Estimation Of Propagation Velocity Research Articles

Principal Stress Measurement by Propagation Velocity Estimation at No Stress Using Surface Anisotropy in Surface SH Wave Acoustoelasticity

Principal Stress Measurement by Propagation Velocity Estimation at No Stress Using Surface Anisotropy in Surface SH Wave Acoustoelasticity

Study of the wave scattering in geological environments for the propagation velocity estimation

Diffraction is a naturally physical phenomenon which plays an extremely key role in forming some theoretical foundations of analyzing geophysical data such as seismic reflection and high frequency electromagnetic, Ground Penetrating Radar to study geological objects. In this phenomenon, when a wave field propagates from a source to an object with small size or a rough surface, its wave energy receivers act as the secondary sources and send their energy parts back to geophones on the ground surface. The relationship between the wave propagation time and the receiver coordinates is formulated as a diffraction hyperbola. This paper reported examples of the high frequency electromagnetic and seismic scattering phenomena with their applications in the study of the wave propagation velocity, location of civil underground objects and seabed depth. The research on scattering phenomenon for the electromagnetic waves has been known and widely applied; however, studying the wave velocity model by the diffraction analysis from the high resolution reflection seismic data for a fixed source receiver distance can be firstly considered in Vietnam and in the world. To determine the two wave velocity types, two graphs of their energy and entropy attributes were built and then calculated from their Kirchhoff migrated data in velocity ranges in order to find out their attributes’ extremes versus velocity variables. Their migrated sections with correct wave velocities could correctly locate diffractors as underground anomalies and produced the maximum energy and minimum entropy values in the peaks of diffraction hyperbolae and the surrounding zones of the diffractors, respectively. These geophysical data were measured at the urban and coastal area of Can Gio district, Ho Chi Minh city, Vietnam.

Subsurface Propagation Velocity Estimation Methods in Ground-Penetrating Radar: A review

Velocity estimation is one of the most crucial tasks in ground-penetrating radar (GPR) surveys. It is an integral part of GPR data analysis for interpreting GPR-generated images of subsurface media. Error in velocity estimation leads to wrong interpretations of underground scenarios. Since the beginning of GPR development, researchers have proposed various velocity estimation procedures. In this article, a survey of different subsurface propagation velocity estimation techniques is presented. Based on the survey methods, GPR environment, and mathematical models involved, different available techniques are presented in a classified manner. A few techniques are experimentally validated and analyzed for their performance. Finally, the impact of wave velocity on GPR imaging is demonstrated on practical GPR measurement data.

Experimental research on hydrodynamic instabilities during condensation of the pro-ecological refrigerant R1234yf in tubular minichannels

The following paper presents the results of preliminary experimental research on the influence of instabilities of a hydrodynamic type on the condensation phase change process in tubular minichannels. The research was focused on a new pro-ecological refrigerant, R1234yf, intended as a substitute for R134a that currently is being phased out. The flow condensation phase change process was investigated for both steady and un-steady conditions in singular tubular minichannels with an internal diameter d = {1,44; 2,30; 3,30} mm. The scope of the analysis of the experimental data covered an estimation of propagation velocities for both pressure and temperature instabilities as well as the shrinkage of the condensation zone. The results were also compared with the previous results obtained for the flow condensation phase change of R134a refrigerant in tubular minichannels with the same internal diameters.

Two-Terminal Traveling-Wave-Based Transmission-Line Protection

This paper proposes a two-terminal traveling-wave-based transmission-line protection using only the first wavefront arrival time at each line terminal (polarity and magnitude of transients are not required), leading to a simple, accurate, and fast protection. In real time, the protection system detects internal and external faults and identifies the fault directionality. In addition, the protection zone and the protection operating time are also formulated. The effects of the sampling rate and the traveling-wave propagation velocity estimation are considered, and some paradigms, such as the need of a high-sampling frequency and an accurate traveling-wave propagation velocity estimation are properly addressed. Two traveling-wave-based protective relays were implemented and evaluated in realistic real-time hardware-in-the-loop simulations considering the communication equipment between the relays, in which reliability and protection operating time could be assessed accordingly.

Velocity and directionality of the electrohysterographic signal propagation.

ObjectiveThe initiation of treatment for women with threatening preterm labor requires effective distinction between true and false labor. The electrohysterogram (EHG) has shown great promise in estimating and classifying uterine activity. However, key issues remain unresolved and no clinically usable method has yet been presented using EHG. Recent studies have focused on the propagation velocity of the EHG signals as a potential discriminator between true and false labor. These studies have estimated the propagation velocity of individual spikes of the EHG signals. We therefore focus on estimating the propagation velocity of the entire EHG burst recorded during a contraction in two dimensions.Study DesignEHG measurements were performed on six women in active labor at term, and a total of 35 contractions were used for the estimation of propagation velocity. The measurements were performed using a 16-channel two-dimensional electrode grid. The estimates were calculated with a maximum-likelihood approach.ResultsThe estimated average propagation velocity was 2.18 (±0.68) cm/s. No single preferred direction of propagation was found.ConclusionThe propagation velocities estimated in this study are similar to those reported in other studies but with a smaller intra- and inter-patient variation. Thus a potential tool has been established for further studies on true and false labor contractions.

Evaluation of arterial propagation velocity based on the automated analysis of the Pulse Wave Shape

This paper proposes the automatic estimation of the arterial propagation velocity from the pulse wave raw records measured in the region of the radial artery. A fully automatic process is proposed to select and analyze typical pulse cycles from the raw data. An adaptive neuro-fuzzy inference system, together with a heuristic search is used to find a functional approximation of the pulse wave. The estimation of the propagation velocity is carried out via the analysis of the functional approximation obtained with the fuzzy model. The analysis of the pulse wave records with the proposed methodology showed small differences compared with the method used so far, based on a strong interaction with the user. To evaluate the proposed methodology, we estimated the propagation velocity in a population of healthy men from a wide range of ages. It has been found in these studies that propagation velocity increases linearly with age and it presents a considerable dispersion of values in healthy individuals. We conclude that this process could be used to evaluate indirectly the propagation velocity of the aorta, which is related to physiological age in healthy individuals and with the expectation of life in cardiovascular patients.

A Sound Sources Locating Method of Constrained Least Squares Based on Time Delay Estimation

The sound sources positioning method based on time delay estimation is through the iteration of a group of nonlinear equation to solve the target position. Most of the existing methods is to solve under the hypothesis that the sound spread velocity in air is known. This paper puts forward several effective methods of source orientation and propagation velocity estimation. These methods are only using the time delay which comes from the received signal between sensors separated in space to deduce the solving method of sound source location and sound’s speed estimation based on least squares, total least squares, limited data not sure and constraint least squares method, and then compare the characteristics of these methods through the computer simulation.

Neural mechanism of activity spread in the cat motor cortex and its relation to the intrinsic connectivity

Motor cortical points are linked by intrinsic horizontal connections having a recurrent network topology. However, it is not known whether neural activity can propagate over the area covered by these intrinsic connections and whether there are spatial anisotropies of synaptic strength, as opposed to synaptic density. Moreover, the mechanisms by which activity spreads have yet to be determined. To address these issues, an 8 × 8 microelectrode array was inserted in the forelimb area of the cat motor cortex (MCx). The centre of the array had a laser etched hole ∼500 μm in diameter. A microiontophoretic pipette, with a tip diameter of 2-3 μm, containing bicuculline methiodide (BIC) was inserted in the hole and driven to a depth of 1200-1400 μm from the cortical surface. BIC was ejected for ∼2min from the tip of the micropipette with positive direct current ranging between 20 and 40 nA in different experiments. This produced spontaneous nearly periodic bursts (0.2-1.0 Hz) of multi-unit activity in a radius of about 400 μm from the tip of the micropipette. The bursts of neural activity spread at a velocity of 0.11-0.24 ms⁻¹ (mean=0.14 mm ms⁻¹, SD=0.05)with decreasing amplitude.The area activated was on average 7.22 mm² (SD=0.91 mm²), or ∼92% of the area covered by the recording array. The mode of propagation was determined to occur by progressive recruitment of cortical territory, driven by a central locus of activity of some 400 μm in radius. Thus, activity did not propagate as a wave. Transection of the connections between the thalamus and MCx did not significantly alter the propagation velocity or the size of the recruited area, demonstrating that the bursts spread along the routes of intrinsic cortical connectivity. These experiments demonstrate that neural activity initiated within a small motor cortical locus (≤ 400 μm in radius) can recruit a relatively large neighbourhood in which a variety of muscles acting at several forelimb joints are represented. These results support the hypothesis that the MCx controls the forelimb musculature in an integrated and anticipatory manner based on a recurrent network topology

A constant influx model for dike propagation: Implications for magma reservoir dynamics

Most observations of seismicity rate during dike propagation on basaltic volcanoes show (1) rate stationarity despite possible variations of the dike tip velocity, (2) frequent lack of clear and monotonic hypocenter migration following dike propagation, and (3) event occurrences located backward with respect to the dike tip position. On these bases, the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation. Seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix. The volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir. The consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir. We consider a two‐phase dike propagation model, including a first vertical propagation followed by a lateral migration along a lithological discontinuity. We explore (1) under which geophysical conditions the vertical dike is fed at constant flow rate of magma and (2) dike propagation patterns. Implications entailed by constant volumetric flux on the Piton de la Fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2.2 MPa. Considering similar magma inflow rates during vertical and lateral dike propagation phases, we reproduce independent estimates of propagation velocities, rise times, and injected volumes when applying the model to the August 2003 Piton de la Fournaise eruption.

Robust propagation velocity estimation of gastric electrical activity by least mean p-norm blind channel identification

The propagation of the gastric slow wave is one of the most important spatial characteristics of gastric electrical activity (GEA). The time delay estimation (TDE) is an effective approach to quantitatively assessing the propagation velocity of GEA. Traditional TDE analyses are developed under the condition reported that the background noise in GEA analysis is Gaussian distributed. Due to the effects of spikes and/or motion artifacts, the GEA obtained from gastric serosal electrodes often contains sharp transitions. This paper proposes robust time delay estimation based on least mean p-norm blind channel identification (BCILMP) under alpha-stable noise condition. Compared with the least mean square time delay estimation (LMSTDE), the BCILMP provides better performance in the impulsive noise environments. The robustness of the proposed method is demonstrated through computer simulations in both Gaussian and alpha-stable noise environments. The results of the propagation velocity of real data obtained from gastric serosal electrodes in gastroparetic patients show that the propagation velocity in gastroparetic patients is slower than in the normal subjects reported in the literature, and the slow-wave propagation is directed proximally to distally from the corpus toward the pylorus but not all the variability of the propagation velocity increases monotonously.

Studies of the plume emission during the femtosecond and nanosecond ablation of graphite in nitrogen

Comparative studies of the pulsed laser ablation of graphite in 20mTorr of N2 using both 15ns and 450fs pulses at a wavelength of 248nm are reported. Emissions from the resulting ablation plumes, and from collisions with ablated material and the background N2 gas molecules, have been investigated by wavelength-, space-, and time-resolved optical emission spectroscopy (OES), and the observations correlated with the results of the analyses of films formed when such material is incident on a silicon substrate. Wavelength-dispersed spectra of the plume arising in nanosecond ablation reveal CI, CII, and C2 emissions—concentrated close to the target—and, at greater distances, strong CN and weak N2+ emissions. N2+(B–X) emission dominates in the case of femtosecond ablation. Time-gated imaging studies have allowed estimation of propagation velocities for these various emissions. Possible production routes for secondary emitters such as CN and N2+ are discussed, and arguments presented to show that measurements of the apparent propagation “velocities” of such emissions are unlikely to provide meaningful measures of the velocities (or energies) with which these carriers impact on a substrate surface. Laser Raman spectroscopy confirms nitrogen incorporation within the films grown by both nanosecond and femtosecond ablations; the former films are deduced to be both thicker and to have higher N content—findings that accord with the OES analyses.

Analysis of multi‐offset GPR data: a case study in a coarse‐grained gravel aquifer

ABSTRACTMulti‐offset ground‐penetrating radar (GPR) data were collected in a coarse‐grained gravel aquifer located in a glacial delta environment within dipping foresets (at the Tettnang aquifer test site, SW Germany). We apply prestack processing techniques and normal‐moveout (NMO) velocity analysis in preparation for stacking. The estimation of propagation velocities is of considerable importance for converting time‐domain radargrams into depth‐sections and for an interpretation in terms of petrophysical properties. In our case, interval velocity determination is difficult because reflector dip angles are variable, and stacking and NMO velocities differ significantly since the antenna offset is comparable to the reflector depth. Using a synthetic two‐layer model, we systematically study possible errors in interval velocity determination. We compare the cases of decreasing velocity with depth (typical for ground‐penetrating (GPR) surveys of aquifers) and increasing velocity with depth (typical for seismic surveys). In the case of decreasing velocity with depth, the discrepancy between stacking and NMO velocity is considerable and, consequently, interval velocities calculated with the Dix equation or the more accurate 2D NMO approximation for dipping layers show unacceptably high errors. The errors are much smaller in comparable models with increasing velocity with depth. Thus, the small‐offset approximation inherent in the NMO concept is not appropriate for the first case. Consequently, it is necessary to model the true common‐midpoint (CMP) raypaths to determine realistic interval velocities from our GPR field data.Stacked GPR sections of multi‐offset data show significant improvements in imaging of reflectors and depth of investigation compared with a standard constant‐offset section. This allows a more reliable interpretation of geological structures. Simultaneous acquisition of four channels, which is possible with some commercial GPR systems, yields significantly better results than constant‐offset standard acquisition without increasing the efforts for data acquisition. Major reflectors in the GPR section can be correlated with distinct contrasts of porosity, represented by the base of open‐framework gravels and sand beds within poorly sorted gravels.

Simultaneous observations of the quasi 2-day wave at Mawson, Antarctica, and Adelaide, South Australia

Observations of the Austral quasi 2-day wave at Mawson, Antarctica (67°S, 63°E) are presented and compared with those from Adelaide (35°S, 138°E). The data were obtained from partial-reflection radars which have been measuring winds continuously since mid-1984, and the results presented here are the first to record the 2-day wave in middle atmosphere winds from Mawson. They show that 2-day period oscillations of 10–15 m s −1 are a regular feature of the high latitude southern hemisphere summer. The wide longitude and latitude separation of the radar stations permits estimates of propagation velocity and latitude phase structure, and results are consistent with the passage of a westward travelling Rossby-gravity (3, 3) wave.

Pulmonary vascular input impedance in the newborn and infant pig.

The input impedance of the main pulmonary artery in 26 pigs aged from 1 h to 2 weeks has been calculated from measurements of pressure and flow. From these data we have derived estimates of the hydraulic power output of the right heart. The impedance spectra were similar in form to those in many other studies and were consistent with the presence of a single reflection site within the lung. The frequency of the (single) minimum decreased steadily with increasing age as did the corresponding zero crossing point on the phase curve. From estimates of propagation velocity the position of this "reflection site" was found to coincide with the position of the lung periphery in each age group. An overall fall in characteristic impedance with increasing age was found to be due to the increasing diameter of the pulmonary artery rather than to changes in its elasticity. The total power output/body weight of the right heart fell from 10.4 to 4.8 mW X kg-1 from birth to 4 weeks of age. During this period the ratio of pulsatile to steady power fell from 0.5 to 0.31. We conclude that this fall is related to a reduction in the effective reflection of pressure and flow waves within the lung due to increasing attenuation and possibly to a reduction in the magnitude of the lumped reflection coefficient itself.

Seismic velocity estimation

The estimate of propagation velocities in the reflection or refraction seismic method is essential to the effective imaging of the subsurface. Wave propagation in a fully elastic medium gives rise to several propagation modes, among them are the longitudinal and transverse compressional waves (P-waves and S-waves), which are commonly used in the reflection and refraction seismic methods. With appropriately sorted data, the arrival time of a wave returning from a particular reflecting interface in the subsurface will vary as a function of source-receiver offset. This variation in arrival time with offset is called "moveout" and is controlled by the propagation velocity. The velocity of propagation enters the processing of reflection seismic data first as an essential parameter of a time coordinate transformation required before data of varying source-receiver offsets can be stacked to enhance signal-to-noise ratio. Velocities estimated in this manner are called "moveout velocities." Velocities also enter the processing sequence as a parameter of an imaging operation called "migration." Early efforts at velocity estimation were only accurate enough to provide parameters to process data, but high-quality data collected using present-day technology allow us to make accurate enough estimates of propagation velocity to infer subsurface geology. Complications arise, however, due to the effects of reflector structure and lateral velocity gradients. Current developments in seismic velocity estimation include measurement of shear wave (S-wave) velocities, use of wide-angle arrivals for more accurate P-wave velocity estimates, and methods requiring areal coverage (three-dimensional seismic).

Propagation Velocity of Turbulent Slugs and Streaks in Transition Pipe Flow

Taking account of experimental observations on the transition process, an elementary theory is developed for estimation of propagation velocity of the rear end of turbulent slugs and streaks which constitute a major feature of the transition process in pipe flow. The theory gives a lower propagation velocity than observed experimentally within the lower range of transition Reynolds numbers while at higher Reynolds numbers the theory gives a value about 7% higher than obtained experimentally. These deviations are due to approximations in the analysis which cannot be avoided at the present level of information on the structure of turbulent shear.