bluuebunny/crossref_metadata_2025 huggingface dataset:
Forward masking in different cochlear implant systems
Authors: Boëx Colette , Kós Maria-Izabel , Pelizzone Marco
Published: October 2003

The goal of this study was to evaluate, from a psychophysical standpoint, the neural spread of excitation produced by the stimulation of different types of intracochlear electrode arrays: the Ineraid™, the Clarion™ S-Series on its own or with the Electrode Positioning System (EPS), and the Clarion™ HiFocus-I with the EPS. The EPS is an independent silicone part designed to bring the electrode array close to the modiolus. Forward masking was evaluated in 12 adult subjects (3 Ineraid™, 4 Clarion™ S-Series, 3 Clarion™ S-Series+EPS, 3 HiFocus-I+EPS) by psychophysical experiments conducted using trains of biphasic stimuli (813 pulses per second, 307.6 μs/phase). Masker signals (+8 dB re: threshold, 300 ms) were applied to the most apical electrode. Probe signals (30 ms, 10-ms postmasker) were delivered to more basal electrodes. Masked and unmasked detection thresholds of probe signals were measured. For both Clarion™ HiFocus-I subjects, measurements were conducted in both monopolar and bipolar stimulus configurations. No major differences were found in forward masking between the different intracochlear electrode arrays tested in the monopolar configuration at suprathreshold levels equivalent to those used in speech-coding strategies, but significant differences were found between subjects. A significant negative correlation also was found between the level of forward masking and the consonant identification performance. These measurements showed that the neural spread of excitation was more restricted in the bipolar configuration than in the monopolar configuration for HiFocus-I subjects. It was found that CIS strategies implemented without using apical electrodes, which showed high levels of masking, could improve consonant identification.
Two-dimensional streaming flows induced by resonating, thin beams
Authors: Açıkalın Tolga , Raman Arvind , Garimella Suresh V.
Published: October 2003

Miniaturized resonating slender beams are finding increased applications as fluidic actuators for portable electronics cooling. Piezoelectric and ultrasonic “fans” drive a flexural mode of the beam into resonance thus inducing a streaming flow, which can be used to cool microelectronic components. This paper presents analytical, computational, and experimental investigations of the incompressible two-dimensional streaming flows induced by resonating thin beams. Closed-form analytical streaming solutions are presented first for an infinite beam. These are used to motivate a computational scheme to predict the streaming flows from a baffled piezoelectric fan. Experiments are conducted to visualize the asymmetric streaming flows from a baffled piezoelectric fan and the experimental results are found to be in close agreement with the predicted results. The findings are expected to be of relevance in the optimal design and positioning of these solid-state devices in cooling applications.
Nonlinear Fresnel diffraction of weak shock waves
Authors: Coulouvrat François , Marchiano Régis
Published: October 2003

Fresnel diffraction at a straight edge is revisited for nonlinear acoustics. Considering the penumbra region as a diffraction boundary layer governed by the KZ equation and its associated jump relations for shocks, similarity laws are established for the diffraction of a step shock, an “N” wave, or a periodic sawtooth wave. Compared to the linear case described by the well-known Fresnel functions, it is shown that weak shock waves penetrate more deeply into the shadow zone than linear waves. The thickness of the penumbra increases as a power of the propagation distance, power 1 for a step shock, or 34 for an N wave, as opposed to power 12 for a periodic sawtooth wave or a linear wave. This is explained considering the frequency spectrum of the waveform and its nonlinear evolution along the propagation, and is confirmed by direct numerical simulations of the KZ equation. New formulas for the Rayleigh/Fresnel distance in the case of nonlinear diffraction of weak shock waves by a large, finite aperture are deduced from the present study.
An angle-by-angle approach to predicting broadband high-frequency sound fields in rectangular enclosures with experimental comparison
Authors: Franzoni Linda P. , Elliott Christopher M.
Published: October 2003

Experiments were performed on an elongated rectangular acoustic enclosure with different levels of absorptive material placed on side walls and an end wall. The acoustic source was a broadband high-frequency sound from a loudspeaker flush-mounted to an end wall of the enclosure. Measurements of sound-pressure levels were averaged in cross sections of the enclosure and then compared to theoretical results. Discrepancies between the experimental results and theoretical predictions that treated all incidence angles as equally probable led to the development of an angle-by-angle approach. The new approach agrees well with the experimentally obtained values. In addition, treating the absorptive material as bulk reacting rather than point reacting was found to significantly change the theoretical value for the absorption coefficient and to improve agreement with experiment. The new theory refines an earlier theory based on power conservation and locally diffuse assumptions. Furthermore, the new theory includes both the angle of incidence effects on the resistive and reactive properties of the absorptive material, and the effects of angle filtering, i.e., that reflecting waves associated with shallow angles become relatively stronger than those associated with steep angles as a function of distance from the source.
A measure of internal noise based on sample discrimination
Authors: Jesteadt Walt , Nizami Lance , Schairer Kim S.
Published: October 2003

Internal noise is often inferred from the difference between observed performance and optimum performance in detection and discrimination tasks. It can be measured directly in some cases by observing the extent to which a change in external variability impacts performance. In the studies reported here, external variability was added to an intensity discrimination task by adding a Gaussian random variable with zero mean to the overall level presented in each interval of a two-interval forced-choice task. The standard deviation of the random variable was set to half the mean difference between the levels in the two intervals, resulting in dideal′=2. As the mean difference and the corresponding standard deviation of the random variable decreased in size, performance was increasingly limited by internal noise, permitting a reliable estimate of internal noise to be obtained. This can be viewed as a sample discrimination task, with one component per sample. In the first study, performance was measured using 2-kHz tones presented at an average level of 70 dB SPL, with mean differences between distributions ranging from 0.1 to 2.2 dB in steps of 0.3 dB. The distributions were either Gaussian in level or in power. Conditions with no external variability were used to obtain a psychometric function. In the second study, performance was measured using 2-kHz tones presented at average levels of 50 and 90 dB SPL, with mean differences ranging from 0.4 to 2.2 dB in steps of 0.6 dB. In both studies, the measure of internal noise was highly reliable and in good agreement with the intensity difference limen (DL) estimated from the psychometric function. Analyses suggest that this measure could be used to estimate the mean difference between the decision distributions as well as the amount of internal noise in cases where the mean difference between the distributions is unknown.
Numerical simulation of shock wave focusing at fold caustics, with application to sonic boom
Authors: Marchiano Régis , Coulouvrat François , Grenon Richard
Published: October 2003

Weak shock wave focusing at fold caustics is described by the mixed type elliptic/hyperbolic nonlinear Tricomi equation. This paper presents a new and original numerical method for solving this equation, using a potential formulation and an “exact” numerical solver for handling nonlinearities. Validation tests demonstrate quantitatively the efficiency of the algorithm, which is able to handle complex waveforms as may come out from “optimized” aircraft designed to minimize sonic booms. It provides a real alternative to the approximate method of the hodograph transform. This motivated the application to evaluate the ground track focusing of sonic boom for an accelerating aircraft, by coupling CFD Euler simulations performed around the mock-up on an adaptated mesh grid, atmospheric propagation modeling, and the Tricomi algorithm. The chosen configuration is the European Eurosup mock-up. Convergence of the focused boom at the ground level as a function of the matching distance is investigated to demonstrate the efficiency of the numerical process. As a conclusion, it is indicated how the present work may pave the way towards a study on sonic superboom (focused boom) mitigation.
A modified Khokhlov–Zabolotskaya equation governing shear waves in a prestrained hyperelastic solid
Authors: Cramer M. S. , Andrews M. F.
Published: October 2003

Weakly nonlinear, weakly diffracting, two-dimensional shear waves propagating in a prestrained hyperelastic solid are examined. A modification of the classical Khokhlov–Zabolotskaya equation is derived using a systematic perturbation scheme. Both dissipative and nondissipative materials were considered. The principal effect of the prestrain was seen to be the inclusion of a quadratic nonlinearity to the cubic nonlinearity found in the case of zero prestrain. Further new results include the shock jump relations and the prediction of shocks having a speed which is identical to the nonlinear wave speed ahead of or behind the shock. Explicit expressions for the nonlinearity coefficients for the special case of a Blatz–Ko material were provided.
Experimental setup for measurement of acoustic power dissipation in lined ducts for higher order modes propagation with air mean-flow conditions
Authors: Ville Jean-Michel , Foucart Felix
Published: October 2003

A flow duct acoustic facility was developed to measure liner efficiency in attenuating higher order acoustic duct modes propagation conditions with mean air flow. The method is based on measurement, upstream and downstream of a liner, of the acoustic power produced by a periodic source. Directly measured total or modal acoustic powers are deduced from the local measurement, in both cross sections, of acoustic pressure, axial acoustic particle velocity, and axial mean flow velocity which are supplied by a probe made of a microphone and a single hot film. In this paper, the equipment, signal processing, and the data treatment process of this facility are first described. Then, information on the accuracy of the methodology is provided by a validation test performed with a rigid wall duct section. Finally, the results of an experiment carried out with a locally reacting liner and a mean flow velocity of 20 m/s will be presented. Measurements of the main attenuation frequency and of the main total acoustic power dissipated agree with the values for which the liner was designed. These results point out the limitations of the method presented to sources with high-level periodic sounds to provide a sufficient signal-to-noise ratio, the noise being produced by fluctuations of the turbulent flow.
Nonlinear dynamics of phonations in excised larynx experiments
Authors: Jiang Jack J. , Zhang Yu , Ford Charles N.
Published: October 2003

Nonlinear dynamic methods including correlation dimension and Lyapunov exponents are applied to quantitatively analyze phonations in excised larynx experiments. Irregular phonations are typically characterized by aperiodic waveforms and broadband spectra. Finite correlation dimensions and positive Lyapunov exponents of irregular phonations demonstrate the existence of chaos in excised larynx phonations. Furthermore, the correlation dimension, maximal Lyapunov exponent, jitter, shimmer, and peak prominence ratio are used to statistically distinguish irregular phonations from normal phonations. The correlation dimension and maximal Lyapunov exponent indicate a significant difference between irregular and normal phonations; however, jitter, shimmer, and peak prominence ratio do not reveal such a significant difference and thus are unsuitable to differentiate between irregular phonations and normal phonations. These findings might potentially assist investigators in understanding rough phonations and developing clinically valuable methodologies for the diagnosis of voice disorders.
Speech segregation based on sound localization
Authors: Roman Nicoleta , Wang DeLiang , Brown Guy J.
Published: October 2003

At a cocktail party, one can selectively attend to a single voice and filter out all the other acoustical interferences. How to simulate this perceptual ability remains a great challenge. This paper describes a novel, supervised learning approach to speech segregation, in which a target speech signal is separated from interfering sounds using spatial localization cues: interaural time differences (ITD) and interaural intensity differences (IID). Motivated by the auditory masking effect, the notion of an “ideal” time–frequency binary mask is suggested, which selects the target if it is stronger than the interference in a local time–frequency (T–F) unit. It is observed that within a narrow frequency band, modifications to the relative strength of the target source with respect to the interference trigger systematic changes for estimated ITD and IID. For a given spatial configuration, this interaction produces characteristic clustering in the binaural feature space. Consequently, pattern classification is performed in order to estimate ideal binary masks. A systematic evaluation in terms of signal-to-noise ratio as well as automatic speech recognition performance shows that the resulting system produces masks very close to ideal binary ones. A quantitative comparison shows that the model yields significant improvement in performance over an existing approach. Furthermore, under certain conditions the model produces large speech intelligibility improvements with normal listeners.
Sensor array beamforming using random channel sampling: The aggregate beamformer
Authors: Havelock David I.
Published: October 2003

The aggregate (AGG) beamformer can provide significant savings in hardware and software cost and complexity relative to conventional beamformers while retaining equivalent directional performance. The key to achieving the savings is collecting data from array channels in a random sequence, rather than simultaneously or sequentially. This allows the AGG beamformer to convert unwanted off-beam signals into wideband noise that can then be reduced by filtering. The total sampling rate is chosen to obtain the desired residual noise level and signal bandwidth. It is independent of the number of sensors. Analog anti-alias filters normally are not required, since the Nyquist frequency is determined by the total sampling rate, not the (lower) per-channel sampling rate. Beamformer delay quantization and steering resolution are greatly improved relative to conventional beamforming without the need for data interpolation. The beamformed signal, prior to decimation filtering, is obtained without arithmetic operations on the data. Low front-end hardware-complexity makes the AGG beamformer suitable for highly integrated systems. The number of sensors in the array can be altered without re-configuring buffers or altering the sampling rate. The principles of the AGG beamformer are introduced, and simulation and experimental results demonstrate performance.
Blind deconvolution applied to acoustical systems identification with supporting experimental results
Authors: Roan Michael J. , Gramann Mark R. , Erling Josh G. , Sibul Leon H.
Published: October 2003

Many acoustical applications require the analysis of a signal that is corrupted by an unknown filtering function. Examples arise in the areas of noise or vibration control, room acoustics, structural vibration analysis, and speech processing. Here, the observed signal can be modeled as the convolution of the desired signal with an unknown system impulse response. Blind deconvolution refers to the process of learning the inverse of this unknown impulse response and applying it to the observed signal to remove the filtering effects. Unlike classical deconvolution, which requires prior knowledge of the impulse response, blind deconvolution requires only reasonable prior estimates of the input signal’s statistics. The significant contribution of this work lies in experimental verification of a blind deconvolution algorithm in the context of acoustical system identification. Previous experimental work concerning blind deconvolution in acoustics has been minimal, as previous literature concerning blind deconvolution uses computer simulated data. This paper examines experiments involving three classical acoustic systems: driven pipe, driven pipe with open side branch, and driven pipe with Helmholtz resonator side branch. Experimental results confirm that the deconvolution algorithm learns these systems’ inverse impulse responses, and that application of these learned inverses removes the effects of the filters.
Threshold differences for interaural time delays carried by double vowels
Authors: Akeroyd Michael A.
Published: October 2003

Experimental measurements were made of threshold interaural time differences (ITDs) for a “target” vowel presented simultaneously with a fixed-ITD “distracter” vowel. Three double-vowel pairs were used, comprising an “er” (/ə/) together with either an “ai,” “ar,” or “oo” (respectively, /e/, /ɔ/, and /u/). Threshold ITDs were found to be larger for the target vowel when it was part of a double-vowel pair than in control conditions in which it was presented alone. The effect size depended upon the choice of target vowel and distracter vowel, the level of the target relative to the distracter, and whether the two vowels had the same or different fundamental frequencies. The experiment was analyzed using a multichannel modification of Heller and Trahiotis’ [J. Acoust. Soc. Am. 99, 3632–3637 (1996)] model, which used a weighted combination of the detectabilities of the ITD of the target and the distracter. It gave predictions consistent with the observed effects of level and with some of the effects of the choice of target vowel, but it could not describe the effect of the target–distracter differences in fundamental frequency. It was found that a single-channel version of the model, in which the chosen channel was allowed to depend upon fundamental frequency (which could be derived using a monaural autocorrelation model) did give a set of predictions in qualitative accord with the data.
A cascade thermoacoustic engine
Authors: Gardner D. L. , Swift G. W.
Published: October 2003

A cascade thermoacoustic engine is described, consisting of one standing-wave stage plus two traveling-wave stages in series. Most of the acoustic power is produced in the efficient traveling-wave stages. The straight-line series configuration is easy to build and allows no Gedeon streaming. The engine delivers up to 2 kW of acoustic power, with an efficiency (the ratio of acoustic power to heater power) of up to 20%. An understanding of the pressure and volumevelocity waves is very good. The agreement between measured and calculated powers and temperatures is reasonable. Some of the measured thermal power that cannot be accounted for by calculation can be attributed to Rayleigh streaming in the two thermal buffer tubes with the largest aspect ratios. A straightforward extension of this work should yield cascade thermoacoustic engines with efficiencies of around 35–40% of the Carnot efficiency.
Echo strength and density structure of Hawaiian mesopelagic boundary community patches
Authors: Benoit-Bird Kelly J. , Au Whitlow W. L.
Published: October 2003

A broadband sonar system and digital camera with strobe lights were mounted on a vertically profiling frame with a depth sensor. The echo strengths and densities of animals within individual mesopelagic boundary community patches were investigated as a function of depth. Time and distance from shore were also investigated. Simultaneous surface echosounder surveys permitted comparison of density estimates from two techniques. Echo strength values suggest nearshore boundary community animals are primarily myctophid fishes, which was confirmed by preliminary photographic evidence. Echo strength varied significantly as a function of distance from the shoreline and time. These measures of echo strength are important for estimating density from a surface echosounder. Density estimates from these revised echo strengths compare well with those made with echo highlight counting, which is independent of echo strength. These density measures suggest that previous density estimates were too low but do not change the conclusions of these studies. Vertical microstructure in density was apparent but animal size and compositional structure was not evident within a patch. Patch edges were abrupt, with no differences in the density or echo strength from patch interiors. These edges were generally straight, with a sharp drop in density to the background density of zero. Estimates of animal size as a function of time provide information about the diel migration patterns of these mesopelagic animals.
Bubble oscillations driven by aspherical ultrasound in liquid
Authors: Wang Wenjie , Chen Weizhong , Lu Meijun , Wei Rongjue
Published: October 2003

In this paper we study the bubble dynamics driven by an aspherical acoustic field, based on the theory of hydrodynamics. Evolution equations for an aspherical bubble are derived under the aspherical acoustic driving. The numerical calculations show that the aspherical bubble can oscillate stably and periodically under suitable conditions, which is out of the explanation of spherical perturbation theory. Furthermore, under some controlling parameters, the aspherical distortion can either grow rapidly, leading to the bubble’s breakdown, or decay gradually making the bubble spherical, which is similar to the result of the perturbation theory driven by a spherical ultrasound.
Cutoff frequencies and cross fingerings in baroque, classical, and modern flutes
Authors: Wolfe Joe , Smith John
Published: October 2003

Baroque, classical, and modern flutes have successively more and larger tone holes. This paper reports measurements of the standing waves in the bores of instruments representing these three classes. It presents the frequency dependence of propagation of standing waves in lattices of open tone holes and compares these measurements with the cutoff frequency: the frequency at which, in an idealized system, the standing waves propagate without loss in such a lattice. It also reports the dependence of the sound field in the bore of the instrument as a function of both frequency and position along the bore for both simple and “cross fingerings” (configurations in which one or more tone holes are closed below an open hole). These measurements show how “cross fingerings” produce a longer standing wave, a technique used to produce the nondiatonic notes on instruments with a small number of tone holes closed only by the unaided fingers. They also show why the changes from baroque to classical to modern gave the instruments a louder, brighter sound and a greater range.
Application of loudness models to sound processing for cochlear implants
Authors: McDermott Hugh J. , McKay Colette M. , Richardson Louise M. , Henshall Katherine R.
Published: October 2003

A new paradigm for processing sound signals for multiple-electrode cochlear implants is introduced, and results are presented from an initial psychophysical evaluation of its effect on the perceived loudness of complex sounds. A real-time processing scheme based on this paradigm, called SpeL, has been developed primarily to improve control of loudness for implant users. SpeL differs from previous schemes in several ways. Most importantly, it incorporates a published numerical model which predicts the loudness perceived by implant users for complex patterns of pulsatile electric stimulation as a function of the pulses’ physical parameters. This model is controlled by the output of a corresponding model that estimates the loudness perceived by normally hearing listeners for complex sounds. The latter model produces an estimate of the specific loudness arising from an acoustic signal. In SpeL, the specific loudness function, which describes the contribution to total loudness of each of a number of frequency bands (or cochlear positions), is converted to a pattern of electric stimulation on an appropriate set of electrodes. By application of the loudness model for electric stimulation, this pattern is designed to produce a specific loudness function for the implant user which approximates that produced by the normal-hearing model for the same input signal. The results of loudness magnitude estimation experiments with five users of the SpeL scheme confirmed that the psychophysical functions relating overall loudness perceived to input sound level for five complex acoustic signals were, on average, very similar to those for normal hearing.
Modulation masking produced by complex tone modulators
Authors: Verhey Jesko L. , Ewert Stephan D. , Dau Torsten
Published: October 2003

Thresholds were measured for detecting sinusoidal amplitude modulation in the presence of a complex-tone masker modulation. Both modulations were applied to the same sinusoidal carrier. Two different masker modulations were used: (i) a pair of components beating at the difference frequency and (ii) a three-tone complex producing a sinusoidal amplitude modulation of the modulation depth at the difference frequency between adjacent components. Both maskers show a periodicity in the waveform that is not contained in the envelope spectrum itself but can be observed when the envelope of the envelope, referred to as the “venelope” [Ewert et al., J. Acoust. Soc. Am. 112, 2921–2931 (2002)], is calculated. For a signal frequency equal to the masker-venelope periodicity, modulation depth at threshold was measured as a function of the signal phase relative to the phase of the masker-venelope component. Signal frequencies of 5, 30, and 90 Hz were used. It was found that masking was phase dependent for all three signal frequencies. Thresholds were lower for the in-phase condition, where maxima in the signal waveform coincided with maxima in the masker-venelope waveform, than for the antiphase condition. The maximum threshold difference was 15 dB. The results are in contrast to recent data [Moore et al., J. Acoust. Soc. Am. 106, 908–918 (1999)], where lowest thresholds were reported for the antiphase condition in a similar experiment. The present data are in line with the idea that a nonlinearity prior to a modulation filterbank extracts the venelope of the masker modulator. However, a compressive nonlinearity such as that associated with the processing on the basilar membrane cannot account for the empirical findings, since it predicts the opposite phase effect.
Desynchronization of electrically evoked auditory-nerve activity by high-frequency pulse trains of long duration
Authors: Litvak Leonid M. , Smith Zachary M. , Delgutte Bertrand , Eddington Donald K.
Published: October 2003

Rubinstein et al. [Hear. Res. 127, 108–118 (1999)] suggested that the neural representation of the waveforms of electric stimuli might be improved by introducing an ongoing, high-rate, desynchronizing pulse train (DPT). A DPT may desynchronize neural responses to electric stimulation in a manner similar to spontaneous activity in a healthy ear. To test this hypothesis, responses of auditory-nerve fibers (ANFs) to 10-min-long electric pulse trains (5 kpps) were recorded from acutely deafened, anesthetized cats. Stimuli were delivered via an intracochlear electrode, and their amplitude was chosen to elicit a response in most ANFs. Responses to pulse trains showed pronounced adaptation during the first 1–2 min, followed by either a sustained response or cessation of spike discharges for the remainder of the stimulus. The adapted discharge rates showed a broad distribution across the ANF population like spontaneous activity. However, a higher proportion of fibers (46%) responded to the DPT at rates below 5 spikes/s than for spontaneous activity, and 12% of the fibers responded at higher rates than any spontaneously active fiber. Interspike interval histograms of sustained responses for some fibers had Poisson-like (exponential) shapes, resembling spontaneous activity, while others exhibited preferred intervals and, occasionally, bursting. Simultaneous recordings from pairs of fibers revealed no evidence of correlated activity, suggesting that the DPT does desynchronize the auditory nerve activity. Overall, these results suggest that responses to an ongoing DPT resemble spontaneous activity in a normal ear for a substantial fraction of the ANFs.
Improved temporal coding of sinusoids in electric stimulation of the auditory nerve using desynchronizing pulse trains
Authors: Litvak Leonid M. , Delgutte Bertrand , Eddington Donald K.
Published: October 2003

Rubinstein et al. [Hearing Res. 127, 108–118 (1999)] suggested that the representation of electric stimulus waveforms in the temporal discharge patterns of auditory-nerve fiber (ANF) might be improved by introducing an ongoing, high-rate, desynchronizing pulse train (DPT). To test this hypothesis, activity of ANFs was studied in acutely deafened, anesthetized cats in response to 10-min-long, 5-kpps electric pulse trains that were sinusoidally modulated for 400 ms every second. Two classes of responses to sinusoidal modulations of the DPT were observed. Fibers that only responded transiently to the unmodulated DPT showed hyper synchronization and narrow dynamic ranges to sinusoidal modulators, much as responses to electric sinusoids presented without a DPT. In contrast, fibers that exhibited sustained responses to the DPT were sensitive to modulation depths as low as 0.25% for a modulation frequency of 417 Hz. Over a 20-dB range of modulation depths, responses of these fibers resembled responses to tones in a healthy ear in both discharge rate and synchronization index. This range is much wider than the dynamic range typically found with electrical stimulation without a DPT, and comparable to the dynamic range for acoustic stimulation. These results suggest that a stimulation strategy that uses small signals superimposed upon a large DPT to encode sounds may evoke temporal discharge patterns in some ANFs that resemble responses to sound in a healthy ear.
Improved neural representation of vowels in electric stimulation using desynchronizing pulse trains
Authors: Litvak Leonid , Delgutte Bertrand , Eddington Donald
Published: October 2003

Current cochlear implant processors poorly represent sound waveforms in the temporal discharge patterns of auditory-nerve fibers (ANFs). A previous study [Litvak et al., J. Acoust. Soc. Am. 114, 2079–2098 (2003)] showed that the temporal representation of sinusoidal stimuli can be improved in a majority of ANFs by encoding the stimuli as small modulations of a sustained, high-rate (5 kpps), desynchronizing pulse train (DPT). Here, these findings are extended to more complex stimuli by recording ANF responses to pulse trains modulated by bandpass filtered vowels. Responses to vowel modulators depended strongly on the discharge pattern evoked by the unmodulated DPT. ANFs that gave sustained responses to the DPT had period histograms that resembled the modulator waveform for low (<5%) modulation depths. Spectra of period histograms contained peaks near the formant frequencies. In contrast, ANFs that gave a transient (<1 min) response to the DPT poorly represented the formant frequencies. A model incorporating a linear modulation filter, a noisy threshold, and neural refractoriness predicts the shapes of period histograms for both types of fibers. These results suggest that a DPT-enhanced strategy may achieve good representation of the stimulus fine structure in the temporal discharge patterns of ANFs for frequencies up to 1000 Hz. It remains to be seen whether these temporal discharge patterns can be utilized by cochlear implant subjects.
Investigation of bubble dynamics and heating during focused ultrasound insonation in tissue-mimicking materials
Authors: Yang Xinmai
Published: October 2003

The deposition of ultrasonic energy in tissue can cause tissue damage due to local heating. For pressures above a critical threshold, cavitation will occur in tissue and bubbles will be created. These oscillating bubbles can induce a much larger thermal energy deposition in the local region. The present work is an attempt to control and utilize this bubble-enhanced heating. First, by applying appropriate bubble dynamic models, limits on the asymptotic bubble size distribution are obtained for different driving pressures at 1 MHz. The size distributions are bounded by two thresholds: the bubble shape instability threshold and the rectified diffusion threshold. The growth rate of bubbles in this region is also given, and the resulting time evolution of the heating in a given insonation scenario is modeled. Experimental results have been obtained to investigate the bubble-enhanced heating in an agar and graphite based tissue-mimicking material. By fitting appropriate bubble densities in the ultrasound field, the peak temperature changes observed in experiments are simulated. Finally, a simple bubbly liquid model is presented to estimate shielding effects which may be important even for low void fraction during high intensity focused ultrasound (HIFU) treatment.

Thesis advisor: R. Glynn Holt

Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu
Sonoluminescence in varying acceleration environments
Authors: Wyatt Sean C.
Published: October 2003

In order to prepare for experiments in variable-g environments, some of the multiple effects caused by the time-varying acceleration of acoustic resonators used in bubble levitation experiments are considered. The coupled effects of the induced changes in ambient pressure (due to a changing hydrostatic head) and bubble position (due to a change in buoyant body force) were modeled. Changing the ambient pressure, while holding the acoustic pressure amplitude constant, causes changes in the radial bubble response and diffusive equilibrium requirements. Changing the bubble levitation position causes both the local acoustic pressure amplitude and gradient to change, which will again impact bubble response. If the bubble remains in a stable diffusive equilibrium, both of these effects will force the bubble’s equilibrium radius to change. By using an empirical relation for emitted sonoluminescence intensity versus bubble response, the variation of emitted light intensity as a function of the changing ambient acceleration can be predicted. The predicted results are shown to agree quantitatively with existing experimental data from other research groups. An experiment was designed and built to fly onboard a KC-135 aircraft that has been reinforced for parabolic flight maneuvers to simulate micro and hyper gravity acceleration.

Thesis advisor: R. Glynn Holt

Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu
Design, fabrication and use of a KC-135 experiment for studying sonoluminescence
Authors: Thomas Charles Robert
Published: October 2003

The effects of many external parameters on single-bubble sonoluminescence (SBSL) have been studied since its discovery 13 years ago in 1990. These studies include the effects due to host water temperature, dissolved gas, ambient pressure, and even magnetic fields. Because the stability of the bubble depends in part on gravity, through its buoyancy, it is natural to study SBSL in microgravity. This is the subject of this thesis: the design and fabrication of an experiment to study the effects of gravity on SBSL for use on the NASA KC-135 aircraft. The KC-135 aircraft flies in a parabolic trajectory to simulate weightlessness for about 20 s per parabolic maneuver, performing roughly 40 parabolas per flight. During those flights, the bubble’s size, position in the imposed sound field, and emitted light intensity were measured. The apparatus and techniques used to make these measurements, along with the constraints imposed by the unique environment afforded by experimentation aboard the KC-135, are discussed in detail. Preliminary results are reported, and a full uncertainty analysis is presented for each measurement.

Thesis advisor: R. Glynn Holt

Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu
Development of a handheld bistatic imaging sonar system for underwater search and survey
Authors: Chiang Alice , Broadstone Steven , Impagliazzo John
Published: October 2003

A high resolution, handheld imaging sonar system is under development by Teratech Corporation for the U.S. Navy. This is a 192 channel, dual frequency bistatic sonar for Navy divers performing search and survey missions for underwater explosives. Our goal is to provide the most compact and energy efficient imaging system for the divers. The system consists of a self-contained handheld unit and a head mounted display integrated into the divers mask. The low power and small volume are a result of the development of Teratechs Charge Domain Processing (CDP) technology. This technology has led to the development of a low power 64-channel beamformer chip. As a result, only three beamformer chips will be required for the 192 channels. Until now, the implementation of small, low power sonar systems containing this many elements and forming enough beams to create an image was considered impossible. Progress in the development of this product will be presented. In-water testing is planned for late summer 2003. Experimental results and test images available will be presented at the conference. [Work sponsored by ONR and OSD Small Business Innovative Research Program, Program manager, Mr. Bruce Johnson, Naval Explosive Ordnance Disposal Technology Division.]
Feasibility of nonlinear acoustic technique with ultrasonic guided waves for nondestructive defect evaluation
Authors: Jung Kyung-il , Yoon Suk Wang
Published: October 2003

Feasibility of nonlinear acoustic modulation technique [K. I. Jung and S. W. Yoon, Proceedings of Internoise 2000, Nice, France, p. 205 (2000)] was discussed for nondestructive defect evaluation. Such nonlinear acoustic technique can be applied to localize a defect in a solid rod and also extended to layer-structured media. In this study, nonlinear acoustic technique with ultrasonic guided waves is introduced. Nonlinear acoustic responses from a defect are observed with guided waves in a 2-D structure. The defect was oriented in the direction of guided wave propagation. The experimental results show that the nonlinear acoustic technique with ultrasonic guided waves seems feasible for nondestructive evaluation of 2-D structure. [Work supported by BK21 Program in Korea and by the Basic Research Program of KOSEF (R01-2000-000-00014-0).]
Acoustic inversions from an explosive source of opportunity in the ASIAEX SCS experiment
Authors: Lin Ying-Tsong , Lynch James F. , Chotiros Nicholas P. , Turgut Altan , Chiu Ching-Sang , Schock Steven G.
Published: October 2003

An acoustic inversion for bottom geoacoustic properties from an unexpected explosion in the South China Sea (SCS) is presented. Horizontal beamforming is performed to find the source azimuthal direction and the water wave part of the modal dispersion curve is used to find the source range. The localization result shows that the detonation occurred in the direction of east–north east and about 40 km distant from the receiver. To perform the bottom inverse, we use a broadband linear inverse technique employing the modal group velocity, which is inferred from the modal arrival time and source range. In the end, a four-layered bottom model is created, which is consistent with both our explosion data and independent source tow data. The resolution and variance of the estimate are also presented. In conclusion, this bottom model should be widely applicable for modeling broadband sound propagation in the ASIAEX SCS experiment site.
Localization and environmental inversion in a soft sediment environment using rotated coordinates
Authors: Newman Rebecca , Koch Robert
Published: October 2003

SARI is used to simultaneously invert data for environmental and source track parameters. The acoustic data were recorded on a bottom mounted, horizontal line array at a soft sediment, shallow water site in the Gulf of Mexico off Port Aransas, Texas. SARI [T. B. Neilsen, J. Acoust. Soc. Am. 113, 2217 (2003)] is a simulated annealing program that uses rotated coordinates, which represent the coupling and optimal variation of the annealing parameters, to invert for source track and environmental parameters. While previously tested on simulated hard sediment data, soft sediments give rise to significant coupling between source and geoacoustic parameters. A comparison of the inversion results obtained for the Gulf of Mexico annealing with rotated coordinates and without will be presented. [Work supported by ONR.]
Evaluating prediction methods for the spectral evolution of finite-amplitude jet noise
Authors: Gee Kent L. , Sparrow Victor W.
Published: October 2003

David Blackstock has made substantial contributions to the understanding of the propagation of broadband, finite-amplitude noise. His work with Pestorius, Theobald, Webster, and Menounou, among others, has given us an understanding of much of the underlying physics. Even so, there are still gaps in our knowledge of the noise propagation from supersonic jet flows. A recent study was undertaken to compare several methods for the far field progression of a finite-amplitude broadband spectrum. This paper will provide initial results for that comparison. For each method tested, a Gaussian spectrum and experimental jet noise data were utilized as inputs. [Work supported by Strategic Environmental Research and Development Program.]
Induction of APOBEC3G Ubiquitination and Degradation by an HIV-1 Vif-Cul5-SCF Complex
Authors: Yu Xianghui , Yu Yunkai , Liu Bindong , Luo Kun , Kong Wei , Mao Panyong , Yu Xiao-Fang
Published: October 2003

Human immunodeficiency virus–1 (HIV-1) Vif is essential for viral evasion of host antiviral factor CEM15/APOBEC3G. We report that Vif interacts with cellular proteins Cul5, elongins B and C, and Rbx1 to form an Skp1-cullin-F-box (SCF)–like complex. The ability of Vif to suppress antiviral activity of APOBEC3G was specifically dependent on Cul5-SCF function, allowing Vif to interact with APOBEC3G and induce its ubiquitination and degradation. A Vif mutant that interacted with APOBEC3G but not with Cul5-SCF was functionally inactive. The Cul5-SCF was also required for Vif function in distantly related simian immunodeficiency virus mac. These results indicate that the conserved Cul5-SCF pathway used by Vif is a potential target for antiviral development.
Mechanical and psychosocial factors predict new onset shoulder pain: a prospective cohort study of newly employed workers
Authors: Harkness E F , Macfarlane G J , Nahit E S , Silman A J , McBeth J
Published: October 2003

Aim:To test the hypothesis that work related mechanical and psychosocial factors predict new onset shoulder pain in newly employed workers.

Methods:Two year prospective study of newly employed workers from 12 diverse occupational settings. At baseline, 1081 subjects provided information on work related mechanical and psychosocial risk factors, and current pain status.

Results:In all, 803 (74%) subjects were free from shoulder pain at baseline. Of those, 638 (79%) responded at 12 months and 476 (88%) at 24 months. New onset shoulder pain was reported by 93 (15%) and 73 (15%) subjects respectively. An increased risk of symptom onset was found in subjects reporting mechanical exposures involving heavy weights including lifting with one or two hands, carrying on one shoulder, lifting at or above shoulder level, and pushing or pulling. Working with hands above shoulder level was also predictive of new onset shoulder pain. Of the psychosocial factors examined, the strongest predictor was monotonous work. Those individuals with any other previous pain also had an increased risk of new onset shoulder pain at follow up. In multivariate analysis, lifting heavy weights with one or two hands, pushing or pulling heavy weights, working with hands above shoulder level, and monotonous work were independently associated with new onset shoulder pain.

Conclusions:This study supports the hypothesised relation between mechanical risk factors and shoulder pain. In general, work related psychosocial factors were modestly associated with new onset shoulder pain. However, monotonous work was a strong risk factor for new onset shoulder pain.
Risk factors for incident neck and shoulder pain in hospital nurses
Authors: Smedley J , Inskip H , Trevelyan F , Buckle P , Cooper C , Coggon D
Published: October 2003

Aim:To assess the incidence and risk factors for neck and shoulder pain in nurses.

Methods:A longitudinal study of neck and shoulder pain was carried out in female nurses at two hospitals in England. Personal and occupational risk factors were assessed at baseline. The self reported incidence of symptoms in the neck and shoulder region was ascertained at three-monthly intervals over two years. A Cox regression model was used to estimate hazard ratios (HRs) for incident neck/shoulder pain during follow up in nurses who had been pain free for at least one month at baseline.

Results:The baseline response rate was 56%. Of 903 women who were pain free at baseline, 587 (65%) completed at least one follow up while still in the same job. During an average of 13 months, 34% of these (202 women) reported at least one episode of neck/shoulder pain. The strongest predictor of pain in the neck/shoulder was previous history of the symptom (HRs up to 3.3). For physical exposures at work, the highest risks (HRs up to 1.7) were associated with specific patient handling tasks that involved reaching, pushing, and pulling. Nurses who reported low mood or stress at baseline were more likely to develop neck/shoulder pain later (HR 1.5). Workplace psychosocial factors (including job demands, satisfaction, and control) were not associated with incident neck/shoulder symptoms.

Conclusions:Neck/shoulder pain is common among hospital nurses, and patient handling tasks that involve reaching and pulling are the most important target for risk reduction strategies.