bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffraction by a hard half-plane: Useful and simple frequency forms to an exact time-domain solution
Authors: Ouis Djamel
Published: July 2002

The general case of diffraction of a spherical wave by a hard half-plane is considered. The calculations are based on Biot and Tolstoy’s exact and explicit form of the solution to the diffraction problem by a hard wedge. This solution is given in the time domain but its Fourier transform is not available. It is the aim of this paper to present some useful and simple approximations for the early time diffracted field which when transformed into the frequency domain is shown to be satisfactory in comparison to numerical integration. This could give some valuable contributions to calculations on scattering by noise barriers and the like. The results of some experiments are also presented.
A discussion on nonradiating sources
Authors: Musafir Ricardo E.
Published: July 2002

The fact that a given source sound field can be generated by more than one source distribution is quite well known but is frequently given an overexaggerated importance. This paper discusses the structure of sources of silence, the name given by Doak [Proc. I.O.A., 10-2, 693–700 (1988)] to the reactive part of a source distribution, i.e., to the part with no far field and which is responsible for the ambiguity. It is shown that, since all ambiguities can always be traced back to the impossibility of distinction between the sound fields of a point monopole and of an isotropic point quadrupole, a simple criteria can be established for identifying a general source distribution as active or reactive. The particular case of the velocity field due to a point dipole (i.e., to a point force) in an homogeneous medium at rest is worked out in detail, since it contains a source of silence (associated with the vorticity at the source point) which is frequently mishandled. The concepts presented are applied to aeroacoustic wave equations, to discuss optimization of the choice of dependent variable as well as some case of identification of nonradiating sources found in the literature.
Longitudinal structural relaxation of glass-forming epoxy oligomer
Authors: Matsukawa Mami , Ohtori Norikazu
Published: July 2002

The glass transition process of a common epoxy oligomer (diglycidyl ether of bisphenol A) has been characterized by Brillouin scattering (GHz range) and ultrasonic pulse spectroscopy (MHz range). As the temperature decreases, longitudinal wave velocity rapidly increased. It showed a large frequency dispersion at temperatures higher than the thermodynamical glass transition temperature (Tg). At Tg, velocity changes showed a clear kink. Wave attenuation also showed a peak of the main (alfa) relaxation at temperatures higher than Tg. The peak temperature shifted to lower temperatures in the MHz range, following the VFT type relaxation behavior, which is very common in the main relaxation. The velocities, however, still showed a clear frequency dispersion at temperatures lower than Tg. Because the main relaxation usually results from a large-scale conformational rearrangement of the polymer chain backbone, the effect of this relaxation seems to be neglected at these temperatures. Taking into account the frequency changes of attenuation peak widths, the effect of other subrelaxations at lower temperatures is discussed. These results are not in contradiction with the acoust-optic dispersion measurements of this oligomer [Kruger et al., Phase Transition (to be published)].
High temporal resolution of the acoustic transients associated with optical cavitation in water using a large area piezoelectric transducer
Authors: Emmony David C. , Alcock Robin D.
Published: July 2002

A PVDF piezoelectric transducer has been used to study the shock wave associated with a laser generated cavitation bubble in water. The measurements depend upon the accurate recording of the voltage developed in a large (3 mm) diameter but thin (9* m) piezoelectric film transducer placed close to a Nd YAG laser-generated cavity in water. The spherical shock transients excite the film over the duration of the passage of the wave through the transducer, and an invertion algorithm of the voltage trace gives the pressure profile along a radius. Pressure profiles due to initial breakdown and first collapse are in excellent agreement with those obtained using full field high-speed optical interferometry of the laser–liquid interaction.
Acoustical characteristics of the noise radiated from supersonic multijets
Authors: Umeda Yoshikuni , Ishii Ryuji
Published: July 2002

The acoustical characteristics of the noise radiated from combined jets exhausted from one main nozzle and 1, 2, 4, or 8 subnozzles which were placed asymmetrically or symmetrically to the main nozzle were investigated experimentally. The diameter d of the main nozzle was 5 mm and that of subnozzle a/d was 0.2 or 0.6, where a is the diameter of the subnozzle. The center-to-center spacing b of the main and subnozzles was fixed to 5 mm (b/d=1.0). In this experiment, the pressure ratio R of the jets was varied from 2.00 to 6.33. From the frequency characteristics of the screech tone, it is found that in almost all cases, two oscillation modes appear, but when eight subjets with a/d=0.6 were used, the screech tone disappeared completely. Although the total cross-sectional area of the multiple nozzles was larger than that of a single jet, it is found that the sound-pressure level radiated from multijets becomes the same or lower than that from the single jet. [Work supported by the Ministry of Education and Culture of Japan, Grant No. C2-09650187.]
Acoustic wave scattering from a coated cylindrical shell
Authors: Ko Sung H.
Published: July 2002

A theoretical model was developed to evaluate the effect of a coating on a cylindrical shell. The coating is designed to reduce the flexural wave noise generated by the vibration of the cylindrical shell. In underwater applications, this coating is called an inner decoupler. The outer surface of the composite structure, which consists of the cylindrical shell and the inner decoupler, is in contact with water; the core (cavity) of the structure contains air. The analysis of the problem is made for a double-layer cylindrical structure that is immersed in water. The theory of elasticity, the elastic wave propagation, the acoustic wave propagation, and pertinent boundary conditions are used in formulating the problem. The two-dimensional problem is treated in this study. This implies that all the quantities are independent of the axial coordinate. Numerically calculated results for both coated and uncoated cylindrical shells are presented to compare these two directivity patterns.
Acoustically induced cavitation fusion
Authors: Crum Lawrence A.
Published: July 2002

In 1982, Hugh Flynn was issued a patent (No. 4,333,796) for a Method of Generating Energy by Acoustically Induced Cavitation Fusion and Reactor Therefor. Although it was largely ignored at the time, there have been several recent papers that treat the subject of acoustically induced fusion as quite plausible. Such prescience in the area of cavitation research was typical of Hugh’s work. This patent shows such an enormous grasp of detail, and suggests Hugh must have given a great deal of thought and energy to its composition. The author will review some of the interesting aspects of this patent as well as describe some of the most recent activity on this topic. He will also reflect on his many rewarding and stimulating experiences with Hugh over the past 30 years.
Cavitation and capillary wave from a parametric decay scheme
Authors: Sato Masanori , Fujii Toshitaka
Published: July 2002

Acoustic cavitation in liquids and capillary waves which cause ultrasonic atomization are considered to be related to the 1/2 subharmonic of ultrasonic surface waves via parametric decay instability. The cavitation bubble oscillation mode is an asymmetric surface bubble oscillation that does not easily emit ultrasonic waves into water and accumulates acoustic energy from longitudinal waves. The capillary waves accumulate acoustic energy in a surface of liquid, enough to be used not only for atomization but also the separation of water-ethanol solution. These were confirmed by experiments using ultrasonic longitudinal waves in water.
Uncertainty in modeling the dynamics of structures in midfrequency range
Authors: Machens Kai-Ulrich , Brechlin Eike
Published: July 2002

Based on measurements of the energy contents in single struts in a complex truss structure (109 struts, 35 joints) [Machens, Dyer. Acustica 81 (1995)], a numerical simulation of the truss dynamics using the direct dynamic stiffness method was performed. Great care was taken to account for flexural, longitudinal, and torsional waves in the struts, moments of inertia and masses of the joints, complex coupling stiffness (translational and rotational) including a loss factor between joints and struts, as well as material damping in the struts. The struts were modeled as Euler–Bernoulli–Beams and additionally as Rayleigh–Timoshenko–Beams. Frequency averaging proved to be important in the midfrequency range as a meaningful comparison with the measured data depends on a high accuracy in modeling and choice of material parameters. The broadband frequency averaged energy in single struts show a high sensitivity towards various factors such as small random variations of the geometry and of the complex coupling stiffnesses as well as the use of first- and second-order beam theory. The results show that a truss, which is built up from simple elements, becomes fuzzy merely by its high number of coupled elements.
Assessment of construction vibration impacts on historic structures
Authors: Balachandran Chetlur G.
Published: July 2002

This paper addresses construction-related ground vibration impacts to historic structures located in an area where three options are being considered for providing capacity improvement to an existing roadway. Historic structures within the project area are: a Fort, a Legislature building, an electrical substation, and an auxiliary building. The above fragile structures are more likely to be affected by construction-related ground vibration impacts than by operational traffic-induced vibration impacts. The buildings are in close proximity to the existing heavily traveled roadway and are already experiencing moderate levels of ground vibration from road traffic. Potential vibration effects from heavy construction equipment include annoyance to people inside these buildings and potential for minor damage to the buildings. The particular concern in the present study is to comply with ground-vibration criteria to safeguard identified structures within the project corridor against construction-induced ground vibration. The various national and international criteria that were used to assess vibration impacts together with the results of vibration impact assessment will be presented. Construction of the roadway alternative that would cause the least vibration impact was identified and mitigation was considered.
Multichannel audio signal compression and quality assessment for AV communications
Authors: Hong Jin-Woo , Jang Dae-Young , Kim Seong-Han
Published: July 2002

This paper describes an algorithm for multichannel audio signal compression using the psychoacoustic model, an implementation and the result on quality assessment of real-time operating multichannel audio codec, and a multiplexing technique of synchronization for AV communication. The algorithm which is based on the MPEG-2 audio standard, utilizes psychoacoustic modeling, sub-band analysis and synthesis, and bit allocation for information as key technology. The audio codec was implemented on real-time operation by using a flexible DSP system in which an encoder and a decoder are independently designed for processing a formatted digital audio bit stream, and can compress the multichannel audio data of about 3848 kbits/s into 384 kbits/s. A subjective test for quality assessment of multichannel audio codec was performed using double blind and triple stimuli with hidden reference method. In the test condition with 17 subjects and ten test materials, the test result with 95% confidence intervalshows that all test materials except one (pitch pipe sound) are awarded mean difference grades better than −0.6 and this audio codec is acceptable for AV communication or broadcasting. Finally, a multiplexing method to control time stamp for synchronization of AV communication is, in this paper, introduced from the implementation of HDTV system using this codec.
High-resolution, three-dimensional measurements of low-frequency sound propagation in shallow water
Authors: Frisk George V. , Becker Kyle M. , Connor Laurence N. , Doutt James A. , Sellers Cynthia J.
Published: July 2002

An overview is presented of the modal mapping experiment (MOMAX), which was conducted in March 1997 in the vicinity of the East Coast STRATAFORM site. Both fixed and moving source configurations were used to transmit several pure tones in the frequency range 50–300 Hz. The magnitudes and phases of these signals were recorded on several freely drifting buoys, each containing a hydrophone, GPS and acoustic navigation, and radio telemetry. High-resolution, three-dimensional measurements of the sound field were made out to ranges of 10 km and illustrate the influence of the laterally varying seabed, measured with a chirp sonar system. The precision navigation also enabled the creation of a two-dimensional, synthetic aperture planar array, parallel to the ocean surface. The pressure field data measured on the array were transformed into the wave number domain, where the lateral variability of the waveguide manifests itself in the spatially evolving spectral content of the modal field. Finally, the phases of the measured signals show remarkable stability and regularity, even in the context of complex, multimodal fields. This behavior can be exploited to make accurate estimates of the relative source/receiver speed from measurements of the time rate-of-change of the phase. [Work supported by ONR.]
Validation of source region energy partition calculations with small-scale explosive experiments
Authors: Clarke Douglas B. , Harben Philip E. , Hunter Steven L. , Rock Donald W.
Published: July 2002

The decrease in signal energy as the location of a nuclear explosion varies from deep in the ocean to above the ocean surface is a concern for the planned ocean monitoring component of the Comprehensive Test Ban Treaty. Small-scale experiments were designed to validate predictions of energy coupling by nuclear explosions in the ‘‘source region,’’ the origin of the signals that propagate in the deep underwater sound (SOFAR) channel. The experiments were performed in a biologically dead lake at a scale length of 1/50 (1/125 000 in explosive energy) relative to one kiloton using 6.82-kg charges of Pentolite 50/50. The acoustic energy coupled into the water was monitored at a 60-m range by a hydrophone string with eight piezoelectric sensors spaced from near-surface to a 30-m depth. Useful data were obtained at five burst locations: 5, 2, 0, −2, and −15 m. Results from the experiments and new calculations support the predicted energy partitioning for above-surface explosions with model and experiment peak pressures agreeing within a factor of two over three orders of magnitude variation. [Work performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under Contract W-7405-ENG-48.]
Field trials using an acoustic buoy to measure fish response to vessel and trawl noise
Authors: Wilson Chris D.
Published: July 2002

A freely drifting acoustic buoy was constructed to evaluate the response of fish to vessel and trawl noise. The buoy contains an echosounder and split beam transducer operating at 38 kHz. Transducer heading data from the buoy are collected to assess the directivity of the fish response (i.e., movement relative to vessel and trawl). Geographic position of the buoy is monitored via GPS. Data are stored onboard the buoy and telemetered directly to the support vessel. The radio link between the buoy and vessel is used to control the echosounder, receive buoy positions, and remotely generate echograms in real time. GPS data from the buoy are also transmitted via the Argos satellite system to the vessel to locate the buoy in the event that visual, radar, and direct radio contact are lost. Field trials include repeated passes by the NOAA research vessel Miller Freeman past the buoy at different ship speeds while free-running and trawling to determine the behavioral response of walleye pollock (Theragra chalcogramma) to vessel and trawl noise. Performance of the buoy and interpretation of the results will be discussed.
Sensitivity of transiently evoked otoacoustic emission to a long-term exposure of impulsive noise
Authors: Duvdevany Amnon , Furst Miriam
Published: July 2002

In spite of the regular use of ear protectors, 30%–40% of the soldiers that are often exposed to impulsive blast noise are suffering from hearing loss. The purpose of the present study is to find in what ears click-evoked otoacoustic emissions (COAEs) were influenced by the noise exposure. The preliminary study included testing of 15 healthy soldiers. They were exposed to blast noise (M-16 riffles) accompanied by replicas from a semi-enclosed firing range in two consecutive sessions, followed by half a year of exposure to continuous blast noise (service period). In each stage COAEs were measured. The blast noise was precisely measured with microphones located next to the shooters’ ears. None of the soldiers acquired a hearing loss. In most subjects COAE levels have significantly changed in the frequency range 2.5–4 kHz. It decreased in the postexposure condition relative to the preexposure by ∼3 dB. It increased before the second training session by ∼8 dB, and it decreased in the last measurement by ∼5 dB. A protection and a destruction mechanism are possibly operating. The protection mechanism reduces the cochlear amplification and causes a reduction in COAE level. The destruction mechanism increases the cochlear nonuniformity which causes an increase in COAE level.
Effects of impulse noise on the hearing of fetal sheep in utero
Authors: Gerhardt Kenneth J. , Huang Xinyan , Abrams Robert M.
Published: July 2002

Knowledge of the transmission of exogenous sounds to the fetal head and the effects that these sounds have on fetal hearing is incomplete. The purposes of this study were to measure the transmission of impulse noise into the uterus and to evaluate the effects of impulse noise delivered to pregnant sheep on the hearing of the fetus in utero. A shock tube produced impulses that averaged 169.7 dB peak sound pressure level (pSPL) in air. In the uterus, the pSPL varied as a function of fetal head location. When the fetal head was against the abdominal wall, peak levels were within 2 dB of airborne levels and the stimulus resembled a Friedlander wave. When the fetal head was deep within the uterus, the duration of the impulse increased and the peak amplitude decreased. In some instances the decrease in pSPL exceeded 10 dB. Slight elevations of evoked potential thresholds were noted but only for low-frequency stimuli. The integrity of hair cells from these animals was assessed using scanning electron microscopy.
Vibration transmission via a nonideal beam junction: FEM and analytical combined methods
Authors: Grouchetski Igor , Rébillard Eric
Published: July 2002

The study is devoted to the calculation of the vibration transmission via a nonideal junction; the example considered is an L-beam system including two steel beams and an elastic block between them. A combination of two calculation methods is used. A finite element method (package ABAQUS) is used to determine the stiffness characteristics of the elastic block having a rectangular parallelpiped shape. These stiffness characteristics are substituted into the calculation for the vibrational behavior of the L-beam system. For such a calculation, the transfer matrix method (TMM) is applied. The experimental approach of the study is divided into two different parts. First the tension-compression and the shear stiffnesses of the elastic block are measured, and, second, the transfer mobility through the complete L-beam system with the rubber elastic block between the two beams is measured. For the two cases, calculated and measured results are compared.
The condition for beam-bending modes to dominate in the vibro-acoustic behavior of a circular cylindrical shell
Authors: Wang Chong , Lai Joseph C. S.
Published: July 2002

The acoustic radiation from circular cylindrical shells is of fundamental and applied interest primarily because cylindrical shells are widely used in industries. However, according to previous studies, only a few special cases, for example, a cylindrical shell under the assumption of beam bending, can be solved analytically. Obviously, in practice, the vibration behavior of a cylindrical shell may not be assumed to be beam bending in the whole frequency range of interest. This is because the vibration behavior of a cylindrical shell changes with frequency. Therefore, it is important to determine the condition under which a circular cylindrical shell would behave like beam bending so that the analytical solution could be used correctly. In this paper, an analysis of the basic vibration behavior of circular cylindrical shells using the Love’s equations shows that for an infinite length cylindrical shell, the beam-bending wave would always be propagating with other flexural waves of different circumferential mode numbers. However, for a finite-length circular cylindrical shell, below the cutoff frequency of n=2 mode, beam-bending modes would dominate the vibration response so that it can be treated as a beam with reasonable accuracy. This analytical result is supported by calculations obtained using the boundary element method.
A simple model for structure-borne sound transmission based on direct wave and first reflections
Authors: Liang Jian , Petersson Bjorn A. T.
Published: July 2002

In finite structures, the total wave field is composed of the direct wave, the first reflections as well as multiple, higher-order reflections. When the structural damping is significant and the divergence of the wave is considered, it is reasonable to assume that those waves reflected more than once only contribute marginally to the total field, and thus can be ignored to a first approximation. This suggests a simple description of the field which takes the direct wave and the first reflections into account. The semi-infinite system realizes an example of such models. The question addressed herein is the performance of those simple descriptions. This contribution first presents an investigation of the performance for one-dimensional systems. It is shown that the corresponding semi-infinite system can be used to: (1) predict the nodal lines in the spatial domain and the locations of deep troughs in the frequency domain; (2) obtain accurate motion transmissibilities. Second, the extrapolation to two-dimensional systems is presented, accompanied by results for platelike structures.
Pressure-flow relationship in a biophysical model of phonation
Authors: Alipour Fariborz , Titze Ingo
Published: July 2002

Simulation data are presented from a computer model that combines vocal fold tissue mechanics, laryngeal aerodynamics, and vocal tract acoustics. These simulations are based upon the laws of physics that govern airflow, vibration of the vocal folds, and wave propagation in the vocal tract. The tissue mechanics was modeled with the finite element method with 100 nodes and 166 elements in each layer of the 15-layer model. The laryngeal aerodynamics was modeled by the solution of two-dimensional unsteady Navier–Stokes equations with a finite volume method with a 64×82 nonuniform staggered grid. The model has been used to demonstrate self-oscillatory characteristics of the vocal folds and the flow pattern in the larynx. In this study, simulations were performed for lung pressure ranging from 4 to 24 cm of water. Adduction control was simulated with activation of thyroarytenoid (TA) muscle that caused increased tension and bulging of the vocal folds. Results are reported for glottal waveform, nodal coordinates, and velocity distributions in the larynx. Preliminary data suggest that the relationship between mean pressure and mean flow is almost linear. Frequency and amplitude contours of the model as functions of the lung’s pressure and TA activation level reveal their increasing pattern with these parameters.
The analysis and classification of small-scale tissue structures using the generalized spectrum
Authors: Donohue Kevin D. , Forsberg Flemming , Halpern Ethan J.
Published: July 2002

Conventional ultrasonic imaging systems primarily use backscattered signals for creating qualitative images that reveal large-scale structures, such as tissue boundaries. Efforts to extract additional quantitative information have resulted in limited success. The nonstationarities of the scatterers comprising biological tissue often violate conditions for applying common signal characterization and estimation methods. In addition, ultrasonic tissue properties (such as attenuation, velocity, scatterer density, size, and structure) ambiguously encode information into the backscattered signal, making it difficult or impossible to extract and quantify a single property. This paper presents the generalized spectrum (GS) as a method for analyzing and quantifying the properties of small-scale resolvable structures (on the order of 1 to 4 mm), which result from tissue structures such as lobules, ducts, and vessels. The GS extends the capabilities of power spectral density to include meaningful phase information that results from small-scale structure. The relevant properties of the GS include its ability to reduce the effects’ diffuse scatterers (speckle), and permit normalization schemes that significantly limit the effects of system response and attenuation from the overlying tissue. An implementation of the GS in an analysis and classification of normal and metastic liver tissues is also described.
A Wold decomposition-based autonomous system for detecting breast lesions in ultrasound images of the breast
Authors: Georgiou Georgia , Cohen Fernand S.
Published: July 2002

This paper presents an autonomous system for detecting lesions in the breast. The Wold decomposition algorithm described is used to decompose the RF echo of the breast into its diffuse and coherent components. The coherent component is modeled as a periodic sequence and the diffuse component is modeled as an autoregressive time series of low order. The parameters of the model are estimated from selected regions of the RF image and used as detection features. The database of images that was used contained 370 B-scan images from 52 patients, obtained in the Radiology department of the Thomas Jefferson Hospital. The pathologies of interest are carcinoma fibrocystic and stromal fibrosis disease and fibroadenoma. Empirical ROC techniques were used to evaluate the detection rate on single parameters of the model, such as the residual error variance and the autoregressive parameters of the diffuse component of the RF echo. The area under the empirical ROC curve for detecting lesion regions versus normal RF regions is 0.901. The area under the ROC curve for detecting carcinoma versus normal regions is 0.904. The corresponding areas for normal regions versus stromal fibrosis/fibrocystic regions and fibroadenoma regions are 0.942 and 0.899, respectively.
Wavefront distortion measurements in the human breast
Authors: Gauss R. C. , Trahey G. E. , Soo M. S.
Published: July 2002

Published wavefront distortion (phase aberration) measurements for the human breast have been inconsistent, ranging from mild phase aberrations (8 ns rms) to severe phase aberrations (67 ns rms). These measurements are required to specify arrays and assess the potentials of and appropriate algorithms for adaptive imaging. They require high interelement uniformity so that receive signal variations between elements can be attributed to wave propagation effects. Array elements must be small to minimize the integration of the arriving wavefront across the face of the element. The array aperture must be large enough to allow target visualization and to provide high correlations between neighboring elements for pulse-echo measurements. An apparatus to make concurrent pulse-echo and pitch-catch (through transmission) waveform measurements in a clinical setting has been developed. The breast is stabilized between opposing transducers with light compression. After fixing the position of the transducers, pulse-echo and pitch-catch snapshots are captured sequentially with tissue and reference phantom targets. Data were collected from four views of the left breast in 12 volunteers. The rms phase error was significantly smaller for pulse-echo measurements (25±14 ns rms) than for pitch-catch measurements (60±23 ns rms). [Work supported by NIH.]
Radiation impedance of resonant ultrasound spectroscopy modes in fused silica
Authors: Zhang Hong , Sorbello R. S. , Hucho Carsten , Herro Joseph , Feller Jeffrey R. , Beck D. E. , Levy Moises , Isaak D. , Carnes J. D. , Anderson O.
Published: July 2002

The pressure dependence of the resonance frequency of several resonant ultrasound spectroscopy modes in a sample of fused silica has been measured at UCLA in atmospheres of air, helium, and argon near ambient temperature. For both compressional and torsional modes, the radiation resistance is linearly dependent upon pressure and increases with the molecular mass of the surrounding gas. The effects are larger for breathing modes than for torsional modes. They also increase with the molecular mass of the gas. A radiation impedance model is presented which explains some of these data qualitatively and quantitatively.
A comparison of bistatic scattering from two geologically distinct mid-ocean ridges
Authors: Chia Chin Swee , Fialkowski Laurie T.
Published: July 2002

A comparison is made of bistatic scattering from two distinct deep-ocean ridges. The ridges are located along a segment valley on the western flank of the Mid-Atlantic Ridge (MAR). The acoustic data sets were acquired during the Main Acoustics Experiment of the Acoustic Reverberation Special Research Program. Detailed analysis of bistatic scattering from one of these ridges, named B′, has been previously presented by some of the authors. The purpose of this paper is to present a similar analysis for the second ridge, C′, for comparative purposes. This comparison is important because the ridges span the two geologically distinct classes found in the MAR. There is a possibility, therefore, that their scattering characteristics may be extrapolated to ridges throughout the MAR. For example, B′ is an ‘‘outside corner’’ and therefore is composed of highly lineated scarps and terraces, while C′ is an ‘‘inside corner’’ that is characteristically amorphous with irregular large-throw normal faults. While major scarps on these ridges can be easily resolved by the towed-array system, smaller-scale anomalies such as gullies and trellises are often underresolved by nearly an order of magnitude. These anomalies are found to introduce large variances in the bistatic scattering characteristics of a given scarp.
Sound waves attenuation in shallow water with rough boundaries
Authors: Katsnelson Boris G. , Pereselkov Sergey A. , Kuz’kin Venedict M. , Petnikov Valery G.
Published: July 2002

Here the object is to estimate the effect of scattering by randomly rough seabed and surface waves on attenuation of low-frequency sound waves in shallow water. The experiment was pursued with CW signals (100 and 230 Hz) in Barents Sea. The transmission loss and interference pattern of a sound field were measured within 100 km of the acoustic sources. Mesoscale relief of the bottom with spatial resolution 10 m and wind parameters were recorded as well. The experimental results (the average sound intensity) were compared with theoretical ones calculated with and without taking into account seabed and surface roughness. The calculation was carried out on the base of modal theory of sound scattering by rough boundaries in a waveguide. It was demonstrated that the random roughness substantially affects the transmission loss for long distances. In this paper the method is suggested for bottom parameter estimation using the statistical attributes of sound field in shallow water with random rough boundaries as well. [The work was supported by Russian Foundation of Basic Research (Grant 96-02-17194).]
Classroom acoustics II: Acoustical conditions in elementary school classrooms
Authors: Gold Martin A. , Lee Hee Won , Siebein Gary W. , Lehde Mitchell , Ashby John , Ermann Michael , Hasell Mary Jo , Abbott Philip , Crandell Carl C.
Published: July 2002

Acoustical measurements of speech transmission index, reverberation time, early reverberation time, early-to-late energy ratios, loudness (or relative strength), articulation index, background noise levels, and signal-to-noise ratios were made in a number of elementary school classrooms in one school district to see how many rooms actually had acceptable acoustical conditions. The source and receiver locations for the acoustical measurements were determined through the participatory action research (PAR) described in Classroom Acoustics I. Measurements were made using a TEF analyzer with custom software to compute additional acoustical measurements. Both omni-directional and directional loudspeakers were used for the source signals. The acoustical measurements were conducted in a variety of source receiver conditions as observed in the PAR studies in the classrooms. General observations are related regarding the relationship between the measurements and the PAR. For example, the STI was always greater than 0.75 for the conditions under which the teachers actually taught. Speaker-to-listener distances of 4 m or less were observed for many classroom activities. Likewise the teachers employed many creative ways to control the behavior of the students to reduce background noise levels while they actually spoke.
Classroom acoustics III: Acoustical model studies of elementary school classrooms
Authors: Siebein Gary W. , Lehde Mitchell , Lee Hee Won , Ashby John , Ermann Michael , Gold Martin A. , Hasell Mary Jo , Abbott Philip , Crandell Carl C.
Published: July 2002

A 1:4 scale model was constructed with a series of interchangeable wall and ceiling panels to allow a battery of acoustical tests to be conducted for a variety of classroom designs. The walls and ceiling of the room could be changed from sound absorbent to sound reflective materials quickly. Scale furniture was also constructed for the room. The walls of the model could be adjusted from approximately 7 to 10 meters in length and from 2.5 m in height to 7 m in height. Acoustical measurements of speech transmission index, reverberation time, early reverberation time, early-to-late energy ratios, loudness (or relative strength), and articulation index were made in a number of simulated elementary school classrooms using both a TEF analyzer and impulse spark techniques. Classrooms where field measurements were taken as described in Classroom Acoustics II were modified to attempt to improve acoustical conditions in the rooms. The location and amount of absorbent material, the location and amount of sound reflective material, and the room volume were the major variables considered. In general rooms that followed good architectural acoustics design principles produced favorable acoustical measurements.
Combined beam tracing and Biot transfer-matrix model for predicting sound fields in enclosed spaces
Authors: Hodgson Murray , Wareing Andrew , Campbell Callum
Published: July 2002

Numerous methods exist for predicting sound fields in enclosed spaces such as rooms, aircraft cabins, and the sea. These are generally energetic approaches which ignore phase and associated wave effects, and which describe sound reflection from surfaces by the energy absorption coefficient. Many, such as ray tracing, require long calculation times. In the work reported here, a new model is presented which is computationally efficient, includes phase, and decribes surface reflection by the angularly varying surface impedance. It is a triangular-beam-tracing algorithm, combined with a Biot-theory transfer-matrix model for laterally homogeneous, multilayer, poroelastic surfaces. The Biot model has been validated in the case of plates, porous materials, and seabeds. The combined approach is being validated in comparison with predictions by analytic and numerical approaches, and with experiment. The model is being used to study the effect of surface extended reaction on enclosed sound fields.
Dependence of accuracy of reverberation time measurement on input filters
Authors: Sumarac Dragana S.
Published: July 2002

In this paper, attention was paid to the standard method for measuring frequency characteristics of reverberation time in rooms. The influence of transfer function characteristics of 1/1 and 1/3 digital octave input filters on differences in measuring values of reverberation time was studied. Procedures for complete digital analysis of recorded impulse response of the room were designed. All procedures were designed by the matlab software package. The verification of that measuring software was performed on a great number of recorded impulses in real rooms. The several classes of 1/1 and 1/3 digital octave FIR and IIR filters were designed according to the international standard IEC 225. The complete analysis was performed using the recorded reverberation decay curve in 20 rooms significantly different in volume and reverberation time values. The rooms were excited with broadband pink noise and short duration impulses. The values of measured reverberation times were statistically analyzed to show the expected variance that can appear due to differences of applied 1/1 and 1/3 digital input filters.
Sound field in long enclosures with diffusely reflecting boundaries
Authors: Picaut Judicaël , Simon Laurent , Polack Jean-Dominique
Published: July 2002

The sound field modelization by a diffusion equation is used to predict the sound propagation in long enclosures with diffusely reflecting boundaries. The diffusion equation is solved for time-varying sources and particularly in the steady state. Analytical expressions of sound attenuation and reverberation in infinite enclosures are given. Their simplicity makes them easy to apply to realistic diffusing long enclosures. For wide cross sections of enclosures and when absorption at the beginning and at the end walls is high, solutions for finite enclosures are also proposed. The source location and the absorption of each wall are taken into account in the model. Comparisons between analytical solutions, numerical simulations, and classical theory of diffuse sound field show good agreements. [Work supported by the PIR-Villes CNRS.]
Reverberance of an existing hall in relation to subsequent reverberation time and SPL
Authors: Hase Shigeo , Takatsu Akio , Sato Shin-ichi , Sakai Hiroyuki , Ando Yoichi
Published: July 2002

Psychological tests in relation to reverberance of sound fields were conducted in an existing hall which is a medium-sized multipurpose hall with 400 seats. Music and speech as sound sources were radiated from an omnidirectional dodecahedron loudspeaker on the stage. Paired-comparison tests were applied for the sound fields changing two orthogonal factors. These factors were the subsequent reverberation time Tsub and the SPL. The Tsub were adjusted by a hybrid system involving the reverberation control room and an electroacoustic system. 21 subjects took part in this test. The results indicate that the reverberance is influenced independently on the Tsub and the SPL. The reverberance increases with increasing both the Tsub and the SPL.
Searching for species identifiers in multifrequency target strength variability
Authors: Dawson James
Published: July 2002

Acoustic research has shown that the species of some schooling fish can be assigned based solely on measurement parameters from acoustic returns. For single targets, this process is complicated by the high variability of in-situ target strength (TS) measurements. Attempts at speciation based on the patterns of TS variability were confounded by interactions between acoustic frequency and fish directivity. Initial attempts at defining speciation parameters based on multifrequency target strength measures look promising. This paper reports on the results of simultaneously measuring the in-situ target strength of fish at 38-, 120-, and 420-kHz acoustic frequencies, and proposes the definition of several speciation parameters.
Fish’n krill: A 38/120-kHz acoustic separation
Authors: Simard Yvan
Published: July 2002

Volume backscattering data (Sv) at 38 and 120 kHz were collected in the Gulf of St. Lawrence, during daylight, in regions where krill scattering layers (SL) and pelagic fish (mainly capelin) were present. The SLs and fish aggregations were sampled with the Bioness zooplankton samples and with small-mesh pelagic trawls equipped with acoustic monitoring systems. Echointegration was performed on small bins of ∼5 m vertically and ∼50 m horizontally. Comparisons of Sv at the two frequencies indicated that krill SLs had stronger backscattering at 120 than at 38 kHz, as expected. The ratio was relatively constant within the same SL, but varied from one SL to the other in parallel with the size of krill. The backscattering from fish schools or fish aggregations or fish layers was stronger at 38 kHz than at 120 kHz. This permitted the separation of fish from krill on the echograms, even for complex cases where fish were embedded in krill SL or had structural patterns that mimic the signature of krill SL. The 38/120-kHz backscattering ratio appears therefore useful to separate krill from fish, or vice-versa, for better interpretation and estimation of these taxa individually.
Shock wave measuring techniques in liquids
Authors: Eisenmenger Wolfgang
Published: July 2002

The parameters of shock waves in liquids as used for lithotripsy have been measured with needle-, membrane-, and fiber optic probe hydrophones. The true rise times of planar shock waves are determined by surface detection or by the transient response of piezoelectric crystals. The different measuring techniques are compared with respect to their suitability for the determination of shock wave parameters, such as risetime, pulse width, positive and negative pressure amplitudes, and also with respect to aging, calibration sensitivity lifetime, etc. The fiber optic probe hydrophone appears as an optimum high precision standard for calibrated shock wave measurements in lithotripsy. Finally, aspects of the shock parameters with respect to the stone destruction efficiency are discussed.
Intensity measurements in various rooms: A new intensity probe
Authors: Druyvesteyn W. F. , de Bree H. E.
Published: July 2002

The main advantage of acoustic intensity measurements is that in a reverberant room the direct and the reverberant sound field can be determined. This property has been tested using the Bruel & Kjaer p-p probe in four different rooms (anechoic, reverberant and two listening rooms). As compared to the results in the anechoic room, small deviations, which can be positive and negative, were found. The deviations can be explained using a model of early reflections. A new intensity probe consisting of a microphone and a sound velocity sensor has been tested and compared with the Bruel & Kjaer p-p probe. The sound (particle) velocity sensor contains the Microflown, a novel micro-machined sensor. This silicon-based velocity microphone operates on a thermal principle. The dimensions of the Microflown are on the order of a cubic millimeter. For symmetry considerations, however, the sensors were packaged in a quarter inch package. Experiments were done in the anechoic and in the reverberation room. A good agreement was found.
Gas dynamics of mixtures within sonoluminescence bubbles
Authors: Szeri Andrew , Storey Brian
Published: July 2002

Sonoluminescence experiments are often conducted using mixtures of gases intentionally dissolved in the liquid, and, presumably, resident in the bubble interior. Even when only a single gas is dissolved in the host liquid, vapor is undoubtedly present within the bubble in addition to the intended gas. Hence, all sonoluminescence experiments can be assumed to involve gas mixtures even though the contents of the bubbles cannot be directly assayed. Two constituents of a gas mixture will have differing solubility in the host liquid, which complicates the amount of each species one would expect is resident within a bubble, depending on how the experiment was prepared. Moreover, there is little opportunity for mixing of the bubble contents due to the highly spherically symmetric nature of single-bubble sonoluminescence. Using the methods of computational fluid dynamics, the fate of gas mixtures within a strongly driven bubble is investigated. [Work was supported by a grant from the National Science Foundation.]
Observations of single-bubble sonoluminescence in simulated microgravity and hypergravity
Authors: Young Jeremy E. , Hicks Nathaniel K. , Binner A. C. , Richardson Susan , Marr-Lyon Mark J. , Marston Philip L.
Published: July 2002

Single-bubble sonoluminescence (SBSL) in water occurs when a bubble undergoes highly nonlinear volume oscillations in a sound field. In the presence of gravity, the SBSL bubble experiences a buoyancy force described by ρgV(t). There is also a Bjerknes force from the sound field. The time average of these two forces balances at the equilibrium location. If the SBSL apparatus is in normal gravity the bubble is displaced from the pressure antinode of the acoustic standing wave [Matula et al., J. Acoust. Soc. Am. 102, 1522–1524 (1997)]. Because of this displacement, the bubble has a vertical oscillation. One method of exploring the effects of the translational oscillations is to compare the light output of SBSL in microgravity to the light output of SBSL in normal or hypergravity. These were examined by an experiment performed aboard NASA’s KC-135A. The airplane performs parabolic maneuvers, giving short periods of microgravity and hypergravity (approximately 0 and 2 g, respectively). The results suggest a correlation of higher light output in microgravity than in hypergravity. [Work supported by Flags Up Feed, Inc., Space Grant Consortium, NASA, and W.S.U.]
Experimental measurement and numerical modeling of nonlinear propagation in biological fluids
Authors: Humphrey Victor F. , Verma Prashant K. , Duck Francis A.
Published: July 2002

The nonlinear pressure fields generated in three biological fluids (amniotic fluid, urine, and a 4.5% human albumin solution) by a circular 2.25-MHz transducer have been investigated experimentally using a flexible measurement facility and compared with numerical predictions. The acoustic field was generated by a single element 38-mm-diameter transducer coupled to a PMMA lens with a focal gain of 12 in water for source pressures from 0.007 to 0.244 MPa. The experimental results illustrate significant harmonic generation in all three fluids which may have safety and imaging implications. In addition, the facility was used to make low level measurements of the acoustic parameters of the fluids, including the frequency dependence of attenuation, at both room and physiological temperature. This data has been used in conjunction with a finite difference model based on the Khokhlov–Zabolotskaya–Kuznetsov equation (the Bergen Code) to model the experiments. The agreement with experiment was found to be generally good, indicating that this type of model may be useful for predicting in-vivo pressure distributions given an accurate knowledge of the medium parameters. [Work supported by EPSRC].