bluuebunny/crossref_metadata_2025 huggingface dataset:
Scramble in behaviour and ecology
Authors: Parker G. A.
Published: July 2002

Nicholson's distinction between ‘scramble’ and ‘contest’ modes of competition has received widespread attention in ecology and in behaviour, though the emphasis has been different between the two disciplines. In ecology the focus has been on the effects on population; in behavioural ecology the focus has been on the consequences at the individual level. This paper reviews and develops a theory of scramble competition at the individual level, deriving a general evolutionarily stable strategy (ESS) for individual scramble expenditure in a patchy habitat in which individuals compete in local groups for available resources, and examines two population consequences. The critical parameter determining the relationship between individual scramble expenditure and the number of competitors in a patch is the expected resource per capita. If resource input,R, to a patch is constant and independent of the number of competitors,n, then as the number of competitors increases, the per–capita resources declines asR/n, and the ESS scramble level declines (in proportion to (n−1)/n2). However, if the resource input to a patch is positively related to the number of competitors in the patch, scramble expenditure may increase with the number of competitors. In the case where the per–capita resource input stays constant (i.e.R(n) =Rn), the scramble level increases with competitor number (in proportion to (n−1)/n). There are plausible ecological reasons why either of these extreme limits may be approached in nature, making it important to ascertain the relationship between R and n before predicting individual scramble expenditure. For example, resource input may be constant when groups of competitors are constrained to remain together in given patches, and constant per–capita resources may be approached when ideal–free foraging rules apply. However, in the latter case, scramble expenditure must be accounted for in determining the idealfree distribution. An analysis shows that this leads to ‘undermatching’, i.e. the ratio of numbers of competitors for good/bad patches becomes progressively less than the ratio of input rates for good/bad patches as the difference between the good and bad patches increases. A second population consequence of the scramble ESS relates to the fact that scrambles may dramatically affect fitness. The per–capita gain in energy can be reduced by a factor of up to 1/nas a result of scramble expenditure, potentially reducing realized population size to as little as the square root of the maximum potential carrying capacity, though reasons are given why such large reductions are unlikely.
Functional control of the binuclear metal site in the metallo‐β‐lactamase‐like fold by subtle amino acid replacements
Authors: Gomes Cláudio M. , Frazão Carlos , Xavier António V. , Legall Jean , Teixeira Miguel
Published: July 2002

At present there are three protein families that share a common structural domain, the αβ/βα fold of class B β‐lactamases: zinc β‐lactamases, glyoxalases II, and A‐type flavoproteins. A detailed inspection of their superimposed structures was undertaken and showed that although these proteins contain binuclear metal sites in spatially equivalent positions, there are some subtle differences within the first ligand sphere that determine a distinct composition of metals. Although zinc β‐lactamases contain either a mono or a di‐zinc center, the catalytically active form of glyoxalase II contains a mixed iron–zinc binuclear center, whereas A‐type flavoproteins contain a di‐iron site. These variations on the type of metal site found within a common fold are correlated with the subtle variations in the nature of the ligating amino acid residues and are discussed in terms of the different reactions catalyzed by each of the protein families. Correlation of these observations with sequence data results in the definition of a sequence motif that comprises the possible binuclear metal site ligands in this broad family. The evolution of the proteins sharing this common fold and factors modulating reactivity are also discussed.
A dose‐point‐kernel model for a low energy gamma‐emitting stent in a heterogeneous medium
Authors: Janicki Christian , Duggan Dennis M. , Rahdert David A.
Published: July 2002

A computer dose model for a low energy gamma‐emitting stent in a heterogeneous medium is described. The method is based on the Sievert model which is adapted to the dose‐point‐kernel (DPK) model to compute the dose distribution about filtered gamma sources (Sievert‐DPK model). The new gamma stent model can take into account effects such as the metallic wire attenuation and the presence of dense calcified plaque in a stented artery. The Sievert‐DPK model is tested against numerical simulations around cylindrical shell sources with dimensions comparable to those of a stent using a Monte Carlo transport code. For low energy gamma sources (Cs‐131 and Pd‐103), it is shown that the Sievert‐DPK model is consistent with the Monte Carlo results to about 5%–10% for distances up to 5 mm from the cylindrical surface and 2.5 mm beyond the cylinder edges. These results indicate that the Sievert‐DPK model may be useful to predict the dose in intravascular therapy applications for heterogeneous systems consisting of soft tissue, metal and dense plaque.
An iterative transmission algorithm incorporating cross‐talk correction for SPECT
Authors: Narayanan Manoj V. , King Michael A. , Byrne Charles L.
Published: July 2002

Simultaneous emission/transmission acquisitions in cardiac SPECT with a source combination offer the capability for nonuniform attenuation correction. However, cross‐talk of photons downscattered into the energy window contaminates the reconstructed transmission map used for attenuation correction. The estimated cross‐talk contribution can be subtracted prior to transmission reconstruction or incorporated in the reconstruction algorithm itself. In this work, we propose an iterative transmission algorithm (MLTG‐S) based on the maximum‐likelihood gradient algorithm (MLTG) that explicitly accounts for this cross‐talk estimate. Clinical images were acquired on a three‐headed SPECT camera, acquiring emission and transmission images simultaneously. Subtracting the cross‐talk estimate prior to transmission reconstruction can result in negative and zero values if the estimate is larger than or equal to the count in the transmission projection bin, especially with increased attenuator size or amount of cross‐talk. This results in inaccurate attenuation coefficients for MLTG reconstructions with cross‐talk subtraction. MLTG‐S reconstructions on the other hand, yield better estimates of attenuation maps, by avoiding the subtraction of the cross‐talk estimate. Comparison of emission slices corrected for nonuniform attenuation reveals that inaccuracies in the reconstructed attenuation map caused by cross‐talk can artificially enhance the extra‐cardiac activity, confounding the ability to visualize the left‐ventricular walls.
Optimization of relative weights and wedge angles in treatment planning
Authors: Xing Lei , Pelizzari C. , Kuchnir F. T. , Chen G. T. Y.
Published: July 2002

An efficient technique to optimize beam weights and wedge angles in radiotherapy treatment planning has been developed. Based on the fact that a wedged field can be regarded as a superposition of an open field and a nominal wedged field, this approach reduces the problem of finding beam weights and the corresponding wedge angles to optimizing a linear system with unknowns (weights of open beams and nominal wedged beams), where is the total number of incident beam directions. Two iterative algorithms similar to the iterative‐least‐square technique in image reconstruction are used to optimize the system. Application of the algorithms to two specific examples shows that this technique can reduce treatment planning time and effort, and promises to create a better solution for an arbitrarily complex treatment plan.
Variations in temporal patterns of speech production among speakers of English
Authors: Smith Bruce L.
Published: July 2002

In many languages, some segments are longer/shorter than others due to phonetic context, position within an utterance, etc. However, results from most such studies have typically considered group averages. The present study examined productions by ten subjects to assess the extent to which they individually showed various temporal patterns viewed as characteristic of English. While all subjects demonstrated most of the patterns considered, there were instances in which one or more of them did not. Even when they did manifest expected patterns, there was typically quite a large range of performance across speakers.
Effects of oscillation of a mechanical hemilarynx model on mean transglottal pressures and flows
Authors: Alipour Fariborz , Scherer Ronald C.
Published: July 2002

This study introduces a mechanical model of the larynx for investigating dynamic aerodynamic effects of phonation. The model mimics the hemilarynx. The tracheal inlet section was rectangular (25-mm width, 20-mm height). The vocal fold was fabricated with precision machinery from hard plastic with an attached oscillating plunger. A speaker assembly and audio amplifier drove the plunger, mimicking one-dimensional vocal-fold motion toward a flat wall. The glottal shape was rectangular. The glottal diameter was well specified or dynamically followed with a laser system. The air was sucked through the channel using a vacuum with controlled speed. Frequency and amplitude of the glottis were varied. The mean pressure and mean flow data were recorded. For steady-flow conditions, the glottal gap ranged from 0.39 to 2.58 mm. The pressure coefficient for steady flow had a range of 3.1 to 1.3 for Reynolds numbers between 300 and 9000. For oscillation conditions (a) the frequency was varied from 75 to 150 Hz while the amplitude was held relatively constant, and (b) the amplitude was varied to 0.3 mm for a fixed frequency of 100 Hz. The results indicate that the hemilarynx model provides mean pressure-flow data similar in form to other models with two vocal folds. Furthermore, the dimensional and non-dimensional pressure coefficient is sensitive to variations in glottal gap and glottal amplitude, but relatively insensitive to the frequency of oscillation.
Coupled-mode sound propagation in a range-dependent, moving fluid
Authors: Godin Oleg A.
Published: July 2002

Full-field acoustic methods for current velocity inversion require accurate and efficient mathematical models of sound propagation in a range-dependent waveguide with flow. In this paper, an exact coupled-mode representation of the acoustic field is derived. To account for the physics of the problem, normal modes in a corresponding range-independent waveguide are chosen as the local basis. In the absence of currents, mode shape functions form a complete orthogonal basis. This property is heavily used in coupled-mode theories of sound propagation in motionless fluid. Unlike in the motionless case, however, vertical dependencies of acoustic pressure in individual normal modes are not orthogonal in the presence of currents. To overcome this difficulty, linearized equations of hydrodynamics are rewritten in terms of a state vector. Its five components are expressed in terms of acoustic pressure and particle displacement due to the wave. Orthogonality of the state vectors corresponding to individual normal modes is established. Coupled differential equations are derived for range-dependent mode amplitudes, leading to a remarkably simple result. The mode-coupling equations have the same form as those known for the motionless case, but of course the values of the mode-coupling coefficients differ as long as the range dependence of the flow velocity contributes to mode coupling in addition to the range dependence of sound speed and fluid density. The mode-coupling formulation is verified against known coupled-mode equations for certain limiting cases and an exact analytic solution of a benchmark problem.
Tomographic reconstruction of shallow-water bubble fields observed in the Scripps Pier bubble experiment
Authors: Rouseff Daniel , Henyey Frank S. , Caruthers Jerald W. , Stanic Steven J.
Published: July 2002

An experiment was performed in the Spring of 1997 off the pier at the Scripps Institute of Oceanography. The objective was to measure the near-shore properties of bubble fields. A major component of the experiment was the Delta frame designed at NRL-SSC. The triangular frame, 9.4 m on each side, supported two sources and eight hydrophones. Measurements of acoustic travel time and attenuation were made at eight frequencies between 39 and 244 kHz. Details of the measurement apparatus will be presented elsewhere at this meeting [J. W. Caruthers et al., ‘‘Observations of attenuation during the Scripps Pier bubble experiment’’]. In this paper, a tomography algorithm [D. Rouseff and F. S. Henyey, J. Acoust. Soc. Am. 101, 3032 (1997)] is applied to a sampling of the data to produce cross-sectional mappings of attenuation. The bubble concentrations are shown to be inhomogeneous and carried across the frame by rip currents. Possible improvements to the tomography algorithm for imaging strongly attenuating structures are discussed. [Work supported by ONR.]
Measurements of macrosonic standing waves in oscillating cavities
Authors: Lawrenson Christopher C. , Lipkens Bart , Lucas Timothy S. , Perkins David K. , Van Doren Thomas W.
Published: July 2002

Measurements of macrosonic standing waves in oscillating closed cavities are shown. These cavities (resonators) were designed by MacroSonix using resonant macrosonic synthesis (RMS) to shape the resultant waveform. By controlling the nonlinear processes by which energy is transferred to harmonic frequencies, RMS allows design of resonators that give high-amplitude shock-free waveforms. Measurements in cavities designed with RMS show standing-wave overpressures in excess of 340% of ambient pressure, compared to maximum overpressures in cylindrical cavities of about 17%. Power is delivered by oscillating the entire resonator along its axis with a linear actuator (entire resonator drive). Measurements are shown for four axisymmetric resonator shapes: cylinder, cone, horn-cone hybrid, and bulb. Resonators were filled with nitrogen, propane, or refrigerant R-134a (1,1,1,2-tetrafluoroethane). Ratios of peak-to-minimum pressures of 27 were observed. Since practical compressors for air, refrigerants, or other gases require pressure ratios (discharge to suction) of 3 or more, RMS technology can be used in a wide range of applications. Frequency sweeps show softening or hardening behavior, depending on resonator shape. High-amplitude resonance sweeps show significant hysteresis.
A theoretical model of nonlinear standing waves in an oscillating cavity
Authors: Ilinskii Yurii A. , Lipkens Bart , Lucas Timothy S. , Van Doren Thomas W. , Zabolotskaya Evgenia A.
Published: July 2002

A theoretical investigation of nonlinear standing waves in an acoustical resonator is presented. The motivation for this research stems from the new technology of resonant macrosonic synthesis (RMS) developed at MacroSonix. RMS creates high amplitude standing waves, e.g., overpressures in excess of 300% of ambient pressure. The analysis is based on a one-dimensional model equation for the velocity potential that is derived from the fundamental gas dynamics equations for an ideal gas. Nonlinearity, gas viscosity, and entire resonator driving are included. The resonator is assumed to be of an axisymmetric, but otherwise arbitrary, shape. Nonlinear spectral equations are integrated numerically for a two-point boundary-value problem. The harmonic amplitudes and phases of the velocity potential wave are obtained directly from the solution of the frequency-domain equations. The pressure wave shape, the harmonic amplitudes of the pressure wave, and harmonic amplitude distribution along the resonator axis are then calculated. Results are presented for three resonator geometries: a cylinder, a cone, and a bulb. Both hardening and softening behaviors are observed and shown to be geometry dependent. At high amplitude, hysteresis effects are present in the frequency-response curves. Comparisons between measured and calculated waveforms show good agreement.
Interaction between wave-number pairs
Authors: Ille Jean-François , Ginsberg Jerry H.
Published: July 2002

When acoustic-structure interaction is analyzed according to the wave-number-based version of the surface variational principle (SVP), considerable computational effort is required to generate each coefficient in the quadratic sum forming the variational quantity. Examination of the wet-surface impedance, which represents the spectrum of pressure amplitudes generated by a specified spectrum of surface velocity amplitudes, reveals that many cross-impedance terms are very small. This suggests that some coefficients need not be computed. The paper introduces several a prioricriteria for selecting the impedance terms to be omitted, based on the supersonic cutoff wave number. Each scheme is assessed by comparing its predictions to the convergent SVP solution. For the nonsymmetric azimuthal harmonics, the field quantities and the radiated power are well predicted if subsonic waves are ignored. In contrast, for the axisymmetric component, substantial errors (6 dB or more) for radiated power arise, unless a broad spectrum of subsonic waves are included in the formulation. The power is mostly reactive, being associated with an evanescent field, even for the supersonic spectrum. The study shows that small interactions between subsonic waves in the axisymmetric case can result in substantial radiative effects that are not modeled in ray theory analyses.
The radiation and vibratory response of a fluid-loaded structure with high internal complexity
Authors: Houston B. H. , Photiadis D. M. , Bucaro J. A.
Published: July 2002

Recently, experiments were reported in which complex internal structure was shown to dramatically influence the scattering cross section of fluid-loaded shells [Photiadis et al., J. Acoust. Soc. Am. 101, 895–899 (1997)] and where spatially varying local admittances were proposed to explain the observed scattering details [Bucaro et al., J. Acoust. Soc. Am. 100, 2721 (1996)]. Here, measurements of the vibratory response of this same structure [a ribbed shell with a large number (∼1000) of internal oscillators] are shown. Comparisons are made to the response of an identical shell with no internal oscillators. For the complex structure, no distinct pass and stop bands for any of the circumferential orders is seen, and a high degree of localization at all circumferential orders and frequencies is observed. Generally speaking, the wave-number-frequency plots associated with the complex structure are significantly different than those for the simple framed cylinder at all but the highest azimuthal components (n>17). Moreover, the wave-number decompositions of these data reveal a strong dominance of local bending in the response of the complex structure and evidence that strong coupling between the circumferential orders contributes to the significantly enhanced radiation levels. [Work supported by the Office of Naval Research.]
Local modeling of complex elastic structures
Authors: Photiadis Douglas M.
Published: July 2002

Several recent results, both numerical and experimental, have indicated that the structural acoustic response of large vibratory systems with complex internal structure is dominated by local response in the midfrequency range. These results have clear implications regarding control strategies for noise control, but also may have a significant impact on the acoustic scattering characteristics of complex structures. In this paper, this phenomena is analyzed theoretically using two disparate models, a conventional stochastic wave scattering model and a new type of model, which treats the system instead as a set of coupled, local resonators. This local model more naturally accommodates the observations concerning the generally localized response but is somewhat more difficult to associate with the geometrical characteristics of the ‘‘base structure’’ than a more conventional elastic wave scattering model. A number of aspects involving the vibration are analyzed and contrasted between the two models; the occurrence of simple, relatively isotropic spreading of energy, increased damping resulting from the internals, increased damping resulting from radiation into the surrounding fluid, and last but not necessarily least, the impact of local resonance behavior.
Feature extraction based on eigenvector analysis applied to the monostatic scattered field of a ribbed finite cylinder
Authors: Sarkissian Angie
Published: July 2002

Feature extraction based on eigenvector analysis is applied to the monostatic response of a ribbed finite cylindrical shell with hemispherical end caps. The method, which is based on the Karhunen–Loeve expansion, is applied in the frequency domain to extract features for optimal representation of the data. An orthonormal set of eigenvectors that form a set of basis functions are computed by diagonalizing the correlation matrix. The expansion of the monostatic scattered field with the resultant set of basis functions is optimal because a small number of the functions is required to approximate the scattered field at each orientation of the scatterer. Such a representation reduces the dimensionality of the problem by more than an order of magnitude. The method is applied to two frequency ranges. In the first case, enhancements in target strength are present due to the phase matching of the elastic waves to the acoustic waves in the exterior fluid. In the second case, Bloch wave resonances are present due to the periodicity of the ribs. It is shown that as larger variations are present in target strength as a function of frequency, a larger number of eigenvectors are necessary to approximate the scattering response.
On the use of the instantaneous frequency to understand phenomena in polyphonic piano sounds
Authors: Rossi Lucile , Girolami Gerard
Published: July 2002

The extraction of amplitudes and frequencies of partials from musical tones have been developed over the past ten years in order to carry out statistical studies on spectral parameters [Ando, J. Acoust. Soc. Am. 94, 37–45 (1993)] and/or to measure the frequency ratios of spectral components [Brown, J. Acoust. Soc. Am. 99, 1210–1218 (1996)]. This paper presents a study of the temporal evolution of the amplitude and frequency of piano sounds’ partials in order to take into account the eventual frequential fluctuations in the identification method of polyphonic piano sounds developed by the authors [Rossi and Girolami, J. Acoust. Soc. Am. 100, 2842 (1996)]. The notion of analytical signal and instantaneous frequency is used to find the characteristics of beats appearing in the evolution of the amplitude of single notes and single notes’ partials. In the case of polyphonic piano sounds, pertubations in the temporal evolution of frequency and amplitude of a given partial, due to the presence of a close partial belonging to another note, are presented.
Ultrasonic properties of aluminosilicate glass
Authors: So J. H. , Green D. H. , Yun S. S.
Published: July 2002

An ultrasonic study of attenuation and sound velocity was carried out in aluminosilicate glasses including annealed samples at 800 and 900 °C for 10 h as functions of temperature and frequency with the pulse–echo method. The temperature and frequency ranges employed here were 100–300 K and 5–50 MHz. The original sample has the largest attenuation coefficient in the temperature range compared to that of samples annealed. In all samples, the longitudinal and shear-wave velocities decrease linearly with temperature. Young’s, shear, and bulk moduli decrease linearly with temperature also. In this temperature range, Lame’s parameter, Poisson’s ratio, and the velocity anisotropy factor were determined using velocity data. The ultrasonic attenuation coefficient increases linearly with frequency and monotonically with decreasing temperature and is independent of pulse amplitudes. These results imply a linear loss mechanism producing a frequency-independent Q.
Backscattering enhancement for tilted plastic cylinders in water due to the caustic-merging transition: Ultrasonic observations
Authors: Blonigen Florian J. , Marston Philip L.
Published: July 2002

Typical plastics do not support leaky Rayleigh waves in water because the shear velocity is less than the speed of sound in water. Consequently, backscattering from plastic cylinders is ordinarily small. If the shear-wave attenuation is sufficiently small, there is, however, a mechanism for enhanced backscattering by tilted circular cylinders. At a certain tilt angle, rainbow caustics merge in the meridional plane defined by the incident wave vector and the cylinder’s axis. The merged caustics are associated with rays internally reflected off an end of the cylinder but are analogous to a merging of caustics observed [C. M. Mount and P. L. Marston, Light and Color in the Open Air (OSA, Washington, DC, 1997), pp. 14–16] in optical experiments with long plastic fibers. Ultrasonic observations of the backscattering enhancement are reported for a plastic cylinder in water with ka=25. The enhancement mechanism should also apply to liquid cylinders in a thin shell if the speed of sound for the liquid is less than that of water. [Work supported by the Office of Naval Research.]
FDTD boundary treatment for scattering from penetrable objects
Authors: Wang Shuozhong , Wang Tong , Wang Rongqing
Published: July 2002

The finite-difference time-domain (FDTD) formulation [S. Wang, J. Acoust. Soc. Am. 99, 1924–1931 (1996)] and the least-squares absorbing boundary conditions [S. Wang, Chin. J. Acoust. 16, 121–134 (1997)] have been successfully applied to deal with sound scattering from ideally soft and ideally rigid objects with arbitrary shapes. To expand the scope of application to more realistic cases, an effective boundary treatment for interfaces penetrable to sound waves is introduced. The FDTD boundary condition expressions take a form similar to that in continuous and uniform media, except for a modification to the material-related constants. This is achieved by using a suitable averaging scheme based on a second-order discretization of the basic acoustic equations on boundaries. The proposed method is consistent with the ideal cases at both soft and rigid ends, giving a unified approach to the solution of scattering from nonelastic objects. Numerical experiments on scattering from various objects submerged in water are presented, showing a good agreement with theoretical solutions and previously obtained results. The object materials used in the computation cover a wide range of acoustic impedance from very soft to very rigid. [Work supported by NNSFC.]
Overview of multipole-based acoustic infinite elements
Authors: Burnett David S.
Published: July 2002

There is a rapidly growing interest in using infinite elements based on multipole expansions for modeling acoustic wave propagation in unbounded domains, either time harmonic or transient. The technology has exhibited many advantages, foremost among them being a very high computational efficiency, convergence and, therefore, unlimited accuracy throughout the entire fluid domain, broadband capability, and a conventional finite-element software implementation. The latter enables these infinite elements, along with conventional finite-size acoustic elements and coupling elements, to be easily added to standard structural element libraries to convert structural codes to structural acoustic codes for fast, accurate modeling of scattering and/or radiation problems in exterior regions. The talk will cover: basic concepts of multipoles, multipole expansions, and the related infinite elements; past contributions to the field; current research, including the author’s; and an assessment of the most promising direction for this technology.
Megameter-scale oceanography of internal waves: Past, present, and future
Authors: Flatté Stanley M.
Published: July 2002

Measurements of internal-wave strengths are reviewed for their contribution to our understanding of megameter-scale behavior. Past measurements are sparse. Recent acoustic measurements have provided large-scale averages, with both temporal and spatial information. Future experiments could provide some insight into the place of internal waves in oceanography.
Just how stochastic are coastal oceanographic fields?
Authors: Colosi John , Rehmann Chris , Lynch Jim
Published: July 2002

A key question one must answer before doing an inverse procedure is: ‘‘How deterministic versus stochastic are the fields that are wished to be inverted?’’ In this talk, this question is addressed for the coastal processes of solibores, fronts, and coastal eddies, using data from both the SWARM and the shelfbreak front PRIMER experiments, as well as computer models of the processes and acoustic propagation through them. Acoustic propagation over 50-km ranges and frequencies of 50–500 Hz will be considered. Issues concerning the eventual inversion of such data will be discussed in detail.
Numerical simulation of the parametric array application for the Fram Strait acoustic monitoring
Authors: Naugolnykh Konstantin A , Shang E. C. , Wang Yun-yu
Published: July 2002

An important part of the general problem of the Arctic climate change is the monitoring of the Fram Strait, which lies between Greenland and Spitsbergen. For this reason, it is reasonable to apply acoustic methods which are proven to be effective in acoustic ocean thermometry, acoustic tomography, etc. Knowledge of the main peculiarities of sound signal propagation in this region is needed to estimate the feasibility of applying remote acoustic methods. Due to the extremely complex propagation environment, strong mode coupling takes place which leads to mode repopulation (variation of the modal structure of a sound field with distance). The application of a parametric array as a mode selective source could be useful in this case providing better spatial resolution of the probing area. The results of numerical simulation of parametric array performance in the Fram Strait environment is considered in the present paper.
Application of ultrasonic stress measurement to engineering components
Authors: Bray Don E.
Published: July 2002

Ultrasonic techniques offer several unique advantages in nondestructive stress measurement. Most importantly, the ultrasonic energy propagates below the material surface, giving information on stress distributions away from the surface effects. Additionally, surface preparation requirements are minimal, enabling rapid collection of stress information from several locations in a component. Finally, the instrumentation necessary to collect and analyze the ultrasonic traveltimes required for stress evaluation is available in relatively light, compact, computer driven units that are easily moved into the industrial or laboratory work space. A brief overview will be given of the acoustoelastic effect, which is the basis for ultrasonic stress measurement. Both the acousticbirefringence (shear wave) and the critically refracted longitudinal wave (LCR) methods will be described. Examples of applications of the latter method for stress measurement in turbine components, rolled plate, ductile iron, and railroad rail and wheels will be described.
Vibrational modes of clarinet reeds
Authors: Lindevald Ian M. , Gower Jason
Published: July 2002

The role of the lowest frequency reed resonance in sound production by single reed instruments has been well established [S. C. Thompson, J. Acoust. Soc. Am. 66, 1299–1307 (1979)]. However, the acoustical significance of the reed’s higher vibrational modes remains an open question. Recently, several higher frequency modes have been identified for a clarinet reed [P. L. Hoekje and G. Matthew Roberts, J. Acoust. Soc. Am. 99, 2462(A) (1996)]. The present study examines several reeds and extends Hoekje’s results to higher frequencies. Holographic interferometry was used to locate the frequencies and to image the vibrational patterns of higher vibrational modes of three nominally equivalent commercial clarinet reeds. Dry reeds were clamped to a specially designed reed holder allowing the reeds to vibrate freely when driven by an acoustic sound field. In all, six or seven distinct modes with frequencies below 7.5 kHz were located on each of the three reeds. Four of the modes (including the fundamental) appear to be similar to the one-dimensional modes of a cantilevered beam. The other three modes show two-dimensional vibrations indicating twisting motion. Variations in modal frequencies among the three reeds studied range from 3%–12% over the different modes.
Observations of backscattering of obliquely incident plane waves by composite cylindrical shells constructed from isotropic and transversely isotropic layers
Authors: Kaduchak Gregory
Published: July 2002

Acoustic backscatteirng from finite, composite cylindrical shells in water is examined. The shells are comprised of N layers, which may be described by orthotropic or transversely isotropic materials. The present research examines experimental observations of the scattering signatures obtained from obliquely incident plane waves in the mid- and high-frequency regions. Scattering effects are viewed in both the time and frequency domains. Attention will be given to the similarities (and dissimilarities) of the scattering signatures, which are the chief contributors to the backscattering form function as the symmetry axis of the transversely isotropic layers is rotated away from the axial direction. To localize the sources of scattered radiation at oblique incidence, scattering effects are viewed with high-resolution techniques, which include narrow transmit/receive beams as well as synthetic aperture sonar. [Work supported by the Office of Naval Research.]
Acoustic excitation of generalized normal-mode vibrations on hemispherically endcapped and on infinite elliptic cylinders
Authors: Maze G. , Lanfranchi J. , Décultot D. , Ripoche J. , Überall H.
Published: July 2002

The concept of normal-mode vibrations of elastic objects, and their resonant acoustic excitation, can be straightforwardly demonstrated ana-lytically for objects of canonical shape (spheres, circular cylinders) only, but it evidently remains valid for objects of completely general shapes. Mode analysis may be extended to these by invoking the principle of phase matching of surface waves (circumferential waves) that encircle the object after their acoustic excitation [H. Überall, L. R. Dragonette, and L. Flax, J. Acoust. Soc. Am. 61, 711 (1977)], thereby creating standing waves around the object (resonances) that correspond to its normal modes of vibration. Experiments have been performed leading to the excitation of resonances of submerged spherically-endcapped circular cylinders, and of infinite elliptic cylinders, which were interpreted according to the phase-matching concept, thus leading to a description of their vibrations as generalized normal modes.
Structural sensitivity analysis in structure-fluid interaction problems
Authors: Hahn Steven R. , Ferri Aldo A.
Published: July 2002

Using a finite-element formulation with infinite elements to approximate the external fluid, well-developed structural sensitivity analysis techniques can be applied to acoustic radiation and scattering problems. Changes to a nominal structure are introduced through a structural perturbation matrix, εΔS, which modifies the system matrix, S, of the nominal system. The perturbed surface pressures and normal velocities are expressed as a binomial series in ΔS. The convergence criteria for the series is examined for structural-acoustic systems. A perturbation consisting of a change in the Young’s modulus is examined for two numerical examples. First, a one-dimensional problem of plane-wave scattering from a viscoelastic layer is examined. The results of the 1-D problem are then extended to the multidimensional problem of plane-wave scattering from a cylindrical shell. The perturbations consist of varying the Young’s modulus of the layer and the shell. It is shown that the convergence of the binomial series is strongly linked to the amount of damping in the nominal system, but not to the damping in the perturbation. Furthermore, the use of a truncated series is shown to be a valid approximation in many cases, even when the series does not converge.
Exploration of the perceptual magnet effect using the mismatch negativity auditory evoked potential
Authors: Sharma Anu , Dorman Michael F.
Published: July 2002

This study assessed the replicability of the ‘‘perceptual magnet effect (PME)’’ [Kuhl, Percept. Psychophys. 50, 93–107 (1991)] and investigated underlying neurophysiologic processes using the mismatch negativity (MMN) evoked potential. A stimulus continuum from /i/–/e/ was synthesized by varying F1 and F2 in equal mel steps. Subjects categorized, rated the goodness of stimuli, and discriminated between stimulus pairs. Results revealed that Kuhl’s prototype was identified and rated as a good (albeit, not the best) exemplar of /i/, whereas, Kuhl’s nonprototype (NP) was identified as /i/ only 20% of the time, and therefore, was not a suitable NP. In this study, the prototype was the stimulus with the lowest F1 and highest F2 values and the NP was close to the category boundary. Discrimination accuracy was not significantly different in the prototype and NP conditions. That is, no perceptual magnet effect was observed. Furthermore, despite equal mel differences between the stimulus pairs, the MMN was largest for the pair with lowest F1 and highest F2 values. Therefore, the MMN appears to be sensitive to within category acoustic differences. The behavioral and electrophysiologic results indicate that discrimination of stimuli near a prototype is based on the auditory structure of those stimuli.
Perceptual-magnet effect as categorical perception
Authors: Lotto Andrew J. , Holt Lori L. , Kluender Keith R.
Published: July 2002

The perceptual-magnet effect has received a great deal of attention in recent years as a possible foundation for phonetic category acquisition. This effect is based upon studies showing that category goodness affects intracategory discriminability. Unfortunately, there is a possible confound in many of these demonstrations. Whereas category identity and goodness ratings are collected for stimuli presented in isolation, discrimination scores are obtained for stimulus pairs. In the present study, vowel identification and goodness ratings were obtained from the same stimulus pairs that would later be presented in an AX discrimination task. Stimuli were identical to the vowel vector used by Iverson and Kuhl [J. Acoust. Soc. Am. 97, 553–561 (1995)]. Identification functions varied substantially as a function of the pairings in a manner that may be described as contrastive. Vowels labeled as /e/ when presented with a good /i/ exemplar were labeled as /i/ when presented with a good /e/. These identification functions were used to predict discrimination scores based solely on perceived phonemic identity. Predictions accounted for all of the difference in discriminability between prototypical and nonprototypical exemplars. Perceptual-magnet effects appear to be little more than classic categorical perception. [Work supported by NSF.]
Effects of the uvula and the epiglottis on measurements of vowel production: Assessment by synthesis
Authors: Magen Harriet , Kang Min
Published: July 2002

The acoustic shape of vowels is determined by the cross-sectional areas along the vocal tract. These areas can be predicted from the midsagittal distance, given certain assumptions about the relation of that distance to the area [P. Mermelstein, J. Acoust. Soc. Am. 53, 1070–1082 (1973)]. The present study used midsagittal MRI images of the vocal tract during sustained vowel production to provide areas as input to an articulatory synthesizer. The acoustic consequences of two methods of measuring distance will be assessed: computing distance with and without the epiglottis and with and without the uvula. For some vowels, the uvula extended into the oral cavity to different degrees across repetitions, resulting in large within-vowel variability for that region. Similarly, distances in the region of the epiglottis depended on the degree to which the epiglottis is detached from the root of the tongue, though this tended to be more consistent across repetitions. Closer matches, both in terms of formant frequencies and perceptual similarity, will indicate which method best represents the effective area predicted by the midsagittal distance. [Work supported by NIH Grant DC-02717.]
Spectral transition in the perception of English segments
Authors: Warner Natasha
Published: July 2002

There is a long-standing debate on whether speech is perceived through steady states or transitions [D. Kewley-Port and D. Pisoni, J. Acoust. Soc. Am. 73, 1779–1793 (1983)]. Furui [S. Furui, J. Acoust. Soc. Am. 80, 1016–1025 (1986)], gating Japanese monomoraic syllables, found listeners identified syllables correctly when they heard the point of maximal spectral transition (maximum D, a measure based on cepstral coefficients). In this paper, this work is extended to English, and to a wider variety of transitions. 128 English words, representing transitions between all manners of articulation, were gated at 20-ms intervals. VC, CC, and VV transitions were used in addition to Furui’s CV and CjV syllables. The results show that for almost all transitions (diphones), there is a clear point at which listener’s identification of the second segment becomes highly accurate. For many diphones (54%), this point is within 15 ms of the maximum D. However, for other diphones (especially those with far-reaching perceptual cues), the point of recognition is farther from the maximum D. This paper will discuss reasons for the discrepancies between Furui’s experiment and the current one, including language-specific factors, and will address implications for the dynamic theory of speech perception.
Effect of relative amplitude manipulation on perception of voiceless fricatives by normal and impaired listeners
Authors: Hedrick Mark S.
Published: July 2002

In the present study, previous work on the relative amplitude and presentation level was extended to include the voiceless fricative /s/–/■/ contrast. Synthetic CV stimuli were used, in which format transitions, frication duration, and relative amplitude were manipulated. For the relative amplitude manipulation, the amplitude of friction relative to vowel onset in the F3 frequency range was varied across a 20-dB range. Frication duration was varied from 140–50 ms. Stimuli were presented at 90 dB SPL. Eight listeners with normal hearing and three listeners with moderate sensorineural hearing loss participated in the experiment. Results showed that listeners with sensorineural hearing loss gave significantly more /s/ responses for lower relative amplitude values. Results from this study and previous studies [Hedrick et al., J. Acoust. Soc. Am. 98, 1292–1303 (1995); M. S. Hedrick and W. Jesteadt, J. Acoust. Soc. Am. 100, 3398–3407 (1996)] suggest that perception of acoustic cues for consonants by listeners with sensorineural hearing loss may differ from that of listeners with normal hearing, even when the cues are audible.
Predicting the intelligibility of speech transmitted over nonideal channels
Authors: Rankovic Christine M.
Published: July 2002

Speech is the most efficient auditory code for conveying abstract information. Hence, high-fidelity speech transmission is an important goal for some multimedia applications. Problems may arise when the signal processing used to create the artificial auditory display inadvertently alters the spectral/temporal properties of the speech or when competing signals mask out portions of the speech. In cases where the distortion amounts to linear filtering and/or noise masking, the degrading effect on intelligibility can be predicted using an elaborate calculation scheme known as articulation theory [H. Fletcher and R. H. Galt, J. Acoust. Soc. Am. 22, 89–151 (1950)]. The theory assumes that the audible spectrum can be divided into a number of bands that contribute independently to speech reception; and the band contributions are additive. Acoustical measurements are translated into their perceptual correlates via transformations derived from psychophysical experiments. These terms are combined to give the articulation index a number which is directly related to the expected percent-correct score for an articulation test. The theory will be described and examples presented. [Work supported by NIH R29 DC02127.]
Overview of tracking techniques and developments for naval undersea tracking ranges
Authors: Smith Dean J.
Published: July 2002

The recent shift in the naval warfare climate from deep-water open-ocean scenarios to littoral waters has resulted in a need for the development of shallow-water training ranges that can augment the deep-water ranges that presently exist. The inherent characteristics of littoral environments (time variability, nonhomogeneity, reverberation, sound velocity variation, etc.) provide significant challenges for developing robust shallow-water tracking systems that can meet range operation and accuracy requirements. These requirements can only be met through advances in tracking techniques and technology. This presentation will provide an overview of traditional deep-water tracking range techniques and then focus on the challenges that shallow-water tracking environments bring. Finally, new tracking techniques that are being developed to overcome these challenges will be discussed.
Acoustic modeling of narrow waters
Authors: Bergh Nilssen Ashild
Published: July 2002

The problem of sound propagation in narrow waters can readily be related to room acoustic problems. Different methods from room acoustics were investigated for a possible application to the underwater acoustics of fjords and straits. The frequency range of interest is 1 Hz–100 kHz, and the sound field at ranges to ∼1000 m from the source is computed. For the very low-frequency range both near-field and far-field propagation must be considered. In the very-low-frequency range, 1 to ∼50 Hz (possibly 500 Hz), finite-element methodology is applied. In the medium-frequency range ∼50 Hz to ∼10 kHz, room acoustic methods are applied. In the high-frequency range ∼10 to 100 kHz, conventional underwater acoustic methods are used. The room acoustic method chosen is a hybrid model combining image source modeling and ray tracing, and with the most important quality; a diffusivity parameter of the boundaries, which makes it unnecessary to know the exact geometry of the area modeled. However, the diffusivity parameter cannot be computed, it must be assessed from experimental data. Numerous experiments have been carried out in several fjords in western Norway to validate and optimize the methods.
Exploring the surf zone using ambient sound
Authors: Nystuen Jeffrey A. , Kolaini Ali R.
Published: July 2002

Can the underwater ambient sound field be used to explore the oceanography of the surf zone? A preliminary examination of the ambient sound field from 1-100 kHz along the Scripps Institution of Oceanography Pier reveals two principal sound sources: breaking waves and snapping shrimp. While local wave breaking can be loud, higher-frequency sound levels within the surf zone and in rip currents are generally very quiet, confirming high-acoustic attenuation for frequencies as low as 2 kHz. Outside the surf zone, the sound field is dominated by snapping shrimp. These creatures live on the pilings (rather than free swimming), and thus present themselves as potential sound sources at distributed locations along the pier. Individual ‘‘snaps’’ are distinctive, broadband (3–100 kHz), loud, and can be tracked for over 30 m. Can these ‘‘signals’’ be used to probe the near-surf zone environment? [Work supported by ONR.]