Ratio Of Wave Speed Research Articles

Continuous shear wave measurements for dynamic cardiac stiffness evaluation in pigs

Ultrasound-based shear wave elastography is a promising technique to non-invasively assess the dynamic stiffness variations of the heart. The technique is based on tracking the propagation of acoustically induced shear waves in the myocardium of which the propagation speed is linked to tissue stiffness. This measurement is repeated multiple times across the cardiac cycle to assess the natural variations in wave propagation speed. The interpretation of these measurements remains however complex, as factors such as loading and contractility affect wave propagation. We therefore applied transthoracic shear wave elastography in 13 pigs to investigate the dependencies of wave speed on pressure–volume derived indices of loading, myocardial stiffness, and contractility, while altering loading and inducing myocardial ischemia/reperfusion injury. Our results show that diastolic wave speed correlates to a pressure–volume derived index of operational myocardial stiffness (R = 0.75, p < 0.001), suggesting that both loading and intrinsic properties can affect diastolic wave speed. Additionally, the wave speed ratio, i.e. the ratio of systolic and diastolic speed, correlates to a pressure–volume derived index of contractility, i.e. preload-recruitable stroke work (R = 0.67, p < 0.001). Measuring wave speed ratio might thus provide a non-invasive index of contractility during ischemia/reperfusion injury.

Modal characteristics of sagged-cable-crosstie systems. Part 2: parametric analysis

Analysis of key parameters is an effective means to understanding modal characteristics of a system. However, because of the large number of components, there are various geometric, material, and physical parameters in a sagged-cable-crosstie structure, which inevitably hinders the reasonable selection of key parameters. Based on the companion (Part 1) paper, the effect of four fundamental key parameters, i.e., the Irvine parameter, position and stiffness of crosstie(s), and wave speed ratio, on the modal characteristics of three representative models: double-cable-single-crosstie, three-cable-single-crosstie, and double-cable-double-crosstie, are investigated by mechanical modeling-based parametric analysis. The simultaneous existence of cross-over and veering phenomena that commonly wouldn’t co-exist in single classical cables is found in sagged-cable-crosstie structures. Generally, the frequency curves of all the in-phase modes, out-of-phase modes with symmetrically arranged crossties, and specific out-of-phase modes with crossties just at modal nodes show cross-over phenomena, while that of out-of-phase modes with non-symmetrically arranged crossties show veering phenomena. Setting one or two crossties can only significantly increase the out-of-phase modal frequencies of specific orders, and the increment limits of dimensionless frequency for systems with identical sagged cables are found to be 1 and 2 respectively, no matter how the crosstie stiffness and position are adjusted and how many cables are connected. However, the wave speed difference between sagged cables can enhance the effect of crosstie(s) to further increase modal frequencies, especially for high-order ones, and hence break through the above increment limits. Moreover, the more cables with wave speed differences connected by crossties and the greater the difference in wave speed, the more the system frequency increases.

Prostate Cancer Detection Using 3-D Shear Wave Elasticity Imaging

Transrectal ultrasound (TRUS) B-mode imaging provides insufficient sensitivity and specificity for prostate cancer (PCa) targeting when used for biopsy guidance. Shear wave elasticity imaging (SWEI) is an elasticity imaging technique that has been commercially implemented and is sensitive and specific for PCa. We have developed a SWEI system capable of 3-D data acquisition using a dense acoustic radiation force (ARF) push approach that leads to enhanced shear wave signal-to-noise ratio compared with that of the commercially available SWEI systems and facilitates screening of the entire gland before biopsy. Additionally, we imaged and assessed 36 patients undergoing radical prostatectomy using 3-D SWEI and determined a shear wave speed threshold separating PCa from healthy prostate tissue with sensitivities and specificities akin to those for multiparametric magnetic resonance imaging fusion biopsy. The approach measured the mean shear wave speed in each prostate region to be 4.8 m/s (Young's modulus E = 69.1 kPa) in the peripheral zone, 5.3 m/s (E = 84.3 kPa) in the central gland and 6.0 m/s (E = 108.0 kPa) for PCa with statistically significant (p < 0.0001) differences among all regions. Three-dimensional SWEI receiver operating characteristic analyses identified a threshold of 5.6 m/s (E = 94.1 kPa) to separate PCa from healthy tissue with a sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and area under the curve (AUC) of 81%, 82%, 69%, 89% and 0.84, respectively. Additionally, a shear wave speed ratio was assessed to normalize for tissue compression and patient variability, which yielded a threshold of 1.11 to separate PCa from healthy prostate tissue and was accompanied by a substantial increase in specificity, PPV and AUC, where the sensitivity, specificity, PPV, NPV and AUC were 75%, 90%, 79%, 88% and 0.90, respectively. This work illustrates the feasibility of using 3-D SWEI data to detect and localize PCa and demonstrates the benefits of normalizing for applied compression during data acquisition for use in biopsy targeting studies.

Effects of non-Fourier heat conduction and surface heating rate on thermoelastic waves in semi-infinite ceramics subject to thermal shock

Non-Fourier heat conduction has been observed in many fast heating experiments. This paper studies the thermoelastic fields of semi-infinite ceramics subjected to surface heating shock based on non-Fourier C–V model, which may have its root application for future thermal protection system of space vehicles. To simulate the surface heating process, a family of exponential functions is presented. Furthermore, the ratio of heating duration to thermal relaxation time, and the ratio of thermal wave speed to elastic wave speed are introduced to study the coupling effects of heating rate, non-Fourier heat conduction and inertia. Firstly, the time horizon and spatial scale where the non-Fourier effect is significant has been delimited. Secondly, it is demonstrated that the thermal stress component along depth increases and converges as the depth increasing. Thirdly, the domain where the maximum thermal stresses influenced by non-Fourier heat conduction are drawn by the critical lines in the plane of dimensionless heating duration vs thermoelastic wave speed. This study may be useful for designs of ceramic heat insulations.

A non–invasive technique for evaluating carpal tunnel pressure with ultrasound vibro–elastography for patients with carpal tunnel syndrome: A pilot clinical study

Carpal tunnel syndrome (CTS) is a disorder that affects the median nerve at the wrist sufficient to cause impairment of nerve function. Elevated carpal tunnel pressure (CTP) leads to median nerve pathology, sensory, and motor changes in CTS patient. The techniques to quantify CTP used in clinic are invasive. This study aimed to investigate the feasibility of a noninvasive ultrasound vibro–elastography (UVE) to predict CTP in CTS patients and healthy individuals. The magnitudes of shear wave speed ratio (rSWS) of the 10 CTS patients (10 hands) and 6 healthy individuals (12 hands), and 10 cadaveric hands were compared using UVE. The ratios of intra to extra-carpal tunnel SWS in CTS patients was significantly higher than those in the healthy individuals (p = 0.0008) and cadaveric hands (p = 0.0015) with 500-g tendon tension. We estimated the CTP in the carpal tunnel using the mean rSWS of each group obtained from the present study and the linear approximation obtain from cadaveric hands data with 500-g tendon tension (y = 0.0036x + 1.1413). These results indicated that the elevated pressure applied to the 3rd flexor digitorum superficialis tendon in the carpal tunnel of CTS patients resulted in faster shear wave propagation. These results show that UVE was useful to indirectly estimate the CTP by measuring the rSWS; thus, they are potentially useful for the early diagnosis and assessment of CTS.

Aftershocks localization and shallow crustal velocity structure following the &amp;lt;italic&amp;gt;M&amp;lt;/italic&amp;gt;s6.9 Mainling earthquake in Tibet, China

At 06:34 CST on November 18, 2017, an M s6.9 earthquake struck Mainling prefecture, Nyingchi City, Tibet. The earthquake occurred at the frontier zone of collision and subduction in the eastern Himalayan syntaxis, a region of persistently strong compression between India and Eurasia. To monitor aftershock activity, the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, installed 28 broadband seismic stations around the epicentral area and obtained 180 days of seismic observation data. The average spacing between stations was approximately 5 km, which yielded good coverage of the source area and enriched the seismic data for the Eastern Himalayan syntaxis. In this paper, the hypodense events are refined by the hypoDD double-difference seismic location method and the local tomography software (LOTOS-12), an algorithm for seismic location and velocity structure imaging joint inversion. The hypoDD seismic localization method uses waveform cross-correlation technology to achieve positioning using the minimum residuals of the actual and theoretical travel times of two earthquakes. It is widely used for close-range earthquakes and is suitable for regional earthquake research; the LOTOS algorithm is more appropriate for velocity structure inversion in regions with significant differences in physical properties. The results show that the aftershock zone is approximately 50 km long and 30 km wide and trends NW-SE. According to the aftershock distribution, three active faults are basically consistent with the strike of the Xixingla fault zone. These active fractures are similar in shape and have a NE dip direction, and the dip angles of the active faults gradually become steeper from NW to SE. Under the continuous NE thrusting action of the Namche Barwa syntaxis, the three secondary fractures have undergone bending deformation. This deformation is associated with the adjustment mode of the eastern Himalayan syntaxis where the Indian plate continues to push Eurasia northward. At the same time, combining these results with those of the LOTOS-12 algorithm, the distribution of the Pg wave and Sg wave velocity disturbance in the shallow crust (20 km) and the wave speed ratio ( V p/ V s) are obtained. The main shock was located in an abnormal transition zone of body wave velocity, and the aftershocks mostly occurred in the negative anomaly zone for P wave and S wave velocities, which reflects the characteristics of stratigraphic fractures and faults in the area with concentrated earthquakes. We suggest that this area should be avoided in the future when construction of engineering facilities is required north of Namche Barwa Peak. Overall, with Namche Barwa Peak as the boundary, the P wave and the S wave are generally characterized by high-speed anomalies in the north and low-speed anomalies in the south. This phenomenon may be related to the geological structure and petrophysical properties in this area, as the lithologies of the Lhasa terrane are old and cold; meanwhile, the metamorphic body in the south and the Namche Barwa syntaxis are relatively broken, the ages of rock formation are relatively young, and the lithologies are relatively hot and soft. In addition, high-speed P wave anomalies in the northwestern part of Namche Barwa Peak may be related to enrichment in garnet minerals in this area. The higher wave velocity ratio on the southwest side of the epicentral area, the lower P wave velocity on the right side of profile 1–1′ and the P wave on the left side of profile 2–2′ may be related to the fragmentation of the terrain in this area and the development of valley glaciers. The area where the wave velocity ratio is relatively large may also be related to the upwelling of asthenospheric and lithospheric material in the deep mantle.

Singularity characteristic analysis for anti-plane accelerated propagating V-notches

By introducing the displacement asymptotic expansion around the vertex of an anti-plane V-notch into the elasto-dynamics equation, the singularity characteristic analysis for an accelerated propagating V-notch is transformed into a problem of solving a characteristic ordinary differential equation. The singularity can be generated once the interpolating matrix method is applied to solve the established characteristic equation. The singularities for anti-plane single material and bi-material propagating V-notches are investigated under different initial propagating velocities and accelerations respectively. For the single material anti-plane V-notch, the singularity becomes stronger with the decrease of notch opening angle, and it becomes stronger with the increase of the direction angle of initial propagating velocity and acceleration. It turns stronger with the increase of propagating speed when the propagating direction of initial velocity is greater than 45°, otherwise, the opposite conclusion may be drawn on the other hand. For the bi-material anti-plane V-notch, the singularity becomes weaker with the increase of propagating acceleration and it becomes stronger with the increase of the ratio of transverse wave speed.

Comparison of two ways of altering carpal tunnel pressure with ultrasound surface wave elastography

Higher carpal tunnel pressure is related to the development of carpal tunnel syndrome. Currently, the measurement of carpal tunnel pressure is invasive and therefore, a noninvasive technique is needed. We previously demonstrated that speed of wave propagation through a tendon in the carpal tunnel measured by ultrasound elastography could be used as an indicator of carpal tunnel pressure in a cadaveric model, in which a balloon had to be inserted into the carpal tunnel to adjust the carpal tunnel pressure. However, the method for adjusting the carpal tunnel pressure in the cadaveric model is not applicable for the in vivo model. The objective of this study was to utilize a different technique to adjust carpal tunnel pressure via pressing the palm and to validate it with ultrasound surface wave elastography in a human cadaveric model. The outcome was also compared with a previous balloon insertion technique. Results showed that wave speed of intra-carpal tunnel tendon and the ratio of wave speed of intra-and outer-carpal tunnel tendons increased linearly with carpal tunnel pressure. Moreover, wave speed of intra carpal tunnel tendon via both ways of altering carpal tunnel pressure showed similar results with high correlation. Therefore, it was concluded that the technique of pressing the palm can be used to adjust carpal tunnel pressure, and pressure changes can be detected via ultrasound surface wave elastography in an ex vivo model. Future studies will utilize this technique in vivo to validate the usefulness of ultrasound surface wave elastography for measuring carpal tunnel pressure.

An SPH multi‐fluid model based on quasi buoyancy for interface stabilization up to high density ratios and realistic wave speed ratios

SummaryWe introduce a smoothed particle hydrodynamics (SPH) concept for the stabilization of the interface between 2 fluids. It is demonstrated that the change in the pressure gradient across the interface leads to a force imbalance. This force imbalance is attributed to the particle approximation implicit to SPH. To stabilize the interface, a pressure gradient correction is proposed. In this approach, the multi‐fluid pressure gradients are related to the (gravitational and fluid) accelerations. This leads to a quasi‐buoyancy correction for hydrostatic (stratified) flows, which is extended to nonhydrostatic flows. The result is a simple density correction that involves no parameters or coefficients. This correction is included as an extra term in the SPH momentum equation. The new concept for the stabilization of the interface is explored in 5 case studies and compared with other multi‐fluid models. The first case is the stagnant flow in a tank: The interface remains stable up to density ratios of 1:1000 (typical for water and air), in combination with artificial wave speed ratios up to 1:4. The second and third cases are the Rayleigh‐Taylor instability and the rising bubble, where a reasonable agreement between SPH and level‐set models is achieved. The fourth case is an air flow across a water surface up to density ratios of 1:100, artificial wave speed ratios of 1:4, and high air velocities. The fifth case is about the propagation of internal gravity waves up to density ratios of 1:100 and artificial wave speed ratios of 1:4. It is demonstrated that the quasi‐buoyancy model may be used to stabilize the interface between 2 fluids up to high density ratios, with real (low) viscosities and more realistic wave speed ratios than achieved by other weakly compressible SPH multi‐fluid models. Real wave speed ratios can be achieved as long as the fluid velocities are not very high. Although the wave speeds may be artificial in many cases, correct and realistic wave speed ratios are essential in the modelling of heat transfer between 2 fluids (eg, in engineering applications such as gas turbines).

SPH Particle Collisions for the Reduction of Particle Clustering, Interface Stabilisation and Wall Modelling

The pair-wise forces in the SPH momentum equation guarantee the conservation of momentum, but they cannot prevent particle clustering and wall penetration. Particle clustering may occur for several reasons. A fundamental issue is the tensile instability, which is caused by negative numerical pressures. Clustering may also occur due to certain properties of the kernel gradient. Discontinuities in the pressure and its gradient, due to surface tension and gravity, may cause particle instabilities near the interface between two fluids. Wall penetration is also a form of particle clustering. In this paper the particle collision concept is introduced to suppress particle clustering. Here, the use of kinematic conditions (motion) rather than dynamic conditions (forces) is explored. These kinematic conditions are obtained from kinetic collision theory. Conservation of momentum is maintained, and under elastic conditions conservation of energy as well. The particle collision model only becomes active when needed. It may be seen as a particle shifting method, in the sense that the velocities are changed, and as a consequence of that the particle positions change. It is demonstrated in several case studies that the particle collision model allows for realistic (low) viscosities. It was also found to stabilise the interface between two fluids up to high, realistic density ratios (1000:1) in typical liquid-gas applications. As such it can be used as a multi-fluid model. The concept allows for real wave speed ratios (and far beyond), which, as well as real viscosities, are essential in the modelling of heat transfer applications. The collisions with walls allow for no-slip conditions at real viscosities while wall penetration is suppressed. In summary, the particle collision model makes SPH more robust for engineering.

Diffuse scattered field of elastic waves from randomly rough surfaces using an analytical Kirchhoff theory

We develop an elastodynamic theory to predict the diffuse scattered field of elastic waves by randomly rough surfaces, for the first time, with the aid of the Kirchhoff approximation (KA). Analytical expressions are derived incorporating surface statistics, to represent the expectation of the angular distribution of the diffuse intensity for different modes. The analytical solutions are successfully verified with numerical Monte Carlo simulations, and also validated by comparison with experiments. We then apply the theory to quantitatively investigate the effects of the roughness and the shear-to-compressional wave speed ratio on the mode conversion and the scattering intensity, from low to high roughness within the valid region of KA. Both the direct and the mode converted intensities are significantly affected by the roughness, which leads to distinct scattering patterns for different wave modes. The mode conversion effect is very strong around the specular angle and it is found to increase as the surface appears to be more rough. In addition, the 3D roughness induced coupling between the out-of-plane shear horizontal (SH) mode and the in-plane modes is studied. The intensity of the SH mode is shown to be very sensitive to the out-of-plane correlation length, being influenced more by this than by the RMS value of the roughness. However, it is found that the depolarization pattern for the diffuse field is independent of the actual value of the roughness.

Mantle‐driven uplift of Hangai Dome: New seismic constraints from adjoint tomography

AbstractThe origin of Hangai Dome, an unusual large‐scale, high‐elevation low‐relief landform in central Mongolia, remains enigmatic partly due to lack of constraints on its underlying seismic structure. Using adjoint tomography—a full waveform tomographic technique—and a large seismic waveform data set in East Asia, we discover beneath the dome a deep low shear wave speed (low‐V) conduit indicating a slightly warmer (54 K to 127 K) upwelling from the transition zone. This upwelling is spatially linked to a broader uppermost mantle low‐V region underlying the dome. Further observations of high compressional to shear wave speed ratios and positive radial anisotropy in the low‐V region suggest partial melting and horizontal melt transport. We propose that the mantle upwelling induced decompression melting in the uppermost mantle and that excess heat associated with melt transport modified the lithosphere that isostatically compensates the surface uplift at upper mantle depths (&gt;80 km).

Pulse-Like Rupture Induced by Three-Dimensional Fault Zone Flower Structures

Faults are often embedded in low-velocity fault zones (LVFZ) caused by material damage. Previous 2D dynamic rupture simulations (Huang and Ampuero, 2011; Huang et al., 2014) showed that if the wave velocity contrast between the LVFZ and the country rock is strong enough, ruptures can behave as pulses, i.e. with local slip duration (rise time) much shorter than whole rupture duration. Local slip arrest (healing) is generated by waves reflected from the LVFZ–country rock interface. This effect is robust against a wide range of fault zone widths, absence of frictional healing, variation of initial stress conditions, attenuation, and off-fault plasticity. These numerical studies covered two-dimensional problems with fault-parallel fault zone structures. Here, we extend previous work to 3D and geometries that are more typical of natural fault zones, including complexities such as flower structures with depth-dependent velocity and thickness, and limited fault zone depth extent. This investigation requires high resolution and flexible mesh generation, which are enabled here by the high-order accurate arbitrary high-order derivatives discontinuous Galerkin method with an unstructured tetrahedral element discretization (Peltieset al., 2012). We show that the healing mechanism induced by waves reflected in the LVFZ also operates efficiently in such three-dimensional fault zone structures and that, in addition, a new healing mechanism is induced by unloading waves generated when the rupture reaches the surface. The first mechanism leads to very short rise time controlled by the LVFZ width to wave speed ratio. The second mechanism leads to generally longer, depth-increasing rise times, is also conditioned by the existence of an LVFZ, and persists at some depth below the bottom of the LVFZ. Our simulations show that the generation of slip pulses by these two mechanisms is robust to the depth extent of the LVFZ and to the position of the hypocenter. The first healing mechanism is dominant for events with hypocenter inside the LVFZ. The second one is dominant if the hypocenter is deeper than a shallow LVFZ. These results suggest that the depth-dependence of rise time might help constrain the depth extent of the LVFZ. We also show that ruptures can spontaneously stop in flower-like LVFZs with uniform velocity reduction, but continue propagating as slip pulses if velocity reduction is depth-dependent.

Coupled axisymmetric vibration of nonlocal fluid-filled closed spherical membrane shell

In this paper, the axisymmetric vibration of a fluid-filled spherical membrane shell is studied based on nonlocal elasticity theory. The membrane shell is considered elastic, homogeneous and isotropic. The shell model is reformulated using the nonlocal differential constitutive relations of Eringen. The membrane shell is completely filled with an inviscid fluid. The motion of the fluid is governed by the wave equation. Nonlocal governing equations of motion for the fluid-filled spherical membrane shell are derived. Along the contact surface between the membrane and the fluid, the compatibility requirement is applied and Legendre polynomials, associated Legendre polynomials and spherical Bessel functions are used to obtain the natural frequencies of the fluid-filled spherical membrane shells. The frequencies for both empty and fluid-filled spherical membrane shell are evaluated, and their comparisons are performed to confirm the validity and accuracy of the proposed method. An excellent agreement is found between the present and previous ones available in the literature. The variations of the natural frequencies with the small-scale parameter, density ratio, wave speed ratio and Poisson’s ratio are also examined. It is observed that the frequencies are affected when the size effect is taken into consideration.

Research on the Hydrodynamic Forces of the Torsional Wave Propulsion by Extended Large-Amplitude Elongated-Body Theory

Torsional wave propulsion is different from transversal wave propulsion. Based on the characteristic feature of fin ray’s motion, we divide the dorsal fin along the radial direction into a series of long narrow bands. For each band, the analysis method is the same as the method computing hydrodynamic force of transversal wave propulsion. Then we give an integral calculation over fin ray’ length. We analyze the influence of the swing amplitude, frequency and length of fin as well as wave numbers and ratio of wave speed to swimming speed on hydrodynamic force. The calculated results show that: 1. the average thrust on the dorsal fin is directly proportional to the square of swing amplitude and frequency of fin ray. 2. The average thrust on the dorsal fin is directly proportional to the biquadrate of ray’s length. 3. As the wave numbers increase, the average thrust begins with a little increase and then turns to decrease. When the wave number roughly equals to 1.5, it reaches to a maximum. 4. If the fin frequency is fixed, the average thrust is of maximum when the ratio of wave speed to swimming speed roughly equals to 1.4.

Shear and compressional wave speeds in Hertzian granular media

It is shown that the shear wave speed in a granular medium is less than that in an elastic solid of the same shear modulus-to-density ratio. Shear and compressional wave speeds are derived for granular media using a conservation of energy approach. The grains are assumed to be spherical with elastic Hertzian contacts of constant stiffness. The affine approximation is used to determine the relative displacements of grain centers, and it is also assumed that the grains are small compared to a wavelength, consistent with the effective medium approximation. Potential and kinetic energies associated with linear motion are the same as those in an elastic solid, but it is found that shear wave propagation in a granular medium involves additional energies associated with grain rotation. The partition of energies results in a reduction in the shear wave speed, relative to an elastic solid of the same shear modulus-to-density ratio. It is shown that the reduction is an inherent property of granular media, independent of any departure from the affine approximation or fluctuations in coordination number or contact stiffness. The predicted wave speed ratios are consistent with published measurements.

A Network Flow Algorithm for the Cell-Based Single-Destination System Optimal Dynamic Traffic Assignment Problem

The cell-transmission model-based single-destination system optimal dynamic traffic assignment problem proposed by Ziliaskopoulos was mostly solved by standard linear programming (LP) methods, e.g., simplex and interior point methods, which produce link-based flows involving vehicle-holding phenomenon. In this paper we present a network flow algorithm for this problem. We show that the problem is equivalent to the earliest arrival flow and then solve the earliest arrival flow on a time-expanded network. In particular, a scaled flow scheme is proposed to deal with the situation in which the ratio of backward wave speed to forward wave speed is less than one. The proposed algorithm produces path-based flows exhibiting realistic nonvehicle-holding properties. Complexity and numerical analyses show that the algorithm runs more efficiently than LP.

Role of fault gouge dilatancy on aseismic deformation transients

In the vicinity of episodic aseismic transients in several subduction zones, the presence of interstitial fluids and near‐lithostatic pore pressure has been proposed to interpret seismic observations of high P to S wave speed ratio and high Poisson's ratio. Under such conditions, fault stabilization by dilatancy‐induced suction during increased shear strain rates becomes very efficient. We analyze the frictional and hydraulic conditions for spontaneous transients on a fluid‐infiltrated fault including dilatancy and pore compaction in the framework of rate and state friction with a “membrane diffusion” approximation. In both a simplified spectral model and a 2‐D Cascadia‐like subduction fault model, the fault response is mainly controlled by three nondimensional parameters: (1) W/h*, the along‐dip width of the high pore pressure, velocity‐weakening fault relative to a characteristic nucleation size, (2) a drainage parameter U, the relative time scales for fluid diffusion and friction evolution, and (3) a dilatancy parameter E, the relative contributions to stress drop from dilatancy and friction evolution. The incorporation of dilatancy enables aseismic transients at much larger values of W/h* than is possible under conditions of constant pore pressure. An analytic estimate of the maximum slip velocity as a function of W/h*, E, and U is derived and agrees reasonably well with the simulation results. The dependence of the properties of modeled transients on the drainage parameter U is similar to that on the dilatancy parameter E. For U (E) less than 1, maximum velocity decreases, while recurrence period remains relatively constant. For U (E) greater than 1, maximum velocity approaches the steady state velocity, and recurrence period approaches the period at neutral stability. In the subduction fault model using gabbro gouge friction properties, the slip per episode and the recurrence period increase with W/h*, generally following the trend defined without dilatancy. The maximum velocity with dilatancy can be several orders of magnitude smaller than that without, in particular for larger values of E and values of W/h* near the no‐dilatancy stability limit.

Arbitrary amplitude solitary waves and double layers in an ultra-relativistic degenerate dense dusty plasma

Arbitrary amplitude solitary waves (SWs) and double layers (DLs) in an ultra-relativistic degenerate dense dusty plasma (containing ultra-relativistic degenerate ultra-cold electron fluid, inertial ultra-cold ion fluid, and negatively charged static dust) have been investigated by the pseudo-potential approach. It has been found that for δ = 1 (where δ is the ratio of nonlinear wave speed to linear wave phase speed) extremely large amplitude DLs with negative potential exist for μ = 0.537 (where μ is the ratio of dust charge density to ion charge density) and SWs with negative potential exist for 1 > μ > 0.537 . It is also shown that for δ > 1 only SWs with positive potential exist for 0 ⩾ μ < 0.537 , but SWs with positive potential coexist with SWs or DLs with a negative potential for 0.537 > μ > 0.851 . The implications of our results in some compact astrophysical objects, particularly, in white dwarfs and neutron stars, have been briefly discussed.

A stacking approach to estimate VP/VS from receiver functions

This note documents an approach to process a suite of receiver function (RF) traces in order to identify discontinuity-generated P-to-S (Ps) conversions based on the timing of their associated reverberations. It is inspired by Kumar and Bostock's method to estimate absolute P wave speeds. From RF estimates recorded in the typical source range for direct P arrivals, the method yields P to S wave speed ratios (VP/VS) without knowledge of crustal VP or thickness.