bluuebunny/crossref_metadata_2025 huggingface dataset:
Localized Mixing Due to an Interfacial Solitary Wave Breaking on Seabed Topography in Different Ridge Heights
Authors: Chen Chen-Yuan , Chen Cheng-Wu , Tseng I-Fan
Published: July 2007

Experiments were carried out in a wave flume on internal solitary wave (ISW) of depression-type propagating over a submarine ridge in triangular shape. Tests were arranged in series from combinations of submarine ridges in different height and ISW in different wave amplitudes. The resultant wave motions were found differing from that of surface gravity waves. Experimental results suggested the blockage parameter ζ can be applied to classify various degrees of ISW–ridge interaction, i.e., ζ<0.5 for weak encounter, 0.5<ζ<0.7 for moderate encounter, and 0.7<ζ for wave breaking. In addition, three categories of ISW–ridge interaction were also employed by the relationship between the degree of blocking B and dimensionless wave amplitude ai∕H2.
Ice Loads Acting on a Model Podded Propeller Blade
(OMAE2005-67416)
Authors: Wang Jungyong , Akinturk Ayhan , Jones Stephen J. , Bose Neil , Kim Moon-Chan , Chun Ho-Hwan
Published: July 2007

With the increase in popularity of podded propulsors and arctic navigation, understanding the interaction between a podded propulsor and ice has become more important. Propeller-ice interaction itself is a complicated process with a high level of uncertainty resulting from the uncertainties associated with the properties of the ice and with the propeller-ice interaction conditions. Model tests provide relatively well-controlled ice properties and interaction conditions to reduce the uncertainties. In order to improve the understanding of this interaction and to develop numerical models of it, a model podded propulsor was used in “Puller” mode, and ice loads were measured on its instrumented blade and propeller shaft. The results of the experiments conducted to simulate the interactions (milling) of the instrumented blade with ice in different operating conditions are reported in this paper. Loads measured during the milling consist of ice milling loads, “inseparable” hydrodynamic loads, and “separable” hydrodynamic loads. The sample results presented here include ice milling and inseparable hydrodynamic loads for various advance coefficients and depths of cut (amount of blade penetration into ice). Some results are compared with existing ice load models.
Hydroelastic Response of a Matlike Floating Circular Plate Advancing in Waves
Authors: Matsui Tetsuya
Published: July 2007

The boundary value problem is formulated to predict the hydroelastic response of a matlike floating circular plate advancing slowly in waves. The plate is idealized as an elastic plate with zero draught, and the potential flow theory is employed with low forward-speed assumptions. These assumptions allow the steady disturbance potential due to forward speed to be neglected, simplifying the problem considerably. By applying the eigenfunction-expansion domain-matching method, analytical solutions are derived for the scattering and radiation potentials up to the leading-order terms of the speed-dependent parts. The far-field approach is adopted to obtain the expression for the wave drift force. Numerical results are also presented for the typical plate geometry, which demonstrates the significant effect of the forward speed on the hydroelastic response and wave drift force.
Tensile Properties of Cold Bends for Line Pipes
Authors: Fukuda Naoki , Yatabe Hiroshi , Masuda Tomoki , Toyoda Masao
Published: July 2007

To comprehensively investigate the tensile properties of cold bends, full-scale cold bending experiments, tensile tests using prestrained small-scale specimens, and finite element (FE) analyses of the cold bending processes were conducted on API 5L X60 and X80 grade line pipes. The tensile tests revealed that the tensile properties of the cold bends were comparable to the uniaxially prestrained specimens machined from the straight part of the pipes. A FE model simulating the cold bending process was verified with the full-scale experimental results in terms of the distributions of residual strains. These results supported a procedure for estimating the tensile properties of the cold bends with a combination of the FE model and the tensile tests using the prestrained specimens; the residual strains obtained from the FE model are transformed into the tensile properties based on the relationship between the residual strains and the tensile properties. This study clarified that the tensile properties come close to being uniformly distributed by reducing the distance between the bending locations; the distance between the bending locations has a significant influence on the overlap of adjacent deformed areas, which governs the distribution of the tensile properties of the cold bends.
Two Benchmark Problems for Three-Dimensional, Linear Hydroelasticity
Authors: Riggs H. R. , Niimi K. M. , Huang L. L.
Published: July 2007

There has been substantial development in computer codes for three-dimensional linear hydroelasticity, but to the authors’ knowledge, there are no problems of sufficient complexity put forth in the open literature to serve as appropriate benchmark problems for a floating structure. We present in this paper detailed descriptions of two such problems for three-dimensional hydroelastic computer codes. The first structure is a rectangular, box-shaped “barge” with dimensions 100 m×10 m×2 m. The second is a Wigley hull with dimensions 100 m×10 m×4.5 m. In both cases, the deformational response is primarily global. Detailed descriptions of each structure, the finite element structural shell models, and the hydrodynamic fluid models, based on the constant panel Green’s function method, are provided. Fine meshes are used to minimize discretization errors. Detailed results, including dry natural periods and modes, wet natural periods, and wave-induced displacements and stresses, are presented. The detail is sufficient for others to use the problems as benchmarks for computer codes.
A Numerical Feasibility Study of a Parametric Roll Advance Warning System
Authors: Shaw McCue Leigh , Bulian Gabriele
Published: July 2007

This work studies the practicality of using finite-time Lyapunov exponents (FTLEs) to detect the inception of parametric resonance for vessels operating in irregular longitudinal seas. Parametrically excited roll motion is modeled as a single-degree-of-freedom system, with nonlinear damping and restoring terms. FTLEs are numerically calculated at every integration time step. Using this numerical model of parametric roll and through tracking trends in the FTLE time series behavior, warnings of parametric roll are identified. This work serves as a proof of concept of the FTLE technique’s viability in detecting parametric resonance. The ultimate aim of the research contained in this paper, along with future work, is the development of a real-time, onboard aid to warn of impending danger allowing for avoidance of severe, even catastrophic, vessel instabilities.
On the Mechanics of Residual Stresses in Girth Welds
Authors: Dong P.
Published: July 2007

In this paper, some of the important controlling parameters governing weld residual stress distributions are presented for girth welds in pipe and vessel components, based on a large number of residual stress solutions available to date. The focus is placed upon the understanding of some of the overall characteristics in through-wall residual stress distributions and their generalization for vessel and pipe girth welds. In doing so, a unified framework for prescribing residual stress distributions is outlined for fitness-for-service assessment of vessel and pipe girth welds. The effects of various joint geometry and welding procedure parameters on through thickness residual stress distributions are also demonstrated in the order of their relative importance.
Stresses in a Cylinder Subjected to an Internal Shock
Authors: Leishear Robert A.
Published: July 2007

Hoop stresses due to a moving shock front in either a gas or liquid filled cylinder can be approximated using vibration theory. The equation of motion can be combined with hoop stress equations to describe the dynamic changes in hoop stress to provide insight into the phenomenon of flexural resonance, which creates pipe stresses significantly in excess of the stresses expected from a slowly applied, or static, pressure loading. To investigate flexural resonance, vibration equations were successfully compared to available experimental results. At shock velocities, the maximum hoop stress is related to a vibration equation for a suddenly applied load. Consideration of structural and fluid damping, as well as pipe constraints at the end of the pipe, were considered in the derivation of the vibration equations. In short, vibration equations are presented in this paper and are compared to available experimental work. The equations describe hoop stresses in a pipe when a step increase in pressure travels the bore of a pipe at sonic or supersonic velocities.
Combination of Longitudinal and Transverse Ultrasonic Waves for In Situ Control of the Tightening of Bolts
Authors: Chaki Salim , Corneloup Gilles , Lillamand Ivan , Walaszek Henri
Published: July 2007

The feasibility of an absolute ultrasonic measurement of the tightening force in bolts was investigated. For this purpose, we used both longitudinal and transverse ultrasonic waves (bi-wave method) to remove the time-of-flight measurement of waves in the unstressed state. To avoid the systematic calibration tests (generally carried out before tightening control), an experimental method has been applied. This method allows determination of the effective length under stress and the difference between longitudinal and transverse acoustoelastic coefficients of a tightened bolt. The results show that the proposed method can provide absolute measurement of the tightening force without either loosening the bolt or performing systematically calibration tests with an uncertainty estimated on the order of ±10% at 95% reliability.
Three-Dimensional Identification of Semi-Elliptical Surface Crack by Means of Direct-Current Electrical Potential Difference Method With Multiple-Probe Sensor
Authors: Tada Naoya , Okada Masayoshi , Iwamoto Jun
Published: July 2007

A method of three-dimensional identification of a semi-elliptical surface crack by direct-current electrical potential difference method with a multiple-probe sensor was proposed and its validity was numerically examined. The condition of the surface crack embedded in a conductive plate was specified by the two-dimensional location of the crack center, length, and depth of the crack, and the surface and inward angles of the crack plane. Identification was carried out based on the distribution of the electrical potential difference around the crack measured on the surface of the plate with the “multiple-probe sensor” which is composed of many probes aligned in two orthogonal directions. The location and surface angle were evaluated using the point symmetry of the potential difference distribution. The inward angle was determined by the magnitude of symmetry of potential difference distribution with reference to the evaluated crack line. Finally, length and depth of the crack were determined using the exact solution of potential difference for an inclined inner elliptical crack which yields similar potential difference to that of the inclined semi-elliptical surface crack. The validity of the method was numerically confirmed by carrying out the evaluation based on the result obtained by finite element analysis.
Influence of Data Analysis Method and Allowable Stress Criterion on Allowable Stress of Gr.122 Heat Resistant Steel
Authors: Maruyama Kouichi , Yoshimi Kyosuke
Published: July 2007

Long-term creep rupture life is usually evaluated from short-term data by a time-temperature parameter (TTP) method. The allowable stress of Gr.122 steel listed in the ASME code has been evaluated by this method and is recognized to be overestimated. The objective of the present study is to understand the causes of the overestimation and propose appropriate methodology for avoiding the overestimation. The apparent activation energy Q for rupture life of the steel changes from a high value of short-term creep to a low value of long-term creep. However, the decrease in Q is ignored in the conventional TTP analyses, resulting in the overestimation of rupture life. A multiregion analysis of creep rupture data is employed to avoid the overestimation; in the analysis creep rupture data are divided into a couple of regions so that the Q value is unique in each divided region. The multiregion analysis provides a good fit to the data and the lowest value of 105h creep rupture strength among the three ways of data analysis examined. A half of 0.2% proof stress cannot provide an appropriate boundary for dividing data to be used in the multiregion analysis. In the 2001 edition of the ASME code an F average concept has been proposed as a substitution for the safety factor of 2∕3 for average rupture stress. The allowable stress of Gr.122 steel changes significantly depending on the allowable stress criteria as well as the methods of rupture data analysis: i.e., from 74MPato48MPa.
High Temperature Oxidation of Cr-Mo Steels in the Context of Accelerated Rupture Testing for Creep Life Prediction
Authors: Al-Mazrouee A. , Singh Raman R. K.
Published: July 2007

Accelerated creep rupture testing is used to aid in assessing the remaining life for components such as pipes and tubes used in high temperature plants. At the high temperatures, oxide growth can affect the creep results by diameter reduction and, thus, increase the stress. This paper includes the study of oxide-scale growth and diameter reduction kinetics during air oxidation of two Cr-Mo steels used in the manufacture of boiler tubing. Tests were at 500–700°C for times up to 1000h for 1.25Cr-0.5Mo and 2.25Cr-1Mo steels (using cylindrical specimens similar to those used for creep testing). At 500–600°C, 2.25Cr-1Mo steels showed a superior oxidation resistance than 1.25Cr-0.5Mo steels. However, at 700°C, the oxidation resistance of 1.25Cr-0.5Mo and 2.25Cr-1Mo steels was similar. Multilayer oxide formation was observed to occur in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, involving oxides with various compositions. It is suggested that inaccuracies in creep data may arise as a result of the cross-sectional losses of the specimens. This inaccuracy may also cause discrepancies in life assessment.
Quantitative Prediction of EAC Crack Growth Rate of Sensitized Type 304 Stainless Steel in Boiling Water Reactor Environments Based on EPFEM
Authors: Xue He , Shoji Tetsuo
Published: July 2007

The quantitative prediction of environmentally assisted cracking (EAC) or stress corrosion cracking (SCC) is essential in order to predict service life and also the structural integrity and safety assessment of light water reactors. During the last 3 decades many of the research results obtained on the quantitative prediction of the EAC crack growth rate have been based on linear fracture mechanics. In order to investigate EAC behavior in the high strain zone of important structures in light water reactors, the approach taken in this paper is one in which quantitative calculations of the EAC crack growth rate, incorporating the SCC deformation /oxidation model and the elastic-plastic finite element method (EPFEM), are carried out. This approach can be used for the quantitative prediction of EAC crack growth rate in both the low and high strain zones of key structures in light water reactors. The crack growth behavior of sensitized type 304 stainless steel with a 1T-CT specimen in simulated boiling water reactor (BWR) environments is analyzed based on this approach. The effect of several environmental, material, and mechanical parameters on the EAC crack growth rate of nickel based alloys in high-temperature aqueous environments is also discussed.
Hybrid Expansion Revisited
Authors: Yokell Stanley
Published: July 2007

This paper describes new hitherto unused procedures that combine hydraulic and explosive expanding to produce tube-to-tubesheet joints in tubular heat transfer equipment with thick tubesheets. This paper also interprets shear load test results and microscopic examination of polished and sectioned specimens used to validate the adequacy of the method for producing strong, leak tight joints. It concludes that the method is successful.
Critical Velocity of a Nonlinearly Supported Multispan Tube
Bundle
Authors: Au-Yang M. K. , Burgess J. A.
Published: July 2007

The phenomenon of fluid-elastic instability and the velocity at which a heat exchanger tube bundle becomes unstable, known as the critical velocity, was discovered and empirically determined based upon single-span, linearly supported tube bundles. In this idealized configuration, the normal modes are well separated in frequency with negligible cross-modal contribution to the critical velocity. As a result, a critical velocity can be defined and determined for each mode. In an industrial heat exchanger or steam generator, not only do the tube bundles have multiple spans, they are also supported in oversized holes. The normal modes of a multispan tube bundle are closely spaced in frequency and the nonlinear effect of the tube-support plate interaction further promotes cross-modal contribution to the tube responses. The net effect of cross-modal participation in the tube vibration is to delay the instability threshold. Tube bundles in industrial exchangers often have critical velocities far above what were determined in the laboratory based upon single-span, linearly supported tube bundles. In this paper, the authors attempt to solve this nonlinear problem in the time domain, using a time history modal superposition method. Time history forcing functions are first obtained by inverse Fourier transform of the power spectral density function used in classical turbulence-induced vibration analyses. The fluid-structure coupling force, which is dependent on the cross-flow velocity, is linearly superimposed onto the turbulence forcing function. The tube responses are then computed by direct integration in the time domain. By gradually increasing the cross-flow velocity, a threshold value is obtained at which the tube response just starts to diverge. The value of the cross-flow velocity at which the tube response starts to diverge is defined as the critical velocity of this nonlinearly supported, multispan tube bundle.
Limit Load Analysis of Cracked Components Using the Reference Volume Method
Authors: Adibi-Asl R. , Seshadri R.
Published: July 2007

Cracks and flaws occur in mechanical components and structures, and can lead to catastrophic failures. Therefore, integrity assessment of components with defects is carried out. This paper describes the Elastic Modulus Adjustment Procedures (EMAP) employed herein to determine the limit load of components with cracks or crack-like flaw. On the basis of linear elastic Finite Element Analysis (FEA), by specifying spatial variations in the elastic modulus, numerous sets of statically admissible and kinematically admissible distributions can be generated, to obtain lower and upper bounds limit loads. Due to the expected local plastic collapse, the reference volume concept is applied to identify the kinematically active and dead zones in the component. The Reference Volume Method is shown to yield a more accurate prediction of local limit loads. The limit load values are then compared with results obtained from inelastic FEA. The procedures are applied to a practical component with crack in order to verify their effectiveness in analyzing crack geometries. The analysis is then directed to geometries containing multiple cracks and three-dimensional defect in pressurized components.
Design and Stress Analysis of a New Quick-Opening Seal Device Connected by D-Shaped Shearing Bolts
Authors: Chen Ping , Qian Caifu , Zhang Yunxiao
Published: July 2007

Because of large scale and heavy weight, end closures of high pressure vessels are usually hard to assemble and disassemble. In this paper, a new quick-opening seal device connected by D-shaped shearing bolts is introduced. This device is compact in structure, reliable in sealing, easy in assembly and disassembly, and very appropriate for end closures of pressure vessels or for pipe joints. Strength calculation formulas for the major parts are proposed analytically, and stress analysis using the finite element method for a C-ring seal has been performed. An application of this device shows that its sealing and strength is reliable.
Frequency dependence and intensity fluctuations due to shallow water internal waves
Authors: Badiey Mohsen , Katsnelson Boris G. , Lynch James F. , Pereselkov Serguey
Published: July 2007

A theory and experimental results for sound propagation through an anisotropic shallow water environment are presented to examine the frequency dependence of the scintillation index in the presence of internal waves. The theory of horizontal rays and vertical modes is used to establish the azimutal and frequency behavior of the sound intensity fluctuations, specifically for shallow water broadband acoustic signals propagating through internal waves. This theory is then used to examine the frequency dependent, anisotropic acoustic field measured during the SWARM'95 experiment. The frequency dependent modal scintillation index is described for the frequency range of 30–200Hz on the New Jersey continental shelf.
Pseudo-damping in undamped plates and shells
Authors: Carcaterra A. , Akay A. , Lenti F.
Published: July 2007

Pseudo-damping is a counter-intuitive phenomenon observed in a special class of linear structures that exhibit an impulse response characterized by a decaying amplitude, even in the absence of any dissipation mechanism. The conserved energy remains within but designated parts of the system. Pseudo-damping develops when the natural frequency distribution of the system includes condensation points. The recently formulated theoretical foundation of this phenomenon, based on mathematical properties of special trigonometric series, makes it possible to describe a class of mechanical systems capable of displaying pseudo-damping characteristics. They include systems with discrete oscillators and one-dimensional continuous beamlike structures already reported by the authors in recent studies. This paper examines development of pseudo-damping phenomenon in two-dimensional structures, using plates and shells as examples, and shows how a preloaded plate on an elastic foundation can lead to pseudo-damping. Moreover, in the case of curved shell elements examined here, pseudo-damping can result due to the curvature of the structure, which naturally introduces condensation points in the modal density.
Analytical approximations for the modal acoustic impedances of simply supported, rectangular plates
Authors: Graham W. R.
Published: July 2007

Coupling of the in vacuo modes of a fluid-loaded, vibrating structure by the resulting acoustic field, while known to be negligible for sufficiently light fluids, is still only partially understood. A particularly useful structural geometry for the study of this problem is the simply supported, rectangular flat plate, since it exhibits all the relevant physical features while still admitting an analytical description of the modes. Here the influence of the fluid can be expressed in terms of a set of doubly infinite integrals over wave number: the modal acoustic impedances. Closed-form solutions for these impedances do not exist and, while their numerical evaluation is possible, it greatly increases the computational cost of solving the coupled system of modal equations. There is thus a need for accurate analytical approximations. In this work, such approximations are sought in the limit where the modal wavelength is small in comparison with the acoustic wavelength and the plate dimensions. It is shown that contour integration techniques can be used to derive analytical formulas for this regime and that these formulas agree closely with the results of numerical evaluations. Previous approximations [Davies, J. Sound Vib. 15(1), 107–126 (1971)] are assessed in the light of the new results and are shown to give a satisfactory description of real impedance components, but (in general) erroneous expressions for imaginary parts.
Wave model of the cat tympanic membrane
Authors: Parent Pierre , Allen Jont B.
Published: July 2007

In order to better understand signal propagation in the ear, a time-domain model of the tympanic membrane (TM) and of the ossicular chain (OC) is derived for the cat. Ossicles are represented by a two-port network and the TM is discretized into a series of transmission lines, each one characterized by its own delay and reflection coefficient. Volume velocity samples are distributed along the ear canal, the eardrum, and the middle ear, and are updated periodically to simulate wave propagation. The interest of the study resides in its time-domain implementation—while most previous related works remain in the frequency domain—which provides not only a direct observation of the propagating wave at each location, but also insight about how the wave behaves at the ear canal/TM interface. The model is designed to match a typical impedance behavior and is compared to previously published measurements of the middle ear (the canal, the TM, the ossicles and the annular ligament). The model matches the experimental data up to 15kHz.
Transmission matrix analysis of the chinchilla middle ear
Authors: Songer Jocelyn E. , Rosowski John J.
Published: July 2007

Despite the common use of the chinchilla as an animal model in auditory research, a complete characterization of the chinchilla middle ear using transmission matrix analysis has not been performed. In this paper we describe measurements of middle-ear input admittance and stapes velocity in ears with the middle-ear cavity opened under three conditions: intact tympano-ossicular system and cochlea, after the cochlea has been drained, and after the stapes has been fixed. These measurements, made with stimulus frequencies of 100–8000Hz, are used to define the transmission matrix parameters of the middle ear and to calculate the cochlear input impedance as well as the middle-ear output impedance. This transmission characterization of the chinchilla middle ear will be useful for modeling auditory sensitivity in the normal and pathological chinchilla ear.
Wild African elephants (Loxodonta africana) discriminate between familiar and unfamiliar conspecific seismic alarm calls
Authors: O’Connell-Rodwell Caitlin E. , Wood Jason D. , Kinzley Colleen , Rodwell Timothy C. , Poole Joyce H. , Puria Sunil
Published: July 2007

The ability to discriminate between call types and callers as well as more subtle information about the importance of a call has been documented in a range of species. This type of discrimination is also important in the vibrotactile environment for species that communicate via vibrations. It has recently been shown that African elephants (Loxodonta africana) can detect seismic cues, but it is not known whether they discriminate seismic information from noise. In a series of experiments, familiar and unfamiliar alarm calls were transmitted seismically to wild African elephant family groups. Elephants respond significantly to the alarm calls of familiar herds (p=0.004) but not to the unfamiliar calls and two different controls, thus demonstrating the ability of elephants to discriminate subtle differences between seismic calls given in the same context. If elephants use the seismic environment to detect and discriminate between conspecific calls, based on the familiarity of the caller or some other physical property, they may be using the ground as a very sophisticated sounding board.
Monitoring near-shore shingle transport under waves using a passive acoustic technique
Authors: Mason T. , Priestley D. , Reeve D. E.
Published: July 2007

Passive acoustic techniques have been used to measure shingle (gravel) sediment transport in very shallow water, near the wave breaking zone on a beach. The experiments were conducted at 1:1 scale in the Large Wave Flume, Große Wellen Kanal (GWK) at Hannover, Germany. The frequency spectrum induced by shingle mobilized under breaking waves can be distinguished from other ambient noise, and is found to be independent of water depth and wave conditions. The inverse relationship between centroid frequency and representative grain size is shown to remain valid in shallow water wave conditions. Individual phases of onshore and offshore transport can be identified. Analysis of the acoustic frequency spectrum provides insight into the mechanics of phase-resolved shingle transport.
Oscillation and extinction thresholds of the clarinet: Comparison of analytical results and experiments
Authors: Dalmont Jean-Pierre , Frappé Cyrille
Published: July 2007

In the context of a simplified model of the clarinet in which the losses are assumed to be frequency independent the analytic expressions of the various thresholds have been calculated in a previous paper [Dalmont et al., J. Acoust. Soc. Am. 118, 32–94 (2005)]. The present work is a quantitative comparison between “theoretical” values of the thresholds and their experimental values measured by using an artificial mouth. It is shown that the “Raman” model, providing that nonlinear losses are taken into account, is reliable and able to predict the values of thresholds.
Automatic classification of killer whale vocalizations using dynamic time warping
Authors: Brown Judith C. , Miller Patrick J. O.
Published: July 2007

A set of killer whale sounds from Marineland were recently classified automatically [Brown et al., J. Acoust. Soc. Am. 119, EL34–EL40 (2006)] into call types using dynamic time warping (DTW), multidimensional scaling, and kmeans clustering to give near-perfect agreement with a perceptual classification. Here the effectiveness of four DTW algorithms on a larger and much more challenging set of calls by Northern Resident whales will be examined, with each call consisting of two independently modulated pitch contours and having considerable overlap in contours for several of the perceptual call types. Classification results are given for each of the four algorithms for the low frequency contour (LFC), the high frequency contour (HFC), their derivatives, and weighted sums of the distances corresponding to LFC with HFC, LFC with its derivative, and HFC with its derivative. The best agreement with the perceptual classification was 90% attained by the Sakoe-Chiba algorithm for the low frequency contours alone.
The ontogeny of echolocation in a Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis)
Authors: Li Songhai , Wang Ding , Wang Kexiong , Xiao Jianqiang , Akamatsu Tomonari
Published: July 2007

Acoustic and concurrent behavioral data from one neonatal male Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) in captivity were presented. The calf click train was first recorded at 22days postnatal, and the frequency of hydrophone-exploration behavior with head scanning motions in conjunction with emissions of click trains by the calf increased gradually with age. The echolocation clicks in the first recorded click train were indistinguishable from those of adults. Calf echolocation trains were found to decrease in maximum click-repetition rate, duration, and number of clicks per train with age while the minimum click-repetition rate remained more consistent.
Direct observations of ultrasound microbubble contrast agent interaction with the microvessel wall
Authors: Caskey Charles F. , Stieger Susanne M. , Qin Shengping , Dayton Paul A. , Ferrara Katherine W.
Published: July 2007

Many thousands of contrast ultrasound studies have been conducted in clinics around the world. In addition, the microbubbles employed in these examinations are being widely investigated to deliver drugs and genes. Here, for the first time, the oscillation of these microbubbles in small vessels is directly observed and shown to be substantially different than that predicted by previous models and imaged within large fluid volumes. Using pulsed ultrasound with a center frequency of 1MHz and peak rarefactional pressure of 0.8 or 2.0MPa, microbubble expansion was significantly reduced when microbubbles were constrained within small vessels in the rat cecum (p<0.05). A model for microbubble oscillation within compliant vessels is presented that accurately predicts oscillation and vessel displacement within small vessels. As a result of the decreased oscillation in small vessels, a large resting microbubble diameter resulting from agent fusion or a high mechanical index was required to bring the agent shell into contact with the endothelium. Also, contact with the endothelium was observed during asymmetrical collapse, not during expansion. These results will be used to improve the design of drug delivery techniques using microbubbles.
Measurement and modeling of the acoustic field near an underwater vehicle and implications for acoustic source localization
Authors: Lepper Paul A. , D’Spain Gerald L.
Published: July 2007

The performance of traditional techniques of passive localization in ocean acoustics such as time-of-arrival (phase differences) and amplitude ratios measured by multiple receivers may be degraded when the receivers are placed on an underwater vehicle due to effects of scattering. However, knowledge of the interference pattern caused by scattering provides a potential enhancement to traditional source localization techniques. Results based on a study using data from a multi-element receiving array mounted on the inner shroud of an autonomous underwater vehicle show that scattering causes the localization ambiguities (side lobes) to decrease in overall level and to move closer to the true source location, thereby improving localization performance, for signals in the frequency band 2–8kHz. These measurements are compared with numerical modeling results from a two-dimensional time domain finite difference scheme for scattering from two fluid-loaded cylindrical shells. Measured and numerically modeled results are presented for multiple source aspect angles and frequencies. Matched field processing techniques quantify the source localization capabilities for both measurements and numerical modeling output.
Relationship between perception of spectral ripple and speech recognition in cochlear implant and vocoder listeners
Authors: Litvak Leonid M. , Spahr Anthony J. , Saoji Aniket A. , Fridman Gene Y.
Published: July 2007

Spectral resolution has been reported to be closely related to vowel and consonant recognition in cochlear implant (CI) listeners. One measure of spectral resolution is spectral modulation threshold (SMT), which is defined as the smallest detectable spectral contrast in the spectral ripple stimulus. SMT may be determined by the activation pattern associated with electrical stimulation. In the present study, broad activation patterns were simulated using a multi-band vocoder to determine if similar impairments in speech understanding scores could be produced in normal-hearing listeners. Tokens were first decomposed into 15 logarithmically spaced bands and then re-synthesized by multiplying the envelope of each band by matched filtered noise. Various amounts of current spread were simulated by adjusting the drop-off of the noise spectrum away from the peak (40–5dB∕octave). The average SMT (0.25 and 0.5cycles∕octave) increased from 6.3 to 22.5dB, while average vowel identification scores dropped from 86% to 19% and consonant identification scores dropped from 93% to 59%. In each condition, the impairments in speech understanding were generally similar to those found in CI listeners with similar SMTs, suggesting that variability in spread of neural activation largely accounts for the variability in speech perception of CI listeners.
Experimental detection and focusing in shallow water by decomposition of the time reversal operator
Authors: Prada Claire , de Rosny Julien , Clorennec Dominique , Minonzio Jean-Gabriel , Aubry Alexandre , Fink Mathias , Berniere Lothar , Billand Philippe , Hibral Sidonie , Folegot Thomas
Published: July 2007

A rigid 24-element source-receiver array in the 10–15kHz frequency band, connected to a programmable electronic system, was deployed in the Bay of Brest during spring 2005. In this 10- to 18-m-deep environment, backscattered data from submerged targets were recorded. Successful detection and focusing experiments in very shallow water using the decomposition of the time reversal operator (DORT method) are shown. The ability of the DORT method to separate the echo of a target from reverberation as well as the echo from two different targets at 250m is shown. An example of active focusing within the waveguide using the first invariant of the time reversal operator is presented, showing the enhanced focusing capability. Furthermore, the localization of the scatterers in the water column is obtained using a range-dependent acoustic model.
A
mode interaction with a plate free edge: Theory and experiments at very low frequency by thickness product
Authors: Ribay Guillemette , Catheline Stefan , Clorennec Dominique , Ing Ros Kiri , Fink Mathias
Published: July 2007

When a plane acoustic wave reaches a medium with an impedance infinite or null, it experiences a phase shift of zero or π and its amplitude on the edge is maximum or vanishes. The case of a flexion wave (A0 Lamb wave) at a free end is also simple; its amplitude is multiplied by a factor 22 and the phase shift is π∕2. The evanescent wave at the origin of these phenomena, perfectly described by the classical flexural plate theory, is identified as the imaginary A1 mode of the exact Rayleigh-Lamb theory. The experiences confirm the theoretical predictions.
Characterization of dense bovine cancellous bone tissue microstructure by ultrasonic backscattering using weak scattering models
Authors: Deligianni D. D. , Apostolopoulos K. N.
Published: July 2007

A weak scattering model was proposed for the ultrasonic frequency-dependent backscatter in dense bovine cancellous bone, using two autocorrelation functions to describe the medium: one with discrete homogeneities (spherical distribution of equal spheres) and another, which considers tissue as an inhomogeneous continuum (densely populated medium). The inverse problem to estimate trabecular thickness of bone tissue has been addressed. A combination of the two autocorrelation functions was required to closely approximate the backscatter from bovine bone with various microarchitecture, given that the shape of trabeculae ranges from a rodlike to a platelike shape. Because of the large variation in trabecular thickness, both at an intraspecimen and an interspecimen level, thickness distributions for individual trabeculae for each bone specimen were obtained, and dominant trabecular sizes were determined. Comparison of backscatter measurements to theoretical predictions indicated that there were more than one dominant trabecular sizes that scatter sound for most specimens. Linear regression, performed between dominant trabecular thickness and estimated correlation length, showed significant linear correlation (R2=0.81). Attenuation due to scattering by a continuous distribution of scatterers was predicted to be linear over a frequency range from 0.3 to 0.9MHz, suggesting a possibility that scattering may be a significant source of attenuation.
Design guidelines of 1-3 piezoelectric composites dedicated to ultrasound imaging transducers, based on frequency band-gap considerations
Authors: Wilm M. , Khelif A. , Laude V. , Ballandras S.
Published: July 2007

Periodic piezoelectric composites are widely used for imaging applications such as biomedical imaging or nondestructive evaluation. In this paper such structures are considered as phononic crystals, and their properties are investigated with respect to periodicity. This approach is based on the investigation of band gaps, that strongly depend on the properties of the considered composites (geometry, size, nature of materials). It is motivated by the fact that band gaps in principle allow one to excite the thickness mode without exciting other parasitic propagating waves. The used plane-wave-expansion method has already been applied to periodic piezoelectric composites, but, in contrast to previous approaches, not only waves propagating in the symmetry plane of the composite are considered, but also waves propagating with a nonzero angle of incidence with this plane. The method is applied to a representative 1-3 connectivity piezocomposite in order to demonstrate its potentialities for design purposes. The evolution of band gaps is explored with respect to the wave vector component parallel to piezoelectric transducer-rod axis. All bulk waves that contribute to the setting up of plate modes in the vicinity of the thickness mode are found and identified.
Modeling of the roundabout noise impact
Authors: Makarewicz Rufin , Golebiewski Roman
Published: July 2007

A roundabout is a very popular tool used by town planners for carrying smooth and stationary road traffic flow. In this study it is shown that the replacement of a classical road intersection by a roundabout, under certain conditions, may produce a traffic noise decrease. These conditions are expressed in terms of the roundabout speed and the receiver location. The A-weighted sound exposure level is used to describe noise reduction.
Companding to improve cochlear-implant speech recognition in speech-shaped noise
Authors: Bhattacharya Aparajita , Zeng Fan-Gang
Published: July 2007

Nonlinear sensory and neural processing mechanisms have been exploited to enhance spectral contrast for improvement of speech understanding in noise. The “companding” algorithm employs both two-tone suppression and adaptive gain mechanisms to achieve spectral enhancement. This study implemented a 50-channel companding strategy and evaluated its efficiency as a front-end noise suppression technique in cochlear implants. The key parameters were identified and evaluated to optimize the companding performance. Both normal-hearing (NH) listeners and cochlear-implant (CI) users performed phoneme and sentence recognition tests in quiet and in steady-state speech-shaped noise. Data from the NH listeners showed that for noise conditions, the implemented strategy improved vowel perception but not consonant and sentence perception. However, the CI users showed significant improvements in both phoneme and sentence perception in noise. Maximum average improvement for vowel recognition was 21.3 percentage points (p<0.05) at 0dB signal-to-noise ratio (SNR), followed by 17.7 percentage points (p<0.05) at 5dB SNR for sentence recognition and 12.1 percentage points (p<0.05) at 5dB SNR for consonant recognition. While the observed results could be attributed to the enhanced spectral contrast, it is likely that the corresponding temporal changes caused by companding also played a significant role and should be addressed by future studies.
Effects of cochlear implant processing and fundamental frequency on the intelligibility of competing sentences
Authors: Stickney Ginger S. , Assmann Peter F. , Chang Janice , Zeng Fan-Gang
Published: July 2007

Speech perception in the presence of another competing voice is one of the most challenging tasks for cochlear implant users. Several studies have shown that (1) the fundamental frequency (F0) is a useful cue for segregating competing speech sounds and (2) the F0 is better represented by the temporal fine structure than by the temporal envelope. However, current cochlear implant speech processing algorithms emphasize temporal envelope information and discard the temporal fine structure. In this study, speech recognition was measured as a function of the F0 separation of the target and competing sentence in normal-hearing and cochlear implant listeners. For the normal-hearing listeners, the combined sentences were processed through either a standard implant simulation or a new algorithm which additionally extracts a slowed-down version of the temporal fine structure (called Frequency-Amplitude-Modulation-Encoding). The results showed no benefit of increasing F0 separation for the cochlear implant or simulation groups. In contrast, the new algorithm resulted in gradual improvements with increasing F0 separation, similar to that found with unprocessed sentences. These results emphasize the importance of temporal fine structure for speech perception and demonstrate a potential remedy for difficulty in the perceptual segregation of competing speech sounds.
Cortical responses to the 2f1-f2 combination tone measured indirectly using magnetoencephalography
Authors: Purcell David W. , Ross (ß) Bernhard , Picton Terence W. , Pantev Christo
Published: July 2007

The simultaneous presentation of two tones with frequencies f1 and f2 causes the perception of several combination tones in addition to the original tones. The most prominent of these are at frequencies f2-f1 and 2f1-f2. This study measured human physiological responses to the 2f1-f2 combination tone at 500Hz caused by tones of 750 and 1000Hz with intensities of 65 and 55dB SPL, respectively. Responses were measured from the cochlea using the distortion product otoacoustic emission (DPOAE), and from the auditory cortex using the 40-Hz steady-state magnetoencephalographic (MEG) response. The perceptual response was assessed by having the participant adjust a probe tone to cause maximal beating (“best-beats”) with the perceived combination tone. The cortical response to the combination tone was evaluated in two ways: first by presenting a probe tone with a frequency of 460Hz at the perceptual best-beats level, resulting in a 40-Hz response because of interaction with the combination tone at 500Hz, and second by simultaneously presenting two f1 and f2 pairs that caused combination tones that would themselves beat at 40Hz. The 2f1-f2 DPOAE in the external auditory canal had a level of 2.6 (s.d. 12.1) dB SPL. The 40-Hz MEG response in the contralateral cortex had a magnitude of 0.39 (s.d. 0.1) nA m. The perceived level of the combination tone was 44.8 (s.d. 11.3) dB SPL. There were no significant correlations between these measurements. These results indicate that physiological responses to the 2f1-f2 combination tone occur in the human auditory system all the way from the cochlea to the primary auditory cortex. The perceived magnitude of the combination tone is not determined by the measured physiological response at either the cochlea or the cortex.
Frequency modulation detection with simultaneous amplitude modulation by cochlear implant users
Authors: Luo Xin , Fu Qian-Jie
Published: July 2007

To better represent fine structure cues in cochlear implants (CIs), recent research has proposed varying the stimulation rate based on slowly varying frequency modulation (FM) information. The present study investigated the abilities of CI users to detect FM with simultaneous amplitude modulation (AM). FM detection thresholds (FMDTs) for 10-Hz sinusoidal FM and upward frequency sweeps were measured as a function of standard frequency (75–1000Hz). Three AM conditions were tested, including (1) No AM, (2) 20-Hz Sinusoidal AM (SAM) with modulation depths of 10%, 20%, or 30%, and (3) Noise AM (NAM), in which the amplitude was randomly and uniformly varied over a range of 1, 2, or 3dB, relative to the reference amplitude. Results showed that FMDTs worsened with increasing standard frequencies, and were lower for sinusoidal FM than for upward frequency sweeps. Simultaneous AM significantly interfered with FM detection; FMDTs were significantly poorer with simultaneous NAM than with SAM. Besides, sinusoidal FMDTs significantly worsened when the starting phase of simultaneous SAM was randomized. These results suggest that FM and AM in CI partly share a common loudness-based coding mechanism and the feasibility of “FM+AM” strategies for CI speech processing may be limited.