bluuebunny/crossref_metadata_2025 huggingface dataset:
Entrainment Characteristics of Transient Turbulent Round, Radial and Wall-Impinging Jets: Theoretical Deductions
Authors: Song Lijun , Abraham John
Published: August 2003

Expressions for the mass entrained in transient turbulent radial and wall-impinging jets are derived by employing scaling laws derived for quasi-steady jets. Quantitative values of the mass entrained in these jets are compared with that in the round jet through an analytical study. In the case of the round jet, the expression has been derived and reported in the literature. It is shown that the ratio of mass entrained in transient radial and round jets for the same mass and momentum flow rates has a constant value with respect to time. In the case of the wall-impinging jet, it is shown that the ratio of the mass entrained in the jet to that in the round jet is a function of the impinging distance and time. The increase in entrained mass with increase in jet penetration in the fully developed region is slower in the wall-impinging jet than in the round jet.
An Evaluation of a Two-Fluid Eulerian-Liquid Eulerian-Gas Model for Diesel Sprays
Authors: Iyer Venkatraman , Abraham John
Published: August 2003

A two fluid Eulerian-liquid Eulerian-gas (ELEG) model for diesel sprays is developed. It is employed to carry out computations for diesel sprays under a wide range of ambient and injection conditions. Computed and measured results are compared to assess the accuracy of the model in the far field, i.e., at axial distances greater than 300 orifice diameters, and in the near field, i.e., at axial distances less than 100 orifice diameters. In the far field, the comparisons are of drop mean velocities and drop fluctuation velocities and in the near field they are of entrainment velocities and entrainment constants. Adequate agreement is obtained quantitatively, within 30 percent, and qualitatively as parameters are changed. Unlike in traditional Lagrangian-drop Eulerian-fluid (LDEF) approaches that are employed for diesel spray computations, adequate resolution can be employed in the near field to achieve numerical grid independence when the two-fluid model is employed. A major source of uncertainty in the near field is in the modeling of liquid jet breakup and atomization.
A Criterion to Define Cross-Flow Fan Design Parameters
Authors: Lazzaretto A.
Published: August 2003

The paper presents an original criterion to parameterize systematically a cross-flow fan configuration according to the most significant variables defining the geometry and then affecting performance and efficiency. This choice of parameters has proved to be effective in a systematic series of experimental tests aimed at investigating directions for design improvement.
A Systematic Experimental Approach to Cross-Flow Fan Design
Authors: Lazzaretto A. , Toffolo A. , Martegani A. D.
Published: August 2003

A systematic investigation of cross-flow fan performances is presented according to an original criterion for the parameterization of fan geometry. Test facility and procedures are set up following ISO standards. The aim is to find which are the parameters most affecting fan performances and the effects of their design choice. Indications are found to design fans according to the desired objectives, such as maximum total pressure, total efficiency, and flow rate.
Concentration Probe Measurements in a Mach 4 Nonreacting Hydrogen Jet
Authors: Buttsworth D. R. , Jones T. V.
Published: August 2003

A new probe technique is introduced for the measurement of concentration in binary gas flows. The new technique is demonstrated through application of the probe in a Mach 4 nonreacting jet of hydrogen injected into a nominally quiescent air environment. Previous concentration probe devices have mostly used hot wires or hot films within an aspirating probe tip. However, the new technique relies on Pitot pressure and stagnation point transient thin film heat flux probe measurements. The transient thin film heat flux probes are operated at a number of different temperatures and thereby provide stagnation temperature and heat transfer coefficient measurements with an uncertainty of around ±5 K and ±4% respectively. When the heat transfer coefficient measurements are combined with the Pitot pressure measurements, it is demonstrated that the concentration of hydrogen within the mixing jet can be deduced. The estimated uncertainty of the reported concentration measurements is approximately ±5% on a mass fraction basis.
Application of an Angular Momentum Balance Method for Investigating Numerical Accuracy in Swirling Flow
Authors: Nilsson H. , Davidson L.
Published: August 2003

This work derives and applies a method for the investigation of numerical accuracy in computational fluid dynamics. The method is used to investigate discretization errors in computations of swirling flow in water turbines. The work focuses on the conservation of a subset of the angular momentum equations that is particularly important to swirling flow in water turbines. The method is based on the fact that the discretized angular momentum equations are not necessarily conserved when the discretized linear momentum equations are solved. However, the method can be used to investigate the effect of discretization on any equation that should be conserved in the correct solution, and the application is not limited to water turbines. Computations made for two Kaplan water turbine runners and a simplified geometry of one of the Kaplan runner ducts are investigated to highlight the general and simple applicability of the method.
Experimental Study of the Flow in a Compact Heat Exchanger Channel With Embossed-Type Vortex Generators
Authors: Dupont F. , Gabillet C. , Bot P.
Published: August 2003

The isothermal flow in a model channel of plate-fin heat exchanger with periodically arranged embossed-like vortex generators is investigated. Velocity measurements are performed by LDA in the transitional regime (Reynolds number from 1000 up to 5000). Strong longitudinal vortices are observed downstream of each generator. The vortex rollup process is highlighted by the evolution of the velocity vector field in the cross section of the flow. The modifications of the vortex characteristics after successively encountered generators are investigated. This work shows most of the flow features which are known to produce heat transfer enhancement, and shows that these smooth shaped vortex generators are very promising for enhanced heat exchangers.
Influence of Roughness on the Two-Phase Flow Structure of Sheet Cavitation
Authors: Stutz B.
Published: August 2003

The purpose of this work is to describe the two-phase flow structure of sheet cavitation. The experimental study is performed in a cavitation tunnel equipped with a Venturi-type test section. Data treatments based on the analysis of transit time histograms and local time fraction histograms have been used. The rate of vapor production required to sustain the cavities is estimated. Wall pressure measurements and visualization techniques are also used to perform momentum balance. The influences of the roughness and the geometry of the divergent part located beneath the cavity on the internal two-phase flow are investigated.
Intensity of Singular Stress Fields at the End of a Cylindrical Inclusion
Authors: Noda N.-A. , Genkai T. , Wang Q.
Published: August 2003

In short fiber reinforced composite it is known that the singular stress at the end of fibers causes crack initiation, propagation, and final failure. The singular stress field is controlled by the generalized stress intensity factors defined at the end of the inclusion. In this study the stress intensity factors are discussed for an elastic cylindrical inclusion in an infinite body under (A) asymmetric uniaxial tension in the x direction, and (B) symmetric uniaxial tension in the z direction. These problems are formulated as a system of integral equations with Cauchy-type or logarithmic-type singularities, where densities of body force distributed in infinite bodies having the same elastic constants as those of the matrix and inclusion are unknown. In the numerical analysis, the unknown body force densities are expressed as fundamental density functions and weight functions. Here, fundamental density functions are chosen to express the symmetric and skew-symmetric stress singularities. Then, the singular stress fields at the end of a cylindrical inclusion are discussed with varying the fiber length and elastic ratio. The results are compared with the ones of a rectangular inclusion under longitudinal and transverse tension.
On the Strain Saturation Conditions for Polycrystalline Ferroelastic Materials
Authors: Landis C. M.
Published: August 2003

A phenomenological constitutive law is developed for the deformation of polycrystalline ferroelastic materials. The model is framed within a thermodynamic setting common to internal variable plasticity. The two significant inputs to this model are a switching (yield) surface, and a hardening potential. To maintain simplicity, the shape of the switching surface is assumed to be spherical in a modified deviatoric stress space. In order to ascertain the functional form of the hardening potential, micromechanical self-consistent simulations of multiple single crystals, with tetragonal crystal structure, embedded in an effective polycrystalline matrix, are performed for differing loading paths in remanent (plastic) strain space. As a result of the asymmetry in the tension versus compression behavior of these materials, it is shown that pure shear loading does not result in pure shear straining. This feature of the material behavior is demonstrated with the self-consistent simulations and predicted by the phenomenological constitutive law. Ultimately, the phenomenological theory is able to capture the complex constitutive behavior of ferroelastic materials predicted by the micromechanical model.
Measurements of the longitudinal wave speed in thin materials using a wideband PVDF transducer
Authors: Kim Kwang Yul , Zou Wei , Holland Steve , Sachse Wolfgang
Published: August 2003

A flat transducer was constructed, using a 9-μm-thick PVDF (polyvinylidene fluoride) film for generation and detection of high-frequency ultrasonic waves, and used for measurements of the phase velocity of longitudinal waves traveling along the thickness direction in a very thin material. The transducer has a useful wideband frequency characteristic extending from 10 MHz to over 150 MHz. Measurements of the phase velocity of the longitudinal waves are carried out using a 0.212-mm-thick glass slide and a 0.102-mm-thick stainless-steel shim, using water as a coupling medium. The thickness limit for this measurement appears to be approximately 20 μm. The phase velocity of the longitudinal mode is obtained as a function of frequency in the frequency domain by using a modified sampled continuous wave (cw) technique. It can also be measured in the time domain by using a broadband pulse of short duration.
Pitch of amplitude-modulated irregular-rate stimuli in acoustic and electric hearing
Authors: van Wieringen Astrid , Carlyon Robert P. , Long Christopher J. , Wouters Jan
Published: August 2003

The pitch of stimuli was studied under conditions where place-of-excitation was held constant, and where pitch was therefore derived from “purely temporal” cues. In experiment 1, the acoustical and electrical pulse trains consisted of pulses whose amplitudes alternated between a high and a low value, and whose interpulse intervals alternated between 4 and 6 ms. The attenuated pulses occurred after the 4-ms intervals in condition A, and after the 6-ms intervals in condition B. For both normal-hearing subjects and cochlear implantees, the period of an isochronous pulse train equal in pitch to this “4–6” stimulus increased from near 6 ms at the smallest modulation depth to nearly 10 ms at the largest depth. Additionally, the modulated pulse trains in condition A were perceived as being lower in pitch than those in condition B. Data are interpreted in terms of increased refractoriness in condition A, where the larger pulses are more closely followed by the smaller ones than in condition B. Consistent with this conclusion, the A-B difference was reduced at longer interpulse intervals. These findings provide a measure of supra-threshold effects of refractoriness on pitch perception, and increase our understanding of coding of temporal information in cochlear implant speech processing schemes.
Cure monitoring using ultrasonic guided waves in wires
Authors: Vogt T. , Lowe M. , Cawley P.
Published: August 2003

The possibility of using ultrasonic guided waves for monitoring the cure process of epoxy resins is investigated. The two techniques presented use a wire waveguide which is partly embedded in the resin. The first technique is based on the measurement of attenuation due to leakage of bulk waves into the resin surrounding the waveguide. The second technique measures the reflection of the guided wave that occurs at the point where the waveguide enters the resin. Both the attenuation and the reflection coefficient change significantly during cure, and the numerical methods to relate these to the material properties of the curing resin are presented in this paper. The results from the modeling are experimentally verified and show good agreement. The applicability of each testing method is discussed, and typical cure-monitoring curves are presented.
The acoustical Klein–Gordon equation: The wave-mechanical step and barrier potential functions
Authors: Forbes Barbara J. , Pike E. Roy , Sharp David B.
Published: August 2003

The transformed form of the Webster equation is investigated. Usually described as analogous to the Schrödinger equation of quantum mechanics, it is noted that the second-order time dependency defines a Klein–Gordon problem. This “acoustical Klein–Gordon equation” is analyzed with particular reference to the acoustical properties of wave-mechanical potential functions, U(x), that give rise to geometry-dependent dispersions at rapid variations in tract cross section. Such dispersions are not elucidated by other one-dimensional—cylindrical or conical—duct models. Since Sturm–Liouville analysis is not appropriate for inhomogeneous boundary conditions, the exact solution of the Klein–Gordon equation is achieved through a Green’s-function methodology referring to the transfer matrix of an arbitrary string of square potential functions, including a square barrier equivalent to a radiation impedance. The general conclusion of the paper is that, in the absence of precise knowledge of initial conditions on the area function, any given potential function will map to a multiplicity of area functions of identical relative resonance characteristics. Since the potential function maps uniquely to the acoustical output, it is suggested that the one-dimensional wave physics is both most accurately and most compactly described within the Klein–Gordon framework.
At-sea measurements of sound penetration into sediments using a buried vertical synthetic array
Authors: Simpson Harry J. , Houston Brian H. , Liskey Steve W. , Frank Philip A. , Berdoz Alain R. , Kraus Larry A. , Frederickson Carl K. , Stanic Steve
Published: August 2003

Acoustic bottom penetration experiments were carried out in a medium-grain sandy bottom at a site in St. Andrews Bay, Florida. These investigations used a new buried, vertical, one-dimensional synthetic array system where a small hydrophone was water-jetted into the sediment to a depth of ∼2 m. Once buried, this hydrophone was mounted to a vertical robotics stage that translated the hydrophone upward in 1-cm increments. A broadband (3 to 80 kHz) spherical source, positioned 50 cm above the sediment–water interface, was used to insonify the sediment. Measurements were made with insonification angles above and below the critical angle by changing the horizontal distance of the source relative to the insertion point. This new measurement system is detailed, and results are presented that include temporal, frequency, and wavenumber analysis for natural and roughened interfaces. The measured compressional sound speed and attenuation are shown to be self-consistent using the Kramers–Kronig relation. Furthermore, only a single fast compressional wave was observed. There was no observation of a second slower compressional wave as predicted by some applications of the Biot model to unconsolidated water-saturated porous media.
Forward scattering of pulses from a rough sea surface by Fourier synthesis of parabolic equation solutions
Authors: Miles David A. , Hewitt Robin N. , Donnelly Marcus K. , Clarke Timothy
Published: August 2003

A variable depth step implementation of the range-dependent acoustic model (RAM) is applied to the modeling of forward scattering from a rough sea surface. The sea surface is treated within RAM simply as an internal interface between a water layer and an air upper halfspace. A comparison with a numerically exact integral equation is undertaken for the scattering of single frequencies from Pierson–Moskowitz sea surfaces. The method is extended to model the variability of linear frequency modulated pulses from a series of frozen sea surfaces in a shallow water waveguide. The subsequent effect of rough boundary scattering on the replica correlation process is investigated.
Predictability of noise indices in a high-rise residential environment (L)
Authors: Tang S. K. , Chan W. Y.
Published: August 2003

In the present investigation, daily noise level measurements were carried out at 12 independent sites within the closely packed high-rise residential areas in Hong Kong. Various environmental noise indices are calculated. Their cross-relationships and correlations with the population density and the daily traffic volume are also examined. Results suggest that the Ldn and Lden correlate very well with a multiple regression model, which involves both the population density and traffic volume, for the present site conditions.
Outer hair cell piezoelectricity: Frequency response enhancement and resonance behavior
Authors: Weitzel Erik K. , Tasker Ron , Brownell William E.
Published: August 2003

Stretching or compressing an outer hair cell alters its membrane potential and, conversely, changing the electrical potential alters its length. This bi-directional energy conversion takes place in the cell’s lateral wall and resembles the direct and converse piezoelectric effects both qualitatively and quantitatively. A piezoelectric model of the lateral wall has been developed that is based on the electrical and material parameters of the lateral wall. An equivalent circuit for the outer hair cell that includes piezoelectricity shows a greater admittance at high frequencies than one containing only membrane resistance and capacitance. The model also predicts resonance at ultrasonic frequencies that is inversely proportional to cell length. These features suggest all mammals use outer hair cell piezoelectricity to support the high-frequency receptor potentials that drive electromotility. It is also possible that members of some mammalian orders use outer hair cell piezoelectric resonance in detecting species-specific vocalizations.
The broadband social acoustic signaling behavior of spinner and spotted dolphins
Authors: Lammers Marc O. , Au Whitlow W. L. , Herzing Denise L.
Published: August 2003

Efforts to study the social acoustic signaling behavior of delphinids have traditionally been restricted to audio-range (<20 kHz) analyses. To explore the occurrence of communication signals at ultrasonic frequencies, broadband recordings of whistles and burst pulses were obtained from two commonly studied species of delphinids, the Hawaiian spinner dolphin (Stenella longirostris) and the Atlantic spotted dolphin (Stenella frontalis). Signals were quantitatively analyzed to establish their full bandwidth, to identify distinguishing characteristics between each species, and to determine how often they occur beyond the range of human hearing. Fundamental whistle contours were found to extend beyond 20 kHz only rarely among spotted dolphins, but with some regularity in spinner dolphins. Harmonics were present in the majority of whistles and varied considerably in their number, occurrence, and amplitude. Many whistles had harmonics that extended past 50 kHz and some reached as high as 100 kHz. The relative amplitude of harmonics and the high hearing sensitivity of dolphins to equivalent frequencies suggest that harmonics are biologically relevant spectral features. The burst pulses of both species were found to be predominantly ultrasonic, often with little or no energy below 20 kHz. The findings presented reveal that the social signals produced by spinner and spotted dolphins span the full range of their hearing sensitivity, are spectrally quite varied, and in the case of burst pulses are probably produced more frequently than reported by audio-range analyses.
Auditory and behavioral responses of California sea lions (Zalophus californianus) to single underwater impulses from an arc-gap transducer
Authors: Finneran James J. , Dear Randall , Carder Donald A. , Ridgway Sam H.
Published: August 2003

A behavioral response paradigm was used to measure underwater hearing thresholds in two California sea lions (Zalophus californianus) before and after exposure to underwater impulses from an arc-gap transducer. Preexposure and postexposure hearing thresholds were compared to determine if the subjects experienced temporary shifts in their masked hearing thresholds (MTTS). Hearing thresholds were measured at 1 and 10 kHz. Exposures consisted of single underwater impulses produced by an arc-gap transducer referred to as a “pulsed power device” (PPD). The electrical charge of the PPD was varied from 1.32 to 2.77 kJ; the distance between the subject and the PPD was varied over the range 3.4 to 25 m. No MTTS was observed in either subject at the highest received levels: peak pressures of approximately 6.8 and 14 kPa, rms pressures of approximately 178 and 183 dB re: 1 μPa, and total energy fluxes of 161 and 163 dB re: 1 μPa2s for the two subjects. Behavioral reactions to the tests were observed in both subjects. These reactions primarily consisted of temporary avoidance of the site where exposure to the PPD impulse had previously occurred.
Evaluation of an auditory model for echo delay accuracy in wideband biosonar
Authors: Sanderson Mark I. , Neretti Nicola , Intrator Nathan , Simmons James A.
Published: August 2003

In a psychophysical task with echoes that jitter in delay, big brown bats can detect changes as small as 10–20 ns at an echo signal-to-noise ratio of ∼49 dB and 40 ns at ∼36 dB. This performance is possible to achieve with ideal coherent processing of the wideband echoes, but it is widely assumed that the bat’s peripheral auditory system is incapable of encoding signal waveforms to represent delay with the requisite precision or phase at ultrasonic frequencies. This assumption was examined by modeling inner-ear transduction with a bank of parallel bandpass filters followed by low-pass smoothing. Several versions of the filterbank model were tested to learn how the smoothing filters, which are the most critical parameter for controlling the coherence of the representation, affect replication of the bat’s performance. When tested at a signal-to-noise ratio of 36 dB, the model achieved a delay acuity of 83 ns using a second-order smoothing filter with a cutoff frequency of 8 kHz. The same model achieved a delay acuity of 17 ns when tested with a signal-to-noise ratio of 50 dB. Jitter detection thresholds were an order of magnitude worse than the bat for fifth-order smoothing or for lower cutoff frequencies. Most surprising is that effectively coherent reception is possible with filter cutoff frequencies well below any of the ultrasonic frequencies contained in the bat’s sonar sounds. The results suggest that only a modest rise in the frequency response of smoothing in the bat’s inner ear can confer full phase sensitivity on subsequent processing and account for the bat’s fine acuity or delay.
Acoustic detection of manatee vocalizations
Authors: Niezrecki Christopher , Phillips Richard , Meyer Michael , Beusse Diedrich O.
Published: August 2003

The West Indian manatee (trichechus manatus latirostris) has become endangered partly because of a growing number of collisions with boats. A system to warn boaters of the presence of manatees, that can signal to boaters that manatees are present in the immediate vicinity, could potentially reduce these boat collisions. In order to identify the presence of manatees, acoustic methods are employed. Within this paper, three different detection algorithms are used to detect the calls of the West Indian manatee. The detection systems are tested in the laboratory using simulated manatee vocalizations from an audio compact disk. The detection method that provides the best overall performance is able to correctly identify ∼96% of the manatee vocalizations. However, the system also results in a false alarm rate of ∼16%. The results of this work may ultimately lead to the development of a manatee warning system that can warn boaters of the presence of manatees.
Informational masking and musical training
Authors: Oxenham Andrew J. , Fligor Brian J. , Mason Christine R. , Kidd Gerald
Published: August 2003

The relationship between musical training and informational masking was studied for 24 young adult listeners with normal hearing. The listeners were divided into two groups based on musical training. In one group, the listeners had little or no musical training; the other group was comprised of highly trained, currently active musicians. The hypothesis was that musicians may be less susceptible to informational masking, which is thought to reflect central, rather than peripheral, limitations on the processing of sound. Masked thresholds were measured in two conditions, similar to those used by Kidd et al. [J. Acoust. Soc. Am. 95, 3475–3480 (1994)]. In both conditions the signal was comprised of a series of repeated tone bursts at 1 kHz. The masker was comprised of a series of multitone bursts, gated with the signal. In one condition the frequencies of the masker were selected randomly for each burst; in the other condition the masker frequencies were selected randomly for the first burst of each interval and then remained constant throughout the interval. The difference in thresholds between the two conditions was taken as a measure of informational masking. Frequency selectivity, using the notched-noise method, was also estimated in the two groups. The results showed no difference in frequency selectivity between the two groups, but showed a large and significant difference in the amount of informational masking between musically trained and untrained listeners. This informational masking task, which requires no knowledge specific to musical training (such as note or interval names) and is generally not susceptible to systematic short- or medium-term training effects, may provide a basis for further studies of analytic listening abilities in different populations.
Infrasonic wind-noise reduction by barriers and spatial filters
Authors: Hedlin Michael A. H. , Raspet Richard
Published: August 2003

This paper reports experimental observations of wind speed and infrasonic noise reduction inside a wind barrier. The barrier is compared with “rosette” spatial filters and with a reference site that uses no noise reduction system. The barrier is investigated for use at International Monitoring System (IMS) infrasound array sites where spatially extensive noise-reducing systems cannot be used because of a shortage of suitable land. Wind speed inside a 2-m-high 50%-porous hexagonal barrier coated with a fine wire mesh is reduced from ambient levels by 90%. If the infrasound wind-noise level reductions are all plotted versus the reduced frequency given by f*L/ν, where L is the characteristic size of the array or barrier, f is the frequency, and ν is the wind speed, the reductions at different wind speeds are observed to collapse into a single curve for each wind-noise reduction method. The reductions are minimal below a reduced frequency of 0.3 to 1, depending on the device, then spatial averaging over the turbulence structure leads to increased reduction. Above the reduced corner frequency, the barrier reduces infrasonic noise by up to 20 to 25 dB. Below the corner frequency the barrier displays a small reduction of about 4 dB. The rosettes display no reduction below the corner frequency. One other advantage of the wind barrier over rosette spatial filters is that the signal recorded inside the barrier enters the microbarometer from free air and is not integrated, possibly out of phase, after propagation through a system of narrow pipes.
The masking level difference for signals placed in masker envelope minima and maxima
Authors: Buss Emily , Hall Joseph W. , Grose John H.
Published: August 2003

Previous data on the masking level difference (MLD) have suggested that NoSπ detection for a long-duration signal is dominated by signal energy occurring in masker envelope minima. This finding was expanded upon using a brief 500-Hz tonal signal that coincided with either the envelope maximum or minimum of a narrow-band Gaussian noise masker centered at 500 Hz, and data were collected at a range of masker levels. Experiment 1 employed a typical MLD stimulus, consisting of a 30-ms signal and a 50-Hz-wide masker with abrupt spectral edges, and experiment 2 used stimuli generated to eliminate possible spectral cues. Results were quite similar for the two types of stimuli. At the highest masker level the MLD for signals coinciding with masker envelope minima was substantially larger than that for signals coinciding with envelope maxima, a result that was primarily due to decreased NoSπ thresholds in masker minima. For most observers this effect was greatly reduced or eliminated at the lowest masker level. These level effects are broadly consistent with the presence of physiological background noise and with a level-dependent binaural temporal window. Comparison of these results with predictions of a published model suggest that basilar-membrane compression alone does not account for this level effect.
Particle drift in a resonance tube—a numerical study
Authors: Alexeev A. , Gutfinger C.
Published: August 2003

The paper considers longitudinal drift of small particles in a resonance tube, caused by periodic shock waves, and its effect on particle agglomeration. It is found that depending on particle size, drift is caused by shock waves and/or gas acceleration and compression. It is also shown that the drift velocity and direction can be controlled by the frequency of the piston that causes gas oscillations in the resonance tube. The obtained numerical solutions indicate that particle drift in a resonance tube enhances aerosol agglomeration. An agglomeration kernel is derived for this case, accounting for particle drift, leading to an estimate of agglomeration time. The time predicted by present model is of the same order of magnitude as that obtained from experiments in the literature.
Effects of interaural frequency difference on binaural fusion evidenced by electrophysiological versus psychoacoustical measures
Authors: Zhou Jianxun , Durrant John D.
Published: August 2003

The binaural interaction component (BIC=sum of monaural−true binaural) of the auditory brainstem response appears to reflect central binaural fusion/lateralization processes. Auditory middle-latency responses (AMLRs) are more robust and may reflect more completely such binaural processing. The AMLR also demonstrates such binaural interaction. The fusion of dichotically presented tones with an interaural frequency difference (IFD) offers another test of the extent to which electrophysiological and psychoacoustical measures agree. The effect of IFDs on both the BIC of the AMLR and a psychoacoustical measure of binaural fusion thus were examined. The perception of 20-ms tone bursts at/near 500 Hz with increasing IFDs showed, first, a deviated sound image from the center of the head, followed by clearly separate pitch percepts in each ear. Thresholds of detection of sound deviation and separation (i.e., nonfusion) were found to be 57 and 209 Hz, respectively. However, magnitudes of BICs of the AMLR were found to remain nearly constant for IFDs up to the 400-Hz (limit of range tested), suggesting that the AMLR-BIC does not provide an objective index of this aspect of binaural processing, at least not under the conditions examined. The nature of lateralization due to IFDs and the concept of critical bands for binaural fusion are also discussed. Further research appears warranted to investigate the significance of the lack of effect of IFDs on the AMLR-BIC. Finally, the IFD paradigm itself would seem useful in that it permits determination of the limit for nonfusion of sounds presented binaurally, a limit not accessible via more conventional paradigms involving interaural time, phase, or intensity differences.
Extending the domain of center frequencies for the compressive gammachirp auditory filter
Authors: Patterson Roy D. , Unoki Masashi , Irino Toshio
Published: August 2003

The gammatone filter was imported from auditory physiology to provide a time-domain version of the roex auditory filter and enable the development of a realistic auditory filterbank for models of auditory perception [Patterson et al., J. Acoust. Soc. Am. 98, 1890–1894 (1995)]. The gammachirp auditory filter was developed to extend the domain of the gammatone auditory filter and simulate the changes in filter shape that occur with changes in stimulus level. Initially, the gammachirp filter was limited to center frequencies in the 2.0-kHz region where there were sufficient “notched-noise” masking data to define its parameters accurately. Recently, however, the range of the masking data has been extended in two massive studies. This paper reports how a compressive version of the gammachirp auditory filter was fitted to these new data sets to define the filter parameters over the extended frequency range. The results show that the shape of the filter can be specified for the entire domain of the data using just six constants (center frequencies from 0.25 to 6.0 kHz and levels from 30 to 80 dB SPL). The compressive, gammachirp auditory filter also has the advantage of being consistent with physiological studies of cochlear filtering insofar as the compression of the filter is mainly limited to the passband and the form of the chirp in the impulse response is largely independent of level.
Effect of coupled oscillations on microbubble behavior
Authors: Allen John S. , Kruse Dustin E. , Dayton Paul A. , Ferrara Katherine W.
Published: August 2003

Ultrasound contrast agents are encapsulated microbubbles whose nonlinear acoustic scattering signatures have been the foundation of their use in diagnostic imaging. The coupled oscillations of microbubbles along their lines of center are investigated theoretically using radial equations in the monopole approximation and an energy balance, which is obtained for the system. Coupled microbubble pairs of different initial radii are investigated numerically relative to the normal modes for the linearized system. For microbubble pairs of different size bubbles driven below the mode of the smaller bubble and above the mode of the larger bubble, it is shown that oscillations of the smaller agent are affected substantially more by the coupling than those of the larger one. For separation distances of 10 and 500 microns, a difference of approximately 10 dB occurs in the second harmonic output of a 1.0-micron radius agent coupled with a 2.2-micron radius agent forced at 2.0 MHz and 0.3 MPa. The subharmonic spectral peak is shown to decrease approximately 19 dB for the coupling of 1.5- and 2.2-micron radius agents at 10- and 500-micron distances under the same acoustic forcing conditions. These coupling effects on the radiated pressure and its spectral power are highlighted for contrast agent imaging applications.
Optimization of structural variables of a flextensional transducer by the statistical multiple regression analysis method
Authors: Kang Kookjin , Roh Yongrae
Published: August 2003

The performance of an acoustic transducer is determined by the effects of many structural variables, and in most cases the influences of these variables are not linearly independent of each other. To achieve optimal performance of an acoustic transducer, we must consider the cross-coupled effects of its structural variables. In this study, with the finite-element method, the variation of the operation frequency and sound pressure of a flextensional transducer in relation to its structural variables is analyzed. Through statistical multiple regression analysis of the results, functional forms of the operation frequency and sound pressure of the transducer in terms of the structural variables were derived, with which the optimal structure of the transducer was determined by means of a constrained optimization technique, the sequential quadratic programming method of Phenichny and Danilin. The proposed method can reflect all the cross-coupled effects of multiple structural variables, and can be extended to the design of general acoustic transducers.
Evaluation of the integrals of target/seabed scattering using the method of complex images
Authors: Fawcett John A. , Lim Raymond
Published: August 2003

In this paper the integrals which arise in target/seabed scattering problems are examined. These are the integrals which express the propagation of a spherical harmonic term in a fluid above or below a half-space and the integrals which compute the conversion coefficients of outgoing spherical harmonics into incident spherical harmonics after a seabed reflection. A very efficient and accurate method of computing these integrals, using the method of complex images, is derived. Numerical comparisons with the exact integral expressions show the accuracy of this approach.
A theoretical study of the vibration and acoustics of ancient Chinese bells
Authors: Jing M.
Published: August 2003

In this paper, the acoustics of an ancient Chinese bell, which was made some 3000 years B. C., is studied theoretically. In ancient times, a set of the bells was used as a musical instrument. Unlike a western church bell and an ancient Indian bell, an ancient Chinese bell has two interesting acoustics. First, two tones can be heard separately as the bell is struck at two special points. The interval between the two pitches is always a minor or major third. Second, tones of the bell attenuate quickly, which is necessary for a musical instrument. So, an ancient Chinese bell is sometimes called a two-tone bell or a music bell. Although a three-dimensional model should be used to simulate the acoustics of the bell, a simplified model proposed in this paper does give some insight. Based on the lens-shaped cross section of an ancient Chinese bell, two tones of an ancient Chinese bell can be simulated by the vibration of a double-circular arch and the quick attenuation of tones can be simulated by acoustics of a cylinder with the lens-shaped cross section like a double-circular arch. Numerical results on the vibration and acoustics of the models are presented.
Diffraction and attenuation of a tone burst in mono-relaxing media
Authors: Dain Yefim , Lueptow Richard M.
Published: August 2003

The influence of intrinsic absorption in a relaxing medium and the resulting three-dimensional diffraction correction of the magnitude of the acoustic pressure averaged over the surface of a receiver is investigated for a tone burst. A rigorous formula for the damped acoustic pressure average at the receiver was obtained for arbitrary pulsed waves in a mono-relaxing medium. Depending on the pulse oscillation frequency, envelope duration, and relaxation frequency of the media, the plane wave burst envelope can be reduced, amplified, or otherwise deformed.
The role of auditory feedback in sustaining vocal vibrato
Authors: Leydon Ciara , Bauer Jay J. , Larson Charles R.
Published: August 2003

Vocal vibrato and tremor are characterized by oscillations in voice fundamental frequency (F0). These oscillations may be sustained by a control loop within the auditory system. One component of the control loop is the pitch-shift reflex (PSR). The PSR is a closed loop negative feedback reflex that is triggered in response to discrepancies between intended and perceived pitch with a latency of ∼100 ms. Consecutive compensatory reflexive responses lead to oscillations in pitch every ∼200 ms, resulting in ∼5-Hz modulation of F0. Pitch-shift reflexes were elicited experimentally in six subjects while they sustained /u/ vowels at a comfortable pitch and loudness. Auditory feedback was sinusoidally modulated at discrete integer frequencies (1 to 10 Hz) with ±25 cents amplitude. Modulated auditory feedback induced oscillations in voice F0 output of all subjects at rates consistent with vocal vibrato and tremor. Transfer functions revealed peak gains at 4 to 7 Hz in all subjects, with an average peak gain at 5 Hz. These gains occurred in the modulation frequency region where the voice output and auditory feedback signals were in phase. A control loop in the auditory system may sustain vocal vibrato and tremorlike oscillations in voice F0.
Stimulus presentation order and the perception of lexical tones in Cantonese
Authors: Francis Alexander L. , Ciocca Valter
Published: August 2003

Listeners’ auditory discrimination of vowel sounds depends in part on the order in which stimuli are presented. Such presentation order effects have been argued to be language independent, and to result from psychophysical (not speech- or language-specific) factors such as the decay of memory traces over time or increased weighting of later-occurring stimuli. In the present study, native Cantonese speakers’ discrimination of a linguistic tone continuum is shown to exhibit order of presentation effects similar to those shown for vowels in previous studies. When presented with two successive syllables differing in fundamental frequency by approximately 4 Hz, listeners were significantly more sensitive to this difference when the first syllable was higher in frequency than the second. However, American English-speaking listeners with no experience listening to Cantonese showed no such contrast effect when tested in the same manner using the same stimuli. Neither English nor Cantonese listeners showed any order of presentation effects in the discrimination of a nonspeech continuum in which tokens had the same fundamental frequencies as the Cantonese speech tokens but had a qualitatively non-speech-like timbre. These results suggest that tone presentation order effects, unlike vowel effects, may be language specific, possibly resulting from the need to compensate for utterance-related pitch declination when evaluating fundamental frequency for tone identification.
Drum silencer with shallow cavity filled with helium
Authors: Choy Y. S. , Huang Lixi
Published: August 2003

The motivation of this study is twofold: (a) to produce a flow-through silencer with zero pressure loss for pressure-critical applications, and (b) to tackle low frequency noise with limited sideway space using cavities filled with helium. The work represents a further development of our recently conceived device of a drum-like silencer with conventional air cavity [Huang, J. Acoust. Soc. Am. 112, 2014–2025 (2002); Choy and Huang, ibid. 112, 2026–2035 (2002)]. Theoretical predictions are validated by experimental data. The new silencer consists of two highly tensioned membranes lining part of a duct, and each membrane is backed by a cavity filled with helium. For a typical configuration of a duct with height h, membrane length L=7h, cavity depth hc=0.2h, and tension T=0.52ρ0c02h2, where ρ0 and c0 are the ambient density and speed of sound in air, respectively, the transmission loss has a continuous stop band of TL>6.35 dB for frequency 0.03c0/h to 0.064c0/h, which is much better than traditional duct lining. In addition to the mechanisms at work for drum silencers with air cavity, the low density of helium reduces the masslike reactance of the cavity on the second in vacuo mode of membrane vibration. The reduction greatly enhances the membrane response at this mode, which is found to be critical for achieving a broadband performance in the low-frequency regime.
The interlanguage speech intelligibility benefit
Authors: Bent Tessa , Bradlow Ann R.
Published: August 2003

This study investigated how native language background influences the intelligibility of speech by non-native talkers for non-native listeners from either the same or a different native language background as the talker. Native talkers of Chinese (n=2), Korean (n=2), and English (n=1) were recorded reading simple English sentences. Native listeners of English (n=21), Chinese (n=21), Korean (n=10), and a mixed group from various native language backgrounds (n=12) then performed a sentence recognition task with the recordings from the five talkers. Results showed that for native English listeners, the native English talker was most intelligible. However, for non-native listeners, speech from a relatively high proficiency non-native talker from the same native language background was as intelligible as speech from a native talker, giving rise to the “matched interlanguage speech intelligibility benefit.” Furthermore, this interlanguage intelligibility benefit extended to the situation where the non-native talker and listeners came from different language backgrounds, giving rise to the “mismatched interlanguage speech intelligibility benefit.” These findings shed light on the nature of the talker–listener interaction during speech communication.
Behavior of rigid-porous layers at high levels of continuous acoustic excitation: Theory and experiment
Authors: Umnova O. , Attenborough K. , Standley E. , Cummings A.
Published: August 2003

A model for the propagation of high amplitude continuous sound through hard-backed rigid-porous layers has been developed which allows for Forchheimer’s correction to Darcy’s law. The nonlinearity associated with this is shown to be particularly important in the range of frequencies around layer resonance. The model is based on the introduction of particle velocity dependent flow resistivity into the equivalent fluid model expression for complex tortuosity. Thermal effects are accounted for by means of a linear complex compressibility function. The model has been used to derive analytical expressions for surface impedance and reflection coefficient as a function of incident pressure amplitude. Depending on the material parameters, sample thickness, and frequency range the model predicts either growth or decrease of reflection coefficient with sound amplitude. Good agreement between model predictions and data for three rigid-porous materials is demonstrated.
Experimental and numerical study of air-coupled surface waves generated above strips of finite impedance
Authors: Zhu Wenhao , Daigle Gilles A. , Stinson Michael R.
Published: August 2003

A series of laboratory experiments are described in which air coupled surface waves are generated from a point source in the frequency range between 800 and 1700 Hz above a surface composed of a lattice of small cavities. Since the sound pressure near the lattice of cavities can be greater than if the surface was rigid, passive amplification is obtained. Moreover, directional receivers can be designed by restricting the lattice of cavities to a strip of finite width. These directional receivers are shown to provide more amplification than would be obtained with a semi-infinite lattice of cavities. Theoretical calculations using a boundary element method predict gains of up to 6 dB, relative to the pressure on a rigid plane when the strip width is of the order of 1 wavelength. The strips are further modified by changing their shape or by adding reflectors to further enhance the amplification. Gains of 12 dB have been measured and predictions show that gains of 20 dB are theoretically possible.