Sound radiation from a circular cylinder subjected to elastic collision by a sphere

Sound radiation from a steel cylinder impacted by a steel sphere from the longitudinal or the transverse direction is studied. In order to analyze the vibration of the cylinder, Hertz's theory is incorporated to obtain an approximate value of the contact force. The influence of the impact speed and the slenderness of the cylinder on the radiation of sound waves from the vibrating cylinder is analyzed. An experimental apparatus was constructed and vibrations of the cylinder as well as the acoustic pressure radiated were measured to demonstrate the analytical results. It is shown that, no matter whether dispersion in the wave propagation in the impacted cylinder is significant as in the case of a transverse impact, or not as in the case of a longitudinal impact, a decaying sound pulse is predominantly generated by the rigid motion of the cylinder provided that the product of the contact time T and the fundamental natural frequency of the cylinder ω₁i.e., ω₁T, is larger than 4π, while a periodic sound due to the free vibration of the cylinder is predominant provided that ω₁T is smaller than 4π.     

On sound transmission into a thin cylindrical shell under “flight conditions”

In the context of the transmission of airborne noise into an aircraft fuselage, a mathematical model for sound transmission into a thin cylindrical shell is used to study sound transmission under “flight conditions”: i.e., under conditions of external air flow past a pressurized cylinder at flight altitude. Numerical results for different incidence angles are presented for a typical narrow-bodied jet in cruising flight at 10 660 m (35 000 ft) with interior pressure at 2440 m (8000 ft). A comparison is made between no-flow sound transmission at standard conditions on the ground to sound transmission under flight conditions. It is shown that at M = 0, the cylinder transmission loss has dips at f_R (cylinder ring frequency) and f_c (critical frequency for a flat panel of same material and thickness as shell). Below f_R cylinder resonances affect TL. Between f_R and f_c, cylinder TL follows a masslaw behavior. Flow provides a modest increase in TL in the mass-law region, and strongly interacts with the cylinder resonances below f_R. For normally-incident waves, TL is unaffected by flow.     

Anomalies in the longitudinal ultrasonic attenuation and the velocity variation in the mixed state of a V3Si single crystal

In addition to sharp attenuation peaks of longitudinal sound waves propagating along the [001] axis of a V₃Si single crystal at the upper critical fields H_c2, new large attenuation and broad velocity peaks were observed in the mixed state. The new anomaly is explained by a mechanism related to the anisotropy of flux in the crystal tetragonally deformed by the band Jahn-Teller effect.     

Brillouin scattering in ice and deuterated ice as a function of temperature

The elastic constants c₁₁, c₃₃, c₄₄ for ordinary ice and c₁₁ for D₂O ice between 12 and 250°K are deduced from light scattering Brillouin measurements for sound waves of wavevector q = 2.35 × 10⁵cm^?1. A range of temperature is found between 70 and 130°K where the elastic constants display an abnormal behaviour.     

Ultrasonic attenuation determination of Hc1 and Hc2 for ErRh4B4 at 1.5 K

The attenuation coefficient of longitudinal sound waves propagating in ErRh₄B₄ has been measured as a function of applied magnetic field where the propagation direction (q) of the sound waves was oriented either parallel or perpendicular to H_applied. For both orientations there is evidence of a type II-1 superconducting transition at H_c1 for T ≈ 1.5 K. In addition, when q ⊥ H an increase in attenuation is evident at H_c2, which does not appear when q 6 H, consistent with theories developed by Tachiki et al. utilizing supercurrent screening of the internal magnetic fields.     

Propagation of sound waves through a spatially homogeneous but smoothly time-dependent medium

The propagation of sound through a spatially homogeneous but non-stationary medium is investigated within the framework of fluid dynamics. For a non-vortical fluid, especially, a generalized wave equation is derived for the (scalar) potential of the fluid velocity distribution in dependence of the equilibrium mass density of the fluid and the sound wave velocity. A solution of this equation for a finite   transition period τ$\tau$ is determined in terms of the hypergeometric function for a phenomenologically realistic, sigmoidal change of the mass density and sound wave velocity. Using this solution, it is shown that the energy flux of the sound wave is not conserved but increases always   for the propagation through a non-stationary medium, independent of whether the equilibrium mass density is increased or decreased. It is found, moreover, that this amplification of the transmitted wave arises from an energy exchange with the medium and that its flux is equal to the (total) flux of the incident and the reflected wave. An interpretation of the reflected wave as a propagation of sound backward in time is given in close analogy to Feynman and Stueckelberg for the propagation of anti-particles. The reflection and transmission coefficients of sound propagating through a non-stationary medium is analyzed in more detail for hypersonic waves with transition periods τ$\tau$ between 15 and 200 ps as well as the transformation of infrasound waves in non-stationary oceans.     

Gravitational radiation by a particle with nonzero orbital angular momentum falling into a Kerr black hole

We have computed the energy of the gravitational waves induced by a particle with nonzero orbital angular momentum μL_z plunging into a Kerr black hole in an equatorial plane. It is found that for the same |L_z| a corotating particle emits more energy than a counter-rotating one, which is due to the change of the frequency of the quasi-normal mode with the increase of the angular momentum of the black hole.     

Sound velocity in shallow water bodies with gas-saturated water-bottom (ice) interfaces

Sound velocity variations in shallow water bodies with gas-saturated water-bottom (ice) interfaces are investigated. The effect of air inclusions in water and water-like bottoms (ice) on the velocity of longitudinal sound waves is qualitatively and quantitatively estimated. It is shown that changes in the sound velocity are mainly governed by the radial resonance, which at low frequencies depends on the quality factor of the zeroth mode of bubble oscillation. For real concentrations of bubbles, the velocity of longitudinal waves may become very low. This may lead to considerable distortions of boundary conditions at rough surfaces and, hence, to enhancement of scattering and absorption of sound waves and additional leakage of acoustic energy into the bottom (ice), as well as considerable changes in the sound velocity profile in surface layers with a change of sign of the velocity gradient from negative to positive, which results in the formation of a subsurface channel or an increase in its power. It is found that water-like bottoms (sediments) and ice (“liquid” ice), which are characterized by shear wave velocities of an order of 15 m/s or less, behave in the kilohertz range almost as a vacuum (C _l → 0) when the air content in them reaches several percent. As a result, the propagation of first normal modes in shallow water or in subsurface layers of arctic and oceanic waveguides noticeably changes.     

Generating mechanism of the energy-stream loops for the evanescent waves in a left-handed material slab

The generating mechanism of the energy-stream loops (ESLs) for the evanescent waves around the interfaces of a left-handed material (LHM) slab has been investigated with a finite-difference time-domain (FDTD) method. The simulations have shown that these ESLs originate from standing waves, attributed to the intervention of counter-propagating evanescent waves. Large numbers of ESLs can appear because of the numerous values of wave vectors k_y. The larger ESLs die out more quickly than the smaller ones in time after the source is switched off, the ESLs shrink continuously with increasing delay, and the oscillated distributions of the evanescent waves between the surfaces can also be validated. It is greatly helpful for the further comprehension on energy fluxes of evanescent waves in the LHM slab.     

Ultrasonic attenuation anomalies at the two transitions in antiferromagnetic FeGe2

The attenuation of longitudinal and shear sound waves is measured through the Néel temperature, T_N≈286 K, and the lower transition temperature, T_K≈265 K, of FeGe₂. Longitudinal sound with wavevector q along the [100] axis of this tetragonal antiferromagnetic metal shows an attenuation peak at T_N, which is reversibly suppressed by compressive uniaxial stress σ along [010]. The estimated pressure dependence of T_N is dT_N/dp=(?2.8±0.3) mK bar^?1. The peak at T_N shows thermal and stress hysteresis, which suggests that it is associated with domain wall motion and that this transition is first order.     

Influence of superconductivity on the sound propagation in disordered metals

The velocity of sound has been investigated in the disordered metal Nb₂₀Zr₈₀ which contains low energy excitations. From measurements in the superconducting as well as in the normal state the interaction between these excitations and conduction electrons has been studied in detail.     

Nonlinear drift waves in a plasma with Ti⪢Te

It is found that nonlinear ion drift waves in a plasma with ion temperature much larger than the electron temperature (T_i?T_e) satisfy certain well-known model evolution equations. The nonlinear development of the ion waves as well as their turbulent behaviour is therefore known in the light of these equations.     

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.     

Temperature-dependent Brillouin scattering studies of surface acoustic modes in Nd0.5Sr0.5MnO3

Brillouin scattering experiments are carried out to study the surface acoustic waves in Nd_0.5Sr_0.5MnO₃ as a function of temperature in the range of 40-300 K covering the metal-insulator and charge-ordering phase transitions. The surface modes include surface Rayleigh wave, pseudo-surface acoustic wave (PSAW) and high velocity PSAW. The observed softening of the sound velocities for the surface modes below paramagnetic to ferromagnetic transition, T_c is related to the softening of the C₄₄ elastic constant. The subsequent hardening of the sound velocity below the charge ordering transition temperature T_co is attributed to the coupling of the acoustic phonon to the charge ordered state via long range ordering of the strong Jahn-Teller (JT) distortion.     

Phase shift analysis of Kp scattering

We have analyzed data on K⁺p elastic scattering at 21 momenta covering the range 0.5–2.5 GeV/c. We present results of three phase shift analyses. One of these is an energy independent accelerated convergence expansion (ACE) analysis in which high partial waves are included through use of conformal mapping as suggested by analytic approximation theory. The other two are an energy independent and an energy smoothed conventional analysis. The ACE method gave, with the same number of parameters, a 20% average improvement in x² as well as more unique phase shift solutions. The high partial waves gave significant contributions to total and inelastic cross sections. The ACE method is also sensitive to the value of g_ΛΣ² = g_KΛN² + g_KΣN²; we have obtained the value g_ΛΣ² = 15.2 ± 2.3.     

Shock waves and mach cones in fast nucleus-nucleus collisions

Mach shock waves and head shock waves occur during the interpenetration of a light high energetic nucleus with a heavy one. Collisions of¹⁶O,¹²C and⁴He ions at energies between 0.25 and 2.1 GeV/N with Ag and Cl nuclei have been investigated. The theoretical concepts and the experiment are presented and interpreted. From that a velocity of first sound in nuclear matterc _s ≈0.19c, a Mach shock velocityv _s ≈0.58c and a nuclear compression constantK=300 MeV are deduced.     

Influence of magnetic fields on sound velocity of V3 Si

It is found that the velocity of longitudinal sound waves propagating along [100] of a single crystal of V₃Si increases quadratically with magnetic field and the relative change Δν/νH² by magnetic field has a maximum value at 35 K.     

The anisotropy of the basic characteristics of Lamb waves in a (001)-Bi<Subscript>12</Subscript>SiO<Subscript>20</Subscript> piezoelectric crystal

The orientation dependences of the phase velocity, the effective electromechanical coupling coefficient, and the angle between the wave normal and the energy flux vector are numerically calculated for zeroand first-order Lamb waves propagating in the (001) basal plane of a Bi₁₂SiO₂₀ cubic piezoelectric crystal. It is shown that the anisotropies of these modes are different and depend on the plate thickness h and the wavelength λ. For h/λ < 1, the mode anisotropy can exceed the anisotropy of the corresponding characteristics of surface acoustic waves propagating in the same plane; for h/λ > 1, it approximately coincides with the SAW anisotropy for all the characteristics.     

Rectification of the dipole force in a monochromatic field created by elliptically polarized waves

The rectification of the force of induced light pressure in laser fields formed by elliptically polarized running waves in zero magnetic field is considered. Explicit analytic expressions for the induced and spontaneous forces of light pressure exerted on a stationary atom are obtained for two classes of closed optical transitions: J _g=J→J _e=J+1 and J _g=J→J _e=J (J is half-integral), where J _g and J _e are the total angular momenta of the ground and excited energy levels. It is shown that the ellipticity of waves is the necessary condition for the emergence of the rectification of the induced force in a monochromatic field. The optimal parameters of the field and the maximum rectification coefficient are calculated for a number of optical transitions. The dependence of the rectified force on the velocity is investigated analytically and numerically for the simplest 1/2→1/2 transition.