bluuebunny/crossref_metadata_2025 huggingface dataset:
The range of existence of reflected homogeneous and surface waves in elastic orthotropic materials
Authors: Nair Sudhakar , Sotiropoulos Dimitrios A.
Published: October 2005

Reflection of elastic waves from the free surface of orthotropic incompressible materials is examined under plane strain conditions in a material symmetry plane. Use of the physically allowable energy flux vectors in conjunction with the propagation condition and the generalized Snell’s law, yields formulas for the range of existence of the different types of reflected waves with respect to the two elastic parameters: the material orientation of the free surface and the angle of incidence. It is the consideration of the energy flux vectors that, in general, introduces the second elastic parameter and enlarges the range for the existence of either two homogeneous shear plane waves or one homogeneous and one supersonic surface wave. In the special case of transverse isotropy, the above formalas yield a homogeneous shear wave and a surface wave which diminishes when the angle of incidence is 45°, the wave-number vector coincides with the energy flux vector, and there enters only one elastic parameter.
Gap detection in infants, children, and adults
Authors: Trehub Sandra E. , Schneider Bruce A. , Henderson Joanna L.
Published: October 2005

Listeners who were 6.5 months, 12 months, 5 years, and 21 years of age were required to discriminate a pair of 500-Hz, Gaussian-enveloped tone pips from a short 500-Hz tone of the same duration and total energy. Groups of 6.5-month-old infants were tested on a single gap duration: 8, 12, 16, 20, 28, or 40 ms. Groups of 12-month-olds were also tested on a single gap duration: 8, 12, 16, or 20 ms. The 5-year-old children and adults were tested on gap durations of 8, 12, and 16 ms. The mean performance of 6.5-month-olds significantly exceeded chance levels on all gap durations except 8 ms, and that of 12-month-olds was above chance levels on all gap durations. For 5-year-old children and adults, mean performance also exceeded chance levels for all gap durations tested. Adults performed significantly better than 5-year-old children on gap durations of 12 and 16 ms. Gap-detection thresholds, defined by a performance criterion of d′=0.5, were estimated at 11, 5.6, and 5.2 ms for infants, children, and adults, respectively. It is likely that smaller adult–infant differences in the present study compared to those reported in previous research stem from our use of Gaussian-enveloped tone pips and the consequent minimization of adaptation effects.
Sound cancellation by the use of secondary multipoles
Authors: Bolton J. Stuart , Gardner Bryce K. , Beauvilain Thierry A.
Published: October 2005

In this paper, global free-field cancellation in the region exterior to a single compact primary source is discussed. The nature of the secondary source or sources required to achieve such cancellation, either globally or in particular regions, is a subject of current interest. In particular, results are presented that relate to global cancellation of a primary monopole’s sound field by the use of a single, multipole secondary source. The secondary multipole component source strengths required to achieve global cancellation can be found in a number of ways. For example, they may be obtained directly from a multipole expansion of the primary monopole sound field, as originally suggested by Kempton. However, improved attenuation can be achieved by choosing the secondary multipole component source strengths to minimize the total sound power radiated by the combination of primary and secondary sources. Closed form solutions for secondary multipole component strengths have been derived for both the latter case and for Kempton’s approach and are presented here along with formulae for the corresponding reductions of sound power and sound pressure. It will also be shown that it is more efficient in some instances to use a secondary multipole than an array of secondary monopoles for global cancellation. However, the primary conclusion of the present work is that useful levels of global far-field cancellation may be obtained by using secondary sources of higher than monopole order placed at a relatively large fraction of a wavelength from the primary source.
Accurate vibration frequencies of circular cylinders from three-dimensional analysis
Authors: Leissa Arthur W. , So Jinyoung
Published: October 2005

A three-dimensional (3-D) method of analysis developed in a companion paper [A. W. Leissa and J. So, J. Acoust Soc. Am. 98, 2122–2135 (1995)] is used to obtain free-vibration frequencies of completely free-elastic cylinders. Extensive, accurate data are presented for the first 20 frequencies of each circumferential wave number 0–5 for free–free cylinders having length-to-diameter ratios (L/D) of 1, 1.5, 2, 3, and 5 with a Poisson’s ratio (ν) of 0.3. An additional study for L/D=1 over the full range (0≤ν<0.5) possible for isotropic materials shows that Poisson’s ratio effects can be quite important. The first known values of frequencies from 3-D analysis of cylinders having one end fixed, with all other boundaries free, are also presented in considerable detail. For free–free cylinders, comparisons are made with less accurate 3-D results published previously by other researchers.
Acoustic scattering from a circular aperture in a thick hard screen
Authors: Jun Kyung H. , Eom Hyo J.
Published: October 2005

Acoustic plane-wave scattering from a circular aperture in a thick hard screen is reexamined. The Hankel transform is applied to express the scattered field in the spectral domain and the boundary conditions are enforced to obtain simultaneous equations for the transmitted field inside the thick hard screen. The simultaneous equations are solved to represent the transmitted and scattered fields in series forms. Numerical computations are performed to illustrate the behavior of scattering and transmission in terms of the aperture size, frequency, and incident angle. It is found that scattering from a circular pit exhibits the resonance versus the pit depth when the pit radius is larger than a wavelength. The numerical comparisons to other available data show excellent agreement. The presented series solution is numerically efficient and general in that it includes scattering from a circular aperture, pit, and semi-infinite pipe altogether.
The stimulus duration required to identify vowels, their octave, and their pitch chroma
Authors: Robinson Ken , Patterson Roy D.
Published: October 2005

Computational models of sound segregation typically include the assumption that pitch plays a key role in timbre identification. This hypothesis was investigated by presenting listeners with short segments of static vowel sounds and asking them to identify the vowel quality (timbre), the octave (tone height), or the note (tone chroma) of the sound. There were four vowel categories (/a/, /i/, /u/, and /eh/), four octave categories (centered on C1, C2, C3, and C4) and four note categories (C, D, E, and F), and performance was measured as a function of the number of glottal periods of the vowel sound. The results show that at all stimulus durations, it was easiest to identify the vowel quality (mean 94% correct), followed by the octave (71%), and finally the note (52%). The results indicate that timbre can be extracted reliably from segments of vowels that are too short to support equivalent pitch judgments, be they note identification, or the less precise judgment of the octave of the sound. Thus it is unlikely that pitch plays a key role in timbre extraction, at least at short durations.
The damping of sound by wall turbulent shear layers
Authors: Howe M. S.
Published: October 2005

A frequency-dependent model is proposed for the eddy viscosity controlling the momentum and thermal wall boundary layers formed when an acoustic wave interacts with a low Mach number turbulent boundary layer whose thickness is much smaller than the acoustic wavelength. This is used to determine the effective acoustic admittance of the boundary layer, and to predict the attenuation of sound reflecting from a plane wall boundary layer, and low-frequency sound propagating in fully developed turbulent pipe flow. The predictions are shown to compare well with a recent experimental study of acoustic attenuation in pipe flows.
Full-field optimum detection in an uncertain, anisotropic random wave scattering environment
Authors: Premus V. , Alexandrou D. , Nolte L. W.
Published: October 2005

The optimum detection of an unknown object in an uncertain random wave scattering environment is considered. A physics-based approach to the design of the optimum detector is presented which merges statistical physical modeling of the acoustic scattering medium with a probabilistic description of environmental prior knowledge within a Bayesian decision-theoretic framework. For the high-frequency, shallow water, reverberation-limited environment considered herein, the parametrization of the acoustic medium is essentially limited to modeling acoustic interaction with anisotropic seafloor microroughness with unknown horizontal wave-number spectrum parameters. Simulation results, presented in terms of receiver operation characteristic (ROC) curves, aim to illustrate three principal points: (1) the cost of ignoring the bottom reverberation spatial coherence when it is present in the data; (2) the sensitivity of the likelihood ratio detector for a known environment to incorrect prior knowledge of the microroughness wave-number spectrum; and (3) the robust performance realizable by the optimum detection algorithm that properly accounts for environmental uncertainty within a Bayesian framework.
Variational principle and energy integrals in a complex sound intensity field
Authors: Zhe Jiang
Published: October 2005

The information about sound energy distribution and transfer is contained in a complex sound intensity field. The fundamental variables are the auto-spectrum and the phase of sound pressure. From the point of view of a differential, applying the mechanical laws, the differential equations expressing change of the variables are given. From the point of view of an energy integral, applying the variational method, a variational principle for the variables in a complex sound intensity field is established. The paper also discusses energy integrals and explains the meaning of the reactive sound intensity.
Modeling of three-dimensional seismoacoustic reverberation from anisotropic roughness patches
Authors: Schmidt Henrik , Fan Huaiyu
Published: October 2005

A perturbation approach to narrow- and wideband modeling of scattering from roughness patches on an interface separating a fluid and an elastic half-space has previously been developed [LePage and Schmidt, J. Acoust. Soc. Am. 89, 1941(A) (1991)]. However, based on a 2-D Fourier transform formulation it allows for modeling of the scattered near-field only, and it prohibits incorporation of waveguide effects. Here, a coordinate transformation is presented, yielding a representation of the virtual seismic moment sources for the scattered field in cylindrical coordinates. This source representation is compatible with the 3-D version of the OASES/SAFARI code, which has consequently been modified to provide extremely efficient numerical simulation of seismoacoustic reverberation in shallow- and deep-water waveguides. This new model has been applied to model the reverberation from horizontal roughness patches in the ARSRP mid-Atlantic environment. The model’s efficiency has allowed for Monte Carlo estimation of the statistical properties of the reverberation from patches with anisotropic roughness statistics, including mean reverberation intensity and spatial correlation. The effects of roughness anisotropy, bottom elasticity and the waveguide physics are discussed. The principal result of this theoretical analysis is the conclusion that Lambert’s law is totally inadequate for representing bistatic bottom reverberation. This conclusion is consistent with the results of the analysis of the bistatic data from the ARSRP experiment, as discussed in the companion paper by Bondaryk etal. [Work supported by ONR.]
Measurement microphone calibrations and their uncertainty
Authors: Frederiksen Erling
Published: October 2005

Today, there is an increasing need for obtaining legal acceptance of and confidence in calibrations performed by laboratories in other countries. This is especially true and clearly observable in Europe where the number of accredited laboratories and calibrations per year are rapidly increasing. To obtain accreditation the laboratories must analyze and state their calibration uncertainty. This leads to focus on uncertainty of microphone sensitivity and sound level calibrations. The overall calibration uncertainty valid for ordinary measurement microphones and pistonphones have been determined by studying error sources and their influence on the calibration results. The uncertainties of the methods, which directly and indirectly influence the uncertainty valid for the user of a Bruel & Kjær transducer calibration, are discussed. The methods include free-field and pressure reciprocity calibration of refrence standard microphones performed by the Danish Primary Laboratory of Acoustics (operated by Bruel & Kjær in cooperation with the Danish Technical University, Lyngby) and the electrostatic actuator method which is widely applied by the Bruel & Kjær Production Department and Calibration Service Centers. Contributions to the uncertainty which are due to the free-field and diffuse-field corrections and to the influence of microphone protection grids will be presented.
Extracting modal structure from vertical array ambient noise data in shallow water
Authors: Hursky Paul , Kuperman William A. , Hodgkiss William S.
Published: October 2005

Measurements of the acoustic mode structure in shallow water can be inverted to determine ocean environmental acoustic parameters. This modal stucture is embedded in shallow-water ambient noise [Kuperman and Ingenito, J. Acoust. Soc. Am. 67, 1988–1996 (1980)]. Ambient noise measurements (SWellEx 1) using a vertical array spanning the lower duct of a summer sound-speed environment were used to extract the acoustic modal structure of a coastal water environment off southern California. The experimental results derived from eigenvector processing are consistent with simulations using the measured environmental parameters.
Numerical study of the effective impedance of an idealized thermoacoustic stack
Authors: Worlikar A. S. , Klein R. , Knio O. M.
Published: October 2005

A low-Mach-number, compressible flow, simulation model is used to compute unsteady oscillatory flow in the neighborhood of a thermoacoustic stack. The model relies on a vorticity-based formulation of the mass, momentum, and energy conservation equations. The numerical scheme incorporates a highly efficient construction which combines a domain decomposition boundary Green’s function formulation with fast Fourier inversion methods. Computed results are used to calculate the effective impedance of the device, which accounts for contributions of both linearized acoustic phenomena and nonlinear inertial effects. The dependence of this effective impedance on stack configuration and on acoustic driving amplitudes and frequencies is also analyzed. [Work supported by the Office of Naval Research.]
Vibrational characteristics of pipe organ reed tongues
Authors: Plitnik G. R. , Knox Ronald
Published: October 2005

Pipe organ reed pipes sound when a fixed-free curved brass reed mounted on a shallot is forced to vibrate by an impressed static air pressure. The frequency dependence of these vibrating reed tongues was determined as a function of three variables. These were the thickness of the reed, the static air pressure within the reed boot, and the length of the reed allowed to vibrate. For each trial, two of these variables were kept constant while the third was altered. Experiments were conducted using three different types of shallots: The American (standard) style, the French style, and the German style. The results show that for each shallot, the frequency increases linearly with thickness and linearly with air pressure (over the normal operating range of the reed). For each of the shallots, frequency varies inversely with length when the other variables are held constant.
Rough sea surface scattering in the presence of an upward-refracting bubble layer
Authors: Gilbert Kenneth E. , Bekker Kathy K. , Kulbago Lucy J.
Published: October 2005

Perturbation theory for scattering from rough surfaces is generalized to account for nonplanar insonifying waves. The generalized theory is applied to low-frequency (50–1500 Hz) sea surface scattering in the presence of an upward-refracting bubble layer. Using an exact numerical solution for the insonifying wave, it is shown that although the sea surface backscatter is enhanced by the upward-refracting bubble layer, the enhancement is not nearly enough to account for the experimentally observed backscatter. Several analytic approximations (plane wave, WKB, Snell’s law) are considered to gain some physical insight into the numerical calculation. At frequencies below a few hundred Hertz, the plane-wave approximation is adequate, that is, the bubble layer becomes acoustically transparent. At higher frequencies, the WKB approximation, which conserves energy, is surprisingly accurate. At low grazing angles and all frequencies, simply using the local wave number (i.e., Snell’s law) is a very poor approximation that does not conserve energy and grossly overestimates the effects of upward refraction. It is concluded that even with upward refraction present, scattering from the rough air–water interface is a minor contributor to the total acoustic backscatter. [Work supported by the Office of Naval Research.]
On the scattering of sound from a submerged thin walled cylinder coated with a compliant layer
Authors: Jarzynski Jacek , Bogle John R. , McCall George S. , Gray Michael D. , Caille Gary W.
Published: October 2005

There is currently an abundance of both mathematical and finite-element models of the scattering of underwater sound from cylindrical bodies treated with compliant coatings. However, there is a significant lack of corresponding scattering measurements. This paper presents the results of a set of simple measurements of the monostatic backscatter from a coated, thin, ribbed cylindrical shell with flat endcaps for ka of 2–8. The coating layer had an input impedance approximately one-fifth that of water, providing a near pressure-release boundary condition. Of particular interest is a minimum in the measured target strength which results from the resonant interaction of the coating and the shell. Results from finite-element and modal expansion models of the coated shell are also presented with the aim of providing a physical understanding of the resonance. [Work supported by ONR.]
Reference sensor selection for automotive active noise control applications
Authors: LePage Kevin D. , Remington P. J. , Curtis Alan R. D. , Knight Scott
Published: October 2005

BBN has obtained a comprehensive set of road noise measurements for the purpose of investigating the potential performance of an automotive active noise control application. Measurements were collected over a total of 20 reference sensors on or near the suspension and four residual sensors in the cabin. Analysis shows that while the reference sensors can account for much of what is received at the microphones, some of the reference sensors provide more residual information than others. For control applications the optimum reference sensors for the available number of input channels are desired. Two reference sensor performance metrics are compared. The first is a suboptimal greedy algorithm where reference channels are iteratively selected via an orthogonalization procedure. The second technique is an exhaustive search over candidate reference sensors sets where the coherent power is maximized. Results show that the greedy procedure generally identifies the majority of the sensors shown to be optimum through the exhaustive search. [Work supported by ARPA.]
A measurement and interpretation of the temporal coherence of acoustic continuous wave propagation in the Barents Sea
Authors: Miller James H. , Lynch James F. , Pierce David D. , Miller Christopher W.
Published: October 2005

As part of the Barents Sea Polar Experiment in the summer of 1992, a continuous wave transmission at 224 Hz was made for 1 h from a near-bottom-moored source to a navigated, vertical array separated by approximately 35 km. The waveguide was approximately 200 m in depth, and its oceanography was dominated by the Barents Sea Polar Front separating the cold, fresh polar water from the warm, saline Atlantic water and a strong thermocline due to surface insolation. Following the methods described by Dahl etal. [J. Acoust. Soc. Am. 83, 2175–2179 (1988)], the variance of the phase rate (ν2) is found for single hydrophones, for beam-formed (plane wave) data, and for mode-formed data. The parameter ν governs the frequency spread and is a measurement of the dynamic effects of the ocean on acoustic propagation. The estimates of ν are related to measured ocean temperature fluctuations and sea surface conditions from the experiment and compared with estimates from the MIZEX data of Dahl etal. The implications of the measurements for sonar system performance including matched field and matched mode techniques are presented. [Research supported by ONR Code 322, High Latitude Dynamics.]
Organization of acoustic singularities in running speech
Authors: Harsin Charles Andrew , Green Kerry P.
Published: October 2005

Investigating speech rhythm by examining an utterance’s syllabic-beat organization seems natural, but is problematic. An utterance must first be divided into syllables, then each syllable’s beat must be located through mathematical modeling or the collection of subjects’ judgments. This study approaches the problem in a more straightforward way by examining the organization of singularities, specifically acoustic envelope amplitude and amplitude rate-of-change maxima, in the acoustic speech wave. These acoustic features are the basis for some acoustic models of syllabic beat location, and so are plausible candidates for more directly measurable correlates of speech rhythm. So far, qualitative analyses suggest that these acoustic features are organized in a quasiperiodic manner which is neither strictly periodicity nor random and that is similar to the organization found in the behaviors of other physical and biological systems. Quantitative analyses will be discussed that further specify the organization of the data. [Work supported by National Multipurpose Research and Training Center Grant DC-01409 from the National Institute on Deafness and Other Communication Disorders.]
Intelligibility assessment of Chinese-accented English
Authors: Rogers Catherine L. , Dalby Jonathan M.
Published: October 2005

Although it is generally accepted that a strong foreign accent renders a speaker less intelligible to native listeners, few studies have attempted to investigate specific sources of this deficit. The present study explores the diagnostic effectiveness of a minimal-pairs test of intelligibility. An inventory of phonemic errors was compiled from careful transcriptions of the spoken English of two native speakers of Mandarin Chinese. Minimal pairs were constructed for each error, using the intended phoneme and the closest English phoneme transcribed. Eight additional native speakers of Mandarin Chinese were recorded reading the target words in the minimal-pairs list and a set of 20 sentences. The minimal-pair target words were presented to groups of native listeners in a forced-choice task; in a second task, listeners were presented with the sentences and asked to write down what they understood. Preliminary results from listener groups for three of the speakers demonstrate (1) no significant differences across listener groups for a control speaker, indicating test reliability, (2) significant differences across listener groups for the three speakers, indicating test sensitivity, and (3) percent-correct scores on the minimal-pairs test are predictive of percent of words correctly identified in the sentence-listening task. [Work supported by NIH-NIDCD Grant ♯2R44DC02213.]
Acoustic scattering by a pair of spheres
Authors: Gaunaurd G. C. , Huang H. , Strifors H. C.
Published: October 2005

If acoustic scattering by a single sphere is the most basic problem of scalar scattering, then sound scattering by a pair of spheres is next in the hierarchy of complexity. The problem has been formulated by several approaches in the past, but no actual detailed studies have been openly published so far. Two spheres insonified by plane waves at arbitrary angles of incidence are considered. The solution of this simplest of multiple-scattering problems is generated by exactly accounting for the interaction between the two spheres, which can be strong or weak depending on their separation, compositions, frequency, and directions of observation. The tools to attack this type of problem are the (forward/backward) addition theorems for the spherical wave functions, which permit the field expansions—all referred to the center of one of the spheres—by means of Wigner (3-j) symbols. The fields scattered by each sphere are obtained as pairs of (double) sums in the spherical wave functions, with coefficients that are coupled through an infinite set of two linear, complex, algebraic equations. These are then solved (by truncation) and used to obtain (i) the scattered fields and (ii) the scattering cross section of the pair of spheres. These exact results are illustrated with many plots of the form functions at various relevant incidence angles, separations, frequencies, etc. Finally, some asymptotic approximations for this problem that are analytically simple are obtained. They are displayed and compared to the exact solutions found above, with quite satisfactory results, even for the simple approximations used here. Thus the phenomenon is described, explained, graphically displayed, physically interpreted, and reduced to a simple accurate approximation in some important cases.
Psychometric functions for level discrimination in cochlearly impaired and normal listeners with equivalent-threshold masking
Authors: Buus So/ren , Florentine Mary , Zwicker Tilmann
Published: October 2005

The purpose of this study was to determine whether the form of the psychometric functions for level discrimination (also known as intensity discrimination) measured in a two-interval, two-alternative forced-choice paradigm changes with hearing impairment. Measurements of sensitivity, d′, as a function of ΔL (=20 log[(p+Δp)/p], where p is pressure) were obtained in six listeners with cochlear impairments, five normal listeners tested in the quiet, and two masked-normal listeners. Stimuli were chosen to encompass a wide range of conditions and difference limens. Results show that the d′ is nearly proportional to ΔL over the entire range of stimuli. This simple relationship is not changed by cochlear impairments or masking noise. These findings indicate that if the transformation from stimulus intensity to decision variable is affected by hearing impairment or masking, the change affects both the mean and the standard deviation in the same manner—i.e., the standard deviation may be proportional to the derivative of the transformation as was suggested by Zwislocki and Jordan [J. Acoust. Soc. Am. 79, 772–780 (1986)]. The results also lend support to the notion that ΔL—plotted on a logarithmic scale—is an appropriate representation of level-discrimination performance.
Interaural cross-correlation, lateral fraction, and low- and high-frequency sound levels as measures of acoustical quality in concert halls
Authors: Hidaka Takayuki , Beranek Leo L. , Okano Toshiyuki
Published: October 2005

Subjective ratings of acoustical quality in concert halls were determined from interviews of conductors, musicians, music critics, and informed listeners during which they were asked to judge the quality of the acoustics and to rank the order of those halls each knew. Subjective ratings on 34 halls were divided into three principal groups: excellent, very good, and less good. No bad halls were studied. The use of the interaural cross-correlation coefficient (IACC) and lateral efficiency (LF) as correlates with the subjective ratings were analyzed in depth. In order to make IACC sensitive to quality ratings, a multi-octave-band average was developed, based on Blauert et al. [Acustica 59, 292 (1986)] and on a subjectively derived set of equal apparent source width (ASW) contours that showed the 0.5-, 1.0-, and 2.0-kHz octave bands to be of equal and principal importance to ASW. This IACC3 was divided into two components, IACCE3, integrated over the first 0.08 s after arrival of the direct sound, and IACCL3, integrated over 0.08–1 s. Subjective judgments were also performed to determine the effects of increased sound levels of symphonic music at frequencies above or below 355 Hz on ASW. It was found that changes in the low-frequency levels (GL) made greater changes in ASW than changes in the high-frequency levels (GH). Because the difference between the low- and high-frequency levels in real halls does not exceed ±5 dB and because both are inversely related to [EDT/Volume], it suffices to measure GL.

Thus IACCL3 and GL appear valuable for determining ASW and the degree of sound-field diffusion in the frequency range from 100 to 3000 Hz for symphonic music in concert halls. The measured quantity [1−IACCE3] alone was found to separate exactly the 17 concert halls for which data were available into three category groups. The constituents of these three groups were the same as those determined from the interviews. The measured lateral fraction (LF) for the 24 halls for which data were available was also compared to the subjective groupings. The average measured values of LF for these halls covered a small range and there were so many overlaps among halls when separation of the halls into three rating groups was attempted that LF was judged not to be suitable for rating the acoustical quality of occupied concert halls.
Time-domain modeling of peripheral auditory processing: A modular architecture and a software platform
Authors: Patterson Roy D. , Allerhand Mike H. , Giguère Christian
Published: October 2005

A software package with a modular architecture has been developed to support perceptual modeling of the fine-grain spectro-temporal information observed in the auditory nerve. The package contains both functional and physiological modules to simulate auditory spectral analysis, neural encoding, and temporal integration, including new forms of periodicity-sensitive temporal integration that generate stabilized auditory images. Combinations of the modules enable the user to approximate a wide variety of existing, time-domain, auditory models. Sequences of auditory images can be replayed to produce cartoons of auditory perceptions that illustrate the dynamic response of the auditory system to everyday sounds.
Binaural advantage for sound pattern identification
Authors: Kidd Gerald , Mason Christine R. , Rohtla Tanya L.
Published: October 2005

Listeners were trained to identify six patterns of eight sequentially presented 48-ms tone bursts. The variation in frequency forming the patterns was confined to a relatively narrow range around the nominal center frequency, which was either 500, 1000, or 3000 Hz, or was selected randomly on each presentation from a range of 450–3300 Hz. Detection (500 and 3000 Hz only) and identification of the six patterns masked by Gaussian noise was measured in two interaural presentation conditions: masker in-phase and signal in-phase (NoSo), and masker in-phase and signal π rad out-of-phase (NoSπ). The differences in performance in the two interaural presentation conditions for detection and identification are referred to as ‘‘masking-level differences’’ (MLDs) and ‘‘identification-level differences’’ (IDLDs), respectively. At 500 Hz, MLDs and IDLDs were about 11–13 dB. At 3000 Hz, the MLDs and IDLDs were about 1–3 dB. For the random-center-frequency condition, the slopes of the identification-level functions were much shallower for the NoSπ condition than for the NoSo condition so the binaural advantage was large at low signal-to-noise ratios and declined as signal-to-noise ratio increased.

This finding was due to the broad frequency range over which the information was distributed and the decline in the binaural advantage with increasing frequency, a conclusion consistent with that reported for the binaural advantage for speech intelligibility. A second experiment demonstrated that MLDs and IDLDs could be manipulated independently: A 500-Hz tone was added to each element of the 3000-Hz patterns. A large MLD was found—due to detection of the 500-Hz tone—while the identification-level functions were determined solely by the high-frequency information, which produced small IDLDs. Finally, the Gaussian noise masker was replaced by an informational masker comprised of eight randomly chosen eight-tone bursts played simultaneously with the signal-pattern elements which were centered at 1000 Hz. Large amounts of informational masking were found for identification. The slopes of the identification-level functions were much shallower than found for the Gaussian noise masker and a relatively small binaural advantage (about 5 dB) was observed.
Lord Rayleigh’s contributions to musical acoustics
Authors: Rossing Thomas D.
Published: October 2005

Rayleigh’s work touched virtually every area of acoustics in some way; musical acoustics is certainly no exception. Besides laying the groundwork for all subsequent research on musical instruments with his informative discussions of the vibrations of strings, bars, membranes, plates, air columns, and resonators, he did important theoretical and experimental work on bells and kettledrums. He identified the vibrational modes that radiated the most prominent partials in the sounds of both of these instruments, and he recognized that the nominal pitch of a church bell lies one octave below the fifth partial. He compared organ pipes with and without flanges, and he determined the effect of blowing pressure on pitch. In the reflected sound from a grove of trees, he observed an acoustic analogue of Rayleigh scattering of light. In the area of music perception, his most important contributions were his studies of absolute pitch and sound source localization.
Multiple cues for the discrimination of narrow-band sounds
Authors: Southworth Curt , Berg Bruce G.
Published: October 2005

The ability to discriminate spectral changes in narrow-band sounds on the basis of multiple cues is examined. The task is to discriminate a sound consisting of three equal-intensity tones with frequencies of 960, 1000, and 1040 Hz from a sound with an increment in the level of the center component. In different conditions, listeners are instructed to discriminate the stimuli according to either ‘‘loudness,’’ ‘‘pitch,’’ or ‘‘roughness’’ cues. Spectral weights are estimated in each condition by the method of COSS analysis [B. G. Berg, J. Acoust. Soc. Am. 86, 1743–1746 (1989)]. Relative to a condition without instructions, systematic changes in the pattern of weight estimates are found for each condition. Weight estimates for the loudness and pitch conditions follow patterns predicted by respective models that base discriminations on overall level and on the envelope-weighted average of instantaneous frequency [L. L. Feth and H. O’Malley, J. Acoust. Soc. Am. 62, 940–947 (1977)] with off-frequency listening. Weight estimates for the roughness condition change relative to other conditions, but do not follow the predictions of a model which uses information about the envelope of the temporal waveform. However, when loudness and pitch information are degraded in a post hoc condition, weight estimates are consistent with those predicted by the envelope model. Changes in weight patterns with instructions are interpreted as changes in listeners’ decision strategies among multiple cues. Departures of weight patterns from model predictions suggest that the processes that underlie dimensions of pitch and roughness are not independent of loudness.
Auditory attentional bandwidth: Effect of level and frequency range
Authors: Botte Marie-Claire
Published: October 2005

This study investigated the relations between theoretical auditory filters and ‘‘attentional filters’’ observed when measuring the detectability in noise of tones of expected or unexpected (probe) frequency. The effect of the level of the noise and the frequency range (narrow or wide) of the probes was assessed. For each 2IFC trial, a tone of the expected target frequency was presented as a cue preceding the two observation intervals—the signal was more often the expected than an unexpected frequency. For the narrow frequency range of probe frequencies, increasing the masker level resulted in a broadening of the probe-signal contour (percent correct as a function of probe frequency); however, detection was significantly better only for probe frequencies farthest from the target frequency. For the wide range of probe frequencies, the percentage of correct detections depended less systematically on masker level; however, detection was better and the attentional band wider than in the narrow frequency range. The results suggest that attentional focusing does not simply reflect auditory filtering: A more central and adaptive process may operate from the outputs of adjacent or more distant auditory filters.
An excitation-pattern model for the starling (Sturnus vulgaris)
Authors: Buus So/ren , Klump Georg M. , Gleich Otto , Langemann Ulrike
Published: October 2005

This paper develops and tests an excitation-pattern model for the starling. Like excitation-pattern models for humans [e.g., Zwicker, Acustica 6, 365–381 (1956); Florentine and Buus, J. Acoust. Soc. Am. 70, 1646–1654 (1981)], the model for starlings provides a unified account of a large body of data. The foundation of the model is a critical-band scale, which is derived as an equal-distance scale according to a cochlear-map function. The cochlear-map function is determined as a best-fitting function to physiological data relating characteristic frequency (CF) of auditory-nerve fibers to their place of innervation on the basilar papilla. Excitation patterns are derived from auditory-nerve measurements of levels at CF necessary to produce firing rates equal to those evoked by a test tone. The shape of these excitation patterns is independent of level and frequency when plotted on a cochlear-distance scale. The resulting model indicates that 10-dB bandwidths of auditory-nerve tuning curves and frequency DLs can be approximated as equal distances along the basilar papilla. Predictions of level discrimination are in good agreement with the data, except below 20 dB SL. Overall, the present work indicates that excitation-pattern models account for a wide range of auditory phenomena in both humans and starlings, when the models take into account differences in critical-band scales, absolute thresholds, excitation-pattern slopes, and growth of excitation, which is linear in starlings, but nonlinear in humans.
Diversification of DNA Sequences in the Symbiotic Genome of
Rhizobium etli
Authors: Flores Margarita , Morales Lucia , Avila Agustín , González Víctor , Bustos Patricia , García Delfino , Mora Yolanda , Guo Xianwu , Collado-Vides Julio , Piñero Daniel , Dávila Guillermo , Mora Jaime , Palacios Rafael
Published: October 2005

Bacteria of the genus
Rhizobium
and related genera establish nitrogen-fixing symbioses with the roots of leguminous plants. The genetic elements that participate in the symbiotic process are usually compartmentalized in the genome, either as independent replicons (symbiotic plasmids) or as symbiotic regions or islands in the chromosome. The complete nucleotide sequence of the symbiotic plasmid of
Rhizobium etli
model strain CFN42, symbiont of the common bean plant, has been reported. To better understand the basis of DNA sequence diversification of this symbiotic compartment, we analyzed the distribution of single-nucleotide polymorphisms in homologous regions from different
Rhizobium etli
strains. The distribution of polymorphisms is highly asymmetric in each of the different strains, alternating regions containing very few changes with regions harboring an elevated number of substitutions. The regions showing high polymorphism do not correspond with discrete genetic elements and are not the same in the different strains, indicating that they are not hypervariable regions of functional genes. Most interesting, some highly polymorphic regions share exactly the same nucleotide substitutions in more than one strain. Furthermore, in different regions of the symbiotic compartment, different sets of strains share the same substitutions. The data indicate that the majority of nucleotide substitutions are spread in the population by recombination and that the contribution of new mutations to polymorphism is relatively low. We propose that the horizontal transfer of homologous DNA segments among closely related organisms is a major source of genomic diversification.
Competition and Coexistence betweenStreptococcus mutansandStreptococcus sanguinisin the Dental Biofilm
Authors: Kreth Jens , Merritt Justin , Shi Wenyuan , Qi Fengxia
Published: October 2005

The human mucosal surface is colonized by the indigenous microflora, which normally maintains an ecological balance among different species. Certain environmental or biological factors, however, may trigger disruption of this balance, leading to microbial diseases. In this study, we used two oral bacterial species,Streptococcus mutansandStreptococcus sanguinis(formerlyS. sanguis), as a model to probe the possible mechanisms of competition/coexistence between different species which occupy the same ecological niche. We show that the two species engage in a multitude of antagonistic interactions temporally and spatially; occupation of a niche by one species precludes colonization by the other, while simultaneous colonization by both species results in coexistence. Environmental conditions, such as cell density, nutritional availability, and pH, play important roles in determining the outcome of these interactions. Genetic and biochemical analyses reveal that these interspecies interactions are possibly mediated through a well-regulated production of chemicals, such as bacteriocins (produced byS. mutans) and hydrogen peroxide (produced byS. sanguinis). Consistent with the phenotypic characteristics, production of bacteriocins and H2O2are regulated by environmental conditions, as well as by juxtaposition of the two species. These sophisticated interspecies interactions could play an essential part in balancing competition/coexistence within multispecies microbial communities.
Stationary-Phase Regulation of RpoS Translation in
Escherichia coli
Authors: Hirsch Matthew , Elliott Thomas
Published: October 2005

In enteric bacteria, adaptation to a number of different stresses is mediated by the RpoS protein, one of several sigma factors that collectively allow a tailored transcriptional response to environmental cues. Stress stimuli including low temperature, osmotic shock, nutrient limitation, and growth to stationary phase (SP) all result in a substantial increase in RpoS abundance and activity. The mechanism of regulation depends on the specific signal but may occur at the level of transcription, translation, protein activity, or targeted proteolysis. In both
Escherichia coli
and
Salmonella enterica
, SP induction of RpoS in rich medium is >30 fold and includes effects on both transcription and translation. Recently, we found that SP control of
rpoS
transcription in
S. enterica
involves repression of the major
rpoS
promoter during exponential phase by the global transcription factor Fis. Working primarily with
E. coli
, we now show that 24 nucleotides of the
rpoS
ribosome-binding site (RBS) are necessary and sufficient for a large part of the increase in
rpoS
translation as cells grow to SP. Genetic evidence points to an essential role for the leader nucleotides just upstream of the Shine-Dalgarno sequence but is conflicted on the question of whether sequence or structure is important. SP regulation of
rpoS
is conserved between
E. coli
and
S. enterica
. When combined with an
fis
mutation to block transcriptional effects, replacement of the
rpoS
RBS sequence by the
lacZ
RBS eliminates nearly all SP induction of RpoS.
Insights into Genome Plasticity and Pathogenicity of the Plant Pathogenic BacteriumXanthomonas campestrispv. vesicatoria Revealed by the Complete Genome Sequence
Authors: Thieme Frank , Koebnik Ralf , Bekel Thomas , Berger Carolin , Boch Jens , Büttner Daniela , Caldana Camila , Gaigalat Lars , Goesmann Alexander , Kay Sabine , Kirchner Oliver , Lanz Christa , Linke Burkhard , McHardy Alice C. , Meyer Folker , Mittenhuber Gerhard , Nies Dietrich H. , Niesbach-Klösgen Ulla , Patschkowski Thomas , Rückert Christian , Rupp Oliver , Schneiker Susanne , Schuster Stephan C. , Vorhölter Frank-Jörg , Weber Ernst , Pühler Alfred , Bonas Ulla , Bartels Daniela , Kaiser Olaf
Published: October 2005

The gram-negative plant-pathogenic bacteriumXanthomonas campestrispv. vesicatoria is the causative agent of bacterial spot disease in pepper and tomato plants, which leads to economically important yield losses. This pathosystem has become a well-established model for studying bacterial infection strategies. Here, we present the whole-genome sequence of the pepper-pathogenicXanthomonas campestrispv. vesicatoria strain 85-10, which comprises a 5.17-Mb circular chromosome and four plasmids. The genome has a high G+C content (64.75%) and signatures of extensive genome plasticity. Whole-genome comparisons revealed a gene order similar to bothXanthomonas axonopodispv. citri andXanthomonas campestrispv. campestris and a structure completely different fromXanthomonas oryzaepv. oryzae. A total of 548 coding sequences (12.2%) are unique toX. campestrispv. vesicatoria. In addition to a type III secretion system, which is essential for pathogenicity, the genome of strain 85-10 encodes all other types of protein secretion systems described so far in gram-negative bacteria. Remarkably, one of the putative type IV secretion systems encoded on the largest plasmid is similar to the Icm/Dot systems of the human pathogensLegionella pneumophilaandCoxiella burnetii. Comparisons with other completely sequenced plant pathogens predicted six novel type III effector proteins and several other virulence factors, including adhesins, cell wall-degrading enzymes, and extracellular polysaccharides.