bluuebunny/crossref_metadata_2025 huggingface dataset:
Moment and force mobilities of semi-infinite tapered beams
Authors: Nijman Eugene J. M. , Petersson Bjorn A. T.
Published: July 2002

The implications of spatially varying structural properties for flexural vibrations will be addressed for beamlike systems. Under the assumption of pure bending, closed-form expressions for the mobilities of a semi-infinite wedge have been derived. The influence of tapering on the energy flow is analyzed for the structural system constituted by a finite length taper attached to a semi-infinite, uniform beam. It is found that the main distinction from the uniform case is a comparatively broadbanded transition from flexural vibrations governed by the properties of the deep part of the system to vibrations governed by those of the slender part. This transition region is featured by a stiffness-controlled global behavior in the case of a moment-to-rotational response, whereas a global resonant behavior is found in the case of force-to-translational response. It is also demonstrated that constructive and destructive interferences due to reflections from the discontinuity between the two structural members are superimposed on the global behavior. Based on the complete expressions for the configurations studied, estimation procedures for the mobilities will be proposed. In addition, experimental results will be presented which corroborate the description developed and the parameter influence established.
Measurement of flexural intensity using a dual-mode fiber-optic sensor
Authors: Sklanka Bernard J. , Reichard Karl M. , McDevitt Timothy E.
Published: July 2002

An experiment was performed which demonstrated the use of distributed optical fiber sensors to measure power flow in a damped cantilevered beam. Dual-mode optical fiber sensors are an implementation of an optical fiber interferometer in which one fiber acts as both the sensing and reference arms. When bonded to the surface of a structure the sensor provides a distributed measurement of the strain along the length of the sensor. The sensors output is proportional to the integral of the axial component of the strain along the length of the fiber. Two optical fiber sensors were used to measure power flow in a damped cantilevered beam. Finite difference and finite sum approximations were used to determine bending moment and rotational velocity from the output of the fiber sensors. These quantities were then used to calculate the far-field structural intensity. The structural intensity measured using the optical fiber sensors was compared to the structural intensity measured using a two-accelerometer method.
Improving convergence in scattering problems by smoothing discrete constraints using an approximate convolution with a smoothed composite Green’s function
Authors: Loftman Rickard C. , Bliss Donald B.
Published: July 2002

A method for efficiently treating discrete structural constraints using an approximate Green’s function approach to smooth the constraint influence is presented. A method called analytical/numerical matching is used to formulate a composite Green’s function that captures the local high-resolution content associated with the discrete force in a separate analytic local solution. This local solution in turn implies a smooth replacement for the original discrete force. This replacement is approximately integrated following the Green’s function formalism modified by a Taylor expansion of the forcing strength function. A smooth replacement for the discrete constraint results. This new smoothed problem converges more rapidly than the original discrete one. However, the difference between the smooth solution and the original is retained in the analytic local solution. The result is a composite solution of the original system that is more accurate for a given computational resolution compared with treating the discrete constraint influence directly. In the present example, a modal method is used. Therefore, a given computational resolution is measured by number of modes calculated. The method is demonstrated in the case of beam incident scattering from an infinite thin elastic shell periodically constrained by rings. [Work supported by ONR.]
Models of volume and roughness scattering in stratified seabeds
Authors: Ivakin Anatoliy N.
Published: July 2002

At high frequencies, two mechanisms of seabed scattering are usually taken into account which are due to roughness of the seabed surface (sediment–water interface) and volume inhomogeneities of near-surface sediment. The mean parameters of bottom medium are usually considered as independent from spatial coordinates. This corresponds to the assumption that sound penetration into the sediment is sufficiently small because of strong absorption. In this paper, more general models are considered where seabeds are assumed as statistically stratified (plane-layered on the average) with the mean parameters taken as various functions of depth. In particular, they can be step functions corresponding to different types of sediments in different layers. Another type of stratification corresponds to continuous depth-dependences and involve gradients of mean parameters. Effects of stratification are shown to be important at lower frequences due to scattering from internal interfaces and volume inhomogeneities of deep layers as well as the influence of regular refraction and reflection within seabed medium. As numerical examples, angular dependencies of the scattering strength in both monostatic and bistatic cases at different frequencies are calculated for seabeds of various types. Comparison with available data is presented and discussed. [Work supported by ONR.]
Nonlinear acoustic method for bubble density measurements in water
Authors: Sutin A. M. , Yoon S. W. , Kim E. J. , Didenkulov I. N.
Published: July 2002

Nonlinear scattering due to bubble oscillations was theoretically and experimentally investigated for bubble size distribution measurements in water. If two primary acoustic waves of different frequencies are incident on a bubble, the difference frequency component of primary waves is produced in the scattered field. The incoherent scattering at the difference frequency from bubbles was theoretically studied. It was shown that the difference frequency amplitude is proportional to the density of bubbles having resonance frequencies close to the difference frequency. It allows the use of difference frequency measurements to determine the bubble density in water. For experimental investigations two focused transducers were used to increase the levels of primary waves in the interaction zone. One of the primary frequencies was kept constant 2.25 MHz while another was changed from 2.22 to 1.93 MHz, so that the observed difference frequency was varied from 30 to 320 kHz. This frequency band corresponds to the resonant bubble radii from 109 to 10 μm. For the bubble clouds produced in a laboratory tank by an electrolysis-type and a slit-type bubble maker the bubble densities were well estimated with the present nonlinear acoustic method.
Projection data error estimation and correction for high-resolution tomographic acoustic microscopy
Authors: Chiao Richard Y. , Kent Davis , Lee Hua
Published: July 2002

In scanning tomographic acoustic microscopy (STAM), projection error correction is necessary for high-resolution tomographic reconstruction. In this paper, both phase and alignment errors are examined. These errors arise from several sources, including the quadrature receiver channels, the unknown initial phase term, and any misalignment in the rotational scan. The data acquisition process and the image formation algorithm for the STAM are reviewed, and a description of error estimation and correction is also presented. Experimental results from the STAM are included to demonstrate the capability and effectiveness of the error-removal techniques.
Analysis of the performance of a model-based optimal auditory signal processor
Authors: Gresham Lisa C. , Collins Leslie M.
Published: July 2002

Traditionally, psychophysical data have been predicted either by constructing models of the peripheral auditory system or by applying signal detection theory (SDT). Frequently, the theoretical detection performance predicted by SDT is greater than that observed experimentally and a nonphysiologically based “internal noise” source is often added to the system to compensate for the discrepancy. A more appropriate explanation may be that traditional SDT approaches either incorporate little or no physiology or make simplifying assumptions regarding the density functions describing the physiological data. In the work presented here, an integrated approach, which combines SDT and a physiologically based model of the human auditory system, is proposed as an alternate method of quantifying detection performance. To validate this approach, the predicted detection performance for a simultaneous masking task is compared to predictions obtained from traditional methods and to experimental data. Additionally, the sensitivity of the integrated method is thoroughly investigated. The results suggest that by combining SDT with a physiologically based auditory model, thereby capitalizing on the strengths of each individual method, the previously observed discrepancies can be partially explained as the result of physical processes inherent in the auditory system rather than unspecified “internal noise” and more accurate predictions of psychophysical behavior can be obtained.
Response to: “Comments on ‘Biot model of sound propagation in water-saturated sand’ ” [J. Acoust. Soc. Am. 103, 2723–2725 (1998)]
Authors: Chotiros N. P.
Published: July 2002

The approach advocated by Prof. Stoll, which lead to the parameter values marked “Historical,” has worked well for porous materials with cemented frames, such as fused glass beads and sandstone, but it does not work for sand. The parameter values, marked “Chotiros,” are uniquely able to match all four. The main issue lies with the values of the frame and grain moduli.
Sound strength in concert halls: The role of the early sound field on objective and subjective measures
Authors: Hyde Jerald R.
Published: July 2002

A very important objective parameter in the acoustical understanding of concert halls is the total sound strength G which is essentially the acoustical ‘‘gain’’ of the space, normalized to source power. Measurement data are not well predicted by current theories and indicate that there must be other component factors of G in addition to the factors of distance (r) and room constant (A) of current theory. Measurements show that significant changes in G, independent of distance, are found to be directly proportional to the variation in the early reflected level G50 (refl.). To check this finding, a test was conducted by adding a reflector within the reverberant boundary of a hall. A significant increase in G was found in the seating area where the G50 (refl.) was increased. While this may seem obvious, current theory does not predict this. The factor G is therefore also found to be a function of early reflected energy where such energy acts in effect as an amplification of the source. The area receiving this early energy is energized by this amplification factor. Measurements show that specific design to provide the early reflected energy can increase G50 (refl.) by 2 to 3 dB and effectively amplify G by up to 2 dB. Subjective tests on the perception of loudness will be reported showing that these increases are quite significant and well above the subjective limit for loudness. A relationship with hall quality and improved ‘‘intimacy’’ is suggested with this design approach.
A fast room acoustical simulation algorithm based on the free path distribution
Authors: Vorlaender Michael
Published: July 2002

A new algorithm is presented which provides estimates of impulse responses in arbitrary shaped rooms. It is applicable to any kind of room shape including nondiffuse spaces like workrooms or offices where, for instance, sound propagation curves are of interest. In the case of concert halls and opera houses it enables very fast predictions of room acoustical criteria like reverberation time, strength, or clarity. The algorithm is based on a conventional statistical ray tracing. However, a very low number of rays is used. During the ray tracing procedure, the distribution of free paths is recorded by considering the entire series of reflections per ray. Furthermore, the transition probabilities between free path classes and the absorption coefficients involved are stored. After the ray tracing, the free path distributions are evaluated by post-processing to create echograms. They include receiver-dependent direct sound and superposed exponential functions corresponding to classes of free paths. It is also possible to create reverberation tails without assuming a-priori diffuse sound fields and purely exponential decays.
Coupled-mode sound propagation in a range-dependent, moving fluid
Authors: Godin Oleg A.
Published: July 2002

Full-field acoustic methods for current velocity inversion require accurate and efficient mathematical models of sound propagation in a range-dependent waveguide with flow. In this paper, an exact coupled-mode representation of the acoustic field is derived for the corresponding 2-D problem. To account for the physics of the problem, normal modes in a corresponding range-independent waveguide are chosen as the local basis. Unlike the motionless case, vertical dependencies of acoustic pressure in individual normal modes are not orthogonal in the presence of currents. To overcome this difficulty, a five-dimensional state vector is introduced. Orthogonality of the state vectors corresponding to individual normal modes is established. In terms of the state vector, the set of linearized equations of the hydrodynamics becomes a single differential equation of the first order with respect to the range coordinate. By using the orthogonality, coupled equations are derived for range-dependent mode amplitudes. The resulting mode-coupling equations have the same form as those known for motionless case, but values of mode-coupling coefficients differ. The contributions to mode coupling from horizontal gradients in the sound speed, density, and flow velocity are isolated and analyzed. [Work suported by NSERC and ONR.]
Integral equation method for bistatic volume scattering from the seafloor
Authors: Jones Christopher D. , Jackson Darrell R.
Published: July 2002

In most theoretical developments of sediment volume scattering, the medium is assumed to have weak fluctuations in sound speed and density and is assumed to be statistically homogeneous. An exact integral equation method has been developed and is used to test these assumptions. Small perturbation theory results for single frequency bistatic scattering from the seafloor are compared with Monte Carlo simulations. Half-space and multiple scattering effects not included in most previous treatments are observed.
Numerical study on sound absorption characteristics of brick/block absorbing walls
Authors: Sakamoto Shinichi , Joe Dong-Jun , Tachibana Hideki , Mukai Hikari
Published: July 2002

The brick/block absorbing walls with openings and backing air space with porous materials are often used for absorption in low frequencies. The absorption in low frequencies can be explained by the well-known theory of Helmholtz resonance. In some measurement results of absorption coefficient, however, high absorption coefficients are seen in high frequencies. Regarding this problem, the authors have been investigating theoretically and experimentally as presented at the last ASA meeting (at Penn. State). Following these studies, further numerical analysis was carried out on simple 2-D models. The wave phenomena in the cavity and backing space/material were formulated by combining the FEM with the scattering wave theory. Comparison between the calculated result and the result of a 1/10 scale model experiment has indicated the validity of the numerical analysis.
Evaluation of spatial information from artificial head and four-microphone array measurements
Authors: Becker Joerg , Sapp Markus
Published: July 2002

Examinations on the acoustic qualities of enclosures are mostly restricted to the evaluation of single-number quantities like ‘‘reverberation time’’ and ‘‘gravity time’’ or criteria which qualify the perceptual qualities, for example, ‘‘definition’’ or ‘‘clarity index.’’ Most of these criteria are measured monaurally, although the spatial distribution of the reflections is essential for the acoustic quality of rooms. Spatial information can be registered with multimicrophone arrays or artificial heads. On the one hand it is easier to get the spatial information by using microphone arrays and on the other hand aurally adequate recordings can only be made with artifical heads. This paper focuses on the further development of algorithms for detecting virtual sound sources and compares evaluations of artifical head recordings with those made by a 4-microphone array.
Directivity patterns of small explosions
Authors: Arana Miguel
Published: July 2002

There are methods and equipment for the generation, amplification, and emission of acoustic impulses in order to evaluate the acoustic characteristics of a room by means of the Fourier transform from its impulse response. However, the responses of this equipment (especially the inertia of the loudspeakers and its lack of linearity) produce acoustic signals that do not reproduce reliably the necessary acoustic impulses. A notable dispersion was found in the measurements accomplished with these systems. The directivity patterns of small explosions have been measured and analyzed with the purpose of using them as impulsive acoustic sources. The typical durations of these impulses are between 0.1 and 0.2 ms. The sound power spectrum is relatively smooth from 1 to 10 kHz. The mean acoustic power is around 200 W (143 dB, Ref. 1 pW). For this an experimental device with 16 channels and software based on LabView were used. This communication will show the experimental device as well as the obtained results (mainly the dispersion of both the acoustic power and directivity patterns). [Work supported by Education Department of Government of Navarra.]
Qualitative evaluations of the acoustics of rooms: Real room studies and headphone studies
Authors: Gold Martin A.
Published: July 2002

This pilot study attempts to qualify the use of headphones to evaluate the listening conditions of existing and proposed architectural spaces. Qualitative listening evaluations of speech and music were conducted in multiple locations in three different listening environments: a 2000-seat multipurpose concert hall, a 600-seat lecture room, and a 120-seat lecture room. Groups of college age students were asked to evaluate loudness, clarity, reverberance, spatial impression, and background noise using a questionnaire with a seven-point bipolar rating scale [Cervone (1990)]. The speech and music sources were played through two adjacent loudspeakers at the front of the respective rooms while the students completed the evaluation forms. The speech and music sources were binaurally recorded on a DAT at the listener locations in the respective rooms. At a later time, students were asked to evaluate the acoustical qualities of the binaural recordings made in the rooms using the same questionnaire. The recordings were presented to the listeners in a random order in a blind subjective evaluation. Data from real room evaluations and headphone studies are compared and conclusions are drawn regarding the potential for headphone listening experiments as a means to study qualitative aspects of room acoustics.
Bioacoustic resonance absorption spectroscopy
Authors: Diachok Orest
Published: July 2002

Absorption losses at the resonance frequencies of sardines up to about 18 dB at 1.3 kHz at night, 15 dB at 1.7 kHz during the day and 35 dB at 2.7 kHz at dawn were observed at a range of 12 km during Modal Lion, a multidisciplinary experiment designed to isolate absorptivity due to fish from other effects on long-range propagation at a relatively shallow (83 m) site in the Gulf of Lion. Comparison of transmission loss measurements with a numerical sound propagation model that incorporates absorption layers in the water column permitted estimation of the average absorption coefficient, depth, and thickness of absorption layers. The depths and thickness of layers estimated from sound propagation measurements were in good agreement with echo sounder data. The measured resonance frequencies of dispersed fish at night were within 13% of theoretical computations, based on swim bladder dimensions which were derived from near coincident samples of adult (∼16 cm long) sardines. A smaller absorption line at 3.9 kHz at night is consistent with the resonance frequency of dispersed juvenile sardines, which are known to be ∼6 cm long, based on historical data. Measured resonance frequencies of sardines in schools were about 0.59 times the resonance frequency of dispersed sardines. The observed frequency shift is analogous to previously observed frequency shifts associated with ‘‘clouds’’ of bubbles. The results presented here suggest the possibility of long-term tomographic mapping of fish parameters over large areas using transmission loss measurements. [This work was supported by The Office of Naval Research.]
Pulse compression processing of zooplankton echoes
Authors: Warren Joseph D. , Stanton Timothy K. , Chu Dezhang , McGehee Duncan E.
Published: July 2002

A pulse compression process was used to analyze echoes from individual animals of three distinct morphological groups of zooplankton. The groups studied were fluidlike animals (Euphausiids, decapod shrimp), elastic-shelled (Gastropods), and animals containing a gas inclusion (Siphonophores). A broadband chirp signal was used to insonify freshly collected animals that were then tethered in a seawater tank either in the laboratory or on the deck of a ship. The decapod shrimp was tethered to a stepper motor and was rotated in 1-deg increments. The other experiments had some animals fixed and others moving freely. The pulse compression processing of the echoes from the animals temporally resolved multiple returns from an individual. Using existing scattering models [Stanton et al., J. Acoust. Soc. Am. (to be published)], the temporal and amplitude differences of the returns were used to estimate size and orientation. Estimates of the size of the animal were made for the Euphausiids, Gastropods, and Siphonophores, while orientation estimates were made for the decapod shrimp. These results agreed well with the actual dimensions of the animals.
Multistatic, multifrequency scattering from zooplankton
Authors: Greenlaw C. F. , Holliday D. V. , McGehee D. E.
Published: July 2002

Very satisfactory results have been obtained in estimating size abundances of small zooplankton such as copepods from inversion of multifrequency backscattering measurements. Application of this method has become almost routine in many situations. Fluctuations in the scatterer physical properties (density and compressibility) tend principally to cause errors in the abundance estimates whereas size estimates are largely unaffected. The model commonly employed for small crustacean scatterers, a truncated-mode version of the Anderson fluid sphere model, predicts bistatic scattering as well as monostatic backscattering. The behavior of bistatic scattering at angles approaching 90 deg predicted by this model shows that scattering spectra at these angles are quite sensitive to physical properties. This suggests that simultaneous measurements at multiple frequencies and one or more off-axis angles might permit estimation of the physical properties of zooplanktonic scatterers as well as their sizes. Preliminary modeling has been done for a single fluid scatterer to illustrate the potential for simultaneous estimation of size, density, and compressibility of zooplanktonic organisms in a laboratory setting. The character of the bistatic scattering may argue for nontraditional methods for inverting this sort of data.
Laboratory studies and theoretical modeling of bistatic scattering of fish
Authors: Ding Li , Ye Zhen
Published: July 2002

Bistatic scattering of fish, in particular forward scattering (scattering in the forward direction), has been identified as a potential means of detecting fish, supplementary to the traditional backscattering. A series of laboratory experiments has been conducted over the past 2 years to measure bistatic scattering characteristics of fish, including forward scattering strength and scattering patterns around the forward direction. It is observed that the forward scattering strength increases rapidly with acoustic frequency and is much stronger than the backscattering strength. The measured scattering patterns (at 120 and 200 kHz) suggest that the scattering is strongest in the forward direction when the incident wave is normal to the fish, and drops by 10–20 dB when the scattering angle deviates from the forward direction by a few degrees. In the latter case, the scattering strength is still much stronger than backscattering strength. These results are compared with a recently developed deformed cylinder model, and with a shelled cylinder model currently under development. [Work supported by the Science and Technology Agency of Japan, the Department of Fisheries and Oceans of Canada, and the National Central University of Taiwan.]
Numerical solution of the linearized Euler equations with high-order centered schemes
Authors: Ekaterinaris John A.
Published: July 2002

The unsteady, linearized Euler equations governing propagation of acoustic disturbances in the presence of a uniform free stream or sound scattering from solid surfaces are solved numerically. The governing equations are discretized in space using the standard fourth- and sixth-order central-difference schemes, and compact finite-difference schemes with spectrallike resolution are also used. The semidiscrete system of equations obtained after space discretization is marched in time using high-order, Runge–Kutta schemes. Numerical boundary conditions are applied at the far field in order to limit the extent of the computational domain. Solutions are computed first on Cartesian, equally spaced grids. Computed results for propagation of a pulse in a uniform medium are compared with existing analytic solutions. Next, sound scattering from a cylinder surface is computed using a nonuniform body-fitted numerical mesh. The effects of grid spacing, time accuracy, the method used for space discretization, and the boundary conditions on the computed solutions are investigated.
In situ absorption measurements using a transfer function technique and MLS
Authors: Dutilleux G. , Kristiansen U. R. , Vigran T. E.
Published: July 2002

The transfer function (or two-microphone) technique is a tool for measuring materials absorption related parameters as impedance or absorption coefficients. But this method is laboratory bound in its original form due to free field assumption and practical issues. It is shown that after proper modifications the transfer function technique can be used successfully in noisy and reverberating fields and work well at low frequency even in small measurement rooms, becoming therefore a really in situ measurement technique. A wide frequency range implementation is presented, based on a two-channel MLS measurement system, ‘‘energy ratio invariant’’ time windowing, a basic specular reflection propagation model with spherical decoupling, and a particular geometrical configuration. The measurement method is tested on a wide range of absorbers. For impedance measurements using infinite surface propagation models the uniqueness of the inversion procedure is investigated using the conformal mapping technique. In addition, faster inversion and model computation routines are proposed. Measurement results obtained under realistic in situ conditions are provided and compared with reference methods.
Energy focusing in bubbly flows
Authors: Putterman Seth , Weninger Keith , Hiller Robert A. , Barber Bradley P.
Published: July 2002

Sonoluminescence, cavitation damage at surfaces, and cavitation in accelerating flows are realizations of spectacular levels of energy focusing in nature. In a resonant sound field a single trapped bubble of gas can focus the ambient sound energy by 12 orders of magnitude to generate a clocklike string of picosecond flashes of ultraviolet light. [Barber et al., ‘‘Defining the unknowns of sonoluminescence,’’ Phys. Rep. 281, 65 (1977)]. In more complicated geometries a high level of sound leads to the formation of hemispherical bubbles attached to an exposed surface. These bubbles also emit light and in addition damage the surface. Measurements show that the pulsation of these bubbles maintains the hemispherical symmetry [Weninger et al., ‘‘Sonoluminescence from an isolated bubble on a solid surface,’’ Phys. Rev. E 56, 6745 (1997)], thus raising the question as to whether cavitation damage is due to (micro)jets or imploding (hemispherical) shock waves. Finally, flow through a Venturi tube generates a stream of bubbles which also emit subnanosecond flashes of light [F. B. Peterson and T. P. Anderson, Phys. Fluids 10, 874 (1967)]. Luminescence from an isolated trapped bubble in water seems to work well with any noble gas, whereas luminescence from cavitating flows and surface bubbles is quite dependent on xenon [argon bubbles appear to give no light at all]. The width of the SL flash [Gompf et al., Phys. Rev. Lett. 79, 1405 (1997), Hiller et al., Phys. Rev. Lett. 80, 1090 (1998)] has been found to be independent of wavelength suggesting that light is emitted from a new high energy phase of matter-probably a cold dense nano-plasma. The key unknowns of SL are the size and temperature of the hot spot from which the light is emitted. Experiments aimed at measuring these quantities will be discussed. [Research supported by the NSF.] a)Present address: CMS, Los Alamos National Laboratories, Los Alamos, NM. b)Present address: Lucent Technologies, Murray Hill, NJ.
Evolution of a sonoluminescence bubble under a magnetic field
Authors: Young J. B. , Cho H. , Kang W.
Published: July 2002

Studies of sonoluminescence (SL) in magnetic fields up to 20 T have revealed a striking magnetic field dependence. The intensity of emitted light is suppressed under increasing magnetic fields and vanishes above threshold magnetic field that depends on the applied sound pressure. Further increase in the magnetic field leads to the destruction of the bubble through dissolution. At a constant magnetic field, the light intensity is found to increase roughly linearly with increasing sound pressure until the bubble disappears above a cut-off pressure which depends on the strength of the magnetic field. The cut-off pressure is found to approximately double between 0 and 20 T. Further study of the SL bubble through the measurement of the phase of the emitted radiation relative to acoustic drive shows a large increase in phase under magnetic fields. These results suggest that the bubble grows significantly in size and that there may be a substantial modification of bubble dynamics under magnetic field. The origin of the observed effects, possibly due to magnetic field-induced anisotropies in the SL bubble, will be discussed in light of our recent anisotropy studies under magnetic fields.
Luminescence from spherically and aspherically collapsing laser-induced bubbles
Authors: Ohl Claus-Dieter , Lindau Olgert , Lauterborn Werner
Published: July 2002

Luminescence from laser-induced cavitation bubbles (SCBL) is investigated experimentally. This experimental technique offers several advantages over the acoustical driving technique for luminescence studies: The optical resolution of the imaging system allows the investigation of the shape of the luminescence spot. This technique facilitates the study of the spherical asymmetries during the bubble collapse phase. Finally, complications due to gas diffusion and Bjerknes forces are avoided. Comparison with theory gives good agreement between the size of the luminescence spot and the observed minimum bubble size for spherical symmetry. A rigid boundary greatly influences the light output; SCBL is only observed for a mildly aspherical bubble collapse.
Asymptotically unified exact solutions of the Khokhlov–Zabolotskaya equation
Authors: Makov Yuri N.
Published: July 2002

For the large distance traversed by the sonic beam the exact analytical and physically realistic solutions of the Khokhlov–Zabolotskaya (KZ) equation were found for the first time. The procedure of finding these solutions as the self-similar traveling waves identifies their asymptotical generality with respect to the initial arbitrary wave profiles. The resulting solutions consist of the periodically repeating parts of the second-order curvers such as hyperbolas, ellipses, and, in particular, parabolas. The boundaries between these parts are defined with the use of the preserved integrals of the KZ equation. The influence of nonlinearity, diffraction, which is seen in many-dimensional cases, and initial curvature of the phase front of the wave beam on the forming of the typical form of a specific asymptotical wave profile (N shaped or U shaped) was discussed. A comparison was made between analytical solutions with the numerical results for the KZ equation and the experimental data and a full agreement was discovered. These solutions play the same role among all the variations of solutions of the KZ equation, such as the well-known sawtoothlike wave for the equation of the simple waves (Riemann’s equation). [Work supported by CRDF.]
Binaural coherence and the localization of sound in rooms
Authors: Hartmann William M. , Constan Zachary A. , Rakerd Brad
Published: July 2002

The absorption coefficient of materials tends to decrease with decreasing frequency. Therefore, the ratio of direct to reverberant sound is normally least favorable at low frequency, and binaural coherence tends to be a minimum. However, the ability to localize sounds using interaural time differences (ITD) in the steady-state waveform requires binaural coherence, especially at low frequency. Lateralization experiments, using a forced-choice staircase technique, indicate that adequate localization based on ITD requires binaural coherence of at least 0.2. Measurements of binaural coherence in rooms find that binaural coherence is often less than that, which means that ITD cues can only be used on the transient portions of a signal. By contrast, interaural level differences are perceptually useful at high frequencies and increasingly dominate the localization of steady-state sounds as the environment becomes more reverberant. [Work supported by the NIDCD, Grant No. DC00181.]
Modeling the ‘‘effective’’ binaural signal processing
Authors: Zerbs Carsten , Dau Torsten , Kollmeier Birger
Published: July 2002

This paper describes a quantitative model for binaural processing in the auditory system. To overcome shortcomings of several proposed models, a monaural stage is employed for signal preprocessing [Dau et al., J. Acoust. Soc. Am. 99, 3615–3622 (1996)], which is able to simulate a large variety of monaural detection data. A binaural processing stage is added following Durlach’s EC model which is also a simple functional unit with a small set of constant parameters unit. The decision algorithm for both the monaural and the binaural channel is realized as an optimal detector in the same way as described in the monaural model. In the simulations the whole adaptive measurement procedure with the actual signals is realized. The model describes both monaural as well as binaural thresholds. The typical binaural masking experiments with the following stimulus parameters and their combinations were examined: signal frequency, signal duration, masker bandwidth, interaural masker and signal phase, interaural masker correlation, and delay in simultaneous and forward masking conditions. The model describes the experimental data with an accuracy of a few dB with some exceptions. Model predictions are discussed and compared to the performance of human observers and to predictions of other binaural models.
The influence of masker variability on estimates of monaural and binaural critical bandwidths
Authors: Kohlrausch Armin , van de Par Steven , Breebaart Jeroen
Published: July 2002

If integration bandwidths are derived from band-widening masking experiments, binaural estimates are usually a factor 2 to 3 larger than monaural estimates, at least at high levels. It is proposed that this difference does not reflect ‘‘different critical bandwidths,’’ but that it is a consequence of detection statistics. In monaural experiments, the variability in the masker energy limits detectability of the signal. Therefore with increasing subcritical bandwidths, the S/N ratio at threshold decreases. In binaural NoSπ experiments, the S/N ratio at subcritical bandwidths remains constant because the masker correlation is always 1 without uncertainty. Due to this absence of external variability in the masker correlation, detection must be limited by internal noise. Binaural detection in narrow-band conditions can gain from the spread of excitation across several critical bands, assuming that the internal noises are uncorrelated. The wider binaural critical band is then caused by masking the off-frequency spread through masker components outside the central critical band (for binaural model simulations, see Breebaart et al.). In this study it is shown that this scheme also applies to monaural frozen-noise maskers, which do not have external variability. In agreement with results from binaural experiments, the integration bandwidths increase considerably with masker level.
The effect of immersion on second language productions: The acquisition of American English /r/ and /l/ by Japanese children
Authors: Downs-Pruitt Jesica C. , Akahane-Yamada Reiko , Mazuka Reiko , Hayashi Akiko
Published: July 2002

Many studies have shown that the American English (AE) /r/ and /l/ are difficult for adult native speakers of Japanese to perceive and produce, sometimes even after substantial experience and/or intense training. In fact, there are many reports of first language (L1) effects on second language (L2) learning. Common lore promotes immersion as the best method of second language learning, particularly for overcoming L1 biases. The current study examined the effect of English-language immersion on Japanese children’s productions of AE /r/ and /l/. We studied productions from children in three age groups, 4-, 6-, and 8-year-olds. Native Japanese children, who had been immersed in an English-language environment, nonimmersed Japanese children, and native English children produced English-language words and nonwords which included /r/, /l/, and /w/ in three positions. The productions were evaluated by categorizing them into one of seven categories, which included a ‘‘correct’’ and ‘‘distorted’’ category for each intended gesture, as well as an ‘‘other’’ category. Significant differences in intelligibility were found dependent upon the age and language-experience group. Furthermore, the children in the three language-experience groups showed different substitution patterns. The results are discussed in the context of recent theories of L1 development and L2 learning.
Perceptual assimilation of Hindi dental and retroflex stop-consonants by native English and Japanese speakers
Authors: Pruitt John S. , Akahane-Yamada Reiko , Strange Winifred
Published: July 2002

Previous research has shown that English speakers have great difficulty distinguishing the dental and retroflex stop-consonants of the Hindi language. However, native Japanese speakers have somewhat less difficulty perceiving this contrast even though it is not employed in the Japanese language. Best and colleagues have attributed similar differences in the perception of non-native speech sounds to differences in the assimilation of such sounds to native-language speech categories [Best, McRoberts, and Sithole, J. Exp. Psych: Human Percept. Perform. 14 (1988)]. According to Best’s Perceptual Assimilation Model (PAM), four patterns of assimilation have been described which are purportedly predictive of perceptual difficulty. To determine if this model could be applied to the present case, native speakers of English and Japanese transcribed multiple instances of the Hindi consonants in different voicing/manner classes, produced with different vowels. Marked differences were found between the responses of the two language groups which were partially dependent upon the voicing/manner class of the contrast. Interestingly, an assimilation pattern emerged which was different from those discussed in PAM. Implications of these findings for PAM and for perceptual training of non-native speech sounds will be discussed. [Work supported in part by NIDCD.]
Cross-linguistic evidence for the acquisition of accent by the onset of word use
Authors: DePaolis Rory A. , Vihman Marilyn M. , Lefkovitch Leonard P.
Published: July 2002

An investigation of the acoustic correlates of stress or accent in infant vocalizations was undertaken using five English- and five French-learning participants at two developmental points, the onset of word use (10–13 months) and late in the single-word period (14–19 months). A data base of 555 disyllabic utterances (words and babble) was digitized from naturalistic recordings and quantified acoustically by indices of duration, amplitude, and fundamental frequency (F0). Cluster analysis as well as the results of perceptual judgments (i.e., both a bottom-up and a top-down approach) revealed a developmental trend toward the adult prosodic system. In addition, acoustic comparisons of French and American infants at both developmental points revealed differences in their use of amplitude, F0, and duration to accent a syllable. The differences were traceable to the adult patterns for the respective adult languages. These results suggest that infants’ perceptual attunement to prosody in the prelinguistic period manifests itself in the beginnings of adultlike production as early as the onset of word use. [Work supported in part by the UK Economic and Social Research Council.]
Statistical characteristics of bistatic sea surface scatter
Authors: Neumann Peter D. , Culver R. Lee
Published: July 2002

The characterization of reverberation, from the surface, the bottom, and/or the volume, is important in advancing the understanding of the mechanisms involved in underwater sound scattering. Numerous experiments and much theoretical work have been done in the area of monostatic reverberation, but the area of bistatic reverberation has been much less researched. This certainly is a result of the much more complex geometries involved in bistatic reverberation. This work studies the statistics of bistatic sea surface reverberation data from the FLIP experiment conducted in January of 1992. The data were verified as homogeneous and normally distributed using the Kolmogorov–Smirnov two-sample test with a confidence interval, α, equal to 0.1. Using a technique by which ensembles from different times were combined, meaningful deviations from a normal distribution were observed at the highest wind speed of 7.2 m/s. The bistatic surface scattering strengths were calculated from the data and compared with the predictions of a theory developed by S. T. McDaniel for the prediction of bistatic surface scattering strengths. The comparison showed good agreement with a rms deviation of about 3 dB. [Work supported by ONR.]
Stacking and averaging techniques for bottom echo characterization
Authors: Sternlicht Daniel D. , deMoustier Christian P.
Published: July 2002

Bottom-looking sonars operating at frequencies greater than 30 kHz transmit acoustic signals which penetrate at most a few meters into seafloor sediments, making them well suited to characterize the water/sediment interface. Acoustic wavelengths at these frequencies are small compared to the rms relief of the interface, resulting in bottom echoes dominated by incoherent energy and varying significantly in amplitude and shape as the sonar translates longitudinally above the interface. Because of this variability, echoes must be treated stochastically and determining the average shape of the bottom echo involves careful selection of stacking and averaging algorithms. Comparisons of a geoacoustic temporal model with 33- and 93-kHz backscatter echoes from sand and silt substrates reveal that a representative echo shape is obtained by averaging echoes along-track over a distance roughly equivalent to the 6-dB footprint diameter of the sonar beam pattern. To be meaningful, such averaging must be performed on echoes that have been aligned in time, thus removing effects due to transducer heave as well as small depth variations over consecutive pings. Echo alignment techniques based on thresholding minima, maxima, or half energy, on low-pass filtering techniques and on carrier frequency phase tracking, have been investigated and their relative merits are discussed. [Work supported by ONR N00014-94-1-0121.]
Effects of the modulated delay-time interval of the single reflection on subjective preference
Authors: Atagi Junko , Ando Yoichi , Ueda Yasutaka
Published: July 2002

In the past, experimental results of the sound-pressure level (SPL) were obtained which showed that the indoor sound field is regarded as a time-variant system due to an air current. Using the time-variant model represented by the direct sound and the varying delay time of single reflection, an experiment was performed on an effect on subjective preference. This experiment was focused on the effect of the modulation interval (Δ) of the delay time of the single reflection. The delay time of reflection (Δt1) was adjusted to the most preferred delay time of reflection which was obtained by the experiments for the time-invariant sound field. In the case of fast tempo music, where the minimum value of the effective duration of the autocorrelation function is τemin=43 ms, the scale value of subjective preference is higher in a time-variant sound field than a time-invariant one. On the other hand, in the case of slow tempo music, τemin=127 ms, such an effect could not be found. It is suggested that a time-variant sound field might have a positive effect on subjective preference in the performance of a fast tempo music.
Ultrasound contrast agent enhances vascular damage in mouse intestines
Authors: Gies Richard A. , Miller Douglas L.
Published: July 2002

Either Albunex®, a gas-body based contrast agent, or 5% albumin in saline without gas bodies was administered to anesthetized hairless mice at 10 ml/kg by retro-orbital injection. The mice then were exposed at the midsection to 1.09 MHz of ultrasound for 100 s, either continuous (cw) or pulsed (pw, 10 μs pulses repeated at 1 kHz), in a 37 °C water bath. After exposure, the intestines were examined to count petechiae and hemorrhages into the intestinal lumen. cw thresholds for statistically significant petechiae production were 0.7 MPa spatial peak pressure amplitude without added gas bodies, and 0.5 MPa with added gas bodies. At 0.7 MPa the mean counts (five mice) were 22 without and 120 with added gas bodies. A statistically significant number of hemorrhages occurred at 0.7 MPa (three per mouse) with the contrast agent. The pw thresholds with added agent were 1.4 MPa for petechiae and 2.8 MPa for hemorrhage. At 2.8 MPa, average counts were 227 petechiae and 2.4 hemorrhages. No statistically significant vascular damage occurred for pw exposure up to 2.8 MPa without contrast agent. In terms of mechanisms, the effects appeared to be partly thermal for cw, but primarily associated with ultrasonic cavitation for pw exposure. [Work supported by NIH CA42947.]