bluuebunny/crossref_metadata_2025 huggingface dataset:
Sonochemistry—A demonstration lecture
Authors: Mason Timothy J.
Published: July 2002

The potential uses of sonochemistry for the processing and chemical industries of the future have been established already in the chemical laboratory. The driving force for this technology is acoustic cavitation and a deeper understanding of this phenomenon will be required to help sonochemistry achieve more widespread acceptance and implementation in industry. For this reason a coordinated research effort is needed involving not only chemists but engineers, physicists, and mathematicians. In the past interaction between these disciplines has been limited due to the different scientific circles in which they move, but a few conferences, including this one, have sought to bring such disciplines together to promote cooperation. This presentation incorporates a series of demonstrations which illustrate the types of physical and chemical effects of cavitation and ultrasound which interest the chemist. These will include degassing, the generation of free radicals, the effects of cavitation near a surface, the dispersion of solids, emulsification, and particle manipulation in an acoustic field. Hopefully these will serve not only as an introduction to sonochemistry for those whose main discipline is not chemistry, but also as a focus for the powerful effects of cavitation which need deeper coordinated exploration.
Principles and applications of nonlinear acoustic nondestructive testing
Authors: Sutin Alexander M. , Donskoy Dimitri M.
Published: July 2002

Nonlinear acoustic techniques have recently been introduced as a new tool for nondestructive inspection and evaluation of fatigued, defective, and fractured materials. Various defects such as cracks, debonding, fatigue, etc., lead to anomalously high levels of nonlinearity as compared with flawless structures. One of the acoustic manifestations of such nonlinearity is the modulation of ultrasound by vibration. This effect is explained by using a model of the defect as contact between two rough surfaces. The vibration varies the contact area modulating the ultrasonic probing wave passing through the defect. A theoretical model considering interaction of different modes of vibrations and probing waves is discussed. Two methods employing the nonlinear interaction of ultrasound and vibration were developed, namely vibro-modulation (VM) and impact-modulation (IM) methods. The VM method employs forced harmonic vibration of the tested structure, while the IM method uses impact excitation of the structures natural modes of vibration. The crack detection tests were carried out for different objects made out of steel, plastic, glass, concrete, and carbon. These nonlinear techniques demonstrated certain advantages as compared with the conventional linear acoustic technique, specifically high sensitivity and applicability to highly inhomogeneous structures. [First author was supported in part by RFBR, Grant No. 96-05-64459.]
Pulsed nonlinear surface acoustic waves in crystals
Authors: Kumon R. E. , Hamilton M. F. , Il’inskii Yu. A. , Zabolotskaya E. A. , Hess P. , Lomonosov A. M. , Mikhalevich V. G.
Published: July 2002

A theoretical model developed recently for the propagation of nonlinear surface acoustic waves in crystals [Hamilton et al., Nonlinear Acoustics in Perspective, edited by R. J. Wei (Nanjing U.P., Nanjing, 1996), pp. 64–69] is used to investigate transient effects associated with pulses. The present work extends an earlier theoretical investigation of pulsed nonlinear Rayleigh waves in isotropic solids [Knight et al., J. Acoust. Soc. Am. 96, 3322(A) (1994)]. The latter was verified via comparison with measurements of laser-generated nonlinear Rayleigh waves with shocks in fused quartz [Lomonosov et al., J. Acoust. Soc. Am. 101, 3080(A) (1997)]. Here simulations of waveform distortion and shock formation are presented for pulses in real crystals, including Si, KCl, and Ni, and for a variety of surface cuts and propagation directions. The second- and third-order elastic moduli in the nonlinearity matrix are taken from measurements reported in the literature. Attention is focused on waveforms corresponding to recent measurements of laser-generated nonlinear surface waves propagating in Si along the 〈112〉 direction in the (111) plane [Lomonosov and Hess, Nonlinear Acoustics in Perspective (Nanjing U.P., Nanjing, 1996), pp. 106–111]. Preliminary comparisons of theory with measurements obtained in related experiments are in good agreement. [Work supported by ONR and the RFBR Foundation.]
An algorithm for calculation of material loss factors using single degree of freedom method and digital data measured by FFT analyzer
Authors: Maeda Toshiyuki
Published: July 2002

The half-power band-width method that is conventionally used to calculate material loss factors cooperated with one single degree of freedom method using data of each resonance response of a material bring out estimation errors caused by approximation of resonance frequency due to discrete frequency when data are measured with FFT analyzer. The proposed new algorithm is able to determine the actual resonance frequency, and its amplitude directly from digital data and loss factors without approximation.
Improvement of damping via analysis of viscoelastic composites
Authors: Sow Ibrahima , Nicolas Jean , Vu-Khanh Toan
Published: July 2002

High damping materials allow vibration and noise to be suppressed or at least reduced. Unfortunately, materials with high loss tangents also exhibit low modulus of elasticity. A new composite damping material is investigated, which consists of specially designed fibers embedded in a viscoelastic matrix. This new approach not only enhances damping through improvement of matrix loss tangent by the addition of elastomer, but also through selection of adequate ply orientation, ply stacking, geometry of fibers, and fraction of fibers. Theoretical analysis of the viscoelastic properties of this composite is presented in order to identify the optimum material with high stiffness and high loss tangent according to all parameters. To address validation theoretical developments are compared to experimental results.
Characteristics for vibration damping of the concrete included secondary subject
Authors: Ishikawa Noboru , Shimoda Hidemaro
Published: July 2002

A concrete structural material with damping performance for vibration has been investigated. It is proposed that in order to reduce the sound propagation in the solid material, the concrete material disperses many small cells in which many easy moving particles are included. It is expected that the vibration energy which is applied to the material is absorbed by the impaction and friction of the particles alternatively and between particles and cell’s wall. The preliminary experiment to confirm the capability of the high damping material on the basis of this concept has been carried out. It was shown that damping performance of the specimen depended on the size, the density, and the volume fraction of the particles by the impact vibration testing for the coupon-sized test specimen. The effect of the easy moving particles for reduction of the sound propagation in the solid was confirmed by the sound propagation testing for the middle-sized panel specimen.
Rapid gains in the speed and efficiency of word recognition by infants in the second year
Authors: Fernald Anne , Pinto John P. , Swingley Daniel
Published: July 2002

Toward the end of the second year, during the period of rapid development in productive vocabulary known as the ‘‘vocabulary explosion,’’ infants also make dramatic gains in the speed and efficiency with which they are able to recognize familiar words in fluent speech. Here several studies using an on-line measure of speech processing by infants from 15 to 24 months of age are presented. In this research, an auditory-visual matching procedure, in which infants looked at two familiar pictures while hearing a target word that matched one of the pictures, was used. Monitoring infants’ eye movements from the onset of the target word, word recognition was assessed by measuring infants’ latency to look to the matching picture in response to the spoken word. These studies show that by the end of the second year, children are progressing toward the highly efficient performance of adults, using incomplete acoustic information to make rapid and accurate decisions about the identity of spoken words. [Work supported by NIMH.]
Use of Scholte waves to determine the shear wave velocity structure in marine sediments
Authors: Kawashima Sayuri , Kimura Masao
Published: July 2002

Scholte waves propagating in marine sediments exhibit velocity dispersion, if the shear wave velocity of the sediment under the seabed surface depends on the depth. Therefore, it is possible to obtain the shear wave velocity profile of marine sediment, using velocity dispersion characteristics of Scholte waves. In this study, in situ experiments of Scholte waves in marine sediments are conducted off the coast of Shizuoka. A weight-drop system, lifting a weight and releasing it, was used as the source. Propagated signals are detected by gimbaled geophones. Group velocity dispersion characteristics are obtained from the recorded signals using the multiple filter method. Next, the depth dependence of shear wave velocity is obtained from the group velocity dispersion curves of Scholte waves using an inversion method. Furthermore, the estimated depth dependence of shear wave velocity is investigated.
Simplex simulated annealing: A hybrid approach to geoacoustic inversion
Authors: Fallat Mark R. , Dosso Stan E.
Published: July 2002

The problem of matched-field inversion of acoustic fields for ocean-bottom geoacoustic properties has received considerable attention in recent years. In order to avoid the large number of local minima typical of multidimensional geoacoustic parameter spaces, many inversions apply global optimization methods, such as simulated annealing (SA), to minimize the mismatch between measured and modeled fields. However, the random manner in which SA searches the parameter space can be quite inefficient, particularly near convergence and/or in cases where the minima represent narrow valleys not aligned with the parameter axes. In addition, standard SA has no memory, so a good solution may be discarded at the early stages and never revisited. In order to improve the efficiency and effectiveness of SA, a local inversion component based on the downhill simplex method within a global approach to geoacoustic inversion has been incorporated. The simplex method is sensitive to local gradients, and provides efficient perturbations at all stages which are independent of the coordinate axes. Also, the simplex of models carried through the inversion retains good models and provides a memory for the algorithm. The hybrid approach of simplex simulated annealing will be described and illustrated for geoacoustic inversion. [For Underwater Acoustics Best Student Paper Award.]
Performance evaluation of horizontal and vertical vector sensor arrays in shallow water environments
Authors: Gerstoft Peter , Goh Joo Thiam
Published: July 2002

In planning an experiment it is essential to have as diverse information as possible in order to obtain a good estimate of the relevant parameters. Traditionally, the inversion for waveguide parameters as well as the source location is done exclusively using pressure measurements. Recently, it has been suggested by Nehorai and Paldi [IEEE Trans. Signal Process. 42, 2481–2491 (1994)] that arrays of vector sensors (sensors that measure both pressure and velocities) could be used. Experiments have also been conducted in deep water by D’Spain et al. [IEEE Oceans (1992)]. In a realistic shallow-water environment the use of either vector or pressure sensors on a linear horizontal/vertical array with amplitude-only or complex-valued data at a number of discrete frequencies are discussed. Based on developed maximum-likelihood functions, the performance for the above type of data will be classified using either a global or a deterministic approach. For the deterministic approach, the Cramer Rao lower bound (CRLB), based on derivatives of the likelihood function, is used. For the global approach the a posteriori distributions are examined. These are based on Monte Carlo integration of the likelihood function. [Work supported by DSO National Laboratories, Singapore.]
Application of coordinate rotation to inversion for sediment parameters
Authors: Perkins John S. , Collins Michael D. , Fialkowski Laurie T.
Published: July 2002

A global optimization technique (e.g., simulated annealing), combined with an accurate acoustic simulation capability, provides the means to invert measured acoustic data for unknown environmental parameters (e.g., sediment properties). Two problems are often encountered: (1) Which parameters are actually important to the solution? and (2) What are the parameter couplings? These problems can be regarded as difficulties in navigating through a multidimensional landscape to find the global minimum of the cost function (the error between the measured data and the simulated acoustic field corresponding to a given set of parameter values). A coordinate rotation technique based on the eigenvectors of the covariance matrix of the gradient of the cost function has been developed [M. D. Collins and L. Fishman, J. Acoust. Soc. Am. 98, 1637–1644 (1995)]. In applying this technique to low-frequency (<200 Hz) SWellEX-96 data involving a drifting source of known position and a 32-element vertical receiver, a 12-parameter representation of the sediment structure and properties leads to a frequency-dependent parameter hierarchy and parameter couplings. The resulting environmental inversions are compared with previous characterizations and are used in matched-field processing to locate the source at other times during the experiment. [Work supported by ONR.]
Chemopotential by low-level ultrasound
Authors: Harrison George H. , Balcer-Kubiczek Elizabeth K.
Published: July 2002

Recent laboratory studies have identified a new approach to cancer therapy: the potential of drug action by ultrasound. Both standard chemotherapeutic cytotoxins and relatively nontoxic compounds related to those used in photodynamic tumor therapy are being investigated. Common to most reported investigations has been the use of continuous wave ultrasound at spatial peak, temporal average intensities exceeding 0.5 W/cm2, implying the likelihood of temperature elevation in insonated tissue, and usually involving cytotoxicity from the action of ultrasound alone. On the other hand, for potentiation of chemotherapy using tone-burst or pulsed ultrasound at spatial average, time average intensities less than 0.3 W/cm2 has been demonstrated [G. H. Harrison, E. K. Balcer-Kubiczek, and P. L. Gutierrez, Ultrasound Med. Biol. 22, 355–362 (1996)]. Chemopotentiation data will be presented for several biological test systems with emphasis on human prostate tumor cell lines. Mechanistic evidence will be analyzed; fluid streaming and shear stress are likely important determinants of chemopotentiation and the cell membrane can be expected to be an important site in this process. Ultrasound-induced modification of drug resistance may have important apoptotic links. These factors suggest the importance of treatment-induced differential expression of membrane-related genes.
Research on inhomogeneous 1-3 PZT/polymer composite transducer
Authors: Xu DaLun , Zhou TieYing
Published: July 2002

An improved equal stress physical model [W. A. Smith and A. Shaulov, Ultrasonics Symposium, 642–647 (1985)] for the inhomogeneous 1-3 PZT/polymer composite material is presented. This model calculates the properties that determine the thickness-mode oscillations in thin plates. Based on this model, together with the constitutive relations for polymer and PZT, expressions are derived for the effective material parameters such as electromechanical coupling constant, acoustic impedance, etc., in terms of the properties of constituents. A relation between the vibration amplitude of the transducer’s surface and the volume fraction of the piezoceramic is also deduced. The distribution of the vibration of the transducer’s surface, hence the distribution of the acoustic field, can be precisely controlled by adjusting the distribution of the volume fraction of the PZT phase in the transducer. To test our model experimentally, a number of special transducers were made. The measurements of the acoustic field that is produced by the transducers are in good agreement with the theory. The research provides guidelines for the transducer engineer to design inhomogeneous 1-3 PZT/polymer composite transducer, such as transducers of Gauss type, Bessel type, or other special types.
Sentential prosodic contour facilitates adults’ short-term memory for nonsense syllable strings
Authors: Schenck Diana L.
Published: July 2002

Recent linguistic theories propose that prosodic contour functions to facilitate encoding, processing, and storing of information in the speech signal. To date, most evidence for these theories comes from studies of infant perception and processing of prosodic speech. The present study employed a short-term memory CV nonsense syllable recall task in order to attempt to replicate with adults the findings for infants that have supported these theories. Ten adult subjects listened to nonsense CVs in two sets, one presented with sentential prosodic contour, the other presented in list form, and recalled as many syllables, in order, from each string as they could. Results were significant at the p<0.05 level and supported the hypothesis that subjects would better recall those syllable strings presented in prosodic contour, as the number of errors was fewer for the prosodic set than for the list set. Small familiarity/order of presentation effects and individual differences were found for all subjects. These results suggest that (1) adults use processing and coding strategies similar to those employed by infants in response to linguistic stimuli; and (2) sentential prosody does, in fact, facilitate short-term memory for these stimuli, possibly by enhancing the perceptual saliency of the linguistic input.
Two-phase theory of acoustic wave propagation in magnetic liquids
Authors: Hornowski Tomasz , Kaczmarek Mariusz , L/abowski Mikol/aj , Skumiel Andrzej
Published: July 2002

A new theoretical approach to ultrasonic wave propagation in magnetic liquids is proposed on the basis of a two-phase model in which the solid phase (magnetic particles coagulating to clusters forming a rigid skeleton) and the liquid phase (carrier liquid) are described by separate sets of equations for the balance of mass, momentum, and angular momentum. Interaction between clusters is described by components of the stress and strain tensors in the solid phase whereas interaction between the clusters and the liquid is accounted for as Stokes, Basset, and added mass forces and the respective angular momenta. Expressions are derived for the velocity and attenuation as functions of the wave frequency and the angle between the propagation direction of the ultrasonic wave and the magnetic field. Moreover, the expressions obtained are checked experimentally for several ultrasonic wave frequencies versus the strength and direction of the magnetic field under various conditions. [Work supported by KBN Research Grant No. 2PO3B 07912.]
Experimental and theoretical analysis of the nonlinear dynamics and acoustics of a rattling plate
Authors: Fegelman Karen J. , Grosh Karl
Published: July 2002

Rattle has become an important issue in the motive and aerospace industries. Design for the prevention and reduction of rattle noise requires that the underlying mechanisms be understood and powerful, flexible numerical tools be developed. In this paper, the focus is on the former, developing a basic theoretical and experimental foundation for determining the vibroacoustic behavior arising from the nonlinear dynamics associated with the rattle process. In order to understand the fundamental mechanics of rattle, a model problem was formulated involving a hinged plate rattling against a stiff contact point excited by base motion. The plate was modeled as a flexible beam and the resulting equations of motion were solved explicitly. It was found that the calculated accelerations at the tip of the beam quantitatively agree with those measured from an experimental test stand. In addition, the predicted and measured sound pressure levels (SPL) at various points were found to agree qualitatively. Finally, the closed form flexible body solutions were analyzed with regard to stability to predict transitions from periodic to chaotic rattling behavior. In particular, the sensitivity of the transition region to chaos on the base motion amplitude and frequency are investigated experimentally and theoretically.
Automatic noise source recognition
Authors: Dufournet Didier , Jouenne Philippe , Rozwadowski Adam
Published: July 2002

MADRAS is an acoustic monitoring system that features the automatic recognition of noise sources. It is based on a tree classifier able to use different classification techniques like signal processing, morphology, fractional analysis, and neural networking. A very high accuracy of recognition is achieved due to the optimization of the choice of real-time technique applied and to the intrinsic performance of each algorithm. MADRAS can learn the characteristics of new sources and also use a database of previously processed cases and typical events. The paper presents the results of multiple source recognition in a complex acoustic environment. Implemented on a real time PC-based measuring analyzer called Symphonie, MADRAS has been able to distinguish all noise sources. Acquired data may then be processed to obtain the energy contribution of each source and a list of the frequency of each appearance. Simulations may be viewed and modified.
Signal models for broadband model-based array processors
Authors: Sullivan Edmund J. , Candy James V.
Published: July 2002

The recently developed theory for broadband model-based acoustic array processing is based on a Kalman-type estimation scheme. Here two sets of equations are required; the state equations and the measurement equations. In the narrow-band case, the measurement equation is based on either a plane wave or curved wavefront monochromatic signal model. In the broadband case the signal model, i.e., the measurement equation, is represented as an autoregressive moving average (ARMA) process. In this approach the parameters of interest, which are the bearing and range, are combined with the ARMA parameters in a single state vector. This provides a scheme wherein these parameters are adaptively estimated in a recursive manner. However, the order of the ARMA process depends upon the spectral characteristics of the signal. In this study, various realistic broadband signal spectra are examined in terms of the required ARMA representations. Examples will be shown for several cases of representative surface ship radiation spectra.
A simple genetic algorithm for active noise control
Authors: Minguez Antonio , Recuero Manuel
Published: July 2002

Genetic algorithms in active noise control (ANC) eliminates the need to know the cancellation path, necessary for a conventional gradient descent-type algorithm (such as filtered-x and filtered-U) to remain stable. However, genetic algorithms show some disadvantages: slow convergence, high residual error noise, and high computational complexity. This paper presents a simple genetic algorithm that improves these quality factors, simplifying the basic stages of the genetic algorithm: population size, selection, reproduction, and mutation. To reduce the algorithm computation the population size is low, 6 chromosomes (filter coefficients) maximum, and only the best chromosome is selected so the reproduction stage disappears. Next generation of chromosomes is generated mutating the selected chromosome with a variable random number which amplitude is directly proportional to the mean-squared error in the current generation. This variable mutation is the most important parameter because it determines the stability, the convergence, and the final residual level. Good results have been obtained for narrow-band signals in single (SISO) and multiple (MIMO) ANC configurations and with FIR or IIR filters. These results shows fast convergence, only four or five generations are necessary with very reduced populations (6 chromosomes in SISO systems and 2 to 3 chromosomes in MIMO systems) and an attenuation better than 20 dB.
Machine recognition of Hindi consonants and distinctive features using vector quantization
Authors: Das Pradip K. , Agrawal S. S.
Published: July 2002

This paper describes the results of experiments conducted to test the efficiency of the VQ algorithms to recognize and distinguish minute differences among consonant features of Hindi. The database was created by combining all the frequently occurring 29 Hindi consonants with vowel /a/ to form CV-type syllables and recorded by 20 male Hindi speakers. The acoustic features in the form of cepstral vectors were derived for each syllable file in the training set. For each syllable, the set of 20 codebooks for 20 speakers were first clubbed to form the universe for that syllable. The LBG algorithm was used to generate the codebook of size 64. Using the codebooks as reference templates the recognition rate was found to be 73.28% out of the total of 580 (29*20) test samples. Further analysis was carried out to see how different consonants were recognized when they were clubbed into different groups according to the manner and place of their articulation. The average recognition rate for the consonants corresponding to the same place of articulation and the same manner of articulation was found to be 83.38% and 76.25%, respectively. Results of detailed distinctive feature analysis carried out to find the differences in the rate of recognition are also discussed.
Small-scale modeling of stage to pit balance: A pilot study
Authors: O’Keefe John P.
Published: July 2002

Measurements in full-scale auditoria have demonstrated that the acoustical balance between stage and orchestra pit sound sources is influenced by the seat dip phenomenon. In general, low-frequency balance favors the orchestra pit for listeners on the orchestra level and is about even for listeners on the balcony. Full scale measurements suggest that the rake of the floor and the presence of local (early) reflectors increase balance to the benefit of the singers on stage. A simple 1:24 scale model has been built to test these and other phenomena in a controlled fashion. Measurements have also been performed in small-scale models of existing theaters. Early findings confirm the influence of seat dip on stage to pit balance.
Measurements and modeling of commonly used resilient channels in lightweight floor structures
Authors: Brunskog Jonas , Hammer Per
Published: July 2002

A common part in lightweight floor structures is resilient channels between the joists and the ceiling. The purpose of the channels is to lower impact sound transmission in a broad frequency band. The channels are normally complicated to describe accurately from a structural acoustic point of view. The intention in this paper is to describe the channels by means of a simple structural acoustical model. The channels are divided into two types of elements. The first element is a beam. The second con-stitutes the mounting of the channels to the joist. The two elements are treated and analyzed both separately and connected to each other. The measurements are done by mainly measuring the accelerations on stiff bodies on the top and bottom of the test sample. The procedure is then repeated with a new set of stiff bodies. From these measured values (four different) one can determine the global two-port description. As a check there is also the reciprocity. As a comparison a method is used where the actual point force acting on the spring is measured and used. The model can be used as a base for analyzing the acoustical behavior of the resilient channels.
Optimizing techniques for field testing of buildings
Authors: Dodd George
Published: July 2002

As national building codes and acoustic comfort standards become more common as tools for quantifying and promoting acoustical quality in dwellings there is a greater need for field testing of buildings. The intent of this project is the promotion of a greater use of field testing by providing more convenient measurement methods. Primarily the focus has been on identifying the ideal sound source. Explosive sources using charges produced for use in powder powered tools have emerged as satisfying the majority of our needs. Continuing study is aimed at optimizing such a source. In particular, it needs to produce adequate power for measuring at the low frequencies required for implementing the new spectrum adaptation terms for the traditional single-figure ratings of building insulation.
A statistical theory of low-frequency sound propagation through internal waves
Authors: Voronovich Alexander G.
Published: July 2002

A statistical theory of propagation of low-frequency sound waves through stochastic internal wave (IW) field is suggested. This theory is based solely on the weakness of sound scattering over distances of the order of correlation radius of IW field. Estimates show that a corresponding small parameter is of the order of a few percent for sound frequencies up to 50–100 Hz. Hence the theory is quite adequate for practically interesting cases. The governing equations include both average field and cross correlators of acoustic modes and are generally 3D. Those equations are finite difference rather then differential. This allows one to avoid making rather restrictive assumptions which can be easily violated. However, in the appropriate limit those equations reduce to standard ‘‘couple power equations’’ by Dozier and Tappert. Decrement of attenuation of average mode amplitudes is linearly related to the spacial spectrum of IW. Thus, by measuring propagation of tonal low-power sound signals over distances of a few hundred kilometers with the help of mode-resolving line vertical arrays, it is possible to infer in detail spacial spectrum of different IW modes (a task which would be extremely expensive to solve with the help of traditional contact measurements).
Inverse imaging of the breast using a conjugate gradient-neural network technique
Authors: Zhang Xiaodong , Broschat Shira L. , Flynn Patrick J.
Published: July 2002

Early detection of a breast tumor greatly improves the chances of survival. Thus it is important to develop high-resolution imaging techniques capable of detecting small tumors. In this paper, an ultrasound imaging technique is presented that is based on solving the two-dimensional inverse scattering problem. An object is reconstructed using an iterative algorithm that combines the conjugate gradient method and a neural network (CGNN) approach. The neural network technique exploits prior knowledge of the statistical characteristics of the different tissues inside the breast to enhance the performance of the conjugate gradient (CG) method. The CGNN algorithm has been tested on two small models simulating a breast tumor surrounded by glandular tissue. One model presents a tumor 3 mm in size and the other a tumor 1 mm in size. Results show that the CGNN algorithm is more accurate than the CG method. In addition, convergence occurs more rapidly; with the CGNN algorithm approximately 40% fewer iterations are needed to obtain the inverse solution. The CGNN method also appears to be robust to noise. Results are still reasonably good for a signal-to-noise ratio of 35 dB. Numerical results will be presented and discussed. [Work supported by NSF and the Carl M. Hansen Foundation.]
Main error sources in ultrasound transmission tomography imaging
Authors: Opielinski Krzysztof J. , Gudra Tadeusz
Published: July 2002

Ultrasound transmission tomography (UTT) consists in the usage of information included in ultrasonic pulses penetrating through an object in order to reconstruct sectional images of its inner structure. The contrast in the images corresponds to the distribution of local values of the acoustic parameter measured in projections. The measurement errors usually distort the tomographic image of the inner object structure. How different measurement errors are manifested and how big the changes they bring about in the reconstructed tomographic image can be fundamental for the determination of the ultrasound transmission tomography application range. The main sources of errors in ultrasound transmission tomography are the measurement accuracy and geometry, the ultrasonic refraction, the changing of measurement conditions, the measurement method, the reconstruction algorithm, and the disappearance of the receiving signal. Some different tomographic measurement errors (caused by the above-mentioned sources) were computer simulated and compared with the real ones. The influence of these errors on the ultrasonic tomographic imaging was shown. All of these errors refer to the run-time measurements in the parallel ray projection geometry using the convolution and backprojection algorithm for the image reconstructions.
Acoustic propagation in gassy sediments
Authors: Richardson Michael D. , Wood Warren T. , Anderson Aubrey L. , Wilkens Roy H.
Published: July 2002

Measurements of values of sediment physical properties, bubble volume, and bubble size distribution are used to predict sound speed and attenuation in the fine-grained, gassy sediments of Eckernförde Bay, Baltic Sea. The predicted results are compared to in situ and laboratory measurements of sound speed and attenuation over the frequency range of 5–400 kHz. Dispersion of sound speed is used to determine the upper limit of methane bubble resonance near 20 kHz. These data combined with bubble size distribution measured using CT scans of sediments held under ambient conditions yield an estimate of effective bubble size of 0.3–5.0-mm equivalent radii. Histograms of bubble size distribution are then used to predict frequency-dependent sound speed and attenuation based on the model of Anderson and Hampton [J. Acoust. Soc. Am. 67, 1865–1903 (1980)]. Given the highly variable spatial distribution of bubble volume and size, the agreement between theory and measurement is remarkably good.
An optimization technique applied to the recovery of acoustic impedance profiles
Authors: Magalhaes Marcelo , Tenenbaum Roberto
Published: July 2002

A method based on a global optimization technique is used to solve the inverse (identification) problem of one-dimensional wave propagation in transversely infinite inhomogenous media. The scheme consists of minimizing a cost function given by the square distance (according to the Euclidean norm) between a measured and a synthetic signal, the latter produced by an arbitrary impedance profile. This cost function imposes several difficulties, since the model for the synthetic signal causes it to be polynomial whose degree is at least equal to the number of layers in which the profile is discretized. The optimization method used is a secant one, which, instead of making use of information about the second derivatives of the cost function, which is too time consuming, generates sucessive approximations of its Hessian matrix, based on information gathered as the procedure progresses. Moreover, in order to guarantee that the method follows a descent direction, that is, the cost function is always reduced, a BFGS (Broyden–Fletcher–Goldfarb–Shanno) updating rule is used, together with a Wolfe line search procedure. Results are shown for some continuous as well as stratified media, showing that the method works well with both smooth and nonsmooth profiles.
Acoustical design of the Tokyo Opera City (TOC) Concert Hall
Authors: Hidaka Takayuki , Beranek Leo L. , Masuda Sadahiro , Nishihara Noriko , Okano Toshiyuki
Published: July 2002

The TOC Concert Hall, called ‘‘Takemitsu Memorial’’ in honor of the late composer Toru Takemitsu, was opened September 10, 1997. With a seating capacity of 1636 and a volume of 15 300 m3, the hall is sized to cover the musical range from recitals to orchestral concerts. The plan is rectangular in shape but, by request of the architect Takahiko Yanagisawa, the ceiling is a distorted pyramid, with its peak nearer the stage than the rear of the wall. This unique shape had to be analyzed using a CAD model and a 1:10 scale model so that all interior surfaces would be adjusted in shape and absorption to yield optimum values for RT, EDT, IACCE3, surface diffusion, initial time delay gap, and loudness [Beranek, Concert and Opera Halls (ASA, New York, 1996)]. To provide a better ensemble condition for the musicians on stage and to provide early reflections to several other regions, a square canopy, almost 10 m on a side, is suspended above the stage. The pyramidal ceiling has diffusing elements added to simulate coffers. Schroeder QRDs on the ceiling surface facing the orchestra are used to control echo and to add sound diffusion. With audience, RT=1.95 s, G=6.4 dB, and [1−IACCE3]=0.72.
Stochastic resonance in the amphibian auditory system? It’s just a matter of time
Authors: Narins P. M.
Published: July 2002

Noise has traditionally been a factor to minimize or eliminate for optimum performance of a communication system. Recently, it has been proposed that in some cases, noise may benefit information transfer and that its existence in sensory systems may be an adaptation to enhance detection of weak signals. One possible mechanism that could take advantage of noise to enhance signal transmission is a physical phenomenon known as stochastic resonance (SR). In order to study such effects in auditory neurons, use was made of the ability of amphibians to function over a range of ambient temperatures, and thus over a range of internal noise levels. The goal of the present study was to determine the effect of temperature (and internal noise) on information transmission in the frog. To this end, core temperature shifts were induced experimentally and the resulting changes in signal-to-noise ratio (S/N) were quantified. Although our results do not demonstrate SR in the sense that the S/N passes through a maximum at a particular internal noise intensity, we do demonstrate the profound influence of the internal noise on the S/N derived from the neural spike trains. Moreover, recent field and behavioral data will be presented and interpreted in the framework of stochastic resonance. [Work supported by NIH Grant DC-00222 to PMN.]
Characterization of vehicle noise in Hong Kong
Authors: Ng W. T. , Yuen M. M. F. , To W. M.
Published: July 2002

There is a common perception among residents of high-rise buildings facing expressways that noise emitted from moving vehicles would be dominated by tire/road interaction and at high-frequency regions. Local government officials believe that the impact on residents of low-frequency noise radiated from car engines would be insignificant, especially after the corrections for the A-weighting scale are applied. This paper reports on an extensive survey and some in situ sound measurements. It was found that road noise in Hong Kong is dominated by low-frequency noise emitted from heavy vehicles in expressways and by low-frequency noise emitted from heavy and light vehicles driven at a speed below 50 km/h in streets. The measured data were characterized by using time-averaged 1/1 octave band analysis, time-averaged 1/3 octave band analysis, and time-frequency analysis. The Doppler effect was clearly observed at low-frequency regions in joint time-frequency distributions. It is suggested that the A-weighting scale would not reflect the true annoyance level of traffic noise. Noisiness should be used to quantify the annoyance caused by moving vehicles. A new noise model is proposed to give a realistic description of noise radiated from a moving vehicle.
Active control of structural sound using an active constrained layer damping treatment
Authors: Yang Jun , Tian Jing , Li Xiaodong
Published: July 2002

In this paper active constrained layer damping (ACLD) treatments are applied to control the noise transmitted into a cavity through a panel. Five of the enclosure walls are rigid and the other wall, which is flexible, is a simply supported panel. The panel is treated with ACLD, which consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the panel. The piezoelectric layer is utilized to control the panel vibration and the shear deformation of the viscoelastic layer to enhance its energy dissipation characteristics. The coupled structural sound equation of the composite panel and the cavity is derived and analyzed by the Galerkin approximation. The results indicate that combining active and passive controls, as in the case of ACLD treatment, is more effective in controlling the noise transmission. Moreover, such a control strategy is found to require lower control inputs than when the active and passive control actions are used separately.
Hugh Guthrie Flynn, 1912–1997
Authors: Blackstock David T.
Published: July 2002

Hugh Flynn spent most of his first three decades in Columbus, Ohio. During the 1930s he was a newspaper crime reporter and also studied physics at Ohio State University. After graduating from Ohio State in 1939, he took a job with the Navy’s Bureau of Ordnance and was a Naval officer during WWII. While working for the NAS Committee on Undersea Warfare after the war, he met F. V. Hunt, who encouraged him to study acoustics at Harvard. There Hugh became interested in cavitation, the beginning of a lifelong love affair with bubbles. After his doctoral degree in 1956, he stayed on as one of Hunt’s postdocs. The year 1960 was a propitious one. He married Prudence Turgeon and joined the faculty of the new Electrical Engineering Department at the University of Rochester. He spent the rest of his life in Rochester, where he solidified his international reputation as a respected authority on cavitation and fathered three children, Kitty, Molly, and Nathaniel. Despite retiring as Professor Emeritus in 1978, he stayed active in research for the rest of his life. His projects during retirement included bubble phenomena in medical ultrasonics and nuclear fusion from cavitation.
Resolution of the convected Helmholtz’s equation by integral equations
Authors: Beldi M. , Monastir F. S.
Published: July 2002

Using the free-field convected Green’s function, the integral formulation for the acoustic velocity potential and its normal derivatives associated with Helmholtz’s equation in a uniform flow is established. An original development for the calculation of the Cauchy principal value in the singular integrals is presented. As far as the finite part in the hypersingular integral is concerned, a new transformation of the convected double-layer potential normal derivative is proposed. The result of this transformation avoids the explicit calculation of the finite part. Moreover, it generalizes the famous works [M. P. Stallybrass, J. Math. Mech. 16, 247–1286 (1967)] [A. W. Maue, Zeit. für Phys. 126, 601 (1949)] on the resolution of the Helmholtz’s equation, by integral equations, in a fluid with null veloc- ity. This new variational method by integral equations can easily be coupled with the variational formulation for studying the convection and refraction effects of the acoustic waves in a nonuniform flow [M. Beldi, Third International Conference on Theoretical and Computational Acoustics, Newark (14–18 Aug. 1997)]. The numerical results shows the importance of these effects.
Experimental study on the vortex-shedding sound from a yawed circular cylinder
Authors: Choi Jong-Soo , Hong Hoon-Bin
Published: July 2002

For a cylinder in a uniform flow stream, sound is generated by the fluctuating pressure on the surface of a cylinder due to the vortex shedding behind the cylinder. It is known that the major parameters in predicting the acoustic pressure at the far field are the flow velocity, the correlation length, and the fluctuating lift coefficient. In this experimental study, the correlation length of the wake is measured with hot-wire sensors and compared to the one obtained with pressure sensors on the cylinder surface. A new measurement technique for the unsteady lift estimation by using a pressure sensor rotating circumferentially is used to show reasonably good results. The surface pressure and the radiated sound are also measured simultaneously for different yaw angles and showed that the reduced normal velocity component to the cylinder axis reduces the unsteady lift fluctuation which results in lowered sound-pressure level. However, experimental result shows that ‘‘the cosine law’’ which uses the normal velocity component as a characteristic velocity for noise generation from a yawed cylinder needs to be carefully reviewed.
Methods of processing laser Doppler anemometry signals to extract sound field information
Authors: Cullen John S. , Hann David B. , Greated Clive A. , Campbell D. Murray
Published: July 2002

For several years laser Doppler anemometry (LDA) has been used to measure mean flow rates in gaseous and liquid flows. It is only recently that LDA has been developed as a technique for recording instantaneous particle velocities, enabling nonintrusive measurements to be made in sound fields. The paper describes a typical experimental setup and discusses various methods of digitally processing the LDA photodetector signals to extract the required velocity information. Particular emphasis is placed on the zero counting and Hilbert transformation techniques. The problem of signal dropout is also addressed. LDA measurements of acoustic particle velocity amplitudes are compared with acoustic velocity amplitudes deduced from probe microphone and impedance measurements. It is found that LDA measurements could be made not only in monofrequency sound fields but also in more complex sound fields containing a fundamental component and additional harmonics. Theoretical and practical limitations of the techniques are investigated and used to assess the viability of applying them to studies in the bores and mouthpieces of brass instruments.
Acoustic parameters of high functional plastics. I. Measurement of acoustic velocities (wave propagation velocities)
Authors: Gakumazawa Masahide , Akiyama Minoru
Published: July 2002

Recently, high functional plastics (so-called engineering plastics) which improved the weak point of conventional plastics have been used in the industry. The acoustic parameters of these engineering plastics in the high frequency have been sparsely reported in the literature using a variety of experimental techniques. In this study the acoustic velocities (wave propagation velocities) of engineering plastics are measured using the scanning acoustic microscopy in the range from 50 to 200 MH, and the velocities were compared with the velocities reported in the literature in the lower frequencies.