bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy conservation via coupled modes in waveguides with an impedance boundary condition
Authors: Stotts Steven A. , Koch Robert A.
Published: October 2014

A statement of energy conservation for a coupled mode formulation with real mode functions and eigenvalues has been demonstrated to be consistent with the statement of conservation derivable from the Helmholtz equation. The restriction to real mode functions and eigenvalues precludes coupled mode descriptions with waveguide absorption or untrapped modes. The demonstration, along with the derivation of the coupled mode range equation, relies on orthonormality in terms of a product of two modal depth functions integrated to infinite depth. This paper shows that energy conservation and the derivation of the coupled mode range equation can be extended to complex mode functions and eigenvalues, and that energy is conserved for ocean waveguides with a penetrable bottom boundary at a finite depth beneath any range dependence. For this, the penetrable bottom boundary is specified by an impedance condition for the mode functions. The new derivations rely on completeness and a modified orthonormality statement. Mode coupling is driven solely by waveguide range dependence. Thus, the form of the range equation and the values of the coupling coefficients are unaffected by a finite depth waveguide. Applications of energy conservation to examine the accuracy of a numerical coupled mode calculation are presented.
Effect of channel impulse response on matched filter performance in the 2013 Target and Reverberation Experiment
Authors: Colin Mathieu E. , Ainslie Michael A. , Dahl Peter H. , Dall'Osto David R. , Pecknold Sean , van Vossen Robbert
Published: October 2014

Active sonar performance is determined by the characteristics of the target, the sonar system and the effect of the environment on the received waveform. The two main influences of the environment are propagation effects and the contamination of the target echo with a background. The ambient noise and reverberation are mitigated by means of signal processing, mostly through beamforming and matched-filtering. The improvement can be quantified by the signal to noise ratios before and after processing. Propagation effects can have a large influence on the gains obtained by the processing. To study the effect of the channel on the matched filter performance, broadband channel impulse responses were modeled and compared to measurements acquired during the Office of Naval Research-funded 2013 Target and Reverberation Experiment (TREX). In shallow water, a large time spread is often observed, reducing the effectiveness of the matched filter. TREX data show, however, a limited time spread. Model predictions indicate that this could be caused by a rough sea-surface, which while increasing propagation loss, at the same time increases matched filter gain.
Using physical oceanography to improve transmission loss calculations in undersampled environments
Authors: Tollefsen Cristina , Pecknold Sean
Published: October 2014

The vertical sound speed profile (SSP) is a critical input to any acoustic propagation model. However, even when measured SSPs are available they are frequently noisy “snapshots” of the SSP at a single moment in time and space and do not fully capture changes such as solar heating and wind-driven mixing that can significantly affect shallow water propagation on time scales of less than a day. Furthermore, SSPs measured in the field may not extend to the ocean bottom and are often based on measured profiles of temperature with an implicit assumption of constant salinity. In April–May 2013, the Target and Reverberation Experiment (TREX) was conducted in the Northeastern Gulf of Mexico near Panama City, Florida, a region strongly affected by local wind forcing, freshwater inputs, and the presence of a warm-core Gulf of Mexico Loop Current eddy ("Eddy Kraken") offshore of the experimental site. “Synthetic” SSPs were constructed for the trial area by combining knowledge of the physical oceanography and water masses in the area with the measured SSPs that were available. Transmission loss was modelled using both synthetic and measured SSPs and the results will be compared with measured transmission loss.
Objective identification of the dominant seabed scattering mechanism
Authors: Steininger Gavin , Holland Charles W. , Dosso Stan E. , Dettmer Jan
Published: October 2014

This paper develops and applies a quantitative inversion procedure for scattering-strength data to determine the dominant scattering mechanism (surface and/or volume scattering) and to estimate the relevant scattering parameters and their uncertainties. The classification system is based on trans-dimensional Bayesian inversion with the deviance information criterion used to select the dominant scattering mechanism. Scattering is modeled using first-order perturbation theory as due to one of three mechanisms: interface scattering from a rough seafloor, volume scattering from a heterogeneous sediment layer, or mixed scattering combining both interface and volume scattering. The classification system is applied to six simulated test cases where it correctly identifies the true dominant scattering mechanism as having greater support from the data in five cases; the remaining case is indecisive. The approach is also applied to measured backscatter-strength data from the Malta Plateau where volume scattering is determined as the dominant scattering mechanism. This conclusion and the scattering/geoacoustic parameters estimated in the inversion are consistent with properties from previous inversions and/or with core measurements from the site. In particular, the scattering parameters are converted from the continuous scattering models used in the inversion to the equivalent discrete scattering parameters, which are found to be consistent with properties of the cores. [Work supported by ONR.]
Laboratory measurements of backscattering strengths from two-types of artificially roughened sandy bottoms
Authors: Son Su-Uk , Cho Sungho , Choi Jee Woong
Published: October 2014

In the case of sandy bottom, the backscattering from the interface roughness is significantly dominant compared to that from the volume inhomogeneities, and the power spectrum of interface roughness thus becomes the most important factor to control the scattering mechanism. Backscattering strength measurements with a 50-kHz signal were made for two types of roughness (smooth and rough interfaces) which were artificially formed on a 0.5-m thick sandy bottom in a 5-m deep water tank. The roughness profiles were estimated by the arrival time analysis of 5-MHz backscattering signals emitted by the transducer moving parallel to the interface at a speed of 1 cm/s, which were then Fourier transformed to yield power spectra. In this talk, the measurements of backscattering strength as a function of grazing angle in a range of 35 to 90° are presented. Finally, the effect of different roughness types on the scattering strength will be discussed in comparison with the predictions obtained by theoretical scattering model including the perturbation and Kirchhoff approximations. [This research was supported by the Agency for Defense Development, Korea.]
Twinkling exponents for backscattering by spheres in the vicinity of airy caustics associated with reflections by corrugated surfaces
Authors: Marston Philip L.
Published: October 2014

High frequency sound reflected by corrugated surfaces produce caustic networks relevant to sea surface reflection [Williams et al., J. Acoust. Soc. Am. 96, 1687–1702 (1994)]. When a sphere is positioned sufficiently far from the reflecting surface, it may be close to an Airy caustic which causes a significant increase in the backscattering [Dzikowicz and Marston, J. Acoust. Soc. Am. 116, 2751–2758 (2004)] for signals that bounce only once off of the focusing surface. For simplicity, here, it is assumed that those signals may be distinguished from the earlier direct echo from the sphere and the later (and sometimes stronger) doubly focused echo from the sphere [Dzikowicz and Marston, J. Acoust. Soc. Am. 118, 2811–2819 (2005)]. In 1977, M. V. Berry noticed that the third and higher intensity moments of wavefields containing caustics can increase in proportion to k ν, where k is the wavenumber and ν is a “twinkling exponent” determined by the dependencies of the intensity and focal volume on k. Assuming that the sphere is impenetrable and sufficiently large that its direct scattering depends only weakly on k, for the single-bounce backscattering by a sphere considered here (the easiest situation for applying Berry’s analysis) the predicted exponent for the third moment is ν = 1/3.
Passive acoustic mapping of stable and inertial cavitation during ultrasound therapy
Authors: Coviello Christian , Choi James , Collin Jamie , Carlisle Robert , Gyongy Miklos , Coussios Constantin C.
Published: October 2014

Accurate spatio-temporal characterization, quantification, and control of the type and extent of cavitation activity is crucial for a wide range of therapeutic ultrasound applications, ranging from ablation to sonothrombolysis, opening of the blood-brain barrier and drug delivery for cancer. Passive Acoustic Mapping (PAM) is a technique that utilizes arrays of acoustic detectors, typically coaxially aligned or coincident with the therapeutic elements, to receive acoustic emissions outside the main frequency band of the therapy pulse. The signals received by each detector are then filtered in the frequency domain into harmonics and ultra/subharmonics of the fundamental therapeutic frequency and other broadband components, and subsequently beamformed using a multi-correlation algorithm, which uses measures of similarity between the signals rather than time-of-flight information in order to map sources of non-linear emissions in real time. 2D and 3D cavitation maps obtained using time exposure acoustics beamforming will be presented, and juxtaposed to the greater spatial resolution but increased computational complexity afforded by more advanced algorithms such as the Robust Capon Beamformer (RCB). The spatial correlation between cavitation maps produced using PAM and the associated therapeutic effect will also be discussed in the context of cavitaion-enhanced ablation and drug delivery.
Image-guided sonothrombolysis in a stroke model with a cavitation delivery and monitoring system
Authors: Vignon Francois , Shi William T. , Powers Jeffry , Xie Feng , Wu Juefei , Gao Shunji , Lof John , Porter Thomas R.
Published: October 2014

Microbubbles (MB) and ultrasound (US) can dissolve intra-arterial thrombi. In order to reproducibly deliver the correct cavitation dose and ensure treatment efficacy and safety, we designed a therapeutic US mode with cavitation monitoring. Therapy delivery and recording of the MB signal are achieved with a sector imaging probe. Monitoring is achieved by spectrally analyzing the MB signal: ultraharmonics are a marker of stable cavitation (SC) and broadband noise characterizes inertial cavitation (IC). We used the system in a pig model. Thrombotic occlusions were created by injecting 4-hour old clots bilaterally into the internal carotids. Forty pigs were randomized to either 2.4 MI, 5 μs pulses with MBs; 1.7 MI, 20 μs pulses with MBs; and 2.4 MI, 5 μs pulses without MBs. Angiographic recanalization rates were compared. Cavitation as a function of MI was estimated in vivo. Dominant SC started at an applied MI of 0.6 (0.3MI in situ after derating by skull attenuation). Dominant IC was estimated to start at an applied MI of 0.9 (0.6 in situ). Thus, all therapy settings were in the IC regime. The 2.4MI + MB setting was the most effective (100% recanalization) vs 38% for the 1.7MI + MB and 50% for 2.4 MI without MBs (both p<0.05 compared to 2.4MI + MB). No signs of hemorrhage were found in any animal. In conclusion, higher IC levels are most effective for thrombus dissolution. Spectral analysis techniques can be used to plan and monitor the therapy.
Cavitation threshold determination —Can we do it?
Authors: ter Haar Gail , Civale John , Rivens Ian , Costa Marcia
Published: October 2014

As clinical applications, which harness acoustic cavitation, become more commonplace, it becomes more and more important to be able to determine the threshold pressures at which it is likely to occur. In our studies, we have used a suite of different detection techniques in an effort to determine these thresholds. These include passive cavitation detection, transducer impedance monitoring, and visual appearance. Different methods of acoustic signal processing have been compared. The resultant cavitation thresholds will be discussed.
Control of cavitation through coalescence of cavitation nuclei
Authors: Hall Timothy L. , Duryea Alex , Tamaddoni Hedieh
Published: October 2014

Therapeutic ultrasound in the form of SWL, HIFU, or histotripsy frequently generates cavitation nuclei (bubbles 1–10 um radius), which can persist up to about 1 s before dissolving. These nuclei can attenuate and reflect propagation of acoustic fields reducing SWL efficiency, enhancing HIFU heating, or shifting the location of a histotripsy focal zone making procedures less predictable. Depending on their location, nuclei can also directly cause tissue damage when a high amplitude sound field causes them to undergo inertial cavitation. These undesirable effects can be reduced by using a low amplitude sound field (MI <1) to stimulate coalescence of nuclei through primary and secondary Bjerknes forces. We will show nuclei coalescence significantly reduces sound field attenuation, improves SWL breakup of model kidney stones, and reduces collateral damage in soft tissues. We also show techniques for designing the non-focal acoustic fields for efficient coalescence with 3D printed acoustic lenses. Timothy Hall has a consulting arrangement with Histosonics, Inc., which has licensed intellectual property related to this abstract.
Instigation and monitoring of inertial cavitation from nanoscale particles using a diagnostic imaging platform and passive acoustic mapping
Authors: Coviello Christian , Kwan James , Graham Susan , Myers Rachel , Shah Apurva , Probert Smith Penny , Carlisle Robert , Coussios Constantin
Published: October 2014

Inertial cavitation nucleated by microbubble contrast agents has been recently shown to enhance extravasation and improve the distribution of anti-cancer agents during ultrasound (US)-enhanced delivery. However, microbubbles require frequent replenishment due to their rapid clearance and destruction upon US exposure and are unable to extravasate into tumor tissue due to their large size. A new generation of gas-stabilizing polymeric cup-shaped nanoparticles, or “nanocups” (NCs), have been formulated to a size that enables exploitation of the enhanced permeability and retention effect for intratumoral accumulation. NCs provide sustained inertial cavitation, as characterized by broadband emissions, at peak rarefactional pressures readily achievable by diagnostic ultrasound systems. This enables the use of a single low-cost system for B-mode treatment guidance, instigation of cavitation, and real-time passive acoustic mapping (PAM) of the location and extent of cavitation activity during therapy. The significant lowering of the inertial cavitation threshold in the presence of NCs as characterized by PAM is first quantified in-vitro. In-vivo and ex-vivo results in xenograft-implanted tumor bearing mice further evidence the strong presence of inertial cavitation detectable in the tumor at diagnostic levels of US intensity, as confirmed by PAM images overlaid on B-mode in real-time.
Passive cavitation imaging with nucleic acid-loaded microbubbles in mouse tumors
Authors: Nguyen Man M. , Kopechek Jonathan A. , Hasjim Bima , Villanueva Flordeliza S. , Kim Kang
Published: October 2014

Ultrasound-targeted microbubble (MB) destruction has been used to deliver nucleic acids to cancer cells for therapeutic effect. Identifying both the location and cavitation activities of the MBs is needed for efficient and effective treatment. In this study, we implemented passive cavitation imaging into a commercially available ultrasound open platform (Verasonics) for a 128-element linear array transducer, centered at 5 MHz, and applied it to an in-vivo mouse tumor model. Cationic lipid MBs were loaded with a transcription factor decoy that suppresses STAT3 signaling and inhibits tumor growth in murine squamous cell carcinomas. During systemic MB infusion, ultrasound pulses (4 or 20 cycles) were delivered with a 1-MHz single-element transducer (0.4–1.4MPa peak pressures). Channel data were offline beamformed, band-pass filtered, subtracted from reference images acquired without MBs, and co-registered with B-mode images. During MB infusion, harmonics and broadband emissions were detected in the tumor with both frequency spectra and cavitation images. For 4-cycle 0.4 MPa pulses, harmonic signals at 5 MHz and broadband signals 3–7 MHz were 23 dB and at least 5 dB greater with MBs than without MBs, respectively. These preliminary results demonstrate the feasibility of in-vivo passive cavitation imaging and could lead to further studies for optimizing US/MB-mediated delivery of nucleic acids to tumors.
Non-focal acoustic lens designs for cavitation bubble consolidation
Authors: Tamaddoni Hedieh A. , Duryea Alexander , Hall Timothy L.
Published: October 2014

During shockwave lithotripsy, cavitation bubbles form on the surface of urinary stones aiding in the fragmentation process. However, shockwaves can also produce pre-focal bubbles, which may shield or block subsequent shockwaves and potentially induce collateral tissue damage. We have previously shown in-vitro that low amplitude acoustic waves can be applied to actively stimulate bubble coalescence and help alleviate this effect. A traditional elliptical transducer lens design produces the maximum focal gain possible for a given aperture. From experiments and simulation, we have found that this design is not optimal for bubble consolidation as the primary and secondary Bjerknes forces may act against each other and the effective field volume is too small. For this work, we designed and constructed non-focal transducer lenses with complex surface geometries using rapid prototyping stereolithography to produce more effective acoustic fields for bubble consolidation during lithotripsy or ultrasound therapy. We demonstrate a design methodology using an inverse problem technique to map the desired acoustic field back to the surface of the transducer lens to determine the correct phase shift at every point on the lens surface. This method could be applied to other acoustics problems where non-focused acoustic fields are desired.
Scavenging dissolved oxygen via acoustic droplet vaporization
Authors: Radhakrishnan Kirthi , Holland Christy K. , Haworth Kevin J.
Published: October 2014

Acoustic droplet vaporization (ADV) has been investigated for capillary hemostasis, thermal ablation, and ultrasound imaging. The maximum diameter of a microbubble produced by ADV depends on the gas saturation of the surrounding fluid. This dependence is due to diffusion of dissolved gases from the fluid into the perfluoropentane (PFP) microbubble. This study investigated the change in oxygen concentration in the surrounding fluid after ADV. Albumin-shelled PFP droplets in air-saturated saline (1:30, v/v) were continuously pumped through a flow system and insonified by a focused 2-MHz single-element transducer to induce ADV. B-mode image echogenicity was used to determine the ADV threshold pressure amplitude. The dissolved oxygen concentration in the fluid upstream and downstream of the insonation region was measured using inline sensors. Droplet size distributions were measured before and after ultrasound exposure to determine the ADV transition efficiency. The ADV pressure threshold at 2 MHz was 1.7 MPa (peak negative). Exposure of PFP droplets to ultrasound at 5 MPa peak negative pressure caused the dissolved oxygen content in the surrounding fluid to decrease from 88 ± 3% to 20 ± 4%. The implications of oxygen scavenging during ADV will be discussed.
Effects of rose bengal on cavitation cloud behavior in optically transparent gel phantom investigated by high-speed observation
Authors: Yasuda Jun , Miyashita Takuya , Taguchi Kei , Yoshizawa Shin , Umemura Shin-ichiro
Published: October 2014

Sonodynamic treatment is a non-thermal ultrasonic method using sonochemical effect of cavitation bubbles. Rose bengal (RB) is sonochemically active and reduces cavitation threshold and therefore has potential to be an agent for sonodynamic treatment. For the effectiveness and safety of the treatment, controlling cavitation is crucial. In our previous study, we have suggested high-intensity focused ultrasound (HIFU) employing second-harmonic superimposition, which can control cavitation cloud generation by superimposing the second harmonic onto the fundamental. In this study, to investigate the effects of RB on cavitation behavior, a polyacrylamide gel phantom containing RB was exposed to second-harmonic superimposed ultrasound and the generated cavitation bubbles were observed by a high-speed camera. The gel contained three different concentrations of RB, 0, 1, and 10 mg/L. The ultrasonic intensity and exposure duration were 40 kW/cm2 and 100 μs, respectively. The fundamental frequency was 0.8 MHz. In the results, the amount of the incepted cloud became higher and the lifetime of bubbles became longer as the RB concentration increased at high reproducibility. The observed RB concentration dependence suggests that the amount of cavitation bubbles can be controlled using second-harmonic superimposition. The observed lifetime extension of bubbles can not only promote sonochemical but also enhance thermal bioeffect.
Impact of AMX-A1 military aircraft operations on the acoustical environment close to a Brazilian airbase
Authors: de Souza Olmiro C. , Paul Stephan
Published: October 2014

Military aircraft operating on airbases usually have a considerable impact on the neighborhood. While the impact of civil aircraft operations can be modeled by commercially available software, the same is hardly possible for military aircraft as no EPNL data are available for such aircraft and flight path are not restricted to those used by civilian operations. Therefore, in this work, the noise impact of AMX-A1 aircraft operating at a Brazilian airbase was evaluated from measurements originally intended for calibration of the noise map of an university that is in the vicinity. From the data, it was possible to obtain LAeq10min with and without jet noise to see how much does AMX operations influence in the total measurement. Sound exposure levels (SEL) were also calculated. It was found that depending of AMX procedure (Approach, Departure, Touch, Go, etc.), jet noise increases the LAeq10min up to 10 dB and SEL values reaches 96, 6 dBA in sensitive areas. It will be discussed if A-weighted sound power level can be estimated form the data considering the aircraft as a point source in free field.
The effect of long-range propagation on contra-rotating open rotor en-route noise levels
Authors: Islam Upol
Published: October 2014

The purpose was to calculate the en-route noise level produced by an advanced contra-rotating open rotor (CROR) powered aircraft. The en-route noise is defined as the noise produced by an aircraft in high altitude operation (>3000 m) measured by a microphone 1.2 m above ground level. Calculations were performed for three different aircraft operating conditions—cruise, climb, and descent. For each calculation, the aircraft noise source was modeled as an isolated CROR engine. This noise model was determined from experimental measurements made in a transonic wind tunnel using a 1/6th-scale open rotor rig. En-route noise levels were calculated using the whole aircraft noise prediction code SOPRANO. The CROR noise model were input into SOPRANO and long-distance propagation was calculated using the ray-tracing code APHRODITE, which is implemented within SOPRANO. This ray tracing code requires atmospheric wind speed, wind direction, temperature, and humidity profiles, which were collected from historical data around Europe. The ray tracing method divides the atmosphere up into a number of layers. Meteorological parameters were assumed to vary linearly between the values specified at the boundaries of each layer. Numerous simulations are conducted using different atmospheres in order to assess the impact of atmospheric conditions on the en-route noise levels.
Gaps in the literature on the effects of aircraft noise on children’s cognitive performance
Authors: Kamrath Matthew , Vigeant Michelle C.
Published: October 2014

In the past two decades, several major studies have indicated that chronic aircraft noise exposure negatively impacts children’s cognitive performance. For example, the longitudinal Munich airport study (Hygge, Am. Psychol. Soc., 2002) demonstrated that noise adversely affects reading ability, memory, attention, and speech perception. Moreover, the cross-sectional RANCH study (Stansfeld, Lancet, 2005) found a linear correlation between extended noise exposure and reduced reading comprehension and recognition memory. This presentation summarizes these and other recent studies and discusses four key areas in need of further research (ENNAH Final Report Project No. 226442, 2013). First, future studies should account for all of the following confounding factors: socioeconomic variables, daytime and nighttime aircraft, road, and train noise, and air pollution. Second, multiple noise metrics should be evaluated to determine if the character of the noise alters the relationship between noise and cognition. Third, future research should explore the mitigating effects of improved classroom acoustics and exterior sound insulation. Finally, additional longitudinal studies are necessary: (1) to establish a causal relationship between aircraft noise and cognition; and (2) to understand how changes in the duration of the exposure and in the age of the students influence the relationship. [Work supported by FAA PARTNER Center of Excellence.]
The perceived annoyance of urban soundscapes
Authors: Craig Adam , Knox Don , Moore David
Published: October 2014

Annoyance is one of the main factors that contribute to a negative view of environmental noise, and can lead to stress-related health conditions. Subjective perception of environmental sounds is dependent upon a variety of factors related to the sound, the geographical location, and the listener. Noise maps used to communicate information to the public about environmental noise in a given geographic location are based on simple noise level measurements and do not include any information regarding how perceptually annoying or otherwise the noise might be. This study involved subjective assessment by a large panel of listeners (N = 200) of a corpus of 60 pre-recorded urban soundscapes collected from a variety of locations around Glasgow City Centre. Binaural recordings were taken at three points during each 24 hour period in order to capture urban noise during day, evening, and night. Perceived annoyance was measured using Likert and numerical scales and each soundscape measured in terms of arousal and positive/negative valence. The results shed light on the subjective annoyance of environmental sound in a range of urban locations around Glasgow, and form the basis for development of environmental noise maps, which more fully communicate the effects of environmental noise to the public.
What comprises a healthy soundscape for the captive Southern White Rhinoceros (Ceratotherium simum simum)?
Authors: Wiseman Suzi , Wilson Preston S. , Sepulveda Frank
Published: October 2014

Many creatures, including the myopic rhinoceros, depend upon hearing and smell to determine their environment. Nature is dominated by meaningful biophonic and geophonic information quickly absorbed by soil and vegetation, while anthrophonic urban soundscapes exhibit vastly different physical and semantic characteristics, sound repeatedly reflecting off hard geometric surfaces, distorting and reverberating, and becoming noise. Noise damages humans physiologically, including reproductively, and likely damages other mammals. Rhinos vocalize sonically and infrasonically, but audiograms are unavailable. They generally breed poorly in urban zoos, where infrasonic noise can be chronic. Biological and social factors are studied, but little attention if any is paid to soundscape. We present a methodology to analyze the soundscapes of captive animals according to their hearing range. Sound metrics determined from recordings at various institutions can then be compared and correlations with the health and wellbeing of their animals can be sought. To develop this methodology we studied the sonic, infrasonic, and seismic soundscape experienced by the white rhinos at Fossil Rim Wildlife Center, one of the few U.S. facilities to successfully breed this species in recent years. Future analysis can seek particular parameters known to be injurious to human mammals, plus parameters known to invoke response in animals.
Shape optimization of acoustic horns using few design variables
Authors: Barbieri Nilson , Barbieri Renato , Vitorino Clebe T. , Lima Key F.
Published: October 2014

The main steps for design of the optimal geometry of acoustic horns employing numerical methods are: the definition of the domain and the restrictions and control of the boundary, the definition of the objective function and the frequency range of interest, the evaluation of the objective function value, and the selection of a robust optimization technique to calculate the optimal value. During the optimization process, the profile is changing continuously until obtaining the optimal horn profile. The main focus of this work was to obtain optimal geometries with the use of few design variables. Two different methods to control the horn profile during the optimization process are used: approximation of the contour of the horn with Hermite polynomials and sinusoidal functions. The numerical results show the efficiency of these methods and it was also found (at least from the engineering point of view) that the solution is not unique to the geometry of the horn to single-frequency. The results for the optimization for more than one frequency are also shown.
Parametric study of a PULSCO vent silencer
Authors: Tohid Usama
Published: October 2014

We have conducted a parametric study via numerical simulations of a PULSCO vent silencer. The overall objective is to demonstrate the existence of an optimum system performance for a given set of operating conditions by modifying the corresponding geometry of the device. The vent silencer under consideration consists of a perforated diffuser, the silencer body, and a tube module. The tube module consists of a set of tubes through which the working fluid passes. The flow tubes are perforated and surrounded with acoustic packing that is responsible for the attenuation. The mathematical model of the vent silencer is built upon Helmholtz equation for the plane wave solution, and the Delany-Bazley model for the acoustic packing. The geometrical parameters chosen for the parametric study include: the porosity of the diffuser and the flow tubes, the type of packing material used for the tube module, bulk density for the acoustic packing, and the hole diameter of the perforated diffuser and flow tubes. The equations of the mathematical model are discretized over the computational domain and solved with a finite element method. Numerical results in terms of transmission loss, for the system, indicate that diffuser hole size of 1/4” with porosity of 0.1, flow tube hole size of 1/8” with porosity of 0.23, packing density of 16 kg/m3 for TRS-10 and 100 kg/m3 for Advantex provided the optimum results for the chosen set of conditions. The numerical results were found to be in agreement with experimental data.
Characterization of cochlear implant-related artifacts during sound-field recording of the auditory steady state response using an amplitude modulated stimulus: A comparison among normal hearing adults, cochlear implant recipients, and implant-in-a-box
Authors: Deshpande Shruti B. , Scott Michael P. , Zhang Fawen , Keith Robert W. , Dimitrijevic Andrew
Published: October 2014

Recent work has investigated the use of electric stimuli to evoke auditory steady state response (ASSR) in cochlear implant (CI) users. While more control can be exerted using electric stimuli, acoustic stimuli present natural listening environment for CI users. However, ASSR using acoustic stimuli in the presence of a CI could lead to artifacts. Five experiments investigated the presence and characteristics of CI-artifacts during sound-field ASSR using amplitude modulated (AM) stimulus (carrier frequency: 2 kHz; modulation frequency: 82.031 Hz). Experiment 1 investigated differences between 10 normal hearing (NH) and 10 CI participants in terms of ASSR amplitude versus intensity and onset phase versus intensity. Experiment 2 explored similar relationships for an implant-in-a-box. Experiment 3 investigated correlations between electrophysiological ASSR thresholds (ASSRe) and behavioral thresholds to the AM stimulus (BTAM) for the NH and CI groups. Mean threshold differences (ASSRe-BTAM) were computed for each group and group differences were studied. Experiment 4 investigated the presence of transducer-related artifacts using masking. Experiment 5 investigated the effect of manipulation of intensity and external components of the CI on the ASSR. Overall, results of this study provide the first comprehensive description of the characteristics of CI-artifacts during sound-field ASSR. Implications for future research to further characterize CI-artifacts, thereby leading to strategies to minimize them are discussed.
Speech spectral intensity discrimination at frequencies above 6 kHz
Authors: Monson Brian B. , Lotto Andrew J. , Story Brad H.
Published: October 2014

Hearing aids and other communication devices (e.g., mobile phones) have made some recent efforts to extend their bandwidths to represent higher frequencies. The impact of this expansion on speech perception is not well characterized. To assess human sensitivity to speech high-frequency energy (HFE, defined here as energy in the 8- and 16-kHz octave bands), difference limens for HFE level changes in male and female speech and singing were obtained. Listeners showed significantly greater ability to detect level changes in singing vs. speech, but not in female vs. male speech. Mean differences limen scores for speech and singing were about 5 dB in the 8-kHz octave (5.6–11.3 kHz) but 8–10 dB in the 16-kHz octave (11.3–22 kHz). These scores are lower (better) than scores previously reported for isolated vowels and some musical instruments, and similar to scores previously reported for white noise.
The effect of experience on environmental sound identification
Authors: Bash Rachel E. , Cash Brandon J. , Loebach Jeremy
Published: October 2014

The perception of environmental stimuli was compared across normal hearing (NH) listeners exposed to an eight-channel sinewave vocoder and experienced bilateral, unilateral, and bimodal cochlear implant (CI) users. Three groups of NH listeners underwent no training (control), one day of training with environmental stimuli (exposure), or four days of training with a variety of speech and environmental stimuli (experimental). A significant effect of training was observed. The experimental group performed significantly better than exposure or control groups, equal to bilateral CI users, but worse than bimodal users. Participants were divided into low, medium and high-performing groups using a two-step cluster algorithm. High-performing members were only observed for the CI and experimental conditions, and significantly more low-performing members were observed for exposure and control conditions, demonstrating the effectiveness of training. A detailed item-analysis revealed that the most accurately identified sounds were often temporal in nature or contained iconic repeating patterns (e.g., a horse galloping). Easily identified stimuli were common across all groups, with experimental subjects identifying more short or spectrally driven stimuli, and CI users identifying more animal vocalizations. These data demonstrate that explicit training in identifying environmental stimuli improves sound perception, and could be beneficial for new CI users.
The U.S. National Hearing Test, a 2013–2014 progress report
Authors: Watson Charles S. , Kidd Gary R. , Miller James D. , Preminger Jill E. , Crowley Alex , Maki Daniel P.
Published: October 2014

A telephone-administered screening test for sensorineural hearing loss was made publically available in the United States in September 2013. This test is similar to the digits-in-noise test developed by Smits and colleagues in the Netherlands, versions of which are now in use in most European countries and in Australia. The test was initially offered in the United States for a small fee ($8, then $4) but after a year of promotion it became clear that either the fee or the complexity of paying it was inhibiting. During the first month in which the test was subsequently offered free of charge, 31,806 calls were made to the test line, of which 26,507 were completed tests. Analyses of test performance suggest that about 81% of the test takers had at least a mild hearing loss, and 40% had a substantial loss (estimated to be in excess of 45 dB PTA). Follow-up studies are being conducted to determine whether those who failed the test sought a full-scale hearing assessment, and whether those advised to obtain hearing aids did so. [Work funded by Grant No. 5R44DC009719 from the National Institute for Deafness and other Communication Disorders.]
Modest, reliable spectral peaks in preceding sounds influence vowel perception
Authors: Stilp Christian , Anderson Paul
Published: October 2014

Sensory systems excel at extracting predictable signal properties in order to be optimally sensitive to unpredictable, more informative properties. Studies of auditory perceptual calibration (Kiefte & Kluender, 2008 JASA; Alexander & Kluender, 2010 JASA) showed that when precursor sounds were filtered to emphasize frequencies matching the second formant (F2) of the subsequent target vowel, vowel perception decreased its reliance on F2 (predictable cue) and increased reliance on spectral tilt (unpredictable cue). Perceptual calibration occurred when reliable spectral peaks were 20 dB or larger, but findings in profile analysis and spectral contrast detection predict sensitivity to more modest spectral peaks. The present experiments tested identification of vowels varying in F2 (1000–2200 Hz) and spectral tilt (-12-0 dB/octave), perceptually varying from /u/ to /i/. Listeners first identified vowels in isolation, then following a sentence filtered to add a reliable + 2 to + 15 dB spectral peak centered at F2 of the target vowel. Changes in perceptual weights (standardized logistic regression coefficients) across sessions were indices of perceptual calibration. Vowel identification weighted F2 significantly less when reliable peaks were at least + 5 dB, but increases in spectral tilt weights were very modest. Results demonstrate high sensitivity to predictable acoustic properties in the sensory environment.
The role of onsets and envelope fluctuations in binaural cue use
Authors: Stecker G. Christopher , Diedesch Anna C.
Published: October 2014

Effective localization of real sound sources requires neural mechanisms to accurately extract and represent binaural cues, including interaural time and level differences (ITD and ILD) in the sound arriving at the ears. Many studies have explored the relative effectiveness of these cues, and how that effectiveness varies with the acoustical features of a sound such as spectral frequency and modulation characteristics. In particular, several classic and recent studies have demonstrated relatively greater sensitivity to ITD and ILD present at sound onsets and other positive-going fluctuations of the sound envelope. The results of those studies have clear implications for how spatial cues are extracted from naturally fluctuating sounds such as human speech, and how that process is altered by echoes, reverberation, and competing sources in real auditory scenes. Here, we review the results of several recent studies to summarize and critique the evidence for envelope-triggered extraction of ITD and ILD across a wide range of spectral frequencies. A number of competing models for cue extraction in fluctuating envelopes are also considered in light of this evidence. [Work supported by NIH R01-DC011548.]
Computing interaural differences using idealized head models
Authors: Cai Tingli , Rakerd Brad , Hartmann William
Published: October 2014

The spherical model of the human head, attributable to Lord Rayleigh, accounts for important features of observed interaural time differences (ITD) and interaural level differences (ILD), but it also fails to capture many details. To gain an intuitive understanding of the failures, we computed ITDs and ILDs for a succession of idealized shapes approximating the human head: sphere, ellipsoid, ellipsoid plus cylindrical neck, ellipsoid plus cylindrical neck plus disk torso. Calculations were done as a function of frequency (100–2500 Hz) and for source azimuths from 10 to 90 degrees using finite-element models. The computations were compared to free-field measurements on a KEMAR manikin. The spherical head model approximated many measured interaural features, but the frequency dependence tended to be too flat in both ITD and ILD. The ellipsoidal head produced greater variation with frequency and therefore agreed better with the measurements, reducing the RMS discrepancies in both ITD and ILD by 35%. Adding a neck further increased the frequency variation. Adding the disk torso further improved the agreement, especially below 1000 Hz, decreasing the ITD discrepancy by another 21\%. The evolution of models enabled us to associate details of interaural differences with overall anatomical features. [Work supported by the AFOSR grant 11NL002.]
Acoustic reflex attenuation in phon loudness measurements
Authors: Goldstein Julius L.
Published: October 2014

Equal Loudness-level Contours, ELC(f, L), represent the sound pressure level in dB SPL of tones at frequency f that are perceived by normal-hearing listeners as equally loud as a 1 kHz tone at L dB SPL. Loudness is defined relatively as L phons (Fletcher & Munson, 1933). ELC measurements by Lydolf and Møller (1997) included in the current ISO standard (Suzuki & Takeshima, JASA vol. 116, 2004), show systematic increases in ELC growth rate with loudness above 60 phons and below 1 kHz, which suggests middle-ear attenuation by the acoustic reflex (AR). A steady-state ELC model was assembled including known mechanisms: (1) middle ear transmission modified by a head-related-transfer-function, (2) compressive cochlear amplification (CA) for signaling loudness, (3) a negative feedback model for AR attenuation by CA inputs exceeding AR threshold, and (4) attenuation of pressure-field stimuli by trans-eardrum static pressure. Model parameters were calculated from ELC data using minimum-square-error estimation. AR attenuation below 1 kHz depends on AR attenuation at the 1 kHz loudness reference frequency, but predicted ELCs are relatively insensitive to it. An earlier psychophysical study of AR attenuation, including 1 kHz, is consistent with subject-dependent model predictions (Rabinowitz & Goldstein, JASA vol. 54, 1973; Rabinowitz, 1977). [NIH-Funded.]
Effects of tinnitus and hearing loss on functional brain networks involved in auditory and visual short-term memory
Authors: Husain Fatima T. , Akrofi Kwaku , Carpenter-Thompson Jake
Published: October 2014

Brain imaging data were acquired from three subject groups—persons with hearing loss and tinnitus (TIN), individuals with similar hearing loss without tinnitus (HL) and those with normal hearing without tinnitus (NH)—to test the hypothesis that TIN and control subjects use different functional brain networks for short-term memory. Previous studies have provided evidence of a link between hearing disorders such as tinnitus and the reorganization of auditory and extra-auditory functional networks. Greater knowledge of this reorganization could lead to the development of more effective therapies. Data analysis was conducted on fMRI data obtained while subjects performed short-term memory tasks with low or high attentional loads, using both auditory and visual stimuli in separate scanning sessions. Auditory stimuli were pure tones with frequencies between 500 and 1000 Hz. Visual stimuli were Korean fonts, unfamiliar to the subjects. We found similar behavioral response across the three groups for both modalities and tasks. However, the groups differed in their brain response, with these differences being more marked for the auditory tasks and not for the tasks involving visual stimuli.
Preliminary results of a two-interval forced-choice method for assessing infant hearing sensitivity
Authors: Werner Lynne
Published: October 2014

Current methods for assessing infants' hearing are yes-no, single interval procedures. Although bias-free statistics can be used to describe the results of such procedures, with the limited number of trials typically available from an individual infant, use of these statistics can be problematic. A two-interval forced choice method based on infants' anticipatory eye movements toward an interesting visual event is currently under development. Preliminary results indicate that a high proportion of both 3- and 7-month-old infants achieve over 80% correct in the detection of a 70 dB SPL 1000 Hz tone presented through an insert earphone. Infants continue to perform better than expected by chance at levels as low as 25 dB SPL. Thus, a test method based on infant eye movements holds potential as an efficient behavioral method for assessing infant hearing.
Vocal effort, coordination, and balance
Authors: Fuhrman Robert A. , Barbosa Adriano , Vatikiotis-Bateson Eric
Published: October 2014

Manipulating speaking and discourse requirements allows us to asses the time-varying correspondences between various subsystems within a talker at different levels of vocal effort. These subsystems include fundamental frequency (F0) and acoustic amplitude, rigid body (6D) motion of the head, motion (2D) of the body, and postural forces and torques measured at the feet. Analysis of six speakers has confirmed our hypothesis that as vocal effort increases coordination among sub-systems simplifies, as shown by greater correspondence (e.g., the instantaneous correlation) between the various time-series measures. However, at the two highest levels of vocal effort, elicited by having talkers shout to and yell at someone located appropriately far away, elements of the postural force, notably one or more torque components, often show a reduction in correspondence with the other measures. We interpret this result as evidence that talkers become more rigidly coordinated at the highest levels of vocal effort, which can interfere with their balance. Furthermore, the discourse type—shouting at someone to carry on a conversation vs. yelling at someone not expected to reply—can be associated with differing amounts of imbalance.