Visualization of surface acoustic wave scattering by dislocations

Stroboscopic X-ray topography at the synchrotron beam line was used to visualize the propagation of a 580 MHz surface acoustic waves (SAW) in LiNbO3 crystals. For this purpose, the X-ray bursts coming from the synchrotron storage ring with periodicity of 5.68 MHz were synchronized with the SAW frequency in a phase-locked mode. This method allowed us to "stop" the SAW in time and to observe the X-ray diffraction contrast caused by the dynamic deformation field of SAW. The X-ray topographic images showed well-resolved individual acoustic wave fronts of 6 microm SAW as well as their distortions due to SAW scattering by linear dislocations. Some of the images revealed an exceptional contrast of the concentric rings about the dislocation line, which is caused by coherent interaction of the secondary elastic waves. This contrast is similar to the Fresnel zones in optics, and this conclusion is confirmed by direct summation of secondary waves emitted by local elements of a vibrating dislocation string.     

New visualization method of progressive acoustic wavefronts using a Köster prism

Visualization of a progressive acoustic wave is explained and verified experimentally. A Köster prism set in an image-forming system works so that the optical wave fields emerging from two points across the exit plane of an acoustic column may be superposed at a point in the image plane. The image intensity changes with a period of half the acoustic wavelength magnified suitably. The visibility of the image intensity takes values between 0 and 0.54 if the acoustic power is made to change. No practical frequency limitation is present in the lower frequency range of the acoustic wave.     

Visualization of human umbilical vein endothelial cells by acoustic microscopy

The morphology and acoustic properties of the human umbilical vein endothelial cells (HUVECs) were evaluated using a scanning acoustic microscope system. HUVECs were cultured for 4 days and exposed to the endotoxin for 4 h. The frequency of the scanning acoustic microscope was variable between 100 and 210 MHz. By changing the measuring frequency, ultrasonic amplitude and phase were measured and the quantitative value of attenuation was calculated. Before and after endotoxin stimuli, HUVECs were observed by scanning acoustic microscopy and the attenuation was measured. The acoustic images were successfully obtained to identify the outer shape of the HUVEC and the location of the nucleus in the cell. The attenuation of the nucleus is higher than that of the cytoplasm. The attenuation of the cytoplasm was increased and became inhomogeneous after endotoxin exposure. This finding would be related to the change of F-actin filaments, which is the main component of the cytoskeleton. Scanning acoustic microscopy is useful for assessing the cellular viscoelastic properties since it can detect both the morphological and acoustic changes without contacting the cellular surface.     

用阴影法观察水声模型的声场

我们建立了一套用于显示模拟海底反射声场的光学系统。实验水声模型是由水-玻璃粉-玻璃-铝组成的三层模拟海底结构,声源是一个管状换能器,其轴线平行于分界面。实验用这套系统记录了从水下三个界面反射的六组波的声场图像。并且分辨出了它们各自的传播路径。从声场图像也可以得出水-玻璃粉界面、玻璃粉-玻璃界面的面波声速,玻璃粉和玻璃中的体波声速以及它们的厚度,结果与预先测出的参数符合。     

Visualization of shock-vortex interaction radiating acoustic waves

Unsteady compressible flow fields past a wedge and a cone, evolved by propagation and interaction of shock waves, slip lines, and vortices, are studied by shadowgraphs and holographic interferograms taken during the shock tube experiment. The supplementary numerical calculation also presented time-accurate solution of the shock wave physics which was essential to recognize the similarity and dissimilarity between the wedge and the conical flows. The decelerated shock detained by the vortex interacts with the small vortexlets along the slip layer, producing diverging acoustics: this phenomenon is more distinct in the case of wedge flow for a given shock Mach number. The decelerated shock penetrated through the vortex core constitutes a transmitted shock, which eventually merges with the diaphragm shock that bridges the vortex pair/vortex ring. This phenomenon became remarkably salient in the case of conical flow.     

Visualization by means of coherent light sheets: application to different flows

Light-sheet generator systems using a sweeping, focused laser beam and spherocylindrical optical components are described and their respective performances discussed. They allow the visualization of supersonic air flows by means of light scattering. Tomographic recordings give a three-dimensional reconstruction of the flow (especially the stationary structures) and can be realized in real-time.     

Visualization of meiotic events in intact living anthers by means of two-photon microscopy

In this paper we describe the application of two-photon microscopy (2 PM) to the study of meiosis in plants. Fresh, unfixed anthers of Agapanthus umbelatus were briefly incubated on a minimal medium containing the DNA fluorophore DAPI. DAPI incorporation took place in about 30 min and nuclei and other DNA-containing organelles kept their fluorescence for more than 24 h. Using PM it was possible to optically section the whole, unfixed anthers to a depth of approximately 200 microm. This was up to the mid sagital section and into the sporogenic tissue. Several meiotic figures were observed with unparalleled resolution. Sequences of nuclear dynamics and division were occasionally observed in the surrounding tissues and epidermal layer of cells. However we could not optimize the procedures up to the level of observing the dynamics of division on the meiotic nuclei as well. We hypothesize that either (1) meiotic cells are sensitive to the reasonably high excitation levels of infrared light needed to attain such penetration in the tissue, or (2) that our incubation procedures are not sufficiently non-invasive for meiosis to remain unperturbed. To the best of our knowledge this is the first report on direct observation of living meiotic cells in plants and establishes the potential of 2 PM for intact organ research.     

Correlation of underwater acoustic signals simultaneously received by omnidirectional and directional means

A comparison of experimental data on the spatial correlation between acoustic signals simultaneously received by an omnidirectional hydrophone and a directional vertical array is carried out. The spatial correlation was measured between the signals received at different distances in a deep ocean. The points of reception were positioned in two convergence zones along the path of sound propagation with a point-to-point distance of about 64 km. Pseudonoise signals were emitted in the frequency range (0.8–2.0) kHz and received by a vertical array, whose beam had a width of ∼2°. Concurrently, multipath signals received with the central hydrophone of the array were recorded. Signals in the first and second convergence zones were received at different times. Nevertheless, in the case of the directional reception, the coefficients of spatial correlation between such signals appeared to be as high as 0.64–0.74 even under the conditions of incomplete resolution of signals in the angle of arrival in the vertical plane. At the same time, in the case of omnidirectional reception, the coefficients of spatial correlation were below 0.32.     

Absolute calibration of Hartmann-Shack wavefront sensor by spherical wavefronts

A method for absolute calibration of Hartmann-Shack wavefront sensor (HSWFS), in which the wavefront differences of several spherical wavefronts are used to determine parameters of HSWFS, is proposed in this paper. The calibration method is introduced and the experiment results and error analysis are presented. Across a pupil with diameter of 2.6 mm, a lenslet array of 20 × 20 sub-apertures with square configuration, and focal length 4 mm, is used to sample the incident wave. The results indicate the uncertainty of the Hartmann-Shack wavefront sensor calibrated by the proposed method, is improved to less than λ/60 PV value and λ/500 RMS value (λ = 635 nm) with modal reconstruction method. Furthermore, the factors affected the results are analyzed. The error analysis suggested that the influences of the factors on the accuracy of reconstruction can be controlled to an accept level.     

Production of monochromatic radiation in an argon plasma by means of acoustic waves

It is shown that monochromatic radiation (λ₁=5888 Å, λ₂=5882 Å, and λ₃=4876 Å) can be obtained in a gas-discharge plasma in argon with the use of acoustic waves. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 5, 355–357 (10 March 1999)     

Phase conjugated wavefronts by stimulated brillouin and Raman scattering

Experimental investigations were made of wavefront reproduction (WFR) by backward stimulated Raman scattering (SRS) and backward stimulated Brillouin scattering (SBS) in CS₂ with a linearly polarized ruby pump beam. The experimental studies were carried out as a function of the optical waveguide diameter and photographic records comparing the pump beam with the backscattered SBS and SRS beams are presented. In all of the cases studied there was a high degree of replication between the SBS and pump beams; however, a deterioration in the quality of the replicated SRS beam was observed, and it increased as the cross-sectional area of the waveguide increased.     

Visualization of acoustic radiation from a vibrating bowling ball.

This paper presents visualization of acoustic radiation from a vibrating bowling ball using the Helmholtz equation least squares (HELS) method. In conducting the experiments, the ball is excited by a vibration shaker using stationary random signals. The radiated acoustic pressures are measured using two microphones and taken as input to the HELS formulations. The reconstructed acoustic pressures on the bowling ball surface are compared with those measured at the same locations. Also shown are comparisons of the reconstructed and measured acoustic pressure spectra at various locations on the bowling ball surface. Results demonstrate that the accuracy of reconstruction based on measurements over a conformal surface is much higher than that over a finite planar surface. This is because the latter often extends beyond the near-field region, making the accuracy of measurements inconsistent. Nevertheless, satisfactory reconstruction of acoustic pressure fields over the entire bowling ball surface can still be obtained based on the measurements taken over a finite planar surface on one side of the source. In a similar manner, the normal component of the surface velocity is reconstructed. Once these acoustic quantities are determined, the time-averaged acoustic intensity is calculated. Also presented are the formulations for estimating a priori the numbers of expansion functions and measurements required by the HELS method and the guidelines for determining the reconstruction error and optimum measurement locations, given the overall dimensions of the source and the highest frequency of interest in reconstruction.     

Analysis of acoustic networks including cavities by means of a linear finite volume method

A procedure allowing for the analysis of complex acoustic networks, including three-dimensional cavities described in terms of zero-dimensional equivalent elements, is presented and validated. The procedure is based on the linearization of the finite volume method often used in gas-dynamics, which is translated into an acoustic network comprising multi-ports accounting for mass exchanges between the finite volumes, and equivalent 2-ports describing momentum exchange across the volume surfaces. The application of the concept to a one-dimensional case shows that it actually converges to the exact analytical solution when a sufficiently large number of volumes are considered. This has allowed the formulation of an objective criterion for the choice of a mesh providing results with a prefixed error up to a certain Helmholtz number, which has been generalized to three-dimensional cases. The procedure is then applied to simple but relevant three-dimensional geometries in the absence of a mean flow, showing good agreement with experimental and other computational results.     

Numerical simulation of wavefronts diffracted by apertures with circular symmetry

The numerical simulation of the wavefronts diffracted by apertures with circular symmetry is realized by a numerical method. It is based on the angular spectrum of plane waves, which ignored the vector nature of light. The on-axial irradiance distributions of plane wavefront and Gauss wavefront diffracted by the circular aperture have been calculated along the propagation direction. Comparisons of the simulation results with the analytical results and the experimental results tell us that it is a feasible method to calculate the diffraction of apertures.     

衍射法测量低频液体表面波的衰减系数

提出了一种可用于几百赫兹低频液体表面声波研究的激光衍射法测量新技术。在实验上采用入射光掠入射到表面波上在远场得到了中间亮,两边暗的高反衬度的衍射条纹,实验中发现对频率为几百赫兹的低频衰减液体表面波,当移动振源改变激光入射点与振源间距离时发现零级条纹消失,这意味着此时的衍射效率接近100%。在理论上给出了衍射光强度与表面波振幅的解析关系,并利用所提出的新技术实现了对几百赫兹液体表面波的衰减系数的实时测量。     

Determination of acoustic attenuation in the Hudson River Estuary by means of ship noise observations

Analysis of sound propagation in a complex urban estuary has application to underwater threat detection systems, underwater communication, and acoustic tomography. One of the most important acoustic parameters, sound attenuation, was analyzed in the Hudson River near Manhattan using measurements of acoustic noise generated by passing ships and recorded by a fixed hydrophone. Analysis of the ship noise level for varying distances allowed estimation of the sound attenuation in the frequency band of 10-80 kHz. The effective attenuation coefficient representing the attenuation loss above cylindrical spreading loss had only slight frequency dependence and can be estimated by the frequency independent value of 0.058 dBm.