bluuebunny/crossref_metadata_2025 huggingface dataset:
Three‐dimensional ultrasound imaging of the prostate
Authors: Tong Shidong
Published: July 2002

Prostate cancer is the most commonly diagnosed cancer in men in North America. Since its introduction in 1971, transrectal ultrasound (TRUS) has evolved into one of the primary tools for the evaluation of prostate disease. However, with conventional TRUS, diagnosticians must mentally integrate a series of 2D images in order to develop an impression of the 3D anatomy, and the accurate and precise estimation of prostate volume is difficult. Moreover, an examination takes 10–20 min, often resulting in patient discomfort. We propose using 3D TRUS to overcome these problems. In this thesis, we describe a 3D ultrasound imaging system, analyze the distortion in its images due to miscalibration, and study its performance in estimating prostate volume. Our system consists of three elements: (i) a conventional ultrasound machine and TRUS probe; (ii) a custom‐built assembly for rotating the probe under microcomputer control; and (iii) a microcomputer with an 8‐bit video frame grabber. A typical scan of 200 2D B‐mode images takes 13 s, so that the entire examination takes under 5 min. These images can then be rapidly reconstructed into a 3D image using an algorithm we describe, and interactively displayed using standard software. Also, we describe procedures for accurately calibrating the reconstruction parameters, so that distortions in the shape, length, area, and volume of the 3D image of an object are all less than 1%. We also show that manual planimetry of 3D TRUS images can be used to estimate prostate volumes in vitro with 2.6% accuracy and 2.5% precision, and in vivo with 5.1% intra‐observer variability and 11.4% inter‐observer variability. By comparison, with the height‐width‐length method (Volume=π/6HWL) with conventional 2D TRUS images, in vivo estimates had 11.5% intra‐observer variability and 13.5% inter‐observer variability. Thus 3D TRUS overcomes some of the limitations of 2D TRUS, and has great potential as a tool for the diagnosis, study, and management of prostate disease.
Monte Carlo simulations of prostate implants to improve dosimetry and compare planning methods
Authors: Taschereau Richard , Roy Jean , Pouliot Jean
Published: July 2002

The objective of this study is to use Monte Carlo simulations to assess the sensitivity of implant planning methods to seed misplacement. A model of seed misplacement is first developed. It is based upon data gathered after a study on source migration performed on 30 patients treated with I‐125 transperineal implants. It consists of applying elementary transformations to every needle in a loading plan to produce a distorted implant mimicking the effect of migration. After being validated, the model has been used to tune the inverse planning system in use at our institution. The new planning system is now used clinically and actual results are compared with those predicted by simulations. Simulations were also used to compare our planning method with others. The new planning system increased the average postimplant dose–volume histogram DVH(160) from 82% to 93%, which is the value predicted by the simulations. This improvement is due to an increased dose margin providing coverage even in the presence of migration. At the same time, the dose to the urethra remained at 267 Gy because of a special protection feature included in the planning system. Some other implant planning methods are not as robust [average DVH(160) ranging from 76% to 85%] and deliver a higher dose to the urethra (close to 400 Gy). To conclude, a simple model of source migration can provide realistic feedback about sensitivity to migration of planning methods. It allowed a significant clinical improvement at our institution. The improved inverse planning system provided better coverage with fewer seeds (but equal total activity) than a manual method. Hence, a properly tuned inverse planning system has the potential to deliver the less sensitive plans. The model also helped demonstrate that planning methods are not equally robust to migration and that they should not be evaluated solely by the plans they produce, but also by their clinical (or simulated) results.
The Duffing oscillator: A precise electronic analog chaos demonstrator for the undergraduate laboratory
Authors: Jones B. K. , Trefan G.
Published: July 2002

A simple electronic circuit is described which can be used in the student laboratory to demonstrate and study nonlinear effects and chaos. The circuit shows the changes to the dynamical properties of the system with respect to three control parameters: the applied voltage amplitude and frequency and the circuit damping. The response voltage and its derivative can be displayed to give the phase space plot and the bifurcation diagram against any control parameter. The circuit is sufficiently ideal and stable to allow comparison of its analog output with the output obtained from standard digital computer simulations. As examples, the routes to chaos with respect to the control parameters and the bifurcation route to chaos, which follows the Feigenbaum scenario, are shown.
The relation between physical and computer-generated point spread functions and optical transfer functions
Authors: Lucke Robert L.
Published: July 2002

A review of how a point spread function and an optical transfer function are derived from the exit pupil function of an imaging system is given and the relation between computer-generated functions and their physical counterparts is developed in detail. Useful normalizations and integral relations are presented.
The attractive nonlinear delta-function potential
Authors: Molina M. I. , Bustamante C. A.
Published: July 2002

We solve the one-dimensional nonlinear Schrödinger equation for an attractive delta-function potential at the origin, [(p2/2m)−Ωδ(x)|φ(x)|α]φ(x)=Eφ(x), and obtain the bound state in closed form as a function of the nonlinear exponent α. The bound state probability profile decays exponentially away from the origin, with a profile width that increases monotonically with α, becoming an almost completely extended state when α→2−. At α=2, the bound state suffers a discontinuous change to a delta function-like profile. A further increase of α increases the width of the probability profile, although the bound state is stable only for α<2. The transmission of plane waves across the potential increases monotonically with α and is insensitive to the sign of the opacity Ω.
Solution of the one-dimensional Dirac equation with a linear scalar potential
Authors: Hiller John R.
Published: July 2002

We solve the Dirac equation in one spatial dimension for the case of a linear, Lorentz-scalar potential. This extends earlier work of Bhalerao and Ram [Am. J. Phys. 69 (7), 817–818 (2001)] by eliminating unnecessary constraints. The spectrum is shown to match smoothly to the nonrelativistic spectrum in a weak-coupling limit.
Evaluation of sound propagation models used in bottom volume scattering studies
Authors: Li Dan , Tang Dajun , Frisk George V.
Published: July 2002

The proper evaluation of sound propagation between sources/receivers and scatterers is important in characterizing bottom volume scattering. In this article, several sound propagation models used in bottom volume scattering studies are evaluated and their results compared to the exact solution obtained through a numerical wave number integration technique. It is found that Hines’ approach [J. Acoust. Soc. Am. 88, 324–334 (1990)] works well for the two isovelocity half-space case except when the grazing angle is close to the critical angle. The far-field approximation, given by Ivakin [Sov. Phys. Acoust. 32(6), 492–496 (1986)] and Mourad and Jackson [J. Acoust. Soc. Am. 94, 344–358 (1993)], has a performance depending upon the sound speed structure in the sediment. For an isovelocity slow bottom, it agrees well with the exact solution. However, discrepancies arise for an isovelocity fast bottom or a bottom with a complex sound speed structure. In addition, the appropriateness of using the equivalent surface scattering strength as a function of grazing angle in volume scattering characterizations is studied. In conclusion, precautions need to be taken in modeling both the propagation effects and the scattering mechanisms associated with the bottom volume scattering process.
Analyses of axisymmetric waves in layered piezoelectric rods and their composites
Authors: Nayfeh Adnan H. , Abdelrahman Wael G. , Nagy Peter B.
Published: July 2002

An exact treatment of the propagation of axisymmetric waves in coaxial anisotropic assembly of piezoelectric rod systems is presented. The rod system consists of an arbitrary number of coaxial layers, each possessing transversely isotropic symmetry properties. The treatment, which is based on the transfer matrix technique, is capable of deriving the dispersion relations for a variety of situations. These include the case of a single rod system that is either embedded in an infinitely extended solid or fluid host or kept free. The procedure is also adapted to derive approximate solutions for the cases of a periodic fiber distribution in a matrix material, which model unidirectional fiber-reinforced composites. The results are numerically illustrated for a widely used piezoelectric-polymer composite. It is seen that piezoelectric coupling can significantly change the morphology of the dispersive behavior of the composite.
Noise transmission from a curved panel into a cylindrical enclosure: Analysis of structural acoustic coupling
Authors: Henry James K. , Clark Robert L.
Published: July 2002

Much of the research on sound transmission through the aircraft fuselage into the interior of aircraft has considered coupling of the entire cylinder to the acoustic modes of the enclosure. Yet, much of the work on structural acoustic control of sound radiation has focused on reducing sound radiation from individual panels into an acoustic space. Research by the authors seeks to bridge this gap by considering the transmission of sound from individual panels on the fuselage to the interior of the aircraft. As part of this research, an analytical model of a curved panel, with attached piezoelectric actuators, subjected to a static pressure load was previously developed. In the present work, the analytical model is extended to consider the coupling of a curved panel to the interior acoustics of a rigid-walled cylinder. Insight gained from an accurate analytical model of the dynamics of the noise transmission from the curved panels of the fuselage into the cylindrical enclosure of an aircraft is essential to the development of feedback control systems for the control of stochastic inputs, such as turbulent boundary layer excitation. The criteria for maximal structural acoustic coupling between the modes of the curved panel and the modes of the cylindrical enclosure are studied. For panels with aspect ratios typical of those found in aircraft, results indicate that predominately axial structural modes couple most efficiently to the acoustic modes of the enclosure. The effects of the position of the curved panel on the cylinder are also studied. Structural acoustic coupling is found to not be significantly affected by varying panel position. The impact of the findings of this study on structural acoustic control design is discussed.
Temporal pitch perception and the binaural system
Authors: Carlyon Robert P. , Demany Laurent , Deeks John
Published: July 2002

Two experiments examined the relationship between temporal pitch (and, more generally, rate) perception and auditory lateralization. Both used dichotic pulse trains that were filtered into the same high (3900–5400-Hz) frequency region in order to eliminate place-of-excitation cues. In experiment 1, a 1-s periodic pulse train of rate Fr was presented to one ear, and a pulse train of rate 2Fr was presented to the other. In the “synchronous” condition, every other pulse in the 2Fr train was simultaneous with a pulse in the opposite ear. In each trial, subjects concentrated on one of the two binaural images produced by this mixture: they matched its perceived location by adjusting the interaural level difference (ILD) of a bandpass noise, and its rate/pitch was then matched by adjusting the rate of a regular pulse train. The results showed that at low Fr (e.g., 2 Hz), subjects heard two pulse trains of rate Fr, one in the “higher rate” ear, and one in the middle of the head. At higher Fr (>25 Hz) subjects heard two pulse trains on opposite sides of the midline, with the image on the higher rate side having a higher pitch than that on the “lower rate” side. The results were compared to those in a control condition, in which the pulses in the two ears were asynchronous. This comparison revealed a duplex region at Fr>25 Hz, where across-ear synchrony still affected the perceived locations of the pulse trains, but did not affect their pitches. Experiment 2 used a 1.4-s 200-Hz dichotic pulse train, whose first 0.7 s contained a constant interaural time difference (ITD), after which the sign of the ITD alternated between subsequent pulses. Subjects matched the location and then the pitch of the “new” sound that started halfway through the pulse train. The matched location became more lateralized with increasing ITD, but subjects always matched a pitch near 200 Hz, even though the rate of pulses sharing the new ITD was only 100 Hz. It is concluded from both experiments that temporal pitch perception is not driven by the output of binaural mechanisms.
Acoustic transmission across a roughened fluid–fluid interface
Authors: Lim Raymond , Paustian Iris C. , Lopes Joseph L.
Published: July 2002

A set of tank experiments was performed to investigate acoustic transmission across a roughened fluid–fluid interface with the intention to test heuristic Bragg scattering predictions used to explain observations of anomalous transmission in field experiments. In the tank experiments, two immiscible fluids (vegetable oil floating on glycerin) formed the layers. Small polystyrene beads were floated at the interface to simulate roughness. An array of hydrophones placed in the bottom layer (glycerin) was used to measure the acoustic levels transmitted across the interface. This array was also employed as a beamformer to determine the apparent angle and sound speed of the scattered signals. Data were acquired at subcritical grazing angles in the frequency range of 100–200 kHz for three different bead diameters and for various configurations in which the locations of the beads floating on the interface were varied. Results of these measurements demonstrated that a significant amount of acoustic energy can be scattered into the bottom layer by beads floating at the interface. The scattered levels increased with increasing bead diameter. However, discrepancies occurred between observed propagation properties and the Bragg predictions. By comparing the processed tank data to a computer simulation of the same it was determined that these discrepancies are a consequence of near-field reception of the scattering by the bead array and ignoring the directionality of the scattering by the beads. Consequences to observations made in field experiments are discussed.
On the group velocity of guided waves in drill strings
Authors: Poletto Flavio , Carcione José M.
Published: July 2002

A key element to verify the drill-bit signal processing is the estimation of the time delay of the guided waves transmitted through the drill string from the bit to the surface. This delay can be measured from drill-bit vibrations or calculated using the mechanical properties of the drill string. The calculation of the complete solution and the exact dispersion relations requires expensive numerical modeling. In this work, a simple approach to compute the group velocity of extensional and torsional waves by averaging the drill-string properties in the low-frequency approximation is used. The result is a generalization of the group velocity for periodic systems in which stationary distribution of properties is assumed. Results obtained with real strings show that the group velocity in the bottom-hole assembly is greater than the velocity in a uniform rod and lower than the velocity in the drill pipes.
The effect of basilar-membrane nonlinearity on the shapes of masking period patterns in normal and impaired hearing
Authors: Wojtczak Magdalena , Schroder Anna C. , Kong Ying-Yee , Nelson David A.
Published: July 2002

Masking period patterns (MPPs) were measured in listeners with normal and impaired hearing using amplitude-modulated tonal maskers and short tonal probes. The frequency of the masker was either the same as the frequency of the probe (on-frequency masking) or was one octave below the frequency of the probe (off-frequency masking). In experiment 1, MPPs were measured for listeners with normal hearing using different masker levels. Carrier frequencies of 3 and 6 kHz were used for the masker. The probe had a frequency of 6 kHz. For all masker levels, the off-frequency MPPs exhibited deeper and longer valleys compared with the on-frequency MPPs. Hearing-impaired listeners were tested in experiment 2. For some hearing-impaired subjects, masker frequencies of 1.5 kHz and 3 kHz were paired with a probe frequency of 3 kHz. MPPs measured for listeners with hearing loss had similar shapes for on- and off-frequency maskers. It was hypothesized that the shapes of MPPs reflect nonlinear processing at the level of the basilar membrane in normal hearing and more linear processing in impaired hearing. A model assuming different cochlear gains for normal versus impaired hearing and similar parameters of the temporal integrator for both groups of listeners successfully predicted the MPPs.
Finite-element vibration analysis of a cantilever plate with a central circular hole subject to an in-plane moving (rotating) load
Authors: El-Saeidy Fawzi M. A.
Published: July 2002

In rotating radial ball bearings supported on elastic casings with the bearing outer ring lightly fitted into the housing, the force due to the ball elastic contact is indeed a rotating load vector rolling over the housing. For accurate estimation of the casing annulus (circular hole) dynamic deformations, which in turn affect bearing tolerances and the magnitude of the generated forces, the effect of the load rotation (motion) on the housing vibration should be considered. Considering the integral casing and outer ring to be a plate, an isoparametric plane stress finite-element (FE) based analytical procedure is presented for dynamic analysis of housing as affected by load vector rotation. The equations of motion are obtained using Lagrange’s equations and decoupled using the normal coordinates representation and solved using a special numerical integration scheme. The computations are carried out using the FE program DAMRO 1. Results in both time and frequency domains are discussed and it is found that higher load rotational speeds decrease deformations and increase the smoothness of the annulus surface. With lower speeds, the deformations are always positive (contraction), and at higher speeds they exhibit both contraction and expansion around the annulus circumference. The vibrations measured at the casing outer surface show that the spectrum in the direction of casing rigid support attracts more system natural frequencies compared to the orthogonal direction spectrum. This underlines the importance of the vibration measuring probe(s) orientation with respect to the casing rigid support direction to capture all the important vibrations.
Low-frequency long-range propagation and reverberation in the central Arctic: Analysis of experimental results
Authors: Duckworth Greg , LePage Kevin , Farrell Ted
Published: July 2002

BBN and the ASW Environmental Acoustic Support program office of ONR conducted a low-frequency reverberation and transmission loss experiment in the central Arctic during the spring of 1992. In this article we report analysis of these data which extracts the controlling propagation and reverberation characteristics. The recorded source levels are combined with the received levels recorded at range to estimate the dependence of the scattering strength of the ice canopy on incident and backscattered grazing angle in frequency bands between 10 and 70 Hz. Results show that the monostatic backscattering strength is roughly proportional to frequency and angle squared, with a nominal value of −47 dB at 40 Hz and 8.5° grazing.
On scattering from a bubble located near a flat air–water interface: Laboratory measurements and modeling
Authors: Kapodistrias George , Dahl Peter H.
Published: July 2002

Scattering by a single bubble near a flat air–water interface is investigated theoretically and experimentally. A ray-acoustic interpretation is used to describe the four scattering paths, from source to bubble to receiver, that determine the response of the bubble. Multiple scattering effects are accounted for using a closed-form solution derived from the multiple scattering series. Experiments are performed by placing a bubble with radius a≈425 μm on a fine nylon thread, which is approximately 100 μm in diameter and practically transparent to sound, at a distance d from the interface. The primary variable is d and it ranges from 1a to 100a. The bubble is excited by tone bursts with a center frequency of 120 kHz, with the transducers arranged in both bistatic and monostatic configurations. Theory and experiment are in good agreement, verifying the dominant effect of the four paths in the response of the bubble, with multiple scattering playing a role for kd<1, where k is the wave number of the medium. In the long-range limit our simulations agree with those of Ye and Feuillade [J. Acoust. Soc. Am. 102, 798–805 (1997)] including the shifting of the bubble’s resonant frequency. The dependence of scattering on transducer arrangement, range to bubble, grazing angle, and phase relation among the four paths, vis-à-vis monostatic and bistatic scattering, is discussed.
Detection and monitoring of cracks using mechanical impedance of rotor-bearing system
Authors: Prabhakar S. , Sekhar A. S. , Mohanty A. R.
Published: July 2002

The dynamic behavior of structures, in particular, that of a rotor, containing cracks is a subject of considerable current interest. In the present study, the influence of a transverse surface crack, both open and breathing conditions, on the mechanical impedance of the rotor-bearing system, has been investigated by FEM analysis for flexural vibrations. The results show that the mechanical impedance changes substantially due to the presence of crack and follow definite trends with the crack parameters (depth and location) and force location. The normalized mechanical impedance of rotor system is more sensitive to the breathing crack when compared to the open crack. The sudden changes in mechanical impedance have been observed at the multiples of the running frequency for the breathing crack. The measurement of mechanical impedance has been suggested for crack detection and condition monitoring of rotor-bearing systems.
Transverse, normal modes of vibration of a cantilever Timoshenko beam with a mass elastically mounted at the free end
Authors: Rossit C. A. , Laura P. A. A.
Published: July 2002

An exact solution for the title problem is obtained by means of the classical eigenfunction approach. The natural frequencies are computed for a wide range of the intervening mechanical and geometric parameters. Normal modes of transverse vibration are plotted for some cases of practical interest. The problem is technically important in several areas of applied science and technology.
An acoustic-logging transmission-network model
Authors: Fa Lin , Castagna John P. , Hovem Jens M. , Dong Daqun
Published: July 2002

The acoustic logging process can be described as a signal transmission system with a corresponding transmission network model. This model gives the relations between driving-voltage signal, the electrical-acoustic conversion at the source, acoustic properties of the propagation media (borehole fluid and formation around borehole), the pressure response in the borehole, the acoustic-electrical conversion at the receiver and recorded logging signal.
The effect of internal oscillators on the acoustic response of a submerged shell
Authors: Photiadis Douglas M. , Bucaro J. A. , Houston Brian H.
Published: July 2002

The effect of a large number (≈1000) of internal mechanical oscillators on the acoustic backscattering cross section of a submerged ribbed shell has been experimentally investigated. A comparison of the backscattering cross section of the shell with oscillators to that of a simple ribbed shell with no oscillators shows a number of significant effects arising from the internal structure and overall a significantly increased average scattering strength. These results are presented and several physical mechanisms which can account for the salient aspects of the observations are discussed.
Comments on “Elastic wave radiation and diffraction of a piston source” [J. Acoust. Soc. Am. 87, 1894 (1990)]
Authors: Wang Enyu , Du Gonghuan
Published: July 2002

It is noted that the second item in Eq. (12) [J. Acoust. Soc. Am. 87, 1894 (1990)] could not be ignored at low frequencies. Meanwhile, a precise solution for Eq. (1) without overflow problems is proposed at high frequencies.
Are normal hearing thresholds a sufficient condition for click-evoked otoacoustic emissions?
Authors: Kapadia Sarosh , Lutman Mark E.
Published: July 2002

Transiently evoked otoacoustic emissions (TEOAE) have been reported in several studies as absent in a small minority of normal ears. Other studies have reported TEOAEs in all normal ears. Differences between studies may arise directly from criteria for TEOAE identification, criteria for selection of normals, or statistically due to limited sample sizes. In order to understand and model cochlear processes involved in TEOAE generation, it needs to be known whether the presence of normal hearing leads automatically to generation of TEOAEs. The present study set out to establish in a large sample if any ears could be found that lacked TEOAEs despite normal hearing threshold levels (HTL). A total of 397 ears from highly cooperative adult subjects were examined under laboratory conditions. Using cross correlation between replicate nonlinear waveforms as the criterion, TEOAEs were present in 99.2% of the sample (lower CI 98.1%). However, careful visual assessment of the recorded waveforms for the remaining ears did not unequivocally show absence of TEOAE characteristics in any ear with normal HTLs. While TEOAE strength varies widely among ears, no clear evidence was found to show that TEOAEs can be absent when HTLs are normal.
A probe-signal study of auditory discrimination of complex tones
Authors: Hill Nicholas I. , Bailey Peter J. , Hodgson Philip
Published: July 2002

The present experiments used an analogue of the probe-signal method of Greenberg and Larkin [J. Acoust. Soc. Am. 44, 1513–1523 1968 to investigate the extent to which listeners direct attention to a particular spectral region when discriminating complex tones. The listeners’ task was to discriminate between two seven-component complex tones on the basis of an increment in the level of a single component. On two-thirds of trials the increment was achieved by adding a fixed primary signal to one component of the complex. The primary-signal trials were relatively easy and were intended to cue listeners to attend to the component to which the primary was added. On the remaining trials a smaller probe signal was added either to the cued component, or to one of three other components. The results of the first experiment, in which the complex tones had a flat spectrum, showed significantly better performance for probe signals applied to the cued component compared to the other three components. To control for the possibility that the observed pattern of results was due to the use of timbral cues, a second experiment was conducted in which the spectral profile of the tones was randomized between trials. The results for the second experiment were similar to those of the first experiment and are consistent with the idea that listeners were focusing attention on the spectral region defined by the primary signal.
Leaky waves and the elastic wave resonance reflection on a crystal–thin solid layer interface
Authors: Darinskii A. N.
Published: July 2002

When a Rayleigh wave becomes “supersonic” for a given geometry of propagation, a thin solid layer coated on the surface of the medium can bring about the transformation of this wave into a leaky wave. In such a case in the sagittal plane there emerges a narrow interval of angles of incidence within which the phase of the reflection coefficient suffers abrupt changes, and the reflection is accompanied by excitation of surface vibrations with amplitudes greatly exceeding the amplitude of the incident wave. The effect is due to the resonance excitation of the leaky wave. The critical angle of incidence and the width of the resonance interval are determined by the real and imaginary parts of the leaky wave speed. Approximate expressions for the leaky wave speed and for the coefficients of plane wave conversion are derived and analyzed without any assumptions about the crystallographic symmetry of both the substrate and the layer.
Elastic waves in orthotropic incompressible materials and reflection from an interface
Authors: Nair Sudhakar , Sotiropoulos Dimitrios A.
Published: July 2002

The propagation of elastic plane waves in orthotropic incompressible materials is examined under plane strain conditions in a plane of symmetry. The slowness surface is obtained by aligning a material axis of symmetry with the direction of minimum phase speed. The existence of incident homogeneous waves and reflected homogeneous and nonhomogeneous waves in the presence of a planar interface separating two half-spaces is subsequently examined. A surface which separates the range of existence of two homogeneous reflected waves from that of one homogeneous and one nonhomogeneous is obtained in terms of the angle of incidence, the orientation of the interface with respect to the material axis of symmetry, and one elastic parameter. The critical orientation beyond which there exist two homogeneous reflected waves is derived in explicit form in terms of the elastic parameter. Reflection coefficients are obtained and discussed when the interface is a free surface. Exclusion points are defined in the range of existence of the reflected waves as points for which only one reflected (homogeneous) wave exists. The analysis is complemented with numerical examples.
Increased off-axis energy deposition due to diffraction and nonlinear propagation of ultrasound from rectangular sources
Authors: Cahill Mark D. , Baker Andrew C.
Published: July 2002

An existing model, the Bergen code, is used to simulate the propagation of ultrasonic beams of finite amplitude, due to rectangular and square sources. It is found that the edges of the source give rise to peaks in the diffraction pattern at the fundamental frequency, which can cause the strongest shockwaves to form off-axis. These tend to be sharply bounded, causing rapid variation in heat deposition and streaming pressure across even an unfocused beam, and suppressing axial maxima in the pressure field.
Acoustic scattering on an elastic plate described by the Timoshenko model: Contact conditions and uniqueness of the solution
Authors: Andronov I. V. , Belinskiy B. P.
Published: July 2002

It is shown that the known solution of the acoustic scattering problem on a supported elastic plate, described by the Timoshenko model, should be corrected. The general formulation of the contact conditions that imply the reciprocity principle is given. Sommerfeld’s formula and the “optical” theorem for the model are formulated. They lead to the uniqueness of the solution. The numerical comparison of the effective cross section of scattering from supported elastic plate described by the Kirchhoff and by the Timoshenko models is presented.
Evolution of phonon noise and phonon state preparation in a model for generation of hypersonic phonons by laser
Authors: Chai Jin-Hua , Guo Guang-Can
Published: July 2002

The evolution of phonon noise and the quantum correlation between phonon and photon in a model of the generation of hypersonic phonons by laser have been analyzed according to the quantum theory. The cases of perfect phase matching, phase mismatch, and losses have been discussed, respectively. It is shown that the phonon state preparation can be performed by measuring a quadrature component of the idle light field under certain conditions.
Temporal deconvolution of laser-generated longitudinal acoustic waves for optical characterization and precise longitudinal acoustic velocity evaluation
Authors: Enguehard Franck , Bertrand Lionel
Published: July 2002

The laser thermoelastic generation of ultrasound is a promising technique with many potential applications, but it is also a complicated process with many physical phenomena involved. Contrary to a conventional piezoelectric transducer generation, which is a surface phenomenon, a laser generation can activate acoustic sources within the material by optical penetration of the excitation wavelength, resulting in asynchronous wave arrivals at a given point. More generally, in the ideal case of a nondispersive isotropic material, the laser-ultrasonics displacement signals result from temporal convolutions between optical penetration, laser pulse duration, and laser spot extension effects. In this paper, a deconvolution technique is presented that extracts the laser pulse duration contribution from the experimental displacement signals. This deconvolution scheme applied to one-dimensional experiments, in which the laser excitation is spread over a sufficiently large area on the front side of the sample, allows the measurement of the optical absorption coefficient of the material at the excitation wavelength and also a precise evaluation of its longitudinal acoustic velocity.
Nonlinear inversion of the SH wave equation in a half-space for density and shear modulus determination
Authors: Zhu Wenhao , Jun Xu , Rose Joseph L.
Published: July 2002

This paper deals with the problem of multi-parameter nonlinear inversion of the SH wave equation in an elastic half-space. A numerical approach combining Born iteration and a regularizing technique is presented for simultaneously reconstructing 2-D distributions of density and shear modulus in a scatterer embedded in a half-space. The well-to-well source–receiver scheme commonly used in geophysical exploration is considered in the model in which two incident frequencies are used to uncouple the parameters in frequency domain. The weighted residual method, along with bilinear interpolating functions, are used in the discretization procedure. Computer simulations have been conducted on several examples with different density and shear modulus configurations. The numerical results show that the approach proposed has a uniformly convergence for the given objects and has a feature of treating the limited-source well-to-well scheme that causes a more ill-conditioned equation in the inversion procedure.
A note on transient underwater bubble sound
Authors: Leander Johan L.
Published: July 2002

This Letter considers scattered sound from transiently oscillating gas bubbles in liquids. The full transient problem including the finite duration of the excitation is analyzed. As a result, the wave front of the radiated sound pulse involving information about the excitation is also studied. The model presented is used to simulate sound pulses from sea-surface bubbles which have been generated by, for example, spilling breakers, capillary-gravity waves, and rain drops. Although very simple in relation to the actual physical process of excitation, this model enables us to predict some of the essential properties of scattered pulses observed experimentally. It is suggested that the time scale of duration of the initial driving that enters into the present analysis might be of some use in a further physical understanding of bubble generation and excitation.
Analytical/numerical matching for efficient calculation of scattering from cylindrical shells with lengthwise constraints
Authors: Loftman R. C. , Bliss D. B.
Published: July 2002

Structural discontinuities in highly coupled fluid–structure systems are modeled by an approach called analytical/numerical matching (ANM). This method separates the low-resolution global influence of a discontinuity from the relatively high-resolution local effects. A continuous, smoothed replacement for a fundamental structural discontinuity is constructed so that the system is identically unchanged beyond a small smoothing region. Simultaneously, the precise local effect of smoothing the discontinuity is retained in analytical form. The smoothed problem is solved by numerical techniques, with rapid convergence and reduced computational cost. The original discontinuous character is restored using the analytical expression for the local difference between the smoothed and the original problems. ANM has been successfully applied to two-dimensional cases of acoustic scattering from a thin, infinitely long cylindrical shell, with multiple structural discontinuities. Local solutions for longitudinal line discontinuities with radial, tangential, and rotational constraints have been formulated using ANM. Line constrained scattering problems, as well as line driven problems, are investigated. The ability of analytical/numerical matching to replace a discontinuous physical problem by a well behaved continuous one for numerical evaluation, while ultimately retaining the original geometry and physical behavior, is illustrated.
Intensity discrimination for precedence effect stimuli
Authors: Freyman Richard L. , McCall Daniel D. , Clifton Rachel K.
Published: July 2002

When two identical stimuli are presented from two loudspeakers with a brief delay between them, a single image is heard near the source of the leading sound. The delayed sound or echo appears to be suppressed whereas the preceding sound determines perceived location, hence the name, the precedence effect. This study investigated normal-hearing listeners’ sensitivity to changes in the intensity of the lagging sound. Pairs of 2-ms white noise bursts, with a 2-ms delay between the onsets of lead and lag, were presented from two loudspeakers 45° left and right of midline in an anechoic chamber. A 2AFC procedure was used to test discrimination of intensity changes in the lead, lag, and both sounds together. The untreated results showed discrimination to be poorest for changes in the lag stimulus. However, when the intensity differences were transformed into predictions of equivalent monaural level based on KEMAR measurements and binaural loudness summation, discrimination for the lag was equal to the other two conditions. A follow-up experiment found that listeners were highly sensitive to the presence of the lag, more sensitive than would be predicted from loudness changes. It is concluded that the precedence effect does not consist of a general suppression or attenuation of the lagging sound, but rather that suppression may be limited to directionality cues.
Auditory and linguistic factors in the perception of voice offset time as a cue for preaspiration
Authors: Pind Jörgen
Published: July 2002

Previous research [J. Pind, Acta Psychol. 89, 53–81 (1995)] has shown that preaspiration in Icelandic, an [h]-like sound inserted between a vowel and the following closure, can be cued by Voice Offset Time (VOffT), a speech cue which is the mirror image of Voice Onset Time (VOT). Research has also revealed that VOffT is much more sensitive to the duration of the neighboring vowel than is VOT [J. Pind, Q. J. Exp. Psychol. 49A, 745–764 (1996)]. This paper explores the hypothesis that it is primarily the perceived quantity of the vowel that is responsible for the effect of the vowel on the perception of preaspiration. This hypothesis is based on the linguistic fact that preaspiration can only follow a phonemically short vowel. This linguistic hypothesis is contrasted with an auditory hypothesis in terms of forward masking. Perceptual experiments show that the perceptual boundaries for preaspiration can be affected either by changing the preceding vowel’s duration or its spectrum. If the spectrum of the vowel changes towards that of a long vowel, longer VOffT’s are needed for listeners to perceive preaspiration, thus lending support to the linguistic hypothesis.
Ultrasonic air-coupled capacitance transducers using thin mica films
Authors: Ingleby Paul , Hutchins David A. , Bashford Andrew G. , Schindel David W.
Published: July 2002

Micromachined air-coupled capacitance transducers have been manufactured using anisotropically etched silicon backplates and commercially available mica films. Devices developed using 20-μm-thick insulating layers have yielded frequencies of up to 400 kHz. However, new devices using mica with a thickness of approximately 4 μm will deliver characteristics similar to existing transducers employing polymeric dielectric films. This will result in wideband behavior and bandwidths extending from approximately 100 kHz to 2 MHz. Mica-based devices have several advantages over capacitance transducers with polymer films due to the robust physical characteristics exhibited by this type of material. Improved thermal characteristics and lower porosity allow this type of device to be employed in a variety of conditions in which the performance of the polymer films would be impaired. Results of experiments performed in air at a range of temperatures from ambient to 400 °C will be presented. This will demonstrate the versatility of such devices in terms of both sensitivity and bandwidth.
The effect of wall materials on the timbre of brass instruments
Authors: Pyle Robert W.
Published: July 2002

It has long been thought by players and instrument makers that the material from which a brass instrument is made influences the tone quality and playing characteristics of the instrument. For instance, the brochure of a maker of custom trombones describes bells made of three alloys: yellow brass (70% Cu, 30% Zn), having the ‘‘clearest sound, sharpest articulation,’’ gold brass (85% Cu, 15% Zn), with ‘‘warm sound, rounded articulation,’’ and red brass (90% Cu, 10% Zn), with ‘‘warmer sound, covered articulation.’’ The bells are made in three metal thicknesses: light weight, with ‘‘flexible tone, rapid response,’’ standard weight, with ‘‘balanced tone, even response,’’ and heavy weight, with ‘‘firm tone, stable response.’’ Most players agree with these statements. This model of trombone is made so that bell sections can be interchanged while leaving the remainder of the instrument intact. The present paper reports the results of measurements under playing conditions on several different bells. Comparisons of steady-state behavior are made via the transfer function between sound pressure in the mouthpiece cup and an on-axis point outside the bell. An attempt will also be made at the rather more difficult task of characterizing the attack transient.
The effect of wall properties on the timbre of organ pipes
Authors: Angster Judit , Paal Gyvrgy , Garen Walter , Miklss Andras
Published: July 2002

The influence of the wall vibrations on the timbre of flue organ pipes is one of the most disputed questions of organ building. Wall vibrations of metal and wooden labial pipes have been investigated by using miniature piezoelectric accelerometers and optical noncontact vibrometers. Both free and forced vibrations have been studied. Two sets of diapason pipes that were built with different wall properties but identical dimensions have been voiced to very similar speech and timbre, then vibration and sound spectra and attack transients were recorded. While large differences have been found in vibration spectra, hardly any change in the sound signal was observed. Similar investigations have been performed on wooden pipes. In this case the voicer ‘‘tuned’’ the side wall resonances in order to make the sound richer in overtones. The effect of this ‘‘tuning’’ on the vibration and sound spectra has been investigated. The ‘‘tuning’’ resulted in a significant increase of the vibration amplitude, while the radiated sound-pressure level decreased and the overtones became relatively stronger.
Interpretation of shear material properties of vocal fold mucosal tissues with Fung’s quasilinear viscoelastic theory
Authors: Chan Roger W. , Titze Ingo R.
Published: July 2002

Fung’s quasilinear viscoelastic theory (QLV) [Y. C. Fung, Biomechanics (Springer-Verlag, New York, 1993), pp. 277–292] has been successfully applied to model the time- and history-dependent properties of a variety of biological soft tissues in the passive state. In particular, the hysteresis or damping curves of many soft tissues remain relatively insensitive to the rate of deformation (strain rate or frequency) across several decades of variation. This insensitivity to frequency cannot readily be accounted for by traditional discrete models of linear viscoelasticity. Rather, Fung’s QLV provides a mathematically powerful framework in which a continuous stress relaxation spectrum can be used to model the relatively flat damping characteristics. The shear properties of human vocal fold mucosal tissues were measured with a rotational rheometer. Data on complex dynamic shear modulus, complex dynamic viscosity, and damping ratio as functions of frequency were obtained. It was found that vocal fold mucosal tissues show the shear-thinning behavior and have a relatively flat damping curve typical of biological soft tissues. Theoretical predictions based on the QLV matched well with the empirical data. The results suggest that the vocal fold mucosa can be modeled by the QLV under small-amplitude oscillation conditions. [Work supported by NIH Grant No. P60 DC00976.]
Material and obsolescence on flute tone quality
Authors: Cocchi Alessandro , Tronchin Lamberto
Published: July 2002

The rule of material and obsolescence on flute tone quality has been discussed for a long time among musicians and flute makers. Mozart himself made use of crystal flutes in some of his works (Rondo’, K617, Adagio, K356). From an acoustical point of view, since Boehm’s work of 1832, the effect of material on flute tone quality has not been investigated, until researches of recent years [Coltman (1971); Chapuis (1991)]. In this work the research has been carried out measuring impulse responses inside the tube of the flute. Two different flutes have been utilized, i.e., a light-alloy flute and a silver flute. The MLS sequences, with homemade software, have been utilized, gathering impulse responses in two different positions in the tube, in order to verify the variation of sound field. From the impulse responses a frequency analysis has been obtained, which pointed out that the silver flute contains more high frequency and shorter transient than the light-alloy flute. Starting from the impulse responses, sound example of difference in sound quality has finally been obtained.