First and second sound in cylindrically trapped gases

We investigate the propagation of density and temperature waves in a cylindrically trapped gas with radial harmonic confinement. Starting from two-fluid hydrodynamic theory we derive effective 1D equations for the chemical potential and the temperature which explicitly account for the effects of viscosity and thermal conductivity. Differently from quantum fluids confined by rigid walls, the harmonic confinement allows for the propagation of both first and second sound in the long wavelength limit. We provide quantitative predictions for the two sound velocities of a superfluid Fermi gas at unitarity. For shorter wavelengths we discover a new surprising class of excitations continuously spread over a finite interval of frequencies. This results in a nondissipative damping in the response function which is analytically calculated in the limiting case of a classical ideal gas.     

Transmission of complex sound signals in the human respiratory system as a function of sound velocity in the utilized gas mixture

The previously revealed effect of the simultaneous existence of two sound transmission paths in human lungs is confirmed on an expanded sampling of 25 people for three different types of sounding signals during respiration of three gas mixtures. The obtained dependences of sounding signal arrival times above the trachea and the lower right zone of the lungs on sound velocity in the respiratory gas mixture filling human lungs have made it possible to link the first of these paths to partial sound propagation over lumens of respiratory ways (air-structural mechanism), and the second, to sound propagation over lung tissue (structural mechanism). We have evaluated the length of the sound propagation path along the lung parenchyma for the part of the sounding signal transmitted to the lower right zone of the lungs via the air-structural mechanism; this length during respiration is within the limits of 3.6–2.0 cm.     

Experimental estimation of the viscous component of ultrasound attenuation in suspensions of bovine skeletal muscle myofibrils

It has been suggested that viscous losses, caused by the motion of myofibrils relative to their environmental fluid, could be the major cause of ultrasound attenuation in muscle. This Paper presents theoretical and experimental estimates of the viscous component of attenuation in suspensions of myofibrils. Experimental estimates were made by monitoring the effects of varying the viscosity and density of the suspending fluid and ranged from 0.55 to 0.72 cm2 g-1 protein at 7 MHz, when expressed as mass attenuation coefficients. This represented 16-22% of the total attenuation measured in suspensions. Corresponding theoretical calculations were lower: 0.44 and 0.21 cm2 g-1 protein, respectively, for suspensions with the myofibrils aligned along and across the direction of sound propagation. It was concluded that most of the attenuation was caused by other absorption processes.     

Lattice-Boltzmann Simulation of Particle Suspensions in Shear Flow

Inclusion of short-range particle–particle interactions for increased numerical stability in a lattice-Boltzmann code for particle-fluid suspensions, and handling of the particle phase for an effective implementation of the code for parallel computing, are discussed and formulated. In order to better understand the origin of the shear-thickening behavior observed in real suspensions, two simplified cases are considered with the code thus developed. A chain-like cluster of suspended particles is shown to increase the momentum transfer in a shear flow between channel walls, and thereby the effective viscosity of the suspension in comparison with random configurations of particles. A single suspended particle is also shown to increase the effective viscosity under shear flow of this simple suspension for particle Reynolds numbers above unity, due to inertial effects that change the flow configuration around the particle. These mechanisms are expected to carry over to large-scale particle-fluid suspensions.     

双横波声速法检测单向受压混凝土构件永存应力*

该文力求寻找一种高效准确检测混凝土构件永存应力的方法。基于声弹性理论提出了一种双横波声速法检测单向受压混凝土构件永存应力的方法,该方法通过测试受力构件第一波速和第二波速,以第一波速和第二波速的平方差为基础构建综合声学参数来检测单向受压混凝土构件永存应力。所述第一波速为声波传播方向与应力方向垂直、质点振动方向与应力方向平行的横波波速,第二波速为声波传播方向及质点振动方向均与应力方向垂直的横波波速。实验结果显示,该声学参数用于检测混凝土单向受压构件永存应力的效果与使用单一声速参数相比,对应力的敏感性有所提高,受混凝土黏滞性及材质离散性的影响更小,并且测试结果基本不受温度和湿度变化影响。     

Hysteresis curves and loops for harmonic and impulse perturbations in some non-equilibrium gases

Evolution of sound in a relaxing gas whose properties vary in the course of wave propagation, is studied. A relaxing medium may reveal normal acoustic properties or be acoustically active. In the first case, losses in acoustic energy lead to an increase in internal energy of a gas similarly as it happens in Newtonian fluids. In the second case, acoustic energy increases in the course of sound propagation, and the internal energy of a medium decreases. Variations in the internal energy of a gas are proportional to some generic parameter, the sign of which is responsible for acoustical activity, and depends on intensity and shape of the sound waveform. Hysteresis curves in the plane of thermodynamic states are plotted. Curves for harmonic and several aperiodic sound impulses are plotted, discussed and compared.     

Ultrasonic waves in diluted and densified suspensions

A theory of propagation of stress waves in diluted and densified suspensions is developed to make the theoretical basis for analysis of ultrasonic waves through these media. The formulae for the phase velocity and the attenuation coefficient are determined as the function of wave frequency and the suspension structure parameter, which is the volume or mass fraction of the solid phase. These formulae can be use, after suitable calibration, for determination of the solid volume fraction in diluted suspensions, and the solid mass fraction or the water content in densified suspensions, that is, parameters that characterize the structure of a suspension. These structure parameters can be determined by measuring the transition time of ultrasonic wave through a given distance of suspension. The phase velocity dispersion curves and the attenuation coefficients determined theoretically and experimentally are plotted as a function of the volume fraction of the solid phase for dilute suspension, or the solid mass fraction for densified suspension.     

Ultrasonic waves in diluted and densified suspensions

A theory of propagation of stress waves in diluted and densified suspensions is developed to make the theoretical basis for analysis of ultrasonic waves through these media. The formulae for the phase velocity and the attenuation coefficient are determined as the function of wave frequency and the suspension structure parameter, which is the volume or mass fraction of the solid phase. These formulae can be use, after suitable calibration, for determination of the solid volume fraction in diluted suspensions, and the solid mass fraction or the water content in densified suspensions, that is, parameters that characterize the structure of a suspension. These structure parameters can be determined by measuring the transition time of ultrasonic wave through a given distance of suspension. The phase velocity dispersion curves and the attenuation coefficients determined theoretically and experimentally are plotted as a function of the volume fraction of the solid phase for dilute suspension, or the solid mass fraction for densified suspension.     

稠密可压缩气粒两相流动中的等熵声速计算建模及物理规律

气体相与颗粒相混合流场的声速研究, 由于具有重要的基础理论价值与广泛的工程应用背景, 逐渐受到人们重视. 针对稠密可压缩气粒两相流动, 综合考虑颗粒相所占空间体积以及颗粒间相互作用, 推导给出了新的等熵声速计算公式; 新公式包含了已有的纯气体、稀疏气粒两相流情形的计算公式作为其特例, 一方面验证了公式推导的正确性, 另一方面说明新公式更具有通用性; 分析了不同颗粒质量分数条件下的声速变化规律, 相应结果与普朗特的理论分析符合, 特别对于稠密气粒两相流动工况得到了一些新的物理认识; 开展了颗粒间相互作用建模参数的物理分析, 揭示了其对气粒两相流动声速的影响机理. 本文取得的成果为稠密可压缩气粒两相流动研究以及相关工程应用提供理论支撑.     

Polarization and transmission of microwaves in the magnetic suspension in the applied magnetic field

The production method of magnetic suspension consisting of ferromagnetic particles dispersed in cedarwood oil is presented at the beginning of this article. Next, the set-up for microwaves generation using a klystron is described. The main part of this paper concerning microwave transmission and polarization during its passage in samples of the produced magnetic suspension placed in a magnetic field is based on the following parameters: induction of this field, filling factor of magnetic suspension by ferromagnetic particles, dimensions of particles, viscosity of liquid carrier, and ratio of the magnetic field changes. Conducted investigations show that microwaves are damped and polarized in these magnetic suspensions. Obtained results are discussed and observed effects are explained by ordering of ferromagnetic particles in magnetic suspension by applied magnetic field.     

Sound waves in a nonequilibrium molecular gas

We consider relaxation processes of dynamics of a nonequilibrium vibrationally excited gas (T_v>T₀). It is shown that the effective heat capacities can become negative in such a medium. This leads to anomalous effects during propagation of long-wave sound: there exist regions (in the parameter T_v/T₀) of sharp enhancement and reduction of its speed, as well as regions where low-frequency sound can generally not propagate. Instability conditions are investigated for various temperature dependences of vibrational relaxation times. It is shown that in a certain region of T_v/T₀ values one has amplification of sound waves, related to the formation of second viscosity in these media. In this case a change in the amount of medium nonequilibrium can vary the sound frequency corresponding to maximum amplification.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–58, July, 1986.     

Sound Attenuation in a Circular Duct of a Viscous Medium in the Absence of Mean Flow

Abstract

An analytical method to study the effect of viscosity of a medium and the wave number on sound propagation and sound attenuation numbers in circular ducts has been presented. The method is based on the variation of parameters of the solution corresponding to the case of inviscid acoustic waves in circular ducts and axisymmetric modes. A mathematical model is constructed to describe the physical problem in general. Three basic assumptions have been considered, namely, each flow quantity has been written as the sum of a steady mean flow and an unsteady acoustic flow quantity. The effect of thermal conductivity of the gas has been neglected as well as no mean flow. The results for a wide range of wave numbers and Reynolds numbers show that for a viscous medium, the propagation number is a weak function of the Reynolds number, and as the Reynolds number increases, the propagation number approaches its inviscid value. Also the propagation number is independent of the wave number. For the attenuation number, it decreases monotonically with the increase of the Reynolds number and it vanishes when Reynolds number exceeds 10⁴.     

Viability of yeast cells in well controlled propagating and standing ultrasonic plane waves

Recent studies have shown that there is no loss of cell viability when the cells are subjected to ultrasonic standing wave fields in acoustic cell retention systems. These systems are characterised by waves that spatially vary in pressure amplitude in the direction of sound propagation. In this work an anechoic 'one-dimensional' sonication chamber has been developed that produces propagating waves, which differ from standing waves in that the pressure amplitude remains constant as the wave travels in a medium with negligible attenuation. The viability of yeast cell suspensions as a function of treatment time was investigated during exposure to both standing and propagating wave fields with frequencies slightly above 2 MHz. The influence of 12% (vol/vol) of ethanol in water on the spatial arrangement of the cells in suspension was also studied. Changes in yeast cell morphology caused by the different types of suspension media and the ultrasonic treatment were examined by transmission electron microscopy (TEM). The agglomeration of yeast cells within the pressure nodal planes appears to minimise damaging effects due to ultrasonic fields.     

Energy and momentum of sound pulses

The energy and momentum of three-dimensionally localized sound pulses are shown to be constant in time for propagation in fluids of negligible viscosity. Further, the energy always exceeds the product of the momentum and the speed of sound. This property follows from the fact that three-dimensionally localized pulses are necessarily converging or spreading (they have a focal region). A consequence of this convergence/divergence is that the associated pressure gradient, density gradient and particle velocity are not purely longitudinal, as they are for pulses localized in only one dimension. The velocity remains curl-free up to second order, however. Analytic values of energy and momentum are obtained from a particular localized solution of the wave equation.     

Elastic waves in suspensions

A model of heterogeneous medium taking into account the friction between the particles and liquid, as well as the relaxation of the small-size particles to the equilibrium on the stress, has been proposed to describe the propagation of the elastic waves in a suspension. A system of wave equations describing the propagation of a plane longitudinal wave has been formulated for the components of the medium. Analytical expressions for the sound velocity in a suspension has been obtained in the approximation in which the particles are completely carried away by liquid in the limiting cases in which the particles are in equilibrium under stress with the liquid or equilibrium is absent. The dependence of the sound velocity in the medium on the volumetric portion and the size of the inclusions has been studied. The obtained results agree with the experimental data and obtained analytical expressions for the sound velocity. The dynamics of the components of the medium at the propagation of the plane longitudinal monochromatic wave has been studied.     

Sound propagation and relaxation processes in the isotropic phase of cholesteryl miristate

The propagation and absorption of high-frequency sound in the isotropic phase of cholesteryl miristate is studied in a wide frequency range using the data of both Brillouin spectroscopy and acoustooptic measurements. The parameters of the relaxation process associated with the volume viscosity relaxation are calculated using the experimental data on the velocity and absorption of sound.     

Photoelektrische Registrierung der Linienprofile thermisch angeregter He I-Linien

The self-energies defined in a preceding paper are calculated explicitly for a dilute Bose gas with weak repulsive interaction. The transport equations are written down and the coupled system of kinetic equations are solved in order to calculate the propagation of normal and second sound.     

含气泡液体中的非线性声传播

考虑到分布在液体中的气泡是声波在含气泡液体中传播时引起非线性的一个很重要的因素,本文研究了声波在含气泡液体中的非线性传播.将气体含量的影响引入到声波在液体中传播的方程中,从而得到声波在气液混合物中传播的数学模型.通过对该模型进行数值模拟发现,气体含量、驱动声场声压幅值及驱动声场作用时间均会影响到气液混合物中的声场分布及声压幅值大小.液体中的气泡会"阻滞"液体中声场的传播并将能量"聚集"在声源附近.对于连续大功率的驱动声场来说,液体中的气泡会"阻滞"气液混合物中声场及其能量的传播.