bluuebunny/crossref_metadata_2025 huggingface dataset:
A Comparison Between Recent Advances in Cylindrical Nodal Diffusion Methods
Authors: Colameco David V. , Ivanov Kostadin N. , Prinsloo Rian H. , Tomasevic Djordje I. , Theron Suzanne
Published: December 2009

The resurgence of high temperature reactor (HTR) technology has prompted the development and application of modern calculation methodologies, many of which are already utilized in the existing power reactor industry, to HTR designs. To this end, the use of nodal diffusion methods for full core neutronic analysis is once again considered for both their performance and accuracy advantages. Recently a number of different approaches to two-dimensional and 3D multigroup cylindrical nodal diffusion methods were proposed by various institutions for use in HTR and, specifically, pebble-bed modular reactor (PBMR) calculations. In this regard, we may mention the NEM code from the Pennsylvania State University based on the nodal expansion method and the OSCAR-4 code from NECSA, utilizing a conformal mapping approach to the analytic nodal method. In this work we will compare these two approaches in terms of accuracy and performance. Representative problems, selected to test the methods thoroughly, were devised and based on both a modified version of the PBMR 400 MW benchmark problem and a “cylindrisized” version of the IAEA two-group problem. The comparative results between OSCAR-4 and NEM are given, focusing on global reactivity estimation, as well as power and flux errors as compared with reference finite-difference solutions. These results indicate that both OSCAR-4 and NEM recover the global reference solution for the IAEA problem and show power errors, which are generally acceptable for nodal methods. For the PBMR problem the accuracy is similar, but some convergence difficulties are experienced at the outer boundaries of the system due to the very large dimensions of the reflector (when compared with typical water-moderated reactors). For both codes a significant performance increase was found, as compared with finite-difference calculations, which is the method currently employed by the PBMR (Pty) Ltd. In conclusion it seems that nodal methods have potential for use in the HTR analysis and, specifically, the PBMR calculational arena, although cylindrical geometry based nodal methods will have to develop toward maturity before becoming the industry standard.
An Analytical Approach for the Evaluation of the Optimal Combustion Phase in Spark Ignition Engines
Authors: Beccari A. , Beccari S. , Pipitone E.
Published: December 2009

It is well known that the spark advance is one of the most important parameters influencing the efficiency of a spark ignition engine. A change in this parameter causes a shift in the combustion phase, whose optimal position, with respect to the piston motion, implies the maximum brake mean effective pressure for given operative conditions. The best spark timing is usually estimated by means of experimental trials on the engine test bed or by means of thermodynamic simulations of the engine cycle. In this work, instead, the authors developed, under some simplifying hypothesis, an original theoretical formulation for the estimation of the optimal combustion phase. The most significant parameters involved with the combustion phase are taken into consideration; in particular, the influence of the combustion duration, of the heat release law, of the heat transfer to the combustion chamber walls, and of the mechanical friction losses is evaluated. The theoretical conclusion, experimentally proven by many authors, is that the central point of the combustion phase (known as the location of the 50% of mass fraction burnt, here called MFB50) must be delayed with respect to the top dead center as a consequence of both heat exchange between gas and chamber walls and friction losses.
A Comparison of the Different Methods of Using Jatropha Oil as Fuel in a Compression Ignition Engine
Authors: Kumar M. Senthil , Ramesh A. , Nagalingam B.
Published: December 2009

Different methods to improve the performance of a jatropha oil based compression ignition engine were tried and compared. A single cylinder water-cooled, direct injection diesel engine was used. Base data were generated with diesel and neat jatropha oil. Subsequently, jatropha oil was converted into its methyl ester by transesterification. Jatropha oil was also blended with methanol and orange oil in different proportions and tested. Further, the engine was modified to work in the dual fuel mode with methanol, orange oil, and hydrogen being used as the inducted fuels and the jatropha oil being used as the pilot fuel. Finally, experiments were conducted using additives containing oxygen, like dimethyl carbonate and diethyl ether. Neat jatropha oil resulted in slightly reduced thermal efficiency and higher emissions. Brake thermal efficiency was 27.3% with neat jatropha oil and 30.3% with diesel. Performance and emissions were considerably improved with the methyl ester of jatropha oil. Dual fuel operation with methanol, orange oil, and hydrogen induction and jatropha oil injection also showed higher brake thermal efficiency. Smoke was significantly reduced from 4.4 BSU with neat jatropha oil to 2.6 BSU with methanol induction. Methanol and orange oil induction reduced the NO emission and increased HC and CO emissions. With hydrogen induction, hydrocarbon and carbon monoxide emissions were significantly reduced. The heat release curve showed higher premixed rate of combustion with all the inducted fuels mainly at high power outputs. Addition of oxygenates like diethyl ether and dimethyl carbonate in different proportions to jatropha oil also improved the performance of the engine. It is concluded that dual fuel operation with jatropha oil as the main injected fuel and methanol, orange oil, and hydrogen as inducted fuels can be a good method to use jatropha oil efficiently in an engine that normally operates at high power outputs. Methyl ester of jatropha oil can lead to good performance at part loads with acceptable levels of performance at high loads also. Orange oil and methanol can be also blended with jatropha oil to improve viscosity of jatropha oil. These produce acceptable levels of performance at all outputs. Blending small quantity of diethyl ether and dimethyl carbonate with jatropha oil will enhance the performance. Diethyl ether seems to be the better of the two.
Producing Hydrogen and Power Using Chemical Looping Combustion and Water-Gas Shift
Authors: McGlashan Niall R. , Childs Peter R. N. , Heyes Andrew L. , Marquis Andrew J.
Published: December 2009

A cycle capable of generating both hydrogen and power with “inherent” carbon capture is proposed and evaluated. The cycle uses chemical looping combustion to perform the primary energy release from a hydrocarbon, producing an exhaust of CO. This CO is mixed with steam and converted to H2 and CO2 using the water-gas shift reaction (WGSR). Chemical looping uses two reactions with a recirculating oxygen carrier to oxidize hydrocarbons. The resulting oxidation and reduction stages are preformed in separate reactors—the oxidizer and reducer, respectively, and this partitioning facilitates CO2 capture. In addition, by careful selection of the oxygen carrier, the equilibrium temperature of both redox reactions can be reduced to values below the current industry standard metallurgical limit for gas turbines. This means that the irreversibility associated with the combustion process can be reduced significantly, leading to a system of enhanced overall efficiency. The choice of oxygen carrier also affects the ratio of CO versus CO2 in the reducer’s flue gas, with some metal oxide reduction reactions generating almost pure CO. This last feature is desirable if the maximum H2 production is to be achieved using the WGSR reaction. Process flow diagrams of one possible embodiment using a zinc based oxygen carrier are presented. To generate power, the chemical looping system is operated as part of a gas turbine cycle, combined with a bottoming steam cycle to maximize efficiency. The WGSR supplies heat to the bottoming steam cycle, and also helps to raise the steam necessary to complete the reaction. A mass and energy balance of the chemical looping system, the WGSR reactor, steam bottoming cycle, and balance of plant is presented and discussed. The results of this analysis show that the overall efficiency of the complete cycle is dependent on the operating pressure in the oxidizer, and under optimum conditions exceeds 75%.
Low-cost interference lithography
Authors: Fucetola Corey P. , Korre Hasan , Berggren Karl K.
Published: December 2009

The authors report demonstration of a low-cost (∼1000 USD) interference lithography system based on a Lloyd’s mirror interferometer that is capable of ∼300nm pitch patterning. The components include only a 405nm GaN diode-laser module, a machinist’s block, a chrome-coated silicon mirror, substrate, and double-sided carbon scanning electron microscopy (SEM) tape. The laser and the machinist’s block were assembled in a linear configuration, and to complete the system, the mirror and substrate were taped to perpendicular surfaces of the machinist’s block. Approximately 50 silicon substrates were prepared, exposed, and developed, after which some were inspected in a SEM. The associated laser spectrum was also measured, enabling calculation of the laser’s fringe visibility as it varied along the substrate surface. To compare the exposed resist pattern to the fringe visibility, the authors measured the first order diffraction efficiency as a function of position along the grating surface. Their measurements indicated that artifacts seen in both the optical spectrum and resulting grating patterns arose from the laser diode source, thus improving the source characteristics will be the topic of future work.
Numerical study on bubble trapping in UV nanoimprint lithography
Authors: Morihara Daisuke , Nagaoka Yoshinori , Hiroshima Hiroshi , Hirai Yoshihiko
Published: December 2009

Resist filling process in UV-nanoimprint lithography is investigated by numerical simulation. A resist droplet on a substrate is pressed by a template and the resist flows laterally with constant velocity. The resist filling processes into the patterned cavity are simulated by various contact angles of template and substrate to the resist. Two kinds of defect modes are observed. A typical defect is induced by branching of the resist flow at the edge of the patterned cavity when the contact angle between the resist and the template is large. The other one is nonfilling into the patterned cavity for low viscosity resist and low contact angle between the resist and substrate, where the resist flows along the substrate and does not flow into the pattern.
Microstructure and chemical wet etching characteristics of AlN films deposited by ac reactive magnetron sputtering
Authors: Tanner S. M. , Felmetsger V. V.
Published: December 2009

The influence of the surface morphology of a molybdenum underlayer on the crystallinity and etchability of reactively sputtered c-axis oriented aluminum nitride thin films was investigated. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, high resolution x-ray diffraction, and defect selective chemical etching were used to characterize the microstructure of the Mo and AlN films. 1000nm thick films of AlN with a full width at half maximum (FWHM) of the x-ray rocking curve ranging from 1.1° to 1.9° were deposited on 300nm thick Mo underlayers with a FWHM of around 1.5°. The Ar pressure during the Mo deposition had a critical effect on the Mo film surface morphology, affecting the structure of the subsequently deposited AlN films and, hence, their wet etching characteristics. AlN films deposited on Mo sputtered at a relatively high pressure could not be etched completely, while AlN films deposited on low pressure Mo etched more easily. Postdeposition etching of the Mo surface in Ar rf discharge prior to deposition of the AlN film was found to influence the formation of AlN residuals that were difficult to etch. Optimal rf plasma etching conditions were found, which minimized the formation of these residuals.
The player and the bowed string: Coordination of bowing parameters in violin and viola performance
Authors: Schoonderwaldt E.
Published: December 2009

An experiment was conducted with four violin and viola players, measuring their bowing performance using an optical motion capture system and sensors on the bow. The measurements allowed for a detailed analysis of the use and coordination of the main bowing parameters bow velocity, bow force, and bow-bridge distance. An analysis of bowing strategies in détaché playing of notes of three durations (0.2, 2, and 4 s) at three dynamic levels (pp, mf, and f) on all four strings is presented, focusing on the “steady” part of the notes. The results revealed clear trends in the coordinated variations of the bowing parameters depending on the constraints of the task, reflecting a common behavior as well as individual strategies. Furthermore, there were clear indications that the players adapted the bowing parameters to the physical properties of the string and the instrument, respecting the limits of the playable control parameter space.
Ultrasonic field modeling by distributed point source method for different transducer boundary conditions
Authors: Yanagita Tamaki , Kundu Tribikram , Placko Dominique
Published: December 2009

Several investigators have modeled ultrasonic fields in front of transducers by Huygens–Fresnel superposition principle that integrates the contributions of a number of point sources distributed on the transducer face. This integral solution, also known as the Rayleigh integral or Rayleigh–Sommerfeld Integral solution, assumes the strengths of the point sources distributed over the transducer face. A newly developed technique called distributed point source method (DPSM) offers an alternative approach for modeling ultrasonic fields. DPSM is capable of modeling the field for prescribed source strength distribution as well as for prescribed interface conditions with unknown source strengths. It is investigated how the ultrasonic field in front of the transducer varies in different situations: (1) when the point source strengths are known, (2) when the point source strengths are unknown but obtained from the interface condition that only the normal component of the transducer velocity is continuous across the fluid-solid interface, (3) when all three components of velocity are assumed to be continuous across the interface for the no-slip condition, and (4) when the pressure instead of the velocity is prescribed on the transducer face. Results for these different interface conditions are compared with the analytical solutions along the central axis.
Enhancing sensitivity to interaural time differences at high modulation rates by introducing temporal jitter
Authors: Goupell Matthew J. , Laback Bernhard , Majdak Piotr
Published: December 2009

Sensitivity to interaural time differences (ITDs) in high-frequency bandpass-filtered periodic and aperiodic (jittered) pulse trains was tested at a nominal pulse rate of 600pulses per second (pps). It was found that random binaurally-synchronized jitter of the pulse timing significantly increases ITD sensitivity. A second experiment studied the effects of rate and place. ITD sensitivity for jittered 1200-pps pulse trains was significantly higher than for periodic 600-pps pulse trains, and there was a relatively small effect of place. Furthermore, it could be concluded from this experiment that listeners were not solely benefiting from the longest interpulse intervals (IPIs) and the instances of reduced rate by adding jitter, because the two types of pulse trains had the same longest IPI. The effect of jitter was studied using a physiologically-based model of auditory nerve and brainstem (medial superior olive neurons). It was found that the random timing of the jittered pulses increased firing synchrony in the auditory periphery, which caused an improved rate-ITD tuning for the 600-pps pulse trains. These results suggest that a recovery from binaural adaptation induced by temporal jitter is possibly related to changes in the temporal firing pattern, not spectral changes.
Ultra-wide sensor arcs for low frequency sonar detection with a baffled cylindrical array
Authors: Bertilone Derek C. , Bao Chaoying , Travaglione Ben C. , Killeen Damien S.
Published: December 2009

Passive detection with a baffled cylindrical array can potentially be improved at low frequencies by exploiting signal diffraction around the baffle. A model based on infinite rigid cylinder scattering suggests that large gains in signal-to-noise ratio are potentially available to adaptive beamformers if the sensor arc is widened to include sensors in the acoustic shadow. However, elastic scatter effects become increasingly important as frequency decreases, so the gains obtained in practice are unknown. The gains in detection performance are examined in this letter by analyzing data recorded at sea from a platform-mounted sonar array.
Modified Škvor/Starr approach in the mechanical-thermal noise analysis of condenser microphone
Authors: Tan Chee Wee , Miao Jianmin
Published: December 2009

Simple analytical expressions of mechanical resistance, such as those formulated by Škvor/Starr, are widely used to describe the mechanical-thermal noise performance of a condenser microphone. However, the Škvor/Starr approach does not consider the location effect of acoustic holes in the backplate and overestimates the total equivalent mechanical resistance and mechanical-thermal noise. In this paper, a modified form of the Škvor/Starr approach is proposed to address this hole location dependent effect. A mode shape factor, which consists of the zero order Bessel and modified Bessel functions, is included in Škvor’s mechanical resistance formulation to consider the effect of the hole location in the backplate. With reference to two B&K microphones, the theoretical results of the A-weighted mechanical-thermal noise obtained by the modified Škvor/Starr approach are in good agreements with those reported experimental ones.
Bistatic scattering from submerged unexploded ordnance lying on a sediment
Authors: Bucaro J. A. , Simpson H. , Kraus L. , Dragonette L. R. , Yoder T. , Houston B. H.
Published: December 2009

The broadband bistatic target strengths (TSs) of two submerged unexploded ordnance (UXO) targets have been measured in the NRL sediment pool facility. The targets—a 5 in. rocket and a 155 mm projectile—were among the targets whose monostatic TSs were measured and reported previously by the authors. Bistatic TS measurements were made for 0° (target front) and 90° (target side) incident source directions, and include both backscattered and forward scattered echo angles over a complete 360° with the targets placed proud of the sediment surface. For the two source angles used, each target exhibits two strong highlights: a backscattered specular-like echo and a forward scattered response. The TS levels of the former are shown to agree reasonably well with predictions, based on scattering from rigid disks and cylinders, while the levels of the latter with predictions from radar cross section models, based on simple geometric optics appropriately modified. The bistatic TS levels observed for the proud case provide comparable or higher levels of broadband TS relative to free-field monostatic measurements. It is concluded that access to bistatic echo information in operations aimed at detecting submerged UXO targets could provide an important capability.
Acoustic radiation patterns of mating calls of the túngara frog (Physalaemus pustuosus): Implications for multiple receivers
Authors: Bernal Ximena E. , Page Rachel A. , Ryan Michael J. , Argo Theodore F. , Wilson Preston S.
Published: December 2009

In order for a signal to be transmitted from a sender to a receiver, the receiver must be within the active space of the signal. If patterns of sound radiation are not omnidirectional, the position as well as the distance of the receiver relative to the sender is critical. In previous measurements of the horizontal directivity of mating calls of frogs, the signals were analyzed using peak or root-mean-square analysis and resulted in broadband directivities that ranged from negligible to a maximum of approximately 5dB. Idealized laboratory measurements of the patterns of acoustic radiation of the mating calls of male túngara frogs (Physalaemus pustulosus), along axes relevant to three receivers in this communication network, female frogs in the horizontal plane, and frog-eating bats and blood-sucking flies above the ground, are reported. The highest sound pressure level was radiated directly above the frog, with a 6dB reduction radiated along the horizontal direction. Band-limited directivities were significantly greater than broadband directivities, with a maximum directivity of 20dB in the vertical plane for harmonics near 6kHz. The implications with regard to mating and predator-prey interactions are discussed.
Model optimization of orthotropic distributed-mode loudspeaker using attached masses
Authors: Lu Guochao , Shen Yong
Published: December 2009

The orthotropic model of the plate is established and the genetic simulated annealing algorithm is developed for optimization of the mode distribution of the orthotropic plate. The experiment results indicate that the orthotropic model can simulate the real plate better. And optimization aimed at the equal distribution of the modes in the orthotropic model is made to improve the corresponding sound pressure responses.
Effects of masker envelope coherence on intensity discrimination
Authors: Buss Emily , Hall Joseph W.
Published: December 2009

Masked detection threshold for a pure tone signal depends on the coherence of masker envelope fluctuation across frequency, with lower thresholds for coherent fluctuation under some conditions. The benefit of coherent masker modulation is larger for detection than for suprathreshold tasks, such as pure tone intensity discrimination [Hall, J. W. and Grose, J. H. (1995). J. Acoust. Soc. Am. 98, 847–852]. In the present study, sensitivity to increments in signal intensity was measured for a 1000-Hz signal, either a tone or a 20-Hz-wide narrowband noise. In one set of conditions the masker was one or more bands of noise, each 20 Hz wide, and in another set of conditions the masker was a single 1620-Hz-wide band of Gaussian noise or noise multiplied by the envelope of a 20-Hz bandpass noise. Coherent masker envelope fluctuation improved detection thresholds in all conditions. Intensity discrimination for a tonal standard in comodulated noise was elevated for standard levels near detection threshold and improved with increasing signal-to-noise ratio, whereas performance was uniformly poor across level for the noise standard. Results are most consistent with the interpretation that the reduced benefit of coherent masker modulation in suprathreshold intensity discrimination is due to the disruptive effects of envelope fluctuation.
Automatic detection of articulation disorders in children with cleft lip and palate
Authors: Maier Andreas , Hönig Florian , Bocklet Tobias , Nöth Elmar , Stelzle Florian , Nkenke Emeka , Schuster Maria
Published: December 2009

Speech of children with cleft lip and palate (CLP) is sometimes still disordered even after adequate surgical and nonsurgical therapies. Such speech shows complex articulation disorders, which are usually assessed perceptually, consuming time and manpower. Hence, there is a need for an easy to apply and reliable automatic method. To create a reference for an automatic system, speech data of 58 children with CLP were assessed perceptually by experienced speech therapists for characteristic phonetic disorders at the phoneme level. The first part of the article aims to detect such characteristics by a semiautomatic procedure and the second to evaluate a fully automatic, thus simple, procedure. The methods are based on a combination of speech processing algorithms. The semiautomatic method achieves moderate to good agreement (κ≈0.6) for the detection of all phonetic disorders. On a speaker level, significant correlations between the perceptual evaluation and the automatic system of 0.89 are obtained. The fully automatic system yields a correlation on the speaker level of 0.81 to the perceptual evaluation. This correlation is in the range of the inter-rater correlation of the listeners. The automatic speech evaluation is able to detect phonetic disorders at an experts’level without any additional human postprocessing.
Perceptual learning of time-compressed and natural fast speech
Authors: Adank Patti , Janse Esther
Published: December 2009

Speakers vary their speech rate considerably during a conversation, and listeners are able to quickly adapt to these variations in speech rate. Adaptation to fast speech rates is usually measured using artificially time-compressed speech. This study examined adaptation to two types of fast speech: artificially time-compressed speech and natural fast speech. Listeners performed a speeded sentence verification task on three series of sentences: normal-speed sentences, time-compressed sentences, and natural fast sentences. Listeners were divided into two groups to evaluate the possibility of transfer of learning between the time-compressed and natural fast conditions. The first group verified the natural fast before the time-compressed sentences, while the second verified the time-compressed before the natural fast sentences. The results showed transfer of learning when the time-compressed sentences preceded the natural fast sentences, but not when natural fast sentences preceded the time-compressed sentences. The results are discussed in the framework of theories on perceptual learning. Second, listeners show adaptation to the natural fast sentences, but performance for this type of fast speech does not improve to the level of time-compressed sentences.
Acoustic measurement of overall voice quality: A meta-analysis
Authors: Maryn Youri , Roy Nelson , De Bodt Marc , Van Cauwenberge Paul , Corthals Paul
Published: December 2009

Over the past several decades, many acoustic markers have been proposed to be sensitive to and measure overall voice quality. This meta-analysis presents a retrospective appraisal of scientific reports, which evaluated the relation between perceived overall voice quality and several acoustic-phonetic correlates. Twenty-five studies met the inclusion criteria and were evaluated using meta-analytic techniques. Correlation coefficients between perceptual judgments and acoustic measures were computed. Where more than one correlation coefficient for a specific acoustic marker was available, a weighted average correlation coefficient was calculated. This was the case in 36 acoustic measures on sustained vowels and in 3 measures on continuous speech. Acoustic measures were ranked according to the strength of the correlation with perceptual voice quality ratings. Acoustic markers with more than one correlation value available in literature and yielding a homogeneous weighted r of 0.60 or above were considered to be superior. The meta-analysis identified four measures that met these criteria in sustained vowels and three measures in continuous speech. Although acoustic measures are routinely utilized in clinical voice examinations, the results of this meta-analysis suggest that caution is warranted regarding the concurrent validity and thus the clinical utility of many of these measures.
Real-time calculation of a limiting form of the Renyi entropy applied to detection of subtle changes in scattering architecture
Authors: Hughes M. S. , McCarthy J. E. , Wickerhauser M. V. , Marsh J. N. , Arbeit J. M. , Fuhrhop R. W. , Wallace K. D. , Thomas T. , Smith J. , Agyem K. , Lanza G. M. , Wickline S. A.
Published: December 2009

Previously a new method for ultrasound signal characterization using entropy Hf was reported, and it was demonstrated that in certain settings, further improvements in signal characterization could be obtained by generalizing to Renyi entropy-based signal characterization If(r) with values of r near 2 (specifically r=1.99) [M. S. Hughes et al., J. Acoust. Soc. Am. 125, 3141–3145 (2009)]. It was speculated that further improvements in sensitivity might be realized at the limit r→2. At that time, such investigation was not feasible due to excessive computational time required to calculate If(r) near this limit. In this paper, an asymptotic expression for the limiting behavior of If(r) as r→2 is derived and used to present results analogous to those obtained with If(1.99). Moreover, the limiting form If,∞ is computable directly from the experimentally measured waveform f(t) by an algorithm that is suitable for real-time calculation and implementation.
On the assimilation-discrimination relationship in American English adults’ French vowel learning
Authors: Levy Erika S.
Published: December 2009

A quantitative “cross-language assimilation overlap” method for testing predictions of the Perceptual Assimilation Model (PAM) was implemented to compare results of a discrimination experiment with the listeners’ previously reported assimilation data. The experiment examined discrimination of Parisian French (PF) front rounded vowels /y/ and /œ/. Three groups of American English listeners differing in their French experience (no experience [NoExp], formal experience [ModExp], and extensive formal-plus-immersion experience [HiExp]) performed discrimination of PF /y-u/, /y-o/, /œ-o/, /œ-u/, /y-i/, /y-ɛ/, /œ-ɛ/, /œ-i/, /y-œ/, /u-i/, and /a-ɛ/. Vowels were in bilabial /rabVp/ and alveolar /radVt/ contexts. More errors were found for PF front vs back rounded vowel pairs (16%) than for PF front unrounded vs rounded pairs (2%). Overall, ModExp listeners did not perform more accurately (11% errors) than NoExp listeners (13% errors). Extensive immersion experience, however, was associated with fewer errors (3%) than formal experience alone, although discrimination of PF /y-u/ remained relatively poor (12% errors) for HiExp listeners. More errors occurred on pairs involving front vs back rounded vowels in alveolar context (20% errors) than in bilabial (11% errors). Significant correlations were revealed between listeners’ assimilation overlap scores and their discrimination errors, suggesting that the PAM may be extended to second-language (L2) vowel learning.
Contralateral acoustic stimulation alters the magnitude and phase of distortion product otoacoustic emissions
Authors: Deeter Ryan , Abel Rebekah , Calandruccio Lauren , Dhar Sumitrajit
Published: December 2009

Activation of medial olivocochlear efferents through contralateral acoustic stimulation (CAS) has been shown to modulate distortion product otoacoustic emission (DPOAE) level in various ways (enhancement, reduction, or no change). The goal of this study was to investigate the effect of a range of CAS levels on DPOAE fine structure. The 2f1-f2 DPOAE was recorded (f2/f1=1.22, L1=55 dB, and L2=40 dB) from eight normal-hearing subjects, using both a frequency-sweep paradigm and a fixed frequency paradigm. Contamination due to the middle ear muscle reflex was avoided by monitoring the magnitude and phase of a probe in the test ear and by monitoring DPOAE stimulus levels throughout testing. Results show modulations in both level and frequency of DPOAE fine structure patterns. Frequency shifts observed at DPOAE level minima could explain reports of enhancement in DPOAE level due to efferent activation. CAS affected the magnitude and phase of the DPOAE component from the characteristic frequency region to a greater extent than the component from the overlap region between the stimulus tones. This differential effect explains the occasional enhancement observed in DPOAE level as well as the frequency shift in fine structure patterns.
Vocalizations of wild Asian elephants (Elephas maximus): Structural classification and social context
Authors: Nair Smita , Balakrishnan Rohini , Seelamantula Chandra Sekhar , Sukumar R.
Published: December 2009

Elephants use vocalizations for both long and short distance communication. Whereas the acoustic repertoire of the African elephant (Loxodonta africana) has been extensively studied in its savannah habitat, very little is known about the structure and social context of the vocalizations of the Asian elephant (Elephas maximus), which is mostly found in forests. In this study, the vocal repertoire of wild Asian elephants in southern India was examined. The calls could be classified into four mutually exclusive categories, namely, trumpets, chirps, roars, and rumbles, based on quantitative analyses of their spectral and temporal features. One of the call types, the rumble, exhibited high structural diversity, particularly in the direction and extent of frequency modulation of calls. Juveniles produced three of the four call types, including trumpets, roars, and rumbles, in the context of play and distress. Adults produced trumpets and roars in the context of disturbance, aggression, and play. Chirps were typically produced in situations of confusion and alarm. Rumbles were used for contact calling within and among herds, by matriarchs to assemble the herd, in close-range social interactions, and during disturbance and aggression. Spectral and temporal features of the four call types were similar between Asian and African elephants.
Vocal cues to identity and relatedness in giant pandas (Ailuropoda melanoleuca)
Authors: Charlton Benjamin D. , Zhihe Zhang , Snyder Rebecca J.
Published: December 2009

A range of acoustic characteristics typically carry information on individual identity in mammalian calls. In addition, physical similarities in vocal production anatomy among closely related individuals may result in similarities in the acoustic structure of vocalizations. Here, acoustic analyses based on source-filter theory were used to determine whether giant panda bleats are individually distinctive, to investigate the relative importance of different source-(larynx) and filter-(vocal tract) related acoustic features for coding individuality, and to test whether closely related individuals have similarities in call structure. The results revealed that giant panda bleats are highly individualized and indicate that source-related features, in particular, mean fundamental frequency, amplitude variation per second, and the mean extent of each amplitude modulation, contribute the most to vocal identity. In addition, although individual pairwise relatedness was not correlated with overall acoustic similarity, it was highly correlated with amplitude modulation rate and fundamental frequency range, suggesting that these acoustic features are heritable components of giant panda bleats that could be used as a measure of genetic relatedness. The ecological relevance of acoustically signaling information on caller identity and the potential practical implications for acoustic monitoring of population levels in this endangered species are discussed.
Microscopic prediction of speech recognition for listeners with normal hearing in noise using an auditory model
Authors: Jürgens Tim , Brand Thomas
Published: December 2009

This study compares the phoneme recognition performance in speech-shaped noise of a microscopic model for speech recognition with the performance of normal-hearing listeners. “Microscopic” is defined in terms of this model twofold. First, the speech recognition rate is predicted on a phoneme-by-phoneme basis. Second, microscopic modeling means that the signal waveforms to be recognized are processed by mimicking elementary parts of human’s auditory processing. The model is based on an approach by Holube and Kollmeier [J. Acoust. Soc. Am. 100, 1703–1716 (1996)] and consists of a psychoacoustically and physiologically motivated preprocessing and a simple dynamic-time-warp speech recognizer. The model is evaluated while presenting nonsense speech in a closed-set paradigm. Averaged phoneme recognition rates, specific phoneme recognition rates, and phoneme confusions are analyzed. The influence of different perceptual distance measures and of the model’s a-priori knowledge is investigated. The results show that human performance can be predicted by this model using an optimal detector, i.e., identical speech waveforms for both training of the recognizer and testing. The best model performance is yielded by distance measures which focus mainly on small perceptual distances and neglect outliers.
Investigating possible mechanisms behind the effect of threshold fine structure on amplitude modulation perception
Authors: Heise Stephan J. , Mauermann Manfred , Verhey Jesko L.
Published: December 2009

Detection thresholds for sinusoidal amplitude modulation at low levels are higher (worse) when the carrier of the signal falls in a region of high pure-tone sensitivity (a minimum of the fine structure of the threshold in quiet) than when it falls at a fine-structure maximum. This study explores possible mechanisms behind this phenomenon by measuring modulation detection thresholds as a function of modulation frequency (experiment 1) and of carrier level for tonal carriers (experiment 2) and for 32-Hz wide noise carriers (experiment 3). The carriers could either fall at a fine-structure minimum, a fine-structure maximum, or in a region without fine structure. Modulation frequencies varied between 8 Hz and one fine-structure cycle, and carrier levels varied between 7.5 and 37.5 dB sensation levels. A large part of the results can be explained by assuming a reduction in effective modulation depth by spontaneous otoacoustic emissions—or more generally cochlear resonances—that synchronize to the carrier at fine-structure minima. Beating between cochlear resonances and the stimulus (“monaural diplacusis”) may hamper the detection task, but this cannot account for the whole effect.
Travel-time sensitivity kernels in long-range propagation
Authors: Skarsoulis E. K. , Cornuelle B. D. , Dzieciuch M. A.
Published: December 2009

Wave-theoretic travel-time sensitivity kernels (TSKs) are calculated in two-dimensional (2D) and three-dimensional (3D) environments and their behavior with increasing propagation range is studied and compared to that of ray-theoretic TSKs and corresponding Fresnel-volumes. The differences between the 2D and 3D TSKs average out when horizontal or cross-range marginals are considered, which indicates that they are not important in the case of range-independent sound-speed perturbations or perturbations of large scale compared to the lateral TSK extent. With increasing range, the wave-theoretic TSKs expand in the horizontal cross-range direction, their cross-range extent being comparable to that of the corresponding free-space Fresnel zone, whereas they remain bounded in the vertical. Vertical travel-time sensitivity kernels (VTSKs)—one-dimensional kernels describing the effect of horizontally uniform sound-speed changes on travel-times—are calculated analytically using a perturbation approach, and also numerically, as horizontal marginals of the corresponding TSKs. Good agreement between analytical and numerical VTSKs, as well as between 2D and 3D VTSKs, is found. As an alternative method to obtain wave-theoretic sensitivity kernels, the parabolic approximation is used; the resulting TSKs and VTSKs are in good agreement with normal-mode results. With increasing range, the wave-theoretic VTSKs approach the corresponding ray-theoretic sensitivity kernels.
Attention modulates auditory adaptation produced by amplitude modulation
Authors: Kawashima Takayuki
Published: December 2009

The effect of attention on adaptation produced by amplitude modulation (AM) was examined. In different experimental conditions, listeners’ AM detection thresholds for a 2 kHz test tone were measured after exposing them to an adapting sound that was presented simultaneously with speech distractors. Magnitude of an aftereffect, calculated as the elevation of the thresholds caused by adaptation, was smaller when the listeners shift attention away from the adaptor to the distractor voice than when they attended to the adaptor. The results suggest that the AM of unattended sounds may not be fully analyzed compared to that of attended sounds.
High-rate envelope information in many channels provides resistance to reduction of speech intelligibility produced by multi-channel fast-acting compression
Authors: Stone Michael A. , Füllgrabe Christian , Moore Brian C. J.
Published: December 2009

The intelligibility of speech in a competing-speech background was measured for signals that were subjected to multi-channel compression and then tone vocoded. The lowpass filter used to extract the envelopes in the vocoder preserved only low-rate envelope cues (E filter) or also preserved pitch-related cues (P filter). Intelligibility worsened with increasing number of compression channels and compression speed, but this effect was markedly reduced when the P filter was used and the number of vocoder channels was 16 as compared to 8. Thus, providing high-rate envelope cues in many channels provides resistance to the deleterious effects of fast compression.
Long range sound propagation over a sea surface
Authors: Bolin Karl , Boué Mathieu , Karasalo Ilkka
Published: December 2009

This paper describes methodology and results from a model-based analysis of data on sound transmission from controlled sound sources at sea to a 10-km distant shore. The data consist of registrations of sound transmission loss together with concurrently collected atmospheric data at the source and receiver locations. The purpose of the analysis is to assess the accuracy of methods for transmission loss prediction in which detailed data on the local geography and atmospheric conditions are used for computation of the sound field. The results indicate that such sound propagation predictions are accurate and reproduce observed variations in the sound level as function of time in a realistic way. The results further illustrate that the atmospheric model must include a description of turbulence effects to ensure predicted noise levels to remain realistically high during periods of sound shadow.
Localization interference between components in an auditory scene
Authors: Lee Adrian K. C. , Deane-Pratt Ade , Shinn-Cunningham Barbara G.
Published: December 2009

Some past studies suggest that when sound elements are heard as one object, the spatial cues in the component elements are integrated to determine perceived location, and that this integration is reduced when the elements are perceived in separate objects. The current study explored how object localization depends on the spatial, spectral, and temporal configurations of sound elements in an auditory scene. Localization results are interpreted in light of results from a series of previous experiments studying perceptual grouping of the same stimuli, e.g., Shinn-Cunningham et al. [Proc. Natl. Acad. Sci. U.S.A. 104, 12223–12227 (2007)]. The current results suggest that the integration (pulling) of spatial information across spectrally interleaved elements is obligatory when these elements are simultaneous, even though past results show that these simultaneous sound elements are not grouped strongly into a single perceptual object. In contrast, perceptually distinct objects repel (push) each other spatially with a strength that decreases as the temporal separation between competing objects increases. These results show that the perceived location of an attended object is not easily predicted by knowledge of how sound elements contribute to the perceived spectro-temporal content of that object.
Role of binaural hearing in speech intelligibility and spatial release from masking using vocoded speech
Authors: Garadat Soha N. , Litovsky Ruth Y. , Yu Gongqiang , Zeng Fan-Gang
Published: December 2009

A cochlear implant vocoder was used to evaluate relative contributions of spectral and binaural temporal fine-structure cues to speech intelligibility. In Study I, stimuli were vocoded, and then convolved through head related transfer functions (HRTFs) to remove speech temporal fine structure but preserve the binaural temporal fine-structure cues. In Study II, the order of processing was reversed to remove both speech and binaural temporal fine-structure cues. Speech reception thresholds (SRTs) were measured adaptively in quiet, and with interfering speech, for unprocessed and vocoded speech (16, 8, and 4 frequency bands), under binaural or monaural (right-ear) conditions. Under binaural conditions, as the number of bands decreased, SRTs increased. With decreasing number of frequency bands, greater benefit from spatial separation of target and interferer was observed, especially in the 8-band condition. The present results demonstrate a strong role of the binaural cues in spectrally degraded speech, when the target and interfering speech are more likely to be confused. The nearly normal binaural benefits under present simulation conditions and the lack of order of processing effect further suggest that preservation of binaural cues is likely to improve performance in bilaterally implanted recipients.
Modeling of acoustic penetration into sandy sediments: Physical and geometrical aspects
Authors: Aleshin V. , Guillon L.
Published: December 2009

Two different approaches to the problem of acoustic penetration into sandy marine sediments are considered: application of the Buckingham constitutive model for sediment with a plane surface and boundary element analysis of a rough surface of sediment represented as a homogeneous fluid. By a careful modeling of the constitutive behavior for plane seafloors, it is possible to partly reproduce some features of known experimental dependencies for acoustical pressure. However, accounting for roughness appears to be more important. Accordingly, the authors present a detailed numerical analysis of penetration into rough sediments using the boundary element method. The simulation results support conclusions reached by other investigators and demonstrate how local surface irregularities violate the evanescence condition that holds for a plane interface at subcritical incidence, thus considerably increasing penetration. The results apply to the frequency range 0.5–50 kHz and grazing angles larger than approximately 6°–8° at 10–50 kHz. For lower frequencies, when diffraction becomes important, the lowest possible grazing angle strongly depends on the range covered by the incident beam and is, in general, considerably larger. The authors provide several characteristic examples with frequencies 5 and 15 kHz and grazing angles 15°–30° illustrating the impact of roughness on penetration.
A large-aperture low-cost hydrophone array for tracking whales from small boats
Authors: Miller B. , Dawson S.
Published: December 2009

A passive sonar array designed for tracking diving sperm whales in three dimensions from a single small vessel is presented, and the advantages and limitations of operating this array from a 6 m boat are described. The system consists of four free floating buoys, each with a hydrophone, built-in recorder, and global positioning system receiver (GPS), and one vertical stereo hydrophone array deployed from the boat. Array recordings are post-processed onshore to obtain diving profiles of vocalizing sperm whales. Recordings are synchronized using a GPS timing pulse recorded onto each track. Sensitivity analysis based on hyperbolic localization methods is used to obtain probability distributions for the whale’s three-dimensional location for vocalizations received by at least four hydrophones. These localizations are compared to those obtained via isodiachronic sequential bound estimation. Results from deployment of the system around a sperm whale in the Kaikoura Canyon in New Zealand are shown.