Decrease In Phase Velocity Research Articles

Using Vehicle‐Induced DAS Signals for Near‐Surface Characterization With High Spatiotemporal Resolution

AbstractVehicle‐induced seismic waves, generated as vehicles traverse the ground surface, carry valuable information for imaging the underlying near‐surface structure. These waves propagate differently in the subsurface depending on soil properties at various spatial locations. By leveraging wave propagation characteristics, such as surface‐wave velocity and attenuation, this study presents a novel method for near‐surface monitoring. Our method employs passing vehicles as active, non‐dedicated seismic sources and leverages pre‐existing telecommunication fibers as large‐scale and cost‐effective roadside sensors empowered by Distributed Acoustic Sensing (DAS) technology. A specialized Kalman filter algorithm is integrated for automated DAS‐based traffic monitoring to accurately determine vehicles' location and speed. Then, our approach uniquely leverages vehicle trajectories to isolate space‐time windows containing high‐quality surface waves. With known vehicle (i.e., seismic source) locations, we can effectively mitigate artifacts associated with suboptimal distribution of sources in conventional ambient noise interferometry. Compared to ambient noise interferometry, our approach enables the synthesis of virtual shot gathers with a high signal‐to‐noise ratio and spatiotemporal resolution at reduced computational costs. We validate the effectiveness of our method using the Stanford DAS‐2 array, with a focus on capturing spatial heterogeneity and monitoring temporal variations in soil seismic properties during rainfall events. Specifically, in non‐built‐up areas, we observed an evident decrease in phase velocity and group velocity and an increase in attenuation due to the rainfall. Our findings illustrate our method's sensitivity and resolution in discerning variations across different spatial locations and demonstrate that our method is a promising advancement for high‐resolution near‐surface imaging in urban settings.

GAA-FGF14 disease: defining its frequency, molecular basis, and 4-aminopyridine response in a large downbeat nystagmus cohort

BackgroundGAA-FGF14 disease/spinocerebellar ataxia 27B is a recently described neurodegenerative disease caused by (GAA)≥250 expansions in the fibroblast growth factor 14 (FGF14) gene, but its phenotypic spectrum, pathogenic threshold, and evidence-based treatability remain to be established. We report on the frequency of FGF14 (GAA)≥250 and (GAA)200-249 expansions in a large cohort of patients with idiopathic downbeat nystagmus (DBN) and their response to 4-aminopyridine. MethodsRetrospective cohort study of 170 patients with idiopathic DBN, comprising in-depth phenotyping and assessment of 4-aminopyridine treatment response, including re-analysis of placebo-controlled video-oculography treatment response data from a previous randomised double-blind 4-aminopyridine trial. FindingsFrequency of FGF14 (GAA)≥250 expansions was 48% (82/170) in patients with idiopathic DBN. Additional cerebellar ocular motor signs were observed in 100% (82/82) and cerebellar ataxia in 43% (35/82) of patients carrying an FGF14 (GAA)≥250 expansion. FGF14 (GAA)200-249 alleles were enriched in patients with DBN (12%; 20/170) compared to controls (0·87%; 19/2,191; OR, 15·20; 95% CI, 7·52 to 30·80; p<0·0001). The phenotype of patients carrying a (GAA)200-249 allele closely mirrored that of patients carrying a (GAA)≥250 allele. Patients carrying a (GAA)≥250 or a (GAA)200-249 allele had a significantly greater clinician-reported (80%, 33/41 vs 31%, 5/16; RR, 2·58; 95% CI, 1·23 to 5·41; Fisher’s exact test, p=0·0011) and self-reported (59%, 32/54 vs 11%, 2/19; RR, 5·63; 95% CI, 1·49 to 21·27; Fisher’s exact test, p=0·00033) response to 4-aminopyridine treatment compared to patients carrying a (GAA)<200 allele. Placebo-controlled video-oculography data, available for four patients carrying an FGF14 (GAA)≥250 expansion, showed a significant decrease in slow phase velocity of DBN with 4-aminopyridine, but not placebo. InterpretationThis study confirms that FGF14 GAA expansions are a frequent cause of DBN syndromes. It provides preliminary evidence that (GAA)200-249 alleles might be pathogenic. Finally, it provides large real-world and preliminary piloting placebo-controlled evidence for the efficacy of 4-aminopyridine in GAA-FGF14 disease. FundingThis work was supported by the Clinician Scientist program "PRECISE.net" funded by the Else Kröner-Fresenius-Stiftung (to CW, AT, and MSy), the grant 779257 “Solve-RD” from the European’s Union Horizon 2020 research and innovation program (to MSy), and the grant 01EO 1401 by the German Federal Ministry of Education and Research (BMBF) (to MSt). This work was also supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) N° 441409627, as part of the PROSPAX consortium under the frame of EJP RD, the European Joint Programme on Rare Diseases, under the EJP RD COFUND-EJP N° 825575 (to MSy, BB and – as associated partner – SZ), the NIH National Institutes of Neurological Disorders and Stroke (grant 2R01NS072248-11A1 to SZ), the Fondation Groupe Monaco (to BB), and the Montreal General Hospital Foundation (grant PT79418 to BB). The Care4Rare Canada Consortium is funded in part by Genome Canada and the Ontario Genomics Institute (OGI-147 to KMB), the Canadian Institutes of Health Research (CIHR GP1-155867 to KMB), Ontario Research Fund, Genome Quebec, and the Children’s Hospital of Eastern Ontario Foundation. The funders had no role in the conduct of this study.

Porosity-dependent wave propagation in multi-directional functionally graded nanoplate with nonlinear temperature-dependent characteristics on Kerr-type substrate

The present study investigates the wave propagation characteristics of porous, multi-directional, functionally graded (FG) nanoplates embedded in a Kerr-elastic substrate. A first-order shear deformation model (FSDM) and the nonlocal strain gradient approach (NSGA) are utilized to address this issue. The NSGA is enhanced by considering softening and hardening material effects, leading to improved accuracy in the obtained results. In accordance with the law of mixing, the material properties of the nanoplates exhibit nonlinear temperature-dependent variations along the structural axes. Both even and uneven porosity profiles are considered in this study. The nonclassical governing equations for the proposed structure are derived using Hamilton's approach. The phase velocity and wave frequency are determined through the analytical solution of an eigenvalue problem, which depends on the wave number. The dispersion properties of waves in porous FG nanoplates are examined with respect to various factors, including porosity distributions, wave numbers, nonlocal and strain gradient effects, elastic foundation coefficients, and volume fraction index. The main findings of the study indicate that increasing the volume fraction index in the thickness direction leads to a decrease in the phase velocity and frequency of wave propagation in a porous FG nanoplate for a given wave number. Additionally, regardless of the porosity pattern, an increase in the porosity coefficient results in a decrease in wave frequency and phase velocity.

Dispersive landslide

Considering the non-hydrostatic mass flow model (Pudasaini, 2022 [1]), here, I derive a novel dispersive wave equation for landslide. The new dispersive wave for landslide recovers the classical dispersive water waves as a special case. I show that the frequency dispersion relation for landslide is inherently different than the classical frequency dispersion for water waves. The wave frequency with dispersion increases non-linearly as a function of the wave number. For dispersive landslide, the wave frequency without dispersion appears to heavily overestimate the dispersive wave frequency for higher wave number. Due to the dispersion term emerging from the non-hydrostatic contribution for landslide, the phase velocity becomes a function of the wave number. This gives rise to the group velocity that is significantly different from the phase velocity, characterizing the dispersive mass flow. The dispersive phase velocity and group velocity decrease non-linearly with the wave number. Yet, the group velocity is substantially lower than the phase velocity. I analytically derive a dispersion number as the ratio between the phase velocity and the group velocity, which measures the deviation of the group velocity from the phase velocity, provides a dynamic scaling between them and summarizes the overall effect of dispersion in the mass flow. The dispersion number for landslide increases rapidly with the wave number, which is in contrast to the dispersion in water waves. With the definition of the effective dispersive lateral stress, I prove the existence of an anti-restoring force in landslide. I reveal the fact that due to the anti-restoring force, landslides are more dispersive than the piano strings. So, the wave dispersion in landslide is fundamentally different than the wave dispersion in the piano string. My model constitutes a foundation for the wave phenomenon in dispersive mass flows.

Multimode Design and Piezoelectric Substrate Anisotropy Use to Improve Performance of Acoustic Liquid Sensors.

Using acoustic wave modes propagation in piezoelectric plates loaded with conductive liquids, peculiarities of the mode-liquid acoustoelectric interaction are studied. It is found that (i) in contrast to bulk and surface acoustic waves propagating in piezoelectric semiconductors, the acoustoelectric attenuation of the modes is not symmetric in respect to its maximum, (ii) a large increase in attenuation may be accompanied by a small decrease in phase velocity and vice versa, (iii) the peculiarities are valid for “pure” (without beam steering) and “not pure” (with beam steering) modes, as well as for modes of different orders and polarizations, and (iv) conductivity of test liquid increases electromagnetic leakage between input and output transducers, affecting results of the measurements. To decrease the leakage, the liquid should be localized between transducers, outside the zone over them. If so, the mode sensitivity may be as large as 8.6 dB/(S/m) for amplitude and 107°/(S/m) for phase. However, because of comparable cross-sensitivity towards viscosity and dielectric permittivity, modes with selective detection of liquid conductivity are not found.

A Method of Investigating the Phenomenon of Bifurcation Memory in the Dynamics of River Vessels

The phenomenon of “bifurcation memory”, which can be detected during the steering of river vessels, is considered by researchers with the questions of equilibrium point’s bifurcations. It was noticed that in some dynamic systems during saddle-node bifurcation, areas are formed on the phase plane (so-called “phase spot”), passing through which the phase velocity of the representative point decreases. A decrease in phase velocity (e. g. during the steering of river vessel) can cause navigation accidents during shallow waters navigation. In order to improve sailing safety, it is necessary to investigate topological features of phase spots under any possible environmental conditions and steering angle values. In this paper, we propose a new method that makes it easy to get information about the localization of regions with decreased phase velocity. We gained the results related to the topology of areas of different types of motion (accelerated or decelerated) of representative point. In addition, the paper presents the process of evolution of these regions, according to the change of steering angles, as well as before and after the bifurcation. The new method, offered in the article, is more accurate for determining the boundaries of the areas compared to the methods of Feigin and Chirkova. This will allow us to make more correct predictions of changes in the dynamics of the object. The practical implication of the suggested method is that by using it, we can get information about the location of areas with different types of motion of the representative point on the phase plane for different values of steering angle and environmental conditions. This information can be used in the control algorithm of the driving object, for example, in order to predict the decreasing of phase velocities.

Asymptotic Analytical Solution on Lamb Waves in Functionally Graded Nano Copper Layered Wafer

In this study, the feasibility of using Lamb waves in functionally graded (FG) nano copper layered wafers in nondestructive evaluation is evaluated. The elastic parameters and mass densities of these wafers vary with thickness due to the variation in grain size. The power series technique is used to solve the governing equations with variable coefficients. To analyze multilayered structures, of which the material parameters are continuous but underivable, a modified transfer matrix method is proposed and combined with the power series method. Results show that multiple modes of Lamb waves exist in FG nano copper wafers. Moreover, the gradient property leads to a decrease in phase velocity, and the absolute value of the phase velocity variation is positively correlated with the gradient coefficient. The phase velocity variation and variation rate in Mode 2 are smaller than those in other modes. The findings indicate that Mode 4 is recommended for nondestructive evaluation. However, if the number of layers is greater than four, the dispersion curves of the Lamb waves in the multilayer structures tend to coincide with those in the equivalent uniform structures. The results of this study provide theoretical guidance for the nondestructive evaluation of FG nanomaterial layered structures.

Analysis of the Effect of Sio2 Film on the Characteristics of Rayleigh Wave in Zno/Sic Structure

The influence of SiO2 film on the phase velocity and the electromechanical coupling coefficient of ZnO/SiC structure was analyzed by finite element method. The results show that the middle SiO2 film layer reduces the phase velocity of Rayleigh wave and significantly increases the electromechanical coupling coefficient. When the top SiO2 film layer thickness is larger than the ZnO film thickness, the Rayleigh wave phase velocity increases. Otherwise, the Rayleigh wave phase velocity decreases. The electromechanical coupling coefficient increases first and then decreases. These conclusions can guide the development of surface acoustic wave devices with high phase velocity and high electromechanical coupling coefficient.

Laser plasma accelerators

An ultrafast intense laser pulse drives coherent wakefields of relativistic amplitude with a high phase velocity robustly supported by the plasma. The structures of wakes and sheaths in plasma are contrasted. While the large amplitude of wakefields involves collective resonant oscillations of the eigenmode of the entire population of plasma electrons, the wake phase velocity ~c and ultrafast nature of the laser pulse introduce the wake stability and rigidity. When the phase velocity decreases, wakefields turn into sheaths, which are more suitable for ion acceleration. This short review reports on 4 decades of discoveries on laser plasma accelerators.

Longitudinal Wave in a Thermally Conducting Elastic Medium

The longitudinal wave propagation in a thermally conducting elastic medium has been investigated. Considering the equations of motions of longitudinal wave in displacement and temperature field, the frequency equation has been derived. The dispersion and damping equations have been derived for the propagation of longitudinal wave in four materials i.e Copper, Steel, Aluminum, and Lead. Effect of Phase velocity and damping coefficient are shown graphically. It is found that the increase in wave number results the decrease in Phase velocity and increase in damping coefficient.

Wave propagation analysis of a spinning porous graphene nanoplatelet-reinforced nanoshell

In this article, wave propagation behavior of a size-dependent spinning graphene nanoplatelet-reinforced composite (GNPRC) cylindrical nanoshell with porosity is presented. The effects of small scale are analyzed based on nonlocal strain gradient theory (NSGT), this accurate theory employs exact length scale parameter and nonlocal constant. The governing equations of GNPRC cylindrical nanoshell coupled with piezoelectric actuator (PIAC) are evolved by minimum potential energy principle and solved by the analytical method. For the first time in the current study, wave propagation-porosity behavior of a GNPRC cylindrical nanoshell coupled with PIAC is examined based on NSGT. The results show that, as the angular velocity increases, the difference between the minimum and maximum values of the phase velocity decreases. Another important result of this paper is that, by increasing the radius, extremum values of phase velocity occur in the lower values of the wave number. Finally, the influences of porosity, angular velocity, wave number and different graphene platelet distribution patterns on the phase velocity are investigated using the mentioned continuum mechanics theory. The outputs of the present work can be used in structural health monitoring and ultrasonic inspection techniques.

Novel Substrate-Integrated Waveguide Phase Shifter and its Application to Six-Port Junction

A complementary split-ring resonator (CSRR)-loaded substrate-integrated waveguide (SIW) phase shifter and its application to a six-port junction is presented and demonstrated in this article. Different from the prior evanescent-mode analysis, this article concentrates on the TE10-mode analysis of CSRR-loaded SIW, and a slow-wave effect is observed. The CSRR offers a simple resolution to a slow-wave structure in SIW and can be verified by the CSRR equivalent-circuit model theory. Hence, an equal-length wideband 90° phase shifter (35%) can be realized by a proper design of the fast-slow-wave hybrid transmission line (TL). The phase velocity decrease caused by the slow-wave effect contributes to the length reduction of the phase shifter as well and makes it more compact. Furthermore, the widespread application of CSRR also helps generalize the slow-wave effect, and a more compact phase- shifter-based half-mode substrate-integrated waveguide (HMSIW) is obtained. To experimentally validate this concept, a dual-layer six-port- junction-based HMSIW is designed, simulated, and fabricated. The application of the slow-wave TL in a six-port design helps in the bandwidth enhancement and size reduction of the component, which makes it more applicable to demanding systems with complex requirements such as detecting and transceiver systems. The measured results are in accordance with the simulated data.

Effects of Soil Parameters Uncertainties on the Behaviour of Anisotropic Porous Media to Shear Waves

In the present study, the wave equations for shear waves propagating in anisotropic fluid-saturated porous media are established in order to obtain the solutions in terms of displacements and dispersion equation. The wave velocities in the vertical and horizontal directions are derived. The uncertainties of the soil parameters due to their spatial variability are taken into account via Monte Carlo Simulations. The results are restricted to the effects of the porosity and permeability uncertainties on the phase velocity and attenuation for SH wave in addition to the anisotropy for Love wave. Results show that the mean velocities are more sensitive to the random variations of the permeability than to that of the porosity, but both phase velocity and attenuation decrease as the uncertainties increase. On the other hand, the anisotropy level and the randomness significantly affect the dispersion of Love waves. The present approach which converts a deterministic solution in a probabilistic one may be used as an everyday tool for practical applications of shear wave propagation in random media.

Wave propagation characteristics of the electrically GNP-reinforced nanocomposite cylindrical shell

In this article, wave propagation characteristics of a size-dependent graphene nanoplatelet (GNP) reinforced composite cylindrical nanoshell coupled with piezoelectric actuator (PIAC) and surrounded with viscoelastic foundation is presented. The effects of small scale are analyzed based on nonlocal strain gradient theory (NSGT) which is an accurate theory employing exact length scale parameter and nonlocal constant. The governing equations of the GNP composite cylindrical nanoshell coupled with PIAC have been evolved using Hamilton’s principle and solved with assistance of the analytical method. For the first time in the current study, wave propagation electrical behavior of a GNP composite cylindrical nanoshell coupled with PIAC based on NSGT is examined. The results show that, by decreasing the PIAC thickness, extremum values of phase velocity occur in the lower values of the wave number. Another important result is that, by increasing GPL%, the effects of PIAC thickness on the phase velocity decrease. Finally, influence of PIAC thickness, wave number, applied voltage, and different GPL distribution patterns on phase velocity is investigated using mentioned continuum mechanics theory. Useful suggestion of this research is that for designing of a nanostructure coupled with PIAC attention should be given to PIAC thickness and applied voltage, simultaneously. The outputs of the current study can be used in the structural health monitoring and ultrasonic inspection techniques.

RESEARCH OF PROCESSES IN A PIPE STRING AT A WELLHEAD PULSE INJECTION OF LIQUID TO A WELL

Studying the processes during the pressure pulses movement in the column of injected impulse liquid from the wellhead to the formation, it is necessary to assume, for simplification, that the wavelength significantly exceeds the diameter of the wells. These conditions are revealed in all cases of pulsed non-stationary liquid injection. It is necessary to take into account the dynamic solution at the low-frequency limit and to determine the displacement of the media with known parameters of size and voltage fields. The obtained results will be compared with the measurements got by various authors. The obtained data will allow to approximate the low- frequency range of waves, with the help of which it will be possible with sufficient error to determine the required parameters in situations where it is impossible to investigate them. A wave equation describing the motion of a column of a pumped liquid in a thick-walled tube is obtained, from which it follows that the column of a pumped liquid in a thick-walled tube is capable of supporting pulses of any waveform passing in either direction without dispersion or damping. Expressions are also obtained for describing the behavior of pulsed waves propagating along the pipe wall. Reflected waves appear in any case: when the change in velocity is caused by a change in pipe thickness, a change in Young's modulus, or a change in shear stiffness in the environment. Changes in the density or volumetric modulus of the injected fluid or well radius also generate reflected waves, and all of them can be combined in one expression. When evaluating the phase velocity and wave attenuation for four porous rocks, it is seen that at frequencies below 100 Hz the phase velocity decreases and the damping is very strong.

On modeling of wave propagation in a thermally affected GNP-reinforced imperfect nanocomposite shell

Due to rapid development of process manufacturing, composite materials with porosity have attracted commercial attention in promoting engineering applications. For this regard, in this research wave propagation-thermal characteristics of a size-dependent graphene nanoplatelet-reinforced composite (GNPRC) porous cylindrical nanoshell in thermal environment are investigated. The effects of small scale are analyzed based on nonlocal strain gradient theory (NSGT). The governing equations of the laminated composite cylindrical nanoshell in thermal environment have been evolved using Hamilton’s principle and solved with the assistance of the analytical method. For the first time, wave propagation-thermal behavior of a GNPRC porous cylindrical nanoshell in thermal environment based on NSGT is examined. The results show that by increasing the thickness, the effect of porosity on the phase velocity decreases. Another important result is that by increasing the value of the radius, the difference between the minimum and maximum values of the phase velocity increases. Finally, influence of temperature change, wave number, angular velocity and different types of porosity distribution on phase velocity are investigated using the mentioned continuum mechanics theory. As a useful suggestion, for designing of a GPLRC nanostructure should be attention to the GNP weight function and radius, simultaneously.

Wave propagation analysis in viscoelastic thick composite plates resting on Visco-Pasternak foundation by means of quasi-3D sinusoidal shear deformation theory

In this research, the wave propagation in a viscoelastic composite thick plate resting on a Visco-Pasternak foundation is analyzed by means of sinusoidal shear deformation theory (SSDT). The viscoelastic properties of the plate are considered by using Kelvin-Voigt model. The material properties of composite plate are assumed viscoelastic based on Kelvin-Voigt model. The governing equations of motion are derived by Hamilton's principle. The analytical solution is applied to obtain the effects of the structural and foundation damping coefficients, wave number, aspect ratios, elastic properties and number of layers on the wave propagation behavior of the viscoelastic composite plate including the dimensionless phase velocity, cut-off and escape frequencies. The obtained results indicate that the dimensionless phase velocity and natural frequency decrease with increasing the damping coefficient. Also, it is observed that the effect of layups on the phase velocity becomes more sensible for small wave numbers. However, the effect of the damping coefficient on the dimensionless phase velocity and natural frequency is only observed at large dimensionless wave numbers.

Cross-Correlation of Station-to-Station Free Surface Elevation Time Series for Breaking Water Waves

Free surface elevation time series of breaking water waves were measured in a laboratory flume. This was done in order to analyze changes in wave characteristics as the waves propagated from deep water to the shore. A pair of parallel- wire capacitive wave gages was used to simultaneously measure free surface elevations at different positions along the flume. One gage was kept fixed near the wave generator to provide a reference while the other was moved in steps of 0.1 m in the vicinity of the break point. Data from these two wave gages measured at the same time constitute station-to-station free surface elevation time series. Fast Fourier Transform (FFT) based cross-correlation techniques were employed to determine the time lag between each pair of the time series. The time lag was used to compute the phase shift between the reference wave gage and that at various points along the flume. Phase differences between two points spaced 0.1 m apart were used to calculate local mean wave phase velocity for a point that lies in the middle. Results show that moving from deep water to shallow water, the measured mean phase velocity decreases almost linearly from about 1.75 m/s to about 1.50 m/s at the break point. Just after the break point, wave phase velocity abruptly increases to a maximum value of 1.87 m/s observed at a position 30 cm downstream of the break point. Thereafter, the phase velocity decreases, reaching a minimum of about 1.30 m/s.

Is there a role for approximations to the Kramers-Kronig relations in understanding the propagation of ultrasound in bone?

Clinical measurements of the speed of sound (SOS) usually exhibit moderately large site-to-site variations within a given individual, leading to rather wide ranges for osteoporosis, osteopenia, and normal. Consequently, the rather modest variation of phase velocity over 200 kHz to 800 kHz predicted by the approximate form of the Kramers-Kronig relations developed in our laboratory would appear to be of limited interest. However, whereas the Kramers-Kronig relations predict a systematic increase in phase velocity with frequency, laboratories in Kyoto, Paris, and Washington, D.C., each reported a systematic decrease in phase velocity with increasing frequency. We suggested that this “anomalous” (negative) decrease in velocity with frequency was actually the consequence of interference between two waves, each of which satisfied the Kramers-Kronig-predicted positive dispersion, with one wave sufficiently stronger than the other that the combination appeared to be only a single wave. Although separation of the fast and slow waves by Bayesian, Prony’s, and other methods has provided substantial insight, significant unexplained results remain and are a focus of this presentation. The author wishes to acknowledge significant contributions by former colleagues: C. Anderson, A. Bauer, G. Brandenburger, L. Bretthorst, A. Groopman, J. Hoffman, S. Handley, M. Holland, M. Hughes, E. Jaynes, J. Katz, K. Marutyan, J. Mobley, R. Norberg, M. O’Donnell, R. Trousil, and K. Waters.

Role of superconductivity in superconducting transmission line resonator

In order to understand the role of superconductivity in superconducting transmission line resonator, we derive the mode equations using the macroscopic wavefunction of the Cooper pairs. We make an appropriate scaling to obtain the dimensionless form of equations and establish the validity of good conductor approximation under most circumstances. Quantization of superconducting transmission line resonator is realized by the black-box principle. We also briefly discuss that the deviation from good conductor behavior would result in the observable effects, such as the considerable decrease of phase velocity and the soliton.