bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrative physiological and computational approaches to understand autonomic control of cerebral autoregulation
Authors: Tan Can Ozan , Taylor J. Andrew
Published: October 2013

New Findings

What is the topic of this review?

This review focuses on the autonomic control of the cerebral vasculature in health and disease from an integrative physiological and computational perspective.

What advances does it highlight?

This review highlights recent studies exploring autonomic effectors of cerebral autoregulation as well as recent advances in experimental and analytical approaches to understand cerebral autoregulation.

The brain requires steady delivery of oxygen and glucose, without which neurodegeneration occurs within minutes. Thus, the ability of the cerebral vasculature to maintain relatively steady blood flow in the face of changing systemic pressure, i.e. cerebral autoregulation, is critical to neurophysiological health. Although the study of autoregulation dates to the early 20th century, only the recent availability of cerebral blood flow measures with high temporal resolution has allowed rapid, beat‐by‐beat measurements to explore the characteristics and mechanisms of autoregulation. These explorations have been further enhanced by the ability to apply sophisticated computational approaches that exploit the large amounts of data that can be acquired. These advances have led to unique insights. For example, recent studies have revealed characteristic time scales wherein cerebral autoregulation is most active, as well as specific regions wherein autonomic mechanisms are prepotent. However, given that effective cerebral autoregulation against pressure fluctuations results in relatively unchanging flow despite changing pressure, estimating the pressure–flow relationship can be limited by the error inherent in computational models of autoregulatory function. This review focuses on the autonomic neural control of the cerebral vasculature in health and disease from an integrative physiological perspective. It also provides a critical overview of the current analytical approaches to understand cerebral autoregulation.
The possible mechanisms by which maternal hypothyroidism impairs insulin secretion in adult male offspring in rats
Authors: Karbalaei Narges , Ghasemi Asghar , Hedayati Mehdi , Godini Aliashraf , Zahediasl Saleh
Published: October 2013

New Findings

What is the central question of this study?

Thyroid hormones play key roles in somatic growth and metabolism. Previous studies have recently shown that maternal hypothyroidism leads to impaired glucose metabolism and reduced insulin secretion in adult offspring in rats, but the mechanistic basis of the secretory defect in maternal hypothyroid islets is unknown.

What is the main finding and its importance?

Our findings demonstrate that reduction in the availability of thyroid hormones during fetal life leads to impaired insulin secretion that is probably related to alterations in different steps of the insulin secretion pathway, including abnormalities in glycolytic pathways and altered behaviour of ATP‐sensitive K+ channels and Ca2+ L‐type channels of β‐cells.

Previous studies have recently shown that maternal hypothyroidism leads to impaired glucose metabolism and reduced insulin secretion in adult offspring in rats. The aim of this study was to locate the defect in the insulin secretion pathway induced by maternal hypothyroidism. Pregnant Wistar rats were divided into two groups; the control group consumed water, while the hypothyroid (FH) group received water containing 0.025% 6‐propyl‐2‐thiouracil during gestation. An intravenous glucose tolerance test was carried out on 5‐month‐old male offspring. In in vitro studies, the effects of various secretagogues and inhibitors acting at different levels of the insulin secretion cascade were investigated, and insulin content, insulin secretion and glucokinase activity of the islets were compared. Although insulin content of the FH islets did not differ from that of control islets, insulin secretion from FH islets was reduced when it was challenged by glucose or arginine. Compared with control islets, activities of both hexokinase and glucokinase were also significantly decreased in the FH islets. Although, in both groups, increasing glibenclamide and nifedipine concentrations in the presence of 16.7 mmol l−1 glucose increased and decreased insulin secretion, respectively, the percentage of changes in secretion of FH islets was significantly lower compared with control islets. The response of FH islets to high extracellular potassium concentration and diazoxide was also significantly lower than that of the control islets. These findings demonstrate that impaired insulin secretion in the FH group is probably related to alterations in different steps of the insulin secretion pathway and not in the insulin pool of β‐cells.
Haptic Hand Exoskeleton for Precision Grasp Simulation
Authors: Fontana Marco , Fabio Salsedo , Marcheschi Simone , Bergamasco Massimo
Published: October 2013

This paper outlines the design and the development of a novel robotic hand exoskeleton (HE) conceived for haptic interaction in the context of virtual reality (VR) and teleoperation (TO) applications. The device allows exerting controlled forces on fingertips of the index and thumb of the operator. The new exoskeleton features several design solutions adopted with the aim of optimizing force accuracy and resolution. The use of remote centers of motion mechanisms allows achieving a compact and lightweight design. An improved stiffness of the transmission and reduced requirements for the electromechanical actuators are obtained thanks to a novel principle for integrating speed reduction into torque transmission systems. A custom designed force sensor and integrated electronics are employed to further improve performances. The electromechanical design of the device and the experimental characterization are presented.
Complete Switched Generalized Function Projective Synchronization of a Class of Hyperchaotic Systems With Unknown Parameters and Disturbance Inputs
Authors: Yu Fei , Song Yun
Published: October 2013

The concept of complete switched generalized function projective synchronization (CSGFPS) in practical type is introduced and the CSGFPS of a class of hyperchaotic systems with unknown parameters and disturbance inputs are investigated. By Lyapunov stability theory, the adaptive control law and the parameter update law are derived to make the states of a class of hyperchaotic systems asymptotically synchronized up to a desired scaling function and the unknown parameters are also estimated. In numerical simulations, the scaling function factors discussed in this paper are more complicated. Finally, the hyperchaotic Lorenz and hyperchaotic Lü systems are taken, for example, and the numerical simulations are presented to verify the effectiveness and robustness of the proposed control scheme.
Robust Separation of Signal Domain From Single Channel Mixed Signal Output of Automotive Urea Based Selective Catalytic Reduction Systems
Authors: Upadhyay D. , Van Nieuwstadt M.
Published: October 2013

There is a class of sensor constrained, uncertain, chemical reactor systems that pose unique challenges with regard to the feedback signal. We refer specifically to the urea based selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the engine exhaust of diesel powertrains. These catalysts rely on adsorbed ammonia (NH3), produced from aqueous urea, for the catalytic reduction of NOx to N2. Typically, underinjection of urea will result in the slip of NOx, whereas overinjection will induce NH3 slip. The ideal control objective of such a plant is, therefore, to regulate urea injection such that the net slip over the catalyst is minimized. Meeting these control objectives is made difficult due to the presence of an output sensor that is cross sensitive to both NOx and NH3, thereby producing a mixed feedback signal. This signal confounding poses significant challenges with regard to the stability and robustness of both closed loop control as well as on board diagnostics. In the absence of a robust NH3 sensor, it becomes necessary to create alternate methods of signal disambiguation. However, so far in open literature, there has not been a detailed discussion of this problem nor has a concrete solution been proposed to robustly and continuously identify the nature of slip as NOx or NH3. In this paper, we discuss the systematic development of a new method that allows a robust and continuous determination of the slip regime from the mixed signal output of a standard NOx sensor. The full scope of the practical problem is discussed and the performance of the proposed method is shown via experimental data.
Effect of temporal decay on perception of heavy-weight floor impact sounds
Authors: Kim Jae Ho , Ryu Jong Kwan , Jeon Jin Yong
Published: October 2013

This study investigates the effect of temporal decay on perception of heavy-weight floor impact sounds through auditory experiments. Heavy-weight impact sounds were recorded in apartment buildings with a box-framed type reinforced concrete structure using a rubber ball. Temporal decay was quantified by using the decay rate (DR), defined as the sound pressure level (SPL) decrease per second [dB/s], and the distribution of DR for heavy-weight impact sounds was calculated. An auditory experiment was conducted in order to examine the just noticeable difference (JND) of DR, which was determined by the criteria of 75% correct answers by subjects. It was found that the JND of DR is around 11 dB/s. Based on the distribution and JND of DR, another experiment was conducted to investigate the effect of DR on annoyance perception of heavy-weight floor impact sounds in relation to the level differences. The results indicate that SPL and DR significantly influence annoyance perception; the scale value of annoyance increases with decreasing DR and increasing SPL. It was also found that the degree of satisfaction with regards to impact sounds can be improved by increasing DR, by controlling the sound field of the receiving room.
Acoustic interaction between the right and left piriform fossae in generating spectral dips
Authors: Takemoto Hironori , Adachi Seiji , Mokhtari Parham , Kitamura Tatsuya
Published: October 2013

It is known that the right and left piriform fossae generate two deep dips on speech spectra and that acoustic interaction exists in generating the dips: if only one piriform fossa is modified, both the dips change in frequency and amplitude. In the present study, using a simple geometrical model and measured vocal tract shapes, the acoustic interaction was examined by the finite-difference time-domain method. As a result, one of the two dips was lower in frequency than the two independent dips that appeared when either of the piriform fossae was occluded, and the other dip was higher in frequency than the two dips. At the lower dip frequency, the piriform fossae resonated almost in opposite phase, while at the higher dip frequency, they resonated almost in phase. These facts indicate that the piriform fossae and the lower part of the pharynx can be modeled as a coupled two-oscillator system whose two normal vibration modes generate the two spectral dips. When the piriform fossae were identical, only the higher dip appeared. This is because the lower mode is not acoustically coupled to the main vocal tract enough to generate an absorption dip.
Strategies adopted by talkers faced with fluctuating and competing-speech maskers
Authors: Aubanel Vincent , Cooke Martin
Published: October 2013

Studying how interlocutors exchange information efficiently during conversations in less-than-ideal acoustic conditions promises to both further the understanding of links between perception and production and inform the design of human-computer dialogue systems. The current study explored how interlocutors' speech changes in the presence of fluctuating noise. Pairs of talkers were recorded while solving puzzles cooperatively in quiet and with modulated-noise or competing speech maskers whose silent intervals were manipulated to produce either temporally sparse or dense maskers. Talkers responded to masked conditions by both increasing the amount of speech produced and locally changing their speech activity patterns, resulting in a net reduction in the proportion of speech in temporal overlap with the maskers, with larger relative reductions for sparse maskers. An analysis of talker activity in the vicinity of masker onset and offset events showed a significant reduction in onsets following masker onsets, and a similar increase in onsets following masker offsets. These findings demonstrate that talkers are sensitive to masking noise and respond to its fluctuations by adopting a “wait-and-talk” strategy.
Development and evaluation of a linguistically and audiologically controlled sentence intelligibility test
Authors: Uslar Verena N. , Carroll Rebecca , Hanke Mirko , Hamann Cornelia , Ruigendijk Esther , Brand Thomas , Kollmeier Birger
Published: October 2013

To allow for a systematic variation of linguistic complexity of sentences while acoustically controlling for intelligibility of sentence fragments, a German corpus, Oldenburg linguistically and audiologically controlled sentences (OLACS), was designed, implemented, and evaluated. Sentences were controlled for plausibility with a questionnaire survey. Verification of the speech material was performed in three listening conditions (quiet, stationary, and fluctuating noise) by collecting speech reception thresholds (SRTs) and response latencies as well as individual cognitive measures for 20 young listeners with normal hearing. Consistent differences in response latencies across sentence types verified the effect of linguistic complexity on processing speed. The addition of noise decreased response latencies, giving evidence for different response strategies for measurements in noise. Linguistic complexity had a significant effect on SRT. In fluctuating noise, this effect was more pronounced, indicating that fluctuating noise correlates with stronger cognitive contributions. SRTs in quiet correlated with hearing thresholds, whereas cognitive measures explained up to 40% of the variance in SRTs in noise. In conclusion, OLACS appears to be a suitable tool for assessing the interaction between aspects of speech understanding (including cognitive processing) and speech intelligibility in German.
Nonadditivity of forward and simultaneous masking
Authors: Svec Adam , Joshi Suyash N. , Jesteadt Walt
Published: October 2013

The current study measured the additional masking obtained for combinations of forward and simultaneous maskers as a function of forward masker bandwidth, signal delay, and simultaneous masker level. The effects of the two individual maskers were equated in all conditions. Additional masking increased with increasing masker level, increasing signal delay, and decreasing masker bandwidth. The portion of the simultaneous masker that made the greater contribution to additional masking was the part that overlapped with the signal, not with the forward masker. The changes in additional masking observed as a function of forward masker bandwidth and the interaction between the effects of forward and simultaneous maskers call into question the use of additional masking as a measure of basilar membrane compression and present problems for the use of simultaneous noise to simulate hearing loss.
Symmetric airfoil geometry effects on leading edge noise
Authors: Gill James , Zhang X. , Joseph P.
Published: October 2013

Computational aeroacoustic methods are applied to the modeling of noise due to interactions between gusts and the leading edge of real symmetric airfoils. Single frequency harmonic gusts are interacted with various airfoil geometries at zero angle of attack. The effects of airfoil thickness and leading edge radius on noise are investigated systematically and independently for the first time, at higher frequencies than previously used in computational methods. Increases in both leading edge radius and thickness are found to reduce the predicted noise. This noise reduction effect becomes greater with increasing frequency and Mach number. The dominant noise reduction mechanism for airfoils with real geometry is found to be related to the leading edge stagnation region. It is shown that accurate leading edge noise predictions can be made when assuming an inviscid meanflow, but that it is not valid to assume a uniform meanflow. Analytic flat plate predictions are found to over-predict the noise due to a NACA 0002 airfoil by up to 3 dB at high frequencies. The accuracy of analytic flat plate solutions can be expected to decrease with increasing airfoil thickness, leading edge radius, gust frequency, and Mach number.
Behavioral measures of cochlear compression and temporal resolution as predictors of speech masking release in hearing-impaired listeners
Authors: Gregan Melanie J. , Nelson Peggy B. , Oxenham Andrew J.
Published: October 2013

Hearing-impaired (HI) listeners often show less masking release (MR) than normal-hearing listeners when temporal fluctuations are imposed on a steady-state masker, even when accounting for overall audibility differences. This difference may be related to a loss of cochlear compression in HI listeners. Behavioral estimates of compression, using temporal masking curves (TMCs), were compared with MR for band-limited (500–4000 Hz) speech and pure tones in HI listeners and age-matched, noise-masked normal-hearing (NMNH) listeners. Compression and pure-tone MR estimates were made at 500, 1500, and 4000 Hz. The amount of MR was defined as the difference in performance between steady-state and 10-Hz square-wave-gated speech-shaped noise. In addition, temporal resolution was estimated from the slope of the off-frequency TMC. No significant relationship was found between estimated cochlear compression and MR for either speech or pure tones. NMNH listeners had significantly steeper off-frequency temporal masking recovery slopes than did HI listeners, and a small but significant correlation was observed between poorer temporal resolution and reduced MR for speech. The results suggest either that the effects of hearing impairment on MR are not determined primarily by changes in peripheral compression, or that the TMC does not provide a sufficiently reliable measure of cochlear compression.
Relating traffic, construction, and ventilation noise to cognitive performances and subjective perceptions
Authors: Lee Pyoung Jik , Jeon Jin Yong
Published: October 2013

The present study investigates the cognitive performance and subjective perceptions in the context of road traffic noise alone and multiple noises, including construction and ventilation noises. A total of 20 university students were exposed to seven noise conditions. Laboratory experiments employed semantic and episodic memory tasks. Self-reports of perception were collected from the participants. It was found that multiple noise sources impaired the free recall of words, and free recall scores were affected by noise type. Significant differences in free recall scores were found when the noise level difference between the individual noise and multiple noise sources was more than 5 dB. In contrast, word comprehension did not mediate the effects of noise on semantic memory. Annoyance caused by multiple noise sources correlated highly with the results of the free recall and word comprehension tasks. Moreover, loudness and roughness were found to account for the annoyance ratings of combinations of road traffic noise with construction or ventilation noises.
On horizontal coherence estimates from path integral theory for sound propagation through random ocean sound-speed perturbations
Authors: Colosi John A.
Published: October 2013

Previously published results from path integral theory for the horizontal coherence length utilized an empirical relation for the phase structure function density that was quite different from path integral results obtained for depth and time coherence where the phase structure function density was expanded to second order in the lag. This letter presents a result for horizontal coherence length which carries out the quadratic expansion and analytically solves the integral equations. Some simple calculations of horizontal coherence length demonstrate the differences between the present and old expressions. In contrast to the empirical result the present expression shows the expected one over square-root range and one over frequency scalings. The results also show more clearly how transverse coherence is sensitive to the space-time scales of internal waves and other environmental parameters.
Coupled mode transport theory for sound transmission through an ocean with random sound speed perturbations: Coherence in deep water environments
Authors: Colosi John A. , Chandrayadula Tarun K. , Voronovich Alexander G. , Ostashev Vladimir E.
Published: October 2013

Second moments of mode amplitudes at fixed frequency as a function of separations in mode number, time, and horizontal distance are investigated using mode-based transport equations and Monte Carlo simulation. These second moments are used to study full-field acoustic coherence, including depth separations. Calculations for low-order modes between 50 and 250 Hz are presented using a deep-water Philippine Sea environment. Comparisons between Monte Carlo simulations and transport theory for time and depth coherence at frequencies of 75 and 250 Hz and for ranges up to 500 km show good agreement. The theory is used to examine the accuracy of the adiabatic and quadratic lag approximations, and the range and frequency scaling of coherence. It is found that while temporal coherence has a dominant adiabatic component, horizontal and vertical coherence have more equal contributions from coupling and adiabatic effects. In addition, the quadratic lag approximation is shown to be most accurate at higher frequencies and longer ranges. Last the range and frequency scalings are found to be sensitive to the functional form of the exponential decay of coherence with lag, but temporal and horizontal coherence show scalings that fall quite close to the well-known inverse frequency and inverse square root range laws.
Observations of sound-speed fluctuations in the western Philippine Sea in the spring of 2009
Authors: Colosi John A. , Van Uffelen Lora J. , Cornuelle Bruce D. , Dzieciuch Matthew A. , Worcester Peter F. , Dushaw Brian D. , Ramp Steven R.
Published: October 2013

As an aid to understanding long-range acoustic propagation in the Philippine Sea, statistical and phenomenological descriptions of sound-speed variations were developed. Two moorings of oceanographic sensors located in the western Philippine Sea in the spring of 2009 were used to track constant potential-density surfaces (isopycnals) and constant potential-temperature surfaces (isotherms) in the depth range 120–2000 m. The vertical displacements of these surfaces are used to estimate sound-speed fluctuations from internal waves, while temperature/salinity variability along isopycnals are used to estimate sound-speed fluctuations from intrusive structure often termed spice. Frequency spectra and vertical covariance functions are used to describe the space-time scales of the displacements and spiciness. Internal-wave contributions from diurnal and semi-diurnal internal tides and the diffuse internal-wave field [related to the Garrett–Munk (GM) spectrum] are found to dominate the sound-speed variability. Spice fluctuations are weak in comparison. The internal wave and spice frequency spectra have similar form in the upper ocean but are markedly different below 170-m depth. Diffuse internal-wave mode spectra show a form similar to the GM model, while internal-tide mode spectra scale as mode number to the minus two power. Spice decorrelates rapidly with depth, with a typical correlation scale of tens of meters.
Long-range asymptotic behavior of vertical travel-time sensitivity kernels
Authors: Skarsoulis E. K. , Cornuelle B. D. , Dzieciuch M. A.
Published: October 2013

Vertical travel-time sensitivity kernels (VTSKs) describe the effect of horizontally uniform sound-speed changes on travel times in range-independent ocean environments. Wave-theoretic VTSKs can be obtained either analytically, through perturbation of the normal-mode representation, or numerically, as horizontal marginals of the corresponding two-dimensional and three-dimensional travel-time sensitivity kernels. In previous works, it has been observed that wave-theoretic finite-frequency VTSKs approach the corresponding ray-theoretic sensitivity kernels as the propagation range increases. The present work is an attempt to explain this behavior. A stationary-phase approach is used to obtain a long-range asymptotic expression for the wave-theoretic VTSKs. The resulting asymptotic VTSKs are very close to the corresponding ray-theoretic ones. The smoothness condition, required for the stationary-phase approximation to hold, is used to obtain an estimate for the range beyond which the asymptotic behavior sets in.
Using a numerical model to understand the connection between the ocean and acoustic travel-time measurements
Authors: Powell Brian S. , Kerry Colette G. , Cornuelle Bruce D.
Published: October 2013

Measurements of acoustic ray travel-times in the ocean provide synoptic integrals of the ocean state between source and receiver. It is known that the ray travel-time is sensitive to variations in the ocean at the transmission time, but the sensitivity of the travel-time to spatial variations in the ocean prior to the acoustic transmission have not been quantified. This study examines the sensitivity of ray travel-time to the temporally and spatially evolving ocean state in the Philippine Sea using the adjoint of a numerical model. A one year series of five day backward integrations of the adjoint model quantify the sensitivity of travel-times to varying dynamics that can alter the travel-time of a 611 km ray by 200 ms. The early evolution of the sensitivities reveals high-mode internal waves that dissipate quickly, leaving the lowest three modes, providing a connection to variations in the internal tide generation prior to the sample time. They are also strongly sensitive to advective effects that alter density along the ray path. These sensitivities reveal how travel-time measurements are affected by both nearby and distant waters. Temporal nonlinearity of the sensitivities suggests that prior knowledge of the ocean state is necessary to exploit the travel-time observations.
Experimental demonstration of multiuser communication in deep water using time reversal
Authors: Shimura T. , Ochi H. , Song H. C.
Published: October 2013

Multiuser communication is demonstrated using experimental data (450–550 Hz) collected in deep water, south of Japan. The multiple users are spatially distributed either in depth or range while a 114 -m long, 20-element vertical array (i.e., base station) is deployed to around the sound channel axis (∼1000 m). First, signals received separately from ranges of 150 km and 180 km at various depths are combined asynchronously to generate multiuser communication sequences for subsequent processing, achieving an aggregate data rate of 300 bits/s for up to three users. Adaptive time reversal is employed to separate collided packets at the base station, followed by a single channel decision feedback equalizer. Then it is demonstrated that two users separated by 3 km in range at ∼1000 m depth can transmit information simultaneously to the base station at ∼500 km range with an aggregate data rate of 200 bits/s.
Estimating uncertainty in subsurface glider position using transmissions from fixed acoustic tomography sources
Authors: Van Uffelen Lora J. , Nosal Eva-Marie , Howe Bruce M. , Carter Glenn S. , Worcester Peter F. , Dzieciuch Matthew A. , Heaney Kevin D. , Campbell Richard L. , Cross Patrick S.
Published: October 2013

Four acoustic Seagliders were deployed in the Philippine Sea November 2010 to April 2011 in the vicinity of an acoustic tomography array. The gliders recorded over 2000 broadband transmissions at ranges up to 700 km from moored acoustic sources as they transited between mooring sites. The precision of glider positioning at the time of acoustic reception is important to resolve the fundamental ambiguity between position and sound speed. The Seagliders utilized GPS at the surface and a kinematic model below for positioning. The gliders were typically underwater for about 6.4 h, diving to depths of 1000 m and traveling on average 3.6 km during a dive. Measured acoustic arrival peaks were unambiguously associated with predicted ray arrivals. Statistics of travel-time offsets between received arrivals and acoustic predictions were used to estimate range uncertainty. Range (travel time) uncertainty between the source and the glider position from the kinematic model is estimated to be 639 m (426 ms) rms. Least-squares solutions for glider position estimated from acoustically derived ranges from 5 sources differed by 914 m rms from modeled positions, with estimated uncertainty of 106 m rms in horizontal position. Error analysis included 70 ms rms of uncertainty due to oceanic sound-speed variability.
Measuring the Kuroshio Current with ocean acoustic tomography
Authors: Taniguchi Naokazu , Huang Chen-Fen , Kaneko Arata , Liu Cho-Teng , Howe Bruce M. , Wang Yu-Huai , Yang Yih , Lin Ju , Zhu Xiao-Hua , Gohda Noriaki
Published: October 2013

Ocean current profiling using ocean acoustic tomography (OAT) was conducted in the Kuroshio Current southeast of Taiwan from August 20 to September 15, 2009. Sound pulses were transmitted reciprocally between two acoustic stations placed near the underwater sound channel axis and separated by 48 km. Based on the result of ray simulation, the received signals are divided into multiple ray groups because it is difficult to resolve the ray arrivals for individual rays. The average differential travel times from these ray groups are used to reconstruct the vertical profiles of currents. The currents are estimated with respect to the deepest water layer via two methods: An explicit solution and an inversion with regularization. The strong currents were confined to the upper 200 m and rapidly weakened toward 500 m in depth. Both methods give similar results and are consistent with shipboard acoustic Doppler current profiler results in the upper 150 m. The observed temporal variation demonstrates a similar trend to the prediction from the Hybrid Coordinate Ocean Model.
Estimating the horizontal and vertical direction-of-arrival of water-borne seismic signals in the northern Philippine Sea
Authors: Freeman Simon E. , D'Spain Gerald L. , Lynch Stephen D. , Stephen Ralph A. , Heaney Kevin D. , Murray James J. , Baggeroer Arthur B. , Worcester Peter F. , Dzieciuch Matthew A. , Mercer James A.
Published: October 2013

Conventional and adaptive plane-wave beamforming with simultaneous recordings by large-aperture horizontal and vertical line arrays during the 2009 Philippine Sea Engineering Test (PhilSea09) reveal the rate of occurrence and the two-dimensional arrival structure of seismic phases that couple into the deep ocean. A ship-deployed, controlled acoustic source was used to evaluate performance of the horizontal array for a range of beamformer adaptiveness levels. Ninety T-phases from unique azimuths were recorded between Yeardays 107 to 119. T-phase azimuth and S-minus-P-phase time-of-arrival range estimates were validated using United States Geological Survey seismic monitoring network data. Analysis of phases from a seismic event that occurred on Yearday 112 near the east coast of Taiwan approximately 450 km from the arrays revealed a 22° clockwise evolution of T-phase azimuth over 90 s. Two hypotheses to explain such evolution—body wave excitation of multiple sources or in-water scattering—are presented based on T-phase origin sites at the intersection of azimuthal great circle paths and ridge/coastal bathymetry. Propagation timing between the source, scattering region, and array position suggests the mechanism behind the evolution involved scattering of the T-phase from the Ryukyu Ridge and a T-phase formation/scattering location estimation error of approximately 3.2 km.
Deep seafloor arrivals in long range ocean acoustic propagation
Authors: Stephen Ralph A. , Thompson Bolmer S. , Udovydchenkov Ilya A. , Worcester Peter F. , Dzieciuch Matthew A. , Andrew Rex K. , Mercer James A. , Colosi John A. , Howe Bruce M.
Published: October 2013

Ocean bottom seismometer observations at 5000 m depth during the long-range ocean acoustic propagation experiment in the North Pacific in 2004 show robust, coherent, late arrivals that are not readily explained by ocean acoustic propagation models. These “deep seafloor” arrivals are the largest amplitude arrivals on the vertical particle velocity channel for ranges from 500 to 3200 km. The travel times for six (of 16 observed) deep seafloor arrivals correspond to the sea surface reflection of an out-of-plane diffraction from a seamount that protrudes to about 4100 m depth and is about 18 km from the receivers. This out-of-plane bottom-diffracted surface-reflected energy is observed on the deep vertical line array about 35 dB below the peak amplitude arrivals and was previously misinterpreted as in-plane bottom-reflected surface-reflected energy. The structure of these arrivals from 500 to 3200 km range is remarkably robust. The bottom-diffracted surface-reflected mechanism provides a means for acoustic signals and noise from distant sources to appear with significant strength on the deep seafloor.
Structure and stability of wave-theoretic kernels in the ocean
Authors: Dzieciuch Matthew A. , Cornuelle Bruce D. , Skarsoulis Emmanuel K.
Published: October 2013

Wave-theoretic modeling can be applied to obtain travel-time sensitivity kernels (TSKs) representing the amount ray travel times are affected by sound-speed variations anywhere in the medium. This work explores the spatial frequency content of the TSK compared to expected ocean variability. It also examines the stability of the TSK in environments that produce strong sensitivity of ray paths to initial conditions. The conclusion is that the linear TSK model is an effective predictor of travel-time changes and that the rays perform nearly as well as the full-wave kernel. The TSK is examined in physical space and in wavenumber space, and it is found that this is the key to understanding how the travel time reacts to ocean perturbations. There are minimum vertical and horizontal length scales of ocean perturbations that are required for the travel time to be affected. The result is that the correspondence between true travel times and those calculated from the kernel is high for large-scale perturbations and somewhat less for the small scales. This demonstrates the validity of ray-based inversion of travel time observations for the cases under study.
Reduced rank models for travel time estimation of low order mode pulses
Authors: Chandrayadula Tarun K. , Wage Kathleen E. , Worcester Peter F. , Dzieciuch Matthew A. , Mercer James A. , Andrew Rex K. , Howe Bruce M.
Published: October 2013

Mode travel time estimation in the presence of internal waves (IWs) is a challenging problem. IWs perturb the sound speed, which results in travel time wander and mode scattering. A standard approach to travel time estimation is to pulse compress the broadband signal, pick the peak of the compressed time series, and average the peak time over multiple receptions to reduce variance. The peak-picking approach implicitly assumes there is a single strong arrival and does not perform well when there are multiple arrivals due to scattering. This article presents a statistical model for the scattered mode arrivals and uses the model to design improved travel time estimators. The model is based on an Empirical Orthogonal Function (EOF) analysis of the mode time series. Range-dependent simulations and data from the Long-range Ocean Acoustic Propagation Experiment (LOAPEX) indicate that the modes are represented by a small number of EOFs. The reduced-rank EOF model is used to construct a travel time estimator based on the Matched Subspace Detector (MSD). Analysis of simulation and experimental data show that the MSDs are more robust to IW scattering than peak picking. The simulation analysis also highlights how IWs affect the mode excitation by the source.
Deep water towed array measurements at close range
Authors: Heaney Kevin D. , Campbell Richard L. , Murray James J. , Baggeroer Arthur B. , Scheer Eddie K. , Stephen Ralph A. , D'Spain Gerald L. , Mercer James A.
Published: October 2013

During the North Pacific Acoustic Laboratory Philippine Sea 2009 experiment, towed array receptions were made from a towed source as the two ships transited from a separation of several Convergence Zones through a Closest Point of Approach at 3 km. A combination of narrowband tones and broadband pulses were transmitted covering the frequency band 79–535 Hz. The received energy arrives from two general paths—direct path and bottom bounce. Bearing-time records of the narrowband arrivals at times show a 35° spread in the angle of arrival of the bottom bounce energy. Doppler processing of the tones shows significant frequency spread of the bottom bounce energy. Two-dimensional modeling using measured bathymetry, a geoacoustic parameterization based upon the geological record, and measured sound-speed field was performed. Inclusion of the effects of seafloor roughness and surface waves shows that in-plane scattering from rough interfaces can explain much of the observed spread in the arrivals. Evidence of out-of-plane scattering does exist, however, at short ranges. The amount of out-of-plane scattering is best observed in the broadband impulse-beam response analysis, which in-plane surface roughness modeling cannot explain.
Modal density and modal distribution of bending wave vibration fields in ribbed plates
Authors: Dickow Kristoffer Ahrens , Brunskog Jonas , Ohlrich Mogens
Published: October 2013

Plates reinforced by ribs or joists are common elements in lightweight building structures, as well as in other engineering structures such as vehicles, ships, and aircraft. These structures, however, are often not well suited for simple structural acoustic prediction models such as statistical energy analysis. One reason is that the modal density is not uniformly distributed due to the spatial periodicity introduced by the ribs. This phenomenon is investigated in the present paper, using a modal model of a ribbed plate. The modal model uses the Fourier sine modes, and the coupling between the plate and ribs is incorporated using Hamilton's principle. This model is then used to investigate the modal density of the considered spatially periodic structure, and a grouping of the modes in different dominating directions is proposed. Suggestions are also given regarding how to proceed towards a simplified prediction model for ribbed plates.
Investigating the relationship between average speaker fundamental frequency and acoustic vowel space size
Authors: Weirich Melanie , Simpson Adrian
Published: October 2013

The purpose of this study is to investigate the potential relationship between speaking fundamental frequency and acoustic vowel space size, thus testing a possible perceptual source of sex-specific differences in acoustic vowel space size based on the greater inter-harmonic spacing and a poorer definition of the spectral envelope of higher pitched voices. Average fundamental frequencies and acoustic vowel spaces of 56 female German speakers are analyzed. Several parameters are used to quantify the size and shape of the vowel space defined by /iː ε aː ɔ uː/ such as the area of the polygon spanned by the five vowels, the absolute difference in F1 or F2 between /iː/ and /uː/ or /aː/, and the Euclidian distance between /iː/ and /aː/. In addition, the potential impact of nasality on the vowel space size is examined. Results reveal no significant correlation between fundamental frequency and vowel space size suggesting other factors must be responsible for the larger female acoustic vowel space.
Modeling and detection of oil in sea water
Authors: Xenaki Angeliki , Gerstoft Peter , Mosegaard Klaus
Published: October 2013

The challenge of a deep-water oil leak is that a significant quantity of oil remains in the water column and possibly changes properties. There is a need to quantify the oil settled within the water column and determine its physical properties to assist in the oil recovery. There are currently no methods to map acoustically submerged oil in the sea. In this paper, high-frequency acoustic methods are proposed to localize the oil polluted area and characterize the parameters of its spatial covariance, i.e., variance and correlation. A model is implemented to study the underlying mechanisms of backscattering due to spatial heterogeneity of the medium and predict backscattering returns. An algorithm for synthetically generating stationary, Gaussian random fields is introduced which provides great flexibility in implementing the physical model of an inhomogeneous field with spatial covariance. A method for inference of spatial covariance parameters is proposed to describe the scattering field in terms of its second-order statistics from the backscattered returns. The results indicate that high-frequency acoustic methods not only are suitable for large-scale detection of oil contamination in the water column but also allow inference of the spatial covariance parameters resulting in a statistical description of the oil field.
T-wave generation and propagation: A comparison between data and spectral element modeling
Authors: Jamet Guillaume , Guennou Claude , Guillon Laurent , Mazoyer Camille , Royer Jean-Yves
Published: October 2013

T-waves are underwater acoustic waves generated by earthquakes. Modeling of their generation and propagation is a challenging problem. Using a spectral element code—SPECFEM2D, this paper presents the first realistic simulations of T-waves taking into account major aspects of this phenomenon: The radiation pattern of the source, the propagation of seismic waves in the crust, the seismic to acoustic conversion on a non-planar seafloor, and the propagation of acoustic waves in the water column. The simulated signals are compared with data from the mid-Atlantic Ridge recorded by an array of hydrophones. The crust/water interface is defined by the seafloor bathymetry. Different combinations of water sound-speed profiles and sub-seafloor seismic velocities, and frequency content of the source are tested. The relative amplitudes, main arrival-times, and durations of simulated T-phases are in good agreement with the observed data; differences in the spectrograms and early arrivals are likely due to too simplistic source signals and environmental model. These examples demonstrate the abilities of the SPECFEM2D code for modeling earthquake generated T-waves.
Differences in short-term training for interaural phase difference discrimination between two different forced-choice paradigms
Authors: King Andrew , Hopkins Kathryn , Plack Christopher J.
Published: October 2013

Improvement in interaural phase difference (IPD) discrimination over 2 to 3 h was compared for two two-alternative forced-choice paradigms: A three-interval paradigm, in which the IPD was in interval two or three, and a paradigm with two intervals of four stimuli in which the IPD was in the second and fourth stimuli of one interval (AAAA vs ABAB). The difference in performance between the beginning and end of the testing period was smaller for the two-interval paradigm, supporting the use of this paradigm for fast measurement of discrimination thresholds without the need for a long period of training.
Infrasonic interferometry of stratospherically refracted microbaroms—A numerical study
Authors: Fricke Julius T. , El Allouche Nihed , Simons Dick G. , Ruigrok Elmer N. , Wapenaar Kees , Evers Läslo G.
Published: October 2013

The atmospheric wind and temperature can be estimated through the traveltimes of infrasound between pairs of receivers. The traveltimes can be obtained by infrasonic interferometry. In this study, the theory of infrasonic interferometry is verified and applied to modeled stratospherically refracted waves. Synthetic barograms are generated using a raytracing model and taking into account atmospheric attenuation, geometrical spreading, and phase shifts due to caustics. Two types of source wavelets are implemented for the experiments: blast waves and microbaroms. In both numerical experiments, the traveltimes between the receivers are accurately retrieved by applying interferometry to the synthetic barograms. It is shown that microbaroms can be used in practice to obtain the traveltimes of infrasound through the stratosphere, which forms the basis for retrieving the wind and temperature profiles.
Inversions of statistical parameters of an acoustic signal in range-dependent environments with applications in ocean acoustic tomography
Authors: Taroudakis Michael I. , Smaragdakis Costas
Published: October 2013

The paper presents an application of a method for the characterization of underwater acoustic signals based on the statistics of the wavelet transform sub-band coefficients in range-dependent environments. As it was illustrated in previous work, this statistical characterization scheme is a very efficient tool for obtaining observables to be exploited in problems of ocean acoustic tomography and geoacoustic inversion, when range-independent environments are considered. Now the scheme is applied in range-dependent environments for the estimation of range-dependent features in shallow water. A simple denoising strategy, also presented in the paper, is shown to enhance the quality of the inversion results as it helps to keep the signal characterization to the energy a significant part of it. The results presented for typical test cases are encouraging and indicative of the potential of the method for the treatment of inverse problems in acoustical oceanography.
Effect of metabolic presbyacusis on cochlear responses: A simulation approach using a physiologically-based model
Authors: Saremi Amin , Stenfelt Stefan
Published: October 2013

In the presented model, electrical, acoustical, and mechanical elements of the cochlea are explicitly integrated into a signal transmission line where these elements convey physiological interpretations of the human cochlear structures. As a result, this physiologically-motivated model enables simulation of specific cochlear lesions such as presbyacusis. The hypothesis is that high-frequency hearing loss in older adults may be due to metabolic presbyacusis whereby age-related cellular/chemical degenerations in the lateral wall of the cochlea cause a reduction in the endocochlear potential. The simulations quantitatively confirm this hypothesis and emphasize that even if the outer and inner hair cells are totally active and intact, metabolic presbyacusis alone can significantly deteriorate the cochlear functionality. Specifically, in the model, as the endocochlear potential decreases, the transduction mechanism produces less receptor current such that there is a reduction in the battery of the somatic motor. This leads to a drastic decrease in cochlear amplification and frequency sensitivity, as well as changes in position-frequency map (tuning pattern) of the cochlea. In addition, the simulations show that the age-related reduction of the endocochlear potential significantly inhibits the firing rate of the auditory nerve which might contribute to the decline of temporal resolution in the aging auditory system.