bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonstationary chaos in acoustic emission from lathes
Authors: Bukkapatnam Satish T. S. , Lakhtakia Akhlesh , Kumara Soundar R. T.
Published: July 2002

Acoustic emission (AE) signals have tremendous promise for monitoring machining processes, but current understanding of AE generation is very limited. In addition, existing techniques to analyze these signals are inadequate. Presented here is a new approach to analyze AE signals based on thorough characterization of the dynamics underlying the signals. The signals were collected from extensive experimentation on five different lathes, performed under various cutting conditions, with different tool–work combinations and sampling rates. First, a battery of statistical tests was applied on the collected AE signals. Tests revealed that AE in turning is chaotic with fractal dimensions ranging between three and six. But owing to nonstationarity, chaos was not clearly revealed in the lag plots. Next, the transients were quantified, based on a compact representation scheme that was developed—called suboptimal wavelet packet representation—that captured all salient features of the AE signals. This representation scheme was used in developing a neural network-based estimator for on-line monitoring of tool wear.
Scattering from rough fluid–fluid interfaces using the finite-difference time-domain method
Authors: Hastings Frank D. , Schneider John B. , Broschat Shira L. , Thorsos Eric I.
Published: July 2002

The finite-difference time-domain (FDTD) method is a numerical technique that can be used to solve a wide variety of problems via time-domain simulations. Results have been presented for scattering from pressure-release surfaces [F. Hastings et al., IEEE Trans. Antennas Propagat. 43, 1183–1191 (1995)] based on the FDTD method. This paper describes the use of the FDTD technique to study scattering from rough fluid–fluid interfaces. Precise results are obtained by employing several enhancements to the FDTD algorithm. Most importantly, a grid conforming to the rough interface is used to achieve accurate results at a reasonable computational cost. This is in contrast to a traditional stair-stepped model of the interface which gives spurious overprediction of the backscattered field. Numerical results are presented for the scattering strength obtained using a Monte Carlo technique and are compared with results obtained using a Monte Carlo integral equation approach. For both methods, the incident field is a tapered plane wave, and 50 surface realizations are used to obtain the average scattering strength. One advantage of the FDTD method is that it allows the addition of heterogeneities at little extra computational cost. [Work supported by ONR.]
Medical ultrasonic imaging
Authors: Miller James G.
Published: July 2002

Diagnostic ultrasound has become a standard tool in the delivery of healthcare. Although some work was carried out at least as early as the 1940s, medical imaging with ultrasound grew from a modest novelty in the early 1970s to become the widely used and still rapidly growing diagnostic modality of today. In this tutorial lecture, the use of ultrasonic imaging will be illustrated with the aid of video tapes and large-screen projection of representative diagnostic studies. Some of the physics and engineering underlying the generation of clinical images will be reviewed at an intuitive, nonmathematical level. Some of the advantages and limitations of ultrasound in comparison with alternative diagnostic modalities will also be highlighted. Specific applications used to diagnose heart disease will provide opportunities to illustrate ultrasonic imaging of the beating heart. Real-time two-dimensional ultrasonic images of the heart with superimposed color encoded visualizations of Doppler-based estimates of blood flow in the cardiac chambers, which have become the standard for the diagnosis and management of most forms of heart disease, will be shown.
Diagnostic assessment of speech intelligibility in auditoria with the STI
Authors: Houtgast Tammo , Steeneken Herman J. M.
Published: July 2002

The quality of speech transmission in an auditorium equipped with a public address system is determined by the characteristics of both the electro-acoustic system and the acoustics of the auditorium. Potentially, various types of distortions and interferences in the sound transmission from talker to listener may have a negative effect on speech intelligibility. Assessment of the intelligibility by means of subjective tests with speakers and listeners offers a representative quality measure of the total chain, without however providing diagnostic information on the underlying type of distortion. Objective methods, like the speech transmission index (STI) [H. J. M. Steeneken and T. Houtgast, J. Acoust. Soc. Am. 67, 318–326 (1980)] may not only predict overall speech intelligibility, but may also provide valuable diagnostic information. However, in order to properly represent the effect of all potential types of distortion in a single index, and to obtain relevant diagnostic information, the test signal and the measuring procedure should be chosen very careful. In this context the STI and other methods, like the use of impulse response measurements (MLSSA), will be discussed. Examples will be presented of results obtained in various environments (e.g., railway stations, highway tunnels, and aircraft cabins). [See NOISE-CON Proceedings for full paper.]
Limitations of speech intelligibility assessment methods
Authors: Mapp Peter
Published: July 2002

Although there are a number of electronic/acoustically based objective intelligibility rating methods (as opposed to subject based word score tests), each suffers from a number of limitations. The essentially nonlinear behavior of most sound systems can and does affect the accuracy of electronically based assessment methods, yet such effects receive little or no mention in the literature. The paper sets out to redress the balance and highlights, and discusses many of the practical limitations of carrying out such measurements. In particular, %Alcons, RASTI, and STI methods are reviewed. The paper describes how system nonlinearities, distortion, compression, digital signal processing, and bandwidth restrictions, as well as late acoustic reflections, can all affect and possibly corrupt the final result. The choice of test stimulus and method of analysis are also shown to affect the apparent result. [See NOISE-CON Proceedings for full paper.]
Self-noise: The relationship between a transducer and its electronics
Authors: Gabrielson Thomas B.
Published: July 2002

The dominant source of self-noise in a sensor system is often assumed to be the first-stage preamplifier. While this can be a poor assumption especially for new-technology sensors, the relationship between the transducer and its electronics is a critical one to consider in the design process. A poor choice for the electronics can negate any potential gains in noise performance from the transducer. This paper explores the inter-relationships between the transducer and its electronics for the important varieties of receiving transducers whether those transducers are simple, self-generating transducers, or complex, feedback-controlled, ac-biased transducers. While this paper will approach the problem from fundamentals, the common figures-of-merit will also be examined and their limitations noted. A number of design guidelines and comparison charts will be presented to facilitate identification of the dominant noise source early in the design process and to permit rough estimation of the achievable noise performance of a particular sensor configuration.
Noise in fiber-optic sensors and sensor systems
Authors: Dandridge A.
Published: July 2002

Over the past decade there has been considerable interest in using fiber-optic sensors for a variety of applications. One area which has attracted substantial attention is the use of these sensors for underwater acoustic arrays. In this paper the fundamental noise performance of these sensors will be discussed. The primary focus will be the noise associated with the transducer itself; however, attention will be paid to the noise associated with the interrogation and multiplexing of these sensors. Transducer noise is usually determined by the thermal noise associated with the structure to which the sensing fiber is attached and the intrinsic thermal noise of the fiber itself. The noise associated with the interrogation of these sensors is usually associated with the characteristics of the optical source. In many systems noise generated by frequency, amplitude, and polarization modulation of the light as it passes through the telemetry cable will also limit the systems noise performance. Consequently, ultimate system noise is a complex trade-off of many parameters and can lead to different solutions for particular applications.
Development and testing of courseware in acoustic phonetics
Authors: Jackson Michel T. T.
Published: July 2002

Sensimetrics Corporation has been engaged in developing and testing interactive, multimedia educational software in acoustic phonetics for more than three years. The course software contains a nonmathematical presentation of major topics in acoustic phonetics, a lab in which students can record and analyze their own speech, and a library in which students can look up technical terms, hear and see spectrograms of IPA examples, and find readings related to the topics covered in the course software. Topics covered in the software include reading spectrograms, basic vowel acoustics, articulatory-acoustic relations in vowels, speaker differences in vowels, acoustic characteristics of constants, aerodynamic effects in consonant production, perception of acoustic cues, identification and discrimination experiments, native and nonnative perception of consonants, and perceptual normalization of vowels. Faculty volunteers at various educational institutions used components of the course and solicited anonymous, written feedback from over 200 graduate and undergraduate students in Communication Disorders/Speech and Hearing Science during the ’94–’95 and ’95–’96 academic years. The volunteers also provided written comments on the course software. The results indicate that the course software is a useful adjunct to traditional teaching methods. [Work supported by NIH Grant No. 9 R44 MH 51970-02.]
Drop dynamics in microgravity
Authors: Jankovsky Joseph C. , Ketterling Jeffrey A. , Apfel Robert E. , Holt R. Glynn
Published: July 2002

The dynamics of liquid drops in microgravity were observed in the Drop Physics Module flown aboard the second United States Microgravity Laboratory (USML-2) in 1995. Water drops with varying concentrations of the surfactants Triton-X 100 and Bovine Serum Albumin were suspended in air and deformed by an acoustic standing wave. When the deforming force was removed, the drops oscillated freely about a spherical equilibrium shape, as opposed to the oblate equilibrium shape of a drop levitated in 1-g. Drop diameters between 1 and 3 cm were observed. Frequencies and decays for the dynamics have been extracted from the data. Results are compared to theoretical models and experiments in 1-g. Results for frequency shifts due to large amplitude oscillations are also presented. [Work supported by NASA through JPL, contract 958722.]
Impact of hearing loss on children in typical school environments
Authors: Nelson Peggy B.
Published: July 2002

Every school can expect to have children with hearing loss. Every teacher in the early grades can expect that every day there is a child in that classroom who has trouble hearing. Ear infections (otitis media, or OM) are the most frequent medical diagnosis for children. The National Center for Health Care Statistics estimates that (per 100 children per year) there are 70 OM cases in children under the age of 5 years, and 14 cases in children ages 5–17 years. Additionally, two have other permanent hearing losses. Hearing loss causes significant educational problems. Academic delays occur in children with mild hearing loss as early as first grade. Traditional classrooms are noisy. In many classrooms, the child in the middle of the room functions at 0-dB signal-to-noise or worse. Noise and reverberation combine to produce adverse effects on speech understanding by hard-of-hearing children. As S/N and reverberation times get worse, the performance gap between children with and without hearing loss increases. Children with hearing loss require 10–12 dB more favorable S/N than others to achieve the same word recognition scores. Hearing loss and poor classroom acoustics adversely impact learning for significant numbers of children.
Pilot studies of speech communication in elementary school classrooms
Authors: Crandell Carl C. , Gold Martin A. , Hasell M. Joyce , Herr Christopher R. , Lee Hee Won , Lehde Mitchell , Siebein Gary W.
Published: July 2002

Numerous investigations [Crandell, Smaldino, and Flexer (1995); Nabelek and Nabelek (1994); Olsen (1998)] have demonstrated that the acoustical environment in a classroom is an important variable contributing to the academic and psychosocial achievement of children. Additional studies have shown that children do not obtain adultlike abilities to perceive speech in noise or reverberation until approximately 15 years of age [Crandell (1992); Elliott (1979); Neuman and Horchberg (1985)]. Despite these data, there is very little literature concerning appropriate classroom acoustics for young children. Acoustical measures of reverberation time, early reverberation time, early-to-late energy ratios, loudness (or relative strength), Alcons, speech transmission index, background noise levels, and signal-to-noise ratios were made across a range of elementary school classrooms to document the acoustical conditions. Speech recognition of children in the rooms was assessed by nonsense syllables and monosyllabic words. Relations among the speech recognition measures, acoustical measurements, and the architectural design features of the classrooms were examined. Observations of teachers’ methods and children’s behavior were also conducted to analyze the relationships between the acoustical tests and the actual communication processes that occur in daily teaching. Data obtained will be discussed in view of developing appropriate classroom acoustics for elementary school children. [See NOISE-CON Proceedings for full paper.]
A short history of the dynamic loudspeaker, with comments
Authors: Villchur Edgar
Published: July 2002

The history of the dynamic speaker, a speaker in which the signal is applied to a voice coil that is part of the moving system, begins with the Rice and Kellog paper [Trans. AIEE 44, 461–475 (1925)] and the ‘‘Radiola’’ loudspeaker of 1926. Innovations since then include the ported or bass reflex enclosure of Thuras, patented in 1932, and the acoustic suspension system. (The author received a patent for the latter in 1956, but a court later ruled that is had been anticipated by prior art.) Present design practice often departs, for good or ill—in the author’s opinion, mostly for ill—from design approaches of the past. For example, some current designs are aimed at creating directional sound rather than wide dispersion; some designs are aimed at controlling phase; and there is an explosion of design meant to influence loudspeaker performance through accessories such as speaker cables and speaker stands.
PANEL: A novel piezoelectric air acoustic transducer
Authors: Kugel V. D. , Chandran Sanjay , Cross L. E.
Published: July 2002

The PANEL (Piezoelectric Acoustic Noise ELiminator) transducer was developed for air acoustic noise cancellation in the frequency range of 200–1000 Hz. It has a thin panel structure, occupies less volume, and is lighter than an equivalent electromagnetic transducer. This device consists of a U-shaped configuration of piezoelectric bimorph and unimorph actuators bridged by a triangular amplifying diaphragm, which acts as an effective source of the sound radiation into air. The role of the diaphragm is twofold: it amplifies by a factor of 5–20 the tip displacement of the piezoelectric actuators and it also increases the sound emitting area. Amplitude of the vibrations and usable frequency range of the transducer depend on the dimensions and material of the actuators and diaphragm. The overall dimensions of the device fabricated were 52×50×24 mm. Soft PZT ceramics were used. The diaphragm was made of a carbon fiber reinforced composite. The diaphragm vibrations reach 500 μm rms well below the fundamental resonant frequency of bending vibrations which lies between 200 and 500 Hz. Above resonance, the amplitude of vibrations gradually decreases to 25 μm rms at 1000 Hz. The experimental results indicate that the transducer developed is promising as a sound transmitter for acoustic noise canceling devices.
Development of a sound audit program for a high-volume product
Authors: Comparin Robert J.
Published: July 2002

Once sound has been identified as an important product feature, it becomes necessary to ensure that the sound levels of the product remain within the desired specification. A method for developing a sound audit program for a high-volume product is presented. The audit program is based on the use of statistical process control techniques. The sound audit program is used to monitor sound performance, improve quality control, and as an aid in the design of new products and new manufacturing processes. [See NOISE-CON Proceedings for full paper.]
Influence of modulated complex tones on power window regulator noise quality
Authors: Shadden Richard D. , Lim Teik C.
Published: July 2002

The influence of amplitude and frequency-modulated complex tones on the perceived quality of power window regulator noise is examined in this paper. Modulation characteristics of sounds generated by electro-mechanical actuators in automotive components, such as power window regulators, play a major role in affecting the perceived overall quality of a vehicle system. Annoying noise with a high degree of modulation tends to create the impression of an inferior product with inherent design flaws and manufacturing problems. Current subjective quality rating methods based on simple jury evaluation schemes and idealized metrics cannot be used to quantify modulation effects accurately. This is because modulated tones are temporal phenomena that are closely related to the rotational velocities of motors that are not typically accounted for in existing time-averaged sound quality metrics. A new time-varying based index is developed that incorporates operational velocity, noise spectrum, and binaural effects to quantify sound quality from acoustic signals measured using a binaural head system and rotational velocity data of the window regulator mechanism. Numerical simulations based on the proposed algorithm are subsequently used to predict the noise quality of various systems. [See NOISE-CON Proceedings for full paper.]
Acoustic solitons in elastic media
Authors: Ostrovsky Lev A.
Published: July 2002

Theoretical models involving acoustic solitons in elastic media with dispersion were first developed for nonlinear longitudinal waves in rods [Ostrovsky and Sutin (1975); Samsonov (1984)]. Recently, the interest to this problem has considerably grown. At the same time, experimental realizations of elastic solitons are scarce [e.g., the works by Lazaridi and Nesterenko (1985) where strong (nonacoustic) solitons were created in contacting spheres, and by Dreiden et al. (1989), where a localized elastic pulse was observed in a rod]. Here, possibilities of soliton existence in different elastic media and some practically interesting values of their parameters are discussed. Three basic models are considered: (1) a thin elastic rod in which dispersion is due to the finiteness of its diameter; (2) a porous medium where dispersion is due to resonance properties of pores (similar to the known mechanism in a liquid with bubbles); and (3) a grainy medium with random packing of spherical grains in which nonlinearity is due to grain contacts and dispersion is due to finite grain sizes. It is shown that in all these cases, acoustic solitons may exist under realistic conditions. Possible realizations of such waves and their applications for medium–structure diagnostics are also evaluated.
Numerical simulations of the absorption of sound by noise in one dimension
Authors: Mital Vivek , Denardo Bruce , Jang Hyeon , Larraza Andrés
Published: July 2002

The absorption of a small-amplitude monofrequency signal by finite-amplitude shockless noise in one dimension has been predicted [O. Rudenko and A. Chirkin, Sov. Phys. JETP 40, 945 (1975)] and experimentally measured [Larraza et al., J. Acoust. Soc. Am. 100, 3554 (1996)] to cause the signal amplitude to decrease as a Gaussian in the distance from the source. Numerical simulations based on Riemann’s exact implicit solution for the unidirectional propagation of sound are presented, where the noise at the source is composed of 50 equally spaced equal-amplitude frequency components with random phases. The Gaussian attenuation is confirmed and is extended to the case where the signal is injected downstream from the noise source. When the phases of the spectral components of the noise are equal, the attenuation of the signal is dramatically reduced. The extent to which the Gaussian attenuation is restored due to small random variations of the amplitudes, phases, and frequencies of the spectral components of the noise is investigated. Preliminary results show that this is specified by the statistical nature of the noise at the source; specifically, by the degree to which the instantaneous amplitude is normally distributed. [Work supported by ONR.]
Coupled-mode modeling of acoustic scattering from axisymmetric, three-dimensional objects
Authors: Fawcett John A.
Published: July 2002

A coupled-mode method for computing the wavefield scattered by three-dimensional, axisymmetric objects is presented. Only the compressional properties of the object and the medium are modeled. The method provides a unified approach to solving three-dimensional scattering problems for axisymmetric objects in free-space, in a waveguide, or partially or fully buried in a basement. In the cases of an infinite space, the computational domain is truncated and an artificial attenuation profile added near the boundaries to attenuate artificial reflections. Galerkin’s method is used to construct the mode set in this case. Numerical examples of scattering from cylindrical disks surrounded by a homogeneous space and from disks partially buried in an underlying basement are presented. A benchmark case of scattering from an infinitely long cylinder, for which analytic solutions can be constructed, is also discussed.
A multilayer 1-3 piezoelectric composite underwater projector
Authors: Howarth Thomas , Ting Robert
Published: July 2002

An underwater acoustic projector for synthetic aperture SONAR (SAS) application on an AUV has recently been developed. The transducer features a two layered 1-3 piezoelectric composite material stacked in mechanical series and electrically wired in parallel. This arrangement was selected in order to maximize the source level output. The transducer is resonant at 100 kHz but has been designed to deliver high sound-pressure levels for operation over the frequency range of 10 to 100 kHz. The center electrode of the monolithic 1-3 piezoelectric composite layers has been segmented to offer four individual elements such that combinations of the sectors offer the ability to access nine different apertures. The basic design of the piezoelectric composite material will be shown along with the methods used to accomplish the successful multilayering effect. The fabrication of the prototype array and the measured transmitting voltage responses (TVRs), source levels (SL), and beampatterns will also be presented. [Work supported by the NSWC/Coastal Systems Station.]
Vowel production by a child with developmental apraxia of speech
Authors: Famoso Christina F. , Bell-Berti Fredericka
Published: July 2002

Vowel production is only rarely considered in discussions of articulation disorders, and the most widely used clinical tests of articulation provide only minimal evaluation of vowel articulation. Indeed, even the literature devoted to the mastery of vowel production by children without articulation disorder is limited, although several recent studies have demonstrated that vowel acquisition does not occur as easily or as early as had been suggested. The subject for the study reported here is an 8-year-old boy diagnosed with developmental apraxia of speech who has been treated for his speech difficulties since the age of 2 years 10 months. At this time his speech is intelligible, although still distorted. This study will evaluate his vowel production in two ways. First, listeners will identify words from minimally contrastive word sets; this to allow us to examine his ability to produce distinctively different and identifiable English vowels. Second, measurements will be made of vowel duration for English long-short vowel pairs and formant frequency for the ten English simple vowels. The latter will be compared to the children’s formant frequency data reported by Peterson and Barney [G. E. Peterson and H. L. Barney, J. Acoust. Soc. Am. 24, 175–184 (1952)].
A large excursion planar magnetic loudspeaker
Authors: Mitchell Kelton D.
Published: July 2002

Planar magnetic loudspeakers with wide diaphragms, such as woofers and midranges, are usually constructed using vertical rows of magnets with each row alternating between north and south poles. Narrow planar magnetic loudspeakers, usually called ribbons, are constructed with the diaphragm directly between the north and south poles of the magnet so it is totally immersed in the magnetic field. In this project, a loudspeaker with a 31/2-in.-wide diaphragm was designed and constructed with the ribbon configuration since the magnetic field is more linear with diaphragm excursion and is distributed more evenly over the surface of the diaphragm. A smaller emphasis was placed on the efficiency so that the speaker would have a diaphragm surface area and excursion that is comparable with cone-type speakers.
Fatigue monitoring of a thin laminated composite using nonlinearity parameter and ultrasonic C-scan
Authors: Darvennes Corinne M. , Johnson Bryant K. , Woodward Michael J.
Published: July 2002

Previous research [X. Hou and C. Darvennes, J. Acoust. Soc. Am. 100, 2568(A) (1996)] has shown that fatigue cycles can affect the nonlinearity parameter of laminated composites. In this research a thin laminated composite plate is put under fatigue until it fails. The fatigue test is stopped at regular intervals, when a C-scan picture is taken and the material nonlinearity is measured. To determine the nonlinearity parameter, the growth of a second harmonic is measured in the material. A monochromatic ultrasonic signal is sent into the sample via a contact transducer placed on the top surface. The growth of the second harmonic is recorded, with a second transducer placed on the bottom face, as the amplitude of the input signal is gradually increased. The nonlinearity parameter is then plotted as a function of the number of fatigue cycles. The C-scan images provide a visual clue about changes in the material structure that can be correlated to changes in nonlinearity. Hopefully this method will provide a means of predicting failure in advance. [Work supported by TTU Research Planning Grant program.]
Increment detection and sensitivity to amplitude modulation
Authors: Wojtczak M. , Viemeister N. F.
Published: July 2002

It is clear that the ability to detect amplitude modulation (AM) is related to intensity resolution but the nature of this relationship is unclear. To address this issue, increment thresholds and modulation detection thresholds were measured under comparable conditions using the same subjects. The pedestal/carrier was a 1-kHz tone presented continuously throughout each block of trials. To ensure a substantial range of thresholds, the level of the pedestal/carrier was varied over a wide range (6–85 dB SPL). The duration of the increment and of the AM was 500 ms. Sinusoidal AM at a modulation frequency of 4 Hz was used. At this low frequency, modulation detection presumably was not affected by temporal resolution. As expected, the observed thresholds decreased with increased pedestal/carrier level. Over the range of measured modulation thresholds (about −33 to −5 dB, in 20 log m), the following well-describes the data: 10 log(ΔI/I)=0.5(20 log m)+3, where ΔI/I is the Weber fraction for increment detection and m is the modulation index at modulation threshold. The generality of this relationship and its theoretical interpretation will be discussed. [Work supported by Grant No. DC00683 from NIDCD, NIH.]
Measurements of precedence phenomena in binaural and monaural conditions
Authors: Litovsky R. Y. , Hawley M. L. , Dizon R. M. , Colburn H. S.
Published: July 2002

The precedence effect is a compelling auditory illusion which is thought to negotiate competition for perception and localization between the direct sound and its reflections. Three perceptual phenomena that have been related to the precedence effect are known to occur: (1) the two sounds are fused into one auditory event (fusion); (2) the perceived location of the fused auditory event is dominated by the leading source (localization dominance); and (3) directional information from the lagging source is inaccessible (discrimination suppression). Performance was measured on the above tasks under both binaural and monaural conditions, in both the azimuthal and median-sagittal planes, and in listeners with profound monaural deafness. Results suggest that: (1) Fusion occurs at similar delays under monaural and binaural conditions; (2) discrimination suppression is strong under binaural conditions but weak or absent under monaural conditions; (3) localization dominance is similar in the azimuthal and median-sagittal planes. It is tentatively concluded that the precedence effect may not be mediated solely by binaural circuits, but that monaural pathways may be involved as well. [Work supported by NIH Grant Nos. DC02692 and DC00100.]
Musical acoustics in teaching engineering
Authors: Everbach E. Carr
Published: July 2002

Musical acoustics provides attractive examples that can be used to introduce engineering majors and nonmajors alike to critical concepts in engineering practice. Foremost among these is the concept of the eigenmodes and accompanying eigenfrequencies of a linear system. These can be wonderfully demonstrated via analysis of the overtone series of brass instruments (a one-dimensional system) and circular drumhead vibrations (a two-dimensional system). As an added bonus, important practical engineering concepts can be explored with these systems, such as the effect of nonlinearities and of nonideal properties on system behavior. Other natural topics include impedance, regenerative feedback, modal coupling, and frequency-dependent boundary conditions. [Work supported by NSF.]
Active control of jet engine inlet noise
Authors: Smith Jerome P. , Burdisso Ricardo A. , Fuller Chris R.
Published: July 2002

This paper summarizes the recent advances in the active control of tonal inlet noise from an operational Pratt and Whitney JT15D turbofan engine. The most recent results show that multiple circumferential control source arrays reduce the radiation spillover to the sideline that is often observed with a single control array. An optimal control configuration results in near global attenuation in all directions of the directivity field, and a sound power reduction of 5.1 dB. A power reduction of 4.1 dB was obtained over a desired sector spanning the angles from 40 to 60 degrees in the far field using a properly configured control system. Results using a hybrid passive-active inlet have also been obtained showing that a passive liner in combination with an active control system will eliminate much of the sideline control spillover. An inlet-mounted sensing strategy using a wave-number observation technique was implemented and the preliminary results show the potential of the method for eliminating far-field microphones. The latest results utilizing hybrid passive-active control with far-field and inlet mounted sensors will be presented and discussed. [Work supported by NASA Langley Research Center.]
Multi-channel active control of acoustic energy density
Authors: Sommerfeldt Scott D. , Parkins John W. , Tichy Jiri
Published: July 2002

Previous numerical work has indicated the potential advantages of minimizing the acoustic energy density for active control of sound in enclosures. Preliminary experimental results have generally confirmed this numerical work. A computerized scanning system has recently been implemented in an enclosure at Penn State Univ. University that provides greatly improved scanning capabilities to investigate the uncontrolled and controlled fields for active control experiments. Using this system, the active control of enclosed fields using energy density has been further investigated for both single-channel and multi-channel implementations. With the scanning capabilities, it is also possible to represent the experimentally measured field in terms of its modal components. Recent results that have been obtained will be presented, to show the control achieved using energy density, both in terms of the spatial dependence of the field, as well as in terms of its modal components.
Effect of unlined duct reflections on coherence for active noise control applications
Authors: Marks Patrick , Schweitzer Chad
Published: July 2002

Because of a major concern regarding internal air quality (IAQ) issues, much of the current work at Digisonix involves unlined duct for HVAC systems. In addition to the well-known problems associated with these systems, such as an abundance of high-frequency noise, the large number of reflective surfaces in the acoustic paths of unlined duct systems can create long reflection times. This can lead to decreased measured coherence between input and error microphones, and may also result in poor cancellation performance. This paper will show that for a particular unlined duct system, a substantial increase in measured coherence can be achieved through changes in the way in which the coherence measurements are made. These changes and their practical implementation will be discussed.
Acoustic and cavitation fields of a pressure release ellipsoidal reflector
Authors: Bailey Michael R.
Published: July 2002

In an electrohydraulic lithotripter (device to treat kidney stones), an underwater spark at the near focus of a rigid ellipsoidal reflector produces acoustic cavitation at the far focus. A reflector made of pressure release foam, however, dramatically reduces cavitation with little change in acoustic pressure amplitude (∼ +35 MPa, ∼−10 MPa). The pressure waveform at the focus of a rigid reflector is a positive spike followed by a negative tail. The negative tail sets bubbles into a growth-and-collapse cycle hundreds of ms long. With a pressure release reflector, a negative phase precedes a positive spike. Bubble growth induced by the negative phase is quickly (<10μs) snuffed by the spike, and collapse is weak. Cavitation was measured by (1) listening for bubble collapse and (2) recording bubble-induced pits on aluminum foil placed along the reflector axis. Pit size was used as an experimental measure of cavitation intensity. Intensity was reduced 3–10 times by the pressure release reflector. Results are in agreement with calculations from the Gilmore equation. Comparing the bioeffects of the two reflectors provides a way to assess cavitation’s role in lithotripsy. [Work supported by ONR, ARL:UT IR & D, and NIH.]
Acoustic reflex decay for pulse train signals
Authors: Pai Namrata , Hall Joseph W. , Grose John
Published: July 2002

Currently, the acoustic reflex decay (ARD) test is useful in testing for auditory nerve tumors, but only at low frequencies, as even normal-hearing subjects show ARD to pure tones at frequencies higher than 1000 Hz. The purpose of this study is to develop a reliable high-frequency test of ARD and to achieve a better understanding of the mechanism underlying ARD. ARD was measured in eighteen normal-hearing subjects using pulse trains with rates of 50, 100, 200, 400, and 800 Hz. Each of these pulse trains was then bandpass filtered with a fixed high-pass setting of 4.5 kHz, and a variable low-pass setting of 5, 6, 8, or 10 kHz. In addition, random noise filtered to similar bandwidths was also tested. Results suggest that the acoustic reflex is resistant to decay for high-frequency pulse train stimuli with rates of 200 Hz and below, whereas rates of 400 Hz and above, as well as high-pass filtered noise, result in significant decay. There seems to be little effect of stimulus bandwidth. These data indicate a strong temporal component to acoustic reflex decay. [Work supported by the American Hearing Research Foundation.]
The effect of probe frequency on ipsilateral acoustic reflex thresholds
Authors: Rawool Vishakha W.
Published: July 2002

This study was designed to evaluate the effect of probe frequency on the ipsilateral acoustic reflex thresholds. Five young female subjects with normal hearing participated in the study. Ipsilateral acoustic reflex thresholds were established for each subject using 226-, 678-, and 1000-Hz probe tones. The criteria for reflex thresholds were based on the lowest hearing levels (HL) at which the following minimum changes in baseline admit- tance were apparent on at least two trials: for 226 Hz, 0.02 ml; for 678 Hz, 0.06 mmho; and for 1000 Hz, 0.09 mmho. The reflex activator frequencies were 0.5, 1, and 2 kHz. The repeated measures multivariate analyses of variance were performed on the data. The results revealed a significant effect of probe frequency and a significant activator and probe interaction. Further analyses with the least significant difference (LSD) test revealed that the reflex thresholds obtained with the 678-Hz probe were significantly higher than those obtained with the 226- and 1000-Hz probes. In addition, for the activator frequency of 1 kHz, the lowest reflex thresholds were obtained with the 226-Hz probe, and for the activator frequency of 2000 Hz the lowest acoustic reflex thresholds were obtained with the 1000-Hz probe tone. [Work supported by a Bloomsburg University Grant for Research and Disciplinary projects.]
Timing of pitch movements and accentuation of syllables in Dutch
Authors: Hermes Dik J.
Published: July 2002

In this study, the relation between the timing of a rising or falling pitch movement and the syllable it accentuates is investigated. The five-syllable utterance /mamamamama/ was provided with a relatively fast rising or falling pitch movement. The timing of the movement was systematically varied and Dutch subjects were asked to indicate which syllable they perceived as accented. In order to find out where in the pitch movement the cue which induces the percept of accentuation is located, the duration of the pitch movement was varied. In order to find out which segments of the utterance this characteristic is linked to, the duration of the /m/ was varied. The results showed that the percept of accentuation is induced by a change in pitch at the start of the movement. The moment at which the course of pitch starts to change significantly determines which syllable is perceived as accented. If this moment lies some tens of milliseconds before the P-center, i.e., the perceptual moment of occurrence of the syllable, the preceding syllable is perceived as accented. For a rise, a high accent is perceived; for a fall, a low accent. If the pitch change occurs after this moment, the syllable with this P-center is perceived as accented. For the rise, a low accent is then perceived; for the fall, a high accent. This will be discussed in the light of earlier research on accentuation and of theoretical knowledge about pitch accents.
Acoustoelastic measurements on aluminium alloy by means of a contact and a non-contact (LFB acoustic microscopy) technique
Authors: Berruti T. , Gola M. M. , Briggs G. A. D.
Published: July 2002

Two independent experimental techniques for measuring the acoustoelastic effect on a sample of AA 6082 T6 aluminium alloy are tested and compared. A non-contact technique using acoustic microscopy and a contact technique using two point wedges as receivers are employed. The two techniques use different approaches in the velocity measurements. The wave frequency is also different—225 MHz for the microsocpy technique and 5 MHz for the contact device. Two different systems to load the sample are also employed. The results confirm the validity of the measurements and of the techniques employed.
The impact of early onset otitis media on babbling and early language development
Authors: Rvachew Susan , Slawinski Elzbieta B. , Williams Megan , Green Carol L.
Published: July 2002

Numerous studies have shown that otitis media (OM) during infancy has a negative impact on language development later in life. Few studies have examined the effect of OM on linguistic and prelinguistic behavior during infancy. The purpose of this study was to investigate the impact of OM on the development of canonical babble in children who experienced at least one episode during the period birth through 6 months of age, in comparison with children who did not experience OM during this period. The results show a consistently lower rate of canonical syllable production among children with early onset OM, when compared to children with later onset OM, during the period 6 through 18 months of age. In addition, a relationship between canonical babbling ability and expressive vocabulary size was observed at 18 months of age.
Time-evolution modeling of seafloor scatter. II. Numerical and experimental evaluation
Authors: Bergem O. , Pouliquen E. , Canepa G. , Pace N. G.
Published: July 2002

A time-evolution model of seafloor scatter is numerically implemented and experimentally evaluated. The model is based on analytically expressing the elementary time-backscattered response of every seafloor surface and every seafloor volume infinitesimal element. The implementation of the model is based on a statistical realization of the seabed interface and volume inhomogeneities, from which the time series are computed by coherent summation of the scatter from small elements over the insonified area and volume. The analytical expressions and the implementation are evaluated for the image solution case, for which an almost perfect agreement is found. Examples are shown of how the beam width and seabed roughness affect the time-series return from both the surface and from the volume. The results of the model are compared with data from two different bottom types recorded with a parametric sonar. Reasonable accordance is found between the model and the data.
Viscoelastic Hysteresis. Part II. Numerical and Experimental Examples
Authors: Marsh B. Duane
Published: July 2002

Several types of viscoelastic shear stress hysteresis loops were obtained for three forms of time-dependent shear rate inputs and four different polymer solutions. A correlation plot based on two dimensionless groups from the Bird-Carreau nonliner viscoelastic model demonstrates the experimental conditions required to obtain the various types of loops. The data were used to evaluate the predictive capabilities of the Bird-Carreau model and a “slowly varying flow” approximation to the same model. The “slow flow” model predicted the hysteresis response for experiments where the time of the experiment was larger than a characteristic time of the fluid. The model was qualitatively correct for a much wider range of experimental conditions. Five types of primary normal stress difference hysteresis loops are reported along with a demonstration of a method to calculate the “zero shear rate” limiting value of the primary normal stress material function θ0.
The Viscosity of Concentrated Suspensions
Authors: Lee Do Ik
Published: July 2002

Vand’s modified equation has been extended to include the effect of three-body collisions of spheres under shear. Brinkman’s equation has also been extended to derive an equation for the relative viscosity of concentrated suspensions of spheres by considering the dynamic formation of shear-induced doublets and triplets of the suspended particles under shear. Vand’s estimation of the immobilized liquid during collisions has been critically examined and the equations derived have been modified on the assumption that only a fraction of Vand’s estimation is actually immobilized. Some deviations of experimental data from theory have been discussed and all the equations derived are compared with the data.
Constitutive Equations for Viscoelastic Solids under Finite Uniaxial and Biaxial Deformations
Authors: McGuirt Charles W. , Lianis George
Published: July 2002

A constitutive equation is proposed for incompressible materials under isothermal conditions which gives very satisfactory results for the styrene-butadiene rubber that was investigated. The material functions in this equation are evaluated from the results of uniaxial and equal biaxial stress relaxation tests. Theoretical expressions are developed for a number of deformation histories and compared to experimental results. The uniaxial histories which are investigated are the constant stretch-rate loading, the exponential loading, and the constant stretch-rate unloading.
Creep of glassy polymers in the α- and β-retardation regions. Physical aging and nonlinear behavior
Authors: Read B. E.
Published: July 2002

Methods are summarized for analyzing the tensile creep curves of glassy polymers over wide time ranges at 23 °C. The methods account for contributions to the creep compliance from secondary (β) and glass–rubber (α) retardation processes, and also allow for the effects of physical aging. With increasing physical age of a polymer, a decrease is found in the magnitude or relaxed compliance of the β process and an increase in mean retardation time for the α process. Quantitative relationships have been established for each of these effects. Nonlinear creep behavior at elevated stresses can be described by functions which account for a rapid stress-induced decrease in α-retardation time and a subsequent increase in this quantity during the creep ascribed to a reactivation of the aging. The nonlinear behavior is illustrated by recent creep data for poly(vinyl chloride) and poly(butylene terephthalate). The effects of aging and nonlinearity may be correlated with changes in structural temperature within the polymer.
Dynamic inflation of hyperelastic spherical membranes
Authors: Verron E. , Khayat R. E. , Derdouri A. , Peseux B.
Published: July 2002

The dynamic inflation of hyperelastic spherical membranes of a Mooney–Rivlin material is analyzed in this study. Various inflation regimes are identified through ranges of the material parameters and driving pressure. In particular, the conditions for oscillatory inflation around the static fixed point are examined. It is found that, for a given material, the frequency of oscillation exhibits a maximum at some pressure level, which tends to increase for materials closer to neo-Hookean behavior.