bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsatile Flow and Oxygen Transport Past Cylindrical Fiber Arrays for an Artificial Lung: Computational and Experimental Studies
Authors: Zierenberg Jennifer R. , Fujioka Hideki , Cook Keith E. , Grotberg James B.
Published: May 2008

The influence of time-dependent flows on oxygen transport from hollow fibers was computationally and experimentally investigated. The fluid average pressure drop, a measure of resistance, and the work required by the heart to drive fluid past the hollow fibers were also computationally explored. This study has particular relevance to the development of an artificial lung, which is perfused by blood leaving the right ventricle and in some cases passing through a compliance chamber before entering the device. Computational studies modeled the fiber bundle using cylindrical fiber arrays arranged in in-line and staggered rectangular configurations. The flow leaving the compliance chamber was modeled as dampened pulsatile and consisted of a sinusoidal perturbation superimposed on a steady flow. The right ventricular flow was modeled to depict the period of rapid flow acceleration and then deceleration during systole followed by zero flow during diastole. Experimental studies examined oxygen transfer across a fiber bundle with either steady, dampened pulsatile, or right ventricular flow. It was observed that the dampened pulsatile flow yielded similar oxygen transport efficiency to the steady flow, while the right ventricular flow resulted in smaller oxygen transport efficiency, with the decrease increasing with Re. Both computations and experiments yielded qualitatively similar results. In the computational modeling, the average pressure drop was similar for steady and dampened pulsatile flows and larger for right ventricular flow while the pump work required of the heart was greatest for right ventricular flow followed by dampened pulsatile flow and then steady flow. In conclusion, dampening the artificial lung inlet flow would be expected to maximize oxygen transport, minimize work, and thus improve performance.
Design of an Ex Vivo Culture System to Investigate the Effects of Shear Stress on Cardiovascular Tissue
Authors: Sucosky Philippe , Padala Muralidhar , Elhammali Adnan , Balachandran Kartik , Jo Hanjoong , Yoganathan Ajit P.
Published: May 2008

Mechanical forces are known to affect the biomechanical properties of native and engineered cardiovascular tissue. In particular, shear stress that results from the relative motion of heart valve leaflets with respect to the blood flow is one important component of their mechanical environment in vivo. Although different types of bioreactors have been designed to subject cells to shear stress, devices to expose biological tissue are few. In an effort to address this issue, the aim of this study was to design an ex vivo tissue culture system to characterize the biological response of heart valve leaflets subjected to a well-defined steady or time-varying shear stress environment. The novel apparatus was designed based on a cone-and-plate viscometer. The device characteristics were defined to limit the secondary flow effects inherent to this particular geometry. The determination of the operating conditions producing the desired shear stress profile was streamlined using a computational fluid dynamic (CFD) model validated with laser Doppler velocimetry. The novel ex vivo tissue culture system was validated in terms of its capability to reproduce a desired cone rotation and to maintain sterile conditions. The CFD results demonstrated that a cone angle of 0.5deg, a cone radius of 40mm, and a gap of 0.2mm between the cone apex and the plate could limit radial secondary flow effects. The novel cone-and-plate permits to expose nine tissue specimens to an identical shear stress waveform. The whole setup is capable of accommodating four cone-and-plate systems, thus concomitantly subjecting 36 tissue samples to desired shear stress condition. The innovative design enables the tissue specimens to be flush mounted in the plate in order to limit flow perturbations caused by the tissue thickness. The device is capable of producing shear stress rates of up to 650dyncm−2s−1 (i.e., maximum shear stress rate experienced by the ventricular surface of an aortic valve leaflet) and was shown to maintain tissue under sterile conditions for 120h. The novel ex vivo tissue culture system constitutes a valuable tool toward elucidating heart valve mechanobiology. Ultimately, this knowledge will permit the production of functional tissue engineered heart valves, and a better understanding of heart valve biology and disease progression.
Injury Tolerance and Moment Response of the Knee Joint to Combined Valgus Bending and Shear Loading
Authors: Bose Dipan , Bhalla Kavi S. , Untaroiu Costin D. , Ivarsson B. Johan , Crandall Jeff R. , Hurwitz Shepard
Published: May 2008

Valgus bending and shearing of the knee have been identified as primary mechanisms of injuries in a lateral loading environment applicable to pedestrian-car collisions. Previous studies have reported on the structural response of the knee joint to pure valgus bending and lateral shearing, as well as the estimated injury thresholds for the knee bending angle and shear displacement based on experimental tests. However, epidemiological studies indicate that most knee injuries are due to the combined effects of bending and shear loading. Therefore, characterization of knee stiffness for combined loading and the associated injury tolerances is necessary for developing vehicle countermeasures to mitigate pedestrian injuries. Isolated knee joint specimens (n=40) from postmortem human subjects were tested in valgus bending at a loading rate representative of a pedestrian-car impact. The effect of lateral shear force combined with the bending moment on the stiffness response and the injury tolerances of the knee was concurrently evaluated. In addition to the knee moment-angle response, the bending angle and shear displacement corresponding to the first instance of primary ligament failure were determined in each test. The failure displacements were subsequently used to estimate an injury threshold function based on a simplified analytical model of the knee. The validity of the determined injury threshold function was subsequently verified using a finite element model. Post-test necropsy of the knees indicated medial collateral ligament injury consistent with the clinical injuries observed in pedestrian victims. The moment-angle response in valgus bending was determined at quasistatic and dynamic loading rates and compared to previously published test data. The peak bending moment values scaled to an average adult male showed no significant change with variation in the superimposed shear load. An injury threshold function for the knee in terms of bending angle and shear displacement was determined by performing regression analysis on the experimental data. The threshold values of the bending angle (16.2deg) and shear displacement (25.2mm) estimated from the injury threshold function were in agreement with previously published knee injury threshold data. The continuous knee injury function expressed in terms of bending angle and shear displacement enabled injury prediction for combined loading conditions such as those observed in pedestrian-car collisions.
Numerical Simulation of Mass Transport in a Microchannel Bioreactor With Cell Micropatterning
Authors: Zeng Yan , Lee Thong-See , Yu Peng , Low Hong-Tong
Published: May 2008

Micropatterning of two different cell types based on surface modification allows spatial control over two distinct cell subpopulations. This study considers a micropatterned coculture system, which has release and absorption parts alternately arranged at the base, and each part has a single cell type. A micropattern unit was defined and within each unit, there are one release part and one absorption part. The cells in the absorption parts consume species, which are secreted by the cells in the release parts. The species concentrations at the micropatterned cell base were computed from a three-dimensional numerical flow model incorporating mass transport. Different combined parameters were developed for the release and absorption parts to make the data collapse in each part. Combination of the collapse data in the release and absorption parts can be used to predict the concentration distribution through the whole channel. The correlated results were applied to predict the critical length ratio of the release and absorption parts for an actual micropatterned system (Bhatia et al., 1999, “Effect of Cell-Cell Interactions in Preservation of Cellular Phenotype: Co-Cultivation of Hepatocytes and Nonparenchymal Cell,” FASEB J. 13, pp. 1883–1900) to avoid species insufficiency based on basic fibroblast growth factor (bFGF). The mass transfer effectiveness was found to be higher with more numbers of micropattern units. The optimal condition for micropatterned coculture bioreactors is achieved by having the product of the length ratio and the reaction ratio equal to 1. This condition was used to optimize the mass transfer in the micropatterned system (Bhatia et al., 1999, “Effect of Cell-Cell Interactions in Preservation of Cellular henotype: Co-Cultivation of Hepatocytes and Nonparenchymal Cell,” FASEB J. 13, pp. 1883–1900) based on bFGF.
Numerical Analysis of the Cooling Effect of Blood Over Inflamed Atherosclerotic Plaque
Authors: Kim Taehong , Ley Obdulia
Published: May 2008

Atherosclerotic plaques with high likelihood of rupture often show local temperature increase with respect to the surrounding arterial wall temperature. In this work, atherosclerotic plaque temperature was numerically determined during the different levels of blood flow reduction produced by the introduction of catheters at the vessel lumen. The temperature was calculated by solving the energy equation and the Navier–Stokes equations in 2D idealized arterial models. Arterial wall temperature depends on three basic factors: metabolic activity of the inflammatory cells embedded in the plaque, heat convection due to luminal blood flow, and heat conduction through the arterial wall and plaque. The calculations performed serve to simulate transient blood flow reduction produced by the presence of thermography catheters used to measure arterial wall temperature. The calculations estimate the spatial and temporal alterations in the cooling effect of blood flow and plaque temperature during the measurement process. The mathematical model developed provides a tool for analyzing the contribution of factors known to affect heat transfer at the plaque surface. Blood flow reduction leads to a nonuniform temperature increase ranging from 0.1°Cto0.25°Celsius in the plaque/lumen interface of the arterial geometries considered in this study. The temperature variation as well as the Nusselt number calculated along the plaque surface strongly depended on the arterial geometry and distribution of inflammatory cells. The calculations indicate that the minimum required time to obtain a steady temperature profile after arterial occlusion is 6s. It was seen that in arteries with geometries involving bends, the temperature profiles appear asymmetrical and lean toward the downstream edge of the plaque.
Experimental Validation of a Finite Element Model of a Human Cadaveric Tibia
Authors: Gray Hans A. , Taddei Fulvia , Zavatsky Amy B. , Cristofolini Luca , Gill Harinderjit S
Published: May 2008

Finite element (FE) models of long bones are widely used to analyze implant designs. Experimental validation has been used to examine the accuracy of FE models of cadaveric femurs; however, although convergence tests have been carried out, no FE models of an intact and implanted human cadaveric tibia have been validated using a range of experimental loading conditions. The aim of the current study was to create FE models of a human cadaveric tibia, both intact and implanted with a unicompartmental knee replacement, and to validate the models against results obtained from a comprehensive set of experiments. Seventeen strain rosettes were attached to a human cadaveric tibia. Surface strains and displacements were measured under 17 loading conditions, which consisted of axial, torsional, and bending loads. The tibia was tested both before and after implantation of the knee replacement. FE models were created based on computed tomography (CT) scans of the cadaveric tibia. The models consisted of ten-node tetrahedral elements and used 600 material properties derived from the CT scans. The experiments were simulated on the models and the results compared to experimental results. Experimental strain measurements were highly repeatable and the measured stiffnesses compared well to published results. For the intact tibia under axial loading, the regression line through a plot of strains predicted by the FE model versus experimentally measured strains had a slope of 1.15, an intercept of 5.5 microstrain, and an R2 value of 0.98. For the implanted tibia, the comparable regression line had a slope of 1.25, an intercept of 12.3 microstrain, and an R2 value of 0.97. The root mean square errors were 6.0% and 8.8% for the intact and implanted models under axial loads, respectively. The model produced by the current study provides a tool for simulating mechanical test conditions on a human tibia. This has considerable value in reducing the costs of physical testing by pre-selecting the most appropriate test conditions or most favorable prosthetic designs for final mechanical testing. It can also be used to gain insight into the results of physical testing, by allowing the prediction of those variables difficult or impossible to measure directly.
Yellow He–Ne going red: A one-minute optics demonstration
Authors: Hopper Christopher , Sieradzan Andrzej
Published: May 2008

A sudden change in the emission wavelength is observed for some types of helium-neon lasers, when their beams are retroreflected. We discuss the physics behind the effect, and propose a novel classroom demonstration for use in optics courses.
Diet Coke and Mentos: What is really behind this physical reaction?
Authors: Coffey Tonya Shea
Published: May 2008

The Diet Coke and Mentos reaction is a fun demonstration in chemistry and physics classes of many important concepts in thermodynamics, fluid dynamics, surface science, and the physics of explosions. The reaction has been performed numerous times on television and the Internet, but has not been systematically studied. We report on an experimental study of the Diet Coke and Mentos reaction, and consider many aspects of the reaction, including the ingredients in the candy and soda, the roughness of the candy, the temperature of the soda, and the duration of the reaction.
Collective bubble oscillations as a component of surf infrasound
Authors: Park Joseph , Garcés Milton , Fee David , Pawlak Geno
Published: May 2008

Plunging surf is a known generator of infrasound, though the mechanisms have not been clearly identified. A model based on collective bubble oscillations created by demise of the initially entrained air pocket is examined. Computed spectra are compared to infrasound data from the island of Kauai during periods of medium, large, and extreme surf. Model results suggest that bubble oscillations generated by plunging waves are plausible generators of infrasound, and that dynamic bubble plume evolution on a temporal scale comparable to the breaking wave period may contribute to the broad spectral lobe of dominant infrasonic energy observed in measured data. Application of an inverse model has potential to characterize breaking wave size distributions, energy, and temporal changes in seafloor morphology based on remotely sensed infrasound.
Focus, prosodic context, and phonological feature specification: Patterns of variation in fricative production
Authors: Silbert Noah , de Jong Kenneth
Published: May 2008

Because they consist, in large part, of random turbulent noise, fricatives present a challenge to attempts to specify the phonetic correlates of phonological features. Previous research has focused on temporal properties, acoustic power, and a variety of spectral properties of fricatives in a number of contexts [Jongman et al., J. Acoust. Soc. Am. 108, 1252–1263 (2000); Jesus and Shadle, J. Phonet. 30, 437–467 (2002); Crystal and House, J. Acoust. Soc. Am. 83, 1553–1573 (1988a)]. However, no systematic investigation of the effects of focus and prosodic context on fricative production has been carried out. Manipulation of explicit focus can serve to selectively exaggerate linguistically relevant properties of speech in much the same manner as stress [de Jong, J. Acoust. Soc. Am. 97, 491–504 (1995); de Jong, J. Phonet. 32, 493–516 (2004); de Jong and Zawaydeh, J. Phonet. 30, 53–75 (2002)]. This experimental technique was exploited to investigate acoustic power along with temporal and spectral characteristics of American English fricatives in two prosodic contexts, to probe whether native speakers selectively attend to subsegmental features, and to consider variability in fricative production across speakers. While focus in general increased noise power and duration, speakers did not selectively enhance spectral features of the target fricatives.
Pitch strength decreases as F0 and harmonic resolution increase in complex tones composed exclusively of high harmonics
Authors: Timothy Ives D. , Patterson Roy D.
Published: May 2008

A melodic pitch experiment was performed to demonstrate the importance of time-interval resolution for pitch strength. The experiments show that notes with a low fundamental (75Hz) and relatively few resolved harmonics support better performance than comparable notes with a higher fundamental (300Hz) and more resolved harmonics. Two four note melodies were presented to listeners and one note in the second melody was changed by one or two semitones. Listeners were required to identify the note that changed. There were three orthogonal stimulus dimensions: F0 (75 and 300Hz); lowest frequency component (3, 7, 11, or 15); and number of harmonics (4 or 8). Performance decreased as the frequency of the lowest component increased for both F0’s, but performance was better for the lower F0. The spectral and temporal information in the stimuli were compared using a time-domain model of auditory perception. It is argued that the distribution of time intervals in the auditory nerve can explain the decrease in performance as F0, and spectral resolution increase. Excitation patterns based on the same time-interval information do not contain sufficient resolution to explain listener’s performance on the melody task.
Cubic nonlinearity in shear wave beams with different polarizations
Authors: Wochner Mark S. , Hamilton Mark F. , Ilinskii Yurii A. , Zabolotskaya Evgenia A.
Published: May 2008

A coupled pair of nonlinear parabolic equations is derived for the two components of the particle motion perpendicular to the axis of a shear wave beam in an isotropic elastic medium. The equations account for both quadratic and cubic nonlinearity. The present paper investigates, analytically and numerically, effects of cubic nonlinearity in shear wave beams for several polarizations: linear, elliptical, circular, and azimuthal. Comparisons are made with effects of quadratic nonlinearity in compressional wave beams.
What marks the beat of speech?
Authors: Kochanski Greg , Orphanidou Christina
Published: May 2008

Which acoustic properties of the speech signal differ between rhythmically prominent syllables and non-prominent ones? A production experiment was conducted to identify these acoustic properties. Subjects read out repetitive text to a metronome, trying to match stressed syllables to its beat. The analysis searched for the function of the speech signal that best predicts the timing of the metronome ticks. The most important factor in this function is found to be the contrast in loudness between a syllable and its neighbors. The prominence of a syllable can be deduced from the specific loudness in an (approximately) 360ms window centered on the syllable in question relative to an (approximately) 800-ms-wide symmetric window.
Mathematics of pulsed vocalizations with application to killer whale biphonation
Authors: Brown Judith C.
Published: May 2008

Formulas for the spectra of pulsed vocalizations for both the continuous and discrete cases are rigorously derived from basic formulas for Fourier analysis, a topic discussed qualitatively in Watkins’ classic paper on “the harmonic interval” [“The harmonic interval: Fact or artifact in spectral analysis of pulse trains,” in Marine Bioacoustics 2, edited by W. N. Tavogla (Pergamon, New York, 1967), pp. 15–43]. These formulas are summarized in a table for easy reference, along with most of the corresponding graphs. The case of a “pulse tone” is shown to involve multiplication of two temporal wave forms, corresponding to convolution in the frequency domain. This operation is discussed in detail and shown to be equivalent to a simpler approach using a trigonometric formula giving sum and difference frequencies. The presence of a dc component in the temporal wave form, which implies physically that there is a net positive pressure at the source, is discussed, and examples of the corresponding spectra are calculated and shown graphically. These have application to biphonation (two source signals) observed for some killer whale calls and implications for a source mechanism. A MATLAB program for synthesis of a similar signal is discussed and made available online.
Intra- versus intermodal integration in young and older adults
Authors: Spehar Brent P. , Tye-Murray Nancy , Sommers Mitchell S.
Published: May 2008

The ability to integrate information across sensory channels is critical for both within- and between-modality speech processing. The present study evaluated the hypothesis that inter- and intramodal integration abilities are related, in young and older adults. Further, the investigation asked if intramodal integration (auditory+auditory), and intermodal integration (auditory+visual) resist changes as a function of either aging or the presence of hearing loss. Three groups of adults (young with normal hearing, older with normal hearing, and older with hearing loss) were asked to identify words in sentence context. Intramodal integration ability was assessed by presenting disjoint passbands of speech (550–750 and 1650–2250Hz) to either ear. Integration was indexed by factoring monotic from dichotic scores to control for potential hearing- or age-related influences on absolute performance. Intermodal integration ability was assessed by presenting the auditory and visual signals. Integration was indexed by a measure based on probabilistic models of auditory-visual integration, termed integration enhancement. Results suggested that both types of integration ability are largely resistant to changes with age and hearing loss. In addition, intra- and intermodal integration were shown to be not correlated. As measured here, these findings suggest that there is not a common mechanism that accounts for both inter- and intramodal integration performance.
Frequency and level dependent masking of the multiple auditory steady-state response in the bottlenose dolphin (Tursiops truncatus)
Authors: Branstetter Brian K. , Finneran James J. , Houser Dorian S.
Published: May 2008

The potential for interactions between steady-state evoked responses to simultaneous auditory stimuli was investigated in two bottlenose dolphins (Tursiops truncatus). Three experiments were conducted using either a probe stimulus (probe condition) or a probe in the presence of a masker (probe-plus-masker condition). In the first experiment, the probe and masker were sinusoidal amplitude-modulated (SAM) tones. Probe and masker frequencies and masker level were manipulated to provide variable masking conditions. Probe frequencies were 31.7, 63.5, 100.8, and 127.0kHz. The second experiment was identical to the first except only the 63.5kHz probe was used and maskers were pure tones. For the third experiment, thresholds were measured for the probe and probe-plus-masker conditions using two techniques, one based on the lowest detectable response and the other based on a regression analysis. Results demonstrated localized masking effects where lower frequency maskers suppressed higher frequency probes and higher amplitude maskers produced a greater masking effect. The pattern of pure tone masking was nearly identical to SAM tone masking. The two threshold estimates were similar in low masking conditions, but in high masking conditions the lowest detectable response tended to overestimate thresholds while the regression-based analysis tended to underestimate thresholds.
Acoustic cues to tonal contrasts in Mandarin: Implications for cochlear implants
Authors: Kuo Yu-Ching , Rosen Stuart , Faulkner Andrew
Published: May 2008

The present study systematically manipulated three acoustic cues—fundamental frequency (f0), amplitude envelope, and duration—to investigate their contributions to tonal contrasts in Mandarin. Simplified stimuli with all possible combinations of these three cues were presented for identification to eight normal-hearing listeners, all native speakers of Mandarin from Taiwan. The f0 information was conveyed either by an f0-controlled sawtooth carrier or a modulated noise so as to compare the performance achievable by a clear indication of voice f0 and what is possible with purely temporal coding of f0. Tone recognition performance with explicit f0 was much better than that with any combination of other acoustic cues (consistently greater than 90% correct compared to 33%–65%; chance is 25%). In the absence of explicit f0, the temporal coding of f0 and amplitude envelope both contributed somewhat to tone recognition, while duration had only a marginal effect. Performance based on these secondary cues varied greatly across listeners. These results explain the relatively poor perception of tone in cochlear implant users, given that cochlear implants currently provide only weak cues to f0, so that users must rely upon the purely temporal (and secondary) features for the perception of tone.
Influence of spatial correlation function on attenuation of ultrasonic waves in two-phase materials
Authors: Liu Dalie , Turner Joseph A.
Published: May 2008

Successful processing of materials by powder sintering relies on the creation of strong interparticle bonds. During certain critical stages of the sintering process, the medium may be modeled as two phases consisting of the particles and a surrounding matrix. Ultrasonic methods have been proposed as a potential tool for monitoring such sintering processes. Thus, an understanding of the propagation and scattering of elastic waves in two-phase solids is of fundamental importance to these monitoring techniques. In this article, expressions for the ultrasonic attenuations are developed based on the spatial statistics of the density and Lamé parameters of the material constituents under assumptions of statistical homogeneity and statistical isotropy. The formulation is based on the solution of the elastodynamic Dyson equation within the limits of the first-order smoothing approximation. Since the geometric two-point correlation function plays a central role in the model, numerical models are developed using Voronoi polycrystals surrounded by a matrix of different material properties. The spatial statistics of the medium are extracted from these models. The results presented suggest new ultrasonic techniques may be developed to extract multiple correlation lengths for such two-phase microstructures.
Effect of combined source (F) and filter (formant) variation on red deer hind responses to male roars
Authors: Charlton Benjamin D. , Reby David , McComb Karen
Published: May 2008

Studying female response to variation in single acoustic components has provided important insights into how sexual selection operates on male acoustic signals. However, since vocal signals are typically composed of independent components, it is important to account for possible interactions between the studied parameter and other relevant acoustic features of vocal signals. Here, two key components of the male red deer roar, the fundamental frequency and the formant frequencies (an acoustic cue to body size), are independently manipulated in order to examine female response to calls characterized by different combinations of these acoustic components. The results revealed that red deer hinds showed greater overall attention and had lower response latencies to playbacks of roars where lower formants simulated larger males. Furthermore, female response to male roars simulating different size callers was unaffected by the fundamental frequency of the male roar when it was varied within the natural range. Finally, the fundamental frequency of the male roar had no significant separate effect on any of the female behavioral response categories. Taken together these findings indicate that directional intersexual selection pressures have contributed to the evolution of the highly mobile and descended larynx of red deer stags and suggest that the fundamental frequency of the male roar does not affect female perception of size-related formant information.
Human listeners attend to size information in domestic dog growls
Authors: Taylor Anna M. , Reby David , McComb Karen
Published: May 2008

The acoustic features of vocalizations have the potential to transmit information about the size of callers. Most acoustic studies have focused on intraspecific perceptual abilities, but here, the ability of humans to use growls to assess the size of adult domestic dogs was tested. In a first experiment, the formants of growls were shifted to create playback stimuli with different formant dispersions (Δf), simulating different vocal tract lengths within the natural range of variation. Mean fundamental frequency (F0) was left unchanged and treated as a covariate. In a second experiment, F0 was resynthesized and Δf was left unchanged. In both experiments Δf and F0 influenced how participants rated the size of stimuli. Lower formant and fundamental frequencies were rated as belonging to larger dogs. Crucially, when F0 was manipulated and Δf was natural, ratings were strongly correlated with the actual weight of the dogs, while when Δf was varied and F0 was natural, ratings were not related to the actual weight. Taken together, this suggests that participants relied more heavily on Δf, in accordance with the fact that formants are better predictors of body size than F0.
Compensation for coarticulation, /u/-fronting, and sound change in standard southern British: An acoustic and perceptual study
Authors: Harrington Jonathan , Kleber Felicitas , Reubold Ulrich
Published: May 2008

The aim of the study was to establish whether /u/-fronting, a sound change in progress in standard southern British, could be linked synchronically to the fronting effects of a preceding anterior consonant both in speech production and speech perception. For the production study, which consisted of acoustic analyses of isolated monosyllables produced by two different age groups, it was shown for younger speakers that /u/ was phonetically fronted and that the coarticulatory influence of consonants on /u/ was less than in older speakers. For the perception study, responses were elicited from the same subjects to two minimal word-pair continua that differed in the direction of the consonants’ coarticulatory fronting effects on /u/. Consistent with their speech production, young listeners’ /u/ category boundary was shifted toward /i/ and they compensated perceptually less for the fronting effects of the consonants on /u/ than older listeners. The findings support Ohala’s model in which certain sound changes can be linked to the listener’s failure to compensate for coarticulation. The results are also shown to be consistent with episodic models of speech perception in which phonological frequency effects bring about a realignment of the variants of a phonological category in speech production and perception.
Effect of spectral normalization on different talker speech recognition by cochlear implant users
Authors: Liu Chuping , Galvin John , Fu Qian-Jie , Narayanan Shrikanth S.
Published: May 2008

In cochlear implants (CIs), different talkers often produce different levels of speech understanding because of the spectrally distorted speech patterns provided by the implant device. A spectral normalization approach was used to transform the spectral characteristics of one talker to those of another talker. In Experiment 1, speech recognition with two talkers was measured in CI users, with and without spectral normalization. Results showed that the spectral normalization algorithm had small but significant effect on performance. In Experiment 2, the effects of spectral normalization were measured in CI users and normal-hearing (NH) subjects; a pitch-stretching technique was used to simulate six talkers with different fundamental frequencies and vocal tract configurations. NH baseline performance was nearly perfect with these pitch-shift transformations. For CI subjects, while there was considerable intersubject variability in performance with the different pitch-shift transformations, spectral normalization significantly improved the intelligibility of these simulated talkers. The results from Experiments 1 and 2 demonstrate that spectral normalization toward more-intelligible talkers significantly improved CI users’ speech understanding with less-intelligible talkers. The results suggest that spectral normalization using optimal reference patterns for individual CI patients may compensate for some of the acoustic variability across talkers.
Information transfer analysis: A first look at estimation bias
Authors: Sagi Elad , Svirsky Mario A.
Published: May 2008

Information transfer analysis [G. A. Miller and P. E. Nicely, J. Acoust. Soc. Am. 27, 338–352 (1955)] is a tool used to measure the extent to which speech features are transmitted to a listener, e.g., duration or formant frequencies for vowels; voicing, place and manner of articulation for consonants. An information transfer of 100% occurs when no confusions arise between phonemes belonging to different feature categories, e.g., between voiced and voiceless consonants. Conversely, an information transfer of 0% occurs when performance is purely random. As asserted by Miller and Nicely, the maximum-likelihood estimate for information transfer is biased to overestimate its true value when the number of stimulus presentations is small. This small-sample bias is examined here for three cases: a model of random performance with pseudorandom data, a data set drawn from Miller and Nicely, and reported data from three studies of speech perception by hearing impaired listeners. The amount of overestimation can be substantial, depending on the number of samples, the size of the confusion matrix analyzed, as well as the manner in which data are partitioned therein.
Spatio-temporal quantification of vocal fold vibrations using high-speed videoendoscopy and a biomechanical model
Authors: Schwarz Raphael , Döllinger Michael , Wurzbacher Tobias , Eysholdt Ulrich , Lohscheller Jörg
Published: May 2008

Pathologic changes within the organic constitution of vocal folds or a functional impairment of the larynx may result in disturbed or even irregular vocal fold vibrations. The consequences are perturbations of the acoustic speech signal which are perceived as a hoarse voice. By means of appropriate image processing techniques, the vocal fold dynamics are extracted from digital high-speed videos. This study addresses the approach to obtain a parametric description of the spatio-temporal characteristics of the vocal fold oscillations for the aim of classification. For this purpose a biomechanical vocal fold model is introduced. An automatic optimization procedure is developed for fitting the model dynamics to the observed vocal fold oscillations. Thus, the resulting parameter values represent a specific vibration pattern and serve as an objective quantification measure. Performance and reliability of the optimization procedure are validated with synthetically generated data sets. The high-speed videos of two normal voice subjects and six patients suffering from different voice disorders are processed. The resulting model parameters represent a rough approximation of physiological parameters along the entire vocal folds.
High-Reynolds-number turbulent-boundary-layer wall pressure fluctuations with skin-friction reduction by air injection
Authors: Winkel Eric S. , Elbing Brian R. , Ceccio Steven L. , Perlin Marc , Dowling David R.
Published: May 2008

The hydrodynamic pressure fluctuations that occur on the solid surface beneath a turbulent boundary layer are a common source of flow noise. This paper reports multipoint surface pressure fluctuation measurements in water beneath a high-Reynolds-number turbulent boundary layer with wall injection of air to reduce skin-friction drag. The experiments were conducted in the U.S. Navy’s Large Cavitation Channel on a 12.9-m-long, 3.05-m-wide hydrodynamically smooth flat plate at freestream speeds up to 20m∕s and downstream-distance-based Reynolds numbers exceeding 200×106. Air was injected from one of two spanwise slots through flush-mounted porous stainless steel frits (∼40μm mean pore diameter) at volume flow rates from 17.8 to 142.5l∕s per meter span. The two injectors were located 1.32 and 9.78m from the model’s leading edge and spanned the center 87% of the test model. Surface pressure measurements were made with 16 flush-mounted transducers in an “L-shaped” array located 10.7m from the plate’s leading edge. When compared to no-injection conditions, the observed wall-pressure variance was reduced by as much as 87% with air injection. In addition, air injection altered the inferred convection speed of pressure fluctuation sources and the streamwise coherence of pressure fluctuations.
Stimulus-frequency otoacoustic emission: Measurements in humans and simulations with an active cochlear model
Authors: Choi Yong-Sun , Lee Soo-Young , Parham Kourosh , Neely Stephen T. , Kim Duck O.
Published: May 2008

An efficient method for measuring stimulus-frequency otoacoustic emissions (SFOAEs) was developed incorporating (1) stimulus with swept frequency or level and (2) the digital heterodyne analysis. SFOAEs were measured for 550–1450Hz and stimulus levels of 32–62dB sound pressure level in eight normal human adults. The mean level, number of peaks, frequency spacing between peaks, phase change, and energy-weighted group delays of SFOAEs were determined. Salient features of the human SFOAEs were stimulated with an active cochlear model containing spatially low-pass filtered irregularity in the impedance. An objective fitting procedure yielded an optimal set of model parameters where, with decreasing stimulus level, the amount of cochlear amplification and the base amplitude of the irregularity increased while the spatial low-pass cutoff and the slope of the spatial low-pass filter decreased. The characteristics of the human cochlea were inferred with the model. In the model, an SFOAE consisted of a long-delay component originating from irregularity in a traveling-wave peak region and a short-delay component originating from irregularity in regions remote from the peak. The results of this study should be useful both for understanding cochlear function and for developing a clinical method of assessing cochlear status.
Pipe wall damage detection by electromagnetic acoustic transducer generated guided waves in absence of defect signals
Authors: Vasiljevic Milos , Kundu Tribikram , Grill Wolfgang , Twerdowski Evgeny
Published: May 2008

Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper.
Effect of sound masking on workers in an open office
Authors: Haapakangas Annu , Hongisto Valtteri O.
Published: May 2008

Appropriate masking sound is necessary for reaching acceptable speech privacy in open offices. However, the electronic masking systems have not become very popular although the importance of masking is emphasized in design guidelines worldwide. One reason may be that very few scientific field experiments have been published in this area. The aim of this pilot study was to investigate the effects of artificial masking sound on workers in a small department of 15 workers. Measurements and questionnaires were conducted before and after launching the system. Masking sound 44 dBA was produced using centralized pink noise generator and ceiling loudspeakers. The spectrum reminded ventilation noise. Initial background noise level was 36 dBA. Acoustic measurements showed that masking sound reduced the radius of distraction rD from 15 m to 7 m, i.e. acoustic privacy improved significantly. The questionnaire revealed several positive changes attributable to masking. Distraction caused by speech and other varying office sounds was reduced. Noise-related stress was reduced. Evaluations of acoustic environment, speech privacy and self-rated work efficiency were improved. The results showed no adverse effects of masking on workers.
Room acoustical measures for open plan spaces
Authors: Nilsson Erling , Hellström Björn , Berthelsen Björn
Published: May 2008

In an ongoing Nordic cooperation project the acoustical conditions in open-plan spaces are investigated. Of special interest is to find suitable acoustical parameters that reveal the acoustical conditions in these spaces and also are of importance for the subjective perceived acoustics. Measurements have so far been carried out in five open plan offices accompanied with an inquiry gathering the subjective judgments by the staff. A program for the acoustical measurements was designed specifying how to perform the measurements, which type of parameters to measure and how to report the results. The acoustical parameters included in the measurements are Reverberation time T20, Early Decay Time (EDT), Deutlichkeit (D50), Speech transmission index (STI), Speech intelligibility index (SII), Privacy Index (PI), Rate of spatial decay of sound pressure levels per distance doubling (DL2), Excess of sound pressure level with respect to a reference curve (DLf), background noise levels in occupied and unoccupied offices. The behavior of these parameters will be discussed and suitable parameters for evaluation of open plan spaces will be suggested.
Characterization of acoustics in open offices - four case studies
Authors: Keränen Jukka S. , Virjonen Petra , Hongisto Valtteri O.
Published: May 2008

Acoustic design in open offices aims to reduction of distractions and improvement of speech privacy. Room acoustical design includes high room absorption, high and absorptive screens and appropriate masking sound level. The aim of this study is to show, how these individual design components can affect on room acoustics, using modern room acoustical descriptors. Individual acoustical remedies were studied in four case studies independently. The implemented room acoustical changes were increased ceiling absorption, sound-absorptive screens, curtains between workers and increased masking sound level. Radius of distraction, rD, spatial decay rate of speech, DL2, and speech level at 4 m from speaker, Lp,S,4m, were determined before and after the room acoustical change. These three simple and robust single-number parameters are recommended to characterize the acoustic conditions of open offices because they react logically to room acoustical changes.
Virtual acoustic environments for music performance, rehearsal, and recording
Authors: Woszczyk Wieslaw , Ko Doyuen , Beghin Tom , De Francisco Martha , Tusz Jeremy , Miller Ryan
Published: May 2008

A comprehensive 24-channel sound field rendering system was built at McGill University's CIRMMT Centre to immerse scholar/performer Tom Beghin in virtual concert spaces where Haydn composed and performed his keyboard sonatas, or expected them to be performed. The virtual rooms were reconstructed from detailed measurements made in Haydn's historical rooms in Europe using a high-resolution 24 bit/96 kHz impulse-response measuring system. In an acoustically treated laboratory, 24 custom loudspeaker arrays were arranged on a surface of a hemisphere surrounding the performer. Multiple fast DSP engines convolved live signals with 24 impulse responses allowing the performer to rehearse and record in each room with low-latency virtual acoustics. This paper describes the details of system design, the method of measurement, and discusses various aspects of recording and performing in virtual acoustic environments. The method has also been tested in a large room during public performance by having virtual-room responses and high-definition photo images projected from the stage. Surround sound recordings of Haydn's complete solo keyboard music made in several virtual rooms and matched to specific historical instruments will be released in a collection of 13 commercial SA-CD's by the end of 2008.
Investigating noise effects on the call amplitude of endangered Southern Resident killer whales (Orcinus orca)
Authors: Holt Marla , Veirs Val , Veirs Scott
Published: May 2008

Anthropogenic sound exposure has been identified as a potential threat to endangered Southern Resident killer whales (SRKWs). Such exposure can mask important biological sounds including those used for social functions. Vocal animals might compensate for increased background noise by calling louder (the Lombard effect). In this study, amplitude compensation was investigated in SRKW communication calls recorded off of San Juan Island, WA, U.S.A. Data were obtained from two calibrated recording systems, a shore-based hydrophone array [V. Veirs, J. Acoust. Soc. Am., 116, 2615 (2004)] and a boat-based vertical array. Calls were localized using time of arrival differences to estimate range and apparent source levels after background levels were subtracted from the signal. Call levels were calculated assuming spreading loss functions determined from sound propagation observations made in situ. Results demonstrated a positive relationship between call levels and background levels. Costs of such vocal flexibility are unknown, but may include changes in energetic demand and/or communicative functionality. Within the data ranges measured in this study, killer whales communicatively adjusted for fluctuating background noise levels. However, other sounds detected during passive listening (e.g. prey sounds) might be more susceptible to masking effects [Work supported by NOAA and Colorado College.]