A Highly Similar Mathematical Model for Cerebral Blood Flow Velocity in Geriatric Patients with Suspected Cerebrovascular Disease

NASA Astrophysics Data System (ADS)

Liu, Bo; Li, Qi; Wang, Jisheng; Xiang, Hu; Ge, Hong; Wang, Hui; Xie, Peng

2015-10-01

Cerebral blood flow velocity(CBFV) is an important parameter for study of cerebral hemodynamics. However, a simple and highly similar mathematical model has not yet been established for analyzing CBFV. To alleviate this issue, through TCD examination in 100 geriatric patients with suspected cerebrovascular disease (46 males and 54 females), we established a representative eighth-order Fourier function Vx(t) that simulates the CBFV. The measured TCD waveforms were compared to those derived from Vx(t), an illustrative Kolmogorov-Smirnov test was employed to determine the validity. The results showed that the TCD waves could been reconstructed for patients with different CBFVs by implementing their variable heart rates and the formulated maximum/minimum of Vx(t). Comparisons between derived and measured TCD waveforms suggest that the two waveforms are very similar. The results confirm that CBFV can be well-modeled through an eighth-order Fourier function. This function Vx(t) can be used extensively for a prospective study of cerebral hemodynamics in geriatric patients with suspected cerebrovascular disease.

Doppler indexes of left ventricular systolic and diastolic flow and central pulse pressure in relation to renal resistive index.

PubMed

Kuznetsova, Tatiana; Cauwenberghs, Nicholas; Knez, Judita; Thijs, Lutgarde; Liu, Yan-Ping; Gu, Yu-Mei; Staessen, Jan A

2015-04-01

The cardio-renal interaction occurs via hemodynamic and humoral factors. Noninvasive assessment of renal hemodynamics is currently possible by assessment of renal resistive index (RRI) derived from intrarenal Doppler arterial waveforms as ((peak systolic velocity - end-diastolic velocity)/peak systolic velocity). Limited information is available regarding the relationship between RRI and cardiac hemodynamics. We investigated these associations in randomly recruited subjects from a general population. In 171 participants (48.5% women; mean age, 52.2 years), using pulsed wave Doppler, we measured RRI (mean, 0.60) and left ventricular outflow tract (LVOT) and transmitral (E and A) blood flow peak velocities and its velocity time integrals (VTI). Using carotid applanation tonometry, we measured central pulse pressure and arterial stiffness indexes such as augmentation pressure and carotid-femoral pulse wave velocity. In stepwise regression analysis, RRI independently and significantly increased with female sex, age, body weight, brachial pulse pressure, and use of β-blockers, whereas it decreased with body height and mean arterial pressure. In multivariable-adjusted models with central pulse pressure and arterial stiffness indexes as the explanatory variables, we observed a significant and positive correlation of RRI only with central pulse pressure (P < 0.0001). Among the Doppler indexes of left ventricular blood flow, RRI was significantly and positively associated with LVOT and E peak velocities (P ≤ 0.012) and VTIs (P ≤ 0.010). We demonstrated that in unselected subjects RRI was significantly associated with central pulse pressure and left ventricular systolic and diastolic Doppler blood flow indexes. Our findings imply that in addition to the anthropometric characteristics, cardiac hemodynamic factors influence the intrarenal arterial Doppler waveform patterns. © American Journal of Hypertension, Ltd 2014. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Modeling measured glottal volume velocity waveforms.

PubMed

Verneuil, Andrew; Berry, David A; Kreiman, Jody; Gerratt, Bruce R; Ye, Ming; Berke, Gerald S

2003-02-01

The source-filter theory of speech production describes a glottal energy source (volume velocity waveform) that is filtered by the vocal tract and radiates from the mouth as phonation. The characteristics of the volume velocity waveform, the source that drives phonation, have been estimated, but never directly measured at the glottis. To accomplish this measurement, constant temperature anemometer probes were used in an in vivo canine constant pressure model of phonation. A 3-probe array was positioned supraglottically, and an endoscopic camera was positioned subglottically. Simultaneous recordings of airflow velocity (using anemometry) and glottal area (using stroboscopy) were made in 3 animals. Glottal airflow velocities and areas were combined to produce direct measurements of glottal volume velocity waveforms. The anterior and middle parts of the glottis contributed significantly to the volume velocity waveform, with less contribution from the posterior part of the glottis. The measured volume velocity waveforms were successfully fitted to a well-known laryngeal airflow model. A noninvasive measured volume velocity waveform holds promise for future clinical use.

Pulsatility of Lenticulostriate Arteries Assessed by 7 Tesla Flow MRI-Measurement, Reproducibility, and Applicability to Aging Effect.

PubMed

Schnerr, Roald S; Jansen, Jacobus F A; Uludag, Kamil; Hofman, Paul A M; Wildberger, Joachim E; van Oostenbrugge, Robert J; Backes, Walter H

2017-01-01

Characterization of flow properties in cerebral arteries with 1.5 and 3 Tesla MRI is usually limited to large cerebral arteries and difficult to evaluate in the small perforating arteries due to insufficient spatial resolution. In this study, we assessed the feasibility to measure blood flow waveforms in the small lenticulostriate arteries with 7 Tesla velocity-sensitive MRI. The middle cerebral artery was included as reference. Imaging was performed in five young and five old healthy volunteers. Flow was calculated by integrating time-varying velocity values over the vascular cross-section. MRI acquisitions were performed twice in each subject to determine reproducibility. From the flow waveforms, the pulsatility index and damping factor were deduced. Reproducibility values, in terms of the intraclass correlation coefficients, were found to be good to excellent. Measured pulsatility index of the lenticulostriate arteries significantly increased and damping factor significantly decreased with age. In conclusion, we demonstrate that blood flow through the lenticostriate arteries can be precisely measured using 7 Tesla MRI and reveal effects of arterial stiffness due to aging. These findings hold promise to provide relevant insights into the pathologies involving perforating cerebral arteries.

Hemodynamic transition driven by stent porosity in sidewall aneurysms.

PubMed

Bouillot, Pierre; Brina, Olivier; Ouared, Rafik; Lovblad, Karl-Olof; Farhat, Mohamed; Pereira, Vitor Mendes

2015-05-01

The healing process of intracranial aneurysms (IAs) treated with flow diverter stents (FDSs) depends on the IA flow modifications and on the epithelization process over the neck. In sidewall IA models with straight parent artery, two main hemodynamic regimes with different flow patterns and IA flow magnitude were broadly observed for unstented and high porosity stented IA on one side, and low porosity stented IA on the other side. The hemodynamic transition between these two regimes is potentially involved in thrombosis formation. In the present study, CFD simulations and multi-time lag (MTL) particle imaging velocimetry (PIV) measurements were combined to investigate the physical nature of this transition. Measurable velocity fields and non-measurable shear stress and pressure fields were assessed experimentally and numerically in the aneurysm volume in the presence of stents with various porosities. The two main regimes observed in both PIV and CFD showed typical flow features of shear and pressure driven regimes. In particular, the waveform of the averaged IA velocities was matching both the shear stress waveform at IA neck or the pressure gradient waveform in parent artery. Moreover, the transition between the two regimes was controlled by stent porosity: a decrease of stent porosity leads to an increase (decrease) of pressure differential (shear stress) through IA neck. Finally, a good PIV-CFD agreement was found except in transitional regimes and low motion eddies due to small mismatch of PIV-CFD running conditions. Copyright © 2015 Elsevier Ltd. All rights reserved.

Use of a Doppler pulmonary artery catheter for continuous measurement of right ventricular pump function and contractility during single lung transplantation.

PubMed

Heerdt, P M; Pond, C G; Kussman, M K; Triantafillou, A N

1993-01-01

Despite numerous technologic advances in intraoperative monitoring, the only methods routinely available for assessment of right ventricular function in lung transplant recipients are continuous measurement of right heart pressures and intermittent thermodilution determination of cardiac output and ejection fraction. Additional data may now be obtained with transesophageal echocardiography, although this technology is expensive and not widely available and requires diverting attention from a potentially unstable patient for data acquisition and analysis. Recently, a Doppler pulmonary artery catheter was introduced that measures beat-to-beat pulmonary artery blood flow-velocity, cross sectional area, and volume flow. Because of data indicating that acceleration of blood in the pulmonary artery (measured as the first derivative of either the velocity or flow waveform) is a sensitive indicator of right ventricular contractility, we have used waveforms obtained with the catheter for assessment of right ventricular pump function (stroke volume and peak pulmonary artery flow rate) and contractility in heart surgery patients. We report here our experience with this method in two patients undergoing left single lung transplantation.

Velocity Field Measurements of Human Coughing Using Time Resolved Particle Image Velocimetry

NASA Astrophysics Data System (ADS)

Khan, T.; Marr, D. R.; Higuchi, H.; Glauser, M. N.

2003-11-01

Quantitative fluid mechanics analysis of human coughing has been carried out using new Time Resolved Particle Image Velocimetry (TRPIV). The study involves measurement of velocity vector time-histories and velocity profiles. It is focused on the average normal human coughing. Some work in the past on cough mechanics has involved measurement of flow rates, tidal volumes and sub-glottis pressure. However, data of unsteady velocity vector field of the exiting highly time-dependent jets is not available. In this study, human cough waveform data are first acquired in vivo using conventional respiratory instrumentation for various volunteers of different gender/age groups. The representative waveform is then reproduced with a coughing/breathing simulator (with or without a manikin) for TRPIV measurements and analysis. The results of this study would be useful not only for designing of indoor air quality and heating, ventilation and air conditioning systems, but also for devising means of protection against infectious diseases.

Characteristics of the umbilical artery velocity waveform as function of measurement site.

PubMed

Ruissen, C J; von Drongelen, M M; Hoogland, H J; Jager, W; Hoeks, A P

1990-01-01

In 30 uncomplicated singleton pregnancies, varying in duration between 24 and 40 weeks, the variability of the flow velocity waveform (FVW) along the course of the umbilical artery was investigated. Blood flow velocities were recorded at 4 locations in the vessel: within the fetal abdomen, 0-5 cm from the origin of the umbilical cord, in the free-floating part, and 0-5 cm from its insertion in the placenta. From the Doppler signals recorded, the pulsatility index (PI) and a parameter for the frequency distribution index (FDI) were calculated. PI values differed among the locations, but no unequivocal tendency could be demonstrated. Statistical analysis, including multiple regression analysis for maternal and menstrual age and fetal heart rate, showed no significant difference in PI and FDI values for any of the 4 locations. It can be concluded that in uncomplicated pregnancies, possible changes in FVW (quantified by PI) along the course of the umbilical artery have no clinical relevance. Therefore, standardization for the sampling site when measuring PI in this vessel seems to be unnecessary.

The effect of inlet boundary conditions in image-based CFD modeling of aortic flow

NASA Astrophysics Data System (ADS)

Madhavan, Sudharsan; Kemmerling, Erica Cherry

2016-11-01

CFD of cardiovascular flow is a growing and useful field, but simulations are subject to a number of sources of uncertainty which must be quantified. Our work focuses on the uncertainty introduced by the selection of inlet boundary conditions in an image-based, patient-specific model of the aorta. Specifically, we examined the differences between plug flow, fully developed parabolic flow, linear shear flows, skewed parabolic flow profiles, and Womersley flow. Only the shape of the inlet velocity profile was varied-all other parameters were held constant between simulations, including the physiologically realistic inlet flow rate waveform and outlet flow resistance. We found that flow solutions with different inlet conditions did not exhibit significant differences beyond 1 . 75 inlet diameters from the aortic root. Time averaged wall shear stress (TAWSS) was also calculated. The linear shear velocity boundary condition solution exhibited the highest spatially averaged TAWSS, about 2 . 5 % higher than the fully developed parabolic velocity boundary condition, which had the lowest spatially averaged TAWSS.

PLATELET ADHESION TO POLYURETHANE UREA UNDER PULSATILE FLOW CONDITIONS

PubMed Central

Navitsky, Michael A.; Taylor, Joshua O.; Smith, Alexander B.; Slattery, Margaret J.; Deutsch, Steven; Siedlecki, Christopher A.; Manning, Keefe B.

2014-01-01

Platelet adhesion to a polyurethane urea surface is a precursor to thrombus formation within blood-contacting cardiovascular devices, and platelets have been found to adhere strongly to polyurethane surfaces below a shear rate of approximately 500 s−1. The aim of the current work is to determine platelet adhesion properties to the polyurethane urea surface as a function of time varying shear exposure. A rotating disk system is used to study the influence of steady and pulsatile flow conditions (e.g. cardiac inflow and sawtooth waveforms) for platelet adhesion to the biomaterial surface. All experiments retain the same root mean square angular rotation velocity (29.63 rad/s) and waveform period. The disk is rotated in platelet rich bovine plasma for two hours with adhesion quantified by confocal microscopy measurements of immunofluorescently labeled bovine platelets. Platelet adhesion under pulsating flow is found to exponentially decay with increasing shear rate. Adhesion levels are found to depend upon peak platelet flux and shear rate regardless of rotational waveform. In combination with flow measurements, these results may be useful for predicting regions susceptible to thrombus formation within ventricular assist devices. PMID:24721222

Conversion of umbilical arterial Doppler waveforms to cardiac cycle triggering signals: a preparatory study for online motion-gated three-dimensional fetal echocardiography.

PubMed

Deng, J; Birkett, A G; Kalache, K D; Hanson, M A; Peebles, D M; Linney, A D; Lees, W R; Rodeck, C H

2001-01-01

To remove motion artefacts, a device was built to convert "noisy" umbilical arterial Doppler waveforms (UADWs) from an ultrasound (US) system into sharp ECG R-wave-like cardiac cycle triggering signals (CCTSs). These CCTSs were then used to gate a simultaneous (online) 3-D acquisition of sectional fetal echocardiograms from another US system. To test the conversion performance, a study was carried out in sheep fetal twins. Pulmonary arterial flow waveforms (PAFWs) from implanted probes were traced, in the meantime, to determine the reference cardiac cycle. Interference caused by running the two nonsynchronised US systems was controlled to three degrees (not-noticeable, moderate, and severe), together with high (> or = 40 cm/s) and low (< 40) flow velocities on UADWs. The conversion efficiency, assessed by the percentage of UADWs converted into CCTSs, was in the range of 83% to 100% for not-noticeable and moderate interference, and 0% to 71% for severe interference. The triggering accuracy, assessed by [(time lag mean between the onsets of PAFWs and corresponding CCTSs) -- (its 99% confidence level)] / the mean, was 90% to 96% for the not-noticeable interference high- and low-flow groups and for the moderate interference high-flow group; 19% to 93% for the moderate interference low-flow group; and from not obtainable up to 90% for the severe interference groups. The results show that UADWs can be used as a satisfactory online motion-gating source even in the presence of moderate interference. The major problems are from severe interference or moderate interference with low-flow velocity, which can be minimised/eliminated by the integration of the individual systems involved.

Parameterization of the Voice Source by Combining Spectral Decay and Amplitude Features of the Glottal Flow.

ERIC Educational Resources Information Center

Alku, Paavo; Vilkman, Erkki; Laukkanen, Anne-Maria

1998-01-01

A new method is presented for the parameterization of glottal volume velocity waveforms that have been estimated by inverse filtering acoustic speech pressure signals. The new technique combines two features of voice production: the AC value and the spectral decay of the glottal flow. Testing found the new parameter correlates strongly with the…

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

USGS Publications Warehouse

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

2011-01-01

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.

A multi-component parallel-plate flow chamber system for studying the effect of exercise-induced wall shear stress on endothelial cells.

PubMed

Wang, Yan-Xia; Xiang, Cheng; Liu, Bo; Zhu, Yong; Luan, Yong; Liu, Shu-Tian; Qin, Kai-Rong

2016-12-28

In vivo studies have demonstrated that reasonable exercise training can improve endothelial function. To confirm the key role of wall shear stress induced by exercise on endothelial cells, and to understand how wall shear stress affects the structure and the function of endothelial cells, it is crucial to design and fabricate an in vitro multi-component parallel-plate flow chamber system which can closely replicate exercise-induced wall shear stress waveforms in artery. The in vivo wall shear stress waveforms from the common carotid artery of a healthy volunteer in resting and immediately after 30 min acute aerobic cycling exercise were first calculated by measuring the inner diameter and the center-line blood flow velocity with a color Doppler ultrasound. According to the above in vivo wall shear stress waveforms, we designed and fabricated a parallel-plate flow chamber system with appropriate components based on a lumped parameter hemodynamics model. To validate the feasibility of this system, human umbilical vein endothelial cells (HUVECs) line were cultured within the parallel-plate flow chamber under abovementioned two types of wall shear stress waveforms and the intracellular actin microfilaments and nitric oxide (NO) production level were evaluated using fluorescence microscope. Our results show that the trends of resting and exercise-induced wall shear stress waveforms, especially the maximal, minimal and mean wall shear stress as well as oscillatory shear index, generated by the parallel-plate flow chamber system are similar to those acquired from the common carotid artery. In addition, the cellular experiments demonstrate that the actin microfilaments and the production of NO within cells exposed to the two different wall shear stress waveforms exhibit different dynamic behaviors; there are larger numbers of actin microfilaments and higher level NO in cells exposed in exercise-induced wall shear stress condition than resting wall shear stress condition. The parallel-plate flow chamber system can well reproduce wall shear stress waveforms acquired from the common carotid artery in resting and immediately after exercise states. Furthermore, it can be used for studying the endothelial cells responses under resting and exercise-induced wall shear stress environments in vitro.

Non-invasive determination of instantaneous brachial blood flow using the oscillometric method.

PubMed

Liu, Shing-Hong; Wang, Jia-Jung; Cheng, Da-Chuan

2009-08-01

The oscillometric method has been widely used to measure arterial systolic and diastolic blood pressures, but its potential for arterial blood flow measurements still remains to be explored. The aim of this study was to non-invasively determine arterial blood flow using an oscillometric blood flow measurement system. The system consists of a pneumatic elastic cuff, an air-pumping motor, a releaser valve, a pressure transducer, and an airflow meter. To build a non-linear cuff model, we measured airflow pumped into the pneumatic cuff and cuff pressure using an airflow meter and pressure transducer during the inflation period, respectively. During the deflation period, only the pressure transducer was used to record cuff pressure. Based on the cuff model, the oscillometric blood flow waveform was obtained by integrating the oscillometric pressure waveform. We compared arterial blood flow derived from the maximum amplitude of the oscillometric blood flow waveform with Doppler-measured blood flow calculated with the diameters and blood velocities of the brachial arteries in 32 subjects who underwent diagnostic evaluations for peripheral arterial embolism. A linear correlation coefficient of r = 0.716 was found between the oscillometry- and Doppler-based blood flow measurements in the 32 subjects. These results suggest that blood flow passing through the brachial artery can be quantified non-invasively using the oscillometric approach after appropriate calibration.

Mantle plumes and associated flow beneath Arabia and East Africa

NASA Astrophysics Data System (ADS)

Chang, Sung-Joon; Van der Lee, Suzan

2011-02-01

We investigate mantle plumes and associated flow beneath the lithosphere by imaging the three-dimensional S-velocity structure beneath Arabia and East Africa. This image shows elongated vertical and horizontal low-velocity anomalies down to at least mid mantle depths. This three-dimensional S-velocity model is obtained through the joint inversion of teleseismic S- and SKS-arrival times, regional S- and Rayleigh waveform fits, fundamental-mode Rayleigh-wave group velocities, and independent Moho constraints from receiver functions, reflection/refraction profiles, and gravity measurements. In the resolved parts of our S-velocity model we find that the Afar plume is distinctly separate from the Kenya plume, showing the Afar plume's origin in the lower mantle beneath southwestern Arabia. We identify another quasi-vertical low-velocity anomaly beneath Jordan and northern Arabia which extends into the lower mantle and may be related to volcanism in Jordan, northern Arabia, and possibly southern Turkey. Comparing locations of mantle plumes from the joint inversion with fast axes of shear-wave splitting, we confirm horizontal mantle flow radially away from Afar. Low-velocity channels in our model support southwestward flow beneath Ethiopia, eastward flow beneath the Gulf of Aden, but not northwestwards beneath the entire Red Sea. Instead, northward mantle flow from Afar appears to be channeled beneath Arabia.

AC Electroosmotic Pumping in Nanofluidic Funnels.

PubMed

Kneller, Andrew R; Haywood, Daniel G; Jacobson, Stephen C

2016-06-21

We report efficient pumping of fluids through nanofluidic funnels when a symmetric AC waveform is applied. The asymmetric geometry of the nanofluidic funnel induces not only ion current rectification but also electroosmotic flow rectification. In the base-to-tip direction, the funnel exhibits a lower ion conductance and a higher electroosmotic flow velocity, whereas, in the tip-to-base direction, the funnel has a higher ion conductance and a lower electroosmotic flow velocity. Consequently, symmetric AC waveforms easily pump fluid through the nanofunnels over a range of frequencies, e.g., 5 Hz to 5 kHz. In our experiments, the nanofunnels were milled into glass substrates with a focused ion beam (FIB) instrument, and the funnel design had a constant 5° taper with aspect ratios (funnel tip width to funnel depth) of 0.1 to 1.0. We tracked ion current rectification by current-voltage (I-V) response and electroosmotic flow rectification by transport of a zwitterionic fluorescent probe. Rectification of ion current and electroosmotic flow increased with increasing electric field applied to the nanofunnel. Our results support three-dimensional simulations of ion transport and electroosmotic transport through nanofunnels, which suggest the asymmetric electroosmotic transport stems from an induced pressure at the junction of the nanochannel and nanofunnel tip.

Imaging hydrothermal roots along the Endeavour segment of the Juan de Fuca ridge using elastic full waveform inversion.

NASA Astrophysics Data System (ADS)

Arnulf, A. F.; Harding, A. J.; Kent, G. M.

2016-12-01

The Endeavour segment is a 90 km-long, medium-spreading-rate, oceanic spreading center located on the northern Juan de Fuca ridge (JDFR). The central part of this segment forms a 25-km-long volcanic high that hosts five of the most hydrothermally active vent fields on the MOR system, namely (from north to south): Sasquatch, Salty Dawg, High Rise, Main Endeavour and Mothra. Mass, heat and chemical fluxes associated to vigorous hydrothermal venting are large, however the geometry of the fluid circulation system through the oceanic crust remains almost completely undefined. To produce high-resolution velocity/reflectivity structures along the axis of the Endeavour segment, here, we combined a synthetic ocean bottom experiment (SOBE), 2-D traveltime tomography, 2D elastic full waveform and reverse time migration (RTM). We present velocity and reflectivity sections along Endeavour segment at unprecedented spatial resolutions. We clearly image a set of independent, geometrically complex, elongated low-velocity regions linking the top of the magma chamber at depth to the hydrothermal vent fields on the seafloor. We interpret these narrow pipe-like units as focused regions of hydrothermal fluid up-flow, where acidic and corrosive fluids form pipe-like alteration zones as previously observed in Cyprus ophiolites. Furthermore, the amplitude of these low-velocity channels is shown to be highly variable, with the strongest velocity drops observed at Main Endeavour, Mothra and Salty Dawg hydrothermal vent fields, possibly suggesting more mature hydrothermal cells. Interestingly, the near-seafloor structure beneath those three sites is very similar and highlights a sharp lateral transition in velocity (north to south). On the other hand, the High-Rise hydrothermal vent field is characterized by several lower amplitudes up-flow zones and relatively slow near-surface velocities. Last, Sasquatch vent field is located in an area of high near-surface velocities and is not characterized by an obvious low-velocity up-flow region, in good agreement with an extinct vent field.

Flow characteristics around a deformable stenosis under pulsatile flow condition

NASA Astrophysics Data System (ADS)

Choi, Woorak; Park, Jun Hong; Byeon, Hyeokjun; Lee, Sang Joon

2018-01-01

A specific portion of a vulnerable stenosis is deformed periodically under a pulsatile blood flow condition. Detailed analysis of such deformable stenosis is important because stenotic deformation can increase the likelihood of rupture, which may lead to sudden cardiac death or stroke. Various diagnostic indices have been developed for a nondeformable stenosis by using flow characteristics and resultant pressure drop across the stenosis. However, the effects of the stenotic deformation on the flow characteristics remain poorly understood. In this study, the flows around a deformable stenosis model and two different rigid stenosis models were investigated under a pulsatile flow condition. Particle image velocimetry was employed to measure flow structures around the three stenosis models. The deformable stenosis model was deformed to achieve high geometrical slope and height when the flow rate was increased. The deformation of the stenotic shape enhanced jet deflection toward the opposite vessel wall of the stenosis. The jet deflection in the deformable model increased the rate of jet velocity and turbulent kinetic energy (TKE) production as compared with those in the rigid models. The effect of stenotic deformation on the pulsating waveform related with the pressure drop was analyzed using the TKE production rate. The deformable stenosis model exhibited a phase delay of the peak point in the waveform. These results revealed the potential use of pressure drop waveform as a diagnostic index for deformable stenosis.

Geophysical well-log analysis of fractured crystalline rocks at East Bull Lake, Ontario, Canada

USGS Publications Warehouse

Paillet, Frederick L.; Hess, A.E.

1986-01-01

Various conventional geophysical borehole measurements were made in conjunction with measurements using a recently designed, low-frequency, acoustic-waveform probe and slow velocity flowmeter for characterization of a fractured mafic intrusion in southern Ontario, Canada. Conventional geophysical measurements included temperature, caliper, gamma, acoustic, single-point resistance, and acoustic televiewer logs. Hole stability problems prevented the use of neutron and gamma-gamma logs, because these logs require that a radioactive source be lowered into the borehole. Measurements were made in three boreholes as much as 850 m deep and penetrating a few tens of meters into granitic basement. All rocks within the mafic intrusion were characterized by minimal gamma radiation and acoustic velocities of about 6.9 km/sec. The uniformity of the acoustic velocities and the character of acoustic-waveform logs made with a conventional high-frequency logging source correlated with the density of fractures evident on televiewer logs. Sample intervals of high-frequency waveform logs were transformed into interpretations of effective fracture opening using a recent model for acoustic attenuation in fractured rocks. The new low-frequency sparker source did not perform as expected at depths below 250 m because of previously unsuspected problems with source firing under large hydrostatic heads. A new heat-pulse, slow velocity flowmeter was used to delineate in detail the flow regime indicated in a general way by temperature logs. The flowmeter measurements indicated that water was entering 2 of the boreholes at numerous fractures above a depth of 200 m, with flow in at least 2 of the boreholes exiting through large isolated fractures below a depth of 400 m. (Author 's abstract)

Concentration and Velocity Measurements of Both Phases in Liquid-Solid Slurries

NASA Astrophysics Data System (ADS)

Altobelli, Stephen; Hill, Kimberly; Caprihan, Arvind

2007-03-01

Natural and industrial slurry flows abound. They are difficult to calculate and to measure. We demonstrate a simple technique for studying steady slurries. We previously used time-of-flight techniques to study pressure driven slurry flow in pipes. Only the continuous phase velocity and concentration fields were measured. The discrete phase concentration was inferred. In slurries composed of spherical, oil-filled pills and poly-methyl-siloxane oils, we were able to use inversion nulling to measure the concentration and velocity fields of both phases. Pills are available in 1-5mm diameter and silicone oils are available in a wide range of viscosities, so a range of flows can be studied. We demonstrated the technique in horizontal, rotating cylinder flows. We combined two tried and true methods to do these experiments. The first used the difference in T1 to select between phases. The second used gradient waveforms with controlled first moments to produce velocity dependent phase shifts. One novel processing method was developed that allows us to use static continuous phase measurements to reference both the continuous and discrete phase velocity images. ?

Acoustic-televiewer and acoustic-waveform logs used to characterize deeply buried basalt flows, Hanford site, Benton County, Washington

USGS Publications Warehouse

Paillet, Frederick L.

1985-01-01

Acoustic-waveform and acoustic-televiewer logs were obtained for a 400-meter interval of deeply buried basalt flows in three boreholes, and over shorter intervals in two additional boreholes located on the U.S. Department of Energy 's Hanford site in Benton County, Washington. Borehole-wall breakouts were observed in the unaltered interiors of a large part of individual basalt flows; however, several of the flows in one of the five boreholes had almost no breakouts. The distribution of breakouts observed on the televiewer logs correlated closely with the incidence of core disking in some intervals, but the correlation was not always perfect, perhaps because of the differences in the specific fracture mechanisms involved. Borehole-wall breakouts were consistently located on the east and west sides of the boreholes. The orientation is consistent with previous estimates of the principal horizontal-stress field in south-central Washington, if breakouts are assumed to form along the azimuth of the least principal stress. The distribution of breakouts repeatedly indicated an interval of breakout-free rock at the top and bottom of flows. Because breakouts frequently terminate at major low-angle fractures, the data indicate that fracturing may have relieved some of the horizontal stresses near flow tops and bottoms. Unaltered and unfractured basalt appeared to have a uniform compressional velocity of 6.0 + or - 0.1 km/sec and a uniform shear velocity of 3.35 + or - 0.1 km/sec throughout flow interiors. Acoustics-waveform logs also indicated that borehole-wall breakouts did not affect acoustic propagation along the borehole; so fracturing associated with the formation of breakouts appeared to be confined to a thin annulus of stress concentration around the borehole. Televiewer logs obtained before and after hydraulic fracturing in these boreholes indicated the extent of induced fractures, and also indicated minor changes to pre-existing fractures that may have been inflated during fracture generation. (USGS)

A multi-frequency receiver function inversion approach for crustal velocity structure

NASA Astrophysics Data System (ADS)

Li, Xuelei; Li, Zhiwei; Hao, Tianyao; Wang, Sheng; Xing, Jian

2017-05-01

In order to constrain the crustal velocity structures better, we developed a new nonlinear inversion approach based on multi-frequency receiver function waveforms. With the global optimizing algorithm of Differential Evolution (DE), low-frequency receiver function waveforms can primarily constrain large-scale velocity structures, while high-frequency receiver function waveforms show the advantages in recovering small-scale velocity structures. Based on the synthetic tests with multi-frequency receiver function waveforms, the proposed approach can constrain both long- and short-wavelength characteristics of the crustal velocity structures simultaneously. Inversions with real data are also conducted for the seismic stations of KMNB in southeast China and HYB in Indian continent, where crustal structures have been well studied by former researchers. Comparisons of inverted velocity models from previous and our studies suggest good consistency, but better waveform fitness with fewer model parameters are achieved by our proposed approach. Comprehensive tests with synthetic and real data suggest that the proposed inversion approach with multi-frequency receiver function is effective and robust in inverting the crustal velocity structures.

Fluid flow through the larynx channel

NASA Astrophysics Data System (ADS)

Miller, J. A.; Pereira, J. C.; Thomas, D. W.

1988-03-01

The classic two-mass model of the larynx channel is extended by including the false vocal folds and the laryngeal ventricle. Several glottis profiles are postulated to exist which are the result of the forces applied to the mucus membrane due to intraglottal pressure variation. These profiles constrain the air flow which allows the formation of one or two "venae contractae". The location of these influences the pressure in the glottis and layrngeal ventricle and also gives rise to additional viscous losses as well as losses due to flow enlargement. Sampled waveforms are calculated from the model for volume velocity, glottal area, Reynolds number and fluid forces over the vocal folds for various profiles. Results show that the computed waveforms agree with physiological data [1,2] and that it is not necessary to use any empirical constants to match the simulation results. Also, the onset of phonation is shown to be possible either with abduction or adduction of the vocal folds.

Comparison of PIV with 4D-Flow in a physiological accurate flow phantom

NASA Astrophysics Data System (ADS)

Sansom, Kurt; Balu, Niranjan; Liu, Haining; Aliseda, Alberto; Yuan, Chun; Canton, Maria De Gador

2016-11-01

Validation of 4D MRI flow sequences with planar particle image velocimetry (PIV) is performed in a physiologically-accurate flow phantom. A patient-specific phantom of a carotid artery is connected to a pulsatile flow loop to simulate the 3D unsteady flow in the cardiovascular anatomy. Cardiac-cycle synchronized MRI provides time-resolved 3D blood velocity measurements in clinical tool that is promising but lacks a robust validation framework. PIV at three different Reynolds numbers (540, 680, and 815, chosen based on +/- 20 % of the average velocity from the patient-specific CCA waveform) and four different Womersley numbers (3.30, 3.68, 4.03, and 4.35, chosen to reflect a physiological range of heart rates) are compared to 4D-MRI measurements. An accuracy assessment of raw velocity measurements and a comparison of estimated and measureable flow parameters such as wall shear stress, fluctuating velocity rms, and Lagrangian particle residence time, will be presented, with justification for their biomechanics relevance to the pathophysiology of arterial disease: atherosclerosis and intimal hyperplasia. Lastly, the framework is applied to a new 4D-Flow MRI sequence and post processing techniques to provide a quantitative assessment with the benchmarked data. Department of Education GAANN Fellowship.

Flow Field of a Human Cough

NASA Astrophysics Data System (ADS)

Hertzberg, Jean

2005-11-01

Cough generated infectious aerosols are of interest while developing strategies for the mitigation of disease risks ranging from the common cold to SARS. In this work, the velocity field of human cough was measured using particle image velocimetry (PIV). The project subjects (total 29) coughed into an enclosure seeded with stage fog for most measurements. Cough flow speed profiles, average widths of the cough jet, waveform, and maximum cough speeds were measured. Maximum cough speeds ranged from 1.5 m/s to 28.8 m/s. No correlation was found for maximum cough flow speeds to height or gender. The slow growth of the width of the cough flow suggests that a cough may penetrate farther into a room than a steady jet of similar volume. The velocity profile was found to scale with the square root of downstream distance.

Digital signal processing and interpretation of full waveform sonic log for well BP-3-USGS, Great Sand Dunes National Park and Preserve, Alamosa County, Colorado

USGS Publications Warehouse

Burke, Lauri

2011-01-01

Along the Great Sand Dunes National Park and Preserve boundary (fig. 1), 10 monitoring wells were drilled by the National Park Service in order to monitor water flow in an unconfined aquifer spanning the park boundary. Adjacent to the National Park Service monitoring well named Boundary Piezometer Well No. 3, or BP-3, the U.S. Geological Survey (USGS) drilled the BP-3-USGS well. This well was drilled from September 14 through 17, 2009, to a total depth of 99.4 meters (m) in order to acquire additional subsurface information. The BP-3-USGS well is located at lat 37 degrees 43'18.06' and long -105 degrees 43'39.30' at a surface elevation of 2,301 m. Approximately 23 m of core was recovered beginning at a depth of 18 m. Drill cuttings were also recovered. The wireline geophysical logs acquired in the well include natural gamma ray, borehole caliper, temperature, full waveform sonic, density, neutron, resistivity, and induction logs. The BP-3-USGS well is now plugged and abandoned. This report details the full waveform digital signal processing methodology and the formation compressional-wave velocities determined for the BP-3-USGS well. These velocity results are compared to several velocities that are commonly encountered in the subsurface. The density log is also discussed in context of these formation velocities.

Volumetric blood flow via time-domain correlation: experimental verification.

PubMed

Embree, P M; O'Brien, W R

1990-01-01

A novel ultrasonic volumetric flow measurement method using time-domain correlation of consecutive pairs of echoes has been developed. An ultrasonic data acquisition system determined the time shift between a pair of range gated echoes by searching for the time shift with the maximum correlation between the RF sampled waveforms. Experiments with a 5-MHz transducer indicate that the standard deviation of the estimate of steady fluid velocity through 6-mm-diameter tubes is less than 10% of the mean. Experimentally, Sephadex (G-50; 20-80 mum dia.) particles in water and fresh porcine blood have been used as ultrasound scattering fluids. Two-dimensional (2-D) flow velocity can be estimated by slowly sweeping the ultrasonic beam across the blood vessel phantom. Volumetric flow through the vessel is estimated by integrating the 2-D flow velocity field and then is compared to hydrodynamic flow measurements to assess the overall experimental accuracy of the time-domain method. Flow rates from 50-500 ml/min have been estimated with an accuracy better than 10% under the idealized characteristics used in this study, which include straight circular thin-walled tubes, laminar axially-symmetric steady flow, and no intervening tissues.

Doppler velocity measurements from large and small arteries of mice

PubMed Central

Reddy, Anilkumar K.; Madala, Sridhar; Entman, Mark L.; Michael, Lloyd H.; Taffet, George E.

2011-01-01

With the growth of genetic engineering, mice have become increasingly common as models of human diseases, and this has stimulated the development of techniques to assess the murine cardiovascular system. Our group has developed nonimaging and dedicated Doppler techniques for measuring blood velocity in the large and small peripheral arteries of anesthetized mice. We translated technology originally designed for human vessels for use in smaller mouse vessels at higher heart rates by using higher ultrasonic frequencies, smaller transducers, and higher-speed signal processing. With these methods one can measure cardiac filling and ejection velocities, velocity pulse arrival times for determining pulse wave velocity, peripheral blood velocity and vessel wall motion waveforms, jet velocities for the calculation of the pressure drop across stenoses, and left main coronary velocity for the estimation of coronary flow reserve. These noninvasive methods are convenient and easy to apply, but care must be taken in interpreting measurements due to Doppler sample volume size and angle of incidence. Doppler methods have been used to characterize and evaluate numerous cardiovascular phenotypes in mice and have been particularly useful in evaluating the cardiac and vascular remodeling that occur following transverse aortic constriction. Although duplex ultrasonic echo-Doppler instruments are being applied to mice, dedicated Doppler systems are more suitable for some applications. The magnitudes and waveforms of blood velocities from both cardiac and peripheral sites are similar in mice and humans, such that much of what is learned using Doppler technology in mice may be translated back to humans. PMID:21572013

Multi Plumes and Their Flows beneath Arabia and East Africa

NASA Astrophysics Data System (ADS)

Chang, S.; van der Lee, S.

2010-12-01

The three-dimensional S-velocity structure beneath Arabia and East Africa is estimated down to the lower mantle to investigate vertical and horizontal extension of low-velocity anomalies that bear out the presence of mantle plumes and their flows beneath lithosphere. We estimated this model through joint inversion of teleseismic S- and SKS-arrival times, regional S- and Rayleigh waveform fits, fundamental-mode Rayleigh-wave group velocities, and independent Moho constraints from receiver functions, reflection/refraction profiles, and gravity measurements. With the unprecedented resolution in our S-velocity model, we found different flow patterns of hot materials upwelling beneath Afar beneath the Red Sea and the Gulf of Aden. While the low-velocity anomaly from Afar is well confined beneath the Gulf of Aden, inferring mantle flow along the gulf, N-S channel of low velocity is found beneath Arabia, not along the Red Sea. The Afar plume is distinctively separate from the Kenya plume, showing its origin in the lower mantle beneath southwestern Arabia. We identified another low-velocity extension to the lower mantle beneath Jordan and northern Arabia, which is thought to have caused volcanism in Jordan, northern Arabia, and possibly southern Turkey. Comparing locations of mantle plumes from the joint inversion with fast axes of shear-wave splitting, we confirmed horizontal plume flow from Afar in NS direction beneath Arabia and in NE-SW direction beneath Ethiopia as a likely cause of the observed seismic anisotropy.

Angular velocity of gravitational radiation from precessing binaries and the corotating frame

NASA Astrophysics Data System (ADS)

Boyle, Michael

2013-05-01

This paper defines an angular velocity for time-dependent functions on the sphere and applies it to gravitational waveforms from compact binaries. Because it is geometrically meaningful and has a clear physical motivation, the angular velocity is uniquely useful in helping to solve an important—and largely ignored—problem in models of compact binaries: the inverse problem of deducing the physical parameters of a system from the gravitational waves alone. It is also used to define the corotating frame of the waveform. When decomposed in this frame, the waveform has no rotational dynamics and is therefore as slowly evolving as possible. The resulting simplifications lead to straightforward methods for accurately comparing waveforms and constructing hybrids. As formulated in this paper, the methods can be applied robustly to both precessing and nonprecessing waveforms, providing a clear, comprehensive, and consistent framework for waveform analysis. Explicit implementations of all these methods are provided in accompanying computer code.

Sensitivity analyses of acoustic impedance inversion with full-waveform inversion

NASA Astrophysics Data System (ADS)

Yao, Gang; da Silva, Nuno V.; Wu, Di

2018-04-01

Acoustic impedance estimation has a significant importance to seismic exploration. In this paper, we use full-waveform inversion to recover the impedance from seismic data, and analyze the sensitivity of the acoustic impedance with respect to the source-receiver offset of seismic data and to the initial velocity model. We parameterize the acoustic wave equation with velocity and impedance, and demonstrate three key aspects of acoustic impedance inversion. First, short-offset data are most suitable for acoustic impedance inversion. Second, acoustic impedance inversion is more compatible with the data generated by density contrasts than velocity contrasts. Finally, acoustic impedance inversion requires the starting velocity model to be very accurate for achieving a high-quality inversion. Based upon these observations, we propose a workflow for acoustic impedance inversion as: (1) building a background velocity model with travel-time tomography or reflection waveform inversion; (2) recovering the intermediate wavelength components of the velocity model with full-waveform inversion constrained by Gardner’s relation; (3) inverting the high-resolution acoustic impedance model with short-offset data through full-waveform inversion. We verify this workflow by the synthetic tests based on the Marmousi model.

Four-dimensional Doppler ultrasound measurements in carotid bifurcation models: effect of concentric versus eccentric stenosis

NASA Astrophysics Data System (ADS)

Poepping, Tamie L.; Rankin, Richard N.; Holdsworth, David W.

2001-05-01

A unique in-vitro system has been developed that incorporates both realistic phantoms and flow. The anthropomorphic carotid phantoms are fabricated in agar with stenosis severity of 30% or 70% (by NASCET standards) and one of two geometric configurations- concentric or eccentric. The phantoms are perfused with a flow waveform that simulates normal common carotid flow. Pulsed Doppler ultrasound data are acquired at a 1 mm grid spacing throughout the lumen of the carotid bifurcation. To obtain a half-lumen volume, symmetric about the mid plane, requires a 13 hour acquisition over 3238 interrogation sites, producing 5.6 Gbytes of data. The spectral analysis produces estimates of parameters such as the peak velocity, mean velocity, spectral-broadening index, and turbulence intensity. Color-encoded or grayscale-encoded maps of these spectral parameters show distinctly different flow patterns resulting from stenoses of equal severity but different eccentricity. The most noticeable differences are seen in the volumes of the recirculation zones and the paths of the high-velocity jets. Elevated levels of turbulence intensity are also seen distal to the stenosis in the 70%-stenosed models.

Unsteady flow in the nasal cavity with high flow therapy measured by stereoscopic PIV

NASA Astrophysics Data System (ADS)

Spence, C. J. T.; Buchmann, N. A.; Jermy, M. C.

2012-03-01

Nasal high flow (NHF) cannulae are used to deliver heated and humidified air to patients at steady flows ranging from 5 to 50 l/min. In this study, the flow velocities in the nasal cavity across the complete respiratory cycle during natural breathing and with NHF has been mapped in vitro using time-resolved stereoscopic particle image velocimetry (SPIV). An anatomically accurate silicone resin model of a complete human nasal cavity was constructed using CT scan data and rapid prototyping. Physiological breathing waveforms were reproduced in vitro using Reynolds and Womersley number matching and a piston pump driven by a ball screw and stepper motor. The flow pattern in the nasal cavity with NHF was found to differ significantly from natural breathing. Velocities of 2.4 and 3.3 ms-1 occurred in the nasal valve during natural breathing at peak expiration and inspiration, respectively; however, on expiration, the maximum velocity of 3.8 ms-1 occurred in the nasopharynx. At a cannula flow rate of 30 l/min, maximal velocities of 13.6 and 16.5 ms-1 at peak expiration and inspiration, respectively, were both located in the cannula jet within the nasal valve. Results are presented that suggest the quasi-steady flow assumption is invalid in the nasal cavity during natural breathing; however, it was valid with NHF. Cannula flow has been found to continuously flush the nasopharyngeal dead space, which may enhance carbon dioxide removal and increase oxygen fraction.

Subduction zone guided waves in Northern Chile

NASA Astrophysics Data System (ADS)

Garth, Thomas; Rietbrock, Andreas

2016-04-01

Guided wave dispersion is observed in subduction zones as high frequency energy is retained and delayed by low velocity structure in the subducting slab, while lower frequency energy is able to travel at the faster velocities associated with the surrounding mantle material. As subduction zone guided waves spend longer interacting with the low velocity structure of the slab than any other seismic phase, they have a unique capability to resolve these low velocity structures. In Northern Chile, guided wave arrivals are clearly observed on two stations in the Chilean fore-arc on permanent stations of the IPOC network. High frequency (> 5 Hz) P-wave arrivals are delayed by approximately 2 seconds compared to the low frequency (< 2 Hz) P-wave arrivals. Full waveform finite difference modelling is used to test the low velocity slab structure that cause this P-wave dispersion. The synthetic waveforms produced by these models are compared to the recorded waveforms. Spectrograms are used to compare the relative arrival times of different frequencies, while the velocity spectra is used to constrain the relative amplitude of the arrivals. Constraining the waveform in these two ways means that the full waveform is also matched, and the low pass filtered observed and synthetic waveforms can be compared. A combined misfit between synthetic and observed waveforms is then calculated following Garth & Rietbrock (2014). Based on this misfit criterion we constrain the velocity model by using a grid search approach. Modelling the guided wave arrivals suggest that the observed dispersion cannot be solely accounted for by a single low velocity layer as suggested by previous guided wave studies. Including dipping low velocity normal fault structures in the synthetic model not only accounts for the observed strong P-wave coda, but also produces a clear first motion dispersion. We therefore propose that the lithospheric mantle of the subducting Nazca plate is highly hydrated at intermediate depths by dipping low velocity normal faults. Additionally, we show that the low velocity oceanic crust persists to depths of up to 200 km, well beyond the depth range where the eclogite transition is expected to have occurred. Our results suggest that young subducting lithosphere also has the potential to carry much larger amounts of water to the mantle than has previously been appreciated.

Optimization of an electrokinetic mixer for microfluidic applications.

PubMed

Bockelmann, Hendryk; Heuveline, Vincent; Barz, Dominik P J

2012-06-01

This work is concerned with the investigation of the concentration fields in an electrokinetic micromixer and its optimization in order to achieve high mixing rates. The mixing concept is based on the combination of an alternating electrical excitation applied to a pressure-driven base flow in a meandering microchannel geometry. The electrical excitation induces a secondary electrokinetic velocity component, which results in a complex flow field within the meander bends. A mathematical model describing the physicochemical phenomena present within the micromixer is implemented in an in-house finite-element-method code. We first perform simulations comparable to experiments concerned with the investigation of the flow field in the bends. The comparison of the complex flow topology found in simulation and experiment reveals excellent agreement. Hence, the validated model and numerical schemes are employed for a numerical optimization of the micromixer performance. In detail, we optimize the secondary electrokinetic flow by finding the best electrical excitation parameters, i.e., frequency and amplitude, for a given waveform. Two optimized electrical excitations featuring a discrete and a continuous waveform are discussed with respect to characteristic time scales of our mixing problem. The results demonstrate that the micromixer is able to achieve high mixing degrees very rapidly.

Optimization of an electrokinetic mixer for microfluidic applications

PubMed Central

Bockelmann, Hendryk; Heuveline, Vincent; Barz, Dominik P. J.

2012-01-01

This work is concerned with the investigation of the concentration fields in an electrokinetic micromixer and its optimization in order to achieve high mixing rates. The mixing concept is based on the combination of an alternating electrical excitation applied to a pressure-driven base flow in a meandering microchannel geometry. The electrical excitation induces a secondary electrokinetic velocity component, which results in a complex flow field within the meander bends. A mathematical model describing the physicochemical phenomena present within the micromixer is implemented in an in-house finite-element-method code. We first perform simulations comparable to experiments concerned with the investigation of the flow field in the bends. The comparison of the complex flow topology found in simulation and experiment reveals excellent agreement. Hence, the validated model and numerical schemes are employed for a numerical optimization of the micromixer performance. In detail, we optimize the secondary electrokinetic flow by finding the best electrical excitation parameters, i.e., frequency and amplitude, for a given waveform. Two optimized electrical excitations featuring a discrete and a continuous waveform are discussed with respect to characteristic time scales of our mixing problem. The results demonstrate that the micromixer is able to achieve high mixing degrees very rapidly. PMID:22712034

Anomalous waveforms observed in laboratory-formed gas hydrate-bearing and ice-bearing sediments

PubMed Central

Lee, Myung W.; Waite, William F.

2011-01-01

Acoustic transmission measurements of compressional, P, and shear, S, wave velocities rely on correctly identifying the P- and S-body wave arrivals in the measured waveform. In cylindrical samples for which the sample is much longer than the acoustic wavelength, these body waves can be obscured by high-amplitude waveform features arriving just after the relatively small-amplitude P-body wave. In this study, a normal mode approach is used to analyze this type of waveform, observed in sediment containing gas hydrate or ice. This analysis extends an existing normal-mode waveform propagation theory by including the effects of the confining medium surrounding the sample, and provides guidelines for estimating S-wave velocities from waveforms containing multiple large-amplitude arrivals. PMID:21476628

Study on law of negative corona discharge in microparticle-air two-phase flow media

NASA Astrophysics Data System (ADS)

He, Bo; Li, Tianwei; Xiu, Yaping; Zhao, Heng; Peng, Zongren; Meng, Yongpeng

2016-03-01

To study the basic law of negative corona discharge in solid particle-air two-phase flow, corona discharge experiments in a needle-plate electrode system at different voltage levels and different wind speed were carried out in the wind tunnel. In this paper, the change law of average current and current waveform were analyzed, and the observed phenomena were systematically explained from the perspectives of airflow, particle charging, and particle motion with the help of PIV (particle image velocity) measurements and ultraviolet observations.

Pulsed-wave Doppler ultrasonographic evaluation of hepatic vein in dogs with tricuspid regurgitation

PubMed Central

Kim, Jaehwan; Kim, Soyoung

2017-01-01

This study was performed to identify the relationships between hepatic vein (HV) measurements, including flow velocity and waveform, using pulsed-wave (PW) Doppler ultrasonography, and the severity of tricuspid regurgitation (TR) in dogs. The study included 22 dogs with TR and 7 healthy dogs. The TR group was subdivided into 3 groups according to TR jet profile obtained by echocardiography. The hepatic venous waveform was obtained and classified into 3 types. A variety of HV measurements, including the maximal velocities of the atrial systolic, systolic (S), end ventricular systolic, and diastolic (D) waves and the ratio of the S- and D- wave velocities (S/D ratio), were acquired. TR severity was significantly correlated with the S- (r = −0.380, p = 0.042) and D- (r = 0.468, p = 0.011) wave velocities and the S/D ratio (r = −0.747, p < 0.001). Receiver operating characteristic curve analysis revealed the highest sensitivity and specificity for the S/D ratio (89% and 75%, respectively) at a threshold of 0.97 with excellent accuracy (AUC = 0.911, p < 0.001). In conclusion, PW Doppler ultrasonography of the HV can be used to identify the presence of significant TR and to classify TR severity in dogs. PMID:27515264

Pulsed-wave Doppler ultrasonographic evaluation of hepatic vein in dogs with tricuspid regurgitation.

PubMed

Kim, Jaehwan; Kim, Soyoung; Eom, Kidong

2017-03-30

This study was performed to identify the relationships between hepatic vein (HV) measurements, including flow velocity and waveform, using pulsed-wave (PW) Doppler ultrasonography, and the severity of tricuspid regurgitation (TR) in dogs. The study included 22 dogs with TR and 7 healthy dogs. The TR group was subdivided into 3 groups according to TR jet profile obtained by echocardiography. The hepatic venous waveform was obtained and classified into 3 types. A variety of HV measurements, including the maximal velocities of the atrial systolic, systolic (S), end ventricular systolic, and diastolic (D) waves and the ratio of the S- and D- wave velocities (S/D ratio), were acquired. TR severity was significantly correlated with the S- ( r = -0.380, p = 0.042) and D- ( r = 0.468, p = 0.011) wave velocities and the S/D ratio ( r = -0.747, p ＜ 0.001). Receiver operating characteristic curve analysis revealed the highest sensitivity and specificity for the S/D ratio (89% and 75%, respectively) at a threshold of 0.97 with excellent accuracy (AUC = 0.911, p ＜ 0.001). In conclusion, PW Doppler ultrasonography of the HV can be used to identify the presence of significant TR and to classify TR severity in dogs.

Parametric Characterization of Flow Inside Cererbal Aneurysms Treated with Flow-Diverting Stents

NASA Astrophysics Data System (ADS)

Barbour, Michael; Levitt, Michael; Geindreau, Christian; Johnson, Luke; Chivukula, Keshav; Aliseda, Alberto

2017-11-01

Cerebral aneurysms are often treated with a flow-diverting stent (FDS) to reduce blood flow into the aneurysm sac, promoting the development of a stable thrombus. Successful treatment is highly dependent on the degree of flow reduction and the altered hemodynamics inside the aneurysm sac following treatment. Establishing a causal connection between hemodynamic metrics of FDS-treated CAs and long-term clinical outcomes requires a rigorous parametric characterization of this flow environment. We use 3D particle image velocimetry (PIV) to measure the flow inside idealized aneurysm models treated with FDS. Physiologically realistic Reynolds numbers and increasing levels of parent vessel curvature are analyzed to understand the effect of inertia on flow development. The flow velocity into the aneurysm and the topology of the flow inside the sac is shown to be highly dependent on parent vessel Dean number (De). The role of flow pulsatility is then added to the study via time-dependent waveforms. Velocity measurements at 2 values of parent vessel Womersley number (Wo) allow us to parameterize flow inside of CAs treated with FDS as a function of De, Re and Wo, improving the fundamental understanding of how FDS alter CA hemodynamics and aiding in the development of new treatments.

An in vitro experimental study of flow past aortic valve under varied pulsatile conditions

NASA Astrophysics Data System (ADS)

Zhang, Ruihang; Zhang, Yan

2017-11-01

Flow past aortic valve represents a complex fluid-structure interaction phenomenon that involves pulsatile, vortical, and turbulent conditions. The flow characteristics immediately downstream of the valve, such as the variation of pulsatile flow velocity, formation of vortices, distribution of shear stresses, are of particular interest to further elucidate the role of hemodynamics in various aortic diseases. However, the fluid dynamics of a realistic aortic valve is not fully understood. Particularly, it is unclear how the flow fields downstream of the aortic valve would change under varied pulsatile inlet boundary conditions. In this study, an in vitro experiment has been conducted to investigate the flow fields downstream of a silicone aortic valve model within a cardiovascular flow simulator. Phased-locked Particle Image Velocimetry measurements were performed to map the velocity fields and Reynolds normal and shear stresses at different phases in a cardiac cycle. Temporal variations of pressure across the valve model were measured using high frequency transducers. Results have been compared for different pulsatile inlet conditions, including varied frequencies (heart rates), magnitudes (stroke volumes), and cardiac contractile functions (shapes of waveforms).

Crustal velocity structure of central Gansu Province from regional seismic waveform inversion using firework algorithm

NASA Astrophysics Data System (ADS)

Chen, Yanyang; Wang, Yanbin; Zhang, Yuansheng

2017-04-01

The firework algorithm (FWA) is a novel swarm intelligence-based method recently proposed for the optimization of multi-parameter, nonlinear functions. Numerical waveform inversion experiments using a synthetic model show that the FWA performs well in both solution quality and efficiency. We apply the FWA in this study to crustal velocity structure inversion using regional seismic waveform data of central Gansu on the northeastern margin of the Qinghai-Tibet plateau. Seismograms recorded from the moment magnitude ( M W) 5.4 Minxian earthquake enable obtaining an average crustal velocity model for this region. We initially carried out a series of FWA robustness tests in regional waveform inversion at the same earthquake and station positions across the study region, inverting two velocity structure models, with and without a low-velocity crustal layer; the accuracy of our average inversion results and their standard deviations reveal the advantages of the FWA for the inversion of regional seismic waveforms. We applied the FWA across our study area using three component waveform data recorded by nine broadband permanent seismic stations with epicentral distances ranging between 146 and 437 km. These inversion results show that the average thickness of the crust in this region is 46.75 km, while thicknesses of the sedimentary layer, and the upper, middle, and lower crust are 3.15, 15.69, 13.08, and 14.83 km, respectively. Results also show that the P-wave velocities of these layers and the upper mantle are 4.47, 6.07, 6.12, 6.87, and 8.18 km/s, respectively.

Experimental study of physiological flow in a cerebral saccular basilar tip aneurysm

NASA Astrophysics Data System (ADS)

Tsai, William; Savas, Omer; Ortega, Jason; Maitland, Duncan; Saloner, David

2008-11-01

The subject matter of the research is the flow within cerebral saccular basilar tip aneurysms and exploring correlations with their growth and rupture. The flow phantom consists of an inlet pipe branching out 90^o into two outlets, simulating the basilar artery bifurcation and a nearly spherical dome at the flow divider simulating the aneurysm. Input flow is a physiological waveform for the basilar artery. Flow outlet branching ratios are controlled at will. Experiments are done at Reynolds numbers 221-376 and Sexl-Wormersley number 4.46. Flow visualization and particle image velocimetry are used to study velocity, vorticity, and wall shear stress. All flows can be characterized by an off-center inlet jet and a circulation region, whose transient strength and behavior depends on the outflow ratios.

Simultaneous inversion of seismic velocity and moment tensor using elastic-waveform inversion of microseismic data: Application to the Aneth CO2-EOR field

NASA Astrophysics Data System (ADS)

Chen, Y.; Huang, L.

2017-12-01

Moment tensors are key parameters for characterizing CO2-injection-induced microseismic events. Elastic-waveform inversion has the potential to providing accurate results of moment tensors. Microseismic waveforms contains information of source moment tensors and the wave propagation velocity along the wavepaths. We develop an elastic-waveform inversion method to jointly invert the seismic velocity model and moment tensor. We first use our adaptive moment-tensor joint inversion method to estimate moment tensors of microseismic events. Our adaptive moment-tensor inversion method jointly inverts multiple microseismic events with similar waveforms within a cluster to reduce inversion uncertainty for microseismic data recorded using a single borehole geophone array. We use this inversion result as the initial model for our elastic-waveform inversion to minimize the cross-correlated-based data misfit between observed data and synthetic data. We verify our method using synthetic microseismic data and obtain improved results of both moment tensors and seismic velocity model. We apply our new inversion method to microseismic data acquired at a CO2-enhanced oil recovery field in Aneth, Utah, using a single borehole geophone array. The results demonstrate that our new inversion method significantly reduces the data misfit compared to the conventional ray-theory-based moment-tensor inversion.

Lithospheric structure of the Arabian Shield and Platform from complete regional waveform modelling and surface wave group velocities

NASA Astrophysics Data System (ADS)

Rodgers, Arthur J.; Walter, William R.; Mellors, Robert J.; Al-Amri, Abdullah M. S.; Zhang, Yu-Shen

1999-09-01

Regional seismic waveforms reveal significant differences in the structure of the Arabian Shield and the Arabian Platform. We estimate lithospheric velocity structure by modelling regional waveforms recorded by the 1995-1997 Saudi Arabian Temporary Broadband Deployment using a grid search scheme. We employ a new method whereby we narrow the waveform modelling grid search by first fitting the fundamental mode Love and Rayleigh wave group velocities. The group velocities constrain the average crustal thickness and velocities as well as the crustal velocity gradients. Because the group velocity fitting is computationally much faster than the synthetic seismogram calculation this method allows us to determine good average starting models quickly. Waveform fits of the Pn and Sn body wave arrivals constrain the mantle velocities. The resulting lithospheric structures indicate that the Arabian Platform has an average crustal thickness of 40 km, with relatively low crustal velocities (average crustal P- and S-wave velocities of 6.07 and 3.50 km s^-1 , respectively) without a strong velocity gradient. The Moho is shallower (36 km) and crustal velocities are 6 per cent higher (with a velocity increase with depth) for the Arabian Shield. Fast crustal velocities of the Arabian Shield result from a predominantly mafic composition in the lower crust. Lower velocities in the Arabian Platform crust indicate a bulk felsic composition, consistent with orogenesis of this former active margin. P- and S-wave velocities immediately below the Moho are slower in the Arabian Shield than in the Arabian Platform (7.9 and 4.30 km s^-1 , and 8.10 and 4.55 km s^-1 , respectively). This indicates that the Poisson's ratios for the uppermost mantle of the Arabian Shield and Platform are 0.29 and 0.27, respectively. The lower mantle velocities and higher Poisson's ratio beneath the Arabian Shield probably arise from a partially molten mantle associated with Red Sea spreading and continental volcanism, although we cannot constrain the lateral extent of a zone of partially molten mantle.

Vortex propagation around a wall-mounted obstacle in pulsatile flow

NASA Astrophysics Data System (ADS)

Carr, Ian A.; Plesniak, Michael W.

2015-11-01

Wall-mounted obstacles are prevalent in nature and engineering applications. Physiological flows observed in human vocal fold pathologies, such as polyps, can be modeled by flow over a wall-mounted protuberance. Despite their prevalence, studies of wall-mounted obstacles have been restricted to steady (constant velocity) freestream flow. In biological and geophysical applications, pulsatile flow is much more common, yet effects of pulsatility on the wake of a wall-mounted obstacle remain to be extensively studied. This study aims to characterize the complex physics produced in this unsteady, separated flow. Experiments were performed in a low-speed wind tunnel with a set of rotating vanes, which produce the pulsatile inflow waveform. Instantaneous and phase-averaged particle image velocimetry (PIV) results acquired around a hemispherical obstacle are presented and compared. A mechanism based on self-induced vortex propagation, analogous to that in vortex rings, is proposed to explain the observed dynamics of coherent structures. Predictions of the propagation velocity based on analytical expressions for vortex rings in a viscous fluid are compared to the experimentally measured propagation velocity. Effects of the unsteady boundary layer on the observed physics are explored. This material is based in part upon work supported by the National Science Foundation under Grant Number CBET-1236351, and GW Center for Biomimetics and Bioinspired Engineering (COBRE).

Anomalous waveforms observed in laboratory-formed gas hydrate-bearing and ice-bearing sediments

USGS Publications Warehouse

Lee, M.W.; Waite, W.F.

2011-01-01

Acoustic transmission measurements of compressional, P, and shear, S, wave velocities rely on correctly identifying the P- and S-body wave arrivals in the measured waveform. In cylindrical samples for which the sample is much longer than the acoustic wavelength, these body waves can be obscured by high-amplitude waveform features arriving just after the relatively small-amplitude P-body wave. In this study, a normal mode approach is used to analyze this type of waveform, observed in sediment containing gas hydrate or ice. This analysis extends an existing normal-mode waveform propagation theory by including the effects of the confining medium surrounding the sample, and provides guidelines for estimating S-wave velocities from waveforms containing multiple large-amplitude arrivals. ?? 2011 Acoustical Society of America.

Active unsteady aerodynamic suppression of rotating stall in an incompressible flow centrifugal compressor with vaned diffuser

NASA Technical Reports Server (NTRS)

Lawless, Patrick B.; Fleeter, Sanford

1991-01-01

A mathematical model is developed to analyze the suppression of rotating stall in an incompressible flow centrifugal compressor with a vaned diffuser, thereby addressing the important need for centrifugal compressor rotating stall and surge control. In this model, the precursor to to instability is a weak rotating potential velocity perturbation in the inlet flow field that eventually develops into a finite disturbance. To suppress the growth of this potential disturbance, a rotating control vortical velocity disturbance is introduced into the impeller inlet flow. The effectiveness of this control is analyzed by matching the perturbation pressure in the compressor inlet and exit flow fields with a model for the unsteady behavior of the compressor. To demonstrate instability control, this model is then used to predict the control effectiveness for centrifugal compressor geometries based on a low speed research centrifugal compressor. These results indicate that reductions of 10 to 15 percent in the mean inlet flow coefficient at instability are possible with control waveforms of half the magnitude of the total disturbance at the inlet.

A Waveform Archiving System for the GE Solar 8000i Bedside Monitor.

PubMed

Fanelli, Andrea; Jaishankar, Rohan; Filippidis, Aristotelis; Holsapple, James; Heldt, Thomas

2018-01-01

Our objective was to develop, deploy, and test a data-acquisition system for the reliable and robust archiving of high-resolution physiological waveform data from a variety of bedside monitoring devices, including the GE Solar 8000i patient monitor, and for the logging of ancillary clinical and demographic information. The data-acquisition system consists of a computer-based archiving unit and a GE Tram Rac 4A that connects to the GE Solar 8000i monitor. Standard physiological front-end sensors connect directly to the Tram Rac, which serves as a port replicator for the GE monitor and provides access to these waveform signals through an analog data interface. Together with the GE monitoring data streams, we simultaneously collect the cerebral blood flow velocity envelope from a transcranial Doppler ultrasound system and a non-invasive arterial blood pressure waveform along a common time axis. All waveform signals are digitized and archived through a LabView-controlled interface that also allows for the logging of relevant meta-data such as clinical and patient demographic information. The acquisition system was certified for hospital use by the clinical engineering team at Boston Medical Center, Boston, MA, USA. Over a 12-month period, we collected 57 datasets from 11 neuro-ICU patients. The system provided reliable and failure-free waveform archiving. We measured an average temporal drift between waveforms from different monitoring devices of 1 ms every 66 min of recorded data. The waveform acquisition system allows for robust real-time data acquisition, processing, and archiving of waveforms. The temporal drift between waveforms archived from different devices is entirely negligible, even for long-term recording.

Measurement of acoustic velocity components in a turbulent flow using LDV and high-repetition rate PIV

NASA Astrophysics Data System (ADS)

Léon, Olivier; Piot, Estelle; Sebbane, Delphine; Simon, Frank

2017-06-01

The present study provides theoretical details and experimental validation results to the approach proposed by Minotti et al. (Aerosp Sci Technol 12(5):398-407, 2008) for measuring amplitudes and phases of acoustic velocity components (AVC) that are waveform parameters of each component of velocity induced by an acoustic wave, in fully turbulent duct flows carrying multi-tone acoustic waves. Theoretical results support that the turbulence rejection method proposed, based on the estimation of cross power spectra between velocity measurements and a reference signal such as a wall pressure measurement, provides asymptotically efficient estimators with respect to the number of samples. Furthermore, it is shown that the estimator uncertainties can be simply estimated, accounting for the characteristics of the measured flow turbulence spectra. Two laser-based measurement campaigns were conducted in order to validate the acoustic velocity estimation approach and the uncertainty estimates derived. While in previous studies estimates were obtained using laser Doppler velocimetry (LDV), it is demonstrated that high-repetition rate particle image velocimetry (PIV) can also be successfully employed. The two measurement techniques provide very similar acoustic velocity amplitude and phase estimates for the cases investigated, that are of practical interest for acoustic liner studies. In a broader sense, this approach may be beneficial for non-intrusive sound emission studies in wind tunnel testings.

3-D characterization of high-permeability zones in a gravel aquifer using 2-D crosshole GPR full-waveform inversion and waveguide detection

NASA Astrophysics Data System (ADS)

Klotzsche, Anja; van der Kruk, Jan; Linde, Niklas; Doetsch, Joseph; Vereecken, Harry

2013-11-01

Reliable high-resolution 3-D characterization of aquifers helps to improve our understanding of flow and transport processes when small-scale structures have a strong influence. Crosshole ground penetrating radar (GPR) is a powerful tool for characterizing aquifers due to the method's high-resolution and sensitivity to porosity and soil water content. Recently, a novel GPR full-waveform inversion algorithm was introduced, which is here applied and used for 3-D characterization by inverting six crosshole GPR cross-sections collected between four wells arranged in a square configuration close to the Thur River in Switzerland. The inversion results in the saturated part of this gravel aquifer reveals a significant improvement in resolution for the dielectric permittivity and electrical conductivity images compared to ray-based methods. Consistent structures where acquisition planes intersect indicate the robustness of the inversion process. A decimetre-scale layer with high dielectric permittivity was revealed at a depth of 5-6 m in all six cross-sections analysed here, and a less prominent zone with high dielectric permittivity was found at a depth of 7.5-9 m. These high-permittivity layers act as low-velocity waveguides and they are interpreted as high-porosity layers and possible zones of preferential flow. Porosity estimates from the permittivity models agree well with estimates from Neutron-Neutron logging data at the intersecting diagonal planes. Moreover, estimates of hydraulic permeability based on flowmeter logs confirm the presence of zones of preferential flow in these depth intervals. A detailed analysis of the measured data for transmitters located within the waveguides, revealed increased trace energy due to late-arrival elongated wave trains, which were observed for receiver positions straddling this zone. For the same receiver positions within the waveguide, a distinct minimum in the trace energy was visible when the transmitter was located outside the waveguide. A novel amplitude analysis was proposed to explore these maxima and minima of the trace energy. Laterally continuous low-velocity waveguides and their boundaries were identified in the measured data alone. In contrast to the full-waveform inversion, this method follows a simple workflow and needs no detailed and time consuming processing or inversion of the data. Comparison with the full-waveform inversion results confirmed the presence of the waveguides illustrating that full-waveform inversion return reliable results at the highest resolution currently possible at these scales. We envision that full-waveform inversion of GPR data will play an important role in a wide range of geological, hydrological, glacial and periglacial studies in the critical zone.

Flow pumping system for physiological waveforms.

PubMed

Tsai, William; Savaş, Omer

2010-02-01

A pulsatile flow pumping system is developed to replicate flow waveforms with reasonable accuracy for experiments simulating physiological blood flows at numerous points in the body. The system divides the task of flow waveform generation between two pumps: a gear pump generates the mean component and a piston pump generates the oscillatory component. The system is driven by two programmable servo controllers. The frequency response of the system is used to characterize its operation. The system has been successfully tested in vascular flow experiments where sinusoidal, carotid, and coronary flow waveforms are replicated.

The effect of flow recirculation on abdominal aortic aneurysm

NASA Astrophysics Data System (ADS)

Taib, Ishkrizat; Amirnordin, Shahrin Hisham; Madon, Rais Hanizam; Mustafa, Norrizal; Osman, Kahar

2012-06-01

The presences of flow recirculation at the abdominal aortic aneurysm (AAA) region yield the unpredictable failure of aneurismal wall. The failure of the aneurismal wall is closely related to the hemodynamic factor. Hemodynamic factor such as pressure and velocity distribution play a significance role of aneurysm growth and rupture. By using the computational approach, the influence of hemodynamic factor is investigated using computational fluid dynamic (CFD) method on the virtual AAA model. The virtual 3D AAAs model was reconstructed from Spiral Computed Tomography scan (CT-scan). The blood flow is assumed as being transient, laminar and Newtonian within a rigid section of the vessel. The blood flow also driven by an imposed of pressure gradient in the form of physiological waveform. The pulsating blood flow is also considered in this simulation. The results on pressure distribution and velocity profile are analyzed to interpret the behaviour of flow recirculation. The results show the forming of vortices is seen at the aneurysm bulge. This vortices is form at the aneurysm region then destroyed rapidly by flow recirculation. Flow recirculation is point out much higher at distal end of aneurysm closed to iliac bifurcation. This phenomenon is managed to increase the possibility of aneurysm growth and rupture.

Velocity structure of a bottom simulating reflector offshore Peru: Results from full waveform inversion

USGS Publications Warehouse

Pecher, I.A.; Minshull, T.A.; Singh, S.C.; von Huene, Roland E.

1996-01-01

Much of our knowledge of the worldwide distribution of submarine gas hydrates comes from seismic observations of Bottom Simulating Reflectors (BSRs). Full waveform inversion has proven to be a reliable technique for studying the fine structure of BSRs using the compressional wave velocity. We applied a non-linear full waveform inversion technique to a BSR at a location offshore Peru. We first determined the large-scale features of seismic velocity variations using a statistical inversion technique to maximise coherent energy along travel-time curves. These velocities were used for a starting velocity model for the full waveform inversion, which yielded a detailed velocity/depth model in the vicinity of the BSR. We found that the data are best fit by a model in which the BSR consists of a thin, low-velocity layer. The compressional wave velocity drops from 2.15 km/s down to an average of 1.70 km/s in an 18m thick interval, with a minimum velocity of 1.62 km/s in a 6 m interval. The resulting compressional wave velocity was used to estimate gas content in the sediments. Our results suggest that the low velocity layer is a 6-18 m thick zone containing a few percent of free gas in the pore space. The presence of the BSR coincides with a region of vertical uplift. Therefore, we suggest that gas at this BSR is formed by a dissociation of hydrates at the base of the hydrate stability zone due to uplift and subsequently a decrease in pressure.

A model of the instantaneous pressure-velocity relationships of the neonatal cerebral circulation.

PubMed

Panerai, R B; Coughtrey, H; Rennie, J M; Evans, D H

1993-11-01

The instantaneous relationship between arterial blood pressure (BP) and cerebral blood flow velocity (CBFV), measured with Doppler ultrasound in the anterior cerebral artery, is represented by a vascular waterfall model comprising vascular resistance, compliance, and critical closing pressure. One min recordings obtained from 61 low birth weight newborns were fitted to the model using a least-squares procedures with correction for the time delay between the BP and CBFV signals. A sensitivity analysis was performed to study the effects of low-pass filtering (LPF), cutoff frequency, and noise on the estimated parameters of the model. Results indicate excellent fitting of the model (F-test, p < 0.0001) when the BP and CBFV signals are LPF at 7.5 Hz. Reconstructed CBFV waveforms using the BP signal and the model parameters have a mean correlation coefficient of 0.94 with the measured flow velocity tracing (N = 232 epochs). The model developed can be useful for interpreting clinical findings and as a framework for research into cerebral autoregulation.

The compression and expansion waves of the forward and backward flows: an in-vitro arterial model.

PubMed

Feng, J; Khir, A W

2008-05-01

Although the propagation of arterial waves of forward flows has been studied before, that of backward flows has not been thoroughly investigated. The aim of this research is to investigate the propagation of the compression and expansion waves of backward flows in terms of wave speed and dissipation, in flexible tubes. The aim is also to compare the propagation of these waves with those of forward flows. A piston pump generated a flow waveform in the shape of approximately half-sinusoid, in flexible tubes (12 mm and 16 mm diameter). The pump produced flow in either the forward or the backward direction by moving the piston forward, in a 'pushing action' or backward, in a 'pulling action', using a graphite brushes d.c. motor. Pressure and flow were measured at intervals of 5 cm along each tube and wave speed was determined using the PU-loop method. The simultaneous measurements of diameter were also taken at the same position of the pressure and flow in the 16 mm tube. Wave intensity analysis was used to determine the magnitude of the pressure and velocity waveforms and wave intensity in the forward and backward directions. Under the same initial experimental conditions, wave speed was higher during the pulling action (backward flow) than during the pushing action (forward flow). The amplitudes of pressure and velocity in the pulling action were significantly higher than those in the pushing action. The tube diameter was approximately 20 per cent smaller in the pulling action than in the pushing action in the 16 mm tube. The compression and expansion waves resulting from the pushing and pulling actions dissipated exponentially along the travelling distance, and their dissipation was greater in the smaller than in the larger tubes. Local wave speed in flexible tubes is flow direction- and wave nature-dependent and is greater with expansion than with compression waves. Wave dissipation has an inverse relationship with the vessel diameter, and dissipation of the expansion wave of the pulling action was greater than that of the pushing action.

Upper Mantle Velocity Structure beneath the Northeastern Philippine Sea Constrained by Waveform Modeling of P Triplicated Phases

NASA Astrophysics Data System (ADS)

Cho, S.; Rhie, J.; Lee, S. H.; Kim, S.; Kang, T. S.

2017-12-01

A study on the detailed velocity structures of the stagnant Pacific slab is important to understand the complex processes happening in the upper mantle. Although waveform modeling of P triplicated phases can reveal the detailed velocity structures especially for the discontinuities, the regions where the method can be applied are limited due to uneven distribution of earthquakes and stations. In this study, we used waveforms generated by two deep earthquakes near Izu-Bonin Trench and recorded by stations in South Korea. These event-station pairs are appropriate to study the upper mantle structures beneath the northeastern Philippine Sea, where no previous results by triplicated waveform modeling have been reported. In this region, the subducting Pacific slab seems to hit the 660 km discontinuity and become stagnant. We applied the reflectivity method to calculate waveforms and found the best fitting model by trial-and-error and manual inspection. In general, our best model is similar to M3.11, which is widely accepted 1D model for the regions where the stagnant slab exists and the 660 km discontinuity is depressed by the slab. The most noticeable feature of our model is that P wave velocities of inside and above the slab are considerably higher and lower than ones for M3.11, respectively. This specific velocity model is necessary to explain arrivals of two distinct phases identified in observed waveforms; one refracts inside the slab and the other reflects on the upper boundary of the slab. To understand the cause of the differences between our model and M3.11, further studies including thermal and mechanical modelling of the slab in this region will be recommended.

Pacific slab beneath northeast China revealed by regional and teleseismic waveform modeling

NASA Astrophysics Data System (ADS)

WANG, X.; Chen, Q. F.; Wei, S.

2015-12-01

Accurate velocity and geometry of the slab is essential for better understanding of the thermal, chemical structure of the mantle earth, as well as geodynamics. Recent tomography studies show similar morphology of the subducting Pacific slab beneath northeast China, which was stagnant in the mantle transition zone with thickness of more than 200km and an average velocity perturbation of ~1.5% [Fukao and Obayashi, 2013]. Meanwhile, waveform-modeling studies reveal that the Pacific slab beneath Japan and Kuril Island has velocity perturbation up to 5% and thickness up to 90km [Chen et al., 2007; Zhan et al., 2014]. These discrepancies are probably caused by the smoothing and limited data coverage in the tomographic inversions. Here we adopted 1D and 2D waveform modeling methods to study the fine structure of Pacific slab beneath northeast China using dense regional permanent and temporary broadband seismic records. The residual S- and P-wave travel time, difference between data and 1D synthetics, shows significant difference between the eastern and western stations. S-wave travel time residuals indicate 5-10s earlier arrivals for stations whose ray path lies within the slab, compared with those out of the slab. Teleseimic waveforms were used to rule out the major contribution of the possible low velocity structure above 200km. Furthermore, we use 2D finite-difference waveform modeling to confirm the velocity perturbation and geometry of the slab. Our result shows that the velocity perturbation in the slab is significantly higher than those reported in travel-time tomography studies. ReferencesChen, M., J. Tromp, D. Helmberger, and H. Kanamori (2007), Waveform modeling of the slab beneath Japan, J. Geophys. Res.-Solid Earth, 112(B2), 19, doi:10.1029/2006jb004394.Fukao, Y., and M. Obayashi (2013), Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity, J. Geophys. Res.-Solid Earth, 118(11), 5920-5938, doi:10.1002/2013jb010466.Zhan, Z. W., D. V. Helmberger, and D. Z. Li (2014), Imaging subducted slab structure beneath the Sea of Okhotsk with teleseismic waveforms, Phys. Earth Planet. Inter., 232, 30-35, doi:10.1016/j.pepi.2014.03.008.

Non-Newtonian blood flow dynamics in a right internal carotid artery with a saccular aneurysm

NASA Astrophysics Data System (ADS)

Valencia, Alvaro; Zarate, Alvaro; Galvez, Marcelo; Badilla, Lautaro

2006-02-01

Flow dynamics plays an important role in the pathogenesis and treatment of cerebral aneurysms. The temporal and spatial variations of wall shear stress in the aneurysm are hypothesized to be correlated with its growth and rupture. In addition, the assessment of the velocity field in the aneurysm dome and neck is important for the correct placement of endovascular coils. This work describes the flow dynamics in a patient-specific model of carotid artery with a saccular aneurysm under Newtonian and non-Newtonian fluid assumptions. The model was obtained from three-dimensional rotational angiography image data and blood flow dynamics was studied under physiologically representative waveform of inflow. The three-dimensional continuity and momentum equations for incompressible and unsteady laminar flow were solved with a commercial software using non-structured fine grid with 283 115 tetrahedral elements. The intra-aneurysmal flow shows complex vortex structure that change during one pulsatile cycle. The effect of the non-Newtonian properties of blood on the wall shear stress was important only in the arterial regions with high velocity gradients, on the aneurysmal wall the predictions with the Newtonian and non-Newtonian blood models were similar.

Nonlinear 1D and 2D waveform inversions of SS precursors and their applications in mantle seismic imaging

NASA Astrophysics Data System (ADS)

Dokht, R.; Gu, Y. J.; Sacchi, M. D.

2016-12-01

Seismic velocities and the topography of mantle discontinuities are crucial for the understanding of mantle structure, dynamics and mineralogy. While these two observables are closely linked, the vast majority of high-resolution seismic images are retrieved under the assumption of horizontally stratified mantle interfaces. This conventional correction-based process could lead to considerable errors due to the inherent trade-off between velocity and discontinuity depth. In this study, we introduce a nonlinear joint waveform inversion method that simultaneously recovers discontinuity depths and seismic velocities using the waveforms of SS precursors. Our target region is the upper mantle and transition zone beneath Northeast Asia. In this region, the inversion outcomes clearly delineate a westward dipping high-velocity structure in association with the subducting Pacific plate. Above the flat part of the slab west of the Japan sea, our results show a shear wave velocity reduction of 1.5% in the upper mantle and 10-15 km depression of the 410 km discontinuity beneath the Changbaishan volcanic field. We also identify the maximum correlation between shear velocity and transition zone thickness at an approximate slab dip of 30 degrees, which is consistent with previously reported values in this region.To validate the results of the 1D waveform inversion of SS precursors, we discretize the mantle beneath the study region and conduct a 2D waveform tomographic survey using the same nonlinear approach. The problem is simplified by adopting the discontinuity depths from the 1D inversion and solving only for perturbations in shear velocities. The resulting models obtained from the 1D and 2D approaches are self-consistent. Low-velocities beneath the Changbai intraplate volcano likely persist to a depth of 500 km. Collectively, our seismic observations suggest that the active volcanoes in eastern China may be fueled by a hot thermal anomaly originating from the mantle transition zone.

Evaluation of third trimester uterine artery flow velocity indices in relationship to perinatal complications.

PubMed

Ghosh, G; Breborowicz, A; Brazert, M; Maczkiewicz, M; Kobelski, M; Dubiel, M; Gudmundsson, S

2006-09-01

Uterine artery Doppler is becoming a routine part of pregnancy surveillance in high-risk pregnancies. Which blood flow velocity waveform index to measure is debated and the 'notch' in early diastole is not widely accepted, as it is a subjective measure. The aim of the present study was to evaluate the different indices in the prediction of adverse outcome of pregnancies suspected for intrauterine fetal growth restriction (IUGR). Uterine artery blood flow was recorded in 217 pregnancies admitted for Doppler ultrasound surveillance due to suspected IUGR. The median gestational age at examination was 38 weeks (range 25-42 weeks). Only cases having bilateral uterine artery notching were included in the evaluation. The uterine artery Doppler spectrum was analyzed for different indices, including evaluation of notch and end-diastolic velocities. Umbilical artery Doppler velocimetry was also performed. The outcome variables chosen were: a small-for-gestational-age (SGA) newborn, preterm birth, and abdominal delivery. ROC-curve calculations were used to compare the different indices. The uterine artery blood velocity pulsatility index (PI) and resistance indices (RI) were the best predictors of adverse outcome of pregnancy. Apart from premature birth, the systolic/end-diastolic ratio was less predictive of adverse outcome. The indices including only diastolic blood velocities were the least predictive of adverse outcome. The group with notch velocity above end-diastolic velocity was compared with those having notch velocity below the end-diastolic velocity. No difference in outcome was seen between the two groups. RI and PI as measures of third trimester utero-placental vascular impedance are the best predictors of adverse outcome of IUGR-suspected pregnancies.

Cardiac surgery during pregnancy: continuous fetal monitoring using umbilical artery Doppler flow velocity indices.

PubMed

Mishra, Manisha; Sawhney, Ravindra; Kumar, Anil; Bapna, Kumar Ramesh; Kohli, Vijay; Wasir, Harpreet; Trehan, Naresh

2014-01-01

The fetal death rate associated with cardiac surgery with cardiopulmonary bypass (CPB) is as high as 9.5-29%. We report continuous monitoring of fetal heart rate and umbilical artery flow-velocity waveforms by transvaginal ultrasonography and their analyses in relation to events of the CPB in two cases in second trimester of pregnancy undergoing mitral valve replacement. Our findings suggest that the transition of circulation from corporeal to extracorporeal is the most important event during surgery; the associated decrease in mean arterial pressure (MAP) at this stage potentially has deleterious effects on the fetus, which get aggravated with the use of vasopressors. We suggest careful management of CPB at this stage, which include partial controlled CPB at initiation and gradual transition to full CPB; this strategy maintains high MAP and avoids the use of vasopressors. Maternal and fetal monitoring can timely recognize the potential problems and provide window for the required treatment.

Two-dimensional model of vocal fold vibration for sound synthesis of voice and soprano singing

NASA Astrophysics Data System (ADS)

Adachi, Seiji; Yu, Jason

2005-05-01

Voiced sounds were simulated with a computer model of the vocal fold composed of a single mass vibrating both parallel and perpendicular to the airflow. Similarities with the two-mass model are found in the amplitudes of the glottal area and the glottal volume flow velocity, the variation in the volume flow waveform with the vocal tract shape, and the dependence of the oscillation amplitude upon the average opening area of the glottis, among other similar features. A few dissimilarities are also found in the more symmetric glottal and volume flow waveforms in the rising and falling phases. The major improvement of the present model over the two-mass model is that it yields a smooth transition between oscillations with an inductive load and a capacitive load of the vocal tract with no sudden jumps in the vibration frequency. Self-excitation is possible both below and above the first formant frequency of the vocal tract. By taking advantage of the wider continuous frequency range, the two-dimensional model can successfully be applied to the sound synthesis of a high-pitched soprano singing, where the fundamental frequency sometimes exceeds the first formant frequency. .

Application of Carbonate Reservoir using waveform inversion and reverse-time migration methods

NASA Astrophysics Data System (ADS)

Kim, W.; Kim, H.; Min, D.; Keehm, Y.

2011-12-01

Recent exploration targets of oil and gas resources are deeper and more complicated subsurface structures, and carbonate reservoirs have become one of the attractive and challenging targets in seismic exploration. To increase the rate of success in oil and gas exploration, it is required to delineate detailed subsurface structures. Accordingly, migration method is more important factor in seismic data processing for the delineation. Seismic migration method has a long history, and there have been developed lots of migration techniques. Among them, reverse-time migration is promising, because it can provide reliable images for the complicated model even in the case of significant velocity contrasts in the model. The reliability of seismic migration images is dependent on the subsurface velocity models, which can be extracted in several ways. These days, geophysicists try to obtain velocity models through seismic full waveform inversion. Since Lailly (1983) and Tarantola (1984) proposed that the adjoint state of wave equations can be used in waveform inversion, the back-propagation techniques used in reverse-time migration have been used in waveform inversion, which accelerated the development of waveform inversion. In this study, we applied acoustic waveform inversion and reverse-time migration methods to carbonate reservoir models with various reservoir thicknesses to examine the feasibility of the methods in delineating carbonate reservoir models. We first extracted subsurface material properties from acoustic waveform inversion, and then applied reverse-time migration using the inverted velocities as a background model. The waveform inversion in this study used back-propagation technique, and conjugate gradient method was used in optimization. The inversion was performed using the frequency-selection strategy. Finally waveform inversion results showed that carbonate reservoir models are clearly inverted by waveform inversion and migration images based on the inversion results are quite reliable. Different thicknesses of reservoir models were also described and the results revealed that the lower boundary of the reservoir was not delineated because of energy loss. From these results, it was noted that carbonate reservoirs can be properly imaged and interpreted by waveform inversion and reverse-time migration methods. This work was supported by the Energy Resources R&D program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 2009201030001A, No. 2010T100200133) and the Brain Korea 21 project of Energy System Engineering.

Imaging Crustal Structure with Waveform and HV Ratio of Body-wave Receiver Function

NASA Astrophysics Data System (ADS)

Chong, J.; Chu, R.; Ni, S.; Meng, Q.; Guo, A.

2017-12-01

It is known that receiver function has less constraint on the absolute velocity, and joint inversion of receiver function and surface wave dispersion has been widely applied to reduce the non-uniqueness of velocity and interface depth. However, some studies indicate that the receiver function itself is capable for determining the absolute shear wave velocity. In this study, we propose to measure the receiver function HV ratio which takes advantage of the amplitude information of the radial and vertical receiver functions to constrain the shear-wave velocity. Numerical analysis indicates that the receiver function HV ratio is sensitive to the average shear wave velocity in the depth range it samples, and can help to reduce the non-uniqueness of receiver function waveform inversion. A joint inversion scheme has been developed, and both synthetic tests and real data application proved the feasibility of the joint inversion. The method has been applied to the dense seismic array of ChinArray program in SE Tibet during the time period from August 2011 to August 2012 in SE Tibet (ChinArray-Himalaya, 2011). The measurements of receiver function HV ratio reveals the lateral variation of the tectonics in of the study region. And main features of the velocity structure imagined by the new joint inversion method are consistent with previous studies. KEYWORDS: receiver function HV ratio, receiver function waveform inversion, crustal structure ReferenceChinArray-Himalaya. 2011. China Seismic Array waveform data of Himalaya Project. Institute of Geophysics, China Earthquake Administration. doi:10.12001/ChinArray.Data. Himalaya. Jiajun Chong, Risheng Chu*, Sidao Ni, Qingjun Meng, Aizhi Guo, 2017. Receiver Function HV Ratio, a New Measurement for Reducing Non-uniqueness of Receiver Function Waveform Inversion. (under revision)

Cardiac-driven Pulsatile Motion of Intracranial Cerebrospinal Fluid Visualized Based on a Correlation Mapping Technique.

PubMed

Yatsushiro, Satoshi; Sunohara, Saeko; Hayashi, Naokazu; Hirayama, Akihiro; Matsumae, Mitsunori; Atsumi, Hideki; Kuroda, Kagayaki

2018-04-10

A correlation mapping technique delineating delay time and maximum correlation for characterizing pulsatile cerebrospinal fluid (CSF) propagation was proposed. After proofing its technical concept, this technique was applied to healthy volunteers and idiopathic normal pressure hydrocephalus (iNPH) patients. A time-resolved three dimensional-phase contrast (3D-PC) sampled the cardiac-driven CSF velocity at 32 temporal points per cardiac period at each spatial location using retrospective cardiac gating. The proposed technique visualized distributions of propagation delay and correlation coefficient of the PC-based CSF velocity waveform with reference to a waveform at a particular point in the CSF space. The delay time was obtained as the amount of time-shift, giving the maximum correlation for the velocity waveform at an arbitrary location with that at the reference location. The validity and accuracy of the technique were confirmed in a flow phantom equipped with a cardiovascular pump. The technique was then applied to evaluate the intracranial CSF motions in young, healthy (N = 13), and elderly, healthy (N = 13) volunteers and iNPH patients (N = 13). The phantom study demonstrated that root mean square error of the delay time was 2.27%, which was less than the temporal resolution of PC measurement used in this study (3.13% of a cardiac cycle). The human studies showed a significant difference (P < 0.01) in the mean correlation coefficient between the young, healthy group and the other two groups. A significant difference (P < 0.05) was also recognized in standard deviation of the correlation coefficients in intracranial CSF space among all groups. The result suggests that the CSF space compliance of iNPH patients was lower than that of healthy volunteers. The correlation mapping technique allowed us to visualize pulsatile CSF velocity wave propagations as still images. The technique may help to classify diseases related to CSF dynamics, such as iNPH.

Characteristics of time-varying intracranial pressure on blood flow through cerebral artery: A fluid-structure interaction approach.

PubMed

Syed, Hasson; Unnikrishnan, Vinu U; Olcmen, Semih

2016-02-01

Elevated intracranial pressure is a major contributor to morbidity and mortality in severe head injuries. Wall shear stresses in the artery can be affected by increased intracranial pressures and may lead to the formation of cerebral aneurysms. Earlier research on cerebral arteries and aneurysms involves using constant mean intracranial pressure values. Recent advancements in intracranial pressure monitoring techniques have led to measurement of the intracranial pressure waveform. By incorporating a time-varying intracranial pressure waveform in place of constant intracranial pressures in the analysis of cerebral arteries helps in understanding their effects on arterial deformation and wall shear stress. To date, such a robust computational study on the effect of increasing intracranial pressures on the cerebral arterial wall has not been attempted to the best of our knowledge. In this work, fully coupled fluid-structure interaction simulations are carried out to investigate the effect of the variation in intracranial pressure waveforms on the cerebral arterial wall. Three different time-varying intracranial pressure waveforms and three constant intracranial pressure profiles acting on the cerebral arterial wall are analyzed and compared with specified inlet velocity and outlet pressure conditions. It has been found that the arterial wall experiences deformation depending on the time-varying intracranial pressure waveforms, while the wall shear stress changes at peak systole for all the intracranial pressure profiles. © IMechE 2015.

3D analysis of vortical structures in an abdominal aortic aneurysm by stereoscopic PIV

NASA Astrophysics Data System (ADS)

Deplano, Valérie; Guivier-Curien, Carine; Bertrand, Eric

2016-11-01

The present work presents an experimental in vitro three-dimensional analysis of the flow dynamics in an abdominal aortic aneurysm (AAA) through stereoscopic particle image velocimetry (SPIV) measurements. The experimental set-up mimics the pathophysiological context involving a shear thinning blood analogue fluid, compliant AAA and aorto-iliac bifurcation walls and controlled inlet and outlet flow rate and pressure waveforms as well as working fluid temperature. SPIV was carefully calibrated and conducted to assess the three velocity components in the AAA volume. For the first time in the literature, the 3D vortex ring genesis, propagation, and vanishing in the AAA bulge are experimentally described and quantified. In comparison with classical 2-component PIV measurements (2C PIV), the third component of the velocity vector was shown to be of importance in such a geometry, especially, during the deceleration phase of the flow rate. The 3D velocity magnitude reached up more than 20 % of the 2D one showing that 2C PIV are definitively not accurate enough to provide a complete description of flow behaviour in an AAA. In addition to potential clinical implications of a full 3D vortex ring description in AAA evolution, the 3D in vitro experimental quantification of the flow dynamics carried out in the present study offers an interesting tool for the validation of fluid-structure interaction numerical studies dealing with AAA.

Local pulse wave velocity estimated from small vibrations measured ultrasonically at multiple points on the arterial wall

NASA Astrophysics Data System (ADS)

Ito, Mika; Arakawa, Mototaka; Kanai, Hiroshi

2018-07-01

Pulse wave velocity (PWV) is used as a diagnostic criterion for arteriosclerosis, a major cause of heart disease and cerebrovascular disease. However, there are several problems with conventional PWV measurement techniques. One is that a pulse wave is assumed to only have an incident component propagating at a constant speed from the heart to the femoral artery, and another is that PWV is only determined from a characteristic time such as the rise time of the blood pressure waveform. In this study, we noninvasively measured the velocity waveform of small vibrations at multiple points on the carotid arterial wall using ultrasound. Local PWV was determined by analyzing the phase component of the velocity waveform by the least squares method. This method allowed measurement of the time change of the PWV at approximately the arrival time of the pulse wave, which discriminates the period when the reflected component is not contaminated.

NEW APPLICATIONS IN THE INVERSION OF ACOUSTIC FULL WAVEFORM LOGS - RELATING MODE EXCITATION TO LITHOLOGY.

USGS Publications Warehouse

Paillet, Frederick L.; Cheng, C.H.; Meredith, J.A.

1987-01-01

Existing techniques for the quantitative interpretation of waveform data have been based on one of two fundamental approaches: (1) simultaneous identification of compressional and shear velocities; and (2) least-squares minimization of the difference between experimental waveforms and synthetic seismograms. Techniques based on the first approach do not always work, and those based on the second seem too numerically cumbersome for routine application during data processing. An alternative approach is tested here, in which synthetic waveforms are used to predict relative mode excitation in the composite waveform. Synthetic waveforms are generated for a series of lithologies ranging from hard, crystalline rocks (Vp equals 6. 0 km/sec. and Poisson's ratio equals 0. 20) to soft, argillaceous sediments (Vp equals 1. 8 km/sec. and Poisson's ratio equals 0. 40). The series of waveforms illustrates a continuous change within this range of rock properties. Mode energy within characteristic velocity windows is computed for each of the modes in the set of synthetic waveforms. The results indicate that there is a consistent variation in mode excitation in lithology space that can be used to construct a unique relationship between relative mode excitation and lithology.

Assessing waveform predictions of recent three-dimensional velocity models of the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Bao, Xueyang; Shen, Yang

2016-04-01

Accurate velocity models are essential for both the determination of earthquake locations and source moments and the interpretation of Earth structures. With the increasing number of three-dimensional velocity models, it has become necessary to assess the models for accuracy in predicting seismic observations. Six models of the crustal and uppermost mantle structures in Tibet and surrounding regions are investigated in this study. Regional Rayleigh and Pn (or Pnl) waveforms from two ground truth events, including one nuclear explosion and one natural earthquake located in the study area, are simulated by using a three-dimensional finite-difference method. Synthetics are compared to observed waveforms in multiple period bands of 20-75 s for Rayleigh waves and 1-20 s for Pn/Pnl waves. The models are evaluated based on the phase delays and cross-correlation coefficients between synthetic and observed waveforms. A model generated from full-wave ambient noise tomography best predicts Rayleigh waves throughout the data set, as well as Pn/Pnl waves traveling from the Tarim Basin to the stations located in central Tibet. In general, the models constructed from P wave tomography are not well suited to predict Rayleigh waves, and vice versa. Possible causes of the differences between observed and synthetic waveforms, and frequency-dependent variations of the "best matching" models with the smallest prediction errors are discussed. This study suggests that simultaneous prediction for body and surface waves requires an integrated velocity model constructed with multiple seismic waveforms and consideration of other important properties, such as anisotropy.

Method to produce American Thoracic Society flow-time waveforms using a mechanical pump.

PubMed

Hankinson, J L; Reynolds, J S; Das, M K; Viola, J O

1997-03-01

The American Thoracic Society (ATS) recently adopted a new set of 26 standard flow-time waveforms for use in testing both diagnostic and monitoring devices. Some of these waveforms have a higher frequency content than present in the ATS-24 standard volume-time waveforms, which, when produced by a mechanical pump, may result in a pump flow output that is less than the desired flow due to gas compression losses within the pump. To investigate the effects of gas compression, a mechanical pump was used to generate the necessary flows to test mini-Wright and Assess peak expiratory flow (PEF) meters. Flow output from the pump was measured by two different independent methods, a pneumotachometer and a method based on piston displacement and pressure measured within the pump. Measuring output flow based on piston displacement and pressure has been validated using a pneumotachometer and mini-Wright PEF meter, and found to accurately measure pump output. This method introduces less resistance (lower back-pressure) and dead space volume than using a pneumotachometer in series with the meter under test. Pump output flow was found to be lower than the desired flow both with the mini-Wright and Assess meters (for waveform No. 26, PEFs 7.1 and 10.9% lower, respectively). To compensate for losses due to gas compression, we have developed a method of deriving new input waveforms, which, when used to drive a commercially available mechanical pump, accurately and reliably produces the 26 ATS flow-time waveforms, even those with the fastest rise-times.

Real-Time seismic waveforms monitoring with BeiDou Navigation Satellite System (BDS) observations for the 2015 Mw 7.8 Nepal earthquake

NASA Astrophysics Data System (ADS)

Geng, T.

2015-12-01

Nowadays more and more high-rate Global Navigation Satellite Systems (GNSS) data become available in real time, which provide more opportunities to monitor the seismic waveforms. China's GNSS, BeiDou Navigation Satellite System (BDS), has already satisfied the requirement of stand-alone precise positioning in Asia-Pacific region with 14 in-orbit satellites, which promisingly suggests that BDS could be applied to the high-precision earthquake monitoring as GPS. In the present paper, real-time monitoring of seismic waveforms using BDS measurements is assessed. We investigate a so-called "variometric" approach to measure real-time seismic waveforms with high-rate BDS observations. This approach is based on time difference technique and standard broadcast products which are routinely available in real time. The 1HZ BDS data recorded by Beidou Experimental Tracking Stations (BETS) during the 2015 Mw 7.8 Nepal earthquake is analyzed. The results indicate that the accuracies of velocity estimation from BDS are 2-3 mm/s in horizontal components and 8-9 mm/s in vertical component, respectively, which are consistent with GPS. The seismic velocity waveforms during earthquake show good agreement between BDS and GPS. Moreover, the displacement waveforms is reconstructed by an integration of velocity time series with trend removal. The displacement waveforms with the accuracy of 1-2 cm are derived by comparing with post-processing GPS precise point positioning (PPP).

PKP Waveform Complexity and Its Implications to Fine Structure Near the Edge of African Large Low Shear Velocity Province

NASA Astrophysics Data System (ADS)

Song, Teh-Ru Alex; Tanaka, Satoru; Takeuchi, Nozomu

2010-05-01

P wave traveling through the Earth's core typically includes three distinct phases, PKPdf (or PKIKP), PKPbc and PKPab and these waves have been frequently analyzed to study the structure of the outer-core and inner-core. It is well known that PKPab waveform suffers a 90-degree phase shift when encountering an internal acoustics in the outer-core and it is theoretically equivalent to Hilbert-transformed PKPbc (or PKPdf) waveform. Here, we report a dataset from an intermediate-depth earthquake in Vanuatu Islands recorded by a PASSCAL broadband array in Cameroon, West Africa. Two anomalous features stand out in this record section. First, in the period of a few seconds and longer, most PKPab waveforms recorded by this array are anomalous in a way that they do not display a 90-degree phase shift that is observed in other stations in Europe. Secondly, in the high frequency band of 0.5 Hz to 2 Hz, two large arrivals separated by about 3.4 seconds are observed in the time window of PKPab phase and they are often absent in the time window of PKPdf and PKPbc phases. In addition, the second arrival seems suffer some degree of phase shift relative to the first arrival. We examine several other record sections from nearby events in Tonga and they do not show such an anomalous feature, suggesting that receiver structures are probably not the cause of this observation. Note that the take-off angle of PKPab is typically 9-12 degrees shallower than that of PKPdf and PKPbc and it is possible that near-source scattering from the slab may account for such an anomalous feature. We make Hilbert transform of P waveforms recorded at shorter range of less than 90 degrees and compare them with these anomalous PKPab waveforms. However, these Hilbert-transformed P wave show a clear 90-degree phase shift relative to PKPdf and PKPbc and they are different from PKPab waveforms, despite a difference in take-off angles of less than 5 degrees in some cases. It appears that near-source scatterings and receiver-side structure do not play a predominant role in generating these anomalous PKPab waveforms. We then look into structural anomaly near the core-mantle-boundary (CMB) since PKPab grazes the CMB at a very shallow angle and it can effectively interact with it and possibly produce anomalous PKPab waveforms. We first explore 1-D model space by introducing velocity anomaly directly above the CMB, with a velocity perturbation up to a few tens of percents in S wave velocity and P wave velocity. We calculate synthetics up to 2 Hz by Direct Solution Method (DSM) and Reflectivity Method to examine waveform anomaly at long period band (0.01-0.2 Hz) as well as short-period band (0.5-2 Hz). Our preliminary result indicates that the model with a thin (~ 15 km) ultra-low velocity zone (ULVZ, 30% reduction in P wave and S wave velocity) is capable of reproducing characteristics of these anomalous PKPab waveforms at both frequency bands. The pierce points of PKPab in the source side at CMB are near the southeast Indian Ocean where S wave velocity is only slightly faster than PREM. On the other hand, the pierce points in the receiver side are at the eastern edge of the African Large Low Shear Velocity Province (LLSVP). One interesting feature of our ULVZ model is that dlnVs/dlnVp is about 1, which is different from most ULVZ models where dlnVs/dlnVp is about 3.

4D Magnetic Resonance Velocimetry in a 3D printed brain aneurysm

NASA Astrophysics Data System (ADS)

Amili, Omid; Schiavazzi, Daniele; Coletti, Filippo

2016-11-01

Cerebral aneurysms are of great clinical importance. It is believed that hemodynamics play a critical role in the development, growth, and rupture of brain arteries with such condition. The flow structure in the aneurysm sac is complex, unsteady, and three-dimensional. Therefore the time-resolved measurement of the three-dimensional three-component velocity field is crucial to predict the clinical outcome. In this study magnetic resonance velocimetry is used to assess the fluid dynamics inside a 3D printed model of a giant intracranial aneurysm. We reach sub-millimeter resolution while resolving sixteen instances within the cardiac cycle. The physiological flow waveform is imposed using an in-house built pump in a flow circuit where the cardiovascular impedance is matched. The flow evolution over time is reconstructed in detail. The complex flow structure is characterized by vortical and helical motions that reside in the aneurysm for most part of the cycle. The 4D pressured distribution is also reconstructed from the velocity field. The present case study was used in a previous CFD challenge, therefore these results may provide useful experimental comparison for simulations performed by other research groups.

Control of end-tidal PCO2 reduces middle cerebral artery blood velocity variability: implications for physiological neuroimaging.

PubMed

Harris, Ashley D; Ide, Kojiro; Poulin, Marc J; Frayne, Richard

2006-02-15

Breath-by-breath variability of the end-tidal partial pressure of CO2 (Pet(CO2)) has been shown to be associated with cerebral blood flow (CBF) fluctuations. These fluctuations can impact neuroimaging techniques that depend on cerebrovascular blood flow. We hypothesized that controlling Pet(CO2) would reduce CBF variability. Dynamic end-tidal forcing was used to control Pet(CO2) at 1.5 mm Hg above the resting level and to hold the end-tidal partial pressure of oxygen (Pet(O2)) at the resting level. Peak blood velocity in the middle cerebral artery (MCA) was measured by transcranial Doppler ultrasound (TCD) as an index of CBF. Blood velocity parameters and timing features were determined on each waveform and the variance of these parameters was compared between Normal (air breathing) and Forcing (end-tidal gas control) sessions. The variability of all velocity parameters was significantly reduced in the Forcing session. In particular, the variability of the average velocity over the cardiac cycle was decreased by 18.2% (P < 0.001). For the most part, the variability of the timing parameters was unchanged. Thus, we conclude that controlling Pet(CO2) is effective in reducing CBF variability, which would have important implications for physiologic neuroimaging.

The OSCAR experiment: using full-waveform inversion in the analysis of young oceanic crust

NASA Astrophysics Data System (ADS)

Silverton, Akela; Morgan, Joanna; Wilson, Dean; Hobbs, Richard

2017-04-01

The OSCAR experiment aims to derive an integrated model to better explain the effects of heat loss and alteration by hydrothermal fluids, associated with the cooling of young oceanic crust at an axial ridge. High-resolution seismic imaging of the sediments and basaltic basement can be used to map fluid flow pathways between the oceanic crust and the surrounding ocean. To obtain these high-resolution images, we undertake full-waveform inversion (FWI), an advanced seismic imaging technique capable of resolving velocity heterogeneities at a wide range of length scales, from background trends to fine-scale geological/crustal detail, in a fully data-driven automated manner. This technology is widely used within the petroleum sector due to its potential to obtain high-resolution P-wave velocity models that lead to improvements in migrated seismic images of the subsurface. Here, we use the P-wave velocity model obtained from travel-time tomography as the starting model in the application of acoustic, time-domain FWI to a multichannel streamer field dataset acquired in the east Pacific along a profile between the Costa Rica spreading centre and the Ocean Drilling Program (ODP) borehole 504B, where the crust is approximately six million years old. FWI iteratively improves the velocity model by minimizing the misfit between the predicted data and the field data. It seeks to find a high-fidelity velocity model that is capable of matching individual seismic waveforms of the original raw field dataset, with an initial focus on matching the low-frequency components of the early arriving energy. Quality assurance methods adopted during the inversion ensure convergence in the direction of the global minimum. We demonstrate that FWI is able to recover fine-scale, high-resolution velocity heterogeneities within the young oceanic crust along the profile. The highly resolved FWI velocity model is useful in the identification of the layer 2A/2B interface and low-velocity layers that may represent zones of enhanced fluid movement. With FWI we are able to better explain the non-linear changes in velocity as the crust evolves with distance from the spreading centre and image the effects of any alteration by hydrothermal fluids. This model provides valuable insight and new constraints on the thermal processes involved, at spreading centres, setting a new benchmark for integrated multi-physics experiments at similar ocean ridge systems. This research is part of a major, interdisciplinary NERC-funded collaboration entitled: Oceanographic and Seismic Characterisation of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

Full-waveform Inversion of Crosshole GPR Data Collected in Strongly Heterogeneous Chalk: Challenges and Pitfalls

NASA Astrophysics Data System (ADS)

Keskinen, Johanna; Looms, Majken C.; Nielsen, Lars; Klotzsche, Anja; van der Kruk, Jan; Moreau, Julien; Stemmerik, Lars; Holliger, Klaus

2015-04-01

Chalk is an important reservoir rock for hydrocarbons and for groundwater resources for many major cities. Therefore, this rock type has been extensively investigated using both geological and geophysical methods. Many applications of crosshole GPR tomography rely on the ray approximation and corresponding inversions of first break traveltimes and/or maximum first-cycle amplitudes. Due to the inherent limitations associated with such approaches, the resulting models tend to be overly smooth and cannot adequately capture the small-scale heterogeneities. In contrast, the full-waveform inversion uses all the information contained in the data and is able to provide significantly improved images. Here, we apply full-waveform inversion to crosshole GPR data to image strong heterogeneity of the chalk related to changes in lithology and porosity. We have collected a crosshole tomography dataset in an old chalk quarry in Eastern Denmark. Based on core data (including plug samples and televiewer logging data) collected in our four ~15-m-deep boreholes and results from previous related studies, it is apparent that the studied chalk is strongly heterogeneous. The upper ~7 m consist of variable coarse-grained chalk layers with numerous flint nodules. The lower half of the studied section appears to be finer-grained and contains less flint. However, still significant porosity variations are also detected in the lower half. In general, the water-saturated (watertable depth ~2 m) chalk is characterized by high porosities, and thus low velocities and high attenuation, while the flint is essentially non-porous and has correspondingly high velocities and low attenuation. Together these characteristics form a strongly heterogeneous medium, which is challenging for the full-waveform inversion to recover. Here, we address the importance of (i) adequate starting models, both in terms of the dielectric permittivity and the electrical conductivity, (ii) the estimation of the source wavelet, (iii) and the effects of data sampling density when imaging this rock type. Moreover, we discuss the resolution of the bedding recovered by the full-waveform approach. Our results show that with proper estimates of the above-mentioned prior parameters, crosshole GPR full-waveform tomography provides high-resolution images capturing a high degree of variability that standard methods cannot resolve in chalk. This in turn makes crosshole full-waveform inversion a promising tool to support time-lapse flow modelling.

Towards seismic waveform inversion of long-offset Ocean-Bottom Seismic data for deep crustal imaging offshore Western Australia

NASA Astrophysics Data System (ADS)

Monnier, S.; Lumley, D. E.; Kamei, R.; Goncharov, A.; Shragge, J. C.

2016-12-01

Ocean Bottom Seismic datasets have become increasingly used in recent years to develop high-resolution, wavelength-scale P-wave velocity models of the lithosphere from waveform inversion, due to their recording of long-offset transmitted phases. New OBS surveys evolve towards novel acquisition geometries involving longer offsets (several hundreds of km), broader frequency content (1-100 Hz), while receiver sampling often remains sparse (several km). Therefore, it is critical to assess the effects of such geometries on the eventual success and resolution of waveform inversion velocity models. In this study, we investigate the feasibility of waveform inversion on the Bart 2D OBS profile acquired offshore Western Australia, to investigate regional crustal and Moho structures. The dataset features 14 broadband seismometers (0.01-100 Hz) from AuScope's national OBS fleet, offsets in excess of 280 km, and a sparse receiver sampling (18 km). We perform our analysis in four stages: (1) field data analysis, (2) 2D P-wave velocity model building, synthetic data (3) modelling, and (4) waveform inversion. Data exploration shows high-quality active-source signal down to 2Hz, and usable first arrivals to offsets greater than 100 km. The background velocity model is constructed by combining crustal and Moho information in continental reference models (e.g., AuSREM, AusMoho). These low-resolution studies suggest a crustal thickness of 20-25 km along our seismic line and constitute a starting point for synthetic modelling and inversion. We perform synthetic 2D time-domain modelling to: (1) evaluate the misfit between synthetic and field data within the usable frequency band (2-10 Hz); (2) validate our velocity model; and (3) observe the effects of sparse OBS interval on data quality. Finally, we apply 2D acoustic frequency-domain waveform inversion to the synthetic data to generate velocity model updates. The inverted model is compared to the reference model to investigate the improved crustal resolution and Moho boundary delineation that could be realized using waveform inversion, and to evaluate the effects of the acquisition parameters. The inversion strategies developed through the synthetic tests will help the subsequent inversion of sparse, long-offset OBS field data.

Toward Near Real-Time Tomography of the Upper Mantle

NASA Astrophysics Data System (ADS)

Debayle, E.; Dubuffet, F.

2014-12-01

We added a layer of automation to the Debayle and Ricard (2012)'s waveform modeling scheme for fundamental and higher mode surface waves in the period range 50-160s. We processed all the Rayleigh waveforms recorded on the LHZ channel by the virtual networks GSN_broadband, FDSN_all, and US_backbone between January 1996 and December 2013. Six millions of waveforms were obtained from IRIS DMC. We check that all the necessary information (instrument response, global CMT determination) is available and that each record includes a velocity window which encompasses the surface wave. Selected data must also have a signal-to-noise ratio greater than 3 in a range covering at least the periods between 50 and 100 s. About 3 millions of waveforms are selected (92% of the rejections are due to the signal to noise ratio criterion) and processed using Debayle and Ricard (2012)'s scheme, which allows the successful modeling of about 1.5 millions of waveforms. We complete this database with 60,000 waveforms recorded between 1976 and 1996 or after 1996 during various temporary experiments and with 161,730 Rayleigh waveforms analyzed at longer period, between 120 and 360 s. The whole data set is inverted using Debayle and Sambridge (2004)'s scheme to produce a 3D shear velocity model. A simple shell command "update_tomo" can then update our seismic model in an entirely automated way. Currently, this command checks from the CMT catalog what are the potential data available at the GSN_broadband, FDSN_all, and US_backbone virtual networks, uses web services to request these data from IRIS DMC and applies the processing chain described above to update our seismic model. We plan to update our seismic model on a regular basis in a near future, and to make it available on the web. Our most recent seismic model includes azimuthal anisotropy, achieves a lateral resolution of few hundred kilometers and a vertical resolution of a few tens of kilometers. The correlation with surface tectonics is very strong in the uppermost 200 km. Regions deeper than 400 km show no velocity contrasts larger than 1%, except for high velocity slabs which produce broad high velocity regions within the transition zone. The use of higher modes and long period surface waves allows us to extract the shear velocity structure down to about 1000 km depth.

Imaging Faults in Carbonate Reservoir using Full Waveform Inversion and Reverse Time Migration of Walkaway VSP Data

NASA Astrophysics Data System (ADS)

Takam Takougang, E. M.; Bouzidi, Y.

2016-12-01

Multi-offset Vertical Seismic Profile (walkaway VSP) data were collected in an oil field located in a shallow water environment dominated by carbonate rocks, offshore the United Arab Emirates. The purpose of the survey was to provide structural information of the reservoir, around and away from the borehole. Five parallel lines were collected using an air gun at 25 m shot interval and 4 m source depth. A typical recording tool with 20 receivers spaced every 15.1 m, and located in a deviated borehole with an angle varying between 0 and 24 degree from the vertical direction, was used to record the data. The recording tool was deployed at different depths for each line, from 521 m to 2742 m depth. Smaller offsets were used for shallow receivers and larger offsets for deeper receivers. The lines merged to form the input dataset for waveform tomography. The total length of the combined lines was 9 km, containing 1344 shots and 100 receivers in the borehole located half-way down. Acoustic full waveform inversion was applied in the frequency domain to derive a high resolution velocity model. The final velocity model derived after the inversion using the frequencies 5-40 Hz, showed good correlation with velocities estimated from vertical incidence VSP and sonic log, confirming the success of the inversion. The velocity model showed anomalous low values in areas that correlate with known location of hydrocarbon reservoir. Pre-stack depth Reverse time migration was then applied using the final velocity model from waveform inversion and the up-going wavefield from the input data. The final estimated source signature from waveform inversion was used as input source for reverse time migration. To save computational memory and time, every 3 shots were used during reverse time migration and the data were low-pass filtered to 30 Hz. Migration artifacts were attenuated using a second order derivative filter. The final migration image shows a good correlation with the waveform tomography velocity model, and highlights a complex network of faults in the reservoir, that could be useful in understanding fluid and hydrocarbon movements. This study shows that the combination of full waveform tomography and reverse time migration can provide high resolution images that can enhance interpretation and characterization of oil reservoirs.

Viterbi sparse spike detection and a compositional origin to ultralow-velocity zones

NASA Astrophysics Data System (ADS)

Brown, Samuel Paul

Accurate interpretation of seismic travel times and amplitudes in both the exploration and global scales is complicated by the band-limited nature of seismic data. We present a stochastic method, Viterbi sparse spike detection (VSSD), to reduce a seismic waveform into a most probable constituent spike train. Model waveforms are constructed from a set of candidate spike trains convolved with a source wavelet estimate. For each model waveform, a profile hidden Markov model (HMM) is constructed to represent the waveform as a stochastic generative model with a linear topology corresponding to a sequence of samples. The Viterbi algorithm is employed to simultaneously find the optimal nonlinear alignment between a model waveform and the seismic data, and to assign a score to each candidate spike train. The most probable travel times and amplitudes are inferred from the alignments of the highest scoring models. Our analyses show that the method can resolve closely spaced arrivals below traditional resolution limits and that travel time estimates are robust in the presence of random noise and source wavelet errors. We applied the VSSD method to constrain the elastic properties of a ultralow- velocity zone (ULVZ) at the core-mantle boundary beneath the Coral Sea. We analyzed vertical component short period ScP waveforms for 16 earthquakes occurring in the Tonga-Fiji trench recorded at the Alice Springs Array (ASAR) in central Australia. These waveforms show strong pre and postcursory seismic arrivals consistent with ULVZ layering. We used the VSSD method to measure differential travel-times and amplitudes of the post-cursor arrival ScSP and the precursor arrival SPcP relative to ScP. We compare our measurements to a database of approximately 340,000 synthetic seismograms finding that these data are best fit by a ULVZ model with an S-wave velocity reduction of 24%, a P-wave velocity reduction of 23%, a thickness of 8.5 km, and a density increase of 6%. We simultaneously constrain both P- and S-wave velocity reductions as a 1:1 ratio inside this ULVZ. This 1:1 ratio is not consistent with a partial melt origin to ULVZs. Rather, we demonstrate that a compositional origin is more likely.

Improved Pulse Wave Velocity Estimation Using an Arterial Tube-Load Model

PubMed Central

Gao, Mingwu; Zhang, Guanqun; Olivier, N. Bari; Mukkamala, Ramakrishna

2015-01-01

Pulse wave velocity (PWV) is the most important index of arterial stiffness. It is conventionally estimated by non-invasively measuring central and peripheral blood pressure (BP) and/or velocity (BV) waveforms and then detecting the foot-to-foot time delay between the waveforms wherein wave reflection is presumed absent. We developed techniques for improved estimation of PWV from the same waveforms. The techniques effectively estimate PWV from the entire waveforms, rather than just their feet, by mathematically eliminating the reflected wave via an arterial tube-load model. In this way, the techniques may be more robust to artifact while revealing the true PWV in absence of wave reflection. We applied the techniques to estimate aortic PWV from simultaneously and sequentially measured central and peripheral BP waveforms and simultaneously measured central BV and peripheral BP waveforms from 17 anesthetized animals during diverse interventions that perturbed BP widely. Since BP is the major acute determinant of aortic PWV, especially under anesthesia wherein vasomotor tone changes are minimal, we evaluated the techniques in terms of the ability of their PWV estimates to track the acute BP changes in each subject. Overall, the PWV estimates of the techniques tracked the BP changes better than those of the conventional technique (e.g., diastolic BP root-mean-squared-errors of 3.4 vs. 5.2 mmHg for the simultaneous BP waveforms and 7.0 vs. 12.2 mmHg for the BV and BP waveforms (p < 0.02)). With further testing, the arterial tube-load model-based PWV estimation techniques may afford more accurate arterial stiffness monitoring in hypertensive and other patients. PMID:24263016

Global and local waveform simulations using the VERCE platform

NASA Astrophysics Data System (ADS)

Garth, Thomas; Saleh, Rafiq; Spinuso, Alessandro; Gemund, Andre; Casarotti, Emanuele; Magnoni, Federica; Krischner, Lion; Igel, Heiner; Schlichtweg, Horst; Frank, Anton; Michelini, Alberto; Vilotte, Jean-Pierre; Rietbrock, Andreas

2017-04-01

In recent years the potential to increase resolution of seismic imaging by full waveform inversion has been demonstrated on a range of scales from basin to continental scales. These techniques rely on harnessing the computational power of large supercomputers, and running large parallel codes to simulate the seismic wave field in a three-dimensional geological setting. The VERCE platform is designed to make these full waveform techniques accessible to a far wider spectrum of the seismological community. The platform supports the two widely used spectral element simulation programs SPECFEM3D Cartesian, and SPECFEM3D globe, allowing users to run a wide range of simulations. In the SPECFEM3D Cartesian implementation the user can run waveform simulations on a range of pre-loaded meshes and velocity models for specific areas, or upload their own velocity model and mesh. In the new SPECFEM3D globe implementation, the user will be able to select from a number of continent scale model regions, or perform waveform simulations for the whole earth. Earthquake focal mechanisms can be downloaded within the platform, for example from the GCMT catalogue, or users can upload their own focal mechanism catalogue through the platform. The simulations can be run on a range of European supercomputers in the PRACE network. Once a job has been submitted and run through the platform, the simulated waveforms can be manipulated or downloaded for further analysis. The misfit between the simulated and recorded waveforms can then be calculated through the platform through three interoperable workflows, for raw-data access (FDSN) and caching, pre-processing and finally misfit. The last workflow makes use of the Pyflex analysis software. In addition, the VERCE platform can be used to produce animations of waveform propagation through the velocity model, and synthetic shakemaps. All these data-products are made discoverable and re-usable thanks to the VERCE data and metadata management layer. We demonstrate the functionality of the VERCE platform with two use cases, one using the pre-loaded velocity model and mesh for the Maule area of Chile using the SPECFEM3D Cartesian workflow, and one showing the output of a global simulation using the SPECFEM3D globe workflow. It is envisioned that this tool will allow a much greater range of seismologists to access these full waveform inversion tools, and aid full waveform tomographic and source inversion, synthetic shakemap production and other full waveform applications, in a wide range of tectonic settings.

Accoustic waveform logging--Advances in theory and application

USGS Publications Warehouse

Paillet, F.L.; Cheng, C.H.; Pennington , W.D.

1992-01-01

Full-waveform acoustic logging has made significant advances in both theory and application in recent years, and these advances have greatly increased the capability of log analysts to measure the physical properties of formations. Advances in theory provide the analytical tools required to understand the properties of measured seismic waves, and to relate those properties to such quantities as shear and compressional velocity and attenuation, and primary and fracture porosity and permeability of potential reservoir rocks. The theory demonstrates that all parts of recorded waveforms are related to various modes of propagation, even in the case of dipole and quadrupole source logging. However, the theory also indicates that these mode properties can be used to design velocity and attenuation picking schemes, and shows how source frequency spectra can be selected to optimize results in specific applications. Synthetic microseismogram computations are an effective tool in waveform interpretation theory; they demonstrate how shear arrival picks and mode attenuation can be used to compute shear velocity and intrinsic attenuation, and formation permeability for monopole, dipole and quadrupole sources. Array processing of multi-receiver data offers the opportunity to apply even more sophisticated analysis techniques. Synthetic microseismogram data is used to illustrate the application of the maximum-likelihood method, semblance cross-correlation, and Prony's method analysis techniques to determine seismic velocities and attenuations. The interpretation of acoustic waveform logs is illustrated by reviews of various practical applications, including synthetic seismogram generation, lithology determination, estimation of geomechanical properties in situ, permeability estimation, and design of hydraulic fracture operations.

2-D traveltime and waveform inversion for improved seismic imaging: Naga Thrust and Fold Belt, India

NASA Astrophysics Data System (ADS)

Jaiswal, Priyank; Zelt, Colin A.; Bally, Albert W.; Dasgupta, Rahul

2008-05-01

Exploration along the Naga Thrust and Fold Belt in the Assam province of Northeast India encounters geological as well as logistic challenges. Drilling for hydrocarbons, traditionally guided by surface manifestations of the Naga thrust fault, faces additional challenges in the northeast where the thrust fault gradually deepens leaving subtle surface expressions. In such an area, multichannel 2-D seismic data were collected along a line perpendicular to the trend of the thrust belt. The data have a moderate signal-to-noise ratio and suffer from ground roll and other acquisition-related noise. In addition to data quality, the complex geology of the thrust belt limits the ability of conventional seismic processing to yield a reliable velocity model which in turn leads to poor subsurface image. In this paper, we demonstrate the application of traveltime and waveform inversion as supplements to conventional seismic imaging and interpretation processes. Both traveltime and waveform inversion utilize the first arrivals that are typically discarded during conventional seismic processing. As a first step, a smooth velocity model with long wavelength characteristics of the subsurface is estimated through inversion of the first-arrival traveltimes. This velocity model is then used to obtain a Kirchhoff pre-stack depth-migrated image which in turn is used for the interpretation of the fault. Waveform inversion is applied to the central part of the seismic line to a depth of ~1 km where the quality of the migrated image is poor. Waveform inversion is performed in the frequency domain over a series of iterations, proceeding from low to high frequency (11-19 Hz) using the velocity model from traveltime inversion as the starting model. In the end, the pre-stack depth-migrated image and the waveform inversion model are jointly interpreted. This study demonstrates that a combination of traveltime and waveform inversion with Kirchhoff pre-stack depth migration is a promising approach for the interpretation of geological structures in a thrust belt.

Prototype Earthquake Early Warning System for Areas of Highest Seismic Risk in the Western U.S.

NASA Astrophysics Data System (ADS)

Bock, Y.; Geng, J.; Goldberg, D.; Saunders, J. K.; Haase, J. S.; Squibb, M. B.; Melgar, D.; Crowell, B. W.; Clayton, R. W.; Yu, E.; Walls, C. P.; Mann, D.; Mencin, D.; Mattioli, G. S.

2015-12-01

We report on a prototype earthquake early warning system for the Western U.S. based on GNSS (GPS+GLONASS) observations, and where available collocated GNSS and accelerometer data (seismogeodesy). We estimate with latency of 2-3 seconds GNSS displacement waveforms from more than 120 stations, focusing on the southern segment of the San Andreas fault, the Hayward and Rodgers Creek faults and Cascadia. The displacements are estimated using precise point positioning with ambiguity resolution (PPP-AR), which provides for efficient processing of hundreds of "clients" within the region of interest with respect to a reference frame well outside the expected zone of deformation. The GNSS displacements are useful for alleviating magnitude saturation concerns, rapid earthquake magnitude estimation using peak ground displacements, CMT solutions and finite fault slip models. However, GNSS alone is insufficient for strict earthquake early warning (i.e., P wave detection). Therefore, we employ a self-contained seismogeodetic technique, where collocations of GNSS and accelerometer instruments are available, to estimate real-time displacement and velocity waveforms using PPP-AR with accelerometers (PPP-ARA). Using the velocity waveforms we can detect the P wave arrival for earthquakes of interest (>M 5.5), estimate a hypocenter, S wave propagation, and earthquake magnitude using Pd scaling relationships within seconds. Currently we are gearing up to receive observatory-grade accelerometer data from the CISN. We have deployed 25 inexpensive MEMS accelerometers at existing GNSS stations. The SIO Geodetic Modules that control the flow of the GNSS and accelerometer data are being upgraded with in situ PPP-ARA and P wave picking. In situ processing allows us to use the data at the highest sampling rate of the GNSS receiver (10 Hz or higher), in combination with the 100 Hz accelerometer data. Adding the GLONASS data allows for increased precision in the vertical, an important factor in P wave detection, and by reducing outliers, increasing the number of visible satellites and significantly reducing the time required for reinitialization of phase ambiguities. We plan to make our displacement and velocity waveforms available to the USGS ShakeAlert system and others in Earthworm format.

Electroosmotic flow in microchannels with arbitrary geometry and arbitrary distribution of wall charge.

PubMed

Xuan, Xiangchun; Li, Dongqing

2005-09-01

General solutions are developed for direct current (DC) and alternating current (AC) electroosmotic flows in microfluidic channels with arbitrary cross-sectional geometry and arbitrary distribution of wall charge (zeta potential). The applied AC electric field can also be of arbitrary waveform. By proposing a nondimensional time scale varpi defined as the ratio of the diffusion time of momentum across the electric double-layer thickness to the period of the applied electric field, we demonstrate analytically that the Helmholtz-Smoluchowski electroosmotic velocity is an appropriate slip condition for AC electroosmotic flows in typical microfluidic applications. With this slip condition approach, electroosmotic flows in rectangular and asymmetric trapezoidal microchannels with nonuniform wall charge, as examples, are investigated. The unknown constants in the proposed general solutions are numerically determined with a least-squares method through matching the boundary conditions. We find that the wall charge affects significantly the electroosmotic flow while the channel geometry does not. Moreover, the flow feature is characterized by another nondimensional time scale Omega defined as the ratio of the diffusion time of momentum across the channel hydraulic radius to the period of the applied electric field. The onset of phase shift between AC electroosmotic velocity and applied electric field is also examined analytically.

Numerical analysis of the pressure drop across highly-eccentric coronary stenoses: application to the calculation of the fractional flow reserve.

PubMed

Agujetas, R; González-Fernández, M R; Nogales-Asensio, J M; Montanero, J M

2018-05-30

Fractional flow reverse (FFR) is the gold standard assessment of the hemodynamic significance of coronary stenoses. However, it requires the catheterization of the coronary artery to determine the pressure waveforms proximal and distal to the stenosis. On the contrary, computational fluid dynamics enables the calculation of the FFR value from relatively non-invasive computed tomography angiography (CTA). We analyze the flow across idealized highly-eccentric coronary stenoses by solving the Navier-Stokes equations. We examine the influence of several aspects (approximations) of the simulation method on the calculation of the FFR value. We study the effects on the FFR value of errors made in the segmentation of clinical images. For this purpose, we compare the FFR value for the nominal geometry with that calculated for other shapes that slightly deviate from that geometry. This analysis is conducted for a range of stenosis severities and different inlet velocity and pressure waveforms. The errors made in assuming a uniform velocity profile in front of the stenosis, as well as those due to the Newtonian and laminar approximations, are negligible for stenosis severities leading to FFR values around the threshold 0.8. The limited resolution of the stenosis geometry reconstruction is the major source of error when predicting the FFR value. Both systematic errors in the contour detection of just 1-pixel size in the CTA images and a low-quality representation of the stenosis surface (coarse faceted geometry) may yield wrong outcomes of the FFR assessment for an important set of eccentric stenoses. On the contrary, the spatial resolution of images acquired with optical coherence tomography may be sufficient to ensure accurate predictions for the FFR value.

Mantle flow beneath Arabia offset from the opening Red Sea

NASA Astrophysics Data System (ADS)

Chang, Sung-Joon; Merino, Miguel; Van der Lee, Suzan; Stein, Seth; Stein, Carol A.

2011-02-01

Continental rifting involves a poorly understood sequence of lithospheric stretching, volcanism, and mantle flow that evolves to seafloor spreading. We present new insight from inversion of seismic traveltimes and waveforms beneath Arabia and surroundings. Low velocities occur beneath the southern Red Sea and Gulf of Aden, consistent with active spreading. However, hot material extends not below the northern Red Sea, but is offset eastward beneath Arabia, showing mantle flow from the Afar hotspot. The location of this channel beneath volcanic rocks erupted since rifting began 30 million years ago indicates that flow moves with Arabia. We propose that the absence of seafloor spreading in the northern Red Sea reflects the offset flow. This geometry may evolve to spreading in the Northern Red Sea, rifting of Arabia, or both. This situation has aspects of both active and passive rifting, showing that both can occur before coalescing to seafloor spreading.

DOE Office of Scientific and Technical Information (OSTI.GOV)

bedle, H; Matzel, E; Flanagan, M

This report summarizes the data analysis achieved during Heather Bedle's eleven-week Technical Scholar internship at Lawrence Livermore National Labs during the early summer 2006. The work completed during this internship resulted in constraints on the crustal and upper mantle S-velocity structure in Northern Africa, the Mediterranean, the Middle East, and Europe, through the fitting of regional waveform data. This data extends current raypath coverage and will be included in a joint inversion along with data from surface wave group velocity measurements, S and P teleseismic arrival time data, and receiver function data to create an improved velocity model of themore » upper mantle in this region. The tectonic structure of the North African/Mediterranean/Europe/Middle Eastern study region is extremely heterogeneous. This region consists of, among others, stable cratons and platforms such as the West Africa Craton, and Baltica in Northern Europe; oceanic subduction zones throughout the Mediterranean Sea where the African and Eurasian plate collide; regions of continental collision as the Arabian Plate moves northward into the Turkish Plate; and rifting in the Red Sea, separating the Arabian and Nubian shields. With such diverse tectonic structures, many of the waveforms were difficult to fit. This is not unexpected as the waveforms are fit using an averaged structure. In many cases the raypaths encounter several tectonic features, complicating the waveform, and making it hard for the software to converge on a 1D average structure. Overall, the quality of the waveform data was average, with roughly 30% of the waveforms being discarded due to excessive noise that interfered with the frequency ranges of interest. An inversion for the 3D S-velocity structure of this region was also performed following the methodology of Partitioned Waveform Inversion (Nolet, 1990; Van der Lee and Nolet, 1997). The addition of the newly fit waveforms drastically extends the range of the model. The model now extends as far east in Africa to cover Chad and Niger, and reaches south to cover Zambia. The model is also stretched eastward to cover the eastern half of India, and northward to cover the southern portion of Scandinavia.« less

Micro-seismic imaging using a source function independent full waveform inversion method

NASA Astrophysics Data System (ADS)

Wang, Hanchen; Alkhalifah, Tariq

2018-03-01

At the heart of micro-seismic event measurements is the task to estimate the location of the source micro-seismic events, as well as their ignition times. The accuracy of locating the sources is highly dependent on the velocity model. On the other hand, the conventional micro-seismic source locating methods require, in many cases manual picking of traveltime arrivals, which do not only lead to manual effort and human interaction, but also prone to errors. Using full waveform inversion (FWI) to locate and image micro-seismic events allows for an automatic process (free of picking) that utilizes the full wavefield. However, full waveform inversion of micro-seismic events faces incredible nonlinearity due to the unknown source locations (space) and functions (time). We developed a source function independent full waveform inversion of micro-seismic events to invert for the source image, source function and the velocity model. It is based on convolving reference traces with these observed and modeled to mitigate the effect of an unknown source ignition time. The adjoint-state method is used to derive the gradient for the source image, source function and velocity updates. The extended image for the source wavelet in Z axis is extracted to check the accuracy of the inverted source image and velocity model. Also, angle gathers is calculated to assess the quality of the long wavelength component of the velocity model. By inverting for the source image, source wavelet and the velocity model simultaneously, the proposed method produces good estimates of the source location, ignition time and the background velocity for synthetic examples used here, like those corresponding to the Marmousi model and the SEG/EAGE overthrust model.

Analysis of vibration waveforms of electromechanical response to determine piezoelectric and electrostrictive coefficients.

PubMed

Izumi, Tatsuya; Hagiwara, Manabu; Hoshina, Takuya; Takeda, Hiroaki; Tsurumi, Takaaki

2012-08-01

We developed a possible method to determine both coefficients of piezoelectricity (d) and electrostriction (M) at the same time by a waveform analysis of current and vibration velocity in the resonance state. The waveforms of the current and vibration velocity were theoretically described using the equations of motion and piezoelectric constitutive equations, considering the dissipation effect. The dissipation factor of the d coefficient and M coefficient is dielectric loss tangent tan δ. The waveforms measured in all of the ceramics, such as Pb(Zr,Ti)O(3) (PZT), Pb(Mg,Nb)O(3) (PMN), and 0.8Pb(Mg(1/3)Nb2/3)O(3)-0.2PbTiO(3) (PMN-PT), were well fitted with the calculated waveform. This fitting produced both the d and M coefficients, which agreed with those determined via the conventional methods. Moreover, the respective contributions of both piezoelectricity and electrostriction to the d value determined in the resonance-antiresonance method were clarified.

Adaptive multi-step Full Waveform Inversion based on Waveform Mode Decomposition

NASA Astrophysics Data System (ADS)

Hu, Yong; Han, Liguo; Xu, Zhuo; Zhang, Fengjiao; Zeng, Jingwen

2017-04-01

Full Waveform Inversion (FWI) can be used to build high resolution velocity models, but there are still many challenges in seismic field data processing. The most difficult problem is about how to recover long-wavelength components of subsurface velocity models when seismic data is lacking of low frequency information and without long-offsets. To solve this problem, we propose to use Waveform Mode Decomposition (WMD) method to reconstruct low frequency information for FWI to obtain a smooth model, so that the initial model dependence of FWI can be reduced. In this paper, we use adjoint-state method to calculate the gradient for Waveform Mode Decomposition Full Waveform Inversion (WMDFWI). Through the illustrative numerical examples, we proved that the low frequency which is reconstructed by WMD method is very reliable. WMDFWI in combination with the adaptive multi-step inversion strategy can obtain more faithful and accurate final inversion results. Numerical examples show that even if the initial velocity model is far from the true model and lacking of low frequency information, we still can obtain good inversion results with WMD method. From numerical examples of anti-noise test, we see that the adaptive multi-step inversion strategy for WMDFWI has strong ability to resist Gaussian noise. WMD method is promising to be able to implement for the land seismic FWI, because it can reconstruct the low frequency information, lower the dominant frequency in the adjoint source, and has a strong ability to resist noise.

Eruption mass estimation using infrasound waveform inversion and ash and gas measurements: Evaluation at Sakurajima Volcano, Japan [Comparison of eruption masses at Sakurajima Volcano, Japan calculated by infrasound waveform inversion and ground-based sampling

DOE PAGES

Fee, David; Izbekov, Pavel; Kim, Keehoon; ...

2017-10-09

Eruption mass and mass flow rate are critical parameters for determining the aerial extent and hazard of volcanic emissions. Infrasound waveform inversion is a promising technique to quantify volcanic emissions. Although topography may substantially alter the infrasound waveform as it propagates, advances in wave propagation modeling and station coverage permit robust inversion of infrasound data from volcanic explosions. The inversion can estimate eruption mass flow rate and total eruption mass if the flow density is known. However, infrasound-based eruption flow rates and mass estimates have yet to be validated against independent measurements, and numerical modeling has only recently been appliedmore » to the inversion technique. Furthermore we present a robust full-waveform acoustic inversion method, and use it to calculate eruption flow rates and masses from 49 explosions from Sakurajima Volcano, Japan.« less

Eruption mass estimation using infrasound waveform inversion and ash and gas measurements: Evaluation at Sakurajima Volcano, Japan [Comparison of eruption masses at Sakurajima Volcano, Japan calculated by infrasound waveform inversion and ground-based sampling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fee, David; Izbekov, Pavel; Kim, Keehoon

Eruption mass and mass flow rate are critical parameters for determining the aerial extent and hazard of volcanic emissions. Infrasound waveform inversion is a promising technique to quantify volcanic emissions. Although topography may substantially alter the infrasound waveform as it propagates, advances in wave propagation modeling and station coverage permit robust inversion of infrasound data from volcanic explosions. The inversion can estimate eruption mass flow rate and total eruption mass if the flow density is known. However, infrasound-based eruption flow rates and mass estimates have yet to be validated against independent measurements, and numerical modeling has only recently been appliedmore » to the inversion technique. Furthermore we present a robust full-waveform acoustic inversion method, and use it to calculate eruption flow rates and masses from 49 explosions from Sakurajima Volcano, Japan.« less

Helioseismic Constraints on the Depth Dependence of Large-Scale Solar Convection

NASA Astrophysics Data System (ADS)

Woodard, Martin F.

2017-08-01

A recent helioseismic statistical waveform analysis of subsurface flow based on a 720-day time series of SOHO/MDI Medium-l spherical-harmonic coefficients has been extended to cover a greater range of subphotospheric depths. The latest analysis provides estimates of flow-dependent oscillation-mode coupling-strength coefficients b(s,t;n,l) over the range l = 30 to 150 of mode degree (angular wavenumber) for solar p-modes in the approximate frequency range 2 to 4 mHz. The range of penetration depths of this mode set covers most of the solar convection zone. The most recent analysis measures spherical harmonic (s,t) components of the flow velocity for odd s in the angular wavenumber range 1 to 19 for t not much smaller than s at a given s. The odd-s b(s,t;n,l) coefficients are interpreted as averages over depth of the depth-dependent amplitude of one spherical-harmonic (s,t) component of the toroidal part of the flow velocity field. The depth-dependent weighting function defining the average velocity is the fractional kinetic energy density in radius of modes of the (n,l) multiplet. The b coefficients have been converted to estimates of root velocity power as a function of l0 = nu0*l/nu(n,l), which is a measure of mode penetration depth. (nu(n,l) is mode frequency and nu0 is a reference frequency equal to 3 mHz.) A comparison of the observational results with simple convection models will be presented.

Nonlinear model for offline correction of pulmonary waveform generators.

PubMed

Reynolds, Jeffrey S; Stemple, Kimberly J; Petsko, Raymond A; Ebeling, Thomas R; Frazer, David G

2002-12-01

Pulmonary waveform generators consisting of motor-driven piston pumps are frequently used to test respiratory-function equipment such as spirometers and peak expiratory flow (PEF) meters. Gas compression within these generators can produce significant distortion of the output flow-time profile. A nonlinear model of the generator was developed along with a method to compensate for gas compression when testing pulmonary function equipment. The model and correction procedure were tested on an Assess Full Range PEF meter and a Micro DiaryCard PEF meter. The tests were performed using the 26 American Thoracic Society standard flow-time waveforms as the target flow profiles. Without correction, the pump loaded with the higher resistance Assess meter resulted in ten waveforms having a mean square error (MSE) higher than 0.001 L2/s2. Correction of the pump for these ten waveforms resulted in a mean decrease in MSE of 87.0%. When loaded with the Micro DiaryCard meter, the uncorrected pump outputs included six waveforms with MSE higher than 0.001 L2/s2. Pump corrections for these six waveforms resulted in a mean decrease in MSE of 58.4%.

Surface wave tomography of North America and the Caribbean using global and regional broad-band networks: Phase velocity maps and limitations of ray theory

USGS Publications Warehouse

Godey, S.; Snieder, R.; Villasenor, A.; Benz, H.M.

2003-01-01

We present phase velocity maps of fundamental mode Rayleigh waves across the North American and Caribbean plates. Our data set consists of 1846 waveforms from 172 events recorded at 91 broad-band stations operating in North America. We compute phase velocity maps in four narrow period bands between 50 and 150 s using a non-linear waveform inversion method that solves for phase velocity perturbations relative to a reference Earth model (PREM). Our results show a strong velocity contrast between high velocities beneath the stable North American craton, and lower velocities in the tectonically active western margin, in agreement with other regional and global surface wave tomography studies. We perform detailed comparisons with global model results, which display good agreement between phase velocity maps in the location and amplitude of the anomalies. However, forward modelling shows that regional maps are more accurate for predicting waveforms. In addition, at long periods, the amplitude of the velocity anomalies imaged in our regional phase velocity maps is three time larger than in global phase velocity models. This amplitude factor is necessary to explain the data accurately, showing that regional models provide a better image of velocity structures. Synthetic tests show that the raypath coverage used in this study enables one to resolve velocity features of the order of 800-1000 km. However, only larger length-scale features are observed in the phase velocity maps. The limitation in resolution of our maps can be attributed to the wave propagation theory used in the inversion. Ray theory does not account for off-great-circle ray propagation effects, such as ray bending or scattering. For wavelengths less than 1000 km, scattering effects are significant and may need to be considered.

Southern Africa seismic structure and source studies

NASA Astrophysics Data System (ADS)

Zhao, Ming

1998-09-01

The upper mantle seismic velocity structure beneath southern Africa is investigated using travel time and waveform data. Waveform and travel time data used in this study come mainly from a large mine tremor in South Africa (msb{b} 5.6) recorded on stations of the southern Africa and the Tanzania Broadband Seismic Experiment. Auxiliary data along similar profiles are obtained from other moderate events within eastern and southern Africa. The waveform data from the large tremor show upper mantle triplications for both the 400 and 670-km discontinuities between 18sp° and 27sp° distance. The most notable feature of the data is a large, late P phase that propagates to at least 27sp°. This phase is striking because of its late arrival time (as much as 15 seconds after direct P at 27sp°) and high amplitude relative to the first arrival. Travel times from all available stations are used to invert for the P wave velocity structure down to 800 km depth and S wave velocity structure down to 200 km using the Wiechert-Herglotz (W-H) inversion technique. The P wave velocities from the uppermost mantle down to 300 km are as much as 3% higher than the global average and are slightly slower than the global average between 300 and 400 km depths. The velocity gradient between 300 and 400 km is 0.0015 1/s. The S wave travel time data yield fast velocities above 200-km depth. The S wave velocity structure appears inconsistent with the P wave structure model indicating varying Poisson's ratio in the upper mantle. Little evidence is found for a pronounced upper mantle low velocity zone. Both sharp and gradual-change 400-km discontinuities are favored by the waveform data. The 670-km discontinuity appears as a gradual-change zone. The source mechanism of the mb 5.6 mining tremor itself is important for seismic discrimination and insight into mining tremor sources. Source parameters for this event as well as some other large mining tremors from the South African gold mines are studied using detailed waveform modeling. All these events (mb > 4.8) indicate normal-faulting slip with P wave nodal planes striking approximately NS. Tectonic stress is essential to control the mining seismicity of large magnitude. Mining geometry also plays an important role in influencing the seismicity. The crustal velocity structure at the study area is investigated in detail using teleseismic receiver function and regional surface wave dispersion data. The results indicate some lateral variation in the shallow crust. The thickness of the crust beneath the GSN station BOSA is 33-36 km. Gradually increasing velocities with depth in the crust are preferred. A thin layer with rather low velocity at the top of the crust beneath BOSA is important for generating the regional waveforms. The crust beneath LBTB is a few kilometers thicker than at BOSA and the Moho there is likely to be dipping. (Abstract shortened by UMI.)

Non-Linear Seismic Velocity Estimation from Multiple Waveform Functionals and Formal Assessment of Constraints

DTIC Science & Technology

2011-09-01

tectonically active regions such as the Middle East. For example, we previously applied the code to determine the crust and upper mantle structure...Objective Optimization (MOO) for Multiple Datasets The primary goal of our current project is to develop a tool for estimating crustal structure that...be used to obtain crustal velocity structures by modeling broadband waveform, receiver function, and surface wave dispersion data. The code has been

Elastic and anelastic structure of the lowermost mantle beneath the Western Pacific using waveform inversion

NASA Astrophysics Data System (ADS)

Konishi, K.; Deschamps, F.; Fuji, N.

2015-12-01

We investigate quasi-2D elastic and anelastic structure of the lowermost mantle beneath the Western Pacific by inverting S and ScS waveforms. The transverse component data were obtained from F-net for 32 deep sources beneath Tonga and Fiji, filtered between 12.5 and 200 s. We observe a regional variation of S and ScS arrival times and amplitude ratio, according to which we divide our region of interest into four sub-regions and perform 1D waveform inversion for S-wave velocity and Qμ value simultaneously. We find S-shaped structure of S-wave velocity beneath the whole region with sub-regional variation of S-wave velocity peak depths, which can explain regional difference in travel times. Qμ structure varies with sub-regions as well, but the physical interpretation has not yet done.

Interpreting Continental Break-Up From Surface Observations: Analysis of 1D Partial Melting Using Synthetic Waveform Propagation

NASA Astrophysics Data System (ADS)

Franken, T.; Armitage, J. J.; Fuji, N.; Fournier, A.

2017-12-01

Low shear-wave velocity zones underneath margins of continental break-up are believed to be related to the presence of melt. Many models attempt to model the process of melt production and transportation during mantle upwelling, yet there is a disconnect between geodynamic models, seismic observations, and petrological studies of melt flow velocities. Geodynamic models that emulate melt retention of 2 %, suggested by shear-wave velocity anomalies (Forsyth & MELT Seismic Team, 1998), fail to adequately reproduce the seismic signal as seen in receiver functions (Rychert, 2012; Armitage et al., 2015). Furthermore, numerical models of melt migration conclude mean melt flow velocities up to 1,3 m yr-1(Weatherley & Katz, 2015), whereas Uranium isotope migration rates advocate velocities up to two orders of magnitude higher. This study aims to reconcile the diverting assertions on the partial melting process by analysing the effect of melt presence on the coda of the seismic signal. A 1D forward model has been created to emulate melt production and transportation in an upwelling mantle environment. Scenarios have been modelled for variable upwelling velocities v (1 - 100 mm yr-1), initial temperatures T0 (1200 - 1800 °C) and permeabilities k0 (10-9 - 10-5 m2). The 1D model parameters are converted to anharmonic seismic parameters using look-up tables from phase diagrams (Goes et al., 2012) to generate synthetic seismograms with the Direct Solution Method. The maximum frequency content of the synthetics is 1,25 Hz, sampled at 20 Hz with a low-pass filter of 0,1 Hz. A comparison between the synthetics and seismic observations of the La Reunion mantle plume from the RER Geoscope receiver is performed using a Monte-Carlo approach. The synthetic seismograms show highest sensitivity to the presence of melt in S-waves within epicentral distances of 0-20 degrees. In the 0-10 degree range only a time-shift is observed proportional to the melt fraction at the onset of melting. Within the 10-20 degree range the presence of melt causes an additional change in the coda of the signal compared to a no-melt model. By analysing these altered synthetic waveforms we search for a seismic signature corresponding to melt presence to form a benchmark for the comparison between the Monte-Carlo results and the seismic observations.

Estimation of Dynamic Friction Process of the Akatani Landslide Based on the Waveform Inversion and Numerical Simulation

NASA Astrophysics Data System (ADS)

Yamada, M.; Mangeney, A.; Moretti, L.; Matsushi, Y.

2014-12-01

Understanding physical parameters, such as frictional coefficients, velocity change, and dynamic history, is important issue for assessing and managing the risks posed by deep-seated catastrophic landslides. Previously, landslide motion has been inferred qualitatively from topographic changes caused by the event, and occasionally from eyewitness reports. However, these conventional approaches are unable to evaluate source processes and dynamic parameters. In this study, we use broadband seismic recordings to trace the dynamic process of the deep-seated Akatani landslide that occurred on the Kii Peninsula, Japan, which is one of the best recorded large slope failures. Based on the previous results of waveform inversions and precise topographic surveys done before and after the event, we applied numerical simulations using the SHALTOP numerical model (Mangeney et al., 2007). This model describes homogeneous continuous granular flows on a 3D topography based on a depth averaged thin layer approximation. We assume a Coulomb's friction law with a constant friction coefficient, i. e. the friction is independent of the sliding velocity. We varied the friction coefficients in the simulation so that the resulting force acting on the surface agrees with the single force estimated from the seismic waveform inversion. Figure shows the force history of the east-west components after the band-pass filtering between 10-100 seconds. The force history of the simulation with frictional coefficient 0.27 (thin red line) the best agrees with the result of seismic waveform inversion (thick gray line). Although the amplitude is slightly different, phases are coherent for the main three pulses. This is an evidence that the point-source approximation works reasonably well for this particular event. The friction coefficient during the sliding was estimated to be 0.38 based on the seismic waveform inversion performed by the previous study and on the sliding block model (Yamada et al., 2013), whereas the frictional coefficient estimated from the numerical simulation was about 0.27. This discrepancy may be due to the digital elevation model, to the other forces such as pressure gradients and centrifugal acceleration included in the model. However, quantitative interpretation of this difference requires further investigation.

A comparison of earthquake backprojection imaging methods for dense local arrays

NASA Astrophysics Data System (ADS)

Beskardes, G. D.; Hole, J. A.; Wang, K.; Michaelides, M.; Wu, Q.; Chapman, M. C.; Davenport, K. K.; Brown, L. D.; Quiros, D. A.

2018-03-01

Backprojection imaging has recently become a practical method for local earthquake detection and location due to the deployment of densely sampled, continuously recorded, local seismograph arrays. While backprojection sometimes utilizes the full seismic waveform, the waveforms are often pre-processed and simplified to overcome imaging challenges. Real data issues include aliased station spacing, inadequate array aperture, inaccurate velocity model, low signal-to-noise ratio, large noise bursts and varying waveform polarity. We compare the performance of backprojection with four previously used data pre-processing methods: raw waveform, envelope, short-term averaging/long-term averaging and kurtosis. Our primary goal is to detect and locate events smaller than noise by stacking prior to detection to improve the signal-to-noise ratio. The objective is to identify an optimized strategy for automated imaging that is robust in the presence of real-data issues, has the lowest signal-to-noise thresholds for detection and for location, has the best spatial resolution of the source images, preserves magnitude, and considers computational cost. Imaging method performance is assessed using a real aftershock data set recorded by the dense AIDA array following the 2011 Virginia earthquake. Our comparisons show that raw-waveform backprojection provides the best spatial resolution, preserves magnitude and boosts signal to detect events smaller than noise, but is most sensitive to velocity error, polarity error and noise bursts. On the other hand, the other methods avoid polarity error and reduce sensitivity to velocity error, but sacrifice spatial resolution and cannot effectively reduce noise by stacking. Of these, only kurtosis is insensitive to large noise bursts while being as efficient as the raw-waveform method to lower the detection threshold; however, it does not preserve the magnitude information. For automatic detection and location of events in a large data set, we therefore recommend backprojecting kurtosis waveforms, followed by a second pass on the detected events using noise-filtered raw waveforms to achieve the best of all criteria.

A remote and non-contact method for obtaining the blood-pulse waveform with a laser Doppler vibrometer

NASA Astrophysics Data System (ADS)

Desjardins, Candida L.; Antonelli, Lynn T.; Soares, Edward

2007-02-01

The use of lasers to remotely and non-invasively detect the blood pressure waveform of humans and animals would provide a powerful diagnostic tool. Current blood pressure measurement tools, such as a cuff, are not useful for burn and trauma victims, and animals require catheterization to acquire accurate blood pressure information. The purpose of our sensor method and apparatus invention is to remotely and non-invasively detect the blood pulse waveform of both animals and humans. This device is used to monitor an animal or human's skin in proximity to an artery using radiation from a laser Doppler vibrometer (LDV). This system measures the velocity (or displacement) of the pulsatile motion of the skin, indicative of physiological parameters of the arterial motion in relation to the cardiac cycle. Tests have been conducted that measures surface velocity with an LDV and a signal-processing unit, with enhanced detection obtained with optional hardware including a retro-reflector dot. The blood pulse waveform is obtained by integrating the velocity signal to get surface displacement using standard signal processing techniques. Continuous recording of the blood pulse waveform yields data containing information on cardiac health and can be analyzed to identify important events in the cardiac cycle, such as heart rate, the timing of peak systole, left ventricular ejection time and aortic valve closure. Experimental results are provided that demonstrates the current capabilities of the optical, non-contact sensor for the continuous, non-contact recording of the blood pulse waveform without causing patient distress.

Hemodynamics in a giant intracranial aneurysm characterized by in vitro 4D flow MRI

PubMed Central

Schiavazzi, Daniele; Moen, Sean; Jagadeesan, Bharathi; Van de Moortele, Pierre-François; Coletti, Filippo

2018-01-01

Experimental and computational data suggest that hemodynamics play a critical role in the development, growth, and rupture of cerebral aneurysms. The flow structure, especially in aneurysms with a large sac, is highly complex and three-dimensional. Therefore, volumetric and time-resolved measurements of the flow properties are crucial to fully characterize the hemodynamics. In this study, phase-contrast Magnetic Resonance Imaging is used to assess the fluid dynamics inside a 3D-printed replica of a giant intracranial aneurysm, whose hemodynamics was previously simulated by multiple research groups. The physiological inflow waveform is imposed in a flow circuit with realistic cardiovascular impedance. Measurements are acquired with sub-millimeter spatial resolution for 16 time steps over a cardiac cycle, allowing for the detailed reconstruction of the flow evolution. Moreover, the three-dimensional and time-resolved pressure distribution is calculated from the velocity field by integrating the fluid dynamics equations, and is validated against differential pressure measurements using precision transducers. The flow structure is characterized by vortical motions that persist within the aneurysm sac for most of the cardiac cycle. All the main flow statistics including velocity, vorticity, pressure, and wall shear stress suggest that the flow pattern is dictated by the aneurysm morphology and is largely independent of the pulsatility of the inflow, at least for the flow regimes investigated here. Comparisons are carried out with previous computational simulations that used the same geometry and inflow conditions, both in terms of cycle-averaged and systolic quantities. PMID:29300738

Echocardiographic Assessment of Aortic Pulse-Wave Velocity: Validation against Invasive Pressure Measurements.

PubMed

Styczynski, Grzegorz; Rdzanek, Adam; Pietrasik, Arkadiusz; Kochman, Janusz; Huczek, Zenon; Sobieraj, Piotr; Gaciong, Zbigniew; Szmigielski, Cezary

2016-11-01

Aortic pulse-wave velocity (PWV) is a measure of aortic stiffness that has a prognostic role in various diseases and in the general population. A number of methods are used to measure PWV, including Doppler ultrasound. Although echocardiography has been used for PWV measurement, to the authors' knowledge, it has never been tested against an invasive reference method at the same time point. Therefore, the aim of this study was to compare prospectively an echocardiographic PWV measurement, called echo-PWV, with an invasive study. Forty-five patients (mean age, 66 years; 60% men) underwent simultaneous intra-arterial pressure recording and echocardiographic Doppler flow evaluation during elective cardiac catheterization. Proximal pressure and Doppler waveforms were acquired in the aortic arch. Distal pressure waveforms were registered in the right and distal Doppler waveforms in the left external iliac artery. Transit time was measured as a delay of the foot of pressure or Doppler waveform in the distal relative to the proximal location. Distance was measured on the catheter for invasive PWV and over the surface for echo-PWV. Echo-PWV was calculated as distance divided by transit time. In the whole group, mean invasive PWV was 9.38 m/sec and mean echo-PWV was 9.51 m/sec (P = .78). The Pearson' correlation coefficient between methods was 0.93 (P < .0001). A Bland-Altman plot revealed a mean difference between invasive PWV and echo-PWV of 0.13 ± 0.79 m/sec. Echo-PWV, based on Doppler echocardiography, is a reliable method of aortic PWV measurement, with a close correlation with invasive assessment. Wider implementation of the echo-PWV method for the evaluation of aortic wall stiffness can further expand the clinical and scientific utility of echocardiography. Copyright © 2016 American Society of Echocardiography. Published by Elsevier Inc. All rights reserved.

On the role of glottis-interior sources in the production of voiced sound.

PubMed

Howe, M S; McGowan, R S

2012-02-01

The voice source is dominated by aeroacoustic sources downstream of the glottis. In this paper an investigation is made of the contribution to voiced speech of secondary sources within the glottis. The acoustic waveform is ultimately determined by the volume velocity of air at the glottis, which is controlled by vocal fold vibration, pressure forcing from the lungs, and unsteady backreactions from the sound and from the supraglottal air jet. The theory of aerodynamic sound is applied to study the influence on the fine details of the acoustic waveform of "potential flow" added-mass-type glottal sources, glottis friction, and vorticity either in the glottis-wall boundary layer or in the portion of the free jet shear layer within the glottis. These sources govern predominantly the high frequency content of the sound when the glottis is near closure. A detailed analysis performed for a canonical, cylindrical glottis of rectangular cross section indicates that glottis-interior boundary/shear layer vortex sources and the surface frictional source are of comparable importance; the influence of the potential flow source is about an order of magnitude smaller. © 2012 Acoustical Society of America

Microseismic event location by master-event waveform stacking

NASA Astrophysics Data System (ADS)

Grigoli, F.; Cesca, S.; Dahm, T.

2016-12-01

Waveform stacking location methods are nowadays extensively used to monitor induced seismicity monitoring assoiciated with several underground industrial activities such as Mining, Oil&Gas production and Geothermal energy exploitation. In the last decade a significant effort has been spent to develop or improve methodologies able to perform automated seismological analysis for weak events at a local scale. This effort was accompanied by the improvement of monitoring systems, resulting in an increasing number of large microseismicity catalogs. The analysis of microseismicity is challenging, because of the large number of recorded events often characterized by a low signal-to-noise ratio. A significant limitation of the traditional location approaches is that automated picking is often done on each seismogram individually, making little or no use of the coherency information between stations. In order to improve the performance of the traditional location methods, in the last year, alternative approaches have been proposed. These methods exploits the coherence of the waveforms recorded at different stations and do not require any automated picking procedure. The main advantage of this methods relies on their robustness even when the recorded waveforms are very noisy. On the other hand, like any other location method, the location performance strongly depends on the accuracy of the available velocity model. When dealing with inaccurate velocity models, in fact, location results can be affected by large errors. Here we will introduce a new automated waveform stacking location method which is less dependent on the knowledge of the velocity model and presents several benefits, which improve the location accuracy: 1) it accounts for phase delays due to local site effects, e.g. surface topography or variable sediment thickness 2) theoretical velocity model are only used to estimate travel times within the source volume, and not along the whole source-sensor path. We finally compare the location results for both synthetics and real data with those obtained by using classical waveforms stacking approaches.

New method for estimating arterial pulse wave velocity at single site.

PubMed

Abdessalem, Khaled Ben; Flaud, Patrice; Zobaidi, Samir

2018-01-01

The clinical importance of measuring local pulse wave velocity (PWV), has encouraged researchers to develop several local methods to estimate it. In this work, we proposed a new method, the sum-of-squares method [Formula: see text], that allows the estimations of PWV by using simultaneous measurements of blood pressure (P) and arterial diameter (D) at single-location. Pulse waveforms generated by: (1) two-dimensional (2D) fluid-structure interaction simulation (FSI) in a compliant tube, (2) one-dimensional (1D) model of 55 larger human systemic arteries and (3) experimental data were used to validate the new formula and evaluate several classical methods. The performance of the proposed method was assessed by comparing its results to theoretical PWV calculated from the parameters of the model and/or to PWV estimated by several classical methods. It was found that values of PWV obtained by the developed method [Formula: see text] are in good agreement with theoretical ones and with those calculated by PA-loop and D 2 P-loop. The difference between the PWV calculated by [Formula: see text] and PA-loop does not exceed 1% when data from simulations are used, 3% when in vitro data are used and 5% when in vivo data are used. In addition, this study suggests that estimated PWV from arterial pressure and diameter waveforms provide correct values while methods that require flow rate (Q) and velocity (U) overestimate or underestimate PWV.

Efficient waveform tomography for lithospheric imaging: implications for realistic, two-dimensional acquisition geometries and low-frequency data

NASA Astrophysics Data System (ADS)

Brenders, A. J.; Pratt, R. G.

2007-01-01

We provide a series of numerical experiments designed to test waveform tomography under (i) a reduction in the number of input data frequency components (`efficient' waveform tomography), (ii) sparse spatial subsampling of the input data and (iii) an increase in the minimum data frequency used. These results extend the waveform tomography results of a companion paper, using the same third-party, 2-D, wide-angle, synthetic viscoelastic seismic data, computed in a crustal geology model 250 km long and 40 km deep, with heterogeneous P-velocity, S-velocity, density and Q-factor structure. Accurate velocity models were obtained using efficient waveform tomography and only four carefully selected frequency components of the input data: 0.8, 1.7, 3.6 and 7.0 Hz. This strategy avoids the spectral redundancy present in `full' waveform tomography, and yields results that are comparable with those in the companion paper for an 88 per cent decrease in total computational cost. Because we use acoustic waveform tomography, the results further justify the use of the acoustic wave equation in calculating P-wave velocity models from viscoelastic data. The effect of using sparse survey geometries with efficient waveform tomography were investigated for both increased receiver spacing, and increased source spacing. Sampling theory formally requires spatial sampling at maximum interval of one half-wavelength (2.5 km at 0.8 Hz): For data with receivers every 0.9 km (conforming to this criterion), artefacts in the tomographic images were still minimal when the source spacing was as large as 7.6 km (three times the theoretical maximum). Larger source spacings led to an unacceptable degradation of the results. When increasing the starting frequency, image quality was progressively degraded. Acceptable image quality within the central portion of the model was nevertheless achieved using starting frequencies up to 3.0 Hz. At 3.0 Hz the maximum theoretical sample interval is reduced to 0.67 km due to the decreased wavelengths; the available sources were spaced every 5.0 km (more than seven times the theoretical maximum), and receivers were spaced every 0.9 km (1.3 times the theoretical maximum). Higher starting frequencies than 3.0 Hz again led to unacceptable degradation of the results.

Quantifying the influence of respiration and cardiac pulsations on cerebrospinal fluid dynamics using real-time phase-contrast MRI.

PubMed

Yildiz, Selda; Thyagaraj, Suraj; Jin, Ning; Zhong, Xiaodong; Heidari Pahlavian, Soroush; Martin, Bryn A; Loth, Francis; Oshinski, John; Sabra, Karim G

2017-08-01

To validate a real-time phase contrast magnetic resonance imaging (RT-PCMRI) sequence in a controlled phantom model, and to quantify the relative contributions of respiration and cardiac pulsations on cerebrospinal fluid (CSF) velocity at the level of the foramen magnum (FM). To validate the 3T MRI techniques, in vitro studies used a realistic model of the spinal subarachnoid space driven by pulsatile flow waveforms mimicking the respiratory and cardiac components of CSF flow. Subsequently, CSF flow was measured continuously during 1-minute RT-PCMRI acquisitions at the FM while healthy subjects (N = 20) performed natural breathing, deep breathing, breath-holding, and coughing. Conventional cardiac-gated PCMRI was obtained for comparison. A frequency domain power ratio analysis determined the relative contribution of respiration versus cardiac ([r/c]) components of CSF velocity. In vitro studies demonstrating the accuracy of RT-PCMRI within 5% of input values showed that conventional PCMRI measures only the cardiac component of CSF velocity (0.42 ± 0.02 cm/s), averages out respiratory effects, and underestimates the magnitude of CSF velocity (0.96 ± 0.07 cm/s). In vivo RT-PCMRI measurements indicated the ratio of respiratory to cardiac velocity pulsations averaged over all subjects as [r/c = 0.14 ± 0.27] and [r/c = 0.40 ± 0.47] for natural and deep breathing, respectively. During coughing, the peak CSF velocity increased by a factor of 2.27 ± 1.40. RT-PCMRI can noninvasively measure instantaneous CSF velocity driven by cardiac pulsations, respiration, and coughing in real time. A comparable contribution of respiration and cardiac pulsations on CSF velocity was found during deep breathing but not during natural breathing. 1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:431-439. © 2017 International Society for Magnetic Resonance in Medicine.

A system for rapid analysis of the femoral blood velocity waveform at the bedside.

PubMed

Capper, W L; Amoore, J N; Clifford, P C; Immelman, E J; Harries-Jones, E P

1986-01-01

The shape of the arterial blood velocity waveform varies with atherosclerotic disease and several methods of quantifying the shape in order to predict the severity of the disease have been described. These methods include pulsatility index, the Laplace transform method, and principal component analysis. This paper describes the development of a system which allows the operator to acquire, display, and store waveforms from each limb and then to quantify the waveforms at the bedside within a few minutes. The system includes a 10 MHz bi-directional Doppler unit, an instantaneous mean frequency processor, and an Apple II microcomputer fitted with an accelerator card. Both the Laplace transform parameters and the pulsatility index are computed and each result is printed in tabular form together with the averaged results of five waveforms from each limb. The printout is suitable for inclusion in the patient's folder. In initial clinical studies Laplace transform analysis exhibited a good correlation with aorto-iliac stenosis as assessed angiographically (R = 0.73 P less than 0.001 t test).

Of Mantle Plumes, Their Existence, and Their Nature: Insights from Whole Mantle SEM-Based Seismic Waveform Tomography

NASA Astrophysics Data System (ADS)

Romanowicz, B. A.; French, S. W.

2014-12-01

Many questions remain on the detailed morphology of mantle convection patterns. While high resolution P wave studies show a variety of subducted slab behaviors, some stagnating in the transition zone, others penetrating into the lower mantle (e.g. Fukao & Obayashi, 2013), low velocity structures - the upwelling part of flow - are more difficult to resolve at the same scale. Indeed, depth extent and morphology of the low velocity roots of hotspot volcanoes is still debated, along with the existence of "mantle plumes". Using spectral element waveform tomography, we previously constructed a global, radially anisotropic, upper mantle Vs model (SEMum2, French et al., 2013) and have now extended it to the whole mantle by adding shorter period waveform data (SEMUCB-WM1, French & Romanowicz, GJI, in revision). This model shows long wavelength structure in good agreement with other recent global Vs models derived under stronger approximations (Ritsema et al. 2011; Kustowski, et al. 2008), but exhibits better focused, finer scale structure throughout the mantle. SEMUCB-WM1 confirms the presence in all major ocean basins of the quasi-periodic, upper mantle low velocity anomalies, previously seen in SEMum2. At the same time, lower mantle low velocity structure is dominated by a small number (~15 globally) of quasi-vertical anomalies forming discrete "column"" rooted at the base of the mantle. Most columns are positioned near major hotspots, as defined by buoyancy flux, and are wider (~800-1000 km diameter) than expected from the thermal plume model - suggestive of thermo-chemical plumes, which may be stable for long times compared to purely thermal ones. Some columns reach the upper mantle, while others deflect horizontally near 1000 km - the same depth where many slabs appear to stagnate. As they reach the transition zone, the wide columnar structure can be lost, as these "plumes" appear to meander through the upper mantle, perhaps entrained by more vigorous, lower viscosity, convection. Most "plumes" in the Pacific LLSVP region appear as isolated columns rising from the CMB, such as beneath Hawaii (rooted near a known ultra low velocity zone, Cottaar & Romanowicz, 2012). Conversely, the African LLSVP region appears more massive up to mid-mantle depths, with isolated "plumes" at its borders, including that beneath Iceland.

Seismic Waveform Modeling of Broadband Data From a Temporary High-Density Deployment in the Los Angeles Basin

NASA Astrophysics Data System (ADS)

Herrman, M.; Polet, J.

2016-12-01

A total of 73 broadband seismometers were deployed for a passive source seismic experiment called the Los Angeles Syncline Seismic Interferometry Experiment (LASSIE) from September to November of 2014. The purpose of this experiment was to collect high density seismic data for the Los Angeles Basin (LAB) to better understand basin structure and response. This research will use the data collected from LASSIE to assess and refine current velocity models of the LAB using a full waveform modeling approach. To this end we will compare seismograms recorded by LASSIE for a subset of the 53 earthquakes and quarry blasts located by the Southern California Seismic Network (SCSN) that occurred within or near the LAB during the deployment period to synthetic seismograms generated by the Frequency-Wavenumber (FK) code developed by Zhu and Rivera (2002). A first analysis of the data indicates that roughly 25 of the 53 events have waveforms with sufficiently high signal to noise ratio, providing approximately 500 seismograms that are of suitable quality for comparison. We observe significant changes in waveform characteristics between stations with a very small separation distance of approximately 1 km. Focal mechanisms for most of these events have been obtained from Dr. Egill Hauksson (personal communication). We will show comparisons between the broadband velocity waveforms recorded by stations across the LASSIE array and FK synthetics determined for a variety of 1D velocity models that have been developed for the LAB area (such as Hadley and Kanamori, 1977; Hauksson, 1989, 1995 and Magistrale, 1992). The results of these comparisons will be analyzed to provide additional constraints on the subsurface seismic velocity structure within the Los Angeles basin.

Arterial pulse wave velocity but not augmentation index is associated with coronary artery disease extent and severity: implications for arterial transfer function applicability.

PubMed

Hope, Sarah A; Antonis, Paul; Adam, David; Cameron, James D; Meredith, Ian T

2007-10-01

The aim of this study was to test the hypothesis that coronary artery disease extent and severity are associated with central aortic pressure waveform characteristics. Although it is thought that central aortic pressure waveform characteristics, particularly augmentation index, may influence cardiovascular disease progression and predict cardiovascular risk, little is known of the relationship between central waveform characteristics and the severity and extent of coronary artery disease. Central aortic waveforms (2F Millar pressure transducer-tipped catheters) were acquired at the time of coronary angiography for suspected native coronary artery disease in 40 patients (24 male). The severity and extent of disease were assessed independently by two observers using two previously described scoring systems (modified Gensini's stenosis and Sullivan's extent scores). Relationships between disease scores, aortic waveform characteristics, aorto-radial pulse wave velocity and subject demographic features were assessed by regression techniques. Both extent and severity scores were associated with increasing age and male sex (P < 0.001), but no other risk factors. Both scores were independently associated with aorto-radial pulse wave velocity (P < 0.001), which entered a multiple regression model prior to age and sex. This association was not dependent upon blood pressure. Neither score was associated with central aortic augmentation index, by either simple or multiple linear regression techniques including heart rate, subject demographic features and cardiovascular risk factors. Aorto-radial pulse wave velocity, but not central aortic augmentation index, is associated with both the extent and severity of coronary artery disease. This has potentially important implications for applicability of a generalized arterial transfer function.

Real-time display of flow-pressure-volume loops.

PubMed

Morozoff, P E; Evans, R W

1992-01-01

Graphic display of respiratory waveforms can be valuable for monitoring the progress of ventilated patients. A system has been developed that can display flow-pressure-volume loops as derived from a patient's respiratory circuit in real time. It can also display, store, print, and retrieve ventilatory waveforms. Five loops can be displayed at once: current, previous, reference, "ideal," and previously saved. Two components, the data-display device (DDD) and the data-collection device (DCD), comprise the system. An IBM 286/386 computer with a graphics card (VGA) and bidirectional parallel port is used for the DDD; an eight-bit microprocessor card and an A/D convertor card make up the DCD. A real-time multitasking operating system was written to control the DDD, while the DCD operates from in-line assembly code. The DCD samples the pressure and flow sensors at 100 Hz and looks for a complete flow waveform pattern based on flow slope. These waveforms are then passed to the DDD via the mutual parallel port. Within the DDD a process integrates the flow to create a volume signal and performs a multilinear regression on the pressure, flow, and volume data to calculate the elastance, resistance, pressure offset, and coefficient of determination. Elastance, resistance, and offset are used to calculate Pr and Pc where: Pr[k] = P[k]-offset-(elastance.V[k]) and Pc[k] = P[k]-offset-(resistance.F[k]). Volume vs. Pc and flow vs. Pr can be displayed in real time. Patient data from previous clinical tests were loaded into the device to verify the software calculations. An analog waveform generator was used to simulate flow and pressure waveforms that validated the system.(ABSTRACT TRUNCATED AT 250 WORDS)

Waveform inversion for D″ structure beneath northern Asia using Hi-net tiltmeter data

NASA Astrophysics Data System (ADS)

Kawai, Kenji; Sekine, Shutaro; Fuji, Nobuaki; Geller, Robert J.

2009-10-01

We invert shear-wave waveform data for the radial variation of (isotropic) shear-velocity in D″ beneath Northern Asia. We reduce source and receiver effects by using data for intermediate and deep events beneath Italy and Japan recorded respectively at stations in East Asia and Europe. Relative to PREM, we find a significantly higher S-wave velocity in the depth range from 150 to 300 km above the core-mantle boundary (CMB) and a slightly lower S-wave velocity in the depth range 0-150 km above the CMB. As our previous studies of D″ structure beneath Central America and the Arctic obtained similar S-wave velocity models, we suggest that this pattern of vertical dependence of shear wave velocity in D″ may be a general phenomenon, at least in relatively cold regions.

SPE-5 Ground-Motion Prediction at Far-Field Geophone and Accelerometer Array Sites and SPE-5 Moment and Corner-Frequency Prediction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xiaoning; Patton, Howard John; Chen, Ting

2016-03-25

This report offers predictions for the SPE-5 ground-motion and accelerometer array sites. These predictions pertain to the waveform and spectral amplitude at certain geophone sites using Denny&Johnson source model and a source model derived from SPE data; waveform, peak velocity and peak acceleration at accelerometer sites using the SPE source model and the finite-difference simulation with LLNL 3D velocity model; and the SPE-5 moment and corner frequency.

Lava Fountaining Discharge Regime driven by Slug-to-Churn Flow Transition. (Invited)

NASA Astrophysics Data System (ADS)

Ripepe, M.; Pioli, L.; Marchetti, E.; Ulivieri, G.

2013-12-01

Lava fountaining episodes at Etna volcano appear characterized by the transition between Strombolian and Hawaiian end-member eruptive styles. There is no evidence for this transition in the seismic (i.e. seismic tremor) signal. However, infrasonic records provide unprecedented evidence on this flow transition. Each eruptive episode is characterized by distinctive common trend in the amplitude, waveform and frequency content of the infrasonic wavefield, which evidences the shift from discrete, and transient, strombolian to sustained, and oscillatory, lava fountain dynamics. Large scale experiments on the dynamics of two-phase flow of basaltic magmas show how the transition between different regimes mainly depends on gas volume flow, which in turn controls pressure distribution within the conduit and also magma vesicularity. In particular, while regular large bubble bursting is associated with slug flow regime, large amplitude and low frequency column oscillations are associated with churn flow. In large pipes, transition from slug to churn flow regime is independent on conduit diameter and it is reached at high superficial gas velocity. Lava fountaining episodes at Etna can be thus interpreted as induced by the transition from the slug (discrete strombolian) to churn flow (sustained lava fountain) regimes that is reflecting an increase in the gas discharge rate. Based on laboratory experiments, we calculate that transition between these two end-member explosive regimes at Etna occurs when gas superficial velocity is 76 m/s for near-the-vent stagnant magma conditions.

Seismic Structure of the Antarctic Upper Mantle and Transition Zone Unearthed by Full Waveform Adjoint Tomography

NASA Astrophysics Data System (ADS)

Lloyd, A. J.; Wiens, D.; Zhu, H.; Tromp, J.; Nyblade, A.; Anandakrishnan, S.; Aster, R. C.; Huerta, A. D.; Winberry, J. P.; Wilson, T. J.; Dalziel, I. W. D.; Hansen, S. E.; Shore, P.

2017-12-01

The upper mantle and transition zone beneath Antarctica and the surrounding ocean are among the poorest seismically imaged regions of the Earth's interior. Over the last 1.5 decades researchers have deployed several large temporary broadband seismic arrays focusing on major tectonic features in the Antarctic. The broader international community has also facilitated further instrumentation of the continent, often operating stations in additional regions. As of 2016, waveforms are available from almost 300 unique station locations. Using these stations along with 26 southern mid-latitude seismic stations we have imaged the seismic structure of the upper mantle and transition zone using full waveform adjoint techniques. The full waveform adjoint inversion assimilates phase observations from 3-component seismograms containing P, S, Rayleigh, and Love waves, including reflections and overtones, from 270 earthquakes (5.5 ≤ Mw ≤ 7.0) that occurred between 2001-2003 and 2007-2016. We present the major results of the full waveform adjoint inversion following 20 iterations, resulting in a continental-scale seismic model (ANT_20) with regional-scale resolution. Within East Antarctica, ANT_20 reveals internal seismic heterogeneity and differences in lithospheric thickness. For example, fast seismic velocities extending to 200-300 km depth are imaged beneath both Wilkes Land and the Gamburtsev Subglacial Mountains, whereas fast velocities only extend to 100-200 km depth beneath the Lambert Graben and Enderby Land. Furthermore, fast velocities are not found beneath portions of Dronning Maud Land, suggesting old cratonic lithosphere may be absent. Beneath West Antarctica slow upper mantle seismic velocities are imaged extending from the Balleny Island southward along the Transantarctic Mountains front, and broaden beneath the southern and northern portion of the mountain range. In addition, slow upper mantle velocities are imaged beneath the West Antarctic coast extending from Marie Byrd Land to the Antarctic Peninsula. This region of slow velocity only extends to 150-200 km depth beneath the Antarctic Peninsula, while elsewhere it extends to deeper upper mantle depths and possibly into the transition zone as well as offshore, suggesting two different geodynamic processes are at play.

Resolvability of regional density structure

NASA Astrophysics Data System (ADS)

Plonka, A.; Fichtner, A.

2016-12-01

Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convectivemotion. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravityprovide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling,making strong assumptions on the origin of structural heterogeneities, which may not necessarily be correct. Our goal is to assessif 3D density structure may be resolvable with emerging full-waveform inversion techniques. We have previously quantified the impact of regional-scale crustal density structure on seismic waveforms with the conclusion that reasonably sized density variations within thecrust can leave a strong imprint on both travel times and amplitudes, and, while this can produce significant biases in velocity and Q estimates, the seismic waveform inversion for density may become feasible. In this study we performprincipal component analyses of sensitivity kernels for P velocity, S velocity, and density. This is intended to establish theextent to which these kernels are linearly independent, i.e. the extent to which the different parameters may be constrainedindependently. Since the density imprint we observe is not exclusively linked to travel times and amplitudes of specific phases,we consider waveform differences between complete seismograms. We test the method using a known smooth model of the crust and seismograms with clear Love and Rayleigh waves, showing that - as expected - the first principal kernel maximizes sensitivity to SH and SV velocity structure, respectively, and that the leakage between S velocity, P velocity and density parameter spaces is minimal in the chosen setup. Next, we apply the method to data from 81 events around the Iberian Penninsula, registered in total by 492 stations. The objective is to find a principal kernel which would maximize the sensitivity to density, potentially allowing for independent density resolution, and, as the final goal, for direct density inversion.

Full Waveform Inversion of Diving & Reflected Waves based on Scale Separation for Velocity and Impedance Imaging

NASA Astrophysics Data System (ADS)

Brossier, Romain; Zhou, Wei; Operto, Stéphane; Virieux, Jean

2015-04-01

Full Waveform Inversion (FWI) is an appealing method for quantitative high-resolution subsurface imaging (Virieux et al., 2009). For crustal-scales exploration from surface seismic, FWI generally succeeds in recovering a broadband of wavenumbers in the shallow part of the targeted medium taking advantage of the broad scattering-angle provided by both reflected and diving waves. In contrast, deeper targets are often only illuminated by short-spread reflections, which favor the reconstruction of the short wavelengths at the expense of the longer ones, leading to a possible notch in the intermediate part of the wavenumber spectrum. To update the velocity macromodel from reflection data, image-domain strategies (e.g., Symes & Carazzone, 1991) aim to maximize a semblance criterion in the migrated domain. Alternatively, recent data-domain strategies (e.g., Xu et al., 2012, Ma & Hale, 2013, Brossier et al., 2014), called Reflection FWI (RFWI), inspired by Chavent et al. (1994), rely on a scale separation between the velocity macromodel and prior knowledge of the reflectivity to emphasize the transmission regime in the sensitivity kernel of the inversion. However, all these strategies focus on reflected waves only, discarding the low-wavenumber information carried out by diving waves. With the current development of very long-offset and wide-azimuth acquisitions, a significant part of the recorded energy is provided by diving waves and subcritical reflections, and high-resolution tomographic methods should take advantage of all types of waves. In this presentation, we will first review the issues of classical FWI when applied to reflected waves and how RFWI is able to retrieve the long wavelength of the model. We then propose a unified formulation of FWI (Zhou et al., 2014) to update the low wavenumbers of the velocity model by the joint inversion of diving and reflected arrivals, while the impedance model is updated thanks to reflected wave only. An alternate inversion of high wavenumber impedance model and low wavenumber velocity model is performed to iteratively improve subsurface models. References : Brossier, R., Operto, S. & Virieux, J., 2014. Velocity model building from seismic reflection data by full waveform inversion, Geophysical Prospecting, doi:10.1111/1365-2478.12190 Chavent, G., Clément, F. & Gomez, S., 1994.Automatic determination of velocities via migration-based traveltime waveform inversion: A synthetic data example, SEG Technical Program Expanded Abstracts 1994, pp. 1179--1182. Ma, Y. & Hale, D., 2013. Wave-equation reflection traveltime inversion with dynamic warping and full waveform inversion, Geophysics, 78(6), R223--R233. Symes, W.W. & Carazzone, J.J., 1991. Velocity inversion by differential semblance optimization, Geophysics, 56, 654--663. Virieux, J. & Operto, S., 2009. An overview of full waveform inversion in exploration geophysics, Geophysics, 74(6), WCC1--WCC26. Xu, S., Wang, D., Chen, F., Lambaré, G. & Zhang, Y., 2012. Inversion on reflected seismic wave, SEG Technical Program Expanded Abstracts 2012, pp. 1--7. Zhou, W., Brossier, R., Operto, S., & Virieux, J., 2014. Acoustic multiparameter full-waveform inversion through a hierachical scheme, in SEG Technical Program Expanded Abstracts 2014, pp. 1249--1253

Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion

NASA Astrophysics Data System (ADS)

Davy, R. G.; Morgan, J. V.; Minshull, T. A.; Bayrakci, G.; Bull, J. M.; Klaeschen, D.; Reston, T. J.; Sawyer, D. S.; Lymer, G.; Cresswell, D.

2018-01-01

Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterized by a complex pattern of faulting, thin continental fault blocks and the serpentinization, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Traveltime tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here, we demonstrate the application of 2-D time-domain acoustic full-waveform inversion (FWI) to deep-water seismic data collected at the Deep Galicia Margin, in order to attain a high-resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modeled waveforms, checkerboard tests, testing of parameter and inversion strategy and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector, there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinization. This study supports the hypothesis that normal faulting acts to hydrate the upper-mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinization. Our results confirm the feasibility of applying the FWI method to sparse, deep-water crustal data sets.

Observations of changes in waveform character induced by the 1999 Mw7.6 Chi-Chi earthquake

USGS Publications Warehouse

Chen, K.H.; Furumura, T.; Rubinstein, J.; Rau, R.-J.

2011-01-01

We observe changes in the waveforms of repeating earthquakes in eastern Taiwan following the 1999 Mw7.6 Chi-Chi earthquake, while their recurrence intervals appear to be unaffected. There is a clear reduction in waveform similarity and velocity changes indicated by delayed phases at the time of the Chi-Chi event. These changes are limited to stations in and paths that cross the 70 × 100 km region surrounding the Chi-Chi source area, the area where seismic intensity and co-seismic surface displacements were largest. This suggests that damage at the near-surface is responsible for the observed waveform changes. Delays are largest in the late S-wave coda, reaching approximately 120 ms. This corresponds to a path averaged Swave velocity reduction of approximately 1%. There is also evidence that damage in the fault-zone caused changes in waveform character at sites in the footwall, where source-receiver paths propagate either along or across the rupture. The reduction in waveform similarity persists through the most recent repeating event in our study (November 15, 2007), indicating that the subsurface damage induced by the Chi-Chi earthquake did not fully heal within the first 8 years following the Chi-Chi earthquake.

Observations of changes in waveform character induced by the 1999 M w7.6 Chi-Chi earthquake

USGS Publications Warehouse

Chen, K.H.; Furumura, T.; Rubinstein, J.; Rau, R.-J.

2011-01-01

We observe changes in the waveforms of repeating earthquakes in eastern Taiwan following the 1999 Mw7.6 Chi-Chi earthquake, while their recurrence intervals appear to be unaffected. There is a clear reduction in waveform similarity and velocity changes indicated by delayed phases at the time of the Chi-Chi event. These changes are limited to stations in and paths that cross the 70 ?? 100 km region surrounding the Chi-Chi source area, the area where seismic intensity and co-seismic surface displacements were largest. This suggests that damage at the near-surface is responsible for the observed waveform changes. Delays are largest in the late S-wave coda, reaching approximately 120 ms. This corresponds to a path averaged S wave velocity reduction of approximately 1%. There is also evidence that damage in the fault-zone caused changes in waveform character at sites in the footwall, where source-receiver paths propagate either along or across the rupture. The reduction in waveform similarity persists through the most recent repeating event in our study (November 15, 2007), indicating that the subsurface damage induced by the Chi-Chi earthquake did not fully heal within the first 8 years following the Chi-Chi earthquake. ?? 2011 by the American Geophysical Union.

Transdimensional inversion of scattered body waves for 1D S-wave velocity structure - Application to the Tengchong volcanic area, Southwestern China

NASA Astrophysics Data System (ADS)

Li, Mengkui; Zhang, Shuangxi; Bodin, Thomas; Lin, Xu; Wu, Tengfei

2018-06-01

Inversion of receiver functions is commonly used to recover the S-wave velocity structure beneath seismic stations. Traditional approaches are based on deconvolved waveforms, where the horizontal component of P-wave seismograms is deconvolved by the vertical component. Deconvolution of noisy seismograms is a numerically unstable process that needs to be stabilized by regularization parameters. This biases noise statistics, making it difficult to estimate uncertainties in observed receiver functions for Bayesian inference. This study proposes a method to directly invert observed radial waveforms and to better account for data noise in a Bayesian formulation. We illustrate its feasibility with two synthetic tests having different types of noises added to seismograms. Then, a real site application is performed to obtain the 1-D S-wave velocity structure beneath a seismic station located in the Tengchong volcanic area, Southwestern China. Surface wave dispersion measurements spanning periods from 8 to 65 s are jointly inverted with P waveforms. The results show a complex S-wave velocity structure, as two low velocity zones are observed in the crust and uppermost mantle, suggesting the existence of magma chambers, or zones of partial melt. The upper magma chambers may be the heart source that cause the thermal activity on the surface.

Nonlinear dynamics of shells conveying pulsatile flow with pulse-wave propagation. Theory and numerical results for a single harmonic pulsation

NASA Astrophysics Data System (ADS)

Tubaldi, Eleonora; Amabili, Marco; Païdoussis, Michael P.

2017-05-01

In deformable shells conveying pulsatile flow, oscillatory pressure changes cause local movements of the fluid and deformation of the shell wall, which propagate downstream in the form of a wave. In biomechanics, it is the propagation of the pulse that determines the pressure gradient during the flow at every location of the arterial tree. In this study, a woven Dacron aortic prosthesis is modelled as an orthotropic circular cylindrical shell described by means of the Novozhilov nonlinear shell theory. Flexible boundary conditions are considered to simulate connection with the remaining tissue. Nonlinear vibrations of the shell conveying pulsatile flow and subjected to pulsatile pressure are investigated taking into account the effects of the pulse-wave propagation. For the first time in literature, coupled fluid-structure Lagrange equations of motion for a non-material volume with wave propagation in case of pulsatile flow are developed. The fluid is modeled as a Newtonian inviscid pulsatile flow and it is formulated using a hybrid model based on the linear potential flow theory and considering the unsteady viscous effects obtained from the unsteady time-averaged Navier-Stokes equations. Contributions of pressure and velocity propagation are also considered in the pressure drop along the shell and in the pulsatile frictional traction on the internal wall in the axial direction. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior of a pressurized Dacron aortic graft conveying blood flow. A pulsatile time-dependent blood flow model is considered by applying the first harmonic of the physiological waveforms of velocity and pressure during the heart beating period. Geometrically nonlinear vibration response to pulsatile flow and transmural pulsatile pressure, considering the propagation of pressure and velocity changes inside the shell, is here presented via frequency-response curves, time histories, bifurcation diagrams and Poincaré maps. It is shown that traveling waves of pressure and velocity cause a delay in the radial displacement of the shell at different values of the axial coordinate. The effect of different pulse wave velocities is also studied. Comparisons with the corresponding ideal case without wave propagation (i.e. with the same pulsatile velocity and pressure at any point of the shell) are here discussed. Bifurcation diagrams of Poincaré maps obtained from direct time integration have been used to study the system in the spectral neighborhood of the fundamental natural frequency. By increasing the forcing frequency, the response undergoes very complex nonlinear dynamics (chaos, amplitude modulation and period-doubling bifurcation), here deeply investigated.

Waveform Tomography Applied to Long Streamer MCS Data from the Scotian Slope

NASA Astrophysics Data System (ADS)

Delescluse, Matthias; Louden, Keith; Nedimovic, Mladen

2010-05-01

Detailed velocity models of the earth subsurface can be obtained through waveform tomography, a method that relies on using information from the full wavefield. Such models can be of significantly higher resolution than the corresponding models formed by more generic traveltime tomography methods, which are constrained only by the wave arrival times. However, to derive the detailed subsurface velocity, the waveform method is sensitive to modelling low-frequency refracted waves that have long paths through target structures. Thus field examples primarily have focused on the analysis of long-offset wide-angle datasets collected using autonomous receivers, in which refractions arrive at earlier times than reflections and there is a significant separation between the two wave arrivals. MCS datasets with shorter offsets typically lack these important features, which result in methodological problems (e.g. Hicks and Pratt, 2001), even though they benefit from a high density of raypaths and uniformity of receiver and shot properties. Modern marine seismic acquisition using long streamers now offers both the ability to record refracted waves at far offsets arriving ahead of the seafloor reflection, and the ability to do this at great density using uniform sources. In this study, we use 2D MCS data acquired with a 9-km-long streamer by ION GX-Technology over the Nova Scotia Slope in water depths of ~1600 m. We show that the refracted arrivals, although restricted to receivers between offsets of 7.5 and 9 km, provide sufficient information to successfully invert for a high-resolution velocity field. Using a frequency domain acoustic code (Pratt, 1999) over frequencies from 8 Hz to 24 Hz on two crossing profiles (45 and 20 km long), we detail how the limited refracted waves can constrain the velocity field above the depth of the turning waves (~1.5 km below seafloor). Several important features are resolved by the waveform velocity model that are not present in the initial travel-time model. In particular, a high velocity layer due to gas hydrates is imaged along the entire profile even where a characteristic BSR is not visible. The velocity increase in the gas hydrate layer is very small (< 100 m/s). In addition, a strong velocity increase of ~ 300 m/s exists below a deeper, gently dipping reflector along which discontinuous low-velocity zones, probably related to gas, are present. Velocity models are consistent at the crossing point between the two profiles. The depth limitation of the detailed MCS waveform tomography imaging could be extended by even longer streamers (e.g. 15 km) or by joint inversion with OBS data.

A compositional origin to ultralow-velocity zones

NASA Astrophysics Data System (ADS)

Brown, Samuel P.; Thorne, Michael S.; Miyagi, Lowell; Rost, Sebastian

2015-02-01

We analyzed vertical component short-period ScP waveforms for 26 earthquakes occurring in the Tonga-Fiji trench recorded at the Alice Springs Array in central Australia. These waveforms show strong precursory and postcursory seismic arrivals consistent with ultralow-velocity zone (ULVZ) layering beneath the Coral Sea. We used the Viterbi sparse spike detection method to measure differential travel times and amplitudes of the postcursor arrival ScSP and the precursor arrival SPcP relative to ScP. We compare our measurements to a database of 340,000 synthetic seismograms finding that these data are best fit by a ULVZ model with an S wave velocity reduction of 24%, a P wave velocity reduction of 23%, a thickness of 8.5 km, and a density increase of 6%. This 1:1 VS:VP velocity decrease is commensurate with a ULVZ compositional origin and is most consistent with highly iron enriched ferropericlase.

Receiver function HV ratio: a new measurement for reducing non-uniqueness of receiver function waveform inversion

NASA Astrophysics Data System (ADS)

Chong, Jiajun; Chu, Risheng; Ni, Sidao; Meng, Qingjun; Guo, Aizhi

2018-02-01

It is known that a receiver function has relatively weak constraint on absolute seismic wave velocity, and that joint inversion of the receiver function with surface wave dispersion has been widely applied to reduce the trade-off of velocity with interface depth. However, some studies indicate that the receiver function itself is capable for determining the absolute shear-wave velocity. In this study, we propose to measure the receiver function HV ratio which takes advantage of the amplitude information of the receiver function to constrain the shear-wave velocity. Numerical analysis indicates that the receiver function HV ratio is sensitive to the average shear-wave velocity in the depth range it samples, and can help to reduce the non-uniqueness of receiver function waveform inversion. A joint inversion scheme has been developed, and both synthetic tests and real data application proved the feasibility of the joint inversion.

Fault-zone waves observed at the southern Joshua Tree earthquake rupture zone

USGS Publications Warehouse

Hough, S.E.; Ben-Zion, Y.; Leary, P.

1994-01-01

Waveform and spectral characteristics of several aftershocks of the M 6.1 22 April 1992 Joshua Tree earthquake recorded at stations just north of the Indio Hills in the Coachella Valley can be interpreted in terms of waves propagating within narrow, low-velocity, high-attenuation, vertical zones. Evidence for our interpretation consists of: (1) emergent P arrivals prior to and opposite in polarity to the impulsive direct phase; these arrivals can be modeled as headwaves indicative of a transfault velocity contrast; (2) spectral peaks in the S wave train that can be interpreted as internally reflected, low-velocity fault-zone wave energy; and (3) spatial selectivity of event-station pairs at which these data are observed, suggesting a long, narrow geologic structure. The observed waveforms are modeled using the analytical solution of Ben-Zion and Aki (1990) for a plane-parallel layered fault-zone structure. Synthetic waveform fits to the observed data indicate the presence of NS-trending vertical fault-zone layers characterized by a thickness of 50 to 100 m, a velocity decrease of 10 to 15% relative to the surrounding rock, and a P-wave quality factor in the range 25 to 50.

Velocity and Attenuation Structure of the Earth's Inner Core Boundary From Semi-Automatic Waveform Modeling

NASA Astrophysics Data System (ADS)

Jin, J.; Song, X.; Sun, D.; Helmberger, D. V.

2013-12-01

The structure of the Earth's inner core boundary (ICB) is complex. Hemispherical differences and local variations of velocity and attenuation structures, as well as the ICB topography have been reported in previous studies. We are using an automatic waveform modeling method to improve the resolution of the ICB structures. The full waveforms of triplicated PKP phases at distance ranges from 120 to 165 degrees are used to model the lowermost 200 km of the outer core and the uppermost 600km of the inner core. Given a 1D velocity and attenuation model, synthetic seismograms are generated by Generalized Ray Theory. We are also experimenting 2D synthetic methods (WKM, AXISEM, and 2D FD) for 2D models (in the mantle and the inner core). The source time function is determined by observed seismic data. We use neighborhood algorithm to search for a group of models that minimize the misfit between predictions and observations. Tests on synthetic data show the efficiency of this method in resolving detailed velocity and attenuation structures of the ICB simultaneously. We are analyzing seismic record sections at dense arrays along different paths and will report our modeling and inversion results in the meeting.

Waveform Tomography of the South Atlantic Region

NASA Astrophysics Data System (ADS)

Celli, N. L.; Lebedev, S.; Schaeffer, A. J.; Gaina, C.

2016-12-01

The rapid growth in broadband seismic data, along with developments in waveform tomography techniques, allow us to greatly improve the data sampling in the southern hemisphere and resolve the upper-mantle structure beneath the South Atlantic region at a new level of detail. We have gathered a very large waveform dataset, including all publicly available data from permanent and temporary networks. Our S-velocity tomographic model is constrained by vertical-component waveform fits, computed using the Automated Multimode Inversion of surface, S and multiple S waves. Each seismogram fit provides a set of linear equations describing 1D average velocity perturbations within approximate sensitivity volumes, with respect to a 3D reference model. All the equations are then combined into a large linear system and inverted jointly for a model of shear- and compressional-wave speeds and azimuthal anisotropy within the lithosphere and underlying mantle. The isotropic-average shear speeds are proxies for temperature and composition at depth, while azimuthal anisotropy provides evidence on the past and present deformation in the lithosphere and asthenosphere beneath the region. We resolve the complex boundaries of the mantle roots of South America's and Africa's cratons and the deep low-velocity anomalies beneath volcanic areas in South America. Pronounced lithospheric high seismic velocity anomalies beneath the Argentine Basin suggest that its anomalously deep seafloor, previously attributed to dynamic topography, is mainly due to anomalously cold, thick lithosphere. Major hotspots show low-velocity anomalies extending substantially deeper than those beneath the mid-ocean ridge. The Vema Hotspot shows a major, hot asthenospheric anomaly beneath thick, cold oceanic lithosphere. The mantle lithosphere beneath the Walvis Ridge—a hotspot track—shows normal cooling. The volcanic Cameroon Line, in contrast, is characterized by thin lithosphere beneath the locations of recent volcanism.

Effect of non-linearity in predicting doppler waveforms through a novel model

PubMed Central

Gayasen, Aman; Dua, Sunil Kumar; Sengupta, Amit; Nagchoudhuri, D

2003-01-01

Background In pregnancy, the uteroplacental vascular system develops de novo locally in utero and a systemic haemodynamic & bio-rheological alteration accompany it. Any abnormality in the non-linear vascular system is believed to trigger the onset of serious morbid conditions like pre-eclampsia and/or intrauterine growth restriction (IUGR). Exact Aetiopathogenesis is unknown. Advancement in the field of non-invasive doppler image analysis and simulation incorporating non-linearities may unfold the complexities associated with the inaccessible uteroplacental vessels. Earlier modeling approaches approximate it as a linear system. Method We proposed a novel electrical model for the uteroplacental system that uses MOSFETs as non-linear elements in place of traditional linear transmission line (TL) model. The model to simulate doppler FVW's was designed by including the inputs from our non-linear mathematical model. While using the MOSFETs as voltage-controlled switches, a fair degree of controlled-non-linearity has been introduced in the model. Comparative analysis was done between the simulated data and the actual doppler FVW's waveforms. Results & Discussion Normal pregnancy has been successfully modeled and the doppler output waveforms are simulated for different gestation time using the model. It is observed that the dicrotic notch disappears and the S/D ratio decreases as the pregnancy matures. Both these results are established clinical facts. Effects of blood density, viscosity and the arterial wall elasticity on the blood flow velocity profile were also studied. Spectral analysis on the output of the model (blood flow velocity) indicated that the Total Harmonic Distortion (THD) falls during the mid-gestation. Conclusion Total harmonic distortion (THD) is found to be informative in determining the Feto-maternal health. Effects of the blood density, the viscosity and the elasticity changes on the blood FVW are simulated. Future works are expected to concentrate mainly on improving the load with respect to varying non-linear parameters in the model. Heart rate variability, which accounts for the vascular tone, should also be included. We also expect the model to initiate extensive clinical or experimental studies in the near future. PMID:14561227

Upper mantle velocity structure beneath southern Africa from modeling regional seismic data

NASA Astrophysics Data System (ADS)

Zhao, Ming; Langston, Charles A.; Nyblade, Andrew A.; Owens, Thomas J.

1999-03-01

The upper mantle seismic velocity structure beneath southern Africa is investigated using travel time and waveform data which come from a large mine tremor in South Africa (mb 5.6) recorded by the Tanzania broadband seismic experiment and by several stations in southern Africa. The waveform data show upper mantle triplications for both the 410- and 670-km discontinuities between distances of 2100 and 3000 km. Auxiliary travel time data along similar profiles obtained from other moderate events are also used. P wave travel times are inverted for velocity structure down to ˜800-km depth using the Wiechert-Herglotz technique, and the resulting model is evaluated by perturbing it at three depth intervals and then testing the perturbed model against the travel time and waveform data. The results indicate a typical upper mantle P wave velocity structure for a shield. P wave velocities from the top of the mantle down to 300-km depth are as much as 3% higher than the global average and are slightly slower than the global average between 300- and 420-km depth. Little evidence is found for a pronounced low-velocity zone in the upper mantle. A high-velocity gradient zone is required above the 410-km discontinuity, but both sharp and smooth 410-km discontinuities are permitted by the data. The 670-km discontinuity is characterized by high-velocity gradients over a depth range of ˜80 km around 660-km depth. Limited S wave travel time data suggest fast S wave velocities above ˜150-km depth. These results suggest that the bouyant support for the African superswell does not reside at shallow depths in the upper mantle.

Difference in perception of angular displacement according to applied waveforms.

PubMed

Kushiro, Keisuke; Goto, Fumiyuki

2013-05-01

This study shows that the differences in the waveforms of angular rotation affect the perception and memory of angular displacement. During daily life, when we turn our head during various activities, our brain calculates how much angular displacement our head has undergone. However, how we obtain an accurate estimation of this angular displacement remains unclarified. This study aims to clarify this issue by investigating the perception and memory of passive rotation for three different waveforms of angular velocity rotation (sinusoidal (sine), triangle, and step). Thirteen healthy young subjects sitting on a servo-controlled chair were passively rotated at 60° or 120° about the earth-vertical axis by using one of these three angular velocity waveforms. They then attempted to reproduce the rotation angle by rotating the chair in the same direction in which they had been passively rotated using a handheld controller. The gain (reproduced angle/passively rotated angle) was calculated and used for the evaluation of the perception and memory of angular rotation. The gain for step rotation was larger than that for sine and triangle rotations, with statistical significance. This confirms that the difference in the waveforms of angular rotation affects the perception and memory of angular displacement.

Is amplitude loss of sonic waveforms due to intrinsic attenuation or source coupling to the medium?

USGS Publications Warehouse

Lee, Myung W.

2006-01-01

Sonic waveforms acquired in gas-hydrate-bearing sediments indicate strong amplitude loss associated with an increase in sonic velocity. Because the gas hydrate increases sonic velocities, the amplitude loss has been interpreted as due to intrinsic attenuation caused by the gas hydrate in the pore space, which apparently contradicts conventional wave propagation theory. For a sonic source in a fluid-filled borehole, the signal amplitude transmitted into the formation depends on the physical properties of the formation, including any pore contents, in the immediate vicinity of the source. A signal in acoustically fast material, such as gas-hydrate-bearing sediments, has a smaller amplitude than a signal in acoustically slower material. Therefore, it is reasonable to interpret the amplitude loss in the gas-hydrate-bearing sediments in terms of source coupling to the surrounding medium as well as intrinsic attenuation. An analysis of sonic waveforms measured at the Mallik 5L-38 well, Northwest Territories, Canada, indicates that a significant part of the sonic waveform's amplitude loss is due to a source-coupling effect. All amplitude analyses of sonic waveforms should include the effect of source coupling in order to accurately characterize the formation's intrinsic attenuation.

Seismic wave propagation through an extrusive basalt sequence

NASA Astrophysics Data System (ADS)

Sanford, Oliver; Hobbs, Richard; Brown, Richard; Schofield, Nick

2016-04-01

Layers of basalt flows within sedimentary successions (e.g. in the Faeroe-Shetland Basin) cause complex scattering and attenuation of seismic waves during seismic exploration surveys. Extrusive basaltic sequences are highly heterogeneous and contain strong impedance contrasts between higher velocity crystalline flow cores (˜6 km s-1) and the lower velocity fragmented and weathered flow crusts (3-4 km s-1). Typically, the refracted wave from the basaltic layer is used to build a velocity model by tomography. This velocity model is then used to aid processing of the reflection data where direct determination of velocity is ambiguous, or as a starting point for full waveform inversion, for example. The model may also be used as part of assessing drilling risk of potential wells, as it is believed to constrain the total thickness of the sequence. In heterogeneous media, where the scatter size is of the order of the seismic wavelength or larger, scattering preferentially traps the seismic energy in the low velocity regions. This causes a build-up of energy that is guided along the low velocity layers. This has implications for the interpretation of the observed first arrival of the seismic wave, which may be a biased towards the low velocity regions. This will then lead to an underestimate of the velocity structure and hence the thickness of the basalt, with implications for the drilling of wells hoping to penetrate through the base of the basalts in search of hydrocarbons. Using 2-D acoustic finite difference modelling of the guided wave through a simple layered basalt sequence, we consider the relative importance of different parameters of the basalt on the seismic energy propagating through the layers. These include the proportion of high to low velocity material, the number of layers, their thickness and the roughness of the interfaces between the layers. We observe a non-linear relationship between the ratio of high to low velocity layers and the apparent velocity of the first arrival suggesting that such a sequence may cause a reduction of the apparent velocity by as much as 1 km s-1. We also find that the rate of amplitude decay in the higher velocity layer is related to the interface roughness between the basalt layers.

3-D S-velocity structure in the lowermost mantle beneath the Northern Pacific

NASA Astrophysics Data System (ADS)

Suzuki, Y.; Kawai, K.; Geller, R. J.; Borgeaud, A. F. E.; Konishi, K.

2017-12-01

We previously (Suzuki et al., EPS, 2016) reported the results of waveform inversion to infer the three-dimensional (3-D) S-velocity structure in the lowermost 400 km of the mantle (the Dʺ region) beneath the Northern Pacific region. Our dataset consists of about 20,000 transverse component broadband body-wave seismograms observed at North American stations (mainly USArray) for 131 intermediate and deep earthquakes which occurred beneath the western Pacific subduction region. Synthetic resolution tests indicate that our methods and dataset can resolve the velocity structure in the target region with a horizontal scale of about 150 km and a vertical scale of about 50 km. The 3-D S-velocity model obtained in that study shows three prominent features: (i) horizontal high-velocity anomalies up to about 3 per cent faster than the Preliminary Reference Earth Model (PREM) with a thickness of a few hundred km and a lower boundary which is at most about 150 km above the core-mantle boundary (CMB), (ii) low-velocity anomalies about 2.5 per cent slower than PREM beneath the high-velocity anomalies at the base of the lower mantle, (iii) a thin (about 150 km) low-velocity structure continuous from the base of the low-velocity zone to at least 400 km above the CMB. We interpret these features respectively as: (i) remnants of slab material where the Mg-perovskite to Mg-post-perovskite phase transition could have occurred within the slab, (ii, iii) large amounts of hot and less dense materials beneath the cold Kula or Pacific slab remnants immediately above the CMB which ascend and form a passive plume upwelling at the edge of the slab remnants. Since our initial work we subsequently conducted waveform inversion using both the transverse- and radial-component horizontal waveform data to infer the isotropic shear velocity structure in the lowermost mantle beneath the Northern Pacific in more detail. We also compute partial derivatives with respect to the 5 independent elastic constants (A, C, F, L, N) of a transversely isotropy (TI) medium, and conduct a synthetic resolution test to examine the ability of our methods and dataset to resolve the anisotropic structure in this region using two-component waveform data.

Velocity Structure of the Subducted Yakutat Terrane, Alaska: Insights from Guided Waves

NASA Astrophysics Data System (ADS)

Coulson, S.; Garth, T.; Rietbrock, A.

2017-12-01

Subduction zone guided wave arrivals from intermediate depth earthquakes provide insight into the fine scale velocity structure of the subducting oceanic crust as it dehydrates. These observations can be used to determine the average velocity and thickness of the crustal low velocity layer (LVL) at depth, allowing inferences to be drawn about composition and degree of hydration. We constrain guided wave dispersion by comparing waveforms recorded in the subduction forearc with simulated waveforms, produced using a 2D finite difference waveform propagation model. The structure of the Aleutian arc is complex due to the accretion of the Yakutat Terrane (YT) to the east, which is partially coupled with the subducting Pacific plate. An unusually thick LVL associated with the YT has been inferred down to 140 km depth by receiver function studies and travel time tomography. Focussing on a profile running NNW-SSE close to Anchorage, we constrain slab geometry using global and local catalogues, as well as the curvature inferred from receiver functions (Kim et al., 2014). P-wave arrivals from 41 earthquakes (2012-2015) show significant guided wave dispersion on at least one station; high frequency (>1-3 Hz) energy is delayed by up to 2-3 seconds. Choosing the clearest dispersion observations, we systematically vary both LVL width and P-wave velocity, to find the lowest misfit between the observed and synthetic waveforms. Multiple modelled events show the thickness of the LVL associated with subducted YT to be 6-10 km, significantly thinner than inferred by receiver function studies. Most events are accounted for by an LVL velocity contrast of 12.5-15% with overriding mantle material, however, observations of the deepest event in the northern corner of the YT require a velocity contrast of 6%. Lower velocities in the shallower slab (70-120 km) cannot be accounted for by reacted or unreacted MORB or gabbro compositions. We postulate the presence of interbedded sediments within the YT reducing the bulk velocity of the LVL. Increased velocities seen at the northern edge of the YT can be explained by reacted MORB or gabbro assemblages. This may be explained by a lack of interbedded sediments in this part of the YT, or the warmer conditions at the edge of the subducted terrane causing a faster pace of metamorphic reaction in this part of the slab.

Low crustal velocities and mantle lithospheric variations in southern Tibet from regional Pnl waveforms

NASA Astrophysics Data System (ADS)

Rodgers, Arthur J.; Schwartz, Susan Y.

We report low average crustal P-wave velocities (5.9-6.1 km/s, Poisson's ratio 0.23-0.27, thickness 68-76 km) in southern Tibet from modelling regional Pnl waveforms recorded by the 1991-1992 Tibetan Plateau Experiment. We also find that the mantle lithosphere beneath the Indus-Tsangpo Suture and the Lhasa Terrane is shield-like (Pn velocity 8.20-8.25 km/s, lid thickness 80-140 km, positive velocity gradient 0.0015-0.0025 s-1). Analysis of relative Pn travel time residuals requires a decrease in the mantle velocities beneath the northern Lhasa Terrane, the Banggong-Nujiang Suture and the southern Qiangtang Terrane. Tectonic and petrologic considerations suggest that low bulk crustal velocities could result from a thick (50-60 km) felsic upper crust with vertically limited and laterally pervasive partial melt. These results are consistent with underthrusting of Indian Shield lithosphere beneath the Tibetan Plateau to at least the central Lhasa Terrane.

Pulse pressure waveform in hydrocephalus: what it is and what it isn't.

PubMed

Czosnyka, Marek; Czosnyka, Zofia; Keong, Nicole; Lavinio, Andreas; Smielewski, Piotr; Momjian, Shahan; Schmidt, Eric A; Petrella, Gianpaolo; Owler, Brian; Pickard, John D

2007-04-15

Apart from its mean value, the pulse waveform of intracranial pressure (ICP) is an essential element of pressure recording. The authors reviewed their experience with the measurement and interpretation of ICP pulse amplitude by referring to a database of recordings in hydrocephalic patients. The database contained computerized pressure recordings from 2100 infusion studies (either lumbar or intraventricular) or overnight ICP monitoring sessions in patients suffering from hydrocephalus of various types (both communicating and noncommunicating), origins, and stages of management (shunt or no shunt). Amplitude was calculated from ICP waveforms by using a spectral analysis methodology. The appearance of a pulse waveform amplitude is positive evidence of a technically correct recording of ICP and helps to distinguish between postural and vasogenic variations in ICP. Pulse amplitude is significantly correlated with the amplitude of cerebral blood flow velocity (R = 0.4, p = 0.012) as assessed using Doppler ultrasonography. Amplitude is positively correlated with a mean ICP (R = 0.21 in idiopathic normal-pressure hydrocephalus [NPH]; number of cases 131; p < 0.01) and resistance to cerebrospinal fluid outflow (R = 0.22) but does not seem to be correlated with cerebrospinal elasticity, dilation of ventricles, or severity of hydrocephalus (NPH score). Amplitude increases slightly with age (R = 0.39, p < 0.01; number of cases 46). A positive association between pulse amplitude and increased ICP during an infusion study is helpful in distinguishing between hydrocephalus and predominant brain atrophy. A large amplitude is associated with a good outcome after shunting (positive predictive power 0.9), whereas a low amplitude has no predictive power in outcome prognostication (0.5). Pulse amplitude is reduced by a properly functioning shunt. Proper recording, detection, and interpretation of ICP pulse waveforms provide clinically useful information about patients suffering from hydrocephalus.

Velocity Structure Determination Through Seismic Waveform Modeling and Time Deviations

NASA Astrophysics Data System (ADS)

Savage, B.; Zhu, L.; Tan, Y.; Helmberger, D. V.

2001-12-01

Through the use of seismic waveforms recorded by TriNet, a dataset of earthquake focal mechanisms and deviations (time shifts) relative to a standard model facilitates the investigation of the crust and uppermost mantle of southern California. The CAP method of focal mechanism determination, in use by TriNet on a routine basis, provides time shifts for surface waves and Pnl arrivals independently relative to the reference model. These shifts serve as initial data for calibration of local and regional seismic paths. Time shifts from the CAP method are derived by splitting the Pnl section of the waveform, the first arriving Pn to just before the arrival of the S wave, from the much slower surface waves then cross-correlating the data with synthetic waveforms computed from a standard model. Surface waves interact with the entire crust, but the upper crust causes the greatest effect. Whereas, Pnl arrivals sample the deeper crust, upper mantle, and source region. This natural division separates the upper from lower crust for regional calibration and structural modeling and allows 3-D velocity maps to be created using the resulting time shifts. Further examination of Pnl and other arrivals which interact with the Moho illuminate the complex nature of this boundary. Initial attempts at using the first 10 seconds of the Pnl section to determine upper most mantle structure have proven insightful. Two large earthquakes north of southern California in Nevada and Mammoth Lakes, CA allow the creation of record sections from 200 to 600 km. As the paths swing from east to west across southern California, simple 1-D models turn into complex structure, dramatically changing the waveform character. Using finite difference models to explain the structure, we determine that a low velocity zone is present at the base of the crust and extends to 100 km in depth. Velocity variations of 5 percent of the mantle in combination with steeply sloping edges produces complex waveform variations. Characteristics of this complex propagation appear from the southern Sierra Nevada Mountains, in the west, to Death Valley in the east. The structure does not cross the Garlock fault to the south, but we are unsure of the structures northern extent.

Novel wave intensity analysis of arterial pulse wave propagation accounting for peripheral reflections

PubMed Central

Alastruey, Jordi; Hunt, Anthony A E; Weinberg, Peter D

2014-01-01

We present a novel analysis of arterial pulse wave propagation that combines traditional wave intensity analysis with identification of Windkessel pressures to account for the effect on the pressure waveform of peripheral wave reflections. Using haemodynamic data measured in vivo in the rabbit or generated numerically in models of human compliant vessels, we show that traditional wave intensity analysis identifies the timing, direction and magnitude of the predominant waves that shape aortic pressure and flow waveforms in systole, but fails to identify the effect of peripheral reflections. These reflections persist for several cardiac cycles and make up most of the pressure waveform, especially in diastole and early systole. Ignoring peripheral reflections leads to an erroneous indication of a reflection-free period in early systole and additional error in the estimates of (i) pulse wave velocity at the ascending aorta given by the PU–loop method (9.5% error) and (ii) transit time to a dominant reflection site calculated from the wave intensity profile (27% error). These errors decreased to 1.3% and 10%, respectively, when accounting for peripheral reflections. Using our new analysis, we investigate the effect of vessel compliance and peripheral resistance on wave intensity, peripheral reflections and reflections originating in previous cardiac cycles. PMID:24132888

Ultrasonic assessment of hepatic blood flow as a marker of mouse hepatocarcinoma.

PubMed

Bonnin, Philippe; Villemain, Aude; Vincent, François; Debbabi, Haythem; Silvestre, Jean Sébastien; Contreres, Jean Olivier; Levy, Bernard I; Tobelem, Gérard; Dupuy, Evelyne

2007-04-01

Two-dimensional color-coded pulsed Doppler ultrasonography (US) with a 12-MHz linear transducer was used to follow tumor growth and neoangiogenesis development in 12 transgenic mice developing a whole liver hepatocellular carcinoma (HCC) induced by the expression of SV40-T antigen. In this model, male mice developed HCC at various temporal and histologic stages (hyperplastic, four-eight wk; nodular, 12 wk; diffuse carcinoma, 16-20 wk), whereas female mice remained tumor free. Seven age-matched tumor-free mice were used as controls. Liver volume was calculated from B-mode images of the abdomen. Blood flow waveforms were recorded from the hepatic tumor-feeding artery upstream from the tumor vessels, allowing quantitative blood flow velocity measurements. Measurements were performed every four weeks from four to 20 weeks. As early as the hyperplastic stage (eight weeks), liver volume was increased by 2.7-fold, hepatic artery peak-systolic blood flow velocities (BFV) by 1.5-fold, end-diastolic BFV by 1.6-fold and mean BFV by 2.0-fold compared with control values (p < 0.001). Differences increased until 20 weeks and peak-systolic reached 90 +/- 6, end-diastolic 54 +/- 5 and mean BFV 48 +/- 5 cm s(-1). Successive measurements of BFV were reproducible and intraobserver repeatability coefficient values were <3 cm s(-1). In contrast, mesenteric artery BFV, which did not supply tumor region, did not show any significant difference with respect to control values. Thus, an increase in BFV constitutes a functional evaluation of tumor vascularity. In preclinical studies in small animals, measurements of liver volume and blood flow velocities in hepatic tumor-feeding artery provide a useful, reproducible, noninvasive, easy-to-repeat tool to monitor tumor growth and neoangiogenesis in hepatocellular carcinoma in mice.

Velocity structure around the 410 km discontinuity beneath the East China Sea based on the waveform modeling method

NASA Astrophysics Data System (ADS)

Li, W.; Cui, Q.; Gao, Y.; Wei, R.; Zhou, Y.; Yu, J.

2017-12-01

The 410 km discontinuity is the upper boundary of the mantle transition zone. Seismic detections on the structure and morphology of the 410 km discontinuity are helpful to understand the compositions of the Earth's interior and the relevant geodynamics. In this paper, we select the broadband P waveforms of an intermediate earthquake that occurred in the Ryukyu subduction zone and retrieved from the China Digital Seismograph Network, and study the fine velocity structure around the 410 km discontinuity by matching the observed triplicated waveforms with the theoretical ones. Our results reveal that (1) the 410 km discontinuity beneath the East China Sea is mostly a sharp boundary with a small-scale uplift of 8-15 km and a gradient boundary up to 20 km in the most southern part, and (2) there exist a low velocity layer atop the 410 km discontinuity with the thickness of 50-62 km and P-wave velocity decrease of 0.5%-1.5%, and (3) a high velocity anomaly with P-wave decrease of 1.0%-3.0% below 440 km. Combining with the previous topographic results in this area, we speculate that the high velocity anomaly is relevant to the stagnancy of the western Pacific slab in the mantle transition zone, the decomposition of phase E in the slab results in the increase of water content, which would cause the uplift of the 410 km discontinuity, and the low velocity layer atop the discontinuity should be related to the partial melting of the mantle peridotite induced by the dehydration of the hydrous minerals.

SDOCT Doppler velocimetry for investigating the morphological influences on blood flow in the developing chick embryo heart

NASA Astrophysics Data System (ADS)

Davis, Anjul M.; Rothenberg, Florence G.; Law, Tzuo H.; Taber, Larry A.; Izatt, Joseph A.

2007-02-01

The onset of congenital heart disease (CHD) is believed to occur at very early stages of development. Investigations in the initiation and development of CHD has been hampered by the inability to image early stage heart structure and function, in vivo. Imaging small animals using optical coherence tomography (OCT) has filled a niche between the limited penetration depth of confocal microscopy and insufficient resolution from ultrasound. Previous demonstrations of chick heart imaging using OCT have entailed excision of, or arresting the heart to prevent motion artifacts. In this summary, we introduce SDOCT Doppler velocimetry as an enhancement of Doppler OCT for in vivo measurement of localized temporal blood flow dynamics. With this technique, dynamic velocity waveforms were measured in the outflow tract of the heart tube. These flow dynamics correlate to a finite element model of pulsatile flow and may lead to a further understanding of morphological influences on early heart development.

Computational solution of the velocity and wall shear stress distribution inside a left carotid artery under pulsatile flow conditions

NASA Astrophysics Data System (ADS)

Arslan, Nurullah; Turmuş, Hakan

2014-08-01

Stroke is still one of the leading causes for death after heart diseases and cancer in all over the world. Strokes happen because an artery that carries blood uphill from the heart to the head is clogged. Most of the time, as with heart attacks, the problem is atherosclerosis, hardening of the arteries, calcified buildup of fatty deposits on the vessel wall. In this study, the fluid dynamic simulations were done in a left carotid bifurcation under the pulsatile flow conditions computationally. Pulsatile flow waveform is given in the paper. In vivo geometry and boundary conditions were obtained from a patient who has stenosis located at external carotid artery (ECA) and internal carotid artery (ICA) of his common carotid artery (CCA). The location of critical flow fields such as low wall shear stress (WSS), stagnation regions and separation regions were detected near the highly stenosed region and at branching region.

Absent end diastolic flow of umbilical artery Doppler: pregnancy outcome in 62 cases.

PubMed

Poulain, P; Palaric, J C; Milon, J; Betremieux, P; Proudhon, J F; Signorelli, D; Grall, J Y; Giraud, J R

1994-02-01

We retrospectively studied the outcome of pregnancy in 62 cases of absent end diastolic flow (AEDF) of umbilical artery Doppler flow velocity waveform. The history of pregnancies revealed that nearly all were of high risk. Many cases presented cerebral (65%) or uterine (55.5%) Doppler flow abnormalities, or both (38%). We noted 10 fetal deaths and decided 7 pregnancy terminations. Malformation and chromosomal defect rate was 16%. We noted 44 (71%) live-births, a very high rate of cesarean section (86%), prematurity (75%), small for gestational age (39%). Forty-five percent of the neonates had a 1-min Apgar score under 7, which dropped to 27% at 5 min. Neonate mortality rate was 6.9% and the total mortality rate was 34% (21/62). Morbidity was significant (7 cases with severe morbidity, 2 cases with chromosomal abnormality of poor prognosis). We compared different sub-groups with a view to looking for some prenatal factors which predict poor neonatal outcome in case of AEDF.

A Quantitative Evaluation of SCEC Community Velocity Model Version 3.0

NASA Astrophysics Data System (ADS)

Chen, P.; Zhao, L.; Jordan, T. H.

2003-12-01

We present a systematic methodology for evaluating and improving 3D seismic velocity models using broadband waveform data from regional earthquakes. The operator that maps a synthetic waveform into an observed waveform is expressed in the Rytov form D(ω ) = {exp}[{i} ω δ τ {p}(ω ) - ω δ τ {q}(ω )]. We measure the phase delay time δ τ p(ω ) and the amplitude reduction time δ τ q(ω ) as a function of frequency ω using Gee & Jordan's [1992] isolation-filter technique, and we correct the data for frequency-dependent interference and frequency-independent source statics. We have applied this procedure to a set of small events in Southern California. Synthetic seismograms were computed using three types of velocity models: the 1D Standard Southern California Crustal Model (SoCaL) [Dreger & Helmberger, 1993], the 3D SCEC Community Velocity Model, Version 3.0 (CVM3.0) [Magistrale et al., 2000], and a set of path-averaged 1D models (A1D) extracted from CVM3.0 by horizontally averaging wave slownesses along source-receiver paths. The 3D synthetics were computed using K. Olsen's finite difference code. More than 1000 measurements were made on both P and S waveforms at frequencies ranging from 0.2 to 1 Hz. Overall, the 3D model provided a substantially better fit to the waveform data than either laterally homogeneous or path-dependent 1D models. Relative to SoCaL, CVM3.0 provided a variance reduction of about 64% in δ τ p, and 41% in δ τ q. Relative to A1D, the variance reduction is about 46% and 20%, respectively. The same set of measurements can be employed to invert for both seismic source properties and seismic velocity structures. Fully numerical methods are being developed to compute the Fréchet kernels for these measurements [L. Zhao et. al., this meeting]. This methodology thus provides a unified framework for regional studies of seismic sources and Earth structure in Southern California and elsewhere.

Artificial Intelligence Estimation of Carotid-Femoral Pulse Wave Velocity using Carotid Waveform.

PubMed

Tavallali, Peyman; Razavi, Marianne; Pahlevan, Niema M

2018-01-17

In this article, we offer an artificial intelligence method to estimate the carotid-femoral Pulse Wave Velocity (PWV) non-invasively from one uncalibrated carotid waveform measured by tonometry and few routine clinical variables. Since the signal processing inputs to this machine learning algorithm are sensor agnostic, the presented method can accompany any medical instrument that provides a calibrated or uncalibrated carotid pressure waveform. Our results show that, for an unseen hold back test set population in the age range of 20 to 69, our model can estimate PWV with a Root-Mean-Square Error (RMSE) of 1.12 m/sec compared to the reference method. The results convey the fact that this model is a reliable surrogate of PWV. Our study also showed that estimated PWV was significantly associated with an increased risk of CVDs.

Assessment of uterine artery and arcuate artery blood flow by transvaginal color Doppler ultrasound on the day of human chorionic gonadotropin administration as predictors of pregnancy in an in vitro fertilization program.

PubMed

Ivanovski, M; Damcevski, N; Radevska, B; Doicev, G

2012-01-01

To investigate whether success rates of IVF/ICSI could be predicted by using the Color Doppler technique by measuring the uterine artery and arcuate artery pulsatility (PI), resistance (RI), and velocity (Vs) indices on the day of hCG injection. This was a prospective observational study at the St Lazar Hospital, Skopje; 106 patients with an indication for IVF or ICSI according to departmental protocol underwent controlled ovarian hyperstimulation followed by IVF/ICSI and embryo transfer. Using Color Doppler in the two-dimensional (2D) mode, flow velocity waveforms were obtained from the ascending main branch of the uterine artery on the right and left sides of the cervix in a longitudinal plane and arcuate arteries, before they entered the uterus. The PI, RI and peak systolic velocity (PSV) of the uterine arteries and arcuate arteries were calculated electronically when similar consecutive waveforms of good quality were obtained and results were compared between patients who conceived and those who did not. In total, 106 patients, aged 24-42 years were included in the study. The patients were divided into two groups according to successful outcome, defined as pregnancy and failure of implantation, where no pregnancy was detected. A total of 40 pregnancies resulted; a crude pregnancy rate was 40/106 (37.7%). There were no significant differences between either group in patients' age, type and duration of infertility; basal levels of FSH, LH and E2; number of gonadotropin ampoules used for ovulation induction; number of retrieved oocytes and number of transferred embryos. No cycle was canceled after initiation of gonadotropin stimulation. In our results, there were statistically significant lower mean uterine artery PI and RI in the pregnant group than in the non-pregnant group (P < 0.05). Arcuate artery PI value was lower in the pregnant group than in the non-pregnant group, but this did not reach statistical significance. Peak systolic velocity (Vs) values in both the mean uterine artery and arcuate artery were higher in the pregnant group than in the non-pregnant group; however, the difference was not statistically significant. Vascular impedance was calculated with PI, RI, and Vs values, among which PI was found to be the most important. Optimal uterine receptivity can be accomplished by reduced vascular resistance and increased blood flow, which will improve pregnancy success. We suggest the use of transvaginal color Doppler ultrasonography to measure the blood flow in uterine arteries and arcuate arteries before hCG in IVF cycles.

Long-period GPS waveforms. What can GPS bring to Earth seismic velocity models?

NASA Astrophysics Data System (ADS)

Kelevitz, Krisztina; Houlié, Nicolas; Boschi, Lapo; Nissen-Meyer, Tarje; Giardini, Domenico

2014-05-01

It is now commonly admitted that high rate GPS observations can provide reliable surface displacement waveforms (Cervelli, et al., 2001; Langbein, et al., 2006; Houlié, et al., 2006; Houlié et al., 2011). For long-period (T>5s) transients, it was shown that GPS and seismometer (STS-1) displacements are in agreement at least for vertical component (Houlié, et al., Sci. Rep. 2011). We propose here to supplement existing long-period seismic networks with high rate (>= 1Hz) GPS data in order to improve the resolution of global seismic velocity models. GPS measurements are providing a wide range of frequencies, going beyond the range of STS-1 in the low frequency end. Nowadays, almost 10.000 GPS receivers would be able to record data at 1 Hz with 3000+ stations already streaming data in Real-Time (RT). The reasons for this quick expansion are the price of receivers, their low maintenance, and the wide range of activities they can be used for (transport, science, public apps, navigation, etc.). We are presenting work completed on the 1Hz GPS records of the Hokkaido earthquake (25th of September, 2003, Mw=8.3). 3D Waveforms have been computed with an improved, stabilised inversion algorithm in order to constrain the ground motion history. Through the better resolution of inversion of the GPS phase observations, we determine displacement waveforms of frequencies ranging from 0.77 mHz to 330 mHz for a selection of sites. We compare inverted GPS waveforms with STS-1 waveforms and synthetic waveforms computed using 3D global wave propagation with SPECFEM. At co-located sites (STS-1 and GPS located within 10km) the agreement is good for the vertical component between seismic (both real and synthetic) and GPS waveforms.

Radiation from a current filament driven by a traveling wave

NASA Technical Reports Server (NTRS)

Levine, D. M.; Meneghini, R.

1976-01-01

Solutions are presented for the electromagnetic fields radiated by an arbitrarily oriented current filament located above a perfectly conducting ground plane and excited by a traveling current wave. Both an approximate solution, valid in the fraunhofer region of the filament and predicting the radiation terms in the fields, and an exact solution, which predicts both near and far field components of the electromagnetic fields, are presented. Both solutions apply to current waveforms which propagate along the channel but are valid regardless of the actual waveshape. The exact solution is valid only for waves which propagate at the speed of light, and the approximate solution is formulated for arbitrary velocity of propagation. The spectrum-magnitude of the fourier transform-of the radiated fields is computed by assuming a compound exponential model for the current waveform. The effects of channel orientation and length, as well as velocity of propagation of the current waveform and location of the observer, are discussed. It is shown that both velocity of propagation and an effective channel length are important in determining the shape of the spectrum.

Waveform inversion for 3-D earth structure using the Direct Solution Method implemented on vector-parallel supercomputer

NASA Astrophysics Data System (ADS)

Hara, Tatsuhiko

2004-08-01

We implement the Direct Solution Method (DSM) on a vector-parallel supercomputer and show that it is possible to significantly improve its computational efficiency through parallel computing. We apply the parallel DSM calculation to waveform inversion of long period (250-500 s) surface wave data for three-dimensional (3-D) S-wave velocity structure in the upper and uppermost lower mantle. We use a spherical harmonic expansion to represent lateral variation with the maximum angular degree 16. We find significant low velocities under south Pacific hot spots in the transition zone. This is consistent with other seismological studies conducted in the Superplume project, which suggests deep roots of these hot spots. We also perform simultaneous waveform inversion for 3-D S-wave velocity and Q structure. Since resolution for Q is not good, we develop a new technique in which power spectra are used as data for inversion. We find good correlation between long wavelength patterns of Vs and Q in the transition zone such as high Vs and high Q under the western Pacific.

2-dimensional triplicated waveform modeling of the mantle transition zone beneath Northeast Asia

NASA Astrophysics Data System (ADS)

Lai, Y.; Chen, L.; Wang, T.

2017-12-01

The Mantle Transition Zone (MTZ) of Northeast Asia has long been investigated by geoscientists for its critical importance where the subducted Pacific slab is stagnant above the 660km discontinuity, accompanied by complicated mantle processes. Taking advantages of the frequent occurrent deep earthquakes in subduction zone and dense seismic arrays in Northeast China, we successfully constructed the fine-scale P and SH velocity structure of a narrow azimuthal fan area based on 2-Dimensional (2D) triplicated waveform modeling for three deep close earthquakes, in which the triplicated waveforms are very sensitive to MTZ velocity structure in general, particularly the morphology of the stagnant slab in Northeast Asia. In our 2D triplication study, for the first time, we show a quite consistent feature of a high velocity layer for both Vp and Vs with the thickness of 140km and the length of 1200km just atop the 660km discontinuity, the western edge of the stagnant slab intersect with the North-South Gravity Lineament in China and has the subducting age of 30 Ma. Compared with a quite normal Vp, the Shear wave velocity reduction of -0.5% in the slab and -2.5% in the upper MTZ is required to reconcile the SH waves featured by the broad BOD. The high Vp/Vs ratio beneath Northeast Asia may imply a water-rich MTZ with the H2O content of 0.1-0.3 wt%. Particularly, a low velocity anomaly of about 150km wide was detected in the overall high-velocity stagnant slab by both P and SH triplicated waveform modeling, with the velocity anomaly value of -1% and -3%, respectively. The gap/window in the stagnant slab may provide a passage for hot deeper mantle materials to penetrate through the thick slab and feed the surface Changbaishan volcano. We also speculate that the existence of such a gap can be the manifestation of the original heterogeneity in the subducted slab and will further exacerbatethe impending gravitational instability and speed up mantle avalanche.

Investigating source processes of isotropic events

NASA Astrophysics Data System (ADS)

Chiang, Andrea

This dissertation demonstrates the utility of the complete waveform regional moment tensor inversion for nuclear event discrimination. I explore the source processes and associated uncertainties for explosions and earthquakes under the effects of limited station coverage, compound seismic sources, assumptions in velocity models and the corresponding Green's functions, and the effects of shallow source depth and free-surface conditions. The motivation to develop better techniques to obtain reliable source mechanism and assess uncertainties is not limited to nuclear monitoring, but they also provide quantitative information about the characteristics of seismic hazards, local and regional tectonics and in-situ stress fields of the region . This dissertation begins with the analysis of three sparsely recorded events: the 14 September 1988 US-Soviet Joint Verification Experiment (JVE) nuclear test at the Semipalatinsk test site in Eastern Kazakhstan, and two nuclear explosions at the Chinese Lop Nor test site. We utilize a regional distance seismic waveform method fitting long-period, complete, three-component waveforms jointly with first-motion observations from regional stations and teleseismic arrays. The combination of long period waveforms and first motion observations provides unique discrimination of these sparsely recorded events in the context of the Hudson et al. (1989) source-type diagram. We examine the effects of the free surface on the moment tensor via synthetic testing, and apply the moment tensor based discrimination method to well-recorded chemical explosions. These shallow chemical explosions represent rather severe source-station geometry in terms of the vanishing traction issues. We show that the combined waveform and first motion method enables the unique discrimination of these events, even though the data include unmodeled single force components resulting from the collapse and blowout of the quarry face immediately following the initial explosion. In contrast, recovering the announced explosive yield using seismic moment estimates from moment tensor inversion remains challenging but we can begin to put error bounds on our moment estimates using the NSS technique. The estimation of seismic source parameters is dependent upon having a well-calibrated velocity model to compute the Green's functions for the inverse problem. Ideally, seismic velocity models are calibrated through broadband waveform modeling, however in regions of low seismicity velocity models derived from body or surface wave tomography may be employed. Whether a velocity model is 1D or 3D, or based on broadband seismic waveform modeling or the various tomographic techniques, the uncertainty in the velocity model can be the greatest source of error in moment tensor inversion. These errors have not been fully investigated for the nuclear discrimination problem. To study the effects of unmodeled structures on the moment tensor inversion, we set up a synthetic experiment where we produce synthetic seismograms for a 3D model (Moschetti et al., 2010) and invert these data using Green's functions computed with a 1D velocity mode (Song et al., 1996) to evaluate the recoverability of input solutions, paying particular attention to biases in the isotropic component. The synthetic experiment results indicate that the 1D model assumption is valid for moment tensor inversions at periods as short as 10 seconds for the 1D western U.S. model (Song et al., 1996). The correct earthquake mechanisms and source depth are recovered with statistically insignificant isotropic components as determined by the F-test. Shallow explosions are biased by the theoretical ISO-CLVD tradeoff but the tectonic release component remains low, and the tradeoff can be eliminated with constraints from P wave first motion. Path-calibration to the 1D model can reduce non-double-couple components in earthquakes, non-isotropic components in explosions and composite sources and improve the fit to the data. When we apply the 3D model to real data, at long periods (20-50 seconds), we see good agreement in the solutions between the 1D and 3D models and slight improvement in waveform fits when using the 3D velocity model Green's functions. (Abstract shortened by ProQuest.).

Frequency-domain ultrasound waveform tomography breast attenuation imaging

NASA Astrophysics Data System (ADS)

Sandhu, Gursharan Yash Singh; Li, Cuiping; Roy, Olivier; West, Erik; Montgomery, Katelyn; Boone, Michael; Duric, Neb

2016-04-01

Ultrasound waveform tomography techniques have shown promising results for the visualization and characterization of breast disease. By using frequency-domain waveform tomography techniques and a gradient descent algorithm, we have previously reconstructed the sound speed distributions of breasts of varying densities with different types of breast disease including benign and malignant lesions. By allowing the sound speed to have an imaginary component, we can model the intrinsic attenuation of a medium. We can similarly recover the imaginary component of the velocity and thus the attenuation. In this paper, we will briefly review ultrasound waveform tomography techniques, discuss attenuation and its relations to the imaginary component of the sound speed, and provide both numerical and ex vivo examples of waveform tomography attenuation reconstructions.

Magnetic plethysmograph transducers for local blood pulse wave velocity measurement.

PubMed

Nabeel, P M; Joseph, Jayaraj; Sivaprakasam, Mohanasankar

2014-01-01

We present the design of magnetic plethysmograph (MPG) transducers for detection of blood pulse waveform and evaluation of local pulse wave velocity (PWV), for potential use in cuffless blood pressure (BP) monitoring. The sensors utilize a Hall effect magnetic field sensor to capture the blood pulse waveform. A strap based design is performed to enable reliable capture of large number of cardiac cycles with relative ease. The ability of the transducer to consistently detect the blood pulse is verified by in-vivo trials on few volunteers. A duality of such transducers is utilized to capture the local PWV at the carotid artery. The pulse transit time (PTT) between the two detected pulse waveforms, measured along a small section of the carotid artery, was evaluated using automated algorithms to ensure consistency of measurements. The correlation between the measured values of local PWV and BP was also investigated. The developed transducers provide a reliable, easy modality for detecting pulse waveform on superficial arteries. Such transducers, used for measurement of local PWV, could potentially be utilized for cuffless, continuous evaluation of BP at various superficial arterial sites.

Crustal structure of the Kaapvaal craton and its significance for early crustal evolution

NASA Astrophysics Data System (ADS)

James, David E.; Niu, Fenglin; Rokosky, Juliana

2003-12-01

High-quality seismic data obtained from a dense broadband array near Kimberley, South Africa, exhibit crustal reverberations of remarkable clarity that provide well-resolved constraints on the structure of the lowermost crust and Moho. Receiver function analysis of Moho conversions and crustal multiples beneath the Kimberley array shows that the crust is 35 km thick with an average Poisson's ratio of 0.25. The density contrast across the Moho is ˜15%, indicating a crustal density about 2.86 gm/cc just above the Moho, appropriate for felsic to intermediate rock compositions. Analysis of waveform broadening of the crustal reverberation phases suggests that the Moho transition can be no more than 0.5 km thick and the total variation in crustal thickness over the 2400 km 2 footprint of the array no more than 1 km. Waveform and travel time analysis of a large earthquake triggered by deep gold mining operations (the Welkom mine event) some 200 km away from the array yield an average crustal thickness of 35 km along the propagation path between the Kimberley array and the event. P- and S-wave velocities for the lowermost crust are modeled to be 6.75 and 3.90 km/s, respectively, with uppermost mantle velocities of 8.2 and 4.79 km/s, respectively. Seismograms from the Welkom event exhibit theoretically predicted but rarely observed crustal reverberation phases that involve reflection or conversion at the Moho. Correlation between observed and synthetic waveforms and phase amplitudes of the Moho reverberations suggests that the crust along the propagation path between source and receiver is highly uniform in both thickness and average seismic velocity and that the Moho transition zone is everywhere less than about 2 km thick. While the extremely flat Moho, sharp transition zone and low crustal densities beneath the region of study may date from the time of crustal formation, a more geologically plausible interpretation involves extensive crustal melting and ductile flow during the major craton-wide Ventersdorp tectonomagmatic event near the end of Archean time.

ADVANCED WAVEFORM SIMULATION FOR SEISMIC MONITORING EVENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Helmberger, Donald V.; Tromp, Jeroen; Rodgers, Arthur J.

Earthquake source parameters underpin several aspects of nuclear explosion monitoring. Such aspects are: calibration of moment magnitudes (including coda magnitudes) and magnitude and distance amplitude corrections (MDAC); source depths; discrimination by isotropic moment tensor components; and waveform modeling for structure (including waveform tomography). This project seeks to improve methods for and broaden the applicability of estimating source parameters from broadband waveforms using the Cut-and-Paste (CAP) methodology. The CAP method uses a library of Green’s functions for a one-dimensional (1D, depth-varying) seismic velocity model. The method separates the main arrivals of the regional waveform into 5 windows: Pnl (vertical and radialmore » components), Rayleigh (vertical and radial components) and Love (transverse component). Source parameters are estimated by grid search over strike, dip, rake and depth and seismic moment or equivalently moment magnitude, MW, are adjusted to fit the amplitudes. Key to the CAP method is allowing the synthetic seismograms to shift in time relative to the data in order to account for path-propagation errors (delays) in the 1D seismic velocity model used to compute the Green’s functions. The CAP method has been shown to improve estimates of source parameters, especially when delay and amplitude biases are calibrated using high signal-to-noise data from moderate earthquakes, CAP+.« less

Flow characteristics in a canine aneurysm model: A comparison of 4D accelerated phase-contrast MR measurements and computational fluid dynamics simulations

PubMed Central

Jiang, Jingfeng; Johnson, Kevin; Valen-Sendstad, Kristian; Mardal, Kent-Andre; Wieben, Oliver; Strother, Charles

2011-01-01

Purpose: Our purpose was to compare quantitatively velocity fields in and around experimental canine aneurysms as measured using an accelerated 4D PC-MR angiography (MRA) method and calculated based on animal-specific CFD simulations. Methods: Two animals with a surgically created bifurcation aneurysm were imaged using an accelerated 4D PC-MRA method. Meshes were created based on the geometries obtained from the PC-MRA and simulations using “subject-specific” pulsatile velocity waveforms and geometries were then solved using a commercial CFD solver. Qualitative visual assessments and quantitative comparisons of the time-resolved velocity fields obtained from the PC-MRA measurements and the CFD simulations were performed using a defined similarity metric combining both angular and magnitude differences of vector fields. Results: PC-MRA and image-based CFD not only yielded visually consistent representations of 3D streamlines in and around both aneurysms, but also showed good agreement with regard to the spatial velocity distributions. The estimated similarity between time-resolved velocity fields from both techniques was reasonably high (mean value >0.60; one being the highest and zero being the lowest). Relative differences in inflow and outflow zones among selected planes were also reasonable (on the order of 10%–20%). The correlation between CFD-calculated and PC-MRA-measured time-averaged wall shear stresses was low (0.22 and 0.31, p < 0.001). Conclusions: In two experimental canine aneurysms, PC-MRA and image-based CFD showed favorable agreement in intra-aneurismal velocity fields. Combining these two complementary techniques likely will further improve the ability to characterize and interpret the complex flow that occurs in human intracranial aneurysms. PMID:22047395

Preliminary analysis of seismic anisotropy in the uppermost mantle beneath NW Pacific reveled by the Normal Oceanic Mantle project

NASA Astrophysics Data System (ADS)

Takeo, A.; Isse, T.; Nishida, K.; Kawakatsu, H.; Shiobara, H.; Sugioka, H.; Ito, A.; Utada, H.

2013-12-01

Seismic structure including anisotropy in the oceanic uppermost mantle is essential for understanding deformation related to plate tectonics. Recent reports of a sharp discontinuity between the high velocity LID and the low velocity zone (LVZ) especially emphasize the importance of observation in oceanic basins apart from ridges and hotspots for determining the structure including LID and LVZ. In this study, we analyzed records of four broadband ocean bottom seismometers (BBOBSs) deployed in the northwest of Shatsky Rise by the pilot observation of the Normal Oceanic Mantle (NOMan) project in 2010-2011. We first measured average phase velocities of surface waves at periods of 5-30 s by the ambient-noise cross correlation method. Based on the method of Takeo et al. (in prep. GJI), we analyzed fundamental- and first higher- mode Rayleigh waves and fundamental-mode Love wave simultaneously by waveform fitting after the correction of clock delay. At periods of 25-100 s, we measured phase velocities of fundamental-mode surface waves by the array analysis of teleseismic waveforms. We then determined one-dimensional radially anisotropic structure beneath the array by the method of Takeo et al. (2013, JGR). The obtained structure shows transition from LID to LVZ at depths of 50-80km, which is marginally consistent with the depth of ~80 km estimated by a receiver function analysis at WP2 station situated at east of the studies area (Kawakatsu et al., 2009). The velocity gradient in the LID is almost zero and inconsistent with the simple cooling model of homogeneous oceanic plate. The average intensity of S-wave radial anisotropy at depths of ~10-220 km is ~3% (VSH>VSV). We further estimated S-wave azimuthal anisotropy at depths of ~30-100 km by analyzing teleseismic fundamental-mode Rayleigh waves at periods of 25-50 s. The intensity of anisotropy is 2-3%. The fastest direction is about N35W, close to that of Sn-wave velocity around WP2 station obtained by a refraction survey (Shinohara et al., 2008), and indicates the presence of past mantle flow almost perpendicular to the ancient mid ocean ridge or the presence of current mantle flow parallel to the plate motion at depths of 30-100 km. We will further analyze new records after the recovery of 13 BBOBSs in August 2013 and will present more detailed structure around Shatsky Rise. BBOBS stations of pilot observation of NOMan project (white crosses), WP2 station (circle), isochrons (white lines). Black bars show the fastest directions of Rayleigh wave at periods of 25-50 s and the fastest direction of Sn-wave velocity (Shinohara et al. 2008).

Teleseismic tomography for imaging Earth's upper mantle

NASA Astrophysics Data System (ADS)

Aktas, Kadircan

Teleseismic tomography is an important imaging tool in earthquake seismology, used to characterize lithospheric structure beneath a region of interest. In this study I investigate three different tomographic techniques applied to real and synthetic teleseismic data, with the aim of imaging the velocity structure of the upper mantle. First, by applying well established traveltime tomographic techniques to teleseismic data from southern Ontario, I obtained high-resolution images of the upper mantle beneath the lower Great Lakes. Two salient features of the 3D models are: (1) a patchy, NNW-trending low-velocity region, and (2) a linear, NE-striking high-velocity anomaly. I interpret the high-velocity anomaly as a possible relict slab associated with ca. 1.25 Ga subduction, whereas the low-velocity anomaly is interpreted as a zone of alteration and metasomatism associated with the ascent of magmas that produced the Late Cretaceous Monteregian plutons. The next part of the thesis is concerned with adaptation of existing full-waveform tomographic techniques for application to teleseismic body-wave observations. The method used here is intended to be complementary to traveltime tomography, and to take advantage of efficient frequency-domain methodologies that have been developed for inverting large controlled-source datasets. Existing full-waveform acoustic modelling and inversion codes have been modified to handle plane waves impinging from the base of the lithospheric model at a known incidence angle. A processing protocol has been developed to prepare teleseismic observations for the inversion algorithm. To assess the validity of the acoustic approximation, the processing procedure and modelling-inversion algorithm were tested using synthetic seismograms computed using an elastic Kirchhoff integral method. These tests were performed to evaluate the ability of the frequency-domain full-waveform inversion algorithm to recover topographic variations of the Moho under a variety of realistic scenarios. Results show that frequency-domain full-waveform tomography is generally successful in recovering both sharp and discontinuous features. Thirdly, I developed a new method for creating an initial background velocity model for the inversion algorithm, which is sufficiently close to the true model so that convergence is likely to be achieved. I adapted a method named Deformable Layer Tomography (DLT), which adjusts interfaces between layers rather than velocities within cells. I applied this method to a simple model comprising a single uniform crustal layer and a constant-velocity mantle, separated by an irregular Moho interface. A series of tests was performed to evaluate the sensitivity of the DLT algorithm; the results show that my algorithm produces useful results within a realistic range of incident-wave obliquity, incidence angle and signal-to-noise level. Keywords. Teleseismic tomography, full waveform tomography, deformable layer tomography, lower Great Lakes, crust and upper mantle.

Waveform Retrieval and Phase Identification for Seismic Data from the CASS Experiment

NASA Astrophysics Data System (ADS)

Li, Zhiwei; You, Qingyu; Ni, Sidao; Hao, Tianyao; Wang, Hongti; Zhuang, Cantao

2013-05-01

The little destruction to the deployment site and high repeatability of the Controlled Accurate Seismic Source (CASS) shows its potential for investigating seismic wave velocities in the Earth's crust. However, the difficulty in retrieving impulsive seismic waveforms from the CASS data and identifying the seismic phases substantially prevents its wide applications. For example, identification of the seismic phases and accurate measurement of travel times are essential for resolving the spatial distribution of seismic velocities in the crust. Until now, it still remains a challenging task to estimate the accurate travel times of different seismic phases from the CASS data which features extended wave trains, unlike processing of the waveforms from impulsive events such as earthquakes or explosive sources. In this study, we introduce a time-frequency analysis method to process the CASS data, and try to retrieve the seismic waveforms and identify the major seismic phases traveling through the crust. We adopt the Wigner-Ville Distribution (WVD) approach which has been used in signal detection and parameter estimation for linear frequency modulation (LFM) signals, and proves to feature the best time-frequency convergence capability. The Wigner-Hough transform (WHT) is applied to retrieve the impulsive waveforms from multi-component LFM signals, which comprise seismic phases with different arrival times. We processed the seismic data of the 40-ton CASS in the field experiment around the Xinfengjiang reservoir with the WVD and WHT methods. The results demonstrate that these methods are effective in waveform retrieval and phase identification, especially for high frequency seismic phases such as PmP and SmS with strong amplitudes in large epicenter distance of 80-120 km. Further studies are still needed to improve the accuracy on travel time estimation, so as to further promote applicability of the CASS for and imaging the seismic velocity structure.

3-D velocity structure model for long-period ground motion simulation of the hypothetical Nankai Earthquake

NASA Astrophysics Data System (ADS)

Kagawa, T.; Petukhin, A.; Koketsu, K.; Miyake, H.; Murotani, S.; Tsurugi, M.

2010-12-01

Three dimensional velocity structure model of southwest Japan is provided to simulate long-period ground motions due to the hypothetical subduction earthquakes. The model is constructed from numerous physical explorations conducted in land and offshore areas and observational study of natural earthquakes. Any available information is involved to explain crustal structure and sedimentary structure. Figure 1 shows an example of cross section with P wave velocities. The model has been revised through numbers of simulations of small to middle earthquakes as to have good agreement with observed arrival times, amplitudes, and also waveforms including surface waves. Figure 2 shows a comparison between Observed (dash line) and simulated (solid line) waveforms. Low velocity layers have added on seismological basement to reproduce observed records. The thickness of the layer has been adjusted through iterative analysis. The final result is found to have good agreement with the results from other physical explorations; e.g. gravity anomaly. We are planning to make long-period (about 2 to 10 sec or longer) simulations of ground motion due to the hypothetical Nankai Earthquake with the 3-D velocity structure model. As the first step, we will simulate the observed ground motions of the latest event occurred in 1946 to check the source model and newly developed velocity structure model. This project is partly supported by Integrated Research Project for Long-Period Ground Motion Hazard Maps by Ministry of Education, Culture, Sports, Science and Technology (MEXT). The ground motion data used in this study were provided by National Research Institute for Earth Science and Disaster Prevention Disaster (NIED). Figure 1 An example of cross section with P wave velocities Figure 2 Observed (dash line) and simulated (solid line) waveforms due to a small earthquake

Full waveform inversion using a decomposed single frequency component from a spectrogram

NASA Astrophysics Data System (ADS)

Ha, Jiho; Kim, Seongpil; Koo, Namhyung; Kim, Young-Ju; Woo, Nam-Sub; Han, Sang-Mok; Chung, Wookeen; Shin, Sungryul; Shin, Changsoo; Lee, Jaejoon

2018-06-01

Although many full waveform inversion methods have been developed to construct velocity models of subsurface, various approaches have been presented to obtain an inversion result with long-wavelength features even though seismic data lacking low-frequency components were used. In this study, a new full waveform inversion algorithm was proposed to recover a long-wavelength velocity model that reflects the inherent characteristics of each frequency component of seismic data using a single-frequency component decomposed from the spectrogram. We utilized the wavelet transform method to obtain the spectrogram, and the decomposed signal from the spectrogram was used as transformed data. The Gauss-Newton method with the diagonal elements of an approximate Hessian matrix was used to update the model parameters at each iteration. Based on the results of time-frequency analysis in the spectrogram, numerical tests with some decomposed frequency components were performed using a modified SEG/EAGE salt dome (A-A‧) line to demonstrate the feasibility of the proposed inversion algorithm. This demonstrated that a reasonable inverted velocity model with long-wavelength structures can be obtained using a single frequency component. It was also confirmed that when strong noise occurs in part of the frequency band, it is feasible to obtain a long-wavelength velocity model from the noise data with a frequency component that is less affected by the noise. Finally, it was confirmed that the results obtained from the spectrogram inversion can be used as an initial velocity model in conventional inversion methods.

Structures of Xishan village landslide in Li County, Sichuan, China, inferred from high-frequency receiver functions of local earthquakes

NASA Astrophysics Data System (ADS)

Wei, Z.; Chu, R.

2017-12-01

Teleseismic receiver function methods are widely used to study the deep structural information beneath the seismic station. However, teleseismic waveforms are difficult to extract the high-frequency receiver function, which are insufficient to constrain the shallow structure because of the inelastic attenuation effect of the earth. In this study, using the local earthquake waveforms collected from 3 broadband stations deployed on the Xishan village landslide in Li County in Sichuan Province, we used the high-frequency receiver function method to study the shallow structure beneath the landslide. We developed the Vp-k (Vp/Vs) staking method of receiver functions, and combined with the H-k stacking and waveform inversion methods of receiver functions to invert the landslide's thickness, S-wave velocity and average Vp/Vs ratio beneath these stations, and compared the thickness with the borehole results. Our results show small-scale lateral variety of velocity structure, a 78-143m/s lower S-wave velocity in the bottom layer and 2.4-3.1 Vp/Vs ratio in the landslide. The observed high Vp/Vs ratio and low S-wave velocity in the bottom layer of the landslide are consistent with low electrical resistivity and water-rich in the bottom layer, suggesting a weak shear strength and potential danger zone in landslide h1. Our study suggest that the local earthquake receiver function can obtain the shallow velocity structural information and supply some seismic constrains for the landslide catastrophe mitigation.

Beat-to-Beat Blood Pressure Monitor

NASA Technical Reports Server (NTRS)

Lee, Yong Jin

2012-01-01

This device provides non-invasive beat-to-beat blood pressure measurements and can be worn over the upper arm for prolonged durations. Phase and waveform analyses are performed on filtered proximal and distal photoplethysmographic (PPG) waveforms obtained from the brachial artery. The phase analysis is used primarily for the computation of the mean arterial pressure, while the waveform analysis is used primarily to obtain the pulse pressure. Real-time compliance estimate is used to refine both the mean arterial and pulse pressures to provide the beat-to-beat blood pressure measurement. This wearable physiological monitor can be used to continuously observe the beat-to-beat blood pressure (B3P). It can be used to monitor the effect of prolonged exposures to reduced gravitational environments and the effectiveness of various countermeasures. A number of researchers have used pulse wave velocity (PWV) of blood in the arteries to infer the beat-to-beat blood pressure. There has been documentation of relative success, but a device that is able to provide the required accuracy and repeatability has not yet been developed. It has been demonstrated that an accurate and repeatable blood pressure measurement can be obtained by measuring the phase change (e.g., phase velocity), amplitude change, and distortion of the PPG waveforms along the brachial artery. The approach is based on comparing the full PPG waveform between two points along the artery rather than measuring the time-of-flight. Minimizing the measurement separation and confining the measurement area to a single, well-defined artery allows the waveform to retain the general shape between the two measurement points. This allows signal processing of waveforms to determine the phase and amplitude changes.

Computational assessment of model-based wave separation using a database of virtual subjects.

PubMed

Hametner, Bernhard; Schneider, Magdalena; Parragh, Stephanie; Wassertheurer, Siegfried

2017-11-07

The quantification of arterial wave reflection is an important area of interest in arterial pulse wave analysis. It can be achieved by wave separation analysis (WSA) if both the aortic pressure waveform and the aortic flow waveform are known. For better applicability, several mathematical models have been established to estimate aortic flow solely based on pressure waveforms. The aim of this study is to investigate and verify the model-based wave separation of the ARCSolver method on virtual pulse wave measurements. The study is based on an open access virtual database generated via simulations. Seven cardiac and arterial parameters were varied within physiological healthy ranges, leading to a total of 3325 virtual healthy subjects. For assessing the model-based ARCSolver method computationally, this method was used to perform WSA based on the aortic root pressure waveforms of the virtual patients. Asa reference, the values of WSA using both the pressure and flow waveforms provided by the virtual database were taken. The investigated parameters showed a good overall agreement between the model-based method and the reference. Mean differences and standard deviations were -0.05±0.02AU for characteristic impedance, -3.93±1.79mmHg for forward pressure amplitude, 1.37±1.56mmHg for backward pressure amplitude and 12.42±4.88% for reflection magnitude. The results indicate that the mathematical blood flow model of the ARCSolver method is a feasible surrogate for a measured flow waveform and provides a reasonable way to assess arterial wave reflection non-invasively in healthy subjects. Copyright © 2017 Elsevier Ltd. All rights reserved.

Cine phase-contrast MRI measurement of CSF flow in the cervical spine: a pilot study in patients with spinal cord injury

NASA Astrophysics Data System (ADS)

Negahdar, MJ; Shakeri, M.; McDowell, E.; Wells, J.; Vitaz, T.; Harkema, S.; Amini, A.

2011-03-01

MRI velocimetry (also known as phase-contrast MRI) is a powerful tool for quantification of cerebrospinal fluid (CSF) flow in various regions of the brain and craniospinal junction and has been accepted as a diagnostic tool to assist with the diagnosis of certain conditions such as hydrocephalus and chiari malformations. Cerebrospinal fluid is continually produced in the ventricles of the brain, flows through the ventricular system and then out and around the brain and spinal cord and is reabsorbed over the convexity of the brain. Any disease process which either impedes the normal pattern of flow or restricts the area where flow occurs can change the pattern of these waveforms with the direction and velocity of flow being determined by the pressure transmitted from the pulsation of the heart and circulation of blood within the central nervous system. Therefore, we hypothesized that phase-contrast MRI could eventually be used as a diagnostic aid in determining the degree of spinal cord compression following injury to the cervical or thoracic spine. In this study, we examined CSF flow in 3 normal subjects and 2 subjects with non-acute injuries in the cervical spine using Cine phasecontrast MRI. CSF flow analysis was performed using an in-house developed software. The flow waveform was calculated in both normal subjects (n=3) as well as subjects with spinal cord injury in the cervical spine (n=2). The bulk flow at C2 was measured to be 0.30 +/- 0.05 cc, at 5 cm distal to C2, it was 0.19+/- 0.07 cc, and at 10 cm distal to C2, it was 0.17+/- 0.05 cc. These results were in good agreement with previously published results. In patients with spinal cord injury, at the site of injury in the cervical spine, bulk flow was found to be 0.08 +/- 0.12 cc, at 5 cm proximal to the site of injury it was found to be 0.18 +/- 0.07 cc, and at 5 cm distal to the site of injury, it was found to be 0.12 +/- 0.01 cc.

A strategy for the application of frequency domain acoustic waveform tomography to marine Walkaway VSP data

NASA Astrophysics Data System (ADS)

Bouzidi, Y.; Takam Takougang, E. M.

2016-12-01

Two dimensional frequency domain acoustic waveform tomography was applied to walkaway VSP data from an oil field in a shallow water environment, offshore the United Arab Emirates, to form a high resolution velocity model of the subsurface around and away from the borehole. Five close parallel walkaway VSP lines were merged to form a 9 km line, with 1344 shots at 25 m shot interval and 4 m shot depth. Each line was recorded using a typical recording tool with 20 receivers at 15.1 m receiver intervals. The recording tool was deployed in a deviated borehole at different depths for each line (521-2742 m depth). Waveform tomography was performed following a specific inversion strategy to mitigate non-linearity. Three parameters were critical for the success of the inversion: the starting model obtained from traveltime tomography, the preconditioning of the input data used for amplitudes correction to remove of shear waves and noise, and a judicious selection of the time damping constant τ to suppress late arrivals in the Laplace-Fourier domain. Several values of the time damping constant were tested, and 2 values, 0.5 s and 0.8 s that suppress waveforms arriving after 1.2 s and 2 s respectively, were retained. The inversion was performed in 2 stages, with frequencies ranging from 5 Hz to 40 Hz. The values of the time damping term τ = 0.5 s and τ = 0.8 s were used in sequence for the frequencies 5-25 Hz, and τ = 0.8 s was used for the frequencies 25-40 Hz. A group of 5 frequencies at 0.5 Hz intervals were used and 6 iterations were performed. A velocity model that generally correlates well with the sonic log and estimated velocities from normal incidence VSP was obtained. The results confirmed the success of the inversion strategy. The velocity model shows zones with anomalous low velocities below 2000 m depth that correlate with known locations of hydrocarbons reservoirs. with known locations of hydrocarbon reservoirs. However, between 500 m and 1200 m depth, the velocity model appears to be slightly underestimated, which can be explained by possible elastic effects and out-of-plane structures not considered during the inversion. This result shows that acoustic waveform tomography can be successfully applied to walkaway VSP data when a good preconditioning of the input data and inversion strategy are used.

Lower Crstal Reflectity bands and Magma Emplacement in Norweigian sea, NE Atlantic

NASA Astrophysics Data System (ADS)

Rai, A.; Breivik, A. J.; Mjelde, R.

2013-12-01

In this study we present the OBS data collected along seismic profiles in the norweigian sea. The traveltime modelling of the OBS data provides first-hand information about seismic structure of the subsurface. However, waveform modelling is used to further constrain the fine scale structure, velocity constrast and velocity gradients. By forward modelling and inversion of the seismic waveforms, we show that the multiple bands of reflectivity could be due to multiple episodes of magma emplacements that might have frozen in the form of sills. These mafic intrusions probably intruded into the ductile lower crust during the main rifting phase of Europe and Greenland.

Application of deconvolution interferometry with both Hi-net and KiK-net data

NASA Astrophysics Data System (ADS)

Nakata, N.

2013-12-01

Application of deconvolution interferometry to wavefields observed by KiK-net, a strong-motion recording network in Japan, is useful for estimating wave velocities and S-wave splitting in the near surface. Using this technique, for example, Nakata and Snieder (2011, 2012) found changed in velocities caused by Tohoku-Oki earthquake in Japan. At the location of the borehole accelerometer of each KiK-net station, a velocity sensor is also installed as a part of a high-sensitivity seismograph network (Hi-net). I present a technique that uses both Hi-net and KiK-net records for computing deconvolution interferometry. The deconvolved waveform obtained from the combination of Hi-net and KiK-net data is similar to the waveform computed from KiK-net data only, which indicates that one can use Hi-net wavefields for deconvolution interferometry. Because Hi-net records have a high signal-to-noise ratio (S/N) and high dynamic resolution, the S/N and the quality of amplitude and phase of deconvolved waveforms can be improved with Hi-net data. These advantages are especially important for short-time moving-window seismic interferometry and deconvolution interferometry using later coda waves.

High-Frequency Normal Mode Propagation in Aluminum Cylinders

USGS Publications Warehouse

Lee, Myung W.; Waite, William F.

2009-01-01

Acoustic measurements made using compressional-wave (P-wave) and shear-wave (S-wave) transducers in aluminum cylinders reveal waveform features with high amplitudes and with velocities that depend on the feature's dominant frequency. In a given waveform, high-frequency features generally arrive earlier than low-frequency features, typical for normal mode propagation. To analyze these waveforms, the elastic equation is solved in a cylindrical coordinate system for the high-frequency case in which the acoustic wavelength is small compared to the cylinder geometry, and the surrounding medium is air. Dispersive P- and S-wave normal mode propagations are predicted to exist, but owing to complex interference patterns inside a cylinder, the phase and group velocities are not smooth functions of frequency. To assess the normal mode group velocities and relative amplitudes, approximate dispersion relations are derived using Bessel functions. The utility of the normal mode theory and approximations from a theoretical and experimental standpoint are demonstrated by showing how the sequence of P- and S-wave normal mode arrivals can vary between samples of different size, and how fundamental normal modes can be mistaken for the faster, but significantly smaller amplitude, P- and S-body waves from which P- and S-wave speeds are calculated.

Distinct endothelial phenotypes evoked by arterial waveforms derived from atherosclerosis-susceptible and -resistant regions of human vasculature

NASA Astrophysics Data System (ADS)

Dai, Guohao; Kaazempur-Mofrad, Mohammad R.; Natarajan, Sripriya; Zhang, Yuzhi; Vaughn, Saran; Blackman, Brett R.; Kamm, Roger D.; García-Cardeña, Guillermo; Gimbrone, Michael A., Jr.

2004-10-01

Atherosclerotic lesion localization to regions of disturbed flow within certain arterial geometries, in humans and experimental animals, suggests an important role for local hemodynamic forces in atherogenesis. To explore how endothelial cells (EC) acquire functional/dysfunctional phenotypes in response to vascular region-specific flow patterns, we have used an in vitro dynamic flow system to accurately reproduce arterial shear stress waveforms on cultured human EC and have examined the effects on EC gene expression by using a high-throughput transcriptional profiling approach. The flow patterns in the carotid artery bifurcations of several normal human subjects were characterized by using 3D flow analysis based on actual vascular geometries and blood flow profiles. Two prototypic arterial waveforms, "athero-prone" and "athero-protective," were defined as representative of the wall shear stresses in two distinct regions of the carotid artery (carotid sinus and distal internal carotid artery) that are typically "susceptible" or "resistant," respectively, to atherosclerotic lesion development. These two waveforms were applied to cultured EC, and cDNA microarrays were used to analyze the differential patterns of EC gene expression. In addition, the differential effects of athero-prone vs. athero-protective waveforms were further characterized on several parameters of EC structure and function, including actin cytoskeletal organization, expression and localization of junctional proteins, activation of the NF-B transcriptional pathway, and expression of proinflammatory cytokines and adhesion molecules. These global gene expression patterns and functional data reveal a distinct phenotypic modulation in response to the wall shear stresses present in atherosclerosis-susceptible vs. atherosclerosis-resistant human arterial geometries.

Post-stenotic plug-like jet with a vortex ring demonstrated by 4D flow MRI.

PubMed

Kim, Guk Bae; Ha, Hojin; Kweon, Jihoon; Lee, Sang Joon; Kim, Young-Hak; Yang, Dong Hyun; Kim, Namkug

2016-05-01

To investigate the details of the flow structure of a plug-like jet that had a vortex ring in pulsatile stenotic phantoms using 4D flow MRI. Pulsatile Newtonian flows in two stenotic phantoms with 50% and 75% reductions in area were scanned by 4D flow MRI. Blood analog working fluid was circulated via the stenotic phantom using a pulsatile pump at a constant pulsating frequency of 1Hz. The velocity and vorticity fields of the plug-like jet with a vortex ring were quantitatively analyzed in the spatial and temporal domains. Pulsatile stenotic flow showed a plug-like jet at the specific stenotic degree of 50% in our pulsatile waveform design. This plug-like jet was found at the decelerating period in the post-stenotic region of 26.4mm (1.2 D). It revealed a vortex ring structure with vorticity strength in the range of ±100s(-1). We observed a plug-like jet with a vortex ring in pulsatile stenotic flow by in vitro visualization using 4D flow MRI. In this plug-like jet, the local fastest flow region occurred at the post-systole phase in the post-stenotic region, which was distinguishable from a typical stenotic jet flow at systole phase. Copyright © 2015 Elsevier Inc. All rights reserved.

One-dimensional model for the intracranial pulse morphological analysis during hyperventilation and CO2 inhalation tests

NASA Astrophysics Data System (ADS)

Ryu, Jaiyoung; Hu, Xiao; Shadden, Shawn C.

2015-11-01

The brain's CO2 reactivity mechanism is coupled with cerebral autoregulation and other unique features of cerebral hemodynamics. We developed a one-dimensional nonlinear model of blood flow in the cerebral arteries coupled to lumped parameter (LP) networks. The LP networks incorporate cerebral autoregulation, CO2 reactivity, intracranial pressure, cerebrospinal fluid, and cortical collateral blood flow models. The model was used to evaluate hemodynamic variables (arterial deformation, blood velocity and pressure) in the cerebral vasculature during hyperventilation and CO2 inhalation test. Tests were performed for various arterial blood pressure (ABP) representing normal and hypotensive conditions. The increase of the cerebral blood flow rates agreed well with the published measurements for various ABP measurements taken during clinical CO2 reactivity tests. The changes in distal vasculature affected the reflected pulse wave energy, which caused the waveform morphological changes at the middle cerebral, common and internal carotid arteries. The pulse morphological analysis demonstrated agreement with previous clinical measurements for cerebral vasoconstriction and vasodilation.

Turbofan forced mixer lobe flow modeling. 1: Experimental and analytical assessment

NASA Technical Reports Server (NTRS)

Barber, T.; Paterson, R. W.; Skebe, S. A.

1988-01-01

A joint analytical and experimental investigation of three-dimensional flowfield development within the lobe region of turbofan forced mixer nozzles is described. The objective was to develop a method for predicting the lobe exit flowfield. In the analytical approach, a linearized inviscid aerodynamical theory was used for representing the axial and secondary flows within the three-dimensional convoluted mixer lobes and three-dimensional boundary layer analysis was applied thereafter to account for viscous effects. The experimental phase of the program employed three planar mixer lobe models having different waveform shapes and lobe heights for which detailed measurements were made of the three-dimensional velocity field and total pressure field at the lobe exit plane. Velocity data was obtained using Laser Doppler Velocimetry (LDV) and total pressure probing and hot wire anemometry were employed to define exit plane total pressure and boundary layer development. Comparison of data and analysis was performed to assess analytical model prediction accuracy. As a result of this study a planar mixed geometry analysis was developed. A principal conclusion is that the global mixer lobe flowfield is inviscid and can be predicted from an inviscid analysis and Kutta condition.

A computer system for analysis and transmission of spirometry waveforms using volume sampling.

PubMed

Ostler, D V; Gardner, R M; Crapo, R O

1984-06-01

A microprocessor-controlled data gathering system for telemetry and analysis of spirometry waveforms was implemented using a completely digital design. Spirometry waveforms were obtained from an optical shaft encoder attached to a rolling seal spirometer. Time intervals between 10-ml volume changes (volume sampling) were stored. The digital design eliminated problems of analog signal sampling. The system measured flows up to 12 liters/sec with 5% accuracy and volumes up to 10 liters with 1% accuracy. Transmission of 10 waveforms took about 3 min. Error detection assured that no data were lost or distorted during transmission. A pulmonary physician at the central hospital reviewed the volume-time and flow-volume waveforms and interpretations generated by the central computer before forwarding the results and consulting with the rural physician. This system is suitable for use in a major hospital, rural hospital, or small clinic because of the system's simplicity and small size.

Surface-wave amplitude analysis for array data with non-linear waveform fitting: Toward high-resolution attenuation models of the upper mantle

NASA Astrophysics Data System (ADS)

Hamada, K.; Yoshizawa, K.

2013-12-01

Anelastic attenuation of seismic waves provides us with valuable information on temperature and water content in the Earth's mantle. While seismic velocity models have been investigated by many researchers, anelastic attenuation (or Q) models have yet to be investigated in detail mainly due to the intrinsic difficulties and uncertainties in the amplitude analysis of observed seismic waveforms. To increase the horizontal resolution of surface wave attenuation models on a regional scale, we have developed a new method of fully non-linear waveform fitting to measure inter-station phase velocities and amplitude ratios simultaneously, using the Neighborhood Algorithm (NA) as a global optimizer. Model parameter space (perturbations of phase speed and amplitude ratio) is explored to fit two observed waveforms on a common great-circle path by perturbing both phase and amplitude of the fundamental-mode surface waves. This method has been applied to observed waveform data of the USArray from 2007 to 2008, and a large-number of inter-station amplitude and phase speed data are corrected in a period range from 20 to 200 seconds. We have constructed preliminary phase speed and attenuation models using the observed phase and amplitude data, with careful considerations of the effects of elastic focusing and station correction factors for amplitude data. The phase velocity models indicate good correlation with the conventional tomographic results in North America on a large-scale; e.g., significant slow velocity anomaly in volcanic regions in the western United States. The preliminary results of surface-wave attenuation achieved a better variance reduction when the amplitude data are inverted for attenuation models in conjunction with corrections for receiver factors. We have also taken into account the amplitude correction for elastic focusing based on a geometrical ray theory, but its effects on the final model is somewhat limited and our attenuation model show anti-correlation with the phase velocity models; i.e., lower attenuation is found in slower velocity areas that cannot readily be explained by the temperature effects alone. Some former global scale studies (e.g., Dalton et al., JGR, 2006) indicated that the ray-theoretical focusing corrections on amplitude data tend to eliminate such anti-correlation of phase speed and attenuation, but this seems not to work sufficiently well for our regional scale model, which is affected by stronger velocity gradient relative to global-scale models. Thus, the estimated elastic focusing effects based on ray theory may be underestimated in our regional-scale studies. More rigorous ways to estimate the focusing corrections as well as data selection criteria for amplitude measurements are required to achieve a high-resolution attenuation models on regional scales in the future.

Automated seismic waveform location using Multichannel Coherency Migration (MCM)-I. Theory

NASA Astrophysics Data System (ADS)

Shi, Peidong; Angus, Doug; Rost, Sebastian; Nowacki, Andy; Yuan, Sanyi

2018-03-01

With the proliferation of dense seismic networks sampling the full seismic wavefield, recorded seismic data volumes are getting bigger and automated analysis tools to locate seismic events are essential. Here, we propose a novel Multichannel Coherency Migration (MCM) method to locate earthquakes in continuous seismic data and reveal the location and origin time of seismic events directly from recorded waveforms. By continuously calculating the coherency between waveforms from different receiver pairs, MCM greatly expands the available information which can be used for event location. MCM does not require phase picking or phase identification, which allows fully automated waveform analysis. By migrating the coherency between waveforms, MCM leads to improved source energy focusing. We have tested and compared MCM to other migration-based methods in noise-free and noisy synthetic data. The tests and analysis show that MCM is noise resistant and can achieve more accurate results compared with other migration-based methods. MCM is able to suppress strong interference from other seismic sources occurring at a similar time and location. It can be used with arbitrary 3D velocity models and is able to obtain reasonable location results with smooth but inaccurate velocity models. MCM exhibits excellent location performance and can be easily parallelized giving it large potential to be developed as a real-time location method for very large datasets.

Lagrangian transport properties of pulmonary interfacial flows

PubMed Central

Smith, Bradford J.; Lukens, Sarah; Yamaguchi, Eiichiro; Gaver, Donald P.

2012-01-01

Disease states characterized by airway fluid occlusion and pulmonary surfactant insufficiency, such as respiratory distress syndrome, have a high mortality rate. Understanding the mechanics of airway reopening, particularly involving surfactant transport, may provide an avenue to increase patient survival via optimized mechanical ventilation waveforms. We model the occluded airway as a liquid-filled rigid tube with the fluid phase displaced by a finger of air that propagates with both mean and sinusoidal velocity components. Finite-time Lyapunov exponent (FTLE) fields are employed to analyse the convective transport characteristics, taking note of Lagrangian coherent structures (LCSs) and their effects on transport. The Lagrangian perspective of these techniques reveals flow characteristics that are not readily apparent by observing Eulerian measures. These analysis techniques are applied to surfactant-free velocity fields determined computationally, with the boundary element method, and measured experimentally with micro particle image velocimetry (μ-PIV). We find that the LCS divides the fluid into two regimes, one advected upstream (into the thin residual film) and the other downstream ahead of the advancing bubble. At higher oscillatory frequencies particles originating immediately inside the LCS experience long residence times at the air–liquid interface, which may be conducive to surfactant transport. At high frequencies a well-mixed attractor region is identified; this volume of fluid cyclically travels along the interface and into the bulk fluid. The Lagrangian analysis is applied to velocity data measured with 0.01 mg ml−1 of the clinical pulmonary surfactant Infasurf in the bulk fluid, demonstrating flow field modifications with respect to the surfactant-free system that were not visible in the Eulerian frame. PMID:23049141

Elastic-Waveform Inversion with Compressive Sensing for Sparse Seismic Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Youzuo; Huang, Lianjie

2015-01-28

Accurate velocity models of compressional- and shear-waves are essential for geothermal reservoir characterization and microseismic imaging. Elastic-waveform inversion of multi-component seismic data can provide high-resolution inversion results of subsurface geophysical properties. However, the method requires seismic data acquired using dense source and receiver arrays. In practice, seismic sources and/or geophones are often sparsely distributed on the surface and/or in a borehole, such as 3D vertical seismic profiling (VSP) surveys. We develop a novel elastic-waveform inversion method with compressive sensing for inversion of sparse seismic data. We employ an alternating-minimization algorithm to solve the optimization problem of our new waveform inversionmore » method. We validate our new method using synthetic VSP data for a geophysical model built using geologic features found at the Raft River enhanced-geothermal-system (EGS) field. We apply our method to synthetic VSP data with a sparse source array and compare the results with those obtained with a dense source array. Our numerical results demonstrate that the velocity models produced with our new method using a sparse source array are almost as accurate as those obtained using a dense source array.« less

Dune migration in a steep, coarse-bedded stream

USGS Publications Warehouse

Dinehart, Randy L.

1989-01-01

During 1986 and 1987, migrating bed forms composed of coarse sand and fine gravel (d50=1.8 to 9.1 mm) were documented in the North Fork Toutle River at Kid Valley, Washington, at flow velocities ranging from 1.6 to 3.4 m s−1 and depths of 0.8 to 2.2 m. The bed forms (predominantly lower regime dunes) were studied with a sonic depth sounder transducer suspended in the river at a stationary point. Twelve temporal depth-sounding records were collected during storm runoff and nearly steady, average streamflow, with record durations ranging from 37 to 261 min. Waveform height was defined by dune front heights, which ranged from 12 to 70 cm. A weak correlation between flow depth and the standard deviation of bed elevation was noted. Dune front counts and spectral analyses of the temporal records showed that dune crests passed the observation point every 2 to 5 min. Dunes were often superposed on larger bed forms with wave periods between 10 and 30 min. Gradual changes in waveform height and periodicity occurred over several hours during storm runoff. The processes of dune growth and decay were both time-dependent and affected by changes in streamflow. Rates of migration for typical dunes were estimated to be 3 cm s−1, and dune wavelengths were estimated to be 6 to 7 m.

Extended target recognition in cognitive radar networks.

PubMed

Wei, Yimin; Meng, Huadong; Liu, Yimin; Wang, Xiqin

2010-01-01

We address the problem of adaptive waveform design for extended target recognition in cognitive radar networks. A closed-loop active target recognition radar system is extended to the case of a centralized cognitive radar network, in which a generalized likelihood ratio (GLR) based sequential hypothesis testing (SHT) framework is employed. Using Doppler velocities measured by multiple radars, the target aspect angle for each radar is calculated. The joint probability of each target hypothesis is then updated using observations from different radar line of sights (LOS). Based on these probabilities, a minimum correlation algorithm is proposed to adaptively design the transmit waveform for each radar in an amplitude fluctuation situation. Simulation results demonstrate performance improvements due to the cognitive radar network and adaptive waveform design. Our minimum correlation algorithm outperforms the eigen-waveform solution and other non-cognitive waveform design approaches.

Development and validation of an improved mechanical thorax for simulating cardiopulmonary resuscitation with adjustable chest stiffness and simulated blood flow.

PubMed

Eichhorn, Stefan; Spindler, Johannes; Polski, Marcin; Mendoza, Alejandro; Schreiber, Ulrich; Heller, Michael; Deutsch, Marcus Andre; Braun, Christian; Lange, Rüdiger; Krane, Markus

2017-05-01

Investigations of compressive frequency, duty cycle, or waveform during CPR are typically rooted in animal research or computer simulations. Our goal was to generate a mechanical model incorporating alternate stiffness settings and an integrated blood flow system, enabling defined, reproducible comparisons of CPR efficacy. Based on thoracic stiffness data measured in human cadavers, such a model was constructed using valve-controlled pneumatic pistons and an artificial heart. This model offers two realistic levels of chest elasticity, with a blood flow apparatus that reflects compressive depth and waveform changes. We conducted CPR at opposing levels of physiologic stiffness, using a LUCAS device, a motor-driven plunger, and a group of volunteers. In high-stiffness mode, blood flow generated by volunteers was significantly less after just 2min of CPR, whereas flow generated by LUCAS device was superior by comparison. Optimal blood flow was obtained via motor-driven plunger, with trapezoidal waveform. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

Waveform inversion of very long period impulsive signals associated with magmatic injection beneath Kilauea Volcano, Hawaii

USGS Publications Warehouse

Ohminato, T.; Chouet, B.A.; Dawson, P.; Kedar, S.

1998-01-01

We use data from broadband seismometers deployed around the summit of Kilauea Volcano to quantify the mechanism associated with a transient in the flow of magma feeding the east rift eruption of the volcano. The transient is marked by rapid inflation of the Kilauea summit peaking at 22 ??rad 4.5 hours after the event onset, followed by slow deflation over a period of 3 days. Superimposed on the summit inflation is a series of sawtooth displacement pulses, each characterized by a sudden drop in amplitude lasting 5-10 s followed by an exponential recovery lasting 1-3 min. The sawtooth waveforms display almost identical shapes, suggesting a process involving the repeated activation of a fixed source. The particle motion associated with each sawtooth is almost linear, and its major swing shows compressional motion at all stations. Analyses of semblance and particle motion are consistent with a point source located 1 km beneath the northeast edge of the Halemaumau pit crater. To estimate the source mechanism, we apply a moment tensor inversion to the waveform data, assuming a point source embedded in a homogeneous half-space with compressional and shear wave velocities representative of the average medium properties at shallow depth under Kilauea. Synthetic waveforms are constructed by a superposition of impulse responses for six moment tensor components and three single force components. The origin times of individual impulses are distributed along the time axis at appropriately small, equal intervals, and their amplitudes are determined by least squares. In this inversion, the source time functions of the six tensor and three force components are determined simultaneously. We confirm the accuracy of the inversion method through a series of numerical tests. The results from the inversion show that the waveform data are well explained by a pulsating transport mechanism operating on a subhorizontal crack linking the summit reservoir to the east rift of Kilauea. The crack acts like a buffer in which a batch of fluid (magma and/or gas) accumulates over a period of 1-3 min before being rapidly injected into a larger reservoir (possibly the east rift) over a timescale of 5-10 s. The seismic moment and volume change associated with a typical batch of fluid are approximately 1014 N m and 3000 m3, respectively. Our results also point to the existence of a single force component with amplitude of 109 N, which may be explained as the drag force generated by the flow of viscous magma through a narrow constriction in the flow path. The total volume of magma associated with the 4.5-hour-long activation of the pulsating source is roughly 500,000 m3 in good agreement with the integrated volume flow rate of magma estimated near the eruptive site.

Empirical transfer functions: Application to determination of outermost core velocity structure using SmKS phases

NASA Astrophysics Data System (ADS)

Alexandrakis, Catherine; Eaton, David W.

2007-11-01

SmKS waves provide good resolution of outer-core velocity structure, but are affected by heterogeneity in the D'' region. We have developed an Empirical Transfer Function (ETF) technique that transforms a reference pulse (here, SmKS) into a target waveform (SKKS) by: (1) time-windowing the respective pulses, (2) applying Wiener deconvolution, and (3) convolving the output with a Gaussian waveform. Common source and path effects are implicitly removed by this process. We combine ETFs from 446 broadband seismograms to produce a global stack, from which S3KS-SKKS differential time can be measured accurately. As a result of stacking, the scatter in our measurements (0.43 s) is much less than the 1.29 s scatter in previous compilations. Although our data do not uniquely constrain outermost core velocities, we show that the fit of most standard models can be improved by perturbing the outermost core velocity. Our best-fitting model is formed using IASP91 with PREM-like velocity at the top of the core.

A Contribution to the Understanding of the Regional Seismic Structure in the Eastern Mediterranean

NASA Astrophysics Data System (ADS)

Di Luccio, F.; Thio, H.; Pino, N.

2001-12-01

Regional earthquakes recorded by two digital broadband stations (BGIO and KEG) located in the Eastern Mediterranean have been analyzed in order to study the seismic structure in this region. The area consists of different tectonic provinces, which complicate the modeling of the seismic wave propagation. We have modeled the Pnl arrivals using the FK-integration technique (Saikia, 1994) along different paths at the two stations, at several distances, ranging from 400 to 1500 km. Comparing the synthetics obtained by using several models compiled by other authors, we have constructed a velocity model, considering the informations deriving from group velocity distribution, in order to determine the finer structure in the analyzed paths. The model has been perturbed by trial and error until a compressional velocity profile has been found producing the shape of the observed waveforms. The crustal thickness, upper mantle P-wave velocity and 410-km discontinuity determine the shape of the observed waveform portions.

Full-waveform Inversion for Localized 3-D S-velocity Structure in D" Beneath the Caribbean using US-Array Data

NASA Astrophysics Data System (ADS)

Borgeaud, A. F. E.; Konishi, K.; Kawai, K.; Geller, R. J.

2015-12-01

The region beneath Central America is known to have significant lateral velocity heterogeneities from the upper mantle down to the lowermost mantle. It is also known for its long history of subducting oceanic plates and fragmented plate remnants that sunk to the lowermost mantle (e.g., Ren et al., 2007). In this study, we use localized full-waveform inversion to invert for the 3-D S-velocity beneath the Caribbean. We use the DSM (Kawai et al., 2006) to compute 1-D synthetic seismograms and the first-order Born approximation to compute the partial derivatives for 3-D structure. We use a larger dataset with better coverage than Kawai et al. (2014), consisting of S and ScS phases from US-Array data for events in South America. The resulting 3-D model can contribute to understanding whether the cause of the velocity anomalies is thermal, chemical, or due to phase transitions.

Mantle Discontinuities under Iranian Plateau and Turan Shield from the Modeling of Seismic Triplications

NASA Astrophysics Data System (ADS)

Tseng, Tai-Lin; Chi, Hui-Ching; Huang, Bor-Shouh; Godoladze, Tea; Javakhishvili, Zurab; Karakhanyan, Arkadi

2015-04-01

Recent studies of seismic tomography show velocity anomalies in the mantle transition zone (TZ) under Zagros and Iranian Plateau, which are created by active collision between Africa and Eurasia. Remnants of Neo-Tethys slab that subducted before the collision might had experienced a break-off and likely be rested in the deep mantle. In this study, we utilize triplicate arrivals of high-resolution P waveforms to investigate the velocity structure of mantle beneath this continental collision zone and the surroundings. By combining several broadband arrays in eastern Turkey and Caucasus, we construct a fan of profiles, each about 800 km long, which consist of triplicate waveforms generated from the 410- and 660-km discontinuities. The method is particularly sensitive to the size of the velocity contrast for the sampled regions, including the central Iranian Plateau, Turan shield and part of South Caspian basin. Our results show that the lower TZ under the stable Turan shield is fast. The corresponding 660-km contrast is about 4.5% only, smaller than the value in global average model IASP91, but fairly close to that under the northern Indian shield in Precambrian age. For profiles sampling Iran, we observe azimuthal changes in the waveforms which require further data division or grouping. The preliminary analysis suggests that the velocity near the bottom of the TZ is comparable to model appropriate for Turan and probably has a slightly shallower 660-km discontinuity. We hope the comparisons between velocity structures under different terranes can improve our understandings to the lithosphere-mantle dynamics under the process of continental collision.

Retrieving rupture history using waveform inversions in time sequence

NASA Astrophysics Data System (ADS)

Yi, L.; Xu, C.; Zhang, X.

2017-12-01

The rupture history of large earthquakes is generally regenerated using the waveform inversion through utilizing seismological waveform records. In the waveform inversion, based on the superposition principle, the rupture process is linearly parameterized. After discretizing the fault plane into sub-faults, the local source time function of each sub-fault is usually parameterized using the multi-time window method, e.g., mutual overlapped triangular functions. Then the forward waveform of each sub-fault is synthesized through convoluting the source time function with its Green function. According to the superposition principle, these forward waveforms generated from the fault plane are summarized in the recorded waveforms after aligning the arrival times. Then the slip history is retrieved using the waveform inversion method after the superposing of all forward waveforms for each correspond seismological waveform records. Apart from the isolation of these forward waveforms generated from each sub-fault, we also realize that these waveforms are gradually and sequentially superimposed in the recorded waveforms. Thus we proposed a idea that the rupture model is possibly detachable in sequent rupture times. According to the constrained waveform length method emphasized in our previous work, the length of inverted waveforms used in the waveform inversion is objectively constrained by the rupture velocity and rise time. And one essential prior condition is the predetermined fault plane that limits the duration of rupture time, which means the waveform inversion is restricted in a pre-set rupture duration time. Therefore, we proposed a strategy to inverse the rupture process sequentially using the progressively shift rupture times as the rupture front expanding in the fault plane. And we have designed a simulation inversion to test the feasibility of the method. Our test result shows the prospect of this idea that requiring furthermore investigation.

Technical Note: A new phantom design for routine testing of Doppler ultrasound.

PubMed

Grice, J V; Pickens, D R; Price, R R

2016-07-01

The objective of this project is to demonstrate the principle and operation for a simple, inexpensive, and highly portable Doppler ultrasound quality assurance (QA) phantom intended for routine QA testing. A prototype phantom has been designed, fabricated, and evaluated. The phantom described here is powered by gravity alone, requires no external equipment for operation, and produces a stable fluid velocity useful for quality assurance. Many commercially available Doppler ultrasound testing systems can suffer from issues such as a lengthy setup, prohibitive cost, nonportable size, or difficulty in use. This new phantom design aims to address some of these problems and create a phantom appropriate for assessing Doppler ultrasound stability. The phantom was fabricated using a 3D printer. The basic design of the phantom is to provide gravity-powered flow of a Doppler fluid between two reservoirs. The printed components were connected with latex tubing and then seated in a tissue mimicking gel. Spectral Doppler waveforms were sampled to evaluate variations in the data, and the phantom was evaluated using high frame rate video to find an alternate measure of mean fluid velocity flowing in the phantom. The current system design maintains stable flow from one reservoir to the other for approximately 7 s. Color Doppler imaging of the phantom was found to be qualitatively consistent with laminar flow. Using pulsed spectral Doppler, the average fluid velocity from a sample volume approximately centered in the synthetic vessel was measured to be 56 cm/s with a standard deviation of 3.2 cm/s across 118 measurements. An independent measure of the average fluid velocity was measured to be 51.9 cm/s with a standard deviation of 0.7 cm/s over 4 measurements. The developed phantom provides stable fluid flow useful for frequent clinical Doppler ultrasound testing and attempts to address several obstacles facing Doppler phantom testing. Such an ultrasound phantom can make routine testing more approachable for institutions that wish to initiate a Doppler QA program or complement a previously existing QA program.

Multi-parameter Full-waveform Inversion for Acoustic VTI Medium with Surface Seismic Data

NASA Astrophysics Data System (ADS)

Cheng, X.; Jiao, K.; Sun, D.; Huang, W.; Vigh, D.

2013-12-01

Full-waveform Inversion (FWI) attracts wide attention recently in oil and gas industry as a new promising tool for high resolution subsurface velocity model building. While the traditional common image point gather based tomography method aims to focus post-migrated data in depth domain, FWI aims to directly fit the observed seismic waveform in either time or frequency domain. The inversion is performed iteratively by updating the velocity fields to reduce the difference between the observed and the simulated data. It has been shown the inversion is very sensitive to the starting velocity fields, and data with long offsets and low frequencies is crucial for the success of FWI to overcome this sensitivity. Considering the importance of data with long offsets and low frequencies, in most geologic environment, anisotropy is an unavoidable topic for FWI especially at long offsets, since anisotropy tends to have more pronounced effects on waves traveled for a great distance. In VTI medium, this means more horizontal velocity will be registered in middle-to-long offset data, while more vertical velocity will be registered in near-to-middle offset data. Up to date, most of real world applications of FWI still remain in isotropic medium, and only a few studies have been shown to account for anisotropy. And most of those studies only account for anisotropy in waveform simulation, but not invert for those anisotropy fields. Multi-parameter inversion for anisotropy fields, even in VTI medium, remains as a hot topic in the field. In this study, we develop a strategy for multi-parameter FWI for acoustic VTI medium with surface seismic data. Because surface seismic data is insensitivity to the delta fields, we decide to hold the delta fields unchanged during our inversion, and invert only for vertical velocity and epsilon fields. Through parameterization analysis and synthetic tests, we find that it is more feasible to invert for the parameterization as vertical and horizontal velocities instead of inverting for the parameterization as vertical velocity and epsilon fields. We develop a hierarchical approach to invert for vertical velocity first but hold epsilon unchanged and only switch to simultaneous inversion when vertical velocity inversion are approaching convergence. During simultaneous inversion, we observe significant acceleration in the convergence when incorporates second order information and preconditioning into inversion. We demonstrate the success of our strategy for VTI FWI using synthetic and real data examples from the Gulf of Mexico. Our results show that incorporation of VTI FWI improves migration of large offset acquisition data, and produces better focused migration images to be used in exploration, production and development of oil fields.

Changes in seismic velocity during the first 14 months of the 2004-2008 eruption of Mount St. Helens, Washington

NASA Astrophysics Data System (ADS)

Hotovec-Ellis, A. J.; Vidale, J. E.; Gomberg, J.; Thelen, W.; Moran, S. C.

2015-09-01

Mount St. Helens began erupting in late 2004 following an 18 year quiescence. Swarms of repeating earthquakes accompanied the extrusion of a mostly solid dacite dome over the next 4 years. In some cases the waveforms from these earthquakes evolved slowly, likely reflecting changes in the properties of the volcano that affect seismic wave propagation. We use coda-wave interferometry to quantify small changes in seismic velocity structure (usually <1%) between two similar earthquakes and employed waveforms from several hundred families of repeating earthquakes together to create a continuous function of velocity change observed at permanent stations operated within 20 km of the volcano. The high rate of earthquakes allowed tracking of velocity changes on an hourly time scale. Changes in velocity were largest near the newly extruding dome and likely related to shallow deformation as magma first worked its way to the surface. We found strong correlation between velocity changes and the inverse of real-time seismic amplitude measurements during the first 3 weeks of activity, suggesting that fluctuations of pressure in the shallow subsurface may have driven both seismicity and velocity changes. Velocity changes during the remainder of the eruption likely result from a complex interplay of multiple effects and are not well explained by any single factor alone, highlighting the need for complementary geophysical data when interpreting velocity changes.

Changes in seismic velocity during the first 14 months of the 2004–2008 eruption of Mount St. Helens, Washington

USGS Publications Warehouse

Hotovec-Ellis, A.J.; Vidale, J.E.; Gomberg, Joan S.; Thelen, Weston A.; Moran, Seth C.

2015-01-01

Mount St. Helens began erupting in late 2004 following an 18 year quiescence. Swarms of repeating earthquakes accompanied the extrusion of a mostly solid dacite dome over the next 4 years. In some cases the waveforms from these earthquakes evolved slowly, likely reflecting changes in the properties of the volcano that affect seismic wave propagation. We use coda-wave interferometry to quantify small changes in seismic velocity structure (usually <1%) between two similar earthquakes and employed waveforms from several hundred families of repeating earthquakes together to create a continuous function of velocity change observed at permanent stations operated within 20 km of the volcano. The high rate of earthquakes allowed tracking of velocity changes on an hourly time scale. Changes in velocity were largest near the newly extruding dome and likely related to shallow deformation as magma first worked its way to the surface. We found strong correlation between velocity changes and the inverse of real-time seismic amplitude measurements during the first 3 weeks of activity, suggesting that fluctuations of pressure in the shallow subsurface may have driven both seismicity and velocity changes. Velocity changes during the remainder of the eruption likely result from a complex interplay of multiple effects and are not well explained by any single factor alone, highlighting the need for complementary geophysical data when interpreting velocity changes.

Pulse transit time differential measurement by fiber Bragg grating pulse recorder.

PubMed

Umesh, Sharath; Padma, Srivani; Ambastha, Shikha; Kalegowda, Anand; Asokan, Sundarrajan

2015-05-01

The present study reports a noninvasive technique for the measurement of the pulse transit time differential (PTTD) from the pulse pressure waveforms obtained at the carotid artery and radial artery using fiber Bragg grating pulse recorders (FBGPR). PTTD is defined as the time difference between the arrivals of a pulse pressure waveform at the carotid and radial arterial sites. The PTTD is investigated as an indicator of variation in the systolic blood pressure. The results are validated against blood pressure variation obtained from a Mindray Patient Monitor. Furthermore, the pulse wave velocity computed from the obtained PTTD is compared with the pulse wave velocity obtained from the color Doppler ultrasound system and is found to be in good agreement. The major advantage of the PTTD measurement via FBGPRs is that the data acquisition system employed can simultaneously acquire pulse pressure waveforms from both FBGPRs placed at carotid and radial arterial sites with a single time scale, which eliminates time synchronization complexity.

Constraining the Size and Depth of a Shallow Crustal Magma Body at Newberry Volcano Using P-Wave Tomography and Finite-Difference Waveform Modeling

NASA Astrophysics Data System (ADS)

Beachly, M. W.; Hooft, E. E.; Toomey, D. R.; Waite, G. P.

2011-12-01

Imaging magmatic systems improves our understanding of magma ascent and storage in the crust and contributes to hazard assessment. Seismic tomography reveals crustal magma bodies as regions of low velocity; however the ability of delay-time tomography to detect small, low-velocity bodies is limited by wavefront healing. Alternatively, crustal magma chambers have been identified from secondary phases including P and S wave reflections and conversions. We use a combination of P-wave tomography and finite-difference waveform modeling to characterize a shallow crustal magma body at Newberry Volcano, central Oregon. Newberry's eruptions are silicic within the central caldera and mafic on its periphery suggesting a central silicic magma storage system. The system may still be active with a recent eruption ~1300 years ago and a drill hole temperature of 256° C at only 932 m depth. A low-velocity anomaly previously imaged at 3-5 km beneath the caldera indicates either a magma body or a fractured pluton. With the goal of detecting secondary arrivals from a magma chamber beneath Newberry Volcano, we deployed a line of densely-spaced (~300 m), three-component seismometers that recorded a shot of opportunity from the High Lava Plains Experiment in 2008. The data record a secondary P-wave arrival originating from beneath the caldera. In addition we combine travel-time data from our 2008 experiment with data collected in the 1980's by the USGS for a P-wave tomography inversion to image velocity structure to 6 km depth. The inversion includes 16 active sources, 322 receivers and 1007 P-wave first arrivals. The tomography results reveal a high-velocity, ring-like anomaly beneath the caldera ring faults to 2 km depth that surrounds a shallow low-velocity region. Beneath 2.5 km high-velocity anomalies are concentrated east and west of the caldera. A central low-velocity body lies below 3 km depth. Tomographic inversions of synthetic data suggest that the central low-velocity body beneath 3 km depth is not well resolved and that, for example, an unrealistically large low-velocity body with a volume up to 72 km3 at 40% velocity reduction (representing 30±7% partial melt) could be consistent with the observed travel-times. We use the tomographically derived velocity structure to construct 2D finite difference models and include synthetic low-velocity bodies in these models to test various magma chamber geometries and melt contents. Waveform modeling identifies the observed secondary phase as a transmitted P-wave formed by delaying and focusing P-wave energy through the low-velocity region. We will further constrain the size and shape of the low-velocity region by comparing arrival times and amplitudes of observed and synthetic primary and secondary phases. Secondary arrivals provide compelling evidence for an active crustal magmatic system beneath Newberry volcano and demonstrate the ability of waveform modeling to constrain the nature of magma bodies beyond the limits of seismic tomography.

Aortic pulse wave velocity and reflecting distance estimation from peripheral waveforms in humans: detection of age- and exercise training-related differences.

PubMed

Pierce, Gary L; Casey, Darren P; Fiedorowicz, Jess G; Seals, Douglas R; Curry, Timothy B; Barnes, Jill N; Wilson, DeMaris R; Stauss, Harald M

2013-07-01

We hypothesized that demographic/anthropometric parameters can be used to estimate effective reflecting distance (EfRD), required to derive aortic pulse wave velocity (APWV), a prognostic marker of cardiovascular risk, from peripheral waveforms and that such estimates can discriminate differences in APWV and EfRD with aging and habitual endurance exercise in healthy adults. Ascending aortic pressure waveforms were derived from peripheral waveforms (brachial artery pressure, n = 25; and finger volume pulse, n = 15) via a transfer function and then used to determine the time delay between forward- and backward-traveling waves (Δtf-b). True EfRDs were computed as directly measured carotid-femoral pulse wave velocity (CFPWV) × 1/2Δtf-b and then used in regression analysis to establish an equation for EfRD based on demographic/anthropometric data (EfRD = 0.173·age + 0.661·BMI + 34.548 cm, where BMI is body mass index). We found good agreement between true and estimated APWV (Pearson's R² = 0.43; intraclass correlation = 0.64; both P < 0.05) and EfRD (R² = 0.24; intraclass correlation = 0.40; both P < 0.05). In young sedentary (22 ± 2 years, n = 6), older sedentary (62 ± 1 years, n = 24), and older endurance-trained (61 ± 2 years, n = 14) subjects, EfRD (from demographic/anthropometric parameters), APWV, and 1/2Δtf-b (from brachial artery pressure waveforms) were 52.0 ± 0.5, 61.8 ± 0.4, and 60.6 ± 0.5 cm; 6.4 ± 0.3, 9.6 ± 0.2, and 8.1 ± 0.2 m/s; and 82 ± 3, 65 ± 1 and 76 ± 2 ms (all P < 0.05), respectively. Our results demonstrate that APWV derived from peripheral waveforms using age and BMI to estimate EfRD correlates with CFPWV in healthy adults. This method can reliably detect the distal shift of the reflecting site with age and the increase in APWV with sedentary aging that is attenuated with habitual endurance exercise.

Waveform shape analysis: extraction of physiologically relevant information from Doppler recordings.

PubMed

Ramsay, M M; Broughton Pipkin, F; Rubin, P C; Skidmore, R

1994-05-01

1. Doppler recordings were made from the brachial artery of healthy female subjects during a series of manoeuvres which altered the pressure-flow characteristics of the vessel. 2. Changes were induced in the peripheral circulation of the forearm by the application of heat or ice-packs. A sphygmomanometer cuff was used to create graded occlusion of the vessel above and below the point of measurement. Recordings were also made whilst the subjects performed a standardized Valsalva manoeuvre. 3. The Doppler recordings were analysed both with the standard waveform indices (systolic/diastolic ratio, pulsatility index and resistance index) and by the method of Laplace transform analysis. 4. The waveform parameters obtained by Laplace transform analysis distinguished the different changes in flow conditions; they thus had direct physiological relevance, unlike the standard waveform indices.

Non-contact hemodynamic imaging reveals the jugular venous pulse waveform

NASA Astrophysics Data System (ADS)

Amelard, Robert; Hughson, Richard L.; Greaves, Danielle K.; Pfisterer, Kaylen J.; Leung, Jason; Clausi, David A.; Wong, Alexander

2017-01-01

Cardiovascular monitoring is important to prevent diseases from progressing. The jugular venous pulse (JVP) waveform offers important clinical information about cardiac health, but is not routinely examined due to its invasive catheterisation procedure. Here, we demonstrate for the first time that the JVP can be consistently observed in a non-contact manner using a photoplethysmographic imaging system. The observed jugular waveform was strongly negatively correlated to the arterial waveform (r = -0.73 ± 0.17), consistent with ultrasound findings. Pulsatile venous flow was observed over a spatially cohesive region of the neck. Critical inflection points (c, x, v, y waves) of the JVP were observed across all participants. The anatomical locations of the strongest pulsatile venous flow were consistent with major venous pathways identified through ultrasound.

Non-contact hemodynamic imaging reveals the jugular venous pulse waveform

PubMed Central

Amelard, Robert; Hughson, Richard L.; Greaves, Danielle K.; Pfisterer, Kaylen J.; Leung, Jason; Clausi, David A.; Wong, Alexander

2017-01-01

Cardiovascular monitoring is important to prevent diseases from progressing. The jugular venous pulse (JVP) waveform offers important clinical information about cardiac health, but is not routinely examined due to its invasive catheterisation procedure. Here, we demonstrate for the first time that the JVP can be consistently observed in a non-contact manner using a photoplethysmographic imaging system. The observed jugular waveform was strongly negatively correlated to the arterial waveform (r = −0.73 ± 0.17), consistent with ultrasound findings. Pulsatile venous flow was observed over a spatially cohesive region of the neck. Critical inflection points (c, x, v, y waves) of the JVP were observed across all participants. The anatomical locations of the strongest pulsatile venous flow were consistent with major venous pathways identified through ultrasound. PMID:28065933

Amplitude loss of sonic waveform due to source coupling to the medium

NASA Astrophysics Data System (ADS)

Lee, Myung W.; Waite, William F.

2007-03-01

In contrast to hydrate-free sediments, sonic waveforms acquired in gas hydrate-bearing sediments indicate strong amplitude attenuation associated with a sonic velocity increase. The amplitude attenuation increase has been used to quantify pore-space hydrate content by attributing observed attenuation to the hydrate-bearing sediment's intrinsic attenuation. A second attenuation mechanism must be considered, however. Theoretically, energy radiation from sources inside fluid-filled boreholes strongly depends on the elastic parameters of materials surrounding the borehole. It is therefore plausible to interpret amplitude loss in terms of source coupling to the surrounding medium as well as to intrinsic attenuation. Analyses of sonic waveforms from the Mallik 5L-38 well, Northwest Territories, Canada, indicate a significant component of sonic waveform amplitude loss is due to source coupling. Accordingly, all sonic waveform amplitude analyses should include the effect of source coupling to accurately characterize a formation's intrinsic attenuation.

Amplitude loss of sonic waveform due to source coupling to the medium

USGS Publications Warehouse

Lee, Myung W.; Waite, William F.

2007-01-01

In contrast to hydrate-free sediments, sonic waveforms acquired in gas hydrate-bearing sediments indicate strong amplitude attenuation associated with a sonic velocity increase. The amplitude attenuation increase has been used to quantify pore-space hydrate content by attributing observed attenuation to the hydrate-bearing sediment's intrinsic attenuation. A second attenuation mechanism must be considered, however. Theoretically, energy radiation from sources inside fluid-filled boreholes strongly depends on the elastic parameters of materials surrounding the borehole. It is therefore plausible to interpret amplitude loss in terms of source coupling to the surrounding medium as well as to intrinsic attenuation. Analyses of sonic waveforms from the Mallik 5L-38 well, Northwest Territories, Canada, indicate a significant component of sonic waveform amplitude loss is due to source coupling. Accordingly, all sonic waveform amplitude analyses should include the effect of source coupling to accurately characterize a formation's intrinsic attenuation.

Computational Modeling of Seismic Wave Propagation Velocity-Saturation Effects in Porous Rocks

NASA Astrophysics Data System (ADS)

Deeks, J.; Lumley, D. E.

2011-12-01

Compressional and shear velocities of seismic waves propagating in porous rocks vary as a function of the fluid mixture and its distribution in pore space. Although it has been possible to place theoretical upper and lower bounds on the velocity variation with fluid saturation, predicting the actual velocity response of a given rock with fluid type and saturation remains an unsolved problem. In particular, we are interested in predicting the velocity-saturation response to various mixtures of fluids with pressure and temperature, as a function of the spatial distribution of the fluid mixture and the seismic wavelength. This effect is often termed "patchy saturation' in the rock physics community. The ability to accurately predict seismic velocities for various fluid mixtures and spatial distributions in the pore space of a rock is useful for fluid detection, hydrocarbon exploration and recovery, CO2 sequestration and monitoring of many subsurface fluid-flow processes. We create digital rock models with various fluid mixtures, saturations and spatial distributions. We use finite difference modeling to propagate elastic waves of varying frequency content through these digital rock and fluid models to simulate a given lab or field experiment. The resulting waveforms can be analyzed to determine seismic traveltimes, velocities, amplitudes, attenuation and other wave phenomena for variable rock models of fluid saturation and spatial fluid distribution, and variable wavefield spectral content. We show that we can reproduce most of the published effects of velocity-saturation variation, including validating the Voigt and Reuss theoretical bounds, as well as the Hill "patchy saturation" curve. We also reproduce what has been previously identified as Biot dispersion, but in fact in our models is often seen to be wave multi-pathing and broadband spectral effects. Furthermore, we find that in addition to the dominant seismic wavelength and average fluid patch size, the smoothness of the fluid patches are a critical factor in determining the velocity-saturation response; this is a result that we have not seen discussed in the literature. Most importantly, we can reproduce all of these effects using full elastic wavefield scattering, without the need to resort to more complicated squirt-flow or poroelastic models. This is important because the physical properties and parameters we need to model full elastic wave scattering, and predict a velocity-saturation curve, are often readily available for projects we undertake; this is not the case for poroelastic or squirt-flow models. We can predict this velocity saturation curve for a specific rock type, fluid mixture distribution and wavefield spectrum.

Pulmonary Vascular Input Impedance is a Combined Measure of Pulmonary Vascular Resistance and Stiffness and Predicts Clinical Outcomes Better than PVR Alone in Pediatric Patients with Pulmonary Hypertension

PubMed Central

Hunter, Kendall S.; Lee, Po-Feng; Lanning, Craig J.; Ivy, D. Dunbar; Kirby, K. Scott; Claussen, Lori R.; Chan, K. Chen; Shandas, Robin

2011-01-01

Background Pulmonary vascular resistance (PVR) is the current standard for evaluating reactivity in children with pulmonary arterial hypertension (PAH). However, PVR measures only the mean component of right ventricular afterload and neglects pulsatile effects. We recently developed and validated an method to measure pulmonary vascular input impedance, which revealed excellent correlation between the zero-harmonic impedance value and PVR, and suggested a correlation between higher harmonic impedance values and pulmonary vascular stiffness (PVS). Here we show that input impedance can be measured routinely and easily in the catheterization laboratory, that impedance provides PVR and PVS from a single measurement, and that impedance is a better predictor of disease outcomes compared to PVR. Methods Pressure and velocity waveforms within the main PA were measured during right-heart catheterization of patients with normal PA hemodynamics (n=14) and those with PAH undergoing reactivity evaluation (49 subjects; 95 conditions). A correction factor needed to transform velocity into flow was obtained by calibrating against cardiac output. Input impedance was obtained off-line by dividing Fourier-transformed pressure and flow waveforms. Results Exceptional correlation was found between the indexed zero harmonic of impedance and indexed PVR (y=1.095·x+1.381, R2=0.9620). Additionally, the modulus sum of the first two harmonics of impedance was found to best correlate with indexed pulse pressure over stroke volume (PP/SV) (y=13.39·x-0.8058, R2=0.7962). Amongst a subset of PAH patients (n=25), cumulative logistic regression between outcomes to total indexed impedance was better (RL2=0.4012) than between outcomes and indexed PVR (RL2=0.3131). Conclusions Input impedance can be consistently and easily obtained from PW Doppler and a single catheter pressure measurement, provides comprehensive characterization of the main components of RV afterload, and better predicts patient outcomes compared to PVR alone. PMID:18082509

Pulmonary vascular input impedance is a combined measure of pulmonary vascular resistance and stiffness and predicts clinical outcomes better than pulmonary vascular resistance alone in pediatric patients with pulmonary hypertension.

PubMed

Hunter, Kendall S; Lee, Po-Feng; Lanning, Craig J; Ivy, D Dunbar; Kirby, K Scott; Claussen, Lori R; Chan, K Chen; Shandas, Robin

2008-01-01

Pulmonary vascular resistance (PVR) is the current standard for evaluating reactivity in children with pulmonary arterial hypertension (PAH). However, PVR measures only the mean component of right ventricular afterload and neglects pulsatile effects. We recently developed and validated a method to measure pulmonary vascular input impedance, which revealed excellent correlation between the zero harmonic impedance value and PVR and suggested a correlation between higher-harmonic impedance values and pulmonary vascular stiffness. Here we show that input impedance can be measured routinely and easily in the catheterization laboratory, that impedance provides PVR and pulmonary vascular stiffness from a single measurement, and that impedance is a better predictor of disease outcomes compared with PVR. Pressure and velocity waveforms within the main pulmonary artery were measured during right heart catheterization of patients with normal pulmonary artery hemodynamics (n = 14) and those with PAH undergoing reactivity evaluation (49 subjects, 95 conditions). A correction factor needed to transform velocity into flow was obtained by calibrating against cardiac output. Input impedance was obtained off-line by dividing Fourier-transformed pressure and flow waveforms. Exceptional correlation was found between the indexed zero harmonic of impedance and indexed PVR (y = 1.095x + 1.381, R2 = 0.9620). In addition, the modulus sum of the first 2 harmonics of impedance was found to best correlate with indexed pulse pressure over stroke volume (y = 13.39x - 0.8058, R2 = 0.7962). Among a subset of patients with PAH (n = 25), cumulative logistic regression between outcomes to total indexed impedance was better (R(L)2 = 0.4012) than between outcomes and indexed PVR (R(L)2 = 0.3131). Input impedance can be consistently and easily obtained from pulse-wave Doppler and a single catheter pressure measurement, provides comprehensive characterization of the main components of RV afterload, and better predicts patient outcomes compared with PVR alone.

P wave velocity of Proterozoic upper mantle beneath central and southern Asia

NASA Astrophysics Data System (ADS)

Nyblade, Andrew A.; Vogfjord, Kristin S.; Langston, Charles A.

1996-05-01

P wave velocity structure of Proterozoic upper mantle beneath central and southern Africa was investigated by forward modeling of Pnl waveforms from four moderate size earthquakes. The source-receiver path of one event crosses central Africa and lies outside the African superswell while the source-receiver paths for the other events cross Proterozoic lithosphere within southern Africa, inside the African superswell. Three observables (Pn waveshape, PL-Pn time, and Pn/PL amplitude ratio) from the Pnl waveform were used to constrain upper mantle velocity models in a grid search procedure. For central Africa, synthetic seismograms were computed for 5880 upper mantle models using the generalized ray method and wavenumber integration; synthetic seismograms for 216 models were computed for southern Africa. Successful models were taken as those whose synthetic seismograms had similar waveshapes to the observed waveforms, as well as PL-Pn times within 3 s of the observed times and Pn/PL amplitude ratios within 30% of the observed ratio. Successful models for central Africa yield a range of uppermost mantle velocity between 7.9 and 8.3 km s-1, velocities between 8.3 and 8.5 km s-1 at a depth of 200 km, and velocity gradients that are constant or slightly positive. For southern Africa, successful models yield uppermost mantle velocities between 8.1 and 8.3 km s-1, velocities between 7.9 and 8.4 km s-1 at a depth of 130 km, and velocity gradients between -0.001 and 0.001 s-1. Because velocity gradients are controlled strongly by structure at the bottoming depths for Pn waves, it is not easy to compare the velocity gradients obtained for central and southern Africa. For central Africa, Pn waves turn at depths of about 150-200 km, whereas for southern Africa they bottom at ˜100-150 km depth. With regard to the origin of the African superswell, our results do not have sufficient resolution to test hypotheses that invoke simple lithospheric reheating. However, our models are not consistent with explanations for the African superswell invoking extensive amounts of lithospheric thinning. If extensive lithospheric thinning had occurred beneath southern Africa, as suggested previously, then upper mantle P wave velocities beneath southern Africa would likely be lower than those in our models.

Earthquake focal parameters and lithospheric structure of the anatolian plateau from complete regional waveform modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodgers, A

2000-12-28

This is an informal report on preliminary efforts to investigate earthquake focal mechanisms and earth structure in the Anatolian (Turkish) Plateau. Seismic velocity structure of the crust and upper mantle and earthquake focal parameters for event in the Anatolian Plateau are estimated from complete regional waveforms. Focal mechanisms, depths and seismic moments of moderately large crustal events are inferred from long-period (40-100 seconds) waveforms and compared with focal parameters derived from global teleseismic data. Using shorter periods (10-100 seconds) we estimate the shear and compressional velocity structure of the crust and uppermost mantle. Results are broadly consistent with previous studiesmore » and imply relatively little crustal thickening beneath the central Anatolian Plateau. Crustal thickness is about 35 km in western Anatolia and greater than 40 km in eastern Anatolia, however the long regional paths require considerable averaging and limit resolution. Crustal velocities are lower than typical continental averages, and even lower than typical active orogens. The mantle P-wave velocity was fixed to 7.9 km/s, in accord with tomographic models. A high sub-Moho Poisson's Ratio of 0.29 was required to fit the Sn-Pn differential times. This is suggestive of high sub-Moho temperatures, high shear wave attenuation and possibly partial melt. The combination of relatively thin crust in a region of high topography and high mantle temperatures suggests that the mantle plays a substantial role in maintaining the elevation.« less

High-resolution near-surface velocity model building using full-waveform inversion—a case study from southwest Sweden

NASA Astrophysics Data System (ADS)

Adamczyk, A.; Malinowski, M.; Malehmir, A.

2014-06-01

Full-waveform inversion (FWI) is an iterative optimization technique that provides high-resolution models of subsurface properties. Frequency-domain, acoustic FWI was applied to seismic data acquired over a known quick-clay landslide scar in southwest Sweden. We inverted data from three 2-D seismic profiles, 261-572 m long, two of them shot with small charges of dynamite and one with a sledgehammer. To our best knowledge this is the first published application of FWI to sledgehammer data. Both sources provided data suitable for waveform inversion, the sledgehammer data containing even wider frequency spectrum. Inversion was performed for frequency groups between 27.5 and 43.1 Hz for the explosive data and 27.5-51.0 Hz for the sledgehammer. The lowest inverted frequency was limited by the resonance frequency of the standard 28-Hz geophones used in the survey. High-velocity granitic bedrock in the area is undulated and very shallow (15-100 m below the surface), and exhibits a large P-wave velocity contrast to the overlying normally consolidated sediments. In order to mitigate the non-linearity of the inverse problem we designed a multiscale layer-stripping inversion strategy. Obtained P-wave velocity models allowed to delineate the top of the bedrock and revealed distinct layers within the overlying sediments of clays and coarse-grained materials. Models were verified in an extensive set of validating procedures and used for pre-stack depth migration, which confirmed their robustness.

Dynamics of temporal variations in phonatory flow.

PubMed

Krane, Michael H; Barry, Michael; Wei, Timothy

2010-07-01

This paper addresses the dynamic relevance of time variations of phonatory airflow, commonly neglected under the quasisteady phonatory flow assumption. In contrast to previous efforts, which relied on direct measurement of glottal impedance, this work uses spatially and temporally resolved measurements of the velocity field to estimate the unsteady and convective acceleration terms in the unsteady Bernoulli equation. Theoretical considerations suggest that phonatory flow is inherently unsteady when two related conditions apply: (1) that the unsteady and convective accelerations are commensurate, and (2) that the inertia of the glottal jet is non-negligible. Acceleration waveforms, computed from experimental data, show that unsteady and convective accelerations to be the same order of magnitude, throughout the cycle, and that the jet flow contributes significantly to the unsteady acceleration. In the middle of the cycle, however, jet inertia is negligible because the convective and unsteady accelerations nearly offset one another in the jet region. These results, consistent with previous findings treating quasisteady phonatory flow, emphasize that unsteady acceleration cannot be neglected during the final stages of the phonation cycle, during which voice sound power and spectral content are largely determined. Furthermore, glottal jet dynamics must be included in any model of phonatory airflow.

Dynamics of temporal variations in phonatory flow1

PubMed Central

Krane, Michael H.; Barry, Michael; Wei, Timothy

2010-01-01

This paper addresses the dynamic relevance of time variations of phonatory airflow, commonly neglected under the quasisteady phonatory flow assumption. In contrast to previous efforts, which relied on direct measurement of glottal impedance, this work uses spatially and temporally resolved measurements of the velocity field to estimate the unsteady and convective acceleration terms in the unsteady Bernoulli equation. Theoretical considerations suggest that phonatory flow is inherently unsteady when two related conditions apply: (1) that the unsteady and convective accelerations are commensurate, and (2) that the inertia of the glottal jet is non-negligible. Acceleration waveforms, computed from experimental data, show that unsteady and convective accelerations to be the same order of magnitude, throughout the cycle, and that the jet flow contributes significantly to the unsteady acceleration. In the middle of the cycle, however, jet inertia is negligible because the convective and unsteady accelerations nearly offset one another in the jet region. These results, consistent with previous findings treating quasisteady phonatory flow, emphasize that unsteady acceleration cannot be neglected during the final stages of the phonation cycle, during which voice sound power and spectral content are largely determined. Furthermore, glottal jet dynamics must be included in any model of phonatory airflow. PMID:20649231

In Vitro MRV-based Hemodynamic Study of Complex Helical Flow in a Patient-specific Jugular Model

NASA Astrophysics Data System (ADS)

Kefayati, Sarah; Acevedo-Bolton, Gabriel; Haraldsson, Henrik; Saloner, David

2014-11-01

Neurointerventional Radiologists are frequently requested to evaluate the venous side of the intracranial circulation for a variety of conditions including: Chronic Cerebrospinal Venous Insufficiency thought to play a role in the development of multiple sclerosis; sigmoid sinus diverticulum which has been linked to the presence of pulsatile tinnitus; and jugular vein distension which is related to cardiac dysfunction. Most approaches to evaluating these conditions rely on structural assessment or two dimensional flow analyses. This study was designed to investigate the highly complex jugular flow conditions using magnetic resonance velocimetry (MRV). A jugular phantom was fabricated based on the geometry of the dominant jugular in a tinnitus patient. Volumetric three-component time-resolved velocity fields were obtained using 4D PC-MRI -with the protocol enabling turbulence acquisition- and the patient-specific pulsatile waveform. Flow was highly complex exhibiting regions of jet, high swirling strength, and strong helical pattern with the core originating from the focal point of the jugular bulb. Specifically, flow was analyzed for helicity and the level of turbulence kinetic energy elevated in the core of helix and distally, in the post-narrowing region.

Fine Scale Structure of Low and Ultra-Low Velocity Patches in the Lowermost Mantle: Some Case Studies

NASA Astrophysics Data System (ADS)

Yuan, K.; Romanowicz, B. A.; French, S.

2015-12-01

The lowermost part of the mantle, which is roughly halfway to the center of the earth, plays a key role as a thermal and chemical boundary layer between the solid, silicate mantle and fluid, iron outer core. Constraining the seismic velocity structure in this region provides important insights on mantle dynamics, and core-mantle interactions. Recently, global shear wave velocity tomography has confirmed the presence of broad plume conduits extending vertically through the lower mantle in the vicinity of major hotspots (SEMUCB-WM1, French and Romanowicz, 2015). These conduits are rooted in D" in patches of strongly reduced shear velocity, at least some of which, such as Hawaii, appear to contain known ultra low velocity zones (e.g. Cottaar and Romanowicz, 2012). We seek to determine whether these patches generally contain ULVZs, and to contrast them with less extreme structures such as the PERM anomaly (Lekic et al., 2012). Because global tomography cannot resolve such fine scale structure, we apply forward modeling of higher frequency (10-20s) Sdiff waveforms in 3D complex structures using the Spectral Element Method. We focus on Iceland, Hawaii and the PERM anomaly, and Sdiff observations at USArray and/or dense broadband arrays in Europe. In all three cases, Sdiff waveforms are clearly distorted by these anomalies, with either a complex coda and/or evidence for amplitude focusing. As a start, we design simple cylindrical models of shear velocity reduction, and contrast the best fitting ones at each location considered in terms of diameter, height above the core-mantle boundary and strength of velocity reduction. We refine previously obtained models for Hawaii and the Perm Anomaly. For Iceland, the waveforms show a strong azimuthally dependent post-cursor, with maximum travel time delay of ~20s and focusing effects. The preliminary best fitting model shows a structure of 700km in diameter, ~15% reduction in shear wave velocity, extending ~40 km above the core-mantle boundary, in a location close to the Iceland hotspot which is in agreement with the low velocity patch in model SEMUCB_WM1.

Aging Wire Insulation Assessment by Phase Spectrum Examination of Ultrasonic Guided Waves

NASA Technical Reports Server (NTRS)

Anastasi, Robert F.; Madaras, Eric I.

2003-01-01

Wire integrity has become an area of concern to the aerospace community including DoD, NASA, FAA, and Industry. Over time and changing environmental conditions, wire insulation can become brittle and crack. The cracks expose the wire conductor and can be a source of equipment failure, short circuits, smoke, and fire. The technique of using the ultrasonic phase spectrum to extract material properties of the insulation is being examined. Ultrasonic guided waves will propagate in both the wire conductor and insulation. Assuming the condition of the conductor remains constant then the stiffness of the insulator can be determined by measuring the ultrasonic guided wave velocity. In the phase spectrum method the guided wave velocity is obtained by transforming the time base waveform to the frequency domain and taking the phase difference between two waveforms. The result can then be correlated with a database, derived by numerical model calculations, to extract material properties of the wire insulator. Initial laboratory tests were performed on a simple model consisting of a solid cylinder and then a solid cylinder with a polymer coating. For each sample the flexural mode waveform was identified. That waveform was then transformed to the frequency domain and a phase spectrum was calculated from a pair of waveforms. Experimental results on the simple model compared well to numerical calculations. Further tests were conducted on aircraft or mil-spec wire samples, to see if changes in wire insulation stiffness can be extracted using the phase spectrum technique.

Pulsed-DC DBD Plasma Actuators

NASA Astrophysics Data System (ADS)

Duong, Alan; Corke, Thomas; Thomas, Flint

2017-11-01

A power system for dielectric barrier discharge (DBD) plasma actuators that utilizes a pulsed-DC waveform is presented. The plasma actuator arrangement is identical to most typical AC-DBD designs with staggered electrodes that are separated by a dielectric insulator. A key difference is that the pulsed-DC actuator utilizes a DC voltage source to drive the actuator instead of an AC voltage input. The DC source is supplied to both electrodes. The exposed electrode remains constant in time while the encapsulated electrode is periodically grounded for short instances then is allowed to rise to the source DC level. Further investigation of the pulsed-DC plasma actuator was conducted. Time-resolved velocity measurements were done to characterize the induced velocity field generated by the pulsed-DC plasma actuator. A model of the pulsed-DC plasma actuator is developed in LTspice for further study. The work presented are intended in developing a model to be used in CFD flow control simulations. NASA SBIR NNX14CC12C.

Numerical simulation of self-sustained oscillation of a voice-producing element based on Navier-Stokes equations and the finite element method.

PubMed

de Vries, Martinus P; Hamburg, Marc C; Schutte, Harm K; Verkerke, Gijsbertus J; Veldman, Arthur E P

2003-04-01

Surgical removal of the larynx results in radically reduced production of voice and speech. To improve voice quality a voice-producing element (VPE) is developed, based on the lip principle, called after the lips of a musician while playing a brass instrument. To optimize the VPE, a numerical model is developed. In this model, the finite element method is used to describe the mechanical behavior of the VPE. The flow is described by two-dimensional incompressible Navier-Stokes equations. The interaction between VPE and airflow is modeled by placing the grid of the VPE model in the grid of the aerodynamical model, and requiring continuity of forces and velocities. By applying and increasing pressure to the numerical model, pulses comparable to glottal volume velocity waveforms are obtained. By variation of geometric parameters their influence can be determined. To validate this numerical model, an in vitro test with a prototype of the VPE is performed. Experimental and numerical results show an acceptable agreement.

Earthquake rupture below the brittle-ductile transition in continental lithospheric mantle

PubMed Central

Prieto, Germán A.; Froment, Bérénice; Yu, Chunquan; Poli, Piero; Abercrombie, Rachel

2017-01-01

Earthquakes deep in the continental lithosphere are rare and hard to interpret in our current understanding of temperature control on brittle failure. The recent lithospheric mantle earthquake with a moment magnitude of 4.8 at a depth of ~75 km in the Wyoming Craton was exceptionally well recorded and thus enabled us to probe the cause of these unusual earthquakes. On the basis of complete earthquake energy balance estimates using broadband waveforms and temperature estimates using surface heat flow and shear wave velocities, we argue that this earthquake occurred in response to ductile deformation at temperatures above 750°C. The high stress drop, low rupture velocity, and low radiation efficiency are all consistent with a dissipative mechanism. Our results imply that earthquake nucleation in the lithospheric mantle is not exclusively limited to the brittle regime; weakening mechanisms in the ductile regime can allow earthquakes to initiate and propagate. This finding has significant implications for understanding deep earthquake rupture mechanics and rheology of the continental lithosphere. PMID:28345055

Earthquake rupture below the brittle-ductile transition in continental lithospheric mantle.

PubMed

Prieto, Germán A; Froment, Bérénice; Yu, Chunquan; Poli, Piero; Abercrombie, Rachel

2017-03-01

Earthquakes deep in the continental lithosphere are rare and hard to interpret in our current understanding of temperature control on brittle failure. The recent lithospheric mantle earthquake with a moment magnitude of 4.8 at a depth of ~75 km in the Wyoming Craton was exceptionally well recorded and thus enabled us to probe the cause of these unusual earthquakes. On the basis of complete earthquake energy balance estimates using broadband waveforms and temperature estimates using surface heat flow and shear wave velocities, we argue that this earthquake occurred in response to ductile deformation at temperatures above 750°C. The high stress drop, low rupture velocity, and low radiation efficiency are all consistent with a dissipative mechanism. Our results imply that earthquake nucleation in the lithospheric mantle is not exclusively limited to the brittle regime; weakening mechanisms in the ductile regime can allow earthquakes to initiate and propagate. This finding has significant implications for understanding deep earthquake rupture mechanics and rheology of the continental lithosphere.

Detailed structure of the top of the melt body beneath the East Pacific Rise at 9°40'N from waveform inversion of seismic reflection data

NASA Astrophysics Data System (ADS)

Collier, J. S.; Singh, S. C.

1997-01-01

We have applied waveform inversion to multichannel seismic reflection data collected at the East Pacific Rise at 9°40'N in order to determine the precise velocity structure of the magma body causing the axial magma chamber reflection. Our analysis supports the idea of a molten sill as previously suggested from forward modeling of seismic data from this location. Our inverted solution has a 30-m-thick sill with a P wave seismic velocity of 2.6 km s-1. Although not well constrained by the data we believe that the S wave velocity in the sill is not significantly different from 0.0 km s-1. The low P- and S wave velocities in the sill imply that it contains less than 30% crystals. The molten sill is underlain by a velocity gradient in which the P wave velocity increases from 2.6 to 3.5 km s-1 over a vertical distance of 50-m. The shape of our velocity-depth profile implies that accretion of material to the roof of the sill is minor compared to accretion to the floor. The underlying velocity gradient zone may represent crystal settling under gravity. We suggest that only material from the 30-m-thick layer can erupt.

Lightning Return-Stroke Current Waveforms Aloft, From Measured Field Change, Current, and Channel Geometry

NASA Technical Reports Server (NTRS)

Willett, J. C.; LeVine, D. M.

2002-01-01

Direct current measurements are available near the attachment point from both natural cloud-to-ground lightning and rocket-triggered lightning, but little is known about the rise time and peak amplitude of return-stroke currents aloft. We present, as functions of height, current amplitudes, rise times, and effective propagation velocities that have been estimated with a novel remote-sensing technique from data on 24 subsequent return strokes in six different lightning flashes that were triggering at the NASA Kennedy Space Center, FL, during 1987. The unique feature of this data set is the stereo pairs of still photographs, from which three-dimensional channel geometries were determined previously. This has permitted us to calculate the fine structure of the electric-field-change (E) waveforms produced by these strokes, using the current waveforms measured at the channel base together with physically reasonable assumptions about the current distributions aloft. The computed waveforms have been compared with observed E waveforms from the same strokes, and our assumptions have been adjusted to maximize agreement. In spite of the non-uniqueness of solutions derived by this technique, several conclusions seem inescapable: 1) The effective propagation speed of the current up the channel is usually significantly (but not unreasonably) faster than the two-dimensional velocity measured by a streak camera for 14 of these strokes. 2) Given the deduced propagation speed, the peak amplitude of the current waveform often must decrease dramatically with height to prevent the electric field from being over-predicted. 3) The rise time of the current wave front must always increase rapidly with height in order to keep the fine structure of the calculated field consistent with the observations.

Microfluidic perfusion system for automated delivery of temporal gradients to islets of Langerhans.

PubMed

Zhang, Xinyu; Roper, Michael G

2009-02-01

A microfluidic perfusion system was developed for automated delivery of stimulant waveforms to cells within the device. The 3-layer glass/polymer device contained two pneumatic pumps, a 12 cm mixing channel, and a 0.2 microL cell chamber. By altering the flow rate ratio of the pumps, a series of output concentrations could be produced while a constant 1.43 +/- 0.07 microL/min flow rate was maintained. The output concentrations could be changed in time producing step gradients and other waveforms, such as sine and triangle waves, at different amplitudes and frequencies. Waveforms were analyzed by comparing the amplitude of output waveforms to the amplitude of theoretical waveforms. Below a frequency of 0.0098 Hz, the output waveforms had less than 20% difference than input waveforms. To reduce backflow of solutions into the pumps, the operational sequence of the valving program was modified, as well as differential etching of the valve seat depths. These modifications reduced backflow to the point that it was not detected. Gradients in glucose levels were applied in this work to stimulate single islets of Langerhans. Glucose gradients between 3 and 20 mM brought clear and intense oscillations of intracellular [Ca(2+)] indicating the system will be useful in future studies of cellular physiology.

Estimation of coronary wave intensity analysis using noninvasive techniques and its application to exercise physiology

PubMed Central

Nijjer, Sukhjinder; Sen, Sayan; Petraco, Ricardo; Jones, Siana; Al-Lamee, Rasha; Foin, Nicolas; Al-Bustami, Mahmud; Sethi, Amarjit; Kaprielian, Raffi; Ramrakha, Punit; Khan, Masood; Malik, Iqbal S.; Francis, Darrel P.; Parker, Kim; Hughes, Alun D.; Mikhail, Ghada W.; Mayet, Jamil; Davies, Justin E.

2015-01-01

Wave intensity analysis (WIA) has found particular applicability in the coronary circulation where it can quantify traveling waves that accelerate and decelerate blood flow. The most important wave for the regulation of flow is the backward-traveling decompression wave (BDW). Coronary WIA has hitherto always been calculated from invasive measures of pressure and flow. However, recently it has become feasible to obtain estimates of these waveforms noninvasively. In this study we set out to assess the agreement between invasive and noninvasive coronary WIA at rest and measure the effect of exercise. Twenty-two patients (mean age 60) with unobstructed coronaries underwent invasive WIA in the left anterior descending artery (LAD). Immediately afterwards, noninvasive LAD flow and pressure were recorded and WIA calculated from pulsed-wave Doppler coronary flow velocity and central blood pressure waveforms measured using a cuff-based technique. Nine of these patients underwent noninvasive coronary WIA assessment during exercise. A pattern of six waves were observed in both modalities. The BDW was similar between invasive and noninvasive measures [peak: 14.9 ± 7.8 vs. −13.8 ± 7.1 × 104 W·m−2·s−2, concordance correlation coefficient (CCC): 0.73, P < 0.01; cumulative: −64.4 ± 32.8 vs. −59.4 ± 34.2 × 102 W·m−2·s−1, CCC: 0.66, P < 0.01], but smaller waves were underestimated noninvasively. Increased left ventricular mass correlated with a decreased noninvasive BDW fraction (r = −0.48, P = 0.02). Exercise increased the BDW: at maximum exercise peak BDW was −47.0 ± 29.5 × 104 W·m−2·s−2 (P < 0.01 vs. rest) and cumulative BDW −19.2 ± 12.6 × 103 W·m−2·s−1 (P < 0.01 vs. rest). The BDW can be measured noninvasively with acceptable reliably potentially simplifying assessments and increasing the applicability of coronary WIA. PMID:26683900

Estimation of coronary wave intensity analysis using noninvasive techniques and its application to exercise physiology.

PubMed

Broyd, Christopher J; Nijjer, Sukhjinder; Sen, Sayan; Petraco, Ricardo; Jones, Siana; Al-Lamee, Rasha; Foin, Nicolas; Al-Bustami, Mahmud; Sethi, Amarjit; Kaprielian, Raffi; Ramrakha, Punit; Khan, Masood; Malik, Iqbal S; Francis, Darrel P; Parker, Kim; Hughes, Alun D; Mikhail, Ghada W; Mayet, Jamil; Davies, Justin E

2016-03-01

Wave intensity analysis (WIA) has found particular applicability in the coronary circulation where it can quantify traveling waves that accelerate and decelerate blood flow. The most important wave for the regulation of flow is the backward-traveling decompression wave (BDW). Coronary WIA has hitherto always been calculated from invasive measures of pressure and flow. However, recently it has become feasible to obtain estimates of these waveforms noninvasively. In this study we set out to assess the agreement between invasive and noninvasive coronary WIA at rest and measure the effect of exercise. Twenty-two patients (mean age 60) with unobstructed coronaries underwent invasive WIA in the left anterior descending artery (LAD). Immediately afterwards, noninvasive LAD flow and pressure were recorded and WIA calculated from pulsed-wave Doppler coronary flow velocity and central blood pressure waveforms measured using a cuff-based technique. Nine of these patients underwent noninvasive coronary WIA assessment during exercise. A pattern of six waves were observed in both modalities. The BDW was similar between invasive and noninvasive measures [peak: 14.9 ± 7.8 vs. -13.8 ± 7.1 × 10(4) W·m(-2)·s(-2), concordance correlation coefficient (CCC): 0.73, P < 0.01; cumulative: -64.4 ± 32.8 vs. -59.4 ± 34.2 × 10(2) W·m(-2)·s(-1), CCC: 0.66, P < 0.01], but smaller waves were underestimated noninvasively. Increased left ventricular mass correlated with a decreased noninvasive BDW fraction (r = -0.48, P = 0.02). Exercise increased the BDW: at maximum exercise peak BDW was -47.0 ± 29.5 × 10(4) W·m(-2)·s(-2) (P < 0.01 vs. rest) and cumulative BDW -19.2 ± 12.6 × 10(3) W·m(-2)·s(-1) (P < 0.01 vs. rest). The BDW can be measured noninvasively with acceptable reliably potentially simplifying assessments and increasing the applicability of coronary WIA. Copyright © 2016 the American Physiological Society.

Advanced Waveform Simulation for Seismic Monitoring

DTIC Science & Technology

2008-09-01

velocity model. The method separates the main arrivals of the regional waveform into 5 windows: Pnl (vertical and radial components), Rayleigh (vertical and...ranges out to 10°, including extensive observations of crustal thinning and thickening and various Pnl complexities. Broadband modeling in 1D, 2D...existing models perform in predicting the various regional phases, Rayleigh waves, Love waves, and Pnl waves. Previous events from this Basin-and-Range

Fault zone reverberations from cross-correlations of earthquake waveforms and seismic noise

NASA Astrophysics Data System (ADS)

Hillers, Gregor; Campillo, Michel

2016-03-01

Seismic wavefields interact with low-velocity fault damage zones. Waveforms of ballistic fault zone head waves, trapped waves, reflected waves and signatures of trapped noise can provide important information on structural and mechanical fault zone properties. Here we extend the class of observable fault zone waves and reconstruct in-fault reverberations or multiples in a strike-slip faulting environment. Manifestations of the reverberations are significant, consistent wave fronts in the coda of cross-correlation functions that are obtained from scattered earthquake waveforms and seismic noise recorded by a linear fault zone array. The physical reconstruction of Green's functions is evident from the high similarity between the signals obtained from the two different scattered wavefields. Modal partitioning of the reverberation wavefield can be tuned using different data normalization techniques. The results imply that fault zones create their own ambiance, and that the here reconstructed reverberations are a key seismic signature of wear zones. Using synthetic waveform modelling we show that reverberations can be used for the imaging of structural units by estimating the location, extend and magnitude of lateral velocity contrasts. The robust reconstruction of the reverberations from noise records suggests the possibility to resolve the response of the damage zone material to various external and internal loading mechanisms.

The Influence of the External Signal Modulation Waveform and Frequency on the Performance of a Photonic Forced Oscillator.

PubMed

Sánchez-Castro, Noemi; Palomino-Ovando, Martha Alicia; Estrada-Wiese, Denise; Valladares, Nydia Xcaret; Del Río, Jesus Antonio; de la Mora, Maria Beatriz; Doti, Rafael; Faubert, Jocelyn; Lugo, Jesus Eduardo

2018-05-21

Photonic crystals have been an object of interest because of their properties to inhibit certain wavelengths and allow the transmission of others. Using these properties, we designed a photonic structure known as photodyne formed by two porous silicon one-dimensional photonic crystals with an air defect between them. When the photodyne is illuminated with appropriate light, it allows us to generate electromagnetic forces within the structure that can be maximized if the light becomes localized inside the defect region. These electromagnetic forces allow the microcavity to oscillate mechanically. In the experiment, a chopper was driven by a signal generator to modulate the laser light that was used. The driven frequency and the signal modulation waveform (rectangular, sinusoidal or triangular) were changed with the idea to find optimal conditions for the structure to oscillate. The microcavity displacement amplitude, velocity amplitude and Fourier spectrum of the latter and its frequency were measured by means of a vibrometer. The mechanical oscillations are modeled and compared with the experimental results and show good agreement. For external frequency values of 5 Hz and 10 Hz, the best option was a sinusoidal waveform, which gave higher photodyne displacements and velocity amplitudes. Nonetheless, for an external frequency of 15 Hz, the best option was the rectangular waveform.

The Influence of the External Signal Modulation Waveform and Frequency on the Performance of a Photonic Forced Oscillator

PubMed Central

Sánchez-Castro, Noemi; Palomino-Ovando, Martha Alicia; Estrada-Wiese, Denise; Valladares, Nydia Xcaret; del Río, Jesus Antonio; Doti, Rafael; Faubert, Jocelyn; Lugo, Jesus Eduardo

2018-01-01

Photonic crystals have been an object of interest because of their properties to inhibit certain wavelengths and allow the transmission of others. Using these properties, we designed a photonic structure known as photodyne formed by two porous silicon one-dimensional photonic crystals with an air defect between them. When the photodyne is illuminated with appropriate light, it allows us to generate electromagnetic forces within the structure that can be maximized if the light becomes localized inside the defect region. These electromagnetic forces allow the microcavity to oscillate mechanically. In the experiment, a chopper was driven by a signal generator to modulate the laser light that was used. The driven frequency and the signal modulation waveform (rectangular, sinusoidal or triangular) were changed with the idea to find optimal conditions for the structure to oscillate. The microcavity displacement amplitude, velocity amplitude and Fourier spectrum of the latter and its frequency were measured by means of a vibrometer. The mechanical oscillations are modeled and compared with the experimental results and show good agreement. For external frequency values of 5 Hz and 10 Hz, the best option was a sinusoidal waveform, which gave higher photodyne displacements and velocity amplitudes. Nonetheless, for an external frequency of 15 Hz, the best option was the rectangular waveform. PMID:29883393

Validating Whole-Airway CFD Predictions of DPI Aerosol Deposition at Multiple Flow Rates.

PubMed

Longest, P Worth; Tian, Geng; Khajeh-Hosseini-Dalasm, Navvab; Hindle, Michael

2016-12-01

The objective of this study was to compare aerosol deposition predictions of a new whole-airway CFD model with available in vivo data for a dry powder inhaler (DPI) considered across multiple inhalation waveforms, which affect both the particle size distribution (PSD) and particle deposition. The Novolizer DPI with a budesonide formulation was selected based on the availability of 2D gamma scintigraphy data in humans for three different well-defined inhalation waveforms. Initial in vitro cascade impaction experiments were conducted at multiple constant (square-wave) particle sizing flow rates to characterize PSDs. The whole-airway CFD modeling approach implemented the experimentally determined PSDs at the point of aerosol formation in the inhaler. Complete characteristic airway geometries for an adult were evaluated through the lobar bronchi, followed by stochastic individual pathway (SIP) approximations through the tracheobronchial region and new acinar moving wall models of the alveolar region. It was determined that the PSD used for each inhalation waveform should be based on a constant particle sizing flow rate equal to the average of the inhalation waveform's peak inspiratory flow rate (PIFR) and mean flow rate [i.e., AVG(PIFR, Mean)]. Using this technique, agreement with the in vivo data was acceptable with <15% relative differences averaged across the three regions considered for all inhalation waveforms. Defining a peripheral to central deposition ratio (P/C) based on alveolar and tracheobronchial compartments, respectively, large flow-rate-dependent differences were observed, which were not evident in the original 2D in vivo data. The agreement between the CFD predictions and in vivo data was dependent on accurate initial estimates of the PSD, emphasizing the need for a combination in vitro-in silico approach. Furthermore, use of the AVG(PIFR, Mean) value was identified as a potentially useful method for characterizing a DPI aerosol at a constant flow rate.

Validating Whole-Airway CFD Predictions of DPI Aerosol Deposition at Multiple Flow Rates

PubMed Central

Tian, Geng; Khajeh-Hosseini-Dalasm, Navvab; Hindle, Michael

2016-01-01

Abstract Background: The objective of this study was to compare aerosol deposition predictions of a new whole-airway CFD model with available in vivo data for a dry powder inhaler (DPI) considered across multiple inhalation waveforms, which affect both the particle size distribution (PSD) and particle deposition. Methods: The Novolizer DPI with a budesonide formulation was selected based on the availability of 2D gamma scintigraphy data in humans for three different well-defined inhalation waveforms. Initial in vitro cascade impaction experiments were conducted at multiple constant (square-wave) particle sizing flow rates to characterize PSDs. The whole-airway CFD modeling approach implemented the experimentally determined PSDs at the point of aerosol formation in the inhaler. Complete characteristic airway geometries for an adult were evaluated through the lobar bronchi, followed by stochastic individual pathway (SIP) approximations through the tracheobronchial region and new acinar moving wall models of the alveolar region. Results: It was determined that the PSD used for each inhalation waveform should be based on a constant particle sizing flow rate equal to the average of the inhalation waveform's peak inspiratory flow rate (PIFR) and mean flow rate [i.e., AVG(PIFR, Mean)]. Using this technique, agreement with the in vivo data was acceptable with <15% relative differences averaged across the three regions considered for all inhalation waveforms. Defining a peripheral to central deposition ratio (P/C) based on alveolar and tracheobronchial compartments, respectively, large flow-rate-dependent differences were observed, which were not evident in the original 2D in vivo data. Conclusions: The agreement between the CFD predictions and in vivo data was dependent on accurate initial estimates of the PSD, emphasizing the need for a combination in vitro–in silico approach. Furthermore, use of the AVG(PIFR, Mean) value was identified as a potentially useful method for characterizing a DPI aerosol at a constant flow rate. PMID:27082824

Resolvability of regional density structure and the road to direct density inversion - a principal-component approach to resolution analysis

NASA Astrophysics Data System (ADS)

Płonka, Agnieszka; Fichtner, Andreas

2017-04-01

Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convective motion. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravity provide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling, making strong assumptions on the origin of structural heterogeneities, which may not necessarily be correct. Our goal is to assess if 3D density structure may be resolvable with emerging full-waveform inversion techniques. We have previously quantified the impact of regional-scale crustal density structure on seismic waveforms with the conclusion that reasonably sized density variations within the crust can leave a strong imprint on both travel times and amplitudes, and, while this can produce significant biases in velocity and Q estimates, the seismic waveform inversion for density may become feasible. In this study we perform principal component analyses of sensitivity kernels for P velocity, S velocity, and density. This is intended to establish the extent to which these kernels are linearly independent, i.e. the extent to which the different parameters may be constrained independently. We apply the method to data from 81 events around the Iberian Penninsula, registered in total by 492 stations. The objective is to find a principal kernel which would maximize the sensitivity to density, potentially allowing for as independent as possible density resolution. We find that surface (mosty Rayleigh) waves have significant sensitivity to density, and that the trade-off with velocity is negligible. We also show the preliminary results of the inversion.

Total variation regularization for seismic waveform inversion using an adaptive primal dual hybrid gradient method

NASA Astrophysics Data System (ADS)

Yong, Peng; Liao, Wenyuan; Huang, Jianping; Li, Zhenchuan

2018-04-01

Full waveform inversion is an effective tool for recovering the properties of the Earth from seismograms. However, it suffers from local minima caused mainly by the limited accuracy of the starting model and the lack of a low-frequency component in the seismic data. Because of the high velocity contrast between salt and sediment, the relation between the waveform and velocity perturbation is strongly nonlinear. Therefore, salt inversion can easily get trapped in the local minima. Since the velocity of salt is nearly constant, we can make the most of this characteristic with total variation regularization to mitigate the local minima. In this paper, we develop an adaptive primal dual hybrid gradient method to implement total variation regularization by projecting the solution onto a total variation norm constrained convex set, through which the total variation norm constraint is satisfied at every model iteration. The smooth background velocities are first inverted and the perturbations are gradually obtained by successively relaxing the total variation norm constraints. Numerical experiment of the projection of the BP model onto the intersection of the total variation norm and box constraints has demonstrated the accuracy and efficiency of our adaptive primal dual hybrid gradient method. A workflow is designed to recover complex salt structures in the BP 2004 model and the 2D SEG/EAGE salt model, starting from a linear gradient model without using low-frequency data below 3 Hz. The salt inversion processes demonstrate that wavefield reconstruction inversion with a total variation norm and box constraints is able to overcome local minima and inverts the complex salt velocity layer by layer.

Beat-to-Beat Blood Pressure Monitor

NASA Technical Reports Server (NTRS)

Lee, Yong Jin

2012-01-01

This device provides non-invasive beat-to-beat blood pressure measurements and can be worn over the upper arm for prolonged durations. Phase and waveform analyses are performed on filtered proximal and distal photoplethysmographic (PPG) waveforms obtained from the brachial artery. The phase analysis is used primarily for the computation of the mean arterial pressure, while the waveform analysis is used primarily to obtain the pulse pressure. Real-time compliance estimate is used to refine both the mean arterial and pulse pressures to provide the beat-to-beat blood pressure measurement. This wearable physiological monitor can be used to continuously observe the beat-to-beat blood pressure (B3P). It can be used to monitor the effect of prolonged exposures to reduced gravitational environments and the effectiveness of various countermeasures. A number of researchers have used pulse wave velocity (PWV) of blood in the arteries to infer the beat-to-beat blood pressure. There has been documentation of relative success, but a device that is able to provide the required accuracy and repeatability has not yet been developed. It has been demonstrated that an accurate and repeatable blood pressure measurement can be obtained by measuring the phase change (e.g., phase velocity), amplitude change, and distortion of the PPG waveforms along the brachial artery. The approach is based on comparing the full PPG waveform between two points along the artery rather than measuring the time-of-flight. Minimizing the measurement separation and confining the measurement area to a single, well-defined artery allows the waveform to retain the general shape between the two measurement points. This allows signal processing of waveforms to determine the phase and amplitude changes. Photoplethysmography, which measures changes in arterial blood volume, is commonly used to obtain heart rate and blood oxygen saturation. The digitized PPG signals are used as inputs into the beat-to-beat blood pressure measurement algorithm.

Cerebral Hemodynamics in the Elderly: A Transcranial Doppler Study in the Einstein Aging Study Cohort.

PubMed

Yang, Dixon; Cabral, Digna; Gaspard, Emmanuel N; Lipton, Richard B; Rundek, Tatjana; Derby, Carol A

2016-09-01

We sought to describe the relationship between age, sex, and race/ethnicity with transcranial Doppler hemodynamic characteristics from major intracerebral arterial segments in a large elderly population with varying demographics. We analyzed 369 stroke-free participants aged 70 years and older from the Einstein Aging Study. Single-gate, nonimaging transcranial Doppler sonography, a noninvasive sonographic technique that assesses real-time cerebrovascular hemodynamics, was used to interrogate 9 cerebral arterial segments. Individual Doppler spectra and cerebral blood flow velocities were acquired, and the pulsatility index and resistive index were calculated by the device's automated waveform-tracking function. Multiple linear regression models were used to examine the independent associations of age, sex, and race/ethnicity with transcranial Doppler measures, adjusting for hypertension, history of myocardial infarction or revascularization, and history of diabetes. Among enrolled participants, 303 individuals had at least 1 vessel insonated (mean age [SD], 80 [6] years; 63% women; 58% white; and 32% black). With age, transcranial Doppler measures of mean blood flow velocity were significantly decreased in the basilar artery (P = .001) and posterior cerebral artery (right, P = .003; left, P = .02). Pulsatility indices increased in the left middle cerebral artery (P = .01) and left anterior cerebral artery (P = .03), and the resistive index was increased in the left middle cerebral artery (P = .007) with age. Women had higher pulsatility and resistive indices compared to men in several vessels. We report a decreased mean blood flow velocity and weakly increased arterial pulsatility and resistance with aging in a large elderly stroke-free population. These referential trends in cerebrovascular hemodynamics may carry important implications in vascular diseases associated with advanced age, increased risk of cerebrovascular disease, cognitive decline, and dementia.

Three-Dimensional Anisotropic Acoustic and Elastic Full-Waveform Seismic Inversion

NASA Astrophysics Data System (ADS)

Warner, M.; Morgan, J. V.

2013-12-01

Three-dimensional full-waveform inversion is a high-resolution, high-fidelity, quantitative, seismic imaging technique that has advanced rapidly within the oil and gas industry. The method involves the iterative improvement of a starting model using a series of local linearized updates to solve the full non-linear inversion problem. During the inversion, forward modeling employs the full two-way three-dimensional heterogeneous anisotropic acoustic or elastic wave equation to predict the observed raw field data, wiggle-for-wiggle, trace-by-trace. The method is computationally demanding; it is highly parallelized, and runs on large multi-core multi-node clusters. Here, we demonstrate what can be achieved by applying this newly practical technique to several high-density 3D seismic datasets that were acquired to image four contrasting sedimentary targets: a gas cloud above an oil reservoir, a radially faulted dome, buried fluvial channels, and collapse structures overlying an evaporate sequence. We show that the resulting anisotropic p-wave velocity models match in situ measurements in deep boreholes, reproduce detailed structure observed independently on high-resolution seismic reflection sections, accurately predict the raw seismic data, simplify and sharpen reverse-time-migrated reflection images of deeper horizons, and flatten Kirchhoff-migrated common-image gathers. We also show that full-elastic 3D full-waveform inversion of pure pressure data can generate a reasonable shear-wave velocity model for one of these datasets. For two of the four datasets, the inclusion of significant transversely isotropic anisotropy with a vertical axis of symmetry was necessary in order to fit the kinematics of the field data properly. For the faulted dome, the full-waveform-inversion p-wave velocity model recovers the detailed structure of every fault that can be seen on coincident seismic reflection data. Some of the individual faults represent high-velocity zones, some represent low-velocity zones, some have more-complex internal structure, and some are visible merely as offsets between two regions with contrasting velocity. Although this has not yet been demonstrated quantitatively for this dataset, it seems likely that at least some of this fine structure in the recovered velocity model is related to the detailed lithology, strain history and fluid properties within the individual faults. We have here applied this technique to seismic data that were acquired by the extractive industries, however this inversion scheme is immediately scalable and applicable to a much wider range of problems given sufficient quality and density of observed data. Potential targets range from shallow magma chambers beneath active volcanoes, through whole-crustal sections across plate boundaries, to regional and whole-Earth models.

Accumulated energy norm for full waveform inversion of marine data

NASA Astrophysics Data System (ADS)

Shin, Changsoo; Ha, Wansoo

2017-12-01

Macro-velocity models are important for imaging the subsurface structure. However, the conventional objective functions of full waveform inversion in the time and the frequency domain have a limited ability to recover the macro-velocity model because of the absence of low-frequency information. In this study, we propose new objective functions that can recover the macro-velocity model by minimizing the difference between the zero-frequency components of the square of seismic traces. Instead of the seismic trace itself, we use the square of the trace, which contains low-frequency information. We apply several time windows to the trace and obtain zero-frequency information of the squared trace for each time window. The shape of the new objective functions shows that they are suitable for local optimization methods. Since we use the acoustic wave equation in this study, this method can be used for deep-sea marine data, in which elastic effects can be ignored. We show that the zero-frequency components of the square of the seismic traces can be used to recover macro-velocities from synthetic and field data.

Global seismic attenuation imaging using full-waveform inversion: a comparative assessment of different choices of misfit functionals

NASA Astrophysics Data System (ADS)

Karaoǧlu, Haydar; Romanowicz, Barbara

2018-02-01

We present the results of synthetic tests that aim at evaluating the relative performance of three different definitions of misfit functionals in the context of 3-D imaging of shear wave attenuation in the earth's upper mantle at the global scale, using long-period full-waveform data. The synthetic tests are conducted with simple hypothetical upper-mantle models that contain Qμ anomalies centred at different depths and locations, with or without additional seismic velocity anomalies. To build synthetic waveform data sets, we performed simulations of 50 events in the hypothetical (target) models, using the spectral element method, filtered in the period range 60-400 s. The selected events are chosen among 273 events used in the development of radially anisotropic model SEMUCB-WM1 and recorded at 495 stations worldwide. The synthetic Z-component waveforms correspond to paths and time intervals (fundamental mode and overtone Rayleigh waves) that exist in the real waveform data set. The inversions for shear attenuation structure are carried out using a Gauss-Newton optimization scheme in which the gradient and Hessian are computed using normal mode perturbation theory. The three different misfit functionals considered are based on time domain waveform (WF) and waveform envelope (E-WF) differences, as well as spectral amplitude ratios (SA), between observed and predicted waveforms. We evaluate the performance of the three misfit functional definitions in the presence of seismic noise and unresolved S-wave velocity heterogeneity and discuss the relative importance of physical dispersion effects due to 3-D Qμ structure. We observed that the performance of WF is poorer than the other two misfit functionals in recovering attenuation structure, unless anelastic dispersion effects are taken into account in the calculation of partial derivatives. WF also turns out to be more sensitive to seismic noise than E-WF and SA. Overall, SA performs best for attenuation imaging. Our tests show that it is important to account for 3-D elastic effects (focusing) before inverting for Qμ. Additionally, we show that including high signal-to-noise ratio overtone wave packets is necessary to resolve Qμ structure at depths greater than 250 km.

Source Process of the 2007 Niigata-ken Chuetsu-oki Earthquake Derived from Near-fault Strong Motion Data

NASA Astrophysics Data System (ADS)

Aoi, S.; Sekiguchi, H.; Morikawa, N.; Ozawa, T.; Kunugi, T.; Shirasaka, M.

2007-12-01

The 2007 Niigata-ken Chuetsu-oki earthquake occurred on July 16th, 2007, 10:13 JST. We performed a multi- time window linear waveform inversion analysis (Hartzell and Heaton, 1983) to estimate the rupture process from the near fault strong motion data of 14 stations from K-NET, KiK-net, F-net, JMA, and Niigata prefecture. The fault plane for the mainshock has not been clearly determined yet from the aftershock distribution, so that we performed two waveform inversions for north-west dipping fault (Model A) and south-east dipping fault (Model B). Their strike, dip, and rake are set to those of the moment tensor solutions by F-net. Fault plane model of 30 km length by 24 km width is set to cover aftershock distribution within 24 hours after the mainshock. Theoretical Green's functions were calculated by the discrete wavenumber method (Bouchon, 1981) and the R/T matrix method (Kennett, 1983) with the different stratified medium for each station based on the velocity structure including the information form the reflection survey and borehole logging data. Convolution of moving dislocation was introduced to represent the rupture propagation in an each subfault (Sekiguchi et al., 2002). The observed acceleration records were integrated into velocity except of F-net velocity data, and bandpass filtered between 0.1 and 1.0 Hz. We solved least-squared equation to obtain slip amount of each time window on each subfault to minimize squared residual of the waveform fitting between observed and synthetic waveforms. Both models provide moment magnitudes of 6.7. Regarding Model A, we obtained large slip in the south-west deeper part of the rupture starting point, which is close to Kashiwazaki-city. The second or third velocity pulses of observed velocity waveforms seem to be composed of slip from the asperity. Regarding Model B, we obtained large slip in the southwest shallower part of the rupture starting point, which is also close to Kashiwazaki-city. In both models, we found small slip near the rupture starting point, and largest slip at about ten kilometer in the south-west of the rupture starting point with the maximum slip of 2.3 and 2.5 m for Models A and B, respectively. The difference of the residual between observed and synthetic waveforms for both models is not significant, therefore it is difficult to conclude which fault plane is appropriate to explain. The estimated large-slip regions in the inverted source models with the Models A and B are located near the cross point of the two fault plane models, which should have similar radiation pattern. This situation may be one of the reasons why judgment of the fault plane orientation is such difficult. We need careful examinations not only strong motion data but also geodetic data to further explore the fault orientation and the source process of this earthquake.

Modelling guided waves in the Alaskan-Aleutian subduction zone

NASA Astrophysics Data System (ADS)

Coulson, Sophie; Garth, Thomas; Reitbrock, Andreas

2016-04-01

Subduction zone guided wave arrivals from intermediate depth earthquakes (70-300 km depth) have a huge potential to tell us about the velocity structure of the subducting oceanic crust as it dehydrates at these depths. We see guided waves as the oceanic crust has a slower seismic velocity than the surrounding material, and so high frequency energy is retained and delayed in the crustal material. Lower frequency energy is not retained in this crustal waveguide and so travels at faster velocities of the surrounding material. This gives a unique observation at the surface with low frequency energy arriving before the higher frequencies. We constrain this guided wave dispersion by comparing the waveforms recorded in real subduction zones with simulated waveforms, produced using finite difference full waveform modelling techniques. This method has been used to show that hydrated minerals in the oceanic crust persist to much greater depths than accepted thermal petrological subduction zone models would suggest in Northern Japan (Garth & Rietbrock, 2014a), and South America (Garth & Rietbrock, in prep). These observations also suggest that the subducting oceanic mantle may be highly hydrated at intermediate depth by dipping normal faults (Garth & Rietbrock 2014b). We use this guided wave analysis technique to constrain the velocity structure of the down going ~45 Ma Pacific plate beneath Alaska. Dispersion analysis is primarily carried out on guided wave arrivals recorded on the Alaskan regional seismic network. Earthquake locations from global earthquake catalogues (ISC and PDE) and regional earthquake locations from the AEIC (Alaskan Earthquake Information Centre) catalogue are used to constrain the slab geometry and to identify potentially dispersive events. Dispersed arrivals are seen at stations close to the trench, with high frequency (>2 Hz) arrivals delayed by 2 - 4 seconds. This dispersion is analysed to constrain the velocity and width of the proposed waveguide. The velocity structure of this relatively young subducting plate is compared to the velocity structure resolved in the older oceanic lithosphere subducted beneath Northern Japan. We also use guided wave observations to investigate the thickness and low velocity structure of the subducting Yakutat terrain. Additionally we discuss the dependence of the inferred slab geometry on the earthquake catalogues that are used.

Cough-Associated Changes in CSF Flow in Chiari I Malformation Evaluated by Real-Time MRI.

PubMed

Bhadelia, R A; Patz, S; Heilman, C; Khatami, D; Kasper, E; Zhao, Y; Madan, N

2016-05-01

Invasive pressure studies have suggested that CSF flow across the foramen magnum may transiently decrease after coughing in patients with symptomatic Chiari I malformation. The purpose of this exploratory study was to demonstrate this phenomenon noninvasively by assessing CSF flow response to coughing in symptomatic patients with Chiari I malformation by using MR pencil beam imaging and to compare the response with that in healthy participants. Eight symptomatic patients with Chiari I malformation and 6 healthy participants were studied by using MR pencil beam imaging with a temporal resolution of ∼50 ms. Patients and healthy participants were scanned for 90 seconds (without cardiac gating) to continuously record cardiac cycle-related CSF flow waveforms in real-time during resting, coughing, and postcoughing periods. CSF flow waveform amplitude, CSF stroke volume, and CSF flow rate (CSF Flow Rate = CSF Stroke Volume × Heart Rate) in the resting and immediate postcoughing periods were determined and compared between patients and healthy participants. There was no significant difference in CSF flow waveform amplitude, CSF stroke volume, and the CSF flow rate between patients with Chiari I malformation and healthy participants during rest. However, immediately after coughing, a significant decrease in CSF flow waveform amplitude (P < .001), CSF stroke volume (P = .001), and CSF flow rate (P = .001) was observed in patients with Chiari I malformation but not in the healthy participants. Real-time MR imaging noninvasively showed a transient decrease in CSF flow across the foramen magnum after coughing in symptomatic patients with Chiari I malformation, a phenomenon not seen in healthy participants. Our results provide preliminary evidence that the physiology-based imaging method used here has the potential to be an objective clinical test to differentiate symptomatic from asymptomatic patients with Chiari I malformation. © 2016 by American Journal of Neuroradiology.

Azimuthal anisotropy of the Pacific region

NASA Astrophysics Data System (ADS)

Maggi, Alessia; Debayle, Eric; Priestley, Keith; Barruol, Guilhem

2006-10-01

Azimuthal anisotropy is the dependence of local seismic properties on the azimuth of propagation. We present the azimuthally anisotropic component of a 3D SV velocity model for the Pacific Ocean, derived from the waveform modeling of over 56,000 multi-mode Rayleigh waves followed by a simultaneous inversion for isotropic and azimuthally anisotropic vsv structure. The isotropic vsv model is discussed in a previous paper (A. Maggi, E. Debayle, K. Priestley, G. Barruol, Multi-mode surface waveform tomography of the Pacific Ocean: a close look at the lithospheric cooling signature, Geophys. J. Int. 166 (3) (2006). doi:10.1111/j.1365-246x.2006.03037.x). The azimuthal anisotropy we find is consistent with the lattice preferred orientation model (LPO): the hypothesis of anisotropy generation in the Earth's mantle by preferential alignment of anisotropic crystals in response to the shear strains induced by mantle flow. At lithospheric depths we find good agreement between fast azimuthal anisotropy orientations and ridge spreading directions recorded by sea-floor magnetic anomalies. At asthenospheric depths we find a strong correlation between fast azimuthal anisotropy orientations and the directions of current plate motions. We observe perturbations in the pattern of seismic anisotropy close to Pacific hot-spots that are consistent with the predictions of numerical models of LPO generation in plume-disturbed plate motion-driven mantle flow. These observations suggest that perturbations in the patterns of azimuthal anisotropy may provide indirect evidence for plume-like upwelling in the mantle.

Lithospheric layering in the North American craton revealed by including Short Period Constraints in Full Waveform Tomography

NASA Astrophysics Data System (ADS)

Roy, C.; Calo, M.; Bodin, T.; Romanowicz, B. A.

2017-12-01

Recent receiver function studies of the North American craton suggest the presence of significant layering within the cratonic lithosphere, with significant lateral variations in the depth of the velocity discontinuities. These structural boundaries have been confirmed recently using a transdimensional Markov Chain Monte Carlo approach (TMCMC), inverting surface wave dispersion data and converted phases simultaneously (Calò et al., 2016; Roy and Romanowicz 2017). The lateral resolution of upper mantle structure can be improved with a high density of broadband seismic stations, or with a sparse network using full waveform inversion based on numerical wavefield computation methods such as the Spectral Element Method (SEM). However, inverting for discontinuities with strong topography such as MLDS's or LAB, presents challenges in an inversion framework, both computationally, due to the short periods required, and from the point of view of stability of the inversion. To overcome these limitations, and to improve resolution of layering in the upper mantle, we are developing a methodology that combines full waveform inversion tomography and information provided by short period seismic observables. We have extended the 30 1D radially anisotropic shear velocity profiles of Calò et al. 2016 to several other stations, for which we used a recent shear velocity model (Clouzet et al., 2017) as constraint in the modeling. These 1D profiles, including both isotropic and anisotropic discontinuities in the upper mantle (above 300 km depth) are then used to build a 3D starting model for the full waveform tomographic inversion. This model is built after 1) homogenization of the layered 1D models and 2) interpolation between the 1D smooth profiles and the model of Clouzet et al. 2017, resulting in a smooth 3D starting model. Waveforms used in the inversion are filtered at periods longer than 30s. We use the SEM code "RegSEM" for forward computations and a quasi-Newton inversion approach in which kernels are computed using normal mode perturbation theory. The resulting volumetric velocity perturbations around the homogenized starting model are then added to the discontinuous 3D starting model by dehomogenizing the model. We present here the first results of such an approach for refining structure in the North American continent.

Seismic signatures of up- and down-going hydrothermal pathways along the East Pacific Rise 9ºN

NASA Astrophysics Data System (ADS)

Marjanovic, M.; Fuji, N.; Singh, S. C.; Belahi, T.

2016-12-01

Hydrothermal circulation along divergent plate boundaries plays an important role in the transfer of heat between Earth's lithosphere and deep ocean, evidenced by the presence of hydrothermal vents on the seafloor. Although the spatial distribution of different types of vents or fluid discharge zones is well documented, the distribution of fluid recharge zones and its flow pattern within the oceanic crust are still elusive. Here, we apply seismic elastic full waveform inversion techniques to extrapolated high-fidelity 2D along-axis seismic data collected in 2008 to characterise the nature of zero-age upper crust formed at the East Pacific Rise (EPR) within 9º15-57'N. The resulting velocity model shows prominent perturbation in background velocity in the northern part of the profile, where prolific hydrothermal and volcanic activities have been observed. This, 22 km wide region is represented by five low velocity anomalies (for 300 m/s lower) that are 3 km wide and can be tracked to up to 1 km below the seafloor. Two of the low velocity zones seem to underlay vent clusters centered at 9º47' and 9º50' that we relate to the presence of up-going pathways of the fluid. The three remaining low velocity zones (centered at 9º44', 9º48.5', 9º51') are more prominent and their extent roughly coincides with the previously identified fine-scale tectonic discontinuities. The results suggest these deviations of axial orientation observed in the seafloor, coupled with upper crustal fracturing that can be sustained for several 100s of years as ideal locations for seawater to penetrate more permeable crust on the ridge-axis and establish down-going pathway of hydrothermal flow. Similar scenario was suggested by micro-earthquakes within one small portion of the region during the last eruption. The presence of a strong axial melt lens and associated anomalous velocity zone indicate enhanced thermal regime within the area responsible for establishing and sustaining hydrothermal flow in the upper crust. Although similar low velocity regions are imaged in the vicinity of prominent third-order discontinuities at 9º17' and 9º37'N the underlying AML is shown to be mostly cristalized hindering the hydrothermal circulation process in the area.

Lithospheric structure of the Western Alps as seen by full-waveform inversion of CIFALPS teleseismic data

NASA Astrophysics Data System (ADS)

Beller, Stephen; Monteiller, Vadim; Operto, Stéphane; Nolet, Guust; Paul, Anne; Zhao, Liang

2017-04-01

Full-waveform inversion (FWI) is a powerful but constitutionally intensive technique that aims to recover 3D multiparameter images of the subsurface by minimising the waveform difference between the full recorded and modelled seismograms. This method has recently been adapted and successfully applied in lithospheric settings by tackling teleseismic waveform modelling with hybrid methods. For each event, a global scale simulation is performed once and for all to store the wavefield solutions on the edges of the lithospheric target. Then, for each modelling involved in the FWI process, these global scale solutions are injected within the lithospheric medium from the boundaries. We present the results of the application of teleseismic FWI to the data acquired by the CIFALPS experiment that was conducted in the Western Alps to gain new insights its lithospheric structure and geodynamic evolution of the alpine range. Nine teleseismic events were inverted to infer 3D models of density, P-wave velocity and S-wave velocity of the crust and the upper-mantle down to 200 km depth. Our models show clear evidences of continental subduction during the alpine orogeny. They outline a dipping European Moho down to 75 km depth and finely delineate the geometry of the Ivrea body at the suture between European and Adriatic plates. Deeper, in the mantle a slow S-wave velocity anomaly might indicate the location of the European slab detachment. Overall, FWI models give access to new seismic images that fill the resolution gap between smooth tomographic model and sharp receiver function images of the lithosphere and enable integrated interpretations of crustal and upper-mantle structures.

3-D Waveform Modeling of the 11 September 2001 World Trade Center Collapse Events in New York City

NASA Astrophysics Data System (ADS)

Yoo, S.; Rhie, J.; Kim, W.

2010-12-01

The seismic signals from collapse of the twin towers of World Trade Center (WTC), NYC were well recorded by the seismographic stations in the northeastern United States. The building collapse can be represented by a vertical single force which does not generate tangential component seismic signals during the source process. The waveforms recorded by the Basking Ridge, NJ (BRNJ) station located due west of the WTC site show that the amplitude on tangential component is negligible and indicates that a vertical single force assumption is valid and the velocity structure is more or less homogeneous along the propagation path. However, 3-component seismograms recorded at Palisades, NY (PAL), which is located 33.8 km due north of the WTC site along the Hudson River (azimuth = 15.2°), show abnormal features. The amplitude on tangential component is larger than on vertical- or on radial-component. This observation may be attributable to the complex energy conversion between Rayleigh and Love waves due to the strong low velocity anomaly associated with unconsolidated sediments under the Hudson River. To test the effects of the low velocity anomaly on the enhanced amplitude in tangential component, we developed a 3D velocity model by considering local geology such as unconsolidated sediment layer, Palisades sill, Triassic sandstone, and crystalline basement and simulated waveforms at PAL. The preliminary synthetic results show that 3D velocity structure can significantly enhance the amplitude in tangential component but it is not as large as the observation. Although a more precise 3D model is required to better explain the observations, our results confirm that the low velocity layer under the Hudson River can enhance the amplitude in tangential component at PAL. This result suggests that a good understanding of the amplitude enhancements for specific event-site pairs may be important to evaluate seismic hazard of metropolitan New York City.

Decreased steady-state cerebral blood flow velocity and altered dynamic cerebral autoregulation during 5-h sustained 15% O2 hypoxia.

PubMed

Nishimura, Naoko; Iwasaki, Ken-ichi; Ogawa, Yojiro; Aoki, Ken

2010-05-01

Effects of hypoxia on cerebral circulation are important for occupational, high-altitude, and aviation medicine. Increased risk of fainting might be attributable to altered cerebral circulation by hypoxia. Dynamic cerebral autoregulation is reportedly impaired immediately by mild hypoxia. However, continuous exposure to hypoxia causes hyperventilation, resulting in hypocapnia. This hypocapnia is hypothesized to restore impaired dynamic cerebral autoregulation with reduced steady-state cerebral blood flow (CBF). However, no studies have examined hourly changes in alterations of dynamic cerebral autoregulation and steady-state CBF during sustained hypoxia. We therefore examined cerebral circulation during 5-h exposure to 15% O2 hypoxia and 21% O2 in 13 healthy volunteers in a sitting position. Waveforms of blood pressure and CBF velocity in the middle cerebral artery were measured using finger plethysmography and transcranial Doppler ultrasonography. Dynamic cerebral autoregulation was assessed by spectral and transfer function analysis. As expected, steady-state CBF velocity decreased significantly from 2 to 5 h of hypoxia, accompanying 2- to 3-Torr decreases in end-tidal CO2 (ETCO2). Furthermore, transfer function gain and coherence in the very-low-frequency range increased significantly at the beginning of hypoxia, indicating impaired dynamic cerebral autoregulation. However, contrary to the proposed hypothesis, indexes of dynamic cerebral autoregulation showed no significant restoration despite ETCO2 reductions, resulting in persistent higher values of very-low-frequency power of CBF velocity variability during hypoxia (214+/-40% at 5 h of hypoxia vs. control) without significant increases in blood pressure variability. These results suggest that sustained mild hypoxia reduces steady-state CBF and continuously impairs dynamic cerebral autoregulation, implying an increased risk of shortage of oxygen supply to the brain.

Full seismic waveform tomography for upper-mantle structure in the Australasian region using adjoint methods

NASA Astrophysics Data System (ADS)

Fichtner, Andreas; Kennett, Brian L. N.; Igel, Heiner; Bunge, Hans-Peter

2009-12-01

We present a full seismic waveform tomography for upper-mantle structure in the Australasian region. Our method is based on spectral-element simulations of seismic wave propagation in 3-D heterogeneous earth models. The accurate solution of the forward problem ensures that waveform misfits are solely due to as yet undiscovered Earth structure and imprecise source descriptions, thus leading to more realistic tomographic images and source parameter estimates. To reduce the computational costs, we implement a long-wavelength equivalent crustal model. We quantify differences between the observed and the synthetic waveforms using time-frequency (TF) misfits. Their principal advantages are the separation of phase and amplitude misfits, the exploitation of complete waveform information and a quasi-linear relation to 3-D Earth structure. Fréchet kernels for the TF misfits are computed via the adjoint method. We propose a simple data compression scheme and an accuracy-adaptive time integration of the wavefields that allows us to reduce the storage requirements of the adjoint method by almost two orders of magnitude. To minimize the waveform phase misfit, we implement a pre-conditioned conjugate gradient algorithm. Amplitude information is incorporated indirectly by a restricted line search. This ensures that the cumulative envelope misfit does not increase during the inversion. An efficient pre-conditioner is found empirically through numerical experiments. It prevents the concentration of structural heterogeneity near the sources and receivers. We apply our waveform tomographic method to ~1000 high-quality vertical-component seismograms, recorded in the Australasian region between 1993 and 2008. The waveforms comprise fundamental- and higher-mode surface and long-period S body waves in the period range from 50 to 200 s. To improve the convergence of the algorithm, we implement a 3-D initial model that contains the long-wavelength features of the Australasian region. Resolution tests indicate that our algorithm converges after around 10 iterations and that both long- and short-wavelength features in the uppermost mantle are well resolved. There is evidence for effects related to the non-linearity in the inversion procedure. After 11 iterations we fit the data waveforms acceptably well; with no significant further improvements to be expected. During the inversion the total fitted seismogram length increases by 46 per cent, providing a clear indication of the efficiency and consistency of the iterative optimization algorithm. The resulting SV-wave velocity model reveals structural features of the Australasian upper mantle with great detail. We confirm the existence of a pronounced low-velocity band along the eastern margin of the continent that can be clearly distinguished against Precambrian Australia and the microcontinental Lord Howe Rise. The transition from Precambrian to Phanerozoic Australia (the Tasman Line) appears to be sharp down to at least 200 km depth. It mostly occurs further east of where it is inferred from gravity and magnetic anomalies. Also clearly visible are the Archean and Proterozoic cratons, the northward continuation of the continent and anomalously low S-wave velocities in the upper mantle in central Australia. This is, to the best of our knowledge, the first application of non-linear full seismic waveform tomography to a continental-scale problem.

Alterations of Blood Flow Through Arteries Following Atherectomy and the Impact on Pressure Variation and Velocity.

PubMed

Plourde, Brian D; Vallez, Lauren J; Sun, Biyuan; Nelson-Cheeseman, Brittany B; Abraham, John P; Staniloae, Cezar S

2016-09-01

Simulations were made of the pressure and velocity fields throughout an artery before and after removal of plaque using orbital atherectomy plus adjunctive balloon angioplasty or stenting. The calculations were carried out with an unsteady computational fluid dynamic solver that allows the fluid to naturally transition to turbulence. The results of the atherectomy procedure leads to an increased flow through the stenotic zone with a coincident decrease in pressure drop across the stenosis. The measured effect of atherectomy and adjunctive treatment showed decrease the systolic pressure drop by a factor of 2.3. Waveforms obtained from a measurements were input into a numerical simulation of blood flow through geometry obtained from medical imaging. From the numerical simulations, a detailed investigation of the sources of pressure loss was obtained. It is found that the major sources of pressure drop are related to the acceleration of blood through heavily occluded cross sections and the imperfect flow recovery downstream. This finding suggests that targeting only the most occluded parts of a stenosis would benefit the hemodynamics. The calculated change in systolic pressure drop through the lesion was a factor of 2.4, in excellent agreement with the measured improvement. The systolic and cardiac-cycle-average pressure results were compared with measurements made in a multi-patient study treated with orbital atherectomy and adjunctive treatment. The agreements between the measured and calculated systolic pressure drop before and after the treatment were within 3%. This excellent agreement adds further confidence to the results. This research demonstrates the use of orbital atherectomy to facilitate balloon expansion to restore blood flow and how pressure measurements can be utilized to optimize revascularization of occluded peripheral vessels.

Initial rupture of earthquakes in the 1995 Ridgecrest, California sequence

USGS Publications Warehouse

Mori, J.; Kanamori, H.

1996-01-01

Close examination of the P waves from earthquakes ranging in size across several orders of magnitude shows that the shape of the initiation of the velocity waveforms is independent of the magnitude of the earthquake. A model in which earthquakes of all sizes have similar rupture initiation can explain the data. This suggests that it is difficult to estimate the eventual size of an earthquake from the initial portion of the waveform. Previously reported curvature seen in the beginning of some velocity waveforms can be largely explained as the effect of anelastic attenuation; thus there is little evidence for a departure from models of simple rupture initiation that grow dynamically from a small region. The results of this study indicate that any "precursory" radiation at seismic frequencies must emanate from a source region no larger than the equivalent of a M0.5 event (i.e. a characteristic length of ???10 m). The size of the nucleation region for magnitude 0 to 5 earthquakes thus is not resolvable with the standard seismic instrumentation deployed in California. Copyright 1996 by the American Geophysical Union.

Near-surface versus fault zone damage following the 1999 Chi-Chi earthquake: Observation and simulation of repeating earthquakes

USGS Publications Warehouse

Chen, Kate Huihsuan; Furumura, Takashi; Rubinstein, Justin L.

2015-01-01

We observe crustal damage and its subsequent recovery caused by the 1999 M7.6 Chi-Chi earthquake in central Taiwan. Analysis of repeating earthquakes in Hualien region, ~70 km east of the Chi-Chi earthquake, shows a remarkable change in wave propagation beginning in the year 2000, revealing damage within the fault zone and distributed across the near surface. We use moving window cross correlation to identify a dramatic decrease in the waveform similarity and delays in the S wave coda. The maximum delay is up to 59 ms, corresponding to a 7.6% velocity decrease averaged over the wave propagation path. The waveform changes on either side of the fault are distinct. They occur in different parts of the waveforms, affect different frequencies, and the size of the velocity reductions is different. Using a finite difference method, we simulate the effect of postseismic changes in the wavefield by introducing S wave velocity anomaly in the fault zone and near the surface. The models that best fit the observations point to pervasive damage in the near surface and deep, along-fault damage at the time of the Chi-Chi earthquake. The footwall stations show the combined effect of near-surface and the fault zone damage, where the velocity reduction (2–7%) is twofold to threefold greater than the fault zone damage observed in the hanging wall stations. The physical models obtained here allow us to monitor the temporal evolution and recovering process of the Chi-Chi fault zone damage.

Measurement and Modeling of Dispersive Pulse Propagation in Drawn Wire Waveguides

NASA Technical Reports Server (NTRS)

Madaras, Eric I.; Kohl, Thomas W.; Rogers, Wayne P.

1995-01-01

An analytical model of dispersive pulse propagation in semi-infinite cylinders due to transient axially symmetric end conditions has been experimentally investigated. Specifically, the dispersive propagation of the first axially symmetric longitudinal mode in thin wire waveguides, which have ends in butt contact with longitudinal piezoelectric ultrasonic transducers, is examined. The method allows for prediction of a propagated waveform given a measured source waveform, together with the material properties of the cylinder. Alternatively, the source waveform can be extracted from measurement of the propagated waveform. The material properties required for implementation of the pulse propagation model are determined using guided wave phase velocity measurements. Hard tempered aluminum 1100 and 304 stainless steel wires, with 127, 305, and 406 micron diam., were examined. In general, the drawn wires were found to behave as transversely isotropic media.

Measurement and modeling of dispersive pulse propagation in draw wire waveguides

NASA Technical Reports Server (NTRS)

Madaras, Eric I.; Kohl, Thomas W.; Rogers, Wayne P.

1995-01-01

An analytical model of dispersive pulse propagation in semi-infinite cylinders due to transient axially symmetric end conditions has been experimentally investigated. Specifically, the dispersive propagation of the first axially symmetric longitudinal mode in thin wire waveguides, which have ends in butt contact with longitudinal piezoelectric ultrasonic transducers, is examined. The method allows for prediction of a propagated waveform given a measured source waveform, together with the material properties of the cylinder. Alternatively, the source waveform can be extracted from measurement of the propagated waveform. The material properties required for implementation of the pulse propagation model are determined using guided wave phase velocity measurements. Hard tempered aluminum 1100 and 304 stainless steel wires, with 127, 305, and 406 micron diam., were examined. In general, the drawn wires were found to behave as transversely isotropic media.

Developing Regionalized Models of Lithospheric Thickness and Velocity Structure Across Eurasia and the Middle East from Jointly Inverting P-Wave and S-Wave Receiver Functions with Rayleigh Wave Group and Phase Velocities

DTIC Science & Technology

2011-09-01

modeling of regional waveforms at station ANTO , in UNIFIED region #14. The velocity models (left) and the corresponding predictions (middle and right) are...models, Geophy. J. Int. 118: 245–254. Rychert, C. A. and P. M. Shearer (2009). A global view of the lithosphere-asthenosphere boundary, Science 324 : 495

Peripheral Artery Disease and Continuous Flow Left Ventricle Assist Device: An Engaging Complement Analysis May Help to Guide Treatment.

PubMed

Falletta, Calogero; Pasta, Salvatore; Raffa, Giuseppe Maria; Crinò, Francesca; Sciacca, Sergio; Clemenza, Francesco

2018-02-13

Use of continuous flow left ventricle assist device (CF-LVAD) in advanced heart failure (HF) patients results in clinically relevant improvements in survival, functional capacity, and quality of life. Peripheral artery disease (PAD) can occur in patients with CF-LVAD due to the high rate of concomitance between risk factors for atherosclerosis and HF. Diagnosis of PAD can be difficult in the specific setting of a patient supported by this kind of device because of the marked alteration in waveform morphology and velocity created by the artificial physiology of an LVAD. We report the case of a 53-year-old man with HF secondary to ischemic cardiomyopathy supported by the HeartWare HVAD as bridge to transplant, who after the implant developed symptoms suggestive of PAD. We describe additional computational flow analysis for the study of PAD-related hemodynamic disturbances induced by a CF-LVAD. Flow simulations enhance the information of clinical image data, and may have an application in clinical investigations of the risk of hemodynamic disturbances induced by LVAD implantation. © 2018 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Abnormal arterial flows by a distributed model of the fetal circulation.

PubMed

van den Wijngaard, Jeroen P H M; Westerhof, Berend E; Faber, Dirk J; Ramsay, Margaret M; Westerhof, Nico; van Gemert, Martin J C

2006-11-01

Modeling the propagation of blood pressure and flow along the fetoplacental arterial tree may improve interpretation of abnormal flow velocity waveforms in fetuses. The current models, however, either do not include a wide range of gestational ages or do not account for variation in anatomical, vascular, or rheological parameters. We developed a mathematical model of the pulsating fetoumbilical arterial circulation using Womersley's oscillatory flow theory and viscoelastic arterial wall properties. Arterial flow waves are calculated at different arterial locations from which the pulsatility index (PI) can be determined. We varied blood viscosity, placental and brain resistances, placental compliance, heart rate, stiffness of the arterial wall, and length of the umbilical arteries. The PI increases in the umbilical artery and decreases in the cerebral arteries, as a result of increasing placental resistance or decreasing brain resistance. Both changes in resistance decrease the flow through the placenta. An increased arterial stiffness increases the PIs in the entire fetoplacental circulation. Blood viscosity and peripheral bed compliance have limited influence on the flow profiles. Bradycardia and tachycardia increase and decrease the PI in all arteries, respectively. Umbilical arterial length has limited influence on the PI but affects the mean arterial pressure at the placental cord insertion. The model may improve the interpretation of arterial flow pulsations and thus may advance both the understanding of pathophysiological processes and clinical management.

Characterization of a viscoelastic heterogeneous object with an effective model by nonlinear full waveform inversion

NASA Astrophysics Data System (ADS)

Mesgouez, A.

2018-05-01

The determination of equivalent viscoelastic properties of heterogeneous objects remains challenging in various scientific fields such as (geo)mechanics, geophysics or biomechanics. The present investigation addresses the issue of the identification of effective constitutive properties of a binary object by using a nonlinear and full waveform inversion scheme. The inversion process, without any regularization technique or a priori information, aims at minimizing directly the discrepancy between the full waveform responses of a bi-material viscoelastic cylindrical object and its corresponding effective homogeneous object. It involves the retrieval of five constitutive equivalent parameters. Numerical simulations are performed in a laboratory-scale two-dimensional configuration: a transient acoustic plane wave impacts the object and the diffracted fluid pressure, solid stress or velocity component fields are determined using a semi-analytical approach. Results show that the retrieval of the density and of the real parts of both the compressional and the shear wave velocities have been carried out successfully regarding the number and location of sensors, the type of sensors, the size of the searching space, the frequency range of the incident plane pressure wave, and the change in the geometric or mechanical constitution of the bi-material object. The retrieval of the imaginary parts of the wave velocities can reveal in some cases the limitations of the proposed approach.

Pockets, conduits, channels, and plumes: links to volcanism and orogeny in the rollback dominated western Mediterranean

NASA Astrophysics Data System (ADS)

Miller, Meghan S.; Sun, Daoyuan; O'Driscoll, Leland; Becker, Thorsten W.; Holt, Adam; Diaz, Jordi; Thomas, Christine

2015-04-01

Detailed mantle and lithospheric structure from the Canary Islands to Iberia have been imaged with data from recent temporary deployments and select permanent stations from over 300 broadband seismometers. The stations extended across Morocco and Spain as part of the PICASSO, IberArray, and Morocco-Münster experiments. We present results from S receiver functions (SRF), shear wave splitting, waveform modeling, and geodynamic models that help constrain the tectonic evolution of the westernmost Mediterranean, including orogenesis of the Atlas Mountains and occurrence of localized alkaline volcanism. Our receiver function images, in agreement with previous geophysical modeling, show that the lithosphere is thin (~65 km) beneath the Atlas, but thickens (~100 km) over a very short length scale at the flanks of the mountains. We find that these dramatic changes in lithospheric thickness also correspond to dramatic decreases in delay times inferred from S and SKS splitting observations of seismic anisotropy. Pockets and conduits of low seismic velocity material below the lithosphere extend along much of the Atlas to Southern Spain and correlate with the locations of Pliocene-Quaternary magmatism. Waveform analysis from the USC linear seismic array across the Atlas Mountains constrains the position, shape, and physical characteristics of one localized, low velocity conduit that extends from the uppermost mantle (~200 km depth) up to the volcanoes in the Middle Atlas. The shape, position and temperature of these seismically imaged low velocity anomalies, topography of the base of the lithosphere, morphology of the subducted slab beneath the Alboran Sea, position of the West African Craton and correlation with mantle flow inferred from shear wave splitting suggest that the unusually high topography of the Atlas Mountains and isolated recent volcanics are due to active mantle support that may be from material channeled from the Canary Island plume.

Acoustic Measurement of Potato Cannon Velocity

ERIC Educational Resources Information Center

Courtney, Michael; Courtney, Amy

2007-01-01

Potato cannon velocity can be measured with a digitized microphone signal. A microphone is attached to the potato cannon muzzle, and a potato is fired at an aluminum target about 10 m away. Flight time can be determined from the acoustic waveform by subtracting the time in the barrel and time for sound to return from the target. The potato…

Eruption mass estimation using infrasound waveform inversion and ash and gas measurements: Evaluation at Sakurajima Volcano, Japan

NASA Astrophysics Data System (ADS)

Fee, David; Izbekov, Pavel; Kim, Keehoon; Yokoo, Akihiko; Lopez, Taryn; Prata, Fred; Kazahaya, Ryunosuke; Nakamichi, Haruhisa; Iguchi, Masato

2017-12-01

Eruption mass and mass flow rate are critical parameters for determining the aerial extent and hazard of volcanic emissions. Infrasound waveform inversion is a promising technique to quantify volcanic emissions. Although topography may substantially alter the infrasound waveform as it propagates, advances in wave propagation modeling and station coverage permit robust inversion of infrasound data from volcanic explosions. The inversion can estimate eruption mass flow rate and total eruption mass if the flow density is known. However, infrasound-based eruption flow rates and mass estimates have yet to be validated against independent measurements, and numerical modeling has only recently been applied to the inversion technique. Here we present a robust full-waveform acoustic inversion method, and use it to calculate eruption flow rates and masses from 49 explosions from Sakurajima Volcano, Japan. Six infrasound stations deployed from 12-20 February 2015 recorded the explosions. We compute numerical Green's functions using 3-D Finite Difference Time Domain modeling and a high-resolution digital elevation model. The inversion, assuming a simple acoustic monopole source, provides realistic eruption masses and excellent fit to the data for the majority of the explosions. The inversion results are compared to independent eruption masses derived from ground-based ash collection and volcanic gas measurements. Assuming realistic flow densities, our infrasound-derived eruption masses for ash-rich eruptions compare favorably to the ground-based estimates, with agreement ranging from within a factor of two to one order of magnitude. Uncertainties in the time-dependent flow density and acoustic propagation likely contribute to the mismatch between the methods. Our results suggest that realistic and accurate infrasound-based eruption mass and mass flow rate estimates can be computed using the method employed here. If accurate volcanic flow parameters are known, application of this technique could be broadly applied to enable near real-time calculation of eruption mass flow rates and total masses. These critical input parameters for volcanic eruption modeling and monitoring are not currently available.

Mössbauer spectra linearity improvement by sine velocity waveform followed by linearization process

NASA Astrophysics Data System (ADS)

Kohout, Pavel; Frank, Tomas; Pechousek, Jiri; Kouril, Lukas

2018-05-01

This note reports the development of a new method for linearizing the Mössbauer spectra recorded with a sine drive velocity signal. Mössbauer spectra linearity is a critical parameter to determine Mössbauer spectrometer accuracy. Measuring spectra with a sine velocity axis and consecutive linearization increases the linearity of spectra in a wider frequency range of a drive signal, as generally harmonic movement is natural for velocity transducers. The obtained data demonstrate that linearized sine spectra have lower nonlinearity and line width parameters in comparison with those measured using a traditional triangle velocity signal.

Central Pulsatile Pressure and Flow Relationship in the Time and Frequency Domain to Characterise Hydraulic Input to the Brain and Cerebral Vascular Impedance.

PubMed

Kim, Mi Ok; O'Rourke, Michael F; Adji, Audrey; Avolio, Alberto P

2016-01-01

In the time domain, pulsatile flow and pressure can be characterised as the ratio of the late systolic boost of flow or pressure to the pulse amplitude so as to estimate the hydraulic input to the brain. While vascular impedance has been widely used to represent the load presented to the heart by the systemic circulation, it has not been applied to the cerebral circulation.We set out to study the relationship between the pressure and the flow augmentation index (AIx) in the time domain and to determine cerebral vascular impedance using aortic blood pressure and cerebral blood flow waveforms in the frequency domain. Twenty-four young subjects (aged 21-39 years) were recruited; aortic pressure was derived using SphygmoCor from radial pressure. Flow waveforms were recorded from the middle cerebral artery. In three subjects, we performed the Valsalva manoeuvre to investigate their response to physiological intervention. There was a linear relationship between flow and pressure AIx, and cerebral impedance values were similar to those estimated for low resistance vascular beds. Substantial change in pressure and flow wave contour was observed during the Valsalva manoeuvre; however, the relationship in both the time and the frequency domains were unchanged. This confirms that aortic pressure and cerebral flow waveform can be used to study cerebral impedance.

Long-period Ground Motion Characteristics Inside and Outside of the Osaka Basin during the 2011 Great Tohoku Earthquake and Its Largest Aftershock

NASA Astrophysics Data System (ADS)

Sato, K.; Iwata, T.; Asano, K.; Kubo, H.; Aoi, S.

2013-12-01

The 2011 great Tohoku earthquake (Mw 9.0) occurred on March 11, 2011, and the largest aftershock (Mw 7.7) at the region adjacent to south boundary of the mainshock's source region. Long-period ground motions (1-10s) of large amplitude were observed in the Osaka sedimentary basin about 550-800km away from the source regions during both events. We studied propagation and site characteristics of these ground motions, and found some common features between these two events in the Osaka basin. (1) The amplitude of horizontal components of the ground motion at the site-specific period is amplified at each sedimentary station. The predominant period is around 7s in the bayside area where the largest pSv were observed. (2) The velocity Fourier spectra have their peak values around 7s at the bedrock sites surrounding the Osaka basin. (3) Two remarkable wave packets separated by 30s propagating from stations around the Nobi plain to the bedrock sites near the Osaka basin were seen in the pasted-up velocity waveforms from the source regions to the Osaka basin for both events (Sato et al., 2012). Therefore, large long-period ground motions in the Osaka basin are generated by the combination of propagation-path and basin effects. Firstly, we simulate ground motions due to the largest aftershock using three-dimensional FDM (GMS; Aoi and Fujiwara, 1999). The reason we focus on the largest aftershock is that this event has a relatively small rupture area and simple rupture process compared to the mainshock. The source model is based on the model estimated by Kubo et al. (2013). The velocity structure model is a three-dimensional velocity structure based on the Japan Integrated Velocity Structure Model (Koketsu et al., 2012) and the layer of Vs 350m/s in this model is replaced with one of Vs 500m/s. The minimum effective period in this computation is 3s. Then, we compare synthetic waveforms with observed ones. At CHBH14, the nearest station to the source and 60km away from the epicenter, the synthetic waveforms of the period-band 5-50s, where Kubo et al. (2013) studied, fit well to the observed ones. However, in our target period-band 5-8s, the earlier portion of the synthetic waveform of the main packet has smaller amplitude than the observation. At the bedrock sites near the Osaka basin, two wave packets which are appeared in the observation are qualitatively reproduced in the synthetics. However, the amplitudes are not well reproduced. Moreover, the amplitude ratio of horizontal components of synthetics between the rock and the bayside stations is underestimated compared to the observed one. Improvements of the source and velocity structure models for propagation-path and basin are needed. For that sake, we will analyze the characteristics of the synthetic waveforms, study how those wave packets are generated, and discuss the discrepancy between the synthetic and observed waveforms. We will also simulate the ground motion for the mainshock to study propagation characteristics of the mainshock. ACKNOWLEDGEMENTS We used strong motion data recorded by K-NET, KiK-net and F-net of NIED, CEORKA, BRI, JMA, and Osaka prefecture. GMS provided by NIED is used for the computation.

Time-reversal imaging techniques applied to tremor waveforms near Cholame, California to locate tectonic tremor

NASA Astrophysics Data System (ADS)

Horstmann, T.; Harrington, R. M.; Cochran, E. S.

2012-12-01

Frequently, the lack of distinctive phase arrivals makes locating tectonic tremor more challenging than locating earthquakes. Classic location algorithms based on travel times cannot be directly applied because impulsive phase arrivals are often difficult to recognize. Traditional location algorithms are often modified to use phase arrivals identified from stacks of recurring low-frequency events (LFEs) observed within tremor episodes, rather than single events. Stacking the LFE waveforms improves the signal-to-noise ratio for the otherwise non-distinct phase arrivals. In this study, we apply a different method to locate tectonic tremor: a modified time-reversal imaging approach that potentially exploits the information from the entire tremor waveform instead of phase arrivals from individual LFEs. Time reversal imaging uses the waveforms of a given seismic source recorded by multiple seismometers at discrete points on the surface and a 3D velocity model to rebroadcast the waveforms back into the medium to identify the seismic source location. In practice, the method works by reversing the seismograms recorded at each of the stations in time, and back-propagating them from the receiver location individually into the sub-surface as a new source time function. We use a staggered-grid, finite-difference code with 2.5 ms time steps and a grid node spacing of 50 m to compute the rebroadcast wavefield. We calculate the time-dependent curl field at each grid point of the model volume for each back-propagated seismogram. To locate the tremor, we assume that the source time function back-propagated from each individual station produces a similar curl field at the source position. We then cross-correlate the time dependent curl field functions and calculate a median cross-correlation coefficient at each grid point. The highest median cross-correlation coefficient in the model volume is expected to represent the source location. For our analysis, we use the velocity model of Thurber et al. (2006) interpolated to a grid spacing of 50 m. Such grid spacing corresponds to frequencies of up to 8 Hz, which is suitable to calculate the wave propagation of tremor. Our dataset contains continuous broadband data from 13 STS-2 seismometers deployed from May 2010 to July 2011 along the Cholame segment of the San Andreas Fault as well as data from the HRSN and PBO networks. Initial synthetic results from tests on a 2D plane using a line of 15 receivers suggest that we are able to recover accurate event locations to within 100 m horizontally and 300 m depth. We conduct additional synthetic tests to determine the influence of signal-to-noise ratio, number of stations used, and the uncertainty in the velocity model on the location result by adding noise to the seismograms and perturbations to the velocity model. Preliminary results show accurate show location results to within 400 m with a median signal-to-noise ratio of 3.5 and 5% perturbations in the velocity model. The next steps will entail performing the synthetic tests on the 3D velocity model, and applying the method to tremor waveforms. Furthermore, we will determine the spatial and temporal distribution of the source locations and compare our results to those by Sumy and others.

Imaging the lithosphere and underlying mantle of the South Atlantic, South America and Africa using waveform tomography with massive datasets

NASA Astrophysics Data System (ADS)

Celli, N. L.; Lebedev, S.; Schaeffer, A. J.; Ravenna, M.; Gaina, C.

2017-12-01

Recent growth in global seismic station coverage has created dense data sampling of the previously poorly constrained lithosphere and underlying mantle beneath the South Atlantic, South America and Africa. The new data enable us to image the vast region at a new level of detail and address important open questions regarding its lithospheric architecture and mantle dynamics. In order to fully exploit the data sampling, we use an efficient, multimode waveform tomography scheme that enables the extraction of structural information from millions of seismograms and use the inherent data redundancy to minimize effects of errors in the data. Our tomographic model is constrained by waveform fits of over 1.2 million vertical-component seismograms, computed using the Automated Multimode Inversion of surface, S- and multiple S-waves. Each successful seismogram fit provides a set of linear equations describing 1D average velocity perturbations within approximate sensitivity volumes, with respect to a 3D reference model. We then combine all equations into a large linear system and invert jointly for a model of S- and P-wave speeds and azimuthal anisotropy within the lithosphere and underlying mantle. We are now able to image the detailed structure of various African shields. For example, in West Africa, two clearly separate high-velocity units underlay the Reguibat and Man-Léo Shields; in the Congo area, a single high-velocity body, formed by three main units correspond to the Gabon-Cameroon, Bomu-Kibali and Kasai Shields. Strong low-velocity anomalies underlay the Afar Hotspot and the East African Rift; pronounced low velocities are also seen beneath parts of the Sahara Desert. We discuss the shape of the deep Afar anomaly and its possible relationships with the Saharan volcanism and the neighboring Tanzania Craton. In the South Atlantic, we retrieve fine-scale velocity structure along the Mid-Atlantic Ridge (MAR), indicative of hotspot-ridge interactions. Major hotspots show low-velocity anomalies extending substantially deeper than those beneath the MAR, with the Vema Hotspot showing especially pronounced low-velocity anomalies under the thick, cold lithosphere of the Cape Basin. The offshore segment of the Cameroon line shows strong low-velocity anomalies that extend from the Sahara volcanic province to the MAR.

Uncertainty quantification of wall shear stress in intracranial aneurysms using a data-driven statistical model of systemic blood flow variability.

PubMed

Sarrami-Foroushani, Ali; Lassila, Toni; Gooya, Ali; Geers, Arjan J; Frangi, Alejandro F

2016-12-08

Adverse wall shear stress (WSS) patterns are known to play a key role in the localisation, formation, and progression of intracranial aneurysms (IAs). Complex region-specific and time-varying aneurysmal WSS patterns depend both on vascular morphology as well as on variable systemic flow conditions. Computational fluid dynamics (CFD) has been proposed for characterising WSS patterns in IAs; however, CFD simulations often rely on deterministic boundary conditions that are not representative of the actual variations in blood flow. We develop a data-driven statistical model of internal carotid artery (ICA) flow, which is used to generate a virtual population of waveforms used as inlet boundary conditions in CFD simulations. This allows the statistics of the resulting aneurysmal WSS distributions to be computed. It is observed that ICA waveform variations have limited influence on the time-averaged WSS (TAWSS) on the IA surface. In contrast, in regions where the flow is locally highly multidirectional, WSS directionality and harmonic content are strongly affected by the ICA flow waveform. As a consequence, we argue that the effect of blood flow variability should be explicitly considered in CFD-based IA rupture assessment to prevent confounding the conclusions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Full waveform seismic modelling of Chalk Group rocks from the Danish North Sea - implications for velocity analysis

NASA Astrophysics Data System (ADS)

Montazeri, Mahboubeh; Moreau, Julien; Uldall, Anette; Nielsen, Lars

2015-04-01

This study aims at understanding seismic wave propagation in the fine-layered Chalk Group, which constitutes the main reservoir for oil and gas production in the Danish North Sea. The starting point of our analysis is the Nana-1XP exploration well, which shows strong seismic contrasts inside the Chalk Group. For the purposes of seismic waveform modelling, we here assume a one-dimensional model with homogeneous and isotropic layers designed to capture the main fluctuations in petrophysical properties observed in the well logs. The model is representative of the stratigraphic sequences of the area and it illustrates highly contrasting properties of the Chalk Group. Finite-difference (FD) full wave technique, both acoustic and elastic equations are applied to the model. Velocity analysis of seismic data is a crucial step for stacking, multiple suppression, migration, and depth conversion of the seismic record. Semblance analysis of the synthetic seismic records shows strong amplitude peaks outside the expected range for the time interval representing the Chalk Group, especially at the base. The various synthetic results illustrate the occurrence and the impact of different types of waves including multiples, converted waves and refracted waves. The interference of these different wave types with the primary reflections can explain the strong anomalous amplitudes in the semblance plot. In particular, the effect of strongly contrasting thin beds plays an important role in the generation of the high anomalous amplitude values. If these anomalous amplitudes are used to pick the velocities, it would impede proper stacking of the data and may result in sub-optimal migration and depth conversion. Consequently this may lead to erroneous or sub-optimal seismic images of the Chalk Group and the underlying layers. Our results highlight the importance of detailed velocity analysis and proper picking of velocity functions in the Chalk Group intervals. We show that application of standard front mutes in the mid- and far-offset ranges does not significantly improve the results of the standard semblance analysis. These synthetic modelling results could be used as starting points for defining optimized processing flows for the seismic data sets acquired in the study area with the aim of improving the imaging of the Chalk Group.

Lattice Boltzmann modeling to explain volcano acoustic source.

PubMed

Brogi, Federico; Ripepe, Maurizio; Bonadonna, Costanza

2018-06-22

Acoustic pressure is largely used to monitor explosive activity at volcanoes and has become one of the most promising technique to monitor volcanoes also at large scale. However, no clear relation between the fluid dynamics of explosive eruptions and the associated acoustic signals has yet been defined. Linear acoustic has been applied to derive source parameters in the case of strong explosive eruptions which are well-known to be driven by large overpressure of the magmatic fluids. Asymmetric acoustic waveforms are generally considered as the evidence for supersonic explosive dynamics also for small explosive regimes. We have used Lattice-Boltzmann modeling of the eruptive fluid dynamics to analyse the acoustic wavefield produced by different flow regimes. We demonstrate that acoustic waveform well reproduces the flow dynamics of a subsonic fluid injection related to discrete explosive events. Different volumetric flow rate, at low-Mach regimes, can explain both the observed symmetric and asymmetric waveform. Hence, asymmetric waveforms are not necessarily related to the shock/supersonic fluid dynamics of the source. As a result, we highlight an ambiguity in the general interpretation of volcano acoustic signals for the retrieval of key eruption source parameters, necessary for a reliable volcanic hazard assessment.

Developing Regionalized Models of Lithospheric Thickness and Velocity Structure Across Eurasia and the Middle East from Jointly Inverting P-Wave and S-Wave Receiver Functions with Rayleigh Wave Group and Phase Velocities

DTIC Science & Technology

2010-09-01

lithospheric velocity structure for a wide variety of tectonic regions throughout Eurasia and the Middle East. We expect the regionalized models will improve...constructed by combining the 1D joint inversion models within each tectonic region and validated through regional waveform modeling. The velocity models thus...important differences in lithospheric structure between the cratonic regions of Eastern Europe and the tectonic regions of Western Europe and the

Anisotropy effects on 3D waveform inversion

NASA Astrophysics Data System (ADS)

Stekl, I.; Warner, M.; Umpleby, A.

2010-12-01

In the recent years 3D waveform inversion has become achievable procedure for seismic data processing. A number of datasets has been inverted and presented (Warner el al 2008, Ben Hadj at all, Sirgue et all 2010) using isotropic 3D waveform inversion. However the question arises will the results be affected by isotropic assumption. Full-wavefield inversion techniques seek to match field data, wiggle-for-wiggle, to synthetic data generated by a high-resolution model of the sub-surface. In this endeavour, correctly matching the travel times of the principal arrivals is a necessary minimal requirement. In many, perhaps most, long-offset and wide-azimuth datasets, it is necessary to introduce some form of p-wave velocity anisotropy to match the travel times successfully. If this anisotropy is not also incorporated into the wavefield inversion, then results from the inversion will necessarily be compromised. We have incorporated anisotropy into our 3D wavefield tomography codes, characterised as spatially varying transverse isotropy with a tilted axis of symmetry - TTI anisotropy. This enhancement approximately doubles both the run time and the memory requirements of the code. We show that neglect of anisotropy can lead to significant artefacts in the recovered velocity models. We will present inversion results of inverting anisotropic 3D dataset by assuming isotropic earth and compare them with anisotropic inversion result. As a test case Marmousi model extended to 3D with no velocity variation in third direction and with added spatially varying anisotropy is used. Acquisition geometry is assumed as OBC with sources and receivers everywhere at the surface. We attempted inversion using both 2D and full 3D acquisition for this dataset. Results show that if no anisotropy is taken into account although image looks plausible most features are miss positioned in depth and space, even for relatively low anisotropy, which leads to incorrect result. This may lead to misinterpretation of results. However if correct physics is used results agree with correct model. Our algorithm is relatively affordable and runs on standard pc clusters in acceptable time. Refferences: H. Ben Hadj Ali, S. Operto and J. Virieux. Velocity model building by 3D frequency-domain full-waveform inversion of wide-aperture seismic data, Geophysics (Special issue: Velocity Model Building), 73(6), P. VE101-VE117 (2008). L. Sirgue, O.I. Barkved, J. Dellinger, J. Etgen, U. Albertin, J.H. Kommedal, Full waveform inversion: the next leap forward in imaging at Valhall, First Brake April 2010 - Issue 4 - Volume 28 M. Warner, I. Stekl, A. Umpleby, Efficient and Effective 3D Wavefield Tomography, 70th EAGE Conference & Exhibition (2008)

Kinematic measurements of the vocal-fold displacement waveform in typical children and adult populations: quantification of high-speed endoscopic videos.

PubMed

Patel, Rita; Donohue, Kevin D; Unnikrishnan, Harikrishnan; Kryscio, Richard J

2015-04-01

This article presents a quantitative method for assessing instantaneous and average lateral vocal-fold motion from high-speed digital imaging, with a focus on developmental changes in vocal-fold kinematics during childhood. Vocal-fold vibrations were analyzed for 28 children (aged 5-11 years) and 28 adults (aged 21-45 years) without voice disorders. The following kinematic features were analyzed from the vocal-fold displacement waveforms: relative velocity-based features (normalized average and peak opening and closing velocities), relative acceleration-based features (normalized peak opening and closing accelerations), speed quotient, and normalized peak displacement. Children exhibited significantly larger normalized peak displacements, normalized average and peak opening velocities, normalized average and peak closing velocities, peak opening and closing accelerations, and speed quotient compared to adult women. Values of normalized average closing velocity and speed quotient were higher in children compared to adult men. When compared to adult men, developing children typically have higher estimates of kinematic features related to normalized displacement and its derivatives. In most cases, the kinematic features of children are closer to those of adult men than adult women. Even though boys experience greater changes in glottal length and pitch as they mature, results indicate that girls experience greater changes in kinematic features compared to boys.

Muscle Velocity and Inertial Force from Phase Contrast Magnetic Resonance Imaging

PubMed Central

Wentland, Andrew L.; McWalter, Emily J.; Pal, Saikat; Delp, Scott L.; Gold, Garry E.

2014-01-01

Purpose To evaluate velocity waveforms in muscle and to create a tool and algorithm for computing and analyzing muscle inertial forces derived from 2D phase contrast (PC) MRI. Materials and Methods PC MRI was performed in the forearm of four healthy volunteers during 1 Hz cycles of wrist flexion-extension as well as in the lower leg of six healthy volunteers during 1 Hz cycles of plantarflexion-dorsiflexion. Inertial forces (F) were derived via the equation F = ma. The mass, m, was derived by multiplying voxel volume by voxel-by-voxel estimates of density via fat-water separation techniques. Acceleration, a, was obtained via the derivative of the PC MRI velocity waveform. Results Mean velocities in the flexors of the forearm and lower leg were 1.94 ± 0.97 cm/s and 5.57 ± 2.72 cm/s, respectively, as averaged across all subjects; the inertial forces in the flexors of the forearm and lower leg were 1.9 × 10-3 ± 1.3 × 10-3 N and 1.1 × 10-2 ± 6.1 × 10-3 N, respectively, as averaged across all subjects. Conclusion PC MRI provided a promising means of computing muscle velocities and inertial forces—providing the first method for quantifying inertial forces. PMID:25425185

Analyzing the subsurface structure using seismic refraction method: Case study STMKG campus

NASA Astrophysics Data System (ADS)

Wibowo, Bagus Adi; Ngadmanto, Drajat; Daryono

2015-04-01

A geophysic survey is performed to detect subsurface structure under STMKG Campus in Pondok Betung, South Tangerang, Indonesia, using seismic refraction method. The survey used PASI 16S24-U24. The waveform data is acquired from 3 different tracks on the research location with a close range from each track. On each track we expanded 24 geofons with spacing between receiver 2 meters and the total length of each track about 48 meters. The waveform data analysed using 2 different ways. First, used a seismic refractionapplication WINSISIM 12 and second, used a Hagiwara Method. From both analysis, we known the velocity of P-wave in the first and second layer and the thickness of the first layer. From the velocity and the thickness informations we made 2-D vertical subsurface profiles. In this research, we only detect 2 layers in each tracks. The P-wave velocity of first layer is about 200-500 m/s with the thickness of this layer about 3-6 m/s. The P-wave velocity of second layer is about 400-900 m/s. From the P-wave velocity data we interpreted that both layer consisted by similar materials such as top soil, soil, sand, unsaturated gravel, alluvium and clay. But, the P-wave velocity difference between those 2 layers assumed happening because the first layer is soil embankment layer, having younger age than the layer below.

Assessment of Hemodynamic Conditions in the Aorta Following Root Replacement with Composite Valve-Conduit Graft.

PubMed

Cheng, Zhuo; Kidher, Emaddin; Jarral, Omar A; O'Regan, Declan P; Wood, Nigel B; Athanasiou, Thanos; Xu, Xiao Yun

2016-05-01

This paper presents the analysis of detailed hemodynamics in the aortas of four patients following replacement with a composite bio-prosthetic valve-conduit. Magnetic resonance image-based computational models were set up for each patient with boundary conditions comprising subject-specific three-dimensional inflow velocity profiles at the aortic root and central pressure waveform at the model outlet. Two normal subjects were also included for comparison. The purpose of the study was to investigate the effects of the valve-conduit on flow in the proximal and distal aorta. The results suggested that following the composite valve-conduit implantation, the vortical flow structure and hemodynamic parameters in the aorta were altered, with slightly reduced helical flow index, elevated wall shear stress and higher non-uniformity in wall shear compared to normal aortas. Inter-individual analysis revealed different hemodynamic conditions among the patients depending on the conduit configuration in the ascending aorta, which is a key factor in determining post-operative aortic flow. Introducing a natural curvature in the conduit to create a smooth transition between the conduit and native aorta may help prevent the occurrence of retrograde and recirculating flow in the aortic arch, which is particularly important when a large portion or the entire ascending aorta needs to be replaced.

Aerodynamic excitation and sound production of blown-closed free reeds without acoustic coupling: the example of the accordion reed.

PubMed

Ricot, Denis; Caussé, René; Misdariis, Nicolas

2005-04-01

The accordion reed is an example of a blown-closed free reed. Unlike most oscillating valves in wind musical instruments, self-sustained oscillations occur without acoustic coupling. Flow visualizations and measurements in water show that the flow can be supposed incompressible and potential. A model is developed and the solution is calculated in the time domain. The excitation force is found to be associated with the inertial load of the unsteady flow through the reed gaps. Inertial effect leads to velocity fluctuations in the reed opening and then to an unsteady Bernoulli force. A pressure component generated by the local reciprocal air movement around the reed is added to the modeled aerodynamic excitation pressure. Since the model is two-dimensional, only qualitative comparisons with air flow measurements are possible. The agreement between the simulated pressure waveforms and measured pressure in the very near-field of the reed is reasonable. In addition, an aeroacoustic model using the permeable Ffowcs Williams-Hawkings integral method is presented. The integral expressions of the far-field acoustic pressure are also computed in the time domain. In agreement with experimental data, the sound is found to be dominated by the dipolar source associated by the strong momentum fluctuations of the flow through the reed gaps.

Aerodynamic excitation and sound production of blown-closed free reeds without acoustic coupling: The example of the accordion reed

NASA Astrophysics Data System (ADS)

Ricot, Denis; Caussé, René; Misdariis, Nicolas

2005-04-01

The accordion reed is an example of a blown-closed free reed. Unlike most oscillating valves in wind musical instruments, self-sustained oscillations occur without acoustic coupling. Flow visualizations and measurements in water show that the flow can be supposed incompressible and potential. A model is developed and the solution is calculated in the time domain. The excitation force is found to be associated with the inertial load of the unsteady flow through the reed gaps. Inertial effect leads to velocity fluctuations in the reed opening and then to an unsteady Bernoulli force. A pressure component generated by the local reciprocal air movement around the reed is added to the modeled aerodynamic excitation pressure. Since the model is two-dimensional, only qualitative comparisons with air flow measurements are possible. The agreement between the simulated pressure waveforms and measured pressure in the very near-field of the reed is reasonable. In addition, an aeroacoustic model using the permeable Ffowcs Williams-Hawkings integral method is presented. The integral expressions of the far-field acoustic pressure are also computed in the time domain. In agreement with experimental data, the sound is found to be dominated by the dipolar source associated by the strong momentum fluctuations of the flow through the reed gaps. .

Spiral blood flows in an idealized 180-degree curved artery model

NASA Astrophysics Data System (ADS)

Bulusu, Kartik V.; Kulkarni, Varun; Plesniak, Michael W.

2017-11-01

Understanding of cardiovascular flows has been greatly advanced by the Magnetic Resonance Velocimetry (MRV) technique and its potential for three-dimensional velocity encoding in regions of anatomic interest. The MRV experiments were performed on a 180-degree curved artery model using a Newtonian blood analog fluid at the Richard M. Lucas Center at Stanford University employing a 3 Tesla General Electric (Discovery 750 MRI system) whole body scanner with an eight-channel cardiac coil. Analysis in two regions of the model-artery was performed for flow with Womersley number=4.2. In the entrance region (or straight-inlet pipe) the unsteady pressure drop per unit length, in-plane vorticity and wall shear stress for the pulsatile, carotid artery-based flow rate waveform were calculated. Along the 180-degree curved pipe (curvature ratio =1/7) the near-wall vorticity and the stretching of the particle paths in the vorticity field are visualized. The resultant flow behavior in the idealized curved artery model is associated with parameters such as Dean number and Womersley number. Additionally, using length scales corresponding to the axial and secondary flow we attempt to understand the mechanisms leading to the formation of various structures observed during the pulsatile flow cycle. Supported by GW Center for Biomimetics and Bioinspired Engineering (COBRE), MRV measurements in collaboration with Prof. John K. Eaton and, Dr. Chris Elkins at Stanford University.

Human sperm steer with second harmonics of the flagellar beat.

PubMed

Saggiorato, Guglielmo; Alvarez, Luis; Jikeli, Jan F; Kaupp, U Benjamin; Gompper, Gerhard; Elgeti, Jens

2017-11-10

Sperm are propelled by bending waves traveling along their flagellum. For steering in gradients of sensory cues, sperm adjust the flagellar waveform. Symmetric and asymmetric waveforms result in straight and curved swimming paths, respectively. Two mechanisms causing spatially asymmetric waveforms have been proposed: an average flagellar curvature and buckling. We image flagella of human sperm tethered with the head to a surface. The waveform is characterized by a fundamental beat frequency and its second harmonic. The superposition of harmonics breaks the beat symmetry temporally rather than spatially. As a result, sperm rotate around the tethering point. The rotation velocity is determined by the second-harmonic amplitude and phase. Stimulation with the female sex hormone progesterone enhances the second-harmonic contribution and, thereby, modulates sperm rotation. Higher beat frequency components exist in other flagellated cells; therefore, this steering mechanism might be widespread and could inspire the design of synthetic microswimmers.

Method of electric field flow fractionation wherein the polarity of the electric field is periodically reversed

DOEpatents

Stevens, Fred J.

1992-01-01

A novel method of electric field flow fractionation for separating solute molecules from a carrier solution is disclosed. The method of the invention utilizes an electric field that is periodically reversed in polarity, in a time-dependent, wave-like manner. The parameters of the waveform, including amplitude, frequency and wave shape may be varied to optimize separation of solute species. The waveform may further include discontinuities to enhance separation.

ParamAP: Standardized Parameterization of Sinoatrial Node Myocyte Action Potentials.

PubMed

Rickert, Christian; Proenza, Catherine

2017-08-22

Sinoatrial node myocytes act as cardiac pacemaker cells by generating spontaneous action potentials (APs). Much information is encoded in sinoatrial AP waveforms, but both the analysis and the comparison of AP parameters between studies is hindered by the lack of standardized parameter definitions and the absence of automated analysis tools. Here we introduce ParamAP, a standalone cross-platform computational tool that uses a template-free detection algorithm to automatically identify and parameterize APs from text input files. ParamAP employs a graphic user interface with automatic and user-customizable input modes, and it outputs data files in text and PDF formats. ParamAP returns a total of 16 AP waveform parameters including time intervals such as the AP duration, membrane potentials such as the maximum diastolic potential, and rates of change of the membrane potential such as the diastolic depolarization rate. ParamAP provides a robust AP detection algorithm in combination with a standardized AP parameter analysis over a wide range of AP waveforms and firing rates, owing in part to the use of an iterative algorithm for the determination of the threshold potential and the diastolic depolarization rate that is independent of the maximum upstroke velocity, a parameter that can vary significantly among sinoatrial APs. Because ParamAP is implemented in Python 3, it is also highly customizable and extensible. In conclusion, ParamAP is a powerful computational tool that facilitates quantitative analysis and enables comparison of sinoatrial APs by standardizing parameter definitions and providing an automated work flow. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

High frequency seismic monitoring of debris flows at Chalk Cliffs (CO), USA

NASA Astrophysics Data System (ADS)

Coviello, Velio; Kean, Jason; Smith, Joel; Coe, Jeffrey; Arattano, Massimo; McCoy, Scott

2015-04-01

A growing number of studies adopt passive seismic monitoring techniques to investigate slope instabilities and landslide processes. These techniques are attractive and convenient because large areas can be monitored from a safe distance. This is particularly true when the phenomena under investigation are rapid and infrequent mass movements like debris flows. Different types of devices are used to monitor debris flow processes, but among them ground vibration detectors (GVDs) present several, specific advantages that encourage their use. These advantages include: (i) the possibility to be installed outside the channel bed, (ii) the high adaptability to different and harsh field conditions, and (iii) the capability to detect the debris flow front arrival tens of seconds earlier than contact and stage sensors. Ground vibration data can provide relevant information on the dynamics of debris flows such as timing and velocity of the main surges. However, the processing of the raw seismic signal is usually needed, both to obtain a more effective representation of waveforms and to decrease the amount of data that need to be recorded and analyzed. With this objective, the methods of Amplitude and Impulses are commonly adopted to transform the raw signal to a 1-Hz signal that allows for a more useful representation of the phenomenon. In that way, peaks and other features become more visible and comparable with data obtained from other monitoring devices. In this work, we present the first debris flows seismic recordings gathered in the Chalk Cliffs instrumented basin, central Colorado, USA. In May 2014, two 4.5-Hz, three-axial geophones were installed in the upper part of the catchment. Seismic data are sampled at 333 Hz and then recorded by a standalone recording unit. One geophone is directly installed on bedrock, the other one mounted on a 1-m boulder partially buried in colluvium. This latter sensor integrates a heavily instrumented cross-section consisting of a 225 cm2 force plate recording basal impact forces at 333 Hz, a laser distance meter recording flow stage over the plate at 10 Hz, and a high definition video camera (24 frames per seconds). This combination of instrumentation allows for a comparison of the amplitude and spectral response of the geophones to flow depth, impact force, and video recordings. On July 4, 2014 a debris flow event occurred in the basin that was recorded by the whole monitoring system. Both geophone installation methods and channel bed characteristics largely influenced the seismic records. One geophone exhibits a broad frequency response during all debris flow surges, while the energy recorded by the other one is mainly concentrated in the 40-80 Hz band. Furthermore, erosion and entrainment processes have a crucial effect on the recorded waveforms. The presence of channel bed sediment damps the Amplitude waveforms during the first surges, when the flow is not yet erosive. The typical proportionality between the Amplitude curve and the flow stage is observed only after the entrainment of the channel bed sediment by the debris flow, when the flow is directly on bedrock. The processing of the signal with the Impulse transformation displays the same damping effect when a high threshold is adopted. However, the use of a high threshold entails the disappearance of the first surge and causes a less effective early detection of the flow. On the contrary, the adoption of a lower threshold impedes the observation of sediment damping effect.

Moment tensor inversions using strong motion waveforms of Taiwan TSMIP data, 1993–2009

USGS Publications Warehouse

Chang, Kaiwen; Chi, Wu-Cheng; Gung, Yuancheng; Dreger, Douglas; Lee, William H K.; Chiu, Hung-Chie

2011-01-01

Earthquake source parameters are important for earthquake studies and seismic hazard assessment. Moment tensors are among the most important earthquake source parameters, and are now routinely derived using modern broadband seismic networks around the world. Similar waveform inversion techniques can also apply to other available data, including strong-motion seismograms. Strong-motion waveforms are also broadband, and recorded in many regions since the 1980s. Thus, strong-motion data can be used to augment moment tensor catalogs with a much larger dataset than that available from the high-gain, broadband seismic networks. However, a systematic comparison between the moment tensors derived from strong motion waveforms and high-gain broadband waveforms has not been available. In this study, we inverted the source mechanisms of Taiwan earthquakes between 1993 and 2009 by using the regional moment tensor inversion method using digital data from several hundred stations in the Taiwan Strong Motion Instrumentation Program (TSMIP). By testing different velocity models and filter passbands, we were able to successfully derive moment tensor solutions for 107 earthquakes of Mw >= 4.8. The solutions for large events agree well with other available moment tensor catalogs derived from local and global broadband networks. However, for Mw = 5.0 or smaller events, we consistently over estimated the moment magnitudes by 0.5 to 1.0. We have tested accelerograms, and velocity waveforms integrated from accelerograms for the inversions, and found the results are similar. In addition, we used part of the catalogs to study important seismogenic structures in the area near Meishan Taiwan which was the site of a very damaging earthquake a century ago, and found that the structures were dominated by events with complex right-lateral strike-slip faulting during the recent decade. The procedures developed from this study may be applied to other strong-motion datasets to compliment or fill gaps in catalogs from regional broadband networks and teleseismic networks.

Effect of low-sodium diet on uteroplacental circulation.

PubMed

Delemarre, F M; van Leest, L A; Jongsma, H W; Steegers, E A

2000-01-01

To study the influence of chronic dietary sodium restriction on uteroplacental circulation. In a randomized trial, Doppler flow velocity waveforms of the uterine and umbilical artery were studied at monthly intervals during pregnancy in 59 women on a low-sodium diet and in 68 controls. Pulsatility index (PI), resistance index (RI), and A/B ratio of the uterine artery were significantly lower during sodium restriction, whereas PI, RI, and A/B ratio of the umbilical artery were significantly higher. The lower resistance indices of the uterine artery during sodium restriction might reflect an increase in pulse pressure/impedance ratio as a result of activation of the renin-angiotensin system. The increase in umbilical artery resistance indices supports the hypothesis that fetal circulation might be altered by chronic dietary sodium restriction.

MO-DE-207A-12: Toward Patient-Specific 4DCT Reconstruction Using Adaptive Velocity Binning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morris, E.D.; Glide-Hurst, C.; Wayne State University, Detroit, MI

2016-06-15

Purpose: While 4DCT provides organ/tumor motion information, it often samples data over 10–20 breathing cycles. For patients presenting with compromised pulmonary function, breathing patterns can change over the acquisition time, potentially leading to tumor delineation discrepancies. This work introduces a novel adaptive velocity-modulated binning (AVB) 4DCT algorithm that modulates the reconstruction based on the respiratory waveform, yielding a patient-specific 4DCT solution. Methods: AVB was implemented in a research reconstruction configuration. After filtering the respiratory waveform, the algorithm examines neighboring data to a phase reconstruction point and the temporal gate is widened until the difference between the reconstruction point and waveformmore » exceeds a threshold value—defined as percent difference between maximum/minimum waveform amplitude. The algorithm only impacts reconstruction if the gate width exceeds a set minimum temporal width required for accurate reconstruction. A sensitivity experiment of threshold values (0.5, 1, 5, 10, and 12%) was conducted to examine the interplay between threshold, signal to noise ratio (SNR), and image sharpness for phantom and several patient 4DCT cases using ten-phase reconstructions. Individual phase reconstructions were examined. Subtraction images and regions of interest were compared to quantify changes in SNR. Results: AVB increased signal in reconstructed 4DCT slices for respiratory waveforms that met the prescribed criteria. For the end-exhale phases, where the respiratory velocity is low, patient data revealed a threshold of 0.5% demonstrated increased SNR in the AVB reconstructions. For intermediate breathing phases, threshold values were required to be >10% to notice appreciable changes in CT intensity with AVB. AVB reconstructions exhibited appreciably higher SNR and reduced noise in regions of interest that were photon deprived such as the liver. Conclusion: We demonstrated that patient-specific velocity-based 4DCT reconstruction is feasible. Image noise was reduced with AVB, suggesting potential applications for low-dose acquisitions and to improve 4DCT reconstruction for irregular breathing patients. The submitting institution holds research agreements with Philips Healthcare.« less

Nature and Role of Subducting Sediments on the Megathrust and Forearc Evolution in the 2004 Great Sumatra Earthquake Rupture Zone: Results from Full Waveform Inversion of Long Offset Seismic Data

NASA Astrophysics Data System (ADS)

Singh, S. C.; Qin, Y.

2015-12-01

On active accretionary margins, the nature of incoming sediments defines the locking mechanism on the megathrust, and the development and evolution of the accretionary wedge. Drilling is the most direct method to characterise the nature of these sediments, but the drilling is very expensive, and provide information at only a few locations. In north Sumatra, an IODP drilling is programmed to take place in July-August 2016. We have performed seismic full waveform inversion of 12 km long offset seismic reflection data acquired by WesternGeco in 2006 over a 35 km zone near the subduction front in the 2004 earthquake rupture zone area that provide detailed quantitative information on the characteristics of the incoming sediments. We first downward continue the surface streamer data to the seafloor, which removes the effect of deep water (~5 km) and brings out the refraction arrivals as the first arrivals. We carry out travel time tomography, and then performed full waveform inversion of seismic refraction data followed by the full waveform inversion of reflection data providing detailed (10-20 m) velocity structure. The sediments in this area are 3-5 km thick where the P-wave velocity increases from 1.6 km/s near the seafloor to more than 4.5 km/s above the oceanic crust. The high velocity of sediments above the basement suggests that the sediments are highly compacted, strengthened the coupling near the subduction front, which might have been responsible for 2004 earthquake rupture propagation up to the subduction front, enhancing the tsunami. We also find several thin velocity layers within the sediments, which might be due to high pore-pressure fluid or free gas. These layers might be responsible for the formation of pseudo-decollement within the forearc sediments that acts as a conveyer belt between highly compacted subducting lower sediments and accreted sediments above. The presence of well intact sediments on the accretionary prism supports this interpretation. Our results provide first hand information about the sediments properties, which will be ground toothed by drilling.

The influence of underlying topography on lava channel networks and flow behavior (Invited)

NASA Astrophysics Data System (ADS)

Dietterich, H. R.; Cashman, K. V.; Rust, A.

2013-12-01

New high resolution mapping of historical lava flows in Hawai';i reveals complex topographically controlled channel networks. Network morphologies range from distributary systems dominated by branching around local obstacles, to tributary systems constricted by topographic confinement. Because channel networks govern the distribution of lava within the flow, they can dramatically alter the effective volumetric flux, which affects both flow length and advance rate. The influence of flow bifurcations is evidenced by (1) channelized flows from Pu';u ';O';o episodes 1-20 at Kilauea Volcano, where flow front velocities decreased by approximately half each time a flow split, and (2) the length of confined flows, such as the Mauna Loa 1859 flow, which traveled twice as far as the distributary Mauna Loa 1984 flow, despite similar effusion rates and durations. To study the underlying controls on flow bifurcations, we have undertaken a series of analogue experiments with golden syrup (a Newtonian fluid) to better understand the physics of obstacle interaction and its influence on flow behavior and morphology. Controlling the effusion rate and surface slope, we extrude flows onto a surface with a cylindrical or V-shaped obstacle of variable angle. When the flow is sufficiently fast, a stationary wave forms upslope of the obstacle; if the stationary wave is sufficiently high, the flow can overtop, rather than split around, the obstacle. The stationary wave height increases with flow velocity and with the effective obstacle width. Evidence for stationary waves in Hawaiian lava flows comes from both photographs of active flows and waveforms frozen into solidified flows. We have also performed a preliminary set of similar experiments with molten basalt to identify the effect of cooling and investigate flow merging. In these experiments, a stationary wave develops upslope of the obstacle, which allows the surface to cool and thicken. After splitting, the syrup experiments show minimal impact of the split on flow advance, except in cases where the flow is very thin, and surface tension controls the flow behavior. In contrast, the experiments with molten basalt slow markedly, as measured by both flow front and surface velocities. This difference demonstrates the effect of cooling and crust formation on flowing lava. Crust formation also controls the ability of split flows to merge below an obstacle, such that flows can converge only at high flow rates, which limits time for crust formation, and at narrow obstacle angles, which limits the lateral spreading required for convergence. Our experiments qualitatively support theoretical descriptions of crustal controls on flow spreading and levee development, but our poor knowledge of the appropriate parameter values, particularly that of the strength of the viscoelastic crust, prevents a quantitative comparison. These experiments, and our observations from natural systems, have significant implications for predicting lava flow behavior and inform efforts to mitigate flow hazards with diversion barriers.

Waveform Modeling of the Crust and Upper Mantle Using S, Sp, SsPmP, and Shear-Coupled PL Waves

DTIC Science & Technology

2008-05-10

and excitation of shear-coupled Pl waves with distance and corresponding phase velocity ( Vph )-period (T) curve: αN and βN are the P and S wave...Pulliam and Sen, 2005) (b) Propagation characteristics and excitation of shear-coupled Pl waves with distance and corresponding phase velocity ( Vph

Full Waveform Inversion for Seismic Velocity And Anelastic Losses in Heterogeneous Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Askan, A.; /Carnegie Mellon U.; Akcelik, V.

2009-04-30

We present a least-squares optimization method for solving the nonlinear full waveform inverse problem of determining the crustal velocity and intrinsic attenuation properties of sedimentary valleys in earthquake-prone regions. Given a known earthquake source and a set of seismograms generated by the source, the inverse problem is to reconstruct the anelastic properties of a heterogeneous medium with possibly discontinuous wave velocities. The inverse problem is formulated as a constrained optimization problem, where the constraints are the partial and ordinary differential equations governing the anelastic wave propagation from the source to the receivers in the time domain. This leads to amore » variational formulation in terms of the material model plus the state variables and their adjoints. We employ a wave propagation model in which the intrinsic energy-dissipating nature of the soil medium is modeled by a set of standard linear solids. The least-squares optimization approach to inverse wave propagation presents the well-known difficulties of ill posedness and multiple minima. To overcome ill posedness, we include a total variation regularization functional in the objective function, which annihilates highly oscillatory material property components while preserving discontinuities in the medium. To treat multiple minima, we use a multilevel algorithm that solves a sequence of subproblems on increasingly finer grids with increasingly higher frequency source components to remain within the basin of attraction of the global minimum. We illustrate the methodology with high-resolution inversions for two-dimensional sedimentary models of the San Fernando Valley, under SH-wave excitation. We perform inversions for both the seismic velocity and the intrinsic attenuation using synthetic waveforms at the observer locations as pseudoobserved data.« less

Seismic Waveform Tomography of the Iranian Region

NASA Astrophysics Data System (ADS)

Maggi, A.; Priestley, K.; Jackson, J.

2001-05-01

Surprisingly little is known about the detailed velocity structure of Iran, despite the region's importance in the tectonics of the Middle East. Previous studies have concentrated mainly on fundamental mode surface wave dispersion measurements along isolated paths (e.g.~Asudeh, 1982; Cong & Mitchell, 1998; Ritzwoller et.~al, 1998), and the propagation characteristics of crust and upper mantle body waves (e.g. Hearn & Ni 1994; Rodgers et.~al 1997). We use the partitioned waveform inversion method of Nolet (1990) on several hundred regional waveforms crossing the Iranian region to produce a 3-D seismic velocity map for the crust and upper mantle of the area. The method consists of using long period seismograms from earthquakes with well determined focal mechanisms and depths to constrain 1-D path-averaged shear wave models along regional paths. The constraints imposed on the 1-D models by the seismograms are then combined with independent constraints from other methods (e.g.~Moho depths from reciever function analysis etc.), to solve for the 3-D seismic velocity structure of the region. A dense coverage of fundamental mode rayleigh waves at a period of 100~s ensures good resolution of lithospheric scale structure. We also use 20~s period fundamental mode rayleigh waves and some Pnl wavetrains to make estimates of crustal thickness variations and average crustal velocities. A few deeper events give us some coverage of higher mode rayleigh waves and mantle S waves, which sample to the base of the upper mantle. Our crustal thickness estimates range from 45~km in the southern Zagros mountains, to 40~km in central Iran and 35~km towards the north of the region. We also find inconsistencies between the 1-D models required to fit the vertical and the tranverse seismograms, indicating the presence of anisotropy.

Recovering Long-wavelength Velocity Models using Spectrogram Inversion with Single- and Multi-frequency Components

NASA Astrophysics Data System (ADS)

Ha, J.; Chung, W.; Shin, S.

2015-12-01

Many waveform inversion algorithms have been proposed in order to construct subsurface velocity structures from seismic data sets. These algorithms have suffered from computational burden, local minima problems, and the lack of low-frequency components. Computational efficiency can be improved by the application of back-propagation techniques and advances in computing hardware. In addition, waveform inversion algorithms, for obtaining long-wavelength velocity models, could avoid both the local minima problem and the effect of the lack of low-frequency components in seismic data. In this study, we proposed spectrogram inversion as a technique for recovering long-wavelength velocity models. In spectrogram inversion, decomposed frequency components from spectrograms of traces, in the observed and calculated data, are utilized to generate traces with reproduced low-frequency components. Moreover, since each decomposed component can reveal the different characteristics of a subsurface structure, several frequency components were utilized to analyze the velocity features in the subsurface. We performed the spectrogram inversion using a modified SEG/SEGE salt A-A' line. Numerical results demonstrate that spectrogram inversion could also recover the long-wavelength velocity features. However, inversion results varied according to the frequency components utilized. Based on the results of inversion using a decomposed single-frequency component, we noticed that robust inversion results are obtained when a dominant frequency component of the spectrogram was utilized. In addition, detailed information on recovered long-wavelength velocity models was obtained using a multi-frequency component combined with single-frequency components. Numerical examples indicate that various detailed analyses of long-wavelength velocity models can be carried out utilizing several frequency components.

Geographic boundary of the “Pacific Anomaly” near the Earth’s core-mantle boundary

NASA Astrophysics Data System (ADS)

He, Y.; Wen, L.

2009-12-01

Seismic tomography have revealed a broad, seismically low velocity anomaly in the Earth’s lower mantle beneath the Pacific (we term it the “Pacific Anomaly”), surrounded by the circum-Pacific high velocity zone. Here, we determine geographical boundary and average shear velocity structure of the Pacific Anomaly near the core-mantle boundary based on travel time analysis of ScSH-SH and ScS2-SS phases. We further constrain the detailed structure of the transition from the base of the Pacific Anomaly to the northern high velocity zone along two perpendicular cross sections on the basis of forward waveform modeling of the seismic data. Two cross-sections include one great arc across the Anomaly from New Zealand to Alaska and another from Solomon Islands to North America. Our seismic data are collected from those recorded in the China National Digital Seismographic Network, and many permanent and temporal arrays from the Incorporated Research Institutions for Seismology. The observed ScS-SH and ScS2-SS differential travel time residuals allow the entire geographic boundary of the anomaly to be clearly defined. The seismic data suggest that the average shear velocity reduction inside the anomaly reaches -5% in the lowermost 300 km of the mantle. Waveform analysis of the seismic data sampling the edge of the anomaly further validates the model of the boundary previously deduced by differential-travel-time-residual data, and suggests that the northern boundary is characterized by a shear velocity model with the low-velocity region accompanied by a high velocity structure.

Single source photoplethysmograph transducer for local pulse wave velocity measurement.

PubMed

Nabeel, P M; Joseph, Jayaraj; Awasthi, Vartika; Sivaprakasam, Mohanasankar

2016-08-01

Cuffless evaluation of arterial blood pressure (BP) using pulse wave velocity (PWV) has received attraction over the years. Local PWV based techniques for cuffless BP measurement has more potential in accurate estimation of BP parameters. In this work, we present the design and experimental validation of a novel single-source Photoplethysmograph (PPG) transducer for arterial blood pulse detection and cycle-to-cycle local PWV measurement. The ability of the transducer to continuously measure local PWV was verified using arterial flow phantom as well as by conducting an in-vivo study on 17 volunteers. The single-source PPG transducer could reliably acquire dual blood pulse waveforms, along small artery sections of length less than 28 mm. The transducer was able to perform repeatable measurements of carotid local PWV on multiple subjects with maximum beat-to-beat variation less than 12%. The correlation between measured carotid local PWV and brachial BP parameters were also investigated during the in-vivo study. Study results prove the potential use of newly proposed single-source PPG transducers in continuous cuffless BP measurement systems.

Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms

PubMed Central

Avrahami, Idit; Kersh, Dikla

2016-01-01

Arterial wall shear stress (WSS) parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity—known as the pulsatility index (PI)—which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV). The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%]), oscillating shear index (OSI) and the ratio of minimum to maximum shear stress rates (min/max), are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS. PMID:27893801

Seismic Observations of the Mid-Pacific Large Low Shear Velocity Province

NASA Astrophysics Data System (ADS)

Chan, A.; Helmberger, D. V.; Sun, D.; Li, D.; Jackson, J. M.

2015-12-01

Seismic data from earthquakes originating in the Fiji-Tonga region exhibits waveform complexity of a number of phases which may be attributed to various structures along ray paths to stations of USArray, including anomalous structures at the core-mantle boundary. The data shows variation in multipathing, that is, the presence of secondary arrivals following the S phase at diffracted distances (Sdiff) which suggests that the waveform complexity is due to structures at the eastern edge of the mid-Pacific Large Low Shear Velocity Province (LLSVP). This study examines data from earthquake events while the Transportable Array portion of USArray was situated in the midwest United States, reinforcing previous studies that indicate late arrivals occurring as long as 26 seconds after the primary arrivals (To et al., 2011). Using earth flattening transformations and finite difference methods, simulations of tapered wedge structures of low velocity material allow for wave energy trapping, producing the observed waveform complexity and delayed arrivals at large distances, with such structures having characteristic properties of, for example, a height of 70 km, in-plane extent more than 1000 km, and shear wave velocity drop of 3% at the top to 15% at the bottom relative to PREM. Differential arrival times for SH and SV components suggest anisotropy and possible wave propagation through downgoing slabs beneath the source region. The arrivals of the SPdKS phase further support the presence of an ultra-low velocity zone (ULVZ) within a two-humped LLSVP. Some systematic delays in arrival times of multiple phases for distances less than 102º are accounted for and attributed to the presence of a mantle slab underneath the continental United States. Comparisons to seismic data from earthquakes originating from other locations further constrain depths of the deep mantle structures. Possible explanations include iron-enrichment of deep mantle phases.

Waveform control of orientation-dependent ionization of DCl in few-cycle laser fields.

PubMed

Znakovskaya, I; von den Hoff, P; Schirmel, N; Urbasch, G; Zherebtsov, S; Bergues, B; de Vivie-Riedle, R; Weitzel, K-M; Kling, M F

2011-05-21

Strong few-cycle light fields with stable electric field waveforms allow controlling electrons on time scales down to the attosecond domain. We have studied the dissociative ionization of randomly oriented DCl in 5 fs light fields at 720 nm in the tunneling regime. Momentum distributions of D(+) and Cl(+) fragments were recorded via velocity-map imaging. A waveform-dependent anti-correlated directional emission of D(+) and Cl(+) fragments is observed. Comparison of our results with calculations indicates that tailoring of the light field via the carrier envelope phase permits the control over the orientation of DCl(+) and in turn the directional emission of charged fragments upon the breakup of the molecular ion. © The Owner Societies 2011

bop5 mutations reveal new roles for the IC138 phosphoprotein in the regulation of flagellar motility and asymmetric waveforms

PubMed Central

VanderWaal, Kristyn E.; Yamamoto, Ryosuke; Wakabayashi, Ken-ichi; Fox, Laura; Kamiya, Ritsu; Dutcher, Susan K.; Bayly, Phillip V.; Sale, Winfield S.; Porter, Mary E.

2011-01-01

I1 dynein, or dynein f, is a highly conserved inner arm isoform that plays a key role in the regulation of flagellar motility. To understand how the IC138 IC/LC subcomplex modulates I1 activity, we characterized the molecular lesions and motility phenotypes of several bop5 alleles. bop5-3, bop5-4, and bop5-5 are null alleles, whereas bop5-6 is an intron mutation that reduces IC138 expression. I1 dynein assembles into the axoneme, but the IC138 IC/LC subcomplex is missing. bop5 strains, like other I1 mutants, swim forward with reduced swimming velocities and display an impaired reversal response during photoshock. Unlike mutants lacking the entire I1 dynein, however, bop5 strains exhibit normal phototaxis. bop5 defects are rescued by transformation with the wild-type IC138 gene. Analysis of flagellar waveforms reveals that loss of the IC138 subcomplex reduces shear amplitude, sliding velocities, and the speed of bend propagation in vivo, consistent with the reduction in microtubule sliding velocities observed in vitro. The results indicate that the IC138 IC/LC subcomplex is necessary to generate an efficient waveform for optimal motility, but it is not essential for phototaxis. These findings have significant implications for the mechanisms by which IC/LC complexes regulate dynein motor activity independent of effects on cargo binding or complex stability. PMID:21697502

Rupture process of the September 12, 2007 Southern Sumatra earthquake from tsunami waveform inversion

NASA Astrophysics Data System (ADS)

Lorito, S.; Romano, F.; Piatanesi, A.

2007-12-01

The aim of this work is to infer the slip distribution and mean rupture velocity along the rupture zone of the 12 September 2007 Southern Sumatra, Indonesia from available tide-gauge records of the tsunami. We select waveforms from 12 stations, distributed along the west coast of Sumatra and in the whole Indian Ocean (11 GLOSS stations and 1 DART buoy). We assume the fault plane and the slip direction to be consistent with both the geometry of the subducting plate and the early focal mechanism solutions. Then we subdivide the fault plane into several subfaults (both along strike and down dip) and compute the corresponding Green's functions by numerical solution of the shallow water equations through a finite difference method. The slip distribution and rupture velocity are determined simultaneously by means of a simulated annealing technique. We compare the recorded and synthetic waveforms in the time domain, using a cost function that is a trade-off between the L1 and L2 norms. Preliminary synthetic checkerboard tests, using the station coverage and the sampling interval of the available data, indicate that the main features of the rupture process may be robustly inverted.

Predictive value of uterine Doppler waveform during pregnancies complicated by diabetes.

PubMed

Haddad, B; Uzan, M; Tchobroutsky, C; Uzan, S; Papiernik-Berkhauer, E

1993-01-01

Diabetes, whether or not it is insulin deficient, is frequently associated with vascular complications during pregnancies. It is accepted nowadays that the uterine artery velocity waveform is predictive concerning pregnancy-induced hypertension (PIH) and its complications. It thus seemed interesting to analyse the predictivity of vascular complications of diabetes by using uterine artery velocity waveforms. We have thus explored 37 diabetic patients [group 1: insulin-deficient diabetes (IDD), n = 10; group 2: gestational IDD, n = 6; and gestational non-IDD, n = 21). We have found vascular complications for 10 patients, divided between all 2 groups: 2 pre-eclampsia, 2 fetal suffering before any labour, 2 cases of intra-uterine growth retardation (including a trisomy 18) and 5 PIH. The uterine artery velocimetry measurement has been found to be pathological 5 times, and always in patients who later developed vascular complications. Among this selected population and excluding the trisomy 18, the sensitivity is of 44.5%, the specificity of 100%, the positive predictive value of 100%, and the negative predictive value of 84.3%. If these results are confirmed, this examination could be an excellent marker of the vascular risk and thus would have its place during systematic survey of pregnancies complicated by diabetes.

Full waveform ambient noise tomography of Mount Rainer

NASA Astrophysics Data System (ADS)

Flinders, A. F.; Shen, Y.

2014-12-01

Mount Rainier towers over the landscape of western Washington, ranking with Fuji-yama in Japan, Mt. Pinatubo in the Philippines, and Mt. Vesuvius in Italy, as one of the great stratovolcanoes of the world. Notwithstanding it's picturesque stature, Mt. Rainier is potentially the most devastating stratovolcano in North America, with more than 3.5 million people living beneath its shadow in the Seattle-Tacoma area. The primary hazard posed by the volcano is in the form of highly destructive volcanic debris flows (lahars). These lahars form when water and/or melted ice erode away and entrain preexisting volcanic sediment. At Mt. Rainier these flows are often initiated by sector collapse of the volcano's hydrothermally rotten flanks and compounded from Mt. Rainier's extensive snow and glacial ice coverage. It is therefore imperative to ascertain the extent of summit hydrothermal alteration within the volcano, and determine areas prone to collapse. Despite being one of the sixteen volcanoes globally designated by the International Association of Volcanology and Chemistry of the Earth's Interior as warranting detailed and focused study, Mt. Rainier remains enigmatic both in terms of shallow internal structure and the degree of summit hydrothermal alteration. We image this shallow internal structure and areas of possible summit alteration using ambient noise tomography. Our full waveform forward modeling includes high-resolution topography, allowing us to accurately account for the effects of topography on the propagation of short-period Rayleigh waves. Empirical Green's functions were extracted from 80 stations within 200 km of Mount Rainier and compared with synthetic greens functions over multiple frequency bands from 2-28 seconds. The preliminary model shows a broad (60 km wide) low shear-wave velocity anomaly in the mid-crust beneath the volcano. The mid-crust low-velocity body extends to the surface beneath the volcano summit in a narrow near-vertical conduit, the likely path of magma ascent. There is a peculiar aseismic high Vs and low Vp/Vs zone (possibly indicative of a high quartz bearing lithology) beneath the eastern edifice. We interpret it as a possible remnant of a more felsic (and perhaps more explosive) proto Mount Rainier volcano.

Noninvasive Intracranial Pressure Determination in Patients with Subarachnoid Hemorrhage.

PubMed

Noraky, James; Verghese, George C; Searls, David E; Lioutas, Vasileios A; Sonni, Shruti; Thomas, Ajith; Heldt, Thomas

2016-01-01

Intracranial pressure (ICP) should ideally be measured in many conditions affecting the brain. The invasiveness and associated risks of the measurement modalities in current clinical practice restrict ICP monitoring to a small subset of patients whose diagnosis and treatment could benefit from ICP measurement. To expand validation of a previously proposed model-based approach to continuous, noninvasive, calibration-free, and patient-specific estimation of ICP to patients with subarachnoid hemorrhage (SAH), we made waveform recordings of cerebral blood flow velocity in several major cerebral arteries during routine, clinically indicated transcranial Doppler examinations for vasospasm, along with time-locked waveform recordings of radial artery blood pressure (APB), and ICP was measured via an intraventricular drain catheter. We also recorded the locations to which ICP and ABP were calibrated, to account for a possible hydrostatic pressure difference between measured ABP and the ABP value at a major cerebral vessel. We analyzed 21 data records from five patients and were able to identify 28 data windows from the middle cerebral artery that were of sufficient data quality for the ICP estimation approach. Across these windows, we obtained a mean estimation error of -0.7 mmHg and a standard deviation of the error of 4.0 mmHg. Our estimates show a low bias and reduced variability compared with those we have reported before.

Plasma-based Compressor Stall Control

NASA Astrophysics Data System (ADS)

McGowan, Ryan; Corke, Thomas

2017-11-01

The use of dielectric barrier discharge (DBD) plasma actuator casing treatment to prevent or delay stall inception in an axial fan is examined. The actuators are powered by a pulsed-DC waveform which induces a larger peak velocity than a purely AC waveform such as a sine or sawtooth wave. With this system, a high-voltage DC source is supplied to both electrodes, remaining constant in time for the exposed electrode. Meanwhile, the covered electrode is periodically grounded for several microseconds and allowed to rise back to the source DC level. To test the actuators' ability to interact with and modify the formation of stall cells, a facility has been designed and constructed around nonconductive fan blades. The actuators are installed in the fan casing near the blade tips. The instrumentation allows for the measurement of rotating pressure disturbances (traveling stall cells) in this tip gap region as well as fan performance characteristics including pressure rise and flow rate. The casing plasma actuation is found to reduce the correlation of the rotating stall cells, thereby extending the stall margin of the fan. Various azimuthal arrangements of the plasma actuator casing treatment is explored, as well as input voltage levels to the actuator to determine optimum conditions. NASA SBIR Contract NNX14CC12C.

A photoelectric technique for measuring lightning-channel propagation velocities from a mobile laboratory

NASA Technical Reports Server (NTRS)

Mach, Douglas M.; Rust, W. David

1989-01-01

The present device for lightning channel propagation-velocity determination employs eight photodetectors mounted behind precision horizontal slits in the focal plane of a photographic camera lens. The eight photodetector pulses, IRIG-B time, and slow and fast electric field-change waveforms are recorded on a 14-track analog tape recorder. A comparison of the present results with those obtained by a streaking camera shows no significant differences between the velocities obtained from the same strokes with the two systems; neither is there any difference in pulse characteristics or in the velocities calculated from them.

An EPG waveform library for sharpshooters and preliminary effects of applied voltage on behaviors controlling Xylella fastidiosa inoculation

USDA-ARS?s Scientific Manuscript database

Electropenetrography (EPG) waveforms represent electrical conductivity of fluids flowing through an insect’s mouthparts. Over the 50 years since its invention, EPG has undergone three major electronic transformations. The newest, third generation of electropenetrograph, the AC-DC EPG monitor, offers...

Crosshole Tomography, Waveform Inversion, and Anisotropy: A Combined Approach Using Simulated Annealing

NASA Astrophysics Data System (ADS)

Afanasiev, M.; Pratt, R. G.; Kamei, R.; McDowell, G.

2012-12-01

Crosshole seismic tomography has been used by Vale to provide geophysical images of mineralized massive sulfides in the Eastern Deeps deposit at Voisey's Bay, Labrador, Canada. To date, these data have been processed using traveltime tomography, and we seek to improve the resolution of these images by applying acoustic Waveform Tomography. Due to the computational cost of acoustic waveform modelling, local descent algorithms are employed in Waveform Tomography; due to non-linearity an initial model is required which predicts first-arrival traveltimes to within a half-cycle of the lowest frequency used. Because seismic velocity anisotropy can be significant in hardrock settings, the initial model must quantify the anisotropy in order to meet the half-cycle criterion. In our case study, significant velocity contrasts between the target massive sulfides and the surrounding country rock led to difficulties in generating an accurate anisotropy model through traveltime tomography, and our starting model for Waveform Tomography failed the half-cycle criterion at large offsets. We formulate a new, semi-global approach for finding the best-fit 1-D elliptical anisotropy model using simulated annealing. Through random perturbations to Thompson's ɛ parameter, we explore the L2 norm of the frequency-domain phase residuals in the space of potential anisotropy models: If a perturbation decreases the residuals, it is always accepted, but if a perturbation increases the residuals, it is accepted with the probability P = exp(-(Ei-E)/T). This is the Metropolis criterion, where Ei is the value of the residuals at the current iteration, E is the value of the residuals for the previously accepted model, and T is a probability control parameter, which is decreased over the course of the simulation via a preselected cooling schedule. Convergence to the global minimum of the residuals is guaranteed only for infinitely slow cooling, but in practice good results are obtained from a variety of finite-time cooling schedules. We present the results of this approach for real and synthetically generated elastic TI data. After traveltime modelling, near offset data satisfied the half-cycle criterion. This gave us confidence that our horizontal velocity model was satisfactory, and we kept it constant while simulated annealing was run to determine the best-fit anisotropy profile. Once a low temperature was reached (so that minimizations to the objective function became rare), we constructed an average anisotropy model using accepted models which possessed a |E| within one standard deviation of the best fit model. This anisotropy model allowed the starting model for Waveform Tomography to satisfy the half-cycle first break criterion at large offsets. We believe that the success of this method is explained by the multipath nature of finite difference wave propagation, which does not suffer from the errors experienced by traveltime ray-tracing along the sharp velocity gradients present in the model.

Near-Melting Condition of the Inner Core Boundary Revealed from Antipodal Seismic Waves

NASA Astrophysics Data System (ADS)

Cormier, V. F.; Attanayake, J.; de Silva, S. M. S.; Miller, M. S.; Thomas, C.

2014-12-01

First-principles calculations1 have suggested that the inner core's low shear velocity (3.5 km/sec) is a consequence of its temperature being very close to its melting temperature throughout its volume. Near the inner core's freezing or melting boundary, the shear modulus could possibly approach zero. A test of this is made from observations of the amplitude of PKIIKP waves at antipodal (>175o) ranges. These underside reflections are very sensitive to the S velocity beneath the inner core boundary due to energy subtracted from PKIIKP by converted S energy. This sensitivity is exploited by modeling PKIIKP waveforms observed by a transportable array in Morocco, which recorded many high-quality antipodal waveforms from Tonga. Differences in the in the sampling of the upper inner core between PKIIKP arriving from the short (<180o) and long (>180o) distances make it feasible to investigate lateral differences in the elastic and anelastic states of uppermost inner core from the amplitude and frequency content of the waveforms. In computational experiments, we show that a zero or small shear modulus in the uppermost inner core is the most effective way of matching large amplitude PKIIKP's observed from antipodal paths from Tonga to Morocco. The correlation of this bright spot in the PKIIKP reflection with a thin zone of low P velocity identified from multi-pathed PKIKP waves sampling a portion of the equatorial eastern hemisphere2suggests that at least this region of the inner core is near its melting temperature. Waveform modeling of PKIKP and PKIIKP from the combined effects of viscoelasticity and forward scattering is performed to determine whether this region of low shear modulus is consistent with freezing or melting. 1Martorell, B., L. Vocadlo, J.P. Brodholt, and I.G.Wood, (2013) Science, 342 (6157), doi: 10.1126/science.1243651. 2Stroujkova, A., and V.F. Cormier (2004), J. Geophys. Res., 109(B10), doi:10.1029/2004JB002976.

Shear velocity and intrinsic Q structure of the shallow crust in southeastern New England from Rg wave dispersion

NASA Astrophysics Data System (ADS)

Saikia, Chandan K.; Kafka, Alan L.; Gnewuch, Scott C.; McTigue, John W.

1990-06-01

In this study, we analyzed 0.5-2.0 s period Rayleigh waves (Rg) generated by quarry and construction blasting in southern New England (CNE). We investigated group velocity dispersion and attenuation of the observed Rg waves. The paths crossing the Hartford Rift basin (HRB) show an obvious correlation between geology and Rg dispersion. The entire region in the southeastern New England comprising a wide range of geological structures and rock types from the Bronson Hill Anticlinorium to the Avalonian Terrane can be represented as one dispersion region. Therefore the relationship between lateral changes in geologic structures mapped on the surface and Rg dispersion is not as straightforward as might be expected for a best fitting flat-layered model of the shallow crust. The shear wave velocities appear to vary between 2.55 and 3.63 km/s within the upper 2.5 km except for the central HRB where the variation is between 2.12 and 2.7 km/s. Intrinsic Q structure is considered to be the primary means for the loss of energy in the shallow crust and was analyzed by modelling the waveforms of several of the observed seismograms. For this aspect of our study, we used a modal summation of Rayleigh waves assuming a far-field radiation approximation. The observed seismograms were dominated primarily by contributions from the fundamental mode, but higher modes were also included in the synthesis of the waveform. We were unable to model the absolute amplitudes of the waveforms because of the problems with the instrument calibration. It is clear, however, that to predict correct waveforms, the shear wave Q values in the upper few tenths of a kilometer of the crust must be about an order of magnitude smaller than Q values at the depth of 1-3 km which is of order of 100-250.

Surface wave tomography of the Ontong Java Plateau: Seismic probing of the largest igneous province

NASA Astrophysics Data System (ADS)

Richardson, William Philip

1998-12-01

Large igneous provinces (LIP), such as the gigantic Cretaceous oceanic plateaus, the Ontong-Java, the Manihiki and the Kerguelen, are part of a globally distributed diverse suite of massive crustal features considered to be episodic representations of mantle dynamics (Coffin and Eldholm, 1994). The Ontong Java Plateau in the central western Pacific is by far the largest (and presumably thickest) of these provinces and is believed to have been emplaced rapidly in the Aptian, ˜122 Ma (Tarduno et al., 1991). From 1994 to 1996 four PASSCAL broadband seismic stations were deployed in an array north of the OJP. Analysis was conducted on vertical component broadband seismograms from events recorded on the Micronesian Seismic Experiment array between January 1994 and March 1996. The purpose of this experiment is to investigate the crustal and upper mantle structure of the Ontong Java Plateau (OJP) employing surface wave tomographic methods. Using the partitioned waveform inversion method (Nolet, 1990) and earthquakes with published Centroid Moment Tensor (Dziewonski et al., 1981) solutions, we produce waveform fits from source-to-receiver paths that primarily sample the OJP. From these waveform fits, linearized constraints on shear velocity suggest: (1) a massively thickened crust over the center of the OJP-greater than 35km over central areas of the plateau while thinning off-center; (2) a pronounced low-velocity zone down to ˜300km depth-a robust result in agreement with recent geochemical predictions (Neal et al., 1997); (3) the probability of lateral heterogeneity across the OJP. Finally, by combining many single waveform inversions (van der Lee and Nolet, 1997b) a 3-D shear velocity model can be computed for the Ontong Java Plateau and the nearby Caroline Basin. New constraints on the crustal thickness (and hence the volume extruded) are presented, thereby adding to the understanding of the overall tectonic setting and possible emplacement mechanism of the structure.

Reverse-Time Imaging Based on Full-Waveform Inverted Velocity Model for Nondestructive Testing of Heterogeneous Engineered Structures

NASA Astrophysics Data System (ADS)

Nguyen, L. T.; Modrak, R. T.; Saenger, E. H.; Tromp, J.

2017-12-01

Reverse-time migration (RTM) can reconstruct reflectors and scatterers by cross-correlating the source wavefield and the receiver wavefield given a known velocity model of the background. In nondestructive testing, however, the engineered structure under inspection is often composed of layers of various materials and the background material has been degraded non-uniformly because of environmental or operational effects. On the other hand, ultrasonic waveform tomography based on the principles of full-waveform inversion (FWI) has succeeded in detecting anomalous features in engineered structures. But the building of the wave velocity model of the comprehensive small-size and high-contrast defect(s) is difficult because it requires computationally expensive high-frequency numerical wave simulations and an accurate understanding of large-scale background variations of the engineered structure.To reduce computational cost and improve detection of small defects, a useful approach is to divide the waveform tomography procedure into two steps: first, a low-frequency model-building step aimed at recovering background structure using FWI, and second, a high-frequency imaging step targeting defects using RTM. Through synthetic test cases, we show that the two-step procedure appears more promising in most cases than a single-step inversion. In particular, we find that the new workflow succeeds in the challenging scenario where the defect lies along preexisting layer interface in a composite bridge deck and in related experiments involving noisy data or inaccurate source parameters. The results reveal the potential of the new wavefield imaging method and encourage further developments in data processing, enhancing computation power, and optimizing the imaging workflow itself so that the procedure can efficiently be applied to geometrically complex 3D solids and waveguides. Lastly, owing to the scale invariance of the elastic wave equation, this imaging procedure can be transferred to applications in regional scales as well.

Analyzing the subsurface structure using seismic refraction method: Case study STMKG campus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wibowo, Bagus Adi, E-mail: bagusadiwibowo1993@gmail.com; Ngadmanto, Drajat; Daryono

2015-04-24

A geophysic survey is performed to detect subsurface structure under STMKG Campus in Pondok Betung, South Tangerang, Indonesia, using seismic refraction method. The survey used PASI 16S24-U24. The waveform data is acquired from 3 different tracks on the research location with a close range from each track. On each track we expanded 24 geofons with spacing between receiver 2 meters and the total length of each track about 48 meters. The waveform data analysed using 2 different ways. First, used a seismic refractionapplication WINSISIM 12 and second, used a Hagiwara Method. From both analysis, we known the velocity of P-wavemore » in the first and second layer and the thickness of the first layer. From the velocity and the thickness informations we made 2-D vertical subsurface profiles. In this research, we only detect 2 layers in each tracks. The P-wave velocity of first layer is about 200-500 m/s with the thickness of this layer about 3-6 m/s. The P-wave velocity of second layer is about 400-900 m/s. From the P-wave velocity data we interpreted that both layer consisted by similar materials such as top soil, soil, sand, unsaturated gravel, alluvium and clay. But, the P-wave velocity difference between those 2 layers assumed happening because the first layer is soil embankment layer, having younger age than the layer below.« less

Relationship of D'' structure with the velocity variations near the inner-core boundary

NASA Astrophysics Data System (ADS)

Luo, Sheng-Nian; Ni, Sidao; Helmberger, Don

2002-06-01

Variations in regional differential times between PKiKP (i) and PKIKP (I) have been attributed to hemispheric P-velocity variations of about 1% in the upper 100 km of the inner core (referred to as HIC). The top of the inner core appears relatively fast beneath Asia where D'' is also fast. An alternative interpretation could be the lateral variation in P velocity at the lowermost outer core (HOC) producing the same differential times. To resolve this issue, we introduce the diffracted PKP phase near the B caustic (Bdiff) in the range of 139-145° epicenter distances, and the corresponding differential times between Bdiff and PKiKP and PKIKP as observed on broadband arrays. Due to the long-wavelength nature of Bdiff, we scaled the S-wave tomography model with k values (k ≡ dlnVs/dlnVp) to obtain large-scale P-wave velocity structure in the lower mantle as proposed by earlier studies. Waveform synthetics of Bdiff constructed with small k's predict complex waveforms not commonly observed, confirming the validity of large scaling factor k. With P-velocity in lower mantle constrained at large scale, the extra travel-time constraint imposed by Bdiff helps to resolve the HOC-HIC issue. Our preliminary results suggest k > 2 for the lowermost mantle and support HIC hypothesis. An important implication is that there appears to be a relationship of D'' velocity structures with the structures near the inner core boundary via core dynamics.

Real-time capture of seismic waves using high-rate multi-GNSS observations: Application to the 2015 Mw 7.8 Nepal earthquake

NASA Astrophysics Data System (ADS)

Geng, Tao; Xie, Xin; Fang, Rongxin; Su, Xing; Zhao, Qile; Liu, Gang; Li, Heng; Shi, Chuang; Liu, Jingnan

2016-01-01

The variometric approach is investigated to measure real-time seismic waves induced by the 2015 Mw 7.8 Nepal earthquake with high-rate multi-GNSS observations, especially with the contribution of newly available BDS. The velocity estimation using GPS + BDS shows an additional improvement of around 20% with respect to GPS-only solutions. We also reconstruct displacements by integrating GNSS-derived velocities after a linear trend removal (IGV). The displacement waveforms with accuracy of better than 5 cm are derived when postprocessed GPS precise point positioning results are used as ground truth, even if those stations have strong ground motions and static offsets of up to 1-2 m. GNSS-derived velocity and displacement waveforms with the variometric approach are in good agreement with results from strong motion data. We therefore conclude that it is feasible to capture real-time seismic waves with multi-GNSS observations using the IGV-enhanced variometric approach, which has critical implications for earthquake early warning, tsunami forecasting, and rapid hazard assessment.

Subsurface fault geometries in Southern California illuminated through Full-3D Seismic Waveform Tomography (F3DT)

NASA Astrophysics Data System (ADS)

Lee, En-Jui; Chen, Po

2017-04-01

More precise spatial descriptions of fault systems play an essential role in tectonic interpretations, deformation modeling, and seismic hazard assessments. The recent developed full-3D waveform tomography techniques provide high-resolution images and are able to image the material property differences across faults to assist the understanding of fault systems. In the updated seismic velocity model for Southern California, CVM-S4.26, many velocity gradients show consistency with surface geology and major faults defined in the Community Fault Model (CFM) (Plesch et al. 2007), which was constructed by using various geological and geophysical observations. In addition to faults in CFM, CVM-S4.26 reveals a velocity reversal mainly beneath the San Gabriel Mountain and Western Mojave Desert regions, which is correlated with the detachment structure that has also been found in other independent studies. The high-resolution tomographic images of CVM-S4.26 could assist the understanding of fault systems in Southern California and therefore benefit the development of fault models as well as other applications, such as seismic hazard analysis, tectonic reconstructions, and crustal deformation modeling.

Velocities and Attenuations of Gas Hydrate-Bearing Sediments

USGS Publications Warehouse

Lee, Myung W.

2007-01-01

Monopole and dipole logging data at the Mallik 5L-38, Mackenzie Delta, Canada, provide a challenge for sonic velocity and attenuation models used to remotely estimate pore-space gas hydrate content. Velocity and attenuation are linked, with velocity dispersion causing increased attenuation. Sonic waveforms for Mallik 5L-38, however, show no velocity dispersion in gas hydrate-bearing layers, yet are highly attenuated. Attenuation models applied to Mallik 5L-38 data are shown to be inconsistent with the observed velocity measurements, and therefore are suspect in their ability to predict gas hydrate content. A model explicitly linking velocity and attenuation data is presented, accurately predicting gas hydrate content from velocity data alone while demonstrating that the attenuation mechanisms at the Mallik 5L-38 site have not yet been identified.

Kinematic Measurements of the Vocal-Fold Displacement Waveform in Typical Children and Adult Populations: Quantification of High-Speed Endoscopic Videos

PubMed Central

Donohue, Kevin D.; Unnikrishnan, Harikrishnan; Kryscio, Richard J.

2015-01-01

Purpose This article presents a quantitative method for assessing instantaneous and average lateral vocal-fold motion from high-speed digital imaging, with a focus on developmental changes in vocal-fold kinematics during childhood. Method Vocal-fold vibrations were analyzed for 28 children (aged 5–11 years) and 28 adults (aged 21–45 years) without voice disorders. The following kinematic features were analyzed from the vocal-fold displacement waveforms: relative velocity-based features (normalized average and peak opening and closing velocities), relative acceleration-based features (normalized peak opening and closing accelerations), speed quotient, and normalized peak displacement. Results Children exhibited significantly larger normalized peak displacements, normalized average and peak opening velocities, normalized average and peak closing velocities, peak opening and closing accelerations, and speed quotient compared to adult women. Values of normalized average closing velocity and speed quotient were higher in children compared to adult men. Conclusions When compared to adult men, developing children typically have higher estimates of kinematic features related to normalized displacement and its derivatives. In most cases, the kinematic features of children are closer to those of adult men than adult women. Even though boys experience greater changes in glottal length and pitch as they mature, results indicate that girls experience greater changes in kinematic features compared to boys. PMID:25652615

In vivo and in vitro measurements of cerebral aneurysm hemodynamics

NASA Astrophysics Data System (ADS)

Amili, Omid; Toloui, Mostafa; van de Moortele, Pierre-Francois; Jagadeesan, Bharathi; Coletti, Filippo

2017-11-01

The hemodynamics of cerebral aneurysms is thought to play a critical role in their formation, growth, and potential rupture. Our understanding in this area, however, comes mostly from in vitro experiments and numerical simulations, which have limited realism. In vivo measurements of the intracranial blood flow can be obtained by Magnetic Resonance Imaging (MRI), but they typically suffer from limited accuracy and inadequate resolution. Here we present a direct comparison between in vivo and in vitro measurements of the flow inside an internal carotid artery aneurysm. For both, we use 4D (i.e. volumetric and time-resolved) MRI velocimetry performed in a 7 Tesla magnet at sub-millimeter resolution. The in vitro measurements are carried out in a 3D printed aneurysm replica scaled up by a factor three, effectively increasing the spatial resolution. The patient-specific inflow waveform and the corresponding Reynolds and Womersley numbers are matched in a flow loop that mimics the impedance of the vascular bed. Direct comparison of the velocity fields allows assessing the robustness of the in vivo measurements, while highlighting the insight achievable in vitro. The data also represents a comprehensive test case for numerical simulations.

Parametric Study of Wall Shear Stress in Idealized Avian Airways

NASA Astrophysics Data System (ADS)

Farnsworth, Michael S.; Riede, Tobias; Thomson, Scott L.

2017-11-01

Because wall shear stress (WSS) affects cell response, WSS patterns in avian respiratory airways may be related to the origin of the syrinx and corresponding voice-producing tissue structures (e.g., membranes or vocal folds) in birds. To explore possible linkages between WSS patterns and the locations of avian voice-producing structures, a computational model of flow through an idealized portion of the avian respiratory airway, including trachea and primary bronchi sections, has been developed. The flow is governed by the Navier-Stokes equations, with velocity boundary conditions derived from pressure-flow data in an adult zebra finch during quiet respiration. Geometric parameters such as tracheal/bronchial diameter and length, as well as bronchial branching angle, are parametrically varied based on data for different avian species. Simulation results predict elevated WSS in the vicinity of the tracheobronchial juncture, the location at which voice-producing tissues are found in avian species. In this presentation, the model will be described and spatial distributions of WSS during inspiration and expiration will be presented and compared for different geometric configurations and respiration rates and waveforms. Funding for this project from the Gordon and Betty Moore Foundation (Grant 4498) is gratefully acknowledged.

Time domain viscoelastic full waveform inversion

NASA Astrophysics Data System (ADS)

Fabien-Ouellet, Gabriel; Gloaguen, Erwan; Giroux, Bernard

2017-06-01

Viscous attenuation can have a strong impact on seismic wave propagation, but it is rarely taken into account in full waveform inversion (FWI). When viscoelasticity is considered in time domain FWI, the displacement formulation of the wave equation is usually used instead of the popular velocity-stress formulation. However, inversion schemes rely on the adjoint equations, which are quite different for the velocity-stress formulation than for the displacement formulation. In this paper, we apply the adjoint state method to the isotropic viscoelastic wave equation in the velocity-stress formulation based on the generalized standard linear solid rheology. By applying linear transformations to the wave equation before deriving the adjoint state equations, we obtain two symmetric sets of partial differential equations for the forward and adjoint variables. The resulting sets of equations only differ by a sign change and can be solved by the same numerical implementation. We also investigate the crosstalk between parameter classes (velocity and attenuation) of the viscoelastic equation. More specifically, we show that the attenuation levels can be used to recover the quality factors of P and S waves, but that they are very sensitive to velocity errors. Finally, we present a synthetic example of viscoelastic FWI in the context of monitoring CO2 geological sequestration. We show that FWI based on our formulation can indeed recover P- and S-wave velocities and their attenuation levels when attenuation is high enough. Both changes in velocity and attenuation levels recovered with FWI can be used to track the CO2 plume during and after injection. Further studies are required to evaluate the performance of viscoelastic FWI on real data.

Microseismic imaging using a source function independent full waveform inversion method

NASA Astrophysics Data System (ADS)

Wang, Hanchen; Alkhalifah, Tariq

2018-07-01

At the heart of microseismic event measurements is the task to estimate the location of the source microseismic events, as well as their ignition times. The accuracy of locating the sources is highly dependent on the velocity model. On the other hand, the conventional microseismic source locating methods require, in many cases, manual picking of traveltime arrivals, which do not only lead to manual effort and human interaction, but also prone to errors. Using full waveform inversion (FWI) to locate and image microseismic events allows for an automatic process (free of picking) that utilizes the full wavefield. However, FWI of microseismic events faces incredible nonlinearity due to the unknown source locations (space) and functions (time). We developed a source function independent FWI of microseismic events to invert for the source image, source function and the velocity model. It is based on convolving reference traces with these observed and modelled to mitigate the effect of an unknown source ignition time. The adjoint-state method is used to derive the gradient for the source image, source function and velocity updates. The extended image for the source wavelet in Z axis is extracted to check the accuracy of the inverted source image and velocity model. Also, angle gathers are calculated to assess the quality of the long wavelength component of the velocity model. By inverting for the source image, source wavelet and the velocity model simultaneously, the proposed method produces good estimates of the source location, ignition time and the background velocity for synthetic examples used here, like those corresponding to the Marmousi model and the SEG/EAGE overthrust model.

PIV-measured versus CFD-predicted flow dynamics in anatomically realistic cerebral aneurysm models.

PubMed

Ford, Matthew D; Nikolov, Hristo N; Milner, Jaques S; Lownie, Stephen P; Demont, Edwin M; Kalata, Wojciech; Loth, Francis; Holdsworth, David W; Steinman, David A

2008-04-01

Computational fluid dynamics (CFD) modeling of nominally patient-specific cerebral aneurysms is increasingly being used as a research tool to further understand the development, prognosis, and treatment of brain aneurysms. We have previously developed virtual angiography to indirectly validate CFD-predicted gross flow dynamics against the routinely acquired digital subtraction angiograms. Toward a more direct validation, here we compare detailed, CFD-predicted velocity fields against those measured using particle imaging velocimetry (PIV). Two anatomically realistic flow-through phantoms, one a giant internal carotid artery (ICA) aneurysm and the other a basilar artery (BA) tip aneurysm, were constructed of a clear silicone elastomer. The phantoms were placed within a computer-controlled flow loop, programed with representative flow rate waveforms. PIV images were collected on several anterior-posterior (AP) and lateral (LAT) planes. CFD simulations were then carried out using a well-validated, in-house solver, based on micro-CT reconstructions of the geometries of the flow-through phantoms and inlet/outlet boundary conditions derived from flow rates measured during the PIV experiments. PIV and CFD results from the central AP plane of the ICA aneurysm showed a large stable vortex throughout the cardiac cycle. Complex vortex dynamics, captured by PIV and CFD, persisted throughout the cardiac cycle on the central LAT plane. Velocity vector fields showed good overall agreement. For the BA, aneurysm agreement was more compelling, with both PIV and CFD similarly resolving the dynamics of counter-rotating vortices on both AP and LAT planes. Despite the imposition of periodic flow boundary conditions for the CFD simulations, cycle-to-cycle fluctuations were evident in the BA aneurysm simulations, which agreed well, in terms of both amplitudes and spatial distributions, with cycle-to-cycle fluctuations measured by PIV in the same geometry. The overall good agreement between PIV and CFD suggests that CFD can reliably predict the details of the intra-aneurysmal flow dynamics observed in anatomically realistic in vitro models. Nevertheless, given the various modeling assumptions, this does not prove that they are mimicking the actual in vivo hemodynamics, and so validations against in vivo data are encouraged whenever possible.

The effects of aortic coarctation on cerebral hemodynamics and its importance in the etiopathogenesis of intracranial aneurysms.

PubMed

Singh, Pankaj K; Marzo, Alberto; Staicu, Cristina; William, Matt G; Wilkinson, Iain; Lawford, Patricia V; Rufenacht, Daniel A; Bijlenga, Philippe; Frangi, Alejandro F; Hose, Rodney; Patel, Umang J; Coley, Stuart C

2010-01-01

Hemodynamic changes in the cerebral circulation in presence of coarctation of aorta (CoA) and their significance in the increased intracranial aneurysms (IAs) formation in these patients remain unclear. In the present study, we measured the flow-rate waveforms in the cerebral arteries of a patient with CoA, followed by an analysis of different hemodynamic indices in a coexisting IA. Phase-contrast Magnetic Resonance (pc-MR) volumetric flow-rate (VFR) measurements were performed in cerebral arteries of a 51 years old woman with coexisting CoA, and five healthy volunteers. Numerical predictions of a number of relevant hemodynamic indices were performed in an IA located in sub-clinoid part of left internal carotid artery (ICA) of the patient. Computations were performed using Ansys(®)-CFX(™) solver using the VFR values measured in the patient as boundary conditions (BCs). A second analysis was performed using the average VFR values measured in healthy volunteers. The VFR waveforms measured in the patient and healthy volunteers were compared followed by a comparison of the hemodynamic indices obtained using both approaches. The results are discussed in the background of relevant literature. Mean flow-rates were increased by 27.1% to 54.9% (2.66-5.44 ml/sec) in the cerebral circulation of patients with CoA as compared to healthy volunteers (1.2-3.95 ml/sec). Velocities were increased inside the IA by 35-45%. An exponential rise of 650% was observed in the area affected by high wall shear stress (WSS>15Pa) when flow-rates specific to CoA were used as compared to population average flow-rates. Absolute values of space and time averaged WSS were increased by 65%. Whereas values of maximum pressure on the IA wall were increased by 15% the area of elevated pressure was actually decreased by 50%, reflecting a more focalized jet impingement within the IA of the CoA patient. IAs can develop in patients with CoA several years after the surgical repair. Cerebral flow-rates in CoA patients are significantly higher as compared to average flow-rates in healthy population. The increased supra-physiological WSS (>15Pa), OSI (>0.2) and focalized pressure may play an important role in the etiopathogenesis of IAs in patients with CoA.

The Effects of Aortic Coarctation on Cerebral Hemodynamics and its Importance in the Etiopathogenesis of Intracranial Aneurysms

PubMed Central

Singh, Pankaj K; Marzo, Alberto; Staicu, Cristina; William, Matt G; Wilkinson, Iain; Lawford, Patricia V; Rufenacht, Daniel A; Bijlenga, Philippe; Frangi, Alejandro F; Hose, Rodney; Patel, Umang J; Coley, Stuart C

2010-01-01

Objectives: Hemodynamic changes in the cerebral circulation in presence of coarctation of aorta (CoA) and their significance in the increased intracranial aneurysms (IAs) formation in these patients remain unclear. In the present study, we measured the flow-rate waveforms in the cerebral arteries of a patient with CoA, followed by an analysis of different hemodynamic indices in a coexisting IA. Materials and Methods: Phase-contrast Magnetic Resonance (pc-MR) volumetric flow-rate (VFR) measurements were performed in cerebral arteries of a 51 years old woman with coexisting CoA, and five healthy volunteers. Numerical predictions of a number of relevant hemodynamic indices were performed in an IA located in sub-clinoid part of left internal carotid artery (ICA) of the patient. Computations were performed using Ansys®-CFX™ solver using the VFR values measured in the patient as boundary conditions (BCs). A second analysis was performed using the average VFR values measured in healthy volunteers. The VFR waveforms measured in the patient and healthy volunteers were compared followed by a comparison of the hemodynamic indices obtained using both approaches. The results are discussed in the background of relevant literature. Results: Mean flow-rates were increased by 27.1% to 54.9% (2.66–5.44 ml/sec) in the cerebral circulation of patients with CoA as compared to healthy volunteers (1.2–3.95 ml/sec). Velocities were increased inside the IA by 35–45%. An exponential rise of 650% was observed in the area affected by high wall shear stress (WSS>15Pa) when flow-rates specific to CoA were used as compared to population average flow-rates. Absolute values of space and time averaged WSS were increased by 65%. Whereas values of maximum pressure on the IA wall were increased by 15% the area of elevated pressure was actually decreased by 50%, reflecting a more focalized jet impingement within the IA of the CoA patient. Conclusions: IAs can develop in patients with CoA several years after the surgical repair. Cerebral flow-rates in CoA patients are significantly higher as compared to average flow-rates in healthy population. The increased supra-physiological WSS (>15Pa), OSI (>0.2) and focalized pressure may play an important role in the etiopathogenesis of IAs in patients with CoA. PMID:22518256

Surface-wave tomography of Ireland and surroundings using ambient noise and teleseismic data

NASA Astrophysics Data System (ADS)

Bonadio, Raffaele; Arroucau, Pierre; Lebedev, Sergei; Meier, Thomas; Schaeffer, Andrew; Licciardi, Andrea; Piana Agostinetti, Nicola

2016-04-01

Ireland's geology is dominated by northeast-southwest structural trends and suture zones, mostly inferred from geological mapping and a few active source seismic experiments. However, their geometry and extent at depth and their continuity across the Irish Sea are still poorly known. Important questions also remain unanswered regarding the thickness and bulk properties of the sedimentary cover at the regional scale, the deformation and flow of the deep crust during the formation of Ireland, the thickness of Ireland's lithosphere today, and the thermal structure and dynamics of the asthenosphere beneath Ireland. In this work, we take advantage of abundant, newly available broadband data from temporary array deployments and permanent seismic networks in Ireland and Great Britain to produce high-resolution models of seismic velocity structure and anisotropy of the lithosphere. We combine Rayleigh and Love phase velocity measurements from waveform cross-correlation using both ambient noise and teleseismic data in order to produce high-quality dispersion curves for periods ranging from 1 to 300 s. The phase velocity measurement procedures are adapted from Meier et al.[2], Lebedev et al.[1] and Soomro et al.[3] and are automated in order to deal with the large amount of data and ensure consistency and reproducibility. For the nearly 200 stations used in this study, we obtain a very large number of dispersion curves from both ambient noise and teleseimic data. Dispersion measurements are then inverted in a tomographic procedure for surface-wave phase velocity maps in a very broad period range. The maps constrain the 3D seismic-velocity structure of the crust and upper mantle underlying Ireland and the Irish Sea. {9} Lebedev, S., T. Meier, R. D. van der Hilst. Asthenospheric flow and origin of volcanism in the Baikal Rift area, Earth Planet. Sci. Lett., 249, 415-424, 2006. Meier, T., K. Dietrich, B. Stockhert, H.P. Harjes, One-dimensional models of shear wave velocity for the eastern Mediterranean obtained from the inversion of Rayleigh wave phase velocities and tectonic implications, Geophys. J. Int. 156, 45-58, 2004. Soomro, R.A., C. Weidle, L. Cristiano, S. Lebedev, T. Meier. Phase velocities of Rayleigh and Love waves in central and northern Europe from automated, broadband, inter-station measurements, Geophys. J. Int., 204, 517-534, 2016.

Finite-frequency sensitivity kernels for head waves

NASA Astrophysics Data System (ADS)

Zhang, Zhigang; Shen, Yang; Zhao, Li

2007-11-01

Head waves are extremely important in determining the structure of the predominantly layered Earth. While several recent studies have shown the diffractive nature and the 3-D Fréchet kernels of finite-frequency turning waves, analogues of head waves in a continuous velocity structure, the finite-frequency effects and sensitivity kernels of head waves are yet to be carefully examined. We present the results of a numerical study focusing on the finite-frequency effects of head waves. Our model has a low-velocity layer over a high-velocity half-space and a cylindrical-shaped velocity perturbation placed beneath the interface at different locations. A 3-D finite-difference method is used to calculate synthetic waveforms. Traveltime and amplitude anomalies are measured by the cross-correlation of synthetic seismograms from models with and without the velocity perturbation and are compared to the 3-D sensitivity kernels constructed from full waveform simulations. The results show that the head wave arrival-time and amplitude are influenced by the velocity structure surrounding the ray path in a pattern that is consistent with the Fresnel zones. Unlike the `banana-doughnut' traveltime sensitivity kernels of turning waves, the traveltime sensitivity of the head wave along the ray path below the interface is weak, but non-zero. Below the ray path, the traveltime sensitivity reaches the maximum (absolute value) at a depth that depends on the wavelength and propagation distance. The sensitivity kernels vary with the vertical velocity gradient in the lower layer, but the variation is relatively small at short propagation distances when the vertical velocity gradient is within the range of the commonly accepted values. Finally, the depression or shoaling of the interface results in increased or decreased sensitivities, respectively, beneath the interface topography.

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

NASA Astrophysics Data System (ADS)

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

2012-04-01

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.

Ultra-low velocity zones beneath the Philippine and Tasman Seas revealed by a trans-dimensional Bayesian waveform inversion

NASA Astrophysics Data System (ADS)

Pachhai, Surya; Dettmer, Jan; Tkalčić, Hrvoje

2015-11-01

Ultra-low velocity zones (ULVZs) are small-scale structures in the Earth's lowermost mantle inferred from the analysis of seismological observations. These structures exhibit a strong decrease in compressional (P)-wave velocity, shear (S)-wave velocity, and an increase in density. Quantifying the elastic properties of ULVZs is crucial for understanding their physical origin, which has been hypothesized either as partial melting, iron enrichment, or a combination of the two. Possible disambiguation of these hypotheses can lead to a better understanding of the dynamic processes of the lowermost mantle, such as, percolation, stirring and thermochemical convection. To date, ULVZs have been predominantly studied by forward waveform modelling of seismic waves that sample the core-mantle boundary region. However, ULVZ parameters (i.e. velocity, density, and vertical and lateral extent) obtained through forward modelling are poorly constrained because inferring Earth structure from seismic observations is a non-linear inverse problem with inherent non-uniqueness. To address these issues, we developed a trans-dimensional hierarchical Bayesian inversion that enables rigorous estimation of ULVZ parameter values and their uncertainties, including the effects of model selection. The model selection includes treating the number of layers and the vertical extent of the ULVZ as unknowns. The posterior probability density (solution to the inverse problem) of the ULVZ parameters is estimated by reversible jump Markov chain Monte Carlo sampling that employs parallel tempering to improve efficiency/convergence. First, we apply our method to study the resolution of complex ULVZ structure (including gradually varying structure) by probabilistically inverting simulated noisy waveforms. Then, two data sets sampling the CMB beneath the Philippine and Tasman Seas are considered in the inversion. Our results indicate that both ULVZs are more complex than previously suggested. For the Philippine Sea data, we find a strong decrease in S-wave velocity, which indicates the presence of iron-rich material, albeit this result is accompanied with larger parameter uncertainties than in a previous study. For the Tasman Sea data, our analysis yields a well-constrained S-wave velocity that gradually decreases with depth. We conclude that this ULVZ represents a partial melt of iron-enriched material with higher melt content near its bottom.

S-Wave Normal Mode Propagation in Aluminum Cylinders

USGS Publications Warehouse

Lee, Myung W.; Waite, William F.

2010-01-01

Large amplitude waveform features have been identified in pulse-transmission shear-wave measurements through cylinders that are long relative to the acoustic wavelength. The arrival times and amplitudes of these features do not follow the predicted behavior of well-known bar waves, but instead they appear to propagate with group velocities that increase as the waveform feature's dominant frequency increases. To identify these anomalous features, the wave equation is solved in a cylindrical coordinate system using an infinitely long cylinder with a free surface boundary condition. The solution indicates that large amplitude normal-mode propagations exist. Using the high-frequency approximation of the Bessel function, an approximate dispersion relation is derived. The predicted amplitude and group velocities using the approximate dispersion relation qualitatively agree with measured values at high frequencies, but the exact dispersion relation should be used to analyze normal modes for full ranges of frequency of interest, particularly at lower frequencies.

Low frequency full waveform seismic inversion within a tree based Bayesian framework

NASA Astrophysics Data System (ADS)

Ray, Anandaroop; Kaplan, Sam; Washbourne, John; Albertin, Uwe

2018-01-01

Limited illumination, insufficient offset, noisy data and poor starting models can pose challenges for seismic full waveform inversion. We present an application of a tree based Bayesian inversion scheme which attempts to mitigate these problems by accounting for data uncertainty while using a mildly informative prior about subsurface structure. We sample the resulting posterior model distribution of compressional velocity using a trans-dimensional (trans-D) or Reversible Jump Markov chain Monte Carlo method in the wavelet transform domain of velocity. This allows us to attain rapid convergence to a stationary distribution of posterior models while requiring a limited number of wavelet coefficients to define a sampled model. Two synthetic, low frequency, noisy data examples are provided. The first example is a simple reflection + transmission inverse problem, and the second uses a scaled version of the Marmousi velocity model, dominated by reflections. Both examples are initially started from a semi-infinite half-space with incorrect background velocity. We find that the trans-D tree based approach together with parallel tempering for navigating rugged likelihood (i.e. misfit) topography provides a promising, easily generalized method for solving large-scale geophysical inverse problems which are difficult to optimize, but where the true model contains a hierarchy of features at multiple scales.

Density reconstruction in multiparameter elastic full-waveform inversion

NASA Astrophysics Data System (ADS)

Sun, Min'ao; Yang, Jizhong; Dong, Liangguo; Liu, Yuzhu; Huang, Chao

2017-12-01

Elastic full-waveform inversion (EFWI) is a quantitative data fitting procedure that recovers multiple subsurface parameters from multicomponent seismic data. As density is involved in addition to P- and S-wave velocities, the multiparameter EFWI suffers from more serious tradeoffs. In addition, compared with P- and S-wave velocities, the misfit function is less sensitive to density perturbation. Thus, a robust density reconstruction remains a difficult problem in multiparameter EFWI. In this paper, we develop an improved scattering-integral-based truncated Gauss-Newton method to simultaneously recover P- and S-wave velocities and density in EFWI. In this method, the inverse Gauss-Newton Hessian has been estimated by iteratively solving the Gauss-Newton equation with a matrix-free conjugate gradient algorithm. Therefore, it is able to properly handle the parameter tradeoffs. To give a detailed illustration of the tradeoffs between P- and S-wave velocities and density in EFWI, wavefield-separated sensitivity kernels and the Gauss-Newton Hessian are numerically computed, and their distribution characteristics are analyzed. Numerical experiments on a canonical inclusion model and a modified SEG/EAGE Overthrust model have demonstrated that the proposed method can effectively mitigate the tradeoff effects, and improve multiparameter gradients. Thus, a high convergence rate and an accurate density reconstruction can be achieved.

Seismic Constraints on Geometry, Seismic Velocity and Anisotropy of the "African Anomaly"

NASA Astrophysics Data System (ADS)

Wang, Y.; Wen, L.

2006-05-01

Seismic evidence shows that the "African Anomaly", a prominent low-velocity structure in the lower mantle beneath Africa, has a broad base near the core-mantle boundary (CMB) and extends at least 1000 km upward into the mid-lower mantle. Waveform modeling results indicate that its base is a very-low velocity province (VLVP) in the lowermost 200-300 km of the Earth's mantle with rapidly varying geometries and a strong Vs reduction gradient of -2% - -12% from top to bottom. These features unambiguously indicate the VLVP is compositionally distinct and can be best explained by partial melting driven by a compositional change produced in the early Earth's history [Wen, 2001; Wen et. al, 2001; Wang and Wen, 2004]. Seismic structure for the mid-lower mantle portion of the "African Anomaly" and the anisotropic behavior related to the VLVP remain unclear. In this presentation, we will present seismic data to constrain geometry and both P- and S- velocity perturbations for the "African Anomaly" along the great arc from the East Pacific Rise to the Japan Sea, and discuss seismic anisotropic behavior inside the VLVP and in the surrounding areas. We collected direct S, ScS, SKS, and SKKS waveforms data sets for 9 earthquakes recorded at the temporary broadband Kaapvaal, Tanzania, and Ethiopia/Kenya seismic arrays in Africa. These seismic data provide reasonably good coverage for the "African Anomaly" along a great circle path in opposite directions. We corrected for the effects of the earthquake mislocation and the seismic heterogeneities outside the anomaly. Seismic data suggest that the "African Anomaly" exhibits a "cusp-like" shape along the great arc and continuously extends from the CMB to about 1300 km above the CMB with both sides tilting toward its center beneath southern Africa. The magnitude of these travel time residuals can be best explained by a shear velocity structure with average Vs reductions of -5% for the basal layer and -2% - -3% for the portion in the lower mantle. A uniform Vs to Vp perturbation ratio of 3:1 can best explain the travel time residuals for the P wave data. The geometry and the inferred S to P velocity perturbation ratio of the anomaly indicate that the "African anomaly" in the lower mantle likely, like the VLVP at its base, is compositionally distinct. We also measured the apparent anisotropic parameters (the fast polarization direction and the split time) for selected 503 SKS and 88 SKKS waveform splits of 118 earthquakes (focal depth > 50 km) recorded by stations in Africa and Europe. We observed a good correlation with stations of apparent anisotropy measurements and consistent measurements from SKS and SKKS phases originated from the same earthquakes when seismic phases sample away from the edges of the VLVP. However, we did not find correlation with stations and consistency for the SKS and SKKS phases sampling near the edges of the VLVP. Because the SKS and SKKS phases have similar propagation paths in the shallow Earth and quite different sampling areas at the CMB, the anisotropy in the lithosphere and asthenosphere should have similar influence on the SKS and SKKS phases. Our observations suggest that part of shear wave splitting for the SKS and SKKS phases sampling at the edges of the VLVP has to originate from the lowermost mantle near the exit points of these phases at the CMB, possibly associated with a complex flow pattern near the edges of the VLVP, while the interior of the VLVP is likely isotropic or weakly anisotropic.

Anatomy of Old Faithful hydrothermal system from subsurface seismic imaging of the Yellowstone Upper Geyser Basin

NASA Astrophysics Data System (ADS)

Wu, S. M.; Lin, F. C.; Farrell, J.; Ward, K. M.; Karplus, M. S.; Smith, R. B.

2017-12-01

The Upper Geyser Basin (UGB) in Yellowstone National Park contains one of the highest concentrations of hydrothermal features on Earth including the iconic Old Faithful Geyser (OFG). Although this system has been the focus of many geological, geochemical, and geophysical studies, the shallow (<200 m) subsurface structure and the hydrothermal tremor behavior remain poorly characterized. To probe the detailed structure that relates to the hydrothermal plumbing of the UGB, we deployed dense arrays of 3-C 5-Hz geophones in both November of 2015 and 2016, composed of 133 stations with 50 m spacing, and 519 station locations, with an 20 m spacing, respectively. By applying seismic interferometry techniques, we extracted Rayleigh-wave signals between 1-10 Hz via seismic signals excited by nearby hydrothermal features (e.g. geysers and pools). We observe a clear lateral velocity boundary at 3.3 Hz frequency that delineates a higher phase velocity of 1.6 km/sec in the NE and a lower phase velocity of 1.0 km/sec in the SW corresponding to the local geologic formation of rhyolitic and glacial deposits, respectively. We also image a relatively shallow (20-60 m deep) large reservoir with an estimated porosity 30% located 100 meters southwest of the OFG from the significant spatial-dependent waveform distortions and delays between 5-10 Hz frequency. This reservoir is likely controlled by the local geology with a rhyolitic deposit in the NE acting as a relatively impermeable barrier to vertical fluid ascent. To understand the pre-eruption tremor signals from OFG, we first study the seismic waveforms recorded at the closest station to the OFG cone. Many highly repetitive seismic pulses associated with bubble collapse, which compose the tremor signal, can be identified. Using a reference event template and the cross-correlation method, we can determine the onset of each individual bubbling event using a cross-correlation coefficient threshold of 0.8. Based on the detected timing, we then inspect the spatial and temporal variation of the event waveforms across the dense arrays. Clear correlation between temporal waveform variation and air temperature is observed. In this presentation, we will discuss the potential mechanisms of tremor waveform variation and how that can be used to improve our understanding of geyser dynamics.

Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

USGS Publications Warehouse

Han, Liang; Hole, John; Stock, Joann; Fuis, Gary S.; Williams, Colin F.; Delph, Jonathan; Davenport, Kathy; Livers, Amanda

2016-01-01

Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65–90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ∼7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ∼1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ∼3 km depth in most of the valley, but at only ∼1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7–8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.

Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

NASA Astrophysics Data System (ADS)

Han, Liang; Hole, John A.; Stock, Joann M.; Fuis, Gary S.; Williams, Colin F.; Delph, Jonathan R.; Davenport, Kathy K.; Livers, Amanda J.

2016-11-01

Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65-90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ˜7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ˜1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ˜3 km depth in most of the valley, but at only ˜1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7-8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.

Seismic Evidence for Fluid/Gas Beneath the Mentawai Fore-Arc Basin, Central Sumatra

NASA Astrophysics Data System (ADS)

Huot, Gabriel; Singh, Satish C.

2018-02-01

Since 2004, there have been three great interplate earthquakes (Mw > 8.0) offshore Sumatra. In addition to rupturing the megathrust, these earthquakes might also have ruptured the backthrusts that bound the Andaman Islands to the Mentawai Islands toward the forearc basins. Here we apply a combination of traveltime tomography and seismic full waveform inversion to an ultralong offset seismic reflection profile from the Mentawai forearc basin, in the region of the 2007 Mw 8.4 Bengkulu earthquake. We perform a waveform inversion of far-offset data followed by a waveform inversion of near-offset data using the starting model derived from the traveltime tomography. Our results show the presence of a large, low-velocity anomaly above the backthrust. The seismic reflection image indicates that this low-velocity anomaly lies either within highly compacted sediments from the accretionary wedge or within highly deformed sediments from the forearc basin. The porosity estimation, using the effective medium theory, suggests that a small amount of gas (from 2 to 13%) or a significant amount of fluid (from 17 to 40%) could generate this low-velocity zone. The presence of fluids and the observation of bottom simulating reflector below a push-up ridge might be associated with mud diapirism. The fluids could originate locally from the dewatering of the sediments from the accretionary wedge or forearc basin. The high reflectivity of the backthrust in this region might also indicate deeper fluid origin, either from underplated sediments on the subduction interface or from the serpentinized mantle wedge.

Performance Bounds on Micro-Doppler Estimation and Adaptive Waveform Design Using OFDM Signals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sen, Satyabrata; Barhen, Jacob; Glover, Charles Wayne

We analyze the performance of a wideband orthogonal frequency division multiplexing (OFDM) signal in estimating the micro-Doppler frequency of a target having multiple rotating scatterers (e.g., rotor blades of a helicopter, propellers of a submarine). The presence of rotating scatterers introduces Doppler frequency modulation in the received signal by generating sidebands about the transmitted frequencies. This is called the micro-Doppler effects. The use of a frequency-diverse OFDM signal in this context enables us to independently analyze the micro-Doppler characteristics with respect to a set of orthogonal subcarrier frequencies. Therefore, to characterize the accuracy of micro-Doppler frequency estimation, we compute themore » Cram er-Rao Bound (CRB) on the angular-velocity estimate of the target while considering the scatterer responses as deterministic but unknown nuisance parameters. Additionally, to improve the accuracy of the estimation procedure, we formulate and solve an optimization problem by minimizing the CRB on the angular-velocity estimate with respect to the transmitting OFDM spectral coefficients. We present several numerical examples to demonstrate the CRB variations at different values of the signal-to-noise ratio (SNR) and the number of OFDM subcarriers. The CRB values not only decrease with the increase in the SNR values, but also reduce as we increase the number of subcarriers implying the significance of frequency-diverse OFDM waveforms. The improvement in estimation accuracy due to the adaptive waveform design is also numerically analyzed. Interestingly, we find that the relative decrease in the CRBs on the angular-velocity estimate is more pronounced for larger number of OFDM subcarriers.« less

Real-time detector for hypervelocity microparticles using piezoelectric material (II)

NASA Astrophysics Data System (ADS)

Miyachi, T.; Mdm Team

This report is concerned with results on response of a piezoelectric lead-zirconate-titanate (PZT) element, by which a possible relation of output waveform to velocity at impact is studied. At first, we point out a meaning of output waveform, in particular, a behavior of the output signal within a few hundred nanoseconds immediately after impact (named as ``first one cycle''), which is free from interference with reflected waves and could contain impact hysteresis. Accordingly, we deal with the first one cycle, and analyze it with respect to its amplitude and frequency components. We obtain the following results: 1. Output amplitude is proportional to the momentum of particles below 6 km/s. 2. Its rise-time is related to the particle velocity above 10km/s. 3. There exists a transition region in between. 4. The sensitivity is confirmed to be independent of the element thickness, contrary to the results in [1,2], in which the amplitude was defined as the maximum peak-to-peak amplitude, which was outside the first one cycle. We propose that a single PZT element can be used as a velocity sensitive detector if the output signal is measured at a sampling rate of ˜ 50MHz. We discuss a PZT detector that is to be employed as a real-time dust monitor to onboard the BepiColombo mission, MDM. This could discriminate real and junk events by analyzing the waveform. [1] T.Miyachi et al., to be published in Adv. Space Rev. ( JASR 6550). [2] T.Miyachi et al., Jpn.J.Appl.Phys.42(2003)1496.

Ultrasonic monitoring of spontaneous imbibition experiments: Acoustic signature of fluid migration

NASA Astrophysics Data System (ADS)

David, Christian; Barnes, Christophe; Desrues, Mathilde; Pimienta, Lucas; Sarout, Joël.; Dautriat, Jérémie

2017-07-01

Capillary rise experiments (spontaneous imbibition tests) were conducted in the laboratory with ultrasonic and X-ray monitoring on the Sherwood sandstone and the Majella grainstone. The aim was to provide a direct comparison between the variation in seismic attributes (amplitude, velocity, spectral content, and energy) and the actual fluid distribution in the rock. Two pairs of ultrasonic P wave sensors located at different heights on a cylindrical rock specimen recorded every 5 s the waveforms when capillary forces make water rise up into the rock from the bottom in contact with a water tank. Simultaneously, computerized tomography scan images of a vertical cross section were also recorded. Two important results were found. (i) The amplitude of the first P wave arrival is impacted by the upward moving fluid front before the P wave velocity is, while the fluid front has not yet reached the sensors level. In contrast, the P wave velocity decreases when the fluid front reaches the Fresnel clearance zone. The spectral analysis of the waveforms shows that the peak frequency amplitude is continuously decreasing without noticeable frequency shift. (ii) A methodology based on the calculation of the analytical signal and instantaneous phase was designed to decompose each waveform into discrete wavelets associated with direct or reflected waves. The energy carried by the wavelets is very sensitive to the fluid substitution process: the coda wavelets related to reflections on the bottom end face of the specimen are impacted as soon as imbibition starts and can be used as a precursor for the arriving fluid.

Comparison of the Cut-and-Paste and Full Moment Tensor Methods for Estimating Earthquake Source Parameters

NASA Astrophysics Data System (ADS)

Templeton, D.; Rodgers, A.; Helmberger, D.; Dreger, D.

2008-12-01

Earthquake source parameters (seismic moment, focal mechanism and depth) are now routinely reported by various institutions and network operators. These parameters are important for seismotectonic and earthquake ground motion studies as well as calibration of moment magnitude scales and model-based earthquake-explosion discrimination. Source parameters are often estimated from long-period three- component waveforms at regional distances using waveform modeling techniques with Green's functions computed for an average plane-layered models. One widely used method is waveform inversion for the full moment tensor (Dreger and Helmberger, 1993). This method (TDMT) solves for the moment tensor elements by performing a linearized inversion in the time-domain that minimizes the difference between the observed and synthetic waveforms. Errors in the seismic velocity structure inevitably arise due to either differences in the true average plane-layered structure or laterally varying structure. The TDMT method can account for errors in the velocity model by applying a single time shift at each station to the observed waveforms to best match the synthetics. Another method for estimating source parameters is the Cut-and-Paste (CAP) method. This method breaks the three-component regional waveforms into five windows: vertical and radial component Pnl; vertical and radial component Rayleigh wave; and transverse component Love waves. The CAP method performs a grid search over double-couple mechanisms and allows the synthetic waveforms for each phase (Pnl, Rayleigh and Love) to shift in time to account for errors in the Green's functions. Different filtering and weighting of the Pnl segment relative to surface wave segments enhances sensitivity to source parameters, however, some bias may be introduced. This study will compare the TDMT and CAP methods in two different regions in order to better understand the advantages and limitations of each method. Firstly, we will consider the northeastern China/Korean Peninsula region where average plane-layered structure is well known and relatively laterally homogenous. Secondly, we will consider the Middle East where crustal and upper mantle structure is laterally heterogeneous due to recent and ongoing tectonism. If time allows we will investigate the efficacy of each method for retrieving source parameters from synthetic data generated using a three-dimensional model of seismic structure of the Middle East, where phase delays are known to arise from path-dependent structure.

Effects of water drinking test on ocular blood flow waveform parameters: A laser speckle flowgraphy study.

PubMed

Bhatti, Mehwish Saba; Tang, Tong Boon; Laude, Augustinus

2017-01-01

The water-drinking test (WDT) is a provocative test used in glaucoma research to assess the effects of elevated intraocular pressure (IOP). Defective autoregulation due to changes in perfusion pressure may play a role in the pathophysiology of several ocular diseases. This study aims to examine the effects of WDT on ocular blood flow (in the form of pulse waveform parameters obtained using laser speckle flowgraphy) to gain insight into the physiology of ocular blood flow and its autoregulation in healthy individuals. Changes in pulse waveform parameters of mean blur rate (MBR) in the entire optic nerve head (ONH), the vasculature of the ONH, the tissue area of the ONH, and the avascular tissue area located outside of the ONH were monitored over time. Significant increases in the falling rate of MBR over the entire ONH and its tissue area and decreases in blowout time (BOT) of the tissue area were observed only at 10 minutes after water intake. Significant increases in the skew of the waveform and the falling rate were observed in the vasculature of the ONH at 40 and 50 minutes after water intake, respectively. In the avascular region of the choroid, the average MBR increased significantly up to 30 minutes after water intake. Furthermore, the rising rate in this region increased significantly at 20 and 40 minutes, and the falling rate and acceleration-time index were both significantly increased at 40 minutes after water intake. Our results indicate the presence of effective autoregulation of blood flow at the ONH after WDT. However, in the choroidal region, outside of the ONH, effective autoregulation was not observed until 30 minutes after water intake in healthy study participants. These pulse waveform parameters could potentially be used in the diagnosis and/or monitoring of patients with glaucoma.

Effects of water drinking test on ocular blood flow waveform parameters: A laser speckle flowgraphy study

PubMed Central

Bhatti, Mehwish Saba; Laude, Augustinus

2017-01-01

The water-drinking test (WDT) is a provocative test used in glaucoma research to assess the effects of elevated intraocular pressure (IOP). Defective autoregulation due to changes in perfusion pressure may play a role in the pathophysiology of several ocular diseases. This study aims to examine the effects of WDT on ocular blood flow (in the form of pulse waveform parameters obtained using laser speckle flowgraphy) to gain insight into the physiology of ocular blood flow and its autoregulation in healthy individuals. Changes in pulse waveform parameters of mean blur rate (MBR) in the entire optic nerve head (ONH), the vasculature of the ONH, the tissue area of the ONH, and the avascular tissue area located outside of the ONH were monitored over time. Significant increases in the falling rate of MBR over the entire ONH and its tissue area and decreases in blowout time (BOT) of the tissue area were observed only at 10 minutes after water intake. Significant increases in the skew of the waveform and the falling rate were observed in the vasculature of the ONH at 40 and 50 minutes after water intake, respectively. In the avascular region of the choroid, the average MBR increased significantly up to 30 minutes after water intake. Furthermore, the rising rate in this region increased significantly at 20 and 40 minutes, and the falling rate and acceleration-time index were both significantly increased at 40 minutes after water intake. Our results indicate the presence of effective autoregulation of blood flow at the ONH after WDT. However, in the choroidal region, outside of the ONH, effective autoregulation was not observed until 30 minutes after water intake in healthy study participants. These pulse waveform parameters could potentially be used in the diagnosis and/or monitoring of patients with glaucoma. PMID:28742142

Seismic Full Waveform Modeling & Imaging in Attenuating Media

NASA Astrophysics Data System (ADS)

Guo, Peng

Seismic attenuation strongly affects seismic waveforms by amplitude loss and velocity dispersion. Without proper inclusion of Q parameters, errors can be introduced for seismic full waveform modeling and imaging. Three different (Carcione's, Robertsson's, and the generalized Robertsson's) isotropic viscoelastic wave equations based on the generalized standard linear solid (GSLS) are evaluated. The second-order displacement equations are derived, and used to demonstrate that, with the same stress relaxation times, these viscoelastic formulations are equivalent. By introducing separate memory variables for P and S relaxation functions, Robertsson's formulation is generalized to allow different P and S wave stress relaxation times, which improves the physical consistency of the Qp and Qs modelled in the seismograms.The three formulations have comparable computational cost. 3D seismic finite-difference forward modeling is applied to anisotropic viscoelastic media. The viscoelastic T-matrix (a dynamic effective medium theory) relates frequency-dependent anisotropic attenuation and velocity to reservoir properties in fractured HTI media, based on the meso-scale fluid flow attenuation mechanism. The seismic signatures resulting from changing viscoelastic reservoir properties are easily visible. Analysis of 3D viscoelastic seismograms suggests that anisotropic attenuation is a potential tool for reservoir characterization. To compensate the Q effects during reverse-time migration (RTM) in viscoacoustic and viscoelastic media, amplitudes need to be compensated during wave propagation; the propagation velocity of the Q-compensated wavefield needs to be the same as in the attenuating wavefield, to restore the phase information. Both amplitude and phase can be compensated when the velocity dispersion and the amplitude loss are decoupled. For wave equations based on the GSLS, because Q effects are coupled in the memory variables, Q-compensated wavefield propagates faster than the attenuating wavefield, and introduce unwanted phase shift. Numerical examples show that there are phase (depth) shifts in the Q-compensated RTM images from the GSLS equation. An adjoint-based least-squares reverse-time migration is proposed for viscoelastic media (Q-LSRTM), to compensate the attenuation losses in P and S images. The viscoelastic adjoint operator, and the P and S modulus perturbation imaging conditions are derived using the adjoint-state method and an augmented Lagrangian functional. Q-LSRTM solves the viscoelastic linearized modeling operator for synthetic data, and the adjoint operator is used for back propagating the data residual. Q-LSRTM is capable of iteratively updating the P and S modulus perturbations,in the direction of minimizing data residuals, and attenuation loss is iteratively compensated. A novel Q compensation approach is developed for adjoint seismic imaging by pseudodifferential scaling. With a correct Q model included in the migration algorithm, propagation effects, including the Q effects, can be compensated with the application of the inverse Hessian to the RTM image. Pseudodifferential scaling is used to efficiently approximate the action of the inverse Hessian. Numerical examples indicate that the adjoint RTM images with pseudodifferential scaling approximate the true model perturbation, and can be used as well-conditioned gradients for least-squares imaging.

Rupture process of the 2016 Mw 7.8 Ecuador earthquake from joint inversion of InSAR data and teleseismic P waveforms

NASA Astrophysics Data System (ADS)

Yi, Lei; Xu, Caijun; Wen, Yangmao; Zhang, Xu; Jiang, Guoyan

2018-01-01

The 2016 Ecuador earthquake ruptured the Ecuador-Colombia subduction interface where several historic megathrust earthquakes had occurred. In order to determine a detailed rupture model, Interferometric Synthetic Aperture Radar (InSAR) images and teleseismic data sets were objectively weighted by using a modified Akaika's Bayesian Information Criterion (ABIC) method to jointly invert for the rupture process of the earthquake. In modeling the rupture process, a constrained waveform length method, unlike the traditional subjective selected waveform length method, was used since the lengths of inverted waveforms were strictly constrained by the rupture velocity and rise time (the slip duration time). The optimal rupture velocity and rise time of the earthquake were estimated from grid search, which were determined to be 2.0 km/s and 20 s, respectively. The inverted model shows that the event is dominated by thrust movement and the released moment is 5.75 × 1020 Nm (Mw 7.77). The slip distribution extends southward along the Ecuador coast line in an elongated stripe at a depth between 10 and 25 km. The slip model is composed of two asperities and slipped over 4 m. The source time function is approximate 80 s that separated into two segments corresponding to the two asperities. The small magnitude of the slip occurred in the updip section of the fault plane resulted in small tsunami waves that were verified by observations near the coast. We suggest a possible situation that the rupture zone of the 2016 earthquake is likely not overlapped with that of the 1942 earthquake.

Intercorrelation of P and Pn Recordings for the North Korean Nuclear Tests

NASA Astrophysics Data System (ADS)

Lay, T.; Voytan, D.; Ohman, J.

2017-12-01

The relative waveform analysis procedure called Intercorrelation is applied to Pn and P waveforms at regional and teleseismic distances, respectively, for the 5 underground nuclear tests at the North Korean nuclear test site. Intercorrelation is a waveform equalization procedure that parameterizes the effective source function for a given explosion, including the reduced velocity potential convolved with a simplified Green's function that accounts for the free surface reflections (pPn and pP), and possibly additional arrivals such as spall. The source function for one event is convolved with the signal at a given station for a second event, and the recording at the same station for the first event is convolved with the source function for the second event. This procedure eliminates the need to predict the complex receiver function effects at the station, which are typically not well-known for short-period response. The parameters of the source function representation are yield and burial depth, and an explosion source model is required. Here we use the Mueller-Murphy representation of the explosion reduced velocity potential, which explicitly depends on yield and burial depth. We then search over yield and burial depth ranges for both events, constrained by a priori information about reasonable ranges of parameters, to optimize the simultaneous match of multiple station signals for the two events. This procedure, applied to the apparently overburied North Korean nuclear tests (no indications of spall complexity), assuming simple free surface interactions (elastic reflection from a flat surface), provides excellent waveform equalization for all combinations of 5 nuclear tests.

Near Fault Strong Ground Motion Records in the Kathmandu Valley during the 2015 Gorkha Nepal Earthquake

NASA Astrophysics Data System (ADS)

Takai, N.; Shigefuji, M.; Rajaure, S.; Bijukchhen, S.; Ichiyanagi, M.; Dhital, M. R.; Sasatani, T.

2015-12-01

Kathmandu is the capital of Nepal and is located in the Kathmandu Valley, which is formed by soft lake sediments of Plio-Pleistocene origin. Large earthquakes in the past have caused significant damage as the seismic waves were amplified in the soft sediments. To understand the site effect of the valley structure, we installed continuous recording accelerometers in four different parts of the valley. Four stations were installed along a west-to-east profile of the valley at KTP (Kirtipur; hill top), TVU (Kirtipur; hill side), PTN (Patan) and THM (Thimi). On 25 April 2015, a large interplate earthquake Mw 7.8 occurred in the Himalayan Range of Nepal. The focal area estimated was about 200 km long and 150 km wide, with a large slip area under the Kathmandu Valley where our strong motion observation stations were installed. The strong ground motions were observed during this large damaging earthquake. The maximum horizontal peak ground acceleration at the rock site was 271 cm s-2, and the maximum horizontal peak ground velocity at the sediment sites reached 112 cm s-1. We compared these values with the empirical attenuation formula for strong ground motions. We found the peak accelerations were smaller and the peak velocities were approximately the same as the predicted values. The rock site KTP motions are less affected by site amplification and were analysed further. The horizontal components were rotated to the fault normal (N205E) and fault parallel (N115E) directions using the USGS fault model. The velocity waveforms at KTP showed about 5 s triangular pulses on the N205E and the up-down components; however the N115E component was not a triangular pulse but one cycle sinusoidal wave. The velocity waveforms at KTP were integrated to derive the displacement waveforms. The derived displacements at KTP are characterized by a monotonic step on the N205E normal and up-down components. The displacement waveforms of KTP show permanent displacements of 130 cm in the fault normal direction and 60 cm in the upward direction; the vector sum of these is 143 cm. Inside the Kathmandu Valley, 147 cm deformation and the same moving direction as the USGS fault normal direction were reported using with GPS data. Our results derived from the KTP records are consistent with these observations.

Abnormal umbilical cord Doppler sonograms may predict impending demise in fetuses with sacrococcygeal teratoma. A report of two cases.

PubMed

Olutoye, Oluyinka O; Johnson, Mark P; Coleman, Beverly G; Crombleholme, Timothy M; Adzick, N Scott; Flake, Alan W

2004-01-01

To identify factors predictive of fetal demise in fetuses with sacrococcygeal teratoma (SCT). The recent management of monochorionic twins discordant for a large SCT and a singleton with a large SCT was reviewed. Serial fetal echocardiography and ultrasonography with Doppler flow measurements documented rapid growth of the SCT in both cases with a relatively modest increase in combined cardiac output. No placentomegaly or hydrops was observed at any time. In both fetuses with SCT, evolution of abnormal umbilical artery waveforms was observed with the ultimate development of reversed end-diastolic umbilical arterial flow that was followed by sudden fetal demise. Death in these 2 fetuses with large SCTs in the absence of placentomegaly/hydrops or hemodynamic changes suggestive of evolving high-output failure suggests a previously unrecognized mechanism of death in fetuses with large rapidly growing SCTs. In these cases, fetal demise may only be heralded by abnormal umbilical artery waveforms that progress to the premorbid observation of reversed diastolic umbilical artery blood flow. Umbilical artery waveform analysis should be closely monitored with other hemodynamic parameters in fetuses with large SCTs. In such fetuses, depending on the gestational age, abnormalities in umbilical artery waveform should be considered indications for early delivery or in utero intervention to prevent fetal demise. Copyright 2004 S. Karger AG, Basel

Abnormal umbilical cord Dopplers may predict impending demise in fetuses with sacrococcygeal teratoma. A report of 2 cases.

PubMed

Olutoye, Oluyinka O; Johnson, Mark P; Coleman, Beverly G; Crombleholme, Timothy M; Adzick, N Scott; Flake, Alan W

2003-01-01

To identify factors predictive of fetal demise in fetuses with sacrococcygeal teratoma (SCT). The recent management of monochorionic twins discordant for a large SCT and a singleton with a large SCT were reviewed. Serial fetal echocardiography and ultrasonography with Doppler flow measurements documented rapid growth of the SCT in both cases with a relatively modest increase in combined cardiac output. No placentomegaly or hydrops was observed at any time. In both fetuses with SCT, evolution of abnormal umbilical artery waveforms was observed with the ultimate development of reversed end-diastolic umbilical arterial flow that was followed by sudden fetal demise. Death in these 2 fetuses with large SCTs in the absence of placentomegaly/hydrops or hemodynamic changes suggestive of evolving high-output failure suggests a previously unrecognized mechanism of death in fetuses with large rapidly growing SCTs. In these cases, fetal demise may only be heralded by abnormal umbilical artery waveforms that progress to the premorbid observation of reversed diastolic umbilical artery blood flow. Umbilical artery waveform analysis should be closely monitored with other hemodynamic parameters in fetuses with large SCTs. In such fetuses, depending on the gestational age, abnormalities in umbilical artery waveform should be considered indications for early delivery or in utero intervention to prevent fetal demise. Copyright 2003 S. Karger AG, Basel

A Gauss-Newton full-waveform inversion in PML-truncated domains using scalar probing waves

NASA Astrophysics Data System (ADS)

Pakravan, Alireza; Kang, Jun Won; Newtson, Craig M.

2017-12-01

This study considers the characterization of subsurface shear wave velocity profiles in semi-infinite media using scalar waves. Using surficial responses caused by probing waves, a reconstruction of the material profile is sought using a Gauss-Newton full-waveform inversion method in a two-dimensional domain truncated by perfectly matched layer (PML) wave-absorbing boundaries. The PML is introduced to limit the semi-infinite extent of the half-space and to prevent reflections from the truncated boundaries. A hybrid unsplit-field PML is formulated in the inversion framework to enable more efficient wave simulations than with a fully mixed PML. The full-waveform inversion method is based on a constrained optimization framework that is implemented using Karush-Kuhn-Tucker (KKT) optimality conditions to minimize the objective functional augmented by PML-endowed wave equations via Lagrange multipliers. The KKT conditions consist of state, adjoint, and control problems, and are solved iteratively to update the shear wave velocity profile of the PML-truncated domain. Numerical examples show that the developed Gauss-Newton inversion method is accurate enough and more efficient than another inversion method. The algorithm's performance is demonstrated by the numerical examples including the case of noisy measurement responses and the case of reduced number of sources and receivers.

Uterine artery velocity waveforms as predictors of pregnancy outcome in patients with antiphospholipid syndrome: a review.

PubMed

De Carolis, Sara; Botta, Angela; Garofalo, Serafina; Ferrazzani, Sergio; Martino, Carmelinda; Fatigante, Gabriella; Caforio, Leonardo; Caruso, Alessandro

2007-06-01

In pregnant women, antiphospholipid syndrome (APS) is associated with an increased risk for preeclampsia, fetal intrauterine growth restriction, and other complications related to uteroplacental insufficiency. In normal pregnancy, impedance to flow in the uterine arteries decreases with gestation, as the likely consequence of the physiologic change of spiral arteries into low-resistance vessels. The presence of antiphospholipid antibodies can impair this vascular adaptation, resulting in a reduced placental perfusion. Doppler investigation provides a noninvasive method for the study of uteroplacental blood flow. Several studies were performed to detect the predictive role of uterine artery Doppler velocimetry in relation to pregnancy outcome in APS patients. In some studies, a high resistance index in the uterine arteries strongly predicted the subsequent development of obstetric complications. In other studies, persistent bilateral uterine artery notches identified the risk of preeclampsia and fetal intrauterine growth restriction. To date, the uterine artery Doppler velocimetry resulted to be a useful tool for identifying APS pregnancies at risk for adverse pregnancy outcome. These findings might have important implications for the management of these patients.

Regularized Stokeslet representations for the flow around a human sperm

NASA Astrophysics Data System (ADS)

Ishimoto, Kenta; Gadelha, Hermes; Gaffney, Eamonn; Smith, David; Kirkman-Brown, Jackson

2017-11-01

The sperm flagellum does not simply push the sperm. We have established a new theoretical scheme for the dimensional reduction of swimming sperm dynamics, via high-frame-rate digital microscopy of a swimming human sperm cell. This has allowed the reconstruction of the flagellar waveform as a limit cycle in a phase space of PCA modes. With this waveform, boundary element numerical simulation has successfully captured fine-scale sperm swimming trajectories. Further analyses on the flow field around the cell has also demonstrated a pusher-type time-averaged flow, though the instantaneous flow field can temporarily vary in a more complicated manner - even pulling the sperm. Applying PCA to the flow field, we have further found that a small number of PCA modes explain the temporal patterns of the flow, whose core features are well approximated by a few regularized Stokeslets. Such representations provide a methodology for coarse-graining the time-dependent flow around a human sperm and other flagellar microorganisms for use in developing population level models that retain individual cell dynamics.

Symmetry of the gradient profile as second experimental dimension in the short-time expansion of the apparent diffusion coefficient as measured with NMR diffusometry.

PubMed

Laun, Frederik Bernd; Kuder, Tristan Anselm; Zong, Fangrong; Hertel, Stefan; Galvosas, Petrik

2015-10-01

The time-dependent apparent diffusion coefficient as measured by pulsed gradient NMR can be used to estimate parameters of porous structures including the surface-to-volume ratio and the mean curvature of pores. In this work, the short-time diffusion limit and in particular the influence of the temporal profile of diffusion gradients on the expansion as proposed by Mitra et al. (1993) is investigated. It is shown that flow-compensated waveforms, i.e. those whose first moment is zero, are blind to the term linear in observation time, which is the term that is proportional to mean curvature and surface permeability. A gradient waveform that smoothly interpolates between flow-compensated and bipolar waveform is proposed and the degree of flow-compensation is used as a second experimental dimension. This two-dimensional ansatz is shown to yield an improved precision when characterizing the confining domain. This technique is demonstrated with simulations and in experiments performed with cylindrical capillaries of 100 μm radius. Copyright © 2015 Elsevier Inc. All rights reserved.

Seismic Anisotropy Beneath the Eastern Flank of the Rio Grande Rift

NASA Astrophysics Data System (ADS)

Benton, N. W.; Pulliam, J.

2015-12-01

Shear wave splitting was measured across the eastern flank of the Rio Grande Rift (RGR) to investigate mechanisms of upper mantle anisotropy. Earthquakes recorded at epicentral distances of 90°-130° from EarthScope Transportable Array (TA) and SIEDCAR (SC) broadband seismic stations were examined comprehensively, via the Matlab program "Splitlab", to determine whether SKS and SKKS phases indicated anisotropic properties. Splitlab allows waveforms to be rotated, filtered, and windowed interactively and splitting measurements are made on a user-specified waveform segment via three independent methods simultaneously. To improve signal-to-noise and improve reliability, we stacked the error surfaces that resulted from grid searches in the measurements for each station location. Fast polarization directions near the Rio Grande Rift tend to be sub-parallel to the RGR but then change to angles that are consistent with North America's average plate motion, to the east. The surface erosional depression of the Pecos Valley coincides with fast polarization directions that are aligned in a more northerly direction than their neighbors, whereas the topographic high to the east coincides with an easterly change of the fast axis.The area above a mantle high velocity anomaly discovered separately via seismic tomography which may indicate thickened lithosphere, corresponds to unusually large delay times and fast polarization directions that are more closely aligned to a north-south orientation. The area of southeastern New Mexico that falls between the mantle fast anomaly and the Great Plains craton displays dramatically smaller delay times, as well as changes in fast axis directions toward the northeast. Changes in fast axis directions may indicate flow around the mantle anomaly; small delay times could indicate vertical or attenuated flow.

Quantifying Biofilm in Porous Media Using Rock Physics Models

NASA Astrophysics Data System (ADS)

Alhadhrami, F. M.; Jaiswal, P.; Atekwana, E. A.

2012-12-01

Biofilm formation and growth in porous rocks can change their material properties such as porosity, permeability which in turn will impact fluid flow. Finding a non-intrusive method to quantify biofilms and their byproducts in rocks is a key to understanding and modeling bioclogging in porous media. Previous geophysical investigations have documented that seismic techniques are sensitive to biofilm growth. These studies pointed to the fact that microbial growth and biofilm formation induces heterogeneity in the seismic properties. Currently there are no rock physics models to explain these observations and to provide quantitative interpretation of the seismic data. Our objectives are to develop a new class of rock physics model that incorporate microbial processes and their effect on seismic properties. Using the assumption that biofilms can grow within pore-spaces or as a layer coating the mineral grains, P-wave velocity (Vp) and S-wave (Vs) velocity models were constructed using travel-time and waveform tomography technique. We used generic rock physics schematics to represent our rock system numerically. We simulated the arrival times as well as waveforms by treating biofilms either as fluid (filling pore spaces) or as part of matrix (coating sand grains). The preliminary results showed that there is a 1% change in Vp and 3% change in Vs when biofilms are represented discrete structures in pore spaces. On the other hand, a 30% change in Vp and 100% change in Vs was observed when biofilm was represented as part of matrix coating sand grains. Therefore, Vp and Vs changes are more rapid when biofilm grows as grain-coating phase. The significant change in Vs associated with biofilms suggests that shear velocity can be used as a diagnostic tool for imaging zones of bioclogging in the subsurface. The results obtained from this study have significant implications for the study of the rheological properties of biofilms in geological media. Other applications include assessing biofilms used as barriers in CO2 sequestration studies as well as assisting in evaluating microbial enhanced oil recovery methods (MEOR), where microorganisms are used to plug highly porous rocks for efficient oil production.

Tomographic inversion of P-wave velocity and Q structures beneath the Kirishima volcanic complex, Southern Japan, based on finite difference calculations of complex traveltimes

USGS Publications Warehouse

Tomatsu, T.; Kumagai, H.; Dawson, P.B.

2001-01-01

We estimate the P-wave velocity and attenuation structures beneath the Kirishima volcanic complex, southern Japan, by inverting the complex traveltimes (arrival times and pulse widths) of waveform data obtained during an active seismic experiment conducted in 1994. In this experiment, six 200-250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex. We use first-arrival times for the shots, which were hand-measured interactively. The waveform data are Fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first-arrival phases. A non-linear inversion method is used to invert 893 first-arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex. Wavefronts for the inversion are calculated with a finite difference method based on the Eikonal equation, which is well suited to estimating the complex traveltimes for the structures of the Kirishima volcano complex, where large structural heterogeneities are expected. The attenuation structure is derived using ray paths derived from the velocity structure. We obtain 3-D velocity and attenuation structures down to 1.5 and 0.5 km below sea level, respectively. High-velocity pipe-like structures with correspondingly low attenuation are found under the summit craters. These pipe-like structures are interpreted as remnant conduits of solidified magma. No evidence of a shallow magma chamber is visible in the tomographic images.

Non-linear and plastic soil response from strong ground motion detected using the ambient seismic field

NASA Astrophysics Data System (ADS)

Viens, L.; Denolle, M.; Hirata, N.

2017-12-01

Strong ground motion can induce dynamic strains large enough for the shallow subsurface to respond non-linearly and cause permanent velocity changes during earthquakes. We investigate the behavior of the near-surface in the Tokyo metropolitan area during the 2011 Mw 9.0 Tohoku-Oki earthquake using continuous records from 234 seismometers of the Metropolitan Seismic Observation network (MeSO-net). This network, which was deployed in shallow 20-m depth boreholes, recorded horizontal accelerations up to 236 cm/s2 during the mainshock. For each MeSO-net station, we compute the near-surface response using the single-station cross-correlation technique between vertical and horizontal components, every 6 hours for 2.5 months around the main event. Comparing each near-surface response against the pre-event reference, we find seismic velocity drops up to 10% in the near-surface of the Tokyo metropolitan area during the mainshock. The amplitude of the coseismic velocity drop increases with increasing ground shaking and decreasing VS30, which is the S-wave velocity the first 30-m of the ground. Furthermore, the waveforms experience a loss of coherence that recovers exponentially over a time. This recovery rate also increases with the acceleration levels. While most of the velocity changes and waveform coherence recover within a few days, we also find permanent changes at stations that experienced liquefaction and the strongest ground motions. The ambient seismic field captures the coseismic velocity changes in the shallow structure and the following healing process, and may be used to detect permanent damage.

Pulse waveform analysis on temporal changes in ocular blood flow due to caffeine intake: a comparative study between habitual and non-habitual groups.

PubMed

Ismail, Aishah; Bhatti, Mehwish S; Faye, Ibrahima; Lu, Cheng Kai; Laude, Augustinus; Tang, Tong Boon

2018-06-06

To evaluate and compare the temporal changes in pulse waveform parameters of ocular blood flow (OBF) between non-habitual and habitual groups due to caffeine intake. This study was conducted on 19 healthy subjects (non-habitual 8; habitual 11), non-smoking and between 21 and 30 years of age. Using laser speckle flowgraphy (LSFG), three areas of optical nerve head were analyzed which are vessel, tissue, and overall, each with ten pulse waveform parameters, namely mean blur rate (MBR), fluctuation, skew, blowout score (BOS), blowout time (BOT), rising rate, falling rate, flow acceleration index (FAI), acceleration time index (ATI), and resistive index (RI). Two-way mixed ANOVA was used to determine the difference between every two groups where p < 0.05 is considered significant. There were significant differences between the two groups in several ocular pulse waveform parameters, namely MBR (overall, vessel, tissue), BOT (overall), rising rate (overall), and falling rate (vessel), all with p < 0.05. In addition, the ocular pulse waveform parameters, i.e., MBR (overall), skew (tissue), and BOT (tissue) showed significant temporal changes within the non-habitual group, but not within the habitual group. The temporal changes in parameters MBR (vessel, tissue), skew (overall, vessel), BOT (overall, vessel), rising rate (overall), falling rate (overall, vessel), and FAI (tissue) were significant for both groups (habitual and non-habitual) in response to caffeine intake. The experiment results demonstrated caffeine does modulate OBF significantly and response differently in non-habitual and habitual groups. Among all ten parameters, MBR and BOT were identified as the suitable biomarkers to differentiate between the two groups.

Investigating the Local Three-dimensional Velocity Structure of the 2008 Taoyuan Earthquake Sequence of Kaohsiung, Taiwan

NASA Astrophysics Data System (ADS)

Shih, M. H.; Huang, B. S.

2016-12-01

March 4, 2008, a moderate earthquake (ML 5.2) occurred in Taoyuan district of Kaohsiung County in the southern Taiwan. It was followed by numerous aftershocks in the following 48 hours, including three events with magnitude larger than 4. The Taoyuan earthquake sequence occurred during the TAIGER (Taiwan Integrated Geodynamic Research) project which is to image lithospheric structure of Taiwan orogeny. The high-resolution waveform data of this sequence were well-recorded by a large number of recording stations belong to several different permanent and TAIGER networks all around Taiwan. We had collected the waveform data and archived to a mega database. Then, we had identified 2,340 events from database in the preliminary locating process by using 1-D velocity model. In this study, we applied the double-difference tomography to investigate not only the fault geometry of the main shock but also the detailed 3-D velocity structure in this area. A total of 3,034 events were selected from preliminary locating result and CWBSN catalog in the vicinity. The resulting aftershocks are extended along the NE-SW direction and located on a 45° SE-dipping plane which agrees to one of the nodal planes of Global CMT solution (strike = 45°, dip = 40° and rake = 119°). We can identify a clear low-velocity area which is enclosed by events next to the main shock in the final 3D velocity model. We also recognized a 45°-dipping zone which is extended to the ground surface with low-velocity; meanwhile, velocity structure variation in study area correspond with major geologic units in Taiwan.

Matching the oculomotor drive during head-restrained and head-unrestrained gaze shifts in monkey.

PubMed

Bechara, Bernard P; Gandhi, Neeraj J

2010-08-01

High-frequency burst neurons in the pons provide the eye velocity command (equivalently, the primary oculomotor drive) to the abducens nucleus for generation of the horizontal component of both head-restrained (HR) and head-unrestrained (HU) gaze shifts. We sought to characterize how gaze and its eye-in-head component differ when an "identical" oculomotor drive is used to produce HR and HU movements. To address this objective, the activities of pontine burst neurons were recorded during horizontal HR and HU gaze shifts. The burst profile recorded on each HU trial was compared with the burst waveform of every HR trial obtained for the same neuron. The oculomotor drive was assumed to be comparable for the pair yielding the lowest root-mean-squared error. For matched pairs of HR and HU trials, the peak eye-in-head velocity was substantially smaller in the HU condition, and the reduction was usually greater than the peak head velocity of the HU trial. A time-varying attenuation index, defined as the difference in HR and HU eye velocity waveforms divided by head velocity [alpha = (H(hr) - E(hu))/H] was computed. The index was variable at the onset of the gaze shift, but it settled at values several times greater than 1. The index then decreased gradually during the movement and stabilized at 1 around the end of gaze shift. These results imply that substantial attenuation in eye velocity occurs, at least partially, downstream of the burst neurons. We speculate on the potential roles of burst-tonic neurons in the neural integrator and various cell types in the vestibular nuclei in mediating the attenuation in eye velocity in the presence of head movements.

Large-scale shear velocity structure of the upper mantle beneath Africa and surrounding regions

NASA Astrophysics Data System (ADS)

Legendre, Cédric; Meier, Thomas; Lebedev, Sergei; Friederich, Wolfgang; Egelados Working Group

2010-05-01

The automated multimode waveform inversion technique developed by Lebedev et al. (2005) was applied to available data of broadband stations in Africa and surrounding regions. It performs a fitting of the complete waveform starting from the S-wave onset to the surface wave. Assuming the location and focal mechanism of a considered earthquake as known, the first basic step is to consider each available seismogram separately and to find the velocity perturbations that can explain the filtered seismogram best. In a second step, each velocity perturbations serves as a linear constraint in an inversion for a 3D S-wave velocity model of the upper mantle. We collected data for the years from 1990 to 2006 from all permanent stations for which data were available via the data centers of ORFEUS, GEOFON and IRIS, and from others that build the Virtual European Seismological Network (VEBSN) as well as all available African stations. Just recently we were also able to add the data recorded by the temporary broadband EGELADOS network in the southern Aegean. This represents a huge dataset with all available stations in Africa and surroundings regions. The resulting models exhibit an overwhelming structural detail in relation to the size of the region considered in the inversion. They are to our knowledge the most detailed models of shear wave velocity currently available for the African upper mantle and surroundings. Most prominent features are an extremely sharp demarcation of the Dead Sea Rift System. Narrow high velocity regions follow the Hellenic arc and the Ionian trench toward the north. Low velocity zones are found at depths around 150 km in the Middle East region. The hotspots in North Africa are also clearly imaged.

Detailed seismic velocity of the incoming subducting sediments in the 2004 great Sumatra earthquake rupture zone from full waveform inversion of long offset seismic data

NASA Astrophysics Data System (ADS)

Qin, Yanfang; Singh, Satish C.

2017-04-01

The nature of incoming sediments defines the locking mechanism on the megathrust, and the development and evolution of the accretionary wedge. Here we present results from seismic full waveform inversion of 12 km long offset seismic reflection data within the trench in the 2004 Sumatra earthquake rupture zone area that provide detailed quantitative information on the incoming oceanic sediments and the trench-fill sediments. The thickness of sediments in this area is 3-4 km, and P wave velocity is as much as 4.5 km/s just above the oceanic crust, suggesting the presence of silica-rich highly compacted and lithified sediments leading to a strong coupling up to the subduction front. We also find an 70-80 m thick low-velocity layer, capped by a high-velocity layer, at 0.8 km above the subducting plate. This low-velocity layer, previously identified as high-amplitude negative polarity reflection, could have porosity of up to 30% containing overpressured fluids, which could act as a protodécollement seaward from the accretionary prism and décollement beneath the forearc. This weak protodécollement combined with the high-velocity indurated sediments above the basement possibly facilitated the rupture propagating up to the front during the 2004 earthquake and enhancing the tsunami. We also find another low-velocity layer within the sediments that may act as a secondary décollement observed offshore central Sumatra, forming bivergent pop-up structures and acting as a conveyer belt in preserving these pop-up structures in the forearc region.

High-resolution Imaging of the Philippine Sea Plate subducting beneath Central Japan

NASA Astrophysics Data System (ADS)

Padhy, S.; Furumura, T.

2016-12-01

Thermal models predict that the oceanic crust of the young (<20 Ma) and warmer Philippine-sea plate (PHP) is more prone to melting. Deriving a high-resolution image of the PHP, including slab melting and other features of the subduction zone, is a key to understand the basics of earthquake occurrence and origin of magma in complex subduction zone like central Japan, where both the PHP and Pacific (PAC) Plates subduct. To this purpose, we analyzed high-resolution waveforms of moderate sized (M 4-6), intermediate-to-deep (>150 km) PAC earthquakes occurring in central Japan and conducted numerical simulation to derive a fine-scale PHP model, which is not constrained in earlier studies. Observations show spindle-shaped seismograms with strong converted phases and extended coda with very slow decay from a group of PAC events occurring in northern part of central Japan and recorded by high-sensitivity seismograph network (Hi-net) stations in the region. We investigate the mechanism of propagation of these anomalous waveforms using the finite difference method (FDM) simulation of wave propagation through the subduction zone. We examine the effects on waveform changes of major subduction zone features, such as the melting of oceanic crust in PHP, serpentinized mantle wedge, hydrated layer on the PAC due to slab dehydration, and anomaly in upper mantle between the PAC and PHP. Simulation results show that the waveform anomaly is primarily explained by strong scattering and absorption of high-frequency energy by the low-velocity anomalous mantle structure, with a strong coda excitation yielding spindle-shaped waveforms. The data are secondarily explained by melting of PHP in the basaltic crust. The location of the mantle anomaly is tightly constrained by the observation and evidence of PAC thinning in the region; these localized low-velocity structures aid in ascending the slab-derived fluids around the slab thinning. We expect that the results of this study will enhance our present understanding on the mechanism of intermediate to deep earthquakes in the region.

Turbulence significantly increases pressure and fluid shear stress in an aortic aneurysm model under resting and exercise flow conditions.

PubMed

Khanafer, Khalil M; Bull, Joseph L; Upchurch, Gilbert R; Berguer, Ramon

2007-01-01

The numerical models of abdominal aortic aneurysm (AAA) in use do not take into account the non-Newtonian behavior of blood and the development of local turbulence. This study examines the influence of pulsatile, turbulent, non-Newtonian flow on fluid shear stresses and pressure changes under rest and exercise conditions. We numerically analyzed pulsatile turbulent flow, using simulated physiological rest and exercise waveforms, in axisymmetric-rigid aortic aneurysm models (AAMs). Discretization of governing equations was achieved using a finite element scheme. Maximum turbulence-induced shear stress was found at the distal end of an AAM. In large AAMs (dilated to undilated diameter ratio = 3.33) at peak systolic flow velocity, fluid shear stress during exercise is 70.4% higher than at rest. Our study provides a numerical, noninvasive method for obtaining detailed data on the forces generated by pulsatile turbulent flow in AAAs that are difficult to study in humans and in physical models. Our data suggest that increased flow turbulence results in increased shear stress in aneurysms. While pressure readings are fairly uniform along the length of an aneurysm, the kinetic energy generated by turbulence impacting on the wall of the distal half of the aneurysm increases fluid and wall shear stress at this site. If the increased fluid shear stress results in further dilation and hence further turbulence, wall stress may be a mechanism for aneurysmal growth and eventual rupture.

The effect of inlet waveforms on computational hemodynamics of patient-specific intracranial aneurysms.

PubMed

Xiang, J; Siddiqui, A H; Meng, H

2014-12-18

Due to the lack of patient-specific inlet flow waveform measurements, most computational fluid dynamics (CFD) simulations of intracranial aneurysms usually employ waveforms that are not patient-specific as inlet boundary conditions for the computational model. The current study examined how this assumption affects the predicted hemodynamics in patient-specific aneurysm geometries. We examined wall shear stress (WSS) and oscillatory shear index (OSI), the two most widely studied hemodynamic quantities that have been shown to predict aneurysm rupture, as well as maximal WSS (MWSS), energy loss (EL) and pressure loss coefficient (PLc). Sixteen pulsatile CFD simulations were carried out on four typical saccular aneurysms using 4 different waveforms and an identical inflow rate as inlet boundary conditions. Our results demonstrated that under the same mean inflow rate, different waveforms produced almost identical WSS distributions and WSS magnitudes, similar OSI distributions but drastically different OSI magnitudes. The OSI magnitude is correlated with the pulsatility index of the waveform. Furthermore, there is a linear relationship between aneurysm-averaged OSI values calculated from one waveform and those calculated from another waveform. In addition, different waveforms produced similar MWSS, EL and PLc in each aneurysm. In conclusion, inlet waveform has minimal effects on WSS, OSI distribution, MWSS, EL and PLc and a strong effect on OSI magnitude, but aneurysm-averaged OSI from different waveforms has a strong linear correlation with each other across different aneurysms, indicating that for the same aneurysm cohort, different waveforms can consistently stratify (rank) OSI of aneurysms. Copyright © 2014 Elsevier Ltd. All rights reserved.

Research on the photoelectric measuring method of warhead fragment velocity

NASA Astrophysics Data System (ADS)

Liu, Ji; Yu, Lixia; Zhang, Bin; Liu, Xiaoyan

2016-09-01

The velocity of warhead fragment is the key criteria to determine its mutilation efficiency. But owing to the small size, larger quantity, irregular shape, high speed, arbitrary direction, large dispersion of warhead fragment and adverse environment, the test of fragment velocity parameter is very difficult. The paper designed an optoelectronic system to measure the average velocity of warhead fragments accurately. The apparatus included two parallel laser screens spaced apart at a known fixed distance for providing time measurement between start and stop signals. The large effective screen area was composed of laser source, retro-reflector and large area photo-diode. Whenever a moving fragment interrupted two optical screens, the system would generate a target signal. Due to partial obscuration of the incident energy and the poor test condition of the explosion, fragment target signal is easily disturbed. Therefore, fragments signal processing technology has become a key technology of the system. The noise of signal was reduced by employing wavelet decomposition and reconstruction. The time of fragment passing though the target was obtained by adopting peak detection algorithm. Based on the method of search peak in different width scale and waveform trend by using optima wavelet, the problem of rolling waveform was solved. Lots of fragments experiments of the different types of the warheads were conducted. Experimental results show that: warhead fragments capture rate of system is better than 98%, which can give velocity of each fragment in the density of less than 20 pieces per m2.

Ultrasonic surface measurements at the Porta Nigra, Trier, and the Neptungrotte, Park Sanssouci Potsdam

NASA Astrophysics Data System (ADS)

Meier, Thomas; Auras, Michael; Fehr, Moritz; Köhn, Daniel

2015-04-01

Ultrasonic measurements along profiles at the surface of an object are well suited to characterize non-destructively weathering of natural stone near the surface. Ultrasonic waveforms of surface measurements in the frequency range between 10 kHz and 300 kHz are often dominated by the Rayleigh wave - a surface wave that is mainly sensitive to the velocity and attenuation of S-waves in the upper 0.3 cm to 3 cm. The frequency dependence of the Rayleigh wave velocity may be used to analyze variations of the material properties with depth. Applications of ultrasonic surface measurements are shown for two buildings: the Roman Porta Nigra in Trier from the 3rd century AD and the Neptungrotte at Park Sanssouci in Potsdam designed by von Knobelsdorff in the 18th century. Both buildings belong to the world cultural heritage and restorations are planned for the near future. It is interesting to compare measurements at these two buildings because they show the applicability of ultrasonic surface measurements to different natural stones. The Porta Nigra is made of local sandstones whereas the facades of the Neptungrotte are made of Carrara and Kauffunger marble. 71 and 46 surface measurements have been carried out, respectively. At both buildings, Rayleigh-wave group velocities show huge variations. At the Porta Nigra they vary between ca. 0.4 km/s and 1.8 km/s and at the Neptungrotte between ca. 0.7 km/s and 3.0 km/s pointing to alterations in the Rayleigh- and S-wave velocities of more than 50 % due to weathering. Note that velocities of elastic waves may increase e.g. because of the formation of black crusts like at the Porta Nigra or they may be strongly reduced due to weathering. The accuracy of the ultrasonic surface measurements, its reproducibility, and the influence of varying water saturation are discussed. Options for the analysis of ultrasonic waveforms are presented ranging from dispersion analysis to full waveform inversions for one-dimensional and two-dimensional models of the outermost layers of the object under investigation. Furthermore, results of non-destructive ultrasonic surface measurements are compared to results of destructive investigation techniques.

Depth-dependence of time-lapse seismic velocity change detected by a joint interferometric analysis of vertical array data

NASA Astrophysics Data System (ADS)

Sawazaki, K.; Saito, T.; Ueno, T.; Shiomi, K.

2015-12-01

In this study, utilizing depth-sensitivity of interferometric waveforms recorded by co-located Hi-net and KiK-net sensors, we separate the responsible depth of seismic velocity change associated with the M6.3 earthquake occurred on November 22, 2014, in central Japan. The Hi-net station N.MKGH is located about 20 km northeast from the epicenter, where the seismometer is installed at the 150 m depth. At the same site, the KiK-net has two strong motion seismometers installed at the depths of 0 and 150 m. To estimate average velocity change around the N.MKGH station, we apply the stretching technique to auto-correlation function (ACF) of ambient noise recorded by the Hi-net sensor. To evaluate sensitivity of the Hi-net ACF to velocity change above and below the 150 m depth, we perform a numerical wave propagation simulation using 2-D FDM. To obtain velocity change above the 150 m depth, we measure response waveform from the depths of 150 m to 0 m by computing deconvolution function (DCF) of earthquake records obtained by the two KiK-net vertical array sensors. The background annual velocity variation is subtracted from the detected velocity change. From the KiK-net DCF records, the velocity reduction ratio above the 150 m depth is estimated to be 4.2 % and 3.1 % in the periods of 1-7 days and 7 days - 4 months after the mainshock, respectively. From the Hi-net ACF records, the velocity reduction ratio is estimated to be 2.2 % and 1.8 % in the same time periods, respectively. This difference in the estimated velocity reduction ratio is attributed to depth-dependence of the velocity change. By using the depth sensitivity obtained from the numerical simulation, we estimate the velocity reduction ratio below the 150 m depth to be lower than 1.0 % for both time periods. Thus the significant velocity reduction and recovery are observed above the 150 m depth only, which may be caused by strong ground motion of the mainshock and following healing in the shallow ground.

Application of the Lienard-Wiechert solution to a lightning return stroke model

NASA Technical Reports Server (NTRS)

Meneghini, R.

1983-01-01

The electric and magnetic fields associated with the lightning return stroke are expressed as a convolution of the current waveform shape and the fields generated by a moving charge of amplitude one (i.e., the Lienard-Wiechert solution for a unit charge). The representation can be used to compute the fields produced by a current waveform of non-uniform velocity that propagates along a filament of arbitrary, but finite, curvature. To study numerically the effects of linear charge acceleration and channel curvature two simple channel models are used: the linear and the hyperbolic.

Application of the Lienard-Wiechert solution to a lightning return stroke model

NASA Technical Reports Server (NTRS)

Meneghini, R.

1984-01-01

The electric and magnetic fields associated with the lightning return stroke are expressed as a convolution of the current waveform shape and the fields generated by a moving charge of amplitude one (i.e., the Lienard-Wiechert solution for a unit charge). The representation can be used to compute the fields produced by a current waveform of non-uniform velocity that propagates along a filament of arbitrary, but finite, curvature. To study numerically the effects of linear charge acceleration and channel curvature two simple channel models are used: the linear and the hyperbolic.

Application of an iterative least-squares waveform inversion of strong-motion and teleseismic records to the 1978 Tabas, Iran, earthquake

USGS Publications Warehouse

Hartzell, S.; Mendoza, C.

1991-01-01

An iterative least-squares technique is used to simultaneously invert the strong-motion records and teleseismic P waveforms for the 1978 Tabas, Iran, earthquake to deduce the rupture history. The effects of using different data sets and different parametrizations of the problem (linear versus nonlinear) are considered. A consensus of all the inversion runs indicates a complex, multiple source for the Tabas earthquake, with four main source regions over a fault length of 90 km and an average rupture velocity of 2.5 km/sec. -from Authors

Comparison of five different defibrillators using recommended energy protocols.

PubMed

Zelinka, M; Buić, D; Zelinka, I

2007-09-01

Biphasic defibrillators represent a great step ahead in defibrillation. The manufacturers claim that biphasic defibrillators are able to compensate for differences in transthoracic impedance. That should mean that all patients should be defibrillated with approximately the same amount of current, regardless of their transthoracic impedance. We assessed one monophasic and four biphasic defibrillators. The defibrillators were discharged into resistive loads of 50, 90 and 130 Omega, simulating transthoracic impedance. For each waveform we used energy protocols recommended by the manufacturers and guidelines 2005. Waveforms were observed with on a digitising oscilloscope on a current sensing resistor. We compared the electrical properties of different waveforms and two defibrillators with the same type of waveform. The influence of different impedance on shape, duration and amplitude of current flow were also observed for each waveform. Measurements showed a significant difference in current flow at different impedance loads. At low impedance the mean current is well above expectations for all the defibrillators studied and at high impedance load we observed a big reduction of current amplitude. We can conclude that the compensating mechanisms of biphasic defibrillators are, from electrical point of view, negligible. From the laws of physics it is practically impossible to keep same level of current at given time with same energy at higher impedance. That is why we should reconsider the use of different energy equivalents between patients with different transthoracic impedance and not between different defibrillation impulses.

Normal-mode and free-Air gravity constraints on lateral variations in velocity and density of Earth's mantle

PubMed

Ishii; Tromp

1999-08-20

With the use of a large collection of free-oscillation data and additional constraints imposed by the free-air gravity anomaly, lateral variations in shear velocity, compressional velocity, and density within the mantle; dynamic topography on the free surface; and topography on the 660-km discontinuity and the core-mantle boundary were determined. The velocity models are consistent with existing models based on travel-time and waveform inversions. In the lowermost mantle, near the core-mantle boundary, denser than average material is found beneath regions of upwellings centered on the Pacific Ocean and Africa that are characterized by slow shear velocities. These anomalies suggest the existence of compositional heterogeneity near the core-mantle boundary.

Seismic Structure of India from Regional Waveform Matching

NASA Astrophysics Data System (ADS)

Gaur, V.; Maggi, A.; Priestley, K.; Rai, S.

2003-12-01

We use a neighborhood adaptive grid search procedure and reflectivity synthetics to model regional distance range (500-2000~km) seismograms recorded in India and to determine the variation in the crust and uppermost mantle structure across the subcontinent. The portions of the regional waveform which are most influenced by the crust and uppermost mantle structure are the 10-100~s period Pnl and fundamental mode surface waves. We use the adaptive grid search algorithm to match both portions of the seismogram simultaneously. This procedure results in a family of 1-D path average crust and upper mantle velocity and attenuation models whose propagation characteristics closely match those of the real Earth. Our data set currently consist of ˜20 seismograms whose propagation paths are primarily confined to the Ganges Basin in north India and the East Dharwar Craton of south India. The East Dharwar Craton has a simple and uniform structure consisting of a 36+/-2 km thick two layer crust, and an uppermost mantle with a sub-Moho velocity of 4.5~km/s. The structure of northern India is more complicated, with pronounced low velocities in the upper crustal layer due to the large sediment thicknesses in the Ganges basin.

Anisotropic Rayleigh-wave Phase-velocity Maps in Northern Vietnam

NASA Astrophysics Data System (ADS)

Zhao, L.; Legendre, C. P.; Huang, W.; Huang, B.

2013-12-01

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.

Design and operation of a bio-inspired micropump based on blood-sucking mechanism of mosquitoes

NASA Astrophysics Data System (ADS)

Leu, Tzong-Shyng; Kao, Ruei-Hung

2018-05-01

The study is to develop a novel bionic micropump, mimicking blood-suck mechanism of mosquitos with a similar efficiency of 36%. The micropump is produced by using micro-electro-mechanical system (MEMS) technology, PDMS (polydimethylsiloxane) to fabricate the microchannel, and an actuator membrane made by Fe-PDMS. It employs an Nd-FeB permanent magnet and PZT to actuate the Fe-PDMS membrane for generating flow rate. A lumped model theory and the Taguchi method are used for numerical simulation of pulsating flow in the micropump. Also focused is to change the size of mosquito mouth for identifying the best waveform for the transient flow processes. Based on computational results of channel size and the Taguchi method, an optimization actuation waveform is identified. The maximum pumping flow rate is 23.5 μL/min and the efficiency is 86%. The power density of micropump is about 8 times of that produced by mosquito’s suction. In addition to using theoretical design of the channel size, also combine with Taguchi method and asymmetric actuation to find the optimization actuation waveform, the experimental result shows the maximum pumping flowrate is 23.5 μL/min and efficiency is 86%, moreover, the power density of micropump is 8 times higher than mosquito’s.

Infrasound reveals transition to oscillatory discharge regime during lava fountaining: Implication for early warning

NASA Astrophysics Data System (ADS)

Ulivieri, Giacomo; Ripepe, Maurizio; Marchetti, Emanuele

2013-06-01

present the analysis of ~4 million infrasonic signals which include 39 episodes of lava fountains recorded at 5.5 km from the active vents. We show that each eruptive episode is characterized by a distinctive trend in the amplitude, waveform, and frequency content of the acoustic signals, reflecting different explosive levels. Lava fountain starts with an ~93 min long violent phase of acoustic transients at ~1.25 Hz repeating every 2-5 s. Infrasound suddenly evolves into a persistent low-frequency quasi-monochromatic pressure oscillation at ~0.4 Hz. We interpret this shift as induced by the transition from the slug (discrete Strombolian) to churn flow (sustained lava fountain) regime that is reflecting an increase in the gas discharge rate. We calculate that infrasonic transition can occur at a gas superficial velocity of ≤76 m/s and it can be used to define infrasonic-based thresholds for an efficient early warning system.

Harmony Behind the Trumped-Shaped Vessel: the Essential Role of the Ductus Venosus in Fetal Medicine.

PubMed

Turan, Sifa; Turan, Ozhan M

2018-03-15

The ductus venosus is a fetal vessel that functions importantly in the transfer of oxygen-and nutrient-rich blood from the umbilical vein to vital organs. Its control under active regulation and its anatomy result in a flow-velocity profile that is typically forward throughout the cardiac cycle. This forward cardiac function reflects afterload, cardiac contractility, compliance, and vascular volume changes. Ductus venosus assessment gives valuable information under different fetal conditions. For example, during first trimester screening, an abnormal ductus venosus measurement changes the screening result. Assessment of ductus venosus in twin-to-twin transfusion syndrome is an essential element of staging. In fetal growth restriction, an abnormal waveform mandates imminent delivery. In this review, we will discuss the role of ductus venosus assessment and its role in antenatal management and outcome prediction in certain fetal conditions throughout pregnancy.

The Lethality Test System

NASA Astrophysics Data System (ADS)

Parsons, W. M.; Sims, J. R.; Parker, J. V.

1986-11-01

The Lethality Test System (LTS) under construction at Los Alamos is an electromagnetic launcher facility designed to perform impact experiments at velocities up to 15 km/sec. The launcher is a 25 mm round bore, plasma armature railgun 22 m in length. Preinjection is accomplished with a two-stage light gas gun capable of 7 km/sec. The railgun power supply utilizes traction motors, vacuum interrupters, and pulse transformers. An assembly of 28 traction motors, equipped with flywheels, stores approximately 80 MJ at 92 percent of full speed and energizes the primary windings of three pulse transformers at a current of 50 kA. At peak current an array of vacuum interrupters disconnects the transformer primary windings and forces the current to flow in the secondary windings. The secondary windings are connected to the railgun, and by staging the vacuum interrupter openings, a 1-1.3 MA ramped current waveform will be delivered to the railgun.

Harmony Behind the Trumped-Shaped Vessel: the Essential Role of the Ductus Venosus in Fetal Medicine

PubMed Central

Turan, Sifa; Turan, Ozhan M.

2018-01-01

The ductus venosus is a fetal vessel that functions importantly in the transfer of oxygen-and nutrient-rich blood from the umbilical vein to vital organs. Its control under active regulation and its anatomy result in a flow-velocity profile that is typically forward throughout the cardiac cycle. This forward cardiac function reflects afterload, cardiac contractility, compliance, and vascular volume changes. Ductus venosus assessment gives valuable information under different fetal conditions. For example, during first trimester screening, an abnormal ductus venosus measurement changes the screening result. Assessment of ductus venosus in twin-to-twin transfusion syndrome is an essential element of staging. In fetal growth restriction, an abnormal waveform mandates imminent delivery. In this review, we will discuss the role of ductus venosus assessment and its role in antenatal management and outcome prediction in certain fetal conditions throughout pregnancy. PMID:29553462

Control volume based hydrocephalus research; analysis of human data

NASA Astrophysics Data System (ADS)

Cohen, Benjamin; Wei, Timothy; Voorhees, Abram; Madsen, Joseph; Anor, Tomer

2010-11-01

Hydrocephalus is a neuropathophysiological disorder primarily diagnosed by increased cerebrospinal fluid volume and pressure within the brain. To date, utilization of clinical measurements have been limited to understanding of the relative amplitude and timing of flow, volume and pressure waveforms; qualitative approaches without a clear framework for meaningful quantitative comparison. Pressure volume models and electric circuit analogs enforce volume conservation principles in terms of pressure. Control volume analysis, through the integral mass and momentum conservation equations, ensures that pressure and volume are accounted for using first principles fluid physics. This approach is able to directly incorporate the diverse measurements obtained by clinicians into a simple, direct and robust mechanics based framework. Clinical data obtained for analysis are discussed along with data processing techniques used to extract terms in the conservation equation. Control volume analysis provides a non-invasive, physics-based approach to extracting pressure information from magnetic resonance velocity data that cannot be measured directly by pressure instrumentation.

Shear wave transducer for boreholes

DOEpatents

Mao, N.H.

1984-08-23

A technique and apparatus is provided for estimating in situ stresses by measuring stress-induced velocity anisotropy around a borehole. Two sets each of radially and tangentially polarized transducers are placed inside the hole with displacement directions either parallel or perpendicular to the principal stress directions. With this configuration, relative travel times are measured by both a pulsed phase-locked loop technique and a cross correlation of digitized waveforms. The biaxial velocity data are used to back-calculate the applied stress.

Shear wave transducer for stress measurements in boreholes

DOEpatents

Mao, Nai-Hsien

1987-01-01

A technique and apparatus for estimating in situ stresses by measuring stress-induced velocity anisotropy around a borehole. Two sets each of radially and tangentially polarized transducers are placed inside the hole with displacement directions either parallel or perpendicular to the principal stress directions. With this configuration, relative travel times are measured by both a pulsed phase-locked loop technique and a cross correlation of digitized waveforms. The biaxial velocity data is used to back-calculate the applied stress.

Comparison of Velocity Models for South America through Seismic Wave Modeling of Ten Andean Earthquakes Recorded by the Brazilian Seismographic Network using the Spectral Element Method

NASA Astrophysics Data System (ADS)

Ciardelli, C.; Assumpcao, M.

2016-12-01

In this work, we carried out simulations of seismic waves propagation for ten large earthquakes occurred in Chile between 2011 and 2016,using the SPECFEM3D Global software (Komatitsch and Tromp, 2000) and the Centroid Moment Tensor solutions from the global catalog (Dziewonski, Chou and Woodhouse, 1981; Ekström, Nettles and Dziewonski, 2012). For each event, the complete wave field was calculated using the spectral element method and recorded at the coordinates of the Brazilian Seismographic Network, thus we can compare the synthetic seismograms with the real data. Initially, we assess the differences between CRUST1.0 and CRUST2.0 models using the transversely isotropic PREM for the internal part of the planet. We will also compare the PREM velocity model plus CRUST1.0 with the Feng's velocity model for South America (Feng, Van der Lee and Assumpção, 2007), calculated using Partitioned Waveform Inversion. For each model, we will evaluate the misfit for all stations of the network. The similarity can be estimated by pure RMS or combining it with cross-correlation. Travel-time residuals can also be used to better constrain velocity anomalies and avoid cycle-skipping. The results will help to assess which model is more appropriated to start a Full-waveform Tomography of the South American continent and the surrounding oceans.

Effect of the α(2)-adrenoceptor antagonist yohimbine on vascular regulation of the middle cerebral artery and the ophthalmic artery in healthy subjects.

PubMed

Kaya, S; Kolodjaschna, J; Berisha, F; Polska, E; Pemp, B; Garhöfer, G; Schmetterer, L

2011-01-01

There is evidence that vascular beds distal to the ophthalmic artery (OA) show vasoconstriction in response to a step decrease in systemic blood pressure (BP). The mediators of this response are mostly unidentified. The aim of the current study was to test the hypothesis that α2-adrenoreceptors may contribute to the regulatory process in response to a decrease in BP. In this randomized, double-masked, placebo-controlled study 14 healthy male volunteers received either 22mg yohimbine hydrochloride or placebo. Beat-to-beat BP was measured by analysis of arterial pressure waveform; blood flow velocities in the middle cerebral artery (MCA) and the OA were measured with Doppler ultrasound. Measurements were done before, during and after a step decrease in BP. The step decrease in BP was induced by bilateral thigh cuffs at a suprasystolic pressure followed by a rapid cuff deflation. After cuff deflation, BP returned to baseline after 7-8 pulse cycles (PC). Blood velocities in the MCA returned to baseline earlier (4 PC) than BP indicating peripheral vasodilatation. Blood velocities in the OA returned to baseline later (15-20 PC) indicating peripheral vasoconstriction. Yohimbine did not affect the blood velocity response in the MCA, but significantly shortened the time of OA blood velocities to return to baseline values (6-7 PC, p<0.05). In conclusion, our results indicate that yohimbine did not alter the regulatory response in the MCA, but modified the response of vascular beds distal to the OA. This suggests that α2-adrenoceptors play a role in the vasoconstrictor response of the vasculatures distal to the OA. 2010 Elsevier Inc. All rights reserved.

Seismic Velocity Assessment In The Kachchh Region, India, From Multiple Waveform Functionals

NASA Astrophysics Data System (ADS)

Ghosh, R.; Sen, M. K.; Mandal, P.; Pulliam, J.; Agrawal, M.

2014-12-01

The primary goal of this study is to estimate well constrained crust and upper mantle seismic velocity structure in the Kachchh region of Gujarat, India - an area of active interest for earthquake monitoring purposes. Several models based on 'stand-alone' surface wave dispersion and receiver function modeling exist in this area. Here we jointly model the receiver function, surface wave dispersion and, S and shear-coupled PL wavetrains using broadband seismograms of deep (150-700 km), moderate to-large magnitude (5.5-6.8) earthquakes recorded teleseismically at semi-permanent seismograph stations in the Kachchh region, Gujarat, India. While surface wave dispersion and receiver function modeling is computationally fast, full waveform modeling makes use of reflectivity synthetic seismograms. An objective function that measures misfit between all three data is minimized using a very fast simulated annealing (VFSA) approach. Surface wave and receiver function data help reduce the model search space which is explored extensively for detailed waveform fitting. Our estimated crustal and lithospheric thicknesses in this region vary from 32 to 41 km and 70 to 80 km, respectively, while crustal P and S velocities from surface to Moho discontinuity vary from 4.7 to 7.0 km/s and 2.7 to 4.1 km/s, respectively. Our modeling clearly reveals a zone of crustal as well as an asthenospheric upwarping underlying the Kachchh rift zone relative to the surrounding unrifted area. We believe that this feature plays a key role in the seismogenesis of lower crustal earthquakes occurring in the region through the emanation of volatile CO2 into the hypocentral zones liberating from the crystallization of carbonatite melts in the asthenosphere. Such a crust-mantle structure might be related to the plume-lithosphere interaction during the Deccan/Reunion plume episode (~65 Ma).

Improving waveform inversion using modified interferometric imaging condition

NASA Astrophysics Data System (ADS)

Guo, Xuebao; Liu, Hong; Shi, Ying; Wang, Weihong; Zhang, Zhen

2017-12-01

Similar to the reverse-time migration, full waveform inversion in the time domain is a memory-intensive processing method. The computational storage size for waveform inversion mainly depends on the model size and time recording length. In general, 3D and 4D data volumes need to be saved for 2D and 3D waveform inversion gradient calculations, respectively. Even the boundary region wavefield-saving strategy creates a huge storage demand. Using the last two slices of the wavefield to reconstruct wavefields at other moments through the random boundary, avoids the need to store a large number of wavefields; however, traditional random boundary method is less effective at low frequencies. In this study, we follow a new random boundary designed to regenerate random velocity anomalies in the boundary region for each shot of each iteration. The results obtained using the random boundary condition in less illuminated areas are more seriously affected by random scattering than other areas due to the lack of coverage. In this paper, we have replaced direct correlation for computing the waveform inversion gradient by modified interferometric imaging, which enhances the continuity of the imaging path and reduces noise interference. The new imaging condition is a weighted average of extended imaging gathers can be directly used in the gradient computation. In this process, we have not changed the objective function, and the role of the imaging condition is similar to regularization. The window size for the modified interferometric imaging condition-based waveform inversion plays an important role in this process. The numerical examples show that the proposed method significantly enhances waveform inversion performance.

Improving waveform inversion using modified interferometric imaging condition

NASA Astrophysics Data System (ADS)

Guo, Xuebao; Liu, Hong; Shi, Ying; Wang, Weihong; Zhang, Zhen

2018-02-01

Similar to the reverse-time migration, full waveform inversion in the time domain is a memory-intensive processing method. The computational storage size for waveform inversion mainly depends on the model size and time recording length. In general, 3D and 4D data volumes need to be saved for 2D and 3D waveform inversion gradient calculations, respectively. Even the boundary region wavefield-saving strategy creates a huge storage demand. Using the last two slices of the wavefield to reconstruct wavefields at other moments through the random boundary, avoids the need to store a large number of wavefields; however, traditional random boundary method is less effective at low frequencies. In this study, we follow a new random boundary designed to regenerate random velocity anomalies in the boundary region for each shot of each iteration. The results obtained using the random boundary condition in less illuminated areas are more seriously affected by random scattering than other areas due to the lack of coverage. In this paper, we have replaced direct correlation for computing the waveform inversion gradient by modified interferometric imaging, which enhances the continuity of the imaging path and reduces noise interference. The new imaging condition is a weighted average of extended imaging gathers can be directly used in the gradient computation. In this process, we have not changed the objective function, and the role of the imaging condition is similar to regularization. The window size for the modified interferometric imaging condition-based waveform inversion plays an important role in this process. The numerical examples show that the proposed method significantly enhances waveform inversion performance.

Frequency Domain Full-Waveform Inversion in Imaging Thrust Related Features

NASA Astrophysics Data System (ADS)

Jaiswal, P.; Zelt, C. A.

2010-12-01

Seismic acquisition in rough terrain such as mountain belts suffers from problems related to near-surface conditions such as statics, inconsistent energy penetration, rapid decay of signal, and imperfect receiver coupling. Moreover in the presence of weakly compacted soil, strong ground roll may obscure the reflection arrivals at near offsets further diminishing the scope of estimating a reliable near surface image though conventional processing. Traveltime and waveform inversion not only overcome the simplistic assumptions inherent in conventional processing such as hyperbolic moveout and convolution model, but also use parts of the seismic coda, such as the direct arrival and refractions, that are discarded in the latter. Traveltime and waveform inversion are model-based methods that honour the physics of wave propagation. Given the right set of preconditioned data and starting model, waveform inversion in particular has been realized as a powerful tool for velocity model building. This paper examines two case studies on waveform inversion using real data from the Naga Thrust Belt in the Northeast India. Waveform inversion in this paper is performed in the frequency domain and is multiscale in nature i.e., the inversion progressively ascends from the lower to the higher end of the frequency spectra increasing the wavenumber content of the recovered model. Since the real data are band limited, the success of waveform inversion depends on how well the starting model can account for the missing low wavenumbers. In this paper it is observed that the required starting model can be prepared using the regularized inversion of direct and reflected arrival times.

Platform for Postprocessing Waveform-Based NDE

NASA Technical Reports Server (NTRS)

Roth, Don

2008-01-01

Taking advantage of the similarities that exist among all waveform-based non-destructive evaluation (NDE) methods, a common software platform has been developed containing multiple- signal and image-processing techniques for waveforms and images. The NASA NDE Signal and Image Processing software has been developed using the latest versions of LabVIEW, and its associated Advanced Signal Processing and Vision Toolkits. The software is useable on a PC with Windows XP and Windows Vista. The software has been designed with a commercial grade interface in which two main windows, Waveform Window and Image Window, are displayed if the user chooses a waveform file to display. Within these two main windows, most actions are chosen through logically conceived run-time menus. The Waveform Window has plots for both the raw time-domain waves and their frequency- domain transformations (fast Fourier transform and power spectral density). The Image Window shows the C-scan image formed from information of the time-domain waveform (such as peak amplitude) or its frequency-domain transformation at each scan location. The user also has the ability to open an image, or series of images, or a simple set of X-Y paired data set in text format. Each of the Waveform and Image Windows contains menus from which to perform many user actions. An option exists to use raw waves obtained directly from scan, or waves after deconvolution if system wave response is provided. Two types of deconvolution, time-based subtraction or inverse-filter, can be performed to arrive at a deconvolved wave set. Additionally, the menu on the Waveform Window allows preprocessing of waveforms prior to image formation, scaling and display of waveforms, formation of different types of images (including non-standard types such as velocity), gating of portions of waves prior to image formation, and several other miscellaneous and specialized operations. The menu available on the Image Window allows many further image processing and analysis operations, some of which are found in commercially-available image-processing software programs (such as Adobe Photoshop), and some that are not (removing outliers, Bscan information, region-of-interest analysis, line profiles, and precision feature measurements).

Detection of sinkholes or anomalies using full seismic wave fields : phase II.

DOT National Transportation Integrated Search

2016-08-01

A new 2-D Full Waveform Inversion (FWI) software code was developed to characterize layering and anomalies beneath the ground surface using seismic testing. The software is capable of assessing the shear and compression wave velocities (Vs and Vp) fo...

Surface Wave Tomography across the Alpine-Mediterranean Mobile Belt

NASA Astrophysics Data System (ADS)

El-Sharkawy, A. M. M. E.; Meier, T. M.; Lebedev, S.; Weidle, C.; Cristiano, L.

2017-12-01

The Alpine-Mediterranean mobile belt is, tectonically, one of the most complicated and active regions in the world. Since the Mesozoic, collisions between Gondwana-derived continental blocks and Eurasia, due to the closure of a number of rather small ocean basins, have shaped the Mediterranean geology. Despite the numerous studies that have attempted to characterize the lithosphere-asthenosphere structure in that area, details of the lithospheric structure and dynamics, as well as flow in the asthenosphere are, however, poorly known. The purpose of this study is to better define the 3D shear-wave velocity structure of the lithosphere-asthenosphere system in the Mediterranean using new tomographic images obtained from surface wave tomography. An automated algorithm for inter-station phase velocity measurements is applied here to obtain Rayleigh fundamental mode phase velocities. We utilize a database consisting of more than 4000 seismic events recorded by more than 3000 broadband seismic stations within the area (WebDc/EIDA, IRIS). Moreover, for the first time, data from the Egyptian National Seismological Network (ENSN), recorded by up to 25 broad band seismic stations, are also included in the analysis. For each station pair, approximately located on the same great circle path, the recorded waveforms are cross correlated and the dispersion curves of fundamental modes are calculated from the phase of the cross correlation functions weighted in the time-frequency plane. Path average dispersion curves are obtained by averaging the smooth parts of single-event dispersion curves. We calculate maps of Rayleigh phase velocity at more than 100 different periods. The phase-velocity maps provide the local phase-velocity dispersion curve for each geographical grid node of the map. Each of these local dispersion curves is inverted individually for 1D shear wave velocity model using a newly implemented Particle Swarm Optimization (PSO) algorithm. The resulted 1D velocity models are then combined to construct the 3D shear-velocity model. Horizontal and vertical slices through the 3D isotropic model reveal significant variations in shear wave velocity with depth, and lateral changes in the crust and upper mantle structure emphasizing the processes associated with the convergence of the Eurasian and African plates

Permittivity and conductivity parameter estimations using full waveform inversion

NASA Astrophysics Data System (ADS)

Serrano, Jheyston O.; Ramirez, Ana B.; Abreo, Sergio A.; Sadler, Brian M.

2018-04-01

Full waveform inversion of Ground Penetrating Radar (GPR) data is a promising strategy to estimate quantitative characteristics of the subsurface such as permittivity and conductivity. In this paper, we propose a methodology that uses Full Waveform Inversion (FWI) in time domain of 2D GPR data to obtain highly resolved images of the permittivity and conductivity parameters of the subsurface. FWI is an iterative method that requires a cost function to measure the misfit between observed and modeled data, a wave propagator to compute the modeled data and an initial velocity model that is updated at each iteration until an acceptable decrease of the cost function is reached. The use of FWI with GPR are expensive computationally because it is based on the computation of the electromagnetic full wave propagation. Also, the commercially available acquisition systems use only one transmitter and one receiver antenna at zero offset, requiring a large number of shots to scan a single line.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yu; Gao, Kai; Huang, Lianjie

Accurate imaging and characterization of fracture zones is crucial for geothermal energy exploration. Aligned fractures within fracture zones behave as anisotropic media for seismic-wave propagation. The anisotropic properties in fracture zones introduce extra difficulties for seismic imaging and waveform inversion. We have recently developed a new anisotropic elastic-waveform inversion method using a modified total-variation regularization scheme and a wave-energy-base preconditioning technique. Our new inversion method uses the parameterization of elasticity constants to describe anisotropic media, and hence it can properly handle arbitrary anisotropy. We apply our new inversion method to a seismic velocity model along a 2D-line seismic data acquiredmore » at Eleven-Mile Canyon located at the Southern Dixie Valley in Nevada for geothermal energy exploration. Our inversion results show that anisotropic elastic-waveform inversion has potential to reconstruct subsurface anisotropic elastic parameters for imaging and characterization of fracture zones.« less

Constant flow-driven microfluidic oscillator for different duty cycles

PubMed Central

Kim, Sung-Jin; Yokokawa, Ryuji; Lesher-Perez, Sasha Cai; Takayama, Shuichi

2012-01-01

This paper presents microfluidic devices that autonomously convert two constant flow inputs into an alternating oscillatory flow output. We accomplish this hardware embedded self-control programming using normally closed membrane valves that have an inlet, an outlet, and a membrane-pressurization chamber connected to a third terminal. Adjustment of threshold opening pressures in these 3-terminal flow switching valves enabled adjustment of oscillation periods to between 57–360 s with duty cycles of 0.2–0.5. These values are in relatively good agreement with theoretical values, providing the way for rational design of an even wider range of different waveform oscillations. We also demonstrate the ability to use these oscillators to perform temporally patterned delivery of chemicals to living cells. The device only needs a syringe pump, thus removing the use of complex, expensive external actuators. These tunable waveform microfluidic oscillators are envisioned to facilitate cell-based studies that require temporal stimulation. PMID:22206453

Evolution of the lithosphere in the Indian Ocean from combined earthquake and ambient noise tomography

NASA Astrophysics Data System (ADS)

Ma, Zhitu; Dalton, Colleen A.

2017-01-01

Rayleigh wave dispersion extracted from ambient seismic noise has been widely used to image crustal and uppermost mantle structure. Applications of this approach in continental settings are abundant, but there have been relatively few studies within ocean basins. By cross-correlating ambient noise recorded at broadband seismic stations around the Indian Ocean, we demonstrate the feasibility of extracting high-quality, long-period (10-30 mHz) Rayleigh waves that traverse the entire ocean basin. High-quality Rayleigh wave cross-correlation functions can be obtained from stacking waveforms over less than 2 years at land stations and less than 4 years at island stations. We show that adding the dispersion information extracted from ambient noise to a global earthquake data set can improve the resolution of phase velocity maps by about 20% in the northern Indian Ocean, where the station distribution is the best. We find that a plate cooling model with a potential temperature of 1450°C and plate thickness of 125 km can fit both the seismic observations and seafloor topography. The Seychelles-Mascarene Plateau is characterized by anomalously slow velocity at 30 mHz. The inclusion of ambient noise data in the tomographic inversion shifts the slow velocity anomaly into better agreement with the topographic relief, allowing us to estimate its crustal thickness and confirm that the plateau's elevation is supported by thick crust. The 10 and 20 mHz phase velocity maps show a strong asymmetry across the Central Indian Ridge that is best explained by eastward asthenospheric flow emanating from nearby hot spots.

Phase Velocity and Full-Waveform Analysis of Co-located Distributed Acoustic Sensing (DAS) Channels and Geophone Sensor

NASA Astrophysics Data System (ADS)

Parker, L.; Mellors, R. J.; Thurber, C. H.; Wang, H. F.; Zeng, X.

2015-12-01

A 762-meter Distributed Acoustic Sensing (DAS) array with a channel spacing of one meter was deployed at the Garner Valley Downhole Array in Southern California. The array was approximately rectangular with dimensions of 180 meters by 80 meters. The array also included two subdiagonals within the rectangle along which three-component geophones were co-located. Several active sources were deployed, including a 45-kN, swept-frequency, shear-mass shaker, which produced strong Rayleigh waves across the array. Both DAS and geophone traces were filtered in 2-Hz steps between 4 and 20 Hz to obtain phase velocities as a function of frequency from fitting the moveout of travel times over distances of 35 meters or longer. As an alternative to this traditional means of finding phase velocity, it is theoretically possible to find the Rayleigh-wave phase velocity at each point of co-location as the ratio of DAS and geophone responses, because DAS is sensitive to ground strain and geophones are sensitive to ground velocity, after suitable corrections for instrument response (Mikumo & Aki, 1964). The concept was tested in WPP, a seismic wave propagation program, by first validating and then using a 3D synthetic, full-waveform seismic model to simulate the effect of increased levels of noise and uncertainty as data go from ideal to more realistic. The results obtained from this study provide a better understanding of the DAS response and its potential for being combined with traditional seismometers for obtaining phase velocity at a single location. This analysis is part of the PoroTomo project (Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology, http://geoscience.wisc.edu/feigl/porotomo).

Near surface velocity and Q S structure of the Quaternary sediment in Bohai basin, China

NASA Astrophysics Data System (ADS)

Chong, Jiajun; Ni, Sidao

2009-10-01

Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation ( Q P and Q S) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1-10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0-500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 M W4.9 Wen’an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average ν P and ν S of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high ν P/ ν S ratio of 4.3. We also modeled surface reflected wave with propagating matrix method to constrain Q S and the near surface velocity structure. Our modeling indicates that Q S is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q (˜10), but consistent with Q S modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0-50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation.

Arduino control of a pulsatile flow rig.

PubMed

Drost, S; de Kruif, B J; Newport, D

2018-01-01

This note describes the design and testing of a programmable pulsatile flow pump using an Arduino micro-controller. The goal of this work is to build a compact and affordable system that can relatively easily be programmed to generate physiological waveforms. The system described here was designed to be used in an in-vitro set-up for vascular access hemodynamics research, and hence incorporates a gear pump that delivers a mean flow of 900 ml/min in a test flow loop, and a peak flow of 1106 ml/min. After a number of simple identification experiments to assess the dynamic behaviour of the system, a feed-forward control routine was implemented. The resulting system was shown to be able to produce the targeted representative waveform with less than 3.6% error. Finally, we outline how to further increase the accuracy of the system, and how to adapt it to specific user needs. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

Change in Coronary Blood Flow After Percutaneous Coronary Intervention in Relation to Baseline Lesion Physiology Results of the JUSTIFY-PCI Study

PubMed Central

Nijjer, Sukhjinder S.; Petraco, Ricardo; van de Hoef, Tim P.; Sen, Sayan; van Lavieren, Martijn A.; Foale, Rodney A.; Meuwissen, Martijn; Broyd, Christopher; Echavarria-Pinto, Mauro; Al-Lamee, Rasha; Foin, Nicolas; Sethi, Amarjit; Malik, Iqbal S.; Mikhail, Ghada W.; Hughes, Alun D.; Mayet, Jamil; Francis, Darrel P.; Di Mario, Carlo; Escaned, Javier; Piek, Jan J.; Davies, Justin E.

2016-01-01

Background Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters. Methods and Results Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (P<0.001). In significant stenoses, flow velocity over the resting wave-free period and hyperemic flow velocity did not differ statistically. After PCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P<0.01). The greatest increase in hyperemic flow velocity was observed when treating stenoses below physiological cut points; treating stenoses with fractional flow reserve ≤0.80 gained Δ28.5±3.8 cm/s, whereas those fractional flow reserve >0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; P<0.001). The change in pressure-only physiological indices demonstrated a curvilinear relationship to the change in hyperemic flow velocity but was flat for resting flow velocity. Conclusions Pre-PCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI. PMID:26025217

Change in coronary blood flow after percutaneous coronary intervention in relation to baseline lesion physiology: results of the JUSTIFY-PCI study.

PubMed

Nijjer, Sukhjinder S; Petraco, Ricardo; van de Hoef, Tim P; Sen, Sayan; van Lavieren, Martijn A; Foale, Rodney A; Meuwissen, Martijn; Broyd, Christopher; Echavarria-Pinto, Mauro; Al-Lamee, Rasha; Foin, Nicolas; Sethi, Amarjit; Malik, Iqbal S; Mikhail, Ghada W; Hughes, Alun D; Mayet, Jamil; Francis, Darrel P; Di Mario, Carlo; Escaned, Javier; Piek, Jan J; Davies, Justin E

2015-06-01

Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters. Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (P<0.001). In significant stenoses, flow velocity over the resting wave-free period and hyperemic flow velocity did not differ statistically. After PCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P<0.01). The greatest increase in hyperemic flow velocity was observed when treating stenoses below physiological cut points; treating stenoses with fractional flow reserve ≤0.80 gained Δ28.5±3.8 cm/s, whereas those fractional flow reserve >0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; P<0.001). The change in pressure-only physiological indices demonstrated a curvilinear relationship to the change in hyperemic flow velocity but was flat for resting flow velocity. Pre-PCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI. © 2015 American Heart Association, Inc.

Gain and phase of perceived virtual rotation evoked by electrical vestibular stimuli

PubMed Central

Peters, Ryan M.; Rasman, Brandon G.; Inglis, J. Timothy

2015-01-01

Galvanic vestibular stimulation (GVS) evokes a perception of rotation; however, very few quantitative data exist on the matter. We performed psychophysical experiments on virtual rotations experienced when binaural bipolar electrical stimulation is applied over the mastoids. We also performed analogous real whole body yaw rotation experiments, allowing us to compare the frequency response of vestibular perception with (real) and without (virtual) natural mechanical stimulation of the semicircular canals. To estimate the gain of vestibular perception, we measured direction discrimination thresholds for virtual and real rotations. Real direction discrimination thresholds decreased at higher frequencies, confirming multiple previous studies. Conversely, virtual direction discrimination thresholds increased at higher frequencies, implying low-pass filtering of the virtual perception process occurring potentially anywhere between afferent transduction and cortical responses. To estimate the phase of vestibular perception, participants manually tracked their perceived position during sinusoidal virtual and real kinetic stimulation. For real rotations, perceived velocity was approximately in phase with actual velocity across all frequencies. Perceived virtual velocity was in phase with the GVS waveform at low frequencies (0.05 and 0.1 Hz). As frequency was increased to 1 Hz, the phase of perceived velocity advanced relative to the GVS waveform. Therefore, at low frequencies GVS is interpreted as an angular velocity signal and at higher frequencies GVS becomes interpreted increasingly as an angular position signal. These estimated gain and phase spectra for vestibular perception are a first step toward generating well-controlled virtual vestibular percepts, an endeavor that may reveal the usefulness of GVS in the areas of clinical assessment, neuroprosthetics, and virtual reality. PMID:25925318

Gain and phase of perceived virtual rotation evoked by electrical vestibular stimuli.

PubMed

Peters, Ryan M; Rasman, Brandon G; Inglis, J Timothy; Blouin, Jean-Sébastien

2015-07-01

Galvanic vestibular stimulation (GVS) evokes a perception of rotation; however, very few quantitative data exist on the matter. We performed psychophysical experiments on virtual rotations experienced when binaural bipolar electrical stimulation is applied over the mastoids. We also performed analogous real whole body yaw rotation experiments, allowing us to compare the frequency response of vestibular perception with (real) and without (virtual) natural mechanical stimulation of the semicircular canals. To estimate the gain of vestibular perception, we measured direction discrimination thresholds for virtual and real rotations. Real direction discrimination thresholds decreased at higher frequencies, confirming multiple previous studies. Conversely, virtual direction discrimination thresholds increased at higher frequencies, implying low-pass filtering of the virtual perception process occurring potentially anywhere between afferent transduction and cortical responses. To estimate the phase of vestibular perception, participants manually tracked their perceived position during sinusoidal virtual and real kinetic stimulation. For real rotations, perceived velocity was approximately in phase with actual velocity across all frequencies. Perceived virtual velocity was in phase with the GVS waveform at low frequencies (0.05 and 0.1 Hz). As frequency was increased to 1 Hz, the phase of perceived velocity advanced relative to the GVS waveform. Therefore, at low frequencies GVS is interpreted as an angular velocity signal and at higher frequencies GVS becomes interpreted increasingly as an angular position signal. These estimated gain and phase spectra for vestibular perception are a first step toward generating well-controlled virtual vestibular percepts, an endeavor that may reveal the usefulness of GVS in the areas of clinical assessment, neuroprosthetics, and virtual reality. Copyright © 2015 the American Physiological Society.

Imaging paleoslabs in the D″ layer beneath Central America and the Caribbean using seismic waveform inversion.

PubMed

Borgeaud, Anselme F E; Kawai, Kenji; Konishi, Kensuke; Geller, Robert J

2017-11-01

D″ (Dee double prime), the lowermost layer of the Earth's mantle, is the thermal boundary layer (TBL) of mantle convection immediately above the Earth's liquid outer core. As the origin of upwelling of hot material and the destination of paleoslabs (downwelling cold slab remnants), D″ plays a major role in the Earth's evolution. D″ beneath Central America and the Caribbean is of particular geodynamical interest, because the paleo- and present Pacific plates have been subducting beneath the western margin of Pangaea since ~250 million years ago, which implies that paleoslabs could have reached the lowermost mantle. We conduct waveform inversion using a data set of ~7700 transverse component records to infer the detailed three-dimensional S-velocity structure in the lowermost 400 km of the mantle in the study region so that we can investigate how cold paleoslabs interact with the hot TBL above the core-mantle boundary (CMB). We can obtain high-resolution images because the lowermost mantle here is densely sampled by seismic waves due to the full deployment of the USArray broadband seismic stations during 2004-2015. We find two distinct strong high-velocity anomalies, which we interpret as paleoslabs, just above the CMB beneath Central America and Venezuela, respectively, surrounded by low-velocity regions. Strong low-velocity anomalies concentrated in the lowermost 100 km of the mantle suggest the existence of chemically distinct denser material connected to low-velocity anomalies in the lower mantle inferred by previous studies, suggesting that plate tectonics on the Earth's surface might control the modality of convection in the lower mantle.

Waveform tomography of crustal structure in the south San Francisco Bay region

USGS Publications Warehouse

Pollitz, F.F.; Fletcher, J.P.

2005-01-01

We utilize a scattering-based seismic tomography technique to constrain crustal tructure around the southern San Francisco Bay region (SFBR). This technique is based on coupled traveling wave scattering theory, which has usually been applied to the interpretation of surface waves in large regional-scale studies. Using fully three-dimensional kernels, this technique is here applied to observed P, S, and surface waves of intermediate period (3-4 s dominant period) observed following eight selected regional events. We use a total of 73 seismograms recorded by a U.S. Geological Survey short-period seismic array in the western Santa Clara Valley, the Berkeley Digital Seismic Network, and the Northern California Seismic Network. Modifications of observed waveforms due to scattering from crustal structure include (positive or negative) amplification, delay, and generation of coda waves. The derived crustal structure explains many of the observed signals which cannot be explained with a simple layered structure. There is sufficient sensitivity to both deep and shallow crustal structure that even with the few sources employed in the present study, we obtain shallow velocity structure which is reasonably consistent with previous P wave tomography results. We find a depth-dependent lateral velocity contrast across the San Andreas fault (SAF), with higher velocities southwest of the SAF in the shallow crust and higher velocities northeast of the SAF in the midcrust. The method does not have the resolution to identify very slow sediment velocities in the upper approximately 3 km since the tomographic models are smooth at a vertical scale of about 5 km. Copyright 2005 by the American Geophysical Union.

Modeling and validation of a 3D velocity structure for the Santa Clara Valley, California, for seismic-wave simulations

USGS Publications Warehouse

Hartzell, S.; Harmsen, S.; Williams, R.A.; Carver, D.; Frankel, A.; Choy, G.; Liu, P.-C.; Jachens, R.C.; Brocher, T.M.; Wentworth, C.M.

2006-01-01

A 3D seismic velocity and attenuation model is developed for Santa Clara Valley, California, and its surrounding uplands to predict ground motions from scenario earthquakes. The model is developed using a variety of geologic and geophysical data. Our starting point is a 3D geologic model developed primarily from geologic mapping and gravity and magnetic surveys. An initial velocity model is constructed by using seismic velocities from boreholes, reflection/refraction lines, and spatial autocorrelation microtremor surveys. This model is further refined and the seismic attenuation is estimated through waveform modeling of weak motions from small local events and strong-ground motion from the 1989 Loma Prieta earthquake. Waveforms are calculated to an upper frequency of 1 Hz using a parallelized finite-difference code that utilizes two regions with a factor of 3 difference in grid spacing to reduce memory requirements. Cenozoic basins trap and strongly amplify ground motions. This effect is particularly strong in the Evergreen Basin on the northeastern side of the Santa Clara Valley, where the steeply dipping Silver Creek fault forms the southwestern boundary of the basin. In comparison, the Cupertino Basin on the southwestern side of the valley has a more moderate response, which is attributed to a greater age and velocity of the Cenozoic fill. Surface waves play a major role in the ground motion of sedimentary basins, and they are seen to strongly develop along the western margins of the Santa Clara Valley for our simulation of the Loma Prieta earthquake.

Inadequate peak expiratory flow meter characteristics detected by a computerised explosive decompression device.

PubMed

Miller, M R; Atkins, P R; Pedersen, O F

2003-05-01

Recent evidence suggests that the frequency response requirements for peak expiratory flow (PEF) meters are higher than was first thought and that the American Thoracic Society (ATS) waveforms to test PEF meters may not be adequate for the purpose. The dynamic response of mini-Wright (MW), Vitalograph (V), TruZone (TZ), MultiSpiro (MS) and pneumotachograph (PT) flow meters was tested by delivering two differently shaped flow-time profiles from a computer controlled explosive decompression device fitted with a fast response solenoid valve. These profiles matched population 5th and 95th centiles for rise time from 10% to 90% of PEF and dwell time of flow above 90% PEF. Profiles were delivered five times with identical chamber pressure and solenoid aperture at PEF. Any difference in recorded PEF for the two profiles indicates a poor dynamic response. The absolute (% of mean) flow differences in l/min for the V, MW, and PT PEF meters were 25 (4.7), 20 (3.9), and 2 (0.3), respectively, at PEF approximately 500 l/min, and 25 (10.5), 20 (8.7) and 6 (3.0) at approximately 200 l/min. For TZ and MS meters at approximately 500 l/min the differences were 228 (36.1) and 257 (39.2), respectively, and at approximately 200 l/min they were 51 (23.9) and 1 (0.5). All the meters met ATS accuracy requirements when tested with their waveforms. An improved method for testing the dynamic response of flow meters detects marked overshoot (underdamping) of TZ and MS responses not identified by the 26 ATS waveforms. This error could cause patient misclassification when using such meters with asthma guidelines.

Validation of color Doppler ultrasonography for evaluating the uterine blood flow and perfusion during late normal pregnancy and uterine torsion in buffaloes.

PubMed

Hussein, Hassan A

2013-04-15

The aim of this study was to verify the efficacy of color Doppler ultrasonography for diagnosis of degree and duration of uterine torsion in buffaloes. In Assiut province/Upper Egypt, 65 buffaloes (37 with uterine torsion, 28 with normal late pregnancy) were examined clinically and using Doppler ultrasonography. The Doppler indices including resistance index (RI), pulsatility index (PI), time-averaged maximum velocity (TAMV), and blood flow volume (BFV) in the arteries ipsilateral to the uterine torsion (IPUT) and in arteries contralateral to the uterine torsion (COUT) were recorded. Methods of correction were documented along with dam and calf survival. Torsion was recorded postcervically with vaginal involvement in 35/37 (94.6%) of the cases. The degrees of uterine torsion were light and high in 9/37 (24.3%) and 28/37 (75.7%) of the cases, respectively (P = 0.001). Right uterine torsion was present in 36/37 (97.3%) of the cases (P = 0.0001). Pulsatility index, RI, TAMV, and BFV in IPUT and COUT did not differ significantly (P > 0.05) in normal late pregnancy. The PI and RI in IPUT were significantly higher (P < 0.01) than in COUT, and the TAMV and BFV in IPUT were less (P < 0.001) than that in COUT in uterine torsion. The PI and RI of torsion cases in IPUT were higher (P < 0.001) than that in normal pregnancy. Time-averaged maximum velocity and BFV in torsion cases were lower (P < 0.01) than that of normal pregnancy in IPUT. There was approximately 50% of RI and PI higher than in light degree uterine torsion in IPUT (P < 0.001). Consequently, TAMV and BFV were greatly lower (P < 0.0001) than that in light degree in IPUT. Pulsatility index and RI were positively correlated (r = 0.856; P < 0.001) with the duration and degree of the uterine torsion, and TAMV and BFV were negatively correlated (r = -0.763; P < 0.001). In all cases of uterine torsion the uterine flow velocity waveform showed high systolic flow and absence of early diastolic flow and poor uterine and placentomal blood perfusion. In conclusion, depicting blood flow within the middle uterine artery using color Doppler sonography could be helpful in correct diagnosis of duration and degree of uterine torsion and concurrently predicting the viability of the fetus and dam. Copyright © 2013 Elsevier Inc. All rights reserved.

Study on of Seepage Flow Velocity in Sand Layer Profile as Affected by Water Depth and Slope Gradience

NASA Astrophysics Data System (ADS)

Han, Z.; Chen, X.

2017-12-01

BACKGROUND: The subsurface water flow velocity is of great significance in understanding the hydrodynamic characteristics of soil seepage and the influence of interaction between seepage flow and surface runoff on the soil erosion and sediment transport process. OBJECTIVE: To propose a visualized method and equipment for determining the seepage flow velocity and measuring the actual flow velocity and Darcy velocity as well as the relationship between them.METHOD: A transparent organic glass tank is used as the test soil tank, the white river sand is used as the seepage test material and the fluorescent dye is used as the indicator for tracing water flow, so as to determine the thickness and velocity of water flow in a visualized way. Water is supplied at the same flow rate (0.84 L h-1) to the three parts with an interval of 1m at the bottom of the soil tank and the pore water velocity and the thickness of each water layer are determined under four gradient conditions. The Darcy velocity of each layer is calculated according to the water supply flow and the discharge section area. The effective discharge flow pore is estimated according to the moisture content and porosity and then the relationship between Darcy velocity and the measured velocity is calculated based on the water supply flow and the water layer thickness, and finally the correctness of the calculation results is verified. RESULTS: According to the velocity calculation results, Darcy velocity increases significantly with the increase of gradient; in the sand layer profile, the flow velocity of pore water at different depths increases with the increase of gradient; under the condition of the same gradient, the lower sand layer has the maximum flow velocity of pore water. The air-filled porosity of sand layer determines the proportional relationship between Darcy velocity and pore flow velocity. CONCLUSIONS: The actual flow velocity and Darcy velocity can be measured by a visualized method and the relationship between Darcy velocity and pore velocity can be expressed well by the air-filled porosity of sand layer. The flow velocity measurement and test method adopted in the research is effective and feasible. IMPLICATIONS: The visualized flow velocity measurement method can be applied to simulate and measure the characteristics of subsurface water flow in the soil.

Maximizing fluid delivered by bubble-free electroosmotic pump with optimum pulse voltage waveform.

PubMed

Tawfik, Mena E; Diez, Francisco J

2017-03-01

In generating high electroosmotic (EO) flows for use in microfluidic pumps, a limiting factor is faradaic reactions that are more pronounced at high electric fields. These reactions lead to bubble generation at the electrodes and pump efficiency reduction. The onset of gas generation for high current density EO pumping depends on many parameters including applied voltage, working fluid, and pulse duration. The onset of gas generation can be delayed and optimized for maximum volume pumped in the minimum time possible. This has been achieved through the use of a novel numerical model that predicts the onset of gas generation during EO pumping using an optimized pulse voltage waveform. This method allows applying current densities higher than previously reported. Optimal pulse voltage waveforms are calculated based on the previous theories for different current densities and electrolyte molarity. The electroosmotic pump performance is investigated by experimentally measuring the fluid volume displaced and flow rate. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Waveform inversion for 3-D S-velocity structure of D'' beneath the Northern Pacific: possible evidence for a remnant slab and a passive plume

NASA Astrophysics Data System (ADS)

Suzuki, Yuki; Kawai, Kenji; Geller, Robert J.; Borgeaud, Anselme F. E.; Konishi, Kensuke

2016-12-01

We conduct waveform inversion to infer the three-dimensional (3-D) S-velocity structure in the lowermost 400 km of the mantle (the D'' region) beneath the Northern Pacific region. Our dataset consists of about 20,000 transverse component broadband body-wave seismograms observed at North American stations for 131 intermediate and deep earthquakes which occurred beneath the western Pacific subduction region. We use S, ScS, and other phases that arrive between them. Resolution tests indicate that our methods and dataset can resolve the velocity structure in the target region with a horizontal scale of about 150 km and a vertical scale of about 50 km. The 3-D S-velocity model obtained in this study shows three prominent features: (1) prominent sheet-like lateral high-velocity anomalies up to ˜3% faster than the Preliminary Reference Earth Model (PREM) with a thickness of ˜200 km, whose lower boundary is ˜150 km above the core-mantle boundary (CMB). (2) A prominent low-velocity anomaly block located to the west of the Kamchatka peninsula, which is ˜2.5% slower than PREM, immediately above the CMB beneath the high-velocity anomalies. (3) A relatively thin (˜300 km) low-velocity structure continuous from the low-velocity anomaly "(2)" to at least 400 km above the CMB. We also detect a continuous low-velocity anomaly from the east of the Kamchatka peninsula at an altitude of 50 km above the CMB to the far east of the Kuril islands at an altitude of 400 km above the CMB. We interpret these features respectively as: (1) remnants of slab material where the bridgmanite to Mg-post-perovskite phase transition may have occurred within the slab, (2, 3) large amounts of hot and less dense materials beneath the cold Kula or Pacific slab remnants just above the CMB which ascend and form a passive plume upwelling at the edge of the slab remnants.[Figure not available: see fulltext.

Upper mantle P velocity structure beneath the Baikal Rift from modeling regional seismic data

NASA Astrophysics Data System (ADS)

Brazier, Richard A.; Nyblade, Andrew A.

2003-02-01

Uppermost mantle P wave velocity structure beneath the Baikal rift and southern margin of the Siberian Platform has been investigated by using a grid search method to model Pnl waveforms from two moderate earthquakes recorded by station TLY at the southwestern end of Lake Baikal. The results yielded a limited number of successful models which indicate the presence of upper mantle P wave velocities beneath the rift axis and the margin of the platform that are 2-5% lower than expected. The magnitude of the velocity anomalies and their location support the presence of a thermal anomaly that extends laterally beyond the rift proper, possibly created by small-scale convection or a plume-like, thermal upwelling.

Fluid-structure interaction for nonlinear response of shells conveying pulsatile flow

NASA Astrophysics Data System (ADS)

Tubaldi, Eleonora; Amabili, Marco; Païdoussis, Michael P.

2016-06-01

Circular cylindrical shells with flexible boundary conditions conveying pulsatile flow and subjected to pulsatile pressure are investigated. The equations of motion are obtained based on the nonlinear Novozhilov shell theory via Lagrangian approach. The flow is set in motion by a pulsatile pressure gradient. The fluid is modeled as a Newtonian pulsatile flow and it is formulated using a hybrid model that contains the unsteady effects obtained from the linear potential flow theory and the pulsatile viscous effects obtained from the unsteady time-averaged Navier-Stokes equations. A numerical bifurcation analysis employs a refined reduced order model to investigate the dynamic behavior. The case of shells containing quiescent fluid subjected to the action of a pulsatile transmural pressure is also addressed. Geometrically nonlinear vibration response to pulsatile flow and transmural pressure are here presented via frequency-response curves and time histories. The vibrations involving both a driven mode and a companion mode, which appear due to the axial symmetry, are also investigated. This theoretical framework represents a pioneering study that could be of great interest for biomedical applications. In particular, in the future, a more refined model of the one here presented will possibly be applied to reproduce the dynamic behavior of vascular prostheses used for repairing and replacing damaged and diseased thoracic aorta in cases of aneurysm, dissection or coarctation. For this purpose, a pulsatile time-dependent blood flow model is here considered by applying physiological waveforms of velocity and pressure during the heart beating period. This study provides, for the first time in literature, a fully coupled fluid-structure interaction model with deep insights in the nonlinear vibrations of circular cylindrical shells subjected to pulsatile pressure and pulsatile flow.

Changes in transthoracic impedance during sequential biphasic defibrillation.

PubMed

Deakin, Charles D; Ambler, Jonathan J S; Shaw, Steven

2008-08-01

Sequential monophasic defibrillation reduces transthoracic impedance (TTI) and progressively increases current flow for any given energy level. The effect of sequential biphasic shocks on TTI is unknown. We therefore studied patients undergoing elective cardioversion using a biphasic waveform to establish whether this is a phenomenon seen in the clinical setting. Adults undergoing elective DC cardioversion for atrial flutter or fibrillation received sequential transthoracic shocks using an escalating protocol (70J, 100J, 150J, 200J, and 300J) with a truncated exponential biphasic waveform. TTI was calculated through the defibrillator circuit and recorded electronically. Successful cardioversion terminated further defibrillation shocks. A total of 58 patients underwent elective cardioversion. Cardioversion was successful in 93.1% patients. First shock TTI was 92.2 [52.0-126.0]Omega (n=58) and decreased significantly with each sequential shock. Mean TTI in patients receiving five shocks (n=5) was 85.0Omega. Sequential biphasic defibrillation decreases TTI in a similar manner to that seen with monophasic waveforms. The effect is likely during defibrillation during cardiac arrest by the quick succession in which shocks are delivered and the lack of cutaneous blood flow which limits the inflammatory response. The ability of biphasic defibrillators to adjust their waveform according to TTI is likely to minimise any effect of these findings on defibrillation efficacy.

Molecular dynamics simulations of ejecta production from sinusoidal tin surfaces under supported and unsupported shocks

NASA Astrophysics Data System (ADS)

Wu, Bao; Wu, FengChao; Zhu, YinBo; Wang, Pei; He, AnMin; Wu, HengAn

2018-04-01

Micro-ejecta, an instability growth process, occurs at metal/vacuum or metal/gas interface when compressed shock wave releases from the free surface that contains surface defects. We present molecular dynamics (MD) simulations to investigate the ejecta production from tin surface shocked by supported and unsupported waves with pressures ranging from 8.5 to 60.8 GPa. It is found that the loading waveforms have little effect on spike velocity while remarkably affect the bubble velocity. The bubble velocity of unsupported shock loading remains nonzero constant value at late time as observed in experiments. Besides, the time evolution of ejected mass in the simulations is compared with the recently developed ejecta source model, indicating the suppressed ejection of unmelted or partial melted materials. Moreover, different reference positions are chosen to characterize the amount of ejecta under different loading waveforms. Compared with supported shock case, the ejected mass of unsupported shock case saturates at lower pressure. Through the analysis on unloading path, we find that the temperature of tin sample increases quickly from tensile stress state to zero pressure state, resulting in the melting of bulk tin under decaying shock. Thus, the unsupported wave loading exhibits a lower threshold pressure causing the solid-liquid phase transition on shock release than the supported shock loading.

Ultrasonic transient bounded-beam propagation in a solid cylinder waveguide embedded in a solid medium.

PubMed

Laguerre, Laurent; Grimault, Anne; Deschamps, Marc

2007-04-01

A semianalytical solution alternative and complementary to modal technique is presented to predict and interpret the ultrasonic pulsed-bounded-beam propagation in a solid cylinder embedded in a solid matrix. The spectral response to an inside axisymmetric velocity source of longitudinal and transversal cylindrical waves is derived from Debye series expansion of the embedded cylinder generalized cylindrical reflection/transmission coefficients. So, the transient guided wave response, synthesized by inverse double Fourier-Bessel transform, is expressed as a combination of the infinite medium contribution, longitudinal, transversal, and coupled longitudinal and transversal waveguide sidewall interactions. Simulated (f, 1/lambdaz) diagrams show the influence of the number of waveguide sidewall interactions to progressively recover dispersion curves. Besides, they show the embedding material filters specific signal portions by concentrating the propagating signal in regions where phase velocity is closer to phase velocity in steel. Then, simulated time waveforms using broadband high-frequency excitation show that signal leading portions exhibit a similar periodical pattern, for both free and embedded waveguides. Debye series-based interpretation shows that double longitudinal/transversal and transversal/longitudinal conversions govern the time waveform leading portion as well as the radiation attenuation in the surrounding cement grout. Finally, a methodology is deduced to minimize the radiation attenuation for the long-range inspection of embedded cylinders.

Building a good initial model for full-waveform inversion using frequency shift filter

NASA Astrophysics Data System (ADS)

Wang, Guanchao; Wang, Shangxu; Yuan, Sanyi; Lian, Shijie

2018-05-01

Accurate initial model or available low-frequency data is an important factor in the success of full waveform inversion (FWI). The low-frequency helps determine the kinematical relevant components, low-wavenumber of the velocity model, which are in turn needed to avoid FWI trap in local minima or cycle-skipping. However, in the field, acquiring data that <5 Hz is a challenging and expensive task. We attempt to find the common point of low- and high-frequency signal, then utilize the high-frequency data to obtain the low-wavenumber velocity model. It is well known that the instantaneous amplitude envelope of a wavelet is invariant under frequency shift. This means that resolution is constant for a given frequency bandwidth, and independent of the actual values of the frequencies. Based on this property, we develop a frequency shift filter (FSF) to build the relationship between low- and high-frequency information with a constant frequency bandwidth. After that, we can use the high-frequency information to get a plausible recovery of the low-wavenumber velocity model. Numerical results using synthetic data from the Marmousi and layer model demonstrate that our proposed envelope misfit function based on the frequency shift filter can build an initial model with more accurate long-wavelength components, when low-frequency signals are absent in recorded data.

Surface Wave Tomography of South China Sea from Ambient Seismic Noise and Two-station Measurements

NASA Astrophysics Data System (ADS)

Liang, W.-T.; Gung, Y.-C.

2012-04-01

We have taken the cross-correlation of seismic ambient noise technique as well as the two-station method to analyze the velocity structure in the South China Sea region. The dataset used in this study includes broadband waveforms recorded at the Taiwan BATS (Broadband Array in Taiwan for Seismology), Japan OHP (Ocean Hemisphere Project), Malaysia and Vietnam seismic networks. We remove the instrument response from daily data and filter the waveform with various frequency bands according to the length of each station-pair. Then we apply the commonly used 1-bit normalization to minimize the effect of earthquakes, instrumental irregularities, and non-stationary noise sources near to the stations. With the derived daily cross correlation function (CCF), we are able to examine the timing quality for each station-pair. We then obtain the surface Rayleigh wave dispersion curves from the stacked CCF for each station-pair. To cover the longer period band in the dispersion curves, we adopt the two-station method to compute both the group and phase velocities of surface waves. A new surface wave tomography based on ambient seismic noise study and traditional two-station technique has been achieved in this study. Raypaths that travel through the Central basin present higher velocity, which is in agreement with the idea of thin crust. On the other hand, the slower velocity between Taiwan and Northern Luzon, Philippine is mainly due to a thick accretionary prism above the Manila trench.

Experimental assessment of valve performance in healthy and diseased right ventricular outflow tracts using magnetic resonance velocimetry

NASA Astrophysics Data System (ADS)

Schiavone, Nicole; Elkins, Christopher; McElhinney, Doff; Eaton, John K.; Marsden, Alison

2017-11-01

Tetralogy of Fallot (ToF), the most common type of cyanotic congenital heart defect, affects 1 in every 2500 newborns annually and typically requires surgical repair of the right ventricular outflow tract (RVOT) and placement of an artificial pulmonary valve. All artificial valves are subject to dysfunction, but their longevity is highly variable. Clinical observation reveals large variations in RVOT anatomy in ToF patients, which may affect longevity. This work aims to experimentally assess the performance of artificial pulmonary valves in anatomically realistic healthy and diseased RVOT geometries using magnetic resonance velocimetry (MRV). With MRV, we can capture 3D, three-component, phase-averaged velocity fields in 3D printed RVOT geometries. The experiment is designed to ensure physiological flow rate and pressure waveforms, while the RVOT geometries are based on anatomies seen clinically in ToF patients. Two models are used in the current work: an idealized RVOT based on healthy subjects aged eleven to thirteen and a diseased geometry with a dilation of 150% in vessel diameter downstream of the pulmonary valve. We will also present preliminary rigid-wall blood flow simulations in each model, towards the ultimate goal of experimental validation of valve simulations.

Surface wave tomography applied to the North American upper mantle

NASA Astrophysics Data System (ADS)

van der Lee, Suzan; Frederiksen, Andrew

Tomographic techniques that invert seismic surface waves for 3-D Earth structure differ in their definitions of data and the forward problem as well as in the parameterization of the tomographic model. However, all such techniques have in common that the tomographic inverse problem involves solving a large and mixed-determined set of linear equations. Consequently these inverse problems have multiple solutions and inherently undefinable accuracy. Smoother and rougher tomographic models are found with rougher (confined to great circle path) and smoother (finite-width) sensitivity kernels, respectively. A powerful, well-tested method of surface wave tomography (Partitioned Waveform Inversion) is based on inverting the waveforms of wave trains comprising regional S and surface waves from at least hundreds of seismograms for 3-D variations in S wave velocity. We apply this method to nearly 1400 seismograms recorded by digital broadband seismic stations in North America. The new 3-D S-velocity model, NA04, is consistent with previous findings that are based on separate, overlapping data sets. The merging of US and Canadian data sets, adding Canadian recordings of Mexican earthquakes, and combining fundamental-mode with higher-mode waveforms provides superior resolution, in particular in the US-Canada border region and the deep upper mantle. NA04 shows that 1) the Atlantic upper mantle is seismically faster than the Pacific upper mantle, 2) the uppermost mantle beneath Precambrian North America could be one and a half times as rigid as the upper mantle beneath Meso- and Cenozoic North America, with the upper mantle beneath Paleozoic North America being intermediate in seismic rigidity, 3) upper-mantle structure varies laterally within these geologic-age domains, and 4) the distribution of high-velocity anomalies in the deep upper mantle aligns with lower mantle images of the subducted Farallon and Kula plates and indicate that trailing fragments of these subducted oceanic plates still reside in the transition zone. The thickness of the high-velocity layer beneath Precambrian North America is estimated to be 250±70 km thick. On a smaller scale NA04 shows 1) high-velocities associated with subduction of the Pacific plate beneath the Aleutian arc, 2) the absence of expected high velocities in the upper mantle beneath the Wyoming craton, 3) a V-shaped dent below 150 km in the high-velocity cratonic lithosphere beneath New England, 4) the cratonic lithosphere beneath Precambrian North America being confined southwest of Baffin Bay, west of the Appalachians, north of the Ouachitas, east of the Rocky Mountains, and south of the Arctic Ocean, 5) the cratonic lithosphere beneath the Canadian shield having higher S-velocities than that beneath Precambrian basement that is covered with Phanerozoic sediments, 6) the lowest S velocities are concentrated beneath the Gulf of California, northern Mexico, and the Basin and Range Province.

Non-linear 3-D Born shear waveform tomography in Southeast Asia

NASA Astrophysics Data System (ADS)

Panning, Mark P.; Cao, Aimin; Kim, Ahyi; Romanowicz, Barbara A.

2012-07-01

Southeast (SE) Asia is a tectonically complex region surrounded by many active source regions, thus an ideal test bed for developments in seismic tomography. Much recent development in tomography has been based on 3-D sensitivity kernels based on the first-order Born approximation, but there are potential problems with this approach when applied to waveform data. In this study, we develop a radially anisotropic model of SE Asia using long-period multimode waveforms. We use a theoretical 'cascade' approach, starting with a large-scale Eurasian model developed using 2-D Non-linear Asymptotic Coupling Theory (NACT) sensitivity kernels, and then using a modified Born approximation (nBorn), shown to be more accurate at modelling waveforms, to invert a subset of the data for structure in a subregion (longitude 75°-150° and latitude 0°-45°). In this subregion, the model is parametrized at a spherical spline level 6 (˜200 km). The data set is also inverted using NACT and purely linear 3-D Born kernels. All three final models fit the data well, with just under 80 per cent variance reduction as calculated using the corresponding theory, but the nBorn model shows more detailed structure than the NACT model throughout and has much better resolution at depths greater than 250 km. Based on variance analysis, the purely linear Born kernels do not provide as good a fit to the data due to deviations from linearity for the waveform data set used in this modelling. The nBorn isotropic model shows a stronger fast velocity anomaly beneath the Tibetan Plateau in the depth range of 150-250 km, which disappears at greater depth, consistent with other studies. It also indicates moderate thinning of the high-velocity plate in the middle of Tibet, consistent with a model where Tibet is underplated by Indian lithosphere from the south and Eurasian lithosphere from the north, in contrast to a model with continuous underplating by Indian lithosphere across the entire plateau. The nBorn anisotropic model detects negative ξ anomalies suggestive of vertical deformation associated with subducted slabs and convergent zones at the Himalayan front and Tien Shan at depths near 150 km.

Validation of Broadband Ground Motion Simulations for Japanese Crustal Earthquakes by the Recipe

NASA Astrophysics Data System (ADS)

Iwaki, A.; Maeda, T.; Morikawa, N.; Miyake, H.; Fujiwara, H.

2015-12-01

The Headquarters for Earthquake Research Promotion (HERP) of Japan has organized the broadband ground motion simulation method into a standard procedure called the "recipe" (HERP, 2009). In the recipe, the source rupture is represented by the characterized source model (Irikura and Miyake, 2011). The broadband ground motion time histories are computed by a hybrid approach: the 3-D finite-difference method (Aoi et al. 2004) and the stochastic Green's function method (Dan and Sato, 1998; Dan et al. 2000) for the long- (> 1　s) and short-period (< 1 s) components, respectively, using the 3-D velocity structure model. As the engineering significance of scenario earthquake ground motion prediction is increasing, thorough verification and validation are required for the simulation methods. This study presents the self-validation of the recipe for two MW6.6 crustal events in Japan, the 2000 Tottori and 2004 Chuetsu (Niigata) earthquakes. We first compare the simulated velocity time series with the observation. Main features of the velocity waveforms, such as the near-fault pulses and the large later phases on deep sediment sites are well reproduced by the simulations. Then we evaluate 5% damped pseudo acceleration spectra (PSA) in the framework of the SCEC Broadband Platform (BBP) validation (Dreger et al. 2015). The validation results are generally acceptable in the period range 0.1 - 10 s, whereas those in the shortest period range (0.01-0.1 s) are less satisfactory. We also evaluate the simulations with the 1-D velocity structure models used in the SCEC BBP validation exercise. Although the goodness-of-fit parameters for PSA do not significantly differ from those for the 3-D velocity structure model, noticeable differences in velocity waveforms are observed. Our results suggest the importance of 1) well-constrained 3-D velocity structure model for broadband ground motion simulations and 2) evaluation of time series of ground motion as well as response spectra.

High-resolution surface wave tomography of the European crust and uppermost mantle from ambient seismic noise

NASA Astrophysics Data System (ADS)

Lu, Yang; Stehly, Laurent; Paul, Anne; AlpArray Working Group

2018-05-01

Taking advantage of the large number of seismic stations installed in Europe, in particular in the greater Alpine region with the AlpArray experiment, we derive a new high-resolution 3-D shear-wave velocity model of the European crust and uppermost mantle from ambient noise tomography. The correlation of up to four years of continuous vertical-component seismic recordings from 1293 broadband stations (10° W-35° E, 30° N-75° N) provides Rayleigh wave group velocity dispersion data in the period band 5-150 s at more than 0.8 million virtual source-receiver pairs. Two-dimensional Rayleigh wave group velocity maps are estimated using adaptive parameterization to accommodate the strong heterogeneity of path coverage. A probabilistic 3-D shear-wave velocity model, including probability densities for the depth of layer boundaries and S-wave velocity values, is obtained by non-linear Bayesian inversion. A weighted average of the probabilistic model is then used as starting model for the linear inversion step, providing the final Vs model. The resulting S-wave velocity model and Moho depth are validated by comparison with previous geophysical studies. Although surface-wave tomography is weakly sensitive to layer boundaries, vertical cross-sections through our Vs model and the associated probability of presence of interfaces display striking similarities with reference controlled-source (CSS) and receiver-function sections across the Alpine belt. Our model even provides new structural information such as a ˜8 km Moho jump along the CSS ECORS-CROP profile that was not imaged by reflection data due to poor penetration across a heterogeneous upper crust. Our probabilistic and final shear wave velocity models have the potential to become new reference models of the European crust, both for crustal structure probing and geophysical studies including waveform modeling or full waveform inversion.

Flow over bedforms in a large sand-bed river: A field investigation

USGS Publications Warehouse

Holmes, Robert R.; Garcia, Marcelo H.

2008-01-01

An experimental field study of flows over bedforms was conducted on the Missouri River near St. Charles, Missouri. Detailed velocity data were collected under two different flow conditions along bedforms in this sand-bed river. The large river-scale data reflect flow characteristics similar to those of laboratory-scale flows, with flow separation occurring downstream of the bedform crest and flow reattachment on the stoss side of the next downstream bedform. Wave-like responses of the flow to the bedforms were detected, with the velocity decreasing throughout the flow depth over bedform troughs, and the velocity increasing over bedform crests. Local and spatially averaged velocity distributions were logarithmic for both datasets. The reach-wise spatially averaged vertical-velocity profile from the standard velocity-defect model was evaluated. The vertically averaged mean flow velocities for the velocity-defect model were within 5% of the measured values and estimated spatially averaged point velocities were within 10% for the upper 90% of the flow depth. The velocity-defect model, neglecting the wake function, was evaluated and found to estimate thevertically averaged mean velocity within 1% of the measured values.  

Laplace-domain waveform modeling and inversion for the 3D acoustic-elastic coupled media

NASA Astrophysics Data System (ADS)

Shin, Jungkyun; Shin, Changsoo; Calandra, Henri

2016-06-01

Laplace-domain waveform inversion reconstructs long-wavelength subsurface models by using the zero-frequency component of damped seismic signals. Despite the computational advantages of Laplace-domain waveform inversion over conventional frequency-domain waveform inversion, an acoustic assumption and an iterative matrix solver have been used to invert 3D marine datasets to mitigate the intensive computing cost. In this study, we develop a Laplace-domain waveform modeling and inversion algorithm for 3D acoustic-elastic coupled media by using a parallel sparse direct solver library (MUltifrontal Massively Parallel Solver, MUMPS). We precisely simulate a real marine environment by coupling the 3D acoustic and elastic wave equations with the proper boundary condition at the fluid-solid interface. In addition, we can extract the elastic properties of the Earth below the sea bottom from the recorded acoustic pressure datasets. As a matrix solver, the parallel sparse direct solver is used to factorize the non-symmetric impedance matrix in a distributed memory architecture and rapidly solve the wave field for a number of shots by using the lower and upper matrix factors. Using both synthetic datasets and real datasets obtained by a 3D wide azimuth survey, the long-wavelength component of the P-wave and S-wave velocity models is reconstructed and the proposed modeling and inversion algorithm are verified. A cluster of 80 CPU cores is used for this study.

Physiological interpretation of Doppler shift waveforms: the femorodistal segment in combined disease.

PubMed

Campbell, W B; Baird, R N; Cole, S E; Evans, J M; Skidmore, R; Woodcock, J P

1983-01-01

A new method is presented for assessing the femorodistal segment in multisegmental arterial disease, using the Laplace transform technique of Doppler waveform analysis. Blood velocity/time waveforms were obtained at femoral and ankle levels in three groups of limbs--50 without arterial disease, 12 with isolated aortoiliac stenoses, and 32 with femoropopliteal occlusions, with and without proximal disease. The waveforms were analysed for Laplace transform and pulsatility index values. The omega 0 coefficients of the Laplace transform analysis at femoral and ankle levels were compared in each subject, as the omega 0 gradient (femoral/ankle omega 0): and pulsatility index damping factor (femoral/ankle P1) was also calculated. The omega 0 gradient was shown to detect femoropopliteal occlusion in the presence of multisegmental arterial disease and to give some indication of its haemodynamic significance. The diagnostic accuracy of the omega 0 gradient was superior to that of pulsatility index damping factor. When combined with its existing ability to detect aortoiliac stenosis, this new application of the Laplace transform method offers the possibility both of a system for complete localisation of significant arterial lesions, and potential for follow-up of vascular surgical procedures in the lower limb, from two simple Doppler recordings.

Three-dimensional laser radar modeling

NASA Astrophysics Data System (ADS)

Steinvall, Ove K.; Carlsson, Tomas

2001-09-01

Laser radars have the unique capability to give intensity and full 3-D images of an object. Doppler lidars can give velocity and vibration characteristics of an objects. These systems have many civilian and military applications such as terrain modelling, depth sounding, object detection and classification as well as object positioning. In order to derive the signal waveform from the object one has to account for the laser pulse time characteristics, media effects such as the atmospheric attenuation and turbulence effects or scattering properties, the target shape and reflection (BRDF), speckle noise together with the receiver and background noise. Finally the type of waveform processing (peak detection, leading edge etc.) is needed to model the sensor output to be compared with observations. We have developed a computer model which models performance of a 3-D laser radar. We will give examples of signal waveforms generated from model different targets calculated by integrating the laser beam profile in space and time over the target including reflection characteristics during different speckle and turbulence conditions. The result will be of help when designing and using new laser radar systems. The importance of different type of signal processing of the waveform in order to fulfil performance goals will be shown.

Seismic evidence of the lithosphere-asthenosphere boundary beneath Izu-Bonin area

NASA Astrophysics Data System (ADS)

Cui, H.; Gao, Y.; Zhou, Y.

2016-12-01

The lithosphere-asthenosphere boundary (LAB), separating the rigid lithosphere and the ductile asthenosphere layers, is the seismic discontinuity with the negative velocity contrast of the Earth's interior [Fischer et al., 2010]. The LAB has been also termed the Gutenberg (G) discontinuity that defines the top of the low velocity zone in the upper mantle [Gutenberg, 1959; Revenaugh and Jordan, 1991]. The seismic velocity, viscosity, resistivity and other physical parameters change rapidly with the depths across the boundary [Eaton et al., 2009]. Seismic detections on the LAB in subduction zone regions are of great help to understand the interactions between the lithosphere and asthenosphere layers and the geodynamic processes related with the slab subductions. In this study, the vertical broadband waveforms are collected from three deep earthquake events occurring from 2000 to 2014 with the focal depths of 400 600 km beneath the Izu-Bonin area. The waveform data is processed with the linear slant stack method [Zang and Zhou, 2002] to obtain the vespagrams in the relative travel-time to slowness domain and the stacked waveforms. The sP precursors reflected on the LAB (sLABP), which have the negative polarities with the amplitude ratios of 0.17 0.21 relative to the sP phases, are successfully extracted. Based on the one-dimensional modified velocity model (IASP91-IB), we obtain the distributions for six reflected points of the sLABP phases near the source region. Our results reveal that the LAB depths range between 58 and 65 km beneath the Izu-Bonin Arc, with the average depth of 62 km and the small topography of 7 km. Compared with the results of the tectonic stable areas in Philippine Sea [Kawakatsu et al., 2009; Kumar and Kawakatsu, 2011], the oceanic lithosphere beneath the Izu-Bonin Arc shows the obvious thinning phenomena. We infer that the lithospheric thinning is closely related with the partial melting, which is caused by the volatiles continuously released from the subducted western Pacific slab in deep Earth, and the strong erosions of the small-scale mantle convection in the back-arc mantle wedge.

Core-Mantle Boundary Complexities beneath the Mid-Pacific

NASA Astrophysics Data System (ADS)

Sun, D.; Helmberger, D. V.; Jackson, J. M.

2016-12-01

The detailed core-mantle boundary (CMB) structures beneath the Mid-Pacific are important to map the boundary of Large Low Shear Velocity Province (LLSVP) and the location of ultra-low velocity zone (ULVZ) related to the LLSVP and the D" layer, which are crucial for answering the key questions regarding to the mantle dynamics. Seismic data from deep earthquakes in the Fiji-Tonga region recorded by stations of USArray provide great sampling of the CMB beneath the Mid-Pacific. Here we explore the USArray data with different seismic phases to study the CMB complexities beneath the Mid-Pacific. First, we examined the differential travel time and amplitude between ScS and S for data at western US and confirm the northeastern boundary of the mid-Pacific LLSVP. The delayed ScS-S travel times and smaller amplitude of ScS require the existence of ULVZ locally. Secondly, the Sdiff data recorded by stations at central US shows variation in multi-pathing, that is, the presence of secondary arrivals following the S phase at diffracted distances (Sdiff) which suggests that the waveform complexity is due to structures at the eastern edge of the mid-Pacific LLSVP. This study reinforces previous studies that indicate late arrivals occurring after the primary Sdiff arrivals. A tapered wedge structure with low shear velocity allows for wave energy trapping, producing the observed waveform complexity and delayed arrivals at large distances. The location of the low velocity anomaly agrees with that inferred from the ScS-S measurements. We also observed advanced SV arrivals, which can be explained by the emerging of the D" discontinuity to the east of the boundary of the LLSVP to produce a "pseudo anisotropy". Thirdly, the arrivals of the SPdKS phase support the presence of an ULVZ within a two-humped LLSVP. A sharp 10 secs jump of the differential travel time between S and SKS (TS-SKS) across distance range of 5° is observed. The associated SKS waveform distortions suggest that the differential travel time anomaly is mainly controlled by the SKS, which is explained by a possible slab subducted to the lower mantle.

Incorporating geometrically complex vegetation in a computational fluid dynamic framework

NASA Astrophysics Data System (ADS)

Boothroyd, Richard; Hardy, Richard; Warburton, Jeff; Rosser, Nick

2015-04-01

Vegetation is known to have a significant influence on the hydraulic, geomorphological, and ecological functioning of river systems. Vegetation acts as a blockage to flow, thereby causing additional flow resistance and influencing flow dynamics, in particular flow conveyance. These processes need to be incorporated into flood models to improve predictions used in river management. However, the current practice in representing vegetation in hydraulic models is either through roughness parameterisation or process understanding derived experimentally from flow through highly simplified configurations of fixed, rigid cylinders. It is suggested that such simplifications inadequately describe the geometric complexity that characterises vegetation, and therefore the modelled flow dynamics may be oversimplified. This paper addresses this issue by using an approach combining field and numerical modelling techniques. Terrestrial Laser Scanning (TLS) with waveform processing has been applied to collect a sub-mm, 3-dimensional representation of Prunus laurocerasus, an invasive species to the UK that has been increasingly recorded in riparian zones. Multiple scan perspectives produce a highly detailed point cloud (>5,000,000 individual data points) which is reduced in post processing using an octree-based voxelisation technique. The method retains the geometric complexity of the vegetation by subdividing the point cloud into 0.01 m3 cubic voxels. The voxelised representation is subsequently read into a computational fluid dynamic (CFD) model using a Mass Flux Scaling Algorithm, allowing the vegetation to be directly represented in the modelling framework. Results demonstrate the development of a complex flow field around the vegetation. The downstream velocity profile is characterised by two distinct inflection points. A high velocity zone in the near-bed (plant-stem) region is apparent due to the lack of significant near-bed foliage. Above this, a zone of reduced velocity is found where the bulk of the vegetation blockage is more evenly distributed. Finally, flow rapidly recovers towards the free-stream region. Analysis of the pressure field demonstrates that drag force is non-linearly distributed over the vegetation. In the downstream direction, the drag force decreases through the vegetation. The experiment is extended to emulate vegetation reconfiguration in the flow, and is achieved through rotation of the vegetation about a fixed position (roots) on the bed. The experiment demonstrates a reduction in the total drag force and a shift in the contribution of different drag mechanisms as the degree of rotation increases. In the upright state, form drag dominates, but with additional rotation, the contribution of viscous drag increases. Consequently, the total drag force is found to decrease by approximately one third between the upright and fully rotated states of reconfiguration. Explicit representation of vegetation geometry therefore enables a re-evaluation of vegetative flow resistance. This presents an opportunity to move away from the conventional methods of representing vegetation in hydraulic models, i.e. roughness parameterisation, in favour of a more physically determined approach.

A baseline for upper crustal velocity variations along the East Pacific Rise at 13 deg N

NASA Astrophysics Data System (ADS)

Kappus, Mary E.; Harding, Alistair J.; Orcutt, John A.

1995-04-01

A wide aperture profile of the East Pacific Rise at 13 deg N provides data necessary to make a high-resolution seismic velocity profile of the uppermost crust along a 52-km segment of ridge crest. Automated and objective processing steps, including r-p analysis and waveform inversion, allow the construction of models in a consistent way so that comparisons are meaningful. A continuous profile is synthesized from 70 independent one-dimensional models spaced at 750-km intervals along the ridge. The resulting seismic velocity structure of the top 500 m of crust is remarkable in its lack of variability. The main features are a thin low-velocity layer 2A at the top with a steep gradient to layer 2B. The seafloor velocity is nearly constant at 2.45 km/s +/- 3% along the entire ridge. The velocity at the top of layer 2B is 5.0 km/s +/- 10%. The depth to the 4 km/s isovelocity contour within layer 2A is 130 +/- 20 m from 13 deg to 13 deg 20 min N, north of which it increases to 180 m. The increase in thickness is coincident with a deviation from axial linearity (DEVAL) noted by both a slight change in axis depth and orientation and in geochemistry. The waveform inversion, providing more details plus velocity gradient information, shows a layer 2A with about 80 m of constant-velocity material underlain by 150 m of high velocity gradient material, putting the base of layer 2A at approximately 230 m depth south of 13 deg 20 min N and about 50 m thicker north of the DEVAL. The overall lack of variability, combined with other recent measurements of layer 2A thickness along and near the axis, indicates that the thickness of volcanic extrusives is controlled not by levels of volcanic productivity, but the dynamics of emplacement. The homogeneity along axis also provides a baseline of inherent variability in crustal structure of about 10% against which other observed variations in similar regimes can be compared.

3-D Velocity Model of the Coachella Valley, Southern California Based on Explosive Shots from the Salton Seismic Imaging Project

NASA Astrophysics Data System (ADS)

Persaud, P.; Stock, J. M.; Fuis, G. S.; Hole, J. A.; Goldman, M.; Scheirer, D. S.

2014-12-01

We have analyzed explosive shot data from the 2011 Salton Seismic Imaging Project (SSIP) across a 2-D seismic array and 5 profiles in the Coachella Valley to produce a 3-D P-wave velocity model that will be used in calculations of strong ground shaking. Accurate maps of seismicity and active faults rely both on detailed geological field mapping and a suitable velocity model to accurately locate earthquakes. Adjoint tomography of an older version of the SCEC 3-D velocity model shows that crustal heterogeneities strongly influence seismic wave propagation from moderate earthquakes (Tape et al., 2010). These authors improve the crustal model and subsequently simulate the details of ground motion at periods of 2 s and longer for hundreds of ray paths. Even with improvements such as the above, the current SCEC velocity model for the Salton Trough does not provide a match of the timing or waveforms of the horizontal S-wave motions, which Wei et al. (2013) interpret as caused by inaccuracies in the shallow velocity structure. They effectively demonstrate that the inclusion of shallow basin structure improves the fit in both travel times and waveforms. Our velocity model benefits from the inclusion of known location and times of a subset of 126 shots detonated over a 3-week period during the SSIP. This results in an improved velocity model particularly in the shallow crust. In addition, one of the main challenges in developing 3-D velocity models is an uneven stations-source distribution. To better overcome this challenge, we also include the first arrival times of the SSIP shots at the more widely spaced Southern California Seismic Network (SCSN) in our inversion, since the layout of the SSIP is complementary to the SCSN. References: Tape, C., et al., 2010, Seismic tomography of the Southern California crust based on spectral-element and adjoint methods: Geophysical Journal International, v. 180, no. 1, p. 433-462. Wei, S., et al., 2013, Complementary slip distributions of the largest earthquakes in the 2012 Brawley swarm, Imperial Valley, California: Geophysical Research Letters, v. 40, no. 5, p. 847-852.

Arbitrary waveform generator to improve laser diode driver performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fulkerson, Jr, Edward Steven

2015-11-03

An arbitrary waveform generator modifies the input signal to a laser diode driver circuit in order to reduce the overshoot/undershoot and provide a "flat-top" signal to the laser diode driver circuit. The input signal is modified based on the original received signal and the feedback from the laser diode by measuring the actual current flowing in the laser diode after the original signal is applied to the laser diode.

Modeling of acoustic wave dissipation in gas hydrate-bearing sediments

NASA Astrophysics Data System (ADS)

Guerin, Gilles; Goldberg, David

2005-07-01

Recent sonic and seismic data in gas hydrate-bearing sediments have indicated strong waveform attenuation associated with a velocity increase, in apparent contradiction with conventional wave propagation theory. Understanding the reasons for such energy dissipation could help constrain the distribution and the amounts of gas hydrate worldwide from the identification of low amplitudes in seismic surveys. A review of existing models for wave propagation in frozen porous media, all based on Biot's theory, shows that previous formulations fail to predict any significant attenuation with increasing hydrate content. By adding physically based components to these models, such as cementation by elastic shear coupling, friction between the solid phases, and squirt flow, we are able to predict an attenuation increase associated with gas hydrate formation. The results of the model agree well with the sonic logging data recorded in the Mallik 5L-38 Gas Hydrate Research Well. Cementation between gas hydrate and the sediment grains is responsible for the increase in shear velocity. The primary mode of energy dissipation is found to be friction between gas hydrate and the sediment matrix, combined with an absence of inertial coupling between gas hydrate and the pore fluid. These results predict similar attenuation increase in hydrate-bearing formations over most of the sonic and seismic frequency range.

Upper mantle anisotropic attenuation of the Sierra Nevada and surroundings

NASA Astrophysics Data System (ADS)

Bernardino, M. J.; Jones, C. H.; Monsalve, G.

2016-12-01

We investigate the contribution of anelasticity in the generation of seismic velocity variations within the upper mantle of the Sierra Nevada and surrounding regions through teleseismic shear-wave attenuation. Given that anelastic effects are most sensitive to temperature and hydration and less to composition and small degrees of partial melt, we aim constrain the thermal structure beneath this region and identify locations where elevated upper mantle temperatures dominate. We also investigate the dependence of shear-wave attenuation on direction by accounting for seismic anisotropy in our measurements. S-wave t* values are determined from teleseismic S- and SKS- phases recorded on permanent and temporary deployments within the California region with particular focus on the Sierra Nevada Earthscope Project (SNEP) and the Sierran Paradox Experiment (SPE) stations. S-waveforms are rotated into the Sierran SFast, N75°E, and SSlow, N15°W, components. Following the method of Stachnik et al., (2004), S-wave spectra for each event are jointly inverted for a single seismic moment, M0k, and corner frequency, fck, for each event, and separate t* for each ray path. The resulting t*Fast and t*Slow measurements are then inverted for three-dimensional variations in (1/QFast) and (1/QSlow). Results are compared with previous magnetotelluric, surface heat flow, and body-wave velocity inversion studies.

A double-gaussian, percentile-based method for estimating maximum blood flow velocity.

PubMed

Marzban, Caren; Illian, Paul R; Morison, David; Mourad, Pierre D

2013-11-01

Transcranial Doppler sonography allows for the estimation of blood flow velocity, whose maximum value, especially at systole, is often of clinical interest. Given that observed values of flow velocity are subject to noise, a useful notion of "maximum" requires a criterion for separating the signal from the noise. All commonly used criteria produce a point estimate (ie, a single value) of maximum flow velocity at any time and therefore convey no information on the distribution or uncertainty of flow velocity. This limitation has clinical consequences especially for patients in vasospasm, whose largest flow velocities can be difficult to measure. Therefore, a method for estimating flow velocity and its uncertainty is desirable. A gaussian mixture model is used to separate the noise from the signal distribution. The time series of a given percentile of the latter, then, provides a flow velocity envelope. This means of estimating the flow velocity envelope naturally allows for displaying several percentiles (e.g., 95th and 99th), thereby conveying uncertainty in the highest flow velocity. Such envelopes were computed for 59 patients and were shown to provide reasonable and useful estimates of the largest flow velocities compared to a standard algorithm. Moreover, we found that the commonly used envelope was generally consistent with the 90th percentile of the signal distribution derived via the gaussian mixture model. Separating the observed distribution of flow velocity into a noise component and a signal component, using a double-gaussian mixture model, allows for the percentiles of the latter to provide meaningful measures of the largest flow velocities and their uncertainty.

Kinematic Source Rupture Process of the 2008 Iwate-Miyagi Nairiku Earthquake, a MW6.9 thrust earthquake in northeast Japan, using Strong Motion Data

NASA Astrophysics Data System (ADS)

Asano, K.; Iwata, T.

2008-12-01

The 2008 Iwate-Miyagi Nairiku earthquake (MJMA7.2) on June 14, 2008, is a thrust type inland crustal earthquake, which occurred in northeastern Honshu, Japan. In order to see strong motion generation process of this event, the source rupture process is estimated by the kinematic waveform inversion using strong motion data. Strong motion data of the K-NET and KiK-net stations and Aratozawa Dam are used. These stations are located 3-94 km from the epicenter. Original acceleration time histories are integrated into velocity and band- pass filtered between 0.05 and 1 Hz. For obtaining the detailed source rupture process, appropriate velocity structure model for Green's functions should be used. We estimated one dimensional velocity structure model for each strong motion station by waveform modeling of aftershock records. The elastic wave velocity, density, and Q-values for four sedimentary layers are assumed following previous studies. The thickness of each sedimentary layer depends on the station, which is estimated to fit the observed aftershock's waveforms by the optimization using the genetic algorithm. A uniform layered structure model is assumed for crust and upper mantle below the seismic bedrock. We succeeded to get a reasonable velocity structure model for each station to give a good fit of the main S-wave part in the observation of aftershocks. The source rupture process of the mainshock is estimated by the linear kinematic waveform inversion using multiple time windows (Hartzell and Heaton, 1983). A fault plane model is assumed following the moment tensor solution by F-net, NIED. The strike and dip angle is 209° and 51°, respectively. The rupture starting point is fixed at the hypocenter located by the JMA. The obtained source model shows a large slip area in the shallow portion of the fault plane approximately 6 km southwest of the hypocenter. The rupture of the asperity finishes within about 9 s. This large slip area corresponds to the area with surface break reported by the field survey group (e.g., AIST/GSJ, 2008), which supports the existence of the large slip close to the ground surface. But, most of surface offset found by the field survey are less than 0.5 m whereas the slip amount of the shallow asperity of the source inversion result is 3-4 m. In north of the hypocenter, the estimated slip amount is small. Slip direction is almost pure dip-slip for the entire fault (Northwest side goes up against southeast side). Total seismic moment is 2.6× 1019 Nm (MW 6.9). Acknowledgments: Strong motion data of K-NET and KiK-net operated by the National Research Institute for Earth Science and Disaster Prevention are used. Strong motion data of Aratozawa Dam obtained by Miyagi prefecture government is also used in the study.

Seismic Wavefield Imaging of Long-Period Ground Motion in the Tokyo Metropolitan Area, Japan

NASA Astrophysics Data System (ADS)

Nagao, H.; Kano, M.; Nagata, K.; Ito, S. I.; Sakai, S.; Nakagawa, S.; Hori, M.; Hirata, N.

2017-12-01

Long-period ground motions due to large earthquakes can cause devastating disasters, especially in urbanized areas located on sedimentary basins. To assess and mitigate such damage, it is essential to rapidly evaluate seismic hazards for infrastructures, which can be simulated by seismic response analyses that use waveforms at the base of each infrastructure as an input ground motion. The present study reconstructs the seismic wavefield in the Tokyo metropolitan area located on the Kanto sedimentary basin, Japan, from seismograms of the Metropolitan Seismic Observation network (MeSO-net). The obtained wavefield fully explains the observed waveforms in the frequency band of 0.10-0.20 Hz. This is attributed to the seismic wavefield imaging technique proposed by Kano et al. (2017), which implements the replica exchange Monte Carlo method to simultaneously estimate model parameters related to the subsurface structure and source information. Further investigation shows that the reconstructed seismic wavefield lower than 0.30 Hz is of high quality in terms of variance reduction (VR), which quantifies a misfit in waveforms but that the VR rapidly worsens in higher frequencies. Meanwhile, the velocity response spectra show good agreement with observations up to 0.90 Hz in terms of the combined goodness of fit (CGOF), which is a measure of misfit in the velocity response spectra. Inputting the reconstructed wavefield into seismic response analyses, we can rapidly assess the overall damage to infrastructures immediately after a large earthquake.

Resolving Isotropic Components from Regional Waves using Grid Search and Moment Tensor Inversion Methods

NASA Astrophysics Data System (ADS)

Ichinose, G. A.; Saikia, C. K.

2007-12-01

We applied the moment tensor (MT) analysis scheme to identify seismic sources using regional seismograms based on the representation theorem for the elastic wave displacement field. This method is applied to estimate the isotropic (ISO) and deviatoric MT components of earthquake, volcanic, and isotropic sources within the Basin and Range Province (BRP) and western US. The ISO components from Hoya, Bexar, Montello and Junction were compared to recently well recorded recent earthquakes near Little Skull Mountain, Scotty's Junction, Eureka Valley, and Fish Lake Valley within southern Nevada. We also examined "dilatational" sources near Mammoth Lakes Caldera and two mine collapses including the August 2007 event in Utah recorded by US Array. Using our formulation we have first implemented the full MT inversion method on long period filtered regional data. We also applied a grid-search technique to solve for the percent deviatoric and %ISO moments. By using the grid-search technique, high-frequency waveforms are used with calibrated velocity models. We modeled the ISO and deviatoric components (spall and tectonic release) as separate events delayed in time or offset in space. Calibrated velocity models helped the resolution of the ISO components and decrease the variance over the average, initial or background velocity models. The centroid location and time shifts are velocity model dependent. Models can be improved as was done in previously published work in which we used an iterative waveform inversion method with regional seismograms from four well recorded and constrained earthquakes. The resulting velocity models reduced the variance between predicted synthetics by about 50 to 80% for frequencies up to 0.5 Hz. Tests indicate that the individual path-specific models perform better at recovering the earthquake MT solutions even after using a sparser distribution of stations than the average or initial models.

Detailed Velocity and Density models of the Cascadia Subduction Zone from Prestack Full-Waveform Inversion

NASA Astrophysics Data System (ADS)

Fortin, W.; Holbrook, W. S.; Mallick, S.; Everson, E. D.; Tobin, H. J.; Keranen, K. M.

2014-12-01

Understanding the geologic composition of the Cascadia Subduction Zone (CSZ) is critically important in assessing seismic hazards in the Pacific Northwest. Despite being a potential earthquake and tsunami threat to millions of people, key details of the structure and fault mechanisms remain poorly understood in the CSZ. In particular, the position and character of the subduction interface remains elusive due to its relative aseismicity and low seismic reflectivity, making imaging difficult for both passive and active source methods. Modern active-source reflection seismic data acquired as part of the COAST project in 2012 provide an opportunity to study the transition from the Cascadia basin, across the deformation front, and into the accretionary prism. Coupled with advances in seismic inversion methods, this new data allow us to produce detailed velocity models of the CSZ and accurate pre-stack depth migrations for studying geologic structure. While still computationally expensive, current computing clusters can perform seismic inversions at resolutions that match that of the seismic image itself. Here we present pre-stack full waveform inversions of the central seismic line of the COAST survey offshore Washington state. The resultant velocity model is produced by inversion at every CMP location, 6.25 m laterally, with vertical resolution of 0.2 times the dominant seismic frequency. We report a good average correlation value above 0.8 across the entire seismic line, determined by comparing synthetic gathers to the real pre-stack gathers. These detailed velocity models, both Vp and Vs, along with the density model, are a necessary step toward a detailed porosity cross section to be used to determine the role of fluids in the CSZ. Additionally, the P-velocity model is used to produce a pre-stack depth migration image of the CSZ.

Imaging paleoslabs in the D″ layer beneath Central America and the Caribbean using seismic waveform inversion

PubMed Central

Borgeaud, Anselme F. E.; Kawai, Kenji; Konishi, Kensuke; Geller, Robert J.

2017-01-01

D″ (Dee double prime), the lowermost layer of the Earth’s mantle, is the thermal boundary layer (TBL) of mantle convection immediately above the Earth’s liquid outer core. As the origin of upwelling of hot material and the destination of paleoslabs (downwelling cold slab remnants), D″ plays a major role in the Earth’s evolution. D″ beneath Central America and the Caribbean is of particular geodynamical interest, because the paleo- and present Pacific plates have been subducting beneath the western margin of Pangaea since ~250 million years ago, which implies that paleoslabs could have reached the lowermost mantle. We conduct waveform inversion using a data set of ~7700 transverse component records to infer the detailed three-dimensional S-velocity structure in the lowermost 400 km of the mantle in the study region so that we can investigate how cold paleoslabs interact with the hot TBL above the core-mantle boundary (CMB). We can obtain high-resolution images because the lowermost mantle here is densely sampled by seismic waves due to the full deployment of the USArray broadband seismic stations during 2004–2015. We find two distinct strong high-velocity anomalies, which we interpret as paleoslabs, just above the CMB beneath Central America and Venezuela, respectively, surrounded by low-velocity regions. Strong low-velocity anomalies concentrated in the lowermost 100 km of the mantle suggest the existence of chemically distinct denser material connected to low-velocity anomalies in the lower mantle inferred by previous studies, suggesting that plate tectonics on the Earth’s surface might control the modality of convection in the lower mantle. PMID:29209659

Peak Stress Intensity Factor Governs Crack Propagation Velocity In Crosslinked UHMWPE

PubMed Central

Sirimamilla, P. Abhiram; Furmanski, Jevan; Rimnac, Clare

2013-01-01

Ultra high molecular weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax-Kmin, MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax, during cyclic loading, rather than by ΔK. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasi-static manner. The current study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax. The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components. PMID:23165898

SeisFlows-Flexible waveform inversion software

NASA Astrophysics Data System (ADS)

Modrak, Ryan T.; Borisov, Dmitry; Lefebvre, Matthieu; Tromp, Jeroen

2018-06-01

SeisFlows is an open source Python package that provides a customizable waveform inversion workflow and framework for research in oil and gas exploration, earthquake tomography, medical imaging, and other areas. New methods can be rapidly prototyped in SeisFlows by inheriting from default inversion or migration classes, and code can be tested on 2D examples before application to more expensive 3D problems. Wave simulations must be performed using an external software package such as SPECFEM3D. The ability to interface with external solvers lends flexibility, and the choice of SPECFEM3D as a default option provides optional GPU acceleration and other useful capabilities. Through support for massively parallel solvers and interfaces for high-performance computing (HPC) systems, inversions with thousands of seismic traces and billions of model parameters can be performed. So far, SeisFlows has run on clusters managed by the Department of Defense, Chevron Corp., Total S.A., Princeton University, and the University of Alaska, Fairbanks.

Seismic Velocity Structure of the Pacific Upper Mantle in the NoMelt Region from Finite-Frequency Traveltime Tomography

NASA Astrophysics Data System (ADS)

Hung, S. H.; Lin, P. Y.; Gaherty, J. B.; Russell, J. B.; Jin, G.; Collins, J. A.; Lizarralde, D.; Evans, R. L.; Hirth, G.

2017-12-01

Surface wave dispersion and magnetotelluric survey from the NoMelt Experiment conducted on 70 Ma central Pacific seafloor revealed an electrically resistive, high shear wave velocity lid of 80 km thick underlain by a non-highly conductive, low-velocity layer [Sarafian et al., 2015; Lin et al., 2016]. The vertical structure of the upper mantle consistent with these observational constraints suggests a plausible convection scenario, where the seismically fast, dehydrated lithosphere preserving very strong fossil spreading fabric moves at a constant plate speed over the hydrated, melt-free athenospheric mantle with the presence of either pressure-driven return flow or thermally-driven small scale circulation. To explore 3-D variations in compressional shear wave velocities related to the lithospheric and asthenospheric mantle dynamics, we employ a multichannel cross correlation method to measure relative traveltime residuals based on the vertical P and traverse S waveforms filtered at 10-33 s from telseismic earthquakes at epicentral distance between 30 and 98 degrees. The obtained P and S residuals show on average peak-to-peak variations of ±0.5 s and ±1 s, respectively, across the NoMelt OBS array. Particularly, the P residuals for most of the events display an asymmetrical pattern with respect to an axis oriented nearly N-S to NE-SW through the array. Preliminary ray-based P tomography results reveal similar asymmetric variations in the uppermost 100 km mantle. To verify the resulting structural features, we will further perform both the P and S traveltime tomography and resolution tests based on a multiscale finite-frequency approach which properly takes into account both the 3D off-path sensitivities of the measured residuals and data-adaptive resolution of the model.

Rupture process of the M 7.9 Denali fault, Alaska, earthquake: Subevents, directivity, and scaling of high-frequency ground motions

USGS Publications Warehouse

Frankel, A.

2004-01-01

Displacement waveforms and high-frequency acceleration envelopes from stations at distances of 3-300 km were inverted to determine the source process of the M 7.9 Denali fault earthquake. Fitting the initial portion of the displacement waveforms indicates that the earthquake started with an oblique thrust subevent (subevent # 1) with an east-west-striking, north-dipping nodal plane consistent with the observed surface rupture on the Susitna Glacier fault. Inversion of the remainder of the waveforms (0.02-0.5 Hz) for moment release along the Denali and Totschunda faults shows that rupture proceeded eastward on the Denali fault, with two strike-slip subevents (numbers 2 and 3) centered about 90 and 210 km east of the hypocenter. Subevent 2 was located across from the station at PS 10 (Trans-Alaska Pipeline Pump Station #10) and was very localized in space and time. Subevent 3 extended from 160 to 230 km east of the hypocenter and had the largest moment of the subevents. Based on the timing between subevent 2 and the east end of subevent 3, an average rupture velocity of 3.5 km/sec, close to the shear wave velocity at the average rupture depth, was found. However, the portion of the rupture 130-220 km east of the epicenter appears to have an effective rupture velocity of about 5.0 km/ sec, which is supershear. These two subevents correspond approximately to areas of large surface offsets observed after the earthquake. Using waveforms of the M 6.7 Nenana Mountain earthquake as empirical Green's functions, the high-frequency (1-10 Hz) envelopes of the M 7.9 earthquake were inverted to determine the location of high-frequency energy release along the faults. The initial thrust subevent produced the largest high-frequency energy release per unit fault length. The high-frequency envelopes and acceleration spectra (>0.5 Hz) of the M 7.9 earthquake can be simulated by chaining together rupture zones of the M 6.7 earthquake over distances from 30 to 180 km east of the hypocenter. However, the inversion indicates that there was relatively little high-frequency energy generated along the 60-km portion of the Totschunda fault on the east end of the rupture.

High-order numerical simulations of pulsatile flow in a curved artery model

NASA Astrophysics Data System (ADS)

Cox, Christopher; Liang, Chunlei; Plesniak, Michael W.

2016-11-01

Cardiovascular flows are pulsatile, incompressible and occur in complex geometries with compliant walls. Together, these factors can produce an environment that can affect the progression of cardiovascular disease by altering wall shear stresses. Unstructured high-order CFD methods are well suited for capturing unsteady vortex-dominated viscous flows, and these methods provide high accuracy for similar cost as low-order methods. We use an in-house three-dimensional flux reconstruction Navier-Stokes solver to simulate secondary flows and vortical structures within a rigid 180-degree curved artery model under pulsatile flow of a Newtonian blood-analog fluid. Our simulations use a physiological flowrate waveform taken from the carotid artery. We are particularly interested in the dynamics during the deceleration phase of the waveform, where we observe the deformed-Dean, Dean, Lyne and Wall vortices. Our numerical results reveal the complex nature of these vortices both in space and time and their effect on overall wall shear stress. Numerical results agree with and complement experimental results obtained in our laboratory using particle image velocimetry. Supported by the GW Center for Biomimetics and Bioinspired Engineering.

Viscoacoustic anisotropic full waveform inversion

NASA Astrophysics Data System (ADS)

Qu, Yingming; Li, Zhenchun; Huang, Jianping; Li, Jinli

2017-01-01

A viscoacoustic vertical transverse isotropic (VTI) quasi-differential wave equation, which takes account for both the viscosity and anisotropy of media, is proposed for wavefield simulation in this study. The finite difference method is used to solve the equations, for which the attenuation terms are solved in the wavenumber domain, and all remaining terms in the time-space domain. To stabilize the adjoint wavefield, robust regularization operators are applied to the wave equation to eliminate the high-frequency component of the numerical noise produced during the backward propagation of the viscoacoustic wavefield. Based on these strategies, we derive the corresponding gradient formula and implement a viscoacoustic VTI full waveform inversion (FWI). Numerical tests verify that our proposed viscoacoustic VTI FWI can produce accurate and stable inversion results for viscoacoustic VTI data sets. In addition, we test our method's sensitivity to velocity, Q, and anisotropic parameters. Our results show that the sensitivity to velocity is much higher than that to Q and anisotropic parameters. As such, our proposed method can produce acceptable inversion results as long as the Q and anisotropic parameters are within predefined thresholds.

A Study of Regional Waveform Calibration in the Eastern Mediterranean Region.

NASA Astrophysics Data System (ADS)

di Luccio, F.; Pino, A.; Thio, H.

2002-12-01

We modeled Pnl phases from several moderate magnitude events in the eastern Mediterranean to test methods and to develop path calibrations for source determination. The study region spanning from the eastern part of the Hellenic arc to the eastern Anatolian fault is mostly interested by moderate earthquakes, that can produce relevant damages. The selected area consists of several tectonic environment, which produces increased level of difficulty in waveform modeling. The results of this study are useful for the analysis of regional seismicity and for seismic hazard as well, in particular because very few broadband seismic stations are available in the selected area. The obtained velocity model gives a 30 km crustal tickness and low upper mantle velocities. The applied inversion procedure to determine the source mechanism has been successful, also in terms of discrimination of depth, for the entire range of selected paths. We conclude that using the true calibration of the seismic structure and high quality broadband data, it is possible to determine the seismic source in terms of mechanism, even with a single station.

Adaptive OFDM Radar Waveform Design for Improved Micro-Doppler Estimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sen, Satyabrata

Here we analyze the performance of a wideband orthogonal frequency division multiplexing (OFDM) signal in estimating the micro-Doppler frequency of a rotating target having multiple scattering centers. The use of a frequency-diverse OFDM signal enables us to independently analyze the micro-Doppler characteristics with respect to a set of orthogonal subcarrier frequencies. We characterize the accuracy of micro-Doppler frequency estimation by computing the Cramer-Rao bound (CRB) on the angular-velocity estimate of the target. Additionally, to improve the accuracy of the estimation procedure, we formulate and solve an optimization problem by minimizing the CRB on the angular-velocity estimate with respect to themore » OFDM spectral coefficients. We present several numerical examples to demonstrate the CRB variations with respect to the signal-to-noise ratios, number of temporal samples, and number of OFDM subcarriers. We also analysed numerically the improvement in estimation accuracy due to the adaptive waveform design. A grid-based maximum likelihood estimation technique is applied to evaluate the corresponding mean-squared error performance.« less

Upper crustal structure beneath East Java from ambient noise tomography: A preliminary result

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martha, Agustya Adi; Graduate Research on Earthquakes and Active Tectonics, Institut Teknologi Bandung, Bandung; Widiyantoro, Sri

East Java has a fairly complex geological structure. Physiographically East Java can be divided into three zones, i.e. the Southern Mountains zone in the southern part, the Kendeng zone in the middle part, and the Rembang zone in the northern part. Most of the seismic hazards in this region are due to processes in the upper crust. In this study, the Ambient Noise Tomography (ANT) method is used to image the upper crustal structure beneath East Java. We have used seismic waveform data recorded by 8Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 16 portable seismographs installed formore » 2 to 8 weeks. The data were processed to obtain waveforms fromnoise cross-correlation between pairs of seismographic stations. Our preliminary results indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly as shown by our tomographic images.« less

Seismic Observations Indicating That the 2015 Ogasawara (Bonin) Earthquake Ruptured Beneath the 660 km Discontinuity

NASA Astrophysics Data System (ADS)

Kuge, Keiko

2017-11-01

The termination of deep earthquakes at a depth of 700 km is a key feature for understanding the physical mechanism of deep earthquakes. The 680 km deep 30 May 2015, Ogasawara (Bonin) earthquake (Mw 7.9) and its aftershocks were recorded by seismic stations at distances from 7° to 19°. Synthetic seismograms indicate that the P waveforms depend on whether the earthquake is located above or below the 660 km discontinuity. In this study, I show that broadband recordings indicate that the 2015 earthquake may have occurred below the 660 km velocity discontinuity. Recordings of the P wave from the strongest aftershock lack evidence for wave triplication expected when a subhorizontal discontinuity underlies the hypocenter. Theoretical waveforms computed with a 660 km discontinuity above the aftershock and mainshock match the observed waveforms more accurately. These observations may indicate earthquake ruptures due to mantle minerals other than olivine or strong deformation of the 660 km phase transition.

Simulations of Ground Motion in Southern California based upon the Spectral-Element Method

NASA Astrophysics Data System (ADS)

Tromp, J.; Komatitsch, D.; Liu, Q.

2003-12-01

We use the spectral-element method to simulate ground motion generated by recent well-recorded small earthquakes in Southern California. Simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than twenty thousand kilometers of seismic reflection profiles. The numerical simulations account for 3D variations of seismic wave speeds and density, topography and bathymetry, and attenuation. Simulations for several small recent events demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 seconds and longer inside the Los Angeles basin and 6 seconds and longer elsewhere. Peak ground displacement, velocity and acceleration maps illustrate that significant amplification occurs in the basin. Centroid-Moment Tensor mechanisms are obtained based upon Pnl and surface waveforms and numerically calculated 3D Frechet derivatives. We use a combination of waveform and waveform-envelope misfit criteria, and facilitate pure double-couple or zero-trace moment-tensor inversions.

Improved source inversion from joint measurements of translational and rotational ground motions

NASA Astrophysics Data System (ADS)

Donner, S.; Bernauer, M.; Reinwald, M.; Hadziioannou, C.; Igel, H.

2017-12-01

Waveform inversion for seismic point (moment tensor) and kinematic sources is a standard procedure. However, especially in the local and regional distances a lack of appropriate velocity models, the sparsity of station networks, or a low signal-to-noise ratio combined with more complex waveforms hamper the successful retrieval of reliable source solutions. We assess the potential of rotational ground motion recordings to increase the resolution power and reduce non-uniquenesses for point and kinematic source solutions. Based on synthetic waveform data, we perform a Bayesian (i.e. probabilistic) inversion. Thus, we avoid the subjective selection of the most reliable solution according the lowest misfit or other constructed criterion. In addition, we obtain unbiased measures of resolution and possible trade-offs. Testing different earthquake mechanisms and scenarios, we can show that the resolution of the source solutions can be improved significantly. Especially depth dependent components show significant improvement. Next to synthetic data of station networks, we also tested sparse-network and single station cases.

An Alternating Current Electroosmotic Pump Based on Conical Nanopore Membranes.

PubMed

Wu, Xiaojian; Ramiah Rajasekaran, Pradeep; Martin, Charles R

2016-04-26

Electroosmotic flow (EOF) is used to pump solutions through microfluidic devices and capillary electrophoresis columns. We describe here an EOF pump based on membrane EOF rectification, an electrokinetic phenomenon we recently described. EOF rectification requires membranes with asymmetrically shaped pores, and conical pores in a polymeric membrane were used here. We show here that solution flow through the membrane can be achieved by applying a symmetrical sinusoidal voltage waveform across the membrane. This is possible because the alternating current (AC) carried by ions through the pore is rectified, and we previously showed that rectified currents yield EOF rectification. We have investigated the effect of both the magnitude and frequency of the voltage waveform on flow rate through the membrane, and we have measured the maximum operating pressure. Finally, we show that operating in AC mode offers potential advantages relative to conventional DC-mode EOF pumps.

Effect of Stagger on the Vibroacoustic Loads from Clustered Rockets

NASA Technical Reports Server (NTRS)

Rojo, Raymundo; Tinney, Charles E.; Ruf, Joseph H.

2016-01-01

The effect of stagger startup on the vibro-acoustic loads that form during the end- effects-regime of clustered rockets is studied using both full-scale (hot-gas) and laboratory scale (cold gas) data. Both configurations comprise three nozzles with thrust optimized parabolic contours that undergo free shock separated flow and restricted shock separated flow as well as an end-effects regime prior to flowing full. Acoustic pressure waveforms recorded at the base of the nozzle clusters are analyzed using various statistical metrics as well as time-frequency analysis. The findings reveal a significant reduction in end- effects-regime loads when engine ignition is staggered. However, regardless of stagger, both the skewness and kurtosis of the acoustic pressure time derivative elevate to the same levels during the end-effects-regime event thereby demonstrating the intermittence and impulsiveness of the acoustic waveforms that form during engine startup.

Experimental validation of numerical simulations on a cerebral aneurysm phantom model

PubMed Central

Seshadhri, Santhosh; Janiga, Gábor; Skalej, Martin; Thévenin, Dominique

2012-01-01

The treatment of cerebral aneurysms, found in roughly 5% of the population and associated in case of rupture to a high mortality rate, is a major challenge for neurosurgery and neuroradiology due to the complexity of the intervention and to the resulting, high hazard ratio. Improvements are possible but require a better understanding of the associated, unsteady blood flow patterns in complex 3D geometries. It would be very useful to carry out such studies using suitable numerical models, if it is proven that they reproduce accurately enough the real conditions. This validation step is classically based on comparisons with measured data. Since in vivo measurements are extremely difficult and therefore of limited accuracy, complementary model-based investigations considering realistic configurations are essential. In the present study, simulations based on computational fluid dynamics (CFD) have been compared with in situ, laser-Doppler velocimetry (LDV) measurements in the phantom model of a cerebral aneurysm. The employed 1:1 model is made from transparent silicone. A liquid mixture composed of water, glycerin, xanthan gum and sodium chloride has been specifically adapted for the present investigation. It shows physical flow properties similar to real blood and leads to a refraction index perfectly matched to that of the silicone model, allowing accurate optical measurements of the flow velocity. For both experiments and simulations, complex pulsatile flow waveforms and flow rates were accounted for. This finally allows a direct, quantitative comparison between measurements and simulations. In this manner, the accuracy of the employed computational model can be checked. PMID:24265876

A comparison of the wavelet and short-time fourier transforms for Doppler spectral analysis.

PubMed

Zhang, Yufeng; Guo, Zhenyu; Wang, Weilian; He, Side; Lee, Ting; Loew, Murray

2003-09-01

Doppler spectrum analysis provides a non-invasive means to measure blood flow velocity and to diagnose arterial occlusive disease. The time-frequency representation of the Doppler blood flow signal is normally computed by using the short-time Fourier transform (STFT). This transform requires stationarity of the signal during a finite time interval, and thus imposes some constraints on the representation estimate. In addition, the STFT has a fixed time-frequency window, making it inaccurate to analyze signals having relatively wide bandwidths that change rapidly with time. In the present study, wavelet transform (WT), having a flexible time-frequency window, was used to investigate its advantages and limitations for the analysis of the Doppler blood flow signal. Representations computed using the WT with a modified Morlet wavelet were investigated and compared with the theoretical representation and those computed using the STFT with a Gaussian window. The time and frequency resolutions of these two approaches were compared. Three indices, the normalized root-mean-squared errors of the minimum, the maximum and the mean frequency waveforms, were used to evaluate the performance of the WT. Results showed that the WT can not only be used as an alternative signal processing tool to the STFT for Doppler blood flow signals, but can also generate a time-frequency representation with better resolution than the STFT. In addition, the WT method can provide both satisfactory mean frequencies and maximum frequencies. This technique is expected to be useful for the analysis of Doppler blood flow signals to quantify arterial stenoses.

Swarms of repeating long-period earthquakes at Shishaldin Volcano, Alaska, 2001-2004

USGS Publications Warehouse

Petersen, Tanja

2007-01-01

During 2001–2004, a series of four periods of elevated long-period seismic activity, each lasting about 1–2 months, occurred at Shishaldin Volcano, Aleutian Islands, Alaska. The time periods are termed swarms of repeating events, reflecting an abundance of earthquakes with highly similar waveforms that indicate stable, non-destructive sources. These swarms are characterized by increased earthquake amplitudes, although the seismicity rate of one event every 0.5–5 min has remained more or less constant since Shishaldin last erupted in 1999. A method based on waveform cross-correlation is used to identify highly repetitive events, suggestive of spatially distinct source locations. The waveform analysis shows that several different families of similar events co-exist during a given swarm day, but generally only one large family dominates. A network of hydrothermal fractures may explain the events that do not belong to a dominant repeating event group, i.e. multiple sources at different locations exist next to a dominant source. The dominant waveforms exhibit systematic changes throughout each swarm, but some of these waveforms do reappear over the course of 4 years indicating repeatedly activated source locations. The choked flow model provides a plausible trigger mechanism for the repeating events observed at Shishaldin, explaining the gradual changes in waveforms over time by changes in pressure gradient across a constriction within the uppermost part of the conduit. The sustained generation of Shishaldin's long-period events may be attributed to complex dynamics of a multi-fractured hydrothermal system: the pressure gradient within the main conduit may be regulated by temporarily sealing and reopening of parallel flow pathways, by the amount of debris within the main conduit and/or by changing gas influx into the hydrothermal system. The observations suggest that Shishaldin's swarms of repeating events represent time periods during which a dominant source is activated.

System identification based on deconvolution and cross correlation: An application to a 20‐story instrumented building in Anchorage, Alaska

USGS Publications Warehouse

Wen, Weiping; Kalkan, Erol

2017-01-01

Deconvolution and cross‐correlation techniques are used for system identification of a 20‐story steel, moment‐resisting frame building in downtown Anchorage, Alaska. This regular‐plan midrise structure is instrumented with a 32‐channel accelerometer array at 10 levels. The impulse response functions (IRFs) and correlation functions (CFs) are computed based on waveforms recorded from ambient vibrations and five local and regional earthquakes. The earthquakes occurred from 2005 to 2014 with moment magnitudes between 4.7 and 6.2 over a range of azimuths at epicenter distances of 13.3–183 km. The building’s fundamental frequencies and mode shapes are determined using a complex mode indicator function based on singular value decomposition of multiple reference frequency‐response functions. The traveling waves, identified in IRFs with a virtual source at the roof, and CFs are used to estimate the intrinsic attenuation associated with the fundamental modes and shear‐wave velocity in the building. Although the cross correlation of the waveforms at various levels with the corresponding waveform at the first floor provides more complicated wave propagation than that from the deconvolution with virtual source at the roof, the shear‐wave velocities identified by both techniques are consistent—the largest difference in average values is within 8%. The median shear‐wave velocity from the IRFs of five earthquakes is 191  m/s for the east–west (E‐W), 205  m/s for the north–south (N‐S), and 176  m/s for the torsional responses. The building’s average intrinsic‐damping ratio is estimated to be 3.7% and 3.4% in the 0.2–1 Hz frequency band for the E‐W and N‐S directions, respectively. These results are intended to serve as reference for the undamaged condition of the building, which may be used for tracking changes in structural integrity during and after future earthquakes.

Seismic anisotropy in the uppermost mantle beneath oceanic regions from data of broadband OBSs

NASA Astrophysics Data System (ADS)

Takeo, A.; Nishida, K.; Isse, T.; Kawakatsu, H.; Shiobara, H.; Sugioka, H.; Ito, A.; Kanazawa, T.; Suetsugu, D.

2011-12-01

For improving vertical resolution of seismic-anisotropy structure at depths of 10-100 km beneath oceanic regions, we measured phase velocities of surface waves in a broadband frequency range by two methods: the ambient noise interferometry in frequency higher than 0.035 Hz, and array analysis of event waveforms in lower frequency. We use seismograms recorded by broadband ocean bottom seismometers (BBOBSs) in two regions: (i) the Shikoku Basin in the Philippine Sea by Stagnant Slab Project, and (ii) east of Tahiti Island by a project called the tomographic investigation by seafloor array experiment for Society hotspot (TIARES). The frequency ranges of phase-velocity measurements in each region are summarized in Table. For the case of Shikoku Basin, we invert phase velocities for radially anisotropic structure. The resultant structure shows decrease of shear-wave velocity by 6-8 % at depths of 50-70 km, and intensification of radial anisotropy (VSH>VSV) from 1-2 % at 10-20 km depth to 4-6 % at 40-70 km depth. These results indicate increasing amount of preferred-oriented olivine crystal, and/or horizontal layering of partial melt near the boundary between the lithosphere and the asthenosphere. The azimuthal anisotropy of phase velocity in the Shikoku Basin is also investigated by array analysis of event waveforms for the fundamental mode of Rayleigh wave at 0.03 Hz. The fastest direction is NW, and consistent with direction of present plate motion. The velocity difference between fastest and slowest directions is 1-2 %. These results mainly reflect shear-wave velocity at depth of 30-60 km, and imply that lattice preferred orientation is, at least, partly (though may not be fully) responsible for the anisotropy in the depth range. We will obtain radially anisotropic structure and azimuthal anisotropy in Tahiti region, and will present difference between two regions.
Frequency range of phase-velocity measurements for two regions of analyses.

Effects of Isotropic and Anisotropic Structure in the Lowermost Mantle on High-Frequency Body Waveforms

NASA Astrophysics Data System (ADS)

Parisi, L.; Ferreira, A. M. G.; Ritsema, J.

2015-12-01

It has been observed that vertically (SV) and horizontally (SH) polarised S waves crossing the lowermost mantle sometimes are split by a few seconds The splitting of such waves is often interpreted in terms of seismic anisotropy in the D" region. Here we investigate systematically the effects of elastic, anelastic, isotropic and anisotropic structure on shear-wave splitting, including 3-D variations in some of these physical properties. Taking advantage of accurate waveform modeling techniques such as Gemini and the Spectral Element Method we generate three-component theoretical waveforms in a wide set of 1-D and 3-D, isotropic and radially anisotropic earth models, accurate down to a wave period of T~5.6s. Our numerical simulations in isotropic earth models show that the contamination of S waves by other phases can generate an apparent splitting between SH and SV waves. In particular, in the case of very shallow sources, the sS phase can interfere with the direct S phase, resulting in split SH and SV pulses when the SH and SV (or sSH and sSV) waves have different polarity or a substantial amplitude difference. In the case of deep earthquake sources, a positive shear velocity jump at the top of the D" can cause the triplication of S waves and the ScSH and ScSV phases can have different polarity. Thus, when the triplicated S wave is combined with the ScS phase, the resulting SH-ScSH and SV-ScSV phases may seem split. On the other hand, in the absence of a sharp vertical variation in the shear wave velocity, the difference in polarity between ScSH and ScSV can make the SH pulse larger than SV and thus also lead to apparent splitting between these phases. This effect depends on the thickness of the D" and the Vs gradient within it. S waveforms simulated in radially anisotropic models reveal that a radial anisotropy of ξ=1.07 in the D" seems to be necessary to explain the 2-3s of splitting observed in waveforms recorded in Tanzania from an event in the Banda Sea. However, our analysis also shows that other factors such as sharp vertical variations at the top of D" and gradients of Vs and η within the D'' may also affect the observed waveforms. This study suggests that caution should be taken when interpreting SH-SV splitting of deep mantle body waves exclusively in terms of anisotropy in the lowermost mantle.

Effect of a Flared Renal Stent on the Performance of Fenestrated Stent-Grafts at Rest and Exercise Conditions.

PubMed

Kandail, Harkamaljot; Hamady, Mohamad; Xu, Xiao Yun

2016-10-01

To quantify the hemodynamic impact of a flared renal stent on the performance of fenestrated stent-grafts (FSGs) by analyzing flow patterns and wall shear stress-derived parameters in flared and nonflared FSGs in different physiologic scenarios. Hypothetical models of FSGs were created with and without flaring of the proximal portion of the renal stent. Flared FSGs with different dilation angles and protrusion lengths were examined, as well as a nonplanar flared FSG to account for lumbar curvature. Laminar and pulsatile blood flow was simulated by numerically solving Navier-Stokes equations. A physiologically realistic flow rate waveform was prescribed at the inlet, while downstream vasculature was modeled using a lumped parameter 3-element windkessel model. No slip boundary conditions were imposed at the FSG walls, which were assumed to be rigid. While resting simulations were performed on all the FSGs, exercise simulations were also performed on a flared FSG to quantify the effect of flaring in different physiologic scenarios. For cycle-averaged inflow of 2.94 L/min (rest) and 4.63 L/min (exercise), 27% of blood flow was channeled into each renal branch at rest and 21% under exercise for all the flared FSGs examined. Although the renal flow waveform was not affected by flaring, flow within the flared FSGs was disturbed. This flow disturbance led to high endothelial cell activation potential (ECAP) values at the renal ostia for all the flared geometries. Reducing the dilation angle or protrusion length and exercise lowered the ECAP values for flared FSGs. Flaring of renal stents has a negligible effect on the time dependence of renal flow rate waveforms and can maintain sufficient renal perfusion at rest and exercise. Local flow patterns are, however, strongly dependent on renal flaring, which creates a local flow disturbance and may increase the thrombogenicity at the renal ostia. Smaller dilation angles, shorter protrusion lengths, and moderate lower limb exercise are likely to reduce the risk of thrombosis in flared geometries. © The Author(s) 2016.

Focal Depth of the WenChuan Earthquake Aftershocks from modeling of Seismic Depth Phases

NASA Astrophysics Data System (ADS)

Luo, Y.; Zeng, X.; Chong, J.; Ni, S.; Chen, Y.

2008-12-01

After the 05/12/2008 great WenChuan earthquake in Sichuan Province of China, tens of thousands earthquakes occurred with hundreds of them stronger than M4. Those aftershocks provide valuable information about seismotectonics and rupture processes for the mainshock, particularly accurate spatial distribution of aftershocks is very informational for determining rupture fault planes. However focal depth can not be well resolved just with first arrivals recorded by relatively sparse network in Sichuan Province, therefore 3D seismicity distribution is difficult to obtain though horizontal location can be located with accuracy of 5km. Instead local/regional depth phases such as sPmP, sPn, sPL and teleseismic pP,sP are very sensitive to depth, and be readily modeled to determine depth with accuracy of 2km. With reference 1D velocity structure resolved from receiver functions and seismic refraction studies, local/regional depth phases such as sPmP, sPn and sPL are identified by comparing observed waveform with synthetic seismograms by generalized ray theory and reflectivity methods. For teleseismic depth phases well observed for M5.5 and stronger events, we developed an algorithm in inverting both depth and focal mechanism from P and SH waveforms. Also we employed the Cut and Paste (CAP) method developed by Zhao and Helmberger in modeling mechanism and depth with local waveforms, which constrains depth by fitting Pnl waveforms and the relative weight between surface wave and Pnl. After modeling all the depth phases for hundreds of events , we find that most of the M4 earthquakes occur between 2-18km depth, with aftershocks depth ranging 4-12km in the southern half of Longmenshan fault while aftershocks in the northern half featuring large depth range up to 18km. Therefore seismogenic zone in the northern segment is deeper as compared to the southern segment. All the aftershocks occur in upper crust, given that the Moho is deeper than 40km, or even 60km west of the Longmenshan fault. Absence of mid-lower crustal shocks supports the model of lower crustal flow beneath eastern Tibetan plateau, which is probably responsible for Longmenshan uplifting and hence the Wenchuan earthquake.

Investigation of Seismic Events associated with the Sinkhole at Napoleonville Salt Dome, Louisiana

NASA Astrophysics Data System (ADS)

Nayak, A.; Dreger, D. S.

2015-12-01

This study describes the ongoing efforts in analysis of the intense sequence of complex seismic events associated with the formation of a large sinkhole at Napoleonville Salt Dome, Assumption Parish, Louisiana in August 2012. Point source centroid seismic moment tensor (MT) inversion of these events using data from a temporary network of broadband stations established by the United States Geological Survey had previously revealed large volume-increase components. We investigate the effect of 3D velocity structure of the salt dome on wave propagation in the frequency range of interest (0.1-0.3 Hz) by forward modeling synthetic waveforms using MT solutions that were computed using Green's functions assuming two separate 1D velocity models for stations over the salt dome and stations on the sedimentary strata surrounding the salt dome separately. We also use a matched filter technique to detect smaller events that went undetected by the automated grid-search based scanning and MT inversion algorithm using the waveforms of the larger events as templates. We also analyze the change in spectral content of the events, many of which exhibit a spectral peak at 0.4 Hz with a duration of > 60 seconds. The decrease in spectral amplitudes with distance also gives an estimate of high anelastic attenuation that damps reverberations within the shallow low velocity layers. Finally, we use noise cross-correlation analysis to explore changes in the green's functions during the development of the sinkhole and verify the sediment velocity model by comparing observed and synthetic surface wave dispersion.

Towards Crustal Structure of Java Island (Sunda Arc) from Ambient Seismic Noise Tomography

NASA Astrophysics Data System (ADS)

Widiyantoro, Sri; Zulhan, Zulfakriza; Martha, Agustya; Saygin, Erdinc; Cummins, Phil

2015-04-01

In our previous studies, P- and S-wave velocity structures beneath the Sunda Arc were successfully imaged using a global data set and a nested regional-global tomographic method was employed. To obtain more detailed P- and S-wave velocity structures beneath Java, in the central part of the Sunda Arc, we then used local data sets, i.e. newline from the MErapi AMphibious EXperiment (MERAMEX) and the Meteorological, Climatological and Geophysical Agency (MCGA), as well as employed a double-difference technique for tomographic imaging. The results of the imaging show e.g. that P- and S-wave velocities are significantly reduced in the uppermost mantle beneath central Java. In order to obtain detailed crustal structure information beneath Java, the Ambient Noise Tomography (ANT) method was used. The application of this method to the MERAMEX data has produced a good crustal model beneath central Java. We continue our experiment to image crustal structure of eastern Java. We have used seismic waveform data recorded by 22 MCGA stationary seismographic stations and 25 portable seismographs installed for 2 to 8 weeks. The data were processed to obtain waveforms of cross-correlated noise between pairs of seismographic stations. Our preliminary results presented here indicate that the Kendeng zone, an area of low gravity anomaly, is associated with a low velocity zone. On the other hand, the southern mountain range, which has a high gravity anomaly, is related to a high velocity anomaly (as shown by our tomographic images). In future work we will install more seismographic stations in eastern Java as well as in western Java to conduct ANT imaging for the whole of Java Island. The expected result combined with the mantle velocity models resulting from our body wave tomography will allow for accurate location of earthquake hypocenters and determination of regional tectonic structures. Both of these are valuable for understanding seismic hazard in Java, the most densely populated island in the world.

Velocity models and images using full waveform inversion and reverse time migration for the offshore permafrost in the Canadian shelf of Beaufort Sea, Arctic

NASA Astrophysics Data System (ADS)

Kang, S. G.; Hong, J. K.; Jin, Y. K.; Kim, S.; Kim, Y. G.; Dallimore, S.; Riedel, M.; Shin, C.

2015-12-01

During Expedition ARA05C (from Aug 26 to Sep 19, 2014) on the Korean icebreaker RV ARAON, the multi-channel seismic (MCS) data were acquired on the outer shelf and slope of the Canadian Beaufort Sea to investigate distribution and internal geological structures of the offshore ice-bonded permafrost and gas hydrates, totaling 998 km L-km with 19,962 shots. The MCS data were recorded using a 1500 m long solid-type streamer with 120 channels. Shot and group spacing were 50 m and 12.5 m, respectively. Most MCS survey lines were designed perpendicular and parallel to the strike of the shelf break. Ice-bonded permafrost or ice-bearing sediments are widely distributed under the Beaufort Sea shelf, which have formed during periods of lower sea level when portions of the shelf less than ~100m water depth were an emergent coastal plain exposed to very cold surface. The seismic P-wave velocity is an important geophysical parameter for identifying the distribution of ice-bonded permafrost with high velocity in this area. Recently, full waveform inversion (FWI) and reverse time migration (RTM) are commonly used to delineate detailed seismic velocity information and seismic image of geological structures. FWI is a data fitting procedure based on wave field modeling and numerical analysis to extract quantitative geophysical parameters such as P-, S-wave velocities and density from seismic data. RTM based on 2-way wave equation is a useful technique to construct accurate seismic image with amplitude preserving of field data. In this study, we suggest two-dimensional P-wave velocity model (Figure.1) using the FWI algorithm to delineate the top and bottom boundaries of ice-bonded permafrost in the Canadian shelf of Beaufort Sea. In addition, we construct amplitude preserving migrated seismic image using RTM to interpret the geological history involved with the evolution of permafrost.

Imaging the density distributions at the regional scale using full waveform and gravity data inversion - Application to the Pyrenees

NASA Astrophysics Data System (ADS)

Martin, Roland; Chevrot, Sébastien; Wang, Yi; Spangenberg, Hannah; Goubet, Marie; Monteiller, Vadim; Komatitsch, Dimitri; Seoane, Lucia; Dufréchou, Grégory

2017-04-01

We present a hybrid inversion method that allows us to image density distributions at the regional scale using both seismic and gravity data. One main goal is to obtain densities and seismic wave velocities (P and S) in the lithosphere with a fine resolution to get important constraints on the mineralogic composition and thermal state of the lithosphere. In the context of the Pyrenees (located between Spain and France), accurate Vp and Vs seismic velocity models are computed first on a 3D spectral element grid at the scale of the Pyrenees by inverting teleseismic full waveforms. In a second step, Vp velocities are mapped to densities using empirical relations to build an a priori density model. BGI and BRGM Bouguer gravity anomaly data sets are then inverted on the same 3D spectral element grid as the Vp model at a resolution of 1-2 km by using high-order numerical integration formulae. Solutions are compared to those obtained using classical semi-analytical techniques. This procedure opens the possibility to invert both teleseismic and gravity data on the same finite-element grid. It can handle topography of the free surface in the same spectral-element distorted mesh that is used to solve the wave equation, without performing extra interpolations between different grids and models. WGS84 curvature, SRTM or ETOPO1 topographies are used.

Crustal and Upper Mantle S-velocity Structure From Receiver Functions Analisys Around Terra Nova Bay Base, Antartica

NASA Astrophysics Data System (ADS)

Piana Agostinetti, N.; Amato, A.; Cattaneo, M.; de Gori, P.; di Bona, M.

In the framework of the italian PNRA (Progetto Nazionale di Ricerche in Antartide), we have started to re-analize teleseismic waveforms recorded, using three-components seismometers (equipped with 5 seconds sensors, Lennartz 3D-5s), during five summer campaings, from 1993 to 2000. Seismic stations were deployed around Terra Nova Bay (TNB) italian base, from the sea to reach the interior of the Transantartic Moun- tains (TAM), the most striking example of nocontractional mountain belt. During the last campaingn (1999-2000) seismic stations were deployed deep into Northern Vic- toria Land to reach Rennik and Lillie Glaciers Area and George V coast region, the northest part of TAM. Our main goals were: to compute, using frequency-domanin deconvolution method by Di Bona [1998], Receiver Functions covering all the area around TNB italian antartic base; to map of Moho-depth and intercrustal S-waves ve- locity discontinuity from 1-D velocity model computed using Sambridge's inversion scheme [Sambridge,1999]; to analize new teleseimic waveforms recorded near TNB base: continuos recording, from 1999 to present, permits more accurate modelling S-velocity crustal structure in this critical area situated at the edge of the ipothetic rift [Stern and ten Brik, 1989; Stump and Fitzgerald, 1992; ten Brik et al., 1997]; to present final results from BACKTAM expedition.

Extension of the Helmholtz-Smoluchowski velocity to the hydrophobic microchannels with velocity slip.

PubMed

Park, H M; Kim, T W

2009-01-21

Electrokinetic flows through hydrophobic microchannels experience velocity slip at the microchannel wall, which affects volumetric flow rate and solute retention time. The usual method of predicting the volumetric flow rate and velocity profile for hydrophobic microchannels is to solve the Navier-Stokes equation and the Poisson-Boltzmann equation for the electric potential with the boundary condition of velocity slip expressed by the Navier slip coefficient, which is computationally demanding and defies analytic solutions. In the present investigation, we have devised a simple method of predicting the velocity profiles and volumetric flow rates of electrokinetic flows by extending the concept of the Helmholtz-Smoluchowski velocity to microchannels with Navier slip. The extended Helmholtz-Smoluchowski velocity is simple to use and yields accurate results as compared to the exact solutions. Employing the extended Helmholtz-Smoluchowski velocity, the analytical expressions for volumetric flow rate and velocity profile for electrokinetic flows through rectangular microchannels with Navier slip have been obtained at high values of zeta potential. The range of validity of the extended Helmholtz-Smoluchowski velocity is also investigated.

Deformation of Tibetan Crust and Mantle and the Uplift of the Plateau: Insights from Broadband Surface Waves

NASA Astrophysics Data System (ADS)

Agius, M. R.; Lebedev, S.

2013-12-01

Seismic deployments over the last two decades have produced dense broadband data coverage across the Tibetan Plateau. Yet, the lithospheric dynamics of Tibet is still debated, with very different end-member models advocated to this day. Uncertainties over the anomalies in seismic tomography models contribute to the uncertainty of their interpretations, ranging from the subduction of India as far as northern Tibet to subduction of Asia there and to extreme viscous thickening of the entire Tibetan lithosphere. Within the lithosphere itself, a low-viscosity layer in the mid-lower crust is evidenced by many observations. It is still unclear, however, whether this layer accommodates a large-scale channel flow (which may have uplifted northern and eastern Tibet, according to one model) or if, instead, deformation within it is similar to that observed at the surface (which implies different uplift mechanisms). Broad-band surface waves provide resolving power from the upper crust down to the asthenosphere, for both isotropic-average shear-wave speeds (proxies for composition and temperature) and the radial and azimuthal shear-wave anisotropy (indicative of the patterns of deformation and flow). We measured highly accurate Love- and Rayleigh-wave phase-velocity curves in broad period ranges (up to 5-200 s) for a few tens of pairs and groups of stations across Tibet, combining, in each case, hundreds to thousands of inter-station measurements, made with cross-correlation and waveform-inversion methods. Robust shear-velocity profiles were then determined by series of non-linear inversions, yielding depth-dependent ranges of shear speeds and radial anisotropy consistent with the data. Temperature anomalies in the upper mantle were estimated from shear-velocity ones using accurate petro-physical relationships. Azimuthal anisotropy in the crust and upper mantle was determined by surface-wave tomography and, also, by sub-array analysis targeting the anisotropy amplitude. Our results show that the prominent high-velocity anomalies in the upper mantle are most consistent with the presence of subducted Indian lithosphere beneath large portions of Tibet. Estimated thermal anomalies within the high-velocity features match those expected for subducted India. The morphology of India's subduction beneath Tibet is complex and shows pronounced west-east variations. Beneath eastern and northeastern Tibet, in particular, the subducted Indian lithosphere appears to have subducted, at a shallow angle, hundreds of km NNE-wards. Azimuthal anisotropy beneath Tibet is distributed in multiple layers with different fast-propagations directions, which accounts for the complexity of published shear-wave splitting observations. The fast directions within the mid-lower crust are parallel to the extensional components of the current strain rate field at the surface, consistent with similar deformation through the entire crust, rather than channel flow. Anisotropy within the asthenosphere beneath northeastern Tibet (sandwiched between the Tibetan lithosphere above and the subducted Indian lithosphere below) indicates SSW-NNE flow, parallel to the direction of motion of the Indian Plate, including its subducted leading edge.

Experimental studies on flow visualization and velocity field of compression ramp with different incoming boundary layers

NASA Astrophysics Data System (ADS)

Wu, Yu; Yi, Shi-He; He, Lin; Chen, Zhi; Zhu, Yang-Zhu

2014-11-01

Experimental studies which focus on flow visualization and the velocity field of a supersonic laminar/turbulent flow over a compression ramp were carried out in a Mach 3.0 wind tunnel. Fine flow structures and velocity field structures were obtained via NPLS (nanoparticle-tracer planar laser scattering) and PIV (particle image velocimetry) techniques, time-averaged flow structures were researched, and spatiotemporal evolutions of transient flow structures were analyzed. The flow visualization results indicated that when the ramp angles were 25°, a typical separation occurred in the laminar flow, some typical flow structures such as shock induced by the boundary layer, separation shock, reversed flow and reattachment shock were visible clearly. While a certain extent separation occurred in turbulent flow, the separation region was much smaller. When the ramp angles were 28°, laminar flow separated further, and the separation region expanded evidently, flow structures in the separation region were complex. While a typical separation occurred in turbulent flow, reversed flow structures were significant, flow structures in the separation region were relatively simple. The experimental results of velocity field were corresponding to flow visualization, and the velocity field structures of both compression ramp flows agreed with the flow structures well. There were three layered structures in the U component velocity, and the V component velocity appeared like an oblique “v”. Some differences between these two compression ramp flows can be observed in the velocity profiles of the shear layer and the shearing intensity.

Source mechanism of small long-period events at Mount St. Helens in July 2005 using template matching, phase-weighted stacking, and full-waveform inversion

USGS Publications Warehouse

Matoza, Robin S.; Chouet, Bernard A.; Dawson, Phillip B.; Shearer, Peter M.; Haney, Matthew M.; Waite, Gregory P.; Moran, Seth C.; Mikesell, T. Dylan

2015-01-01

Long-period (LP, 0.5-5 Hz) seismicity, observed at volcanoes worldwide, is a recognized signature of unrest and eruption. Cyclic LP “drumbeating” was the characteristic seismicity accompanying the sustained dome-building phase of the 2004–2008 eruption of Mount St. Helens (MSH), WA. However, together with the LP drumbeating was a near-continuous, randomly occurring series of tiny LP seismic events (LP “subevents”), which may hold important additional information on the mechanism of seismogenesis at restless volcanoes. We employ template matching, phase-weighted stacking, and full-waveform inversion to image the source mechanism of one multiplet of these LP subevents at MSH in July 2005. The signal-to-noise ratios of the individual events are too low to produce reliable waveform-inversion results, but the events are repetitive and can be stacked. We apply network-based template matching to 8 days of continuous velocity waveform data from 29 June to 7 July 2005 using a master event to detect 822 network triggers. We stack waveforms for 359 high-quality triggers at each station and component, using a combination of linear and phase-weighted stacking to produce clean stacks for use in waveform inversion. The derived source mechanism pointsto the volumetric oscillation (~10 m3) of a subhorizontal crack located at shallow depth (~30 m) in an area to the south of Crater Glacier in the southern portion of the breached MSH crater. A possible excitation mechanism is the sudden condensation of metastable steam from a shallow pressurized hydrothermal system as it encounters cool meteoric water in the outer parts of the edifice, perhaps supplied from snow melt.

Ventricular Fibrillation Waveform Changes during Controlled Coronary Perfusion Using Extracorporeal Circulation in a Swine Model.

PubMed

Gazmuri, Raúl J; Kaufman, Christopher L; Baetiong, Alvin; Radhakrishnan, Jeejabai

2016-01-01

Several characteristics of the ventricular fibrillation (VF) waveform have been found predictive of successful defibrillation and hypothesized to reflect the myocardial energy state. In an open-chest swine model of VF, we modeled "average CPR" using extracorporeal circulation (ECC) and assessed the time course of coronary blood flow, myocardial metabolism, and myocardial structure in relation to the amplitude spectral area (AMSA) of the VF waveform without artifacts related to chest compression. VF was induced and left untreated for 8 minutes in 16 swine. ECC was then started adjusting its flow to maintain a coronary perfusion pressure of 10 mmHg for 10 minutes. AMSA was calculated in the frequency domain and analyzed continuously with a 2.1 s timeframe and a Tukey window that moved ahead every 0.5 s. AMSA progressively declined during untreated VF. With ECC, AMSA increased from 7.0 ± 1.9 mV·Hz (at minute 8) to 12.8 ± 3.3 mV·Hz (at minute 14) (p < 0.05) without subsequent increase and showing a modest correlation with coronary blood flow of borderline statistical significance (r = 0.489, p = 0.0547). Myocardial energy measurements showed marked reduction in phosphocreatine and moderate reduction in ATP with increases in ADP, AMP, and adenosine along with myocardial lactate, all indicative of ischemia. Yet, ischemia did not resolve during ECC despite a coronary blood flow of ~ 30% of baseline. AMSA increased upon return of coronary blood flow during ECC. However, the maximal level was reached after ~ 6 minutes without further change. The significance of the findings for determining the optimal timing for delivering an electrical shock during resuscitation from VF remains to be further explored.

Genesis of the characteristic pulmonary venous pressure waveform as described by the reservoir-wave model

PubMed Central

Bouwmeester, J Christopher; Belenkie, Israel; Shrive, Nigel G; Tyberg, John V

2014-01-01

Conventional haemodynamic analysis of pulmonary venous and left atrial (LA) pressure waveforms yields substantial forward and backward waves throughout the cardiac cycle; the reservoir wave model provides an alternative analysis with minimal waves during diastole. Pressure and flow in a single pulmonary vein (PV) and the main pulmonary artery (PA) were measured in anaesthetized dogs and the effects of hypoxia and nitric oxide, volume loading, and positive-end expiratory pressure (PEEP) were observed. The reservoir wave model was used to determine the reservoir contribution to PV pressure and flow. Subtracting reservoir pressure and flow resulted in ‘excess’ quantities which were treated as wave-related. Wave intensity analysis of excess pressure and flow quantified the contributions of waves originating upstream (from the PA) and downstream (from the LA and/or left ventricle (LV)). Major features of the characteristic PV waveform are caused by sequential LA and LV contraction and relaxation creating backward compression (i.e. pressure-increasing) waves followed by decompression (i.e. pressure-decreasing) waves. Mitral valve opening is linked to a backwards decompression wave (i.e. diastolic suction). During late systole and early diastole, forward waves originating in the PA are significant. These waves were attenuated less with volume loading and delayed with PEEP. The reservoir wave model shows that the forward and backward waves are negligible during LV diastasis and that the changes in pressure and flow can be accounted for by the discharge of upstream reservoirs. In sharp contrast, conventional analysis posits forward and backward waves such that much of the energy of the forward wave is opposed by the backward wave. PMID:25015922

Improved MIMO radar GMTI via cyclic-shift transmission of orthogonal frequency division signals

NASA Astrophysics Data System (ADS)

Li, Fuyou; He, Feng; Dong, Zhen; Wu, Manqing

2018-05-01

Minimum detectable velocity (MDV) and maximum detectable velocity are both important in ground moving target indication (GMTI) systems. Smaller MDV can be achieved by longer baseline via multiple-input multiple-output (MIMO) radar. Maximum detectable velocity is decided by blind velocities associated with carrier frequencies, and blind velocities can be mitigated by orthogonal frequency division signals. However, the scattering echoes from different carrier frequencies are independent, which is not good for improving MDV performance. An improved cyclic-shift transmission is applied in MIMO GMTI system in this paper. MDV performance is improved due to the longer baseline, and maximum detectable velocity performance is improved due to the mitigation of blind velocities via multiple carrier frequencies. The signal model for this mode is established, the principle of mitigating blind velocities with orthogonal frequency division signals is presented; the performance of different MIMO GMTI waveforms is analysed; and the performance of different array configurations is analysed. Simulation results by space-time-frequency adaptive processing proves that our proposed method is a valid way to improve GMTI performance.

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

USGS Publications Warehouse

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

1996-01-01

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.

Extent of the low-velocity region in the lowermost mantle beneath the western Pacific detected by the Vietnamese Broadband Seismograph Array

NASA Astrophysics Data System (ADS)

Takeuchi, N.; Morita, Y.; Xuyen, N. D.; Zung, N. Q.

2008-03-01

We present evidence showing the extent of the low-velocity region in the lowermost mantle beneath the western Pacific. We analyzed S, sS, ScS-S, and sScS-sS travel times observed by the Vietnamese broadband seismograph array deployed as part of the Ocean Hemisphere Project. The abrupt changes in ScS-S and sScS-sS travel times suggest that the western geographical boundary of the low-velocity region is located around 140°E and is sharp (more than 4% velocity contrast within 200 km). The dependency of S and sS travel time anomalies of epicentral distances suggests that the strong low-velocity region is confined to within 400 km from the CMB (core-mantle boundary). The existence of lateral heterogeneities with a 100 km scale inside the low-velocity region is also suggested by the abrupt changes in S and ScS waveforms.

Analysis of flow and LDL concentration polarization in siphon of internal carotid artery: Non-Newtonian effects.

PubMed

Sharifi, Alireza; Niazmand, Hamid

2015-10-01

Carotid siphon is known as one of the risky sites among the human intracranial arteries, which is prone to formation of atherosclerotic lesions. Indeed, scientists believe that accumulation of low density lipoprotein (LDL) inside the lumen is the major cause of atherosclerosis. To this aim, three types of internal carotid artery (ICA) siphon have been constructed to examine variations of hemodynamic parameters in different regions of the arteries. Providing real physiological conditions, blood considered as non-Newtonian fluid and real velocity and pressure waveforms have been employed as flow boundary conditions. Moreover, to have a better estimation of risky sites, the accumulation of LDL particles has been considered, which has been usually ignored in previous relevant studies. Governing equations have been discretized and solved via open source OpenFOAM software. A new solver has been built to meet essential parameters related to the flow and mass transfer phenomena. In contrast to the common belief regarding negligible effect of blood non-Newtonian behavior inside large arteries, current study suggests that the non-Newtonian blood behavior is notable, especially on the velocity field of the U-type model. In addition, it is concluded that neglecting non-Newtonian effects underestimates the LDL accumulation up to 3% in the U-type model at the inner side of both its bends. However, in the V and C type models, non-Newtonian effects become relatively small. Results also emphasize that the outer part of the second bend at the downstream is also at risk similar to the inner part of the carotid bends. Furthermore, from findings it can be implied that the risky sites strongly depend on the ICA shape since the extension of the risky sites are relatively larger for the V-type model, while the LDL concentrations are higher for the C-type model. Copyright © 2015 Elsevier Ltd. All rights reserved.

The propagation characteristics of the plate modes of acoustic emission waves in thin aluminum plates and thin graphite/epoxy composite plates and tubes. Ph.D. Thesis - Johns Hopkins Univ., 1991

NASA Technical Reports Server (NTRS)

Prosser, William H.

1991-01-01

Acoustic emission was interpreted as modes of vibration in plates. Classical plate theory was used to predict dispersion curves for the two fundamental modes and to calculate the shapes of flexural waveforms produced by vertical step function loading. There was good agreement between theoretical and experimental results for aluminum. Composite materials required the use of a higher order plate theory (Reissner-Mindlin) to get good agreement with the measured velocities. Four composite plates with different laminate stacking sequences were studied. The dispersion curves were determined from phase spectra of the time dependent waveforms. Plate modes were shown to be useful for determining the direction of source motion. Aluminum plates were loaded by breaking a pencil lead against their surface. By machining slots at angles to the plane of a plate, the direction in which the force acted was varied. Changing the source motion direction produced regular variations in the waveforms. To demonstrate applicability beyond simple plates, waveforms produced by lead breaks on a thin walled composite tube were also shown to be interpretable as plate modes. The tube design was based on the type of struts proposed for Space Station Freedom's trussed structures.

Inversion of ocean-bottom seismometer (OBS) waveforms for oceanic crust structure: a synthetic study

NASA Astrophysics Data System (ADS)

Li, Xueyan; Wang, Yanbin; Chen, Yongshun John

2016-08-01

The waveform inversion method is applied—using synthetic ocean-bottom seismometer (OBS) data—to study oceanic crust structure. A niching genetic algorithm (NGA) is used to implement the inversion for the thickness and P-wave velocity of each layer, and to update the model by minimizing the objective function, which consists of the misfit and cross-correlation of observed and synthetic waveforms. The influence of specific NGA method parameters is discussed, and suitable values are presented. The NGA method works well for various observation systems, such as those with irregular and sparse distribution of receivers as well as single receiver systems. A strategy is proposed to accelerate the convergence rate by a factor of five with no increase in computational complexity; this is achieved using a first inversion with several generations to impose a restriction on the preset range of each parameter and then conducting a second inversion with the new range. Despite the successes of this method, its usage is limited. A shallow water layer is not favored because the direct wave in water will suppress the useful reflection signals from the crust. A more precise calculation of the air-gun source signal should be considered in order to better simulate waveforms generated in realistic situations; further studies are required to investigate this issue.