bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Springback of Metal-Polymer-Metal Laminates
Authors: Liu Li , Wang Jyhwen
Published: September 2004

Metal-polymer-metal laminate is an emerging material that has many potential applications. The laminated structure consists of two outer layers of sheet metal and a polymeric center core. The material offers excellent sound deadening properties and is being introduced to applications where noise reduction is desired. Part manufacturing for laminates involves converting a flat sheet into a deformed body. Springback has been a major concern in shape control. While bending of a single layered sheet metal does not exhibit significant sidewall curl, the problem is pronounced in bending laminates. This paper presents an analytical approach to predict springback and sidewall curl of laminates due to wiper die bending. Based on the integration of a straight beam and a curved beam models, the springback factor Ks is calculated. It is shown that the prediction is in good agreement with the published experimental data. Application of the integrated model to minimize the springback and side wall curl is demonstrated. The analytical model leads to a simple expression that predicts the springback factor. The ability to predict the shape analytically is significant, since other methods require extensive finite element simulation of the deformation process.
Roundness Errors in BTA Drilling and a Model of Waviness and Lobing Caused by Resonant Forced Vibrations of Its Long Drill Shaft
Authors: Deng Chyn-Shu , Chin Jih-Hua
Published: September 2004

The original purpose of this work was to propose an equation system to describe the kind of drilling in which the tools are with pronounced shaft length. The equation system turned out to disclose the low frequency mechanism of hole lobes. The proposed system is composed of Euler-Bernoulli beam equation representing tool shaft, and an excitation force in form of Fourier series. An empirical cutting force was established and related cutting force components were calculated. And the accumulated contribution of modes and harmonics was evaluated. The solution for the proposed equation system allowed a prediction of hole roundness which was consistent with experimental results for different conditions. The solution also allowed an investigation into the waviness and lobes. The results suggested that the bizarre phenomenon of lobes on hole is in reality waviness described by Tlusty for milling. The rigorous mathematical nature of the proposed equation built solid foundation for former empirical observation of waviness and lobes on work pieces.
Nanoparticle Additive Manufacturing of Ni-H13 Steel Injection Molds
Authors: Nair, Rajeev , Jiang, and Wenping , Molian Pal
Published: September 2004

This paper reports a novel solid freeform fabrication process, Nanoparticle Additive Manufacturing (NAM), for dispersing nanoparticles into molten matrix for improved mechanical properties. In addition, it also presents the characterization of microstructure and hardness of the fabricated Ni-nanoparticles dispersed H13 steel gear-shaped molds.
Electrophotographic Layered Manufacturing
Authors: Kumar Ashok V. , Dutta Anirban
Published: September 2004

A layered manufacturing technique that uses electrophotography is described where powder is picked up and deposited using a charged photoconducting surface and deposited layer by layer on a build platform. A test bed was designed and constructed to study the application of electrophotography to layered manufacturing. The test bed can precisely deposit powder in the desired shape on each layer. The feasibility of printing powder layer by layer was demonstrated. The electric field required to transfer the powder on to the platform (or onto previously printed layers) was studied. It was found that corona charging the top layer of the part is necessary to continue printing powder as the part height increases.
Flank Wear of Edge-Radiused Cutting Tools Under Ideal Straight-Edged Orthogonal Conditions
Authors: Kountanya Raja K. , Endres William J.
Published: September 2004

Understanding the effects of tool wear is critical to predicting tool life, the point at which tool performance, in terms of power requirement, dimensional error, surface finish, burring, or chatter, is no longer acceptable. To achieve the long cuts that are required for wear testing while maintaining a clear view of the basic process geometry effects, ideal straight-edged orthogonal conditions are realized in a bar-turning arrangement by employing a specially designed two-tool setup. The data show that increasing edge radius tends to increase wear rate, especially at the initial cut-in wear phase. The data also show that when the uncut chip thickness is less than or equal to the edge radius, forces actually decrease substantially with flank wear until most of the edge radius has been worn away. At that point the forces begin to increase with flank wear in a power-law fashion. This decreasing-then-increasing trend is a result of the parasitic (non chip removing) wear-land force increasing more slowly than the chip-removal force is decreasing. The decrease in chip-removal force with an increase in flank wear results from the blunt edge being effectively sharpened as it is removed by the growing wear land. An empirical model structure is formulated, guided by specific elements of the data, to well represent the force trends with respect to wear and edge radius and to assist in their interpretation. The edge-sharpening concept is further supported by a special experiment in which the edge sharpening effect is studied in the absence of wear land.
Character and Behavior of Mist Generated by Application of Cutting Fluid to a Rotating Cylindrical Workpiece, Part 1: Model Development
Authors: Yue Y. , Sun J. , Gunter K. L. , Michalek D. J. , Sutherland J. W.
Published: September 2004

Increasing attention is being devoted to the airborne emissions resulting from a variety of manufacturing processes because of health, safety, and environmental concerns. In this two-part paper, a model is presented for the amount of cutting fluid mist produced by the interaction of the fluid with the rotating cylindrical workpiece during a turning operation. This model is based on relationships that describe cutting fluid atomization, droplet settling, and droplet evaporation. Experiments are performed to validate the model. In Part 1 of the paper, the emphasis is on model development. In the model, thin film theory is used to determine the maximum fluid load that can be supported by a rotating cylindrical workpiece; rotating disk atomization theory is applied to the turning process to predict the mean size of the droplets generated by atomization; and expressions for both the evaporation and settling behavior are established. Droplet size distribution and mass concentration predictions are used to characterize the fluid mist. Model predictions indicate that the droplet mean diameter is affected by both fluid properties and operating conditions, with cutting speed having the most significant affect. Model predictions and experimental results show that the number distribution of droplets within the control volume is dominated by small droplets because of the settling and evaporation phenomena. In Part 2 of the paper, the cutting fluid mist behavior model is validated using the results obtained from a series of experiments.
Upper and Lower Bounds for Incipient Failure in a Body Under Gravitational Loading
Authors: Chamberlain, J. A. , Horrobin, D. J. , Landman, and K. A. , Sader J. E.
Published: September 2004

Recent numerical work has investigated incipient failure of yield stress materials under gravitational loading, for both the rectangular block and cylinder geometries [Chamberlain et al.; 2001, Int. J. Mech. Sci. 43(3):793-815, 2002, Int. J. Mech. Sci. 44(8):1779-1800]. While the rectangular block solution is exact, the cylinder solutions give lower bounds on the height of incipient failure. Consequently, we construct upper bound solutions for the height of incipient failure of a cylinder under gravitational loading. This closes the cylinder problem and quantifies the accuracy of the Haar-Karman hypothesis used in slip-line analysis. For completeness, we also give a simple lower bound solution for the cylinder, as well as upper and lower bound solutions for the two-dimensional rectangular block. These results have the advantage of being analytical, in contrast to the previous purely numerical results.
Buckling of a Rotating Rod Under Axial Force
Authors: Wang C. Y.
Published: September 2004

The difference equations governing the rotation of a segmented rod under axial force is formulated. The stability boundaries are found to be highly dependent on the number of links, the rotation rate and the compressive force. For a large number of links, the result approaches to that of the continuous elastic rod through some fractional power. The analysis is applicable to segmented drill shafts.
A Long Crack Penetrating a Transforming Inhomogeneity
Authors: Wang and Yuping , Ballarini Roberto
Published: September 2004

This note presents the stress intensity factors of a long crack penetrating a circular transforming inhomogeneity. Using the Greens functions of dislocations interacting with a circular inhomogeneity experiencing an isotropic (free expansion) eigenstrain, the elasticity solution is reduced to a system of singular integral equations representing the traction boundary condition along the crack surfaces. The normalized stress intensity factor, obtained through a numerical solution of the integral equations, has a strong dependence on the elastic mismatch, and can be either negative or positive depending on the crack-tip location. The formulation and results generalize a previously published transformation-toughening model that assigns equal elastic moduli to the inhomogeneity and the surrounding medium.
Nonlinear Vibrations of Beams, Strings, Plates, and Membranes Without Initial Tension
Authors: Bao Zhongping , Mukherjee Subrata , Roman Max , Aubry Nadine
Published: September 2004

The subject of this paper is nonlinear vibrations of beams, strings (defined as beams with very thin uniform cross sections), plates and membranes (defined as very thin plates) without initial tension. Such problems are of great current interest in minute structures with some dimensions in the range of nanometers (nm) to micrometers (μm). A general discussion of these problems is followed by finite element method (FEM) analyses of beams and square plates with different boundary conditions. It is shown that the common practice of neglecting the bending stiffness of strings and membranes, while permissible in the presence of significant initial tension, is not appropriate in the case of nonlinear vibrations of such objects, with no initial tension, and with moderately large amplitude (of the order of the diameter of a string or the thickness of a plate). Approximate, but accurate analytical expressions are presented in this paper for the ratio of the nonlinear to the linear natural fundamental frequency of beams and plates, as functions of the ratio of amplitude to radius of gyration for beams, or the ratio of amplitude to thickness for square plates, for various boundary conditions. These expressions are independent of system parameters—the Young’s modulus, density, length, and radius of gyration for beams; the Young’s modulus, density, length of side, and thickness for square plates. (The plate formula exhibits explicit dependence on the Poisson’s ratio.) It is expected that these results will prove to be useful for the design of macro as well as micro and nano structures.
Collinear and Periodic Electrode-Ceramic Interfacial Cracks in Piezoelectric Bimaterials
Authors: Ha¨usler Christoph , Gao Cun-Fa , Balke Herbert
Published: September 2004

Field singularities of collinear and collinear periodic interface cracks between an electrode and a piezoelectric matrix are studied in terms of the Stroh formalism for mixed boundary conditions. In contrast to the relevant work done previously on this subject, the problem is solved based on the assumption that the upper and lower planes embedding the electrode consist of two arbitrary piezoelectric materials, and the cracks are assumed to be permeable. The problem is reduced to an interfacial crack problem equivalent to that in purely elastic media. Explicit expressions are presented for the complex potentials and field intensity factors. All the field variables exhibit oscillatory singularities, and their intensities are dependent on the material properties and the applied mechanical loads, but not on the applied electric loads.
On the Acoustic Nonlinearity of Solid-Solid Contact With Pressure-Dependent Interface Stiffness
Authors: Biwa S. , Nakajima S. , Ohno N.
Published: September 2004

Nonlinear interaction between elastic wave and contact interface, known to result in the so-called contact acoustic nonlinearity, is examined in a one-dimensional theoretical framework. The present analysis is based on a nonlinear interface stiffness model where the stiffness property of the contact interface is described as a function of the nominal contact pressure. The transmission/reflection coefficients for a normally incident harmonic wave, and the amplitudes of second harmonics as well as DC components arising at the contact interface are derived in terms of the interface stiffness properties and other relevant acoustic parameters. Implications of power-law relations between the linear interface stiffness and the contact pressure are examined in detail regarding the linear and nonlinear acoustic responses of the contact interface. Also, a plausible range of the relevant power-law exponent is provided from considerations based on the rough-surface contact mechanics. The analysis clarifies the qualitative contact-pressure dependence of various nonlinearity parameters based on different definitions. A particular power law is identified from existing experimental data for aluminum-aluminum contact, for which some explicit nonlinear characteristics are demonstrated. The theoretical contact-pressure dependence of the second harmonic generation at the contact interface is found to be in qualitative agreement with previous measurements.
Evaluation of Tension Field Theory for Wrinkling Analysis With Respect to the Post-Buckling Study
Authors: Iwasa T. , Natori M. C. , Higuchi K.
Published: September 2004

A comparative study of two representative wrinkling theories, a bifurcation theory and a tension field theory, is carried out for quantitative evaluation of the tension field theory regarding wrinkling analysis. Results obtained from the bifurcation theory show the limitations of tension field theory on the wrinkling analysis. Existence of compressive stresses caused by wrinkling phenomena, which is not accounted for tension field theory, is quantitatively presented. Considering strain energy due to these compressive stresses and geometrical boundary constraints, it is clarified that there are regions, in which the tension field theory is not properly applied.
Port-Compatibility and Connectability Based Assembly Design
Authors: Singh Palwinder , Bettig Bernhard
Published: September 2004

In Computer-Aided Design, when creating the solid model of a part, the designer knows how the part will interface with other parts, however this information is not stored with the part model. For catalog parts, it would be useful to be able to embed this assembly information into the part model in order to automate the process of applying mating constraints, to reduce the assembly designer’s effort or to allow for automated exploration of alternative configurations. This research evaluates and compares different schemes for capturing the attributes of assembly interfaces and appending that information to solid models. To evaluate the various schemes, this research work introduces the concept of assembly ports, which are defined as a group of one or more low-level geometric entities that undergo mating constraints in order to join parts in a CAD assembly. The schemes studied involve (i) different combinations of ways to constitute ports and include labeling, (ii) different bases for determining port compatibility with respect to design intent, and (iii) different ways of evaluating connectability with respect to part geometry. The scheme that we conclude is best minimizes the number of ways the system will try to put parts together at the expense of effort from the solid model designer to provide more information.
Constant-beamwidth and constant-powerwidth wideband robust Capon beamformers for acoustic imaging
Authors: Wang Zhisong , Li Jian , Stoica Petre , Nishida Toshikazu , Sheplak Mark
Published: September 2004

The standard Capon beamformer (SCB) is sensitive to the mismatch between the assumed and actual array steering vector, which occurs often in practice. Recently a robust Capon beamformer (RCB) was proposed by extending the SCB to the case of uncertain array steering vectors. In certain applications such as acoustic imaging, it is desirable that the beamwidth is constant across the frequency bins. This prevents future corrections for different frequencies and contributes to consistent sound pressure level (SPL) estimation, which means that for an acoustic wideband monopole source with a flat spectrum the acoustic image for each frequency bin stays the same. However, the beamwidth of RCB decreases with frequency, which can lead to inconsistent imaging results across the frequencies. In this paper two beamformers are proposed, namely a constant-beamwidth robust Capon beamformer (CBRCB) and a constant-powerwidth robust Capon beamformer (CPRCB), as extensions of RCB for consistent wideband acoustic imaging. Both CBRCB and CPRCB are more robust against array steering vector errors and finite sample size problems than SCB and have better resolution and interference suppression capability than data-independent beamformers. Moreover, they both can be efficiently implemented. The effectiveness of CBRCB and CPRCB is demonstrated via a number of simulated and experimental examples.
Correlation of ultrasonic scatterer size estimates for the statistical analysis and optimization of angular compounding
Authors: Gerig Anthony , Chen Quan , Zagzebski James , Varghese Tomy
Published: September 2004

Ultrasonic scatterer size estimates generally have large variances due to the inherent noise of spectral estimates used to calculate size. Compounding partially correlated size estimates associated with the same tissue, but produced with data acquired from different angles of incidence, is an effective way to reduce the variance without making dramatic sacrifices in spatial resolution. This work derives theoretical approximations for the correlation between these size estimates, and the coherence between their associated spectral estimates, as functions of ultrasonic system parameters. A Gaussian spatial autocorrelation function is assumed to adequately model scatterer shape. Both approximations compare favorably with simulation results, which consider validation near the focus. Utilization of the correlation/coherence expressions for statistical analysis and optimization is discussed. Approximations, such as the invariance of phase and amplitude terms with angle, are made to obtain closed-form solutions to the derived spectral coherence near the focus and permit analytical optimization analysis. Results indicate that recommended parameter adjustments for performance improvement generally depend upon whether, for the system under consideration, the primary source of change in total coherence with rotation is phase term variation due to the change in the relative position of scattering sites, or field amplitude term variation due to beam movement.
A fast Fourier transform on multipoles (FFTM) algorithm for solving Helmholtz equation in acoustics analysis
Authors: Ong Eng Teo , Lee Heow Pueh , Lim Kian Meng
Published: September 2004

This article presents a fast algorithm for the efficient solution of the Helmholtz equation. The method is based on the translation theory of the multipole expansions. Here, the speedup comes from the convolution nature of the translation operators, which can be evaluated rapidly using fast Fourier transform algorithms. Also, the computations of the translation operators are accelerated by using the recursive formulas developed recently by Gumerov and Duraiswami [SIAM J. Sci. Comput. 25, 1344–1381 (2003)]. It is demonstrated that the algorithm can produce good accuracy with a relatively low order of expansion. Efficiency analyses of the algorithm reveal that it has computational complexities of O(Na), where a ranges from 1.05 to 1.24. However, this method requires substantially more memory to store the translation operators as compared to the fast multipole method. Hence, despite its simplicity in implementation, this memory requirement issue may limit the application of this algorithm to solving very large-scale problems.
Estimated transmission beam pattern of clicks recorded from free-ranging white-beaked dolphins (Lagenorhynchus albirostris)
Authors: Rasmussen Marianne H. , Wahlberg Magnus , Miller Lee A.
Published: September 2004

Recordings were made from white-beaked dolphins in Icelandic waters using a four-hydrophone array in a star configuration. The acoustic signals were amplified and sampled to a hard disk at a rate of 800 kHz per channel. The 3 and 10 dB beamwidths were calculated to be 8° and 10°, respectively, indicating a narrower transmission beam for white-beaked dolphins than that reported for bottlenose dolphins (Tursiops truncatus). The beamwidth was more similar to that found for belugas (Delphinapterus lucas). The measured beam pattern included large side lobes, perhaps due to the inclusion of off-axis clicks, even after applying several criteria to select only on-axis clicks. The directivity index was calculated to be 18 dB when using all data for angles from 0°–50°. The calculated sound radiation from a circular piston with a radius of 6 cm driven by a white-beaked dolphin click had a beam pattern very similar to the measured beam pattern for the main transmission lobe of the white-beaked dolphin. The directivity index was 29 dB. This is the first attempt to estimate the directionality index of dolphins in the field. [Work supported by the Oticon Foundation and the Danish National Research Council.]
Listening difficulty as a subjective measure for evaluation of speech transmission performance in public spaces
Authors: Morimoto Masayuki , Sato Hiroshi , Kobayashi Masaaki
Published: September 2004

Listening difficulty ratings, using words with high word familiarity, are proposed as a new subjective measure for the evaluation of speech transmission in public spaces to provide realistic and objective results. Two listening tests were performed to examine their validity, compared with intelligibility scores. The tests included a reverberant signal and noise as detrimental sounds. The subject was asked to repeat each word and simultaneously to rate the listening difficulty into one of four categories: (1) not difficult, (2) a little difficult, (3) fairly difficult, and (4) extremely difficult. After the tests, the four categories were reclassified into, not difficult [response (1)] and some level of difficulty, (the other 3 responses). Listening difficulty is defined as the percentage of the total number of responses indicating some level of difficulty [i.e. not (1)]. The results of two listening tests demonstrated that listening difficulty ratings can evaluate speech transmission performance more accurately and sensitively than intelligibility scores for sound fields with higher speech transmission performance.
Method of evaluating dipole sound source in a finite computational domain
Authors: Takaishi T. , Ikeda M. , Kato C.
Published: September 2004

Numerical prediction of dipole sound based on Lighthill–Curle’s equation gives little information on the structure of sound sources. On the other hand, a hybrid method that combines the large eddy simulation (LES) and the compact Green’s function proposed by Howe provides detailed information on the vortices in the flow that most contribute to the generation of sound. However, when the dipole sound is evaluated from the momentum change in fluid inside a finite computational domain, the result does not in general agree with the sound evaluated from the fluctuating pressure on the body surface because contribution from vortices outside the computational domain is not taken into account. In this study, the balance of momentum in a finite computational domain is considered strictly, and the effect of outer vortices is replaced with contribution from inner properties by using an imaginary velocity potential φi. This process avoids sudden termination of Lighthill’s stress tensor at the outer boundary and extracts the net contribution from dipole sound sources. With this new method, this paper simulates dipole sound sources around pantograph horns numerically, and clarifies how strong dipole sound sources are formed in the shear layer close to the model surface and how the flow through holes plays an important role in cancellation of sound sources.
Fredholm integral equation for shape reconstruction of an underwater object using backscattered ramp response signatures
Authors: Li Wei , Liu G. R. , Varadan V. K.
Published: September 2004

Inverse scattering problems for identifying underwater objects are of importance for all kinds of applications in seas that occupy more than two-thirds of the surface of the earth. The physical optics approximation has been applied to the acoustic scattering integral representation, yielding an inverse scattering equation which relates the profile function of a submerged object to the Fourier transform of the complex backscattered acoustic field. This technique is the so-called ramp response technique and usually requires the full scattering information for all frequencies to obtain accurate profile function of an object. In order to retrieve the shape information of an object from the band-limited backscattered frequency data, a Fredholm integral equation is formulated in this paper for calculating the ramp response of the submerged object. This Fredholm integral equation is for the unknown ramp response of an object in terms of the known incomplete scattering information. The kernel of this integral equation is the inverse Fourier transform of the known characteristic function of the scattering information aperture. In order to simulate the real experiment environment, a computer-generated Gauss noise is added directly to the simulated impulse response. This noise-contaminated impulse response is then used for the inverse identification of the underwater object. It is found that adding noise would lead to the ill-posedness of this inverse scattering problem. To deal with the ill-posedness, the regularization method by filtering is employed. Numerical examples have confirmed that the method presented in this paper can successfully reconstruct the shape of an underwater object using an incomplete set of backscattered frequency data with or without noise contamination. Meanwhile, the effect of bandwidth to the ramp response is also discussed in the numerical examples.
A note on measurement of sound pressure with intensity probes
Authors: Juhl Peter , Jacobsen Finn
Published: September 2004

The effect of scattering and diffraction on measurement of sound pressure with “two-microphone” sound intensity probes is examined using an axisymmetric boundary element model of the probe. Whereas it has been shown a few years ago that the sound intensity estimated with a two-microphone probe is reliable up to 10 kHz when using 0.5 in. microphones in the usual face-to-face arrangement separated by a 12 mm spacer, the sound pressure measured with the same instrument will typically be underestimated at high frequencies. It is shown in this paper that the estimate of the sound pressure can be improved under a variety of realistic sound field conditions by applying a different weighting of the two pressure signals from the probe. The improved intensity probe can measure the sound pressure more accurately at high frequencies than an ordinary sound intensity probe or an ordinary sound level meter.
Implicit methods of solution to integral formulations in boundary element method based nearfield acoustic holography
Authors: Valdivia Nicolas , Williams Earl G.
Published: September 2004

Two integral equation methods are considered which can be inverted to provide the surface velocity and/or pressure given a measurement of the pressure on an imaginary surface in the nearfield of a vibrating or scattering body. This problem is central to nearfield acoustical holography (NAH). The integral equations are discretized using boundary element methods (BEMs). The integral equation methods considered are (1) an indirect formulation method based on the single layer integral equation and (2) a direct formulation method based on a system of equations derived from the Helmholtz–Kirchhoff integral equation. The formation of integral equations from the mentioned methods will not involve the explicit inversion of matrices, but instead will require this inversion to be done implicitly. Since these methods back-track the sound field from the measurement surface to the surface of the source/vibrator they are ill-posed in nature and Tikhonov regularization are used to stabilize the reconstruction. Problems are noted with the use of higher order shape functions in the BEM discretization which are detrimental to the inversion, and it is shown that the breakdown of the method at the interior resonance frequencies can be mitigated successfully. These two approaches are compared with the conventional direct method using measured experimental data from a point-driven rectangular plate.
Spectral methods for modelling guided waves in elastic media
Authors: Adamou A. T. I. , Craster R. V.
Published: September 2004

An efficient, accurate, and flexible numerical scheme based on spectral methods is developed here to determine dispersion curves and displacement/stress profiles for modes in elastic guiding structures, possibly curved, layered, damped, inhomogeneous, or anisotropic. Numerical examples and comparisons with existing techniques are given to demonstrate the efficiency and flexibility of the scheme.
Frequency specificity of distortion-product otoacoustic emissions produced by high-level tones despite inefficient cochlear electromechanical feedback
Authors: Carvalho Sirley , Mom Thierry , Gilain Laurent , Avan Paul
Published: September 2004

Distortion product otoacoustic emissions (DPOAEs) are thought to stem from the outer hair cells (OHCs) around the normally narrow place tuned to the primary tone stimuli. They are thus said to be frequency-specific: their local absence should accurately pinpoint local OHC damage. Yet the influence of impaired tuning on DPOAE frequency specificity is poorly documented. Mice with local damage to OHCs were examined. Their DPOAEs were frequency-specific in that audiometric notches were accurately tracked. The same cochleae were further impaired by ischemia or furosemide injection inducing strial dysfunction with flat loss of sensitivity and tuning, while the preexisting pattern of damaged OHCs remained unaltered. Despite the loss of cochlear activity, DPOAEs produced by high-level (⩾70 dB SPL) primaries remained large in about the same interval where they had been initially normal, i.e., that with nondamaged OHCs, albeit with a slight frequency shift, of −1.1 kHz on average. Thus, the ability of DPOAEs to map structurally intact OHCs cannot be a mere consequence of cochlear tuning as it largely persists in its absence. The key element for this correct mapping is likely part of intact OHC structures (e.g., stereocilia bundles) and must have some tuning of its own.
A wide-angle on-surface radiation condition applied to scattering by spheroids
Authors: Calvo David C.
Published: September 2004

A rational approximation of the pseudo-differential Dirichlet-to-Neumann operator for a circular cylinder is made using zero placement. For an acoustically hard circular cylinder, this zero corresponds to the dominant creeping-wave singularity in the residue series for the time-harmonic free-space surface Green’s function. Based on this operator, a wide-angle on-surface radiation condition (OSRC) is developed first for two-dimensional slender convex bodies. For the object scattering problem, this OSRC is accurate for wide-scattering angles relative to the surface normal. The notion of creeping waves is then used to develop a wide-angle, three-dimensional OSRC applicable to smooth convex bodies. Application to both hard and soft, prolate and oblate spheroids is presented, and excellent agreement is found in comparison with a more costly technique.
On the dichotomy in auditory perception between temporal envelope and fine structure cues (L)
Authors: Zeng Fan-Gang , Nie Kaibao , Liu Sheng , Stickney Ginger , Del Rio Elsa , Kong Ying-Yee , Chen Hongbin
Published: September 2004

It is important to know what cues the sensory system extracts from natural stimuli and how the brain uses them to form perception. To explore this issue, Smith, Delgutte, and Oxenham [Nature (London) 416, 87–90 (2002)] mixed one sound’s temporal envelope with another sound’s fine temporal structure to produce auditory chimaeras and found that “the perceptual importance of the envelope increases with the number of frequency bands, while that of the fine structure diminishes.” This study addressed two technical issues related to natural cochlear filtering and artificial filter ringing in the chimaerizing algorithm. In addition, this study found that the dichotomy in auditory perception revealed by auditory chimaeras is an epiphenomenon of the classic dichotomy between low- and high-frequency processing. Finally, this study found that the temporal envelope determines sound location as long as the interaural level difference cue is present. The present result reinforces the original hypothesis that the temporal envelope is critical for speech perception whereas temporal fine structure is critical for pitch perception, but does not support the assertion regarding the temporal envelope and fine structure as the acoustic basis for the “what” and “where” mechanisms.
Thin, lightweight electroacoustic projector for low frequency underwater applications
Authors: Tressler James F. , Howarth Thomas R. , Carney Walter L.
Published: September 2004

A thin, lightweight oil-filled electroacoustic projector has been designed and fabricated for application on unmanned underwater vehicles (UUVs) and autonomous unmanned vehicles (AUVs) used in littoral environments. The projector has dimensions of 381 mm×280 mm×64 mm and weighs 26 N in water. The acoustic aperture consists of 294 cymbal-type miniature Class V flextensional drivers. These 294 elements are divided into six independent modules of 49 cymbals wired together electrically in parallel. The six modules, in turn, are wired so that they can be easily combined together electrically either in parallel, series, or as a combination of both. Based on the VA power curve and a low duty cycle input voltage, an acoustic source level of at least 180 dB (re: 1 μPa @ 1 m) is attainable across the frequency span ∼3–15 kHz. This particular design is best suited for shallow water, but is shown to still be operable at water depths up to 200 meters without significant degradation in performance.
Resonance frequency of microbubbles: Effect of viscosity
Authors: Khismatullin Damir B.
Published: September 2004

The transmitted frequency at which a gas bubble of millimeter or submillimeter size oscillates resonantly in a low-viscosity liquid is approximately equal to the undamped natural frequency (referred to as the Minnaert frequency if surface tension effects are disregarded). Based on a theoretical analysis of bubble oscillation, this paper shows that such an approximation cannot be validated for microbubbles used in contrast-enhanced ultrasound imaging. The contrast-agent microbubbles represent either encapsulated bubbles of size less than 10 μm or free (nonencapsulated) bubbles of submicron size. The resonance frequency of the microbubbles deviates significantly from the undamped natural frequency over the whole range of microbubble sizes due to the increased viscous damping coefficient. The difference between these two frequencies is shown to have a tremendous impact on the resonant backscatter by the microbubbles. In particular, the first and second harmonics of the backscattered signal from the microbubbles are characterized by their own resonance frequencies, equal to neither the microbubble resonance frequency nor the undamped natural frequency.
Time reversal and the spatio-temporal matched filter (L)
Authors: Chambers D. H. , Candy J. V. , Lehman S. K. , Kallman J. S. , Poggio A. J. , Meyer A. W.
Published: September 2004

It is known that focusing of an acoustic field by a time-reversal mirror (TRM) is equivalent to a spatio-temporal matched filter under conditions where the Green’s function of the field satisfies reciprocity and is time invariant, i.e., the Green’s function is independent of the choice of time origin. In this letter, it is shown that both reciprocity and time invariance can be replaced by a more general constraint on the Green’s function that allows a TRM to implement the spatio-temporal matched filter even when conditions are time varying.
The discrimination of baboon grunt calls and human vowel sounds by baboons
Authors: Hienz Robert D. , Jones April M. , Weerts Elise M.
Published: September 2004

The ability of baboons to discriminate changes in the formant structures of a synthetic baboon grunt call and an acoustically similar human vowel (/ɛ/) was examined to determine how comparable baboons are to humans in discriminating small changes in vowel sounds, and whether or not any species-specific advantage in discriminability might exist when baboons discriminate their own vocalizations. Baboons were trained to press and hold down a lever to produce a pulsed train of a standard sound (e.g., /ɛ/ or a baboon grunt call), and to release the lever only when a variant of the sound occurred. Synthetic variants of each sound had the same first and third through fifth formants (F1 and F3–5), but varied in the location of the second formant (F2). Thresholds for F2 frequency changes were 55 and 67 Hz for the grunt and vowel stimuli, respectively, and were not statistically different from one another. Baboons discriminated changes in vowel formant structures comparable to those discriminated by humans. No distinct advantages in discrimination performances were observed when the baboons discriminated these synthetic grunt vocalizations.
Auditory stream segregation in monkey auditory cortex: effects of frequency separation, presentation rate, and tone duration
Authors: Fishman Yonatan I. , Arezzo Joseph C. , Steinschneider Mitchell
Published: September 2004

Auditory stream segregation refers to the organization of sequential sounds into “perceptual streams” reflecting individual environmental sound sources. In the present study, sequences of alternating high and low tones, “…ABAB…,” similar to those used in psychoacoustic experiments on stream segregation, were presented to awake monkeys while neural activity was recorded in primary auditory cortex (A1). Tone frequency separation (ΔF), tone presentation rate (PR), and tone duration (TD) were systematically varied to examine whether neural responses correlate with effects of these variables on perceptual stream segregation. “A” tones were fixed at the best frequency of the recording site, while “B” tones were displaced in frequency from “A” tones by an amount=ΔF. As PR increased, “B” tone responses decreased in amplitude to a greater extent than “A” tone responses, yielding neural response patterns dominated by “A” tone responses occurring at half the alternation rate. Increasing TD facilitated the differential attenuation of “B” tone responses. These findings parallel psychoacoustic data and suggest a physiological model of stream segregation whereby increasing ΔF, PR, or TD enhances spatial differentiation of “A” tone and “B” tone responses along the tonotopic map in A1.
Pseudo-surface waves above thin porous layers (L)
Authors: Allard Jean F. , Henry Michel , Gareton Vincent
Published: September 2004

The total monopole field above thin porous layers for small source-receiver distances is a complex superposition of different contributions. It is shown that the dependence of the amplitude on the distance from the layer is exponential, close to the layer, and the same as for the surface wave related to the pole located at an angle of incidence θp close to π/2. The localization of this pole obtained for a thin layer from this property is compared to measurements performed with a recent transfer function method based on pressure measurements at different source-receiver distances. In this paper, we evaluate cos θp from pressure measurements on an axis perpendicular to the surface of the layer at small source-receiver offsets, thus this method can be used with small sample sizes.
An acoustic description of the vowels of Northern and Southern Standard Dutch
Authors: Adank Patti , van Hout Roeland , Smits Roel
Published: September 2004

A database is presented of measurements of the fundamental frequency, the frequencies of the first three formants, and the duration of the 15 vowels of Standard Dutch as spoken in the Netherlands (Northern Standard Dutch) and in Belgium (Southern Standard Dutch). The speech material consisted of read monosyllabic utterances in a neutral consonantal context (i.e., /sVs/). Recordings were made for 20 female talkers and 20 male talkers, who were stratified for the factors age, gender, and region. Of the 40 talkers, 20 spoke Northern Standard Dutch and 20 spoke Southern Standard Dutch. The results indicated that the nine monophthongal Dutch vowels /a ɑ ɛ i ɪ ɔ u y ʏ/ can be separated fairly well given their steady-state characteristics, while the long mid vowels /e o ø/ and three diphthongal vowels /ɛɪ ɔu y/ also require information about their dynamic characteristics. The analysis of the formant values indicated that Northern Standard Dutch and Southern Standard Dutch differ little in the formant frequencies at steady-state for the nine monophthongal vowels. Larger differences between these two language varieties were found for the dynamic specifications of the three long mid vowels, and, to a lesser extent, of the three diphthongal vowels.
The acoustic analysis of tone differentiation as a means for assessing tone production in speakers of Cantonese
Authors: Barry Johanna G. , Blamey Peter J.
Published: September 2004

This paper reports on a methodology for acoustically analyzing tone production in Cantonese. F0 offset versus F0 onset are plotted for a series of tokens for each of the six tones in the language. These are grouped according to tone type into a set of six ellipses. Qualitative visual observations regarding the degree of differentiation of the ellipses within the tonal space are summarized numerically using two indices, referred to here as Index 1 and Index 2. Index 1 is a ratio of the area of the speaker’s tonal space and the average of the areas of the ellipses of the three target tones making up the tonal space. Index 2 is a ratio of the average distance between all six tonal ellipses and the average of the sum of the two axes for all six tone ellipses. Using this methodology, tonal differentiation is compared for three groups of speakers; normally hearing adults; normally hearing children aged from 4–6 years; and, prelinguistically deafened cochlear implant users aged from 4–11 years. A potential conundrum regarding how tone production abilities can outstrip tone perception abilities is explained using the data from the acoustic analyses. It is suggested that young children of the age range tested are still learning to normalize for pitch level differences in tone production. Acoustic analysis of the data thus supports results from tone perception studies and suggests that the methodology is suitable for use in studies investigating tone production in both clinical and research contexts.
Sound generation by steady flow through glottis-shaped orifices
Authors: Zhang Zhaoyan , Mongeau Luc , Frankel Steven H. , Thomson Scott , Park Jong Beom
Published: September 2004

Although the signature of human voice is mostly tonal, it also includes a significant broadband component. Quadrupolelike sources due to turbulence in the region downstream of the glottis, and dipolelike sources due to the force applied by the vocal folds onto the surrounding fluid are the two primary broadband sound generating mechanisms. In this study, experiments were conducted to characterize the broadband sound emissions of confined stationary jets through rubber orifices formed to imitate the approximate shape of the human glottis at different stages during one cycle of vocal fold vibrations. The radiated sound pressure spectra downstream of the orifices were measured for varying flow rates, orifice shapes, and gas mixtures. The nondimensional sound pressure spectra were decomposed into the product of three functions: a source function F, a radiation efficiency function M, and an acoustic response function G. The results show that, as for circular jets, the quadrupole source contributions dominated for straight and convergent orifices. For divergent jets, whistling tonal sounds were emitted at low flow rates. At high flow rates for the same geometry, dipole contributions dominated the sound radiated by free jets. However, possible source-load acoustic feedback may have hampered accurate source identification in confined flows.
Spectral loudness summation and simple reaction time
Authors: Wagner Eva , Florentine Mary , Buus Søren , McCormack Joseph
Published: September 2004

The present study evaluates the relation between loudness and simple reaction time (RT). Loudness matches between a narrowband noise (125 Hz wide) and a broadband noise (1500 Hz) were made at levels from near threshold to near 100 dB SPL. Over a similarly wide range of levels, RT to each of the noise bands was also measured. As reported often in previous loudness-matching studies, loudness summation depended strongly on level. With increasing SPL, the level difference between the noises needed to keep them equally loud first increased, to around 10 dB at moderate levels, and then decreased. Except for one listener, the RT data show the same pattern. The level difference needed to keep RT to the two noises the same first increased and then decreased. These results show that RT is closely related to loudness, but not to sensation level. If RT depended on sensation level, the level difference between the two noises needed to achieve equal RT would not change with SPL because the difference in sensation level between two sounds is a constant. Overall, the average results provide strong support for the contention that simple RT and loudness are closely related.
Electromagnetoacoustic surface waves on dispersive piezoelectric layered media
Authors: Romeo Maurizio
Published: September 2004

A full electromagnetic approach is employed to study the propagation of SH surface waves on a piezoelectric solid layer superimposed on a piezoelectric solid substrate. The materials of the layered structure allow for dielectric dispersion and two different boundary conditions are considered at the free surface. The dispersion laws for both boundary conditions are derived in a general form and some special cases are discussed. The solutions of the dispersion equations reveal that besides the expected quasi-acoustic dispersive waves, new quasi-electromagnetic modes exist which propagate at high speeds and depths within the layered structure. These dispersive modes occur also in nondispersive materials. Moreover, in addition to subsonic quasi-acoustic modes, accounting for dielectric dispersion gives rise to quasi-acoustic surface modes whose speed exceeds the bulk wave speed of the layer. Special electroelastic surface waves are also discussed which are characterized by the absence of mechanical perturbation in the substrate.