Search

Surface acoustic wave (SAW) resonators are essential components of mobile communication technology. Advanced performance SAW resonators are needed to support beyond fifth-generation mobile communication technology, which aims to achieve unprecedentedly high data rates and low latency using wide frequency bands in the RF spectrum. This study theoretically investigates the propagation characteristics of a non-leaky Rayleigh-type SAW (RSAW) propagating in a c-axis-tilted ScAlN film/3C-SiC substrate structure. By appropriately selecting the c-axis tilt angle and the film thickness of the ScAlN film, a high electromechanical coupling coefficient (K2) value was obtained in the second-mode RSAW (Sezawa wave). The maximum K2 value for the Sezawa wave was 8.03%, with a phase velocity of 7456 m/s and a power flow angle of 0° under the structural conditions where the K2 value was maximized. These properties offer significant advantages for achieving wide frequency bands, high operating frequencies, and ease of design for SAW resonators. The structural conditions under which good propagation characteristics were obtained in the Sezawa waves were found to coincide with the conditions that maximize the electromechanical coupling coefficient of the quasi-longitudinal wave in the ScAlN film, and a significant increase in the shear vertical component of Sezawa wave particle displacement was observed. Additionally, ScAlN films with a 40% Sc concentration can be fabricated using sputtering and molecular beam epitaxy. Recent advancements have reported the production of high-quality 3C-SiC wafers and large 3C-SiC film/silicon wafers. Therefore, the c-axis-tilted ScAlN film/3C-SiC substrate structure shows great potential as a candidate for next-generation SAW resonators. [ABSTRACT FROM AUTHOR]

Crossed-Field Vacuum Electron Devices are ubiquitous in the High-Power Microwave field in either an oscillator/source or amplifier variant. A typical configuration consists of a magnetically insulated laminar electron flow in an anode–cathode gap with crossed electric (∝ V , voltage) and magnetic (B-) fields and a series of open resonant cavities/vanes located on the anode block that serve as a slow-wave structure (SWS). The SWS slows the phase velocity of the electromagnetic signal down so that the wave becomes synchronous with a layer of the electron flow but is often neglected when calculating the Hull magnetic field necessary to insulate the electrons. In particular, the guiding design equation for the critical cutoff B-field assumes a smooth anode wall. In this paper, we show that such an assumption severely narrows the operating regime in B–V space and that upon inclusion of a revised Hull Cutoff condition taking into account the SWS, operation at lower B and higher V is possible. This revised Hull Cutoff criterion for magnetic insulation in crossed-field devices is corroborated by Particle-in-Cell simulations using CST Particle Studio. [ABSTRACT FROM AUTHOR]

Magnetic skyrmion bags are composite topological spin textures with arbitrary topological charges. Here, we computationally study the transient rotational motion of skyrmion bags, which is characterized by a global rotation of inner skyrmions around the central point. Distinct from conventional rotational modes found in skyrmions, the observed rotation is a forced motion associated with the breathing mode induced solely by vertical microwave fields. The driving force behind this rotation originates from the interactions between outer and inner skyrmions, with the angular velocity determined by the phase difference resulting from their asynchronous breathing behaviors. It is also found that skyrmion bags with larger skyrmion numbers are more conducive to the occurrence of the rotation. Our results are useful for understanding the cluster dynamics of complex topological spin textures driven by dynamic fields. [ABSTRACT FROM AUTHOR]

Near-surface in seismic exploration generally refers to the low deceleration zone and a section of stratum below it, which can be described in geophysical language as "low velocity", "low Q", and "Free surface", etc. Due to the presence of low-velocity layers in near-surface, shallow seismic simulation is plagued by numerical dispersion. Numerical dispersion affects the accuracy of seismic wave simulation, especially severe in shallow areas containing low-velocity layers. To improve the simulated quality, denser grids or higher-order difference schemes are used, but both of which would seriously reduce computational efficiency, especially for frequency-domain numerical modeling. Differentiation is replaced by difference in wave field simulation, which would inevitably result in numerical errors. These numerical errors are manifested as the difference between the phase velocity of the discretized wave field and the medium velocity. The waves with different wavenumber components have different phase velocities, and the larger the wavenumber, the more that its phase velocity lags the group velocity. Based on this theoretical analysis, a regularization factor is added to the frequency-domain acoustic wave equation to correct the phase velocity of high wavenumber components. According to the Von Neumann stability requirements, a regularization factor that adaptively changes with simulation parameters is derived. Compared to the fixed regularization factor, adaptive regularization factor can better match the velocity field and protect the effective wave field to the maximum extent while suppressing numerical dispersion. The improved acoustic wave equation can effectively suppress numerical dispersion without increasing the number of grids. Different numerical models demonstrate the effectiveness and efficiency of the improved acoustic equation with the adaptive regularization factor for suppressing numerical dispersion. [ABSTRACT FROM AUTHOR]

The recent developments in array-based surface-wave tomography have made it possible to directly measure apparent phase velocities through wave front tracking. While directionally dependent measurements have been used to infer intrinsic |$2\psi $| azimuthal anisotropy (with a 180° periodicity), a few studies have also demonstrated strong but spurious |$1\psi $| azimuthal anisotropy (360° periodicity) near major structure boundaries particularly for long period surface waves. In such observations, Rayleigh waves propagating in the direction perpendicular to the boundary from the slow to the fast side persistently show a higher apparent velocity compared to waves propagating in the opposite direction. In this study, we conduct numerical and theoretical investigations to explore the effect of scattering on the apparent Rayleigh-wave phase velocity measurement. Using 2-D spectral-element numerical wavefield simulations, we first reproduce the observation that waves propagating in opposite directions show different apparent phase velocities when passing through a major velocity contrast. Based on mode coupling theory and the locked mode approximation, we then investigate the effect of the scattered fundamental-mode Rayleigh wave and body waves interfering with the incident Rayleigh wave separately. We show that scattered fundamental-mode Rayleigh waves, while dominating the scattered wavefield, mostly cause short wavelength apparent phase velocity variations that could only be studied if the station spacing is less than about one tenth of the surface wave wavelength. Scattered body waves, on the other hand, cause longer wavelength velocity variations that correspond to the existing real data observations. Because of the sensitivity of the |$1\psi $| apparent anisotropy to velocity contrasts, incorporating such measurements in surface wave tomography could improve the resolution and sharpen the structural boundaries of the inverted model. [ABSTRACT FROM AUTHOR]

Train noise is a kind of green, non‐destructive and strong‐energy artificial seismic sources, which is widely used in railway safety monitoring, near‐surface imaging and urban underground space exploration. Distributed acoustic sensing is a new seismic acquisition technology, which has the advantages of dense sampling, simple deployment and strong anti‐electromagnetic interference ability. In recent years, distributed acoustic sensing has been gradually applied in the fields of urban traffic microseism monitoring, crack detection and underground space imaging. However, previous studies mainly focused on microseism interferometry using train event coda noise, and there is limited research on the workflow of interferometry imaging using distributed acoustic sensing–based heavy train events noise (with short coda windows), which produces an abundant of near‐source interference. Aiming at proving the effectiveness of this idea, we investigated a process workflow to get underground shear‐velocity structure based on distributed acoustic sensing recorded heavy traffic noise near Qinhuangdao train station. A weighted sliding absolute average method is used to weaken the strong amplitude to the coda wave level and reduce the near‐source influence. We demonstrated that the cross‐coherence interferometry method, after spectral whitening, has the best effect on sidelobe suppression in the virtual source surface wave shot gathers, through a comparative analysis of cross‐correlation and cross‐coherence results. For obtaining concentrated energy and strong continuity in phase velocity spectra, we selected the time windows with high spatial coherence and signal‐to‐noise ratio not less than 1.2 for stacking from 720 time windows in F–K domain. When dividing subarrays to extract pseudo‐two‐dimensional profile, we set the overlap rate between adjacent time windows to 80% to increase stacking times, enhancing the precision of phase velocity spectra and reducing the errors of picking dispersion curve. Our results show that heavy traffic train events noise (non‐pure coda) can be used to detect underground velocity structure with clear dispersion and high inversion reliability. This research provides a new processing flow for distributed acoustic sensing train noise imaging and can be applied in future urban underground space exploration. [ABSTRACT FROM AUTHOR]

Accurate seismic models with anisotropy and attenuation characteristics are crucial to accurately imaging subsurface structures. However, the anisotropic viscoelastic equations are complex and require significant computational resources. In addition, the single‐mode waves have been sufficient for most practical exploration needs. However, separating the qP‐ and qSV‐waves in anisotropic viscoelastic wavefields is challenging. Thus, we propose a new method to approximate and efficiently separate the qP‐ and qSV‐waves in attenuated transversely isotropic media. First, we obtain the decoupled approximate phase velocities of qP‐ and qSV‐waves by a curve‐fitting method. Consequently, based on the average and maximum relative error analysis, our approximate qP‐ and qSV‐wave phase velocities are more accurate than the existing approximations. Additionally, our approximations have broader applicability, resulting in acceptable errors during their application. Second, based on the approximate qP‐ and qSV‐wave phase velocities, we derive the corresponding qP‐ and qSV‐wave equations for a complete decoupling of the qP‐ and qSV‐wave components in transversely isotropic media. Third, to combine the attenuation and anisotropy characteristics, we incorporate the Kelvin–Voigt attenuation model and obtain the decoupled qP‐ and qSV‐wave equations in attenuated transversely isotropic media. Then, we use an efficient and stable hybrid finite‐difference and pseudo‐spectral method to solve the new decoupled qP‐ and qSV‐wave equations. Finally, several numerical examples demonstrate the separability and high accuracy of the proposed qP‐ and qSV‐wave equations. We obtain a qP‐wave wavefield entirely devoid of SV‐wave artefacts. In addition, the decoupled approximate qP‐ and qSV‐wave equations are accurate and stable in heterogeneous media with different velocities and attenuation. The decoupled, approximated qP‐wave and qSV‐wave equations proposed in this paper can effectively separate the qP‐wave and qSV‐wave components, resulting in fully decoupled qP‐ and qSV‐wave wavefields in attenuated transversely isotropic media. [ABSTRACT FROM AUTHOR]

To investigate the local damage characteristics and properties of stiffness degradation in aluminum structures under vibration fatigue, an evaluation method of the fatigue property for local areas has been proposed by identifying the stiffness from the phase velocity obtained by the laser ultrasonic system. First, vibration fatigue tests were conducted on 2024‐O aluminum alloy components under four different stress levels. To address the issue of local damage characteristics under vibration fatigue, a scan window to achieve the local phase velocities within a small local region was employed, and then, the local stiffness can be calculated. By tracking the residual stiffness of the weakest region, the local damage factor was calculated. A unified model with normalized periods at different stress levels was carried out to predict the evolutionary trend. This approach offers a more efficient alternative to estimate local fatigue damage and residual life through the monitoring of local stiffness during maintenance. Highlights: A method for quantifying local damage induced by vibration fatigue is proposed.Local stiffness obtained from the phase velocity acquired by the laser ultrasonic system is used for fatigue assessment.The focus on the most vulnerable area is achieved using a local damage factor.The fatigue life of the specimen is predicted by a normalized model under different stress levels. [ABSTRACT FROM AUTHOR]

Chiral light emission plays a key role in sensing, tomography, quantum communication, among others. Whereas, achieving highly pure, tunable chirality emission across a broad spectrum currently presents significant challenges. Free‐electron radiation emerges as a promising solution to surpass these barriers, especially in hard‐to‐reach regimes. Here, chiral free‐electron radiation is presented by exploiting the spin‐momentum locking (SML) property of spoof surface plasmons (SSPs). When the phase velocity of free electrons matches that of the SSPs, the SSPs can be excited. By implementing wavenumber compensation through perturbations, the confined SSPs are transformed into free‐space free‐electron radiation. Owing to the law of angular momentum conservation, this process converts the transverse spin angular momentum of SSPs into the longitudinal spin angular momentum of free‐electron radiation during the process, producing pure, tunable, and chiral free‐electron radiation across a broad spectrum. This method achieves an optimal degree of circular polarization approaching −1. The innovative methodology can be adapted to SML‐enabled guided states or silicon photonics platforms, offering new avenues for achieving chiral emission. [ABSTRACT FROM AUTHOR]

A first theoretical attempt is made to understand the characteristics of dust acoustic shock waves (DASWs) in a polarized electron-depleted plasma with a mixed nonextensive high energy–tail ion distribution and to examine the impact of the generalized nonthermal polarization force on DASWs in an electron-depleted dusty plasma. First, a short numerical investigation illustrating the behavior of the mixed nonextensive high energy–tail (or Cairns–Tsallis) ion distribution and the domain of validity of its two parameters (q and α) is carried out. Next, the generalized nonthermal polarization acting on dust grain in electron-depleted dusty plasma is determined within the context of Tsallis' statistical mechanics. The behavior of this generalized polarization force is significantly affected by the nonextensive character of the nonthermal ions. Specifically, we have shown that, for both space and experimental dusty plasmas, the magnitude of the polarization force (in the case where − 1 < q < 1) decreases as the nonextensivity of the nonthermal ions becomes significant. As an application, we have analyzed the changes caused by the nonthermal nonextensive polarization force on the main characteristics of DASW (viz. phase velocity, polarity, amplitude, width, etc.). Numerical results showed that our plasma model supports rarefactive and compressive DASWs that are significantly affected by the effects of nonthermal ion nonextensivity and polarization force. In particular, we have shown that for large values of the nonthermal parameter α , the increase in q allows the transition from rarefactive to compressive DASW structures. The present theoretical investigation is helpful to fully understand electrostatic disturbances in space and experimental dusty plasmas. [ABSTRACT FROM AUTHOR]

The severe damage observed in the Kathmandu Basin, Nepal, during past earthquakes necessitates a thorough study of the seismic behavior of the basin sediments. As the shear-wave velocity is directly related to the elastic shear modulus of the material, it is essential to determine it to incorporate the behavior of the soil in the design of the structure. Hence, we determined average shear-wave velocity in upper 30 m (Vs30) of soil in Bhaktapur district in the eastern part of the Kathmandu Basin at 73 observation points, employing two methods involving the use of non-invasive microtremor array measurements (MAMs). These MAMs are widely used for determining subsurface soil characteristics by analyzing the ambient vibrations of the ground. The first method involves inversion using a genetic algorithm, and the second is a method for obtaining Vs30 directly from the dispersion curve. We found that Vs30 in the southeastern part of the study area was higher than that in other parts. Conversely, Vs30 in the western region was lower. The calculated Vs30 values were used to classify the sites. The elevated eastern and southeastern areas with high Vs30 were categorized as dense soil or soft rock, whereas the areas with low Vs30 that had suffered significant damage during the 2015 Gorkha earthquake were classified as soft soil sites. [ABSTRACT FROM AUTHOR]

Many heart diseases can change the elasticity of myocardial tissues, making elastography a potential medical imaging strategy for heart disease diagnosis and cardiovascular risk assessment. Among the existing elastography methods, ultrasound elastography is an appealing choice because of ultrasound’s inherent advantages of low cost, high safety, wide availability, and deep penetration. The existing investigations of cardiac ultrasound elastography were implemented based on a bulk model of heart tissue, treating the waves generated in the myocardial tissues as shear waves. In this pilot study, we considered the distinct geometric characteristics of heart tissue, i.e., being a layered structure and its dispersive nature as biological tissue. Based on these considerations, we modeled heart tissues as a layered-dispersive structure and developed a new ultrasound elastography method, ultrasonic guided wave elastography, to characterize the myocardial elasticity. The validity of this layered-dispersive model and the reliability of the developed guided wave elastography were first verified on tissue-mimicking phantoms. Then, the guided wave elastography was applied to an ex vivo imaging of a rat heart tissue specimen in real-time during the biaxial planar mechanical testing. The comparison of the real-time myocardial elasticity obtained from guided wave elastography and mechanical testing demonstrated strong matching, verifying the reliability of the developed cardiac guided wave elastography as a potential method for characterizing myocardial elasticity. [ABSTRACT FROM AUTHOR]

Detecting buried active faults presents the challenge of precisely locating the upper breakpoint, the shallowest point in the Quaternary system where faults occur. Microtremor survey technology, unaffected by urban electromagnetic interference, offers an eco-friendly and efficient method for investigating buried faults and stratigraphic structures in urban areas. This research uses microtremor survey technology to identify the upper breakpoint of the buried Nankou-Sunhe Fault in Changping, Beijing. For data collection, 17 microtremor survey points were deployed across the northern section of the Nankou-Sunhe fault, employing a three-point nested circular array with a point spacing of approximately 200 m to form a profile spanning approximately 320 m. For data analysis, the spatial autocorrelation method was utilized. Each measurement point was divided into 9 sets of radii, ranging from a minimum of approximately 4 m to a maximum of 28 m. The correlation coefficients for each set were calculated, and the dispersion curve for each measurement point was generated by fitting the average coefficients with the Bessel function of the first kind of order zero. The apparent S-wave velocity was determined directly from the dispersion curve using empirical formulas and interpolated to generate the contour cross-section map. Integrating the section and inverted S-wave velocity data can significantly enhance interpretation accuracy, and based on these data, the spatial development characteristics and upper breakpoint locations of the Nankou-Sunhe fault zone were analyzed, and the strata shallower than 100 m were deduced. The results align well with known geological data, such as luminescence dating and 14C dating from boreholes at nearby locations. [ABSTRACT FROM AUTHOR]

On 15 January 2022, a massive underwater eruption occurred at the Hunga Tonga‐Hunga Ha'apai Volcano. The plume reached the mesosphere, and the eruption excited a significant atmospheric Lamb wave, which forced the tsunami. The complicated tsunami waveforms due to ocean‐atmosphere coupling prevented inferring the force history of the excitation. To address this, we analyze ocean surface gravity waves (OSWs) from 15 to 40 mHz, which are decoupled from the Lamb wave due to their slower phase velocities. Modeling these OSWs, we infer that the excitation started at 4:00 UTC with an amplitude of 1010 $1{0}^{10}$ N and lasted for 5 hr, followed by a sub‐event at 8:40 UTC. The observations suggest an initial blowout of seawater above the summit and a subsequent outflow that excited a tsunami below 5 mHz. The 2 hr delayed OSW excitation from 6 to 15 mHz may indicate seawater inflow into the crater. Plain Language Summary: On 15 January 2022, the Hunga Tonga‐Hunga Ha'apai volcano experienced a massive underwater eruption. This eruption sent a plume into the atmosphere and produced a powerful atmospheric wave that caused an early arrival of the tsunami. The complex tsunami propagation coupled with the atmospheric wave prevents us from understanding the excitation processes. To address this, we focussed on ocean surface gravity waves (OSWs) in an oscillatory period from 25 to 67 s, also interpreted as short‐period tsunamis. These OSWs are less affected by these atmospheric waves because of the slow propagation speed. Because the OSWs are less influenced by ocean depth, they are easier to model. The observed OSWs show that the eruption started at 4:00 UTC with a vertical force of approximately 1010 $1{0}^{10}$ N and continued for about 5 hr. Another significant sub‐event occurred around 8:40 UTC. Furthermore, the OSWs in an oscillatory period from 67 to 167 s arrived about 2 hr after the short‐period OSWs. These observations suggest that the eruption blew seawater above the volcano's summit and a subsequent outflow that excited a tsunami. The 2 hr delay in low‐frequency OSW could indicate that seawater flowed into the crater. Key Points: Ocean surface gravity waves at 15–40 mHz were excited at 4:00 UTC when an underwater eruption occurred at Hunga Tonga‐Hunga Ha'apai VolcanoA significant sub‐event at about 8:40 UTC followed the main event, and the ocean surface gravity waves lasted for half a dayThe observations of ocean surface gravity waves suggest a blowout of seawater above the summit and the inflow of seawater into the crater [ABSTRACT FROM AUTHOR]

The two circular structures with local resonance resonant hammers proposed in this paper have the comprehensive performance of small size, easy fabrication and low frequency vibration and sound damping. In the study, Bloch's theorem is used to calculate the energy band curves of the two structures and to analyze the vibration forms of the structures at the edge of the band gap. At the same time, the integrated analysis means of phase constant surface, group velocity and phase velocity are innovatively used to explore the real propagation path of waves and provide experience for topology optimization. The position of resonant hammers, the mirror symmetry structure and the size of resonant hammers are adjusted to optimize the band gap for both structures. Finally, the vibration transmission characteristics of the finite period structure are calculated to verify the band gap and evaluate the vibration isolation performance. The results show that the new structure has low-frequency noise reduction performance, and the band gap frequency can be further reduced by topology optimization. This study presents an innovative approach for achieving low-frequency noise reduction, analysis of wave propagation paths and lightweight design. [ABSTRACT FROM AUTHOR]

AbstractWith the size reduction of structures into micro/nanoscale, the size-dependent effect arises in mechanical properties. For micro/nanostructures working in transient thermal environment, the thermal relaxation needs to be considered in heat conduction. Functionally graded carbon nanotubes/graphene platelets reinforced composite (FG-CNTRC/GPLRC) materials as new generation of advanced materials have attracted much attention due to their excellent mechanical or thermoelastic performance. Though the mechanical or non-coupled thermoelastic behaviors of beam, plate and shell made of FG-CNTRC/GPLRC materials have been extensively studied, there lacks of investigations on the coupled thermoelastic behaviors of micro/nanostructures of FG-CNTRC/GPLRC in the context of generalized thermoelasticity where both the elastic nonlocality and thermal relaxation need to be considered. To fill this gap, in this work, the Lord–Shulman (L-S) type generalized thermoelasticity incorporating the fractional-order nonlocal theory is applied to investigating the thermoelastic bending wave propagation characteristics of a nanocomposite microbeam reinforced by GPLs and CNTs simultaneously for the first time. The Halpin–Tsai micromechanical model is used to assess the effective elastic modulus and the other properties are evaluated by the rule of mixture. Then, the governing equations are formulated based on the Euler–Bernoulli beam model. By assuming the wave-type solutions, the governing equations are solved and the dispersion relation between frequency and wave number and the relation between phase velocity and wave number are determined, respectively. In calculation, the effects of the thermal relaxation time, the elastic nonlocal parameter, the fractional order parameter and the mass fractions of GPLs and CNTs on the dimensionless frequency and phase velocity are analyzed and discussed in detail. [ABSTRACT FROM AUTHOR]

Driven by the versatility and adaptability of next-generation soft robotic devices, investigating the vibrational behavior under fluid-electromechanical coupling represented by a soft dielectric elastomer actuator (DEA) tube filled with fluid evokes much attention. Here, we investigate the axisymmetric vibration of an inviscid compressible fluid-filled thin DEA tube by using the Gent model to define the behavior of the tube under multi-fields. We consider the effect of the fluid by exploiting the relation of the radial fluid pressure at the fluid-solid interface. Following the general incremental theory of nonlinear electro-elasticity, we formulate the incremental governing and constitutive equations needed for vibration analysis and solve them numerically using the state-space method (SSM). The results demonstrate the influence of the applied voltage, overcritical circumferential stretch, higher frequency modes, and phase velocity modes on the early development of axisymmetric instability and dielectric breakdown. The existence of the fluid contributes to more reduction in the frequency and phase velocity compared to the fluid-free case due to the added mass effect. Moreover, the results show the role of fluid in the partial self-healing of the soft DEA. A parametric study on specific variables deduces that increasing the thickness of the soft DEA tube reduces the frequency effectively, whereas applying higher voltages causes a thinning in the thickness, leading to the need for thicker tubes. [ABSTRACT FROM AUTHOR]

A new modified three-dimensional (3D) nonlinear Schrödinger equation (3DMNLSE) is derived for gravity waves in the presence of wind, dissipation, and two-dimensional slowly varying currents, which include transverse and longitudinal currents in finite water depth. The effect of currents on modulational instability (MI) is investigated. The divergence (convergence) effect of longitudinal favorable (adverse) currents decreases (increases) the MI growth rate and region of instability while suppressing (enhancing) the formation of freak waves. Meanwhile, the transverse currents hardly affect the occurrence of MI. Furthermore, some results from the simulations with the space evolution of 3DMNLSE are presented. The results show the ubiquitous occurrence of freak waves in 3D wave fields under certain sets of initial conditions. We demonstrate that larger waves can be triggered when a weakly modulated wave train enters a region of adverse currents. The maximum amplitude of a freak wave depends on the ratio of the current velocity to the wave phase velocity. [ABSTRACT FROM AUTHOR]

This study investigates the gas–liquid two-phase flow characteristics in a stirred tank equipped with a double-layer punched impeller. Numerical simulations are conducted to analyze flow dynamics, gas holdup, bubble sizes, and distributions under various operational conditions. The results show a high degree of agreement between experimental and simulated power values and gas holdup distributions, validating the reliability of the computational fluid dynamics–population balance model coupling approach. The combination of the punched four-inclined-blade up-pumping turbine and the punched Rushton impeller exhibits excellent bubble dispersion characteristics, with overall small bubble sizes. Increasing the rotational speed can enhance turbulence within the flow field and accelerate the liquid phase velocity, which facilitates gas diffusion and improves gas–liquid mixing efficiency. Additionally, higher rotational speed further intensifies the shear effect of the punched impeller, resulting in a reduction in average bubble size. [ABSTRACT FROM AUTHOR]

Paroxysmal positional nystagmus frequently occurs in lesions involving the cerebellum, and has been ascribed to disinhibition and enhanced canal signals during positioning due to cerebellar dysfunction. This study aims to elucidate the mechanism of central positional nystagmus (CPN) by determining the effects of baclofen on the intensity of paroxysmal positional downbeat nystagmus due to central lesions. Fifteen patients with paroxysmal downbeat CPN were subjected to manual straight head-hanging before administration of baclofen, while taking baclofen 30 mg per day for at least one week, and two weeks after discontinuation of baclofen. The maximum slow phase velocity (SPV) and time constant (TC) of the induced paroxysmal downbeat CPN were analyzed. The positional vertigo was evaluated using an 11-point numerical rating scale (0 to 10) in 9 patients. After treatment with baclofen, the median of the maximum SPV of paroxysmal downbeat CPN decreased from 30.1°/s [interquartile range (IQR) = 19.6—39.0°/s] to 15.2°/s (IQR = 11.2—22.0°/s, Wilcoxon signed rank test, p < 0.001) with the median decrement ratio at 40.2% (IQR = 28.2—50.6%). After discontinuation of baclofen, the maximum SPV re-increased to 24.6°/s (IQR = 13.1—34.4°/s, Wilcoxon signed rank test, p = 0.001) with the median increment ratio at 23.5% (IQR = 5.2—87.9%). In contrast, the TCs of paroxysmal downbeat CPN remained unchanged at approximately 3.0 s throughout the evaluation. The positional vertigo also decreased with the medication (Wilcoxon signed rank test, p = 0.020), and remained unchanged even after discontinuation of medication (Wilcoxon signed rank test, p = 0.737). The results of this study support the prior presumption that paroxysmal CPN is caused by enhanced responses of the semicircular canals during positioning due to cerebellar disinhibition. Baclofen may be tried in symptomatic patients with paroxysmal CPN. [ABSTRACT FROM AUTHOR]

After transporting oil with a mobile pipeline, it is necessary to empty the oil within the pipeline. A common method is to inject water into the inlet to push the oil out. However, due to the effects of buoyancy and surface tension, the oil within the pipeline tends to accumulate at the elevated section, forming a stagnant oil layer, which will limit the evacuation efficiency. Based on the multiphase flow theory, a hydrodynamic model of oil–water flow was utilized to describe the pressure distribution and the thickness of the stagnant oil layer within the pipeline. A numerical model for oil-carrying water flow in a downward-inclined mobile pipeline was established, and the model was solved under given initial and boundary conditions to obtain the characteristics of the oil-carrying water flow within the pipeline. The calculation results indicate that the initial water phase velocity has a promoting effect on the oil-carrying capacity of water flow. The pipe diameter is negatively correlated with the capacity. The initial thickness of the oil is not directly related to the capacity but can increase the oil phase front velocity, which can enable the oil phase to be emptied more quickly. When the initial water phase velocity is lower than the critical water phase velocity, an increase in the inclination angle will weaken the capacity of water flow to carry oil. Conversely, when the velocity of the initial water phase is higher than the critical water phase velocity, an increase in the inclination angle will enhance the capacity. [ABSTRACT FROM AUTHOR]

In the past two decades or so, ambient noise tomography (ANT) has emerged as a powerful tool for investigating high-resolution crustal and upper-mantle structures. A crucial step in the ANT involves extracting phase velocities from cross-correlation functions (CCFs). However, obtaining precise phase velocities can be a formidable challenge, particularly when significant lateral velocity variations exist in shallow subsurface imaging that relies on short-period surface waves from ambient noise. To address this challenge, we propose an unwrapping correction method that enables the accurate extraction of short-period dispersion curves. Our method relies on the examination of the continuity of phase velocities extracted from CCFs between a common station and other neighbouring stations along a linear array. We demonstrate the effectiveness of our approach by applying our method to both synthetic and field data. Both applications suggest our unwrapping correction method can identify and correct unwrapping errors in phase velocity measurements, ensuring the extraction of accurate and reliable dispersion curves at short periods from ambient noise, which is essential for subsequent inversion for subsurface structures. [ABSTRACT FROM AUTHOR]

Taiwan, one of the most active orogenic belts in the world, undergoes orogenic processes that can be elucidated by the doubly vergent wedge model, explaining the extensive island-wide geological deformation. To provide a clearer depiction of its cross-island orogenic architecture, we apply ambient noise tomography across an east–west linear seismic array in central Taiwan, constructing the first high-resolution 2-D shear velocity model of the upper crust in the region. We observe robust fundamental- and higher-mode Rayleigh waves, with the latter being mainly present in the western Coastal Plain. We develop a multimode double-beamforming method to determine local phase velocities across the array between 2- and 5-s periods. For each location, we jointly invert all available fundamental- and higher-mode phase velocities using a Bayesian-based inversion method to obtain a 1-D model. All 1-D models are then combined to form a final 2-D model from the surface to ∼10 km depth. Our newly developed 2-D model clearly delineates major structural boundaries and fault geometries across central Taiwan, thereby corroborating the previously proposed pro-wedge and retro-wedge models while offering insight into regional seismic hazards. [ABSTRACT FROM AUTHOR]

We present an approach, based on cross-coupling of quadrupole and monopole borehole acoustic modes caused by anisotropy, to investigate the in situ stress state, a critical parameter for effective CO2 sequestration and for determining subsurface injection bounds in general. We focus on in situ stress states where the vertical direction is a principal stress direction, and we aim at determining the minimum and maximum horizontal stresses. Because of non-linear elastic effects, three unequal principal stresses in an otherwise isotropic rock may create three orthogonal planes of symmetry, which characterize an orthorhombic elastic medium. Near a wellbore, where the stress field is perturbed, a stress sensitive material causes material axes and moduli to form a spatial distribution to which sonic logging is sensitive. We present a method for differentiating between stress induced and intrinsic anisotropy. Using finite element modelling, we demonstrate that in either case the quadrupole fundamental mode includes an axis-symmetric (monopole) component. We demonstrate that the acoustic amplitude at the borehole centre divided by the maximum acoustic amplitude at the wellbore periphery (dominated by the acoustic profile |$\cos(2\theta)$|⁠) is an indicator of elastic anisotropy. We denote this ratio |$I_A$| and argue that |$I_A\gt 0$| when the elastic anisotropy is of entirely intrinsic origin (meaning the elastic moduli are in -sensitive to stress), and further that |$I_A$| increases for decreasing frequency for such cases. We demonstrate that |$I_A$| attains negative values for increasing frequency in stress-sensitive formations where a cross-over (from negative to positive values) is attributed to the perturbed velocity/moduli/stress fields near the wellbore. In synthetic data, we show that the ratio |$I_A$|⁠ , in combination with the phase velocity dispersion, uniquely determines the state of stress in stress-sensitive formations. In stress in-sensitive formations, we argue that |$I_A$| at lower frequencies, that is at frequencies slightly above the cut-off frequency, is very sensitive to elastic anisotropy. We argue that in quadrupole eigenmodes, evidence of intrinsic anisotropy is present at low frequencies whereas stress induced anisotropy is better gauged at moderate to high frequencies. Finally, we discuss the practical implications of these findings. [ABSTRACT FROM AUTHOR]

Seismic velocity models provide important constraints on Greenland's deep structure, which, in turn, has profound implications for our understanding of the tectonic history of this region. However, the resolution of seismic models has been limited by a sparse network, particularly in northern and central Greenland. We address these limitations by generating new high-resolution Rayleigh-wave phase velocity maps encompassing Greenland and northeastern Canada by processing over three decades of teleseismic earthquake records and incorporating recently added stations in Greenland and Arctic Canada. These phase velocity maps are sensitive to structure from the lower crust down to the sub-lithospheric mantle (25–185 s period). We find significant heterogeneity and a strong correlation between isotropic and anisotropic seismic velocities with inferred geological structure. High seismic velocities associated with cratonic lithosphere are broadly divided into two regions, with a belt of reduced velocity spanning central Greenland, which we interpret as lithospheric erosion resulting from interaction between the Greenland continental keel and the Iceland plume. Within each region, we identify tectonic subdivisions that suggest fundamental differences between the blocks that make up Precambrian Greenland. In the south, the North Atlantic craton (NAC) has a high-velocity keel exhibiting anisotropic stratification. Between the NAC and the cratonic lithosphere further north, the Proterozoic Nagssugtoqidian orogenic belt shows a distinct signature of reduced seismic velocity to |$\sim$| 75 s period, but then appears to pinch out at depth. The northern Greenland lithosphere exhibits significant isotropic heterogeneity, with a distinct core of high velocities in the northwest (⁠|$\sim$| 55–75 s period) giving way to a set of distinct east-west trending high-velocity belts at longer periods. At all periods sensitive to the lithospheric mantle in this region, anisotropic fast orientations are E–W, consistent with a north–south Precambrian assembly of the Greenland shield. In contrast to the NAC, there is no evidence of anisotropic stratification in the northern part of the cratonic keel. Based on both isotropic and anisotropic phase-velocity anomalies, we suggest that the Phanerozoic Caledonian and Ellesmerian-Franklinian fold belts are relatively thin-skinned features onshore Greenland, though the Caledonian belt may have a stronger signature off the east coast. At the longest periods, a prominent low-velocity anomaly initially centred on Iceland migrates northwards and spreads beneath central-eastern Greenland. Coupled with NW–SE trending anisotropy, this feature is interpreted as the effect of mantle flow radiating outward from the Iceland plume and interacting with the eroded Greenland lithosphere. [ABSTRACT FROM AUTHOR]

Background: Neuro-otological factors that influence changes in spontaneous nystagmus (SN) during vertigo attacks in Ménière's disease (MD) remain unclear. Objective: To identify neuro-otological factors that might influence the initial direction of SN and the directional change of SN. Methods: A prospective, observational study of 22 patients with definite MD to evaluate the initial direction and directional change of SN during vertigo attacks, endolymphatic hydrops (EH) volume, and the function of horizontal semicircular canal and hearing levels. Results: SN consistently began as irritative in 17 of 22 cases, and 9 of 17 cases showed a definite change in direction after onset. SN consistently began as paralytic in 5 of 22 cases, and 3 of 5 cases showed a definite change in direction after onset. Subjects in the irritative initial SN group had less severe degrees of hearing loss, smaller cochlear and vestibular EH volume than the paralytic initial SN group (P = 0.017, < 0.001, and 0.009, respectively). Subjects in the SN direction change group had significantly smaller maximum slow phase velocity, percentage of caloric weakness and canal paresis than the no SN direction change group (P = 0.001, 0.006, and 0.001, respectively). Simple logistic regression analysis showed that smaller EH volume was significantly associated with initial irritative SN (OR = 0.867, 95% CI 0.762–0.988, P = 0.032) and that the degree of canal paresis was negatively associated with the presence of directional change of SN (OR = 0.022, 95% CI 0.002–0.289, P = 0.004). Conclusions: The morphology of EH and canal paresis may independently affect the characteristics of SN in patients with MD. [ABSTRACT FROM AUTHOR]

The suppression of low-frequency vibration and noise has always been an important issue in a wide range of engineering applications. To address this concern, a novel square hierarchical honeycomb metamaterial capable of reducing low-frequency noise has been developed. By combining Bloch's theorem with the finite element method, the band structure is calculated. Numerical results indicate that this metamaterial can produce multiple low-frequency bandgaps within 500 Hz, with a bandgap ratio exceeding 50%. The first bandgap spans from 169.57 Hz to 216.42 Hz. To reveal the formation mechanism of the bandgap, a vibrational mode analysis is performed. Numerical analysis demonstrates that the bandgap is attributed to the suppression of elastic wave propagation by the vibrations of the structure's two protruding corners and overall expansion vibrations. Additionally, detailed parametric analyses are conducted to investigate the effect of θ, i.e., the angle between the protruding corner of the structure and the horizontal direction, on the band structures and the total effective bandgap width. It is found that reducing θ is conducive to obtaining lower frequency bandgaps. The propagation characteristics of elastic waves in the structure are explored by the group velocity, phase velocity, and wave propagation direction. Finally, the transmission characteristics of a finite periodic structure are investigated experimentally. The results indicate significant acceleration amplitude attenuation within the bandgap range, confirming the structure's excellent low-frequency vibration suppression capability. [ABSTRACT FROM AUTHOR]

In this paper, wave propagation in functionally graded (FG) porous plates resting on Winkler-Pasternak foundation is studied using a quasi-3D shear deformation theory. The proposed theory has a new displacement field that includes indeterminate integral terms and contains fewer unknown variables taking into account the effect of transverse shear and thickness stretching. The parameters of the elastic foundation are introduced in the present formulation following the mathematical model of Pasternak. In addition, the effect of porosity is studied. The material of the FG plate is inhomogeneous and the material properties are assumed to vary continuously in the thickness direction according to a power law of the volume fraction. The equations governing wave propagation in the plates resting on an elastic foundation are derived using Hamilton's principle. Then, the dispersion relationship between frequency and wave number is solved analytically. A comprehensive numerical result is accomplished to evaluate the effects of the volume fraction index, the porosity, thickness ratio (h/a), and the wave number on the wave propagation in functionally graded porous plates are discussed in detail. [ABSTRACT FROM AUTHOR]

The paper deals with a new model based on Eringen's nonlocal thermoelasticity. The propagation of Rayleigh waves in a nonlocal thermoelastic layer which is lying over a nonlocal thermoelastic half-space is considered in the context of energy dissipation theory. The normal mode analysis is employed to the considered equations to obtain vector matrix differential equation which is then solved by state space approach.The frequency equation of Rayleigh surface wave is derived. The effect of the nonlocal parameter on phase velocity, attenuation coefficient, specific loss and penetration depth of Rayleigh surface waves is presented graphically. [ABSTRACT FROM AUTHOR]

An analysis of the propagation behavior of Rayleigh wave has been conducted in an anisotropic layer, such as reservoir rocks overlying a sandy medium. The layer and lower half-space interface have been considered imperfect, whereas a corrugated upper boundary has been assumed. A closed relation of phase velocity and wave number has been obtained as a determinant form. For the numerical interpretation of results, reservoir rocks of triclinic type have been modeled. Some special cases are taken into account. The study examines the simultaneous simulated results of several physical parameters and illustrates the effects of thickness, sandiness parameter, phase velocity, corrugation amplitude, corrugation wavelength, and imperfect Rayleigh wave interface distribution in the structure under consideration, which was created using Mathematica 7. For variations in wave number and phase velocity, diagrams are drawn. [ABSTRACT FROM AUTHOR]

The objective functions adopted by earthquake early warning (EEW) location algorithms are inadequate for out-of-network earthquakes. As a result, the real-time locations of these earthquakes are often erroneous. The consequences of mislocating out-of-network earthquakes are that their magnitudes are miscalculated, and the loci of their shaking predictions map are shifted. Given that the largest earthquakes occur in subduction settings, improving real-time out-of-network earthquake location is of great importance. In this study, the Virtual Dynamically Assembled Array Algorithm (ViDA³) is introduced, which addresses the location issue of offshore and off-network earthquakes. The guiding principle underlying the new EEW location algorithm is that standard seismic networks may be viewed as a collection of medium-sized seismic arrays, with each array consisting of three or more network stations. The potential of array seismology for EEW against out-of-network earthquakes stems primarily from the slowness vector, which points at the direction of the epicentral region. Thus, this region may be constrained merely by intersecting two or more such vectors. In addition, the length of the slowness vector depends on the hypocentral distance and depth and is thus vital for addressing an acute problem in a subduction setting--discriminating between upper crust and deep slab earthquakes. Furthermore, when the slowness of the P phase is known, the slowness of the S phase is deduced, and the S-phase arrival is searched for using the shift-and-sum practice. What makes ViDA³ so attractive is that, in locations where a real-time network is already in place, these added values may be achieved without extra hardware or substantial budget requirements. We present the result of ViDA³ real-time operation on a shallow earthquake offshore Vancouver Island and the result of its replay on a deep slab earthquake in northern Chile. performance is further assessed using a dataset of seismograms from the Mendocino Triple Junction area. It is concluded that ViDA³ location scheme outperforms currently available EEW location algorithms for out-of-network earthquakes. [ABSTRACT FROM AUTHOR]

Velocity-based resistance training is a fundamental component of sports science, offering a systematic approach to investigating the load variables of resistance exercises. This research focused on assessing the load across various resistance exercises by examining the barbell velocity during the concentric phase. The study involved 11 male athletes representing the China badminton team, who underwent 1RM testing for bench press, hip thrust, back squat, and single leg press exercises and the maximum repetition testing at load intensities of 60%, 70%, 80%, and 90% of 1RM. Simultaneously, measurements were taken of the barbell's concentric phase velocity during each exercise. The findings revealed a robust negative correlation between barbell velocity and load intensity. Furthermore, exercises engaging greater muscle strength displayed smoother fitting curves. Analysis of velocity loss rates indicated that the hip thrust exhibited a higher completion percentage compared to the back squat and the bench press. Similarly, the non-dominant leg press showed a higher completion percentage than the dominant leg press. The study emphasizes the significance of delineating barbell velocity distributions in resistance training involving large muscle groups, as well as the accurate determination of load intensity. Precise load determination can be facilitated by employing fitting curves derived from distinct movement patterns and varying load intensities. The utilization of velocity data offers a quantifiable approach to achieving targeted training outcomes. [ABSTRACT FROM AUTHOR]

The NE Tibet experienced complex and distinct basin developments and uplifts in different areas. However, the reasons for such distinct surface deformation and their relationship to deep crustal geodynamic processes are not well understood. Here, we obtain a crust model of NE Tibet by jointly inverting Rayleigh wave ellipticity and phase velocity. Our results reveal that deep crustal strength contrasts across NE Tibet play an important role in controlling basin development. Extrusion of the significantly weak Qilian crust is obstructed by rigid Alxa block, resulting in deep foreland basin with dramatic topographic step. In contrast, the relatively weak crust of Longzhong absorbs outward extrusion of NE Tibet within a wide transition zone, leading to small intermontane basins. Furthermore, the systematic thinning of basins from north to south around the western Ordos Block demonstrates the tectonic transformation from extension to compression due to expansion of NE Tibet since the late Miocene. Plain Language Summary: In this study, we obtain a high‐resolution model of NE Tibet by jointly inverting Rayleigh wave phase velocity and ellipticity (the radial‐to‐vertical amplitude ratio), which provides complementary constraints to the shallow structure. Our results show a clear correlation between velocity variations in the deep crust and basin structures at the surface. We infer that the extrusion of mechanically weak mid‐to‐lower crust of Qilian is obstructed by the strong Alxa block, leading to the steep topography and deep foreland Hexi Basin. To the east, in contrast, the outward extrusion of Songpan‐Ganzi is absorbed in a wide range by the relatively weak Longzhong region, developing gently sloping topography and small intermontane basins. Furthermore, the significant structural differences of rift basins from north to south around the western Ordos likely result from tectonic regime transformation induced by the continuous expansion of NE Tibet since the late Miocene. Our results improve the understanding of how deep crustal geodynamic processes influence surface uplift and basin developments in the expanding NE Tibet. Key Points: A high‐resolution 3‐D crustal model of NE Tibet is obtained by joint inversion of Rayleigh wave ellipticity and phase dispersionWe infer that deep crust extrusion and strength differences across plateau boundaries control distinct surface deformation in NE TibetThe systematic thinning of basins in west Ordos indicates tectonic regime transformation due to expansion of Tibet since Miocene [ABSTRACT FROM AUTHOR]

Upstream propagating waves are observed to correlate with the reflected ions in the foot of a high Mach number quasi‐perpendicular collisionless shock. The respective wavefronts show time varying amplitude matching the variation of the reflected ions and the shock reformation cycles. We interpret this process in terms of the fast two‐stream instability and investigate the results of the PIC simulation as compared with the prediction of the linear analysis. Evidence for upstream propagating whistler waves supported by two‐stream instability is continuously growing, see for example, recent surveys based on MMS in‐situ observations of the Earth bow‐shock. The present study suggests that upstream propagating waves are consistent with and in particular supported by the mechanism of fast two‐stream instability developing in the upstream region of the shock foot. Plain Language Summary: By using particle‐in‐cell simulations, a highly non‐stationary quasi‐perpendicular collisionless shock exhibits reformation cycles characterized by extensions and compressions of the foot, ramp, and overshoot. Waves with upstream propagation are crossing the foot, with large variation of their phase velocities with respect to the rest frame of the shock, repeated periodically. Additionally, strong downstream propagating waves driven by incoming ions ‐ incoming electrons two‐stream instability (or slow two‐stream instability) are observed close to the end of each shock cycle. In a system attached to the electron flow (regarded as proxy for the system used in the study of two‐stream instabilities), the variations of the phase velocities appear to be significantly smaller. The linear theory based on dispersion analysis supports, in our case, the use of a 1‐D code for exploring upstream whistler propagation driven by the fast two‐stream instability, associated by former studies with 2‐D configuration. At the same time, the analytical examination of the real part of the dispersion relation shows good agreement with the simulation results, while the imaginary part indicates a significant local growth rate of the fast two‐stream instability, that can presumably compensate the otherwise strong damping of the oblique whistler waves. Key Points: Fast two‐stream instability excited in the foot of a collisionless shock by using 1‐D PIC simulationsCyclic emissions of whistler waves in the foot of the shocks are supported by fast and slow two‐stream instabilityConvergence of three independent approaches: simulations, analytical, and observations (MMS) [ABSTRACT FROM AUTHOR]

We report on experimental observation of unidirectional propagation of zero-momentum magnons in synthetic antiferromagnet consisting of strained CoFeB/Ru/CoFeB trilayer. Inherent non-reciprocity of spin waves in synthetic antiferromagnets with uniaxial anisotropy results in smooth and monotonous dispersion relation around Gamma point, where the direction of the phase velocity is reversed, while the group velocity direction is conserved. The experimental observation of this phenomenon by intensity-, phase-, and time-resolved Brillouin light scattering microscopy is corroborated by analytical models and micromagnetic simulations. [ABSTRACT FROM AUTHOR]

AbstractThis paper investigates Love-type wave propagation in a multilayered, elastic, prestressed solid half-space with voids. Using the Haskell matrix method, the dispersion relation is derived for a stress-free boundary surface. Two distinct dispersive fronts of Love-type waves, propagating at different speeds, are identified. One behaves like waves in a prestressed elastic half-space, while the other is novel due to voids. Analytical expressions for three-layered and two-layered models are provided. Graphical representations compare the dispersion curves, highlighting differences and dependencies. The study explores how void parameters, initial stress, and layer thickness influence phase velocity, with applications in various engineering fields. [ABSTRACT FROM AUTHOR]

Recently, non-local configurations have been proposed by adding beyond nearest neighbour couplings among elements in lattices to obtain roton-like dispersion relations and phase and group velocities with opposite signs. Even though the introduction of non-local elastic links in metamaterials has unlocked unprecedented possibilities, literature models and prototypes seem neither to provide criteria to compare local and non-local lattices nor to discuss any related rules governing the transition between the two configurations. A physically reasonable principle that monoatomic one-dimensional chains must obey to pass from single- to multi-connected systems is here proposed through a mass conservation law for elastic springs thereby introducing a suitable real dimensionless parameter α to tune stiffness distribution. Therefore, the dispersion relations as a function of α and of the degree of non-locality P are derived analytically, demonstrating that the proposed principle can be rather interpreted as a general mechanical consistency condition to preserve proper dynamics, involving the spring-to-bead mass ratio. Finally, after discussing qualitative results and deriving some useful inequalities, numerical simulations and two-dimensional FFTs are performed for some paradigmatic examples to highlight key dynamics features exhibited by chains with finite length as the parameters α and P vary. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'. [ABSTRACT FROM AUTHOR]

A relativistic version of the correspondence principle, a limit in which classical electrodynamics may be derived from quantum electrodynamics (QED), has never been clear, especially when including gravitational mass. Here we introduce a novel classical field theory formulation of electromagnetism, and then show that it approximates QED in the limit of a quantum state which corresponds to a classical charged continua. Our formulation of electromagnetism features a Lagrangian which is gauge invariant, includes a classical complex field from which a divergenceless four-current may be derived, and reproduces all aspects of the classical theory of charged massive continua without any quantum effects. Taking a geometric approach, we identify the four-current as being in the direction of extremal phase velocity of the classical field; the field equations of motion determine this phase velocity as being equal to the mass, which makes the rest density proportional to the squared modulus of the field. [ABSTRACT FROM AUTHOR]

Wave propagation and vibration state in the sports balls have important effects on the stability in movement and accuracy of hits. In some sports, similar to football and volleyball, the balls are subjected to continuous strong hits from players. In the current study, the wave propagation in a beach volleyball ball under the effect of temperature change, different material characteristics, different thicknesses, and the total mass is investigated. In this regard, the ball is modeled using a spherical shell structure and a higher-order displacement field is considered. The classical theory of elasticity is employed along with Hamilton's principle for the spherical shell. The outcome equations with different boundary conditions are solved by engaging the discrete singular convolution method (DSCM). In addition, the finite element method is used to obtain the modal shape and natural frequency. The formulations and solution method are utilized in different steps of convergence examination, validation, and parametric study to acquire a comprehensive insight into the behavior of beach volleyball balls under the effect of the dynamic loading conditions. In specific, we are more interested in the phase velocity of the ball. The results are presented for different temperature changes and geometrical and material properties. [ABSTRACT FROM AUTHOR]

The traditional specific storage coefficient (Ss) was defined under two assumptions. One is that aquifer rock deforms only in the vertical direction, and the other is that the average rock stress remains unchanged. Consequently, Ss is irrelevant to the shear modulus of rock (G). In this paper, the Biot theory is used to derive a new specific storage coefficient (Ss∗) with the natural deformation of rock. Ss∗ appears to be relevant to G. Compressed glass beads and Berea sandstone are used for illustration. At frequencies lower than 10 kHz, the equation of groundwater flow with Ss∗ yields the same phase velocity and quality factor as the Biot theory, and therefore, it is capable of accurately predicting fluid pressure diffusion in the low‐frequency regime. The results also show that Ss is 16%–17% higher than Ss∗. In conclusion, the latter one is superior to the former in its consistency with the Biot theory and unconstraint by the aforementioned two assumptions. [ABSTRACT FROM AUTHOR]

This work numerically explores the anisotropy, impact phase wave propagation, buckling resistance, and natural vibration of ultra-high performance concrete (UHPC) and UHPC-steel interpenetrating phase composite (IPC) with triply periodic minimal surfaces (TPMSs), including sheet and solid gyroid, primitive, diamond, and the Schoen I-graph-wrapped package (I-WP). The experiment is conducted to verify the accuracy of the numerical model in terms of Young's modulus of polylactic acid (PLA)-based TPMS lattices and PLA-cement IPCs with TPMS cores, with the highest percent difference of 15% found for IPCs and 17% found for lattice. The results indicate that UHPC material with sheet gyroid exhibits the least extreme anisotropy in response to the varying orientation among other lattices regardless of the change of solid density, making it the ideal candidate for construction materials. Interestingly, compared to UHPC-based TPMS lattice, IPCs possess a much smaller anisotropy and exhibit almost isotropy regardless the variation of solid density and TPMS topology, offering a free selection of TPMS type to fabricate IPCs without much care of anisotropy. The phase wave velocity and buckling resistance of UHPC- and IPC-based beams with TPMSs nonlinearly decrease with a drop of TPMS solid density, but it is the almost linear pattern for the case of natural vibration frequency. UHPC material and IPC with sheet gyroid lattice are found to possess the lowest phase wave velocity and exhibit the least anisotropy of wave propagation, showing it as an ideal candidate for UHPC material to suppress the destructive energy induced by the external impact. [ABSTRACT FROM AUTHOR]

Starting from the classical quasi-geostrophic potential vorticity equation with equal depth two-layer fluid, the coupled cylindrical Kadomtsev–Petviashvili (KP) equations with variable coefficients for Rossby waves are studied. To be more general, the phase velocity is considered an indefinite integral about time and improves the analysis procedure. So the variable coefficients are obtained and some previous studies are reasonably explained. The cylindrical wave theory is therewith utilized to reduce the coupled cylindrical KP equations with variable coefficients, and based on the modified Hirota bilinear method, the lump solutions and interaction solutions are found. Through numerical simulations, the Rossby lump waves on both sides of the y axis move closer to the center, and their amplitude gradually decreases and tends to flatten with the generalized Rossby parameter growth. In the Rossby waves flow field, the dipole structures propagate to the east and lead to the appearance of the compress phenomenon during barotropic–baroclinic interaction. It is possibly useful for further theoretical research on atmospheric phenomena. [ABSTRACT FROM AUTHOR]

In this manuscript, a theoretical investigation of SPPs generated at magnetized plasma–graphene interface is presented. To model graphene conductivity, Kubo formula is utilized, and impedance boundary conditions are applied to obtain dispersion relation. In the presence of strong anisotropy of the plasma medium, the behaviors of the lower and upper plasmon modes are demonstrated. By examining the dispersion relation, it has been shown that upper and lower modes strongly depend on graphene and plasma features. It has been shown that effective mode index and phase velocity of proposed structure can be tuned by tuning graphene and magnetized plasma features. The proposed model may be exploited for a variety of applications, including sensing and integrated plasmonic circuits in the THz spectrum. [ABSTRACT FROM AUTHOR]

The basic design of a Love wave (LW) bio-sensor contains the loading of a viscoelastic liquid on top of a layered structure with distinct viscoelastic properties. Changes in the characteristics of the propagating acoustic wave caused by biochemical interactions at the sensing area can be detected at the output Inter digital transducer (IDT). The propagation of the anti-plane (AP) wave is discussed in this work in a layered structure of piezo-flexo-electric (PFE) layer bonded with a PFE half-space having a soft reinforced layer at the interface. The free surface of the PFE layer is loaded with viscous liquid. The viscosity of the loaded liquid introduces losses and results in the damping of the wave. For the formulation of the problem with interface energy, the Gurtin–Murdoch approach is used. Using suitable conditions, a dispersion relation for propagating waves is derived in complex form. On separating the dispersion relation in real and non-real parts, the expressions relating the phase and damp velocities with wave number are derived. The obtained theoretical results are portrayed for the numerical data of PFE materials and distinct data of the interface layer. The obtained results are validated with pre-existing literature. [ABSTRACT FROM AUTHOR]

We analyze the dynamics of small two-dimensional disturbances in stable plane-parallel inviscid shear flows under linear theory. Using a velocity profile V x = U (y) with an inflection point but stable according to Fjørtoft's theorem, we illustrate that the continuum spectrum of van Kampen modes, possessing real phase velocities c = ω / k , aggregates into Landau damping solutions or "quasi-modes," which exhibit exponential decay. It was found that the real part of the complex phase velocity c L (k) of these solutions may lie outside the allowable range for van Kampen modes, suggesting a non-resonant damping mechanism for these quasi-modes. This conclusion was reached by solving the eigenvalue problem and observing the evolution of initial perturbations, calculated by directly solving the evolutionary equation for vorticity as well as by decomposing the initial disturbance into van Kampen modes. Landau damping of the total vorticity across the channel emerges as an intermediate stage before transitioning to power-law damping. [ABSTRACT FROM AUTHOR]

In this work, laser-induced florescent particle image velocimetry was performed to measure simultaneously the liquid and vapor velocity fields at the mid-span of a small-scale Venturi type section to determine the presence of a slip velocity between the phases. Various dynamic behavior and Kelvin–Helmholtz (K-H) instability involved in the cloud cavity shedding regime are discussed at four different cavitation numbers. The velocity, vorticity, and turbulence field information of the two phases are analyzed. The liquid–vapor mixture in a cavitating flow is usually considered a homogeneous medium in currently used computational models, but it is shown in this study that the two phases have very different dynamics. The measurements of the time-averaged velocities highlight the existence of a noteworthy slippage between the liquid and the vapor phases, especially in the upstream part of the cavitation region, where the slippage between the two phases can reach about 50% of the liquid velocity. Using phase-locked average, it is shown that the slip velocity in the upstream region is mainly located at the upper liquid–vapor interface, while the slip velocity in the closure area is near the bottom wall, due to the reentrant jet. These results contradict a primary assumption of the current models, where the medium is usually considered as a homogeneous mixture with a unique velocity field, thus providing a reference for future computational model improvement. [ABSTRACT FROM AUTHOR]

A modification to the dual paddle wave generation method for internal solitary waves (ISWs) has been achieved through the implementation of the adjusted high-order unidirectional (aHOU) model and the Miyata–Choi–Camassa (MCC) model. This modified method utilizes layer-averaged horizontal velocities from ISWs in both the upper and lower fluid layers to control the operational velocities of the corresponding paddles. Experimental investigations conducted in a two-layer fluid with varied stratification conditions were employed to evaluate the applicability of the aHOU and MCC models. The validation of this approach involved examining the stability of generated ISWs by comparing experimental waveforms with theoretical predictions, demonstrating good agreement with prior research. Furthermore, evaluation of the modified wave generation method included an analysis of dimensionless phase velocity and characteristic frequency. The study also explored the quasi-linear relationship between the designed wave amplitude and the actual wave amplitude, establishing a polynomial fit between the actual wave amplitude and the layer thickness ratio. This approach offers a new method for stable and controllable laboratory generation of ISWs. Under finite water depth conditions, the method can produce ISWs that propagate stably over long distances and effectively control parameters such as wave amplitude and wave profile across a broad range of wave amplitudes and stratifications. These results confirm the effectiveness of the modified method and underscore its practical applicability in ISWs generation. [ABSTRACT FROM AUTHOR]

Qingshankou shale (Gulong area, China) exhibits strong acoustic anisotropy characteristics, posing significant challenges to its exploration and development. In this study, the five full elastic constants and multipole response law of the Qingshankou shale were studied using experimental measurements. Analyses show that the anisotropy parameters ϵ and γ in the study region are greater than 0.4, whereas the anisotropy parameter δ is smaller, generally 0.1. Numerical simulations show that the longitudinal and transverse wave velocities of these strong anisotropic rocks vary significantly with inclination angle, and significant differences in group velocity and phase velocity are also present. Acoustic logging measures the group velocity in dipped boreholes; this differs from the phase velocity to some extent. As the dip angle increases, the longitudinal and SH wave velocities increase accordingly, while the qSV-wave velocity initially increases and then decreases, reaching its maximum value at a dip of approximately 40°. These results provide an effective guide for the correction and modeling of acoustic logging time differences in the region. [ABSTRACT FROM AUTHOR]

The eastward extrusion of the Tibetan Plateau materials has caused intricate tectonic deformations and frequent seismic activities in the Sanjiang lateral collision zone (SLCZ). To reveal crust structures and deformation mechanisms, we investigate high‐resolution structural features of crustal depth (≤40 km). A 3‐D S‐wave velocity and azimuthal anisotropy model is constructed by the direct tomography method with Rayleigh phase velocity at periods of 2–40 s from multiple temporary seismic arrays and regional permanent network. In the middle‐to‐lower crust, an obvious low‐velocity zone is confined by the large‐scale fault systems of Jinhe‐Qinghe fault and Chenhai fault (CHF) to the northeast and east, Lancangjiang fault (LCJF) and Red River fault (RRF) to the west, with strong N‐S‐oriented anisotropy, which evident differs from the ENE‐WSW‐oriented weak anisotropy in the high‐velocity zone on the northeastern side. We consider that the weak material may be obstructed by large faults and the high‐velocity zone, resulting in complex crustal deformation and tectonic boundary. The crustal low‐velocity materials beneath the Tengchong volcano (TCV) are probably separated with those from the Tibetan Plateau. The low‐velocity beneath the Chuxiong basin (CXB) may be combinations of partial melts and fluid derived from shear deformation and deep material upwelling. The segmented anisotropy at the NW end of the RRF suggests complex deformation by crustal flow, emphasizing the important influence of faults on anisotropic pattern. The complex anisotropy in the fault intersection of the Lijiang‐Xiaojinhe fault and RRF also highlights the important role of these faults in shaping crustal deformation. Plain Language Summary: The Sanjiang lateral collision zone in the SE margin of the Tibetan Plateau has experienced a complex, multistage tectonic evolution and witnessed frequent seismic activity. A meticulous high‐resolution 3‐D S‐wave velocity and azimuthal anisotropy is undeniably obtained due to adding up two elaborate temporary seismic arrays. Our model shows that the low‐velocity with strong anisotropy in the middle‐to‐lower crust is probably related to the eastward extrusion of the Tibetan Plateau material blocked by large faults and high‐velocity body, leading to complicated crustal deformation and distinct boundaries between tectonic blocks. Interestingly, the low‐velocity from the Tibetan Plateau is seen to be well separated from the low‐velocity under the Tengchong volcano. At the NW end of the Red River fault, the segmented anisotropic pattern, indicating that the complex deformation is caused by the southeastward movement of the crust and the nature of the fault itself. The complex anisotropy in the fault intersection also highlights the important role of these faults in shaping crustal deformation. Key Points: An unprecedented high‐resolution 3‐D azimuthal anisotropy Vs model reveals the low‐velocity from the Tibetan PlateauMiddle‐to‐lower crustal low‐velocity materials from Tibetan Plateau spreading southeast are confined by Jinhe‐Qinghe faultLow‐velocity materials under the Tengchong volcano seem to be separated with those from the Tibetan Plateau [ABSTRACT FROM AUTHOR]

We investigate the continent‐size lithospheric structures of paleo rift around the central Korean Peninsula using ambient noise tomography and earthquake‐based Eikonal tomography based on dense seismic networks. We determine Rayleigh‐wave group velocities at periods of 1–15 s from ambient noise tomography and Rayleigh‐wave phase velocities at periods of 20–80 s from earthquake‐based Eikonal tomography. We determine a 3‐D shear‐wave velocity model in the lithosphere from the Rayleigh wave velocities. The model exhibits high lateral variations ranging from ∼ ${\sim} $‒9% to ∼ ${\sim} $8%, depending on depth. The shear‐wave velocities at shallow depths (≤ ${\le} $2 km) are relatively high in mountain regions and low in coastal and basin regions. Strong velocity contrasts are observed around major earthquake hypocenters at depths of 3–20 km, which may be due to the presence of seismogenic faults. Shear‐wave velocities at depths of ∼ ${\sim} $30–40 km are high along the east coast, suggesting uplifted mantle that is responsible for the opening of the East Sea (Sea of Japan). High velocity structures beneath Moho around the coast may suggest solidified underplated magma caused by the paleo rifting. The root of coast‐parallel high‐mountain range (Taebaek Mountain Range) is bounded by the uplifted mantle, presenting mountain range development in rift flank along paleo‐rift axis. Low shear‐wave velocities along the coast at depths ≥60 ${\ge} 60$ km may imply elevated temperature beneath the solidified underplated magma. The continent‐side paleo rift affects the geological, thermal, and seismological properties around the continental margin at present. Plain Language Summary: It is crucial to understand the subsurface seismogenic and tectonic structures to mitigate the seismic hazards. This study investigates the lithospheric structure in the central Korean Peninsula. We use ambient noise tomography and Eikonal tomography. Dense seismic stations allow us to determine high‐resolution 3‐D seismic velocity models. The velocity models present strong lateral variation due to geological structures. The lateral heterogeneities around seismicity regions extend to the midcrust. Shear‐wave velocities at depths of ∼30–40 km are high along the east coast, suggesting uplifted mantle that is responsible for the opening of the East Sea (Sea of Japan). The tomography presents mantle upwelling signature along paleo‐rifting structure. The root of coast‐parallel high‐mountain range (Taebaek Mountain Range) is bounded by the uplifted mantle, presenting mountain range development in rift flank along paleo‐rift axis. The shear‐wave velocities in the middle to lower lithosphere (>=50 km) are low in the eastern central Korean Peninsula, which may be attributed to elevated temperature associated with paleo‐volcanic activity. The present and paleotectonic activities leave signatures in seismic structures. Key Points: Lithospheric structures in the central Korean Peninsula are explored using combined seismic tomographyContinental‐size uplifted mantle is present along a paleo rift in East SeaGeological structures in the lithosphere are interpreted from tomographic features [ABSTRACT FROM AUTHOR]