These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Shear-wave velocity variation in jointed rock: an attempt to measure tide-induced variations  

SciTech Connect

The use of the perturbation of seismic wave velocities by solid earth tides as a possible method of exploration for fractured media is discussed. Velocity of compressional seismic waves in fractured homogeneous rock has been observed to vary through solid earth tide cycles by a significant 0.5-0.9%. This variation of seismic velocities may be attributed to the opening and closing of joints by tidal stresses. In an attempt to see if shear-wave velocities show a similar velocity variation, a pneumatic shear-wave generator was used for the source. The 5 receivers, 3-component, 2.0 Hz, moving-coil geophones, were connected to a GEOS digital recorder. The two receivers located 120 m and 110 m from the source showed large shear-to-compression amplitude ratio and a high signal-to-noise ratio. A glaciated valley was chosen for the experiment site, since topography is flat and the granodiorite is jointed by a set of nearly orthogonal vertical joints, with superimposed horizontal sheeting joints. A slight velocity variation was noted in the first 200 consecutive firings; after which, the amplitude of the shear-wave begun to increase. This increase has been attributed to the compacting of the soil beneath the shear-wave generator (SWG). In the future, the soil will be compacted prior to placing the SWG or the SWG will be coupled directly to the rock to alleviate the amplitude fluctuation problem. This research may have application in exploration for fracture permeability in the rock mass between existing wells, by measuring seismic velocities from well to well through the tidal cycle.

Beem, L.I.

1987-08-01

2

Mapping of shallow three dimensional variations of P-wave velocity in Garhwal Himalaya  

Microsoft Academic Search

A set of short aperture seismic arrays was operated in the Garhwal Himalaya close to the Main Central Thrust and recorded a large number of small local earthquakes. This study pertains to the inversion of the body wave arrival time data of these earthquakes to construct a seismic velocity model for the region. The analysis indicates a systematic variation in

I. Sarkar; R. Jain; K. N. Khattri

2001-01-01

3

Variation of Fundamental Mode Surface Wave Group Velocity Dispersion in Iran and the Surrounding Region  

NASA Astrophysics Data System (ADS)

We present group velocity 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 group velocity 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 group velocity studies. We observe variations in short-period wave group velocity which is consistent with the surface geology. Low group velocities (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 group velocity (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) group velocities 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 group velocities remain low (3.25-3.70 km/s) over most of Iran, but there are even lower velocities (2.80-3.00 km/s) still associated with the thick sediments of the south Caspian basin, the surrounding shield areas have much higher group velocities (3.90-4.45 km/s) at these periods. A similar pattern is seen for longer period Rayleigh waves, with low velocities (2.85-3.60 km/s) beneath the Alpine-Himalaya belt, compared to the velocities (3.80-4.10 km/s) of the Turan and Arabian shields, to the north and south respectively, no large anomaly beneath the south Caspian is observed for these longer period Rayleigh waves.

Rham, D. J.; Preistley, K.; Tatar, M.; Paul, A.

2006-12-01

4

Mapping of shallow three dimensional variations of P-wave velocity in Garhwal Himalaya  

NASA Astrophysics Data System (ADS)

A set of short aperture seismic arrays was operated in the Garhwal Himalaya close to the Main Central Thrust and recorded a large number of small local earthquakes. This study pertains to the inversion of the body wave arrival time data of these earthquakes to construct a seismic velocity model for the region. The analysis indicates a systematic variation in the P-wave velocities of the upper crustal rocks. We estimate (i) significantly lower seismic velocities within the Middle-Lesser Garhwal Himalaya, and (ii) higher seismic velocities in the interface zone between the Middle-Lesser and Higher Garhwal Himalaya. Seismic activity is mostly confined to a relatively narrow north-east dipping zone in the upper 4 km of the crust characterized by a relatively higher P-wave velocity. This active seismicity represents reverse thrusting along steep north-easterly dipping parallel slip surfaces within this zone forming a ramp in the crystalline formations of Higher Himalaya. The lower velocity zone exhibits a low level of seismicity but appears to be associated with an increased landslide hazard.

Sarkar, I.; Jain, R.; Khattri, K. N.

2001-02-01

5

Variation of fundamental mode Rayleigh wave group velocity dispersion in Iran and the surrounding region  

NASA Astrophysics Data System (ADS)

We present group velocity 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 group velocity 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 group velocity studies. We observe variations in short-period group velocity which is consistent with the surface geology. Low group velocity (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 group velocity (2.60-2.70~km/s) at these periods occurs in central Iran. At intermediate periods (30-40~s) group velocities over most of the region are low (2.90-3.10~km/s) compared to Arabia. At longer periods (50-60~s) group velocities remain low (3.35-3.45~km/s) over most of Iran but there is a suggestion of higher group velocities beneath the northern and central Zagros.

Rham, D.; Priestley, K.; Tatar, M.; Paul, A.; Hatzfeld, D.; Radjaee, A.; Nowrouzi, G.; Kaviani, A.; Tiberi, C.

2005-12-01

6

Apparent changes in seismic wave velocity related to microseism noise source variations  

NASA Astrophysics Data System (ADS)

Currently there is a strong interest of using cross correlation of ambient noise for imaging of the subsurface or monitoring of various geological settings where we expect rapid changes (e.g. reservoirs or volcanoes). Through cross correlation retrieved Green's function is usually used to calculate seismic velocities of the subsurface. The assumption of this method is that the wavefields which are correlated must be diffuse. That means that the ambient noise sources are uniformly distributed around the receivers or the scattering in the medium is high enough to mitigate any source directivity. The location of the sources is usually unknown and it can change in time. These temporal and spatial variations of the microseism noise sources may lead to changes in the retrieved Green's functions. The changed Green's functions will then cause apparent changes in the calculated seismic velocity. We track the spatial and temporal distribution of the noise sources using seismic arrays, located in Ireland. It is a good location in which to study these effects, as it is tectonically very quiet and is relatively close to large microseism noise sources in the North Atlantic, allowing a quantification of noise source heterogeneity. Temporal variations in seismic wave velocity are calculated using data recorded in Ireland. The results are compared to the variations in microseism source locations. We also explore the minimum noise trace length required in Ireland for the Green's functions to converge. We quantify the degree to which apparent velocity variations using direct arrivals are caused by changes in the sources and assess if and at what frequencies the scattering of the medium in Ireland is high enough to homogenise the coda wavefield.

Friderike Volk, Meike; Bean, Christopher; Lokmer, Ivan; Craig, David

2014-05-01

7

Variation of P-wave velocity before the Bear Valley, California, earthquake of 24 February 1972  

USGS Publications Warehouse

Residuals for P-wave traveltimes at a seismograph station near Bear Valley, California, for small, precisely located local earthquakes at distances of 20 to 70 kilometers show a sharp increase of nearly 0.3 second about 2 months before a magnitude 5.0 earthquake that occurred within a few kilometers of the station. This indicates that velocity changes observed elsewhere premonitory to earthquakes, possibly related to dilatancy, occur along the central section of the San Andreas fault system.

Robinson, R.; Wesson, R.L.; Ellsworth, W.L.

1974-01-01

8

Velocities under Water Waves  

NSDL National Science Digital Library

This site from the Center of Applied Coastal Research at the University of Delaware features an interactive animation of wave form that users can modify then watch the results of their input. Parameters include wave height, wave period, and local depth. The resulting animation shows the associated water particle motion, plus the velocity vector of the user's chosen wave.

Robert A. Dalrymple

9

Spatial variation in coda Q around the Nobi fault zone, central Japan: relation to S-wave velocity and seismicity  

NASA Astrophysics Data System (ADS)

We investigate the spatial variation in coda Q around the Nobi fault zone in a high strain rate zone to assess the relation between coda Q, shear wave velocity, and seismicity. Waveform data were obtained from dense seismic observations. Low coda Q that follows the Niigata-Kobe Tectonic Zone in the high strain rate zone is distinct at the lowest frequency band of 1 to 2 Hz. However, at higher frequencies, such a spatial pattern in coda Q is unclear. A good positive correlation was found between coda Q at the 1- to 2-Hz frequency band and the S-wave velocity perturbation at 25-km depth, which suggests that the coda Q reflects the ductile deformation below the brittle-ductile transition zone. Furthermore, coda Q at the 1- to 2-Hz frequency band correlates negatively with seismicity at 10- to 15-km depth, which implies that there is a high stressing rate in the low coda Q area. These facts, together with results of previous studies, imply that a high deformation rate below the brittle-ductile transition zone produces the high strain rate observed by the Global Positioning System (GPS) on the surface in this region.

Tsuji, Sugane; Hiramatsu, Yoshihiro

2014-12-01

10

Rapid lateral variation of P-wave velocity at the base of the mantle near the edge of the Large-Low Shear Velocity Province beneath the western Pacific  

NASA Astrophysics Data System (ADS)

We examine P-wave velocity structure at the base of the mantle beneath the western Pacific, near the western edge of the Pacific Large-Low Shear Velocity Province (LLSVP), using high-quality seismograms provided by a large-scale mobile broad-band seismic observation in northeastern China (the NECESSArray project). Forward modelling using the reflectivity method is conducted to explain the variation of P-wave traveltimes as a function of epicentral distance near the core shadow zone. Additionally, PcP-P traveltimes are examined to enlarge the survey area. As a result, a rapid variation of P-wave velocity is detected at the base of the mantle. Regions of thin (20-50 km thick) and low velocity (-2 to -5 per cent) layers at the base of the mantle are intersected by an 80-km-thick region with a high velocity (+2 per cent). A slightly fast region exists at the northwest of the region with the thin low-velocity layer. These layers are typically separated by several hundred kilometres and would be difficult to explain by thermal effects alone. These observations suggest that very complicated thermochemical reactions occur near the edge of the Pacific LLSVP.

Tanaka, Satoru; Kawakatsu, Hitoshi; Obayashi, Masayuki; Chen, Y. John; Ning, Jieyuan; Grand, Stephen P.; Niu, Fenglin; Ni, James

2015-02-01

11

Study of stress-induced velocity variation in concrete under direct tensile force and monitoring of the damage level by using thermally-compensated Coda Wave Interferometry.  

PubMed

In this paper, we describe an experimental study of concrete behavior under a uniaxial tensile load by use of the thermally-compensated Coda Wave Interferometry (CWI) analysis. Under laboratory conditions, uniaxial tensile load cycles are imposed on a cylindrical concrete specimen, with continuous ultrasonic measurements being recorded within the scope of bias control protocols. A thermally-compensated CWI analysis of multiple scattering waves is performed in order to evaluate the stress-induced velocity variation. Concrete behavior under a tensile load can then be studied, along with CWI results from both its elastic performance (acoustoelasticity) and plastic performance (microcracking corresponding to the Kaiser effect). This work program includes a creep test with a sustained, high tensile load; the acoustoelastic coefficients are estimated before and after conducting the creep test and then used to demonstrate the effect of creep load. PMID:22989948

Zhang, Yuxiang; Abraham, Odile; Grondin, Frédéric; Loukili, Ahmed; Tournat, Vincent; Le Duff, Alain; Lascoup, Bertrand; Durand, Olivier

2012-12-01

12

Joint Inversion of Receiver Functions and Surface Wave Group Velocities from the MANAS data set to Determine Custal Thickness Variations in theTien Shan  

NASA Astrophysics Data System (ADS)

The Tien Shan is the largest active intracontinental orgogenic belt on the Earth. To better understand the processes causing mountains to form in this location distant from a plate boundary, we analyze passive source seismic data collected on 40 broad band stations of the MANAS project (2005-2007) to determine variations in crustal thickness and wavespeed across the range. The linear MANAS array transects the Tien Shan just to the east of the Talas Fergana fault and extends from the Tarim Basin north over the Kokshal Range and across the Naryn Valley to the Kyrgyz Range and the Kazakh Shield. This data set has a denser station spacing (~10 km) than that available in previous studies. We combine P- and S-wave receiver functions with surface wave observations from both earthquakes and ambient noise analysis to reduce the ambiguity inherent in the images obtained from the techniques applied individually. In particular, fundamental-mode surface-wave dispersion observations are sensitive to absolute wavespeed averages rather than contrasts, while receiver functions are primarily sensitive to wavespeed contrasts and vertically integrated travel times rather than absolute wavespeeds. Moreover, analysis of the ambient noise allows dispersion measurements at shorter periods which improves constraints for the upper crust. We jointly invert P- and S-wave receiver functions, fundamental mode Rayleigh wave group velocity determined from 1.75 years of continuous seismic ambient noise for periods 4-28s, and group velocity data for periods 10-70s from the surface wave study of Acton et al. (2010). The resulting crustal model show a strong variation in the Moho depth across the range. We find the thickest crust (~60 km) beneath the Kokshal range, while that beneath the Naryn Valley, in the middle of the Tien Shan is thin (~45 km) and is of similar thickness to that beneath the Tarim Basin and Kazakh shield. This suggests a lack of crustal shortening, or shortening of a previously thinned crust, in the middle of the range.

Gilligan, A.; Priestley, K. F.; Roecker, S. W.

2012-12-01

13

Arterial pulse wave velocity in coronary arteries  

Microsoft Academic Search

Pulse wave velocity is related to arterial stiffness. Pulse wave velocity changes with age and disease and is a useful indicator of cardiovascular disease. Different methods are used for evaluating pulse wave velocity in systemic vessels, but none is applicable to coronary arteries. In this study we first compare values of wave speed (c) calculated from measurements of pressure (P)

J. Aguado-Sierra; K. H. Parker; J. E. Davies; D. Francis; A. D. Hughes; J. Mayer

2006-01-01

14

Shear wave velocities in the earth's mantle.  

NASA Technical Reports Server (NTRS)

Direct measurement of the travel time gradient for S waves together with travel time data are used to derive a shear velocity model for the earth's mantle. In order to satisfy the data it is necessary to discard the usual assumption of lateral homogeneity below shallow depths. A shear velocity differential is proposed for a region between western North America and areas of the Pacific Ocean. Distinctive features of the velocity model for the upper mantle beneath western North America are a low-velocity zone centered at 100 km depth and zones of high velocity gradient beginning at 400, 650, and 900 km.

Robinson, R.; Kovach, R. L.

1972-01-01

15

Irregular wave induced velocities in shallow water  

E-print Network

IRREGULAR WAVE INDUCED VELOCITIES IN SHALLOW WATER A Thesis by NELS JOHN SULTAN Submitted to the Office of Graduate Studies of Texas ASM University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE December... 1991 Major Subject: Ocean Engineering IRREGULAR WAVE INDUCED VELOCITIES IN SHALLOW WATER A Thesis by NELS JOHN SULTAN Approved as to style and co tent by: Steven A. Hug s (Co-Chair of Committee) Robert E. Ra n dali (Co-Chair o mmittee...

Sultan, Nels John

1991-01-01

16

Copernicus observations of Iota Herculis velocity variations  

NASA Technical Reports Server (NTRS)

Observations of Iota Her at 109.61-109.67 nm obtained with the U1 channel of the Copernicus spectrophotometer at resolution 5 pm during 3.6 days in May, 1979, are reported. Radial-velocity variations are detected and analyzed as the sum of two sinusoids with frequencies 0.660 and 0.618 cycles/day and amplitudes 9.18 and 8.11 km/s, respectively. Weak evidence supporting the 13.9-h periodicity seen in line-profile variations by Smith (1978) is found.

Rogerson, J. B., Jr.

1984-01-01

17

MEASUREMENT OF OCEAN WAVES VELOCITY FIELDS FROM A SINGLE SPOT-5 DATASET USING CORRELATION BETWEEN  

E-print Network

MEASUREMENT OF OCEAN WAVES VELOCITY FIELDS FROM A SINGLE SPOT-5 DATASET USING CORRELATION BETWEEN Energies Alternatives, Siège-Saclay, 75000, Paris, France 1. ABSTRACT Ocean waves represent an important of the local ocean waves' velocity field and its temporal variation can provide invaluable information about

Paris-Sud XI, Université de

18

Upper mantle P-wave velocity structure beneath southern Scandinavia  

NASA Astrophysics Data System (ADS)

This study images upper mantle structure beneath different tectonic and geomorphological provinces in southern Scandinavia by P-wave travel time tomography based on teleseismic events. We present integrated results using data from several projects (CALAS, MAGNUS, SCANLIPS, CENMOVE and Tor) with a total of 202 temporary seismological stations deployed in southern Norway, southern Sweden, Denmark and the northernmost part of Germany. These stations, together with 18 permanent stations, yield a high density data coverage enabling presentation of the first high resolution 3D seismic P-wave velocity model for the upper mantle for this region, which includes areas of Baltic Shield, Scandinavian Caledonides, the entire northern part of the prominent Tornquist Zone and the Southern Scandes Mountains. P-wave arrival time residuals of up to ±1 s are observed reflecting large seismic velocity contrasts at depths. Relative regional as well as absolute global tomographic inversion is carried out and consistently show upper mantle velocity variations relative to the ak135 reference model of up to ± 2-3 % corresponding to P-wave velocity differences of about 0.4 km/s from depths of about 100 km to more than 300 km. High upper mantle velocities are observed to great depth to the east in Baltic Shield areas of southwestern Sweden. Lower velocities are found to the west and southwest beneath the Danish and North German sedimentary basins and in most of southern Norway. A well-defined, generally narrow deep boundary is observed between areas of contrasting upper mantle seismic velocity. In basin areas, low upper mantle velocities are associated with thinned lithosphere and velocity contrasts are interpreted to represent differences between deep shield lithosphere and shallow basin asthenosphere with a deep lithospheric boundary running close to the Sorgenfrei-Tornquist Zone. Differences in P-wave velocity are here likely to arise mainly from temperature differences. To the north, the boundary crosses various tectonic and geomorphologic units including shield units, the Caledonides as well as areas of high topography, and a structural and geodynamic interpretation is more complex. Reduced upper mantle velocities below southern Norway also appear to be associated with a thinner lithosphere compared to shield areas to the east. Velocity contrasts may be explained to a higher degree by both compositional and temperature differences and a geodynamic origin including both Proterozoic and Phanerozoic events. Below southern Norway, a regional contribution to buoyancy from reduced density in the upper mantle is likely to exist, but we observe no clear correlation between reduced upper mantle seismic velocity and high topography of the southern Scandes Mountains.

Medhus, A. B.; Balling, N.; Jacobsen, B. H.; England, R. W.; Kind, R.; Weidle, C.; Voss, P.; Thybo, H.

2012-04-01

19

Variational Principles for Water Waves  

E-print Network

We describe the Hamiltonian structures, including the Poisson brackets and Hamiltonians, for free boundary problems for incompressible fluid flows with vorticity. The Hamiltonian structure is used to obtain variational principles for stationary gravity waves both for irrotational flows as well as flows with vorticity.

Boris Kolev; David H. Sattinger

2007-12-01

20

S-wave velocity structure of the North China from inversion of Rayleigh wave phase velocity  

NASA Astrophysics Data System (ADS)

We constructed the S-wave velocity structure of the crust and uppermost mantle (10-100 km) beneath the North China based on the teleseismic data recorded by 187 portable broadband stations deployed in this region. The traditional two-step inversion scheme was adopted. Firstly, we measured the interstation fundamental Rayleigh wave phase velocity of 10-60 s and imaged the phase velocity distributions using the Tarantola inversion method. Secondly, we inverted the 1-D S-wave velocity structure with a grid spacing of 0.25° × 0.25° and constructed the 3-D S-wave velocity structure of the North China. The 3-D S-wave velocity model provides valuable information about the destruction mechanism and geodynamics of the North China Craton (NCC). The S-wave velocity structures in the northwestern and southwestern sides of the North-South Gravity Lineament (NSGL) are obviously different. The southeastern side is high velocity (high-V) while the northeastern side is low velocity (low-V) at the depth of 60-80 km. The upwelling asthenosphere above the stagnated Pacific plate may cause the destruction of the Eastern Block and form the NSGL. A prominent low-V anomaly exists around Datong from 50 to 100 km, which may due to the upwelling asthenosphere originating from the mantle transition zone beneath the Western Block. The upwelling asthenosphere beneath the Datong may also contribute to the destruction of the Eastern Block. The Zhangjiakou-Penglai fault zone (ZPFZ) may cut through the lithosphere and act as a channel of the upwelling asthenosphere. A noticeable low-V zone also exists in the lower crust and upper mantle lid (30-50 km) beneath the Beijing-Tianjin-Tangshan (BTT) region, which may be caused by the upwelling asthenosphere through the ZPFZ.

Chen, Hao-peng; Zhu, Liang-bao; Wang, Qing-dong; Zhang, Pan; Yang, Ying-hang

2014-07-01

21

Propagation of a constant velocity fission wave  

NASA Astrophysics Data System (ADS)

The ideal nuclear fuel cycle would require no enrichment, minimize the need fresh uranium, and produce few, if any, transuranic elements. Importantly, the latter goal would be met without the reprocessing. For purely physical reasons, no reactor system or fuel cycle can meet all of these objectives. However, a traveling-wave reactor, if feasible, could come remarkably close. The concept is simple: a large cylinder of natural (or depleted) uranium is subjected to a fast neutron source at one end, the neutrons would transmute the uranium downstream and produce plutonium. If the conditions were right, a self-sustaining fission wave would form, producing yet more neutrons which would breed more plutonium and leave behind little more than short-lived fission products. Numerical studies have shown that fission waves of this type are also possible. We have derived an exact solution for the propagation velocity of a fission wave through fertile material. The results show that these waves fall into a class of traveling wave phenomena that have been encountered in other systems. The solution places a strict conditions on the shapes of the flux, diffusive, and reactive profiles that would be required for such a phenomenon to persist. The results are confirmed numerically.

Deinert, Mark

2011-10-01

22

3D Shear-wave Velocity Model of The East Sea using Long Period Rayleigh-wave Group Velocity Dispersion Data  

NASA Astrophysics Data System (ADS)

This study presents 3D shear-wave velocity model beneath the East Sea (Sea of Japan). The region, which lies between the Korean peninsula and Japanese arc, plays important role to understand the crustal evolution at the continental margin. Long-period waveforms from 292 earthquake recorded on 251 stations of IRIS, F-net, and KS Networks were analyzed to estimate group arrival velocities of Rayleigh waves. A careful determination of the group velocities were carried out by determining velocity deviation to theoretical dispersion curves, and 3,666 dispersion curves were finally selected. A surface wave tomography technique using the fast marching method was applied to examine spatial group velocity variations between 10 s and 100 s. 3D shear-wave velocity model is constructed after inversion of the group velocities. Our shear-wave velocity model shows a shallow crust of the East Sea and a relatively thick crust of the Korean peninsula and Japanese arc. Depths of Moho-discontinuity inferred from steepest velocity gradient of the vertical velocity profiles were estimated. Estimated depths are 15-25 km beneath the East Sea and ~35 km beneath the Korean peninsula, respectively. Differences of Moho-depths are clearly depicted between sea basins and highs. Crustal thickness of the Yamato rise and Korea plateau, which are known as continental fragments formed during the East Sea opening, are found to be ~25 km, while 3 major basins, Japan, Ulleung, and Yamato show about 15 km-thick crust. Shear-wave velocities of the uppermost mantle down to 100 km show ±4% variation to 4.3 km/s of the average velocity. There exist a low velocity zone with -4% perturbation at ~70 km-depth beneath the East Sea. We consider that the thin crustal thickness and the low velocity zones are strong indications that the origin of the East Sea is the back-arc opening.

Jo, B. G.; Jung, S.; Jang, Y.

2013-05-01

23

Shear wave crustal velocity model of the Western Bohemian Massif from Love wave phase velocity dispersion  

NASA Astrophysics Data System (ADS)

We propose a new quantitative determination of shear wave velocities for distinct geological units in the Bohemian Massif, Czech Republic (Central Europe). The phase velocities of fundamental Love wave modes are measured along two long profiles (~200 km) crossing three major geological units and one rift-like structure of the studied region. We have developed a modified version of the classical multiple filtering technique for the frequency-time analysis and we apply it to two-station phase velocity estimation. Tests of both the analysis and inversion are provided. Seismograms of three Aegean Sea earthquakes are analyzed. One of the two profiles is further divided into four shorter sub-profiles. The long profiles yield smooth dispersion curves; while the curves of the sub-profiles have complicated shapes. Dispersion curve undulations are interpreted as period-dependent apparent velocity anomalies caused both by different backazimuths of surface wave propagation and by surface wave mode coupling. An appropriate backazimuth of propagation is found for each period, and the dispersion curves are corrected for this true propagation direction. Both the curves for the long and short profiles are inverted for a 1D shear wave velocity model of the crust. Subsurface shear wave velocities are found to be around 2.9 km/s for all four studied sub-profiles. Two of the profiles crossing the older Moldanubian and Teplá-Barrandian units are characterized by higher velocities of 3.8 km/s in the upper crust while for the Saxothuringian unit we find the velocity slightly lower, around 3.6 km/s at the same depths. We obtain an indication of a shear wave low velocity zone above Moho in the Moldanubian and Teplá-Barrandian units. The area of the Eger Rift (Teplá-Barrandian-Saxothuringian unit contact) is significantly different from all other three units. Low upper crust velocities suggest sedimentary and volcanic filling of the rift as well as fluid activity causing the earthquake swarms. Higher velocities in the lower crust together with weak or even missing Moho implies the upper mantle updoming.

Kolínský, Petr; Málek, Ji?í; Brokešová, Johana

2011-01-01

24

Compressional and shear wave velocities in granular materials to 2.5 kilobars  

NASA Technical Reports Server (NTRS)

The velocities of seismic compressional waves and, for the first time, shear wave velocities in silica sand, volcanic ash, and basalt powder were determined under hydrostatic confining pressures to 2.5 kb. Simultaneously, the porosity of these materials was obtained as a function of confining pressure. The presented results have important implications for the self-compaction hypothesis that has been postulated to explain the lunar near-surface seismic velocity variation.

Talwani, P.; Nur, A.; Kovach, R. L.

1973-01-01

25

S velocity variations beneath North America Heather Bedle1,2  

E-print Network

S velocity variations beneath North America Heather Bedle1,2 and Suzan van der Lee1 Received 23 S and Rayleigh wave trains generated by earthquakes around North America that occurred between the years 2000 variations beneath North America, J. Geophys. Res., 114, B07308, doi:10.1029/2008JB005949. 1. Introduction [2

van der Lee, Suzan

26

Anisotropic Rayleigh wave phase velocity maps of eastern China  

NASA Astrophysics Data System (ADS)

We explore the variations of Rayleigh wave phase velocity beneath eastern China in a broad period range (20-200 s). Rayleigh wave dispersion curves are measured by the two-station technique for a total of 734 interstation paths using vertical component broadband waveforms at 39 seismic stations in eastern China from 466 global earthquakes. In addition, 599 waveform inversion interstation measurements were added to this data set. The interstation dispersion curves are then inverted for high-resolution isotropic and azimuthally anisotropic phase velocity maps at periods between 20 and 200 s. At shorter periods sampling the crustal depth range, phase velocities are higher in the southeastern part of the region, reflecting the thinner crust there. The Jiangnan Belt separates Cathaysia from the Yangtze Craton, the latter with thicker crust and a deep, high-velocity cratonic root. The eastern part of Yangtze Craton, however, east of 115-116°E, does not display a deep root and has a thin lithosphere. Azimuthal anisotropy at long periods (>120 s) shows fast propagation directions broadly similar to that of the absolute plate motion. Beneath Cathaysia and eastern Yangtze Craton, anisotropy in the asthenosphere is strong and suggests coast-perpendicular flow. Asthenospheric flow from beneath China's thick continental lithosphere toward the thinner lithosphere of the margin and the resulting decompression melting may be the fundamental causes of the intraplate basaltic volcanism along the eastern coast of China.

Legendre, C. P.; Deschamps, F.; Zhao, L.; Lebedev, S.; Chen, Q.-F.

2014-06-01

27

A simple method of predicting S-wave velocity  

USGS Publications Warehouse

Prediction of shear-wave velocity plays an important role in seismic modeling, amplitude analysis with offset, and other exploration applications. This paper presents a method for predicting S-wave velocity from the P-wave velocity on the basis of the moduli of dry rock. Elastic velocities of water-saturated sediments at low frequencies can be predicted from the moduli of dry rock by using Gassmann's equation; hence, if the moduli of dry rock can be estimated from P-wave velocities, then S-wave velocities easily can be predicted from the moduli. Dry rock bulk modulus can be related to the shear modulus through a compaction constant. The numerical results indicate that the predicted S-wave velocities for consolidated and unconsolidated sediments agree well with measured velocities if differential pressure is greater than approximately 5 MPa. An advantage of this method is that there are no adjustable parameters to be chosen, such as the pore-aspect ratios required in some other methods. The predicted S-wave velocity depends only on the measured P-wave velocity and porosity. ?? 2006 Society of Exploration Geophysicists.

Lee, M.W.

2006-01-01

28

Wave equation migration velocity analysis by differential semblance optimization  

NASA Astrophysics Data System (ADS)

Differential semblance measures the deviation from flatness or focus of image gathers. The differential semblance objective function posed on the sub-surface offset domain responds smoothly to velocity changes. Therefore gradient descent methods are uniquely attractive for velocity updating by differential semblance optimization. Because of their kinematic fidelity, wave equation (depth extrapolation) migration methods are natural platforms for velocity analysis in complex structures. The gradient of the objective function with respect to velocity is fomulated through the adjoint of differential migration. Limited memory BFGS algorithm is used for the velocity optimization. The method for wave equation velocity analysis developed in this thesis study is applied to both synthetic and real data examples.

Shen, Peng

2005-11-01

29

Using a phonocardiography in a pulse wave velocity measurement  

Microsoft Academic Search

A data acquisition is realised using purely non-invasive measuring mode, i.e. phonocardiography, in this project. A blood pulse wave velocity (PWV) in human arterial tree is determined by analysing phonocardiographic (PCG) records. Two signals are needed at minimum for an estimation of the pulse wave velocity. All of these signals have to be measured simultaneously from different points on a

Martin Jelinek; J. Dobes; Lubomir PouSek; K. Hana

2003-01-01

30

Thin-film zero-group-velocity Lamb wave resonator  

NASA Astrophysics Data System (ADS)

A concept for the development of thin film micro-acoustic resonators is demonstrated. The basic principles for the design and fabrication of zero-group-velocity Lamb acoustic wave resonators on c-textured thin aluminum nitride films are presented. The experimental results demonstrate that the zero-group-velocity waves can be employed in high frequency resonators with small form factors.

Yantchev, Ventsislav; Arapan, Lilia; Katardjiev, Ilia; Plessky, Victor

2011-07-01

31

Crustal P and Pn Wave Velocity Perturbations Beneath Caucasus Region  

NASA Astrophysics Data System (ADS)

In presented study we invert crustal P and Pn velocities as well as Moho depth simultaneously applying the joint inversion method developed by Zhen et al. (2009). In this method all those three parameters are jointly inverted. It's using a spherical pseudo-bending ray tracing method and includes secondary Pg wave data at large distances. We applied the method to the Caucasus region and adjusted territories for reconstruction of the crust structure and uppermost mantle. New digital seismic network in Georgia was developed from 2003 and because of that we selected data from 2004 to 2010. Also we add data of past earthquakes from the time interval 1960-1990, with local magnitude more than 3.5. Before 1960 and during 1990-2004 seismic station coverage and hypocenter determination were very poor, so it was better not to use data from this time windows to avoid big errors in hypocenter locations. Final data set includes information about more than six thousand earthquakes. It includes Pg and Pn wave arrivals from the seismograms recorded by seismic stations of the regional seismic network of Georgia, Central Caucasus Local Network (installed in 2007), regional seismic networks of Turkey, Azerbaijan and Armenia. We applied the checkerboard resolution test to estimate the spatial resolution of the tomographic images. The results of the checkerboard test indicate that the initial model with passive and negative values is well reconstructed for all depths. The results of tomography show some significant features, well seen heterogeneities in upper crust, high and low Pn velocity zones. The depth of Moho discontinuity is relatively big in northern and southern part of Georgia, beneath the Greater and Smaller Caucasus, it has relatively large variations in this region. We can see the similar results in previous studies. Our tomography results in upper crust also show correlation among the velocity variations, seismicity, active faults and quaternary volcanic centers. At shallow depth are visible low velocity zones, which may be related to the thick sedimentary layer. The biggest depth of earthquakes in this region is about 40 kilometers, from our study is clearly shown that they are related with high velocity area at that depth.

Mumladze, T.; Wu, Y. M.

2012-04-01

32

Numeric implementation of wave-equation migration velocity analysis operators  

Microsoft Academic Search

Wave-equation migration velocity analysis (MVA) is a technique similar to wave- equation tomography because it is designed to update velocity models using infor- mation derived from full seismic wavefields. On the other hand, wave-equation MVA is similar to conventional, traveltime-based MVA because it derives the information used for model updates from properties of migrated images, e.g. focusing and moveout. The

Paul Sava; Ioan Vlad

2008-01-01

33

Group velocity of cylindrical guided waves in anisotropic laminate composites.  

PubMed

An explicit expression for the group velocity of wave packets, propagating in a laminate anisotropic composite plate in prescribed directions, is proposed. It is based on the cylindrical guided wave asymptotics derived from the path integral representation for wave fields generated in the composites by given localized sources. The expression derived is theoretically confirmed by the comparison with a known representation for the group velocity vector of a plane guided wave. Then it is experimentally validated against laser vibrometer measurements of guided wave packets generated by a piezoelectric wafer active sensor in a composite plate. PMID:24437754

Glushkov, Evgeny; Glushkova, Natalia; Eremin, Artem; Lammering, Rolf

2014-01-01

34

Blood pressure evaluation based on arterial pulse wave velocity  

Microsoft Academic Search

Pulse wave transit time assessment and peripheral pressure waveform analysis are being developed for noninvasive estimation of arterial blood pressure. In the present work we investigate the dependence of the pulse wave velocity from the aortic pressure by an appropriate mathematical model and by an ad hoc developed computerised acquisition system of blood pressure waveform and sphygmic wave during cath-lab

D. Franchi; R. Bedini; F. Manfredini; S. Berti; G. Palagi; S. Ghione; A. Ripoli

1996-01-01

35

Diffraction correction for precision surface acoustic wave velocity measurements  

E-print Network

Diffraction correction for precision surface acoustic wave velocity measurements Alberto Ruiz M is the diffraction of the surface acoustic wave SAW as it travels over the surface of the specimen. The results suggest that a diffraction correction may be introduced to increase the accuracy of surface wave

Nagy, Peter B.

36

The energy of waves in the photosphere and lower chromosphere. I. Velocity statistics  

NASA Astrophysics Data System (ADS)

Context: Acoustic waves are one of the primary suspects besides magnetic fields for the chromospheric heating process to temperatures above radiative equilibrium (RE). Aims: We derived the mechanical wave energy as seen in line-core velocities on disc centre to obtain a measure of mechanical energy flux with height for a comparison with the energy requirements in a semi-empirical atmosphere model, the Harvard-Smithsonian reference atmosphere (HSRA). Methods: We analyzed a 1-hour time series and a large-area map of Ca II H spectra on the traces of propagating waves. We analyzed the velocity statistics of several spectral lines in the wing of Ca II H, and the line-core velocity of Ca II H. We converted the velocity amplitudes into volume (? ? v^2) and mass energy densities (? v^2). For comparison, we used the increase of internal energy (? R ? ? T) necessary to lift a RE atmosphere to the HSRA temperature stratification. Results: We find that the velocity amplitude grows in agreement with linear wave theory and thus slower with height than predicted from energy conservation. The mechanical energy of the waves above around z ~ 500 km is insufficient to maintain on a long-term average the chromospheric temperature rise in the semi-empirical HSRA model. The intensity variations of the Ca line core (z ~ 1000 km) can, however, be traced back to the velocity variations of the lowermost forming spectral line considered (z ~ 250 km). Conclusions: The chromospheric intensity, and hence, (radiation) temperature variations are seen to be induced by passing waves originating in the photosphere. The wave energy is found to be insufficient to maintain the temperature stratification of the semi-empirical HSRA model above 500 km. We will in a following paper of this series investigate the energy contained in the intensity variations to see if the semi-empirical model is appropriate for the spectra.

Beck, C.; Khomenko, E.; Rezaei, R.; Collados, M.

2009-11-01

37

Implications of elastic wave velocities for Apollo 17 rock powders  

NASA Technical Reports Server (NTRS)

Ultrasonic P- and S-wave velocities of lunar rock powders 172701, 172161, 170051, and 175081 were measured at room temperature and to 2.5 kb confining pressure. The results compare well with those of terrestrial volcanic ash and powdered basalt. P-wave velocity values up to pressures corresponding to a lunar depth of 1.4 km preclude cold compaction alone as an explanation for the observed seismic velocity structure at the Apollo 17 site. Application of small amounts of heat with simultaneous application of pressure causes rock powders to achieve equivalence of seismic velocities for competent rocks.

Talwani, P.; Nur, A.; Kovach, R. L.

1974-01-01

38

Local variations of seismic velocity in the Imperial Valley, California  

SciTech Connect

The authors inverted local earthquake arrival times to estimate spatial variations of seismic velocity. Their model consisted of near-surface station corrections and local perturbations to a standard crustal velocity model. The authors found a zone of relatively high-velocity trending southeast from the Salton Sea. This zone corresponds to the region of thickest sediments. The authors compared results with those of teleseismic studies by Savino et al (1977). The agreement was excellent, suggesting that the teleseismic delays are caused primarily by crustal velocity variations. Residual delays between the teleseismic observations and predicted crustal delays imply crustal thinning of 3 or 4 km along the axis of the valley. Known geothermal resource areas at Salton Sea (or Obsidian Buttes), Brawley, and East Mesa, lie on the axis of a zone of thin crust, and they may be intimately related to the Brawley fault. Neither local earthquake nor teleseismic arrival times can discriminate between these hypotheses, but the issue might be resolved by combining both types of data. Known geothermal resource areas at Heber, Dunes, and Glamis, lie away from the projected trace of the Brawley fault. These areas are nearly aseismic, and overlie crust with apparent seismic velocities only mildly higher than the regional average. These apparent velocity anomalies could be related to crustal thinning, but because of the very mild Bouguer gravity anomalies in these areas, it seems more likely that the velocity anomalies occur entirely within the crust. 7 references, 6 figures, 3 tables.

Jackson, D.D.; Lee, W.B.

1981-12-01

39

Equipment for continuous measurements of pulse wave velocities  

Microsoft Academic Search

Equipment that measures continously ‘foot to foot’ time intervals between two peripheral arterial pulse waves is described.\\u000a To calculate the pulse wave velocity one has to know, besides this time interval, the distance between the sites of the proximal\\u000a and distal pulse wave transducers. The foot of the proximal and the distal pulse waves is detected by differantiation and\\u000a by

J. Weinman; D. Sapoznikov

1971-01-01

40

Rayleigh wave group velocity dispersion across Northern Africa, Southern Europe and the Middle East  

SciTech Connect

THis report presents preliminary results from a large scale study of surface wave group velocity dispersion throughout Northern Africa, the Mediterranean, Southern Europe and the Middle East. Our goal is to better define the 3D lithospheric shear-wave velocity 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 velocity 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 group velocity measurements since valuable measurements can be made without knowledge of the source. In order to obtain Rayleigh wave group velocity 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 group velocities 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 group velocity variation throughout the region. These results are preliminary, however, Rayleigh wave group velocity maps for a range of periods (10-95 sec) are presented and initial interpretations are discussed. Significant lateral group velocity variation is apparent at all periods. In general, shorted periods (10-45 sec) are sensitive to crustal structure as seen by the relatively low velocities associated with large sedimentary features (eastern Arabian shield, Persian Gulf, Eastern Mediterranean, Caspian Sea). At longer periods (50-95 sec), Rayleigh waves are most sensitive to topography on the Moho and upper mantle shear-wave velocity structure. This is observed in the group velocity maps as low velocities associated with features such as the Zagros Mountains, Iranian Plateau and the Red Sea. Analysis will eventually be expanded to include Love wave group and phase velocity. Knowledge of the lateral variation of group velocity and phase velocity will allow us to invert for shear velocity at each grid point. A detailed regionalization of shear-wave velocity will potentially lower the threshold for Ms determinations and improve event location capabilities throughout the region. Better Ms estimates and locations will improve our ability to reliably monitor the Comprehensive Test Ban Treaty (CTBT).

McNamara, D.E.; Walter, W.R.

1997-07-15

41

Calculating wave-generated bottom orbital velocities from surface-wave parameters  

USGS Publications Warehouse

Near-bed wave orbital velocities and shear stresses are important parameters in many sediment-transport and hydrodynamic models of the coastal ocean, estuaries, and lakes. Simple methods for estimating bottom orbital velocities from surface-wave statistics such as significant wave height and peak period often are inaccurate except in very shallow water. This paper briefly reviews approaches for estimating wave-generated bottom orbital velocities from near-bed velocity data, surface-wave spectra, and surface-wave parameters; MATLAB code for each approach is provided. Aspects of this problem have been discussed elsewhere. We add to this work by providing a method for using a general form of the parametric surface-wave spectrum to estimate bottom orbital velocity from significant wave height and peak period, investigating effects of spectral shape on bottom orbital velocity, comparing methods for calculating bottom orbital velocity against values determined from near-bed velocity measurements at two sites on the US east and west coasts, and considering the optimal representation of bottom orbital velocity for calculations of near-bed processes. Bottom orbital velocities calculated using near-bed velocity data, measured wave spectra, and parametric spectra for a site on the northern California shelf and one in the mid-Atlantic Bight compare quite well and are relatively insensitive to spectral shape except when bimodal waves are present with maximum energy at the higher-frequency peak. These conditions, which are most likely to occur at times when bottom orbital velocities are small, can be identified with our method as cases where the measured wave statistics are inconsistent with Donelan's modified form of the Joint North Sea Wave Project (JONSWAP) spectrum. We define the 'effective' forcing for wave-driven, near-bed processes as the product of the magnitude of forcing times its probability of occurrence, and conclude that different bottom orbital velocity statistics may be appropriate for different problems. ?? 2008 Elsevier Ltd.

Wiberg, P.L.; Sherwood, C.R.

2008-01-01

42

Anisotropic parameter estimation using velocity variation with offset analysis  

SciTech Connect

Seismic anisotropy is defined as velocity dependent upon angle or offset. Knowledge about anisotropy effect on seismic data is important in amplitude analysis, stacking process and time to depth conversion. Due to this anisotropic effect, reflector can not be flattened using single velocity based on hyperbolic moveout equation. Therefore, after normal moveout correction, there will still be residual moveout that relates to velocity information. This research aims to obtain anisotropic parameters, ? and ?, using two proposed methods. The first method is called velocity variation with offset (VVO) which is based on simplification of weak anisotropy equation. In VVO method, velocity at each offset is calculated and plotted to obtain vertical velocity and parameter ?. The second method is inversion method using linear approach where vertical velocity, ?, and ? is estimated simultaneously. Both methods are tested on synthetic models using ray-tracing forward modelling. Results show that ? value can be estimated appropriately using both methods. Meanwhile, inversion based method give better estimation for obtaining ? value. This study shows that estimation on anisotropic parameters rely on the accuracy of normal moveout velocity, residual moveout and offset to angle transformation.

Herawati, I.; Saladin, M.; Pranowo, W.; Winardhie, S.; Priyono, A. [Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung, 40132 (Indonesia)] [Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Jalan Ganesa 10, Bandung, 40132 (Indonesia)

2013-09-09

43

Variational Wave Functions for Frustrated Magnetic Models  

Microsoft Academic Search

\\u000a Variational wave functions containing electronic pairing and suppressed charge fluctuations (i.e., projected BCS states) have\\u000a been proposed as the paradigm for disordered magnetic systems (including spin liquids). Here, we discuss the general properties\\u000a of these states in one and two dimensions, and show that different quantum phases may be described with high accuracy by the\\u000a same class of variational wave

Federico Becca; Luca Capriotti; Alberto Parola; Sandro Sorella

2009-01-01

44

Common Genetic Variation in the 3-BCL11B Gene Desert Is Associated With Carotid-Femoral Pulse Wave Velocity and Excess Cardiovascular Disease Risk The AortaGen Consortium  

PubMed Central

Background Carotid-femoral pulse wave velocity (CFPWV) is a heritable measure of aortic stiffness that is strongly associated with increased risk for major cardiovascular disease events. Methods and Results We conducted a meta-analysis of genome-wide association data in 9 community-based European ancestry cohorts consisting of 20,634 participants. Results were replicated in 2 additional European ancestry cohorts involving 5,306 participants. Based on a preliminary analysis of 6 cohorts, we identified a locus on chromosome 14 in the 3?-BCL11B gene desert that is associated with CFPWV (rs7152623, minor allele frequency = 0.42, beta=?0.075±0.012 SD/allele, P = 2.8 x 10?10; replication beta=?0.086±0.020 SD/allele, P = 1.4 x 10?6). Combined results for rs7152623 from 11 cohorts gave beta=?0.076±0.010 SD/allele, P=3.1x10?15. The association persisted when adjusted for mean arterial pressure (beta=?0.060±0.009 SD/allele, P = 1.0 x 10?11). Results were consistent in younger (<55 years, 6 cohorts, N=13,914, beta=?0.081±0.014 SD/allele, P = 2.3 x 10?9) and older (9 cohorts, N=12,026, beta=?0.061±0.014 SD/allele, P=9.4x10?6) participants. In separate meta-analyses, the locus was associated with increased risk for coronary artery disease (hazard ratio [HR]=1.05, confidence interval [CI]=1.02 to 1.08, P=0.0013) and heart failure (HR=1.10, CI=1.03 to 1.16, P=0.004). Conclusions Common genetic variation in a locus in the BCL11B gene desert that is thought to harbor one or more gene enhancers is associated with higher CFPWV and increased risk for cardiovascular disease. Elucidation of the role this novel locus plays in aortic stiffness may facilitate development of therapeutic interventions that limit aortic stiffening and related cardiovascular disease events. PMID:22068335

Mitchell, Gary F.; Verwoert, Germaine C.; Tarasov, Kirill V.; Isaacs, Aaron; Smith, Albert V.; Yasmin; Rietzschel, Ernst R.; Tanaka, Toshiko; Liu, Yongmei; Parsa, Afshin; Najjar, Samer S.; O’Shaughnessy, Kevin M.; Sigurdsson, Sigurdur; De Buyzere, Marc L.; Larson, Martin G.; Sie, Mark P.S.; Andrews, Jeanette S.; Post, Wendy S.; Mattace-Raso, Francesco U.S.; McEniery, Carmel M.; Eiriksdottir, Gudny; Segers, Patrick; Vasan, Ramachandran S.; van Rijn, Marie Josee E.; Howard, Timothy D.; McArdle, Patrick F.; Dehghan, Abbas; Jewell, Elizabeth; Newhouse, Stephen J.; Bekaert, Sofie; Hamburg, Naomi M.; Newman, Anne B.; Hofman, Albert; Scuteri, Angelo; De Bacquer, Dirk; Ikram, Mohammad Arfan; Psaty, Bruce; Fuchsberger, Christian; Olden, Matthias; Wain, Louise V.; Elliott, Paul; Smith, Nicholas L.; Felix, Janine F.; Erdmann, Jeanette; Vita, Joseph A.; Sutton-Tyrrell, Kim; Sijbrands, Eric J.G.; Sanna, Serena; Launer, Lenore J.; De Meyer, Tim; Johnson, Andrew D.; Schut, Anna F.C.; Herrington, David M.; Rivadeneira, Fernando; Uda, Manuela; Wilkinson, Ian B.; Aspelund, Thor; Gillebert, Thierry C.; Van Bortel, Luc; Benjamin, Emelia J.; Oostra, Ben A.; Ding, Jingzhong; Gibson, Quince; Uitterlinden, André G.; Abecasis, Gonçalo R.; Cockcroft, John R.; Gudnason, Vilmundur; De Backer, Guy G.; Ferrucci, Luigi; Harris, Tamara B.; Shuldiner, Alan R.; van Duijn, Cornelia M.; Levy, Daniel; Lakatta, Edward G.; Witteman, Jacqueline C.M.

2012-01-01

45

The continuous measurement of arterial pulse wave velocity  

Microsoft Academic Search

It has long been known that arterial pulse wave velocity (PWV) depends on arterial extensibility. Since extensibility is a\\u000a function of arterial pressure, as well as of various pathological states, the measurement of PWV provides a promising approach\\u000a to the indirect monitoring of the cardiovascular system. The present paper describes a Pulse Wave Velocity Computer designed\\u000a to measure and record

Gershon Weltman; George Sullivan; Dale Bredon

1964-01-01

46

Pressure wave vs. tracer velocities through unsaturated fractured rock  

NASA Astrophysics Data System (ADS)

Rapid fluid pressure changes in unsaturated media due to perturbations at or near the earth-atmosphere interface are commonly attributed to preferential or bypass flow. An alternative mechanism for the rapid propagation of pressure perturbations in unsaturated media is the kinematic response, which results from the nonlinear relationship between unsaturated hydraulic conductivity and water content. The relationship between pressure wave velocities and fluid velocities is described using kinematic wave theory, presented for the Brooks—Corey and van Genuchten—Mualem formulations. The kinematic mechanism predicts fluid pressure pulse velocities to be substantially faster than unsaturated fractured rock tracer velocities for both formulations. A hydraulic form of the advection-diffusion equation based on Richards' Equation is presented that uses the hydraulic diffusivity and kinematic velocity to predict the hydraulic response in unsaturated fractured rock to pressure head perturbations. Pressure pulse velocity monitoring may be an additional tool for estimating unsaturated hydraulic properties in low permeability media.

Rasmussen, Todd C.

47

Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet  

NASA Technical Reports Server (NTRS)

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5 S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and accelerations over distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of approx 140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7 N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n = 75 to 100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7 +/- 0.7-day period. This oscillating motion has a wavelength of approx 20 and a speed of 101 +/- 3 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of mUltiple wave modes, the difference in dominant cloud appearance between 7 deg N and 7.5 deg S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

Simon-Miller, Amy A.; Choi, David; Rogers, John H.; Gierasch, Peter J.; Allison, Michael D.; Adamoli, Gianluigi; Mettig, Hans-Joerg

2012-01-01

48

Detection of periodic variations in vertical velocities of Galactic masers  

E-print Network

We have collected literature data on Galactic masers with trigonometric parallaxes measured by means of VLBI. We have obtained series of residual tangential, \\Delta V_{circ}, and radial, \\Delta V_R, velocities for 107 masers. Based on these series, we have re-determined parameters of the Galactic spiral density wave using the method of spectral (periodogram) analysis. The tangential and radial perturbation amplitudes are f_\\theta=6.0+/-2.6 km/s and f_R=7.2+/-2.2 km/s, respectively; the perturbation wavelengths are \\lambda_\\theta=3.2+/-0.5 kpc and \\lambda_R=3.0+/-0.6 kpc for a four-armed spiral model, m=4. The phase of the Sun \\chi_0 in the spiral density wave is -79^\\circ+/-14^\\circ and -199^\\circ+/-16^\\circ from the residual tangential and radial velocities, respectively. The most interesting result of this work is detecting a wave in vertical spatial velocities W versus distance R from the Galactic rotation axis. From the spectral analysis, we have found the following characteristics of this wave: the pertu...

Bobylev, V V

2014-01-01

49

Correlation Analysis in a Pulse Wave Velocity Evaluation  

Microsoft Academic Search

In this paper, methods for a time delay evalu- ation of phonocardiographic (PCG) signals are presented to estimate a pulse wave velocity (PWV) in a cardiovascu- lar system of a human body, especially in arterial segments of an arterial tree selected. A measuring method used for the pulse wave registration is fully non-invasive. Electronic phonendoscopes - pressure\\/acoustic converters - were

Martin JELÍNEK; Josef DOBEŠ

50

Upper crustal compressional wave velocity in the Garhwal Himalaya  

NASA Astrophysics Data System (ADS)

A value of 5.2 km/s is obtained for compressional wave velocity in the upper crust in the vicinity of the Main Central Thrust where it crosses the Yamuna and Bhagirathi valleys in the Garhwal Himalaya. The data used consisted of the arrival times of compressional waves; recorded at five portable stations from nine earthquakes occurring in the region.

Chander, Ramesh; Sarkar, I.; Khattri, K. N.; Gaur, V. K.

1986-04-01

51

Estimation of near-surface shear-wave velocity by inversion of Rayleigh waves  

USGS Publications Warehouse

The shear-wave (S-wave) velocity of near-surface materials (soil, rocks, pavement) and its effect on seismic-wave propagation are of fundamental interest in many groundwater, engineering, and environmental studies. Rayleigh-wave phase velocity of a layered-earth model is a function of frequency and four groups of earth properties: P-wave velocity, S-wave velocity, density, and thickness of layers. Analysis of the Jacobian matrix provides a measure of dispersion-curve sensitivity to earth properties. S-wave velocities are the dominant influence on a dispersion curve in a high-frequency range (>5 Hz) followed by layer thickness. An iterative solution technique to the weighted equation proved very effective in the high-frequency range when using the Levenberg-Marquardt and singular-value decomposition techniques. Convergence of the weighted solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Synthetic examples demonstrated calculation efficiency and stability of inverse procedures. We verify our method using borehole S-wave velocity measurements.Iterative solutions to the weighted equation by the Levenberg-Marquardt and singular-value decomposition techniques are derived to estimate near-surface shear-wave velocity. Synthetic and real examples demonstrate the calculation efficiency and stability of the inverse procedure. The inverse results of the real example are verified by borehole S-wave velocity measurements.

Xia, J.; Miller, R.D.; Park, C.B.

1999-01-01

52

Minimizers with discontinuous velocities for the electromagnetic variational method  

SciTech Connect

The electromagnetic two-body problem has neutral differential delay equations of motion that, for generic boundary data, can have solutions with discontinuous derivatives. If one wants to use these neutral differential delay equations with arbitrary boundary data, solutions with discontinuous derivatives must be expected and allowed. Surprisingly, Wheeler-Feynman electrodynamics has a boundary value variational method for which minimizer trajectories with discontinuous derivatives are also expected, as we show here. The variational method defines continuous trajectories with piecewise defined velocities and accelerations, and electromagnetic fields defined by the Euler-Lagrange equations on trajectory points. Here we use the piecewise defined minimizers with the Lienard-Wierchert formulas to define generalized electromagnetic fields almost everywhere (but on sets of points of zero measure where the advanced/retarded velocities and/or accelerations are discontinuous). Along with this generalization we formulate the generalized absorber hypothesis that the far fields vanish asymptotically almost everywhere and show that localized orbits with far fields vanishing almost everywhere must have discontinuous velocities on sewing chains of breaking points. We give the general solution for localized orbits with vanishing far fields by solving a (linear) neutral differential delay equation for these far fields. We discuss the physics of orbits with discontinuous derivatives stressing the differences to the variational methods of classical mechanics and the existence of a spinorial four-current associated with the generalized variational electrodynamics.

De Luca, Jayme [Departamento de Fisica Rodovia Washington Luis, Universidade Federal de Sao Carlos, km 235 Caixa Postal 676, Sao Carlos, Sao Paulo 13565-905, SP (Brazil)

2010-08-15

53

Lithology and shear-wave velocity in Memphis, Tennessee  

USGS Publications Warehouse

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

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

2003-01-01

54

Linking sperm length and velocity: the importance of intramale variation  

PubMed Central

Selection imposed through sperm competition is commonly thought to promote the evolution of longer sperm, since sperm length is assumed to be positively associated with sperm swimming velocity. Yet, the basis for this assumption remains controversial, and there is surprisingly little intraspecific evidence demonstrating such a link between sperm form and function. Here, we show that sperm length and velocity are highly correlated in the sea urchin Heliocidaris erythrogramma, but importantly we report that failure to account for within-male variation in these sperm traits can obscure this relationship. These findings, in conjunction with the mounting evidence for extremely high levels of intra-specific variance in sperm traits, suggest that a functional link between sperm morphology and velocity may be more prevalent than what current evidence suggests. Our findings also suggest that selection for faster swimming sperm may promote the evolution of longer sperm, thereby supporting recent findings from macroevolutionary studies. PMID:20484233

Fitzpatrick, John L.; Garcia-Gonzalez, Francisco; Evans, Jonathan P.

2010-01-01

55

Uppermost mantle P wave velocities beneath Turkey and Iran  

SciTech Connect

The uppermost mantle P wave velocities beneath Turkey and Iran were estimated by applying the conventional travel time-distance relation method to arrival times of well located earthquakes recorded at a few stations. The average uppermost mantle P wave velocity under Turkey is estimated from two stations of the World Wide Standardized Seismograph Network (WWSSN), Istanbul and Tabriz. The data are consistent with a crust of uniform, but poorly determined, thickness and an uppermost mantle P wave velocity of 7.73 +- 0.08 km/s. This velocity is very similar to that for the Aegean Sea and suggests that its structure could be closely related to that beneath Turkey. For Iran, the results calculated from travel times to three WWSSN stations, Meshed, Shiraz, and Tabriz, can be explained by a crust dipping toward the south-southeast at about 1/sup 0/ with an uppermost mantle P wave velocity of 8.0 +- 0.1 km/s. If the crustal thickness were 34 km in the north it would reach about 49 km in the south. Based on these uppermost mantle velocities, the temperature at Moho beneath Turkey is probably close to the melting temperature of peridotite but that beneath Iran is probably lower.

Chen, C.; Chen, W.; Molnar, P.

1980-01-01

56

Constraints on shear velocity in the cratonic upper mantle from Rayleigh wave phase velocity  

NASA Astrophysics Data System (ADS)

The standard model of the thermal and chemical structure of cratons has been scrutinized in recent years as additional data have been collected. Recent seismological and petrological studies indicate that the notion of cratonic lithosphere as a thick thermal boundary layer with a very depleted and dehydrated composition may be too simplistic and does not fully explain all aspects of the seismological and petrological observations. We hypothesized that the cratonic lithosphere may be more complicated and designed an experiment to investigate its thermal, chemical, and mineralogical properties using a global database of fundamental mode Rayleigh surface waves. To test this hypothesis, the phase velocities of Rayleigh wave that travel paths primarily over cratons were selected. A 1-D global craton phase velocity profile was generated from these observations and compared to predicted phase-velocity curves using two different forward modeling techniques. With the first approach, profiles of shear velocity were generated based on educated guesses of upper mantle temperatures using geotherms. With the second approach, profiles of shear velocity were generated using random permutations about 1-D global model STW105. In total 5,625 geotherm and 80,000 random 1-D forward models were generated for comparison. Each shear velocity model was converted to phase velocity and compared to the observed range of cratonic phase velocities, defined as within one standard deviation of the mean. This method was able to constrain shear velocity in cratons relatively well though the 1-D profiles deviate at depths shallower than 100 km. Shear velocity is faster than PREM/STW105 to depths greater than 200 km with constantly increasing velocity with depth in the random model and a low velocity layer at 100-150 km.

Hirsch, Aaron C.

57

Dip-movement processing for depth-variable velocity. [Correction for variation of velocity with depth  

SciTech Connect

Dip-moveout correction (DMO) has become commonplace in the seismic processing flow. The goal of DMO processing is to transform the NMO-corrected data to zero-offset, so that the application of zero-offset (poststack) migration is equivalent to full prestack migration of the recorded data. Nearly all DMO implementations assume that the seismic velocity is constant. Usually, this is an acceptable tradeoff because of the tremendous cost savings of DMO and poststack migration versus prestack migration. Where the velocity changes rapidly with depth, however, this constant velocity theory can yield inadequate results. For many areas, such as the Gulf Coast, a velocity function that varies with depth is a reasonable approximation to the true velocity field. Using ray tracing, I find the raypaths from the source and receiver to the reflection point with the given recording time. The time along the corresponding zero-offset ray gives the DMO correction. The relationships between the three rays are expressed by a system of nonlinear equations. By simultaneously solving the equations via Newton-Raphson iteration, I determine the mapping that transforms nonzero-offset data to zero-offset. Unlike previous schemes that approximately handle vertical velocity variation, this method makes no assumptions about the offset, dip, or hyperbolic moveout.

Artley, C.T.

1992-12-01

58

Local earthquake travel times and spatial variations of crustal velocity in southern California  

NASA Astrophysics Data System (ADS)

Measurements of P-wave arrival times from local earthquakes contain information about differences in crustal velocity within a region. Using 32,000 arrival times recorded by a seismic array in southern California, these spatial variations in velocity were estimated. A statistical model of the behavior of travel time residuals derived from a laterally homogeneous velocity model accounts for the major sources of error in the recording and hypocenter location processes, and leads to a set of editing procedures to remove aberrant data. Edited data were inverted under a variety of assumptions to estimate a laterally varying veocity model using a variation on a method originally developed for teleseismic data. The improvement in the residuals due to the new velocity models is statistically significant. The inversion method appears to underestimate the size of the velocity contrasts, but the results are generally consistent with those obtained using other types of data. A major result is that the Peninsular Ranges have substantially higher average velocity than nearby regions, probably due to differences in crustal tickness and composition.

Ergas, R. A.

59

The Effect of Area Variation on Wave Rotor Elements  

NASA Technical Reports Server (NTRS)

The effect of varying the cross-sectional flow area of the passages of a wave rotor is examined by means of the method of characteristics. An idealized expansion wave, an idealized inlet port, and an idealized compression stage are considered. It is found that area variation does not have a very significant effect on the expansion wave, nor on the compression stage. For the expansion wave, increasing the passage area in the flow direction has the same effect as a diffuser, so that the flow emerges at a lower velocity than it would for the constant area case. This could be advantageous. The inlet is strongly affected by the area variation, as it changes the strength of the hammer shock wave, thereby changing the pressure behind it. In this case, reduction in the passage area in the flow direction leads to increased pressure. However, this result is dependent on the assumption that the inlet conditions remain constant with area variation. This may not be the case.

Wilson, Jack

1997-01-01

60

Optimization of wave phase velocity in oscillators of orotron type  

NASA Astrophysics Data System (ADS)

Smooth functions of desynchronization between the inital electron-beam velocity in an orotron and the variable phase velocity of the synchronous wave are found numerically. This approach leads to maximization of the quality functional which includes both the electronic efficiency and the self-excitation condition. In addition, an auxiliary functional is introduced which accounts for the standard deviation of the derivative of the desynchronization with respect to the interaction space.

Tarasov, M. M.; Tret'iakov, O. A.; Shmat'ko, A. A.

1987-06-01

61

Reconfigurable Wave Velocity Transmission Lines for Phased Arrays  

NASA Technical Reports Server (NTRS)

Phased array antennas showcase many advantages over mechanically steered systems. However, they are also more complex, heavy and most importantly costly. This presentation paper presents a concept which overcomes these detrimental attributes by eliminating all of the phase array backend (including phase shifters). Instead, a wave velocity reconfigurable transmission line is used in a series fed array arrangement to allow phase shifting with one small (100mil) mechanical motion. Different configurations of the reconfigurable wave velocity transmission line are discussed and simulated and experimental results are presented.

Host, Nick; Chen, Chi-Chih; Volakis, John L.; Miranda, Felix

2013-01-01

62

An inexpensive instrument for measuring wave exposure and water velocity  

USGS Publications Warehouse

Ocean waves drive a wide variety of nearshore physical processes, structuring entire ecosystems through their direct and indirect effects on the settlement, behavior, and survivorship of marine organisms. However, wave exposure remains difficult and expensive to measure. Here, we report on an inexpensive and easily constructed instrument for measuring wave-induced water velocities. The underwater relative swell kinetics instrument (URSKI) is a subsurface float tethered by a short (<1 m) line to the seafloor. Contained within the float is an accelerometer that records the tilt of the float in response to passing waves. During two field trials totaling 358 h, we confirmed the accuracy and precision of URSKI measurements through comparison to velocities measured by an in situ acoustic Doppler velocimeter and those predicted by a standard swell model, and we evaluated how the dimensions of the devices, its buoyancy, and sampling frequency can be modified for use in a variety of environments.

Figurski, J.D.; Malone, D.; Lacy, J.R.; Denny, M.

2011-01-01

63

Estimating Pulse Wave Velocity using Mobile Phone Sensors  

Microsoft Academic Search

Pulse wave velocity has been recognised as an important physiological phenomenon in the human body, and its measurement can aid in the diagnosis and treatment of chronic diseases. It is the gold standard for arterial stiffness measurements, and it also shares a positive relationship with blood pressure and heart rate. There exist several methods and devices via which it can

Rohan Anchan

2011-01-01

64

The Velocity of Radio Waves over Short Paths  

Microsoft Academic Search

The velocity of radio waves was measured directly in the following manner. Two radio stations were set up on frequencies of 3492.5 and 2398 kilocycles, respectively. One station was fixed while the other was portable. The fixed station sent out pulses which were received at the portable station. A thyratron control set off return pulses which came back to the

R. C. Colwell; H. Atwood; J. E. Bailey; C. O. Marsh

1942-01-01

65

Quasi-periodic variations in Doppler velocities of H ? spicules  

NASA Astrophysics Data System (ADS)

New series of CCD spectral observations of spicules were obtained using 53-cm Lyot coronagraph of Abastumani Astrophysical Observatory (Georgia) at 5500 km height above the solar limb on October 17, 2012 in H ? spectral line. The line-of-sight Doppler velocities of 34 spicules were measured with the cadence of 4.5 s and standard error equal to ±0.3 km/s. Life times of almost all measured spicules were 5-6 min (and longer), therefore they resemble the type I spicules. No short lived structures (similar to type II spicules) were identified during the time series neither inside nor outside the observed spicules. The Doppler velocity time series were processed using Lomb Periodogram Algorithm revealing 4 types of dominating period intervals centered around: 254 s, 136 s, 94 s and 65 s having confidence levels over 95 %. The oscillations with periods around 254 s can be caused by quasi-periodic rebound shocks after the propagation of photospheric pulses. The oscillations with periods around 136 s can be caused by the oscillation of spicules axis at the kink cut-off frequency in gravitationally stratified magnetic tubes. In this case, seismological estimations give the density scale height as 380-540 km for the kink wave speed of 70-100 km/s in spicules. Shorter period oscillations are probably caused by propagating kink waves in spicules.

Khutshishvili, E.; Kulidzanishvili, V.; Kvernadze, T.; Zaqarashvili, T. V.; Kakhiani, V.; Khutsishvili, D.; Sikharulidze, M.

2014-12-01

66

Hydrodynamic forces and surface topography: Centimeter-scale spatial variation in wave forces  

E-print Network

Hydrodynamic forces and surface topography: Centimeter-scale spatial variation in wave forces forces. The intertidal zone of wave-swept rocky shores is one of the most physically stressful (Denny et al. 2003). The high water velocities in the intertidal zone can impose large hydrody- namic

Denny, Mark

67

Lithospheric structure beneath the East China Sea revealed by Rayleigh-wave phase velocities  

NASA Astrophysics Data System (ADS)

We explore the variations of Rayleigh-wave phase-velocity beneath the East China Sea in a broad period range (5-200 s). Rayleigh-wave dispersion curves are measured by the two-station technique for a total of 373 interstation paths using vertical-component broad-band waveforms at 32 seismic stations around the East China Sea from 6891 global earthquakes. The resulting maps of Rayleigh-wave phase velocity and azimuthal anisotropy provide a high resolution model of the lithospheric mantle beneath the East China Sea. The model exhibits four regions with different isotropic and anisotropic patterns: the Bohai Sea, belonging to the North China Craton, displays a continental signature with fast velocities at short periods; the Yellow Sea, very stable unit associated with low deformation, exhibits fast velocities and limited anisotropy; the southern part of the East China Sea, with high deformation and many fractures and faults, is related to slow velocities and high anisotropic signature; and the Ryukyu Trench shows high-velocity perturbations and slab parallel anisotropy.

Legendre, C. P.; Chen, Q.-F.; Zhao, L.

2014-12-01

68

Crustal shear-wave velocity structure beneath northeast India from teleseismic receiver function analysis  

NASA Astrophysics Data System (ADS)

We investigated the seismic shear-wave velocity structure of the crust beneath nine broadband seismological stations of the Shillong-Mikir plateau and its adjoining region using teleseismic P-wave receiver function analysis. The inverted shear wave velocity models show ?34-38 km thick crust beneath the Shillong Plateau which increases to ?37-38 km beneath the Brahmaputra valley and ?46-48 km beneath the Himalayan foredeep region. The gradual increase of crustal thickness from the Shillong Plateau to Himalayan foredeep region is consistent with the underthrusting of Indian Plate beyond the surface collision boundary. A strong azimuthal variation is observed beneath SHL station. The modeling of receiver functions of teleseismic earthquakes arriving the SHL station from NE backazimuth (BAZ) shows a high velocity zone within depth range 2-8 km along with a low velocity zone within ?8-13 km. In contrast, inversion of receiver functions from SE BAZ shows high velocity zone in the upper crust within depth range ?10-18 km and low velocity zone within ?18-36 km. The critical examination of ray piercing points at the depth of Moho shows that the rays from SE BAZ pierce mostly the southeast part of the plateau near Dauki fault zone. This observation suggests the effect of underthrusting Bengal sediments and the underlying oceanic crust in the south of the plateau facilitated by the EW-NE striking Dauki fault dipping 300 toward northwest.

Bora, Dipok K.; Hazarika, Devajit; Borah, Kajaljyoti; Rai, S. S.; Baruah, Saurabh

2014-08-01

69

Shear Wave Velocity Imaging Using Transient Electrode Perturbation: Phantom and ex vivo Validation  

PubMed Central

This paper presents a new shear wave velocity imaging technique to monitor radio-frequency and microwave ablation procedures, coined electrode vibration elastography. A piezoelectric actuator attached to an ablation needle is transiently vibrated to generate shear waves that are tracked at high frame rates. The time-to-peak algorithm is used to reconstruct the shear wave velocity and thereby the shear modulus variations. The feasibility of electrode vibration elastography is demonstrated using finite element models and ultrasound simulations, tissue-mimicking phantoms simulating fully (phantom 1) and partially ablated (phantom 2) regions, and an ex vivo bovine liver ablation experiment. In phantom experiments, good boundary delineation was observed. Shear wave velocity estimates were within 7% of mechanical measurements in phantom 1 and within 17% in phantom 2. Good boundary delineation was also demonstrated in the ex vivo experiment. The shear wave velocity estimates inside the ablated region were higher than mechanical testing estimates, but estimates in the untreated tissue were within 20% of mechanical measurements. A comparison of electrode vibration elastography and electrode displacement elastography showed the complementary information that they can provide. Electrode vibration elastography shows promise as an imaging modality that provides ablation boundary delineation and quantitative information during ablation procedures. PMID:21075719

Varghese, Tomy; Madsen, Ernest L.

2011-01-01

70

P, S wave velocity model of the crust and upper most mantle of Albania region  

NASA Astrophysics Data System (ADS)

This paper describes the one-dimensional (1D) velocity model computed by VELEST in the SEISAN seismic analysis system, inverting re-picked P-wave and S-wave arrival times recorded during 2002-2006 by the Albanian, Montenegro, Thessalonica and Macedonia seismic networks. The re-picked data yield P-wave and S-wave velocities proved to be more suitable compared to bulletin data for this detailed inversion study. Seismic phases recorded by the Albania seismic network and integrated with data from the Montenegro, Thessalonica and Macedonia networks are used to prepare the Albanian seismic bulletin. Earthquake hypocenters from the Albanian bulletins have also location errors that are negligible for civil protection purposes, large scale seismotectonic analyses and more accurate hypocentral determinations which are necessary for detailed seismotectonic and geodynamic studies. It was noted that the smoothness of the velocity variation increased with depth. A velocity of 5.5 km/s was calculated for the upper crust, 6.1 km/s was calculated for the middle crust and 6.9 km/s was computed for the lower crust. P wave velocity was 7.85 km/s at depth of 50 km and for the upper mantle it is 8.28 km/s. Using the improved velocity model, the earthquakes which occurred in Albania in the past 5 years were able to be relocated, achieving constrained hypocentral determinations for events in Albania. The interpretation of the 1 D velocity models infers interesting features of the deep structure of Albania. These results represent an important step towards more detailed seismotectonic analyses.

Ormeni, Rrapo

2011-01-01

71

Automatic measurements of surface wave phase velocities and body wave travel times: New data for new seismic reference Earth models  

NASA Astrophysics Data System (ADS)

In the past several years we have systematically analysed long-period seismograms for the study of large-scale P and S velocity variations in the mantle [J. Ritsema, H.J. van Heijst, and J. H. Woodhouse, Science, 286, 1925--1928, 1999; J. Ritsema and H.J. van Heijst, Geophysical Journal International, submitted, 2001]. This new data set consists of 250,000 travel times and more than 2 million phase velocities. It is several orders of magnitude larger than seismic data sets available two decades ago due to the expansion of digital seismic networks. When combined with data from other research groups (e.g., free-oscillation splitting measurements), it will enable the construction of better constrained reference 1-D and 3-D Earth models. In our presentation we demonstrate that reliable surface-wave phase-velocity and body-wave travel-time measurements can be obtained with automatic procedures by systematic presentation of phase velocity maps and the spatial characteristics of differential travel times. We point out characteristics of the Preliminary Reference Earth model (e.g., 220-km discontinuity, upper mantle P velocity structure) that are inconsistent with our data. Furthermore, we compare our 3-D models of S and P velocity (obtained by joint inversion) with models from other groups to indicate robust features in global seismic models.

Ritsema, J.; van Heijst, H.

2001-05-01

72

Rayleigh Wave Phase Velocity Maps in South-central Mongolia  

NASA Astrophysics Data System (ADS)

Mongolia orogenic is located between the Siberian platform, Sino-Korean platform and Tarim platform, and thousands of kilometers away from the Indian-Asian continental collision front. Geological structure in this area is influenced by the complicated orogeny. Active tectonics is marked by the progressive transition from south to north. We collected the vertical component data recorded by 69 broadband seismic stations deployed in the south-central Mongolia from August 2011 to July 2013. By using the frequency-time analysis of wavelet transformation method, we extracted the inter-station phase velocity dispersion curves of fundamental Rayleigh wave and then constructed the phase velocity maps at periods from 12s to 70s. At shorter periods (e.g. 12s), the results show that the phase velocity distributions are well correlated with the large crustal structural domains, with low phase velocities in the gobi basin, while high phase velocities in the mountainous areas. The distributions at middle periods (e.g. 30s) show that low phase velocities are located in the central region and high phase velocities in the southeast and north, which corresponds well with the crustal thickness. The maps at long periods (e.g. 50s, 60s), reveal that a obvious low velocity zone at 106°N, which may indicate the high temperatures and be related with mantle upwelling. In contrast, the southeast region still shows high velocity. This suggests that the shear velocity structure in our study area may be not as simple as previously thought. This study was supported by the international cooperation project of the Ministry of Science and Technology of China (2011DFB20120).

Yu, D.; Wu, Q.; Gao, M.; Munkhuu, U.; Demberel, S. G.

2013-12-01

73

Adaptive blood pressure estimation from wearable PPG sensors using peripheral artery pulse wave velocity measurements and multi-channel blind identification of local arterial dynamics  

Microsoft Academic Search

A method for estimating pulse wave velocity (PWV) using circulatory waveform signals derived from multiple photoplethysmograph (PPG) sensors is described. The method employs two wearable in-line PPG sensors placed at a known distance from one another at the ulnar and digital artery. A technique for calibrating the measured pulse wave velocity to arterial blood pressure using hydrostatic pressure variation is

Devin B. McCombie; Andrew T. Reisner; H. Harry Asada

2006-01-01

74

Measurements of parallel electron velocity distributions using whistler wave absorption  

SciTech Connect

We describe a diagnostic to measure the parallel electron velocity distribution in a magnetized plasma that is overdense ({omega}{sub pe} > {omega}{sub ce}). This technique utilizes resonant absorption of whistler waves by electrons with velocities parallel to a background magnetic field. The whistler waves were launched and received by a pair of dipole antennas immersed in a cylindrical discharge plasma at two positions along an axial background magnetic field. The whistler wave frequency was swept from somewhat below and up to the electron cyclotron frequency {omega}{sub ce}. As the frequency was swept, the wave was resonantly absorbed by the part of the electron phase space density which was Doppler shifted into resonance according to the relation {omega}-k{sub ||v||} = {omega}{sub ce}. The measured absorption is directly related to the reduced parallel electron distribution function integrated along the wave trajectory. The background theory and initial results from this diagnostic are presented here. Though this diagnostic is best suited to detect tail populations of the parallel electron distribution function, these first results show that this diagnostic is also rather successful in measuring the bulk plasma density and temperature both during the plasma discharge and into the afterglow.

Thuecks, D. J.; Skiff, F.; Kletzing, C. A. [Department of Physics and Astronomy, University of Iowa, 203 Van Allen Hall, Iowa City, Iowa 52242 (United States)

2012-08-15

75

Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations  

NASA Technical Reports Server (NTRS)

Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering

Vinas, A.F.; Gurgiolo, C.; Nieves-Chinchilla, T.; Gary, S. P.; Goldstein, M. L.

2010-01-01

76

Measurement of Pulse Wave Velocity Using Pulse Wave Doppler Ultrasound: Comparison with Arterial Tonometry  

Microsoft Academic Search

Pulse wave velocity (PWV), the speed of propagation of arterial pressure waves through the arterial tree, is related to arterial stiffness and is an important prognostic marker for cardiovascular events. In clinical practice PWV is commonly determined by arterial tonometry, with a noninvasive pressure sensor applied sequentially over carotid and femoral arteries. The electrocardiogram (ECG) is used as a timing

Benyu Jiang; Baoming Liu; Karen L. McNeill; Philip J. Chowienczyk

2008-01-01

77

P wave velocity structure beneath Greenland using teleseismic events  

NASA Astrophysics Data System (ADS)

A three-dimensional P-wave velocity model was inverted with 3032 ray paths from 416 events observed on the GLISN network from 2009 to 2013. The relative travel times were computed with respect to the IASP91 global reference model using the multi-channel cross correlation method (MCCC) by VanDecar and Crosson {, 1990 #1}. Our model space was parameterized laterally with 1°×1° from 55°N to 85°N in latitude and from 20°W to 80°W in longitude. This high latitude model space causes spatial distortion in the model parameters on the spherical coordinate for the teleseismic body wave tomography. To minimize a distortion in the model parameters the spherical coordinate system was rotated as the referent stations SUMG and SCO, located on the middle of Greenland, to equator, and all stations and seismic events were converted to this new coordinate system. All ray paths were computed by a three dimensional ray tracing algorithm developed with pseudobending technique and Snell's law {Zhao, 1992 #1}, and travel times were corrected by ice and crustal thicknesses for each observed station as well. Our inverted model shows a broad low velocity anomaly ( -1.5%) in the mid-eastern parts of Greenland, which is connected to the low velocity anomaly beneath Iceland. Another low velocity anomaly was observed below 300km in the middle of Greenland where the Icelandic mantle plume was located in 60Ma. P wave velocity anomaly depth slices from 150 km to 400 km on the rotated coordinate from the center of Green land to the equator.

Park, Y.; Lee, W.; Yoo, H.

2013-12-01

78

Photospheric Logarithmic Velocity Spirals as MHD Wave Generation Mechanisms  

E-print Network

High-resolution observations of the solar photosphere have identified a wide variety of spiralling motions in the plasma. These spirals vary in properties, but are observed to be abundant on the solar surface. In this work these spirals are studied for their potential as magnetohydrodynamic (MHD) wave generation mechanisms. The inter-granular lanes, where these spirals are commonly observed, are also regions where the magnetic field strength is higher than average. This combination of magnetic field and spiralling plasma is a recipe for the generation of Alfv\\'en waves and other MHD waves. This work employs numerical simulations of a self-similar magnetic flux tube embedded in a realistic, gravitationally stratified, solar atmosphere to study the effects of a single magnetic flux tube perturbed by a logarithmic velocity spiral driver. The expansion factor of the logarithmic spiral driver is varied, multiple simulations are run for a range of values of the expansion factor centred around observational data. Th...

Mumford, S J

2015-01-01

79

Shallow S-wave Velocity Structure Based on the ZH Ratio Method Around Los Angeles Basin  

NASA Astrophysics Data System (ADS)

In order to predict seismic ground motion, elucidation of site conditions such as Vs30 is absolutely important. However, in order to predict long-period ground motions (~ 0.1 Hz), the depth range must be extended from 30 m to a much deeper depth, possibly to 5-10 km, as wavelength of seismic waves become long and those waves become sensitive to deeper regions. We developed a method that uses Rayleigh-wave ellipticity data, estimated from seismic noise (the ZH method), to derive shallow S-wave structure (< 10 km in depth) in the Los Angeles area, using broadband data (about 150 stations) recorded at local dense SCSN network. Using two years (2002 and 2003) of continuous data, we tested feasibility of an approach that analyzes low-frequency microseisms about 0.1-0.3 Hz. There is abundant evidence that such low-frequency microseisms are dominated by Rayleigh waves. Depth sensitivity of phase and group velocities of Rayleigh waves can reach almost 20 km for this frequency range, but the ZH ratios' sensitivity is confined to approximately half of those depth ranges (10 km). With the ZH ratios, we thus have a clean data set to derive shallow S-wave structure for the upper 10 km of the Earth. In fact, we observe systematic geographic variations in the ZH ratios between the LA basin and outside of this basin. Application to the urban Los Angeles region indicates that systematic perturbations in S-wave velocity structure are required up to about 50% of the reference velocity model for the region (the SCEC Community Velocity Models) in order to explain our measured ZH ratio values. Patterns of surface ground motion by large earthquakes in the region may dramatically differ from previous ground-motion predictions because of these changes in shallow S-wave velocity structure. We will present the systematic difference of ZH ratio measurements depending on the different area and S-wave structure due to the inversion using ZH ratio measurements.

Hakamata, T.; Yano, T. E.; Tanimoto, T.

2011-12-01

80

Radial Velocity Variations in Pulsating Ap Stars. II. 33 Librae  

E-print Network

We present precise relative radial velocity (RV) measurements for the rapidly oscillating Ap (roAp) star 33 Librae measured from high resolution data spanning the wavelength interval 5000--6200 A. We find that pulsational radial velocity amplitude determined over a broad wavelength range (~100 A) depends on the spectral region that is examined and can be as high as 60 m/s at 5600 A and as low as 7 m/s in the 5900 A region. RV measurements of individual spectral lines can show even higher RV amplitudes. The acoustic cross-sections of the atmosphere, i.e. the phase and amplitude of the pulsations, as a function of optical depth is found for spectral lines of Ca, Cr, Fe, La, Ce, Gd, Er and Nd. This analysis shows that pulsation phase is variable through the atmosphere and that Nd III lines pulsate almost 180 degrees out-of-phase with those of Nd II features and are formed significantly higher in the stellar atmosphere. This conclusively establishes the presence of at least one radial node to the pulsations in the upper stellar atmosphere. The histogram of pulsational phases for all individual spectral feature shows a bi-modal Gaussian distribution with 17% of the lines having a pulsational phase approximatels 165 degrees out-of-phase with most other spectral lines. This is also consistent with the presence of a radial node in the stellar atmosphere. The accumulation of phase due to a running wave component can explain the 165 degree phase difference as well as the broader width (by a factor of two) of one of the Gaussian components of the phase distribution.

David E. Mkrtichian; Artie P. Hatzes; Antonio Kanaan

2003-07-18

81

The effect of stresses on the velocity of propagation for ultrasonic waves in metals  

Microsoft Academic Search

The results of an experimental investigat}on into the effect of uniaxial stresses on the velocity of propagation of transverse ultrasonic waves in steel, aluminum, and titanium alloys are discussed in this paper. As the tension increases, the velocity of the wave polarized along the stress direction decreases, while the velocity of the wave polarized perpendicular to the stress direction increases,

O. I. Gushcha; V. K. Lebedev

1968-01-01

82

Probabilistic Seismic Hazard Maps of Seattle, Washington, Including 3D Sedimentary Basin Effects and Rupture Directivity: Implications of 3D Random Velocity Variations (Invited)  

NASA Astrophysics Data System (ADS)

We have produced probabilistic seismic hazard maps of Seattle for 1 Hz spectral acceleration, using over five hundred 3D finite-difference simulations of earthquakes on the Seattle fault, Southern Whidbey Island fault, and Cascadia subduction zone, as well as for random deep and shallow earthquakes at various locations. The 3D velocity model was validated by modeling the observed waveforms for the 2001 M6.8 Nisqually earthquake and several smaller events in the region. At these longer periods (? 1 sec) that are especially important to the response of buildings of ten stories or higher, seismic waves are strongly influenced by sedimentary basins and rupture directivity. We are investigating how random spatial variations in the 3D velocity model affect the simulated ground motions for M6.7 earthquakes on the Seattle fault. A fractal random variation of shear-wave velocity with a Von Karman correlation function produces spatial variations of peak ground velocity with multiple scale lengths. We find that a 3D velocity model with a 10% standard deviation in shear-wave velocity in the top 1.5 km and 5% standard deviation from 1.5-10 km depth produces variations in peak ground velocities of as much as a factor of two, relative to the case with no random variations. The model with random variations generally reduces the peak ground velocity of the forward rupture directivity pulse for sites near the fault where basin-edge focusing of S-waves occurs. It also tends to reduce the peak velocity of localized areas where basin surface waves are focused. However, the medium with random variations also causes small-scale amplification of ground motions over distances of a few kilometers. We are also evaluating alternative methods of characterizing the aleatory uncertainty in the probabilistic hazard calculations.

Frankel, A. D.; Stephenson, W. J.; Carver, D.; Odum, J.; Williams, R. A.; Rhea, S.

2010-12-01

83

Searching for Radial Velocity Variations in eta Carinae  

NASA Technical Reports Server (NTRS)

A hot companion of eta Carinae has been detected using high resolution spectra (905 - 1180 A) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite (see poster by Sonneborn et al.). Analysis of the far-UV spectrum shows that eta Car B is a luminous hot star. The N II 1084-86 emission feature indicates that the star may be nitrogen rich. The FUV continuum and the S IV 1073 P-Cygni wind line suggest that the effective temperature of eta Car B is at least 25,000 K. FUV spectra of eta Carinae were obtained with the FUSE satellite at 9 epochs between 2000 February and 2005 July. The data consists of 12 observations taken with the LWRS aperture (30x30 arcsec), three with the HIRS aperture (1.25x20 arcsec), and one MRDS aperture (4x20 arcsec). In this paper we discuss the analysis of these spectra to search for radial velocity variations associated with the 5.54-year binary orbit of Eta Car AB.

Iping, R. C.; Sonneborn, G.; Gull, T. R.; Ivarsson, S.; Nielsen, K.

2006-01-01

84

New Hybridized Surface Wave Approach for Geotechnical Modeling of Shear Wave Velocity at Strong Motion Recording Stations  

NASA Astrophysics Data System (ADS)

Strong motion recording (SMR) networks often have little or no shear wave velocity measurements at stations where characterization of site amplification and site period effects is needed. Using the active Spectral Analysis of Surface Waves (SASW) method, and passive H/V microtremor method we have investigated nearly two hundred SMR sites in California, Alaska, Japan, Australia, China and Taiwan. We are conducting these studies, in part, to develop a new hybridized method of site characterization that utilizes a parallel array of harmonic-wave sources for active-source SASW, and a single long period seismometer for passive-source microtremor measurement. Surface wave methods excel in their ability to non-invasively and rapidly characterize the variation of ground stiffness properties with depth below the surface. These methods are lightweight, inexpensive to deploy, and time-efficient. They have been shown to produce accurate and deep soil stiffness profiles. By placing and wiring shakers in a large parallel circuit, either side-by-side on the ground or in a trailer-mounted array, a strong in-phase harmonic wave can be produced. The effect of arraying many sources in parallel is to increase the amplitude of waves received at far-away spaced seismometers at low frequencies so as to extend the longest wavelengths of the captured dispersion curve. The USGS system for profiling uses this concept by arraying between two and eight electro-mechanical harmonic-wave shakers. With large parallel arrays of vibrators, a dynamic force in excess of 1000 lb can be produced to vibrate the ground and produce surface waves. We adjust the harmonic wave through a swept-sine procedure to profile surface wave dispersion down to a frequency of 1 Hz and out to surface wave-wavelengths of 200-1000 meters, depending on the site stiffness. The parallel-array SASW procedure is augmented using H/V microtremor data collected with the active source turned off. Passive array microtremor data reveal the natural and resonance characteristics of the ground by capturing persistent natural vibrations. These microtremors are the result of the interaction of surface waves arriving from distant sources and the stiffness structure of the site under investigation. As such, these resonance effects are effective in constraining the layer thicknesses of the SASW shear wave velocity structure and aid in determining the depth of the deepest layer. Together, the hybridized SASW and H/V procedure provides a complete data set for modeling the geotechnical aspects of ground amplification of earthquake motions. Data from these investigations are available at http://walrus.wr.usgs.gov/geotech.

Kayen, R.; Carkin, B.; Minasian, D.

2006-12-01

85

Phase Velocities of Long-Period Surface Waves and Structure of the Upper Mantle, 1, Great-Circle Love and Rayleigh Wave Data  

Microsoft Academic Search

New long-period dispersion data are obtained from the surface waves generated by the Alaska earthquake of March 28, 1964, and recorded at Isabella, Kipapa, and Stutt- gart. Digital techniques were used to isolate phases and determine spectrums over the period band 80 to 670 seconds. Available phase velocity data are now accurate enough to permit us to discuss regional variations

M. Nafi Toksöz; Don L. Anderson

1966-01-01

86

Petrologic Constraints on Seismic Velocity Variations in the Upper Mantle Beneath Southern Africa  

NASA Astrophysics Data System (ADS)

Three-dimensional tomographic images of seismic velocity perturbations obtained from analyses of P-wave and S-wave data from the southern Africa seismic experiment show that seismic velocities are about 0.5 to 1.0% higher in the upper mantle beneath Archean cratons relative to the upper mantle off-craton and in modified craton. We examine these seismic velocity perturbations quantitatively in terms of mineralogical and petrological constraints, including depth and temperature of origin, obtained from more than 100 well-characterized mantle samples in kimberlite pipes both on and off craton. We use laboratory-determined bulk and shear moduli, as well as their temperature and pressure derivatives, to compute the seismic properties of the mineral aggregates at the estimated depths and temperatures in the mantle from which the samples were derived. Xenolith samples from the Kaapvaal craton are organized by petrologic subgroups: (1) low temperature garnet lherzolites and harzburgites that originate predominantly from depths in the range 100-150 km; (2) high temperature garnet lherzolites originating at depths in excess of 170 km; and (3) spinel lherzolites and harzburgites that are thought to comprise a continuous upper layer (depth < 80 km) of the cratonic lithosphere. Off-craton peridotites of Proterozoic age (ca 1-2 Ga) are typically more fertile (enriched in Al, Ca, and Fe) than on-craton samples, and they tend to lie on a mantle geotherm displaced toward higher temperatures. All of the mantle samples used in the present study consist dominantly of olivine and orthopyroxene, with or without lesser amounts of garnet, clinopyroxene, and spinel. P and S wave velocities are computed for each xenolith sample based on the modal proportions and chemical composition of individual mineral phases. Where possible, each velocity determination is corrected for the pressure and temperature at which the sample was in equilibrium in the mantle. A significant uncertainty in the velocity determinations results from an incomplete, and in some cases inconsistent, elasticity database. Notably absent from the database are a number of temperature derivatives, many compositional and second-order derivatives, and virtually all P-T cross-derivatives. Within the limits of these uncertainties, however, we have selected a representative set of elastic parameters that we apply uniformly to all specimens of the xenolith suite for the computation of seismic velocities. The contributions of varying mineral modes, phase compositions, and geothermal gradient to seismic velocity variations are examined in the terms of observed velocity perturbations across southern Africa. We evaluate the relative importance of the geothermal gradient vs. average rock composition of the upper mantle as factors in producing the seismic velocity variations observed between regions that are on-craton, off-craton, and in disturbed craton.

James, D. E.; Carlson, R. W.; Boyd, F. R.; Janney, P. E.

2001-05-01

87

Predicting S-wave velocities for unconsolidated sediments at low effective pressure  

USGS Publications Warehouse

Accurate S-wave velocities for shallow sediments are important in performing a reliable elastic inversion for gas hydrate-bearing sediments and in evaluating velocity models for predicting S-wave velocities, but few S-wave velocities are measured at low effective pressure. Predicting S-wave velocities by using conventional methods based on the Biot-Gassmann theory appears to be inaccurate for laboratory-measured velocities at effective pressures less than about 4-5 megapascals (MPa). Measured laboratory and well log velocities show two distinct trends for S-wave velocities with respect to P-wave velocity: one for the S-wave velocity less than about 0.6 kilometer per second (km/s) which approximately corresponds to effective pressure of about 4-5 MPa, and the other for S-wave velocities greater than 0.6 km/s. To accurately predict S-wave velocities at low effective pressure less than about 4-5 MPa, a pressure-dependent parameter that relates the consolidation parameter to shear modulus of the sediments at low effective pressure is proposed. The proposed method in predicting S-wave velocity at low effective pressure worked well for velocities of water-saturated sands measured in the laboratory. However, this method underestimates the well-log S-wave velocities measured in the Gulf of Mexico, whereas the conventional method performs well for the well log velocities. The P-wave velocity dispersion due to fluid in the pore spaces, which is more pronounced at high frequency with low effective pressures less than about 4 MPa, is probably a cause for this discrepancy.

Lee, Myung W.

2010-01-01

88

S-wave velocity structure in southwest China from surface wave tomography and receiver functions  

NASA Astrophysics Data System (ADS)

Using the surface wave records of 504 teleseismic events at 50 temporal and 92 permanent seismic stations in southwest China, we extracted the phase velocity dispersion curves with interstation correlation method, and obtained the phase velocity maps at 10, 15, 25, 40, 60 and 75 s with a grid space of 0.5×0.5 from surface wave tomography. Meanwhile, we obtained the S-wave velocity structures beneath three profiles from the joint inversion of receiver functions and surface waves. From the maps at short periods (10 and 15 s) and long periods (40, 60 and 75 s), different distribution features of high velocity zones (HVZs for short) and low velocity zones (LVZs for short) are shown in the study area: HVZs at short periods are shown in the Panzhihua - Emeishan region, Sichuan basin and Weixi-Lijiang region, surrounding the LVZs from Songpan-Ganzi block to the east of Lijiang where there are significant higher elevations; whereas HVZs at long periods are shown in the Weixi-Lijiang region, Panzhihua-Chuxiong basin and Kunming-Tonghai region and forming a line in the center part of the study area, and the fast polarization directions of the shear wave from SKS analysis on the two sides of the line change significantly. These phenomena indicate plateau material flow can be blocked in two different depth intervals and leads to different horizontal extensions. From the maps at long periods and the structures along the profiles, LVZs are shown in the upper mantle beneath rapid slip fault zones, such as Anninghe - Zemuhe - Xiaojiang fault zone, Red River fault zone and Xiaojinhe fault zone, implying these faults are deep penetrating faults. Figure (a-f) Rayleigh wave phase velocity maps at 10, 15, 25,40,60 and 75 s with a resolution of 100 km. The black lines represent faults. The red points represent M?6 earthquakes. The colour scale changes in different panels. Figure (g) Distribution of the seismic stations and regional tectonic features in the study area. Figure (h-j) The S wave velocity structures beneath the profiles AA', BB' and CC' from the joint inversion of receiver functions and surface waves. The results at different stations are vertically projected to the profiles.

Wang, W.; Wu, J.; Fang, L.; Lai, G.; Yang, T.

2013-12-01

89

Variational Water Wave Model with accurate Dispersion and Vertical Vorticity  

E-print Network

free surface potential flow water wave model under gravity is widely used for marine engineering)l(x, y, z, t) · (ii) Classical potential flow water wave model: u = · (iii) New faster water wave modelVariational Water Wave Model with accurate Dispersion and Vertical Vorticity Onno Bokhove Numerical

Al Hanbali, Ahmad

90

Monitoring stress related velocity variation in concrete with a 2 x 10(-5) relative resolution using diffuse ultrasound.  

PubMed

Ultrasonic waves propagating in solids have stress-dependent velocities. The relation between stress (or strain) and velocity forms the basis of non-linear acoustics. In homogeneous solids, conventional time-of-flight techniques have measured this dependence with spectacular precision. In heterogeneous media such as concrete, the direct (ballistic) wave around 500 kHz is strongly attenuated and conventional techniques are less efficient. In this manuscript, the effect of weak stress changes on the late arrivals constituting the acoustic diffuse coda is tracked. A resolution of 2 x 10(-5) in relative velocity change is attained which corresponds to a sensitivity to stress change of better than 50 kPa. Therefore, the technique described here provides an original way to measure the non-linear parameter with stress variations on the order of tens of kPa. PMID:19354358

Larose, Eric; Hall, Stephen

2009-04-01

91

Seasonal Variation in Ablation and Surface Velocity on a Temperate Maritime Glacier: Fox Glacier, New Zealand  

Microsoft Academic Search

Seasonal variations in ablation and surface velocity were investigated on the lower part of Fox Glacier, South Westland, New Zealand. A large variation between summer and winter ablation was recorded, with daily averages of 129 mm d21 and 22 mm d21, respectively. Variations in measured climatic variables were found to account for ,90% of variation in ablation during both summer

H. L. Purdie; M. S. Brook; I. C. Fuller

2008-01-01

92

Determination of the specific area of liquid gas and the velocity of weak pressure waves in aqueous foams  

NASA Technical Reports Server (NTRS)

The specific area of an aqueous foam contained in a tube is obtained by determining the fraction of the quantity of light emitted by a source and diffused by the specific area of the column of the foam. The velocity of the waves of weak pressure (which propagate in the air with the velocity of sound) is measured by noticing the moment when the wave penetrates the column and the moment when, having reached the opposite side, it determines a variation of the light diffused by the area of the latter.

Saint-Cloud, Jean; Guerraud, Claude; Moreau, Michel; Manson, Numa

1988-01-01

93

Feasibility of Using the Near Surface Seismic Waves Velocities to Identify a Fault Location  

NASA Astrophysics Data System (ADS)

Taiwan is located at a geologic complex area between two plates, having very complicated subsurface structures and intensive seismic activities. Currently, thirty-three active faults are found on the island; however, more detailed studies such as excavation and borehole are still needed. Since most of those fault zones are covered by sediments, actual locations of the faults are not clear on the surface. Although the shallow seismic reflection method is useful for obtaining the subsurface image of the faults; however, the image is commonly muted from the ground surface down to the depth around 20 m. Many studies have shown that the velocities variations of the seismic waves at the near surface could be used for locating the accurate fault location. However, limitation of using the seismic wave methods to locate a fault location is not clear. In this paper, we will show feasibility of the seismic wave methods for identifying the fault locations on the surface. The applied seismic methods consist of the P-wave refraction and the multi-channel surface wave analysis methods. The two methods are conducted on three active faults of different fault types. The Hsinhua fault is a strike-slip fault with a flower structure shown on the shallow reflection seismic profile; the Sanchiao fault is a normal fault covered with thick sediments on the hanging wall; and the Henchun fault is a thrust fault covered by sediments and mélange. Each fault was studied by using the shallow seismic reflection method and core borings. This study uses variations of the P-wave and S-wave velocities across the fault zones to compare with boreholes and shallow seismic reflection images. The integrated results will be used to illustrate the feasibility of using the seismic wave methods to identify the actual fault location. Data collected for this study were recorded by using 4.5-Hz geophones of 24-channel, down to the depth of 18 m were analyzed. From the preliminary result of the Hsinhua fault, we may see that low velocities were observed in the fault zone, which is well correlated to the results from core borings. The data collected across the Sanchiao fault and Henchun fault are ongoing.

Chen, C.; Chang, Y.; Shih, R.

2012-12-01

94

Shear wave velocity structure in North America from large-scale waveform inversions of surface waves  

USGS Publications Warehouse

A two-step nonlinear and linear inversion is carried out to map the lateral heterogeneity beneath North America using surface wave data. The lateral resolution for most areas of the model is of the order of several hundred kilometers. The most obvious feature in the tomographic images is the rapid transition between low velocities in the technically active region west of the Rocky Mountains and high velocities in the stable central and eastern shield of North America. The model also reveals smaller-scale heterogeneous velocity structures. A high-velocity anomaly is imaged beneath the state of Washington that could be explained as the subducting Juan de Fuca plate beneath the Cascades. A large low-velocity structure extends along the coast from the Mendocino to the Rivera triple junction and to the continental interior across the southwestern United States and northwestern Mexico. Its shape changes notably with depth. This anomaly largely coincides with the part of the margin where no lithosphere is consumed since the subduction has been replaced by a transform fault. Evidence for a discontinuous subduction of the Cocos plate along the Middle American Trench is found. In central Mexico a transition is visible from low velocities across the Trans-Mexican Volcanic Belt (TMVB) to high velocities beneath the Yucatan Peninsula. Two elongated low-velocity anomalies beneath the Yellowstone Plateau and the eastern Snake River Plain volcanic system and beneath central Mexico and the TMVB seem to be associated with magmatism and partial melting. Another low-velocity feature is seen at depths of approximately 200 km beneath Florida and the Atlantic Coastal Plain. The inversion technique used is based on a linear surface wave scattering theory, which gives tomographic images of the relative phase velocity perturbations in four period bands ranging from 40 to 150 s. In order to find a smooth reference model a nonlinear inversion based on ray theory is first performed. After correcting for the crustal thickness the phase velocity perturbations obtained from the subsequent linear waveform inversion for the different period bands are converted to a three-layer model of S velocity perturbations (layer 1, 25-100 km; layer 2, 100-200 km) layer 3, 200-300 km). We have applied this method on 275 high-quality Rayleigh waves recorded by a variety of instruments in North America (IRIS/USGS, IRIS/IDA, TERRAscope, RSTN). Sensitivity tests indicate that the lateral resolution is especially good in the densely sampled western continental United States, Mexico, and the Gulf of Mexico.

Alsina, D.; Woodward, R.L.; Snieder, R.K.

1996-01-01

95

Average shear-wave velocity structure of the Kamchatka peninsula from the dispersion of surface waves  

NASA Astrophysics Data System (ADS)

An average shear-wave velocity structure has been estimated for the path between the Kamchatka Isthmus and Petropavlovsk-Kamchatski. It is obtained from the Monte Carlo inversion of the Rayleigh and Love wave group velocity dispersion curves measured using broad-band seismograms of events in Northern Kamchatka recorded by the IRIS station PET in Petropavlovsk-Kamchatski. The Moho interface was found at a depth of 35±5 km and the Konrad one at 18±4 km. An important feature of the found structure is a low velocity in the upper mantle. This result is coherent with the recent and present-% day volcanic activity in Kamchatka. Synthetic long period seismograms computed for the obtained structure are in good agreement with observed ones.

Shapiro, N. M.; Gorbatov, A. V.; Gordeev, E.; Dominguez, J.

2000-09-01

96

A seismic waves velocity model for Gran Canaria Island from ambient noise correlations  

NASA Astrophysics Data System (ADS)

We have analysed continuous ambient seismic noise recorded by a temporary array in Gran Canaria (Canary Islands, Spain) in order to find a velocity model for the top few kilometers. The SISTEVOTENCAN-IGN seismic array consisted of five broadband stations surrounding a sixth central one placed close to Pico de las Nieves, at the center of the island. The array had a radius of 12-14 km, with interstation distances ranging from 10 to 27 km. This network was operative from December 2009 to November 2011. The Green's functions between the 15 pairs of stations have been estimated in the time domain by stacking cross-correlations of 60-s time windows for the whole recording period (~2 years). The effects of several processing adjustments such as 1-bit normalization and spectral whitening are discussed. We observe significant differences (mainly in amplitude) between causal and acausal parts of the estimated Green's functions, which can be associated to an uneven distribution of the seismic noise sources. The application of a phase-matched filter based on an average dispersion curve allowed the effective reduction of some spurious early arrivals and the selection of fundamental-mode Rayleigh wave pulses, making possible an automatic extraction of their group velocities. Then, Rayleigh-wave dispersion curves were retrieved for the set of paths by using frequency-time analysis (FTAN) as well as by following the procedure described by Herrin and Goforth (1977, BSSA) based on the iterative fitting of a phase-matched filter which optimally undisperses the signal. Reliable curves were obtained from 1 s to 6-7 s with group velocities ranging between 1.5 and 2.2 km/s. Some lateral variations in velocity have been detected in spite of the limited spatial coverage and path density, which substantially restricted the resolution. A mean S-wave velocity model has been inverted for this area down to ~3 km.

García-Jerez, Antonio; Almendros, Javier; Martínez-Arévalo, Carmen; de Lis Mancilla, Flor; Luzón, Francisco; Carmona, Enrique; Martín, Rosa; Sánchez, Nieves

2014-05-01

97

Shear Wave Velocity Structure of the Sinai Peninsula from Rayleigh Wave Analysis  

NASA Astrophysics Data System (ADS)

The lithospheric structure of the Sinai Peninsula is shown by means of nine shear velocity profiles for depths ranging from zero to 50 km, determined from the Rayleigh wave analysis. The traces of 30 earthquakes, which occurred from 1992 to 1999 in and around the study area, have been used to obtain Rayleigh wave dispersion. These earthquakes were registered by a broadband station located in Egypt (KEG station). The dispersion curves were obtained for periods between 3 and 40 s, by digital filtering with a combination of MFT and TVF filtering techniques. After that, all seismic events were grouped in source zones to obtain a dispersion curve for each source-station path. These dispersion curves were inverted according to generalized inversion theory, to obtain shear wave velocity models for each source-station path, which is the main goal of this study. The shear velocity structure obtained for the Sinai Peninsula is shown through the shear velocity distributions with depth. These results agree well with the geology and other geophysical results, previously obtained from seismic and gravity data. The obtained velocity models suggest the existence of lateral and vertical heterogeneity. The shear velocity increases generally with depth for all paths analyzed in the study area. Nevertheless, in some paths a small low velocity channel in the upper or lower crust occurs. Along these profiles, it is found that the crustal structure of the Sinai Peninsula consists of three principal layers: upper crust with a sedimentary layer and lower crust. The upper crust has a sedimentary cover of 2 km thick with an average S-velocity of 2.53 km/s. This upper crust has a variable thickness ranging from 12 to 18 km, with S-wave velocity ranging from 3.24 to 3.69 km/s. The Moho discontinuity is located at a depth of 30 km, which is reflected by a sharp increase in the S-velocity values that jump from 3.70-4.12 to 4.33-4.61 km/s.

Corchete, V.; Chourak, M.; Hussein, H. M.

2007-07-01

98

Note on the velocity and related fields of steady irrotational two-dimensional surface gravity waves.  

PubMed

The velocity and other fields of steady two-dimensional surface gravity waves in irrotational motion are investigated numerically. Only symmetric waves with one crest per wavelength are considered, i.e. Stokes waves of finite amplitude, but not the highest waves, nor subharmonic and superharmonic bifurcations of Stokes waves. The numerical results are analysed, and several conjectures are made about the velocity and acceleration fields. PMID:22393109

Clamond, Didier

2012-04-13

99

Reproducibility of Regional Pulse Wave Velocity in Healthy Subjects  

PubMed Central

Background/Aims Despite the clinical importance and widespread use of pulse wave velocity (PWV), there are no standards for pulse sensors or for system requirements to ensure accurate pulse wave measurement. We assessed the reproducibility of PWV values using a newly developed PWV measurement system. Methods The system used in this study was the PP-1000, which simultaneously provides regional PWV values from arteries at four different sites (carotid, femoral, radial, and dorsalis pedis). Seventeen healthy male subjects without any cardiovascular disease participated in this study. Two observers performed two consecutive measurements in the same subject in random order. To evaluate the reproducibility of the system, two sets of analyses (within-observer and between-observer) were performed. Results The means±SD of PWV for the aorta, arm, and leg were 7.0±1.48, 8.43±1.14, and 8.09±0.98 m/s as measured by observer A and 6.76±1.00, 7.97±0.80, and 7.97±0.72 m/s by observer B, respectively. Between-observer differences for the aorta, arm, and leg were 0.14±0.62, 0.18±0.84, and 0.07±0.86 m/s, respectively, and the correlation coefficients were high, especially for aortic PWV (r=0.93). All the measurements showed significant correlation coefficients, ranging from 0.94 to 0.99. Conclusions The PWV measurement system used in this study provides accurate analysis results with high reproducibility. It is necessary to provide an accurate algorithm for the detection of additional features such as flow wave, reflection wave, and dicrotic notch from a pulse waveform. PMID:19270477

Lee, Nak Bum

2009-01-01

100

Variation of the upper mantle velocity structure along the central-south Andes  

NASA Astrophysics Data System (ADS)

Variations in the subduction angle of the Nazca plate beneath the South American plate has lead to different modes of deformation and volcanism along the Andean active margin. The volcanic gap between the central and southern Andean volcanic zones is correlated with the Pampean flat-slab subduction zone, where the subducting Nazca slab changes from a 30-degree dipping slab beneath the Puna plateau to a horizontal slab beneath the Sierras Pampeanas, and then to a 30-degree dipping slab beneath the south Andes from north to south. The Pampean flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of crustal deformation. A major Pliocene delamination event beneath the southern Puna plateau has previously been inferred from geochemical and geological and preliminary geophysical data. The mechanisms for the transition between dipping- and flat-subduction slab and the mountain building process of the central Andean plateau are key issues to understanding the Andean-type orogenic process. We use a new frequency-time normalization approach with non-linear stacking to extract very-broadband (up to 300 second) empirical Green's functions (EGFs) from continuous seismic records. The long-period EGFs provide the deeper depth-sensitivity needed to constrain the mantle structure. The broadband waveform data are from 393 portable stations of four temporary networks: PUNA, SIEMBRA, CHARGE, RAMP, East Sierras Pampeanas, BANJO/SEDA, REFUCA, ANCORP, and 31 permanent stations accessed from both the IRIS DMC and GFZ GEOFON DMC. A finite difference waveform propagation method is used to generate synthetic seismograms from 3-D velocity model. We use 3-D traveltime sensitivity kernels, and traveltime residuals measurement by waveform cross-correlation to directly invert the upper mantle shear-wave velocity structure. The preliminary model shows strong along-strike velocity variations within in the mantle wedge and the subducting NAZCA slab. Low upper mantle velocities are north of 29°S and south of 35°S, corresponding to the low velocity mantle wedge of dipping-subduction. The upper mantle beneath the Sierras Pampeanas has a higher velocity than that beneath the central and south volcanic zones, which is consistent with the Pampeanas flat-slab. Though we observe substantial heterogenity within this flat-slab zone.

Liang, Xiaofeng; Sandvol, Eric; Shen, Yang; Gao, Haiying

2014-05-01

101

Analysis of wave velocity patterns in black cherry trees and its effect on internal decay detection  

E-print Network

Analysis of wave velocity patterns in black cherry trees and its effect on internal decay detection March 2014 Accepted 21 March 2014 Keywords: Stress wave Velocity pattern Trees Internal decay detection that the analytical model can be used to diagnose internal conditions of trees when a stress wave testing method

102

Surface wave tomography with USArray: Rayleigh wave phase velocity, ellipticity, and local amplification  

NASA Astrophysics Data System (ADS)

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 velocity, 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 velocity 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 velocity 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 velocity, 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 velocity and H/V ratio measurements.

Lin, F.; Schmandt, B.; Tsai, V. C.

2012-12-01

103

S-wave velocity structure beneath the High Lava Plains, Oregon, from Rayleigh-wave dispersion inversion  

NASA Astrophysics Data System (ADS)

The High Lava Plains (HLP) "hotspot" track is a prominent volcanic lineament that extends from the southeast corner of Oregon in the northern Great Basin to Newberry volcano in the eastern Cascades. With the age of silicic volcanism decreasing along track to the northwest, the HLP and Newberry volcano are a rough mirror image to the Eastern Snake River Plain and Yellowstone but, in the case of the HLP, at an orientation strongly oblique to North American plate motion. Since this orientation is incompatible with plate motion over a fixed hotspot, other proposed origins for the HLP, such as asthenospheric inflow around a steepening slab, residual effects of a Columbia River/Steens plume, backarc spreading, and Basin and Range extension, relate it to various tectonic features of the Pacific Northwest. To begin distinguishing between these hypotheses, we image upper-mantle structure beneath the HLP and adjacent tectonic provinces with fundamental-mode Rayleigh waves recorded by stations of the USArray Transportable Array, the recently-initiated HLP seismic experiment, the United States National Seismograph Network, and the Berkeley seismic network. We estimate phase velocities along nearly 300 two-station propagation paths that lie within and adjacent to the HLP and cross the region along two azimuths, parallel to and perpendicular to the HLP track. The dispersion curves, which typically give robust results over the period range 16-171 seconds, are grouped by tectonic region, and the composite curves are inverted for S-wave velocity as a function of depth. We also fit a single plane wave to phase delays across the region to identify laterally homogeneous subregions. The resulting variations in upper-mantle structure correlate with variations in surface volcanism and tectonics. The lowest velocities (˜ 4.1 km/s) occur at ˜ 50 km depth in the SE corner of Oregon, where there has been extensive basaltic volcanism in the past 2-5 kyr, and suggest uppermost mantle temperatures sufficient to produce basaltic partial melting. While the seismic velocities of the uppermost mantle beneath the volcanic High Lava Plains are low relative to the standard Tectonic North America (TNA) model, they are only slightly lower than those found for the adjacent northern Great Basin and they appear to be significantly higher than upper-mantle velocities beneath the Eastern Snake River Plain. Our results provide no evidence for a residual plume signature beneath the HLP region, leaving open questions as to the origin of the HLP volcanic track itself.

Warren, Linda M.; Snoke, J. Arthur; James, David E.

2008-09-01

104

Ultrasonic Velocity Variations with Soil Composition for Moisture Measurement  

NASA Technical Reports Server (NTRS)

Soil moisture content may be measured by many methods, but the presently available techniques all have drawbacks when used in ground truth measurements for remote sensing. Ultrasonic velocity varies with soil moisture content, and may be used as the basis of a new measurement technique. In order to characterize a sensor capable of field use, soil particle size distribution data are compared to ultrasonic velocity in a variety of soils over a wide moisture range.

Metzl, R.; Choi, J.; Aggarwal, M. D.; Manu, A.

1998-01-01

105

Constraints on Crustal Shear Wave Velocity Structure beneath Central Tibet from 3-D Multi-scale Finite-frequency Rayleigh Wave Travel-time Tomography  

NASA Astrophysics Data System (ADS)

Surface wave travel-time tomography has been widely used as a powerful strategy to image shear wave velocity structure of the Earth's crust and upper mantle, providing comparable information other than body wave tomography. Traditionally, lateral variations of dispersive phase velocities are first obtained at multiple frequencies and then used to invert for shear wave velocity 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 tomography 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 velocity 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 velocity beneath the Qiangtang terrane is generally very slow. The velocities beneath the Lhasa terrane appear to be relatively higher. The distinct velocity contrast across the BNS has also been observed previously in the tomographic models constrained by body-wave travel times. The absence of pervasive low velocity anomalies in the mid-to-lower crust revealed in our model indicates that the ductile channel flow of the lower crust is not active beneath southern Tibet. By integrating longer-period surface data from distant earthquakes, we will improve the model resolution in the lithospheric mantle and provide better constrains on the geodynamic process of the Himalayan-Tibetan orogeny involved in both the crust and lithospheric mantle.

Jheng, Y.; Hung, S.; Zhou, Y.; Chang, Y.

2012-12-01

106

Illumination Profile & Dispersion Variation Effects on Radial Velocity Measurements  

NASA Astrophysics Data System (ADS)

The Multi-object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS) measures radial velocities using a fiber-fed dispersed fixed-delay interferometer (DFDI) with a moderate dispersion spectrograph. This setup allows a unique insight into the 2D illumination profile from the fiber on to the dispersion grating. Illumination profile investigations show large changes in the profile over time and fiber location. These profile changes are correlated with dispersion changes and long-term radial velocity offsets, a major problem within the MARVELS radial velocity data. Characterizing illumination profiles creates a method to both detect and correct radial velocity offsets, allowing for better planet detection. Here we report our early results from this study including improvement of radial velocity data points from detected giant planet candidates. We also report an illumination profile experiment conducted at the Kitt Peak National Observatory using the EXPERT instrument, which has a DFDI mode similar to MARVELS. Using profile controlling octagonal-shaped fibers, long term offsets over a 3 month time period were reduced from ~50 m/s to within the photon limit of ~4 m/s.

Grieves, Nolan; Ge, Jian; Thomas, Neil B.; Ma, Bo; Li, Rui; SDSS-III

2015-01-01

107

Imaging seismic velocities for hydrate-bearing sediments using converted waves near Yuan-An Ridge, off southwest Taiwan  

NASA Astrophysics Data System (ADS)

Data from P-waves and from S-waves generated by P-S conversion on reflection from airgun shots recorded along four lines of ocean bottom seismometers were used to construct 2-D velocity sections near the Yuan-An Ridge, off southwest Taiwan. The locations of the ocean bottom seismometers were determined to high accuracy by an inversion based on the shot traveltimes. Traveltime inversion and forward modeling of multicomponent wide-angle seismic data result in detailed P-wave (Vp) and S-wave (Vs) velocities of hydrate-bearing sediment layers. The inversion indicates a relatively high P-wave velocity beneath topographic ridges which represent a series of thrust-cored anticlines develop in the accretionary wedge. S-wave velocities of the sediments over the entire section, down to 400 m below seafloor, range from 320 to 570 ms-1. We suggested the lateral variation in Vp/Vs profiles in the hydrate-affected zones may be related to the migration conduit of gas-rich fluid and a characteristic of hydrate content. We model Vp using equations based on a modification of Wood’s equation to estimate the gas hydrate saturation. The hydrate saturation varies from 5% at the top ?200 m below the seafloor to 10-15% of pore space close to the bottom simulating reflector (BSR) in the survey area.

Cheng, W. B.; Shih, T. Y.; Lin, W. Y.; Wang, T. K.; Liu, C. S.; Wang, Y.

2014-10-01

108

The correlations between the saturated and dry P-wave velocity of rocks.  

PubMed

Sometimes engineers need to estimate the wet-rock P-wave velocity from the dry-rock P-wave velocity. An estimation equation embracing all rock classes will be useful for the rock engineers. To investigate the predictability of wet-rock P-wave velocity from the dry-rock P-wave velocity, P-wave velocity measurements were performed on 41 different rock types, 11 of which were igneous, 15 of which were sedimentary and 15 of which was metamorphic. In addition to the dry- and wet-rock P-wave velocity measurements, the P-wave velocity changing as a function of saturation degree was studied. Moreover, dry-rock S-wave velocity measurements were conducted. The test results were modeled using Gassmann's and Wood's theory and it was seen that the measured data did not fit the theories. The unconformity is due to the fact that the theories are valid for high-porosity unconsolidated sediments at low frequencies. Gassmann's equation was modified for the rocks except high-porosity unconsolidated sediments. The dry- and wet-rock P-wave velocity values were evaluated using regression analysis. A strong linear correlation between the dry- and wet-rock P-wave velocities was found. Regression analyses were repeated for the rock classes and it was shown that correlation coefficients were increased. Concluding remark is that the derived equations can be used for the prediction of wet-rock P-wave velocity from the dry-rock P-wave velocity. PMID:17624388

Kahraman, S

2007-11-01

109

Imaging the Anisotropic Shear-wave Velocity in the Earth's Mantle using Free Oscillations, Body Waves, Surface Waves and Long-period Waveforms  

NASA Astrophysics Data System (ADS)

We incorporate normal-mode splitting functions into a framework containing surface-wave phase anomalies, long-period waveforms, and body-wave travel times to investigate the three-dimensional structure of anisotropic shear-wave velocity in the Earth's mantle. In contrast with earlier studies, our modeling approach spans a wider spectrum (0.3-50 mHz) of seismological observables, jointly inverts for velocity and anisotropy apart from the discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the nonlinear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+, an update to S362ANI, gives better fits to the recently measured splitting functions of spheroidal and toroidal modes that are modeled in this study. The splitting functions require additional isotropic variations in the transition zone and the mid mantle that are geographically distributed in the southern hemisphere. The level of agreement in the isotropic shear-velocity structure is higher between S362ANI+ and other recent studies than in the earlier generation of models. The anisotropic part of S362ANI+ is similar to S362ANI and is restricted to the upper 300 km in the mantle since only small improvements in fits are observed on adding anisotropy at depth. We also show that modeling the splitting functions reduces the tradeoffs between lateral variations in velocity and anisotropy in the lowermost mantle. Therefore, more data should be included to constrain any radial anisotropy in the transition zone and in the lower mantle.

Moulik, P.; Ekstrom, G.

2013-12-01

110

Spectral analysis of surface waves method to assess shear wave velocity within centrifuge models  

NASA Astrophysics Data System (ADS)

The method of the spectral analysis of surface waves (SASW) is tested out on reduced scale centrifuge models, with a specific device, called the mini Falling Weight, developed for this purpose. Tests are performed on layered materials made of a mixture of sand and clay. The shear wave velocity VS determined within the models using the SASW is compared with the laboratory measurements carried out using the bender element test. The results show that the SASW technique applied to centrifuge testing is a relevant method to characterize VS near the surface.

Murillo, Carol Andrea; Thorel, Luc; Caicedo, Bernardo

2009-06-01

111

Stochastic simulation for the propagation of high-frequency acoustic waves through a random velocity field  

NASA Astrophysics Data System (ADS)

In-service inspection of Sodium-Cooled Fast Reactors (SFR) requires the development of non-destructive techniques adapted to the harsh environment conditions and the examination complexity. From past experiences, ultrasonic techniques are considered as suitable candidates. The ultrasonic telemetry is a technique used to constantly insure the safe functioning of reactor inner components by determining their exact position: it consists in measuring the time of flight of the ultrasonic response obtained after propagation of a pulse emitted by a transducer and its interaction with the targets. While in-service the sodium flow creates turbulences that lead to temperature inhomogeneities, which translates into ultrasonic velocity inhomogeneities. These velocity variations could directly impact the accuracy of the target locating by introducing time of flight variations. A stochastic simulation model has been developed to calculate the propagation of ultrasonic waves in such an inhomogeneous medium. Using this approach, the travel time is randomly generated by a stochastic process whose inputs are the statistical moments of travel times known analytically. The stochastic model predicts beam deviations due to velocity inhomogeneities, which are similar to those provided by a determinist method, such as the ray method.

Lu, B.; Darmon, M.; Leymarie, N.; Chatillon, S.; Potel, C.

2012-05-01

112

Elastic wave velocities in anorthosite and anorthositic gabbros from Apollo 15 and 16 landing sites  

NASA Technical Reports Server (NTRS)

Laboratory measurements of ultrasonic velocities in lunar samples 15065, 15555, 15415, 60015, and 61016 as well as in synthetic materials corresponding to compositions of anorthositic gabbros are presented as a function of hydrostatic pressure to about 7 kb. The author examined the seismic velocity distributions in the moon with reference to the variations to be expected in a homogeneous medium. The lunar mantle begins about 60 km, and the velocity of P waves in this area is about 7.7 km/sec. Variation of the seismic parameter with depth in the upper crust (about 20 km thick) is much too rapid to be explained by compression of a uniform material and the departure from expectation is so great that no reasonable adjustment of the material parameters can bring agreement; therefore, this author concludes that this result in this region of the moon is not due to self-compression but to textural gradients. In the lower crust (about 40 km thick), the region is shown to be relatively homogeneous, consisting probably of anorthositic rocks.

Chung, D. H.

1973-01-01

113

Measurement of shear-wave velocity by ultrasound critical-angle reflectometry (UCR)  

NASA Technical Reports Server (NTRS)

There exists a growing body of research that relates the measurement of pressure-wave velocity in bone to different physiological conditions and treatment modalities. The shear-wave velocity has been less studied, although it is necessary for a more complete understanding of the mechanical properties of bone. Ultrasound critical-angle reflectometry (UCR) is a noninvasive and nondestructive technique previously used to measure pressure-wave velocities both in vitro and in vivo. This note describes its application to the measurement of shear-wave velocity in bone, whether directly accessible or covered by soft tissue.

Mehta, S.; Antich, P.; Blomqvist, C. G. (Principal Investigator)

1997-01-01

114

Feasibility of waveform inversion of Rayleigh waves for shallow shear-wave velocity using a genetic algorithm  

USGS Publications Warehouse

Conventional surface wave inversion for shallow shear (S)-wave velocity relies on the generation of dispersion curves of Rayleigh waves. This constrains the method to only laterally homogeneous (or very smooth laterally heterogeneous) earth models. Waveform inversion directly fits waveforms on seismograms, hence, does not have such a limitation. Waveforms of Rayleigh waves are highly related to S-wave velocities. By inverting the waveforms of Rayleigh waves on a near-surface seismogram, shallow S-wave velocities can be estimated for earth models with strong lateral heterogeneity. We employ genetic algorithm (GA) to perform waveform inversion of Rayleigh waves for S-wave velocities. The forward problem is solved by finite-difference modeling in the time domain. The model space is updated by generating offspring models using GA. Final solutions can be found through an iterative waveform-fitting scheme. Inversions based on synthetic records show that the S-wave velocities can be recovered successfully with errors no more than 10% for several typical near-surface earth models. For layered earth models, the proposed method can generate one-dimensional S-wave velocity profiles without the knowledge of initial models. For earth models containing lateral heterogeneity in which case conventional dispersion-curve-based inversion methods are challenging, it is feasible to produce high-resolution S-wave velocity sections by GA waveform inversion with appropriate priori information. The synthetic tests indicate that the GA waveform inversion of Rayleigh waves has the great potential for shallow S-wave velocity imaging with the existence of strong lateral heterogeneity. ?? 2011 Elsevier B.V.

Zeng, C.; Xia, J.; Miller, R.D.; Tsoflias, G.P.

2011-01-01

115

Comparision between crustal density and velocity variations in Southern California  

USGS Publications Warehouse

We predict gravity from a three-dimensional Vp model of the upper crust and compare it to the observed isostatic residual gravity field. In general this comparison shows that the isostatic residual gravity field reflects the density variations in the upper to middle crust. Both data sets show similar density variations for the upper crust in areas such as the Peninsular Ranges and the Los Angeles basin. Both show similar variations across major faults, such as the San Andreas and Garlock faults in the Mojave Desert. The difference between the two data sets in regions such as the Salton Trough, the Eastern California Shear Zone, and the eastern Ventura basin (where depth to Moho is <30 km), however, suggests high-density middle to lower crust beneath these regions. Hence the joint interpretation of these data sets improves the depth constraints of crustal density variations.

Langenheim, V.E.; Hauksson, E.

2001-01-01

116

Crustal structure and anisotropy of Greenland from surface-wave group-velocity tomography  

NASA Astrophysics Data System (ADS)

Studies of the geology of Greenland - largely restricted to the edge of the continent due to the presence of the inland ice sheet - show that a significant portion of the continent is underlain by Archean and Paleoproterozoic rocks. The Greenland craton is bounded by numerous younger fold belts, continental margins and basins, and the Iceland hotspot is thought to have had an impact on the lithosphere at the time of North Atlantic opening. The crustal structure of certain regions of Greenland has been studied through receiver function analysis at permanent and temporary broadband seismograph stations; the continental margins and surrounding ocean basins have also been sampled by controlled-source seismic profiles. However, the 3D structure of the crust and uppermost mantle across the continent remains poorly resolved. In order to shed further light on the structure and tectonic evolution of the Greenland continent, we analysed group velocities from earthquakes on the Mid-Atlantic Ridge and northern Canada, recorded at broadband stations of the GEOFON, GSN, CNSN, GLATIS and GLISN seismograph networks. The region covered by the study spans the entire Greenland continent as well as the surrounding oceanic lithosphere. The dense path coverage afforded by the data set allows for a tomographic inversion for maps of group velocity variation and azimuthal anisotropy across the region, sampling over a depth range from the mid crust to the uppermost lithospheric mantle. In addition to the expected first-order difference between oceanic and continental crust beneath the region, we note substantial lateral variations in group velocity across periods ranging from 10 to 60 seconds. Certain zones of relatively low group velocity correspond to sediment infill in large extensional basins at the edge of the Greenland continent; local variations for periods sampling the uppermost mantle are more enigmatic. Reconstruction of group velocities at each well-resolved grid point in the inversion allows the modelling of isotropic 1D shear-wave velocity structure using linearised inversion and Monte-Carlo sampling. The models are combined into a 3D model of the crust and uppermost mantle of the region. We use the 3D velocity model to investigate the structural relationships between the Greenland craton and its surroundings, and search for evidence of pervasive lithospheric modification by the Iceland hotspot.

Darbyshire, F. A.; Dahl-Jensen, T.; Larsen, T.; Voss, P.

2013-12-01

117

On the Formation of Shock Waves in Subsonic Flows With Local Supersonic Velocities  

NASA Technical Reports Server (NTRS)

In the flow about a body with large subsonic velocity if the velocity of the approaching flow is sufficiently large, regions of local supersonic velocities are formed about the body. It is known from experiment that these regions downstream of the flow are always bounded by shock waves; a continuous transition of the supersonic velocity to the subsonic under the conditions indicated has never been observed. A similar phenomenon occurs in pipes. If at two cross sections of the pipe the velocity is subsonic and between these sections regions of local supersonic velocity are formed without completely occupying a single cross section, these regions are always bounded by shock waves.

Frankl, F. I.

1950-01-01

118

Estimation of shear wave velocity in gelatin phantoms utilizing PhS-SSOCT  

NASA Astrophysics Data System (ADS)

We report a method for measuring shear wave velocity in soft materials using phase stabilized swept source optical coherence tomography (PhS-SSOCT). Wave velocity was measured in phantoms with various concentrations of gelatin and therefore different stiffness. Mechanical waves of small amplitudes (˜10 ?m) were induced by applying local mechanical excitation at the surface of the phantom. Using the phase-resolved method for displacement measurement described here, the wave velocity was measured at various spatially distributed points on the surface of the tissue-mimicking gelatin-based phantom. The measurements confirmed an anticipated increase in the shear wave velocity with an increase in the gelatin concentrations. Therefore, by combining the velocity measurements with previously reported measurements of the wave amplitude, viscoelastic mechanical properties of the tissue such as cornea and lens could potentially be measured.

Manapuram, Ravi Kiran; Aglyamov, S.; Menodiado, F. M.; Mashiatulla, M.; Wang, Shang; Baranov, S. A.; Li, Jiasong; Emelianov, S.; Larin, K. V.

2012-09-01

119

Effects of soil moisture variations on deposition velocities above vegetation.  

SciTech Connect

The parameterized subgrid-scale surface flux (PASS) model provides a simplified means of using remote sensing data from satellites and limited surface meteorological information to estimate the influence of soil moisture on bulk canopy stomatal resistances to the uptake of gases over extended areas. PASS-generated estimates of bulk canopy stomatal resistance were used in a dry deposition module to compute gas deposition velocities with a horizontal resolution of 200 m for approximately 5000 km{sup 2} of agricultural crops and rangeland. Results were compared with measurements of O{sub 3} flux and concentrations made during April and May 1997 at two surface stations and from an aircraft. The trend in simulated O{sub 3} deposition velocity during soil moisture drydown over a period of a few days matched the trend observed at the two surface stations. For areas under the aircraft flight paths, the variability in simulated O{sub 3} deposition velocity was substantially smaller than the observed variability, while the averages over tens of kilometers were usually in agreement within 0.1 cm s{sup -1}. Model results indicated that soil moisture can have a major role in deposition of O{sub 3} and other substances strongly affected by canopy stomatal resistance.

Wesely, M. L.; Song, J.; McMillen, R. T.; Meyers, T. P.; Environmental Research; Northern Illinois Univ.; National Oceanic and Atmospheric Administration

2001-01-01

120

Estimation of near-surface shear-wave velocities and quality factors using multichannel analysis of surface-wave methods  

NASA Astrophysics Data System (ADS)

This overview article gives a picture of multichannel analysis of high-frequency surface (Rayleigh and Love) waves developed mainly by research scientists at the Kansas Geological Survey, the University of Kansas and China University of Geosciences (Wuhan) during the last eighteen years by discussing dispersion imaging techniques, inversion systems, and real-world examples. Shear (S)-wave velocities of near-surface materials can be derived from inverting the dispersive phase velocities of high-frequency surface waves. Multichannel analysis of surface waves—MASW used phase information of high-frequency Rayleigh waves recorded on vertical component geophones to determine near-surface S-wave velocities. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that inversion with higher modes and the fundamental mode simultaneously can increase model resolution and an investigation depth. Multichannel analysis of Love waves—MALW used phase information of high-frequency Love waves recorded on horizontal (perpendicular to the direction of wave propagation) component geophones to determine S-wave velocities of shallow materials. Because of independence of compressional (P)-wave velocity, the MALW method has some attractive advantages, such as 1) Love-wave dispersion curves are simpler than Rayleigh wave's; 2) dispersion images of Love-wave energy have a higher signal to noise ratio and more focused than those generated from Rayleigh waves; and 3) inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves.

Xia, Jianghai

2014-04-01

121

Temporal changes of surface wave velocity associated with major Sumatra earthquakes from ambient noise correlation  

PubMed Central

Detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis. Here we report temporal changes of surface wave velocity over a large area associated with 3 major Sumatra earthquakes in 2004, 2005, and 2007. We use ambient noise correlation to retrieve empirical Green's function (EGF) of surface waves between stations. Because the process is completely repeatable, the technique is powerful in detecting possible temporal change of medium. We find that 1 excellent station pair (PSI in Indonesia and CHTO in Thailand) shows significant time shifts (up to 1.44 s) after the 2004 and 2005 events in the Rayleigh waves at 10–20 s but not in the Love waves, suggesting that the Rayleigh time shifts are not from clock error. The time shifts are frequency dependent with the largest shifts at the period band of 11–16 s. We also observe an unusual excursion ?1 month before the 2004 event. We obtain a total of 17 pairs for June, 2007 to June, 2008, which allow us to examine the temporal and spatial variation of the time shifts. We observed strong anomalies (up to 0.68 s) near the epicenter after the 2007 event, but not in the region further away from the source or before the event or 3 months after the event. The observations are interpreted as stress changes and subsequent relaxation in upper-mid crust in the immediate vicinity of the rupture and the broad area near the fault zone. PMID:19667205

Xu, Zhen J.; Song, Xiaodong

2009-01-01

122

Resonances and wave propagation velocity in the subglottal airways.  

PubMed

Previous studies of subglottal resonances have reported findings based on relatively few subjects, and the relations between these resonances, subglottal anatomy, and models of subglottal acoustics are not well understood. In this study, accelerometer signals of subglottal acoustics recorded during sustained [a:] vowels of 50 adult native speakers (25 males, 25 females) of American English were analyzed. The study confirms that a simple uniform tube model of subglottal airways, closed at the glottis and open at the inferior end, is appropriate for describing subglottal resonances. The main findings of the study are (1) whereas the walls may be considered rigid in the frequency range of Sg2 and Sg3, they are yielding and resonant in the frequency range of Sg1, with a resulting ~4/3 increase in wave propagation velocity and, consequently, in the frequency of Sg1; (2) the "acoustic length" of the equivalent uniform tube varies between 18 and 23.5 cm, and is approximately equal to the height of the speaker divided by an empirically determined scaling factor; (3) trachea length can also be predicted by dividing height by another empirically determined scaling factor; and (4) differences between the subglottal resonances of males and females can be accounted for by height-related differences. PMID:21973365

Lulich, Steven M; Alwan, Abeer; Arsikere, Harish; Morton, John R; Sommers, Mitchell S

2011-10-01

123

Finite element solution for pressure and velocity wave propagation  

SciTech Connect

As part of the development of utility thermal-hydraulics capabilities, the microcomputer is becoming a more powerful tool for analysis. Water-hammer and single-phase flow problems have been analyzed with large computer codes such as RELAP5, TRAC, or method of characteristics codes. These analyses can now be performed on a microcomputer for a fraction of the manpower as before and at essentially no cost. This can be done by using finite element (weighted residual) types of methods. A finite element (weighted residual) type of solution is outlined for solving the continuity (mass) and momentum equations for pressure wave propagation. The method uses a staggered grid. A staggered grid is one in which the scalar variables (such as pressure) and the vector variables (velocity, mass flux) are solved for at different points in the computational grid. The method presented here is termed the elimination method, since for two equations (mass and momentum), one of the dependent variables is eliminated in terms of the other, resulting in, essentially, a higher order equation in one dependent variable.

Lucas, S.

1987-01-01

124

Intima media thickness, pulse wave velocity, and flow mediated dilation  

PubMed Central

The identification of vascular alterations at the sub-clinical, asymptomatic stages are potentially useful for screening, prevention and improvement of cardiovascular risk stratification beyond classical risk factors. Increased intima-media thickness of the common carotid artery is a well-known marker of early atherosclerosis, which significantly correlates with the development of cardiovascular diseases. More recently, other vascular parameters evaluating both structural and functional arterial proprieties of peripheral arteries have been introduced, for cardiovascular risk stratification and as surrogate endpoints in clinical trials. Increased arterial stiffness, which can be detected by applanation tonometry as carotid-femoral pulse wave velocity, has been shown to predict future cardiovascular events and to significantly improve risk stratification. Finally, earlier vascular abnormalities such as endothelial dysfunction in the peripheral arteries, detected as reduced flow-mediated dilation of the brachial artery, are useful in the research setting and as surrogate endpoints in clinical trials and have also been suggested for their possible clinical use in the future. This manuscript will briefly review clinical evidence supporting the use of these different vascular markers for cardiovascular risk stratification, focusing on the correct methodology, which is a crucial issue to address in order to promote their use in future for routine clinical practice. PMID:25148901

2014-01-01

125

Helmholtz tomography of ambient noise surface wave data to estimate Scholte wave phase velocity at Valhall Life of the Field  

E-print Network

Helmholtz tomography of ambient noise surface wave data to estimate Scholte wave phase velocity , and Olav I. Barkved4 ABSTRACT We applied the Helmholtz tomography technique to 6.5 hours of continuous by Lin and Ritzwoller (2011) as "Helmholtz tomogra- phy." It is based on tracking of surface wave fronts

Shapiro, Nikolai

126

Automatic brachial ankle pulse wave velocity measurements for vascular damage assessments  

Microsoft Academic Search

An automatic brachial ankle pulse wave velocity device was developed using plethysmographic method based on blood pressure cuffs wrapped on arm brachial artery and tibial artery of ankle. Three electrodes of electrocardiogram were placed on ventral surface of both wrists and medial side of right ankle. The acquired signals of automatic brachial ankle pulse wave velocity device was developed using

R. Gonzalez; O. Morales; J. Delgado; J. M. Padilla; J. M. Ferrero; J. Saiz

2008-01-01

127

Temporal changes of surface wave velocity associated with major Sumatra earthquakes from  

E-print Network

Temporal changes of surface wave velocity associated with major Sumatra earthquakes from ambient temporal changes of surface wave velocity over a large area associated with 3 major Sumatra earthquakes earthquakes in Sumatra, Indonesia in recent years (Fig. 1), occurring on De- cember 26, 2004 (Mw 9.0); March

Song, Xiaodong

128

Signals embedded in the radial velocity noise. Periodic variations in the ? Ceti velocities  

NASA Astrophysics Data System (ADS)

Context. The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. Aims: We study an extensive set of radial velocities for the star HD 10700 (? Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. Methods: We performed Bayesian comparisons of statistical models describing the radial velocity data to quantify the number of significant signals and the magnitude and properties of the excess noise in the data. We reached our goal by adding artificial signals to the "flat" radial velocity data of HD 10700 and by seeing which one of our statistical noise models receives the greatest posterior probabilities while still being able to extract the artificial signals correctly from the data. We utilised various noise components to assess properties of the noise in the data and analyse the HARPS, AAPS, and HIRES data for HD 10700 to quantify these properties and search for previously unknown low-amplitude Keplerian signals. Results: According to our analyses, moving average components with an exponential decay with a timescale from a few hours to few days, and Gaussian white noise explains the jitter the best for all three data sets. Fitting the corresponding noise parameters results in significant improvements of the statistical models and enables the detection of very weak signals with amplitudes below 1 m s-1 level in our numerical experiments. We detect significant periodicities that have no activity-induced counterparts in the combined radial velocities. Three of these signals can be seen in the HARPS data alone, and a further two can be inferred by utilising the AAPS and Keck data. These periodicities could be interpreted as corresponding to planets on dynamically stable close-circular orbits with periods of 13.9, 35.4, 94, 168, and 640 days and minimum masses of 2.0, 3.1, 3.6, 4.3, and 6.6 M?, respectively. Radial velocities are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A79

Tuomi, M.; Jones, H. R. A.; Jenkins, J. S.; Tinney, C. G.; Butler, R. P.; Vogt, S. S.; Barnes, J. R.; Wittenmyer, R. A.; O'Toole, S.; Horner, J.; Bailey, J.; Carter, B. D.; Wright, D. J.; Salter, G. S.; Pinfield, D.

2013-03-01

129

A Variational Property of the Velocity Distribution in a System of Material Particles  

ERIC Educational Resources Information Center

A simple variational property concerning the velocity distribution of a set of point particles is illustrated. This property provides a full characterization of the velocity distribution which minimizes the kinetic energy of the system for prescribed values of linear and angular momentum. Such a characterization is applied to discuss the kinetic…

Siboni, S.

2009-01-01

130

Parameterization and simulation of near bed orbital velocities under irregular waves in shallow water  

USGS Publications Warehouse

A set of empirical formulations is derived that describe important wave properties in shallow water as functions of commonly used parameters such as wave height, wave period, local water depth and local bed slope. These wave properties include time varying near-bed orbital velocities and statistical properties such as the distribution of wave height and wave period. Empirical expressions of characteristic wave parameters are derived on the basis of extensive analysis of field data using recently developed evolutionary algorithms. The field data covered a wide range of wave conditions, though there were few conditions with wave periods greater than 15 s. Comparison with field measurements showed good agreement both on a time scale of a single wave period as well as time averaged velocity moments.

Elfrink, B.; Hanes, D.M.; Ruessink, B.G.

2006-01-01

131

The shear wave velocity of the upper mantle beneath the Bay of Bengal, Northeast Indian Ocean from interstation phase velocities of surface waves  

NASA Astrophysics Data System (ADS)

The Bay of Bengal evolved along the eastern margin of the Indian subcontinent about 130 Ma with the breakup of India from eastern Gondwanaland. Since then the Indian lithospheric Plate has moved northward, along with the Bay of Bengal, and eventually collided with the Eurasian Plate. The age of the lithosphere beneath the central Bay of Bengal is ˜110 Ma. We evaluate the shear wave velocity structure of the upper mantle beneath the central Bay through inversion of phase velocities of fundamental mode Rayleigh and Love waves along two wave paths: (i) between Port Blair (PBA) and VIS (Visakhapatnam) and (ii) between DGPR (Diglipur) and VIS. The seismological observatories PBA and DGPR are located on the Andaman Island and to the east of the Bay and the observatory at VIS in located on the eastern coast of India to the west of the Bay. Using broad-band records of earthquakes, which lie along the great circle arc joining each pair of observatories, we obtain phase velocities between 20 and 240 s periods for Rayleigh waves and between 23 and 170 s for Love waves. These phase velocities are inverted to find the S-wave velocity structure of the upper mantle down to 400 km. The crustal structure is based on previous studies of the Bay and kept fixed in the inversion. We obtain a radially anisotropic upper-mantle structure, where the SH-wave velocity (VSH) is greater than the SV-wave velocity (VSV) down to 400 km. The S-wave velocity decreases sharply by ˜4.5 per cent for VSV and ˜1.5 per cent for VSH at a depth 110 km, which is considered as the Lithosphere-Asthenosphere boundary (LAB), that is, the bottom of the mantle lid. Based on recent studies, such sharp fall of S-wave velocity below the mantle lid appears to indicate a partially molten thin layer (G-discontinuity) at this depth. The thickness of the mantle lid is intermediate between oceanic and continental regions. The lid is also characterized by low radial anisotropy, which decreases to near isotropy at the bottom of the lid. These two characteristics show a `continental-like' mantle lid beneath the Bay. Rapid northward motion of the Indian Plate before its collision with Eurasia might have caused the large radial anisotropy observed below the mantle lid.

Bhattacharya, S. N.; Mitra, Supriyo; Suresh, G.

2013-06-01

132

Determination of relationship between Rayleigh wave velocity and stress with laser Doppler velocimeter  

NASA Astrophysics Data System (ADS)

A non-contact measurement technique of Rayleigh wave velocity is proposed. In the non-contact measurement system, a laser Doppler velocimeter is used to determine wave motions. With above technique, the relationship between Rayleigh wave velocity and stress for an aluminum alloy 5052 and steel SS400 is determined, and the results are in good agreement with that obtained by contact measurement method.

He, Lingfeng; Kobayashi, Shoichi

2002-05-01

133

Imaging subtle microstructural variations in ceramics with precision ultrasonic velocity and attenuation measurements  

NASA Technical Reports Server (NTRS)

Acoustic images of a silicon carbide ceramic disk were obtained using a precision scanning contact pulse echo technique. Phase and cross-correlation velocity, and attenuation maps were used to form color images of microstructural variations. These acoustic images reveal microstructural variations not observable with X-ray radiography.

Generazio, Edward R.; Roth, Don J.; Baaklini, George Y.

1987-01-01

134

Surface wave phase velocities from 2-D surface wave tomography studies in the Anatolian plate  

NASA Astrophysics Data System (ADS)

We study the Rayleigh and Love surface wave fundamental mode propagation beneath the Anatolian plate. To examine the inter-station phase velocities 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 velocity 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 velocity curves, remove outliers and average over many measurements. We discard these average phase velocity 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 velocity 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 Tomography (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 azimuthal coverage of the respective two-station paths is proper to analyze the observed dispersion curves in terms of both azimuthal and radial anisotropy beneath the study region. This research is supported by Joint Research Project of the Scientific and Research Council of Turkey (TUB?TAK- Grant number 111Y190) and the Russian Federation for Basic Research (RFBR).

Arif Kutlu, Yusuf; Erduran, Murat; Çak?r, Özcan; Vinnik, Lev; Kosarev, Grigoriy; Oreshin, Sergey

2014-05-01

135

Error analysis of the converted wave deduced by equivalent velocity assumption  

NASA Astrophysics Data System (ADS)

Based on the assumption of the equivalent velocity and offset, the converted wave travel-time equation, which has a double square root due to the asymmetric ray-path of the down-going P-wave and the up-coming S-wave, can be transformed into a single square root equation if the common scatterpoint (CSP) gathers are binned. This method simplifies the equation and decreases the errors of converted wave migration transferred by P-wave velocity error, compared to the equivalent offset method (EOM) migration proposed by Bancroft, Geiger and Foltinek . In this paper, the errors caused by the introduction of equivalent velocity for the PS-wave are analysed in detail. The discrete errors and effects introduced by discretization of the equivalent offset are presented, and finally the conditions for applying CSP gathers for PS-wave processing under the control of reasonable error limits are derived.

Wang, Wei; Wang, Yun; Yin, Junjie; Gao, Xing

2012-05-01

136

Trench-parallel variations in Pacific and Indo-Australian crustal velocity structure due to Louisville Ridge seamount subduction  

NASA Astrophysics Data System (ADS)

Variations in trench and forearc morphology, and lithospheric velocity structure are observed where the Louisville Ridge seamount chain subducts at the Tonga-Kermadec Trench. Subduction of these seamounts has affected arc and back-arc processes along the trench for the last 5 Myr. High subduction rates (80 mm/yr in the north, 55 mm/yr in the south), a fast southwards migrating collision zone (~180 km/myr), and the obliquity of the subducting plate and the seamount chain to the trench, make this an ideal location to study the effects of seamount subduction on lithospheric structure. The "before and after" subduction regions have been targeted by several large-scale geophysical projects in recent years; the most recent being the R/V Sonne cruise SO215 in 2011. The crust and upper mantle velocity structure observed in profiles along strike of the seamount chain and perpendicular to the trench from this study, are compared to a similar profile from SO195, recorded ~100 km to the north. The affects of the passage of the seamounts through the subduction system are indicated by velocity anomalies in the crust and mantle of the overriding plate. Preliminary results indicate that in the present collision zone, mantle velocities (Pn) are reduced by ~5%. Around 100 km to the north, where seamounts are inferred to have subducted ~1 Myr ago, a reduction of 7% in mantle P-wave velocity is observed. The width of the trench slope and elevation of the forearc also vary along strike. At the collision zone a >100 km wide collapse region of kilometre-scale block faults comprise the trench slope, while the forearc is elevated. The elevated forearc has a 5 km think upper crust with a Vp of 2.5-5.5 km/s and the collapse zone also has upper crustal velocities as low as 2.5 km/s. To the east in the Pacific Plate, lower P-wave velocities are also observed and attributed to serpentinization due to deep fracturing in the outer trench high. Large bending faults permeate the crust and the Osbourn Seamount, currently on the verge of subduction, is fractured stepwise down into the trench. Pn velocities in the hinge zone of the Pacific Plate are as low as 7.3 km/s indicating that fracturing and serpentinization may also extend to sub-crustal depths. Finally, trench-parallel variations in subduction zone velocity structure are used to infer the degree to which seamount subduction has altered the physical state of the Pacific and Indo-Australian plates both pre- and post subduction.

Stratford, W. R.; Knight, T. P.; Peirce, C.; Watts, A. B.; Grevemeyer, I.; Paulatto, M.; Bassett, D.; Hunter, J.; Kalnins, L. M.

2012-12-01

137

The velocities and accelerations accompanying ocean waves can impose large hydrodynamic forces on marine organisms,  

E-print Network

The velocities and accelerations accompanying ocean waves can impose large hydrodynamic forces no guarantee, however, that these plants will not be broken. Indeed, wave forces imposed during storms tear (Koehl and Wainwright, 1977; Seymour et al. 1989). Despite the recognition of wave-induced hydrodynamic

Denny, Mark

138

Lithospheric structure of the Chinese mainland determined from joint inversion of regional and teleseismic Rayleigh-wave group velocities  

NASA Astrophysics Data System (ADS)

We processed a large number of vertical-component seismograms recorded by broadband seismic stations in and around China and ultimately retrieved ˜33 140 regional and ˜10 360 teleseismic fundamental-mode group-velocity measurements at 40 s periods, with fewer measurements for shorter and longer periods. We directly inverted the processed group-velocity measurements for a three-dimensional lithospheric S-velocity model of the Chinese mainland. Synthetic test results and data fit or misfit analysis demonstrated the reliability of our surface-wave tomographic inversion. The imaged upper-crustal low velocities are consistent with variations in sediment thickness; for example, the Tarim Basin, which contains a great thickness of sediments, is characterized by a strong, shallow, low-velocity anomaly. High lithospheric velocities are observed to varying depths in the North China Craton, Yangtze Craton, and Tarim Craton, indicating varying thicknesses of the lithosphere beneath these cratonic areas. Low asthenospheric velocities are widely imaged in eastern and southern China, around the Tarim Basin, and along a roughly north-south belt in central China. The low asthenospheric velocities in eastern and southern China are attributed to partial melting of a subducted slab associated with the westward subduction of an oceanic plate, while those in central China and around the Tarim Basin are attributed to Indian-Eurasian collision.

Feng, Mei; An, Meijian

2010-06-01

139

Shear wave velocities in the Pampean flat-slab region from Rayleigh wave tomography: Implications for slab and upper mantle hydration  

NASA Astrophysics Data System (ADS)

The Pampean flat-slab region, located in central Argentina and Chile between 29° and 34°S, is considered a modern analog for Laramide flat-slab subduction within western North America. Regionally, flat-slab subduction is characterized by the Nazca slab descending to ˜100 km depth, flattening out for ˜300 km laterally before resuming a more "normal" angle of subduction. Flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of deformation and the cessation of volcanism within the region. To better understand flat-slab subduction we combine ambient-noise tomography and earthquake-generated surface wave measurements to calculate a regional 3D shear velocity model for the region. Shear wave velocity variations largely relate to changes in lithology within the crust, with basins and bedrock exposures clearly defined as low- and high-velocity regions, respectively. We argue that subduction-related hydration plays a significant role in controlling shear wave velocities within the upper mantle. In the southern part of the study area, where normal-angle subduction is occurring, the slab is visible as a high-velocity body with a low-velocity mantle wedge above it, extending eastward from the active arc. Where flat-slab subduction is occurring, slab velocities increase to the east while velocities in the overlying lithosphere decrease, consistent with the slab dewatering and gradually hydrating the overlying mantle. The hydration of the slab may be contributing to the excess buoyancy of the subducting oceanic lithosphere, helping to drive flat-slab subduction.

Porter, Ryan; Gilbert, Hersh; Zandt, George; Beck, Susan; Warren, Linda; Calkins, Josh; Alvarado, Patricia; Anderson, Megan

2012-11-01

140

LITHOSTRATIGRAPHY AND SHEAR-WAVE VELOCITY IN THE CRYSTALLIZED TOPOPAH SPRING TUFF, YUCCA MOUNTAIN, NEVADA  

SciTech Connect

Evaluation of the seismic response of the proposed spent nuclear fuel and high-level radioactive waste repository at Yucca Mountain, Nevada, is in part based on the seismic properties of the host rock, the 12.8-million-year-old Topopah Spring Tuff. Because of the processes that formed the tuff, the densely welded and crystallized part has three lithophysal and three nonlithophysal zones, and each zone has characteristic variations in lithostratigraphic features and structures of the rocks. Lithostratigraphic features include lithophysal cavities, rims on lithophysae and some fractures, spots (which are similar to rims but without an associated cavity or aperture), amounts of porosity resulting from welding, crystallization, and vapor-phase corrosion and mineralization, and fractures. Seismic properties, including shear-wave velocity (V{sub s}), have been measured on 38 pieces of core, and there is a good ''first order'' correlation with the lithostratigraphic zones; for example, samples from nonlithophysal zones have larger V{sub s} values compared to samples from lithophysal zones. Some samples have V{sub s} values that are beyond the typical range for the lithostratigraphic zone; however, these samples typically have one or more fractures, ''large'' lithophysal cavities, or ''missing pieces'' relative to the sample size. Shear-wave velocity data measured in the tunnels have similar relations to lithophysal and nonlithophysal rocks; however, tunnel-based values are typically smaller than those measured in core resulting from increased lithophysae and fracturing effects. Variations in seismic properties such as V{sub s} data from small-scale samples (typical and ''flawed'' core) to larger scale traverses in the tunnels provide a basis for merging our understanding of the distributions of lithostratigraphic features (and zones) with a method to scale seismic properties.

D. BUESCH; K.H. STOKOE; M. SCHUHEN

2006-03-20

141

Lithostratigraphy and shear-wave velocity in the crystallized Topopah Spring Tuff, Yucca Mountain, Nevada  

USGS Publications Warehouse

Evaluation of the potential future response to seismic events of the proposed spent nuclear fuel and high-level radioactive waste repository at Yucca Mountain, Nevada, is in part based on the seismic properties of the host rock, the 12.8-million-year-old Topopah Spring Tuff. Because of the processes that formed the tuff, the densely welded and crystallized part has three lithophysal and three nonlithophysal zones, and each zone has characteristic variations in lithostratigraphic features and structures of the rocks. Lithostratigraphic features include lithophysal cavities; rims on lithophysae and some fractures; spots (which are similar to rims but without an associated cavity or aperture); amounts of porosity resulting from welding, crystallization, and vapor-phase corrosion and mineralization; and fractures. Seismic properties, including shear-wave velocity (Vs), have been measured on 38 pieces of core, and there is a good "first order" correlation with the lithostratigraphic zones; for example, samples from nonlithophysal zones have larger Vs values compared to samples from lithophysal zones. Some samples have Vs values that are outside the typical range for the lithostratigraphic zone; however, these samples typically have one or more fractures, "large" lithophysal cavities, or "missing pieces" relative to the sample size. Shear-wave velocity data measured in the tunnels have similar relations to lithophysal and nonlithophysal rocks; however, tunnel-based values are typically smaller than those measured in core resulting from increased lithophysae and fracturing effects. Variations in seismic properties such as Vs data from small-scale samples (typical and "flawed" core) to larger scale transects in the tunnels provide a basis for merging our understanding of the distributions of lithostratigraphic features (and zones) with a method to scale seismic properties.

Buesch, D.C.; Stokoe, K.H., II; Won, K.C.; Seong, Y.J.; Jung, J.L.; Schuhen, M.D.

2006-01-01

142

New statistical analysis of the horizontal phase velocity distribution of gravity waves observed by airglow imaging  

NASA Astrophysics Data System (ADS)

have developed a new analysis method for obtaining the power spectrum in the horizontal phase velocity domain from airglow intensity image data to study atmospheric gravity waves. This method can deal with extensive amounts of imaging data obtained on different years and at various observation sites without bias caused by different event extraction criteria for the person processing the data. The new method was applied to sodium airglow data obtained in 2011 at Syowa Station (69°S, 40°E), Antarctica. The results were compared with those obtained from a conventional event analysis in which the phase fronts were traced manually in order to estimate horizontal characteristics, such as wavelengths, phase velocities, and wave periods. The horizontal phase velocity of each wave event in the airglow images corresponded closely to a peak in the spectrum. The statistical results of spectral analysis showed an eastward offset of the horizontal phase velocity distribution. This could be interpreted as the existence of wave sources around the stratospheric eastward jet. Similar zonal anisotropy was also seen in the horizontal phase velocity distribution of the gravity waves by the event analysis. Both methods produce similar statistical results about directionality of atmospheric gravity waves. Galactic contamination of the spectrum was examined by calculating the apparent velocity of the stars and found to be limited for phase speeds lower than 30 m/s. In conclusion, our new method is suitable for deriving the horizontal phase velocity characteristics of atmospheric gravity waves from an extensive amount of imaging data.

Matsuda, Takashi S.; Nakamura, Takuji; Ejiri, Mitsumu K.; Tsutsumi, Masaki; Shiokawa, Kazuo

2014-08-01

143

Anisotropic P-wave velocity analysis and seismic imaging in onshore Kutch sedimentary basin of India  

NASA Astrophysics Data System (ADS)

The long-offset P-wave seismic reflection data has observable non-hyperbolic moveout, which depend on two parameters such as normal moveout velocity ( Vnmo) and the anisotropy parameter( ?). Anisotropy (e.g., directional dependence of velocity at a fixed spatial location in a medium) plays an important role in seismic imaging. It is difficult to know the presence of anisotropy in the subsurface geological formations only from P-wave seismic data and special analysis is required for this. The presence of anisotropy causes two major distortions of moveout in P-wave seismic reflection data. First, in contrast to isotropic media, normal-moveout (NMO) velocity differs from the vertical velocity; and the second is substantial increase of deviations in hyperbolic moveout in an anisotropic layer. Hence, with the help of conventional velocity analysis based on short-spread moveout (stacking) velocities do not provide enough information to determine the true vertical velocity in a transversely isotropic media with vertical symmetry axis (VTI media). Therefore, it is essential to estimate the single anisotropic parameter ( ?) from the long-offset P-wave seismic data. It has been demonstrated here as a case study with long-offset P-wave seismic data acquired in onshore Kutch sedimentary basin of western India that suitable velocity analysis using Vnmo and ? can improve the stacking image obtained from conventional velocity analysis.

Behera, Laxmidhar; Khare, Prakash; Sarkar, Dipankar

2011-08-01

144

Ultrasonic Velocities of the Dilatational and Shear Waves in Frozen Soils  

NASA Astrophysics Data System (ADS)

Ultrasonic velocities of the dilatational and shear waves in water-saturated frozen soils were measured as a function of temperature by both pulse first arrival and critical angle methods. A strong correlation exists between the dilatational wave velocities and the unfrozen water content. The observed hysteresis in the velocities of silt and clay during a freeze-thaw cycle is considered to be caused by hysteresis in the frozen water content. A general tendency for the shear wave velocity to decrease with ascending temperature exists, but the effect of temperature is not as pronounced as on the dilatational velocity. Calculations based on measured dilatational and shear velocities showed that the Poisson's ratios of sand are almost constant. However, the ratios of silt and clay decrease monotonically with ascending temperature.

Nakano, Yoshisuke; Martin, Randolph J., III; Smith, Martin

1972-08-01

145

Corrosion and erosion monitoring in plates and pipes using constant group velocity Lamb wave inspection.  

PubMed

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 group velocity (CGV) point where the group velocity remains essentially constant over a wide range of wall thickness variation, but the phase velocity 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 tomography. 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

Nagy, Peter B; Simonetti, Francesco; Instanes, Geir

2014-09-01

146

Geomagnetic field variations in seismic waves traveling across a fault  

NASA Astrophysics Data System (ADS)

The results of regular instrumental observations over geomagnetic field variations in the zones of influence of tectonic faults during movement of seismic waves of varied intensity are presented. It has been shown that seismic waves with an amplitude more than 5-10 ?m/s, traveling across the fault zone, always produced geomagnetic field variations. At weaker seismic disturbances, geomagnetic field variations are of the "glimmer" character, and the relative frequency of appearance of the effect drops as the seismic wave amplitude decreases. The quantitative dependence between the maximal value of the full vector of variations in geomagnetic field induction in a fault zone and the amplitude of the seismic disturbance has been found for the first time.

Lukishov, B. G.; Spivak, A. A.; Ter-Semenov, A. A.

2012-01-01

147

Influence of small temperature variations on the ultrasonic velocity in concrete  

NASA Astrophysics Data System (ADS)

Ultrasonic methods are valuable tools for quality assessment and structural imaging of concrete. In such applications, accurate and reliable determination of ultrasonic wave velocities is essential, as they are affected by various experimental and environmental factors. In this research coda wave interferometry (CWI) was used to determine the influence of temperature (0 to 50 °C) on ultrasonic wave velocity in concrete samples. A resolution of better than 10-4 was achieved in the measurement of relative velocity changes. Reversibility and repeatability as well as the influence of moisture were taken into account. In addition the influence of sensor (transmitter and receiver) positioning errors on the results of the interferometric algorithm was evaluated as well as the benefit of newly developed, permanently embedded sensors. The presented results can be used to evaluate and refine data from ultrasonic monitoring systems.

Niederleithinger, E.; Wunderlich, C.

2013-01-01

148

Rayleigh wave phase velocity maps from the ambient noise tomography in central Mongolia  

NASA Astrophysics Data System (ADS)

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 tomography 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 tomography methods of surface waves, ambient noise tomography 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 velocity dispersion curves of Rayleigh wave were extracted from EGFs. High resolution phase velocity 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 tomography results reveal lateral heterogeneity of shear wave structure in the crust and upper mantle in the study region. For periods shorter than 10 s, the phase velocity variations are well correlated with the principal geological units, with low-speed anomalies corresponding to the sedimentary basins and high-speed anomalies coinciding with the main mountain ranges. Within the period range from 20 s to 30 s, phase velocity distribution is correlated to the crust thickness. However, the value of phase velocities have little lateral changes with ~0.15km/s on each map for the whole period band ranging from 5 s to 30 s, indicating that it doesn't have big lateral heterogeneity for shear wave structure in the crust and upper mantle in the study region.This study was supported by the international cooperation project of the Ministry of Science and Technology of China (2011DFB20120) and NSFC (41104029)

Pan, J.; Wu, Q.; Gao, M.; Li, Y.; Demberel, S. G.; Munkhuu, U.

2013-12-01

149

Precise continuous monitoring of seismic velocity variations and their possible connection to solid earth tides  

Microsoft Academic Search

Seismic velocities in the siting area of the Norwegian Seismic Array (Norsar) have been monitored over a time period of 1 week by using a hydroelectric power plant as a continuous wave generator. Propagational phase angle differences have been measured over travel distances ranging from 4.7 to 13.7 km, and group velocities of the order of 3.5 km\\/s are derived.

Hilmar Bungum; Torben Risbo; Erik Hjortenberg

1977-01-01

150

Thermal dehydration reactions characterized by combined measurements of electrical conductivity and elastic wave velocities  

NASA Astrophysics Data System (ADS)

Combined laboratory measurements of seismic velocities and electrical conductivity as a function of PT and drainage conditions have been performed on various rocks containing hydrous minerals. This paper presents experimental results for evaporite rocks containing gypsum (CaSO4 x 2H2O) and carnallite (KMgCl3 x 6H2O) and for serpentinite. The experiments on the evaporite rocks were carried out in a triaxial cell in the range 20-130 C and 5.0-24.0 MPa confining pressure. The measurements on serpentinite covered the range 20-750 C at pressures of up to 200 MPa and were performed in a cubic pressure apparatus. The thermally induced onset of dehydration was indicated by the pronounced discontinuous behaviour of conductivity, corresponding to a marked drop in the elastic wave velocities. The respective Poisson ratios were inversely correlated with permeability and seem to be a sensitive parameter to describe the reaction-related variations of pore space. The seismic properties can be satisfactory modelled by using the self-consistent approximation of O'Connell and Budiansky, illustrating the effects of variations in pore space and saturation. The dehydration behavior of the various hydrous rock types was found to be different because the changes in the rock physical properties are closely linked to the internally created pore fluid, to the changes in the porosity and pore geometry, and to the resulting pore pressure. Progressive thermal dehydration reactions induce an opening of pore space accompanied by lowered saturation conditions whereby the rate of fluid release depends mainly on temperature and also on the drainage conditions of the system. Our findings, as reflected by the variations in the geophysical parameters, may be of importance for the interpretation of natural dehydration processes in the crust caused by prograde metamorphism.

Popp, T.; Kern, H.

1993-11-01

151

Anomalous translational velocity of vortex ring with finite-amplitude Kelvin waves  

SciTech Connect

We consider finite-amplitude Kelvin waves on an inviscid vortex assuming that the vortex core has infinitesimal thickness. By numerically solving the governing Biot-Savart equation of motion, we study how the frequency of the Kelvin waves and the velocity of the perturbed ring depend on the Kelvin wave amplitude. In particular, we show that, if the amplitude of the Kelvin waves is sufficiently large, the perturbed vortex ring moves backwards.

Barenghi, C. F. [School of Mathematics, University of Newcastle, Newcastle NE1 7RU (United Kingdom); Haenninen, R.; Tsubota, M. [Department of Physics, Osaka City University, Sugimoto 3-3-138, 558-8585 Osaka (Japan)

2006-10-15

152

Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet  

NASA Technical Reports Server (NTRS)

We have conducted a detailed study of the cloud features in the strong southern equatorial wind jet near 7.5 S planetographic latitude. To understand the apparent variations in average zonal wind jet velocity at this latitude [e.g.. 1,2,3], we have searched for variations iIi both feature latitude and velocity with longitude and time. In particular, we focused on the repetitive chevron-shaped dark spots visible on most dates and the more transient large anticyclonic system known as the South Equatorial Disturbance (SED). These small dark spots are interpreted as cloud holes, and are often used as material tracers of the wind field.

Simon-Miller, A. A.; Rogers, John H.; Gierasch, Peter J.; Choi, David; Allison, Michael; Adamoli, Gianluigi; Mettig, Hans-Joerg

2012-01-01

153

Guided wave observations and evidence for the low-velocity subducting crust beneath Hokkaido, northern Japan  

NASA Astrophysics Data System (ADS)

At the western side of the Hidaka Mountain range in Hokkaido, we identify a clear later phase in seismograms for earthquakes occurring at the uppermost part of the Pacific slab beneath the eastern Hokkaido. The later phase is observed after P-wave arrivals and has a larger amplitude than the P wave. In this study, we investigate the origin of the later phase from seismic wave observations and two-dimensional numerical modeling of wave fields and interpret it as a guided P wave propagating in the low-velocity subducting crust of the Pacific plate. In addition, the results of our numerical modeling suggest that the low-velocity subducting crust is in contact with a low-velocity material beneath the Hidaka Mountain range. Based on our interpretation for the later phase, we estimate P-wave velocity in the subducting crust beneath the eastern part of Hokkaido by using the differences in the later phase travel times and obtain velocities of 6.8 to 7.5 km/s at depths of 50 to 80 km. The obtained P-wave velocity is lower than the expected value based on fully hydrated mid-ocean ridge basalt (MORB) materials, suggesting that hydrous minerals are hosted in the subducting crust and aqueous fluids may co-exist down to depths of at least 80 km.

Shiina, Takahiro; Nakajima, Junichi; Toyokuni, Genti; Matsuzawa, Toru

2014-12-01

154

Abnormal temperature-dependent variation in sound velocity for the molecular liquids benzene and hexafluorobenzene  

Microsoft Academic Search

In this paper we give the results of sound-velocity measurements by accurate Brillouin techniques in pure liquid benzene and hexafluorobenzene in the temperature range 20-60 °C. For both fluids, we find a clear change in the slope of the variation of the sound velocity with temperature. A change in the Landau-Placzek ratio was also detected. These experimental facts seem to

L. Letamendia; M. Belkadi; O. Eloutassi; C. Vaucamps; G. Nouchi; S. Iakovlev; N. B. Rozhdestvenskaya; L. V. Smirnova; J. E. Runova

1993-01-01

155

PARTICLE ACCELERATION BY ELECTROSTATIC WAVES WITH SPATIALLY VARYING PHASE VELOCITIES  

Microsoft Academic Search

We present here the results of numerical calculations connected with a mechanism recently proposed [Swift, 1968] for the acceleration of charged particles in a strong dc magnetic field. An electrostatic plasma wave propagates nearly perpendicularly to the magnetic field, and a weak density gradient exists parallel to the magnetic field. The wave propagates into the region of increasing plasma density

S. Peter Gary; David Montgomery; Daniel W. Swift

1968-01-01

156

Observation of Wave Packet Distortion during a Negative-Group-Velocity Transmission  

PubMed Central

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 velocity 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 group velocity. 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-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity 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 group velocity physically meaningless in the anomalously dispersive region. PMID:25631746

Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin

2015-01-01

157

Observation of Wave Packet Distortion during a Negative-Group-Velocity Transmission.  

PubMed

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 velocity 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 group velocity. 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-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity 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 group velocity physically meaningless in the anomalously dispersive region. PMID:25631746

Ye, Dexin; Salamin, Yannick; Huangfu, Jiangtao; Qiao, Shan; Zheng, Guoan; Ran, Lixin

2015-01-01

158

Measurements of plasma temperature in indirect drive targets from the shock wave velocity in aluminum in the Iskra-5 facility  

NASA Astrophysics Data System (ADS)

Results are presented from the development of a method for measuring plasma temperature in indirect (X-ray) drive targets by recording the shock wave velocity in the Iskra-5 facility. The samples under investigation were irradiated by X-rays in a converter box, and the shock wave velocity was determined from the time at which the wave reached the back surface of the sample and the surface began to emit visible radiation. This emission, in turn, was detected by a streak camera. The results of experiments on the interaction of X radiation with a hot dense plasma, as well as the accompanying gas-dynamic processes in aluminum samples, are analyzed both theoretically and numerically. In experiments with Al and Pb samples, the shock wave velocity was measured to vary in the range U = 8-35 km/s, and the range of variation of the temperature of the box walls was measured to be T e = 140-170 eV.

Vatulin, V. V.; Zhidkov, N. V.; Kravchenko, A. G.; Kuznetsov, P. G.; Litvin, D. N.; Mis'ko, V. V.; Pinegin, A. V.; Pleteneva, N. P.; Senik, A. V.; Starodubtsev, K. V.; Tachaev, G. V.

2010-05-01

159

Measurements of plasma temperature in indirect drive targets from the shock wave velocity in aluminum in the Iskra-5 facility  

SciTech Connect

Results are presented from the development of a method for measuring plasma temperature in indirect (X-ray) drive targets by recording the shock wave velocity in the Iskra-5 facility. The samples under investigation were irradiated by X-rays in a converter box, and the shock wave velocity was determined from the time at which the wave reached the back surface of the sample and the surface began to emit visible radiation. This emission, in turn, was detected by a streak camera. The results of experiments on the interaction of X radiation with a hot dense plasma, as well as the accompanying gas-dynamic processes in aluminum samples, are analyzed both theoretically and numerically. In experiments with Al and Pb samples, the shock wave velocity was measured to vary in the range U = 8-35 km/s, and the range of variation of the temperature of the box walls was measured to be T{sub e} = 140-170 eV.

Vatulin, V. V.; Zhidkov, N. V.; Kravchenko, A. G.; Kuznetsov, P. G.; Litvin, D. N.; Mis'ko, V. V.; Pinegin, A. V.; Pleteneva, N. P.; Senik, A. V.; Starodubtsev, K. V.; Tachaev, G. V. [Russian Federal Nuclear Center, All-Russia Research Institute of Experimental Physics (Russian Federation)

2010-05-15

160

A comprehensive dispersion model of surface wave phase and group velocity for the globe  

NASA Astrophysics Data System (ADS)

A new method is developed to measure Rayleigh- and Love-wave phase velocities 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 velocity and azimuthal anisotropy, we include the effect of azimuthal anisotropy in our inversions in order to obtain reliable isotropic phase velocity. We use b-splines to combine these isotropic phase velocity maps with our previous group velocity maps to produce an internally consistent global surface wave dispersion model.

Ma, Zhitu; Masters, Guy; Laske, Gabi; Pasyanos, Michael

2014-10-01

161

Variation of Seismic Velocity Structure around the Mantle Transition Zone and Conjecture of Deep Water Transport by Subducted Slabs  

NASA Astrophysics Data System (ADS)

Seismic tomography models published in the past two decades determined common long-wavelength features of subducting plates as high velocity anomalies and upwelling plumes as low velocity anomalies, and have led to a new class of high-resolution three-dimensional (3D) modeling of global mantle convection with a link to tomography models [e.g., Becker and Boschi, 2002; Ritsema et al., 2007; Schuberth et al., 2009a,b]. However, even such high resolution numerical models do not account for the variation associated with different behaviors of subducting plates as they enter the mantle transition zone (MTZ), i.e., some flatten to form stagnant slabs with a large lateral extent and others descend further into the lower mantle. There are conventional interpretations applied for the cause of variation of the subducted slab behaviors, i.e., temperature difference due to different plate age, different geochemical compositions, different water content and subsequent possible reduction of viscosity etc., which could be taken as non-unique and somewhat equivocal. These parameters and conditions have been tested in two-dimensional numerical simulations, while the water content in the MTZ or the mechanisms of hydration and dehydration through subduction process are still in the realm of conjecture. Recent models of seismic P- and SH-wave velocities derived for the mantle structure beneath northeast China [Wang and Niu, 2010; Ye et al., 2011] using reflectivity synthetics with data from the dense Chinese networks of broadband seismic instruments, show a broader 660 km discontinuity (by about 30 to 70 km) and slower shear velocities above the MTZ than a global standard model iasp91 (Kennett and Engdahl, 1991). These features were interpreted with a mixture of different chemical properties which show delayed phase transformation, and effects of water above the flattened slab. Nonetheless, the SH-wave model has a structure similar to model TNA above the MTZ, which was derived for the structure beneath tectonic North America [Grand and Helmberger, 1984] and has a sharp discontinuity. Tajima and Nakagawa [2006] have already shown that SH waveforms which sampled the stagnant slab in the northwestern Pacific subduction zone could be modeled with TNA well. The reflectivity synthetic approaches attempted to model a large number of waveform data obtained from an array with a layered structure, and tend to average the discontinuity depth variation and other features. Our 3D finite difference waveform modeling clearly suggests variation of relatively sharp phase transformation depths beneath stagnant slabs. The results were interpreted with variation of geochemical properties under wet condition at the base of MTZ. Accordingly we explore how well the hydrous and dry conditions can be delineated for varying chemical properties from seismic waveform analysis.

Tajima, F. C.; Stahler, S. C.; Ohtani, E.; Yoshida, M.; Sigloch, K.

2011-12-01

162

Referential ZMP Trajectory for Minimizing Variation of COG Velocity in Single Support Phase of Biped Robot  

NASA Astrophysics Data System (ADS)

The referential ZMP (Zero-Moment Point) trajectory that minimizes the variation of COG (Center of Gravity) velocity in the single support phase of a biped robot is shown. Two advantages of using this ZMP trajectory are discussed. The first advantage is that the variation of COG velocity is gradual. The second advantage is that the biped robot enables the heel-contact motion and the toe-off motion in the single support phase. The trajectory planning based on this ZMP trajectory is proposed. In simulation and experiment, the validity of the proposed method was confirmed.

Sato, Tomoya; Ohnishi, Kouhei

163

Shear Wave Velocity Structure Beneath the Western Basin and Range Province, Eastern California: Implications for Crustal-scale Tectonic Models  

NASA Astrophysics Data System (ADS)

Broadband seismic data from three seismic stations located within the western Basin and Range Province of eastern California were analyzed in order to image the shear wave velocity structure of the crust and upper mantle in the region. The stations include: (1) Manual Prospect Mines, Trona, (2) Cottonwood Creek, Lone Pine, and (3) Slate Mountain, Trona. The area of the study is characterized by a complex geologic history predominantly involving the Mesozoic emplacement of the Sierra Nevada batholith and Cenozoic extension, uplift, and volcanism. Lateral and vertical velocity variations deduced from receiver-function analyses indicate complex lithospheric structure in this region. The crustal configuration beneath the stations depicts a low-velocity zone (LVZ) that is present between 16-18 km depth and the Moho at about 30-km depth. These results are consistent with extensional models of the region involving lateral flow of mid- to lower-crustal material and/or delamination of the lower crust.

Kamath, N.; Leslie, S.; Mooney, W. D.

2007-12-01

164

The relationship between shear wave velocity, temperature, attenuation and viscosity in the shallow part of the mantle  

NASA Astrophysics Data System (ADS)

Surface wave tomography, using the fundamental Rayleigh wave velocities and those of higher modes between 1 and 4 and periods between 50 and 160 s, is used to image structures with a horizontal resolution of ˜250 km and a vertical resolution of ˜50 km to depths of ˜300 km in the mantle. A new model, PM_v2_2012, obtained from 3×106 seismograms, agrees well with earlier lower resolution models. It is combined with temperature estimates from oceanic plate models and with pressure and temperature estimates from the mineral compositions of garnet peridotite nodules to generate a number of estimates of SV(P,T) based on geophysical and petrological observations alone. These are then used to estimate the unrelaxed shear modulus and its derivatives with respect to pressure and temperature, which agree reasonably with values from laboratory experiments. At high temperatures relaxation occurs, causing the shear wave velocity to depend on frequency. This behaviour is parameterised using a viscosity to obtain a Maxwell relaxation time. The relaxation behaviour is described using a dimensionless frequency, which depends on an activation energy E and volume Va. The values of E and Va obtained from the geophysical models agree with those from laboratory experiments on high temperature creep. The resulting expressions are then used to determine the lithospheric thickness from the shear wave velocity variations. The resolution is improved by about a factor of two with respect to earlier models, and clearly resolves the thick lithosphere beneath active intracontinental belts that are now being shortened. The same expressions allow the three dimensional variations of the shear wave attenuation and viscosity to be estimated.

Priestley, Keith; McKenzie, Dan

2013-11-01

165

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

166

Phase and group velocities for Lamb waves in DOP-26 iridium alloy sheet  

SciTech Connect

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 group velocities 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 velocities so that accurate flaw location is ensured. We describe a numerical technique for computing the phase velocities of Lamb waves (or of any other type of guided wave) and derive the group velocities from this information. A frequency-domain method is described for measuring group velocity when multiple Lamb modes are present and mutually interfering in the time domain, and experimental confirmation of the group velocity is presented for the capsule material.

Simpson, W.A.; McGuire, D.J.

1994-07-01

167

Longshore sediment transport rate calculated incorporating wave orbital velocity fluctuations  

E-print Network

distinct zones of longshore transport were observed across the surf zone: the incipient breaker zone, inner surf zone, and swash zone. Transport at incipient breaking was influenced by breaker type; inner surf zone transport was dominated by wave height...

Smith, Ernest Ray

2006-10-30

168

Vertical Energy Propagation of Inertial Waves: A Vector Spectral Analysis of Velocity Profiles  

Microsoft Academic Search

Vertical propagation of near-inertial period waves has been detected in a series of recent velocity profiles by a technique of vector spectral analysis. This method, previously applied to vector series in time, has been used to study the vertical spatial structure of velocity profiles obtained in the Mid-Ocean Dynamics Experiment (MODE). Prior to the use of spectral analysis, however, it

KEVIN D. LEAMANAND; Thomas B. Sanford

1975-01-01

169

Correlation between ultrasonic shear wave velocity and Poisson’s ratio for isotropic solid materials  

Microsoft Academic Search

A new correlation between ultrasonic shear wave velocity and Poisson’s ratio has been established for isotropic solid materials, based on the data generated experimentally and collected from the literature. Poisson’s ratio has been found to decrease with increasing ultrasonic velocity in various solid materials such as metals and alloys, ceramics and glasses, intermetallics and polymers. The slope of the plot

Anish Kumar; T. Jayakumar; Baldev Raj; K. K. Ray

2003-01-01

170

Rayleigh wave phase velocity analysis of the Ross Sea, Transantarctic Mountains, and East Antarctica  

E-print Network

, and a transition between the two between 50 and 150 km inland. The EA phase velocities in the region adjacent Rayleigh wave phase velocities in order to seismically image the crustal and upper mantle structure beneath., 1991a; Fitzgerald et al., 1986]. This study images the WARS in the western part of the Ross Sea

171

Shear velocity model for the Kyrgyz Tien Shan from joint inversion of receiver function and surface wave data  

NASA Astrophysics Data System (ADS)

The Tien Shan is the largest active intracontinental orogenic belt on Earth. To better understand the processes causing mountains to form at great distances from a plate boundary, we analyse passive source seismic data collected on 40 broad-band stations of the MANAS project (2005-2007) and 12 stations of the permanent KRNET seismic network to determine variations in crustal thickness and shear wave speed across the range. We jointly invert P- and S-wave receiver functions with surface wave observations from both earthquakes and ambient noise to reduce the ambiguity inherent in the images obtained from the techniques applied individually. Inclusion of ambient noise data improves constraints on the upper crust by allowing dispersion measurements to be made at shorter periods. Joint inversion can also reduce the ambiguity in interpretation by revealing the extent to which various features in the receiver functions are amplified or eliminated by interference from multiples. The resulting wave speed model shows a variation in crustal thickness across the range. We find that crustal velocities extend to ˜75 km beneath the Kokshaal Range, which we attribute to underthrusting of the Tarim Basin beneath the southern Tien Shan. This result supports the plate model of intracontinental convergence. Crustal thickness elsewhere beneath the range is about 50 km, including beneath the Naryn Valley in the central Tien Shan where previous studies reported a shallow Moho. This difference apparently is the result of wave speed variations in the upper crust that were not previously taken into account. Finally, a high velocity lid appears in the upper mantle of the Central and Northern part of the Tien Shan, which we interpret as a remnant of material that may have delaminated elsewhere under the range.

Gilligan, Amy; Roecker, Steven W.; Priestley, Keith F.; Nunn, Ceri

2014-10-01

172

Increased Pulse Wave Velocity Reflecting Arterial Stiffness in Patients with Colorectal Adenomas  

PubMed Central

The obese patients with diabetes or cardiovascular risk factors are associated with increased risk of colorectal cancer as well as adenomas under the shared pathogenesis related to atherosclerosis. Here we determined the association between increased arterial stiffness and colorectal adenomas incorporating parameters including age, gender, waist circumference, body mass index, lipid profiles, fasting glucose, and blood pressure. Subjects who simultaneously underwent colonoscopies and pulse wave velocity (PWV) determinations between July 2005 and September 2006 were analyzed, based on which the subjects were classified into two groups as patients group with colorectal adenomas (n = 49) and control group (n = 200) with normal, non-polypoid benign lesions or hyperplastic polyps. Uni- and multi-variate analyses were performed to calculate the odd ratio for colon adenomas. Based on uni-variate analysis, age, waist circumference, body mass index, heart-femoral PWV (hfPWV), and brachial-ankle PWV were significantly associated with adenomas (p<0.05) and multiple logistic regression analysis showed that the heart-femoral PWV, waist circumference, and the levels of LDL-C were significant risk factor for colorectal adenoma. However, arterial stiffness did not affect the progression of colon adenoma. The finding that hfPWV, reflecting aortic stiffness, was increased in patients with colorectal adenomas lead to conclusion that patients who have prominently increased arterial stiffness can be recommended to undergo colonoscopic examinations and at the same time we also recommend counseling about the risk for atherosclerosis in those who have colorectal adenomas. PMID:21103036

Lim, Yun Jeong; Kwack, Won Gun; Lee, Youg-Sup; Hahm, Ki Baik; Kim, Young-Kwon

2010-01-01

173

Multiparameter full waveform inversion of multicomponent ocean-bottom-cable data from the Valhall field. Part 2: imaging compressive-wave and shear-wave velocities  

NASA Astrophysics Data System (ADS)

Multiparameter elastic full waveform inversion (FWI) is a promising technology that allows inferences to be made on rock and fluid properties, which thus narrows the gap between seismic imaging and reservoir characterization. Here, we assess the feasibility of 2-D vertical transverse isotropic visco-elastic FWI of wide-aperture multicomponent ocean-bottom-cable data from the Valhall oil field. A key issue is to design a suitable hierarchical data-driven and model-driven FWI workflow, the aim of which is to reduce the nonlinearity of the FWI. This nonlinearity partly arises because the shear (S) wavespeed can have a limited influence on seismic data in marine environments. In a preliminary stage, visco-acoustic FWI of the hydrophone component is performed to build a compressional (P)-wave velocity model, a density model and a quality-factor model, which provide the necessary background models for the subsequent elastic inversion. During the elastic FWI, the P and S wavespeeds are jointly updated in two steps. First, the hydrophone data are inverted to mainly update the long-to-intermediate wavelengths of the S wavespeeds from the amplitude-versus-offset variations of the P-P reflections. This S-wave velocity model is used as an improved starting model for the subsequent inversion of the better-resolving data recorded by the geophones. During these two steps, the P-wave velocity model is marginally updated, which supports the relevance of the visco-acoustic FWI results. Through seismic modelling, we show that the resulting visco-elastic model allows several P-to-S converted phases recorded on the horizontal-geophone component to be matched. Several elastic quantities, such as the Poisson ratio, and the ratio and product between the P and S wavespeeds, are inferred from the P-wave and S-wave velocity models. These attributes provide hints for the interpretation of an accumulation of gas below lithological barriers.

Prieux, Vincent; Brossier, Romain; Operto, Stéphane; Virieux, Jean

2013-09-01

174

Aortic Pulse Wave Analysis is not a surrogate for central arterial Pulse Wave Velocity.  

PubMed

Arterial Stiffness (AS) is a primary cardiovascular risk factor. AS increases myocardial oxygen demand and LV work and decreases coronary perfusion. Pulse Wave Velocity (PWV) is considered the gold standard for assessing AS. However, PWV testing is time consuming and impractical in the clinical setting. The purpose of this study was to determine if Pulse Wave Analysis (PWA) parameters obtained with applanation tonometry can be used to predict PWV. Radial artery PWA testing and aortic PWV measurements were performed on 77 apparently healthy subjects. A correlation matrix between all the studied variables and a stepwise multiple regression were performed. The best regression equation was obtained with central PWV as the dependent variable and Age, Height, Weight, Brachial Systolic and Diastolic Blood pressures, normalized and non-normalized Augmentation Index, Cardiac Cycle time, Ejection Duration, reflected wave round trip travel time, and time to peak pressure as independent variables. Finally, a Bland-Altman test was performed to determine the agreement between measured and predicted PWV. No significant correlations between PWV and PWA parameters were found. The resulting stepwise regression equation was PWV = 1.76 + 0.044*Age + 0.023*SBP (R = 0.544, Adj-R(2) = 0.28, P < 0.001). No agreement between measured and predicted PWV was observed using the Bland-Altman test. Although the regression equation is significant, the adjusted coefficient of determination shows that the model could explain just 28% of PWV variability. These findings suggest that PWA should not be used as a surrogate measure for assessing aortic PWV and stiffness. PMID:19657066

Gurovich, Alvaro N; Beck, Darren T; Braith, Randy W

2009-11-01

175

An automatic pulse wave velocity estimation using a blood pressure sensor for invasive measurement  

Microsoft Academic Search

The compliance and stiffness of artery are closely related to the disease of arteries. Pulse wave velocity (PWV) in the blood vessel is a basic and common parameter in the hemodynamic. Blood pressure (BP) and blood flow wave traveling in arteries are important because the PWV is affected directly by the condition of blood vessels. However, there is no standardized

Junghyeon Choi; Junho Park; Jongman Cho

2008-01-01

176

Measurement of local pulse wave velocity on aorta for noninvasive diagnosis of arteriosclerosis  

Microsoft Academic Search

Small vibrations are simultaneously measured at two adjacent points on the aortic wall near the aortic valve by electronically alternating the directions of the ultrasonic beam. The transit delay time of the pulse wave between these two points is determined from two vibration signals obtained by this alternation beam method. The local pulse wave velocity at several millimeters on the

Ryoji Murata; Hiroshi Kanai; Noriyoshi Chubachi; Yoshiro Koiwa

1994-01-01

177

Pulse wave velocity in patients with severe head injury a pilot study  

Microsoft Academic Search

The study aimed to determine the potential of pulse wave velocity measurements to reflect changes in compliant cerebral arteries\\/arterioles in head injured patients. The approach utilizes the electrocardiogram and intracranial pressure signals to measure the wave transit time between heart and cranial cavity. Thirty five clinical records of nineteen head injured patients, with different levels of cerebrovascular pressure-reactivity response, were

S. Shahsavari; T. McKelvey; B. Rydenhag; C. E. Ritzen

2010-01-01

178

Array signal processing approaches to ultrasound-based arterial pulse wave velocity estimation  

Microsoft Academic Search

Assessment of the arterial pulse wave velocity (PWV) has long been an area of interest in physiology, and ultrasound has long been used to provide measurements for such assessments. Recently, new signal processing approaches for ultrasound data have emerged. However, these methods suffer from inaccuracies due to pulse wave reflections, which are always present and can strongly bias the PWV

R. T. Hoctor; A. M. Dentinger; K. E. Thomenius

2005-01-01

179

Array signal processing for local arterial pulse wave velocity measurement using ultrasound  

Microsoft Academic Search

A new signal processing approach to estimation of local arterial pulse wave velocity (PWV) in superficial arterial segments using long-axis ultrasound measurements is proposed. The method is designed to be resistant to estimation bias due to pulse wave reflections. It is evaluated using a laboratory test tank, and it appears to estimate local PWV with less bias than previously accepted

Ralph T. Hoctor; Aaron M. Dentinger; Kai E. Thomenius

2007-01-01

180

Variational two fermion wave equation in QED  

NASA Astrophysics Data System (ADS)

We consider a reformulation of QED in which covariant Green function are used to solve for the electromagnetic field in terms of the fermion fields. The resulting modified Hamiltonian contains the photon propagator directly. A simple Fock-state variational trial function is used to derive relativistic two-fermion equations variationaly from the expectation value of the Hamiltonian of the quantum field theory. We require the trial state to be an eigen-state of the square of the total relativistic angular momentum operator, its projection and parity. The interaction kernels of the equations are shown to be, in essence, the invariant M matrix in the lowest order. Solutions of the two-body equations are presented for positronium and muonium-like systems. For small coupling constants the fine structure up to the fourth order for all states and mass ratios is calculated. Comparison with results using other formalisms will be presented.

Terekidi, Andrei; Darewych, Jurij

2002-04-01

181

Gain-Scheduled Control: Relaxing Slow Variation Requirements by Velocity-Based Douglas J. Leith  

E-print Network

@icu.strath.ac.uk 2 The effective elevator deflection, , may represent the combined action of several control surfacesGain-Scheduled Control: Relaxing Slow Variation Requirements by Velocity-Based Design Douglas J of the gain-scheduling approach to flight control tasks where the conditions required by conventional

Duffy, Ken

182

Monitoring velocity variations in the crust using earthquake doublets: An application to the Calaveras fault, California  

Microsoft Academic Search

We present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet, or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates. We compute differences in arrival times between seismograms recorded at the same station in the frequency domain by cross correlation

G. Poupinet; V. L. Ellsworth; J. Frechet

1984-01-01

183

The chromospheric line-of-sight velocity variations in a solar microflare  

NASA Astrophysics Data System (ADS)

The variations of the chromospheric line-of-sight velocity in the active region NOAA 11024 are studied before, during, and after a solar microflare on 2009 July 4. At the day of the observations the main emergence phase was in this active region. The new emerging flux has interacted with the pre-existing magnetic field. The spectropolarimetric observations were carried out with the French-Italian THEMIS telescope (Spain, Tenerife). We used H? spectra of the high resolution obtained over 21 min. The spatial resolution was ?1 arcsec. The time interval between the spectra was 2.84 s. Doppler velocities were measured in the microflare location and its surroundings. We have revealed strong temporal variations of the line-of-sight velocity in the chromosphere. The velocities changed in the range -33-10 km/s. We revealed the velocity oscillations with the amplitude of 4-5 km/s. 12-14 min before the microflare both upward and downward motions with velocity values reaching about 20 km/s are found on the outer edge of the region studied. The amplitude of the oscillations increased. It may be the signature of the magnetic reconnection.

Leiko, U. M.; Kondrashova, N. N.

2015-02-01

184

Estimation of pseudo-2D shear-velocity section by inversion of high frequency surface waves  

USGS Publications Warehouse

A scheme to generate pseudo-2D shear-velocity sections with high horizontal resolution and low field cost by inversion of high frequency surface waves is presented. It contains six steps. The key step is the joint method of crossed correlation and phase shift scanning. This joint method chooses only two traces to generate image of dispersion curve. For Rayleigh-wave dispersion is most important for estimation of near-surface shear-wave velocity, it can effectively obtain reliable images of dispersion curves with a couple of traces. The result of a synthetic example shows the feasibility of this scheme. ?? 2005 Society of Exploration Geophysicists.

Luo, Y.; Liu, J.; Xia, J.; Xu, Y.; Liu, Q.

2006-01-01

185

Negative group velocity Lamb waves on plates and applications to the scattering of sound by shells  

NASA Astrophysics Data System (ADS)

Symmetric Lamb waves on plates exhibit anomalies for certain regions of frequency. The phase velocity appears to be double-valued [M. F. Werby and H. Überall, J. Acoust. Soc. Am. 111, 2686-2691 (2002)] with one of the branches having a negative group velocity relative to the corresponding phase velocity. The classification of the symmetric plate modes for frequencies appearing to have a double-valued phase velocity is reviewed here. The complication of a double-valued velocity is avoided by examining mode orthogonality and the complex wave-number spectra. Various authors have noted an enhancement in the backscattering of sound by elastic shells in water that occurs for frequencies where symmetric leaky Lamb waves (generalized to case of a shell) have contra-directed group and phase velocities. The ray diagram for negative group velocity contributions to the scattering by shells [G. Kaduchak, D. H. Hughes, and P. L. Marston, J. Acoust. Soc. Am. 96, 3704-3714 (1994)] is unusual since for this type of mode the energy on the shell flows in the opposite direction of the wave vector. Circumnavigation of the shell is not required for the leaky ray to be backward directed.

Marston, Philip L.

2003-05-01

186

INFLUENCE OF TEMPERATURE VARIATIONS AND ACOUSTIC WAVES ON THE COLUMN  

E-print Network

REPORT INFLUENCE OF TEMPERATURE VARIATIONS AND ACOUSTIC WAVES ON THE COLUMN DENSITY. CALCULATIONS position x at fixed column density N = 5 Ã? 1017 cm-2 . . 12 1.5 Number density n(x) vs position x at fixed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1 #12;List of Tables 1.1 Injection pressure Pin throughput q and number density N vs temperature

Sharipov, Felix

187

A three-dimensional P wave velocity model for the Charlevoix seismic zone, Quebec, Canada  

NASA Astrophysics Data System (ADS)

A three-dimensional P wave velocity model has been developed for the Charlevoix seismic zone (CSZ). The CSZ is located along the St. Lawrence River ˜100 km northeast of Quebec City, Canada, and is one of the most active seismic zones in eastern North America. Five earthquakes with magnitudes equal to or exceeding 6.0 have occurred in the CSZ in historic time, and around 200 earthquakes occur annually. Hypocenters are located in Precambrian basement rocks. Basement rocks have been affected by numerous tectonic events including Grenvillian collision, Iapetan rifting, and meteor impact. We performed a sequential, tomographic inversion for P wave velocity structure based upon 3093 P wave arrivals from 489 earthquakes recorded by 12 stations. High velocity is associated with the center of the impact crater. The region of high velocity is surrounded by low velocities interpreted to be highly disrupted rocks. An elongated, high-velocity region is present at midcrustal depths that trends parallel to the St. Lawrence River. Earthquakes avoid the high-velocity body and separate into two bands, one on either side of the feature. Larger earthquakes (magnitude ? 4) have occurred along the northern edges of the high-velocity region.

Vlahovic, Gordana; Powell, Christine; Lamontagne, Maurice

2003-09-01

188

Shear wave velocities from noise correlation at local scale  

SciTech Connect

Cross correlations of ambient seismic noise recordings have been studied to infer shear seismic velocities with depth. Experiments have been done in the crowded and noisy historical centre of Napoli over inter-station distances from 50 m to about 400 m, whereas active seismic spreadings are prohibitive, even for just one receiver. Group velocity dispersion curves have been extracted with FTAN method from the noise cross correlations and then the non linear inversion of them has resulted in Vs profiles with depth. The information of near by stratigraphies and the range of Vs variability for samples of Neapolitan soils and rocks confirms the validity of results obtained with our expeditious procedure. Moreover, the good comparison of noise H/V frequency of the first main peak with 1D and 2D spectral amplifications encourages to continue experiments of noise cross-correlation. If confirmed in other geological settings, the proposed approach could reveal a low cost methodology to obtain reliable and detailed Vs velocity profiles.

De Nisco, G.; Nunziata, C. [Dipartimento di Scienze della Terra, Univ. Napoli Federico II (Italy); Vaccari, F. [Dipartimento di Scienze della Terra, Univ. Trieste (Italy); Panza, G. F. [Dipartimento di Scienze della Terra, Univ. Trieste (Italy); The Abdus Salam International Center for Theoretical Physics, ESP-SAND Group, Trieste (Italy)

2008-07-08

189

S-velocity upper mantle structure beneath the NW Pacific from surface-wave tomography  

NASA Astrophysics Data System (ADS)

The three-dimensional lithospheric structure in the north-western Pacific region is investigated by multimode surface wave tomography, incorporating finite frequency effects. The data are collected from the IRIS (Incorporated Research Institutions for Seismology) network in the north-western Pacific region. Three- component broad-band seismograms of FARM (Fast Archive Recovery Method) data recorded from seismic events with magnitudes greater than 6.0 from 1990 to 2005 are used in this study. The initial data set is composed of 23 stations and 271 events. The recorded waveforms are processed by the three-stage inversion technique of Yoshizawa & Kennett (2004), which comprises three independent steps: (1) to estimate a path-specific multi-mode phase dispersion from a fully non-linear waveform inversion, (2) to construct phase velocity maps as a function of frequency and mode, incorporating effects of finite frequency as well as off-great-circle propagation, and (3) to combine the phase velocity maps for a model of 3-D shear wave velocity. The 3-D shear wave velocity maps are obtained down to 200 km, using 740 paths. The subducting Pacific plate is clearly imaged as a high velocity anomaly up to 6 percents. A low velocity anomaly beneath Japan Sea and Okhotsk Sea is associated to the mantle wedge. The absolute S wave velocities in the mantle wedge are approximately 4 km/s, probably indicating the presence of partial melt in this area. A small-scale high velocity anomaly is located in the northern part of the Okhotsk Sea. The position of this anomaly correlates well with the high velocity anomaly found in the P-wave tomography of Gorbatov et al. (2000), which may be interpreted as a relict of the subducted Okhotsk plate.

Litvina, E.; Yoshizawa, K.; Yomogida, K.

2006-12-01

190

Detection of periodic variations in the vertical velocities of Galactic masers  

NASA Astrophysics Data System (ADS)

We have collected literature data on Galactic masers with trigonometric parallaxes measured by means of very-long-baseline interferometry (VLBI). We have obtained series of residual tangential (?Vcirc) and radial (?VR) velocities for 107 masers. Based on these series, we have re-determined the parameters of the Galactic spiral density wave using the method of spectral (periodogram) analysis. The tangential and radial perturbation amplitudes are f? = 6.0 ± 2.6 km s-1 and fR = 7.2 ± 2.2 km s-1, respectively; the perturbation wavelengths are ?? = 3.2 ± 0.5 kpc and ?R = 3.0 ± 0.6 kpc for a four-armed spiral model, m = 4. The phase of the Sun, ??, in the spiral density wave is -79° ± 14° and -199° ± 16° from the residual tangential and radial velocities, respectively. The most interesting result of this work is detecting a wave in vertical spatial velocity (W) versus distance R from the Galactic rotation axis. From spectral analysis, we have found the following characteristics for this wave: perturbation wavelength ?W = 3.4 ± 0.7 kpc and amplitude fW = 4.3 ± 1.2 km s-1.

Bobylev, V. V.; Bajkova, A. T.

2015-02-01

191

SHEAR WAVE VELOCITY FIELD TO DETECT ANOMALIES UNDER ASPHALT  

Microsoft Academic Search

Non-invasive mapping of anomalies beneath asphalt at depths from 2 m to as deep as 50 m has been successful using MASW in a variety of near-surface settings. Anomalies that include fracture zones within bedrock, dissolution\\/potential subsidence features, voids associated with old mine works, and erosional channels eched into the bedrock surface have been effectively identified in the shear wave

Richard D. Miller; Jianghai Xia; Choon Byong Park; Julian Ivanov

2001-01-01

192

Time-lapse Measurements of Scholte Wave Velocity Over a Compacting Oil Field  

NASA Astrophysics Data System (ADS)

Acquisition of time-lapse seismic data over producing oil and gas fields is a proven method for optimizing hydrocarbon production. Most current data have been acquired using towed-streamer seismic vessels but new systems incorporating permanent Ocean Bottom Cable (OBC) systems are gaining in popularity, both as a way to achieve better repeatability and also to reduce the cost of acquiring many time-lapse repeats of the baseline survey. Over the last three years, more than seven repeat data sets have been acquired at the permanent OBC system installed (by the operator, BP) over the Valhall oil field located offshore Norway. This system contains ~2400 four-component receiver stations that are recorded using a dense areal shot grid ("carpet" shoot) that provides high fold and has delivered excellent time-lapse signals starting from the first repeat occurring just three months after the baseline. Time-lapse OBC data are conventionally used to measure amplitude and velocity changes of body wave reflections (PP and PS) but other measurements are also possible. In particular, Scholte waves are strongly visible on records acquired everywhere in the field on appropriately processed data and, given the high fold (because of the dense shots), Scholte wave velocity and anisotropy time-lapse changes obtained with both hydrophone and geophone sensors are accurately and robustly estimated. The resulting shallow velocity maps are very sensitive to the seabed strains and show large velocity changes overlying deep production. Also, reconstruction of compressional "head wave" velocity difference measurements and vertically propagating shear wave shallow time-lapse statics produce maps that resemble the Scholte wave maps, with differences that reflect the physics of the propagation modes and effective fold. A reservoir model that includes deep reservoir volume changes together with appropriate geomechanical properties in the overburden and a shallow conversion of strain to velocity is used to successfully predict the measured velocity changes. The strain/velocity conversion requires asymmetry between crack opening and closing as well as velocity hysteresis and, in fact, the measurements provide an excellent laboratory for testing fracture-model/velocity conversion on in-situ rocks. After calibration, the model together with the data can constrain both volume changes in the reservoir, for making drilling decisions as well as the overburden geomechanical rock properties model, which itself is used for well- path selection and facilities decisions. Scholte wave velocity measurements can also be made using an oil platform as a "passive" source, removing the need for a conventional source near the seafloor. Finally, these measurements might be applicable on time- lapse controlled source measurements of greater generality in a wider geophysical context wherever an accurate measurement of a time-varying surface strain is desired.

Wills, P. B.; Hatchell, P. J.

2007-12-01

193

Excitation of solitons by an external resonant wave with a slowly varying phase velocity  

SciTech Connect

A novel mechanism is proposed for the excitation of solitons in nonlinear dispersive media. The mechanism employs an external pumping wave with a varying phase velocity, which provides a continuous resonant excitation of a nonlinear wave in the medium. Two different schemes of a continuous resonant growth (continuous phase-locking) of the induced nonlinear wave are suggested. The first of them requires a definite time dependence of the pumping wave phase velocity and is relatively sensitive to the initial wave phase. The second employs the dynamic autoresonance effect and is insensitive to the exact time dependence of the pumping wave phase velocity. It is demonstrated analytically and numerically, for a particular example of a driven Korteweg-de Vries (KdV) equation with periodic boundary conditions, that as the nonlinear wave grows, it transforms into a soliton, which continues growing and accelerating adiabatically. A fully nonlinear perturbation theory is developed for the driven KdV equation to follow the growing wave into the strongly nonlinear regime and describe the soliton formation.

Aranson, I.; Meerson, B. (Hebrew Univ., Jerusalem (Israel). Racah Inst. of Physics); Tajima, Toshiki (Texas Univ., Austin, TX (United States))

1992-02-01

194

Excitation of solitons by an external resonant wave with a slowly varying phase velocity  

SciTech Connect

A mechanism is proposed for the excitation of solitons in nonlinear dispersive media. The mechanism employs an external pumping wave with a varying phase velocity, which provides a continuous resonant excitation of a nonlinear wave in the medium. Two different schemes of a continuous resonant growth (continuous phase locking) of the induced nonlinear wave are suggested. The first of them requires a definite time dependence of the pumping-wave phase velocity and is relatively sensitive to the initial wave phase. The second employs the dynamic autoresonance effect and is insensitive to the exact time dependence of the pumping-wave phase velocity. It is demonstrated analytically and numerically, for a particular example of a driven Korteweg--de Vries (KdV) equation with periodic boundary conditions, that as the nonlinear wave grows, it transforms into a soliton, which continues growing and accelerating adiabatically. A fully nonlinear perturbation theory is developed for the driven KdV equation to follow the growing wave into the strongly nonlinear regime and describe the soliton formation.

Aranson, I.; Meerson, B. (Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904 (Israel)); Tajima, T. (Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States) Department of Physics, The University of Texas at Austin, Austin, Texas 78712 (United States))

1992-05-15

195

Characteristics of group velocities of backward waves in a hollow cylinder.  

PubMed

It is known that modes in axially uniform waveguides exhibit backward-propagation characteristics for which group and phase velocities have opposite signs. For elastic plates, group velocities of backward Lamb waves depend only on Poisson's ratio. This paper explores ways to achieve a large group velocity of a backward mode in hollow cylinders by changing the outer to inner radius ratio, in order that such a mode with strong backward-propagation characteristics may be used in acoustic logging tools. Dispersion spectra of guided waves in hollow cylinders of varying radii are numerically simulated to explore the existence of backward modes and to choose the clearly visible backward modes with high group velocities. Analyses of group velocity characteristics show that only a small number of low order backward modes are suitable for practical use, and the radius ratio to reach the highest group velocity corresponds to the accidental degeneracy of neighboring pure transverse and compressional modes at the wavenumber k?=?0. It is also shown that large group velocities of backward waves are achievable in hollow cylinders made of commonly encountered materials, which may bring cost benefits when using acoustic devices which take advantage of backward-propagation effects. PMID:24907803

Cui, Hanyin; Lin, Weijun; Zhang, Hailan; Wang, Xiuming; Trevelyan, Jon

2014-06-01

196

On Variational Methods in the Physics of Plasma Waves  

SciTech Connect

A fi rst-principle variational approach to adiabatic collisionless plasma waves is described. The focus is made on one-dimensional electrostatic oscillations, including phase-mixed electron plasma waves (EPW) with trapped particles, such as Bernstein-Greene-Kruskal modes. The well known Whitham's theory is extended by an explicit calculation of the EPW Lagrangian, which is related to the oscillation-center energies of individual particles in a periodic fi eld, and those are found by a quadrature. Some paradigmatic physics of EPW is discussed for illustration purposes. __________________________________________________

I.Y. Dodin

2013-03-08

197

7B.1 A 3-D VARIATIONAL METHOD FOR SINGLE-DOPPLER VELOCITY RETRIEVAL APPLIED TO A SUPERCELL STORM CASE  

E-print Network

with microphysical processes and the effect of terminal velocity. In order to correctly use the reflectivity equation7B.1 A 3-D VARIATIONAL METHOD FOR SINGLE-DOPPLER VELOCITY RETRIEVAL APPLIED TO A SUPERCELL STORM and for diagnostic studies, techniques for single-Doppler velocity retrievals (SDVR) and data assimilation have been

Xue, Ming

198

Velocity of sound behind strong shock waves in 2024 A1  

SciTech Connect

Rarefaction waves were produced by impacting a target with a thin plate. An optical technique was used to determine where the rarefaction from the back surface of the impactor overtook the shock wave induced in a step wedge target. Bromoform was placed on the front surface. When the shock reached the liquid it radiated steadily until the rarefaction from the impactor overtakes it. The times when this occurred were used to determine where the rarefaction just overtook the shock in the target, and thus the sound velocity. The leading edge of this rarefaction wave travels at longitudinal sound velocity in solids. This velocity increases smoothly with pressure until shock heating causes the material to melt. The data indicate that melting on the Hugoniot of 2024 Al begins at about 125 GPa and is completed at 150 GPa.

McQueen, R.G.; Fritz, J.N.; Morris, C.E.

1983-01-01

199

Minimal position-velocity uncertainty wave packets in relativistic and non-relativistic quantum mechanics  

SciTech Connect

We consider wave packets of free particles with a general energy-momentum dispersion relation E(p). The spreading of the wave packet is determined by the velocity v={partial_derivative}{sub p}E. The position-velocity uncertainty relation {delta}x{delta}v{>=}1/2 |<{partial_derivative}{sub p}{sup 2}E>| is saturated by minimal uncertainty wave packets {phi}(p)=Aexp(-{alpha}E(p)+{beta}p). In addition to the standard minimal Gaussian wave packets corresponding to the non-relativistic dispersion relation E(p)=p{sup 2}/2m, analytic calculations are presented for the spreading of wave packets with minimal position-velocity uncertainty product for the lattice dispersion relation E(p)=-cos(pa)/ma{sup 2} as well as for the relativistic dispersion relation E(p)={radical}(p{sup 2}+m{sup 2}). The boost properties of moving relativistic wave packets as well as the propagation of wave packets in an expanding Universe are also discussed.

Al-Hashimi, M.H. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)], E-mail: hashimi@itp.unibe.ch; Wiese, U.-J. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)

2009-12-15

200

Effects of uneven moisture distribution on the strength of and wave velocity in concrete.  

PubMed

Earlier findings showed that the effects of moisture (liquid or free water) in hardened concrete on its behavior, especially the lesser known effects ofuneven moisture distribution, can (a) be significant, and (b) vary from property to property. This distribution, for instance whether or not the surface layer is drier than the overall average moisture content, can be characterized by the difference between the velocity of the longitudinal wave (pulse velocity) measured in the standard through-thickness manner, and the velocity of the longitudinal wave propagating on the concrete surface. The summary of earlier findings on the effects of moisture distribution is followed by a recent investigation on pulse velocity in the special case, occurring frequently in practice, when the distribution is uneven because the liquid is concentrated in cracks in the concrete. PMID:15823317

Popovics, Sandor

2005-05-01

201

Hurricane Directional Wave Spectrum Spatial Variation in the Open Ocean  

NASA Technical Reports Server (NTRS)

The sea surface directional wave spectrum was measured for the first time in all quadrants of a hurricane in open water using the NASA airborne scanning radar altimeter (SRA) carried aboard one of the NOAA WP-3D hurricane hunter aircraft at 1.5 km height. The SRA measures the energetic portion of the directional wave spectrum by generating a topographic map of the sea surface. At 8 Hz, the SRA sweeps a radar beam of 1 deg half-power width (two-way) across the aircraft ground track over a swath equal to 0. 8 of the aircraft height, simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 positions. These slant ranges are multiplied by the cosine of the incidence angles to determine the vertical distances from the aircraft to the sea surface. Subtracting these distances from the aircraft height produces the sea surface elevation map. The sea surface topography is interpolated to a uniform grid, transformed by a two-dimensional FFT, and Doppler corrected. The data presented were acquired on 24 August 1998 when hurricane Bonnie was east of the Bahamas and moving slowly to the north. Wave heights up to 18 m were observed and the spatial variation of the wave field was dramatic. The dominant waves generally propagated at significant angles to the downwind direction and at times there were wave fields traveling at right angles to each other. The NOAA aircraft spent over five hours within 180 km of the hurricane Bonnie eye, and made five eye penetrations. A 2-minute animation of the directional wave spectrum spatial variation over this period will be shown.

Wright, C. W.; Walsh, E. J.; Vandemark, D.; Krabill, W. B.; Garcia, A. W.

1999-01-01

202

Abnormal temperature-dependent variation in sound velocity for the molecular liquids benzene and hexafluorobenzene  

NASA Astrophysics Data System (ADS)

In this paper we give the results of sound-velocity measurements by accurate Brillouin techniques in pure liquid benzene and hexafluorobenzene in the temperature range 20-60 °C. For both fluids, we find a clear change in the slope of the variation of the sound velocity with temperature. A change in the Landau-Placzek ratio was also detected. These experimental facts seem to confirm that a molecular-orientation ordering change occurs in this temperature range for these fluids. We see some similarity in these velocity changes with previous results found for phase changes in fluids. We believe that when the dominant molecular orientation changes in a local order scale, it creates a process strong enough to perturb the hydrodynamic behavior of the fluid, which can then be detected by spontaneous Brillouin light scattering.

Letamendia, L.; Belkadi, M.; Eloutassi, O.; Vaucamps, C.; Nouchi, G.; Iakovlev, S.; Rozhdestvenskaya, N. B.; Smirnova, L. V.; Runova, J. E.

1993-11-01

203

Electromagnetic wave propagation with negative phase velocity in regular black holes  

SciTech Connect

We discuss the propagation of electromagnetic plane waves with negative phase velocity in regular black holes. For this purpose, we consider the Bardeen model as a nonlinear magnetic monopole and the Bardeen model coupled to nonlinear electrodynamics with a cosmological constant. It turns out that the region outside the event horizon of each regular black hole does not support negative phase velocity propagation, while its possibility in the region inside the event horizon is discussed.

Sharif, M., E-mail: msharif.math@pu.edu.pk; Manzoor, R., E-mail: rubabmanzoor9@yahoo.com [University of the Punjab, Department of Mathematics (Pakistan)

2012-12-15

204

Ultrasonic wave velocities, gas permeability and porosity in natural and granular rock salt  

Microsoft Academic Search

Gas-permeability and P- and S-wave velocities were measured simultaneously as a function of pressure in core samples of rock salt from the Gorleben borehole Go 1002. In addition, compaction experiments were carried out on granular salt in order to establish velocity-porosity systematics.The initial permeabilities of the Gorleben rock salt vary between 10?16 and 2?10?20 m2 and are found to be

T. Popp; H. Kern

1998-01-01

205

New look at wave analogy for prediction of bubble terminal velocities  

Microsoft Academic Search

The analogy between waves on the surface of an infinite fluid and bubbles rising in low-viscosity fluids of infinite extent, originally proposed by Mendelson for 3-D bubbles, has been used to predict the terminal velocity, of plane bubbles. In terms of its terminal velocity, a plane bubble rising in a rectangular duct of small aspect (spacing-to-width) ratio behaves as if

Charles C. Maneri

1995-01-01

206

Wave propagation in heterogeneous, porous media: A velocity-stress, finite-difference method  

Microsoft Academic Search

A particle velocity-stress, finite-difference method is developed for the simulation of wave propagation in 2-D heterogeneous poroelastic media. Instead of the prevailing second-order differential equations, the authors consider a first-order hyperbolic system that is equivalent to Biot`s equations. The vector of unknowns in this system consists of the solid and fluid particle velocity components, the solid stress components, and the

N. Dai; E. R. Kanasewich; A. Vafidis

1995-01-01

207

Velocity-curvature relationship of colliding spherical calcium waves in rat cardiac myocytes.  

PubMed Central

Colliding spherical calcium waves in enzymatically isolated rat cardiac myocytes develop new wavefronts propagating perpendicular to the original direction. When investigated by confocal laser scanning microscopy (CLSM), using the fluorescent Ca2+ indicator fluo-3 AM, "cusp"-like structures become visible that are favorably approximated by double parabolae. The time-dependent position of the vertices is used to determine propagation velocity and negative curvature of the wavefront in the region of collision. It is evident that negatively curved waves propagate faster than positively curved, single waves. Considering two perfectly equal expanding circular waves, we demonstrated that the collision of calcium waves is due to an autocatalytic process (calcium-induced calcium release), and not to a simple phenomenon of interference. Following the spatiotemporal organization in simpler chemical systems maintained under conditions far from the thermodynamic equilibrium (Belousov-Zhabotinskii reaction), the dependence of the normal velocity on the curvature of the spreading wavefront is given by a linear relation. The so-called velocity-curvature relationship makes clear that the velocity is enhanced by curvature toward the direction of forward propagation and decreased by curvature away from the direction of forward propagation (with an influence of the diffusion coefficient). Experimentally obtained velocity data of both negatively and positively curved calcium waves were approximated by orthogonal weighted regression. The negative slope of the straight line resulted in an effective diffusion coefficient of 1.2 x 10(-4) mm2/s. From the so-called critical radius, which must be exceeded to initiate a traveling calcium wave, a critical volume (with enhanced [Ca2+]i) of approximately 12 microm3 was calculated. This is almost identical to the volume that is occupied by a single calcium spark. Images FIGURE 2 FIGURE 4 FIGURE 5 FIGURE 6 PMID:9284291

Wussling, M H; Scheufler, K; Schmerling, S; Drygalla, V

1997-01-01

208

Stiffness matrix determination of composite materials using lamb wave group velocity measurements  

NASA Astrophysics Data System (ADS)

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 group velocity. 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 velocities 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 group velocities). This paper proposes determination of the stiffness matrix from the measured group velocities, 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 group velocity 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.

Putkis, O.; Croxford, A. J.

2013-04-01

209

Measurement of elastic modulus and ultrasonic wave velocity by piezoelectric resonator  

NASA Astrophysics Data System (ADS)

A piezoelectric ceramic resonator is used for the ‘electrical’ measurement of elastic properties, i.e. Young’s modulus and ultrasonic wave velocity in metallic materials. Piezoelectric response is precisely calculated for the piezoelectric ceramic ring fixed at the end of a metallic rod. The piezoelectric ring serves as both an actuator as well as a sensor. The experimental setup and method of measurement using higher overtones is explained in detail and practically demonstrated for a set of different metallic materials. Young’s moduli and ultrasonic wave velocities are measured within 3% relative error. The presented method is suitable for an advanced engineering class or physics laboratory training.

Erhart, Ji?í

2015-01-01

210

Single Tracking Location Methods Suppress Speckle Noise in Shear Wave Velocity Estimation  

PubMed Central

In ultrasound-based elastography methods, the estimation of shear wave velocity typically involves the tracking of speckle motion due to an applied force. The errors in the estimates of tissue displacement, and thus shear wave velocity, are generally attributed to electronic noise and decorrelation due to physical processes. We present our preliminary findings on another source of error, namely, speckle-induced bias in phase estimation. We find that methods that involve tracking in a single location, as opposed to multiple locations, are less sensitive to this source of error since the measurement is differential in nature and cancels out speckle-induced phase errors. PMID:23493611

Elegbe, Etana C.; McAleavey, Stephen A.

2014-01-01

211

Measuring the acoustic wave velocity and sample thickness using an ultrasonic transducer array  

NASA Astrophysics Data System (ADS)

We suggest a new method for determining the longitudinal and transverse acoustic wave velocities and sample thicknesses, which is based on the measurement and analysis of pulsed echo signals by an array of ultrasonic transducers. Analytical expressions relating the delay of signals detected by the array and the values of parameters to be determined are obtained within the framework of a ray model of the measuring system. Measurements on a reference sample have been performed. The values of ultrasonic wave velocities and sample thickness obtained using the proposed technique agree with the results of measurements using independent methods.

Titov, S. A.; Maev, R. G.; Bogachenkov, A. N.

2009-11-01

212

Nonlinear pulse propagation and phase velocity of laser-driven plasma waves  

SciTech Connect

Laser evolution and plasma wave excitation by a relativistically-intense short-pulse laser in underdense plasma are investigated in the broad pulse limit, including the effects of pulse steepening, frequency red-shifting, and energy depletion. The nonlinear plasma wave phase velocity is shown to be significantly lower than the laser group velocity and further decreases as the pulse propagates owing to laser evolution. This lowers the thresholds for trapping and wavebreaking, and reduces the energy gain and efficiency of laser-plasma accelerators that use a uniform plasma profile.

Schroeder, Carl B.; Benedetti, Carlo; Esarey, Eric; Leemans, Wim

2011-03-25

213

Impact of localized inhomogeneity on the surface-wave velocity and bulk-wave reflection in solids.  

PubMed

The effect of a weak surface, near-surface and interfacial inhomogeneity on the frequency dependence of the surface wave velocity and of the SH (shear horizontal) wave reflectivity in isotropic elastic media is studied analytically and numerically. The inhomogeneity is modeled as an infinite planar layer with continuously varying properties. Weak inhomogeneity may markedly affect the dispersion of the Rayleigh velocity and especially of the reflectivity. It is demonstrated how this effect, particularly pronounced at high frequency, depends on the extent of inhomogeneity. The material data for damaged and ideal concrete and several simple examples of inhomogeneity profiles are utilized for the numerical calculations based on the Peano expansion. The use of explicit low- and high-frequency approximations is also exemplified. Among these, simple WKB asymptotics are shown to be particularly helpful for the Rayleigh velocity in the case of a prominent inhomogeneity attached to the surface and for the reflection on weak interfaces. PMID:17064750

Baron, C; Shuvalov, A L; Poncelet, O

2007-03-01

214

Diffusion in velocity space of solar wind protons exposed to parallel and oblique plasma waves  

NASA Astrophysics Data System (ADS)

The solar wind plasma is permeated by all kinds of waves with a broad range of wavelengths and frequencies. Kinetic plasma waves in particular can resonantly interact with the ions, a process that is described within quasilinear theory as diffusion. The resulting effects on the proton velocity distribution function (VDF) are discussed. Theoretical predictions are compared with detailed measurements made in-situ by Helios, and found to comply favourably with resonant diffusion of the protons in the wave field. The shape of the proton VDF, showing an anisotropic core and a beam at positive velocities in the solar wind frame, can well be explained by scattering of the protons in weakly compressive and obliquely propagating Alfvén/ion-cyclotron and fast/slow-magnetoacoustic waves.

Marsch, Eckart; Tu, Chuanyi

2013-06-01

215

Crustal S-wave velocity structure of the Yellowstone region using a seismic ambient noise method  

NASA Astrophysics Data System (ADS)

The Yellowstone volcano is one of the largest active volcanoes in the world, and its potential hazards demand detailed seismological and geodetic studies. Previous studies with travel time tomography and receiver functions have revealed a low-velocity layer in the crust beneath the Yellowstone volcano, suggesting the presence of a magma chamber at depth. We use ambient seismic noise from regional seismic stations to retrieve short-period surface waves and then study the shallow shear velocity structure of the Yellowstone region by surface wave dispersion analysis. We first obtained a crustal model of the area outside of the Yellowstone volcano and then constructed an absolute shear wave velocity structure in combination with receiver function results for the crust beneath the Yellowstone volcano. The velocity model shows a low-velocity layer with shear velocity at around 1.3 km/s, suggesting that a large-scale magma chamber exists at shallow levels within the crust of the Yellowstone volcanic region.

Lü, Yan; Ni, Sidao; Xie, Jun; Xia, Yingjie; Zeng, Xiangfang; Liu, Bin

2013-10-01

216

Uppermost Mantle S-wave Velocity Structure of the East Anatolian-Caucasus Region  

NASA Astrophysics Data System (ADS)

The East Anatolian-Caucasus region is a part of the orogenic belt which formed as the result of the closure of the Neo Tethys Ocean and the corresponding continental collision of Arabian and Eurasian plates. Our study region includes the southwestern part of the Caspian basin, the Kura basin, the Lesser and Greater Caucasus mountains, and the East Anatolian and North Iranian plateaus. We used the data from the Eastern Turkey Seismic Experiment network (1999-2001) in addition to the data which was recorded by 26 permanent broadband stations located in eastern Turkey and Azerbaijan during January of 2006 - July of 2008 in order to develop a 3D S-wave velocity model of the regional uppermost mantle. We selected total of 62 teleseismic events with surface wave magnitudes larger than 5.8 and with good signal-to-noise ratio to determine the fundamental mode Rayleigh wave phase velocities at 13 periods between 20 and 143 seconds. The phase velocity maps show a broad low velocity zone beneath East Anatolian and North Iranian plateaus and three high velocity zones located under the eastern part of the Greater Caucasus, the Talesh and Pontides. Furthermore, the regional uppermost mantle appears to be relatively isotropic. We inverted the Rayleigh wave phase velocities to obtain the regional 3D S-wave velocity model (0-350 km). The low velocity zone is observed starting right at the moho down to 150 km, which suggests asthenospheric material underlying a very thin lithosphere of eastern Anatolia where widespread Late Miocene - Quaternary calc-alkaline volcanic products of mantle origin are reported. Eastern Arabia and Black Sea each have lithospheric roots reaching depths of 150 km. The high velocity body beneath the eastern Greater Caucasus and Kura Basin lies at depths below the moho down to 180 km, and apparently represents either a thick lithospheric mantle root or a shallow subducting slab associated with the South Caspian block. The high velocity bodies beneath the Talesh and Pontides are observed below 160 km. We believe that these high velocity bodies represent remnant Neo Tethys slabs that broke off after the initiation of continental collision between Arabia and Eurasia and could serve as an evidence of two subduction zones beneath Pontide and Bitlis arcs during the Neogene.

Skobeltsyn, G.; Mellors, R.; Gok, R.; Turkelli, N.; Forsyth, D. W.; Sandvol, E. A.

2011-12-01

217

Signal processing for ultrasound-based arterial pulse wave velocity estimation  

Microsoft Academic Search

In this paper we propose a new signal processing approach for estimating arterial pulse wave velocity (PWV) in a uniform arterial segment based on ultrasound measurements. The new approach compensates for whatever pulse wave reflections are present in the observation. We show that the long-axis PWV estimation problem with reflections is similar to that of direction-of-arrival (DOA) estimation for two

Ralph T. Hoctor; Aaron M. Dentinger; Kai E. Thomenius

2004-01-01

218

Are There Optical Solitary Wave Solutions in Linear Media with Group Velocity Dispersion?  

NASA Technical Reports Server (NTRS)

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 group-velocity-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.

Li, Zhonghao; Zhou, Guosheng

1996-01-01

219

S-Band space traveling-wave tubes employing velocity resynchronization and collector depression  

Microsoft Academic Search

Two related traveling-wave tubes, both of which demonstrate in excess of 50 percent efficiency over the design bandwidth, are introduced. Low dielectric and conductive shield loading are combined with suitable velocity resynchronization techniques to provide effective beam-circuit wave interaction. Use is made of multi-stage depressed collectors to sort the electrons according to energy, thus recovering a portion of the spent

M. K. Schreba

1972-01-01

220

Unexpected rapid decrease in phase velocity of submeter Farley-Buneman waves with altitude  

Microsoft Academic Search

An unexpected and drastic drop in the phase velocity V ph of Farley-Buneman (FB) waves with increasing altitude was observed in the equatorial electrojet over Jicamarca. The effect was detected with the newly employed 430-MHz radar looking vertically. The decrease in V ph was 67 m\\/s and 36 m\\/s over 2.4 km for the FB waves moving towards and away

L. M. Kagan; R. S. Kissack; M. C. Kelley; R. Cuevas

2008-01-01

221

Unexpected rapid decrease in phase velocity of submeter Farley-Buneman waves with altitude  

Microsoft Academic Search

An unexpected and drastic drop in the phase velocity Vph of Farley-Buneman (FB) waves with increasing altitude was observed in the equatorial electrojet over Jicamarca. The effect was detected with the newly employed 430-MHz radar looking vertically. The decrease in Vph was 67 m\\/s and 36 m\\/s over 2.4 km for the FB waves moving towards and away from the

L. M. Kagan; R. S. Kissack; M. C. Kelley; R. Cuevas

2008-01-01

222

A universal wave spectrum for atmospheric temperature and velocity fluctuations in the stratosphere  

SciTech Connect

The first simultaneous power spectral densities of high resolution lower stratospheric temperature and horizontal/vertical velocity fluctuations are presented. Amplitudes are within a factor of 2 or 3 of other observations reported in literature. However, the measured amplitude ratios, which are absolute characteristics of the fluctuating wave field, disagree significantly (multiplicative factor up to 10) with predictions of the saturation theory. These results disagree with the concept of a universal spectrum controlled by saturated waves.

Cot, C.; Barat, J. (Service d'Aeronomie du CNRS, Verrieres le Buisson (France))

1990-09-01

223

A shear-wave velocity model of the European upper mantle from automated inversion of seismic shear and surface waveforms  

NASA Astrophysics Data System (ADS)

Broadband waveforms recorded at stations in Europe and surrounding regions were inverted for shear-wave velocity of the European upper mantle. For events between 1995 and 2007 seismograms were collected from all permanent stations for which data are available via the data centers ORFEUS, GEOFON, ReNaSs and IRIS. In addition, we incorporated data from temporary experiments, including SVEKALAPKO, TOR, Eifel Plume, EGELADOS and other projects. Automated Multimode Inversion of surface and S-wave forms was applied to extract structural information from the seismograms, in the form of linear equations with uncorrelated uncertainties. Successful waveform fits for about 70,000 seismograms yielded over 300,000 independent linear equations that were solved together for a three-dimensional tomographic model. Resolution of the imaging is particularly high in the mantle lithosphere and asthenosphere. The highest velocities in the mantle lithosphere of the East European Craton are found at about 150 km depth. There are no indications for a large scale deep cratonic root below about 330 km depth. Lateral variations within the cratonic mantle lithosphere are resolved by our model as well. The locations of diamond bearing kimberlites correlate with reduced S-wave velocities in the cratonic mantle lithosphere. This anomaly is present in regions of both Proterozoic and Archean crust, pointing to an alteration of the mantle lithosphere after the formation of the craton. Strong lateral changes in S-wave velocity are found at the western margin of the East European Craton and hint to erosion of cratonic mantle lithosphere beneath the Scandes by hot asthenosphere. The mantle lithosphere beneath Western Europe and between the Tornquist-Teyissere Zone and the Elbe Line shows moderately high velocities and is of an intermediate character, between cratonic lithosphere and the thin lithosphere of central Europe. In central Europe, Caledonian and Variscian sutures are not associated with strong lateral changes in the lithosphere-asthenosphere system. Cenozoic anorogenic intraplate volcanism in central Europe and the Circum Mediterranean is found in regions of shallow asthenosphere and close to sharp gradients in the depth of the lithosphere-asthenosphere boundary. Low-velocity anomalies extending vertically from shallow upper mantle down to the transition zone are found beneath the Massive Central, Sinai, Canary Islands and Iceland.

Legendre, C.; Meier, T.; Lebedev, S.; Friederich, W.; Viereck-Götte, L.

2012-04-01

224

The P-wave boundary of the Large-Low Shear Velocity Province beneath the Pacific  

NASA Astrophysics Data System (ADS)

The Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle represent volumetrically significant thermal or chemical or thermo-chemical heterogeneities. Their structure and boundaries have been widely studied, mainly using S-waves, but much less is known about their signature in the P-wavefield. We use an extensive dataset recorded at USArray to create, for the first time, a high-resolution map of the location, shape, sharpness, and extent of the boundary of the Pacific LLSVP using P(Pdiff)-waves. We find that the northern edge of the Pacific LLSVP is shallow dipping (26° relative to the horizontal) and diffuse (?120 km wide transition zone) whereas the eastern edge is steeper dipping (70°) and apparently sharp (?40 km wide). We trace the LLSVP boundary up to ?500 km above the CMB in most areas, and 700 km between 120° and 90°W at the eastern extent of the boundary. Apparent P-wave velocity drops are ?1-3% relative to PREM, indicating a strong influence of LLSVPs on P-wave velocity, at least in the high-frequency wavefield, in contrast to previous studies. A localised patch with a greater velocity drop of ?15-25% is detected, defined by large magnitude gradients of the travel-time residuals. We identify this as a likely location of an Ultra-Low Velocity Zone (ULVZ), matching the location of a previously detected ULVZ in this area. The boundary of a separate low velocity anomaly, of a similar height to the LLSVP, is detected in the north-west Pacific, matching tomographic images. This outlier appears to be connected to the main LLSVP through a narrow channel close to the CMB and may be in the process of joining or splitting from the main LLSVP. We also see strong velocity increases in the lower mantle to the east of the LLSVP, likely detecting subducted material beneath central America. The LLSVP P-wave boundary is similar to that determined in high-resolution S-wave studies and follows the -0.4% ?VS iso-velocity contour in the S40RTS tomography model. Additionally, the LLSVP boundary roughly matches the shape of the -0.4% ?VP iso-velocity contour of the P-wave model GyPSuM but defines an area more similar to that defined by the 0.0% VP iso-velocity contour. High resolution P-wave velocity determination allows for estimation of the ratio of P- and S-wave velocity anomalies (RS,P) which can be used to indicate dominantly thermal or chemical control of seismic velocities. Although the RS,P is found here to be approximately 2.4, which is indicative of a thermo-chemical anomaly. However, this result contains a large amount of uncertainty and the implications for the origin of LLSVPs likely remain inconclusive. Nonetheless, other observations of the Pacific LLSVP are consistent with a thermo-chemical anomaly whose shape and boundary sharpness are controlled by proximity to active and past subduction.

Frost, Daniel A.; Rost, Sebastian

2014-10-01

225

Three-dimensional P-wave velocity structure of Mt. Etna, Italy  

USGS Publications Warehouse

The three-dimensional P-wave velocity structure of Mt. Etna is determined to depths of 15 km by tomographic inversion of first arrival times from local earthquakes recorded by a network of 29 permanent and temporary seismographs. Results show a near-vertical low-velocity zone that extends from beneath the central craters to a depth of 10 km. This low-velocity region is coincident with a band of steeply-dipping seismicity, suggesting a magmatic conduit that feeds the summit eruptions. The most prominent structure is an approximately 8-km-diameter high-velocity body located between 2 and 12 km depth below the southeast flank of the volcano. This high-velocity body is interpreted as a remnant mafic intrusion that is an important structural feature influencing both volcanism and east flank slope stability and faulting.

Villasenor, A.; Benz, H.M.; Filippi, L.; De Luca, G.; Scarpa, R.; Patane, G.; Vinciguerra, S.

1998-01-01

226

Prediction of building limestone physical and mechanical properties by means of ultrasonic P-wave velocity.  

PubMed

The aim of this study was to evaluate ultrasonic P-wave velocity as a feature for predicting some physical and mechanical properties that describe the behavior of local building limestone. To this end, both ultrasonic testing and compressive tests were carried out on several limestone specimens and statistical correlation between ultrasonic velocity and density, compressive strength, and modulus of elasticity was studied. The effectiveness of ultrasonic velocity was evaluated by regression, with the aim of observing the coefficient of determination r(2) between ultrasonic velocity and the aforementioned parameters, and the mathematical expressions of the correlations were found and discussed. The strong relations that were established between ultrasonic velocity and limestone properties indicate that these parameters can be reasonably estimated by means of this nondestructive parameter. This may be of great value in a preliminary phase of the diagnosis and inspection of stone masonry conditions, especially when the possibility of sampling material cores is reduced. PMID:24511286

Concu, Giovanna; De Nicolo, Barbara; Valdes, Monica

2014-01-01

227

Rayleigh wave group velocity distributions for East Asia using ambient seismic noise  

NASA Astrophysics Data System (ADS)

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 group velocity 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 group velocities 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 group velocity regions relative to higher group velocity continental regions. At periods longer than 40 s, a low group velocity region emerges in the Ulleung basin region, and is bounded by the Korean peninsula.

Witek, Michael; van der Lee, Suzan; Kang, Tae-Seob

2014-11-01

228

Using second-sound shock waves to probe the intrinsic critical velocity of liquid helium II  

NASA Technical Reports Server (NTRS)

A critical velocity truly intrinsic to liquid helium II is experimentally sought in the bulk fluid far from the apparatus walls. Termed the 'fundamental critical velocity,' it necessarily is caused by mutual interactions which operate between the two fluid components and which are activated at large relative velocities. It is argued that flow induced by second-sound shock waves provides the ideal means by which to activate and isolate the fundamental critical velocity from other extraneous fluid-wall interactions. Experimentally it is found that large-amplitude second-sound shock waves initiate a breakdown in the superfluidity of helium II, which is dramatically manifested as a limit to the maximum attainable shock strength. This breakdown is shown to be caused by a fundamental critical velocity. Secondary effects include boiling for ambient pressures near the saturated vapor pressure or the formation of helium I boundary layers at higher ambient pressures. When compared to the intrinsic critical velocity discovered in highly restricted geometries, the shock-induced critical velocity displays a similar temperature dependence and is the same order of magnitude.

Turner, T. N.

1983-01-01

229

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

NASA Astrophysics Data System (ADS)

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 São Francisco craton remain. The fading of the Rio Grande do Norte domain fast-velocity anomaly suggests this is a supracrustal structure rather than a lithospheric terrain, and places new constraints on the Precambrian evolution of the Borborema Province.

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

2014-11-01

230

Effect of CO2 hydrate formation on seismic wave velocities of fine-grained sediments  

NASA Astrophysics Data System (ADS)

study examines the effect of gas hydrate formation on seismic wave velocities of fine-grained sediments. Synthesis of gas hydrates in fine-grained sediments has proved to be challenging, and how hydrate formation would affect the seismic wave velocities and stiffness of clay-rich sediments has not yet been fully understood. In this study, CO2 hydrate was synthesized in remolded and partially water-saturated clayey silt sediments that were originally cored from a hydrate occurrence region in the Ulleung Basin, East Sea, offshore Korea. After achieving excess water conditions, compressional wave and shear wave velocities were measured for different hydrate saturations and under different vertical effective stresses. The results reveal that the compressional wave velocity VP and shear wave velocity VS increase, and the stress-dependency of VP and VS decreases as the hydrate saturation SH increases from 0% to ~60%. In particular, the VS-SH trend lies between the grain-cementing model and the load-bearing model, suggesting that gas hydrate formation in clayey silt sediments causes weak cementation from a hydrate saturation less than ~28%. The weak cementation in fine-grained sediments can be explained by the breakage of hydrate bonds that are cementing grains during sediment compression and/or the innate weakness in bonding between hydrate crystals and fine mineral grains owing to the presence of unfrozen water films on clay mineral surfaces. In addition, it is found that at low SH, the cementation effect on VP is masked by the high stiffness of pore-filling phases, but it becomes pronounced at SH greater than 47%.

Kim, Hak-Sung; Cho, Gye-Chun; Kwon, Tae-Hyuk

2013-06-01

231

Velocity Dispersion and Attenuation of Acoustic Waves in Granular Sedimentary Media.  

NASA Astrophysics Data System (ADS)

An experimental and theoretical investigation of the effects of stress, frequency, and clay content on compressional and shear wave velocities and attenuations has been conducted using tight gas sandstone samples. The ultrasonic pulse transmission technique (~ 1 MHz) was used to measure velocities and attenuations and calculate dynamic moduli of fully brine saturated samples with porosities from 3 to 11.9 percent and clay contents from 1 to 38 percent. Simultaneous measurements were carried out to record axial and radial deformation under a biaxial stress state in order to calculate the static elastic moduli. The static moduli were found to be 1 to 6 times smaller than the dynamic moduli under the stress state. The velocities measured at ultrasonic frequency were also compared to the sonic log velocities (~20 KHz) in order to investigate dispersion effects. The trend observed in P and S wave velocities in homogeneous intervals shows that clean sandstone velocities measured in the ultrasonic frequency range deviate systematically from the log derived velocities. Compressional and shear wave amplitude data exhibited a shift in peak frequency toward lower frequencies for clay rich samples as compared to clean samples showing the important role clays play in the dissipative behavior of sandstones. The deviations from the log derived velocities are correlatable in most cases to the clay content and dispersion. The presence of clay softens the rock grain contacts and causes larger contact area values compared to the values for nearly clean rock under the same applied load. The frame moduli of sedimentary rocks are strongly influenced by the properties of the grain contacts. A modified Hertz contact theory is presented for the self consistent calculation of contact deformation, equilibrium separation distance (film thickness) and contact area for two spherical asperities in contact and subjected to an external load. It is shown that surface forces, i.e. electrostatic repulsion, Born, structural, and Van der Waals forces can be incorporated into the contact deformation problem. These forces play an important role in determining seismic wave velocities and attenuations at low confining stresses. The computed equilibrium separation distances and contact radii were used to calculate velocities and attenuations as a function of frequency and compared with measured values for glass beads, Navajo, Berea, Obernkirchner and Fort Union sandstones. The velocities and attenuations calculated as functions of stress, frequency, fluid type and saturation are all in good agreement with reported experimental data.

Tutuncu, Azra Nur

232

Surface acoustic waves with negative group velocity in a thin film structure on silicon  

NASA Astrophysics Data System (ADS)

A surface acoustic wave dispersion curve of a thin film structure on silicon measured with the laser-induced transient grating technique displays a local minimum in frequency at nonzero wavenumber. For a range of wavenumbers to one side of this minimum the dispersion curve is of negative slope, implying the existence of surface waves with negative group velocity. Unlike in the well studied case of "backward traveling" Lamb waves in plates, the anomalous behavior here is exhibited by the lowest acoustic mode of the structure. The existence of the local minimum in the dispersion curve is corroborated by numerical simulations.

Maznev, A. A.; Every, A. G.

2009-07-01

233

Total-variation-based methods for gravitational wave denoising  

E-print Network

We describe new methods for denoising and detection of gravitational waves embedded in additive Gaussian noise. The methods are based on Total Variation denoising algorithms. These algorithms, which do not need any a priori information about the signals, have been originally developed and fully tested in the context of image processing. To illustrate the capabilities of our methods we apply them to two different types of numerically-simulated gravitational wave signals, namely bursts produced from the core collapse of rotating stars and waveforms from binary black hole mergers. We explore the parameter space of the methods to find the set of values best suited for denoising gravitational wave signals under different conditions such as waveform type and signal-to-noise ratio. Our results show that noise from gravitational wave signals can be successfully removed with our techniques, irrespective of the signal morphology or astrophysical origin. We also combine our methods with spectrograms and show how those can be used simultaneously with other common techniques in gravitational wave data analysis to improve the chances of detection.

Alejandro Torres; Antonio Marquina; José A. Font; José M. Ibáñez

2014-09-28

234

Total-variation-based methods for gravitational wave denoising  

NASA Astrophysics Data System (ADS)

We describe new methods for denoising and detection of gravitational waves embedded in additive Gaussian noise. The methods are based on total variation denoising algorithms. These algorithms, which do not need any a priori information about the signals, have been originally developed and fully tested in the context of image processing. To illustrate the capabilities of our methods we apply them to two different types of numerically-simulated gravitational wave signals, namely bursts produced from the core collapse of rotating stars and waveforms from binary black hole mergers. We explore the parameter space of the methods to find the set of values best suited for denoising gravitational wave signals under different conditions such as waveform type and signal-to-noise ratio. Our results show that noise from gravitational wave signals can be successfully removed with our techniques, irrespective of the signal morphology or astrophysical origin. We also combine our methods with spectrograms and show how those can be used simultaneously with other common techniques in gravitational wave data analysis to improve the chances of detection.

Torres, Alejandro; Marquina, Antonio; Font, José A.; Ibáñez, José M.

2014-10-01

235

RESEARCH NOTE : Shear-wave velocity in marine sediments on young oceanic crust: constraints from dispersion analysis of Scholte waves  

NASA Astrophysics Data System (ADS)

An experiment with a newly developed implosive source, located about 1 m above the seafloor at 3665 m depth, revealed a slow interface wave. This wave is attributed to S waves in a soft sediment layer covering the hard rock sub-bottom. Dispersion analysis by means of the multiple-filter technique yields the group velocity as a function of frequency. Model calculations showed that the observed dispersion curve can be reproduced by considering a steep gradient of S velocity within the sediment layer. Nearly perfect agreement of experimental and model data could be achieved with a sediment layer thickness of 21.5 m, an S speed of 225 m s- 1 at the water-sediment interface and an increase by 23 s- 1 within the layer. These values are relatively high compared to data from the literature. However, previous estimates of in situ S-wave velocity have been obtained on old oceanic crust in the vicinity of continents or islands, while our experiment was carried out on young Pacific crust. Therefore, we suggest two mechanisms which could support a relatively high S speed in sediments: (1) the input of hydrothermally generated metalliferous sediments from the adjacent spreading axis; and (2) post-depositional diagenesis which has accelerated the induration of sediments.

Heinz-Essen, H.; Grevemeyer, Ingo; Herber, Rolf; Weigel, Wilfried

1998-01-01

236

An empirical method to estimate shear wave velocity of soils in the New Madrid seismic zone  

USGS Publications Warehouse

In this study, a set of charts are developed to estimate shear wave velocity of soils in the New Madrid seismic zone (NMSZ), using the standard penetration test (SPT) N values and soil depths. Laboratory dynamic test results of soil samples collected from the NMSZ showed that the shear wave velocity of soils is related to the void ratio and the effective confining pressure applied to the soils. The void ratio of soils can be estimated from the SPT N values and the effective confining pressure depends on the depth of soils. Therefore, the shear wave velocity of soils can be estimated from the SPT N value and the soil depth. To make the methodology practical, two corrections should be made. One is that field SPT N values of soils must be adjusted to an unified SPT N??? value to account the effects of overburden pressure and equipment. The second is that the effect of water table to effective overburden pressure of soils must be considered. To verify the methodology, shear wave velocities of five sites in the NMSZ are estimated and compared with those obtained from field measurements. The comparison shows that our approach and the field tests are consistent with an error of less than of 15%. Thus, the method developed in this study is useful for dynamic study and practical designs in the NMSZ region. Copyright ?? 1996 Elsevier Science Limited.

Wei, B.-Z.; Pezeshk, S.; Chang, T.-S.; Hall, K.H.; Liu, H.-P.

1996-01-01

237

perovskite phase suggests slow longitudinal elastic-wave velocities propagating along the  

E-print Network

perovskite phase suggests slow longitudinal elastic-wave velocities propagating along the [010] direction. In addition, it is also inferred that the post-perovskite phase forms a platy crystal habit) observed in the D region (1, 2) is possibly caused by the preferred orientation of the post-perovskite

Hansell, Dennis

238

Effect of a Shallow Water Obstruction on Long Wave Runup and Overland Flow Velocity  

E-print Network

that there was a compelling correlation between coral mining and locally severe tsunami damage. Analytical, experimental:6 455 CE Database subject headings: Tsunamis; Wave runup; Reefs; Numerical models; Velocity; Overland interacts with any coastal features in its path, such as reefs, bars, and dunes. The role of these obstacles

Lynett, Patrick

239

Measurement of Local Pulse Wave Velocity: Effects of Signal Processing on Precision  

Microsoft Academic Search

Pulse wave velocity (PWV) provides information about the mechanical properties of the vessel: the stiffer the artery is, the higher the PWV will be. PWV measured over a short arterial segment facilitates direct characterization of local wall properties corrected for prevailing pressure without the necessity of measuring pulse pressure locally. Current methods for local PWV assessment have a poor precision,

Evelien Hermeling; Koen D. Reesink; Robert S. Reneman; Arnold P. G. Hoeks

2007-01-01

240

Measurement of local pulse wave velocity in arteriosclerosis by ultrasonic Doppler method  

Microsoft Academic Search

This paper presents a new method to measure local pulse wave velocity (PWV), which is an index of the hardness in the range of several millimeters on the aortic wall for diagnosis of the early stage arteriosclerosis. Small vibration signals are measured simultaneously at two adjacent points on the aortic wall near the aortic valve by electronically alternating the direction

N. Chubachi; H. Kanai; R. Murata; Y. Koiwa

1994-01-01

241

ACE stimulated neural network for shear wave velocity determination from well logs  

NASA Astrophysics Data System (ADS)

Shear wave velocity provides invaluable information for geomechanical, geophysical, and reservoir characterization studies. However, measurement of shear wave velocity is time, cost and labor intensive. This study proposes a swift and exact methodology, called ACE stimulated neural network, for prediction of shear wave velocity from available well logs such that it will be able to surpass previous models. The proposed method is composed of two major parts: 1) transforming input/output data space to a higher correlated space using alternative condition expectation (ACE), and 2) making a neural network formulation in transformed data space. Transforming in the first step makes it easier for neural network to find the complicated underlying dependency of input/output data. Therefore, neural network will be able to develop an accurate and strong formulation between conventional well logs and shear wave velocity. The Propounded approach was successfully applied in one of the carbonate gas fields of Iran. A comparison between proposed model and previous models showed superiority of ACE stimulated neural network.

Asoodeh, Mojtaba; Bagheripour, Parisa

2014-08-01

242

P-wave velocity structure of the uppermost mantle beneath Hawaii from traveltime tomography  

USGS Publications Warehouse

We examine the P-wave velocity 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 velocity 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 velocities 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 velocities 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-velocity zone cannot be explained in terms of conductive heating by one primary conduit per volcano but that more complicated melt pathways must exist.

Tilmann, F.J.; Benz, H.M.; Priestley, K.F.; Okubo, P.G.

2001-01-01

243

Crustal thickness variation beneath the Romanian seismic network from Rayleigh wave dispersion and receiver function analysis  

NASA Astrophysics Data System (ADS)

Variations in crustal thickness in Romania where determined by joint inversion of P wave receiver functions (RFs) and Rayleigh wave group velocity dispersion. We present new models of shear wave velocity structure of the crust beneath Romanian broad band stations. The data set consist in more than 500 teleseismic earthquake with epicentral distance between 30° and 95°, magnitude greater than 6 and a signal-to-noise ratio greater than 3 for the P-wave pulse. Most epicenters are situated along the northern Pacific Rim and arrive with backazimuths (BAZs) between 0° and 135° at the Romanian seismic network. We combine receiver functions with fundamental-mode of the Rayleigh wave group velocities to further constrain the shear-wave velocity structure.To extract the group velocities we applied the Multiple Filter Technique analysis to the vertical components of the earthquakes recordings. This technique allowed us to identify the Rayleigh wave fundamental mode and to compute the dispersion curves of the group velocities at periods between 10 and 150 s allowing us to resolve shear wave velocities to a depth of 100 km. The time-domain iterative deconvolution procedure of Ligorr?a and Ammon (1999) was employed to deconvolve the vertical component of the teleseismic P waveforms from the corresponding horizontal components and obtain radial and transverse receiver functions at each broadband station. The data are inverted using a joint, linearized inversion scheme (Hermann, 2002) which accounts for the relative influence of each set of observations, and allows a trade-off between fitting the observations, constructing a smooth model, and matching a priori constraints. The results show a thin crust for stations located inside the Pannonian basin (28-30 km) and a thicker crust for those in the East European Platform (36-40 km). The stations within the Southern and Central Carpathian Orogen are characterized by crustal depths of ~35 km. For stations located in the Northern part of the Eastern Carpathians we found a crustal depth of 32 km. For two station located in the Apuseni Mountains the Moho discontinuity is replace by a transition zone extended between 36 to 40 km depth. For a station located in the Carpathians bent area we identify a double Moho (32 respectively 44 km depth) possible due to the Vrancea subduction process. For the crust of Moesian Platform we get higher values (~35 km) compare to those obtained from seismic refraction profile (VRANCEA'2001). The North Dobrogea crust reaches a thickness of about 44-46 km. For most of the stations the crust-mantle transition zone has a significant gradient, with velocity values varying from 3.8 to 4.7 km/s. Our results are compatible with results from previous studies.

Tataru, Dragos; Grecu, Bogdan; Zaharia, Bogdan

2014-05-01

244

Subduction zones beneath Indonesia imaged by Rayleigh wave phase velocity tomography  

NASA Astrophysics Data System (ADS)

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 derived from these 2-D phase velocity maps at different periods, which is in progress, certainly will sharpen the images of the complex subduction system, unraveling more geodynamic processes in this region.

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

2013-12-01

245

Explicit use of the Biot coefficient in predicting shear-wave velocity of water-saturated sediments  

USGS Publications Warehouse

Predicting the shear-wave (S-wave) velocity is important in seismic modelling, amplitude analysis with offset, and other exploration and engineering applications. Under the low-frequency approximation, the classical Biot-Gassmann theory relates the Biot coefficient to the bulk modulus of water-saturated sediments. If the Biot coefficient under in situ conditions can be estimated, the shear modulus or the S-wave velocity can be calculated. The Biot coefficient derived from the compressional-wave (P-wave) velocity of water-saturated sediments often differs from and is less than that estimated from the S-wave velocity, owing to the interactions between the pore fluid and the grain contacts. By correcting the Biot coefficients derived from P-wave velocities of water-saturated sediments measured at various differential pressures, an accurate method of predicting S-wave velocities is proposed. Numerical results indicate that the predicted S-wave velocities for consolidated and unconsolidated sediments agreewell with measured velocities. ?? 2006 European Association of Geoscientists & Engineers.

Lee, M.W.

2006-01-01

246

Shear wave velocity structure of the Anatolian Plate and surrounding regions using Ambient Noise Tomography  

NASA Astrophysics Data System (ADS)

The Anatolian Plate consists of various lithospheric terranes amalgamated during the closure of the Tethys Ocean, and is currently extruding to the west in response to a combination of the collision of the Arabian plate in the east and the roll back of the Aegean subduction zone in the west. We used Ambient Noise Tomography (ANT) at periods <= 40s to investigate the crust and uppermost mantle structure of the Anatolian Plate. We computed a total of 13,779 unique cross-correlations using one sample-per-second vertical component broadband seismic data from 215 stations from 8 different networks over a period of 7 years to compute fundamental-mode Rayleigh wave dispersion curves following the method of Benson et al. (2007). We then inverted the dispersion data to calculate phase velocity maps for 11 periods from 8 s - 40 s throughout Anatolia and the Aegean regions (Barmin et al. 2001). Using smoothed Moho values derived from Vanacore et al. (2013) in our starting models, we inverted our dispersion curves using a linear least-squares iterative inversion scheme (Herrmann & Ammon 2004) to produce a 3-D shear-wave velocity model of the crust and uppermost mantle throughout Anatolia and the Aegean. We find a good correlation between our seismic shear wave velocities and paleostructures (suture zones) and modern deformation (basin formation and fault deformation). The most prominent crustal velocity contrasts occur across intercontinental sutures zones, resulting from the juxtaposition of the compositionally different basements of the amalgamated terranes. At shallow depths, seismic velocity contrasts correspond closely with surficial features. The Thrace, Cankiri and Tuz Golu basins, and accretionary complexes related to the closure of the Neotethys are characterized by slow shear wave velocities, while the Menderes and Kirsehir Massifs, Pontides, and Istanbul Zone are characterized by fast velocities. We find that the East Anatolia Plateau has slow shear-wave velocities, as expected due to high heat flow and active volcanism. The Tuz Golu fault has a visible seismic signal down to ~15 km below sea level, and the eastern Inner-Tauride Suture corresponding to the Central Anatolian Fault Zone may extend into the mantle. The Isparta Angle separates the actively extending portion of western Anatolia from the plateau regions in the east, and the largest anomaly (slow velocities) extending into the upper mantle is observed under the western flank of the Isparta Angle, corresponding to the Fethiye-Burdur fault zone. We attribute these slow shear-wave velocities to the effects of complex deformations within the crust as a result of the interactions of the African and Anatolian Plates. In the upper mantle, slow shear-wave velocities are consistent with a slab tear along a STEP fault corresponding to the extensions of the Pliny and Strabo Transform faults, allowing asthenosphere to rise to very shallow depths. The upper mantle beneath the Taurides exhibits very slow shear-wave velocities, in agreement with possible delamination or slab-breakoff (Cosentino et al. 2012) causing rapid uplift in the last 8 million years.

Delph, J. R.; Beck, S. L.; Zandt, G.; Biryol, C. B.; Ward, K. M.

2013-12-01

247

Generation of electromagnetic waves in the very low frequency band by velocity gradient  

SciTech Connect

It is shown that a magnetized plasma layer with a velocity gradient in the flow perpendicular to the ambient magnetic field is unstable to waves in the Very Low Frequency band that spans the ion and electron gyrofrequencies. The waves are formally electromagnetic. However, depending on wave vector k{sup ¯}=kc/?{sub pe} (normalized by the electron skin depth) and the obliqueness, k{sub ?}/k{sub ||}, where k{sub ?,||} are wave vectors perpendicular and parallel to the magnetic field, the waves are closer to electrostatic in nature when k{sup ¯}?1 and k{sub ?}?k{sub ||} and electromagnetic otherwise. Inhomogeneous transverse flows are generated in plasma that contains a static electric field perpendicular to the magnetic field, a configuration that may naturally arise in the boundary layer between plasmas of different characteristics.

Ganguli, G., E-mail: Gurudas.Ganguli@nrl.navy.mil; Tejero, E.; Crabtree, C.; Amatucci, W. [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375-5346 (United States)] [Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375-5346 (United States); Rudakov, L. [Icarus Research Inc., P.O. Box 30780, Bethesda, Maryland 20824-0780 (United States)] [Icarus Research Inc., P.O. Box 30780, Bethesda, Maryland 20824-0780 (United States)

2014-01-15

248

A reappraisal of surface wave group velocity tomography in the Subantarctic Scotia Sea and surrounding ridges  

NASA Astrophysics Data System (ADS)

A reappraisal of surface wave tomography in the remote Scotia Sea region and surrounding ridges is presented. New group velocity dispersion curves were obtained from local and regional earthquakes recorded at permanent Antarctic stations from 2001 to 2013 and used to update the measurements reported by Vuan et al. (2000). Rayleigh and Love group velocity maps for periods ranging from 15 to 50 s were retrieved using a tomographic inversion. The group velocity anomalies are clearly associated with the major crustal and upper mantle features of the Antarctic, Scotia and South American plates. The updated dataset allows for considerable decrease of the correlation length of the crustal heterogeneities that can be resolved, especially in the west Scotia Sea, central Scotia Sea and Bransfield Basin. Surface wave tomography results were compared with CRUST 1.0 group velocity maps and revealed specific areas where more detailed information is made available by our regional study. In particular, low group velocity anomalies of the Bransfield Strait rifting and continental fragments that are detached from the Antarctic Peninsula and spreading along the South Scotia ridge are not shown by the reference CRUST 1.0 model. A comparison between the average seismic velocities beneath the west and central Scotia Sea shows that both have an oceanic-type structure; however, the crust of the central sea is thicker (12-14 km) and slower than that of the 20 Ma old western sea.

Vuan, A.; Sugan, M.; Plasencia Linares, M. P.

2014-12-01

249

Second sound shock waves and critical velocities in liquid helium 2. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

Large amplitude second-sound shock waves were generated and the experimental results compared to the theory of nonlinear second-sound. The structure and thickness of second-sound shock fronts are calculated and compared to experimental data. Theoretically it is shown that at T = 1.88 K, where the nonlinear wave steepening vanishes, the thickness of a very weak shock must diverge. In a region near this temperature, a finite-amplitude shock pulse evolves into an unusual double-shock configuration consisting of a front steepened, temperature raising shock followed by a temperature lowering shock. Double-shocks are experimentally verified. It is experimentally shown that very large second-sound shock waves initiate a breakdown in the superfluidity of helium 2, which is dramatically displayed as a limit to the maximum attainable shock strength. The value of the maximum shock-induced relative velocity represents a significant lower bound to the intrinsic critical velocity of helium 2.

Turner, T. N.

1979-01-01

250

Condition assessment of PC tendon duct filling by elastic wave velocity mapping.  

PubMed

Imaging techniques are high in demand for modern nondestructive evaluation of large-scale concrete structures. The travel-time tomography (TTT) technique, which is based on the principle of mapping the change of propagation velocity of transient elastic waves in a measured object, has found increasing application for assessing in situ concrete structures. The primary aim of this technique is to detect defects that exist in a structure. The TTT technique can offer an effective means for assessing tendon duct filling of prestressed concrete (PC) elements. This study is aimed at clarifying some of the issues pertaining to the reliability of the technique for this purpose, such as sensor arrangement, model, meshing, type of tendon sheath, thickness of sheath, and material type as well as the scale of inhomogeneity. The work involved 2D simulations of wave motions, signal processing to extract travel time of waves, and tomography reconstruction computation for velocity mapping of defect in tendon duct. PMID:24737961

Liu, Kit Fook; Chai, Hwa Kian; Mehrabi, Nima; Yoshikazu, Kobayashi; Shiotani, Tomoki

2014-01-01

251

Condition Assessment of PC Tendon Duct Filling by Elastic Wave Velocity Mapping  

PubMed Central

Imaging techniques are high in demand for modern nondestructive evaluation of large-scale concrete structures. The travel-time tomography (TTT) technique, which is based on the principle of mapping the change of propagation velocity of transient elastic waves in a measured object, has found increasing application for assessing in situ concrete structures. The primary aim of this technique is to detect defects that exist in a structure. The TTT technique can offer an effective means for assessing tendon duct filling of prestressed concrete (PC) elements. This study is aimed at clarifying some of the issues pertaining to the reliability of the technique for this purpose, such as sensor arrangement, model, meshing, type of tendon sheath, thickness of sheath, and material type as well as the scale of inhomogeneity. The work involved 2D simulations of wave motions, signal processing to extract travel time of waves, and tomography reconstruction computation for velocity mapping of defect in tendon duct. PMID:24737961

Liu, Kit Fook; Mehrabi, Nima; Yoshikazu, Kobayashi; Shiotani, Tomoki

2014-01-01

252

Seismic velocity variations at TCDP are controlled by MJO driven precipitation pattern and high fluid discharge properties  

NASA Astrophysics Data System (ADS)

Using seismic noise based monitoring techniques we find that seismic velocity variations (dv/v) observed with the borehole array of the Taiwan Chelungpu-fault Drilling Project (TCDP) are controlled by strong precipitation events associated with the Madden-Julian Oscillation (MJO), a dynamic intraseasonal atmospheric pattern in the tropical atmosphere. High-frequency noise (>1 Hz) excited by steady anthropogenic activity in the vicinity of the TCDP allows daily resolution of dv/v time series. Relatively large fluid discharge properties control the equilibration of the ground water table and hence seismic velocities on time scales smaller than the average precipitation recurrence interval. This leads to the observed synchronous 50-80 day periodicity in dv/v and rainfall records in addition to the dominant annual component. Further evidence for the governing role of hydraulic properties is inferred from the similarity of observed dv/v timing, amplitude, and recovery properties with dv/v synthetics generated by a combined model of ground water table changes and diffusive propagation of seismic energy. The lapse time (?) dependent increase of dv/v amplitudes is controlled by the sensitivity of the diffuse wave field sampled at 1100 m depth to shallower water level fluctuations. The significant vertical offset between stations and water level explains the direct ? dependence which is opposite to the trend previously inferred from measurements at the surface.

Hillers, G.; Campillo, M.; Ma, K.-F.

2014-04-01

253

Landstreamer Use for Near-Surface P- and S-Wave Velocities and Poisson's Ratio  

NASA Astrophysics Data System (ADS)

Seismic landstreamer use is becomingly increasingly important in shallow seismic investigations where cost or time efficiency is critical. Applications range from locating underground voids to investigating archaeological sites, and recently to determining engineering parameters such as Poisson's ratio and shear modulus. The advantage of a landstreamer is the capability to drag a geophone array from location to location rather than planting individual geophones by hand each time the array is moved. Comparison studies have shown that data quality from landstreamer geophones and conventionally planted spiked geophones is similar and often practically indistinguishable. The Geophysical Engineering Department at Montana Tech has been using seismic landstreamers to aid data collection for projects that use both diving wave tomographic inversion to produce P-wave velocity images and surface wave dispersion inversion to estimate S-wave velocity images. We then use the P-wave and S-wave velocity images to calculate a Poisson's ratio image. All of these are produced from the same set of recorded shot gathers using vertical component, gimbaled geophones in a landstreamer configuration. This combined use of landstreamers and single mode geophones proves to be an extremely efficient method for determining subsurface parameters of interest. We used this approach to image an open-top buried cement structure at a local geophysical test site. The two velocity images and Poisson's ratio image show good agreement with expected values and clearly show the location of the buried structure. We also used this approach to characterize a leaking earthen mine tailings dam. Results from this investigation highlight areas interpreted to be weak zones associated to known leakage locations.

Link, C. A.; Speece, M. A.

2006-12-01

254

Intima-media thickness of carotid artery and aortic pulse wave velocity as determinants of cerebral blood flow velocity.  

PubMed

The current study aims to check the relationship between parameters derived from brachial blood pressure, the carotid artery intima-media thickness (IMT), pulse wave velocity (PWV) and mean cerebral blood flow velocity (mCBFV) in the middle cerebral artery (MCA). In consecutive adult outpatients we recorded the brachial systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), mean arterial blood pressure (MAP), PWV and IMT. mCBFV was assessed using Doppler ultrasound probe applied to the transtemporal window. The mean±s.d. age of 165 patients (50% women) was 56.7±11.8 years. Women and men differed significantly in SBP, PP, total cholesterol and mCBFV. Age (r=-0.44, P<0.001) and BMI (r=-0.25, P<0.01) were significantly and reversely related to mCBFV. Compared with healthy individuals, hypertensive (P<0.05) and diabetic (P<0.01) patients had lower mCBFV. IMT and PWV were related to mCBFV (IMT, r=-0.36; P<0.001, and PWV, r=-0.34; P<0.001). After adjustment for possible confounders, the relationship between mCBFV and PWV did not retain statistical significance (P=0.54). However, the relationship between mCBFV and IMT remained statistically significant (P=0.02). The association between lower CBFV and higher IMT may constitute a link between increased IMT and risk of cerebrovascular events. PMID:24304708

Kwater, A; G?sowski, J; Grodzicki, T

2014-06-01

255

Seasonal variation of solitary wave properties in Lake Constance  

NASA Astrophysics Data System (ADS)

The properties of internal solitary waves (ISWs) depend on the stratification of the water body. In most climatic regions the stratification in lakes and oceans varies during the year, and hence the properties of the ISWs can also be expected to change over the seasons. On the basis of a long-term temperature time series recorded over 6 years, this paper investigates seasonal changes in the characteristic properties of ISWs in Lake Überlingen, a subbasin of Lake Constance. A large number of ISWs with amplitudes ranging from 3 m to 30 m were identified. More than 15% of the leading ISWs of a wave train were associated with density inversions, often indicating shear instabilities or trapped cores. For all waves the propagation depth and the value of a nonlinearity index nlp providing the degree of nonlinearity were determined, propagation depth being the rest height of the isotherm undergoing maximum displacement and nlp the ratio between wave amplitude and propagation depth. The index nlp was found to be a good parameter for predicting the occurrence of inversions. The statistical analysis of the wave properties derived from the observations revealed that the degree of nonlinearity of the ISWs changes with season. Complementary to the statistical analysis, the seasonally averaged ISW properties were compared with wave prototypes obtained numerically from the Dubreil-Jacotin-Long (DJL) and the stratified Korteweg-deVries (KdV) models. The simulations indicate that the typical stratification and its seasonal variation are responsible for the degree and the seasonality of nonlinearity of the ISWs.

Preusse, M.; Freistühler, H.; Peeters, F.

2012-04-01

256

Solar cycle variation of gravity waves observed in OH airglow  

NASA Astrophysics Data System (ADS)

Airglow imaging provides a unique means by which to study many wave-related phenomena in the 80 to 100 km altitude regime. Two-dimensional image observations reveal quasi-monochromatic disturbances associated with atmospheric gravity waves (AGWs) as well as small-scale instabilities, often called ripples. Image-averaged temperature and intensity measurements can be used to study the response of the airglow layer to tides and planetary waves, as well as monitor longer-term climatological variations. Here we present results of low and mid-latitude OH airglow observations beginning near solar max of solar cycle 23 and continuing through solar max of cycle 24. Aerospace imagers deployed at Alice Springs (23o42'S, 133o53'E) and Adelaide (34o55'S, 138o36'E) have been operating nearly continuously since ~2001. The imagers employ filters measuring OH Meinel (6, 2) and O2 Atmospheric (0, 1) band emission intensities and temperatures, as well as atmospheric gravity wave parameters. The Aerospace Corporation's Infrared Camera deployed at Maui, HI (20.7N,156.3W), collected more than 700 nights of airglow images from 2002-2005. The camera measures the OH Meinel (4,2) emission at 1.6 um using a 1 second exposure at a 3 second cadence, which allows the study of AGW and ripple features over very short temporal and spatial scales. The camera was relocated to Cerro Pachon, Chile (30.1 S, 70.8 W) and has been operating continuously since 2010. Temperature, intensity and gravity wave climatologies derived from the two Australian airglow imagers span a full solar cycle (solar max to solar max). Emission intensities have been calibrated using background stars, and temperatures have been calibrated with respect to TIMED/SABER temperatures, reducing the influence of instrument degradation on the solar cycle climatology. An automated wave detection algorithm is used to identify quasi monochromatic wave features in the airglow data, including wavelength, wave period and propagation direction. Supplemental observations of OH emission brightness and gravity waves (including ripple climatology) at Maui (2002-2005) and Chile (2010-present) will be compared to the Australian observations.

Gelinas, L. J.; Hecht, J. H.; Walterscheid, R. L.; Reid, I. M.; Woithe, J.; Vincent, R. A.

2013-12-01

257

Assessment of Pulse Wave Velocity and Augmentation Index in different arteries in patients with severe coronary heart disease  

Microsoft Academic Search

The aim of this study was to assess pulse wave velocity (PWV) and augmentation index in different arteries in patients with severe coronary heart disease (CHD). Signal measurements were obtained from 28 subjects. Severe coronary heart disease was confirmed by coronary angiography. Aortic PWV and augmentation Index were measured using the TENSIOMed Arteriograph. Four other pulse wave velocities (upper limb

Irina Hlimonenko; Kalju Meigas; Margus Viigimaa; Kristiina Temitski

2007-01-01

258

Three-dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi-net  

E-print Network

Three-dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi seismic noise. We applied this method to the recording of Hi-net tiltmeters in Japan at 679 stations from), Three-dimensional crustal S wave velocity structure in Japan using microseismic data recorded by Hi

Kawakatsu, Hitoshi

259

Mass variation governed by the universe expansion velocity and the cosmic acceleration  

E-print Network

Much effort has been made in trying to solve, or at least evade, the inconsistencies that emerge from general relativity as the framework for a cosmological model. The extradimensional models rise as superb possibilities on this regard. In this work I present Wesson's Space-Time-Matter theory of gravity cosmological solutions. A relation between mass variation at cosmological scales and the expansion velocity of the universe is obtained. Such a novelty on Space-Time-Matter theory of gravity predicts a transition from a decelerated to an accelerated phase of the universe expansion.

Moraes, Pedro H R S

2015-01-01

260

Variations in the electrical short-circuit current decay for recombination lifetime and velocity measurements  

NASA Technical Reports Server (NTRS)

An improved measurement system for electrical short-circuit current decay is presented that extends applicability of the method to silicon solar cells having an effective lifetime as low as 1 microsec. The system uses metal/oxide/semiconductor transistors as voltage-controlled switches. Advances in theory developed here increase precision and sensitivity in the determination of the minority-carrier recombination lifetime and recombination velocity. A variation of the method, which exploits measurements made on related back-surface field and back-ohmic contact devices, further improves precision and sensitivity. The improvements are illustrated by application to 15 different silicon solar cells.

Jung, Tae-Won; Lindholm, Fredrik A.; Neugroschel, Arnost

1987-01-01

261

Variational stereo imaging of oceanic waves with statistical constraints.  

PubMed

An image processing observational technique for the stereoscopic reconstruction of the waveform of oceanic sea states is developed. The technique incorporates the enforcement of any given statistical wave law modeling the quasi-Gaussianity of oceanic waves observed in nature. The problem is posed in a variational optimization framework, where the desired waveform is obtained as the minimizer of a cost functional that combines image observations, smoothness priors and a weak statistical constraint. The minimizer is obtained by combining gradient descent and multigrid methods on the necessary optimality equations of the cost functional. Robust photometric error criteria and a spatial intensity compensation model are also developed to improve the performance of the presented image matching strategy. The weak statistical constraint is thoroughly evaluated in combination with other elements presented to reconstruct and enforce constraints on experimental stereo data, demonstrating the improvement in the estimation of the observed ocean surface. PMID:23807444

Gallego, Guillermo; Yezzi, Anthony; Fedele, Francesco; Benetazzo, Alvise

2013-11-01

262

Variational structure of inverse problems in wave propagation and vibration  

SciTech Connect

Practical algorithms for solving realistic inverse problems may often be viewed as problems in nonlinear programming with the data serving as constraints. Such problems are most easily analyzed when it is possible to segment the solution space into regions that are feasible (satisfying all the known constraints) and infeasible (violating some of the constraints). Then, if the feasible set is convex or at least compact, the solution to the problem will normally lie on the boundary of the feasible set. A nonlinear program may seek the solution by systematically exploring the boundary while satisfying progressively more constraints. Examples of inverse problems in wave propagation (traveltime tomography) and vibration (modal analysis) will be presented to illustrate how the variational structure of these problems may be used to create nonlinear programs using implicit variational constraints.

Berryman, J.G.

1995-03-01

263

Phase velocities and attentuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L)  

PubMed Central

In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb–Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb–Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb–Rayleigh attenuation. Results of numerical simulations in the frequency range 0–500?Hz are presented. PMID:22225009

Nenadic, Ivan Z.; Urban, Matthew W.; Bernal, Miguel; Greenleaf, James F.

2011-01-01

264

Phase velocities and attenuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L).  

PubMed

In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb-Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb-Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb-Rayleigh attenuation. Results of numerical simulations in the frequency range 0-500 Hz are presented. PMID:22225009

Nenadic, Ivan Z; Urban, Matthew W; Bernal, Miguel; Greenleaf, James F

2011-12-01

265

CO-RELATIVE STUDY OF SOLAR WIND STREAMS VELOCITY & COSMIC RAY INTENSITY VARIATIONS DURING 2002-2007  

E-print Network

Abstract: A correlative study of solar wind streams velocity & cosmic ray intensity variations during 2002-2007, using the hourly neutron monitor data of Moscow (R e = 2.39 GV) station. High speed plasma streams identified in the solar wind measurement, which can be separated into two categories: Coronal hole associated streams & flare generated solar streams. It is investigated that; the solar wind streams velocity is inversely related with cosmic ray intensity variation on long-term basis.

S. G. Singh; A. K. Saxena; R. P. Singh; Y. K. Singh

266

Changes in compressional and shear wave velocities and dynamic moduli during operation of a hot dry rock geothermal system  

Microsoft Academic Search

Compressional and shear velocities measured during cross well seismic surveys are found to decrease during operation of a hot dry rock geothermal system. The relative P and S wave velocity decrease is very close to values predicted by O'Connell and Budiansky (1974), who modeled velocities in rocks containing fluid-saturated and dry cracks. Because our data fit their model quite well,

Christopher F. Pearson; Michael C. Fehler; James N. Albright

1983-01-01

267

Changes in Compressional and Shear Wave Velocities and Dynamic Moduli During Operation of a Hot Dry Rock Geothermal System  

Microsoft Academic Search

Compressional and shear velocities measured during cross well seismic surveys are found to decrease during operation of a hot dry rock geothermal system. The relative P and S wave velocity decrease is very close to values predicted by O'Connell and Budiansky (1974), who modeled velocities in rocks containing fluid-saturated and dry cracks. Because our data fit their model quite well,

Christopher F. Pearson; Michael C. Fehler; James N. Albright

1983-01-01

268

Shear wave velocity estimation in the metropolitan area of Málaga (S Spain)  

NASA Astrophysics Data System (ADS)

We carry out a seismic noise study based on array measurements at three sites in the Málaga basin, South Spain, for the further estimation of shear wave velocity profiles. For this purpose, we use both the H/V method and the f-k technique in order to characterize the different materials present in the zone, i.e., Quaternary sediments and Pliocene sedimentary rocks above the bedrock. The H/V analysis shows frequency peaks going from 1 Hz, in areas close to the border of the basin, to 0.3 Hz in places located toward the center of the formation. The f-k analysis allows obtaining the dispersion curves associated with each site and subsequently, estimating the Vs profiles by inversion of the respective group velocities. In this way, the basin basement can be characterized by S-wave velocities greater than 2000 m/s. Regarding the basin fill, it is divided into three layers defined by different wave velocity intervals. The shallowest one is featured by velocities ranging from 150 to 400 m/s and comprises the Quaternary sediments, while velocities going from 550-700 to1200-1600 m/s characterize the two underlying layers composed by Pliocene sediments. Finally, the information provided by the three Vs profiles is integrated in a 2D cross-section of the basin to have a spatial view of its sedimentary structure. The results obtained here, in addition to providing useful information about the infill of the basin near the metropolitan area of Málaga, will be very helpful for future seismic zonation studies in the region.

Clavero, D.; Rosa-Cintas, S.; López-Casado, C.; Delgado, J.; Galiana-Merino, J. J.

2014-10-01

269

Crustal P-wave velocity model for the central-western region of Mexico  

NASA Astrophysics Data System (ADS)

Several studies require a p-wave velocity model to obtain accurate results moreover such models could provide an insight of the tectonic structure of the study area. Accordingly, in this study we estimate the crustal 3D p-wave velocity model for the Jalisco Block located at the central-western region of Mexico. The Jalisco Block is limited on its eastern side by the Colima and Tepic-Zacoalcos Rifts, and the Trans-Mexican Volcanic Belt; while on its western side it is limited by the Mesoamerican Trench. Cocos and Rivera plates are subducting beneath the Jalisco Block conforming a tectonically complex region. We used earthquakes occurring within the limits of lithosphere volume from which we want to estimate the velocity model. Such events were registered by the Mapping the Rivera Subduction Zone experiment (MARS) and the Seismic and Acelerometric Network of Jalisco (RESAJ). During MARS experiment 51broadband stations active from January 2006 to June 2007 were deployed while RESAJ by July of 2012consists of nine active stations however more stations will be deployed until reach 30 stations. The velocity model is estimated using the Fast Marching Tomography (FMTOMO) software. FMTOMO uses the Fast Marching Method (FMM) in order to solve the forward problem; the FMM is a numerical algorithm that tracks the interfaces evolution along a nodes narrow band, and travel times are updated solving the eikonal equation. Finally , the inverse problem is about adjusting the model parameters (interface depth, velocity, hypocenter location) in order to try to satisfy the observed data (travel times). We perform a resolution test using several events that show good resolution results up to a 60 km depth. We present a 3D p-wave velocity model, we compare our results within the MARS data with previous results for greater depths, approximately the upper mantle, finally we also present studies towards the northern portion of the Jalisco Block using the RESAJ data.

Ochoa, J.; Escudero, C. R.; Perez, O. G.; Nunez-Cornu, F. J.

2012-12-01

270

Revision of P-wave velocity and thickness of hydrate layer in Shenhu Area, South China Sea  

NASA Astrophysics Data System (ADS)

To revise P-wave velocity and thickness of the hydrate layer in the Shenhu area of the South China Sea, acoustic and resistivity logging curves are reanalyzed. The waterlogging phenomenon is found in the shallow sediments of five drilling wells, which causes P-wave velocity to approximate the propagation velocity of sea water (about 1500 m s-1). This also affects the identification of the hydrate layer and results in the underestimate of its thickness. In addition, because there could be about a 5 m thick velocity ramp above or below the hydrate layer as interpreted by acoustic and resistivity logging curves, the recalibrated thickness of this layer is less than the original estimated thickness. The recalibrated P-wave velocity of the hydrate layer is also higher than the original estimated velocity. For the drilling well with a relatively thin hydrate layer, the velocity ramp plays a more important role in identifying and determining the thickness of the layer.

Gong, Jianming; Zhang, Xunhua; Zou, Changchun; Chen, Qiang; Wang, Lichen; Yuan, Chunfang; Hu, Gaowei; Jiang, Yubo

2014-10-01

271

Discovery of a surface wave velocity anomaly in the West Sea of South Korea  

NASA Astrophysics Data System (ADS)

Imaging of Rayleigh- and Love-wave velocities is very important in detecting geophysical anomalies within the earth. Surface wave velocity imaging studies using ambient noise have provided enhanced and detailed images of velocity anomalies for sedimentary basins, hotspots, and volcanoes in various regions of the Earth (Yang et al., 2008). Cross-correlations of ambient noises observed from the Korea Meteorological Administration (KMA) seismic network provide the short-period Rayleigh-and Love-wave dispersion characteristics of the Korean Peninsula (Cho et al., 2007). Signal whitening and multiple-filter analysis are used to equalise power in signals from different times before noise processing, such as cross-correlation and stacking to extract group velocities from the estimated Green's functions, which are then used to image the spatially varying dispersion at periods between 1 and 5 s. The analysis method and data used in this paper are the same as those of Cho et al. (2007) except for the addition of the dataset of a new station, HUK. However, this paper notes that Rayleigh- and Love-wave velocity images in short periods show a very different group velocity image for the north-eastern area of the HUK station because additional data was analysed. This velocity anomaly corresponds with the residual anomaly of gravity tomography obtained in prior studies (Yu and Min, 2005; Kim and Oh, 2007). Our results show that a fracture zone concerning the Permo-Triassic collision (Choi et al., 2006; Kwon et al., 2009) exists below the north-eastern sea of the HUK station. In addition, recent studies (de Ridder and Dellinger, 2011; de Ridder and Biondi, 2013; Mordret et al., 2011, 2013a, 2013b, 2013c; Bussat and Kugler, 2011) regarding ambient noise tomography in hydro-carbon fields show that the anomaly might have resulted from the hydro-carbon reservoir. In the near future, the ambient noise tomography (ANT) method can replace seismic survey dominantly using body waves to find oil and gas reservoirs.

Cho, Kwang Hyun

2014-01-01

272

TEMPERATURE VARIATION OF ULTRASONIC ATTENUATION AND PHASE VELOCITY IN VO2 AND V2O3 CRYSTALS  

E-print Network

L-25 TEMPERATURE VARIATION OF ULTRASONIC ATTENUATION AND PHASE VELOCITY IN VO2 AND V2O3 CRYSTALS J. Y. PRIEUR, P. SEZNEC and S. ZIOLKIEWICZ Laboratoire d'Ultrasons (*), Université Pierre et Marie measurements of the change in the ultrasonic attenuation and phase velocity in the vicinity of the phase

Boyer, Edmond

273

Characteristics of Light Reflected from a Dense Ionization Wave with a Tunable Velocity  

SciTech Connect

An optically dense ionization wave (IW) produced by two femtosecond (approx10/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses.

Zhidkov, A.; Fujii, T.; Nemoto, K. [Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa, 240-0196 Japan (Japan); Esirkepov, T.; Koga, J.; Bulanov, S. V. [Kansai Photon Science Institute, Japan Atomic Energy Agency, 8-1 Umemidai, Kizugawa, Kyoto, 619-0215 (Japan)

2009-11-20

274

Characteristics of light reflected from a dense ionization wave with a tunable velocity  

E-print Network

An optically-dense ionization wave (IW) produced by two femtosecond laser pulses focused cylindrically and crossing each other is shown to be an efficient coherent x-ray converter. The resulting velocity of a quasi-plane IW in the vicinity of pulse intersection increases with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing an easy tuning the wavelength of x-rays. The x-ray spectra of a converted, lower frequency coherent light change from the monochromatic to a high order harmonic-like with the duration of ionizing pulses and the intensity of scattered pulses; the spectrum are not symmetrical at Vc.

A. Zhidkov; T. Esirkepov; T. Fujii; K. Nemoto; J. Koga; S. V. Bulanov

2009-04-06

275

Daily variation of the fractal dimension of the velocity components in the turbulent surface layer  

NASA Astrophysics Data System (ADS)

The turbulence is a dominant property within the Planetary Boundary Layer (PBL). It is the main characteristic of the mixing in the lower atmosphere since the atmospheric turbulent fluxes are more efficient than the molecular diffusion. Turbulence can be observed in time series of meteorological variables (wind velocity for example). The sampling rate of observation in that time series has to be high in order to detect the turbulent regime. The analysis of these series presents a self-similarity structure, so the wind velocity can be considered as a fractal magnitude. This work shows a study of the fractal dimension of the wind perturbation series u'and w'components of the wind speed. Fractal dimension of velocity components can be related to others turbulent characteristics of the fluxes close to the ground. Fluctuation of longitudinal and, specially, vertical components depend on stability and, therefore, on the solar cycle. In consequence, the behaviour of fractal dimension should be in agreement with that cycle also. These series have been obtained once it has carried out the necessary transformation to get the mean wind series in short intervals, namely 5 minutes, to ensure the consistent properties of turbulence. The original records available were taken every thirty minutes by sonic anemometers (20 Hz sampling rate) during a week of a field campaign. The data analysed was recorded in the experimental campaign SABLES-98 at the Research Centre for the Lower Atmosphere (CIBA), located in Valladolid province (Spain). It has been calculated the fractal dimension (Komolgorov capacity or box- counting dimension) of the time series of fluctuations of the velocity component along of the mean wind direction and the vertical component (u' = u-U, w' = w -W), both in the physical spaces (velocity-time). It has been studied the time evolution of the fractal dimension during several days and at three levels above the ground (5.8 m, 13.5 m, 32 m). The fractal dimension of theu' and w' components of wind velocity series have been studied, as well as the influence of different turbulent parameters depending on daily cycle: turbulent kinetic energy, friction velocity, difference of temperature between the extreme of the layer studied close of the surface (?T50-0.22m),etc. It has been observed that there is a possible correlation between the fractal dimension and some of these turbulent parameters. Finally, it has been analysed the variation of the fractal dimension versus stability obtained from the Richardson number along of the day.

Tijera, M.; Maqueda, G.; Yagüe, C.; Cano, J. L.

2012-04-01

276

A physical model study of converted wave amplitude variation in a reservoir of systematically aligned vertical fractures  

NASA Astrophysics Data System (ADS)

The existence of fractures not only provides spaces for the residence of oils and gases reside, but it also creates pathways for migration. Characterizing a fractured reservoir thus becomes an important subject and has been widely studied by exploration geophysicists and drilling engineers. In seismic anisotropy, a reservoir of systematically aligned vertical fractures (SAVF) is often treated as a transversely isotropic medium (TIM) with a horizontal axis of symmetry (HTI). Subjecting to HTI, physical properties vary in azimuth. P-wave reflection amplitude, which is susceptible to vary in azimuth, is one of the most popular seismic attributes which is widely used to delineate the fracture strike of an SAVF reservoir. Instead of going further on analyzing P-wave signatures, in this study, we focused on evaluating the feasibility of orienting the fracture strike of an SAVF reservoir using converted (C-) wave amplitude. For a C-wave is initiated by a downward traveling P-wave that is converted on reflection to an upcoming S-wave; the behaviors of both P- and S-waves should be theoretically woven in a C-wave. In our laboratory work, finite offset reflection experiments were carried out on the azimuthal plane of a HTI model at two different offset intervals. To demonstrate the azimuthal variation of C-wave amplitude in a HTI model, reflections were acquired along the principal symmetry directions and the diagonal direction of the HTI model. Inheriting from phenomenon of S-wave splitting in a transversely isotropic medium (TIM), P-waves get converted into both the fast (S1) and slow (S2) shear modes at all azimuths outside the vertical symmetry planes, thus producing split PS-waves (PS1 and PS2). In our laboratory data, the converted PS1- (C1-) wave were observed and identified. As the azimuth varies from the strike direction to the strike normal, C1-wave amplitude exhibits itself in a way of weakening and can be view from the common-reflection-point (CRP) gathers. Therefore, in conjunction with the azimuthal velocity and the amplitude variations in the P-wave and the azimuthal polarization of the S-wave, the azimuthal variation of C-wave amplitude which is experimentally demonstrated could be considered as a valuable seismic attribute in orienting the fracture strike of a SAVF reservoir. (Key words: converted wave, transversely isotropic medium, physical modeling, amplitude, fracture)

Chang, C.; Sun, L.; Lin, C.; Chang, Y.; Tseng, P.

2013-12-01

277

S-wave velocity profiles near the Hayward fault obtained by active and passive surface wave methods  

NASA Astrophysics Data System (ADS)

We measured S-wave velocity (Vs) profiles at five sites the Hayward (Fig.1) using active and passive surface wave methods. The methods are multichannel analysis of surface waves using an active source (MASW), a passive surface wave method using geophones in a linear array (MAM), and a two-station spatial autocorrelation method (2ST-SPAC) using long-period accelerometers. Maximum array size varied from 345 to 565 m depending on the site. Minimum frequency and corresponding maximum wavelength ranged from 0.6 to 2 Hz and 500 to 1500 m, depending on the site. Phase velocities obtained from the three methods were combined to produce a single dispersion curve for each site. A nonlinear inversion consisting of a least squares method and a genetic algorithm was used to estimate Vs profiles from the dispersion curves to a depth of 400 to 700 m depending on the site. Vs profiles (Fig.2) show significant differences across the Hayward fault. On the west side of the fault (Southgate Park to Cemetery), there is a low velocity layer at the surface, with Vs less than 400 m/s to a depth of 40 to 90 m. A thick intermediate velocity layer with Vs ranging from 400 to 1200 m/s lies beneath the low velocity layer. Bedrock with Vs greater than 1200 m/s was measured at depths greater than 450 m. On the east side of the Fault (CSU East Bay), thickness of the low velocity layer (Vs < 400 m/s) is less than 5 m, and depth to bedrock (Vs > 1200 m/s) is less than 170 m. The results of this investigation are generally consistent with existing borehole Vs logs and other geophysical investigations, and indicate that bedrock depth changes approximately 300 m across the fault. To evaluate the effect of a significant change of bedrock depth on surface ground motion due to earthquakes, a representative Vs cross section perpendicular to the fault was constructed and theoretical amplification including two-dimensional structure was calculated using a viscoelastic finite-difference method. Calculation results show that the low frequency (1 to 3 Hz) component of ground motion is locally amplified on the west side of the fault because of the effect of two-dimensional structure.

Hayashi, K.; Craig, M.; Aql, R.; Shuler, S.

2013-12-01

278

Higher Brachial-Ankle Pulse Wave Velocity Is Associated with More Advanced Carotid Atherosclerosis in End-Stage Renal Disease  

Microsoft Academic Search

Brachial-ankle pulse wave velocity is a new measure of arterial stiffness. We examined whether higher brachial-ankle pulse wave velocity is associated with more advanced carotid atherosclerosis and left ventricular hypertrophy in patients with end-stage renal disease, and whether this effect would be mediated by the influence of wave reflection on central arterial pressure. In 68 patients with end stage renal

Masanori Munakata; Junko Sakuraba; Jun Tayama; Takashi Furuta; Akira Yusa; Tohru Nunokawa; Kaoru Yoshinaga; Takayoshi Toyota

2005-01-01

279

Anisotropic Changes in P-Wave Velocity and Attenuation during Deformation and Fluid Infiltration of Granite  

Microsoft Academic Search

4 Abstract. Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic wave propagation characteristics such as V p\\/Vs ratio,

Sergei A. Stanchits; David A. Lockner; Alexander V. Ponomarev

2003-01-01

280

A variational principle for studying fast-wave mode conversion  

NASA Astrophysics Data System (ADS)

A variational principle for studying one-dimensional wave propagation and damping near the ion-ion hybrid conversion region in a tokamak is presented. In its variational form, the wave equation is closely related to the power balance equation: substituting the electric field for the test function in it yields the generalized Poynting theorem. The guiding centre position rather than that of the particle is adopted as the independent variable. Toroidal and oblique incidence effects are retained but the poloidal magnetic field is neglected. A strictly positive power density for Maxwellian plasmas is ensured by starting from a general formalism due to Lamalle (Lamalle P U 1993 Phys. Lett. 175A 45; 1997 Plasma Phys. Control. Fusion 39 1409) and expanding the operator acting on the electric field in the expression for the absorbed power per guiding centre orbit (rather than expanding the dielectric tensor, as is usually done) in terms of the assumed small parameter 0741-3335/40/11/010/img1, where 0741-3335/40/11/010/img2 is the perpendicular wavenumber and 0741-3335/40/11/010/img3 the Larmor radius. The general formulae for the dielectric response are provided and explicit expressions are given for the case where up to second-order corrections in 0741-3335/40/11/010/img4 are retained in the operator. As an illustration, the absorption of radio frequency power in a (H)-D-(Ar) TEXTOR plasma typical for the radiative improved mode is discussed.

Van Eester, D.; Koch, R.

1998-11-01

281

Stress- and damage-induced changes in coda wave velocities in concrete  

NASA Astrophysics Data System (ADS)

Diffuse ultrasonic measurements are used to monitor progressive stress-induced damage in a number of concrete specimens. Each specimen was subjected to uniaxial compression, applied in small steps over one or several load cycles. At each step, the loading was held constant and a series of ultrasonic measurements parallel and perpendicular to the loading were obtained. The measurements were taken during both the loading and unloading phases. The time scale of the signals was chosen such that the diffuse ultrasonic regime could be recorded. Using Coda Wave Interferometry (CWI), the corresponding changes in the velocity of diffuse ultrasonic waves were monitored. The evolution of the slope of the CWI velocity-stress curve with the increased level of damage in concrete is demonstrated.

Shokouhi, P.

2013-01-01

282

Vertical velocities associated with gravity waves measured in the mesosphere and lower thermosphere with the EISCAT VHF radar  

E-print Network

Vertical velocities associated with gravity waves measured in the mesosphere and lower thermosphere. The data reveal a motion ®eld dominated by quasi-monochromatic gravity waves with represen- tative apparent advanced to explain gravity-wave spectra. The spectral slopes evaluated for individual days have a range

Paris-Sud XI, Université de

283

Compositional variation of density and seismic velocities in natural peridotites at STP conditions: Implications for seismic imaging  

E-print Network

Compositional variation of density and seismic velocities in natural peridotites at STP conditions natural spinel- and garnet-peridotite samples (n = 133) at standard temperature (T ) and pressure (P) (STP-members of peridotitic minerals, the variation of elastic moduli with Mg# at STP conditions holds at elevated P and T

Lee, Cin-Ty Aeolus

284

Permeability and P-wave velocity change in granitic rocks under freeze–thaw cycles  

Microsoft Academic Search

An extensive experimental investigation of microstructural changes in granites under freeze–thaw cycles using permeability and P-wave velocity measurements is described. Two types of natural granite rocks are considered and tested under dry and saturated conditions. The specimens were subjected to 200 heating–cooling cycles (??20°C\\/?+?20°C); each cycle had a duration of 24 h. The results indicate that the ageing process decreases the

M. Takarli; W. Prince

2007-01-01

285

Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling  

Microsoft Academic Search

We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas

M. B. Helgerud; J. Dvorkin; A. Nur; A. Sakai; T. Collett

1999-01-01

286

Coronary artery calcification and aortic pulse wave velocity in chronic kidney disease patients  

Microsoft Academic Search

Coronary artery calcification and aortic pulse wave velocity in chronic kidney disease patients.BackgroundPatients with end-stage renal disease (ESRD) are at increased risk of cardiovascular mortality and morbidity. Many complications arise in ESRD patients as a result of the twin arterial pathologies of atherosclerosis and arteriosclerosis. Part of this latter process is calcification of the arterial media, which is thought significantly

Ali A. Haydar; Adrian Covic; Helen Colhoun; Michael Rubens; David J. A. Goldsmith

2004-01-01

287

A wind tunnel study of air flow in waving wheat: Single-point velocity statistics  

Microsoft Academic Search

We analyse single-point velocity statistics obtained in a wind tunnel within and above a model of a waving wheat crop, consisting of nylon stalks 47 mm high and 0.25 mm wide in a square array with frontal area index 0.47. The variability of turbulence measurements in the wind tunnel is illustrated by using a set of 71 vertical traverses made

Y. Brunet; J. J. Finnigan; M. R. Raupach

1994-01-01

288

Three-dimensional P wave velocity model for the San Francisco Bay region, California  

Microsoft Academic Search

A new three-dimensional P wave velocity model for the greater San Francisco Bay region has been derived using the double-difference seismic tomography method, using data from about 5,500 chemical explosions or air gun blasts and approximately 6,000 earthquakes. The model region covers 140 km NE-SW by 240 km NW-SE, extending from 20 km south of Monterey to Santa Rosa and

Clifford H. Thurber; Thomas M. Brocher; Haijiang Zhang; Victoria E. Langenheim

2007-01-01

289

Formulas for Phase Velocity and Damping of Longitudinal Waves in Thick-Walled Viscoelastic Tubes  

Microsoft Academic Search

The frequency equation for longitudinal waves in a viscoelastic tube of infinite length filled with a viscous fluid is solved for the complex wavenumber, k(=k1+ik2). Thus for two modes, Young's mode and Lamb's mode, an explicit expression for k is obtained which yields the phase velocity c(=??k1, ?=radial frequency) and the damping constant k2. The formulas for k, c, and

Willem Klip; PIETER VAN LOONt; Dorothea A. Klip

1967-01-01

290

Line-profile variations in radial-velocity measurements. Two alternative indicators for planetary searches  

NASA Astrophysics Data System (ADS)

Aims: We introduce two methods to identify false-positive planetary signals in the context of radial-velocity exoplanet searches. The first is the bi-Gaussian cross-correlation function fitting (and monitoring of the parameters derived from it), and the second is the measurement of asymmetry in radial-velocity spectral line information content, Vasy. We assess the usefulness of each of these methods by comparing their results with those delivered by current indicators. Methods: We make a systematic analysis of the most used common line profile diagnosis, Bisector Inverse Slope and Velocity Span, along with the two proposed ones. We evaluate all these diagnosis methods following a set of well-defined common criteria and using both simulated and real data. We apply them to simulated cross-correlation functions that are created with the program SOAP and which are affected by the presence of stellar spots. We consider different spot properties on stars with different rotation profiles and simulate observations as obtained with high-resolution spectrographs. We then apply our methodology to real cross-correlation functions, which are computed from HARPS spectra, for stars with a signal originating in activity (thus spots) and for those with a signal rooted on a planet. Results: We demonstrate that the bi-Gaussian method allows a more precise characterization of the deformation of line profiles than the standard bisector inverse slope. The calculation of the deformation indicator is simpler and its interpretation more straightforward. More importantly, its amplitude can be up to 30% larger than that of the bisector span, allowing the detection of smaller-amplitude correlations with radial-velocity variations. However, a particular parametrization of the bisector inverse slope is shown to be more efficient on high-signal-to-noise data than both the standard bisector and the bi-Gaussian. The results of the Vasy method show that this indicator is more effective than any of the previous ones, being correlated with the radial-velocity with more significance for signals resulting from a line deformation. Moreover, it provides a qualitative advantage over the bisector, showing significant correlations with RV for active stars for which bisector analysis is inconclusive. Conclusions: We show that the two indicators discussed here should be considered as standard tests to check for the planetary nature of a radial-velocity signal. We encourage the usage of different diagnosis as a way of characterizing the often elusive line profile deformations.

Figueira, P.; Santos, N. C.; Pepe, F.; Lovis, C.; Nardetto, N.

2013-09-01

291

Joint migration velocity analysis of PP- and PS-waves for VTI media  

NASA Astrophysics Data System (ADS)

Combining PP-waves with mode-converted PS reflections in migration velocity analysis can help build more accurate VTI velocity models. To avoid problems caused by the moveout asymmetry of PS-waves and take advantage of efficient MVA algorithms designed for pure modes, I suggest to generate pure SS-reflections from PP and PS data using the PP+PS=SS method. Then the residual moveout in both PP and SS common-image gathers is minimized during iterative velocity updates. The objective function also includes the differences between the migrated depths of the same reflectors on the PP and SS sections and a regularization term. Synthetic examples confirm that 2D MVA of PP- and PS-waves may be able to resolve all four relevant parameters of VTI media if reflectors with at least two distinct dips are available. The algorithm is also applied to a 2D line from 3D OBS data acquired at Volve field in the North Sea.

Cai, Pengfei

292

Estimation of local pulse wave velocity using arterial diameter waveforms: Experimental validation in sheep  

NASA Astrophysics Data System (ADS)

Increased arterial stiffness is associated with an increased risk of cardiovascular events. Estimation of arterial stiffness using local pulse wave velocity (PWV) promises to be very useful for noninvasive diagnosis of arteriosclerosis. In this work we estimated in an instrumented sheep, the local aortic pulse wave velocity using two sonomicrometry diameter sensors (separated 7.5 cm) according to the transit time method (PWVTT) with a sampling rate of 4 KHz. We simultaneously measured aortic pressure in order to determine from pressure-diameter loops (PWVPDLoop), the "true" local aortic pulse wave velocity. A pneumatic cuff occluder was implanted in the aorta in order to compare both methods under a wide range of pressure levels. Mean pressure values ranged from 47 to 101 mmHg and mean proximal diameter values from 12.5. to 15.2 mm. There were no significant differences between PWVTT and PWVPDLoop values (451±43 vs. 447±48 cm/s, p = ns, paired t-test). Both methods correlated significantly (R = 0.81, p<0.05). The mean difference between both methods was only -4±29 cm/s, whereas the range of the limits of agreement (mean ± 2 standard deviation) was -61 to +53 cm/s, showing no trend. In conclusion, the diameter waveforms transit time method was found to allow an accurate and precise estimation of the local aortic PWV.

Graf, S.; Craiem, D.; Barra, J. G.; Armentano, R. L.

2011-12-01

293

Prediction of rocks thermal conductivity from elastic wave velocities, mineralogy and microstructure  

NASA Astrophysics Data System (ADS)

While knowledge on Thermal Conductivity (TC) of rocks is of interest in many fields, determining this property remains challenging. In this paper, a modelling approach for TC prediction from Elastic Wave Velocity (EWV) measurements is reported. To this end, a new effective TC model for a typical sedimentary rock is introduced that explicitly accounts for the presence of pores, pressure-sensitive microcracks (or grain contacts) and formation fluids. A model of effective elasticity is also devised for this same rock that links its microstructural characteristics to the velocity of elastic waves. The two models are based on the same effective medium approach and involve the same microstructural parameters. A workflow based on this explicit modelling approach is devised that allows for the prediction of the TC of a reservoir rock using (i) the elastic waves velocities, (ii) the dominant mineral content and (iii) the bulk porosity. This workflow is validated using experimental data reported in the literature for dry and water-saturated Fontainebleau and Berea sandstones. The datasets include measurements of TC and EWV as a function of effective pressure. In addition, it is shown that the dependence of TC on the rock microstructure is formally and practically similar to that of EWV. It is also demonstrated that the accuracy of TC predictions from EWV increases with effective pressure (burial depth). The underlying assumptions and limitations of the present approach together with the effect of burial are discussed.

Pimienta, Lucas; Sarout, Joel; Esteban, Lionel; Piane, Claudio Delle

2014-05-01

294

The influence of solid solution on elastic wave velocity determination in (Mg,Fe)O using nuclear inelastic scattering  

NASA Astrophysics Data System (ADS)

Elastic wave velocities of minerals are important for constraining the chemistry, structure and dynamics of the Earth's mantle based on the comparison between laboratory-based measurements and seismic observations. As the second most abundant phase in the Earth's lower mantle, (Mg,Fe)O ferropericlase has been the focus of numerous studies measuring the elastic wave velocities using various methods such as Brillouin spectroscopy and ultrasonic measurements. Recently, nuclear inelastic scattering (NIS) has been used to determine elastic wave velocities of iron-bearing phases. However, the elastic wave velocities of ferropericlase obtained using NIS are considerably lower than the velocities obtained by other methods, even at ambient conditions. One possible source of this discrepancy is the local nature of the NIS method. In order to test this hypothesis, we have investigated six ferropericlase samples with various iron contents using NIS. The Debye sound velocities calculated using the conventional method of NIS analysis are consistent with previous results obtained using NIS, yet the values are significantly lower than those obtained using ultrasonics and Brillouin spectroscopy. If the Debye sound velocities are re-calculated based on a mixture of different iron next-neighbour configurations with different compositions, the Debye sound velocities determined by NIS agree well with the results from other methods. Our new model was also successfully applied to high-pressure NIS data taken from the literature. Our results demonstrate that NIS is a reliable experimental method to determine elastic wave velocities of iron-bearing mantle minerals.

Sinmyo, R.; Glazyrin, K.; McCammon, C. A.; Kupenko, I.; Kantor, A.; Potapkin, V.; Chumakov, A.; Rüffer, R.; Dubrovinsky, L. S.

2013-12-01

295

Structure of the Crust beneath Cameroon, West Africa, from the Joint Inversion of Rayleigh Wave Group Velocities and Receiver Functions  

SciTech Connect

The Cameroon Volcanic Line (CVL) is a major geologic feature that cuts across Cameroon from the south west to the north east. It is a unique volcanic lineament which has both an oceanic and a continental sector and consists of a chain of Tertiary to Recent, generally alkaline volcanoes stretching from the Atlantic island of Pagalu to the interior of the African continent. The oceanic sector includes the islands of Bioko (formerly Fernando Po) and Sao Tome and Principe while the continental sector includes the Etinde, Cameroon, Manengouba, Bamboutos, Oku and Mandara mountains, as well as the Adamawa and Biu Plateaus. In addition to the CVL, three other major tectonic features characterize the region: the Benue Trough located northwest of the CVL, the Central African Shear Zone (CASZ), trending N70 degrees E, roughly parallel to the CVL, and the Congo Craton in southern Cameroon. The origin of the CVL is still the subject of considerable debate, with both plume and non-plume models invoked by many authors (e.g., Deruelle et al., 2007; Ngako et al, 2006; Ritsema and Allen, 2003; Burke, 2001; Ebinger and Sleep, 1998; Lee et al, 1994; Dorbath et al., 1986; Fairhead and Binks, 1991; King and Ritsema, 2000; Reusch et al., 2010). Crustal structure beneath Cameroon has been investigated previously using active (Stuart et al, 1985) and passive (Dorbath et al., 1986; Tabod, 1991; Tabod et al, 1992; Plomerova et al, 1993) source seismic data, revealing a crust about 33 km thick at the south-western end of the continental portion of the CVL (Tabod, 1991) and the Adamawa Plateau, and thinner crust (23 km thick) beneath the Garoua Rift in the north (Stuart et al, 1985) (Figure 1). Estimates of crustal thickness obtained using gravity data show similar variations between the Garoua rift, Adamawa Plateau, and southern part of the CVL (Poudjom et al., 1995; Nnange et al., 2000). In this study, we investigate further crustal structure beneath the CVL and the adjacent regions in Cameroon using 1-D shear wave velocity models obtained from the joint inversion of Rayleigh wave group velocities and P-receiver functions for 32 broadband seismic stations. From the 1-D shear wave velocity 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.

Tokam, A K; Tabod, C T; Nyblade, A A; Julia, J; Wiens, D A; Pasyanos, M E

2010-02-18

296

Variation in the dispersion of axisymmetric waves in infinite circular rods with crystallographic wire texture  

SciTech Connect

This paper presents the solution to the frequency equation for a number of polycrystalline, textured circular rods having transverse isotropy. The effective, second-order elastic stiffness tensors were estimated using the recursive general Hill arithmetic mean (GHAM). The velocity dispersion curves for a number of combinations of materials and crystallographic fiber or wire textures were calculated and the variation due to texture displayed. At large wavelengths, the velocity dispersion of fiber textured materials exhibits a lowest-order axisymmetric mode which varies only with the directional Poisson[close quote]s ratios in a manner similar to that of isotropic aggregates. In this wavelength regime, the waves propagate nondispersively at the wave speed, C[sub 0], as dictated by the directional Young[close quote]s modulus. At wavelengths smaller than the rod radius, the dispersion curves were more influenced by the full anisotropy of the wire textures. At these wavelengths, the dispersion curves for the anisotropic materials deviated significantly from those of the isotropic materials and one another with the higher axisymmetric vibration modes exhibiting extreme differences. This deviation is a function of the single crystal anisotropy and nature of the wire textures. < --[AN] -->

Mason, T.A. (Materials Science and Technology Division, MS G755, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

1999-09-01

297

Generation of lower hybrid and whistler waves by an ion velocity ring distribution  

SciTech Connect

Using fully kinetic simulations in two and three spatial dimensions, we consider the generation and nonlinear evolution of lower hybrid waves produced by a cold ion ring velocity distribution in a low beta plasma. We show that the initial development of the instability is very similar in two and three dimensions and not significantly modified by electromagnetic effects, consistent with linear theory. At saturation, the level of electric field fluctuations is a small fraction of the background thermal energy; the electric field and corresponding density fluctuations consist of long, field-aligned striations. Energy extracted from the ring goes primarily into heating the background ions and the electrons at comparable rates. The initial growth and saturation of the magnetic components of the lower hybrid waves are related to the electric field components, consistent with linear theory. As the growing electric field fluctuations saturate, parallel propagating whistler waves develop by the interaction of two lower hybrid waves. At later times, these whistlers are replaced by longer wavelength, parallel propagating whistlers that grow through the decay of the lower hybrid fluctuations. Wave matching conditions demonstrate these conversion processes of lower hybrid waves to whistler waves. The conversion efficiency (=ratio of the whistler wave energy to the energy in the saturated lower hybrid waves) is computed and found to be significant ({approx}15%) for the parameters of the three-dimensional simulation (and even larger in the two-dimensional simulation), although when normalized in terms of the initial kinetic energy in the ring ions the overall efficiency is very small (<10{sup -4}). The results are compared with relevant linear and nonlinear theory.

Winske, D.; Daughton, W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-07-15

298

Comparison of an Oscillometric Method with Cardiac Magnetic Resonance for the Analysis of Aortic Pulse Wave Velocity  

PubMed Central

Objectives Pulse wave velocity (PWV) is the proposed gold-standard for the assessment of aortic elastic properties. The aim of this study was to compare aortic PWV determined by a recently developed oscillometric device with cardiac magnetic resonance imaging (CMR). Methods PWV was assessed in 40 volunteers with two different methods. The oscillometric method (PWVOSC) is based on a transfer function from the brachial pressure waves determined by oscillometric blood pressure measurements with a common cuff (Mobil-O-Graph, I.E.M. Stolberg, Germany). CMR was used to determine aortic PWVCMR with the use of the transit time method based on phase-contrast imaging at the level of the ascending and abdominal aorta on a clinical 1.5 Tesla scanner (Siemens, Erlangen, Germany). Results The median age of the study population was 34 years (IQR: 24–55 years, 11 females). A very strong correlation was found between PWVOSC and PWVCMR (r = 0.859, p < 0.001). Mean PWVOSC was 6.7 ± 1.8 m/s and mean PWVCMR was 6.1 ± 1.8 m/s (p < 0.001). Analysis of agreement between the two measurements using Bland-Altman method showed a bias of 0.57 m/s (upper and lower limit of agreement: 2.49 m/s and -1.34 m/s). The corresponding coefficient of variation between both measurements was 15%. Conclusion Aortic pulse wave velocity assessed by transformation of the brachial pressure waveform showed an acceptable agreement with the CMR-derived transit time method. PMID:25612307

Feistritzer, Hans-Josef; Reinstadler, Sebastian J.; Klug, Gert; Kremser, Christian; Seidner, Benjamin; Esterhammer, Regina; Schocke, Michael F.; Franz, Wolfgang-Michael; Metzler, Bernhard

2015-01-01

299

Spin-wave velocity and specific heat of the Hubbard model at half filling with a path-integral approach  

NASA Astrophysics Data System (ADS)

A path-integral formulation of the two-dimensional Hubbard model is used in which scattering of electrons across the magnetic Brillouin zone by spin fluctuations (umklapp processes) is included. With this formulation, we have calculated the spin-wave velocity cs and the specific heat Cv for the half-filled-band case. For the quadratic form of the Hubbard model due to Schrieffer, we obtain cs=1.5c0 in the large-U limit (U is the intrasite Coulomb repulsion, c0= ?2 J is the spin-wave velocity in linear-spin-wave theory, J=4t2/U is the superexchange interaction, and t is the hopping integral for nearest neighbors). Our result is in good agreement with various numerical calculations based on the Heisenberg model, e.g., cs=1.22c0 by Liu and Manousakis [Phys. Rev. B 40, 11 437 (1989)], with use of the variational Monte Carlo technique. Our present calculation differs from previous path-integral calculations, which lead to cs~t in the large-U limit. A general free-energy formula, which includes all kinds of fluctuation, is obtained. At low temperature, the specific heat in the large-U limit is given by Cv~=0.51(T/J)2. The present calculation can also be applied to the Hubbard model written in other quadratic forms, in one of which the saddle-point approximation leads to the Hartree-Fock solution and cs=c0 and Cv=1.15(T/J)2 in the large-U limit.

Chi, Hongguang; Nagi, A. D. S.

1992-10-01

300

Shear wave group velocity inversion in MR elastography of human skeletal muscle.  

PubMed

In vivo quantification of the anisotropic shear elasticity of soft tissue is an appealing objective of elastography techniques because elastic anisotropy can potentially provide specific information about structural alterations in diseased tissue. Here a method is introduced and applied to MR elastography (MRE) of skeletal muscle. With this method one can elucidate anisotropy by means of two shear moduli (one parallel and one perpendicular to the muscle fiber direction). The technique is based on group velocity inversion applied to bulk shear waves, which is achieved by an automatic analysis of wave-phase gradients on a spatiotemporal scale. The shear moduli are then accessed by analyzing the directional dependence of the shear wave speed using analytic expressions of group velocities in k-space, which are numerically mapped to real space. The method is demonstrated by MRE experiments on the biceps muscle of five volunteers, resulting in 5.5+/-0.9 kPa and 29.3+/-6.2 kPa (P<0.05) for the medians of the perpendicular and parallel shear moduli, respectively. The proposed technique combines fast steady-state free precession (SSFP) MRE experiments and fully automated processing of anisotropic wave data, and is thus an interesting MRI modality for aiding clinical diagnosis. PMID:16894586

Papazoglou, Sebastian; Rump, Jens; Braun, Jürgen; Sack, Ingolf

2006-09-01

301

A global shear velocity model of the mantle from normal modes and surface waves  

NASA Astrophysics Data System (ADS)

We present SEISGLOB1, a new global shear wave velocity model of the mantle based on the inversion of all published normal mode, splitting and coupling coefficients, and the large surface wave dataset measured by Debayle & Ricard (2012). Normal mode and surface wave data are sensitive to lateral heterogeneities of elastic parameters (Vs, Vp, ?, ?, ?) and density. We first only consider spheroidal modes and Rayleigh waves and restrict the inversion to Vsv (imposing an a priori correlation between Vp-Vsv and density-Vsv). Before the inversion, we correct the data from the crust effect using 3SMAC (Nataf & Ricard ,1996). The data are inverted up to the degree 20 of spherical harmonics. Vertical smoothing is imposed by splines and we discuss the effect of coupling/decoupling the inverted structure above and below the '670' discontinuity. The obtained model is in good agreement with existing ones and an interesting result is that the high velocity slabs do cross the '670' discontinuity and are still observed down to 800 km depth whatever the parameterization is, coupled or not at the '670' discontinuity.

durand, stephanie; debayle, eric; ricard, yanick; lambotte, sophie

2014-05-01

302

Upper mantle structure of South America from joint inversion of waveforms and fundamental mode group velocities of Rayleigh waves  

NASA Astrophysics Data System (ADS)

A new tomographic S wave velocity model for the upper mantle beneath South America is presented. We developed and applied a new method of simultaneously inverting regional S and Rayleigh waveforms and fundamental mode Rayleigh wave group velocities, to better constrain upper mantle S velocity structure and Moho depth. We used ˜5700 Rayleigh wave group velocity dispersion curves and 1537 regional wave trains with paths principally passing through the South American continent. The joint inversion of this data set provided a new three-dimensional (3-D) upper mantle S velocity model and a Moho depth model for South America, which fits both the group velocity and regional waveform data sets well. New features of the final three-dimensional (3-D) S velocity and Moho depth model correlate well with known geotectonic units on a regional scale. The Moho depth ranges from 30 km in the central Chaco basin to 42 km beneath the Amazonian craton and 45-70 km beneath the orogenic Andean belt. The imaged S velocity indicates an average lithosphere thickness of around 160 km for the Amazonian craton. High velocities are imaged beneath the Amazon and part of the Paraná and Parnaíba basins down to about 150 km. Low to very low velocities are imaged beneath the central Andes and the Chaco, Pantanal, and northwestern Paraná basins.

Feng, Mei; van der Lee, Suzan; AssumpçãO, Marcelo

2007-04-01

303

Upper Mantle Structure of South America from Joint Inversion of Waveforms and Fundamental-mode Group Velocities of Rayleigh Waves  

NASA Astrophysics Data System (ADS)

A new tomographic S-wave velocity model for the upper mantle beneath South America is presented. We developed and applied a new method of simultaneously inverting regional S & Rayleigh waveforms and fundamental-mode Rayleigh-wave group velocities, to better constrain upper mantle S-velocity structure and Moho depth. We used about 5700 Rayleigh wave group velocity dispersion curves and 1537 regional wave trains with paths principally passing through the South American continent. The joint inversion of this data set provided a new 3D upper mantle S-velocity model and a Moho depth model for South America, which fits both the group velocity and regional waveform data sets well. New features of the final 3D S-velocity and Moho depth model correlate well with known geotectonic units on a regional scale. The Moho depth ranges from 30 km in the central Chaco basin to 42 km beneath the Amazonian craton and 45-70 km beneath the orogenic Andean belt. The imaged S-velocity indicates an average lithosphere thickness of around 160 km for the Amazonian craton. High velocities are imaged beneath the Amazon and São Francisco cratons and part of the Paraná and Parnaíba basins down to about 150 km. Low to very low velocities are imaged beneath the central Andes and the Chaco, Pantanal and northwestern Paraná basins.

Feng, M.; van der Lee, S.; Assumpcao, M.

2007-05-01

304

On-chip laser Doppler vibrometer for arterial pulse wave velocity measurement  

PubMed Central

Pulse wave velocity (PWV) is an important marker for cardiovascular risk. The Laser Doppler vibrometry has been suggested as a potential technique to measure the local carotid PWV by measuring the transit time of the pulse wave between two locations along the common carotid artery (CCA) from skin surface vibrations. However, the present LDV setups are still bulky and difficult to handle. We present in this paper a more compact LDV system integrated on a CMOS-compatible silicon-on-insulator substrate. In this system, a chip with two homodyne LDVs is utilized to simultaneously measure the pulse wave at two different locations along the CCA. Measurement results show that the dual-LDV chip can successfully conduct the PWV measurement. PMID:23847745

Li, Yanlu; Segers, Patrick; Dirckx, Joris; Baets, Roel

2013-01-01

305

The nonlinear theory of slow-wave electron cyclotron masers with inclusion of the beam velocity spread  

SciTech Connect

The nonlinear theory of slow-wave electron cyclotron masers (ECM) with an initially straight electron beam is developed. The evolution equation of the nonlinear beam electron energy is derived. The numerical studies of the slow-wave ECM efficiency with inclusion of Gaussian beam velocity spread are presented. It is shown that the velocity spread reduces the interaction efficiency. -- Highlights: •The theory of slow-wave electron cyclotron masers is considered. •The calculation of efficiency under the resonance condition is presented. •The efficiency under Gaussian velocity spreads has been obtained.

Kong, Ling-Bao, E-mail: konglingbao@gmail.com [School of Science, Beijing University of Chemical Technology, Beijing 100029 (China) [School of Science, Beijing University of Chemical Technology, Beijing 100029 (China); Beijing Key Laboratory of Environmentally Harmful Chemicals Assessment, Beijing University of Chemical Technology, Beijing 100029 (China); Wang, Hong-Yu [School of Physics, Anshan Normal University, Anshan 114005 (China)] [School of Physics, Anshan Normal University, Anshan 114005 (China); Hou, Zhi-Ling, E-mail: houzl@mail.buct.edu.cn [School of Science, Beijing University of Chemical Technology, Beijing 100029 (China) [School of Science, Beijing University of Chemical Technology, Beijing 100029 (China); Beijing Key Laboratory of Environmentally Harmful Chemicals Assessment, Beijing University of Chemical Technology, Beijing 100029 (China); Jin, Hai-Bo [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China)] [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); Du, Chao-Hai [Institute of Electronics, Chinese Academy of Sciences, Beijing 100190 (China)] [Institute of Electronics, Chinese Academy of Sciences, Beijing 100190 (China)

2013-12-15

306

Temporal variations of Seismic Velocities after the 2006 Mw6.1 Taitung Earthquake in Taiwan  

NASA Astrophysics Data System (ADS)

Impulse response (Green’s function) of a diffusive medium retrieved from cross-correlation of ambient noise at two stations has become widely used in monitoring small temporal changes of subsurface seismic velocities associated with earthquake and volcanic activities. Eastern Taiwan is a seismically very active region resulting from oblique collision between the Eurasian plate under the Philippine Sea plate. A Mw 6.1 shallow earthquake struck eastern Taiwan near Taitung in the southern Longitudinal Valley fault and caused significant coseismic deformation. To detect potential variations in subsurface seismic velocities associated with internal strain change before and after the quake, we construct the Green’s functions from auto-correlation of continuous, one-day long seismic noise on the vertical component in the two months before and after the quake, recorded by seven short-period stations of Central Weather Bureau (CWB) within less than 50 km from the epicenter. Before computing autocorrelation functions (ACF) in frequent domain at each station two months before and after the quake, we employ the time-domain normalization to eliminate earthquake-related signals. A three-order Butterworth band-pass filter between 2 and 8 Hz is then applied to the retrieved ACFs. The spectra of some ACFs within 2-8 Hz show very narrow band-limited resonant peaks which are further removed by a band-stop filter. All the filtered autocorrelation functions with waveform correlation coefficients greater than 0.5 are stacked to obtain reference Green’s function (RGF). We compare the time shift of each daily-long autocorrelation function between 2 and 15-s lapse times with the corresponding RGF. The station TWG, located ~6 km apart from the epicenter on the southern part of the rupture zone yields a clear step-wise time shift after the quake, which corresponds to the increase in seismic velocity by about 1.66% assuming the velocity change in the medium is uniform. The station TTN located on the Taitung city, ~15 km southeast to the epicenter show a slightly decrease by -0.06%. We will further investigate the cause of temporal seismic velocity change by comparing our result with the coseismic displacement measured by GPS and leveling, strong motion records, and volumetric strain perturbations near the rupture zone.

Yu, T.; Hung, S.

2010-12-01

307

Rayleigh Wave Group Velocity Tomography of Siberia, China and the Vicinity  

NASA Astrophysics Data System (ADS)

Rayleigh waves are used in a tomographic inversion to obtain group velocity maps of East Asia (40° E-160° E and 20° N-70° N). The period range studied is 30 to 70 seconds. Seismograms used for this study were recorded at CDSN stations, at a temporary broadband seismic array in Tibet, at several SRO stations, and Kirnos-equipped stations established in Asia by the former Soviet Union, in Siberia, in the Sakhalin and in Mongolia. Altogether more than 1200 paths were available in the tomographic inversion. The study area includes the Angara craton, the geologically ancient core of Asia, and the subsequently accreted units, the Altaids (a Paleozoic collision complex), the Sino-Korean platform (a chain of Archaen terranes separated by belts of active structures), the south China platform (a collage of Precambrian, Paleozoic and Mesozoic metamorphic and igneous terranes), as well as the Tibetan plateau (an active tectonic feature created in late Cenozoic through collision of the Indian subcontinent and the Asian continent). Many of these main units are recognizable in the tomographic images as distinctive units; Tibet appears as a prominent low velocity (about -15% from the average) structure, with western and central Tibet often appearing as the areas with the lowest velocities, the Central Asian fold-belt, and the Angara craton are consistently high group velocity areas. Some lesser tectonic features are also recognizable. For example, Lake Baikal is seen as a high velocity feature at periods greater than 40 seconds. However, the high group velocity feature does not stop near the southern end of Lake Baikal; it extends south-southwestward across Mongolia. The North China Plain, a part of the platform where extensional tectonics dominate, is an area of high velocities as a result of relatively thin crust. The south China block, the least tectonically active region of China, is generally an area of high velocity. For periods longer than 40 seconds, a NNE trending high group velocity gradient clearly exists in eastern China; the velocities are noticeably higher in the east. From the group velocity maps, average dispersion curves at twelve locations were determined and inverted to obtain velocity structures. Main results of group velocity inversion include: (1) a Tibetan crust of around 60km thick, with low crustal and upper mantle shear velocities, at 3.3km/s and 4.2km/s, respectively; (2) with the Moho constrained at 40-43km, the Angara craton and the Central Asian foldbelt have a VS in excess of 4.6km/s (3) relatively low shear velocities are obtained for tectonically active areas. In many parts of the study area, where Precambrian basement is exposed, the process in the crust and upper mantle due to recent tectonic activities have modified the crust and upper mantle velocity structures under the Precambrian terranes, they are no longer underlain by high velocity crust and mantle.

Wu, F. T.; Levshin, A. L.; Kozhevnikov, V. M.

308

Compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near-surface sedimentary rocks  

SciTech Connect

Laboratory ultrasonic measurements of compressional wave velocity and attenuation were made as a function of effective pressure on samples of limestone, sandstone and siltstone taken from a shallow borehole test site. The results indicate that the sandstones are pervaded by grain contact microcracks which dramatically affect their compressional wave attenuations. Clean sandstone shows a compressional wave quality factor (Q{sub p}) of 24 {+-} 2 at 5 MPa effective pressure (close to the estimated in situ burial pressure) and a Q{sub p} of 83 {+-} 29 at 60 MPa. The Q{sub p} of limestones and siltstones at the site show negligible and small increases with pressure in the laboratory, respectively. The strong pressure dependence of Q{sub p} in clean sandstone was used to infer the presence of in situ microcracks. Sediment velocities measured in the laboratory at about 1 MHz were compared with those from the full waveform sonic log at about 10 kHz implies that they must also be highly attenuating over a significant part of the frequency range 10 kHz to 1 MHz, to account for the magnitude of the observed velocity dispersion. Assuming the laboratory Q{sub p} values measured at 5 MPa remain constant down to 10 kHz predicts the observed dispersion quite well. Furthermore, the sonic log velocities of sandstones, limestones and siltstones (after normalizing each lithology for porosity and clay content) were found to reflect the same pressure (depth) trends observed in the laboratory. The results provide evidence for the existence of in situ microcracks in near-surface sediments.

Best, A.I. [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology] [Univ. of Reading (United Kingdom). Postgraduate Research Inst. for Sedimentology; Sams, M.S. [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology] [Imperial College of Science, Technology and Medicine, London (United Kingdom). Dept. of Geology

1997-03-01

309

Two-dimensional PP/PS-stereotomography: P- and S-waves velocities estimation from OBC data  

NASA Astrophysics Data System (ADS)

We present the extension of stereotomography to P- and S-wave velocity estimation from PP- and PS-reflected/diffracted waves. In this new context, we greatly benefit from the use of locally coherent events by stereotomography. In particular, when applied to S-wave velocity estimation from PS-data, no pairing of PP- and PS-events is a priori required. In our procedure the P-wave velocity model is obtained first using stereotomography on PP-arrivals. Then the S-wave velocity model is obtained using PS-stereotomography on PS-arrivals fixing the P-wave velocity model. We present an application to an `ideal' synthetic data set demonstrating the relevance of the approach, which allows us to recover depth consistent P- and S-waves velocity models even if no pairing of PP- and PS-events is introduced. Finally, results to a real data set from the Gulf of Mexico are presented demonstrating the potential of the method in a noisy data context.

Alerini, M.; Lambaré, G.; Baina, R.; Podvin, P.; Le Bégat, S.

2007-08-01

310

Alternative dust-ion acoustic waves in a magnetized charge varying dusty plasma with nonthermal electrons having a vortex-like velocity distribution  

NASA Astrophysics Data System (ADS)

Alternative localized dust-ion acoustic waves are investigated in a magnetized charge varying dusty plasma with nonthermal electrons having a vortex-like velocity distribution. The correct non-Maxwellian charging currents are obtained based on the well-known orbit limited motion theory. Following the standard reductive perturbation technique, a Schamel-Zakharov Kuznetsov Burgers (S-ZKB) equation is derived. It is shown that due to an interplay between trapping and nonthermality, our dusty plasma model may support solitary as well as shock waves the main quantities (phase velocity, amplitude and width) of which are drastically influenced by trapping, nonthermality and charge variation. Due to the flexibility provided by the outlined distribution function (two concepts of non isothermality), we stress that our model should provide a good fit of the space observations.

Hadjaz, Idir; Tribeche, Mouloud

2014-06-01

311

Variations in Gravitational Field, Tidal Force, Electromagnetic Waves and Earthquakes  

NASA Astrophysics Data System (ADS)

This paper is the report on an experiment carried out between the month of December 2009 and the month of April 2010 between the Venetian Lagoon and the Northern Apennines in Italy, to check on a potential relationship between earthquakes and variations in the local gravitational field, the effect on the tide exercised by the interaction between the moon and the Sun, the appearance of anomalous light effects in the atmosphere ("Earth lights"), and the emission of radio waves caused by stresses in the Earth's crust. The cases studied show that there is indeed some concomitance between the periodic rising and falling of the sea level and the terrestrial tide effect, due to the gravitational attraction of the moon and sun on the Earth. In fact, changes in the local force of gravity coincided with the cycle of high and low tides and, in certain cases, with a variation in the electromagnetic field that preceded the occurrence of a seismic event by just a few hours. The o! bservations in the article are limited to the magnitude range discussed in the paper.

Strasser, Valentino

2010-12-01

312

3-D Shear Wave Velocity Structure of the Crust and Upper Mantle in South China Sea and its Surrounding Regions by Surface Wave Dispersion Analysis  

NASA Astrophysics Data System (ADS)

In this study, we construct a 3-D shear wave velocity structure of the crust and upper mantle in South China Sea and its surrounding regions by surface wave dispersion analysis. We use the multiple filter technique to calculate the group velocity dispersion curves of fundamental mode Rayleigh and Love waves with periods from 14 s to 120 s for earthquakes occurred around the Southeast Asia. We divide the study region (80° E-140° E, 16° S-32° N) into 3° × 3° blocks and use the constrained block inversion method to get the regionalized dispersion curve for each block. At some chosen periods, we put together laterally the regionalized group velocities from different blocks at the same period to get group velocity image maps. These maps show that there is significant heterogeneity in the group velocity of the study region. The dispersion curve of each block was then processed by surface wave inversion method to obtain the shear wave velocity structure. Finally, we put the shear wave velocity structures of all the blocks together to obtain the three-dimensional shear wave velocity structure of crust and upper mantle. The three-dimensional shear wave velocity structure shows that the shear wave velocity distribution in the crust and upper mantle of the South China Sea and its surrounding regions displays significant heterogeneity. There are significant differences among the crustal thickness, the lithospheric thickness and the shear wave velocity of the lid in upper mantle of different structure units. This study shows that the South China Sea Basin, southeast Sulu Sea Basin and Celebes Sea Basin have thinner crust. The thickness of crust in South China Sea Basin is 5-10 km; in Indochina is 25-40 km; in Peninsular Malaysia is 30-35 km; in Borneo is 30-35 km; in Palawan is 35 km; in the Philippine Islands is 30-35 km, in Sunda Shelf is 30-35 km, in Southeast China is 30-40 km, in West Philippine Basin is 5-10 km. The South China Sea Basin has a lithosphere with thickness of about 45-50 km, and the shear wave velocity of its lid is about 4.3-4.7 km/s; Indochina has a lithosphere with thickness of about 55-70 km, and the shear wave velocity of its lid is about 4.3-4.5 km/s; Borneo has a lithosphere with thickness of about 55-60 km, and the shear wave velocity of its lid is about 4.1-4.3 km/s; the Philippine Islands has a lithosphere with thickness of about 55-60 km, and the shear wave velocity of its lid is about 4.2-4.3 km/s, West Philippine Basin has a lithosphere with thickness of about 50-55 km, and the shear wave velocity of its lid is about 4.7-4.8 km/s, Sunda Self has a lithosphere with thickness of about 55-65 km, and the shear wave velocity of its lid is about 4.3 km/s. The Red-River Fault Zone probably penetrates to a depth of at least 200 km and is plausibly the boundary between the South China Block and the Indosinia Block.

Wu, Hsin-Hung; Tsai, Yi-Ben; Lee, Tung-Yi; Lo, Ching-Hua; Hsieh, Chao-Hui; Toan, Dinh Van

2004-03-01

313

P-wave velocity changes in freezing hard low-porosity rocks: a laboratory-based time-average model  

NASA Astrophysics Data System (ADS)

P-wave refraction seismics is a key method in permafrost research but its applicability to low-porosity rocks, that constitute alpine rock walls, has been denied in prior studies. These explain p-wave velocity changes in freezing rocks exclusively due to changing velocities of pore infill, i.e. water, air and ice. In existing models, no velocity increase is expected for low-porosity bedrock. We postulate, that mixing laws apply for high-porosity rocks, but freezing in confined space in low-porosity bedrock also alters physical rock matrix properties. In the laboratory, we measured p-wave velocities of 22 decimeter-large low-porosity (<6 %) metamorphic, magmatic and sedimentary permafrost rock samples with a natural texture (>100 micro-fissures) from 25 °C to -15 °C in 0.3 °C increments close to the freezing point. P-wave velocity increases by 7-78 % when freezing parallel to cleavage/bedding and matrix velocity increases from 5-59 % coincident to an anisotropy decrease in most samples. The expansion of rigid bedrock upon freezing is restricted and ice pressure will increase matrix velocity and decrease anisotropy while changing velocities of the pore infill are insignificant. Here, we present a modified Timur's 2-phase equation implementing changes in matrix velocity dependent on lithology and demonstrate the physical basis for refraction seismics in low-porosity bedrock.

Draebing, D.; Krautblatter, M.

2012-02-01

314

P-wave velocity changes in freezing hard low-porosity rocks: a laboratory-based time-average model  

NASA Astrophysics Data System (ADS)

P-wave refraction seismics is a key method in permafrost research but its applicability to low-porosity rocks, which constitute alpine rock walls, has been denied in prior studies. These studies explain p-wave velocity changes in freezing rocks exclusively due to changing velocities of pore infill, i.e. water, air and ice. In existing models, no significant velocity increase is expected for low-porosity bedrock. We postulate, that mixing laws apply for high-porosity rocks, but freezing in confined space in low-porosity bedrock also alters physical rock matrix properties. In the laboratory, we measured p-wave velocities of 22 decimetre-large low-porosity (< 10%) metamorphic, magmatic and sedimentary rock samples from permafrost sites with a natural texture (> 100 micro-fissures) from 25 °C to -15 °C in 0.3 °C increments close to the freezing point. When freezing, p-wave velocity increases by 11-166% perpendicular to cleavage/bedding and equivalent to a matrix velocity increase from 11-200% coincident to an anisotropy decrease in most samples. The expansion of rigid bedrock upon freezing is restricted and ice pressure will increase matrix velocity and decrease anisotropy while changing velocities of the pore infill are insignificant. Here, we present a modified Timur's two-phase-equation implementing changes in matrix velocity dependent on lithology and demonstrate the general applicability of refraction seismics to differentiate frozen and unfrozen low-porosity bedrock.

Draebing, D.; Krautblatter, M.

2012-10-01

315

On measuring surface wave phase velocity from station-station cross-correlation of ambient signal  

NASA Astrophysics Data System (ADS)

We apply two different algorithms to measure surface wave phase velocity, as a function of frequency, from seismic ambient noise recorded at pairs of stations from a large European network. The two methods are based on consistent theoretical formulations, but differ in the implementation: one method involves the time-domain cross-correlation of signal recorded at different stations; the other is based on frequency-domain cross-correlation, and requires finding the zero-crossings of the real part of the cross-correlation spectrum. Furthermore, the time-domain method, as implemented here and in the literature, practically involves the important approximation that interstation distance be large compared to seismic wavelength. In both cases, cross-correlations are ensemble-averaged over a relatively long period of time (1 yr). We verify that the two algorithms give consistent results, and infer that phase velocity can be successfully measured through ensemble-averaging of seismic ambient noise, further validating earlier studies that had followed either approach. The description of our experiment and its results is accompanied by a detailed though simplifed derivation of ambient-noise theory, writing out explicitly the relationships between the surface wave Green's function, ambient-noise cross-correlation and phase and group velocities.

Boschi, Lapo; Weemstra, Cornelis; Verbeke, Julie; Ekström, Göran; Zunino, Andrea; Giardini, Domenico

2013-01-01

316

Fast simulated annealing inversion of surface waves on pavement using phase-velocity spectra  

USGS Publications Warehouse

The conventional inversion of surface waves depends on modal identification of measured dispersion curves, which can be ambiguous. It is possible to avoid mode-number identification and extraction by inverting the complete phase-velocity spectrum obtained from a multichannel record. We use the fast simulated annealing (FSA) global search algorithm to minimize the difference between the measured phase-velocity spectrum and that calculated from a theoretical layer model, including the field setup geometry. Results show that this algorithm can help one avoid getting trapped in local minima while searching for the best-matching layer model. The entire procedure is demonstrated on synthetic and field data for asphalt pavement. The viscoelastic properties of the top asphalt layer are taken into account, and the inverted asphalt stiffness as a function of frequency compares well with laboratory tests on core samples. The thickness and shear-wave velocity of the deeper embedded layers are resolved within 10% deviation from those values measured separately during pavement construction. The proposed method may be equally applicable to normal soil site investigation and in the field of ultrasonic testing of materials. ?? 2006 Society of Exploration Geophysicists.

Ryden, N.; Park, C.B.

2006-01-01

317

Pn wave velocity and anisotropy beneath Pamir and its adjacent regions  

NASA Astrophysics Data System (ADS)

As the western end point of continental collision between the Indian and Eurasian plates, Pamir is an ideal place to research uplifting mechanisms in the Tibetan plateau. In this study, 141 644 Pn arrivals were used to obtain seismic wave velocities and anisotropy in the uppermost mantle beneath Pamir and its adjacent regions by performing tomographic inversion of Pn travel times. The data were selected from multiple databases, including ISC/EHB, the Annual Bulletin of Chinese Earthquakes, and regional bulletins of Xinjiang. The tomography results reveal significant features with high resolution and correlate well with geological structures. The main results are as follows: (1) The Pn wave velocities are particularly high in the old stable blocks such as Tarim basin, Indian plate and Tajik basin, while the low Pn velocities always lie in tectonically active regions like the western Tibetan plateau, Pamir, Tianshan and Hindu Kush. (2) Strong Pn anisotropy is found beneath the Indian-Eurasian collision zone; its direction is parallel to the collision arc and nearly perpendicular to both the direction of maximum compression stress and relative crustal movement. The result is probably caused by the pure shear deformation in the uppermost mantle of the collision zone. (3) A geodynamic continent-continent collision model is proposed to show anisotropy and collision mechanisms between the Indian plate and the Tarim and Tajik basins.

Feng, Biao; Pei, Shunping

2012-12-01

318

Spatial parallelism of a 3D finite difference, velocity-stress elastic wave propagation code  

SciTech Connect

Finite difference methods for solving the wave equation more accurately capture the physics of waves propagating through the earth than asymptotic solution methods. Unfortunately, finite difference simulations for 3D elastic wave propagation are expensive. The authors model waves in a 3D isotropic elastic earth. The wave equation solution consists of three velocity components and six stresses. The partial derivatives are discretized using 2nd-order in time and 4th-order in space staggered finite difference operators. Staggered schemes allow one to obtain additional accuracy (via centered finite differences) without requiring additional storage. The serial code is most unique in its ability to model a number of different types of seismic sources. The parallel implementation uses the MPI library, thus allowing for portability between platforms. Spatial parallelism provides a highly efficient strategy for parallelizing finite difference simulations. In this implementation, one can decompose the global problem domain into one-, two-, and three-dimensional processor decompositions with 3D decompositions generally producing the best parallel speedup. Because I/O is handled largely outside of the time-step loop (the most expensive part of the simulation) the authors have opted for straight-forward broadcast and reduce operations to handle I/O. The majority of the communication in the code consists of passing subdomain face information to neighboring processors for use as ghost cells. When this communication is balanced against computation by allocating subdomains of reasonable size, they observe excellent scaled speedup. Allocating subdomains of size 25 x 25 x 25 on each node, they achieve efficiencies of 94% on 128 processors. Numerical examples for both a layered earth model and a homogeneous medium with a high-velocity blocky inclusion illustrate the accuracy of the parallel code.

Minkoff, S.E.

1999-12-01

319

An explicit relation for the apparent phase velocity of Rayleigh waves in a vertically heterogeneous elastic half-space  

NASA Astrophysics Data System (ADS)

This paper presents the mathematical derivation of an explicit relation for the apparent (or effective) phase velocity of Rayleigh waves in a vertically heterogeneous, isotropic elastic half-space for harmonic excitation. As a kinematical feature, the apparent phase velocity captures the superposition, in a spatial Fourier series, of the individual modes of propagation of Rayleigh waves and describes the speed of propagation of a composite waveform generated by a vertically oscillating point load. The relation, which is a function of the distance from the source, frequency and depth, depends explicitly on the modal phase and group velocities of Rayleigh waves, and their corresponding wavenumbers and eigenfunctions, which can be computed directly from the solution of the Rayleigh-wave eigenproblem. A practical scenario for the application of the notion of apparent Rayleigh-wave phase velocity is the modelling of the dispersion curve in the well-known surface wave measurement methods `spectral analysis of surface waves' (SASW) and `multichannel analysis of surface waves' (MASW). Apart from a theoretical motivation, the availability in surface wave testing of an explicit formula for the calculation of the apparent Rayleigh-wave phase velocity may lead to the development of a new class of inversion algorithms capable of taking into account the influence of all the modes of surface wave propagation. To demonstrate the exactness of the explicit relation, the predicted values of apparent phase velocity are compared to those computed synthetically from a numerical simulation of SASW and MASW testing for three case studies, which show both single as well as multiple mode dominance effects.

Lai, Carlo G.; Mangriotis, Maria-Daphne; Rix, Glenn J.

2014-11-01

320

Upper mantle S wave velocity structure of the East Anatolian-Caucasus region  

NASA Astrophysics Data System (ADS)

processes occurring in the upper mantle such as slab break off and lithosphere delamination often result in high rates of lithospheric deformation and rapid tectonic uplift of large areas. The continent-continent collision zone between Arabia and Eurasia has been widely studied in this context, but several different viable geodynamic models exist to explain the uplift and deformation of the Anatolian Plateau and the Caucasus Mountains. We have imaged the uppermost mantle shear wave velocity structure of the East Anatolian-Caucasus region using surface wave tomography to better understand the regional tectonic activity since the onset of the collision between the Arabian and Eurasian Plates. Furthermore, we used our tomographic models to better understand the processes, which are responsible for the formation of the 2 km high plateau and the widespread volcanism in eastern Turkey, as well as reactivation of deformation and deep seismicity in the eastern Greater Caucasus. Our model of regional upper mantle shear wave velocity structure supports subduction of the northern and southern branches of Neo-Tethys lithosphere between Eurasia and Gondwana and suggests a possible underthrusting of the Kura Basin lithosphere beneath the Greater Caucasus.

Skolbeltsyn, Gleb; Mellors, Robert; Gök, Rengin; Türkelli, Niyazi; Yetirmishli, Gurban; Sandvol, Eric

2014-03-01

321

Measurements of Spatially Resolved Velocity Variations in Shock Compressed Heterogeneous Materials Using a Line-Imaging Velocity Interferometer  

SciTech Connect

Relatively straightforward changes in the optical design of a conventional optically recording velocity interferometer system (ORVIS) can be used to produce a line-imaging velocity interferometer wherein both temporal and spatial resolution can be adjusted over a wide range. As a result line-imaging ORVIS can be tailored to a variety of specific applications involving dynamic deformation of heterogeneous materials as required by the characteristic length scale of these materials (ranging from a few {micro}m for ferroelectric ceramics to a few mm for concrete). A line-imaging ORVIS has been successfully interfaced to the target chamber of a compressed gas gun driver and fielded on numerous tests in combination with simultaneous measurements using a dual delay-leg, ''push-pull'' VISAR system. These tests include shock loading of glass-reinforced polyester composites, foam reverberation experiments (measurements at the free surface of a thin aluminum plate impacted by foam), and measurements of dispersive velocity in a shock-loaded explosive simulant (sugar). Comparison of detailed spatially-resolved material response to the spatially averaged VISAR measurements will be discussed.

ASAY,JAMES R.; CHHABILDAS,LALIT C.; KNUDSON,MARCUS D.; TROTT,WAYNE M.

1999-09-01

322

RESEARCH PAPERS : Wave-theoretical inversion of teleseismic surface waves in a regional network: phase-velocity maps and a three-dimensional upper-mantle shear-wave-velocity model for southern Germany  

NASA Astrophysics Data System (ADS)

Using teleseimic surface-wave data from 110 selected earthquakes recorded at 10broad-band stations in southern Germany we construct phase-velocity maps of Rayleigh waves for southern Germany. In a further step these maps are inverted for a three-dimensional model of the SV velocity of the upper 200 km of the mantle. We attempt to take into account the effect of heterogeneous structure outside the study region by jointly inverting the data for heterogeneous phase velocity inside the study region and the distortion of the incoming wavefields by the surrounding structure. The total wavefield in the study region is computed with a scattering formalism which includes multiple forward scattering and single backscattering. Since, in principle, the data can be perfectly fit by the incoming wavefields without any heterogeneous structure inside the study area, we impose additional constraints on the incoming wavefields to reduce the non-uniqueness. The most important constraint is an energy criterion which states that the energy of the modelled wavefield in the study area, averaged over many events, should be equal to the energy sampled by the stations. We demonstrate that enforcing this criterion generates phase-velocity maps with heterogeneous structure. Nevertheless, we are able to satisfy the energy criterion without any heterogeneous structure at the price of an only slightly increased data misfit. Hence, it must be concluded that a seismic network of size and station density such as the one used in this study is still insufficient to demonstrate convincingly the existence of heterogeneities in the network area using teleseismic surface waves. Any reasonable structure combined with the appropriate incoming wavefields would allow an acceptable fit of our data. This frustrating conclusion, of course, applies to all other comparable studies which use teleseismic surface waves. Although we cannot convincingly show that any phase-velocity map we find should be preferred over others, we are able to obtain good reconstructions of test structures from realistic synthetic data with the same station and event distribution as the real data. Moreover, we find that the geometric pattern of the phase-velocity maps obtained from real data depends only weakly on the constraints applied in the inversion, while the amplitude of the phase-velocity perturbations is almost completely determined by the constraints. For all periods considered the fit to the data is extremely good. The reduction of the quadratic misfit relative to the case of plane incoming waves and no structure is dramatic for the shorter periods. The 3-D model of vertical shear-wave velocity down to a depth of 200 km exhibits a basic division into four quadrants separated by a vertical plane intersecting the surface along a nearly west-east line and a horizontal plane at about 130 km depth. The northern rants show high velocities in the top 120 km and low velocities below 140 km. The opposite is the case for the southern quadrants. An exception to this general feature is a pronounced low-velocity zone in the northwestern corner of the region.

Friederich, Wolfgang

1998-01-01

323

Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling  

USGS Publications Warehouse

We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions: (a) hydrate modifies the pore fluid elastic properties without affecting the frame; (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data. We apply the model to sonic and VSP data from ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consistent with estimates obtained from resistivity, chlorinity and evolved gas data. Copyright 1999 by the American Geophysical Union.

Helgerud, M.B.; Dvorkin, J.; Nur, A.; Sakai, A.; Collett, T.

1999-01-01

324

Characteristics of light reflected from a dense ionization wave with a tunable velocity.  

PubMed

An optically dense ionization wave (IW) produced by two femtosecond (approximately 10/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses. PMID:20366045

Zhidkov, A; Esirkepov, T; Fujii, T; Nemoto, K; Koga, J; Bulanov, S V

2009-11-20

325

Large-scale Observations of a Subauroral Polarization Stream by Midlatitude SuperDARN Radars: Instantaneous Longitudinal Velocity Variations  

NASA Technical Reports Server (NTRS)

We present simultaneous measurements of flow velocities inside a subauroral polarization stream (SAPS) made by six midlatitude high-frequency SuperDARN radars. The instantaneous observations cover three hours of universal time and six hours of magnetic local time (MLT). From velocity variations across the field-of-view of the radars we infer the local 2D flow direction at three different longitudes. We find that the local flow direction inside the SAPS channel is remarkably constant over the course of the event. The flow speed, however, shows significant temporal and spatial variations. After correcting for the radar look direction we are able to accurately determine the dependence of the SAPS velocity on magnetic local time. We find that the SAPS velocity variation with magnetic local time is best described by an exponential function. The average velocity at 00 MLT was 1.2 km/s and it decreased with a spatial e-folding scale of two hours of MLT toward the dawn sector. We speculate that the longitudinal distribution of pressure gradients in the ring current is responsible for this dependence and find these observations in good agreement with results from ring current models. Using TEC measurements we find that the high westward velocities of the SAPS are - as expected - located in a region of low TEC values, indicating low ionospheric conductivities.

Clausen, L. B. N.; Baker, J. B. H.; Sazykin, S.; Ruohoniemi, J. M.; Greenwald, R. A.; Thomas, E. J.; Shepherd, S. G.; Talaat, E. R.; Bristow, W. A.; Zheng, Y.; Coster, A. J.

2012-01-01

326

Combined ultrasonic elastic wave velocity and microtomography measurements at high pressures  

NASA Astrophysics Data System (ADS)

Combined ultrasonic and microtomographic measurements were conducted for simultaneous determination of elastic property and density of noncrystalline materials at high pressures. A Paris-Edinburgh anvil cell was placed in a rotation apparatus, which enabled us to take a series of x-ray radiography images under pressure over a 180° angle range and construct accurately the three-dimensional sample volume using microtomography. In addition, ultrasonic elastic wave velocity measurements were carried out simultaneously using the pulse reflection method with a 10° Y-cut LiNbO3 transducer attached to the end of the lower anvil. Combined ultrasonic and microtomographic measurements were carried out for SiO2 glass up to 2.6 GPa and room temperature. A decrease in elastic wave velocities of the SiO2 glass was observed with increasing pressure, in agreement with previous studies. The simultaneous measurements on elastic wave velocities and density allowed us to derive bulk (Ks) and shear (G) moduli as a function of pressure. Ks and G of the SiO2 glass also decreased with increasing pressure. The negative pressure dependence of Ks is stronger than that of G, and as a result the value of Ks became similar to G at 2.0-2.6 GPa. There is no reason why we cannot apply this new technique to high temperatures as well. Hence the results demonstrate that the combined ultrasonic and microtomography technique is a powerful tool to derive advanced (accurate) P-V-Ks-G-(T) equations of state for noncrystalline materials.

Kono, Yoshio; Yamada, Akihiro; Wang, Yanbin; Yu, Tony; Inoue, Toru

2011-02-01

327

Experimental demonstration of noncontact pulse wave velocity monitoring using multiple Doppler radar sensors.  

PubMed

In this paper, two Doppler radars are used to monitor the pulse movements at the heart and the calf in order to measure the pulse wave velocity (PWV) wirelessly. Both simulation and experiment have been performed to demonstrate the feasibility of the proposed noncontact PWV monitoring. A three-stage calibration procedure, including DC offset calibration, circuit delay calibration and antenna radiation pattern calibration, has been developed for reliable long-term PWV monitoring. The measurement results have been verified by wired contact measurement with pulse transducers. PMID:21096684

Lu, Li; Li, Changzhi; Lie, Donald Y C

2010-01-01

328

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles  

DOEpatents

An apparatus for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously.

Benjamin, R.F.

1983-10-18

329

Optical pin apparatus for measuring the arrival time and velocity of shock waves and particles  

DOEpatents

An apparatus is disclosed for the detection of the arrival and for the determination of the velocity of disturbances such as shock-wave fronts and/or projectiles. Optical pins using fluid-filled microballoons as the light source and an optical fiber as a link to a photodetector have been used to investigate shock-waves and projectiles. A microballoon filled with a noble gas is affixed to one end of a fiber-optic cable, and the other end of the cable is attached to a high-speed streak camera. As the shock-front or projectile compresses the microballoon, the gas inside is heated and compressed producing a bright flash of light. The flash of light is transmitted via the optic cable to the streak camera where it is recorded. One image-converter streak camera is capable of recording information from more than 100 microballoon-cable combinations simultaneously. 3 figs.

Benjamin, R.F.

1987-03-10

330

Relationship between compressional-wave velocity and porosity of sediments along subduction plate interface  

NASA Astrophysics Data System (ADS)

Evolution of physical properties of sediments along subduction interface has effects on wedge strength, wedge geometry, dewatering and dehydration processes, and seismic behavior. Sediments have initially more than 70% of porosity prior to subduction. Through underthrusting and accretion, porosity of sediments decreases by compaction and cementation to be lithified sediments. The purpose of this study is to understand evolution of physical properties from a state before subduction to a state within a wedge using a relationship between compressional-wave velocity and porosity. In this study, we obtained new data for sediments from a reference site in IODP NanTroSEIZE, Expedition 333. In addition to that, we have complied velocity-porosity relationships for the samples and also for previous studies from NanTroSEIZE (off Kumano) (Hashimoto et al., 2010, 2011), ODP Leg 190 (off Shikoku) (Hoffman and Tobin, 2004) and ODP Leg 170 (off Costa Rica) (Gettemy and Tobin, 2003). Velocity measurement procedure in this study to obtain new data is as following: Two pumps were used to control pore fluid pressure and confining pressure. The pore pressure of 1000kPa was kept under drained conditions. Confining (effective) pressure was increased stepwise in the measurements. Velocity measurements were conducted under isotropic pressure conditions. Confining pressure was pressurized in tens seconds and kept for more than 8 hours for next step to obtain equilibrium conditions between effective pressure and sediments strain. Lead zirconate titanate (PZT) shear wave transducers (500kHz) were used in a source-receiver pair to measure wave speed. Porosity and P-wave velocity ranges about 27 - 75% and 1.4 - 2.2 km/s in this study, respectively. In the comparison in Vp-porosity relationships between sedimetns from reference sites and others, sediments were classified into two, simply compacted sediments (reference site and slope sediments) and wedge sediments. Different trends in Vp-porosity relationships were observed for the classified sediments. For compacted sediments, Vp-porosity relationships are along the global empirical relationships (Erickson and Jarrard 1988) and almost within the area between normal and highly compaction curves. On the other hand, some of Vp-porosity relationships for wedge sediments represent trends with higher velocity at a porosity. Such trend was observed for wedge sediments from Site C0001 and C0004. Those higher Vp trend in Vp-porosity relationship for wedge sediments can be explained by shear strain of sediments and/or cementation. Even though the velocity measurements was conducted under hydrostatic condition, we examined the void ratio-porosity curve as a kind of compaction curve. On the basis of the curves, break points were observed at the pressure which corresponds to the effective pressure assuming the hydrostatic pore fluid pressure. The result suggests that the sediments were under condition of normal compaction. Some of void ratio-porosity curve represent a evidence of weak cement which can correspond with anomaly in porosity-depth curve in the shallow portion of the reference sites.

Yamaguchi, M.; Hashimoto, Y.

2012-12-01

331

High propagating velocity of spin waves and temperature dependent damping in a CoFeB thin film  

E-print Network

lm as depicted in Fig. 1. A 5 nm thick layer of Al2O3 was grown by atomic layer deposition onto; published online 29 June 2012) Spin wave propagation in a magnetron-sputtered CoFeB thin filmHigh propagating velocity of spin waves and temperature dependent damping in a CoFeB thin film

Grundler, Dirk

332

Stress-wave velocity of wood-based panels: Effect of moisture, product type, and material direction  

Microsoft Academic Search

The effect of moisture on longitudinal stress-wave veloc­ ity (SWV), bending stiffness. and bending strength of com­ mercial oriented strandboard, plywood. particleboard. and southern pine lumber was evaluated. It was shown that the stress-wave verocity decreased in general with increases in panel moisture content (MC). At a given MC level. SWV var­ ied with panel type and test directions. Regression

Guangping Han; Qinglin Wu; Xiping Wang

2006-01-01

333

The thin section rock physics: Modeling and measurement of seismic wave velocity on the slice of carbonates  

NASA Astrophysics Data System (ADS)

This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave velocity of rock.

Wardaya, P. D.; Noh, K. A. B. M.; Yusoff, W. I. B. W.; Ridha, S.; Nurhandoko, B. E. B.

2014-09-01

334

Compositional variation of density and seismic velocities in natural peridotites at STP conditions: Implications for seismic imaging of compositional heterogeneities in the upper mantle  

NASA Astrophysics Data System (ADS)

Densities and elastic properties of solid natural spinel- and garnet-peridotite samples (n = 133) at standard temperature (T) and pressure (P) (STP) conditions were calculated for compositions ranging from Mg# (100 × Mg/(Mg + Fe)) of 86-94. The physical properties were used to investigate how natural compositional variations control density and seismic velocity. A corresponding set of compositional derivatives (d/dMg#) of density and seismic velocity is provided. Because the P and T derivatives of elastic moduli are very similar for different compositional end-members of peridotitic minerals, the variation of elastic moduli with Mg# at STP conditions holds at elevated P and T. Increased Mg# leads to a significant increase in VS because of the sensitivity of mineral shear moduli to this parameter (dVS/dMg# = 0.0143 ± 0.0009 km s-1). In contrast, the compressional wave velocity (VP) is insensitive to Mg# and, instead, correlates weakly with increasing olivine abundance at STP conditions. The ratio VP/VS therefore exhibits a significant negative correlation with Mg# (d(VP/VS)/dMg# = -0.00407 ± 0.00038). Because the temperature dependency of VP/VS is small (<˜0.04%/100°C) compared to the compositional dependency (1.7%/Mg# unit), the variation in VP/VS is a fairly robust measure of compositional variation even when temperature varies. Finally, a new density versus Mg# parameterization is derived. Combined with a compilation of bulk-rock Mg#s of peridotite xenoliths from cratonic lithospheric mantle, it is shown that the intrinsic density of cratonic mantle balances to within error its negative thermal buoyancy imposed by its cooler thermal state relative to upwelling asthenospheric mantle.

Lee, Cin-Ty Aeolus

2003-09-01

335

The use of driver inserts to reduce non-ideal pressure variations behind reflected shock waves  

Microsoft Academic Search

Non-ideal shock tube facility effects, such as incident shock wave attenuation, can cause variations in the pressure histories\\u000a seen in reflected shock wave experiments. These variations can be reduced, and in some cases eliminated, by the use of driver\\u000a inserts. Driver inserts, when designed properly, act as sources of expansion waves which can counteract or compensate for\\u000a gradual increases in

Zekai Hong; Genny A. Pang; Subith S. Vasu; David F. Davidson; Ronald K. Hanson

2009-01-01

336

The effects of pressure, temperature, and pore water on velocities in Westerly granite. [for seismic wave propagation  

NASA Technical Reports Server (NTRS)

A description is presented of an experimental assembly which has been developed to conduct concurrent measurements of compressional and shear wave velocities in rocks at high temperatures and confining pressures and with independent control of the pore pressure. The apparatus was used in studies of the joint effects of temperature, external confining pressure, and internal pore water on sonic velocities in Westerly granite. It was found that at a given temperature, confining pressure has a larger accelerating effect on compressional waves in dry rock, whereas at a given confining pressure, temperature has a larger retarding effect on shear waves.

Spencer, J. W., Jr.; Nur, A. M.

1976-01-01

337

Simultaneous measurement of the phase and group velocities of Lamb waves in a laser-generation based imaging method.  

PubMed

This paper describes a novel approach to the simultaneous measurement of the phase and group velocities of Lamb waves based on images of their propagation. The laser-generation based imaging method was first introduced to obtain images of Lamb wave propagation. The time series of snapshot images is used to make a position-time diagram, and the velocities can be estimated based on the slopes of the position curves. Thus, the phase and group velocities can be obtained by measuring the phase advance and energy flow of the Lamb wave, respectively. Details of the principle of simultaneous measurement are presented herein. Experimental verification was also performed in the range of 0.2-3.0 MHz-mm using aluminum plates. The average errors between experiment and theory in the phase and group velocities were 3.31% and 5.68%, respectively. PMID:22225595

Nishino, Hideo; Tanaka, Toshiro; Yoshida, Kenichi; Takatsubo, Junji

2012-04-01

338

Elastic constants measured from acoustic wave velocities in barium titanate piezoelectric ceramics  

NASA Astrophysics Data System (ADS)

The longitudinal and transverse wave velocities in barium titanate (BT) ceramics sintered at different firing temperatures were measured using an ultrasonic precision thickness gauge with high-frequency pulse generation to evaluate elastic constants, such as Young’s modulus and Poisson’s ratio. With increasing firing temperature, the longitudinal and transverse wave velocities increased; as a result, Young’s modulus increased because of BT ceramics being mechanically hard. Poisson’s ratio after DC poling, however, was almost independent of the firing temperature. It was confirmed that there was an important factor for generating piezoelectricity regarding changes in Young’s modulus and Poisson’s ratio after DC poling compared with those before DC poling, that is, lowering Young’s modulus and increasing Poisson’s ratio. Furthermore, the modulus of rigidity and bulk modulus increased with the firing temperature because of the increase in ceramic bulk density. The modulus of rigidity decreased and the bulk modulus increased during DC poling because of domain alignment.

Ogawa, Toshio; Ikegaya, Taiki

2015-01-01

339

Anisotropic Rayleigh-wave Phase-velocity Maps in Northern Vietnam  

NASA Astrophysics Data System (ADS)

Northern Vietnam is the location of both the Song Ma Complex, the suture between the Indochina and South China Blocks, and the southern end of the giant Red River Shear Zone. Lithospheric structure provides important clues to the evolutions of the tectonic boundary zone and the interaction between the Indochina and South China Blocks. During 2006-2008, an array of 24 broadband stations were deployed in northern Vietnam in a collaborative project between the Institute of Geophysics of the Vietnam Academy of Science and Technology and the Institute of Earth Sciences of Academic Sinica in Taiwan. In this study, we use Rayleigh waveforms recorded at those stations from globally distributed earthquakes to construct the regional isotropic and azimuthally anisotropic phase velocity maps. Rayleigh-wave dispersion curves in the period range of 10-200 sec are obtained manually by the two-station method using vertical-component broadband waveforms. The dispersion curves along the densely distributed crossing paths are inverted via the LSQR algorithm for the isotropic and azimuthally anisotropic phase-velocity maps at a number of periods. Results will be compared with previous studies in this region based on body-wave traveltimes, SKS splitting observations and receiver functions, and with the tectonic features observed in the region.

Zhao, L.; Legendre, C. P.; Huang, W.; Huang, B.

2013-12-01

340

The 24-hour pulse wave velocity, aortic augmentation index, and central blood pressure in normotensive volunteers.  

PubMed

The purpose of this study was to examine the pulse wave velocity, aortic augmentation index corrected for heart rate 75 (AIx@75), and central systolic and diastolic blood pressure during 24-hour monitoring in normotensive volunteers. Overall, 467 subjects (206 men and 261 women) were recruited in this study. Participants were excluded from the study if they were less than 19 years of age, had blood test abnormalities, had a body mass index greater than 2 7.5 kg/m(2), had impaired glucose tolerance, or had hypotension or hypertension. Ambulatory blood pressure monitoring (ABPM) with the BPLab(®) device was performed in each subject. ABPM waveforms were analyzed using the special automatic Vasotens(®) algorithm, which allows the calculation of pulse wave velocity, AIx@75, central systolic and diastolic blood pressure for "24-hour", "awake", and "asleep" periods. Circadian rhythms and sex differences in these indexes were identified. Pending further validation in prospective outcome-based studies, our data may be used as preliminary diagnostic values for the BPLab ABPM additional index in adult subjects. PMID:24812515

Kuznetsova, Tatyana Y; Korneva, Viktoria A; Bryantseva, Evgeniya N; Barkan, Vitaliy S; Orlov, Artemy V; Posokhov, Igor N; Rogoza, Anatoly N

2014-01-01

341

The 24-hour pulse wave velocity, aortic augmentation index, and central blood pressure in normotensive volunteers  

PubMed Central

The purpose of this study was to examine the pulse wave velocity, aortic augmentation index corrected for heart rate 75 (AIx@75), and central systolic and diastolic blood pressure during 24-hour monitoring in normotensive volunteers. Overall, 467 subjects (206 men and 261 women) were recruited in this study. Participants were excluded from the study if they were less than 19 years of age, had blood test abnormalities, had a body mass index greater than 2 7.5 kg/m2, had impaired glucose tolerance, or had hypotension or hypertension. Ambulatory blood pressure monitoring (ABPM) with the BPLab® device was performed in each subject. ABPM waveforms were analyzed using the special automatic Vasotens® algorithm, which allows the calculation of pulse wave velocity, AIx@75, central systolic and diastolic blood pressure for “24-hour”, “awake”, and “asleep” periods. Circadian rhythms and sex differences in these indexes were identified. Pending further validation in prospective outcome-based studies, our data may be used as preliminary diagnostic values for the BPLab ABPM additional index in adult subjects. PMID:24812515

Kuznetsova, Tatyana Y; Korneva, Viktoria A; Bryantseva, Evgeniya N; Barkan, Vitaliy S; Orlov, Artemy V; Posokhov, Igor N; Rogoza, Anatoly N

2014-01-01

342

Relations of Pulse Wave Velocity to Waist Circumference Independent of Hip Circumference  

PubMed Central

OBJECTIVES Little is known about the effect of waist circumference (WC) on brachial artery pulse wave velocity (baPWV) independent of hip circumference (HC). Therefore, this study aimed to dissociate specific effect of WC on baPWV independent of HC. METHODS Of 1,053 rural residents (2004-2005), 777 subjects with no known history of coronary artery diseases or diabetes mellitus over 40 yr were included. To reduce collinearity, we assessed the independent effect of WC with HC on PWV by residual method (WC [RM]). RESULTS In women, most correlation coefficients were significant between measures of abdominal obesity and baPWV, with the highest (0.32) in waist to hip ratio (WHR), whereas no significance was found in men. All mean values of baPWV among the abdominally obese were higher than those of normal group in women, which were in the order of WHR, WC (RM), and WC. Adjusted OR with 95% CI for baPWV was significantly elevated by increase of WC (RM) upto 4.8 (95% CI: 2.1-11.2), and as 4.3 by WHR (95% CI: 1.6-11.4). CONCLUSION Considering the difficulty in biologically interpreting WHR, WC (RM) may be a useful indicator of abdominal obesity among females in that it reflects the risk of pulse wave velocity. PMID:21191457

Ko, Min Jung; Kim, Mi Kyung; Shin, Jinho

2010-01-01

343

Prediction of shear wave velocity using empirical correlations and artificial intelligence methods  

NASA Astrophysics Data System (ADS)

Good understanding of mechanical properties of rock formations is essential during the development and production phases of a hydrocarbon reservoir. Conventionally, these properties are estimated from the petrophysical logs with compression and shear sonic data being the main input to the correlations. This is while in many cases the shear sonic data are not acquired during well logging, which may be for cost saving purposes. In this case, shear wave velocity is estimated using available empirical correlations or artificial intelligent methods proposed during the last few decades. In this paper, petrophysical logs corresponding to a well drilled in southern part of Iran were used to estimate the shear wave velocity using empirical correlations as well as two robust artificial intelligence methods knows as Support Vector Regression (SVR) and Back-Propagation Neural Network (BPNN). Although the results obtained by SVR seem to be reliable, the estimated values are not very precise and considering the importance of shear sonic data as the input into different models, this study suggests acquiring shear sonic data during well logging. It is important to note that the benefits of having reliable shear sonic data for estimation of rock formation mechanical properties will compensate the possible additional costs for acquiring a shear log.

Maleki, Shahoo; Moradzadeh, Ali; Riabi, Reza Ghavami; Gholami, Raoof; Sadeghzadeh, Farhad

2014-06-01

344

Effects of exciting frequencies, grain sizes, and damage upon P-wave velocity for ultrasonic NDT of concrete  

NASA Astrophysics Data System (ADS)

This paper focuses on the experimental study of the effects of exciting frequencies, grain (aggregate) sizes, and damage upon the ultrasonic P-wave velocity when performing the ultrasonic nondestructive testing (NDT) for concrete specimens. Two batches of concrete and mortar specimens were prepared in the laboratory for the investigation of the effects from the stated factors upon the P-wave velocity. Damage here mostly refers to microcracks and microvoids in concrete. Five different aggregate sizes, 0' (mortar), 3/8', 1/2', 3/4', and 1', were selected to demonstrate the grain (aggregate) size effect. Exciting frequencies of the ultrasonic wave were set to range from 100 kHz to 1,000 kHz, with increment of 50 kHz, to demonstrate the frequency effect. Styrofoam particles were mixed into the comparison concrete and mortar specimens to simulate the distributed microvoids (damage). Different volume fractions of styrofoam particles were mixed into the mortar specimens in order to study the effect of different porosities (damage) upon the P-wave velocity. The experimental observations show that, for mortar and concrete specimens with aggregate sizes from 0 to 1 inch, the P-wave velocity would not be affected significantly within the tested frequency range (100 - 1000 kHz). The normalized P-wave velocity exhibits almost identical pattern upon the exciting frequencies for all specimens.

Ju, Jiann W.; Weng, Lisheng

2000-05-01

345

Shear-wave Velocity Structure of Surabaya, Indonesia, Inferred from Microtremor Observation  

NASA Astrophysics Data System (ADS)

Surabaya, the second-largest city of Indonesia, is located on the northern shore of eastern Java at the mouth of the Mas River and along the edge of the Madura Strait. Though there are not many occurrences of large earthquakes, the region has been exposed to moderate earthquakes frequently. Moreover, Surabaya lies over the alluvium deposit that can be critical for the amplification of seismic waves. Towards the southwestern part of the study area, there is the exposure of sedimentary rocks. Shear wave velocity (Vs) is an important parameter for evaluating the dynamic soil behavior of subsurface structures. Small array measurements of microtremor at 36 sites in the city of Surabaya were carried to estimate the shallow Vs profiles for site effect analysis. The spatial autocorrelation coefficient (SPAC) method was used to determine the phase velocity in the period ranging from 0.1 s to 0.5 s and the iterative inversion technique was subsequently applied to determine the Vs profiles at each site. Large array measurements of microtremor at 11 sites were also carried out to estimate deep Vs profiles. Based on the previous shallow Vs profiles from SPAC, the frequency wavenumber (FK) method was subsequently used to determine the phase velocity in the period from 0.5 s to 3 s and depth of soil profiles down to 800 m. Vs30, the average shear wave velocity in the top 30 m of soil profiles, is a representative value to classify the site condition. It was calculated at each site according to definition in the International Building Code (IBC 2006). The maps of site classification are proposed with Kriging interpolations. Site class D is assigned in southwest corner part while site class E is assigned to the rest of Surabaya. The low Vs values confirms well with the loose soil deposit of the area. Additionally, the regression analysis between topographic elevation and Vs in the logarithm shows a linear relationship. However, it is difficult to conclude the relationship between Vs and slope, since most area of the test region are flat lying (slope gradient range from 0 to 2 degree).

Deng, X.; Megawati, K.; Yamanaka, H.

2010-12-01

346

On the Nature of the Radial Velocity Variability of Aldebaran: A Search for Spectral Line Bisector Variations  

E-print Network

The shape of the Ti I 6303.8 A spectral line of Aldebaran as measured by the line bisector was investigated using high signal-to-noise, high resolution data. The goal of this study was to understand the nature of the 643-day period in the radial velocity for this star reported by Hatzes and Cochran. Variations in the line bisector with the radial velocity period would provide strong evidence in support of rotational modulation or stellar pulsations as the cause of the 643-day period. A lack of any bisector variability at this period would support the planet hypothesis. Variations in the line asymmetries are found with a period of 49.93 days. These variations are uncorrelated with 643-day period found previously in the radial velocity measurements. It is demonstrated that this 50-day period is consistent with an m=4 nonradial sectoral g-mode oscillation. The lack of spectral variability with the radial velocity period of 643 days may provide strong evidence in support of the hypothesis that this variability stems from the reflex motion of the central star due to a planetary companion having a mass of 11 Jupiter masses. However, this long-period variability may still be due to a low order (m=2) pulsation mode since these would cause bisector variations less than the error measurement.

Artie P. Hatzes; William D. Cochran

1997-12-23

347

Letter to the Editor Inter-ear variations in the eardrum impedance and stapes velocity in the  

E-print Network

Letter to the Editor Inter-ear variations in the eardrum impedance and stapes velocity in the human middle ear Douglas H. Keefe * Boys Town National Research Hospital, 555 N. 30th Street, Omaha, NE 68131, USA Received 11 May 2001; accepted 5 June 2001 In a study elucidating many aspects of middle-ear

Allen, Jont

348

Millimeter-wave Velocity Modulation Spectroscopy as a Technique to Selectively Detect Molecular Ions  

NASA Astrophysics Data System (ADS)

Molecular ions are usually very unstable and reactive species. As a result, their spectroscopic features can be difficult to identify and distinguish from those of neutral species, which tend to be more stable and thus have stronger signals. The technique of velocity modulation allows this disadvantage to be removed. This method uses the alternating plus and minus polarity of an electric field created by an AC discharge, which also produces the molecular ions, to selectively detect the molecular ions, while eliminating the neutral features. This technique has been applied at infrared and optical wavelengths for many years with much success. Recently, we designed and built a millimeter-wave velocity modulation spectrometer, the first ever constructed. This instrument has been used to create and study multiple molecular ions, including metal-bearing molecular ions. The rotational spectrum of these species, such as TiCl^+, VCl^+, TiF^+, FeO^+, FeCO^+, and SiCl^+, has been investigated with this new machine in our laboratory. Results of these studies along with a description of the velocity modulation technique and instrument will be presented.

Halfen, Dewayne; Ziurys, Lucy

2009-05-01

349

Measuring air-sea gas exchange velocities in a large scale annular wind-wave tank  

NASA Astrophysics Data System (ADS)

In this study we present gas exchange measurements conducted in a large scale wind-wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, ? = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.8 to 15 m s-1 conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of three) was observed for N2O under a surfactant covered water surface. In contrast, the surfactant affected CH3OH, the high solubility tracer only weakly.

Mesarchaki, E.; Kräuter, C.; Krall, K. E.; Bopp, M.; Helleis, F.; Williams, J.; Jähne, B.

2014-06-01

350

S-Wave Velocities of the Lithosphere-Asthenosphere System in the Caribbean Region  

NASA Astrophysics Data System (ADS)

An overview of the S-wave velocity ( V s) structural model of the Caribbean with a resolution of 2° × 2° is presented. New tomographic maps of Rayleigh wave group velocity dispersion at periods ranging from 10 to 40 s were obtained as a result of the frequency time analysis of seismic signals of more than 400 ray-paths in the region. For each cell of 2° × 2°, group velocity dispersion curves were determined and extended to 150 s by adding data from a larger scale tomographic study ( Vdovin et al., Geophys. J. Int 136:324-340, 1999). Using, as independent a priori information, the available geological and geophysical data of the region, each dispersion curve has been inverted by the "hedgehog" non-linear procedure ( Valyus, Determining seismic profiles from a set of observations (in Russian), Vychislitielnaya Seismologiya 4, 3-14. English translation: Computational Seismology (V.I. Keylis-Borok, ed.) 4:114-118, 1968), in order to compute a set of V s versus depth models up to 300 km of depth. Because of the non-uniqueness of the solutions for each cell, a local smoothness optimization has been applied to the whole region in order to choose a three-dimensional model of V s, satisfying this way the Occam's razor concept. Several known and some new main features of the Caribbean lithosphere and asthenosphere are shown on these models such as: the west directed subduction zone of the eastern Caribbean region with a clear mantle wedge between the Caribbean lithosphere and the subducted slab; the complex and asymmetric behavior of the crustal and lithospheric thickness in the Cayman ridge; the predominant oceanic crust in the region; the presence of continental type crust in Central America, and the South and North America plates; as well as the fact that the bottom of the upper asthenosphere gets shallower going from west to east.

González, O'leary F.; Alvarez, José Leonardo; Moreno, Bladimir; Panza, Giuliano F.

2012-01-01

351

The microscopic state of the solar wind--links between composition, velocity distributions and waves  

SciTech Connect

An overview is given of the microscopic state of the solar wind with emphasis on recent Ulysses high-latitude observations and previous Helios in-ecliptic observations. Emphasis is placed on the connection of interplanetary kinetic-scale phenomena with their generating microscopic processes in the corona. The fast streams seem to consist of mesoscale pressure-balanced magnetic flux tubes, reminiscent of the supergranular or smaller structures building the open corona, from which copious Alfven waves emanate. The wind from the magnetically structured and active corona shows considerable abundance and ionization state variations. Some modelling attempts to explain the observed element fractionation are mentioned. The nonthermal particle features, such as proton-ion differential streaming, ion beams, temperature anisotropies, and skewed electron distributions associated with collisionless heat conduction, and the related wave-particle interactions are discussed.

Marsch, E. [Max-Planck-Institut fuer Aeronomie, D-37191 Katlenburg-Lindau (Germany)

1996-07-20

352

Robust segmentation methods with an application to aortic pulse wave velocity calculation.  

PubMed

Aortic stiffness has proven to be an important diagnostic and prognostic factor of many cardiovascular diseases, as well as an estimate of overall cardiovascular health. Pulse wave velocity (PWV) represents a good measure of the aortic stiffness, while the aortic distensibility is used as an aortic elasticity index. Obtaining the PWV and the aortic distensibility from magnetic resonance imaging (MRI) data requires diverse segmentation tasks, namely the extraction of the aortic center line and the segmentation of aortic regions, combined with signal processing methods for the analysis of the pulse wave. In our study non-contrasted MRI images of abdomen were used in healthy volunteers (22 data sets) for the sake of non-invasive analysis and contrasted magnetic resonance (MR) images were used for the aortic examination of Marfan syndrome patients (8 data sets). In this research we present a novel robust segmentation technique for the PWV and aortic distensibility calculation as a complete image processing toolbox. We introduce a novel graph-based method for the centerline extraction of a thoraco-abdominal aorta for the length calculation from 3-D MRI data, robust to artifacts and noise. Moreover, we design a new projection-based segmentation method for transverse aortic region delineation in cardiac magnetic resonance (CMR) images which is robust to high presence of artifacts. Finally, we propose a novel method for analysis of velocity curves in order to obtain pulse wave propagation times. In order to validate the proposed method we compare the obtained results with manually determined aortic centerlines and a region segmentation by an expert, while the results of the PWV measurement were compared to a validated software (LUMC, Leiden, the Netherlands). The obtained results show high correctness and effectiveness of our method for the aortic PWV and distensibility calculation. PMID:24405817

Babin, Danilo; Devos, Daniel; Pižurica, Aleksandra; Westenberg, Jos; Vansteenkiste, Ewout; Philips, Wilfried

2014-04-01

353

The dynamics of the observed solar granulation: spatio-temporal variations of line of sight velocity and thermodynamic parameters  

NASA Astrophysics Data System (ADS)

We investigated the dynamics of solar granulation, using the neutral iron line ??639.3 nm profiles from high-spatial resolution observations around the centre of the solar disc, in the non-perturbed region. We reproduced spatio-temporal variations of kinematic and thermodynamic parameters of solar convection at different heights of the solar photosphere (h=-25..550 km). The acoustic waves were removed by k-? filtration. We analysed the temporal changes of these variations within convective cells.

Baran, O. A.

2014-12-01

354

Non-Contact Determination of Antisymmetric Plate Wave Velocity in Ceramic Matrix Composites  

NASA Technical Reports Server (NTRS)

A 13 mJ NdYAG 1064 nm, 4 ns, laser pulse was employed to produce ultrasonic plate waves in 20 percent porous SiC/SiC composite tensile specimens of three different architectures. An air coupled 0.5 MHz transducer was used to detect and collect the waveforms which contained first antisymmetric plate wave pulses for determining the shear wave velocity (VS). These results were compared to VS values determined on the same specimens with 0.5 MHz ultrasonic transducers with contact coupling. Averages of four noncontact determinations on each of 18 specimens were compared to averages of four contact values. The noncontact VS's fall in the same range as the contact. The standard deviations for the noncontact VS's averaged 2.8 percent. The standard deviations for the contact measurements averaged 2.3 percent, indicating similar reproducibility. Repeated laser pulsing at the same location always lead to deterioration of the ulu-"nic signal. The signal would recover in about 24 hr in air however, indicating that no permanent damage was produced.

Kautz, Harold E.

1996-01-01

355

Laser Light Scattering Diagnostic for Measurement of Flow Velocity in Vicinity of Propagating Shock Waves  

NASA Technical Reports Server (NTRS)

A laser light scattering diagnostic for measurement of dynamic flow velocity at a point is described. The instrument is being developed for use in the study of propagating shock waves and detonation waves in pulse detonation engines under development at the NASA Glenn Research Center (GRC). The approach uses a Fabry-Perot interferometer to measure the Doppler shift of laser light scattered from small (submicron) particles in the flow. The high-speed detection system required to resolve the transient response as a shock wave crosses the probe volume uses fast response photodetectors, and a PC based data acquisition system. Preliminary results of measurements made in the GRC Mach 4, 10 by 25 cm supersonic wind tunnel are presented. Spontaneous condensation of water vapor in the flow is used as seed. The tunnel is supplied with continuous air flow at up to 45 psia and the flow is exhausted into the GRC laboratory-wide altitude exhaust system at pressures down to 0.3 psia.

Seasholtz, Richard G.; Buggele, Alvin E.

2002-01-01

356

Structure of the Northern Cascadia Subduction Zone: A 3-D Tomographic P-wave Velocity Model  

NASA Astrophysics Data System (ADS)

A large-scale 3D P-wave velocity model to ~60 km depth has been constructed for SW British Columbia and NW Washington through tomographic inversion of first-arrival times from controlled source experiments together with local and regional earthquake travel-time data recorded at permanent stations. 150000 first-arrival times recorded at 225 temporary stations from the 1998 Seismic Hazards Investigation in Puget Sound (SHIPS) experiment, and 60000 first-arrival times from 3000 earthquakes recorded at 91 permanent recording stations are inverted for a minimum structure velocity model. The RMS residuals for the initial and final models are 764 and 132 ms, respectively, which represents a 97% variance reduction. Checkerboard resolution tests indicate a horizontal resolution of 30 km down to 20 km depth, and 50 km down to 60 km depth. The velocity model images the structure of the forearc crust/upper mantle, and the subducting Juan de Fuca plate geometry beneath the region. The sedimentary basins in the Straits of Georgia and Juan de Fuca and Puget Sound are well defined by the velocity model. The mafic Eocene Crescent Terrane (Metchosin Igneous Complex in southern Vancouver Island) is shown to dip beneath the margin to at least 20 km depth. This terrane is regionally extensive beneath the Strait of Juan de Fuca and the Puget lowland, with higher than average velocities of ~7 km/s at approximately 15 km depth. Beneath the Olympic Peninsula, the Core rocks (accretionary sedimentary prism) are under-thrust beneath the Crescent Terrane to a depth of at least 30 km. At this location most seismicity lies within the overlying Crescent Terrane; the under-thrusting Core rocks are aseismic. The strong Crescent terrane seismicity may be due to deformation induced by the underthrusting. Beneath southern Vancouver Island, the subduction thrust zone above the Juan de Fuca plate is characterized by low velocities of 6.4-6.6 km/s at a depth of 25-35 km. Such low velocities may be due to trapped fluids, sheared lower crustal rocks, and possibly underthrust accretionary sedimentary or metamorphic rocks. This low velocity region coincides with the high conductivity region mapped in previous magneto-telluric studies and with a dipping band of seismic reflectors; it is devoid of seismicity. It probably represents a zone of aseismic slip. Low velocities of 7.2-7.6 km/s are observed in the forearc upper mantle beneath the Strait of Georgia and Puget Sound. Such low upper mantle velocities are interpreted to be due to regional serpentinization of cool forearc mantle peridotite by fluids rising from the dehydrating underlying Juan de Fuca crust. The Tertiary sedimentary basins in the Strait of Georgia and Puget lowland lie directly above the zone of forearc upper mantle serpentinization. In contrast, the sedimentary basins in the Strait of Juan de Fuca lie in a synclinal depression in the Crescent volcanic Terrane.

Ramachandran, K.; Hyndman, R. D.; Brocher, T. M.

2004-12-01

357

Variational water wave model -with accurate dispersion and vertical vorticity  

E-print Network

oscillator Euler equations incompressible fluid with free surface Potential flow water waves New model: potential flow water waves with horizontal circulation Discontinuous Galerkin finite element models Potential flow water waves Conclusions and future work B (SFFF) UT Free University A'dam 09-12-2009 2 / 33

Al Hanbali, Ahmad

358

The effect of impactor location and velocity variation on validation of an advanced human body finite element model.  

PubMed

Finite Element Modeling (FEM) is increasingly used as a tool in the field of injury biomechanics. One challenge in validating human body FEMs is quantifying the effect that variability of input parameters from experiments can have on the model?s predictions. The objective of this study was to conduct a parametric study on a validation simulation of the Global Human Body Models Consortium?s 50th percentile male model. The selected case was an oblique hub impact to the thoracoabdominal region of the model?s right side. The hub impactor was a 23.4 kg cylinder, with a 15cm diameter, given an initial velocity. The location and velocity of the impactor were varied based on the reported variance of the experiments used as the basis of these simulations. The effect that these changes have on the peak force was observed. Fifteen cases were simulated, giving results for five locations and three velocities based on a nominal velocity (6.7 m/s) and placement. The nominal impactor location was 7.5 cm below the xiphoid process and 30° from lateral, as described in the literature. The nominal velocity was varied ± 2 standard deviations from the average experimental velocity. The study results indicate that there were both location-based and velocity-based dependencies. There was a 5.5% increase in peak force when increasing the velocity by 0.3 m/s and a 6.4% decrease in peak force when decreasing the velocity by 0.3 m/s. Additionally, the Force vs. Time curves of the same impactor location showed a trend of similar curve shapes. The impactor location also had an impact on the number of rib fractures predicted by the model as well as the time of the peak force. The parameters used in this study represent typical experimental variation in location and velocity and show the model is reasonably robust within range of plausible impacts. PMID:22846319

Vavalle, Nicholas A; Moreno, Daniel P; Stitzel, Joel D; Gayzik, F Scott

2012-01-01

359

Interseasonal Variations in the Middle Atmosphere Forced by Gravity Waves  

NASA Technical Reports Server (NTRS)

In our Numerical Spectral Model (NSM), which incorporates Hines' Doppler Spread Parameterization, gravity waves (GW) propagating in the east/west direction can generate the essential features of the observed equatorial oscillations of the zonal circulation and in particular the QBO (quasi-biennial oscillation) extending from the stratosphere into the upper mesosphere. We report here that the NSM also produces inter-seasonal variations in the zonally symmetric meridional circulation. A distinct meridional oscillation (MO) is generated, which appears to be the counterpart to the QBO. With a vertical grid-point resolution of about 0.5 km, the NSM produces the MO through momentum deposition of GW's propagating in the north/south direction. This process is inherently non-linear, of third (odd) order, which enables the oscillation. Since the meridional winds are relatively small compared to the zonal winds, the vertical wavelength required to maintain the MO is also smaller, i.e., only about 10 km instead of the 30 km for the QBO. The corresponding viscous stress is then larger, and the period of the MO is thus short compared with that of the QBO, i.e., only about 3 to 4 months. Depending on the strength of the GW forcing, the computed amplitudes of the meridional wind oscillation are typically 5 m/s in the upper stratosphere and mesosphere, and the associated temperature amplitudes are between about 2 and 3 K. These amplitudes may be observable with the instruments on the TIMED spacecraft. Extended computer simulations with the NSM in 2D and 3D reveal that the MO at low latitudes is modulated by the QBO and in turn can influence it to produce a hemispherically asymmetric component. The annual circulation from the summer to the winter hemisphere is likely to play an important role.

Mayr, H. G.; Mengel, J. G.; Drob, D. P.; Porter, H. S.; Bhartia, P. K. (Technical Monitor)

2002-01-01

360

Interseasonal Variations in the Middle Atmosphere Forced by Gravity Waves  

NASA Technical Reports Server (NTRS)

In our Numerical Spectral Model (NSM), which incorporates Hines' Doppler Spread Parameterization, gravity waves (GW) propagating in the east/west direction can generate the essential features of the observed equatorial oscillations in the zonal circulation and in particular the QBO (quasi-biennial oscillation) extending from the stratosphere into the upper mesosphere. We report here that the NSM also produces inter-seasonal variations in the zonally symmetric (m = 0) meridional circulation. A distinct but variable meridional wind oscillation (MWO) is generated, which appears to be the counterpart to the QBO. With a vertical grid-point resolution of about 0.5 km, the NSM produces the MWO through momentum deposition of GWs propagating in the north/south direction. The resulting momentum source represents a third (generally odd) order non-linear function of the meridional winds, and this enables the oscillation, as in the case of the QBO for the zonal winds. Since the meridional winds are relatively small compared to the zonal winds, however, the vertical wavelength that maintains the MWO is much smaller, i.e., only about 10 km instead of 40 km for the QBO. Consistent with the associated increase of the viscous stress, the period of the MWO is then short compared with that of the QBO, i.e., only about two to four months. Depending on the strength of the GW forcing, the computed amplitudes of the MWO are typically 4 m/s in the upper stratosphere and mesosphere, and the associated temperature amplitudes are between about 2 and 3 K. These amplitudes may be observable with the instruments on the TIMED spacecraft. Extended computer simulations with the NSM in 2D (two-dimensional) and 3D (three-dimensional) reveal that the MWO is modulated by and in turn influences the QBO.

Mayr, H. G.; Mengel, J. G.; Drob, D. P.; Porter, H. S.; Chan, K. L.; Bhartia, P. K. (Technical Monitor)

2002-01-01

361

Estimation of shallow S-wave velocity structure in the Puli basin, Taiwan, using array measurements of microtremors  

NASA Astrophysics Data System (ADS)

The September 21, 1999, Chi-Chi earthquake induced strong shaking, resulting in severe damage in the Puli area. According to Huang and Tarng (2005), the collapse of many structures during the earthquake was very closely related to site effects. Shallow shear-wave velocities are widely used for earthquake ground-motion site characterization. Thus, we investigate S-wave velocity structures for the Puli area by performing microtremor array measurements at 16 sites. Dispersion curves at these sites are calculated using the F-K method (Capon, 1969) for the vertical component; S-wave velocity structures for the Puli area are then estimated by surface wave inversion (Herrmann, 1991). If the S-wave velocity of the bedrock is assumed to be 2000 m/s, the depths of the Quaternary sediments in the Puli area are between 300 m (FAL, PIP) and 870 m (DAH). Moreover, there are 3˜6 distinct interfaces in the shallow velocity structure (0˜1000 m). The depth of the bedrock gradually increases from the edge (SIN, PIP) to the center (PUL, DAH) of the basin and the thickest Quaternary sediments appear near Heng-Chih-Cheng (DAH).

Wu, C.-F.; Huang, H.-C.

2012-05-01

362

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)

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.

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

2014-09-01

363

The influence of solid solution on elastic wave velocity determination in (Mg,Fe)O using nuclear inelastic scattering  

NASA Astrophysics Data System (ADS)

Elastic wave velocities of minerals are important for constraining the chemistry, structure and dynamics of the Earth's mantle based on the comparison between laboratory-based measurements and seismic observations. As the second most abundant phase in the Earth's lower mantle, (Mg,Fe)O ferropericlase has been the focus of numerous studies measuring the elastic wave velocities using various methods such as Brillouin spectroscopy and ultrasonic measurements. Recently, nuclear inelastic scattering (NIS) has been used to determine elastic wave velocities of iron-bearing phases. However, the elastic wave velocities of ferropericlase obtained using NIS are considerably lower than the velocities obtained by other methods, even at ambient conditions. One possible source of this discrepancy is the local nature of the NIS method. In order to test this hypothesis, we have investigated six ferropericlase samples with various iron contents using NIS. The Debye sound velocities calculated using the conventional method of NIS analysis are consistent with previous results obtained using NIS, yet the values are significantly lower than those obtained using ultrasonics and Brillouin spectroscopy. If the Debye sound velocities are re-calculated based on a mixture of different iron next-neighbour configurations with different compositions, the Debye sound velocities determined by NIS agree well with the results from other methods. Our new model was also successfully applied to high-pressure NIS data taken from the literature. Our results constitute an important step towards a better understanding of how to obtain reliable sound velocities of iron-bearing mantle minerals from NIS measurements.

Sinmyo, R.; Glazyrin, K.; McCammon, C.; Kupenko, I.; Kantor, A.; Potapkin, V.; Chumakov, A. I.; Rüffer, R.; Dubrovinsky, L.

2014-04-01

364

Nonlinear low frequency wave propagation in electronegative dusty plasma: Effects of adiabatic and nonadiabatic charge variations  

SciTech Connect

The effects of both adiabatic and nonadiabatic charge variations on small but finite amplitude nonlinear dust acoustic wave (DAW) have been investigated in an electronegative dusty plasma in presence of a static magnetic field. It is found that in case of adiabatic charge variations, the nonlinear wave is governed by the Zakharov-Kuznetsov (ZK) equation which yields the usual solitary wave solution. On the other hand, in case of nonadiabatic charge variations, the dynamics is governed by the Zakharov-Kuznetsov-Burgers' (ZKB) equation which exhibits shock like structures. The results are discussed in the context of cometary plasma.

Sarkar, Subrata; Khan, Manoranjan; Gupta, M. R. [Department of Instrumentation Science, Jadavpur University, Kolkata-700 032 (India); Ghosh, Samiran [Department of Applied Mathematics, University of Calcutta 92, Acharya Prafulla Chandra Road, Kolkata-700 009 (India)

2011-09-15

365

A method to measure a relative transverse velocity of source-lens-observer system using gravitational lensing of gravitational waves  

E-print Network

Gravitational waves propagate along null geodesics like light rays in the geometrical optics approximation, and they may have a chance to suffer from gravitational lensing by intervening objects, as is the case for electromagnetic waves. Long wavelength of gravitational waves and compactness of possible sources may enable us to extract information in the interference among the lensed images. We point out that the interference term contains information of relative transverse velocity of the source-lens-observer system, which may be obtained by possible future space-borne gravitational wave detectors such as BBO/DECIGO.

Yousuke Itoh; Toshifumi Futamase; Makoto Hattori

2009-08-03

366

Method to measure a relative transverse velocity of a source-lens-observer system using gravitational lensing of gravitational waves  

SciTech Connect

Gravitational waves propagate along null geodesics like light rays in the geometrical optics approximation, and they may have a chance to suffer from gravitational lensing by intervening objects, as is the case for electromagnetic waves. Long wavelengths of gravitational waves and compactness of possible sources may enable us to extract information in the interference among the lensed images. We point out that the interference term contains information of relative transverse velocity of the source-lens-observer system, which may be obtained by possible future space-borne gravitational wave detectors such as BBO/DECIGO.

Itoh, Yousuke; Futamase, Toshifumi; Hattori, Makoto [Astronomical Institute, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan)

2009-08-15

367

Ambient noise analysis along the North Anatolian Fault Zone in Turkey: Lateral variations of the crustal velocity field  

NASA Astrophysics Data System (ADS)

We analyze the ambient seismic noise field in order to investigate crustal structure and seismic anisotropy at the North Anatolian Fault Zone (NAFZ) in NW Turkey. We focus on the eastern Sea of Marmara section of the NAFZ representing a pre-seismic phase of the seismic cycle just prior to an expected major (M>7) earthquake. We apply cross-correlation analysis of the seismic ambient noise to determine spectral dependence of the seismic velocity in order to image crustal structure at seismogenic depths. Time-domain cross correlations are calculated for all available stations pairs in the target area. Inter-station distances span 0.3-90 km. Only the vertical component is analyzed in order to recover fundamental mode Rayleigh waves in the frequency range of 0.05-1.1 Hz. Group velocity dispersion curves are obtained for selected correlation paths in particular to address the directional dependency of the velocity field. In the frequency band of interest, average group velocities range between ~1.8 and 3.5 km/s. Dispersion curves corresponding to the NS-trending paths crossing the main NAFZ fault branch below the eastern Sea of Marmara show low group velocities between ~1.5 and 1.8 km/s well explained by the 3-4 km-deep Çinarcik Basin directly south of the fault. In contrast, ray paths restricted to within the mainland Istanbul and Armutlu peninsulas (primarily trending EW) show higher group velocities up to 3.2 km/s. By averaging the dispersion curves we determine an optimized 1-D S-wave velocity model for the eastern Sea of Marmara region allowing for a significant improvement in hypocenter determination.

Acarel, D.; Bulut, F.; Bohnhoff, M.

2013-12-01

368

High resolution 3D Sv wave velocity model of China and surrounding area  

NASA Astrophysics Data System (ADS)

In our study we determine the three dimensional Sv wave speed and azimuthal anisotropy model by analyzing vertical component multimode Rayleigh wave seismograms. We use data of broadband stations from in and around China. We construct the three dimensional model using a 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. We have used the 3SMAC model (as a crustal part) and smooth version of PREM for the upper mantle velocity structure as an initial model. In the second stage we combine the 1-D velocity models in a tomographic inversion to obtain the three dimensional Sv wave speed structure and the azimuthal anisotropy as a function of depth. China is sitting at a triple junction of three major plates: the Eurasian plate, the Indo-Australian plate and the Philippine Sea plate. China itself has three major Precambian cratons: the North China craton (also called Sino-Korean craton), the Yangtze craton (also called South China craton) and the Tarim block. The interactions among different blocks have formed the tectonic features today and caused many intraplate earthquakes. These tectonics setting have made China an interesting place for various kind of study as all of these events have left their imprint on the upper mantle structure. 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. The upper most part of our model is in good agreement with the finding from the deep seismic profile. It is also evident that the extent of crustal flow of Tibet is being restricted by Tarim in the north and Ordos, Sichuan in the east. Various receiver function and SS precursor results are also comparable with our results in terms of the lithosphere extent.

Pandey, S.; Yuan, X.; Debayle, E.; Priestley, K. F.; Kind, R.; Li, X.

2011-12-01

369

Downward Link of Solar Activity Variations Through Wave Driven Equatorial Oscillations (QBO and SAO)  

NASA Technical Reports Server (NTRS)

Signatures of the 11-year solar activity/irradiance cycle are observed in the Quasi Biennial Oscillation (QBO) of the lower stratosphere. At these altitudes, the QBO is understood to be the result of "downward control" exerted by the wave mean flow interactions that drive the phenomenon. It is reasonable then to speculate that the QBO is a natural conduit to lower altitudes of solar activity variations in radiance (SAV). To test this hypothesis, we conducted experiments with a 2D version of our Numerical Spectral Model that incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). To account for the SAV, we change the solar heating rate on a logarithmic scale from 0.1% at the surface to 1% at 50 kin to 10% at 100 km. With the same GW flux, we then conduct numerical experiments to evaluate the magnitude of the solar activity irradiance effect (SAE) on the zonal circulation at low latitudes. The numerical results obtained show that, under certain conditions, the SAE is significant in the zonal circulation and does extend to lower altitudes where the SAV is small. The differences in the wind velocities can be as large as 5 m/s at 20 kin. We carried out two numerical experiments with integrations over more than 20 years: 1) With the QBO period "tuned" to be 30 months, of academic interest but instructive, the seasonal cycle in the solar forcing [through the Semi-annual Oscillation (SAO)] acts as a strong pacemaker to produce a firm lock on the period and phase of the QBO. The SAE then shows up primarily as a distinct but relatively weak amplitude modulation. 2) With the QBO period between 30 and 34 (or less than 30, presumably) months, the seasonal phase lock is weak compared with (1). The SAV in the seasonal cycle then causes variations in the QBO period and phase, and this amplifies the SAE to produce relatively large variations in the wind field. We conclude that, under realistic conditions as in (2), the solar seasonal forcing, with activity variations in radiance, causes the phase and period of the QBO to change to produce a relatively large solar activity effect in the zonal circulation at low latitudes and low altitudes.

Mengel, J. G.; Mayr, H. G.; Chan, K. L.; Porter, H. S.; Einaudi, Franco (Technical Monitor)

2000-01-01

370

Surface acoustic wave velocity of gold films deposited on silicon substrates at different temperatures  

SciTech Connect

Au thin films have been deposited by DC magnetron sputtering on Si (001) substrates at different substrate temperatures, ranging from 200 K to 450 K. With increasing temperature, the expected crystallinity and morphology of the Au thin film are clearly improved, as shown by x ray diffraction, atomic force microscopy and scanning electron microscopy experiments. Parallel to this, the surface acoustic wave propagation velocity shows a clear enhancement toward the ideal values obtained from numerical simulations of a Au thin film on Si (001) substrate. Moreover, a very thin and slightly rough interlayer between the Si (001) substrate and the Au thin film is developed for temperatures above 350 K. The composition and nature of this interlayer is not known. This interlayer may be responsible for the steep change in the structural and elastic properties of the Au thin films at the higher temperatures and possibly also for an improvement of the adhesion properties of the Au on the Si (001) substrate.

Salas, E.; Jimenez Rioboo, R. J.; Prieto, C. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Cantoblanco, Madrid 28049 (Spain); Every, A. G. [School of Physics, University of the Witwatersrand, Wits 2050 (South Africa)

2011-07-15

371

Low-velocity zones along the San Jacinto Fault, Southern California, from body waves recorded in dense linear arrays  

NASA Astrophysics Data System (ADS)

derive high-resolution information on low-velocity fault zone (FZ) structures along the San Jacinto Fault Zone (SJFZ), Southern California, using waveforms of local earthquakes that are recorded at multiple linear cross-fault arrays. We observe clear across-fault delays of direct P and S waves, indicating damage zones at different segments of the SJFZ. We then compute synthetic traveltimes and waveforms using generalized ray theory and perform forward modeling to constrain the FZ parameters. At the southern section near the trifurcation area, the low-velocity zone (LVZ) of the Clark branch has a width of ~200 m, 30-45% reduction in Vp, and ~50% reduction in Vs. From array data across the Anza seismic gap, we find a LVZ with ~200 m width and ~50% reduction in both Vp and Vs, nearly as prominent as that on the southern section. We only find prominent LVZs beneath three out of the five arrays, indicating along-strike variations of the fault damage. FZ-reflected phases are considerably less clear than those observed above the rupture zone of the 1992 Landers earthquake shortly after the event. This may reflect partially healed LVZs with less sharp boundaries at the SJFZ, given the relatively long lapse time from the last large surface-rupturing event. Alternatively, the lack of observed FZ-reflected phases could be partially due to the relatively small aperture of the arrays. Nevertheless, the clear signatures of damage zones at Anza and other locations indicate very slow healing process, at least in the top few kilometers of the crust.

Yang, Hongfeng; Li, Zefeng; Peng, Zhigang; Ben-Zion, Yehuda; Vernon, Frank

2014-12-01

372

Quantitative Assessment of In-situ Salt Karstification Using Shear Wave Velocity, Dead Sea  

NASA Astrophysics Data System (ADS)

The Dead Sea (DS) coastal areas have been dramatically affected by sinkhole formation since around 1990. Such sinkholes along both Israeli and Jordanian shores are linked to karst cavities that form through slow salt dissolution. A quantitative estimate of such in-situ salt karstification would be an important indicator of sinkhole hazard. One of the indications of salt karstification is its increased hydraulic conductivity, caused by the development of dissolution cavities forming conducting channels within the salt layer. We measured the hydraulic conductivity (K) versus shear-wave velocity (Vs) of DS salt in situ for estimating the actual salt karstification in areas of sinkhole development. These parameters were measured with the Magnetic Resonance Sounding (MRS) and Multichannel Analysis of Surface Waves (MASW) methods, respectively. Understanding of the field relationships was augmented by similar inter-relations obtained in the laboratory on samples of DS salt. In-situ salt velocities Vs vary from 750 m/s to over 1650 m/s, while hydraulic conductivity (K) in the same zones varies between about 10- 4 m/s to slightly over 10- 8 m/s. Both field and laboratory K and Vs values fit the exponential function ln(K) = - 0.0045 ? Vs - 5.416 with a determination coefficient (R2) of 0.88. A classification based on Vs and K was generated for salt conditions and the corresponding degrees of sinkhole hazard, which was verified in the Mineral Beach sinkhole development area. The mapping of sinkhole sites shows that they form within highly conductive zones with K ? 5.5 ? 10- 5. It is suggested that this methodology, with some modification, can be used for evaluating the conductive properties of karstified rock and associated sinkhole hazards.

Ezersky, Michael; Legchenko, Anatoly

2014-09-01

373

MEASUREMENT OF COMPRESSIONAL-WAVE SEISMIC VELOCITIES IN 29 WELLS AT THE HANFORD SITE  

SciTech Connect

Check shot seismic velocity surveys were collected in 100 B/C, 200 East, 200-PO-1 Operational Unit (OU), and the Gable Gap areas in order to provide time-depth correlation information to aid the interpretation of existing seismic reflection data acquired at the Hanford Site (Figure 1). This report details results from 5 wells surveyed in fiscal year (FY) 2008, 7 wells in FY 2009, and 17 wells in FY 2010 and provides summary compressional-wave seismic velocity information to help guide future seismic survey design as well as improve current interpretations of the seismic data (SSC 1979/1980; SGW-39675; SGW-43746). Augmenting the check shot database are four surveys acquired in 2007 in support of the Bechtel National, Inc. Waste Treatment Plant construction design (PNNL-16559, PNNL-16652), and check shot surveys in three wells to support seismic testing in the 200 West Area (Waddell et al., 1999). Additional sonic logging was conducted during the late 1970s and early 1980s as part of the Basalt Waste Isolation Program (BWIP) (SSC 1979/1980) and check shot/sonic surveys as part of the safety report for the Skagit/Hanford Nuclear project (RDH/10-AMCP-0164). Check shot surveys are used to obtain an in situ measure of compressional-wave seismic velocity for sediment and rock in the vicinity of the well point, and provide the seismic-wave travel time to geologic horizons of interest. The check shot method deploys a downhole seismic receiver (geophone) to record the arrival of seismic waves generated by a source at the ground surface. The travel time of the first arriving seismic-wave is determined and used to create a time-depth function to correlate encountered geologic intervals with the seismic data. This critical tie with the underlying geology improves the interpretation of seismic reflection profile information. Fieldwork for this investigation was conducted by in house staff during the weeks of September 22, 2008 for 5 wells in the 200 East Area (Figure 2); June 1, 2009 for 7 wells in the 200-PO-1 OU and Gable Gap regions (see Figure 3 and Figure 4); and March 22, 2010 and April 19, 2010 for 17 wells in the 200 East, The initial scope of survey work was planned for Wells 299-EI8-1, 699-2-E14, 699-12-18, 699-16-51, 699-42-30, 699-53-55B, 699-54-18D, and 699-84-34B. Well 299-E18-1 could not be entered due to bent casing (prevented removal of the pump), wells 699-12-18 and 699-42-30 could not be safely reached by the logging truck, Well 699-16-51 was decommissioned prior to survey start, Well 699-53-55B did not have its pump pulled, and Wells 699-2-EI4, 699-54-18D, and 699-84-34B are artesian and capped with an igloo structure. Table 1 provides a list of wells that were surveyed and Figure 1 through Figure 5 show the well locations relative to the Hanford Site.

PETERSON SW

2010-10-08

374

Dual-beam laser Doppler vibrometer for measurement of pulse wave velocity in elastic vessels  

NASA Astrophysics Data System (ADS)

When a fluid flowing through an elastic vessel is subjected to a sudden change in pressure gradient, pressure pulses will propagate through the fluid. Velocity of these pulse waves (PWV) can be determined by simultaneous detection of wall distension on two separate points on the vessel wall, along its trajectory. PWV depends on wall stiffness, and under certain circumstances, wall stiffness can be calculated from the propagation velocity. Optical interferometry is a noncontacting technique that allows measurement of wall distension on discrete locations. In this work we propose a miniaturized dual-beam laser Doppler vibrometer (LDV) to measure wall distension simultaneously at two locations. Our dual-beam LDV is based on a single laser source and one acousto-optic modulator with as much as possible of the interferometer optics shared among the different beams. The dual-beam LDV was used for simultaneous detection of wall distension of several elastic vessels of different stiffness. We found that PWV as measured in elastic vessels agrees well with theoretically expected values, and measurement precision is better than 5%. Moreover, the dual-beam LDV performs almost as good as commercial systems for detection of PWV. The dual-beam LDV can have applications in cardiovascular risk management. Stiffness of large arteries has a very good predictive value for cardiovascular disease and overall mortality. This parameter can be estimated from arterial PWV. Current methods to measure arterial PWV suffer from several shortcomings. A dual-beam LDV can offer substantial advantages over existing techniques.

Campo, Adriaan; Dirckx, Joris

2011-08-01

375

Assessment of aortic pulse wave velocity by ultrasound: a feasibility study in mice  

NASA Astrophysics Data System (ADS)

Pulse wave velocity (PWV) is considered a surrogate marker of arterial stiffness and could be useful for characterizing cardiovascular disease progression even in mouse models. Aim of this study was to develop an image process algorithm for assessing arterial PWV in mice using ultrasound (US) images only and test it on the evaluation of age-associated differences in abdominal aorta PWV (aaPWV). US scans were obtained from six adult (7 months) and six old (19 months) wild type male mice (strain C57BL6) under gaseous anaesthesia. For each mouse, diameter and flow velocity instantaneous values were achieved from abdominal aorta B-mode and PW-Doppler images; all measurements were obtained using edge detection and contour tracking techniques. Single-beat mean diameter and velocity were calculated and time-aligned, providing the lnD-V loop. aaPWV values were obtained from the slope of the linear part of the loop (the early systolic phase), while relative distension (relD) measurements were calculated from the mean diameter signal. aaPWV values for young mice (3.5±0.52 m/s) were lower than those obtained for older ones (5.12±0.98 m/s) while relD measurements were higher in young (25%±7%) compared with older animals evaluations (15%±3%). All measurements were significantly different between the two groups (P<0.01 both). In conclusion, the proposed image processing technique well discriminate between age groups. Since it provides PWV assessment just from US images, it could represent a simply and useful system for vascular stiffness evaluation at any arterial site in the mouse, even in preclinical small animal models.

Faita, Francesco; Di Lascio, Nicole; Stea, Francesco; Kusmic, Claudia; Sicari, Rosa

2014-03-01

376

Dip-moveout error in transversely isotropic media with linear velocity variation in depth  

SciTech Connect

Levin (1990) modeled the moveout, within Common-midpoint (CMP) gathers, of reflections from plane-dipping reflectors beneath homogeneous, transversely isotropic media. For some media, when the axis of symmetry for the anisotropy was vertical, he found departures in stacking velocity from predictions based upon the familiar cosine-of-dip correction for isotropic media. Here, I do similar tests, again with transversely isotropic models with vertical axis of symmetry, but now allowing the medium velocity to vary linearly with depth. Results for the same four anisotropic media studied by Levin show behavior of dip-corrected stacking velocity with reflector dip that, for all velocity gradients considered, differs little from that for the counterpart homogeneous media. As with isotropic media, traveltimes in an inhomogeneous, transversely isotropic medium can be modeled adequately with a homogeneous model with vertical velocity equal to the vertical rms velocity of the inhomogeneous medium. In practice, dip-moveout (DMO) is based on the assumption that either the medium is homogeneous or its velocity varies with depth, but in both cases isotropy is assumed. It turns out that for only one of the transversely isotropic media considered here --shale-limestone -- would v(z) DMO fail to give an adequate correction within CMP gathers. For the shale-limestone, fortuitously the constant-velocity DMO gives a better moveout correction than does the v(z) DMO.

Larner, K.

1992-10-01

377

Dip-moveout error in transversely isotropic media with linear velocity variation in depth  

SciTech Connect

Levin (1990) modeled the moveout, within Common-midpoint (CMP) gathers, of reflections from plane-dipping reflectors beneath homogeneous, transversely isotropic media. For some media, when the axis of symmetry for the anisotropy was vertical, he found departures in stacking velocity from predictions based upon the familiar cosine-of-dip correction for isotropic media. Here, I do similar tests, again with transversely isotropic models with vertical axis of symmetry, but now allowing the medium velocity to vary linearly with depth. Results for the same four anisotropic media studied by Levin show behavior of dip-corrected stacking velocity with reflector dip that, for all velocity gradients considered, differs little from that for the counterpart homogeneous media. As with isotropic media, traveltimes in an inhomogeneous, transversely isotropic medium can be modeled adequately with a homogeneous model with vertical velocity equal to the vertical rms velocity of the inhomogeneous medium. In practice, dip-moveout (DMO) is based on the assumption that either the medium is homogeneous or its velocity varies with depth, but in both cases isotropy is assumed. It turns out that for only one of the transversely isotropic media considered here --shale-limestone -- would v(z) DMO fail to give an adequate correction within CMP gathers. For the shale-limestone, fortuitously the constant-velocity DMO gives a better moveout correction than does the v(z) DMO.

Larner, K.

1992-01-01

378

Augmentation index and aortic pulse wave velocity in patients with abdominal aortic aneurysms  

PubMed Central

Background: Abdominal aortic aneurysm (AAA) is a severe disease that can prove fatal. Factors such as advanced age, male gender, family history and cigarette use increase the risk of AAA. These factors associated with AAA development also increase arterial stiffness. Aortic pulse-wave velocity (PWV) was measured as an index of aortic stiffness. The heart rate-corrected augmentation index (AIx@75) was estimated as a composite marker of wave reflections and arterial stiffness. Elevated arterial stiffness increases the risk of development of cardiovascular events and impairs cardiovascular functions. In this study we investigated whether arterial stiffness rises in patients with AAA by measuring aortic PWV and AIx@75 parameters. Methods: Eighteen patients with AAA (age 69 ± 4 years) and 20 patients with no aneurysm (age 66 ± 6) were included. AAA was diagnosed using computerized tomography. Arterial stiffness was measured non-invasively in all patients using a SphygmoCor device. Aortic PWV and AIx@75 were used as arterial stiffness parameters. Results: There was no significant difference between the two groups in terms of demographic characteristics. AIx@75 (33.2 ± 8.9 vs 25.1 ± 7.8, p=0.008) and aortic PWV (14.8 ± 4.9 vs 10.0 ± 1.7, p=0.002) were significantly elevated in the AAA group compared to the control group. Conclusion: Elevated AIx@75 and aortic PWV shows that arterial stiffness increases in patients with AAA. PMID:24600499

Durmus, Ismet; Kazaz, Zeynep; Altun, Gokalp; Cansu, Aysegul

2014-01-01

379

A comparison of four geophysical methods for determining the shear wave velocity of soils  

USGS Publications Warehouse

The Missouri Department of Transportation (MoDOT) routinely acquires seismic cone penetrometer (SCPT) shear wave velocity control as part of the routine investigation of soils within the Mississippi Embayment. In an effort to ensure their geotechnical investigations are as effective and efficient as possible, the SCPT tool and several available alternatives (crosshole [CH]; multichannel analysis of surface waves [MASW]; and refraction microtremor [ReMi]) were evaluated and compared on the basis of field data acquired at two test sites in southeast Missouri. These four methods were ranked in terms of accuracy, functionality, cost, other considerations, and overall utility. It is concluded that MASW data are generally more reliable than SCPT data, comparable to quality ReMi data, and only slightly less accurate than CH data. However, the other advantages of MASW generally make it a superior choice over the CH, SCPT, and ReMi methods for general soil classification purposes to depths of 30 m. MASW data are less expensive than CH data and SCPT data and can normally be acquired in areas inaccessible to drill and SCPT rigs. In contrast to the MASW tool, quality ReMi data can be acquired only in areas where there are interpretable levels of "passive" acoustic energy and only when the geophone array is aligned with the source(s) of such energy.

Anderson, N.; Thitimakorn, T.; Ismail, A.; Hoffman, D.

2007-01-01

380

Variational wave equations for relativistic few-body systems in QFT  

NASA Astrophysics Data System (ADS)

The variational method in a reformulated Hamiltonian formalism of quantum field theory is used to derive relativistic few-body wave equations for scalar and Fermion fields. Analytic and approximate solutions of some two-body bound states are presented.

Darewych, J. W.

2006-06-01

381

Variation in Differential and Total Cross Sections Due to Different Radial Wave Functions  

ERIC Educational Resources Information Center

Three sets of analytical wave functions are used to calculate the Na (3s---3p) transition differential and total electron excitation cross sections by Born approximations. Results show expected large variations in values. (Author/CP)

Williamson, W., Jr.; Greene, T.

1976-01-01

382

Ultrasonic elastic wave velocity measurements of polycrystalline pyrope garnet up to 20 GPa and 1700 K  

NASA Astrophysics Data System (ADS)

Pyrope Mg3Al2(SiO4)3 garnet is considered a significant magnesium end-member of garnets group. Elastic properties of pyrope garnet for both single crystal and synthetic polycrystalline samples have been measured by various techniques, including ultrasonic interferometry, Brillouin scattering and static compression methods. However, to date, direct measurements of the elastic wave velocities of pyrope garnet based on in situ high P-T experiments have been still limited. Previous studies were carried out either at high pressure or high temperature. Moreover, the earlier studies on the elastic properties, i.e. the pressure and temperature dependence of bulk modulus and shear modulus are not well constrained. It is thus of great importance to carry out further studies for pyrope garnet at elevated pressures and temperatures. Recently, the elasticity and sound velocities of synthetic polycrystalline pyrope garnet have been measured up to 20 GPa and 1700 K, equivalent to the middle part of the mantle transition zone, by using ultrasonic interferometry combined with energy-dispersive synchrotron X-ray diffraction in a Kawai-type multi-anvil apparatus. Compressional (VP) and shear wave (VS) velocities as well as the bulk (KS) and shear (G) moduli exhibit monotonic increase with pressure, and decrease with temperature, respectively. Two-dimensional linear fittings yield the following parameters: KS0 = 170.0(2) GPa, dKs/dP = 4.51(2), dKs/dT = -0.0170(1) GPa/K, G0= 93.2(1) GPa, dG/dP = 1.51(2), and dG/dT = -0.0107(1) GPa/K. Moreover, we have observed a linear temperature dependence in both VP and VS, which is consistent with that in grossular (Kono et al. 2010), but in contrast to that in pyrolite majorite where a non-linear temperature dependence was observed (Irifune et al. 2008). The non-linear temperature dependence may be due to the effect of the complex multi-component system, but not the garnet structure itself.

Zou, Y.; Irifune, T.; Greaux, S.; Whitaker, M. L.; Ohfuji, H.; Shinmei, T.; Higo, Y.; Li, B.

2012-12-01

383

Stereoscopy of dust density waves under microgravity: Velocity distributions and phase-resolved single-particle analysis  

NASA Astrophysics Data System (ADS)

Experiments on dust-density waves have been performed in dusty plasmas under the microgravity conditions of parabolic flights. Three-dimensional measurements of a dust density wave on a single particle level are presented. The dust particles have been tracked for many oscillation periods. A Hilbert analysis is applied to obtain trajectory parameters such as oscillation amplitude and three-dimensional velocity amplitude. While the transverse motion is found to be thermal, the velocity distribution in wave propagation direction can be explained by harmonic oscillations with added Gaussian (thermal) noise. Additionally, it is shown that the wave properties can be reconstructed by means of a pseudo-stroboscopic approach. Finally, the energy dissipation mechanism from the kinetic oscillation energy to thermal motion is discussed and presented using phase-resolved analysis.

Himpel, Michael; Bockwoldt, Tim; Killer, Carsten; Ole Menzel, Kristoffer; Piel, Alexander; Melzer, André

2014-03-01

384

Damage Evaluation of Unsaturated Polyester Resin Using Zero-Group Velocity Lamb Waves in Non-Contact Matter  

NASA Astrophysics Data System (ADS)

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-group-velocity (ZGV) Lamb waves. The energy of ZGV Lamb waves does not propagate while the phase velocity 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

Cho, Hideo; Oka, Daichi; Matsuo, Takuma

385

Stereoscopy of dust density waves under microgravity: Velocity distributions and phase-resolved single-particle analysis  

SciTech Connect

Experiments on dust-density waves have been performed in dusty plasmas under the microgravity conditions of parabolic flights. Three-dimensional measurements of a dust density wave on a single particle level are presented. The dust particles have been tracked for many oscillation periods. A Hilbert analysis is applied to obtain trajectory parameters such as oscillation amplitude and three-dimensional velocity amplitude. While the transverse motion is found to be thermal, the velocity distribution in wave propagation direction can be explained by harmonic oscillations with added Gaussian (thermal) noise. Additionally, it is shown that the wave properties can be reconstructed by means of a pseudo-stroboscopic approach. Finally, the energy dissipation mechanism from the kinetic oscillation energy to thermal motion is discu