bluuebunny/crossref_metadata_2025 huggingface dataset:
Depth‐segmented detector for x‐ray absorptiometry
Authors: Stevens Grant M. , Pelc Norbert J.
Published: July 2002

A new energy‐dependent multi‐cell detector, which is a generalization of the conventional front–back detector, was studied using computer simulations. The noise performance of the detector for bone quantitation was examined in comparison to an ideal energy discriminating detector, and front–back detectors with and without inter‐detector filters. The front–back detectors were optimized for a reference object composed of water and bone, and then compared to the new detector over a range of object compositions. In this paper, precision in calculated bone thickness is used as the criterion for evaluating detector performance. Simulations show that the segmented detector always performs better than the front–back detector without an inter‐detector filter. It outperforms the detector incorporating a filter by an amount that depends on the heterogeneity of the x‐ray spectrum. In addition, for single component radiographic images, this multi‐cell detector retains information which is lost in the front–back detector with a filter layer.
Density of states on a staircase
Authors: Zypman Fredy R.
Published: July 2002

The concept of density of states (DOS) is introduced via a gravitational problem, which is solved exactly and, for comparison, under various approximations. It consists of a collection of hard spheres in a two-dimensional container. One of the container’s walls is vertical, and the other is inclined with a height that varies in steps. This problem is well suited in physics courses as a preamble to topics in which the idea of DOS is required, but not fully appreciated by students.
The origin of the conduction band in table salt
Authors: de Boer P. K. , de Groot R. A.
Published: July 2002

A long-standing misinterpretation of the origin of the conduction band in sodium chloride is corrected. We show that this band is primarily derived from chlorine states, and not from sodium states as is generally believed. The anion character of the conduction band holds for the other alkali halides as well. The reinterpretation of this band clarifies why the size of the band gap in these insulators does not depend on the alkali metal in a first-order approximation.
Synchrotron radiation and symmetries
Authors: Rivera R. , Villarroel D.
Published: July 2002

The total power of radiation emitted by a monoenergetic electron in circular orbit is derived by calculating the instantaneous energy flux of the electron field across the surfaces of spheres and tori that enclose the orbit. These surfaces are such that the positions of the electron at different times are indistinguishable with respect to them, which in turn permits the choice of special spheres and tori that greatly simplify the calculations. The total power of radiation of an electron is usually derived in textbooks with the help of the relativistic formalism. But for the particular motion in a synchrotron, the total power of radiation is obtained here working in the ordinary three-dimensional physical space, where the calculations are conceptually easier to follow than in Minskowski space, especially for students who are taking a first course of electrodynamics.
Projection operator approach to time-independent perturbation theory in quantum mechanics
Authors: Yao Demin , Shi Jicong
Published: July 2002

The time-independent perturbation theory in quantum mechanics is formulated using projection operator techniques. The determination of the perturbed eigenvalue can be decoupled from that of the perturbed eigenstate. Both the Brillouin–Wigner theory and the Rayleigh–Schrödinger theory come out straightforwardly. Both degenerate and nondegenerate cases can be treated in a unified way for arbitrarily high order perturbations.
Mode-selective resonance ultrasound spectroscopy of a layered parallelepiped
Authors: Ogi Hirotsugu , Heyliger Paul , Ledbetter Hassel , Kim Sudook
Published: July 2002

The resonance frequencies of mechanical free vibration of a three-layer material calculated by a discrete-layer model and measured by acoustic-resonance methods were compared. The material was composed of an aluminum parallelepiped sandwiched by two stainless-steel parallelepipeds. The discrete-layer model developed here used linear Lagrange basis functions through the layered dimension and continuous global power-series basis functions in the plane perpendicular to the layer thickness. Using such a basis function for the layer-thickness direction allows discontinuity in the elastic properties across the interface between dissimilar layers. The resonance frequencies were measured using two methods: mode-selective electromagnetic acoustic resonance (EMAR) and resonance ultrasound spectroscopy (RUS). The measurements agreed with the calculations typically within 1%. The EMAR method allows the selective detection of vibrational modes possessing particular displacement patterns. This selectivity was supported by the model calculation. Thus, using the EMAR method makes mode identification clear and this is essential for developing and improving the model calculation of such a complicated structure. Internal friction was also measured by the two acoustic methods, which reveals the mechanical-contact effect on the internal-friction measurement in the RUS method.
Aeroacoustics of diffusers: An experimental study of typical industrial diffusers at Reynolds numbers of O(105)
Authors: van Lier L. , Dequand S. , Hirschberg A. , Gorter J.
Published: July 2002

Diffusers as used in gas transport systems have an optimal pressure recovery but are unstable due to marginal flow separation. Coupling of diffuser flow oscillation with acoustic modes in a pipe has been demonstrated in a recent work by Kwong and Dowling [J. Fluids Eng. 116, 842 (1994)] to drive flow unsteadiness. Considered here in addition to the diffuser at a pipe termination is the aeroacoustic response of a diffuser in a long pipe. In both cases reflection coefficient measurements show that at moderate and low amplitudes of the acoustical particle velocity compared to the main flow velocity, diffusers are aeroacoustic sources similar to the whistler nozzle and the horn. This confirms the observations of Kwong and Dowling. At higher acoustical velocity amplitudes diffusers become strong absorbers, which can be explained in terms of a quasistationary flow model. Finally, an indication is provided for possible remedial measures when a stable flow is needed.
Improved solution for the vortical and acoustical mode coupling inside a two-dimensional cavity with porous walls
Authors: Majdalani Joseph
Published: July 2002

This work presents an improved solution to a former study that analyzes the oscillatory motion of gases prescribed by vortico-acoustical mode coupling inside a two-dimensional porous cavity. The physical problem arises in the context of an oscillating gas inside a rectangular enclosure with wall transpiration, sublimation, or sweating. Previously, a multiple-scale solution was derived for the temporal field. The asymptotic formulation was based on an unconventional choice of scales. Its accuracy was also commensurate with the size of ε, a parameter that captured the effect of small viscosity. Currently, an exact solution is derived and compared to the previous formulation. A simple WKBJ solution is also constructed for validation purposes. Unlike both asymptotic formulations, the exact solution remains accurate regardless of the range of physical parameters.
Response to “Ants are deaf ” [J. Acoust. Soc. Am. 109, 3080 (2001)]
Authors: Hickling Robert , Brown Richard L.
Published: July 2002

We reply to the preceding Letter to the Editor.
The effects of pressure loading on the dynamics of a curved piezostructure
Authors: Henry James K. , Clark Robert L.
Published: July 2002

In an article previously published in this journal by the authors, a state-space model of a curved piezostructure was developed and used to investigate the effects of curvature on panel dynamics. Panel curvature was shown to increase control system bandwidth and to affect transducer coupling. In the present work, the model is extended to include the effects of internal pressure loading on the dynamics of a curved piezostructure. The impact of internal pressure loading on the dynamics of a curved piezostructure, and subsequently on active structural acoustic control (ASAC) of sound transmission through it, are reviewed.
Decision strategies of hearing-impaired listeners in spectral shape discrimination
Authors: Lentz Jennifer J. , Leek Marjorie R.
Published: July 2002

The ability to discriminate between sounds with different spectral shapes was evaluated for normal-hearing and hearing-impaired listeners. Listeners detected a 920-Hz tone added in phase to a single component of a standard consisting of the sum of five tones spaced equally on a logarithmic frequency scale ranging from 200 to 4200 Hz. An overall level randomization of 10 dB was either present or absent. In one subset of conditions, the no-perturbation conditions, the standard stimulus was the sum of equal-amplitude tones. In the perturbation conditions, the amplitudes of the components within a stimulus were randomly altered on every presentation. For both perturbation and no-perturbation conditions, thresholds for the detection of the 920-Hz tone were measured to compare sensitivity to changes in spectral shape between normal-hearing and hearing-impaired listeners. To assess whether hearing-impaired listeners relied on different regions of the spectrum to discriminate between sounds, spectral weights were estimated from the perturbed standards by correlating the listener’s responses with the level differences per component across two intervals of a two-alternative forced-choice task. Results showed that hearing-impaired and normal-hearing listeners had similar sensitivity to changes in spectral shape. On average, across-frequency correlation functions also were similar for both groups of listeners, suggesting that as long as all components are audible and well separated in frequency, hearing-impaired listeners can use information across frequency as well as normal-hearing listeners. Analysis of the individual data revealed, however, that normal-hearing listeners may be better able to adopt optimal weighting schemes. This conclusion is only tentative, as differences in internal noise may need to be considered to interpret the results obtained from weighting studies between normal-hearing and hearing-impaired listeners.
Acoustic scattering from a rectangular aperture in a thick hard screen
Authors: Park Hyun H. , Eom Hyo J.
Published: July 2002

Acoustic scattering from a rectangular aperture in a thick hard screen is examined. The Fourier transform is used to represent the scattered wave in the spectral domain and the boundary conditions are enforced to represent a solution in closed form. Numerical computations are performed to illustrate the behavior of the scattered wave from a thick rectangular aperture. The solution is represented in series which are numerically efficient.
Estimating acoustic radiation from a Bernoulli–Euler beam using shaped polyvinylidene flouride film
Authors: Scott Brian L. , Sommerfeldt Scott D.
Published: July 2002

This paper examines numerically the use of arrayed shaped polyvinylidene fluoride film sensors to obtain an estimate of the far-field radiated power from a clamped-clamped Bernoulli–Euler beam excited by a sinusoidal point force. Distributed sensors are designed that are sensitive to the radiated power. Fourier analysis of point and distributed sensor outputs is used to estimate the beam’s radiated power. The numerical results of the estimated power obtained from the point and distributed sensors are compared to those predicted by the theoretical model and the performance of the two sensor types is assessed. The results show that the shaped sensors provide a reasonable estimate of the strain transforms over the region of interest, when compared to the exact theoretical predictions, for the first five beam resonance frequencies and for frequencies located approximately midway between resonance frequencies. The distributed sensors also give consistently better predictions of the strain transforms for all frequencies considered when compared to the point sensor results. The power predictions using shaped sensors range from −1 to 3 dB relative to the exact theoretical results for most of the frequencies analyzed. This contrasts to the 36–68 dB range of relative power estimates using point sensors.
Absolute pitch and sex affect event-related potential activity for a melodic interval discrimination task
Authors: Hantz Edwin C. , Kreilick Kelley G. , Marvin Elizabeth W. , Chapman Robert M.
Published: July 2002

Absolute pitch is a special ability which allows for special perceptual/cognitive strategies. Studies have shown differences in event-related scalp potentials between absolute-pitch (AP) and relative-pitch (RP) subjects of equal musical training. In this study, highly trained musicians (15 females/15 males) performed a melodic interval discrimination task, using intervals on-pitch in equal-tempered tuning (A4=440 Hz) and tuned a half-semitone sharp. Subjects identified target intervals (probability 0.2) in a series of 400 randomly transposed intervals. AP subjects were expected to perform differently across intonation conditions, whereas RP subjects were not. Event-related potentials (ERPs) were recorded from three midline sites and two lateral sites. ERPs were analyzed by principal component analysis and analysis of variance. Sex was also considered as an independent subject variable. Performance was not significantly different either by absolute pitch or sex. Reaction times did not reveal any significant interactions involving AP or sex, but showed a significant effect by response type (target/nontarget). Strong P3 activity appeared to the target melodic intervals regardless of subject group or intonation. PCA factors with maxima at 352, 511, and 709 ms were sensitive to task relevance. Males showed greater positivity than females along the midline. A significant intonation by response type by sex interaction indicated a greater spread of values for females than males, and greater similarity in response by sex for the sharp than the on-pitch intervals. AP subjects showed reduced P3 activity along the midline, but increased over lateral sites. In a difficult musical task, the ERPs were sensitive to the sex of the listeners, as well as to whether they had absolute pitch.
The resonances of finite-length elastic cylinders and elastic spheroids excited by sound scattering
Authors: Bao X. L. , Überall H. , Niemiec J. , Décultot D. , Lecroq F. , Maze G. , Ripoche J.
Published: July 2002

The predictions of resonance frequencies for elongated elastic cylinders and spheroids, based on various methods of approach, were discussed in a number of papers in recent years. In the present study, the regions of applicability of the phase matching method for surface waves and of the longitudinal bar wave approximation are examined by comparing the predicted results with the results of T-matrix calculations or with the results of scattering experiments.
Three-dimensional noise field directionality estimation from single-line towed array data
Authors: Wagstaff Ronald A. , Newcomb J.
Published: July 2002

For many reasons, the three-dimensional (3-D) arrival structure of the undersea ambient noise field is of interest to the research and development community. One reason is that the arrival structure can be used to estimate the beam noise of an array, which may be required to estimate the performance of the array as an operational Navy asset or a scientific measurement tool. Another reason is that there are clues inherent in the vertical arrival structure that relate to the nature of the acoustic propagation along the azimuths of the noise sources. Similarly, there are also clues in the horizontal arrival structure of the undersea ambient noise field that relate to the azimuthal distribution of the noise sources. Both of these classes of clues are important in the verification and validation of undersea ambient noise models. The ideal measurement tool to measure the 3-D arrival structure of the noise field is a high-resolution volumetric array sonar system. Unfortunately, such a system is not generally available. However, towed horizontal line arrays are available and can be used, even though they are far from ideal. The beam patterns of a line array are conically symmetric about the axis of the array. When the axis of a horizontal line array is tilted slightly from an elevation angle of 0°, the vertical character of the beam cones can be used to discriminate between various vertical arrival angles. Combined with measurements made on several different towed array headings, an estimate of the 3-D directionality of the noise field can be obtained. An algorithm that uses such a technique on single-line towed array data to generate an estimate of the 3-D directionality of the noise field is described herein. Some results using measured data from a recent noise measurement exercise are presented and discussed.
Matched-field evaluation of acoustic scattering from Arctic ice
Authors: Kapoor Tarun K. , Schmidt Henrik
Published: July 2002

This paper investigates the three-dimensional acoustic scatter from large-scale features under the Arctic ice cover using field data collected during the CEAREX experiments in April 1989. The analysis involves the identification and isolation of the features under the ice canopy, and the simultaneous evaluation of their spatial scattering characteristics. A two-step matched-field processing (MFP) algorithm is used to solve this complex multiparameter estimation problem. Using one large (∼1200 m) and four short (∼300 m) vertical line arrays, and a crossed horizontal hydrophone array in a matched-field processing scheme, beamforming under the ice sheet was performed to obtain an approximate map of the rough interface between ice and water. This analysis yields estimates for scattering strengths for frequencies ranging between 25 and 105 Hz. It is shown that scatter from the elastic ice surface is a frequency selective phenomenon. This beamformed map is then used to isolate a single discrete scatterer, and subsequently, its scattering characteristics are evaluated. Simultaneously, an idealized environmental model is developed to compute scatter from a canonical protuberance. Matching the theoretical results from the analytical model with the experimental data, which consists of contributions from multiple scatterers, yields the statistics of the distribution of ice protuberances.
An improved approximation for wave propagation above an impedance ground in a medium with a linear sound-speed profile
Authors: Li Y. L. , White Michael J. , Tai Jianfeng
Published: July 2002

The atmospheric profile whose sound speed varies linearly with height is simple in concept, but leads to complications when solving for the sound pressure. Its effects are commonly approximated by a similar profile whose squared refractive index is a linear function of height. In this paper, the validity of the approximation has been examined for sound propagation above an impedance ground and an improved approximation is given. The new approximation is based on a WKB-type analysis using Airy functions as the general solution to the wave equation. Numerical examples show that this new approximation more adequately models the sound field for the linear sound-speed profile for a wide range of detector heights and gradients and for both upward and downward refracting atmospheres.
Binaural detection with spectrally nonoverlapping signals and maskers: Evidence for masking by aural distortion products
Authors: van der Heijden Marcel , Trahiotis Constantine , Kohlrausch Armin , van de Par Steven
Published: July 2002

Thresholds were measured for diotic tonal signals in the presence of interaurally delayed bands of Gaussian noise. When the signal frequency was 525 Hz, the spectrum of the noise was either below (highest frequency, 450 Hz) or above (lowest frequency, 600 Hz) the frequency of the signal. When the signal frequency was 450 Hz, the spectrum of the noise was always above the signal frequency (lowest frequency, 600 Hz). Signals had a 250-ms duration and were temporally centered within the 300-ms long bursts of noise. The spectrum level of the noise was 60 dB. Thresholds obtained in all three conditions varied essentially sinusoidally with the interaural delay of the noise. For signals below the spectrum of the noise, the periodicities within the data were close to, but not identical with, the periodicities of the signals. This outcome is discussed in terms of masking produced by aural distortion products stemming from interactions within the bands of noise [cf. van der Heijden and Kohlrausch, J. Acoust. Soc. Am. 98, 3125–3134 (1995)]. For signals above the spectrum of the noise, the periodicities in the data suggested that masking was produced by components within the band of noise. Patterns within the data are also discussed in terms of limitations concerning the magnitude of external delays that can be matched by internal delays that are incorporated in modern models of binaural processing.
The PVDF-based wave number domain sensing techniques for active sound radiation control from a simply supported beam
Authors: Wang Bor-Tsuen
Published: July 2002

This work presents a novel wave number domain sensing approach which applies polyvinylidene fluoride (PVDF) films for active structural acoustic control. An array of PVDF strip films is equally distributed over a beam to measure the structural response. The PVDF voltage wave number transform functions can then be obtained by performing the discrete wave number transform on the sensing signals. The cost function can be defined as the sum of mean square values of the supersonic components of the wave number transform function. The linear quadratic optimization process can be applied to obtain the optimal control inputs, thereby minimizing the cost function. This work also considers the simply supported beam with infinite rigid baffle subjected to a harmonic point force disturbance. The PVDF-based wave number domain sensing approach is applied, while piezoelectric actuators are used as control inputs. In addition, the sensing method’s performance is evaluated by comparing with an accelerometer based wave number domain sensing approach. Both continuous and discrete wave number transform approaches are presented as well. Analysis results demonstrate that the wave number domain sensing approach cannot only provide efficient signals that are related to the structure-borne sound, but is also quite effective in controlling sound radiation. This work advances current efforts to apply the sensing ability of intelligent material structure systems to actively control structural sound radiation.
The role of the chinchilla pinna and ear canal in electrophysiological measures of hearing thresholds
Authors: Murphy W. J. , Davis R. R.
Published: July 2002

Measurements of the acoustic transfer function (ATF) of the pinnae of 8 chinchillas were compared with the auditory-evoked potential (AEP) thresholds of 16 chinchillas measured in free field and with insert earphones. The ATF was measured in anesthetized chinchillas in a far-field condition in a semi-anechoic room using a logarithmic frequency sweep from 100 Hz to 20 kHz. Probe microphone measurements were collected with the probe opening at the tympanic membrane and in the same approximate position with the chinchilla removed from the sound field. For each animal’s acoustic transfer function, the average of five in-the-ear and three free-field measurements were determined. The ATF exhibited a 5-dB passive gain at about 1 kHz and a broad resonance between 2.5 and 6 kHz of about a 10-dB gain. AEP thresholds were obtained from monaural chronically implanted chinchillas at 0.5, 1, 2, 4, and 8 kHz using first free-field and then insert earphone stimuli. The free-field sound pressure was measured with a microphone in the approximate position of the chinchilla’s head. The earphone sound pressures were measured with a probe microphone positioned near the tympanic membrane. The free-field AEP hearing thresholds exhibited +10-dB gain at 4 kHz compared to the insert earphone AEP thresholds. The agreement between the ATF and AEP derived transfer function suggested that the threshold differences at 4 kHz between the two testing configurations can be accounted for by the pinna and ear canal gain.
Fluid dynamic aspects of human voice and brass instruments: Implications for sound synthesis
Authors: Pelorson Xavier , Msallam Regis , Gilbert Joel , Hirschberg Avraham
Published: July 2002

The challenge of physical models of musical instruments is to provide a global description of a highly complex instrument which has to be accurate but simple enough to be numerically implemented. For this purpose, a logical approach is to extract, from a theoretical or experimental study, what are the most important phenomenon involved which are thus to be taken into account. Two examples of such an approach are given by the physical models of human voice and brass instruments presented here. Although both instruments share in common the same basic principle, a self-oscillating source coupled with a resonator, crucial physical aspects are quite different. It is shown that, for brass instruments, the lips’ self-sustained oscillations are mainly driven by the acoustical coupling, therefore the simpliest one degree of freedom model for the lips is sufficient. In the case of voicing, the acoustical feedback, although effective, is not sufficient to maintain self-sustained oscillations. A more elaborated vocal-folds model is needed. Regardless of the sound source, the description of the resonator is also discussed. While, for voice simulations, significant improvement can be gained using a two-dimensional linear theory, nonlinear propagation is sometimes to be taken into account for brass instruments.
Noise and vibration characteristics of cleanroom fan filter units
Authors: Wu Mei Q. , Gordon Colin G.
Published: July 2002

Fan filter units (FFU’s) are used increasingly by the microelectronics industry to provide recirculation air in cleanrooms. Such units usually consist of one or more direct-drive blowers located in a small discharge plenum and a HEPA or ULPA filter. There may be several hundred FFU’s in a large cleanroom. The noise and vibration generated by FFU’s differ greatly between manufacturers. Since it is difficult to apply external noise and vibration mitigation, it is important to select an FFU model with appropriate noise and vibration levels, so that a cleanroom served by these units will meet the prespecified noise and vibration criteria. Unfortunately, FFU manufacturers usually do not provide enough information for predicting the FFU generated sound-pressure spectrum or vibration in a cleanroom. In this paper, simple noise and vibration measurement methods will be described, which can be used as a basis for specifying FFU performance without special testing facilities. Measured data will be presented for a number of units. Procedures will be demonstrated to predict the performance of a cleanroom which uses FFU’s as the primary source of recirculation air.
Aural method of speech intelligibility enhancement
Authors: Majewski Wojciech J.
Published: July 2002

Among a variety of speech enhancement techniques, one subjective technique, called the Hollien binaural filtered (HBF) approach [Hollien, The Acoustics of Crime (Plenum, New York, 1990)], was proposed. It utilizes a special binaural hearing technique: The modified (usually filtered) speech signal is fed to the listener’s dominant ear at a relatively high level and a low-energy unprocessed speech signal is simultaneously sent to the contralateral ear. Unfortunately, there were no investigations related to the effectiveness of this technique of speech enhancement. In the present paper the results of the experiments performed in order to quantitatively evaluate this method are presented. The speech material consisted of nonsense word lists. For each measuring condition, one list containing 100 nonsense words was presented to five experienced listeners. Due to possible applications of the HBF technique in forensic phonetics, poor quality recordings were examined. The major difficulty in the experiments as to obtain the improvement of speech intelligibility by means of conventional speech enhancement techniques. When, however, such technique yielded an increase in speech intelligibility score (the largest increase was 5%), then the HBF technique provided further speech enhancement, the largest increase was 8% and 12%, respectively, in relation to modified and unprocessed speech.
Elliptical wave radiation from a curved waveguide
Authors: Fehlmann Rolphe F.
Published: July 2002

This paper deals with the investigation of the wave radiation properties of the resonance modes in 3-D curved waveguides. With the finite element method (FEM), a curved waveguide has been modeled and the computer simulations have shown that the wave radiation changes from circular waves in two dimensions to spherical waves in three dimensions, respectively, to beam formation. Interestingly enough, however, for some certain modes there exist elliptical and ellipsoidal waves, respectively. A visualization of these waves emanating from such nonaxisymmetric waveguide geometries is presented as pressure fields as well as phase fronts. This so far unknown elliptical field radiation is a phenomenon which future acousticians of the 21st century will have to cope with.
Glottal source parameter estimation by comparison of measured signals with simulated signals
Authors: Druker David G. , Titze Ingo R. , Story Brad H.
Published: July 2002

Oral flow, electroglottographic (EGG), and photoglottographic (PGG) signals were simultaneously digitized from a single subject phonating sustained vowels. Analogous simulated signals—oral flow, vocal fold contact area, and glottal area, respectively—were produced by a driven, kinematic glottal source model coupled to a wave-reflection-type vocal tract. The vocal tract area function used in the simulation was estimated from magnetic resonance imaging (MRI) data previously published for the subject. This essentially removed the vocal tract as a confounding factor in the analysis. The measured and simulated signals were compared and an attempt was made to adjust model parameters so that the least-squared differences between the signals were minimized. The model parameters, which included subglottal pressure, vocal fold adduction, vocal fold convergence, and fundamental frequency were observed to be estimates for the glottal configuration and control parameters used by the subject.
Modeling the transitory behavior of speech using a time-varying transmission line
Authors: Rane Amit S. , Wei Derrick C. , Falkson Lisa E. , Alwan Abeer A.
Published: July 2002

In this study, a transmission-line model of speech production [Rael et al., J. Acoust. Soc. Am. 97, S1(5) (1995)] is modified so that changes in the vocal-tract (VT) area functions, reflecting changes in the VT shape from one sound to another, are properly modeled. Each VT shape is divided into uniform cylindrical sections and each section is modeled by its equivalent transmission line comprising resistors (R), capacitors (C), and inductors (L). A radiation impedance terminates the transmission-line sections. For voiced sounds, the KLSYN88 glottal waveform [D. H. Klatt and L. C. Klatt, J. Acoust. Soc. Am. 87, 820–857 (1990)] is used as input. The model is simulated in time and frequency by using the analog-circuit simulator HSPICE. To simulate the transitory characteristics of speech, different interpolations such as linear, cubic, and Fourier transform are used for area transitions. The interpolated values result in a ‘‘sampled‘‘ area function and the RLC elements of each section are varied according to these time-sampled values. These variations are accomplished by utilizing time-varying independent voltage sources. Examples using American English dipthongs will be presented. Formant frequencies (both steady state and transitions) of the synthesized and natural dipthongs are in close agreement. [Work supported by NSF Award IRI-95-03089.]
The study of evaporation of multicomponent drops using the acoustoelectric levitator
Authors: Zheng Yibing , Apfel Robert , Tian Yuren
Published: July 2002

The evaporation of single drops and drop arrays of multicomponent liquids is investigated using a novel acoustoelectric levitator. By simultaneous levitation and charging of the drops, 2D drop arrays with the drop diameters varying from 0.2 to 1 mm can be formed. Also by controlling both the acoustic and electric field intensities, arrays with different drop sizes and spaces between drops can be created. This allows us to study the interference effects among drops in an evaporating dense spray. Mixtures of different liquids such as alkanes (heptane, dodecane, and hexadecane) are studied. The evaporation rates of those mixtures with different molar ratios of components and different numbers of drops in an array are measured. The drop size and spacing are carefully controlled and varied. A video camera is used to record the drop size change with time, and the diameters of drops are calculated from the pictures. The results are compared with a theoretical analysis based on the diffusion-controlled evaporation model. [Work supported by NASA through JPL Grant No. 958722.]
The two-dimensional acoustic standing wave and its application in coagulation of aerosols
Authors: Czyż Henryka
Published: July 2002

The problem of motion of small solid or liquid particles suspended in gaseous medium (aerosols and smokes) has been studied intensively in connection with the technical application of acoustic coagulation for precipitation of gases. Along with its technical applications, the problem of motion of small particles in acoustic field (called the drift) is interesting by itself as one of the fundamental physical effects of sound. For theoretical and practical reasons, the two-dimensional standing-wave configuration seems to be of special interest. In the case when nodal and antinodal surfaces of the standing wave are convex, the particles move along some curves and gather in some particular points and not only in some planes. This means that one can obtain much greater concentration of particles in some definite regions than in the case of the plane standing wave. As a configuration of special theoretical interest it proposes the standing wave in a rigid elliptical cylinder with a strip-shaped source of uniform velocity distribution placed in the symmetry plane of the system. Some numerical examples will be presented during the conference [H. Czyż, Acustica 70, 23–29 (1990)].
Physical effects of macrosonic standing waves in oscillating cavities
Authors: Lawrenson Christopher C. , Van Doren Thomas W. , Lipkens Bart
Published: July 2002

Previous work has demonstrated resonant macrosonic synthesis (RMS) for shaping pressure waves in oscillating closed cavities. Additional measurements of pressure waves are presented, with peak overpressures in excess of 400% of ambient pressure. Characteristic power consumption of various resonator shapes is presented. Resonator shape as well as pressure amplitude is shown to be important in determining power consumption. For a change in resonator geometry, one example shows a 765% increase in pressure amplitude for a fixed power delivery. The dependence on resonator geometry of hardening and softening resonance behavior is demonstrated by showing results for both different resonator shapes and different gases in the resonators. Physical effects of macrosonic pressures and particle velocities are demonstrated with pulverization of objects placed in the resonator cavity.
Optical techniques for sound generation and detection in acoustic resonators
Authors: Benedetto Giuliana , Gavioso Roberto M. , Spagnolo Renato
Published: July 2002

The most reliable method for sound-speed measurement in gases is based on the use of acoustical resonators. The measurement consists of the determination of the resonance frequencies of the cavity in the presence of a stationary acoustic field. Usually, the source and the receiver are condenser microphones. The main limit of these transducers is their inability to be used in a hostile environment, so there is an increasing interest to develop remote optical techniques for sound generation and detection. In this paper it is shown that it is possible to generate the acoustical field through a photoacoustic effect on the interior surface of the resonator, achieving a measurement precision comparable to that obtained when the source is a 1/4-in. condenser microphone. As a further improvement, it is also shown that sound can be generated by a silicon micromembrane facing the cavity, optically excited at the rear side. Measurements have been performed in a cylindrical stainless steel resonator of about 572 cm3; the light source is the 514-nm line of an Ar+ laser. An effort is being made to investigate the possibility of also substituting the receiving transducer with an optical detection scheme, based on laser beam deflection.
Comparing the accuracy of monotic and dichotic repetition pitch
Authors: Bilsen Frans A. , Dols Han H. , Raatgever Johan
Published: July 2002

When white noise is added to its delayed replica, a pitch is evoked corresponding to the reciprocal value of the delay time (T). When the delayed replica is fed to the same ear, the pitch (monotic repetition pitch: MRP) is rather salient; when, instead, it is fed to the contralateral ear, the pitch (dichotic repetition pitch: DRP) is rather faint. MRP is readily explained by spectral information processing in the cochlea. For reasons of parsimony, DRP is assumed to be the result of central spectrum processing preceded by interaural (temporal) processing. The present paper reports measurements on the accuracy of pitch matching for both MRP and DRP. Because of the difference in saliency, a difference in accuracy might be expected, if pitch saliency and pitch accuracy would be positively correlated. It turned out that pitch accuracy, expressed as the relative standard deviation, is dependent on the delay time and the stimulus type. For T larger than about 20 ms (the infra pitch range) the accuracy is about 10% for both MRP and DRP. For T smaller than 20 ms (the pitch range), accuracy is about 0.5% for MRP and 3% for DRP.
Accentuation of spectral pitch
Authors: Deutsch Werner A.
Published: July 2002

Lower harmonics of steady-state complex tones are resolved and produce individual spectral pitches when attention is focused to them. Attention to individual harmonics is enforced by sharp onset cues as simply switching partials on and off. Periodically rising and falling changes of the fundamental frequency of a complex tone (range: 1 oct, rate: 1–0.5 s) results in concurrent percepts. Initially accentuated spectral pitches of short duration are perceived followed by continuing integration of the partials into the complex tone according to the ‘‘common fate’’ rule. In comparison to the falling fundamental frequency phase higher partials accentuated during the rising phase are integrated faster. Concurrent spectral and fundamental frequency information exhibit a distinct pitch ambiguity transition immediately after the onset of the spectral pitch. The duration of the transition stage is assumed to reflect a kind of ‘‘Gestalt’’ generation time constant until the complex tone accepts its new incoming component. Raising the rate of fundamental frequency change to 4/s and more reduces the effect of the spectral pitch progressively. The pitch change of the complex tone dominates the spectral information. The concurrence is reduced furthermore when onsets are smoothed and consequently changes of timbre are perceived.
Jagged-edge noise barriers
Authors: Menounou Penelope , Busch-Vishniac Ilene J. , Blackstock David T.
Published: July 2002

Experimental, numerical, and analytical investigations have shown that noise barrier performance can be improved by making the top edge randomly jagged. The incident noise is a spherical N wave (produced by a spark in our model experiments). See Ho et al. [J. Acoust. Soc. Am. 101, 2669–2676 (1997)], and oral papers by (i) Menounou et al., (ii) Ohm et al., and (iii) Rosenberg et al., all in J. Acoust. Soc. Am. 101, 3075(A) (1997). In many, but not all, cases the jagged edge improves insertion loss by up to 5 dB. The most promising theoretical approach is to model the edge as a directive, crooked line source [paper (i) above]. Besides yielding predictions that agree favorably with measurements [paper (iii) above], the line source model helps in understanding the following results: (1) the jagged edge smears out the diffracted signal and makes the tail ragged, (2) insertion loss varies significantly with receiver position, and (3) the portion of the edge on the most direct path between source and receiver plays a very important role. Because the model is easy to apply, it is a promising and powerful tool for further research on jagged barriers. [Work supported by Texas Advanced Technology Program.]
Rubber crumb as an absorbent acoustical material
Authors: Pfretzschner Jaime , Rodriguez Rosa M.
Published: July 2002

In order to contribute to the solution of the environmental problem created by the tire wasteways, the possibilities of using rubber crumbs of waste tires as acoustic absorbent materials have been studied in a systematic way. Experimental absorption coefficients of rubber crumb granulates with mesh diameters between 1.4 and 7 mm have been tested in Kundt’s tube and in a reverberation room. Absorption coefficient values so obtained are compared with computational values afforded through mathematical prediction models that use the intrinsical parameters of porous material such as porosity, tortuosity, and flow resistivity, which were measured on layers of the respective materials. The good broadband acoustic absorption of the material encourages its use as an alternative to the current absorbent acoustic screens, used for the protection against traffic noise.
Effect of waveform distortion on sonic boom noise penetration into a flat ocean
Authors: Ferguson Tracie J. , Sparrow Victor W.
Published: July 2002

The penetrating underwater sound field due to an N-shaped sonic boom incident on a flat ocean surface is well described by existing theory. However, in realistic situations, most of the waves that hit the surface are not perfect N waves but are distorted by such processes as atmospheric turbulence. In the present research, N waves are created that contain the same amount of energy as experimentally measured sonic booms produced by aircraft in the U.S. Air Force. Each signature is input to an algorithm recently presented by Sparrow and Ferguson [AIAA Paper 97-0486 (1997)] to calculate the respective underwater sound fields. By comparing the underwater wave shapes and plots of peak pressure with respect to depth, initial results of the effect of waveform distortion on sonic boom noise penetration into a flat ocean are determined. Preliminary figures show that waveform distortions at the surface cause a slightly greater penetration depth underwater. However, the magnitude of the effect is dependent on the incident sonic boom. [Work supported by Armstrong Laboratory, Air Force Materiel Command, USAF, under Grant No. F41624-96-1-0003.]
Sonic boom in the shadow zone
Authors: Coulouvrat François
Published: July 2002

The classical geometrical acoustics theory predicts the amplitude of sonic booms only within the carpet. Inside the geometrical shadow, the sound field is known to emanate from rays shed by creeping waves propagating along the ground. A new, nonlinear, time-domain formulation of diffraction effects inside the shadow zone is given. The resulting equation is analogous to an unsteady, two-dimensional, transonic equation. In the linear case, it can be solved, so that the dispersion equation for creeping waves is recovered. If only the least attenuated one is taken into account, an approximate equation of Burgers-type describing the nonlinear propagation of the creeping wave can be deduced. A dimensional study indicates that nonlinear effects are small, except for small sound-speed gradients. A numerical simulation shows that the amplitude decay of the signal compares favorably with Concorde measurements made by ISL at Biscarosse in 1973, at least sufficiently deep within the shadow zone. [Work supported by Aérospatiale Aéronautique–Toulouse.]
The effect of mass transfer on sound propagation in cylindrical tubes using the low reduced frequency approximation
Authors: Hickey Craig J. , Raspet Richard
Published: July 2002

The theory for sound propagation in a gas/vapor mixture contained in a cylindrical tube is investigated. The tube is assumed to have a rigid wall covered by a thin film of water. This thin film of water acts as a source/sink for the mass and the heat associated with the vapor. This problem has been previously solved in the high- and low-frequency limits using the Rayleigh eigenmode method [Y. Mao and J. M. Sabatier, J. Acoust. Soc. Am. 96, 3254(A) (1994)]. However, the interpretation of these results is limited by their complexity. This formulation of the problem parallels the low reduced frequency approximation work of Tijdeman [J. Sound Vib. 39, 1–33 (1975)]. In contrast to the earlier results an easily interpreted analytical solution for the propagation constant is obtained. The parameters governing the propagation of the sound waves are the shear wave number, Prandtl number, Schmitt number, and the reduced frequency. The limits of small and large shear wave number provide useful insight into the behavior of the gas/vapor mixture. Examples of air/water and helium/water mixtures will be discussed. [Work supported by ONR.]
Boundary-integral-equation methods for accurate calculation of acoustic fields
Authors: Mehl James B.
Published: July 2002

Acoustic fields near solid boundaries can be approximated by solutions of the Helmholtz equation subject to Neumann boundary conditions on the boundaries. For closed, axisymmetric geometries, the boundary-value problem can be expressed as a one-dimensional integral equation. Boundary shapes can be represented exactly in this formalism. With current code, numerical solutions can be obtained for shapes formed by rotating plane figures made up of mixtures of straight and circular line segments. Numerical solutions to the integral equation were determined by using cubic-spline approximations to the velocity potential Ψ. This procedure enabled both Ψ and the tangential acoustic velocity Ψ′ to be determined with high precision. In calculations of the fields within ducts near the orifices, with modest (∼200) numbers of boundary elements, approximate values of Ψ′ were found which were smooth over five orders of magnitude. The technique was used to calculate fields near the duct ends and to evaluate inertial and resistive end effects, for both baffled and unbaffled duct ends. The effects of rounding sharp edges has been evaluated through the use of circular-arc boundary elements. [Work supported in part by the Office of Naval Research.]