bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying rain noise on three different roof structures
Authors: Patel Sunil , Wang Lily M.
Published: October 2013

A system for measuring rain noise has been constructed, consisting of a 3.4-m3 structure with a slanted roof and an artificial rain generation apparatus using PVC pipes and an appropriate spray nozzle. Three different roof structures have been tested for the level of rain noise generated within the structure: a shingle roof, one made with an EPDM membrane, and a corrugated metal panel roof system. Measurements show that the shingle and EPDM membrane roofs perform approximately the same and outperform the corrugated metal panel system by at least 13 dB across the frequency bands of 250 to 5000 Hz. The test system and detailed results are presented, as well as compared to guidelines provided in a draft ISO standard on measuring rain noise. [Work supported by UNL UCARE Grant.]
An experimental laboratory investigation of the low-frequency acoustics of seagrasses
Authors: Wilson Preston S. , Dunton Kenneth H.
Published: October 2013

The acoustics of seagrass beds can impact sonar operation in shallow water and may also be exploited for remotely assessing the health of estuarine and littoral ecosystems. The acoustics are dominated by air channels (aerenchyma) within the plants and air bubbles produced by the plants during photosynthesis. In situ studies of seagrass beds have confirmed their unique acoustic properties with respect to side-scan sonar backscatter and propagation effects. The results of these studies suggest a richness of exploitable phenomena, but corresponding forward theoretical models have yet to appear. To address this question, low-frequency acoustic laboratory experiments were conducted on three freshly collected seagrass species, Thalassia testudinum, Syringodium filiforme, and Halodule wrightii. A one-dimensional acoustic resonator technique was used to assess the effective acoustic properties and gas content of individual plants, leaves, and rhizomes. We successfully tracked bubble formation and transport from above- to below-ground tissues and present our results with respect to model predictions based on independent optical gas content estimates obtained via microscopic cross-section imagery. [Work supported by the UT College of Engineering and the Texas Sea Grant College Program Grant R/ES-87.]
Audiovisual asymmetries in speech and nonspeech
Authors: Brown Julie M.
Published: October 2013

The individual contribution of the various perceptual systems to multimodal perception is typically examined by placing information from the various perceptual systems in conflict and measuring how much each contributes to the resulting perception. When one perceptual system dominates perception more than another, it is called intersensory bias. The present research examines intersensory bias using a tapping task in which participants were asked to tap to the frequency of either an auditory or visual stimulus. The stimuli that were used were either nonspeech stimuli, such as a tone and a flashing ellipse, or speech, such as a visual or auditory syllable. In past experiments that have used nonspeech stimuli, audition has been shown to dominate visual temporal perception. Based on the influence of visible speech on auditory speech perception found in the McGurk effect, it was thought that vision might influence temporal perception more when using speech stimuli than nonspeech stimuli. It was found that the speech and nonspeech distinction did not affect intersensory bias. Rather, the amount of information provided by the auditory and visual stimuli predicted the occurrence of intersensory bias. [This research was supported by a NIH grant through Haskins Laboratories, New Haven, CT.
Graduate level acoustics at Brown University 1950–1955
Authors: Elder Samuel A.
Published: October 2013

When Sam Elder considered graduate school he had in mind going into some exotic field like low-temperature physics, but when Dr. Lindsay offered him a good deal on a teaching assistantship, he could not turn it down. Then, when he started there in 1950, he began to realize that Brown was becoming known as a powerhouse of research in acoustics, so he happily changed his direction in order to study under that great man. As editor of JASA, Lindsay and the other acoustics experts he had gathered around him were at the very heart of the Society and it was an exciting time to be there.
Quantifying ocean acoustic environmental sensitivity
Authors: Dosso Stan E. , Giles Peter , Brooke Gary H. , McCammon Diana F. , Pecknold Sean , Hines Paul C.
Published: October 2013

This paper examines the sensitivity of acoustic propagation data required for sonar performance predictions to physical parameters of the ocean environment. Sensitivity is quantified here by an appropriate measure of the relative uncertainty of the acoustic data due to realistic uncertainties in environmental parameters. Within a linear approximation, Gaussian-distributed environmental parameter uncertainties lead directly to Gaussian data uncertainties which scale linearly with the parameter uncertainties. However, the actual data uncertainties, which can be estimated numerically via Monte Carlo methods, do not necessarily possess these desirable linear properties. The applicability of the linearized approximation and the relative magnitude of acoustic sensitivities are examined for realistic uncertainties in seabed geoacoustic parameters and oceanographic features of the water-column sound-speed profile. Sensitivities are considered as a function of source and receiver depth, range, and source frequency for various shallow-water environments. [Funding provided by DRDC-Atlantic Rapid Environmental Assessment Project.]
Lexical influences on the progressive facilitation during perception of assimilated speech
Authors: Munson Cheyenne , McMurray Bob , Gow David
Published: October 2013

Phonological processes such as place assimilation, in which coronal sounds partially adopt the place of a subsequent noncoronal (e.g., green boat becomes green/m boat), may create ambiguity during speech comprehension, but may also paradoxically facilitate word recognition. Gow (2001) demonstrated that partial assimilation facilitates perception of postassimilation context. Two eye-tracking experiments investigated whether this progressive effect is influenced by lexical processes. Assimilated and nonassimilated adjectives (e.g., green) were spliced onto coronal or noncoronal nouns (e.g., boat or dog) to create phonologically plausible and implausible assimilation. In experiment 1, assimilation resulted in nonwords; in experiment 2, words assimilated into other words, cuing lexical competition (e.g., cat box became cat/p box). Subjects viewed a screen showing 4 pictures: a coronal noun, 1 noncoronal, and 2 fillers. Eye movements were monitored as subjects heard instructions to select a picture with a mouse. In both experiments subjects were reliably faster to look at the noncoronal target following the assimilated adjective than the nonassimilated one. This progressive effect occurred approximately 100 ms later when assimilation created competitors (experiment 2). These results support an interactive view of word recognition in which lexical processing interacts in real time with phonological and perceptual grouping and integration processes.
Across-channel gap detection in cochlear implant listeners
Authors: Grose John H. , Buss Emily , Hall Joseph W.
Published: October 2013

In normal hearing, gap detection thresholds are elevated when the leading and trailing markers of a gap differ widely in frequency or are presented to different ears; thresholds are also elevated by the introduction of amplitude modulation (AM) to the markers. This study assessed whether similar effects can be observed in a group of high-performing, MED-EL COMBI 40+ cochlear implant users, a subset of whom are bilaterally implanted. In experiment 1, markers were equal-amplitude 3-kHz pulse trains of random duration (40–80 ms) delivered through a research interface. Thresholds were low (<1 to 6 ms) when the two markers were presented on a single electrode channel and increased when the markers were on different channels within an ear or across ears. In experiment 2, markers were AM pulse trains of random duration (100–150 ms). These were generated by multiplying a 3-kHz, equal-amplitude pulse train with the envelope of a 50- or a 300-Hz bandpass filtered Gaussian noise; the envelope was either uncompressed or compressed with an exponent of 0.2. Thresholds were elevated by AM at both rates, with larger effects for the uncompressed envelope. These patterns of results are similar to those observed in normal hearing. [Work supported by NIDCD 5R01DC1507.]
Nonlinear oscillation of microbubble in microtubes for ultrasound imaging and drug delivery
Authors: Qin Shengping , Ferrara Katherine
Published: October 2013

Ultrasound-assisted microbubble drug delivery is under intensive investigation due to the potential for enhanced local delivery without systemic adverse effects. The efforts in modeling bubble oscillation have been largely focused on using various modified forms of the Rayleigh-Plesset bubble dynamics equation, of which the cornerstone assumption is that a bubble oscillates in an unbounded liquid field and remains spherical until it collapses. Here, nonlinear oscillation of a bubble confined inside a microtube with diameters comparable with capillaries is studied numerically and experimentally. In numerical simulation, the liquid is treated as incompressible viscid fluid and contrast agent is treated as gas bubble obeying the polytropic law. Microbubble oscillation is shown to decrease in a small vessel as compared with oscillation in an infinite fluid or a larger vessel diameter. For the same bubble size, the natural oscillation frequency of a bubble deceases with the decrease of tube size. The natural frequency of a bubble with an equilibrium diameter of 2.5 μm decreases from 3.56 MHz, in unbounded liquid field, to 1.16 MHz in an 8-μm tube. Decreasing the ultrasound center frequency can increase the amplitude of bubble oscillation and thereby produce a higher pressure on the tube.
Reexamining loudness at and near threshold
Authors: Epstein Michael , Florentine Mary
Published: October 2013

This talk reviews two sets of data that support the contention that loudness at threshold is not zero, consistent with the new loudness standard. Both sets of data examine the form of the loudness function in normal listeners at low levels. The first set of data was derived from loudness-matching experiments between equally loud tones and tone complexes (i.e., spectral integration of loudness). Listeners matched the loudness of tone complexes comprised of subthreshold components with pure tones above threshold. Results show that a tone complex composed of components at threshold can easily be heard and can be relatively loud. This result is only possible if all tones had some probability of detection (some contribution to loudness), even those below threshold. The second set of data consists of the slopes of the loudness function at threshold, which average 1.3. These data are consistent with loudness functions obtained with a wide variety of methods that yield a slope close to unity. A slope close to unity indicates a positive loudness at threshold in accord with the new loudness standard. [Work supported by NIH/NIDCD Grant R01DC02241.]
The contribution of envelope and carrier to cues for tone-in-noise detection in narrow-band reproducible noises
Authors: Davidson Sean A. , Gilkey Robert H. , Colburn H. Steven , Carney Laurel H.
Published: October 2013

To elucidate the roles of envelope and carrier cues in detection of a 500-Hz tone in 50-Hz bandwidth noise under N0Sπ conditions, hit- and false-alarm rates were collected for 4 sets of reproducible stimuli. The envelopes and carriers from two sets of stimuli (each with 25 signal-plus-noise and 25 noise-alone waveforms) were extracted and recombined to form 2 new sets (each having the carriers from one of the original sets and the envelopes from the other). Noises were preselected to produce minimal spectral splatter in the recombination processes. Preliminary results for signal-plus-noise trials suggest that carrier cues (e.g., temporal fine structure) are dominant over envelope cues (i.e., response patterns were more similar between sets with the same carriers but different envelopes, than between sets with the same envelopes but different carriers); however, carrier cues cannot completely explain the data. Results for noise-alone trials suggest that both envelope cues and carrier cues contribute to listener responses. Further analyses will explore potential interactions between monaural and binaural stimulus properties, as well as interactions between interaural envelope cues and carrier cues. [Supported by NIH DC007798(SAD), DC001641(LHC), and DC00100(HSC).]
Nonlinear mechanisms of heating by high-intensity focused ultrasound
Authors: Khokhlova Vera A. , Bailey Michael R. , Canney Michael S. , Kaczkowski Peter J. , Crum Lawrence A.
Published: October 2013

Two major nonlinear mechanisms are known to influence HIFU heating: acoustic nonlinearity and cavitation. Heating may also result in formation of boiling vapor bubbles that grow much larger than the cavitation bubbles. The relevant role of these phenomena was investigated experimentally and numerically in a gel phantom. HIFU pressure thresholds for shock formation, cavitation, and boiling were measured using a fiber-optic probe hydrophone, passive cavitation detection, ultrasound and optical imaging, and thermocouples. The KZK and Bio-heat equations were employed to simulate experimental conditions. Elevated static pressure was applied to suppress bubbles and increase the boiling temperature, thus isolating the pure effect of acoustic nonlinearity in comparison of heating between short, high-amplitude and long, low-amplitude pulses of equal average intensity. The experimental results indicated that both nonlinear mechanisms accelerated lesion production with acoustic nonlinearity responsible for the greater effect. It was observed that lesion distortion and migration was due to boiling detected in as little as 40 ms within the center of the lesion, in agreement with nonlinear acoustic simulations. These data indicate that acoustic nonlinearity and the boiling play a significant role earlier in HIFU treatments than previously anticipated. [Work supported by the NSBRI-SMS00402, RFBR, NIH FIRCA and DK43881.]
Perception of object features by echolocating big brown bats
Authors: DeLong Caroline M. , Bragg Rebecca , Simmons James A.
Published: October 2013

Big brown bats can discriminate among objects using wideband FM sonar sounds. They can perceive only the acoustic dimensions of echoes (e.g., delay, frequency, amplitude), or they can use those dimensions to reconstruct object features (e.g., distance, shape, size). To investigate this question, bats were presented with two-alternative (left/right) forced-choice sonar discrimination tasks. In experiment 1, the stimuli were a one-cylinder monopole target and a two-cylinder dipole target that were presented at all aspect angles. In experiment 2, the stimuli were multiple two-cylinder dipole targets presented at all aspect angles. In both experiments, the positive target was the dipole with a 5-cm separation (negative targets had separations of 1–7 cm). Acoustic dimensions of the dipole echoes change depending on the aspect angle. If the bats represent only acoustic dimensions, they should have difficulty selecting the positive target at many aspects. If the bats represent object features, they should be able to select the positive target independent of aspect angle. Bats perform well, suggesting that they reconstruct object features from echo acoustic dimensions. Errors appear due to masking of either the monopole glint with the dipole glints or the dipole glints with each other. [Work supported by NIH and ONR.]
Multiple frequency acoustic propagation through clusters of bubbles
Authors: Weber Thomas C. , Lyons Anthony P. , Bradley David L.
Published: October 2013

A numerical study has been conducted in order to examine the effect of bubble clustering on acoustic propagation through bubble clouds. Commonly used effective medium theories make the assumption that the positions of bubbles are statistically independent from each other. It is plausible, however, that there are some scenarios in which this assumption does not apply. For example, bubbles may become preferentially concentrated or clustered as they cross fluid flow streamlines due to their density difference from that of the surrounding liquid. In order to help understand the acoustic implications of bubble clustering, propagation through two types of bubble clouds was investigated numerically. In the first type of bubble cloud the positions of the bubbles were statistically independent from each other. In the second type the bubbles were clustered. Both the average attenuation and the variance in the acoustic pressure amplitude were recorded at nine different frequencies for each type of bubble cloud. It was found that clustering has the effect of reducing the average attenuation from that observed in the nonclustered bubble cloud while increasing the variance. This contrasting behavior suggests a method for detecting the presence of bubble clustering using multiple frequency acoustic propagation measurements.
Monaural and binaural cues to signal detection
Authors: Culling John F.
Published: October 2013

When a signal is added to random noise in the NoSπ configuration it has two effects on the stimulus at the signal frequency: the correlation is reduced and the energy is increased. Both changes may contribute to the detection and discrimination of signals. A signal-level discrimination task (2I-FC) was used to measure the strength of each cue and their combination across a wide range of signal-to-noise ratios (−20–0 dB). The signal was a band of noise (462–539 Hz). The masker was a broadband noise (10–3000 Hz) of fixed sound level. Conditions were NoSπ, NoSo, and correlation manipulation within the target band equivalent to NoSπ. At low signal-to-noise ratios, performance was determined by the correlation change, but at higher signal levels both cues became ustable and discrimination was better in NoSπ than in the correlation-manipulation condition. Analysis using signal-detection theory indicated that these data could not be explained by assuming the two cues were independent.
Contribution of cross talk to the uncertainty of microphone calibrations by the electrostatic actuator method
Authors: Zuckerwar Allan J. , Faison Richard M.
Published: October 2013

Cross talk in electrostatic actuator calibrations is defined as the response of a test microphone to the actuator excitation voltage when the   microphone membrane is frozen, i.e., when the actuator polarization voltage is zero—an unavoidable nuisance effect that contributes to the calibration uncertainty. Two models for the cross talk are considered. In the first, the actuator excitation voltage is coupled to the microphone output through the stray capacitance between the actuator electrode and the microphone backplate; in the second, it is coupled through the ground resistance, which provides a common element between the input and output loops. In the stray capacitance model, at frequencies below the membrane resonance, the cross talk is independent of frequency, but in the ground resistance model it varies inversely with frequency. The frequency dependence of the cross talk thus serves as a discriminator between the two models. Measurements on condenser microphones of various sizes yield results that favor the stray capacitance model. The ratio of cross-talk signal to actuator pressure signal (at 94 dB re: 20 mPa) is found experimentally to be −74 dB for a 1-in. condenser microphone and nearly the same for 1/2-in. and 1/4-in. microphones.
Trends in detection in earthquake seismology
Authors: Harris David B.
Published: October 2013

Detection methods in earthquake seismology have been dominated in the past by simple energy detectors, often combined with array processing (beamforming) to detect at lower thresholds. Increasingly, correlation detectors now are being employed to exploit the additional gain possible with coherent detection methods. Coherent detection of transient seismic signals is complicated by the fact that earthquake signals generally cannot be predicted with certainty in advance, except for those cases where observations of previous events are available. One approach to solving this problem is to employ subspace detectors that allow variation in the correlation template to match the range of signals anticipated from a specific source region. Subspace templates have been produced empirically from past observations of repeating sources. The current challenge is to compute the templates in areas without past event observations. One approach to doing so calculates the target signal space by forward simulation through many earth realizations drawn from a stochastic earth model. In this talk, we present the results of empirical subspace detection with arrays of sensors (combining array gain with coherent matched-signal gain) and discuss preliminary results from the use of computed subspaces. [This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.]
Practical issues in designing strings for different-sized bowed instruments
Authors: Tao Fan-Chia
Published: October 2013

The playing length and frequency of musical strings are fixed by the design of the instrument. The playing tensions of commercially available strings for standard bowed instruments follow an approximately linear scaling law in relation to string length. However, the string designer can adjust the playing tension to yield different results, and playing tensions have changed throughout history as string technology and playing techniques have evolved. Another string property that can be varied by the string designer is damping. Empirical data suggest that over a wide variety of bowed instruments and frequency ranges, strings with similar damping give similar playing characteristics.
Depth/range localization of diving sperm whales using passive acoustics on a single hydrophone disregarding seafloor reflections
Authors: Laplanche Christophe , Adam Olivier , Lopatka Maciej , Motsch Jean-François
Published: October 2013

Depth and range of sound sources can be estimated using a single hydrophone. Such a passive acoustic technique requires the detection of direct path transmitted, sea surface, and seafloor reflected source signals, so as to measure their time of arrival differences (TOADs). Sperm whales almost continuously emit powerful, directional echolocation sounds (usual clicks) when diving. Sperm whales often dive in deep water, and click seafloor reflections are usually well detected only at the beginning of the dive. Surface echoes may be detected during the entire dive. If the measurement of the surface reflection TOAD of a single click is not enough for estimating the depth/range of the sperm whale at the time when this click was emitted, the joint consideration of delays emitted during the whole dive may provide this estimation. Such delays are indeed the measurements of a single phenomenon: the underwater movements of a single-clicking sperm whale. One can merge such data using a Bayesian technique, as well as use prior information (e.g., range when fluking-up). Such a method could make the single-hydrophone localization technique usable regardless of the properties of the sea bottom, e.g., in deep or high relief areas.
Coherent backscattering without a source
Authors: Larose Eric , Lobkis Oleg I. , Weaver Richard L.
Published: October 2013

Coherent backscattering is due to constructive interferences of reciprocal paths and leads to an enhancement of the intensity (by factors of up to 2 or 3, typically) of a multiply scattered field near its source. To observe this enhancement an array of receivers must be placed close to the source, within one or two wavelengths. It has been proposed that the effect may be used for the assessment of mean free paths against scattering. Here, we propose and demonstrate a passive technique that allows observation of the enhancement without need of sources. It is performed using time correlation of diffuse fields [Weaver and Lobkis, Phys. Rev. Lett. 87, 134301 (2001)] obtained by receive-only transducers. It is shown that this passive enhancement cone has an excellent spatial resolution, comparable to active cones previously obtained by others [Tourin et al., Phys. Rev. Lett. 79, 3637–3639 (1997), Lobkis and Weaver, Phys. Rev. Lett. 90, 254302 (2003)].
Modified modal analysis for damped enclosures.
Authors: Xu Buye , Sommerfeldt Scott
Published: October 2013

Modal analysis (MA) has been widely used to model and understand acoustic fields in undamped or lightly damped enclosures. When additional damping is introduced, MA is known to fail in predicting acoustic quantities close to the boundaries and to exhibit a much slower speed of convergence. Modifications have been introduced into a standard MA approach to partially match the damped boundary conditions and source conditions. Notable improvements in both accuracy and convergence speed are observed when using this modified modal analysis. The theoretical derivation of the model will be discussed briefly, and several examples will be shown to demonstrate the improved accuracy of the model.
Adding art to an artless space: case studies in refitting existing buildings as performance facilities.
Authors: Miller Gregory , Way Evelyn , Harrison Byron , Talaske Richard
Published: October 2013

Performing artists will find ways to present their work, often in spaces that they find and adapt for their own use. This paper will provide a number of historic examples of the use of “found spaces” for theatrical performance (specifically referencing the work of Peter Brook and CIRT), as well as contemporary case studies of buildings that have undergone significant renovations. Contemporary projects will include the Lookingglass Theatre (a former municipal pumping station), the Steppenwolf Garage (a parking structure), and the Lincoln Park Music Theatre (a former bank building).
Scattering of a helicoidal Bessel beam by a sphere: The effect of an azimuthal phase gradient.
Authors: Marston Philip
Published: October 2013

In prior work [P. L. Marston, J. Acoust. Soc. Am. 121, 753–758 (2007)] the partial wave series for the scattering by a sphere centered on an ordinary Bessel beam was derived. The present work extends the analysis of the far field scattering to the case of a helicoidal Bessel beam having an angular phase ramp equal to the azimuthal angle. Helicoidal beams possess an axial null and have an azimuthal phase gradient. Some of the resulting modifications of the scattering are illustrated for an empty steel shell in water. In agreement with symmetry arguments given previously [B. T. Hefner and P. L. Marston, J. Acoust. Soc. Am. 106, 3313–3316 (1999)] the backward scattering and forward scattering vanish. For some directions the scattering increases when shifting from ordinary to a helicoidal beam illumination. In addition to describing the scattering by acoustic beams, there are potential applications of this analysis to the description of acoustic radiation forces and torques. [Work supported in part by ONR and by NASA.]
Causality and mathematical models in vibration and acoustics: A realistic perspective.
Authors: Pierce Allan D.
Published: October 2013

Acoustic and vibrations applications require stricter causality conceptions than primitive causality (effect never precedes cause). Relativistic causality (nothing travels faster than light) is irrelevant; there is no practical reason that a satisfactory continuum-mechanical model, holding for low to moderate frequencies, be relativistically invariant. Modifying the requirement so that the speed of light is replaced by some acoustic speed is not satisfactory, as the insertion of dissipative mechanisms into any continuum-mechanical model invariably results in small precursors which may precede sonic-velocity wavefronts. These are small, but they are formally nonzero at arbitrarily large distances in advance of the front. The present paper follows Ginzberg (1955) and advocates acoustic causality: the requirements that (i) the precursors die out rapidly with distance, (ii) up to some frequency of interest acoustic disturbances genuinely propagate, with the attenuation per wavelength being substantially less than unity, and (iii) vibrations and propagation are governed by coupled partial differential equations. With these principles as a guide, approximate relations involving extrapolations into the complex plane are derived, and it is shown how error bounds can be placed on applications of various members of a derived family of Kramers–Kronig relations. Very low-frequency relaxation processes account for proportional damping in vibrations.
Developmental study of the relationship between F0 and formant frequencies.
Authors: Assmann Peter F. , Nearey Terrance M. , Bharadwaj Sneha V. , Hubbard Daniel , Jayaraman Anu
Published: October 2013

There is a systematic relationship between fundamental frequency (F0) and formant frequencies in natural speech across adult talkers, associated with anatomical differences in the length of the vocal tract and vocal folds. In the present study we examined developmental trends in this relationship using a database of vowel recordings from adults and children ranging from 5 to 18 years of age from the Dallas, Texas region. A moderate correlation was found between the geometric mean of the formant frequencies (F1–F3) across all of the vowels for a given speaker (a measure related to vocal tract length) and the geometric mean F0. Overall the correlation was higher in males (r=0.87) than in females (r=0.46) and increased as a function of age. The presence of systematic covariation between F0 and formant frequencies is consistent with studies showing a perceptual contribution of F0 to vowel identification.
Card-house theory of mud sediments containing kaolinite and its acoustical implications.
Authors: Pierce Allan D. , Carey William M. , Porter Tyrone M.
Published: October 2013

A major component of harbor mud is the clay mineral kaolinite, Al2Si2O5(OH)4. Isomorphous substitution, Al atoms occasionally replacing Si atoms, causes a net positive charge of roughly one electronic charge per 400 Si atoms. Kaolinite platelets have diameters and thicknesses of the order of 1 μm and 20 nm. The platelet’s positive charge induces a thin negative charge layer of suspended negative ions on both sides, layer thickness dependent on temperature, creating a continuous sheet of transversely aligned longitudinal electrical quadrupoles. Platelets repel each other weakly when placed face to face. The natural configuration is where the only connection between platelets are with the edge of one touching the center of the face of another. The resulting configuration resembles a house of cards. Because the platelets are thin, the porosity is close to unity, and the sound speed is slightly less than the sound speed in water. This type of mud weakly resists shear because any shearing leads to an increase in electrostatic energy within the card house. Theories are presented to answer why bubbles in mud tend to have a flattened shape and to explain the small but nonzero attenuation of sound in mud. [Work sponsored by Strategic Environmental Research and Development Program.]
Active control of diffuse sound fields using generalized energy density.
Authors: Xu Buye , Sommerfeldt Scott
Published: October 2013

In enclosures, the total acoustic energy density (ED) has been shown both theoretically and experimentally to be more spatially uniform than the squared pressure. The generalized energy density (GED) has even more uniform properties than the acoustic energy density. In active noise control applications, the standard approach taken is to minimize the squared pressure response in the field. However, the use of ED as the minimization quantity has been demonstrated to yield improved performance in low modal density acoustic fields, often resulting in improved global attenuation. For diffuse acoustic fields (high modal density), local “quiet zones” can be achieved, with the volume of this quiet zone typically being characterized as a sphere with a diameter of about one-tenth of a wavelength when the squared pressure is minimized. It has been found that this performance can also be improved through the use of GED. By controlling GED instead of squared pressure, one cannot only increase the size of the quiet zone but also decrease the acoustic power added into the system. Results will be shown to illustrate the improved performance.
Consonant landmarks: Automatic detection and interpretation.
Authors: Park Chiyoun , Chen Nancy
Published: October 2013

Consonant landmarks are acoustic discontinuities in the speech signal that correspond to the closures and releases in speech production, and have been proposed as critical elements in speech processing [Stevens (2002)]. The three types of consonant landmarks represent the onset and offset of salient acoustic events: glottal vibration, turbulence noise, and sonorancy (e.g., nonvocalic voicing). While earlier work [Liu, (1996)] evaluated the success of identifying single candidate landmarks of all three types, this work focuses on two tools for evaluating strings of landmark candidates. First, a bigram model representing the physiologically feasible sequences of consonant landmarks is used to evaluate candidate strings. Second, a graphical method is used to identify the regions where the landmarks are reliably detected versus where they are ambiguous. Together these tools substantially improve the performance for landmark detection, identify regions in need of further acoustic analysis, and model the ‘grammatical’ structure of landmark sequences. Furthermore, the reliable regions in the proposed representation often correspond to structural elements such as lexical stress and word boundaries. Thus, the proposed representation is potentially useful in analyzing speech not only at the phoneme level but also at the word and phrase levels. [This work was supported by NIH/NIDCD DC02978 and T32DC00038.]
Evaluation of a singular-spectrum analysis algorithm for detecting two types of brachytherapy seeds commonly used to treat prostate cancer.
Authors: Mamou Jonathan , Ramachandran Sarayu , Feleppa Ernest J.
Published: October 2013

Brachytherapy for prostate-cancer treatment involves permanent implantation of radioactive seeds into the gland. Reliable imaging of implanted seeds is needed to correct dosimetry errors in the operating room. A singular-spectrum analysis algorithm previously was able to detect palladium seeds over various angles between the seed and ultrasound-beam axes. We subsequently evaluated algorithm performance with iodine seeds. The algorithm extracts pairs of eigenvalues from the autocorrelation matrix of seed echo signals. Selected eigenvalues are used to compute a P-value for seed presence. The algorithm was applied to echo signals obtained using a 5-MHz transducer to scan seeds implanted into an acoustically transparent gel pad and a piece of ex vivo beef. The angle of the seed axis with respect to the beam axis was varied from normal to the beam axis to 20 deg from normal. Algorithm performance was denoted by a score computed from P-values. Scores for both seed types in beef varied from 70 to 40 dB over the range of angles studied. Scores computed from B-mode images were approximately 30 dB lower indicating superior contrast with the SSA algorithm. The SSA algorithm was successful in detecting palladium and iodine seeds over a range of angles to the ultrasound beam.
Acoustic tomography of the atmosphere at the Boulder Atmospheric Observatory.
Authors: Ostashev Vladimir E. , Bedard Alfred J. , Vecherin Sergey N. , Wilson D. Keith
Published: October 2013

An array for acoustic tomography of the atmosphere has been built at the NOAA Boulder Atmospheric Observatory. In this paper, a short description of the array and some acoustic tomography results are presented. The array consists of three speaker and five microphone towers located along the perimeter of a square with a side length of 80 m. The towers are 9.1 m high. The speakers and microphones can be located at different (multiple) levels on the towers to do three-dimensional tomography. The transducers are connected via cables with the central command and data acquisition computer. The array enables measurements of travel times of sound propagation between different pairs of speakers and microphones. The measurements are done repeatedly within a short time interval so that the information about the temporal change in the travel times can be employed in tomographic reconstruction. Then, these travel times are used as input data in a time-dependent stochastic inversion for reconstruction of temperature and wind velocity fields. Examples of the reconstructed turbulence fields are presented and discussed. [Work supported by the Army Research Office.]
Inversion of ocean environmental variations via time reversal acoustics.
Authors: Xu Wen , Li Jianlong
Published: October 2013

Time reversal (TR) processing is derived from the invariance of the wave equation for lossless medium to change in the sign of the time variable. By retransmitting the TR version of the time-dispersed received signal propagated from a probe source (PS) to a source-receiver array, one can reacquire the transmitted pulse at the PS location (time compression and spatial focusing) when the waveguide environment is time invariant. However, if some environmental variations occur between the two transmissions, the retrofocusing signal will be defocused. This paper presents a new method of environmental parameter inversion by comparing the difference of the focused signals measured at the PS location with/without environmental perturbations. Because the sound speed profile (SSP) plays a critical role in an uncertainty ocean environment, inversion of the SSP represented in terms of the empirical orthogonal functions is developed and discussed in detail. Simulations demonstrate some advantages of environmental inversion via TR: (1) great signal-to-noise ratios can be obtained at the PS location; (2) variations of the environment at different times can be directly inverted by repeatedly retransmitting either the same received signal generated by one PS transmission or the updated received signals generated by updated PS transmissions.
Improving biomedical ultrasonic imaging systems through coded excitation and pulse compression.
Authors: Oelze Michael , Sanchez Jose
Published: October 2013

Coded excitation and pulse compression techniques are being employed in biomedical ultrasonic imaging systems in order to improve image quality. Traditionally, the rationale for using coded excitation techniques in biomedical ultrasonic imaging was to increase the signal-to-noise ratio (SNR) of backscattered signals without increasing the pressure amplitudes above the thresholds predicted to produce bioeffects. Furthermore, coding schemes combined with pulse compression would allow the spatial resolution to be preserved. Recently, unique coded excitation schemes have been developed [i.e., the resolution enhancement compression (REC) technique] that not only produce a significant increase in SNR but also a doubling of the bandwidth of the ultrasonic imaging system. In conventional ultrasound B-mode imaging, the increased bandwidth provided by the REC technique could be used to improve the axial resolution of the ultrasonic imaging system or traded off to improve the contrast resolution of the ultrasonic imaging system through frequency compounding. In quantitative imaging techniques using spectral analysis (e.g., scatterer size imaging), the increased bandwidth from REC could be used to increase the trade-off between spatial resolution and estimate variance. An overview of these coded excitation techniques and their application to biomedical ultrasonic imaging will be presented. [This work is supported by NIH EB006741.]
High-frequency one-way propagation experiments in Portsmouth Harbor, NH.
Authors: Weber Thomas C. , Weirathmueller Michelle , Mayer Larry
Published: October 2013

Portsmouth Harbor is a shallow water estuary with 3-m tide heights and 2-m/s tidal currents, exhibiting strong mixing between ocean water and several fresh water inputs. In order to help characterize the limitations for underwater acoustic positioning systems in this environment, high-frequency (40 kHz) one-way acoustic propagation measurements were made at ranges up to 1 km in an area where the maximum depth reached 25 m. Synchronized acoustic transmissions were made from a bottom mounted projector as well as from a near-surface projector mounted on a moving research vessel. The signals were received at a pier-mounted hydrophone. Measurements of signal levels and arrival times show strong signatures from a variety of phenomenon including changes in tide height, changes in sound speed gradients in response to the tidal forcing functions, and turbulent mixing in the water. Each of these will be discussed in relation to signal fluctuations and constraints on measuring pulse arrival times.
Detection and localization performance using a forward scattering tripwire concept for harbor surveillance.
Authors: Folegot Thomas
Published: October 2013

An innovative technique has been developed to localize intruders crossing an acoustic underwater tripwire surveillance system in shallow water chokepoints. In the context of defence against terrorism, an sample application would be the permanent autonomous detection and localization of small underwater vehicles or divers surreptitiously entering a friendly harbor. The proposed method uses forward propagation and produces an acoustic image of the whole underwater entrance of a harbor, scanning and checking for intrusion in the area of interest. It is anticipated that the system could provide a high image rate and improved performance in noisy, reverberating, and changing environment. This paper discusses results obtained from a scaled tank experiment and shows preliminary results at sea.
Bayesian localization and tracking with environmental and array-element uncertainties.
Authors: Dosso Stan , Tollefsen Dag , Wilmut Michael
Published: October 2013

This paper considers matched-field source localization and tracking when environmental parameters and/or array-element positions are not well known. A Bayesian formulation is applied in which source, array, and environmental parameters are considered unknown random variables constrained by noisy acoustic data and by prior information on parameter values (e.g., physical limits for environmental properties and element positions) and on interparameter relationships (e.g., limits on source speed and interelement spacing). The goal then is to extract source information from the posterior probability density (PPD). One approach is based on maximizing the PPD over all parameters to obtain optimal source locations. A key to solving this problem efficiently is that the VITERBI algorithm is applied to compute the highest-probability source track for each environment/array realization: this provides the optimal track, while requiring the optimization is applied only over the nuisance parameters. A second approach involves integrating the PPD over unknown environmental and array parameters to represent source-location information as a series of joint marginal probability surfaces over range and depth. Given the strong nonlinearity of this problem, marginal PPDs are computed numerically using efficient Markov-chain Monte Carlo importance sampling methods. The approaches are illustrated with examples based on simulated and measured acoustic data.
Discovery of temporal patterns in continuous nonrandom sound sequences.
Authors: Singh Rita , Raj Bhiksha
Published: October 2013

The problem addressed is that of automatically determining the minimal structures in structured sounds such as human speech. It is well established that human speech comprises consistent sound units (such as phonemes), a fact that is exploited by speech recognition systems, which only model the units, characterizing all speech as sequences of units. Currently, the units are typically manually defined, and their statistical models are assigned structures based on subjective judgments. In this work it is attempted to identify these units automatically through an analysis of data. The problem is treated as one of entropy minimization. The minimum entropy estimation principle assumes a structured universe and dictates the estimation of the most predictable model that the observations used to train the model will allow. For the current problem, this amounts to identifying a set of units such that every word can be represented by a minimum-perplexity network over them. Experiments demonstrate that this procedure identifies units with consistent structures that, although not always identical to phonemes, are nevertheless able to explain the data just as well as quantified by recognition accuracy. More interestingly, the algorithm is generic and may be employed to learn component units of other natural sounds besides speech.
Evidence for interaction between speech rhythm and gesture.
Authors: Tilsen Sam
Published: October 2013

Temporal patterns in speech occur on multiple timescales. Speech gestures generally occur on a fast timescale; previous work has found evidence for a c-center effect in complex syllable onsets (e.g. /spa/), whereby initiations of tongue blade and lip movements associated with /s/ and /p/ are equally displaced in opposite directions from initiation of tongue body movement associated with the vowel [C. Browman and L. Goldstein, Phonetica 45, 140–155 (1988)]. Speech rhythms occupy a slower timescale; in metronome-driven phrase repetition tasks, rhythmic timing is more variable for higher-order target ratios of intervals between stressed syllables and phrases [F. Cummins and R. Port, J. Phonetics 26, 145–171 (1998)]. An experiment was conducted to investigate how these gestural and rhythmic patterns interact. Gestural kinematics were recorded using electromagnetic articulometry during a repetition task with the phrase “take on a spa.” Significantly greater variance in relative timing of tongue and lower lip movements associated with /s/ and /p/ was observed with the more difficult (less harmonic) target rhythms. Within-gesture effector synergies between jaw and tongue differed systematically across rhythmic conditions. These results demonstrate a substantial interaction between rhythmic and gestural systems. Observed variability patterns are simulated with a dynamical model of phase-coupled oscillators.
Finite element studies of hand bell modes.
Authors: Hansen Uwe J.
Published: October 2013

Hand bell modes are identified by indices m and n (m, n), where m refers to the number of nodal lines crossing the crown and n refers to the number of circumferential nodal lines. For high m values, depending on the bell size, no n = 0 modes exist. For such large m modes, the n = 1 nodal line is located very close to the mouth of the bell, rather than near the middle of the bell as is the case for (m,1) modes, where for the same value of m, an n = 0 mode exists. These modes are generally labeled as (m, 1*) modes. Finite element studies of mode sections of increasing complexity indicate that only when two curvatures are introduced, conditions are adequate to give rise to (m, 1*) modes. Computer generated images and animations of mode patterns corresponding to increasingly complex geometries will be illustrated.