Decrease In Sound Velocity Research Articles

Equation of State and Spin Crossover of (Al, Fe)‐Phase H

AbstractThe transport of hydrogen into Earth's deep interior may have an impact on lower mantle dynamics as well as on the seismic signature of subducted material. Due to the stability of the hydrous phases δ‐AlOOH (delta phase), MgSiO2(OH)2 (phase H), and ε‐FeOOH at high temperatures and pressures, their solid solutions may transport significant amounts of hydrogen as deep as the core‐mantle boundary. We have constrained the equation of state, including the effects of a spin crossover in the Fe3+ atoms, of (Al, Fe)‐phase H: Al0.84Fe3+ 0.07Mg0.02Si0.06OOH, using powder X‐ray diffraction measurements to 125 GPa, supported by synchrotron Mössbauer spectroscopy measurements on (Al, Fe)‐phase H and δ‐(Al, Fe)OOH. The changes in spin state of Fe3+ in (Al, Fe)‐phase H results in a significant decrease in bulk sound velocity and occurs over a different pressure range (48–62 GPa) compared with δ‐(Al, Fe)OOH (32–40 GPa). Changes in axial compressibilities indicate a decrease in the compressibility of hydrogen bonds in (Al, Fe)‐phase H near 30 GPa, which may be associated with hydrogen bond symmetrization. The formation of (Al, Fe)‐phase H in subducted oceanic crust may contribute to scattering of seismic waves in the mid‐lower mantle (∼1,100–1,550 km). Accumulation of 1–4 wt.% (Al, Fe)‐phase H could reproduce some of the seismic signatures of large, low seismic‐velocity provinces. Our results suggest that changes in the electronic structure of phases in the (δ‐AlOOH)‐(MgSiO2(OH)2)‐(ε‐FeOOH) solid solution are sensitive to composition and that the presence of these phases in subducted oceanic crust could be seismically detectable throughout the lower mantle.

Thermo-physical properties and thermal energy storage performance of two vegetable oils

Sensible heat storage materials are cheaper than latent heat storage materials for small storage volumes. Vegetable oils are cheap and readily available sensible heat storage materials produced locally in most countries in Sub-Saharan Africa. In this paper, the refractive indices, sound velocities, densities, specific heat capacities, and thermal conductivities of Sunflower oil and Roki oil (a blend of Palm oil and Sunflower oil) are determined experimentally. These two vegetable oils are locally produced in Uganda. Isentropic compressibility and thermal expansion coefficient are derived from the physical properties for the first time. The results show the refractive index, sound velocity, density, and thermal conductivity decrease with the increase in temperature, whereas isentropic compressibility, thermal expansion coefficient, and specific heat capacity increase with the increase in temperature for both oils. Roki oil shows higher thermal conductivity values than Sunflower oil at various temperatures. Additionally, an experimental setup to compare the performance of Roki oil and Sunflower oil as sensible heat storage materials for domestic medium temperature applications is presented. Roki oil and Sunflower oil are experimentally compared using charging and discharging experiments. The charging/heating cycles are first simulated with electrical energy followed by experimental tests with solar energy using parabolic dish solar cookers. The thermal comparison is made in terms of the temperature profiles during charging, discharging and heat utilization processes. During charging, the results show that Roki oil attains higher maximum temperatures (170–233 °C) compared to Sunflower oil (160–210 °C). Roki oil shows higher temperatures (71–78 °C) during cooling compared to Sunflower oil (67–76 °C). Roki oil shows higher heat utilization temperatures compared to Sunflower oil. The results provide insights on the utilization of locally available materials in Uganda as sensible heat thermal energy storage which are cheaper than commercial solar heat transfer oils.

Accretion around cloud of strings in 4D Einstein–Gauss–Bonnet black hole

In this paper, we study the accretion process of a charged black hole in the background of cloud of strings in the framework of 4D Einstein–Gauss–Bonnet (EGB) gravity theory. Firstly, the steady spherical accretion process of ideal fluid on 4D cloud of strings EGB black hole is studied from the aspects of the radial velocity, the energy density, the mass accretion rate and the sound speed. Then, the general analytical expressions of the accretion process are determined, and the effects of the black hole parameters on the radial velocity, the energy density, the mass accretion rate and the sound velocity are discussed. When the GB coupling constant increases, the energy density and mass accretion rate increase, and the sound velocity and radial speed decrease. EGB gravity and charge have similar physical effects on the accretion process of black hole.

The porosity dependence of sound velocities in ceramic materials

The porosity dependence of transverse and longitudinal sound wave velocities is studied in statistically isotropic porous ceramics. Based on the model relations for elastic moduli six model relations are constructed for the prediction of the porosity dependence of these velocities. All of them predict a decrease of sound wave velocities with increasing porosity, but the Maxwell / Mori-Tanaka / MMT model leads to unrealistic predictions for high porosity. A velocity ratio function is defined which contains the porosity dependence of the effective Poisson ratio and enables the prediction of longitudinal wave velocities. A comparison with literature data shows that most data lie below the exponential prediction and above the numerical prediction for concave pores. The correlation of the normalized longitudinal wave velocities and relative transverse wave velocities shows that essentially all values are above the highest lower bound and are reasonably predicted by the differential, exponential and self-consistent models.

Investigation of acoustic characterization of ultrasonic air coupling testing of NEPE propellant under strain control

To explore the acoustic characterization of composite solid propellant materials, the wave equation of the viscoelastic body was derived based on the linear viscoelastic constitutive model, and the theoretical relationship between ultrasonic sound velocity and attenuation coefficient, which are closely related to mechanical properties, such as elastic modulus, viscosity coefficient, and complex modulus, was obtained. Ultrasonic air-coupled testing experiments of the NEPE (Nitrate Ester Plasticized Polyether) propellant under different tensile strain states were carried out to obtain the variation law of ultrasonic transmission wave peak amplitude, sound velocity, and attenuation coefficient with strain variables in combination with the variation in propellant porosity under tensile strain. Furthermore, the acoustic parameters with strain and porosity were fitted by the regression equation, and the effect of mesoscopic damage on macroscopic mechanical properties was analyzed. The results show that with the increase in NEPE propellant tensile strain, the porosity increases exponentially. With the increase in porosity, the sound velocity decreases by first polynomials, the wave amplitude decreases by second polynomials, and the attenuation coefficient increases by third polynomials.

Thermal Equations of State of Corundum and Rh2O3 (II)‐Type Al2O3 up to 153 GPa and 3400 K

AbstractIn this study, we present new experimental constraints on the thermal equations of state of corundum and Rh2O3(II)‐type Al2O3 up to 153 GPa and 3400 K using synchrotron X‐ray diffraction in laser‐heated diamond anvil cells. Corundum was observed to transform into a mixture of corundum and Rh2O3(II)‐type Al2O3 at 106 GPa and 2300 K, accompanied by a strong kinetic barrier. The Rh2O3(II)‐type Al2O3 further transforms into the CaIrO3‐phase at 156 GPa and 3700 K. The transition from corundum to Rh2O3(II)‐type Al2O3 along a normal mantle geotherm could lead to a 1.9(5)% increase in density (ρ) but a 0.6(3)% decrease in bulk sound velocity (VΦ). Al2O3 is one of the major components of the anorthositic crust once this old crust was subducted to the deep mantle. Using the obtained thermoelastic parameters, we further modeled ρ and VΦ profiles of primordial anorthositic crust and found that the subducted fate of the primordial anorthositic crust depended strongly on its temperature. Our modeling reveals that primordial anorthositic crust along a normal mantle geotherm could descend to the transition zone but be trapped at the topmost lower mantle with a greater VΦ. Sinking of the anorthositic crust to the lower mantle can only occur along a 500–1000 K colder slab geotherm.

Structure, stress, and mechanical properties of Mo-Al-N thin films deposited by dc reactive magnetron cosputtering: Role of point defects

In this work, the structural and mechanical properties of ternary Mo-Al-N alloys are investigated by combining thin film growth experiments and density functional theory (DFT) calculations. Mo1−xAlxNy thin films (∼300 nm thick), with various Al fractions ranging from x = 0 to 0.5 and nitrogen-to-metal (Al + Mo) ratio ranging from y = 0.78 to 1.38, were deposited by direct-current reactive magnetron cosputtering technique from elemental Mo and Al targets under Ar + N2 plasma discharges. The Al content was varied by changing the respective Mo and Al target powers, at a fixed N2 (20 SCCM) and Ar (25 SCCM) flow rate, and using two different substrate temperatures Ts = 350 and 500 °C. The elemental composition, mass density, crystal structure, residual stress state, and intrinsic (growth) stress were examined by wavelength dispersive x-ray spectroscopy, x-ray reflectivity, x-ray diffraction, including pole figure and sin2ψ measurements, and real-time in situ wafer curvature. Nanoindentation tests were carried out to determine film hardness H and elastic modulus EIT, while the shear elastic constant C44 was measured selectively by surface Brillouin light spectroscopy. All deposited Mo1−xAlxNy films have a cubic rock-salt crystal structure and exhibit a fiber-texture with a [001] preferred orientation. The incorporation of Al is accompanied by a rise in nitrogen content from 44 to 58 at. %, resulting in a significant increase (2%) in the lattice parameter when x increases from 0 to 0.27. This trend is opposite to what DFT calculations predict for cubic defect-free stoichiometric Mo1−xAlxN compounds and is attributed to variation in point defect concentration (nitrogen and metal vacancies) when Al substitutes for Mo. Increasing Ts from 350 to 500 °C has a minimal effect on the structural properties and phase composition of the ternary alloys but concurs to an appreciable reduction of the compressive stress from −5 to −4 GPa. A continuous increase and decrease in transverse sound velocity and mass density, respectively, lead to a moderate stiffening of the shear elastic constant from 130 to 144 GPa with increasing Al fraction up to x = 0.50, and a complex and nonmonotonous variation of H and EIT is observed. The maximum hardness of ∼33 GPa is found for the Mo0.81Al0.19N1.13 film, with nitrogen content close to the stoichiometric composition. The experimental findings are explained based on structural and elastic constant values computed from DFT for defect-free and metal- or nitrogen-deficient rock-salt MoAlN compounds.

Dispersion and Damping of Phononic Excitations in Fermi Superfluid Gases in 2D

We calculate the sound velocity and the damping rate of the collective excitations of a 2D fermionic superfluid in a non-perturbative manner. Specifically, we focus on the Anderson–Bogoliubov excitations in the BEC-BCS crossover regime, as these modes have a sound-like dispersion at low momenta. The calculation is performed within the path-integral formalism and the Gaussian pair fluctuation approximation. From the action functional, we obtain the propagator of the collective excitations and determine their dispersion relation by locating the poles of this propagator. We find that there is only one kind of collective excitation, which is stable at T = 0 and has a sound velocity of v F / 2 for all binding energies, i.e., throughout the BEC-BCS crossover. As the temperature is raised, the sound velocity decreases and the damping rate shows a non-monotonous behavior: after an initial increase, close to the critical temperature T C the damping rate decreases again. In general, higher binding energies provide higher damping rates. Finally, we calculate the response functions and propose that they can be used as another way to determine the sound velocity.

Limit of Fuel Injection Rate in the Common Rail System under Ultra-High Pressures

The common rail injection system with higher injection pressure can improve injection characteristics. However, relevant researches for injection characteristics under ultra-high pressures are insufficient. In this article, the results of experiments with a maximum injection pressure of 390 MPa for nine different injectors of four types are presented. The experiment showed the existence of supercritical pressure during injection. At pressures below the supercritical pressure, the injection quantity increases with increasing injection pressure, however, when the injection pressure is over supercritical pressure, the injection quantity does not increase. According to the experiment results, the supercritical injection pressure is about 300 ∼ 350 MPa. Under ultra-high pressures, fuel is strongly heated and the local sound velocity decreases, and the adiabatic flow velocity reaches the sound velocity. Under supercritical pressure, the injection rate ceases to increase and even begins to fall. The traditional equations for calculating the injection rate cannot correctly describe the injection under ultrahigh pressures. A new mathematic model with considering the fuel heating for describing the injection quantity of compressible fluid was developed, this model is not only suitable for calculating the injection quantity under ultra-high pressures, but under traditional injection pressures.

One-dimensional sonic black holes: Exact analytical solution and experiments

We discuss results of experiments made in the 2000s with two different models of acoustic (sonic) black holes. Both structures provide linear decrease of sound velocity. The first one is a series of rigid discs fixed on a rod and placed inside the tube, diameters of discs gradually increase according to a parabolic law. The second one is a tube where effective density of the medium increases due to mass layers placed inside, the concentration of these layers grows toward the end of the tube. If these structures were “perfect”, the sound velocity would decrease so that the wave would never reach the end of the tube. For imperfect (real) models, small addition of absorbers makes absorption very efficient. What is essential, both structures have exact analytical solutions for the wave propagation equation. We study these theoretical results and juxtapose them with the experiments.

Theoretical model of hydrodynamic jet formation from accretion disks with turbulent viscosity

We develop the theoretical model for the analytic description of hydrodynamic jets from protostellar disks employing the Beltrami-Bernoulli flow configuration of disk-jet structure. For this purpose we extend the standard turbulent viscosity prescription and derive several classes of analytic solutions using the flow parametrization in self-similar variables. Derived solutions describe the disk-jet structure, where for the first time jet properties are analytically linked with the properties of the accretion disk flow. The ratio of the jet ejection and disk accretion velocities is controlled by the turbulence parameter, while the ejection velocity increases with the decrease of local sound velocity and the jet launching radius. Derived solutions can be used to analyze the astrophysical jets from protostellar accretion disks and link the properties of outflows with the local observational properties of accretion disk flows.

Elastic Properties of a FeGe2 Single Crystal

The report presents the results of studying the temperature dependences of the velocities of propagation of longitudinal and torsion waves and the internal friction in a tetragonal FeGe2 single crystal along crystallographic axes [100], [110], and [001]. At temperatures of magnetic phase transitions of T1 ≈ 263 K and T2 ≈ 289 K an abrupt decrease of sound velocities is detected. A high anisotropy of the internal friction is observed in the region of existence of an incommensurate magnetic structure (T1 ≤ T ≤ T2).

Упругие свойства монокристалла FeGe-=SUB=-2-=/SUB=-

The results of the investigation of temperature dependences of longitudinal and torsional sound wave velocities and the internal friction of FeGe2 tetragonal single crystal along [100], [110] and [001] crystallographic axes have been presented. At temperatures of magnetic phase transitions of T1≈263 K and T2≈289 K an abrupt decrease of sound velocities is observed. The profound anisotropy of the internal friction is detected in the region of the existence of incommensurate magnetic structure (T1≤T≤T2).

A simple analysis of Brillouin spectra from opaque liquids and its application to aqueous suspensions of poly-N-isopropylacrylamide microgel particles

Brillouin spectroscopy is a powerful technique to probe the viscoelastic properties of materials. However, the phenomenon of multiple scattering makes getting information from opaque liquids quite difficult, thus limiting the use of this spectroscopy. In this paper we present a new method that greatly simplifies the problem of analyzing Brillouin spectra affected by multiple scattering from samples of moderate opacity. Our approach is based on the observation that multiple-scattered contributions broaden the spectrum acquired in external backscattering geometry, while preserving in the external side the information related to internally backscattered light. The new strategy avoids unnecessary approximations and requires minimum numerical effort to extract physical information. Here, we show the results of two Brillouin light scattering experiments performed on prototypical hard and soft colloidal systems. First, measurements on latex suspensions as a function of depth are used to validate the method and to derive new relations between the back-scattered and multiple-scattered components of the Brillouin spectrum. Second, measurements on poly-N-isopropylacrylamide (PNIPAM) microgels in water as a function of temperature are used as a testing ground to demonstrate the method's capabilities. Our analysis confirms that sound waves are extremely sensitive to the volume-phase transition of thermoresponsive particles. The presented approach, however, shows that a marked increase of attenuation is accompanied by only a moderate decrease of sound velocity. The study revises the viscoelastic properties of PNIPAM suspensions; more generally, it provides a new guideline in the characterization of moderately opaque media and fosters new theoretical investigations.

Continuous Sound Velocity Measurements along the Shock Hugoniot Curve of Quartz.

We report continuous measurements of the sound velocity along the principal Hugoniot curve of α quartz between 0.25 and 1.45TPa, as determined from lateral release waves intersecting the shock front as a function of time in decaying-shock experiments. The measured sound velocities are lower than predicted by prior models, based on the properties of stishovite at densities below ∼7 g/cm^{3}, but agree with density functional theory molecular dynamics calculations and an empirical wide-regime equation of state presented here. The Grüneisen parameter calculated from the sound velocity decreases from γ∼1.3 at 0.25TPa to 0.66 at 1.45TPa. In combination with evidence for increased (configurational) specific heat and decreased bulk modulus, the values of γ suggest a high thermal expansion coefficient at ∼0.25-0.65 TPa, where SiO_{2} is thought to be a bonded liquid. From our measurements, dissociation of the molecular bonds persists to ∼0.65-1.0 TPa, consistent with estimates by other methods. At higher densities, the sound velocity is close to predictions from previous models, and the Grüneisen parameter approaches the ideal gas value.

Effect of soil particle and pore orientations on sound velocity

The main purpose of compressing soil dams, highway constructions, bridge abutments and fillings behind retaining walls is to increase the bearing capacity, reduce consolidation settlement and permeability of clayey soils. However, the soil particles and pore orientation could be somehow anisotropic due to a compaction-induced anisotropic structure. Orientations of particles, pores and other constituents during compaction of a mixed mica schist clayey soil with fly ash were studied to investigate how soil structure, and in turn, sound velocity change during compaction of a cohesive soil at different moisture contents on all three sides at three are perpendicular to each other. Ultrasonic sound velocity measurements of the cube samples compressed in the optimum water content were investigated perpendicular to each other. The results showed that the ultrasonic sound velocity decreased in the compression direction of the soil samples, namely the overall degree of preferred orientation increases as opposed to the compression direction. On the other hand, the overall degree of preferred horizontal orientation increases and ultrasonic sound velocity decreases.

Effect of acoustic impedance matching on kinetics of titanium phase transformation

The phase transition experiments under ramp wave compression of titanium have been done by using a magnetic diven device CQ-4, and the influence of the acoustic impedance of the back surface of titanium on the phase transition has been studied. The experimental results show that when the acoustic impedance of the window is low, free surface or LiF, the particle velocity corresponding to the beginning of phase transition is about 408.9 m/s, while at the high impedance sapphire window, is about 373.9 m/s. The pressures corresponding to the characteristic velocities are not the phase change onset pressures. A simulation was done to well describe this complicated dynamic response including physical models of multi-phase equation of state based on Helmholtz free energy, strength model, and non-equilibrium dynamic equation of phase transition. The calculated results are in excellent agreement with the experimental data, and they exhibit the dynamic physical characteristics of Tin involving the elastoplastic transition and evolution of mass fraction of different phase. The results show that the velocity wave forms of the samples near the loading surface are the same, but the amplitude of the wave forms varies greatly due to the impedance matching of Tin and windows in the vicinity of Tin’s rear surface. The phase transition pressure of Ti is about 10.5 GPa, which is a rate dependent non-equilibrium dynamic process. In the pressure-volume thermodynamic plane, the calculated isentrope coincides with Hugoniot before phase transition, but is below the Hugoniot after phase change. The obvious decrease in sound velocity after phase transition is due to the discontinuity of the specific volume due to phase transition.

Elastic properties of a La0.5Pr0.2Ca0.3MnO3 single crystal

The temperature dependences of the velocity of longitudinal sound and internal friction in the ferromagnetic La0.5Pr0.2Ca0.3MnO3 single crystal with magnetic first-order phase transition were studied. It was found that the sound velocity decreases by ≈20% in transition from the ferromagnetic to paramagnetic state. In the paramagnetic region, the extended temperature hysteresis of the sound velocity and the internal friction was observed. It was shown that La0.5Pr0.2Ca0.3MnO3 has two paramagnetic phases with different sound velocities.

Thermodynamic and acoustical study of zinc oxide-nematic liquid crystals mixtures

Thermodynamical and acoustical studies have been carried out in nematic liquid crystal (8CB) and zinc oxide (ZnO) nanoparticle doped 8CB mixtures. The effect of nanoparticle concentration on the ultrasonic velocity and density has been studied using density and sound velocity analyzer. Adiabatic compressibility, molar compressibility, sound velocity, acoustic impedance and intermolecular free length have been estimated. Density and sound velocity decrease with the increase of the temperature and ZnO concentration, however intermolecular free length increases with increasing the temperature and ZnO concentration. The results have been compared with pure nematic liquid crystal mixture.

Vibration characteristics of rectangular plate in compressible inviscid fluid

This paper presents a mathematical derivation of the vibration characteristics of an elastic thin plate placed at the bottom of a three dimensional rectangular container filled with compressible inviscid fluid. A set of beam functions is used as the admissible functions of the plate in a fluid–plate system, and the motion of the fluid induced by the deformation of the plate is obtained from a three-dimensional acoustic equation. Pressure from the fluid over the fluid–plate interface is integrated to form a virtual mass matrix. The frequency equation of the fluid–plate system is derived by combining mass, stiffness, and the virtual mass matrix. Solving the frequency equation makes it possible to obtain the dynamic characteristic of the fluid–plate system, such as resonant frequencies, corresponding mode shapes, and velocity of the fluid. Numerical calculations were performed for plates coupled with fluids with various degrees of compressibility to illustrate the difference between compressible and incompressible fluids in a fluid–plate system. The proposed method could be used to predict resonant frequencies and mode shapes with accuracy compared to that of incompressible fluid theory (IFT). The proposed method can be used to analyze cases involving high value of sound velocity, such as incompressible fluids. When the sound velocity approaches infinity, the results obtained for compressible fluids are similar to those of incompressible fluids. We also examined the influence of fluid compressibility on vibration characteristics in which a decrease in sound velocity was shown to correspond to a decrease in resonant frequency. Additional modes, not observed in incompressible fluids, were obtained in cases of low sound velocity, particularly at higher resonant frequencies. Fluid velocity plots clearly reveal that the additional resonant modes can be attributed to the compressible behavior of the fluid.