bluuebunny/crossref_metadata_2025 huggingface dataset:
Blood Flow in Stented Arteries: A Parametric Comparison of Strut Design Patterns in Three Dimensions
Authors: He Yong , Duraiswamy Nandini , Frank Andreas O. , Moore James E.
Published: January 2006

Background: Restenosis after stent implantation varies with stent design. Alterations in secondary flow patterns and wall shear stress (WSS) can modulate intimal hyperplasia via their effects on platelet and inflammatory cell transport toward the wall, as well as direct effects on the endothelium. Method of Approach: Detailed flow characteristics were compared by estimating the WSS in the near-strut region of realistic stent designs using three-dimensional computational fluid dynamics (CFD), under pulsatile high and low flow conditions. The stent geometry employed was characterized by three geometric parameters (axial strut pitch, strut amplitude, and radius of curvature), and by the presence or lack of the longitudinal connector. Results: Stagnation regions were localized around stent struts. The regions of low WSS are larger distal to the strut. Under low flow conditions, the percentage restoration of mean axial WSS between struts was lower than that for the high flow by 10–12%. The largest mean transverse shear stresses were 30–50% of the largest mean axial shear stresses. The percentage restoration in WSS in the models without the longitudinal connector was as much as 11% larger than with the connector. The mean axial WSS restoration between the struts was larger for the stent model with larger interstrut spacing. Conclusion: The results indicate that stent design is crucial in determining the fluid mechanical environment in an artery. The sensitivity of flow characteristics to strut configuration could be partially responsible for the dependence of restenosis on stent design. From a fluid dynamics point of view, interstrut spacing should be larger in order to restore the disturbed flow; struts should be oriented to the flow direction in order to reduce the area of flow recirculation. Longitudinal connectors should be used only as necessary, and should be parallel to the axis. These results could guide future stent designs toward reducing restenosis.
The matched-lag filter: Detecting broadband multipath signals with auto- and cross-correlation functions
Authors: Spiesberger John L.
Published: January 2006

Signal detection is considered for uncertain noise variance and a broadband source of unknown waveform and emission time. The signal travels to the receivers along paths with unknown delays. Using a new “matched-lag filter,” the presence or absence of the signal is estimated from the auto- and cross-correlation functions of the receptions. Like a matched filter, correlation functions provide the first stage of gain in signal-to-noise ratio because the paths are assumed to be partially coherent. The second stage achieves additional gain by searching only over physically possible arrangements of signals in the auto- and cross-correlation functions while excluding forbidden arrangements. These stages enable the matched-lag filter to behave like a matched filter within a matched filter. In an ideal case, simulations of the matched-lag filter yield probabilities of detection that are, with one and two receivers, 4.1 and 366 times, respectively, that obtained from the conventional energy detector at a false-alarm probability of 0.001. The matched-lag filter has applications to wireless communications and the detection of acoustic signals from animals, vehicles, ships, and nuclear blasts. The matched-lag filter more completely describes signal structure than stochastic detection and communication theories whose specified auto-correlation function does not prohibit forbidden arrangements.
The relationship between frequency selectivity and overshoot
Authors: Strickland Elizabeth A.
Published: January 2006

Under some conditions, threshold for a brief tone is higher at the onset of a broadband masker than it is if it is delayed from the onset of the masker. Evidence suggests that this “overshoot” is related to active processing in the auditory system. The present experiments examined this question, by measuring frequency selectivity under the same conditions in which overshoot was measured. The first experiment demonstrated that the growth of masking with masker level was approximately linear for a 1-kHz signal with or without a precursor (which was identical to the masker), and a 4-kHz signal with a precursor. For the 4-kHz signal with no precursor, an elevation in signal-to-masker ratio was seen at mid masker levels, relative to the other conditions. Frequency selectivity was then measured for a fixed-level signal, with and without a precursor. Relative frequency selectivity was highest for the 4-kHz signal with no precursor, lower for the 1-kHz signal with no precursor, and lowest for the 1- or 4-kHz signal with a precursor. The overshoot results and the frequency selectivity results would be consistent with stronger active processing at 4 kHz than at 1 kHz, and a decrease in active processing following a broadband noise precursor.
Tomography of joint P-wave traveltime and polarization data: A simple approach for media with low to moderate velocity gradients
Authors: Song Lin-Ping , Every A. G. , Wright C.
Published: January 2006

An elastic wave tomography method utilizing joint traveltime and polarization data is proposed that is computationally simpler than the existing methods [Hu and Menke, Geophys. J. Int. 110, 63 (1992); Farra and Begat, Geophys. J. Int. 121, 371 (1995)]. In the linearization problem for the use of polarization data, we start with ray perturbation theory and assume that the medium is weakly inhomogeneous. Then the problem formulation for polarization data is approximately expressed as a linear integral of the gradient of the medium slowness perturbation along a reference ray. We call this a quasi-linear approximation which ignores the effect of the perturbation of the ray position on the first-order perturbation of the ray slowness vector. To efficiently obtain the solution for multi-data sets, a quadratic objective functional is constructed by including the data misfit terms and a model constraint term. Then a new conjugate gradient type of iterative reconstruction algorithm is developed to solve this minimization problem. This algorithm is also an extension of the conjugate gradient approach for standard least-squares problems. The feasibility and capability of the proposed tomography method is illustrated by conducting both noise-free and noisy synthetic experiments in a cross-hole geometry. The numerical results demonstrate that the additional use of polarization data not only improves the image quality, but also has a stabilizing effect on the iterative tomography solution. However, the limitation of the method is that it becomes inaccurate if the velocity variations in the medium change rapidly with position.
Simulations of the thermo-acoustic lens effect during focused ultrasound surgery
Authors: Hallaj Ibrahim M. , Cleveland Robin O. , Hynynen Kullervo
Published: January 2006

Laboratory measurements of soft tissue properties show a dependence of background propagation properties on temperature. For typical focused ultrasound surgery (FUS) applications, only the slow variations in tissue background parameters need to be accounted for when computing the outcome of a FUS sonication. The cumulative effect of slowly varying sound speed has been referred to in the literature as a thermal lens, or a thermo-acoustic lens because of its beam-distorting properties. An algorithm to solve the coupled acoustic-thermal problem is described, and numerical results are presented to illustrate the effects of dynamic sound-speed profiles in layered tissues undergoing FUS. The results of simulations in liver with and without a fat layer indicate that the thermal-acoustic interaction results in more complex dynamics in FUS than a simple model will predict. Both the size and the position of the lesions predicted from the simulations are affected by the thermo-acoustic lens effect. However, the overall effect from short sonications at high power from sharply focused single element sources (F-no. from 0.8 to 1.3) around 1 MHz similar to those used in clinical setups is found to be small.
The effect of speechreading on masked detection thresholds for filtered speech
Authors: Grant Ken W.
Published: January 2006

Detection thresholds for spoken sentences in steady-state noise are reduced by 1–3 dB when synchronized video images of movements of the lips and other surface features of the face are provided. An earlier study [K. W. Grant and P. F. Seitz, J. Acoust. Soc. Am. 108, 1197–1208 (2000)], showed that the amount of masked threshold reduction, or bimodal coherence masking protection (BCMP), was related to the degree of correlation between the rms amplitude envelope of the target sentence and the area of lip opening, especially in the mid-to-high frequencies typically associated with the second (F2) and third (F3) speech formants. In the present study, these results are extended by manipulating the cross-modality correlation through bandpass filtering. Two filter conditions were tested corresponding roughly to the first and second speech formants: F1 (100–800 Hz) and F2 (800–2200 Hz). Results for F2-filtered target sentences were comparable to those of unfiltered speech, yielding a BCMP of roughly 2–3 dB. Results for F1-filtered target sentences showed a significantly smaller BCMP of approximately 0.7 dB. These results suggest that the magnitude of the BCMP depends on both the spectral and temporal properties of the target speech signal.
Probabilistic solutions of the Helmholtz equation
Authors: Budaev B. V. , Bogy D. B.
Published: January 2006

Solutions of the Schrödinger and Helmholtz equations are represented as mathematical expectations of functionals on paths in a complex space. Formulas obtained for the Helmholtz equation appear as direct improvements of the ray-method approximations to the exact solution. Presented numerical results confirm the efficiency of the suggested description of wave propagation phenomena.
Investigating trends in acoustics research from 1970–1999
Authors: Viator John A. , Pestorius F. Michael
Published: January 2006

Text data mining is a burgeoning field in which new information is extracted from existing text databases. Computational methods are used to compare relationships between database elements to yield new information about the existing data. Text data mining software was used to determine research trends in acoustics for the years 1970, 1980, 1990, and 1999. Trends were indicated by the number of published articles in the categories of acoustics using the Journal of the Acoustical Society of America (JASA) as the article source. Research was classified using a method based on the Physics and Astronomy Classification Scheme (PACS). Research was further subdivided into world regions, including North and South America, Eastern and Western Europe, Asia, Africa, Middle East, and Australia/New Zealand. In order to gauge the use of JASA as an indicator of international acoustics research, three subjects, underwater sound, nonlinear acoustics, and bioacoustics, were further tracked in 1999, using all journals in the INSPEC database. Research trends indicated a shift in emphasis of certain areas, notably underwater sound, audition, and speech. JASA also showed steady growth, with increasing participation by non-US authors, from about 20% in 1970 to nearly 50% in 1999.
Aerodynamic excitation and sound production of blown-closed free reeds without acoustic coupling: The example of the accordion reed
Authors: Ricot Denis , Caussé René , Misdariis Nicolas
Published: January 2006

The accordion reed is an example of a blown-closed free reed. Unlike most oscillating valves in wind musical instruments, self-sustained oscillations occur without acoustic coupling. Flow visualizations and measurements in water show that the flow can be supposed incompressible and potential. A model is developed and the solution is calculated in the time domain. The excitation force is found to be associated with the inertial load of the unsteady flow through the reed gaps. Inertial effect leads to velocity fluctuations in the reed opening and then to an unsteady Bernoulli force. A pressure component generated by the local reciprocal air movement around the reed is added to the modeled aerodynamic excitation pressure. Since the model is two-dimensional, only qualitative comparisons with air flow measurements are possible. The agreement between the simulated pressure waveforms and measured pressure in the very near-field of the reed is reasonable. In addition, an aeroacoustic model using the permeable Ffowcs Williams–Hawkings integral method is presented. The integral expressions of the far-field acoustic pressure are also computed in the time domain. In agreement with experimental data, the sound is found to be dominated by the dipolar source associated by the strong momentum fluctuations of the flow through the reed gaps.
Perception of aperiodicity in pathological voice
Authors: Kreiman Jody , Gerratt Bruce R.
Published: January 2006

Although jitter, shimmer, and noise acoustically characterize all voice signals, their perceptual importance in naturally produced pathological voices has not been established psychoacoustically. To determine the role of these attributes in the perception of vocal quality, listeners were asked to adjust levels of jitter, shimmer, and the noise-to-signal ratio in a speech synthesizer, so that synthetic voices matched naturally produced tokens. Results showed that, although listeners agreed well in their judgments of the noise-to-signal ratio, they did not agree with one another in their chosen settings for jitter and shimmer. Noise-dependent differences in listeners’ ability to detect changes in amounts of jitter and shimmer implicate both listener insensitivity and inability to isolate jitter and shimmer as separate dimensions in the overall pattern of aperiodicity in a voice as causes of this poor agreement. These results suggest that jitter and shimmer are not useful as independent indices of perceived vocal quality, apart from their acoustic contributions to the overall pattern of spectrally shaped noise in a voice.
The effect of spatial separation on informational masking of speech in normal-hearing and hearing-impaired listeners
Authors: Arbogast Tanya L. , Mason Christine R. , Kidd Gerald
Published: January 2006

The ability to understand speech in a multi-source environment containing informational masking may depend on the perceptual arrangement of signal and masker objects in space. In normal-hearing listeners, Arbogast et al. [J. Acoust. Soc. Am. 112, 2086–2098 (2002)] found an 18-dB spatial release from a primarily informational masker, compared to 7 dB for a primarily energetic masker. This article extends the earlier work to include the study of listeners with sensorineural hearing loss. Listeners performed closed-set speech recognition in two spatial conditions: 0° and 90° separation between signal and masker. Three maskers were tested: (1) the different-band sentence masker was designed to be primarily informational; (2) the different-band noise masker was a control for the different-band sentence; and (3) the same-band noise masker was designed to be primarily energetic. The spatial release from the different-band sentence was larger than for the other maskers, but was smaller (10 dB) for the hearing-impaired group than for the normal-hearing group (15 dB). The smaller benefit for the hearing-impaired listeners can be partially explained by masker sensation level. However, the results suggest that hearing-impaired listeners can use the perceptual effect of spatial separation to improve speech recognition in the presence of a primarily informational masker.
Quantifying the acoustic repertoire of a population: The vocalizations of free-ranging bottlenose dolphins in Fiordland, New Zealand
Authors: Boisseau Oliver
Published: January 2006

Quantification of the vocal repertoire of a species is critical for subsequent analysis of signal functionality, geographical variation, social relevance, and transmission. While signal repertoires have been documented for numerous animal species, detailed descriptions for the cetaceans are rare. This study describes the vocalizations of free-ranging bottlenose dolphins resident to the waters of Fiordland, New Zealand. The field recordings presented in this paper were made using both audio band and broadband apparatus. Subsequent classification of vocalizations using multivariate parameters enabled a quantification of the entire vocal output of the focal animals. These results were used to propose a meaningful repertoire of signals employed by this species. A total of 12 individual signal types were described, comprising four broad structural classes: “tonal,” “single bursts,” “click bursts,” and “repeat bursts.” The proposed repertoire will allow subsequent investigation into vocal behavior. It appears that the successful description of a species’ repertoire is dependent on the use of appropriate recording systems, a high number of representative recordings with good signal-to-noise ratio, and subsequent validation of the original classification system.
Dispersion of waves in porous cylinders with patchy saturation: Formulation and torsional waves
Authors: Berryman James G. , Pride Steven R.
Published: January 2006

Laboratory experiments on wave propagation through saturated and partially saturated porous media have often been conducted on porous cylinders that were initially fully saturated and then allowed to dry while continuing to acquire data on the wave behavior. Since it is known that drying typically progresses from outside to inside, a sensible physical model of this process is concentric cylinders having different saturation levels—the simplest example being a fully dry outer cylindrical shell together with a fully wet inner cylinder. We use this model to formulate the equations for wave dispersion in porous cylinders for patchy saturation (i.e., drainage) conditions. In addition to multiple modes of propagation obtained numerically from these dispersion relations, we find two distinct analytical expressions for torsional wave modes. We solve the resulting torsional wave dispersion relation for two examples: Massillon sandstone and Sierra White granite. One essential fact that comes to light during the analysis is that the effective shear moduli of the gas- and liquid-saturated regions must differ, otherwise it is impossible to account for the laboratory torsional wave data. Furthermore, the drainage analysis appears to give improved qualitative and quantitative agreement with the data for both of the materials considered.
A Speech Intelligibility Index-based approach to predict the speech reception threshold for sentences in fluctuating noise for normal-hearing listeners
Authors: Rhebergen Koenraad S. , Versfeld Niek J.
Published: January 2006

The SII model in its present form (ANSI S3.5-1997, American National Standards Institute, New York) can accurately describe intelligibility for speech in stationary noise but fails to do so for nonstationary noise maskers. Here, an extension to the SII model is proposed with the aim to predict the speech intelligibility in both stationary and fluctuating noise. The basic principle of the present approach is that both speech and noise signal are partitioned into small time frames. Within each time frame the conventional SII is determined, yielding the speech information available to the listener at that time frame. Next, the SII values of these time frames are averaged, resulting in the SII for that particular condition. Using speech reception threshold (SRT) data from the literature, the extension to the present SII model can give a good account for SRTs in stationary noise, fluctuating speech noise, interrupted noise, and multiple-talker noise. The predictions for sinusoidally intensity modulated (SIM) noise and real speech or speech-like maskers are better than with the original SII model, but are still not accurate. For the latter type of maskers, informational masking may play a role.
Modulation masking produced by second-order modulators
Authors: Füllgrabe Christian , Moore Brian C. J. , Demany Laurent , Ewert Stephan D. , Sheft Stanley , Lorenzi Christian
Published: January 2006

Recent studies suggest that an auditory nonlinearity converts second-order sinusoidal amplitude modulation (SAM) (i.e., modulation of SAM depth) into a first-order SAM component, which contributes to the perception of second-order SAM. However, conversion may also occur in other ways such as cochlear filtering. The present experiments explored the source of the first-order SAM component by investigating the ability to detect a 5-Hz, first-order SAM probe in the presence of a second-order SAM masker beating at the probe frequency. Detection performance was measured as a function of masker-carrier modulation frequency, phase relationship between the probe and masker modulator, and probe modulation depth. In experiment 1, the carrier was a 5-kHz sinusoid presented either alone or within a notched-noise masker in order to restrict off-frequency listening. In experiment 2, the carrier was a white noise. The data obtained in both carrier conditions are consistent with the existence of a modulation distortion component. However, the phase yielding poorest detection performance varied across experimental conditions between 0° and 180°, confirming that, in addition to nonlinear mechanisms, cochlear filtering and off-frequency listening play a role in second-order SAM perception. The estimated magnitude of the modulation distortion component ranges from 5%–12%.
Acoustic pulse propagation through a fluctuating stably stratified atmospheric boundary layer
Authors: Chunchuzov Igor , Kulichkov Sergey , Otrezov Alexander , Perepelkin Vitaly
Published: January 2006

Mesoscale wind speed and temperature fluctuations with periods from 1 min to a few hours significantly affect temporal variability and turbulent regime of the stable atmospheric boundary layer (ABL). Their statistical characteristics are still poorly understood, although the knowledge of such statistics is required when modeling sound propagation through the stable ABL. Several field experiments have been conducted to study the influence of mesoscale wind speed fluctuations on acoustic pulse propagation through the stable ABL. Some results of these experiments are described in this paper. A special acoustic source was used to generate acoustic pulses by the detonation of an air–propane mixture with a repetition period 30 s. The mean wind speed and temperature profiles were continuously measured by Doppler sodar and temperature profiler, whereas mesoscale wind fluctuations were measured by anemometers placed on a 56-m mast. From the measurements of the pulse travel time fluctuations at different distances from the source, the statistical characteristics of the mesoscale wind fluctuations, such as frequency spectra, coherences, horizontal phase speeds and scales, have been obtained. Some of the obtained results are interpreted with the use of a recently developed model for the internal wave spectrum in a stably stratified atmosphere.
Coherence and the speech intelligibility index
Authors: Kates James M. , Arehart Kathryn H.
Published: January 2006

The speech intelligibility index (SII) (ANSI S3.5-1997) provides a means for estimating speech intelligibility under conditions of additive stationary noise or bandwidth reduction. The SII concept for estimating intelligibility is extended in this paper to include broadband peak-clipping and center-clipping distortion, with the coherence between the input and output signals used to estimate the noise and distortion effects. The speech intelligibility predictions using the new procedure are compared with intelligibility scores obtained from normal-hearing and hearing-impaired subjects for conditions of additive noise and peak-clipping and center-clipping distortion. The most effective procedure divides the speech signal into low-, mid-, and high-level regions, computes the coherence SII separately for the signal segments in each region, and then estimates intelligibility from a weighted combination of the three coherence SII values.
Smart panels with velocity feedback control systems using triangularly shaped strain actuators
Authors: Gardonio Paolo , Elliott Stephen J.
Published: January 2006

In this paper we present a theoretical study on the active structural acoustic control of a new smart panel with sixteen triangularly shaped piezoelectric patch actuators, having their base edges evenly distributed along the perimeter of the panel, and velocity sensors positioned at the vertices opposite the base edges. The performance is assessed and contrasted with that of a conventional smart panel using a 4×4 array of square piezoelectric patch actuators evenly distributed over the surface of the panel with velocity sensors at their centers. For both systems the control effectiveness and stability of MIMO decentralized or SISO direct velocity feedback control architectures have been analyzed. The two control systems are arranged to generate active damping which reduces the response and sound radiation of the panel in the lightly damped and well separated low-frequency resonances. In particular the new control system can be seen as a set of sixteen “active wedges” which absorb energy from the incident flexural waves to the borders of the panel so that the panel could be considered anechoic. This study shows that the new arrangement with triangularly shaped actuators can achieve better control than the corresponding system using square actuators.
Modeling high-frequency electromotility of cochlear outer hair cell in microchamber experiment
Authors: Liao Zhijie , Popel Aleksander S. , Brownell William E. , Spector Alexander A.
Published: January 2006

Cochlear outer hair cells (OHC) are critically important for the amplification and sharp frequency selectivity of the mammalian ear. The microchamber experiment has been an effective tool to analyze the OHC high-frequency performance. In this study, the OHC electrical stimulation in the microchamber is simulated. The model takes into account the inertial and viscous properties of fluids inside and outside the cell as well as the viscoelastic and piezoelectric properties of the cell composite membrane (wall). The closed ends of the cylindrical cell were considered as oscillatory rigid plates. The final solution was obtained in terms of Fourier series, and it was checked against the available results of the microchamber experiment. The conditions of the interaction between the cell and pipette was analyzed, and it was found that the amount of slip along the contact surface has a significant effect on the cell electromotile response. The cell’s length changes were computed as a function of frequency, and their dependence on the viscosities of both fluids and the cell wall was analyzed. The distribution of the viscous losses inside the fluids was also estimated. The proposed approach can help in a better understanding of the high-frequency OHC electromotility under experimental and physiological conditions.
Multi-mode Lamb wave tomography with arrival time sorting
Authors: Leonard Kevin R. , Hinders Mark K.
Published: January 2006

Lamb wave tomography has been shown to be an effective nondestructive evaluation technique for platelike structures. A series of pitch-catch measurements between ultrasonic transducers can be taken from different orientations across the sample to create a map of a particular feature of interest such as plate thickness. Most previous work has relied solely on the first arriving mode for the time-of-flight measurements and tomographic reconstructions. The work described here demonstrates the capability of the Lamb wave tomography system to generate accurate reconstructions from multiple modes. Because each mode has different through-thickness displacement values, each is sensitive to different types of flaws, and the information gained from a multi-mode analysis can improve understanding of the structural integrity of the inspected material. However, one of the problems with the extraction of multi-mode arrival times is that destructive interference between two modes may cause one of the modes to seemingly disappear in the signal. The goal of the sorting algorithm presented in this work is to try and counteract this problem by using multiple frequency scans—also known as frequency walking—to sort the arrival times into their correct mode series.
Analysis of the sound field in finite length infinite baffled cylindrical ducts with vibrating walls of finite impedance
Authors: Shao Wei , Mechefske Chris K.
Published: January 2006

This paper describes an analytical model of finite cylindrical ducts with infinite flanges. This model is used to investigate the sound radiation characteristics of the gradient coil system of a magnetic resonance imaging (MRI) scanner. The sound field in the duct satisfies both the boundary conditions at the wall and at the open ends. The vibrating cylindrical wall of the duct is assumed to be the only sound source. Different acoustic conditions for the wall (rigid and absorptive) are used in the simulations. The wave reflection phenomenon at the open ends of the finite duct is described by general radiation impedance. The analytical model is validated by the comparison with its counterpart in a commercial code based on the boundary element method (BEM). The analytical model shows significant advantages over the BEM model with better numerical efficiency and a direct relation between the design parameters and the sound field inside the duct.
Instrumenting free-swimming dolphins echolocating in open water
Authors: Martin Stephen W. , Phillips Michael , Bauer Eric J. , Moore Patrick W. , Houser Dorian S.
Published: January 2006

Dolphins within the Navy Marine Mammal Program use echolocation to effectively locate underwater mines. They currently outperform manmade systems at similar tasks, particularly in cluttered environments and on buried targets. In hopes of improving manmade mine-hunting sonar systems, two instrumentation packages were developed to monitor free-swimming dolphin motion and echolocation during open-water target detection tasks. The biosonar measurement tool (BMT) is carried by a dolphin and monitors underwater position and attitude while simultaneously recording echolocation clicks and returning echoes through high-gain binaural receivers. The instrumented mine simulator (IMS) is a modified bottom target that monitors echolocation signals arriving at the target during ensonification. Dolphin subjects were trained to carry the BMT in open-bay bottom-object target searches in which the IMS could serve as a bottom object. The instrumentation provides detailed data that reveal hereto-unavailable information on the search strategies of free-swimming dolphins conducting open-water, bottom-object search tasks with echolocation.
The acoustics of Japanese wooden drums called “mokugyo”
Authors: Sunohara Masahiro , Furihata Kenji , Asano David K. , Yanagisawa Takesaburo , Yuasa Atsuyoshi
Published: January 2006

A drumlike traditional Japanese instrument, the mokugyo, is experimentally discussed. First, the acoustic characteristics of 176 mokugyos with diameters ranging from 7.5 to 120 cm and three drumsticks were measured. Results show that (a) the sound spectra consist of two common peaks [F1 (Hz): first peak frequency, F2 (Hz): second peak frequency] close together, with an average ratio (F2/F1) of 1.15, and (b) a drumstick beating the mokugyo is translated into an impact force applied over a period of time from 1 to 6 ms related to the mass and stiffness of the material wrapped around the tip of the drumstick. Second, to evaluate the acoustic response of a mokugyo in the final tuning process, the mechanical and acoustical analogy between the mokugyo and a bass reflex loudspeaker is theoretically and experimentally discussed. Results show that the model can be estimated within a relative error of 0.52% from the mass of wood chips. Finally, from a psychological experiment, the timbre of the mokugyo shows higher scores on psychological scales when the ratio (F2/F1) becomes 1.15.
Simultaneous acoustic channel measurement via maximal-length-related sequences
Authors: Xiang Ning , Daigle John N. , Kleiner Mendel
Published: January 2006

A wide variety of acoustic systems has multiple sources and receivers. This paper proposes a technique for making acoustic measurements simultaneously for multiple sources. The proposed technique features a collection of excitation signals of the maximum-length sequence (MLS) and MLS-related classes. Each signal in the set has a pulse-like autocorrelation function, and the cross-correlation functions between arbitrary pairs of signals drawn from the set have peak values that are significantly lower than the peak magnitude of the autocorrelation functions. The proposed method is particularly valuable when characterization of multisource, multireceiver system must be accomplished in a limited time period. Both simulation and experimental results are presented that demonstrate the feasibility and fidelity of the proposed techniques in characterizing acoustic systems.
Protocols for calibrating multibeam sonar
Authors: Foote Kenneth G. , Chu Dezhang , Hammar Terence R. , Baldwin Kenneth C. , Mayer Larry A. , Hufnagle Lawrence C. , Jech J. Michael
Published: January 2006

Development of protocols for calibrating multibeam sonar by means of the standard-target method is documented. Particular systems used in the development work included three that provide the water-column signals, namely the SIMRAD SM2000/90- and 200-kHz sonars and RESON SeaBat 8101 sonar, with operating frequency of 240 kHz. Two facilities were instrumented specifically for the work: a sea well at the Woods Hole Oceanographic Institution and a large, indoor freshwater tank at the University of New Hampshire. Methods for measuring the transfer characteristics of each sonar, with transducers attached, are described and illustrated with measurement results. The principal results, however, are the protocols themselves. These are elaborated for positioning the target, choosing the receiver gain function, quantifying the system stability, mapping the directionality in the plane of the receiving array and in the plane normal to the central axis, measuring the directionality of individual beams, and measuring the nearfield response. General preparations for calibrating multibeam sonars and a method for measuring the receiver response electronically are outlined. Advantages of multibeam sonar calibration and outstanding problems, such as that of validation of the performance of multibeam sonars as configured for use, are mentioned.
A phase-space Gaussian beam summation representation of rough surface scattering
Authors: Gordon Goren , Heyman Ehud , Mazar Reuven
Published: January 2006

A Gaussian beam (GB) summation representation for rough surface scattering is introduced. In this scheme, the coherent and incoherent scattered fields are described by a phase-space summation of GBs that emanate from the rough surface at discrete set of points and directions. It thus involves stochastic GB2GB scattering matrices for the coherent and incoherent fields, and deterministic GB propagators. It benefits from the simplicity and accuracy of the latter, and can be used in applications involving propagation in complex scenarios comprising inhomogeneous media with rough surface boundaries. The GB2GB matrices are calculated from the statistical moments of the scattering amplitude, which are given either analytically or empirically. An analytical and numerical example for weakly rough surface is presented and discussed. Applications to the more complicated propagation scenario of doubly rough surface waveguide with multiple reflection phenomena will be presented in a follow-up publication.
A first-order statistical smoothing approximation for the coherent wave field in random porous media
Authors: Müller Tobias M. , Gurevich Boris
Published: January 2006

An important dissipation mechanism for waves in randomly inhomogeneous poroelastic media is the effect of wave-induced fluid flow. In the framework of Biot’s theory of poroelasticity, this mechanism can be understood as scattering from fast into slow compressional waves. To describe this conversion scattering effect in poroelastic random media, the dynamic characteristics of the coherent wavefield using the theory of statistical wave propagation are analyzed. In particular, the method of statistical smoothing is applied to Biot’s equations of poroelasticity. Within the accuracy of the first-order statistical smoothing an effective wave number of the coherent field, which accounts for the effect of wave-induced flow, is derived. This wave number is complex and involves an integral over the correlation function of the medium’s fluctuations. It is shown that the known one-dimensional (1-D) result can be obtained as a special case of the present 3-D theory. The expression for the effective wave number allows to derive a model for elastic attenuation and dispersion due to wave-induced fluid flow. These wavefield attributes are analyzed in a companion paper.
Difference between diotic and dichotic presentations on audiovisual synchronization
Authors: Nakamura Rie , Aikawa Kiyoaki
Published: January 2006

Significant differences were found between diotic and dichotic presentations of auditory stimuli on audiovisual synchronization. Two types of moving sphere were used for visual stimuli; (a) a sphere moved straight from left to right at a constant velocity, and (b) it moved up and right and then turned down and right at the midpoint. Auditory stimuli included (1) a continuous pure tone (1000 Hz), (2) a sequence of two short tones of 30 ms (1000 Hz), (3) a sweep tone (500 Hz → 1500 Hz), and (4) a Frequency-Modulated tone (500 Hz → 1500 Hz → 500 Hz). The duration of these stimuli was 240 ms each. Visual stimuli were presented on a Liquid-Crystal Display. Auditory stimuli were presented by headphones. The time difference between auditory and visual stimuli was changed between −360 ms and +360 ms. The sound source linearly moved from left to right in case of dichotic presentation. Subjective tests, using the forced-choice of synchronized or not, clarified the significant differences between diotic and dichotic presentations when the auditory stimulus (1) or (4) was presented with the visual stimulus (b). No significance was obtained for other combinations of auditory and visual stimuli. [Work supported by NTT.]
Global active control of broadband noise from small axial cooling fans
Authors: Green Matthew J. , Sommerfeldt Scott D.
Published: January 2006

The filtered-x LMS algorithm has previously been used for feed-forward control of the tonal noise of a small axial cooling fan. This system consists of four actuator-sensor pairs surrounding the small fan. The ideal placement of these elements has been previously determined by Gee and Sommerfeldt [Gee and Sommerfeldt, J. Acoust. Soc. Am. 115, 228–236 (2004)]. With success in reducing tonal noise to about the same level as broadband noise it now becomes desirable to control the broadband noise of the small axial cooling fan. This is accomplished with active feedback control. The performance of the broadband control system will be reviewed, and the results of a hybrid (feed-forward and feedback) system for overall reduction of cooling fan noise will be discussed. Ideal methods and configurations for feedback control will also be discussed.
Interpolation noise in a hard-limited beamformer
Authors: Young J. W.
Published: January 2006

Beamforming typically requires sampling of individual hydrophone outputs at a rate substantially higher than Nyquist for bandpass processes. One approach to minimizing the sampling rate is the use of an interpolation filter for reconstruction of intermediate sample values [R. G. Pridham and R. A. Mucci, J. Acoust. Soc. Am. 63, 425–434 (1978)]. In principle, the required samples can be determined without error from the Nyquist rate samples since the latter contain complete information on the band-limited element signal. When the element signals are hard-limited, all amplitude information is lost and errors are introduced into the interpolation process. Information in a hard-limited signal (HLS) is contained in the zero-crossing times. Basically, sampling a HLS obliterates the information necessary to determine exact zero-crossing times between sample values. In this paper, we present an analysis of the mean square error (interpolation noise) associated with estimating the values of the HLS at intermediate times. We compute the increase in beam noise power due to this error and show that this imposes a limit on our ability to perform adaptive null steering with such an array.
On the use of focused horizontal arrays as mode separation and source location devices in ocean acoustics-numerical modeling results
Authors: Lynch James F. , Schwartz Daniel K.
Published: January 2006

It has been shown theoretically that one can perform normal mode separation and source location using focused horizontal arrays [J. F. Lynch, J. Acoust. Soc. Am. (to be published)]. To illustrate this theory, numerical modeling results are displayed for both line and convex circulaly curved arrays in range-dependent and range-independent waveguide environments, both in the presence and absence of source motion. Various topics to be discussed include: direct measurement of modal group velocities from moving cw source measurements, determination of environmental range variations, mode interference effects and ray theory multipath focusing, and the intercomparison of focused array mode filtration with other standard techniques, e.g., steering.
Discovery of a solitary, localized, stationary water wave
Authors: Wu Junru , Keolian Robert , Rudnick Isadore
Published: January 2006

When a trough, 15×1 in., is filled with water to a depth of 2 cm and driven parametrically by oscillating it vertically with an amplitude of about 0.06 cm at a frequency, 10 Hz, where the half-wavelength of the surface wave is equal to the width of the trough, a striking phenomenon is observed. In a strongly localized region, which may be centered almost anywhere along the trough, a standing wave of very high amplitude is seen to oscillate across the width of the channel. Surprisingly, its amplitude drops off exponentially at its edges with a 1/e length of only 0.9 cm. It oscillates at subharmonic frequencies. This energy packet has particle-like behavior. When the trough is tilted the wave packet moves toward the shallow end. Two solitary waves of opposite phase, pair. Those of like phase combine or form an oscillating pair. [Work supported by ONR.]
Sidelobe level of hyperbolic frequency modulated (HFM) waveforms
Authors: Chou S. I.
Published: January 2006

As large time-bandwidth products are employed for the widely used LFM (linear frequency-modulated) waveforms, the loss due to the phase mismatch of the peak output of a single matched filter becomes excessive even for very moderate target radial speeds. HFM (hyperbolic frequency modulated) waveforms can eliminate this loss. An early result on sidelobe level of HFM waveform [J. J. Kroszczynski, Proc. IEEE 57, 1260–1266 (1969)] apparently has errors in its derivation in applying asymptotic approximation techniques. The only numerical result provided there did not agree well with the analytically derived result, despite the claim to the contrary. In the present paper, new asymptotic results have been derived using integration by parts in the correct direction, so that terms discarded are smaller than the quantity being approximated. Computer simulations using several sets of parameters, including the one mentioned above, compare well with the new analytic approximations. The increased sidelobe level of HFM waveform over that of the LFM one is much less than indicated by the early approximation.
A ray theory simulator of a moving broadband source
Authors: Ratliff James D. , Penrod Clark S.
Published: January 2006

A computer model is described which simulates and processes the time series received from a moving broadband source. Ray theory is used to compute the set of eigenrays instantaneously valid at each source emission time in a range invariant environment characterized by an arbitrarily depth-dependent water-column sound-speed profile atop a single sediment layer with linear sound speed and attenuation profiles overlying a semi-infinite homogeneous substrate. The received time series is obtained by a discrete time domain convolution of an arbitrary source waveform with a set of impulse responses which depend on emission time and propagation path. The received time series can be autocorrelated or crosscorrelated to examine the impact on broadband signal processing due to environmental (particularly bottom interaction) effects, source motion effects (Doppler and multipath structure evolution), and the choice of signal processing parameters. Example correlation functions are shown to illustrate the effects of some of these mechanisms. [Work supported by Naval Ocean Research and Development Activity, Code 530.]
The influence of environment and source motion on broadband acoustic correlations: A normal mode approach
Authors: Gragg Robert
Published: January 2006

We deal with a source which emits a broadband signal S(t) while moving through a shallow (⩽300 m), range-invariant environment at constant speed, depth, and bearing. The received signal is constructed from the result [K. E. Hawker, J. Acoust. Soc. Am. 63, 675–681 (1979)] for the S(t)∼eiωt case. In terms of Fourier transforms, P(r,z,t)∼  ∑ n (Ŝ(ω)exp{[ikn(ω) − δn(ω)] × [1 − εn(ω)cos θ (t)]|r − r0(t)|} × Un*[z,ωn(ω,t)]Un [z0,ωn (ω,t)])″ is the signal at r,z,t from a source on trajectory r0(t) at depth z0 and speech ν0. θ(t) is the source-receiver angle, εn(ω) = ν0/νngp(ω)<1, and ωn(ω,t) = ω − ν0kn (ω)[cos θ(t) − εn (ω)] is a Doppler-shifted frequency. We model subkilohertz-band signals in this way for fixed explosive sources (SUS) and for moving noise sources. The signal and its autocorrelation are compared with experimental data to determine the importance of environmental factors (gross SVP features, finer SVP details, bottom attentuation profile) and source motion (speed and cpa range), as well as source and receiver depths. [Work supported by DARPATTO and Naval Electronics Systems Command (Code 612).]
Eigenvalue detection threshold statistics
Authors: Mignerey Peter C.
Published: January 2006

A promising method for high-resolution beamforming on underwater arrays is the eigenvector decomposition method which requires knowledge of the expected noise in order for multiple eigenvalues to occur. [D. H. Johnson and S. P. DeGraaf, IEEE Trans. Acoustics Speech Signal Process. 30, 638 (1982).] It is presently not well understood how to objectively separate the signal and noise subspaces. When the correlation matrices are estimated with a finite number of degrees of freedom the rank becomes full and the eigenvalues spread. Under these conditions the classification of eigenvalues may be made using statistical methods. A Gaussian process was applied to the hydrophones of a ten-element filled array and sample noise matrices were generated in the metric of other independent sample noise matrices. Probability densities were obtained based on 106 samples for each eigenvalue and the broadside beam of conventional, maximum likelihood and maximum entropy beamformers. A comparison of ROC curves demonstrates sufficient detection capability by the eigenvalue method to allow the establishment of detection thresholds for the objective classification of eigenvalues.