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In the experiments of measuring the strength of materials under ramp compression, accurately determining in situ particle velocity is crucial for calculating material sound speed during loading–unloading path and materials strength under high pressure. This paper proposes a machine learning approach that utilizes Long Short-Term Memory (LSTM) neural networks and Bayesian optimization algorithms to enhance the analysis of data from ramp compression strength measurement experiments. This method leverages LSTM neural networks to uncover the complex relationship between the rear interface velocity of the sample and the in situ particle velocity in numerical simulations. By using a well-trained network model, it enables direct interpretation of experimental data, leading to accurate predictions of key physical quantities along the loading and unloading paths in ramp compression experiments. A comparative analysis between theoretical curves from numerical simulations and LSTM neural network predictions shows a high degree of consistency. This approach is applied to ramp compression experiments on Ta and CuCrZr materials, demonstrating superior accuracy over the free-surface approximation and incremental impedance matching methods. Additionally, this method relies solely on the equation of state during numerical computations, eliminating the need for the complex constitutive equations required by the transfer function method, thus enhancing data processing efficiency and practicality. [ABSTRACT FROM AUTHOR]

We apply the methodology of Lustig, with which rigorous expressions for all thermodynamic properties can be derived in any statistical ensemble, to derive expressions for the calculation of thermodynamic properties in the path integral formulation of the quantum-mechanical isobaric–isothermal (NpT) ensemble. With the derived expressions, thermodynamic properties such as the density, speed of sound, or Joule–Thomson coefficient can be calculated in path integral Monte Carlo simulations, fully incorporating quantum effects without uncontrolled approximations within the well-known isomorphism between the quantum-mechanical partition function and a classical system of ring polymers. The derived expressions are verified by simulations of supercritical helium above the vapor–liquid critical point at selected state points using recent highly accurate ab initio potentials for pairwise and nonadditive three-body interactions. We observe excellent agreement of our results with the most accurate experimental data for the density and speed of sound and a reference virial equation of state for helium in the region where the virial equation of state is converged. Moreover, our results agree closer with the experimental data and virial equation of state than the results of semiclassical simulations using the Feynman–Hibbs correction for quantum effects, which demonstrates the necessity to fully include quantum effects by path integral simulations. Our results also show that nonadditive three-body interactions must be accounted for when accurately predicting thermodynamic properties of helium by solely theoretical means. [ABSTRACT FROM AUTHOR]

We study the elastic behavior of hexagonal close-packed (hcp) Fe at the high temperature and pressure conditions of the Earth Core, using an embedded-atom method interatomic potential adjusted to those conditions. We calculate diffusivity, elastic constants, density, bulk modulus, shear modulus, and sound velocities vs temperature. We obtain reasonable agreement with ab initio simulations and with other empirical potential simulations. Our densities and shear modulus are slightly higher than those in the preliminary reference earth model for the core. Phase stability is discussed in terms of the Born criteria and free energies, finding that hcp is mechanically stable and that the free energy difference between hcp and body-centered cubic (bcc) is very small compared to the thermal energy. We compare our simulated shear modulus G to several analytical models, obtaining excellent agreement with the Atom in Jelium model by Swift and co-workers. Assuming that the yield strength Y is equal to the shear modulus G , Y = G / 30 , we find reasonable agreement with a recent parametrization of the Steinberg–Guinan model. These results can lead to future large-scale, multi-million simulations of Fe under core conditions for samples with microstructure like grain boundaries and twins, which might be present under those conditions. [ABSTRACT FROM AUTHOR]

We present ab initio simulations of a large system of 2400 particles of molten NaCl to investigate the behavior of collective mode dispersion beyond the hydrodynamic regime. In particular, we aim to explain the unusually strong increase in the apparent speed of sound with wave number, which significantly exceeds the typical positive sound dispersion of 10%–25% observed in simple liquids. We compare dispersions of "bare" acoustic and optic modes in NaCl with ab initio simulations of other ionic melts such as CuCl and LiBr, metallic liquid alloys such as Pb44Bi56 and Li4Tl, and the regular Lennard-Jones KrAr liquid simulated by classical molecular dynamics. Analytical expressions for the "bare" acoustic and optic branches of collective excitations help us to identify the impact of the high-frequency optic branch on the emergence of "fast sound" in binary melts. Our findings show that in ionic melts, the high-frequency speed of sound is much larger than in the simple Lennard-Jones liquids and metallic melts, leading to an observed strong viscoelastic increase in the apparent speed of sound—more than double its adiabatic value. [ABSTRACT FROM AUTHOR]

As elastography, an emerging medical imaging strategy, advances, surface acoustic waves have been utilized to examine superficial tissues quantitatively. So far, most studies are experimental, and a numerical method is needed to cost-effectively investigate surface acoustic wave generation and propagation for technical development and optimization purposes. This study aims to develop a reliable numerical method for simulating impulse-induced surface acoustic waves using the k-wave simulation toolbox. According to the physical process of surface acoustic wave based elastography, the proposed simulation method consists of two stages: compressional wave simulation and elastic wave simulation, which aim to generate acoustic radiation force impulse and elastic waves, respectively. The technical procedures were demonstrated by a wave simulation on a water–tissue model. Meanwhile, three acoustic radiation force modeling methods were adopted. The compressional wave simulation showed that the three force modeling methods could produce similar force distribution in space but largely different amplitudes. The elastic wave simulation confirmed the feasibility of numerically generating surface acoustic waves. The reliability of the simulated waves was verified by a quantitative comparison between the numerically acquired sound speeds and their theoretical expectations and by a qualitative comparison between the numerically generated waves and the experimental observations under similar conditions. In summary, this study confirms k-wave as an effective numerical method for simulating surface acoustic waves for elastography purposes. This study provides an immediate simulation platform for investigating Scholte waves, the surface acoustic wave at a liquid–solid interface, and also, a potential numerical framework to investigate other surface acoustic waves. [ABSTRACT FROM AUTHOR]

Three third-order dielectric constants, 8 electrostrictive constants, 13 third-order piezoelectric constants, and 14 third-order elastic constants for lithium tantalate (LiTaO3) single crystals, which are mainly used in surface acoustic wave (SAW) devices, were determined as part of basic research to realize SAW devices with a low degree of nonlinearity. The third-order dielectric constants were determined by measuring the change in capacitance along selected directions when an alternating electric field was applied to the crystal. The electrostrictive constants were determined by measuring the change in capacitance when static stress was applied. Some of the piezoelectric constants were determined directly from the change in sound velocity due to the application of an alternating electric field, whereas others were obtained from the measured dielectric constants, electrostrictive constants, and the change in sound velocity due to an alternating electric field. In addition, the elastic constants (compliance) were determined using the three aforementioned determined nonlinear constants and the measured small-amplitude ultrasonic velocity change as a function of applied static stress. The measurements performed in the present study are more advanced than those reported for LiNbO3 single crystals in 1987 due to the adoption of the d-form nonlinear piezoelectric equation (instead of the e-form) and a higher degree of precision using dynamic measurement methods. The use of the d-form of the nonlinear piezoelectric equation allows many nonlinear constants to be determined independently from other nonlinear constants, eliminating measurement errors associated with these other constants. The d-form nonlinear constants obtained in the present study were converted to e-form constants to make them applicable to the analysis of nonlinear phenomena in piezoelectric devices. [ABSTRACT FROM AUTHOR]

Picosecond ultrasonics is a technique where coherent acoustic phonons are generated with frequencies in the GHz frequency range. When optical detection is operated in a transparent medium, the interaction of these phonons with the probe pulses yields oscillations in the time domain that reveal Brillouin scattering. Their frequency is at the Brillouin frequency shift, commensurate with the phonon velocity. As the pump–probe experiments are time-resolved, changes in the Brillouin frequency with time can be attributed to changes in sound velocity with depth. As sound velocity is temperature-dependent in liquids, we show that the picosecond ultrasonics technique can be used for temperature depth profiling in liquids. In this work, the concept is proved using the pump absorption itself as a heat source and confronting measured changes in Brillouin frequency with depth with data resulting from the derivation of a 3D modeling of the temperature rise in the liquid. We demonstrate the remote depth profiling of temperature, with measured data spaced at a distance less than the optical wavelength. [ABSTRACT FROM AUTHOR]

Within the low-frequency limit, this work analyzes the viscous absorbing properties of circular clusters and semi-infinite slabs made of rigid scatterers embedded in a fluid, such as air or water. These structures are made of rigid scatterers distributed in a hexagonal lattice, and they are proposed as useful absorbing devices in the core of acoustic black holes or acoustic metasurfaces. It is demonstrated that in both types of structures, an optimum value of the filling fraction produces the maximum absorption in a given frequency band. To avoid heavy numerical simulations, the broadband absorbing power has been obtained using a homogenization theory providing not only the effective acoustic parameters (effective mass and effective sound speed) but also the decay coefficient due to viscosity. An enhancement of the broadband sound absorption can be obtained by using a refractive index gradient allowing an increase of the acoustic energy into the semi-infinite slabs. The theoretical predictions are well supported by numerical simulations based on the finite-element and boundary-element methods, respectively, for the semi-infinite slabs and clusters. These predictions have potential applications in the design of structures and metasurfaces with enhanced absorbing power at low frequencies. The analytical model is further supported by experiments made with a 3D-printed sample. [ABSTRACT FROM AUTHOR]

Experimental studies of the shock wave properties of two epoxy resins with the same composition but different curing temperatures (160 and 200 °C) at up to 330 GPa pressure have been carried out. Laser interferometry was used to record particle velocity profiles at up to 73 GPa pressure while measuring the shock wave velocity. The release sound velocity was experimentally determined in the 3–73 GPa pressure range. Cumulative explosive shock wave generators were used to study the shock Hugoniot of epoxy resins at pressures above 100 GPa. It was shown that the shock compressibility data of both samples are approximated by a single shock Hugoniot within the experimental error. A kink on Hugoniot recorded close to 25 GPa pressure indicates a chemical decomposition in epoxy resin. Above this kink, a change in the shock wave front structure was recorded. Hugoniots of epoxy resin and unidirectional carbon/epoxy composite were compared at up to 370 GPa pressure. [ABSTRACT FROM AUTHOR]

We present the ab initio thermoelastic properties of body-centered cubic molybdenum under extreme conditions obtained within the quasi-harmonic approximation including both the vibrational and electronic thermal excitation contributions to the free energy. The quasi-harmonic temperature-dependent elastic constants are calculated and compared with existing experiments and with the quasi-static approximation. We find that the quasi-harmonic approximation allows for a much better interpretation of the experimental data, confirming the trend found previously in other metals. Using the Voigt–Reuss–Hill average, we predict the compressional and shear sound velocities of polycrystalline molybdenum as a function of pressure for several temperatures, which might be accessible in experiments. [ABSTRACT FROM AUTHOR]

The thermophysical properties and elemental abundances of the noble gases in terrestrial materials can provide unique insights into the Earth's evolution and mantle dynamics. Here, we perform extensive ab initio molecular dynamics simulations to determine the melting temperature and sound velocity of neon up to 370 GPa and 7500 K to constrain its physical state and storage capacity, together with to reveal its implications for the deep interior of the Earth. It is found that solid neon can exist stably under the lower mantle and inner core conditions, and the abnormal melting of neon is not observed under the entire temperature (T) and pressure (P) region inside the Earth owing to its peculiar electronic structure, which is substantially distinct from other heavier noble gases. An inspection of the reduction for sound velocity along the Earth's geotherm evidences that neon can be used as a light element to account for the low-velocity anomaly and density deficit in the deep Earth. A comparison of the pair distribution functions and mean square displacements of MgSiO3–Ne and Fe–Ne alloys further reveals that MgSiO3 has a larger neon storage capacity than the liquid iron under the deep Earth condition, indicating that the lower mantle may be a natural deep noble gas storage reservoir. Our results provide valuable information for studying the fundamental behavior and phase transition of neon in a higher T–P regime, and further enhance our understanding for the interior structure and evolution processes inside the Earth. [ABSTRACT FROM AUTHOR]

We report a kind of coiled-up meta-liners with nonuniform cross sections (CMNC), which can efficiently attenuate low-frequency sound waves under grazing flow with a deep subwavelength thickness (e.g., ∼λ/17 at 500 Hz). At a grazing flow Mach number of 0.26, the average transmission loss of the meta-liner is 12.6 dB at 500–1000 Hz, which is twice as much as that of a double-degree-of-freedom acoustic liner of the same size. Physically, the nonuniform cross-sectional distribution and significant cross-sectional area ratio enhances vortex shedding, thus resulting in severe acoustic energy dissipation. The excellent low-frequency acoustic attenuation performance of CMNC is investigated thoroughly with experimental, theoretical, and numerical methods. This work provides an avenue for low-frequency noise reduction in grazing flow scenarios (e.g., in a high bypass ratio turbofan engine). [ABSTRACT FROM AUTHOR]

Isotropic materials are required to adhere to various mechanical principles due to their limited thermal stability. For instance, it is essential for Poisson's ratio to be within the range of −1 to 0.5, and the longitudinal wave velocity must exceed the transverse wave velocity. Nevertheless, perfect crystals, as anisotropic materials, have the ability to defy conventional rules. Through the integration of high-throughput processes and first-principles calculations, a comprehensive exploration of known materials was conducted, resulting in the establishment of a database featuring an extreme anisotropic mechanism. This included the identification of abnormal Poisson's ratios (with the directional Poisson's ratio ranging from −3.00 to 3.67), the discovery of extreme negative linear compressibility, the determination of the upper and lower limits of the sound velocity, and other associated properties. Several materials with abnormal Poisson's ratios (<−1 or >0.5) were listed, and their peculiar mechanical behavior, wherein the volume decreased counterintuitively with uniaxial tension, was discussed. Finally, this study focused on the velocities of longitudinal and transverse waves, with specific emphasis on materials exhibiting transverse wave velocities that exceeded the longitudinal wave velocities. [ABSTRACT FROM AUTHOR]

The motivation of the present study is to gain insights into the evolution of elastic properties of cemented tungsten carbides (WC) shock compressed to 100 GPa. Seven plate impact experiments—two front surface impact and five release wave overtake—are conducted to make simultaneous measurements of Hugoniot states and longitudinal sound speeds in shocked WC with 3.7wt.% cobalt binder. The sound speeds along with estimates for bulk sound speeds, obtained using the Birch–Murnaghan EoS, are analyzed to determine the elastic moduli—longitudinal, bulk, and shear—as a function of Hugoniot stress. The longitudinal and bulk sound speeds at Hugoniot states of interest are found to increase linearly with longitudinal stress. Consistent with the increase in sound speeds, the longitudinal and bulk moduli also increase with Hugoniot stress; however, the increase in longitudinal modulus is modest when compared to predictions of theoretical models that account for pressure and temperature dependence of elastic moduli, but with no damage. The shear moduli remain nearly constant at ∼ 318 GPa over the range of Hugoniot states investigated. These values are, however, much lower than those predicted by the Steinberg–Guinan model with no damage. Poisson's ratio decreases initially from its ambient value of 0.208 to ∼ 0.199 for Hugoniot stress ≤ 10 GPa indicating consolidation of the WC microstructure with low initial stress; however, with an increase in Hugoniot stress to ∼ 100 GPa, Poisson's ratio increases to ∼ 0.317, indicating degradation of shear moduli with increasing stress. The product of density and Grüneisen parameter (ρ Γ), after an initial spike, remains nearly constant for volumetric strains ≥ 0.07. The maximum average temperature rise is estimated to be ∼ 286 ° C at the highest Hugoniot stress employed in the study. [ABSTRACT FROM AUTHOR]

Water is one of the most abundant substances on earth, but it is still not entirely understood. It shows unusual behavior, and its properties present characteristic extrema unlike any other fluid. This unusual behavior has been linked to the two-state theory of water, which proposes that water forms different clusters, one with a high density and one with a low density, which may even form two distinct phases at low temperatures. Models incorporating the two-state theory manage to capture the unusual extrema of water, unlike traditional equations of state, which fail. In this work, we have derived the framework to incorporate the two-state theory of water into the Statistical-Associating-Fluid-Theory (SAFT). More specifically, we have assumed that water is an ideal solution of high density water molecules and low density water molecules that are in chemical equilibrium. Using this assumption, we have generalized the association term SAFT to allow for the simultaneous existence of the two water types, which have the same physical parameters but different association properties. We have incorporated the newly derived association term in the context of the Perturbed Chain-SAFT (PC-SAFT). The new model is referred to as PC-SAFT-Two-State (PC-SAFT-TS). Using PC-SAFT-TS, we have succeeded in predicting the characteristic extrema of water, such as its density and speed of sound maximum, etc., without loss of accuracy compared to the original PC-SAFT. This new framework is readily extended to mixtures, and PC-SAFT-TS manages to capture the solubility minimum of hydrocarbons in water in a straightforward manner. [ABSTRACT FROM AUTHOR]

Cerium is regarded as one of the few metals that exhibit a first-order liquid–liquid phase transition (LLPT). However, despite the theoretical attribution of the LLPT to the localized-itinerant transition of f-electrons, there is still a lack of compelling experimental evidence to support this important scientific inquiry. In this study, we investigate the evolution of sound velocity in molten cerium along the isothermal and isobaric paths under static compression. Drawing parallels with the extensively studied γ–α isostructural phase transition, the V-shaped trend of temperature-dependent sound velocity in liquid suggests the existence of LLPT and identifies an associated mechanism predominating liquids' compressibility. [ABSTRACT FROM AUTHOR]

The viscosity ($\eta $ η) and speed of sound ($u$ u) of binary pentyl acetate (1) + isomers of butanol (2) mixtures were reported at T = 298.15 K to 318.15 K and at 0.1 MPa pressure. Using the experimental data, deviation in viscosity ($\Delta \eta $ Δη), deviation in speed of sound ($\Delta u$ Δu), and excess isentropic compressibility (${\kappa _s}^E$ κ s E ) were determined and these were fitted with the RK equation. The findings suggest that the behaviour of a mixture is affected by intermolecular interactions (dipole – dipole, H – bonding, dispersive, and cohesive force) and structural aspects of the molecule. The $\Delta \eta $ Δη and ${\kappa _s}^E$ κ s E curves were predicted well with the Singh model and ab – initio approach. At each temperature, the ${\kappa _s}^E$ κ s E values were positive for binary mixtures, whereas the $\Delta \eta $ Δη and $\Delta u$ Δu values were negative. The numeric values of $u$ u were determined through numerous correlations. This study delves into the relative importance of these relations with the experimental values of $u$ u. [ABSTRACT FROM AUTHOR]

Changes in pore pressure within geological reservoirs, due to, for example hydrocarbon production, CO2 and energy storage or wastewater disposal, may cause substantial stress changes in the overburden, altering propagation velocities of elastic waves. The corresponding time-shifts are detected and quantified using time-lapse (4-D) seismic analysis. To invert seismic time-shifts for changes in stress and strains, stress sensitivity of rocks is studied in laboratory experiments on core plugs. Such measurements are typically conducted at ultrasonic frequencies. However, previous studies indicate that the stress sensitivity of velocities at seismic frequencies could be higher than that at ultrasonic frequencies. Therefore, calibration based on laboratory ultrasonic data may lead to inaccurate prediction of stresses and strains when applied to 4-D seismic data. To study the influence of frequency on stress sensitivity of acoustic wave velocities, a series of laboratory experiments was performed on two overburden shales with different petrophysical properties. In a low-frequency apparatus—a triaxial pressure cell that combines measurements at low (seismic) and high (ultrasonic) frequencies—the shale samples underwent stress changes with different ratios of horizontal to vertical stress amplitudes to mimic stress variations across the overburden. High-frequency velocity changes were directly recorded, while low-frequency velocity changes were obtained indirectly from the elastic parameters measured at seismic frequency by applying a rock physics inversion using third-order elasticity model. The experiments were conducted at undrained conditions, a representative state for reservoir overburden composed of shales. The results suggest that the stress sensitivities and strain sensitivities (R-factor) of P -wave velocities could be two to four times greater at seismic frequencies than at ultrasonic frequencies. Furthermore, it was found that the previously reported linear relation between the stress sensitivity and stress-path parameter (horizontal/vertical stress change) at ultrasonic frequencies also holds for seismic frequencies. We discuss the theoretical background for frequency-dependent stress sensitivity of wave velocities that supports the experimental findings. The effect of frequency when using laboratory-based calibrations should be taken into account when inverting time-lapse seismic data for changes in stresses and strains. [ABSTRACT FROM AUTHOR]

The materials with a perovskite phase have been in the limelight due to their power conversion efficiency (PSC) in solar cells. New perovskite materials are essential to predict the abundant availability of efficient materials for technological applications. Mechanical properties can predict the mechanical stability of crystals. Therefore, it is very important to know their mechanical parameters. So, in this work, the elastic constants C11, C12 and C44 of the cubic chloride perovskites (ABCl3) have been determined through first principles study using density functional theory by using the Chirpan method integrated with WIEN2k. After calculating the elastic constants, we have also calculated different moduli like Shear, Bulk and Young moduli, different parameters like Kleinman’s constant, Lame constants, Chung–Buessem anisotropy index, universal anisotropic index, acoustic behavior and its anisotropy, hardness, melting temperature, Poisson ratios by using different formulas in connection with the elastic constants. It has been found that the studied compounds possess low resistance to the plastic deformations. It has also been found that the majority of the materials possess a central type of force because Poisson’s ratio is greater than 0.25. It has been studied that six out of eighteen new perovskites were brittle and the rest were ductile. The anisotropy of the materials was checked and found that all the materials are anisotropic elastically. This work is useful for the synthesis of these new perovskites. [ABSTRACT FROM AUTHOR]

We establish local-in-time and global-in-time well-posedness for small data, for a coupled system of nonlinear acoustics-structure interactions. The model consists of the nonlinear Westervelt equation on a bounded domain with nonhomogeneous boundary conditions, coupled with a fourth-order linear equation defined on a lower dimensional interface occupying a part of the boundary of the domain, with transmission boundary conditions matching acoustic velocities and acoustic pressures. While the well-posedness of the Westervelt model has been well studied in the literature, there has been no works in the literature on well-posedness of acoustics-structure interaction models involving the Westervelt equation. Another contribution of this work, is a novel variational weak formulation of the linearized system and a consideration of various boundary conditions. [ABSTRACT FROM AUTHOR]

The strong-field gravity in general relativity (GR) realized in neutron stars (NSs) renders the equation of state (EOS) P (ε) of supradense neutron star matter to be essentially nonlinear and refines the upper bound for ϕ ≡ P / ε to be much smaller than the special relativity (SR) requirement with linear EOSs, where P and ε are respectively the pressure and energy density of the system considered. Specifically, a tight bound ϕ ≲ 0.374 is obtained by perturbatively anatomizing the intrinsic structures of the scaled Tolman–Oppenheimer–Volkoff (TOV) equations without using any input nuclear EOS. New insights gained from this novel analysis provide EOS-model-independent constraints on the properties (e.g., density profiles of the sound speed squared s 2 = d P / d ε and trace anomaly Δ = 1 / 3 − ϕ) of cold supradense matter in NS cores. Using the gravity-matter duality in theories describing NSs, we investigate the impact of gravity on supradense matter EOS in NSs. In particular, we show that the NS mass M NS , radius R , and compactness ξ ≡ M NS / R scale with certain combinations of its central pressure and energy density (encapsulating its central EOS). Thus, observational data on these properties of NSs can straightforwardly constrain NS central EOSs without relying on any specific nuclear EOS model. [ABSTRACT FROM AUTHOR]

The present work discusses the topic of cosmic evolution in an intriguing framework of f(Q)$f(Q)$ theory of gravity (with Q$Q$ as a non‐metricity (NM) scalar which controls the gravitational interaction) by using some recently proposed holographic dark energy (HDE) models. To achieve this goal, the dynamical equations for locally rotationally symmetric (LRS) Bianchi type‐I (BI) geometry are formulated with matter contents as a mixture of dust and anisotropic fluids. By assuming that the time‐redshift relation follows a Lambert function, the cosmological model is constructed by using Rényi HDE (RHDE), Sharma–Mittal HDE (SMHDE) and Generalized HDE (GHDE) as separate cases where Hubble horizon is taken as an infrared (IR) cutoff. Cosmological characteristics of these models are then examined through graphs of energy densities, skewness parameter (γ)$(\gamma)$, deceleration, and EoS parameters. The evolution of the EoS parameter is also studied, i.e., ω′$\omega ^{^{\prime }}$ to discuss the dynamical characteristics of constructed DE models and assess the stability of models via the squared speed of sound parameter. It is found that the ω−ω′$\omega -\omega ^{^{\prime }}$ plane shows the freezing region for RHDE and GHDE models while the thawing region for the SMHDE case. Also, it is concluded that all constructed models exhibit cosmologically viable and stable behavior. [ABSTRACT FROM AUTHOR]

In this work, a time-domain model of the two-dimensional acoustic field in a bubble-containing fluid medium is established. The finite-difference time-domain (FDTD) method is used to simulate sound field bubbly liquids with a non-homogeneous bubble distribution. The distribution of the sound field in two-dimensional space when sound waves propagate in a special equivalent medium is analyzed in detail. The results show that bubbles affect not only the speed of sound and attenuation of sound waves in the medium but also the nonlinear phenomenon can be clearly observed during numerical analysis. [ABSTRACT FROM AUTHOR]

This paper considers the problem of flying a UAV along a given trajectory at speeds close to the speed of sound and above. A novel pitch channel control system is presented using the example of a trajectory with rapid and large changes in flight height. The control system uses a proportional–integral–differential (PID) controller, whose gains were first determined using the Ziegler-Nichols II method. The determined gains were then optimised to minimise height error using a recurrent back-propagation neural network (PIDNN), with which new controller gains were determined, which is also a novelty of this study. Simulations were carried out for flights at subsonic speeds close to the speed of sound and supersonic speeds, at low and high altitudes. The simulations showed that determining controller gains using a recurrent neural network significantly minimises height errors and increases the flexibility of the PID controller. [ABSTRACT FROM AUTHOR]

Negative velocity discontinuities are often observed at the base of the D'' layer, yet their formation mechanisms remain elusive. Here, we present the first investigation of thermoelastic properties of SiO2‐seifertite under 30–200 GPa and 1,000–4,000 K using first‐principles molecular dynamics simulations. We find that the compressional and shear wave velocities of seifertite are 2.0%–4.3% and 7.4%–11.3% lower, respectively, than those of CaCl2‐type SiO2 in the D'' layer. The reductions in VS across the phase transition are significantly larger than previous estimates from density functional theory results. Incorporating the elastic properties of other minerals, we demonstrate that the presence of SiO2 in the accumulated subducted oceanic crust and the associated VS reductions can contribute to the negative velocity discontinuities observed in the D'' layer. The observed low seismic velocities at the base of the lower mantle can be matched if 19–27 vol.% SiO2 is present in the D'' region. Plain Language Summary: Geochemical and seismic observations suggest that subducted oceanic crust can accumulate at the core‐mantle boundary, but its effects on the seismic velocity of the D'' layer remain poorly constrained. In fact, the thermoelastic properties of seifertite, which is a major mineral in the deeply subducted oceanic crust at the lowermost mantle, have not been previously investigated at high pressure‐temperature conditions. Using first‐principles molecular dynamics simulations, we computed the thermoelastic properties of seifertite under high pressures and temperatures up to 200 GPa and 4000 K. Our findings shows that seifertite has lower compressional and shear wave velocities than the CaCl2‐type SiO2, but has slightly higher density and bulk sound velocity. Thus, the reductions in VS of SiO2‐bearing mantle assemblages, such as the subducted oceanic crust, upon transition from CaCl2‐type SiO2 to seifertite, could contribute to the negative velocity discontinuities observed in certain regions of the D'' layer. Key Points: Thermoelastic properties of seifertite were determined using first‐principles molecular dynamics simulationsSeifertite has lower compressional and shear wave velocities than the CaCl2‐type SiO2 in the D'' layerCombined effects of SiO2 phase transition and temperature increase may lead to large shear velocity reductions in the D'' layer [ABSTRACT FROM AUTHOR]

The bar properties (elastic modulus, density, Poisson's ratio, and sound speed) necessary for exploiting bar impact tests were calibrated via two methods called the 1D method (which combines the iterative dispersion correction with 1D approximation) and 3D method (which resorts to the simulation-based reverse engineering of the strain profile in a circular 3D bar). The two methods cross-verified one another for a maraging steel bar with 19.1 mm in diameter. This paper also considers the method of calibrating measured strain and finally presents a method of determining the impact velocity with reference to a reliably measured strain profile for a bar calibrated via the 1D method. [ABSTRACT FROM AUTHOR]

Acoustic tweezers can trap and manipulate a target along a desired path without physical contact. Potential applications of this technology may require the propagation of acoustic waves through non-homogeneous media. It is typically assumed that the acoustic impedance of media is the same. However, this assumption leads to reduced efficiency in both the trapping accuracy and strength of the acoustic tweezers. In this study, we propose a method to derive phases driving an 8x8 array of ultrasonic transducers using generalized Snell's law to account for the variation in the speed of sound between media layers of planar or non-planar interfaces. The results indicate that the tweezers formed with our approach maintain their patterns and trapping capability at selected trapping locations. In addition, our method significantly enhances the trapping accuracy and force, achieving up to ten times greater force and more accurate alignment with the selected trapping points compared to the previous method that assumes a uniform speed of sound. [ABSTRACT FROM AUTHOR]

Based on experimental data from the deep-sea sound channel axis in the Western Pacific, the statistical distribution law of cluster structure and channel delay spread characteristics are analyzed for three typical receiving depths near the sound channel axis in this paper. A ray theory-based underwater acoustic channel model is used to explain the variations in channel parameters over time and the receiving depth. The results indicate that the underwater acoustic communication channel at the channel axis depth over a 20-km range exhibits a clustered structure that depends on the emission angles of sound rays. For the amplitude characteristics, the amplitude of each cluster follows an inverse Gaussian distribution, with the maximum average amplitude observed when the receiver and transmitter depths are similar. The amplitude of each cluster fluctuation decreases as the receiving depth increases. Regarding delay spread characteristics, the delay spread of each cluster, as well as the maximum and root mean square delay spread of the channel, conform to a Gaussian mixture distribution. The mean and fluctuation of the delay spread parameters increase with the receiving depth. Variations in the cluster structure and channel delay spread characteristics above are primarily attributed to the time-varying sound speed along the propagation paths of sound rays emitted at small upward angles. [ABSTRACT FROM AUTHOR]

We reveal the specific structural and bonding features that result in anisotropic thermal transport for CsPbBr3 by directional single-crystal measurements and elucidate the bases for the low Debye temperature and speed of sound. This work enhances the research on perovskites and reveals the structural features governing the thermal properties. [ABSTRACT FROM AUTHOR]

Telecommunication of the next generation demands filters that can operate in the 10 GHz range with sufficient bandwidths. For surface-acoustic-wave (SAW) devices this prerequisite translates into high sound velocities and high piezoelectric couplings. Wurtzite AlN on diamond, which exploits the strong piezoelectricity of AlN with the very high SAW velocity of diamond, has been considered a promising platform. A significant boost (up to a factor of 4) of the piezoelectric response can be obtained by alloying AlN with Sc. Here, the main challenge lies in the synthesis of highly-oriented thin (Sc,Al)N films on diamond. In this work, we aim at establishing a platform for SAW devices using plasma-assisted molecular beam epitaxy for the deposition of Sc0.2Al0.8N on diamond. We investigate the structural properties related to SAW generation gearing towards applications at high frequencies. To this end, we prepare (Sc,Al)N thin films on polished polycrystalline diamond wafers and demonstrate the efficient generation of SAW modes with frequencies up to 8 GHz. Systematic studies of the dependence of the SAW velocity and electromechanical coupling coefficient on the Sc0.2Al0.8N film thickness is presented for various SAW modes. Our result demonstrates the potential of this material combination for future application that requires large bandwidth in the ultra-high frequency range. [ABSTRACT FROM AUTHOR]

As representative compositions of the mold flux used in the continuous casting of steel, the temperature and composition dependence of the thermal conductivity of alkali silicate glasses and melts was investigated in the range of 300–1700 K using molecular dynamics (MD) simulations. MD simulations can exclude disturbances such as radiation, convection, and impurities, and extract only the effect of phonons on the thermal conduction. Thermal conductivity determined by the laser flash (LF) method was reported to be three times higher than that obtained by the unsteady hot wire (HW) method in the high‐temperature range of 1250–1550 K for 33.3Na2O–66.7SiO2 (mol%). This study shows that (1) the thermal conductivity estimated by MD simulations was closer to the experimental value of the LF method than those of the HW method above 1200 K, which suggests that the LF method is reliable and that the effect of radiation on the thermal conductivity is not significant. (2) The decrease in the thermal conductivity measured by the LF method in the range of 1250–1550 K was attributed to the decrease in the bulk modulus of the 33.3Na2O–66.7SiO2 melt. (3) In a series of Na2O–SiO2 melts, the sound velocity calculated by MD decreased with increasing Na2O content, which is consistent with Shiraishi's ultrasonic wave measurements. [ABSTRACT FROM AUTHOR]

We reveal the specific structural and bonding features that result in anisotropic thermal transport for CsPbBr3 by directional single-crystal measurements and elucidate the bases for the low Debye temperature and speed of sound. This work enhances the research on perovskites and reveals the structural features governing the thermal properties. [ABSTRACT FROM AUTHOR]

Density (ρ), and speed of sound (W) of natural mineral waters from the region of south Russia (North Caucasus, Essentuki wells ES№1, ES№2, ES№4, and ES№17) have been measured as a function of temperature. The measurements were made over the temperature range from (278 to 343) K at atmospheric pressure. Anton Paar DSA 5000 М sound-speed analyzer has been employed to the simultaneously measurements of the density and speed of sound of the mineral water samples. The combined expanded uncertainty of the density, speed of sound, atmospheric pressure (P0), and temperature (T) measurements at the 95 % confidence level with a coverage factor of k = 2 is estimated to be ± 0.005 kg∙m-3 (or 0.01 %), 0.1 %, and 15 mK, respectively. The measured temperature behavior of density, and speed of sound for natural mineral waters were compared with the values for pure water (IAPW formulation) and for various binary aqueous salt (NaCl, Na2CO3, Na2SO4, etc.) solutions. The measured values of density, and speed of sound were used to develop correlation models for the temperature and ion species concentration dependences (Riedel’s characteristic constants of the ions determination). The measured properties as a function temperature at atmospheric pressure have been used as a reference data for prediction of the high-pressure thermodynamic behavior. [ABSTRACT FROM AUTHOR]

Bright sources of mega-electron volt (MeV) x-rays have many unique applications, including nuclear physics, radiation oncology, and imaging high areal density systems. High intensity lasers (> 10 18 W cm−2) incident on mm-thick metal targets can deliver MeV x-rays via the bremsstrahlung process, providing sources with ultrashort duration (∼ ps) and small source size (∼ 100 μ m). Here, we report on a reproducible regime of laser-driven MeV x-ray sources, where the x-ray dose can be further increased by 60% by coating the metal target with micrometers of plastic. High fidelity numerical simulations indicate that the interaction is a result of relativistic transparency in the preplasma. Though relativistic transparency is present in both cases, the greater sound speed and smaller ion inertia of the plastic target allow the laser to more deeply penetrate and couple more efficiently to electrons. Radiography with this system demonstrates a resolving power < 300 μ m, important for imaging applications. [ABSTRACT FROM AUTHOR]

This work presents a fundamental equation of state for calculations of the thermodynamic properties of R-1132(E), which is a potential refrigerant for residential or mobile air conditioners. The equation of state has a functional form expressed explicitly in the Helmholtz energy with temperature and density as the independent variables, and the form is fitted to consistent experimental datasets, including the critical parameters, vapor pressure, saturated liquid and vapor densities, (p , ρ , T) behavior, vapor-phase sound speed, and ideal gas isobaric heat capacity. The equation of state is valid between temperatures from 240 K and 400 K, with pressures up to 6.5 MPa. In this range, expected relative uncertainties at the 95 % confidence interval ( k = 2 ) are 0.1 % for liquid densities, 0.4 % for vapor densities, and 0.1 % for vapor-phase sound speeds, except at the saturation states and in the critical region where larger deviations of up to 2 % are possible in densities due to higher experimental uncertainties. The uncertainty in calculated vapor pressures is 0.15 % above 275 K, which is larger at lower temperatures due to their small values. Various plots of derived properties from the equation of state show that the equation exhibits qualitatively correct behavior over wide ranges of temperature and pressure. [ABSTRACT FROM AUTHOR]

This article presents a spatial environmental inversion scheme using broadband impulse signals with deep learning (DL) to model a single spatially-varying sediment layer over a fixed basement. The method is applied to data from the Seabed Characterization Experiment 2022 (SBCEX22) in the New England Mud-Patch (NEMP). Signal Underwater Sound (SUS) explosive charges generated impulsive signals recorded by a distributed array of bottom-moored hydrophones. The inversion scheme is first validated on a range-dependent synthetic test set simulating SBCEX22 conditions, then applied to experimental data to predict the lateral spatial structure of sediment sound speed and its ratio with the interfacial water sound speed. Traditional geoacoustic inversion requires significant computational resources. Here, a neural network enables rapid single-signal inversion, allowing the processing of 1836 signals along 722 tracks. The method is applied to both synthetic and experimental data. Results from experimental data suggest an increase in both absolute compressional sound speed and sound speed ratio from southwest to northeast in the NEMP, consistent with published coring surveys and geoacoustic inversion results. This approach demonstrates the potential of DL for efficient spatial geoacoustic inversion in shallow water environments. [ABSTRACT FROM AUTHOR]

An acoustic propagation experiment was conducted in the western continental shelf of India (off Kollam, Kerala) in water depth of ∼71 m with seafloor consisting of hard sandy sediments. The multipath arrival times are obtained from peaks in acoustic impulse response measurements made on a single hydrophone for two source-receiver ranges of 245 m and 320 m. The arrival times are used for inverting the water column sound speed profile (SSP) utilizing the empirical orthogonal functions (EOFs), which can completely describe large datasets. The EOFs are generated from a seasonal dataset consisting of 12 SSPs collected once every month of the year at the same location. Inversion is formulated as an optimization problem and solved by employing the method of Differential Evolution Algorithm. A ray-theory based forward propagation model is implemented to model multipath arrival times with candidate SSPs, reconstructed from the EOFs as input for the two source receiver ranges. The objective function measures mismatch between the observed and modeled travel time estimates. The SSP estimated from modeled arrival times with EOFs as search space is found to agree reasonably well with in situ SSP for the two ranges. [ABSTRACT FROM AUTHOR]

Confidence intervals of location of calling marine mammals, derived from time differences of arrival (TDOA) between receivers, depend on errors of TDOAs, receiver location, clocks, sound speeds, and location method. Simulations demonstrate Ishmael, a TDOA locator based on uncorrected least squares minimization (ULSM), yields errors with mean, standard deviation, and maximum of 0.1, 0.2, and 0.9 km, respectively, due to sensitivity to inputs and numerical implementation when applied to scenarios with minuscule errors; e.g., five clock-synchronized receivers residing on the vertices of a square with one in its center. This sensitivity can mask other causes of location error due to small uncertainties in receiver location and sound speed. Realistic uncertainties of sound speed up to ±7.5 m/s lead to errors up to 4 km. With unsynchronized clocks and common practice of correcting TDOA from synchronization measurements at the start and end of an experiment, errors of location are 10 to 1000 km. These problems occur because ULSM was not designed to account for all errors. ULSM is also available in PAMGuard and other systems and is used to study behavior and abundance of calling marine mammals. ULSM is briefly compared to another method designed to account for errors. [ABSTRACT FROM AUTHOR]

The present study provides an experimental method for measuring acoustic velocity components (amplitude and spatial phase shift) in the presence of turbulent flows using either low-frequency particle image velocimetry (PIV) or laser Doppler velocimetry (LDV). The approach leverages compressed sensing (CS) principles to overcome the limitations of classical PIV techniques, such as the need for a reference signal for synchronization, large data size and long measurement duration. Theoretical aspects of CS for extracting acoustic components from PIV and LDV measurements are discussed. The proposed method is applied to both PIV and LDV systems, and the results are compared with microphone measurements. The results show the ability of the proposed experimental method to accurately measure acoustic velocity components at different frequencies and sound pressure levels in the presence of turbulent flow. The presented experimental method offers several advantages, including reduced data size, no need for phase-locking measurements and reduced measurement duration. The actual limitation is the need for a low noise-to-signal ratio (NSR). The effects of high NSR can be mitigated by increasing acquisition time in some cases. The non-intrusive nature of the method makes it valuable for aeroacoustic research. Ongoing research focuses on applying the method to higher-order duct modes and investigating its potential for modal decomposition using optical techniques. [ABSTRACT FROM AUTHOR]

The star matter composed of nucleons deep inside compact stars, such as neutron stars, is believed to be very dense, such that various types of new concepts and physical phenomena are naturally expected due to the nontrivial strong correlations between hadrons. The possibility of revealing the hidden scale symmetry in dense baryonic matter has been discussed recently, to uncover the pseudo-conformal phase in dense star matter. In the pseudo-conformal phase, the trace of the energy–momentum tensor becomes density-independent, and the speed of sound approaches the conformal velocity in scale symmetric matter. Interestingly, it is also observed that the effective nucleon mass becomes a density-independent finite quantity, which can be identified as the chiral invariant mass of the parity doublet model, indicating that the parity doubling is an emergent phenomenon. In this paper, we will discuss how parity-doubling symmetry emerges inside the core of a compact star as a consequence of the interplays between ω vector mesons and nucleons (or dilaton, χ , equivalently) and between the chiral symmetry and the scale symmetry. [ABSTRACT FROM AUTHOR]

To refine the melting curve, equation of state, and physical properties of MgO we performed plate impact experiments spanning ∼ ${\sim} $170–250 GPa on <100> ${< } 100 > $ MgO single crystals, preheated to 2300 K. A controlled thermal gradient in ∼ ${\sim} $20 mm long samples enabled radiative temperature (± $\pm $3%–4%) and rarefaction overtake observations (yielding sound speed ± $\pm $2%) close to the hot Mo driver with a free surface below ∼ ${\sim} $2000 K that minimized evaporation. Ta flyers were launched by two‐stage light‐gas gun up to 7.6 km/s and sample radiance was recorded with a 6‐channel (500–850 nm) pyrometer. Shock front reflectivity was measured at 198 and 243 GPa using ∼ ${\sim} $50/50 sapphire beam‐splitters. Most experiments show monotonic increases of shock temperature with pressure, from (168 GPa, 7100 K) to (243 GPa, 9400 K), in good agreement with predictions of our MgO B1 phase equation of state. Measured sound speeds are parallel to but ∼ ${\sim} $10% higher than model predictions for bulk sound speed of solid B1 MgO, confirming ductile behavior of preheated MgO. Two experiments, at 238 and 246 GPa, showed anomalously low shock temperature and sound speed, suggesting melting. Using reported MgO melting data up to 120 GPa and our data at 232–246 GPa, we constructed a maximum‐likelihood Simon‐Glatzel fit. At Earth's core‐mantle boundary pressure (135 GPa), our best‐fit interpolated MgO melting point is Tm=(7.77±0.03)·103 ${T}_{m}=(7.77\pm 0.03)\cdot {10}^{3}$ K. Our proposed melting line falls within the envelope of theoretical predictions but does not completely agree with any particular model curve. Our results reduce the uncertainty on MgO melting temperature at Earth's core‐mantle boundary by a factor of ∼ ${\sim} $17 and provide an anchor for extension to multicomponent systems. Plain Language Summary: Magnesium Oxide (MgO) has the highest melting temperature among the abundant components of rocky planet interiors. Hence its melting temperature extending up to Earth's core‐mantle boundary pressure is a key constraint on deep Earth melting, early planetary evolution, and core‐mantle interactions throughout Earth history. Large rocky exoplanets are tied to MgO melting at even higher pressures. However, discrepancies among proposed melting curves for MgO are immense, with differences of 1000's of K among experimental, semi‐empirical, and computed results. We used a novel shock compression technique to probe states along the melting curve of B1 MgO (periclase) in a key pressure range never before sampled experimentally: single crystals preheated to 2300 K before impact yield shock‐compressed states at high temperature and pressure. We measured shock temperature using radiant light emission and inferred sound speed in the shocked material by observing a release wave overtaking the shock. Decreases in both temperature and sound speed in our highest‐pressure experiments show that we reached and constrained the melting curve. These new data, combined with selected experimental data from lower pressure, define the most accurate melting curve for MgO. This experimentally derived result helps to distinguish among the various published computational predictions and lower‐pressure experimental results. Key Points: Accurate temperature and sound speed data extending up to the melting curve of B1 phase MgO were obtained from 168 to 246 GPaThe new observation of melting, together with previous data up to 120 GPa, allowed us to construct a reliable high‐P melting curve for MgOThe proposed maximum‐likelihood MgO melting curve improves the accuracy at Earth's core‐mantle boundary pressure by a factor of ∼ ${\sim} $17 [ABSTRACT FROM AUTHOR]

An analytical investigation was conducted to examine a linearized heat release response of a premixed annular enveloped M-flame to velocity disturbances. The flame transfer function (FTF) of the M-flame, consisting of a converging and a diverging part with equal tip angles, acts as a low pass filter with frequency in an overall manner. The FTF magnitude of the M-flame exhibits the smallest magnitude, compared with that of a one-sided (converging or diverging) flame subject to acoustic velocity disturbance, and it vanishes at some periodic frequencies in the same manner as the flame tip fluctuation does. The phase of the FTF of the M-flame undergoes some uncertain variations, which are bounded roughly by the phase of each of the inner and the outer part of the flame. The time lag of the FTF of the M-flame is estimated as an average of two characteristic time scales in a low frequency regime, beyond which the time lag is bounded between these two characteristic time scales. [ABSTRACT FROM AUTHOR]

Velocity information is important for describing the motion state of an object. Modern underwater navigation systems use the Doppler effect to extract the absolute velocity to the bottom or relative velocity to the water layer from the acoustic backscattering signal. Suppressing interference from sidelobe coupling is very important to improve the accuracy of phased-array acoustic Doppler Velocity Log (DVL) and to realize autonomous navigation in complex ocean environments. This paper proposes an interference suppression method based on optimizing the correlation delay of the pulse-pair algorithm to reduce the sidelobe coupling interference. The results of simulations and experiments show that the proposed method reduces the effect of sidelobe coupling on velocity measurements by 70% on average, which is expected to be useful for improving the autonomous navigation performance of unmanned vehicles in complex underwater environments. [ABSTRACT FROM AUTHOR]

Since Biot's first work on acoustic waves in non-dissipative solid media, it has been known that the group velocity of bulk acoustic waves coincides with the velocity of wave energy transport. The recent studies on these types of velocities for electromagnetic waves reveal that (i) these can differ, and (ii) the superluminal group velocities may exist. The current research demonstrates that in the case of Lamb waves propagating in sandwich clamped–clamped plates, the group velocity can exceed the largest longitudinal bulk wave velocity, and, moreover, the group velocity can be infinitely large, similarly to electromagnetic waves. [ABSTRACT FROM AUTHOR]

The Airy phase is the frequency at which group velocity of a surface acoustic wave (SAW) attains a stationary value. In turn, a stationary value of the group velocity causes SAW to propagate with a lesser attenuation than at other frequencies. At present, no conditions for the appearance of stationary values of the group velocity are known for dispersive modes of Lamb waves propagating in stratified plates. Herein, the closed form solutions are derived for double zero group velocity (ZGV) belonging to the same Lamb mode. It is also found that the double ZGV leads to the appearance of the Airy phase located between the twofold ZGV. The analysis relies on the Cauchy formalism and the exponent fundamental matrix method. [ABSTRACT FROM AUTHOR]

This paper considers the viscous/inviscid Moore–Gibson–Thompson (MGT) equations with memory of type I in the whole space ℝn$$ {\mathrm{\mathbb{R}}}&#x0005E;n $$. For one thing, associating with a new condition on initial data, we derive the optimal L2$$ {L}&#x0005E;2 $$ estimates and the optimal leading term of the acoustic velocity potential for large time, where we analyze different contributions from viscous, thermally relaxing, as well as hereditary fluids on large time asymptotic behavior for the acoustic waves models. For another, by using the multiscale analysis and energy methods in the Fourier space, we demonstrate the L∞$$ {L}&#x0005E;{\infty } $$ inviscid limits (i.e., as the diffusivity of sound tends to zero), which match our Wentzel‐Kramers‐Brillouin (WKB) expansion of the solution. Finally, we give a further application of our results on large time behavior for the nonlinear Jordan‐MGT equation in viscous hereditary fluids. [ABSTRACT FROM AUTHOR]

The underwater environment introduces uncertainty into the acoustic velocity, which affects the performance of traditional direction of arrival (DOA) estimation methods. This research proposes a cascaded neural network based underwater DOA estimate approach to address this issue. In this method, the cascade neural network is composed of a velocity regressor and a velocity classifier. To determine the estimated value of acoustic velocity, the velocity classifier first breaks down the input data into distinct velocity domains. It then regulates the velocity regression process. Then, the array steering matrix predicted by the blind source separation algorithm is utilized to determine the angle, and the acoustic velocity is modiffed by the cascaded neural network. Eventually, it is possible to derive the DOA estimation value under the calculated acoustic velocity. The suggested method has a high estimation accuracy especially when the acousitc velocity is unknown, as shown by the simulation results. [ABSTRACT FROM AUTHOR]