bluuebunny/crossref_metadata_2025 huggingface dataset:
Komornik’s feedback stabilization: An experimental realization
Authors: Bourquin Frederic , Joly Michel , Collet Manuel
Published: July 2002

Most active control strategies applied in mechanical engineering are, in fact, active damping or suboptimal stabilization implemented with the help of new transducers. Indeed, it is very difficult to apply real optimal active control feedback on a distributed structure like a beam, plate, or shell. The infinite number of degrees of freedom puts forward the intrinsic problems of exact controllability and observability. The physical properties corresponding to their results are the observation of spill-over and the lack of efficiency of many experimental devices. An original solution to obtain a prescribed energy decay is to use aversion of Komornik’s feedback. Although it is a pure product of mathematical developments, Komornik’s algorithm can be implemented on line on a real structure. This method should really prove of interest in mechanical engineering. After a short overview of Komornik’s feedback, this paper presents the experimental characteristics of this control strategy. By comparing with data associated with alternative control strategies like DVF or IFF, some specific properties of Komornik’s method can be shown. Indeed, the real efficiency of this feedback and a large capability of eliminating modal spill-over instabilities is emphasized. As a conclusion, the principles for potential experimental developments on large-scale structures are introduced.
Active fiber composite actuators for reducing acoustic radiation from cylindrical shells
Authors: McDowell Donald , Plunkett Stephen , Goddu Gregory , Bent Aaron
Published: July 2002

Active fiber composites were developed to provide a mechanically robust method for large-area, orthotropic actuation and sensing in active structures. This presentation will describe the application of active fiber composite actuators to the reduction of acoustic radiation from a cylindrical shell by active control. The composite actuation layer is formed by small diameter piezoelectric fibers that are unidirectionally aligned and imbedded in a resin matrix system. A separate, etched, interdigital electrode layer makes the electrical connections. By nature of its structure, an active fiber composite actuator or sensor allows use of the primary piezoelectric effect in the plane of the composite. Active fiber composites are inherently tolerant of damage and can be conformed to a wide range of structural shapes. To control acoustic radiation from a cylindrical shell, active fiber composite actuators are used to generate a strain field that counteracts the strain associated with acoustically efficient shell motions. Optimal placement of the actuators is determined using numerical models verified by an experimental characterization of the shell dynamics. The control signal applied to the actuator is determined, in real time, using adaptive control. Error sensing methods using accelerometers or active fiber composite sensors were considered. [Work supported by DARPA.]
Two unique approaches for actively controlling the interior acoustic response of a cylindrical aircraft enclosure using active constrained layer damping and end actuation
Authors: Herdic Peter C. , Houston Brian H. , Baz Amr M.
Published: July 2002

Experimental results are reported involving the use of 12 active constrained layer damping (ACLD) patches instrumented on a fuselage section under radial point excitation. ACLD utilizes an active piezo film constraining layer over a viscoelastic layer to increase damping and apply restoring moments. Results reported to date showed that performance was achieved both in the reduction of the interior acoustic response and of the structural vibratory response. A more detailed analysis is reported here of the uncontrolled/controlled structural acoustics derived from high spatially sampled surface velocity and interior pressure measurements. A second control approach is reported where interior acoustic levels are reduced by control of the efficient end cap coupling to the interior by placing control actuators on each end. Analytic and numeric models are used to identify three dominate interior acoustic mechanisms: (1) a forced response on the interior by purely structural modes, (2) purely normal acoustic cavity modes, and (3) mixed structural/acoustic modes. Numeric control ‘‘experiments’’ are reported where both interior acoustic minimization and end-constraint control laws are employed. Good performance was found and discussion will involve the effectiveness of the control laws on each of these mechanisms. [Work supported in part by NASA, Langley.] a)Also SFA, Inc.
Active noise control in aircraft cabins
Authors: Ross Colin F.
Published: July 2002

There is significant interest from the aircraft industry to reduce the noise and vibration levels in aircraft cabins. In the last 5 years, active noise and vibration control systems have been introduced and have been shown to have transformed the environment of turboprop aircraft. These systems have provided significant reductions in cabin noise and vibration and further improvements are being sought. Tonal noise control was the most important objective and also the easiest to implement. Further improvements in the reduction of propeller and engine tones can be achieved, but the focus is beginning to shift to the control of broadband noise. This paper will review the performance of current systems and identify the areas where improvement will be required to meet the industrial objective. It will also review the available technology and identify the areas which are most likely to be successful with the practical constraints of an aircraft environment.
Active noise control procedures in a generic composite helicopter cabin
Authors: Simon Frank , Pauzin Simone
Published: July 2002

Composite materials are used more and more in the helicopter domain, instead of metal structures, which leads toward a degradation of the acoustic comfort in the cabin because of the decreasing mass and low performances of composites. So, active control procedures can be used in addition to passive treatments. The paper deals with the feasibility of active noise control procedures in order to reduce the radiated noise generated in a composite helicopter cabin, through the mechanical deck. A generic composite fuselage is excited by four shakers to simulate the noise produced by the four gear box fastenings. Four decorrelated random signals are generated to produce forces equal to about 1 N into the 500–3000 Hz band. Modal analysis and structural intensity measurements are achieved on the mechanical deck, and pressure fields are acquired in two parallel planes. Moreover, theoretical acoustic modes of the cavity are computed with a FEM model. These different data allow one to analyze the structural behavior of the mechanical desk and the structure–cavity coupling. Four piezoelectric actuators, located in front of the excitations, are controlled by feedforward algorithms to reduce the pressure fields with different types of error sensors and cost functions.
Assessment of BOTOX effects on adductor spasmodic dysphonia using LTAS-guided analysis
Authors: Buder Eugene H. , Cannito Michael P. , Taylor Merlin , Woodson Gayle E. , Murry Thomas
Published: July 2002

Connected speech samples from 17 women with adductor spasmodic dysphonia before and one month after unilateral botulinum toxin (BOTOX) injection of the thyroarytenoid muscle were analyzed using long-term averaged spectra (LTAS). Respiratory noises were removed prior to analysis but consonants were not. Prior LTAS research on this disorder before and after unilateral recurrent laryngeal nerve resection [K. Izdebski, Acta Otolaryngol. 97, 373–378 (1984)] predicts similar strengthening of lower-frequency harmonics and weakening of upper-frequency harmonics following chemodenervation using BOTOX. Pre- to post-treatment differences between standardized spectral magnitudes in LTAS frequency bins below 5 kHz revealed these effects for BOTOX treatment. Repeated measures ANOVA indicated a significant treatment-by-frequency band interaction (p less than 0.001). Discriminant analysis yielded 79% overall classification success for pre/post treatment conditions using only four frequency bands of approximately 250 Hz width, one in the f0 region and three in the 1–3 kHz region. These results support the hypothesized treatment effect. Furthermore, the LTAS-based discriminations motivated case-by-case analyses of harmonic magnitude measures. For example, examinations of relative magnitudes of first harmonics and formant-excited harmonic groups further our understanding of differing treatment effects on individual voices. [Work supported by NIH.]
A longitudinal investigation of formant frequency development in childrens’ speech production
Authors: Smith Bruce L. , Kenney Mary Kay , Sobecks Jana
Published: July 2002

While cross-sectional/group investigations provide important findings about the development of speech production, such studies do not furnish details regarding the development of individual children across time. However, such information is necessary for understanding childrens’ speech production development more thoroughly and for evaluating, from a somewhat different perspective, ideas that have been proposed on the basis of cross-sectional findings. In the present study, four subjects were recorded at approximately one-year intervals for four to six years as they produced about 20 repetitions (per session) of each of several target stimuli; three of the children were approximately 11/2 years old at the onset of the study, and the other was about 4 years of age. Measurements of F1 and F2 for three different vowels for all four children showed some patterns supporting the general notion that formant frequencies tend to decrease with increased age. However, there were also a number of instances in which a particular child’s formant frequency values showed little or no change across the entire 4–6 years. These longitudinal data suggest that childrens’ formant frequency values do not necessarily decrease in a consistent fashion with increases in age and physical size.
Classroom acoustics and vocal efficiency
Authors: Canning David , Hirson Allen , Arnold Paul
Published: July 2002

The modern school classroom predicated upon the premise that effective vocal communication can take place. Such communication depends upon intact processes of speech production and reception. Numerous studies have demonstrated the inadequate acoustic conditions of classrooms and the impact of this situation on the reception of speech. A smaller number of studies indicate high levels of vocal damage within the teaching profession. This study examines the vocal efficiency of teachers in classrooms before and after acoustic treatments of the teaching space. The paper will present acoustic measurements of the teaching voice with and without amplification and in acoustically treated and untreated classrooms. The impact of both physical and electro-acoustic modifications will be presented. [The authors gratefully acknowledge the support of Luton Unitary Education Authority’s Service for the Hearing Impaired, facilities of the Speech Acoustics Laboratory at City University, and the support of BioAcoustics Ltd. UK.]
Spectrographic analysis of stuttering episodes
Authors: Kuniszyk-Jóźkowiak Wiesl/awa , Suszyński Waldemar
Published: July 2002

Changes in time of frequencies and formant levels were measured in disturbed phoneme articulation. Ten stutterers read the same text in two situations: with simultaneous auditory feedback (SAF) and delayed auditory feedback (DAF). Words chosen for the analyses were ones uttered nonfluently with SAF and fluently with DAF. Frequency characteristics of the phonemes uttered nonfluently and realized fluently were made using computer procedures. These characteristics were analyzed in time intervals of 10 ms. Time evolutions of frequencies and formant levels were made in the cases of fluent and nonfluent articulation of the same phonemes. Results for the stutterers were compared with the ones for fluent speakers in identical utterances. The analysis of time evolution of formant allowed for a description of the vocal tract dynamics in the moments of stuttering. Studying the behavior of these formants in the conditions of forced fluency, that is, with DAF, afforded for anticipating the possible changes in the dynamics of the vocal tract leading to proper pronunciation. The significance of the measures of the parameters was shown for diagnosing and treatment of stuttering.
A review of modern ultrasonic diagnostic systems
Authors: Reid John M.
Published: July 2002

Modern ultrasonic imaging systems used in medical diagnosis have taken full advantage of digital technology, to the limits set by the fundamental acoustic properties of tissue. These properties set the penetration and resolution that is obtainable. The architecture of these systems now resembles that of a computer, since software control and data manipulation are essential parts of the imaging process. Many types of image processing are now done during the image formation and display process. New types of imaging use the Doppler and nonlinear effects to advantage. Many of these advances depend not only on the older types of video image memories, but also on direct storage of the rf data. Although the details of operation are proprietary information, the general structure of these systems is known. A knowledge of the hardware and software operation could assist in further efforts at image enhancement.
Matched-field imaging of laser ultrasound using a novel correlation cancelling approach
Authors: Candy James V. , Huber Robert , Chambers David H. , Thomas Graham H.
Published: July 2002

Matched-field imaging (MFI), which has evolved from various underwater acoustic applications, provides a solution to the inverse problem through forward modeling. In terms of investigating parts for flaws during nondestructive evaluation (NDE), the matched-field approach offers a reasonable technique for imaging provided the necessary preprocessing and parameter estimation can be accomplished. In this paper the results of controlled NDE experiments are described which are aimed at detecting a well-defined flaw in an aluminum part. By heating with a pulsed laser an ultrasonic wave is generated and received by a synthetic array of interferometers. It is demonstrated how these displacement measurements coupled to MFI can be used to detect the flaw. Preprocessing is accomplished by a correlation cancelling scheme designed to separate correlated (reference) from uncorrelated (flaw) measurements. The reference signals are generated by using a known flawless part of the same dimensions and material. The canceller then provides the ‘‘optimal’’ separation removing the wash, etc., and leaving just information about the flaw. Further basic processing is accomplished (filtering, etc.) and the underlying arrivals and velocities are estimated using a semblance processor providing a set of parameters required for MFI. The results of this approach applied to experimental data are promising.
Acoustic measurements of air entrainment by a plunging free water jet
Authors: Hahn Thomas R. , Berger Thomas K. , Buckingham Michael J.
Published: July 2002

Low-frequency acoustic emissions of a free plunging water jet were studied to determine the volumetric rate of gas transfer across the pool surface. At the studied jet velocities, up to 10 m/s, air bubbles are entrained at the interface and form well-defined bubble clouds penetrating up to 20 cm into the pool. The resulting biphasic region of the submerged jet was found to be an efficient acoustic resonator. The radiated sound field was recorded with hydrophones close to the region of the submerged jet and strong resonances were found below 1 kHz. The frequencies of the lowest modes were measured for a given jet diameter as a function of the jet velocity. The observed acoustic eigenfrequencies are unique functions of the jet velocity and the gas flux, independent of the details of the gas entrainment. This functional dependence was investigated both experimentally and theoretically, allowing an inversion of the acoustic data for the air flux across the interface as a function of the jet velocity. Reference measurements of the air flux were made to calibrate the inversions. Using this technique, measurements of the air flux were made for a variety of jet diameters, lengths, and velocities. [Work supported by ONR.]
Under-ice noise resulting from thermally induced fracturing of the arctic ice pack: Theory and a test case application
Authors: Stein Peter J. , Lewis James K. , Parinella James C.
Published: July 2002

A theory is presented relating thermally induced fracturing of pack ice to under-ice noise. The thermomechanics of pack ice relates thermally induced strain rates to stresses within various layers of the floe. Paradigms are used to specify the relative quantity of fracturing and stress relief as the ice tensile yield strength ice is exceeded. The thermomechanics is complemented by an acoustic model that relates the number of fracture events to acoustic levels at arbitrary frequency and depth below the ice. This theory assumes each fracture acts as a monopole source, the fractures are evenly distributed horizontally, and the energy of each fracture propagates through the ice and water as elastic waves in a stratified media. Noise from fracturing occurring over the top 40 cm of a 160-cm-thick floe will propagate over distances of ∼100 km. However, noise from fracturing occurring in the lower 100 cm of the floe will only propagate ∼10 km. The theories were used to develop a numerical model for predicting under-ice noise for a given thermal forcing. The model was used to simulate stresses in a multiyear floe and under-ice noise levels. Model-predicted ice stresses and under-ice noise compare well with observed stresses and noise.
The modeling of acoustic wave scattering on fractal seabed surface
Authors: Lubniewski Zbigniew , Stepnowski Andrzej
Published: July 2002

The one-dimensional model of a plane wave scattering on a corrugated seabed surface was analyzed in order to investigate the process of transferring the fractal structure of the bottom surface onto bottom scattering impulse response. The investigation evaluates the adequacy of the fractal dimension of a bottom impulse response as a descriptive parameter of a bottom type. The Kirchhoff approximation was used in the model. Several types of sea bottom surfaces with different fractal dimensions were used in modeling and the relation between fractal dimension of a bottom surface and fractal dimension of its impulse response was found.
Scattering and reflection of sound by random rough surfaces
Authors: Rabau Guy
Published: July 2002

The classical underwater acoustical models for shallow or deep water configuration (Lambert’s law, facet’s model, etc.) generally use a simple approximation to take into account the real nature of the bottom (and, in particular, the roughness of the surface). When the wavelength and the dimensions of the roughness are equivalent (1 kHz<frequency<5 kHz), it is difficult to validate these models through lack of calibrated measures. In this paper, the influence of a rough and inhomogeneous bottom on the propagation is shown. Therefore, on different types of rough or/and inhomogeneous bottoms, the diffusion diagram generated by an incident plane wave was measured. The experiment was done on a 1 to 100 scale with a 250-kHz source. Original synthetic materials were used to simulate the sea bottom. Besides the interest of the experimental setup, this paper reports comparisons between results from theoretical model and experimental results, and it describes the limits of the theoretical model and its defects. In particular, it describes the impact of the scattering in shallow or deep water propagation due to the rough and inhomogeneous bottom.
Sound transmission loss of double-glazed window panes—an empirical approach
Authors: Koch Siegfried
Published: July 2002

There are only a few contributions to the theory of sound transmission loss (STL) of double-glazed window panes, e.g., by M. Rehfeld et al. (1996). The situation is nearly the same with the empirical approach of reducing data from laboratory measurements to a simple formula, as done by K. Goesele (1977). Goesele inferred a result in terms of the single-number rating according to ISO 717 based on many laboratory STL measurements as described in DIN 52210 and ISO 140. In particular, measurements of air-filled double-glazed window panes had been used. Meanwhile, the gas fillings changed, because the thermal insulation of the window panes had to be increased. In the last five years a large number of STL measurements of double-glazed window panes with different dimensions (pane thicknesses, gap between the panes) and gas fillings have been carried out at the Fraunhofer-Institut fuer Bauphysik. From these measurements some typical behaviors of STL versus frequency belonging to specific pane configurations could be derived. This should allow an approximate prediction of the STL for given physical dimensions of double-glazed window panes.
The use of agglomerated cork as an underlay for improvement of impact sound insulation in buildings
Authors: Carvalho Antonio , Vafiadis Constantinos , Borrego Hugo
Published: July 2002

The cork-oak is only abundant in the Western part of the Mediterranean and is an important feature of Portuguese landscape and heritage. Portugal has about 30% of the world’s cork-oak trees and accounts for more than half of the world’s cork production. Agglomerated cork has natural cork granules (the by-products from the production of other cork products) as its base material. The project goal was to test and characterize the use of agglomerated cork as underlay to increase the impact sound insulation. Eight different cork agglomerate products were tested to assess their impact sound insulation quality when used as underlays with four different floor coverings (linoleum, ceramic tile, and two types of wood parquet). The measurements were made on-site (with flanking transmissions) on a coffered concrete floor without a fastened ceiling and according to International, Portuguese, and American standards (ISO-140/6 and 717, NP-669 and 2073, and ASTM-E989 and 1007). The results show that the use of this underlay improves the weighted index (Ln, w, or IIC) for each respective reference floor up to 19 (for ceramic tiles), 20 (thin parquet), 21 (linoleum), and 26 dB (thick parquet). Prediction formulas, determined by statistical analysis, are also presented.
Background noise levels in classrooms
Authors: Siebein Gary W. , Gold Martin A. , Lehde Mitchell , Ashby John
Published: July 2002

Field measurements of background noise levels produced by air-conditioning systems were taken in a sample of 47 elementary school classrooms. Noise levels were grouped by air-conditioning system type and resulting noise criterion (NC) levels. Eight computer models of classrooms were constructed with varying combinations of absorbent materials on the surfaces of the rooms. A sound source was configured to approximate the normal speaking voice of a teacher in the room. RASTI measures were estimated for six seating locations in each room for background noise levels from 0 dB to NC- 55 in 5-NC point increments. RASTI values remained above 0.8 in seven of the eight rooms at NC levels of 32 and below. RASTI levels decreased to 0.50 and less in all eight rooms at levels of NC- 45. The one exception to this was the room constructed with a gypsum board ceiling, vinyl tile floor, and gypsum board walls. Even with no background noise, RASTI values in this room never exceeded 0.60. Background noise levels of NC 32 or less appear to be necessary in most typical classrooms to maintain reasonable RASTI values. Very few of the actual classrooms visited achieved these noise levels.
Acoustic censusing of sperm whales at Kaikoura, New Zealand—An inexpensive method to count clicks and whales automatically
Authors: Jaeke Olaf , Dawson Stephen
Published: July 2002

Special DSP software was developed to automatically count sperm whale clicks recorded along acoustic transects, and to facilitate the calibration of these counts through automated and interactive analyses of dive cycle and range experiments. Minimum pulse width and maximum interpulse interval are used as criteria for automated click detection. In addition to these criteria, interclick intervals and click amplitudes can be used for the tracing of clicks during interactive analyses. Interactive analysis of a dive of a single whale recorded under almost ideal conditions gave the following results: The mean of all interclick intervals measured within bouts of regular clicks was 0.801 s (n=2203 intervals, cv 27.5%), the reciprocal of which corresponds to c. 1.25 clicks per second. Including 10 s between fluke-up and the first click recorded, silences between bouts of regular clicks, and a silence between the last regular click detected and two surface clicks found 3:37 min after the last regular click, the average click rate over a dive time of 42:23 min is 0.88 per second (n=2244 clicks). In several dive cycles analyzed, interclick intervals were found to oscillate periodically during bouts of regular clicks. These oscillations correlated with click amplitude.
Specific food-related calling in dolphins
Authors: Konstantin Kebkal G.
Published: July 2002

The results of acoustical observation of feeding behavior of bottlenose dolphins demonstrated the high degree of correlation between feeding events and very specific food signals related to every feeding act. In the paper, the features of such signals are described. They consist of specific click trains (recognizable as ‘‘creaks’’ or ‘‘squeaks’’). Working normally for echolocation, in this case, however, the use of such click series for echolocation is physically impossible. Whether the food signals serve as an anaesthetization of a prey or merely as emotional signals is not clear. The fact is that they are in any case produced before and also shortly after the moment of catching a prey, and their intensities are high enough to provide their reliable detection even in a dolphin’s back fin area. The food signals consist of some distinctive parts: (1) the stage of gaining a click’s repetition rate and their power, (2) the sector with a short gap of acoustic activity, and (3) the part of highest repetition rate of low powerful clicks. Parameters of every such signal’s sector may somewhat vary for different individuals staying, however, stable enough to be mathematically modeled and separated from any other click trains not related to feeding events.
Subsurface classification of shallow gassy river sediments using broadband seismic data
Authors: Bloomer Stephen F. , Chapman N. Ross , Collins William T. , Simpkin Peter G.
Published: July 2002

Acoustic seabed classification from sonar data has generally focused on attributes of the return echo from the seafloor. For many shallow-water engineering applications, such as dredging, detailed knowledge of the shallow sub-bottom is also required. Consequently, acoustic classification of the sub-bottom is also often essential. In 1995, a shallow-water, high-resolution seismic predredging survey was conducted on the St. Lawrence River in water depths of 10–15 m using the IKB SEISTEC high-resolution profiler, which has a bandwidth of 1–12 kHz and subsurface penetration in excess of 10 m. In these river sediments, it was found that shallow gas had a controlling effect on the appearance of the seismic sections in some places. The shallow gas could often be identified as a curtain in which there are no acoustic returns below a strong subsurface reflector with a phase reversal relative to the seafloor reflection. The frequency dependency of the ratio of the signal amplitude between the seafloor and sub-bottom reflectors may also be diagnostic of gas reflectors in that, instead of attenuation, resonances may occur. Using the spectral-ratio method, the attenuation between successive reflectors characteristic of the sediment between the reflectors can be determined. Results of classifying sub-surface sediments between distinct reflectors from this survey will be presented.
Bottom layers’ structure influence on ocean shelf water low-frequency source sound field numerical modeling
Authors: Semenov Andrew G. , Derzjavin Alexander M. , Kudryavtzev Oleg V.
Published: July 2002

The low-frequency vector wave field modeling method for the predic-tion of fields in layered inhomogeneous ocean and the ocean bottom en-vironment is proposed. The method is especially stable to vertically cut media multiple arbitrary thickness layers. Based on integral presentation of 2-D cylindrically symmetric source wave fields in elastic media, the method accounts for all wave types involved. Inhomogeneous media in the problem are cut in N horizontally homogeneous layers, for which 4 (N−1) equations were derived, accounting for conditions on both layers boundaries. Equation factors found by the Schmidt global matrix method are introduced in Fourier–Bessel integral expressions for local field parameters. Expressions were calculated numerically to obtain values of acoustic pressure and elastic stress, vertical and horizontal particle velocity component in liquid and elastic media, respectively. Deviations fromexact solutions expressed in modeling stability losses were obliged mainly to layers’ excessive thickness choice. A simple enough ‘‘benchmark’’ problem solution, where results for the conventional and the proposed method were compared to the exact solution, demonstrates method advan-tages. Point source of frequency 0.01–10.0 Hz, situated in a water-layer field model is presented. The influence of the bottom elastic layers’ structure on model parameters is demonstrated. The geological–acoustic bottom model depending on frequency is proposed.
Controlled and forced collapse of inertial cavitation bubbles during SWL
Authors: Zhong Pei , Xi Xufeng
Published: July 2002

The dynamics of inertial cavitation induced by current clinical lithotripters is uncontrolled. Recently, it has been shown [Zhong et al., J. Urol. 158, 2323–2328 (1997)] that a second shock wave generated in a few hundred microseconds following the standard lithotripter pulse can be used to control and force the collapse of cavitation bubbles toward the target stones, leading to increased stone comminution. Different approaches of generating the second shock wave have been tested, including combination of two EH generators and modification of ellipsoidal reflectors. To provide a unit that can be combined with clinical EH lithotripters, a piezoelectric annular array (PEAA) generator was designed and fabricated. This PEAA generator consists of eight 50-mm PZT4 elements of 200-kHz resonant frequency, which produce a peak compressive pressure of ∼8 MPa with a −6-dB beam diameter of 5 mm. A fiber-optic link was used to trigger the release of the PEAA generator (jitter less than 10 μs). The combined shock-wave generator, with optimal time delay between the release of the lithotripter and the second pulses, was found to increase stone fragmentation in vitro by 48% to 67%, as compared to the standard lithotripter. [Work supported by NIH RO1 DK 52985.]
In vivo modeling of the HM3 lithotripter
Authors: Cleveland Robin O.
Published: July 2002

A computer model for the propagation of shock waves in the HM3 lithotripter has recently been developed using the KZK equation [Averkiou and Cleveland, J. Acoust. Soc. Am., submitted]. The model has been extended to account for propagation through inhomogeneous tissue. The tissue was modeled as a layered medium with properties varying in the direction of acoustic propagation. Tissue absorption was modeled as consisting of four relaxation processes which provided an excellent fit to empirical absorption characteristics. Results were compared to waveforms measured in pigs [Cleveland et al., Ultrasound Med. Biol. 24, 293–306 (1998)]. Measured and calculated waveforms were in good agreement, including the rise time of the shock. However, at the focus measured, peak pressure was less than calculated numerically. It is supposed that small-scale arbitrary inhomogeneities, that the model does not account for, produced aberration effects that lead to the reduction in measured amplitude. The model predicted large negative pressures in the perirenal fat where cavitation events have been detected. [Work supported by NIH PO1-DK43881.]
Factors influencing the subjective rating of tonal components in noise
Authors: Vormann Matthias , Verhey Jesko L.
Published: July 2002

If environmental or artificial noises contain tonal components, they are more annoying than noises without tonal components. Therefore the German norm, DIN 45681 (draft): ‘‘Detection of tonal components of noise and determination of a tone adjustment for the assessment of noise immisions’’ was proposed to quantify this increased annoyance. Within this definition the effects of the tonal components are reduced to the increasing annoyance of the signals. In the literature no satisfying data exists about the subjective ratings of tonal components in noises (in German called ‘‘Tonhaltigkeit’’). For this reason the present study investigates the influence of selected physical parameters on subjective ratings of the ‘‘Tonhaltigkeit.’’ An adaptive procedure is used to adjust the hearing impression ‘‘Tonhaltigkeit’’ of different noises to a reference signal consisting of a single sinusoidal.
Bifurcation and chaos in flexural vibration of a baffled plate in mean flow
Authors: Wu Sean F. , Zhu Jason
Published: July 2002

This paper presents the results of an analytic and numerical investigation of flexural vibration of a finite plate clamped to an infinite baffle in mean flow. Attention of the present paper is focused on: (1) the physical mechanisms that lead to unstable conditions for a clamped plate in mean flow; (2) the effects of mean flow, plate aspect ratio and length to thickness ratio, and the structural nonlinearities on the instabilities; and (3) the onset of bifurcation and chaos in plate flexural vibration beyond critical mean flow speeds. In carrying out these analyses, the plate flexural displacements are solved by the Galerkin method. The critical mean flow speeds are determined by a general stability theory and the Routh algorithm. Results show that the instabilities of a baffled plate are mainly caused by an added stiffness due to acoustic radiation in mean flow, but controlled by the structural nonlinearities. The added stiffness is shown to be negative and increase quadratically with the mean flow speed. Hence, as the mean flow speed approaches a critical value, the added stiffness may null the overall stiffness of a plate, leading to an unstable condition. Note that without the inclusion of the structural nonlinearities, the plate has only one equilibrium position, namely, its undeformed flat position. Under this condition, the amplitude of plate flexural vibration would grow exponentially in time everywhere, known as absolute instability. With the inclusion of structural nonlinearities, the plate may possess multiple equilibria. When the mean flow speed exceeds the critical values, the plate may be unstable around all equilibria, jumping from one equilibrium position to another. Since this jumping is random, the plate flexural vibration may seem chaotic. This chaotic behavior disappears, however, when viscous damping is introduced. Accordingly, the plate settles down to a “buckled-down” position owning to the hydraulic fluid-loading effect.
New subjective and objective data on 20 opera houses of the world
Authors: Beranek Leo L. , Hidaka Takayuki
Published: July 2002

Acoustical measurements have been made in opera houses of Europe, Japan, the United States, and Argentina using the same equipment: dodecahedron loudspeaker, stretched impulses, and monaural and binaural sensing devices. The measuring positions were 3 on-stage and 2 in-pit for sources, and 8 to 17 in audience areas for sensors. Quantities measured as a function of frequency were reverberation time RT, early decay time EDT, clarity C80, deutlichkeit D, time gravity Tg, early to reverberant energy ratio as a function of cutoff time C(t), strength G, interaural cross correlation IACC, IACCE, and IACCL, stage support ST1 and ST2, initial-time-delay gap ITDG, and reflectograms. International opera conductors were contacted by mail to rate 20 opera houses, with satisfactory responses. An attempt is made to correlate the objective data with the subjective ratings. Early results indicate that IACCE3 and ITDG are definite indicators. Others seem important in a certain type of opera house.
Measuring the role of masker-correlation uncertainty in binaural masking experiments
Authors: Kohlrausch Armin , Breebaart Jeroen
Published: July 2002

Masked thresholds of a 500-Hz sinusoid were measured in an NρSπ condition for both running and frozen-noise maskers using a 3IFC procedure. The nominal masker correlation varied between 0.64 and 1, and the bandwidth of the masker was either 10, 100, or 1000 Hz. The running-noise thresholds were expected to be higher than the frozen-noise thresholds because of interaural correlation uncertainty of the masker intervals for running-noise conditions. Since this correlation uncertainty decreases with increasing masker bandwidth, differences between running- and frozen-noise conditions should decrease with increasing bandwidth for interaural correlations smaller than +1. For an interaural correlation close to +1, no difference between frozen-noise and running-noise thresholds is expected for all values of the masker bandwidth. These expectations are supported by the experimental data. For the 10-Hz running-noise condition, the thresholds can be accounted for in terms of interaural correlation uncertainty. For the frozen-noise conditions and both the 100- and 1000-Hz running-noise conditions, it is likely that the limits of accuracy of the internal representation determine the detection thresholds. [Work supported by the Dutch Organisation for Scientific Research (NWO).]
Analysis of different pointing methods in localization experiments of sound sources
Authors: Pörschmann Christoph , Djelani Thomas
Published: July 2002

Sound localization experiments are described which aim to analyze and compare different pointing methods for sound-source localization in virtual and real environments. In the first experiment, subjects indicated the perceived direction of sound incidence by pointing directly to the source with their hands. In the second experiment, the direction was indicated using the GELP (Gods eye localization pointing) technique, i.e., by pointing at a spherical model of the auditory space. In the third experiment, a head-pointing task was applied, that is to say the direction of localization was indicated by turning the head toward the direction of the source. All the localization tests were carried out in a virtual auditory environment. Individually measured HRTFs were used for the auralization; the stimuli (pulsed white noise) were presented via headphones. The subjects were allowed to perform small head movements in order to improve the localization capability. The results of the experiments are discussed. The systematic errors that occur when using the different pointing methods are analyzed. It is shown that the localization blur averaged over all the directions is smaller using the GELP technique, while the blur for the front directions is smaller when the subjects point directly to the source.
Novel electrostrictive poly(vinylidene fluoride-trifluoroethylene) copolymer actuators
Authors: Zhang Q. M. , Bharti Vivek , Cheng Z-Y. , Romotowski T. , Tito Frank , Ting R. Y.
Published: July 2002

Electroactive materials for applications in active noise and vibration control should possess a high displacement capability, high reliability, and be easily fabricated to conform to complicated surfaces and shapes. Apparently, almost all the current available materials cannot meet these requirements. It was discovered recently that a massive electrostriction (strain level ∼5%) can be achieved in specially treated P(VDF-TrFE) copolymers [Q. M. Zhang, Vivek Bharti, and X. Zhao, Science 280, 2101 (1998)]. More significantly, because of the high elastic modulus, the material also exhibits high elastic energy and power density, an order of magnitude higher than those from the conventional piezoceramic and magnetostrictive materials. In addition to the large longitudinal strain, the transverse strain can be tuned over a broad range by varying the processing and irradiation conditions, from near zero in unstretched samples to more than the longitudinal strain in stretched samples. In this paper, the electromechanical properties of this class of material and the performance under different external conditions will be presented. The results on the unimorph and multilayer actuator performance fabricated using the new electrostrictive polymers with different electrode materials will also be presented. [Work supported by ONR.]
Piezo actuators for active vibration control and isolation—principles and practical experiences
Authors: Schirmacher Rolf
Published: July 2002

Piezoelectric actuators based on PZT ceramics are a widely used drive system and are also often used for active noise and vibration control applications. They offer high static and dynamic forces, are very stiff, allow high-frequency dynamic applications, and contain no moving parts. But they also have severe disadvantages: They are very sensitive to bending moments and pulling forces and have to be driven by electrical fields of some kV/mm to obtain displacements of about 1%. The actuators have a high capacitance, which is a challenge for the power amplifiers, and the material exhibits hysteresis which shows up as nonlinearities. Based on these restrictions, different concepts for the application of piezo actuators for active vibration control and isolation systems are presented, and mechanical as well as electrical aspects are discussed. For a real life application, it was decided to use one of the concepts at an experimental stage. The design of this actuator system will be presented. Experimental results and experiences will be shown, including test stand results of the entire active vibration control system. The main problem proved to be with the nonlinearities of the actuator response, which are prohibitive for at least some applications.
The time course of lexical involvement in phonetic categorization
Authors: McQueen James M. , Norris Dennis , Cutler Anne
Published: July 2002

Two experiments in Dutch examined how the influence of lexical knowledge on phonetic decisions changes over time. A [f]–[s] continuum (edited natural speech) was placed in initial position in monosyllables to make word–nonword and nonword–word continua: flauw (dull)–slauw and flaap–slaap (sleep). Syllable-final continua were made in the same way: maf (silly)–mas and jaf–jas (coat). Materials were low-pass filtered at 3 kHz. In experiment 1 there was a significant lexical effect for both initial and final fricatives: throughout the continua there were more [f] responses in the word–nonword than in the nonword–word continua. Lexical involvement was strongest in the listeners’ fastest responses but disappeared in their slowest responses, both for the final fricatives (in line with previous findings) and the initial fricatives (contradicting earlier studies showing the strongest effects in the slowest responses). Experiment 2 tested whether listeners would still use lexical knowledge in their fastest responses under severe time pressure. They were asked to respond before a tone, presented 500 ms after fricative offset. The results replicated experiment 1. Lexical knowledge appears to be used in phonetic decision-making only within a limited time frame.
The perception of German syllabic [n]
Authors: Pompino-Marschall Bernd , Janker Peter M.
Published: July 2002

Perception of syllabic [n] was studied using different inflectional forms of the German indefinite article, i.e., ‘‘ein’’ (nom. sing. masc.) versus ‘‘einen’’ (acc. sing. masc.). Inspection of a larger corpus of spoken German revealed that the most frequent pronunciation of ‘‘einen’’ is the allegro form with only a lengthened—not literally bisyllabic—[n]. Identification tests were run with manipulated items of a naturally spoken ‘‘einen.’’ The original utterance consisted of a glottalized [a] segment of 68-, a diphthong of 65-, and a [n] of 49-ms duration produced at a fundamental frequency of about 200 Hz by a female speaker. The duration of the diphthong and the nasal were varied in five steps of approximately 10 ms by doubling/cutting pairs of individual pitch periods. A second set of 25 stimuli was produced by cutting the initial glottalized segment. Analyses of variance revealed highly significant effects of nasal duration and glottalization independent of diphthong duration: Longer nasal segments as well as the presence of glottalization resulted in an increase in ‘‘einen’’ responses. The identification seems to be independent of rate of articulation but not of general speaking rate when the test items are embedded in larger utterances.
An active approach to interior noise reduction for a modern electrical locomotive
Authors: Viscardi M. , Fontana M. , Vecchio A. , Mocerino B. , Lecce L.
Published: July 2002

The present work deals with the noise measurement and characterization inside the cabin of an electric locomotive and the first results of an active control approach aimed at noise suppression to improve the acoustic comfort of drivers during the service. Characterization of each single source contributing to the measured overall level has at first been performed on an experimental basis, through a set of microphones located inside the cabin and directly near the main sources at the engine cooler fan, the air conditioning system, and also, during travel, on the exteriors to measure the airborne and the rail–wheels contact noise. During this stage the engine cooler fan has been identified as the main source strongly contributing to increase the noise level in the cabin. First experimental activities have so been planned and performed to assess an active noise control system reducing the annoyance on this last source. Technical reasons have pushed to prefer a system directly working on the acoustic interior more than at the noise source, mainly based on loudspeakers and microphones distributed in the cabin. By the use of active digital filters some of the tonal peaks presented in the noise spectra were so suppressed in the range 0–1000 Hz, producing an overall noise reduction in the band of 5 dB for both seats.
Biased lead zirconate titanate as a high-power transduction material
Authors: Moffett Mark B. , Jevnager Michael D. , Gilardi Stephen S. , Powers James M.
Published: July 2002

High-power, underwater transducers utilizing polarized piezoelectric ceramic material are usually limited in drive amplitude so that depolarization does not occur, but application of a dc bias field in the polarization direction allows the use of higher ac drive fields. To demonstrate the feasibility of biased operation as a means of achieving higher power, a thin-walled, spherical-shell transducer was constructed of Channel 5800 and tested in NUWC’s Acoustic Pressure Tank Facility at a hydrostatic pressure of 1400 psig (9.65 MPa). The transducer was successfully driven to 33 V/mil (1.3 MV/m) rms with an accompanying bias field of 31 V/mil (1.2 MV/m). The source level was 206 dB re: 1 μPa⋅m at 61 kHz, corresponding to a 10-dB improvement over the unbiased drive limit of 10 V/mil (0.4 MV/m) rms and 196 dB re: 1 μPa⋅m.