bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral investigation of spatial scales associated with substructures on a fluid-loaded plate
Authors: Cunefare Kenneth A. , Shepard W. Steve , Ginsberg Jerry H.
Published: October 2005

A wave-number-based formulation of the surface variational principle is used to investigate the effects of substructures on fluid-loaded systems. The paper examines issues of scale associated with the spatial distribution and representation of substructure attachments. The primary emphasis is suspended discrete spring-mass systems. A further extension considers an elastic beam attached at multiple locations. The main structure is a simply supported plate of infinite width contained in an infinite baffle and exposed to water on one side. Scales are introduced to the formulation by using a spectral Fourier series to represent point attachments. Previous work had considered the case where line masses are fastened to the plate. The concept that evolved entailed comparing the displacement and surface pressure obtained from analyses whose only difference is the number of terms in the spectral series used to represent the attached masses. The difference between such analyses is an indicator of the significance of the scales associated with the additional terms in the series. The work reported here increases the complexity of the system by allowing for the masses to be flexibly attached to the plate. This generalized problem is comparable to the types of systems considered to form fuzzy structures. However, the viewpoint here is deterministic. Results to be presented examine the influence of the scales associated with substructure attachments when the parameters of the suspended substructures have a range of values.
The theory of fuzzy structures—A statistical continuum mechanics interpretation
Authors: McCoy J. J.
Published: October 2005

The theory of fuzzy structures is demonstrated to follow from a renormalization of a more fundamental continuum mechanics formulation. The derivation accepts an explicitly statistical interpretation of the attached fuzzy and the achieved renormalization applies for estimating the ensemble averaged response of the master structure. An alternative interpretation of the attached fuzzy acting on a much smaller length scale than that required for describing the master structure response is briefly discussed. Several issues are identified that suggest the theory cannot be rigorously justified as a general mathematical framework. These issues relate to the uniqueness of predictions, to the independence of the effective impedance operator that reflects the presence of the fuzzy structure attachments to the master structure, and to the well-posedness of the inverse problem for determining this effective impedance from experiments of the response of the master structure. The case of point-connected fuzzy structures is investigated in detail and a distinction between an added inertia force and an added stiffness is emphasized. The simplification of the renormalization required for the added inertia forces is shown to reproduce a result of a statistical independence assumption.
Bragg-modulated hybrid ray-mode acoustics for plane wave sound scattering from a periodically ribbed submerged cylindrical elastic shell
Authors: Felsen Leopold B. , Shaya Ronald
Published: October 2005

The ray-acoustically parametrized formal spectral integral solution presented in the companion paper [L. B. Felsen and R. Shaya, preceding paper] is evaluated by asymptotic procedures structured around saddle point methods, contour deformations, and pole residue extractions in the complex spectral wave-number (ν,β) domains pertaining to the scattering configuration. Saddle points give rise to geometrical reflections, whereas intercepted poles give rise to shell-guided leaky, trapped, and creeping wave fields, both for the bare-shell and rib-induced contributions. The resulting scattered field ray-acoustic algorithm contains (a) specular and Bragg-modulated diffracted ray fields; (b) Bragg-modulated helically traveling shell-guided mode fields that are phase-matched to the fluid; and (c) helically resonant shell-guided modes formed by phase coherent circumnavigations of the modes in (b). The propagation and leakage characteristics of the shell-guided modes are determined by the dispersion equation for the rib-loaded cylindrical shell.
Toward local effective parameter theories using multiresolution decomposition
Authors: Steinberg B. Z. , McCoy J. J.
Published: October 2005

Using the recently developed theory of multiresolution decomposition, a formulation that governs the response of a linear dynamical system with nonstationary microscale heterogeneity is reduced to two coupled formulations, one governing the smoothed response, on an arbitrary chosen reference scale with the response fine details as forcing, and one governing the detail response with the smoothed response as a forcing. By substituting the formal solution of the latter in the former, a new framework, specifically tuned to macroscale variations of the response, in which the effects of the nonstationary microscale heterogeneity are described via a macroscale-effectivematerialoperator, is obtained. Localization of across-scale couplings, as well as the dependence of the smoothed response and the effective material operator on the microscale and macroscale geometries are investigated via general asymptotic considerations and specific numerical examples. The latter concerns the response of a fluid-loaded elastic plate with nonstationary microscale mass heterogeneity.
Response of a pseudo-periodically ribbed shell to a point drive
Authors: Photiadis Douglas , Houston Brian , Williams Earl , Bucaro Joseph
Published: October 2005

Near periodic arrays of discontinuities have been predicted to have a significant impact on the acoustic properties of elastic structures. Recent experimental results obtained at the Naval Research Laboratory have demonstrated the importance of the multiple scattering of flexural waves on the acoustic far field, but the surface propagation characteristics of such structures are still uncertain. Near-field pressure measurements of the response of an irregularly ribbed cylindrical shell to a point drive have now been performed. Using near-field acoustic holography (NAH), the surface velocity field of the structure is reconstructed, and further data analysis, modal and wave-number decomposition, is performed. The dispersion relations and the associated apparent damping factors for the propagating waves on the structure are hence experimentally determined. These results and interpretation of the data will be presented.
Role of articulation in speech perception: Clues from production studies
Authors: Lindblom Bjorn
Published: October 2005

The relative roles that signal properties and nonsignal information play in speech perception are examined first. The evidence strongly suggests that ‘‘the input is never into a quiescent or static system.’’ Thus phonetic percepts are never knowledge-innocent records of the raw signal. Drawing this conclusion not only with reference to ‘‘higher’’ levels of language processing, but also for the perception of elementary phonetic stimuli, a broad range of facts about production are considered. Is it organized to permit listeners to recover articulations? Or is it shaped by a demand for (relative or absolute) acoustic stability despite articulatory imprecisions? Is it controlled to generate auditory invariants? The search for answers highlights the adaptive nature of speech production, which suggests that the signal does not encode articulatory, acoustic, or auditory invariants but plays the role of supplementing the multi-modal information already in place in the listener’s speech processing system. Phonetic signals are not invariants wrapped in ‘‘noise’’ but are products of listener-dependent adaptations that transform speech patterns in principled, and therefore interpretable, ways. Do listeners recover articulations? The present review leads one to doubt that they do.
Global acoustics
Authors: Munk Walter H.
Published: October 2005

Spiesberger etal. [J. Acoust. Soc. Am. (to be published)] has demonstrated the feasibility of phase-coherent processing of 250-Hz coded acoustic signals transmitted from Hawaii to the West Coast over ranges of 3000 to 4000 km. The Heard Island Test [W. Munk etal., J. Acoust. Soc. Am. (to be published)] extended the range for 57-Hz transmission to antipodal distances. Such low-frequency long-range acoustics transmissions are well suited for monitoring ocean climate variability. The acoustic travel time between two fixed points are a measure of the average temperature of the intervening ocean. Basin scale averages suppress the intense mesocale eddies (order 100 km) that would otherwise dominate over the climatic variations. Propagation problems that are peculiar to global-scale transmissions will be discussed. Acoustic thermometry of ocean climate (ATOC) is scheduled for the North, Central, and South Pacific starting 1994 as a beginning of a global network. [Work supported by ONR, ARPA, NOA, NSF, and DOE.]
Experimental design for acoustic thermometry of ocean climate (ATOC)
Authors: Spindel Robert C. , Howe Bruce , Worcester Peter F.
Published: October 2005

The ATOC demonstration experiment involves the installation of two fixed acoustic sources, one near Hawaii and the other near Pt. Sur, California, the instrumentation of several Navy receiver systems in the North Pacific, and the deployment of autonomous and cabled-to-short vertical arrays. Extension of the experiment to other oceans may require the installation of eight to ten additional sources and as many as 40 receivers. In this paper the ATOC network and site selection criteria are described for the demonstration phase as well as for its extension, the design of the sources and receivers to be used for the demonstration phase, and the technologies currently being considered for long-term, world-wide use.
Global acoustic mapping of ocean temperatures (GAMOT)
Authors: Spiesberger John L. , Frye Dan , Hurlburt Harley , McCaffrey Joe , Johnson Mark , O’Brien James
Published: October 2005

The GAMOT group is developing two instruments that will economically map temperatures in the global oceans at a resolution suitable for understanding natural variability in climate and separating that from a global warming trend. The status of these instruments, a surface suspended acoustic receiver and an autonomous source mooring, will be presented. According to state-of-the-art models of the ocean. changes in climate can be easily detected with acoustic thermometers. These types of models represent climatic variability quite well since they replicate variations in climate measured from satellite altimeters and infrared sensors. The fastest way to detect global warming is to subtract off natural variability and examine the residual for trends. [Work supported by the Advanced Research Projects Agency.]
A new scheme of the acoustic tomography of the ocean
Authors: Voronovich A. G. , Shang E. C.
Published: October 2005

Using horizontal antennas composed out of mode resolving long vertical arrays has powerful potentials in the study of ocean acoustics. The new scheme for acoustic tomography of the ocean is presented based on the measurements of horizontal refraction of horizontal rays related to different acoustic modes. The horizontal refraction angle (HRA) of a given mode equals the transverse gradient of the refraction index averaged over the depth interval embraced by this mode and integrated over the acoustic path. Using HRA offers the following advantages. (a) Only simple tonal signals are involved. (b) There is no need for exact positioning of the source. (c) As rays are straight lines with great accuracy, the linear procedures of inversion are adequate in the 2-D stage. (d) Since tomography reconstruction is two dimensional for any given mode number, the processing and interpretation of the data are greatly simplified; a precise 3-D picture of inhomogeneities is calculated as the next stage after 2-D reconstruction. An experiment involving two pairs of LVA and a towed tonal source which allowed the reconstruction of a 3-D picture of the ocean inner structure in the area of 1000 nm×1000 nm for about 2 weeks, is discussed. [Work partly supported by NRC and ARPA.]
Trans-Arctic propagation for ocean climate studies
Authors: Mikhalevsky Peter N.
Published: October 2005

Long-term observations over many years of the changes in acoustic phase, travel time, and amplitude for many trans-Arctic paths could provide synoptic measurements of Arctic Ocean temperature and sea ice properties (particularly average ice thickness), crucial elements of the Arctic climate that plays a significant role in the Earth’s climate system as well as being a sensitive indicator of global climate change. The response of acoustic phase and amplitude to changes in Arctic Ocean temperature, and changes in sea ice coverage and thickness have been estimated for a trans-Arctic path of 2700 km at 30 Hz. Low frequencies (<40 Hz) are required in the Arctic due to the large scattering losses from the ice (indeed, one of the observables). The travel time and phase ‘‘noise’’ caused by ‘‘short-term’’ mesoscale and internal wave modulation of the Arctic Ocean temperature are calculated to be negligible. Phase measurements made in the Arctic over a 320-km path at 30 Hz [P. N. Mikhalevsky, J. Acoust. Soc. Am. 70, 1717–1722 (1981)] demonstrated phase detection to better than one hundredth of a cycle with observed short-term phase fluctuations consistent with the mesoscale calculations. However, these observations were too short in time and in range for any definitive conclusions regarding trans-Arctic paths. An experiment is planned in late April to transmit signals at 20 Hz from a Russian ice camp off Spitzbergen to a vertical array in the Lincoln Sea, and horizontal and vertical arrays at an ice camp in the Beaufort Sea.
Dual use potentials of the U.S. Navy’s integrated undersea surveillance system
Authors: Williams Harold A.
Published: October 2005

The U.S. Navy is interested in further exploring the potential additional uses of the integrated undersea surveillance system. The system consists of both high-gain long fixed arrays in the deep ocean basins, and mobile ships equipped with long towed arrays. Significant signal processing is incorporated, together with expert operators. Applications for the data could include marine mammals, seismic research, global warming, weather research, fisheries enforcement, and drug enforcement. At the same time, due to the reduced security demands of the Defense department, funding for this personnel-intensive, expensive system has been greatly reduced. Future opportunities for collaborative initiatives between the U.S. Navy and other agencies will be explored.
Dual uses of the Navy undersea surveillance system
Authors: Conlon Dennis M.
Published: October 2005

The U.S. Navy’s integrated undersea surveillance system (IUSS) consists of a fixed component, the sound surveillance system (SOSUS), and a mobile component, the surveillance towed array sensor system (SURTASS). Access to these systems is being granted to researchers who possess the proper security clearance (i.e., SECRET), and whose work can be accommodated within the framework of the system’s primary mission of national defense. Working with IUSS, progress has been achieved in studies of whale migration (WHALES ’93 Experiment) and the remote detection of subsurface geophysical events (NOAA VENTS Program). Future uses include a role in the acoustic thermometry of ocean climate (ATOC) Experiment. The mechanics of gaining access to and working within the IUSS are discussed.
The nation’s fixed undersea surveillance assets—A national resource for the future
Authors: Evans Kirk
Published: October 2005

Following the Cold War, the Navy’s extensive undersea surveillance tracking net, SOSUS, provides an unparalleled opportunity for converting defense infrastructure into a civilian national asset. Designed to track submarines by their faint acoustic signals, SOSUS enjoyed tremendous success during the Cold War and was a major factor in the United States’ dominance in antisubmarine warfare. The SOSUS hydrophone arrays in both the Atlantic and Pacific face an uncertain future of shutdowns and closings. Yet those arrays and associated signal processing provide a unique acoustic ‘‘window’’ into the deep ocean—the volume of data collected is enormous. Over the last two years some limited experiments in tracking marine mammals, detecting seismic activity, and law enforcement have confirmed a tremendous civilian potential for this data. This paper reviews the history and characteristics of SOSUS, its potential for civilian use, and calls for the conversion of unused SOSUS assets into a National Acoustic Observatory. Using modern computers and networking technology, such an observatory could provide data from SOSUS arrays for research, law enforcement, and unparalleled synoptic pictures of marine mammal and seismic activity. However, to make this a reality will take the timely and cooperative efforts of defense, civilian agencies, and universities.
Opportunities for industrial and academic partnering with the Naval Undersea Warfare Center Division, Newport
Authors: LaPlante Robert F.
Published: October 2005

With the continuing defense drawdown, the Clinton administration policy of defense technology conversion, and the emphasis on development of dual use technologies, the Naval Undersea Warfare Center (NUWC) Division, Newport in Newport, RI is seeking partnerships with industry, academia, and other government activities. Division, Newport is the Navy’s principal laboratory for research, development, test and evaluation (RDT&E), engineering, and Fleet support for submarine and surface ship sonars, submarine combat and communications systems, autonomous underwater vehicles, undersea offensive and defensive weapons systems, and countermeasures associates with undersea warfare. To support this mission, the Division maintains a staff of technical experts in many areas including acoustics, signal processing, oceanography, hydrodynamics, large scale numerical analysis, structural acoustics, advanced materials, guidance and control. The Division also operates many world class acoustic and engineering facilities including acoustic test, transient flow loop, integrated transducer design, acoustic display, and propulsion test facilities. The Divison also operates several underwater acoustic measurement and test facilities such as the Atlantic Undersea Test and Evaluation Center (AUTEC). Mechanisms for industry, academia, and other Government activities to partner with the Division, make use of facilities/expert, or use Division patents are described.
Neurophysiological studies of acoustic processing in the ventral auditory cortex of the FM bat, Eptesicus fuscus
Authors: Fritz Jonathan B. , Simmons James A.
Published: October 2005

A focus of recent experiments on the functional organization of the auditory cortex in the big brown bat has been the characterization of neurons in the newly identified ventral auditory area (VAC). The observations indicate that VAC neurons display significantly higher spontaneous activity, longer response latency and duration than cells in dorsal auditory cortex [Dear etal., J. Neurophysiol. 70, 1988–2009 (1993)]. In VAC there is a higher percentage of physiological cell types whose spectral tuning and echo-delay tuning varies dynamically with stimulus amplitude and context, and cells whose frequency tuning curves are multipeaked. These latter cells may play a functional role in encoding spectral notches in multiple echoes, which are known to carry information about the shape, fine range structure, and textures of a target. Averaged evoked potentials of cells in VAC to tonebursts or FM sweeps show oscillatory responses (150–400 Hz). The role of temporal response patterns in cortical processing of acoustic information will be discussed. The results indicate that the VAC may be a higher auditory processing center. [Work supported by NSF.]
A wavelet representation of acoustic information in the auditory cortex
Authors: Dear Steven P. , Simmons James A.
Published: October 2005

A previous study demonstrated that a subpopulation of cortical neurons comprised a multiresolution decomposition of target range information in the big brown bat [Dear etal., Nature 364, 620–622 (1993)]. Given the strong relationship between a multiresolution decomposition and wavelets, it was wondered if acoustic information is represented as wavelets in the auditory cortex. Here, the existence of Daubechies wavelets in the auditory cortex in response to multiharmonic FM sweeps simulating the type of signals used by the big brown bat for echolocation is reported. The Daubechies wavelets exist as continuous analog voltages that appear to be evoked by a local ensemble of cortical neurons. The wavelets are sensitive to manipulations of multiple synthetic echoes and suggest an orthogonal representation of acoustic echo information in the auditory cortex. [Work supported by NSF.]
Transient-evoked otoacoustic emission suppression tuning curves in human adults and infants
Authors: Folsom Richard C. , Burns Edward M. , Zettner Erika M. , Morrison Robert B.
Published: October 2005

Suppression tuning curves (STCs) were obtained for transient-evoked otoacoustic emissions (TEOAEs) from infants 1-to-3 months of age and from normal-hearing young adults. TEOAEs were elicited by tone-pip probes at frequencies ranging from 1000 to 4000 Hz. Suppressors were pure tones presented simultaneously with the probes. STCs, based on a criterion suppression of 6 dB, were constructed using from four to seven suppressor frequencies per probe, depending on how long the infant remained quiet. Suppressor frequencies ranged from one octave below, to one-half octave above, the probe frequency. In agreement with previous studies on OAE suppression, tuning curve tips were usually at frequencies from one-eighth to one-quarter octave above the probe frequency. Overall STC shapes, Q10’s, and upper and lower slopes were similar in infants and adults at all probe frequencies. In general, STCs were similar to ABR tuning curves obtained from infants and adults, but broader than adult (nonsimultaneous) psychophysical tuning curves which have been reported in the literature. [Work supported by NIDCD.]
Mass per unit natural frequency as a descriptor of internal fuzzy structure
Authors: Pierce Allan D.
Published: October 2005

Previous work by the author with Sparrow and Russell, and by Strasberg and Feit, has suggested that internal mass per unit natural frequency is the appropriate prime descriptor of the internal structure of a complex system enclosed by a shell. In the simplest idealization one conceives of many one-degree-of-freedom (dof) spring-mass systems, coupled only through the outer shell, and which are attached at random points on the interior surface of the shell, and one specifies for any small area just how much suspended mass is associated with a narrow band of natural frequencies. The assumption of large numbers allows the use of an idealized limit of mass per unit natural frequency per unit area. The present paper shows from basic principles that this concept still applies when the individual attachments have multi-dof complexity. The question is then addressed of how one can deduce this mass-frequency density when the internal structure is largely apriori unknown (fuzzy internal structure). A possibility is the sampling of the impedance presented to small surface areas of the outer shell by the internal structure. Algorithms for processing the (complex) impedance versus frequency curves yield estimates of the required information.
Vibration damping of large structures induced by attached small substructures each with multiple degrees of freedom
Authors: Strasberg M. , Feit D.
Published: October 2005

At the previous meeting [J. Acoust. Soc. Am. 94, 1814 (A) (1993)] a relatively simple method was described for estimating the vibration damping introduced into a large structure by a multitude of small substructures compliantly connected to the large structure. The analysis in that talk assumed that the substructures behaved as sprung masses with different but closely spaced frequencies of resonance, each mass having a single frequency of resonance corresponding to one degree of freedom. The analysis is now extended to attached substructures each with multiple degrees of freedom. As an example, calculations are presented of the damping of flexural vibrations induced in a large undamped beam by a large number of small cantilevered strips of gradually varying length attached to the beam. The calculated results are compared with experimental data for this arrangement described some years ago by M. Heckl. [Work supported by ONR.]
Plane wave radiation resistance of a source in a duct with mean flow
Authors: Muehleisen Ralph T. , Swanson David C.
Published: October 2005

A theoretical investigation into the effects of mean flow (of Mach number M) on the plane wave radiation resistance of a source mounted in the side of a duct is made. The radiation resistance is an important parameter in the design of active noise control systems. It is found when the source is in a nonturbulent region the overall radiation resistance is increased by a factor of 1+6M2. If the source is in a region of turbulence the radiation resistance is only increased by a factor of 1+M2. Without turbulence the downstream radiated power is decreased by a factor of 1/(1+M)3 while the upstream radiated power is increased by the factor 1/(1−M)3. With turbulence the factors are reduced to 1/(1±M). The difference in the turbulent and nonturbulent expressions is because of a velocity discontinuity at the edges of the piston that is modified in the presence of turbulence. Because the downstream radiated power is reduced, an active noise control system that works primarily by out-of-phase cancellation will be less efficient. However, since the upstream radiated power is increased, a system that works primarily by mutual coupling of the sources may be enhanced.
Prediction of impulsive noise levels: A different approach
Authors: Lewis Nelson D.
Published: October 2005

There is a need for a simple model that can be used to predict the noise levels from impulsive events. These data are needed for Environmental Assessments and Impact Statements. This paper presents a model that fills this need. It can be used to predict either the expected mean level and its standard deviation at a fixed location or the distance to a fixed sound level. The model includes corrections for terrain, and buried or elevated explosions.
A transmission method for estimating the specific acoustic impedance of a porous material: Modelization
Authors: Amédin Celse K. , Champoux Yvan , Berry Alain
Published: October 2005

A new method is suggested for the characterization of porous materials; it is based on a measurement of the sound transmission through a layer of the material. This paper presents two theoretical models to evaluate the potential of the method. In these models, a thin layer of the material lies on a horizontal baffle; the acoustic source is a waveguide mounted vertically under the baffle with its end flush to the baffle and the sound is transmitted through the layer to the half-space above the layer. The two models calculate the transfer function between the volume velocity of the waveguide and the sound pressure over the layer. The first model is based on the integral method and collocation in which the appropriate Green’s functions are used to describe the sound field. The second model uses a method of decomposition into plane waves. The details of each model are described; results, comparisons, and validations are presented. Finally, the potential of the method to evaluate the characteristics of the porous layer is discussed.
Impulse measurements compared to rigid-frame and dual-wave predictions for foam
Authors: Lawrence David E. P. , Don Charles G.
Published: October 2005

Impedance and wave-number predictions from a rigid-frame model of a porous medium, where only a single wave is assumed to propagate through the permeating fluid, are compared with results from a dual-wave theory where there is both a fast and a slow wave present. Both results are matched against experimental data obtained by acoustic impulse techniques that allowed both the characteristic impedance and the layer impedance to be deduced from 200 Hz to 10 kHz. The complex wave number was determined by placing two microphones a known distance apart inside a foam block and recording the waveforms as a pulse passed. The high-frequency wave-number limit permits the tortuosity to be established, while the effect of a pore shape factor is more evident in the attenuation data. The position and magnitude of the maxima in the layer impedance are very sensitive to the tortuosity and the shape factor. Both models adequately predict the experimental impedance curves, however, for a foam with a flow resistivity of 25100 N s m−4 the presence of a slow wave is required to fit the low-frequency attenuation and wave speed results. An improved incorporation of the shape factor into the dual wave model is suggested.
On the influence of ground porosity on acoustic/seismic coupling spectra
Authors: Taherzadeh Shahram , Attenborough Keith
Published: October 2005

An airborne sound wave striking the ground surface can produce seismic excitation in the ground. The acoustic-to-seismic coupling spectra show distinctive structure. The structure is mainly attributed to wave resonances within the ground layers. This phenomenon has been studied extensively in the past. Here the extent to which certain parameters influence the position of maxima of acoustic-to-seismic coupling are investigated. The ground has been modeled as a vertically layered porous-elastic medium using the modified Biot–Stoll theory. Predictions based on this theory and also some previously derived expressions are compared with data. It is shown that for some typical ground types, only the full Biot–Stoll theory rather than a low velocity elastic layer model is required to predict the acoustic-to-seismic coupling spectra adequately.
Propagation over rough finite impedance boundaries
Authors: Attenborough Keith , Taherzadeh Shahram
Published: October 2005

Previous studies of the boundary wave associated with near-grazing propagation over randomly rough surfaces have been concerned with high-frequency (2.5–30 kHz) pulses and acoustically rigid surfaces [see, for example, Medwin etal., J. Acoust. Soc. Am. 66, 1131–1134 (1979)]. Continuous wave measurements of the excess attenuation spectrum by means of maximum length sequence signal analysis have been carried out. These have enabled study of roughness effects in the frequency range 500 to 2500 Hz. Data have been obtained over rough wooden surfaces and over a thin polymer foam layer to which rectangular 3 cm by 0.5 cm strips have been attached. These data have been compared with predictions due to Howe [J. Sound Vib. 98, 83–94 (1985)] modified for effects of roughness shape according to Tolstoy [J. Acoust. Soc. Am. 66, 1135–1143 (1989)]. [Work supported by S.E.R.C. (UK).]
Estimation of the time-varying phase (instantaneous frequency) in atmospheric sound propagation
Authors: Burgess John C. , Havelock David I.
Published: October 2005

Atmospheric turbulence affects both the amplitude and phase (instantaneous frequency) of transmitted sound. The effect is similar to that of random variations in sound propagation velocity. Two methods to estimate the time-varying phase are discussed, one based on an FFT with optimum data windows and the other based on the discrete Hilbert transform. Accuracy of the two methods is compared using synthesized single-frequency test signals. Comparisons are made between the methods applied to acoustic data obtained from sound propagating through a turbulent atmosphere. a)On leave from the University of Hawaii.
Integral formulation of wave propagation through a turbulent medium
Authors: Kaneko Hirobumi
Published: October 2005

A novel technique for approximate computation of transient waveforms through weakly inhomogeneous media is described. It has some of the features of ray acoustics formulations, but largely circumvents the problems associated with caustics and allows the incorporation of diffraction effects. The prototype for a single step in propagation range is that where the acoustic pressure is specified as a function of time and lateral position on a planar surface, with the desire to determine the acoustic pressure on some further surface at a distance Δx in the general direction of propagation. To determine the pressure versus time at a typical point on the second surface, an approximate integral solution is developed in terms of a Green’s function for a point source in the inhomogeneous medium. Such a Green’s function is determined by matching a ray acoustics solution in the far field to Blokhintzev’s well-known solution for a point source in a homogeneous moving medium. Although the overall wave field may encounter a caustic in the intervening slab, such is not as likely to occur for the Green’s function because of its intrinsic spherical spreading.
Comparison of the spatial coherence in a refractive shadow as calculated using measurement and simulation data
Authors: Havelock David I. , Di Xiao
Published: October 2005

In an upward refracting atmosphere an acoustic shadow is generated near the ground. Sound arrives deep within a shadow region by scattering from atmospheric turbulence. The Green’s function method for the parabolic equation (GF-PE) can be used to simulate the (complex) sound field in such a shadow region. Signals from an array of microphones can be beamformed to detect coherent signals. To better understand the performance of a beamforming array within an acoustic shadow, knowledge of the coherence of the sound field is important. The transverse and longitudinal coherence of a sound field within a shadow region near the ground are examined using the GF-PE and experimental measurements obtained with a 24-element array. Propagation distances of 400–700 m and signal frequencies of 100–1000 Hz are considered. The simulation and measurements are in good agreement and show greater longitudinal coherence than transverse coherence. Variations with frequency and range are also observed. a)Present address: 503 Walker Bldg., Penn State Univ., University Park, PA 16804.
Nonlinear–nonstationary propagation of acoustic waves
Authors: Maestrello L.
Published: October 2005

A study is made of the complex acoustic wave field emanating from a supersonic turbulent jet at constant or accelerated speeds and its interaction with a nearby flexible structure. The acoustic wave propagation from the jet and from the structure manifests period doubling, shock harmonics, and nonstationarity, all superimposed on a broadband random response field. At accelerated speeds, aperiodic (random appearing) transient multi-shock signals highly sensitive to initial conditions dominate the broadband radiation field with positive Lyapunov exponent. The shock harmonics achieve noticeable amplitude with distance with respect to the fundamental. The loading is a combination of continuous broadband stochastic-type excitation and discontinuous events from the shock impact. Transient loading plays a major role in the response dynamics of accelerated supersonic flights due to great stress/strain amplitude and high-intensity noise.
On sound diffraction by an impedance wedge
Authors: Osipov Andrey V.
Published: October 2005

Diffraction of waves by a wedge is a problem of modern acoustics whose mathematical solutions provide a theoretical basis in analyzing sound radiation and scattering phenomena. Considerable attention has previously been attracted to this class of diffraction problems, especially to the particular cases of a perfectly reflecting wedge and half-plane. The model of an impedance wedge [G. D. Malyuzhinets, 1958 Dokl. Akad. Nauk SSSR 121, 436 (1958) in Russian] is a more general and realistic one that gives new opportunities for treating acoustic diffraction by irregular surfaces [A. D. Pierce and W. J. Hadden, J. Acoust. Soc. Am. 63, 17 (1978); A. V. Osipov, Sov. Phys. Acoust. 36, 287 (1990)]. This paper investigates the wave field excited by a line source in the presence of a wedge with arbitrary values of face impedances. Based on the Malyuzhinets’ solution, various exact representations for the Green’s function are deduced to generate a system of convenient formulas for any relative positions of the source and point of observation. A new representation of the Malyuzhinets’ solution in the form of double series [A. V. Osipov, Sov. Phys. Acoust. 37, 381 (1991)] is exploited to describe the wave field of the line source placed in the vicinity of edge. In the opposite case of large distances from the edge, a uniform asymptotic expansion is presented. Applications of the obtained results to problems of sound attenuation by wedge-like barriers and sound radiation from a line source located at the edge of a corrugated surface are described.
Level dependence of AC and DC magnitude transfer functions in the cochlea: Implications for intensity and frequency coding
Authors: Chatterjee Monita , Zwislocki Jozef J.
Published: October 2005

AC and DC magnitude transfer functions were recorded from cells in the organ of Corti in the middle turn of the gerbil cochlea. It was found that a healthier cochlea shows more compression around the BF, a greater intensity-dependent BF shift, and a stronger DC response. Both AC and DC magnitude transfer functions show a shift in the BF. The shift exceeds an octave as intensity is raised from 40 to 100 dB SPL. Both the DC and the AC transfer functions exhibit an identical high-frequency cutoff that remains constant up to 80 kB SPL. These results further support the conclusion that the changing BF cannot encode the pitch of a pure tone, but that the high-frequency response cutoff (the apical cutoff in the spatial excitation pattern) could. At the same time, the strong compression in both the AC and DC I/O functions measured around the frequency of greatest sensitivity confirms that, for pure tone inputs, the growth of the response at one location in the cochlea cannot encode the entire range of audible intensities. [Work supported by NIDCD.]
Variability of voltage dependency of the outer hair cell (OHC) motility voltage sensor
Authors: Santos-Sacchi J. , Huang G.-J. , Kakehata S.
Published: October 2005

The OHC is a motile cell in the organ of Corti that functions to mechanically modulate inner hair cell responses. OHC length is voltage dependent; its magnitude varies as a sigmoidal function of voltage. The voltage sensing elements of the mechanical effectors have been evaluated by means of the nonlinear capacitance presented by the sensor’s charge movement. The nonlinear capacitance is a bell-shaped function of voltage. The voltage sensitivities of mechanical response and nonlinear capacitance correspond, with the peak capacitance occurring at voltages where the mechanical response is maximal. This voltage (Vh) lies between −40 and −20 mV, on average. The variability of this value within single cells has been studied using a peak capacitance tracking method. It was found that in addition to variability among cells, with Vh ranging from 0 to −80 mV, individual cells also demonstrate variability over time, sometimes hovering within a range of 20 to 30 mV. In some cases, preferred voltage levels are held for several seconds to minutes, thereafter moving to new voltage levels. Since the sensitivity of OHC motility should follow that of the voltage sensor, these results indicate that the motility function may be non-static. [Work supported by NIDCD.]
Violin acoustics
Authors: Weinreich Gabriel
Published: October 2005

The almost magical sound of a well-played violin, whose expressive capacity approaches that of a human voice while its technical possibilities far exceed it, has always excited the intellectual curiosity of people who cannot resist asking: ‘‘How in the world is it done?’’ In fact, although developed primarily by trial and error, the violin represents a surprisingly complex piece of machinery, some of whose detailed workings are only now beginning to yield to scientific investigation. This talk will outline, on a popular nontechnical level, the present understanding of the physical mechanisms that operate when a violin is played, commenting also on important aspects that are not yet understood. [Work partially supported by NSF.]
Ultrasonic cleaning of the skin surface
Authors: Qi Quan , Johnson Robert E. , O’Brien William D.
Published: October 2005

A model of ultrasonic cleaning of the skin surface is discussed in this presentation. The model assumes that the primary cleaning mechanism is associated with the collapse of cavitation bubble near the skin surface. First, bubble behavior near a deforming surface is briefly reviewed. Based on an available analytical solution, it is shown that when a bubble collapses near the skin surface, a jet formed by the collapsing bubble is directed at the surface. Consequently, it is believed that the flow field induced by bubble jetting plays a central role in the cleaning process. This flow field is modeled as a stagnation point flow and the mean transport of dirt due to this flow field is investigated. Specifically, the removal rate, i.e., mass flux, of dirt from the skin surface is found and is shown to be higher for ideal flows than for viscous flows. Finally, the relation between the stagnation point flow and the Kelvin impulse associated with a single bubble collapse is examined. By assuming a known distribution of bubble sizes, an overall removal rate estimate is obtained.
The effects of aging on vibrotactile threshold in glabrous skin
Authors: Hall Karen L. , Hoffman Katy E. , Gescheider George A. , Bolanowski Stanley J. , Verrillo Ronald T.
Published: October 2005

Thresholds were measured for the detection of vibratory stimuli in subjects ranging in age from 10 to 89 years (n=168). Vibratory stimuli of 1, 10, and 300 Hz were delivered to the thenar eminence of the right hand through a small (0.008 cm2) and a large (2.9 cm2) contactor. These stimuli have been shown to selectively isolate the NP I, NP II, NP III, and P channels in glabrous skin (Bolanowski etal., 1988). The results show a substantial reduction in the sensitivity of the P channel with increasing age. The NP I, NP II, and NP III channels show comparatively less reduction in sensitivity as age increases. Therefore, the P channel, which is mediated by Pacinian corpuscle (PC) fibers, shows a greater loss in sensitivity with age than the NP I, NP II, and NP III channels, which are thought to be mediated by RA, SA II, and SA I fibers, respectively. Women were found to be more sensitive than men in all but the youngest subjects. [Work supported by NIH, NIDCD.]
Effects of signal duration on vibrotactile intensity discrimination
Authors: Gescheider George A. , Zwislocki Jozef J. , Rasmussen Andrea L.
Published: October 2005

Vibrotactile intensity DLs were measured by the continuous pedestal and gated pedestal methods. In both cases, the relative DL decreased as a function of the sensation level of the stimulus and the results, in most cases, could be described as a near miss to Weber’s law. DLs measured by the continuous pedestal method were found to decrease substantially as a function of increases in stimulus duration over a range of 12 to 1000 ms and the results could be described by a temporal summation function derived from Zwislocki’s theory of temporal summation [J. J. Zwislocki, J. Acoust. Soc. Am. 32, 1046–1060 (1960)]. In contrast, DLs measured by the gated pedestal method were only slightly affected by changes in stimulus duration. These findings are consistent with the hypothesis that, at suprathreshold levels of stimulation, the effects of temporal summation tend to be cancelled by the effects of adaptation.
Three periods of flextensional transducer evolution
Authors: Jones Dennis F.
Published: October 2005

About 65 years ago the first flextensional transducers for aeroacoustic applications were constructed and tested by naval researchers. This first period of flextensional transducer development spanned the late 1920s to mid 1930s. Twenty years later, research on flextensional transducers for the generation of low-frequency underwater sound began. This second period of development extended from the mid 1950s into the late 1970s. A third period of flextensional transducer development began in the early 1980s when advances in acoustic quieting of submarines caused a renewed interest in low-frequency active sonar systems. This third period continues today. In successive periods there were an increasing number of countries, laboratories, industries, universities, and researchers contributing to the development of the flextensional transducer. All periods, however, were driven by naval requirements. Also, in each period there were technical advances and discoveries in many areas that influenced the evolution of the flextensional transducer. The purpose of this paper is to review the evolution of the flextensional transducer by focusing on the discoveries, advances, and motivations that distinguished the three development periods. In addition, new ideas for the future of the flextensional projector will be discussed.
Developments in electromagnetic (variable reluctance) transducers for the generation of low-frequency, high-power underwater sound
Authors: Massa Donald P.
Published: October 2005

There is a need to develop improved methods for generating low-frequency, high-power sound in the ocean. Electromagnetic transducers can have many advantages over other transduction technologies in the design of transmitters to meet this need. An historical overview of various electromagnetic transducers that have been developed will be presented, including the 300 000-lb. megawatt array manufactured for project Artemis in the early 1960s. Several high-power, low-frequency electromagnetic transducer designs will also be discussed that can be fabricated by using multiple push–pull driver modules as building blocks to produce the final structure. They can be configured into a wide variety of different array configurations, including linear, planar, cylindrical, conformal, or volumetric. These transducers possess many desirable characteristics, including immunity to explosive shock damage; no corona problems because transducers use low voltage drive; mechanical Q<1 when array loaded; no temperature sensitive components; and linear responses with low distortion due to push–pull design.
Transient response of arrays of linear and nonlinear transducers
Authors: Benthien George W. , Barach Don
Published: October 2005

In this paper a method is presented for the time-domain analysis of the mutual interaction effects in transducer arrays. This method is applicable to a large class of linear and nonlinear devices. Most analyses of array acoustic interactions to date have utilized a frequency-domain approach. However, a time-domain approach is more natural when the transducer elements are nonlinear or when it is desired to study transient effects. A method for calculating array acoustic interaction effects in the time domain is presented that can be easily coupled to models for many linear and nonlinear transducer elements. The boundary integral equation program CHIEF is used to generate acoustic interaction coefficients in the frequency domain which are then Fourier transformed to the time domain. When coupled with the transducer equations the result is a coupled set of integral-differential equations that can be solved by an explicit time-stepping procedure. Numerical results are presented for a small closely packed array of simple linear transducer elements and for an array of nonlinear hydraulically driven transducers. [Work supported by SPAWAR, PMW 183.]