Dispersion Of Sound Waves Research Articles

Analysis of Space Charge Signal Spatial Resolution Determined with PEA Method in Flat Samples including Attenuation Effects

The constant development of the electrical engineering sector, especially in the transmission of electrical energy under high-voltage direct current (HVDC), requires research on new insulation materials and investigations of physical phenomena under ultrahigh electrical fields in solid dielectrics. One of the current problematic issues is the formation of space charge in HV insulation systems, which affects the operational electrical field distribution and can lead to faster insulation degradation. There are several problems that have to be considered before every space charge measurement, such as the attenuation and dispersion of sound waves in tested dielectric materials, reflections at the interfaces, and the spatial resolution of the measured charge profile. The spatial resolution is one of the most important technical factors of the PEA measurement stand. The spatial resolution, as it is assumed, depends on several factors, such as the width of the pulser and the pulse rise time, the thickness of the piezoelectric sensor, and the dispersion of the tested material. The article presents the laboratory measurement results of the impact of pulser parameters, such as pulse width and rise time, and sensor thickness on the equivalent thickness of the measured net charge layer corresponding to the resolution of the method. The dispersion in the tested LDPE material is also presented and analysed. The results show that with an increase in the pulser rise time, a higher resolution of the pea method can be achieved.

Топологические моды в неэрмитовых фононных кристаллах, индуцированных оптически в массиве квантовых ям

We study theoretically propagation of acoustic waves in an array of quantum wells, where a spatially modulated amplification and attenuation of sound is realized by optical excitation with a frequency close to the exciton resonance. The dispersion of sound waves near Bragg resonances corresponding to the modulation wave vector is calculated. The appearance of "imaginary" stop bands, where the imaginary parts of the Bloch mode frequencies are split, is described. The emergence of acoustic topological modes at the edge of the structure is demonstrated.

A Renormalization-Group Study of Interacting Bose–Einstein Condensates: Absence of the Bogoliubov Mode below Four (T > 0) and Three (T = 0) Dimensions

We derive exact renormalization-group equations for the $n$-point vertices ($n=0,1,2,\cdots$) of interacting single-component Bose-Einstein condensates based on the vertex expansion of the effective action. They have a notable feature of automatically satisfying Goldstone's theorem (I), which yields the Hugenholtz-Pines relation $\Sigma(0)-\mu=\Delta(0)$ as the lowest-order identity. Using them, it is found that the anomalous self-energy $\Delta(0)$ vanishes below $d_{\rm c}=4$ ($d_{\rm c}=3$) dimensions at finite temperatures (zero temperature), contrary to the Bogoliubov theory predicting a finite "sound-wave" velocity $v_{\rm s}\propto [\Delta(0)]^{1/2}>0$. It is also argued that the one-particle density matrix $\rho({\bf r})\equiv\langle\hat\psi^\dagger({\bf r}_1)\hat\psi({\bf r}_1+{\bf r})\rangle$ for $d<d_{\rm c}$ dimensions approaches the off-diagonal-long-range-order value $N_{\bf 0}/V$ asymptotically as $r^{-d+2-\eta}$ with an exponent $\eta>0$. The anomalous dimension $\eta$ at finite temperatures is predicted to behave for $d=4-\epsilon$ dimensions ($0<\epsilon\ll 1$) as $\eta\propto\epsilon^2$. Thus, the interacting Bose-Einstein condensates are subject to long-range fluctuations similar to those at the second-order transition point, and their excitations in the one-particle channel are distinct from the Nambu-Goldstone mode with a sound-wave dispersion in the two-particle channel.

Propagation of acoustic waves in multifractional polydisperse gas suspension

The propagation of acoustic waves in multifractional polydisperse gas suspension is studied. A mathematical model is presented, the dispersion equation is obtained, dispersion curves are calculated. The influence of the particle size and the parameters of the dispersed phase for multifractional gas mixture with ice particles, aluminum and sand on dissipation and dispersion of sound waves is analyzed.

Acoustic waves in multifractional gas mixture with the inclusion of different materials and dimensions without Phase Transformations

The propagation of acoustic waves in mixtures of gas and particle fractions of different materials and sizes is studied. A mathematical model is presented, the dispersion equation is obtained, dispersion curves are calculated. The influence of the particle size and the parameters of the dispersed phase for multifractional gas mixture with ice particles, aluminum and sand on dissipation and dispersion of sound waves is analyzed. A comparison with experiment is conducted.

Spatial stochasticity and non-continuum effects in gas flows

We investigate the relationship between spatial stochasticity and non-continuum effects in gas flows. A kinetic model for a dilute gas is developed using strictly a stochastic molecular model reasoning, without primarily referring to either the Liouville or the Boltzmann equations for dilute gases. The kinetic equation, a stochastic version of the well-known deterministic Boltzmann equation for dilute gas, is then associated with a set of macroscopic equations for the case of a monatomic gas. Tests based on a heat conduction configuration and sound wave dispersion show that spatial stochasticity can explain some non-continuum effects seen in gases.

ELECTROSTATIC LOUDSPEAKER CAPABLE OF DISPERSING SOUND BOTH HORIZONTALLY AND VERTICALLY

An electrostatic loudspeaker (ESL) assembly providing curvature in two directions for improved dispersion of sound waves. The ESL comprises at least one stator panel, a flexible diaphragm and a spacer that impedes contact between the stator panel and the diaphragm. The stator is formed from a material that comprises an array of apertures. Furthermore, the material can be annealed. The material temper, along with the aperture geometry and patter, affect the stretchability of the material. The two-axis curved structure enables a compact form of ESL to be realized, including bookshelf type loudspeakers whereas all known commercial units are comparable in height to that of a human listener. The individual curved ESL panels can also be readily combined to create larger transducer assemblies including omni-directional units.

Ultrasonic propagation in molten lithium, sodium and potassium silicates

Velocity and attenuation of ultrasonic wave in molten alkaline silicates of lithium, sodium and potassium were measured at a temperature range between their liquidus and ∼200 K higher than their liquidus. Measurements were carried out by the pulse transmission method using a couple of ultrasonic pulse generator and receiver. Composition of the silicate sample was selected for covering the enough temperature range and for getting the correct knowledge of composition dependence of alkaline silicate. Measured velocity of ultrasound decreases with the increase in temperature in all samples. Composition dependence were similar between sodium and potassium silicates but little different in lithium silicate. Absorption of ultrasound depends both on the sound frequencies and temperatures. It suggests that there is some dispersion of sound waves propagating in the silicate medium. Since the lithium silicate melt behaves in a dissimilar way from those of other alkaline silicates, the authors tried the additional measurement on the pseudobinary system of lithium and sodium disilicate system. The results are discussed from the structural aspect comparing with the previous work on Ni ion colour indicator.

Ioffe–Regel’ crossover and boson peaks in disordered solid solutions and similar anomalies in heterogeneous crystalline structures

Low-frequency features of the phonon spectra of disordered solid solutions and heterogeneous crystalline structures are analyzed at the microscopic level. It is shown that boson-peak type excitations can arise in disordered solid solutions whose sites have only translational degrees of freedom. Thus it is established that such excitations appear mainly because of the additional positional dispersion of sound waves which is due to the disordering. The influence of boson-peak excitations on the low-temperature specific heat is investigated. It is found that in a number of cases the specific heat is more sensitive to excitations of this kind than the low-frequency density of states is. It is shown that anomalies similar to Ioffe–Regel’ crossover and boson peaks can also arise in disordered heterogeneous crystalline structures with a complicated lattice.

Sound propagation in the mixtures of liquid and solid aggregate; similarities at micro- and nanoscales.

Sound propagation phenomena in certain liquid and solid aggregate mixtures, at micrometer scales, in some cases resemble the wave propagation behaviors of materials observed at nanometer and atomic scales. For example, it can be shown that the sound wave dispersion, attenuation, and cutoff-frequency effects depend on the same structural parameters as those observed at nano or atomic levels and are similar at both scales. Therefore, to investigate theoretical models of wave and matter interactions it is more convenient to use, as experimental tools, the readily analyzable models of wave propagation, in mixtures of solid and liquid, constructed at micrometer scales. Theoretical findings on sound propagation in the mixtures of liquid and solid particles at micrometer scales will be discussed. These results show the resemblance to the behavior of acoustic phonons, the lattice thermal vibrations of crystalline structures, at radically different scales. Experimental data on wave dispersion, attenuation, band-pass, and cutoff frequency effects, measured for sound propagation, in inhomogeneous materials consisting of mixtures of solid and liquid will be presented, showing the similarities of wave propagation behaviors at micro- and nanoscales.

Transport properties of cascading gauge theories

Cascading gauge theories of Klebanov et al. provide a model within a framework of gauge theory/string theory duality for a four-dimensional nonconformal gauge theory with a spontaneously generated mass scale. Using the dual supergravity description, we study sound wave propagation in strongly coupled cascading gauge theory plasma. We analytically compute the speed of sound and the bulk viscosity of cascading gauge theory plasma at a temperature much larger than the strong coupling scale of the theory. The sound wave dispersion relation is obtained from the hydrodynamic pole in the stress-energy tensor two-point correlation function. The speed of sound extracted from the pole of the correlation function agrees with its value computed in Phys. Rev. D 72, 066003 (2005), using the equation of state. We find that the bulk viscosity of the hot cascading gauge theory plasma is nonzero at the leading order in the deviation from conformality.

Effect of Air Viscosity on Sound Propagation in Human Bronchial Tree

A physical model of sound propagation in a transitional zone of human respiratory tract has been developed within the long-wave approximation. A basic notice was given to analyzing the influence of viscous interaction between the bronchial air, oscillating owing to acoustic excitation, and bronchial wall. To avoid a considering of the effects of wall compliance and sound radiation into pulmonary parenchyma, within this study the respiratory airways were modeled by the tubes with rigid walls. It is shown that the allowance for air viscosity results in not only attenuation, but also profound dispersion of sound waves propagating in the elements of the bronchial tree. These phenomena rapidly increase with the decrease of the bronchus caliber. Also, the viscosity essentially alters frequency dependencies of the input impedance of terminal bronchioles loaded on the system of respiratory airways. Moreover, the impedance of terminal bronchiole depends on boundary conditions at the entrance of the respiratory tract - the glottis (open or closed vocal chords).

Dynamics of supercooled liquids: densityfluctuations and mode coupling theory

We write equations of motion for density variables that areequivalent to Newton's equations. We then propose a set of trialequations parametrized by two unknown functions to describe theexact equations. These are chosen to best fit the exactNewtonian equations. Following established ideas, we choose toseparate these trial functions into a set representingintegrable motions of density waves, and a set containing alleffects of non-integrability. The density waves are found tohave the dispersion of sound waves, and this ensures that theinteractions between the independent waves are minimized.Furthermore, it transpires that the static structure factor isfixed by this minimum condition to be the solution of theYvon-Born-Green equation. The residual interactionsbetween density waves are explicitly isolated in their Newtonianrepresentation and expanded by choosing the dominant objects inthe phase space of the system, that can be represented by adissipative term with memory and a random noise. This provides amapping between deterministic and stochastic dynamics. Imposingthe fluctuation-dissipation theorem allows us to calculatethe memory kernel. We write exactly the expression for it,following two different routes, i.e. using explicitly Newton'sequations, or instead, their implicit form, that must beprojected onto density pairs, as in the development of thewell established mode coupling theory. We compare thesetwo ways of proceeding, showing the necessity to enforce a newequation of constraint for the two schemes to be consistent. Thus, while in the first `Newtonian' representation a simpleGaussian approximation for the random process leads easily tothe mean spherical approximation for the statics and toMCT for the dynamics of the system, in the second case higherlevels of approximation are required to have a fully consistenttheory.

Sound waves in a rotating solid

The Coriolis force in rotating solids changes the sound wave dispersion. The equations for the propagation of sound are solved for a rotating isotropic elastic medium and the effects of rotation on the wave dispersion are analyzed.

Thermal attenuation and dispersion of sound in a periodic emulsion.

We investigate the attenuation and dispersion of sound waves in suspensions and emulsions caused by the thermal-transport process. They combine to constitute the effective compressibility of the system. We begin with an attempt to justify the Isakovich formula for calculating the effective compressibility. The formula is then rewritten in terms of the interfacial heat flux. Isakovich's analysis is simply an independent-particle approximation. It is the purpose of this paper to consider the effect of interparticle interactions. The effective compressibility is calculated for an array of spherical particles or droplets centered at the points of a periodic lattice, immersed in a fluid of different species. Ewald's method of fast-convergent lattice sums in electrostatics is extended to a technique for the heat-conduction problem in a periodic emulsion. The computation for cubic lattices reveals that the interparticle interactions act to reduce, in the lower-frequency range, both the attenuation coefficient and the departure of the sound velocity from its high-frequency limit. The striking feature is that a drastic change in attenuation occurs when the thermal conductivity of the particle is substantially larger than that of the ambient fluid.

Ultrasonic attenuation in incommensurate solids due to order parameter fluctuations

Abstract A theory for the dispersion and attenuation of sound waves due to amplitude and phase fluctuations of the order parameter in incommensurate solids is developed. Using Langevin equations for acoustic and order parameter modes we obtain a Debye behavior for the elastic response at “high” frequencies and a strongly non-Debye behavior at “low” frequencies due to infrared divergences of simple perturbation theory. The divergences are treated by summing up the leading diagrams of a 1/N expansion where N is the number of components of the order parameter. At low frequencies the dispersion of sound waves is only little affected by the divergences; however their absorption increases dramatically in pure systems, leading to diverging viscosities throughout the incommensurate phase and an anomalous ω3/2 law for the ultrasonic attenuation coefficient. We discuss also how the anomalous elastic response at low frequencies changes if a finite coherence length due to pinning effects is taken into account. Finall...

Combination acoustic conditioner and light fixture

A combination light fixture and acoustic conditioner assembly particularly useful in modular room enclosures wherein the ceiling is spaced above the enclosure walls. The invention provides for indirect lighting means and means for masking external sounds in the vicinity of the light fixture assembly. The assembly includes a reflector positioned so that light and sound waves contacting the reflector are dispersed in a plurality of directions due to the concavity of the reflector and undulations therein and eventually contact the ceiling where they are further reflected and spread. Dispersion of sound waves in this manner provides a pleasant, unintelligible sound which masks external sounds that might otherwise distract occupants of the modular room enclosures.

Method and means for loudspeaker sound wave distribution

A loudspeaker having a totally integrated acoustic system which reduces unwanted cabinet diffraction of the sound waves to minimum; resulting in maximum sound wave dispersion with directional accuracy.

Anomalous absorption and dispersion of sound waves in diethylamine melanin

Longitudinal and shear mechanical relaxation data are reported for a hydration of 20% of synthetic diethylamine melanin. The longitudinal attenuations per wavelength αλ at frequencies between 1 and 5 MHz show an enormously large amount of absorption above room temperature. The amount αλ/2π=0.55–0.95 at a temperature of 60 °C in the frequency of 1 MHz has never been found in usual polymeric substances where αλ/2π∼0.1. The longitudinal data are interpreted in terms of a combined relaxation and resonance process. Measurements of the shear impedance in the temperature range from −10 to +60 °C, with frequencies ranging from 5.2 to 362 MHz, indicate a distribution of relaxation times, represented by the Davidson-Cole spectrum. Temperature dependency of limiting shear modulus is found to obey the Hirai-Eyring equation.

Dynamics of nuclear fluid. IV. Some spin and isospin properties in the hydrodynamical model

In the hydrodynamical model, the nuclear spin and isospin symmetry energies and the speeds of spin sound and isospin sound are pertinent to the determination of the static and dynamic properties of finite nuclei. We examine these quantities with a generalized Skyrme interaction. From the explicit expressions we obtain for these quantities, we find an interesting algebraic relation connecting the symmetry energies and likewise the sound speeds. Relevant collective vibrational energies of various types and different multipolarities are evaluated with the known sets of Skyrme interactions, in order to provide information for future amendments or selections among the sets of interactions and for the confrontation of the hydrodynamical model with experiment. We further investigate the dispersion of sound waves due to the range of the nuclear interaction. In particular, the "plasma oscillation" arising from the long-range Coulomb interaction is found to lead to a simple modification of the energies of the isoscalar and isovector collective vibrational states. When applied to the nuclear giant dipole and monopole resonances, the inclusion of the plasma oscillation gives an improved agreement between the hydrodynamical and the experimental giant dipole state energies and modifies the nuclear incompressibility extracted from measured giant monopole energies by as much as 15%.NUCLEAR STRUCTURE Nuclear hydrodynamical model. Symmetry energies, and their algebraic relations. Speeds of different sound waves, and their algebraic relations. Giant multipole resonances in the hydrodynamical model. Plasma oscillations in finite nuclei. Energy of nuclear giant dipole states. Energy of giant monopole states. Nuclear incompressibility.