependence, an alternate means of estimating absolute flow <span class="hlt">velocity</span> is presented. The design and development of a dual-beam (db) system incorporating an optical switch mechanism for signal discrimination of two spatially disparate points enabling quasi-simultaneous multiple specimen scanning is described. A crosscorrelation (c</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S31B4404B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S31B4404B"><span id="translatedtitle">3-D Crustal <span class="hlt">Velocity</span> Structure of Central Idaho/ Eastern Oregon from Joint Inversion of Rayleigh Wave <span class="hlt">Group</span> and Phase <span class="hlt">Velocities</span> Derived from Ambient Seismic Noise: Newest Results from the IDOR Project</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bremner, P. M.; Panning, M. P.; Russo, R. M.; Mocanu, V. I.; Stanciu, A. C.; Torpey, M. E.; Hongsresawat, S.; VanDecar, J. C.</p> <p>2014-12-01</p> <p>We present the latest 3-D isotropic crustal <span class="hlt">velocity</span> model beneath central Idaho and eastern Oregon. We produced the <span class="hlt">velocity</span> model from vertical component Rayleigh wave <span class="hlt">group</span> and phase <span class="hlt">velocity</span> measurements on data from the IDaho/ORegon (IDOR) Passive seismic network, 86 broadband seismic stations, using ambient noise <span class="hlt">tomography</span> and the methods of Gallego et. al (2010) and Lin et. al (2008). We calculated inter-station <span class="hlt">group</span>/phase <span class="hlt">velocities</span> in narrow frequency bands from travel-time measurements of the stacked cross-correlations (bandpass filtered between 2 and 30 seconds), which we used to invert for <span class="hlt">velocity</span> structure beneath the network. Goals of our work include refining models of crustal structure in the accreted Blue Mountain terranes in the western study area; determining the depth extent of the Salmon River Suture/West Idaho Shear Zone (WISZ), which crosses north-south through the middle of the network; determining the architecture of the Idaho batholith, an extensive largely crustal-derived pluton; and examining the nature of the autochthonous (?) North American crust and lithosphere beneath and east of the batholith. We derived Rayleigh wave <span class="hlt">group</span> and phase <span class="hlt">velocity</span> maps for each frequency band using the damped least-squares inversion method of Tarantola (2005), and then jointly inverted for <span class="hlt">velocity</span> with depth. Moho depths are prescribed in the joint inversions based on receiver functions, also from the IDOR seismic data, and provides a starting crustal <span class="hlt">velocity</span> model. 3-D checkerboard resolution tests indicate lateral resolution of better than 40 km. Preliminary results show higher S wave <span class="hlt">velocities</span> in the western study area, and lower <span class="hlt">velocities</span> in the lower crust on the east side of the network, consistent with Basin-and-Range style extension there. A tabular <span class="hlt">velocity</span> anomaly juxtaposing higher above lower seismic <span class="hlt">velocities</span> dips shallow west in the midcrust on the west side of the network.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoRL..41.8045W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoRL..41.8045W"><span id="translatedtitle">Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> distributions for East Asia using 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>Witek, Michael; van der Lee, Suzan; Kang, Tae-Seob</p> <p>2014-11-01</p> <p>Vertical component data from 206 broadband seismometer stations from Korean networks Korean Institute of Geoscience and Mineral Resources and Korea Meteorological Administration, the Japanese F-net network, and the Chinese New China Digital Seismograph Network and Northeast China Extended Seismic Array network are collected for the year 2011, and the ambient seismic noise is analyzed. Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> distribution maps are created in the period range 10 to 70 s. Our results are largely consistent with previous studies of the area but provide greater detail in the Korean peninsula and the Sea of Japan. Low <span class="hlt">group</span> <span class="hlt">velocities</span> are observed in the Ulleung basin, and the Chubu-Kanto and Kyushu regions in Japan. At 10 s period, sediment basins in the Sea of Japan appear as low <span class="hlt">group</span> <span class="hlt">velocity</span> regions relative to higher <span class="hlt">group</span> <span class="hlt">velocity</span> continental regions. At periods longer than 40 s, a low <span class="hlt">group</span> <span class="hlt">velocity</span> region emerges in the Ulleung basin region, and is bounded by the Korean peninsula.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PApGe.tmp..172O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PApGe.tmp..172O"><span id="translatedtitle">P-Wave <span class="hlt">Velocity</span> <span class="hlt">Tomography</span> from Local Earthquakes in Western Mexico</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ochoa-Chávez, Juan A.; Escudero, Christian R.; Núñez-Cornú, Francisco J.; Bandy, William L.</p> <p>2015-11-01</p> <p>In western Mexico, the subduction of the Rivera and Cocos plates beneath the North America plate has deformed and fragmented the overriding plate, forming several structural rifts and crustal blocks. To obtain a reliable subsurface image of the continental crust and uppermost mantle in this complex area, we used P-wave arrivals of local earthquakes along with the Fast Marching Method <span class="hlt">tomography</span> technique. We followed an inversion scheme consisting of (1) the use of a high-quality earthquake catalog and corrected phase picks, (2) the selection of earthquakes using a maximum location error threshold, (3) the estimation of an improved 1-D reference <span class="hlt">velocity</span> model, and (4) the use of checkerboard testing to determine the optimum configuration of the <span class="hlt">velocity</span> nodes and inversion parameters. Surprisingly, the <span class="hlt">tomography</span> results show a very simple δVp distribution that can be described as being controlled by geologic structures formed during two stages of the separation of the Rivera and Cocos plates. The earlier period represents the initial stages of the separation of the Rivera and Cocos plates beneath western Mexico; the later period represents the more advanced stage of rifting where the Rivera and Cocos plates had separated sufficiently to allow melt to accumulate below the Colima Volcanic complex. During the earlier period (14 or 10-1.6 Ma), NE-SW-oriented structures/lineaments (such as the Southern Colima Rift) were formed as the two plates separated. During the second period (1.6 Ma to the present), the deformation is attributed to magma, generated within and above the tear zone between the Rivera and Cocos plates, rising beneath the region of the Colima Volcanic Complex. The rising magma fractured the overlying crust, forming a classic triple-rift junction geometry. This triple-rift system is confined to the mid- to lower crust perhaps indicating that this rifting process is still in an early stage. This fracturing, along with fluid circulation and associated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015520','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015520"><span id="translatedtitle">High <span class="hlt">velocity</span> anomaly beneath the Deccan volcanic province: Evidence from seismic <span class="hlt">tomography</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>Iyer, H.M.; Gaur, V.K.; Rai, S.S.; Ramesh, D.S.; Rao, C.V.R.; Srinagesh, D.; Suryaprakasam, K.</p> <p>1989-01-01</p> <p>Analysis of teleseismic P-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the <span class="hlt">velocity</span> is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first <span class="hlt">group</span> of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second <span class="hlt">group</span> roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third <span class="hlt">group</span> of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to-1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of the P-wave residual data delineate the presence of a 600 km long approximately N-S trending anomalous region of high <span class="hlt">velocity</span> (1-4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion of P-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high <span class="hlt">velocity</span> zone (1-4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low <span class="hlt">velocity</span> region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high <span class="hlt">velocity</span> anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low</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_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_4 --> <div id="page_5" 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_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="81"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.T53D..03Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.T53D..03Y"><span id="translatedtitle">P-Wave <span class="hlt">Velocity</span> Structure Beneath Eastern Eurasia From Finite Frequency Seismic <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, T.; Shen, Y.; Yang, X.</p> <p>2005-12-01</p> <p>Eastern Eurasia is one of the most tectonically complex regions in the world. While the evolution history of continental lithosphere has been well recognized, the fine structure associated with the complicated deformation in this region is far from clear, and deep mantle processes that accompanied shallower lithosphere deformations are poorly understood. In order to improve the resolution of the <span class="hlt">velocity</span> structure in the region, we applied the newly-developed Finite Frequency Seismic <span class="hlt">Tomography</span> (FFST) method, which utilizes the 3D Frechet-Born sensitivity kernels of the travel times of finite frequency seismic waves to account for wavefront healing and off-ray scattering, to eastern Eurasia. In addition to the new technique, we obtained a comprehensive finite-frequency body wave travel time data set from cross-correlation of broadband waveforms. Datasets used in this study include waveforms from the publicly accessible sources (e.g. IRIS, GSN, PASSCAL, and IMS stations) and other seismic networks in the region such as the Japanese Broadband Seismograph Network (F-net), the Japanese International Seismic Network (JISNET), the Taiwan Broadband Seismic Network and China National Digital Seismic Network. Taking advantage of broadband waveforms, we measured relative delays times by waveform cross-correlation in three frequency bands between 0.03 to 2 Hz for P waves. The travel times in the three frequency bands were inverted jointly to take advantage of the `data fusion' made possible by the finite-frequency kernels and separately to understand the resolving power of each data set. Preliminary results are comparable to the <span class="hlt">velocity</span> models obtained in previous tomographic studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003PhDT........25Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003PhDT........25Y"><span id="translatedtitle">Noninvasive microstructural and <span class="hlt">velocity</span> imaging in humans by color Doppler optical coherence <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yazdanfar, Siavash</p> <p></p> <p>The objective of this dissertation is to develop the optical instrumentation, electronics, and signal processing for high-resolution blood flow imaging using optical coherence <span class="hlt">tomography</span> (OCT) in human subjects. In particular, in vivo OCT blood flow imaging, termed color Doppler OCT (CDOCT), is applied for the first time to measurements in human vasculature of the retina and skin. CDOCT is similar to color Doppler ultrasound, whereas depth-resolved flow information is extracted from reflectivity profiles obtained from phase-sensitive, low-coherence interferometry. Although CDOCT has been demonstrated in tissue-mimicking phantoms and in living animal models, the technique has not yet been extended to blood flow imaging in humans. In this project, CDOCT was integrated with a modified slit lamp biomicroscope for imaging of retinal blood flow, and additional technical requirements necessary for retinal flow imaging were met. This system was used to acquire the first high resolution, cross-sectional images of blood flow with OCT in humans. The image acquisition rate was increased to examine retinal hemodynamics in normal subjects. A method was introduced for improving the <span class="hlt">velocity</span> resolution by approximately two orders of magnitude, down to ˜1 micrometer/sec, by calculating the change in the phase across sequential scans. This technique was used to achieve the highest <span class="hlt">velocity</span> resolution to date in scattering media, and applied to imaging the human microvasculature down to the capillary level. Finally, a modification of CDOCT based on differential phase contrast was introduced for high resolution imaging in the presence of motion artifact. This technique measures the differential Doppler frequency between two beams of orthogonal polarization states that are laterally displaced on the sample. Using polarization diversity detection, the common-mode noise was removed, enabling the measurement of flow in scattering media down to the theoretical frequency resolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015WRR....51.9665R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015WRR....51.9665R"><span id="translatedtitle">Application of acoustic <span class="hlt">tomography</span> to reconstruct the horizontal flow <span class="hlt">velocity</span> field in a shallow river</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Razaz, Mahdi; Kawanisi, Kiyosi; Kaneko, Arata; Nistor, Ioan</p> <p>2015-12-01</p> <p>A novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20-35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic <span class="hlt">tomography</span> in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5-3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth-average current <span class="hlt">velocity</span> components from differential travel times. Zeroth-order Tikhonov regularization, in conjunction with L-curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along-channel <span class="hlt">velocities</span> larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.1716G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.1716G"><span id="translatedtitle">Can seismic <span class="hlt">tomography</span> detect weak <span class="hlt">velocity</span> changes? The practical application for the volcanoes in the Tohoku region.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gladkov, Valery; Koulakov, Ivan</p> <p>2016-04-01</p> <p>Temporal variations of seismic <span class="hlt">velocities</span> in the active volcanic areas may give us important information about its evolution and development of geologic processes inside it. Usually we use "direct" method to reveal <span class="hlt">velocity</span> changes with use of body wave's data. In this method, a whole period of observations is divided into a several interesting for us periods. For each period, we obtain a seismic <span class="hlt">velocity</span> model by means of seismic <span class="hlt">tomography</span>. Finally, a seismic <span class="hlt">velocity</span> changes between chosen periods is a difference between inverted <span class="hlt">velocity</span> models for these periods. In case of weak <span class="hlt">velocity</span> changes, this approach fails due to factors of varying events location and "event-station" rays distribution which influence can raise a false and apparent <span class="hlt">velocity</span> changes in the model. With the aim to eliminate these factors and to increase the reliability of <span class="hlt">velocity</span> changes detection, we propose an approach, which improves the similarity of datasets used for seismic <span class="hlt">tomography</span> in different time periods by rejection some input events and rays information. We used this approach to the data of the Japan Meteorological Agency, which includes several years before and after the Mw 9.0 Tohoku-Oki event that occurred on 11.03.2011. We performed careful testing using different synthetic models, showing that the selected data subsets reveal weak <span class="hlt">velocity</span> changes with amplitudes above 0.5%. We detected <span class="hlt">velocity</span> reductions of P-waves on 0.8% and S-waves on 0.6% in the central area of Honshu possibly linked with the fluid system properties changes which triggered by Tohoku-Oki earthquake.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993PhDT.......118C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993PhDT.......118C"><span id="translatedtitle">a Renormalization <span class="hlt">Group</span> Calculation of the <span class="hlt">Velocity</span> - and Density-Density Correlation Functions.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cowan, Mark Timothy</p> <p></p> <p>The <span class="hlt">velocity-velocity</span> correlation function of a free field theory is obtained. The renormalization <span class="hlt">group</span>, along with a 4-varepsilon expansion, is then used to find the leading order behavior of the <span class="hlt">velocity-velocity</span> correlation function for an interacting field theory in the high temperature phase near the critical point. The details of the calculation of the density-density correlation function for Hedgehogs, in the context of a free field theory, is presented next. Finally the renormalization <span class="hlt">group</span>, along with a 4-varepsilon expansion, is used to find the leading order behavior of the density-density correlation function for Hedgehogs in an interacting field theory near the critical point.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012ApPhL.100w3702R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012ApPhL.100w3702R"><span id="translatedtitle">Quantitative imaging of red blood cell <span class="hlt">velocity</span> invivo using optical coherence Doppler <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ren, Hugang; Du, Congwu; Park, Kicheon; Volkow, Nora D.; Pan, Yingtian</p> <p>2012-06-01</p> <p>We present particle counting ultrahigh-resolution optical Doppler <span class="hlt">tomography</span> (pc-μODT) that enables accurate imaging of red blood cell <span class="hlt">velocities</span> (νRBC) of cerebrovascular networks by detecting the Doppler phase transients induced by the passage of a RBC through a capillary. We apply pc-μODT to image the response of capillary νRBC to mild hypercapnia in mouse cortex. The results show that νRBC in normocapnia (νN = 0.72 ± 0.15 mm/s) increased 36.1% ± 5.3% (νH = 0.98 ± 0.29 mm/s) in response to hypercapnia. Due to uncorrected angle effect and low hematocrit (e.g., ˜10%), νRBC directly measured by μODT were markedly underestimated (νN ≈ 0.27 ± 0.03 mm/s, νH ≈ 0.37± 0.05 mm/s). Nevertheless, the measured νRBC increase (35.3%) matched that (36.1% ± 5.3%) by pc-μODT.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JAG...109..140C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JAG...109..140C"><span id="translatedtitle">Application of seismic <span class="hlt">velocity</span> <span class="hlt">tomography</span> in underground coal mines: A case study of Yima mining area, Henan, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cai, Wu; Dou, Linming; Cao, Anye; Gong, Siyuan; Li, Zhenlei</p> <p>2014-10-01</p> <p>A better understanding of geological structures, stress regimes, and rock burst risks around longwall mining panels can allow for higher extraction efficiency with reduced safety concerns. In this paper, the stress change of rock mass was first examined by using ultrasonic technique into laboratory-scale rock samples. Subsequently, the active and passive seismic <span class="hlt">velocity</span> tomograms were simultaneously applied into two study cases with field-scale. Similar characteristics can be found between the active and passive <span class="hlt">tomography</span> results. More specifically, in the first case, a geological discontinuity was clearly indicated by a linear image in both active and passive seismic <span class="hlt">tomography</span> results. The results of the second case suggest that seismic <span class="hlt">tomography</span> can be used to infer stress redistribution, and assess rock burst hazard or locate high-seismicity zones. Ultimately, comparisons have been made between the results of active and passive seismic <span class="hlt">tomography</span>. Active <span class="hlt">tomography</span> is found to be better applied in accurately detecting stress distribution and geological structures prior to the extraction of longwall panels, while passive <span class="hlt">tomography</span> has advantages in continuously monitoring the stress changes and assessing rock burst potential during the mining of longwall panels. This study is expected to increase the safety and efficiency of the underground mining.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.S51A0984R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.S51A0984R"><span id="translatedtitle">Variation of fundamental mode Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion in Iran and the surrounding region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rham, D.; Priestley, K.; Tatar, M.; Paul, A.; Hatzfeld, D.; Radjaee, A.; Nowrouzi, G.; Kaviani, A.; Tiberi, C.</p> <p>2005-12-01</p> <p>We present <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion results from a study of regional fundamental mode Rayleigh waves propagating across Iran and the surrounding region. Data for these measurements come from field deployments within Iran by the University of Cambridge (UK) and the Universite Joseph-Fourier (FRA) in conjunction with International Institute of Earthquake Engineering and Seismology (Iran), within Oman by the Universite Pierre et Marie Curie-Paris (FRA), in addition to data from IRIS and Geofone. 1D path-averaged dispersion measurements have been made for ~800 source-receiver paths using multiple filter analysis. We combine these observations in a tomographic inversion to produce <span class="hlt">group</span> <span class="hlt">velocity</span> images between 15 and 60~s period. Because of the dense path coverage, these images have substantially higher lateral resolution for this region than is currently available from global and regional <span class="hlt">group</span> <span class="hlt">velocity</span> studies. We observe variations in short-period <span class="hlt">group</span> <span class="hlt">velocity</span> which is consistent with the surface geology. Low <span class="hlt">group</span> <span class="hlt">velocity</span> (2.45-2.55~km/s) at short periods (15-20~s) is observed beneath the south Caspian Basin, northern Iran, the Persian Gulf, the Zagros, the Makran, northern Afghanistan and southern Pakistan. Somewhat higher <span class="hlt">group</span> <span class="hlt">velocity</span> (2.60-2.70~km/s) at these periods occurs in central Iran. At intermediate periods (30-40~s) <span class="hlt">group</span> <span class="hlt">velocities</span> over most of the region are low (2.90-3.10~km/s) compared to Arabia. At longer periods (50-60~s) <span class="hlt">group</span> <span class="hlt">velocities</span> remain low (3.35-3.45~km/s) over most of Iran but there is a suggestion of higher <span class="hlt">group</span> <span class="hlt">velocities</span> beneath the northern and central Zagros.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ApPhL.108w1904L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApPhL.108w1904L"><span id="translatedtitle">Simultaneous realization of negative <span class="hlt">group</span> <span class="hlt">velocity</span>, fast and slow acoustic waves in a metamaterial</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Xiao-juan; Xue, Cheng; Fan, Li; Zhang, Shu-yi; Chen, Zhe; Ding, Jin; Zhang, Hui</p> <p>2016-06-01</p> <p>An acoustic metamaterial is designed based on a simple and compact structure of one string of side pipes arranged along a waveguide, in which diverse <span class="hlt">group</span> <span class="hlt">velocities</span> are achieved. Owing to Fabry-Perot resonance of the side pipes, a negative phase time is achieved, and thus, acoustic waves transmitting with negative <span class="hlt">group</span> <span class="hlt">velocities</span> are produced near the resonant frequency. In addition, both fast and slow acoustic waves are also observed in the vicinity of the resonance frequency. The extraordinary <span class="hlt">group</span> <span class="hlt">velocities</span> can be explained based on spectral rephasing induced by anomalous dispersion on the analogy of Lorentz dispersion in electromagnetic waves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoJI.199.1303F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoJI.199.1303F"><span id="translatedtitle">Whole-mantle radially anisotropic shear <span class="hlt">velocity</span> structure from spectral-element waveform <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>French, S. W.; Romanowicz, B. A.</p> <p>2014-12-01</p> <p>The radially anisotropic shear <span class="hlt">velocity</span> structure of the Earth's mantle provides a critical window on the interior dynamics of the planet, with isotropic variations that are interpreted in terms of thermal and compositional heterogeneity and anisotropy in terms of flow. While significant progress has been made in the more than 30 yr since the advent of global seismic <span class="hlt">tomography</span>, many open questions remain regarding the dual roles of temperature and composition in shaping mantle convection, as well as interactions between different dominant scales of convective phenomena. We believe that advanced seismic imaging techniques, such as waveform inversion using accurate numerical simulations of the seismic wavefield, represent a clear path forwards towards addressing these open questions through application to whole-mantle imaging. To this end, we employ a `hybrid' waveform-inversion approach, which combines the accuracy and generality of the spectral finite element method (SEM) for forward modelling of the global wavefield, with non-linear asymptotic coupling theory for efficient inverse modelling. The resulting whole-mantle model (SEMUCB-WM1) builds on the earlier successful application of these techniques for global modelling at upper mantle and transition-zone depths (≤800 km) which delivered the models SEMum and SEMum2. Indeed, SEMUCB-WM1 is the first whole-mantle model derived from fully numerical SEM-based forward modelling. Here, we detail the technical aspects of the development of our whole-mantle model, as well as provide a broad discussion of isotropic and radially anisotropic model structure. We also include an extensive discussion of model uncertainties, specifically focused on assessing our results at transition-zone and lower-mantle depths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006AGUFM.S23D0188R&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006AGUFM.S23D0188R&link_type=ABSTRACT"><span id="translatedtitle">Variation of Fundamental Mode Surface Wave <span class="hlt">Group</span> <span class="hlt">Velocity</span> Dispersion in Iran and the Surrounding Region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rham, D. J.; Preistley, K.; Tatar, M.; Paul, A.</p> <p>2006-12-01</p> <p>We present <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion results from a study of regional fundamental mode Rayleigh and Love waves propagating across Iran and the surrounding region. Data for these measurements comes from field deployments within Iran by the University of Cambridge (GBR) and the Universite Joseph-Fourier (FRA) in conjunction with International Institute of Earthquake Engineering and Seismology (Iran), in addition to data from IRIS and Geofone. 1D path- averaged dispersion measurements have been made for ~5500 source-receiver paths using multiple filter analysis. We combine these observations in a tomographic inversion to produce <span class="hlt">group</span> <span class="hlt">velocity</span> images between 10 and 60 s period. Because of the dense path coverage, these images have substantially higher lateral resolution for this region than is currently available from global and regional <span class="hlt">group</span> <span class="hlt">velocity</span> studies. We observe variations in short-period wave <span class="hlt">group</span> <span class="hlt">velocity</span> which is consistent with the surface geology. Low <span class="hlt">group</span> <span class="hlt">velocities</span> (2.00-2.55 km/s) at short periods (10-20 s), for both Rayleigh and Love waves are observed beneath thick sedimentary deposits; The south Caspian Basin, Black Sea, the eastern Mediterranean, the Persian Gulf, the Makran, the southern Turan shield, and the Indus and Gangetic basins. Somewhat higher <span class="hlt">group</span> <span class="hlt">velocity</span> (2.80-3.15 km/s for Rayleigh, and 3.00-3.40 km/s for Love) at these periods occur in sediment poor regions, such as; the Turkish-Iranian plateau, the Arabian shield, and Kazakhstan. At intermediate periods (30-40 s) <span class="hlt">group</span> <span class="hlt">velocities</span> over most of the region are low (2.65-3.20 km/s for Rayleigh, and 2.80-3.45 km/s for love) compared to Arabia (3.40-3.70 km/s Rayleigh, 3.50-4.0 km/s Love). At longer periods (50-60 s) Love wave <span class="hlt">group</span> <span class="hlt">velocities</span> remain low (3.25-3.70 km/s) over most of Iran, but there are even lower <span class="hlt">velocities</span> (2.80-3.00 km/s) still associated with the thick sediments of the south Caspian basin, the surrounding shield areas have much higher <span class="hlt">group</span> <span class="hlt">velocities</span> (3</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007Optik.118..163L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007Optik.118..163L"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> of the light pulse in an open V-type system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Jingjuan; Fan, Xijun; Tian, Shufen; Liu, Chengpu; Gong, Shangqing; Xu, Zhizhan</p> <p>2007-04-01</p> <p>We investigate the <span class="hlt">group</span> <span class="hlt">velocity</span> of the probe light pulse in an open V-type system with spontaneously generated coherence. We find that, not only varying the relative phase between the probe and driving pulses can but varying the atomic exit rate or incoherent pumping rate also can manipulate dramatically the <span class="hlt">group</span> <span class="hlt">velocity</span>, even make the pulse propagation switching from subluminal to superluminal; the subliminal propagation can be companied with gain or absorption, but the superluminal propagation is always companied with absorption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/611845','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/611845"><span id="translatedtitle">Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion across Northern Africa, Southern Europe and the Middle East</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>McNamara, D.E.; Walter, W.R.</p> <p>1997-07-15</p> <p>THis report presents preliminary results from a large scale study of surface wave <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave <span class="hlt">velocity</span> structure within this region by improving the resolution of global surface wave tomographic studies. We hope to accomplish this goal by incorporating regional data at relatively short periods (less than 40 sec), into the regionalization of lateral <span class="hlt">velocity</span> variation. Due to the sparse distributions of stations and earthquakes throughout the region (Figure 1) we have relied on data recorded at both teleseismic and regions; distances. Also, to date we have concentrated on Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> measurements since valuable measurements can be made without knowledge of the source. In order to obtain Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> throughout the region, vertical component teleseismic and regional seismograms were gathered from broadband, 3-component, digital MEDNET, GEOSCOPE and IRIS stations plus the portable PASSCAL deployment in Saudi Arabia. Figure 1 shows the distribution of earthquakes (black circles) and broadband digital seismic stations (white triangles) throughout southern Europe, the middle east and northern Africa used in this study. The most seismicly active regions of northern Africa are the Atlas mountains of Morocco and Algeria as well as the Red Sea region to the east. Significant seismicity also occurs in the Mediterranean, southern Europe and throughout the high mountains and plateaus of the middle-east. To date, over 1300 seismograms have been analyzed to determine the individual <span class="hlt">group</span> <span class="hlt">velocities</span> of 10-150 second Rayleigh waves. Travel times, for each period, are then inverted in a back projection tomographic method in order to determine the lateral <span class="hlt">group</span> <span class="hlt">velocity</span> variation throughout the region. These results are preliminary, however, Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> maps for a range of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFMNS31B0400G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFMNS31B0400G"><span id="translatedtitle">Use of Seismic Reflection Data and Traveltime <span class="hlt">Tomography</span> to Image the Near Surface <span class="hlt">Velocity</span> Structure in the Mississippi Embayment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ge, J.; Magnani, M.; Waldron, B.; Powell, C.</p> <p>2007-12-01</p> <p>The Memphis aquifer represents one of the highest quality reservoirs of drinking water in the nation and it is separated from the shallow unconfined aquifer by the Upper Claiborne clay. Recent studies show that the confining unit might be discontinuous over the greater Memphis area exposing the Memphis aquifer to potential contamination. We present the results of a seismic reflection profile collected near Memphis, TN with the goal of imaging the structures and potential breaches in the Upper Claiborne confining clay. The imaged area is characterized by a highly heterogeneous shallow <span class="hlt">velocity</span> structure and low P wave <span class="hlt">velocities</span> in the ultrashallow unconsolidated materials. The data were collected using a shotgun source and a 1 m source spacing, 0.25 m receiver spacing and a 168-geophone spread for a max offset of 42 m. Raw seismic data show several reflected arrivals in the first 200ms, widespread ground roll, and air wave energy as well as consistent refracted phases across the 1 km - long profile. In addition to the reflection profile we present the preliminary results of first arrival travel time <span class="hlt">tomography</span> performed along the profile to constrain the <span class="hlt">velocity</span> field in the shallow portion of the profile. The <span class="hlt">velocity</span> was then used to remove the effect of the near surface <span class="hlt">velocity</span> variations. The main data processing steps included elevation statics and frequency and FK filtering. First arrival travel time modeling started with an initial estimate of the 2-layer <span class="hlt">velocity</span> model using the slope/intercept method. We then modeled first-arrival picks on 1095 shot gathers using the Geo TOMO+ package. The algorithm computes travel times by tracing turning rays and is also able to handle raypaths through low-<span class="hlt">velocity</span> zones (blind zones). The final resolution is estimated through a ray-information density map, which shows the cumulative contribution of the ray segments traversing different areas of the model. Synthetic models were generated and tested for the <span class="hlt">tomography</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JPCM...18.3117B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JPCM...18.3117B"><span id="translatedtitle">Propagation of smooth and discontinuous pulses through materials with very large or very small <span class="hlt">group</span> <span class="hlt">velocities</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bigelow, Matthew S.; Lepeshkin, Nick N.; Shin, Heedeuk; Boyd, Robert W.</p> <p>2006-03-01</p> <p>We investigate the propagation of optical pulses through two different solid-state optical materials, ruby and alexandrite, for which the <span class="hlt">group</span> <span class="hlt">velocity</span> can be very small (v_{\\mathrm {g}} \\ll c ) or superluminal (v_{\\mathrm {g}} \\gg c or negative). We find that for smooth pulses the fractional delay or advancement is maximized through the use of pulses with durations comparable to the response time of the physical process—coherent population oscillations—that leads to these extreme <span class="hlt">group</span> <span class="hlt">velocities</span>. However, we find that the transmitted pulse shape becomes distorted unless the pulse is much longer or much shorter than this response time. We also investigate the transmission of pulses that possess an abrupt change in pulse amplitude. We find that, to within experimental accuracy, this nearly discontinuous jump propagates at the usual phase <span class="hlt">velocity</span> of light c/n, even though the smoothly varying portions of the pulse propagate at the <span class="hlt">group</span> <span class="hlt">velocity</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JVGR..122...69S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JVGR..122...69S"><span id="translatedtitle">Seismic <span class="hlt">velocity</span> structure of the central Taupo Volcanic Zone, New Zealand, from local earthquake <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sherburn, Steven; Bannister, Stephen; Bibby, Hugh</p> <p>2003-03-01</p> <p> are unable to determine whether greywacke, which forms the basement beneath the eastern most part of the TVZ continues further west, or is replaced by a volcanic rock such as andesite which has similar Vp and density. Vp/Vs anomalies are much smaller than Vp anomalies and generally have little spatial relationship to the Vp pattern. There is a widespread decrease in Vp/Vs, from >1.76 to 1.70-1.73, between 4 and 6 km depth over much of the study area and Vp/Vs is high southwest of the Okataina caldera, where Vp is low. Hypocentres calculated using the 3-D <span class="hlt">velocity</span> model differ little from those obtained using a 1-D model with station terms, however, some <span class="hlt">groups</span> of earthquakes are more tightly clustered. Following relocation, there is a slight decrease in the estimated thickness of the seismogenic zone, with 73% of hypocentres between 4 and 7 km depth and a slight increase in the depth of the brittle-ductile transition from 6 to 6.5 km.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.7883S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.7883S"><span id="translatedtitle">Cluster analysis applied to <span class="hlt">velocity</span> and attenuation <span class="hlt">tomography</span>: the case study of Mt. Vesuvius</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Siniscalchi, A.; Bianco, F.; Del Pezzo, E.; de Siena, L.; di Giuseppe, M. G.; Petrillo, Z.</p> <p>2009-04-01</p> <p>The interpretation of the results of seismic <span class="hlt">velocity</span> and attenuation inversion are usually based on the qualitative observation and comparison of the different tomographic images. A promising tool to jointly interpret tomographic models based on different parameters resides in the application of statistical classification methods, such as the k-means clustering method, which minimizes the logic distance among each <span class="hlt">group</span> of observations having homogeneous physical properties and maximizes the same quantity between <span class="hlt">groups</span>. The correlation between the models is subsequently examined and significant classes (volumes of high correlation) are identified. Such technique is able to spatially clusterize the zones having similar characteristics in a statistical sense. Each zone is finally identified by the barycenter (centroid) of the corresponding cluster. The Vp <span class="hlt">velocity</span> and Qp and Qs attenuation structures of Mt. Vesuvius, Italy, have been already qualitatively interpreted by a comparison with other similar investigations. To obtain a more quantitative interpretation gathered in a unified model consistent with the entire dataset, a cluster analysis was applied to this models. An optimizing study on the proper number of classes recognizes five clusters corresponding to separate zones inside the volcano structure. - The first cluster can be considered as a "background" cluster, and corresponds to the areas with "average" seismic properties (mainly located below the topographical interface). - The second cluster defines a spatial pattern corresponding to the residual part of the feeding conduit of the volcano. - The third cluster corresponds to two volumes, the first vertically extended between -1000 and -3000 m above the sea level, North-Eastward the cone; the second, in the same depth range Westward the central cone, and linked to the first one at -2000 m. These two volumes may be associated with hydrothermal basins. - The fourth and fifth clusters are described both by</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10171446','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10171446"><span id="translatedtitle">Phase and <span class="hlt">group</span> <span class="hlt">velocities</span> for Lamb waves in DOP-26 iridium alloy sheet</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Simpson, W.A.; McGuire, D.J.</p> <p>1994-07-01</p> <p>The relatively coarse grain structure of iridium weldments limits the ultrasonic inspection of these structures to frequencies in the low megahertz range. As the material thickness is nominally 0.635 mm for clad vent set capsules, the low frequencies involved necessarily entail the generation of Lamb waves m the specimen. These waves are, of course, dispersive and detailed knowledge of both the phase and <span class="hlt">group</span> <span class="hlt">velocities</span> is required in order to determine accurately the location of flaws detected using Lamb waves. Purpose of this study is to elucidate the behavior of Lamb waves propagating in the capsule alloy and to quantify the <span class="hlt">velocities</span> so that accurate flaw location is ensured. We describe a numerical technique for computing the phase <span class="hlt">velocities</span> of Lamb waves (or of any other type of guided wave) and derive the <span class="hlt">group</span> <span class="hlt">velocities</span> from this information. A frequency-domain method is described for measuring <span class="hlt">group</span> <span class="hlt">velocity</span> when multiple Lamb modes are present and mutually interfering in the time domain, and experimental confirmation of the <span class="hlt">group</span> <span class="hlt">velocity</span> is presented for the capsule material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27410269','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27410269"><span id="translatedtitle">Momentum-dependent <span class="hlt">group</span> <span class="hlt">velocity</span> of surface plasmon polaritons in two-dimensional metallic nanohole array.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cao, Z L; Ong, H C</p> <p>2016-06-13</p> <p>We determine the momentum-dependent <span class="hlt">group</span> <span class="hlt">velocities</span> of ( ± 1,0) and (0, ± 1) Bloch-like surface plasmon polaritons (SPPs) in two-dimensional Au nanohole array by measuring their propagation lengths and decay lifetimes at different SPP propagation length via angle- and polarization-resolved reflectivity spectroscopy and real- and Fourier-space microscopy. We find the decay length and lifetime, as well as <span class="hlt">group</span> <span class="hlt">velocity</span>, are highly dependent on the propagation direction. In particular, close to the Γ-M direction where two SPPs begin to interfere, the <span class="hlt">group</span> <span class="hlt">velocity</span> decreases due to the increase of the standing wave character. More importantly, the two SPPs are strongly interacted with each other at the Γ-M direction, resulting in forming the dark and bright modes. We find the <span class="hlt">group</span> <span class="hlt">velocity</span> of the dark mode is higher that of the bright mode despite its higher quality factor, or longer decay lifetime. We attribute such difference to the distinct field symmetries of dark and bright modes, yielding different effective indices. While bright mode has fields mostly concentrated at the flat metal region to produce higher effective index and therefore lower <span class="hlt">velocity</span>, the fields of the dark mode are located near the air hole, resulting in higher <span class="hlt">velocity</span>. PMID:27410269</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014GeoJI.199..113M&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014GeoJI.199..113M&link_type=ABSTRACT"><span id="translatedtitle">A comprehensive dispersion model of surface wave phase and <span class="hlt">group</span> <span class="hlt">velocity</span> for the globe</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Zhitu; Masters, Guy; Laske, Gabi; Pasyanos, Michael</p> <p>2014-10-01</p> <p>A new method is developed to measure Rayleigh- and Love-wave phase <span class="hlt">velocities</span> globally using a cluster analysis technique. This method clusters similar waveforms recorded at different stations from a single event and allows users to make measurements on hundreds of waveforms, which are filtered at a series of frequency ranges, at the same time. It also requires minimal amount of user interaction and allows easy assessment of the data quality. This method produces a large amount of phase delay measurements in a manageable time frame. Because there is a strong trade-off between the isotropic part of the Rayleigh-wave phase <span class="hlt">velocity</span> and azimuthal anisotropy, we include the effect of azimuthal anisotropy in our inversions in order to obtain reliable isotropic phase <span class="hlt">velocity</span>. We use b-splines to combine these isotropic phase <span class="hlt">velocity</span> maps with our previous <span class="hlt">group</span> <span class="hlt">velocity</span> maps to produce an internally consistent global surface wave dispersion model.</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_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_5 --> <div id="page_6" 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_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="101"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19790019265','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19790019265"><span id="translatedtitle">An examination of a <span class="hlt">group-velocity</span> criterion for the breakdown of an idealized vortex flow</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Tsai, C. Y.; Widnall, S. E.</p> <p>1979-01-01</p> <p>The phenomenon of vortex breakdown is believed to be associated with a finite amplitude wave that has become trapped at the critical or breakdown location. The conditions at which the propagating waves become trapped at a certain axial location were examined by use of a <span class="hlt">group-velocity</span> criterion implied by Landahl's general theory of wave trapping. An ideal vortex having constant vorticity and uniform axial <span class="hlt">velocity</span> at the inlet of a slowly diverging duct was studied. The linear wave propagation analysis is applied to the base flow at several axial stations for several values of the ratio of swirl <span class="hlt">velocity</span> to axial <span class="hlt">velocity</span> at the inlet of the divergent duct, assuming a locally parallel flow. The dipsersion relations and hence the <span class="hlt">group</span> <span class="hlt">velocities</span> of both the symmetric (n = 0) and asymmetric modes (n = + or - 1) were investigated. The existence of a critical state in the flow (at which the <span class="hlt">group</span> <span class="hlt">velocity</span> vanishes), and its relationship to the stagnation point on the axis of the duct and to the occurrence of an irregular singularity in the equations governing wave propagation in the flow field are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/678818','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/678818"><span id="translatedtitle">Crust and upper mantle P wave <span class="hlt">velocity</span> structure beneath Valles caldera, New Mexico: Results from the Jemez teleseismic <span class="hlt">tomography</span> experiment</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Steck, Lee K.; Fehler, Michael C.; Roberts, Peter M.; Baldridge, W. Scott; Stafford, Darrik G.; Lutter, William J.; Sessions, Robert</p> <p>1998-10-01</p> <p>New results are presented from the teleseismic component of the Jemez <span class="hlt">Tomography</span> Experiment conducted across Valles caldera in northern New Mexico. We invert 4872 relative {ital P} wave arrival times recorded on 50 portable stations to determine <span class="hlt">velocity</span> structure to depths of 40 km. The three principle features of our model for Valles caldera are: (1) near-surface low <span class="hlt">velocities</span> of {minus}17{percent} beneath the Toledo embayment and the Valle Grande, (2) midcrustal low <span class="hlt">velocities</span> of {minus}23{percent} in an ellipsoidal volume underneath the northwest quadrant of the caldera, and (3) a broad zone of low <span class="hlt">velocities</span> ({minus}15{percent}) in the lower crust or upper mantle. Crust shallower than 20 km is generally fast to the northwest of the caldera and slow to the southeast. Near-surface low <span class="hlt">velocities</span> are interpreted as thick deposits of Bandelier tuff and postcaldera volcaniclastic rocks. Lateral variation in the thickness of these deposits supports increased caldera collapse to the southeast, beneath the Valle Grande. We interpret the midcrustal low-<span class="hlt">velocity</span> zone to contain a minimum melt fraction of 10{percent}. While we cannot rule out the possibility that this zone is the remnant 1.2 Ma Bandelier magma chamber, the eruption history and geochemistry of the volcanic rocks erupted in Valles caldera following the Bandelier tuff make it more likely that magma results from a new pulse of intrusion, indicating that melt flux into the upper crust beneath Valles caldera continues. The low-<span class="hlt">velocity</span> zone near the crust-mantle boundary is consistent with either partial melt in the lower crust or mafic rocks without partial melt in the upper mantle. In either case, this low-<span class="hlt">velocity</span> anomaly indicates that underplating by mantle-derived melts has occurred. {copyright} 1998 American Geophysical Union</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.G11A0913R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.G11A0913R"><span id="translatedtitle">GNSS <span class="hlt">tomography</span>, assembled multi model solution, initial results from first experiment of IAG GNSS <span class="hlt">tomography</span> working <span class="hlt">group</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rohm, W.; Gaiger, A.; Brenot, H.; Bender, M.; Shangguan, M.; Bosy, J.</p> <p>2012-12-01</p> <p>The Global Navigation Satellite Systems (GNSS) troposphere delay, standard product of GNSS processing, among all other applications can be used as a data source for GNSS <span class="hlt">tomography</span>. The path delays in the direction of satellites can be converted to a 3D distribution of atmospheric refractivity (total or wet), or water vapor density using Radon inverse transform. Although problem is linear the ill - conditionedess and ill-posedness of the equations, results in complexity of the problem. In the frame of IAG Sub-Commission SC 4.3 - "Remote sensing and modelling of the atmosphere", we proposed a Working <span class="hlt">Group</span> "Inter-comparison and cross-validation of <span class="hlt">tomography</span> models". The <span class="hlt">group</span> aim is to tackle current challenges of GNSS <span class="hlt">tomography</span> modeling like how to find best way to include space based GNSS observations, to deliver more reliable slant delay processing methods, to test robust algorithms to account for outliers in observations, to determine trustworthy precision and accuracy measures, to address problems linked with near real time processing, and how to provide effective cooperation channels with meteorological agencies. In this study the same GNSS data set has been processed for each tomographic model. To study the differences between obtained solutions, each solution step of GNSS <span class="hlt">tomography</span> has been carefully analyzed. The methodical framework has been developed to allow comprehensive comparison and validation. In the GNSS <span class="hlt">tomography</span> process flow several critical points have been selected, for each node a validation has been performed. This validation was based on meteorological observations carefully selected from in situ measurements, satellite measurements, and Numerical Weather Prediction models. Following nodes of GNSS <span class="hlt">tomography</span> processing have been considered: GNSS raw data processing and preprocessing of path delays, voxel model outline and construction, observation selection, raytracing algorithms, a priori observations, observations noise, inversion</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22058808','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22058808"><span id="translatedtitle">Slow light with low <span class="hlt">group-velocity</span> dispersion at the edge of photonic graphene</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ouyang Chunfang; Dong Biqin; Liu Xiaohan; Zi Jian; Xiong Zhiqiang; Zhao Fangyuan; Hu Xinhua</p> <p>2011-07-15</p> <p>We theoretically study the light propagation at the zigzag edges of a honeycomb photonic crystal (PC), or photonic graphene. It is found that the corresponding edge states have a sinusoidal dispersion similar to those found in PC coupled resonator optical waveguides [CROWs; M. Notomi et al., Nature Photon. 2, 741 (2008)]. The sinusoidal dispersion curve can be made very flat by carefully tuning edge parameters. As a result, low <span class="hlt">group</span> <span class="hlt">velocity</span> and small <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion can be simultaneously obtained for light propagating at the zigzag edge of photonic graphene. Compared with PC CROWs, our slow-light system exhibits no intrinsic radiation loss and has a larger <span class="hlt">group</span> <span class="hlt">velocity</span> bandwidth product. Our results could find applications in on-chip optical buffers and enhanced light-matter interaction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27505834','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27505834"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> locked vector dissipative solitons in a high repetition rate fiber laser.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Luo, Yiyang; Li, Lei; Liu, Deming; Sun, Qizhen; Wu, Zhichao; Xu, Zhilin; Tang, Dingyuan; Fu, Songnian; Zhao, Luming</p> <p>2016-08-01</p> <p>Vectorial nature of dissipative solitons (DSs) with high repetition rate is studied for the first time in a normal-dispersion fiber laser. Despite the fact that the formed DSs are strongly chirped and the repetition rate is greater than 100 MHz, polarization locked and polarization rotating <span class="hlt">group</span> <span class="hlt">velocity</span> locked vector DSs can be formed under 129.3 MHz fundamental mode-locking and 258.6 MHz harmonic mode-locking of the fiber laser, respectively. The two orthogonally polarized components of these vector DSs possess distinctly different central wavelengths and travel together at the same <span class="hlt">group</span> <span class="hlt">velocity</span> in the laser cavity, resulting in a gradual spectral edge and small steps on the optical spectrum, which can be considered as an auxiliary indicator of the <span class="hlt">group</span> <span class="hlt">velocity</span> locked vector DSs. Moreover, numerical simulations well confirm the experimental observations and further reveal the impact of the net cavity birefringence on the properties of the formed vector DSs. PMID:27505834</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4477408','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4477408"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> mismatch-absent nonlinear frequency conversions for mid-infrared femtosecond pulses generation</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zhong, Haizhe; Zhang, Lifu; Li, Ying; Fan, Dianyuan</p> <p>2015-01-01</p> <p>A novel <span class="hlt">group</span> <span class="hlt">velocity</span> mismatch (GVM) absent scheme for nonlinear optical parametric procedure in mid-infrared was developed with type-I quasi phase matching by use of an off-digital nonlinear optical coefficient d31. This was achieved by matching of the <span class="hlt">group</span> <span class="hlt">velocities</span> of the pump and the signal waves, while the phase <span class="hlt">velocities</span> were quasi phase matched. The system employs MgO-doped periodically poled LiNbO3 as the nonlinear medium. Desired <span class="hlt">group-velocity</span> dispersion would be obtained via appropriately temperature regulation. To demonstrate its potential applications in ultrafast mid-infrared pulses generation, aiming at a typical mid-infrared wavelength of ~3.2 μm, design examples of two basic nonlinear frequency conversion procedures are studied for both the narrow-band seeding mid-IR optical parametric amplification (OPA) and the synchronously pumped femtosecond optical parametric oscillation (SPOPO). Compared with the conventional scheme of type-0 QPM, the quantum-efficiency can be more than doubled with nearly unlimited bandwidth. The proposed GVM- absent phase matching design may provide a promising route to efficient and broadband sub-100 fs mid-infrared ultrafast pulses generation without <span class="hlt">group-velocity</span> walk-off. PMID:26099837</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013SPIE.8694E..03P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013SPIE.8694E..03P&link_type=ABSTRACT"><span id="translatedtitle">Stiffness matrix determination of composite materials using lamb wave <span class="hlt">group</span> <span class="hlt">velocity</span> measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Putkis, O.; Croxford, A. J.</p> <p>2013-04-01</p> <p>The use of Lamb waves in Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) is gaining popularity due to their ability to travel long distances without significant attenuation, therefore offering large area inspections with a small number of sensors. The design of a Lamb-wave-based NDE/SHM system for composite materials is more complicated than for metallic materials due to the directional dependence of Lamb wave propagation characteristics such as dispersion and <span class="hlt">group</span> <span class="hlt">velocity</span>. Propagation parameters can be theoretically predicted from known material properties, specifically the stiffness matrix and density. However, in practice it is difficult to obtain the stiffness matrix of a particular material or structure with high accuracy, hence introducing errors in theoretical predictions and inaccuracies in the resulting propagation parameters. Measured Lamb wave phase <span class="hlt">velocities</span> can be used to infer the stiffness matrix, but the measurements are limited to the principal directions due to the steering effect (different propagation directions of phase and corresponding <span class="hlt">group</span> <span class="hlt">velocities</span>). This paper proposes determination of the stiffness matrix from the measured <span class="hlt">group</span> <span class="hlt">velocities</span>, which can be unambiguously measured in any direction. A highly anisotropic carbon-fibre-reinforced polymer plate is chosen for the study. The influence of different stiffness matrix elements on the directional <span class="hlt">group</span> <span class="hlt">velocity</span> profile is investigated. Thermodynamic Simulated Annealing (TSA) is used as a tool for inverse, multi variable inference of the stiffness matrix. A good estimation is achieved for particular matrix elements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4309966','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4309966"><span id="translatedtitle">Observation of Wave Packet Distortion during a Negative-<span class="hlt">Group-Velocity</span> Transmission</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin</p> <p>2015-01-01</p> <p>In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the <span class="hlt">velocity</span> of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative <span class="hlt">group</span> <span class="hlt">velocity</span>. However, Sommerfeld and Brillouin pointed out that the “front” of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-<span class="hlt">group-velocity</span> transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative <span class="hlt">group</span> <span class="hlt">velocity</span> in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of <span class="hlt">group</span> <span class="hlt">velocity</span> physically meaningless in the anomalously dispersive region. PMID:25631746</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25631746','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25631746"><span id="translatedtitle">Observation of wave packet distortion during a negative-<span class="hlt">group-velocity</span> transmission.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin</p> <p>2015-01-01</p> <p>In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the <span class="hlt">velocity</span> of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative <span class="hlt">group</span> <span class="hlt">velocity</span>. However, Sommerfeld and Brillouin pointed out that the "front" of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-<span class="hlt">group-velocity</span> transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative <span class="hlt">group</span> <span class="hlt">velocity</span> in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of <span class="hlt">group</span> <span class="hlt">velocity</span> physically meaningless in the anomalously dispersive region. PMID:25631746</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70036347','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70036347"><span id="translatedtitle">Analysis of <span class="hlt">group-velocity</span> dispersion of high-frequency Rayleigh waves for near-surface applications</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.</p> <p>2011-01-01</p> <p>The Multichannel Analysis of Surface Waves (MASW) method is an efficient tool to obtain the vertical shear (S)-wave <span class="hlt">velocity</span> profile using the dispersive characteristic of Rayleigh waves. Most MASW researchers mainly apply Rayleigh-wave phase-<span class="hlt">velocity</span> dispersion for S-wave <span class="hlt">velocity</span> estimation with a few exceptions applying Rayleigh-wave <span class="hlt">group-velocity</span> dispersion. Herein, we first compare sensitivities of fundamental surface-wave phase <span class="hlt">velocities</span> with <span class="hlt">group</span> <span class="hlt">velocities</span> with three four-layer models including a low-<span class="hlt">velocity</span> layer or a high-<span class="hlt">velocity</span> layer. Then synthetic data are simulated by a finite difference method. Images of <span class="hlt">group-velocity</span> dispersive energy of the synthetic data are generated using the Multiple Filter Analysis (MFA) method. Finally we invert a high-frequency surface-wave <span class="hlt">group-velocity</span> dispersion curve of a real-world example. Results demonstrate that (1) the sensitivities of <span class="hlt">group</span> <span class="hlt">velocities</span> are higher than those of phase <span class="hlt">velocities</span> and usable frequency ranges are wider than that of phase <span class="hlt">velocities</span>, which is very helpful in improving inversion stability because for a stable inversion system, small changes in phase <span class="hlt">velocities</span> do not result in a large fluctuation in inverted S-wave <span class="hlt">velocities</span>; (2) <span class="hlt">group-velocity</span> dispersive energy can be measured using single-trace data if Rayleigh-wave fundamental-mode energy is dominant, which suggests that the number of shots required in data acquisition can be dramatically reduced and the horizontal resolution can be greatly improved using analysis of <span class="hlt">group-velocity</span> dispersion; and (3) the suspension logging results of the real-world example demonstrate that inversion of <span class="hlt">group</span> <span class="hlt">velocities</span> generated by the MFA method can successfully estimate near-surface S-wave <span class="hlt">velocities</span>. ?? 2011 Elsevier B.V.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NJPh...18g3031H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NJPh...18g3031H"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> matching in high-order harmonic generation driven by mid-infrared lasers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hernández-García, C.; Popmintchev, T.; Murnane, M. M.; Kapteyn, H. C.; Plaja, L.; Becker, A.; Jaron-Becker, A.</p> <p>2016-07-01</p> <p>We analyze the role of <span class="hlt">group-velocity</span> matching (GVM) in the macroscopic build up of the high-harmonic signal generated in gas targets at high pressures. A definition of the walk-off length, associated with GVM, in the non-perturbative intensity regime of high-harmonic generation is given. Semiclassical predictions based on this definition are in excellent agreement with full quantum simulations. We demonstrate that <span class="hlt">group</span> <span class="hlt">velocity</span> matching is a relevant factor in high harmonic generation and the isolation of attosecond pulses driven by long wavelength lasers and preferentially selects contributions from the short quantum trajectories.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AIPC..760..970H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AIPC..760..970H"><span id="translatedtitle">Applications of the Zero-<span class="hlt">Group-Velocity</span> Lamb Mode for Air-Coupled Ultrasonic Imaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Holland, Stephen D.; Song, Jun-Ho; Evan, Victoria L.; Chimenti, D. E.</p> <p>2005-04-01</p> <p>Airborne ultrasound couples particularly well into plates at the zero-<span class="hlt">group-velocity</span> point of the first order symmetric (S1) Lamb mode. Applications of this mode to ultrasonic imaging of plate-like structures are discussed. The sensitivity and high Q of this mode makes it ideal for imaging. Images from a wide variety of materials and samples, including composites and honeycomb structures are presented. Transmission at the zero-<span class="hlt">group-velocity</span> frequency is shown to be particularly sensitive to nearby flaws and discontinuities, and is therefore suitable for wide-area scanning for cracks or manufacturing flaws.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25019900','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25019900"><span id="translatedtitle">Measurement of the laser-pulse <span class="hlt">group</span> <span class="hlt">velocity</span> in plasma waveguides.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>van Tilborg, J; Daniels, J; Gonsalves, A J; Schroeder, C B; Esarey, E; Leemans, W P</p> <p>2014-06-01</p> <p>Electrically discharged plasma channels can guide laser pulses, extending the laser-plasma interaction length to many Rayleigh ranges. In applications such as the laser-plasma accelerator, the laser <span class="hlt">group</span> <span class="hlt">velocity</span> in the channel plays a critical role. The laser travel time (and thus the averaged <span class="hlt">group</span> <span class="hlt">velocity</span>) was measured through two-pulse frequency-domain interferometry and was found to depend on the on-axis plasma density and laser spot size. The data is in agreement with theory. PMID:25019900</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21313185','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21313185"><span id="translatedtitle">Phase tunability of <span class="hlt">group</span> <span class="hlt">velocity</span> by modulated-pump-forced coherent population oscillations</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Arrieta-Yanez, Francisco; Melle, Sonia; Calderon, Oscar G.; Anton, M. A.; Carreno, F.</p> <p>2009-07-15</p> <p>We propose a technique to obtain slow and fast light propagations based on coherent population oscillations forced by a modulated pump. This mechanism produces an enhancement of 1 order of magnitude of the delay or advancement of light signals. The relative phase between the pumps to the signal fields is used as a knob for changing light propagation from ultraslow <span class="hlt">group</span> <span class="hlt">velocities</span> to negative <span class="hlt">group</span> <span class="hlt">velocities</span>. The experimental realization of the phenomenon was carried out in an erbium-doped fiber amplifier at room temperature.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22072614','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22072614"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> of extraordinary waves in superdense magnetized quantum plasma with spin-1/2 effects</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Li Chunhua; Ren Haijun; Yang Weihong; Wu Zhengwei; Chu, Paul K.</p> <p>2012-12-15</p> <p>Based on the one component plasma model, a new dispersion relation and <span class="hlt">group</span> <span class="hlt">velocity</span> of elliptically polarized extraordinary electromagnetic waves in a superdense quantum magnetoplasma are derived. The <span class="hlt">group</span> <span class="hlt">velocity</span> of the extraordinary wave is modified due to the quantum forces and magnetization effects within a certain range of wave numbers. It means that the quantum spin-1/2 effects can reduce the transport of energy in such quantum plasma systems. Our work should be of relevance for the dense astrophysical environments and the condensed matter physics.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T51B2579P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T51B2579P"><span id="translatedtitle">Mapping Tectonic features beneath the Gulf of California using Rayleigh and Love Waves <span class="hlt">Group</span> <span class="hlt">Velocities</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Persaud, P.; Di Luccio, F.; Clayton, R. W.</p> <p>2012-12-01</p> <p>This study contributes to our understanding of the Pacific-North America lithospheric structure beneath the Gulf of California and its western and eastern confining regions, by mapping fundamental mode surface wave <span class="hlt">group</span> <span class="hlt">velocities</span>. We measure the dispersion of Rayleigh and Love surface waves to create a series of 2D maps of <span class="hlt">group</span> <span class="hlt">velocities</span>, which provide important information on the earth structure beneath the study region. Although several surface waves studies were published in the last decade, all of them were done using phase <span class="hlt">velocity</span> measurements based on the two stations method. Here we combine dispersion measurements at the regional scale with data at teleseismic distances to provide a more complete dataset for studies of earth structure. We also analyze <span class="hlt">group</span> <span class="hlt">velocities</span> from short to long periods in order to define structural features at both crustal and mantle scales. Our study uses earthquakes recorded by the Network of Autonomously Recording Seismographs (NARS-Baja), a set of 14 broadband seismic stations that flank the Gulf of California. From the NEIC bulletin we selected 140 events recorded by the NARS-Baja array. In order to have dispersion measurements in a wide range of periods, we used regional earthquakes with M > 4.2 and teleseismic events with M > 6.9. We first computed the dispersion curves for the surface wave paths crossing the region. Then, the along path <span class="hlt">group</span> <span class="hlt">velocity</span> measurements for multiple periods are converted into tomographic images using kernels which vary in off-path width with the square root of the period. Dispersion measurements show interesting and consistent features for both Rayleigh and Love waves. At periods equal to or shorter than 15 s, when surface waves are primarily sensitive to shear <span class="hlt">velocity</span> in the upper 15 km of the crust, slow <span class="hlt">group</span> <span class="hlt">velocities</span> beneath the northern-central Gulf reveal the presence of a thick sedimentary layer, relative to the southern Gulf. <span class="hlt">Group</span> <span class="hlt">velocities</span> beneath the northwestern side of Baja</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012GeoJI.189..647W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012GeoJI.189..647W"><span id="translatedtitle">High resolution Rayleigh wave phase <span class="hlt">velocity</span> <span class="hlt">tomography</span> in northern North China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Weilai; Wu, Jianping; Fang, Lihua</p> <p>2012-04-01</p> <p>This study presents the Rayleigh wave phase <span class="hlt">velocity</span> tomographic results in northern North China. The data are from 190 broad-band and 10 very broad-band stations of the North China Seismic Array and 50 permanent stations nearby. All available teleseismic vertical component time-series are used to extract the phase <span class="hlt">velocity</span> dispersion curves of the fundamental mode Rayleigh wave by interstation method. Tomographic maps are obtained at periods of 10, 15, 25 and 60 s with a grid spacing of 0.25°× 0.25°. The short-period phase <span class="hlt">velocity</span> maps show good correlation with the geological and tectonic features. To be specific, lower <span class="hlt">velocities</span> correspond to North China Basin and depression area whereas higher <span class="hlt">velocities</span> are associated with Taihangshan and Yanshan uplifts. At 25 s, there are obvious low-<span class="hlt">velocity</span> anomalies in Jizhong depression and Beijing-Tianjin-Tangshan region, indicating that ascendant low <span class="hlt">velocity</span> channel may be formed beneath these areas and induce the <span class="hlt">velocity</span> difference in the upper crust. The phase <span class="hlt">velocity</span> map at 60 s reflects the upper-mantle information in the study area. High-<span class="hlt">velocity</span> anomalies are observed at Yanshan blocks north to Zhangjiakou-Bohai seismic belt, suggesting that the materials are stable beneath these areas or the asthenosphere is at deeper location. Low-<span class="hlt">velocity</span> anomalies are mainly south to the seismic belt, implying the asthenosphere is shallower and the materials are transformed by the open stretching rift trending NNE, resulting in many NNE-directed fault belts. These structural differences at depth may be controlled by the fault activity and strong tectonic movements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3853P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3853P"><span id="translatedtitle">Applications of detailed 3D P-wave <span class="hlt">velocity</span> crustal model in Poland for local, regional and global seismic <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Polkowski, Marcin; Grad, Marek</p> <p>2015-04-01</p> <p>The 3D P-wave seismic <span class="hlt">velocity</span> model was obtained by combining data from multiple studies during past 50 years. Data sources included refraction seismology, reflection seismology, geological boreholes, vertical seismic profiling, magnetotellurics and gravimetry. Use of many data sources allowed creation of detailed 3D P-wave <span class="hlt">velocity</span> model that reaches to depth of 60 km and includes 6-layers of sediments and 3-layers of the crust. Purpose of this study is to analyze how 3D model influences local (accuracy of location and source time estimation for local events), regional (identification of wide-angle seismic phases) and global (teleseismic <span class="hlt">tomography</span>) seismic travel times. Additionally we compare results of forward seismic wave propagation with signals observed on short period and broadband stations. National Science Centre Poland provided financial support for this work by NCN grant DEC-2011/02/A/ST10/00284.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4932526','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4932526"><span id="translatedtitle">In vivo label-free measurement of lymph flow <span class="hlt">velocity</span> and volumetric flow rates using Doppler optical coherence <span class="hlt">tomography</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>Blatter, Cedric; Meijer, Eelco F. J.; Nam, Ahhyun S.; Jones, Dennis; Bouma, Brett E.; Padera, Timothy P.; Vakoc, Benjamin J.</p> <p>2016-01-01</p> <p>Direct in vivo imaging of lymph flow is key to understanding lymphatic system function in normal and disease states. Optical microscopy techniques provide the resolution required for these measurements, but existing optical techniques for measuring lymph flow require complex protocols and provide limited temporal resolution. Here, we describe a Doppler optical coherence <span class="hlt">tomography</span> platform that allows direct, label-free quantification of lymph <span class="hlt">velocity</span> and volumetric flow rates. We overcome the challenge of very low scattering by employing a Doppler algorithm that operates on low signal-to-noise measurements. We show that this technique can measure lymph <span class="hlt">velocity</span> at sufficiently high temporal resolution to resolve the dynamic pulsatile flow in collecting lymphatic vessels. PMID:27377852</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016NatSR...629035B&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016NatSR...629035B&link_type=ABSTRACT"><span id="translatedtitle">In vivo label-free measurement of lymph flow <span class="hlt">velocity</span> and volumetric flow rates using Doppler optical coherence <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blatter, Cedric; Meijer, Eelco F. J.; Nam, Ahhyun S.; Jones, Dennis; Bouma, Brett E.; Padera, Timothy P.; Vakoc, Benjamin J.</p> <p>2016-07-01</p> <p>Direct in vivo imaging of lymph flow is key to understanding lymphatic system function in normal and disease states. Optical microscopy techniques provide the resolution required for these measurements, but existing optical techniques for measuring lymph flow require complex protocols and provide limited temporal resolution. Here, we describe a Doppler optical coherence <span class="hlt">tomography</span> platform that allows direct, label-free quantification of lymph <span class="hlt">velocity</span> and volumetric flow rates. We overcome the challenge of very low scattering by employing a Doppler algorithm that operates on low signal-to-noise measurements. We show that this technique can measure lymph <span class="hlt">velocity</span> at sufficiently high temporal resolution to resolve the dynamic pulsatile flow in collecting lymphatic vessels.</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_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" 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_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27377852','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27377852"><span id="translatedtitle">In vivo label-free measurement of lymph flow <span class="hlt">velocity</span> and volumetric flow rates using Doppler optical coherence <span class="hlt">tomography</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Blatter, Cedric; Meijer, Eelco F J; Nam, Ahhyun S; Jones, Dennis; Bouma, Brett E; Padera, Timothy P; Vakoc, Benjamin J</p> <p>2016-01-01</p> <p>Direct in vivo imaging of lymph flow is key to understanding lymphatic system function in normal and disease states. Optical microscopy techniques provide the resolution required for these measurements, but existing optical techniques for measuring lymph flow require complex protocols and provide limited temporal resolution. Here, we describe a Doppler optical coherence <span class="hlt">tomography</span> platform that allows direct, label-free quantification of lymph <span class="hlt">velocity</span> and volumetric flow rates. We overcome the challenge of very low scattering by employing a Doppler algorithm that operates on low signal-to-noise measurements. We show that this technique can measure lymph <span class="hlt">velocity</span> at sufficiently high temporal resolution to resolve the dynamic pulsatile flow in collecting lymphatic vessels. PMID:27377852</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1611558B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1611558B"><span id="translatedtitle">The deeper structure of the southern Dead Sea basin derived from neural network analysis of <span class="hlt">velocity</span> and attenuation <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Braeuer, Benjamin; Haberland, Christian; Bauer, Klaus; Weber, Michael</p> <p>2014-05-01</p> <p>The Dead Sea basin is a pull-apart basin at the Dead Sea transform fault, the boundary between the African and the Arabian plates. Though the DSB has been studied for a long time, the available knowledge - based mainly on surface geology, drilling and seismic reflection surveys - gives only a partial picture of its shallow structure. Therefore, within the framework of the international DESIRE (DEad Sea Integrated REsearch) project, a dense temporary local seismological network was operated in the southern Dead Sea area. Within 18 month of recording 650 events were detected. In addition to an already published <span class="hlt">tomography</span> study revealing the distribution of P <span class="hlt">velocities</span> and the Vp/Vs ratios a 2D P-wave attenuation <span class="hlt">tomography</span> (parameter Qp) was performed. The neural network technique of Self-organizing maps (SOM) is used for the joint interpretation of these three parameters (Vp, Vp/Vs, Qp). The resulting clusters in the petrophysical parameter space are assigned to the main lithological units below the southern part of the Dead Sea basin: (1) The basin sediments characterized by strong attenuation, high vp/vs ratios and low P <span class="hlt">velocities</span>. (2) The pre-basin sediments characterized by medium to strong attenuation, low Vp/Vs ratios and medium P <span class="hlt">velocities</span>. (3) The basement characterized by low to moderate attenuation, medium vp/vs ratios and high P <span class="hlt">velocities</span>. Thus, the asymmetric southern Dead Sea basin is filled with basin sediments down to depth of 7 to 12 km. Below the basin sediments, the pre-basin sediments are extending to a depth between 13 and 18 km.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.4786J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.4786J"><span id="translatedtitle">Anisotropic <span class="hlt">velocity</span> structure of the crust and upper mantle in the Taiwan region from local travel time <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jakovlev, Andrey; Koulakov, Ivan; Wu, Yih-Min</p> <p>2014-05-01</p> <p>Taiwan Island located in a contact zone between the Eurasian and Philippine Sea plates, the tectonic processes in this area are mostly controlled by the relative kinematics of these two plates. In the east, the Philippine Sea plate subducts northward under the Eurasian plate along the Ryukyu trench. Off the southern tip of Taiwan, the South China Sea subplate, part of the Eurasian plate, subducts eastward under the Philippine Sea plate underneath the Luzon Island. The Taiwan Island is located at the junction between these two subduction zones. Here we present anisotropic <span class="hlt">velocity</span> model of the crust and upper mantle in the Taiwan region derived from local travel time <span class="hlt">tomography</span>. We use more than 300 000 P and more than 150 000 S rays coming from 12910 earthquakes occurred in the Taiwan region and registered by 816 stations of different local Taiwanese seismic networks. The ANITA algorithm, for iterative nonlinear inversion of local earthquake data in orthorhombic anisotropic media with one predefined vertical orientation, was used for the tomographic inversion. This algorithm presumes anisotropy for only P <span class="hlt">velocity</span> described as horizontally oriented ellipsoid. For S <span class="hlt">velocity</span> we presume an isotropic model. Results show a good agreement with tectonic structure of the region. Obtained isotropic P and S <span class="hlt">velocity</span> models show fit to each other. The most prominent features of the models are Philippine Sea plate characterized by increased <span class="hlt">velocities</span> and decreased <span class="hlt">velocities</span> observed along the Luzon and Ryukyu arcs. We observe that orientation of the fast <span class="hlt">velocity</span> axis within the Philippine Sea plate coincides with direction of its displacement. Along the Luzon and Ryukyu arcs orientation of the fast <span class="hlt">velocities</span> axis coincide with the arcs extension. The results show that upper mantle beneath the eastern Taiwan characterized by decreased <span class="hlt">velocities</span> and N-S orientation of the fast <span class="hlt">velocity</span> axis. The western Taiwan characterized by alteration of the relatively small negative</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=280412','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/Publications.htm?seq_no_115=280412"><span id="translatedtitle">Breed <span class="hlt">group</span> effects for chute exit <span class="hlt">velocity</span> as an indicator trait for temperament in weaner cattle</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p>The objective of this study was to determine breed <span class="hlt">group</span> differences in chute exit <span class="hlt">velocity</span> (CEV) in weaner cattle (n=3176). Data were collected in 2004 through 2008 under procedures of objective 3, Southern Regional Research project S1013 with the following states contributing data: FL, LA, and MS...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoJI.199.1861D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoJI.199.1861D"><span id="translatedtitle">Seismic structure beneath the Gulf of California: a contribution from <span class="hlt">group</span> <span class="hlt">velocity</span> measurements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Di Luccio, F.; Persaud, P.; Clayton, R. W.</p> <p>2014-12-01</p> <p>Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion measurements from local and regional earthquakes are used to interpret the lithospheric structure in the Gulf of California region. We compute <span class="hlt">group</span> <span class="hlt">velocity</span> maps for Rayleigh waves from 10 to 150 s using earthquakes recorded by broad-band stations of the Network of Autonomously Recording Seismographs in Baja California and Mexico mainland, UNM in Mexico, BOR, DPP and GOR in southern California and TUC in Arizona. The study area is gridded in 120 longitude cells by 180 latitude cells, with an equal spacing of 10 × 10 km. Assuming that each gridpoint is laterally homogeneous, for each period the tomographic maps are inverted to produce a 3-D lithospheric shear wave <span class="hlt">velocity</span> model for the region. Near the Gulf of California rift axis, we found three prominent low shear wave <span class="hlt">velocity</span> regions, which are associated with mantle upwelling near the Cerro Prieto volcanic field, the Ballenas Transform Fault and the East Pacific Rise. Upwelling of the mantle at lithospheric and asthenospheric depths characterizes most of the Gulf. This more detailed finding is new when compared to previous surface wave studies in the region. A low-<span class="hlt">velocity</span> zone in northcentral Baja at ˜28ºN which extends east-south-eastwards is interpreted as an asthenospheric window. In addition, we also identify a well-defined high-<span class="hlt">velocity</span> zone in the upper mantle beneath central-western Baja California, which correlates with the previously interpreted location of the stalled Guadalupe and Magdalena microplates. We interpret locations of the fossil slab and slab window in light of the distribution of unique post-subduction volcanic rocks in the Gulf of California and Baja California. We also observe a high-<span class="hlt">velocity</span> anomaly at 50-km depth extending down to ˜130 km near the southwestern Baja coastline and beneath Baja, which may represent another remnant of the Farallon slab.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3149517','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3149517"><span id="translatedtitle">Doppler <span class="hlt">velocity</span> detection limitations in spectrometer-based versus swept-source optical coherence <span class="hlt">tomography</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>Hendargo, Hansford C.; McNabb, Ryan P.; Dhalla, Al-Hafeez; Shepherd, Neal; Izatt, Joseph A.</p> <p>2011-01-01</p> <p>Recent advances in Doppler techniques have enabled high sensitivity imaging of biological flow to measure blood <span class="hlt">velocities</span> and vascular perfusion. Here we compare spectrometer-based and wavelength-swept Doppler OCT implementations theoretically and experimentally, characterizing the lower and upper observable <span class="hlt">velocity</span> limits in each configuration. We specifically characterize the washout limit for Doppler OCT, the <span class="hlt">velocity</span> at which signal degradation results in loss of flow information, which is valid for both quantitative and qualitative flow imaging techniques. We also clearly differentiate the washout effect from the separate phenomenon of phase wrapping. We demonstrate that the maximum detectable Doppler <span class="hlt">velocity</span> is determined by the fringe washout limit and not phase wrapping. Both theory and experimental results from phantom flow data and retinal blood flow data demonstrate the superiority of the swept-source technique for imaging vessels with high flow rates. PMID:21833356</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70023092','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70023092"><span id="translatedtitle">P-wave <span class="hlt">velocity</span> structure of the uppermost mantle beneath Hawaii from traveltime <span class="hlt">tomography</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>Tilmann, F.J.; Benz, H.M.; Priestley, K.F.; Okubo, P.G.</p> <p>2001-01-01</p> <p>We examine the P-wave <span class="hlt">velocity</span> structure beneath the island of Hawaii using P-wave residuals from teleseismic earthquakes recorded by the Hawaiian Volcano Observatory seismic network. The station geometry and distribution of events makes it possible to image the <span class="hlt">velocity</span> structure between ~ 40 and 100 km depth with a lateral resolution of ~ 15 km and a vertical resolution of ~ 30 km. For depths between 40 and 80 km, P-wave <span class="hlt">velocities</span> are up to 5 per cent slower in a broad elongated region trending SE-NW that underlies the island between the two lines defined by the volcanic loci. No direct correlation between the magnitude of the lithospheric anomaly and the current level of volcanic activity is apparent, but the slow region is broadened at ~ 19.8??N and narrow beneath Kilauea. In the case of the occanic lithosphere beneath Hawaii, slow seismic <span class="hlt">velocities</span> are likely to be related to magma transport from the top of the melting zone at the base of the lithosphere to the surface. Thermal modelling shows that the broad elongated low-<span class="hlt">velocity</span> zone cannot be explained in terms of conductive heating by one primary conduit per volcano but that more complicated melt pathways must exist.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoJI.192..310D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoJI.192..310D"><span id="translatedtitle">Uppermost mantle seismic <span class="hlt">velocity</span> and anisotropy in the Euro-Mediterranean region from Pn and Sn <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Díaz, J.; Gil, A.; Gallart, J.</p> <p>2013-01-01</p> <p>In the last 10-15 years, the number of high quality seismic stations monitoring the Euro-Mediterranean region has increased significantly, allowing a corresponding improvement in structural constraints. We present here new images of the seismic <span class="hlt">velocity</span> and anisotropy variations in the uppermost mantle beneath this complex area, compiled from inversion of Pn and Sn phases sampling the whole region. The method of Hearn has been applied to the traveltime arrivals of the International Seismological Center catalogue for the time period 1990-2010. A total of 579 753 Pn arrivals coming from 12 377 events recorded at 1 408 stations with epicentral distances between 220 km and 1 400 km have been retained after applying standard quality criteria (maximum depth, minimum number of recordings, maximum residual values …). Our results show significant features well correlated with surface geology and evidence the heterogeneous character of the Euro-Mediterranean lithosphere. The station terms reflect the existence of marked variations in crustal thickness, consistent with available Moho depths inferred from active seismic experiments. The highest Pn <span class="hlt">velocities</span> are observed along a continuous band from the Po Basin to the northern Ionian Sea. Other high <span class="hlt">velocity</span> zones include the Ligurian Basin, the Valencia Trough, the southern Alboran Sea and central part of the Algerian margin. Most significant low-<span class="hlt">velocity</span> values are associated to orogenic belts (Betics, Pyrenees, Alps, Apennines and Calabrian Arc, Dinarides-Hellenides), and low-<span class="hlt">velocity</span> zones are also identified beneath Sardinia and the Balearic Islands. The introduction of an anisotropic term enhances significantly the lateral continuity of the anomalies, in particular in the most active tectonic areas. Pn anisotropy shows consistent orientations subparallel to major orogenic structures, such as Betics, Apennines, Calabrian Arc and Alps. The Sn tomographic image has lower resolution but confirms independently most of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5446768','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5446768"><span id="translatedtitle">Teleseismic <span class="hlt">tomography</span> of the compressional wave <span class="hlt">velocity</span> structure beneath the Long Valley region, California</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dawson, P.B.; Evans, J.R.; Iyer, H.M. )</p> <p>1990-07-10</p> <p>In 1982 and 1984 the U.S. Geological Survey used several seismic networks, totaling over 90 stations, to record teleseismic P waves and measure travel time residuals in an area centered on the Long Valley caldera. The authors inverted the travel time residuals to obtain a three-dimensional image of the <span class="hlt">velocity</span> structure with resolution of 5-6 km to depths of 70 km beneath the array. Direct inversion of these data indicates that the 2- to 4-km-thick low-<span class="hlt">velocity</span> caldera fill contaminates the signal from any midcrustal <span class="hlt">velocity</span> anomalies beneath the caldera. Thus two methods were used to strip the effects of the upper crust from the travel time residuals: (1) ray tracing through upper crustal <span class="hlt">velocity</span> models provided by seismic refraction experiments and gravity surveys, and (2) an iterative stripping scheme using the inversion itself. The methods produce essentially identical results and adequately remove the effects of the shallowest crustal structures, including the caldera fill and hydrothermal alteration effects. The resulting stripped models show two well-resolved midcrustal low-<span class="hlt">velocity</span> bodies in the Long Valley region. The first body is centered between 7 and 20 km depth beneath the resurgent dome of the Long Valley caldera and has a volume of 150-600 km{sup 3}. The second, with a similar volume, is centered between 10 and 20 km depth beneath the Mono Craters, about 10 km north of Long Valley. <span class="hlt">Velocity</span> contrasts in both of these bodies are about 6-10%, and the features are interpreted as silicic magma chambers. This experiment does not preclude the presence of additional pockets of magma smaller than 5 km across in the upper crust, particularly beneath the resurgent dome of the caldera (which would be removed with the stripping methods). The high eruptive rate of the Mono Craters and these upper mantle structures suggest that the focus of volcanism is shifting north from Long Valley to the Mono Craters</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 id="translatedtitle">Lithospheric shear <span class="hlt">velocity</span> structure of South Island, New Zealand, from amphibious Rayleigh wave <span class="hlt">tomography</span></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 3-D shear <span class="hlt">velocity</span> 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 wave 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 shear wave <span class="hlt">velocity</span> (Vs) model include a low-<span class="hlt">velocity</span> (Vs < 4.4 km/s) body extending from near surface to greater than 75 km depth beneath the Banks and Otago Peninsulas and high-<span class="hlt">velocity</span> (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-<span class="hlt">velocity</span> 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-<span class="hlt">velocity</span> 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/cgi-bin/nph-data_query?bibcode=2013EGUGA..15.4891C&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013EGUGA..15.4891C&link_type=ABSTRACT"><span id="translatedtitle">Uppermost mantle <span class="hlt">velocity</span> from Pn <span class="hlt">tomography</span> in the Gulf of Aden</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corbeau, Jordane; Rolandone, Frédérique; Leroy, Sylvie; Al-Lazki, Ali; Keir, Derek; Stuart, Graham; Stork, Anna</p> <p>2013-04-01</p> <p>We present an analysis of Pn traveltimes to determine lateral variations of <span class="hlt">velocity</span> in the uppermost mantle and crustal thickness beneath the Gulf of Aden and its margins. No detailed tomographic image of the entire Gulf of Aden was available. Previous tomographic studies covered the eastern Gulf of Aden and were thus incomplete or at a large scale with a too low resolution to see the lithospheric structures. From 1990 to 2010, 49206 Pn arrivals were selected from the International Seismological Center catalogue. We also used temporary networks : YOCMAL (Young Conjugate Margins Laboratory) networks with broadband stations located in Oman, Yemen and Socotra from 2003 to 2011, and Djibouti network from 2009 to 2011. From these networks we picked Pn arrivals and selected 4110 rays. Using a least-squares tomographic code (Hearn, 1996), these data were analyzed to solve for <span class="hlt">velocity</span> variations in the mantle lithosphere. We perform different inversions for shorter and longer ray path data sets in order to separate the shallow and deep structure within the mantle lid. In the upper lid, zones of low <span class="hlt">velocity</span> (7.7 km/s) around Sanaa, Aden, Afar, and along the Gulf of Aden are related to active volcanism. Off-axis volcanism and a regional melting anomaly in the Gulf of Aden area may be connected to the Afar plume, and explained by the model of channeling material away from the Afar plume along ridge-axis. Our study validates the channeling model and shows that the influence of the Afar hotspot may extend much farther eastwards along the Aden and Sheba ridges into the Gulf of Aden than previously believed. Still in the upper lid, high Pn <span class="hlt">velocities</span> (>8,2 km/s) are observed in Yemen and may be related to the presence of a magmatic underplating under the volcanic margin of Aden and under the Red Sea margins. In the lower lid, zones of low <span class="hlt">velocities</span> are spatially located differently than in the upper lid. On the Oman margin, a low <span class="hlt">velocity</span> zone (7.6 km/s) suggests deep partial</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S23C4517I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S23C4517I"><span id="translatedtitle">3-D P Wave <span class="hlt">Velocity</span> Structure of Marmara Region Using Local Earthquake <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Işık, S. E.; Gurbuz, C.</p> <p>2014-12-01</p> <p>The 3D P wave <span class="hlt">velocity</span> model of upper and lower crust of the Marmara Region between 40.200- 41.200N and 26.500- 30.500E is obtained by tomographic inversion (Simulps) of 47034 P wave arrivals of local earthquakes recorded at 90 land stations between October 2009 and December 2012 and 30 OBO stations and 14162 shot arrivals recorded at 35 OBO stations (Seismarmara Survey, 2001). We first obtained a 1D minimum model with Velest code in order to obtain an initial model for 3D inversion with 648 well located earthquakes located within the study area. After several 3D inversion trials we decided to create a more adequate initial model for 3D inversion. Choosing the initial model we estimated the 3D P wave <span class="hlt">velocity</span> model representing the whole region both for land and sea. The results are tested by making Checkerboard , Restoring Resolution and Characteristic Tests, and the reliable areas of the resulting model is defined in terms of RDE, DWS, SF and Hit count distributions. By taking cross sections from the resulting model we observed the vertical <span class="hlt">velocity</span> change along profiles crossing both land and sea. All the profiles crossing the basins showed that the high <span class="hlt">velocities</span> of lower crust make extensions towards the basin area which looks like the force that gives a shape to the basins. These extensions of lower crust towards the basins appeared with an average <span class="hlt">velocity</span> of 6.3 km/s which might be the result of the deformation due the shearing in the region. It is also interpreted that the development of these high <span class="hlt">velocities</span> coincide with the development of the basins. Thus, both the basins and the high <span class="hlt">velocity</span> zones around them might be resulted from the entrance of the NAF into the Marmara Sea and at the same time a shear regime was dominated due to the resistance of the northern Marmara Region (Yılmaz, 2010). The seismicity is observed between 5 km and 15 km after the 3D location of the earthquakes. The locations of the earthquakes improved and the seismogenic zone</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AIPC.1096.1386I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AIPC.1096.1386I"><span id="translatedtitle">Constant <span class="hlt">Group</span> <span class="hlt">Velocity</span> Ultrasonic Guided Wave Inspection for Corrosion and Erosion Monitoring in Pipes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Instanes, Geir; Pedersen, Audun; Toppe, Mads; Nagy, Peter B.</p> <p>2009-03-01</p> <p>This paper describes a novel ultrasonic guided wave inspection technique for the monitoring of internal corrosion and erosion in pipes, which exploits the fundamental flexural mode to measure the average wall thickness over the inspection path. The inspection frequency is chosen so that the <span class="hlt">group</span> <span class="hlt">velocity</span> of the fundamental flexural mode is essentially constant throughout the wall thickness range of interest, while the phase <span class="hlt">velocity</span> is highly dispersive and changes in a systematic way with varying wall thickness in the pipe. Although this approach is somewhat less accurate than the often used transverse resonance methods, it smoothly integrates the wall thickness over the whole propagation length, therefore it is very robust and can tolerate large and uneven thickness variations from point to point. The constant <span class="hlt">group</span> <span class="hlt">velocity</span> (CGV) method is capable of monitoring the true average of the wall thickness over the inspection length with an accuracy of 1% even in the presence of one order of magnitude larger local variations. This method also eliminates spurious variations caused by changing temperature, which can cause fairly large <span class="hlt">velocity</span> variations, but do not significantly influence the dispersion as measured by the true phase angle in the vicinity of the CGV point. The CGV guided wave CEM method was validated in both laboratory and field tests.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1987PhRvL..58...37M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987PhRvL..58...37M"><span id="translatedtitle">Laboratory observation of ion conics by <span class="hlt">velocity</span>-space <span class="hlt">tomography</span> of a plasma</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McWilliams, R.; Koslover, R.</p> <p>1987-01-01</p> <p>Laboratory experiments have examined particular elements of proposed mechanisms for ion conic formation seen in the earth's auroral-zone magnetosphere. A laser-induced fluorescence diagnostic measured the ion distribution function at many angles in <span class="hlt">velocity</span> space, allowing tomographic techniques to reconstruct the multidimensional ion distribution function. Ion conics, as well as drifting Maxwellians, were observed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S43B4562W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S43B4562W"><span id="translatedtitle">Seismic <span class="hlt">Velocity</span> and Attenuation <span class="hlt">Tomography</span> of the Tonga Arc and Lau Back-arc Basin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wei, S. S.; Zha, Y.; Wiens, D. A.; Webb, S. C.</p> <p>2014-12-01</p> <p>We apply various techniques to analyze seismic data from the 2009 - 2010 Ridge2000 Lau Spreading Center project to investigate the distribution of partial melt beneath the Tonga arc and Lau back-arc basin. The shear wave <span class="hlt">velocity</span> structure is jointly inverted from the phase <span class="hlt">velocities</span> of teleseismic and ambient-noise Rayleigh waves, as the former is inverted using the two-plane-wave method with finite-frequency kernels, and the latter is obtained from cross-correlation in frequency domain. Additionally, we determine the 3D attenuation structure from t* measurements of P and S waves from local earthquakes. In order to avoid the trade-off between t* and corner frequency, we analyze the spectral ratio of S coda to independently constrain the fc for each event. The QP and QS structures are inverted separately, and QP/QS is jointly inverted from QP and t*(S). Tomographic results show strong signals of low <span class="hlt">velocity</span> and high attenuation within the upper 100-km of the mantle beneath the back-arc basin, suggesting perhaps the lowest shear <span class="hlt">velocity</span> (VSV = 3.5 km/s) and highest seismic attenuation (QP < 35 and QS < 25) known in the mantle. These anomalies require not only the abnormally high temperature but also the existence of partial melt. The inferred partial melt aligns with the spreading centers at shallow depths, but shift westwards away from the slab, implying a passive decompression melting process governed by the mantle wedge flow pattern. The Tonga volcanic arc does not display as strong of <span class="hlt">velocity</span> or attenuation anomalies as the spreading centers, suggesting less magmatism associate with the arc compared to the back-arc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.6157N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.6157N"><span id="translatedtitle">3d <span class="hlt">Velocity</span> <span class="hlt">Tomography</span> of The Kos - Nisyros Volcanic Area - East Aegean Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nikolova, S.; Ilinski, D.; Makris, J.; Chonia, T.; Stavrakakis, J.</p> <p></p> <p>Since June 2000, active and passive seismic observations have been carried out by IfG, GeoPro GmbH, Hamburg and Institute of Geodynamics, Athens within the frame of the project GEOWARN (Geo-Spacial Warning Systems Nisyros Volcano, Greece: An Emergency Case Study of the Volcanic Area of Nisyros) supported by the European Community. In the active experiment 48 recording seismic units were deployed and recorded more than 7000 shots in 3D array. The Nisyros volcano has been identified as an apophytic intrusion of much larger volcanic structure with a caldera of 35 km diameter, extending between the southern coasts of the islands of Kos and Nisyros. To obtain 3-D <span class="hlt">velocity</span> structure of the area a tomographic inversion was made using 6800 rays which probed the area with a very high ray density. The method applied and the high accuracy of active tomographic data allowed to resolve the high <span class="hlt">velocity</span> bodies in the caldera. The complex volcanic structure is identified by high <span class="hlt">velocity</span> rocks in- truding through the upper crust and penetrating the volcanic cone to depth of approx. 1.0 km to 1.8 km below the surface. Particularly high <span class="hlt">velocity</span> bodies were identified below the islands of Yali and the central caldera of Nisyros. The high <span class="hlt">velocity</span> bodies at shallow depth were interpreted as high-density cumulates of solidified magma intru- sion in the caldera. These intrusions explain very high temperature of 300C observed in the lower aquifer in the caldera at 1.5 km depth as confirmed by drilling. The vol- canic edifices of Kos, Yali, Nisyros and Strongily are part of a major volcanic caldera nearly 35 km in diameter. This size of the volcanic caldera explains the large volume of ignimbrites erupted 160 000 years ago. By combining geodetic, geophysical, geo- chemical and geological observations it is intended to correlate magma movements and associated changes of physical and chemical parameters of the recent volcanism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021644','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021644"><span id="translatedtitle">P wave crustal <span class="hlt">velocity</span> structure in the greater Mount Rainier area from local earthquake <span class="hlt">tomography</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>Moran, S.C.; Lees, J.M.; Malone, S.D.</p> <p>1999-01-01</p> <p>We present results from a local earthquake tomographic imaging experiment in the greater Mount Rainier area. We inverted P wave arrival times from local earthquakes recorded at permanent and temporary Pacific Northwest Seismograph Network seismographs between 1980 and 1996. We used a method similar to that described by Lees and Crosson [1989], modified to incorporate the parameter separation method for decoupling the hypocenter and <span class="hlt">velocity</span> problems. In the upper 7 km of the resulting model there is good correlation between <span class="hlt">velocity</span> anomalies and surface geology. Many focal mechanisms within the St. Helens seismic zone have nodal planes parallel to the epicentral trend as well as to a north-south trending low-<span class="hlt">velocity</span> trough, leading us to speculate that the trough represents a zone of structural weakness in which a moderate (M 6.5-7.0) earthquake could occur. In contrast, the western Rainier seismic zone does not correlate in any simple way with anomaly patterns or focal mechanism fault planes, leading us to infer that it is less likely to experience a moderate earthquake. A ???10 km-wide low-<span class="hlt">velocity</span> anomaly occurs 5 to 18 km beneath the summit of Mount Rainier, which we interpret to be a signal of a region composed of hot, fractured rock with possible small amounts of melt or fluid. No systematic <span class="hlt">velocity</span> pattern is observed in association with the southern Washington Cascades conductor. A midcrustal anomaly parallels the Olympic-Wallowa lineament as well as several other geophysical trends, indicating that it may play an important role in regional tectonics. Copyright 1999 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.S41A2351L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.S41A2351L"><span id="translatedtitle">Surface wave <span class="hlt">tomography</span> with USArray: Rayleigh wave phase <span class="hlt">velocity</span>, ellipticity, and local amplification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lin, F.; Schmandt, B.; Tsai, V. C.</p> <p>2012-12-01</p> <p>The deployment of the EarthScope/USArray Transportable Array allows detailed empirical study of the surface-wave wavefield on a large scale. In this presentation, we show that three local properties of Rayleigh waves, i.e. phase <span class="hlt">velocity</span>, ellipticity (or H/V ratio), and local amplification, can be determined across the array in the western US between 24 and 100 sec period based on teleseismic measurements. More than 900 earthquakes are analyzed where phase <span class="hlt">velocity</span> and local amplification are determined based on empirical phase travel time and amplitude mapping. The three Rayleigh wave properties, which are all sensitive to the 1D structure beneath each location, have very distinct depth sensitivity to Vs, Vp/Vs ratio, and density. Joint inversion of these quantities therefore reduces the trade-off between the three different parameters at different depths. Including the H/V ratio, in particular, allows the uppermost (0-3 km) crustal <span class="hlt">velocity</span> and density structure to be constrained, and our new results are in excellent agreement with known surface features. Pronounced low Vs, low density, and high Vp/Vs anomalies are imaged in the locations of several major sedimentary basins including the Williston, Powder River, Green River, Denver, and San Juan basins. Preliminary results on the inverted 3D Vs, Vp/Vs ratio, and density structure in the crust and upper mantle will also be discussed. (a)-(c) 30-sec Rayleigh-wave phase <span class="hlt">velocity</span>, local amplification, and H/V ratio observed across USArray in the western US. The red lines denote the tectonic boundaries and the triangles in (b)-(c) shown the stations used. The thick black lines indicate 3-km sediment contours for several major sedimentary basins (WB: Williston Basin; PR: Powder River Basin; GR: Green River Basin; DB: Denver Basin). (d)-(f) The Vs, density, and Vp/Vs ratio in the uppermost crust (0-3 km) inverted by phase <span class="hlt">velocity</span> and H/V ratio measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22043421','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22043421"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> and pulse lengthening of mismatched laser pulses in plasma channels</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schroeder, C. B.; Benedetti, C.; Esarey, E.; Tilborg, J. van; Leemans, W. P.</p> <p>2011-08-15</p> <p>Analytic solutions are presented to the non-paraxial wave equation describing an ultra-short, low-power, laser pulse propagating in a plasma channel. Expressions for the laser pulse centroid motion and laser <span class="hlt">group</span> <span class="hlt">velocity</span> are derived, valid for matched and mismatched propagation in a parabolic plasma channel, as well as in vacuum, for an arbitrary Laguerre-Gaussian laser mode. The <span class="hlt">group</span> <span class="hlt">velocity</span> of a mismatched laser pulse, for which the laser spot size is strongly oscillating, is found to be independent of propagation distance and significantly less than that of a matched pulse. Laser pulse lengthening of a mismatched pulse owing to laser mode slippage is examined and found to dominate over that due to dispersive pulse spreading for sufficiently long pulses. Analytic results are shown to be in excellent agreement with numerical solutions of the full Maxwell equations coupled to the plasma response. Implications for plasma channel diagnostics are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1048294','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1048294"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> and pulse lengthening of mismatched laser pulses in plasma channels</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schroeder, Carl; Benedetti, Carlo; Esarey, Eric; van Tilborg, Jeroen; Leemans, Wim</p> <p>2011-07-07</p> <p>Analytic solutions are presented to the non-paraxial wave equation describing an ultra-short, low-power, laser pulse propagating in aplasma channel. Expressions for the laser pulse centroid motion and laser <span class="hlt">group</span> <span class="hlt">velocity</span> are derived, valid for matched and mismatchedpropagation in a parabolic plasma channel, as well as in vacuum, for an arbitrary Laguerre-Gaussian laser mode. The <span class="hlt">group</span> <span class="hlt">velocity</span> of amismatched laser pulse, for which the laser spot size is strongly oscillating, is found to be independent of propagation distance andsignificantly less than that of a matched pulse. Laser pulse lengthening of a mismatched pulse owing to laser mode slippage isexamined and found to dominate over that due to dispersive pulse spreading for sufficiently long pulses. Analytic results are shown tobe in excellent agreement with numerical solutions of the full Maxwell equations coupled to the plasma response. Implications for plasmachannel diagnostics are discussed.</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_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" 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_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4585822','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4585822"><span id="translatedtitle">Impact of Substrate and Bright Resonances on <span class="hlt">Group</span> <span class="hlt">Velocity</span> in Metamaterial without Dark Resonator</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hokmabadi, Mohammad Parvinnezhad; Kim, Ju-Hyung; Rivera, Elmer; Kung, Patrick; Kim, Seongsin M.</p> <p>2015-01-01</p> <p>Manipulating the speed of light has never been more exciting since electromagnetic induced transparency and its classical analogs led to slow light. Here, we report the manipulation of light <span class="hlt">group</span> <span class="hlt">velocity</span> in a terahertz metamaterial without needing a dark resonator, but utilizing instead two concentric split-ring bright resonators (meta-atoms) exhibiting a bright Fano resonance in close vicinity of a bright Lorentzian resonance to create a narrowband transmittance. Unlike earlier reports, the bright Fano resonance does not stem from an asymmetry of meta-atoms or an interaction between them. Additionally, we develop a method to determine the metamaterial “effective thickness”, which quantifies the influence of the substrate on the metamaterial response and has remained challenging to estimate so far. By doing so, very good agreement between simulated and measured <span class="hlt">group</span> delays and <span class="hlt">velocities</span> is accomplished. The proposed structure and method will be useful in designing optical buffers, delay lines, and ultra-sensitive sensors. PMID:26395071</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JVGR..301..148V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JVGR..301..148V"><span id="translatedtitle">Three-dimensional <span class="hlt">velocity</span> structure of the Galeras volcano (Colombia) from passive local earthquake <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vargas, Carlos Alberto; Torres, Roberto</p> <p>2015-08-01</p> <p>A three-dimensional estimation of the Vp, Vs and Vp/Vs ratio structure at Galeras volcano was conducted by means of passive local earthquake <span class="hlt">tomography</span>. 14,150 volcano-tectonic events recorded by 58 stations in the seismological network established for monitoring the volcanic activity by the Colombian Geological Survey - Pasto Volcano Observatory between the years 1989 and 2015, were inverted by using the LOTOS code. The seismic events are associated with shear-stress fractures in solid rock as a response to pressure induced by magma flow. <span class="hlt">Tomography</span> resolution tests suggest a depth of imaging that yield 10 km from the summit of the main crater, illuminating a large portion of the volcanic structure and the interaction of tectonic features like the Buesaco and Silvia-Pijao faults. Full catalog tomographic inversion, that represents the stacked image of the volcanic structure or the most permanent features underneath the volcano, shows vertical structures aligned with seismicity beneath the main crater. We hypothesize that these structures correspond to a system of ducts or fractures through which magma and fluid phases flow up from deeper levels toward the top and related with the intersection of the surface traces of the Silvia-Pijao and Buesaco faults.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960025080','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960025080"><span id="translatedtitle">Are There Optical Solitary Wave Solutions in Linear Media with <span class="hlt">Group</span> <span class="hlt">Velocity</span> Dispersion?</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Li, Zhonghao; Zhou, Guosheng</p> <p>1996-01-01</p> <p>A generalized exact optical bright solitary wave solution in a three dimensional dispersive linear medium is presented. The most interesting property of the solution is that it can exist in the normal <span class="hlt">group-velocity</span>-dispersion (GVD) region. In addition, another peculiar feature is that it may achieve a condition of 'zero-dispersion' to the media so that a solitary wave of arbitrarily small amplitude may be propagated with no dependence on is pulse width.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/17632631','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17632631"><span id="translatedtitle">Ultrashort Laguerre-Gaussian pulses with angular and <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion compensation.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zeylikovich, I; Sztul, H I; Kartazaev, V; Le, T; Alfano, R R</p> <p>2007-07-15</p> <p>Coherent optical vortices are generated from ultrashort 6.4 fs pulses. Our results demonstrate angular dispersion compensation of ultrashort 6.4 fs Laguerre-Gaussian (LG) pulses as well as what is believed to be the first direct autocorrelation measurement of 80 fs LG amplified pulses. A reflective-mirror-based 4f-compressor is proposed to compensate the angular and <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion of the ultrashort LG pulses. PMID:17632631</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21466497','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21466497"><span id="translatedtitle">Pulsed bismuth fibre laser with the intracavity-compensated <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Krylov, Aleksandr A; Kryukov, P G; Dianov, Evgenii M; Okhotnikov, O G; Guina, M</p> <p>2009-01-31</p> <p>Passive mode locking is achieved in a bismuth-doped fibre laser with the help of a SESAM saturable absorber optimised for operation in the spectra range from 1100 to 1200 nm. Pumping was performed by a 2-W cw ytterbium fibre laser at 1075 nm. The oscillation of the laser with an intracavity <span class="hlt">group-velocity</span>-dispersion compensator based on a pair of diffraction gratings is studied. Laser pulses with the minimum duration of {approx}5 ps are generated. (lasers)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.4181R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.4181R"><span id="translatedtitle">Joint inversion of P-waveforms from teleseismic events and surface waves <span class="hlt">group</span> <span class="hlt">velocities</span> from ambient seismic noise in Bohemian Massif</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruzek, Bohuslav</p> <p>2010-05-01</p> <p>Joint inversion of P-waveforms from distant earthquakes recorded by 41 broadband seismic stations located on the territory of Bohemian Massif and Rayleigh/Love <span class="hlt">group</span> <span class="hlt">velocities</span> gained by using cross-correlation technique applied to seismic noise recorded by the same set of broadband stations has been performed. Together with joint inversion also individual inversions using single data sets have been carried out. All computations were arranged inside isotropic, locally 1D layered models. Remarkable result is indication of horizons just above MOHO in the lower crust below some stations where low-<span class="hlt">velocity</span> S-wave channel is needed in order to ensure correct modeling of measured events. This indication follows both from individual and joint inversions. P-waveform inversion is based on using a set of 271 well-recorded teleseismic events from epicentral distances 3000-10000 km. The inversion was originally based on the popular 'receiver function' methodology, but due to the instability of needed deconvolution it was modified. We search for optimum layered <span class="hlt">velocity</span> model, which correctly projects radial to vertical components (and vice versa, deconvolution is no more needed). Regarding second source of data, both Rayleigh and Love surface waves were extracted from seismic noise by using cross-correlation. Long time series covering the period 2001-2009 were processed. Such measurements provide <span class="hlt">group</span> <span class="hlt">velocities</span> between arbitrary pairs of stations. Local <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion curves were computed by using 2D <span class="hlt">tomography</span>-like approach for periods 4-20 s. The subject of inversion (both individual and joint) were just <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion curves. Inversion required exhaustive computations. We used HPC cluster nemo.ig.cas.cz and ANNI inversion software, capable to run in parallel regime.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JAG....59..337C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JAG....59..337C"><span id="translatedtitle">Numerical simulation of attenuation and <span class="hlt">group</span> <span class="hlt">velocity</span> of guided ultrasonic wave in grouted rock bolts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cui, Y.; Zou, D. H.</p> <p>2006-08-01</p> <p>In this paper, the guided ultrasonic wave propagating in grouted rock bolts was simulated with finite element method. An 800 mm partially grouted cylindrical rock bolt model was created. Dynamic input signals with frequency from 25 to 100 kHz were used to excite ultrasonic wave. The simulated waveform, <span class="hlt">group</span> <span class="hlt">velocity</span> and amplitude ratio matched well with the experimental results. This model made it possible to study the behaviour of the guided waves in the grouted bolt along its central axis. Analysis of the simulated results showed that the <span class="hlt">group</span> <span class="hlt">velocity</span> in grouted rock bolts is constant along the grouted length, and the boundary effect on the <span class="hlt">group</span> <span class="hlt">velocity</span> is negligible. This paper also presents methods to determine the attenuation coefficient from simulation and to determine the boundary effect on attenuation at the bolt ends. The analysis showed that the attenuation of the guided wave propagating inside the grouted bolts is similar to the theoretical solution in steel bar with infinite length. After correction for the boundary effects the grout length of a grouted rock bolt can be determined using the measured attenuation, with sufficient accuracy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhRvA..91f3607N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhRvA..91f3607N"><span id="translatedtitle">Maximum <span class="hlt">group</span> <span class="hlt">velocity</span> in a one-dimensional model with a sinusoidally varying staggered potential</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nag, Tanay; Sen, Diptiman; Dutta, Amit</p> <p>2015-06-01</p> <p>We use Floquet theory to study the maximum value of the stroboscopic <span class="hlt">group</span> <span class="hlt">velocity</span> in a one-dimensional tight-binding model subjected to an on-site staggered potential varying sinusoidally in time. The results obtained by numerically diagonalizing the Floquet operator are analyzed using a variety of analytical schemes. In the low-frequency limit we use adiabatic theory, while in the high-frequency limit the Magnus expansion of the Floquet Hamiltonian turns out to be appropriate. When the magnitude of the staggered potential is much greater or much less than the hopping, we use degenerate Floquet perturbation theory; we find that dynamical localization occurs in the former case when the maximum <span class="hlt">group</span> <span class="hlt">velocity</span> vanishes. Finally, starting from an "engineered" initial state where the particles (taken to be hard-core bosons) are localized in one part of the chain, we demonstrate that the existence of a maximum stroboscopic <span class="hlt">group</span> <span class="hlt">velocity</span> manifests in a light-cone-like spreading of the particles in real space.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/19550877','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/19550877"><span id="translatedtitle">Time-domain upconversion measurements of <span class="hlt">group-velocity</span> dispersion in quantum cascade lasers.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Choi, Hyunyong; Diehl, Laurent; Capasso, Federico; Bour, David; Corzine, Scott; Zhu, Jintian; Hofler, Gloria; Norris, Theodore B</p> <p>2007-11-26</p> <p>A time-resolved mid-infrared upconversion technique based on sum-frequency generation was applied to measure pulse propagation in lambda approximately 5.0 mum quantum cascade lasers operated in continuous wave at 30 K. The wavelength-dependent propagation delay of femtosecond mid-infrared pulses was measured to determine the total <span class="hlt">group-velocity</span> dispersion. The material and waveguide dispersion were calculated and their contributions to the total <span class="hlt">group-velocity</span> dispersion were found to be relatively small and constant. The small-signal gain dispersion was estimated from a measurement of the electroluminescence spectrum without a laser cavity, and was found to be the largest component of the total GVD. A negative <span class="hlt">group-velocity</span> dispersion of beta2 ( =d2beta/d omega2) approximately - 4.6x10-6 ps2/mum was observed at the peak emission wavelength, and good agreement was found for the measured and calculated pulse-broadening. PMID:19550877</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27036254','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27036254"><span id="translatedtitle">Backward waves with double zero-<span class="hlt">group-velocity</span> points in a liquid-filled pipe.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cui, Hanyin; Lin, Weijun; Zhang, Hailan; Wang, Xiuming; Trevelyan, Jon</p> <p>2016-03-01</p> <p>Hollow cylinders often exhibit backward propagation modes whose <span class="hlt">group</span> and phase <span class="hlt">velocities</span> have opposite directions, and these exhibit a minimum possible frequency at which the <span class="hlt">group</span> <span class="hlt">velocity</span> vanishes at a nonzero wavenumber. These zero-<span class="hlt">group-velocity</span> (ZGV) points are associated with resonant conditions in the medium. On the basis of ZGV resonances, a non-contact and laser ultrasound technique has been developed to measure elastic constants of hollow pipes. This paper provides a theoretical and numerical investigation of the influence of the contained liquid on backward waves and associated ZGV modes, in order to explore whether this ZGV technique is suitable for in-service non-destructive evaluations of liquid-filled pipes. Dispersion spectra and excitation properties have been analyzed. It is found that the presence of the liquid causes an increased number of backward modes and ZGVs which are highly excitable by a point source. In addition, several guided modes twice undergo a change of sign in the slopes of their dispersion curves, leading to two ZGV points. This phenomenon of double ZGVs in one backward wave, which is caused by strong mode repulsions, has not been found in isotropic hollow cylinders, but it can be observed in a fluid-filled thin-walled pipe. PMID:27036254</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006GeoRL..33.7303T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006GeoRL..33.7303T"><span id="translatedtitle">Local earthquake (LE) <span class="hlt">tomography</span> with joint inversion for P- and S-wave <span class="hlt">velocities</span> using structural constraints</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tryggvason, Ari; Linde, Niklas</p> <p>2006-04-01</p> <p>In local earthquake (LE) <span class="hlt">tomography</span> for P- and S-wave <span class="hlt">velocities</span> (or Vp/Vs ratios), constraints punishing deviations from a given Vp/Vs ratio are often used. In a synthetic model test we demonstrate that though such constraints inhibit unreasonable Vp/Vs ratio variations, they bias the resulting Vp/Vs ratios. As an alternative approach, structural constraints based on the cross-product of the model gradients can be used to constrain the joint P- and S-wave inversion. We show that the resulting models are as low in artifacts as if a Vp/Vs damping was used, but the resulting Vp/Vs ratios are less biased, which is important for a quantitative interpretation of physical properties and processes in the Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMSM51F4315S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMSM51F4315S"><span id="translatedtitle"><span class="hlt">Velocity</span> and Energy Distributions of Water <span class="hlt">Group</span> Ion Around the Enceladus Plume</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sakai, S.; Cravens, T.; Pothapragada, S.; Kumar, A.</p> <p>2014-12-01</p> <p>Enceladus has a dynamic plume on its south pole which is emitting gas, including water vapor, and dust. The gas is ionized by solar EUV radiation and by electron impacts and extends throughout the inner magnetosphere of Saturn. The dust is negatively charged and forms the E ring. Hence, the inner magnetosphere within 10 RS contains a complex mixture of plasma, neutral gas and dust. Cassini observations show that the plasma <span class="hlt">velocities</span> are less than the co-rotation <span class="hlt">velocity</span>. The <span class="hlt">velocity</span> and energy distributions of this need to be explained in order to understand the inner magnetospheric plasma physics. We have investigated the <span class="hlt">velocity</span> and energy distributions of water <span class="hlt">group</span> ions in the vicinity of Enceladus using test particle and Monte Carlo methods including collisional processes such as charge exchange and ion-neutral chemical reaction. The model results will be constrained by neutral and ion composition data from the Cassini Ion and Neutral Mass Spectrometer and ion energy spectra from the Plasma Spectrometer (CAPS). We will also discuss related plasma processed in the Enceladus torus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.S53F..06M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.S53F..06M"><span id="translatedtitle">A New Global <span class="hlt">Group</span> <span class="hlt">Velocity</span> Dataset for Constraining Crust and Upper Mantle Properties</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Z.; Masters, G.; Laske, G.; Pasyanos, M. E.</p> <p>2010-12-01</p> <p>We are improving our CRUST2.0 to a new LITHO1.0 model, refining the nominal resolution to 1 degree and including lithospheric structure. The new model is constrained by many datasets, including very large datasets of surface wave <span class="hlt">group</span> <span class="hlt">velocity</span> built using a new, efficient measurement technique. This technique starts in a similar fashion to the traditional frequency-time analysis, but instead of making measurements for all frequencies for a single source-station pair, we apply cluster analysis to make measurements for all recordings for a single event at a single target frequency. By changing the nominal frequencies of the bandpass filter, we filter each trace until the centroid frequency of the band-passed spectrum matches the target frequency. We have processed all the LH data from IRIS (and some of the BH data from PASSCAL experiments and the POLARIS network) from 1976 to 2007. The Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocity</span> data set is complete from 10mHz to 40mHz at increments of 2.5mHz. The data set has about 330000 measurements for 10 and 20mHz, 200000 for 30mHz and 110000 for 40mHz. We are also building a similar dataset for Love waves, though its size will be about half that of the Rayleigh wave dataset. The SMAD of the <span class="hlt">group</span> arrival time difference between our global dataset and other more regional datasets is about 12 seconds for 20mHz, 9 seconds for 30mHz, and 7 seconds for 40mHz. Though the discrepancies are about twice as big as our measurement precision (estimated by looking at <span class="hlt">group</span> arrival time differences between closely-spaced stations), it is still much smaller than the signal in the data (e.g., the <span class="hlt">group</span> arrival time for 20mHz can differ from the prediction of a 1D Earth by over 250 seconds). The fact that there is no systematic bias between the datasets encourages us to combine them to improve coverage of some key areas. <span class="hlt">Group</span> <span class="hlt">velocity</span> maps inverted from the combined datasets show many interesting signals though the dominant signal is related to variations</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007AAS...210.0801M&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007AAS...210.0801M&link_type=ABSTRACT"><span id="translatedtitle">Impact of High <span class="hlt">Velocity</span> Interactions on Galaxy Evolution in Galaxy <span class="hlt">Groups</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Machacek, Marie E.; Jones, C.; Forman, W. R.; Kraft, R. P.; Ashby, M. L.; Hardcastle, M. J.</p> <p>2007-05-01</p> <p>Galaxy interactions in cool <span class="hlt">groups</span> dominate galaxy evolution at high redshift. Observations of galaxies interacting in nearby galaxy <span class="hlt">groups</span>, where the same dynamical processes that transform galaxies at high redshift can be studied in detail, are critical to our understanding of galaxy and <span class="hlt">group</span> evolution. X-ray observations of hot gas features, e.g. surface brightness edges and wakes, reveal that high <span class="hlt">velocity</span> interactions play a significant role in the transformation of galaxies in <span class="hlt">groups</span>, yet, because these encounters are difficult to identify in other wavebands, few have been studied. We present two case studies of high <span class="hlt">velocity</span> galaxy-galaxy and galaxy-gas interactions in galaxy <span class="hlt">groups</span>: NGC4782(3C278) and NGC4783 in LGG316, and NGC6872 and NGC6876 in the Pavo <span class="hlt">group</span>. From Chandra and XMM-Newton X-ray data, we measure the hot gas temperature, density and metal abundance in the galaxies and the intragroup medium (IGM) to characterize the thermodynamic state of the <span class="hlt">group</span>, constrain 3D motions of the galaxies through the IGM, and determine the dominant processes transferring matter and energy between the galaxy and <span class="hlt">group</span> gas. We compare these results with VLA observations of NGC4782/3 and Spitzer IRAC observations of NGC6872 and NGC6876 to study the impact of these interactions on nuclear activity, radio jet evolution, and star formation in these galaxies, and on the heating and enrichment of the IGM. This work was supported in part by the Smithsonian Institution, the Chandra Science Center, NASA contracts AR5-6011X, GO6-7068X, NNX06AG34G, JPL1279244 and the Royal Society.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.S51A1259I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.S51A1259I"><span id="translatedtitle">P-wave anisotropic <span class="hlt">velocity</span> <span class="hlt">tomography</span> beneath the Japan islands: Large-scale images and details in the Kanto district</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ishise, M.; Koketsu, K.; Miyake, H.; Oda, H.</p> <p>2006-12-01</p> <p>The Japan islands arc is located in the convergence zone of the North American (NA), Amurian (AM), Pacific (PAC) and Philippine Sea (PHS) plates, and its parts are exposed to various tectonic settings. For example, at the Kanto district in its central part, these four plates directly interact with each, so that disastrous future earthquakes are expected along the plate boundaries and within the inland areas. In order to understand this sort of complex tectonic setting, it is necessary to know the seismological structure in various perspectives. We investigate the seismic <span class="hlt">velocity</span> structure beneath the Japan islands in view of P-wave anisotropy. We improved a hitherto-known P-wave <span class="hlt">tomography</span> technique so that the 3-D structure of isotropic and anisotropic <span class="hlt">velocities</span> and earthquake hypocenter locations are determined from P-wave arrival times of local earthquakes [Ishise and Oda, 2005]. In the <span class="hlt">tomography</span> technique, P-wave anisotropy is assumed to hold hexagonal symmetry with horizontal symmetry axis. The P-wave arrival times used in this study are complied in the Japan University Network Earthquake Catalog. The results obtained are summarized as follows; (1) the upper crust anisotropy is governed by the present-day stress field arising from the interaction between the plates surrounding the Japan islands arc, (2) the mantle anisotropy is caused by the present-day mantle flow induced by slab subduction and continental plate motion, (3) the old PAC slab keeps its original slab anisotropy which was captured when the plate was formed, while the youngest part of the PHS slab has lost the original anisotropy during its subduction and has gained new anisotropy which is controlled by the present-day stress field. We also carried out a further study on high-resolution seismic <span class="hlt">tomography</span> for understanding the specific characteristics of the Kanto district. We mostly focused on the elucidation of the dual subduction formed by the PHS and PAC slabs using seismological data</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/20442022','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/20442022"><span id="translatedtitle">Laser ultrasonic inspection of plates using zero-<span class="hlt">group</span> <span class="hlt">velocity</span> lamb modes.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Clorennec, Dominique; Prada, Claire; Royer, Daniel</p> <p>2010-05-01</p> <p>A noncontact laser-based ultrasonic technique is proposed for detecting small plate thickness variations caused by corrosion and adhesive disbond between two plates. The method exploits the resonance at the minimum frequency of the S(1) Lamb mode dispersion curve. At this minimum frequency, the <span class="hlt">group</span> <span class="hlt">velocity</span> vanishes, whereas the phase <span class="hlt">velocity</span> remains finite. The energy deposited by the laser pulse generates a local resonance of the plate. This vibration is detected at the same point by an optical interferometer. First experiments show the ability to image a 1.5-microm deep corroded area on the back side of a 0.5-mm-thick duralumin plate. Because of the finite wavelength of the S(1)- zero <span class="hlt">group</span> <span class="hlt">velocity</span> (ZGV) mode, the spatial resolution is limited to approximately twice the plate thickness. With the same technique we investigate the state of adhesive bonds between duralumin and glass plates. The S(1)-Lamb mode resonance is strongly attenuated when plates are rigidly bonded. In the case of thin adhesive layers, we observed other resonances, associated with ZGV modes of the multi-layer structure, whose frequencies and amplitudes vary with adhesive thickness. Experiments were carried out on real automotive adhesively bonded structures and the results were compared with images obtained by X-ray radiography. PMID:20442022</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009SPIE.7177E..0YY','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009SPIE.7177E..0YY"><span id="translatedtitle">Simultaneous recovery of chromophore concentrations and ultrasound <span class="hlt">velocity</span> by spectrally resolved photoacoustic <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yuan, Zhen; Zhang, Qizhi; Grobmyer, Stephen; Jiang, Huabei</p> <p>2009-02-01</p> <p>We describe a new spectral approach for inversion of photoacoustic data with multi-wavelength pulsed laser illumination. Multi-spectral PAT provides a means of recovery of different chromophore concentrations and ultrasound <span class="hlt">velocity</span> simultaneously and directly by incorporating prior spectral information into the image reconstruction process. It is demonstrated from simulation tests and small animal experiments that the multi-parameter recovery based on multispectral PAT is reliable and accurate. The reconstructed multiple parameter images may provide us a key tool to quantify physiological function, disease progression, or response to intervention.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.S31A2030P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.S31A2030P"><span id="translatedtitle">Three dimensional Rayleigh wave <span class="hlt">velocity</span> model using multimode surface wave <span class="hlt">tomography</span> of Eastern Asia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pandey, S.; Yuan, X.; Debayle, E.; Priestley, K. F.; Kind, R.; Li, X.</p> <p>2010-12-01</p> <p>The collision of the Eurasian plate, Indian plate and Philippine sea plate resulted in the tectonic feature of todays; like mountain ranges, fold belts, sedimentary basins and high plateaus in China and the surrounding region. In the Northern part this region is supposed to get some resistance from the Siberian shield. But the collision of Indian plate has left its major imprints and the consequence of this was the uplift of Himalayan Mountain and Tibetan Plateau. This triple junction scenario is the main cause for many inter and intra-plate earthquake in this region. It is generally agreed that the lithosphere is thick in west China while much of the lithospheric root was lost beneath some cratons in east China. Still it's an open debate whether the lithosphere beneath the Tibetan plateau has doubled its thickness as did the crust above or much of the thickened lithosphere was removed by mantle convection and delamination. In our study we try to determine the three dimensional Sv wave speed and azimuthal anisotropy model by analyzing the vertical component multimode Rayleigh wave seismogram. The data which we used are from broadband stations from in and around China. We construct the three dimensional model in two step procedure. In the first step we use the automated version of the Cara and Leveque [1987] waveform inversion technique in terms of secondary observables for modeling each multimode Rayleigh waveform to determine the path-average mantle Sv wave speed structure. In the second stage we combine the 1-D <span class="hlt">velocity</span> models in a tomographic inversion to obtain the three dimensional Sv wave speed structure and the azimuthal anisotropy as a function of depth. We have taken a source region specific <span class="hlt">velocity</span> structure from the three dimensional model 3SMAC to improve the source excitation computation. We analyzed the seismograms using a modified (smoothed) version of PREM for the upper mantle <span class="hlt">velocity</span> structure both for the reference model used in extracting the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22039079','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22039079"><span id="translatedtitle">TWO DISTANT HALO <span class="hlt">VELOCITY</span> <span class="hlt">GROUPS</span> DISCOVERED BY THE PALOMAR TRANSIENT FACTORY</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sesar, Branimir; Cohen, Judith G.; Levitan, David; Kirby, Evan N.; Kulkarni, Shrinivas R.; Prince, Thomas A.; Grillmair, Carl J.; Laher, Russ R.; Surace, Jason A.; Juric, Mario; Ofek, Eran O.</p> <p>2012-08-20</p> <p>We report the discovery of two new halo <span class="hlt">velocity</span> <span class="hlt">groups</span> (Cancer <span class="hlt">groups</span> A and B) traced by eight distant RR Lyrae stars and observed by the Palomar Transient Factory survey at R.A. {approx} 129 Degree-Sign , decl. {approx} 20 Degree-Sign (l {approx} 205 Degree-Sign , b {approx} 32 Degree-Sign ). Located at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the most distant substructures in the Galactic halo known to date. Follow-up spectroscopic observations with the Palomar Observatory 5.1 m Hale telescope and W. M. Keck Observatory 10 m Keck I telescope indicate that the two <span class="hlt">groups</span> are moving away from the Galaxy at v-bar{sub gsr}{sup A} = 78.0{+-}5.6 km s{sup -1} (Cancer <span class="hlt">group</span> A) and v-bar{sub gsr}{sup B} = 16.3{+-}7.1 km s{sup -1} (Cancer <span class="hlt">group</span> B). The <span class="hlt">groups</span> have <span class="hlt">velocity</span> dispersions of {sigma}{sub v{sub g{sub s{sub r}{sup A}}}} = 12.4{+-}5.0 km s{sup -1} and {sigma}B{sub v{sub g{sub s{sub r}{sup B}}}} =14.9{+-}6.2 km s{sup -1} and are spatially extended (about several kpc), making it very unlikely that they are bound systems, and more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both <span class="hlt">groups</span> are metal-poor (median metallicities of [Fe/H]{sup A} = -1.6 dex and [Fe/H]{sup B} = -2.1 dex) and have a somewhat uncertain (due to small sample size) metallicity dispersion of {approx}0.4 dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars with <span class="hlt">velocities</span> consistent with those of the Cancer <span class="hlt">groups</span> have been observed {approx}25 Degree-Sign east, suggesting possible extension of the <span class="hlt">groups</span> in that direction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004ApJ...610L..17P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004ApJ...610L..17P"><span id="translatedtitle">Where Are the High-<span class="hlt">Velocity</span> Clouds in Local <span class="hlt">Group</span> Analogs?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pisano, D. J.; Barnes, David G.; Gibson, Brad K.; Staveley-Smith, Lister; Freeman, Ken C.; Kilborn, Virginia A.</p> <p>2004-07-01</p> <p>High-<span class="hlt">velocity</span> clouds (HVCs) are clouds of H I seen around the Milky Way with <span class="hlt">velocities</span> inconsistent with Galactic rotation; they have unknown distances and masses and controversial origins. One possibility is that HVCs are associated with the small dark matter halos seen in models of galaxy formation and distributed at distances of 150 kpc to 1 Mpc. We report on our attempts to detect the analogs to such putative extragalactic clouds in three <span class="hlt">groups</span> of galaxies similar to our own Local <span class="hlt">Group</span> using the Australia Telescope National Facility Parkes Telescope and Compact Array. Eleven dwarf galaxies were found, but no H I clouds lacking stars were detected. Using the population of compact HVCs around the Milky Way as a template, we find that our nondetection of analogs implies that they must be clustered within 160 kpc of the Milky Way (and other galaxies) with an average H I mass <~4×105 Msolar at the 95% confidence level. This is in accordance with recent limits derived by other authors. If our <span class="hlt">groups</span> are true analogs to the Local <span class="hlt">Group</span>, then this makes the original Blitz et al. and Braun & Burton picture of HVCs residing out to 1 Mpc from the Milky Way extremely unlikely. The total H I mass in HVCs, <~108 Msolar, implies that there is not a large reservoir of neutral hydrogen waiting to be accreted onto the Milky Way. Any substantial reservoir of baryonic matter must be mostly ionized or condensed enough as to be undetectable.</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_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" 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_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3673069','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3673069"><span id="translatedtitle">Evaluation of Moisture-Related Attenuation Coefficient and Water Diffusion <span class="hlt">Velocity</span> in Human Skin Using Optical Coherence <span class="hlt">Tomography</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>Lee, Cheng-Kuang; Tsai, Meng-Tsan; Chang, Feng-Yu; Yang, Chih-Hsun; Shen, Su-Chin; Yuan, Ouyang; Yang, Chih-He</p> <p>2013-01-01</p> <p>In this study, time-resolved optical coherence <span class="hlt">tomography</span> (OCT) scanning images of the process of water diffusion in the skin that illustrate the enhancement in the backscattered intensities due to the increased water concentration are presented. In our experiments, the water concentration in the skin was increased by soaking the hand in water, and the same region of the skin was scanned and measured with the OCT system and a commercial moisture monitor every three minutes. To quantitatively analyze the moisture-related optical properties and the <span class="hlt">velocity</span> of water diffusion in human skin, the attenuation coefficients of the skin, including the epidermis and dermis layers, were evaluated. Furthermore, the evaluated attenuation coefficients were compared with the measurements made using the commercial moisture monitor. The results demonstrate that the attenuation coefficient increases as the water concentration increases. Furthermore, by evaluating the positions of center-of mass of the backscattered intensities from OCT images, the diffusion <span class="hlt">velocity</span> can be estimated. In contrast to the commercial moisture monitor, OCT can provide three-dimensional structural images of the skin and characterize its optical property, which together can be used to observe morphological changes and quantitatively evaluate the moisture-related attenuation coefficients in different skin layers. PMID:23529149</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ApPhL.108f1106T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApPhL.108f1106T"><span id="translatedtitle">Reducing the <span class="hlt">group</span> <span class="hlt">velocity</span> of coherent radiation for upconverting the single-cycle electron density modulation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tanaka, Takashi</p> <p>2016-02-01</p> <p>We present an interesting property of broadband coherent radiation emitted by a single microbunch, or a single-cycle density modulation in an electron beam passing through an undulator, and describe its application to a frequency upconversion of the single-cycle modulation. This is based on the fact that a monocycle pulse is generated by focusing the coherent radiation with a unit-magnification optical system, which propagates without diffraction like the Bessel beam, at a reduced <span class="hlt">group</span> <span class="hlt">velocity</span> equal to the average electron <span class="hlt">velocity</span> in the undulator. Calculations show that a single microbunch with a length of 46-nm formed in a 2-GeV and 2-kA electron beam can be upconverted to a 4-nm long microbunch through interaction with focused coherent radiation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhRvB..92l1409B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhRvB..92l1409B"><span id="translatedtitle">Nonperturbative renormalization <span class="hlt">group</span> calculation of quasiparticle <span class="hlt">velocity</span> and dielectric function of graphene</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bauer, Carsten; Rückriegel, Andreas; Sharma, Anand; Kopietz, Peter</p> <p>2015-09-01</p> <p>Using a nonperturbative functional renormalization <span class="hlt">group</span> approach, we calculate the renormalized quasiparticle <span class="hlt">velocity</span> v (k ) and the static dielectric function ɛ (k ) of suspended graphene as functions of an external momentum k . Our numerical result for v (k ) can be fitted by v (k ) /vF=A +B ln(Λ0/k ) , where vF is the bare Fermi <span class="hlt">velocity</span>, Λ0 is an ultraviolet cutoff, and A =1.37 , B =0.51 for the physically relevant value (e2/vF=2.2 ) of the coupling constant. In contrast to calculations based on the static random-phase approximation, we find that ɛ (k ) approaches unity for k →0 . Our result for v (k ) agrees very well with a recent measurement by Elias et al. [Nat. Phys. 7, 701 (2011), 10.1038/nphys2049].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22066656','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22066656"><span id="translatedtitle">Dynamics of frequency-modulated soliton-like pulses in a longitudinally inhomogeneous, anomalous <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion fibre amplifier</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zolotovskii, Igor' O; Korobko, D A; Okhotnikov, Oleg G; Sysolyatin, A A; Fotiadi, A A</p> <p>2012-09-30</p> <p>We examine conditions for the formation and amplification of frequency-modulated soliton-like pulses in longitudinally inhomogeneous, anomalous <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion fibres. The <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion profiles necessary for the existence and amplification of such pulses in active fibres are identified and the pulse duration and chirp are determined as functions of propagation distance. (optical fibres, lasers and amplifiers. properties and applications)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014JGRB..119..519B&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014JGRB..119..519B&link_type=ABSTRACT"><span id="translatedtitle">Phase <span class="hlt">velocity</span> <span class="hlt">tomography</span> of surface waves using ambient noise cross correlation and array processing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boué, Pierre; Roux, Philippe; Campillo, Michel; Briand, Xavier</p> <p>2014-01-01</p> <p>Continuous recordings of ambient seismic noise across large seismic arrays allows a new type of processing using the cross-correlation technique on broadband data. We propose to apply double beamforming (DBF) to cross correlations to extract a particular wave component of the reconstructed signals. We focus here on the extraction of the surface waves to measure phase <span class="hlt">velocity</span> variations with great accuracy. DBF acts as a spatial filter between two distant subarrays after cross correlation of the wavefield between each single receiver pair. During the DBF process, horizontal slowness and azimuth are used to select the wavefront on both subarray sides. DBF increases the signal-to-noise ratio, which improves the extraction of the dispersive wave packets. This combination of cross correlation and DBF is used on the Transportable Array (USArray), for the central U.S. region. A standard model of surface wave propagation is constructed from a combination of the DBF and cross correlations at different offsets and for different frequency bands. The perturbation (phase shift) between each beam and the standard model is inverted. High-resolution maps of the phase <span class="hlt">velocity</span> of Rayleigh and Love waves are then constructed. Finally, the addition of azimuthal information provided by DBF is discussed, to construct curved rays that replace the classical great-circle path assumption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/19506660','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/19506660"><span id="translatedtitle">Zero-<span class="hlt">group-velocity</span> modes in chalcogenide holey photonic-crystal fibers.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Oskooi, Ardavan F; Joannopoulos, J D; Johnson, Steven G</p> <p>2009-06-01</p> <p>We demonstrate that a holey photonic-crystal fiber with chalcogenide-glass index contrast can be designed to have a complete gap at a propagation constant beta = 0 that also extends into the non-zero beta region. This type of bandgap (previously identified only at index contrasts unattainable in glasses) opens up a regime for guiding zero-<span class="hlt">group-velocity</span> modes not possible in holey fibers with the more common finger-like gaps originating from beta-->infinity. Such modes could be used to enhance nonlinear and other material interactions, such as for hollow-core fibers in gas-sensor applications. PMID:19506660</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=55078&keyword=seismic+AND+tomography&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=67184562&CFTOKEN=25351295','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=55078&keyword=seismic+AND+tomography&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=67184562&CFTOKEN=25351295"><span id="translatedtitle">SUBSEQUENT FINAL REPORT. SEISMIC SURFACE-WAVE <span class="hlt">TOMOGRAPHY</span> OF WASTE SITES</span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>Surface-wave <span class="hlt">group-velocity</span> <span class="hlt">tomography</span> is an efficient way to obtain images of the <span class="hlt">group</span> <span class="hlt">velocity</span> over a test area. Because Rayleigh-wave <span class="hlt">group</span> <span class="hlt">velocity</span> depends on frequency, there are separate images for each frequency. Thus, at each point in these images the <span class="hlt">group</span> <span class="hlt">velocities</span> de...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhRvA..90f2314D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhRvA..90f2314D"><span id="translatedtitle">Phase-noise limitations on single-photon cross-phase modulation with differing <span class="hlt">group</span> <span class="hlt">velocities</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dove, Justin; Chudzicki, Christopher; Shapiro, Jeffrey H.</p> <p>2014-12-01</p> <p>A framework is established for evaluating cphase gates that use single-photon cross-phase modulation (XPM) originating from the Kerr nonlinearity. Prior work [J. H. Shapiro, Phys. Rev. A 73, 062305 (2006), 10.1103/PhysRevA.73.062305], which assumed that the control and target pulses propagated at the same <span class="hlt">group</span> <span class="hlt">velocity</span>, showed that the causality-induced phase noise required by a noninstantaneous XPM response function precluded the possibility of high-fidelity π -radian conditional phase shifts. The framework presented herein incorporates the more realistic case of <span class="hlt">group-velocity</span> disparity between the control and target pulses, as employed in existing XPM-based fiber-optical switches. Nevertheless, the causality-induced phase noise identified by Shapiro [J. H. Shapiro, Phys. Rev. A 73, 062305 (2006), 10.1103/PhysRevA.73.062305] still rules out high-fidelity π -radian conditional phase shifts. This is shown to be so for both a reasonable theoretical model for the XPM response function and for the experimentally measured XPM response function of silica-core fiber.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/20707442','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/20707442"><span id="translatedtitle">Estimation of modal <span class="hlt">group</span> <span class="hlt">velocities</span> with a single receiver for geoacoustic inversion in shallow water.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bonnel, Julien; Nicolas, Barbara; Mars, Jérome I; Walker, Shane C</p> <p>2010-08-01</p> <p>Due to the expense associated with at-sea sensor deployments, a challenge in underwater acoustics has been to develop methods requiring a minimal number of sensors. This paper introduces an adaptive time-frequency signal processing method designed for application to a single source-receiver sensor pair. The method involves the application of conjugate time-frequency warping transforms to improve the SNR and resolution of the time-frequency distribution (TFD) of the measured field. Such refined knowledge of the TFD facilitates efforts to extract tomographic information about the propagation medium. Here the method is applied to the case of modal propagation in a shallow ocean range independent environment to extract a refined TFD. Given knowledge of the source-receiver separation, the refined TFD is used to extract the frequency dependent <span class="hlt">group</span> <span class="hlt">velocities</span> of the individual modal components. The extracted <span class="hlt">group</span> <span class="hlt">velocities</span> are then incorporated into a computationally light tomographic inversion method. Simulated and experimental results are discussed. PMID:20707442</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000AAS...196.2809G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000AAS...196.2809G"><span id="translatedtitle">Are Compact High-<span class="hlt">Velocity</span> Clouds The Missing Local <span class="hlt">Group</span> Satellites?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grebel, E. K.; Braun, R.; Burton, W. B.</p> <p>2000-05-01</p> <p>In contrast to high-<span class="hlt">velocity</span> cloud complexes, isolated compact high-<span class="hlt">velocity</span> clouds (CHVCs) are plausibly at distances of 0.5 to 1 Mpc, show infall motion with respect to the Local <span class="hlt">Group</span> barycenter, are rotationally supported and dark-matter dominated. Are CHVCs the missing Local <span class="hlt">Group</span> satellites predicted by hierarchical clustering scenarios? Are they proto-galactic gas clouds or do they contain stars as well? A failure to detect stars would be a very interesting result in itself: the first discovery of pure HI/dark matter halos prior to star formation, i.e., the most basic of galaxy building blocks. A detection of stars will help to refine the HI distances, augment the faint end of the galaxy luminosity function, and open the way to the study of the stellar populations of a new, very dark type of dwarf galaxy. We present results from a targeted multi-color survey for stars in radio-preselected CHVCs with the Mosaic imagers at NOAO. Our findings seem to indicate the detection of the red giant branch of an old stellar population, but contamination by distant starburst galaxies plays a role as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OptCo.363...31V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OptCo.363...31V"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> dispersion of CdSSe/ZnS core-shell colloidal quantum dots measured with white light interferometry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>VanEngen Spivey, Amelia G.</p> <p>2016-03-01</p> <p>We measure the <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion coefficient of CdSSe/ZnS core-shell colloidal quantum dots in liquid suspension in the ∼700-900 nm wavelength range using a white-light Michelson interferometer. Two different sizes of dots are investigated. In both cases, the <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion coefficient decreases with increasing wavelength above the absorption edge in the dots. For quantum dots in which the linear absorption spectrum shows clear peaks, the absorption characteristics of the dots can be used to accurately model the wavelength-dependence of the <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion coefficient.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JOpt...17f5612M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JOpt...17f5612M"><span id="translatedtitle">Phase and <span class="hlt">group</span> <span class="hlt">velocity</span> of focused, pulsed Gaussian beams in the presence and absence of primary aberrations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Major, Balázs; Horváth, Zoltán L.; Porras, Miguel A.</p> <p>2015-06-01</p> <p>This work presents a study on the phase- and <span class="hlt">group-velocity</span> variations of focused, pulsed Gaussian beams during the propagation through the focal region along the optical axis. In the aberration-free case, it is discussed how the wavelength dependence of beam properties alters the <span class="hlt">group</span> <span class="hlt">velocity</span>, and how a chromatic aberration-like effect can arise even when focusing is performed with an element that does not have chromatic aberration. It is also examined what effects primary spherical aberration, astigmatism, coma, curvature of field and distortion, along with chromatic aberration, have on the phase- and <span class="hlt">group-velocity</span> changes occurring during propagation through focus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.S41B2727K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.S41B2727K&link_type=ABSTRACT"><span id="translatedtitle">A 3D Seismic <span class="hlt">Velocity</span> Model Offshore Southern California from Ambient Noise <span class="hlt">Tomography</span> of the ALBACORE OBS Array</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kohler, M. D.; Bowden, D. C.; Tsai, V. C.; Weeraratne, D. S.</p> <p>2015-12-01</p> <p>The Pacific-North America plate boundary in Southern California extends far west of the coastline, and a 12-month ocean bottom seismometer (OBS) array spanned the western side of the plate boundary to image lithospheric seismic <span class="hlt">velocities</span>. <span class="hlt">Velocities</span> are modeled through stacked cross correlations of ambient noise data. Twelve months of continuous data were used from 22 OBS stations and ~30 coastal and island Southern California Seismic Network stations. Particular attention has been paid to improving signal-to-noise ratios in the noise correlations with OBS stations by removing the effects of instrument tilt and infragravity waves. Different applications of preprocessing techniques allow us to distinguish the fundamental and first higher order Rayleigh modes, especially in deep water OBS pairs where the water layer dominates crustal sensitivity of the fundamental mode. Standard time domain and frequency domain methods are used to examine surface wave dispersion curves for <span class="hlt">group</span> and phase <span class="hlt">velocities</span> between 5 and 50 second periods, and these are inverted for 3D <span class="hlt">velocity</span> structure. The results define the transition in three dimensions from continental lithospheric structure in the near-shore region to oceanic structure west of the continental borderland. While the most prominent features of the model relate to thinning of the crust west of the Patton Escarpment, other notable anomalies are present north-to-south throughout the continental borderland and along the coast from the Los Angeles Basin to the Peninsular Ranges. The <span class="hlt">velocity</span> model will help describe the region's tectonic history, as well as provide new constraints for determination of earthquake relocations and rupture styles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3677104','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3677104"><span id="translatedtitle">Quantitative imaging of cerebral blood flow <span class="hlt">velocity</span> and intracellular motility using dynamic light scattering–optical coherence <span class="hlt">tomography</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>Lee, Jonghwan; Radhakrishnan, Harsha; Wu, Weicheng; Daneshmand, Ali; Climov, Mihail; Ayata, Cenk; Boas, David A</p> <p>2013-01-01</p> <p>This paper describes a novel optical method for label-free quantitative imaging of cerebral blood flow (CBF) and intracellular motility (IM) in the rodent cerebral cortex. This method is based on a technique that integrates dynamic light scattering (DLS) and optical coherence <span class="hlt">tomography</span> (OCT), named DLS–OCT. The technique measures both the axial and transverse <span class="hlt">velocities</span> of CBF, whereas conventional Doppler OCT measures only the axial one. In addition, the technique produces a three-dimensional map of the diffusion coefficient quantifying nontranslational motions. In the DLS–OCT diffusion map, we observed high-diffusion spots, whose locations highly correspond to neuronal cell bodies and whose diffusion coefficient agreed with that of the motion of intracellular organelles reported in vitro in the literature. Therefore, the present method has enabled, for the first time to our knowledge, label-free imaging of the diffusion-like motion of intracellular organelles in vivo. As an example application, we used the method to monitor CBF and IM during a brief ischemic stroke, where we observed an induced persistent reduction in IM despite the recovery of CBF after stroke. This result supports that the IM measured in this study represent the cellular energy metabolism-related active motion of intracellular organelles rather than free diffusion of intracellular macromolecules. PMID:23403378</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T33D2690H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T33D2690H"><span id="translatedtitle">Spatial variation and azimuthal anisotropy of the Rayleigh phase <span class="hlt">velocity</span> beneath Northeast China revealed by ambient noise eikonal <span class="hlt">tomography</span>: results and implications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Han, J.; Ning, J.; Chen, Y. J.; Niu, F.; Grand, S.; Kawakatsu, H.; Tanaka, S.; Obayashi, M.; Ni, J. F.</p> <p>2012-12-01</p> <p>Northeast China consists of Songliao Basin in its center, the Great Xing'an Range to the west, the Changbaishan volcano to the east and the Archean Sino-Korean Craton to the south. Although it is generally believed that the evolution of the Songliao Basin and the Cenozoic volcanism in NE China are somehow related to the Pacific plate subduction beneath the area, there are no concrete geodynamical explanations of the genesis of the volcanism. Detailed seismic images are needed to understand the deep structures. We conducted a high-resolution Rayleigh wave <span class="hlt">tomography</span> to study the crustal <span class="hlt">velocity</span> and azimuthal anisotropy beneath NE China. We used continuous broadband records of the 120 NECESSArray stations and 266 CEA stations in NE China to construct Green's functions of ray paths between station pairs. We employed the Eikonal <span class="hlt">tomography</span> method developed by Lin et al. (2009) to invert phase <span class="hlt">velocities</span> in the area. At short periods, isotropic <span class="hlt">velocity</span> is clearly correlated with the tectonic units. Songliao basin is characterized with very low <span class="hlt">velocity</span>, while most mountain belts show relatively higher <span class="hlt">velocity</span> except some sporadically distributed small low <span class="hlt">velocity</span> zones to the east of the Dunhua-Mishan fault. As period increases, those sporadically distributed small low <span class="hlt">velocity</span> zones gradually grow larger into several scattered low <span class="hlt">velocity</span> fingers, northwestward. At period of 40 s, those scattered low <span class="hlt">velocity</span> fingers expand into a singular wide low <span class="hlt">velocity</span> anomaly and the image clearly shows the low <span class="hlt">velocity</span> zone beneath the Songliao Basin. This large feature is located around Tanlu fault, Yilan-Yitong fault and Dunhua-Mishan fault and suggests that these faults penetrate through the lithosphere and possibly form the conduits for melting materials. To the west of the Great Xing'an Range, there is another large deep low <span class="hlt">velocity</span> zone. Edge-driven small-scale convection process may be operating beneath the boundary between the hot and cold mantle and causing</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70025993','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70025993"><span id="translatedtitle">Surface wave <span class="hlt">tomography</span> of North America and the Caribbean using global and regional broad-band networks: Phase <span class="hlt">velocity</span> maps and limitations of ray theory</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Godey, S.; Snieder, R.; Villasenor, A.; Benz, H.M.</p> <p>2003-01-01</p> <p>We present phase <span class="hlt">velocity</span> maps of fundamental mode Rayleigh waves across the North American and Caribbean plates. Our data set consists of 1846 waveforms from 172 events recorded at 91 broad-band stations operating in North America. We compute phase <span class="hlt">velocity</span> maps in four narrow period bands between 50 and 150 s using a non-linear waveform inversion method that solves for phase <span class="hlt">velocity</span> perturbations relative to a reference Earth model (PREM). Our results show a strong <span class="hlt">velocity</span> contrast between high <span class="hlt">velocities</span> beneath the stable North American craton, and lower <span class="hlt">velocities</span> in the tectonically active western margin, in agreement with other regional and global surface wave <span class="hlt">tomography</span> studies. We perform detailed comparisons with global model results, which display good agreement between phase <span class="hlt">velocity</span> maps in the location and amplitude of the anomalies. However, forward modelling shows that regional maps are more accurate for predicting waveforms. In addition, at long periods, the amplitude of the <span class="hlt">velocity</span> anomalies imaged in our regional phase <span class="hlt">velocity</span> maps is three time larger than in global phase <span class="hlt">velocity</span> models. This amplitude factor is necessary to explain the data accurately, showing that regional models provide a better image of <span class="hlt">velocity</span> structures. Synthetic tests show that the raypath coverage used in this study enables one to resolve <span class="hlt">velocity</span> features of the order of 800-1000 km. However, only larger length-scale features are observed in the phase <span class="hlt">velocity</span> maps. The limitation in resolution of our maps can be attributed to the wave propagation theory used in the inversion. Ray theory does not account for off-great-circle ray propagation effects, such as ray bending or scattering. For wavelengths less than 1000 km, scattering effects are significant and may need to be considered.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.8180K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..18.8180K&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Group</span> and phase <span class="hlt">velocities</span> from deterministic and ambient sources measured during the AlpArray-EASI experiment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kolínský, Petr; Zigone, Dimitri; Fuchs, Florian; Bianchi, Irene; Qorbani, Ehsan; Apoloner, Maria-Theresia; Bokelmann, Götz; AlpArray-EASI Working Group</p> <p>2016-04-01</p> <p>The Eastern Alpine Seismic Investigation (EASI) was a complementary experiment to the AlpArray project. EASI was composed of 55 broadband seismic stations deployed in a winding swath of 540 km length along longitude 13.350 E from the Czech-German border to the Adriatic Sea. Average north-south inter-station distance was 10 km, the distance of each station to either side of the central line was 6 km. Such a dense linear network allows for surface wave dispersion measurements by both deterministic and ambient noise sources along the same paths. During the experiment (July 2014 - August 2015), three earthquakes ML = 2.6, 2.9 and 4.2 occurred in Austria and Northern Italy only several kilometers off the swath. We measure Rayleigh and Love wave <span class="hlt">group</span> <span class="hlt">velocities</span> between the source and a single station for the recorded earthquakes, as well as phase <span class="hlt">velocities</span> between selected pairs of stations using the standard two-station method. We also calculate cross-correlations of ambient noise between selected pairs of stations and we determine the corresponding <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion curves. We propose a comparison of phase <span class="hlt">velocities</span> between two stations measured from earthquakes with <span class="hlt">group</span> <span class="hlt">velocities</span> obtained from cross-correlations for the same station pairs. We also compare <span class="hlt">group</span> <span class="hlt">velocities</span> measured at single station using earthquakes, which occurred along the swath, with <span class="hlt">group</span> <span class="hlt">velocities</span> measured from cross-correlations. That way we analyze <span class="hlt">velocities</span> of both deterministic and ambient noise reconstructed surface waves propagating along the same path. We invert the resulting dispersion curves for 1D shear wave <span class="hlt">velocity</span> profiles with depth and we compile a quasi-2D <span class="hlt">velocity</span> model along the EASI swath.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhyB..452...92A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhyB..452...92A"><span id="translatedtitle">Dynamical diffusion and renormalization <span class="hlt">group</span> equation for the Fermi <span class="hlt">velocity</span> in doped graphene</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ardenghi, J. S.; Bechthold, P.; Jasen, P.; Gonzalez, E.; Juan, A.</p> <p>2014-11-01</p> <p>The aim of this work is to study the electron transport in graphene with impurities by introducing a generalization of linear response theory for linear dispersion relations and spinor wave functions. Current response and density response functions are derived and computed in the Boltzmann limit showing that in the former case a minimum conductivity appears in the no-disorder limit. In turn, from the generalization of both functions, an exact relation can be obtained that relates both. Combining this result with the relation given by the continuity equation it is possible to obtain general functional behavior of the diffusion pole. Finally, a dynamical diffusion is computed in the quasistatic limit using the definition of relaxation function. A lower cutoff must be introduced to regularize infrared divergences which allow us to obtain a full renormalization <span class="hlt">group</span> equation for the Fermi <span class="hlt">velocity</span>, which is solved up to order O(ℏ2).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014ApPhL.105b1605M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014ApPhL.105b1605M"><span id="translatedtitle">Non contact probing of interfacial stiffnesses between two plates by zero-<span class="hlt">group</span> <span class="hlt">velocity</span> Lamb modes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mezil, Sylvain; Laurent, Jérôme; Royer, Daniel; Prada, Claire</p> <p>2014-07-01</p> <p>A non contact technique using zero-<span class="hlt">group</span> <span class="hlt">velocity</span> (ZGV) Lamb modes is developed to probe the bonding between two solid plates coupled by a thin layer. The layer thickness is assumed to be negligible compared with the plate thickness and the acoustic wavelength. The coupling layer is modeled by a normal and a tangential spring to take into account the normal and shear interfacial stresses. Theoretical ZGV frequencies are determined for a symmetrical bi-layer structure and the effect of the interfacial stiffnesses on the cut-off and ZGV frequencies are evaluated. Experiments are conducted with two glass plates bonded by a drop of water, oil, or salol, leading to a few micrometer thick layer. An evaluation of normal and shear stiffnesses is obtained using ZGV resonances locally excited and detected with laser ultrasonic techniques.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhyU...55.1239L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhyU...55.1239L"><span id="translatedtitle">Angular beam width of a slit-diffracted wave with noncollinear <span class="hlt">group</span> and phase <span class="hlt">velocities</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lock, Edwin H.</p> <p>2012-12-01</p> <p>Taking magnetostatic surface wave diffraction as an example, this paper theoretically investigates the 2D diffraction pattern arising in the far-field region of a ferrite slab in the case of a plane wave with noncollinear <span class="hlt">group</span> and phase <span class="hlt">velocities</span> incident on a wide, arbitrarily oriented slit in an opaque screen. A universal analytical formula for the angular width of a diffracted beam is derived, which is valid for magnetostatic and other types of waves in anisotropic media and structures (including metamaterials) in 2D geometries. It is shown that the angular width of a diffracted beam in an anisotropic medium can not only take values greater or less than \\lambda _0/D (where \\lambda _0 is the incident wavelength, and D is the slit width), but can also be zero under certain 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_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" 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_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUSMSM32A..06S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUSMSM32A..06S"><span id="translatedtitle">Fast Reconnection Rates Based on <span class="hlt">Group</span> <span class="hlt">Velocity</span> Cones: Whistler Regime and Pair Plasmas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Singh, N.</p> <p>2009-05-01</p> <p>Based on the <span class="hlt">group</span> <span class="hlt">velocity</span> vector of the whistler mode, we predict the range of whistler-regime reconnection rate depending on the half width (w) of the current sheet (CS. During the reconnection process electromagnetic perturbations (EMPs) are generated in the localized diffusion region (DR, which acts like an antenna and radiates whistler waves for certain range of CS widths. The reconnection structure (exhaust) is approximately the radiation pattern of the DR antenna and it is determined by the <span class="hlt">group</span> <span class="hlt">velocity</span> directions. Since the whistler waves originate from the electromagnetic perturbations (EMPs) localized in the DR, we calculate R over a range of the discrete values of the perpendicular wave number (k'') contained in the Fourier spectrum of the EMPs. We have used such calculations to determine the reconnection rates <R> averaged over the wave number spectrum of a Gaussian shaped EMP as a function of the CS width. We find that <R> has a fairly constant value at <R> ˜ 0.23 for CS widths in the range 0.4 < w/di ˜ 1 and for w < 0.3di it decreases with decreasing w and it attains a value <R> ˜ 0.06 in an extremely thin CS with w ˜ 0.05di, where di is the ion skin depth. We compare the values of <R> and R with those found from simulations and experiments, and find them in good agreement. We also report the properties of the whistler waves radiated from the DR into the exhaust region. We also demonstrate that our theoretical method developed for whistler regime reconnection could be easily adopted to predict fast reconnection rates in pair plasmas, which support inertial Alfven waves.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26473520','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26473520"><span id="translatedtitle">Swimming Training Assessment: The Critical <span class="hlt">Velocity</span> and the 400-m Test for Age-<span class="hlt">Group</span> Swimmers.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Zacca, Rodrigo; Fernandes, Ricardo Jorge P; Pyne, David B; Castro, Flávio Antônio de S</p> <p>2016-05-01</p> <p>Zacca, R, Fernandes, RJP, Pyne, DB, and Castro, FAdS. Swimming training assessment: the critical <span class="hlt">velocity</span> and the 400-m test for age-<span class="hlt">group</span> swimmers. J Strength Cond Res 30(5): 1365-1372, 2016-To verify the metabolic responses of oxygen consumption (V[Combining Dot Above]O2), heart rate (HR), blood lactate concentrations [La], and rate of perceived exertion (RPE) when swimming at an intensity corresponding to the critical <span class="hlt">velocity</span> (CV) assessed by a 4-parameter model (CV4par), and to check the reliability when using only a single 400-m maximal front crawl bout (T400) for CV4par assessment in age-<span class="hlt">group</span> swimmers. Ten age-<span class="hlt">group</span> swimmers (14-16 years old) performed 50-, 100-, 200-, 400- (T400), 800-, and 1,500-m maximal front crawl bouts to calculate CV4par. V[Combining Dot Above]O2, HR, [La], and RPE were measured immediately after bouts. Swimmers then performed 3 × 10-minute front crawl (45 seconds rest) at CV4par. V[Combining Dot Above]O2, HR, [La], and RPE were measured after 10 minutes of rest (Rest), warm-up (Pre), each 10-minute repetition, and at the end of the test (Post). CV4par was 1.33 ± 0.08 m·s. V[Combining Dot Above]O2, HR, [La], and RPE were similar between first 10-minute and Post time points in the 3 × 10-minute protocol. CV4par was equivalent to 92 ± 2% of the mean swimming speed of T400 (v400) for these swimmers. CV4par calculated through a single T400 (92%v400) showed excellent agreement (r = 0.30; 95% CI: -0.04 to 0.05 m·s, p = 0.39), low coefficient of variation (2%), and root mean square error of 0.02 ± 0.01 m·s when plotted against CV4par assessed through a 4-parameter model. These results generated the equation CV4par = 0.92 × v400. A single T400 can be used reliably to estimate the CV4par typically derived with 6 efforts in age-<span class="hlt">group</span> swimmers. PMID:26473520</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27410366','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27410366"><span id="translatedtitle">Design of chirped distributed Bragg reflector for octave-spanning frequency <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion compensation in terahertz quantum cascade laser.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Xu, Chao; Ban, Dayan</p> <p>2016-06-13</p> <p>The strategies and approaches of designing chirped Distributed Bragg Reflector for <span class="hlt">group</span> <span class="hlt">velocity</span> compensation in metal-metal waveguide terahertz quantum cascade laser are investigated through 1D and 3D models. The results show the depth of the corrugation periods plays an important role on achieving broad-band <span class="hlt">group</span> <span class="hlt">velocity</span> compensation in terahertz range. However, the deep corrugation also brings distortion to the <span class="hlt">group</span> delay behavior. A two-section chirped DBR is proposed to provide smoother <span class="hlt">group</span> delay compensation while still maintain the broad frequency range (octave) operation within 2 THz to 4 THz. PMID:27410366</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.S42B..02B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.S42B..02B"><span id="translatedtitle">Three-Dimensional Seismic <span class="hlt">Velocity</span> Structure in a High-Injection Region in The Northwest Geysers, California, from Standard and Double-Difference Seismic <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boyle, K. L.; Jarpe, S.</p> <p>2011-12-01</p> <p>The Northwest Geysers contains some of the highest-volume injection and production wells in the Geysers geothermal field. These wells coincide spatially with dense clusters of microseismicity with exception of a sub-region central to several injectors which has shown lower rates of seismicity over the past 10 years. This low-seismicity region is underlain by a cluster of deep seismicity extending up to 4.2km below sea level (b.s.l.). The low-seismicity region has been imaged to 610 m resolution using passive-source 3D seismic <span class="hlt">tomography</span> and co-location of hypocenters. The results indicate a low-<span class="hlt">velocity</span> (2.9 km/s) anomaly that extends from the surface to approximately 1.5km b.s.l. in both P- and S- <span class="hlt">velocity</span> models. It lies just above and to the Northwest of the low-seismicity region. The high-injection/production region is bounded on the southeast by higher <span class="hlt">velocities</span> (range 4.0 km/s to 5.3 km/s), although it is dominated by <span class="hlt">velocities</span> in the 3.8 km/s range. The low-<span class="hlt">velocity</span> feature persists over our 5-year study period from 2005 to 2010, but appears to diminish spatially in 2010. Mean <span class="hlt">velocity</span> values vary nominally from year to year, as do the extent of high and low <span class="hlt">velocity</span> regions, but it is yet unknown whether this effect is temporal, an artifact of topography, or related to differences in data quality during different monitoring periods. The the low-<span class="hlt">velocity</span> feature is being confirmed and re-imaged using double-difference <span class="hlt">tomography</span> with a node-spacing of 150 m, and the feature's evolution over time will be correlated with injection and production rates in the surrounding area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21301438','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21301438"><span id="translatedtitle">ARE NEWLY DISCOVERED H I HIGH-<span class="hlt">VELOCITY</span> CLOUDS MINIHALOS IN THE LOCAL <span class="hlt">GROUP</span>?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Giovanelli, Riccardo; Haynes, Martha P.; Adams, Elizabeth A. K.; Kent, Brian R. E-mail: haynes@astro.cornell.edu E-mail: bkent@nrao.edu</p> <p>2010-01-01</p> <p>A set of H I sources extracted from the north Galactic polar region by the ongoing ALFALFA survey has properties that are consistent with the interpretation that they are associated with isolated minihalos in the outskirts of the Local <span class="hlt">Group</span> (LG). Unlike objects detected by previous surveys, such as the compact high-<span class="hlt">velocity</span> clouds of Braun and Burton, the H I clouds found by ALFALFA do not violate any structural requirements or halo scaling laws of the {lambda}CDM structure paradigm, nor would they have been detected by extant H I surveys of nearby galaxy <span class="hlt">groups</span> other than the LG. At a distance of d Mpc, their H I masses range between 5 x 10{sup 4} d {sup 2} and 10{sup 6} d {sup 2} M {sub sun} and their H I radii between <0.4d and 1.6d kpc. If they are parts of gravitationally bound halos, the total masses would be on the order of 10{sup 8}-10{sup 9} M {sub sun}, their baryonic content would be significantly smaller than the cosmic fraction of 0.16 and present in a ionized gas phase of mass well exceeding that of the neutral phase. This study does not however prove that the minihalo interpretation is unique. Among possible alternatives would be that the clouds are shreds of the Leading Arm of the Magellanic Stream.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016SPIE.9719E..0OB&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016SPIE.9719E..0OB&link_type=ABSTRACT"><span id="translatedtitle">Label-free in-vivo measurement of lymph flow <span class="hlt">velocity</span> using Doppler optical coherence <span class="hlt">tomography</span> (Conference Presentation)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blatter, Cedric; Meijer, Eelco F. J.; Nam, Ahhyun S.; Jones, Dennis; Padera, Timothy P.; Vakoc, Benjamin J.</p> <p>2016-03-01</p> <p>Alterations in lymphatic network function contribute to the lymphedema development, cancer progression and impairment in regional immune function. However, there are limited tools available to directly measure lymphatic vessel function and transport in vivo. Existing approaches such as fluorescence recovery after photo-bleaching (FRAP) require injection of exogenous labels which intrinsically alter the physiology of the local lymphatic network. A label-free approach to imaging lymph flow in vivo would provide direct and unaltered measurements of lymphatic vessel transport and could catalyze research in lymphatic biology. Here, we demonstrate and validate the use of Doppler optical coherence <span class="hlt">tomography</span> (DOCT) to measure lymph flow in vivo at speeds as low as 50µm/s. Compared to blood, lymph is relatively acellular (under normal conditions), but contains similar soluble components to blood plasma. We demonstrate that the small but detectable scattering signal from lymph can be used to extract fluid <span class="hlt">velocity</span> using a dedicated algorithm optimized for Doppler analysis in low signal-to-noise settings (0 to 6 dB typical). We demonstrate the accuracy of this technique by comparing DOCT to FRAP measurements, using an intralipid lymph proxy in microfluidic devices and in vivo in the mouse ear. Finally, we demonstrate the label free measurement of lymph speed in the hind-limb of mice with a temporal resolution of 0.25s that agree well with prior literature reports. We anticipate that DOCT can become a powerful new tool in preclinical lymphatic biology research—including the relationship between lymphatic function and metastasis formation—with the potential to later expand also to clinical settings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016OptCo.371..196I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016OptCo.371..196I"><span id="translatedtitle">Dependence of light pulse propagation on its temporal width: Transition from <span class="hlt">group</span> <span class="hlt">velocity</span> to c-propagation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ignesti, Emilio; Tommasi, Federico; Fini, Lorenzo; Cavalieri, Stefano</p> <p>2016-07-01</p> <p>We show how the <span class="hlt">velocity</span> of an optical pulse propagating through a dispersive medium depends on the pulse duration. A transition from the <span class="hlt">group</span> <span class="hlt">velocity</span> for long pulses to the in-vacuum <span class="hlt">velocity</span> for short pulses is shown both in experimental results and in theoretical predictions. The temporal duration of the experimental pulses are 150 ps and 3.5 ns. A description of the pulse propagation in terms of the time "center of mass" of the energy flow allows an intuitive overview of the results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4882591','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4882591"><span id="translatedtitle">Subluminal <span class="hlt">group</span> <span class="hlt">velocity</span> and dispersion of Laguerre Gauss beams in free space</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Bareza, Nestor D.; Hermosa, Nathaniel</p> <p>2016-01-01</p> <p>That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s <span class="hlt">group</span> <span class="hlt">velocity</span> vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space. PMID:27231195</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015OptCo.353...96M&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015OptCo.353...96M&link_type=ABSTRACT"><span id="translatedtitle">Generation of tunable ultrafast ultraviolet third harmonic by collinear compensation of <span class="hlt">group-velocity</span> mismatch</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Meng, Xianghao; Liu, Huagang; Huang, Jianhong; Wu, Hongchun; Deng, Jing; Dai, Shutao; Weng, Wen; Lin, Wenxiong</p> <p>2015-10-01</p> <p>We demonstrate a high efficient frequency tripling configuration of Ti: sapphire amplifier system for wavelength-tunable ultrafast ultraviolet laser generation. A new nonlinear crystal Ba1-xB2-y-zO4SixAlyGaz and a type-II phase-matched β-BaB2O4 crystal are employed for the second and the third harmonic generation, respectively. Significant improvement in conversion efficiency of frequency tripling is achieved by using a 65°-cut, 3-mm-long β-BaB2O4 crystal as the collinear <span class="hlt">group</span> <span class="hlt">velocity</span> compensation plate. Tunable ultraviolet pulse within the wavelength range from 256.7 to 276.7 nm have been produced, with a maximum average power of 212 mW, corresponding to a conversion efficiency of 8.48% for the third harmonic generation with 2.5 W fundamental power. The maximum pulse energy of the third harmonic is up to 0.21 mJ and it is estimated that the peak power is above 1 GW at 266.7 nm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008PhRvE..78a1117D&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008PhRvE..78a1117D&link_type=ABSTRACT"><span id="translatedtitle">Transport in a Lévy ratchet: <span class="hlt">Group</span> <span class="hlt">velocity</span> and distribution spread</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dybiec, B.; Gudowska-Nowak, E.; Sokolov, I. M.</p> <p>2008-07-01</p> <p>We consider the motion of an overdamped particle in a periodic potential lacking spatial symmetry under the influence of symmetric, white, Lévy noise, being a minimal setup for a “Lévy ratchet.” Due to the nonthermal character of the Lévy noise, the particle exhibits a motion with a preferred direction even in the absence of whatever additional time-dependent forces. The examination of the Lévy ratchet has to be based on the characteristics of directionality which are different from typically used measures such as mean current and the dispersion of particle positions, since these become inappropriate when the moments of the noise diverge. To overcome this problem, we discuss robust measures of directionality of transport such as the position of the median of the particle displacement distribution characterizing the <span class="hlt">group</span> <span class="hlt">velocity</span> and the interquantile distance giving the measure of the distribution width. Moreover, we analyze the behavior of splitting probabilities for leaving an interval of a given length, unveiling qualitative differences between the noises with Lévy indices below and above unity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27231195','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27231195"><span id="translatedtitle">Subluminal <span class="hlt">group</span> <span class="hlt">velocity</span> and dispersion of Laguerre Gauss beams in free space.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bareza, Nestor D; Hermosa, Nathaniel</p> <p>2016-01-01</p> <p>That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein's postulate in special relativity. This has been a basic assumption in light's various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light's <span class="hlt">group</span> <span class="hlt">velocity</span> vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam's divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space. PMID:27231195</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016NatSR...626842B&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016NatSR...626842B&link_type=ABSTRACT"><span id="translatedtitle">Subluminal <span class="hlt">group</span> <span class="hlt">velocity</span> and dispersion of Laguerre Gauss beams in free space</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bareza, Nestor D.; Hermosa, Nathaniel</p> <p>2016-05-01</p> <p>That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s <span class="hlt">group</span> <span class="hlt">velocity</span> vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.S41A2350J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.S41A2350J"><span id="translatedtitle">Constraints on Crustal Shear Wave <span class="hlt">Velocity</span> Structure beneath Central Tibet from 3-D Multi-scale Finite-frequency Rayleigh Wave Travel-time <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jheng, Y.; Hung, S.; Zhou, Y.; Chang, Y.</p> <p>2012-12-01</p> <p>Surface wave travel-time <span class="hlt">tomography</span> has been widely used as a powerful strategy to image shear wave <span class="hlt">velocity</span> structure of the Earth's crust and upper mantle, providing comparable information other than body wave <span class="hlt">tomography</span>. Traditionally, lateral variations of dispersive phase <span class="hlt">velocities</span> are first obtained at multiple frequencies and then used to invert for shear wave <span class="hlt">velocity</span> with 1-D depth-dependent sensitivity kernels. However, this approach runs short on considering the directional- and depth-dependence of scattering while surface wave propagating through laterally heterogeneous Earth. To refrain from these shortcomings, we here provide a fully 3-D finite-frequency method based on the Born scattering theory formulated with surface wave mode summation, and apply it to regional fundamental Rayleigh wave travel-time <span class="hlt">tomography</span> in central Tibet. Our data were collected from Project Hi-CLIMB, which deployed an N-S trending linear array of over 100 broadband seismic stations with a large aperture of 800 km and very dense spacing of ~3-8 km across the Lhasa and Qiangtang terranes during 2004-2005. We follow a standard procedure of ambient noise cross correlation to extract empirical Green's functions of fundamental Rayleigh waves at 10-33 s between station pairs. A multi-taper method is employed to measure the phase differences as a function of period between observed and synthetic Rayleigh waves as well as the corresponding sensitivity kernels for the measured phase delays to 3-D shear wave <span class="hlt">velocity</span> perturbations in a spherically-symmetric model suitable for central Tibet. A wavelet-based, multi-scale parameterization is invoked in the tomographic inversion to deal with the intrinsically multi-scale nature of unevenly distributed data and resolve the structure with data-adaptive spectral and spatial resolutions. The preliminary result shows that to the north of the Banggong-Nujiang suture (BNS), the crustal shear wave <span class="hlt">velocity</span> beneath the Qiangtang terrane is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/24247747','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/24247747"><span id="translatedtitle">In vitro and in vivo three-dimensional <span class="hlt">velocity</span> vector measurement by three-beam spectral-domain Doppler optical coherence <span class="hlt">tomography</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Trasischker, Wolfgang; Werkmeister, René M; Zotter, Stefan; Baumann, Bernhard; Torzicky, Teresa; Pircher, Michael; Hitzenberger, Christoph K</p> <p>2013-11-01</p> <p>We developed a three-beam Doppler optical coherence <span class="hlt">tomography</span> (OCT) system that enables measurement of the <span class="hlt">velocity</span> vector of moving particles in three-dimensions (3-D). The spatial orientation as well as the magnitude of motion can be determined without prior knowledge of the geometry of motion. The system combines three spectral-domain OCT interferometers whose sample beams are focused at the sample by a common focusing lens at three different angles. This provides three spatially independent <span class="hlt">velocity</span> components simultaneously from which the <span class="hlt">velocity</span> vector can be reconstructed. We demonstrate the system in a simple test object (rotating disc), a flow phantom, and for blood flow measurements in the retina of a healthy human subject. Measurements of blood flow at a venous bifurcation achieve a good agreement between in- and outflow and demonstrate the reliability of the method. PMID:24247747</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25836695','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25836695"><span id="translatedtitle">Patient <span class="hlt">grouping</span> for dose surveys and establishment of diagnostic reference levels in paediatric computed <span class="hlt">tomography</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vassileva, J; Rehani, M</p> <p>2015-07-01</p> <p>There has been confusion in literature on whether paediatric patients should be <span class="hlt">grouped</span> according to age, weight or other parameters when dealing with dose surveys. The present work aims to suggest a pragmatic approach to achieve reasonable accuracy for performing patient dose surveys in countries with limited resources. The analysis is based on a subset of data collected within the IAEA survey of paediatric computed <span class="hlt">tomography</span> (CT) doses, involving 82 CT facilities from 32 countries in Asia, Europe, Africa and Latin America. Data for 6115 patients were collected, in 34.5 % of which data for weight were available. The present study suggests that using four age <span class="hlt">groups</span>, <1, >1-5, >5-10 and >10-15 y, is realistic and pragmatic for dose surveys in less resourced countries and for the establishment of DRLs. To ensure relevant accuracy of results, data for >30 patients in a particular age <span class="hlt">group</span> should be collected if patient weight is not known. If a smaller sample is used, patient weight should be recorded and the median weight in the sample should be within 5-10 % from the median weight of the sample for which the DRLs were established. Comparison of results from different surveys should always be performed with caution, taking into consideration the way of <span class="hlt">grouping</span> of paediatric patients. Dose results can be corrected for differences in patient weight/age <span class="hlt">group</span>. PMID:25836695</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T11C2452Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T11C2452Y"><span id="translatedtitle">Upper-mantle <span class="hlt">velocity</span> models beneath the east Qingling orogenic belt from finite-frequency <span class="hlt">tomography</span> of a portable seismic array</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Y.; Chen, Y. J.; An, M.; Feng, Y.; Liang, X.; Dong, S.</p> <p>2013-12-01</p> <p>The east Qinling orogenic belt is located between the North China Craton and the South China Block, and is also at the northeastern boundary of Tibetan Plateau. A temporal seismic array of over 110 portable seismic stations was deployed by Peking University and the Chinese Academy of Geological Sciences (CAGS) from July 2011 to October 2013 to study the complex tectonics of this region. We used earthquake data recorded at 65 stations from this array between July 2011 and October 2012 to image the seismic <span class="hlt">velocity</span> variations of the region using finite-frequency <span class="hlt">tomography</span> method. The travel times used in the inversion contain 10876 P-waves and 5945 S-waves at 3 different frequencies. Preliminary results show that <span class="hlt">velocity</span> structures of P-waves and S-waves are quite similar. The upper mantle <span class="hlt">velocities</span> under the east Qinling orogenic belt are higher in general in the east than that in the west at depth around 80 km. A higher <span class="hlt">velocity</span> anomaly is observed under the southern Ordos plateau from 40 km to 360km deep and a low <span class="hlt">velocity</span> anomaly is seen beneath the Taihang uplift from the depth of 40km to the depth of 200km. These <span class="hlt">velocity</span> anomalies in the lithosphere and the upper mantle will be interpreted with the geologic observations and tectonic process of the region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT.......331A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT.......331A"><span id="translatedtitle">Multi-Scale Imaging of the Fault Zone <span class="hlt">Velocity</span> Structure: Double-difference <span class="hlt">Tomography</span>, Inversion of Fault Zone Headwaves, and Fault Zone Sensitivity Kernels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Allam, Amir A.</p> <p></p> <p>In spite of the close relationship between fault zone structure and earthquake mechanics, fault zone structure at seismogenic depths remains poorly understood. How does localization of the primary slip zone vary with depth? Is there a signature of broad persistent damage zones at seismogenic depths? How does fault zone structure merge with regional structure? To answer these questions, we utilize multiple imaging techniques. We apply high-resolution double-difference <span class="hlt">tomography</span> to the San Jacinto fault zone, invert for <span class="hlt">velocity</span> structure along the Hayward fault using fault zone head waves, and use analytical results for idealized geometries to validate sensitivity kernels of fault zone phases for use in adjoint tomographic inversions. Double-difference <span class="hlt">tomography</span> uses the arrival times of P and S waves to invert simultaneously for compressional <span class="hlt">velocity</span>, shear wave <span class="hlt">velocity</span>, and source location in three dimensions. We present results in the southern California plate-boundary area, with a focus on the San Jacinto fault zone, which incorporate arrival times of 247,472 P- and 105,448 S-wave picks for 5493 earthquakes recorded at 139 stations. Starting with a layered 1D model, and continuing in later iterations with various updated initial models, we invert the data for Vp and Vs in a 270 km long, 105 km wide and 35 km deep volume using a spatially variable grid with higher density around the San Jacinto. Our final <span class="hlt">velocity</span> results show zones of low-<span class="hlt">velocity</span> and high Vp/Vs ratios associated with various fault strands and sedimentary basins, along with clear <span class="hlt">velocity</span> contrasts across the San Jacinto. While both features are limited to the upper 10km, the low <span class="hlt">velocity</span> zones generally have higher amplitude and broader distribution in geometrically complex areas, while the <span class="hlt">velocity</span> contrasts are more pronounced for Vp than Vs. Along the Hayward fault in the San Francisco Bay region, we identify fault zone head waves at eight stations on the northeastern side of the fault</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1175404','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1175404"><span id="translatedtitle">Dielectric waveguide with transverse index variation that support a zero <span class="hlt">group</span> <span class="hlt">velocity</span> mode at a non-zero longitudinal wavevector</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Ibanescu, Mihai; Joannopoious, John D.; Fink, Yoel; Johnson, Steven G.; Fan, Shanhui</p> <p>2005-06-21</p> <p>Optical components including a laser based on a dielectric waveguide extending along a waveguide axis and having a refractive index cross-section perpendicular to the waveguide axis, the refractive index cross-section supporting an electromagnetic mode having a zero <span class="hlt">group</span> <span class="hlt">velocity</span> for a non-zero wavevector along the waveguide axis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAESc.115..273C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAESc.115..273C"><span id="translatedtitle">Crustal S-wave structure beneath Eastern Black Sea Region revealed by Rayleigh-wave <span class="hlt">group</span> <span class="hlt">velocities</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Çınar, Hakan; Alkan, Hamdi</p> <p>2016-01-01</p> <p>In this study, the crustal S-wave structure beneath the Eastern Black Sea Region (including the Eastern Black Sea Basin (EBSB) and Eastern Pontides (EP)) has been revealed using inversion of single-station, fundamental-mode Rayleigh-wave <span class="hlt">group</span> <span class="hlt">velocities</span> in the period range of 4-40 seconds. We used digital broadband recordings of 13 regional earthquakes that recently occurred in the easternmost EBSB recorded at stations of the Kandilli Observatory and Earthquake Research Institute (KOERI). The average <span class="hlt">group-velocity</span>-dispersion curves were generated from 26 paths for the EBSB, and 16 paths for the EP, and they were inverted to determine the average 1-D shear-wave structure of the region. We have created a pseudo-section, roughly depicting the crustal structure of the region based on the <span class="hlt">group</span> <span class="hlt">velocity</span> inversion results of all station-earthquake paths. The thickness of the sedimentary layer reaches 12 km in the center of EBSB (Vs = 2.5-3.1 km/s) and decreases 4 km in the EP. There is a thin sedimentary layer in the EP (Vs = 2.7 km/s). A consolidated thin crust that exists in the EBSB possesses a high seismic <span class="hlt">velocity</span> (Vs = 3.8 km/s). While a thin (∼26 km) and transitional crust exists beneath the EBSB, a thick (about 42 km) continental crust exists beneath the EP where the Conrad is clearly seen at about a 24 km depth. Thick continental crust in the EP region is clearly distinguished from a gradational <span class="hlt">velocity</span> change (Vs = 3.4-3.8 km/s). The Moho dips approximately southwards, and the Vs <span class="hlt">velocity</span> (4.25-4.15 km/s) beneath the Moho discontinuity decreases from the EBSB to the EP in the N-S direction. This may be an indication of a southward subduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26548467','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26548467"><span id="translatedtitle">[(18)F]-<span class="hlt">Group</span> 13 fluoride derivatives as radiotracers for positron emission <span class="hlt">tomography</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chansaenpak, Kantapat; Vabre, Boris; Gabbaï, François P</p> <p>2016-02-21</p> <p>The field of (18)F chemistry is rapidly expanding because of the use of this radionuclide in radiotracers for positron emission <span class="hlt">tomography</span> (PET). Until recently, most [(18)F]-radiotracers were generated by the direct attachment of (18)F to a carbon in the organic backbone of the radiotracer. The past decade has witnessed the emergence of a new strategy based on the formation of an (18)F-<span class="hlt">group</span> 13 element bond. This approach, which is rooted in the field of fluoride anion complexation/coordination chemistry, has led to the development of a remarkable family of boron, aluminium and gallium [(18)F]-fluoride anion complexing agents which can be conjugated with peptides and small molecules to generate disease specific PET radiotracers. This review is dedicated to the chemistry of these <span class="hlt">group</span> 13 [(18)F]-fluorides anion complexing agents and their use in PET. Some of the key fluoride-binding motifs covered in this review include the trifluoroborate unit bound to neutral or cationic electron deficient backbones, the BF2 unit of BODIPY dyes, and AlF or GaF3 units coordinated to multidentate Lewis basic ligands. In addition to describing how these moieties can be converted into their [(18)F]-analogs, this review also dicusses their incorporation into bioconjugates for application in PET. PMID:26548467</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_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" 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_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016IJTP...55.2942Q&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016IJTP...55.2942Q&link_type=ABSTRACT"><span id="translatedtitle">Phase Control of <span class="hlt">Group</span> <span class="hlt">Velocity</span> in a Doppler-Broadened Λ-Type Three-Level System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Qiu, Tian-Hui; Xie, Min</p> <p>2016-06-01</p> <p>We theoretically investigate the phase control role on the <span class="hlt">group</span> <span class="hlt">velocity</span> of a weak probe field in a Doppler-broadened Λ-type three-level atomic system with the spontaneously generated coherence effect enhanced by an incoherence pump. We find that the absorption-dispersion of the probe field behaves phase and Doppler broadening-dependent phenomena, and testify that the quite large <span class="hlt">group</span> index can be realized. The <span class="hlt">group</span> <span class="hlt">velocity</span> of the probe field can be switched from subluminal to superluminal or vice versa by modulating the relative phase of the two applied light fields. In contrast to the counterpropagating setting, the copropagating case is more suitable for the purpose considered in this paper due to the effectiveness of Doppler-free.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012ApJ...753....8V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012ApJ...753....8V"><span id="translatedtitle">The M31 <span class="hlt">Velocity</span> Vector. II. Radial Orbit toward the Milky Way and Implied Local <span class="hlt">Group</span> Mass</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van der Marel, Roeland P.; Fardal, Mark; Besla, Gurtina; Beaton, Rachael L.; Sohn, Sangmo Tony; Anderson, Jay; Brown, Tom; Guhathakurta, Puragra</p> <p>2012-07-01</p> <p>We determine the <span class="hlt">velocity</span> vector of M31 with respect to the Milky Way and use this to constrain the mass of the Local <span class="hlt">Group</span>, based on Hubble Space Telescope proper-motion measurements of three fields presented in Paper I. We construct N-body models for M31 to correct the measurements for the contributions from stellar motions internal to M31. This yields an unbiased estimate for the M31 center-of-mass motion. We also estimate the center-of-mass motion independently, using the kinematics of satellite galaxies of M31 and the Local <span class="hlt">Group</span>, following previous work but with an expanded satellite sample. All estimates are mutually consistent, and imply a weighted average M31 heliocentric transverse <span class="hlt">velocity</span> of (vW , vN ) = (- 125.2 ± 30.8, -73.8 ± 28.4) km s-1. We correct for the reflex motion of the Sun using the most recent insights into the solar motion within the Milky Way, which imply a larger azimuthal <span class="hlt">velocity</span> than previously believed. This implies a radial <span class="hlt">velocity</span> of M31 with respect to the Milky Way of V rad, M31 = -109.3 ± 4.4 km s-1, and a tangential <span class="hlt">velocity</span> of V tan, M31 = 17.0 km s-1, with a 1σ confidence region of V tan, M31 <= 34.3 km s-1. Hence, the <span class="hlt">velocity</span> vector of M31 is statistically consistent with a radial (head-on collision) orbit toward the Milky Way. We revise prior estimates for the Local <span class="hlt">Group</span> timing mass, including corrections for cosmic bias and scatter, and obtain M LG ≡ M MW, vir + M M31, vir = (4.93 ± 1.63) × 1012 M ⊙. Summing known estimates for the individual masses of M31 and the Milky Way obtained from other dynamical methods yields smaller uncertainties. Bayesian combination of the different estimates demonstrates that the timing argument has too much (cosmic) scatter to help much in reducing uncertainties on the Local <span class="hlt">Group</span> mass, but its inclusion does tend to increase other estimates by ~10%. We derive a final estimate for the Local <span class="hlt">Group</span> mass from literature and new considerations of M LG = (3.17 ± 0.57) × 1012 M </p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22036965','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22036965"><span id="translatedtitle">THE M31 <span class="hlt">VELOCITY</span> VECTOR. II. RADIAL ORBIT TOWARD THE MILKY WAY AND IMPLIED LOCAL <span class="hlt">GROUP</span> MASS</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Van der Marel, Roeland P.; Sohn, Sangmo Tony; Anderson, Jay; Brown, Tom; Fardal, Mark; Besla, Gurtina; Beaton, Rachael L.; Guhathakurta, Puragra</p> <p>2012-07-01</p> <p>We determine the <span class="hlt">velocity</span> vector of M31 with respect to the Milky Way and use this to constrain the mass of the Local <span class="hlt">Group</span>, based on Hubble Space Telescope proper-motion measurements of three fields presented in Paper I. We construct N-body models for M31 to correct the measurements for the contributions from stellar motions internal to M31. This yields an unbiased estimate for the M31 center-of-mass motion. We also estimate the center-of-mass motion independently, using the kinematics of satellite galaxies of M31 and the Local <span class="hlt">Group</span>, following previous work but with an expanded satellite sample. All estimates are mutually consistent, and imply a weighted average M31 heliocentric transverse <span class="hlt">velocity</span> of (v{sub W} , v{sub N} ) = (- 125.2 {+-} 30.8, -73.8 {+-} 28.4) km s{sup -1}. We correct for the reflex motion of the Sun using the most recent insights into the solar motion within the Milky Way, which imply a larger azimuthal <span class="hlt">velocity</span> than previously believed. This implies a radial <span class="hlt">velocity</span> of M31 with respect to the Milky Way of V{sub rad,M31} = -109.3 {+-} 4.4 km s{sup -1}, and a tangential <span class="hlt">velocity</span> of V{sub tan,M31} = 17.0 km s{sup -1}, with a 1{sigma} confidence region of V{sub tan,M31} {<=} 34.3 km s{sup -1}. Hence, the <span class="hlt">velocity</span> vector of M31 is statistically consistent with a radial (head-on collision) orbit toward the Milky Way. We revise prior estimates for the Local <span class="hlt">Group</span> timing mass, including corrections for cosmic bias and scatter, and obtain M{sub LG} {identical_to} M{sub MW,vir} + M{sub M31,vir} = (4.93 {+-} 1.63) Multiplication-Sign 10{sup 12} M{sub Sun }. Summing known estimates for the individual masses of M31 and the Milky Way obtained from other dynamical methods yields smaller uncertainties. Bayesian combination of the different estimates demonstrates that the timing argument has too much (cosmic) scatter to help much in reducing uncertainties on the Local <span class="hlt">Group</span> mass, but its inclusion does tend to increase other estimates by {approx}10%. We</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoJI.194..961O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoJI.194..961O"><span id="translatedtitle">The uppermost mantle shear wave <span class="hlt">velocity</span> structure of eastern Africa from Rayleigh wave <span class="hlt">tomography</span>: constraints on rift evolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Donnell, J. P.; Adams, A.; Nyblade, A. A.; Mulibo, G. D.; Tugume, F.</p> <p>2013-08-01</p> <p>An expanded model of the 3-D shear wave <span class="hlt">velocity</span> 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 <span class="hlt">velocities</span> 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 <span class="hlt">velocity</span> model of the uppermost mantle. New features in the model include (1) a low-<span class="hlt">velocity</span> region in western Zambia, (2) a high-<span class="hlt">velocity</span> region in eastern Zambia, (3) a low-<span class="hlt">velocity</span> region in eastern Tanzania and (4) low-<span class="hlt">velocity</span> 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-<span class="hlt">velocity</span> 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 <span class="hlt">velocity</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Ap.....59..246E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Ap.....59..246E"><span id="translatedtitle">Kinematics and <span class="hlt">Velocity</span> Ellipsoid Parameters of Stellar <span class="hlt">Groups</span> and Open Star Clusters: II Cool Stars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elsanhoury, W. H.</p> <p>2016-06-01</p> <p>Based on the galactic space <span class="hlt">velocity</span> components (U, V, W) and with aid of the vector and matrix analyses, we computed the <span class="hlt">velocity</span> ellipsoid parameters for 790 late-type stars from CoRoT (Convection, Rotation and Transits) observations and 290 L dwarf stars. We ran the calculations for spectral types F, G, and K for late-type stars and L0, L1, L2, and L3 for L dwarf stars. We found that the ratio of the middle to the major axis in the galaxy ranged from 0.35 to 0.73. The vertex deviation from the galactic center was very small for the samples under investigation, which agrees well with earlier calculations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GGG....16..681B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GGG....16..681B"><span id="translatedtitle">P and S <span class="hlt">velocity</span> <span class="hlt">tomography</span> of the Mariana subduction system from a combined land-sea seismic deployment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barklage, Mitchell; Wiens, Douglas A.; Conder, James A.; Pozgay, Sara; Shiobara, Hajime; Sugioka, Hiroko</p> <p>2015-03-01</p> <p>Seismic imaging provides an opportunity to constrain mantle wedge processes associated with subduction, volatile transport, arc volcanism, and back-arc spreading. We investigate the seismic <span class="hlt">velocity</span> structure of the upper mantle across the Central Mariana subduction system using data from the 2003-2004 Mariana Subduction Factory Imaging Experiment, an 11 month deployment consisting of 20 broadband seismic stations installed on islands and 58 semibroadband ocean bottom seismographs. We determine the three-dimensional VP and VP/VS structure using over 25,000 local and over 2000 teleseismic arrival times. The mantle wedge is characterized by slow <span class="hlt">velocity</span> and high VP/VS beneath the fore arc, an inclined zone of slow <span class="hlt">velocity</span> underlying the volcanic front, and a strong region of slow <span class="hlt">velocity</span> beneath the back-arc spreading center. The slow <span class="hlt">velocities</span> are strongest at depths of 20-30 km in the fore arc, 60-70 km beneath the volcanic arc, and 20-30 km beneath the spreading center. The fore-arc slow <span class="hlt">velocity</span> anomalies occur beneath Big Blue seamount and are interpreted as resulting from mantle serpentinization. The depths of the maximum <span class="hlt">velocity</span> anomalies beneath the arc and back arc are nearly identical to previous estimates of the final equilibrium depths of mantle melts from thermobarometry, strongly indicating that the low-<span class="hlt">velocity</span> zones delineate regions of melt production in the mantle. The arc and back-arc melt production regions are well separated at shallow depths, but may be connected at depths greater than 80 km.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T41D2929B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T41D2929B"><span id="translatedtitle">Lithospheric Shear <span class="hlt">Velocity</span> Structure of South Island, New Zealand from Rayleigh Wave <span class="hlt">Tomography</span> of Amphibious Array Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ball, J. S.; Sheehan, A. F.; Stachnik, J. C.; Lin, F. C.; Collins, J. A.</p> <p>2015-12-01</p> <p>We present the first 3D shear <span class="hlt">velocity</span> model extending well offshore of New Zealand's South Island, imaging the lithosphere beneath 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 wave dispersion measurements. We augment an array of 29 ocean-bottom instruments deployed off the South Island's east and west coasts in 2009-2010 with 28 New Zealand land-based seismometers. The ocean-bottom seismometers and 4 of the land seismometers were part of the Marine Observations of Anisotropy Near Aotearoa (MOANA) experiment, and the remaining land seismometers are from New Zealand's permanent GeoNet array. Major features of our shear wave <span class="hlt">velocity</span> (Vs) model include a low-<span class="hlt">velocity</span> (Vs<4.3km/s) body extending to at least 75km depth beneath the Banks and Otago peninsulas, a high-<span class="hlt">velocity</span> (Vs~4.7km/s) upper mantle anomaly underlying the Southern Alps to a depth of 100km, and discontinuous lithospheric <span class="hlt">velocity</span> structure between eastern and western Challenger Plateau. Using the 4.5km/s contour as a proxy for the lithosphere-asthenosphere boundary, our model suggests that the lithospheric thickness of Challenger Plateau is substantially greater than that of Campbell Plateau. The high-<span class="hlt">velocity</span> anomaly we resolve beneath the central South Island exhibits strong spatial correlation with subcrustal earthquake hypocenters along the Alpine Fault (Boese et al., 2013). The ~400km-long low <span class="hlt">velocity</span> zone we image beneath eastern South Island underlies Cenozoic volcanics and mantle-derived helium observations (Hoke et al., 2000) on the surface. The NE-trending low-<span class="hlt">velocity</span> zone dividing Challenger Plateau in our model underlies a prominent magnetic discontinuity (Sutherland et al., 1999). The latter feature has been interpreted to represent a pre-Cretaceous crustal boundary, which our results suggest may involve the entire mantle lithosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015JGRB..120.1708A&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015JGRB..120.1708A&link_type=ABSTRACT"><span id="translatedtitle">Lithospheric instability and the source of the Cameroon Volcanic Line: Evidence from Rayleigh wave phase <span class="hlt">velocity</span> <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adams, Aubreya N.; Wiens, Douglas A.; Nyblade, Andrew A.; Euler, Garrett G.; Shore, Patrick J.; Tibi, Rigobert</p> <p>2015-03-01</p> <p>The Cameroon Volcanic Line (CVL) is a 1800 km long volcanic chain, extending SW-NE from the Gulf of Guinea into Central Africa, that lacks the typical age progression exhibited by hot spot-related volcanic tracks. This study investigates the upper mantle seismic structure beneath the CVL and surrounding regions to constrain the origin of volcanic lines that are poorly described by the classic plume model. Rayleigh wave phase <span class="hlt">velocities</span> are measured at periods from 20 to 182 s following the two-plane wave methodology, using data from the Cameroon Seismic Experiment, which consists of 32 broadband stations deployed between 2005 and 2007. These phase <span class="hlt">velocities</span> are then inverted to build a model of shear wave <span class="hlt">velocity</span> structure in the upper mantle beneath the CVL. Results show that phase <span class="hlt">velocities</span> beneath the CVL are reduced at all periods, with average <span class="hlt">velocities</span> beneath the CVL deviating more than -2% from the regional average and +4% beneath the Congo Craton. This distinction is observed for all periods but is less pronounced for the longest periods measured. Inversion for shear wave <span class="hlt">velocity</span> structure indicates a tabular low <span class="hlt">velocity</span> anomaly directly beneath the CVL at depths of 50 to at least 200 km and a sharp vertical boundary with faster <span class="hlt">velocities</span> beneath the Congo Craton. These observations demonstrate widespread infiltration or erosion of the continental lithosphere beneath the CVL, most likely caused by mantle upwelling associated with edge-flow convection driven by the Congo Craton or by lithospheric instabilities that develop due to the nearby edge of the African continent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005PhRvE..72a6604M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005PhRvE..72a6604M"><span id="translatedtitle">Causal determination of acoustic <span class="hlt">group</span> <span class="hlt">velocity</span> and frequency derivative of attenuation with finite-bandwidth Kramers-Kronig relations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mobley, Joel; Waters, Kendall R.; Miller, James G.</p> <p>2005-07-01</p> <p>Kramers-Kronig (KK) analyses of experimental data are complicated by the extrapolation problem, that is, how the unexamined spectral bands impact KK calculations. This work demonstrates the causal linkages in resonant-type data provided by acoustic KK relations for the <span class="hlt">group</span> <span class="hlt">velocity</span> (cg) and the derivative of the attenuation coefficient (α') (components of the derivative of the acoustic complex wave number) without extrapolation or unmeasured parameters. These relations provide stricter tests of causal consistency relative to previously established KK relations for the phase <span class="hlt">velocity</span> (cp) and attenuation coefficient (α) (components of the undifferentiated acoustic wave number) due to their shape invariance with respect to subtraction constants. For both the <span class="hlt">group</span> <span class="hlt">velocity</span> and attenuation derivative, three forms of the relations are derived. These relations are equivalent for bandwidths covering the entire infinite spectrum, but differ when restricted to bandlimited spectra. Using experimental data from suspensions of elastic spheres in saline, the accuracy of finite-bandwidth KK predictions for cg and α' is demonstrated. Of the multiple methods, the most accurate were found to be those whose integrals were expressed only in terms of the phase <span class="hlt">velocity</span> and attenuation coefficient themselves, requiring no differentiated quantities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006GGG.....7.7005W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006GGG.....7.7005W"><span id="translatedtitle">P and S <span class="hlt">velocity</span> structure of the upper mantle beneath the Transantarctic Mountains, East Antarctic craton, and Ross Sea from travel time <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Watson, Timothy; Nyblade, Andrew; Wiens, Douglas A.; Anandakrishnan, Sridhar; Benoit, Margaret; Shore, Patrick J.; Voigt, Donald; Vandecar, John</p> <p>2006-07-01</p> <p>P and S wave travel times from teleseismic earthquakes recorded by the Transantarctic Mountains Seismic Experiment (TAMSEIS) have been used to tomographically image upper mantle structure beneath portions of the Transantarctic Mountains (TAM), the East Antarctic (EA) craton, and the West Antarctic rift system (WARS) in the vicinity of Ross Island, Antarctica. The TAM form a major tectonic boundary that divides the stable EA craton and the tectonically active WARS. Relative arrival times were determined using a multichannel cross-correlation technique on teleseismic P and S phases from earthquakes with mb ≥ 5.5. 3934 P waves were used from 322 events, and 2244 S waves were used from 168 events. Relative travel time residuals were inverted for upper mantle structure using VanDecar's method. The P wave <span class="hlt">tomography</span> model reveals a low-<span class="hlt">velocity</span> anomaly in the upper mantle of approximately δVp = -1 to -1.5% in the vicinity of Ross Island extending laterally 50 to 100 km beneath the TAM from the coast, placing the contact between regions of fast and slow <span class="hlt">velocities</span> well inland from the coast beneath the TAM. The magnitude of the low-<span class="hlt">velocity</span> anomaly in the P wave model appears to diminish beneath the TAM to the north and south of Ross Island. The depth extent of the low-<span class="hlt">velocity</span> anomaly is not well constrained, but it probably is confined to depths above ˜200 km. The S wave model, within resolution limits, is consistent with the P wave model. The low-<span class="hlt">velocity</span> anomaly within the upper mantle can be attributed to a 200-300 K thermal anomaly, consistent with estimates obtained from seismic attenuation measurements. The presence of a thermal anomaly of this magnitude supports models invoking a thermal buoyancy contribution to flexurally driven TAM uplift, at least in the Ross Island region of the TAM. Because the magnitude of the anomaly to the north and south of Ross Island may diminish, the thermal contribution to the uplift of the TAM could be variable along strike</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1810068S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1810068S"><span id="translatedtitle">Crustal high-<span class="hlt">velocity</span> anomaly at the East European Craton margin in SE Poland (TESZ) modelled by 3-D seismic <span class="hlt">tomography</span> of refracted and reflected arrivals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Środa, Piotr; Dec, Monika</p> <p>2016-04-01</p> <p>The area of Trans-European Suture Zone in SE Poland represents a contact of major tectonic units of different consolidation age - from the Precambrian East European Craton, through Palaeozoic West European Platform to Cenozoic Carpathian orogen. The region was built by several phases of crustal accretion, which resulted in a complex collage of tectonic blocks. In 2000, this region was studied by several seismic wide-angle profiles of CELEBRATION 2000 experiment, providing a dense coverage of seismic data in SE Poland and allowing for detailed investigations of the crustal structure and properties in this area. Beneath the marginal part of the EEC, the 2-D modelling of in-line data form several CELEBRATION profiles revealed a prominent high P-wave <span class="hlt">velocity</span> anomaly in the upper crust, with Vp of 6.7-7.1 km/s, starting at 10-16 km depth (e.g., Środa et al., 2006). Anomalously high <span class="hlt">velocities</span> are observed in the area located approximately beneath Lublin trough, to the NE of Teisseyre-Tornquist Zone. Based on 3-D <span class="hlt">tomography</span> of first arrivals of in- and off-line CELEBRATION 2000 recordings (Malinowski et al., 2008), elevated <span class="hlt">velocities</span> are also reported in the same area and seem to continue to the SW, off the craton margin. Gravimetric modelling also revealed anomalously high density in the same region at similar depths. High seismic <span class="hlt">velocities</span> and densities are interpreted as indicative for a pronounced mafic intrusion, possibly related to extensional processes at the EEC margin. Previous 3-D models of the high-<span class="hlt">velocity</span> intrusion were based on first arrivals (crustal refractions) only. In this study, also off-line reflections (not modelled up to now) are used, in order to enlarge the data set and to better constrain the geometry and properties of the <span class="hlt">velocity</span> anomaly. A code for 3-D joint tomographic inversion of refracted and reflected arrivals, with model parametrization allowing for <span class="hlt">velocity</span> discontinuities was used (Rawlinson, 2007). With this approach, besides the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2939199','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2939199"><span id="translatedtitle">Fundus Autofluorescence and Optical Coherence <span class="hlt">Tomography</span> of Congenital <span class="hlt">Grouped</span> Albinotic Spots</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kim, David Y.; Hwang, John C.; Moore, Anthony T.; Bird, Alan C.; Tsang, Stephen H.</p> <p>2010-01-01</p> <p>Purpose To describe fundus autofluorescence (FAF) and optical coherence <span class="hlt">tomography</span> (OCT) in a series of patients with congenital <span class="hlt">grouped</span> albinotic spots (CGAS). Methods Three eyes of three patients with CGAS were evaluated with FAF and OCT imaging to evaluate the nature of the albinotic spots. Results In all three eyes with CGAS, FAF imaging revealed autofluorescent spots corresponding to the albinotic spots seen on stereo biomicroscopy. One eye also had additional spots detected on FAF imaging that were not visible on stereo biomicroscopy or color fundus photographs. FAF imaging of the spots demonstrated decreased general autofluorescence as well as decreased peripheral autofluorescence surrounding central areas of retained or increased autofluorescence. OCT revealed a disruption in signal from the hyper-reflective layer corresponding to the photoreceptor inner and outer segment junction as well as increased signal backscattering from the choroid in the area of the spots. Fluorescein angiography (FA) demonstrated early and stable hyperfluorescence of the spots without leakage. Conclusion In this case series, FAF demonstrated decreased autofluorescence of the spots consistent with focal RPE atrophy or abnormal material blocking normal autofluorescence as well as areas of increased autofluorescence suggesting RPE dysfunction. OCT and FA findings suggest photoreceptor and RPE layer abnormalities. FAF and OCT are useful noninvasive diagnostic adjuncts that can aid in the diagnosis of GCAS, help determine extent of disease, and contribute to our understanding of its pathophysiology. PMID:20539258</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S51B4461P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S51B4461P"><span id="translatedtitle">Shear <span class="hlt">velocity</span> model for the westernmost Mediterranean from ambient noise and ballistic finite-frequency Rayleigh wave <span class="hlt">tomography</span></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.; Villasenor, A.; Thurner, S.; Levander, A.; Gallart, J.; Harnafi, M.</p> <p>2014-12-01</p> <p>The westernmost Mediterranean comprises the Iberian Peninsula and Morocco, separated by the Alboran Sea and the Algerian Basin. From north to south this region consists of the Pyrenees, resulting from Iberia-Eurasia collision; the Iberian Massif, which has been undeformed since the end of the Paleozoic; the Central System and Iberian Chain, regions with intracontinental Oligocene-Miocene deformation; the Gibraltar Arc (Betics, Rif and Alboran terranes), resulting from post-Oligocene subduction roll-back; and the Atlas Mountains. We analyzed data from recent broad-band array deployments and permanent stations in the area (IberArray and Siberia arrays, the PICASSO array, the University of Munster array, and the Spanish, Portuguese and Moroccan National Networks) to characterize its lithospheric structure. The combined array of 350 stations has an average interstation spacing of ~60 km. We calculated the Rayleigh waves phase <span class="hlt">velocities</span> from ambient noise (periods 4 to 40 s) and teleseismic events (periods 20 to 167 s). We inverted the phase <span class="hlt">velocities</span> to obtain a shear <span class="hlt">velocity</span> model for the lithosphere to ~200 km depth. Our results correlate well with the surface expression of the main structural units with higher crustal <span class="hlt">velocity</span> for the Iberian Massif than for the Alpine Iberia and Atlas Mountains. The Gibraltar Arc has lower crustal shear <span class="hlt">velocities</span> than the regional average at all crustal depths. It also shows an arc shaped anomaly with high upper mantle <span class="hlt">velocities</span> (>4.6 km/s) at shallow depths (<65 km) interpreted as the subducting Alboran slab. The hanging slab is depressing the crust of the Gibraltar arc to ~55 km depth, as seen in receiver function data and active source seismic profiles. Low upper mantle <span class="hlt">velocities</span> (<4.2 km/s) are observed beneath the Atlas, the northeastern end of the Betic Mountains and the Late Cenozoic volcanic fields in Iberia and Morocco, indicative of high temperatures at relatively shallow depths, and suggesting that the lithosphere</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22113687','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22113687"><span id="translatedtitle">Light bullets and supercontinuum spectrum during femtosecond pulse filamentation under conditions of anomalous <span class="hlt">group-velocity</span> dispersion in fused silicalicati</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chekalin, Sergei V; Kompanets, V O; Smetanina, E O; Kandidov, V P</p> <p>2013-04-30</p> <p>We report the results of theoretical and experimental research on spectrum transformation and spatiotemporal distribution of the femtosecond laser radiation intensity during filamentation in fused silica. The formation of light bullets with a high power density is first observed in a femtosecond laser pulse in the anomalous <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion regime at a wavelength of 1800 nm. The minimum duration of the light bullet is about two oscillation cycles of the light field. (extreme light fields and their applications)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JAP...117h4305M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JAP...117h4305M"><span id="translatedtitle">Reduction of heat capacity and phonon <span class="hlt">group</span> <span class="hlt">velocity</span> in silicon nanowires</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marchbanks, Christopher; Wu, Zhigang</p> <p>2015-02-01</p> <p>We report on ab initio linear-response calculations of lattice vibrations in narrow silicon nanowires on the order of 1 nm along the [001], [011], and [111] growth directions. The confinement and nanowire structure substantially alter phonon distributions, resulting in an 15% to 23% reduction in heat capacity and an averaged decrease of 31% in acoustic <span class="hlt">velocities</span> compared with bulk silicon. Based on these, we estimate an improvement up to 4 fold on thermoelectric performance due solely to the modified lattice vibrations in narrow silicon nanowires over bulk silicon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EP%26S...68..132P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EP%26S...68..132P&link_type=ABSTRACT"><span id="translatedtitle">Investigating P- and S-wave <span class="hlt">velocity</span> structure beneath the Marmara region (Turkey) and the surrounding area from local earthquake <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Polat, Gulten; Özel, Nurcan Meral; Koulakov, Ivan</p> <p>2016-07-01</p> <p>We investigated the crustal structure beneath the Marmara region and the surrounding area in the western part of the North Anatolian fault zone. These areas have high seismicity and are of critical significance to earthquake hazards. The study was based on travel-time <span class="hlt">tomography</span> using local moderate and micro-earthquakes occurring in the study area recorded by the Multi-Disciplinary Earthquake Research in High Risk Regions of Turkey project and Kandilli Observatory and Earthquake Research Institute. We selected 2131 earthquakes and a total of 92,858 arrival times, consisting of 50,044 P-wave and 42,814 S-wave arrival times. We present detailed crustal structure down to 50 km depth beneath the Marmara region for P- and S-wave <span class="hlt">velocities</span> using the LOTOS code based on iterative inversion. We used the distributions of the resulting seismic parameters ( Vp, Vs) to pick out significant geodynamical features. The high-<span class="hlt">velocity</span> anomalies correlate well with fracturing segments of the North Anatolian fault. High seismicity is mostly concentrated in these segments. In particular, low <span class="hlt">velocities</span> were observed beneath the central Marmara Sea at 5 km depth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.9513M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.9513M"><span id="translatedtitle">Full waveform seismic modelling of Chalk <span class="hlt">Group</span> rocks from the Danish North Sea - implications for <span class="hlt">velocity</span> analysis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Montazeri, Mahboubeh; Moreau, Julien; Uldall, Anette; Nielsen, Lars</p> <p>2015-04-01</p> <p>This study aims at understanding seismic wave propagation in the fine-layered Chalk <span class="hlt">Group</span>, which constitutes the main reservoir for oil and gas production in the Danish North Sea. The starting point of our analysis is the Nana-1XP exploration well, which shows strong seismic contrasts inside the Chalk <span class="hlt">Group</span>. For the purposes of seismic waveform modelling, we here assume a one-dimensional model with homogeneous and isotropic layers designed to capture the main fluctuations in petrophysical properties observed in the well logs. The model is representative of the stratigraphic sequences of the area and it illustrates highly contrasting properties of the Chalk <span class="hlt">Group</span>. Finite-difference (FD) full wave technique, both acoustic and elastic equations are applied to the model. <span class="hlt">Velocity</span> analysis of seismic data is a crucial step for stacking, multiple suppression, migration, and depth conversion of the seismic record. Semblance analysis of the synthetic seismic records shows strong amplitude peaks outside the expected range for the time interval representing the Chalk <span class="hlt">Group</span>, especially at the base. The various synthetic results illustrate the occurrence and the impact of different types of waves including multiples, converted waves and refracted waves. The interference of these different wave types with the primary reflections can explain the strong anomalous amplitudes in the semblance plot. In particular, the effect of strongly contrasting thin beds plays an important role in the generation of the high anomalous amplitude values. If these anomalous amplitudes are used to pick the <span class="hlt">velocities</span>, it would impede proper stacking of the data and may result in sub-optimal migration and depth conversion. Consequently this may lead to erroneous or sub-optimal seismic images of the Chalk <span class="hlt">Group</span> and the underlying layers. Our results highlight the importance of detailed <span class="hlt">velocity</span> analysis and proper picking of <span class="hlt">velocity</span> functions in the Chalk <span class="hlt">Group</span> intervals. We show that application of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016GeoJI.205..715W&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016GeoJI.205..715W&link_type=ABSTRACT"><span id="translatedtitle">Correction of phase <span class="hlt">velocity</span> bias caused by strong directional noise sources in high-frequency ambient noise <span class="hlt">tomography</span>: a case study in Karamay, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Kai; Luo, Yinhe; Yang, Yingjie</p> <p>2016-05-01</p> <p>We collect two months of ambient noise data recorded by 35 broad-band seismic stations in a 9 × 11 km area (1-3 km station interval) near Karamay, China, and do cross-correlation of noise data between all station pairs. Array beamforming analysis of the ambient noise data shows that ambient noise sources are unevenly distributed and the most energetic ambient noise mainly comes from azimuths of 40°-70°. As a consequence of the strong directional noise sources, surface wave components of the cross-correlations at 1-5 Hz show clearly azimuthal dependence, and direct dispersion measurements from cross-correlations are strongly biased by the dominant noise energy. This bias renders that the dispersion measurements from cross-correlations do not accurately reflect the interstation <span class="hlt">velocities</span> of surface waves propagating directly from one station to the other, that is, the cross-correlation functions do not retrieve empirical Green's functions accurately. To correct the bias caused by unevenly distributed noise sources, we adopt an iterative inversion procedure. The iterative inversion procedure, based on plane-wave modeling, includes three steps: (1) surface wave <span class="hlt">tomography</span>, (2) estimation of ambient noise energy and biases and (3) phase <span class="hlt">velocities</span> correction. First, we use synthesized data to test the efficiency and stability of the iterative procedure for both homogeneous and heterogeneous media. The testing results show that: (1) the amplitudes of phase <span class="hlt">velocity</span> bias caused by directional noise sources are significant, reaching ˜2 and ˜10 per cent for homogeneous and heterogeneous media, respectively; (2) phase <span class="hlt">velocity</span> bias can be corrected by the iterative inversion procedure and the convergence of inversion depends on the starting phase <span class="hlt">velocity</span> map and the complexity of the media. By applying the iterative approach to the real data in Karamay, we further show that phase <span class="hlt">velocity</span> maps converge after 10 iterations and the phase <span class="hlt">velocity</span> maps obtained using</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GeoJI.183.1061T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GeoJI.183.1061T"><span id="translatedtitle">Structure of the crust beneath Cameroon, West Africa, from the joint inversion of Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocities</span> and receiver functions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tokam, Alain-Pierre K.; Tabod, Charles T.; Nyblade, Andrew A.; Julià, Jordi; Wiens, Douglas A.; Pasyanos, Michael E.</p> <p>2010-11-01</p> <p>The Cameroon Volcanic Line (CVL) consists of a linear chain of Tertiary to Recent, generally alkaline, volcanoes that do not exhibit an age progression. Here we study crustal structure beneath the CVL and adjacent regions in Cameroon using 1-D shear wave <span class="hlt">velocity</span> models obtained from the joint inversion of Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocities</span> and P-receiver functions for 32 broad-band seismic stations deployed between 2005 January and 2007 February. We find that (1) crustal thickness (35-39km) and <span class="hlt">velocity</span> structure is similar beneath the CVL and the Pan African Oubanguides Belt to the south of the CVL, (2) crust is thicker (43-48km) under the northern margin of the Congo Craton and is characterized by shear wave <span class="hlt">velocities</span> >=4.0kms-1 in its lower part and (3) crust is thinner (26-31km) under the Garoua rift and the coastal plain. In addition, a fast <span class="hlt">velocity</span> layer (Vs of 3.6-3.8kms-1) in the upper crust is found beneath many of the seismic stations. Crustal structure beneath the CVL and the Oubanguides Belt is very similar to Pan African crustal structure in the Mozambique Belt, and therefore it appears not to have been modified significantly by the magmatic activity associated with the CVL. The crust beneath the coastal plain was probably thinned during the opening of the southern Atlantic Ocean, while the crust beneath the Garoua rift was likely thinned during the formation of the Benue Trough in the early Cretaceous. We suggest that the thickened crust and the thick mafic lower crustal layer beneath the northern margin of the Congo Craton may be relict features from a continent-continent collision along this margin during the formation of Gondwana.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012JSMME...6..678C&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012JSMME...6..678C&link_type=ABSTRACT"><span id="translatedtitle">Damage Evaluation of Unsaturated Polyester Resin Using Zero-<span class="hlt">Group</span> <span class="hlt">Velocity</span> Lamb Waves in Non-Contact Matter</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cho, Hideo; Oka, Daichi; Matsuo, Takuma</p> <p></p> <p>In this study we attempted to evaluate the degree of degradation of an unsaturated polyester resin when it was degraded by exposing it to hot water at 90°C, using the frequency of zero-<span class="hlt">group-velocity</span> (ZGV) Lamb waves. The energy of ZGV Lamb waves does not propagate while the phase <span class="hlt">velocity</span> remains finite. We generated ZGV Lamb waves with a Q-switched YAG laser and detected them with a focused air-coupled transducer at the same area of an irradiation point of the YAG laser in con-contact matter. A change in measured frequencies of ZGV Lamb waves decreased with increase of exposed period to hot water and are corresponding to the change in Young's modulus and thickness of the plate near the exposed surface</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_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" 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_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMMR13A2255G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMMR13A2255G"><span id="translatedtitle">3D Anisotropic <span class="hlt">Velocity</span> <span class="hlt">Tomography</span> of a Water Saturated Rock under True-Triaxial Stress in the Laboratory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ghofrani Tabari, M.; Goodfellow, S. D.; Nasseri, M. B.; Young, R.</p> <p>2013-12-01</p> <p>A cubic specimen of water saturated Fontainebleau Sandstone is tested in the laboratory under true-triaxial loading where three different principal stresses are applied under drained conditions. Due to the loading arrangement, closure and opening of the pre-existing cracks in the rock, as well as creation and growth of the aligned cracks cause elliptical anisotropy and distributed heterogeneities. A Geophysical Imaging Cell equipped with an Acoustic Emission monitoring system is employed to image <span class="hlt">velocity</span> structure of the sample during the experiment through repeated transducer to transducer non-destructive ultrasonic surveys. Apparent P-wave <span class="hlt">velocities</span> along the rock body are calculated in different directions and shown in stereonet plots which demonstrate an overall anisotropy of the sample. The apparent <span class="hlt">velocities</span> in the main three orthogonal cubic directions are used as raw data for building a mean spatial distribution model of anisotropy ratios. This approach is based on the concept of semi-principal axes in an elliptical anisotropic model and appointing two ratios between the three orthogonal <span class="hlt">velocities</span> in each of the cubic grid cells. The spatial distribution model of anisotropy ratios are used to calculate the anisotropic ray-path segment matrix elements (Gij). These contain segment lengths of the ith ray in the jth cell in three dimensions where, length of each ray in each cell is computed for one principal direction based on the dip and strike of the ray and these lengths differ from the ones in an isotropic G Matrix. 3D strain of the squeezed rock and the consequent geometrical deformation is also included in the ray-path segment matrix. A Singular Value Decomposition (SVD) method is used for inversion from the data space of apparent <span class="hlt">velocities</span> to the model space of P-wave propagation <span class="hlt">velocities</span> in the three principal directions. Finally, spatial variation and temporal evolution of induced damages in the rock, representing uniformly distributed or</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..1818160P&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..1818160P&link_type=ABSTRACT"><span id="translatedtitle">Lithospheric structure of the westernmost Mediterranean inferred from finite frequency Rayleigh wave <span class="hlt">tomography</span> S-<span class="hlt">velocity</span> model.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Palomeras, Imma; Villasenor, Antonio; Thurner, Sally; Levander, Alan; Gallart, Josep; Harnafi, Mimoun</p> <p>2016-04-01</p> <p>The Iberian Peninsula and Morocco, separated by the Alboran Sea and the Algerian Basin, constitute the westernmost Mediterranean. From north to south this region consists of the Pyrenees, the result of interaction between the Iberian and Eurasian plates; the Iberian Massif, a region that has been undeformed since the end of the Paleozoic; the Central System and Iberian Chain, regions with intracontinental Oligocene-Miocene deformation; the Gibraltar Arc (Betics, Rif and Alboran terranes) and the Atlas Mountains, resulting from post-Oligocene subduction roll-back and Eurasian-Nubian plate convergence. In this study we analyze data from recent broad-band array deployments and permanent stations on the Iberian Peninsula and in Morocco (Spanish IberArray and Siberia arrays, the US PICASSO array, the University of Munster array, and the Spanish, Portuguese, and Moroccan National Networks) to characterize its lithospheric structure. The combined array of 350 stations has an average interstation spacing of ~60 km, comparable to USArray. We have calculated the Rayleigh waves phase <span class="hlt">velocities</span> from ambient noise for short periods (4 s to 40 s) and teleseismic events for longer periods (20 s to 167 s). We inverted the phase <span class="hlt">velocities</span> to obtain a shear <span class="hlt">velocity</span> model for the lithosphere to ~200 km depth. The model shows differences in the crust for the different areas, where the highest shear <span class="hlt">velocities</span> are mapped in the Iberian Massif crust. The crustal thickness is highly variable ranging from ~25 km beneath the eastern Betics to ~55km beneath the Gibraltar Strait, Internal Betics and Internal Rif. Beneath this region a unique arc shaped anomaly with high upper mantle <span class="hlt">velocities</span> (>4.6 km/s) at shallow depths (<65 km) is observed. We interpret this body as the subducting Alboran slab that is depressing the crust of the western Gibraltar arc to ~55 km depth. Low upper mantle <span class="hlt">velocities</span> (<4.2 km/s) are observed beneath the Atlas, the northeastern end of the Betic Mountains and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70170508','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70170508"><span id="translatedtitle">Three-dimensional seismic <span class="hlt">velocity</span> structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic <span class="hlt">tomography</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>Lin, Guoqing; Shearer, Peter M.; Matoza, Robin S.; Okubo, Paul G.; Amelung, Falk</p> <p>2016-01-01</p> <p>We present a new three-dimensional seismic <span class="hlt">velocity</span> model of the crustal and upper mantle structure for Mauna Loa and Kilauea volcanoes in Hawaii. Our model is derived from the first-arrival times of the compressional and shear waves from about 53,000 events on and near the Island of Hawaii between 1992 and 2009 recorded by the Hawaiian Volcano Observatory stations. The Vp model generally agrees with previous studies, showing high-<span class="hlt">velocity</span> anomalies near the calderas and rift zones and low-<span class="hlt">velocity</span> anomalies in the fault systems. The most significant difference from previous models is in Vp/Vs structure. The high-Vp and high-Vp/Vs anomalies below Mauna Loa caldera are interpreted as mafic magmatic cumulates. The observed low-Vp and high-Vp/Vs bodies in the Kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments. The high-Vp and moderate- to low-Vp/Vs anomalies beneath Kilauea caldera can be explained by a combination of different mafic compositions, likely to be olivine-rich gabbro and dunite. The systematically low-Vp and low-Vp/Vs bodies in the southeast flank of Kilauea may be caused by the presence of volatiles. Another difference between this study and previous ones is the improved Vp model resolution in deeper layers, owing to the inclusion of events with large epicentral distances. The new <span class="hlt">velocity</span> model is used to relocate the seismicity of Mauna Loa and Kilauea for improved absolute locations and ultimately to develop a high-precision earthquake catalog using waveform cross-correlation data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRB..119.4377L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRB..119.4377L"><span id="translatedtitle">Three-dimensional seismic <span class="hlt">velocity</span> structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lin, Guoqing; Shearer, Peter M.; Matoza, Robin S.; Okubo, Paul G.; Amelung, Falk</p> <p>2014-05-01</p> <p>We present a new three-dimensional seismic <span class="hlt">velocity</span> model of the crustal and upper mantle structure for Mauna Loa and Kilauea volcanoes in Hawaii. Our model is derived from the first-arrival times of the compressional and shear waves from about 53,000 events on and near the Island of Hawaii between 1992 and 2009 recorded by the Hawaiian Volcano Observatory stations. The Vp model generally agrees with previous studies, showing high-<span class="hlt">velocity</span> anomalies near the calderas and rift zones and low-<span class="hlt">velocity</span> anomalies in the fault systems. The most significant difference from previous models is in Vp/Vs structure. The high-Vp and high-Vp/Vs anomalies below Mauna Loa caldera are interpreted as mafic magmatic cumulates. The observed low-Vp and high-Vp/Vs bodies in the Kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments. The high-Vp and moderate- to low-Vp/Vs anomalies beneath Kilauea caldera can be explained by a combination of different mafic compositions, likely to be olivine-rich gabbro and dunite. The systematically low-Vp and low-Vp/Vs bodies in the southeast flank of Kilauea may be caused by the presence of volatiles. Another difference between this study and previous ones is the improved Vp model resolution in deeper layers, owing to the inclusion of events with large epicentral distances. The new <span class="hlt">velocity</span> model is used to relocate the seismicity of Mauna Loa and Kilauea for improved absolute locations and ultimately to develop a high-precision earthquake catalog using waveform cross-correlation data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA....11836J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA....11836J"><span id="translatedtitle">SERAPIS project - 3D imaging of the Campi Flegrei caldera (southern Italy) : high resolution P-wave <span class="hlt">velocity</span> <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Judenherc, S.; Zollo, A.; Auger, E.; Boschi, L.; Satriano, C.; Serapis Working Group</p> <p>2003-04-01</p> <p>In September 2001, the SERAPIS project was carried out as an extended active seismic survey in the gulfs of Naples and Pozzuoli. A dense array of 60 three-component on-land stations and 72 sea bottom seismographs (OBS) have been deployed to record more than 5000 air gun shots at a spacing of about 125~m. As a preliminary analysis, the first P-arrival times of a the small offset data in the central part of the region has been inverted using the codes of H.M. Benz. The linearized iterative inversion of 38000 arrival times provided a >80% variance reduction with a node spacing of 250m. At the first order, our model shows a 2-layer structure : low <span class="hlt">velocity</span> volcanic sediments (2.5-3.5km/s) lying on an inclined high <span class="hlt">velocity</span> limestone platform (>6km/s). The caldera itself is very well identified, the rim is characterized by a 500-1000m upward shift of the <span class="hlt">velocity</span> isolines. The whole dataset is expected to provide a wider image with the same resolution (250m). It includes the detailed shape of the refractor beneath the caldera as well as its irregularities out of the bay which have been observered in the seismic sections.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/17325457','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17325457"><span id="translatedtitle">Autopsy radiography: digital radiographs (DR) vs multidetector computed <span class="hlt">tomography</span> (MDCT) in high-<span class="hlt">velocity</span> gunshot-wound victims.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Harcke, H Theodore; Levy, Angela D; Abbott, Robert M; Mallak, Craig T; Getz, John M; Champion, Howard R; Pearse, Lisa</p> <p>2007-03-01</p> <p>This study compared full-body digital radiography (DR) with multidetector computed <span class="hlt">tomography</span> (MDCT) in the postmortem evaluation of gunshot wound (GSW) victims. Thirteen consecutive male GSW victims (mean age, 27 years) had full-body DR and MDCT prior to routine autopsy. DR successfully identified all metallic fragments, but MDCT was superior in its ability to precisely determine location because it provided 3-dimensional anatomic localization. In all cases, MDCT more accurately assessed organ injuries and wound tracks. Both DR and MDCT are limited in classifying multiple wounds and major vessel injury, but MDCT is generally superior to DR. MDCT shows significant advantages over DR in the forensic evaluation of GSW victims. This is particularly advantageous for the pathologist retrieving metallic fragments and for describing fracture detail accurately. Use of MDCT instead of radiographs will require medical examiners to become familiar with reading cross-sectional images. PMID:17325457</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19810002129','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19810002129"><span id="translatedtitle">First Scientific Working <span class="hlt">Group</span> Meeting of Airborne Doppler Lidar Wind <span class="hlt">Velocity</span> Measurement Program</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kaufman, J. W. (Editor)</p> <p>1980-01-01</p> <p>The purpose of the first scientific working <span class="hlt">group</span> meeting was fourfold: (1) to identify flight test options for engineering verification of the MSFC Doppler Lidar; (2) to identify flight test options for gathering data for scientific/technology applications; (3) to identify additional support equipment needed on the CV 990 aircraft for the flight tests; and (4) to identify postflight data processing and data sets requirements. The working <span class="hlt">group</span> identified approximately ten flight options for gathering data on atmospheric dynamics processes, including turbulence, valley breezes, and thunderstorm cloud anvil and cold air outflow dynamics. These test options will be used as a basis for planning the fiscal year 1981 tests of the Doppler Lidar system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/22344142','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/22344142"><span id="translatedtitle">Modulational instability in a silicon-on-insulator directional coupler: role of the coupling-induced <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ding, W; Staines, O K; Hobbs, G D; Gorbach, A V; de Nobriga, C; Wadsworth, W J; Knight, J C; Skryabin, D V; Strain, M J; Sorel, M; De La Rue, R M</p> <p>2012-02-15</p> <p>We report frequency conversion experiments in silicon-on-insulator (SOI) directional couplers. We demonstrate that the evanescent coupling between two subwavelength SOI waveguides is strongly dispersive and significantly modifies modulational instability (MI) spectra through the coupling induced <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion (GVD). As the separation between two 380-nm-wide silicon photonic wires decreases, the increasing dispersion of the coupling makes the GVD in the symmetric supermode more normal and suppresses the bandwidth of the MI gain observed for larger separations. PMID:22344142</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/19829441','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/19829441"><span id="translatedtitle">Temporal compression of cw diode-laser output into short pulses with cesium-vapor <span class="hlt">group-velocity</span> dispersion.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Choi, K; Menders, J; Ross, D; Korevaar, E</p> <p>1993-11-15</p> <p>Using a technique similar to chirped pulse compression, we have compressed the 50-mW cw output of a diode laser into pulses of greater than 500-mW peak power and less than 400-ps duration. By applying a small current modulation to the diode, we induced a small wavelength modulation in the vicinity of the 6s(1/2)-to-6p(3/2) cesium resonance transition at 852 nm. <span class="hlt">Group-velocity</span> dispersion on propagation through a cesium vapor cell then led to pulse compression. We developed a simple model to make predictions of output pulse shapes by using different modulation waveforms. PMID:19829441</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/17471707','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17471707"><span id="translatedtitle">Finite-bandwidth Kramers-Kronig relations for acoustic <span class="hlt">group</span> <span class="hlt">velocity</span> and attenuation derivative applied to encapsulated microbubble suspensions.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mobley, Joel</p> <p>2007-04-01</p> <p>Kramers-Kronig (KK) analyses of experimental data are complicated by the conflict between the inherently bandlimited data and the requirement of KK integrals for a complete infinite spectrum of input information. For data exhibiting localized extrema, KK relations can provide accurate transforms over finite bandwidths due to the local-weighting properties of the KK kernel. Recently, acoustic KK relations have been derived for the determination of the <span class="hlt">group</span> <span class="hlt">velocity</span> (cg) and the derivative of the attenuation coefficient (alpha') (components of the derivative of the acoustic complex wave number). These relations are applicable to bandlimited data exhibiting resonant features without extrapolation or unmeasured parameters. In contrast to twice-subtracted finite-bandwidth KK predictions for phase <span class="hlt">velocity</span> and attenuation coefficient (components of the undifferentiated wave number), these more recently derived relations for cg and alpha' provide stricter tests of causal consistency because the resulting shapes are invariant with respect to subtraction constants. The integrals in these relations can be formulated so that they only require the phase <span class="hlt">velocity</span> and attenuation coefficient data without differentiation. Using experimental data from suspensions of encapsulated microbubbles, the finite-bandwidth KK predictions for cg and alpha' are found to provide an accurate mapping of the primary wave number quantities onto their derivatives. PMID:17471707</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T23A1991A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T23A1991A"><span id="translatedtitle">3-D P-wave <span class="hlt">velocity</span> structure and seismicity in Central Costa Rica from Local Earthquake <span class="hlt">Tomography</span> using an amphibic network</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arroyo, I.; Husen, S.; Flueh, E.; Alvarado, G. E.</p> <p>2008-12-01</p> <p>The Central Pacific sector of the erosional margin in Costa Rica shows a high seismicity rate, coincident with the subduction of rough-relief ocean floor, and generates earthquakes up to Mw 7. Precise earthquake locations and detailed knowledge of the 3-D <span class="hlt">velocity</span> structure provide key insights into the dynamics of subduction zones. To this end, we performed a 3-D Local Earthquake <span class="hlt">Tomography</span> using P-wave traveltimes from 595 selected events recorded by a seismological network of off- and onshore stations, deployed for 6 months in the area. The results reflect the complexity associated to subduction of bathymetric highs and the transition from normal to thickened oceanic crust (Cocos Ridge). The slab is imaged as a high-<span class="hlt">velocity</span> anomaly with a band of low <span class="hlt">velocities</span> (LVB) on top enclosing the intraslab events deeper than ~30 km. Below the margin slope, the LVB is locally thickened by at least two seamounts. We observe an abrupt, eastward widening of the LVB, preceded by a low-<span class="hlt">velocity</span> anomaly under the continental shelf, which we interpret as a big seamount. The thickening coincides with an inverted basin at the inner forearc and a low-<span class="hlt">velocity</span> anomaly under it. The latter appears in a sector where blocks of inner forearc are uplifted, possibly by underplating of eroded material against the base of the crust. The anomaly promotes seismicity by high-friction with the upper plate, and could be linked to a Mw 6.4 earthquake in 2004. In the west part of the area, the interplate seismicity forms a cluster beneath the continental shelf. Its updip limit coincides with the 150° C isotherm and an increase in Vp along the plate boundary. This further supports a proposed model in which the seismicity onset along the plate interface is mainly due to a decrease in the abundance of the fluids released by subducted sediments. Higher seismicity rates locally concur with seamounts present at the seismogenic zone, while seamounts under the margin slope may shallow the onset of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APhy...61..231B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APhy...61..231B"><span id="translatedtitle">Reconstruction of the sound <span class="hlt">velocity</span> and absorption spatial distributions in soft biological tissue phantoms from experimental ultrasound <span class="hlt">tomography</span> data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burov, V. A.; Zotov, D. I.; Rumyantseva, O. D.</p> <p>2015-03-01</p> <p>The paper is devoted to implementing in a specific tomographic device a two-step algorithm designed to reconstruct the spatial distributions of the sound <span class="hlt">velocity</span> and absorption coefficient, primarily in soft biological tissues. To generate the input data of the first and second steps, a correlation algorithm is used based on determination of the time shift in the signal propagation time in the presence of an object. The results of reconstruction are presented, which are based on data measured for objects-phantoms using a developed experimental ultrasound tomograph model. We discuss problems that arise during reconstruction with a low resolution at the first step of the algorithm, and we demonstrate the high spatial resolving power achieved at the second step.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010SoPh..265..245J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010SoPh..265..245J"><span id="translatedtitle">Inclusion of In-Situ <span class="hlt">Velocity</span> Measurements into the UCSD Time-Dependent <span class="hlt">Tomography</span> to Constrain and Better-Forecast Remote-Sensing Observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jackson, B. V.; Hick, P. P.; Bisi, M. M.; Clover, J. M.; Buffington, A.</p> <p>2010-08-01</p> <p>The University of California, San Diego (UCSD) three-dimensional (3-D) time-dependent <span class="hlt">tomography</span> program has been used successfully for a decade to reconstruct and forecast coronal mass ejections from interplanetary scintillation observations. More recently, we have extended this <span class="hlt">tomography</span> technique to use remote-sensing data from the Solar Mass Ejection Imager (SMEI) on board the Coriolis spacecraft; from the Ootacamund (Ooty) radio telescope in India; and from the European Incoherent SCATter (EISCAT) radar telescopes in northern Scandinavia. Finally, we intend these analyses to be used with observations from the Murchison Widefield Array (MWA), or the LOw Frequency ARray (LOFAR) now being developed respectively in Australia and Europe. In this article we demonstrate how in-situ <span class="hlt">velocity</span> measurements from the Advanced Composition Explorer (ACE) space-borne instrumentation can be used in addition to remote-sensing data to constrain the time-dependent tomographic solution. Supplementing the remote-sensing observations with in-situ measurements provides additional information to construct an iterated solar-wind parameter that is propagated outward from near the solar surface past the measurement location, and throughout the volume. While the largest changes within the volume are close to the radial directions that incorporate the in-situ measurements, their inclusion significantly reduces the uncertainty in extending these measurements to global 3-D reconstructions that are distant in time and space from the spacecraft. At Earth, this can provide a finely-tuned real-time measurement up to the latest time for which in-situ measurements are available, and enables more-accurate forecasting beyond this than remote-sensing observations alone allow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013ApJ...768...77A&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2013ApJ...768...77A&link_type=ABSTRACT"><span id="translatedtitle">A Catalog of Ultra-compact High <span class="hlt">Velocity</span> Clouds from the ALFALFA Survey: Local <span class="hlt">Group</span> Galaxy Candidates?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P.</p> <p>2013-05-01</p> <p>We present a catalog of 59 ultra-compact high <span class="hlt">velocity</span> clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s-1, median angular diameters of 10', and median <span class="hlt">velocity</span> widths of 23 km s-1. We show that the full UCHVC population cannot easily be associated with known populations of high <span class="hlt">velocity</span> clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of ~1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of ~105-106 M ⊙, H I diameters of ~2-3 kpc, and indicative dynamical masses within the H I extent of ~107-108 M ⊙, similar to the Local <span class="hlt">Group</span> ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22126806','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22126806"><span id="translatedtitle">A CATALOG OF ULTRA-COMPACT HIGH <span class="hlt">VELOCITY</span> CLOUDS FROM THE ALFALFA SURVEY: LOCAL <span class="hlt">GROUP</span> GALAXY CANDIDATES?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P. E-mail: riccardo@astro.cornell.edu</p> <p>2013-05-01</p> <p>We present a catalog of 59 ultra-compact high <span class="hlt">velocity</span> clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s{sup -1}, median angular diameters of 10', and median <span class="hlt">velocity</span> widths of 23 km s{sup -1}. We show that the full UCHVC population cannot easily be associated with known populations of high <span class="hlt">velocity</span> clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of {approx}1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of {approx}10{sup 5}-10{sup 6} M{sub Sun }, H I diameters of {approx}2-3 kpc, and indicative dynamical masses within the H I extent of {approx}10{sup 7}-10{sup 8} M{sub Sun }, similar to the Local <span class="hlt">Group</span> ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI41A4314L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI41A4314L"><span id="translatedtitle">Layer Stripping Forward <span class="hlt">Tomography</span> with S, ScS, and Sdiff phases to sharpen images of deep mantle shear <span class="hlt">velocity</span> heterogeneity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lai, H.; Garnero, E.; Zhao, C.</p> <p>2014-12-01</p> <p>The Earth's deep mantle has been shown to be heterogeneous at a wide spectrum of scales, from fine scale (e.g.,1-10 km) to degree 2 low <span class="hlt">velocity</span> provinces (1000's of km lateral scale). Principle structures include large low shear <span class="hlt">velocity</span> provinces (LLSVPs) beneath the Pacific Ocean and Africa and southern Atlanic Ocean, and a circum-Pacific higher <span class="hlt">velocity</span> band. At intermediate scales, structures include D" discontinuities and details associated with LLSVPs, such as sharp sides. Shorter scales include ultra-low <span class="hlt">velocity</span> zones (ULVZs) and regions of scattering of high frequency waves. In this study we seek to improve upon our knowledge of global intermediate and small-scale shear wave structure in the lower mantle with an iterative Layer-Stripping Forward <span class="hlt">Tomography</span> approach. This approach iteratively updates a starting tomographic model by mapping travel time residuals (between observations and predictions) from the surface (using shallow S wave phase) down to lowermost mantle depths (using deep S waves, ScS waves, and Sdiff waves). Modifications to the uppermost mantle are primarily aimed at properly correcting deep phases for shallow heterogeneity. Relatively uniform coverage of the deepest mantle is achieved with Sdiff. The core-reflected ScS contributes most strongly to our knowledge of shorter scale heterogeneity, but coverage is more limited that with Sdiff. Deep mantle S waves provide information on the vertical extent of lowermost mantle heterogeneity (e.g., LLSVPs), but similar to ScS, coverage is limited to source-receiver pairs with the proper distance range. We collected near 1200 global earthquakes global earthquakes from the last two decades, with depths greater than 30 km, and focused on data with clear and impulsive phases. In a semi-automatic scheme, we measured all S, ScS, and Sdiff times and document waveshape stability by constructing a mean shape of each phase for each event. Cross-correlation coefficients between individual records and the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27523454','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27523454"><span id="translatedtitle">Defining risk <span class="hlt">groups</span> of patients with cancer of unknown primary site and cervical nodal metastases by F-18 fluorodeoxyglucose positron emission <span class="hlt">tomography</span> and computed <span class="hlt">tomography</span> imaging.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Su, Yung-Yueh; Chen, Shih-Shin; Hsieh, Chia-Hsun; Liao, Chun-Ta; Lin, Chien-Yu; Kang, Chung-Jan; Yen, Tzu-Chen</p> <p>2016-08-01</p> <p>We sought to investigate the clinical utility of F-18 fluorodeoxyglucose (FDG) positron emission <span class="hlt">tomography</span> and computed <span class="hlt">tomography</span> (PET/CT) in Taiwanese patients with cancer of unknown primary site (CUP) and cervical nodal metastases. We also aimed to study the impact of F-18 FDG PET/CT on clinical treatment priority in this patient <span class="hlt">group</span>. Between September 2006 and May 2014, patients with CUP and cervical nodal metastases who underwent F-18 FDG PET/CT imaging study were retrospectively identified. The clinicopathological risk factors and PET parameters were analyzed in relation to 2-year overall survival (OS) rates using univariate and multivariate analyses. Two-year OS curves were plotted with the Kaplan-Meier method. Of the eligible patients (n = 54), 12 (22.2%) had distant metastases (DM) at presentation. A total of 13 (24.1%) and 15 (27.8%) primary tumors were identified by FDG PET/CT imaging and an additional triple biopsy, respectively. The results of multivariate analysis identified smoking [p = 0.033, 95% confidence interval (CI) = 1.197-40.342], a maximum standardized uptake value (SUVmax) of cervical nodes ≥ 14.2 (p = 0.035, 95% CI = 1.134-28.029), and DM at presentation (p = 0.031, 95% CI = 1.257-114.854) as independent predictors of 2-year OS. Specifically, patients who carried ≥ 2 risk factors showed poorer outcomes (70.3% vs. 11.8%, p < 0.001). Fifteen study patients (27.8%) had their treatment modified by FDG PET/CT findings. We conclude that FDG PET/CT is clinically useful in CUP patients not only for tumor staging, but also for modifying treatment regimens. PMID:27523454</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25121882','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25121882"><span id="translatedtitle">Measurement of <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion in a solid-core photonic crystal fiber filled with a nematic liquid crystal.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wahle, Markus; Kitzerow, Heinz</p> <p>2014-08-15</p> <p>Liquid crystal-filled photonic crystal fibers (PCFs) are promising candidates for electrically tunable integrated photonic devices. In this Letter, we present <span class="hlt">group</span> <span class="hlt">velocity</span> measurements on such fibers. A large mode area PCF, LMA8, was infiltrated with the liquid crystal mixture, E7. The measurements were performed with an interferometric setup. The fiber exhibits several spectral transmission windows in the visible wavelength regime that originate from the bandgap guiding mechanism. The dispersion of these windows is very unusual compared to typical fibers. Our measurements show that it can change from -2500 ps km(-1) nm(-1) to +2500 ps km(-1) nm(-1) within a spectral range of only 15 nm. This leads to multiple zero dispersion wavelengths in the visible wavelength range. PMID:25121882</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22395863','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22395863"><span id="translatedtitle">Filamentation of a phase-modulated pulse under conditions of normal, anomalous and zero <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Chekalin, S V; Kompanets, V O; Smetanina, E O; Spirkov, A I; Kandidov, V P</p> <p>2014-06-30</p> <p>We have investigated experimentally and numerically the influence of the initial temporal phase modulation of a pulse on the spatiotemporal intensity distribution and the frequency-angular spectrum of femtosecond laser pulses with self-channelling in a condensed medium. We have detected a decrease in the intensity of divergent anti-Stokes frequency components during filamentation of radiation under conditions of normal <span class="hlt">group-velocity</span> dispersion (GVD) and strong phase modulation. In the zero-GVD regime under conditions of the phase modulation of radiation, the spatiotemporal transformation of the pulse is similar to that in the normal-GVD regime, which leads to a qualitative change in the supercontinuum spectrum. In the anomalous-GVD regime, a sequence of 'light bullets' is formed in the filament for both a phase-modulated and a transform-limited pulse. (extreme light fields and their applications)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014QuEle..44..577C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014QuEle..44..577C"><span id="translatedtitle">Filamentation of a phase-modulated pulse under conditions of normal, anomalous and zero <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chekalin, S. V.; Smetanina, E. O.; Spirkov, A. I.; Kompanets, V. O.; Kandidov, V. P.</p> <p>2014-06-01</p> <p>We have investigated experimentally and numerically the influence of the initial temporal phase modulation of a pulse on the spatiotemporal intensity distribution and the frequency-angular spectrum of femtosecond laser pulses with self-channelling in a condensed medium. We have detected a decrease in the intensity of divergent anti-Stokes frequency components during filamentation of radiation under conditions of normal <span class="hlt">group-velocity</span> dispersion (GVD) and strong phase modulation. In the zero-GVD regime under conditions of the phase modulation of radiation, the spatiotemporal transformation of the pulse is similar to that in the normal-GVD regime, which leads to a qualitative change in the supercontinuum spectrum. In the anomalous-GVD regime, a sequence of 'light bullets' is formed in the filament for both a phase-modulated and a transform-limited pulse.</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_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" 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_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</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_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26233023','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26233023"><span id="translatedtitle">Experimental and numerical study of the excitability of zero <span class="hlt">group</span> <span class="hlt">velocity</span> Lamb waves by laser-ultrasound.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Grünsteidl, Clemens M; Veres, István A; Murray, Todd W</p> <p>2015-07-01</p> <p>The excitability of zero <span class="hlt">group</span> <span class="hlt">velocity</span> (ZGV) Lamb waves using a pulsed laser source is investigated experimentally and through numerical simulation. Experimentally, a laser based ultrasonic technique is used to find the optical spot size on the sample surface that allows an optimal coupling of the optical energy into the ZGV mode. Numerical simulations, using the time domain finite differences technique, are carried out to model the thermoelastic generation process by laser irradiation and the propagation of the generated acoustic waves. The experimental results are in good agreement with the numerical predictions. The experimentally and numerically obtained responses of the plate are investigated by a short-time Fourier transform. The responses show that the source diameter does not affect the fundamental behavior of the temporal decay of the ZGV mode. PMID:26233023</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22130462','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22130462"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> dispersion and relativistic effects on the wakefield induced by chirped laser pulse in parabolic plasma channel</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sohbatzadeh, F.; Akou, H.</p> <p>2013-04-15</p> <p>The excitation of wake field plasma waves by a short laser pulse propagating through a parabolic plasma channel is studied. The laser pulse is assumed to be initially chirped. In this regard, the effects of initial and induced chirp on the plasma wake field as well as the laser pulse parameters are investigated. The <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion and nonlinear relativistic effects were taken into account to evaluate the excited wake field in two dimension using source dependent expansion method. Positive, negative, and un-chirped laser pulses were employed in numerical code to evaluate the effectiveness of the initial chirp on 2-D wake field excitation. Numerical results showed that for laser irradiances exceeding 10{sup 18}W/cm{sup 2}, an intense laser pulse with initial positive chirp generates larger wake field compared to negatively and un-chirped pulses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhPl...20d3101S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhPl...20d3101S"><span id="translatedtitle"><span class="hlt">Group</span> <span class="hlt">velocity</span> dispersion and relativistic effects on the wakefield induced by chirped laser pulse in parabolic plasma channel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sohbatzadeh, F.; Akou, H.</p> <p>2013-04-01</p> <p>The excitation of wake field plasma waves by a short laser pulse propagating through a parabolic plasma channel is studied. The laser pulse is assumed to be initially chirped. In this regard, the effects of initial and induced chirp on the plasma wake field as well as the laser pulse parameters are investigated. The <span class="hlt">group</span> <span class="hlt">velocity</span> dispersion and nonlinear relativistic effects were taken into account to evaluate the excited wake field in two dimension using source dependent expansion method. Positive, negative, and un-chirped laser pulses were employed in numerical code to evaluate the effectiveness of the initial chirp on 2-D wake field excitation. Numerical results showed that for laser irradiances exceeding 1018W/cm2, an intense laser pulse with initial positive chirp generates larger wake field compared to negatively and un-chirped pulses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.S41B2742K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.S41B2742K&link_type=ABSTRACT"><span id="translatedtitle">New Observations of Seismic <span class="hlt">Group</span> <span class="hlt">Velocities</span> in the Western Solomon Islands from Cross-Correlation of 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>Ku, C. S.; You, S. H.; Kuo, Y. T.; Huang, B. S.; Wu, Y. M.; Chen, Y. G.; Taylor, F. W.</p> <p>2015-12-01</p> <p>A MW 8.1 earthquake occurred on 1 April 2007 in the western Solomon Islands. Following this event, a damaging tsunami was induced and hit the Island Gizo where the capital city of Western Province of Solomon Islands located. Several buildings of this city were destroyed and several peoples lost their lives during this earthquake. However, during this earthquake, no near source seismic instrument has been installed in this region. The seismic evaluations for the aftershock sequence, the possible earthquake early warning and tsunami warning were unavailable. For the purpose of knowing more detailed information about seismic activity in this region, we have installed 9 seismic stations (with Trillium 120PA broadband seismometer and Q330S 24bit digitizer) around the rupture zone of the 2007 earthquake since September of 2009. Within a decade, it has been demonstrated both theoretically and experimentally that the Green's function or impulse response between two seismic stations can be retrieved from the cross-correlation of ambient noise. In this study, 6 stations' observations which are more complete during 2011/10 ~ 2012/12 period, were selected for the purpose of the cross-correlation analysis of ambient seismic noise. The <span class="hlt">group</span> <span class="hlt">velocities</span> at period 2-20 seconds of 15 station-pairs were extracted by using multiple filter technique (MFT) method. The analyzed results of this study presented significant results of <span class="hlt">group</span> <span class="hlt">velocities</span> with higher frequency contents than other studies (20-60 seconds in usually cases) and opened new opportunities to study the shallow crustal structure of the western Solomon Islands.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22036442','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22036442"><span id="translatedtitle">Simultaneous measurement of <span class="hlt">group</span> refractive index and thickness of optical samples using optical coherence <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cheng, Hsu-Chih; Liu, Yi-Cheng</p> <p>2010-02-10</p> <p>Optical coherence <span class="hlt">tomography</span> (OCT), based on a Michelson interferometer and utilizing low coherence light as the optical source, is a novel technique for the noninvasive imaging of optical scattering media. A simple OCT scheme based on a 3x3 fiber coupler is presented for the simultaneous measurement of the refractive index and thickness of optical samples. The proposed system enables the refractive index and thickness to be determined without any prior knowledge of the sample parameters and is characterized by a simple and compact configuration, a straightforward measurement procedure, and a low cost. The feasibility of the proposed approach is demonstrated experimentally using BK7 and B270 optical glass samples.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008GeoJI.175..689S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008GeoJI.175..689S"><span id="translatedtitle">P- and SV-<span class="hlt">velocity</span> structure of the South Portuguese Zone fold-and-thrust belt, SW Iberia, from traveltime <span class="hlt">tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmelzbach, C.; Zelt, C. A.; Juhlin, C.; Carbonell, R.</p> <p>2008-11-01</p> <p>Imaging the architecture of the shallow crust of the South Portuguese Zone fold-and-thrust belt is essential to extend surface mapped geological information to depth and to help in developing models of the ore-bearing Iberian Pyrite Belt part of the Variscan orogeny. The recently acquired IBERSEIS seismic-reflection data set provides, for the first time, detailed images of the entire crust, but source-generated noise masks the earliest reflections and limits the shallowest observed signals to depths >500m. We inverted P- and SV first-arrival traveltimes for the smoothest minimum-structure <span class="hlt">velocity</span> models, imaging the shallowest few hundreds of metres along four in total ~60-km-long profiles. A comparison of a 2-D and 2.5-D (3-D forward and 2-D inverse problem) crooked-line inversion scheme revealed that the crooked-line geometry has a negligible effect on the final images. Resolution of the final preferred models was assessed on the basis of an extensive series of checkerboard tests, showing a slightly lower resolution capability of the SV-data due to greater data uncertainty, fewer number of picks and more limited source-receiver offsets compared with the P-data. The preferred final models compare favourably with the mapped surface geology, showing relatively high and uniform <span class="hlt">velocities</span> (>5.25kms-1) for the flysch <span class="hlt">group</span> in the southern part of the investigation area. Low <span class="hlt">velocities</span> (~4.5kms-1) are found for the `La Puebla de Guzman antiform' in the centre of the investigation area, where the phyllite-quartzite <span class="hlt">group</span> is exposed. <span class="hlt">Velocities</span> fluctuate the most along the northernmost ~20km. <span class="hlt">Velocity</span> variations reflect more the state of tectonic deformation than being directly correlated with the mapped lithologies. Based on a comparison with coincident seismic-reflection data along the southern half of the area, we suggest that two areas of low to intermediate ratios (~1.85-1.9) correspond to occurrences of thick and less deformed flysch-<span class="hlt">group</span> units, whereas high</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1010842','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1010842"><span id="translatedtitle">Structure of the Crust beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave <span class="hlt">Group</span> <span class="hlt">Velocities</span> and Receiver Functions</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tokam, A K; Tabod, C T; Nyblade, A A; Julia, J; Wiens, D A; Pasyanos, M E</p> <p>2010-02-18</p> <p> Cameroon using 1-D shear wave <span class="hlt">velocity</span> models obtained from the joint inversion of Rayleigh wave <span class="hlt">group</span> <span class="hlt">velocities</span> and P-receiver functions for 32 broadband seismic stations. From the 1-D shear wave <span class="hlt">velocity</span> models, we obtain new insights into the composition and structure of the crust and upper mantle across Cameroon. After briefly reviewing the geological framework of Cameroon, we describe the data and the joint inversion method, and then interpret variations in crustal structure found beneath Cameroon in terms of the tectonic history of the region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.T51A0304T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.T51A0304T"><span id="translatedtitle">A Detailed 3D Seismic <span class="hlt">Velocity</span> Structure of the Subducting Pacific Slab Beneath Hokkaido, Tohoku and Kanto, Japan, by Double-Difference <span class="hlt">Tomography</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tsuji, Y.; Nakajima, J.; Kita, S.; Okada, T.; Matsuzawa, T.; Hasegawa, A.</p> <p>2007-12-01</p> <p>Three-dimensional heterogeneous structure beneath northeastern (NE) Japan has been investigated by previous studies and an inclined seismic low-<span class="hlt">velocity</span> zone is imaged in the mantle wedge sub-parallel to the down-dip direction of the subducting slab (Zhao et al., 1992, Nakajima et al., 2001). However, the heterogeneous structure within the slab has not been well studied even though it is very important to understand the whole process of water transportation from the slab to the surface. Here we show a detailed 3D seismic <span class="hlt">velocity</span> structure within the subducted Pacific slab around Japan and propose a water-transportation path from the slab to the mantle wedge. In this study, we estimated 3D <span class="hlt">velocity</span> structure within the Pacific slab by the double-difference <span class="hlt">tomography</span> (Zhang and Thurber, 2003). We divided the study area, from Hokkaido to Kanto, into 6 areas due to the limitation of memory and computation time. In each area, arrival-time data of 7,500-17,000 events recorded at 70-170 stations were used in the analysis. The total number of absolute travel-time data was about 140,000-312,000 for P wave and 123,000-268,000 for S wave, and differential data were about 736,000-1,920,000 for P wave and 644,000-1,488,000 for S wave. Horizontal and vertical grid separations are 10-25 km and 6.5 km, respectively. RMS residuals of travel times for P wave decreased from 0.23s to 0.09s and for S wave from 0.35s to 0.13s. The obtained results are as follows: (1) a remarkable low-Vs zone exists in the uppermost part of the subducting slab, (2) it extends down to a depth of about 80 km, (3) the termination of this low-Vs zone almost corresponds to the "seismic belt" recently detected in the upper plane of the double seismic zone (Kita et al.,2006; Hasegawa et al., 2007), (4) at depths deeper than 80 km, a low-Vs and high-Vp/Vs zone is apparently distributed in the mantle wedge, immediately above the slab crust. We consider that these features reflect water-transportation processes</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/24921834','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/24921834"><span id="translatedtitle">Tamm plasmon-polariton with negative <span class="hlt">group</span> <span class="hlt">velocity</span> induced by a negative index meta-material capping layer at metal-Bragg reflector interface.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Cunding; Kong, Mingdong; Li, Bincheng</p> <p>2014-05-01</p> <p>Influence of a negative refractive index meta-material (NIM) capping layer on properties of Tamm plasmon-polariton at the interface of metal-Bragg reflector structure is investigated. Conditions for excitation of the plasmon-polariton is determined from reflectivity mapping calculation and analyzed with cavity mode theory. For specific thicknesses of capping layers, Tamm plasmon-polariton with negative <span class="hlt">group</span> <span class="hlt">velocity</span> is revealed in a wide region of frequency. Different from backward optical propagation induced by negative effective-<span class="hlt">group</span>-refractive-index in dispersive media, negative <span class="hlt">group</span> <span class="hlt">velocity</span> of Tamm plasmon-polariton results from opposite signs of cross-section-integrated field energy and Poynting vector. PMID:24921834</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhRvA..93b3834C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhRvA..93b3834C"><span id="translatedtitle">Modulation instability in noninstantaneous Kerr media with walk-off and cross-phase modulation for mixed <span class="hlt">group-velocity</span>-dispersion regimes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Canabarro, Askery; Santos, B.; de Lima Bernardo, B.; Moura, André L.; Soares, W. C.; de Lima, E.; Gléria, Iram; Lyra, M. L.</p> <p>2016-02-01</p> <p>Taking into account relaxing Kerr nonlinearity and walk-off effects, the conditions and gain spectra of cross-phase modulation-induced modulational instability (XPM-MI) of two incoherently copropagating optical waves of different frequencies and same polarization are investigated. We devote particular attention to the mixed case in which one pulse propagates under the normal <span class="hlt">group-velocity</span> dispersion (GVD) regime, while the second one is under an anomalous GVD regime. We unveil that in the limit of an instantaneuous nonlinear response, the typical frequency with maximum gain converges to a finite value in the mixed GDV regime, while it continuously grows with the <span class="hlt">group-velocity</span> mismatch in the normal GVD regime. As a result, the maximum gain typically decreases with the <span class="hlt">group-velocity</span> mismatch in the mixed regime, contrasting with the opposite trend in the normal GVD regime. Further, we show that besides the mode having maximum gain at a frequency decaying with 1 /τ1 /3 in the slow response limit, there is a second mode having maximum gain with a distinct scaling behavior Ωmax∝1 /τ in the absence of <span class="hlt">group-velocity</span> mismatch. The associated maximum gains scale, respectively, as 1 /τ2 /3 and 1 /τ , thus signaling the corresponding quadratic and linear dispersion relation of these modes in the low-frequency limit. A detailed analysis of the influence of the nonlinear response time and <span class="hlt">group-velocity</span> dispersion on the MI gain spectrum is also provided.</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_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</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_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <center> <div class="footer-extlink text-muted"><small>Some links on this page may take you to non-federal websites. 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