Search

Using the first-principle simulations and the Boltzmann transport equation, our study investigated the properties of single-layer SnBi 2 Se 4 and PbBi 2 Se 4 , including stability, elasticity, electronic and thermoelectric transport properties. We discovered that both 2D materials have acceptable cleavage energies ranging from 0.27 to 0.28 J/m2 and that they are indirect semiconductors with narrow band gaps of 0.68 eV and 0.94 eV, respectively. Interestingly, the valence band maximum exhibits 'multi-valley' energy dispersion. Furthermore, SnBi 2 Se 4 and PbBi 2 Se 4 have comparable electron and hole mobility of about ∼102 cm2/Vs and ∼103 cm2/Vs, respectively resulting in high conductivity and a high thermoelectric power factor. Owing to low group velocities and strong phonon–phonon scattering rates, the materials exhibit low lattice thermal conductivities of 2.59 W/mK (SnBi2Se 4) and 1.73 W/mK (PbBi 2 Se 4). Thus, they demonstrate high thermoelectric figures of merit, namely 0.31 (SnBi2Se 4) and 0.37 (PbBi 2 Se 4) at 300 K, which rise further to 1.22 and 1.82, respectively, at 700 K. Our results suggest that these two single-layer materials are promising candidates for use in nanoelectronics and thermoelectric appliances. [ABSTRACT FROM AUTHOR]

Liver fibrosis has been found to increase the mechanical stiffness of the liver. To mimic different stages of liver fibrosis, commercially available phantoms (Model 039, CIRS, Inc.) have been produced for clinical quality assurance and research purposes. The purpose of this study was to investigate the mechanical property variability of the phantoms in two lots of CIRS Model 039 phantoms. Each lot consisted of phantoms of four stiffness types, and there were 8–10 phantoms of each type. Shear wave elastography measurements were conducted on each phantom at 10 different angles. Group velocity measurements and phase velocity curves were calculated for every SWE acquisition. Multilevel functional principal component analysis (MFPCA) was performed on phase velocity data, which decomposes each phase velocity curve into the sum of eigenfunctions of two levels. The variance of the component scores of levels 1 and 2 were used to represent inter-phantom and intra-phantom variability, respectively. The 95% confidence intervals of phase velocity in a phantom type were calculated to reflect curve variability. The standard deviations of the group velocity for phantoms of any type were less than 0.04 and 0.02 m/s for lots 1 and 2, respectively. For both lots, in every type, the phase velocity curves of most individual phantoms fall within the 95% confidence interval. MFPCA is an effective tool for analyzing the inter- and intra-phantom variability of phase velocity curves. Given the known variability of a fully tested lot, estimation of the variability of a new lot can be performed with a reduced number of phantoms tested. [ABSTRACT FROM AUTHOR]

Bubble size and deformation are important factors for the closure models required in Euler-Euler simulations of bubbly flows. To properly simulate polydisperse bubbly flows where the bubble size spectrum may cover a range of several millimeters, several velocity groups with different sizes have to be considered. To this end, the theory for the particle-center-averaged Euler-Euler model is generalized for the simulation with multiple bubble velocity groups. Furthermore, bubble deformation effects have been included in appropriate bubble force models. The particle-center-averaged Euler-Euler model provides additional freedom to consider the bubble shape during the conversion between the bubble number density and the gas volume fraction. Therefore, the theory is also generalized to consider an oblate ellipsoidal bubble shape in simulations. A bubbly pipe flow is used to validate the theory and to demonstrate the improvements of the proposed generalizations. • Particle-center-averaged Euler-Euler model for polydisperse simulations is formed. • Bubble deformation is considered in the particle-center-averaged Euler-Euler model. • Experimental data for bubbly pipe flows (MTLoop) are used in validation. [ABSTRACT FROM AUTHOR]

• An attempt has been made to understand the effect of electromagnetic induction on the network of neurons. • An excitable slow-fast memristive model has been studied with its various intrinsic dynamics. • We analytically establish the existence and stability of Hopf bifurcation with bifurcating periodic solutions. • We investigate the emergence of multi-arm antispiral waves in the system with proper analytical justification. • A random network architecture is used to study the dynamics of coupled network that generates MMOs and bursting patterns. The diverse firing responses in a single neuron model as well as in a neuronal network play a major role in understanding the collective neuronal dynamics. In this paper, we consider an excitable slow-fast memristive model and study its various intrinsic dynamics by allowing a periodic external stimulus. The single model exhibits various types of spiking, bursting, mixed-mode oscillations (MMOs), and mixed-mode bursting oscillations (MMBOs) depending on the amplitude and frequency of the periodic injected current. Corresponding bifurcation analysis reveals the existence of supercritical and subcritical Hopf bifurcations in the system depending on the major predominant parameters that establish the scenarios of the neuronal responses. We have verified analytically the existence and stability of Hopf bifurcations. The memristive system can produce cascade of period doubling bifurcations for particular parameter regimes. Next, we investigate the emergence of multi-arm antispiral waves in the diffusively coupled system with proper analytical justification. We have also computed the group and phase velocities to discern the spiral and antispiral waves near the Hopf instability. A transition from target wave to multi-arm antispiral wave is observed in the diffusive system. Moreover, we use a random network architecture different from the diffusive network to study the dynamics of the coupled network for certain firing activities. It is observed that the network of heterogeneous desynchronized neurons with higher electrical couplings, can generate MMOs, MMBOs, and bursting for different external stimuli. However, the uncoupled systems cannot reveal such typical dynamics for particular parameters. Further, we introduce a reduced-order model to summarize the complete dynamics of the larger random network and report the findings. [ABSTRACT FROM AUTHOR]

The nonlinear tunneling of the optical similaritons through both dispersion and nonlinear barriers in a non-centrosymmetric waveguide exhibiting second- and third-order nonlinearity is studied. Within the framework of an inhomogeneous quadratic-cubic nonlinear Schrödinger equation with distributed group velocity dispersion, reciprocal of the group velocity, quadratic-cubic nonlinearity, and gain or loss, we demonstrate the existence of a rich variety of exact similariton solutions in the shape of bright, kink, anti-kink, W-shaped, and gray solutions. The results show that these self-similar waves involve certain control parameters in their amplitude, phase, width, and shift of the inverse group velocity, which enables us to control their evolution dynamics in the waveguide system through a suitable choice of these parameters. It is found that the parameter of reciprocal of the group velocity decides the phase shift and group velocity of these self-similar waves. Also, the stability of the solutions is discussed numerically. Results of this paper are helpful for enriching the similariton theory and understanding the dynamics of self-similar waves in systems with quadratic–cubic nonlinearities. • The inhomogeneous quadratic-cubic nonlinear Schrodinger equation is solved analytically. • Exact bright, kink, anti-kink, W-shaped, and gray solitons are reported. • The chirped similaritons in non-centrosymmetric waveguides with quadratic-cubic nonlinearity is studied. [ABSTRACT FROM AUTHOR]

• This study presents, for the first time, the identification of an exceptional metallic material, KNaRb, characterized by an ultralow lattice thermal conductivity of 0.114 W/mK at room temperature, a value comparable to the lowest thermal conductivities reported for metals and metallic materials. • The contribution of phononic thermal conductivity to the overall thermal transport in KNaRb amounts to merely 0.66 %, markedly lower than the typical range observed in other metals and metallic systems. • The ultralow phononic thermal conductivity observed in KNaRb can be attributed to the loose bonding characteristics of Rb. In the domain of metallic systems, electronic thermal conductivity typically governs heat transfer, while lattice (phononic) thermal conductivity (LTC) remains non-negligible magnitude. This study introduces the exceptional metallic material, cubic half-Heusler-type KNaRb, via phonon Boltzmann transport equation (BTE) resolution and first-principles calculations. KNaRb exhibits an ultralow LTC of 0.114 W/mK at room temperature, comparable to the lowest reported for metallic materials, contributing merely 0.66 % to overall thermal transport. Analysis attributes KNaRb's low LTC to low group velocity and strong anharmonicity, originating from its loosely bonded electronic structure. Acoustic modes, primarily from Rb atoms, dominate thermal transport. Examination of mean square displacement and potential energy profiles reveals significant movement of loosely bonded Rb atoms within KNaRb, acting as intrinsic "rattlers," inducing pronounced phonon anharmonicity and ultrashort lifetimes. This study advances understanding of heat conduction in metals, offering insights into materials with extremely low lattice thermal conductivity for potential future applications. [ABSTRACT FROM AUTHOR]

• The wave behaviors of 2D IAMs are regulated by the IA angle. • The negative refraction and refractive steering of elastic waves are realized with the IA mechanism. • The IA angle is the critical parameter that determines the sign of the effective stiffness, inertial and group velocity of the system. • The negative refraction and wave steering are verified in time-domain numerical simulation. Tailoring wave behaviors governed by dispersion relations is a huge challenge in wave manipulation. Inertial amplification (IA) mechanism has been introduced in metamaterials and phononic crystals to obtain a low-frequency bandgap without adding mass to the system. In this work, we demonstrate unique wave propagation behaviors in two-dimensional inertial amplification metamaterials (2D IAMs). Through analytical derivations and numerical simulations, negative refraction and refractive steering of elastic waves are realized with the IA mechanism. The positive (negative) inertia of the system can be tuned by the IA angle, which determines whether the passband of the lattice is positive (negative) group velocity. By analyzing the dispersion relations of the 2D IAMs, we find that the IA angle 45° is the critical point where the group velocity flips. Negative refraction occurs at the interface between two lattices, which have opposite signs of group velocity. We can also achieve a wide range of angles for wave steering in the system. The normalized displacement fields of 2D IAMs are measured via harmonic excitation. We believe that the research results may inspire the design of 'elastic lenses' and multifunctional metamaterial devices. [Display omitted] [ABSTRACT FROM AUTHOR]

This theoretical study reveals that the transfer of coherence (TOC) and the direction of light propagation vector play a crucial role in transitioning from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) in a four-level closed and open cascade (Ξ)-type light-atom interacting systems (LAIS) under both linear as well as nonlinear interaction regimes. It is found that the amplitudes of the coherence signals are distinctly influenced by the system's openness driven by the presence of additional dipole allowed levels not connected by the lasers and the type of interaction regimes. The effect of TOC on the EIT to EIA transition is discussed in detail by the velocity-dependent dressed state analysis and velocity mapping of the probe absorption coefficient. The findings also reveal that the efficiency of the counter-propagation scheme of the coupling fields is higher than the co-propagation scheme. Furthermore, we have estimated the Rydberg blockade effect on the probe absorption profiles for some specific velocity groups of atoms, which exhibit probe gain in the medium along with EIT and EIA patterns. [ABSTRACT FROM AUTHOR]

Zero-Group-Velocity (ZGV) guided mode has recently received particular attention because of its highly sensitive to structural changes, such as defects. Parallel to ZGV, in the present work, we introduce a new guided mode so-called Minimum-Group-Velocity (MGV) that is a remarkable phenomenon in defect detection applications. Strictly speaking, when any two phase-velocity dispersion curves of Lamb modes approach each other without overlapping, we observe this new mode in group-velocity dispersion curves. It is worth noting that this MGV mode has never been addressed in literature. We compute the Lamb-like modes in asymmetric viscoelastic sandwich plates using the Stiffness Matrix Method (SMM). We show that the change in properties of this sandwich can dramatically affect frequency ranges associated with ZGV and MGV modes. However, a linear correlation between phase velocities and this change on viscoelastic properties is discussed, where we observed an interconnection phenomenon in the dispersion curves. This interconnection happens between specific points on the dispersion curves, each corresponding to a ZGV- or MGV-mode. On the other hand, we verify that the detection of changes in level of viscoelastic properties or variations in the thickness of the buffer viscoelastic layer is possible within a limited segment of the damped mode curve. [ABSTRACT FROM AUTHOR]

The present work reports the theoretical background and the capabilities of SEISMIC , a Python code specifically developed to calculate the propagation of the sound waves inside crystalline materials. SEISMIC is a tool integrated in the Quantas package and provides a series of useful information for engineers and geophysicists, such as the phase and group velocities, the power flow angle, the enhancement factors, and the polarization vectors, using as input the elastic moduli and the density of the material. Numerical treatments of the derivatives were avoided, using analytical methods to obtain numerically stable results. The code relies only on Python numerical and graphical libraries to ensure a full cross-platform usability. • Automated software to calculate the propagation of seismic waves in crystalline solids. • Analytical evaluation of the second derivatives, which improve the description. • Entirely coded in Python, with no need of external software for plotting. • Integrated in Quantas, a software suite for the analysis of solid phases. • The code is completely cross-platform. [ABSTRACT FROM AUTHOR]

A new theoretical model is derived to predict wave attenuation in an emerged vegetation domain under current influences by considering the current effects on changing both wave group velocity and energy dissipation rate. Considering the current effect on changing wave group velocity, the theory predicts an asymmetric behavior of wave decay in following and opposing currents, different from the earlier theory that predicts a symmetry decay behavior by ignoring the current effect on wave group velocity. The new theory dictates that as the current speed increases, the rate of wave decay changes from the traditionally reciprocal law to the exponential law, where the mixed exponential and reciprocal decay law exists under intermediate current conditions. Furthermore, the present theory can be reduced to an explicit expression of the drag coefficient for weak and strong current conditions. In addition, the theory shows that the decay rate depends on both incident wave amplitude and current velocity when the current velocity is relatively small to wave orbital velocity, whereas it is independent of incident wave amplitude when the current is strong. All of these wave decaying characteristics predicted by the theory have been confirmed by the available experimental data and the numerical results from a 2D RANS model (NEWFLUME). • A theoretical model is developed to predict wave attenuation by the vegetation under wave-current conditions and validated by the available experiments and numerical results. • For the same magnitude of current velocity, opposing current induces greater wave attenuation. • As the current velocity increases, the decaying law of wave height will change from reciprocal decay to exponential decay. • The wave attenuation rate is independent of the incident wave amplitude when the current is strong. [ABSTRACT FROM AUTHOR]

Topological slow-light in a one-dimensional conjugated topological photonic crystal (CTPhC) is presented. The study shows that extremely slow-light of 26.57 m/s group velocity and 7.52 × 10−7 s group delay are achieved in the proposed CTPhC with 20 μm thick, which is better than traditional approaches of slow-light. Results also show that there are two significant sensitive parameters for slow-light in the CTPhC. Robust and ultra-slow-light is achieved as the refractive index contrast of materials and the number of layers increases. It is worth noting that the CTPhC has a symmetric and wide operating range photonic bandgap, which has better slow-light effects than typical topological photonic crystal. It is expected that the CTPhC can provide an efficient approach to constructing robust and ultra-slow-light devices. • Topological slow-light in a one-dimensional conjugated topological photonic crystal is presented. • The conjugated topological photonic crystal has a symmetric and wide operating range photonic bandgap. • An extraordinary slow-light of 26.57 m/s group velocity and 7.52 × 10-7 s group delay are achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • The innovative metamaterials with high load-bearing capacity and low-frequency multi-bandgaps are proposed and optimized based on assembly concept. • The incorporation of metal pins enhances the local stiffness, thereby improving the load-bearing ability of the metamaterial. • The metal pins play a crucial role in generating low-frequency multi-bandgaps by adjusting the local resonant modes. • The structure of particle damping can conveniently adjust the frequency of the resonant bandgaps and further dissipate the vibration energy. This study presents a novel star-shaped honeycomb meta-material (N-SSHM) that realizes improved static mechanical and vibration properties by introducing rings to the four sides of a traditional star-shaped honeycomb meta-material (T-SSHM). Optimization of the static and vibration suppression properties is achieved using the assembly concept. The static properties of the proposed meta-materials are initially investigated using the finite element method (FEM) and static compression tests. The results demonstrate that the N-SSHM exhibits a superior load-bearing capacity compared to the T-SSHM. Subsequently, the vibration properties of the meta-material are studied using simulations and experiments. The wave propagation characteristics of the meta-materials are explored by introducing the phase velocity and group velocity. The study also examines the effects of design parameters (ring size, metal pin size, and pin material) on the bandgap characteristics, and the vibration suppression properties of the meta-material are further enhanced by introducing particle damping. The simulation and experimental results confirm that the proposed N-SSHM has a lower starting frequency and wider bandwidth for the bandgap than the T-SSHM. In summary, the N-SSHM demonstrates significant improvements in both load-bearing and vibration suppression compared to the T-SSHM. This study provides support for the engineering applications of meta-materials. [ABSTRACT FROM AUTHOR]

• A broadband THz slow light device based on VO 2 metasurface is proposed. • The slow light effect can be achieved in a wide range from 0.35 THz to 1.02 THz, and a maximum transmission of 0.68 is realized at 0.7 THz. • The maximum group delay variation reaches 8.2 ps at 0.35 THz, and the maximum group delay is 9.7 ps. • The group velocity can be regulated within the range of 2.13 × 10 5 m/s to 2 × 10 7 m/s. In addition, this structure has low insertion loss. In the range of 0.52–0.92 THz, the insertion loss is less than 2.5 dB. • Theoretical calculation and simulation show good agreement with the experiment. The terahertz (THz) slow light effect has broad applications in fields of all-optical network communication, optical sensing, and nonlinear optics. Due to the weak response of natural material, it is difficult to achieve slow light effects in the THz broadband range. In this work, we experimentally demonstrated a broadband THz slow light device based on VO 2 metasurface. The slow light effect can be achieved in a wide range from 0.35 THz to 1.02 THz, and a maximum transmission of 0.68 is realized at 0.7 THz. More importantly, the maximum group delay variation reaches 8.2 ps at 0.35 THz, and the maximum group delay is 9.7 ps. The group velocity can be regulated within the range of 2.13 × 10 5 m/s to 2 × 10 7 m/s. In addition, this structure has low insertion loss. In the range of 0.52–0.92 THz, the insertion loss is less than 2.5 dB. Three-level system theory and coupled Lorentz model are introduced to interpret the mechanism of broadband slow light effect at THz band. Theoretical calculation and simulation show good agreement with the experiment. The device has potential applications in THz imaging, communication, and detection. [ABSTRACT FROM AUTHOR]

The Brewster angles and phase shift of both left right circular polarization beams of the probe field is controlled and modified in this manuscript. Subluminal and superluminal propagation of light having group indices of ± 200 has been reported. The group velocities of left circularly polarized (LCP) and right circularly polarized (RCP) beam varies to ± 1. 5 × 1 0 6 m/s while, delay times varies to ± 5 ns. The peak values of Brewster angles of LCP and RCP beams are calculated 0.786 radian. The maximum value phase shift of LCP and RCP is reported to 31.45 radian at length L = 5 λ. Strong oscillation in Brewster angles and phase variations of LCP and RCP beams are investigated with azimuthal quantum number of control field and increasing length of position coordinates. The modified results of this manuscript are useful for interferometry and lasers technology. [ABSTRACT FROM AUTHOR]

By similarity transformation, optical similaritons in a nonlinear birefringent optical fiber are investigated within the framework of two coupled nonlinear Schrödinger equations with space-modulated self- and cross-phase modulation nonlinearities, group velocity dispersion, external electro-optic phase modulation, and gain/loss. We find that the birefringent nonlinear medium with spatial parameter variations supports the existence of linearly chirped similariton structures of the W-shaped-dipole and bright-dipole types. These important results indicate that in addition to the usual single-humped localized waves such as bright-bright and dark-dark type waveforms, multihump chirped similaritons can also exist in the inhomogeneous birefringent fiber in the presence of all physical effects. The similariton parameters such as the amplitude, width, phase, and inverse group velocity are found to be dependent on certain controllable fiber parameters, thus enabling us to manage their intensity and consequently their subsequent dynamical evolution. Finally, we investigate the transmission of similaritons for different choices of material parameters. • Optical similaritons in a nonlinear birefringent optical fiber are investigated. • W-shaped-dipole and bright-dipole types of solitons are reported. • Two coupled nonlinear Schrodinger equations are solved by similarity transformation method. [ABSTRACT FROM AUTHOR]

The achievement of high-quality wave manipulation and energy concentration has always been considered as state-of-the-art technologies, especially for integrated photonics, acoustics, and mechanics. The exploration of the topological phase of matter provides abundant design tools for robust waveguiding that is immune to backscattering at small defects and sharp bends. Recent research has extended the elastic wave manipulation from 2D edge waveguiding to 3D planar waveguiding. However, most of them are limited to single-mode and single-frequency wave propagation along the designed plane. This paper introduces a novel 3D topological metamaterial structure whose geometrical parameters are specifically configured to obtain dual-mode topological states at distinct frequencies. Parametric studies are presented to demonstrate the controllability of bandgaps and to provide a design principle for preventing the effects of unwanted modes. Topological interface modes with either high group velocity or near-zero group velocity along the z direction are found. Full-scale finite element simulations are presented to uncover the elastic wave propagation behavior. The interesting layer-locked and layer-unlocked waveguiding based on excitation polarization and frequency for both straight path and zig-zag path are demonstrated. The outcomes of this work suggest abundant potential applications related to elastic wave control such as wave filters, energy harvesters, mechanical computers, and the like. This work may also help inspire future research on more complex and sophisticated multi-mode waveguiding in 3D spaces. [Display omitted] • Discovery of a 3D topological metamaterial with cylindrical masses and interconnected frameworks. • Dual-mode bandgaps at distinct frequencies. • Dual-mode topologically protected interface mode at different frequencies. • Demonstration of straight path and zig-zag path in 2D models. • Demonstration of layer-, frequency-, and polarization-dependent waveguiding along straight path or zig-zag path in 3D models. [ABSTRACT FROM AUTHOR]

We show that Airy soliton interaction in anomalous dispersion and focussing nonlinear regime provides an effective control on the co-propagating sech soliton dynamics. Cross phase modulation (XPM) induced nonlinear phase results varying group velocity of the sech soliton which leads to its temporal shift towards leading edge. The soliton could be made either advanced or delayed by choosing an appropriate initial time delay between the two co-propagating pulses. The effect of the initial time delay on trapping efficiency is also disclosed. Additionally, we have studied the effect of temporal chirp in Airy pulse on sech soliton dynamics. It is found that introduction of positive chirp inhibits the XPM-induced temporal shift of the soliton, while negative chirp boosts the XPM-induced acceleration. Further, the effect of group delay on the trapping and guiding of the soliton has been investigated. Moreover, the role of relative dispersion and nonlinear length on the soliton pulse acceleration are investigated. These results are expected to provide a better understanding on manipulation of light by light that could be useful in all-optical switching and signal control. • Airy and sech pulse interaction is investigated in anomalous dispersion and focussing nonlinear medium. • Sech soliton pulse is trapped in the optical potential created by Airy pulse through the XPM. • The trapped soliton is shifted towards the leading edge and the amount of temporal shift depends upon the relative strength of the dispersion and nonlinearity. • Time delay between soliton and Airy pulse plays a crucial role in soliton guiding and a large time delay causes to soliton splitting. • Initially chirped Airy pulse provides an extra degree of freedom in controlling the soliton path. [ABSTRACT FROM AUTHOR]

• The role of lattice dynamics to minimize the lattice thermal conductivity is investigated in transition metal nitrides. • Lattice parameters and bond lengths are in good agreement with the available experimental study. • Layered structure of Li 2 MN 2 leads to strong anisotropy in transport properties. • Li 2 ZrN 2 exhibits ultralow lattice thermal conductivity despite of large group velocity. This study systematically examines the lattice dynamics of Li 2 MN 2 (M = Zr or Hf), with the aim of unraveling the factors contributing to its unique thermal transport properties using first-principles calculations. Both compounds are found to be energetically and dynamically stable, and our results for their lattice parameters and bond lengths are in good agreement with the available experimental data. The transport properties exhibit strong anisotropic behavior due to the layered structure. Li 2 ZrN 2 possesses a low lattice thermal conductivity (1.52 Wm−1K−1) along the a -axis at 1000 K, owing to the significant reduction in phonon lifetime caused by the rattling behavior of Zr. The present study may provide valuable insights when exploring the role of lattice dynamics in minimizing the lattice thermal conductivity of transition metal nitrides and their prospective energy harvesting applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The current study focuses on the analysis of propagation characteristics of Love-type waves in a corrugated composite cylindrical structure, with corrugation at the lateral surface. The corrugated cylindrical structure is comprised of two regions of functional gradient fiber-reinforced material media with distinct radii. The amplitude of corrugation at the outermost lateral surface is assumed to be small. The functional gradients in outer and inner cylindrical layers are generated because of radial variation of the elastic parameters and density. An analytical treatment featuring a perturbation method and Debye Asymptotic Expansion is employed to attain the dispersion relation. The obtained dispersion relation is validated with some established standard and classical results through particular cases. The substantial effects of reinforcement, functional gradients, and corrugation parameters on both phase and group velocities of the Love-type wave have been analyzed extensively with the aid of graphical illustrations, accomplished by numerical computations. • Propagation behaviour of Love-type wave in corrugated cylindrical structure. • Cylindrical structure is composed of two functional gradient fibre-reinforced media. • Contour integration, Perturbation method, Asymptotic analysis is used. • Dispersion relation is validated with some established classical results. • Effects of various affecting parameters on phase and group velocities of wave. [ABSTRACT FROM AUTHOR]

• Dispersion relation for discrete heat equation is analyzed. • Real and imaginary parts of the wave vector are obtained as functions of frequency. • Analytical expressions for the phase and group velocities are derived and analyzed. • Continuum limit leads to either Fourier equation or hyperbolic heat equation. • On ultra-short time and space scales the discrete approach is preferable. The dispersion relation in ω-k space has been derived and analyzed for discrete heat conduction equation (DE). The DE is inherently nonlocal both in time and space and can be used to describe non-Fourier heat transport occurring on ultrashort time and length scales. An important distinction between the DE and the continuum description is that the frequencies and wave numbers available to the discrete system are limited, whereas in the continuum description there are no such limitations. Analytical expressions for the attenuation distance, group and phase velocities have been obtained and analyzed as functions of frequency. In the continuum limit, depending on the basic invariant of the continualization procedure, the dispersion relation for the DE reduces to either dispersion relation for the classical Fourier parabolic equation (PE) or to dispersion relation for the hyperbolic heat equation (HE). However, at the moderate and high frequencies the spectrum of the DE differs significantly from the spectra of the PE and HE. This implies that the continuum-based approaches, including both the PE and HE, unable to describe high-frequency and short-wavelength processes and the DE is preferable. This work provides a relatively simple analytical tool to interpret the transient wave-like behavior of heat transport on ultrashort space and time scales. [Display omitted] [ABSTRACT FROM AUTHOR]

Topological structures are well known for their robust and unidirectional wave transportation in acoustic and elastic communities. The rainbow effect in metamaterials is also promising for applications such as buffers, filters, wavelength-division multiplexing devices, and etc. In this work, the combination of topology and rainbow effect, i.e., topological rainbow, is investigated. The topological rainbow trapping and rainbow concentration in valley topological phononic crystal plates with gradient substrate are observed both numerically and experimentally. The topological rainbow guiding, where the elastic waves are guided in a spatial-spectral way, is also presented. The precise control of elastic waves with topological protection and in spatial-spectral way provides a convenient path to design future phononic devices such as elastic energy harvesters, signal storages, and communication devices. [Display omitted] • Valley topological rainbow structures are built up only by tuning the thickness of substrate. • Real rainbow trapping is realized, benefiting from the topological edge states. • The topological rainbow is determined by both the zero group velocity and the band gap. • Topological rainbow concentration and rainbow guiding for elastic wave are achieved. [ABSTRACT FROM AUTHOR]

• We examine wave beaming of the rotational wave propagation with structurally rhombus re-entrant honeycombs (SRRHs). • Sub-preferential wave beaming arises along the short diagonals of SRRHs, driven by symmetry-breaking induced coupling between wave frequency and structural topology. • Analysis using a rigid-spring model unveils an anisotropic coefficient explaining the frequency-structure coupling, illuminating the formation of the sub-preferential rotational wave beaming in SRRHs. Rotational waves frequently manifest in micro-structured materials and are often coupled with classical shear or longitudinal wave modes. In this study, a distinctive isolated optical branch, exhibiting very high polarization index related to joint rotation motion, is found in dispersion diagram of elastic wave propagation in structurally rhombus re-entrant honeycomb (SSRH). Through an analysis of group velocity, we further explore the wave beaming of the rotational wave propagation within the SRRH, and intriguingly, observe the emergence of sub-preferential wave beaming occurring along the short diagonal directions. This dynamic anisotropic phenomenon stems from the intricate interplay between wave frequency and structural topology. To elucidate the underlying dynamic anisotropy of rotational waves, we propose a simple rigid-spring model and derive a modulation function that precisely captures the intricate frequency-structure coupling behavior. The obtained modulation function unveils the formation of sub-preferential directions of the rotational wave within the SRRH. [ABSTRACT FROM AUTHOR]

• Quasi-static components (QSCs) induced by longitudinal waves in isotropic pipes are numerically investigated. • The experiment is carried out to validate the existence of QSCs. • The generation of different levels of corrosion on the surface of the aluminium pipe is investigated. • The sensitivity of QSCs to corrosion is examined by nonlinear acoustic parameter. In this paper, the quasi-static component (QSC) generation of longitudinal waves propagating in an isotropic pipe is investigated numerically and experimentally. The three-dimensional (3D) finite element (FE) simulations are first carried out to gain physical insights into the characteristics of QSC generation from longitudinal wave travelling in an isotropic pipe with weak material nonlinearity. By applying the axial displacement excitation in the FE model, L(0, 1) mode and L(0, 2) mode are excited simultaneously. Then, the generated QSC pulses are extracted using the phase reversal approach for analysis. It is found that the QSC pulses generated by L(0, 2) mode and L(0, 1) mode are L(0, 1) mode. Meanwhile, the shapes of QSC pulses at different locations are extracted and compared. In this study, a data pre-processing method is proposed to handle numerically calculated and subsequent experimentally measured displacement signals, and a nonlinear acoustic parameter is defined to evaluate the incipient damages. After that, an experiment is conducted to measure the QSCs induced by the propagation of longitudinal waves in an aluminum pipe. The experimental results indicate that the propagation of longitudinal waves in the aluminum pipe can induce the QSCs. Different levels of corrosion are created on the surface of the aluminum pipe and are assessed by the generated QSCs. The results show that the nonlinear acoustic parameter has a monotonically increasing trend with the growing severity of corrosion. The QSCs generated by longitudinal wave can be used to detect and evaluate the early-stage surface corrosion in the aluminum pipe. [ABSTRACT FROM AUTHOR]

Functionally graded materials (FGM) are materials in which there is a gradual variation in functional properties of the material so as to make it useful for different purposes. The life span and efficiency of Surface Acoustic Waves (SAW) devices can be increased by taking FGM into consideration. Further, FGM as a substrate can help to improve the structural integrity of a component or device. FGM substrates offer flexibility in design, enabling engineers to tailor the substrate's characteristics for specific functions within a device or system. Rayleigh-type surface waves, known for their numerous advantageous attributes, find extensive applications in various functional devices, and Rayleigh waves in functionally graded porous piezoelectric medium have not been studied so far and for more accurate simulation of field conditions, porous layers should be taken into account when determining the excitation and propagation processes of Rayleigh surface waves. Taking these considerations into account, this paper introduces a new model of composites of 'n' porous piezoelectric layers over functionally graded porous piezoelectric half-space (FGPPHS) and different characteristics of generalized Rayleigh waves in this model are studied. The material properties of the FGPPHS are taken to vary along the vertical direction (thickness). Closed form frequency equations are obtained for electrically short and open boundaries. Computing the model numerically, the impacts of gradation and wavenumber on the phase velocity and group velocity of generalized Rayleigh waves are examined. Also, lateral and vertical fluctuations of the electric potentials, stresses, mechanical displacements and electrical displacements are depicted by plotting 3D surface and contour graphs. In acoustic devices, a crucial measure that reflects the impact of piezoelectricity on wave phase velocity is the electromechanical coupling factor, therefore, the numerical analysis in terms of the electromechanical coupling factor is done and it is observed that the gradation coefficient can be adjusted to produce fairly high electromechanical coupling factor for the structure at a particular wave number. Numerical results are presented for alternating layers of Barium Titanate Crystal, PZT-5H, and PZT-7H and it is found that phase velocity decreases as the number of porous piezoelectric layers above FGPPHS increases for a particular wavenumber. The particle motion, in the layers and the half-space, is also determined and is found to be elliptic, in general, but its eccentricity changes with layer to FGPPHS and with depth. The outcome of the study provides a deeper understanding of the nature of generalized Rayleigh wave propagation in non-homogeneous functionally graded porous materials and may find applications in designing high performance SAW devices and also in the optimization of Rayleigh wave based devices for engineering applications. • Rayleigh wave in a functionally graded porous piezoelectric half-space is examined. • Rayleigh wave behaviour is exhibited by plotting 3D surface and contour graphs. • Retrograde and prograde particle motions of Rayleigh waves are observed. • Phase velocity and group velocity of Rayleigh waves have been examined. • Effects of gradation, porosity and stacking on phase velocity are investigated. [ABSTRACT FROM AUTHOR]

This paper describes the development of a framework for deterministic vessel motion prediction in real-time using an Artificial Neural Network (ANN), with the measurements of vessel motion and upstream wave elevation as the inputs. Instead of relying on sensitivity analysis to select the ANN training dataset, the location and duration of upstream wave elevation is estimated based on group velocity of the incident waves, given a user-specified prediction time horizon for vessel motion. This method is a form of physics-informed feature extraction that only uses correlated information to train the ANN in order to reduce computational effort. The developed framework is promising, as the ANN trained using physics-based numerical results can provide motion predictions with an error down to 6% for surge, heave and pitch motions of a turret-moored Floating Production Storage Offloading (FPSO) vessel. By applying the ANN training using numerical results onto experimental results of the FPSO, an error of 22% was obtained for pitch motions. At an instant of time, up to 120 s of vessel motion can be predicted in real-time. This physics-informed feature extraction method can be automated as part of the framework for the ANN training and testing pipeline in the future. • Combining far field wave and history of vessel motion for motion prediction. • Physics-informed feature extraction to select ANN training dataset. • Prediction horizon is deducible from the predictable zone of far field wave. • Improvements in prediction accuracy compared to brute force approach. [ABSTRACT FROM AUTHOR]

Flow-induced random vibration propagates throughout a plate-like structure and thus contains information about the structural properties and states. Previous research has shown that the group velocity under various frequencies can be estimated by the cross-correlation between two measurement points, in which the prominent peak signifies the travel time of the random guided wave. However, it is found that the performance of this method depends on the sensor placement and the plate size; in some cases, the cross-correlation is contaminated such that the extraction of dispersion curve is problematic. This is because the wave package in the cross-correlation corresponding to the direct propagation between the two sensors overlaps with the coda wave packages associated with complex boundary reflections. This hypothesis is justified by a passive experiment on an ellipse-shaped plate: in the cross-correlation between the foci of the ellipse, the imprints of the direct propagation and various orders of boundary reflections can be clearly separated and precisely predicted by the ray method. Based on these findings, a sensor placement criterion is proposed, by which a robust passive reconstruction of dispersion curve using flow-induced random vibration is guaranteed. • We propose passive reconstruction of dispersion curve using flow-induced vibration. • Boundary reflection and sensor placement decide the accuracy of passive detection. • An ellipse-shaped plate experiment justifies the effect of boundary reflection. • A sensor placement criterion is proposed to guarantee robust passive detection. [ABSTRACT FROM AUTHOR]

Using a subsurface mooring deployed at a depth of ∼2290 m in the northern South China Sea, the characteristics of deep-propagating near-inertial waves (NIWs) (>1500 m) generated by a combination of a winter storm and a typhoon were examined. The NIWs had a large vertical wavelength and showed a high coherence in near-full water depth. Correspondingly, the strong vertical shear and energy of the NIWs were concentrated at vertical scales larger than ∼500 m. The average vertical group velocity was ∼160 m/day. The horizontal wavelength decreased from ∼600 km in the upper layer to a few tens of kilometers below a depth of 1500 m. Interestingly, the near-inertial energy did not decrease obviously at depths of 100–1500 m, where the average downward near-inertial energy flux (F z) was (2.3 ± 0.9) × 10−3 W/m2 and nearly equaled that at 100 m depth. Combined with the slab model, the mean F z at a depth of 100–1500 m can reach 19%–43% of that in the mixed layer. During the deep propagation of NIWs, the near-inertial shear was not strong in the upper layer. However, in the deep layer, the total shear was dominated by deep-propagating NIWs and was significantly enhanced. Correspondingly, the estimated diapycnal diffusivity increased, reaching a maximum value of ∼270% of the averaged value. This study contributes to our understanding of the deep propagation of wind-generated NIWs in the open ocean. • Deep propagation of near-inertial waves (>1500 m) is observed by a subsurface mooring. • The near-inertial waves show a high coherence in near-full observed depth, with a mean vertical wavelength of ∼1262 m. • Approximately 19%–43% of the wind-generated near-inertial energy penetrates the deep ocean. • The enhancement of shear induced by the deep-propagating NIWs is mainly located in the deep layer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ambient noise tomography of the Eastern Indian Shield, performed for the first time, provided a 3D V S structure of the region. • The 3D V S structure highlights a high V S layer (depth 4–20 km) and an ultra-high V S layer (depth > 20 km) within the Singhbhum Craton only. • The V S of the lower layer probably implies the presence of ultramafic composition. • The possible cause of the ultramafic layer may be high-temperature metamorphism due to lithosphere delamination. Singhbhum Craton (SC) in the Eastern Indian Shield (EIS) is known to have preserved Archean crust which might provide insights into the Precambrian tectonics. In this study, ambient noise cross-correlation of about 1 year of continuous data recorded in 15 broadband seismic stations across EIS is performed. Rayleigh wave group velocities at 4–22 s periods obtained by frequency-time analysis of the cross-correlograms were subjected to tomographic inversion to produce group velocity maps. The spatial resolution of these maps was found to be ∼100 km. Inverted 1D shear-wave velocity (V S) models at regular grid points of these tomographic maps were combined to construct the first 3D V S model of the SC and adjoining regions within the EIS. The 3D model highlights a high V S (3.6–3.8 km/s) structure in the 4–20 km depth range and an ultra-high V S (∼4.0–4.2 km/s) structure at depths ≥ 20 km within the SC only. The V S of the upper layer and its regionalisation match with the well-studied granite batholith within the SC. The ultra-high velocity layer in the lower crust, spatially spanning ∼100 km × 150 km, is distinctly imaged for the first time and its V S indicates probable ultramafic composition. The existence of ultramafic composition at ∼800 MPa lithostatic pressure requires ultra-high temperature metamorphism, possible through mantle upwelling/melting. The previous studies of upwarped crust-lithosphere beneath the SC and the lower-crustal ultramafic composition inferred in this study probably confirm the delamination of the lithosphere beneath the SC at some point during the Precambrian eon. [ABSTRACT FROM AUTHOR]

• A novel and universal disturbance wave velocity model was proposed. • Dominant scaling parameter group for wave velocity was revealed. • Entrained droplets effect plays a critical role on wave velocity. • New correlation collapses all entrained conditions within 5% error band. • Scalability and wide scope of application of the model were validated. A full knowledge of the interfacial effect on disturbance wave is vital for accurately predicting disturbance wave velocity in annular flow. However, almost all of the existing disturbance wave velocity models do not ponder the droplet-film mass transfer, which largely limits the applicable scope and prediction accuracy of the model. This article leads into the entrained droplets effect to the interfacial shear modeling, proposing a new disturbance wave velocity model with a widely applied range. The effects of entrainment and liquid film thickness on the characteristics of the gas core mixture (bulk density and velocity) were included, and the mean velocity of the liquid film surface was introduced in the modelling. For the verifying experiments, an annular flow loop with film metering device and electrode sensor was developed, and the entrainment and liquid film thickness were also modelled for the convenience of usage in cases without raw measured data. The new developed disturbance wave velocity model collapses the experiments corresponding to all entrained conditions well within ± 5.0% deviation for an 85.2% confidence interval. The comparative analysis with the existing empirical correlations confirms the critical role of entrained droplets on the disturbance wave velocity. The scalability and wide scope of application were further validated by the open data in the literature, and finally, practical suggestions were given for the disturbance wave velocity prediction on various pressure and pipe diameter conditions. [ABSTRACT FROM AUTHOR]

The lattice thermal conductivity of the CdO monolayer was investigated by density functional theory in combination with Boltzmann transport theory and it was estimated about 3.346 Wm−1K−1 at T = 300 K. Comparing this result with the one reported for the bulk CdO, it was revealed that the lattice thermal conductivity of the monolayer is lower than the bulk CdO. The lower lattice thermal conductivity of the CdO monolayer was attributed to the lower phonon lifetime and phonon group velocity in comparison to the bulk counterpart. Considering the lower lattice thermal conductivity of the monolayer, higher thermoelectric efficiency was estimated in comparison with the reported efficiency for the bulk CdO. At T = 900 K, the maximum zT = 0.76 can be found in p-type for the hole concentrations of 7.2 × 1012 cm−2. • The phonon dispersion of CdO monolayers were investigated with considering Born effective charges. • The contribution of phonon frequency to the k lat , group velocity, and phonon lifetime were investigated. • Thermoelectric efficiency of the CdO monolayer was investigated. [ABSTRACT FROM AUTHOR]

• Scattering of SH wave on an irregular surface of the piezomagnetic stratum-substrate structure is studied. • The expressions of frequency relation and group velocity of SH wave is derived in closed form for both MO and MS cases. • The expressions of mechanical displacement and magnetic potential are derived for three different shaped irregularities. • Validation of the derived results of both cases is found in well agreement with the classical Love wave equation. • The impact of material properties is depicted on the phase velocity and group velocity of SH wave for both MO and MS cases. The present paper investigates the scattering phenomenon of horizontally polarized Shear wave on an irregular surface of the piezomagnetic stratum lying over a piezomagnetic substrate. The expressions of frequency relation and group velocity of scattered Shear wave on the considered piezomagnetic stratum-substrate structure are deduced for magnetically open and magnetically short cases by inducing appropriate boundary conditions. A closed form expressions of reflected mechanical displacement and reflected magnetic potential function related to stratum and substrate are also determined for three different shaped irregularities (rectangular shaped, parabolic shaped and triangular shaped) by employing perturbation technique and residue theorem for both magnetically open and short cases. The efficacy of piezomagnetic coupling parameter, vertical irregular parameter due to presence of surface irregularities is portrayed on the phase velocity, group velocity, reflected mechanical displacement and reflected magnetic potential function related to the stratum for both magnetically open and short conditions graphically. A comparative study is also made to examine the impact of different shaped irregularities on the reflected mechanical displacement and reflected magnetic potential function of the stratum. [ABSTRACT FROM AUTHOR]

Spatially damped continental shelf waves (CSWs) with diurnal tidal frequency outside Lofoten–Vesterålen in north-west Norway are studied theoretically for an idealized shelf topography. Wave damping is caused by the exchange of fluid on the shelf with an inner archipelago through a permeable coastline. This exchange is modelled by the application of a Robin condition at the coastal boundary. It is shown that CSWs with diurnal frequencies are possible in a small wave number range centred around zero group velocity. By calculating the nonlinear radiation stress components in the spatially damped CSWs, we find the time- and depth averaged Lagrangian mean drift current to second order along the coast. We show that the Lagrangian mean drift current is independent of the value of the damping coefficient, however small, as long as it is nonzero. This illustrates the singular behaviour of the Lagrangian wave drift problem for CSWs. [ABSTRACT FROM AUTHOR]

Low dimensional and 2D materials have been considered as promising candidates for thermoelectric applications due to their intrinsic high carrier mobilities. Amongst them, β -SiC 7 has gained interest due to its direct band gap and thermal stability. To further explore the potential of this material, we present a detailed analyses of the lattice thermal conductance (κ L) of 2D β -SiC 7 through a full iterative solution of the Boltzmann transport equation. We find the thermal transport to be anisotropic with κ yy = 97.62 (10−9 W/K), significantly lower than that of graphene due to the presence of Si atom in the lattice which causes distortion and weakening of the acoustic branches. The TA and LA modes to possess the highest phonon group velocities due to their linear nature around the Γ point in the phonon dispersion, while the ZA mode possesses the lowest group velocity as a result of the quadratic shape of the branch within the vicinity of the Γ point. On the other hand, the flexural ZA branch possesses the longest carrier lifetime that is about three orders of magnitude higher than the LA and TA branches, since the mass disorder in the lattice softens the acoustic modes. The thermodynamic limit to the κ L is attained for a sample domain size of ∼45 μ m and nanostructuring emerges as a possibility to reduce the κ L by 50% to enhance the thermoelectric efficiency of the material. [Display omitted] [ABSTRACT FROM AUTHOR]

Shear wave elastography (SWE) is an ultrasonic technique able to quantitatively assess the mechanical properties of tissues by combining acoustic radiation force and ultrafast imaging. While utilizing coherent plane wave compounding enhances echo and shear wave motion signal-to-noise ratio (SNR), it also reduces the effective pulse repetition frequency (PRFe), affecting the accuracy of the measurements of motion and, consequently, of material properties. It is important to maintain both high-motion SNR and PRFe, particularly for the characterization of (material and/or geometrical) dispersive tissues such as arteries. This work proposes a method for SWE measurements with high SNR, while maintaining a high PRFe, using conventional clinical ultrasound scanners. A time alignment process is applied after acquiring data from plane wave transmissions at different angles. The time alignment uses interpolation to obtain data points at higher frame rates, and the time-aligned data are compounded to increase the SNR. The method is used for SWE in tissue-mimicking phantoms of different stiffness and is compared with traditional plane wave compounding. Increases of 58% and 36% in spatial and temporal bandwidth compared with conventional plane wave compounding, respectively, can be achieved for SWE measurements of representative arterial stiffness values. Improvements in phase velocity accuracy and bandwidth in an arterial phantom are also described, to emphasize the beneficial advantage in dispersive cases. [ABSTRACT FROM AUTHOR]

A gas-solid fluidized bed reactor composed of Geldart Group C fine powers with the addition of nano-additives (Group C+) has recently been shown to have higher reaction conversion and better contact efficiency than the same reactor composed of Geldart Group A particles due to the increased gas holdup in the dense phase and the increased gas-solid interfacial area. Based on our earlier findings that significantly smaller bubbles were observed in such a Group C+ particle fluidized bed, the bubbling behavior is fully characterized in this work using the bubble position, diameter, rise velocity and residence time. The results indicated that bubbles were smaller in diameter, lower in rise velocity, and had a longer residence time in the Group C+ fluidized bed when compared with the same bed using Geldart Group A particles. All these factors contributed to better fluidization quality and enhanced gas-solid contact, thus improving reaction performance. [Display omitted] • Less and smaller bubbles in the fluidized bed of Group C+ particles • Lower bubble rise velocity and longer bubble residence time for Group C+ particles • More uniform distributions of the bubble diameter and rise velocity for Group C+ particles • Better fluidization quality and reactor performance of Group C+ fluidized bed [ABSTRACT FROM AUTHOR]

• The method of multiple scales is applied to analysis of internally resonant guided waves. • The amplitudes of the internally resonant guided waves are nonlinearly dependent to propagation distance. • The propagation-distance dependence of the amplitudes is affected by detuning parameters. Taking into account damping effects, the propagation-distance dependence of the amplitude of nonlinear guided waves arising from an internal resonance was investigated. In the analysis of Lamb-wave propagation, we introduced nonlinear quadratic effects derived from both geometric and material nonlinearities, referred to as classical nonlinearities, and damping effects by expressing the Lamé constants as complex numbers. Assuming a small detuning from the phase matching condition with respect to wavenumber and frequency, and using the method of multiple scales and self-adjointness of the governing equations with boundary conditions, the amplitude equations describing the nonlinear coupling of the two wave modes are derived as solvability conditions. This derivation also provides both physical and mathematical insights into both the phase and group velocity matching conditions. Numerical results obtained from these amplitude equations show that because of the nonlinear coupling an internal resonance between the two modes can occur under the above matching conditions. Without detuning, one mode increases monotonically in amplitude while the other decreases monotonically. Nevertheless, their changes gradually decrease with propagation distance, and each amplitude converges to a finite value. However, with wavenumber and frequency detuning, both amplitudes increase and decrease cyclically with propagation distance, resulting in a weakening of this resonance. Furthermore, results with damping effects show an attenuation of both amplitudes with propagation distance, which limits the distance resonance waves can propagate. [ABSTRACT FROM AUTHOR]

Phononic crystals and elastic metamaterials have recently received significant attention due to their potential for unconventional wave control. Despite this interest, one outstanding issue is that their band diagram is typically fixed once the structure is designed. To overcome this limitation, periodic structures with adaptive elastic properties have recently been proposed for Bragg- and local resonance-driven structures. In this context, we report about the effect of an applied external mechanical load on a periodic structure exhibiting band gaps induced by inertial amplification mechanism. If compared to the cases of Bragg scattering and ordinary local resonant metamaterials, we observe here a more remarkable curve shift, modulated through large but fully reversible compression (stretch) of the unit cell, eventually triggering significant (up to two times) enlargement (reduction) of the width of a specific band gap. An important up (down)-shift of some dispersion branches over specific wavenumber values is also observed, showing that this selective variation may lead to negative group velocities over larger (smaller) wavenumber ranges. In addition, the possibility for a non-monotone trend of the lower limit of the first BG under the same type of external applied prestrain is found and explained through an analytical model, which unequivocally proves that this behaviour derives from the different unit cell effective mass and stiffness variations as the prestrain level increases. These peculiarities derive from the hinge-like behaviour of some regions of the unit cell, which is typical of structures exhibiting the inertial amplification mechanism. The effect of the prestress on the dispersion diagram is investigated through the development of a 2-step calculation method: first, an Updated Lagrangian scheme, including a static geometrically nonlinear analysis of a representative unit cell undergoing the action of an applied external load is derived, and then the Floquet-Bloch decomposition is applied to the linearized equations of the acousto-elasticity for the unit cell in the deformed configuration. Finally, the most evident consequence on the dispersion curves of the application of an external prestress, i.e. the band gap shift with respect to the unloaded structure, is demonstrated through nonlinear transient numerical simulations, clearly proving the capability of the structure to switch from a pass- to a stop-band behaviour over the same frequency range. The results presented herein provide insights in the behaviour of band gaps induced by inertial amplification, and suggest new opportunities for real-time tunable wave manipulation. [ABSTRACT FROM AUTHOR]

Ultrasound bladder vibrometry (UBV) parameters have been shown in previous studies to strongly correlate with measurements from urodynamic studies. Just like urodynamic studies, UBV can be performed in supine and sitting positions. The objective of this study is to compare UBV parameters obtained in the two different positions using statistical methods. We recruited eight volunteers with healthy bladders for this purpose. The elasticity, group velocity squared and thickness of the bladder were the UBV parameters of interest, and their values were recorded at different bladder volumes for each volunteer. The results presented indicate that the measurements made in the two positions are in agreement using the Bland-Altman method and a parameter q which compares the values at each bladder volume for each volunteer. UBV parameters were also repeatable for measurements recorded in the supine and sitting positions. [ABSTRACT FROM AUTHOR]

• SH waves at imperfect interface of two transversely isotropic piezoelectric media. • Dispersion equations of SH obtained using method of infinite determinants. • Effect of mechanical/dielectric imperfections on the dispersion curves. • Electromechanical coupling, mass loading sensitivity and group velocity studied. Imperfect mechanical or dielectric interfaces in piezoelectric sensors/actuators reduce the electromechanical efficiency of the system. The major drawback of an imperfect interface in a system is its disability to transfer stress or potential across the surface effectively. This leads to imperfect signal communication and thereby affecting its performance. The present study encapsulates the shear wave (Love wave in low velocity layer and B-G wave) propagation characteristics in an imperfectly bonded piezoelectric layered structure, also subjected to material gradients. The imperfect bonding interface is considered to be mechanically compliant and dielectrically weak (or high) conducting. With help of admissible, but non-traditional, boundary conditions at the interface, the dispersion equations of waves are derived by method of infinite determinants for both electrically open and shorted conditions at the free surface. Phase velocity, electromechanical coupling factor and mass loading sensitivity of shear waves are sketched graphically with special concern on the influence of interface imperfection on them. The results reported can serve to overcome the deficit in the performance of Love wave sensors due to mechanically/dielectrically imperfect interfacial surface. [ABSTRACT FROM AUTHOR]

• The competing affecting mechanism on AlN growth induced from hydrogen flow rate is studied and further confirmed by CFD simulation. • GR increases with MO VM by suppressing parasitic reaction, but uniformity show a deteriorate trend due to the occurrence of turbulence and loss of uniform boundary layer. • High quality 4-μm-thick AlN films with improved crystalline quality and atomic smooth surfaces were achieved on nano-patterned sapphire substrates with a growth rate of 0.82 um/hr. Effect and mechanism of carrier gas velocity, V/III ratio, and carrier gas velocity match of group III to group V (MO VM) on AlN growth rate (GR) were investigated in depth by experiment and computational fluid dynamics (CFD) simulation in Prismo HiT3 MOCVD platform. It is found that AlN growth rate increases with hydrogen flow rate at first, reaches saturation and then shows a monotonic decrease trend. The specific value of turning point depends on the equipment and process. At constant total flow rate of 160 slm, GR increases with MO VM by suppressing parasitic reaction, but uniformity show a deteriorate trend due to the occurrence of turbulence and loss of uniform boundary layer. High quality 4-μm-thick AlN films with improved crystalline quality and atomic smooth surfaces were achieved on nano-patterned sapphire substrates with a growth rate of 0.82 um/hr. The full width at half maximum of the X-ray rocking curve was 162/305 arcsec for (0 0 2)/(1 0 2) planes with total dislocation density ∼ 109 cm−2. [ABSTRACT FROM AUTHOR]

• Topological acoustic rainbow trapping can be realized by regulating topological edge mode dispersion curve and group velocity. • The topological phononic crystal is robust to multiple structural disorders, such as scaling, rotating and removing unit cells. • The proposed gradient phononic crystal is capable of recovering the Gaussian pulse signal from the background noise. In this letter, a gradient phononic crystal (PC) structure is proposed for robust enhanced acoustic sensing. At first, the topologically protected edge states are introduced by breaking the space-inversion symmetry of the PC structure. Then, the topological edge mode dispersion curve and group velocity are demonstrated to be regulated by varying the structure parameters gradually and the edge states can be slowed down to zero group velocity and trapped at different positions. Consequently, topological acoustic rainbow trapping is formed. Furthermore, the robustness and enhancement properties are verified both numerically and experimentally. All the results indicate that the gradient PC structure is able to realize robust enhanced acoustic sensing. This work opens a new vista to improve the robustness of the PC-based enhanced acoustic sensing. [ABSTRACT FROM AUTHOR]

• A highly efficient recursive Legendre orthogonal polynomial approach for prestressed bolts is presented. • The applicability of the "Mechanics of Incremental Deformations" theory is verified by prestressed guided wave experiment. • The group velocity and attenuation on both sides of an intersection frequency exhibit completely opposite trends with the variation of prestress. The magnitude of prestress can reflect the degree of anchor bolt failure, but currently there are relatively limited theoretical research methods for the wave characteristics of prestressed bolts. For this reason, this paper establishes a viscoelastic bolt model with prestress based on the Mechanics of Incremental Deformations theory and the Kelvin-Voight viscoelastic theory, and proposes a recursive Legendre polynomial series method (RLPSM) to solve the longitudinal guided wave propagation characteristics in free bolts with prestress. The dispersion and attenuation curves of longitudinal guided waves in free bolts with various prestresses are given, and the influences of prestress on dispersion curves are analyzed. Meanwhile, the ultrasonic guided wave detection system of free bolts with prestress is established for laboratory research, and compared with the theoretical results. [ABSTRACT FROM AUTHOR]

• The Rayleigh wave generated by the sphere can be measured on the surface of the block. • Wave characterization methods allow to study 1D and 2D dispersion in order to relate information extracted on the sphere and on the block. • Material property of the sphere can be remotely estimated from the waves converted to the surface of the bloc. • Measurement of the space time dispersive nature of the wave on the spheres surface using laser vibrometer. • Mode conversions between the sphere and the surface at the contact point are studied. The monitoring of the integrity of the spherical balls inside a ball bearing can be challenging, as it needs to be disassembled in order to access every element of the structure. In this paper, an ultrasonic method is used to directly interrogate the spherical solids. The interaction wave-solid lets us extract material related information. The complex geometry of the ball bearing is simplified to a repetitive assembly of an elementary unit of a solid sphere setting on a plane surface. Understanding of the interaction between the ultrasonic wave and this elementary block is the key to a more general comprehension of the interaction with the complete ball bearing. To achieve this, the interaction between a Rayleigh Surface Acoustic Waves (SAWs) propagating on a plane and a spherical solid ball setting on that plane is studied, numerically and experimentally. In the experimental configuration, a steel ball is fixed to an aluminum block. Shear wave contact transducers are used to generate SAWs, while a laser vibrometer is employed to precisely measure the ensuing displacements. Subsequently, the collected time series data is carefully visualized and analyzed to discern distinct waves, such as the Rayleigh wave on the block, SAW on the sphere, and the waves generated by the sphere. To complement these experimental findings, a numerical model is created using finite element analysis, faithfully reproducing the experimental conditions. This approach facilitates a comprehensive examination of the displacement field, both on the surface of the sphere and the aluminum block. The extraction of the material related information of the spherical ball is based on the estimation of the resonance frequency of each vibrational mode of the solid sphere. Furthermore, 3D Gabor and dispersion curves from the spatio-temporal signals are used to estimate and analyze these frequencies and to compare the different waves involved in the interaction: the direct Rayleigh waves, the back-generated waves and the waves propagating on the surface of the sphere. The findings demonstrate that the transmitted waves toward the block (back-generated wave) preserve the waveform of the SAW propagating on the sphere, enabling the deduction of the dispersive behavior and extraction of material properties, such as the Rayleigh wave group velocity. The implications of this study are particularly relevant for non-destructive testing and evaluation (NDTE) of ball bearings, as the research provides insights into characterizing their integrity without disassembling them. The ability to extract material information from signals measured at the outer ring of ball bearings holds promise for practical applications in assessing their condition. [ABSTRACT FROM AUTHOR]

• Combination of 1D-GLL-SAFE and 2D-Gauss-SAFE to compute GW. • Compute GW in acoustoelastic and complex waveguide. • Development of freeware SAFEDC. Guided wave (GW)-based techniques have been extensively investigated and applied in material characterization, damage detection, and structural health monitoring. A comprehensive understanding of GW is the cornerstone for the development of such techniques. Based on the semi-analytical finite element (SAFE) method, an open-source dispersion calculator of GW propagating in acoustoelastic and complex waveguides with both isotropic and anisotropic material properties is developed. First, by assuming the simple harmonic motion along the propagation direction and discretizing along the thickness direction, 1D-GLL-SAFE (one-dimensional Gauss-Lobatto-Legendre SAFE) is adopted for the solution of GW in plate waveguide, which is attributed to its superior performance in terms of computational accuracy and efficiency. Different theories on acoustoelasticity are adopted to calculate GWs under loading. Then 2D-Gauss-SAFE (two-dimensional Gauss SAFE) with triangular meshes filling the cross section is adopted for GW in general waveguides considering the ease of convenience in meshing. Finally, based on the 1D-GLL-SAFE and 2D-Gauss-SAFE algorithms, an open-source tool SAFEDC (SAFE-based dispersion calculator) is developed, which not only provides the solution of GW in pre-stressed isotropic waveguide and general cross section, but also extends to GW in laminates with arbitrary layer stacking configurations and hybrid stacking including multiple materials. Most of the GW features, including phase velocity, group velocity, wave number, wave structure in terms of displacement, stress, and strain, and animation of wave propagation are all offered in SAFEDC, which helps the researchers and engineers to understand and utilize GW. [ABSTRACT FROM AUTHOR]

• The greatest pulse delay is observed for low absorption and low anisotropic scattering. • A maximum in relative pulse width is formed at some distance from the source. • A combination of optical parameters and distance results in a minimum in frequency response. • The frequency response minimum position shows monotonous dependence on anisotropy. The paper reports on the numerical study of temporal characteristics, frequency and phase responses of the photon density waves generated by a point-sized source in scattering media with different scattering anisotropy and absorption index. The study is performed with time-resolved Monte-Carlo simulations for a wide range of medium optical properties covering values typical for aerosols and sea water. We demonstrate that although the normalized pulse delay increases monotonically with distance in the course of propagation in the medium, for particular sets of optical properties its normalized width shows a non-monotonous trend with a maximum corresponding to distances where ballistic and multiply scattered photons give comparable contribution to the irradiance field. In the frequency responses of photon density waves for certain combinations of optical properties at particular distances a deep minimum is formed, also associated with the interference of partial waves. The dimensionless frequency corresponding to this minimum monotonically increases with the increase in anisotropy factor. Dependencies of local and averaged phase and group velocities on distance derived from phase responses revealed a formation of a minima in local group velocities dependencies with further increase to the average velocity values at higher distances, which is also associated with relative contribution of low- and multiply scattered photons. The revealed dependencies can be useful for verifying the analytical models of nonstationary radiation transfer and directly for assessing the achievable parameters of optical systems for various purposes operating in natural scattering media, such as the atmosphere and sea water. [ABSTRACT FROM AUTHOR]