bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic Bistable Electroactive Polymers: Large Strain Actuation of Shape Memory Polymers
Authors: Son Seyul , Goulbourne N. C.
Published: April 2011

In this paper, constitutive equations to model the electromechanical behavior of shape memory polymers (SMPs) are introduced for the first time. SMPs are unique material that can be transformed into complicated shapes and recover their original shapes even under large deformations [1]. Above their transition temperature, elastic modulus decreases and they can be easily deformed by mechanical or electrical input. Advantage of this behavior is returning to the deformed shape utilizing a triggering temperature without any applied forces. This can be used to actuate the electroactive polymer to restore the deformed shape without applying an electric field [2]. Therefore in this paper, the equibiaxial extension of two different SMPs (PTBA (poly(tert-butylacrylate)) [2] and Sylgard (Sylgard 184)/PCL (poly(ε-caprolactone)) composite [3]) is simulated numerically to demonstrate the electromechanical behavior with respect to mechanical and electromechanical inputs. For simplification, the response of the SMP above the transition temperature is considered, so that material properties are constant and not a function of temperature. The SMPs are considered a fiber-reinforced membrane with two families of fibers, which enable to tune the material properties of SMPs [3]. To describe the constitutive relation of the SMPs, Mooney-Rivlin and Ogden model for isotropic SMPs, as well as Gasser et al model [4] for anisotropic SMPs, are applied. In the numerical computations, the isotropic and anisotropic electromechanical response of PTBA and Sylgard/PCL composite are presented. PTBA shows larger electromechanical effect in the range of stretch 1.5–2.5. Additionally, the effects of the fiber stiffness, angle, and dispersion on the deformation of the SMPs are observed. According to the result, the fiber stiffness can significantly affect on the electromechanical response and fiber angle and dispersion can influence the anisotropic deformation.
Design of an SMA Actuated Mechanotransductive Implant for Correcting Short Bowel Syndrome
Authors: Utter Brent , Barnes Brian , Luntz Jonathan , Brei Diann , Teitelbaum Daniel H. , Okawada Manabu , Miyasaka Eiichi
Published: April 2011

Short bowel syndrome is a serious medical condition afflicting an estimated 20,000 to 200,000 people in the United States with mortality rates as high as 40%, despite current treatments. Recent research on mechanotransduction, the process through which mechanical load induces tissue growth, has successfully demonstrated permanent growth of healthy, functional bowel in small animals. Unfortunately, the underlying technological approaches limit further research of growth under different load profiles and extension to safe clinical devices. This paper presents a fully implantable bowel extender which expands via a unique Shape Memory Alloy (SMA) driven ratcheting mechanism, measures the bowel tension and load, and enables studies of mechanotransductive bowel tissue growth where the displacement or load may be controlled wirelessly in real-time. The architecture and operation of the bowel extender is illustrated, focusing on the SMA driven ratcheting mechanism that incrementally expands the device. To help visualize the SMA wire and reset spring design, an alternative graphical method is outlined which transforms the SMA material curves into a Reset View based on predictions of the system forces. An analytical model predicts the ratchet mechanism force with tooth and pawl geometry selected based on packaging, load-bearing, and kinematic constraints. Force limits to maintain tissue health are established from ex vivo and in vivo porcine small bowel loading experiments. The Reset View methodology is applied to design a bowel extender prototype which is used to experimentally validate the ratchet force model. The functionality device is demonstrated, operating against loads much larger than specified, validating the device’s ability to enable new studies of mechanotransductive bowel growth in pigs.
Aqueous Magnetorheological Suspensions of Composite Carbonyl Iron Particles
Authors: Cheng H. B. , Zuo L. , Zhang Q. J. , Wereley N. M.
Published: April 2011

Aqueous magnetorheological (MR) suspensions of composite carbonyl iron particles (CCIPs) were prepared with carbonyl iron particles and an organic reagent coating (N-polyether, N, N, N,-acetyloxy) 2, 6-aminion-1, 3, 4-thiadiazole dimer (EAMTD). The properties of the CCIPs, including morphology, structure, and magnetic behaviors, were characterized using scanning electron microscopy (SEM) and a vibrating sample magnetometer (VSM). The MR properties of the aqueous MR suspensions were analyzed via a strain-controlled parallel disk rheometer equipped with a magnetic field source. The results show that the stability and redispersibility of the aqueous MR suspensions were greatly improved, and the yield stress is influenced by the EAMTD coating layer of the CCIPs.
Wind Tunnel Testing of a Helicopter Rotor Trailing Edge Flap Actuated via Pneumatic Artificial Muscles
Authors: Woods Benjamin K. S. , Wereley Norman M. , Kothera Curt S.
Published: April 2011

A novel active trailing edge flap actuation system is under development. This system differs significantly from previous trailing edge flap systems in that it is driven by a pneumatic actuator technology. Pneumatic Artificial Muscles (PAMs) were chosen because of several attractive properties, including high specific work and power output, an expendable operating fluid, and robustness. The actuation system is sized for a full scale active rotor system for a Bell 407 scale helicopter. This system is designed to produce large flap deflections (±20°) at the main rotor rotation frequency (1/rev) to create large amplitude thrust variation for primary control of the helicopter. Additionally, it is designed to produce smaller magnitude deflections at higher frequencies, up to 5/rev (N+1/rev), to provide vibration mitigation capability. The basic configuration has a pair of Pneumatic Artificial Muscles mounted antagonistically in the root of each blade. A bellcrank and linkage system transfers the force and motion of these actuators to a trailing edge flap on the outboard portion of the rotor. A reduced span wind tunnel test model of this system has been built and tested in the Glenn L. Martin Wind Tunnel at the University of Maryland at wind speeds up to M = 0.3. The test article consisted of a 5-ft long tip section of a Bell 407 rotor blade cantilevered from the base of the tunnel with a 34 in, 15% chord plain flap that was driven by the PAM actuation system. Testing over a wide range of aerodynamic conditions and actuation parameters established the considerable control authority and bandwidth of the system at the aerodynamic load levels available in the tunnel. Comparison of quasi-static experimental results shows good agreement with predictions made using a simple system model.
High Specific Power Actuators for Robotic Manipulators
Authors: Robinson R. M. , Woods B. K. S. , Vocke R. D. , Wereley N. M. , Kothera Curt S.
Published: April 2011

Recent advances in actuator technology suggest that the implementation of reliable, high power-to-weight ratio pneumatic actuation systems is now possible for robotic platforms. Current robotic manipulator arms for casualty extraction and patient placement use hydraulic actuation, whereas related robotic prosthetic devices use large, heavy actuator motors. We have developed an alternative solution to robotic manipulation that employs pneumatic artificial muscles (PAMs) to generate desired joint torque and range of motion. The goal of this study is to determine the size and configuration of a robotic manipulator for battlefield casualty extraction. Following characterization and comparison of different-sized PAM actuators, a prototype of a PAM robotic manipulator arm was constructed. A quasi-static model for the PAM actuators is applied to system modeling. This model includes the Gaylord force from pressure effects on the braid, as well as a nonlinear Mooney-Rivlin term that considers the elastic energy of the bladder. Experiments are performed to measure joint torque over the manipulator range of motion. The model developed here is experimentally validated.
A Bending Mode Galfenol Electric Power Harvester
Authors: Yoo Jin-Hyeong , Flatau Alison B.
Published: April 2011

Iron-Gallium alloys (Galfenol) are promising transducer materials that combine high magnetostriction, desirable mechanical properties, high permeability and a wide operational temperature range. In this study, we present results from a proof-of-concept prototype energy harvester that produces an output voltage proportional to the load-induced bending of the Galfenol element. The device consists of a polycrystalline Galfenol strip bonded to an aluminum cantilever beam which has an effective length of 1.5 in. Two brass pieces containing a permanent magnet are used to mass load each end of the beam and to provide a magnetic bias field through the Galfenol strip. An induction coil around the cantilever beam captures the magnetic flux variation of Galfenol as the beam vibrates. The first bending mode resonant frequency of the device was measured at 223 Hz. The power generated from the prototype subjected to 4-g acceleration at 222 Hz frequency was 16.4 mW(RMS), with corresponding power efficiency for output electrical power per input mechanical power of more than 30%.
Modeling of the Nucleation and Growth of Domain Needles
Authors: Li Wenyuan , Landis Chad M.
Published: April 2011

Some recent results on phase-field modeling of the nucleation, growth and interaction of domain needles are presented. First, the nucleation of domains near crack tips is studied within the context of a small-scale switching boundary layer formulation. Combinations of mechanical stress intensity factors and electric displacement intensity factors that cause domain nucleation are reported. After nucleation, domains are allowed to grow. The effects of the new domain structures on the crack growth energy release rate are studied.
“Compression-only” behavior: A second-order nonlinear response of ultrasound contrast agent microbubbles
Authors: Sijl Jeroen , Overvelde Marlies , Dollet Benjamin , Garbin Valeria , de Jong Nico , Lohse Detlef , Versluis Michel
Published: April 2011

Oscillating phospholipid-coated ultrasound contrast agent microbubbles display a so-called “compression-only” behavior, where it is observed that the bubbles compress efficiently while their expansion is suppressed. Here, a theoretical understanding of the source of this nonlinear behavior is provided through a weakly nonlinear analysis of the shell buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499–3505 (2005)]. It is shown that the radial dynamics of the bubble can be considered as a superposition of a linear response at the fundamental driving frequency and a second-order nonlinear low-frequency response that describes the negative offset of the mean bubble radius. The analytical solution deduced from the weakly nonlinear analysis shows that the compression-only behavior results from a rapid change of the shell elasticity with bubble radius. In addition, the radial dynamics of single phospholipid-coated microbubbles was recorded as a function of both the amplitude and the frequency of the driving pressure pulse. The comparison between the experimental data and the theory shows that the magnitude of compression-only behavior is mainly determined by the initial phospholipids concentration on the bubble surface, which slightly varies from bubble to bubble.
A study of acoustic-to-articulatory inversion of speech by analysis-by-synthesis using chain matrices and the Maeda articulatory model
Authors: Panchapagesan Sankaran , Alwan Abeer
Published: April 2011

In this paper, a quantitative study of acoustic-to-articulatory inversion for vowel speech sounds by analysis-by-synthesis using the Maeda articulatory model is performed. For chain matrix calculation of vocal tract (VT) acoustics, the chain matrix derivatives with respect to area function are calculated and used in a quasi-Newton method for optimizing articulatory trajectories. The cost function includes a distance measure between natural and synthesized first three formants, and parameter regularization and continuity terms. Calibration of the Maeda model to two speakers, one male and one female, from the University of Wisconsin x-ray microbeam (XRMB) database, using a cost function, is discussed. Model adaptation includes scaling the overall VT and the pharyngeal region and modifying the outer VT outline using measured palate and pharyngeal traces. The inversion optimization is initialized by a fast search of an articulatory codebook, which was pruned using XRMB data to improve inversion results. Good agreement between estimated midsagittal VT outlines and measured XRMB tongue pellet positions was achieved for several vowels and diphthongs for the male speaker, with average pellet-VT outline distances around 0.15 cm, smooth articulatory trajectories, and less than 1% average error in the first three formants.
The energy ratio mapping algorithm: A tool to improve the energy-based detection of odontocete echolocation clicks
Authors: Klinck Holger , Mellinger David K.
Published: April 2011

The energy ratio mapping algorithm (ERMA) was developed to improve the performance of energy-based detection of odontocete echolocation clicks, especially for application in environments with limited computational power and energy such as acoustic gliders. ERMA systematically evaluates many frequency bands for energy ratio-based detection of echolocation clicks produced by a target species in the presence of the species mix in a given geographic area. To evaluate the performance of ERMA, a Teager-Kaiser energy operator was applied to the series of energy ratios as derived by ERMA. A noise-adaptive threshold was then applied to the Teager-Kaiser function to identify clicks in data sets. The method was tested for detecting clicks of Blainville’s beaked whales while rejecting echolocation clicks of Risso’s dolphins and pilot whales. Results showed that the ERMA-based detector correctly identified 81.6% of the beaked whale clicks in an extended evaluation data set. Average false-positive detection rate was 6.3% (3.4% for Risso’s dolphins and 2.9% for pilot whales).
A field expansions method for scattering by periodic multilayered media
Authors: Malcolm Alison , Nicholls David P.
Published: April 2011

The interaction of acoustic and electromagnetic waves with periodic structures plays an important role in a wide range of problems of scientific and technological interest. This contribution focuses upon the robust and high-order numerical simulation of a model for the interaction of pressure waves generated within the earth incident upon layers of sediment near the surface. Herein described is a boundary perturbation method for the numerical simulation of scattering returns from irregularly shaped periodic layered media. The method requires only the discretization of the layer interfaces (so that the number of unknowns is an order of magnitude smaller than finite difference and finite element simulations), while it avoids not only the need for specialized quadrature rules but also the dense linear systems characteristic of boundary integral/element methods. The approach is a generalization to multiple layers of Bruno and Reitich’s “Method of Field Expansions” for dielectric structures with two layers. By simply considering the entire structure simultaneously, rather than solving in individual layers separately, the full field can be recovered in time proportional to the number of interfaces. As with the original field expansions method, this approach is extremely efficient and spectrally accurate.
Transmission loss of orthogonally rib-stiffened double-panel structures with cavity absorption
Authors: Xin F. X. , Lu T. J.
Published: April 2011

The transmission loss of sound through infinite orthogonally rib-stiffened double-panel structures having cavity-filling fibrous sound absorptive materials is theoretically investigated. The propagation of sound across the fibrous material is characterized using an equivalent fluid model, and the motions of the rib-stiffeners are described by including all possible vibrations, i.e., flexural displacements, bending, and torsional rotations. The effects of fluid-structure coupling are account for by enforcing velocity continuity conditions at fluid-panel interfaces. By taking full advantage of the periodic nature of the double-panel, the space-harmonic approach and virtual work principle are applied to solve the sets of resultant governing equations, which are eventually truncated as a finite system of simultaneous algebraic equations and numerically solved insofar as the solution converges. To validate the proposed model, a comparison between the present model predictions and existing numerical and experimental results for a simplified version of the double-panel structure is carried out, with overall agreement achieved. The model is subsequently employed to explore the influence of the fluid-structure coupling between fluid in the cavity and the two panels on sound transmission across the orthogonally rib-stiffened double-panel structure. Obtained results demonstrate that this fluid-structure coupling affects significantly sound transmission loss (STL) at low frequencies and cannot be ignored when the rib-stiffeners are sparsely distributed. As a highlight of this research, an integrated optimal algorithm toward lightweight, high-stiffness and superior sound insulation capability is proposed, based on which a preliminary optimal design of the double-panel structure is performed.
Miniature photonic-crystal hydrophone optimized for ocean acoustics
Authors: Kilic Onur , Digonnet Michel J. F. , Kino Gordon S. , Solgaard Olav
Published: April 2011

This work reports on an optical hydrophone that is insensitive to hydrostatic pressure, yet capable of measuring acoustic pressures as low as the background noise in the ocean in a frequency range of 1 Hz to 100 kHz. The miniature hydrophone consists of a Fabry–Perot interferometer made of a photonic-crystal reflector interrogated with a single-mode fiber and is compatible with existing fiber-optic technologies. Three sensors with different acoustic power ranges placed within a sub-wavelength sized hydrophone head allow a high dynamic range in the excess of 160 dB with a low harmonic distortion of better than –30 dB. A method for suppressing cross-coupling between sensors in the same hydrophone head is also proposed. A prototype was fabricated, assembled, and tested. The sensitivity was measured from 100 Hz to 100 kHz, demonstrating a sound-pressure-equivalent noise spectral density down to 12 μPa/Hz1/2, a flatband wider than 10 kHz, and very low distortion.
The reflection of guided waves from simple supports in pipes
Authors: Galvagni Andrea , Cawley Peter
Published: April 2011

Successful ultrasonic guided wave detection of flaws at support locations relies on the ability to distinguish between the reflection produced by a simple support on an undamaged pipe and the reflection produced by pipe flaws. Consequently, it is essential to know how the reflections produced by simple supports behave; very little work has so far been reported on this subject. Through finite element simulations and experiments, this study develops a systematic understanding of how ultrasonic guided waves propagating along a pipe, in particular the T(0, 1) mode, interact with simple supports. It is shown that, unlike the T(0, 1) mode in a free pipe, the torsional mode in a supported region has a cut-off frequency, below which it will not propagate; below this frequency the T(0, 1) reflection coefficient is large, and it quickly reduces beyond the cut-off.
Acoustic scattering by a spherical obstacle: Modification to the analytical long-wavelength solution for the zero-order coefficient
Authors: Pinfield Valerie J. , Challis Richard E.
Published: April 2011

Classical long wavelength approximate solutions to the scattering of acoustic waves by a spherical liquid particle suspended in a liquid (an emulsion) show small but significant differences from full solutions at very low kca (typically kca < 0.01) and above at kca > 0.1, where kc is the compressional wavenumber and a the particle radius. These differences may be significant in the context of dispersed particle size estimates based on compression wave attenuation measurements. This paper gives an explanation of how these differences arise from approximations based on the significance of terms in the modulus of the complex zero-order partial wave coefficient, A0. It is proposed that a more accurate approximation results from considering the terms in the real and imaginary parts of the coefficient, separately.
A computational study of asymmetric glottal jet deflection during phonation
Authors: Zheng X. , Mittal R. , Bielamowicz S.
Published: April 2011

Two-dimensional numerical simulations are used to explore the mechanism for asymmetric deflection of the glottal jet during phonation. The model employs the full Navier–Stokes equations for the flow but a simple laryngeal geometry and vocal-fold motion. The study focuses on the effect of Reynolds number and glottal opening angle with a particular emphasis on examining the importance of the so-called “Coanda effect” in jet deflection. The study indicates that the glottal opening angle has no substantial effect on glottal jet deflection. Deflection in the glottal jet is always preceded by large-scale asymmetry in the downstream portion of the glottal jet. A detailed analysis of the velocity and vorticity fields shows that these downstream asymmetric vortex structures induce a flow at the glottal exit which is the primary driver for glottal jet deflection.
Sound speed in water-saturated glass beads as a function of frequency and porosity
Authors: Argo Theodore F. , Guild Matthew D. , Wilson Preston S. , Schröter Matthias , Radin Charles , Swinney Harry L.
Published: April 2011

Sound propagation in water-saturated granular sediments is known to depend on the sediment porosity, but few data in the literature address both the frequency and porosity dependency. To begin to address this deficiency, a fluidized bed technique was used to control the porosity of an artificial sediment composed of glass spheres of 265 μm diameter. Time-of-flight measurements and the Fourier phase technique were utilized to determine the sound speed for frequencies from 300 to 800 kHz and porosities from 0.37 to 0.43. A Biot-based model qualitatively describes the porosity dependence.
Numerical vibroacoustic analysis of plates with constrained-layer damping patches
Authors: Loredo Alexandre , Plessy Arnaud , El Hafidi Ali , Hamzaoui Nacer
Published: April 2011

A numerical vibroacoustic model that can manage multilayered plates locally covered with damping patches is presented. All the layers can have an on-axis orthotropic viscoelastic behavior. Continuity of displacements and transverse shear stresses at each interface is enforced, which permits to write the entire displacement field in function of the displacements of the—common—first layer, leading to a two-dimensional plate model. The problem is then discretized by Rayleigh–Ritz’s method using a trigonometric basis that includes both sine and cosine functions in order to treat various boundary conditions. The excitation can be of mechanical kind (concentrated or distributed forces) or of acoustic kind (plane wave of any incidence, diffuse field, etc.). The model permits to compute different vibroacoustic indicators: the mean square velocity of the plate, the radiation efficiency, and the transmission loss. Comparisons between the present model and numerical results from literature or finite element computations show that the model gives good results in both mechanical and acoustical aspects. Then, a comparison of the effects of different distributions of patches is presented. The role of the surface covering rate is first discussed, followed by a study involving different geometries for the same surface covering rate.
Multiple scattering by random configurations of circular cylinders: Reflection, transmission, and effective interface conditions
Authors: Martin P. A.
Published: April 2011

In a previous paper, Linton and Martin [J. Acoust. Soc. Am. 117, 3413–3423 (2005)] obtained two formulas for the effective wavenumber in a dilute random array of circular scatterers. They emerged from a study of the problem of the reflection of a plane wave at oblique incidence to a half-space containing the scatterers. Here, their study is extended to obtain formulas for the reflection and transmission coefficients and to investigate the average fields near the boundary of the half-space. Comparisons with previous work are made.
Prediction of sound reflection by corrugated porous surfaces
Authors: Allard J.-F. , Dazel O. , Gautier G. , Groby J.-P. , Lauriks W.
Published: April 2011

The coupled mode (CM) and finite-element methods (FEMs) are developed and used to predict the acoustic reflection coefficient of a semi-infinite porous medium with closely spaced two-dimensional (2D) periodical corrugations. These methods are also applied to predict the reflection coefficient of a periodic array of porous corrugations installed on an acoustically rigid surface. It is shown that the predictions by the both methods agree closely. The reflection coefficient and Brewster angle of total refraction for the corrugated semi-infinite medium predicted with these methods are compared against that predicted by the Biot/Tolstoy/Howe/Twersky and extended Twersky models. A similar analysis is carried out for porous corrugations set on a rigid backing. The behavior of the reflection coefficient and the pole in the expression for the reflection coefficient located close to grazing incidence is studied.
Ocean bottom profiling with ambient noise: A model for the passive fathometer
Authors: Traer James , Gerstoft Peter , Hodgkiss William S.
Published: April 2011

A model is presented for the complete passive fathometer response to ocean surface noise, interfering discrete noise sources, and locally uncorrelated noise in an ideal waveguide. The leading order term of the ocean surface noise contribution produces the cross-correlation of vertical multipaths and yields the depth of sub-bottom reflectors. Discrete noise incident on the array via multipaths give multiple peaks in the fathometer response. These peaks may obscure the sub-bottom reflections but can be attenuated with use of minimum variance distortionless response (MVDR) steering vectors. The seabed critical angle introduces discontinuities in the spatial distribution of distant surface noise and may introduce spurious peaks in the passive fathometer response. These peaks can be attenuated by beamforming within a bandwidth limited by the array geometry and critical angle.
Membranous and cartilaginous vocal fold adduction in singing
Authors: Herbst Christian T. , Qiu Qingjun , Schutte Harm K. , Švec Jan G.
Published: April 2011

While vocal fold adduction is an important parameter in speech, relatively little has been known on the adjustment of the vocal fold adduction in singing. This study investigates the possibility of separate adjustments of cartilaginous and membranous vocal fold adduction in singing. Six female and seven male subjects, singers and non-singers, were asked to imitate an instructor in producing four phonation types: “aBducted falsetto” (FaB), “aDducted falsetto” (FaD), “aBducted Chest” (CaB), and “aDducted Chest” (CaD). The phonations were evaluated using videostroboscopy, videokymography (VKG), electroglottography (EGG), and audio recordings. All the subjects showed less posterior (cartilaginous) vocal fold adduction in phonation types FaB and CaB than in FaD and CaD, and less membranous vocal fold adduction (smaller closed quotient) in FaB and FaD than in CaB and CaD. The findings indicate that the exercises enabled the singers to separately manipulate (a) cartilaginous adduction and (b) membranous medialization of the glottis though vocal fold bulging. Membranous adduction (monitored via videokymographic closed quotient) was influenced by both membranous medialization and cartilaginous adduction. Individual control over these types of vocal fold adjustments allows singers to create different vocal timbres.
The enhancement effect: Evidence for adaptation of inhibition using a binaural centering task
Authors: Byrne Andrew J. , Stellmack Mark A. , Viemeister Neal F.
Published: April 2011

The enhancement effect is consistently shown when simultaneously masked stimuli are preceded by the masker alone, with a reduction in the amount of masking relative to when that precursor is absent. One explanation for this effect proposed by Viemeister and Bacon [(1982). J. Acoust. Soc. Am. 71, 1502–1507] is the adaptation of inhibition, which predicts that an enhanced component (the “target”) will be effectively more intense within the auditory system than one that has not been enhanced. Forward masking studies have indicated this effect of increased gain; however, other explanations of the enhancement effect have also been suggested. In order to provide an alternative measure of the amount of effective gain for an enhanced target, a subjective binaural centering task was used in which listeners matched the intensities of enhanced and unenhanced 2-kHz tones presented to opposite ears to produce a centered stimulus. The results showed that the enhancement effect produces an effective 4–5 dB increase in the level of the enhanced target. The enhancement effect was also measured using other enhancement paradigms which yielded similar results over a range of levels for the target, supporting an account based on adaptation of inhibition.
California sea lion (Zalophus californianus) aerial hearing sensitivity measured using auditory steady-state response and psychophysical methods
Authors: Mulsow Jason , Finneran James J. , Houser Dorian S.
Published: April 2011

Although electrophysiological methods of measuring the hearing sensitivity of pinnipeds are not yet as refined as those for dolphins and porpoises, they appear to be a promising supplement to traditional psychophysical procedures. In order to further standardize electrophysiological methods with pinnipeds, a within-subject comparison of psychophysical and auditory steady-state response (ASSR) measures of aerial hearing sensitivity was conducted with a 1.5-yr-old California sea lion. The psychophysical audiogram was similar to those previously reported for otariids, with a U-shape, and thresholds near 10 dB re 20 μPa at 8 and 16 kHz. ASSR thresholds measured using both single and multiple simultaneous amplitude-modulated tones closely reproduced the psychophysical audiogram, although the mean ASSR thresholds were elevated relative to psychophysical thresholds. Differences between psychophysical and ASSR thresholds were greatest at the low- and high-frequency ends of the audiogram. Thresholds measured using the multiple ASSR method were not different from those measured using the single ASSR method. The multiple ASSR method was more rapid than the single ASSR method, and allowed for threshold measurements at seven frequencies in less than 20 min. The multiple ASSR method may be especially advantageous for hearing sensitivity measurements with otariid subjects that are untrained for psychophysical procedures.
Speaker compensation for local perturbation of fricative acoustic feedback
Authors: Casserly Elizabeth D.
Published: April 2011

Feedback perturbation studies of speech acoustics have revealed a great deal about how speakers monitor and control their productions of segmental (e.g., formant frequencies) and non-segmental (e.g., pitch) linguistic elements. The majority of previous work, however, overlooks the role of acoustic feedback in consonant production and makes use of acoustic manipulations that effect either entire utterances or the entire acoustic signal, rather than more temporally and phonetically restricted alterations. This study, therefore, seeks to expand the feedback perturbation literature by examining perturbation of consonant acoustics that is applied in a time-restricted and phonetically specific manner. The spectral center of the alveopalatal fricative [∫] produced in vowel-fricative-vowel nonwords was incrementally raised until it reached the potential for [s]-like frequencies, but the characteristics of high-frequency energy outside the target fricative remained unaltered. An “offline,” more widely accessible signal processing method was developed to perform this manipulation. The local feedback perturbation resulted in changes to speakers’ fricative production that were more variable, idiosyncratic, and restricted than the compensation seen in more global acoustic manipulations reported in the literature. Implications and interpretations of the results, as well as future directions for research based on the findings, are discussed.
Modeling subharmonic response from contrast microbubbles as a function of ambient static pressure
Authors: Katiyar Amit , Sarkar Kausik , Forsberg Flemming
Published: April 2011

Variation of subharmonic response from contrast microbubbles with ambient pressure is numerically investigated for non-invasive monitoring of organ-level blood pressure. Previously, several contrast microbubbles both in vitro and in vivo registered approximately linear (5–15 dB) subharmonic response reduction with 188 mm Hg change in ambient pressure. In contrast, simulated subharmonic response from a single microbubble is seen here to either increase or decrease with ambient pressure. This is shown using the code BUBBLESIM for encapsulated microbubbles, and then the underlying dynamics is investigated using a free bubble model. The ratio of the excitation frequency to the natural frequency of the bubble is the determining parameter—increasing ambient pressure increases natural frequency thereby changing this ratio. For frequency ratio below a lower critical value, increasing ambient pressure monotonically decreases subharmonic response. Above an upper critical value of the same ratio, increasing ambient pressure increases subharmonic response; in between, the subharmonic variation is non-monotonic. The precise values of frequency ratio for these three different trends depend on bubble radius and excitation amplitude. The modeled increase or decrease of subharmonic with ambient pressure, when one happens, is approximately linear only for certain range of excitation levels. Possible reasons for discrepancies between model and previous experiments are discussed.
A computational study of the effect of windscreen shape and flow resistivity on turbulent wind noise reduction
Authors: Xu Ying , Zheng Z. C. , Wilson D. K.
Published: April 2011

In this paper, numerical simulations are used to study the turbulent wind noise reduction effect of microphone windscreens with varying shapes and flow resistivities. Typical windscreen shapes consisting of circular, elliptical, and rectangular cylinders are investigated. A turbulent environment is generated by placing a solid circular cylinder upstream of the microphone. An immersed-boundary method with a fifth-order weighted essentially non-oscillatory scheme is implemented to enhance the simulation accuracy for high-Reynolds number flow around the solid cylinder as well as at the interface between the open air and the porous material comprising the windscreen. The Navier–Stokes equations for incompressible flow are solved in the open air. For the flow inside the porous material, a modified form of the Zwikker–Kosten equation is solved. The results show that, on average, the circular and horizontal ellipse windscreens have similar overall wind noise reduction performance, while the horizontal ellipse windscreen with medium flow resistivity provides the most effective wind noise reduction among all the considered cases. The vertical ellipse windscreen with high flow resistivity, in particular, increases the wind noise because of increased self-generation of turbulence.
Minimizing the thermal losses from perfusion during focused ultrasound exposures with flowing microbubbles
Authors: Zhang Siyuan , Ding Ting , Wan Mingxi , Jiang Hujie , Yang Xu , Zhong Hui , Wang Supin
Published: April 2011

This paper demonstrated the use of flowing microbubbles (MBs) to minimize thermal losses from perfusion during focused ultrasound exposures due to acoustic cavitation. Temperature and cavitation were simultaneously investigated as MBs flowing through a wall-less flow phantom with varying flow velocities (2–55 cm/s) and concentrations (0%–0.1%) when exposed at different acoustic power levels (5–120 W). The peak temperature at the end of ultrasonic exposures in the flow and in the outer of the vessel as well as the cavitation were higher than those pure controls measured at the same exposure parameters and flow velocities but without MBs. All the peak temperatures initially increased with increasing flow velocities of MBs, followed by a decrease of the peak temperatures with increasing flow velocities when the velocity was higher than the inflection velocity. Meanwhile, cavitation showed a trend of increases with increasing flow velocity. The inflection velocity and cavitation increased with increasing acoustic power and MBs concentration. Thermal lesion appeared around the vessel as MBs flow through the vessel, at which lesion was not observed originally without MBs. These results suggested that this may provide an effective way to minimize thermal losses from perfusion during focused ultrasound exposures.
Different sound decay patterns and energy feedback in coupled volumes
Authors: Pu Hongjie , Qiu Xiaojun , Wang Jiqing
Published: April 2011

Different non-exponential decays such as the concave and the convex double sloped decays in the coupled rooms provide distinct sound qualities. These are commonly considered to occur in the less reverberant sub-room and the more reverberant sub-room, respectively. However, numerical simulations and experiments in this paper show that the demarcation line is not located along the physical boundaries (e.g., the partition and the coupling aperture), but in the more reverberant sub-room. The sound field with the concave double sloped decay penetrates into the auxiliary sub-room to an extent which is influenced by the difference between the two natural reverberations of the sub-rooms. Furthermore the sound energy flows in different regions are investigated, demonstrating how energy feedback leads to the concave double sloped decay.
Monitoring stress changes in a concrete bridge with coda wave interferometry
Authors: Stähler Simon Christian , Sens-Schönfelder Christoph , Niederleithinger Ernst
Published: April 2011

Coda wave interferometry is a recent analysis method now widely used in seismology. It uses the increased sensitivity of multiply scattered elastic waves with long travel-times for monitoring weak changes in a medium. While its application for structural monitoring has been shown to work under laboratory conditions, the usability on a real structure with known material changes had yet to be proven. This article presents experiments on a concrete bridge during construction. The results show that small velocity perturbations induced by a changing stress state in the structure can be determined even under adverse conditions. Theoretical estimations based on the stress calculations by the structural engineers are in good agreement with the measured velocity variations.
Acoustic multipath arrivals in the horizontal plane due to approaching nonlinear internal waves
Authors: Badiey Mohsen , Katsnelson Boris G. , Lin Ying-Tsong , Lynch James F.
Published: April 2011

Simultaneous measurements of acoustic wave transmissions and a nonlinear internal wave packet approaching an along-shelf acoustic path during the Shallow Water 2006 experiment are reported. The incoming internal wave packet acts as a moving frontal layer reflecting (or refracting) sound in the horizontal plane. Received acoustic signals are filtered into acoustic normal mode arrivals. It is shown that a horizontal multipath interference is produced. This has previously been called a horizontal Lloyd’s mirror. The interference between the direct path and the refracted path depends on the mode number and frequency of the acoustic signal. A mechanism for the multipath interference is shown. Preliminary modeling results of this dynamic interaction using vertical modes and horizontal parabolic equation models are in good agreement with the observed data.
Distortion-product otoacoustic-emission suppression tuning in human infants and adults using absorbed sound power
Authors: Keefe Douglas H. , Abdala Carolina
Published: April 2011

The greatest difference in distortion product otoacoustic emission (DPOAE) suppression tuning curves (STCs) in infant and adult ears occurs at a stimulus frequency of 6 kHz. These infant and adult STCs are much more similar when constructed using the absorbed power level of the stimulus and suppressor tones rather than using sound pressure level. This procedure incorporates age-related differences in forward and reverse transmission of sound power through the ear canal and middle ear. These results support the theory that the cochlear mechanics underlying DPOAE suppression are substantially mature in full-term infants.
Equivalent contributing depth investigated by a lateral wave with axial transmission in viscoelastic cortical bone
Authors: Haïat Guillaume , Naili Salah , Ba Vu Mai , Desceliers Christophe , Soize Christian
Published: April 2011

Cortical bone is a viscoelastic heterogeneous medium which may be assessed with axial transmission. This work aims at evaluating the average depth investigated by the lateral wave for radial variations of material properties in relatively thick cortical bone. The equivalent contributing depth (ECD) is derived from the finite element simulation results for spatial variations of a viscoelastic coefficient (η11) and of porosity. A value of ECD equal to around 1.6 mm is obtained for a spatial variation of η11. The method fails to predict accurate values of the ECD for a spatial variation of porosity, because all parameters vary simultaneously.
Airframe structural damage detection: A non-linear structural surface intensity based technique
Authors: Semperlotti Fabio , Conlon Stephen C. , Barnard Andrew R.
Published: April 2011

The non-linear structural surface intensity (NSSI) based damage detection technique is extended to airframe applications. The selected test structure is an upper cabin airframe section from a UH-60 Blackhawk helicopter (Sikorsky Aircraft, Stratford, CT). Structural damage is simulated through an impact resonator device, designed to simulate the induced vibration effects typical of non-linear behaving damage. An experimental study is conducted to prove the applicability of NSSI on complex mechanical systems as well as to evaluate the minimum sensor and actuator requirements. The NSSI technique is shown to have high damage detection sensitivity, covering an extended substructure with a single sensing location.
Analysis of high-frequency wind-driven ambient noise in shallow brackish water
Authors: Poikonen Ari
Published: April 2011

Ambient noise spectra in a shallow brackish water environment were found to be steeper than expected at frequencies above 10 kHz. The high-frequency behavior of the spectra was resolved by modeling dispersion and noise in bubbly water. Bubble size distributions fitted to the brackish water spectra exhibit a distinctive maximum in the radius range 0.1–0.3 mm, and a substantial drop in bubble density below a radius of 0.1 mm. The brackish water distributions were tied to an oceanic spectrum with a spectral slope of 5.7 dB/octave obtained with a −3/2 power law dependence of bubble size density on radius.
Coherent backscattering enhancement in cavities. Highlights of the role of symmetry
Authors: Gallot Thomas , Catheline Stefan , Roux Philippe
Published: April 2011

Through experiments and simulations, the consequences of symmetry on coherent backscattering enhancement (CBE) are studied in cavities. Three main results are highlighted. First, the CBE outside the source is observed: (a) on a single symmetric point in a one-dimensional (1-D) cavity, in a disk and in a symmetric chaotic plate; (b) on three symmetric points in a two-dimensional (2-D) rectangle; and (c) on seven symmetric points in a three-dimensional (3-D) parallelepiped cavity. Second, the existence of enhanced intensity lines and planes in 2-D and 3-D simple-shape cavities is demonstrated. Third, it is shown how the anti-symmetry caused by the special boundary conditions is responsible for the existence of a coherent backscattering decrement with a dimensional dependence of R=(12)d, with d=1,2,3 as the dimensionality of the cavity.
Articulatory and acoustic adaptation to palatal perturbation
Authors: Thibeault Mélanie , Ménard Lucie , Baum Shari R. , Richard Gabrielle , McFarland David H.
Published: April 2011

Previous work has established that speakers have difficulty making rapid compensatory adjustments in consonant production (especially in fricatives) for structural perturbations of the vocal tract induced by artificial palates with thicker-than-normal alveolar regions. The present study used electromagnetic articulography and simultaneous acoustic recordings to estimate tongue configurations during production of [s š t k] in the presence of a thin and a thick palate, before and after a practice period. Ten native speakers of English participated in the study. In keeping with previous acoustic studies, fricatives were more affected by the palate than were the stops. The thick palate lowered the center of gravity and the jaw was lower and the tongue moved further backwards and downwards. Center of gravity measures revealed complete adaptation after training, and with practice, subjects’ decreased interlabial distance. The fact that adaptation effects were found for [k], which are produced with an articulatory gesture not directly impeded by the palatal perturbation, suggests a more global sensorimotor recalibration that extends beyond the specific articulatory target.
A wavelet packet adaptive filtering algorithm for enhancing manatee vocalizations
Authors: Gur M. Berke , Niezrecki Christopher
Published: April 2011

Approximately a quarter of all West Indian manatee (Trichechus manatus latirostris) mortalities are attributed to collisions with watercraft. A boater warning system based on the passive acoustic detection of manatee vocalizations is one possible solution to reduce manatee–watercraft collisions. The success of such a warning system depends on effective enhancement of the vocalization signals in the presence of high levels of background noise, in particular, noise emitted from watercraft. Recent research has indicated that wavelet domain pre-processing of the noisy vocalizations is capable of significantly improving the detection ranges of passive acoustic vocalization detectors. In this paper, an adaptive denoising procedure, implemented on the wavelet packet transform coefficients obtained from the noisy vocalization signals, is investigated. The proposed denoising algorithm is shown to improve the manatee detection ranges by a factor ranging from two (minimum) to sixteen (maximum) compared to high-pass filtering alone, when evaluated using real manatee vocalization and background noise signals of varying signal-to-noise ratios (SNR). Furthermore, the proposed method is also shown to outperform a previously suggested feedback adaptive line enhancer (FALE) filter on average 3.4 dB in terms of noise suppression and 0.6 dB in terms of waveform preservation.